microsoft word reviewer.doc thanks to reviewers we greatly appreciate the voluntary contribution that each reviewer gives to the journal. we hope that our reviewers will help in the reviewing process for bibechana in future also. reviewers dr. b.p. singh, univ. dept. of physics, t.m. bhagalpur university, bhagalpur, india dr. r. novakovic, national research council, institute of energetics and interphases, via de marini, 6-16149-genoa, italy dr. b.c. paul, department of physics, university of north bengal, india prof. l.n. jha, central department of physics, tribhuvan university, nepal prof. badiadka narayana, department of studies in chemistry, mangalore university, india dr. bhausaheb k. karale, p.g. & research, department of chemistry, s. s. g. m. college, kopargaon, dist-ahmednagar, india dr. ghanashyam bez, dept of chemistry, north easternn hill university shillong-793022, india prof. bijan das, department of chemistry, north bengal university india prof. ramazan sever, middle east technical university , physics department, turkey prof. pradeep raj pradhan, post-graduate department of physics, m.m.a.m. campus (tribhuvan university), nepal prof. man singh, school of chemical sciences, central university of gujarat gujarat, india dr. yaseen iqbal, ceng, minstp, msgt foreign professor materials research laboratory institute of physics & electronics university of peshawar, khyber pukhtunkhwa, pakistan dr. kambiz shahroudi, department of industrial management, islamic azad university rasht branch,rasht, iran dr. archana gupta, department of engineering and technology, m.j.p. rohilkhand university, bareilly, india dr. i.s. jha, , post-graduate department of physics, m.m.a.m. campus (tribhuvan university), nepal prof. mohan siwakoti, central department of botany, tribhuvan university, nepal a. prof. md. haider ali biswas, mathematics discipline, khulna university, khulna-9208, bangladesh 128-130 k.k. mishra r c o s t n k.k. mishra / bibechana 11(1) (2014) 128-130 (online publication: march, 2014) p.128 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana chromogenomic changes after the use of methyl parathion on ocimum americanum l. in eastern zone of nepal k.k. mishra department of botany m.m.a.m. campus, t.u., biratnagar, nepal accepted for publication: february 04, 2014 abstract fungicide like methyl parathion was able to control the fusarial disease of ocimum americanum l. but it caused chromogenomic changes in the first progeny of the host plant. the parental colour was red, which became to green in the ratio 5-95%. therefore, the use of the fungicide not only control the disease caused by the fusarium oxysporum but also affects the genomes responsible for the colour. the investigation was from 1/11/2012 to 02/12/2013. © 2014 rcost: all rights reserved. keywords: chromogenomic changes; methyl parathion; ocimum americanum l. 1. introduction the host plant showed the presence of microconidia and megaconidia of f. oxysporum in the twig and leaf of ocimum americanum l. under the anatomical study along with the following symptoms: plants height branches symptoms i 60 cm. 16 lesser white ii 55 cm. 11 white vascular tissue very clear iii 35.5 cm. 9 least white, terminating brownish black, presence of air canal. i.e. breakage of xylem & phloem. calculation of spores: a) smallest twig: epidermal and vascular region. (i) micro conidium 1 (ii) mega conidium 1 roothair: (i) mycelium (+) (ii) micro conidium unicellular, no -2 (iii) mega conidium only one. b) inter mediate twig: (i) mycelium (+) (ii) xylem lumen – mycelium, megacondidium – 1, 5 – septate condition. k.k. mishra / bibechana 11(1) (2014) 128-130 (online publication: march, 2014) p.129 c) largest twig: (i) mycelium – (+) (ii) microconidium – (+) (iii) mega conidium – (+) in the cortical region of stem. the identification was followed as described by wollenweber and reinking [1-3], and synder [4]. the pathogens of fusarium oxysporum during its different stages of growth – i.e. mycelia, mat of mycelia, microconidia and megaconidia librates several toxic substances to lnactive the cell, tissues or lysis of different parts particulary xylem and pholoem of the host ocimum americanum l [5]. here, fusaric acid is the most important and viable toxin, secreted by f. oxysporum. it caused vein clearing, epinasty, reduction in respiration and growth. necrosis of cortical tissues overlying the vascular bundles, furrowing of stem, deposition of salts on stem and sometimes bending of stem. kalyansundram & venkatraman [6,7] have shown that a concentration of 10-4m of fusaric acid is reached in the infected plants. this condition is lethal to host tissues [8] described phytotoxins produced by fusaria [9]. the fungicide methyl parathion was used through spraying on the plant, soil and surrounding. it resulted to control the disease fusarial wilt’ on the host plants of ocimum americanum l. the theme or vision 2030 of indian phytopathological society, new delhi, india. methyl parathion parathion is the chemical control of the pathogen and known as methyl parathion 2% d.p. the first progeny obtained by the seeds of treated host plants of ocimum americanum l. were free from the fusarial disease but the colour of the leaves of the plant was mixed condition of red and green, though the parental leaves were red. the different ration of the red and green leaves is given in the following tables. plant red leaves greenleaves ocimum americanum l. (i) 5% 95% (ii) 11% 89% (iii) 20% 80% (iv) 30% 70% (v) 35% 65% (vi) 40% 60% (vii) 50% 50% (viii) 55% 45% (ix) 70% 30% (x) 95% 5% the calculation of green leaves and red leaves was done, counting the number of leaves on each branch of the plants. k.k. mishra / bibechana 11(1) (2014) 128-130 (online publication: march, 2014) p.130 conclusion the use of fungicide is essential to control the fungal diseases but it has some side effects also as chromogenomic changes in the first progeny of the treated host plants of ocimum americanum l. by the fungicide methyl parathion. references [1] w.c. synder, h.n. hansen, amer. j. bot., 27 (1940) 64. [2] w.c. synder, h.n. hansen, amer, j. bot., 28 (1941) 738. [3] w.c. synder, h.n. hansen, amer, j. bot., 32 (1945) 657. [4] w.c. synder, current status of taxonomy in fusarium sp. and their perfect stages phytopathology, 55 (1965) 833. [5] k.k. mishra, date palm without date due to fusarium oxysporum var. toddy in eastern zone of nepal. 95th indian science congress, jan 3-7, 2008, vishakhapatnum, 87. [6] r. kalyansundram, proc. first int. symp. pl. pathology, iari, new delhi, (1970) 135. [7] r. kalyansundaran, some concept of toxin in the plant disease physiology of host pathogen interaction (a. mahadevan ed.) today & tomorrow’s printers & publishers, new delhi, 1977. [8] h. kern, “phytotoxins produced by fusaria” in phytotoxins in plant diseases, 1972. [9] k.k. mishra, the fungicide around the fusarial conidia of ocimum americanum l. at biratnagar nepal, 100th indian science congress, 3-7 jan. 2013, kolkata, 98. microsoft word n.p. sah _126-129_.doc n.p.sah / bibechana 9 (2013) 126-129 : bmhss, p.126 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana about riesz theory of compact operators nagendra pd. sah department of mathematics, m.m.a.m.campus (tribhuvan university) biratnagar, nepal. article history: received 2 october, 2012; accepted 12 november, 2012 abstract in this paper, it is shown that every compact operators are bounded and continuous. the bounded and continuous properties of an operator is sufficient for a riesz operator. for mapping t: kiλ in normed linear space with some extended [1] properties, t becomes compact. keywords: chain length; riesz operators; relatively regular operator 1. introduction for the mapping t = kiλ , in normed linear space, [where i is the identity map, k is compact map and 0≠λ is an arbitrary scalar from φ ], the fredholm alternative theorem is valid. the null spaces and image spaces of t k , where k is natural number, form chains with the same chain length. the image space b(t) is always closed; kiλ is open and the eigenvalues of k form a null sequence, provided infinitely many such eigenvalues exist. an operator which satisfies these properties for all 0≠λ , is known as a riesz operator. if k is a compact map, then t = kiλ possesses a decomposition into an invertible operator r(λ ) and an operator s(λ ) of finite rank. this leads to the decisive definitions. the operators that in the quotient algebra of all continuous maps with respect to the ideal of all finite dimensional maps, they are right or left invertible respectively, such invertible are known as atkinson operators. still another important notion which stands together very closely with the above definitions. if for a continuous operator t, there exists a continuous operator s with t.s.t. = t, then t is called relatively regular operator [2], for a topological characterization of these relatively regular operators, if e is a named linear space and )e(rk∈ ; then put i-k=t and n(t k )=nk, b(t k )=bk for k=0,1,2… 2. some properties of null and image spaces as null spaces form an increasing sequence {0}=n0⊂ n1 ⊂ n2⊂ n3⊂…. 1. nk is closed: this follows from the continuity of t k , k = 0,1,2…. 2. dim n1<∞ : if nx n ∈ , and ||xn||=1, nn∈ , then (i-k)xn=0, therefore xn=k. xn; on account of the compactness of k, the sequence {k.xn} has a subsequence {k.xn} with lim k. xn = lim knx = y ∞→k ∞→k n.p.sah / bibechana 9 (2013) 126-129 : bmhss, p.127 (online publication: nov., 2012) therefore { 1||x||:ex =∈ } 1n∩ is compact, and hence n1 is finite dimensional. 3. dim nk <∞ : since t k = (i-k) k = i     −++ − − − k1k2 k.)1(.....k 2 )1k(k k.k = i kk, nk∈ , holds and kk is compact [3]. from above result it follows that dim nk<∞ for all k = 0,1,2… 4. if there exists 0k ≥ s.t. nk = nk+1, then it follows that nk = nk+1, .nn∈ proof: if 2knx +∈ , then t k+2 .x = t k+1 (t.x)= 0, t.x k1k nn =∈ + , therefore, also t k (t.x)=t k+1 .x=0 i.e., 1knx +∈ hence nk+1 = nk+2 and by complete induction, wet get nk= nk+n. definition (1:1): there exists, either smallest number p = p(t)<∞ satisfying np=np+1 in which case we say that t fulfills the null chain condition with the null chain length p or we always have nk≠ nk+1, therefore p(t) = ∞ in which case we say that t does not fulfill the null chain condition [4]. theorem (2.1): if t = i-k, k )e(r∈ , then nk is closed, dim nk < ∞ for all k = 0,1,2…, and t satisfies the null chain condition. we now verify the corresponding statements for image spaces: bk is closed: in case k = 1, we must show that y 1b∈ , y 1b∈ , in other words yn=t.xn 1b∈ and yn→y, then we must show that y 1b∈ , if (1) ||ux||glb k nu k 1 −=δ ∈ , then we choose an nu k ∈ , s.t. ||xk-uk|| ≤ 2. :kδ we put vk = xk-uk, then (2) ||vk||≤ 2. :kδ and yk = t.xk = t (vk+uk) = t.vk we first of all show that the sequence {uk}is bounded [5]; otherwise let there exists a subsequence which we again denote by {vk} s.t. ||vk|| ∞→ for k ∞→ . for wk = ||v|| v k k . the sequence (3) {t.wk} =       =       ||y|| y ||v|| v .t k k k k converges to 0. since {yk} converges by assumption. since {wk} is a boundend s.t, {k.wk} contains a convergent subsequence {k. jkw }. then by (3) it follows that jkw = (i-k) jkw + k. jkw z→ . and also by (3) lim t. jkw = t.z = 0, hence 1nz∈ from which it follows that. ||wk-z|| = z v ux k kk − − = )z.||v||u(x. ||v|| 1 kkk k +− ≥ ||v|| k kδ ≥ 2 1 n.p.sah / bibechana 9 (2013) 126-129 : bmhss, p.128 (online publication: nov., 2012) since uk + ||vk||.z 1n∈ . this contradicts that lim jkw = z : hence {vk} is bounded. therefore the sequence {k. vk }contains a convergent subsequence {k. ikv } and the sequence{ ikv }= {t. ikv +k. ikv }={ ii kk u.ky + } converges to an element v. it follows that iky = ikv k ikv →v k.v = t.v, hence y = t.v 1b∈ [6]. then from above equation (3) it follows that bk is closed also for k>1. theorem (2.2) a) if t∈l(x) fulfills the null chain condition with the null chain length p≤m iff nr mb∩ = {0} for some r n∈ holds or: nm = nr+m iff nr mb∩ = {0}, r n∈ b) t∈l(x) fulfills the image chain condition with the image chain length q n≤ iff there exists a component cr to br in x which is contained in nn. or : bn = bn+r iff x = cr ⊕ br⊂ nn + br = x, r n∈ [7]. theorem (2.3): if k ),e(r∈ then ∞<−β=−α )ki()ki( , k possesses a representation k = r+s with rs= sr = 0, r )e(r∈ and s )e(r∈ ; i – k possesses a representation (i-r)-s with (i-r)s = s(ir), where i-r possesses a continuous inverse on e. definition (1.2): l φ∈ is called eigenvalue of s ∈l(x), x an arbitrary vector space, if there exists an x∈x, x 0≠ s.t. (s l.i).x = 0, therefore 0)i.ls( >−α , x is then called eigensolution corresponding to l; n(s-l.i) is called the eigenspace corresponding to l and )i.ls( −α the multiplicity of l. theorem (2.4): if k∈r(e), then for every 0≠λ , then a) )ik()ik( λ−β=λ−α b) )ik(q)ik(p λ−=λ− c) )ik(b λ− is closed d) ik λ− is open e) the eigenvalues of k form, provided they are infinite in number, a null sequence. theorem (2.5): if if k∈l(e), then every 0≠λ , then a) )ik()ik( λ−β=λ−α b) )ik(q)ik(p λ−=λ− c) ik λ− is relatively regular. d) the eigenvalues of k form a null sequence, provided they are infinite in number. 3. conclusions k∈l(e) is called a rieszoperators if ik λ− possesses the properties (a) – (e) of theorem (2.4) for each φ∈λ . again k∈l(e) is a riesz operator iff for every 0≠λ , it has the properties (a) – (d) of theorem (2.5). thefore, every compact operator is always a riesz-operator. references [1] a.e. taylor: introduction to functional analysis, new-york john wiley and sons inc london (1956). n.p.sah / bibechana 9 (2013) 126-129 : bmhss, p.129 (online publication: nov., 2012) [2] a.p. robertson and w. robertson: topological vector spaces cambridge university press (1964). [3] j.l kelley: general topology, d.van nostrand, new york (1955). [4] conway, john.b: a course on functional analysis springer, verlang (1985). [5] g. kothe, topological vector space, i and ii, springer, verlang, (1969). [6] m.m. day: normed linear spaces, berlin, springer, verlang, (1958). [7] r.g. cooke: linear operators, macmillan, london, (1953). further readings [8] a.g. ramm, american mathematical monthly journal, (2001) 81. [9] t. kato: perturbation theory for linear operators, springer, verlang (1966). microsoft word n.a. rathar_28-32_.doc n. a. rather and faroz ahmad / bibechana 9 (2013) 28-32 : bmhss, p.28 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana on the critical points of a polynomial n a rather, faroz ahmad * department of mathematics, university of kashmir * corresponding author: email: farozmaths1080@gmail.com article history: received 25 march, 2012; accepted 13 august, 2012 abstract let denote the set of all polynomials of the form with and , . in this paper, we show that in for all polynomials . for , this reduces to a result due to aziz and zargar. keywords: polynomial, critical point; sendove conjecture; walish coincidence theorem. 1. introduction the gauss-lucas theorem states that if s is the set of zeros of a polynomial , then every zero of the derivative is contained in the smallest convex set that contains s. this is best possible, in the sense that, if has all its zeros in , then no proper subset of can be guaranteed to contain even one zero of , (as is shown by the polynomial of the form , since has zeros only at , which can lie anywhere in ). gauss-lucas theorem has been rather thoroughly investigated [8] and sharped in several ways. however, there is one related question that deserves attention, namely given one specific zero of , what can be said about a neighborhood of that will always contain a zero of . n. a. rather and faroz ahmad / bibechana 9 (2013) 28-32: bmhss, p.29 (online publication: nov., 2012) the following conjecture was made by bulgarian mathematician b l sendov in 1962 but became later known as ilief’s conjecture (see [4, problem 4.5] or [6, p.795]) . conjecture 1. let be a polynomial of degree having all its zeros in the unit disk . if is any one of these zeros, then has at least one zero in the disk . since in 1962, when it is first became known, conjecture 1 has been the subject of more than thirty articles. however, it was fully verified only for polynomials of degree (see [13]). a variety of special cases have been dealt with over the years (see [2, 7, 11] for references), among which we mention that of a polynomial with at most five distinct zeros [5], as well as miller’s qualitative result [10], according to which those zeros of lying sufficiently close to the unit circle satisfy an even stronger condition that the one stated in sendov’s conjecture (see also [12]). another stronger conjecture than that of ilief was made in 1969 by goodman, rahman and ratti [3]. conjecture 2. let be a polynomial of degree having all its zeros in the unit disk . if is any one of these zeros, then has at least one zero in the disk conjecture 2 has been proved when [3], but some counter examples have been devised for case by m. j. miller [10]. recently aziz and zargar [2] have proved the following result . theorem a. if is a polynomial of degree with , , then does not vanish in . in this paper we establish a generalized form of above theorem. in fact we prove the following interesting result which extracts that portion of complex plane in which the above polynomial does not vanish. theorem 1. let be a polynomial of degree with and , , then does not vanish in the disk n. a. rather and faroz ahmad / bibechana 9 (2013) 28-32: bmhss, p.30 (online publication: nov., 2012) . the result is best possible as shown by the polynomial , further taking we get theorem a. by using a similar argument, we can prove the following more general result. theorem 2. let be a polynomial of degree with and , where then has fold zero at and remaining zeros of lie in the region . the result is best possible as shown by the polynomial , . for the proof of this theorem we need the following lemma which is the coincidence theorem of walish [8, p.62] (see also [1]). lemma. let be a symmetric -linear form of total degree in and let c be a circular region containing the points , then there exists at least one point belonging to c such that . proof of theorem 2. by hypothesis, where and let , then is a polynomial of degree , having all its zeros in and we have . this implies . n. a. rather and faroz ahmad / bibechana 9 (2013) 28-32: bmhss, p.31 (online publication: nov., 2012) if now is any zero of , then from , we get (2) this is an equation which is linear and symmetric in the zeros of that is, in . hence an application of the above lemma with circular region shows that will also satisfy the equation obtained by substituting into the equation (2) , where is suitably chosen point in the circular region . that is satisfies the equation or equivalently . thus has the values or , where is suitably chosen point in . if , then using the fact that , it follows that if then clearly thus in any case since is an arbitrary zero of , it follows that every zero of lie in the disk this completes the proof of theorem 2. corollary . if we take in theorem 2, we get theorem 1. n. a. rather and faroz ahmad / bibechana 9 (2013) 28-32: bmhss, p.32 (online publication: nov., 2012) references [1] a. aziz, pacific j. math., 118 (1985) 17-26. [2] aziz and zargar, aus. math. soc., 57 (1998) 173-174. [3] a. w. goodman, q. i. rahman and j. s. ratti, proc. amer. math . soc., 21 (1969) 273-274. [4] w. k. hayman, research problems in function theory, athlone press london (1967). [5] s. kumar and b. g. shenoy, j. math. anal. appl., 171 (1992) 595-600. [6] m. marden, much ado about nothing, amer. math. monthly, 83 (1976)788-789. [7] m. marden, amer. math. monthly, 90 (1983) 267-276. [8] m. marden, geometry of polynomials, iind edition math. surveys, 3. amer .math. soc., providence, rhode island (1966). [9] a. meir and a. sharma, pacific j. math., 31 (1969) 459-467. [10] m. j. miller, j. math. anal. appl., 175 (1993) 632-639. [11] g. schmeisser, math. z., 156 (1977) 165-173. [12] v.vajaitu and z. zaharesen, london. math. soc., 25 (1993) 49-54. [13] jonny e. brown and guangping xiang, proof of the sendov conjecture for polynomials of degree at most eight (1965) [14] z. rubinstien, pacific j. math., 26 (1968) 159-161. microsoft word bibechana _final_.doc 1 bibechana vol. 6, march 2010 regular associated solution model for the estimation of heat of mixing of binary liquid alloys d. adhikari a , b.p. singh a , i.s. jha b a univ. dept. of physics, t.m.bhag. university, bhagalpur, bihar, india b dept. of physics, m.m.a.m. campus (tribhuvan university), biratnagar, nepal abstract we have determined the equilibrium constants and pairwise interaction energies between the species and the complexes of liquid cusn, agal and fesi, alloys on the basis of regular associated solution model. these parameters are then used to estimate the heat of mixing of each alloy. the observed asymmetry in the heat of mixing of each alloy with respect to concentration is well explained. key words: free energy of mixing; asymmetry; binary alloys, interaction energy 1. introduction several models have been proposed to solve the difficulties and complexities of obtaining thermodynamic parameters. one of the models successfully used for accounts of the thermodynamic characteristics of binary liquid alloy systems, is the model of regular associated solution model. in regular associated solution model, it is assumed that strong associations among the constituent species exist in the liquid phase close to the melting temperature. these associations are given different names such as 'complexes', 'pseudomolecules', 'clusters', 'associations' etc. this assumption has been used by several researchers [1-12] to explain the asymmetry of the properties of mixing for binary alloys. thus binary alloys in a liquid phase can be considered as a ternary mixture of unassociated atoms of components and complexes, all in chemical equilibrium. jordan [3] proposed that activity of unassociated atoms and the complexes can be estimated by treating the mixture as a ternary system and termed this mixture as regular associated solution. jordan [3] applied this idea in the congruently melting semiconductors zn-te and cd-te and determined thermodynamic equations for liquidus curve (the melting temperature against concentration curve) of these alloys. this model is further extended and applied by other researchers [4, 5, 12] for the determination of thermodynamics and microscopic parameters of different alloy systems in molten state. in present paper, we intend to apply regular associated solution model to obtain the heat of mixing of liquid cusn, agal and fesi alloys. for this, we have assumed cu3sn ,ag3al and 2 d. adhikari et al. fe2si complexes in liquid cusn, agal and fesi alloys respectively by studying their corresponding phase diagram in solid state[13]. theoretical formalism is given in section 2, section 3 deals with the numerical result and discussion. conclusion is provided in section 4. 2. theory suppose there be three species in equilibrium in the liquid alloy, namely, monomers a, b and apb molecules in the respective concentrations ,n,n ba and apbn moles. considering a solution of 1n atoms of a and 2n atoms of b, the formation of apbn complex requires apba1 pnnn += and apbb2 nnn += for conservation of mass in the partially associated solution. when there is association, the thermodynamic behaviour of complexes a and b components is governed by their true mole fractions ax , bx and apbx rather than their gross mole fraction 1x and 2x , where )nn/(nx 2111 += etc. and )nnn/(nx apbbaaa ++= etc. using above relations, the two sets of mole fractions are related to each other by the relations apb21a xpxxx −= , apb22b x)px1(xx −−= (1) in regular associated solution solutions, the gross chemical potentials of components 1 and 2 are equal to the chemical potentials of the monomeric species a and b [14]. the activity coefficients aγ , bγ and apbγ of monomers and complex can be expressed in terms of pairwise interaction energies through [3] )ωωω(xxωxωxγlnrt 132312apbb13 2 apb12 2 ba +−++= (2a) )ωωω(xxωxωxγlnrt 121323apba12 2 a23 2 apbb +−++= (2b) )ωωω(xxωxωxγlnrt 231213apbb23 2 b13 2 apba +−++= (2c) where 12ω , 13ω and 23ω are interaction energies for the species a, b ; a, apb and b, apb respectively, t the temperature and r stands for the universal gas constant. the equilibrium constant in a regular associated can be obtained [6] as ]x)px1(x[ rt ]x)x1(px[ rt ]x)x1(px[ rtx xx lnkln bbapb 23 aaapb 13 abb 12 apb b p a −− ω +−− ω ++− ω +         = (3) 3 bibechana vol. 6, march 2010 now using the equations listed above the integral excess free energy xs g∆ is given by klnrt )px1( x )xlnxxlnx(rt)xlnxxlnxxlnx( )px1( rt )xxxxxx( )px1( 1 g apb apb 2211apbapbbbaa apb 23apbb13apba12ba apb xs + ++−++ × + +ω+ω+ω + =∆ (4) once the expressions for g∆ )]xlnxxlnx(rtg[ 2211 xs ++∆= is obtained, heat of mixing can be found using standard thermodynamic relation p,t t g∆ tg∆h∆         ∂ ∂ −= (4a) the pairwise interaction energies and equilibrium constant are determined by the following method: in a regular associated solution aa11 γxγx = and bb22 γxγx = , where 1γ and 2γ are respective gross activity coefficients of components 1 and 2. thus 1 a a1 x x lnlnln +γ=γ (5a) and 2 b b2 x x lnlnln +γ=γ (5b) the pairwise interaction energies, the equilibrium constants and the activity coefficients at infinite dilution can be written as [9] rt ln 120 1 ω =γ (6a) o 2 o 1 o 2 o 1 13 γγ γγ )rt/ωexp(k − = (6b) where o γ1 and o γ 2 are activity coefficients of component a and that of b at zero concentrations. solving equations (2a) and (2b) we obtain 2 apb 12 bb a 1 b b 2 b 13 x rt )x1(x x a ln)x1( x a lnx rt ω −−      −+      = ω (7) 2 apb 12 aa b 2 a a 1 a 23 x rt )x1(x x a ln)x1( x a lnx rt ω −−      −+      = ω (8) using equations (6), (16) and (17), we can derive         +         −      +              + =+ apb 2 p 112 b 2 apb b a 1 apb a13 x aa ln rt ω x a ln x x x a ln x x1 rt ω kln (9) 4 d. adhikari et al. 3. results and discussion to find heat of mixing of binary alloys, we have found the complex concentration in a regular associated solution of respective alloys by using equations (6), (9) and observed data of corresponding activities [13]. the complex concentration of liquid alloys in molten state are presented in table 1. we have found the equilibrium constants and the pairwise interaction energies between the species and the complexes using equations (3), (4), (6), (7), (8), and observed data of corresponding integral excess free energies of mixing. the equilibrium constants and pairwise interaction energies of different binary alloys are listed in table 2. 3.1 cusn alloys at 1400k it is found from the analysis that the heat of mixing is negative at all concentration. our theoretical calculation shows that the minimum value of the heat of mixing is -4.95 kj at cux = 0.8 which exactly matches with the experimental value [1]. further it is observed that the concentration dependence of asymmetry in h∆ can be explained only when one considers the temperature dependence of the pairwise interaction energies. the agreement between the calculated and experimental values is also good. the calculated and observed values of heat of mixing are compared in figure 1. figure-1: free energy of mixing (∆hrt) versus xcu of liquid cusn solution (1400k) ;(–––) theory, (○○○) experiment [13] 5 bibechana vol. 6, march 2010 3.2 agal alloys at 1273k it is found from the analysis that the enthalpy of mixing is negative at all concentration, being minimum around stoichiometric composition ( h∆ = -0.611rt at xag = 0.72). further it is observed that the concentration dependence of asymmetry in h∆ can be explained only when one considers the temperature dependence of the pairwise interaction energies. the calculated and observed values heat of mixing is compared in figure 2. figure-2: free energy of mixing (∆h/rt) versus xag of liquid agal solution (1273k); (––––) theory, (○○○) experiment [1] 3.3 fesi alloys at 1873k it is found from the analysis that the heat of mixing is negative at all concentration. our theoretical calculation shows that the minimum value of the heat of mixing is -2.585 kj at fex = 0.55. further it is observed that the concentration dependence of asymmetry in h∆ can be explained only when one considers the temperature dependent of the 6 d. adhikari et al. pairwise interaction energies. figure 3 show the comparison between the experimental and calculated values of heat of mixing and entropy of mixing. figure-3: free energy of mixing (∆g/rt) versus xfe of liquid fesi solution (1873k); (––––) theory, (○○○) experiment [13] table 1 xcu/ xag/ xfe sncux 3 alagx 3 sifex 2 0.1 0.001095 0.008257 0.01635 0.2 0.008378 0.03075 0.05294 0.3 0.02658 0.0656 0.1086 0.4 0.05146 0.1138 0.1869 0.5 0.08541 0.1803 0.2903 0.6 0.1240 0.2517 0.3337 0.7 0.1525 0.3075 0.3720 0.8 0.1650 0.2355 0.2968 0.9 0.1192 0.1056 0.1098 -3 -2.5 -2 -1.5 -1 -0.5 0 0.2 0.4 0.6 0.8 1 r t / h ∆ fex 7 bibechana vol. 6, march 2010 table 2 liquid alloy systems parameter cusn at 1400k agal at 1273k fesi at 1873k k 0.1652 0.0494 0.004139 12ω (jmol -1 ) -13500 -11382 -64170 13ω (jmol -1 ) -24900 -617 -14720 23ω (jmol -1 ) -16500 -28064 -45500 4. conclusion the regular associated solution model is found to be suitable to estimate the heat of mixing for both weakly and strongly interacting binary liquid alloys. the observed asymmetries in the heat of mixing of binary liquid alloys with respect to the concentrations are well explained on the basis of regular associated solution models. acknowledgement one of the authors (d. adhikari) is thankful to university grant commission (ugc), nepal, for providing financial support to pursue the research. references [1] bhatia, a.b. and hargoove, w.h. 1974.phys. rev. b-10:316 . [2] singh, r.n. 1987. can j. phys. 65: 309. [3] jordan, a.s. 1970. metall. trans. 1:239. [4] lele, s.and ramchandra rao, p. 1981. metall. trans. 12 b: 659. [5] osmura, k. and predel , b. 1977. tans. j. phys. inst. met. 18 :765 . [6] k. hoshino and w.h. young, j. of phys. f: met. phys. 10,1365 (1980). [7] mcalister, s.p. and crozier, e.d. 1974. j. of phys. c-7:3509. 8 d. adhikari et al. [8] jha, i.s. ,singh, r. n. shrivastava ,p.l. and mitra, n.r. 1990.phil. mag. 61:8445. [9] singh, r. n. , jha, i.s. and pandey, d.k. 1993.j. condens. matter 5: 2469 . [10] bhatia,a.b. and singh, r. n. 1980.phys. letters a-78:460 . [11] gerling, u. pool ,m. j. and predel, 1983.b. z. metallkde 74:616 . [12] adhikari, d., jha, i.s. and singh, b. p. 2010.physica b405 :1861 . [13] hultgren, r. desai, p. d.,hawkins, d.t., gleiser, m. and kelley, k.k. (asm,metal park,1973).selected values of the thermodynamic properties of binary alloys [14] prigogine, i. and defay, r. ,( longmans green and co.london, 1974) chem. thermodynamicsp.257. microsoft word editorial.doc editorial bibechana, volume 9 has been published. the aim of the journal bibechana” is to offer a forum to the scientists, academicians and researchers to exchange and explore recent advancement in science and technology. it is the matter of great pleasure for us that we are receiving very encouraging responses from the scientists, academicians and researchers which is reflected in the contents of the journal. we are grateful to the referees, authors and readers for their noble contribution to the journal. devendra adhikari, ph.d. editor-in-chief 123-127 ajaya bhattarai-chom nath adhikari r c o s t n a. bhattarai et al. / bibechana 11(1) (2014) 1 a multidisciplinary journal of science, technology and mathematics journal homepage: http://nepjol.info/index.php/bi study of critical micelle concentration of bromide (ctab) in pure wa sulphate and sodium sulph ajaya bhattarai*, ghanashyam s department of chemistry, m.m.a.m. c *corresponding author: e accepted for publication: february the precise measurement of specific conductivity of cetyltrimethylammonium bromide room temperature was reported and also the specific conductivity of cetyltrimethylammonium bromide measured in the presence of magnesium sulphate and sodium sulphate using a conductivity meter. the critical micelle concentration of three systems was calculated. the compar keywords: conductivity meter; cetyltrimethylammonium bromide concentration; sodium sulphate 1. introduction cetyltrimethylammonium bromide (ctab) is a highly effective cationic surfactant in daily life. ctab type of compound is found in high concentration in industrial products like detergents industries. the charge on the head group of ctab is positive that is why the surfactant is said to be cationic surfactants. due to the positive charge of the head group, cationic surfactants strongly adsorb on the negatively charged surfaces such as fabric, hair and cell membr softeners, hair conditioners and antibacterial agents. the iupac name of cetyltrimethylammoniumbromide is hexadecyltrimethylammonium bromide having molecular weight 364.45 and it has structure in the shielding of the electrostatic repulsion by the counterions [1]. chung kcl and alcohol on the cmc of cetylpyridinium chloride (cpc). they observed the decrease in the addition of electrolyte and vice versa. in this paper, we report a study of the aggregation process of ctab at room temperature in absence and in presence of sodium sulphate and magnesium sulphate by conductivity method in aqueous media. figure / bibechana 11(1) (2014) 123-127: (online publication: march, 2014) p.1 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana ritical micelle concentration of cetyltrimethylammonium romide (ctab) in pure water in presence and absence of magnesium ate and sodium sulphate by measuring conductivity meter ajaya bhattarai*, ghanashyam shrivastav, chom nath adhikari department of chemistry, m.m.a.m. c., tribhuvan university, biratnagar, nepal *corresponding author: e-mail: bkajaya@yahoo.com accepted for publication: february 18, 2014 abstract the precise measurement of specific conductivity of cetyltrimethylammonium bromide (ctab) in distilled water at reported and also the specific conductivity of cetyltrimethylammonium bromide measured in the presence of magnesium sulphate and sodium sulphate using a conductivity meter. the critical micelle concentration of three systems was calculated. the comparison of cmc among them was also performed. © 2014 rcost: all rights reserved. cetyltrimethylammonium bromide; specific conductivity; sulphate; magnesium sulphate. cetyltrimethylammonium bromide (ctab) is a highly effective cationic surfactant in daily life. ctab type of compound is found in high concentration in industrial products like detergents industries. the e on the head group of ctab is positive that is why the surfactant is said to be cationic surfactants. due to the positive charge of the head group, cationic surfactants strongly adsorb on the negatively charged surfaces such as fabric, hair and cell membrane of bacteria. therefore they are used as a fabric softeners, hair conditioners and antibacterial agents. the iupac name of cetyltrimethylammoniumbromide is hexadecyltrimethylammonium bromide having it has structure in fig.1. the effect of inorganic salt is explained in terms of the shielding of the electrostatic repulsion by the counterions [1]. chung et al.[1,2] studied the effect of kcl and alcohol on the cmc of cetylpyridinium chloride (cpc). they observed the decrease in the addition of electrolyte and vice versa. in this paper, we report a study of the aggregation process of ctab at room temperature in absence and in presence of sodium sulphate and magnesium sulphate by conductivity method in aqueous media. figure 1: cetyltrimethylammonium bromide : (online publication: march, 2014) p.123 cetyltrimethylammonium ter in presence and absence of magnesium ate by measuring conductivity meter biratnagar, nepal (ctab) in distilled water at reported and also the specific conductivity of cetyltrimethylammonium bromide was measured in the presence of magnesium sulphate and sodium sulphate using a conductivity meter. the critical ison of cmc among them was also performed. © 2014 rcost: all rights reserved. ; critical micelle cetyltrimethylammonium bromide (ctab) is a highly effective cationic surfactant in daily life. ctab type of compound is found in high concentration in industrial products like detergents industries. the e on the head group of ctab is positive that is why the surfactant is said to be cationic surfactants. due to the positive charge of the head group, cationic surfactants strongly adsorb on the negatively ane of bacteria. therefore they are used as a fabric the iupac name of cetyltrimethylammoniumbromide is hexadecyltrimethylammonium bromide having the effect of inorganic salt is explained in terms of [1,2] studied the effect of kcl and alcohol on the cmc of cetylpyridinium chloride (cpc). they observed the decrease in cmc with in this paper, we report a study of the aggregation process of ctab at room temperature in absence and in presence of sodium sulphate and magnesium sulphate by conductivity method in aqueous media. a. bhattarai et al. / bibechana 11(1) (2014) 123-127: (online publication: march, 2014) p.124 2. experimental section conductance measurements were carried out on a pye-unicam pw 9509 conductivity meter at a frequency of 2000 hz using a dip-type cell with a cell constant of 1.15 cm-1 and having an uncertainty of 0.01 %. the cell was calibrated by the method of lind and co-workers [3] using aqueous potassium chloride solution. several independent solutions were prepared and runs were performed to ensure the reproducibility of the results. due correction was made for the specific conductance of the solvent by subtracting the specific conductance of the relevant solvent medium from those of the surfactant solutions. cetyltrimethylammonium bromide (ctab) was purchased from loba chemical, india. mgso4 and na2 so4 were purchased from ranbaxy chemical, india. the water used in the experiments was doubly distilled. the solutions prepared at room temperature. 3. results and discussion the specific conductivities of ctab solution increase with increasing the concentration of ctab. there is sharp break in which two straight lines intersect. that point of intersection is known as critical micelle concentration (cmc). the electrical conductivity of a cationic surfactant certltrimethylammonium bromide in distilled water was reported (table 1). the sodium ion (na+) is larger than the magnesium ion (mg2+) due to two effects. the elements sodium and magnesium are in the same period, therefore outer electrons of the mg atom experience greater effective nuclear charge and, more importantly, the magnesium cation, mg2+, has a greater cationic charge than the na+ cation. this second effect is by far the more significant. the conductivities of ctab in presence of na2so4 is more than in presence of mgso4 because the smaller ions are strongly hydrated, so they need to pull more water molecules with them which makes them less mobile. hence the conductivity values of ctab in presence of na2so4 are high in comparison with mgso4 as shown in table 1 (a&b). in water, the cmcs of ctab were reported [4] to be 1.007 mm from conductometry, and 1.102 mm from tensiometry respectively at 308.15 k which verifies our experimental data of cmc of ctab at room temperature (table 2). figures (2-4) show the cmc of ctab in absence and in presence of na2so4 and mgso4. also, the cmc values of ctab in absence and presence of na2so4 and mgso4 at room temperature are shown in table 2. as the salt is added, the electrostatic repulsive force between ionic head groups of the surfactant molecules is reduced by shielding of micelle charge, so that spherical micelles are more closely packed by the surfactant ions [5,6], hence a decrease in the cmc values after adding salts. it is observed that salts decrease the cmc of ionic surfactants [7] due to screening of the electrostatic repulsion among the polar head groups and movement of the hydrophobic alkyl chain away from aqueous environment, so that less electrical work is required to form micelles. salts decrease the cmc in the order: mgso4< na2so4. here mg+ + is least effective in decreasing the cmc due to small size and large hydrated radius and would act as a water-structure promoter decreasing the availability of water to the micelles. therefore, upon addition of mgso4 and na2so4 in ctab, na2so4 is more effective in reducing the cmc of ctab. hence in our case na2so4 decreases the cmc of ctab more than mgso4 (table 2). a. bhattarai et al. / bibechana 11(1) (2014) 123-127: (online publication: march, 2014) p.125 table 1: conductance of ctab in distilled water at room temperature. solvent concentration (mol/ltr) conductance (ohm-1cm-1) distilled water 0.00436 0.00313 0.00224 0.00161 0.00115 0.00083 0.00059 0.00042 0.00030 0.00022 0.00015 0.00011 0.283 0.251 0.226 0.205 0.185 0.174 0.160 0.151 0.142 0.136 0.128 0.121 table 1a: conductance of ctab in presence of na2so4 -water at room temperature. solvent concentration (mol/ltr) conductance (ohm-1cm-1) na2so4-water 0.00600 0.00503 0.00410 0.00310 0.00262 0.00210 0.00169 0.00136 0.00108 0.00088 0.00068 0.00055 0.00044 0.00035 0.00028 0.00018 1.820 1.812 1.805 1.790 1.793 1.789 1.786 1.783 1.781 1.779 1.778 1.777 1.776 1.771 1.768 1.764 a. bhattarai et al. / bibechana 11(1) (2014) 123-127: (online publication: march, 2014) p.126 table 1b: conductance of ctab in presence of mgso4 -water at room temperature. solvent concentration (mol/ltr) conductance (ohm-1cm-1) mgso4-water 0.00671 0.00537 0.00429 0.00343 0.00275 0.00171 0.00140 0.00112 0.00091 0.00075 0.00057 0.00046 0.00036 1.867 1.829 1.790 1.758 1.739 1.704 1.691 1.684 1.677 1.672 1.661 1.651 1.646 fig. 2 fig.3 figure 2: specific conductivities of ctab as a function of the concentration in distilled water at room temperature. figure 3: specific conductivities of ctab as a function of the concentration in na2so4-water at room temperature. 0 0.1 0.2 0.3 0.4 0.5 0 0.001 0.002 0.003 0.004 0.005 cmc =1.10mm concentration (mol/l) c on du ct an ce ( oh m -1 cm -1 ) 1.76 1.78 1.80 1.82 1.84 1.86 0 0.002 0.004 0.006 cmc =0.31mm concentration (mol/l) co du ct an ce ( oh m -1 cm -1 ) a. bhattarai et al. / bibechana 11(1) (2014) 123-127: (online publication: march, 2014) p.127 figure 4: specific conductivities of ctab as a function of the concentration in mgso4-water at room temperature. table 2: critical micelle concentration (cmc) obtained from conductometry of ctab in absence and presence of na2so4 and mgso4 in aqueous media at room temperature. distilled water cmc (mm) na2so4-water cmc (mm) mgso4-water cmc (mm) 1.10 0.31 0.63 4. conclusion the following conclusions have been drawn from above result and discussions. the results showed an increase in conductivity of cetyltrimethylammonium bromide with addition of salts. the conductance of cetyltrimethylammonium bromide is found more in presence of na2so4 than mgso4 in aqueous media whereas in the presence of na2so4, the cmc of cetyltrimethylammonium bromide decreases more in comparison with presence of mgso4. references [1] j. j. chung, s. w. lee, j. h. choi, bull. kor. chem. soc., 12 (1991) 411. [2] j. j. chung, s. w. lee, y. c. kim, bull. kor. chem. soc., 13 (1992) 647. [3] j. e. jr. lind, j. j. zwolenik, r. m. fuoss, j. am. chem. soc., 81 (1959) 1557. [4] t. chakraborty, i. chakraborty, s. ghosh, langmuir, 22 (2006) 9905. [5] d.varade, t. joshi, v.k. aswal, p. s. goyal, p.a. hassan, p. bahadur, colloids and surfaces a: physicochem. eng. aspects, 25 (2005) 95. [6] h.n.singh, s. swarup, s.m. saleem, j. colloid and interface. sci., 68 (1979) 128. [7] l. zang, p. somasundaran, c. maltesh, langmuir, 12 (1996) 2371. 1.6 1.7 1.8 1.9 0 0.002 0.004 0.006 0.008 cmc =0.6mm concentration (mol/l) co nd uc ta nc e (o hm -1 cm -1 ) microsoft word i. koirala _130-135_.doc i. koirala et al. / bibechana 9 (2013) 130-135 : bmhss, p.130 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana thermodynamic and structural properties of k-na liquid alloy i. koirala 1,2 , i. s. jha 3 , b. p. singh 1* 1 university department of physics, t.m. bhagalpur university, india 2 central department of physics, tribhuvan university, nepal 3 m.m.a.m. campus, biratnagar, tribhuvan university, nepal * corresponding author: e-mail : bhrigunandansingh@yahoo.com article history: received 2 october, 2012; accepted 16 november, 2012 abstract the deviation from ideal mixture behavior and concentration dependent symmetry in thermodynamic and structural properties of k-na liquid alloy is investigated within a simple statistical model. the concentration dependence of the free energy of mixing, heat of mixing, entropy of mixing, concentration fluctuation in the long wavelength limit, warren-cowley short range order parameter, ratio of diffusion coefficients of potassium-sodium alloy at 384 k and activity of the components has got special attention to show a tendency of like atom pairing in the mixture. key words: liquid alloy; simple statistical model; thermodynamic properties; diffusion coefficient 1. introduction the properties of mixing of some binary alloys such as, free energy of mixing, heat of mixing, entropy of mixing are symmetrical about the equiatomic composition [1] even though there is large size difference. such behaviour of these liquid alloys is least understood and demands extensive theoretical investigations. since long theoreticians [2-8] are trying to interpret the physical properties of liquid alloys so that their alloying behaviour could adequately be understood. in the present work we intend to explain the alloying behaviour (the free energy of mixing (gm), heat of mixing (hm), entropy of mixing (sm)) of potassium-sodium liquid alloy on the basis of simple statistical model. thermodynamic parameters give us an idea about the stability and bonding strength of the constituent species of the alloy, whereas structural parameters provide the idea about ordering and segregating nature of the alloy. some of the properties of mixing of k-na alloys are symmetrical about equiatomic composition despite the large size difference of na and k [1]. i. koirala et al. / bibechana 9 (2013) 130-135 : bmhss, p.131 (online publication: nov., 2012) the outline of the paper is follows: in section 2, general formalism about the theory is presented. section 3 deals with the result and discussion and conclusion are presented in section 4. 2. formalism simple statistical model developed by singh and mishra [8] for the binary liquid alloys is a model in which grand partition function is used. the grand partition function is solved by assuming that the energy of a given nearest neighbour bond is different if it belongs to the complex than if it does not .the grand partition function for simple binary liquid alloys can be generalized as ) tk enn (exp)t(q)t(q b bbaa e n b n a ba −µ+µ =ξ ∑ (1) where in iq are the partition functions of atoms ( borai = ) associated with inner and vibrational degree of freedom. qi is the same whether the atom i is located in the pure state or in alloy. µa and µb are the chemical potentials; e is the configurational energy; kb, the boltzmann constant and t, the absolute temperature. the standard thermodynamical relation for free energy of mixing is [8] i i ib xs mm clnctnkgg ∑+= (2) but excess of free energy of mixing is bbaa c 0 z b xs m lnclncdcln tnk g γ+γ=σ= ∫ (3) where ( ) c2/)tzk/wexp(1c2 b−−+β=σ 3(a) [ ] 2/z aaa )1(c/)c21( β++−β=γ 3(b) [ ] 2/z bab )1(c/)c21( β+−+β=γ 3(c) [ ]{ } 2/1 bba 1)tzk/w2exp(cc41 −+=β 3(d) using the relations (2) and (3), the free energy of mixing will be )c1ln()c1(clnc tk w )c1(c[tnkg b bm −−++−= or, )c1ln()c1(clnc tk w )c1(c rt g b m −−++−= (4) the warren-cowley chemical short range order parameter 1α for the first coordination shell [9,10] in term of w is 1)tzk/w2exp( cc)1( b ba 2 1 1 −= α− α (5) for the equiatomic composition ( 2 1 cc ba == ), relation (3) reduces to i. koirala et al. / bibechana 9 (2013) 130-135 : bmhss, p.132 (online publication: nov., 2012) 2/z b 2/z b xs m )]tzk/wexp(1[2ln tnk g −−+= (6) from eq. (4), the concentration fluctuation in the long wavelength limit becomes 1 n,p,t2 m 2 bcc ) c g (tnk)0(s − ∂ ∂ = 1 ba )]1)(2/z(1[cc −β−β+= (7) from eqs. (5) and (7), it follows that ]1)1z(s/[)1s(1 +−−=α (8) where, )0(s )0(s cc )0(s s id cc cc ba cc == and z represents the number of atoms in the first coordination shell and is called coordination number. the heat of mixing of binary liquid alloys can be obtained using the standard thermodynamic relation (4): p,n m mm ) t g (tgh ∂ ∂ −= ] dt dw k 1 )c1(c tk w )c1(c[rt bb −−−= (9) the entropy of mixing is t gh ) t g (s mm p,n m m − = ∂ ∂ −= (10) the activity of binary liquid alloys, ai, can be related to the free energy of mixing by the relation n,p,t i m ib ) n g (alntnk ∂ ∂ = (11) the mixing behavior of the alloy forming molten metals can also be studied at the microscopic level in terms of coefficients of diffusion. the scc(0) and diffusion coefficients can be related using darken thermo dynamic equation for diffusion [11] as follows: )0(s )0(s d d cc id cc id m = (12) here idd is the intrinsic diffusion coefficient for an ideal mixture and md is the chemical or mutual diffusion coefficient given by abbam dcdcd += (13) where da and db are the self-diffusion coefficients of pure components a and b respectively. i. koirala et al. / bibechana 9 (2013) 130-135 : bmhss, p.133 (online publication: nov., 2012) 3. results and discussion 3.1 thermodynamic properties the energy parameter used for the calculation for k-na liquid alloys at 384k has been determined from experimental value of xs mg and hm for equiatomic composition (c =1/2 ), using the equations (6) and(9) which are found as 989.0 tk w b = and 077.0 dt dw k 1 b = fig. 1 : free energy of mixing (gm/rt) , heat of mixing (hm/rt) and entropy of mixing (sm/r) versus concentration of na (cna) : theoretical solid curve; experimental circles. fig. 2 : chemical activities (ai) versus concentration of na (cna) : theoretical solid curve; experimental circles. i. koirala et al. / bibechana 9 (2013) 130-135 : bmhss, p.134 (online publication: nov., 2012) the free energy of mixing, heat of mixing and entropy of mixing for k-na liquid alloy at 384k have been computed from equations (4), (9) and (10). the plot of rt/g m , rt/h m and r/sm versus cna are depicted in fig. 1. the theoretical and experimental values of rt/g m , rt/h m and r/sm are in good agreement in all concentrations of na. rt/g m is minimum but rt/h m and r/sm are each maximum at cna =0.5, which show that k-na liquid alloy is symmetric about equiatomic concentration. we have used the same values of the energy parameters in eq. (11) for the evaluation of chemical activities of the components of the alloy. there is well agreement between experimental and theoretical values of the activities of the components k and na of the alloy (fig. 2). 3.2 structural properties ( microscopic properties ) using the estimated energy parameter, the theoretical values of scc(0) are computed from eq. (7). fig. 3 shows a plot of the theoretical and experimental values of scc(0) along with the ideal values. the theoretical values of scc(0) are in good agreement with the experimental values of scc(0). the result can be used to understand the nature of atomic order in binary liquid alloys. at a given composition if )0(s)0(s id cccc < , ordering in liquid alloy is expected while )0(s)0(s id cccc > gives the indication of tendency of segregation. fig. 3 : concentration fluctuation (scc(o)) versus concentration of na (cna) : theoretical solid curve; experimental – circles; idealcrosses and warren –cowley sro parameter ( 1α ) versus concentration of na (cna) the knowledge of α1 provides an immediate insight into the nature of the local arrangement of atoms in the mixture. the minimum possible value of α1 is -1 and it indicates complete ordering of unlike atom pairing at nearest atoms. on the other hand the maximum value of α1 is +1, which implies complete segregation leading to phase separation and α1= 0 corresponds to a random distribution of atoms. figure 3 shows that α1 is positive, maximum at 5.0cna = and )0(s)0(s id cccc > throughout whole concentration range of na, showing that k-na liquid alloy at 384k is segregating.the scc(0) are used in eq. (12). to evaluate the ratio of the mutual and i. koirala et al. / bibechana 9 (2013) 130-135 : bmhss, p.135 (online publication: nov., 2012) intrinsic-diffusion coefficients, id m d d . the value of id m d d is less than 1 in the entire range of concentration (fig.4) which is indicative for the phase separation in the mixture. fig. 4 : diffusion coefficient ratio (dm/did) versus concentration of na (cna) 4. conclusion the thermodynamic and structural properties of the regular k-na alloy at 384k in liquid state are examined on the basis of simple statistical model. the analysis suggests that there is a tendency of like atom pairing in k-na alloy in the whole range of concentration. acknowledgment i.p. koirala would like to acknowledge dr. devendra adhikari, department of physics, m.m.a.m. campus, biratnagar (tribhuvan university) nepal for fruitful suggestions and inspiring discussions. references [1] r. hultgren, p. d. desai, d. t. hawkins, m. gleiser, and k. k. kelly, selected values of the thermodynamic properties of binary alloys, asm, metal park, ( 1973), p. 1057. [2] j. flory, j. chem. phys., 10 (1942) 51. [3] s. lele and p. ramchandrarao, metall. trans., 12 b (1981) 659. [4] a.s. jordan, metall. trans., 1 (1970) 239. [5] d. adhikari, i.s. jha. b.p. singh, physica b, 405 (2010) 1861. [6] a.b. bhatia and w.h. hargoove, phys. rev. b, 10 (1974) 3186. [7] i.s. jha, r.n. singh, p.l. shrivastava, n.r. mitra, philos. mag., 61 (1990) 15. [8] r.n.singh, i.k.mishra, v.n. singh, j.phys.: condensed matter, 2 (1990) 8457. [9] b.e.warren, x-ray diffraction, reading ma: addison-wesley, (1969), p.227. [10] j.m. cowley, phys. rev., 77 (1950) 667. [11] l.s. darken, r.w. gurry physical chemistry of metals, mcgraw hill, new york (1953), p. 535. microsoft word kabita jha et al _28-33__corrected.doc kabita jha et al. / bibechana 10 (2014) 52-57 : bmhss, p.52 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana surface tension studies on the micellization of cetyltrimethylammonium bromide in presence and absence of kcl and nacl in aqueous media at room temperature kabita jha, ajaya bhattarai *, sujeet kumar chatterjee department of chemistry, mahendra morang adarsh multiple campus tribhuvan university, biratnagar, morang, nepal * e-mail: bkajaya@yahoo.com article history: received 30 august, 2013; accepted 5 october, 2013 abstract precise measurements on surface tension of cetyltrimethylammonium bromide in presence and in absence of kcl and nacl in aqueous media are reported. the results showed a sharp decrease in surface tension with increase in concentration of cetyltrimethylammonium bromide and then almost constant value of surface tension was observed. also, the surface tension decreases with addition of salts. the surface tension of cetyltrimethylammonium bromide is found more in presence of kcl than nacl in aqueous media. in presence of monovalent salts, the critical micelle concentration (cmc) value decreases which is explained on the basis of the orientation of the surfactant and reduction of the free energy of the surface, thus decreasing surface tension. the graphs of surface tension versus concentration are used in determining the critical micelle concentration (cmc). keywords: cetyltrimethylammonium bromide, surface tension, critical micelle concentration, aqueous media. 1. introduction the cetyltrimethylammonium bromide (ctab) is a long chain carbon molecule with a polar head group, which is hydrophilic and a hydrophobic carbon tail. the molecular weight of ctab is 364.5 and specific gravity is 0.9. ctab forms spherical micelles above cmc (critical micellar concentration), which is 0.0008 in d2o and is 0.00001 in h2o [1]. the surface of the micelle is charged and is therefore classified as cationic micelle. it is well known that salts (ionic compounds) and non-electrolytes (alcohols, diols, urea, thiourea) can alter the delicate balance of the hydrophobic-hydrophilic interaction of the micelle-forming surfactant in different ways [2-5]. it is, therefore, important to understand the key role of forces that govern the micellization behavior in the presence of various additives. surface tension is a measure of the free energy of the surface per unit area. surfactants are substances which alter the surface properties of liquids, even when present in small quantities. composed of two fractions, a lyophilic group and a lyophobic group, surfactants migrate to the surface, resulting in the lyophilic portion lying within the solution and the lyophobic group orienting itself away from the solution. this orientation of the surfactant reduces the free energy of the surface, thus decreasing surface tension and increasing kabita jha et al. / bibechana 10 (2014) 52-57 : bmhss, p.53 (online publication: dec., 2013) surface viscosity. surfactants reduce the amount of work necessary to create unit surface area i .e. surface tension of a solution is lowered when surfactants are present [6] . the following are a few generalizations regarding surface tension and surfactants, followed by a discussion of surfactants and dynamic surface tension. higher concentrations of surfactants lower the surface tension in comparison to the pure solvent state. the limiting value of surfactant concentration that produces a surface tension decrease is the critical micelle concentration [7]. furthermore; the steeper decrease in surface tension is evident only at high surfactant concentrations. as the temperature increase, the molecular interaction between the liquids molecules are weaker, since hydrogen bond is the main factor for association between two molecules which are very weak bond, so it can be break easily when the temperature increase leading to decrease in surface tension. we found in the literature [8] that surface tension decreases with increasing temperatures. this decrease can be attributed to the higher surface activity at the higher bulk temperatures and adsorption of contaminates in the system was postulated for this anomality. in this paper, we report a study of the aggregation process of ctab at room temperature in absence and in presence of kcl and nacl by surface tension method in aqueous media. 2. experimental surface tension measurements were carried out on a stalagmometer. the surface tension of ctab in absence and presence of salts was measured by drop count method using a stalagmometer. the experimental set up used for determining surface tension by drop count method was of the standard type (stalagmometer) which is an instrument used to determine the surface tension of a liquid. it was designed by troube and consists of a pipette with a capillary outflow to be the end of which is flattened out. this is done to give a larger dropping surface. the surface is carefully ground flat and polished. there are two marks, one just above the bulb a, while the other is just below it. before using the stalagmometer was first carefully washed with a solution of chromic acid and then with distilled water. finally, it was washed with acetone and water and dried. it must be kept in mind that the tip of the lower end should not come in contact with hand, desk or some other thing, as it will be contaminated with trace of grease. slight traces of grease will alter the size of the drops, hence their number. the stalagmometer was held vertical and was not shaken because otherwise the drop will fall out even before attaining its maximum size. in this process, first the stalagmometer was filled with distilled water as above without changing the pressure. then the drop count was started. by following the same process all the liquids or solutions of varied strength of ctab in presence and absence of salt (nacl and kcl) was measured. the calculation of the surface tension was done through the following expression: (1) where, γsoln = surface tension of solution γsolv = surface tension of solvent nsoln = number of drops of solution nsolv = number of drops of solvent dsoln = density of solution dsolv = density of solvent if the surface tension of one of the liquids i.e. known then that of the other can be easily calculated from equation (1). cetyltrimethylammonium bromide (ctab), kcl and nacl were used as purchased from loba chemical, india. the water used in the experiments was doubly distilled. the solutions prepared at kabita jha et al. / bibechana 10 (2014) 52-57 : bmhss, p.54 (online publication: dec., 2013) room temperature (301.15 k). all the measurements were carried out at the same temperature i.e. room temperature. 3. results and discussion a linear decrease in surface tension was observed with increase in surfactant (ctab) concentration up to cmc. the cmc of the surfactant decreased in the presence of nacl and kcl, the decrease being depended upon the concentration of added salt. when an increasing amount of the surfactant is added then the concentration of surfactant on water interface increases. this is manifested as beginning until the concentration at which the cooperative interaction between the surfactant and salt first occurs indicating the onset of the micelle formation. the surface concentration of the surfactant does not increase because all added surfactant associates with salt. this results in a flat part in the surface-tension log [surfactant] curve. this invariance of surface tension with log [surfactant] thus terminates at a surfactant concentration at which the salt becomes saturated by the surfactant and the surface tension starts to decrease again. a concentration of surfactant is finally reached beyond which addition of the surfactant can hardly affect the surface tension of the solution. this inflection marks the surfactant concentration where all the added surfactant starts to form the surfactant micelles. when surfactant and salt are mixed in solution, salting-out phenomenon often happens [9-12]. according to hydration theory [13] salting-out is the result of preferential movement of water molecules, which immobilize and quench their role as solvents, from coordination shells of surfactant molecules to those of salts. the effects of halide salts on the growth of micelles in ionic surfactant solutions have been systematically studied [14,15]. with the addition of inorganic salts, the reduced electrostatic repulsion among the surfactant head groups is a key factor to influence the morphology of aggregates in ionic surfactant solutions. for conventional single-chain cationic surfactants, micelles may change from global to rod like or wormlike with the addition of inorganic salts [16,17]. the surface tension and cmc of ctab in presence of kcl is more than in presence of nacl because the valence and structure of salts play an important role in the aggregation behavior of cationic surfactants. inorganic salts affect surfactant aggregation mainly through reducing the electrostatic interaction among the surfactant head groups, and k + is more efficient to promote the aggregation of the surfactant than na+. thus, the cmc of surfactant in kcl is less than in nacl. in tensiometry, the cmc’s were the threshold surfactant concentrations required to saturate the air/solution interface and were obtained from the sharp breaks in the surface tension ( ) versus log [surfactant] profiles respectively. it is observed that in a given salt-water mixture, the cmc of pure ctab decreases . two factors must be considered to explain this significant influence of salts on the cmc value of ctab: (a) the presence of salt increases the cohesive energy density, or the solubility parameter, of water, thus decreases the solubility of the monomeric form of the surfactant and hence the cmc, and (b) the cosolvent causes an increment in the relative permittivity of the aqueous phase, favouring the mutual attraction of the ionic heads in the micelle, thus supporting micellisation and decreasing the cmc. kabita jha et al. / bibechana 10 (2014) 52-57 : bmhss, p.55 (online publication: dec., 2013) 25 35 45 55 -4.0 -3.5 -3.0 -2.5 log[ctab] γ (d y n e /c m ) fig.1: variation of with log[ctab] for ctab in distilled water at room temperature 22 24 26 28 30 -4.0 -3.5 -3.0 -2.5 log[ctab] γ (d y n e /c m ) fig. 2: variation of with log[ctab]for ctab in nacl at room temperature kabita jha et al. / bibechana 10 (2014) 52-57 : bmhss, p.56 (online publication: dec., 2013) 23.0 24.5 26.0 27.5 29.0 30.5 -3.4 -3.2 -3.0 -2.8 log[ctab] γ (d y n e /c m ) fig.3: variation of with log[ctab]for ctab in kcl at room temperature table 1. the critical micellar concentratiom (cmc) obtained from surface tension of cetyltrimethylammonium bromide in aqueous media at 301.15 k t (k) water cmc (mm) 0.01 mol.l-1 nacl cmc (mm) 0.01 mol.l-1 kcl cmc (mm) 301.15 k 0.95 0.87 0.76 4. conclusions the following conclusions have been drawn from above results and discussion. the results showed an decrease in surface tension of cetyltrimethylammonium bromide with concentration and addition of salts. the surface tension of cetyltrimethylammonium bromide is found more in presence of kcl than nacl in aqueous media. also, in the presence of kcl, the cmc of cetyltrimethylammonium bromide decreases more in comparison with presence of nacl. kabita jha et al. / bibechana 10 (2014) 52-57 : bmhss, p.57 (online publication: dec., 2013) acknowledgements one of the authors (kabita jha) is thankful to the university grant commission (ugc), nepal, for providing grants for m. sc. thesis work and we are grateful to associate professor g.s. shrivastav, head of the department of chemistry, mahendra morang adarsh multiple campus,tribhuvan university, biratnagar for providing the research facilities to conduct this research work. references 1. m. e cates and s. j. candau, j. phys condens matter, 2 (1990) 6869 . 2. g.calvaruso, f. p. cavasino., c. sbriziolo and m. liria turco liveri, j. chem soc faraday trans, 89 (1993) 1373. 3. c. c ruiz and f.g. sanchez, j. colloid interface sci., 165 ( 1994) 110. 4. c. c. ruiz. , colloid polymer sci., 273(1995) 1033. 5. k. gracie, d. turner and r. palepu. , can.j.chem., 74 (1996) 1616. 6. m. austin, b .b. bright and e .a. simpson , j. colloid and interface sci., 23( 1967) 108 . 7. j .a. caskey and w .b. barlage jr., j . colloid and interface sci., 35 (1971) 46. 8. e. tornberg , j. colloid and interface sci., 60(1977) 50. 9. p. mukerjee and c. c. chan, langmuir, 18 ( 2002) 5375. 10. y. defeng, x. huang, m. deng, y. lin, l. jiang, j. huang and yi. wang, j. phys. chem. b, 114 (2010) 14955. 11. f. a. long,and w. f. mcdevit, chem. rev., 51(1952)119. 12. l.wattebled and a. laschewsky, langmuir, 23( 2007)10044. 13. p. k. grover, and r. l. ryall, chem. rev., 105( 2005) 1. 14. m. l. corrin, and w. d. harkins, j. am. chem. soc., 69 (1947) 683. 15. v. k. aswal, and p. s. goyal, chem. phys lett., 364 (2002) 44. 16. j.h.mu, g.z. li, x. l. jia, h.x. wang and g.y. zhang, j. phys chem b, 106 ( 2002) 11685. 17. a. khatory, f. lequeux., f. kern and s. j. candau, langmuir, 9 ( 1993) 1456. microsoft word main.doc 22 narendra kumar chaudhary food additives narendra kumar chaudhary m.m.a.m. campus, biratnagar, tribhuvan university, nepal abstract different types of food additives have been discussed. i have discussed the role of food additives to preserve nutritional values and to maintain desired consistency of the product. the antioxidants and antimicrobials food preservatives have also been studied. keywords: food additives; preservatives; colorants; sweeteners introduction various chemical substances added to foods to produce specific desirable effects are called food additives. additives such as salt, spices, and sulfites have been used since ancient times to preserve foods and make them more palatable. with the increased processing of foods in the 20th century, there came a need for both the greater use of and new types of food additives. many modern products, such as low-calorie, snack, and ready-to-eat convenience foods, would not be possible without food additives. food additives and their metabolites are subjected to rigorous toxicological analysis prior to their approval for use in the industry. feeding studies are carried out using animal species (e.g., rats, mice, dogs) in order to determine the possible acute, short-term and long-term toxic effects of these chemicals. the lowest level of additive producing no toxicological effects is termed the no-effect level (noel). there are four general categories of food additives: nutritional additives, processing agents, preservatives, and sensory agents. nutritional additives nutritional additives are utilized for the purpose of restoring nutrients lost or degraded during production, fortifying or enriching certain foods in order to correct dietary deficiencies, or adding nutrients to food substitutes. the fortification of foods began in 1924 when iodine was added to table salt for the prevention of goitre. vitamins are commonly added to many foods in order to enrich their nutritional value. for example, vitamins a and d are added to dairy and cereal products, several of the b vitamins are added to flour, cereals, baked goods, and pasta, and vitamin c is added to fruit beverages, cereals, dairy products, and confectioneries. other nutritional additives include the essential fatty acid linoleic acid, minerals such as calcium and iron, and dietary fibre. processing agents a number of agents are added to foods in order to aid in processing or to maintain the desired consistency of the product. several of these agents are discussed in more detail below. emulsifiers are used to maintain a uniform dispersion of one liquid in another, such as oil in water. the basic structure of an emulsifying agent includes a hydrophobic portion, usually a long-chain fatty acid, and a hydrophilic portion that may be either charged or uncharged. the hydrophobic portion of the emulsifier dissolves in the oil phase and the hydrophilic portion dissolves in the aqueous phase, forming a dispersion of small oil droplets. emulsifiers thus form and stabilize oil-in 23 bibechana vol. 6, march 2010 water emulsions (e.g., mayonnaise), uniformly disperse oil-soluble flavour compounds throughout a product, prevent large ice crystal formation in frozen products (e.g., ice cream), and improve the volume, uniformity, and fineness of baked products. stabilizers and thickeners have many functions in foods. most stabilizing and thickening agents are polysaccharides, such as starches or gums, or proteins, such as gelatin. the primary function of these compounds is to act as thickening or gelling agents that increase the viscosity of the final product. these agents stabilize emulsions, either by adsorbing to the outer surface of oil droplets or by increasing the viscosity of the water phase. thus, they prevent the coalescence of the oil droplets, promoting the separation of the oil phase from the aqueous phase (i.e., creaming). chelating, or sequestering, agents protect food products from many enzymatic reactions that promote deterioration during processing and storage. preservatives food preservatives are classified into two main groups: antioxidants and antimicrobials. antioxidants are compounds that delay or prevent the deterioration of foods by oxidative mechanisms. antimicrobial agents inhibit the growth of spoilage and pathogenic microorganisms in food. antioxidants the oxidation of food products involves the addition of an oxygen atom to or the removal of a hydrogen atom from the different chemical molecules found in food. two principal types of oxidation that contribute to food deterioration are autoxidation of unsaturated fatty acids and enzyme catalyzed oxidation. the autoxidation of unsaturated fatty acids involves a reaction between the carbon-carbon double bonds and molecular oxygen (o2). the products of autoxidation, called free radicals, are highly reactive, producing compounds that cause the off-flavours and off-odours characteristic of oxidative rancidity. antioxidants that react with the free radicals (called free radical scavengers) can slow the rate of autoxidation. these antioxidants include the naturally occurring tocopherols (vitamin e derivatives) and the synthetic compounds butylated hydroxyanisole (bha), butylated hydroxytoluene (bht), and tertiary butylhydroquinone (tbhq). specific enzymes may also carry out the oxidation of many food molecules. the products of these oxidation reactions may lead to quality changes in the food. for example, enzymes called phenolases catalyze the oxidation of certain molecules (e.g., the amino acid tyrosine) when fruits and vegetables, such as apples, bananas, and potatoes, are cut or bruised. the product of these oxidation reactions, collectively known as enzymatic browning, is a dark pigment called melanin. antioxidants that inhibit enzyme-catalyzed oxidation include agents that bind free oxygen (i.e., reducing agents), such as ascorbic acid (vitamin c), and agents that inactivate the enzymes, such as citric acid and sulfites. antimicrobials antimicrobials are most often used with other preservation techniques, such as refrigeration, in order to inhibit the growth of spoilage and pathogenic microorganisms. sodium chloride (nacl), is probably the oldest known antimicrobial agent. organic acids, including acetic, benzoic, propionic, and sorbic acids, are used against microorganisms in products with a low ph. nitrates and nitrites are used to inhibit the bacterium clostridium botulinum in cured meat products. sulfur dioxide and sulfites are used to control the growth of spoilage microorganisms in dried fruits, fruit juices, and 24 narendra kumar chaudhary wines. nisin and natamycin are preservatives produced by microorganisms. nisin inhibits the growth of some bacteria while natamycin is active against molds and yeasts. sensory agents colorants colour is an extremely important sensory characteristic of foods; it directly influences the perception of both the flavour and quality of a product. the processing of food can cause degradation or loss of natural pigments in the raw materials. in addition, some formulated products, such as soft drinks, confections, ice cream, and snack foods, require the addition of colouring agents. colorants are often necessary to produce a uniform product from raw materials that vary in colour intensity. colorants used as food additives are classified as natural or synthetic. natural colorants most natural colorants are extracts derived from plant tissues. the use of these extracts in the food industry has certain problems associated with it, including the lack of consistent colour intensities, instability upon exposure to light and heat, variability of supply, reactivity with other food components, and addition of secondary flavours and odours. in addition, many are insoluble in water and therefore must be added with an emulsifier in order to achieve an even distribution throughout the food product. synthetic colorants synthetic colorants are water-soluble and are available commercially as powders, pastes, granules, or solutions. special preparations called lakes are formulated by treating the colorants with aluminum hydroxide. they contain approximately 10 to 40 percent of the synthetic dye and are insoluble in water and organic solvents. lakes are ideal for use in dry and oil-based products. the stability of synthetic colorants is affected by light, heat, ph, and reducing agents. a number of dyes have been chemically synthesized and approved for usage in various countries. all synthetic colorants have undergone extensive toxicological analysis. brilliant blue fcf, indigo carmine, fast green fcf, and erythrosine are poorly absorbed and show little toxicity. extremely high concentrations (greater than 10 percent) of allura red ac cause psychotoxicity, and tartrazine induces hypersensitive reactions in some persons. flavourings the flavour of food results from the stimulation of the chemical senses of taste and smell by specific food molecules. taste reception is carried out in specialized cells located in the taste buds. the four basic taste sensations—sweet, salty, bitter, and sour—are detected in separate regions of the tongue, mouth, and throat because the taste cells in each region are specific for certain flavour molecules. in addition to the four basic tastes, the flavouring molecules in food stimulate specific olfactory (smell) cells in the nasal cavity. these cells can detect more than 10,000 different stimuli, thus fine-tuning the flavour sensation of a food. a flavour additive is a single chemical or blend of chemicals of natural or synthetic origin that provides all or part of the flavour impact of a particular food. these chemicals are added in order to 25 bibechana vol. 6, march 2010 replace flavour lost in processing and to develop new products. flavourings are the largest group of food additives, with more than 1,200 compounds available for commercial use. natural flavourings are derived or extracted from plants, spices, herbs, animals, or microbial fermentations. artificial flavourings are mixtures of synthetic compounds that may be chemically identical to natural flavourings. artificial flavourings are often used in food products because of the high cost, lack of availability, or insufficient potency of natural flavourings. flavour enhancers are compounds that are added to a food in order to supplement or enhance its own natural flavour. the concept of flavour enhancement originated in asia, where cooks added seaweed to soup stocks in order to provide a richer flavour to certain foods. the flavour-enhancing component of seaweed was identified as the amino acid l-glutamate, and monosodium glutamate (msg) became the first flavour enhancer to be used commercially. the rich flavour associated with l-glutamate was called umami. umami is often considered the fifth basic taste because it is distinctly different from the other basic tastes (sweet, salty, sour, and bitter) and it is believed to activate a separate set of taste receptors. other compounds that are used as flavour enhancers include the 5′-ribonucleotides, inosine monophosphate (imp), guanosine monophosphate (gmp), yeast extract, and hydrolyzed vegetable protein. flavour enhancers may be used in soups, broths, sauces, gravies, flavouring and spice blends, canned and frozen vegetables, and meats. sweeteners sucrose or table sugar is the standard on which the relative sweetness of all other sweeteners is based. because sucrose provides energy in the form of carbohydrates, it is considered a nutritive sweetener. other nutritive sweeteners include glucose, fructose, corn syrup, high fructose corn syrup, and sugar alcohols (e.g., sorbitol, mannitol, and xylitol). efforts to chemically synthesize sweeteners began in the late 1800s with the discovery of saccharin. since then, a number of synthetic compounds have been developed that provide few or no calories or nutrients in the diet and are termed nonnutritive sweeteners. these sweeteners have significantly greater sweetening power than sucrose, and therefore a relatively low concentration may be used in food products. in addition to saccharin, the most commonly used nonnutritive sweeteners are cyclamates, aspartame, and acesulfame k. the sensation of sweetness is transmitted through specific protein molecules, called receptors, located on the surface of specialized taste cells. all sweeteners function by binding to these receptors on the outside of the cells. the increased sweetness of the nonnutritive sweeteners relative to sucrose may be due to either tighter or longer binding of these synthetic compounds to the receptors. nonnutritive sweeteners are primarily used for the production of low-calorie products including baked goods, confectioneries, dairy products, desserts, preserves, soft drinks, and tabletop sweeteners. they are also used as a carbohydrate replacement for persons with diabetes and in chewing gum and candies to prevent dental caries (i.e., tooth decay). unlike nutritive sweeteners, nonnutritive sweeteners do not provide viscosity or texture to products, so that bulking agents such as polydextrose are often required for manufacture. toxicological analysis of the nonnutritive sweeteners has produced variable results. high concentrations of saccharin and cyclamates in the diets of rats have been shown to induce the development of bladder tumours in the animals. because of these results, the use of cyclamates has been banned in several countries and the use of saccharin must include a qualifying statement regarding its potential health risks. however, no evidence of human bladder cancer has been reported with the consumption of these sweeteners. both aspartame and acesulfame k are relatively safe, with no evidence of carcinogenic potential in animal studies. 26 narendra kumar chaudhary references 1. r. macrae, r.k. robinson and m.j. sadler (eds.), encyclopaedia of food science, food technology, and nutrition, vol. 8 (1993); 2. y.h. hui (ed.), encyclopedia of food science and technology, vol. 4 (1992), 3 p. fellows, food processing technology: principles and practices (1988), 4. a. larry branen, p. michael davidson, and seppo salminen (eds.), food additives (1990), 5. t. e. furia (ed.), crc handbook of food additives, 2nd ed., 2 vol. (1972, reissued 1980), 6. j. a. maga and t. anthony tu (eds.), food additive toxicology (1995), 7. t. smith (ed.), food additive user's handbook (1991), b r c o s t n k. jha et al. / bibechana 11(1) (2014) 131-135: (online publication: march, 2014) p.131 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana determination of critical micelle concentration of cetyltrimethylammonium bromide in presence and absence of kcl and nacl in aqueous media at room temperature by viscosity measurement kabita jha, ajaya bhattarai*, sujeet kumar chatterjee department of chemistry, m.m.a.m.c., tribhuvan university, biratnagar, nepal *corresponding author: e-mail: bkajaya@yahoo.com accepted for publication: february 16, 2014 abstract viscosity measurement of cetyltrimethylammonium bromide in presence and in absence of kcl and nacl in aqueous media is done. the results showed a sharp increase in viscosity with increase in concentration of cetyltrimethylammonium bromide. also, the viscosity increases with addition of salts. the viscosity of cetyltrimethylammonium bromide is found more in presence of kcl than nacl in aqueous media. in presence of monovalent salts, the critical micelle concentration (cmc) value decreases which is explained on the basis of nature and ionic strength of the added ion. the graphs of viscosity versus concentration are used in determining the critical micelle concentration (cmc). © 2014 rcost: all rights reserved. keywords: cetyltrimethylammonium bromide; viscosity; critical micelle concentration. 1. introduction surfactant solutions exhibit complex behavior even at equilibrium. above a critical micelle concentration, several tens of surfactant molecules aggregate to form micelles since the formation of micelles is entropically favorable as compared to a system of unassociated surfactant molecules in solution [1]. micelles could exist in various shapes such as cylindrical, spherical or lamellar depending on the temperature and surfactant concentration in solution [1-6]. micelle formation of a surfactant in solution is induced by the hydrophobic interaction between hydrocarbon parts of the surfactant molecules balanced by their hydration and electrostatic repulsive effects [7]. cationic surfactants offer some additional advantages over other class of surfactants [8–11]. these substances besides their surface activity do show antibacterial properties and are used as cationic softeners, lubricants, retarding agents and antistatic agents and in some cases consumer use. aqueous solution of ctab becomes extremely viscous on addition of small quantity of sodiumsalicylate (nasal). the viscosity of 0.1m ctab with 0.03m nasal is about 1017 centipoise. a similar increase in viscosity is observed with addition of kcl, kbr or nacl with five times higher concentration [12]. the mechanism responsible for this large change in viscosity is expected to be different in two cases [13, 14]. like all other surfactants ctab also shows a rapid change in viscosity when the physical and chemical compositions of the solution are changed. this rise in viscosity has been mainly attributed to the change in the structure of the ctab micelles depending upon the ambient condition to which it has been subjected. the structure change from spherical to rod like phases have been predicted [15]. in order to mailto:bkajaya@yahoo.com k. jha et al. / bibechana 11(1) (2014) 131-135: (online publication: march, 2014) p.132 understand these phenomena considerable research studying have been done and reported. the cmc of ctab depends directly upon the solvent and it has been determined by berr [13] that ctab forms large micelles in d2o than in h2o. the effective factors, such as the addition of electrolytes, buffer ph, temperature, addition of organic modifiers, ionic strength of the aqueous solution, and presence of additives can change the cmc value from that determined in pure water [16-18]. addition of electrolyte in the surfactant solution decreases the cmc value [19]. addition of an electrolyte causes a reduction in the thickness of ionic atmosphere surrounding the polar head groups which consequently decreases repulsion between them, because of the electroviscous effect which will be absent at high ionic strength. the lower the ionic strength thicker the particles diffuse layer and more evident the effect of reduced viscosity in absence of salt. addition of surfactant to solutions lowers the viscosity dramatically [20-27]. abuin and scaiano [28] showed that this viscosity reduction is far stronger than the simple charge screening resulting from the addition of monovalent salt. in this paper, we report a study of the aggregation process of ctab at room temperature in absence and in presence of kcl and nacl by viscometric method in aqueous media. 2. experimental the viscometric measurements were performed at room temperature using an ostwald viscometer. several independent solutions were prepared, and runs were performed to ensure the reproducibility of the results. to check whether the reduced viscosities depend on the shear rate in the concentration range investigated. this did not lead to different values of the reduced viscosity. solvent medium from those of the surfactant solutions in presence and absence of salt was taken. the viscometer was always suspended vertically at room temperature. the viscometer was cleaned and dried every time before each measurement. the flow time for constant volume of solution through the capillary was measured with a calibrated stop watch. the coefficient of viscosity of a given liquid can be calculated according to the following equation: 2 2 1 2 1 1 t t d d η            =η (1) 1η = coefficient of viscosity of the solution 2η = coefficient of viscosity of the solvent t1 = time flow of the solution t2 = time flow of the solvent d1 = density of the solution d2 = density of the solvent the density of any one solution must be known which is calculated by using the expression: 2 2 1 1 d w wd       = (2) d1 = density of liquid d2 = density of water w1= weight of liquid w2= weight of water cetyltrimethylammonium bromide (ctab), kcl and nacl were used as purchased from loba chemical, india. the water used in the experiments was doubly distilled. the solutions prepared at room temperature. k. jha et al. / bibechana 11(1) (2014) 131-135: (online publication: march, 2014) p.133 3. results and discussion the specific viscosity increase with increase of concentration of ctab and there is a pronounced break and then remains constant. the breaking point is known as critical micelle concentration, cmc (fig. 1-3). our results indicate that there is increase in viscosity with increase in concentration of salt added. fig. 1 fig. 2 figure 1: viscosity of ctab in pure water as a function of the surfactant concentration. figure 2: viscosity of ctab in presence of nacl as a function of the surfactant concentration. figure 3: viscosity of ctab in presence of kcl as a function of the surfactant concentration. the viscosity of ctab in presence of kcl is more than in presence of nacl(table1), this is because while nacl is absorbed on the surface of the micelle, kcl remains in the bulk of the solution [29]. addition of salt is known to decrease cmc of the solution [1]. increasing the salt concentration reduces the electrostatic debye screening length around the surfactant, which encourages the formation of longer micelles at equilibrium. this, in turn contributes to the changes in cmc. fujio (1998) [30] found that spherical micelles associated to form into rod-like micelles when salt concentration exceeded a threshold concentration. salts decrease the cmc of surfactant in the order: nacl<kcl [31]. here na+ is least effective in decreasing the cmc due to small size and large hydrated radius and would act as a water 0.80 0.85 0.90 0.95 0.0005 0.001 0.002 log [ctab] η( m p a s) 0.91 0.93 0.95 0.97 0.0001 0.001 0.01 log[ctab] η( m p a s) 1.10 1.12 1.14 1.16 0.001 0.002 0.003 0.004 0.005 log [ctab] η (µ p a s) k. jha et al. / bibechana 11(1) (2014) 131-135: (online publication: march, 2014) p.134 structure promoter decreasing the availability of water to the micelles. therefore, upon addition of nacl and kcl; kcl is more effective in reducing the cmc. hence in our case kcl decrease the cmc more than nacl(table 2). table 1: viscosity of cetyltrimethylammonium bromide in pure water and in presence of nacl and kcl at room temperature solvent concentration (mol/l-1) viscosity [η (mpa.s)] solvent concentration (mol/l-1) viscosity [η (mpa.s)] pure water 0.003150 0.002713 0.002355 0.002045 0.001762 0.001533 0.001335 0.001164 0.001031 0.000865 0.000749 0.000650 0.000563 0.000488 0.9164 0.9042 0.8924 0.8826 0.8756 0.8683 0.8597 0.8527 0.8478 0.8492 0.8492 0.8492 0.8492 0.8492 kcl 0.002400 0.002100 0.001800 0.001594 0.001314 0.001174 0.000829 0.000773 0.000725 0.000649 0.000553 0.000465 1.1474 1.1400 1.1326 1.1258 1.1167 1.1114 1.1068 1.1069 1.1064 1.1072 1.1066 1.1056 nacl 0.002014 0.001787 0.001592 0.001392 0.001205 0.001029 0.000877 0.000775 0.000649 0.9743 0.9629 0.9543 0.9449 0.9357 0.9273 0.9204 0.9200 0.9194 table 2: critical micelle concentratiom (cmc) obtained from viscosity methods of cetyltrimethylammonium bromide in pure water and presence of nacl and kcl at room temperature t (k) water cmc (mm) 0.01 mol.l-1 nacl cmc (mm) 0.01 mol.l-1 kcl cmc (mm) 301.15 k. (room temperature) 0.99 0.90 0.78 4. conclusion the following conclusions have been drawn from above results and discussion. the results showed an increase in viscosity of cetyltrimethylammonium bromide with addition of salts. the viscosity of cetyltrimethylammonium bromide is found more in presence of kcl than nacl in aqueous media whereas in the presence of kcl, the cmc of cetyltrimethylammonium bromide decreases more in comparison with presence of nacl. k. jha et al. / bibechana 11(1) (2014) 131-135: (online publication: march, 2014) p.135 acknowledgments one of the authors (kabita jha) is thankful to the university grants commission (ugc), nepal, for providing grants for m. sc. dissertation work and the authors are grateful to associate professor g.s. shrivastav, head of the department of chemistry, mahendra morang adarsh multiple campus, tribhuvan university, biratnagar for providing the research facilities to conduct this research work. references [1] i. w. hamley, introduction to soft matter polymers, colloids, amphiphiles and liquid crystals, wiley, england, 2000. [2] k. tsujii, surface activity: principles, phenomena, and applications; academic press, london, 1998. [3] t. f. tardos, surfactants, academic press, london, 1984. [4] r. zana, surfactant solutions:new methods of investigation, mercel dekker, newyork, 1987. [5] w. b. russel, d. a. saville, w. r. schowalter, colloidal dispersions, cambridge university press, cambridge, 1989. [6] a. shen, m. vasudevan, c. lee, y. wang, g. z. cao, r. sureshkumar, hydrodynamics and rheology effects in processing of micellar fluids in nanomaterials manufacturing in soft nanomaterials, edited by h.s. nalwa, american scientific publishers, 2007. [7] c. tanford, the hydrophobic effect-formation of micelles and biological membranes, second edition, wiley, new york, 1980. [8] e. jungerman, cationic surfactants, marcel dekker, new york, 1969. [9] j. cross, e.j. singer, cationic surfactants: analytical and biological evaluation, marcel dekker, new york, 1994. [10] p.m. holland, d.n. rubingh (eds.), cationic surfactants: physical chemistry, marcel dekker, new york, 1991. [11] j.m. richmond, cationic surfactants: organic chemistry, marcel dekker, new york, 1990. [12] p.g. cummins, e. staples, j. b. hayter, j. penfold, j. chem. soc. faraday trans.1, 83 (1987) 1851. [13] s.s. berr. j. phys. chem., 91(1998) 4760. [14] u.r.k. rao, c, manohar, b.s. valaulikar and r.m. iyer. j. phys. chem., 91 (1987)3286. [15] p. ekwall, l.coll. int. sci., 35(1971) 519. [16] k. behara, s. pandey. j colloid interface sci., 316(2007)803. [17] a. d. w. carswell, a. m. lowe, s. wei and b. p. grady. colloids surf a., 212( 2003)147. [18] n. m.saeed, f. t. farshad, a. hossein, a.k. hossein. j. surfact deterg., 16( 2013)271. [19] e. fuguet, c. rafols, m. roses, e. bosch. anal chim acta., 548(2005)95. [20] e. b. abuin, j. c. scaiano. j. am. chem. soc., 106 (1984) 6274. [21] a. asnacios, d. langevin, j. f. argillier. macromolecules, 29(1996)7412. [22] a. asnacios, v. bergeron, d. langevin, j. f. argillier. rev. inst. fr. pet.,52 (1997)139. [23] a. asnacios, d. langevin, j. f. argillier. eur. phys. j. b., 5 (1998)905. [24] a. asnacios, r. klitzing, d. langevin. colloids surf. a., 169(2000)189. [25] k. kogej, j. skerjanc. acta chim. slov., 46(1999)481. [26] k. kogej, j. skerjanc, physical chemistry of polyelectrolytes, marcel dekker, new york, 2001. [27] j. fundin, w. brown, i. iliopoulos and p. m. claaesson. colloid polym. sci.,277(1999)25. [28] e. b. abuin and j. c. scaiano. j. am. chem. soc.,106 (1984)6274. [29] p.s. goyal, b.a. dasannacharya, v.k. kelkar, c. manohar, k.s. rao, b.s. valaulikar. physica,174(1991)196. [30] k. fujio. b. chem. soc. jpn., 71(1998)83. [ 31] k.u. din, r.m. abdul, n. z. andleeb. acta phys. chim. sin., 28(2012)885. 161-164 s.n. sah r c o s t n s. n. sah / bibechana 11(1) (2014) 161-164: (online publication: march, 2014) p.161 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana characterization of frechet spaces with nuclear kothe quotients satya narayan sah department of mathematics m.m.a.m. campus, t.u., biratnagar, nepal e-mail: satyanarayansah33@yahoo.com accepted for publication: february 02, 2014 abstract in this paper our result based on the characterization of frechet spaces with nuclear kothe quotients is in terms of the following condition which labeled as ⍟. we show that a frechet spaces e satisfies condition ⍟ if and only if it has a quotient which admits continuous norm and satisfies condition ⍟. for the condition ⍟, there exists ℓ such that for every k there exists j such that the ‖. ‖� closure of eℓ ′ is not closed in e� ′. © 2014 rcost: all rights reserved. keywords: frechet spaces; kothe spaces; quotient. 1. introduction frechet spaces have played an important role in functional analysis from its very beginning. many linear spaces of holomorfic, differentiable or continuous functions which arise in connection with various problems in analysis and its applications are defined by (at most) countably many conditions, whence they carry a natural frechet topology (if they are, in addition, complete). c. bessaga and a. pelczynski showed that a frechet space fails to admit a continuous norm if it has a subspace isomorphic to ω in 1957 [1]. if a frechet space admits a continuous norm then so does every subspace, which simplifies the problem a little. again, in 1959, bessaga, pelczynski and s. rolewicz showed that a frechet space which admits continuous norm has a nuclear kothe subspace iff it is not banach [2]. thus it follows that, in general, a frechet space has a nuclear kothe subspace iff it has a non-banach subspace which admits continuous norm. if we consider only nuclear frechet spaces, then we are looking for kothe quotients and here the problem has a positive solution: every nuclear frechet space not isomorphic to ω has a kothe quotient. the proof is given in [3]. in the present paper we find some characterization of the frechet spaces with nuclear kothe quotients. in view of the open mapping theorem the condition ⍟ has the following equivalent formulation : ∃ ∋∋ ∃ ∋ l k j sup {ǁ.ǁ'k:uϵel', ǁ.ǁ'j≤1} = ∞ in this form our condition is very close to being a dual to the following condition used by bessaga, pelczynski and rolewicz [4] in thier determination of those frechet spaces which have nuclear kothe subspaces: ∋ k ∃ ∋ j sup {||x||j : x ϵ y, ||x||k ≤ 1} = ∞ for every subspace y of e with finite co-dimension. s. n. sah / bibechana 11(1) (2014) 161-164: (online publication: march, 2014) p.162 it is easy to check that this condition ⍟ is independent of the choice of (ǁ·ǁk). for definitions and notations we refer to the book of g. kothe [5]. some of them which are used in this paper are following: 2. notations e' – the dual of e will be considered to have the strong topology from e e* – the completion of e e''– the dual of e' a0 – the polar in e or e' where a⊆ ⊆ e or a e' ||· ||k – the semi-norm on e, where k = 1,2,3,…….. ||· ||' k – the dual norm on e' (||· ||k) – the fundamental sequence of semi-norms e'k – the banach space determined by the unit ball of the dual norm ||· ||' k on e', where k ϵ n 3. definitions definition 3.1. a frechet space is a metrizable, complete cocally convex vector space [6]. # its topology is defined by an increasing sequence of semi norms (ǁ·ǁ)k called a fundamental sequence of semi-norms. if one of these semi-norms is a norm we say that the space admits continuous norm. # a metrizable topological vector space (tvs) is complete if every cauchy sequence is convergent [5,7]. definition 3.2. nuclear kothe spaces are those frechet spaces which have quotients that are nuclear, admit continuous norm and have a basis. definition 3.3. let a linear subspace m of a linear space e, consider the sets x (m) = x + m = {x + y : y ϵ m} for each element x ϵ e. the collection of these so called equivalence classes becomes a linear space e/m, the quotient space of e by m if x(m) + y(m) = x + y + m = {x + y + z : z ϵ m} and αx(m) = αx + m = {αx + z : z ϵ m} [8,9]. 4. theorems theorem 4.1. (open mapping theorem) if e and f are frechet spaces, a:e→f linear, continuous and surjective, then a is open [6]. theorem 4.2. (bipolar theorem) if e is a locally convex and m ⊂ e absolutely convex then m00 =m[6]. theorem 4.3. if e is a frechet space and m ⊂ e a closed subspace then m and e/m are frechet spaces. corollary 4.4. if e is a frechet space then e' is a complete locally convex space which has a countable fundamental system of bounded sets. s. n. sah / bibechana 11(1) (2014) 1 corollary 4.5. if e is isomorphic to a countable product of banach spaces then e does not have a nuclear kothe quotient. corollary 4.6. every frechet montel space not isomorphic to proof: if e is a frechet montel space then e is separable and reflexive. we will prove that e is not a quojection. let e be the projective limit of the surjections a of ek+1 on to the unit ball of ek . also, since e is not isomorphic to dimensional. then, viewing e as the projective limit, it is easy to see that {(x ek∋k} is closed, bounded subset of e. but the projection of this set in e compact [10,11]. hence the set is not compact in e which is a contradiction. we are now ready for the main result of this paper. proposition 4.6. a frechet space e satisfies condition condition ⍟. proof: suppose that the frechet space e satisfies condition let m = ( )°° which, by the bipolar theorem, is the closure of in prove that e/m° is the desired quotient. at first, we check that e/m° admits continuous norm. for this, let x e/m° induced by ǁ·ǁl, annihilates x + m°. this means that ∃ ⊂(yn) m° ϶ limn ǁx let u ϵ m. then, ∃ � ϵ ϶ |u(x)-v(x)| so we have |u(x)| ≤ |v(x)| + |u(x) v(x)| since v ϵ e'l it follows that lim v(x + yk) = o, so |u(x) by ǁ·ǁl, is a norm. next, we verify condition ⍟ for e/m°. we fix k and let u condition ⍟, we have a sequence (u ~ u� so a fortiori un ∉ (uk + m°)°. moreover, if x |nun(x+ y) | =|nun (x)| hence un ϵ � � (uk+1 + m°)°. thus we have prove m and the unit ball of the dual norm of the norm in e/m° induced by ||· ||k is (uk + m°)°. this proves that e/m° satisfies condition ⍟. now, conversely assume that e/f be a quotient of e. e then by general duality, (e/f)' can be represented as a vector subspace of e' and a fundamental / bibechana 11(1) (2014) 161-164: (online publication: march, 2014) p.163 if e is isomorphic to a countable product of banach spaces then e does not have a nuclear kothe space not isomorphic to ω has a nuclear kothe quotient. if e is a frechet montel space then e is separable and reflexive. we will prove that e is not a quojection. let e be the projective limit of the surjections ak: ek+1→ek . we may assume that ak . also, since e is not isomorphic to ω we may assume that e dimensional. then, viewing e as the projective limit, it is easy to see that {(xk)ϵe: xk is in the unit ball of ed, bounded subset of e. but the projection of this set in el is the unit ball so it is not compact [10,11]. hence the set is not compact in e which is a contradiction. we are now ready for the main result of this paper. ace e satisfies condition ⍟ iff it has a quotient which admits continuous norm and satisfies suppose that the frechet space e satisfies condition . we may take ℓ=1 and j = k + 1fo� ° which, by the bipolar theorem, is the closure of in the weak topology from e. now we prove that e/m° is the desired quotient. at first, we check that e/m° admits continuous norm. for this, let x ϵ e and assume that the seminorm in l, annihilates x + m°. this means that ϶ limn ǁx – yn ǁl = 0. v(x)| ≤ 1. v(x)| ≤ |v(x + yn )|+ 1. it follows that lim v(x + yk) = o, so |u(x)| ≤ 1. this shows x ϵ m°, so the semi for e/m°. we fix k and let uk be the unit ball of ǁ·ǁk in e. since e satisfies we have a sequence (un) ⊂ e'l with ǁunǁ'k > 1 and ǁunǁ'k+1 ≤ � � . this implies that, u + m°)°. moreover, if x ϵ uk+1,y ϵ m°, then as un ϵ m, we have |nun(x+ y) | =|nun (x)| ≤ 1. (uk+1 + m°)°. thus we have proved that un ϵ � � (uk+1+ m°)°~ (uk+m°)°. but, (e/m°)' = m and the unit ball of the dual norm of the norm in e/m° induced by ||· ||k is (uk + m°)°. this proves that now, conversely assume that e/f be a quotient of e. if (uk) is a fundamental sequence of nbds. of 0 for e then by general duality, (e/f)' can be represented as a vector subspace of e' and a fundamental publication: march, 2014) p.163 if e is isomorphic to a countable product of banach spaces then e does not have a nuclear kothe if e is a frechet montel space then e is separable and reflexive. we will prove that e is not a quojection. maps the unit ball we may assume that el is infinite is in the unit ball of is the unit ball so it is not iff it has a quotient which admits continuous norm and satisfies 1for this condition. � the weak topology from e. now we e and assume that the seminorm in m°, so the semi-norm induced in e. since e satisfies . this implies that, un ϵ � � u��� m, we have (uk+1+ m°)°~ (uk+m°)°. but, (e/m°)' = m and the unit ball of the dual norm of the norm in e/m° induced by ||· ||k is (uk + m°)°. this proves that if (uk) is a fundamental sequence of nbds. of 0 for e then by general duality, (e/f)' can be represented as a vector subspace of e' and a fundamental s. n. sah / bibechana 11(1) (2014) 1 sequence of equicontinuous sets for (e/f)' is given by ( with l = 1 and j = k+1) then ∃ (un) u��� � ∽∩ f°) (u� �∩f°) . it follows that un > 1. therefore, e satisfies condition 7. conclusion a frechet space which admits continuous norm has a nuclear kothe subspace if and only if it is not banach. thus it follows that, in general, a frechet space has a nuclear kothe subspace iff it has a non banach subspace which admits continuous norm. references [1] c. bessaga, a. pelczynski, bull. acad. polon. sei. cl. ill [2] c. bessaga, a. pelczynski, s. rolewicz, bull. acad. polon. sei. [3] g.l. litvinov, nuclear space, springer [4] c. bessaga and ed dubinsky, arch math. [5] g. kothe, topological vector space i , spiringer [6] d. vogat, lectures on frechet spaces, bergische universitat wuppertal, sommer semester [7] a.e.taylor, introduction to functional analysis, john willey and sons, inc., london,1961. [8] a. pietsch, nuclear locally convex space, springer [9] a.p. robertson, w. robertson, topological vector spaces, cambridge university press, 1964. [10] ed dubinsky, springer-verlag, berlin and new york [11] v.b. moscatelli, bull. london math. soc. [12] l. holmstrom, journal of functional analysis [13] ed. dubinsky, w. robinson, studia math [14] w. sliwa, trans. amer. math. soc. [15] w. sliwa, bull. belg. math. soc. simon stevin / bibechana 11(1) (2014) 161-164: (online publication: march, 2014) p.164 equicontinuous sets for (e/f)' is given by ( u� �∩+-f°) k. so if e/f satisfies condition ) ⊂ f° and a sequence of constants (cn) with un ϵ (c f°) . it follows that unϵ e'l, ||un||'k+1 ≤ but since un ϵ f° then un > 1. therefore, e satisfies condition ⍟. a frechet space which admits continuous norm has a nuclear kothe subspace if and only if it is not . thus it follows that, in general, a frechet space has a nuclear kothe subspace iff it has a non banach subspace which admits continuous norm. [1] c. bessaga, a. pelczynski, bull. acad. polon. sei. cl. ill, 4 (1957) 375. elczynski, s. rolewicz, bull. acad. polon. sei., 9 (1961) 677. [3] g.l. litvinov, nuclear space, springer-verlag, 2001. [4] c. bessaga and ed dubinsky, arch math., 31 (1978) 597. [5] g. kothe, topological vector space i , spiringer-verlag, 1969. at, lectures on frechet spaces, bergische universitat wuppertal, sommer semester [7] a.e.taylor, introduction to functional analysis, john willey and sons, inc., london,1961. [8] a. pietsch, nuclear locally convex space, springer-verlag berlin heidelberg, new york,1972. [9] a.p. robertson, w. robertson, topological vector spaces, cambridge university press, 1964. verlag, berlin and new york, 720 (1979) 123. [11] v.b. moscatelli, bull. london math. soc., 12 (1980) 63. [12] l. holmstrom, journal of functional analysis, 348 (1982) 12. dubinsky, w. robinson, studia math, 63 (1978) 267. trans. amer. math. soc., 362 (2010) 3273. [15] w. sliwa, bull. belg. math. soc. simon stevin, 14 (2007) 1017. publication: march, 2014) p.164 f°) k. so if e/f satisfies condition ⍟ (say ϵ (cnu� � ∩ f°) ∩ ( ∉ u� � ; so || un ||'k a frechet space which admits continuous norm has a nuclear kothe subspace if and only if it is not . thus it follows that, in general, a frechet space has a nuclear kothe subspace iff it has a nonat, lectures on frechet spaces, bergische universitat wuppertal, sommer semester, 2000. [7] a.e.taylor, introduction to functional analysis, john willey and sons, inc., london,1961. berlin heidelberg, new york,1972. [9] a.p. robertson, w. robertson, topological vector spaces, cambridge university press, 1964. microsoft word b. c. kumar-_33-37_.doc b.c. kumar et al. / bibechana 9 (2013) 33-37 : bmhss, p. 33 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana temperature dependence of knight shift for the metals zn and al b. c. kumar * , s. m. rafique, b. p. singh university department of physics, t.m. bhagalpur university, bhagalpur * corresponding author: e-mail : bimal_ckumar@yahoo.com article history: received 22 october, 2012; accepted 4 november, 2012 abstract we have studied the variation of knight shift with temperature using pseudopotential technique for zn and al metals. knight shift occurs due to the hyperfine contact interaction between the nucleus and surrounding conduction electrons. the computed values of zinc is obtained using h-eigen values with α = αvt and β = 1 gives k= 0.374 against kexp = 0.337 at 419 0 c and 0.391 against kexp = 0.399 at 500 0 c. for aluminium with h-eigen values and β = 1 gives k= 0.199 whereas kexp = 0.164 at 360 0 c and k= 0.209 at 400 0 c for kexp = 0.184 have been found. the computed values and experimental values are in good agreement for both metals. it reveals that the knight shift increases with increasing temperatures for zn and al. keywords: pseudopotential; knight shift; h-eigen values 1. introduction it is observed that nuclear magnetic resonance (nmr) associated with a metallic state is higher than the corresponding frequency for non-metallic state. this shift of the nmr frequency is known as the knight shift and this occurs due to the hyperfine contact interaction between the nucleus and the surrounding conduction electrons. the ratio of the frequency shift to the frequency at which the nmr is observed for the metallic state is known as knight shift (k). the hyperfine interaction between conduction electron and nuclear moment in metals provides a rich array of properties that can be studied through nuclear magnetic resonance technique (1-2). although the experimental technique of the measurement of knight shift had been developed much earlier, its theoretical development was developed much later. the previous theoretical work [3-4] on the magnetic properties of metals substantiates the view that like electrical resistivity, the nearly free electron approximation is also valid for the theoretical treatment of various magnetic properties viz,, knight shift, magnetic susceptibility, hall coefficient etc. the study of the plethora of literature on pseudopotential theory and specially harrison’s first principle technique brings out the fact that this property has not been studied through this technique except by singh [5] who has applied it to some multivalent liquid metals. we propose to proceed on this line for the investigation of the knight shift of metals under investigation for which the experimental data is available. it is interesting to note that the previous authors (seymour and styles 1966, heighway and seymour 1971, ford and styles 1972) have observed that the orbital effect of the electrons also contributes even in the b.c. kumar et al. / bibechana 9 (2013) 33-37: bmhss, p.34 (online publication: nov., 2012) simple metals. the experimentally measured knight shift [2] for various metals shows insignificant change in it due to melting. heine (1957) first obtained a simple expression for the knight shift of metals in solid phase. but opw method has only been used by gerstner and cutler (1969) for ba and singh (1988) for mg, al and ga. reasonable qualitative agreement has been obtained for the metals under investigation. due to various approximations involved in the formalism of knight shift and that of the form factor exact agreement is not expected. in the next sections we are presenting the formalism, result and significant observations. 2. formalism in this section of our study the precise theory within the framework of pseudopotential technique is presented. the knight shift [7] may be written as ωχ      π = fp p 3 8 k (1) here pχ is the spin paramagnetic susceptibility of conduction electron per unit volume, ω is the volume of the crystal and fp the average electron density at the site of the nucleus from the conduction electrons with energy fe . this electron density is represented by an average of the form, ∑ ψ= − j 2 ik 1 f )r(np f (2) where, ir is the position vector of the ith ions, n is the total number of ions and fkψ are the electron wave functions. in opw approximation the wave function is expressed in terms of the pseudo wave function )r(kφ and )r(αψ . the core wave function is written as, ( ) ( )      ψφψ−φ=ψ ∑ α αα r,)r(c)r( kkkk (3) here, kc is the normalization factor. since the psedopotential is very weak in nature we can expand kφ according to the first order perturbation theory, ' k 0 kk φ+φ=φ (4) where, )r.kiexp( 10 k −ω=φ (5) ∫ + + φ −π ω =φ 0 qk qkk 3 ' k ee )q,k(w)q(dqa 8 (6) using the above analogy we can express the electron density as, ' f 0 ff ppp += (7) similarly the knight shift may also be written as, 10 kkk += (8) the variation of )r( fk φ in the core region is small. thus the equations (2), (3) and (6) may be used to obtain ∫ +−π ω =φ qd ee )q(a)q,k(w p 8 2 3 qkk 3 ' k (9) )()(re2 0'1 0 ' rrn p p ff k l k f f φφ∑−= b.c. kumar et al. / bibechana 9 (2013) 33-37: bmhss, p.35 (online publication: nov., 2012) where p is the cauchy principal value. assuming the form factor w (k, q) and structure factor a (q) to be spherically symmetric we get, dq k2q k2q lnq)q,k(w)q(a ke4 z3 p p k k 0 f f 2 ff 0 f ' f 0 1 ∫ α − + −== (10) where fe is the fermi energy and fk is the fermi wave vector. the temperature coefficient of knight shift is represented by )rr(r rr m m ttt tt k + − =α (11) where, t is the desired temperature and mt is the melting point of the metal. 3. results and discussion by applying equation (10) we have calculated knight shift using two different eigen values (herman skillman and climenti eigen values). the results have been given in table 1 and table 2 for zn and al respectively. the h-eigenvalues with α = αvt and β =1 we get the values of k= 0.374 (kexp = 0.337) at 419 0 c and at 500 0 c, k was found to be 0.391 (kexp = 0.339) respectively. similarly we have calculated knight shift using c-eigen values; the values of knight shift are slightly different which are shown in table 1. as the other computed values of knight shift opting α = 2/3 and β =1 & 5/8 do not lie in the vicinity of experimental value, hence they are discarded. table 1: results for zn k = 0.540 metal α β єnl αvt 1 αvt 5/8 2/3 1 2/3 5/8 kexp. temp. ( 0 c) h 0.374 0.601 0.399 0.398 c 0.401 0.426 0.405 0.409 0.337 419 h 0.391 0.621 0.399 0.399 zn c 0.478 0.499 0.588 0.589 0.339* 500 fig. 1 : temperature dependence of knight shift of zn b.c. kumar et al. / bibechana 9 (2013) 33-37: bmhss, p.36 (online publication: nov., 2012) table 2: results for al k = 0.18 metal α β єnl αvt 1 αvt 5/8 2/3 1 2/3 5/8 kexp. temp. ( 0 c) h 0.199 0.126 0.119 0.139 0.164 360 al h 0.209 0.142 0.142 0.147 0.184 400 fig. 2 : temperature dependence of knight shift of al we have calculated the knight shift of aluminium at different temperatures by using h-eigen values. the calculated and experimental values of k are very close to each other. since the c-eigen values are not available for al, therefore it was not possible to calculate. the computed values for knight shift come to be 0.126 and 0.142 for α =αvt and β = 5/8 at temperatures 360 0 c and 400 0 c respectively. at the same time the set of values obtained for α = 2/3 and β= 1 & 5/8 are 0.119 & 0.142 and 0.139 & 0.147 respectively. from the above mentioned table it is evident that the closest approach obtained from the computation is for α = αvt and β=1 . the value 0.199 and 0.209 also lie very close to experimental values 0.164 and 0.184 for two different opted temperatures 360 0 c & 400 0 c respectively. the temperature dependence of knight shift of zn and al has been shown in fig. 1 and fig. 2 respectively with two sets of eigen values, and the estimated experimental curve have also been given for comparison. 4. conclusion for zinc, temperature dependence of knight shift with h-eigen values lies closer and has almost the same slope as that of the experimental curve. but the slope of the curve using c-eigen values is slightly different from that of experimental curve. in this case also qualitative agreement has been obtained. in case of aluminium only h-eigen values are available and temperature dependence curve has almost the same slope as that of the experimental curve. it is evident to mention that the different values of k obtained by computation lie very close to experimental values and also the slope has similar inclination in both the cases viz. theoretical and experimental. thus we observe that in spite of various approximations involved in the theoretical framework reasonable qualitative agreement has been obtained for the metals under investigation. from the above mentioned b.c. kumar et al. / bibechana 9 (2013) 33-37: bmhss, p.37 (online publication: nov., 2012) facts it is apparent that the knight shift and its temperature dependence have been reasonably predicted on the basis of the harrison’s first principle technique in conjunction with pake’s formalism. it is to be mentioned that the ziman’s formalism for the electrical resistivity involves the square of the form factor within its integrand hence; it depends only on the magnitude of the form factor. in contrast, the pake’s formalism for the knight shift involves the form factor linearly within its integrand. hence it depends both on the magnitude and the sign of the form factor. however, the electrical resistivity is very sensitive to the nature of the form factor especially in the region where the peak of the structure factor lies. also it has a much larger magnitude. in contrast the knight shift has a very small magnitude, hence the impact of the choice of various input parameters are not as much important as in the case of the electrical resistivity. references [1] s. d. mahanti, magnetic resonance, plenum press ny (1970). [2] knight w.d. et al., ann. phys., 8 (1959) 173. [3] j. m. ziman, solid state physics, 26 (1971) 1. [4] p. k. mishra and l. m. roth, phys. rev., 177 (1969 ) 1089. [5] b. n. singh, ph. d. thesis, t. m. bhagalpur university bhagalpur (1988). further readings [6] j. heighway and seymour, phy. kond. mat., 13 (1971) 1. [7] g. e. pake, phil. mag., 11 (1956) 153. [8] ashwini kumar, ph.d. thesis, t. m. bhagalpur university bhagalpur (2006). [9] r.n.singh and r.b. choudhary, j. phys. f: metal physics, 11 (1981) 1577. [10] ritu, i. s. jha, b.p. singh, v. n. chaudhary and r.n. singh, indian j. phys., 79 (2005) 635. [11] b. p. singh, v. n. choudhary and r. n. singh, phys. chem. liq., 23 (1991) 211. [12] m. mehar khan and s. h. m. rafique, phys. stat. sol.(b), 139 k(1987)131. [13] v. n. choudhary, b. p. singh et al., acta ciencia indica (2010). microsoft word s. shrestha _136-140_.doc s. shrestha / bibechana 9 (2013) 136-140: bmhss, p.136 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana antibiotic susceptibility pattern of resistant escherichia coli from poultry waste s. shrestha central department of biotechnology e mail: smitabiotech01@gmail.com article history: received 8 october, 2012; accepted 16 november, 2012 abstract the study was conducted in kathmandu valley to investigate the relationship between the use of antibiotic and the development of the resistant form of escherichia coli (e.coli), which were isolated from faecal waste of poultry farm. out of 30 samples investigated, 20 samples were found to be e.coli positive. it was further investigated that the resistance pattern for the isolates of e.coli from poultry farm was tetracycline (100%), penicillin (100%), erythromycin (100%), amoxicillin (90%) and chloramphenicol (60%). keywords: antibiotics; resistance pattern; tetracycline; penicillin; erythromycin 1. introduction poultry farming is the practice of raising poultry, such as chickens, turkeys, ducks, and other fowl for the purpose of farming, meat or egg production. nowadays, especially in poultry production antibiotics are widely used as growth promoter and in treatment of infectious disease [1].the use of antibiotics in the poultry production industries, for the promotion of growth, largely contributes to the high resistance to antimicrobial agents in normal flora of poultry [2] and pathogenic microorganisms [3]. besides this the antibiotics are used for the adjustment of intestinal flora, favoring useful bacteria while suppressing other bacterial population which enhances the use of antibiotics as growth promoter. many contend that this puts humans at risk and bacterial strains develop stronger and stronger resistances [4,5]. these resistant microorganisms may act as possible source for the transfer of antimicrobial resistance to human pathogens. plasmid and transposon mediated resistance is widely transmitted between different species and genera including human pathogens [6]. antibiotics are used extensively to prevent or to treat microbial infections in human and veterinary medicine. apart from their use in aquaculture, they are also employed to promote more rapid growth of livestock [7,8]. however, e.coli is the causative agent of human intestinal disease which remains a major cause of morbidity and mortality worldwide. these occur primarily in the developing countries where the access to effective antibiotic therapy is limited. the increase in number of drug resistant strains has also complicated the management of disease caused by e.coli. the emergence of resistance to antibiotic is a relevant matter worldwide, but the retrieval of antibiograms for e.coli is severely delayed when phenotypic methods are used. early identification of drug resistance s. shrestha / bibechana 9 (2013) 136-140: bmhss, p.137 (online publication: nov., 2012) and particularly multidrug resistant strain (mdr) is routine in developed low prevalence countries but the methods are currently unavailable and are too costly for resource poor nations like nepal where the burden of disease is greatest. data on the identification of antibiotic resistant e.coli is crucial in order to permit timely administration of appropriate antibiotic schedule and could potentially improve the efficacy of multidrug resistant treatments. 2. materials and methods sample collection faecal samples of poultry were collected from different poultry farms of kathmandu. bacterial isolation specimens were cultured on mcconkey and eosin methyl blue (emb) agar and the colonies suspected to be e. coli were identified by various biochemical tests. the list of biochemical tests are as follows indole test in this a loopful of bacteria was inoculate in a media containing kovac’s reagent containing n amyl alcohol 75ml, hydrochloric acid (conc.) 25ml and p-dimethylamine benzaldehyde 5gm and observed for color change. methyl red test in this a loop of bacteria was inoculated in a test tube having methyl red voges proskaur(mrvp) broth containing buffered peptone7gm, dextrose 5gm, dipotassium phosphate5gm and ph 7.4 and incubated for 24 to 48 hrs. then methyl red was added for the color change voges proskaur test in this a loop of bacteria were inoculated in a test tube having mrvp broth and incubated for 48 hours. then 20 drops of barrits reagent containing solution a containing 5gm alpha nephthol in 100ml 95% ethanol and solution b containing 40gm potassium hydroxide in 100ml distilled water were added to the test tubes and change in the color was noted citrate utilization test the bacteria were inoculated in the simmon citrate agar containing ammonium dihydrogen phosphate 1gm, dipotassium chloride 1gm, sodium chloride 5gm, magnesium sulphate 0.2gm, sodium citrate 2gm, agar15gm, bromothymol blue .08gm and ph 6.8 slant and incubated for 48 hours. it was then observed for any color change triple sugar iron test (tsi test) in this the bacteria was inoculated in the tsi agar slant containing glucose 0.1gm, sucrose 1gm, lactose1gm and distilled water 100ml and incubated for 24 hrs. then the change in color was observed hydrogen sulphide test in this a loopful of bacteria was inoculated in sim media containing ammonium ferric citrate 0.2gm, casein peptone 20gm, meat peptone 6.6gm, sodium thiosulphate 0.2gm, distilled water 1000ml. the change in color was noted. urease test in this the bacteria was inoculated in the urea agar containing phenol red solution and incubated at 35 0 c for 24 hrs. the urease production was examined by observing change in color. 3. antibiotic susceptibility determination antibiotic susceptibility was done by single disc diffusion method. the following antibiotic discs were applied on mueller hinton media: penicillin(p/10µg), chloramphenicol (c/30 µg), tetracycline(te/30 µg), amoxicillin(amx/10 µg), erythromycin(e/10 µg). interpretation was done according to the criteria recommended in the national committee for clinical laboratory standards (nccls. 1993) s. shrestha / bibechana 9 (2013) 136-140: bmhss, p.138 (online publication: nov., 2012) 4. results and discussion after the samples were collected from kathmandu valley and microorganism were isolated, various biochemical tests were performed. the results of which are shown below table 1: showing different biochemical test organisms indole test mr test vp test citrate test tsi(slant/broth) h2s test urease test e.coli positive positive negative negative yellow color / yellow color negative negative shigella negative negative negative negative red color/yellow color negative negative salmonella negative positive negative negative red color/yellow color positive negative proteus positive positive negative negative red color/yellow color positive positive fig 1 : isolated microorganism from poultry. from the above figure it was found that among 30, 20 (66.66%) was identified as e.coli. 5(16.67%) was identified as shigella spp. 3(10%)was salmonella spp and 2(6.67%)was proteus species. fig 2 : antibiotic susceptibility test. from the above figure it was found that all the isolate were resistant to penicillin(100%), chloramphenicol(60%), tetracycline (100%), amoxycillin(90%) and erythromycin(100%). analysis of the treatment history collected from the poultry farm showed that they used antibiotics mainly for s. shrestha / bibechana 9 (2013) 136-140: bmhss, p.139 (online publication: nov., 2012) treatment purpose. the resistance pattern of 20 isolates of e.coli isolated from poultry wastes clearly demonstrates the high resistance rate to all of the above tested antibiotics. the increased antimicrobial resistance in bacteria especially pathogens, has received worldwide attention. the increasing failure of therapeutic intervention pushed the world health organization (who) to publish the “global strategy for containment of antimicrobial resistance” in 2001[9]. this strategy was intended to minimize the increase of resistant bacterial strains while maintaining the effectiveness of the antibiotics already in use. during recent years poultry industry has expanded very rapidly in nepal and antibiotic resistance has emerged as one of the most severe problem having adverse effects on human health through their faecal waste and consuming their products. this has highlighted the need for taking extensive control measures to save the industry as well as humans. worldwide data show that there is increasing resistance among urinary tract pathogens to conventional drugs especially with various strains of e.coli [10]. although new antibiotics are being developed eg. glycylgycines [11] the level of antimicrobial resistance is not decreasing and it seems that development of resistance keeps pace with the development of new antibiotics. risk management of antimicrobial resistance is heavily biased towards banning the misuse of antibiotics [12]. it is also generally accepted that the high and often inappropriate use of antimicrobials and disinfectants, in both the humans and animals, is the main driver of resistance [13]. increasingly, multiresistant bacteria are being detected in environmental compartments with a high bacterial density [14]. the source of these bacteria as well as the transfer of resistance between different environment compartments, require further investigation and should be included in risk analysis. the results obtained from this research will help in monitoring antimicrobial resistance in environment where there is a high usage antibiotic. however, healthy and preferably antimicrobial naive populations should also be monitored, to have a better overview of the spread of antimicrobial activity in a population. besides this, it will also give a baseline data about the antibiotic susceptibility pattern of some commonly used antibiotics used in poultry farm. references [1] w. wolfgang, medical consequences of antibiotic use in agriculture science, 279 (1998) 996997. [2] b.j. allan, w. van-den-hurk and a.a. potter, characterization of escherichia coli isolates from cases of avian colibacillosis, canadian journal of veterinary research, 57 (1993) 145-151. [3] a. amara, z. ziani and k. bouzoubaa, antibiotic resistance of escherichia coli strains isolated in morrocco from chickens with colibacillosis, veterinary microbiology, 43 (1995) 29-51. [4] a.l. aronson, potential impact of the use of antimicrobial drug in farm animal on public health presented at the meeting on pharmacology in the animal health sector, colorado state university fort collins (1975). [5] d.g. white, c. hudson, j.j. maurer, s. ayers, m. d. lee, l. bolton, t. foley and j. sherwood. characterization of chloramphenicol and florphenicol resistance eschericia coli associated with bovine diarrhea, journal of clinical microbiolgy, 38 (2000) 4593-4598. [6] j. davis, inactivation of antibiotics and the dissemination of resistance genes, science, 264 (1994) 375-382. [7] r.j. wise, k.j. towner, c.a. webster, r.c. slack and t.o. jones, time to ball all antibiotics as animal growth promoting agents, lancet, 348 (1996) 619 [8] k. kummerer, resistance in the environment. journal of antimicrobial chemotherapy, 54 (2004) 311-320. [9] i.k. okele, k.p. klugman, z.a. bhutta, a.g. duse, p.jenkins, t.f. o’brian, a. pablosmendez, r. laxminarayan, antimicrobial resistance in developing countries, part(ii) : strategies for containment, the lancet infectious diseases, 5 (2005) 568-580. [10] a.e. van den bogaard, n. london, c. driessen and e.e. stobberingh, antibiotic resistance of faecal escherichia coli in poultry farmers and poultry slaughterers, journal of antimicrobial chemotherapy, 47 (2001) 763-771. s. shrestha / bibechana 9 (2013) 136-140: bmhss, p.140 (online publication: nov., 2012) [11] i. chopra, glycyclines : third generation tetracycline antibiotics, current opinion in pharmacology, 1 (2001) 464-469. [12] c. grugel, meeting report : first national scientific symposium “risk management for limitation of antibiotic resistance”, international journal of microbiology, 296 (2006) 1-3. [13] who, global strategy for containment of antimicrobial resistance, world health organization geneva switzerland, (2001). [14] d. berry, x. chunwu, l. raskin, microbial ecology of drinking water distribution systems, current opinions in biotechnology, 17 (2006) 297-302. microsoft word hassan_49-56_.doc m.r. hassan and r.r.thapa / bibechana 10 (2014) 44-51 : bmhss, p.44 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana periodic solution of the restricted three body problem m.r. hassan 1 , r. r.thapa 2* 1 dept. of mathematics, s.m. college, bhagalpur, under t.m.b.university, bhagalpur 2dept. of mathematics, p.g.campus, biratnagar, morang, nepal *email: thaparajuram@yahoo.com article history: received 25 august, 2013; accepted 5 october, 2013 abstract the effect of perturbation in centrifugal force on the periodic solution of the restricted three-body problem representing analytic continuation of keplerian rectilinear periodic motion has been examined. however, we have taken the perturbation in the centrifugal force to be of the order of µ , the reduced mass of the smaller primary. we have calculated the first order perturbations also. keywords: elliptic restricted three body problem; generating solution; hamiltonian equations; perturbation; periodic solution; variational equations. introduction considering the two body problem, poincare [1] classified three kinds of periodic solutions of the restricted three body problem. solutions of i and ii kinds are related to the planar case of the three body problem. in the solution of i kind, the eccentricity reduces to zero together with small mass. in the solution of ii kind, the eccentricity does not reduce to zero with the small mass. poincare studied in details the i kind and proved its existence. for the solution of the ii kind, he deduced conditions under which they may exist but regorious proof for the existence of the solution of this kind was not given by him. poincare used the de-launay elements in his study and so he excluded the case when one of the eccentricity of the generating solution is equal to unity. kurcheeva [2] considered the last case. under certain conditions she proved the existence of so called periodic solution of poincare i.e. having equal periods for their perturbed as well as for the unperturbed motions. ahmad [3] studied the elliptic restricted three body problem generalizing the work of kurcheeva. ahmad and khan [4] generalized the work of ahmad with the introduction of perturbation in the coriolis force. in this paper we have studied the generalization of the restricted three body problem introducing perturbation in the centrifugal force. we have examined the existence of the periodic solution taking the perturbation to be of the order of µ , the reduced mass of the smaller primary. we have also calculated first order perturbation. hamiltonian equations of motion using non-dimensional variables and a synodic system of co-ordinates, the hamiltonian equations of motion are m.r. hassan and r.r.thapa / bibechana 10 (2014) 44-51: bmhss, p.45 (online publication: dec., 2013) dx h dy h , dt x dt y dx h dy h , dt x dt y ∂ ∂ = = ∂ ∂ ∂ ∂ = − = − ∂ ∂ (1) where ( ) ( )2 2 1 2 1 1 h x y yx xy 2 r r −µ µ = + + + − − (2) ( ) ( ) 22 2 1 22 2 2 r x y r x 1 y = −µ + = −µ + + (3) in the above equations, the parameter µ is the ratio of the mass of the smaller primary to the total mass of the primaries and 0 1/ 2.< µ ≤ we consider the perturbation in the centrifugal force with the help of the parameter β , the unperturbed value of β being unity. the corresponding hamiltonian function takes the following bhatnagar and hallan form [5] ( ) ( ) ( )( )2 2 2 2 1 2 1 1 1 h x y xy yx 1 x y 2 2 r r −µ µ = + + + + −β + − − here β may be taken as 1 ', ' |β = +∈ ∈ << where '∈ represents the perturbation in the centrifugal force. upto first order, we have ( ) ( ) ( )2 2 2 2 1 2 1 ' 1 h x y xy yx x y 2 2 r r ∈ −µ µ = + + − − + − − (4) limiting case µ=0 for the elimination of singularity at the bigger primary we shall use levi-civita's [6] variables as used by kurcheeva: ( ) ( ) 2 x iy p iq p iq x i y 2(p iq) +µ + = + − − +µ = + (5) ( )2 2dt 4 p q ds = + (6) the regularized canonical equations of motion became dp dq , ds p ds q dp dq , ds p ds q ∂ω ∂ω = = ∂ ∂ ∂ω ∂ω = = ∂ ∂ (7) where ( ) ( ) ( ) ( ) ( ) 2 2 4 4 1 1 2 3 4 4 1 1 1 p q 2r qp pq 4 p q 4 4 4 r / r 2 2cr 2 'r 4 ' p q ω = + + − + µ − − + µ − µ + − ∈ − µ∈ − (8) m.r. hassan and r.r.thapa / bibechana 10 (2014) 44-51: bmhss, p.46 (online publication: dec., 2013) ( ) ( )22 2 2 2 2 2 2 1 2r p q , r 1 2 p q p q= + = − + + + (9) the solution of the system (7) being the solution of the system (8), we must have 0ω = we suppose that '∈ is or the order of µ i.e. 0' '∈ =∈ µ . if we put 0µ = in the system (7) may be integrated. the solutions of the simplified system, which in sideral system of co-ordinates corresponds to collinear motion, has krasinski form [7]. o o o o p sin , q cos p sin , q cos = ρ θ = ρ θ = ρ θ = ρ θɺ ɺ (10) where ( ) ( ) ( ) 0 0 3 0 2 / ccos 2 cs 1 4 cs sin 4 cs 2 2n d n c meanmotion, ds ρ = −φ  θ = + − φ   ρ = = ρ =ɺ the period of such a solution is ( ) ( ) 0 0 k if k m isan even number 2 c s k if k m isan odd number c π + =  π +  (11) the relation between t and s for 0µ = is given by ( ) ( )0 0 1 t 2 4 cs sin 4 c s 2 n  = θ−ω = + − φ   (12) solutions of the variational equations of the generating system the solutions of the variational equations of the system (7) for 0µ = are well known. the solutions given by krasinski are 0 0 1 0 2 0 3 0 0 4 0 0 0 0 0 1 0 2 0 3 0 0 0 4 0 0 0 0 0 1 0 2 0 3 0 0 0 4 0 0 0 0 t q1 2 p q , p p , p p tq , p q p s n n2 c t p1 2 q p , q q , q q t p , q p q s n n2 c t q2 2 p q , p p , p p t q , p 2 c q p s p n n n   δ = δ = δ = + δ = − + −       δ = − δ = δ = − δ = + −       δ = δ = δ = + δ = + + −    ɺ ɺ ɺ ɺ ɺ ɺ (13) 0 0 1 0 2 0 3 0 0 0 4 0 0 0 0 t p2 2 q p , q q , q q t p , q 2 c p q s q n n n   δ = − δ = δ = − δ = − + + +    ɺ ɺ proof of isoperiodic solution we see that our hamiltonian function (8) possesses the same properties as that of kurcheeva. therefore, under the conditions: m.r. hassan and r.r.thapa / bibechana 10 (2014) 44-51: bmhss, p.47 (online publication: dec., 2013) q(o) p(o) o,p(s*) q(s*) 0,s* s/ 4= = = = = (14) and q(o) p(o) o,q(s*) p(s*) 0, s* s / 2= = = = = (15) the general solutions xi (s), (i = 1, 2, 3, 4) are periodic with period s as in kurcheeva where by xi (i = 1, 2, 3, 4), p,q,p,q are respectively denoted. the solutions (10) of the generating system satisfy the conditions (14) when k+m is odd and (15) when k+m is even under the following values of the parameters 0φ and .ω i. 0 0, / 2φ = ω=± π ii. 0 0 / 2, l, l 0,1,2,.......φ = =± π ω = π = we observe that the value of 0ω is the same as in kurcheeva. hence one can follow the work of kurcheeva, step by step, to examine the existence of isoperiodic solutions. the isoperiodic solution exist for 0 0, / 2,k even, m odd.φ = ω = ±π − − for arbitrary k and m, there exist periodic solutions reducing to the generating one for 0.µ = the period of these solutions is an analytic function of µ , s=s*+4s(µ ), s* being the period of the generating solution. perturbation of the first order in the proceeding paragraph the existence of the periodic orbits analytic relative to µ with the period s=s*+ sδ , where s* is the period of the generating solution has been pointed out. let us pass on to such time t the period in which does not depend on µ : s* s* s s* s s* τ = = +δ +α where k s* . 4 c π = then the equations of motion are written as ( ) ( )i i 1 4 dx s* x x ,..........x ,c , i 1,........., 4 d s* +α = = τ (16) the solution of the system (16) may be sought in the form of series in integral positive powers of µ . ( )(0) (i) i k k k i 1 x x x , k 1,....4 ∞ = = + µ =∑ (17) for c and α , we have i i 0 i i i 1 i 1 c c c , ∞ ∞ = = = + µ α = α µ∑ ∑ (18) as it is proved by kurcheeva series (17) and (18) representing solutions of the system (16) converge for sufficiently small value of µ . let us substitute (17), (18) in (16) for the determination of the functions ( )( j) ix τ . we have a system of linear differential equations. (i) 4 (i) (0) (i)k kj j k i k i k j 1 dx p x x h c f d = = + + φ + τ ∑ where by hi we denote i / s*α m.r. hassan and r.r.thapa / bibechana 10 (2014) 44-51: bmhss, p.48 (online publication: dec., 2013) (0) (0) (0) (0)k kj k k 1 4 0 j k k 0 x p , x x (x ,.......x ,c ,0) x x c ∂ = = ∂ ∂ φ = ∂ ( )(i) (i) (0) (i 1) k k i 4 0 i 1 1 i 1 f f x ,......., x ,c ,......,c ,h ,......, h− − −= in particular for i=1, we have (i) 1 (i) 2 (i) 3 '1 1 3 0 13 2 2 f 0 f 0 8qr (1 r )8q f 16q 12 r p. r r = = + = − + + + ∈ (i) 3 ' 21 1 4 0 13 2 2 8pr (1 r )8p f 16p 12 r q. r r − = + − + ∈ (20) 1 2 3 0 4 00, 4p , 4qφ = φ = φ = − φ = − (21) (0) (0) (0) 1 0 0 2 0 0 3 0 0 0 4 0 0 0x p 2rq , x q 2rp , x 2rq 4p c , x 2rp 4q c= + = − = − = − − (22) all the linearly independent solutions of the system 4 i ik k k 1 dy p .y d = = τ ∑ (23) are obtained from the expression (13). let us seek particular solution of the system (19) with the help of the method of variation of arbitrary constant. let 4 (i) j k ik k 1 x l .y = =∑ (24) where { }jk y is a fundamental system of solution of the homogenous system (23) differentiating (24), we obtain 4 (i) (i)k jk j 1 j i j k 1 dl y c x h f d= = φ + + τ∑ (25) now, in order to get rid of yjk from the coefficients with lk depending on the time τ . we shall multiply the expression (25) by zji , where { }jiz is a matrix of solution for conjugate system (23) we shall add then in j from 1 to 4. we have 4 ik k i k 1 a l f = =∑ ɺ where 4 ik ji jk j 1 a z y = =∑ , do not depend on time (the property of the conjugate system) ( ) 4 (o) (i) i k 1 k 1 k ki k 1 f x h c x z = = + φ +∑ (26) as the expression (23) is a system in variation of a cononic sytem, so for the determination of zij we have the following relations 1i 3i 2i 4i 3i 1i 4i 2iz y , z y ,z y ,z y= − = − = − = − m.r. hassan and r.r.thapa / bibechana 10 (2014) 44-51: bmhss, p.49 (online publication: dec., 2013) as the coefficients aij do not depend on time, so for the determination we shall put 0τ = . using the formula (13) for the calculation of yij (0), we find ij 4 0 0 0 c 16 0 0 8 a n 0 8 0 0 4 16 0 0 nc            =    −   − −     thus we have the following system 4 1 3 2 1 0 2 3 1 4 3 0 c 1 1 l f , l f f 4 8 2c 1 c 1 l f , l f f 8 4 2c = = − = − = + ɺ ɺ ɺ ɺ integrating we get, 2 0 1 1 4 3 0 0 0 3t c 1 l c b b c 4c 4 2c  τρ = − + − +    ɺ 0 2 1 1 3 t 1 l b c b 8 8 = τ + − 22 (0) 3 1 2 1 0 1 1 l c b b 4 4 8 2c  ρρ = − + + −     (27) ( ) 4 1 1 1 3 20 2 4 4 ' 31 3 1 0 13 3 3 2 2 20 0 0 c l b 4 1 b 16pqr 1 d r b 0, 0 8r1 1 b 8 p q 2 d 16 tpqr 1 d 12c r d r r r τ τ τ τ =   = − τ       ∂ω ∂ω = − +   ∂µ ∂µ    τ = µ =       = − − + + τ + − τ + τ           ∫ ∫ ∫ ∫ ( ) 1 2 4 0 0 db dbt b tan 2 c 2 / n d n d d τ   = τ −φ − + τ τ  τ τ   ∫ (28) in general, solution of the system (19) m.r. hassan and r.r.thapa / bibechana 10 (2014) 44-51: bmhss, p.50 (online publication: dec., 2013) ( ) ( ) 4 (1) k i i ki i 1 x l a y , k 1,.....4 = = + =∑ (29) there will enter six constraints h,c,ai (i=1,……4) (ai=constants of integration) which must be chosen in such a manner that the following relations are satisfied (1) (1) (1) 2 3 0 4 0 d k x (0) x (0) x (s*) 0,s* d 4 c µ=  ω π = = = = = µ  , if (k+m) is odd (30) and (1) (1) (1) (1) 2 3 1 4 0 d k x (0) x (0) x (s*) x (s*) 0,s* d 4 cµ=  ω π = = = = = = µ  , if k+m is even (31) from the relations (1) (1) 2 3x (0) x (0) 0= = we find immediately that a1=a2=0 we shall write the equations (30) and (31) in the following manner (1) i i1 1 i2 1 i3 3 i4 4 i (1) j j1 1 j2 1 j3 3 j4 4 j x (s*) f* h f* c f* a f* a f* 0 x (s*) f* h f* c f* a f* a f* 0 = + + + + = = + + + + = (32) 1 3 00 0 d 4 16 d c a d c n d µ= τ=    ω ω = + +   µ µ    where i 1, j 4, k m isodd, i 2, j 3, k m is even = = + = = + k1 k2 k3 k3 k4 k4 2 2 2 0 0 k2 k1 k2 k3 0 0 f y , f y , f y 3t t (0) f y y y c 4c 8 4 4 = τ = =    τρ ρ ρ = − + +       0 k 4 3 k1 3 k2 2 1 k3 1 k4 0 0 cc 1 1 1 1 f b b y b y b b y b y 4 2c 8 8 2c 4     = − + − + + +        (33) where h1 are defined by the formula (28). thus we have three equations for the determination of four constants (h1, c1, a3, a4). one of them is chosen arbitrary when k is even m is odd, 0 0, / 2φ = ω = ± π one may require in order that in perturbed as well as in unperturbed motion the period in independent variable t may coincide; then to these equations we shall supplement another. ( ) 0 k t *, m 0, * 4 c π τ µ − π = τ = (34) where t may be put in the form of the series inµ . m.r. hassan and r.r.thapa / bibechana 10 (2014) 44-51: bmhss, p.51 (online publication: dec., 2013) i 0 i i i 1 t t t , t (0) 0 ∞ = = + µ =∑ (35) let us pass in the expression (6) to new independent variation s* s s* τ = +α ( )2 2 1 2 dt s* 4 x x d s* +α = + τ (36) and we shall substitute expression (35) in (36) then for the determination of t1, we have the following equations. ( ) ( )2 2 (0) (0) (0) (1) (0) (1) 1 2 1 1 1 1 1 dt 4 x x h 8 x x x x d = + + + τ integrating we obtain 1 51 1 52 1 53 3 54 4 5t f h f c f a f a f= + + + + . where ( ) ( ) 2 2 51 0 0 2 2 2 0 0 0 00 52 0 0 0 f 4 p q t p q t 4 c sin 2 c 4sin 2 c f 52 c c 3c = + + = + − + ( )2 2 0 0 0 53 0 54 8 p q 2t f 2t , f n n + = = + (37) ( ) ( )2 2 5 2 4 3 0 2 f l l pp qq l p q d n τ  = + + + τ   ∫ ɺ ɺ then to the equation (32) when k is even, m is odd, 0, / 2,φ = ω = ±π one may add also another equation. ( ) * * * * * 1 51 1 52 1 53 3 54 4 5t * f h f c f a f a f 0τ = + + + + = (38) this is the required equation for calculating the first order perturbation in centrifugal forces. acknowledgements we are thankful to prof. dr. mrityunjay jha, prof. and head, university department of mathematics, t.m.b., university; bhagalpur, india for giving us encouragement and his valuable suggestions. references 1. h. poincare, les mathod nouvels dela mecanique cilest., paris, 1892. 2. i.v. kurcheeva, bulletin, inst. of theo. astro. (ita) (1968)149. 3. a. ahmad, ph.d. thesis, bhagalpur university, bhagalpur, 1981. 4. a. ahmad, and a.a. khan, jbms, 10(86) 199-128. 5. k.b. bhatnagar, and p.p. hallen, celestial mechanics 18 (1978) 105. 6. t. levi-civita, periodic orbits, washington, 1906. 7. g.a. krasinski, bulletin, inst. of theo. astro. (ita) 9 (1963) 105. microsoft word main.doc 15 bibechana vol. 6, march 2010 diversity of herpetofauna in and around the koshi tappu wildlife reserve damodar thapa chhetry p.g. campus, biratnagar, tribhuvan university, nepal abstract the paper deals with the herpetofauna of koshi tappu wildlife reserve and its surroundings. a total of 23 species of herpetofauna belonging to 19 genera and 13 families were recorded. of these 8 species belonging to 6 genera and 3 families were amphibians, and 15 species belonging to 13 genera and 10 families were reptiles. keywords: herpetofauna.; gavialis gangeticus; koshi tappu 1. introduction the koshi tappu wildlife reserve is the first ramsar site in nepal. it extends between 86°55'-87°05’e longitude and 26°34'-26°45'n latitudes on the alluvial flood plain of the sapta koshi river which is fed by seven tributaries, the indrawati , bhote koshi , tama koshi , dudh koshi , liku , arun and tamor rivers. the reserve covers part of sunsari, saptari and udayapur districts of the eastern development region. it is touched by twelve village development committees. eastern and western embankments of 5-7 m high were constructed by the koshi dam project to control flood. in and around of koshi tappu wildlife reserve are many notable wetlands like rivers, floodplain, oxbow lakes and riverine marshes, fresh water marshes and ponds, seasonally flooded grassland, swamp forest, reservoir, paddy fields etc. these wetlands are the suitable habitat for the herpetofauna. several herpetologist have provided literature on herpetofauna of nepal (swan and levition,1962; dubois,1974; nonhoe and ouboter, 1987; shah and giri, 1992; schleich, 1993; shah, 1995; schleich and kaestle, 2002). however, very few literature (suwal,1993; wmi/iucn,1994;) are available on herpetofauna of koshi tappu wildlife reserve and its surroundings. 2. materials and methods the herpetofauna was studied from july, 2002 to june, 2004, once in every month at regular interval from koshi tappu wildlife and its surroundings. the amphibians were collected by the help of local people and fisher men. they used different materials like rubber glove, long iron tongue, different nets (cast net, scoop net etc.). the collected specimens were preserved in plastic containers in 10 % formalin for further study. in case of reptiles, long iron tongue, rubber glove, scoop net, plastic container etc. were mainly used for collection. some of the collected specimens were preserved in 10 % formalin for further study. some reptiles were released after taking photographs. informations about snakes were collected from local people. reports about the presence of gavialis gangeticus and crocodylus palustris were also collected from local people. the collected specimens of amphibia 16 damodar thapa chhetry and reptile were identified with standard literature (stebbins, 1966; cochran and goin, 1970; shrestha, 1981; daniel, 1983; conant and collins, 1991; das, 1991; schleich, 1993; murthy, 1995; shrestha, 2001; and schleich and kaestle, 2002). 3. results and discussion the present study recorded altogether 23 species of herpetofauna belonging to 19 genera and 13 families. of these 8 species belonging to 6 genera and 3 families were amphibians, and 15 species belonging to 13 genera and 10 families were reptiles (table 1). among the amphibians, 4 species were found commonly during the whole study period and 4 species were found rarely. five species belonging to the ranidae family was observed. among the ranidae species the sphaerotheca breviceps was found rarely. but the family rhacophoridae and bufonidae included all rarely found species. among the reptiles, 5 species found commonly during the whole study period, 4 species found rarely and 6 species found rarely. according to the local informations, the abundance of herpetofauna are in decreasing trend due to loss of habitat, poaching, killing and cosuming by people. specially, the turtle species: aspideretes hurum, lissemys punctata, pangshura flaviventer kill by local people for meat. similarly, python molurus molurus poach for leather. naja naja is highly poisonous and the people kill this animal when they see. references 1. d.m. cochran and c.j. goin, the new field book of reptiles and amphibians, putnam nature field book, new york (1970). 2. r. conant and j. t. collins, field guide to the reptiles and amphibians (1991). 3. j.c. daniel, the book of indian reptiles. bombay natural history society, india (1983). 4. i. das, colour guide to the turtles and tortoise of the indian sub continent. .a. publishing ltd., england (1991).5. a. dubois, diagnoses de troisespeces nouvelles d’ nepal. bull. zool. soc. france 98(1974) 495. 6. eastern and central north america, 3rd edition. houghton mifflin co., boston, mass. 7. t.s.n. murthy, reptiles of india, r.r. publishing corporation, delhi. (1995). 8. l.m.r. nanhoe and p.e. ouboter, the distribution of reptiles and amphibians in the annapurnadhaulagiri region (nepal). zool. verhandel. leiden. netherland 229(1987) 1. 9. h.h. schleich, contribution to the systematics and to a bibliography of the amphibians and reptiles from nepal . j. nepal res. centre 9(1993) 141. 10. h.h. schleich and w. kaestle, amphibians and reptiles of nepal. koeltz scientific books, koenigstein (2002) 11. k.b. shah, enumeration of the amphibians and reptiles of nepal. publication no. 2. department of national parks and wildlife conservation, ministry of forest and soil conservation, nepal (1995). 12. k.b. shah and m. k. giri, some amphibians and their local uses in arun basin. j. nat. hist. mus. t.u., nepal 12(1992) 9. 13. t.k. shrestha, distribution of amphibians of nepal and their conservation. in: introduction to fauna and wildlife of nepal. (ed. majupuria, t.c.) (1981) 148160, lashkar, kathmandu. 14. t.k. shrestha, herpetology of nepal. mrs. bimala shrestha, kathmandu, nepal (2001). 15. r.c. stebbins, a field guide to western reptiles and amphibians, houghton mifflin co., boston, mass (1966) . 16. r. n. suwal, koshi tappu wildlife reserve: conservation issues and management measures. a survey report submitted to iucn, nepal (1993). 17. l.w. swan and a.e. levition, the herpetology of nepal: a history checklist and zoogeographical analysis of the herpetofauna. proc. calif. acad. sci., san francisco, usa 32(1962) 103. 17 bibechana vol. 6, march 2010 18. wmi/ iucnnepal biodiversity of koshi tappu wildlife reserve and its adjacent area. applied database for integrated biodiversity conservation in nepal. woodland mountain institute / iucn – nepal( 1994). herpetofauna in and around the koshi tappu wildlife reserve. family scientific name common name local name local status ranidae hoplobatrachus crassus (jerdon, 1853) jerdon’s bull frog sandhe bhyaguto commonly found ranidae hoplobatrachus tigerinus (daudin,1802) indian bull frog singare baghe bhyaguto ’’ ranidae euphlyctis cyanophlyctis (schneider, 1799) skittering frog ahale bhyaguto ’’ ranidae limnonectes teraiensis (dubois, 1984) terai cricket frog madhese kithre bhyaguto. ’’ ranidae sphaerotheca breviceps (schneider,1799) indian burrowing frog. bharati khopilte bhyaguto. rarely found rhacophoridae polypedates taeniatus (boulenger, 1906) terai tree frog madhese singare rukh bhyaguto ’’ bufonidae bufo melanostictus (schneider, 1799) common asian toad khasre bhyaguto ’’ bufonidae bufo stomaticus (lutken, 1862) marbled toad khasre bhyguto ’’ agamidae calotes versicolor (daudin,1802) common garden lizard bagaiche chheparo commonly found varanidae varanus bengalensis (daudin,1802) bengal monitor bhaise gohoro very rarely found varanidae varanus flavescens ( hardwicke and gray, 1827) yellow monitor sun gohoro ’’ colubridae xenochrophis piscator (schneider, 1799) checkered keel back water snake kothe dhodia sarpa commonly found colubridae amphiesma stolatum (linnaeus,1758) buff-striped keelback harara sarpa ’’ elapidae bungarus fasciatus (schneider, 1801) banded krait pate gana guwali sarpa ’’ elapidae bungarus caeruleus (schneider,1801) common indian krait karet ’’ elapidae naja naja (linnaeus,1758) spectacled cobra goman very rarely found boidae python molurus molurus (linnaeus,1758) asiatic rock python ajingar ’’ testudinidae indotestudo elongata (blyth , 1853) elongated tortoise kubadi kachhuwa rarely found gavialidae gavialis gangeticus (gmelin, 1789) gharial lamo thutune gohi. very rarely found crocodylidae crocodylus palustris (lesson,1831) mugger crocodile magar gohi ’’ trionychidae aspideretes hurum (gray,1831) indian peacock soft shell turtle naram khabate kachhuwa rarely found trionychidae lissemys punctata (webb,1980) indian flapshell turtle putali kachhuwa ’’ bataguridae pangshura flaviventer (gunther,1864) yellow-bellied tent turtle. pahelo bhude dhuri kachhuwa ’’ 149-156 r.r. thapa r c o s t n r.r. thapa / bibechana 11(1) (2014) 149-156: (online publication: march, 2014) p.149 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana stability of the sitnikov's circular restricted thr ee body problem when the primaries are oblate spheroid r.r. thapa department of mathematics, post graduate campus, biratnagar tribhuvan university, nepal email: thaparajuram@yahoo.com accepted for publication: february 06, 2014 abstract the sitnikov's problem is a special case of restricted three body problem if the primaries are of equal masses (m1 = m2 = 1/2) moving in circular orbits under newtonian force of attraction and the third body of mass m3 moves along the line perpendicular to plane of motion of primaries. here oblate spheroid primaries are taken. the solution of the sitnikov's circular restricted three body problem has been checked when the primaries are oblate spheroid. we observed that solution is depended on oblate parameter a of the primaries and independent variable t.τ = η for this the stability of non-trivial solutions with the characteristic equation is studied. the general equation of motion of the infinitesimal mass under mutual gravitational field of two oblate primaries are seen at equilibrium points. then the stability of infinitesimal third body m3 has been calculated. © 2014 rcost: all rights reserved. keywords: characteristic equation; non-trivial solution; oblate spheroid; sitnikov's restricted three body problem; stability. 1. introduction the primaries in the sitnikov’s problem move on the circumference of the same circle if the primaries are spheroid in shape. but if the primaries are oblate spheroid in shape then due to their oblateness the primaries will not be equidistant from their center of mass. the primaries should be equidistant from their centre of mass. for this principal axes of the oblate bodies should be parallel to the synodic axes andthe masses of both the primaries should be equal. the system consists of two oblate primaries with equal masses (m1 = m2 = 1/2). the third body of mass m3 is much less than the masses of the primaries. thus the potential between two bodies m1 and m2 is given by 1 2 1 2 3 ( )gm m ga m m v r r + ⇒ − = + 2 2 10 a c a −= = oblatenless of the primaries where ai, bi, ci (i = 1, 2) be the semi axes of the primaries. when the primaries are oblate, ai = bi. an integrable case in restricted problem of three bodies by imposing further restrictions on the restricted three body problem, by supposing the two finite bodies of equal masses and an infinitesimal body moving in their common axis of revolution has been studied by macmillan [1]. r.r. thapa / bibechana 11(1) (2014) 149-156: (online publication: march, 2014) p.150 in three body problem two primaries of equal masses and these two moving in (i) circular orbits and (ii) elliptic orbits around their center of mass has obtained by sitnikov [2]. the third body (infinitesimal mass) is moving along a line which is perpendicular to the plane of primaries and passing through the center of mass of the primaries. the stability and bifurcation of sitnikov motion have studied by perdios et.al. [3]. the family of periodic sitnikov motions can be recognized as a special case (µ =1/2) of the family 3 1l of three dimensional orbits emanating at l1 for all admissible values of µ and is denoted by 11l . the existence of such a family offers the opportunity to study the stability of bifurcations of one-dimensional motions under perturbations in two additional dimensions which tends to take the moving particle directly into the full three-dimensional space. the stability of motion in the sitnikov problem have studied by soulis et al. [4]. they have varied the mass of the infinitesimal body 0 < m < 10-3. they have found that as m3 increases, the domain of allowed motion grows significantly and chaotic regions in the phase space appear through a series of saddle-node bifurcations. the equations of motions have the non-trivial solutions obtained by mccuskey [5] 2 3 5 1 8a n r r ⇒ = + the equation of motion of the third body has obtained by suraj et al. [6], as follows 2 2 2 2 2 3/ 2 2 2 5/ 2 2 2 7 / 2 9 15 0 ( ) ( ) ( ) ⇒ + + − = + + + d z z az az dt z r z r z r 2. solutions by lindsted-poincare method equation of motion of third body is ( ) ( ) ( ) 2 2 3/ 2 5/ 2 7 / 22 2 2 2 2 2 2 9 15 0+ + − = + + + d z z az az dt z r z r z r raju ram thapa, et al. [7] has obtained the solution as follows: ( ) ( ) ( ) ( ) 5 3 7 3 5 3 9 cos cos cos3 23cos 24cos3 cos5 64 4096 27 547 297 3 1 cos cos3 cos5 cos7 8 32768 16384 2048 32768 1 3 cos cos3 23cos 24cos3 cos5 32 1024 27 547 297 cos 4 32768 1638 c z c t t t c t t t c t t t t a t t c t t t c t η η η η η η η η η η η η η η η η = + − + − +  + − + −   + − + − + + − 73 1 cos3 cos5 cos7 ... 4 2048 32768 t t t cη η η  + − +      3. stability: the general equations of motion of the infinitesimal mass under the mutual gravitational field of two oblate primaries are r.r. thapa / bibechana 11(1) (2014) 149-156: (online publication: march, 2014) p.151 2 2 x ny x y nx y z z ∂ω− = ∂  ∂ω+ = ∂   ∂ω= ∂  && & && & && (1) where n is the mean angular velocity of the primaries moving on the common circular orbit of radius a/2. here, 2 1 3 5 2 2 2 2 2 22 2 2 1 3 ( ) ( ) ( ) ω = + − + + + a az z r z r z r (2) 16 1 3 b a= + a = oblateness parameter of the primaries. hence from (2), it is clear that ω is independent of x and y and depends only upon z alone hence 0. x y ∂ω ∂ω= = ∂ ∂ 3 3 5 7 2 2 22 2 2 9 15 ( ) ( ) ( ) ∂ω = − − + ∂ + + + z az az z z b z b z b (3) for the equilibrium solution of the restricted three body problem, 0. x y z ∂ω ∂ω ∂ω= = = ∂ ∂ ∂ thus the system of equations (1) can be written as 2 ( , , ) (say) 2 ( , , ) (say) ( , , ) (say) x ny f x y z x y nx g x y z y z h x y z z ∂ω− = = ∂  ∂ω + = = ∂   ∂ω = = ∂  && & && & && at the equilibrium points (4) let us denote the equilibrium point as l(0, 0, z0), we shall now communicate small displacement ξ, η, ζ in the coordinates of l such that x = 0 + ξ, y = 0 + η, z = z0 + ζ satisfy the above equation. r.r. thapa / bibechana 11(1) (2014) 149-156: (online publication: march, 2014) p.152 thus, 2 02 2 02 22 0 02 2 2 (0 ,0 , ) 2 (0 ,0 , ) (0 ,0 , ) where 0. d n f z dt d n g z dt d zd h z dt dt ξ η ξ η ζ η ξ ξ η ζ ζ ξ η ζ ⇒ − = + + + − = + + + = + + + = & & 0 0 00 0 0 00 0 0 2 (0,0, ) higher order infinitesimals 2 (0,0, ) higher order infinitesimals (0,0, ) f f f n f z x y z g g g n g z x y z h h z x ξ η ξ η ζ η ξ ξ η ζ ζ ξ η  ∂ ∂ ∂    ⇒ − = + + + +    ∂ ∂ ∂      ∂ ∂ ∂   + = + + + +    ∂ ∂ ∂     ∂ ∂ = + + ∂  && & &&& && 00 higher order infinitesimals h h y z ζ  ∂ + +   ∂ ∂   since (0, 0, z0) is a solution of the set of equation (4) 0, x y z ∂ω ∂ω ∂ω= = = ∂ ∂ ∂ hence f(0, 0, z0) = g(0, 0, z0) = h(0, 0, z0) = 0 thus, 0 0 0 0 0 0 0 2 higher order infinitesimals 2 higher order infinitesimals n x x y x z x n x y y y z y x z y z ξ η ξ η ζ η ξ ξ η ζ ζ ξ η ∂ ∂ω ∂ ∂ω ∂ ∂ω     − = + + +     ∂ ∂ ∂ ∂ ∂ ∂           ∂ ∂ω ∂ ∂ω ∂ ∂ω+ = + + +     ∂ ∂ ∂ ∂ ∂ ∂      ∂ ∂ω ∂ ∂ω  = + ∂ ∂ ∂ ∂   && & &&& && 0 0 higher order infinitesimals z z ζ ∂ ∂ω  + +   ∂ ∂   neglecting higher order terms of ξ, η, ζ, we get the variational equations as 0 0 0 0 0 0 0 0 0 2 2 xx yx zx xy yy zy xz yz zz n n ξ η ξ η ζ η ξ ξ η ζ ζ ξ η ζ ⇒ − = ω + ω + ω  + = ω + ω + ω   = ω + ω + ω  && & &&& && (5) where 0 0 0, , ,...xx xy xzω ω ω etc represent the value of 0 0 , , x x x y  ∂ ∂ω ∂ ∂ω    ∂ ∂ ∂ ∂    0 ,... x z ∂ ∂ω   ∂ ∂  at the equilibrium points. r.r. thapa / bibechana 11(1) (2014) 149-156: (online publication: march, 2014) p.153 now the system of equations (5) can be written in the form of a single matrix equation as 0 0 0 0 0 0 0 0 0 6 16 1 6 6 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 2 0 2 0 0 0 0 0 xx yx zx xy yy zy zx zy zz n n ξξ ηη ζζ ξξ ηη ζζ ×× ×                              =     ω ω ω          ω ω ω −          ω ω ω      & & & &&& &&& &&& (6) i.e. x ax=& (7) when t ξ η ζ ξ η ζ   & && is a 6 × 1 column matrix of derivatives of the variations of the coordinates of the equilibrium points. 0 0 0 0 0 0 0 0 0 6 6 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 2 0 2 0 0 0 0 0 xx yx zx xy yy zy zx zy zz a n n ×            =  ω ω ω    ω ω ω −    ω ω ω  is a 6×6 square matrix of constants. but 0 x y ∂ω ∂ω= = ∂ ∂ , so 0 0 0 0 0 0 0 0 0 0 0 0 and 0 xx yx zx xy yy zy zx zy zz ω = ω = ω = ω = ω = ω = ω = ω = ω ≠ 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 2 0 0 0 0 2 0 0 0 0 0 0 0zz a n n            =      −    ω  r.r. thapa / bibechana 11(1) (2014) 149-156: (online publication: march, 2014) p.154 if any matrix x satisfies the equation ax = λx (8) the first in the solution of (7) is to found as the value of x. we can write (8) as (a λi) x = 0 (9) where i is the 6×6 unit matrix. the set of six simultaneous linear equations in six unknowns , , , , ,ξ η ζ ξ η ζ& && will have non-trivial solutions provided the determinant of the matrix (a λi) vanishes. i.e. a λi = 0 (10) to check the stability of the (10) non-trivial solutions. let us find values of λ from (10) i.e. from 2 2 2 2 0( 4 )( ) 0zznλ λ λ⇒ + − ω = (11) i.e. there are six values of λ. let 2 2 2 1 2 3, ,λ λ λ be three roots corresponding each factor of (11). the conditions for stable solution are 2 0 for 1,2,3.i iλ ≤ = from (11) 2 1 11 12 2 21 22 2 0 0 3 3 0 0 2 (imaginary) 2 , 2 when 0 = ⇒ = =  ⇒ = ±   ⇒ = = −   − ω = ⇒ = ± ω zz zz ni ni ni λ λ λ λ λ λ λ λ (12) but 3 3 5 7 2 2 2 2 2 22 2 2 9 15 ( ) ( ) ( ) ∂ω = − − + ∂ + + + z az az z z b z b z b 2 2 2 4 3 5 5 7 92 2 2 2 2 2 2 2 2 2 22 2 2 2 2 3 9 90 105 ( ) ( ) ( ) ( ) ( ) ∂ ω ⇒ = − + − + − ∂ + + + + + z z a az az z z b z b z b z b z b r.r. thapa / bibechana 11(1) (2014) 149-156: (online publication: march, 2014) p.155 2 2 2 2 0 0 0 0 0 3 3 5 2 2 4 2 0 0 0 0 5 5 1 3 3 5 9 5 1 ... 1 ... 1 ... 2 2 2 90 7 105 9 1 ... 1 ... 2 2 zz z z z za b b b b b b b z z z za a b b b b b b             ω = − − + + − + − − +                                        + − + − − +                        since z0 is very small in comparison of b hence 0 1 z b << and so 2 3 4 0 0 0, , ,... z z z b b b                   are negligible. thus we get [ ] 0 3 53 5 3 5 2 1 9 1 9 16 16 1 1 3 3 16 16 6a 1 9 1 using 1 3 3 3 1 − −      ω = − − = − +     + +              = − + + + = + =           = − + zz a a b b a a a a a r b a ( ) ( ) 0 2 3 3 31 32 1 1 1 1 ; 1 ω = − + ⇒ = − + ⇒ = ± + ⇒ = + = − + zz a a i a i a i a λ λ λ λ thus, all the six roots of the characteristic equation are 0, 0; 2ni, -2ni, 1 ; 1+ − +i a i a and hence the equilibrium position of the sitnikov restricted three body problem are stable. 4. conclusion the condition of stability is satisfied by solution of the sitnikov's problem the third body is oscillatory in nature. it displaced slightly from its equilibrium position but stayed in the neighbourhood of the equilibrium point. r.r. thapa / bibechana 11(1) (2014) 149-156: (online publication: march, 2014) p.156 acknowledgments the author is grateful to his respected supervisor dr. m.r. hassan, dept. of mathematics, s.m. college, bhagalpur, t.m.b. university, bhagalpur, 812007, india and also would like to gratefully acknowledge prof. dr. devendra adhikari (p.g. department of physics, m.m.a.m. campus, biratnagar, nepal) for inspiring discussion. references [1] w.d. macmillan, astronomical journal, 27 (1913) 11, [2] k.a. stinikov, dokl. akad. nauk, ussr, 133 (1960) 303. [3] e. perdois, et al., celest. mech. & dyn. astron., 42 (1988) 187. [4] p.s. soulis, celest. mech. & dyn. astron., 99 (2007) 129. [5] s.w. mccuskey introduction to cel. mechanics, addison-wesley publishing company, inc., 1963. [6] m.s. suraj, m.r.hassan, proceeding of pas, 50 (2013) 61. [7] r.r. thapa, m.r. hassan, proceedings: modern trends in science and technology, biratnagar (2013) 129. microsoft word harihar paudyal and p.doc harihar paudyal and p.n.s. roy / bibechana 8 (2012) 116-126 : bmhss, p.116 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana fractal approach: quantification of seismicity in south central tibet harihar paudyal 1 and p.n.s. roy 2 1 department of physics, birendra multiple campus, tribhuvan university, chitwan, nepal, email: hariharpaudyal@gmail.com 2 department of applied geophysics,indian school of mines, dhanbad, jharkhand-826 004, india, e-mail: pns_may1@yahoo.com corresponding author: dr. harihar paudyal, department of physics, birendra multiple campus, tribhuvan university, chitwan, nepal email: hariharpaudyal@gmail.com article history: received 22 november, 2011; accepted 10 december, 2011 abstract the south central tibet (sct) region is inferred to be an extensional regime since it is predominantly associated with normal faulting with e-w oriented horizontal tension axis representing extension in eastwest direction. in this paper the fractal analysis is carried out using the seismicity data (mb≥3.5) for last 47 years (1963-2009) in sct to the north of central himalaya. the entire study area is bounded by 29 o -31 o n and 85 o -90 o e. the study escorted to the recognition of a clustering events in two consecutive fifty events window having low spatial fractal correlation dimension (dc) value ranging from 0.3638 to 0.5451 during the period between 07.26.1998 to 03.23.2002. relatively two lower dc obtained prior to strong event. spatial-temporal clustering of events during low dc period actually specifies a highly stressed region, leading to increase of shear strain causing weak zone from where the rupture propagation may ultimately nucleate causing large earthquake. this type of clustering pattern study using the wellconstrained catalogue data for the sct region, which has a record of high seismic activity for the entire last two decades, can assist to enhance the understanding and mitigation of earthquake hazard. keywords: fractal spatial; correlation dimension (dc); clustering; seismicity 1. introduction fractal distributions are the units that are scale invariant and self similar. these behaviors are reflected in several empirical power laws of different branches in geology and geophysics [1]. seismic activity in a region has fractal structure with respect to time, space and magnitude [2] hence a fractal approach can be used to make probabilistic seismic hazard assessment [3]. several authors used this method in various seismically active region to study fractal nature of earthquake occurrence, fault systems and which imposed hazard for example kanto japan [4], mexican subduction zone [5], north anatolian block [6], himalayan region [7], koyanawarna region [8], hokkaido, japan [9], east java-indonesia [10], northwest himalayan region [11]. harihar paudyal and p.n.s. roy / bibechana 8 (2012) 116-126 : bmhss, p.117 the spatial fractal correlation-dimensions (dc) provide a quantitative measure of clustering of seismic events in space indicating the seismicity of a region. such parameter measures quantitative seismicity spatio-temporally from sliding windows with time containing certain number of events. in the present paper, we use the fractal approach to study the seismic hazard of sct region bounded by 29 o -31 o n, 85 o -90 o e to the north of central himalaya. the region is considered for consecutive period with a single entity of 50 events sliding window for which fractal analysis is carried out. 2. seismotectonics characters of the sct region the earthquake activity of sct region lying to the north of central himalaya is influenced by several factors such as highly deformed structures and large crustal thickness, intense geothermal activity as well as high vertical temperature gradient etc. [12]. the region is dominated by normal faulting in which most of the tectonic stresses have orientation along north-south striking normal faults. the indus tsangpo suture (its) separates the himalayas from the gangdise block which lies just north of it. the indus suture reflects the relative motion of indian plate and complex micro-plates towards the north. the tibetan plateau, to the north of the its, has an average elevation of 3 km and some of the hills rise up to 4.5 km. the origin and the evolution of this plateau are directly related to the process of continental collision of indian lithospheric plate with asia along the himalayan arc [13]. this wide tectonic zone consists of tethyan sediments with marine deposits that range in age from the late precambrian to the eocene [14, 15, 16]. the region has a multilayered composition where earthquake activities occur adjacent to the its and north of it. the plateau was uplifted to its present position 10 ma ago [15, 16] with a crustal thickness of about 70 km in the central part of the plateau. by determining the velocities and propagation characteristics of pn and sn waves beneath the tibetan plateau, barazangi and ni [17] reported that the shield like material exists in the uppermost mantle beneath tibet. the tibetan plateau is characterized by predominantly normal faulting with extension in the east-west direction [18]. many transverse lineaments are present between the gangetic fore–deep and the its across the himalaya. strikes of these transverse lineaments, in general, vary from northwest to northeast, and are parallel to the outline of the sub-surface ridges underlying the fore-deep [19]. some of them are reported to be seismically active. the sct region is characterized by the isolated clustering of seismic activity where shallow focus seismic activities occur throughout the region but more frequent in the identified active regions. however, some intermediate seismic activities (from 70 to 110 km) also occur mainly to the north of the its which coincide with the clusters of shallow focus earthquake activity. further, it has been observed that there exists a non-uniform pattern of seismic energy release with depth estimated at 10 km interval, the distribution of maximum seismic energy released (85%) with depth lies 10-20 km in sct [12]. the seismicity in and around tibetan plateau is largely controlled by the convergence of the indian and eurasian plates [13, 20]. the seismic characteristics of the region are reported by several workers mainly using spatialtemporal distribution of events [21, 22, 23]. verma and reddy [22] reported that the tibetan plateau is not behaving as a single seismotectonics unit, whereas several blocks within it, having different seismic characteristics, move relative to each other. sato et al. [23] observed that the seismicity is diffused and bears no long linear trend to the north of the its. the earthquakes are mainly shallow, but some intermediate depth events have also been observed in certain isolated pockets. the tectonic environment of this region is almost uniform with extensive north-south trending normal faulting and the isolated clustering of seismic activities are found in association with these faults. clusters of events was observed to the north of the its and it is evident that this might have been caused by the local normal fault, and the influence of himalayan mega thrusts seems to be remote. the activity has been low for the period 1963-1980, moderate during 1980-1994, and followed by a drastic increase since 1995 [24]. it may be said that the general view of the seismic processes in the sct region governed by the high heat flow associated with large internal temperature gradient and a large crustal thickness. 85 85.5 86 86.5 87 87.5 88 88.5 89 89.5 29.5 30 30.5 harihar paudyal and p.n.s. roy / bibechana 8 (2012) 116-126 : bmhss, p.118 probably, the seismic activities are caused by the change in the physical properties due to the high heat flow associated with plumes prevailing at depths coupled with abnormally large crustal thickness of the region [12]. the distribution of earthquakes in the study region during 1963-2009 is shown in figure 1. although the earthquake frequency is more in recent time, indicating the region is moderately active since large earthquakes are infrequent compared to adjacent himalayan compression zone. in the region to the north of the its concentrated shallow and intermediate events occur frequently. recently moderate size events are also found to be preceded by anomalous seismic activity prior to mainshock [12]. fig. 1: seismicity of south central tibet region (1963-2009). 3. data and method the earthquake data b a s e p r e p a r e d (mb ≥3.5) from all existing catalogs [12] which has been used for the period 1963-2009 for the study of sct region. the consecutive 8 windows formed for each 50 events period totaling t o 400 earthquakes in the region with latitude 29°n-31°n and longitude 85°e90°e. fractal analysis was carried taking 50 events window to investigate the fractal nature of earthquake in the specified region. the scaling range for the linear portion of log r vs. log c(r) plot is about 5km 90km, which is well within the region of the study considered. the value of scaling region is approximately smaller than 1/3 ~ 1/4 of the side length of analysis region complying with the study [ 4 ] ruling out boundary effect on our analysis. in the present paper spatial fractal correlation-dimensions (dc) and their variation with time is determined using correlation integral method [25] on the catalogue of earthquakes of central himalaya. the methodology to compute dc is as follows: the fractal correlation dimension is derived from the correlation integral [25-29] which is a cumulative correlation function that measures the fraction of points in the 2-dimensional space. it is defined as, harihar paudyal and p.n.s. roy / bibechana 8 (2012) 116-126 : bmhss, p.119 ∑∑ +== − − = n ji ij n j rrh nn rc 11 )( )1( 2 )( (1) where n (for 100 events window, n will be 100c2 i.e 2500 and for 50 events window, n will be 50c2 i.e 1225) is the total number of pairs of vectors with respect to one another in the fractal set to determine dc, r is the length scale, rij the distances between the points of a set, h is the heaviside step function. the value of r i j is computed through spherical triangle method [7, 30]. consequently, c(r) is proportional to the number of pairs of points of the fractal set separated by a distance less than r. the fractal correlation dimension is given as )(log )(log lim 10 10 0 r rc dc r→ = ( 2 ) if the system of points examined fits into a fractal set, the graph between c(r) and r in logarithmic coordinates must be a linear function with slope dc equivalent to the fractal dimension of the system. the g r a p h o f c(r) versus r at different stages of the fracture process, with 50 event windows, is shown in fig.2. the curves show a clear self-similar behaviour in a wide range of about two orders of magnitude on the space scale. deviations from linear dependence in the range of large scales are connected with the finite size of samples, while the other deviation in the range of small scales reflects the boundary effect of data for the region of investigation. 4. results the spatial distribution of earthquake depicts that epicenters are clustered in different pockets (fig. 1). hence to quantify such distribution, the present study is carried out using fifty events window. the study of correlation fractal dimension (dc) of all events with mb≥3.5 occurring in the sct region during 1963 to 2009 shows that its value fluctuating with time considerably (fig. 2). the values of variation of spatial correlation dimension with time are given in table 1 for all considered eight windows. the correlation integral method as described above is used to compute the correlation fractal dimension. it provides information how the past events are having correlation with each other. in heterogeneous region like sct, the correlation integral approach helps to recognize the cause of strong events. in the considered sct region, clustering were observed for events with low dc values estimated as 0.3638 (for the window 26/07/1998 -08/09/1998) and 0.5414 (for the window 10/09/1998 -23/03/2002) indicating highly stressed period. the variation in correlation dimension from region to region represents seismic clustering within the study region (fig. 2). the second window having the dc value 0.9401 for the period 06/05/1990 -10/05/1996 led to a moderate event of mb 5.9 in 17 march 1996. the fourth window with the dc value 0.9913 for the period 25/08/1996 -23/07/1998 led to another moderate event of mb 5.8 in 20 july 1998. however, we can see in fig. 2 that prior to fifth window low value of dc indicates shear stress increase. basically after fifth window we have two consecutive low dc in windows six and seven; they may be attributed to large number of aftershocks. harihar paudyal and p.n.s. roy / bibechana 8 (2012) 116-126 : bmhss, p.120 time (indexed) fig. 2: the temporal variation of dc for fifty events window is shown, where point given by a and b represent clustering of events with dc value 0.9401 and 0.9913 for second and fourth windows respectively. table 1: correlation dimension dc variation with time for the events occurred in the region as shown in figure 2. low dc values correspond to fifth and sixth window. sn time for 50 events dc sn time for 50 events dc 1 11/06/1963 -18/02/1990 1.221 5 26/07/1998 -08/09/1998 0.3638 2 06/05/1990 -10/05/1996 0.9401 6 10/09/1998 -23/03/2002 0.5451 3 10/05/1996 -23/08/1996 1.1684 7 23/03/2002 -30/09/2003 0.9181 4 25/08/1996 -23/07/1998 0.9913 8 11/11/2003 -07/11/2009 1.2459 harihar paudyal and p.n.s. roy / bibechana 8 (2012) 116-126 : bmhss, p.121 fig. 3: log c(r) versus log r is shown for fourth time window for the sct region, the slope gives dc 0.9913. the f i t t ing of t rend l ine demarcates the scaling region obeying power law i.e. scale invariance. r2 represents correlation coefficients of the regression line. 5. discussion and conclusion the advances in statistical analysis of seismological data were discussed by several research papers [31-34]. such studies provides a new understanding of the scaling parameters of seismicity, which gives an opportunity to evaluate seismic hazard and to estimate short to long term rate of future seismic activity in a given region. the correlation fractal dimension (dc) provides a quantitative measure of the spatial clustering of epicenters and also of the seismicity of the region. the dc value is inversely related to the degree of clustering and it requires higher degree of accuracy in both space and time of occurrence of events, as the present analysis depends on the spatio-temporal distribution of earthquake sequences. thus, it is utmost important to use well constrained complete and homogeneous catalogue. the sct zone has complex geodynamic process due to combination of several factors such as northward movement of indian plate, resistance provided by the thick tibetan plate and high heat flow [35]. fractal analysis of seismicity for such a region is useful to correlate the seismogenesis and hence indicator for possible cause of large events. clustering of events in a short period is an apparent feature of shallow seismic activity whereas long period clustering must be studied in the presence of a much stronger signal. such clustering for a short period is essential for obtaining the efficient and fruitful model. therefore a model is necessary to explain such clustering pattern, timespace –focal mechanism regularities of events sequences [36]. 85 85.5 86 86.5 87 87.5 88 88.5 89 89.5 29.5 30 30.5 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3 harihar paudyal and p.n.s. roy / bibechana 8 (2012) 116-126 : bmhss, p.122 the time period of increased moment release in moderate size event has correlations with the regional stress field [37]. moreover, the critical point model for regional seismicity hypothesized that during low dc periods the region is in or near to self organized critical (soc) state in which small events fall into larger events. this may be featured to self similarity of earthquakes of different sizes that may allow fractures to self-organize order to gain criticality as computed by the clustering of events in the region of stress accumulation ultimately causing the main shock (figs. 4, 5a, 5b, 6a and 6b). it is clear that for the first five time window the clustering is mainly in the central part (figs. 5a and 5b) where seismic activity is very high with two moderate size events having mb 5.9 (03/17/1996) and 5.8 (20/07/1998). both of these events are followed by large number of aftershocks. fig. 4: dc value contour for the sct of all eight windows of consecutive fifty events. the lowest d values patch represents possible highly stressed region and clustering of events. the dc value varies from region to region however the lowest values are near the center of the region for all the time windows (figs 4, 5b and 6b). a normal fault trending ne-sw located in the region [18, 19]. the activity in near to this fault is swarm like during 1996 to 1998 [12]. these clustering can be monitored by the correlation integral technique for the major events. the presence of high stress regime for the release of accumulated strain accelerates the seismic activity of moderate sized earthquakes which can be accessed by the precursory spatio– temporal dc variation study. 85 85.5 86 86.5 87 87.5 88 88.5 89 89.5 29.5 30 30.5 85 85.5 86 86.5 87 87.5 88 88.5 89 89.5 29.5 30 30.5 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 harihar paudyal and p.n.s. roy / bibechana 8 (2012) 116-126 : bmhss, p.123 fig. 5a: spatial distr ibut ion of f irst f ive t ime windows of fifty events. fig. 5b: dc value contour for the sct of first five windows of consecutive fifty events. the lowest d values patch represents possible highly stressed region and clustering of events. the present study based on fractal pattern of seimsicity showed that dc value drops significantly in two consecutive windows from july 1998 to march 2002. such drops represents higly accumulated stress and can be considered as a numerical warning of strong earthqukaes. strong events following such a period reduces a sufficieent portion of the accumulated regional strain which makes the region out of a soc state. the considered sct region presently have high dc values representing stress accumulation process is quite slow. 85.5 86 86.5 87 87.5 88 88.5 89 89.5 29.5 30 30.5 85.5 86 86.5 87 87.5 88 88.5 89 89.5 29.5 30 30.5 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 harihar paudyal and p.n.s. roy / bibechana 8 (2012) 116-126 : bmhss, p.124 fig. 6a: spatial distr ibution of last three t ime windows of fifty events fig. 6b: dc value contour for the sct of last three windows of consecutive fifty events. the lowest d values patch represents possible highly stressed region and clustering of events. harihar paudyal and p.n.s. roy / bibechana 8 (2012) 116-126 : bmhss, p.125 acknowledgements the present work has been carried out within the framework of the associateship scheme of the abdus salam international centre for theoretical physics (ictp), trieste, italy. the authors are grateful to ictp for providing the necessary facilities and literature for the present work. one of the authors (hp) acknowledges ugc, nepal for fellowship and tribhuvan university for sabbatical leave. pns roy acknowledges moes/p.o./ (seismo)/gps/ 60/2006 project for providing computational facility in developing 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[37] s.c. jaume and l.r. sykes, pure and applied geophysics 155 (1999) 279-306. microsoft word s.k.shah et al. _61-64_.doc s.k. shah et al. / bibechana 7 (2011) 61-64: bmhss 61 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana surfactants, its applications and effects on environment s.k. shah, a. bhattarai , s. k. chatterjee∗∗∗∗ dept. of chemistry, mahendra morang adrash multiple campus, biratnagar, tribhuvan university, nepal article history: received 2 december 2010; accepted 5 december 2010 abstract surfactant is being considered as a very demandable molecule in the field of chemistry. this paper reviews most important factors especially the uses of surfactants and their effects on environment. evaluation of surfactants are based on examining the ability of the surfactant to maintain lower interfacial tension between target contaminant and water, satisfying lower cmcs, and sustaining lower sorption and precipitation to target substrate. surfactant mixtures of anionic and nonionic surfactant are shown to be excellent candidates for robust surfactant cleaners. keywords: surfactant, interfacial tension; critical micelle concentration; anionic surfactant; nonionic surfactant 1. introduction to surfactants surfactants are amphiphilic molecules having a hydrophilic or water soluble moiety (head group) and a hydrophobic, or water insoluble moiety (tail group). at low concentrations, surfactants exist solely as monomers. the formation of micelles, begins at a specific surfactant concentration termed the critical micelle concentration (cmc), where the physical properties of the solution, such as interfacial tension, electrical conductivity, and light scattering behaviour, often changes abruptly due to the existence of micelles[1]. the cmc concentration corresponds also to the point where the surfactant first shows the lowest surface/interfacial tension [2]. interfacial tension is the tensile force that exists at the interface of two immiscible liquids. this force arises as a result of mutual dislike of molecules, such as oil and water, on two sides of the interface. if the two liquids are fully miscible with each other, there is no interfacial tension between them. the amphiphilic nature of surfactants, which results from their water-like and oillike components, causes them to accumulate at interfaces and thus reduce the interfacial tension between oil and water. beyond the cmc, the aqueous monomer concentration will not increase with any further addition of surfactant since the additional surfactant will form micelles. spherical micelles orient with surfactant hydrophobic tails pointed toward the interior and hydrophilic head point outward to the surface of micelles. this creates the hydrophobic interior of ∗ corresponding author: prof. s. k. chatterjee, dept. of chemistry, mahendra morang adrash multiple campus, biratnagar, tribhuvan university, nepal, e-mail: sujeetkumarchatterjee@yahoo.com , tel.: +977 9842059697 s.k. shah et al. / bibechana 7 (2011) 61-64: bmhss 62 the micelle within which hydrophobic organic molecules can partition, thus increasing the aqueous solubility of the none-aqueous liquids (nals) in the solution. this is referred to as micellar solubilization[1]. therefore, below the cmc, micelles do not form and the surfactant solution does not enhance the solubilization for nals. surfactants are classified as ionic and nonionic with varying chemical structures according to their hydrophilic group. for industrial applications, the ionic surfactants are classified based on the charge they carry when dissociated in water at their neutral ph. these classifications are namely anionic, cationic and zwitterionic or amphoteric[1,3]. surfactants are also classified according to the balance between the hydrophilic and hydrophobic, or lipophilic, portions of the surfactant molecule. a lipophilic substance is one with a high affinity for fatty or organic solvents and it is essentially a hydrophobic substance [4]. surfactants with a high hydrophile lipophile balance (hlb) number are more soluble in water, and a low hlb indicates the surfactant is more soluble in an organic solvent [5]. 1.1. surfactants enhanced industries surface-active agents, or surfactants, are widely used in many industrial and commercial products and possessed throughout the world. surfactants are not only related to soaps and detergents in daily life, they are also in heavy demand for industrial processes requiring colloid stability, metal treatments, mineral flotation, pesticides, oil production, pharmaceutical formulation, emulsion polymerization, and particle growth [6, 7]. 1.2. surfactants created environmental problems the broad range of surfactant applications may also cause side effects in the environment and in these industrial processes. the application of surfactants can also produce environmental pollution and raises a series of problems for wastewater treatment plants [8]. the target of surfactant analysis would be twofold: quality assurance for commercial products and pollution control in environment [9]. in assay of surfactant products, the analytical methods should be able to identify surfactants of various types universally in a simple way. in conjunction with pollution control, on the other hand, the techniques to identify and quantify the surfactants released from the surfactant products to the environments would require much lower detection limits at the level of trace analysis [10, 11].the constraint of extremely low detection limit is due to huge dilution and biodegradation of the released surfactants in environments. the currently most important uncharged nonionic surfactants, are the branched-chain and, therefore, biodegradation-resistant alkylphenol ethoxylates (apeos) constituting about 7% of the world surfactant consumption. the apeos [cnh2n+1-c6h4-o-(ch2ch2o)mh] are environmentally persistent organic pollutants (pops) because their biodegradation is very slow and quite often incomplete for a long period of time. moreover, several of their degradation products and metabolites are more toxic to aquatic organisms than the parent homologs and, therefore, their persistence and showing estrogenicendocrine modulating effects in aquatic organisms is a “hot” issue of major healthand environment-related concern worldwide. although there is still not enough evidence to support the hypothesis that exposure to endocrine-disrupting chemicals (edcs) is a global environmental human health problem, the following relevant facts have been established. estrogenic activity of domestic sewage treatment work effluents was shown to occur at levels capable of producing biological effects in fish exposed to this water [12].many of the xenoestrogens, such as the apeos, and their degradation products, such as the carboxylated metabolites [13,14], enter the aquatic environment by means of discharge from municipal sewage treatment works, industrial effluents and untreated sewage and can occur in effluents and rivers from nanogram to mg/l levels [15-17]. s.k. shah et al. / bibechana 7 (2011) 61-64: bmhss 63 although no clearcut evidence of endocrine disruption was demonstrated, a recent study with 4-nonylphenol, a persistent metabolite of apeos, has indicated that this compound and some of its short-chain polyethoxylates may have toxic effects at environmentally realistic concentrations of 0.01-10 ppb [18, 19]. as previously mentioned, the results [20] corroborate these findings and their implications. 1.3 surfactants used in daily life cationic surface active substances (csas) are important class of pollutants of surface waters. csas are frequently used as factors against lumping in artificial fertilizers [21], corrosion protectors [22, 23], and as factors delivering softening effect and static control in washing powders and liquids [24-26]. frequently they are components in cosmetics [27], pharmaceuticals [28], and antiseptic and sanitary products [29]. csas exhibit strong bactericidal and fungicidal activity [30-32]. a result of surfactant pollution include the ability of surfactants to increase the solubility of other toxic organic compounds in soils and when adsorbed to sludge that can have a negative impact on sludge dewatering characteristics at municipal water treatment plants. two suggestions for reducing surfactant pollution include dispensing only the quantity required of the major components for a particular wash cycle or using environmentally friendly detergents [33]. surfactant mixtures of anionic and nonionic surfactant are shown to be excellent candidates for robust surfactant cleaners. at present we are working on the solution properties of cationic surfactant i.e. cetyltrimethylammonium bromide in methanol–water mixture of different percentage composition and also trying to observe the effect on cmc value [34]. 2. summary this review presents the information about surfactants. it has been shown that successful surfactants enhance industries. but some surfactants create the environmental problems. if we use in a proper way, surfactants will be beneficial for daily uses. references: [1] m.j. rosen, surfactants and interfacial phenomena, 4th ed., wiley-interscience, new york. (2004). [2] k. urum and t. pekdemir, chemosphere, 57 (2004) 1139. [3] k. holmberg, b. jonsson, b. kronberg, and b. lindman, surfactants and polymers in aqueous solution, 2nd ed. england, john wiley & sons ltd. (2003). [4] d. myers, surfaces, interfaces, and colloids: principles and applications, 2nd edition, new york: wiley-vch, john wiley and sons (1999). [5] j. childs, e. acosta, j. f. scamehorn and d. a. sabatini, j . energy resour . technol. , 127 (2005)153. [6] p. c. pavan , e. l. crepaldi and j. b. valim, j. colloid interface sci., 229(2000)346. [7] c. e. hoeft and r. l. zollars, j. colloid interface sci., 177(1996)171. [8] n. paxeus, water res., 30(1996)1115. [9] t. m. schmitt, analysis of surfactants in surfactant science series: new york, u.s.a., vol. 40 (1992). [10] g. g. ying, environ. int., 32(2006) 417. [11] w. h.ding, and y. h. liao, anal. chem, 73( 2001) 36. [12] e.j. rutledge, d. sheahan, c. desbrow, g.c. brighty, m. maldoc and j.p. sumpter, environ. sci. technol, 32(1998) 1559. s.k. shah et al. / bibechana 7 (2011) 61-64: bmhss 64 [13] m. ahel, e. mplnar, s. ibric and w. giger, wat. sci. & tech., 42(2000)15. [14] j.a. field and r.l. read, environ. sci. tech., 30 (1996)3544. [15] l.n. britton , j. surfact. deterg., 1 (1998) 109. [16] u. zoller ,toxic. environ. chem., 66(1997) 145. [17] c.g. nylor, j.p. mieure , w.j. adams, j.a. weeks , f.j. castaldi, l.d. ogle and r.r.romano, the alkylphenols and alkylphenol ethoxylates – review, vol. 1, washington, d.c., (1998) pp. 32-43. [18] z. billinghurst, a.s clare, t. fileman, j. mcevoy, readman, j. and m.h. depledge, mar. poll. bull., 36(1998) 833. [19] s. jobling, d. sheahan, a. osborne, p. mathiessen and j.p. sumpter , envir. toxicol. chem., 15 (1996)194. [20] u. zoller, i. plaut and m. hushan, wat. sci. & technol., 50 (2004) (in print). [21] b. brycki, antimicrobial activity and other properties of quaternary ammonium salts; proceedings of iii symposium on quaternary ammonium salts and the fields of their application in industry, poznań, (1997) 24-36 (in polish). [22] l. h. huber, jaocs, 61(1984) 377. [23] j. cross, introduction to cationic surfactants [in]: cationic surfactants, analytical and biological evaluation, marcel dekker: new york-basel-hong kong (1994). [24] s. giol -ando r.a rapaport., chemosphere, 30(1995)1067. [25] j. pernak et al., pol. j chem, 77 (2003)1263. [26] r. lagerman et al., jaocs, 71 (1994)(1)97. [27] a. k. reng, sofw, 4 (1984) 90. [28] s. witek biological activity of quaternary ammonium salts and lysosomotrophic amines; proceedings of iii symposium on quaternary ammonium salts and the fields of their application in industry, poznań, 7(1998) (in polish). [29] w. śliwa, n-substituted piridinium salts; synthesis, properties and application; academic edition wsp , częstochowa, (1996) (in polish). [30] j. pernak , a. zabielsk, j. matejuk and e. urbanik, holtzfforschung, 52 (1998)249. [31] a. skrzypczak et al., eur. j. med. chem., 32 (1997) 661. [32] a. zabielska, j. matejuk, et al., holzforschung, 58(2004)292. [33] j. hack, j. chem. technol. biotechnol., 50(1991) 379. [34] s.k. shah, g. s. srivastav, a.b. bhattarai and s.k. chatterjee, j. nepal chem. soc., 24 (2009) 24. microsoft word achut ram pradhananga et al_141-150_.doc achut ram pradhananga et al./ bibechana 9 (2013) 141-150: bmhss, p.141 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana assessment of physico-chemical parameters of surface water quality of taudaha lake of kathmandu and their comparison with other global published values achut ram pradhananga 1 , ramesh kaji shakya 2 , pawan raj shakya 1* 1 department of chemistry, padma kanya multiple campus, tribhuvan university, kathmandu 2 department of zoology, padma kanya multiple campus, tribhuvan university, kathmandu * corresponding author email: pawansh2003@yahoo.com article history: received 10 novemver; accepted 24 november, 2012 abstract the aim of current study was to evaluate the status of taudaha lake water with respect to different physico-chemical parameters (ph, electrical conductivity, dissolved oxygen, free co2, total dissolved solids (tds), total suspended solids (tss), total solids (ts), total alkalinity, total hardness, chloride, nitrate, sulphate, phosphate, sodium, calcium, magnesium, lead, cadmium, copper and zinc) in monsoon season 2012. results reveal that almost all the physico-chemical parameters including the elemental investigation of the lake water have values within the range of the maximum permissible levels for drinking water. the results were compared with who water quality guidelines as well as with literature values reported for global lake water. key words: physico-chemical parameters; taudaha lake; surface water quality; who guideline values; trace and toxic elements. 1. introduction lakes and surface water reservoirs are the planet’s most important freshwater resources and provide innumerable benefits. they are used for domestic and irrigation purposes, and provide ecosystems for aquatic life especially fish, thereby functioning as a source of essential protein, and for significant elements of the world’s biological diversity. they have important social and economic benefits as a result of tourism and recreation, and are culturally and aesthetically important for people throughout the world. they also play an equally important role in flood control [1]. however, the remarkable increase in population resulted in a considerable consumption of the water reserves world wide [2]. the quality of surface water is largely affected by natural processes (weathering and soil erosion) as well as anthropogenic inputs (municipal and industrial wastewater discharge). the anthropogenic discharges represent a constant polluting source, whereas surface runoff is a seasonal phenomenon, largely affected by climatic conditions [3, 4]. among environmental pollutants, metals are of particular concern, due to their potential toxic effect and ability to bioaccumulation in aquatic ecosystems [5, 6]. therefore, it has public interest [7, 8]. the serious environmental problems have been faced in developing as well as developed countries [9]. dissolved constituents of water bodies are often determined as a major component for baseline limnological studies. the major ions ca 2+ , mg 2+ , na + , k + , cl , so4 2, hco3 , and co3 2 are essential constitute of water and achut ram pradhananga et al./ bibechana 9 (2013) 141-150: bmhss, p.142 (online publication: nov., 2012) responsible for ionic salinity as compared with other ions [10]. contamination of aquatic ecosystems with heavy metals is a serious problem all over the world [11]. water quality monitoring has a high priority for the determination of current conditions and long-term trends for effective management. the supply of safe water has a significant impact on the anticipation of water transmissible diseases [12]. the abundance of organic compounds, radionuclides, toxic chemicals, nitrites and nitrates in water may cause unfavorable effects on the human health especially cancer, other human body malfunctions and chronic illnesses [13]. therefore, it is necessary to frequently monitor water quality, used for drinking purposes. taudaha, the only natural lake in central nepal at an altitude of 1350 m with 27° 38.88’ n latitude and 85° 17.05’ e longitude is located approximately 10 km away from the center of kathmandu [14]. the lake is situated here from the time immemorial holding historical significance of kathmandu valley long before the settlement of human society. according to the legend, the lake was created by god manjushree as a home for the king of serpents karkotak and his wife who lost their home when the valley was drained. it is also believed that karkotak resides to this day in the epicenter of the lake. at present, the mean depth of the lake is approximately 3 m and it covers an area of 4 hectare. it has eight corners with uneven in shape, nine inlets covering north-west agricultural fields and permanent outlet towards southwest. it is reported to have in average 0.12 million liters water inlets per day and outlet in average 0.27 million liters of water per day [14]. because of the religious importance, townspeople come to the lake twice a year for paying homage to this sacred site. presently, karkotak nagraja nagrani resident restoration society (knnrrs) has been safe guarding the place that has now turned into recreation center for visitors and nature lovers as well as for ecological studies. therefore, it has become necessary to monitor water quality to observe the pollution level of the surface water of the lake time to time. several water analyses have been regularly conducted by different scientific groups across the country. the present work is an attempt to examine the water quality status of the lake with respect to different physico-chemical parameters in monsoon season. 2. material and methods study site and sample collection taudaha lake (fig. 1) was selected for the study purpose because it holds the ancient history of kathmandu valley. the sampling network was designed to cover a wide range of determinates of key sites, which reasonably represent the water quality of the lake system. multiple samples for different analytical purposes were collected using separate pet bottles from 6 key sites of the same station in monsoon season. all water samples were delivered on the same day to laboratory and stored at 4°c until further processing and analysis. analytical procedure different physico-chemical parameters were determined using the following methods: the water temperature, ph, electrical conductivity (ec), of each water sample were measured at the sampling points by a mercury thermometer, digital ph meter and ec meter, respectively. in laboratory, tds, tss and ts were determined by drying and weighing method. measurement of do was done by winkler’s iodometric method while free co2 by titrimetric method using standard 0.05 n naoh [15]. for anions and metal analysis, the duplicate aqueous samples of each site were filtered through whatman filter paper no. 42 and the samples were divided into two parts. one part was used for analysis of anions and the remaining physico-chemical parameters, while second part treated with 1ml of concentrated hno3 for metal analysis. total alkalinity was determined by acid titration using methyl-orange as endpoint while total hardness by complexometric titration method [15]. chloride was measured by silver nitrate (agno3) titration using potassium chromate (k2cro4) solution as an indicator and nitrate was measured by phenol disulphonic acid method [15]. similarly, phosphate was determined by molybdate achut ram pradhananga et al./ bibechana 9 (2013) 141-150: bmhss, p.143 (online publication: nov., 2012) ascorbic acid method and sulphate was determined spectrophotometrically by barium sulfate turbidity method [16]. the acid-treated water samples were further diluted 20-time with ultrapure water for analyzing na and ca, using flame photometry, while mg was determined by the flame atomic absorption spectrometer (faas). for trace and toxic elements, the volume of water samples was reduced four-fold at 60°c on an electric hot plate. zinc, copper, lead and cadmium were determined by varian model-aa240fs fast sequential atomic absorption spectrophotometer (aas). reagents and solutions all chemicals used were of analytical reagent grade or the highest purity available. doubly distilled water was used throughout the study. standard solutions of all the elements were prepared by dilution of certified standard solutions 1000 ppm, fluka kamica (buchs sg and switzerland) of corresponding metal ions. the quality of the analytical data was ensured through careful standardization and blank measurements. descriptive statistics using simply mean and standard deviation was used for analysis of the results. 3. results and discussion the physico-chemical parameters and elemental concentrations of water samples collected from 6 sampling sites of the taudaha lake water are presented in table 1, 2 and 3 respectively; the results are compared with the values of world health recommended maximum permissible limits [17] and with other global published values on lakes in different continents. the taudaha lake water recorded 29 o c in average during the study period. the temperature is one of the important factors in aquatic environment since it regulates physicochemical as well as biological activities [18]. mean ph value (8.9) of the lake water was found in the alkaline range (table 1). the ph range (8.69.1) of the water samples were found above the upper limit defined by who guidelines of 6.5-8.5 [17]. high value of ph may result due to waste discharge, microbial decomposition of organic matter in the water body or may be attributed to sewage discharge by surrounding human population [19]. the ions (ca 2+ , mg 2+ , na + , k + , cl , so4 2, hco3 , and co3 2) constitute the total ionic salinity in most fresh water as reported in literature [20]. electrical conductivity is a measure of water capability to transmit electric current and also it is a tool to assess the purity of water. the ec values of the lake water were found to be lower as compared to the maximum permissible levels recommended by who (2004) guidelines for drinking water. the mean conductivity values of the lake water were lower than those reported in literature (table 1) for other lakes [21-23, 31] except in the case of tuskegee lake, usa [30]. mean tds, tss and ts values in the present study were found to be 124.5, 621.4 and 745.8 mg/l respectively. high levels of tds, tss and ts in water used for drinking purposes may lead to many diseases [33]. the who has established water quality standard of 500 mg/l to provide for palatability of drinking water [17]. accordingly, the tds value was found to be lower than the maximum permissible limit. do is of great importance to all living organisms. besides, it is a very important parameter of water quality and an index of physical and biological process going on in water. it may be present in water due to direct diffusion from air and photosynthetic activity of autotrophs [19]. in the present study, the mean concentration of dissolved oxygen (5.8 mg/l) was found to be within the permissible level for drinking water (table 1) [17]. this value was observed in monsoon season, which favours solubility of oxygen in water bodies [19]. moitra and bhattacharya [34] found maximum dissolved oxygen in winter season which they explained due to low temperature. the minimum dissolved oxygen was found in summer due to high temperature, and higher microbial demand of oxygen for decomposition of suspended organic matter [35, 36]. mean free co2 was found to be 21.6 mg/l (table 1), the value higher than the maximum permissible limit as defined by who guidelines [17]. our results are in agreement with that reported by chettry and pal [37]. they observed positive and significant correlation with biological oxygen demand achut ram pradhananga et al./ bibechana 9 (2013) 141-150: bmhss, p.144 (online publication: nov., 2012) but inverse and significant correlation with total alkalinity and total hardness. however, minimum free carbon dioxide was reported during winter season [38]. mean value of the total alkalinity of the lake water was found to be 111.7 mg/l (table 1); the value being well below the maximum permissible limit according to who [17]. the value was also lower than that of manchar lake, pakistan [21] but was higher than tuskegee lake, usa [30]. das and chand [39] also recorded low alkalinity during monsoon supporting our results, which might be due to dilution effect of rainfall. total hardness is the total soluble magnesium and calcium salts present in the water expressed as its caco3 equivalent. the hardness of water increases in the polluted water by the deposition of such salts [19]. the total hardness in the taudaha lake was found to be 106.3 mg/l (table 1). this mean value lies within the range of the who recommended value [17]. khan et al. [40] also found similar results in triveni lake water of amravati district, india during monsoon season. similarly, patralekh [41] recorded minimum quantity in rainy season stating due to more dilution of water. however, maximum total hardness in winter season might be due to low volume of water and slow current of water [42]. the concentrations of cl , so4 2 and po4 3 in taudaha lake water did not exceed the who recommended values (table 2). the value of cl was higher than that of tuskegee lake, usa [30] but significantly lower than manchar lake, pakistan [21]. according to versari et al. [43], chloride concentrations higher than 200 mg/l are considered to be a risk for human health and may cause unpleasant taste of water. munawar [44] has suggested that higher concentration of chloride in water is an index of pollution of animal origin and there is a direct relation between chloride concentration and pollution level. the concentration of so4 2 in the lake water was significantly lower than those of the reported literature [21, 30] but the value was almost similar to siberian ponde [28]. on the contrary, the value of po4 3 was found to be higher than manchar lake, pakistan [21] and tuskegee lake, usa [30] but it was significantly lower than kasumigaura lake, japan [27]. the no3 concentration in the lake was found to be 1.9 mg/l. it has been found that all the elemental investigation of the taudaha lake water have lower values as compared to the maximum permissible levels of these elements in drinking water (table 3). however, the concentration of ca 2+ was higher in the lake water sample as compared to mg 2+ and na + . when compared with other global published values, the ca 2+ concentration was significantly lower than the value reported in the literature [21, 28] but was higher than those reported values in the literature [27, 30]. similarly, the mg 2+ value in the lake water was significantly lower than manchar lake, pakistan [21] and latvian lakes [32] but was higher than kasumigaura lake, japan [27] and tuskegee lake, usa [30]. likewise, the na + value in the lake water was significantly lower than the reported values in the literature [21, 22, 27, 32] but higher than the value of tuskegee lake, usa [30]. it has been reported that high consumption of salts, particularly nacl, may be crucial for the development of hypertension and increases the risk for stroke, left ventricular hypertrophy, osteoporosis, renal stones and asthma [45]. the concentration of toxic elements cd, cu, pb and zn detected in the lake water were found to be multifold lower than the maximum permissible limits of these elements in drinking water (table 3). the level of cd in the lake water was significantly lower than manchar lake (pakistan) [21], lake nakuru (kenya) [22] and nacharam lake (india) [29] while higher than the other lakes [23, 24, 26, 27, 28, 30-32] (table 3). it has been reported that the elevated concentrations of cd can cause nausea, vomiting, salivation and renal failure as well as kidney, liver and blood damages [46]. the concentration of pb in the understudy lake water was higher than other 8 lakes water samples [23, 24, 26, 27, 29-32] but significantly lower than those reported in the literature [21, 28]. the adverse health effects of lead consist of various cancers, adverse reproductive outcomes, cardiovascular and neurological diseases [47]. cu and zn showed almost similar behaviour and their concentrations in the lake water were found to be significantly lower than the maximum permissible levels (table 3). besides, they were also found to be lower than the reported values of the literature [21, 22, 25] but higher than other lake water samples [3032]. both the metals are essential nutrients for plants and animals, occurring naturally in environment. in natural waters, cu and zn are largely bound to dissolved organic compounds. cu is excreted in animal achut ram pradhananga et al./ bibechana 9 (2013) 141-150: bmhss, p.145 (online publication: nov., 2012) table 1: physico-chemical parameters of taudaha lake water and comparison with other global published values (mean ± s.d., n = 6). study area ph conductivity (µs/cm) tds (mg/l) tss (mg/l) ts (mg/l) do (mg/l) free co2(mg/l) t. alkalinity (mg caco3/l) t. hardness (mg caco3/l) who standard [17] 6.5-8.5 800-1000 500 4-6 6 200 80-120 taudah lake, nepal (*p.s.) 8.5 ± 0.2 231.7 ±16.0 124.5±19.2 621.4±23.3 745.8±69.2 5.8±0.9 21.6±5.3 111.7 ± 6.1 106.3 ± 4.6 manchar lake, pakistan [21] 8.4 ± 0.2 5243.6±178.6 157.0±40.3 lake nakuru, kenya [22] 10.3±0.3 27,500 ± 276 mc farlane, canada [23] 8.2 ± 0.0 370 ± 0.6 lake balaton, hungary [24] hazar lake, turkey [25] lake doirani, greece [26] lake kasumigaura, japan [27] 8.0 ± 0.1 siberian ponde [28] 7.7 9.5 nacharam lake, india [29] tuskegee lake, usa [30] 7.4 ± 0.2 82.5 ± 0.7 29.7 ± 1.3 lapland, finland [31] 5.7 1300 latvian lakes [32] 6.5 8.1 * p.s. – present study achut ram pradhananga et al./ bibechana 9 (2013) 141-150: bmhss, p.146 (online publication: nov., 2012) table 2: physico-chemical parameters of taudaha lake water and comparison with other global published values (mean ± s.d., n = 6). study area chloride (mg/l) nitrate (mg/l) sulphate (mg/l) phosphate (mg/l) who standard [17] 250 250 0.8 taudah lake, nepal (*p.s.) 18.6 ± 2.1 1.9 ± 0.2 1.5 ± 0.4 0.6 ± 0.1 manchar lake, pakistan [21] 1260 ± 251 163.8 ± 13.4 0.5 ± 0.2 lake nakuru, kenya [22] mc farlane, canada [23] lakebalaton, hungary [24] hazar lake, turkey [25] lake doirani, greece [26] lake kasumigaura, japan [27] 8.0 siberian ponde [28] 1.3 nacharam lake, india [29] tuskegee lake, usa [30] 9.3 ± 0.6 8.8 ± 2.1 0.07 ± 0.04 lakes in lapland, finland [31] latvian lakes [32] *p.s. – present study achut ram pradhananga et al./ bibechana 9 (2013) 141-150: bmhss, p.147 (online publication: nov., 2012) table 3: physico-chemical parameters of taudaha lake water and comparison with other global published values (mean ± s.d., n = 6). study area ca (mg/l) mg (mg/l) na (mg/l) cd (µg/l) cu (µg/l) pb (µg/l) zn (µg/l) who standard [17] 100 50 200 3 2000 10 3000 taudah lake, nepal (*p.s.) 36.2 ± 3.5 7.8 ± 1.9 6.4 ± 0.7 1.0 ± 0.3 7.8 ± 5.7 5.3 ± 0.2 10.0 ± 1.0 manchar lake, pakistan [21] 219.9 ± 45.9 167.1 ± 53.1 433.1 ± 93.0 5.0 ± 1.4 19.1 ± 4.3 82.2±18.6 720.2 ± 146 lake nakuru, kenya [22] 281.0 ± 22.0 43.0 ± 1.4 100.0 ± 9.7 138 ± 10.6 mc farlane, canada [23] 0.03 ± 0.001 11.0 ± 23.0 0.14±0.03 2.4 ± 0.4 lake balaton, hungary [24] 1.5x10-3 0.04-0.33 0.2 1.9 hazar lake, turkey [25] 18.0 38 71 lake doirani, greece [26] 0.1 0.4 1.0 13.0 1.0 1.6 6.0 66.0 lake kasumigaura, japan [27] 14.8 4.9 11.5 0.02 2.9 0.4 3.8 siberian ponde [28] 38.6 ± 2.4 < 1 2.3 ± 0.4 8.8 ± 3.6 nacharam lake, india [29] 8.9 ± 3.5 0.9 5.0 21 142 tuskegee lake, usa [30] 6.8 ± 1.9 2.4 ± 0.9 3.3 ± 0.2 0.001 ± 0.005 0.5 ± 0.9 0.1 ± 0.3 5.5 ± 4.4 lapland, finland [31] 0.02 0.5 -1.2 1.9 3.6 latvian lakes [32] 1.5 74.1 15.5 ± 0.4 39.0 ± 2.2 0.01 0.08 0.3 ± 0.1 2.3 ± 0.2 0.02 ± 0.02 * p.s. – present study achut ram pradhananga et al./ bibechana 9 (2013) 141-150: bmhss, p.148 (online publication: nov., 2012) waste, which can contaminate water, and may impair human health. zn may also increase the acidity of water [47]. although humans can handle proportionally large concentration of zinc, too much zinc can still cause eminent health problems, such as stomach cramps, skin irritations, vomiting, nausea and anemia [48]. fig. 1: taudaha lake (study area; source: google earth) 4. conclusion as might be evident from the present study that the taudaha lake possesses better water quality status under the study period since all the physico-chemical analyzes indicate the values within the maximum permissible limits for drinking water as recommended by who. besides, the surface water quality of the lake is also found to be in better condition than many of the reported global lake water. nevertheless, the physico-chemical parameters undertaken for the present study may have either positive or negative correlation with one another. further investigation on seasonal variation in the water quality parameters is therefore required to arrive at the specified conclusion. since the lake is of historic importance, it may be suggested for interventions on any kind of anthropogenic activities which bear responsibilities for the lake water quality deterioration. it may be expected that the outcomes of the present investigation may furnish useful information for future planning in using the lake water for drinking purpose. achut ram pradhananga et al./ bibechana 9 (2013) 141-150: bmhss, p.149 (online publication: nov., 2012) acknowledgements the authors are very thankful to department of science, padmakanya multiple campus, tribhuvan university for providing the lab facilities. aastha scientific research service pvt. ltd., dillibazar, kathmandu is also greatly acknowledged for part of analytical services. references [1] y.j. an, d.h. kampbell and g.w. sewell, environ. pollut., 118 (2002) 331. 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[48] t.c. hutchinson and p.m. stokes. am. soc. test. mater. spec. tech. pub. 573 (1975) 320. microsoft word i.s.jha _26-29_.doc i.s. jha et al. / bibechana 7 (2011) 26-29 : bmhss 26 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana free energy of mixing and activity of indium-tin alloy i.s. jhaa, arun k. khan b∗∗∗∗ , b.c. kumar c a dept. of physics, m.m.a.m. campus (tribhuvan university), biratnagar, nepal b dept. of physics, r.m. college (b.n. mandal university), saharsa, bihar, india c university department of physics ,t.m. bhagalpur university, bhagalpur, bihar, india article history: received 10 october 2010; revised 5 november 2010; accepted 12 november 2010 a b s t r a c t flory's model has been used to calculate the free energy of mixing and activity of in in insn liquid alloy at 700 k. the values of these thermodynamic parameters obtained from this model are compared with corresponding experimental values. the computed values are in reasonable agreement with the observed values. keywords: flory's model; activity; indium-tin alloy 1. introduction the indium-tin alloys have been attracting considerable attention due to their several uses. primary applications of indium-tin alloys include bearing assembly, ballast, casting, step soldering, and radiation shielding. in this paper, we intend to study the thermodynamic properties of indium-tin alloys in molten state at 700 k on the basis of flory's model [1]. the thermodynamic mixing properties of liquid alloys are important for understanding process metallurgy and material preparation of metal alloy. the liquidus lines of insn alloys [2] reveal that the constituent species form complexes at one or more stoichiometric composition. the assumptions of complex formation have been used by several researchers [3-10] to study the mixing properties of alloys in liquid state. the theoretical background of flory's model is presented in section 2. section 3 gives the result and discussion of the work and conclusion of the work is given in section 4. 2. flory's model considering nc mole of in atoms and n(1-c) mole of sn atoms mixed in molten state,flory's expression for free energy of mixing of a binary mixture is given by[1] ∗ corresponding author: dr. arun k. khan, dept. of physics, r.m. college (b.n. mandal university), saharsa, bihar, india, email: arunkumarkhan@gmail.com i.s. jha et al. / bibechana 7 (2011) 26-29 : bmhss 27 c1 c1 c)c1ln()1ln(c)c1ln()c1(clnc[rtg m β− − ω+β−−β−+−−+= (1) where 0sn 0in )v( )v( 1−=β , 0in )v( and 0sn )v( being the atomic volumes of in and sn respectively. the standard thermodynamic relation for activity of in in binary liquid is given by c g )c1(galnrt m mal ∂ ∂ −+= (2) differentiating equation (1) with respect to 'c' and substituting the value of c g m ∂ ∂ , one gets 2 2 al )c1( )c1( rtc1 )c1( )c1ln()1ln(clnaln β− −ω + β− −β +β−−β−+= (3) once the expressions for mg is obtained, other thermodynamic functions follow readily. heat of mixing and entropy of mixing are related to mg through standard thermodynamic relations p,t m mm t g tgh         ∂ ∂ −= (4) t gh s mm m − = (5) differentiating equation (1) with respect to t and substituting in equation (4), we get trtc1 c 1c1 )c1(c rt tc1 )c1(c t c1 )c1(c h 2 m ∂ β∂       ω β− − β− β β− − + ∂ ω∂ β− − − β− − ω= (6) where 0sn 0in insn )v( )v( )( t α−α= ∂ β∂ , inα and snα are linear expansivities of indium and tin respectively. 3. results and discussion the value of interchange energy )(ω was determined from the observed data [2] of mg in the concentration range from 0.1 to 0.9. the best fit value of ω used in the present work was found to be -3.65 kj mol -1 . the computed values of mg obtained from equation (1) are plotted against inc (concentration of in) in figure 1 along with its observed values at 700k. the computed and observed values of mg are in reasonable agreement in all concentration range. the computed values are in better agreement with the observed values in higher concentrat ion of in. the computed and observed both values are least at equiatomic composition. the computed and observed values of gm are displayed in table 1. activity is a very important thermodynamic function because it is one of the fortune functions which is obtained directly from experiment and it can be used to obtain other thermodynamic functions. the graph between the experimental and theoretical values of inaln with respect to inc is shown in figure 2. it is clear from the graph that the matching of theoretical values with experimental values is relatively better in lower concentration range of in, i.e.; in the region alc < 0.5 than in higher concentration. the computed and observed values of lnain are displayed in table 1. i.s. jha et al. / bibechana 7 (2011) 26-29 : bmhss 28 figure 1: free energy of mixing (gm) verses concentration of in (cin) of liquid insn alloy at 700 k; ((––––) theory, (…………) experiment [2]. figure 2: activity (lna) versus cin (concentration of al) in the liquid insn solution (1073k); (––––) theory, (………….) experiment [2]. 4. conclusion we have calculated free energy of mixing and activity of in in in-sn alloys in molten state. both of these parameters computed from flory's model were found to be in i.s. jha et al. / bibechana 7 (2011) 26-29 : bmhss 29 rescannable agreement with corresponding observed values. the interaction energy was found to be temperature dependent. table 1 references [1] p.j. flory, j. chem.phys. liq. all., 10(1942)51. [2] r. hultgren, p. d desai, d.t hawkins, m. gleser and k.k. kelley, selected values of the thermodynamic properties of binary alloys (metals park, ohio: american society for metals, (1973). [3] d. adhikari, i. s. jha and b. p. singh, phil. mag., 90 (2010) 2687. [4] d. adhikari , i.s. jha , b.p. singh, physica b, 405(2010) 1861. [5] r.n. singh and l.c. prasad, phys. chem. liquid, 22(1990)1. [6] a.s. jordan, metall. trans., 1 (1970) 239. [7] d. adhikari, b.p. singh, i.s. jha and b.k. singh, j. mol. liqs., 156 (2010) 155. [8] b.p. singh, d. adhikari and i.s. jha, j. non-crystalline solids, 356(2010) 1730. [9] a.b. bhatia and n.h. march, j. phys.f:met. phys., 5(1975) 1100. [10] s. lele and p. ramchandrarao, metall. trans., 12 b (1981) 659. gm(kj mol -1 ) lnain cin theoretical experimental [2] theoretical experimental [2] 0.1 -2.221 -1.902 -2.313 -2.501 0.2 -3.500 3.967 -1.635 -2.032 0.3 -4.329 -4.067 -1.262 -1.635 0.4 -4.805 -4.669 -1.024 -1.234 0.5 -4.963 -4.903 -0.856 -0.896 0.6 -4.812 -4.815 -0.746 -0.664 0.7 -4.341 -4.410 -0.681 -0.460 0.8 -3.513 -3.628 -0.650 -0.279 0.9 -2.231 -2.341 -0.648 -0.123 microsoft word n. sah _115-118_doc.doc n.p. sah / bibechana 10 (2014) 115-117 : bmhss, p.115 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana relation between saturated and normal operators nagendra pd. sah dept. of mathematics, m.m.a.m.campus, biratnagar. . article history: received 6 december, 2013 abstract a vector space x with algebra of all linear maps l(x) from x into itself and the ideal of all finite dimensional linear maps with dual (conjugate) transformation t* to t from x' to itself form a relation in terms of relatively regular and linearly independent which is sufficient for mentioned title. keywords: relatively regular, saturated, normal operator. 1. introduction let x be a vector space, l(x)be the algebra of all linear map of x into itself and be the ideal of all finite dimensional linear maps l(x). let x* be the algebraic dual space x with elements x*, y*,…… and t l(x), then we define by y*(x) = x*(tx), x* x*,a linear form y* x*. the map is called the (algebraic) dual or conjugate transformation t* to t. it is a linear map of x* into itself and is uniquely characterized by < tx, x*> = <x, t* x*>, x x, x* x*[1]. if x' is a linear subspace of x', therefore a vector space of linear forms, we denote by l(x') the set of all t l(x), whose dual transformation t* maps the space x' into itself. properties of dual transformation t* (1) (t1+t2)* = t1* + t2* (2) (αt)* = αt* (3) (t1 t2)*= t2* t1* definition (1): if for a continuous operator t, there exists a continuous operator s with t s t = t, then t is called relatively regular. definition (2): the algebra rrrr of operators on a vector space is called normal, if every finite dimensional operator t from rrrr is relatively rrrr regular. definition (3): an algebra rrrr of operators on vector space x is called saturated, if corresponding to any pair of finite sets {x1,……..xn}, {y1…..yn} ⊂x, where {x1, x2……..xn} is linearly independent and there exists t rrrr with txγ = yγ , γ = 1,2…….n. theorem (1.1): every operator t l(x) is relatively l(x)-regular. proof: we have x = n(t) + u and x = b(t) + c. if p is the projection of x onto b(t) along c, q the projection of x onto n(t) along u and to the restriction of t to u, then to is a bijective linear n.p. sah / bibechana 10 (2014) 115-117 : bmhss, p.116 (online publication: dec., 2013) map of u onto b(t). therefore s = to -1 p l(x). for x = n + u, n = q x n(t), u = (i q) x u, we have s tx = to -1 p tx = to -1 t x = to -1t (n+u) = to -1tu = to -1 tou = u = (t-q)x. therefore, s t = i – q and t s t = t – tq = t. hence t is relatively regular. theorem (1.2): every saturated operator algebrarrrr is normal. proof :let x1,…….xn be a basis of the image space of t yγ ,1≤ γ ≤n, be so chosen that t yγ = xγ , 1≤ γ ≤n, then on account of being saturated, there exist s with s xγ = yγ and hence also with t s xγ = xγ , 1≤ γ ≤n. then for t x =∑ = n 1 )( γ γγα xx we obtain t s t x = xxxxx t)(ts)( n 1 n 1 ==∑∑ == γ γγ γ γγ αα hence t is relatively rrrr -regular. definition (4): if x' be a linear space of linear functionals on x, then we define the set of all finite dimensional maps of the form tx =∑ γγ xxx )(' , 'x' ∈γx and x∈γx by γ (x'). γ (x') is an algebra if e is a topological vector space with dual space e' then γ (e')= f(e). theorem (1.3): if x is a vector space and x' is a total, then γ (x') is saturated; every super algebra. i.e. γ (x') is normal. proof: if {x1,……..,xn} is linearly independent subset and {y1,…….,yn} arbitrary from x, then by definition. (2) corresponding to the elements x1,…….,xn there exist linear forms x'1,…….x'n on x' such that ( ) mm' γγ ∂=xx , 1≤ γ , m≤n[2]. since x' is total, we define t by t x =∑ = n 1 )(' γ γγ yxx , then t γ (x') and txm =∑ = n 1 m )(' γ γ xx = ym, 1≤m≤ n. hence γ (x') is saturated. lemma(1):t*(x') ⊂x'. and l(x') is an algebra containing i. proof: we have γ (x') ⊂ l(x')[4] if t γ (x') then tx = ∑ = >< n 1 ', γ γγ xxx with x'' ∈γx and x∈γx then for arbitrary x'' ∈γx , we have n.p. sah / bibechana 10 (2014) 115-117 : bmhss, p.117 (online publication: dec., 2013) <x, t*x'> = <tx, x'> = <∑ = >< n 1 , '', γ γγ xxxx > = ∑ = ><< n 1 , ''', γ γγγ xxxx > therefore t*x' = ∑ = ∈>< n 1 x''', γ γ xxx theorem (1.4): if x' is a total vector space of linear forms on x, then l(x') is normal. the result follows from lemma (1) and theorem (1.3) [3]. 2. conclusions the super algebra of a saturated operator is again saturated [5]. every saturated operators of algebra rrrr is normal. if e is a topological vector space with total dual space e', then l(e) is always saturated. but if l(e) is not normal for every topological vector space e, then l(e) is not always saturated [6]. references 1. a.e. taylor: introduction to functional analysis, new-york john wiley and sons inc. london, 1956. 2. a.p. robertson and w. robertson, topological vector spaces cambridge university press, 1964. 3. b. conway john, a course on functional analysis springer, verlang, 1985. 4. m.m. day, normed linear spaces, berline, springer, verlag, 1958. 5. m.m. day, normed linear spaces, berlin, springer, verlang, 1958. 6. r.g. cooke, linear operators, macmillan, london, 1953. microsoft word r.r. thapa _121-125_.doc r. r. thapa and m. k. raut. / bibechana 9 (2013) 121-125: bmhss, p.121 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana the sensitivity of l4 and l5 in the framework of restricted problem of three bodies when the primaries are different r. r. thapa, m. k. raut department of mathematics, p.g. campus, biratnagar, nepal article history: received 2 october, 2012; accepted 16 november, 2012 abstract in the paper, the location of liberation points have been observed and triangular liberation points l4 and l5 are determined. keywords: libration points; jacobi integral; triaxial rigid body 1. introduction two primaries the point masses, the bigger one is spherical and the second primary; (smaller primary) is a triaxial rigid body are moving around their centre of mass in circular orbits under the influence of their mutual gravitational attraction and a third body, influenced by the primaries but not influencing their motion moves in the plane defined by the two revolving primaries. if one body is triaxial and other is spherical then the triangular libration points in restricted problem of three bodies are infinitesimal or linearly stable. leontovic [1] established a non-linear stability of the triangular libration point. deprit and palmore [2] established the family of short orbits originating at the equilateral triangular libration point. deprit [2,3] studied geometrically the long periodic and short periodic obits around l4 with the help of d'alembert's series. henrard [4] discovered that the long periodic orbits at l4 doesn't evolve in a continuous way. and discontinuity appears not only at mass ratios but also at singular bifurcation points. tuckness [6] has used all the stability criteria numerically and investigated the sensitivities of third body around l4 when it is given positional deviations away from l4 with a suitable condition. the above mentioned mathematicians studied the different aspects of stability of libration points with different approaches in circular restricted problem of three bodies. here we have taken the bigger primary is a spherical and smaller as a triaxial rigid body under the same condition of mc kanzie and szebehely and tukness. 2. equation of motion the equations of motion of the third body are: r. r. thapa and m. k. raut. / bibechana 9 (2013) 121-125: bmhss, p.122(online publication: nov., 2012) x y2x ∂ ω∂ =η− ••• y x2y ∂ ω∂ =η+ ••• where ( )22 2 1r x y= − µ + (2) ( )22 2 2r x 1 y= − µ + + (3) and ( ) ( ) 2 1 22 2 2 1 2 1 23 5 1 2 2 2 21 3 (1 )r r y 2 r r 2r 2r µ σ − ση − µ µ µ  ω = + µ + µ + + + − σ − σ  (4) 21 21 2 , 2 1 mm mm m ≥≤ + =µ where r1,r2 are distances between first and second primary from third body respectively, and m1,m2 are masses of the first and second primaries respectively. the mean angular motion, ( )212 2 3 1 σση −+= (5) where , 5 , 5 , 5 2 2 32 2 22 2 1322311 r c a r b a r a aandaaandaa ===−=−= σσ a, b, c being semi-axes of triaxial rigid body and r is distance between the primaries. 3. location of libration points from equation (1) ( )yx dt d 2y y x x 2yx dt d 22 ,.. ω=      ∂ ω∂ + ∂ ω∂ =      + •••• integrating w. r. t. t we get c2yx 22 −ω=+ •• (6) which is jacobi's integral. libration points are solutions of the equations ,0,0. = ∂ ω∂ = ∂ ω∂ yx we get, 2 2 1 1 , r y y r r y y r = ∂ ∂ = ∂ ∂ or, ( )( ) ( ) ( ) ( ) ( ) ( ) 2 7 2 21 5 2 21 3 2 3 1 2 1 2 15 1 2 2311 . yx r x rr x r x x x +− − ++− − − +− − −− −= ∂ ω∂ µ σσµ µ σσµµµµµ η (1) r. r. thapa and m. k. raut. / bibechana 9 (2013) 121-125 : bmhss, p.123 (online publication: nov., 2012) ( ) ( ) ( )       − + − −− − −= ∂ ω∂ 2 7 2 21 5 2 21 3 2 3 1 2 2 15 2 3431 . y rrrr y y σσµσσµµµ η 4. triangular libration points the triangular libration points are solutions of the equations: ( )( ) ( ) ( ) ( ) ( ) ( ) 01 2 15 1 2 2311 2 7 2 21 5 2 21 3 2 3 1 2 =+− − ++− − − +− − −− − yx r x rr x r x x µ σσµ µ σσµµµµµ η (7) ( ) ( ) ( ) 0 2 15 2 3431 2 7 2 21 5 2 21 3 2 3 1 2 =      − + − −− − − y rrrr y σσµσσµµµ η (8) multiplying equation (7) by ( )1x +µ− and subtracting the result from equation (8); we set. ( ) ( ) ( ) ( ) 01 31 1 5 2 21 3 1 2 =+− − + − +−− µ σσµµ µη x rr (9) multiplying equation 8 by ( )µ−x and subtracting the result from equation (7) we get, ( )( ) ( ) ( ) 0 2 15 2 2331 2 7 2 21 5 2 21 5 2 21 3 2 2 =      − + − − −− +− y rrr x r σσσσµσσ η (10) if we put 021 ==σσ then equations ( 9) and (10) become 3 2 2 1 r −η =0 and 0 1 3 1 2 =+− r η adding them, we get, 21 rr = (11) using equation 5, we get, 121 === ηrr if 0,0 21 ≠≠ σσ then we get αβµ −+−= 2 1 x (12) ( )    ++±= βα 3 2 1 2 3 y (13) r. r. thapa and m. k. raut. / bibechana 9 (2013) 121-125 : bmhss, p.124 (online publication: nov., 2012) where 1,0,1,1 21 <<<+=+= βαβα rr putting the values of yxrr ,,,, 21η in equations (9) and (11) we get, ( ) ( ) ( ) ( ) ( )( ) ++−−+      −−−++−−+ −−− 5 21 5 21 3 21 12 2 3 1 2 1 312 2 3 1 βσσβαβσσβσσ ( )( ) 7 21 1 2 15 −+− βσσ 0 4 3 =      ++ βα and ( ) ( )( ) ( ) 01 2 1 )(3111 2 3 31 5 21 3 21 =+      −+−++−+−      −+− −− βαβσσµαµµσσ we get 21 8 11 8 11 σσβ +−= and ( ) ( ) 21 12 21 12 32 σ µ µ σ µ µ α       − − +      − +− = respectively from equation (12) ( ) ( ) 21 18 37 18 3 2 1 σ µ µ σ µ µ µ       − − +      − + −−=x and from equation (13) ( ) ( )       − − + − − −±= 21 112 1915 112 2319 1 2 3 σ µ µ σ µ µ y thus, ( )             ++−+−≡ βααβµ 3 2 1 2 3 , 2 1 4l and ( )             ++−−+−≡ βααβµ 3 2 1 2 3 , 2 1 5l can be written as ( ) ( ) ( ) ( ) ( ) ( )             − − + − − − − − + − + −−≡ 21214 112 1915 112 2319 1 2 3 , 18 37 18 3 2 1 σ µ µ σ µ µ σ µ µ σ µ µ µl ( ) ( ) ( ) ( ) ( ) ( )             − − + − − −− − − + − + −−≡ 21215 112 1915 112 2319 1 2 3 , 18 37 18 3 2 1 σ µ µ σ µ µ σ µ µ σ µ µ µl 5. conclusion the triaxial rigid body can be affected by analytical effect on the values of the critical mass. the libration points l4 & l5 are depending on µ , 21 ,σσ . r. r. thapa and m. k. raut. / bibechana 9 (2013) 121-125: bmhss, p.125 (online publication: nov., 2012) references [1] a. m. leontovic, on the stability of the lagrange periodic solutions for the reduced problem of three bodies, soviet math, 3(1962) 425 428. [2] a. deprit and palmore, analytical continuation and first order stability of short period orbits at l4, astron, j.,71(1966 a) 94. [3] a. deprit, limiting orbits around the equilateral centres of libration, astron, j., 71(1966b) 77 87. [4] j. henrard, concerning the genealogy of long period families at l4 , astron, astrophysics, 5(1970) 45-52. microsoft word md. and ali.doc md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.58 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana application of the new approach of generalized )/( gg′ -expansion method to find exact solutions of nonlinear pdes in mathematical physics md. nur alam 1 and m. ali akbar 2* 1 department of mathematics, pabna university of science and technology, bangladesh 2department of applied mathematics, university of rajshahi, bangladesh * email: ali_math74@yahoo.com article history: received 27 october, 2013; accepted 17 november, 2013 abstract the exact solutions of nonlinear evolution equations (nlees) play a crucial role to make known the internal mechanism of complex physical phenomena. in this article, we construct the traveling wave solutions of the zakharov-kuznetsov-benjamin-bona-mahony (zk-bbm) equation by means of the new approach of generalized )/( gg′ -expansion method. abundant traveling wave solutions with arbitrary parameters are successfully obtained by this method and the wave solutions are expressed in terms of the hyperbolic, trigonometric, and rational functions. it is shown that the new approach of generalized )/( gg′ -expansion method is a powerful and concise mathematical tool for solving nonlinear partial differential equations. keywords: new approach of generalized )/( gg′ -expansion method, zk-bbm equation; homogeneous balance, traveling wave solutions, solitary wave solutions, nonlinear evolution equation. 1. introduction nonlinear phenomena arise in several aspects of physics as well as other natural and applied sciences. essentially all the fundamental equations in physical sciences are nonlinear and, in general, such nlees are often very complicated to solve explicitly. the exact solutions of nlees play an important role in the study of nonlinear physical phenomena. therefore, the powerful and efficient methods to find exact solutions of nonlinear equations still have drawn a lot of interest by diverse group of scientists. in the past three decades, there has been significant progress in the development of finding effective methods for obtaining exact solutions of nlees. these methods are the expfunction method [1-3], the generalized riccati equation [4], the miura transformation [5], the jacobi elliptic function expansion method [6, 7], the hirota’s bilinear method [8], the sine-cosine method [9], the tanh-function method [10], the extended tanh-function method [11-12], the homogeneous balance method [13], the modified exp-function method [14], the )/( gg′ -expansion method [15-22], the md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.59 (online publication: dec., 2013) improved )/( gg′ -expansion method [23], the modified simple equation method [24-28], the inverse scattering transform [29] and so on. recently, naher and abdullah [30] established a highly effective extension of the )/( gg′ expansion method, called the new generalized )/( gg′ expansion method to obtain exact traveling wave solutions of nlees. the aim of this article is to look for new study relating to the new generalized )/( gg′ expansion method for solving the renowned zk-bbm equation to make obvious the effectiveness and usefulness of the method. the outline of this paper is organized as follows: in section 2, we give the description of the new generalized )/( gg′ expansion method. in section 3, we apply this method to the zk-bbm equation. in section 4, discussions are given. conclusions are given in section 5. 2. description of the new generalized ( / )g g′ -expansion method let us consider a general nonlinear pde in the form ),,,,,,( … xtttxxxt vvvvvvφ , (1) where ),( txvv = is an unknown function, φ is a polynomial in ),( txv and its derivatives in which highest order derivatives and nonlinear terms are involved and the subscripts stand for the partial derivatives. step 1: we combine the real variables x and t by a complex variable η )(),( ηvtxv = , tvx ±=η , (2) where v is the speed of the traveling wave. the traveling wave transformation (2) converts eq. (1) into an ordinary differential equation (ode) for )(ηvv = : ),,,,( ⋯vvvv ′′′′′′ψ , (3) where ψ is a polynomial of v and its derivatives and the superscripts indicate the ordinary derivatives with respect to η . step 2: according to possibility, eq. (3) can be integrated term by term one or more times, yields constant(s) of integration. the integral constant may be zero, for simplicity. step 3. suppose the traveling wave solution of eq. (3) can be expressed as follows: i n i i i n i i mdmdv − == +++= ∑∑ )()()( 10 βαη , (4) where either n α or n β may be zero, but could be zero simultaneously, i α ),,2,1,0( ni ⋯= and i β ),,2,1( ni ⋯= and d are arbitrary constants to be determined and )(ηm is )/()( ggm ′=η (5) where )(ηgg = satisfies the following auxiliary nonlinear ordinary differential equation: 0)( 22 =′−−′−′′ gcgegbggag , (6) where the prime stands for derivative with respect to η ; a , b ,c and e are real parameters. step 4: to determine the positive integer n , taking the homogeneous balance between the highest order nonlinear terms and the derivatives of the highest order appearing in eq. (3). md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.60 (online publication: dec., 2013) step 5: substitute eq. (4) and eq. (6) including eq. (5) into eq. (3) with the value of n obtained in step 4, we obtain polynomials in n md )( + ),2,1,0( ⋯=n and n md −+ )( ),2,1,0( ⋯=n . subsequently, we collect each coefficient of the resulted polynomials to zero, yields a set of algebraic equations for i α ),,2,1,0( ni ⋯= and i β ),,2,1( ni ⋯= , d and v . step 6: suppose that the value of the constants i α ),,2,1,0( ni ⋯= , i β ),,2,1( ni ⋯= , d and v can be found by solving the algebraic equations obtained in step 5. since the general solutions of eq. (6) are known to us, inserting the values of i α ),,2,1,0( ni ⋯= , i β ),,2,1( ni ⋯= , d and v into eq. (4), we obtain more general type and new exact traveling wave solutions of the nonlinear partial differential equation (1). step 7: using the general solution of eq. (6), we have the following solutions of eq. (5): family 1: when ,0≠b ca −=ω and ,0)(42 >−+=ω caeb         ω +        ω         ω +        ω ω +=      ′ = ηη ηη ωω η a c a c a c a c b g g m 2 sinh 2 cosh 2 cosh 2 sinh 22 )( 21 21 (7) family 2: when ,0≠b ca −=ω and ,0)(42 <−+=ω caeb         ω− +        ω−         ω− +        ω− − ω− +=      ′ = ηη ηη ωω η a c a c a c a c b g g m 2 sin 2 cos 2 cos 2 sin 22 )( 21 21 (8) family 3: when ,0≠b ca −=ω and ,0)(42 =−+=ω caeb ηω η 21 2 2 )( cc cb g g m + +=      ′ = (9) family 4: when ,0=b ca −=ω and ,0>=∆ eω )sinh()cosh( )cosh()sinh( )( 21 21 ηη ηη ω η a c a c a c a c g g m ∆ + ∆ ∆ + ∆ ∆ =      ′ = (10) family 5: when ,0=b ca −=ω and ,0<=∆ eω )sin()cos( )cos()sin( )( 21 21 ηη ηη ω η a c a c a c a c g g m ∆− + ∆− ∆− + ∆− −∆− =      ′ = (11) 3. application of the method in this section, we will put forth the new generalized )/( gg′ expansion method to construct many new and more general traveling wave solutions of the zk-bbm equation. let us consider the zkbbm equation, md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.61 (online publication: dec., 2013) 02 =−−+ txxxxt bvvvavv . (12) we will use the traveling wave transformation eq. (2) into the eq. (12), which yields: 02)1( =′′′−′−′+ vvbvvavv . (13) integrating eq. (13) with respect to η once yields ,0)1( 2 =+′′−−+ kvvbvavv (14) where k is an integration constant which is to be determined. taking the homogeneous balance between highest order nonlinear term 2 v and linear term of the highest order v ′′ in eq. (14), we obtain 2=n . therefore, the solution of eq. (14) is of the form: ,)()()()()( 2 2 1 1 2 210 −− ++++++++= mdmdmdmdv ββαααη (15) where 21210 ,,,, ββααα and d are constants to be determined. substituting eq. (15) together with eqs. (5) and (6) into eq. (14), the left-hand side is converted into polynomials in ( )nmd + ,.......)2,1,0( =n and ( ) n md −+ ),2,1( ⋯=n . we collect each coefficient of these resulted polynomials to zero yields a set of simultaneous algebraic equations (for simplicity, the equations are not presented here) for 0α , 1α , 2α , 1β , 2β d , k and v . solving these algebraic equations with the help of computer algebra, we obtain following: set 1: )2816( 4 1 44242242222222 4 vaavbvbaebvbevb aa k ++−+−−−= ωω , )81212( 2 1 22222 20 bvbvaabvebvbdbvd aa +−−−+−= ωωωα , ,vv = (16) ),232( 6 2223 21 ebdbedbdd aa bv −+−+= ωωωβ ,dd = ,01 =α ,02 =α )222( 6 2222324 22 edbbdeedbdd aa bv ++−−+−= ωωωβ . where ,ca −=ω ,v ,d ,a ,b ,c e are free parameters. set 2: )2816( 4 1 44242242222222 4 vaavbvbaebvbevb aa k ++−+−−−= ωω , )81212( 2 1 22222 20 bvbvaabvebvbdbvd aa +−−−+−= ωωωα , ,vv = (17) )2( 6 2 21 ωωα bd aa bv += , 2 2 2 6 aa bvω α −= , ,01 =β 02 =β . where ,ca −=ω ,v ,d ,a ,b ,c e are free parameters. set 3: )16128256)1(( 4 1 4222222222242 4 bvbebvbeavbav aa k −−−+−= ωω , )28)1(( 2 1 22 20 bvbbveav aa +++= ωα , 2 2 2 6 aa bvω α −= , ,01 =α ,vv = md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.62 (online publication: dec., 2013) ),816( 8 3 4222 222 bebe aa bv ++−= ωω ω β ,01 =β ω2 b d −= (18) where ,ca −=ω ,v ,a ,b ,c e are free parameters. for set 1, substituting eq. (16) into eq. (15), along with eq. (7) and simplifying, yields following traveling wave solutions, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: 2 2 1 101 )) 2 coth( 22 ()) 2 coth( 22 ()( 1 −− ωω +++ ωω +++= η ωω βη ωω βαη a b d a b dv . 2 2 1 101 )) 2 tanh( 22 ()) 2 tanh( 22 ()( 2 −− ωω +++ ωω +++= η ωω βη ωω βαη a b d a b dv . substituting eq. (16) into eq. (15), along with eq. (8) and simplifying, our exact solutions become, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: 2 2 1 101 )) 2 cot( 22 ()) 2 cot( 22 ()( 3 −− ω−ω− +++ ω−ω− +++= η ωω βη ωω βαη a b d a b dv . 2 2 1 101 )) 2 tan( 22 ()) 2 tan( 22 ()( 4 −− ω−ω− −++ ω−ω− −++= η ωω βη ωω βαη a b d a b dv . substituting eq. (16) into eq. (15), together with eq. (9) and simplifying, our obtained solution becomes: .) 2 () 2 ()( 2 21 2 2 1 21 2 1015 −− + +++ + +++= ηω β ηω βαη cc cb d cc cb dv substituting eq. (16) into eq. (15), along with eq. (10) and simplifying, we obtain following traveling wave solutions, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: .))coth(())coth(()( 2 2 1 1016 −− ∆∆ ++ ∆∆ ++= η ω βη ω βαη a d a dv 2 2 1 101 ))tanh(())tanh(()( 7 −− ∆∆ ++ ∆∆ ++= η ω βη ω βαη a d a dv . substituting eq. (16) into eq. (15), together with eq. (11) and simplifying, our obtained exact solutions become, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: 2 2 1 101 ))cot(())cot(()( 8 −− ∆−∆− ++ ∆−∆− ++= η ω βη ω βαη a d a dv 2 2 1 101 ))tan(())tan(()( 9 −− ∆−∆− −+ ∆−∆− −+= η ω βη ω βαη a d a dv , where .vtx −=η again for set 2, substituting eq. (17) into eq. (15), along with eq. (7) and simplifying, our traveling wave solutions become, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.63 (online publication: dec., 2013) )), 2 (coth3)1()4(2( 2 1 )( 222 221 ηωη a bvvaebbv aa v ω ω−+++= )), 2 (tanh3)1()4(2( 2 1 )( 222 222 ηωη a bvvaebbv aa v ω ω−+++= substituting eq. (17) into eq. (15), along with eq. (8) and simplifying yields exact solutions, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: )), 2 (cot3)1()4(2( 2 1 )( 222 223 ηωη a bvvaebbv aa v ω− ω++++= )) 2 (tan3)1()4(2( 2 1 )( 222 224 ηωη a bvvaebbv aa v ω− ω++++= . substituting eq. (17) into eq. (15), along with eq. (9) and simplifying, our obtained solution becomes: ),)(12)1()4(2( 2 1 )( 2 21 2222 225 η ωωη cc c bvvaebbv aa v + −+++= substituting eq. (17) into eq. (15), together with eq. (10) and simplifying, yields following traveling wave solutions, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: )))(coth)coth((12)1()8(( 2 1 )( 222 226 ηηωη aa bbvvaebbv aa v ∆ ∆− ∆ ∆++++−= . )))(tanh)tanh((12)1()8(( 2 1 )( 222 227 ηηωη aa bbvvaebbv aa v ∆ ∆− ∆ ∆++++−= . substituting eq. (17) into eq. (15), along with eq. (11) and simplifying, our exact solutions become, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: ))).(cot)cot((12)1()8(( 2 1 )( 222 228 ηηωη aa ibbvvaebbv aa v ∆− ∆+ ∆− ∆++++−= ))(tan)tan((12)1()8(( 2 1 )( 222 229 ηηωη aa ibbvvaebbv aa v ∆− ∆− ∆− ∆−+++−= , where .vtx −=η similarly, for set 3, substituting eq. (18) into eq. (15), together with eq. (7) and simplifying, yields following traveling wave solutions, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: ) 2 (tanh 4 ) 2 (coth 2 3 )( 2 2 22 2031 η ω ηαη a b aaa bv v ω ω + ωω −= . ) 2 (coth 4 ) 2 (tanh 2 3 )( 2 2 22 2032 η ω ηαη a b aaa bv v ω ω + ωω −= . md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.64 (online publication: dec., 2013) substituting eq. (18) into eq. (15), along with eq. (8) and simplifying, we obtain following solutions, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: ) 2 (tan 4 ) 2 (cot 2 3 )( 2 2 22 2033 η ω ηαη a b aaa bv v ω− ω − ω−ω += . ) 2 (cot 4 ) 2 (tan 2 3 )( 2 2 22 2034 η ω ηαξ a b aaa bv v ω− ω − ω−ω += . substituting eq. (18) into eq. (15), along with eq. (9) and simplifying, our obtained solution becomes: .)()( 6 )( 2 21 2 2 2 21 2 2 2 035 − + + + −= η β η ω αη cc c cc c aa bv v substituting eq. (18) into eq. (15), along with eq. (10) and simplifying, yields following exact traveling wave solutions, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: 2 2 2 2 2 03 ))coth( 2 ())coth( 2 ( 6 )( 6 −∆∆ + − + ∆∆ + − −= η ωω βη ωω ω αη a b a b aa bv v . 2 2 2 2 2 03 ))tanh( 2 ())tanh( 2 ( 6 )( 7 −∆∆ + − + ∆∆ + − −= η ωω βη ωω ω η a b a b aa bv av . substituting eq. (18) into eq. (15), along with eq. (11) and simplifying, our obtained exact solutions become, if 01 =c but ;02 ≠c 02 =c but 01 ≠c respectively: 2 2 2 2 2 03 ))cot( 2 ())cot( 2 ( 6 )( 8 −∆−∆− + − + ∆−∆− + − −= η ωω βη ωω ω αη a b a b aa bv v . 2 2 2 2 2 03 ))tan( 2 ())tan( 2 ( 6 )( 9 −∆−∆− − − + ∆−∆− − − −= η ωω βη ωω ω αη a b a b aa bv v . where .vtx −=η 4. discussions the advantages and validity of the method over the basic )/( gg′ -expansion method and the generalized and improved )/( gg′ -expansion method have been discussed in the following. advantages: the crucial advantage of the new approach against the basic )/( gg′ -expansion method and the generalized and improved )/( gg′ -expansion method is that the method provides more general and abundant new exact traveling wave solutions with many real parameters. the exact solutions have its great importance to expose the inner mechanism of the complex physical phenomena. apart from the physical application, the close-form solutions of nonlinear evolution equations assist the numerical solvers to compare the correctness of their results and help them in the stability analysis. md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.65 (online publication: dec., 2013) validity: in ref. [31] zhang et al. used the linear ordinary differential equation (lode) as auxiliary equation and traveling wave solutions presented in the form ∑ −= ′= m mi i i ggau ,)/()(ξ where 0≠ m a . akbar et al. [17] used same auxiliary equation (lode) and the solution is presented in the form ∑ −= − ′+ = m mn n n ggd e u , ))/(( )(ξ where either m e− or m e may be zero, but both m e− or m e cannot be zero together. it is noteworthy to point out that some of our solutions are coincided with previously published results, if the parameters are taken particular values which validate our solutions. moreover, in ref. [31] zhang et al. investigated the zk-bbm equation to obtain exact solutions via the improved )/( gg′ -expansion method and achieved only six solutions (a.1)-(a.6) (see appendix a). on the other hand, by using the generalized and improved )/( gg′ -expansion method, akbar et al. [17] obtained nine solutions (b.1)-(b.9) (see appendix b) of the zk-bbm equation. but in this article twenty seven exact solutions including (a.1)-(a.6) and (b.1)-(b.2) of the zk-bbm equation are constructed by applying the new approach of generalized )/( gg′ -expansion method. 5. conclusion in this study, we considered the zakharov-kuznetsov-benjamin-bona-mahony (zk-bbm) equation. we employed the new approach of generalized )/( gg′ -expansion method for the exact solution to this equation and constructed some new solutions which are not found in the previous literature. the method offers solutions with free parameters that might be imperative to explain some intricate physical phenomena. this study shows that the new generalized )/( gg′ -expansion method is quite efficient and practically well suited to be used in finding exact solutions of nlees. also, we observe that the new generalized )/( gg′ -expansion method is straightforward and can be applied to many other nonlinear evolution equations. references 1. j.h. he and x.h. wu, chaos, solitons fract., 30 (2006) 700. 2. m.a. akbar and n.h.m. ali, world appl. sci. j., 17(12) (2012) 1603. 3. h. naher, a.f. abdullah and m.a. akbar, j. appl. math., article id 575387 (2012) 14 pages. doi: 10.1155/2012/575387. 4. z. yan and h. zhang, phys. lett. a, 285(5-6) (2001) 355. 5. t.l. bock and m.d. kruskal, phys. lett. a, 74 (1979) 173. 6. d. liu, chaos solitons fract., 24 (2005) 1373. 7. y. chen and q. wang, chaos solitons fract., 24 (2005) 745. 8. a.m. wazwaz, commun nonlinear sci numer simulat., 17 (2012) 491. 9. a.m. wazwaz, appl. math. comput. modeling, 40 (2004) 499. 10. a.m. wazwaz, appl. math.comput., 169 (2005) 321. 11. e. fan, phys lett a, 277(4-5) (2000) 212 . 12. s.a. el-wakil, m.a. abdou, chaos solitons fract., 31(4) (2007) 840. 13. e.g. fan, phys. lett. a, 265 (2000) 353. 14. m. usman, a. nazir, t. zubair, i. rashid, z. naheed and s.t. mohyud-din, int. j. modern math. sci., 5(1) (2013) 27. 15. m.l. wang, x.z. li and j. zhang, phys. lett. a, 372 (2008) 417. 16. m.a. akbar, n.h.m. ali and e.m.e. zayed, commun. theor. phys., 57 (2012) 173. 17. m.a. akbar, n.h.m. ali and e.m.e. zayed, math. prob. engr., vol. 2012 (2012) 22 pages. doi: 10.1155/2012/459879. 18. a. bekir, phys. lett. a, 372 (2008) 3400. md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.66 (online publication: dec., 2013) 19. e.m.e. zayed, j. appl. math. comput., 30 (2009) 89. 20. m.a. akbar, n.h.m. ali and s.t. mohyud-din, world appl. sci. j., 16(11) (2012) 1551. 21. m.a. akbar, n.h.m. ali and s.t. mohyud-din, j. comput. analysis appl., 15(3) (2013) 557. 22. s. zhang, j. tong and w. wang, phys. lett. a, 372 (2008) 2254. 23. j. zhang, f. jiang and x. zhao, int. j. com. math., 87(8) (2010) 1716. 24. a.j.m. jawad, m.d. petkovic and a. biswas, appl. math. comput., 217 (2010) 869. 25. e.m.e. zayed, appl. math. comput., 218 (2011) 3962. 26. e.m.e. zayed and s.a.h. ibrahim, chin. phys. lett., 29 (06) (2012) 060201. 27. k. khan and m.a. akbar, ain shams engr. j., 4(4) (2013) 903. 28. k. khan, m.a. akbar and n.h.m. ali, isrn math. phys., vol. (2013), article id 146704, 5 pages doi: 10.1155/2013/146704. 29. m.j. ablowitz and p.a. clarkson, soliton, nonlinear evolution equations and inverse scattering, cambridge university press, new york, 1991. 30. h. naher and f.a. abdullah, aip advances 3, 032116 (2013) doi: 10. 1063/1.4794947. 31. j. zhang, f. jiang and x. zhao, inter. j. computer math., 87(8) (2010) 1716. appendix a: zhang et al. solutions [31] zhang et al. [31] established exact solutions of the well-known the zk-bbm equation by using the improved )/( gg′ -expansion method which are as follows: when ,042 >− µλ 2 1 2 2 2 1 2 2 2 2 2 1 2 2 2 1 2 2 2 2 1 2 1 6bv u 1 1 c sinh 4 c cosh 4 1 2 2a( ( ) ( 4 )( )) 1 12 2 c cosh 4 c sinh 4 2 2 6bv 1 1 c sinh 4 c cosh 4 1 2 2a( ( ) ( 4 )( )) 1 12 2 c cosh 4 c sinh 4 2 2 bv 8bv v 1 , 2a − µ = − λ − µξ+ λ − µξλ − + λ − µ λ − µξ + λ − µξ − µλ − λ − µξ + λ − µξλ − + λ − µ λ − µξ+ λ − µξ λ + µ − − (a.1) where 21 ,cc are arbitrary constants. when ,042 <− µλ 2 1 2 2 2 1 2 2 2 2 2 1 2 2 2 1 2 2 2 2 1 2 2 6bv u 1 1 c sin 4 c cos 4 1 2 2a( ( ) ( 4 )( )) 1 12 2 c cos 4 c sin 4 2 2 6bv 1 1 c sin 4 c cos 4 1 2 2a( ( ) ( 4 )( )) 1 12 2 c cos 4 c sin 4 2 2 bv 8bv v 1 , 2a − µ = − − µ −λ ξ + µ − λ ξλ − + µ −λ µ − λ ξ + µ − λ ξ − µλ − − µ − λ ξ + µ − λ ξλ − + µ − λ µ −λ ξ + µ −λ ξ λ + µ − − (a.2) where 21 ,cc are arbitrary constants. md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.67 (online publication: dec., 2013) when ,042 =− µλ 2 1 22 2 1 2 1 2 2 2 6bv 6bv u c c a( ( ) ( )) a( ( ) a( ( ) ( )) 2 c c 2 2 c c bv 8bv v 1 , 2a − µ − µλ = − − λ λ λ − + − + − + + ξ + ξ λ + µ − − (a.3) where 21 ,cc are arbitrary constants. when ,042 >− µλ 2 2 2 2 1 2 2 2 2 2 1 2 1 1 1 c sinh 4 c cosh 4 3bv( 4 ) 2 2u ( )) 1 12a c cosh 4 c sinh 4 2 2 bv 8bv v 1 , 2a λ − µξ + λ − µξ− λ − µ = λ − µξ + λ − µξ λ + µ − − − (a.4) where 21 ,cc are arbitrary constants. for ,01 >c 2 2 2 1 cc < above, then the solutions (a.4) turns into 22 2 2 2 01 43bv( 4 ) bv 4bv v 1 u sech ( ) , 2a 2 2a λ − µξ− λ − µ λ − µ − − = + ξ − ),(tanh 2 11 0 c c−=ξ when ,042 <− µλ 2 2 2 2 1 2 2 2 2 2 1 2 2 1 1 c sin 4 c cos 4 3bv( 4 ) 2 2u ( )) 1 12a c cos 4 c sin 4 2 2 2bv 8bv v 1 , 2a − µ −λ ξ + µ − λ ξλ − µ = µ − λ ξ + µ − λ ξ λ − µ + + + (a.5) where 21 ,cc are arbitrary constants. when ,042 =− µλ 2 2 2 2 2 1 2 2 6bvc 2bv 8bv v 1 u , 2aa(c c ) λ − µ + + = + + ξ (a.6) where 21 ,cc are arbitrary constants. appendix b: akbar et al. [17] akbar et al. [17] established a generalized and improved )/( gg′ -expansion method and studied zk-bbm equation, and obtained following solutions: when ,042 >− µλ md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.68 (online publication: dec., 2013) 2 2 3 2 1 2 2 2 2 2 2 2 2 2 2 2 2 1 6bv{ d( d d 2 d 2d 2 )} u 1 1 bsinh 4 acosh 4 1 2 2a(d ( 4 )( )) 1 12 2 bcosh 4 asinh 4 2 2 6bv{ d( 2d 2 d 2 )} 1 1 bsinh 4 acosh 4 1 2 2a(d ( 4 )( 1 12 2 bcosh 4 asinh 2 2 − µ + λ + − λ + µ − λµ = − λ − µξ + λ − µξλ − + λ − µ λ − µξ + λ − µξ − µλ − λ + − λ + µ λ − µξ + λ − µξλ − + λ − µ λ − µξ+ 2 2 )) 4 {(bv 8bv v 1) 12bvd(d ) , 2a − λ − µξ λ + µ − − + −λ (b.1) where ba, are arbitrary constants. when ,042 <− µλ 2 2 3 2 1 2 2 2 2 2 2 2 2 2 2 2 2 2 6bv{ d( d d 2 d 2d 2 )} u 1 1 bsinh 4 acosh 4 1 2 2a(d ( 4 )( )) 1 12 2 bcosh 4 asinh 4 2 2 6bv{ d( 2d 2 d 2 )} 1 1 bsinh 4 acosh 4 1 2 2a(d ( 4 )( 1 12 2 bcosh 4 asinh 2 − µ + λ + − λ + µ − λµ = − − µ −λ ξ + µ − λ ξλ − + µ − λ µ − λ ξ + µ −λ ξ µλ − λ + − λ + µ − µ − λ ξ + µ −λ ξλ − + µ −λ µ −λ ξ + 2 2 )) 4 2 {(bv 8bv v 1) 12bvd(d ) , 2a − µ − λ ξ λ + µ − − + −λ (b.2) where ba, are arbitrary constants. when ,042 =− µλ 2 2 3 2 1 2 2 3 6bv{ d( d d 2 d 2d 2 )} u b a(d ( )) 2 a b {(bv 8bv v 1) 12bvd(d ) , 2a − µ + λ + − λ + µ − λµ = − λ − + + ξ λ + µ − − + −λ (b.3) where ba, are arbitrary constants. when ,042 >− µλ 2 2 2 2 2 2 2 2 1 1 1 bsinh ( 4 ) acosh ( 4 ) 3bv( 4 ) 2 2u ( )) 1 12a bcosh ( 4 ) asinh ( 4 ) 2 2 2bv 8bv v 1 , 2a λ − µξ + λ − µξλ − µ = − λ − µξ + λ − µξ λ − µ + + − (b.4) where ba, are arbitrary constants. md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.69 (online publication: dec., 2013) if ,0>b 22 ba < above, then the solutions (b.4) turns into 22 2 2 2 01 43bv( 4 ) bv 4bv v 1 u sech ( ) , 2a 2 2a λ − µξλ − µ λ − µ − − = + ξ − ),(tanh 1 0 b a−=ξ when ,042 <− µλ , 2 182 )) 4 2 1 sin4 2 1 cos 4 2 1 cos4 2 1 sin ( 2 )4(3 2 2 22 22 2 22 a vbvbv ab ab a bv u ++− + −+− −+−−− −= µλ ξλµξλµ ξλµξλµλµ (b.5) where ba, are arbitrary constants. when ,042 =− µλ 2 2 2 22 6bvb 2bv 8bv v 1 u , 2aa(a b ) λ − µ + + = − + + ξ (b.6) where ba, are arbitrary constants. when ,042 >− µλ 2 2 3 2 2 2 2 2 2 2 2 2 2 2 2 2 1 3bv( 4 ) u 1 1 bsinh 4 acosh 4 1 2 28a(d ( 4 )( )) 1 12 2 bcosh 4 asinh 4 2 2 1 1 bsinh 4 acosh 4 6bv 1 2 2(d ( 4 )( )) 1 1a 2 2 bcosh 4 asinh 4 2 2 (2bv 8bv v v 1) , 2a − λ − µ = λ − µξ + λ − µξλ − + λ − µ λ − µξ + λ − µξ λ − µξ + λ − µξλ − − + λ − µ λ − µξ + λ − µξ λ − µ + + − (b.7) where ba, are arbitrary constants. when ,042 <− µλ 2 2 3 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3bv( 4 ) u 1 1 bsin 4 acos 4 1 2 28a(d ( 4 )( )) 1 12 2 bcos ( 4 ) asin ( 4 ) 2 2 1 1 bsin ( 4 ) acos ( 4 ) 6bv 1 2 2(d ( 4 )( )) 1 1a 2 2 bcos ( 4 ) asin ( 4 ) 2 2 (2bv 8bv v v 1) , 2a λ − µ = − − µ − λ ξ + µ − λ ξλ − + µ −λ µ − λ ξ + µ − λ ξ − µ −λ ξ + µ −λ ξλ − − + µ −λ µ − λ ξ + µ − λ ξ λ − µ + + − (b.8) md. nur alam and m. ali akbar/ bibechana 10 (2014) 58-70 : bmhss, p.70 (online publication: dec., 2013) where ba, are arbitrary constants. when ,042 =− µλ 2 2 2 3 2 2 3 3bv( 4 ) 6bv b u (d ( )) b a 2 a b 8a(d ( )) 2 a b (v 1 2bv 8bv v) , 2a − λ − µ λ = − − + λ + ξ− + + ξ + + λ − µ + (b.9) where ba, are arbitrary constants. microsoft word main.doc 27 bibechana vol. 6, march 2010 dark matter in the universe devendra adhikari1 and krishna raj adhikari2 1m.m.a.m. campus, biratnagar, tribhuvan university, nepal 2western regional campus, ioe, tribhuvan univesity, nepal abstract different physical phenomena, techniques, and evidences which give the proof for the existence of dark matter have been discussed. keywords: baryonic matter; dark mtter; chandra x-ray observatory 1. introduction until about three decades ago, astronomers thought that the universe was composed almost entirely of the “baryonic matter” (matter basically made up of electrons, protons and neutrons), ordinary stuff. however, in the past decade, there has been ever more evidence accumulating that suggests there is something in the universe that we can not see. although it can not be seen, scientists have several reliable evidences that more than 90% of the total mass of the universe is composed of this undetected mass, called dark matter. dark matter is so called because it emits no detectable radiation. carl sagan described it as dark, quintessential, deeply mysterious stuff wholly unknown on earth. there is currently much ongoing research by scientists attempting to discover exactly what the dark matte is; how much there is, and what effect it may have on the future of the universe as a whole. this review article attempts to survey and analyze the evidences of the existence of dark matter in the universe. 2. discussion astronomers can not detect the dark matter directly because it does not emit or absorb light or radiation. the presence of dark matter can be inferred from different physical phenomena, techniques, and evidences. these physical phenomena, techniques and evidences are discussed below: (1) by measuring the motion (more exactly orbital velocity) of stars, gas, and other matters present in the galaxies, astronomers can measure the mass of the galaxies by using kepler’s laws of planetary motion, 28 devendra adhikari and krishna raj adhikari 2 2 24 gmt r and v gm r π = = here, t, r and v are orbital period, average radial distance of the star from the galactic centre and orbital velocity respectively. g is the universal gravitational constant and m is the mass of the stars . in our solar system, we can use the velocity of the earth ( 30 /≈ km s ) around the sun to measure the sun’s mass. if the sun were four times massive then the earth would need to move around the sun at about 60 km/s, otherwise the earth would collapse on the sun. we can use the velocity of the stars to measure the mass of the galaxy (the velocity of stars can be measured from the doppler’s shift of light). similarly, radio and optical observations of gas, stars and other detectable matter in a distant galaxy, enable astronomers to determine the mass of the galaxy. and here major problem arises. the mass that the astronomers infer for the galaxies is at least 5-10 times the mass of all visible stars and other matter in the galaxy. this missing mass component is considered to be the invisible dark matter, which was first suggest in 1993 by astrophysicist fritz zwicky. (2) there is another way to look at the mass problem with the spiral galaxies. one can plot a rotation curve, a group of velocity versus distance from the galactic centre for component stars. the kepler’s law shows that, for solar system, the planet’s velocity decreases as the inverse square root of distance from the sun. but for galaxies, measurements show that the curve is flat, showing constant speed, or even increases slightly with distance. the unexpected nature of the rotation curve was first noted by astronomers vera rubin and kent floyd in 1970, for the andromeda galaxy. this implies that there must be a large amount of dark matter affecting the stellar motion; otherwise, the stellar galaxies would be flying apart. (3) the shortfall in mass is much greater for galaxy cluster (a group of large number of galaxies) than that in individual galaxy. the coma cluster is found to be 90% missing, the virgo cluster 98% missing. (4) the us space agency (nasa) published in 2002 its chandra x-ray observatory has seen filaments of hot gas connecting the galaxies. these visible gas clouds within galaxy clusters also have added to the dark matter requirement. if there were not unseen mass to give the hot cloud of gas, it would quickly leak way from the cluster due to its high speed. (5) the presence of dark matter has also been confirmed by the gravitational lensing, bending of light predicted by einstein’s theory of general relativity. astrophysicists scrutinized and analyzed 29 bibechana vol. 6, march 2010 the gravitational lensing. using time-honored methods of calculating mass and expected velocity dispersion astrophysicists have found that there is much more mass than can be observed directly . using the biggest telescopes in the world, an institute of astronomy, cambridge team of researchers has made detailed 3d maps of galaxies. by analyzing these 3d images, the team has measured the mass of the galaxies very precisely. with the aid of 7000, separate measurements, the researchers have been able to establish that the galaxies contain 400 times the amount of dark matter as they do normal matter. (6) from the virial theorem, which can be applied for a gravitationally stable system and if galaxies are supposed to be gravitationally stable, the mass formula for the galaxy cluster is 23v rm g = here v is the average of the squared radial velocity observed for member of galaxies within the cluster. r is an estimate of the geometric radius of the entire cluster and g is the gravitational constant. this formula provides the mass of albell 1060, a cluster of about 200 galaxies located at 220 million light years away with v is about 57.14 10 m/ s× and r, 6.5 million light years is about 147 10× solar masses. this is about 10 times higher than the known mass. the albell 1060 galaxies probably do not contain this much extra mass. instead the mass may exist as dark matter. a similar numerical discrepancy exists for every galaxy cluster, assuming they obey virial theorem. (7) dark matter is also involved in the popular inflationary big bang model (almost universally accepted model) which predicts that the curvature of the universe must be flat. this means the density of the matter in the universe is exactly balanced with the critical density (the density that would need to have enough gravitational pull to overcome the expansion of the universe). without dark matter, the ratio of actual density of the matter in the universe to the critical density (called omega, ω ) lies somewhere between 0.1 and 0.01. therefore a great amount of dark matter is needed to result in flat curvature of the universe. 3. conclusion it is seen that the dark matter is required if the laws of motion and gravity hold for galaxies, and if the galaxy systems are stable. there is no reason to except the failure of the laws of motion and gravity in the galaxies. similarly, no evidence of instability of galaxies and clusters of galaxies is yet found. moreover, gravitational lensing (modern technique to measure the mass of distant massive 30 devendra adhikari and krishna raj adhikari objects), big bang inflationary model (universally accepted model), virial theorem, all show that there must be much more matter in the universe than that detected till the date. thus, it is concluded that even though the dark matter is invisible and most of its components are yet to be detected there exists dark matter in the galaxies, if not elsewhere. references 1. b.j. bok, scientific american, 244, (1981) 92 2. h. briggs, bbc news online science reporter, ( 1 august 2002 ). 3. m.t. bruck, exercise in practical astronomy using photographs. adam higher, new york,(1990). 4. jeff foust ,spaceflight now (online space news), (march 23, 2001). 5. j.f. hawley and k.a. holcomb, foundations of modem cosmology. oxford university press, new york, (1998). 6 . g. jonson, dark matter lights the void, the new york times,(01/1996). 7. panel on cosmology; cosmology, a research briefly board on physics and astronomy, commission on physical sciences, mathematics and application, national research council, national academy press, washington, d.c., (1995) p.27. 8. r., resnick ,d., hallodayand k.s., krane physics, 4th edition vol-1(1994). 9. c. sagan, nature 400 (6747): (1994),819. 10. whitehouse, d. the light in dark matter, bbc news online science editor,(03/2000). microsoft word main.doc 9 bibechana vol. 6, march 2010 experimental study of free energy of activation of flow and grunberg-nissan parameters in binary liquid mixtures i.s.jha ,r.p. koirala and d. adhikari m.m.a.campus, biratnagar, tribhuvan university, nepal abstract the binary mixtures of cabontetrachloride with isobutylmethylketone and benzaldehyde were studied at 308.15 by measuring viscosities and densities. the derived and excess viscosities, activation energy of flow and grunberg-nissan parameters have been calculated. it was found that these parameters are satisfactorily used to predict the strength and nature of molecular interactions. it was found that the strength of interactions in the systems studied is in the following order : 4 4ccl ibmk ccl bd+ > + kewyords: binry liquid; benzaldehyde; carbontetrachloride 1. introduction compressibility which is a static properly and viscosity which is a transport property, are the most useful and important amongst the properties of the liquid. attempts have been made to relate these properties to the strength of molecular interaction through various models [l]. excess thermodynamics parameters [2–4] and excess ultrasonic parameters [5–8)] have been used by various workers extensively in studying relative strength of intermolecular interaction in pure liquids and binary liquid mixtures. however, very few attempts [9–10] have been made to study molecular interactions through viscosity data. this work attempts to describe the interactions from the result of viscosity measurements in binary mixtures of carbontetrachloride with benzaldehyde and isobutylmethylketone at 308.15k. we know due to viscosity liquids exhibits resistance to flow. in laminar flow molecules flowing ahead must acquire a definite amount of energy. this energy is called the free energy of activation of flow per mole. in general, higher the free energy of activation of flow, moiré viscous is the liquid. however, other factors are also important. eyring [13] developed a simple theory of liquid. he suggested that the fundamental rate process for viscous flow in liquid is the migration of molecules from a lattice site into nearby hole from which it can then move to another site. thus work is required to make the hole against the potential barrier due to the migration of molecules and the process is therefore analogous to chemical reaction proceeding through a transition state higher energy than the initial and final states. the absolute reaction-rate of erying [14] and co-workers relates the viscosity to the energy needed for a molecule to overcome the attractive force field of its neighbours so that it can jump (flow). in this present work attempts have made to describe the interaction from the results of viscosity measurement of the binary mixtures. 2. formalism free energy of activation of flow (g) has been calculated y the following equation : 10 i.s. jha et.al n vg rt l ........................(i) hn η =     where r, t, η , v, h and n are gas constant, absolute temperature, viscosity, molar volume, plank’s constant and avogadro’s number respectively. grunberg-nissan parameter (d) has been calculated using following equation: 1 1 2 2 1 2in x ln x ln x x d .................. (ii)η = η + η + where η is the viscosity of binary mixture, 1 2andη η re the viscosities of ith component of the mixtures with mole fraction x1and ‘d’ is the parameter which is regarded as a measure of the strength of interaction between the components of the mixture. excess parameters have been calculated using the following equation e measured i ip p x p .......................... (iii)= ∑ measuredp is the experimental measured value of the parameter p for the mixture and pi is the value of p for the ith pure liquid having x1 mole fraction in the mixture. comparison of experimentally measured value of the parameter p for the mixture and p1 is the value of p for the ith pure liquid having x1 mole fraction in the mixture. e 2 1 2 1 2 1 2p x x [a b(x x ) c(x x )] .................. (iv)= + − + − where a, b and c are constants, determined by least square fit method. pe represents e e e, v and gη respectively for the system. 3. method and methodology the liquids carbontetrachloride (ccl4), isobutylketone (ibmk) and benzaldehyde were of analytic grade (e-merek) and used as it was supplied. the densities and viscosities of these pure liquids were checked against the literature values published elsewhere [15]. the densities were measured using bicapillary pyknometer of 10cc capacity whereas the masses were measured by using electronic balance of sensitivity 0.001 gm. viscosities were measured by oswald’s viscometer. the binary mixtures of the liquids were prepared according to normal process using mole fractions. table 1 (cabontetrachloride + benzaldehyde) 308.15 k obs x1 x2 η (10-4nm-2) ρ (kgm-3) v(10-6m3) 1 0.000 1.000 11.562 1023.610 103.672 2 0.113 0.887 10.927 1031.350 108.925 3 0.295 0.705 10.045 1086.920 107.161 4 0.376 0.624 9.836 1089.660 111.812 5 0.427 0.573 9.214 1173.540 110.213 6 0.505 0.495 8.824 1208.290 112.567 7 0.601 0.399 8.493 1275.520 109.169 8 0.741 0.259 8.235 1356.910 105.633 9 0.890 0.110 7.991 1434.170 104.067 10 1.000 0.000 7.955 1569.140 98.028 11 bibechana vol. 6, march 2010 table 2 (cabontetrachloride + isobutykmethylketone) 308.15 k obs x1 x2 η (10-4nm-2) ρ (kgm-3) v(10-6m3) 1 0.000 1.000 4.954 786.94 127.277 2 0.143 0.857 5.014 873.62 123.475 3 0.234 0.766 5.154 926.44 121.595 4 0.333 0.667 5.282 961.32 122.805 5 0.461 0.539 5.407 1037.72 120.394 6 0.582 0.416 5.710 1119.81 117.345 7 0.695 0.605 6.101 1270.01 106.265 8 0.801 0.199 6.682 1324.02 106.599 9 0.904 0.096 6.964 1446.10 102.812 10 1.000 0.000 7.955 1569.14 98.028 table 3 (cabontetrachloride + isobutykmethylketone) 308.15 k obs x1 5 2(10 )e nsmη − − 6 3(10 )ev m g(kj/mole) ( / )eg kj mole d 1 0.000 0.000 0.00 13.02 0.00 0.000 2 0.143 -6.701 0.46 12.97 -28.68 -0.439 3 0.234 -5.038 1.27 13.01 -31.88 -0.381 4 0.333 -6.765 5.28 13.09 -23.37 -0.402 5 0.461 -9.303 6.62 13.12 -36.86 -0.503 6 0.582 -9.870 7.09 13.10 -33.96 -0.519 7 0.695 -9.412 1.33 13.14 -56.59 -0.531 8 0.801 -6.813 2.78 13.33 -23.60 -0.447 9 0.904 -7.034 1.98 13.54 -34.65 -0.914 10 1.000 0.000 0.00 13.56 0.00 -0.000 table 4 (cabontetrachloride + benzaldehyde) 308.15 k obs x1 5 2(10 )e nsmη − − 6 3(10 )ev m g(kj/mole) ( / )eg kj mole d 1 0.000 0.00 0.000 14.972 0.00 0.000 2 0.113 -4.10 0.088 14.653 -11.95 -0.015 3 0.295 -8.70 0.009 14.395 -23.04 -0.031 4 0.376 -1.20 3.260 14.450 -22.60 -0.022 5 0.427 -1.25 3.280 14.245 -24.89 -0.067 6 0.505 -1.14 3.320 14.188 -35.89 -0.082 7 0.601 -8.20 2.790 14.186 -57.69 -0.085 8 0.741 -5.60 0.780 13.847 -48.38 -0.064 9 0.890 -2.10 0.800 13.721 -40.74 -0.037 10 1.000 0.00 0.000 13.566 0.00 0.000 12 i.s. jha et. al table 5 (cabontetrachloride + isodutylmethylketone) 308.15 k (redlick-kister equation) obs x1 eη 6 2(10 nsm )− − eδη 5 2(10 nsm )− − ev 6 3(10 m )− evδ 6 3(10 m / mole)− eg (kj / mole) egδ (kj / mole) 1 0.000 0.000 0.0 0.00 0.00 0.00 0.000 2 0.143 -6.701 -1.7 0.46 -0.10 -28.68 0.0037 3 0.234 -5.038 -2.4 1.27 -1.04 -31.88 -0.0020 4 0.333 -6.765 -3.2 5.28 -0.88 -23.37 0.0082 5 0.461 -9.303 -5.9 6.62 -0.54 -36.86 0.0033 6 0.582 -9.870 -2.8 7.09 -1.10 -33.96 0.0037 7 0.695 -9.412 -1.5 1.33 -3.04 -56.59 -0.0015 8 0.801 -6.813 -1.4 2.78 -0.61 -23.60 -0.0037 9 0.904 -7.034 -1.7 1.98 -1.63 -34.65 -0.0063 10 1.000 0.000 0.00 0.00 0.00 0.00 0.0000 table 6 (cabontetrachloride + benzaldehyde) 308.15 k (redlick-kister equation) obs x1 eη 6 2(10 nsm )− − eδη 5 2(10 nsm )− − ev 6 3(10 m )− evδ 6 3(10 m / mole)− eg (kj / mole) egδ (kj / mole) 1 0.000 0.00 0.00 0.000 0.0000 0.00 0.0000 2 0.113 -4.10 0.08 0.088 -0.0004 -11.95 0.0016 3 0.295 -8.70 1.10 0.009 -0.0014 -23.04 0.0029 4 0.376 -1.20 -0.90 3.260 -0.0008 -22.60 -0.0003 5 0.427 -1.25 -1.10 3.280 -0.0004 24.89 -0.0049 6 0.505 -1.14 -0.30 3.320 -0.0002 -35.04 -0.020 7 0.601 -8.20 1.30 2.790 -0.0001 -57.69 -0.0113 8 0.741 -5.60 0.08 0.780 -0.0008 -48.38 -0.0057 9 0.890 -2.10 7.60 0.800 -0.0008 -40.74 -0.0009 10 1.000 0.00 0.00 0.000 0.0000 0.00 0.0000 table 7 (least square parameters) ccl4 + bd ccl4 + ibmk parameter a b c σ a b c σ eη -0.0044 0.0017 0.0028 0.00008 -0.0034 -0.0016 -0.0008 0.0008 ev 0.0125 0.0034 0.0034 0.00070 0.0240 0.0033 -0.0302 0.0156 eg 0.1460 0.194 0.1780 0.00510 -0.1390 -0.0610 -0.2110 0.0078 13 bibechana vol. 6, march 2010 4. result and discussion the basic data of both the systems of binary mixtures ccl4 + ibmk (system i) and ccl4 + bd (system ii) have been given in tables 1 and 2. the observations have been recorded at 308.15 k. the required parameters and their excess values have been calculated using equation (i) to (ii). to fit redlich-kister equation for the prediction of excess values and their standard deviations, the constants for the systems i and ii have been calculated by least square fit methods. the calculated values have been recorded in table 3 to 7. perusal of table 1 and 2 of both the systems indicate that the magnitude of the viscosities decreases in systems ii and increases in system i at the same temperature as the concentration of ccl4 increases. the magnitude of densities increases in both the systems with the increase in concentration of ccl4. in order to study the relative interaction in above systems, we have made use of excess parameters e e e, v and gη . for ideal mixing the excess values should be zero. the deviation, whether positive or negative indicate the non-ideality of the mixtures. the deviation from the ideal behaviour in the mixtures i.e., non-zero values of excess parameters are due to presence of interactions between the constituents of the mixtures. these interactions are of various types. the positive values of excess volume attributed to dispersive forces while negative values of excess derived parameters have been attributed to charge transfer, hydrogen bonding, dipole-dipole and dipole induced dipole interaction [17]. thus we conclude that dispersive forces operate in both the systems. but if additional interactions are also present between the components of the mixtures then the excess values of the derived parameters are the net results of all types of contributions. the non-zero values of different excess parameters in both the systems of mixtures shown in the table 3 and 4 confirm the presence of specific interactions between the components of the mixtures. attempts have been made by various workers [18, 19] to explain the nature and strength of such interactions on the basis of sign and magnitude of excess parameters. if strong interaction is present in a mixture then the molecules of the components come closer after mixing. this will cause a decrease in volume compared to what is expected for an ideal case, ev then will be negative. the excess volume ev , interactions in the systems. the perusal of the sign and magnitude of the excess volume parameter shows that the interaction in the systems follows the following order : 4 4ccl ibmk ccl bd+ > + the negative deviation of eη for both the systems indicates that dispersive forces are primarily responsible for interaction [20]. also the negative deviation of eη implies that the dipole interactions are more probable in these systems. further the negative deviations in excess values of the activation of energy flow also indicate the decrease in the internal energy of viscous flow, thus supporting the presence of weak interaction in the systems studies [21], the sign and magnitude o the nissan-grunberg parameter ‘d’ has been taken as the measure of the strength of interactions. the negative values of the parameter (d) shows the presence of weak interaction in the systems. thus the study of the table 1 to 4 shows that the systems under study contain dispersive interactions of weak magnitude and their strength of interaction can be placed in the following order : ccl4 + ibmk > ccl4 + bd further, we have fitted the redlich-kister equations for parameters e e e, v and gη by using least square fit method. the result has been given in table 5, 6 and 7. we found that our results are satisfactory by comparing the results of other workers [22]. 14 i.s. jha et.al references 1. h.n.v. temperley , j.s. rawlinson, and g.s. rushbroke, physics of simple liquids , john wiley, new york, (1968). 2. d.d .despandev and , l.g., bhutangade, phy. chem 71, (1967) 1277. 3. r.p. rastogi., and j.j.misra, phys.chem 71, (1967) 1277. 4. j.k. halzhaverand w.t. zeigler, j. phys. chem ,79, (1975) 590. 5. fort. r.j. and w.r. ,traus faraday soc. (gb), 61 (1975) 2105. 6. v.tiwari, & j.d. pandey , indian. j. pure & appl. phys. 18, (1980) 51. 7. v.a. tabhane, v. n.badhe, and b. a., pataki, , accustica (gev) 411. 8. v.a. tabhane, v.a badhe and b.a pataki,., ind. j. pure & appl. phys. 20 (1982) 159. 9. d.v.s. jain, m. alstair, and a. pethrie, trans. faraday soc. (gb) 70, (1974) 1293. 10. d. dalwoska, a. dutkiewitz & surma, d. acta. phys. 15, (1977) 719. 11. r.l. misra. and j.d. pandey , ind. j. pure & appl. phys. 15, (1977) 870. 12. g. maijano, and f.j. wandereingh, chem.phys. (usa) 69,(1978)559. 13. h. eyring, and hirschfelder., j. phys. chem.41, (1937) 249. 14. s. glasstone, k.j. laider, and h. eyring, the theory of rate process, mc grow hill, ny (1941). 15. c.r.c table (1960). 16. j.d., pandey, g.p. dubey, b.p. shukla, and s.n.j. dubey, ultrasonic 13, (1991) 74. 17. v.a., tavhane, and b.a pataki, ind. j.pure & appl. phys 22, 447(1984). 18. k.m. singh, v.k. mishra, s.n. sudhanshu and t. sati, proc. solid state phys. sympo.(india),33, (1991) 296. 19. o. prakash, j. raman, t. and e. rajgopal, ind. j. pure & appl. phys. 26, 716(1988). 20. r.k.nigam,. and b.s. maki ind. j. chem. 9(1971)1255. 21. m. chauhan, r. mishra, and a. singh, , pramana 20, (1983)77. 22. a kumar., n. pitamber, and s. prakash, ind. j. pure & appl.phys. 32, 608(1984). 103-112 tulasi niraula r c o s t n t.p. niraula et al. / bibechana 11(1) (2014) 103-112 (online publication: march, 2014) p.103 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana critical micelle concentration of sodium dodecyl sulphate in pure water and in methanol-water mixed solvent media in presence and absence of kcl by surface tension and viscosity methods tulasi prasad niraula, ajaya bhattarai*, sujeet kumar chatterjee department of chemistry, m.m.a.m.c., tribhuvan university , biratnagar, nepal *corresponding author: email: bkajaya@yahoo.com accepted for publication: february 18, 2014 abstract careful measurements of surface tension and viscosity of sodium dodecyl sulphate (sds) in presence and absence of kcl in pure water and methanol-water mixed solvent media containing 0.1, 0.2, 0.3 and 0.4 volume fractions of methanol at 308.15 k are reported. the concentration of kcl is 0.01m. the concentration of sds varies from 4.86×10-3 to 29.56×10-3 mol.l-1. the critical micelle concentration (cmc) increases with increase in percentage of methanol and decreases with addition of salt. © 2014 rcost: all rights reserved. key words: critical micelle concentration; sodium dodecyl sulphate; surface tension; viscosity; methanol-water mixed solvent media. 1. introduction when an ionic surfactant dissolves in water or any other solvent, initially, the molecules or ions of the surfactant move freely in solution. as the concentration of the surfactant is increased, the ions or molecules start to associate, and finally organize into more complex unit, called micelle [1]. generally micelles have spherical shape but sometime they also assume different shapes like cylindrical, conical, rod like etc. [2]. the particular concentration (actually an arbitrary concentration of a narrow range) value, where the aggregation process begins for the formation of micelle, is called critical micelle concentration (cmc). the cmc is one of the most useful physicochemical characteristics of surfactants. chemically, surfactants are mostly low-molecular compounds. when they dissolve in solvent, they form true solutions in concentration ranges below the cmc. micelles are collection of a larger number of simple molecules or ions of surfactants and the resulting size of such structures is in the colloidal range. the cmc of a solution can be determined by measuring different physical properties of the solution like conductance, surface tension, viscosity, uv-vis spectrum, fluorescence emission spectrum etc. [3]. in this paper, surface tension and viscosity methods are used for determination of cmc for sodium dodecyl sulphate. the surface tension is an intensive thermodynamic quantity, which is very important for the determination of cmc of surfactant [4]. on addition of a surfactant, surface tension of solution decreases and at a particular concentration, the surface tension of the solution tends to remain constant. this concentration indicates critical micelle concentration (cmc) of the surfactant. the behaviour of the solution is thus different above and below the cmc. t.p. niraula et al. / bibechana 11(1) (2014) 103-112 (online publication: march, 2014) p.104 another property of surfactants which can be used for the measurement of cmc is viscosity. viscosity can be defined as the internal resistance or friction of liquid or gas to flow. it is one of the most important properties of fluids and has a very important role in petroleum industry. when two or more than two liquids flow on a same surface, they move with different rates or they have different viscosities. viscosity is generally represented by a greek letter eta (η ) [5]. the small change in viscosity causes an unexpected change in different properties of fluids [6]. the surface tension and the viscosity data have been measured with the help of simple instruments like stalagmometer and ostwald viscometer. these instruments consume more time and large amount of chemicals. mansingh survismeter helps to measure these properties in short time with small amount of chemicals. the surface tension and viscosity of hygroscopic as well as poisonous substances can be measured with the help of mansingh survismeter. it means it is cost effective and less hazardous [5]. the surface tension is generally represented by a greek letter gamma (γ) [5], and it is determined by using the following relation: ����� = � � ��� � � (� � � �� )����� (1) where, γsoln = surface tension of solution γsolv = surface tension of solvent nsoln = number of drops of solution nsolv = number of drops of solvent dsoln = density of solution dsolv = density of solvent when surface tension of a solution is plotted against log[c], where c is the concentration of surfactant then it gives a curve. the two fitted lines meet in the curve at the particular point. that point of intersection is known as cmc of the solution. viscosity calculation can be worked out by the following mathematical relation: 2 2 1 2 1 1 t t d d η            =η (2) where, 1η = coefficient of viscosity of the solution 2η = coefficient of viscosity of the solvent t1 = time flow of the solution t2 = time flow of the solvent d1 = density of the solution d2 = density of the solvent when viscosity of a solution is plotted against log[c], where c is the concentration of surfactant then it gives a curve. the two fitted lines meet in the curve at the particular point. that point of intersection is known as cmc of the solution. the curve for surface tension is different from the curve of viscosity. the aggregation of ionic surfactants in aqueous solution is influenced by the presence of electrolytes, temperature, pressure etc. generally, the addition of an electrolyte tends to induce the formation of aggregates at concentration below the cmc of the pure surfactant [7,8] while with many electrolytes, specific interactions between the surfactant ion and electrolyte counter ion will lead to a reduction in solubility [9]. t.p. niraula et al. / bibechana 11(1) (2014) 103-112 (online publication: march, 2014) p.105 sodium dodecyl sulphate is an ionic surfactant. it has different uses like as engine degreaser, floor cleaner etc. in recent studies it is considered as a novel microbicide against different viruses [10, 11]. methanol water mixtures have very special properties, which are different from that of the other alcohol water mixtures. in methanolwater mixture ions association has been found to be negligible up to methanol content of about 80% in the binary solvent. it may be due to the larger dielectric constant of the methanolwater mixture and the smaller size of ion. our interest is to see the effects of concentration and relative permittivity on the viscosity and surface tension of sodium dodecyl sulphate in pure water and methanol-water mixed solvent media in the presence and absence of kcl at 308.15 k., also to compare the calculated cmc of the surfactant solutions. 2. experimental methods methanol (merck, india) was distilled with phosphorous pentoxide and then redistilled over calcium hydride. the purified solvent had a density of 0.77723 ± 0.00004g.cm-3 which was measured by the use of an ostwald-sprengel type pycnometer of about 25 cm3 capacity and a co-efficient of viscosity of 0.47424 ± 0.00005 mpa.s which was determined by the use of the viscometric measurements were performed at 308.15 k using a schultz-immergut-type viscometer [12] with a sintered disc fitted to the widest arm to filter the solution/solvent from dust particles, if any and these values are in good agreement with the literature values [13]. triply distilled water with a specific conductance less than 10-6 s.cm-1 at 308.15 k was used for the preparation of the mixed solvents. sodium dodecyl sulphate employed in these investigations was purchased from merck specialties private limited, mumbai, india. surface tension and viscosity measurements were carried out by using mansingh survismeter. potassium chloride employed in these investigations was purchased from himedia laboratories limited, mumbai, india. the measurements were made in a water bath maintained 308.15 k within ± 0.005 k. for the measurement of surface tension and viscosity mansingh survismeter was washed with chromic acid after that it was washed with tap water, distilled water and then with doubly distilled water followed by triply distilled water and finally washed by acetone for drying and then kept to dry for 24 hours. in dry limb of mansingh survismeter, 30ml solvent was filled and number of drops formed by fixed volume of solution was counted by using a counter machine. to measure the viscosity of surfactant’s solution, the time flow for the given volume of solution was determined by using stop watch. in order to avoid moisture pickup, all solutions were prepared in a dehumidified room with utmost care. in all cases, the experiments were performed in three replicates. 3. results and discussion the experimental surface tension and viscosity of sodium dodecyl sulphate in pure water and four different methanol-water mixtures (containing 0.1, 0.2, 0.3 and 0.4 volume fractions of methanol) in presence and in absence of kcl at 308.15k are represented in the figures 1 to 20. we have also calculated the critical micelle concentration (cmc) from figs. 1 to 20. table 1 shows cmc of sds with change in volume fraction of methanol in presence and in absence of 0.01m kcl. it was observed that the surface tension decreases with increase in concentration but viscosity increases with increase in concentration. after formation of cmc with addition of surfactant the ions or molecules associate with each other but not goes in solution hence viscosity or surface tension remains almost the same. the cmc of sds increases with increase in percentage of methanol and decreases with addition of kcl. the increase in cmc with increase in volume fraction of methanol is due to decrease in polarity of solvent molecule and decrease in hydrophobicity of solvent and surfactant hydrophobic part. the decrease in cmc with addition of kcl is due to inserts of counter ion between surfactant molecules or ions. we have observed the break in the curve of surface tension versus log[c] and viscosity versus log[c]. the breaking points indicate critical micelle concentration (cmc). the cmc of sds calculated by using surface tension and viscosity are found almost same which are shown in table 1. the value of cmc in distilled water is t.p. niraula et al. / bibechana 11(1) (2014) 103-112 (online publication: march, 2014) p.106 experimentally found to be 9.68 mm (table1) which is almost same (9.4mm) which was obtained by khan and shah [14]. it was found from our experiments that the cmc of sds solution decreases in the presence of kcl and our data matched with baloch et.al [15]. the unit used here for surface tension is n/m and that for viscosity is pa.s throughout the experiments. fig. 1 fig. 2 figure 1: variation of surface tension with log[c] of sds in pure water at 308.15 k (indicating cmc). figure 2: variation of surface tension with log[c] of sds in pure water in presence of kcl at 308.15 k (indicating cmc). fig. 3 fig. 4 figure 3: variation of surface tension with log[c] of sds in 10% methanol at 308.15 k (indicating cmc). figure 4: variation of surface tension with log[c] of sds in 10% methanol in presence of kcl at 308.15 k (indicating cmc). 0.037 0.038 0.039 0.040 -2.10 -2.05 -2.00 -1.95 -1.90 -1.85 log [c] s ur fa ce te ns io n 0.031 0.032 0.033 -2.2 -2.1 -2.0 log [c] s ur fa ce te ns io n 0.0320 0.0335 0.0350 0.0365 -2.4 -2.3 -2.2 -2.1 log [c] s ur fa ce te ns io n 0.0320 0.0325 0.0330 -1.9 -1.8 -1.7 -1.6 -1.5 log [c] s ur fa ce te ns io n t.p. niraula et al. / bibechana 11(1) (2014) 103-112 (online publication: march, 2014) p.107 fig. 5 fig. 6 figure 5: variation of surface tension with log[c] of sds in 20% methanol at 308.15 k (indicating cmc). figure 6: variation of surface tension with log[c] of sds in 20% methanol in presence of kcl at 308.15 k (indicating cmc) fig. 7 fig. 8 figure 7: variation of surface tension with log[c] of sds in 30% methanol at 308.15 k (indicating cmc). figure 8: variation of surface tension with log[c] of sds in 30% methanol in presence of kcl at 308.15 k (indicating cmc). 0.0325 0.0330 0.0335 0.0340 0.0345 0.0350 -2.0 -1.9 -1.8 -1.7 log [c] s ur fa ce te ns io n 0.029 0.031 0.033 0.035 0.037 -2.4 -2.3 -2.2 -2.1 -2.0 log [c] s ur fa ce te ns io n 0.033 0.034 0.035 -2.3 -2.2 -2.1 -2.0 log[c] s ur fa ce te ns io n 0.028 0.029 0.030 -2.0 -1.9 -1.8 -1.7 -1.6 log [c] s ur fa ce te ns io n t.p. niraula et al. / bibechana 11(1) (2014) 103-112 (online publication: march, 2014) p.108 fig. 9 fig. 10 figure 9: variation of surface tension with logarithm of concentration of sds in 40% methanol at 308.15 k (indicating cmc). figure 10: variation of surface tension with logarithm of concentration of sds in 40% methanol in presence of kcl at 308.15 k (indicating cmc). fig. 11 fig. 12 figure 11: variation of viscosity with log[c] of sds in pure water at 308.15k (indicating cmc). figure 12: variation of viscosity with log[c] of sds in pure water in presence of 0.01m kcl at 308.15 k (indicating cmc). 0.0314 0.0318 0.0322 0.0326 0.0330 -1.9 -1.8 -1.7 -1.6 -1.5 log [c] s ur fa ce te ns io n 0.0315 0.0320 0.0325 0.0330 -1.90 -1.85 -1.80 -1.75 -1.70 -1.65 log [c] s ur fa ce te ns io n 825 830 835 840 845 850 -2.1 -2.0 -1.9 -1.8 log[c] v is co si ty 850 860 870 880 -2.1 -2.0 -1.9 -1.8 -1.7 log[c] v is co si ty t.p. niraula et al. / bibechana 11(1) (2014) 103-112 (online publication: march, 2014) p.109 fig. 13 fig. 14 figure 13: variation of viscosity with log[c] of sds in 10% methanol at 308.15 k (indicating cmc) . figure 14: variation of viscosity with log[c] of sds in 10% methanol in presence of 0.01m kcl at 308.15 k (indicating cmc). fig. 15 fig. 16 figure 15: variation of viscosity with log[c] of sds in 20% methanol at 308.15 k (indicating cmc). figure 16: variation of viscosity with log[c] of sds in 20% methanol in presence of 0.01m kcl at 308.15 k (indicating cmc) . 990 1000 1010 1020 1030 1040 -1.90 -1.85 -1.80 -1.75 -1.70 -1.65 log [c] v is co si ty 1005 1010 1015 1020 1025 -2.3 -2.2 -2.1 -2.0 -1.9 log[c] v is co si ty 1030 1035 1040 1045 1050 1055 -1.9 -1.8 -1.7 log [c] v is co si ty 1010 1020 1030 1040 -2.4 -2.3 -2.2 -2.1 -2.0 log[c] v is co si ty t.p. niraula et al. / bibechana 11(1) (2014) 103-112 (online publication: march, 2014) p.110 fig. 17 fig. 18 figure 17: variation of viscosity with log[c] of sds in 30% methanol at 308.15 k (indicating cmc). figure 18: variation of viscosity with log[c] of sds in 30% methanol in presence of 0.01m kcl at 308.15 k (indicating cmc). fig. 19 fig. 20 figure 19: variation of viscosity with log[c] of sds in 40% methanol at 308.15 k (indicating cmc). figure 20: variation of viscosity with log[c] of sds in 40% methanol in presence of 0.01m kcl at 308.15 k (indicating cmc). 1152 1156 1160 -2.0 -1.9 -1.8 -1.7 -1.6 log [c] v is co si ty 1140 1144 1148 1152 1156 -2.5 -2.4 -2.3 -2.2 -2.1 log[c] v is co si ty 1200 1210 1220 1230 1240 -1.8 -1.7 -1.6 -1.5 log[c] v is co si ty 1211 1213 1215 1217 -1.9 -1.8 -1.7 -1.6 log [c] v is co si ty t.p. niraula et al. / bibechana 11(1) (2014) 103-112 (online publication: march, 2014) p.111 table 1: critical micelle concentration values of sds in presence and in absence of 0.01m kcl calculated from surface tension and viscosity in pure water and methanol-water mixed solvent media at 308.15 k. s.n. volume fraction of methanol cmc /mm from surface tension from viscosity 308.15 k 308.15 k in absence of kcl in presence of kcl in absence of kcl in presence of kcl 1 zero 9.68 6.03 8.85 6.08 2 0.1 14.13 6.24 15.09 6.40 3 0.2 15.16 6.64 15.24 7.01 4 0.3 16.48 8.18 16.21 8.15 5 0.4 18.19 17.78 18.36 17.60 conclusion effects of concentration and solvent composition on the surface tension and viscosity of sodium dodecyl sulphate in absence and presence of kcl in pure water and methanol-water mixed solvent media have been studied by measuring number of drops and time flow for fixed volume of solution through two different limbs of mansingh survismeter. the following conclusions have been drawn from the above results and discussion. the critical micelle concentration increases with increase in volume fractions of methanol and decreases with addition of kcl in methanol-water mixed solvent media. acknowledgments one of the authors (tulasi prasad niraula) is thankful to nepal academy of science and technology (nast), nepal for providing financial support to pursue ph.d. work. sincere thanks goes to the head of the department of chemistry, mahendra morang adarsh multiple campus, biratnagar (t. u.), nepal for providing the available research facilities to conduct the research work. references [1] y. bayrak, turk. j. chem., 27 (2003) 487. [2] b. halle, m. landgren, b. jönsson, j. phys. france, 49 (1988) 1235. [3] a. domínguez, a. fernández, n. gonzález, e. iglesias, l. montenegro, j. chem. education, 74 (1997) 1227. [4] k. lunkenheimer, a. lind , m. jost, j. phys. chem. b, 107 ( 2003) 7527. [5] a. singh, v.k. mishra, s.k. patel, s. sheikh, k. sahu, n.k. courey. int. j. pharm & life sci., 1 (2010) 182. t.p. niraula et al. / bibechana 11(1) (2014) 103-112 (online publication: march, 2014) p.112 [6] l. m. kushner, b. c. duncan, j. i. hoffman, j. rese, nati. bue. std., 49 (1952) 2346. [7] t. p. niraula, s. k. chatterjee, a. bhattarai, j. nepal chem. soc., 29 (2012) 5. [8] a. j. m. valente, h. d. burrows, r. f. pereira, a. c. f. ribeiro, j. l. g. costa pereira, v. m. m. lobo, langmuir, 22 (2006) 5625. [9] j. mata, j. patel, n. jain, g. ghosh, p. bahadur, j. colloid & interface. sci., 297 (2006) 797. [10] f. c. krebs, s. r. miller, b. j. catalone, p. a. welsh, d. malamud, m. k. howett, b. wigdahl, j. am. soc. for micro, 7 (1954) 44. [11] nutan gupta, s. k. gupta, ind. j. med. res., 134 (2011) 939. [12] j. schulz, e. h. immergut, j. polym. sci., 9 (1952) 279. [13] h. doe, t. kitagawa, k.sasabe, j. phys. chem., 88 (1984) 3341. [14] a.m. khan, s.s. shah, j. chem. soc. pak., 30 (2008) 186. [15] m.k. baloch, g. hameed, a. bano, j. chem. soc. pak., 24 (2002) 77. 86-93 s.k. yadav r c o s t n s.k. yadav et al. / bibechana 11(1) (2014) 86-93: (online publication: march, 2014) p.86 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana segregation in fe-pd melt at 1873 k s. k. yadav1, l. n. jha2, d. adhikari1* 1department of physics, mahendra morang adarsh multiple campus, t. u., biratnagar, nepal 2central department of physics, t. u., kathmandu, nepal corresponding author: *email: adksbdev@yahoo.com accepted for publication: february 10, 2014 abstract the thermodynamic and structural properties of fe-pd liquid alloys at 1873 k have been computed using regular associated solution model. to compute these functions we have estimated the mole fractions of the complex assuming the existence of fepd3 complex in the melt. the thermodynamic properties such as free energy of mixing (gm), heat of mixing (hm), entropy of mixing (sm) and activity (a) of the melt have been estimated. to understand the microscopic structural properties, we have estimated the concentration fluctuation in long wavelength limit (scc(0)) and the warren-cowley short range parameter (α1). the free energy of mixing was found to be negative at all compositions. but the heat of mixing and the entropy of mixing are found to be positive at all compositions. the equilibrium constant (k) is found be less than negative. the interaction energy parameters (w12, w13 and w23) are all found to be positive and temperature dependent. the theoretical estimation of the concentration fluctuation in long wavelength limit (scc (0)) is found to be greater than the ideal values throughout the whole range. the theoretical analysis suggests that the fe-pd liquid alloy at 1873 k near the melting point is segregating (homo-coordinating) system. the warren-cowley short range order parameter is found to be positive which too suggest the homocoordinating (segregating) nature of the system at all compositions. the theoretical analysis also suggests that the fe-pd liquid alloy near melting point is weakly interacting system. © 2014 rcost: all rights reserved. keywords: fe-pd alloy; thermodynamic properties; interaction energy parameters; equilibrium constant; segregation. 1. introduction a number of researchers of present day are concentrated on developing and devising new alloys to meet the demands of today. the alloys comprises of dynamical properties which leads them to multidisciplinary uses. there also appears keen interest in investigating and developing fe-pd alloys as they can be used in shape memory alloys, computational chips, medical purposes and their nanopartiples are used as electro-catalyst for oxygen reduction. the alloys are generally grown from the liquid state at temperatures nearer to their melting points. thus, the thermodynamic and structural properties of initial melt plays important role in understanding the properties of the solid alloys. different theories have long been proposed to explain the thermodynamic and microscopic structural properties of binary liquid alloys. in present work we intend to investigate and to understand the thermodynamic and microscopic structural features of fe-pd liquid alloys at 1873 k on the basis of regular associated solution model [1-4]. according to the regular associated solution model, the existence of chemical complex in the binary solution of the alloy near to their melting point is assumed. according to this model, binary solution is considered to be the ternary mixture of complexes and unassociated atoms. it is assumed that there appears unequal interaction between the complexes and the unassociated atoms and the equations of the thermodynamic and microscopic structural functions are derived on this basis. it can be seen from the s.k. yadav et al. / bibechana 11(1) (2014) 86-93: (online publication: march, 2014) p.87 phase diagram of fe-pd [5] the appearance of different phases such as fepd, �����, �����. among the different phases, in this work we have computed the thermodynamic behavior and microscopic structural properties such as concentration fluctuation in long wavelength limit (scc(0)) and warren-cowley shortrange order parameter (α1) [6,7] assuming the presence of ����� complex in the binary solution of fepd at 1873 k. we have also computed the activities of the unassociated atoms [8] to investigate the strength of complex in the liquid state and ratio of diffusion coefficients for the greater insight of local ordering in the liquid state. in this model the interaction energy parameters are considered to be temperature dependent. the formulations used for the calculations are presented in section 2, the results and discussions are presented in section 3 and the conclusions are presented in section 4. 2. theory consider one mole of a liquid binary alloys of the form a-b (a=pd, b=fe) which consists of �� atoms of species a and �� atoms of species b. according to lele and ramchandrarao [8], it is assumed that the chemical complexes � ( � <=> � + �) exists in the melt, where � is a small integer whose value is determined from the compound forming concentration (= �/ (� +1)) in the solid state. hence, the liquid alloy can be considered to be the ternary mixtures of unassociated atoms a (=pd), b (=fe) and the complex � (= �����) in tranquility, where � =3. let ��, �� and ���� moles are the concentrations of a, b and � in the melt. then according to the conservation of mass, in the partially associated solution the formation of the complex � requires �� = �� + ����� and �� = �� + ����. but the thermodynamic and microscopic structural behaviours of the complexes in the melt are ruled by their true mole fractions��, �� and ���� in spite of their gross mole fractions �� and ��, where �� = �� ��� �� , �� = �� ��� �� (1) �� = �� ��� ������� , �� = �� ��� ������� and ���� = ���� ��� ������� (2) then the relation between the two sets of true mole fractions can be derived using the eqns. (1) and (2) as �� = �� − ������� and �� = �� − (1 − ���)���� (3) following jordan [3], the activity coefficients of monomers !�, !� and !��� and complex can be represented in terms of pairwise interaction energies as rt ln!� = ��� &�� + ����� &�� + �� ���� (&��‒ &�� + &��) (4) rt ln!� = ����� &�� + ���&�� + �� ����(&�� − &�� + &��) (5) rt ln! �� = ���&�� + ���&�� + ����(&�� − &�� + &��) (6) where &��, &�� and &�� represents the pairwise interaction energies for the species a, b; a, � and b, � respectively. temperature and universal gas constant are represented by t and r respectively. following lele and ramchandrarao [8], the equilibrium constant for the reaction � <=> � + � is given by following equation ( = )�� )� *� � *� ) ��� * ��� (7) using eqs. (3) , (4) and (5), the relation for the equilibrium constant can be obtained as s.k. yadav et al. / bibechana 11(1) (2014) 86-93: (online publication: march, 2014) p.88 lnk = ln , )�� )� )��� + .�� /0 + .�� /0 [ p�� (1 ‒ ��) + �� ] + .�4 /0 [ p���� (1 ‒ ��) ‒ �� ] + .�4 /0 [ ���� (1‒ p��) ‒ ��] (8) and the free energy of mixing (56) is given as 56 = � ��7)��� 89 :; ���� .�� /0 + ������ .�4 /0 + ������ .�4 /0 < + ;��ln�� + ��ln�� + ����ln����< + ����lnk= (9) in a regular associated solution model ��!� = ��!� and ��!� = ��!� where !� and !� are the gross activity coefficients of components 1 and 2 respectively. hence it follows >�!� = >�!� + ln ( )� )� ) (10a) and, >�!� = >�!� + ln ( )� )� ) (10b) on solving equations (4) and (5), we get .�4 /0 = )� ?�, @�a� -�( �b )� ) cd, @�a� -b )� (�b )� )e��fg )���� (11) .�4 /0 = )� cd, @� a� �( �b)� ) cd, @�a� b )�( �b )� )e��fg )���� (12) where h� and h� are activities of components 1 and 2 respectively. the pairwise interaction energies, the equilibrium constants and the activity coefficients at infinite dilution can be written as [2] ln !�i = .�� /0 (13a) k exp ( .�4 /0 ) = ( *�l *�l*�l b *�l) (13b) on solving equations (8) and (13), we obtain >�( + .�4 /0 = , ��)� )��� ln ; m� )� < + )� )��� :ln ; m� )� < − .�� /0 = + ln , n��n� )��� (14) the other thermodynamic functions such as heat of mixing (o6), entropy of mixing (p6) and concentration fluctuation in the long wavelength limit ( pqq (0) ) are corelated with free energy of mixing ( 56) by the following standard thermodynamic relations o6 = 56t ( rst r0 )7 (15a) p6 = utv wt0 (15b) pqq (0) = rt ( r�st r)�� ) 0,7b� (15c) pqq (0) = �� h�( rm� r)� ) 0,7b� = �� h�( rm� r)� ) 0,7b� (15d) using equation (9) in equation (15a), the expression for the enthalpy of mixing can be obtained as s.k. yadav et al. / bibechana 11(1) (2014) 86-93: (online publication: march, 2014) p.89 o6 = � �� )��� :; ���� .�� /0 + ������ .�4 /0 + ������ .�4 /0 < – t ; ���� r.�� r0 + ������ r.�4 r0 + ������ r.�4 r0 < − 89� z?�[ z0 = (16) the expression for the concentration fluction in the long-wavelength limit (pqq(0)) can be obtained as using equation (9) in equations (15c) and (15d) as pqq(0) = ] , � �� )��� ^ � _` ;�� a �� a b�� + �� a ����a b�� + �� a ����a b��< + c)�d�)� + )�d� )� + )���d� )��� ef g -1 (17) here, r�st r)�� > 0 for rst r)� = 0. the prime denotes the differentiations with respect to concentrations, and �� a and �� a are obtained by using eqn. (3). ����a is obtained using eqn. (8) by using the condition z?�[ z)� = 0 [1011]. the factor ( 1+ p���� )-1, which appears as a coefficient of all terms containing��, �� and ���� in eqn. (9), (16) and (17), is a result of change in the basis for expressing mole fractions of species a, b and � from that used for �� and ��. the concentration fluctuation in long wavelength limit (pqq (0)) helps to understand the nature of atomic order in the binary liquid alloys. at a given concentration, if pqq (0) < pqqhz (0) then ordering (unlike atoms pairing) is expected and if pqq (0) > pqqhz (0), then segregation (like atoms pairing) is expected, where pqqhz (0) =����. the experimental values of pqq (0) can be obtained from eqn. (15d) [12]. further, the degree of local ordering in the liquid alloys can be studied by estimating warren-cowley short range order parameter (h�) with the knowledge of (pqq(0)) [13-14]. the expression for h� in terms of pqq(0) is h� = i b� i (j b�) � � where, p = ikk (i) ikklm (i) and pqqhz (0) =���� (18) where z is the coordination number and z= 10 is taken for our calculation. the greater insight of microscopic structural properties can be done by evaluating diffusion coefficient which is expressed in terms of pqq (0) by using darken thermodynamic equation [15, 16] as nt nlm = )� )� ikk (i) (19) where o6 stands for the chemical or mutual diffusion coefficient and ohz stands for the intrinsic diffusion coefficient for an ideal mixture which are related as o6 = ohz r?�n� r)� , with o6 = ��o� + ��o� (20) where o� and o� are the self-diffusion coefficient of pure components a and b respectively. 3. results and discussion in the present work, we have used regular associated solution model to compute the thermodynamic and microscopic structural behavior of fe-pd liquid binary alloys at 1873 k. we have assumed the existance of ����� complex in the initial melt at 1873 k. at first, the model parameters .�� /0 and k exp ( .�4 /0 ) were estimated using equations (13a) and(13b) with the help of experimental datas of activities coefficients [5]. with the knowledge of these parameter, the mole fractions of the complexes (����) and unassociated s.k. yadav et al. / bibechana 11(1) (2014) 86-93: (online publication: march, 2014) p.90 atoms of( �� and ��) were calculated using the eqations (14) and (3) respectively. the graph between the mole fraction of pd ( �7z ) vs the mole fractions of the complex (�����) and the unassociated monomers (�7z and �pq) is shown in fig. 1. it is found that the computed value of ����� as a function of concentration shows maximum association at �7z = 0.7, which at 8.1 percentage of pd. this is close to the complex forming composition. then the other interaction energy parameters such as .�4 /0 and .�4 /0 were estimated using the equations (11) and (12) with the help of the values of determined complexes. these values of the interaction energy parameters and the complexes were substituted in equation (8) to estimate the value of the equilibrium constant k. the estimated values of the interaction energy parameters and equilibrium constant have been slightly adjusted to explain the experimental values of the free energy of mixing 56 [5], using equation (9). the best fit values of the equilibrium constant and the interaction energies for fe-pd liquid binary alloys at 1873 k were found to be figure 1: mole fractions fe, pd, fe-pd vs conc. of pd in fe-pd liquid alloys at1873 k. k = 0.192, .�� /0 = +1.03, .�4 /0 = +4.21 and .�4 /0 = + 2.06 the theoretical values of the free energy of mixing (56) were computed using the equation (9) and the best fit model parameters shown above. the theoretical calculations shows that the minimum value of 56 is found to be at �7z = 0.50 (the theoretical value of st /0 = −0.48878 and the experimental value of st /0 = −0.48263 [5]). hence the theoretical analysis suggests that the tendency of complex formation in the fe-pd liquid alloys at 1873 k is weaker. the plot of �7z vs free energies of mixing (56/89) is shown in fig. 2. it is found that both the estimated values and the experimental values of the free energies of mixing are in a good agreement. the other model parameters were estimated by successive approximation by using equation (16) and the experimental values of the enthalpy of mixing (o6) [5]. the best fit values of the parameters {&��/{9, {&��/{9, {&��/{9 and 89�{>�(/{9 were found to be r.�� r0 = 1.20jmol-1k-1, r.�4 r0 = 13.21 j mol-1 k-1, r.�4 r0 = 3.79j mol-1 k-1 and rt2 z?�[ z0 = 39500 ± 3500 j mol-1 using the best fit values of the above parameters and equation (16), the theoretical values of the enthalpy of mixing ( o6/89) were computed. figure 2: free energy of mixing (56/89) vs concentration of pd in fe-pd liquid alloy at 1873 k. the solid line is for the theoretical values and stars in black are for the experimental values. s.k. yadav et al. / bibechana 11(1) (2014) 86-93: (online publication: march, 2014) p.91 the enthalpy of mixing is found to be positive throughout the concentration of pd. the o6/89 is found to be maximum at �7z = 0.50 (the theoretical value of o6/89 =+ 0.143121 and the experimental value of o6/89 = +0.142287 [5]). the positive values of the enthalpy of mixing suggest that the fe-pd melt at 1873 k is segregating in nature. it can be observed that both the theoretical and the experimental values are in a good agreement. the theoretical analysis also suggests that the fe-pd liquid alloy at 1873 k is weakly interacting system. the plot of o6/89 vs concentration of pd is shown in the fig. 3. using the computed values of the free energy of mixing (56/89) and the heat of mixing (o6/89), the entropy of mixing (p6/8) can be calculated from equation (15b). the calculated and the observed values for the fe-pd liquid alloy at 1873 k are found to be positive at all concentrations. it can be observed that both the theoretical and the experimental values [5] of the entropy of mixing (p6/8) are in a good agreement (fig. 4). the activity is an important parameter for the liquid alloys as most of the thermodynamic as well as the microscopic functions depend on it. it can be measured in terms of the alloy composition and the temperature. the deviations of the behaviour determining parameter figure 3: heat of mixing (o6/89) vs concentration of pd in liquid fe-pd alloy at 1873 k; the solid line is for the theoretical values and the stars in black are for the experimental values. from the ideal behavior can be incorporated into the activity. the activities of both the monomers |� and |� (a = pd and b = fe) are estimated using equations (10a) and (10b). both the theoretical and the observed values [5] of the activities are in a good agreement throughout the whole concentrations (fig. 5). to understand the microscopic structural behavior of the liquid alloy, the theoretical values of the concentration fluctuation in longwavelength limit (pqq(0)) were computed using equation (17) and the ideal values of pqq(0) were computed using equation (18). the computed and the figure 4: entropy of mixing (p6/8) vs concentration of pd in fe-pd liquid alloy at 1873 k; the solid line is for the theoretical values and the stars in black are for the experimental values. observed values [5] of the pqq(0) are reasonably in a good agreement. both the theoretical and the observed values [5] of the concentration fluctuation in long-wavelength limit are found to be greater than the ideal values throughout the whole concentrations of pd (fig. 6). hence, the theoretical analysis suggest that the fe-pd liquid alloy at 1873 k is segregating in nature i. e. the associations of like atoms (pd-pd and fe-fe) are favoured in the the liquid state. as a result of which there must be separation of phase in the solid state. for the better insight of the local ordering and the complex forming behavior of the liquid alloy we have computed the warren–cowley short range order parameter (h�) from the equation (18). the normalized value of h� lies between -1 to +1. if the computed values of h� = -1 indicates complete ordering (unlike atoms pairing), if h� = +1 indicates complete segregating (like atoms pairing) and if h�= 0 indicates a randomness of atoms in the liquid state. it has been found that the values of short range parameter (h�) are found to be positive and less than 1 for the entire concentrations of pd (fig. 7) which suggest that the s.k. yadav et al. / bibechana 11(1) (2014) 86-93: (online publication: march, 2014) p.92 figure 5: activities of the monomers a(=pd) and b(=fe) vs concentrations of pd in fe-pd liquid alloys at 1873 k; the solid lines are for the theoretical values and the experimental values are represented by circles in black (for pd) and stars in black (for fe) respectively. figure 6: concentration fluctuation in long-wavelength limit (pqq(0)) vs concentration of pd in fe-pd liquid alloy at 1873 k; the solid lines are for the theoretical values, the circles are for the experimental values and the dotted lines are for the ideal values. figure 7: the ratio of mutual and intrinsic diffusion coefficients (o6/ohz) and warren – cowley short range order parameter (h�) vs concentrations of pd in fe-pd liquid alloy at 1873 k. fe-pd liquid alloy at 1873 k is complete segregating system. also, the ratio of the mutual and intrinsic diffusion coefficients (o6/ohz) were evaluated using equation (19). the theoretical values of o6/ohz are found to be positive and less than one (figure 7) which further verifies the segregating (homocoordinating) nature of fe-pd liquid alloy at 1873 k. s.k. yadav et al. / bibechana 11(1) (2014) 86-93: (online publication: march, 2014) p.93 4. conclusion the theoretical analysis suggests that the fe-pd liquid alloy at 1873 k is weakly interacting system. it also suggests that fe-pd system at 1873 k is segregating (homo-coordinating) system. the interaction energy parameters are found to be positive at all concentrations of pd and are found to be temperature dependent. references [1] k. hoshino, j. phys. f: met. phys., 13 (1983) 1891. [2] w.h. young, rep. prog. phys., 55 (1992) 1769. [3] d. adhikari, b.p. singh, i.s. jha, phys. chem. liq., 48 (2010) 787. [4] h. ruppersberg, h. reiter, j. phys. f; met. phys., 12 (1982) 1311. [5] r. hultgren, p.d. desai, d.t. hawkins, m. gleiser, and k.k. kelley, selected values of the thermodynamic properties of binary alloys, asm, material park, oh, 1973. [6] j.m. cowley, phys. rev., 77 (1950) 667. [7] i. prigogine, r. defay, chem. thermodynamics, longmans green and co., london, 1947. [8] s. lele and p. ramchandrarao, metall. trans. b, 12 (1981) 659. [9] d. adhikari, b. p. singh, i. s. jha, b. k. singh, j. non-cryst. solids, 357 (2010) 2892. [10] b.p. singh, d. adhikari, i.s. jha, j. non-cryst. solids, 356 (2010) 1730. [11] t.s. yih, j.c. thopson, j. phys., 12 (1982) 1625. [12] b.e. warren, x-ray diffraction, addison-wesley, reading ma, 1969. [13] a.b. bhatia, w.h. hargrove, phys. rev., 10 (1974) 3186. [14] r.n. singh, can. j. phys., 65 (1987) 309. [15] r.n. singh, f. sommer, phys. chem. liq., 36 (1998) 17. [16] l.s. darken, r.w. gurry, physical chemistry of metals, mcgraw hill, new york, 1953. microsoft word nagendra sir.doc g.k. palei and n.p. sah / bibechana 8 (2012) 127-130 : bmhss, p.127 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana foundations of the fredholm alternative theorem, equicontinuous operators and completely continuous operators g.k. palei 1 , n.p. sah 2 * 1 department of mathematics, b.n. college, patna university, patna, india 2 department of mathematics m.m.a.m. campus (tribhuvan university), biratnagar, nepal article history: received 25 july, 2011; accepted 27 nov., 2011 abstract the fredholm alternative theorem gives the notion of bounded and continuous operator which makes a family f of elements of c[a, b] bounded and equicontinuous. a continuous operator of finite rank is completely continuous but every continuous operator is not completely continuous operator. keywords: arzela-ascoli's theorem; completely continuous; equicontinuous and fredholm alternative theorem 1. introduction if x be a liner space over the field φ of real or complex numbers, then the set of all linear transformations t from x into itself form a linear space l(x) on x. the linear subspace n(t)={ , 0}x x tx∈ = is called the null space of t and b(t)={ }: ,y x tx y x x∈ = ∈ is called the image space of t. the fredhlom alternative theorem is based on the linear algebra. i.e. if dimx< ∞ and t∈l(x), then the following alternative holds : either the equation tx = 0 has only the trivial solution x = 0 in which case the equation tx = y has a unique solution x∈x for arbitrary y∈x. or the equation tx = 0 has nontrivial solutions in which case the equation tx = y is not always solvable for each y∈x. the above alternative theorem does not hold for infinite dimensional vector spaces. for this, consider the vector space (s) of all sequences of real or complex numbers. the map defined on (s) by t(x1, x2, >) = (0, x1, x2>>>..) is one to one and onto, hence t(x1, x2, >>.) = 0 has the only trivial solution x1 = x2 = >>> = 0 but still the equation tx = y is not solvable for all y∈(s) whose first component is zero. fredhlom has proved in his work (1900-1903) that the alternative theorem[4] is valid for a certain class of linear integral equations. g.k. palei and n.p. sah / bibechana 8 (2012) 127-130 : bmhss, p.128 ( ) ( ) ( )( ) , b z x s k s t x t dt y s− =∫ these equations are known as fredholm integral equations. here k(s, t) is a continuous function on [a, b] x [a, b] and is called the kernel of the integral equation, y(s) is continuous on [a, b], and therefore y∈c[a, b]. as solutions only elements from c[a, b] are allowed. therefore we can write the integral equation also in the following abstract form. ( )x kx i k x y− = − = , where i is the identity map on c[a, b] and where the linear map k : c[a, b]→c[a, b] is defined by ( ) ( ) ( ) ( ), b a kx s k s t x t dt= ∫ . further, if in fredholm aternative theorem we replace t by i-k then in that case it reads[7]: either the equation (i-k)x=0 has only the trivial solution x = 0 in which case the equation (i-k)x=y has a unique solution x∈c[a, b] for arbitrary y∈c[a, b]. or the equation (i-k)x = 0 has non-trivial solution in c[a, b] in which case the equation (i-k)x = y is not necessarily solvable through an x∈c[a, b] for arbitrary y∈c[a, b]. in order to give a refinement of fredholm alternative theorem we introduce the following definitions: 1. definition k∈l(x) is called finite dimensional or of finite rank of dim b(k)<∞. let x, y be vector spaces over the same field of scalars and let l(x, y) denote the vector space of all linear mappings of x into y. let t∈l(x, y). then α(t) = dimn(t) is called the kernel index of t([1][.2]). β(t) = co-dimb(t) = dim y/b(t) is called the deficiency index of t. the following theorem is a refinement of fredholm alternative theorem: theorem: if k is a finite dimensional map of x into itself then α(i-k)= β(i-k)<∞. proof : (a) we first show that α (i-k) ≤ dimb(k), in fact if x∈n(i-k) then x = kx, hence n(i-k)⊆b(k) and α (i-k)≤dimb(k). (b) we put y = b(k). since b(k 2 )⊆b(k), k and hence also i-k map y into itself. we denote the restrictions of i, k to y by �,i kɶ . by (a) we have �( ) ( )i k n i k− = −ɶ , if z is an algebric components space of �( )b i k−ɶ in y then z has finite dimension since dim y<∞. now, since �i k−ɶ is a map of a finite dimensional space into itself, we have α �( ) �( )i k i kβ− = −ɶ ɶ and hence α ( ) dimi k z− = . (c) we show that dinz=b(i-k), from which the result follows due to (b), for this purpose we prove that x = z⊕b(i-k) or equivalent that x = z+b(i-k) and {0}=z∩b(i-k). if y = (i-k)x, x∈x, then for suitable g∈g, z∈y we have x = y + kx = y + (g + (i-k)z) = g + (i-k)(x+z), therefore x = g+b(i-k). if u∈z∩b(i-k) then u = (i-k)v∈z. then v = u + kv∈y, therefore u = (i-k) v∈b(i-k)∩z = {0}. this complete the proof. illustration : the vector space c[a, b] becomes a banach space if we define ||x|| = sup |x(t)| for all t∈[a, b]. as k(s, t) is continuous on the closed rectangle [a, b] x [a, b] g.k. palei and n.p. sah / bibechana 8 (2012) 127-130 : bmhss, p.129 we have |k(s, t)| ≤ µ for all s, t ∈ [a, b], from which we get |(kx)(s)| ≤ ( ) ( ), b a k s t x t dt∫ | | | | ≤ µ . ||x|| . (b-a) therefore ||kx|| ≤ (b a)µ . ||x||. hence k is a bounded operator and therefore, also a continuous operator in other words, k maps every bounded subset of c[a, b] into a bounded subset of c[a, b]. 3. definition a family f of elements of c [a, b] is said to be equicontinuous, if to each ∈>0, there exists a δ = δ(∈) > 0, s.t. for all t1, t2 ∈ x,|t1t2| < δ implies | y(t1)-y(t2) | < ∈ for all y∈ f. lemma : if m is a bounded set in c[a, b] then f = {kx : x ∈ m} is a bounded and equicontinuous family. proof : we have seen above that f is bounded. now, it remains to show that f is equi continuous. as k (s, t) is uniformly continuous on [a, b] x [a, b] given ∈ > 0, there exists a δ>0 s.t. |k(s1, t)-k(s2, t)|< ( )b a γ ∈ − for all t ∈ [a, b] provided |s1 – s2| < δ. hence | y(s1)–y(s2)| = ( ) ( ) ( )1 2, , . b a k s t k s t x t dt − ∫| | ≤ ( ) ( ) ( )1 2, , b a k s t s t x t dt−∫ | | | | < ( ) ( ) b a b a γ γ ∈ − − = ∈, provided |s1-s2|<δ hence f is equicontinuous. for further we need the arzela-ascoli's theorem. arzela – ascoli's theorem if f is a bounded and equicontinuous family in c [a, b] then every sequence of elements of f contains a convergent subsequence[3]. from arzela – ascoli's theorem it follows that the image sequence kx1, kx2, kx3,… of a bounded sequence is c [a, b] contains a convergent sebsequence. riesz has constructed the theory of fredholm integral equations on this property of k[6]. 4. definition if e and f are normed linear spaces then a map k∈l(e, f) is called completely continuous if for every bounded sequence {xn} in e, the image sequence {kxn} in f has a convergent sebsequence. lemma : a completely continuous linear operator k is continuous. suppose if k is not continuous, k is not bounded, sup ||kxn|| = ∞, hence there exists a sequence {xn} with ||xn||≤1 and ||kxn||→∞ which contradicts that k is completely continuous. but every continuous operator is not completely continuous. for example, the identity map i on an infinite dimensional normed linear space is continuous but not completely continuous [2,5]. g.k. palei and n.p. sah / bibechana 8 (2012) 127-130 : bmhss, p.130 theorem: a continuous operator k of finite rank is completely continuous. proof : if {xn} is a bounded sequence in e, then the image sequence {kxn} in f is bounded. now, since b(k) i.e. the image space of k is finite dimensional, hence b(k) is complete. hence applying bolzano. weierstrass theorem it follows that there exists a convergent sebsequence {kxn}. reference [1] bruce biackadar, operator algebras, encyelopedia of mathematical sciences, springer – verlag, 2005. [2] john b conway, a course on funtional analysis springer – verlag, 1985. [3] s. goldberg, unbounded linear operators, mc. graw hill, new yorks, 1966. [4] k hvedelidge : fredholm theorem, encyclopedia of maths, springer – verlag, 2001 [5] g. kothe, top, vector space, i and ii springer verlag, 1969. [6] alena pietro a characterization of riesz operators : in the journal of "mathematiche zeitschrift, springer-berlin, 2005. [7] a.g. ramm, a simple proof of the fredholm alternative and characterization of the fredholm operators, american mathematical monthly journal p.815; 2001. microsoft word binod prasad dhakal _151-158_.doc binod prasad dhakal / bibechana 9 (2013) 151-158 : bmhss, p.151 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana approximation of a generalized lipschitz class function by euler cesàro means of fourier series binod prasad dhakal central department of education mathematics tribhuvan university, nepal e-mail: binod_dhakal2004@yahoomail.com article history: received 19 november, 2011; accepted 27 november, 2012 abstract in this paper, i have taken product of two summability methods, euler and cesàro; and establish a new theorem on the degree of approximation of the function f belonging to w(l p , ξ(t)) classes by euler cesàro method. key words and phrases: degree of approximation; (e,1) (c,1) summability; fourier series. 1. definitions and notations a function f(x)∈ lipα, if ( )α =−+ to)x(f)tx(f for 0 < α ≤ 1 and f ∈ lip (α, p), if ( ),todx)x(f)tx(f p 1 2 0 p α π =      −+∫ 0 < α ≤ 1, p ≥ 1. given a positive increasing function ξ(t), p ≥ 1, f (x) ∈ lip (ξ(t), p), if ))t((odx)x(f)tx(f p 1 2 0 p ξ=      −+∫ π and f ∈ w (l p , ξ(t)), if ( ) ).0()),t((odxxsin)x(f)tx(f p 1 2 0 p ≥βξ=      −+∫ π β [1] it is noted that, α →α →ξ→ξ ∞→=ξ=β α lip)p,(lip)p),t((lip))t(,l(w pt)t(0p so, lip α ⊆lip (α, p)⊆ lip (ξ(t), p) ⊆ w (l p , ξ(t)) for 0 < α ≤ 1 and 1p≥ . binod prasad dhakal / bibechana 9 (2013) 151-158 : bmhss, p.152(online publication: nov., 2012) we define the norm p by 1p,dx)x(ff p 1 p 2 0 p ≥         = ∫ π . the degree of approximation en(f) of function f: r→r is given by pnn ftmin)f(e −= . where tn is trigonometric polynomial of degree n [2]. let f be 2π periodic, integrable over (-π,π) in the sense of lebesgue and belonging to ( ))t(,lw p ξ class, then its “fourier series” is given by )ntsinbntcosa(a 2 1 )t(f nn 1n o ++= ∑ ∞ = . (1) let ∑ ∞ =0n nu be the infinite series whose nth partial sum is given by ∑ = = n 0i in .us the cesåro means (c, 1) of sequence {sn} is .s 1n 1 n 0k kn ∑ =+ =σ if ∞→→σ nas,sn then sequence {sn} or the infinite series ∑ ∞ =0n nu is said to be summable by cesåro means method (c,1) to s. it is denoted by n s(c,1), as n [3].σ → → ∞ the euler means (e, 1) of sequence {sn} is ∑ =       = n 0k kn 1 n s k n 2 1 e if ∞→→ n,asse1 n then sequence {sn} or infinite series ∑ ∞ =0n nu is said to be summable by euler means method (e, 1) to s. it is denoted by 1 n e s(e,1), as n [4].→ →∞ the 1 ne transformation of {σn} is denoted by ,t 11 c,e n which is (e, 1) (c, 1) transformation of {sn} and defined as ∑ = σ      = n 0k kn c,e n k n 2 1 t 11 ∑ ∑ = =+      = n 0k r k or n .s 1k 1 k n 2 1 if ∞→→ nas,st 11 c,e n then sequence {sn} or infinite series ∑ ∞ =0n nu is said to be summable by (e, 1) (c, 1) means method to s. it is denoted by .nas),1,c()1,e(st 11 c,e n ∞→→ we use following notations. )x(f2)tx(f)tx(f)t( −−++=φ (2) 2 t2 2 t2n 0k 1n c,e n sin)1k( )1k(sin k n 2 1 n 11 + +       π = ∑ = + (3) binod prasad dhakal / bibechana 9 (2013) 151-158 : bmhss, p.153 (online publication: nov., 2012) 2. main theorem in present paper, the degree of approximation of a function ( ))t(,lwf p ξ∈ class by (e,1) (c,1) means of a fourier series has been determined in the following form: theorem: if f: r → r is 2π periodic, lebesgue integrable function in ),( ππ− and is w ( ))t(,lp ξ , then the degree of approximation of function f by (e,1)(c,1) means of fourier series (1) satisfies, ( )     ξ+=− + +β 1n 1 p c,e n p 111 )1n(oft , for ..,.........4,3,2,1n = provided ξ(t) satisfy the following conditions;      ξ t )t( is monotonic decreasing (4)       + =                 ξ φ β∫ + 1n 1 odttsin )t( )t(t p 1 p p 0 1n 1 , (5) ( )( )δ δ−π +=                 ξ φ ∫ + 1nodt )t( )t(t p 1 p 1n 1 (6) where δ is an arbitrary number such that q(1-δ)-1> 0, condition (5) and (6) hold uniformly in x. 3. lemmas we need the following lemmas for the proof of our theorem. lemma 1: let ∑ = + + +       π = n 0k 2 t2 2 t2 1n c,e n , sin)1k( )1k(sin k n 2 1 )t(n 11 then )1n(o)t(n 11 c,e n += , for . 1n 1 t0 + << proof: ∑ = + + +       π = n 0k 2 t2 2 t2 1n c,e n sin)1k( )1k(sin k n 2 1 )t(n 11 ∑ = + + +       π ≤ n 0k 2 t2 2 t22 1n sin)1k( sin)1k( k n 2 1 ∑ = + +      π = n 0k 1n )1k( k n 2 1 binod prasad dhakal / bibechana 9 (2013) 151-158 : bmhss, p.154 (online publication: nov., 2012)             +      π = ∑ ∑ = = + n 0k n 0k 1n k n k n k 2 1 [ ]n1n 1n 22n 2 1 + π = − +       π + = 4 2n ( ) π + ≤ 2 1n )1n(o += (7) lemma 2: let 11 c,e nn be given as lemma i, then         + = 2 c,e n t)1n( 1 o)t(n 11 , for π<< + t 1n 1 proof: ∑ = + + +       π ≤ n 0k 2 t2 2 t2 1n c,e n sin)1k( )1k(sin k n 2 1 )t(n 11 ∑ = + + +−       π = n 0k 2 t21n sin)1k(2 t)1k(cos1 k n 2 1 ∑ = + +       π ≤ n 0k 2 t21n sin)1k( 1 k n 2 1 ∑ = + +      π = n 0k 21n )1k( 1 k n t2       + −π = + + 1n 12 t2 1n 21n       − + π = +1n2 2 1 1 t)1n( 2t)1n( + π ≤ . t)1n( 1 o 2         + = (8) 4. proof of the theorem following titchmarsh [5], n th partial sum of fourier series (1) at t = x is given by binod prasad dhakal / bibechana 9 (2013) 151-158 : bmhss, p.155 (online publication: nov., 2012) ( ) dt sin tnsin )t( 2 1 )x(f)x(s 2 t 2 t 0 n + φ π =− ∫ π . (c,1) transform of sn i.e. σn is given by ( ) ( ) dttksin sin )t( )1n(2 1 )x(f)x(s 1n 1 2 t n 0k2 t 0 k n 0k + φ π+ =− + ∑∫∑ = π = dt sin )1n(sin )t( )1n(2 1 )x(f)x( 2 t2 2 t2 0 n + φ π+ =−σ ∫ π . similarly, (e,1) transform of σn i.e. 11 c,e nt is ( ) ( ) dt sin)1k( 1ksin k n )t( 2 1 )x(f)x( k n 2 1 2 t2 2 t2n 0k0 1nk n 0k n + +       φ π =−σ      ∑∫∑ = π + = dt sin)1k( )1k(sin k n 2 1 )t()x(f)x(t 2 t2 2 t2n 0k 1n 0 c,e n 11 + +       π φ=− ∑∫ = + π dt)t(n)t( 11 c,e n 0 φ= ∫ π dt)t(n)t(dt)t(n)t( 11 1n 1 11 1n 1 c,e n c,e n 0 φ+φ= ∫∫ π + + 21 ii += , say. (9) for i1, applying holder inequality and fact that ( ))t(,lw)t( p ξ∈φ , we have p 1 p 0 1 dttsin )t( )t(t i 1n 1                 ξ φ ≤ β∫ + q 1 q c,e n 0 dt)t(n tsint )t( 11 1n 1               ξ β∫ + = ( ) 1 1 +no q 1 1n 1 dt t )1n)(t( 0 q 1               +ξ ∫ + +β = o ( ))( 1 1 +nξ q 1 1n 1 dtt )1(q         ∫ + ε +β− , by the mean value theorem, where 1n 1 0 + <ε< . ( ) q 1 1n 1 1)1(q t )(o 1)1(q 1n 1               ++β− ξ= + ε ++β− + ( ) ( ){ }q 1 1q)1( 1n 1 1n)(o −+β + +ξ= binod prasad dhakal / bibechana 9 (2013) x151-158: bmhss, p.156 (online publication: nov., 2012)      ξ+= + −+β )()1n(o 1n 1 1 q 1      ξ+= + +β )()1n(o 1n 1p 1 . (10) for i2, applying holder’s inequality and taking δ as an arbitrary number such that q (1δ) -1 > 0, we have p 1 p 2 dttsin )t( )t(t i 1n 1                 ξ φ ≤ β δ−π ∫ + q 1 q c,e n dt tsint )t(n)t( 11 1n 1                     ξ βδ− π ∫ + p 1 p dt )t( )t(t 1n 1                 ξ φ = δ−π ∫ + q 1 q 2 dt )1n(t )t( 1n 1               + ξ +β+δ− π ∫ + ( )1)1n(o −δ+= q 1 2 q 2 y 1 1n y dy y )( 1               −        ξ −β−δ + ∫ π = o             + ξ+ δ 1n 1 )1n(                   −δ−β+ + ∫ π q 1 1 dyyo 2)1(q 1n using condition ( 4) = o ( ))()1n( 1n 1 + δ ξ+                         −δ−β+ +−δ−β+ π q 1 1 1n 1)1(q 1)1(q y o =o ( ))()1n( 1n 1 + δ ξ+ ( )               −+ −δ−β+ −δ−β+ π −δ−β+ q 1 1)1(q11)1(q )()1n( 1)1(q 1 o = o ( ))()1n( 1n 1 + δ ξ+ ( )( )q 11 1no −δ−β++ = o      ξ+ + −+β )()1n( 1n 1 1 q 1 = o      ξ+ + +β )()1n( 1n 1p 1 . (11) by (9), (10) and (11), we have      ξ+=− + +β )()1n(ft 1n 1c,e n p 1 11 or p 1 p 111 dx)()1n(oft p 1n 1 2 0p c,e n            ξ+=− + +β π ∫ binod prasad dhakal / bibechana 9 (2013) 151-158 : bmhss, p.157 (online publication: nov., 2012) = o      ξ+ + +β )()1n( 1n 1p 1 p 1 dx 2 0       ∫ π = o      ξ+ + +β )()1n( 1n 1p 1 . (12) this completes the proof of theorem. 5. corollaries corollary 1: if 10,t)t(ando ≤α<=ξ=β α then the degree of approximation of a π2 periodic function f belonging to class )p,(lip α is given by         + =− −α p 1 11 )1n( 1 oft p c,e n proof: ( )     ξ+=− + +β 1n 1 p c,e n p 111 )1n(oft = o      ξ+ + )()1n( 1n 1p 1 = o      + α+ )1n( 1p 1 )1n( = o         + −α p 1 )1n( 1 . (13) corollary 2: if ∞→p in corollary 1 then the degree of approximation of a π2 periodic function f belonging to class )10(lip <α<α is given by 10for, )1n( 1 oft 11 c,e n <α<      + =− α ∞ . (14) remarks: an independent proof of corollary can be developed along the same line as the theorem. example: consider the infinite series, ∑ ∞ = −−− 1n 1n)3(41 . (15) the (e,1) (c,1) means of the sequence {sn} is given by ∑ = σ      = n 0k kn c,e n k n 2 1 t 11 ( )1n)1(1 )1n(2 1 +−− + = . (16) the infinite series (15) is neither (c,1) nor ( e,1) summable. but from (16), it is summable by (e,1) (c,1) method. therefore product summability (e,1) (c,1) is more powerful than the individual methods (c,1) binod prasad dhakal / bibechana 9 (2013) 151-158 : bmhss, p.158 (online publication: nov., 2012) and (e,1). consequently, (e,1) (c,1) means gives the better approximation than individual methods (c,1) and (e,1). references [1] b. e. rhoades, journal of mathematics, 3(2003) 245-247. [2] a .zygmund: trigonometric series, cambridge university press (1959). [3] g. h. hardy: on the summability of fourier series, proc. london math. soc.,12(1913) 365-372. [4] g. h. hardy : divergent series, the university press, oxford ( 1949). [5] e. c. titchmarsh.: the theory of functions, second edition, oxford (1939). 34-39 indra b. karki r c o s t n i.b. karki et al. / bibechana 11(1) (2014) 34-39: (online publication: march, 2014) p.34 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana dye-sensitized solar cells sensitized with natural dye extracted from indian jamun indra b. karki1,2*, jeevan j. nakarmi1, pradeep k. mandal2, suman chatterjee2 1central department of physics, tribhuvan university, kathmandu, nepal 2department of physics, university of north bengal, siliguri-734013, india *corresponding author: e-mail: indrakarky@gmail.com accepted for publication: february 06, 2014 abstract dye sensitized solar cell (dssc) is a device which absorbs light from the sun with a layer of dye molecules and directly converts into electric energy. dsscs based on zno have drawn attention worldwide due to their low cost and easy preparation techniques compared to conventional silicon based photovoltaic devices. silicon based solar cells were the most popular before the emerging of dye-sensitized solar cells. these silicon based solar cells devices have dominated photovoltaic industry until now. the objectives of this study is to make dssc using zno on ito coated glass substrate as anode and characterize the dssc properties such as conversion efficiency, short current density, open circuit voltage, and fill factor. zno thin films have been prepared on indium tin oxide (ito) glass substrate. these films were used to construct ito/zno/natural dye/c/ito, dsscs with natural anthocyanin sensitizer extracted from wild jamun fruits. the cells show open circuit voltage (voc) of 0.58v, short-circuit current (i sc) of 1.66 ma and 0.58 fill factor (ff) with an conversion efficiency (η) of 1.23 %. © 2014 rcost: all rights reserved. keywords: dye sensitized solar cells; zno; jamun natural dyes; electrolyte. 1. introduction dye sensitized solar cell (dssc) is third generation and environmental friendly dye based solar cell. it is the most suitable candidate for the next generation of building integrate photovoltaics [1]. although a light-to-energy conversion exceeding 12% has been achieved with a liquid electrolyte [2], several practical factors such as the leakage or volatilization of the liquid solvent are still limiting their long term stability and industrial application [3]. it is a device which absorbs light from the sun with a layer of dye molecules and directly converts into electric energy. gratzel and o'regan found dye-sensitized solar cells (dssc), which are regarded as the latest technology in solar cells, in 1991 [4]. for this reason, such cell is called gratzel cell. the interest in the dssc has increased with this development. the vision is to produce dssc from cheap materials in low-cost processes, thus resulting in low-cost electricity production from solar radiation [5]. dsscs are generally considered much more environmentally benign to produce than conventional silicon-based solar cells because they use relatively non-toxic materials that require little energy to manufacture. silicon is the primary material comprising today’s solar cells. in the manufacturing of most solar cells, silica (sio2) must be heavily heated to separate the silicon from oxygen, so that it can be i.b. karki et al. / bibechana 11(1) (2014) 34-39: (online publication: march, 2014) p.35 further processed into a solar cell. processing silica to produce silicon is an energy-intensive process. at current efficiencies, it takes years for a conventional solar cell to generate as much energy as was used to make the silicon it contains. recently, some research groups have achieved conversion efficiencies of 11-12 %, for tio2 based dyesensitized solar cells with inorganic dyes [6-7]. however, these cells still suffer from a high recombination rate between the injected electrons and the oxidized dye or ions in solution. the high recombination rate in dsscs is attributed to the small size of the particles, which cannot establish significant band banding [8-12]. that is, an electric field that spatially separates the injected electrons from the holes in the dye or solution is not formed at the electrode-electrolyte interface [10]. until now, the major part of the photoanode dssc research has mainly focused on tio2 nanostructures. however, zno semiconductor can be a good alternative as it can exhibit several advantages in comparison with tio2 semiconductor, such as a direct band gap (3.37 ev), higher exciton binding energy (60 mev) compared to tio2 (4 mev), and higher electron mobility (200 cm2 v-1 s-1) over tio2 (30 cm2v-1 s-1) for similar band gap energy levels [13-14]. in case of natural dye and zno thin film based dssc solar cell, researchers have achieved efficiencies of less than 2% till date [15-16]. recently we successfully [17] demonstrated zno nanorod based dsscs with various dyes. the purpose of this study is to identify the significant i-v curve parameters aspects of the nanocrystalline zno based dssc using natural dyes. the knowledge of the significant i-v curve parameters aspects will be used as input in further research to increase the efficiency of dssc and support the development of solar cells as a sustainable alternative for generating electric energy. in this work, we report significant iv curve parameters and efficiency aspects of the nanocrystalline zno based dssc using natural dye jamun. the coated nanoporous electrode was examined by means of current voltage dependence (i-v) of the dssc solar cell when illuminated and in the dark. 2. materials and method experimental section 2.1. synthesis of zno nanorods thin film and counter electrode zno nanorods were synthesized using sol-gel spin coating technique. in this process, we prepared 5 mm solution of zinc acetate dehydrate, (ch3coo)2zn, 2h2o, (98% merck) with methanol. the solution was spun on indium tin oxide (ito) coated glass substrate at 1000 rpm for 30s. the zinc acetate solution is spread on a rotating substrate according to [18-19]. the substrates were heated to 3500c in conventional oven for 30 min to yield layers of zno islands with their (100) plane parallel to the substrate surface. after evaporation of solvent, a thin zno film was formed as shown in flow chart in figure 1. the process was repeated for five to seven times to control the thickness of the film. concentration of the solution and spinning speed of the substrate also play important roles in adjusting the thickness of the fabricated film. the counter electrode (cathode) is prepared on another ito coated glass by using amorphous carbon dust. 2.2. dssc assembling dsscs were assembled following the procedure described in the literature [19]. the amorphous carbon coated counter electrode was placed on the top so that the conductive side of the counter electrode faces the zno film. the iodide based solution as the liquid electrolyte (0.5m potassium iodide mixed with 0.05m iodine in water-free ethylene glycol) was placed at the edges of the plates. the liquid electrolyte was drawn into the space between the electrodes by capillary action. two binder clips were used to hold the electrodes together as shown in figure 2(a) & 2(b). figure 1: flow chart preparation of zno nanorod i.b. karki et al. / bibechana 11(1) (2014) 34-39: (online publication: march, 2014) p.36 figure 2 : (a) zno nanorods based dsscs with natural dyes (b) liquid electrolyte ki3. 3. results and discussion the morphology of the zno samples was observed using a scanning electron microscope (sem) with a field emission gun operating at 200 kv. figure 3 displays zno nanorod seeds and grow arrays in a wide surface area. the nanorods have an average length of 600 nm diameter ranging from 100 to 200nm and they are mostly vertically aligned with the substrate having hexagonal shapes. the thickness of zno film was around ~50 µm. the solar conversion efficiency (η) of a dssc can be estimated using the conversion efficiency formula: � = ���� �� (1) where pmax and pin denote the maximum output power and the input power respectively. figure 3: sem images of seed zno and seed grow zno. since a dssc usually contains a series resistance, rs and a shunt resistance, rsh, the fill factor (ff) is introduced to count both effects. i.b. karki et al. / bibechana 11(1) (2014) 34 = ���� �� ��� where voc is the open-circuit voltage and a dssc can be calculated by, � = �� ��� ��� �� 3.1. the equivalent circuit model of dssc a solar cell is generally characterized using the equivalent circuit of the single diode model as shown in figure 4 and the relation between the current � = ��� � �� ���� ��� where iph, is, rs, rsh, q, a, kb, and t are the photocurrent, the resistance, the shunt resistance, the electron charge, the ideality factor, the boltzmann constant, and absolute temperature, respectively. using equation (4) and fitting i with jamun dye have found and presented in table 1. 3.2. performance of the dssc we have recorded i-v characteristics of zno nanorods based dsscs using natural dye jamun with varied external resistances under illumination. figure 5 shows the current voltage curve with fitting of dye based on dssc solar cell. the physical parameters open maximum voltage (vmax), maximum current (i from figure 5 and fitted with the raphson’s method. as shown in fig. 5, very good curve fitting, r in voltage range 0 0.55 v results of curve fitting are given in table the parasitic resistances (series and shunt) of dsscs are important parameters that affect cell. the resulting parasitic resistances, series (r figure 4: equivalent circuit diagram of dssc. ideality factor indicates perfectness of the solar cell in the equivalent circuit, and it is 1.0 for a perfect cell. in our observation, an improvement in ideality factor (a) was observed 4.8 for jamun dye based dssc. table 1. the physical parameters open conversion efficiency (η) values calculated from current voltage curve of natural dye dssc cell. after absorbing photon energy from the illuminated white light, the dye molecules in the dssc become excited and inject electrons to the left side of zno nanorods as shown in figure 6. due to favorable energy dssc/dye v oc (v) i sc (ma) jamun 0.58 1.56 / bibechana 11(1) (2014) 34-39: (online publication: march, 2014) p.37 (2) circuit voltage and isc is the short-circuit current. the solar conversion efficiency of (3) the equivalent circuit model of dssc a solar cell is generally characterized using the equivalent circuit of the single diode model as shown in figure 4 and the relation between the current i and the voltage v is given by � ������ !"#$ % � 1' � ����� ��( (4) , and t are the photocurrent, the saturation current of the diode, the series resistance, the shunt resistance, the electron charge, the ideality factor, the boltzmann constant, and absolute temperature, respectively. using equation (4) and fitting i-v curve, physical parameters of dssc th jamun dye have found and presented in table 1. characteristics of zno nanorods based dsscs using natural dye jamun with varied external resistances under illumination. figure 5 shows the current voltage curve with fitting of dye based on dssc solar cell. the physical parameters open-circuit voltage (voc), short circuit current (i ), maximum current (imax), values of dssc cell with natural dye were calculated from figure 5 and fitted with the eq. 4 for one diode equivalent circuit model (fig. 4) by newton . as shown in fig. 5, very good curve fitting, r2 = 0.99 and chi2 = 0.003 were obtained 0.55 v results of curve fitting are given in table-1. the parasitic resistances (series and shunt) of dsscs are important parameters that affect cell. the resulting parasitic resistances, series (rs) and shunt resistance (rsh) were evaluated from fitting i-v curve results. the fill factor (ff) for this cell using natural dye was also evaluated from the i-v characteristics using eq and finally the energy conversion efficiency (η using equation (3). all these results are presented in table the cell parameters like ideality factor (a), fill factor (ff) and energy conversion efficiency (η) of zno nanorod based dsscs with natural dye were calculated and presented in table values were calculated from current voltage curve of dssc cell fabricated with natural jamun dye. equivalent circuit diagram of dssc. s perfectness of the solar cell in the equivalent circuit, and it is 1.0 for a perfect cell. in our observation, an improvement in ideality factor (a) was observed 4.8 for jamun dye based the physical parameters open-circuit voltage (voc), short circuit current (isc), fill factor (ff) and energy ) values calculated from current voltage curve of natural dye dssc cell. after absorbing photon energy from the illuminated white light, the dye molecules in the dssc become excited and inject electrons to the left side of zno nanorods as shown in figure 6. due to favorable energy sc (ma) i 0 (µa) ff r s (ωωωω) r sh kωωωω) ideality factor, a 1.56 21 0.58 62 3.25 4.8 publication: march, 2014) p.37 circuit current. the solar conversion efficiency of a solar cell is generally characterized using the equivalent circuit of the single diode model as shown in saturation current of the diode, the series resistance, the shunt resistance, the electron charge, the ideality factor, the boltzmann constant, and v curve, physical parameters of dssc characteristics of zno nanorods based dsscs using natural dye jamun with varied external resistances under illumination. figure 5 shows the current voltage curve with fitting of dye based ), short circuit current (isc), dye were calculated equivalent circuit model (fig. 4) by newton= 0.003 were obtained the parasitic resistances (series and shunt) of dsscs are important parameters that affect on efficiency of ) were evaluated from fitting curve results. the fill factor (ff) for this cell using natural dye characteristics using equation (2) η) were calculated using equation (3). all these results are presented in table-1. the cell parameters like ideality factor (a), fill factor (ff) and nanorod based dsscs with natural dye were calculated and presented in table-1, where values were calculated from current voltage curve of dssc cell s perfectness of the solar cell in the equivalent circuit, and it is 1.0 for a perfect cell. in our observation, an improvement in ideality factor (a) was observed 4.8 for jamun dye based ), fill factor (ff) and energy ) values calculated from current voltage curve of natural dye dssc cell. after absorbing photon energy from the illuminated white light, the dye molecules in the dssc become excited and inject electrons to the left side of zno nanorods as shown in figure 6. due to favorable energy ideality factor, a ηηηη (%) 4.8 1.23 i.b. karki et al. / bibechana 11(1) (2014) 34-39: (online publication: march, 2014) p.38 difference, electron transfer occurs between the lowest unoccupied molecular orbital (lumo) of the dye and the conduction band of zno. the photogenerated electrons percolate rapidly through the zno nanorods and are collected by the conducting glass support. the highest occupied molecular orbital (homo) of the dye is energetically lower than the redox potential, eredox of the iodide/triiodide couple. the energy difference provides the driving force for hole injection into the electrolyte. recombination of charge carrier is also minimized in such devices since transport of only one type of carrier (electron, in general) is energetically possible from the dye to the semiconductor. the reaction mechanisms (5-10) inside the dssc solar cell are as follows: dye + hν → dye* [5] dye* + zno → zno• + dye+ [6] zno• + ce → zno + ce• + energy [7] dye+ + i→ dye + i3 [8] i3 + ce → i+ ce [9] overall: hν (photon) → energy [10] (ce=counter electrode) the incident photon to current efficiency (ipce) of the ito coated zno based dssc can affect on the collection efficiency. the recombination process is wavelength dependent because the penetration length of the light increases with the decreases of the absorption coefficient of the dye. in other words, illumination at wavelengths in which the dye absorption coefficient is low leads to the photo injection of electrons a long way from the current collector. if such a distance is longer than the electron diffusion length, these electrons are lost in recombination processes. a fit of a one-diode model curve to a measured iv curve is shown in figure 5. the zno nanorod based dssc was prepared at the north bengal university, siliguri and is a 50 µm thick cell with only 1.23% efficiency. the fit parameters are given in the table 1. the fit results give explanations of the low efficiency of figure 5: i-v curve fitting of dssc with jamun dye. the dssc: first of all, the dye content of this cell is too low, probably due to a non-optimized zno electrode. secondly, the electron mobility has a relatively low value, probably due to poor electric contacts between the zno colloids. the high series resistance rs of 62 ohm resulting from the fit may be explained by a nonoptimized cell design and the fact that there are also contact resistances, which are included in the series resistances of the model. in this case, rsh is too high for this dssc and limits its performance. figure 6: working principle of dssc withdye. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 data: data3_c model: dssc1 chi^2 = 0.00303 r^2 = 0.99242 a 1.60183 ±0.04418 b -0.02493 ±0.04794 c 7.92052 ±3.73578 d -0.04917 ±0.03734 f -3.25228 ±7.81718 c ur re nt ( m a ) voltage (v) iv curve fiting of dssc with jamun dye i.b. karki et al. / bibechana 11(1) (2014) 34-39: (online publication: march, 2014) p.39 4. conclusion dye-sensitized solar cells (dsscs) were assembled using extracts from various dyes as sensitizers for nanocrystalline zno photoelectrodes. based on our investigation, it was found that jamun possesses the photosensitization effect among other extracts of natural dyes studied. natural dyes as alternative sensitizers for dsscs are expected to be promising because of many reasons such as the simple preparation technique and low cost. the physical parameters of solar cell: series resistance (rs), ideality factor (n), saturation current (is), shunt resistance (rsh) and photocurrent (iph) were measured from measured current-voltage characteristics. zno thin films have been prepared on indium tin oxide (ito) glass substrate. these films were used to construct ito/zno/natural dye/c/ito, dssc with natural anthocyanin sensitizer extracted from wild jamun fruits. the cell shows open circuit voltage (voc) of 0.58v, short-circuit current (i sc) of 1.66 ma and 0.58 fill factor (ff) with an conversion efficiency (η) of 1.23 %. our research work will help understand the physics of low coast zno based dsscs, predict the efficiency, and facilitate the development of future structures of natural dye based dsscs. acknowledgments the author i.b. karki would like to thank the university grants commission (ugc), nepal for phd fellowship and national academy of science and technology (nast), nepal; and indian national science academy (insa), india, for partial financial and technical support for this work. i.b. karki is also grateful to the north bengal university, darjeeling, siliguri, india and central department of physics, tribhuvan university, kathmandu, nepal for providing laboratory facilities and hospitality to carry out this work. references [1] g.e. tulloch, j. photoc. photobiology a, 164 (2004) 209. [2] a. yella, h. lee, h.n. tsao, c. yi, a.k. chandiran, m.k. nazeeruddin, e.w. diau, c. yeh, s.m. zakeeruddin, m. gratzel, science, 334 (2011) 629. [3] a.f. nogueira, m.a. de paoli, sol. energy mater. sol. cells, 61 (2000) 127. [4] b. o’regan, m. grätzel, nature, 353 (1991) 737. [5] g. smestad, c. bignozzi, r. argazzi, solar energy mater., 32 (1994) 259. [6] y. chiba, a. islam, y. watanabe, r. komiya, n. koide, l.y. han, jpn. j. appl. phys., 45 (2006) l638. [7] r. buscaino, c. baiocchi, c. barolo, c. medana, m. grätzel, md.k. nazeeruddin, g. viscardi, inorg. chim. acta, 361 (2008) 798. [8] l. m. peter, j. phys. chem. c, 111 (2007) 6601. [9] j. bisquert, g. garcia-belmonte, f.j. fabregat-santiago, j. solid state electrochem. 3 (1999) 337. [10] l. m. peter, phys. chem. chem. phys., 9 (2007) 2630. [11] e. bellingeri, d. marre, l. pellegrino, i. pallecchi, g. canu, m. vignolo, c. bernini, a. s. siri, super lattices microstructures, 38 (2005) 446. [12] d. c. look, materials science & engineering, b: solid-state materials for advanced technology b, 80 (2001) 383. [13] u. ozgur, y,i. alivov, c.liu , a. teke, m.a. reshchikov , s. dogan, j appl phys., 98 (2005) 8:04131. [14] s.j. pearton, d.p. norton , ip k, w. heo, t. steiner, prog mater sci., 50 (2005) 293. [15] m. r. narayan, renewable and sustainable energy reviews, 16 (2012) 208. [16] l. a. kosyachenko, solar cells dye-sensitized devices, intech europe, university campus step ri publication, first edition 2011, isbn 978-953-307-735-2. [17] i. b. karki, j. j. nakarmi, p. k. mandal, s. chatterjee, nepal journal of science and technology, 13 (2012) 179. [18] n.j. cherepy, g.p. smestad, m. grätzel, j.z. zhang, j. phys. chem. b, 101 (1997) 9342. [19] b. pradhan, s. kumar, b. amal, j. pal, sol. energy mater. sol. cells, 91 (2007) 769. microsoft word main.doc 18 b.p. singh et.al free energy of mixing and activity of hgk liquid alloy b.p. singh1, i.s. jha2 and d. adhikari2 1university department of physics, t.m. bhagalpur university, india 2m.m.a.m. campus, biratnagar, tribhuvan university, nepal abstract the large asymmetry observed in free energy of mixing of hgk liquid alloy is discussed on basis of flory’s model. the concentration dependence of the free energy of mixing and activity of mercury has got special attention in the discussion. key words: liquid alloy, flory’s model, free energy of mixing, activity. 1. introduction the free energy of mixing and activity of hgk liquid alloy show large deviation from the ideal values [1,5]. the observed values of free energy of mixing (gm) are quite asymmetrical around the equi-atomic composition (c=0.5) and they show large minima near 60% of hg [1]. in the present work, flory’s expression for the free energy of mixing has been used to explain the alloying behavour of hgk liquid alloys. working expressions and the results for free energy of mixing and activity are given in section 2 and 3 receptively. conclusion of the work is given in section 4. 2. general formalism flory’s expression for the free energy of mixing of a binary mixture consisting of nc mole of species a(=hg) and n(1-c) mole of species b(=k) is given by [2]. m 1 cg rt[c ln c (1 c) in (1 c) c ln(1 ) in(1 c)] c , ..............(i) 1 c − = + − − + −β − −β +ω −β where 0 a b v1 v β = − 0 av and 0 bv being the atomic volumes of species a and b respectively 0 0 b av / v 3.3 at 600 k.(simoji 1977) . =  [4] activity is a very important thermodynamic function because it is one of the fortunate functions which are obtained directly from experiment. the activity (a) of an element in a binary liquid is given by bk t ina zfe= − where z = valency of carrier ions of the element f = faraday’s constant kb = boltzmann constant e = electromotive force which is observed directly from the experiment in order to obtain the expression for ‘a’ let us recall the standard thermodynamic relation: 19 bibechana vol. 6, march 2010 m m grt in a g (1 c) . ................(ii) c ∂ = + − ∂ differentiating equation (i) partially with respect to ‘c’ m 2 g 1 2c (1 c)crt in c ln(1 c) in (1 ) ...........(iii) c c 1 c (1 c)   ∂ β − β − = − − + −β + +ω +  ∂ β −β −β    using equations (i) and (iii) in equation (ii), we get 2 2 c(1 ) (1 c) (1 c)in a ln ............(iv) 1 c 1 c rt (1 c) −β β − ω − = + + −β −β −β 3. result and discussion the value of interchange energy is determined form the observed data of gm in the concentration range from 0.1 to 0.9 [1]. the value of / rtω used in the present work is -5.51. the computed values of mg / rt from equation (i) are furnished in table -1 and plotted in fig. – 1 with its observed values at 600 k. as a function of chg. the computed and observed values of the free energy of mixing are in well agreement. it may be noted that the free energy of mixing of hgk liquid alloys exhibits asymmetry around equi-atomic composition. our computed values of gm do not differ from the experimental values by more than 7.6% at any concentration. equation (iv) has been used to compute in ahg, which is tabulated in table-2 and plotted in fig.-2 along with the experimental values of ln ahg at 600k, [3]. the computed and observed values of activity are in reasonable agreement/ it is observed that the activity of hg in the hgk liquid alloys remains quite a small value for most of the concentrations i.e. hgc 0.7≤ and then it rises very fast. there is slightly disagreement between the theoretical and experimental values of ln ahg for small concentrations of mercury but this disagreement reduces considerably at the hg-rich end. 4. conclusion flory’s, model has been considered to study the concentration dependence of free energy of mixing and activity of hgk liquid alloy. our theoretical investigation explains the asymmetry in the free energy of mixing to a great extent. the activity has been successfully explained. references 1. t.e faber, introduction to the theory of liquid metals, cambridge university pres, u.k. (1972). 2. p.j. flory, j. chem. phys. 10, (1942) 51. 3. r. hultgren, o.d desai,, d.t. hawkins, m. gleiser, and k.k., kelley, selected values of the thermodynamics properties of binary alloys, a.s.m., u.s.a. (1973). 4. m. simoji, liquid metals, london acad., u.k. (1977). 5. r.n. singh, and a.b. bhatia, j. phys., f14, (1984) 2309. 20 g m /r t chg b.p. singh et. al tables & graphs table – 1 free energy of mixing of hgk liquid at 600 k gm/rt chg theoretical experimental* 0.1 -0.9053 -0.8181 0.2 -1.6135 -1.4835 0.3 -2.1975 -2.0927 0.4 -2.6573 -2.6491 0.5 -2.9759 -3.0963 0.6 -3.1206 -3.3464 0.7 -3.0368 -3.2809 0.8 -2.6327 -2.7800 0.9 -1.7432 -1.7218 • hultgen et al, 1973 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 theoretical experimental* fig.-1. gm/rt – chg curve for hgk liquid alloy at 600 k 21 in a h g chg bibechana vol. 6, march 2010 table – 2 activity of hg in liquid alloys at 600 k . in ahg chg theoretical experimental* 0.1 -7.9069 -6.9078 0.2 -6.7666 -6.9078 0.3 -5.8626 -6.2146 0.4 -5.0171 -5.8091 0.5 -4.1689 -4.9618 0.6 -3.2883 -3.8167 0.7 -2.3639 -2.4889 0.8 -1.4125 -1.2483 0.9 -0.5220 -0.3538 *hultgren et al, 1973 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 theoretical experimental* fig.-2. in ahg-chg curve for liquid alloy at 600 k. microsoft word l. gurung _108-114_.doc l. gurung et al. / bibechana 10 (2014) 108-114 : bmhss, p.108 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana mixing properties of ni-pd liquid alloy l. gurung, r. p. koirala, d. adhikari * department of physics, mahendra morang adarsh multiple campus, biratnagar, nepal *email: adksbdev@yahoo.com .article history: received 5 december, 2013 abstract in this work, thermodynamic and microscopic properties of ni-pd liquid alloy at 1873 k have been studied using a simple theory of mixture. in thermodynamic properties, free energy of mixing, heat of mixing and entropy of mixing have been studied. to understand the structural behaviour of the alloy concentration fluctuation in long wavelength limit and chemical short range order parameter have been computed. the ni-pd melt at 1873 k is found to be slightly deviated from regular behaviour. the best estimated value of energy parameter is found to be positive. the alloy is found to be weakly segregating system. the symmetric behaviour of all functions has been well explained by the simple theory of mixing keywords: ideal alloys, regular alloys, non-ideal alloys, ni-pd alloy, thermodynamic functions 1. introduction the mixing behaviour of binary liquid alloys may be explained in terms of thermodynamic and microscopic properties. thermodynamic behaviour of the alloys is understood by the knowledge of free energy of mixing (∆gm), heat of mixing (∆hm), entropy of mixing (∆sm) and activity (a). structural behavior is comprehended by the interpretation of concentration fluctuation in long wavelength limit (scc(0)) and chemical short range order parameter (α1). the thermodynamic properties of binary liquid alloys give the information about the maximum stable composition, bonding strength and most mixed state of the alloy. the microscopic properties provide the information about the local arrangement of atoms. it is, therefore, obvious that without having a clear knowledge of the properties of alloys in liquid state it is not possible to understand the energetics of the formation of solid alloys. this requirements demand extensive investigations for understanding the properties of alloys in the liquid state. several theoreticians [1-10] have long been carried out to understand various properties of alloys in their liquid states. the ni-pd alloy is used in hydrogen sensors. this alloy has also glass forming properties at eutectic region around 45% of pd. the knowledge of thermodynamic and structural properties at liquid state is essential for investigating the solidification process. hence, it is important to study different properties of ni-pd liquid alloy for its industrial applications. in this work we intend to study the thermodynamic and structural properties of ni-pd alloy in liquid state at 1873 k by using simple theory of mixing. in next section the theoretical formalism is presented. section 3 deals with results and discussion and conclusions are outlined in section 4. l. gurung et al./ bibechana 10 (2014) 108-114 : bmhss, p.109 (online publication: dec., 2013) 2. theoretical basis 2. theoretical basis for non-ideal solution we have to take an account of the heat of formation ∆hm. let’s account for the heat of formation ∆hm ≠ 0 using a simple model called statistical or quasi-chemical model. in this model the heat of mixing is only related to the bond energies between adjacent atoms. the assumption is that the interatomic distances and bond energies are independent of composition. there may be three types of bonds: (i) a-a bonds (energy eaa): (ii) b-b bonds (energy ebb) (iii) a-b bonds (eab) if there are paa, pbb, pab bonds of each type, the internal energy of the solution is aa aa bb bb ab abe p e p e p e= + + (1) if z is the coordination number of an atom in a crystal, then the number of atoms na and nb are related to the number of bonds a aa abn z 2p p= + (2) b bb abn z 2p p= + (3) a ab aa n z p p 2 2 = − (4) b ab bb n z p p 2 2 = − (5) using these expressions for paa and pbb in the expression for energy, we have a ab b ab aa bb ab ab n z p n z p e e e p e 2 2 2 2 = − + − + (6) a b aa bb aa bb ab ab n z n z e e e e e p e 2 2 2 + = + + −    (7) the first two terms of right hand side of eq. (7) represents the energy of unmixed components. therefore energy of mixing (heat of formation (∆hm)) is given as aa bb m ab ab e e h p e 2 + ∆ = −    (8) for small differences between eab and (eaa+ebb)/2 we can still consider a random arrangement of atoms in a solution and entropy of mixing of the solution is equal to ideal value ( [ ]m 1 1 2 2s r x lnx x lnx∆ = − + ). such solutions are called regular solutions. then ab tot 1 2p zn x x= (9) and m 1 2h x x∆ = θ (10) where aa bb tot ab e e zn e 2 + θ = −    (11) called the exchange parameter. it measures how different ab interactions are from the aa and bb interactions. if all of the interactions among the components are the same, then and there is no energy of mixing. for regular solutions a random arrangement of atoms in a solution is assumed. if there is small deviation from regular solution we may have to correct the exchange parameter. for this case let us consider θ is a linear function of t as [12] l. gurung et al./ bibechana 10 (2014) 108-114 : bmhss, p.110 (online publication: dec., 2013) d t dt ω θ = ω+ (12) here, the term d dt ω is introduced in order to account the small deviation of entropy from ideal behaviour. therefore, the heat of mixing and entropy of mixing may be expressed as m 1 2 d h t x x dt ω ∆ = ω+    (13) ( )m 1 1 2 2 1 2 d s r x ln x x ln x x x dt ω ∆ = − + + (14) then the free energy of mixing of the regular solution is given as [ ]m 1 1 2 2 1 2g rt x ln x x ln x x x∆ = + +ω (15) the activity of pure components a and b in binary solution may be obtained using a standard statistical relation m a m 2 1 g rt ln a g x x ∂∆ = ∆ + ∂ (16) thus, we have 2 a 1 1rt ln a rt ln x (1 x )= +ω − (17) similarly the activity of the component b may be obtained as 2 b 2 2rt ln a rt ln x (1 x )= +ω − (18) the expression for concentration fluctuation in long wavelength limit (scc(0)) has been introduced and derived by bhatia and march [13]. it provides the idea about ordering and segregating nature of a solution. if the computed value of scc(0) is less than ideal values ( =x1 x2) there is tendency of unlike atoms pairing (ordering) and if it is greater than ideal values ( =x1 x2) there is a tendency of like atoms pairing (segregating). according bhatia and march[13] the concentration fluctuation in long wavelength limit may be related with the free energy of mixing by the relation ( ) 1 2 2 cc m 1 t,p,n s (0) rt g x − = ∂ ∆ ∂   (19) therefore scc(0) for regular solution is given as 1 2 cc 1 2 x x s (0) 1 2x x rt = ω − (20) a measure of the tendency to compound formation or phase separation in a molten alloy is also given by the warren-cowley short-range order parameter (sro), α1 [14,15]. this is an important indicator of the degree of ordering in a binary alloy and is given as 1 s 1 s(z 1) 1 − α = − + (21) where cc id cc s (0) s s = (22) z being the coordination number of the alloy. we note that the main effect of z on 1α is to reduce the depth and hence its magnitude, the significant effects of complex formation and phase separation are essentially maintained. l. gurung et al./ bibechana 10 (2014) 108-114 : bmhss, p.111 (online publication: dec., 2013) 3. result and discussion we have estimated the best fit value of ω by the successive approximation using the observed values of free energy of mixing [16] and eq. (15). the value of ω estimated by this method must satisfy all the thermodynamic and microscopic functions. in our case the best fit value of ω is found to be 7350 jmol-1. the value of ω is found to be positive. this indicates that the ni-pd system in liquid state at 1873 k is segregating system, i.e. like atoms tend to form pairs. we have calculated the free energy of mixing of ni-pd liquid alloys at 1873 k using eq. (15) and estimated value of ω. the computed values of free energy of mixing are almost equal to the observed values. both the computed and observed values of free energy of mixing are minimum (computed value = -8951 jmol-1 and observed value = 8928 jmol-1) at equiatomic composition. the free energy of mixing is negative at all composition (fig. 1). fig. 1: excess free energy of mixing ( xs mg∆ ) of ni-pd liquid alloy at 1873 k versus x1 (concentration of ni); solid lines for theoretical values and circles for experimental values. we have computed the heat of mixing of ni-pd liquid alloys at 1873 k on the basis of simple theory of mixing (eq. 13). before this we estimated the best fit value of d dt ω using experimental data. its best value is found to be -1.4 jmol-1k-1. the theoretical and experimental values are in a very good agreement up to x1 = 0.6 ( fig. 32). above this region there are some discrepancies. these discrepancies may be due to greater deviation of solution from regular behaviour. however, the symmetric nature of the experimental results of heat of mixing against the concentration of ni is not violated by the theoretical analysis. both the experimental and theoretical values of heat of mixing are positive at all compositions. the theoretical maximum value of heat of mixing is almost equal to the experimental maximum value (experimental value =1195.5 jmol-1, theoretical value = 1182 jmol-1). we have then computed the entropy of mixing of ni-pd liquid alloys at 1873 k using eq. (14). the computed entropy of mixing is in good agreement with the observed values at all compositions. the entropy of mixing is positive for all compositions. this clearly indicates that the entropy is greater in l. gurung et al./ bibechana 10 (2014) 108-114 : bmhss, p.112 (online publication: dec., 2013) the mixture than that of the pure states of the components. the symmetric behaviour of the observed result of entropy of mixing of ni-pd liquid alloys at 1873 k is well explained by the theoretical analysis. for comparative study the computed and observed values of entropy of mixing of ni-pd liquid alloys at 1873 are plotted against concentration of ni (figure 3). fig. 2 : heat of mixing (∆hm) of ni-pd liquid alloy at 1873 k versus x1 (concentration of ni) ; solid lines for theoretical values and circles for experimental values fig. 3: heat of mixing (∆sm) versus x1 (concentration of ni) for different positive values of d dt ω ; solid lines for theoretical values and circles for experimental values. we have computed the theoretical values of scc(0) for ni-pd liquid alloys at 1873 k using the previously determined value of ω (figure 4). the computed value of scc(0) is greater than ideal values at all compositions. this shows that the alloy under investigation is segregating in nature. this l. gurung et al./ bibechana 10 (2014) 108-114 : bmhss, p.113 (online publication: dec., 2013) result is in agreement with the theoretical and experimental analysis of free energy of mixing and heat of mixing. the symmetric behaviour of scc(0) is well explained by the theoretical analysis. the knowledge of 1α provides an immediate insight into the nature of the local arrangements of atoms in the mixture. at equiatomic composition, one has 1α1 1 ≤≤− . the minimum possible value of 1α is 1α min 1 −= and that implies complete ordering of unlike atoms paring at nearest neighbours. on the other hand the maximum value of 1α is 1αmax 1 += which implies total segregation leading to the phase separation and 1α = 0 corresponds to a random distribution of atoms. here 1α can be estimated from the knowledge of scc(0) as by the eq. (21). it is found positive at all compositions. this shows that ni-pd liquid alloys at 1873 k. fig. 4: concentration fluctuation in long wavelength limit (scc(0)) versus x1 (concentration of ni) for ni-pd liquid alloys at 1873 k; solid lines for theoretical values, circles for experimental values and dotted lines for ideal values. fig. 5: chemical short range order parameter (α1) versus x1 (concentration of ni) for ni-pd liquid alloys at 1873 k l. gurung et al./ bibechana 10 (2014) 108-114 : bmhss, p.114 (online publication: dec., 2013) 4. conclusions based on the above discussion the following conclusions may be drawn about ni-pd liquid alloy at 1873 k: (i) it is not a strictly regular solution. it slightly deviates from the regular behaviour. (ii) it is a weakly interacting system. (iii) it is a segregating alloy, i.e. like atoms tend to pair forming homo-coordination. (iv) all the thermodynamic and structural functions of this alloy are symmetric at equiatomic composition as a function of concentration. references 1. k. hoshino and w.h. young, j. phys. f 10 (1980) 1365. 2. r.n. singh and f. sommer, z.metall. 83 (1992) 553. 3. i.s. jha, r. n. singh, p.l. shrivastava and n.r. mitra, phil. mag. 61 (1990) 15. 4. d.ahhikari, i.s.jha and b.p.singh, physica b, 405(2010)1861 5. j.r. wilson, metallurgical review 10 (1965) 381. 6. a.b. bhatia and n.h. march, j. phys.f:met. phys. 5 (1975) 1100. 7. r. n. singh, i.s. jha and d.k. pandey, j. condens. matter 5(1993) 2469. 8. s. lele and p. ramchandrarao, metall. trans. 12 b (1981) 659. 9. a.s. jordan, metall. trans. 1 (1970) 239. 10. d.ahhikari, b.p.singh and i.s.jha,, phys. chem. liq. (2010) 11. segvi k.o. (2004). physical properties of pd, ni metals and their binary alloys. ph.d. thesis.a. guggenheim,. mixtures, clarendon press, oxford, 1952. 12. a.b. bhatia and n.h. march, j. phys.f:met. phys. 5(1975) 1100. 13. e.warren, x-ray diffraction (reading ma: addison-wesley (1969) p.227. 14. j.m. cowley phys. rev. 77, (1950) 667. 15. r. hultgren, p. d.desai, d.t. hawkins, m. gleiser and k.k. kelley, selected values of the thermodynamic properties of binary alloys (asm,metal park,1973). microsoft word ram p. koirala _14-17_.doc ram p. koirala / bibechana 7 (2011) 14-17 : bmhss 14 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana temperature regulation in animals ram prasad koirala ∗∗∗∗ dept. of physics, m.m.a.m. campus, biratnagar, nepal article history: received 5 september 2010; revised 22 october 2010; accepted 5 november 2010 a b s t r a c t we have studied the rate of evaporation of sweat for the body of human of two different surface areas at different temperatures. we have also studied the rate of evaporation of sweat at different values of heat produced by chemical metabolism. it is found that a thin man perspires at lower temperature than a fat man when they both produce the same heat by chemical metabolism. keywords: chemical metabolism; evaporation of sweat; normal breathing 1. introduction most biological processes are temperature dependent. so the body temperature must be kept within a narrow range. the chemical metabolism of food is the source of body heat. depending on the air temperature and clothing worn, the heat generated may be needed to overcome convective and radiative loss and radiation from the skin and by the evaporation of sweat from the skin and of water from the lungs [1, 2]. the evaporation of sweat is primary cooling mechanism used by the body. the temperature – control mechanisms of many warm blooded animals make use of heat of vaporization, removing heat from the body using it to evaporate from the tongue (panting) or from the skin (sweating). evaporation by perspiration is an important mechanism for temperature control of warm blooded animals evaporating cooling enables humans to maintain normal body temperature in hot, dry desert climates where the air temperature may reach 55 o c (about 130 o f). the skin temperature may be as much as 30 o c cooler than the surrounding air. under these conditions a normal person may perspire several liters per day, and this lost water must be replaced [3]. if the interior temperature begins to increase, the body first increases blood flow near the skin surface to increase convective and radiative losses and then if necessary, uses evaporative loss mechanism. human sweats from glands located over much of the body and thus benefits from evaporation over a large surface area. as much as 1.5 kg sweat per hour can be evaporated from the human body under many conditions. evaporation by perspiration is primary cooling mechanism for temperature control of human body. this mechanism can also be observed in ∗ corresponding author: ram pd. koirala, dept. of physics m.m.a.m. campus, biratnagar, nepal, email:sijuwa_3@yahoo.co.in ram p. koirala / bibechana 7 (2011) 14-17 : bmhss 15 other warm-blooded animals. in this paper we intend to study about the rate of sweat from human body in different conditions in light of physics. 2. theory the various contributions to the rate of heat loss and production of heat for a typical human adult are approximately as follows [4]: if the area a is given in square meter, the skin temperature ts and air temperature ta are given in degree celsius, and the rate r of sweating is in units of kilogram per hour, then =mh rate of heat generated by metabolism ( w1600to80 ; average hm = 300 w) hr = rate of heat lost by radiation = )tt(ad asr − hc = rate of heat lost by convection = )tt(ad asc − (still air) hl = rate of heat lost by evaporation from the lungs = dl hs = rate of heat lost by evaporation of sweat = ds r the d’s are constants whose values are given by 12 c kwm1.7d −− = 12 r kmw5.6d −− = 1 s kghw674d − = w5.10d l = for normal breathing. the value of hl is given for normal breathing; it increases to the proportion of rate of breathing. as the variation is very small, we neglect the variation. for the body temperature to be held constant, the heat loss are related as hm = hs + hr+ h c+ hl lrcms hhhhh −−−= 3. results and discussion for a given value of heat produced by chemical metabolism in a man, the rate of sweating has been found to increase with increase in air temperature. evaporation begins at different temperature depending upon the amount of heat produced by metabolism. with a given surface area, as heat produced by metabolism is increased, sweating is found to begin at lower temperature and the rate of sweat production is higher for larger value of heat of metabolism, hm. for a typical human of a=1.0 m 2 , sweating begins around air temperature of 32 0 c (r =0.0022 kgh -1 ), 16 0 c (r =0.0057 kgh -1 ), 2 0 c(r = 0.0200 kgh -1 ) and below 0 0 c for hm=80w, hm = 300w, hm = 500w and hm = 1000w respectively. for a human of a=1.2m 2 , sweating begins around 33 0 c (r=0.0063 kgh -1 ), 20 0 c (r=0.0179 kgh -1 ), 8 0 c (r=0.02406 kgh -1 ) and far below for hm=80w, 300w, 500w and 1000w respectively. ram p. koirala / bibechana 7 (2011) 14-17 : bmhss 16 figure 1, 2 and 3: rate of evaporation of sweat (r) verses temperature, ( ) for a human of surface area 1.0 square metre and (……..) for human of surface area 1.2 square metre. thus rate of perspiration varies with the heat produced by the chemical metabolism and with the temperature of air. the evaporation of sweat forms an important mechanism for the temperature control of human body. the constant body temperature of other warm blooded animals can also be explained on the principle of evaporation by perspiration. ram p. koirala / bibechana 7 (2011) 14-17 : bmhss 17 4. conclusions a thin man perspires at lower temperature than a fat man when they both produce the same heat by chemical metabolism. at higher temperature rates of sweating are nearly the same for fat and thin man. acknowledgement i gratefully acknowledge associate professor devendra adhikari, presently in t.m. bhagalpur university, for his valuable suggestions and inspiring discussions. references [1] t.c. ruch and h.d. patton; physiology and biophysics vol. 3, w.b. saunders co. philadelphia, chap.5 ( 1973 ). [2] h. bornd, scientific american ( 1981) 146. [3] f.w.sears, zemnasky et.al., university physics, 11th ed. pearson education , delhi, (2004). [5] j .w. kane and m.m. sterntheim, physics, john willey and sons 2nd ed. ( 1948 ) p. 260. further readings j.r. cameron and j. g. skofronick, medical physics, john willey and sons inc. new york ( 1978). microsoft word yub raj dhakal et al _82-91_.doc yub raj dhakal et al. / bibechana 10 (2014) 82-91 : bmhss, p.82 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana investigation on the soil corrosivity towards the buried water supply pipelines in kamerotar town planning area of bhaktapur, nepal yub raj dhakal 1 , kumar p. dahal 2 and jagadeesh bhattarai 2,* 1 department of chemistry, tri-chandra m. campus, saraswoti sadan, kathmandu 2 central department of chemistry, tribhuvan university, kirtipur, kathmandu *e-mail: bhattarai_05@yahoo.com. article history: received 21 august, 2013; accepted 27novemberr, 2013 soil parameters such as moisture content, ph, resistivity, oxidation-reduction potential, chloride and sulfate ions can give an indication of the soil corrosivity towards the buried-galvanized steels and cast-iron pipelines used to supply the drinking water in nepal. present research work was focused to examine such soil parameters collected from kamerotar town planning area of bhaktapur district of nepal. concentrations of these soil parameters measured in this study are found as: moisture content (18-77%), ph (3.0-9.3), resistivity (11600-71400 ohm.cm), oxidation-reduction potential (87-426 mv vs she), chloride (28-135 ppm) and sulfate (20-226 ppm). these soil parameters gave an indication of “moderately corrosive” to “mildly corrosive” behavior of soils on the buried-galvanized steels and cast-iron pipelines used in the study area. it was found a good correlation between the soil resistivity and moisture content as well as the chloride content in soils. the soil resistivity was generally decreased with increasing both the moisture and chloride contents in soils. keywords: chloride & sulfate, moisture content, resistivity, soil corrosion, oxidation-reduction potential. 1. introduction the buried materials like water supply galvanized steel and cast-iron pipelines are corroded due to the corrosive nature of soils. the soil corrosivity towards these buried materials can explain on the basis of two types of soils; one is disturbed soil and the other is undisturbed soil. the disturbed soil is one in which digging, back filling are taking place and oxygen is introduced in such soil. the soil corrosivity towards the buried materials in undisturbed soil is generally negligible as compared with the corrosive nature of the disturbed soil [1]. the difference in the corrosivity of the disturbed and undisturbed soils is mainly attributed to the difference in oxygen content in soils [1,2]. corrosion rate of the buried materials in the disturbed soil is influenced by number soil parameters (i.e., moisture content, ph, resistivity, oxidation-reduction potential, chloride and sulfate so on) [1-4]. estimation of these parameters can give an indication of soil corrosivity towards the buried materials. the buried-pipelines used to supply the drinking water; natural gas and crude oil have been affected by corrosive nature of soils al l around the world [5-24]. when a fai lure of water supply yub raj dhakal et al. / bibechana 10 (2014) 82-91 : bmhss, p.83 (online publication: dec., 2013) buried−pipelines occurs, there is a high degree of environmental and economic consequences. it has been studied the corrosion behavior of galvanized steels, bare steels and zinc metal in different soils of usa [5,6]. clayey soils are characterized by fine texture, high water–holding capacity, poor aeration and drainage, and hence the clayey soils are also prone to be potentially more corrosive towards the buried materials than soils of coarse nature such as sand or gravel. on the other hand, well−drained soils are recognized to be less corrosive than poorly drained ones [1,2,3-6]. it has been reported that the corrosion of mild steel increased when the soil moisture exceeds 50% [5,6,8]. research data strongly suggested that the maximum corrosion rates occur at saturations of 60-85% [5,6,8,17]. soil structure, permeability and porosity determine the moisture content of a soil. when the moisture content of a soil is in the range of 20 to 40 %, the rate of uniform corrosion of the buried materials is increased [25]. below this value, a pitting type of corrosion attack is more likely occurs. soils have a wide range of acidity/alkalinity, reaching from 2.5 to 10 ph values. the ph 5 or below can lead to extreme general corrosion or premature pitting corrosion of the buried materials [1,2] and hence a neutral ph around 7 of soils is most desirable to minimize the soil corrosion of the buried materials. the soil ph range of 5–8 is not usually considered to be a problem for soil corrosion towards the buried materials such as galvanized steels, castiron, zinc coatings and so on [3,4]. the soil ph can also dramatically affect the nature of microbiological activity in soil that can have a large impact on corrosion rates, especially in microbiologically induced corrosion [1]. on the other hand, it has been reported that the soil resistivity decreased with increasing the moisture content [15]. hence, the corrosive nature of the soils towards the buried materials is increased with increasing the moisture content or decreasing the soil resistivity [6,15]. therefore, sand and gravel are considered to be less corrosive towards the galvanized steels, because they showed a high resistivity of 6000 ohm.cm or more. on the other hand, clayey and silty soils with the resistivity value less than 1000 ohm.cm are generally considered to be highly corrosive for the buried-galvanized steels [1,23,25,26]. the oxidation-reduction potential (orp) is a measure of how reduced or oxidized the soil environment is. the measurement of soil orp is significant to explain the soil corrosivity towards the buried materials, because it determines partially the stability of the materials. in general, an anaerobic soils having orp value less than about 100 mv vs she are not helpful for the formation of oxide layers on the surface of the materials, because the anaerobic soils do not contain any free oxygen which is necessary for the passivation of the buried–iron/steels [25-27]. furthermore, the presence of excess amounts of free oxygen in soils is generally indicated from the orp value greater than 100 mv vs she [25-27]. hence, the orp value of a soil is helpful to indicate whether the soil is corrosive or not towards the buried materials. on the other hand, the soil orp indicates whether or not a soil is capable of sustaining sulfate-reducing bacteria, which contribute greatly to the corrosion of soil. a low orp indicates that oxygen content in the soil is low and consequently, the condition is ideal for the proliferation of the sulfate-reducing bacteria, the greater the sulfide content in soils by reducing sulfate to sulfite. this is possible only the orp is less than zero or negative values. it is meaningful to mention here that the presence of sulfide in soils is not beneficial to the buried-galvanized steels and cast-iron pipelines. maslehuddin et al. [17] studied the effect of chloride concentration in soil on the corrosion behavior of reinforcing steels in concrete by measuring the corrosion potential and corrosion current density. the result indicated that the corrosion current density increased with increasing chloride concentration in soil. compared to the corrosive effect of chloride, sulfate is generally considered to yub raj dhakal et al. / bibechana 10 (2014) 82-91 : bmhss, p.84 (online publication: dec., 2013) be more benign in their corrosive action towards the buried-metallic substances [1,2]. however, the presence of sulfate amounts more than 200 ppm in soils can pose a major risk for the buried-structural materials [23-25], because it can readily be converted to highly corrosive sulfides by anaerobic sulfate-reducing bacteria. it is also meaningful to mention here that a high concentration of sodium sulfate in poorly drained soils makes the soil very corrosive to the buried-structural materials. soils are generally considered to be “mildly corrosive” if the sulfate and chloride are below 200 ppm and 100 ppm, respectively, for soils with ph of 5–8 and the resistivity greater than 3,000 ohm.cm [1,2,2325]. the supply of water from water reservoirs to distribution terminal is mostly through the buriedgalvanized steels and cast-iron pipelines in nepal. the buried-galvanized steel and cast-iron pipes, although susceptible to corrosion are widely used in nepal, because of their low cost and high strength. the study of the corrosion behavior of these buried materials in soil is a major importance for the underground corrosion, because thousands of miles of buried-galvanized steels and cast-iron pipelines are used to supply the drinking water in nepal. in this context, it is very urgent to investigate the effects of different soil parameters those affect the corrosion behavior on the buried materials. the main objective of this research work is to investigate the effects of soil parameters to the corrosion of the buried materials like galvanized steel and cast-iron pipelines used to supply the drinking water in kamerotar town planning area of bhaktapur, nepal. 2. materials and experimental methods thirty soil samples were collected from kamerotar town planning area of bhaktapur, nepal which is located within the latitude of 27o 40’ 25”-27o 40’ 50” north and within the longitude of 85o 23’ 30”-85o 24’ 20” east as shown in fig. 1. all soil samples were taken from the depth of about 1 meter from the ground level for the real location of the buried-pipelines for the purpose of the supplying the drinking water. all the soil samples were collected in the months of january to april of 2013. the distance between two samples was taken about 300 to 500 meters. the soil sample was taken in an air tight polyvinyl bag so that the moisture remained same for a period of moisture content analysis in the laboratory. moisture content in soil was determined using weight loss method in accordance with the astm d4959-07 standards [28]. a digital ph meter was used to determine the ph of 1:2 soil-water suspensions of each soil samples in accordance with the astm g51-95 (2012) standards [29]. the conductivity bridge was used to determine the electrical conductivity of the 1:2 soil-water suspensions in accordance with the astm g187-05 standards [30]. the soil resistivity (bulk/saturated paste) was calculated from the conductivity. the oxidation-reduction potential (orp) of the soil samples was measured with the help of a digital potentiometer in accordance with the astm g200-09 standards [31]. the platinum wire and saturated calomel electrodes (she) were used as working and reference electrode, respectively. the recorded orp values vs sce was converted to reference value of the saturated hydrogen electrode (she). argentometric titration was used to determine the amount of chloride content in soil. chloride content in the 1:2 soil-water suspensions was determined by titrating the soil suspension against standard silver nitrate solution using potassium chromate as an indicator. gravimetric method was used to estimate the amounts of sulfate content in soil samples. the details of these methods are discussed elsewhere [32-37]. yub raj dhakal et al. / bibechana 10 (2014) 82-91 : bmhss, p.85 (online publication: dec., 2013) fig. 1: location map of the sampling sites of kamerotar town planning area of bhaktapur. 3. results and discussion moisture content in soil it is found that the moisture content in the collected soil samples ranges from 18-77% which is summarized in table 1. among thirty soil samples from kamerotar area, two soil samples contained 10-20%, twenty samples contained 21-40%, five samples contained 41-60% and only three samples contained more than 60% moisture content as shown in fig. 2(a). these results revealed that most of the soil samples (22 out of 30 soil samples) are assumed to be "mildly corrosive", while eight samples containing more than 40% moisture content are classified to "moderately corrosive" to "highly corrosive" for the galvanized steels and cast-iron pipes. soil ph ph is another important soil parameter that determine the soil corrosivity towards the buriedgalvanized steel and cast-irons pipelines. the ph value of the soil samples collected from kamerotar town panning area is in the range of 4.0-9.3 as shown in fig. 2(b). among thirty soil samples, three yub raj dhakal et al. / bibechana 10 (2014) 82-91 : bmhss, p.86 (online publication: dec., 2013) samples (i.e., k3, k6 and k16) are highly acidic in nature showing the ph value 4.5 or less than and two samples (i.e., k18 and k28) showed the ph value more than 8.5 as shown in table 1. therefore, these five soil samples are assumed to be "highly corrosive "towards the buriedgalvanized steel and cast-iron pipelines. on the other hand, ten samples having the ph value in the range of 6.5-7.4 and the remaining ten samples having the ph value in the range of 7.5-8.4 are considered to be "mildly corrosive" and "moderately corrosive", respectively, towards the buried galvanized steel and cast-iron pipes. these results revealed that most of the soils of the kamerotar town planning area of bhaktapur are "mildly corrosive" to "highly corrosive" in nature towards the various buried materials. table 1: corrosive parameters of soils collected from kamerotar town planning area of bhaktapur, nepal. sample no. moisture content (%) ph resistivity (ohm.cm) chloride content (ppm) sulfate content (ppm) orp (mv vs she) k1 22 5.2 71400 39 63 242 k2 73 4.9 17900 121 46 179 k3 65 3.0 14500 135 112 87 k4 49 7.0 32300 46 22 204 k5 29 6.7 27800 80 24 245 k6 38 3.4 33300 53 164 104 k7 28 6.3 58800 39 35 263 k8 25 7.9 45500 46 200 282 k9 28 7.5 47600 46 44 318 k10 44 7.5 38500 55 192 344 k11 22 7.7 50000 43 29 337 k12 54 6.7 34500 43 189 340 k13 30 6.2 45500 57 149 254 k14 34 7.7 43500 57 33 361 k15 34 7.7 29400 65 37 365 k16 22 4.0 71400 28 226 108 k17 43 8.2 43500 54 79 248 k18 24 9.3 41700 50 31 422 k19 24 8.4 37000 43 20 346 k20 21 7.3 50000 47 23 327 k21 24 7.3 37000 71 41 350 k22 28 7.6 25000 75 60 340 k23 77 7.3 11600 130 70 324 k24 18 7.1 45500 46 34 353 k25 18 7.3 71400 50 72 297 k26 30 4.5 62500 40 93 175 k27 39 7.9 40000 68 178 369 k28 55 8.7 33300 53 137 426 k29 23 7.3 52200 45 205 329 k30 30 7.4 28500 66 153 329 soil resistivity figure 2(c) shows the results of the soil resistivity of all thirty soil samples. among these thirty soil samples, three samples have the soil resistivity between 10,000-20,000 ohm.cm, four samples have yub raj dhakal et al. / bibechana 10 (2014) 82-91 : bmhss, p.87 (online publication: dec., 2013) 20,000-30,000 ohm.cm, eight samples have 30,000-40,000 ohm.cm, while remaining fifteen samples have more than 40,000 ohm.cm resistivity. fig. 2: (a) moisture content (b) soil ph (c) soil resistivity (d) oxidation-reduction potential (e) chloride content and (f) sulfate content in each soil samples collected from kamerotar town planning area of bhaktapur, nepal. yub raj dhakal et al. / bibechana 10 (2014) 82-91 : bmhss, p.88 (online publication: dec., 2013) these results revealed that all soils collected from the kamerotar town planning area of bhaktapur are assumed to be "mildly corrosive" to "non-corrosive" nature towards the buriedgalvanized steel and cast-iron pipelines used to supply the drinking water from water reservoir to consumer's house. this conclusion is based on the classification of the astm and nace standards (23,25,26). there was a clear correlation between the moisture content and the resistivity of soils. it was found that the soil resistivity was generally decreased with increasing the soil moisture content less than about 40% which is not shown here. these results revealed that 40% or less moisture containing soils are not aggressive for the soil corrosion towards the buried materials. oxidation-reduction potential of soil the oxidation-reduction potential (orp) value of all thirty soil samples of kamerotar town planning area is in the range of 87 to 426 mv vs she which is given in table 1. among these thirty samples, one sample has the orp value less than 100 mv vs she, four samples have in the range of 100-200 mv vs she, five samples have in the range of 200-300 mv vs she, nineteen samples have in the range of 301-400 mv vs she and remaining one sample has the orp value more than 400 mv vs she as shown in fig. 2(d). these results revealed that most of the soil samples (except k3) are belonged to "moderately corrosive" to "non-corrosive" for the buried-structural materials based on the johe's classification (table 3) [24, 27]. the k3 sample has the orp of 87 mv vs she and hence it is assumed to be "severely corrosive". chloride content in soil the chloride content in soil samples collected from the study area is shown in fig. 2(e). it is found that most of the soil samples except three samples (i.e., k2, k3 and k23) contained less than 100 ppm which is the upper limit of the chloride content in the soil for showing "mildly corrosive" nature towards the buried materials. the samples k21, k3 and k23 contained 121, 135 and 130 ppm chloride, respectively. these values are also not significantly higher than the upper limit of chloride content in soils for showing the "mildly corrosive" nature towards buried materials and hence these three soil samples are assumed to be "moderately corrosive" in nature. among these thirty soil samples, the chloride content in fifteen samples contained less than 50 ppm chloride, twelve samples contained 50-100 ppm and remaining three samples contained more than 100 ppm chloride. these results revealed that most of the soils of the kamerotar town planning area of bhaktapur district are considered to be "mildly corrosive" towards the buried-galvanized steel and cast-iron pipes used to supply the drinking water in the study area. furthermore, there was a good correlation between the chloride content in soils and soil resistivity (not shown here). it was found that the soil resistivity was increased with decreasing the chloride content in soil. this result revealed that the soil resistivity of kamerotar town planning area is affected by the chloride content in soil. sulfate content in soil amounts of sulfate content in soils of kamerotar town planning area are found in the range of 20 to 226 ppm as tabulated in table 1. figure 2(f) shows that nineteen soil samples contained less than 100 ppm sulfate, nine samples contained 100-200 ppm sulfate and remaining two samples contained more than 200 ppm sulfate which is upper limits of the sulfate content in the soil for showing "mildly corrosive" nature toward the buried materials based on the classification of the astm and nace [23,25,27]. these results revealed that most of the soil samples expect two soil samples (i.e., k16 and k29) of the study area are considered to be "mildly corrosive" to "non-corrosive" for the buried yub raj dhakal et al. / bibechana 10 (2014) 82-91 : bmhss, p.89 (online publication: dec., 2013) galvanized steel and cast-iron pipelines used to supply the drinking water based on the sulfate content results from the present study. table 2: relationship between soil resistivity, chloride, sulfate and soil corrosivity towards the buried materials (23,25,26). soil parameter soil corrosivity 1. soil resistivity (ohm.cm) > 20,000 10,000-20,000 5,000-10,000 3,000-5,000 1,000-3,000 < 1,000 essentially non-corrosive mildly corrosive moderately corrosive corrosive highly corrosive extremely corrosive 2. chloride content (ppm) < 100 mildly corrosive 3. sulfate content (ppm) < 200 mildly corrosive table 3: rating of soil corrosivity based on the oxidation–reduction potential of soils (24,27). 4. conclusions from the above results and discussion on the corrosive nature of the thirty soil samples collected from kamerotar town planning area of bhaktapur, following conclusions are drawn. 1. most of the collected soils (73.3% of 30 samples) contained less than 40% moisture content which is assumed to be "mildly corrosive" nature towards the buried-galvanized steel and castiron pipes. other 26.7% of the total collected samples contained more than 40% moisture content which is assumed to be "moderately corrosive" nature based on the moisture content values. 2. the soil ph value is found to be within the limits of 3.0-9.3 ph for showing "corrosive", "mildly corrosive" and "non-corrosive" towards the buried-galvanized steel and cast-iron pipelines based on the soil ph values. 3. all thirty soil samples showed high soil resistivity (i.e., > 10,000 ohm.cm) which supports the fact that all soils are "mildly corrosive" to "essentially non-corrosive" nature towards the buried materials based on the soil resistivity values. 4. twenty seven soil samples (i.e., 90% of the total collected samples) except three samples (k2, k3 & k23) having chloride content less than 100 ppm are considered to be "mildly corrosive" in oxidation–reduction potential (mv vs she) soil corrosivity >400 201–400 100–200 <100 non–corrosive mildly corrosive moderately corrosive severe corrosive yub raj dhakal et al. / bibechana 10 (2014) 82-91 : bmhss, p.90 (online publication: dec., 2013) nature, while three samples having the chloride content more than 100 ppm are considered to be "moderately corrosive" nature based on the chloride content in soils. 5. twenty eight soil samples (i.e., 93.3% of the total collected samples) except two samples (k16& k29) having the sulfate content is less than 200 ppm are "mildly corrosive" nature, while two soil samples having the sulfate content more than 200 ppm are "moderately corrosive" nature based on the sulfate content in soils. acknowledgements authors are thankful to the head of the central department of chemistry, kirtipur and head as well as the coordinator of m sc program of the department of chemistry, t c campus, tribhuvan university, saraswoti sadan, kathmandu, nepal for 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(2013) 51 + viii pp. 35. p. p. bhandari, k. p. dahal and j. bhattarai, j. inst. sci. technol., 18 (2013) 71. 36. m. gautam and j. bhattarai, nepal j. sci. technol., in press (2013). 37. s. k. regmi and j. bhattarai, scientific world, submitted (2014). microsoft word damodar thapa _30-32_.doc damodar thapa chhetry / bibechana 7 (2011) 30-32 : bmhss 30 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana studies on molluscs of betna wetlands and its surroundings, nepal damodar thapa chhetry∗∗∗∗ department of zoology, p.g. campus (tribhuvan university), biratnagar, nepal article history: received 10 october 2010; revised 11 november 2010; accepted 13 november 2010 abstract this paper deals with 15 freshwater and 1 terrestrial mollusc species collected from betna wetland and its surroundings. among the collected 16 species, 12 species were gastropods representing 3 orders, 6 families, 8 genera and 4 species were bivalves representing 1 order, 2 families and 2 genera. seven species of the total species of molluscs were edible and consume by the local people and 3 species were harmful. key words: molluscs diversity; betna wetland 1. introduction the betna wetland is located at belbari village development committee of morang district. it extends between 26°20' to 26°53’ lattitude and 87°16' to 87°41'e longitude. it covers 5.5 hectors and receives natural water from its upper catchment area. its surrounding area consists forest, small stream, little marsh area, paddy fields etc. due to the presence of wetlands ( lakes) and other suitable habitats, it is rich in molluscan diversity. regarding the diversity of molluscs, very few works has been done in nepal. however, subba and ghosh [1,2] has made reports on molluscs of nepal. majupuria [3] has reported a few species of land and freshwater molluscs from kathmandu valley. investigation on different aspects of population dynamics of fresh water snails have also been carried out by yadav et.al. [4], and pfeiffer et. al. [5] sharma [6] reported some species of molluscs from the various aquatic systems of the koshi river basin belt. subba and pandey [7] studied molluscan diversity of jhapa district of nepal and reported 17 species freshwater and 4 species land molluscs. subba and ghos [8] reported 9 species of terrestrial molluscs from eastern, mideastern and far western regions of nepal. 2. materials and methods the freshwater molluscs were collected from betna wetland (oxbow lakes), paddy fields, marshes area and stream while the land molluscs were collected from shady and moist places. the specimens were collected up to one year from july 2008 to june 2009. the molluscs were ∗ corresponding author: dr. damodar thapa chhetry, department of zoology, p.g. campus (tribhuvuniversity), biratnagar, nepal, email:thp_damodar@rediffhotmail.com . damodar thapa chhetry / bibechana 7 (2011) 30-32 : bmhss 31 mainly collected by hand picking method and also with the help of nylon cloth net (40 meshes/cm 2 ), nylon scoop, forceps etc. the collected specimens were kept in polythene bags and plastic containers. then the animals were preserved in 5 % formalin for further study. dead specimens with dry shells were also collected. identifications were made according to preston [9] mellanby [10] and subba rao [11]. table 1: molluscs species of betna wetlands and its surroundings class order family scientific name gastropoda mesogastropoda pilidae pila globosa (swainson, 1822) gastropoda mesogastropoda pilidae pila theobaldi (hanley, 1875). gastropoda mesogastropoda thiaridae brotia costula (rafinesque, 1833) gastropoda mesogastropoda thiaridae thiara punctata (lamark,1822) gastropoda mesogastropoda thiaridae thiara tuberculata (mullar,1774) gastropoda mesogastropoda thiaridae thiara granifera (lamark,1822) gastropoda mesogastropoda viviparidae bellamya bengalensis (lamark,1882) gastropoda basommatophora lymnaeidae lymnaea luteola (lamark, 1822 ) gastopoda basommatophora lymnaeidae lymnaea acuminata (lamarck, 1822) gastropoda basommatophora planorbidae indoplanorbis exustus (deshayes, 1834) gastropoda basommatophora planorbidae gyraulus convexiusculus (hutton, 1849) gastropoda pulmonata stenogyridae achatina fulica. bivalvia (pelecypoda) unionoida unionidae lamellidens marginalis (lamark,1819) bivalvia (pelecypoda) unionoida amblemidae parreysia favidens (benson, 1862) bivalvia (pelecypoda) unionoida amblemidae parreysia caerulea gaudichaudi (eydoux, 1838) bivalvia (pelecypoda) unionoida amblemidae parreysia caerulea (lee, 1831) 3. results and discussion altogether 16 species of molluscs belonging to 2 classes, 4 orders, 8 families and 10 genera were identified (table 1). among 16 species, 12 species were gastropods representing 3 orders, 6 families, 8 genera, and 4 species were bivalves representing 1 order, 2 families and 2 genera (table 1). seven species of the total species of molluscs were edible and consume by the local people (table 2) and 3 species were harmful (table 3). among three species, achatina damodar thapa chhetry / bibechana 7 (2011) 30-32 : bmhss 32 fulica is more harmful, it destroys all types of plants. among the collected species, bellamya bengalensis and lymnaea acuminata were found abundantly in the study area. table 2: edible molluscs of betna wetland and its surroundings s.n. name of the species tribes who eat molluscs. 1 pila globosa (swainson, 1822) jhangad, bantar, sardar, malaha etc. 2 brotia costula (rafinesque ,1833) jhangad, bantar,sardar, malaha etc. 3 bellamya bengalensis (lamarck,1882) jhangad, bantar, sardar, malaha etc. 4 lamellidens marginalis (lamarck, 1819) jhangad, bantar,sardar, malaha, choudhary etc. 5 parreysia favidens (benson, 1862) jhangad, bantar, sardar, malaha, etc. 6 parreysia caerulea gaudichaudi (eydoux, 1838) jhangad,bantar,sardar, malaha, etc. 7 parreysia caerulea (lee,1831) jhangad, bantar, sardar, malaha, etc. table 3: harmful molluscs of betna wetland and its surroundings s.n. name of the species harmful activities 1 bellamya bengalensis (lamarck,1882) pest of seedlings of paddy 2 lymnaea acuminata (lamarck, 1822) intermediate host of liverfluke. 3 achatina fulica destroy vegetatable and crop pest. references [1] b. r subba and t.k ghos , j. bombay nat. hist. soc. 97(2000):452. [2] b. r. subba and t.k. ghos, j. bombay nat. hist. soc. 97(2001)58. [3] t.c. majupuria, wild is beautiful: introduction to fauna and wildlife of nepal. s. devi, gwalior, india, (198182) p. 507. [4] u.k.r yadav, s.b. karki, and p.n. mishra, j. nat. his. mus. 4(1980)33. [5] m .p. feiffer, s. sharma and b. m. dahal, proc. of iii nat. conf. on sci. and tech. nepal, (1999)1371. [6] u.p. sharma, ecological society (ecos), kathmandu, nepal (1996) 92. [7] b.r. subba and m.r. pandey, j.nat. hist. mus. 22(2005) 22. [8] b.r.subba and t.k. ghos j.nat. hist. mus. 23 (2008) 78. [9] h.b. preston, the fauna of british india including ceylon and burma, taylor and francis , london(1915). [10] h. mellanby, animal life in freshwater, methuen and co., london (1963). [11] n. v. subba rao, handbook of freshwater molluscs of india, zoological survey of india , calcutta(1989). microsoft word forouzanfar et al_46-48_.doc a.m. forouzanfar et al / bibechana 10 (2014) 31-33 : bmhss, p.31 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana uniformly invariant normed spaces a.m. forouzanfar 1 , s. khorshidvandpour 2* and z. bahmani 3 1 faculty of mathematical sciences and computer, shahid chamran university, ahvaz, iran 2faculty of mathematical sciences and computer, shahid chamran university, ahvaz, iran 3 department of mathematics, islamic azad university, genaveh branch, genaveh, iran *email: sajad_khorshidvand@yahoo.com article history: received 4 february, 2013; accepted 27 september, 2013 abstract in this work, we introduce the concepts of compactly invariant and uniformly invariant. also we define sometimes c-invariant closed subspaces and then prove every m-dimensional normed space with has a nontrivial sometimes c-invariant closed subspace. sequentially c-invariant closed subspaces are also introduced. next, an open problem on the connection between compactly invariant and uniformly invariant normed spaces has been posed. finally, we prove a theorem on the existence of a positive operator on a strict uniformly invariant hilbert space. keywords: compactly invariant normed space, uniformly invariant normed space, unitary space, positive operator. 1. introduction the subject of extension of linear operators is one of the important subjects in functional analysis. invariant subspace problem is also. bandyopadeyay and roy [1] have studied uniqueness of invariant hahn-banach extensions. author in [2] has studied invariant subspace problem for banach spaces, in [3, 4] extensions of positive operators has been worked. saccoman [5] has given a necessary and sufficient condition for extension of a linear operator between banach spaces. karapınar [6], has used of invariants to consider the problem of isomorphic classification of pairs of -köthe spaces. in this work, we introduce the new concepts "compactly invariant and uniformly invariant normed spaces " to prove a theorem on the existence of a positive operator on a strict uniformly invariant hilbert space. first of all, we have the following definitions and results. definition 1.1 [7]: let x and y be normed spaces and t: x a linear operator. t is called to be a compact operator if is compact, for every bounded subset m of x. lemma 1.1 [7]: let x be a normed space. if , the identity operator is not compact. definition 1.2: let t be a linear operator on a vector space x. if there is a subspace y of x such that then y is called an invariant subspace of t. throughout this paper, denotes the normed space of all bounded linear operators on a normed space x. further, by we mean that the normed space of all compact operators on x. clearly, is a closed subspace of . a.m. forouzanfar et al / bibechana 10 (2014) 31-33 : bmhss, p.32 (online publication: dec., 2013) definition 1.3 [5]: a normed linear space x is an unitary space if the norm satisfies the parallelogram low, that is, the following theorem gives a necessary and sufficient condition for extension of a linear operator between banach spaces. theorem 1.1 [5]: let x be a banach space and m be a closed subspace of the real banach space x and b is a bounded linear operator which maps m into an arbitrary banach space y. then there exist a bounded linear operator b which maps x into y and if and only if x is a unitary space. 2. main results in this section, we let always x be a normed space over f( ); unless the contrary is specified. we set and definition 2.1: we say that x is compactly invariant when for each there exists nonzero such that dealing with the previous definition we have the following theorem. theorem 2.1: let x be a finite-dimensional normed space. then x is compactly invariant. proof. let be an arbitrary closed subspace of x. it is easy to show that the identity operator on x, say , is compact. this completes the proof. example 2.1: are compactly invariant normed spaces. theorem 2.2: every infinite-dimensional banach space contains infinite many compactly invariant subspaces. proof. it immediately follows from the dvoretzky's theorem.[8,theorem8]. definition 2.2: we say that a closed subspace y of x is sometimes c-invariant, when there is such that t is called fixing operator of y. example 2.2: let be a compact operator. then is a sometimes c-invariant closed subspace of x. the problem of the existence of invariant subspaces of a normed space is attractive for many authors, for example see [9-12]. next, we prove a theorem, in the sense of definition 2.2. theorem 2.3: if x is a m-dimensional normed space with , then it has a nontrivial sometimes c-invariant closed subspace. proof. suppose . let be a basis for x. set . obviously, y is a nontrivial closed subspace of x. the rest of what we need follows from theorem2.1. definition 2.3: we say that a closed subspace y of a x is sequentially c-invariant when there is a sequence of such that for all the sequence is called fixing sequence of y. the next theorem gives an interesting property on invariance in the sense of definition 2.3. theorem 2.4: let y be a sequentially c-invariant closed subspace of x. also, let be fixing sequence of y which then y is an invariant subspace of t. a.m. forouzanfar et al / bibechana 10 (2014) 31-33 : bmhss, p.33 (online publication: dec., 2013) proof. suppose that since for all , so by assumption, on the other hand, since was arbitrary, so .□ the next definition has a key role in the main theorem. definition 2.4: we say that a normed space x is uniformly invariant when there is an operator such that for each . in particular, if x is a hilbert space then we say that it is strict uniformly invariant when furthermore the last assumptions, is positive, for every ; then, t is called uniformly invariant operator and strict uniformly invariant operator, respectively. open problem 2.1: find a normed space which is both uniformly invariant and compactly invariant. now we can now prove the main theorem of this paper. theorem 2.5: let h be a strict uniformly invariant hilbert space with strict uniformly invariant operator t. suppose that s be an linear bounded operator on a closed subspace y of h such that then there exists a positive operator on h such that y is invariant under it. proof. by theorem 1.1, there exists a linear bounded operator which maps h into h. evidently, the restriction of to y is s. since h is strict uniformly invariant, therefore on h. set .then y is an invariant subspace of , as desired. references 1. p. bandyopadhyay and a. k. roy, extracta mathematica, 22 (2007) 93. 2. p. enflo, , acta mathematica, 158 (1987) 213. 3. m. vonkomerova, math. slovaca, 31(1981) 251. 4. c. d. aliprantis and o. burkinshaw, positive operators, springer , usa, 2006. 5. j. saccoman, , ijmms, 28 (2001) 621. 6. e. karapınar, , hacettepe journal of mathematics and statistics, 39 (2010) 337. 7. e. kreyszig, introductory functional analysis with applications, john wiley & sons, canada, 1978. 8. a. slavik, glasgow math. j., 53 (2011) 443. 9. s. brown, int. equ. oper.theory,1(1978) 310. 10. i. gohberg, p. lancaster and l. rodman, invariant subspaces of matrices with applications, wiley-interscience, new york, 1986. 11. h. bercovici and a. tannenbaum, j. math. anal. appl. 156 (1991) 220. 12. w.s.li and v.muller, integr. equ.oper. theory, (1999)197. microsoft word e. haji-ali -final.doc e. haji-ali / bibechana 8 (2012) 46-52 : bmhss, p.46 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana photo and electroluminescence of porous silicon layers e. haji-ali department of physics; imam hussein university; tehran; iran e-mail: ehajiali@yahoo.com article history: received 15 june, 2011; accepted 11 july, 2011 abstract porous silicon layers were prepared by both chemical and electrochemical methods on nand ptype si substrates. in the former technique, light emission was obtained from p-type and n-type samples. it was found that intense light illumination during the preparation process was essential for psi formation on n-type substrates.an efficient electrochemical cell with some useful features was designed for electrochemical etching of silicon. various preparation parameters were studied and photoluminescence emissions ranging from dark red to light blue were obtained from psi samples prepared on p-type substrates. n-type samples produced emissions ranging from dark red to orange-yellow. electroluminescence of porous silicon samples showed that the color of the emission was the same as the photoluminescence color of the sample, and its intensity and duration depended on the current density passed through the sample. the effects of exposure of samples to air, storage in vacuum, and heat-treatment in air on luminescence intensity of the samples and preparation of patterned porous layers were also studied keywords: porous silicon layers; photoluminescence; electroluminescence 1. introduction silicon is the most important material in microelectronics technology. however, it has a major shortcoming that prevents development of large-scale fabrication of fully-integrated optoelectronic circuits based on silicon. the origin of this drawback is the indirect energy band gap of silicon, which leads to very low quantum efficiencies for photoluminescence (pl) and electroluminescence (el) processes in silicon. furthermore, si has a relatively small (~1.1 ev) band gap. therefore, the band-to band luminescence of bulk si occurs in the near-infrared (nir) part of the spectrum. this makes si unsuitable for optical display applications. consequently, si was regarded as an unsuitable material for optical applications for many years. on the other hand, gaas which has a direct band gap and can emit light rather efficiently is expensive and not compatible with the highly developed microelectronics technologies, which are based on silicon. in 1990 canham [1] reported emission of visible light from highly porous silicon (psi) samples. since then the interest on psi has greatly intensified, and during the last five years considerable research has been done on psi. these have been aimed at both understanding the phenomenon from the basic science point of view, and also exploring possible optoelectronics applications of this material. due to a very large surface area, psi layers are highly reactive and can be oxidized at low temperatures. furthermore, psi has a higher resistivity than a comparable sio2 layer. utilizing e. haji-ali / bibechana 8 (2012) 46-52 : bmhss, p.47 these properties, "silicon-on-insulator" (soi) and "fully-isolated-porous-oxided-silicon" (fipos) processes have used psi for device isolation in si integrated circuits. crystalline si can be made porous by partial dissolution in aqueous hydrofluoric (hf) acid. psi layers have been prepared by both chemical and electrochemical methods. in electrochemical technique, the hf solution etches an array of holes (pores) into the surface of the si substrate, when an electrical current passes through the cell. the result is an array of pores that are a few nanometers wide and, in some cases, microns long. the si skeleton that is left behind consists of columnlike structures (a few nm wide) and many si microcrystals (with sizes ranging from ~ 3 – 20 nm) that are not connected with the columnlike structures. both of these columnlike and particlelike structures have been observed by tem and sem studies [2]. the columnlike si structures that are sometimes referred to as "quantum wires" are highly strained, but retain the crystallinity of the substrate. theoretical considerations (based on quantum confinement model) show that when the average width of the si quantum wires become smaller than about 4 nm, the psi layer should emit visible light at room temperature [3]. the color of this emission should vary with change in size of the wires, i.e. by making smaller structures; shorter-wavelength pl emissions should be obtained. these have been confirmed experimentally; si wire dimensions have been varied with changing psi formation parameters. psi pore diameters are increased with increasing current densities for both nand p-type samples. at low-current densities the pores are filamentlike and randomly directed. but at higher current densities, the pores "pipe" i.e. becomes larger and more cylindrically shaped [4]. for p-type samples both the pore diameters and interpore spacings are extremely small (~1-5 nm) with a highly interconnected and homogeneous pore network. the pore diameters and also interpore spacings increase slightly with increasing dopant concentration. for n-type si the pore diameters are considerably larger than p-type si and show a strong tendency to form straight channels at low dopant concentration. as the dopant concentration is increased, both the pore diameters and interpore spacings are decreased, to the point where the pore morphologies and diameters of n+ and p+ samples become comparable [4]. the actual pore formation mechanism shows considerable anisotropy. for example, it is shown that in n-type si, pore formation results in rectangular-shaped pores [4]. 2. experimental results 2.1 chemical method psi layers were prepared by etching of si in a mixture of hf: hno3: h2o (with 1:3:5 ratio) and a small amount of ethanol (~ 3%). si samples were first cleaned with rca1 and rca2 solutions, followed by a dip in a 10% hf solution for one minute. samples were etched for 5 minutes and wear rinsed in deionized water and dried with n2 gas. the etching process was performed under bright light illumination. samples emitted organe light under uv illumination. both nand p type samples showed light emission, but p-type samples had pl intensities greater than that of the n-type specimens. however these intensities were significantly lower than that of samples prepared by electrochanical technique. this is known to be due to the lower psi film thicknesses that are attainable by this preparation technique. the film thickness in this process is self limiting and saturates after several minutes; this happens when dissolution rates of si at the top surface and at the bottom part of the psi layer are balanced. pt si wafer e. haji-ali / bibechana 8 (2012) 46-52 : bmhss, p.48 it is believed that in this case the chemical etching is a two-step process, in which the si surface is first oxidized by hno3 acid, and then the oxide is reacted with hf acid to form h2sif6 which is soluble in water. shih et. al. [5] have proposed a localized electrochemical process for the above psi formation. according to them, anode and cathode sites are momentarily formed on the etched surface, and a local current flow between them during the etching process. the anodeforming reaction consists of the dissolution of si, and the cathode reaction is believed to be a complicated reduction of hno3 that causes holes to be injected in the si. the parameters involved are: hno3 concentration in the enchant mixture, reaction time, stirring condition, and doping level and conductivity type of the substrate. for stronger stirring, a thicker final film is formed; shi et al [5] have reported psi formation with p-type samples only. we also found that when the etching process was carried out in dark (or low-level illumination) psi did not from on n-type samples; however, psi formation on n-type si was possible under rather high illumination intensities. 2.2 electrochemical method figure (1) shows schematic diagram of the cell that was designed and made for electrochemical etching of si samples. an ultrasonic vibrator is used for prevention of gas bubble formation on the sample. this cell needs very little (about 15 cc) etching solution for each sample; and psi layer can be prepared under illumination (total-surface or patterned), or in the dark. a si wafer was first cleaned by rca 1 and rca2 solution followed by dipping in a 10% hf solution, rinsing in deionized water, and drying by n2 gas. immediately after cleaning, the wafer was placed in a vacuum evaporation system, and a layer of ohmic contact metal (al for p-type and ti/al for n-type samples) was evaporated on the back side of the wafer. the wafer was then cut into 2*2 cm. pieces, and each piece was attached by silver conducting paint to a piece of flatplate copper. this assembly was not only strong enough to be put under pressure in the electrochemical cell, but produced a uniform potential over the whole surface of the wafer under bias. (this was necessary for obtaining a uniform psi thickness over the whole area of the substrate). the wafer assembly was then placed in the cell. upon closing the cell cover, an o-ring was pressed onto the surface of si substrate and isolated and inner section of the cell, which was then filled with hf solution. the bias was established between a platinum wire (as the cathode) and the copper base plate. the outer section of the cell was partially filled with water, so that ultrasonic vibrations could effectively reach the inner section. fig. 1: schematic diagram of the electrochemical cell used for preparation of psi layers e. haji-ali / bibechana 8 (2012) 46-52 : bmhss, p.49 at the end of the anodization process, the sample assembly was removed from the cell, washed and dried (by n2 gas), and finally the si substrate was removed from the base plate by using a few drops of acetone to loosen the silver paint. in this method, the major parameters affecting formation and characteristic of psi film are: substrate conductivity type, substrate doping level, current density, anodization time, and hf acid concentration, illumination level during the process, and substrate crystal orientation. the effects of these parameters on psi film have been thoroughly investigated by other workers [6-10]. we also found that psi film thickness essentially determined by the amount of electric charge passed through the cell (per unit area of the substrate) during formation. this charge is the product of the current density and anodization time. at a fixed hf concentration and current density, psi film thickness increases linearly with anodization time; and again at the fixed hf concentration, psi formation rate increases linearly with current density. however, if the anodization current density is increased beyond a certain limit, electropolishing of the si surface occurs. there is a transition region between pore formation and electropolishing domains. at a fixed anodization time, the psi film thickness increases with increasing hf acid concentration in the solution. the etching mechanism of si is a two-step process: first si is oxidized by the water content of the hf solution; and then the oxide is etched away by hf acid. it has been suggested that the etching rate is considerably faster than the oxidation rate [7]. therefore, the amount of the dissolved si is determined by the oxidation reaction. it is also suggested that the si dissolution during anodization is caused by two reactions: an electrochemical reaction to form psi (which is proportional to anodization time), and a nonelectrochemical reaction (which dissolves psi) [7]. since presence of holes is essential in psi formation, exposure of the si substrate to light (with photon energies greater than the si bandgap) during anodization process increases hole concentration and therefore, increases the etching rate. light exposure during the psi formation process increased the pl emission intensity and decreased wavelength of the emitted light. application of an electric field parallel to the surface had a suppressing effect on the pl intensity (which in most cases recovered very slowly when the bias was removed). 3. photoluminescence and electroluminescence results 3.1 photoluminescence emission of p-type samples pl emissions with colors ranging from dark red to light blue were obtained for ptype samples. in a series of experiments, the total amount of charge passing through the unit area of the samples was kept constant and the current density was varied. the substrates [b-doped, (100), 38-63 ωcm] and the hf concentrations (39%) were the same for all the tests in each set. table (1) gives the color of the pl emission of the prepared psi samples under uv illumination. table (1): color of pl emission of psi samples (under uv illumination) prepared on p-type si and under different anodization times. the total charge passed through the cell was constant for all of the cases no etching time(minutes) current(ma/cm2) pl emission color 1 60 5 dark-red 2 30 10 red-orange 3 15 20 orange 4 7.5 40 orange-yellow 5 3.75 80 yellow-green 6 3.53 85 lightblue 7 3 100 -- e. haji-ali / bibechana 8 (2012) 46-52 : bmhss, p.50 the samples with yellow to blue pl emissions persisted only for a short duration, and their pl emission could only be seen if the samples were examined immediately after the preparation. the pl of samples with yellow-green emission was gone after about 5 minutes exposure to air; and the blue emission vanished in much shorter times. on the other hand, the pl intensities of samples with orange or red emissions were not destroyed with storage of samples in room air (even for periods of a year or longer). furthermore, storage of psi samples with shorter wavelength emissions in vacuum did not diminish their pl emission intensities; and even after several hours, no significant change in the intensities was observed. the above observations can be attributed to the extremely small thicknesses of si wires and microcrystals when the anodization current density is large, i.e. approaching the electropolishing domain. these very thin wires eventually oxidize completely during pl emission intensities; and even after several hours, no significant change in the intensities was observed. the above observations can be attributed to the extremely small thicknesses of si wires and microcrystals when the anodization current density is large, i.e. approaching the electropolishing domain. these very thin wires eventually oxidize completely when the psi layer is exposed to air. on the other hand, thick si wires do not oxidize entirely and a thin sio2 layer, which forms on the outer surface of the wires, prevents their further oxidation. of course, if the temperature is increased, the oxidation process will propagate further until the entire si structure is oxidized. this was actually observed experimentally; psi samples with red pl emissions (which are normally stable) were heated in air. when the temperature reached ~ 60 0 c the pl intensity of the sample started to diminish; at ~200 0 c (after 6 minutes total heating time) the emission was completely destroyed. heating similar samples in boiling water also showed the same oxidation effect. at current densities of 100 ma/cm 2 or greater (sample no. 7 in table 1) electropolishing process takes place and psi is not formed. the emission intensities for samples 2 and 3 (table 1) were stronger than the others. the intensities of samples 5 and 6 were lower, though quite visible. viewing the spectrum of the emitted pl emission of psi samples by a spectroscope showed that the light consisted of a range of wavelengths, as is well documented in the literature. 3.2 photoluminescence emission of n-type samples under various preparation conditions, n-type samples did not produce any visible pl emission, when samples were prepared in the dark. however, psi was formed and strong pl emissions were observed when the anodization process was done under illumination. this was well observed when only a part of the substrate was illuminated by a bright light source. the contrast between the two parts was quite evident when the sample was inspected under normal or uv illumination. again, by varying anodization current densities (under a constant-charge condition), various pl colors were obtained from these samples. table (2) shows the results. the samples were illuminated by a 150w mercury-vapor lamp at 30 cm. distance the psi formation. e. haji-ali / bibechana 8 (2012) 46-52 : bmhss, p.51 table (2): color of pl emission of psi samples (under uv illumination) prepared on n-type si and under different anodization times. the total charge passed through the cell was constant for all of the cases no etching time(minutes) current(ma/cm2) pl emission color 1 50 4 dark-red 2 34 6 red-orange 3 25 8 orange-yellow pattered psi layers were generated by two techniques. first, a layer of positive photoresist was patterned by photolithographic method on the substrate surface. in another technique, patternd illumination of the sample (during the anodization process) was used. a mask was placed in the path of light (see fig. 2), and its image was optically projected on the si substrate. however, due to scattering of light in the solution and body of the cell, pattern definition was not as good as the former technique. 3.3 electroluminescence results three kind of el cells (electrolyte/psi, au/psi, and ito/psi) were made and studied. the electrolyte for the first type consisted of acid solutions, usually hno3: h2o (1:5 ratios). the samples were placed in the same cell that was used for preparation of psi samples (see fig. 1). the bias was established between the top pt electrode and the base of the sample, i.e. ohmic contact with si substrate. the amount of gold that was thermally evaporated on the psi layer in vacuum was adjusted so that the au electrode acted as a semi-transparent electrode in au/psi cells. the third kind of el cells were prepared by deposition of an indium oxide (io) or indium-tin-oxide (ito) layer on top of the psi samples. since during the deposition of io or ito layers (by reactive evaporation of in metal in partial pressure of oxygen and spray-hydrolysis methods, respectively) the substrate needed to be heated to several hundred degrees celsius, the psi layer oxidized during the transparent electrode deposition, and therefore, no visible el emission was observed from these cells. of the other two types of el cells, only electrolyte/psi cells produced bright visible el emissions. the intensity of the emission increased with increasing current passing through the cells. the color of the emission was the same as the pl color of the sample. however, due to electrochemical reaction between the electrolyte and psi layer (which dissolves psi), the lifetime of these cells was limited to a few minutes; after which, the el emission sharply reduced to zero. 4. conclusion porous silicon is fast becoming an important research subject. this is not only due to its potential applications in optoelectronic devices and integrated optics circuits, but also because of its significance from the basic solid state science point of view. in this article, we report: (1) by shining intense light on the sample during the psi preparation process, it is possible to form psi layer on n-type silicon substrates as well; (2) features of an efficient electrochemical cell for preparation of psi samples, which is simple to make, but has various useful capabilities; (3) obtaining pl and el emissions ranging from dark red to light blue from psi samples is possible by just changing the preparation parameters during psi formation process (with no need for post-deposition heat-treatment of samples in boiling water). furthermore, preparation and characterization results for various psi samples are discussed. e. haji-ali / bibechana 8 (2012) 46-52 : bmhss, p.52 acknowledgement the author would like to thank dr. mahdi eshghi for the positive suggestions which helped to improve the present work. references [1] l. t. canham, appl. phys. lett. 57(10), (1990) 1046. [2] x. wang, modern phys. lett. b 8 (2), 69 (1994) 1597 [3] l. t. canham, phys. world, 41(march 1992) 1540. [4] r. l. smith and s. d. collins, j. appl. phys. 71 (8), r1 (1992). [5] s. shih, et al., mat. res. soc. symp. proc. 256, 27 (1992) 197. [6] t. asano, et al., jpn. j. appl. phys. 31, l373 (1992) 865. [7] h. unno, k. imai, & s. muramoto, j. electrochem. soc. s. s. & t 134 (3), 645(1987) 645 648. [8] j. t. lue, et al., solid state commun. 86(9), (1993) 593. [9] s. f. chung, s. d. collins, & r. l. smith, appl. phys. lett. 55(7), (1989) 675. [10] o. teschke, m. c. goncalves, & f. galembeck, appl. phys. lett. 63(10), (1993) 1348. microsoft word a. liman et al _72-82_..doc a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.71 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana on the eneström-kakeya theorem a. liman 1 , tawheeda rasool 1 , w.m shah 2 1department of mathematics, national institute of technology, india –190006 2 department of mathematics, jammu and kashmir institute of mathematical sciences-190008 e-mail: wmshah@rediffmail.com, abliman22@yahoo.com article history: received 25 september, 2013; accepted 23 november, 2013 abstract in this paper we present some interesting generalizations of eneström-kakeya type results concerning the location of zeros of a polynomial in the complex plane. we relax the hypothesis and put less restrictive conditions on the coefficients of the polynomial, and thereby generalize some classical results. keywords: polynomials, zeros, eneström-kakeya theorem 1. introduction the following result known as eneström-kakeya theorem (for reference see [1-3]) is well-known in the theory of distribution of zeros of polynomials. theorem a. if ∑ = = n j j j zazp 0 )( is a polynomial of degree n such that (1) 0aa....aa 011nn >≥≥≥≥ − , then all the zeros of p(z) lie in 1.z ≤ joyal, labelle and rahman [4] dropped the restriction on the hypothesis that all the coefficients be positive and proved the following: theorem b. if ∑ = = n j j j zazp 0 )( is a polynomial of degree n such that 1 1 0....n na a a a−≥ ≥ ≥ ≥ , then all the zeros of p(z) lie in 0 0n n a a a z a − + ≤ . more recently aziz and zargar [5] relaxed the hypothesis of eneström kakeya theorem and proved some interesting extensions of theorem b. in fact they proved theorem c. if 1 1 1 0( ) ...n n n np z a z a z a z a− −= + + + + , is a polynomial of degree n such that for some 1k ≥ , a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.72 (online publication: dec., 2013) 1 2 1 0... ,n nka a a a a−≥ ≥ ≥ ≥ ≥ then all the zeros of p(z) lie in 0 0 1 . n n ka a a z k a − + + − ≤ more recently, shah and liman [6] while assuming the coefficients of the polynomials to be complex numbers among other things proved the following generalization of theorem c. theorem d. let ( )p z = 0 n j j j a z = ∑ be a polynomial with complex coefficients. if re j ja α= and im j ja β= for 0,1, 2,...,j n= , 0na ≠ such that for some k 1≥ 1 2 1 0...n n nkα α α α α− −≥ ≥ ≥ ≥ ≥ , 1 1 0.... 0n nβ β β β−≥ ≥ ≥ ≥ > , then all the zeros of ( )p z lie in 0 0 ( 1) n nn n n k z k a a α α α βα − + + + − ≤ in this paper, we prove some enström-kakeya type results which besides generalizing some earlier results proved in this direction, include theorem b, theorem c and theorem d as special cases. we start by proving the following: 2. theorems and proofs theorem 1: let ( )p z = 0 n j j j a z = ∑ be a polynomial of degree n. if re j ja α= , im j ja β= for 0,1, 2,...,j n= , 0na ≠ and if for some positive integer nλ ≤ and 1k ≥ 1 1 1 2 1 1 0... ...n n n n n nk k k kλ λ λ λ λα α α α α α α− + − − − − − −≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ then all the zeros of p(z) lie in 0 0 0 ( 1) ( | |) 2 1 . n n n j j n j j j n k z k λ α α α α α α β α = =     − + + − + − +      + − ≤ ∑ ∑ if we take nλ = we obtain the following : corollary 1.1: let ( )p z = 0 n j j j a z = ∑ be a polynomial of degree n with re j ja α= , im j ja β= for 0,1, 2,...,j n= , 0na ≠ and if for some 1k ≥ 1 2 1 0...n n nkα α α α α− −≥ ≥ ≥ ≥ ≥ then all the zeros of p(z) lie in a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.73 (online publication: dec., 2013) 0 0 0 2 1 . n n j j n k z k α α α β α = − + + + − ≤ ∑ for 1nλ = − and assuming all coefficients real and positive in theorem 1, we obtain the following corollary 1.2: let ( )p z = 0 n j j j a z = ∑ be a polynomial of degree n and if for some 1k ≥ 2 1 2 1 0... 0n n nk a ka a a a− −≥ ≥ ≥ ≥ ≥ > then all the zeros of p(z) lie in 11 2( 1) n n a z k k k a −+ − ≤ + − or equivalently 1 (2 1)z k k k+ − ≤ − remark 1.1: theorem c is a special case of theorem 1, if we take all coefficients real and nλ = . further for all coefficients real, nλ = and 1k = we obtain theorem b. theorem 2: let ( )p z = 0 n j j j a z = ∑ be a polynomial of degree n. if re j ja α= and im j ja β= for 0,1, 2,...,j n= , 0na ≠ and if for some positive integer nλ ≤ and 1k ≥ 1 1 1 2 1 1 0... ...n n n n n nk k k kλ λ λ λ λβ β β β β β β− + − − − − − −≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ then all the zeros of p(z) lie in 0 0 0 ( 1) ( | |) 2 1 n n n j j n j i j n k z k λ β β β β β β α β = =    − + + − + − +     + − ≤ ∑ ∑ next as a generalization of therorem d, we prove theorem 3: let ( )p z = 0 n j j j a z = ∑ be a polynomial of degree n. if re j ja α= and im j ja β= for 0,1, 2,...,j n= , 0na ≠ and if for some positive integer nλ ≤ and 1k ≥ 1 1 1 2 1 1 0... ...n n n n n nk k k kλ λ λ λ λα α α α α α α− + − − − − − −≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ 1 1 0... 0n nβ β β β−≥ ≥ ≥ ≥ > then all the zeros of p(z) lie in 0 0 ( 1) ( ) ( 1) . n n j j n n in n n k z k a a λ α α α α α α β α =    − + + − + − +     + − ≤ ∑ remark 3.1: if we take nλ = in above we obtain theorem d. a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.74 (online publication: dec., 2013) theorem 4: let ( )p z = 0 n j j j a z = ∑ be a polynomial of degree n. if for some positive integer nλ ≤ , 1k ≥ and 1µ ≥ 1 1 1 2 1 1 0... ... n n n n n nk k k k λ λ λ λ λα α α α α α α− + − − − − − −≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ 1 1 0... 0n nµβ β β β−≥ ≥ ≥ ≥ > then all the zeros of p(z) lie in ( )0 0 1 ( ) 1 n n j j n n in n n n k k i z a a λ α α α α α α µβ α µβ =    − + + − + − +  +   + − ≤ ∑ if we take nλ = in above we obtain the following: corollary 4.1: let ( )p z = 0 n j j j a z = ∑ be a polynomial of degree n. if for some positive integer nλ ≤ , 1k ≥ and 1µ ≥ 1 1 0...n nkα α α α−≥ ≥ ≥ ≥ 1 1 0... 0n nµβ β β β−≥ ≥ ≥ ≥ > then all the zeros of ( )p z lie in 0 0 { } 1 n nn n n n kk i z a a α α α µβα µβ − + ++ + − ≤ theorem 5: let ( )p z = 0 n j j j a z = ∑ be a polynomial of degree n. if for some positive integer nλ ≤ and 1k ≥ 1 1 1 2 1 1 0... ...n n n n n nk a k a k a k a a a aλ λ λ λ λ − + − − − − − −≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ and for some real β , arg 2 ja π β α− ≤ ≤ , 0,1, 2,...j = then all the zeros of lie in 1 1 1 1 1 2sin 1 (cos sin ) {( 1) cos ( 1)sin } ( 1) | | . n n j i j i i jn n z k k k k a k a a a aλ λ λ α α α α α − = + = = − + − ≤ + + − + + + − +∑ ∑ ∑ proof of theorem 1: consider a polynomial ( ) (1 ) ( )f z z p z= − 1 1 1 0 0( ) ... ( )n n n n na z a a z a a z a+ −= − + − + + − + { } { } 1 1 1 0 0 1 1 1 0 0 ( ) ... ( ) ( ) ... ( ) n n n n n n n n n n z z z i z z z α α α α α α β β β β β β + − + − = − + − + + − + + − + − + + − + a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.75 (online publication: dec., 2013) 1 1 1 1 1 2 1 1 2 1 1 0 0 1 2 1 1 1 1 0 0 { ( 1) ( ) ( ) ... ( ) ( ) ... ( ) ( 1)( ... )} { ( ) ... ( ) } n n n n n n n n n n n n n n n n n z z k k z k z k z k z z k z z z z i z z zλ λ λ λ λ λ λ λ λ λ α α α α α α α α α α α α α α α α β β β β β β+ − + − − − + − − − − − + + − = − + − + − + − + + − + − + + − + − − + + + + + − + − + + − + 1 1 1 1 1 2 1 1 2 1 1 0 0 1 2 1 1 0 1 1 { ( 1) ( ) ( ) ... ( ) ( ) ... ( ) ( 1)( ... )} ( ) } n n n n n n n n n n n n n n j n j j j z z k k z k z k z k z z k z z z z i z i i zλ λ λ λ λ λ λ λ λ λ α α α α α α α α α α α α α α α α β β β β+ − + − − − + − − − − − + + − = = − + − + − + − + + − + − + + − + − − + + + + − + + −∑ 1 1 2 1 11 1 2 0 1 0 0 11 2 1 1 1 1 ( 1) ( ) ( ) ... ( ) ( ) 1 1 1 ... ( ) ( 1) ... ( ) n n n n n n n n n n n n j jn n n n n j j z z k k k k k z z z k i z i i z z z z z z z λ λ λ λλ λ λ λ α α α α α α α α α α α α β α α α β β β − − − + −− − − − − −− − − = = − + − + − + − + + − + − +   + + − + − − + + + − + + −      ∑ let 1z > so that 1 1 n j z − < , 0,1, 2,...j = 1 2 1 1 1 1 1 0 0 1 2 1 1 2 1 0 1 1 ( ) 1 ... ... 1 ... 1 (| | | |) n n n n n n n n n n n n n n n n j jn n j j k k k f z z z k k z z z k zz z z z z z z z λ λ λ λ λ λ λ λ λ λ α α α α α α α α α α α α α α α α β β β β − − + − − − − − − − + − − − − − − =   − − − ≥ + − − − + + + + +    −  + + + + − + + + +      + + + +   ∑ { 1 1 2 1 1 1 1 0 0 0 1 1 1 ... ... 1 (| | | |) n n n n n n n n j n j j j j z z k k k k k k λ λ λ λ λ α α α α α α α α α α α α α β β β β − − − + − − − = = > + − −  − + − + + − + − +  + + − + + − + + + +   ∑ ∑ { 1 1 2 1 1 1 1 0 0 0 1 1 1 ... ... 1 (| | | |) n n n n n n n n j n j j j j z z k k k k k k λ λ λ λ λ α α α α α α α α α α α α α β β β β − − − + − − − = = = + − −  − + − + + − + − +  + + − + + − + + + +   ∑ ∑ 0 0 0 1 ( 1) ( ) 2 | | n n n n n j j n j j j z z k k λ α α α α α α α β = =          = + − − − + + − + − +               ∑ ∑ a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.76 (online publication: dec., 2013) 0,> if 0 0 0 ( 1) ( | |) | | 2 | | 1 n n n j j n j j j n k z k λ α α α α α α β α = =   − + + − + − +   + − > ∑ ∑ this shows that those zeros of ( )f z for which 1z > lie in 0 0 0 ( 1) ( | |) | | 2 | | 1 . n n n j j n j j j n k z k λ α α α α α α β α = =   − + + − + − +   + − ≤ ∑ ∑ but those zeros of ( )f z for which 1z ≤ already satisfy the above equation. we conclude that all the zeros of ( )f z and hence of ( )p z lie in the disc 0 0 0 ( 1) ( | |) | | 2 | | 1 n n n j j n j i j n k z k λ α α α α α α β α = =   − + + − + − +   + − ≤ ∑ ∑ this completes the proof. proof of theorem 2: the proof follows on the same lines of theorem 1. proof of theorem 3: consider a polynomial ( ) (1 ) ( )f z z p z= − 1 1 1 0 0( ) ... ( ) n n n n na z a a z a a z a + −= − + − + + − + 1 1 1 0 0 1 1 0 0 { ( ) ... ( ) } {( ) ... ( ) } n n n n n n n n a z z z i z z α α α α α β β β β β + − − = − + − + + − + + − + + − + 1 1 1 1 1 1 2 1 1 2 1 1 0 0 1 2 1 1 1 0 0 { ( 1) ( ) ( ) ... ( ) ( ) ... ( ) ( 1)( ... )} {( ) ... ( ) } n n n n n n n n n n n n n n n n n a z z k k z k z k z k z z k z z z z i z zλ λ λ λ λ λ λ λ λ λ α α α α α α α α α α α α α α α α β β β β β+ + − + − − − + − − − − − + − = − − − + − + − + + − + − + + − + − − + + + + + − + + − + 1 1 2 1 1 1 2 1 1 0 01 2 1 1 0 01 1 1 ( 1) ( ) ( ) ... ( ) 1 1 1 ( ) ... ( ) ( 1) ... 1 1 ( ) ... ( ) n n n n n n n n n n n n n n n n n n z a z k k k k z z k k z z z z z z i z z λ λ λ λ λ λ λ λ α α α α α α α α α α α α α α α β β β β β − − − + − − − − − − − − − − = − − − + − + − + + −   + − + + − + − − + + + +     + − + + − +    a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.77 (online publication: dec., 2013) 1 1 2 1 1 1 1 ( 1) ( ) ( ) ... ( )n n n n n n n n z a z k k k k z z λ λ λα α α α α α α− − − + − − = − − − + − + − + + −  1 2 1 1 0 01 2 1 1 1 ( ) ... ( ) ( 1) ...n n n n n n k k zz z z z z λ λ λ λ λ α α α α α α α α − − − − − −   + − + + − + − − + + +    1 1 0 01 1 1 ( ) ... ( )n n n n i z z β β β β β− −  + − + + − +    let 1z > so that 1 1 n j z − < , 0,1, 2,...j = 1 2 1 1 1 0 0 1 2 2 1 2 2 1 0 0 1 1 ( ) ( 1) ... ( 1) ... ... n n n n n n n n n n n n n n n n n k k f z z a z k k z z k zz z z z i z z λ λ λ α α α α α α α α α α α α α β β β β β − − − − − − − − − − −   − −  ≥ + − − − + + + +     −  + + + − + + +      −  + − + + +    0 0( 1) ( 1) ( ) n n n n n j j n n in z a z k k a λ α α α α α α α β =     = + − − − + + − + − +        ∑ 0,> if 0 0 ( 1) ( ) ( 1) n n j j n n in n n k z k a a λ α α α α α α β α =    − + + − + − +     + − > ∑ this shows that the zeros of ( )f z , for which 1z > lie in 0 0 ( 1) ( ) ( 1) . n n j j n n in n n k z k a a λ α α α α α α β α =    − + + − + − +     + − ≤ ∑ but those zeros of ( )f z for which 1z ≤ already satisfy the above equation. we conclude that all the zeros of ( )f z and hence of ( )p z lie in the disc 0 0 ( 1) ( ) ( 1) n n j j n n in n n k z k a a λ α α α α α α β α =    − + + − + − +     + − ≤ ∑ a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.78 (online publication: dec., 2013) proof of theorem 4: consider a polynomial ( ) (1 ) ( )f z z p z= − 1 1 1 0(1 )( ... )n n n nz a z a z a z a− −= − + + + + 1 1 1 0 0( ) ... ( ) n n n n na z a a z a a z a + −= − + − + + − + 1 1 1 0 0 1 1 0 0 { ( ) ... ( ) } { ( ) ... ( ) } n n n n n n n n a z z z i z z α α α α α β β β β β + − − = − + − + + − + + + − + + − + 1 1 1 1 1 1 2 1 1 2 1 1 0 0 1 2 1 1 1 0 0 { ( 1) ( ) ( ) ... ( ) ( ) ... ( ) ( 1)( ... )} {( ) ... ( ) } n n n n n n n n n n n n n n n n n n n a z z k k z k z k z k z z k z z z z i z z λ λ λ λ λ λ λ λ λ λ α α α α α α α α α α α α α α α α µβ β µβ β β β β + + − + − − − + − − − − − + − = − − − + − + − + + − + − + + − + − − + + + + + + − − + + − + 1 1 2 1 2 1 1 0 01 2 1 1 0 01 1 ( ) ( ) ( ) ... 1 1 1 ( ) ( ) ( 1) ... 1 1 ( ) ... ( ) n n n n n n n n n n n n n n n n n n n n z a z k i i k k z k k z z z z z z i z z λ λ λ λ λ α α µβ β α α α α α α α α α α α α µβ β β β β − − − − − − − − − − − = − − + − + + − + − +   + − + + − + − − + + +     + − + + − +    1 1 2 1 2 1 1 0 01 2 1 1 0 01 1 ( ) ( ) ( ) ... 1 1 1 ( ) ... ( ) ( 1) ... 1 1 ( ) ... ( ) n n n n n n n n n n n n n n n n n n n z a z k i a k k z k k z z z z z z i z z λ λ λ λ λ α µβ α α α α α α α α α α α α µβ β β β β − − − − − − − − − − −  = − − − + + − + − +    + − + + − + − − + +       + − + + − +     let 1z > so that 1 1 n j z − < , 0,1, 2,...j = { } 1 1 2 1 1 0 0 1 2 1 1 0 0 ( ) 1 ... ... ( 1)( ... ) ... n n n n n n n n n n n n n k i f z z a z k k k a k λ λ λ α µβ α α α α α α α α α α α α µβ β β β β − − − − − − − + ≥  + − − − + − + + − + + − + + − + + + + − + + − +  0 0 1 ( 1) ( | |) n n n n n n j j n n in k i z a z k a λ α µβ α α α α α α µβ =   +   = + − − − + + − + − +         ∑ 0,> a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.79 (online publication: dec., 2013) 0 0 ( 1) ( | |) 1 n n j j n n in n n n k k i z a a λ α α α α α α µβ α µβ =    − + + − + − +  +   + − > ∑ this shows that the zeros of ( )f z , for which 1z > lie in 0 0 ( 1) ( | |) 1 . n n j j n n in n n n k k i z a a λ α α α α α α µβ α µβ =    − + + − + − +  +   + − ≤ ∑ but those zeros of ( )f z for which 1z ≤ already satisfy the above equation. we conclude that all the zeros of ( )f z and hence of ( )p z lie in the disc. 0 0 ( 1) ( | |) 1 n n j j n n in n n n k k i z a a λ α α α α α α µβ α µβ =    − + + − + − +  +   + − ≤ ∑ proof of theorem 5: consider a polynomial ( ) (1 ) ( )f z z p z= − 1 1 1 0(1 )( ... ) n n n nz a z a z a z a − −= − + + + + 1 1 1 0 0( ) ... ( )n n n n na z a a z a a z a+ −= − + − + + − + 1 1 2 1 1 1 2 1 1 0 01 2 1 1 ( 1) ( ) ( ) ... ( ) 1 1 1 ( ) ( ) ( 1) ... n n n n n n n n n n n n n z a z k ka a ka a ka a z z a a a ka a a a a k z z z z z z λ λ λ λ λ λ λ λ − − − + − − − − − − − − = − + − + − + − + + −   + − + − + − − + + +    let 1z > so that 1 1 n j z − < , 0,1, 2,...j = { } 1 1 2 1 1 1 0 0 1 2 ( ) 1 { ... ... ( 1)(| | | | ... | |) . n n n n n n n n f z z a z k ka a ka a ka a ka a a a a k a a a λ λ λ λ λ − − − + − − − ≥ + − − − + − + + − + − + + − + + − + + + using the fact (for reference see [2]) that for any two complex numbers 0b and 1b such that 0 1 ,b b≥ and arg 2 ja π β α− ≤ ≤ , 0,1, 2j = and β real 0 1 0 1 0 1(| | | |) cos (| | | |) sin .b b b b b bα α− ≤ − + + a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.80 (online publication: dec., 2013) [ { 1 1 1 2 1 2 1 1 1 2 1 2 1 0 1 0 ( ) | | | 1 | cos cos sin sin cos cos sin sin ... cos cos sin sin ... cos cos sin sin ... cos cos sin sin n n n n n n n n n n f z z a z k k a a k a a k a a k a a k a a k a a a a a a a a a a λ λ λ λ λ λ λ λ α α α α α α α α α α α α α α α α α α α α − − − − − − − − − − − − ≥ + − − − + + + − + + + + − + + + + − + + + + − + + 1 0... ( 1) | | n i i a k a λ − =  + + + −   ∑ [ { 1 1 1 2 1 1 0 0 0 | | | 1 | (cos sin ) ( 1) cos ( 1) sin ... ( 1) cos ( 1) sin 2 sin 2 sin ... 2 sin cos sin ( 1) | | n n n n n n i i z a z k k a k a k a k a k a a a a a a a k a λ λ λ λ λ α α α α α α α α α α α − − − − − = = + − − + + − + + + + − + + + + +  + − + + + −   ∑ [ 1 1 1 1 1 0 0 1 1 | | | 1 | { (cos sin ) ( 1) cos | | ( 1)sin 2sin (sin cos ) n n n n n j i i i n j j i j z a z k k a k a a k a a a a λ λ λ λ α α α α α α α − − = + = − = + = −   = + − − + + − +     + + + + − +   ∑ ∑ ∑ ∑ { 1 1 1 0 1 1 (cos sin ) (( 1)cos ( 1)sin ) 2sin (1 sin cos ) ( 1) | | n n n n j i n j i j i z a z k k a k k a a a k a λ λ λ α α α α α α α = + − = − = =  + − − + + − + +  + + + − + −   ∑ ∑ ∑ { 1 1 1 1 1 (cos sin ) (( 1) cos ( 1)sin ) 2sin ( 1) | | n n n n j i n j i j i z a z k k a k k a a k a λ λ λ α α α α α = + − = − =  ≥ + − − + + − + +   + + −   ∑ ∑ ∑ 0,> if 1 1 1 1 1 2sin 1 (cos sin ) {( 1) cos ( 1)sin } ( 1) | | n n j j i i j in n z k k k k a a k a a aλ λ λ α α α α α − = + = − = + − > + + − + + + + −∑ ∑ ∑ this shows that the zeros of ( )f z , for which 1z > lie in a. liman et al. / bibechana 10 (2014) 71-81 : bmhss, p.81 (online publication: dec., 2013) 1 1 1 1 1 2sin 1 (cos sin ) {( 1) cos ( 1)sin } ( 1) | |. n n j j i i j in n z k k k k a a k a a aλ λ λ α α α α α − = + = − = + − ≤ + + − + + + + −∑ ∑ ∑ but those zeros of ( )f z for which 1z ≤ already satisfy the above equation the above equation. we conclude that all the zeros of ( )f z and hence of ( )p z lie in the disc 1 1 1 1 1 2sin 1 (cos sin ) {( 1) cos ( 1)sin } ( 1) | |. n n j j i i j in n z k k k k a a k a a aλ λ λ α α α α α − = + = − = + − ≤ + + − + + + + −∑ ∑ ∑ references 1. m. marden, geometry of polynomials, math. surveys, no. 3; amer. math. soc. providence r.i., (1966). 2. q. i. rahman and g. schmeisser, analytic theory of polynomials. oxford univ. press, (2002). 3. w.m shah and a. liman, on eneström kakeya theorem and related analytic functions, proc. indian acad. sci.( math sci.) vol.117,no. 3,(2007) 359-370. 4. a. joyal, g. labelle and q.i-rahman, on the location of zeros of polynomials, canad. math. bull.,10(1967) 53-63. 5. a.aziz and b.a zargar, some extension of eneström-kakeya theorem,glasnik matematicki, 31(1996) 239-244. 136-140 i. bhagat r c o s t n i. bhagat / bibechana 11(1) (2014) 136-140: (online publication: march, 2014) p.136 bibechana a multidisciplinary jurnal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana management of collar rot of tomato caused by sclerotium rolfsii indramani bhagat department of botany, post graduate campus, biratnagar tribhuvan university, nepal e-mail: drimbhagat@yahoo.com accepted for publication: february 08, 2014 abstract collar rot of tomato (lycopersicum esculentum miller) caused by sclerotium rolfsii sacc. is one of the most destructive diseases in tomato throughout the world. effective and efficient management of the crop disease is generally achieved by the use of synthetic pesticides. these pesticides are known to pollute the environment, soil and water besides causing deleterious effects on human health and biosphere. amendments (neem cake, oil cake, cow dung, rabbit manure and chicken manure) were used in tomato seedlings to observe growth promotion and percentage increase in shoot length in healthy and treated tomato seedlings of two varieties, f1 hybrid arjuna and pahuza s-22. results revealed that growth of the tomato seedlings was significantly increased following amendment with neem cake and oil cake in the treated sclerotium rolfsii inoculated plants than in untreated uninoculated plants as recorded. oil cake had better effect than neem cake. similarly, amendment with cow dung, rabbit manure and chicken manure it has been observed that the growth of tomato seedlings increased in treated uninoculated than treated inoculated tomato seedlings. among the three treatments, cow dung gave better growth of tomato seedlings than that of rabbit manure and chicken manure. © 2014 rcost: all rights reserved. keywords: organic amendment; pathogen; manure. 1. introduction tomato (lycopersium esculentum miller) is one of the second most popular vegetable crops of world. it is attacked by a large number of fungal, viral and bacterial pathogens. sclerotium rolfsii is one of the important fungal pathogens that causes collar rot resulting in substantial yield losses. this disease appears in the nursery grown tomato seedlings. the fungus is a soil borne rotting pathogen of very aggressive nature and causes considerable damage to young tomato seedlings in the nursery which is very common in the plains but rare in the hills. it occurs in diverse soils, has a very wide host range and worldwide distribution [1]. however effective and efficient management of crop diseases is generally achieved by the use of synthetic pesticides. these pesticides are known to pollute the environment, soil and water besides causing deleterious effects on human health and biosphere. the present investigation is related to the study of the management of collar rot disease of tomato by organic amendments. i. bhagat / bibechana 11(1) (2014) 136-140: (online publication: march, 2014) p.137 2. materials and method plant material two tomato varieties f1 hybrid arjuna and pahuza s-22 were grown in pots and were used for experimental purpose. fungal culture source of cultures virulent culture of sclerotium rolfsii sacc was obtained from immuno-phytopathology laboratory, department of botany, north bengal university. this was originally isolated from teen ali-17/1/54 and after completion of kock’s postulate, the organism was identified by global plant clinic, diagnostic and advisory service, cabi bioscience uk and designated as sr-1. maintenance of stock cultures the fungus thus obtained has been sub-cultured on pda slants. after two weeks the culture has been stored under three different conditions (0ºc, 4ºc and at room temperature 28ºc). the culture of s. rolfsii was examined at regular intervals to test its pathogenicity. effect of organic amendments on tomato seedling in pot culture pot culture experiment were conducted with different organic amendments treated in the tomato seedlings to observe growth promotion and percentage increase in shoot length in healthy and treated tomato seedling varieties. the earthen pots were filled with autoclaved 1kg of soil. mustard oil cakes were allowed to decompose for a week in a clay pot covered with polythene. 100 ml of decomposed oil cake solution, 100 g powdered neem cake, 100 g cow dung, 100 g chicken and 100 g rabbit manure were added in pots containing sterilized soil separately and watered. after one week, the seedlings of two varieties of tomato (f1 hybrid arjuna and pahuza s-22) were grown in soil amended with neem cake, oil cake, cow dung, rabbit and chicken manure separately before inoculation with 100 g sclerotium rolfsii and watered lightly. then these pots were inoculated with the test pathogen multiplied on sand-maize medium and watered lightly. the seedlings were planted in the earthen pots without amendments but inoculated with the pathogen and were maintained as control. each treatment consisted of 10 plants, in triplicate and the values are an average of 30 plants. the observations were recorded after two months. results and discussion results (tables 1 & 2) revealed that the growth of the tomato seedlings was significantly increased following amendment with neem cake and oil cakes in the treated s. rolfsii inoculated seedlings than in untreated inoculated seedlings as recorded after two months. oil cake had better effect than neem cake. it had been observed that the percentage increase in shoot length after two months of treatment with neem cake and oil cake in treated inoculated with s. rolfsii the tomato seedlings was more than in the untreated inoculated tomato seedlings. i. bhagat / bibechana 11(1) (2014) 136-140: (online publication: march, 2014) p.138 table 1: growth promotion in tomato seedlings following soil amendment with neem cake and oil cake tomato variety one month two months healthy infected healthy infected increase in height (cm) increase number of compound leaves increase in height (cm) increase number of compound leaves increase in height (cm) increase number of compound leaves increase in height cm increase number of compound leaves f1 hybrid arjuna untreated 29+1.24 10+1.01 20+1.22 7+0.06 36+1.35 12+1.14 34+ 1.29 9+0.07 treated neem cake 20+1.19 7+0.06 19+1.18 6+0.04 32+1.32 11+1.17 40+2.42 13+1.14 oil cake 23+1.26 8+0.05 25+1.23 9+0.08 58+2.12 19+1.19 55+2.11 18+1.17 pahuza s22 untreated 28+1.29 9+0.02 17+1.16 6+0.05 35+1.34 11+1.09 32+1.33 8+0.02 treated neem cake 19+1.13 6+0.03 17+1.15 5+0.04 31+1.30 10+1.02 30+1.34 10+1.09 oil cake 21+1.21 7+0.09 23+1.21 8+0.07 56+2.10 18+1.17 46+2.01 16+1.17 average of 3 replicates + standard error. table 2: percentage increase in shoot length in tomato seedlings following treatment with neem cake and oil cake tomato variety percentage increase in shoot length after two months treatment healthy infected f1 hybrid arjuna untreated 24.14 70.0 treated neem cake 60.0 110.0 oil cake 163.64 120.0 pahuza s-22 untreated 93.94 25 treated neem cake 63.16 73.53 oil cake 176.19 97.83 i. bhagat / bibechana 11(1) (2014) 136-140: (online publication: march, 2014) p.139 it revealed that the growth of tomato seedlings had been increased in treated uninoculated than treated inoculated tomato seedlings (table 3). among the three treatments, cow dung gave very good and healthy growth of tomato seedlings (plate 1: fig. d) than rabbit and chicken manure (plate 1: fig. e & f). table 3: growth promotion in tomato seedlings by different organic components after inoculation with sclerotium rolfsii tomato variety one month two months healthy infected healthy infected increase in height (cm) increase number of compound leaves increase in height (cm) increasenumber of compound leaves increase in height (cm) increase number of compound leaves increase in height (cm) increase number of compound leaves f1 hybrid arjuna untreated 30+1.45 10+1.01 11+1.02 7+0.08 3+0.05 13+1.07 33+1.10 10+1.03 treated cow dung 19+1.25 9+0.02 18+1.23 8+0.06 54+1.49 19+1.04 41+1.20 16+1.07 rabbit manure 18+1.24 7+0.07 15+1.13 4+0.05 42+1.55 14+1.13 28+1.21 11+1.12 chicken manure 27+1.22 10+1.09 24+1.08 9+0.09 47+1.22 15+1.07 45+1.43 14+1.15 pahuza s-22 untreated 28+1.26 9+0.06 17+1.11 6+0.07 35+1.26 12+1.09 30+1.28 9+0.08 treated cow dung 17+1.09 7+0.04 16+1.09 6+0.02 47+1.29 16+1.18 36+1.46 15+1.09 rabbit manure 26+1.31 9+0.05 16+1.03 5+0.02 46+1.23 15+1.14 24+1.20 10+1.01 chicken manure 27+1.22 8+0.07 23+1.33 8+0.09 44+1.46 14+1.16 42+1.38 13+1.15 average of 3 replicates + standard error. a botanist [2] who had reported that mustard cake was found effective in reducing the incidence of fusarium oxysporum f. sp. lycopersici. neem cake was found as effective for the control of f. oxysporum f. sp. cubense in banana [3,4]. organic amendments increase the availability of nutrients besides improving physical condition of soil, increase the yield and reduce the soil-borne diseases [5]. organic soil amendments have also been reported to be effective in controlling the pathogen [6-9]. the superiority of this amendment may be due to release of some inhibitory substances like nimbicidin, nimbin or azadirachtin on the decomposition, effecting the population of pathogen. besides the nutrient content of these amendments may have a possible role in enhancing the host growth and vigour, increasing antagonistic microbial activity and enabling them to resist the attack of pathogen. i. bhagat / bibechana 11(1) (2014) 1 plate 1 (figures a-f): tomato plants following treatment with biocontrol agent and organic amendments. (a) untreated inoculated with (b & c) untreated healthy. (d) amended with cow dung manure. (e) amended with chicken manure. (f) amended with rabbit manure. acknowledgment the author is thankful to university grants commission (ugc), nepal for providing pursue the research. references [1] z. k. punja, annu. rev. phytopathol [1] b. bhagawati, b.k. goswami, c.s. singh, indian j. nematol [3] a. karthikeyan and karunanithi, pl. dis. res. [4] g. saravanan, s. nanda, s. sumitha, pl. dis. res. [5] s. ramarethinam, b. rajagopal, pestology [6] vbs nargund, kulkarn, r.k. hedge, curr. res. [7] r.g. linderman, can. j. pl pathol. [8] y. hadar, b. golodeeki, soil bio. [9] s.a. kulkarni, s. kulkarni, curr. res. / bibechana 11(1) (2014) 136-140: (online publication: march, 2014) p.1 tomato plants following treatment with biocontrol agent and organic amendments. (a) untreated inoculated with s. rolfsii. (b & c) untreated healthy. (d) amended with cow dung manure. (e) amended with chicken manure. (f) amended with rabbit manure. the author is thankful to university grants commission (ugc), nepal for providing necessary phytopathol., 23 (1985) 97. b. bhagawati, b.k. goswami, c.s. singh, indian j. nematol, 30 (2000) 16. [3] a. karthikeyan and karunanithi, pl. dis. res., 71 (1996) 180. [4] g. saravanan, s. nanda, s. sumitha, pl. dis. res., 18 (2004) 35. ramarethinam, b. rajagopal, pestology, 13 (1999) 21. [6] vbs nargund, kulkarn, r.k. hedge, curr. res., 13 (1984) 76. [7] r.g. linderman, can. j. pl pathol., 11 (1989) 180. hadar, b. golodeeki, soil bio. biochem., 23 (1991) 303. . kulkarni, curr. res., 24 (1995) 135. : (online publication: march, 2014) p.140 tomato plants following treatment with biocontrol agent and organic amendments. necessary support to 141-148 milan kharel r c o s t n m. kharel & d. thapa chhetry / bibechana 11(1) (2014) 141-148 (online publication: march, 2014) p.141 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana description on some rescued turtles and their translocation at turtle rescue and conservation centre (trcc), sanischare, jhapa milan kharel1* and damodar thapa chhetry2 1department of zoology, lord buddha college, biratnagar, nepal 2department of zoology, p.g. campus, tribhuvan university, biratnagar, nepal *corresponding author: e-mail: milankharel2000@yahoo.com accepted for publication: february 12, 2014 abstract the present paper deals with the brief introduction of turtle rescue and conservation centre (trcc) and description of some rescued turtles. nine specimens of turtles belonging to five genera were rescued and translocated to the centre till date including 9.3 kg male indian peacock soft-shelled turtle (nilssonia hurum) for the first time from jhapa district. the rescue operations were conducted for the translocation of turtles confiscated from the local market, censorial collectors, fisherman and public residence. the high resolution photographs of captured specimens, their necessary biometry and gps coordinates of location were taken. species identification was done with the help of and pictorial field guide and relevant literatures. climatic data of study area were recorded from gainde irrigation project, maidhar, jhapa. interviews were taken during field visits with the help of structured questionnaire. preliminary rescue data showed that the indian flap-shelled turtle (lissemys punctata) and yellow bellied roofed turtle (pangshura flaviventer) were the most overexploited species in the vicinities of the study area. the climatic condition of the rescue centre and water quality found suitable to support terrestrial and freshwater turtles and other various wetland flora and fauna. however, the rapid population growth and habitat destruction due to deforestation, unmanaged urbanization and expansion of agricultural land are found as the major threats to the survival of turtles and other wetland creatures at the study area and its vicinities. © 2014 rcost: all rights reserved. keywords: nilssonia hurum; lissemys punctata; freshwater turtle; budhoholi wetland; trcc. 1. introduction turtle rescue and conservation centre (trcc), is established for the first time in the eastern nepal having an ample motto of ‘saving turtles for future generations’. the centre is located in the vicinity of wetland cum sal dominated forest area formed by the old course of aduwa river called budho holi or bhimsen pokhari, within the premises of sukhani martyr’s memorial foundation (summef) at sanischare-6, salbari, jhapa district in south-east nepal. the area is about 0.235 sq km (22.4 ha) and geographically located between 88°00 ' 59.04" e to 26°40' 20.64" n at an altitude of 145 m from msl [1]. the centre has been established by the joint venture of amphibians and reptiles conservation nepal (arco-nepal) and sukhani martyr’s memorial foundation (summef) with the legal consent of government of nepal under the ministry of physical planning and construction. it was inaugurated jointly on 15th april 2012 by prof. dr. hermann schleich, chair of arco-nepal and mr. devraj ghimire, president of summef on the auspicious presence of government authority, national and international delegates, subject experts distinguish scholars, locals and media persons. the first author is going m. kharel & d. thapa chhetry / bibechana 11(1) (2014) 141-148 (online publication: march, 2014) p.142 figure 1: location map of study area (trcc), jhapa, nepal to keep the records of rescued turtle scientifically, which are trans-located from various places to the centre; study the physico-chemical parameters of the budhoholi lake and meteorological condition of study area. the study also helps to conclude whether the forest cum wetland site will be appropriate or not, for the development of turtle rescue and conservation centre. the detailed study will help to protect turtles by identifying the root problem of their depletion and their rehabilitation. the centre will have multiple functions as a centre for education and research, conservation-tourism activities related to freshwater and terrestrial turtles. in the future, the centre will serve as “living” laboratories for freshwater and terrestrial turtle and encourage young scientist to conduct research regarding biology of freshwater and terrestrial turtles and threats to their survival in order to develop and implement innovative methods in the conservation of turtles. 1.1 need for the study previous works revealed that the area was the suitable habitat for the various species of aquatic and terrestrial turtles. records show that most of the endangered species of turtles are captured by local fisherman and sensorial collectors. the captured species were found either consumed as food or sell at local market for flesh and medicinal use [3]. turtles have been used as food and in the preparation of traditional medicines since time immortal in nepal [6]. human impacts have affected the survival of turtles since prehistoric man has haunted them and gathered their eggs [4]. the burning poverty pressed the tribal ethnic group of jhapa district such as satar, mushar to involve in catching to substitute their meal. the carapace and plastron was fed to the cattle after grinding [2]. all turtles in nepal are threatened m. kharel & d. thapa chhetry / bibechana 11(1) (2014) 141-148 (online publication: march, 2014) p.143 by international trade, local use, making tourist articles and killed as pests on fishery farms [6]. such type of socio-ecological information is lacking in nepal which has prompted to conduct the present study. genera occurring east and west of nepal like geoclemys, morenia, hardella and the big growing species such as kachugas cannot be found any more in wild [5]. the realization of trcc will be dedicated to the restoration and rehabilitation of depleted wild populations of aquatic and terrestrial turtles in south-east nepal. therefore, a detailed scientific study on the socio-ecological impacts on the turtle felt urgently with appropriate management strategies for their conservation. 2. materials and methods the study is based on survey method. samples of flora and fauna collected were identified with the help of field guide and pictorial literatures. the meteorological data were collected from gainde irrigation project (meteorological centre), maidhar. interviews were conducted with local during field work to gather necessary information. the various turtles were rescued from different places. turtles were transported by vehicle carefully by keeping inside wet cotton sac. necessary biometry and gps coordinates of the place of reception of specimen were recorded. photographs were taken and the species were identified by the help of literatures and experts. table 1: summary of some rescued turtle: d = dorsum, v = venter s n species size (l-b) cm wt (gm) rescued at gps coordinates trans-ocated @ trcc on 1 lissemys punctata d 9.5-9.0 v 9.1-8.8 135 pg college, biratnagar n 26° 25' 43" e 87° 16' 8" 31/8/2012 2 lissemys punctata d 8.0-7.5 v 7.8-7.7 65 pg college, biratnagar n 26° 25' 43" e 87° 16' 8" 31/8/2012 3 lissemys punctata d 7.1-7.0 v 7.0-6.8 45 pg college, biratnagar n 26° 25' 43" e 87°16' 8" 31/8/2012 4 nilssonia hurum d 47.0-37.0 v 42.2-37.5 9300 dipeni river, damak n 26° 39' 43" e 87°41'36" 21/9/2012 5 pangshura flaviventer d 16.0-12.0 v 15.0-11.5 520 koshi barrage, bhantabari n 26° 37' 37" e 87° 01'55" 11/10/2012 7 lissemys punctata d 10.5-9.5 v 10.0-8.5 180 biratnagar-11, madhumara n 26° 27'55" e 87° 17'04" 30/11/2012 8 indotestudo elongata d 20.5-4.0 v 15.0-2.0 1004 bharatganj-6, bara n 27° 12'34" e 85° 13'20" 26/1/2013 9 melanochelys tricarinata d 15.0-11 v 13.0-9.0 530 bharatganj-6, bara n 27° 12'10" e 85° 13'25" 26/1/2013 10 lissemys punctata d 10.5-10 v 10.0-8.5 140 bargachhi biratnagar-4 n 26° 27' 35" e 87° 17'15" 3/9/2013 11 lissemys punctata d 13.5-13 v 12.5-10 290 bargachhi biratnagar-4 n 26° 27' 35" e 87° 17'15" 3/9/2013 l. punctata 64% m. kharel & d. thapa chhetry / bibechana 11(1) (2014) 1 3. results and discussion five species of turtles, of which three belongs to hard tricarinata and pangshura flaviventer and nilssonia hurum have been successfully rescued and translocated to the turtle rescue centre (table 1). of them, iucn has listed and nilssonia hurum as vulnerable species (table during august to november. table 2: status of rescued turtles turtle species recorded no. hard-shelled indotestudo elongata 1 melanochelys tricarinata 1 pangshura flaviventer 1 soft-shelled lissemys punctata 7 nilssonia hurum 1 figure 2: pie-chart showing percentages cover of turtles (species wise). table 3: month-wise records of rescued species (2013). species jan feb mar i. elongata + m. tricarinata + p. flaviventer l. punctata n. hurum i. elongata 9% m. tricraniata 9% p. flaviventer 9% l. punctata 64% n. hurum 9% / bibechana 11(1) (2014) 141-148 (online publication: march, 2014) p.1 five species of turtles, of which three belongs to hard-shelled viz. indotestudo elongata, melanochelys pangshura flaviventer while rest two species belong to soft-shelles viz. have been successfully rescued and translocated to the turtle rescue centre ). of them, iucn has listed indotestudo elongata as endangered and melanochelys tric as vulnerable species (table 2). most of the rescue operations were conducted recorded no. % cover iucn cites arco 9 endangered ii vulnerable 9 vulnerable i endangered 1 9 near threatened ii least concern 64 lower risk ii leastconcern 1 9 vulnerable i endangered chart showing percentages cover of turtles (species wise). wise records of rescued species (2013). mar apr may jun jul aug sep oct + + + + (online publication: march, 2014) p.144 indotestudo elongata, melanochelys shelles viz. lissemys punctata have been successfully rescued and translocated to the turtle rescue centre so far melanochelys tricarinata most of the rescue operations were conducted arco vulnerable endangered least concern leastconcern endangered chart showing percentages cover of turtles (species wise). oct nov dec + + m. kharel & d. thapa chhetry / bibechana 11(1) (2014) 141-148 (online publication: march, 2014) p.145 3.1. description and locality records of some of rescued species indotestudo elongata (blyth 1853) lat. testudo or testa: brick, earthen pot; elongates: elongated status: iucn: endangered, cites: ii, arco: vulnerable (hunted for masks) etymology: e. yellow-headed tortoise; n. bhuin /sun kachhuwa biometry: (l×b) cm: carapace 20.0 × 8.0; plastron: 15.0 × 6.0 weight: 1.4 kg location: bharatganj, bara gps coordinates: n 27° 12'34" / e 85° 13'20" rescued on: 26/1/2013; 1750 hrs (crawling to bank of dipeni river; caught by hand) resource person: om bk, local person identification key: upper jaw tricuspid with pointed tip which is bent downwards limbs: greenish grey to dark grey, with yellow scales; claws yellow to whitish carapace: carapace yellow to grayish or greenish yellow, even reddish brown plastron: large, truncate anteriorly, notched posteriorly egg size: 3 × 5cm incubation period: 135 days 3.1.1. melanochelys tricarinata (blyth, 1853) gr. melas: black; chelys: turtle; tria: three; carina:keel status: iucn: vulnerable, cites: i, arco: endangered etymology: e. three-keeled land tortoise; n. tin-pate pahadi kachhuwa/ thotari biometry: (l×b) cm: carapace 15.0 × 11.0; plastron: 13.0 × 9.0 weight: 530 gm location: bharatganj-6, bara gps coordinates: n 27° 12' 34"; e 85° 13' 20 " rescued on: 20/01/2013; 1830 hrs (caught by hand while hiding beneath wooden log) resource person: om b.k., bara identification key: three narrow keels, prominent due to their yellow coloration coloration: light brown, with yellowish to light brown keels and margin; carapace: convex with three prominent keels runs parallel to each other plastron: light yellow to orange, formula: abd > pect > an > gul> fem> hum. head: posterior part of the upper head is divided in to large shields forelimbs: with elongated or pointed scales, fingers are half webbed; tail short sexual dimorphism: male with concave plastron, large hind limbs, longer / thicker tail diet: crepuscular and omnivorous. nesting: clutch size 1-3 eggs. produce feb/apr,oct/dec hatches after 60-72 days. 3.1.2. pangshura flaviventer (gunther,1864) bengal.pangshura: turtle; lat.flavus: yellow; venter: belly status: iucn: near threatened, cites: ii, arco: least concern etymology: e. yellow-bellied roofed; n. pahelo bhunde dhuri kachhuwa biometry: (l×b) cm: carapace 16.0 × 12.0; plastron: 15.0 × 11.5 weight: 520 gm location: koshi barrage gps coordinates: n 26° 37' 37" ; e 87° 01' 55" rescued on: 11/10/2012; 1400 hrs (trapped by fisherman and kept for sell) resource person: prem narayan yadav identification key: 3rd vertebral plate carries a sharp projection. m. kharel & d. thapa chhetry / bibechana 11(1) (2014) 141-148 (online publication: march, 2014) p.146 coloration: carapace brownish; posterior head pale pink head: grey pigmentation is present around the eyes category: iucn: listed as synonym to p. tentoria; cites: listed as synonym to p. tecta arco-nepal listed as p. flaviventer as an independent own species 3.1.3. lissemys punctata (bonnaterre, 1789) gr.lissa: rage; lat. punctatus: dotted status: iucn: lower risk, cites: ii, arco: least concern etymology: e. indian flapshell turtle; n. dhakani khabate/ putali kachhuwa biometry: (l×b) cm: carapace 13.5 × 13.0; plastron: 12.5 × 10.0 weight: 290 gm location: bargachhi, biratnagar gps coordinates: n 26° 27' 35" ; e 87° 17' 15 " rescued on: 03/09/2013; 0900 hrs (trapped by lab boy and kept in aquarium) resource person: dhan bahadur identification key: carapace dotted with yellow. semicircular flaps on plastron coloration: olive green to dark brown with yellow dots; plastron white sexual dimorphism: tail comparatively longer with thicker base in male nesting: between end of august and mid september in sandy or sand loam soil. eggs: brittle-shelled, spherical, 24-30 mm in diameter clutch size: 2-14 eggs; incubation period 241-412 days diet: omnivorous, voracious, scavenger on animal corpses far from water bodies also takes tadpoles, fish, invertebrates and aquqtic plants. forelimbs: with 5 claws; hind limbs with 4 claws; tail ending in a horny nail. coloration: carapace olive green to dark brown with irregular yellow dots with a dark edge plastron white; head yellowish; limb greenish grey to dark grey. 3.1.4. nilssonia hurum (gray 1832) gr.aspis: shield; eretes: oarsman, rower status: iucn: vulnerable, cites: i, arco: endangered etymology: e. indian peacock soft-shell turtle ; n. mayurpankhi/ chartari kachhuwa biometry: (l×b) cm: carapace 47.0 × 37.0; plastron: 42.2 × 37.5 weight: 9.3 kg; sex: male location: dipeni river, damak, jhapa gps coordinates: n 26° 39' 43" ; e 87° 41' 36 " rescued on: 21/09/2012; 1750 hrs (crawling to bank of dipeni river; caught by hand) resource person: reported by m. kharel for the first time from jhapa district identification key: large aquatic turtle with a snout; juveniles have 4-6 distinct eyes spots on carapace coloration: head with dark green or black lines, with yellow spots. carapace: olive green with black reticulation, normally with 4 spots (5 /6 occasionally) plastron: brownish grey, pales with age. nesting: august-december in clay-sandy soil. egg: spherical, hardshelled, about 30 mm in diameter, 20-30 eggs per clutch sexual dimorphism: male poses comparatively longer and thicker tails than female 0 5 10 15 20 25 30 j f m a m j j a s o n d ave. rainfall (mm) 6 7 8 9 s1 s2 s3 s4 s5 do ( winkler’s method)ave. do (mg/l) sampling stations m. kharel & d. thapa chhetry / bibechana 11(1) (2014) 141-148 (online publication: march, 2014) p.147 male female 3.2. meteorological data during study some of the climatic parameters such as dissolved oxygen of main lake, temperature of water and average rainfall records, it was found that he following climatic factors of the study area were favorable to support their growth and conservation. average do: 7.4* (±0.301) mg/l (max. jan) ave. water temp: 21* (±0.283)˚c ave. rainfall: 6.25*mm (max:25mm) * considered sufficient enough to support aquatic life figure 3: average rainfall recorded in the study area (2013). figure 4: average dissolved oxygen in study area. m. kharel & d. thapa chhetry / bibechana 11(1) (2014) 1 figure 5: average water temperature of study area (month wise). 4. conclusion climatic data shows the average annual temperature and average rainfall pattern of jhapa district is suitable to support the flora and fauna of tropical climatic zone. it could be one of the hotspot for the conservation of turtles. during, preliminary stud translocated in the trcc. a male of district. during field visit, two species punctata (for food and traditional medicine) were found overexploited by local fisherman specially from koshi barrage area. however, the population growth rate is quite high and habitats of wildlife have been decreasing day by day. it indicated the urgent need of p fauna in the study area. largest rescued species: frequently rescued species: rare rescued species: popular pet trade species: most easily captured species: popular area for turtle trade: acknowledgments thanks are due to prof. dr. kalu ram rai ‘khambu’, hod campus, bhadrapur, (t.u.), nepal during field trip and supply of useful literatures. we are grateful to the sukhani martyr’s memorial foundation (summef) for granting my research in the premises of the park area. the first author is grateful to founder of arco-nepal, prof. dr. h. hermann schleich, university of munich (germany) for providing financial assistance to conduct this study. references [1] ddc, district profile, district development committee, jhapa, 2002. [2] m. kharel, general survey of anthropogenic impacts on chelonian fauna in the kankai (mai) river and its vicinities, jhapa, east nepal, m. sc. thesis submitted to department of zoology post-graduate campus, t.u., biratnagar, 2011. [3] k.r. rai, environmental impact systematics and distribution of herpetofauna from east nepal, ph.d. thesis submitted to the central department of zoology, t.u., kritipur, kathmandu, 2003. [4] h.h. schleich, the turtles of nepal, a children coloring book, pub. fuhlrott-museum, 2004. [5] h.h schleich, k. ernst, t.m. maskey and realities (ed. r.b. thapa [6] k.b. shah, j. nat. hist. mus. 13 (2004) 19. 19 20 21 22 23 jan feb mar t e m p . ˚ c / bibechana 11(1) (2014) 141-148 (online publication: march, 2014) p.1 average water temperature of study area (month wise). climatic data shows the average annual temperature and average rainfall pattern of jhapa district is suitable to support the flora and fauna of tropical climatic zone. it could be one of the hotspot for the conservation of turtles. during, preliminary study, five species of turtles have been rescued and translocated in the trcc. a male of nilssonia hurum (9.3kg) reported for the first time from jhapa district. during field visit, two species pangshura flaviventer (as pet and ornament) and (for food and traditional medicine) were found overexploited by local fisherman specially from koshi barrage area. however, the population growth rate is quite high and habitats of wildlife have been decreasing day by day. it indicated the urgent need of protection of turtle and other endangered flora and nilssonia hurum (9.3 kg) lissemys punctata (64%) melanochelys tricarinata pangshura flaviventer indotestudo elongata koshi barrage area thanks are due to prof. dr. kalu ram rai ‘khambu’, hod (department of zoology , (t.u.), nepal for giving us continuous guidance, inspiration, personal assistance during field trip and supply of useful literatures. we are grateful to the sukhani martyr’s memorial ting my research in the premises of the park area. the first author is nepal, prof. dr. h. hermann schleich, university of munich (germany) for providing financial assistance to conduct this study. profile, district development committee, jhapa, 2002. [2] m. kharel, general survey of anthropogenic impacts on chelonian fauna in the kankai (mai) river and its vicinities, jhapa, east nepal, m. sc. thesis submitted to department of zoology graduate campus, t.u., biratnagar, 2011. [3] k.r. rai, environmental impact systematics and distribution of herpetofauna from east nepal, ph.d. thesis submitted to the central department of zoology, t.u., kritipur, kathmandu, 2003. , the turtles of nepal, a children coloring book, pub. arco nepal reg. soc. maskey, urgent call for turtle conservation in nepal, in nepal myths & j. baaden), 1998. , j. nat. hist. mus. 13 (2004) 19. mar apr may june july aug sep oct nov dec month (2013) (online publication: march, 2014) p.148 climatic data shows the average annual temperature and average rainfall pattern of jhapa district is suitable to support the flora and fauna of tropical climatic zone. it could be one of the hotspot for the y, five species of turtles have been rescued and (9.3kg) reported for the first time from jhapa (as pet and ornament) and lissemys (for food and traditional medicine) were found overexploited by local fisherman specially from koshi barrage area. however, the population growth rate is quite high and habitats of wildlife have been rotection of turtle and other endangered flora and zoology), mechi multiple continuous guidance, inspiration, personal assistance during field trip and supply of useful literatures. we are grateful to the sukhani martyr’s memorial ting my research in the premises of the park area. the first author is nepal, prof. dr. h. hermann schleich, university of munich (germany) for [2] m. kharel, general survey of anthropogenic impacts on chelonian fauna in the kankai (mai) river and its vicinities, jhapa, east nepal, m. sc. thesis submitted to department of zoology, [3] k.r. rai, environmental impact systematics and distribution of herpetofauna from east nepal, ph.d. thesis submitted to the central department of zoology, t.u., kritipur, kathmandu, 2003. arco nepal reg. soc. urgent call for turtle conservation in nepal, in nepal myths 40-45 ajaya bhattaraijay n. mitruka r c o s t n a. bhattarai et al. / bibechana 11(1) (2014) 40-45: (online publication: march, 2014) p.40 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana uv-vis investigation of (ctc/orthodox/green) tea in presence of brij 35/water system ajaya bhattarai1*, jay narayan mitruka2, subas kumar chapagain2, prem kumar shrestha2 1department of chemistry, m.m.a.m. campus, tribhuvan university, biratnagar, nepal 2department of chemistry, mechi multiple campus, tribhuvan university, bhadrapur, nepal *corresponding author: bkajaya@yahoo.com accepted for publication: february 04, 2014 abstract the precise measurements of (ctc/orthodox/green) tea absorbance in presence of brij 35/water system at room temperature by uv-vis technique are reported. the concentrations of brij 35 [polyoxyethylene lauryl ether] were varied from 0.01 to 0.02 mol/lt. tea concentration in quvette during uv-vis spectrum registration was the same. obtained results showed a noticeable decreasing of tea absorbance as a function of brij 35 concentration. there is evidence of tea absorbance in the following order: orthodox > ctc >green. © 2014 rcost: all rights reserved. keywords: ctc tea; orthodox tea; green tea; brij 35; water; uv-vis. 1. introduction nonionic surfactants are surface-active compounds that are non-ionizable in aqueous solutions that consist of a lipophilic part (e.g., alkylated phenols, fatty acids, long-chain linear alcohols) and a hydrophilic part (primarily ethylene oxide chains of various lengths). these compounds are second in worldwide surfactant consumption, comprising 35 % of the total surfactant market. the most interesting, commercially-available nonionic surfactants are ethoxylated nonionic surfactants (eons). the analytical grade eons are octylphenol decaethylene glycol ether(triton x-100) and polyethylene glycol(23)lauryl ether (brij 35) [1]. brij 35 is also called polyoxyethylene lauryl ether is one of the nonionic surfactants widely used both in biochemical and chemical processes for its virtues such as high stability, well-dissolved, and easily mixing with other typical surfactants for a mixed use [2]. studies indicate that brij 35 [3] acts as a surfactant in micellar electrokinetic chromatography (mekc). it is known that brij 35 [4] is also beneficial in uv monitoring of solubilized proteins due to their low uv absorbance. this compound is useful in slowing down electro osmotic pumping, which allows users to change ph values without drastically altering the flow rate. the critical micelle concentration of brij 35 in water is 0.0001 mol/lt at room temperature where as in d20 is 0.00011 ± 0.00002 mol/lt [5] and structural formula of brij 35 is given in fig. 1. after water, tea is the most widely consumed beverage in the world [6]. it has a cooling, slightly bitter, and astringent flavour that many people enjoy [7]. tea originated in china as a medicinal drink [8]. two types of tea are manufactured in the factory: orthodox and ctc. a. bhattarai et al. / bibechana 11(1) (2014) 40-45: (online publication: march, 2014) p.41 figure 1: structural formula for brij 35. orthodox tea refers to the process, where the tea is hand-processed or by rolling it in the machines. in nepal, orthodox tea is produced and processed in the mountainous regions of nepal at an altitude ranging from 3,000 – 7,000 feet above the sea level. there are six major districts, primarily in the eastern regions of nepal that are known for producing quality orthodox tea, which are ilam, panchthar, dhankuta, terhathum, sindhulpalchok and kaski. crush tear curl (ctc) tea is a method of processing tea, where three main steps are involved crush, tear and curl, hence the name ctc tea. ctc tea is produced in lower altitudes in the fertile plains of nepal, which are warm and humid, primarily in the jhapa district, which is ideal for the production and processing of ctc tea. the handmade tea or green tea is prepared by drying green tea leaves and crushing with the help of hands. it is especially found in darjeeling, india. recent studies suggest that green tea may help reduce the risk of cardiovascular disease and some forms of cancer, promote oral health, reduce blood pressure, help with weight control, improve antibacterial and antivirasic activity, provide protection from solar ultraviolet light [ 9]. our research is focused on the surfactant and tea interaction. uv-vis technique is very useful technique to see the effects of tea on surfactant. there is lack of information about tea / brij 35/water systems. the aim of the present work is to analyze the influence of concentrations to brij 35 by uv-vis method at room temperature with (ctc/orthodox/green) tea in water. 2. experimental section brij 35 was from sigma-aldrich steinheim, germany, and was dried under vacuum at 25oc, ctc tea was from jhapa, nepal, orthodox tea was from ilam, nepal and green tea was from darjeeling, india. the investigated solutions were prepared gravimetrically at room temperature by dissolving 500 mg each tea in 20 ml of doubled distilled water and used after 5 days for the experiments. brij 35 solution with concentration 0.02 mol/ lt was used as stock solution. uv-vis measurements were realized with the following procedure. before each measurement base line was registered for suitable brij 35/ water and afterwards a tea solution in the same solvent was added. after adding tea solution to the brij 35 once the whole liquid volume was stirred very carefully. the absorption band was registered as a function of brij 35 concentration. we also investigated the absorbance change of (ctc/orthodox/green)tea with water on double beam uv-vis spectrophotometer (lt-2900 model), india. 3. results and discussion 3.1. absorption spectra of orthodox tea / ctc tea / green tea the absorption spectra of orthodox tea show the highest absorbance value in comparison with ctc tea and green tea. the absorbance value is higher in ctc tea than green tea below 500nm but after that it was found the higher value of absorbance of green tea in comparison with ctc tea. the absorption spectra were shown up to 600nm (fig.2). a. bhattarai et al. / bibechana 11(1) (2014) 40-45: (online publication: march, 2014) p.42 figure 2: absorption spectra for orthodox tea in water (top graph), ctc tea (middle graph) and green tea (bottom graph). 3.2. absorption spectra of orthodox tea / ctc tea / green tea in presence of brij 35 the absorption spectra of orthodox tea, ctc tea and green tea in presence of brij 35 show the absorbance value within the range of 300nm to 600nm(fig.3). the absorbance value of brij 35 is the highest in orthodox tea, and then lower in ctc tea and the lowest in green tea. moreover, depending on brij 35, a small shift of the maxima into a longer wave length (red shift) has been noticed in the following order: green tea>ctc tea >orthodox tea. 3.3. absorbance of green tea in absence and presence of brij 35 the absorption band of green tea observed to be the highest in absence of brij 35 and then the absorption band decreases with the presence of brij 35 and further decreases when the concentration of brij 35 increases (fig.4). 3.4. absorbance of ctc tea in absence and presence of brij 35 the absorption band of ctc tea observed to be the highest in absence of brij 35 and then the absorption band decreases with the presence of brij 35 and further decreases when the concentration of brij 35 increases (fig.5). 3.5. absorbance of orthodex tea in absence and presence of brij 35 the absorption band of orthodex tea observed to be the highest in absence of brij 35 and then the absorption band decreases with the presence of brij 35 and further decreases when the concentration of brij 35 increases (fig.6). our investigations were supported by β–carotene absorbance in presence of aot/solvent/water systems at 25oc by uv-vis technique [10] in which the solvents selected were: n-heptane, cyclohexane, and tetrahydrofuran and the concentrations of aot [aerosol-ot (sodium bis(2-ethylhexyl) sulfosuccinate)] were varied from 0.01 to 0.2 mol/kg. 0 2 4 6 8 10 400 500 600 green tea in water orthodox in water ctc tea in water λ[nm] a bs or ba nc e a. bhattarai et al. / bibechana 11(1) (2014) 40-45: (online publication: march, 2014) p.43 figure 3: absorption spectra for 250 micro litre of orthodox tea in 3ml stock brij 35 (top graph), 250 micro litre of ctc tea in 3ml stock brij 35 (middle graph) and 250 micro litre of green tea in 3ml stock brij 35 (bottom graph). figure 4: absorption spectra for 250 micro litre of green tea in 3ml stock brij 35 (top graph), and different concentrations of brij 35 solution in water with 250 micro litre of green tea. 0 0.5 1.0 1.5 2.0 300 400 500 600 λ[nm] a bs or ba nc e 0 1 2 3 4 300 400 500 600 250 microlitre green tea + 2500micro liter stock brij 35+ 500 micro liter water 250 microlitre green tea + 500micro liter stock brij 35+ 2500 micro liter water 250 microlitre green tea + 2000micro liter stock brij 35+ 1000 micro liter water 250 microlitre green tea + 300micro liter stock brij 35+ 2700 micro liter water 250 microlitre green tea + 3ml water λ[nm] a bs or ba nc e a. bhattarai et al. / bibechana 11(1) (2014) 40-45: (online publication: march, 2014) p.44 figure 5: absorption spectra for 250 micro litre of ctc tea in 3ml stock brij 35 (top graph), and different concentrations of brij 35 solution in water with 250 micro litre of ctc tea. figure 6: absorption spectra for 250 micro litre of orthodox tea in 3ml stock brij 35 (top graph), and different concentrations of brij 35 solution in water with 250 micro litre of orthodox tea. 0 1 2 3 4 300 400 500 600 700 250 microlitre ctc tea + 2500micro liter stock brij 35+ 500 micro liter water 250 microlitre ctc tea + 2000micro liter stock brij 35+ 1000 micro liter water 250 microlitre ctc tea + 1000micro liter stock brij 35+ 2000 micro liter water 250 microlitre ctc tea + 300micro liter stock brij 35+ 2700 micro liter water 250 microlitre ctc tea + 500 micro liter stock brij 35+ 2500 micro liter water 250 microlitre ctc tea + 100micro liter stock brij 35+ 2900 micro liter water 250 microlitre ctc tea + 3ml water λ[nm] a bs or ba nc e 0 1 2 3 300 400 500 600 250 microlitre orthodox tea + 1000micro liter stock brij 35+ 2000 micro liter water 250 microlitre orthodox tea + 200micro liter stock brij 35+ 2800 micro liter water 250 microlitre orthodox tea + 100micro liter stock brij 35+ 2900 micro liter water 250 microlitre orthodox tea + 3ml water λ[nm] a bs or ba nc e a. bhattarai et al. / bibechana 11(1) (2014) 40-45: (online publication: march, 2014) p.45 4. conclusion experimental results for the uv-vis measurement of (ctc/orthodox/green) tea in presence of brij 35/ water at room temperature have been presented as a function of brij 35 concentration and wave lengths. it was found the highest absorbance was observed for orthodox tea, lower for ctc tea and the lowest for green tea. the highest absorbance was noted for orthodox tea in water with brij 35 concentration in comparison to ctc tea and green tea. in all investigated systems, the intensity of (ctc/orthodox/green) tea absorption bands decreases with brij 35 concentration increasing. this behaviour suggests that (ctc/orthodox/green) tea molecules dipper penetrate into brij 35. acknowledgments the authors are thankful to the campus chief of mechi multiple campus, tribhuvan university, bhadrapur, nepal for providing us the research facilities to conduct this research work. references [1] d. m. cacic, m. s. bosnar, int. j. electrochem. sci., 6 (2011) 1630. [2] l. cheng, handbook of surfactant application, beijing: beijing polytechnic university press, 1994. [3] n. arnaud, j.georges, spectrochim acta a mol. biomol. spectrosc., 57a (2001) 1085. [4] m. rukhadze , d. dzidziguri, n. giorgobiani, s. kerkenjia, biomed chromatogr., 25 (2011) 1364. [5] c. d. tran, s. yu, j. colloid interface sci., 283 (2005) 613. [6] a. macfarlane, i. macfarlane, the empire of tea, the overlook press, 2004. [7] p. ody, complete guide to medicinal herbs. new york, ny: dorling kindersley publishing, 2000. [8] m. l. heiss, r. j. heiss, the story of tea: a cultural history and drinking guide. random house, 2011. [9] u. heinrich, c. e. moore, s. d. spirt, h. tronnier, w. stahl, j. nutr., 141 (2011) 1202. [10] a. bhattarai, h. wilczura-wachnik, j. applied sol. chem. & model., 2 (2013) 253. 53-59 bhim p. kafle r c o s t n b.p. kafle et al. / bibechana 11(1) (2014) 53-59: (online publication: march, 2014) p.53 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana fabrication of dye-sensitized solar cells from thin films of zinc oxide nanocrystalline particles and organic dye bhim p. kafle1*, babu r. pokhrel2, rajendra gyawali1, prakash lamichhane1, ravi m. adhikari3 1kathmandu university, dhulikhel, kavre, nepal 2patan multiple campus, tribhuvan university, kathmandu, nepal 3angstrom technologies, kentuki, usa *corresponding author: email: bhimkafle@gmail.com accepted for publication: february 8, 2014 abstract photovoltaic solar modules, which are mostly made of silicon based solar cells, are still expensive to the common people of nepal. the high cost is, mainly, due to the processing difficulties to get pure crystalline silicon. here, we present results on devising efficient and low-cost dye sensitized solar cells (dsscs). the solar cells were fabricated from transparent thin film of zinc oxide (zno), as a semiconductor, on top of which a thin layer of synthetic organic dye was deposited for efficient light harvesting. in order to achieve the films with optimum conditions for solar cell fabrication, we prepared transparent thin films of zno of various thicknesses and characterized by measuring their light transmittance by uv-visible spectrophotometry. the results clearly show variation in transmittance curves with variation in film’s thickness. also for finding appropriate sensitizer for zno nanoparticles, we extensively investigated the light absorbance of synthetic organic dyes. among the dye species investigated, green-vs, patent-blue, and black-adli show strong absorbance over the wide range in the visible spectrum, demonstrating prospect of utilizing for dsscs. then prototype solar cells from zno film with various thicknesses were constructed and were sensitized with the mixture of green-vs and black-adli dyes (with 1:1 ratio). the measured photo-voltage and photo-current from solar cell, from our modest zno film, after irradiation with 200 w commercial bulb (calibrated with pyranometer) as a light source, were about 20 mv and 1 µa, respectively. also, with increment of the power of radiation both the measured photo-current and photo-voltage increase. performance of the cell in real sun condition has also been made. with the solar radiation power of 930 w, the observed photo-voltage and photo-current were ca. 230 mv and 50 µa, respectively. © 2014 rcost: all rights reserved. keywords: absorbance; dye; maharanga bicolor; green vs; patent blue; black adli; solar cell. 1. introduction solar energy is considered to be one of the most promising solutions to meet energy demand and environmental challenge as a carbon-neutral energy source in both developed and developing countries. photovoltaic (pv) electric power generation is a technology for generating renewable energy from solar irradiation. due to difficult geographical features (high hills and mountains) of nepal, which create hurdles to extend national electrical grid to remote areas, pv technology is even more important than other countries. b.p. kafle et al. / bibechana 11(1) (2014) recently published report of nepal government reveals that electricity has reached to only 67% of the households for fulfilling their lighting needs. still 18% rely on kerosene lamps while around 7% depend on solar energy technology for lighting [1]. although the later data (use of solar energy) is quite encouraging, the use of the current pv technology is still very expensive to th and is unaffordable unless government provides heavy subsidies for purchasing them. therefore, for efficient harnessing of solar energy at low cost, modification in the present technology must be made. in this connection, current pv devices (solar cells) in market, mostly, are made of crystalline silicon and amorphous silicon. however, because of the considerably high material costs and long energy payback time, effort has been made to find alternative materials such as compound se gallium arsenide (gaas) [2,3], copper indium gallium selenide [4,5] and thin film based solar cells [6 8]). but, for practical use, they still require major breakthroughs to meet the long term goal of very cost and short payback time so that the technology can be affordable to people of developing countries like nepal for its adoption. also long term stability is another problem of solar cells of the later type. the thin film based dye sensitized solar cells (dsscs) are made of metallorganic complex dye (as a sensitizer), liquid electrolyte (medium for charge transfer from elctrode to dye), and two transparent conducting pieces of glass, contacting the particle film and the electrolyte. a thin layer (thickness in the range of hundreds of nanometer to micrometer) of metal oxide is coated on top of conducting glass and on top of zno layer another layer of dye is deposited. then the counter electrode and dye layer are contacted with liquid electrolyte. this electrolyte interface needed for cell operation. operating principle of dssc cell can be understood as: when photons (from sunlight) hit the photosensitive dye layer, the freed electrons accumulate on the layer of compound semiconductor (titanium dioxide or zinc oxide) and create an electrical a liquid electrolyte such as tri-odide anion (i the schematic view of this type of solar cell is the overall process after irradiation with light of energy (h as: here, dye* represents excited dye molecule. the nanoparticle dssc has already a comparable efficiency (meaning that 12 percent of the captured solar energy is converted to electrical energy) to traditional solid state solar cells and is inexpensive to manufacture. however, one of the measure problems of the dsscs is still low solar to light conversion efficiency. also, of their long term stability is another pro however, very recently, yella et al. redox electrolyte in combination with the donor o-c8) as a sensitizer performed well. improvement in efficiency above 12 % with photo / bibechana 11(1) (2014) 53-59: (online publication: march, 2014) p. recently published report of nepal government reveals that electricity has reached to only 67% of the heir lighting needs. still 18% rely on kerosene lamps while around 7% depend on solar energy technology for lighting [1]. although the later data (use of solar energy) is quite encouraging, the use of the current pv technology is still very expensive to the common people of nepal and is unaffordable unless government provides heavy subsidies for purchasing them. therefore, for efficient harnessing of solar energy at low cost, modification in the present technology must be made. pv devices (solar cells) in market, mostly, are made of crystalline silicon and amorphous silicon. however, because of the considerably high material costs and long energy payback time, effort has been made to find alternative materials such as compound semiconductor (for e.g. gallium arsenide (gaas) [2,3], copper indium gallium selenide [4,5] and thin film based solar cells [6 8]). but, for practical use, they still require major breakthroughs to meet the long term goal of very ime so that the technology can be affordable to people of developing countries like nepal for its adoption. also long term stability is another problem of solar cells of the later type. the thin film based dye sensitized solar cells (dsscs) are made of oxide semiconductors and metallorganic complex dye (as a sensitizer), liquid electrolyte (medium for charge transfer from elctrode to dye), and two transparent conducting pieces of glass, contacting the particle film and the electrolyte. a kness in the range of hundreds of nanometer to micrometer) of metal oxide is coated on top of conducting glass and on top of zno layer another layer of dye is deposited. then the counter electrode and dye layer are contacted with liquid electrolyte. this arrangement creates the large particle electrolyte interface needed for cell operation. operating principle of dssc cell can be understood when photons (from sunlight) hit the photosensitive dye layer, the freed electrons accumulate on the compound semiconductor (titanium dioxide or zinc oxide) and create an electrical odide anion (i3 -) carries the electrons from counter electrode to dye layer. the schematic view of this type of solar cell is given in fig. (1). the overall process after irradiation with light of energy (hν), h being planck constant, can be represented represents excited dye molecule. figure (1): schematic view of dye sensit cell. white spheres indicate while black spheres denote dye molecules. the nanoparticle dssc has already a comparable efficiency (meaning that 12 percent of the captured converted to electrical energy) to traditional solid state solar cells and is inexpensive to manufacture. however, one of the measure problems of the dsscs is still low solar to light conversion efficiency. also, of their long term stability is another problem. et al. [8] reported that solar cells fabricated utilizing cobalt (ii/iii) redox electrolyte in combination with the donor-bridge-acceptor zinc porphyrin dye (designated as yd2 c8) as a sensitizer performed well. specifically, solar cells with the later combination showed improvement in efficiency above 12 % with photo-voltage of ~ 1v. the reason of the better performance : (online publication: march, 2014) p.54 recently published report of nepal government reveals that electricity has reached to only 67% of the heir lighting needs. still 18% rely on kerosene lamps while around 7% depend on solar energy technology for lighting [1]. although the later data (use of solar energy) is quite e common people of nepal and is unaffordable unless government provides heavy subsidies for purchasing them. therefore, for efficient harnessing of solar energy at low cost, modification in the present technology must be made. pv devices (solar cells) in market, mostly, are made of crystalline silicon and amorphous silicon. however, because of the considerably high material costs and long energy payback miconductor (for e.g. gallium arsenide (gaas) [2,3], copper indium gallium selenide [4,5] and thin film based solar cells [68]). but, for practical use, they still require major breakthroughs to meet the long term goal of very-low ime so that the technology can be affordable to people of developing countries like nepal for its adoption. also long term stability is another problem of solar cells of the later type. oxide semiconductors and metallorganic complex dye (as a sensitizer), liquid electrolyte (medium for charge transfer from elctrode to dye), and two transparent conducting pieces of glass, contacting the particle film and the electrolyte. a kness in the range of hundreds of nanometer to micrometer) of metal oxide is coated on top of conducting glass and on top of zno layer another layer of dye is deposited. then the counter electrode arrangement creates the large particle-dyeelectrolyte interface needed for cell operation. operating principle of dssc cell can be understood when photons (from sunlight) hit the photosensitive dye layer, the freed electrons accumulate on the compound semiconductor (titanium dioxide or zinc oxide) and create an electrical current. also ) carries the electrons from counter electrode to dye layer. ), h being planck constant, can be represented schematic view of dye sensitized solar zno nanoparticles, while black spheres denote dye molecules. the nanoparticle dssc has already a comparable efficiency (meaning that 12 percent of the captured converted to electrical energy) to traditional solid state solar cells and is inexpensive to manufacture. however, one of the measure problems of the dsscs is still low solar to light conversion [8] reported that solar cells fabricated utilizing cobalt (ii/iii)-based acceptor zinc porphyrin dye (designated as yd2specifically, solar cells with the later combination showed voltage of ~ 1v. the reason of the better performance b.p. kafle et al. / bibechana 11(1) (2014) 53-59: (online publication: march, 2014) p.55 was explained as the use of yd2-o-c8 dye, which greatly retards recombination (the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide (tio2) film to the oxidized cobalt mediator. for the most part tio2 has been the material of choice for dye-sensitized solar cells and so far have shown to exhibit the highest overall light conversion efficiency of 12% (above example). however, zno has also been recently explored as an alternative material, because of its low-cost, having similar bandgap to tio2 and much higher electron mobility than tio2. nevertheless, the highest overall light conversion efficiency obtained so far for zno is only ~ 5-7% depending on the nature of zno composition and dye used for its (zno film) sensitization [9]. here, we report on progress in the direction of producing an efficient and low-cost dye sensitized solar cells (dsscs) from zno thin film as a semiconductor. for cell construction, thin layer of organic dye was deposited on top of zno film. iodine-based redox system was utilized as an electrolyte for efficient charge transfer between counter electrode (cathode) and dye. as quality of zno film (geometry and surface morphology) of the film greatly affect the photovoltaic properties of the cell, optimization of the films is discussed. also, to tackle with efficiency reduction due to charge recombination [9], we have extensively searched natural organic dyes which demonstrate better light absorption coefficient and presented. finally, the performance of our proto-type solar cells in the laboratory conditions is presented. 2. detailed methodology for constructing solar cell with better performance, optimization of prepared zno thin films in terms of size (thickness and surface area) and surface morphology is required. also, identification of a suitable sensitizer with a high molar extinction coefficient in visible region, for improving incident photon to current production, is another necessary condition for efficient solar cell. and, finally, assembling of all the components systematically for fabrication of proto-type dye sensitized solar cell and its characterization with proper care is another important task. below we discuss methods to accomplish all of the above mentioned tasks in five steps. (a) preparation and characterization of zno thin film on conducting glass substrate preparation of transparent thin films of zno performed by depositing the zno precursor solution on conducting glass substrates (~2.5 ×2.5×0.25 cm) by a spray pyrolysis method and details of which is given somewhere else [10,11]. briefly, the setup consists of a cylindrical nebulizer mounted vertically on a horizontal table to spray the aerosol jet aimed upwards at a substrate through a 0.9 mm nozzle. the substrate is mounted on a temperature controlled heating block 25 mm above the nozzle. humid air at atmospheric pressure is used as a carrier gas at a 2-3 ml/h flow rate. the precursor solution consists of 0.2 m acetate dissolved in distilled water and ethanol (at ratio of 1:3). spraying times has been variable to control the thicknesses of the film. alternatively, thicker films can be obtained in shorter times by increasing the concentration of the solution. after deposition, sample is annealed in a standard furnace 450°c for 1h in oxygen. during the time of deposition the substrate temperature was maintained around 425±25. the substrate temperature has been measured by ir thermometer (spectral response 6214 mm) available in our laboratory. transmission measurements have been performed on films supported by glass substrate using genesis-10 uv spectrophotometer (thermo scientific, uk, available in our department) in the wavelength range from 310 to1100 nm. (b) investigation of dye for photo-sensitizer methods for characterization of dye samples have been discussed in our previous article [12]. in brief, the synthetic dye samples were purchased from hindustan ciba geigy ltd. absorbance of the dye was measured on genesis-10 uv-visible spectrophotometer in the wavelength of 310 to 900 nm. b.p. kafle et al. / bibechana 11(1) (2014) 53-59: (online publication: march, 2014) p.56 (c) coating of zno film with dye coating of zno thin film with dye is done by adsorption method for several minutes to 48 hours depending on the dye adsorption on the thin film. here, to tackle the problem of efficiency reduction due to charge recombination we adopted following strategy: we have extensively searched natural organic dye which showed better light absorption coefficient, demonstrated reduced recombination, and higher stability, when compared with zinc porphyrin dye (standard dye). utilizing the dye with above properties, we fabricated solar cells, a foremost component of the pv system. with this configuration, we expect to improve the cell's efficiency and other photovoltaic properties. (d) fabrication of solar cell the solar cell was constructed by sandwitching two electrodes; anode (conducting glass electrode with thin layers of zno nanoparticles and dye molecules) and cathode (counter electrode). then both of the electrodes were then squeezed together, using a spring type clamp. the electrolyte, ki / i2 was attracted into the cavities of the zno electrode by capillary forces. (e) characterization of solar cells measurement of the photocurrent versus photo-voltage (i-v) of the constructed solar cells was carried out in our laboratory condition at ku using multimeter. the light intensity of the radiation was measured by a pyranometer (pma2144). 3. results and discussion (a) thickness dependence transmittance of zno films films of various thicknesses of zno were deposited on conducting glass (fluoride doped glass substrate) purchased from merk, germany. fig. (2) shows precursor solution deposition time dependence of transmittance of zno thin films as a function of radiation wavelength. in other words, the figure resembles thickness dependence of transmittance of transparent films. the concentration of the precursor solution, zinc acetate, was 0.2 m. one can notice clearly that transmittance decreases gradually with the increment of deposition time, as expected, yielding only around 65 % transmittance at the first peak position of spectrum from left for film obtained by our thickest film (20 minutes deposition time). the presence of noticeable oscillations in the transmittance versus wavelength spectra indicates that the films are of good quality. (b) absorbance of naturaland synthetic dyes: prospect of application in dsscs for our solar cell, we attempted to utilize organic synthetic dye. characterization of their optical properties has been discussed in our previous article [12]. in brief, among all the samples, the greenvs and patentblue exhibited superior absorbance in the visible region (around 550 nm to 700 nm). interestingly, both dyes behaved similarly in this region and showed maximum absorbance at 650 nm with a fwhm around 60 nm. on the other hand, blackadli showed fairly good absorbance in wide region extending from uv to visible region of electromagnetic figure 2: precursor solution deposition time dependence of transmittance of light as a function of radiation wavelength. (note the decreasing trend of transmittance in the rising edge region of the curves with increasing in thickness of the films.) b.p. kafle et al. / bibechana 11(1) (2014) 53-59: (online publication: march, 2014) p.57 spectrum (300 nm to 700 nm), with two major peaks at around 310 and 575 nm. indeed, the blackadli is demonstrates even better absorbance than ruthenum dye complex, z917, which have been common dye for dsscs due to its remarkable absorbance in the visible region. (c) fabrication and characterization of proto-type solar cell figure 3: side view (left) and top view of our proto-type dye sensitized solar cell hold by clamps at the ends. both the electrodes of the cell shown at right are connected to multimeter for current and voltage measurements. prototype solar cells from zno film with various thicknesses were constructed. left panel of fig. 3 shows an image of one of the ptoto-type solar cells constructed in our laboratory. both the anode (top) and cathode (buttom) electrodes of the cell are connected with multimeter for current and voltage measurements. anode was constructed by depositing zno nanoparticles on the fto coated conducting glass substrate, utilizing optimized conditions for zno films on quartz substrate (see fig.1). then on top of zno layer a thin layer of organic dye was deposited (for this, zno films were soaked in dye solution for 46 hours). the mixture of green-vs and black-adli dyes (with 1:1 ratio) was used as a sensitizer. then the performance of the cell was tested by measuring photo-voltage and photo-current, after irradiation with light source of various powers in the laboratory. as an example, the measured photovoltage and photo-current obtained from solar cell with intermediate thickness of zno film (40 minutes spray time of zno precursor solution) after irradiation with 200 w commercial bulb as a light source yielded photo-voltage of ca. 20 mv and current of 0.7 µa, respectively. the values of current and voltage obtained from our systematic measurement with various powers from light source are displayed in table (1) and also fig. (4). note that with increment of the power both the measured photo-current and photo-voltage increase and show linear relationship. table (1): measured photo-current and photo-voltage at various radiation powers. the commercial bulbs were used as a light souce, calibrated with the help of pyranometer (pma2144). power (watt) voltage (mv) current ( µa) 25 4.4 0.05 40 6.6 0.1 60 9.0 0.2 100 13.5 0.3 200 19.4 0.7 b.p. kafle et al. / bibechana 11(1) (2014) 53-59: (online publication: march, 2014) p.58 also, we tested our solar cell with above combination (same cell which was used to produce above data) in real sun condition as well (see fig.(5)). with this cell, the best photo-voltage was ca. 230 mv and ca. photocurrent was ca.50 µa. note that both the background current and voltage were zero. the power of radiation was 930 w as displayed by pyranometer. figure 4: measured photo-voltage and photocurrent as a function of radiation power. (note the linear relationship between power and both the measured photo-current and photo-voltage.) figure 5: test of our dye sensitized solar cell (top) in real sun condition. the power of radiation was ca. 930 w. the cell was hold by clamps at the ends and connected to multimeter. the values on display of multimeter associate voltage (left) and current (right). 4. conclusion and future outlook we managed to prepare transparent thin film of zinc oxide on conducting glass. thickness dependence transmittance of the films have been measured and presented in this report. properties such as accurate thickness, surface morphology, crystallinity, and conductivity are yet to be measured to fully characterize them. these measurements along with the transmittance will allow us to find the best condition to fabricate films with optimum properties for solar cells. moreover, among the measured absorption spectra of synthetic dyes green-vs, patent-blue, and black-adli show strong absorbance over the wide range in the visible spectrum, demonstrating the prospect of utilizing in the fabrication of dye sensitized solar cells. b.p. kafle et al. / bibechana 11(1) (2014) 53-59: (online publication: march, 2014) p.59 the solar cells were also tested in real sun condition as well. with solar radiation power of 930 w, the observed photo-voltage and photo-current were ca. 230 mv and 25 µa. the observed values were remarkable in that they were obtained by a proto-type solar cell. evaluation of efficiency and other photovoltaic parameters is in progress. also, from the analysis so far what can be inferred is that, to make these solar cells competitive (or even cheaper) with commercial solar cells, further optimization is required. in particular, the present values of current and voltages have to be improved, at least, by factor of four. this is indeed possible by finely tuning the particle size of zno nanoparticles, film’s thickness and making appropriate choice of sensitizer (dye). also to fully characterize solar cell, photovoltaic parameters should be measured at standard photovoltaic conditions (am 1.5 global sunlight at 1000 w/m2 and a temperature of 298 k) with a calibrated solar simulator. references [1] d. adhikari, energy planning and policy, the himalayan times (daily news paper) jan. 15, 2013. [2] j. s. ward, k. ramanathan, f. s. hasoon, t. j. coutts, j. keane, m. a. contreras, t. moriarty, r. noufi, prog. photovoltaics, 10 (2002) 41. [3] m. afzaal, p. o’brien, j. mater. chem., 16 (2006) 1597. [4] h. w. schock, appl. surf. sci., 92 (1996) 606. [5] r. w. birkmire, energ. mat. sol. c, 65 (2001) 17. [6] b. o’regan, m. grätzel, nature, 353 (1991) 737. [7] m. gratzel, j. photochem. photobiol. c, 4 (2003) 145. [8] a. yella, h-w lee, h. n. tsao, c. yi, a. k. chandiran, md. k. nazeeruddin, e. w-g. diau, c-y yeh, s. m. zakeeruddin, m. grätzel, science, 334 (2011) 629. [9] j. a. anta, e. guillen, r. tena-zaera, j. phys. chem. c, 116 (2012) 11413. [10] a. huczko, a. dabrowska, d. k. madhup, d. p. subedi, s. p. chimouriya, phys. status solidi b, 247 (2010) 3035. [11] b. p. kafle, b. r. pokhrel, p. lamichhane, j. of kathmandu university (2014) (in press). [12] b. p. kafle, b. r. pokhrel, r. gyawali, a. kafle, t. m. shrestha, r. bajracharya, r. m. adhikari, advances in applied science research, 5 (2014) 8. microsoft word akkaldeo mishra.doc a. d. mishra / bibechana 8 (2012) 17-22 : bmhss, p. 17 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana a convenient route for the synthesis of antimicrobial 1, 3, 4thiadiazole derivatives a. d. mishra dept. of chemistry, tribhuvan university, p. n. campus, pokhara ph. no.: 061-540414 / mob, no.: 9846027853 e-mail: mishraad05@hotmail.com article history: received 18 may, 2011; accepted 17 june, 2011 abstract thiosemicarbazide of 6-chloro-2aminobenzothiazole on cyclization with different aromatic carboxylic acids in phosphorus oxychloride provided the corresponding 2-aryl-5-(6’-chloro-1’,3’benzothiazole-2-yl-amino)-1,3,4-thiadiazoles 4a-j. the compounds are characterized by elemental analysis, ir and 1 h nmr spectral data. all the compounds are evaluated in vitro for their antimicrobial activities against several fungal and bacterial strains and showed significant activities. keywords: aminobenzothiazole; 1, 3, 4thiadiazole; antimicrobial; cyclization 1. introduction benzothiozoles are bicyclic ring systems with diverse chemical reactivity and broad spectrum of biological activities such as antimicrobial[1,2],antitumor[3,4],anti-inflammatory[5,6]and antilieshmanial[7,8], etc. several 1, 3, 4thiadiazole derivatives are also known to exhibit diverse biological properties like antimicrobial [9,10] , antitubercular[11,12] , anti-inflammatory[13] and anticonvulsant[14]. the synthesis and biological activities of a few benzothiozole derivatives linked with 1,3,4-thiadiazole systems is reported here owing to their pharmaceutical importance. the reaction sequence leading to the formation of the desired heterocyclic compounds are outlined in scheme 1.the 6-chloro-1,3-benzothiazol-2-yl-thiosemicarbazide 2 was prepared by the reaction of 6-chloro-2-aminobenzothiazole 1 with cs2 and hydrazine in the presence of ethanol. several 2-aryl-5-(6’-chloro-1,’3’-benzothiazol-2-yl-amino)1, 3, 4thiadiazoles 4a-j were synthesized by the reaction of 6-chloro-1,3-benzothiazol-2-yl-thiosemicarbazide 2 with various substituted aromatic carboxylic acids 3a-j in the presence of phosphorous oxychloride. 2. material and methods melting points were measured in open capillary tubes and are uncorrected. ir spectra were recorded on a nicolet, 5pc ft-ir spectrometer in kbr pelletes and 1 h nmr spectra on the bruker drx-300 ft nmr spectrometer using tms as internal reference.chemical shifts are observed with dmso-d 6 solvent in ppm. the purity of the compounds was checked on silica gel a. d. mishra / bibechana 8 (2012) 17-22 : bmhss, p. 18 g plates using iodine vapor as visualizing agents. ofloxacin was used as standard dug for antibacterial activity ketoconazole as standard drug for antifungal activity [15,16]. the precursor 6-chloro-2aminobenzothiazole 1 was synthesized by the already reported procedure [17]. scheme 1 n scl nh2 cs2 c2h5oh nh2 cl n s nh c s nh rcoohpocl3 cl n s nn s nh r 1 2 nh2nh2 a-j3 4a-j ( ) ( ) ( ) ( ) r = a. phenyl b. 4-chlorophenyl c. 2,4-dichlorophenyl d. 4-nitrophenyl e. 2-aminophenyl f. 2,4-dichlorophenoxymethyl g. 2-naphthylmethyl h. 4-methoxyphenyl i. 2-acetoxyphenyl j. 3-pyridyl 2.1 general procedure for the synthesis of 6-chloro-1,3benzothiazol-2-yl thiosemicarbazide (2) the 6-chloro-2aminobenzothiazole 1 (0.01 mole) was dissolved in ethanol (90%, 50ml) and then cs2 (20ml) was added slowly within 10 minutes with constant shaking. the resulted solution was then allowed to stand for 1.0 hr. then 20 ml of 50% hydrazine solution was added to it. the reaction mixture was warmed slowly for 1.30 hr then filtered, washed with cold water and dried. the solid thus obtained was purified by recrystallization from methanol. 2.2 general procedure for the synthesis of 2-aryl-5-(6’-chloro-1’, 3’benzothiazol-2-ylamino) 1,3,4-thiadiazoles (4a-j) a mixture of 6-chloro-1,3benzothiazol-2-ylthiosemicarbazide 2 (0.01 mole), an aromatic acid 3a-j (0.01 mole) and phosphorous oxychloride (25 ml) was refluxed for 3 hr. after cooling to room temperature the reaction mixture was slowly poured over crushed ice and kept for 1 hr. the solid thus separated was filtered, washed with cold water, dried and purified by recrystallization from methanol. 3. results and discussion all the synthesized thiadiazole derivatives 4a-j are confirmed by different spectral analysis (table 2).these compounds have given similar ir and 1 h nmr signals for main moiety with variations for substitutions. the characteristic observations for the substitutions have further supported the formation of mentioned products 4a-j.the ir spectrum of the typical compound 4i showed absorption peak at 1710 cm -1 due to the stretching of c=0. the n-h stretching vibration appeared at 3436 cm -1 . the absorption at 795 cm -1 was obtained due to c-cl stretching vibration. the 1 h a. d. mishra / bibechana 8 (2012) 17-22 : bmhss, p. 19 nmr spectra of this compound displayed on singlet at δ 2.13 showing the presence of occh3 protons of acetyl group. a broad singlet appeared at δ 12.36 showing the presence of nh proton. the seven aromatic protons of benzothiozole and phenyl ring were observed as a multiplet at δ 7.5-8.0. table 1: physical characterization data of compounds (4a-j) comp.no r yield (%) m.p.(˚c) 4a phenyl 65 225 4b 4-chlorophenyl 61 270 4c 2,4-dichlorophenyl 67 283 4d 4-nitrophenyl 72 285 4e 2-aminophenyl 66 227 4f 2,4-dichlorophenoxymethyl 58 215 4g 2-napthylmethyl 73 165 4h 2-methoxyphenyl 61 201 4i 2-acetoxyphenyl 60 272 4j 3-pyridyl 55 242 4. biological evaluation all the compounds have been screened for both antibacterial and antifungal activities using cupplate agar diffusion method by measuring the inhibition zone in mm. ofloxacin(50 µg/ml) was used as a standard drug for antibacterial activity and ketoconazole(50 µg/ml) as a standard drug for antifungal activity. the compounds 4a-j were screened for antibacterial activity against e. coli, s. aureus and p. aerugenosa in nutrient agar medium and for antifungal activity against a. niger and c. albicans in sabouraud’s dextrose agar medium. these sterilized agar media were poured into petri-dishes and allowed to solidify. on the surface of media microbial suspensions were spreaded with the help of sterilized triangular loop. a presterilized stainless steel cylinder of 8 mm diameter was used to bore cavities. all synthesized compounds (50 µg/ml) were placed serially in the cavities with the help of micropipette and allowed to diffuse for 1.00 hr. dmf was used as a solvent for all the compounds and as a control. these plates were incubated at 37˚c for 36 hr. and 28˚c for 48 hr, for antibacterial and antifungal activities respectively. the zone of inhibition observed around the cups after respective incubation was measured and percentage inhibition of a. d. mishra / bibechana 8 (2012) 17-22 : bmhss, p. 20 the compounds was calculated (tables 3&4).the thiadiazole derivative 4i having acetoxyphenyl group showed potent activity against s. aureus(92%), wereas compound 4g having 2 nepthylmethyl group showed maximum inhibition against e. coli(95%), when compared to standard drug ofloxacin. the compound 4c having 2,4-dichlorophenyl group also showed significant antibacterial activity(85, 87 and 82%) against s. aureus, e. coli, and p. aerugenosa respectively. rest of the compounds showed moderate to good antibacterial activity. table 2: spectral data of the compounds (4a-j) comp.no. ir, ν (cm -1 ) 1 h nmr, δ (ppm) 4a 3360(n-h) 3030(c-h) 750(c-cl) 7.35-7.8(m,8h,arh) 8.27(s,1h,nh) 4b 3369(n-h) 3032(c-h) 755(c-cl) 7.30-7.96(m,7h,arh) 10.48(s,1h,nh) 4c 3386(n-h) 3060(c-h) 765(c-cl) 7.34-7.62(m,6h,arh) 10.50(s,1h,nh) 4d 3366(n-h) 3033(c-h) 752(c-cl) 7.37-8.38(m,7h,arh) 13.25(s,1h,nh) 4e 3411(n-h) 3033(c-h) 752(c-cl) 4.5(s,2h,nh2) 7.08-7.86(m,7h,arh) 12.56(s,1h,nh) 4f 3408(n-h) 3028(c-h) 750(c-cl) 4.97(s,2h,ch2o) 7.06-7.89(m,6h,arh) 12.59(s,1h,nh) 4g 3402(n-h) 3021(c-h) 752(c-cl) 3.27(s,2h,ch2) 7.50-7.87(m,10h,arh) 12.34(s,1h,nh) 4h 3399(n-h) 3032(c-h) 752(c-cl) 3.86(s,3h,och3) 7.05-7.86(m,7h,arh) 12.56(s,1h,nh) 4i 3436(n-h) 3038(c-h) 1710(c=o) 795(c-cl) 2.13(s,3h,och3) 7.5-8.0(m,7h,arh) 12.36(s,1h,nh) 4j 3421(n-h) 3036(c-h) 745(c-cl) 7.05-7.89(m,7h,arh) 13.0(s,1h,nh) a. d. mishra / bibechana 8 (2012) 17-22 : bmhss, p. 21 table 3: antibacterial activity of 1, 3, 4-thiadiazole derivatives (4a-j) comp. staphylococcus aureus escherichia coli pseudomonas aerugenosa zone of inhibition (mm) % inhibition zone of inhibition (mm) % inhibition zone of inhibition (mm) % inhibition 4a 10 65 9 63 13 77 4b 12 80 10 69 12 70 4c 15 85 16 87 14 82 4d 11 76 14 85 12 71 4e 11 80 13 71 11 74 4f 14 82 12 65 13 76 4g 13 76 16 95 13 81 4h 10 78 12 75 12 70 4i 16 92 13 72 14 83 4j 12 80 11 69 13 79 table 4: antifungal activity of 1, 3, 4thiadiazole derivatives (4a-j) aspergillus niger candida albicans comp. zone of inhibition (mm) % inhibition zone of inhibition (mm) % inhibition 4a 20 62 12 66 4b 14 55 11 58 4c 13 47 13 62 4d 11 45 11 61 4e 25 87 15 78 4f 23 82 16 83 4g 16 56 14 67 4h 12 46 13 69 4i 13 48 12 63 4j 15 52 14 71 a. d. mishra / bibechana 8 (2012) 17-22 : bmhss, p. 22 the results of antifungal activity of the test compounds were quite different from their antibacterial activity. the 1,3,4thiadiazole derivative 4e having 2-aminophenyl group showed maximum inhibition(87%) against a. niger whereas 4f having 2,4-dichlorophenoxymethyl groups showed maximum inhibition (83%) against c. albicans. furthermore 1, 3, 4thiadiazole dericatives 4e showed 78% inhibition against c. albicans. whereas 4f showed 82% inhibition against a. niger. rest of the thiadiazole derivatives showed moderate to good antifungal activity as compared to the reference drug ketoconazole. thus it is concluded from the screening results that 1,3,4 thiadiazole derivatives 4a-j have been proved to be more effective against all the tested microorganisms at a concentration of 50 µg/ml. 5. conclusion the reaction of 6-chloro-2aminobenzothiazole 1 with hydrazine and carbon disulphide in alcoholic medium yielded corresponding thiosemicarbazide 2 in excellent yield of 82% within 1 hr. thus obtained thiosemicarbazide produced various 1,3,4-thiadiazoles 4a-j, through cyclization upon reaction with carboxylic acids 3a-j in presence of phosphorous oxychloride in 75% yield within 3 hr. all the synthesized thiadiazoles 4a-j, showed excellent to moderate antifungal and antibacterial activities, which has proved the thiadiazoles 4a-j as pharmaceutically valuable heterocycles. this synthetic method is proved to be simple, easier to workup and environment friendly tool in pharmaceutical chemistry. acknowledgements the auther is thankful to the research committee, department of chemistry and department of microbiology, tribhuvan university,p. n. campus, for providing miniresearch grant and available laboratory facilities regarding synthesis and microbial activities of the compounds. thanks are due to the instrumental laboratory, department of chemistry, university of delhi, for assisting in spectral analysis of all the synthesized compounds. references [1] i. yildiz-oren, i. yalein and n. ucartruk, eur j med chem. 39 (2004) 291. [2] f. delmas, a. avellaneda, c.d. gioegia, e.d. robin clereq, and j.p. galy, eur j med chem. 39 (2004)685. [3] n.k. wadoker and m.a. dhiman, indian j chem. 40b (2001) 636. [4] s.h. joshi and m.k. thaker, indian j chem. 44b (2005) 410. [5] h.joshi, p. upadhayaya, d. karia and a.j. baxi, eur j med chem. 38 (2000) 837. [6] m. amir, s.a. javed and h. kumar, indian j chem. 46b (2007) 1014. [7] a.d. mishra, nepal j sc tech. 11 (2010) 153. [8] e.a. gamal, a.m. mohamad and a.g. yehia, indian j chem. 39 (2000) 368. [9] m. kidwai, p. mishra and r.k. bhushan, polyhedron 18 (1999) 2641. [10] a.d. mishra, j nepal chem soc. 25 (2010) 83. [11] o.m. pedro, m.p. jose and i.p. gean, j med chem. 1 (2006) 223. [12] k. mogilaihi and g.r. reddy, j chem res. 10 (2004) 363. [13] k. eger, g. grieb. and s. spatting, j heterocyclic chem. 27 (1990) 2069. [14] a.d. mishra, j institute sc tech. 16 (2010) 135. [15] s. gupta and n. ajmera, indian j chem. 48 (2009) 853. 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[17] m. kidwai, r. venkataraman and b. deve, green chem. 3 (2001) 278. microsoft word tulasi prasad nirula et al_corrected.doc tulasi prasad nirula et al. / bibechana 9 (2013) 159-164 : bmhss, p.159 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana effects of concentration, relative permittivity on the transport properties of sodium dodecyl sulphate in presence and in absence of potassium bromide and sodium chloride in methanol-water mixed solvent media at 308. 15 k tulasi prasad niraula, ajaya bhattarai, sujeet kumar chatterjee* department of chemistry, mahendra morang adarsh multiple campus, tribhuvan university , biratnagar, nepal *corresponding author : sujeetkumarchatterjee@yahoo.com article history: received 7 november, 2012; accepted 25 november, 2012 abstract precise measurements on conductivity of sodium dodecyl sulphate in presence and in absence of kbr and nacl in methanol-water mixed solvent media containing 0.1, 0.2 and 0.4 volume fractions of methanol at 308.15k are reported. the concentrations were varied from ~ 0.001 to ~ 0.03 mol.l -1 . the results showed a sharp increase in conductivity with increase in concentration of sodium dodecyl sulphate. also, the conductivity of sodium dodecyl sulphate increases with addition of salts. the conductivity of sodium dodecyl sulphate decreases with increase in amount of methanol. the conductance of sodium dodecyl sulphate is found more in presence of kbr than nacl in methanol-water mixed solvent media containing 0.1, 0.2 and 0.4 volume fractions of methanol. key words: conductance; sodium dodecyl sulphate; relative permittivity; mixed solvent media 1. introduction several works has been done on conductivity of ionic surfactants [1-5]. the addition of an electrolyte will, in general, tend to induce the formation of aggregates at concentrations below the critical micelle concentration (cmc) of the pure surfactant[6,7], while with many electrolytes, specific interactions between the surfactant ion and electrolyte counterion will lead to a reduction in solubility[8]. the transport properties have been investigated for a wide variety of electrolytes in methanolwater mixed solvent media in great details [9-16]. there are very few works on the transport properties of polyelectrolytes in methanol – water mixed solvent media [17, 18], whereas the transport properties of ionic surfactants in methanol-water mixed solvent media are relatively rare. it is our interest to see the effects of concentration and relative permittivity on the transport properties of sodium dodecyl sulphate in methanol – water mixed solvent media in presence and in absence of kbr and nacl. 2. experimental methods methanol (merck, india) was distilled with phosphorous pentoxide and then redistilled over calcium hydride. the purified solvent had a density of 0.77723 ± 0.00004 g.cm -3 which was measured by the use tulasi prasad nirula et al. / bibechana 9 (2013) 159-164 : bmhss, p.160 (online publication: nov., 2012) of an ostwald-sprengel type pycnometer of about 25 cm 3 capacity. the solvent was transfused into the pycnometer by using a medical syringe. the pycnometer was then tightly fixed in a thermostat at the experimental temperatures within 0.005 k. after thermal equilibrium was attained, the mass of the pycnometer was measured with an electronic balance, and the density was calculated. density measurements are precise within 0.00005g.cm -3 , which is satisfactory for our purpose and a co-efficient of viscosity of 0.47424 ± 0.00005 m pa. s which was determined by the use of the viscometric method. measurements were performed at 308.15 k using a schultz-immergut-type viscometer [19] with a sintered disc fitted to the widest arm to filter the solution/solvent from dust particles, if any and these values are in good agreement with the literature values [20]. triply distilled water with a specific conductance less than 10 -6 s.cm -1 at 308.15 k was used for the preparation of the mixed solvents. the physical properties of methanol-water mixed solvents used in this study at 308.15 k are taken from our published works [5,14,17,21]. the relative permittivity of methanol-water mixtures at the experimental temperatures were obtained by regressing the relative permittivity data as function of solvent composition from the literature [22]. sodium dodecyl sulphate employed in these investigations was purchased from merck specialties private limited, mumbai, india. conductance measurements were carried out on a pye-unicam pw 9509 conductivity meter at a frequency of 2000 hz using a dip-type cell with a cell constant of 1.15 cm -1 and having an uncertainty of 0.01%. the cell was calibrated by the method of lind and co-workers [23] using aqueous potassium chloride solution. sodium chloride and potassium bromide employed in these investigations were purchased from ranbaxy chemical company, mumbai, india. the measurements were made in a water bath maintained 308.15 k within ± 0.005 k. the details of the experimental procedure have been described earlier [24,25]. several independent solutions were prepared and runs were performed to ensure the reproducibility of the results. due correction was made for the specific conductance of the solvent by subtracting the specific conductance of the relevant solvent medium from those of the electrolyte solutions. in order to avoid moisture pickup, all solutions were prepared in a dehumidified room with utmost care. in all cases, the experiments were performed in three replicates. 3. results and discussion the conductivities of sodium dodecyl sulphate in pure water and three different methanol-water mixtures (containing 0.10, 0.20 and 0.40 volume fractions of methanol) at 308.15 k is depicted in fig.1. it is evident from fig.1 that the specific conductivities exhibit a sharp decrease with increasing concentration of methanol within the concentration range investigated here. the decrease in the conductance with increase in concentration of methanol is due to decrease in the dielectric constant of the mixture. the presence of methanol reduces the dielectric constant of the solvent phase and makes easier for the formation of ion pairs in the solution phase. however, solvents with high dielectric constants yield more conducting solutions. fig. 1 also shows that conductance increase with increase in concentration. the increase in conductance with increase in concentration is due to increase in number of ions per unit volume of the solution. it has been studied earlier that the conductivity value decreases with increase of methanol in the system [17]. the conductance decreases with increase of alcohol content for the studied methanol-water mixed solvent system. tulasi prasad nirula et al. / bibechana 9 (2013) 159-164 : bmhss, p.161 (online publication: nov., 2012) 0 0.5 1.0 1.5 0 0.005 0.010 0.015 c s (mole.l -1 ) κ (s .c m -1 ) fig.1: specific conductivities of sodium dodecyl sulphate as a function of concentration (cs) in 308.15 k: closed squares, triangle, open circles and closed circles represent pure water, 0.10, 0.20 and 0.40 volume fractions of methanol in the solvent mixture respectively. figs. 2-5 represent the specific conductivities of sodium dodecyl sulphate as a function of concentration (cs) in absence and presence of 0.1n kbr and 0.1n nacl at 308.15 k: in distilled water and different composition of methanol. from the figs. 2 to 5, it is evident that the specific conductivities of sodium dodecyl sulphate exhibit increase with addition of salt. the conductivity of sodium dodecyl sulphate in presence of kbr is more than in presence of nacl. also, from figs. 2-5, it is clear that the specific conductivities of sodium dodecyl sulphate exhibit a sharp increase with addition of salts in all the measured solvent composition of methanol-water mixture. the increase in conductance of sodium dodecyl sulphate in methanol water mixed solvent media with addition of salts is because of increase in current carrying species in the solution. the conductivities of sodium dodecyl sulphate in presence of kbr is more than in presence of nacl. because the smaller ions are strongly hydrated than larger ions, so they need to pull more water molecules with them that results decrease in mobility of ions. hence the conductivity values for sodium dodecyl sulphate in presence of kbr is more than in comparison with nacl. tulasi prasad nirula et al. / bibechana 9 (2013) 159-165 : bmhss, p.162 (online publication: nov., 2012) 0 0.5 1.0 1.5 2.0 2.5 0 0.005 0.010 0.015 c s (mole.l -1 ) κ (s .c m -1 ) fig. 2: specific conductivities of sodium dodecyl sulphate as a function of concentration (cs) in absence and in presence of 0.1n kbr and 0.1n nacl at 308.15 k: circles, triangles, and squares represent presence of 0.01n kbr, 0.01n nacl and absence of salt in distilled water i.e. in '0' volume fractions of methanol in the solvent mixture respectively. 0 0.5 1.0 1.5 2.0 0 0.005 0.010 0.015 c s (mole.l -1 ) κ (s .c m -1 ) fig. 3: specific conductivities of sodium dodecyl sulphate as a function of concentration (cs) in absence and in presence of 0.1n kbr and 0.1n nacl at 308.15 k: circles, triangles, and squares represent presence of 0.01n kbr, 0.01n nacl and absence of salt in 0.1 volume fractions of methanol in the solvent mixture respectively. tulasi prasad nirula et al. / bibechana 9 (2013) 159-164 : bmhss, p.163 (online publication: nov., 2012) 0 0.5 1.0 1.5 2.0 2.5 0 0.005 0.010 0.015 c s (mole.l -1 ) κ (s .c m -1 ) fig. 4: specific conductivities of sodium dodecyl sulphate as a function of concentration (cs) in absence and in presence of 0.1n kbr and 0.1n nacl at 308.15 k: circles, triangles, and squares represent presence of 0.01n kbr, 0.01n nacl and absence of salt in 0.2 volume fractions of methanol in the solvent mixture respectively. 0 0.5 1.0 1.5 2.0 2.5 0 0.005 0.010 0.015 c s (mole.l -1 ) κ (s .c m -1 ) fig. 5: specific conductivities of sodium dodecyl sulphate as a function of concentration (cs) in absence and in presence of 0.1n kbr and 0.1n nacl at 308.15 k: circles, triangles, and squares represent presence of 0.01n kbr, 0.01n nacl and absence of salt in 0.4 volume fractions of methanol in the solvent mixture respectively. tulasi prasad nirula et al. / bibechana 9 (2013) 159-164 : bmhss, p.164 (online publication: nov., 2012) 4. conclusions the following conclusions have been drawn from the above results and discussion. experimental results for the specific conductivity of solution of sodium dodecyl sulphate in absence and presence of kbr and nacl in methanol-water mixed solvent media have been presented as a function of salt concentration and different percentage composition of (methanol + water) mixed solvent media. the specific conductivities are found to increase with increase in concentration over the entire concentration range investigated whereas the specific conductivities of sodium dodecyl sulphate decrease with decreasing dielectric constant of solvent composition. also, the specific conductivities of sodium dodecyl sulphate in presence of kbr found to be more than in presence of nacl in pure water and three different compositions (0.10, 0.20 and 0.40 volume fractions of methanol) of methanol-water mixed solvent media. acknowledgements one of the authors (tulasi prasad niraula ) is thankful to nepal academy of science and technology (nast) for providing financial support to pursue ph.d. work from the fiscal year 2012.sincere thanks to the head of the department of chemistry, mahendra morang adarsh multiple campus, biratnagar, (tribhuvan university), nepal for providing the available research facilities to conduct the research work. references [1] h. c. evans, j. chem. soc., (1956) 579. 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[25] b. das and d. k. hazra, j. phys. chem., 99 (1995) 269. microsoft word d. adhikari _90-95_.doc d. adhikari / bibechana 8 (2012) 90-95 : bmhss, p.90 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana a theoretical study of thermodynamic properties of cd-bi liquid alloy d. adhikari 1,2 1 university department of physics, t.m. bhagalpur university, india 2 department of physics, m.m.a.m.c. (tribhuvan university), biratnagar, nepal e-mail: adksbdev@yahoo.com article history: received 5 november, 2011 abstract flory’s model has been used for the study of thermodynamic properties of cd-bi liquid alloys. free energy of mixing, heat of mixing, entropy of mixing and activity of cd have been determined. all of these computed quantities have been found to be in a good agreement with observed values. keywords: flory’s model; thermodynamic properties; cd-bi liquid alloy; weakly interacting system; interaction energy parameter 1. introduction the liquid state of matter such as, liquid metal alloys is characterized as disorder system and hence it is much more difficult to understand the properties of liquid alloys than that of crystal. in order to solve the complexity of obtaining thermodynamic properties of binary liquid alloys several models [1-9] have been employed by the theoreticians. moreover cadmium is highly reactive element and it is difficult to conduct diffraction experiment on it. therefore a theoretical investigation giving structural information on a system of cd is highly desirable. experience shows that the thermodynamic properties of binary liquid alloys can be explained by flory’s model [2] if there is larger size mismatch between the constitute metals. in case of bi-cd binary alloy the size factor (ωbi/ωcd =1.63, ω being the atomic volume of the constituent of the alloy) is greater than 1.5. thus, in present investigation, we have used flory’s model to understand the thermodynamic properties of bi-cd liquid alloy at 773 k. theoretical formalism is given in section 2, section 3 deals with the numerical results and discussion. conclusion is provided in section. 2. theory we consider nc mole of cd atoms and n(1-c) mole of bi atoms are mixed in molten state at 773 k. then flory's expression for free energy of mixing of a binary mixture cd-bi is given by [2] d.adhikari / bibechana 8 (2012) 90-95 : bmhss, p.91 m 1 c g rt[c ln c (1 c) ln(1 c) c ln(1 ) ln(1 c)] c 1 c − = + − − + −β − −β +ω −β (1) where cd bi ( ) 1 0.385 ( ) ω β = − = ω the standard thermodynamic relation for activity of cd in binary liquid is given by m cd m g rt ln a g (1 c) c ∂ = + − ∂ (2) differentiating equation (1) with respect to 'c' and substituting the value of c gm ∂ ∂ , one gets 2 cd 2 (1 c) (1 c) ln a ln c ln(1 ) ln(1 c) 1 c rt (1 c) β − ω − = + −β − −β + + −β −β (3) once the expressions for mg is obtained, other thermodynamic functions follow readily. heat of mixing and entropy of mixing are related to mg through standard thermodynamic relations m m m p g h g t t  ∂ = −   ∂  (4) t gh s mm m − = (5) differentiating equation (1) with respect to t and substituting in equation (4), we get trtc1 c 1c1 )c1(c rt tc1 )c1(c t c1 )c1(c h 2 m ∂ β∂       ω β− − β− β β− − + ∂ ω∂ β− − − β− − ω= (6) where cd bi cd bi ( ) t ω∂β = α −α ∂ ω , cd α and bi α are expansivities of cd and bi respectively. 3. results and discussion the value of interchange energy )(ω was determined from the observed data [10] of mg in the concentration range from 0.1 to 0.9. the best fit value of ω used in the present work was found to be 51.4 j mol -1 . the negative value of ω indicates that there is a tendency of compound formation (preferred with unlike atoms pairing) in cd-bi alloy in molten state. the computed values of mg obtained from equation (1) are plotted against cd c (concentration of cd) in figure 1 along with its observed values at 773k. the computed and observed values of mg are in a good agreement in all concentration range. both the theoretical and observed values are minimum at equiatomic composition, cd c = 0.5. theoretical calculation of free energy of mixing for cd-bi liquid alloy shows that it is weakly interacting system. this indicates that the tendency of compound formation is weak. d.adhikari / bibechana 8 (2012) 90-95 : bmhss, p.92 fig.1 : free energy of mixing (gm) versus ccd (concentration of cd) in the liquid cd-bi solution (773k); (–– ––) theory, (ooo) experiment [10]. activity is a very important thermodynamic function because it is one of the fortune functions which is obtained directly from experiment and it can be used to obtain other thermodynamic functions. . the graph between the experimental and theoretical values of cd ln a with respect to cd c is shown in figure 2. it is clear from the graph that theoretical values of cd ln a are in a good agreement with experimental values. fig. 2: activity (ln acd) ) versus ccd (concentration of cd) in the liquid cd-bi solution (773k); (––––) theory, (ooo) experiment [10]. d.adhikari / bibechana 8 (2012) 90-95 : bmhss, p.93 to determine heat of mixing and entropy of mixing we need the variation of interchange energy with temperature [11,12]. for this, observed values of heat of mixing (hm) are used. in present work the value of / t∂ω ∂ = -4.8 jmol -1 k -1 is considered as a best fit value. the heat of mixing at 773k is calculated using equation (6). the minimum value of the heat of mixing show that the intermolecular forces between bi and cd is also small. fig. 3 : heat of mixing (hm) versus ccd in the liquid cd-bi solution (773k); (––––) theory, (ooo) experiment [10]. equation (5) is used to calculate ms for the concentration ccd = 0.1 to 0.9. the computed values of ms are plotted in figure 4 along with their observed values. the computed and observed values of ms are in a good agreement. the calculated and observed both values of entropy of mixing show that cd-bi alloy is not ordered system at 773 k. d.adhikari / bibechana 8 (2012) 90-95 : bmhss, p.94 fig. 4 : entropy of mixing (sm) versus ccd in the liquid cd-bi solution (773k); (––––) theory, (ooo) experiment [10]. 4. conclusion the cd-bi melts at 773 k is weakly interacting system. the interaction energy parameter is temperature dependent. the intermolecular force between like or unlike atoms in cd-bi alloy in liquid state is very weak. acknowledgements the author gratefully acknowledges dr. b.p. singh, t.m. bhagalpur university, india and dr. i.s. jha, m.m.a.m. campus, biratnagar, nepal for their fruitful suggestions. references [1] r.n. singh, f. sommer, j. phys. condens. matter 4 (1992) 5345. [2] p.j. flory, j. chem. phys. 10 (1942)51. [3] f. sommer, j. non-cryst. solids 117 (1990) 505. [4] b.p. singh, i.s. jha, d. adhikari and b.k. singh, bibechana, 7(2011) 1. [5] k. hoshino, j. phys. f: met. phys. 13 (1983) 1891. [6] w.h. young, rep. prog. phys. 55 (1992) 1769. [7] d. adhikari,, b.p. singh, i.s. jha and b.k. singh, j. mol. liq., 156 (2010)155. d.adhikari / bibechana 8 (2012) 90-95 : bmhss, p.95 [8] h. ruppersberg, h. reiter, j. phys. f: met.phys. 12 (1982) 1311. [9] d. adhikari, i.s. jha, and b.p. singh, philos. mag. 90 (2010) 2687. [10] hultgren, r., desai, p. d., hawkins, d.t., gleser, m. and kelley, k.k., , selected values of thethermodynamic properties of binary alloys (metals park, ohio: american society for metals) (1973). [18] a.r miedema, f.r de boer, and r. boom, physica 167 b (1981)7. [19] a.r miedema, p.f de chatel, and f.r. boer, physica 100 b (1980)1. microsoft word ram chandra adhikari _21-25_.doc ram chandra adhikari / bibechana 7 (2011) 21-25 : bmhss 21 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana household solid waste production and its management in biratnagar sub-metropolitan city ram chandra adhikari ∗∗∗∗ department of zoology, tribhuvan university, central campus of science and technology, hattisar, dharan article history: received 2 october 2010; revised 5 november 2010; accepted 10 november 2010 a b s t r a c t the study was conducted from march to may month of 2010 a d in biratnagar regarding the waste production and management. total amount of waste produced was recorded about 46.877 tonnes per day. the highest amount was from urban rural area (44.637 tonnes) and the lowest was from main bazaar (0.689 tonnes). about 69.19 percent households collect waste separately . 45.90 percent households dump degradable waste. 80 percentages of all households sell non degradable waste and only 33.67 percentage people of this town have scientific knowledge of waste management. keywords: solid waste; biodegradable waste; improper settlements 1. introduction biratnagar sub-metropolitan city (26º 28ú n, 86º19ú e and 72 m altitude) is one of four submetropolitan cities of nepal lying in koshi zone, morang district . taking the position as second largest town it locates with the embanked by singia river in east and keshlia in west. it enjoys on sub-tropical and monsoon type of climate. this town covers an area about 59.9 square kilometers. a total of 26,699 households and 1, 80,138 people reside in this town. due to availability of facilities belonging to education, healthcare, employment etc. a lot people are migrating to this town every year. improper settlements, rapidly growing population, industrialization and lack of sufficient awareness result over production of solid waste and that create many problems. this town has been facing growing solid waste problems. any unwanted and discarded materials from residential, commercial, industrial, mining and agricultural activities that cause environmental problems may termed as solid waste. on the other words solid waste can be defined as those wastes which have been rejected for further use and can neither be transported by water into streams nor readily escape into atmosphere . according to rao [1] the waste arising from human and animal actives that normally solid and described as useless or unwanted. solid waste is a byproduct of human activities which tends to increase with rapid urbanization, improved living standards and changing consumption patterns. ∗ corresponding author: ram chandra adhikari, department of zoology, tribhuvan university, central campus of science and technology, hattisar , dharan email: ramchandra.adhikari@gmail.com ram chandra adhikari / bibechana 7 (2011) 21-25 : bmhss 22 management of increasing amounts of solid waste has become a major challenge in many cities in developing countries. the amount of waste generated from every person is increasing day per day as a result of social, economical and technological changes. according to who [2], it varies from 0.2 to 3 kg per person per day. unicef [3] reported that waste production depends on income of people. people with per capita income below 360 us dollar produce about 0.5 kg solid waste. similarly those with per capita income 360 to 3500 dollar produce 1.5 kg and income above 3500 dollar produce up to 4 kg of solid waste per day. on average 58 municipalities in the country are spending about 13 percent of their total budget on waste management related activities but in most cases this amount is not being spent in an efficient manner [4]. according to cbs 1997 [5] only 17 percent of urban households have their waste collected by waste collectors. furthermore, in low-income households, indicated by houses having no toilets, only 2 percent of the households have their waste collected. open waste piles are a common site and the work of municipalities is often limited to sweeping the streets and dumping the waste in the nearest river or vacant land. solid waste can be classified into two categories. they are bio degradable waste and non degradable waste. papers, garbage, dead bodies and compost -able waste are the examples of degradable solid waste and plastics, metals, ceramics etc. are non degradable ones. the waste should be managed properly but in the case of biratnagar there is not suitable dumping site or sanitary landfill site. so problems on the management of solid waste have been rising. waste management comprises of purposeful and systematic control of the generation, storage, collection, transportation, separation, processing, recycling, recovery and disposal of waste [6]. objectives the main objectives of present study were: -to measure the total quantity of waste production -to study management practice of household waste 2. materials and methodology the following important materials, tools or equipments were used for designing experiment scientifically. the materials used in the research are as following :collecting drums, spring balance, shovel, thermometer, gloves, field book, forceps, mask, questionnaires, calculator, camera, tongs, plastic bags, spade etc. firstly biratnagar town was divided into three areas namely main-bazaar ( ward number 8,9,10 and 14), semi-urban ( 3,4,12 and 13) and urban-rural (1,2,5,6,7,11,15,16,17,18,19,20,21 and 22 ). it was done according to municipality profile. after finding total number of households, 10 percent (about 300 households) of total number was taken for the study. special attention was given to include the households of all toles. fifteen individuals were trained as observers and used in the field with researcher. from each sample house, waste production was weighed with the help of spring balance twice a week and amount of average production was calculated. during the study period the waste management methods were also observed. by giving a questionnaire to fill up to the public and direct observation of existing management practice was studied. the period of study was three months from march to may 2010. ram chandra adhikari / bibechana 7 (2011) 21-25 : bmhss 23 3. result and discussion 3.1 waste production the average of solid waste generation from urban-rural region is tabulated in the table 1. table 1 s.n. month types of waste average daily production ( in kg) 1 march bio degredable + non degrdable+mixed 17540+6440+20000=4398 0 2 april bio degredable+non degredable+ mixed 18702+7845+21033=4758 3 3 may bio degredable+ non degredable +mixed 16980+5488+19882=4235 0 average 44637.667 from the above table in march biodegradable waste was produced 17540 kg, non degradable waste 6440 kg and non-separated was 20000 kg. similarly 18702 kg of biodegradable,7845 kg of non degradable and 21033 mixed type of waste was produced and total amount was 47583 kg in april. in the case of may month biodegradable 16980 kg, non degradable 5488 kg mixed 19882 kg and total 42350 kg was generated per day. the sum of total waste generation was found to be 44637.667 kg. the average of solid waste solid waste generation from semi urban region is tabulated in table 2. table 2 s.n. month types of waste average daily production ( in kg) 1 march bio degredable + non degrdable+mixed 540+192+732=1464 2 april bio degredable+non degredable+ mixed 555+243+679=1477 3 may bio degredable+ non degredable +mixed 675+272+765= 1712 average 1551 above table shows that from semi urban area in march 540 kg of bio degradable waste, 192 kg of non degradable and 732 kg of non-separated waste was excreted out per day. the total amount of solid waste produced was about 1464 kg daily. in the month of april 555 kg biodegradable, 243 kg non degradable, 679 kg mixed and total 1477 kg of non separated waste was found to come out from the houses. 675 kg bio degradable, 272 kg non degradable and 765 kg mixed waste and a total of 1712 kg was excreted out daily. in average 1551 kg waste was found to be generated everyday from this area. the average of solid waste solid waste generation from main bazaar region is furnished in table 3. ram chandra adhikari / bibechana 7 (2011) 21-25 : bmhss 24 table 3 s.n. month types of waste average daily production ( in kg) 1 march bio degredable + non degrdable+mixed 240+100+331=671 2 april bio degredable+non degredable+ mixed 385+123+ 342=850 3 may bio degredable+ non degredable +mixed 299+112+235= 546 average 689 above table tells that from main bazaar area in march 240 kg of bio degradable waste, 100 kg of non degradable and 331 kg of non-separated waste was excreted out per day. the total amount is about 671 kg daily. in the month of april 385 kg biodegradable, 123 kg, non degradable 342 kg mixed and total 850 kg of waste comes out from the houses. 299 kg biodegradable, 112 kg non degradable and 546 kg mixed waste and a total of 546 kg was excreted out daily. 689 kg was the average daily waste production. total waste generation from whole biratnagar sub-metropolitan city is displayed in table 4. table 4 s. n. area waste production (in kg per day ) 1 urban rural 44637.667 2 semi urban 1551 3 main bazaar 689 total 46877.667 according to the above table total amount of waste production from this town was found to be about 466877.667 kg or 46.6877 metric tonnes per day . it was made by 44637.667 kg from urban rural as maximum and 689 kg from main bazaar as minimum. 3.2 waste management practice during the study the following practices were observed in whole sub-metropolitan city. data were taken region wise and total of the town is presented here in all the topics. • 69.19 percent households collect biodegradable and non degradable waste separately. • about 45.90 percent households dump degradable waste in the pit in house compound. rest of them throws the solid waste randomly. • 80 percentages of all households sell non degradable waste. • only 33.67 percentage people have scientific knowledge of waste management. 4. conclusion biratnagar sub-metropolitan city is in trouble of solid waste problem. a huge amount of solid waste (46.687 tonnes) has daily been produced. there are not sanitary landfill site, proper ram chandra adhikari / bibechana 7 (2011) 21-25 : bmhss 25 awareness and cultural practices of waste management. some people (69.19 percent) collect waste separately but large population throws them everywhere. about 80 percentages of households sell plastics and metal born waste as they don't have sufficient practice of reuse. according to the study 33.67 percentage people know the method of waste management. this town is seeking for a good guideline, enough budget, proper awareness, skilled human resource etc. for waste management. acknowledgements the author is thankful to sagaramatha community development center (scdc) for financial support to this study. the author is also grateful to dr. damodar thapa for the valuable suggestions and inspiration to conduct the project. references [1] c.s. rao, study of solid waste management for environment pollution control engineering, wiley eastern limited, delhi, (1985). [2] who, solid waste disposal and control, public health papers 38, geneva , (1971). [3] unicef, the state of children and environment, new york, (1990). [4] swmrmc, a diagnostic report on state of solid waste management in municipalities of nepal, solid waste management and resource mobilization centre, lalitpur, (2004). [5] cbs, urban population survey 1996, central bureau of statistics, his majesty's government of nepal, kathmandu, (1997). [6] s.s. dara, a text book of environmental chemistry and pollution control, s. chand and company ltd, new delhi, ( 1998) . further readings [7] a.k deo, environmental chemistry, new age international limited, new delhi, (2001). [8] r.c. adhikari, study of solid waste management, a thesis submitted to p.g. campus biratnagar,(2oo5) . microsoft word s. k. shah _20-27_doc.doc s. k. shah / bibechana 10 (2014) 100-107 : bmhss, p.20 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana water quality assessment of mardi river by using water quality index shailendra kumar shah 1,2 1 i.o.f. pokhara, tribhuwan university, po.box: 43, nepal 2 nepal water supply corporation, tripureshwar, kathmandu, nepal email: erskshah@yahoo.com article history: received 30 november, 2012; accepted 25 september, 2013 abstract the aimed study assesses the water quality of mardi river applying national sanitation foundation (nsf) america developed index called water quality index (wqi). this index is one of effective way to inform about water quality trends to the public and the policy makers for water quality management. as mardi river is primary source of consumption to pokhara city and mardi watershed entities, the water quality is important for public health and ecological aspects. the study starts with five different sampling stations having total fifteen samples along three (april, may, june) months of the year 2012 were analyzed in water laboratory. after the analysis the weight values and sub index were obtained from the nsfwqi method which results that mardi river water has medium degraded water quality ranges in class c and nsfwqi of mardi river scores as 55.02 and there is high correlation between water quality parameters nitrogen and turbidity. keywords: mardi watershed / river, nsfwqi, water quality index. 1. introduction human civilizations of histories have thrived in part because of their ability to find, transport and deliver potable water to their growing urban populations and agricultural centers. the supply of potable water is a great challenge for the world today as well our country nepal too. rivers are large natural stream of water bodies emptying into an ocean, lake, or other bodies of water and usually fed along its course by converging tributaries. although they contain only about 0.0001% of the total amount of water in the world at any given time, rivers are vital carriers of water and nutrients to areas all around the earth [1]. river water quality is an important issue for each stakeholder as it affects human uses as well as plant and animal life. traditional approaches to assessing river water quality are based on the comparison of experimentally determined parameter values with the existing local normative. however, it does not provide a global vision on the spatial and temporal trends in the overall water quality. to overcome these difficulties, a water quality index (wqi) was developed. water quality indices appeared in the literature as early as 1965 (horton 1965). wqi is a mathematical instrument used to transform large quantities of water quality data into a single number, which provides a simple and understandable tool for managers s. k. shah / bibechana 10 (2014) 100-107 : bmhss, p.101 (online publication: dec., 2013) and decision makers on the quality and possible uses of a given water body. the evaluation of wqi requires many physical and chemical parameters to be measured [2, 3]. in the early 1970s, the national sanitation foundation (nsf), in cooperation with over 100 water quality experts, devised a standard index for measuring water quality. this index is known as the water quality index (wqi), consists of nine tests to determine water quality. these nine tests are: temperature, ph, turbidity, total solids, dissolved oxygen, biochemical oxygen demand, phosphates, nitrate, and fecal coliform. a table or graph for each of the nine tests indicates the water quality value (or q-value) corresponding to the data obtained. once the q-value for a test has been determined, it is multiplied by a weighting factor. each of the tests is weighted based on its relative importance to overall water quality. the resulting values for all nine tests are total and used to gauge the health of the water source as excellent, good, medium or average, fair, or poor [4]. study area: the present study area, the mardi river / khola, is located at the northern corner of pokhara valley of kaski district. mardi river situated in the foothills of annapurna mountain range, the mardi watershed (83º50’e to 83º 56’ e and 28º19’n to 28º29’n; area 144 km2) is representative of mid-hill watersheds of western nepal. fig. 1: map of study area ( mardi khola / river ) [5] s. k. shah / bibechana 10 (2014) 100-107 : bmhss, p.102 (online publication: dec., 2013) the elevation ranges from about 1000 m to 5588 m above mean sea level from valley floor to mountain peaks. the climate of the area varies from warm and humid subtropical to cool and dry alpine along with the elevation variation. the temperature in the study area is the range between 20-30 degrees in the summer and 7-18 degrees in winter rainfall is monsoonal with average annual rainfall amounting to 4300 mm, of which 80-85% occurs between june and october [6] . so it is very important to study such a diversify area. 2. material and methods basically, the field visit and sample collections were conducted for their outputs as to carry out research. the research was primarily based on field data supported by secondary data for analyzing, comparison and introduction part. taking the whole mardi river as universe, two kilometer apart of the intake point to intake point of water supply scheme were taken as sampling site for having different samples. the sampling points were divided in 500 m interval, which caused to have total five samples from zero to two kilometer of upstream i.e. naming sample one at zero meter, sample two at 500 meter, sample three at 1000 meter, sample four at 1500 meter and sample five at 2000 meter. all these samples were collected once a month at all intervals in the last week of month from april 2012 to june 2012, which formulated total fifteen samples throughout the sampling. structured and standard data collection method were used as per research methodology practice for their outputs as to carry out research work with different tools prescribed (standard method for the examination of water and waste water, (apha, awwa, wef) 19th edition 1995) and enpho test kit procedures. the field collected samples were tested by using following particular methods and instruments as mentioned in table 1. the data obtained from the field observation were categorized, tabulated, processed and analyzed using nsf wqi methods. the parameters of nsf wqi were tested by using following instruments and test kits with following particular testing methods. table 1: the test methods used for parameters [7] s.n. testing parameters testing methods / instruments remarks 1 ph hanna calibrated electrode probe ph meter 2 temperature mercury thermameter 3 turbidity turbidity meter enpho kit 4 total solids gravimetric 5 nitrate reagent 1,reagent 2,colour chart enpho kit 6 total phosphate reagent 1,reagent 2,colour chart enpho kit 7 ecoli elevated temperature fermentation 8 dissolved oxygen winkler method 9 bod winkler method finally the collected water samples were tested in regional water supply monitoring and supervision office pokhara and nepal water supply corporation pokhara branch as per respective standard guidelines. the analysis of the data was accomplished and presented using tools like ms word, excel and spss v. 16 as required. s. k. shah / bibechana 10 (2014) 100-107 : bmhss, p.103 (online publication: dec., 2013) 3. theory / calculation there are lots of efforts made to know the water quality of different water bodies like lakes and rivers around the world. several organizations in the united states and around the world have adopted the wqi concept for expressing the water quality for their water resources. among them some widely accepted wqi are nsf wqi, canadian council of ministers of the environment (ccme) wqi, alberta agricultural water quality index (aawqi), british columbia wqi etc. in case of nepal little studies found on the wqi. hence the nsf wqi method has been chosen to study the mardi river water quality as it is economical and easy. essentially, a wqi is a compilation of a number of parameters that can be used to determine the overall quality of a river. to measure the water quality, a standard index called the national sanitation foundation water quality index (nsfwqi) is used. the national sanitation foundation wqi consists of dissolved oxygen, fecal coliform, ph, biological oxygen demand, temperature, total phosphate, nitrate, turbidity and total solids parameters. the results of the tests are transferred to a weighting curve chart where their numerical values are obtained. these numerical values are multiplied by a “weighting factor” and then added – an overall water quality index is obtained as of table no 2 and 3. table 2: water quality weight factor of nsf – wqi [8] factors weight dissolved oxygen 0.17 fecal coliform 0.16 ph 0.11 bod 0.11 temperature 0.10 total phosphate 0.10 nitrates 0.10 turbudity 0.08 total solids 0.07 water quality weight factor the mathematical expression for nsf wqi is given by p nsf wqi = σ wi ii i=1 where ii is the sub-index for i th water quality parameters. wi is the weight (in terms of importance) associated with i th water quality parameters. p is the number of water quality parameters. the nsf wqi is an excellent management and general administrative tool in communicating water quality information. the table of classification criteria is very clear that according to the nsf value ranges the descriptor and category denotes the water quality information. this index has been widely tested in field and applied to data from a number of different geographical areas all over the world. s. k. shah / bibechana 10 (2014) 100-107 : bmhss, p.104 (online publication: dec., 2013) table 3: table of classification criteria standards based on nsf – wqi [8] nsf – wqi descriptor category 90 – 100 excellent a 70 – 90 good b 50 – 70 medium c 25 – 50 bad d 0 – 25 very bad e 4. results all the collected samples result were analyzed and presented as follows table 4: statistics of observed nsfwqi parameters parameters min max do 74.00 105.00 fecalcoliform 27.00 50.00 ph 6.80 7.80 bod 18.00 42.00 temperature 22.00 26.00 total phosphate 0.20 1.00 nitrate 25.00 75.00 turbidity 15.00 40.00 totalsolids 130.00 250.00 24.26 ± 0.34 0.62 ± 0.07 46.66 ± 5.38 24.40 ± 2.13 169.67 ± 12.06 average ± s.e. 87.33 ± 2.29 38.13 ± 2.00 7.43 ± 0.082 32.20 ± 1.94 fig. 2: wqi in different months along the different stations s. k. shah / bibechana 10 (2014) 100-107 : bmhss, p.105 (online publication: dec., 2013) according to above wqi values of different stations there is general progressive decline in wqi values which indicated that as the rainy season commence the quality of water get started to degrade. this is also supported by the given below of monthly variation of wqi graph. fig. 3: monthly varation of wqi table 5: correlation coefficient matrix of water quality parameters parameters do fecal coliform ph bod temperature total phosphate nitrate turbidity total solids do 1.000 fecal coliform 0.855** 1.000 ph 0.561* 0.636* 1.000 bod 0.772** 0.936** 0.435 1.000 temperature (-0.832**) (-0.727**) (-0.611*) (-0.654*) 1.000 total phosphate 0.591* 0.627* 0.122 0.744** (-0.524*) 1.000 nitrate 0.853** 0.918** 0.634* 0.814** (-0.672**) 0.667** 1.000 turbidity 0.851** 0.864** 0.536* 0.797** (-0.776**) 0.715** 0.891** 1.000 total solids 0.876** 0.789** 0.602* 0.674** (-0.786**) 0.542* 0.857** 0.895** 1.000 ** correlation is significant at the 0.01 level (2-tailed). * correlation is significant at the 0.05 level (2-tailed). 5. discussion the correlation matrix shows that there is high correlation in parameters nitrate and turbidity with the water quality of mardi river. these two parameters are highly correlated and responsible for degradation of water quality of mardi. so for having corrections in water quality, we should think s. k. shah / bibechana 10 (2014) 100-107 : bmhss, p.106 (online publication: dec., 2013) about the controlling mechanism of nitrate and turbidity. the analysis shows that if we have to give the priority between nitrate and turbidity then nitrate becomes the first parameter, which should be minimized to make less effective role in degradation of mardi’s river water quality. excess amount of nitrogen content in water causes the algae growth, which finally seriously affects the aquatic life as the algal blooms are formed. the eutrophication will be the major problem of water due to excess nitrogen content in water. the long term use of nitrogen contained water cause the blue baby disease which is also known as methemoglobinemia. other health problems like headache, dizziness, weakness or difficulty in breathing also can be caused. turbidity becomes the secondary one which is highly affecting the water quality of mardi river. turbidity is the life span shortening factor of water bodies as it get deposited in the bed and at bank the streams get narrow down. turbidity blocks the natural photosynthesis process which is important part of the life cycle of water bodies. excess turbidity could cause lack of dissolved oxygen which is the most essential thing for survival of aquatic life. so these factors are prime causes of mardi water quality degradation which should be taken in account. 6. conclusion although the study reveals mardi has degraded water quality and it lies in medium level pollution and denoted by c. though it still can be used for agriculture, fishery and for drinking application after proper treatment. rainfall increases the runoff carrying chemical fertilizers, manure and soil particles which get washed away towards the mardi river .this plays vital role for increasing the value of nitrate and turbidity concentration. river water pollution is not only an aesthetic problem, but a serious economic, public health problem and sustaining aquatic life as well. so regular monitoring of the water quality is thus required to assess the condition of river water. wqi is helpful in saving the river from further degradation and maintain the standard of sustaining aquatic life. recommendation based on assumption that the taken stretch of mardi river represents the whole mardi watershed’s mardi river, it clearly shows that there is an urgent need to control the further deterioration of mardi river water quality. the following measures are recommended based on the study: 1. best management practices for fertilizer use can reduce nitrate concentration in the soil. following practices in planning of fertilizer use are recommended: • use soil and water analysis to determine exact nitrogen needs of crop and consider all the potential sources of nitrogen. • set a realistic yield goal for each field. 2. upstream villages should be rewarded through pes mechanism to decrease the contamination to the river by different activities such as helping to construct public toilets, lowering the manure application, public awareness campaigns etc. 3. best practices of watershed management already applied in nepal should be used in this mardi watershed area like: i. terrace improvement and on-farm conservation ii. cascades of conservation ponds s. k. shah / bibechana 10 (2014) 100-107 : bmhss, p.107 (online publication: dec., 2013) iii. water supply focused activity of watershed management iv. community based management v. bioengineering measures 4. anthropogenic actions like open defecation and wastewater discharge, cattle washing and funeral rituals in and near vicinity of mardi river should be stopped. 5. adequate water treatment plant (sedimentation) for mardi water supply scheme should be planned and implemented. acknowledgements the author gratefully acknowledge international tropical timber organization (itto) fellowship programme japan for providing research fund, mr.binod prasad heyojoo, associate professor,t.u. i.o.f. pokhara, nepal, and mr. kishor kumar shrestha, lecturer, t.u. i.o.e.,w.r.c.pokhara, nepal for their valuable support and countless corrective suggestions. references 1. r.g. wetzel,. limnology: lake and river ecosystems, 3rd ed. academic press, 2001. 2. anish dua and ashwini kumar, global journal of environmental science, 8, (2009). 3. http://nnww2011.wordpress.com/2011/02/26/water-quality-mapping-of-bagmati-river-using-gis/ assessed on may 05, 2012 4. www.vernier.com/cmat/esi.html assessed on may 05, 2012. 5. district development committee, kaski, 2012 6. k.d. awasthi, b.k. sitaula, b.r. singh and r.m. bajracharya land-use change in two nepalese watershed: gis and geomorphometric. land degrade develop 13(2002) 495-513. 7. apha-awwa-wpcf, standard methods for examination of water and wastewater, 19th edn. washington, district of columbia: american public health association, american water works association, water pollution control federation 1995. 8. www.water-research.net/watrqualindex/index.htm assessed on may 15, 2012 microsoft word a. panthi _59-62_.doc a. panthi and h.n. singh / bibechana 9 (2013) 59-62 : bmhss, p.59 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana recent seismic status of shillong plateau, northeast india ananta panthi 1* , h. n. singh 2 1 department of physics, butwal multiple campus, butwal 2 department of geophysics, banaras hindu university, varanasi, india *corresponding author: email: apanthi@hotmail.com article history: received 27 october, 2012; accepted 8 november, 2012 abstract seismic status of shillong plateau of northeast india has been studied, considering spatial and temporal pattern of the region and using seismicity data for the period 1808-2008. cutoff magnitude and b-value has been estimated using earthquake data for the period 1963-2008. seismic activity is observed to be very feeble along the major faults of shillong plateau and strong activity is found to occur slightly away from these faults and confined within middle portion at two locations of the region. the temporal pattern shows that the region is due for great earthquake. focal depth distribution of the events shows that all the events are intermediate depth (less than 70 km). keywords: b-value; seismicity; faults; focal depth; temporal; spatial. 1. introduction the shillong plateau is located between the himalaya and bengal basin. the shillong plateau is known as detached area from indian shield comprises the archaean to proterozoic gneisses and is covered by quartzite, grit and slates [1]. this plateau also consists of patchy remnants of a tertiary cover and some unclassified crystalline rocks. the topography of shillong plateau shows a crisscross pattern of faults cutting the ancient rocks of the basement [2]. this plateau has pop-up structure since pliocene because of the loads of himalaya [3]. the shillong plateau has experienced vertical uplift [4] and the upliftment is believed to be ~1 km [3]. the shillong plateau is mostly e–w trending hill. this region consists of several faults with three main directions of orientation i.e. nw-se, ne-sw and n-s. the major faults are mapped in the shillong plateau region such as dauki fault trending e-w to the south [2], chedrang fault and oldhan fault to the north, kopili fault to the east and dhubri and tista fault to the west. shillong plateau region is seismically active in northeast india, where a great earthquake (1897) has occurred in the past. the region has been seismically very active from 1897 to 1930 during which one great earthquake (1897) and three large earthquakes with 7 ≤ m ≤ 7.6 (1918, 1923 and 1930) have rocked the region in just 33 years period (table 3). three of these earthquakes i.e. 1897, 1918 and 1923 are located in a straight line along 91 o e almost in the middle of the plateau whereas 1930 earthquake occurred at a distance of about 1 o to the west of it. the remaining part of the region towards east has been devoid of such seismic hazards in the past. a. panthi and h.n. singh / bibechana 9 (2013) 59-62 : bmhss, p.60 (online publication: nov., 2012) 2. data analysis seismicity data were compiled considering almost all the available earthquake catalogues such as national earthquake information centre (neicusgs), international seismological centre (isc), advanced national seismic systems (anss), incorporated research institutions for seismology (iris), national oceanic atmospheric administration (noaa) and other published records by tandon and srivastava [5], chandra [6], gupta et al. [7] etc. as sources of earthquakes. using the earthquakes records from the above catalogues, a database has been compiled on computer format using a rectangular search method for the period from 1808-2008. critical scrutiny and examination of compiled seismicity data have been carried out and the database was finalized by removing suspected repeated events. the frequency of earthquakes with magnitude and depth of shillong plateau is depicted in table 1. similarly, the estimated b-value and cutoff magnitude of the region is given in table 2. table 1: frequency of earthquakes with respect to magnitude and focal depth in shillong plateau of northeast india from 1963 to 2008. . table 2: estimated a & b-values for shillong plateau for the period 1963 to 2008 with cutoff magnitude. table 3: list of large to great earthquakes for m ≥≥≥≥ 7 that occurred in shillong plateau northeast india during the period 1897 to 1962 [7] (gupta et al., 1986). date origin time epicenter depth m source sl. nos. yyyy mm dd hh:mm:ss long.˚e lat. ˚n km 1 1897 06 12 11:06:00 91.00 26.00 60 8.7 old 2 1918 07 08 10:22:07 91.00 24.50 60 7.6 g-r 3 1923 09 09 22:03:43 91.00 25.20 60 7.1 g-r/bda 4 1930 07 02 21:03:42 90.00 25.50 60 7.1 g-r/bda old[8]; g-r[9];bda[10] number of earthquakes focal depth (km) magnitude (mb) all magnitude mb≥ 4.3 annual frequency ≤ 4.2 ≥ 4.3 ≥ 5.0 ≥ 6.0 ≤40 40–70 >70 shallow intermediate mb≥ 4.3 98 103 22 -145 50 6 103 0 2 bvalue a value r 2 cutoff magnitud e area (x 10 4 km 2 ) 1.27±0.04 7.58±0.2 3 0.98 4.2 008.79 a. panthi and h.n. singh / bibechana 9 (2013) 59-62 : bmhss, p.61 (online publication: nov., 2012) fig. 1: patterns of spatial (a), temporal (b) and focal depth (c) distribution of earthquakes (mb≥4.3) in shillong plateau region during the period 1963 -2008. the compiled seismicity data indicates that shillong plateau region has been mildly active during 19632008. two prominent seismically active centers can be seen from the spatial distribution of earthquakes shown in fig. 1a as: a northwest-southeast trending segment measuring approximately 100 km x 350 km located almost in the middle of the plateau; and the second is of localized nature bounded by 25.5 o -26.5 o n; 91.7 o e93 o e. the larger magnitude earthquakes (mb 5.5-5.9) during this period are concentrated to the southeast portion of the plateau near dauki fault whereas smaller events (m 4.3-5.4) are distributed almost uniformly throughout the plateau. dauki fault, dapshi thrust, kopili fault and sylhet fault are responsible for earthquake generation in this region. during the period 1963-2008, the total number of events occurred in the region is 201 that includes 40% events with mb 4.3-4.9 and 11% with mb ≥ 5.0 (5.0-5.9) (table 1). the focal depth distribution of this region is peculiar, where only shallow focus earthquakes have occurred frequently. temporal pattern (fig. 1b) shows extremely low seismic activity up to 1981 followed by a sudden jump in 1982. although temporal clustering is evident in 1982 (fig. 1b) but these events are not spatially clustered and distributed widely in plateau region. the seismic activity from 1982 increases constantly but not a single moderate event (mb ≥ 6.0) has occurred in the region during the last 46 years. the a. panthi and h.n. singh / bibechana 9 (2013) 59-62 : bmhss, p.62 (online publication: nov., 2012) longitude wise focal depth distribution of events shows the higher concentration at depth greater than 30 km with a clustering of events between 91.7 o 92.3 o e (fig. 1c). it is also observed that about 70% of larger magnitude earthquakes (mb ≥ 5.0) have occurred between the focal depths ranges 30-55 km. 3. result and discussions the seismic activity of a region mainly depends upon the subsurface geologic setup and arrangement of tectonic features. the data set has been critically examined for b-values, the spatio-temporal patterns of seismic activity, the focal depth distribution of events in shillong plateau. the bvalue thus estimated help understanding earthquake occurrence pattern and its relation with other tectonic belts/regions. thus spatio-temporal distribution of earthquakes and their relationships with the regional/ local geological structures constitute an important field of study for understanding the future seismic hazards and its assessment. the seismic activity in shillong plateau is confined within the middle portion in two seismically active segments trending northwest-southeast. temporal pattern shows that the region is due for a great earthquake. the major features of northeast india himalaya and its adjoining regions is the result of collision tectonics of india and eurasia. this part of himalaya is under high compression due to northward movement of indian plate which is eventually subducting beneath the eurasian plate. from the interpretation of observed faulting patterns in shillong plateau, it can be inferred that the region is under compression due to the stresses acting in n to ne directions. due to this action, probably the tectonic features of the region are also affected and it is believed that this could be one of the most promising reasons for intense seismic activity in this part of northeast india. references [1] d. r. nandy, abc publications, calcutta, (2001). [2] p. evans, journal of geological society of india, 5 (1964) 80. [3] r. bilham and p. england, nature, 410 (2001) 806. [4] s. v. deshikachar, journal of geological society of india, 15 (1974) 137. [5] a. n. tandon and h. n. srivastava, ann. di geofis., 28 (1975)13. [6] u. chandra, current science, 62 (1992) 40. [7] h. k. gupta, k. rajendran and h. n. singh, journal of geological society of india, 28 (1986) 345. [8] r. d. oldham, mem. geol. surv. india, 29 (1899) 1. [9] b. gutenberg and c. f. richter, hafner publication ( 1954). [10] m. bath, and s. duda, report no. 1-79, seismological institute, uppsala, sweden (1979) 41. 70-78 i. koirala r c o s t n i. koirala / bibechana 11(1) (2014) 70-78: (online publication: march, 2014) p.70 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana theoretical investigation on ordering nature of cd-bi alloys in the molten state i. koirala1, 2, i.s. jha 3, b.p. singh1 1university department of physics, t.m. bhagalpur university, bhagalpur, india 2central department of physics, tribhuvan university, kirtipur, nepal 3department of physics, m.m.a.m. campus biratnagar, tribhuvan university, nepal e-mail: ishwar_koirala@yahoo.com accepted for publication: february 6, 2014 abstract experimental determination of thermo-physical mixing properties of binary liquid alloys is a long and expensive task that becomes more complicated for some system which may be chemically active or radioactive or even may contain scarce components. theoretical method, on the other hand reduces the time and efforts required, and are of great importance in predicting the properties. now we have focused on theoretical model to study of the alloying behaviour of cd-bi alloys in the molten state at 773k. we have used simple statistical model to report the ordering nature of cd-bi liquid alloys through the study of surface properties, transport properties and various thermodynamic and microscopic functions. the knowledge of surface phenomena like surface segregation and surface tension is essential for the processing of materials and productions in the metallurgical industry. at the microscopic level, transport properties such as viscosity and diffusion coefficient help to understand about the mixing behaviour of the alloys forming molten metals. thermodynamic properties provide information on the interaction, stability and bonding strength among the constituent atoms in the alloys. the microscopic properties are useful in obtaining the microscopic information on structure of molten alloys. our theoretical analysis gives the negative energy parameter, which is found to be temperature dependent. negative deviation from raoultian behaviour is observed in the computed surface tension, thermodynamic and structural parameters of the alloys. but in case of viscosity isotherm positive deviation from ideality is observed. the computed results are in good agreement with experimental data. the analysis concluded that the alloy is of weakly interacting and heterocoordinating system. © 2014 rcost: all rights reserved. keywords: simple statistical model; negative deviation; hetero-coordination; surface properties. 1. introduction it is very difficult to conduct diffraction experiment on cadmium metal because of its highly reactive nature. therefore theoretical investigation giving mixing properties of cadmium alloys are highly desirable. cadmium alloys have been widely used in fabricating solid state electronic components [1]. cadmium-bismuth is one of the eutectic metal alloys, which has potential applications in bearing assemblies, ballasts, casting, step soldering, radiation soldering etc. small content of cadmium lowers the melting point of cadmium-bismuth alloys, improves thermal and electrical conductivities and increases mechanical properties such as hardness, wear resistance, tensile and fatigue strength [1]. for the material preparation of metal alloys, the understandings of mixing properties of liquid alloys are important. several theoretical models [2-8] have long been proposed to understand the thermodynamic, structural, transport and surface properties of binary liquid alloys. in present work, we study the concentration dependent mixing properties of liquid cd-bi at 773k by the simple statistical model [9-11]. the energetic of mixing as well as the positive/negative deviation from raoultian behavior for the various bulk and surface properties have been discussed. i. koirala / bibechana 11(1) (2014) 70-78: (online publication: march, 2014) p.71 it is observed that system cd-bi is characterized by negative interaction energy, indicating the formation of two structures, as shown by their phase diagrams [12].this characteristic behavior is likely to be a reflection of the interplay of the energetic and structural re-adjustment of the constituent elemental atoms. the paper is arranged as follows: we present theoretical formalism in section 2, which is followed by results and discussions in section 3 and finally, conclusion of the paper is presented in section 4. 2. theoretical formalism 2.1. thermodynamic properties in the framework of simple statistical model for regular solution the expression for the excess free energy of mixing [10, 11] is { }xxs z m a b0 g rt in dx rt xin (1 x)in= σ = γ + − γ∫ (1) where ( ) b2x 1 exp( / zk t) / 2xσ= β+ − −ω (1a) [ ] 2/z a )1(x/)x21( β++−β=γ (1b) [ ] 2/z b )1)(x1/()x21( β+−−+β=γ (1c) [ ]{ } 2/1 b 1)tzk/2exp()x1(x41 −ω−+=β (1d) where r is universal molar constant; t, absolute temperature; x, concentration of the component; ω, interchange energy; z, coordination number and kb, boltzmann constant. the ideal free energy of mixing (ω = 0) is { }id mg rt xinx (1 x)in(1 x)= + − − (2) the expression for free energy of mixing [13], one obtains from the standard thermodynamic relation as xs m id mm ggg += { }a brt{x ln x (1 x) ln(1 x)} rt xin (1 x)in= + − − + γ + − γ (3) for the equiatomic composition ( 2 1 x = ), relation (1) reduces to 2/z b 2/z xs m )]tzk/exp(1[2ln rt g −ω−+= (4) the heat of mixing (hm) and entropy of mixing (sm) are obtained from the relations m m m x,p,n g h g t t ∂ = −  ∂  (5) m m ms (h g ) / t= − (6) the activity of binary liquid alloys, fi (i=a or b) ,can be related to the free energy of mixing by the relation m i i t,p,n g rt ln f n  ∂ =  ∂  m m i i t,p,n g g (1 x ) x  ∂ = + −  ∂  (7) then from eq.(8) we have [13], 2 a b ln f ln x (1 x ) k t ω= + − (8a) 2 b b ln f ln(1 x) x k t ω= − + (8b) i. koirala / bibechana 11(1) (2014) 70-78: (online publication: march, 2014) p.72 2.2. structural properties concentration fluctuations in the long-wavelength limit (scc(0)) is an essential structural function which has been widely used to study the nature of atomic order in binary liquid alloys [14,15]. scc(0) is thermodynamically related to free energy of mixing(gm) [14]. it is given as ( ) 12 m cc 2 t,p,n g s 0 rt x −  ∂  =  ∂  (9) equations (3) and (9) gives the theoretical value of scc(0): 1 cc bs (0) x(1 x)[1 x(1 x) 2 / k t ]−= − − − ω (10) the ideal value of concentration-concentration fluctuations, when the ordering energy is zero, is usually computed from: id ccs (0) x(1 x)= − (11) there are difficulties in diffraction experiment, therefore theoretical determination of scc(0) is of great importance when nature of interactions in the melt has to be analyzed. the mixing behavior of liquid alloys can be deduced from the deviation of scc(0) from id ccs (0) . at a given composition if )0(s)0(s id cccc < , ordering in liquid alloy is expected while )0(s)0(s id cccc > gives the indication of tendency of segregation [14]. the warren-cowley [16-17] short-range order parameter (α1) is useful parameter to quantify the degree of chemical order in the alloy melt. it provides insight into the local arrangement of the atoms in the molten alloys. although it is difficult to obtain the experimental values of α1, theoretical values of this parameter are easily obtain via conditional probability [a/b] which defines the probability of finding an a-atom as a nearest neighbor of a given b-atom. it can be evaluated theoretically [16-17]: id 1 cc cc(s 1) / {s (z 1) 1}, s s (0) / s (0)α = − − + = (12) where z is the coordination number, which is taken as 10 for our purposes. for the equiatomic composition, the chemical short range order parameter is found to be -1 ≤ α1 ≤ 1. negative values of α1 indicate ordering in the melt, which is complete if α1= -1. on the other hand, positive values of α1indicate segregation, leading to complete only if α1 = 1. but α1 = 0, corresponds to random distribution of the atoms in the mixture. 2.3 transport properties the mixing behavior of binary liquid alloys can also be studied at the microscopic level in terms of transport properties such as viscosity, chemical diffusion coefficients etc. viscosity (η) of liquid alloys is equally important in the understanding of the atomic level structure and interactions. as in the case of thermodynamic functions, the composition dependence of η of liquid alloys is also found to exhibit either a linear variation, or positive or negative deviations from the linear law. a simple formula for the investigation of viscosity of a binary solution [18] is id b 2 1 x(1 x) k t   ωη = η − −       (13) with 0 0 id a bx (1 x)η = η + − η (14) where 0 iη is the viscosity of pure component i ( = a or b) and ω, as usual, is the interchange energy or order energy. the mixing behavior of the alloys forming molten metal can also be studied at the microscopic level in terms of coefficient of diffusion. the mutual diffusion coefficient (dm) of binary liquid alloys can be i. koirala / bibechana 11(1) (2014) 70-78: (online publication: march, 2014) p.73 expressed in terms of activity (fi) and selfdiffusion coefficient (did) of pure component with the help of darken’s equation [19], i m id i i d ln f d d x dx = (15) we obtain an expression for md in terms of scc(0): )0(s )0(s d d cc id cc id m = (16) with abm d)x1(xdd −+= (17) where da and db are the self-diffusion coefficients of pure components a and b respectively. according to eq. (17), id cc ccs (0) s〈 indicates typical compound forming alloys implying dm ˃ did. a peak on diffusivity curve, dm / did verses x, suggests presence of maximum chemical order in the molten alloys system as well as the composition of the most probable associates formed in the liquid phase. the relationship between scc(0) and the diffusivity expressed by the ratio of the mutual and self-diffusion coefficients, dm / did, indicates the mixing behavior of the alloys, i.e. the tendency for compound formation( dm / did > 1) or phase separation (dm / did < 1) or ideal mixing (dm / did approaches 1). considering only the energetics of the nearestneighbor bond, equation (14) becomes m id b 2 d d 1 x(1 x) k t   ω= − −       (18) 2.4 surface properties many properties of technological importance such as mechanical behavior, kinetics of phase transformation, catalytic activity of alloy catalyst and thin film cannot be explained without understanding surface phenomena i.e. surface segregation and surface tension. surface segregation results from the interaction among the atoms and surface tension, is the enrichment of the surface by the atoms of the particular component element in a binary alloy [4, 5]. in the statistical formulation of prasad et al. [4, 5] binary liquid alloy is considered to have a layered structure near the surface with thermodynamic equilibrium existing between the species at the surface and in the bulk. the surface properties of liquid alloys are influenced by their bulk thermodynamic properties. the surface grand partition function is related to the surface tension τ by the expression [5]. s s b b s n exp exp k t k t   − τ − τξξ = =         (19) where s is the surface area and ξ is the mean area of the surface per atom and is defined as ξ = s/ns , and ns is the total number of atoms at the surface. kb is the boltzmann constant. a pair of equation for surface tension of the binary liquid alloys in terms of activity coefficient (γi) of the alloy components and interchange energy parameter (ω), at the given temperature t, proposed by prasad et al., have been reduced in the simple form, using zeroth approximation as ( ) ( ) s 2 2sb a k t x ln p 1 x (q 1) 1 x x  ωτ = τ + + − + − − ξ ξ   (20a) s s 2 2b b b k t k t ln(1 x ) ln(1 x) {p(x ) (q 1)x } ωτ = τ + − − − + + − ξ ξ ξ (20b) where aτ and τb are the surface tension values for the pure components a and b respectively; x and xs are the bulk and surface concentrations of the alloy component; p and q are the surface coordination i. koirala / bibechana 11(1) (2014) 70-78: (online publication: march, 2014) p.74 fractions, which are defined as the fraction of the total number of nearest neighbors made by atom within its own layer and that in the adjoining layer. for p and q, the following relation is available [4-7]. p + 2q = 1 for closed packed structure, p = 0.5 while q = 0.25 (in view of the disordered structure and relaxation effect of the surface layer p and q should be treated as parameters [5]). the pair of eqs. 20(a) and 20(b) can be solved numerically to obtain xs as a function of x. obviously the surface concentration depends upon the surface tension of the ith component in the pure state (τi) , surface area per atom (ξ), order energy (ω) and the coordination fractions (p and q). this approach is useful because it can be used to investigate the dependence of surface composition on order energy and surface coordination. the mean atomic surface area ξ (=a/ns) is given as i ic (i a,b)ξ = ξ =∑ (21) where the atomic area of hypothetical surface for each component is given as [5]: 2/3 i i 0 1.102 ω ξ =  ν  (22) where iω is the molar volume of the species i and n0 stands for avogadro number. on the basis of assumption of monatomic surface layer, butler’s approach [20] of surface tension τ of liquid solution can be expressed as s b s b s b a a b b i i a b i ....... µ − µ µ − µ µ − µ τ= = = = α α α (23) where s b i i i, andµ µ α represent respectively the chemical potential in the hypothetical surface and that in the bulk and molar surface area of pure component i (a or b). equation(23) yields the expressions for surface tension in terms of partial excess free energy of mixing in bulk ( e,b ig ) and at the surface (e,s ig ), and concentration in the bulk (x) and at the surface (xs) as ( )e e a a ,s ,b a 1 rt rtsg g a a a inx inxτ = τ − + α α α + − (24a) ( )e e b b ,s ,b b b b b 1 rt rtsg g in(1 x ) in(1 x)τ = τ − + α α α + − − − (24b) where τa and τb are surface tension of pure component a and b respectively. the area of monatomic surface layer for the component i can be calculated by the relation [20] 1/3 2/3 i 0 i1.091 nα = ω (25) where n0 is avogadro’s number and ωi stands for molar volume of the component i, can be calculated from its molar mass and density. 3. results and discussion the energy parameter used for the calculation for cd-mg liquid alloys at 773k has been determined from equations (4) and (5) by using experimental value of xs m g and hm for equiatomic composition [12].the best fitting values of parameter are found as: i. koirala / bibechana 11(1) (2014) 70-78: (online publication: march, 2014) p.75 b 0.224 k t ω = − and b 1 d .07084 k dt ω = − (26) the negative value of energy parameter ω/kbt suggests that there is higher tendency for unlike atoms to pair in the alloy which implies a hetero-coordination system. however, the tendency of pairing is weak since energy parameter is small. we have observed that if energy parameters are supposed to be independent of temperature (dω/dt = 0), then sm and hm so obtained are in poor agreement with experimental data. this suggests the importance of temperature dependence of ordering energy, ω. the free energy of mixing, heat of mixing and entropy of mixing for cd-mg liquid alloys at 773k have been computed from equations (3), (5) and (6).the plot of gm/rt, hm/rt and sm/r versus xcd are depicted in fig. 1. the calculated and experimental values of gm/rt, hm/rt and sm/r are in good agreement throughout whole concentrations of cadmium. therefore our choice of ω for the alloy is good because it is confirmed from the qualitative agreement between calculated and experimental values. the value of gm/rt and hm/rt are minimum but sm/r is maximum at xcd =0.5, which show that cd-bi liquid alloy is symmetric about equiatomic concentration. the negative small values of free energy of mixing throughout the entire compositions indicate that the cd-bi alloy at 773k in molten state is weakly interacting system. the activity is one of the important thermodynamic functions which are obtained directly from experiment. the deviation from ideal behaviour is incorporated into activity. we have used the same value of the energy parameter in eq. (8a) and (8b) for the evaluation of chemical activities of the components of the alloy. there is well agreement between calculated and experimental values of the activities of the components cd and bi of the alloy (fig. 2). figure 1: free energy of mixing (gm ), heat of mixing (hm) and and entropy of mixing (sm ) vs concentration of cadmium(xcd ) in liquid cd-bi alloy at 773k. figure 2: chemical activity (fi) versus concentration of cadmium(xcd ) in liquid cd-bi alloy at 773k. we have used eq.(10) to compute the scc(0) for cd-bi. it can also be obtained directly from the measured activity [12] data as 11 cd bi cc cd bi f f s (0) (1 x)f xf x (1 x) −−  ∂ ∂ = − =   ∂ ∂ −    (27) where fcd and fbi are the observed chemical activities of cadmium and bismuth respectively. the scc(0), obtained from eq. (27) are taken as experimental values. figure 3 shows a plot of the calculated and experimental values of scc(0) along with the ideal values. the calculated values of scc(0) are in good agreement with the experimental values of scc(0) except in the region 0.7˂ xbi˂ 0.3. in the region 0.3˂ xbi˂0.7, the computed values lie below the experimental values but in the whole range of concentrations of aluminium, computed values of scc(0) lying below the corresponding ideal values. the result )0(s)0(s id cccc 〈 , clearly described this system as compound forming. 0.2 0.4 0.6 0.8 1.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 c cd experimental theoretical g m / rt s m / r h m / rt fig.1 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 ln f i c cd experimental theoretical 0.2 0.4 0.6 0.8 lnf cd lnf cd fig.2 i. koirala / bibechana 11(1) (2014) 70-78: (online publication: march, 2014) p.76 figure 4 shows the plots of α1 against chemical composition of cadmium, obtained from eq. (12) for cdbi at 773k. it is observed that the plots are symmetrical about equiatomic composition and negative throughout the whole concentration range of cadmium. the negative values of α1 (minimum at xcd = 0.5) throughout whole concentration range are the signatures of hetero-coordination system in the cd-bi liquid alloys at 773k. the viscosity of the cd-bi liquid alloy has been computed numerically from eq. (13). from the plot of η verses bulk concentration of xcd (fig.5) in cd-bi liquid alloy, positive deviation from the linear law (raoult’s law) in viscosity isotherms η(c) have been observed for the regular alloy. the calculated values of scc(0) are used in eq. (16) to evaluate the ratio of the mutual and intrinsicdiffusion coefficients, dm/did. for the consistency of the estimated order energy parameter, ω, we have also calculated dm/did using eq. (18). fig.6 shows plot of dm/did against the concentration of cadmium. in that plot the value of dm/did is found greater than 1 in the entire range of concentration which is indicative for the compound formation in the mixture. a maximum value of dm/did = 1.112 for xcd= 0.5, confirms a weak tendency for chemical ordering, as observed by the scc(0) and csro parameter. figure 3: concentration fluctuation at long wavelength limit (scc(0) ) vs concentration of cadmium (xcd ) in liquid cd-bi alloy at 773k. figure 4: chemical short range order parameter (α1) vs concentration of cadmium (xcd ) in liquid cd-bi alloy at 773k. figure 5: viscosity (η) vs concentration of cadmium (xcd ) in liquid cd-bi alloy at 773k. figure 6: ratio of mutual and intrinsic diffusion coefficients ( dm /did ) vs concentration of cadmium (xcd ) in liquid cd-bi alloy at 773k. 0.2 0.4 0.6 0.8 1.0 0.00 0.05 0.10 0.15 0.20 0.25 s cc ( 0) c cd experimental theoretical ideal fig.3 -0.012 -0.010 -0.008 -0.006 -0.004 -0.002 0.000 c s r o ( αα αα 11 11) 0.2 0.4 0.6 1.00.8 c cd fig.4 0.0 0.2 0.4 0.6 0.8 1.0 1.0 1.2 1.4 1.6 1.8 ηη ηη ( m n sm -1 ) c cd fig.5 0.0 0.2 0.4 0.6 0.8 1.0 1.02 1.04 1.06 1.08 1.10 1.12 d m / d i d c cd fig.6 i. koirala / bibechana 11(1) (2014) 70-78: (online publication: march, 2014) p.77 the surface concentrations and surface tension of cd-bi have been computed numerically from the eqs. 20(a) and 20(b). for this, we need experimental data of density and surface tension of the components at the working temperature. we have calculated the density and surface tension for the components cd and bi [21,22] at the working temperature t=773k by using the following equations 3 cd(t) 8.70904 1.16 10 t−ρ = − × (28a) 3 bi (t) 10.79152 1.33 10 t−ρ = − × (28b) 5 cd(t) 0.585444 2.6 10 t−τ = − × (29a) 5 bi (t) 0.41608 7.0 10 t−τ = − × (29b) the mean atomic surface area ξ has been calculated by using eqs. (21) and (22). for calculating surface tension we used same estimated energy parameter, ω. at first, surface concentrations of cadmium in alloy cd-bi have been obtained as a function of bulk concentration by concurrently solving the eqs. 20(a) and 20(b). using the obtained values of surface concentrations we computed the surface tension of cd-bi liquid alloys at temperature 773k for whole concentration range. for the computation of surface concentration and surface tension of the cd-bi alloy on using butler’s approach, the partial excess free energies of mixing of pure components of the alloys have been taken from the ref. [12]. by concurrently solving the equations 24(a) and24(b) surface concentrations of cd in alloy cd-bi have been obtained as a function of bulk concentration and then using the obtained values of surface concentrations we computed the surface tension of cd-bi liquid alloys at temperature 773k for whole concentration range. figure 7: surface concentration of cadmium (scdx ) vs bulk concentration of cadmium (xcd ) in liquid cd-bi alloy at 773k. figure 8: surface tension (τ) vs bulk concentration of cadmium (xcd ) in liquid cd-bi alloy at 773k. the study of surface concentration shows the usual pattern for surface concentration increasing with increasing bulk compositions (fig. (7). this indicates that bi-atoms (having lower value of surface tension relative to cd-atoms in cd-bi) segregate at the surface of cd-bi liquid alloys in preference to cdatoms throughout the entire compositions. the computed values of surface tension for molten cd-bi alloys at 773k from two approaches, mentioned above are depicted in fig. (8). due to lack of surface tension experimental data we could not compare our computed surface tension with the experimental data, nonetheless, we observed that the isothermal plots of surface tension of the system exhibits negative 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 c s c d c cd prasad's model butler's model ideal fig.7 0.0 0.2 0.4 0.6 0.8 1.0 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50 0.52 0.54 0.56 τ (n m -1 ) c cd prasad's model butler's model ideal fig.8 i. koirala / bibechana 11(1) (2014) 70-78: (online publication: march, 2014) p.78 deviation from the ideal values ( a bx (1 x)τ=τ +τ − ) as it is the case with most binary liquid mixtures [21]. it is noticed that in two approaches computed values of τ and s cdx are found to be smaller than the ideal values throughout bulk concentration of cadmium. 4. conclusion following conclusions are drawn from the theoretical investigation on cd-bi liquid alloys at 773k: • order energy is small, negative and found to temperature dependent. • the alloy is of a weakly interacting nature. • it is of ordering system. • negative departure of thermodynamic and structural parameters from ideality is observed. • viscosity isotherm of the alloy is found to deviate positively from ideality. • consistency is occurred in the values of surface tension obtained from two approaches, negative departure of surface tension from ideality is observed. • the surface of liquid cd-bi alloys is enormously rich with bigger bi atoms. acknowledgments the author acknowledges dr. devendra adhikari (prof., m.m.a.m. campus biratnagar, tribhuvan university, nepal) and dr. lok narayan jha and dr. shekhar gurung (retired professors, tribhuvan university, nepal) for fruitful suggestions and inspiring discussions. references [1] f. habashi (editor), alloys: preparation, properties & applications, john wiley & sons, 2008. [2] b.c. anusionwu, o. akinlade, l.a. hussain, j. alloys and compounds, 175 (1998) 278. [3] o akinlade, r.n. singh, j.alloys and compounds, 84 (2002) 333. [4] l.c. prasad, r.n. singh, v.n. singh, g.p. singh, j. phys. chem. b, 102 (1998) 921. [5] l.c. prasad, r.n. singh, phys. rev. b, 44 (1991) 13768. [6] r. novakovic, j. non-cryst. solids, 356 (2010) 1593. [7] r. novakovic, d. giuranno, e. ricci, a. passerone, surface sci., 175 (2005) 576. [8] b.p. singh, d. adhikari, i.s. jha, adv.mat. lett., 3 (2012) 226. [9] i. koirala, i.s. jha, b.p. singh, d. adhikari, chemxpress, 4 (2014) 179. [10] i. koirala, i.s. jha, b.p. singh, d. adhikari, physica b, 49 (2013) 423. [11] r.n. singh, i.k. mishra, v.n. singh, phys. condens. matter, 2 (1990) 8457. [12] r. hultgren, p.d. desai, d.t. hawkins, m. gleiser, k.k. kelley, selected values the of thermodynamic properties of binary alloys. asm metals park, ohio., 1973. [13] e.a. guggenheim, mixtures, oxford university press, london, 1952. [14] a.b. bhatia, r.n. singh, phys. chem. liq., 11 (1982) 343. [15] a.b. bhatia, w.h. hargoove, phys. rev. b, 10 (1974) 3186. [16] b.e. warren. x-ray diffraction, addison-wesley, reading ma, 1969. [17] j.m. cowley, phys. rev., 77 (1950) 667. [18] e.a. moelevyn-hughes, physical chemistry, oxford, pergamon, 1964. [19] l.s. darken, r.w. gurry, physical chemistry of metals. mcgraw hill, new york, 1953. [20] j.a.v. butler, proc. r. soc. a, 135 (1932) 348. [21] t. iida, r.i.l. guthrie, the physical properties of liquid metals, clarendon press, oxford, 1988. [22] e.a. brandes, smithells, metals reference book, sixth edition 1983. 79-85 kuber limbu-ajaya bhattarai r c o s t n k. limbu et al. / bibechana 11(1) (2014) 79-85: (online publication: march, 2014) p.79 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana micellization behaviour of sodium dodecyl sulphate in presence and absence of sodium sulphate and zinc sulphate in distilled water by surface tension measurement kuber limbu, sujit kumar shah, ajaya bhattarai* department of chemistry, m.m.a.m. c. (tribhuvan university), biratnagar, nepal *corresponding author: e-mail: bkajaya@yahoo.com accepted for publication: february 15, 2014 abstract the accurate measurements of surface tension of sodium dodecyl sulphate (sds) in distilled water and in presence of 0.01m na2so4 and 0.01m znso4 at room temperature were reported by drop weight method using a stalagmometer. the critical micelle concentration (cmc) of sodium dodecyl sulphate (sds) in distilled water was obtained higher than in presence of na2so4 and znso4. the decrease of cmc of sodium dodecyl sulphate in the presence of salts has been discussed. © 2014 rcost: all rights reserved. keywords: stalagmometer; sodium dodecyl sulphate; surface tension; critical micelle concentration; sodium sulphate; zinc sulphate. 1. introduction due to the different environment of molecules located at an interface compared to those from either bulk phase, an interface is associated with a surface free energy. at the air-water surface for example, water molecules are subjected to unequal short-range attraction forces and, thus, undergo a net inward pull to the bulk phase. minimization of the contact area with the gas phase is therefore a spontaneous process, explaining why drops and bubbles are round. the surface free energy per unit area, defined as the surface tension (γ). another, but less intuitive, definition of surface tension is given as the force acting normal to the liquid-gas interface per unit length of the resulting thin film on the surface. surfactants reduce the amount of work necessary to create unit surface area i.e. surface tension of a solution is lowered when surfactants are present [1]. the limiting value of surfactant concentration that produces a surface tension decrease is the critical micelle concentration [2]. furthermore, the steeper decrease in surface tension is evident only at high surfactant concentrations. since, due to the surface activity of the surfactant, surface tension measurement is the major method for the determination of cmc. in tensiometric determination of the cmc of pure surfactants, the surface tensions (γ ) are plotted as a function of logarithm of the surfactant concentration. the following equation is used to calculate the surface tension of required solution. k. limbu et al. / bibechana 11(1) (2014) 79-85: (online publication: march, 2014) p.80 ����� = � � ��� � � (� � � �� )����� (1) where, γsoln = surface tension of solution γsolv = surface tension of solvent nsoln = number of drops of solution nsolv = number of drops of solvent dsoln = density of solution dsolv = density of solvent sodium dodecyl sulphate (sds) is an anionic surfactant. one end of the molecule is charged and therefore has an affinity for water, and the other end is non polar and soluble in fat/oil. sds has a negatively charged sulfonate group as its “hydrophilic” end and a saturated 12-carbon for its “lipophilic” end. sodium dodecyl sulphate has significant application as very effective surfactant in a number of industrial products and in recent studies it is considered as a novel microbicide against different viruses [3, 4]. in this paper, we report a study of the micellization behaviour of sodium dodecyl sulphate (sds) at room temperature in absence and in presence of na2so4 and znso4 by surface tension method in aqueous media. 2. experimental sodium dodecyl sulphate was purchased from loba chemical, india. znso4 and na2so4 were purchased from ranbaxy chemical, india. the water used in the experiments was doubly distilled. the solutions prepared at room temperature. for the preparation of experimental solution of sds in distilled water, 2.8838g of pure sds was weighed accurately with digital balance and was dissolved in 100 ml of distilled water to get 0.1m sds solution. 0.1 m sds solution was used as stock solution (so) for the preparation of different eight solutions of different concentrations viz. 0.08m (s1), 0.06m (s2), 0.04m (s3), 0.024m (s4), 0.018m (s5), 0.012m (s6), 0.00725m (s7), 0.0054m (s8). these different solutions were prepared by diluting the appropriate volume of stock solution (so) with distilled water in 50 ml volumetric flasks. similarly, as described above the same weight of pure sds was weighed and was dissolved in 100 ml of 0.01m na2so4 and 0.01m znso4 separately to get 0.1m sds in non-aqueous environments. here also eight different solutions were prepared for each of solvents with stock solutions: ao, a1, a2, a3, a4, a5, a6, a7, a8 and do, d1, d2, d3, d4, d5, d6, d7, d8 respectively with equivalent concentrations. the weights of the different solutions of sds with different strengths were measured by the pyknometer (specific gravity bottle). for this purpose, the cleaned pyknometer was taken and was first filled with airfree distilled water in it, then the stopper was inserted into its mouth so that the small amount of water flowed out the capillary then the outer surface of it was wiped out with a tissue paper ensuring that outer surface was completely dried. finally, the bottle was weighed and then emptied and dried. then, the same process was repeated for every type of solutions under investigations. after collecting the weights, the densities of related solutions were calculated and tabulated with reference to the standard density of water at 30oc(room temperature) i.e. 0.99571 g/cm3. surface tension measurements were carried out on a stalagmometer. the surface tension of sds in absence and presence of salts was measured by drop count method using a stalagmometer. it was designed by troube and consists of a pipette with a capillary outflow to be the end of which is flattened out. this is done to give a larger dropping surface. the surface is carefully ground flat and polished. before using the stalagmometer was first carefully washed with a solution of chromic acid and then with k. limbu et al. / bibechana 11(1) (2014) 79-85: (online publication: march, 2014) p.81 distilled water. finally it was washed with acetone and dried. the stalagmometer was held vertical and was not shaken because otherwise the drop will fall out even before attaining its maximum size. in this process, first the stalagmometer was filled with distilled water as above without changing the pressure. then the drop count was started. by following the same process all the liquids or solutions of varied strength of sds in presence and absence of na2so4 and znso4 was measured. 3. results and discussion the surface tension of sds in distilled water and in aqueous solution of na2so4 and znso4 were calculated from equation (1) and were tabulated in table 1a, 1b and 1c. the graphical representations of the surface tension of sds in distilled water and in aqueous solution of na2so4 and znso4 with log [sds] are shown in figs. 1-3. since, there was sharp decrease of surface tension on increase of surfactant concentrations. according to the experimental calculations and determinations, the surface tension was found to be decreased in presence of salts .i.e. na2so4 and znso4. the surface tension value was high in case of water because of absence of externally added salts. since, on the addition of inorganic salts, affect surfactant aggregation mainly through reducing the electrostatic interaction among the surfactant head groups and consequently decrease the surface tension of the surfactant molecules. in the case of na2so4 and znso4, the sodium ion (na+) is larger than the zinc ion (zn2+) because, the zinc cation, zn2+, has a greater cationic charge than the na+ cation. the surface tension of sds in presence of na2so4 is more than in presence of znso4 because the smaller ions are strongly hydrated, so they need to pull more water molecules with them which make them less mobile. thus, due to zinc ions (zn2+) .i.e. counter ions reduced largely the electrostatic interaction among the surfactant molecules and decreased surface tension largely. when surface tension of a solution is plotted against log[c], where c is the concentration of surfactant then it gives a curve. the two fitted lines meet in the curve at the particular point. that point of intersection is known as cmc of the solution. table 1a: surface tensions of sds in distilled water. solvent concentration (mol/l-1) surface tension (dyne/cm) distilled water 0.02402 0.01801 0.01351 0.01013 0.00760 0.00570 0.00428 0.00321 0.00241 0.00180 0.00135 0.00102 31.80359 32.11061 32.42408 32.74436 33.40919 35.97611 37.62764 38.96942 39.91825 40.40978 40.91390 41.43103 k. limbu et al. / bibechana 11(1) (2014) 79-85: (online publication: march, 2014) p.82 table 1b: surface tensions of sds in the presence of na2so4. solvent concentration (mol/l-1) surface tension (dyne/cm) na2so4 0.02400 0.02000 0.01667 0.01389 0.01157 0.00965 0.00804 0.00670 0.00558 0.00465 0.00388 0.00323 0.00269 0.00224 0.00187 0.00156 0.00130 29.83293 30.10266 30.66151 31.54318 32.15982 33.13277 33.81490 34.16566 40.99797 43.73001 44.92753 47.53145 50.45586 53.76411 56.54468 58.56345 59.62791 our calculation of cmc of sds in distilled water at room temperature found to be 8.29 mm which is almost matching with 9.00 mm by surface tension method [5]. when surfactant and salt are mixed in solution, salting-out phenomenon often happens [6-9]. according to hydration theory [10] salting-out is the result of preferential movement of water molecules, which immobilize and quench their role as solvents, from coordination shells of surfactant molecules to those of salts. the effects of halide salts on the growth of micelles in ionic surfactant solutions have been systematically studied [11,12]. with the addition of inorganic salts, the reduced electrostatic repulsion among the surfactant head groups is a key factor to influence the morphology of aggregates in ionic surfactant solutions. for conventional single-chain cationic surfactants, micelles may change from global to rod like or wormlike with the addition of inorganic salts [13,14]. salts decrease the cmc in the order: znso4< na2so4. here zn+ + is least effective in decreasing the cmc due to small size and large hydrated radius and would act as a water-structure promoter decreasing the availability of water to the micelles. therefore, upon addition of znso4 and na2so4 in sds, na2so4 is more effective in reducing the cmc of sds. hence in our case na2so4 decreases the cmc of sds more than znso4 (table 2). k. limbu et al. / bibechana 11(1) (2014) 79-85: (online publication: march, 2014) p.83 table 1c: surface tensions of sds in the presence of znso4. solvent concentration (mol/l-1) surface tension (dyne/cm) znso4 0.06017 0.05014 0.04179 0.03482 0.02902 0.02418 0.02015 0.01679 0.01399 0.01166 0.00972 0.00810 0.00675 0.00562 0.00469 0.00391 0.00325 0.00271 0.00226 0.00188 27.16200 27.37816 27.59907 28.06390 28.29980 28.79153 29.56571 30.10506 30.66502 30.95195 31.24480 31.54408 31.84879 34.89688 37.27535 40.00185 41.00095 41.51947 41.51852 41.51804 figure 1: variation of surface tension of sds with log [sds] in distilled water at room temperature. 30 33 36 39 42 -3.0 -2.5 -2.0 -1.5 -1.0 log[sds] su rf ac e te ns io n( dy ne /c m ) k. limbu et al. / bibechana 11(1) (2014) 79-85: (online publication: march, 2014) p.84 figure 2: variation of surface tension of sds with log [sds] in aqueous solution of na2so4 at room temperature. figure 3: variation of surface tension of sds with log [sds] in aqueous solution of znso4 at room temperature. table 2: critical micelle concentrations of sds obtained from surface tension measurement in distilled water, aqueous solution of na2so4 and znso4. solvent distilled water cmc (mm) 0.01m znso4 cmc (mm) 0.01m na2so4 cmc (mm) surface tension 8.29 7.01 6.02 25 30 35 40 45 -2.8 -2.4 -2.0 -1.6 -1.2 log[sds] su rf ac e te ns io n( dy ne /c m ) 20 30 40 50 60 70 -3.0 -2.5 -2.0 -1.5 -1.0 log[sds] su rf ac e te ns io n( dy ne /c m ) k. limbu et al. / bibechana 11(1) (2014) 79-85: (online publication: march, 2014) p.85 4. conclusion the following conclusions have been drawn from above results and discussion. the results showed the decrease in surface tension of sodium dodecyl sulphate (sds) at room temperature in presence of na2so4 and znso4. the surface tension of sodium dodecyl sulphate is found less in presence of znso4 than na2so4 in aqueous media and the cmc of sodium dodecyl sulphate decreases more in na2so4 comparison with presence of znso4. acknowledgments one of the authors (kuber limbu) is thankful to the university grants commission (ugc), nepal, for providing grants for m. sc. dissertation work and the authors are grateful to associate professor g.s. shrivastav, head of the department of chemistry, mahendra morang adarsh multiple campus, tribhuvan university, biratnagar, nepal for providing the research facilities to conduct this research work. references [1] m. austin, b.b. bright, e .a. simpson, j. colloid and interface sci., 23 (1967) 108 . [2] j .a. caskey, w .b. barlage, j. colloid and interface sci., 35 (1971) 46. [3] j. piret, a. désormeaux, m. g. bergeron, curr. drug targets, 3 (2002) 17. [4] j. piret, j. lamontagne, j. bestman-smith, s. roy, p. gourde, a. désormeaux, r.f. omar, j. juhász, m. g. bergeron, j. clin. microbiol., 38 (2000) 110. [5] m. a. bahri, m. hoebeke, a. grammenos, l. delanaye, n. vandewalle, a. seret, colloids and surfaces a: physicochem. eng. aspects, 290 (2006) 206. [6] p. mukerjee, c. c. chan, langmuir, 18 (2002) 5375. [7] y. defeng, x. huang, m. deng, y. lin, l. jiang, j. huang, yi. wang, j. phys. chem. b, 114 (2010) 14955. [8] f. a. long, w. f. mcdevit, chem. rev., 51 (1952) 119. [9] l.wattebled, a. laschewsky, langmuir, 23 (2007) 10044. [10] p. k. grover, r. l. ryall, chem. rev., 105 (2005) 1. [11] m. l. corrin, w. d. harkins, j. am. chem. soc., 69 (1947) 683. [12] v. k. aswal, p. s. goyal, chem. phys lett., 364 (2002) 44. [13] j.h. mu, g.z. li, x. l. jia, h.x. wang, g.y. zhang, j. phys. chem. b, 106 (2002) 11685. [14] a. khatory, f. lequeux., f. kern, s. j. candau, langmuir, 9 (1993) 1456. microsoft word a bhattarai _63-68_.doc a. bhattarai et al. / bibechana 9 (2013) 63-68: bmhss, p. 63 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana effect of solvent composition on the critical micelle concentration of sodium deoxycholate in ethanol-water mixed solvent media ajaya bhattarai*, sujit kumar shah, ashok kumar yadav, janak adhikari department of chemistry, mahendra morang adarsh multiple campus, tribhuvan university, biratnagar, nepal * corresponding author: e mail: bkajaya@yahoo.com article history: received 18 october, 2012; accepted 3 november, 2012 abstract the precise measurement of the specific conductivity of sodium deoxycholate in pure water and ethanolwater mixed solvent media containing 0.10 and 0.20 volume fraction of ethanol at 303.15 k are reported. the concentration were varied from ~ 0.01 mol l -1 to ~ 0.0002 mol l -1 .the conductivity of sodium deoxycholate decreases with the increase in the volume fraction of ethanol. the critical micelle concentration of sodium deoxycholate increases with the increase in the volume fraction of ethanol. keywords: sodium deoxycholate; conductivity; critical micelle concentration; ethanol-water mixed solvent media 1. introduction surfactants are organic substances, which significantly decrease the surface tension of water at relatively low concentrations, are at least partially water soluble. surfactants are amphiphilic materials containing both a polar long-chain hydrocarbon “tail” and polar, usually ionic, “head” groups. in polar solvents, for example water, this dual character of the amphiphile leads to self-association or micellization, the surfactant molecules arrange themselves into organized molecular assemblies known as micelles. the hydro-phobic part of the aggregate forms the core of the micelle, while the polar head groups are located at the micelle–water interface in contact with and hydrated by a number of water molecules. depending on the chemical structure of the surfactant, its micelle can be cationic, anionic, ampholitic (zwitterionic), or nonionic. when dissolving them, after they reach a certain value of concentration, molecules or ions of surfactants begin to associate and to organize themselves into micelles. in colloidal and surface chemistry, the critical micelle concentration (cmc) is defined as the concentration of surfactants above which micelles form and almost all additional surfactants added to the system go to micelles [1]. critical micelle concentration values are important indicators when considering which surfactant will provide optimal performance benefits. the determination of cmc is generally based on the localization of the position of a breaking point in the concentration dependencies a. bhattarai et al. / bibechana 9 (2013) 63-68: bmhss, p. 64 (online publication: nov., 2012) of selected physical or chemical properties of surfactant solutions. because of the surface activity of these substances, measurements of the surface tension of surfactant solutions represent the principal method of cmc determination. however, it is rather tedious and time-consuming procedure. in the case of ionic surfactants, the utilization of electrochemical measurement is much more convenient, especially the measurements of the electrical conductivity of their solutions with varying concentration. the conductometric method is based on the finding of a breaking point on the curves, which describe the concentration dependence of conductivity [2]. it is well-known, that the conductivity of any solution is directly proportional to the concentration of its ions. the point, where the micelle formation starts, is indicated on the concentration dependence of specific conductivity (κ) as a breaking point. it is easy to find the breaking point, because it marks a significant change of the linear slope of the dependence κ =f(c). the requested value of cmc is the intercept of two linear functions with mutually different slopes. sodium deoxycholate (fig.1), the sodium salt of deoxycholic acid, is a water-soluble, bile-acid, ionic detergent commonly used in protein methods. it is most frequently used as a component of cell lysis buffers (e.g., ripa buffer), but also has been used for liposome preparation, isolation of membrane proteins and lipids, preventing nonspecific binding in affinity chromatography and a cell culture media supplement. deoxycholic acid has been used since its discovery in various fields of human medicine. in the human body deoxycholic acid is used in the emulsification of fats for the absorption in the intestine. it has, in some countries (including switzerland) been licensed as an emulsifier in food industry [3]. fig.1: structure of sodium deoxycholate. our aim of this paper is to determine the cmc of sdc in pure water and ethanol-water mixed solvent media containing 0.10 and 0.20 volume fraction of ethanol at 303.15 k by conductometric method. 2. experimental methods ethanol (e. merck, india) was used for the experimental works. the purified solvent had a density of 0.78097 g.cm -3 and a co-efficient of viscosity of 0.9490 mpa.s at 303.15 k; these values are in good agreement with the literature values [4]. distilled water with a specific conductance less than 10 -6 s.cm -1 at 303.15 k was used for the preparation of the mixed solvents. the physical properties of ethanol-water mixed solvents used in this study at 303.15k were taken from the published works [5-8]. a. bhattarai et al. / bibechana 9 (2013) 63-68: bmhss, p. 65 (online publication: nov., 2012) conductance measurements were carried out on a pye-unicam pw 9509 conductivity meter at a frequency of 2000 hz using a dip-type cell with a cell constant of 1.15 cm -1 and having an uncertainty of 0.01%. the cell was calibrated by the method of lind and co-workers in 1959[9], using aqueous potassium chloride solution. the measurements were made at 303.15 k in a jacket containing conductivity cell of cell constant 1.002 cm –1 . water was circulated in the jacket from thermostat and the temperature was maintained within ± 0.1 o c. the details of the experimental procedure have been described earlier [10-11]. several independent solutions were prepared and runs were performed to ensure the reproducibility of the results. due correction was made for the specific conductance of the solvent by subtracting the specific conductance of the relevant solvent medium from those of the electrolyte solutions. in order to avoid moisture pickup, all solutions were prepared in a dehumidified room with utmost care. in all cases, the experiments were performed in three replicates. 3. result and discussions conductivity measurements were performed in pure water and ethanol -water mixed solvent media at 303.15 k in order to evaluate the cmc of sodium deoxycholate. the cmc of sodium deoxycholate found at different volume fraction of ethanol –water mixed solvent media are listed in table 1.the cmc of sodium deoxycholate in pure water was found to be 2.04 mm by fluorescence measurements at 298.15 k[12] which is almost matching with static light scattering measurements[13]. as the temperature increases of the solution of sodium deoxycholate in water,the cmc also increases[13-14] and this is the best evidence for our conductivity measurements of sodium deoxycholate in pure water. the experimental specific conductivities of sodium deoxycholate as a function of the its molar concentration at 303.15 k of pure water and two different ethanol-water mixtures (containing 0.10 and 0.20 volume fractions of ethanol) are depicted in fig. 2 to 4. it was observed that cmc of sodium deoxycholate increases with the increase in the volume fraction of ethanol. this trend is due to decrease in the relative permittivity of the medium. the relative permittivity of the medium decreased at a given temperature with increasing in the ethanol content and similar trends have been observed in the previous works [6-7]. the presence of ethanol reduces the dielectric constant of the solvent phase and makes easier for the formation of ion-pairs in the solution phase. it is also well known that addition of solvent which acts as water structure breakers decrease the hydrophobic effect result in to the increase in the cmc value of ionic surfactants [15]. breaking of water molecules by ethanol molecules would facilitate interation between the hydrophobic tail of the surfactant molecule and the hydrophobic part of the ethanol and consequently the local concentration of ethanol molecules around the surfactants monomers becomes larger than the bulk solvation of the surfactant molecules by the hydrophobic part of the organic solvent would therefore lead to the delay aggregation of the surfactant monomers to form micelle and hence the increase in the cmc of the surfactant [16]. table 1: the critical micellar concentratiom (cmc) obtained from conductometry of sdc in pure water and ethanol-water mixed solvent media containing 0.10, 0.20 volume fraction of ethanol at 303.15 k t (k) water cmc (mm) 0.10 volume fraction of ethanol cmc (mm) 0.20 volume fraction of ethanol cmc (mm) 303.15 2.91 3.74 4.15 a. bhattarai et al. / bibechana 9 (2013) 63-68 : bmhss, p. 66 (online publication: nov., 2012) 0 0.15 0.30 0.45 0.60 0.75 0 0.002 0.004 0.006 0.008 0.010 cmc= 2.91 mm ↑ [sdc] (mol l -1 ) κ ( s c m -1 ) fig. 2: specific conductivities of sdc as a function of the surfactant concentration in 303.15 k: opened circles represent pure water. 0 0.1 0.2 0.3 0.4 0.5 0 0.002 0.004 0.006 0.008 0.010 ↑ cmc= 3.74mm [sdc] (mol l -1 ) κ ( s c m -1 ) fig. 3: specific conductivities of sdc as a function of the surfactant concentration in 303.15 k: opened circles represent 0.10 volume fractions of ethanol in the solvent mixture. a. bhattarai et al. / bibechana 9 (2013) 63-68: bmhss, p. 67 (online publication: nov., 2012) 0 0.1 0.2 0.3 0.4 0.5 0 0.0025 0.0050 0.0075 0.0100 ↑ cmc= 4.15mm [sdc] (mol l -1 ) κ ( s c m -1 ) fig. 4: specific conductivities of sdc as a function of the surfactant concentration in 303.15 k: opened circles represent 0.20 volume fractions of ethanol in the solvent mixture. 4. conclusions the following conclusions have been drawn from the above results and discussion. experimental result for the conductivity of sdc solution in pure water and ethanolwater mixed solvent media has been presented as a function of salt concentration and different percentage composition of ethanol-water mixed solvent media. the cmc of sdc are found to increase with the increase in the volume fraction of ethanol in ethanol-water mixed solvent media. acknowledgements the authors are thankful to professor dr. sujeet kumar chatterjee at the department of chemistry, mahendra morang adarsh multiple campus, tribhuvan university, biratnagar, nepal for the valuable suggestions and discussions. the authors are also thankful to associate professor ghanashyam shrivastav, the head of department of chemistry, mahendra morang adarsh multiple campus,tribhuvan university, biratnagar, nepal for providing us the research facilities to conduct this research work. references [1] a. d. mcnaught and a. wilkinson, compendium of chemical terminology, 2nd ed. blackwell scientific publications, oxford, iupac (1997). [2] a. bhattarai, s.k. shah and a. k. yadav, nepal j. sci. and tech.,13 (2012) 89. [3] h. streuli, et. al, slmb schweizer lebensmittelbuch, chapter 58, 4/3, (1992). [4] n. a. lange and j. a. dean, lange's handbook of chemistry, 10th ed. mcgraw-hill, new york, (1967). [5] j .j. lee and m. d. lee, korean j. chem. eng., 5 (1988) 5. a. bhattarai et al. / bibechana 9 (2013) 63-68: bmhss, p. 68 (online publication: nov., 2012) [6] a. bhattarai and s. k. sah, res. j. chem. sci., 1 (2011) 1. [7] a. bhattarai and j. raut, j. alpine chemistry, 2 (2011) 44. [8] h. s. harned and b. b. owen, the physical chemistry of electrolytic solutions, reinhold, new york, (1957) 234. [9] j. e., jr.lind, j. j. zwolenik and r.m. fuoss, j. am. chem. soc., 81 (1959) 1557. [10] b. das and d. k. hazra, bull. chem. soc. jpn., 65 (1992) 3470. [11] b. das and d. k. hazra, j. phys. chem., 99 (1995) 269. [12] s. das, u. thapa and k. ismail, bull. chem. soc. jpn., 83 (2010) 1352. [13] k. matsuoka and y. moroi, biochimica et biophysica acta, 1580 (2002) 189. [14] l. r. bogdanovaa, o. i. gnezdilovb, b. z. idiyatullina, r. kh. kurbanova, yu. f. zueva, and o. g. usyarovc, colloid j., 74 (2012) 1. [15] k. gracie, d. turner and r. palepu, can. j. chem., 74 (1996) 1616. [16] s.k.shah, t.p. niraula, a.bhattarai and s.k. chatterjee, bibechana, 8 (2012) 37. 25-33 krishna r. adhikari r c o s t n k.r. adhikari et al. / bibechana 11(1) (2014) 25-33: (online publication: march, 2014) p.25 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana empirical model based on meteorological parameters to estimate the global solar radiation in nepal krishna r. adhikari1*, shekhar gurung2, binod k. bhattarai3 1pashchimanchal campus, institute of engineering, tribhuvan university, nepal 2central department of physics, university campus, tribhuvan university, nepal 3central campus, institute of engineering, tribhuvan university, nepal *corresponding author: e-mail: adhikarikrishna@wrc.edu.np accepted for publication: february 02, 2014 abstract solar radiation is the best option and cost effective energy resources of this globe. only a few stations are there in developing and under developed countries including nepal to monitor solar radiation and sunshine hours to generate a rational and accurate solar energy database. in this study, daily global solar radiation, and ubiquitous meteorological data (temperature and relative humidity) rather than rarely available sunshine hours have been used for biratnagar, kathmandu, pokhara and jumla to derive regression constants and hence to develop an empirical model. the model estimated global solar radiation is found to be in close agreement with measured values of respective sites. the estimated values were compared with angstrom-prescott model and examined using the statistical tools. thus, the linear regression technique can be used to develop model at any location in the world. the resultant model may then be used to estimate the missing data of solar radiation for the respective sites and also can be used to estimate global solar radiation for the locations of similar geographic and meteorological characteristic. © 2014 rcost: all rights reserved. keywords: global solar radiation; clearness index; relative humidity; temperature; linear regression relation; empirical model. 1. introduction nepal is a land locked mountainous country with a large area of beautiful landscape situated between 26022' to 30027' north latitude and 80040' to 88012' east longitude [1] within a span of 200 km from south to north and about 800 km in east to west [2]. more than 6000 rivers with all river systems draining north to south towards the ganges [1] in nepal whereas theoretical, technical and economically feasible hydropower potential has been estimated at about 83000 mw, 45000 mw and 42000 mw respectively [2]. the current installed capacity of power plants connected to the national grid is 693 mw. the electricity consumption and the number of consumers increasing at a rate of approximately 9 % per year [3] which project peak demand of power 1163.2 mw for 2012/2013, 2052.00 mw for 2019/2020, and 3679.10 mw for 2027/2028 [4] whereas generation of additional power plant is almost in sluggish. this gap of supply and demand in k.r. adhikari et al. / bibechana 11(1) (2014) 25-33: (online publication: march, 2014) p.26 energy sector forces nepal electricity authority to load-shedding from 4 hours per day in spring and 16 hours per day in dry season [5]. fossil fuel reserves in the world have been depleting rapidly [6], even though their uses create negative impact to environment [7]. the construction period for new power generation projects and new import transmission capacities is very long therefore a rapid improvement of energy supply and an urgent supply of power through diesel power plants cannot be expected. the power supply crisis affects public life and especially economic development negatively [3]. on the other hand biomass technology does not work well enough on the comparatively cold high altitude and small hydro turbines need special topographical conditions [2] to set up and run. all these facts claim the transfer of the emphasis to the new clean alternative energy resources to replace costly and not viable sources and ensure sustainable development of the country. in the fiscal year 2008/09 total energy consumption in nepal was 410,000 tj. the consumption coverage data provided by mof shows 85% coverage by traditional resources (i.e., biomass energy resources), 14 % by commercial sources (petroleum products-9 %, coal-3 % and grid electricity2 %) and about 1% by alternative sources (biogas, solar power, wind and micro/pico level hydropower) [8]. the average global solar radiation in nepal varies from 3.6-6.2 kwh/m2day, sun shines for about 300 days a year, the number of sunshine hours amounts almost 2100 hours per year and average insolation intensity about 4.7 kwhm-2 day-1 (=16.92 mj/m2day) [2] it is greater than 4.38kwh/m2day (15.8 mj/m2day) measured by [7] for lao pdr. thus, nepal lies in a favourable insolation zone in the world even though the data in nepal was based on one year and few sites [2] but that of lao pdr was based on few years and throughout the country. so, a long term and many sites' solar energy data are required to authenticate this statement. solar energy, in the country like nepal, is the best and crucial option among the different energies including alternative energy sources. based on various facts and factors including global warming deforestation, and climate change (which may deplete the sources of water) government of nepal/private sectors have switch the priority of investment to generate the electricity into the solar farming even though per unit cost of electricity from solar energy is relatively higher than that of hydro electricity so far. moreover, for rural electrification in nepal, everyone should have to plan to link up microhydro/pico-hydro with solar energy exploitation [9].thus, an accurate knowledge and database of solar radiation at a particular place and selected sites are important for the development of many solar devices, establishment of solar plant to the proposed site and for estimation of their performance [10]. the radiation reaching the earth surface is modified significantly by clouds [11], water vapor, ice, aerosols, and atmospheric constituents in its intensity and the sunshine duration. the beam radiation (radiation coming directly from the solar disk) is attenuated by the presence of cloud in its path, as well as by the various atmospheric elements. the depletion of the direct beam by the cloud depends on type of cloud, their thickness and number of layers [12]. the radiation scattered by the atmospheric constituents is called diffuse radiation where a portion of this radiation goes back by about 6% of the incident radiation to space, and a portion, about 20% of the incident radiation, reaches the earth surface [13]. the sum of direct and diffuse radiation on the earth surface is known as global/total radiation which is very important for the design of certain solar energy applications [12]. in nepal like developing countries, the facility of ground based measurement of solar radiation is available only at selected sites whereas meteorological and hydrological data are available at different parts of the country. certainly the best way of knowing the amount of global solar radiation at the site of consideration is to install pyranometer at many locations in the given region and look after their day to day maintenance and recording, which is a very expensive venture. the alternative approach is to develop a model based on meteorological parameters, where the data can be collected, to estimate global radiation. k.r. adhikari et al. / bibechana 11(1) (2014) 25-33: (online publication: march, 2014) p.27 the resultant correlation may then be used for locations of similar meteorological characteristics [14]. thus, developing an empirical model to estimate the global solar radiation using various parameters such as sunshine duration, maximum and minimum temperature, relative humidity, rainfall and geographical location etc. is an essential assignment, for the country like nepal, which is a vigorous scientific research. so far various models have been developed by a number of researchers with different regression coefficients using linear regression techniques [15] for various countries and for different locations to estimate solar radiation. the most and commonly used model, including nepal, is angstrom [16] and modified later by prescott [17] which is based on sunshine hours [9]. in almost underdeveloped countries temperature and relative humidity are easily measured but the instrument to measure sunshine hours is in a very few locations. empirical models which have been used to calculate solar radiation are usually based on astronomical factors, geographical factors, geometric factor, physical factors and meteorological factors [18]. available literatures relate that there is a very few and limited study done in nepal to develop the empirical model [9]. in the present study, global solar radiation, meteorological/hydrological data have been used to derive the regression coefficients a, b, c, d to develop a model based on linear regression technique to estimate the monthly mean daily global solar radiation for four sites of nepal and compare the values with the estimations from the ref. [5,9,16,17,19]. 2. materials and method the raw data of daily solar radiation on horizontal surface for biratnagar, kathmandu, pokhara and jumla were collected from the archives of the department of hydrology and meteorology, government of nepal (dhm/gon) and solar radiation and aerosol in himalayan region (sahr) project of institute of engineering, tribhuvan university, nepal. daily sunshine duration, temperature and relative humidity data for these sites were obtained from department of hydrology and meteorology (dhm)/gon. the data obtained covered a period of years from 2007 2012 for biratnagar (latitude 26.4830, longitude 87.2660 and altitude 72m above the sea level), 2010 2012 for kathmandu (latitude 27.70, longitude 86.3660 and altitude 1337m above the sea level), 20082012 for pokhara (latitude 28.2160, longitude 840 and altitude 827m above the sea level) and two years, 2011 2012 for jumla (latitude 29.2830, longitude 82.1660 and altitude 2300m above the sea level). the most widely used origin and microsoft office excel software have been used for the data analysis. 2.1 theory microsoft office excel was used to process the data in useable/desirable form. the proposed linear regression relation i.e., empirical model to estimate global solar radiation which is based on temperature and relative humidity is as below: o m h h = a + b t + c 2t + d rh (1) here, a, b, c, and d are regression constants, t is monthly mean daily maximum temperature in celsius unit, 2t is monthly mean daily square of maximum temperature, rh is monthly mean daily maximum value of relative humidity, the ratio h/h om is monthly mean daily clearness index kt, and oh is the daily extraterrestrial radiation on the horizontal surface given by iqbal [12] as follows: ]sincoscossinsin 180 [ei 24 h ssosco ωδφ+δφωπ π = (2) k.r. adhikari et al. / bibechana 11(1) (2014) 25-33: (online publication: march, 2014) p.28 where, isc = 1000000 36001367× mj/m2h1, (3) is the solar constant, eo = 1+ 0.33cos 365 360n (4) is the eccentricity correction, n is the day number of the year (doy)/ julian day (1 jan, n=1 and 31st dec, n=365), ∅ is the latitude of the site, δ = 23.45 sin [ ] 365 )284(360 +n (5) is the solar declination, ωs = cos-1(-tan )tanδφ (6) is the hour angle, nd = ω=δφ−− s 1 15 2 )tantan(cos 15 2 (7) is the maximum possible sunshine hours. 2.2 developing a model the first order linear regression equation was employed to analyze the data as given below, a + b t + ct2 +d rh = kt (8) this represent an equation of least square line [20] or first order regression [21] where, o m t h h k = is a dependent variable called clearness index, and independent variables as maximum value of temperature t, & maximum value of relative humidity rh. the equation (8) has been multiplied by 1, t, t2, and rh successively and summing both sides, to obtain the regression constants are as given below: an + b∑t + c∑ t2 + d ∑rh = ∑kt (9) a∑t + b∑t2 + c∑t3 + d ∑t rh = ∑ktt (10) a∑t2 + b∑t3 + c∑t4 + d ∑t2rh = ∑kt t 2 (11) a∑ rh + b∑t rh + c∑t2 rh + d ∑rh2 = ∑kt rh (12) three years data of biratnagar (brt), four years data of pokhara (pkr) and two years data of kathmandu (ktm) & jumla (jml) separately were used to evaluate regression constants a, b, c, and d which are presented in table 2. 2.3 data analysis the accuracy of the estimated values by angstrom-prescott model and new model was tested by using the statistical techniques based on the definition devised by iqbal [12] which are given below: 2/1n 1 2 me ]}/n)hh({[rmse ∑ −= (13) n/)]hh[mbe n 1 me∑ −= (14) k.r. adhikari et al. / bibechana 11(1) (2014) 25-33: (online publication: march, 2014) p.29 n/)]100 h hh[mpe n 1 m em ∑ × − = (15) 2 12 mmm 2 mee mmmmee }])hh(}{)hh([{ )hh)(hh(cc −σ−σ −−σ = (16) here n is the total numbers of observations, handh me are monthly mean measured and estimated values and handh memm are mean of measured and estimated values respectively. calculated values of different parameters in organized form with coefficient of regression, r and coefficient of determinant, r2 derived from the plots for the statistical analysis and correlation coefficient (cc) are presented in the table 2. these, earlier stated, statistical indicators are used to examine the performance of the model of solar radiation estimation. in general, low values of root mean square error (rmse), mean bias (mbe) and mean percentage error (mpe) are expected for the better performance of the model. rsme test provides information on the short-term performance at the same time mbe and mpe test provide information on the long-term performance. the positive and negative values of mbe represent the overestimation and the underestimation [22] respectively of the radiations. preferably, for the best performance, correlation coefficient (cc), coefficient of regression (r) and coefficient of determinant (r2) each should be 1. 3. results and discussion regression technique has been used to determine the coefficients for biratnagar, kathmandu, pokhara and jumla, presented in table 2, to develop empirical model. positive value and negative value of coefficients b and d respectively, for all sites, show the better correlation of solar radiation with temperature and relative humidity i.e., greater the temperature more is the solar radiation & vice versa and greater the relative humidity lesser is the solar insolation and vice-versa. table 1 presents the measured and estimated monthly mean daily global solar radiation at four different sites of nepal where their varies altitude from 72m to 2300m above the sea level and location from east to west part of nepal. the values were estimated by using the angstrom-prescott model and by the new model separately. the minimum measured and model estimated value of monthly mean daily radiation on the horizontal surface were observed in january and december characterized by more cloudy/misty days and relatively farther distance of the earth from the sun. figure 1: (a) variation of radiation with months for biratnagar (b) variation of radiation with months for kathmandu k.r. adhikari et al. / bibechana 11(1) (2014) 25-33: (online publication: march, 2014) p.30 table 1. monthly mean daily measured and estimated solar insolation at four sites. month biratnagar kathmandu pokhara jumla hm he he new hm he he new hm he he new hm he he new jan 7.49 8.77 7.42 12.31 12.62 11.27 11.27 12.29 11.09 15.07 15.74 13.96 feb 9.63 10.85 9.98 15.26 14.86 13.71 14.24 14.49 13.78 16.60 17.22 17.11 mar 13.94 13.28 13.95 18.61 17.46 17.73 16.69 17.18 17.58 22.38 21.83 22.35 apr 15.56 15.18 16.59 20.44 19.73 20.76 18.65 19.45 20.31 22.81 22.61 24.44 may 17.18 15.90 17.29 21.64 20.36 21.55 20.95 20.59 21.40 25.21 24.64 26.24 jun 16.60 15.12 16.03 20.74 20.20 21.01 21.25 20.54 21.09 24.97 24.31 25.68 jul 13.11 14.46 15.25 16.09 17.90 19.87 18.82 19.04 20.50 19.99 19.89 22.52 aug 12.95 13.96 14.57 15.96 17.25 18.50 18.71 18.27 19.35 19.23 19.27 21.15 sep 12.25 12.94 13.12 16.09 16.52 16.84 16.98 17.00 17.40 20.54 20.21 19.24 oct 12.59 11.87 11.64 15.31 15.37 14.92 16.69 15.49 14.98 20.03 20.07 18.40 nov 10.90 10.14 9.76 13.27 12.69 12.44 13.07 12.54 12.20 16.73 16.67 15.94 dec 9.40 8.84 7.86 11.10 11.75 10.69 11.19 11.70 10.70 14.31 14.58 13.54 and the maximum value observed in may and june characterizes the relatively shortest distance between the sun and the earth and less aerosols. the greatest value (measured hm = 25.21mj/m2day & estimated henew= 26.26 mj/m2day) was observed at jumla (2300m above the sea level) and the minimum radiation valu (measuredhm = 7.49mj/m2day & estimated henew= 7.42 mj/m2day) was observed at biratnagar (72m above the sea level). the result shows the altitude, aerosol and weather dependency of the radiation. the observed value of solar insolation for all sites is suitable for solar farming, agriculture and forestation. fig. 1( a-d) is linear plot between measured & model estimated monthly mean daily solar radiations and months to compare the date. figures 2-5 are the scatter plot between the measured and model estimated monthly mean daily global solar radiation for different sites to analyze the performance of new model. the plots and table 2 show close agreement of the measured value with new model estimated values. it was found that solar insolation, depends on clearness index, vary with month of the year, weather condition of the sky and the location. the least value of solar insolation and statistical analysis for kathmandu show the more attenuation of radiation due to the presence of aerosol/smokes in the sky of kathmandu valley than other sites. figure 1: (c) variation of radiation with months for pokhara (d) variation of radiation with months for jumla k.r. adhikari et al. / bibechana 11(1) (2014) 25-33: (online publication: march, 2014) p.31 figure 2: measured (���) versus estimation global solar radiation (���) by angstrom-prescott model and new model for biratnagar. figure 3: measured (���) versus estimation global solar radiation (���) by angstrom-prescott model and new model for kathmandu. table 2. regression constants and errors analysis. sn location regression constants rmse mbe mpe % r2 r cc a* b* a** b** c** d** new new new a-p new a-p new new 1 brt 0.301 0.164 0.355 0.024 -0.00038 -0.0039 1.08 0.155 -0.68 0.89 0.90 0.94 0.95 0.95 2 ktm 0.364 0.280 0.677 0.025 -0.00062 -0.0046 1.49 0.20 -0.89 0.93 0.85 0.96 0.92 0.92 3 pkr 0.442 0.169 0.301 0.029 -0.00054 -0.0019 0.97 0.15 -0.33 0.96 0.95 0.98 0.98 0.97 4 jml 0.383 0.394 0.894 0.009 -0.00023 -0.0049 1.3 0.22 -0.65 0.99 0.92 0.99 0.96 0.95 note: *regression coefficients for angstrom-prescott model ** regression coefficients for proposed new model & a-p stands for angstrom-prescott model. k.r. adhikari et al. / bibechana 11(1) (2014) 25-33: (online publication: march, 2014) p.32 moreover, table 2 presents the least values of root mean square error rmse, mean bias error mbe and mean percentage error mpe, from statistical analysis, indicate the best linear regression relations to estimate global solar radiation at biratnagar, kathmandu, pokhara and jumla in nepal. the additional statistical indicators were also used to evaluate the accuracy and performance of new model. all sites have higher values of r & r2 whereas the highest value of r is 0.98 (r2 = 0.95) at pokhara and minimum value of r is 0.92 (r2 = 0.85) at kathmandu, correlation coefficient cc observed 0.92 at kathmandu, 0.95 at biratnagar & jumla and 0.97 at pokhara. figures from 1-5 of the plots of global solar radiations model estimated by the angstrom-prescott and new one also proved the higher performance of the new model in comparison to the value estimated in ref. [5,19,23] and nearly same value as in ref. [9,16,17]. figure 4: measured vs estimation global solar radiation by angstrom-prescott model and new model for pokhara. figure 5: measured (���) versus estimation global solar radiation (���) by angstrom-prescott model and new model for jumla. 4. conclusion solar radiation database of any site is essential for designing and sizing the solar energy systems for that particular locality and ultimately for the broader world community [18] for a sustainable future energy. important finding of this work are as follows: a. development of the linear regression equation (an empirical model) to estimate the global solar insolation based on easily available meteorological parameters; temperature and relative humidity. the model proved that higher the temperature more is the solar radiation but the effect of humidity is in opposite/reverse manner. k.r. adhikari et al. / bibechana 11(1) (2014) 25-33: (online publication: march, 2014) p.33 b. admirable harmony has been found between measured and estimated global solar radiation by new model. the statistical analysis techniques also confirm the better performance of the model at four sites. c. measurements showed that west and high altitude regions in nepal are the places where high potential of global solar radiation was observed and least value of radiation was observed in eastern part and low altitude locations. in general abundant solar radiation is observed at all sites in nepal. d. ubiquitously available data can be used to developed model and hence to estimate daily and monthly mean daily solar radiation for the locations and the locations of similar geographical characteristics. this study also recommends that pokhara, jumla and other places having similar geographical and meteorological parameters are suitable for the endeavor of the solar projects to resolve the energy deficiency in nepal. the model is more useful and rational than the model proposed by adhikari et al. [9]. acknowledgments authors gratefully express sincere thanks to university grants commission, nepal for providing assistance in the form of scholarship and assistantship for this research work and are indebted to solar radiation and aerosol in himalaya region (sahr) project, pulchowk, nepal and department of hydrology and meteorology/gon for making the data available. references [1] napa, national adaptation programme of action, napa twg draft summary report, ministry of environment, gon, 2010. [2] wecs, energy sector synopsis report, nepal, water and energy commission secretariat, govt of nepal, 2010. [3] nepal energy situation 2011 & 2012, https://energypedia.info/wiki/nepal_energy_situation. [4] nepal electricity authority, annual report, ministry of energy, gon, 2011. [5] khem n. poudyal, binod k. bhattarai, balkrishna sapkota, berit kjeldstand, energy and power engineering, 4 (2012) 415. [6] sunday olayinka, international journal of energy and environmental engineering, 2 (2011) 11. [7] assessment of solar energy potentials for lao people’s democratic republic, department of alternative energy development and efficiency, thailand, department of electricity, lao pdr, and solar energy research laboratory, department of physics, silpakorn university, thailand, 2010. [8] mof, annual report-2012, ministry of finance, gon, 2012. [9] krishna r. adhikari, shekhar gurung, binod bhattarai, journal of power and energy engineering, 1 (2013) 1. [10] m. chegaar, a. chibani, rev. energy: chemss, (2000) 111. [11] l. salby murry, fundamental of amospheric physics, academic press, new york, 1996. [12] m. iqbal, an introduction to solar radiation. academic press, new york, 1983. [13] r.h.b. excell, the intensity of solar radiation, king mongkut's university of technology press, thorburi, 2000. [14] c. augustine, m. n. nnabuchi, international journal of physical sciences, 4 ( 2009) 182. [15] s.s. chandel, r. k. agrawal, a. n. pandey, journal of solar engineering, 147 (2005) 417. [16] a. angstromm, quarterly journal of the royal meteorological society, 50 (1924) 121. [17] j. a. prescott, transactions of the royal society of south australia, 64 (1940) 114. [18] dehghan a. ali, besharat fariba, faghig r. ahmad, renewable and sustainable energy review, 21 (2013) 798. [19] khem n. poudyal, binod k. bhattarai, balkrishna sapkota, berit kjeldstand, research journal of chemical sciences, 2 (2012) 20. [20] ekpe j. elom, nnabuchi m. nnamdi, scholarity journals of biotechnology, 1 (2012) 101. [21] b. murray, solar energy 12 (1961) 417. [22] c.k. panday, a.k. katiyar, international journal of energy and environment, 1 (2010) 737. microsoft word binil aryal.doc binil aryal / bibechana 8 (2012) 1-7 : bmhss, p.1 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana asymmetric mass-loss from the white dwarf wd 0253+209: secret revealed binil aryal central department of physics, tribhuvan university, kirtipur, nepal e-mail: binil.aryal@uibk.ac.at article history: received 25 may, 2011; accepted 8 june, 2011 abstract dust structures around the white dwarf wd 0253+209 is studied in 100 and 60 micron infrared image. these images are received from infrared astronomical satellite survey (iras survey). the post asymptotic giant branch (agb) emission of the white dwarf's precursors' wind and the ambient interstellar matter is studied. the distribution of the relative flux density is studied and analyzed in the context of the dust color temperature, mass loading trend and the amount of total mass deposited due the interaction in the interstellar medium. the twisted curved emission structure at 100 micron in the region of interest is probably due to the interaction between the ambient interstellar medium and the he-flashes of the parent planetary nebula of the central white dwarf wd 0253+209. the total mass of the filamentary arc is found to be ~ 5 solar masses, as predicted. the mass loss rate of the post agb star goes up to 10 -5 solar masses per year. it is concluded that the first he-flash occurred at least ~2500 years ago. keywords: white dwarf; interstellar medium; flux density; interstellar dust; mass of the gas 1. introduction when a star exhausts the supply of hydrogen in its core, the core contracts and its temperature increases, causing the outer layers of the star to expand and cool. the star's luminosity increases greatly, and it becomes a red giant, following a track leading into the upper-right hand corner of the hr diagram [5,13]. the asymptotic giant branch is the name given to a region of the hertzsprungrussell diagram populated by evolving low to medium-mass stars. during this phase the star swells up to giant proportions to become a red giant again. the star may become as large as one astronomical unit. after the helium shell runs out of fuel, the tp-agb starts. now the star derives its energy from fusion of hydrogen in a thin shell, inside of which lies in the now inactive helium shell. however, on periods of 10,000 to 100,000 years the helium shell switches on again, and the hydrogen shells switches of, a process known as a helium shell flash [6]. towards the end of their lifetime, almost all (95-98%) stars lose a substantial fraction of their mass on the asymptotic giant branch (agb) in form of massive winds, which compels them into the planetary nebula (pn) phase [13]. the central star of pn is the white dwarf. the massive stellar wind emitted from the agb star interacts with the ambient interstellar medium. thus the structure (gas or the dust) around the white dwarf preserve the history as a fossil record of the early and late agb phase of the star. it is important to understand the shaping process of interstellar clouds as well as the nature of the emission from agb to pn phase. the white dwarf is suspected to reside within giant dust structures which may represent fossil records of its progenitor's transition from spherically symmetric to bipolar or unipolar mass loss [1,2]. it can be suspected that the white dwarf is not the only one where fossil records of ancient mass loss in its neighborhood as well as signs of the resulting shaping binil aryal / bibechana 8 (2012) 1-7 : bmhss, p.2 can be traced. besides being ideal laboratories for the study of various astrophysical processes prevailing in highly excited dilute nebulae, pne and their progenitors are key objects for the understanding of the evolution of stars. in this connection, the transformation from spherically symmetric agb winds to non-spherical pne represents one of the most enduring problems of stellar astrophysics (e.g. aryal, rajbahak & weinberger, 2009; balick, 2002) [3,4]. in this work we present a detailed study of dust structures around white dwarf wd 0253+209 in order to understand the fossil records of its evolution during agb phase. for this, the variation of flux density along the maxima, dust color temperature profile of the region, mass of the gas in the nods and the possible direction of the mass loading have been extensively examined. 2. methods we have carried out following steps to study the dust structure around the white dwarf wd 0253+209. 1. we searched 100 micron dust structure around hot white dwarfs. 2. the past history of the evolution of white dwarfs is studied by carefully examining the dust structure around the white dwarf. 3. the interaction between the stellar wind in the post agb phase is studied. 4. we intended to study the mass loading phenomena around the investigated white dwarf. we adopt the following methods to find the dust color temperature of the region of interest and the mass of the gas in the selected region around the white dwarf. 2.1 temperature estimation we followed the method developed by schnee et al. (2005) to calculate the dust color temperature from the iras 60 micron and 100 micron flux densities [14]. the temperature is determined by the ratio of the 60 micron and 100 micron flux densities. the dust temperature td in each pixel of a fir image can be obtained by assuming that the dust in a single beam is isothermal and that the observed ratio of 60 micron to 100 micron emission is due to black body radiation from dust grains at td, modified by a power law emissivity spectral index. the flux density of emission at a wavelength ν, is given by (1) where nd represents column density of dust grains, α is a constant that relates the flux to the optical depth of the dust, β is the emissivity spectral index, and ωι is the solid angle subtended at λi by the detector. following dupac et al. (2003), we use the equation [8] (2) to describe the observed inverse relationship between temperature and emissivity spectral index. with the assumptions that the dust emission is optically thin at 60 micron and 100 micron and that ωw ≈ ω100 (true for iras image), we can write the ratio, r, of the flux densities at 60 micron and 100 micron as (3) once the appropriate value of β is known, one can use eq. (3) to derive td. the value of β depends on such dust grain properties as composition, size, and compactness. for reference, a pure blackbody would have β = 0, the amorphous layer-lattice matter has β ~ 1, and the metals and crystalline dielectrics have β ~ 2. for a smaller value of td, 1 can be dropped from both numerator and denominator of eq. (3) and it takes the form binil aryal / bibechana 8 (2012) 1-7 : bmhss, p.3 (4) taking natural logarithm on both sides of eq. (4) we find the expression for the temperature as (5) where r is given by (6) f(60 micron) and f(100 micron) are the flux densities in 60 micron and 100 micron respectively. 2.2 mass estimation the dust masses are estimated from the infrared flux densities at 60 micron and 100 micron, following the analysis of meaburn et al. 2000; young et al., 1989, and donofrio et al., 1999 (equation 7) [12, 15, 7]. the infrared flux can be measured from iras sky-view images and images from the groningen using both aladin2.5 and fitsview2.0.1 software. the background subtraction is done by the averaging the background surrounding the object and multiplying by the number of pixels containing the object. the black body intensity can be calculated using the basic expression as given in equation (8). the resulting dust mass depends on the physical and chemical properties of the dust grains, the adopted dust temperature and the distance to the object (7) where, α = weighted grain size, ρ = grain density, qν = grain emissivity, sν = flux density. the planck's function is a well known function, given by this equation, (8) it is clear from the expression (8) that the value of planck function [b(ν,t)] for longer wavelength is higher than that of the shorter wavelength. consequently, the range of b(ν,t) for fixed temperature goes narrower if wavelength of the images increases. 2.3 region of interest we planned to study the region as shown in fig. 1a. this region has one white dwarf, namely wd 0253+209 (see plus mark in fig. 1). the position of this white dwarf is r.a.(j2000)= 02 h 55 m 4.37 s and dec.(j2000)= +21 o 06’ , 08”. 3. result and discussion first we present the results concerning the interaction between the stellar wind emitted from the post agb phase of the white dwarf with the surrounding interstellar medium. the study of relative flux density helps us to know about the inner dynamics of the region. in addition, this study is useful to estimate the dust color temperature and the mass of the dust in the selected region. after getting information regarding the possible energy needed to make the structure, we calculate/estimate whether this amount of energy can be supplied by the white dwarfs or not. binil aryal / bibechana 8 (2012) 1-7 : bmhss, p.4 fig. 1: (a) 100 micron iras image of the region of interest. the symbol ‘+’ represents the position of white dwarf wd 0253+209. (b) contour maps showing the rounded filamentary nodes around the white dwarf. fig. 2: (a) region of interest (roi) showing line joining the maxima of the nodes as shown in fig. 1b. the variation of relative flux density is plotted along the path, starting from northern maxima, i.e., `1' to the southern maxima i.e., `5'. the studied region has one white dwarf, namely wd 0253+209. the position of this white dwarf is r.a.(j2000)= 02 h 55 m 4.37 s and dec.(j2000)= +21 o 06’ , 08”. 100 micron iras image centered at r.a. (j2000) = 02 h 55 m 1.8 s , dec.(j2000)= 21 o 05’ 32” is shown in fig. 1a. the position of the white dwarf is shown by the symbol ‘+'. in the northern part of white dwarf, grey shaded filamentary arc can be seen. the contour map of the image presented in fig. 1b shows five maxima (represented by 1, 2, 4, 6 and 5) from top to bottom. these maxima have 2.5 times greater values of relative flux density binil aryal / bibechana 8 (2012) 1-7 : bmhss, p.5 than that of the background. the minimum and maximum relative flux density is found at maxima ‘2' and ‘5'. fig. 2a shows the path joining all the maxima from ‘1' to ‘5'. the path goes through 1 →2 → 4 →6 → 5 from top to bottom. the value of flux density is measured at all pixels on the path. fig. 2b shows the variation of relative flux. the maximum relative flux density at ‘2' and ‘5' are nearly equal. maxima ‘4' showed less flux than that of ‘2' and ‘5'. interestingly it is found that the path joining the maxima 1 → 2 → 4 → 6 → 5 are point of twisted filamentary arc. it is noticed that the mass at ‘1', ‘2' and ‘4' are growing day by day in equal rate. it is also found that the separation between all the maxima is equal. star with initial masses between `1' and `9' solar masses that end up as white dwarf must lose a substantial fraction of their mass before they leave asymptotic giant branch (agb). most of the mass loss occurs near the end of agb lifetime. these losses of mass are appear in the form of nodes around the white dwarf. as time passes, mass is found to be deposited rapidly around the white dwarf. to study the mass loading on the maxima, we joined the maxima of the infrared clouds and the white dwarf (see fig. 3a). the variation of relative flux density along the path helps us to understand the mass loss pattern. fig. 3: variation of relative flux density along straight line joining the maxima (1, 2, 3, 4, 5 and 6) and the white dwarf wd 0253+209. to calculate the dust color temperature we used the 100 micron and 60 micron iras images in aladin2.5 software. the maximum temperature in the maxima `1' found to be 18.5 ± 1.5 k. this temperature is the background corrected. the maximum value of dust color temperature of the maxima `2', `3', `4', `5' and `6' are estimated as 17.5 ± 0.5 k, 18.5 ± 0.5 k, 17.5 ± 0.5 k, 18.5 ± 1.5 k and 18.0 ± 1.0 k respectively. the error in the temperature is calculated by estimating the minimum temperature of that region. thus, the maxima `1', `3' and `5' is found to be hotter than other maxima. interestingly, the region `2' is found to be colder than that of the region `1', `3' and `5'. it should be noted that the paths 1 → 2 → 4 → 6 → 5 shows a similar temperature fluctuation, suggesting a close connection between the paths (fig. 4). the mass of the dust is estimated using henning et al. (eq. 7). the value of their respective temperature is used in order to calculate the value of the planck function (eq. 8). we used 100 micron iras image for the mass estimation. the region `5' is obviously the massive region. it has a mass of (1.670 ± 0.940) msun. the second and third massive region is found to be region `3' and region `2', where (1.210 ± 0.250) msun and (1.200 ± 0.280) msun are estimated. the least massive maxima in the roia value and the error are estimated using the range of flux density in each maxima region. all together, roia has a mass of (4.732 ± 0.940) msun. now the question is, this amount of mass can be binil aryal / bibechana 8 (2012) 1-7 : bmhss, p.6 fig. 4: the variation of relative flux density is plotted along the path which connects the maxima 1 → 2 → 4 → 6 → 5. the maximum temperature at the maxima is shown. contributed by our white dwarfs or not? obviously not! because white dwarf is the remnant of 1.440 msun star. however, the deposited masses in the ism region is need to be added here. we check whether our white dwarf can displace and load this amount of estimated mass during their evolution or not. in the optical (red) wavelength, the surface brightness of this white dwarf is extremely low. the spectral index of this white dwarf in v band is 17.83 (mcsion & cook 2003). so, this white dwarf is relatively colder. in the catalog, this white dwarf is classified as da, means it has only balmer lines, no he i or metals present. the white dwarf (wd 0252+209) which is at the head of the emission structure is colder (i.e., older) than that of the white dwarf (wd 0258+184) at the tail or bottom of the structure. the difference in the spectral index in v band is, 17.83-15.30 = 2.53. this difference leads age difference of ~ 2500 years. this difference is significant in the context of the total mass of the emission region of the structure, i.e., ~ 5 msun. it is found that the mass-loading is active in the lower part but the contribution of upper white dwarf is dominating in the context of the amount of mass deposition. thus, the structure roia is formed due to the interaction between the post agb winds of the white dwarf. however, this interaction is found to be active in the lower region. we conclude that the twisted curved structure in the region of interest is formed probably due to the interaction between the ambient interstellar medium and the he flashes of the parent planetary nebula of the white dwarf wd 1003-441. 4. conclusion we studied the 100 micron dust structures around white dwarf wd 1003-441. the post asymptotic giant branch (agb) emission of white dwarf's precursors' wind and the ambient interstellar matter is thoroughly studied. for this, distribution of the relative flux density of each pixel of the images are analyzed in the context of the dust color temperature, mass loading trend and the amount of total mass deposited due the interaction in the interstellar medium. the 100 micron far infrared image is provided by the groningen server of infrared astronomical satellite (iras) survey. the spectral index of the white dwarf was taken from mcsion & cook (2003). these images were processed in the image reduction software aladin2.5. the calculations for the dust color temperature (schnee et al. 2005 & dupac et al., 2003) and the mass (young 1989) were carried out using 100 micron iras image. the white dwarf (wd 0252+209) which is at the head of the emission structure is found to be colder (i.e., older) than that of the white dwarf (wd 0258+184) at the tail or bottom of the emission structure (region of interest a). the difference in the spectral index in v (2.53) leads age difference of ~ 2500 years. this difference is noticeable because total mass of the emission region of the structure is not more than 5 solar masses. it can be concluded that the process of mass-loading is active in the lower part but the contribution of northern white dwarf (wd 0253+209) is dominating. the maximum and minimum dust color temperature of the dust structure is found to be 20.0 and 17.0 k, respectively. it can be concluded that the structure is formed due to the interaction between the post agb winds of the white dwarf. binil aryal / bibechana 8 (2012) 1-7 : bmhss, p.7 acknowledgements b. aryal is grateful to the university of innsbruck as well as to its institute of astroand particle physics for financial support for a research stay during october to december 2010. we acknowledge prof. ronald weinberger of innsbruck university for his important suggestion. this research has made use of nasa/ipac extragalactic database (ned) which is operated by the jet propulsion laboratory, california institute of technology, under contract with the national aeronautics and space administration. references [1] b. aryal, r. weinberger, journal astronomy & astrophysics 245 (2006) 306. 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[15] w. young, astrophysical journal 109 (1989) 725. microsoft word g. palei _39-43_.doc g.k. palei and n.p. sah / bibechana 7 (2011) 39-43 : bmhss 39 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana some results on asymptotically normable frechet spaces g.k. paleia , n.p. sahb ∗∗∗∗ a department of mathematics, b.n. college, patna university, patna, india b department of mathematics, m.m.a.m. campus (tribhuvan university), biratnagar, nepal article history: received 8 october 2010; revised 18 november 2010; accepted 20 november 2010 abstract. in this paper, it is shown that the asymptotically normable spaces are the smallest class of frechet spaces which contains the nuclear kothe spaces with continuous norm, the banach spaces and is closed under ε-tensor products and sub-spaces. again our main aim will be to construct an example of a kothe space which is montel, admits a continuous norm, but still is not asymptotically normable. keywords: asymptotically normable; frechet space; kothe space introduction let e be a frechet space, || ||1 ≤ || ||2 ≤ ...... a fundamental system of seminorms on e and uk = { x ∈ e : ||x||k ≤ 1} for every k. e is called asymptotically normable, if there is a ko such that for every k ≥ ko there is a p so that the seminorms || || ok and || || k define equivalent topologies on up. it is easy to see that in this case || || ok is in fact a norm. this class of spaces appears in investigations about the structure of frechet spaces and about the behaviour of their operators as a natural counterpart of the class of quasi-normable spaces introduced by grothendieck [1]. while the quasi-normable frechet spaces e are those which admit an ω-type condition [2] and for which there exists a nontrivial frechet space f with ext 1 (f, e) = 0 [2], the asymptotically normable frechet spaces e are those which admit a dntype condition [3] and for which thee exists a nontrivial frechet space f with ext 1 (e, f) = 0. nontrivial here could mean: an infinite dimensional nuclear kothe space. in [2] it is shown that the quasi-normable spaces are the quotient spaces of standard spaces of the form : for allλ   = ∈ = < + ∞    ∑ j k n j j k j k j, k(a, e) x =(x ) e || x || || x || a where e is a banach space and a = (aj, k) a matrix with o < aj, k ≤ aj, k+1 for all k and ∗ corresponding author: nagendra pd. sah, department of mathematics, m.m.a.m. campus(tribhuvan university), biratnagar, nepal g.k. palei and n.p. sah / bibechana 7 (2011) 39-43 : bmhss 40 ∞∑ j, k j j, k+1 a <+ a we can show that the asymptotically normable spaces are the subspaces of these standard spaces. they are the smallest class of frechet spaces which contains the nuclear kothe spaces with continuous norm, the banach spaces and is closed under ε-tensor products and subspaces. a. we use the standard terminology of the theory of locally convex spaces as in [4]. for the theory of ext & the splitting conditions we refer to [3] & [5]. by (|| ||k) we always denote an increasing sequence of seminorms defining the topology of a frechet space e and uk = {x ∈ e : ||x||k ≤ 1}. in this section we collect some simple results in order to see the concept of asymptotic normability in a proper perspective. let ϕ : (0, ∞) → (0, ∞, be a strictly increasing function. we say e satisfies (dnϕ) if we have a ko with the property that for every k there is a p and c > 0 so that the inequality ||x||k ≤ cϕ(γ) ko || x || + 1 γ ||x||p holds for every x ∈ e and γ > 0 [3]. in the case ϕ(γ) = γ this condition, denoted by (dn), was introduced by d. vog t in [3] to characterize initially the subspaces of the space (s) of rapidly decreasing sequences. subsequently it was proved by him in [5] that every space of type (dn) is isomorphic to a subspace of l∞(i)⊗π (s) for some index set i. consider also the following condition: there is a ko such that for every k ≥ ko we have p ≥ ko with the following property: every sequence in e which is cauchy with respect to || ||p and converges to 0 with respect to || || ok even converges to 0 with respect to || ||k. proposition 1.1 every asymptotically normable frechet space is countably normable. we can obtain the proof from [1], page 176. proposition 1.2 the following are equivalent for a frechet space e : (1) e is asymptotically normable. (2) there is ko such that for every k there is a p such that for every ε > 0 we can choose m > 0 with || ||k ≤ m || || ok + ε|| ||p. (3) e has property (dnϕ) for some ϕ. proposition 1.3 a frechet-schwartz space is asymptotically normable if and only if it is countably normable. the question whether these classes coincide in general we shall answer in the negative in the next section. before we do this let us recall that a frechet space e is called locally normable [6] if there is a ko such that on every bounded set b the topologies induced by e and by || || ok coincide. obviously every asymptotically normable space is locally normable. on the other hand every frechet-montel space admitting a continuous norm is locally normable. hence, in view of proposition 1.3, every frechet-schwartz space admitting a continuous norm but not countably normable [7], gives an example of a locally normable space which is not asymptotically normable (see also section 2). b. in this section we shall consider kothe sequence spaces. our main aim will be to construct an example of a kothe space λ (b) which is montel, admits a continuous norm, but still is not asymptotically normable. in particular, λ (b) will be an example of a locally normable kothe space which is not asymptotically normable. by proposition 1.3, λ (b) cannot be a schwartz space. in this context we should like to mention that the well-known example constructed by kothe in [4] of a montel space which is not ∧ g.k. palei and n.p. sah / bibechana 7 (2011) 39-43 : bmhss 41 a schwartz space, is asymptotically normable by the following proposition which is an immediate consequence of proposition 1.2 and gives a characterization of asymptotically normable kothe spaces in terms of the defining matrix. proposition 2.1 a kothe space λ (a) is asymptotically normable if and only if there is ko such that for every k we have p so that for every ε > 0 there is an m > 0 with ≤ ε ∈ oj, k j, k j, p' a ma + a j n example 2.2 we define (i j v) k for k ≤ v bi j, v; k = i v (j v) k for v < k ≤ j + v ik-j (j v) k for j + v < k then the kothe space λ (b) is montel, admits a continuous norm but is not asymptotically normable. proof.: suppose for some k there is a p such that for every ε > 0 there is m > 0 with bi j, v; k+1 ≤ m bi j, v; k + ε bi j, v; p for all (i, j, k) ∈ n 3 . we may assume p > k + 1, set v = k + 1, j = p – v and obtain (i j v) k+1 ≤ m (i j v) k + ε i k+1 (j v) p for ε < (j v) k+1-p , we let i tend to infinity and get a contradiction. hence the kothe space λ (b) is not asymptotically normable by proposition 1.2. suppose we fix ko and let i ⊂ n 3 be an index set such that for all k we have bi j v; k ≤ ρ(k)bi j, v; k for some ρ(k) > 0 and (i, j, v) ∈ i. if we show that i must be finite, then we have that λ (b) is a montel space [4]. since the exponent of i is increasing with k, we have j v ≤ ρ(ko+1) for all (i, j, v) ∈ i. for any given jo, vo let k > jo + vo + ko. if (i, jo, vo) ∈ i, we get (≤ ρokj i k okk m o o o o (j v ) ) i (j v ) where m is some integer which is strictly less than k – jo in all cases. hence {i : (i, jo, vo) ∈ i} is finite and so i must also be finite. c. this section is devoted to the proof of our main theorem 3.3. for this, we state the following lemma without proof: lemma 3.1 let a = ( ai, k; m) be a doubly indexed matrix and ak = (ai, k; m + ai+1, k; m). we assume that with suitable sequences i(m) and s(m) ≥ m we have the following: (1) ai, k;k = 1 for all i, k. (2) ai, k; m ≥ ai+1, k;m for all i, m ≤ k. ai, k; m ≤ ai+1, k;m for all i ≥ i( m), m > k. (3) ai, k; m = 0 for all m < k. (4) ∞∑ i, k;m i i, k; s(m) a <+ a then there exists an exact sequence 0 → λ (ak) → λ (a) → ω → 0. we will now show that for a given kothe-schwartz space λ (b) there is another such space λ (a) and a surjection of λ (a) onto ω whose kernel is isomorphic to λ (b). proposition 3.2 for every kothe-schwartz space λ (b) with a continuous norm, there exists a kothe-schwartz space λ (a) with a continuous norm and an exact sequence 0 → λ (b) → λ (a) → ω → 0. further, if λ (b) is nuclear, then λ (a) is also nuclear. o lim i sup k g.k. palei and n.p. sah / bibechana 7 (2011) 39-43 : bmhss 42 proof: we assume without loss of generally bj; 1 > 0 for all j and j;m j;m+ b = b 1 0 for all m. we determine inductively disjoint, infinite sets of integers mk = {n(i, k) : i = 1, 2, ...} with ∪mk = n such that the following are true: (5) ≥ n(i,k) ;m n(i+1, k) ;m n(i,k) ;k n(i+1, k) ; k b b b b for m < k (6) ≤ n(i,k) ;m n(i+1, k) ;m n(i,k) ;k n(i+1, k) ; k b b b b for m > k, i ≥ m (7) 2−≤ in(i,k) ;m n(i,k) ;m+1 b b for m ≤ i. for a fixed k, the sequence (n(i, k))i=1,2, ...... can be chosen inductively, starting with n(1, k) = min n \       u k-1 l l=1 m and such that n \       u k l l=1 m remains infinite. we now set n(i,k) ;m n(i,k) ; k b b for m < k ai, k; m = n(i-1,k) ;m n(i-1,k) ;k b b for m > k, i ≥ 2 1 elsewhere since ai, k; k = ai+1, k; k = 1, we note that (ai, k; m) is increasing in m. then (1) ..... (4) of 3.1 lemma are satisfied and hence we have an exact sequence 0 → λ (ak) → λ (a) → ω → 0. one can check easily that λ (a) is a schwartz space or if λ (b) is nuclear, then λ (a) is also nuclear. for m < k and m ≥ k using (5) and (6) are estimate in different ways and obtain 2≤ ≤ n(i,k) ;m n(i,k) ;m i,k;m i+1,k;m n(i,k) ;k n(i,k) ;k b b a +a b b for i > m. therefore λ (ak) is isomorphic to λ (b) by diagonal transformation. theorem 3.3 a frechet space e is asymptotically normable if and ony if there is an index set i and a nuclear kothe space λ (a) with a continuous norm such that e is isomorphic to a subspace of l∞(i)⊗π λ(a). proof: we have a nuclear kothe space λ (b) with a continuous norm such that (e, λ (b) ) ∈ ( )* 1 s by lemma 5.4 in [3]. by the previous result we construct an exact sequence. 0 → λ (b) → λ (a) → ω → 0. if e is a banach space, our theorem is trivial. if e is a proper frechet space, then (e, λ (b) ) ∈ ( ) o * 1 s by lemma 3.3 in [5]. now we choose a set i such that each banach space ek is isomorphic to a subspace of l∞(i), where ek is the completion of (e, || ||k). we identify the tensor product l∞(i)⊗π λ(b) with the space of all y = (yj), such each vj ∈ l∞(i) and for every k ∈ n we have ||y||k = sup ||yj||∞bj;k < + ∞ where || ||∞ denotes the norm of l∞(i). an obvious modification of proposition 3.5 in [5] yields (e, l∞(i)⊗π λ(b) ∈ (s1). taking tensor product with l∞(i) we get an exact sequence lim j ∧ ∧ j g.k. palei and n.p. sah / bibechana 7 (2011) 39-43 : bmhss 43 0 → l∞(i)⊗π λ(b) → l∞(i)⊗π λ(a) → l∞(i) n → 0 since ext (e, l∞(i)⊗π λ(b)) = 0, the natural imbedding t of e into l∞(i) n can be lifted to a continuous linear operator t : e → l∞(i)⊗π λ(a). it is easily checked that t is one-to-one and has a closed range. we would like to point out that the kothe space λ(a) we have constructed actually depends only on ϕ. this is so, because for each strictly increasing function ϕ : (0, ∞) → (0, ∞), an examination of the proof of lemma 5.4 in [3] reveals that there is a nuclear kothe space λ(b) such that (e, λ(b)) ∈ ( )* 1 s for any frechet space e which satisfies (dnϕ). finally, we would like to note that l. holmstrom [8] proved that every nuclear asymptotically normable frechet space is isomorphic to a subspace of some nuclear kothe space which admits a continuous norm. d. finally we use the results of section 3 for another description of the class of asymptotically normable frechet spaces and for a comparison with the class quasi-normable frechet spaces. the first lemma is obvious. lemma 4.1 if e is asymptotically normable and h ⊂ e a subspace then h is asymptotically normable. lemma 4.2 if e and f are asymptotically normable then so is 1 b b l (e , f) . proof: the proof is straightforward if one notices that e being asymptotically normable is equivalent to: there is ko such that for every k there is a p so that for every ε > 0 we can choose m > 0 with ⊂ ε o o o o k k pu mu + u from these lemmas and theorem 3.3, we can obtain: theorem 4.3 the class of asymptotically normable frechet spaces is the smallest class of frechet spaces containing the nuclear kothe spaces with continuous norm the banach spaces and is closed under ε-tensor products and subspaces. for comparison we recall that the class of quasi-normable frechet spaces is the smallest class of frechet spaces containing the nuclear kothe spaces (or nuclear kothe spaces with continuous norms, or schwartz spaces, or countably normable schwartz spaces) and the banach spaces and is closed under π-tensor products and quotient spaces. references [1] a. grothendieck, topological vector spaces, new york – london-paris, (1973). [2] r. meise, d. vogt, math. nachr., 122 (1985) 141. [3] d. vogt, some results on continuous linear maps between frechet spaces, in bierstedt k.d., fuchssteiner b. (eds.), <<functional analysis : surveys and recent results ii>>, north-holland math. studies, 90 (1984), pp. 349-381. [4] g. kothe, topological vector spaces, i, ii, new york-heildelber-berlin, 3 (1969, 1979). [5] d. vogt, studia math., 85 (1987) 163. [6] t. terzioglu, d. vogt, math., 54 (1990)180. [7] e. dubinsky, studia math., 71 (1981) 85. [8] l. holmstrom, proc. amer. math. soc., 89 (1983)453. further reading [1] e. dubinsky, the structure of nuclear frechet spaces, lecture notes in math., 720 (1979), berlin-heildel-berg-new york. [3] e. dubinsky, d. vogt, frechet spaces with quotients failing the bounded approximation property, studia math., 81 (1985), pp.71-77. [11] g.l., litvinov, nuclear space, springer verlag, new york, (2001). ∧ ∧ ∧ ∧ microsoft word h.p. aryal _34-43_.doc h.p. aryal and u. budhathoki / bibechana 10 (2014) 34-43 : bmhss, p.34 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana some wild mushrooms of rupandehi district, west nepal h.p. aryal 1* , u. budhathoki 2 1 bhairahawa multiple campus, siddarthanagar, institute of science and technology, tribhuvan university. 2 central department of botany, kirtipur, kathmandu, tribhuvan university, nepal *e-mail: hahariprasadaryal06@gmail.com 2 email: drushabudathoki@yahoo.com article history: received 25 october, 2012; accepted 1 november, 2013 abstract this mycological investigation carried out at natural as well as community managed forest, of rupandehi district, western terai and siwaliks region of nepal. samples were collected in different area ranging between 90 and 1229 masl in tropical deciduous riverine forest, to subtropical deciduous hill forest. this paper highlights on common wild mushrooms amanita chepangiana, geastrum fimbriatum, macrolepiota procera, pycnoporus cinnabarinus, schizophyllum commune, scleroderma bovista and sparassis crispa. the collected samples represented seven species of basidiomycetes belongs to four order and seven families. the specimens were deposited in the tribhuvan university central herbarium, (tuch), kathmandu, nepal. keywords: basidiomycetes, macrofungi, mushroom diversity, taxonomy. 1. introduction taxonomy of this genus has been based mainly on basidiocarp, macro morphology, basidiospore size & host plant type [1]. the species of mushrooms in nepal is expected to reach more than 3000 due to the large variation in climatic condition and vegetation types [2]. the taxonomic approach has been made here along with distribution. 2. study area the study area (map 1) is the southern belt of west nepal and lies in, lumbini zone, rupandehi district. this area is a tropical to subtropical zone embracing different types of soil and forests. the forest vegetation is dominated by members of the dipterocarpaceae, combretaceae, fagaceae and leguminosae. the study area included 19897 hectares of forested land [3] and lies between 27o20’00’’27o47’25’’n latitude and 83o12’16’’83o38’07’’e longitude. altitude varies between 90 and 1229 masl. the average annual rainfall is 1391 m [4]. 3. materials and methods surveys were under taken and specimens collected from 15 th to 31 st may and from 1 st june to 31 st october in 2011 and 2012 respectively. mushroom samples were photographed in their natural habitat h.p. aryal and u. budhathoki / bibechana 10 (2014) 34-43 : bmhss, p.35 (online publication: dec., 2013) and their morphological characters were noted. the samples were well dried and packed in wax-paper bags wrapped with aluminium foil to prevent external infection and intermixing of the spores and labeled. the habitats including ecological parameters viz. altitude (by altimeter, model no. 7030, japan), vegetation composition, soil type, soil ph (by digital ph meter, model no.335, systronics, ahmedabad, india, serial no. 2719), soil moisture (by nail ph meter, model: takemura, japan), humidity, temperatures and time (by means of thermo-hygrometer-clock, model: temptec, hong kong), with macroscopic and microscopic characters of the specimens were noted. the wax-paper bags were brought to central department of botany, tribhuvan university, for further microscopic examination. map 1: sample collection site. a number of the collected specimens were preserved in 25:5:70 ml rectified alcohol: formalin: distilled water [5]. for microscopic study the specimens were sectioned using a sharp razor blade. the cyanophility was observed by placing the parts of species in cotton blue and mounting in lactophenol reagent. photographs were taken with a digital camera (sony dsc s980 camera, china) and macro and micro characters studied under an olympus microscope (model no. cx 22). latitude and longitude were recorded by means of gps compass (garmin, eterex, germany). the voucher specimens were identified [6-25] and are deposited in tribhuvan university central herbarium, (tuch), and kathmandu, nepal. h.p. aryal and u. budhathoki / bibechana 10 (2014) 34-43 : bmhss, p.36 (online publication: dec., 2013) 4. results and discussion fig. 1: amanita chepangiana tulloss & bhandary [26] common name: chepang slender, caesar (eng.). local name: gobre musa (chepang), salleu (magar), vaam waam moo, naagfum, seto kukhura phooey chyau (nepali.) taxonomic position: basidiomycetes, agaricales, plutaceae. description: pileus: 13-19cm wide, convex at first later umbrella like pure white, sometimes with a slight grayish to brownish or yellowish tint over the center. gills: lamellae free, close to sub crowded, white, and truncate. stipe: 15-18cm x 2cm, cylindrical white, annulus skirt like, white found just below the cap, white. volva: large, membranous, white, saccate. spore: 9-12 x 8-10 µm, white, subglobose, inamyloid. spore print: white. edibility: edible, preferred by chepang ethnic cast, excellent. rs. 250 to 300/kg nc, in the local market. distribution: mostly in shorea robusta forest. occurs in fagaceous forest also-china, south east asia and nepal habit: sporophores growing solitary or scattered, sometimes in clusters. habitat: on soil, mycorrhizal. season: june to august. specimen examined: on the litter of the soil, in shorea robusta dominant forest of karhiya, 223m, paklihawa, 90m, chiliya, 110m, murgiya, 233m , saljhandi, 262m, simalpani,1225m (rupandehi), (2011); voucher no. 100772, aryal, h.p.; new to area of collection. previously reported: from jugedi, chitwan [2, 26, 27, 28, 29, 30]. fig. 2: geastrum fimbriatum fr. butler, e.j. & bisby, g.r. [18, 31]. h.p. aryal and u. budhathoki / bibechana 10 (2014) 34-43 : bmhss, p.37 (online publication: dec., 2013) common name: earthstar, sessile earthstar, geastre fimbrie. local name: tare chyau taxonomic position: basidiomycetes, phallales, geastraceae. description: basidiocarp: close globose, up to 7cm in diameter. exoperidium: opening into 6-9 triangular fringes, turned downward, chamois-colored, thin, membranous, separable, whitish. endoperidium: globose, sessile, same color as exoperidium, with fairly salient apical opening, edge fibrous. gleba: powdery when mature, cocoa-brown. flesh: leathery, odor: not distinctive, spores: 3-4 µm, cocoabrown, rounds, finely warty. edibility: inedible. distribution: europe, japan, north america and nepal. habit: on soil, in clusters or in colonies on moss or pine needles in sandy forest of conifers or in mixed woods. habitat: in groups among leaf-litter, under conifers. saprophyte. season: june to september. specimen examined: on soil, in clusters in mixed forest in murgiya, 233m, saljhandi, 262m, simalpani,1225m, (rupandehi), (2012); voucher no. 1008167, aryal, h.p. new to area of collection. previously recorded: on phoksundo tal [32, 33]. fig. 3: macrolepiota procera (scop.) sing [34]. common name: parasol mushroom. local name: gobbre chyau (nepali.) taxonomic position: basidiomycetes, agaricales, agaricaceae. description: usually 12-25 cm or more high, fruiting body pale colored. pileus: 7-15 cm in diameter, at first ovate, then campanulate, finally becoming expanded with an umbo, grayish brown or reddish brown, surface cracking into large, brown scales which are concentrically arranged except at the umbo and small white scales scattered in between the large ones, adpressed scaly or with reflexed roughening, fibrillose edge. gills: free, crowded but not forked ventricose, white when young and pinkish at maturity, broad in the middle and narrow near the stipe. stipe: slender, cylindrical, broad, with markedly brownstriped surface with a prominent bulbous base, 15-25 x 1.5-2 cm, broad, colour paler than the pileus, covered with minute darker scales, hollow, annulus large, band like, conspicuous thick tough, white, movable up and down flesh: white, soft, in cap and fibrous in stipe, thick. h.p. aryal and u. budhathoki / bibechana 10 (2014) 34-43 : bmhss, p.38 (online publication: dec., 2013) hymenophoral trama: regular basidia: 4-spored, clavate. basidiospores: white, ovate to elliptical, apiculate, smooth, with germ-pore, dextrinoid, 13-16 x 8-10 µm, metachromatic. spore print: white. spore: 15-20 x 10-13 µm. elliptical, smooth, dextrinoid. pleurocystidia: absent. hyphae: thin walled. clamp connections: present. odor: pleasant. edibility: edible, delicious. distribution: europe, japan, china, n. america, india and nepal. habit: sporophores growing solitary or scattered, sometimes in clusters. habitat: on soil, in pastures, lawns, in woods, gardens. saprophyte. season: june to october specimen examined: on soil, in sal forest in karhiya, 223m, paklihawa, 90m, chiliya, 110m, murgiya,233m, saljhandi,262m, simalpani,1225m, (rupandehi), (2011); voucher no. 1008118, aryal, h.p.; new to area of collection. previously recorded: previously recorded from manichur [35], phulchowki [36], nagarjoon [37], growing under pine forest, nagarkot, [38]. fig. 4: pycnoporus cinnabarinus (jacq.: fr.) karst. [23, 39] local name: rato kathe chyau, raktey chyau, sindure chyau. taxonomic position: basidiomycetes, polyporales, polyporaceae. description: fruiting body: semicircular to kidney-shaped; plano convex. carpophore: 3.9 x 1.5-5-7 x 0.5-2.2 cm, bracket-shaped, sessile to sub stipulate, deep orange red , tending to darken dimidiate, at first slightly pubescent then glabrous, fairly rugose, hard on dry in annual, with faint zonation towards margin, thinning from base to periphery, upper surface reddish to almost blackish red at maturity, finely hairy, under surface bright reddish orange with 2-4 round to angular pore; stipe: absent, hymeneal surface: waxy, deep red. tube: 1 3mm long, orange-red; pores: irregular, small, round, pubescent, vermilion 2-4 per mm. flesh: red, leathery, first spongy then suberose. spore print: white spores: white, 5 6 x 2 2.5 µm, hyaline, oblong or short cylindric, smooth, and apiculate, inamyloid, hyphal system: trimitic. cystidia: absent. odor and taste: not distinctive. edibility: inedible, (medicinally used for relief from ear pain and to cure cuts and burns). distribution: worldwide. in tropical to temperate belts. habit: clusters on the dead wood, annual. habitat: on dead broadleaf branches and trunks. saprophyte. season: june to october. specimen examined: on log on syzygium cumini, karhiya, 223m, paklihawa, 90m, chiliya, 110m, murgiya, 233m, saljhandi, 262m, simalpani,1225m (rupandehi), (2012); voucher no. 100711, aryal, h.p., new to area of collection. previously recorded: on dead wood of alnus nepalensis. sundarijal, 1500m, [30], chitwan 200m. [30], ranipauwa 1600m. [30], langtang 2200m. [30]. on dead wood, place not mentioned [40]; khand bari [37]; on betula sp., chheti gaon, darchula dist. [41], darchula dist. [42] and pokhara h.p. aryal and u. budhathoki / bibechana 10 (2014) 34-43 : bmhss, p.39 (online publication: dec., 2013) (900m) [43, 44]. and lamjung [45]. on bark of stump of alnus nepalensis. jhakrey, lumle, 1645m, [46, 47]. fig. 5: schizophyllum commune (fr.:fr.) grev. [27, 48], (fig. 5) local name: mizu chyau, kathe bagale chyau, kanchat chyau, pankhe chyau. taxonomic position: basidiomycetes, agaricales, schizophyllaceae. description: tiny fruiting bodies lack stems and they attached themselves like tiny bracket fungi on the dead wood of deciduous trees. sporophores growing in groups on branches or trunks of trees, on old wood, sometimes on the branches of shorea robusta, usually coriaceous, tough, pliant when fresh, attached laterally to the substratum carpophore: gregarious, 1-5 cm wide, fan or kidney shaped, dry, gray, hairy, whitish gray when dry to brownish gray when moist, margin lobed and hairy; sessile, dry, inclined downward or horizontal, sometimes zoned concentrically gills: grayish white or pink-tinged, split lengthwise into two layers which tend to curve away from each other, converging radially toward base, where they are attached, edge split and revolute. stipe: absent, flesh: tough leathery, gray, becoming whitish and sometimes malodorous as it dries. hymenophoral trama: not bilateral, hyphae: thick walled basidia: 4-spored. basidiospores: hyaline. oblong with obtuse ends, smooth, non-amyloid, 5-7 x 2-3 µm spore print: white. cystidia: absent. spore: 3-4 x 11.5µm. white, straight or curved, smooth. inamyloid clamp connection: present. edibility: edible. it is used to eat mixing with other things e.g. cereals. mostly used by the newar cast during their marriage ceremony as sagun (better happening). used in soups, by magar, newar and tharu (bara district) ethnic casts. this fungus causes a disease known as basidioneuromycois in human being [25]. better to avoid. distribution: worldwide. in tropical to temperate belts. habit: in clusters on log. habitat: on wood, stumps, dead trunks or living trees in poor health. besides growing on wood, it has also been found on animal matter (saprophytic on whalebone or, in mycelia form with no fruitbody, on scar tissue in a human mouth). ecology: saprobic on dead wood or sometimes parasitic on living wood. season: july to september. specimen examined on decay wood (shorea robusta), in sal forest, karhiya, 223m, paklihawa, 90m, chiliya, 110m, murgiya, 233m, saljhandi, 262m, simalpani,1225m, (rupandehi); (2012); voucher no. 101002, aryal, h.p., new to area of collection. previously recorded: on dead wood, place not mentioned [40]; growing on decayed wood, ranipauwa, kaligandaki [33], bagarchhap [49], pokhara [43, 42]. khand bari [37]; on betula sp., chheti gaon, darchula dist. [41] and on the logs, stumps and sticks of alnus nepalensis, jhakrey, lumle, 1645m, [47]. in tropical to temperate belts [43]. on the logs, stumps and sticks of alnus h.p. aryal and u. budhathoki / bibechana 10 (2014) 34-43 : bmhss, p.40 (online publication: dec., 2013) nepalensis, sundarijal, 1440m, sundhara (kath) swayambhu, champadevi, bishalnagar (kath), namobudha (kavre), nagarkot [30]. fig. 6: scleroderma texense berk. [48, 50, 51], (fig.6) local name: kudaki chyau, kutaki chyau, paduke chyau. bhundki, dalle, phutuki. taxonomic position: basidiomycetes, boletales, sclerodermataceae. description: basidiocarp: 1-2 cm, whitish, subterranean or superficial globose, sessile sometimes prolonged into a stem like base. peridium: simple, rarely double smooth or rough with pale brown warts on the upper part outer layer composed of hyaline, loosely and irregularly arranged hyphae of 22.5µm diameter, inner layer whitish, composed of hyaline, anastomosing hyphae of 5 µm diameter and irregular shaped hyaline cells of 7-7.5 µm diameter. gleba: traversed by sterile veins, pale white when young, becoming sooty black with age. dehiscence: irregular. capillitium: rudimentary, consisting of only remnants of sterile hyphae. spores: 6.25-10 µm diameters, globose, purplish brown to black, wall darker, echinulate. edibility: edible. rs. 350 to 450/ per kg, in the local market. very common. eaten raw as well as roasted in fire or cooked as vegetable. distribution: europe, india thailand, nepal. habit: growing buried or on soil in shorea robusta forest. mainly in tropical dipterocarp forest. nepal (east to west: tropical belt of shorea robusta forest). habitat: ectomycorrhizal fungi. specimen examined: on soil, in sal forest, karhiya, 223m, paklihawa, 90m, chiliya, 110m, murgiya, 233m, saljhandi, 262m, simalpani,1225m, (rupandehi), (2011); voucher no. 1009152, aryal, h.p., new to area of collection. previously recorded on chuche khola, hetauda, makawanpur district, growing buried or on soil, [51]. fig.7: sparassis crispa (wulfen) fr. [6, 7, 9, 20, 23]. h.p. aryal and u. budhathoki / bibechana 10 (2014) 34-43 : bmhss, p.41 (online publication: dec., 2013) common name: cauliflower fungus, wood cabbage, coat of wood, brain fungus. local name: cauli chyau, thakre chyau, fursey chyau, chyapkey, fyaleshymo (tamang). taxonomic position: basidiomycetes, agaricales, pluteaceae. description: sporophores growing usually at base of conifer, 15-40 cm high, carpophore 10-60 cm, fleshy, erect, densely branched from a short stout rooting stipe. flattened and curled lobes resembling a cauliflower head from a distance, whitish or ochraceous when young, black with maturity, white to pale yellow in colour. stipe: very short, stout, whitish at first, turning black when old. flesh: firm, tough, elastic, whitish or faintly pale yellow, fragile, brittle. odor: pleasant. hymenium: smooth. basidia: 4-spored basidiospores: white, buff in mass, pip-shaped. spore print: whitish. spores: whitish to light ochre, ovoid, smooth, 6-7 x 3-5µm. inamyloid. clamp connection: present edibility: edible. young fruit bodies are very good in taste. distribution: north america, europe, china, japan, india and nepal. habit: on colonies in dead wood. habitat: on coniferous wood, at the foot of trees or on roots. it grows on the ground near trees or on very rotten wood in broadleaf woodlands. parasitic season: july-october. specimens examined: on log (tectona grandis), karhiya, 223m, paklihawa, 90m, chiliya, 110m, murgiya, 233m, saljhandi, 262m, simalpani,1225m, (rupandehi); (2011); voucher no. 100748; new to area of collection. previously recorded: at the base of quercus lamellose,pahiro,1660m, at the base of quercus semecarpifolia, dhunche, 1960m, lama hotel, 2840m, chandanbari, 3250, at the base of tsuga demosa, thulo syafru, 2120m, ghoda tabela, 3000m, cholangpati, 3585m [52]. 5. conclusion the gathering of mushrooms shows that there are plenty of species, which are said to be edible and of medicinal value. many mushroom species are gathered by local people for their daily livelihood and trade. they are sacked in bags and carried to market even for sell. the tropical species like amanita chepangiana seem to be widespread in the terai and siwaliks belt of nepal. the medicinally important tropical polypore like pycnoporus cinnabarinus has been gathered for the remedy of infectious disease (mump), ear pain etc. the cosmopolitan species like schizophyllum commune the inedible fungi is sometimes used for culinary proposes in food deficit condition. this species has religious value also and is used as ‘sagun’ for better happening in the marriage ceremony in newar community. the dipterocarp inhibiting mycoelements like scleroderma texense has been used both for food and medicine. during surveys, it was found that the population of amanita chepangiana, macrolepiota fuliginosa scleroderma bovista, and sparasis crispa are declining since the last two decades due to deterioration of forest. so, it is visualized from the field survey that some of the important species need special attention to conserve against the threat to avoid their unmanaged and unscientific exploitation by the people. it is therefore necessary to conserve natural habitat of mushroom diversity for the sustainable development. the government should take special attention on these aspects. acknowledgements the authors would like to acknowledge nepal academy of science and technology for providing the ph.d. research grant; thanks are due to the central department of botany, tribhuvan university for providing laboratories facilities. we are also grateful to the institute of science and technology for granting study leave to one of them (mr. h.p. aryal). sincere thanks are extended to local informants of the study area for providing information. h.p. aryal and u. budhathoki / bibechana 10 (2014) 34-43 : bmhss, p.42 (online publication: dec., 2013) references 1. h.h. burdsall and o.k. miller, type studies and nomenclatural considerations in the genus sparassis. mycotaxon, 31(1988)199-206. 2. m christensen, s. bhattarai, s. devkota and h. o larsen, collection and use of wild edible fungi in nepal. eco. bot. 62 (1) (2008) 12-23. 3. d.f.o. 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(1988), pp. 444, 448 & 504. 49. h.r. bhandary, some edible and medicinal fungi from dumre to manag, mustang and pokhara. jour. nat. hist. mus. 12(1-4) (1991) 47-60. 50. k.p. sims, r. watling and p. jeffries, a revised key to the genus scleroderma, mycotaxon, vol. lvi (1995) 403-420. 51. v. manandhar and m. k. adhikari. the family sclerodermataceae: ectomycorhizal fungi from nepal. bull. dept.pl.res. 31(2009) 29-34. 52. s. devkota, distribution and status of highland mushroom: a study from dolpa, nepal. j. nat. hist. mus. 23(2008) 51-59. 53. websites: www.biodiversitylibrary.org, www.indexfungorum.org, www.jstor.org, www.mycobank.org, www.scihub.org, www.scirus.com, www.tropicos.org 60-69 s. pandey-gopi chandra kaphle r c o s t n s. pandey et al. / bibechana 11(1) (2014) 60-69: (online publication: march, 2014) p.60 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana electronic structure and magnetic properties of bulk elements (fe and pd) and ordered binary alloys (fepd and fe3pd):tb-lmto-asa approach suraj pandey1, gopi chandra kaphle2, narayan prasad adhikari2* 1patan multiple campus, patan dhoka, kathmandu, nepal 2central department of physics tribhuvan university, kathmandu, nepal *email: npadhikari@gmail.com accepted for publication: february 05, 2014 abstract the binary alloys formed from the elements of fe and pd like fepd and fe3pd, have the strange electronic and magnetic properties, generally used in shape memory alloys, computational chips, medical purposes as well as modern technological uses. we used tb-lmto-asa approach for the study of band structure and density of states of the transitional elements fe and pd and their ordered alloys fepd and fe3pd. we analyzed metallic and nonmetallic character and occupation of s, p and d electrons from the band structures and magnetic properties through the plot of density of states. our findings show that all the elements and alloys bear metallic nature whereas bulk palladium shows non magnetic behavior. similarly fe and both the ordered alloys fepd and fe3pd are found to be magnetic in nature with values b19.2 µ , b49.3 µ and b01.3 µ respectively. these well agree with experimental as well as previous theoretical calculations. © 2014 rcost: all rights reserved. keywords: binary alloys; density of states; electronic properties; tb-lmto-asa. 1. introduction the physical properties of metal are generally determined through its electronic structure. in solid there are large numbers of electrons and nuclei which are mutually interact with each other, so dynamics of these particles, in general cannot be considered separately. for the simplicity, we have considered frozen core approximation because the nuclei together with core electrons do not take part in bonding. the cohesive, electronic, optical, magnetic and superconducting properties of solids are dominated by the behavior of valance electrons moving in the field of the ion-cores of constituent atoms [1]. alloys are metallic materials consisting of two or more elements combined in such a way that they cannot be readily separated by physicals means. if the alloy is formed by a mixture of only two types of atoms, it is called binary alloy [2]. binary alloys may be ordered or disordered depending upon atomic positions. in ordered alloys atoms are situated by making symmetry in the crystals whereas in disordered alloys atoms are situated randomly in the crystals without any crystal symmetry. in the present work we are dealing with alloys and we are also familiar that more than 90 percent of metals used are in the form of alloys. they represent an enormous family of engineering materials that provide a wide range of products with s. pandey et al. / bibechana 11(1) (2014) 60-69: (online publication: march, 2014) p.61 useful properties. each alloy is distinct from its components, and the properties of each alloy are distinct. indeed the purpose of forming an alloy is to provide a metallic substance with physical, mechanical and chemical properties and characteristics that are different from those of its components. fe3pd alloys are potentially useful ferromagnetic shape memory materials with a maximum predicted strain of up to 6.8%. shape memory materials have found widespread application in engineering and medicine, and recently there has been a great deal of interest in the search for ferromagnetic shape memory alloys capable of large reversible strains under an applied magnetic field [3]. fepd alloys have large magnetization and magneto-crystalline anisotropies and as such are potentially technologically important for applications as permanent magnets or high-density storage media [4]. the large number of experimental and theoretical works have been done regarding the characteristics of fe and pd separately and their alloys. the rest of the paper is organized as follows. section ii describes the computational details of the present study. results and discussions are described in section iii whereas section iv provides the conclusion and finally we present references used in the present study. 2. computational details all the systems considered are studied using tight binding linear muffin-tin orbitals atomic sphere approximation (tb-lmto-asa). the calculations are carried out from self-consistent calculations (scf) based on density functional theory within the framework of the local-density approximation (lda) [5]. the scf solve the kohn-sham equation using the exchange-correlation potential of von barth and hedin [6] with the help of minimal basis sets and partial wave method implemented in tb-lmto-asa code. the crystal potential is constructed of overlapping wigner-seitz spheres for each atom in the unit cell. according to the spirit of the tb-lmto-asa procedure, only the energetically higher-lying valence states have been included in the self-consistent calculations of the effective crystal potential [7]. in such a case, the deeper lying core states are treated as atomic like and hence called frozen core approximation. the band calculation technique are divided into two main approaches; one uses trial wave function, which is formed as linear combinations of basis functions like plane waves in the nearly free-electron (nfe) method expands orthogonalized plane waves function into a set of energy-dependent partial waves and applies a matching condition for partial waves at the muffin-tin sphere like the apw [8] and kkr methods [9]. actually, the linearized muffin-tin orbital (lmto) method developed by anderson [10,11] uses as basis set for expanding the wave function, a set of orbitals that form a complete basis set for a muffin-tin potential. for the calculation of fe (bcc) and pd (fcc) structure same basis set were used at which (8×8×8) kpoints were sampled in the irreducible wedge of brillouin zone (bz). these parameters are sufficient in leading to well converged total energy and other related parameters. the magnetic moment was calculated by differentiating up and down dos. after the convergence of scf we analyzed all the data required for band structure, total energy, dos etc. all the calculations were iterated to self-consistency with accuracy of 10-6 rydberg. 3. results and discussions this section contains the result and discussion of main findings for the band structure and density of states of elemental solid fe, pd and the ordered alloys formed by them like fepd and fe3pd. a. band structure of fe and pd presently, we used bcc structure of iron which belongs to the space group im-3m with space group number 229. the energy minimization curve for fe and pd are shown in fig. 1. s. pandey et al. / bibechana 11(1) (2014) figure 1: plot of energy versus lattice constant for fe (left) and pd (right). from the left panel of fig. (1) we found that the lattice parameter of fe at minimum energy is 2.83 (5.34 a.u.). this value of lattice parameter is 1.39 % less than the experimental value case of palladium we have used fcc structure which belongs to the space group fm minimization curve for it is shown in right panel of fig. minimum energy is 3.86 o a (7.28 a.u.), this value of lattice parameter is 0.77% less than the experimen value 3.89 o a [12]. the band structures and density of states of these clusters are calculated with the base of these parameters. figure 2: energy band structures of fe and pd along symmetry axes with reference to the fermi energy. the band structure of fe and pd are shown in left panel and right panel of fig. (2) respectively, which are plotted with reference to the fermi energy, 0 on vertical axis represents fermi energy of the iron. bands below the fermi energy are valance bands and bands above t chana 11(1) (2014) 60-69: (online publication: march, 2014) p.62 plot of energy versus lattice constant for fe (left) and pd (right). (1) we found that the lattice parameter of fe at minimum energy is 2.83 (5.34 a.u.). this value of lattice parameter is 1.39 % less than the experimental value 2.87 o a case of palladium we have used fcc structure which belongs to the space group fm-3m. the energy curve for it is shown in right panel of fig. (1). we found out that lattice parameter of pd at (7.28 a.u.), this value of lattice parameter is 0.77% less than the experimen [12]. the band structures and density of states of these clusters are calculated with the base energy band structures of fe and pd along symmetry axes with reference to the fermi energy. re of fe and pd are shown in left panel and right panel of fig. (2) respectively, which are plotted with reference to the fermi energy, 0 on vertical axis represents fermi energy of the iron. bands below the fermi energy are valance bands and bands above the fermi energy are conduction bands (1) we found that the lattice parameter of fe at minimum energy is 2.83 o a o a [12]. in 3m. the energy (1). we found out that lattice parameter of pd at (7.28 a.u.), this value of lattice parameter is 0.77% less than the experimental [12]. the band structures and density of states of these clusters are calculated with the base re of fe and pd are shown in left panel and right panel of fig. (2) respectively, which are plotted with reference to the fermi energy, 0 on vertical axis represents fermi energy of the iron. bands he fermi energy are conduction bands. s. pandey et al. / bibechana 11(1) (2014) 60-69: (online publication: march, 2014) p.63 in case of fe there are all together 9 bands. the maximum energy is at conduction band having value 45.36 ev and minimum value of the energy lies at valence band which has the value -8.67ev. the difference between maximum value of energy of conduction band and minimum value of energy in valance band is found to be 54.01 ev. conduction band and valance bands are overlapping within this range showing fe as a metallic nature. due to the high symmetry of the crystal at the maximum energy of the conduction band and minimum value of energy of the valance band occurs at the gamma point. fat band structure calculations were carried out in order to know the s, p and d orbital contributions on the band structure of fe. fig. (3) shows the contribution of s and p orbitals on the band structure of fe. figure 3: fat band structure of s-orbital (left) and p-orbital (right) of fe, horizontal dotted line represents the fermi level. figure 4: fat band structure of t2g-orbital (left) and eg-orbital (right) of fe, horizontal dotted line represents the fermi level. s. pandey et al. / bibechana 11(1) (2014) 60-69: (online publication: march, 2014) p.64 it shows that s and p-orbitals do not contribute much in the band structure of fe, there is a greater contribution of p-orbital to the conduction band in comparison to the valence band, while the contribution of s-orbital is negligible in both conduction and valence band. s band contribution for the electronic structure concerntrayed as the g points . the contribution of p band elongates from n to p and crosses fermi energy through n. figure (4) shows that d-orbitals overlap between the valence bands and conduction band at the fermi energy level, it has a greater occupancy at valence band and less at conduction band, this indicate that d-orbital contributes significantly to the total band structure. it is mainly due to majority of electrons are in d-orbitals of iron. in case of pd, valance bands lie below the fermi energy are found occupied, bands above the fermi energy are unoccupied conduction band. valance bands and conduction bands overlaps with each other. along g axis maximum value of energy of conduction band is 28.17 ev and minimum value of the energy of valance band is -7.72 ev; difference between these two energies is 35.89 ev. maximum value of energy of conduction band is 30.45 ev. fig. (6) shows that energy levels at some points are degenerate. )figure 5: fat band structure of s-orbital (left) and p-orbital (right) of pd , horizontal dotted line represents the fermi level. figure 6: fat band structure of t2 g-orbital(left) and eg-orbital (right) of pd, horizontal dotted line represents the fermi level. s. pandey et al. / bibechana 11(1) (2014) 60-69: (online publication: march, 2014) p.65 we studied the fat band structures of s, p and d orbitals of pd in order to know their contributions on the band structure. dark and shaded portion of fig. (5) shows the occupancy of s and p electron. occupancy of the s-orbital is negligible in comparison with the p orbital, occupancy of p-orbital is greater at conduction band and less at the valence band. fig. (6) shows that the occupancy of the d-orbital occurs at the valence band, while its occupancy at the conduction band is almost negligible due to which it has a significant contribution to the band structure. physical properties of the solid such as electrical and magnetic properties, is contributed due to the d-orbital. b. band structure of fepd and fe3pd we deal with the ordered structure of the fepd and fe3pd alloys, both have a simple cubic structure with the space group pm-3m ( space group no. 221)[13-15]. in the present calculation figure 7: plot of energy vs lattice constant for fepd and fe3pd. figure 8: band structure of simple cubic fepd and fe3pd along symmetry axes with reference to the fermi energy. s. pandey et al. / bibechana 11(1) (2014) 60-69: (online publication: march, 2014) p.66 the lattice constant of fepd for the minimum energy is obtained as 3.01 o a (5.68 a.u.). similarly the lattice parameter for the lowest energy value of fe3pd is found to be 3.56 o a (6.70 a.u.). the energy minimization curves for both fepd and fe3pd are shown in fig. (7). all the further calculations are done using these optimized lattice parameters. the band structure of fepd and fe3pd obtained from the present study is shown in the left and right panel of fig. (8). in case of fepd, we found 18 bands with valence and conduction bands overlapping with each other, showing fepd has metallic nature. the minimum value of energy of valence band is -4.25 ev, and the maximum value of energy of conduction band is 21.25 ev, at g point. similarly, in case of fe3pd we found 36 bands contributing s, p and d orbitals. the valence and conduction bands also found to be overlapped with each other showing metallic nature of fe3pd alloy. the maximum energy of the conduction band lies at g point having value 31.36 ev and minimum energy of valence band at g point which has a value of -6.72 ev. to know the effective contribution of individual orbital we have to analyze density of states. c. density of states for fe and pd the plots of total density of states and partial density of states for s, p and d orbitals calculated using optimized parameters for fe and pd are shown in left and right panel of fig. (9). figure 9: projected density of states of fe and pd with reference to fermi energy. from the figure it is found that there is negligible contribution of s band for the magnetization whereas slight asymmetric nature of p orbital below the fermi level shows that p contributed less. there is great asymmetry in up and down spin of dos of d orbitals indicating that overall magnetic behaviour of fe is dominated by d electrons. the vertical dotted line at zero represents fermi energy. the large number of peaks lies below the fermi energy and few peaks lie above the fermi energy in left panel of fig. (9). the peaks in the dos indicate the large number of states at the certain energy level, which can be occupied by large number of electrons. the magnetic moments are found by integrating the difference of density of states between up and down spin states up to fermi energy. from the present calculation magnetic moment of fe found to be equal to b19.2 µ which is 1.35% less than the experimental 2.22bµ obtained by w. zhong et al. [16] which shows that fe is strongly ferromagnetic. partial density of state plot for the s, p and d orbital of fe shows that there is a significant difference between the up and down spin density of state plot of the d-orbital which give rise to a net magnetic moment. in case of pd, we found up spins and down spins density of states are nearly symmetrical with each other due to which the net magnetic moment of pd is nearly zero, hence pd is non-magnetic in nature. partial density of state plot for s and p orbital shows that it has a minimum difference of energy between up and down spin hence it does not contributes to the magnetic properties while in case of d-orbital up and down spin dos curves are almost symmetrical and there is no any significant differences of energy in the density of state plot and hence contribution to the magnetic moment is almost negligible. this supports the arguments given by band structure plot. s. pandey et al. / bibechana 11(1) (2014) 60-69: (online publication: march, 2014) p.67 d. density of states of fepd and fe3pd. we have performed calculation of density of states of ordered binary alloy fepd and fe3pd. fig. (10) shows the total density of state plot of ordered binary alloy fepd. all the up and down spin density of states of fepd are plotted with reference to the fermi energy at which vertical line at zero in the figure represents fermi energy of the system. density of states on positive side of the vertical axis are for up spin, and on negative side are for down spin states of fepd. fig. (10) shows that there is large number of peaks lies below the fermi energy and few peaks lie above the fermi energy for the up spin. the highest peak of up spins lies above the fermi energy and down spins lies below the fermi energy. figure 10: total and projected density of states of fepd with reference to fermi energy. the dos of down spin shows that the curve above the fermi energy is almost smooth having no peaks while below the fermi level it has a large no of peaks. there is a significant differences between the up and down spin dos in fepd which results in the large magnetic moment. from data obtained for density of states of fepd, the d magnetic moment of fepd was found to be 3.49µb . the density of state plot for s and p-orbital shows that it has a minimum difference of energy between up and down spin hence it does not contributes to the magnetic moment while there is a significant differences between the up and down spin in the dos of d-orbitals indicating that magnetic moment mostly come from the contribution of d electrons. total density of states of the binary ordered alloy fe3pd from the experimental work and present calculation are projected in left and right panel of fig. (11) respectively. from the right panel of fig. (11) we found that there is large number of peaks lie below the fermi energy and few peaks lie above the fermi energy. the highest peaks of up spins as well as down spins are below the fermi energy. the significant differences between the up and down spin density of state in fe3pd up to the fermi energy gives the magnetic moment which is found to be equal to 3.01 µb .s and p contributions are almost negligible. in case of up spin density of state plot of d-orbital has large number of peak lying below the fermi energy and the curve is almost smooth above the fermi energy without any peaks. down spin density of state plot of d-orbital shows that number of peaks below the fermi energy is greater than above the fermi energy. every peaks and nature of the present calculation is exactly matches with the experimental obtained dos by r. a stern et al. [3] shown in left panel of fig. (11). the slight difference in number of states is due to the effect of approximation used in theory and constrained used to experimental works like pressure, temperature etc. from this we considered that overall that dos is dominated by d projected dos in fe3pd and hence reflect same behaviour to magnetic moments. s. pandey et al. / bibechana 11(1) (2014) 60-69: (online publication: march, 2014) p.68 figure 11: tdos (ref:3) and pdos (present calculation) of fe3pd with reference to fermi energy. 4. conclusions and concluding remarks the present work gives the calculation of band structure and density of states of elemental solids fe and pd and ordered binary alloy fepd and fe3pd using tb-lmto-asa approach. in all elemental solids fe and pd along some symmetrical axis we have found nine bands with valance and conduction bands overlapping with each other. this is due to the contribution of minimal basis set used lmto. in case of ordered binary alloys fepd and fe3pd we have found 18 and 36 bands respectively with valance and conduction bands overlapping with each other. this shows that all the elements and their binary alloys behave metallic nature. the band structures and dos plot show that the transition metals have partially filled d-shells and their dbands extend through the fermi surface. since the d-bands are narrow and contain more levels than free electron bands, the density of states at the fermi level become very high. the magnetic moment is due to asymmetric distribution of d bands in the fermi level. the density of states of up and down spins for fe, fepd and fe3pd are found to be quite asymmetric in nature which causes a net magnetic moment and thus they are magnetic in nature. while up and down dos of pd is symmetric in nature giving a total magnetic moment nearly zero, due to which it is non-magnetic in nature. the magnetic moments for fe, fepd and fe3pd are found to be b19.2 µ , b49.3 µ and b01.3 µ respectively, which are comparable to experimentally calculated value. acknowledgments gck is grateful to ictp/oea net-56 program of trieste, italy for financial support and prof. a. mookerjee of s. n. bose national center for basic sciences, kolkata, india for providing computational code and some discussion in the manuscript. references [1] r. m. martin, electronic structure: basic theory and practical methods, cambridge university press, united kingdom, 2004. [2] n. w. ashcroft and n. d. mermin, solid state physics, thomson books, usa, second edition 1976. [3] r. a. stern, s. d willoughby, j. m. maclaren, j. cui, q. pan, r.d. james, j. applied physics, 93 (2003) 8644. s. pandey et al. / bibechana 11(1) (2014) 60-69: (online publication: march, 2014) p.69 [4] s. d willoughby, j. m. maclaren, journal of applied physics, 91 (2002) 8813. [5] p. hohenberg, w. kohn, phys. rev. b, 136 (1964) 864. [6] u. v. barth , l. hedin, j. phys. c : solid state phys, 5 (1972) 1629. [7] h. l. skriver, the lmto method: muffin-tin orbitals and electronic structure , springer verlag, 1984. [8] j. c. slater and g. f. koster. phys. rev. b, 15 (1954) 1498. [9] w. kohn, n. rostoker, phys. rev., 94 (1954) 1111 . [10] o. k. andersen, phys. rev. b, 12 (1975) 3060. [11] o. k. andersen, o. jepsen, phys. rev lett., 53 (1984) 2571. [12] c. kittel, introduction to solid state physics, wiley publication, seventh edition 2009. [13] a. szabo, neil s. ostlund, modern quantum chemistry, dover publication inc., second edition 1996. [14] s. hollos, electronic band structure calculations, exstrom laboratories llc, 1998. [15] b. k. aggrawal, h. prakash, quantum mechanics, prentice hall publication, 2007. [16] w. zohng, g. overny, d. tomanek, phys. rev. b, 47 (1993) 95. microsoft word mahesh chandra _6-13_.doc mahesh chandra and r.c. meena / bibechana 7 (2010) 6-13 : bmhss 6 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana role of reductant for generation of solar energy in photogalvanic cell mahesh chandraa∗∗∗∗ , r.c. meenab a department of chemistry,deshbandhu college,new dehli-110019 b department of chemistry, jai narain vyas university, jodhpur (rajasthan)-342 005 e-mail: rcmeena007@rediffmail.com article history: received 15 october 2010;revised 29 october 2010; accepted 1 november 2010 a b s t r a c t the photo voltages and photocurrents in photo galvanic cell containing a dye rose bengal and oxalic acid as reducing agent have been determined. the photo-outputs with oxalic acid are higher than rose bengal and mannitol system. the efficiency of the rose bengal –oxalic acid photo galvanic cell has been estimated to be 0.981 % .the photo potentials and photocurrent garneted, conversion efficiency, power of the cell and cell performance of the photo galvanic cells were determined. the effects of different parameters on electrical output of the cell were observed .a mechanism has also been proposed for the generation of the photocurrent in photo galvanic cell. keywords: photo galvanic cell; photopotential; rose bengal; oxalic acid,; mannitol; power point 1. introduction today, global warming and the rapid decrease in energy resources caused by the largescale consumption of fossil fuels have become serious. accordingly renewable energy resources are attracting a great deal of attention, and solar energy is one of the most promising future energy resources. the photo effects in electrochemical systems were first reported by becquerel [1, 2] in his investigation on the solar illumination of metal electrodes long back. surash and hercules [3] proved that only negative photo potential should be obtained with carbonyl compounds. alonso et al. [4] reported the use of electrodeposited cdse0-5 te0-5 electrode for solar energy conversion. jana and bhowmik [5] reported enhancement in the power output of a solar cell consisting of mixed dyes. hara et al. [6] investigated design of new coumarin dyes having thiophene moieties for highly efficient organic dye-sensitized solar cells. ameta et al. [7] reported use of toluidine blue nitroloacetic acid (tb-nta) system in photo galvanic cell for solar energy conversion. they also reported the use of micelles in photo galvanic cell for solar energy conversion and storage in azur a-glucose system [8], bromophenol-edta system [9] and fluoroscein-edta system [10]. bohrmann-linde and tausch [11] reported photo galvanic cells ∗ corresponding author: dr. mahesh chandra, asstt. prof., department of chemistry, deshbandhu college, new dehli-110019 [india]. mob.no. +91-09968347362, e-mail: drmahesh100@gmail.com mahesh chandra and r.c. meena / bibechana 7 (2010) 6-13 : bmhss 7 for classroom investigation, and monat and mccusker [12] reported femto-second excited state dynamics of an iron (ii) polypyridyl solar cell. schwarzhurg and willig [13] explored the origin of photo voltage and photocurrent in nanoporous, dye-sensitized, photo electrochemical solar cell. the sensitization of nanoporous films of tio2 with santaline (red sandal wood pigment) and the construction of a dye–sensitized solid-state photovoltaic cell was attempted by tennakone and kumara [14]. yadav et al. [15] reported use of bismarck brown-ascorbic acid (bb-aa) system in photogalvanic cell for solar energy conversion. photo galvanic cells containing reductants and photo sensitizers [16-33] were reported. the research in the field of photogalvanic cells is still in its infancy with respect to its viability and practical applicability and, therefore, requires thorough exploration to increase the conversion efficiency and storage capacity by selecting a suitable redox couple and photo sensitizers. a detailed survey of literature reveals that no attention has been paid to electrochemical behaviour of rose bengal-oxalic acid and mannitol has also been investigated at platinum electrode in presence of these reducing agents; therefore, the present work has been undertaken 2. experimental rose bengal (loba), oxalic acid (loba), mannitol (loba) and sodium hydroxide (s.d. fine) were used without further purification in present work. all the solutions were prepared in doubly distilled water and were kept in amber colored containers to protect them from sunlight. the whole system was set up systematically for photo galvanic studies consists of two thin foilles of electrochemically treated platinum as electrodes and saturated calomel electrodes as a reference electrode the distance between the illuminated and dark electrode is approx 45 mm .an ordinary tungsten lamp of 200 as light source. water filter was used to cut off ir radiations. the photopotetial was obtained as the difference between the initial potential of the system in dark and the equilibrium potential the system attains under constant illumination. the potential was first measured in dark and the change in potential on illumination was measured as a function of time. all the solution was bubbled with prepurified nitrogen gas for nearly twenty minutes to remove dissolved oxygen. solutions of dye, reductant and sodium hydroxide were taken in an htube glass tube. a platinum electrode (1.0x1.0 cm 2 ) was immersed into one arm of h-tube and a saturated calomel electrode (sce) was kept in the other. the whole system was first placed in dark till a stable potential was obtained, then the arm containing the sce was kept in the dark and the platinum electrode was exposed to a 200 w tungsten lamp. a water-filter was used to cut off infrared radiations. the photochemical bleaching of rose bengal was studied potentiometrically. a digital ph meter (systronices) and a micro-ammeter (osaw, india) were used to measure the potential and current generated by the system, respectively. the i-v characteristics of the cells were studied using an external load (log470k) in the circuit. the effect of variation of different parameters has also been observed. the rate of change in potential after removing the source of illumination was 1.20 min in rose bengal-oxalic acid; therefore, the system may be used in photo galvanic cell more successfully than the rose bengal and mannitol system. 3. results and discussion 3.1 rose bengal-oxalic acid systems the photo potential of rose bengal-oxalic acid system was measured at different ph values and maximum photo potential was found at ph 12.6 all the subsequent measurements were made at this ph value. the variation of photo potential with time for this system is shown in figure 1. as can he has seen from the figure, the photo potential increases upon illumination to a mahesh chandra and r.c. meena / bibechana 7 (2010) 6-13 : bmhss 8 value of 1239.0 mv in about 260.0 min. and remains constant on further illumination. when the light is switched-off, the system regains its original potential immediately, thereby showing that the system is perfectly reversible. 3.2 rose bengal-mannitol systems the photo potential of rose bengal-mannitol system was measured at different ph values and maximum photo potential was found at ph 11.0. all the subsequent measurements were made at this ph value. the variation of photo potential with time for this system is shown in figure 2. as can he seen from the figure, the photo potential increases upon illumination to a value of 1080 .0 mv in about 315.0 min. and remains constant on further illumination. when the light is switched-off, the system regains its original potential immediately, thereby showing that the system is perfectly reversible. we have also examined the photocurrent of rose bengal in presence of mannitol. the observed photo potentials and currents are comparable less than that of rose bengal-oxalic acid system (table 1). the photoionduced short circuit currents of rose bengal-oxalic acid and rose bengal-mannitol in photo galvanic cells are shown in fig.3. on illumination maximum photocurrents are obtained 190.0 in 315.0 min in rose bengal – oxalic acid system and 180.0 in 260.0 min in rose bengal-mannitol system. the rose bengalmannitol system takes much smaller time than that of rose bengal-oxalic acid system. the trend in short circuit photocurrents of rose bengal-oxalic acid is much better than rose bengalmannitol system (table 1). 3.3 power conversion efficiency of photo galvanic cell one of the important characteristics of any electrochemical cell is its power conversion efficiency. the i-v characteristics of rose bengaloxalic acid and rose bengal-mannitol photo galvanic cell have been investigated to estimate the power conversion efficiency of the cell. the typical i-v curve shown in figure 3. the possible power output from the cell can be obtained from the rectangle of maximum area which can be drawn under i-v curve. 100 200 300 400 500 600 700 1000 800 900 0 p h o t o p o t e n t ia l (m v ) 1100 1200 1300 1400 1500 1600 50 100 150 200 2500 time (min) figure 1: variation of photo potential with time in rose bengal-oxalic acid in photo galvanic cell mahesh chandra and r.c. meena / bibechana 7 (2010) 6-13 : bmhss 9 the power point (a point on the curve where the product of potential and current was maximum) in i-v curves were determined and their fill factors were also calculated. these data are summarized in table 2. the efficiency of the rose bengal-oxalic acid photo galvanic cell has been calculated to be 0.981 percent, comparable to that of and rose bengal-mannitol photo galvanic cell has been calculated to be 0.744 percent table 1 observations rose bengaloxalic acid system rose bengal-mannitol system open circuit voltage (voc) 1239.0 mv 1080.0 mv photo potential (v) 1137.0 mv 968.0 mv equilibrium photocurrent (ieq) 160.0 µa 160.0 µa maximum photocurrent (imax) 190.0 µa 180.0 µa short circuit current (isc) 175.0 µa 160.0 µa current at power point (ipp) 110.0 µa 100.0 µa potential at power point (vpp) 1022.0 µa 704.0 µa power at power point 64.0 µa/min 62.8 µa/min rate of generation 56.8 µa/min 56.0 µa/min conversion efficiency 0.981% 0.744% charging time 180.0 min 260.0 min t1/2 90.0 min 60.0 min fill factor (n) 0.51 0.44 mahesh chandra and r.c. meena / bibechana 7 (2010) 6-13 : bmhss 10 0 35 70 105 140 175 210 245 280 315 100 200 300 400 500 600 700 1000 800 900 0 1100 p h o t o p o t e n t ia l ( m v ) time (min) figure 2: variation of photo potential with time in rose bengal-mannitol in photo galvanic cell 100 0 200 300 0 35 70 105 140 175 210 245 280 315 time (min) p h o t o c u r r e n t ( a ) µ i ii figure 3 : variation of photo potential with time in (i) rose bengal-oxalic acid and (ii) rose bengalmannitol photo galvanic cell mahesh chandra and r.c. meena / bibechana 7 (2010) 6-13 : bmhss 11 table 2: i-v characteristics of the photogalvanic cells systems voc (mv) isc (µa) vpp (mv) ipp (µa) n rose bengal-oxalic acid 1239 175.0 1022.0 110.0 0.51 rose bengal-mannitol 1080 160.0 704.0 100.0 0.44 the conversion efficiency and sunlight conversion data for these two systems are reported in table 3. table 3 : conversion efficiency and sunlight conversion data sunlight conversion data system fill factor (n) conversion efficiency (%) photo potential (mv) photocurrent ( µ a) rose bengal-oxalic acid 0.51 0.98 1239 190 rose bengal mannitol 0.44 0.74 1080 180 on the basis of these observations, the highest conversion efficiency was found in rose bengaloxalic acid system. 3.3.1 performance of the cell the results obtained have been given in the tables 4. all the two systems were studied by applying the desired external load to have the potential and current corresponding to power point. the time t1/2 was determined after removing the source of light. it is the time taken in reaching half the value of power. the performance of cells was studied and comparative values are summarized in the table 4. table 4: performance of the photogalvanic cells in dark system power ( µ w ) t1/2 (min) rose bengal-oxalic acid 64.0 90.0 rose bengal-mannitol 62.8 60.0 on the basis of the observed data, the rose bengal-oxalic acid is the most efficient from power point of view (electrochemical studies of photo sensitizers). mahesh chandra and r.c. meena / bibechana 7 (2010) 6-13 : bmhss 12 3.3.2 mechanism on the basis of these observations, a mechanism is suggested for the generation of photocurrent in the photo galvanic cell as: illuminated chamber dye dye * (1) dye * + r dye (semi or leuco) + r + (2) at platinum electrode dye dye + e (3) dark chamber dye + e dye (semi or leuco) (4) dye + r + dye + r (5) where dye, dye*, dye , r and r+ are the excited form of dye, semi or leuco dye, reductant and oxidized form of the reductant, respectively. 4. conclusion photo galvanic cells are low cost due to the use of a dye, which are cheap and used in minute quantities reductant like ascorbic acid, is also not that very expensive. so overall working with a photo galvanic cell has lot of scope for its development. on the basis of observation in the whole study it is concluded that photo galvanic cells are better option for solar energy conversion and storage. also this system with better electrical output good performance and storage capacity may be used in near future. according to observed photo galvanic effect in 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[33] manju kumari, ram babu pachwarya, r.c. meena, int j. energy sources, 31(11) (2009) 1. microsoft word main.doc 31 bibechana vol. 6, march 2010 bio-diversity conservation in nepal d. thapa p.g. campus, biratnagar, tribhuvan university, nepal abstract the importance of biodiversity has been explained with examples. the effort applied for the conservation of biodiversity in nepal has been studied. i have also presented the species which are legally protected by the nepal government. keywords: biodiversity; wildlife reserves; aquatic animals 1. introduction bio-diversity means simply the different life forms or varieties of life. the care and management of biological things is called bio-diversity conservation. bio-diversity conservation is one of the most important global responsibilities of the mankind to ensure its safe future. hence the united nations conference on environment and development (unced) has given a prime importance on the agenda of bio-diversity conservation to the earth summit held in rio-de jenerio in june 1992. nepal has great diversity of flora and fauna due to unique geographical location with representative of deciduous and coniferous forests of subtropical and temperate regions to the sub-alpine and alpine , pastures and snow capped himalayan peaks with their cold streams, glaciers and lakes. 2. conservation of biodiversity nepal consist more than 5,000 species of flowering plants, 181 species of mammals, 844 species of birds, 185 species of fishes, about 635 species of butterflies and more than 2252 moths. the concept of bio-diversity conservation was arisen in rana regime when the central zoo was established in nepal. however, the active efforts for the conservation of bio-diversity started about 30 years ago. nowadays, many efforts have been applied for the conservation of biodiversity. the various efforts include protected areas, zoo, different types of law, conventions, non governmental organizations (ngos), local and national authorities, national and international organizations, etc. among them the protected areas is main. the protected areas conserve the biological things in their original place which is called in situ conservation. the protected areas has covered 26,695 km. square (18.32%) of the total area of nepal. the national parks and wildlife conservation act 1973 provides the legal basis for the management of protected areas. the protected areas include nine national parks, three wildlife reserves, one hunting reserve, three conservation areas and six buffer zones. 3. protected areas national park national park is an area set up for the conservation and management flora and fauna, landscapes, and historic objects of an area. the activities like hunting and damaging any animal, grazing, cultivation, felling any tree are prohibited within the national park’s area. 32 d. thapa wildlife reserve it is an area set aside for the conservation and management of animals and plants in their habitat. conservation area it is an area managed with an integrated plan for the conservation of natural environment and the sustainable use of natural resources. hunting reserve: it is an area set aside for the conservation and management of wildlife. it provides legal hunting opportunity. buffer zone: it is a surrounding area of national park and wildlife reserve. the local people can use this zone for collection of forest products. protected areas of nepal table 1 (national parks) s.n. category and name (year of establishment)area (km s. q.)altitude (m) 1 royal chitwan national park (1973) 932 150-815 2 royal bardia national park (1976\1988) 968 152-1494 3 shavipuri national park (2002) 144 1366-2732 4 khaptad national park (1984) 225 1000-3276 5 makalu barun national park (1991) 1500 435-8463 6 sagarmatha national park (1976) 1148 2800-8850 7 langtang national park (1976) 1710 792-7245 8 shey phoskundo national park (1984) 3555 2000-6885 9 rara national park (1976) 106 1800-4048 total 10288 table 2 (wildlife reserves) s.n. category and name (year of establishment) area (km s.q.) altitude (m) 1 koshi tappu wildlife reserve (1976) 175 90 2 parsa wildlife reserve (1984) 499 150-815 3 royal shuklaphanta wildlife reserve (1976) 305 90-270 total 979 33 bibechana vol. 6, march 2010 table 3 (hunting reserve) s.n. category and name (year of establishment) area (km s.q.) altitude (m) 1 dhorpatan hunting reserve 1325 700 -2850 total 1325 table 4 (conservation areas) s.n. category and name (year of establishment) area (km s.q.) altitude (m) 1 kanchanjunga conservation area (1997) 2035 1200-8598 2 mansalu conservation area (1998) 1663 1360-8163 3 annapurna conservation area (1986\1992) 7629 1000-8082 total 11327 table 5 (buffer zones) the protected areas helping to conserve medicinal, fodder, timber and other threatened plants along with wild rare, endangered animals etc. 4. rules and regulation for the conservation of biodiversity zoo is another important tool for the protection of threatened animals. the national zoo of nepal which is situated in kathmandu is helping for the conservation of important animals from different ecological zones of the country. notable animals are rhino, tiger, crocodile, black bear, black buck, clouded leopard etc. for the conservation of biodiversity, many rules (acts) and regulations has been formed by the government of nepal. some of them are: aquatic animals protection act (1961): it is concerned for the protection of wetlands and aquatic animals. s.n. buffer zones area (km s.q.) 1 royal chitwan national park 750 2 royal bardia national park 328 3 makalu barun national park 830 4 langtang national park 420 5 shey phoskundo national park 449 6 sagarmatha national park 275 total 3051 total protected area of nepal 26970 % of nepal territory (18.32) 34 d. thapa national parks and wildlife conservation act (1973): it is the base for the management of protected areas. the other important acts which are helping directly and indirectly for the conservation of biodiversity like forest act (1993), environmental protection act (1996), soil and watershed conservation act (1982), water resource act (1992), electricity act (1992), livestock health and livestock service act (1998). the regulations includes himalayan national park regulations (1979), buffer zone management regulations (1996), environmental protection regulations (1997) etc. these regulations are also concerned for the protection of biodiversity. similarly, environment protection council (1992), ministry of forest and soil conservation, ministry of agriculture, ministry of population and environment, national planning commission, national agriculture research council, nepal academy of science and technology, department of botany and zoology of tribhuvan university, local authorities (village development committee and district development committee) are working for the conservation of biodiversity. non government organizations like ecological society (ecos), natural history society of nepal (nashon), legal and environmental analysis for development and research service (leaders) are also working directly and indirectly for the conservation of biodiversity in nepal. the international conventions like the world heritage convention (1992), convention on international trade in endangered species of fauna and flora (cites),1993, ramsar convention on wetlands of international importance (1971), convention on biological diversity (1992) are also related for the conservation of biodiversity. there are also many international and national organizations which are working on biodiversity research and conservation. some of them are followings: 1) international union for the conservation of nature (iucn) 2) united nations environmental programme (unep). 3) world wildlife fund (wwf). 4) global environmental facility (gef) 5) international centre for integrated mountain development (icimod) 6) international plant genetic resource institute (ipgri) 7) king mahendra trust for nature conservation (kmtnc). the government of nepal has given legal protection to 27 mammal species, 9 bird species, and three reptile species under the national park and wildlife conservation act 1973. the protected animals are listed in table 6, 7, and 8. the government of nepal has protected many plant species under the forest act 1993. the juglans regia (bark of tree), picrorhiza kurroa (kutki), etc, are banned for collection, use, sale and distribution, transportation and export. the other important medicinal plants like valeriana jatamansi (jatamansi) , rauvolfia serpentina (sarpagandha), abies spectabilis (talis patra), taxus baccata (lauth salla), cordyceps sinensis (yarsagumba) are banned for export except processed and permission of department of forest. similarly, michelia champaca (champ), acacia catechu (khayer), shorea rubusta (sal, sakhuwa), bombax malabaricum (simal), dalbergia latifolia (satisal), pterocarpus marsupium (bijayasal), etc, are banned for transportation, export and felling for commercial purposes. 35 bibechana vol. 6, march 2010 table 7protected birds of nepal s.n. english name scientific name 1 gaint hornbill buceros bicornis 2 cheer pheasant catreus wallichii 3 bengal florican hubaropsis bengalensis 4 impeyon pheasant lophophorus impejanus 5 black stork ciconia nigra 6 white stork ciconia ciconia 7 crimson-horned pheasant tragopan satyra 8 lesser florican sypheotides indica 9 sarus crane garus antigone table 6 protected mammals of nepal s.n. english name scientific name 1 red panda ailurus fulgens 2 gaur bos gaurus 3 wild yak bos grunniens 4 grey wolf canis lupus 5 hispid hare caprolagus hispidus 6 swamp deer cervus duvauceli 7 asian wild elephant elephas maximus 8 leopard cat felis bengalensis 9 musk deer moschus chrysogaster 10 clouded leopard neofelis nebulosa 11 great tibetan sheep ovis ammon 12 royal bengal tiger panthera tigris tigris 13 snow leopard uncia uncia 14 tibetan antelope pantholops hodgsoni 15 gangetic dolphin platanista gangetica 16 one horned rhinoceros rhinoceros unicornis 17 pygmy hog sus sulvanius 18 brown beer ursus arctos 19 indian pangolin manis crassicaudata 20 chinese pangolin manis pentadactyla 36 21 assamese monkey macaca assamensis 22 striped hyena hyaena hyaena 23 lynx felis lynx 24 spotted lingsang prionodon pardicolor 25 wild water buffalo bubalus bubalis 26 four horned antelope tetracerus quadricornis 27 black buck antilope cervicapra table 8protected reptiles of nepal s.n. english name scientific name 1 gharial crocodile gavialis gangeticus 2 asiatic rock python python molurus 3 golden monitor lizard varanus flavescens references 1. d. d. bhatt, state of environment and biodiversity in nepal,(1996). 2. s.b., karmacharya, s.r. baral, and p. lacoul (eds), environment and biodiversity in the context of south asia, ecological society (ecos), nepal. pp. 26-33. 3. r.p. chaudhary, biodiversity in nepalstatus and conservation, tec press books, bangkok. (1998) 4. iucn, an inventory of nepal’s wetlands, iucn nepal, kathmandu (1996). 5. mope state of environment of nepal, ministry of population and environment nepal, kathmandu, nepal, (1998) 6. t.c. majupuria, and r.k majupuria, wildlife, national parks and reserves. s. devi saharanpur, india,(1998) 7. n.shrestha, protected wildlife species of nepal. an introductory handbook, iucn (1997). 8. b.n. upreti, conservation of wildlife resources in nepal, national parks and wildlife conservation office, kathmandu. , (1979). 9. v.k. thapa, environmental and economic zoology. durga books, kathmandu nepal (1999). 10. u.k.r. yadav, ecology and physiology, u.k. publisher, kirtipur, kathmandu (2005). 11. p.b. yonzon, and j.t. heinen, nepal’s biodiversity and protected areas, the 1997 protected areas management, workshop of the national biodiversity action plan, kathmandu , nepal, (1997). 1-7 s.k. saha r c o s t n s.k. saha / bibechana 11(1) (2014) 1-7 (online publication: march, 2014) p.1 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana weak interactions-strong effects: key role of hydrophobic interaction in the formation of stimuli-responsive viscoelastic gel of worm-like micelles swapan k. saha*1 department of chemistry, university of north bengal, darjeeling, 734 013, india e-mail: ssahanbu@hotmail.com accepted for publication: february 02, 2014 abstract among all the weak interactions, which are operative in the domain of chemistry, hydrophobic effect is one that leads to new structural motifs like molecular self-assemblies viz., micelles, vesicles etc. worm-like micelles are polymer like aggregates which have been formed in aqueous surfactant solutions in the presence of additives. these are relatively new materials with exciting material properties. these stimuli-responsive viscoelastic materials are interesting from both fundamental understanding as well as application points of view. the physico-chemical properties of worm-like micelles are studied and the morphological transitions to vesicle as functions of various parameters have been investigated. © 2014 rcost: all rights reserved. keywords: hydrophobic effect; vesicles; worm-like micelles; viscoelastic materials. 1. introduction from the days of alchemists, the primary goal of chemistry has been to understand the behavior of molecules and their construction from constituent atoms. in recent years chemists have extended their goal beyond the atomic and molecular chemistry into the realm of supramolecular chemistry controlled by weak interactions. in chemistry, weak interactions are the intermolecular forces mainly governed by (i) vander waals interaction (0.5-2 kcal/mol) (ii) hydrophobic interactions (1-2 kcal/mole) (iii) π—π interaction (2-3 kcal/mole) and (iv) hydrogen bonding (12-16 kcal/mole). among all the weak interactions, which are operative in the domain of chemistry, hydrophobic effect is one that leads to new structural motifs like molecular self-assemblies viz., micelles, vesicles etc. in aqueous media. the unfavorable contact between water and the apolar part of surfactant molecules lead to their congregation into well organized entities, viz., micelles, vesicles, fibers, discs and tubes [1-3]. although micelles are usually spherical in shape, under certain conditions, e.g., concentration, salinity or in the presence of hydrophobic counter ions, etc., they may undergo uniaxial growth. this subsequently results in the formation of significantly long (100 – 500 µm) yet highly flexible aggregates referred to as 1* prof. swapan k. saha, keynote speaker international conference on emerging trends in science and technology (march 22-23, 2014) biratnagar, nepal s.k. saha / bibechana 11(1) (2014) 1-7 (online publication: march, 2014) p.2 “worm-like micelles (wlm)” [4-6]. the research of wlm has drawn considerable interest as its rheology is very challenging due to the presence of multiple pertinent length scales and stress relaxation mechanisms. this relatively new material has many applications including that of fractured fluids in oil fields, efficient drag reducing agent in hydrodynamic engineering and home care, personal care and cosmetic products [7-8]. viscoelastic wlms are formed in various surfactant systems in the presence of different additives [9-12]. most extensively studied system is the cetyltrimethylammonium bromide (ctab) micelles in presence of hydrotrope, sodium salicylate (ss). unlike simple halides, salicylate promotes sphere to wormlike micellar transition at very low concentrations, viz., near the normal critical micelle concentration (cmc, ~1 mm) of ctab. the flexible and elongated wormlike micelles under dilute conditions show complex and unusual rheological phenomena, which include strong viscoelasticity and shear-induced structure (sis) formation. it is particularly interesting that, while a wide variety of wormlike ionic micellar solutions display identical rheological responses, a common element in most of these systems was the presence of salt anions such as ss. in view of the importance of an efficient wlm promoter, which might be effective for various applications at low surfactant concentrations and in the presence of metal ion impurities, organic πconjugated molecules with h-bonding functionality, viz., naphthols are highly promising [13-16]. microstructural transitions of micellar aggregates, especially the nature of transition from ordinary micelles to long worm-like giant micelles and the vesicles, mediated by organic π-electron systems are of fundamental scientific interest and have been reported in several papers only recently [17-18]. moreover, synthetic vesicular systems are interesting from a number of standpoints, not the least being their structural similarity with the constituent of the biomembrane, viz., phospholipid. they offer a convenient way to probe interactions involving membrane systems. vesicle aggregation or adhesion is the primary step for the fusion of the vesicles in membrane. therefore, the elucidation of the molecular mechanism of vesicular aggregation would greatly contribute to a better understanding of these biological phenomena. further, it may be anticipated that a simple and effective route to design a ph responsive microstructure could well be based on the neutral naphthol dopants, which form salts only at high ph (pka ~ 9.2). as a function of ph, ionization of the oh group of naphthol molecules may switch the onset of charge screening, paving the way to effect further morphological transitions (viz., vesicle formation). one of the objectives of the present work is, therefore, to design a simple effective route of ph-responsive morphological transition for the aqueous molecular aggregates of single chain cationic surfactant, viz., ctab from micelles to long wormlike micelle to unilamelar vesicles. 2. historical overview since the pioneering work of prof. h. hoffmann [9] and his group of bayreut university, germany on the unusual rheological property of wlm in the year 1988, quite a large number of physical chemists, physicists and chemical engineers became interested in this fascinating area and have contributed immensely to the advancement of wlm research. among others this list includes prof. s. candau and m. cates [19-20] of louis pasteur university, france; prof. h.t. davis [21], university of minnesota, u.s.a.; prof. d.j. pine [22] and prof. s.l. keller [23], both from the university of california, u.s.a.; prof. e.w. kaler [24], university of delware, u.s.a. and prof. t. imae [25,26] of nagoya university of japan. the coevolution of strong theoretical framework alongside application of a range of sophisticated experimental tools engendered rapid advancement in the study of wlm. presently the main focus of research in this field has been shifted to the development of new surfactant systems and new protocol by which wlm formation could be triggered. prof. s.r. raghavan [27] and his group of university of maryland have developed a series of new shear, temperature and light responsive wlm systems, which are of high technological interests. a mixture of ctab and trans orthomethoxy cinnamic acid (omca) (photo-rheological fluid) form long wormlike micelles leading to strong viscoelasticity under the s.k. saha / bibechana 11(1) (2014) 1-7 (online publication: march, 2014) p.3 influence of uv light. this trans omca is converted to cis isomer of omca, which interacts only weakly with ctab and eventually viscoelasticity disappears. prof. raghavan’s group has also studied wlm to vesicle transition as influenced by heat. prof. a. bose [28] of university of rhode island and prof. v.t. john [28] of tulane university, usa has investigated surfactant solubilization and direct encapsulation of interfacially active phenols in mesoporous silicas. template synthesis of mesoscopic tube silicates using aqueous mixtures of naphthalene diol and ammonium surfactant has been carried out by prof. m. isayama [29] of kyushu university, japan. dr. r. g. shrestha [30] and her groups, also from japan, are involved in extensive research on wlm with the aid of saxs, rheometer, cryo-tem etc. on some novel and interesting systems including poly (oxyethylene) cholesteryl ether. in china, the researchers in the field of wlm include dr. g-z. li [31] of shardong university, dr. s. liu [32] of science and technology university and prof. j. huang [33] of peking university. dr. l. zheng [34] of key laboratory of colloid and interface chemistry has been engaged in wlm research involving surface active ionic liquids (sail). in view of the fascinating rheology and technological applications of wlm, a tunable and efficient method of preparation of wlm is required. in spite of remarkable interests among the scientists on this exciting area of research, there is a major gap in the method of preparation and triggering of the wlm formation from a wide range of surfactants by metal ion inert neutral promoters (hydroxyl aromatic compounds). unless this limitation is addressed properly a complete understanding of the phenomenon, its application and control may prove to be far from complete success. 3. results and discussion despite high promise shown by neutral hydrotropes like naphthols in triggering the formation of wlm from cationic surfactants, surprisingly these hydroxyl aromatic compounds have been used only scarcely. aqueous ctab (2-10 mm) and 1or 2-naphthol (2-10 mm in 2-5% methanol, naphthols being sparingly soluble in water) solutions show viscosities similar to those of water. but as soon as these solutions are mixed together at room temperature, a thick gel-type fluid with high viscoelasticity is developed. from the initial visual observation it was found that the viscosity of the gel was very much dependent on the concentration of ctab and the additives. therefore, we first determined the ctab: dopant mole ratio at which the gel shows maximum viscosity [14]. much like the ctab-nasal system, it was found that ctab-naphthols also display maximum viscoelasticity at a 1:1 molar ratio of surfactant and the promoter (fig. 1). on the other hand the effect of the dihydroxynaphthalenes (2,3-dhn and 2,7-dhn) on micelles of ctab are completely different. equimolar mixtures of only ctab and 2,3-dhn gives a highly viscous gel in aqueous solutions but 2,7-dhn/ctab does not. therefore, further attempts were not made to study the viscosity of 2,7-dhn/ctab system [15]. the argument that an excess or deficiency of charge on the micelles due to adsorption of hydrotrope anions (e.g., nasal) would shorten the micellar life time and size is not apparently true for the present system because under the present experimental condition of solution ph (~6.5), the naphthols and the dihydroxynaphthalenes are mostly protonated, i.e., uncharged (pka’s > 9.0) [16]. therefore, it seems apparent that the symmetrical distribution of surfactant and the promoter molecules leading to highly compact spherical micelles facilitates an optimum surface curvature to attain in presence of h bonding (discussed later), and this results in the sphere to rod transition easily. for further experiments, dopant to surfactant ratio was chosen to produce strongest viscoelasticity, i.e., 1:1 mole ratio. further, the rheological responses for a viscoelastic system (viz., an aqueous ctab-1-naphthol system as a function of concentration (1:1 mol ratio) at 250c (ph ~5.0)) shows a shear thinning property up to a shear rate of 25 s-1 and then the shear thickening phenomenon starts to occur at low concentrations (~2 mm), but above a shear rate of 60, the fluid shows a newtonian type behavior [17]. however, an overall non-newtonian nature is apparent as the concentration of the ctab and naphthol (1:1) system is raised above 2.0 mm. at still higher concentrations (~5.0 mm), the nature of the rheological response s.k. saha / bibechana 11(1) (2014) 1-7 (online publication: march, 2014) p.4 changes dramatically and the system starts displaying an unusual rheology as a function of shear rate. up to a shear rate of 60 s-1, the fluid shear thins. an onset of viscosity rise is observed at the shear rate of 60 s-1, and the system again shear thins, passing through a maximum at 70 s-1. figure 1: variation of viscosity as a function mole ratio of ctab and the dopants (2-naphthol, 1-naphthol and 2,3-dihydroxynaphthelene) that form viscoelastic gels. at further higher concentrations (8.5 mm), the viscosity-shear rate profile again changes feature; the initial shear thinning characteristics disappear. the overall behavior is consistent with building up of long worm-like micellar bundles at relatively high concentrations. spectral modification of micelle-embedded dopants: in view of the differences in the viscoelastic responses and the morphological transitions of ctab micelles induced by neutral naphthols and the methoxynaphthalenes, uv absorption spectra of these dopants may be interesting to study in micellar media. to understand the kind of interactions which are operative in the micelle-dopant systems, the key element of the present study is to compare the spectral characteristics of naphthols (hns which contain oh) with those of methoxy naphthalenes (mns, which do not contain oh) under various conditions in order to visualize a consistent molecular picture eliminating the untenable suggestions. aromatic compounds, e.g., naphthalene, in general, have two strongly overlapped bands in the near uv region, viz., the longitudinally polarized 1la ← 1a band and the transversely polarized 1lb ← 1a band. while the vibrational structure of these bands appears differently in different substituted compounds, effects of extending conjugation in 1 and 2 positions by oh or ch3o groups in naphthol and methoxynaphthalene molecules, respectively, are interesting. both in 1-naphthol and 1-methoxy, naphthalene conjugation is extended in the transverse direction and, therefore, it affects the transverse polarized 1la band. in 2-naphthol and 2-methoxy naphthalene, on the other hand, conjugation is primarily extended in the longitudinal direction, affecting both the intensity and the frequency of the longitudinally polarized 1lb band compared to the unsubstituted naphthalene. it is well-known that the near uv spectra of aromatic compounds are affected by specific interactions like hydrogen bonding. noncovalent interactions like π-π and cation-π also cause shifts in the electron distributions of the molecule. the near uv absorption of 1-naphthol which arises from two strongly overlapped π-π* transitions remains unaffected in the presence of submicellar aqueous ctab solution, indicating the absence of any appreciable interaction. the effect of ctab micelles on the uv spectra of 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 4 8 12 16 20 24 28 32 v is co si ty ( cp ) ctab:dopant 2,3-dhn 1-naphthol 2-naphthol s.k. saha / bibechana 11(1) (2014) 1-7 (online publication: march, 2014) p.5 2-naphthol is also similar (fig. 2). however, interestingly, significant red-shift starts to occur (6.4 nm at λmax ~293 nm) in the presence of ctab just above its cmc (0.96 mm) with a well-defined isobastic point at 296 nm. such shifting of λmax continues until most of the naphthol molecules are partitioned in the micellar phase at high surfactant/ naphthol ratio (80:1). figure 2: absorption spectra of 2-naphthol (0.25 mm) in water at varying concentrations of ctab at 25 °c. [ctab]: (1) 0.0, (2) 0.65, (3) 0.79, (4) 0.94, (5) 1.13, (6) 1.36, (7) 1.63, (8) 1.96, (9) 2.35, (10) 2.82, (11) 3.39, (12) 5.08, (13) 7.63, (14) 11.44, (15) 17.16, (16) 20.60 mm the result suggests that the protruded oh groups of micelle-embedded naphthols form a h-bond with interfacially located (deff ~45) water molecules and act as a h-donor. it may also be argued that at a mole ratio of 1:1 of naphthol and the ctab, at which maximum viscoelastic response is observed under shear due to the presence of entangled worm-like micelles, not all of the naphthol molecules are embedded in the micelles, but some are located in the palisade layer. these naphthols may, however, be involved in hbond network formation with embedded molecules via interfacial water. the relatively less polar and less mobile water molecules compared to bulk water form a strong h-bond with the oh group of embedded naphthols, which act as h-donors and result in an optimum orientation of aromatic π-electron systems in the micelles to shield the surfactant headgroup charges efficiently; may be via cation-π interaction; i.e., the cation charge of surfactant head groups interacts with the quadrupole moment of the aromatic πsystem of naphthols. on the other hand, as the h atom of oh is replaced by a ch3 group (viz., the methoxynaphthalene molecule), the ability of intermolecular h-bond formation disappears. instead, the h-accepting tendency from a potential donor is enhanced. the nature of changes encountered in the uv spectra of methoxynaphthalenes on the addition of ctab above its cmc indicates the permeation of the dopant molecules in the micelles. the small red-shift compared to that in naphthols indicates a weaker noncovalent interaction takes place. the large drop in intensity on first addition of 0.33 mm ctab is the signature of breaking of a h-bond with bulk water molecules. due to their directionality and spatial arrangement, complementary multiple h-bonding interactions at the micellar interface lead to engineering well-defined supramolecular structure via micellar headgroup charge shielding by π-electron systems of naphthols. shear-induced viscosity and ph: the role of neutral hydroxyaromatic dopants, viz., 1and 2naphthol, stimulates the idea of designing a route for ph-responsive vesicle formation. this idea stems from the fact that the dopants, which under neutral conditions activate the formation of worm-like micelles at ph ~5.0, may on partial ionization of the oh group increase the packing parameter further via charge screening. while the viscosity of both, 2as well as 1-hn-ctab systems, is quite high due to s.k. saha / bibechana 11(1) (2014) 1-7 (online publication: march, 2014) p.6 formation of long worm-like micelles at low ph, the viscosity of the former system falls initially, indicating formation of shorter micelles with ph until ph ~5.0 is reached. on the other hand, for 1-hnctab, the onset of viscosity rise as a function of ph is found to occur from very low ph (ph ~2.0). for 2-naphthol-ctab, the onset of viscosity rise is observed at higher ph (~5.0) and the viscosity-ph profile passes through a maximum at ph ~8.5. further increase in ph results in the ionization of oh group further, and the packing parameter probably exceeds the critical value of 1/2 via enhanced charge screening, leading to vesicle formation (for naphthols, pka ~9, which means 50% ionization of the oh group at ph ~9.0). this results in the fall of viscosity of the system. since 1-naphthol could modulate the micellar surface curvature more efficiently, a little dissociation of the oh group (at low ph range) leads to an appreciable decrease of surface curvature via charge screening and promotes long worm-like micelle formation. in fact, for the 1-hn-ctab system, vesicles start to form even at slightly higher than ph ~5.0. a simple and effective route to design ph responsive viscoelastic worm-like micelles and less viscous globular vesicles based on naphthol dopants may be tuned by controlling the degree of charge screening of ctab micelles via controlled ionization of naphtholic oh groups. the result of ph-responsive morphology modification is further investigated by means of cryo-tem. cryogenic transmission electron microscopic study: cryo-tem images of the ctab-2naphthol system at high ph’s is shown in fig. 3. at high ph (ph~9.4), the system contains very long wormlike micelles, which coexist with large unilamellar vesicles. this is undoubtedly due to enhanced charge screening of micelles by naphtholate anions. the field is seen to populate mainly by large vesicles of diameter ~30 nm along with thinly populated smaller vesicles. it is also seen that the long worm-like micelles are highly entangled. sometimes they are found to elongate linearly under shear flow. the solutions are completely transparent. the direct imaging by cryo-tem supports the rheological observation as a function of ph. at low ph, the worm-like micelles are formed via headgroup charge shielding by aromatic π electrons, whereas, at high ph, ionization of oh groups takes place and the packing parameter exceeds the critical value of 1/2 via enhanced charge screening by naphtholate ion. this leads to unilamellar vesicle formation along with long worm-like micelles. figure 3: cryo-tem image of ctab-2-naphthol at a ph of ~ 9.4. 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[34] dong, j. zhang, l. zheng, s. wang, x. li, t. inoue, j. colloid interface sci., 319 (2008) 338. microsoft word mahdi eshghi.doc mahdi eshghi / bibechana 8 (2012) 23-30 : bmhss, p. 23 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana pseudo-spin symmetry in dirac-four-parameter diatomic problem coupled with a coulomb-like tensor potential mahdi eshghi department of basic sciences, central tehran branch, islamic azad university, tehran, iran e-mail: eshgi54@gmail.com article history: received 13 june, 2011; accepted 21 june, 2011 abstract in this work, we use the parametric generalization of the nikiforov-uvarov method to obtain the relativistic bound state energy spectrum and the corresponding spinor wave-functions for fourparameter diatomic potential coupled with a coulomb-like tensor under the condition of the pseudo-spin symmetry. also, some numerical results have given. keywords: dirac equation; four-parameter diatomic potential; coulomb-like tensor 1. introduction since the solutions of the dirac equation with physical potential are very useful to investigate the relativistic effects, especially a strong coupling system [1]. recently, some authors have been solved approximately the dirac equation for some potentials like the eckart potential [2], resenmorse potential [3], poschl-teller potential [4, 5], woods-saxon potential [6], scarf potential [7, 8], etc. the spin and pseudo-spin symmetry concepts in nuclear theory [9, 10], have been used to explain the features of deformed nuclei [11], super-deformation [12], and also to establish an effective nuclear shell-model scheme [13]. ginocchio has been showed that pseudo-spin symmetry is exact when the sum of the vector potential )(rvv and scalar potential )(rvs is equal to zero or a constant, pseudo-spin symmetry occurs in the dirac equation [14, 15]. of course, in real nuclei, .)()( constrvrv sv ≠+ and pseudo-spin symmetry is only an approximation. on the other hands, tensor potentials have been introduced into the dirac equation with the substitution. in this way, a spin-orbit coupling term was added to the dirac hamiltonian [7, 16-23]. the four-parameter diatomic potential (fpdp) [24] following as: 2 ( ) r d v r e qα= − − (1) where ( 1)ed d e ς= − , / erα ς= , ed is the depth of the potential well, er is the equilibrium distance of of the two nuclei, and ς , q are real parameters. mahdi eshghi / bibechana 8 (2012) 23-30 : bmhss, p. 24 recently, c. gang [25] has been studied solution of the dirac equation with this potential by using the supersymmetric quantum mechanics. the motivation of the present work was to solved the dirac equation under the pseudo-spin symmetry for fpdp that including a coulomb-like tensor potential [16] 2 0 ( ) , , 4 a b c z z eh u r h r r r πε = − = ≥ (2) where =cr 7.78 fm is the coulomb radius, az and bz denote the charges of the projectile a and the target nuclei b, respectively. the parametric generalization of the nikiforov-uvarov (nu) method have been used to obtain the dirac equation with this potential. the energy eigenvalues equation and the corresponding unnormalized eigenfunctions have been obtained. 2. nu method we give a brief description of the conventional nu method [26]. this method is based on solving the second-order differential equations by means of special orthogonal functions. the mean equation which is closely associated with the method is given in the following form 0)( )( )(~ )( )( )(~ )( 2 =+′+′′ s s s s s s s nnn ψ σ σ ψ σ τ ψ (3) where )(sσ and )(~ sσ are polynomials, at the most of the second degree, and )(~ sτ is a polynomials, at most of the first degree. let us discuss the exact particular solution of eq. (3) by choosing )()()( syss nn φψ = resulting in a hypergeometric type equation of the form 0)()()()()( =+′+′′ sysyssys nnn λτσ (4) where ( ) ( ) (ln ( )) d s s s ds π σ ϕ= (5) 0)(),(2)(~)( <′+= ssss τπττ (6) where )(rπ is a polynomial of order at most one. the first part of the wave function, i.e. )(syn , is the hypergeometric-type function whose polynomials solutions are given by rodrigue's relation [ ])()( )( )( ss ds d s a sy n n n n n ρσ ρ = (7) where na is a normalization constant and the weight function )(sρ must satisfy the differential equation ( ) ( ) ( ) 0, ( ) s s s s τ ω ω σ   ′ − =    ( ) ( ) ( )s s sω σ ρ= (8) the function )(sπ and the parameterλ in the above equation are defined as follows ( ) ( ) ( ) 2 s s s σ τ π ′ − = ɶ 2 ( ) ( ) ( ) ( ) 2 s s s k s σ τ σ σ ′ − ± − +    ɶ ɶ (9) ( )k sλ π ′= + (10) mahdi eshghi / bibechana 8 (2012) 23-30 : bmhss, p. 25 the determination of k is the essential point in the calculation of )(sπ . it is simply defined by setting the discriminate of the square root which must be zero. the eigenvalues equation have calculated from the above equation ,...2,1,0).( 2 )1( )( =′′− −′−== ns nn snn στλλ . (11) in order to clarify the parametric generalization of the nu method, let us take the following equation, which represents a general form of the schrodinger-like equation written for any potential by an appropriate coordinate transformation )(rss = . thus, we obtain another generalized hypergeometric equation [18] ( ) ( ) ( ) 2 22 2 3 3 1 2 1 2 32 1 1 [ ] ( ) 0n d d s s s s s s s s ds ds α α α α ξ ξ ξ ψ   − + − − + − + − =   (12) when (12) is compared with (3), we get 1 2( )s sτ α α= −ɶ , ( )3( ) 1s s sσ α= − , 2 1 2 3( )s s sσ ξ ξ ξ= − + −ɶ (13) substituting these into (9), we find 4 5( )s sπ α α= + ( ) ( ) 1 2 2 6 3 7 8k s k sα α α α ± − + + +  (14) where the parameter set are ( )4 1 1 1 2 α α= − , ( )5 2 3 1 2 2 α α α= − , 2 6 5 1α α ξ= + , 7 4 5 22α α α ξ= − , 2 8 4 3α α ξ= + (15) we obtain the parameter k from the condition that the function under the square root should be the square of a polynomial ( )1,2 7 3 8 8 92 2k α α α α α= − + ± (16) where 2 9 3 7 3 8 6α α α α α α= + + (17) for each k the following π ’s are obtained. the function )(sπ becomes 4 5 9 3 8 8( ) [( ) ]s s sπ α α α α α α= + − + − (18) for the k-value ( )7 3 8 8 92 2k α α α α α= − + − (19) we also have from ( ) ( ) 2 ( )s s sτ τ π= +ɶ , 1 4 2 5( ) 2 ( 2 )s sτ α α α α= + − − 9 3 8 82[( ) ]sα α α α− + − (20) thus, we impose the following condition to fix the k-value 2 5 9 3 8( ) ( 2 ) 2( )sτ α α α α α′ = − − − + 3 9 3 82 2( ) 0.α α α α= − − + < (21) when (10) is used with (20) and (21) the following equation is derived 3 2 5 9 3 8[( 1) 2 ] (2 1)( )n n nα α α α α α− + − + + + 5 7 3 8 8 92 2 0α α α α α α− + + + = (22) by using (8) 11 10 10 3 1 1 3( ) (1 )s s s α α α αρ α − − −= − (23) and together with (7), we have mahdi eshghi / bibechana 8 (2012) 23-30 : bmhss, p. 26 11 10 10 3 1 , 1 3( ) (1 2 )n ny s p s α α α α α   − − −   = − (24) where 10 1 4 82 2α α α α= + + (25) and 11 2 5 9 3 82 2( )α α α α α α= − + + (26) and ),( βα np are jacobi polynomials. by using (5), we get 13 12 312 3( ) (1 )s s s α α ααφ α − − = − (27) and the total wave function become 1113 10 1012 3312 1 , 1 3 3( ) (1 ) (1 2 )   − − −− −    ψ = − −ns s s p s αα α αα ααα α α (28) where 12 4 8α α α= + and 13 5 9 3 8( )α α α α α= − + . 3. solution of the dirac equation according to the report which have been given in the researcher [4, 7, 16-20], the dirac equation of a nucleon with mass m moving in a scalar and a vector potential including tensor interaction for spin-1/2 particles can be written as ( 1== cℏ ), ( ) ˆ[ ( ) ( )] ( )s nkp m v r i ru r rα β βα ψ⋅ + + − ⋅ �� � � [ ( )] ( ),v nke v r rψ= − � (29) where 0 0 σ α σ   =     � � � , 0 0 i i β   =  −  (30) and e is the relativistic energy of the system and ∇−= �� ip is the three-dimensional momentum operator. in which σ � is vector pauli matrix. in pauli-dirac ( ) ( , )1 ( ) ( ) ( , ) l nk jm nk l nk jm f r y r r ig r y θ ϕ ψ θ ϕ    =    ɶ � (31) where ( )nkf r and ( )nkg r are upperand lower-components of the dirac spinors and k is eigenvalue of the spin-orbit matrix operator [27]. ( , )l jmy θ ϕ and ( , )l jmy θ ϕ are spin pseudospin spherical harmonics, respectively, and m is the projection of the angular momentum on the zaxis. substituting (31) into (29) and using the following relations [28] ).(.).)(.( baibaba ��������� ×+= σσσ (32) ) . .ˆ(ˆ.).( r l iprrp �� ���� σ σσ += (33) and properties ),()1(),().( ~~ φθφθσ l jm l jm ykyl −= �� (34) ),()1(),().( φθφθσ l jm l jm ykyl −−= �� (35) mahdi eshghi / bibechana 8 (2012) 23-30 : bmhss, p. 27 ),(),()ˆ.( ~ φθφθσ l jm l jm yyr −= � (36) ),(),()ˆ.( ~ φθφθσ l jm l jm yyr −= � (37) yields two coupled differential equations as follows [ ]( ) ( ) ( ) ( )  + − = + − ∆    nk nk nk d k u r f r e m r g r dr r (38) [ ]( ) ( ) ( ) ( )  − + = − + σ    nk nk nk d k u r g r m e r f r dr r (39) where ∆ and σ have been assumed to be radial functions, i.e., )()()( rvrvr sv −=∆ and )()()( rvrvr sv +=σ . by substituting ( )nkg r from (38) into (39) and ( )nkf r from (39) into (38), we have been obtained the following two second-order differential equations for the upper and lower components, )( )( )( 2)1( 2 22 2 ru dr rdu ru r k r kk dr d −−+ + −    ))())((( rmerme nknk σ−−∆−++ ( ) ( ) ( ) 0 ( ) nk nk d r d kdr f r m e r dr r ∆ −  + + = + − ∆    (40) )( )( )( 2)1( 2 22 2 ru dr rdu ru r k r kk dr d −++ − −    ))())((( rmerme nknk σ−−∆−++ ( ) ( ) ( ) 0 ( ) σ  + − = − +σ    nk nk d r d kdr g r m e r dr r (41) in the above equations ( 1) ( 1)k k l l+ = + and ( 1) ( 1)k k l l− = +ɶ ɶ . substituting (1) and (2) into (41), considering pseudo-spin symmetry, taking )(r∆ as the fpdp and .)( constcr ps ==σ )0/)(( =σ drrd , [29, 30] i.e., the equation have been obtained for the upper component of the dirac spinor )(rfnk becomes 2 2 2 ( )( 1)d k h k h dr r  + + − −  2 ( )( ) ( ) ( ) 0    + + + − − − − − = −   nk nk ps nk ps nkr d m e m e c e m c f r e qα (42) this equation is describes a particle of spin-1/2 such as the electron in the dirac theory with fpdp potential including a tensor coupling, that can not be solved analytically because of 2( )( 1) /k h k h r+ + − term, we take the following approximation [31, 32] ( ) 1 2 0 22 2 0 1 1 r r c c c r r e q e q α α    ≈ + +  − −  (43) where 0 ,c 1c and 2c are real constant, [ ]0 1 .log 1 2 ( 1) /r aα α α ′ ′= + − , where α , α ′ and a are constant and q is real parameter and constant, also [31]. by using a transformation of the form res α= , we rewrite it as follows mahdi eshghi / bibechana 8 (2012) 23-30 : bmhss, p. 28 2 2 ( ) d s q d ds s s q ds − + − [ ] 2 1 2 32 1 ( ) 0 ( )   + + + = −  nks s f s s s q ξ ξ ξ (44) where ( )( ) ( )( ) 0 1 2 2 2 0 1 nk ps nke m c e mc k h k h r ξ α α − − ++ + − = − , ( )( ) ( ) ( ) 0 1 2 2 2 2 0 [2 ]1 (2 ) nk ps nk e m c q e m dk h k h qc c r ξ α α  − − + −+ + − −  = −    , ( )( ) ( ) ( ) 22 0 1 2 3 2 2 2 0 1 ( ) nk pse m c e m q dqk h k h q c c q c r ξ α α  − − + −+ + − − +  = − (45) by comparing (44) with (12), we have been obtained the parameter set as q−=1α , 2 1α = , 3 1α = , ( )4 1 / 2qα = + , 5 1/ 2α = − , 6 11/ 4α ξ= + , ( )7 21 / 2qα ξ= − + − , ( )2 8 31 / 4qα ξ= + + , 2 9 1 2 3 / 4qα ξ ξ ξ= − + + , ( )2 10 31 2 1 / 4qα ξ= + + + , ( )22 11 1 2 3 3 2 2 / 4 1 / 4 = + − + + + + +    q qα ξ ξ ξ ξ , ( )22 13 1 2 3 3 1 / 4 1 / 4 2  = − − − + + + + +    q qα ξ ξ ξ ξ (46) the energy eigenvalue function is obtained from eq. (22) as follows: [( 1) 2]n n − + ( )22 1 2 3 3(2 1) / 4 1 / 4n q qξ ξ ξ ξ + + − + + + + +    ( )( )2 2 31/ 2 (1 ) / 2 2 1 / 4q qξ ξ+ − + − + + + ( ) ( )( )22 1 2 3 32 / 4 1 / 4 0q qξ ξ ξ ξ+ − + + + + = (47) some numerical results are given in table 1. we use the parameters 6psc = − , 1m = , 0.05α = , 0 0.000208178c = , 1 0.002500011408c = , 2 0.002499999716c = , 30.52a = , 1.5α′ = , 5h = , 1q = , 0.03815d = − . the lower component of the dirac spinor is obtained from (28) as follows: ( ) ( )2 2 3 1 2 3 1 1 /4 /4 2 2( ) (1 ) q q q q nk nkg s b s s ξ ξ ξ ξ + + + + − + − + + = + ( )2 2 3 1 2 32 1 /4 , 2 /4 (1 2 ) q q np s ξ ξ ξ ξ + + − + +   × + (48) where nkb is the normalization constant to be determined from the normalization condition 1 2 21 0 0 ( ) 1 ( )nk nkg r dr b s g s ds ∞ −= =∫ ∫ (49) and 1 2 3ξ ξ ξ− + = ( )( ) ( ) ( )2 0 1 2 2 2 0 1 [ 1 1 ]k h k h c q c q c r α + + − − + − + ( ) ( )( )2 2 [ 1 (1 )]− − + − + − − nk pse m c m e q d q α (50) mahdi eshghi / bibechana 8 (2012) 23-30 : bmhss, p. 29 table 1. the bound state energy eigenvalues ,n ke in unit of fm -1 of the pseudospin symmetry fpdf for several values of n and k . 4. conclusion in this paper, by using the parametric generalization of the nu method, we have been solved analytically the approximate energy eigenvalues equation and the corresponding unnormalized wave-functions of the dirac equation for the fpdp coupled with a coulomb-like tensor under the condition of the pseudo-spin symmetry. some numerical results are given for this potential. acknowledgments the author would like to thank the kind referee for their positive suggestions which have improved the present work. references [1] i.c. wang and c.y. wong, phys. rev. d 38 (1988) 348. 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[32] s.m. ikhdair and r. sever, appl. math. com., 216 (2010) 911. arxiv:1001.4327. microsoft word jb _1-8_ final.doc s. baral and j. bhattarai / bibechana 10 (2014) 1-8 : bmhss, p.1 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana the effect of tantalum addition on the corrosion behavior of w-xta alloys in 1 m naoh solution susil baral , jagadeesh bhattarai* central department of chemistry, tribhuvan university, kathmandu, nepal. *e-mail:bhattarai_05@yahoo.com. article history: received 25 july, 2013; accepted 23 september, 2013 abstract the role of tantalum addition on the corrosion behavior of the sputter–deposited nanocrystalline and amorphous w–xta (x=8–77) alloys was studied in 1 m naoh solution open to air at 25°c using corrosion tests and electrochemical measurements. tungsten and tantalum metals act synergistically in enhancing the corrosion resistant properties of the w–xta alloys and hence addition of 23 at% or more tantalum to the alloys were found to be effective to lower the corrosion rate of the alloys than those of alloy–constituting tungsten and tantalum elements. the corrosion rates of the w-xta alloys containing 23-77 at% tantalum are nearly two orders of magnitude lower than that of tungsten and even slightly lower than that of tantalum in 1 m naoh. addition of tantalum metal in w–xta alloys is effective for ennoblement of the open circuit corrosion potential of the tungsten metal in 1 m naoh solution at 25°c. keywords: sputter-deposited w−xta alloys, corrosion rate, corrosion potential, naoh solution, electrochemical measurement. 1. introduction it is generally believed that the preparation of metallic alloys with a liquid like atomic arrangement requires ultra-rapid quenching of the alloy melt. in the early 1960s, amorphous and supersaturated solid solution of metallic alloys prepared by rapid quenching attracted considerable attention from materials scientists, because of their technologically important properties such as physical, chemically, mechanical, magnetic, electronic and catalytic properties [1]. a novel corrosion resistance properties of the rapidly–quenched alloys even in aggressive environments generated tremendous interest of corrosion scientists last four decades. varieties of corrosion–resistant rapidly quenched alloys were developed in 1970’s [2-6]. since 1990’s, it has been reported that the sputter– deposited binary tungsten–titanium [7-10], tungsten–zirconium [7,11,12], tungsten–chromium [7,13,14], tungsten–niobium [7,15-17], tungsten–tantalum [7,18-20], tungsten–molybdenum [21-24] and tungsten–nickel [21,25,26], and ternary tungsten–based [27-33] alloys showed higher corrosion resistance than those of alloy–constituting elements in different corrosive environments. s. baral and j. bhattarai / bibechana 10 (2014) 1-8 : bmhss, p.2 (online publication: dec., 2013) tungsten and tantalum are regarded as very effective alloying elements for enhancing the corrosion resistance properties of the alloys in aggressive environments. it has been reported that the addition of small amount of tungsten to stainless steels increased the corrosion-resistance of steels and stainless steels [34,35]. several surface studies have been carried out for the better understanding of the role of tungsten in the passivity of stainless steel in aggressive chloride containing medium [3640]. furthermore, it has been also reported that the addition of a small amount of tungsten to amorphous fe-p-c alloys with or without chromium [41-43], to ni-fe [44] alloys and to the amorphous ni-p alloys [45] is effective in improving the corrosion resistance of these alloys in aggressive hydrochloric acid solutions. similarly, the addition of only small amount of tungsten (i.e., less than 10 at%) was enough to cause spontaneous passivation of the sputter-deposited nanocrystalline w-xcr alloys in 12 m hcl solution and they showed about five orders of magnitude lower corrosion rate than the corrosion rate of chromium metal [7,14,46]. on the other hand, tantalum is widely known for its superior corrosion resistance properties in aggressive acidic media. amorphous nickel−base alloys containing certain amounts of tantalum exhibit very high corrosion resistant in boiling acids [47]. it has been reported that a beneficial effect of tantalum to improve the corrosion resistance of nickel−base alloys in 12 m hcl [48]. a series of the sputter−deposited binary tantalum−containing alloys showed higher corrosion resistance than those of alloying elements due to spontaneous passivation in aggressive media [5,20,49-51]. it has been reported that the corrosion resistance of the sputter–deposited amorphous or nanocrystalline w–ta alloys were passivated spontaneously and observed significantly high corrosion resistance in 12 m hcl solution having the ph value of less than 4 [7,18]. it is meaningful for mentioning here that tungsten is hardly corroded by most of acid solutions, except some complex acids like hf acid which attacks it. however, tungsten metal is corroded in neutral and alkaline solutions [52]. on the other hand, tantalum metal is highly corrosion resistance in all ph values [53], mostly due to the formation of stable and diffusion–barrier tantalum oxides. in this context, it is interesting to study the corrosion behavior of the sputter−deposited w–xta alloys in alkaline 1 m naoh solution. the main objectives of this study are to estimate the corrosion rate and study the electrochemical behavior of the sputter–deposited amorphous or nanocrystalline w–xta alloys in 1 m naoh solution open to air at 25°c. 2. materials and experimental methods the sputter–deposited binary w−xta (x=23,60 & 77 at%) alloys were characterized as the single– phase solid solutions of amorphous or/and nanocrystalline structures having apparent grain size ranges from 1.6−22 nm [7,18]. the compositions of the sputter–deposited w–xta alloys hereafter are all denoted in atomic percentage (at%). prior to corrosion tests and electrochemical measurements, the surface of the alloy specimen was mechanically polished with a silicon carbide paper up to grit number 1500 in cyclohexane, rinsed by acetone and dried in air. the average corrosion rate of the alloys was estimated from the weight loss after immersion for 240 h in 1 m naoh solution open to air at 25°c using the formula as described elsewhere (7,54). the time dependence of the corrosion rate of the w–xta alloys was also estimated at various time intervals ranging from 2 to 240 hours. the open circuit potentials of the w–xta alloys were o measured after immersion for 72 hours in 1 m naoh solution open to air at 25°c. a platinum mesh and saturated calomel electrode (sce) were used as counter and reference electrodes, respectively. all the potentials given in this paper are relative to sce. s. baral and j. bhattarai / bibechana 10 (2014) 1-8 : bmhss, p.3 (online publication: dec., 2013) 3. results and discussion figure 1 shows the changes in corrosion rates of the sputter–deposited w–xta alloys including the sputter–deposited tungsten and tantalum metal after immersion for 240 hours in 1 m naoh solution open to air at 25°c. corrosion rates of the binary w–xta alloys containing 23–77 at% tantalum are more than two orders of magnitude lower than that of tungsten and even slightly lower than that of the tantalum. however, the corrosion rate of the w–8ta alloy is slightly higher than that of tantalum metal. in particular, the sputter–deposited w–xta alloys containing 60–77 at% tantalum content, which are composed of either amorphous or nanocrystalline single phase solid solution, show lower corrosion rates than those of alloy-constituting elements (i.e., tungsten and tantalum) even immersion for 240 hours in 1 m naoh solution at 25°c. the corrosion rate of the w–60ta alloy shows lowest among the examined alloys. consequently, the addition of tantalum to the sputter–deposited w–xta alloys is effective in enhancing the corrosion resistance propertied of the alloys in 1 m naoh solution. fig. 1: changes in corrosion rates of the sputter-deposited w-xta alloys including the sputterdeposited tungsten and tantalum metals in 1 m naoh solution open to air at 25°c, as a function of alloy tantalum content. it is important to identify the role of immersion time for better understanding of the corrosion behavior of the alloys. in general, alloys show high corrosion resistance through the active dissolution of the alloys at the initial periods of immersion in the corrosive environments. high s. baral and j. bhattarai / bibechana 10 (2014) 1-8 : bmhss, p.4 (online publication: dec., 2013) chemical reactivity of the alloys leads to the rapid accumulation of a beneficial species in the passive films. this accounts for the high corrosion resistance of the alloys. figure 2 shows the changes in the corrosion rates of all the examined w–xta alloys including the sputter–deposited tantalum in 1 m naoh solution open to air at 25°c, as a function of immersion time. in general, the corrosion rates of all the examined w–xta alloys are significantly high at initial periods (for example, for about 2 h). the corrosion rate is decreased with immersion time till about 2–72 h for all the w–xta alloys. in particular, the corrosion rates of the w–xta alloys become almost steady after immersion for about 72–240 hours. accordingly, initially fast dissolution of the w–xta alloys results in fast passivation by forming a more protective passive films in 1 m naoh solution at 25°c. as a result, the average corrosion rates of the w–xta alloys are lower than that of the tungsten metal after immersion for 240 h as shown above in fig. 1 also. fig.2: changes in corrosion rates of the w-xta alloys including tantalum metal in 1 m naoh solution open to air at 25°c, as a function of immersion time. figure 3 shows the changes in open circuit potentials of the sputter–deposited w–8ta, w–23ta, w– 60ta, w–77ta alloys including tungsten and tantalum metals in 1 m naoh solution open to air at 25°c, as a function of immersion time. the open circuit potential of all the examined sputter– deposited amorphous or/and nanocrystalline w–xta alloys containing 23–77 at % tantalum including pure tantalum metal is shifted towards more positive (noble) direction with immersion time. these results revealed that more stable passive film is formed on the surface of the sputter–deposited w– xta alloys with increasing tantalum content. furthermore, the open circuit potentials of the w–xta alloys containing 60–77 at % tantalum content are almost same as that of tantalum metal after s. baral and j. bhattarai / bibechana 10 (2014) 1-8 : bmhss, p.5 (online publication: dec., 2013) immersion for 72 h in 1 m naoh solution. these results revealed that the stability of the passive films of the w–(23–77)ta alloys is increased with increasing tantalum content in the alloys and the passive films formed on the alloys are more stable than those films formed on the sputter–deposited tungsten and tantalum metals. on the other hand, the open circuit potential of all the examined w-xta alloys in 1 m naoh solution is located between the open circuit potential of tungsten and tantalum metals as shown in fig. 4. it is meaningful to mention here that the open circuit potential of the w-xta alloys containing 60-77 at% chromium content are located slightly more positive direction than that of tantalum metal. accordingly, the addition of tantalum enhances the corrosion resistance properties of the sputterdeposited w-xta alloys. fig.3: changes in open circuit potential for the w–xta alloys including tungsten and tantalum metals in 1 m naoh solution open to air at 25°c, as a function of immersion time. s. baral and j. bhattarai / bibechana 10 (2014) 1-8 : bmhss, p.6 (online publication: dec., 2013) fig.4: changes in corrosion rate and open circuit potential for the w–xta alloys including tungsten and tantalum metals in the given condition, as a function of alloy tantalum content. 4. conclusions in this study, a beneficial effect of tungsten and tantalum in the corrosion behavior of the sputter−deposited binary w−xta alloys was studied using corrosion tests and electrochemical measurements. tantalum metal acts synergistically with tungsten in enhancing the corrosion resistance properties of the sputter–deposited w–xta alloys so as to show lower corrosion rates of the alloys than the corrosion rates of the alloy–constituting elements (i.e., tungsten and tantalum) in 1 m naoh solution open to air at 25°c. more ennoblement of the open circuit potentials of the w– 60ta and w–77ta alloys are observed as compared to those of w–8ta and w–23ta alloys after immersion for 72 h in 1 m naoh and hence more stable passive films were formed on the surface of the sputter–deposited 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(2010) 304 pp. microsoft word a.k. mishra _165-174_.doc a.k. mishra and m. milanarun / bibechana 9 (2013) 165-174: bmhss, p. 165 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana thermodynamic properties of liquid inna alloys a.k. mishra 1 , m. milanarun 2* 1 g.b. college, naugachia – 853 204, bhagalpur, bihar, india 2 b.s.l.i., katihar – 854105, bihar, india * corresponding author: e-mail : mukulmilan@yahoo.co.in article history: received 22 november, 2012 abstract concept of complex formation model has been applied to account for the thermodynamic properties of liquid inna alloy. the theoretical study reveals that the intermetallic compound in3na2 exists at stoichiometric composition. our expressions reproduce successfully the asymmetric behaviour of free energy of mixing, enthalpy of mixing, s-type entropy of mixing, csro and phase separation in liquid inna alloy. it is found that na atoms segregate on the surface. the study reveals that various factors such as size difference and electronegative factor are not sufficient to account for the asymmetry in the system. the low value of order energy suggests that in-na is a weak interacting system. key words: complex formation; stoichiometric composition; phase separation; segregation; order energy. 1. introduction the anomalous behaviour in mixing properties of many binary liquid alloys needs extensive investigations. experimentalists [1 – 6] as well as theoreticians [7 – 12] have been trying to interpret the alloying behaviour of liquid alloys. the search of light weight solutions in the automotive industry [13] and importance in mechanical and technological applications in catalysis coating, high temperature engineering [14] etc. have created renewed interest in liquid binary alloys. concentration dependent information of the thermodynamics, energetics and local atomic order is required for detailed information about the alloying behaviour of the liquid binary alloys. a good understanding of the mixing properties of liquid binary alloys is important from metallurgical point of view since most of the binary solid alloys are formed by cooling from their liquid state. surface phenomena like surface tension play an important role in metallic systems and processes. it intervenes in nucleation from the vapour phase, in casting, coating, wetting and many other processes that include the liquid state [15]. surface segregation is predicted in many binary liquid alloys [11, 12, 16]. surface segregation and surface tension play an important role in metallurgical operation in the study of catalytic activity [1721]. the concentration dependent thermodynamic properties of indium-sodium liquid binary alloys are interesting. the gibbs energy of mixing (gm) and enthalpy of mixing (hm) are asymmetric about its equiatomic composition where as the entropy of mixing (sm) is positive at both indium and sodium rich a.k. mishra and m. milanarun / bibechana 9 (2013) 165-174 : bmhss, p. 166 (online publication: nov., 2012) ends and has negative values in the intermediate region [22]. asymmetry in gm and hm are responsible for promoting complex formation in the liquid binary alloys, but these properties need not necessarily imply complex formation [23]. hence the concentration-concentration fluctuations at the long wavelength limit (scc(0)) are one of the most microscopic functions for understanding the nature of interatomic interactions. the experimental scc(0) [24] shows both complex formation and the existence of phase separation. the contributions from entropy and enthalpy to the free energy of mixing are the physical reason responsible for phase separation [25-28]. the preference for unlike atoms to pair as the nearest neighbours i.e., heterocoordination and preference for like atoms to pair as the nearest neighbours i.e., homocoordination help to analyse the complex formation tendencies and the phase separation in liquid binary alloys. the asymmetry in the thermodynamic properties of in-na liquid alloy can neither be ascribed to the size factor (ωna/ ωin = 1.77 being less than 2.0, the required value to produce these effects [7] nor the electronegativity difference (en = 1 –exp (–0.25d 2 ), d is the difference in the electronegativity values of the two metals) of 0.1478 [29]. so the asymmetric behaviour of various observed properties may be due to short range order. in this study, a statistical thermodynamic model based on complex formation is used to calculate the interdependence of various properties such as free energy of mixing, heat of mixing, entropy of mixing, concentration-concentration fluctuation at long wavelength limit, chemical short range order parameter and surface tension of inna liquid alloy. this concept has been used successfully to explain the mixing properties of a variety of binary liquid alloys [9, 10, 30, 31]. the present paper is presented as follows. a summary of essential equations required for calculations is given in section 2. section 3 deals with results. conclusions are summarized in section 4. 2. formalism 2.1. properties of mixing the model adopted here starts by assuming the existence of a atoms, b atoms of the binary alloy ab and a chemical complexes aµ bν (µ and ν being small integers) in the liquid state i.e., νµ⇔ν+µ baba the grand partition function of an alloy consisting of n1 number of a atoms and n2 numbers of b atoms may be expressed in terms of the configuration energy e as ( )( ) ( )( ) ( )     −µ+µ∑=θ tk enn exptqtq b 2211n 2 n 1 21 (1) where qi(t) and µi are the atomic partition function and the chemical potential of the ith (i = 1, 2) species, respectively kb and t refer, respectively, to the boltzmann’s constant and the absolute temperature. equation (1) can be solved in the framework of quasi-lattice theory [32] to obtain various expressions for the thermodynamic and microscopic functions. after performing some algebra [33], we obtain the free energy of mixing as ii xs mm clncrtgg ∑+= (2) 2222111112122i xs m wwwwccg φ+φ+φ+= (3) )cc2(cc 1 2 1 1 1 2 1 112 −−−− υµ−υµ=φ 2:)cc2(cc 2 2 12 2 111 ≥µυµ−υµ=φ −− 2:)cc2(cc 2 212 2 122 ≥υυµ−υµ=φ −− (4) where w is the order energy and w12, w11, w22 are the interaction energies. c1 and c2 are the concentrations of the first and the second species of the alloys. ijφ is the probability of finding the i – j a.k. mishra and m. milanarun / bibechana 9 (2013) 165-174: bmhss, p. 167 (online publication: nov., 2012) bond as a part of the complex. in choosing an appropriate complex (in3na2) we are guided by experimental considerations [22]. for a weakly interacting system with µ = 3, υ = 2 1 7 1 6 1 5 1 4 1 3 1 2 1 12 c 4 c 7 c5 3 c2 5 c3 2 c3 3 c2 420 13       +−++−+=φ 1 7 1 6 15 1 4 1 3 1 2 1 11 c 8 c 7 c4 c 5 c6 4 c5 3 c2 840 53       −+−+−+−=φ 1 7 1 6 1 4 1 3 1 22 c 8 c 7 c 5 c2 2 c 280 23       −++−=φ (5) the enthalpy of mixing hm can be obtained from equation 2 and the relation n,c,p xs mxs m xs m t g tgh       ∂ ∂−= (6) equations (2) and (6) yield ( )( )             ∂ ∂ −φ∑+∂ ∂−= t w tw t wtwcch ij ijij 2,1 j,i 21 xs m (7) the entropy of mixing is given by ( ) t gh s mm m −= (8) 2.2 concentration-concentration fluctuations in long wavelength limit and short range order parameter concentration-concentration fluctuations in the long wavelength limit, scc(0), have been widely used [23, 31, 34, 35] to understand the alloying behaviour of liquid binary alloys. scc(0) is related to gm as 1 n,p,t 2 1 m 2 cc c g rt)0(s −       ∂ ∂= (9) using equation (2) the value of scc(o) for µ=3 and υ=2 is given by =)0(scc ( )[{ 5 1 4 1 3 1 2 111 1 2121 c7c15c10c6c92c2w2)rt(cc1cc +−++−+−+ − ( ) 2 111 5 1 4 1 3 1 2 11112 cwc7c24c30c24c154cw +−+−+−+ ( ) ]} 1 22 4 1 3 11 wc7c6c86 − −++− (10) the warren-cowley [36, 37] short range order parameter, 1α is evaluated to quantify the degree of order and is computed theoretically [23, 31, 37] as ( ))1)1z(s )1s( 1 +− −=α (11) )0(ids )0(s s cc cc= (12) 21cc cc)0(ids = (13) here z is the coordination number, which is taken as 4 for in-na liquid alloy [8]. a.k. mishra and m. milanarun / bibechana 9 (2013) 165-174: bmhss, p. 168 (online publication: nov., 2012) 2.3 surface tension the surface tension of complex forming liquid alloys is given by [10, 38, 39] =σ ( )             γ γ+      +σ 1 s 1 1 s 1 1 ln c c lnart (14a) = ( )             γ γ+      +σ 2 s 2 2 s 2 2 ln c c lnart (14b) where, )2,1i(i =σ are the surface tensions of the components and a is the mean atomic surface area. s iγ and s ic refer, respectively, to activity coefficients and the concentrations of the ith component at the surface. s iγ is the related to iγ as ( ) i2 s ii1 s i lnnccontaininglnnln γ+γ=γ (15) where n1 and n2, termed as surface coordination fractions, are the fractions of the total numbers of nearest neighbours of an atom within the layer in which it lies and that in the adjoining layer, respectively, so that n1+2n2 = 1. from equation (2) and the usual thermodynamic relation ∫ γ= 1c 0 1 xs m dclnng (16) the activity coefficients for µ = 3 and υ = 2 are given as : ( ) ( ) (       +−+−+ −+   ++−−+    −+−+   −+−       ++−++−=γ − 8 c7 7 c13 c 5 c8 2 c7 c2 280 23w 8 c7 7 c31 c9 5 c54 4 c39 3 c19 c2 840 53w 4 c7 7 c44 3 c25 5 c8 2 c15 3 c22 c 420 13wc1wtkln 8 1 7 16 1 5 1 4 1 3 122 8 1 7 16 1 5 1 4 1 3 12 111 8 1 7 1 6 1 5 1 4 1 3 12 112 2 1 1 b1 (17) ( )       +   −−+   +    −+−+−+   −       +−−+−+=γ − 4 1 4 1 3 11 22 3 1 5 1 4 16 1 2 11 11 3 1 5 1 4 1 3 1 2 11 12 2 1 1 b2 c 8 c7 7 c6 5 c8 2 3wc 8 c9 7 c24 c5 5 c24 4 c15 3 4wc 4 c7 7 c30 3 c10 5 c12 2 c9 3 4wwctkln (18) a.k. mishra and m. milanarun / bibechana 9 (2013) 165-174: bmhss, p. 169 (online publication: nov., 2012) 3. results and discussion: comparison between calculation and experiment 3.1 mixing properties the free energy of mixing ( )mg of liquid in-na alloy at 713 k has been computed through equation (2). those values of order energy and interaction energies are considered which when substituted into equation (2) give us values of gm that are very close to experimentally observed values from [22]. these parameters are independent of concentration although they may depend on temperature and pressure. these computed values are w = 1.66 rt w11 = –18.99 rt w22 = – 6.84 rt w12 = –1.9 rt it is obvious from the value of order energy w that the tenderly of complex formation in the alloy inna is relatively weak. the values of interaction energy suggest that attraction between in atoms is maximum followed by na atoms and in and na atoms. a plot of computed and experimental [22] values of gm/rt for inna liquid alloy at 713k is given in figure 1. figure 1 shows that computed and experimental values are in agreement. a.k. mishra and m. milanarun / bibechana 9 (2013) 165-174: bmhss, p. 170 (online publication: nov., 2012) the enthalpy of mixing (hm) and entropy of mixing (sm) are evaluated through equations (7) and (8) respectively. the energy parameters are considered to vary with temperature to ascertain the variation of enthalpy and entropy of mixing with experimental values [22]. the temperature dependent energies are r9.0 t −=∂ ω∂ r0.1 t 11 −=∂ ω∂ r75.0 t 11 +=∂ ω∂ r6.9 t 12 +=∂ ω∂ the values of enthalpy of mixing hm/rt and entropy of mixing sm/r for in-na liquid alloy at 713 k are shown in figures 2 and 3 respectively along with experimental values [22]. it is seen from figure 2 that the computed values of hm/rt are in reasonable agreement with experiment. it is clear from figure 3 that the pattern of sm/r is reproduced in our computation. but calculated values are not in quantitative agreement with the experiment. it may be because of the fact that slight difference in gm/rt and hm/rt produces more difference between the computed and experimental values of sm/r as is evident from equation 8. however, our computed values are better than that given by chakrabarti et al [40]. 3.2 concentration-concentration fluctuations in the long wavelength limit scc(0) and short range order parameter (α1) scc(0) is an important parameter because any deviation from ideal value scc id (0) is significant in explaining the type of interaction in liquid alloys. there is a tendency for self coordination if scc(0) > scc id (0) and scc (0) >> scc id (0) means the occurrence of phase separation. scc (0) << scc id (0) is an indication of the existence of chemical short range order (csro) or an indication of strong association. the values of scc (0) are computed via equation (10). these are depicted in figure 4 along with experimental values [24], values computed by akinlade [8] and scc id (0). perusal of figure 4 indicates that the computed values of scc (0) predicts csro in the concentration range 0 < cna ~ < 0.7 and phase separation in 0.7 ≤ cna ≤ 1.0. the magnitude of the calculated values beyond cna > 0.7 is lower than the experimental values. a better agreement between the calculated and experimental values may be obtained if the energy parameters are assumed concentration dependent. the dip in scc(0) is found at stoichiometric composition in3na2. a.k. mishra and m. milanarun / bibechana 9 (2013) 165-174: bmhss, p. 171 (online publication: nov., 2012) the short range order parameter α1 has been calculated to quantify the degree of order and these have been represented in figure 5. the negative values of α1 correspond to complex formation while its positive values correspond to the occurrence of segregation resulting in phase separation. a random distribution of atoms is expected by α1= 0. 3.3 surface tension calculation of surface tension through equations (14a, 14b) requires the values of surface concentration ( )2,1ic s i = and activity coefficients in the bulk iγ and on the surface s iγ . the calculated values of 1γ and 2γ along with experimental values [22] and calculated values of s iγ and s 2γ are given in table 1. table 1 shows that there is reasonable resemblance between calculated and experimental values of activity coefficients of in ( 1γ ) and na ( 2γ ) in the bulk in inna liquid alloy at 713k. it is predicted from table 1 that sodium atoms are more active on the surface than in the bulk throughout the whole concentration range except for cna = 0.9. indium atoms are less active on the surface than in the bulk up to cna< 0.5 but become more active on the surface than in the bulk after this concentration. a.k. mishra and m. milanarun / bibechana 9 (2013) 165-174: bmhss, p. 172 (online publication: nov., 2012) table 1 : activity coefficients of in and na in inna liquid alloy at 713 k in the bulk ( 1γ , 2γ ) and on the surface ( s 1γ , s 2γ ) 1γ 2γ c2 theoretical expt. [22] s 1γ theoretical expt. [22] s 2γ 0.1 1.003 0.978 0.871 0.065 0.097 0.165 0.2 0.921 0.900 0.548 0.082 0.151 0.518 0.3 0.727 0.752 0.521 0.252 0.258 0.714 0.4 0.511 0.554 0.509 0.505 0.454 0.855 0.5 0.353 0.365 0.456 0.844 0.765 0.959 0.6 0.268 0.248 0.422 1.044 1.044 1.010 0.7 0.247 0.207 0.412 1.086 1.156 1.021 0.8 0.280 0.227 0.424 1.042 1.126 1.010 0.9 0.347 0.356 0.447 1.003 1.004 1.000 surface tension of inna liquid alloy is calculated at 713 k using equation 14. the surface tension of pure in and na at the specified temperature are taken from smithell’s metals reference book [41]. the mean atomic surface area a is calculated from the relation given by laty et al. [42] as ( ) 3 2 n/v102.1a = where n is the avogadro’s number and v is the volume the alloy. experimental values of v have been taken from the graph given by akinlade [8]. the evaluated values of surface tension of inna liquid alloy with concentration are displayed in table 2 along with its ideal values ( )2211 cc σ+σ=σ and surface concentration of na. table 2 : surface concentration of na ( )sc2 and surface tension (σ ) of inna liquid alloy at 713k. c2 s c2 σ )( 2211 σσσ cc id += 0.1 0.2866 494.713 493.550 0.2 0.5372 430.553 457.407 0.3 0.8569 355.470 420.863 0.4 0.9634 283.708 384.320 0.5 0.9884 233.436 347.777 0.6 0.9954 203.578 311.233 0.7 0.9977 187.859 274.690 0.8 0.9987 179.337 238.146 0.9 0.9994 172.421 201.603 we could not compare our evaluated values for want of experimental values. table 2 shows that the surface tension of in is lowered when alloyed with na, the value of surface tension inna liquid alloy is above its ideal values up to 10% concentration of na and after this the calculated values are less than its ideal values. it is evident from table 2 that na atoms segregate on the surface at all concentrations. a.k. mishra and m. milanarun / bibechana 9 (2013) 165-174: bmhss, p. 173 (online publication: nov., 2012) 4. conclusion the phenomenon of complex formation in inna liquid alloys and its effect on the concentration dependent mixing properties were investigated theoretically on the basis of quasi-lattice theory. the existence of the complex in the form in3na2 has been used to obtain concentration dependent thermodynamic properties and surface tension of inna liquid alloy. the low value of order energy (w/rt) shows that inna liquid alloy is a weak interacting system. the evaluation of scc(0) predicts that csro exists in the region 0 < cna < 0.7 and phase separation in the region 0.7 < cna ≤ 1.0. a better agreement between theoretical and experimental values of scc (0) at cna = 0.8 can be obtained by assuming concentration dependent energy parameters but it may distort the quasi-lattice theory. the same energy parameters have been considered for the study of bulk as well as surface properties. we may conclude that the theory is capable of predicting of negative values of free energy of mixing, enthalpy of mixing, s-type entropy of mixing, the phenomenon of csro and phase separation by considering in3na2 complex in inna liquid binary alloys. references [1] h.e. barleett, a.h. neethling and p.j. growther, j. chem. thermodyn., 2 (1970) 521. 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[42] p. laty, j.c. loud and p. deste, surf. sci., 60 (1976) 109. microsoft word b.p singh.doc b.p.singh et al. / bibechana 8 (2012) 81-89 : bmhss, p.81 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana thermodynamic and structural properties of mg-tl liquid alloy b.p. singh 1 , d. adhikari 1 , i.s. jha 2* , b.c. kumar 1 , s.k. chaudhary 1 , s.k. jayaswal 1 , r.p. koirala 2 1 univ. dept. of physics, t.m.bhag. university, bhagalpur, bihar, india 2 dept. of physics, m.m.a.m. campus (tribhuvan university), biratnagar, nepal (*email address of corresponding author: indusekharjha@yahoo.com) article history: received 25 june, 2011; accepted 24 august, 2011 abstract the concentration dependent asymmetry in mixing properties of mg-tl liquid alloys at 923 k has been investigated on the basis of regular associated solution model. the concentration of apb type complex in a regular associated solution of mg and tl have been determined. we have then used the concentration of complex to calculate the free energy of mixing, enthalpy of mixing, entropy of mixing, activity, concentration fluctuations in long wavelength limit scc(0) and the warren cowley short-range parameter 1α .the analysis suggests that heterocoordination leading to the formation of chemical complex mg2tl is likely to exist in the melt. the analysis reveals that there is a tendency of unlike atom pairing (mg-tl) in mg-tl alloy whole range of concentration. keywords: mg-tl alloy; microscopic structure; pairwise interaction energy; chemical short range order 1. introduction physics and chemistry of liquid alloys, in which the atomic arrangement is not spatially periodic in contrast to the case of crystalline materials, is well-recognized as important and promising area for research. structural and thermodynamic properties of the initial melt play important role in the formation of alloy. thus the properties of alloys in the melt are helpful to understand the alloying behaviour of alloys in solid state. growing technological interest to the nonperiodicity in the atomic arrangement of disordered materials has led to an increasing need for a better description of their atomic scale structures. in this paper, we intend to study the thermodynamic properties of mg-tl alloys in liquid state at 923 k on the basis of regular associated solution model. in regular associated solution model strong interaction among the constituent species of the alloy is assumed [1-5]. such assumptions have been used in different models [6-10] by the investigators. the phase diagram of mg-tl alloys shows the existence of mg-tl and mg2tl intermetallic compounds in its solid state [11].in this paper; we have assumed mg2tl complex is energetically favoured in the liquid state of mg-tl alloy. assuming mg2tl complex, we have determined free b.p.singh et al. / bibechana 8 (2012) 81-89 : bmhss, p.82 energy of mixing (gm), heat of mixing (hm), entropy of mixing (sm), concentration fluctuation in long wavelength limit (scc(0)) and chemical short range order parameter (α1) of mg-tl liquid alloy at 923 k. basic formalism of regular associated solution model is given in section 2 and section 3 deals with the numerical results and discussion. conclusion is provided in section 4. 2. basic formalism let us consider one mole of binary solution comprising of x1 mole of a atoms and x2 moles of b atoms. the presence of apb type complex in the solution results in a depletion of concentration of free atoms of the components of a and b. the liquid solution is thus composed of three species namely free atoms a and b and the complex apb. as a result of associations, the thermodynamic behaviour of the components a and b is governed by the true mole fractions xa and xb rather than the gross mole fraction x1 and x2. thus it is convenient to operate with two frames of references, one referring to gross mole fractions x1 and x2 and other referring to actual mole fractions of each species (xa, xb and xapb). further, it is assumed that there are n1 moles of species a, n2 moles of species b and n3 moles of species apb per mole of the binary solution. from the conservation of mass, the two frames of reference can be interrelated as follows: 311 pnxn −= 322 nxn −= and 3321 pn1nnnn −=++= (1) 3 1 321 1 a pn1 n nnn n x − = ++ = 3 2 321 2 b pn1 n nnn n x − = ++ = and 3 3 321 3 apb pn1 n nnn n x − = ++ = (2) here, apb 3 3 3 px1 pn1 pn 1 pn1 1 n 1 += − += − = (3) now using eq. (2.3) in eq. (2.2), we have, apb a 1 px1 x n + = , apb b 2 px1 x n + = , apb apb 3 px1 x n + = (4) for the sake of convenience one or more of these frames of reference may be used. now xa, xb and xapb can be inter-related with each other as follows 1221 xxxx = using 311 pnxn −= and 322 nxn −= , we get b.p.singh et al. / bibechana 8 (2012) 81-89 : bmhss, p.83 132231 x)nn(x)pnn( +=+ after performing some algebraic operations and rearranging the terms, we obtain )nnn(xnpx)xx(n 321132211 ++=++ and apb21a xpxxx −= (5a) similarly we can obtain apb22b x)px1(xx −−= (5b) the equilibrium constant for the reaction apb ⇔ bpa + is given apbapb b p ab p a x xx k γ γγ = (6) where aγ , bγ and apbγ are activity coefficients of monomers a, b and complex apb. following lele and ramchandrarao [1] the free energy of mixing mg is given by m a b 12 a apb 13 b apb 23 apb apb apb a a b b apb apb apb 1 rt g (x x x x x x ) (1 px ) (1 px ) x (x ln x x ln x x ln x ) rt ln k (1 px ) = ω + ω + ω + × + + + + + + (7) where 12ω , 13ω and 23ω are interaction energies for the species a, b ; a, apb and b, apb respectively, t the temperature and r stands for the universal gas constant. progonine and defay [12] have shown that in associated solutions, the gross chemical potentials of components 1 and 2 are equal to the chemical potentials of the monomeric species a and b. following jordan [2] the activity coefficients aγ , bγ and apbγ of monomers and complex can be expressed in terms of pairwise interaction energies through )ωωω(xxωxωxγlnrt 132312apbb13 2 apb12 2 ba +−++= (8a) )ωωω(xxωxωxγlnrt 121323apba12 2 a23 2 apbb +−++= (8b) 2 2 apb a 13 b 23 b b 13 12 23 rt ln x x x x ( )γ = ω + ω + ω −ω +ω (8c) thus, using equation (5), (6) and (7), one gets ]x)px1(x[ rt ]x)x1(px[ rt ]x)x1(px[ rtx xx lnkln bbapb 23 aaapb 13 abb 12 apb b p a −− ω +−− ω ++− ω +        = (9) once the expressions for mg is obtained, other thermodynamic and microscopic functions follow readily. heat of mixing, entropy of mixing and concentration fluctuations in the long-wavelength limit are related to mg through standard thermodynamic relations b.p.singh et al. / bibechana 8 (2012) 81-89 : bmhss, p.84 m m m t,p g h g t t ∂ = −  ∂  (9) m m m h g s t − = (10) 2 2 1 cc m t,ps (0) rt( g c )−= ∂ ∂ (11a) 1 p,t22 1 p,t11cc ))c1(a(ca )ca(a)c1()0(s − − −∂∂= ∂∂−= (11b) where c (= mgx ) is concentration of a component in the alloy. equation (7) is used in equation (9) and (11), we obtained expressions for mh and )0(scc as m a b 12 a apb 13 b apb 23 apb apb apb 213 2312 a b a apb b apb apb 1 t h (x x x x x x ) (1 px ) (1 px ) x dln k x x x x x x rt t t t (1 px ) dt = ω + ω + ω − × + + ∂ω ∂ω∂ω + + − ∂ ∂ ∂ +  (12) =)0(scc 1 apb 2/ apb b 2/ b a 2/ a 23 / apb / b13 / apb / a12 / b / a apb x x x x x x )xxxxxx( rt 2 )px1( 1 −                         +++ω+ω+ω + (13) here, 2 2 c g∆ ∂ ∂ > 0 for 0 c g∆ = ∂ ∂ where prime denotes the differentiations with respect to concentration and / ax and / bx are determined by using equation (5). / apbx is determined using the equation (9) and the condition 0 dc klnd = [3]. the concentration fluctuation in long wavelength limit (scc(0) ) can be determined from measured activity data following equations (11b) [13]. this is usually considered as the experimental value. in order to fit the degree of order in the liquid alloy, warrencowley short-range parameter 1α [14, 15] can be estimated from the knowledge of concentration-concentration structure factor s cc(q) and the number-number structure factor snn(q). however, in most diffraction experiments these quantities are not easily measurable for all kinds of binary liquid alloy [16, 17]. on the other hand 1α can be estimated from the knowledge of scc(0) [18,19] )0(s )0(s s, 1)1z(s 1s id cc cc 1 = +− − =α ; )1c(csid cc −= (14) where z is coordination number and z =5 is taken for our calculation. we note that varying the value of z does not have any effect on the position of the minima of 1α ; the effect is to vary the depth while the overall feature remains unchanged. b.p.singh et al. / bibechana 8 (2012) 81-89 : bmhss, p.85 the pairwise interaction energies and equilibrium constant are determined by the following method: in a regular associated solution aa11 γxγx = and bb22 γxγx = , where 1γ and 2γ are respective gross activity coefficients of components 1 and 2. thus 1 a a1 x x lnlnln +γ=γ (15a) and 2 b b2 x x lnlnln +γ=γ (15b) following the technique of lee and ramchandrarao [1] the pairwise interaction energies, the equilibrium constants and the activity coefficients at infinite dilution can be written as rt ln 120 1 ω =γ (16a) o 2 o 1 o 2 o 1 13 γγ γγ )rt/ωexp(k − = (16b) where o 1γ and o 2γ are activity coefficients of component a and that of b at zero concentrations. solving equations (8a) and (8b) we obtain 2 apb 12 bb a 1 b b 2 b 13 x rt )x1(x x a ln)x1( x a lnx rt ω −−      −+      = ω (17) 2 apb 12 aa b 2 a a 1 a 23 x rt )x1(x x a ln)x1( x a lnx rt ω −−      −+      = ω (18) where 1a and 2a are respective activities of mg and tl atoms in the liquid alloys. using equations (9), (17) and (18), we can derive         +         −      +              + =+ apb 2 p 112 b 2 apb b a 1 apb a13 x aa ln rt ω x a ln x x x a ln x x1 rt ω kln (19) 3. results and discussion the mole fraction of complex mg tl− is determined using experimental data of activity [9] and equations (16) and (19) employing the iterative procedure. the best fit values of equilibrium constant and pairwise interaction energies for the alloy mg2tl in liquid state at 923 k are found to be k = 0.113, 12ω = -20940 j mol -1 , 13ω = -7870 j mol -1 and 23ω = -29050 j mol -1 all the interaction energies are negative and show that mg and tl atoms are attracted to each other and to the complex. b.p.singh et al. / bibechana 8 (2012) 81-89 : bmhss, p.86 the compositional dependence of various species (fig. 1) shows that the maximum association occurs at 60 at. pct. of mg. at this composition and 923 k, about 21 mol pct. of the liquid alloy is associated. theoretical calculation of free energy of mixing for mg-tl liquid alloy shows that it is moderately interacting system. fig. 2 shows excellent agreement between the experimental and calculated free energies. the free energy of mixing is minimum (= -12.6 kj) at xmg = 0.5 which is almost equal to the experimental result [1]. fig. 2 shows an excellent agreement between the experimental and calculated free energies. on using equation (12) and observed values of mh [1], we have chosen the following values for the given parameters as the best fit values for the heat of formation of mg-tl complex. 1 112 10jmol k t − −∂ω = − ∂ , 1 113 22.5jmol k t − −∂ω = + ∂ , 1 123 2jmol k t − −∂ω = + ∂ and 2 ln k r t t ∂ = ∂ 14250 ± 800 j mol -1 it is found from the analysis that the heat of mixing is negative at all concentration. our theoretical calculation shows that the minimum value of the heat of mixing is -6.87 kj at mgx = 0.6. further it is observed that the concentration dependence of asymmetry in mh can be explained only when one considers the temperature dependence of the pairwise interaction energies. theoretical values of heat of mixing are in very good agreement with observed values. fig.-1 : compositional dependence of mole fractions xa (a=mg), xb (b=tl) and xapb (apb= mg2tl) versus xmg (concentration of mg) at 923k. b.p.singh et al. / bibechana 8 (2012) 81-89 : bmhss, p.87 fig.-2 : upper part : entropy of mixing (sm) versus xmg, lower part : free energy of mixing (gm) and heat of mixing (hm) versus xmg (concentration of mg) at 923k; (––––) theory, (οοο) experiment [1]. we have calculated entropy of mixing of mg-tl alloy in liquid state using equation (10). the calculated values always match in sign with observed values. the calculated values and experimental values are in good agreement in all concentration of mg. the concentration dependence of asymmetry in ms is well explained (fig. 2). the basic inputs for the calculations of activity are pairwise interaction energies and mole fractions of the unassociated atoms of component 1, called a, unassociated atoms of component 2, called b and the complex, apb. we have used the same values of mole fractions and pairwise interaction energies for the evaluation of activity which were used for the evaluation of free energy of mixing, heat of mixing and entropy of mixing. the agreement between observed and calculated values of activity of mg and tl is also good as shown in fig. 3. fig. 4 shows the computed and experimental values of scc(0) as well as ideal values. the calculated values for scc(0) shows excellent agreement with the experimental values. the scc(0) can be used to understand the nature of atomic order in the binary liquid alloys. at a given composition, if scc(0) < )0(sid cc , ordering in liquid alloy is expected and if scc(0) > )0(sid cc , there is tendency of segregation. our theoretical analysis clearly indicates that, there is unlike atoms are pairing as nearest neighbours in full range of concentration of mg, i.e., mg-tl alloy in the liquid state behaves like unlike atoms ordering pair in whole concentration range. the knowledge of 1α provides an immediate insight into the nature of the local arrangements of atoms in the mixture. at equiatomic composition, one has 1α1 1 ≤≤− . the minimum possible value of 1α is 1αmin 1 −= and that implies complete ordering of unlike atoms paring at nearest neighbours. on the other hand the maximum value of 1α is 1αmax 1 += which implies total segregation leading to the phase separation and 1α = 0 corresponds to a random distribution of atoms. the variation of 1α (fig. 4) clearly strengthens the result obtained from the study of scc(0). b.p.singh et al. / bibechana 8 (2012) 81-89 : bmhss, p.89 fig.-3 : activity (a) of mg and tl in liquid mg-tl liquid alloy at 923k versus xmg ; (––––) theory, (○○○) experiment [1]. fig.-4 : upper part : concentration fluctuations in long wavelength limit (scc(0)) versus xmg (concentration of mg) at 923k ; lower part : short range ordering parameter (α1) versus xmg at 923k; (––––) theory, (○○○) experiment, (----) ideal values. b.p.singh et al. / bibechana 8 (2012) 81-89 : bmhss, p.89 4. conclusion the thermodynamic properties and microscopic structure of mg-tl alloy in liquid state are explained assuming mg2tl complex in the melt on the basis of regular associated solution model the analysis suggests that there is a tendency of unlike atom pairing (mg-tl) in mg-tl alloy whole range of concentration. the result also indicates that there exist mg2tl complex in the liquid state of mg-tl alloy. acknowledgement d. adhikari gratefully acknowledges university grant commission (ugc), nepal for providing financial support to pursue this research. references [1] s. lele and p. ramchandra rao, metall. trans. 12b (1981) 659. 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[19] s.p. mcalister and e.d. crozier, j. of phys. c7 (1974)3509. microsoft word article bharat subba-corrected.doc bharat raj subba and satya narayan meheta / bibechana 8 (2012) 96-104 : bmhss, p.96 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana ovarian histomorphology and gonadial cycle of freshwater garfish xenentodon cancila (hemiltonbuchanan) (beloniformes:belonidae) bharat raj subba and satya narayan meheta department of zoology,post graduate campus (tu), biratnagar, nepal email:subbabharat@yahoo.com article history: received 5 december, 2011; accepted 26 december, 2011 abstract the histomorphology and gonadial cycle of a freshwater garfish xenentoton cancila revealed that the ovaries of the fish pass through resting, early maturing advanced maturing ,pre-spawning, spawning and spent phases within one year.the oogenetic activity starts in november and continues upto june(gsi=10.19)-july(gsi=11.38),when ovaries are full of yolky eggs.only young oogonia and oocytes l appeared in september to october.the oocytes of l,ll,lll,lv and v stages were present during november to february.the oocytes vl and vll were seen dominated by ripe oocytes during june to late july when spawning takes place.asychronism mode of oocyte development was recorded in x.cancila. keywords: xenentodon cancila; oocyte development; reproductive cycle; spawning 1. introduction the studies on fish biology encompassing habitat ecology,ovarian morphology,spawning,physiology and reproductive habits have been indespensible for the fish culture development and safeguard of fish species.pisciculture has been an important adjunct to aquaculture on one hand and the conservation of fish has been a global attention because of climate change and population explosion on the other.conserving fish is only possible when the life cycle is fully understood. the study of spawning habit of a fish is carried out in the natural habitat but as fish are aquatic ,it is not possible to observe all the steps taking place during spawning and before that too.therefore, considering the above facts, the study of ovarian histomorphology of the freshwater garfish xenentodon cancila has been made to understand the reproductive potential of the species in the natural habitat. several workers have studied the gonads of fishes. among many, most important contributions on the histological and seasonal changes in the ovary of fishes were made[ 1-11]. shrestha and khanna[12] have worked on structure and histological changes in the ovary of the nepalese snow trout schizothorax. plagiostomus. . rita and nair [13] made studies on oogenesis in a tropical loach, lepidocephalus thermalis and hillstream loach noemachelilus triangular. toshimori, and fumioki [14] studied gap junctions between microvilli of an oocyte and follicle cell in teleosts, plecoglossus attivelis. chakrabarti and mandal [15] studied seasonal histological changes in the vary of puntius japanieus. in spite of large contributions noted above, the study in ovarian structure of freshwater garfish (kauwa) is meager indeed., taking this point in view, subba [16] has carried out an investigation on ovarian histomorphology and gonadial cycle of a hill-stream fish lepidocephalichthys guntea. bharat raj subba and satya narayan meheta / bibechana 8 (2012) 96-104 : bmhss, p.97 2. materials and methods live specimens of xenentodon cancila were collected every month from muriyadhar which runs parallel to east koshi dam in sunsari. the weight of the specimens and their ovaries were recorded in situ.the ovaries taken out were washed in distilled water properly so as to remove blood stains. fresh pieces from anterior, middle and posterior regions of the ovary were taken and fixed separately in bouin's fixative. serial sections were cut at 5 to 6µ and stained in iron haematoxylin using eosion as a counter stain. mallory triple stain was also used to study connective tissues. the gonadosomatic index (gsi) was calculated for every month as below. weight of the ovary gsi = × 100 total weigh of the fish 3. results 3.1 ovarian morphology the ovaries of xenentodon cancila are paired and elongated sac like structures which lie in the abdominal cavity ventral to the kidney. they are attached to the body wall by means of the mesovarium. the anterior portions of the ovary are free, broad but posterior ends are united into one to form oviduct (fig 1). the ovary is of typical teleostean type consisting of an ovarian wall and ovocoel. the ovary is covered with a thin peritoneal covering or serosa. beneath this is the elastic and muscular connective tissue, the connective tissue fibers bear the blood vessels, project into the ovarian lumen, ovocoel to form finger like folds known as the ovigerous lamellae, which encloses numerous ova in different stages of development and growth. the ovaries are of light cream colour during early stages of maturation but become yellow in the breeding season, ripe ova project out of the surface and gonads become semitransparent. as maturity advances the weight of the ovaries also increases gradually and reaches maximum in the mouths of jun-july showing highest gsi value was 11.3772. the weight became minimum in the months of oct-november with gsi 0.9416. after spawning the ovaries became, thin flaccid, and were considerably reduced in size. 3.2. histology the wall of the ovary is composed of an outer thin layer, peritoneal membrane, which is the outermost layer, overlying the tunica albuginea. the tunica albuginea is made of fibrous connective tissue and blood capillaries. the inner most layer is the germinal epithelium which projects into the ovocoel in the form of lamellae. these ovigerous lamellae are the seat for the development of oogonia, which are visible in various stages of development. oogonia of various stages are arranged on either side of these lamellae. these oogonia mature into oocytes. 4. developing oocytes an oogonium has a large nucleus and a thin layer of ooplasm which is chromophobic. each oogonium undergoes successive maturation divisions and form new generation of oocytes. before ripening an ovum, a series of cytonuclear changes take place in the oocyte. bharat raj subba and satya narayan meheta / bibechana 8 (2012) 96-104 : bmhss, p.98 stage oocyte (plate-i a,plate-2 g) :the earliest stage of germ cell in the ovary is the oogonium, which arises from the residual oogonia, occurring in the year. an oogonium has a large nucleus which is single thin layer of ooplasm which does not take basic stain. this stage is also known as chromatin nucleus stage. each oogonium passess through seven different stages called the oocytes, before it becomes a ripe ovum. the following stages of oocytes have been identified in the ovary of this fish. the mean diameter of an oogonium is 0.035 mm. stage i oocyte (plate i a,b plate-2 ): in this stage, the oogonia which acquire larger amount of cytoplasm are called oocytes. an oocyte can be distinguished from an oognium because of a prominent round central nucleus and two or three nucleoli. in this stage, oocyte is encircled by an incomplete layer of simple squamous cells. this is the beginning of the follicular layer. the cytoplasm is basophilic. the oocyte in this stage measured 0.1 mm in diameter. stage ii oocyte (plate i b,d plate-3): with an increased quantity of cytoplasm, increases strong affinity for basic dyes. in this stage many oocytes have a yolk nucleus situated close to the nuclear membrane in the cytoplasm. the yolk nucleolus ,first appears near the nuclear membrane but moves towards the periphery in the later stage. several nucleoli of various sizes are arranged along the periphery of nuclear membrane. this stage is conventionally known as perinucleolus stage. the oocyte measured 0.15 mm. stage iii oocyte (plate ic, plate-2 i) :further development of the oocytes is marked by the formation of a thin layer of follicular cells around the cytoplasm. owing to the differential affinity to the basic dyes, the zonation is exhibited in ooplasm. the oocytes of this stage show an intensely stained inner zone and lightly stained outer portion. a few nucleoli extrude out of the nuclear membrane into the cytoplasm, some of them can be seen emerging through nuclear membrane while others are found in cytoplasm. yolk nucleous is seen frequently at this stage. the oocyte, at this stage was of 0.24 mm in diameter. stage iv oocyte (plate 1 b,): this stage is characterized by the appearance of minute vaculoes in the ooplasm. the vacuoles appear as if they are empty because they don't take basic dyes. the ocyte is now known to have reached the yolk vesicles stage. as oocytes grow further, more yolk vesicles bharat raj subba and satya narayan meheta / bibechana 8 (2012) 96-104 : bmhss, p.99 appear at the periphery and proceed inwards towards the nucleous and fill the entire cytoplasm. at this stage a few of the nucleoli can be seen to pass out of the undulating nuclear membrane. in this stage a vitelline membrane or zona radiata is also recognizable between ooplasm and follicular layer. the oocyte in this stage measured 0.29 mm in diameter. stage v oocyte (plate 1 d) : after the cytoplasm has become full of yolk vesicles, yolk begins to appear in the form of small granules in the extra vesicular ooplasm. most of them are present near the periphery of the oocyte and accumulate in high number. the yolk granules then proceed centripetally to the entire cytoplasm and become impregnated with them. the smaller granules fuse each other in later stage to produce large yolk globules. the process of nuclear extrusion contiunes in some of the oocytes. the zona radiata and follicular layer become more thicker in this stage. the oocytes measured 0.33 mm in diameter at this stage. stage vi oocyte (plate 1 e) :this stage is characterized by the appearance of the yolk globules. the nucleus disappears. the yolk starts depositing in the form of large globules in the extravesicular ooplasm. the entire cytoplasm becomes impregnated with yolk globules or granules proceeded in words. some yolk vesicles of smaller size collect along the periphery of the oocyte and form individual so called cortical alveoli. outside the follicular layer, a thin layer of fibroblast develop. the oocytes measured 0.44 mm in diameter. stage vii oocyte (plate 1f) :at this stage nucleus becomes irregular in outline and smaller in size. the nucleus can be observed gradually migrating towards the periphery of the oocyte. so this stage is known as migratory nucleus stage. the nuclear membrane becomes indistinct and probably after that the contents of the nucleus mingle with cytoplams. the oocyte of this stage measured 0.48 mm in diameter. ripe oocyte: the ripe oocyte is recognized by its largest size, yellowish colour and translucent. large amount of yolk globules and yolk vesicles may lie scattered in it. it is covered over by three distinguishable layers namely theca an external layer, followed by the follicular epithelium (zona granulosa), and the innermost layer ,zona radiata. zona granulosa is made up of follicular epithelium. the ripe oocyte is full of yolk and nucleus is not visible. the ripe, oocyte measured 0.56 mm in diameter. this is the largest size oocyte and the ovary contains several ripe eggs. spawing takes place at this stage. a ripe egg is full of large amount of noncontiguous yolk and numerous yolk vesicles remain scattered in it. 4. reproduction cycle on the basis of histomorphological changes, the ovarian cycle of xenentodon cancila has been divided into the following phases. resting phase ( october to november ) :it extends from october to november. in this phase ovaries are thin translucent, pale and dirty brown in colour, with less vascular supply. histologically, the ovary shows ovigerous lamellae, packed with oogonia. the oogonia are budded off from the germinal epithelium and are arranged in nests. early maturing phase ( december to january ) plate 1 a,b : this phase extends from december to january. during this phase the ovaries become slightly thicker, opaque, yellowish in colour. vascularisation is feeble. the ovigerous lamellae are greatly swollen and laden with oocytes of different stages. tunica albuginea becomes slightly thinner than in previous months. there is an increase in the weight to the ovary. advanced maturing phase (february to march) plate 1 e,f : this phase extends from february to march. in this phase, colour of the ovaries changes into deep yellow. the blood capillaries become inconspicuous because of profuse vascular supply. number of immature oocytes decreases. the ova are tightly held and the ovary can not be striped by applying gentle pressure. the tunica albuginea becomes extremely thin. due to the presence of large number of fully mature ova. the ovocoel is greatly reduced. migratory nucleus reduced in size is seen towards the periphery. the yolk globules become enlarged because of their fusion with one another. there is further increase in the weight and volume of the ovaries. bharat raj subba and satya narayan meheta / bibechana 8 (2012) 96-104 : bmhss, p.100 pre-spawning phase (april to may) plate i e,f : this stage extends from april to may. during this phase the ovaries become deep yellow in colour. vascularisation is extensively developed. both transparent and opaque ova are present and the ovaries attain maximum weight. the fish abdomen seems bulging due to the presence of ripe ova inside. in this phase nuclear extrusion is seen. histological condition is the same as that of previous months. spawning phase (early june to late july) plate 1f,plate-3m : this phase begins in the early june and ends in the late july. during this period the ovaries are yellowish and turgid due to the presence of a large number of translucent eggs. ripe eggs are present in the oviduct to be discharged out side. the fish spawns number of times during this period. vascularisation of the ovary reaches its peak and the ovaries are said to be in running phase. in this phase ova ooze out in the oviduct with slight pressure in the abdomen. tunica albuginea becomes extremely thin and inter follicular space is greatly reduced. the ovigerous lamellae are inconspicuous. histological section of the ovaries in june and july shows a number of discharged follicles, such follicles can be detected up to the end of september. spent phase (august to september) :this phase starts in august and lasts up to september. the ovaries become thin, flaccid, delicate, slender and dull in colour. there is a decrease in the volume and weight of the ovary. vascularisation is reduced. in this phase, oogonia are seen budding from the germinal epithelium. the tunica albuginea again becomes thicker. histologically, the ovary shows some residual oocytes as well as discharged follicles. the nest of oogonia are seen among the ovigerous lamellae. 5. discussion xenentodon cancila (ham.) does not show sexual diamorphism, but during the breeding period, they exhibit notable sexual difference by the presence of relatively enlarged belly in female fishes. in this fish, the ovary is of cystovarian type, because lumen of the ovary is continuous with the oviduct. 5.1 origin of oogonia different authors have expressed different views regarding the origin of the new oogonia, yamamoto [18] believed that the new oogonia originate from the follicular epithelial cells of spent follicles but according to, [,19,20] the new crop of the oogonia are produced by the germinal epithelium.unlikely to the above suggestion some [7-9] suggest that in schizothorax richardsonii the new crop of oogonia arises from the residual oogonia. as observed by rita and nair [13] the new crop of oogonia originates from ovarian lamellae formed by germinal epithelium. shrestha and khanna [12] showed that the crop of oogonia arises from the residual oogonia. in this fish, cancila the crop of oogonia are derived from the residual oogonia. this finding supports the finding of belsare [4,8,12]. 5.2 yolk nucleus the investigators differ in their views regarding the origin and function of the yolk nucleus. according to yamamoto [21] the yolk nucleus is of nuclear in origin, while chopra [22] believed it to be cytoplasm in origin. wallace [17] suggested that the yolk nucleus has the capacity to form yolk in fishes, whereas wheeler [23] suggested that the yolk nucleus remains inactive and takes no visible part in the formation of yolk. khanna [24] has suggested that the yolk nucleus is the initial centre of growth and dispersal of all important cellular inclusions. bara [20] and nayar [25]. reported some relationship between the yolk nucleus, golgi bodies and mitochondrial elements according to rita and nair [13] the yolk nucleus is entirely wanting in any stage of oocyte maturation of lepidocephalus thermalis. in x. cancila the yolk nucleus is present in the periphery of young stage iii oocytes. as it gradually disappears in the maturing oocytes, it may have some relationship with the process of vitellogenesis.a similar view has been expessed by khanna, and sanwal [8] in channa gachua and bisht and joshi [4] in schizothorax richardsonii bharat raj subba and satya narayan meheta / bibechana 8 (2012) 96-104 : bmhss, p.101 bharat raj subba and satya narayan meheta / bibechana 8 (2012) 96-104 : bmhss, p.102 plate -1 a. photomicrograph of t.s. ovary of xenentodon cancila showing oogonium,ooc l, x 40 b. general observation of t.s. ovary of x.cancila showing stage 11 and iv,ooc l x 100. c. general observation of t.s. ovary of x.cancila showing stage iii and yolk nucleus x 200 d. t.s. ovary of x.cancila showing appearance of yolk vesicles in the periphery in stage v&lll oocytes x 200. e. t.s. ovary of xenentodon cancila showing stage vl x 200 f. t.s. ovary of xenentodon cancila showing stage vll x 200 (ge = germinal epithelium, 10 = immature oocyte, mn= migratory nucleus, ns = nest, nu = nucleus, nm = nuclear membrane, 0 = oogonium, ooc = oocyte, vm= vitelline membrane, yv = yolk vesicle, yg = yolk granule) plate -2 g. t.s. mature oocyte of xenentodon cancila. showing stage lv x 50. h. showing fusion of yolk globules x 100 i. stage vii showing migratory nucleus x 100. j. plate of a ripe ovum x 200. k. showing both mature and immature oocytes. l t.s. ovary of x.cancila showing immature oocytes. ovocoel. (fl = follicular layer, 10 = immature oocyte. mn = migratory nucleus, mo = mature oocyte, nu = nucleus,. th = thica, vm = vitelline membrane, yg = yolk globules, yv = yolk vesicles; zr = zona radiata.) plate-3 m. t.s. ovary of xenentodon cancila showing stage vll x 200 yg=yolk globules,mn=migrating nucleus,yv=yolk vesicles , n. ts showing of ovary of x.cancila atretic egg o. ts of ovay of x.cancila showing p= peritoneum,bc-blood capillary,ge=germinal epithelium,io=immature oocyte, ac = atretic egg 5.3 nuclear extrusion there are several views regarding the origin, extrusion and functions of the nucleoli in teleosts. rai [6] believed that large number of nucleoli are produced by division and fragmentation of a single nucleus of an oogonium, contrary to the above view, yamamoto et.al. [8,13,18,20,] did not observe any fragmentation in the fishes examined by them. according to their views, the fusion of minute fulgen positive particles present in peripheral nucleoplasm form peripheral nucleoli. according to bisht [5,9 23] in schizothorax richardsonii the nucleoli are produced by the division and fragmentation of the nucleolus. bharat raj subba and satya narayan meheta / bibechana 8 (2012) 96-104 : bmhss, p.103 in x.cancila many nucleoli of different sizes were observed in the early stages of oocyte, increasing in number by division, but the number diminishes as oocyte advances to maturity. this result corroborates closely with the finding of khanna et. al.[5,8,23, ]. extraction of nucleoli has been studied by several investigators in the past, but there is a great controversy in the origin of extrusion of nucleoli. according to dixit [3] the nuclear membrane does not allow the nucleoli to pass through it. rai et. al [6 ,8] have also observed extrusion of nucleoli into the ooplasm. extrusion of nucleoli is seen in x. cancila. several nucleoli of various sizes are seen in the early stage of oocyte. as oocytes reach maturity the nucleoli are seen increasing in number and their size goes on diminishing. this result agrees with the finding of khanna [5]. as the extrusion of nucleoli was seen more in number during the formation of yolk. it appeared to be associated with the formation of yolk. 5.4 yolk formation according to the mode of yolk formation the fish eggs have been classified into two types by yamamoto [26] uamamoto namely (i) eggs having a continuous mass of yolk, as in oryzia [18] and (ii) eggs having a noncontinuous mass of yolk, as in clupea [27]. in x.cancila yolk appears at the periphery of oocytes, in the form of the globular, later the whole ooplasm is filled with yolk globules. this process is similar to clupea [21] tot tor [6] channa gachua [8], puntius sophore [28] similarly results were obtained in x.cancila, where the yolk vesicles and yolk globules are independent of each other and the former give rise to so called cortical alveoli. and the yolk vesicles as such seen to play no role in the formation of yolk globules. nayar et. al [21,25] have described breaking down the vesicles of the inner side to take place in the formation of yolk globules in cyprinus and gobio which contradicts the above findings. 5.5 spawning there are three modes of oocytes development, according to prabhu [29] in some fishes eg. oncorhynchus masou [20] all the oocytes develop together at the same time in the ovary, such fishes spawn only once in a life time. this phenomenon is called total synchromism, there are some species which spawn once or twice in a season, developing two group of oocytes side by side (group synchronism), as in speckled trout, viadykov [30] still other species spawn several times in a breeding season. in these species large number of oocytes are present at various stages of their development in the same ovary asynchronism) as in channa gachua [8] and puntious sophore [28]. the spawning season of x.cancila extends from early june to late july. since various stages of developing oocytes are found in the same ovary and the fish spawns several times during a breeding season. x. cancila comes under the third group asynchronism. references [1] a .l. craig-bennett,linn. philos. trans. b 219 (1930)197. [2] c.f. hickling, z.j. mar. biol, ass. y.k. 20 (1936)443. [3] r.k. dixit, proc. nat. acad, sci, india b. 30 (1956) 214. [4] d.k.belsare, indian j.fish. 9 (1962)140. [5] s.s. khanna, and pant, m.c. copeil (1967) 83. [6] b.p.rai,acta.zool. 48 ( 1967)289. [7] g.k. lehri, acta anat. 69 (1968) 105. [8] s.s. khanna, and r. sanwal, zool. geitr, floge, 17 (1971)311. [9] j.s.bisht and m.l.joshi, acta, anat. 93 (1975)512. [10] c.p kapoor,acta. anat, 96 (1976)1-8. [11] c.p. kapoor, zekrosk. anat, forach. (leipz) 90 (1978)1049. [12] t.k. shrestha and s.s. khanna, matsya, 5 (1979)23. [13] s.d. kumari rita and n.b. nair, acad. sci. sect.b. 88 (1979)45. bharat raj subba and satya narayan meheta / bibechana 8 (2012) 96-104 : bmhss, p.104 [14] k. toshimori, and y. fumioki, forsch (lepiz) 93 (1979) 458. [15] p.chakrabarti and d.k. mandal,journal of freshwater bil.7 (1995)195. [16] b.r subba,j. freshwater biol.10 (1998)103. [17] w. wallace, quart. j. micr. sci. 47 (1904)161. [18] k.yamamoto,ann.zool.jap.28 (1955)233. [19] v.sriramalu and m. rajalaxmi, z. mikrosk. anat, forsch., 75 (1966)65. [20] g.bara, rev.fac,sci, univ. 25 (1960)50. [21] k.yamamoto, h.kal and r.ished,20 (1959)109. [22] h.c. chopra, experimentia. 17 (1961)120. [23] j.f.c. wheeler, quart. j. micr. sci. 68 (1925)641. [24] h.s. chaudhary, z.zellforosch. 37 (1952)455. [25] r.p.nayar, quart. j. micr, sci. 105 (1964)353. [26] k.yamamoto, j.fac.sci.hokkaido univ.13 (1957)346. [27] k.yamamoto,bull.fac.fish.hokkaido,univ.8 (1958)270. [28] r.k.dixit and n.agrawal,acta.anat.90 (1974)133. [29] m.s.prabhu, indian j.fish 3 (1956)59. [30] v.d.viadykov, j. fish. res. canada 13 (1956)799. microsoft word r.p. koirala_103-112_.doc r. p. koirala et al. / bibechana 9 (2013) 103-112 : bmhss, p.103 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana surface tension of two weakly interacting liquid alloys r. p. koirala 1, 2 , d. adhikari 2 , b. p. singh 1* 1 university department of physics, t.m. bhagalpur university, bhagalpur, india 2 department of physics, m.m.a.m. campus biratnagar, tribhuvan university, nepal * corresponding author: e-mail :bhrigunandansingh@yahoo.com article history: received 22 october, 2012; accepted 14 november, 2012 abstract we report surface tension of two weakly segregating alloys al-ga and cd-in in molten state at temperatures of 1023 k and 800 k respectively using different approaches. our analysis based on different assumptions reveal that the metal with lower surface tension tends to segregate on the surface of molten alloy and the metal with higher surface tension tends to segregate in the bulk. different approaches predict consistency in the values of the surface tension of al-ga liquid alloy that increases with increase in bulk concentration of aluminium in the alloy with all values smaller than the ideal values. in cd-in alloy the models reveal no such regularity in the surface tension; it varies slightly from the ideality. keywords: concentration; surface tension; surface segregation; order energy parameter; activity coefficients 1. introduction the surface tension is one of the important thermo-physical properties of mixing of liquid metallic alloys. a good knowledge of surface tension is required in many fields of engineering and metallurgical science. the processing of materials and the production in metallurgical industry are very important aspects of modern technology. in many phenomena such as, heterogeneous catalysis, welding, corrosion, gas absorption, nucleation of gas bubbles, nucleation and growth of nonmetallic inclusions and slag/metal reaction and kinetics of phase transformation, the role of surface tension is crucial [1]. the motivation of study of surface properties of liquid alloys thus stems from such importance of the surface tension. the study in general leads to expansion of knowledge in the field of material science and engineering for producing construction materials of enhanced properties such as increased mechanical strength, heat and chemical resistance, a wider range of colour not found naturally and even economic from the point of view of production costs. in this context, we have chosen two weakly interacting binary molten alloys, r. p. koirala et al. / bibechana 9 (2013) 103-112 : bmhss, p.104 (online publication: nov., 2012) one of aluminium and the other of cadmium namely al-ga and cd-in for investigation of their surface properties. al-ga alloy is reported to split up water spontaneously to generate hydrogen in large scale on demand which can keep away unnecessary storage of hydrogen [2]. cd-in alloys are common used in applications which include bearing assembly, ballast, casting and radiation shielding. eutectic cd-in alloy (composition 25% cd and 75% in by weight) is known to be a desirable solder in electro-deposition for obtaining superior strength joints in delicate electrical fabrication of transistor electrodes in electronic circuits [3]. the surface tension is very important in physical and chemical contamination, particularly at high temperatures. but the experimental determination of surface tension at different temperatures involves several difficulties in many cases. thus there is a strong need of theoretical studies and for this reason theoreticians have employed several models [4-15] for the study of thermodynamic and surface properties of binary liquid alloys. we have employed the formulations mentioned in the papers of prasad et al. [4], novakovic [5], march and alonso [6], and butler [7-8] for the comparative study of concentration dependence of surface properties for al-ga liquid alloy at 1023 k and the first three formulations for the cd-in alloy at 800 k. most of the theoretical models for determining the surface tension require the inputs from the thermodynamic data. the statistical formulations of prasad et al. and novakovic require order energy input, estimated from thermodynamic data, for the computation of surface concentration and surface tension. the value of the thermodynamic order energy parameter can be obtained from consideration of different theoretical models. as the values of concentration fluctuation, scc(0) computed directly from activity data [16] for the liquid alloys al-ga and cd-in at temperatures of 1023 k and 800 k respectively are all slightly greater than the ideal values, the alloys are weakly segregating; and hence we have used quasi-chemical approximation (qca) for regular alloys [13] to estimate the required thermodynamic parameters for the alloys. the thermodynamical treatment of guggenheim is generally applied to determine the surface tension of the binary liquid alloys in which the surface tension varies with concentration in a monotonic way between the values of the surface tension of two pure metals forming the alloys [6]. in butler’s monolayer model [7], excess free energy of mixing is used to calculate both surface concentration and surface tension. in the next section, the basic expressions for the formalism used in calculations are outlined. section 3 gives the result and discussions of the work and conclusions are presented in section 4. 2. formalism for comparative study of surface properties such as surface concentration and surface tension of al-ga and cd-in alloys in molten state respectively at temperatures of 1023 k and 800 k, we have employed the following treatments. 2.1. consider one mole of a binary liquid alloy a-b consisting of na ( nxa= ) atoms of a-component and nb ( nx b= ) atoms of b-component in the bulk phase, n being the total number atoms, and xa and xb are the concentrations expressed in mole fractions such that .1xx ba =+ in the statistical formulation of prasad et al. [4], a binary liquid alloy is considered to have a layered structure near the surface with a thermodynamic equilibrium existing between the species at the surface r. p. koirala et al. / bibechana 9 (2013) 103-112 : bmhss, p.105 (online publication: nov., 2012) and in the bulk. there is direct influence of bulk thermodynamic properties of liquid alloys on their surface properties. the expressions that connect the surface properties namely surface tension, γ of a binary liquid alloy and surface concentrations of the alloy component metal with the thermodynamic properties such as chemical activity, )b,ai(i =γ and interaction energy parameter, w at a given temperature, t have been derived in this model [4] in the following form: α ++ γα +γ=γ w ])x(q)x(p[ x x nl tk 2 b 2s b aa s ab a (1a) α ++ γα +γ=γ w ])x(q)x(p[ x x nl tk 2 a 2s b bb s bb b (1b) where aγ and bγ are surface tensions of pure components a and b respectively; kb stands for boltzmann constant; xa and xb are bulk concentrations; s ax and s bx are surface concentrations; and aγ and bγ are the bulk activity coefficients of the alloy components a and b respectively. the mean atomic surface area,α is given as ∑ α=α iix )b,ai( = (2) where the atomic area of hypothetical surface for each component is given as [4]: 3/2 aii )n/(102.1 ω=α (3) where iω is the molar volume of species i and na stands for avogadro's number. p and q are surface coordination fractions which are defined as the fractions of the total number of nearest neighbours made by atom within its own layer and that in the adjoining layer. for p and q the following relation is available [4, 9]: 1q2p =+ (4) for closed packed structures the values of these parameters are taken as 0.5 and 0.25 respectively. the ordering energy term w is a temperature dependent quantity and for an alloy at a given temperature, it can be estimated as a model fit parameter in qca [13]. qca for regular binary liquid alloys assumes the homo-coordination of like atoms at equivalent sites that results in the formation of self-associates of types aµ and .bν in qca, the following standard thermodynamic expressions for the free energy of mixing for the binary system, gm and chemical activities of the components, aa and ab are used to estimate the best fit value for w: rt w )xnx()1()]1(lnxlnx[ rt g baba m +ϕ−ϕ+ϕ−+ϕ= (5) r. p. koirala et al. / bibechana 9 (2013) 103-112 : bmhss, p.106 (online publication: nov., 2012) rt w )1( x ln1aln 2 a a ϕ−+ ϕ −ϕ+= (6) rt w n)n1()1(lnaln 2 b ϕ+−ϕ+ϕ−= (7) here, r is molar gas constant; ba a xnx x + =ϕ with µ ν =n = ratio of self-associates. 2.2. the surface tension of regular binary liquid alloys in which no complexes are formed can be examined by the application of quasi-lattice theory [5,17]. the following pair of equations are available for the theoretical investigation of the surface tension of the binary liquid alloys :         λ+ −+λ − −+λλ+ −+λλ+ α + α − +γ=γ a ba ba s s b s a s b a s ab a x)1( )xx( lnq )xx()1( )xx()1( nlp 2 tkz x x nl 2 )pz2(tk (8a)         λ+ −+λ − −+λλ+ −+λλ+ α + α − +γ=γ b ab ab s s a s b s b b s bb b x)1( )xx( lnq )xx()1( )xx()1( nlp 2 tkz x x nl 2 )pz2(tk (8b) here z is co-ordination number in the bulk and all the other notations have the same meaning as those in eqs. (1a-1b), with λ as the concentration dependent auxiliary variable defined in terms of the order energy parameter, w through the following equation [5] 2/12 bba ]}1)tzk/w2(exp{xx41[ −+=λ (9) the function sλ for surface is obtained from eq. (9) by substituting the bulk concentration xa by the surface concentration s ax and the coordination number z by coordination number of the surface atoms, z s . the value of z s is calculated from its relation with z given by [1] z)qp(z s += (10) 2.3. in third approach the standard expression for obtaining the surface tension,γ of a binary liquid alloy which usually varies with concentration x in a smooth way between the surface tension of the two pure metals of the alloy, is expressed as follows [6]: )(expx)(exp)x1()(exp ba γβα−+γβα−−=γβα− (11) here x represents the concentration of the component b with smaller surface tension; aγ and bγ are the surface tensions of the components a and b respectively at the temperature of investigation, t; and the r. p. koirala et al. / bibechana 9 (2013) 103-112 : bmhss, p.107 (online publication: nov., 2012) term tk/1 b=β , kb being boltzmann constant. the symbol α denotes the mean atomic surface area of the alloy, which can be calculated as function of bulk concentration from eq. (2). 2.4. butler’s formulation [7] is based on the assumption of monatomic surface layer which is considered as a separate phase that is in thermodynamic equilibrium with the bulk. the surface tension, γ of a binary liquid solution in this model can be expressed as: i b i s i 2 b b s b 1 b a s a ........... α µ−µ == α µ−µ = α µ−µ =γ (12) where b i s i , µµ and iα denote respectively the chemical potential in the hypothetical surface, and that in the bulk, and the molar surface area of pure component i. from equation (12), the expressions for the surface tension has been derived in terms of partial excess free energy of mixing, b,e ig in the bulk and s,e ig at the surface, and surface concentrations, b ix in the bulk and s ix at the surface ( b,ai = ), in the following forms [8,18]: ] x x lnrtgg[ 1 b a s ab,e a s,e a a a +− α +γ=γ (13a) ] x x lnrtgg[ 1 b b s bb,e b s,e b b b +− α +γ=γ (13b) where aγ and bγ are surface tension of pure metals a and b respectively. the partial excess free energy of mixing of component i at the surface and that in the bulk are related to each other through a parameter β as [8]: b,e i s,e i g g =β (14) the value of β is assumed a constant number in the calculations. the area of monatomic surface layer for the component i is commonly calculated from the following relation [19] 3/2 i 3/1 ai nl ω=α (15) where 091.1l = is called geometrical factor for the closed packed atoms of the surface monolayer, na is avogadro’s constant and iω stands for the molar volume of the component i. the molar volume of a component can be calculated from its molar mass and density. solving eqs. (13a) and (13b) together for the surface concentration using the partial excess free energy of mixing in the bulk, one can work out the surface tension of a binary liquid solution. 3. results and discussion 3. 1. for the computation of surface properties namely surface concentration, surface tension of the binary liquid alloys using the equations (1a) and (1b), we need experimental data of density, surface tension and partial excess free energies of mixing of the components at the working temperature. we calculated the r. p. koirala et al. / bibechana 9 (2013) 103-112 : bmhss, p.108 (online publication: nov., 2012) density and surface tension for each of the components al, ga, cd and in at the respective working temperature by using their temperature coefficients and the values at their respective melting temperatures in the following equations [20]: )tt( t )t( mm − ∂ ρ∂ +ρ=ρ (16) )tt( t )t( mm − ∂ σ∂ +σ=σ (17) where t and tm are respectively the temperature of investigation and melting temperature; and t∂ ρ∂ and t∂ σ∂ represent the temperature coefficient of density and temperature coefficient of surface tension for each component metal of the alloys. the other parameter that is required for calculating surface tension is the interaction energy parameter, w. we have estimated the values of w separately for al-ga and cd-in alloys by simultaneously fitting equations (5), (6) and (7) to the experimental data of free energy of mixing and chemical activities [16] of respective alloy throughout whole concentration range. thus having numerical values of all the terms, surface concentrations of aluminium in al-ga alloy and cadmium in cd-in alloy have been obtained separately as function of bulk concentration by concurrently solving the equations (1a) and (1b). in both cases surface concentrations of a-component of the al-ga and cd-in alloys are found to increase with the increase in their bulk concentrations (fig. 1 & fig. 3). due to a significant difference in the values of surface tension of component metals in the al-ga liquid alloy at 1023 k, the mixing shows strong segregation of the component with smaller surface tension at the surface and the other in the bulk. on the other hand, with very comparable values of the surface tension of the metals in cd-in liquid alloy at 800 k, surface concentrations of components do not differ much from the bulk concentrations. fig. 1: surface concentration versus bulk concentration of al-component in al-ga alloy at 1023 k: broken line -approach 1; circles-approach 2; solid line-approach 4. r. p. koirala et al. / bibechana 9 (2013) 103-112 : bmhss, p.109 (online publication: nov., 2012) . fig. 2: surface tension of al-ga alloy at 1023 k versus bulk concentration of al-component: crosses -approach 1; circles-approach 2; broken curve(lower)-approach 3; solid line-approach 4; broken line (upper)ideal. using the obtained values of surface concentrations, we computed the surface tensions of the al-ga and cd-in liquid alloys at temperatures of 1023 k and 800 k respectively for whole concentration range. this approach predicts that the surface tension of al-ga alloy increases with increase in bulk concentration of aluminium part in the alloy (fig. 2). in contrast, very small variation is noticed in the surface tension of the cd-in alloy with the bulk concentration, through a flat peak around the equiatomic composition (fig. 4). further, it is noted that the computed values are found to be all smaller than the corresponding ideal values ( bbaaid xx γ+γ=γ ) in al-ga alloy but greater in cd-in alloy (from first approach) even though both alloys are weakly segregating. however, the surface tension of the cd-in alloy liquid alloy at 800 k is found to be less than the ideal values computed from the second approach. the sign and size of difference in the surface tension of alloy components a and b and the interaction energy parameter w together thus decide the concentration dependence of surface tension of the alloy. 3.2. eqs. (8a) and (8b) were solved together for the surface concentration of component-a of both the alloys at all bulk concentrations by using their interaction energies obtained from the application of quasichemical approximation to the alloys separately. surface tension and densities of the components calculated above from eqs. (16) and (17) were used in solving the equations for surface concentrations. the surface concentration of al in al-ga alloy at 1023 k have been found to be very nearly equal to those obtained from the above approach at the corresponding concentrations with nonlinear variation with bulk composition of al-component. (fig.1). however, in cd-in alloy at 800 k surface concentration is found to vary almost linearly with bulk composition (fig. 3). this approach predicts extremely matching result for the surface tension of al-ga system with the result of first approach, and for cd-in system, the result shows very small variation in surface tension values (fig. 2 & fig. 4). r. p. koirala et al. / bibechana 9 (2013) 103-112 : bmhss, p.110 (online publication: nov., 2012) fig. 3: surface concentration of cd-component versus bulk concentration in cd-in alloy at 800 k : solid curve -approach 1; broken line-approach 2. 3.3. the concentration dependence of surface tension is studied by computing surface tensions for the alloys from eq. (11). the surface tensions of al-ga are in extremely good agreement with the results of above mentioned approaches. the values of surface tension of cd-in alloy calculated from this approach are found to lie between the results of the above two sections (3.1. & 3.2.) for whole concentration range; and are almost equal to the ideal values (fig. 2 & fig. 4). fig. 4: surface tension of cd-in alloy at 800k versus bulk concentration of cd-component: solid curve approach 1; circles-approach 2; crosses-approach 3; broken line ideal. it is to be noted that for alloys with component metals having large difference in their surface tension values, the theoretical models we are using, give well matching result for the surface properties. for alloys with metals having very comparable surface tensions, the values of surface tension predicted by different approaches are not matching so exactly. r. p. koirala et al. / bibechana 9 (2013) 103-112 : bmhss, p.111 (online publication: nov., 2012) 3.4. finally we employed butler’s model for the computation of surface concentration and surface tension of the al-ga alloy. the partial excess free energies of mixing of the pure components of the alloys at the temperature of investigation were taken from the ref. [16]. both the surface concentration of acomponent and the surface tension of the alloy are found to have nonlinear increment with the increasing bulk concentration (fig. 1 & fig. 2) as observed in the first two approaches. we do not have experimental values of surface tension to compare our result. however, it is mentioned that the models which we have used in present work have been successfully used by several workers to compute the surface tension of metallic solution. 4. conclusion this theoretical study shows that the metal with lower surface tension tends to segregate on the surface of molten alloy while the metal with higher surface tension tends to segregate in the bulk. when there is a larger difference in surface tension between the solvent and solute, the segregating behaviour of the component is more significant. in al-ga system at 1023 k, there is consistency in the values of surface tension obtained from different approaches, with small negative deviations from ideality whereas in cd-in system at 800 k, such consistency is not observed in the computed values of the surface tension. acknowledgements we are grateful to prof. dr. l.n. jha (head, central department of physics, t.u., nepal), prof. dr. pradeep raj pradhan and dr. i.s. jha (post-graduate department of physics, m.m.a.m. campus, biratnagar, nepal) for fruitful suggestions and inspiring discussions. references [1] b.c. anusionwu, c. a. madhu, c. e. orji, pramana, j. physics, 72 (2009) 951. [2] woodall jerry, m.; ziebach, jeffrey; allen charle’s r., the science and technology of al-ga alloys as a material for energy storage, transport and splitting water, proc. of 2nd energy nanotechnology international conference, enic, (2007) 45014. [3] george l. schnable, john g. javes, j. electrochem. soc.,105 (1958) 84. [4] l.c. prasad, r.n. singh, g.p. singh, phys. chem. liq., 27 (1994) 179. [5] r. novakovic, j. non-cryst. solids, 356 (2010) 1593. [6] n.h. march and j.a. alonso, phys. chem. of liq., 46 (2008) 522. [7] j.a. butler, proc. roy. soc. a , 135 (1932) 348. [8] d. adhikari, i.s. jha, b.p. singh, adv. mat. lett., 3 (2012) 226. [9] r. novakovic, e. ricci, d. giuranno, f. gnecco, surface science, 515 (2002) 377. [10] b.p. singh, d. adhikari, i.s. jha , b.c. kumar, s.k. chaudhary, s.k. jayaswal, r.p. koirala, bibechana, 8 (2012) 81. [11] d. adhikari, b.p. singh, i.s. jha, j. molecular liquids , 167c (2012) 52. [12] b. p. singh, d. adhikari, i.s. jha, j. kumar, r. p. koirala, materials sciences and applications, 2 (2011) 1139. [13] r.n. singh, f. sommer, rep. prog. phys., 60 ( 1997) 57. [14] b.p. singh, d. adhikari, i.s. jha, b.k. singh, bibechana, 7 (2011) 1. [15] d. adhikari, physica b, 406 (2011) 445. [16] r. hultgren, p.d. desai, d.t. hawkins, m. gleiser, and k.k. kelly, selected values of the thermodynamic properties of binary alloys, asm, metal park (1973). r. p. koirala et al. / bibechana 9 (2013) 103-112 : bmhss, p.112 (online publication: nov., 2012) [17] e.a. guggenheim, mixtures, oxford university press, london (1952). [18] j. lee, w. shimoda, t. tanaka, materials transactions, 45 (2004) 2864. [19] t.p. hoar, d.a. melford, trans. faraday soc., 53 (1957) 315. [20] brandes, smithells metals reference book, sixth edition, (1983), sec. 14-6. microsoft word jagadeesh bhattarai.doc jagadeesh bhattarai / bibechana 8 (2012) 8-16 : bmhss, p. 8 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana a non–destructive compositional analysis of thin surface films formed on w– xta alloys by angle resolved x–ray photoelectron spectroscopy jagadeesh bhattarai central department of chemistry, tribhuvan university, kathmandu, nepal. e-mail:bhattarai_05@yahoo.com article history: received 22 may, 2011; accepted 11 june, 2011 abstract synergistic effect of the simultaneous additions of tungsten and tantalum in the extremely high corrosion resistance properties of the spontaneously passivated sputter–deposited w–xta alloys was investigated using a non−destructive angle resolved x−ray photoelectron spectroscopy (angle resolved xps) techniques in this study. in−depth surface analyses of the thin passive films formed on the spontaneously passivated amorphous/nanocrystalline w–xta alloys using angle resolved xps analyses revealed that the high corrosion resistance of the alloys is mostly due to the formation of homogeneous passive double oxyhydroxide films consisting of w ox and ta 4+ cations with a small concentration gradients in–depth particularly after immersion between 20– 168 h in 12 m hcl solution open to air at 30°c. consequently, tantalum metal acts synergistically with tungsten in enhancing the spontaneous passivity as well as the high corrosion resistance of the sputter–deposited binary w–xta alloys in 12 m hcl solution. keywords: sputter deposition; w–xta alloys; 12 m hcl; take–off angle 1. introduction an angle resolved xps proves as one of the promising in−depth compositional analyses of thin films to investigate chemical compositions, oxidation states, chemical shifts, binding energies and electronic structures of the surface films [1−7]. for this purpose the non−destructive angle resolved xps technique is widely used by a number of researchers to gain about the in−depth concentration profiles of the passive films. in principle, the in−depth information of the passive film depends on the effective escape depth of the ejected photoelectrons, which increases with an increase in the take−off angle of photoelectrons relative to the surface of the sample specimen [1−8]. therefore, the surface sensitivity is varied by changing the take−off angle of photoelectrons (θ) as explain by equation (1). in general, the surface sensitivity is varied by changing the take−off angle of photoelectrons. at a lower take−off angle of photoelectrons, the intensity signals (i) from the sample species located in the exterior part of the surface films are enhanced. therefore, the apparent compositions of the surface films are changed with the take−off angle of photoelectrons in the angle resolved xps measurements. jagadeesh bhattarai / bibechana 8 (2012) 8-16 : bmhss, p. 9 i = k exp(−z/λ sinθ) (1) where, i is the intensity of the ejected photoelectrons, k is constant, z is the depth of the surface and θ is the take−off angle of the ejected photoelectrons. in recent years, angle resolved xps (arxps) technique is one of the very useful in−depth surface characterization tools for corrosion scientists to study the mechanism of high corrosion resistance of materials during last four decades after a valuable contribution of kai siegbahn and his research groups [9]. it allows us to examine the formation of homogeneous or heterogeneous passive surface films formed on the corrosion−resistant alloys [8,10−19]. tungsten and tantalum are effective elements in enhancing the corrosion resistance of alloys in aggressive environments. several surface studies have been carried out for a better understanding of the role of tungsten in the corrosion resistance properties of the sputter−deposited binary [12,14−16,18,20−37] and ternary [19,38−43] tungsten−based alloys in aggressive environments. it is reported that the addition of tungsten to amorphous fe−p−c alloys with and without chromium [44,45] and to the amorphous ni−p alloys [46] is effective in improving the corrosion resistance in aggressive hydrochloric acid solutions. similarly, tantalum is widely known for its superior corrosion resistance in aggressive acidic media. amorphous nickel−base alloys containing certain amounts of tantalum exhibit very high corrosion resistance in boiling concentrated acids [47,48]. lee et al. reported a beneficial effect of tantalum to improve the corrosion resistance of nickel base alloys in 12 m hcl [48,49]. a series of sputter−deposited binary [11,13,20,50,51] and ternary [52,53] tantalum−containing alloys showed high corrosion resistance due to spontaneous passivation in aggressive media. in particular, the sputter-deposited w-xta alloys were passivated spontaneously and showed significantly high corrosion resistance in 12 m hcl solution. their corrosion rates were found about two orders of magnitude lower than that of sputter-deposited tungsten and even lower than that of tantalum. the conventional xps analyses confirmed that the formation of the spontaneously passivated films formed on the alloys composed of double oxyhydroxide of tungsten and tantalum ions was found to be responsible for their higher corrosion resistance those of alloying elements of the wxta alloys in 12 m hcl solution. in this context, the present work is aimed to clarify the mechanism of the higher corrosion resistance of the sputter–deposited nanocrystalline w–23ta and w–60ta alloys than those of tungsten and tantalum in 12 m hcl solution open to air at 30°c using angel resolved xps techniques. 2. materials and experimental methods the sputter–deposited w–23ta and w–60ta alloys were characterized as nanocrystalline single–phase solid solution having an apparent grain size of 10–20 nm from xrd patterns using scherrer’s formula [54]. the compositions of the alloys hereafter are all denoted in atomic percentage (at%). prior to the corrosion tests and angle resolved xps analyses, the sputter– deposited w–xta alloy specimens were mechanically polished with a silicon carbide paper up to grit number 1500 in cyclohexane, degreased by acetone and dried in air. the average corrosion rate of the alloys was estimated from weight loss after immersion for 168 h in 12 m hcl solution open to air at 30°c. the composition of the spontaneously passivated films formed on the w–xta alloys was analyzed by angle–resolved xps. before and after immersion in 12 m hcl solution, xps spectra were measured by a shimadzu esca–850 photoelectron spectrometer with mg k (hν = 1253.6 ev) radiation for surface analyses including the in–depth surface compositions of the alloys. xps spectra for both the nanocrystalline w–23ta and w–60ta alloys over a wide binding energy region (that is, 0–1000 ev) exhibited peaks of tungsten, tantalum, carbon, oxygen and chlorine. jagadeesh bhattarai / bibechana 8 (2012) 8-16 : bmhss, p. 10 the most intense peaks of the w 4f, ta 4f, c 1s, o 1s and cl 2p electrons were measured in the binding energy range of 20 ev for all spectra except for w 4f and ta 4f electrons. the most intense peaks of the w 4f and ta 4f spectra are located very close to each other and they are partially overlapped as discussed elsewhere [20,55]. hence, the w 4f and ta 4f electrons were measured in the binding energy range of 30 ev [20,55]. the peak shift (chemical shift) caused by the charging effect was corrected using the difference the measured binding energy of the contaminant c 1s peak and assumed value of 285.0 ev. for the alloy specimens after immersed in 12 m hcl solution, a very weak cl 2p spectrum was detected at about 199.0 ev. however, the concentration of the chloride ion was not considered for the quantitative analyses of the surface films in this study because the intensity of the chloride ion is very low for quantitative analyses. the o 1s spectrum was composed of two peaks; the lower binding energy peak at 530.4 ev was assigned to om oxygen, and the higher binding energy peak at 532.3 ev was assigned to oh oxygen [56]. the spectra from the w–xta alloys constituents indicated the presence of the oxidized and metallic species; the former comes from the surface film and the latter from the underlying alloy surface. the measured spectrum of w 4f electron was separated into w ox 4f and w m 4f and the measured spectrum of ta 4f electron was separated into ta 4+ 4f and ta m 4f for the sputter–deposited w–xta alloys. furthermore, the w m 4f spectrum was consisted of w 4+ 4f, w 5+ 4f and w 6+ 4f spectra. the integrated intensities of the w 0 4f, w 4+ 4f, w 5+ 4f, w 6+ 4f, ta m 4f, and ta 4+ 4f were obtained by the same method as those described elsewhere [20,55]. after the integrated intensities of these all spectra observed from the surfaces of the sputter−deposited w−xti alloys were obtained, the compositions and thickness of the passive films and the compositions of the underlying alloy surfaces were quantitatively determined using three layers model proposed by asami et al. [56,57]. the diagrammatic sketch of the three layers model is shown in fig. 1. for angle–resolved xps, the angle between the alloy specimen surface and the direction of photoelectron to the detector (take–off angle of photoelectrons) was changed by using tilted–specimen holders at 30°, 45°, 60° and 90° as discussed elsewhere [55]. the photo–ionization cross–section of the w 4f and t a 4f electrons relative to the o 1s electrons used were 2.97 [58] and 2.617 [59], respectively. fig. 1: a diagrammatic sketch of the three layers model for the quantitative xps analyses of the surface films formed on the sputter–deposited w–xta alloys. jagadeesh bhattarai / bibechana 8 (2012) 8-16 : bmhss, p. 11 3. results and discussion it was reported that the synergistic effect of tungsten and tantalum in forming the double oxyhydroxide was responsible for the higher corrosion resistance of the sputter−deposited amorphous/nanocrystalline w−xta alloys than those of the alloy−constituting elements in 12 m hcl solution open to air at 30°c from the conventional xps analyses. however, the experimental results of the angle resolved xps measurements are presented here to clarify the mechanism of showing the higher corrosion resistance behavior of the sputter−deposited binary w−xta alloys than those of alloy−constituting elements in 12 m hcl. because, the in−depth surface analyses of the spontaneously passivated double oxyhydroxide films formed on the w−xta alloys using angle resolved xps measurements give very important information for a better understanding of the effects of tungsten and tantalum additions in the corrosion−resistant behavior of the alloys. an information about in−depth composition changes of the spontaneously passivated films formed on the w−23ta and w−60ta alloys were obtained by a non−destructive depth profiling technique of the angle resolved xps to know whether the spontaneously passivated films formed on the alloys are homogeneous or not. the spectra from the w–xta alloys constituents indicated the presence of the oxidized and metallic species; the former comes from the surface film and the latter from the underlying alloy surface. the measured spectrum of ta 4f electrons was separated into ta 4+ 4f and ta m 4f spectra as shown in fig. 1 and the measured spectrum of w 4f electrons was separated into w m 4f and w ox 4f as shown in fig. 1 for the sputter–deposited w–45ta alloy in the given conditions [55]. the ta 4+ 4f and ta m 4f spectra were consisted of lower and higher binding energy peaks corresponding to ta 4+ 4f7/2 and ta 4+ 4f5/2 electrons, and ta m 4f7/2 and ta m 4f5/2 electrons, respectively, as shown in fig. 1. furthermore, the w m 4f spectrum was consisted of lower and higher binding energy peaks corresponding to w m 4f7/2 and w m 4f5/2 electrons. similarly, the w ox 4f spectrum was also composed of three doublets of the overlapped spectra of three oxidized species, that is, doublets of w 4+ 4f7/2 and w 4+ 4f5/2 ; w 5+ 4f7/2 and w 5+ 4f5/2 ; and w 6+ 4f7/2 and w 6+ 4f5/2 electrons as shown in fig. 1. the quantitative result of the in−depth compositional change in the surface films formed on the sputter−deposited w−xta alloys using angle resolved xps analysis is shown in fig. 2. figures 2 (a) and 2 (b) show the changes in apparent cationic fractions in the spontaneously passivated films and the apparent atomic fractions in the underlying alloy surfaces of the w−23ta and w−60ta alloys, respectively, after immersion for different periods of time in 12 m hcl solution open to air at 30°c, respectively, as a function of take−off angle of photoelectrons. it is clearly raveled that tantalum is concentrated in the spontaneously passivated films, while tantalum is deficient in the underlying alloy surfaces. the concentration of tantalum ion is slightly higher in the exterior part (at take−off angle of 30°) of the passive films formed on both the sputter−deposited w−23ta and w−60ta alloys by immersion for 20 hours or more in 12 m hcl, while there is also small concentration gradient of cations in−depth of the underlying alloys. on the other hand, the concentration of tungsten is slightly higher in the exterior part (at take−off angle of 90°) of the underlying alloy surfaces and the tungsten concentration decreases with take−off angles after immersion in 12 m hcl solution. jagadeesh bhattarai / bibechana 8 (2012) 8-16 : bmhss, p. 12 fig. 2: changes in the apparent cationic fractions in the passive film and the atomic fractions in the underlying alloy surface for the (a) w−23ta and (b) w−60ta alloy as a function of take−off angle of photoelectrons. for a better understanding of the role of tungsten ions in the passive films formed on the alloys, the changes in the ratios of w 4+ , w 5+ and w 6+ ions in the surface films were determined quantitatively. figure 3 shows the concentration ratios of w 4+ , w 5+ and w 6+ ions to the total tungsten ions in the spontaneously passivated films formed on the w−23ta and w−60ta alloys after immersion for 20 h in 12 m hcl solution open to air at 30°c, as a function of take−off angle of photoelectrons. after immersion for 20 h in 12 m hcl solution, the ratio of w 6+ ions in the passive films formed on both the w−23ta and w−60ta alloys are significantly higher than those of w 4+ and w 5+ ions in the spontaneously passivated films. w 6+ ion decreases with increasing take−off angle of photoelectrons, while w 4+ ion increases with take−off angles. the ratio of w 5+ ion remains almost constant with take−off angle of photoelectrons. accordingly, w 4+ ion is particularly concentrated in the interior (at take−off angle of 90°) of the spontaneously passivated film formed on the sputter−deposited w−xta alloys, while the concentration of w 6+ ion is higher in jagadeesh bhattarai / bibechana 8 (2012) 8-16 : bmhss, p. 13 the exterior (at take−off angles of 30 to 60°) of the spontaneously passivated films. it is generally known that air exposure of the specimen during transfer from the electrolyte to the xps analyzing chamber give rise to oxidation of w 4+ to w 6+ ion. accordingly the relative ratio of w 6+ ion is higher in the exterior of the surface films and decreases with the depth of the passive film. fig. 3: changes in the apparent cationic fractions in the passive film and the atomic fractions in the underlying alloy surface for the (a) w−23ta and (b) w−60ta alloys, as a function of take−off angle of photoelectrons. in general, one of the characteristic of the thin passive films is the concentration of oxygen species in the spontaneously passivated films formed on the corrosion−resistant alloys. figure 4 shows the changes in the ratios of [o 2−]/[cations] and [oh]/[cations] in the spontaneously passivated films formed on the sputter−deposited amorphous w−23ta and w−60ta alloys after immersion for 20 h in 12 m hcl solution open to air at 30°c, as a function of take−off angle of photoelectrons. the ratios of [o 2−]/[cations] slightly increase with the take−off angles and the ratios of [oh]/[cations] significantly decrease with take−off angles in the films formed on the w−xta alloys. consequently, the interior part of the passive films formed on the sputter−deposited w−xta alloys is rather dry and well developed by m−o−m bridging, while the exterior part of the passive films formed on the alloys is slightly wet with oh− ion and h2o. jagadeesh bhattarai / bibechana 8 (2012) 8-16 : bmhss, p. 14 fig. 4: changes in the ratios of [o 2−]/[cations and [oh−]/[cations] in the surface films formed on the w−23ta and w−60ta alloys in the given conditions, as a function of take−off angle of photoelectrons. 4. conclusion the mechanism of the synergistic effect of tungsten and tantalum metals enhancing the higher corrosion resistance of the sputter–deposited nanocrystalline w–23ta and w–60ta alloys than those of alloy–constituting elements has been studied using angle resolved xps measurements in 12 m hcl solution open to air at 30°c. the following conclusions are drawn: 1. the angle–resolved xps measurement revealed that all cations of the binary w−xta alloys are distributed homogeneously in the spontaneously passivated films formed on the alloys. the higher corrosion resistance of the alloys than those of the alloying elements is mostly due to the formation of the homogeneous passive films composed of both w 4+ and ti 4+ ions with a small concentration gradient in–depth. 2. the w 4+ ion is particularly concentrated in the interior of the spontaneously passivated films formed on both the w−23ta and w−60ta alloys, while the concentration of w 6+ ion is higher in the exterior of the passive films. 3. the interior part of the passive films formed on the w−xta alloys is rather dry and well developed by m−o−m bridging, while the exterior part of the passive films formed on the alloys is slightly wet with oh− ion and bound h2o molecule. acknowledgements the author is very thankful to professors emeritus; dr. koji hashimoto 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[59] j. h. kim, h. yoshioka, h. habazaki, a. kawashima, k. asami and k. hashimoto, corros. sci. 33 (1992) 1507. microsoft word n. pahari. _34-44_.doc n.p. pahari / bibechana 10 (2014) 20-30 : bmhss, p.20 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana on 2 normed space valued paranormed null sequence space (c0 ( s, αααα–, u– , ||. , .|| ),t ) narayan prasad pahari central department of mathematics, tribhuvan university, university campus, kirtipur, kathmandu, nepal email: nppahari @ gmail.com article history: received 5 september, 2013; accepted 23 september, 2013 abstract in this paper we introduce and study a new class c0 ( s, α–, u – , ||. , .|| ) of sequences with values in 2normed space as a generalization of basic null sequence space c0. we investigate some conditions pertaining to the containment relations of the class c0 ( s, α–, u– , ||. , .|| ) in terms of different α– and u – and explore the linear topological structures of the space c0 ( s, α–, u– , ||. , .|| ) by endowing it with a suitable natural paranorm. keywords: 2normed space, 2–banach space, paranormed space, sequence space. 1. introduction and preliminaries before proceeding with the main results, we recall some of the basic notations and definitions that are used in this paper. the notion of 2–normed space was initially introduced by s. gäahler [1] as an interesting linear generalization of a normed linear space, which was further studied by j.a. white and y.j. cho [2], k.iseki [3], r. freese et al. [4,5], w.raymond et al. [6] and many others. recently a lot of activities have been started by many researchers to study this concept in different directions, for instances e. savas [7], h. gunawan and h. mashadi [8] , j.k. srivastava and n.p. pahari [9] , m. açikgöz [10] and others. let s be a vector space of dimension d > 1 over k, the field of real or complex numbers. a 2 norm on s is a real valued function ||. , .|| on s × s satisfying the following conditions: 2n1: || ξ, η || ≥ 0 and || ξ, η || = 0 if and only if ξ and η are linearly dependent; 2-n2: || ξ, η || = || η, ξ ||, for all ξ, η ∈ s; 2-n3: || γξ, η || = |γ | ||ξ¸ η ||, where γ∈k and ξ, η ∈ s;and 2-n4 : || ξ1 + ξ2, η || ≤ || ξ1, η || + || ξ2, η || ,for all ξ1 , ξ2 and η∈ s. the pair (x, ||. , .||) is called a 2–normed space. thus the notion of 2–normed space is just a two dimensional analogue of a normed space . recall that (x, ||. , .||) is a 2-banach space if every cauchy sequence in x is convergent to some x0 in x. n.p. pahari / bibechana 10 (2014) 20-30: bmhss, p.21 (online publication: dec., 2013) the pair (s, ||. , .||) is called a 2–normed space. thus the notion of 2–normed space is just a two dimensional analogue of a normed space . recall that (s, ||. , .||) is a 2-banach space if every cauchy sequence in s is convergent to some ξ0 in s. geometrically, a 2-norm function generalizes the concept of area function of parallelogram due to the fact that, in the standard case, it represents the area of the usual parallelogram spanned by the two associated vectors.for example, consider s = r2, being equipped with || ξ, η || = | ξ1η2 – ξ2η1|, where ξ = (ξ1, ξ2) and η = (η1 , η2). then (s, ||. , .||) forms a 2–normed space and || ξ, η || represents the area of the parallelogram spanned by the two associated vectors ξ and η. again, let s = r 3 and define the function ||. , .|| on s × s by || ξ, η || =       det      i j k ξ1 ξ2 ξ3 η1 η2 η3 where ξ = (ξ1, ξ2, ξ3) and y = (η1, η2, η3). obviously (s, ||. , .||) forms a 2–normed space. analogously, if (s , <. , .>) be a finite dimensional inner product space and ||. , .|| defined on s × s by || ξ, η || =      <ξ‚ξ > < ξ‚ η > < η‚ ξ > < η‚ η > , then we can see that (s, ||. , .||) satisfies all the conditions of 2–normed space. the notion of convergence has introduced by white and cho [2]. a sequence (ξn) in a linear 2– normed space s is convergent if there is an ξ ∈ s such that lim n→∞ || ξn – ξ, η || = 0, for each η ∈ s .it is said to be a cauchy if there are η and ν in s such that η and ν are linearly independent and lim m‚n→∞ ||ξm – ξn‚ η|| = 0 and lim m‚n→∞ ||ξm – ξn‚ ν|| = 0. a linear 2–normed space (s, ||.,.||) is called 2–banach space if every cauchy sequence in s is convergent to some ξ ∈ s. the notion of paranormed space is closely related to linear metric space , see a. wilansky [11]. a paranormed space (s, t ) is a linear space s with zero element θ together with a function t : s → r+ (called a paranorm on s) which satisfies the following axioms: pn1: t (θ) = 0; pn2: t (ξ) = t (–ξ) , for all ξ ∈ s; pn3: t (ξ + η) ≤ t (ξ) + t (η) , for all ξ , η ∈ s; and pn4: scalar multiplication is continuous i.e., if (γn) is a sequence of scalars with γn → γ as n → ∞ and (ξn) is a sequence of vectors with t (ξn − ξ) → 0 as n → ∞ then t (γn ξn − γξ) → 0 as n → ∞. note that the continuity of scalar multiplication is equivalent to (i) if t (ξn) → 0 and γn → γ as n → ∞, then t(γn ξn) → 0 as n → ∞ and n.p. pahari / bibechana 10 (2014) 20-30: bmhss, p.22 (online publication: dec., 2013) (ii) if γn → 0 as n → ∞ and ξ be any element in s, then t (γn ξ) → 0, see wilansky [11]. a paranorm is called total if t (ξ) = 0 implies ξ = θ, see a. wilansky [11]. the studies of paranorm on sequence spaces were initiated by maddox [12] and many others. srivastava and et al. [13-15], pahari [16], parashar and choudhary [17], bhardwaj and bala [18] and many others further studied various types of paranormed sequence spaces and function spaces. a sequence space s is said to be normal if ξ – = (ξk) ∈ s and α– = (αk) a sequence of scalars with |αk| ≤ 1, for all k ≥ 1, then α– ξ – = (αk ξk) ∈s . 2. the class c0 ( x, λλλλ – , u – , ||. , .|| ) of 2-normed space valued vector sequences let u– = (uk) and v– = (vk) be any sequences of strictly positive real numbers and λ – = (λk) and µ–= (µk ) be the sequences of non zero complex numbers. let ( x, ||. , .|| ) be the 2 normed space over the field c of complex numbers and θ denotes the zero element of x. let ω(x) denotes the linear space of all sequences x – = (ξk) and y– = (ηk ) with ξk , ηk ∈ x , k ≥ 1 with usual coordinate wise operations i.e., x – + y– = (ξk +ηk) and α x – = (αξk ) ,for each x – , y– ∈ ω (x) and α∈ c. we shall denote ω (c) by ω. further, λ– = (λk ) ∈ ω and x – ∈ ω (x ) we shall write λ– x – = (λk ξk ) . we now introduce the following classes of 2-normed space x–valued sequences c0 ( x, λ – , u– , ||. , .|| ) = {x– = (xk) ∈ ω(x ), xk ∈ x, k ≥ 1 satisfying || λk xk‚ y|| uk → 0 as k→ ∞ , for each y ∈ x }. in fact, this class is a generalization of the familiar sequence spaces, studied in srivastava et al. (1996) [12], srivastava (1996), pahari ( 2011) [16], pahari and et al ( 2011) [11] , using 2-norm . further, when λk = 1 for all k , then c0 ( x, λ – , u– , ||. , .|| ) will be denoted by c0 ( x, u– , ||. , .|| ) and when uk = 1 for all k, then c0 ( x, λ – , u– , ||. , .|| ) will be denoted by c0 ( x, λ – , ||. , .|| ). if uk = λk = 1 for all k , then the class c0 ( x, λ – , u– , ||. , .|| ) will be denoted by c0 ( x, ||. , .|| ) . further, when x = c we simply write c0 ( x, λ – , u– , ||. , .|| ) as c0 (λ – , u– , ||. , .|| ). 3. containment relations in this section, we investigate some inclusion relations of the class c0( s, ||. , .||, α–, u– ) arising in terms of different u– and α– . throughout, we denote sup uk =l for each k and for scalar α, a [α] = max (1, |α|). but when the sequences uk and vk occur, then to distinguish l we use the notations l(u) and l(v) respectively. theorem 3.1: for any u – = (uk), c0 ( s, α – , u – , ||. , .|| ) ⊂⊂⊂⊂ c0 ( s, β – , u – , ||. , .|| ) if and only if lim inf k    αk βk uk > 0. proof: n.p. pahari / bibechana 10 (2014) 20-30: bmhss, p.23 (online publication: dec., 2013) for the necessity, assume that c0 ( s, α– , u– , ||. , .|| ) ⊂ c0 ( s, β – , u– , ||. , .|| ) but lim infk    αk βk uk = 0. then we can find a sequence (k(n)) of integers such that 1 ≤ k(n) < k(n +1), n ≥ 1 for which n 2 |αk(n) | uk(n) < |βk(n)| uk(n) , for all n ≥ 1. ...( 3.1) now, corresponding to ρ ∈ s and ρ ≠ θ, we define the sequence ξ – = ( ξk) by ξk =   αk(n) -1 n-2/uk(n) ρ‚ if k = k(n) ‚ n ≥1 and θ‚ otherwise. ...( 3.2) then for k = k(n), n ≥ 1 ,we have || αk ξk‚ η|| uk = ||n-2/uk(n) ρ‚ η || uk(n) ≤ 1 n2 ||ρ‚ η || uk(n) ≤ 1 n2 a [ ||ρ‚ η|| l(u) ] → 0 as n→ ∞, where ||ρ, η|| uk(n) ≤ a [ || ρ, η|| l(u) ] for each n ≥ 1 is used and || αk ξk‚ η|| u k = 0, for k ≠ k(n) , n ≥ 1. this shows that ξ – ∈ c0 ( s, α–, u– , ||. , .|| ) . on the other hand, let us choose η ∈ s such that || w, η || = 1. then for k = k(n), n ≥ 1, and in view of (3.1) and (3.2) ,we have || βk ξk ‚η|| uk = || β k(n) ξ k(n) ‚η || u k(n) = 1 n 2 || w‚ η||uk(n)    αk(n) βk (n) uk(n) ≥ 1. this shows that ξ – ∉ c0 ( s, β – , u–,||. , .|| ),a contradiction. for the sufficiency, assume that lim infk    αk βk uk > 0.then there exists m > 0 such that m |βk| uk < |αk | uk for all sufficiently large values of k. let ξ – = (ξk) ∈ c0 ( x, α–, u– , ||. , .|| ) . then for each η ∈s, || αk ξk‚ η|| u k → 0 as k→ ∞ . now for each η ∈ s, ||βk ξk‚ η|| uk ≤ |αk| uk m ||ξk ‚η|| uk ≤ 1 m || αk ξk‚ η|| uk → 0 as k → ∞. this clearly implies that ξ – ∈ c0 ( s, β – , u– , ||. , .|| ) and hence c0 ( s, α–, u– , ||. , .|| ) ⊂ c0 ( s, β – , u– , ||. , .|| ). this completes the proof . theorem 3.2: for any u – = (uk), c0 ( s, β – , u – , ||. , .|| ) ⊂ ⊂ ⊂ ⊂ c0 ( s, α – , u – ,||. , .|| ) if and only if lim supk    αk βk uk < ∞∞∞∞. n.p. pahari / bibechana 10 (2014) 20-30: bmhss, p.24 (online publication: dec., 2013) proof: for the necessity, suppose that c0 ( s, β – , u–,||. , .|| ) ⊂ c0 ( s, α– , u– , ||. , .|| ) but lim supk    αk βk uk = ∞. then there exists a sequence (k(n)) of positive integers with 1 ≤ k(n) < k(n + 1) , n ≥ 1 satisfying |αk(n)| uk(n) > n2 |βk(n)| uk(n) ,for each n ≥ 1. ...( 3.3) corresponding to ρ ∈ s and ρ ≠ θ, we define a sequence ξ – = (ξk) by ξk =   βk(n) -1 n-2/uk(n) ρ‚ if k = k(n)‚ n ≥1 and θ‚ otherwise. ...( 3.4) then for k = k(n), n ≥ 1, we have || βk ξk‚ η|| uk = || β k(n) ξ k(n) ‚η || u k(n) = ||n-2/uk(n) ρ‚ η || uk(n) ≤ 1 n2 ||ρ‚ η || uk(n) ≤ 1 n2 a [ ||ρ‚ η || l(u) ] → 0 as n→ ∞ and ||βk ξk‚ η|| uk = 0, for k ≠ k(n) , n ≥ 1. this shows that ξ – ∈ c0 ( s, β – , u–,||. , .|| ) . on the other hand, let us choose η ∈ s such that ||ρ, η|| = 1. then for k = k(n), n ≥ 1, in view of (3.3) and (3.4) ,we have || αk ξk ‚η|| uk =    αk(n) βk (n) uk(n) . 1 n 2 ||ρ‚ η||uk(n) ≥ 1 and so ξ – ∉ c0 ( s, α– , u– , ||. , .|| ) ,a contradiction. for the sufficiency, assume that lim supk    αk βk uk < ∞. then we can find a positive constant d such that d |βk| uk > |αk| uk for all sufficiently large values of k. let ξ – = (ξk) ∈ c0 ( s, β – , u–,||. , .|| ) . then we have ||βk ξk‚ η|| uk → 0 as k→ ∞ , for each η ∈s. now we have ||αk ξk‚ η || uk ≤ d|βk| uk || ξk‚ η|| uk ≤ ||βk ξk‚ η|| uk → 0 as k→ ∞ , for each η ∈s. this clearly implies that ξ – ∈ c0 ( s, α– , u– , ||. , .|| ) and hence c0 ( s, β – , u–,||. , .|| ) ⊂ c0 ( s, α– , u– , ||. , .|| ). the proof is now complete. on combining the theorems 3.1 and 3.2, we get: theorem 3.3: for any u – = (uk), c0 ( s, α – , u – , ||. , .|| ) = c0 ( s, β – , u – ,||. , .|| ) if and only if 0 < lim infk    αk βk uk ≤ ≤ ≤ ≤ lim supk    αk βk uk < ∞.∞.∞.∞. corollary 3.4: for any u – = (uk), n.p. pahari / bibechana 10 (2014) 20-30: bmhss, p.25 (online publication: dec., 2013) (i) c0 ( s, α – , u – , ||. , .|| ) ⊂⊂⊂⊂ c0 ( s, u – ,||. , .|| ) if and only if lim infk |ααααk| uk > 0 ; (ii) c0 ( s, u – ,||. , .|| ) ⊂⊂⊂⊂ c0 ( s, α – , u – , ||. , .|| ) if and only if lim supk |ααααk| uk < ∞∞∞∞;and (iii) c0 ( s, α – , u – , ||. , .|| ) = c0 ( s, u – ,||. , .|| ) if and only if 0 < lim infk |ααααk| uk ≤ ≤ ≤ ≤ lim supk |ααααk| uk < ∞∞∞∞. proof: the proof follows by putting βk = 1 for all k in theorems 3.1, 3.2 and 3.3. theorem 3.5: for any α– = (ααααk), c0 ( s, α – , u – , ||. , .|| ) ⊂⊂⊂⊂ c0 ( s, α – , v – ,||. , .|| ) if and only if lim infk vk uk > 0. proof: for the necessity, suppose that the inclusion holds but lim infk vk uk = 0. then there exists a sequence (k(n)) of positive integers such that 1 ≤ k(n) < k(n + 1), n ≥ 1 for which n vk(n) < uk(n) , for each n ≥ 1. …(3.5) let ρ ∈ s and ρ ≠ θ. we define a sequence ξ – = (ξk) by ξk =   αk(n) -1 n -1/uk(n) ρ‚ for k = k(n) ‚ n ≥1 and θ‚ otherwise. ...( 3.6) then for each η ∈ s, k = k(n), n ≥ 1 , we have ||αk ξk ‚ η|| u k = ||n -1/u k(n) ρ‚ η|| uk(n) = 1 n || ρ‚ η||uk(n) ≤ 1 n a [ ||ρ‚ η || l(u) ] → 0 as n →∞ and ||αk ξk ‚ η|| uk = 0, for k ≠ k(n) , n ≥ 1. this shows that ξ – ∈ c0 ( s, α– , u– , ||. , .|| ). but on the other hand, let us choose η ∈ s such that ||ρ, η|| = 1. then for k = k(n), n ≥ 1, in view of (3.5) and (3.6) ,we have ||αk ξk ‚ η|| v k = ||α k(n) ξ k(n) ‚ η|| vk(n) = || n-1/uk(n) ρ‚ η|| vk(n) ≥ 1 n 1/n || ρ‚ η|| vk(n) ≥ 1 n 1/2 this shows that ξ – ∉ c0 ( s, α–, v–,||. , .|| ) , which contradicts our assumption. for the sufficiency of the condition, suppose that lim infk vk uk > 0. then there exists a m > 0 such that vk > m uk for all sufficiently large values of k. let ξ – = (ξk) ∈ c0 ( s, α–, u– , ||. , .|| ) . then for each η ∈ s ||αk ξk ‚ η|| uk → 0 as k → ∞. hence for a given ε > 0, if we choose 0 < δ < 1 satisfying δ m < ε satisfying n.p. pahari / bibechana 10 (2014) 20-30: bmhss, p.26 (online publication: dec., 2013) ||αk ξk , η || uk < δ < 1 for each η ∈ s and for all sufficiently large values of k.thus ||αk ξk , η || vk ≤ [||αk ξk ‚ η || uk] m ≤ δ m < ε, for each η ∈ s and for all sufficiently large values of k and consequently ξ – ∈ c0 ( s, α–, v–,||. , .|| ). hence c0 ( s, α–, u– , ||. , .|| ) ⊂ c0 ( s, α– , v–,||. , .|| ). this completes the proof of the theorem. theorem 3.6: for any α– = (ααααk), c0 ( s, α – , v – ,||. , .|| ) ⊂⊂⊂⊂ c0 ( s, α – , u – , ||. , .|| ) if and only if lim supk vk uk < ∞∞∞∞. proof: for the necessity, suppose that the inclusion holds but lim supk vk uk = ∞ . then there exists a sequence (k(n)) of positive integers such that 1 ≤ k(n) < k(n+ 1), n ≥ 1 for which vk(n) > n uk(n) ,for all n ≥ 1. ...( 3.7) corresponding to ρ ∈ s and ρ ≠ θ , we define a sequence ξ – = (ξk) by ξk =   αk(n) -1 n -1/vk(n) ρ‚ for k = k(n) ‚ n ≥1 and θ‚ otherwise. ...( 3.8) then for each η ∈ s, k = k(n), n ≥ 1 , we have ||αk ξk ‚η || vk = ||n-1/vk(n) ρ‚η|| vk(n) = 1 n || ρ‚ η||vk(n) ≤ 1 n a [ ||ρ‚ η || l(v) ] → 0 as n →∞ and ||αk ξk ‚ η|| v k = 0, for k ≠ k(n) , n ≥ 1. this shows that ξ – ∈ c0 ( s, α– , v–,||. , .|| ). but on the other hand, let us choose η ∈ s such that || ρ, η|| = 1. then for k = k(n), n ≥ 1, in view of (3.7) and (3.8) ,we have ||αk ξk ‚ η|| u k = || n-1/vk(n) ρ‚ η|| uk(n) ≥ 1 n 1/n || ρ‚ η|| uk(n) ≥ 1 n 1/2 this shows that ξ – ∉ c0 ( s, α– , u– , ||. , .|| ) , a contradiction. for the sufficiency of the condition, assume that lim supk vk uk < ∞. hence there exists d > 0 such that vk < d uk for all sufficiently large values of k. let ξ – = (ξk) ∈ c0 ( s, α– , v–,||. , .|| ). then for each η ∈ s ||αk ξk ‚ η|| v k → 0 as k → ∞. hence for a given ε > 0, if we choose 0 < δ < 1 satisfying δ 1/d < ε satisfying ||αk ξk , η || vk < δ < 1 for each η ∈ s and for all sufficiently large values of k.thus ||αk ξk , η || uk ≤ [||αk ξk ‚ η|| v k] 1/d n.p. pahari / bibechana 10 (2014) 20-30: bmhss, p.27 (online publication: dec., 2013) ≤ δ 1/d < ε, for each η ∈ s and for all sufficiently large values of k and consequently ξ – ∈ c0 ( s, α– , u–,||. , .|| ). hence c0 ( s, α– , v–,||. , .|| ) ⊂ c0 ( s, α– , u– , ||. , .|| ) . this completes the proof. on combining the theorems 3.5 and 3.6, one obtain theorem 3.7: for any α– = (ααααk),c0 ( s, α – , u – , ||. , .|| ) = c0 ( s, α – , v – ,||. , .|| ) if and only if 0 < lim infk vk uk ≤≤≤≤ lim supk vk uk < ∞.∞.∞.∞. corollary 3.8: for any α– = (ααααk), (i) c0 ( s, α – , ||. , .|| ) ⊂ ⊂ ⊂ ⊂ c0 ( s, α – , u – , ||. , .|| ) if and only if lim inf k uk > 0; (ii) c0 ( s, α – , u – , ||. , .|| ) ⊂⊂⊂⊂ c0 ( s, α – , ||. , .|| ) if and only if lim sup k uk < ∞∞∞∞; and (iii) c0 ( s, α – , u – , ||. , .|| ) = c0 ( s, α – , ||. , .|| ) if and only if 0 < lim infk uk ≤≤≤≤ lim supk uk < ∞∞∞∞. proof: proof follows by taking uk = 1 for all k and replacing v– by u– in theorems 3.5 , 3.6 and 3.7. theorem 3.9: for any α– = (ααααk), β – = (ββββk), u – = (uk) and v – = (vk), c0 ( s, α – , u – , ||. , .|| ) ⊂ ⊂ ⊂ ⊂ c0 ( s, β – , v – , ||. , .|| ) if and only if (i) lim infk    αk βk uk > 0 ; and (ii) lim infk vk uk > 0. proof: proof of the theorem follows immediately from the theorems 3.1 and 3.5. in the following example, c0 (s, α–, u– , ||. , .|| ) may strictly be contained in c0 ( s, β – , v–, ||. , .|| ) in spite of the satisfaction of the conditions (i) and (ii) of theorem 3.9. example 3.10: let ( s, ||. , .|| ) be a 2normed space and consider a sequence ξ – = (ξk) defined by ξk = k –k ρ, if k = 1, 2, 3, …, where ρ ∈ s and ρ ≠ θ. further, let uk = k –1, if k is odd integer, uk = k –2, if k is even integer, vk = k –1 for all values of k, αk = 3k, βk = 2k for all values of k. then    αk βk uk = 3 2 or     3 2 1/k according as k is odd or even integer and hence lim infk    αk βk uk > 0. further, vk uk = 1, if k is odd integer, vk uk = k, if k is even integer. therefore lim infk vk uk > 0. hence the conditions (i) and (ii) of theorem 3.9 are satisfied. now for each η ∈ s, we have n.p. pahari / bibechana 10 (2014) 20-30: bmhss, p.28 (online publication: dec., 2013) ||βk ξk ‚ η|| v k = ||2k k –k ρ ‚ η|| 1/k ≤ 1 k 2 || ρ ‚ η|| 1/k ≤ 1 k 2a [ || ρ‚ η || ] → 0 as k → ∞, and it shows that ξ – ∈ c0 ( s, β – , v–, ||. , .|| ). but on the other hand, let us choose η ∈ s such that || ρ, η || = 1. then for each even integer k, we have || αk ξk ‚ η|| uk = ||3k k –k ρ ‚ η|| 1/k 2 = (3/k)1/ k || ρ ‚ η|| 1/k 2 > 1 2 . this implies that ξ – ∉ c0 ( s, α– , u– , ||. , .|| ).thus the containment of c0 ( s, α– , u– , ||. , .|| ) in c0 ( s, β – , v–, ||. , .|| ) is strict inspite of the satisfaction of the conditions (i) and (ii) of the theorem 3.9. 4. linear topological structures of c0 ( s, α – , u – , ||. , .|| ) in this section, we shall investigate some results that characterize the linear topological structure of the class c0 ( s, α–, u– , ||. , .|| ) by endowing it with suitable natural paranorm. throughout we take coordinatewise operations of sequences over the field c of complex numbers i.e.,for ξ – = (ξk ) and η– = (ηk ) and scalar γ, ξ – + η– = (ξk + ηk ) and γ ξ – = (γ ξk ) and we see below that each of these classes forms a complete paranormed linear space over c. moreover, we use frequently | ξ + η | uk ≤ s {|ξ| uk + |η| uk }, where ξ , η ∈ c, 0 < uk ≤ supk uk = l < ∞ and a(α) = max (1, |α| ). theorem 4.1: the space c0 ( s, α – , u – , ||. , .|| ) forms a linear space over c if and only if supk uk is bounded above . proof: for the necessity of the conditions, suppose that c0 ( s, α–, u– , ||. , .|| ) is a linear space over c but supk uk = ∞. then there exists a sequence (k(n)) of positive integers satisfying 1 ≤ k(n) < k(n + 1), n ≥ 1 for which uk(n) > n ,for each n ≥ 1 … .(4.1) now, corresponding to ρ ∈ s and ρ ≠ θ, we define the sequence ξ – = (ξk) by ξk =   αk(n) -1 n-2/uk(n) ρ‚ if k = k(n) ‚ n ≥1 and θ‚ otherwise. … .(4.2) then for k = k(n), n ≥ 1, we have ||αk ξk‚ η|| uk = ||n-2/uk(n) ρ‚ η || uk(n)) ≤ ||ρ‚ η || uk(n) n2 → 0 as n→ ∞, n.p. pahari / bibechana 10 (2014) 20-30: bmhss, p.29 (online publication: dec., 2013) and ||αk ξk‚ η|| uk = 0, for k ≠ k(n) , n ≥ 1 showing that ξ – ∈ c0 ( s, α– , u– , ||. , .|| ). but on the other hand, let us choose η ∈ s such that ||ρ, η|| = 1. then for such η and scalar γ = 4, for k = k(n), n ≥ 1, in view of (4.1) and (4.2), we have || γ αk ξk‚ η || uk = || αk(n) γ ξk(n ) ‚ η || uk(n) = || 4 n–2/ uk(n) ρ ‚η || uk(n) = 4 uk(n) n2 ≥ sup n 4 n n 2 ≥ 1 . this shows that γ ξ – ∉ c0 ( s, α–, u– , ||. , .|| ) , a contradiction. for the sufficiency of the condition, assume that supk uk < ∞. let ξ – , η– ∈ c0 ( s, α–, u– , ||. , .|| ) and γ, ρ ∈ c. then for each η ∈ s, we have ||αk ξk‚ η|| uk → 0 and ||αk ηk‚ η|| uk →0, as k → ∞. we now setting s = max ( 1,2l-1 ), then we have ||αk (γξk + ρηk)‚ η || uk = (|| γαk ξk‚ η || + || ρ αk ηk‚ η || ) uk ≤ ( s || γ αk ξk‚ η || uk + s || ρ αk ηk‚ η || uk ) = s |γ| uk || αk ξk‚ η || uk + s |ρ| uk || αk ηk‚ η || uk which tends to 0 as k → ∞, for each η ∈ s and hence αξ – + ρ η– ∈ c0 ( s, α–, u– , ||. , .|| ). this implies that c0 ( s, α–, u– , ||. , .|| ) forms a linear space over c. this completes the proof. let u– ∈ ℓ∞ i.e., supk uk < ∞ , m = max (1, supk uk ) and consider a real valued function t on c0 ( s, α–, u– , ||. , .|| ) defined by t (x–) ={ sup k || αk ξk ‚ η || u k /m , for each η ∈ s },for ξ – ∈ ℓ∞ ( s, α–, u– , ||. , .|| ). … (4.3) we prove below that c0 ( s, α–, u– , ||. , .|| ) with respect to t forms a paranormed space. theorem: 4.2 (c0 ( s, α – , u – , ||. , .|| ), t ) forms a total paranormed space. proof: since t(ξ – ) ≥ 0 ; t(ξ – ) = 0 if and only if ξ – = θ–; t (–ξ – ) = t (ξ – ) ; and t (ξ – + η–) ≤ t (ξ – ) + t (η –) easily follow. so pn1 , pn2 and pn3 are obvious. for pn4 i.e., the continuity of scalar multiplication, it suffices to show that (a) if ξ – (n) → θ– in t and γn → γ as n → ∞,then γn ξ – (n) → θ– in t; and (b) if γn → 0 and ξ – ∈ c0 ( s, α–, u– , ||. , .|| ) , then γn ξ – → θ– in t . now (a) is easily proved if we suppose |γn| ≤ l for all n ≥ 1 and in view of (4.3) , we have t (γn ξ – (n)) = { sup k || γn αk ξk (n) ‚ η || u k /m , for each η ∈ s } ≤ { sup k |γn| u k /m sup k || αk ξk (n) ‚ η || u k /m , for each η ∈ s } n.p. pahari / bibechana 10 (2014) 20-30: bmhss, p.30 (online publication: dec., 2013) = a(l) { sup k || αk ξk (n) ‚ η || u k /m , for each η ∈ s } ≤ a(l) t (ξ – (n)), implies that t (γn ξ – (n)) → 0, as t (ξ – (n)) → 0 as n → ∞. to prove (b), let ξ – ∈ c0 ( s, α–, u– , ||. , .|| ), |γn| < 1 for all n ≥ n1 and ε > 0. then there exists a positive integer k such that ||αk ξk ‚ η || u k < ε m for all k ≥ k and for each η ∈ s and hence for all k ≥ k and n ≥ n1, we have || γn αk ξk ‚ η || u k = |γn| u k || αk ξk ‚ η || u k < εm, for each η ∈ s. now choose n2 such that for all k = 1, 2, …, k – 1 and n ≥ n2, || γn αk ξk ‚ η || u k = |γn| u k || αk ξk ‚ η || u k < ε m, for each η ∈ s. thus, t (γn ξ – ) ≤ ε, for n ≥ n = max (n1, n2), which proves (b).the totality of t is obvious. references 1. s. gäahler, math. nachr., 6 (1963) 115-148. 2. j.a. white and y.j. cho, bull. korean math. soc., 21(1) (1984) 1–6. 3. k. iseki , bull. korean, math. soc., 13(2) ( 1976) . 4. r. freese and y. cho, nova science publishers, inc. new york, 2001. 5. r.w. freese ,y. j. cho and s.s. kim, j. korean math. soc., 29( 2) (1992) 391 – 400. 6. w. raymond, y. freese and j. cho, geometry of linear 2-normed spaces, n. y. nova science publishers, huntington, 2001. 7. e. savas , abstract and applied analysis, 2011 ( 2010) 10.1155. 8. h. gunawan and h. mashadi, soochow j.math., 27(2001) 321–329. 9. j. k. srivastava and n.p. pahari , south east asian j.math. & math.sc., 10(1) , ( 2011) 39-49. 10. m. açikgöz , int. journal of math. analysis, 1(4) (2007) 187-191. 11. a. wilansky, modern methods in topological vector spaces , mc graw_hill book co.inc.new york , 1978. 12. i. j. maddox, j. math. soc. ,2(1) (1969) 316-322. 13. j. k. srivastava and b. k. srivastava, indian j. pure and appl. math., 27 (1) (1996) 73-84. 14. j.k. srivastava and n.p.pahari, jour. of rajasthan academy of physical sciences, 11(2) ( 2011) 103-116. 15. j.k. srivastava and n.p.pahari , proc. of indian soc. of math. and mathematical sciences, 6 ( 2011) 243-251. 16 . n.p. pahari , nepal jour. of science and tech. , 12 ( 2011) 252-259. 17. s. d. parashar and b. choudhary, indian j. pure appl. maths., 25(4) (1994) 419–428. 18. v.n. bhardwaj and i. bala, j. of pure and appl. maths., 41(5) (2007) 617–626. microsoft word mani raj bhattrai _82-86_.doc mani raj bhattrai / bibechana 7 (2011) 83-86: bmhss 83 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana riemann integral and its relation with lebesgue integral mani raj bhattrai∗∗∗∗ dept. of mathematics, bhanu m.h.s. school, biratnagar, nepal article history: received 29 october 2010; revised 25 november 2010; accepted 5 december 2010 abstract this review explains the limitations of the riemann integral and focuses on the more general concept. it has been suggested that a better route is to abandon the riemann integral for lebesgue integral and explained the importance of lebesgue integral in real analysis and other fields of mathematical science. keywords: riemann integral; lebesgue integral; fourier series 1. introduction as part of a general movement toward rigor in mathematics in the nineteenth century, attempts were made to put the integral calculus on a firm foundation. the riemann integral, proposed by bernhard riemann (1826–1866) [1], is a broadly successful attempt to provide such a foundation. riemann's definition starts with the construction of a sequence of easily-calculated areas which converge to the integral of a given function. this definition is successful in the sense that it gives the expected answer for many already-solved problems, and gives useful results for many other problems. in the branch of mathematics called real analysis, the riemann integral was the first definition of the integral of a function on an interval, created by bernhard riemann,. while the riemann integral is unsuitable for many theoretical purposes, it is one of the easiest integrals to define. some of these technical deficiencies can be remedied by the riemann–satieties integral, and most of them disappear in the lebesgue integral [2]. bernhard riemann,no doubt acquired his interest in problems connected with trigonometric series through contact with dirichlet when he spent a year in berlin. he almost certainly attended dirichlet's lectures. for his habilitationsschrift (1854) riemann under-took to study the representation of functions by trigonometric functions. he concluded that continuous functions are represented by fourier series. he also concluded that functions not covered by dirichlet do not exist in nature. but there were new applications of trigonometric series to number theory and other places in pure mathematics. this provided impetus to pursue these foundational questions. riemann began with the question: when is a function integrable? by that he meant, when do the cauchy sums converge? ∗ corresponding author: mani raj bhattrai, dept. of mathematics, bhanu m.h.s. school, biratnagar, nepal, email: manirb08@yahoo.co.in mani raj bhattrai / bibechana 7 (2011) 83-86: bmhss 84 however, riemann integration does not interact well with taking limits of sequences of functions, making such limiting processes difficult to analyze. this is of prime importance, for instance, in the study of fourier series, fourier transforms and other topics. the lebesgue integral is better able to describe how and when it is possible to take limits under the integral sign. the lebesgue definition considers a different class of easily-calculated areas than the riemann definition, which is the main reason the lebesgue integral is better behaved. the lebesgue definition also makes it possible to calculate integrals for a broader class of functions. in mathematics, lebesgue integration refers to both the general theory of integration of a function with respect to a general measure, and to the specific case of integration of a function defined on a sub-domain of the real line or a higher dimensional euclidean space with respect to the lebesgue measure. 2. limitations of the riemann integral here we discuss the limitations of the riemann integral and the greater scope offered by the lebesgue integral. we presume a working understanding of the riemann integral. with the advent of fourier series, many analytical problems involving integrals came up whose satisfactory solution required interchanging limit processes and integral signs. however, the conditions under which the integrals ( ) ( )k k k k f x dx and f x dx       ∑ ∑∫ ∫ are equally proved quite elusive in the riemann framework. there are some other technical difficulties with the riemann integral. these are linked with the limit taking difficulty discussed above. 2.1 unsuitability for unbounded intervals. the riemann integral can only integrate functions on a bounded interval. it can however be extended to unbounded intervals by taking limits, so long as this doesn't yield an answer such as ∞÷∞ . 3. domain of integration a technical issue in lebesgue integration is that the domain of integration is defined as a set (a subset of a measure space), with no notion of orientation. in elementary calculus, one defines integration with respect to an orientation: ∫ ∫−= a b b a ff . generalizing this to higher dimensions yields integration of differential forms. by contrast, lebesgue integration provides an alternative generalization, integrating over subsets with respect to a measure; this can be notated as ∫ ∫ µ=µ a ]b,a[ fdfd to indicate integration over a subset a. for details on the relation between these generalizations, see differential form: relation with measures. 4. intuitive interpretation to get some intuition about the different approaches to integration, let us imagine that it is desired to find a mountain's volume (above sea level). mani raj bhattrai / bibechana 7 (2011) 83-86: bmhss 85 4.1 the riemann-darboux approach divide the base of the mountain into a grid of 1 meter squares. measure the altitude of the mountain at the center of each square. the volume on a single grid square is approximately 1x1(altitude), so the total volume is the sum of the altitudes. 4.2 the lebesgue approach draw a contour map of the mountain, where each contour is 1 meter of altitude apart. the volume of earth contained in a single contour is approximately that contour's area times its height. so the total volume is the sum of these volumes. folland [1] summarizes the difference between the riemann and lebesgue approaches thus: "to compute the riemann integral of f, one partitions the domain [a, b] into subintervals", while in the lebesgue integral, "one is in effect partitioning the range of f". the riemann integral is a linear transformation; that is, if f and g are riemann-integrable on [a,b] and α and β are constants, then ( ) ( ) ( ) b b b a a a f g dx f x dx g x dxα + β =α + β∫ ∫ ∫ because the riemann integral of a function is a number, this makes the riemann integral a linear functional on the vector space of riemann-integrable functions. it can be shown that a real-valued function f on [a,b] is riemann-integrable if and only if it is bounded and continuous almost everywhere in the sense of lebesgue measure. if a real-valued function on [a,b] is riemann-integrable, it is lebesgue-integrable. if function is a uniformly convergent sequence on [a,b] with limit f, then riemann integrability of all function implies riemann integrability of f, and b b b n n n n a a a f dx lim f dx lim f dx → ∞ → ∞ = =∫ ∫ ∫ if a real-valued function is monotone on the interval [a,b], it is riemann-integrable, since its set of discontinuities is denumerable, and therefore of lebesgue measure zero. 5. alternative formulations it is possible to develop the integral with respect to the lebesgue measure without relying on the full machinery of measure theory. one such approach is provided by daniell integral [3]. there is also an alternative approach to developing the theory of integration via methods of functional analysis. the riemann integral exists for any continuous function f of compact support defined on rn (or a fixed open subset). integrals of more general functions can be built starting from these integrals. let cc be the space of all real-valued compactly supported continuous functions of r. define a norm on cc by ( ) .= ∫f f x d x then cc is a normed vector space (and in particular, it is a metric space.) all metric spaces have hausdorff completions, so let l 1 be its completion. this space is isomorphic to the space of lebesgue integrable functions modulo the subspace of functions with integral zero. furthermore, the riemann integral ∫ is a uniformly continuous functional with respect to the norm on cc, which is dense in l 1 . hence ∫ has a unique extension to all of l 1 . this integral is precisely the lebesgue integral. mani raj bhattrai / bibechana 7 (2011) 83-86: bmhss 86 this approach can be generalized to build the theory of integration with respect to radon measures on locally compact spaces. it is the approach adopted by bourbaki [4] for more details see radon measures on locally compact spaces. references [1] w.k.clifford, “on the hypotheses which lie at the foundation of geometry”, nature, 8 (1873) 183. [2] h.j. wilcox and d.l. myers, an introduction to lebesgue integration and fourier series, dover publications, inc., new york, (1978). [3] p. daniell, "a general form of integral" ann. of math. , 19 (1917) 279. [4] n. bourbaki, elements of mathematics, springer, (2004). microsoft word koirala _9-19_.doc r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.9 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana thermo-physical properties of molten cd-ga alloys r.p. koirala 1, 2 , b.p. singh 2 , d. adhikari 1 * 1department of physics, m.m.a.m. campus (tribhuvan university), biratnagar, nepal 2 university department of physics, t.m. bhagalpur university, bhagalpur, india *email: adksbdev@yahoo.com article history: received 22 june, 2013; accepted 29 september, 2013 abstract we report thermodynamic, microscopic and surface properties of cd-ga alloys in molten state at 700 k. we use quasi-chemical approximation for the computation of thermodynamic and microscopic properties. for the computation of surface we use butler’s approach and quas-chemical approach. we also calculate the surface concentration of the individual component. keywords: binary alloys, entropy of mixing, short range order, surface concentration. 1. introduction the understanding of thermodynamic and surface properties of binary liquid alloys is necessarsy for the design and development of desired materials particularly for high temperature applications. these properties help to know the bonding strength of different species and their local ordering in the alloys. moreover, information about the mixing properties of solid alloys can be derived from the study of the corresponding initial melts. liquid alloys are disordered systems in the sense they have no long range order. the complexity in the behaviour of such systems has long been a challenge for researchers in material science and thus determination of thermo-physical properties for alloys in the liquid state is still an active field of research. advancement in technology of the alloy systems of non-periodicity in the atomic arrangement has led to an increasing need for a better description of their atomic scale structures. in this paper, we intend to study the thermo-physical properties of cd-ga liquid alloy at 700k. cadmium containing alloys are generally important for their wide variety of applications as they possess improved mechanical, thermal and electrical properties such as tensile and fatigue strength, hardness, drawability, heat resistance and electrical conductivity etc. cd-ga alloy has a characteristic melting point and the liquidus line in the phase diagram is monotectic [1]. it possesses large positive heat of mixing and is characterized by miscibility gaps. this binary segregating liquid alloy has been studied previously using various approaches [1-4]. in the present study we employ the quasi-chemical approximation (qca) [2,5]for the estimation of the thermodynamic properties such as free energy of mixing (gm), entropy of mixing (sm), heat of mixing (hm) and activity (ai)); structural properties (concentration fluctuation in the long wavelength limit (scc(0)), the warren–cowley short-range order parameter ( 1α ) and transport properties (ratio of diffusion coefficients); and statistical formulations for the determination surface properties like surface concentration and surface tension of the cd-ga alloy at 700k. in qca, a binary liquid a–b alloy is assumed to consist of homo-pairs (a–a and b–b) which are the clusters of like atoms formed by self-association having a short-range interaction. the self r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.10 (online publication: dec., 2013) associates of types aµ and bν , where µ and ν are the number of atoms in the cluster of types a and b, respectively, are assumed to be located at their equivalent sites in the alloy [3]. the necessary theoretical formalism is given in section 2, which follows, results and discussions, and conclusions in sections 3 and 4, respectively. 2. formalism consider one mole of a binary alloy having nxa atoms of element a and nxb atoms of element b where xa and xb represent the mole fraction concentrations of element a and b. on the basis of this assumption expressions for thermodynamic and microscopic functions have been derived for binary liquid alloys (singh et al., 1997) as given below. 2.1 thermodynamic functions the free energy of mixing, gm for binary liquid alloys at temperature t in quasi-chemical approximation can be obtained using the expression [2]: w)xx()1()]1(lnxlnx[rtg babam γ+φ−φ+φ−+φ= (1) where ba a xx x γ+ =φ ; µ ν γ = and ω= iw (2) here r is universal gas constant; w is ordering energy parameter and ω is the interchange energy. the chemical activities, aa and ab of constituent elements a and b in binary liquid alloys are obtained from the free energy of mixing, gm using following standard thermodynamic relations 12 n,p,t2 m b n,p,t1 m a n g alnrt; n g alnrt       ∂ ∂ =      ∂ ∂ = (3) using eqs. (1) and (3), the working expressions for the activities are obtained as: rt w )1( x ln1aln 2 a a φ−+ φ −φ+= (4) rt w )1()1(lnaln 2 b φγ+γ−φ+φ−= (5) the expression for the entropy of mixing (sm) is derived from the following standard thermodynamic relation: p m m t g s       ∂ ∂ −= (6) using eq. (1), sm can be obtained as: t w )xx()1()]1ln(xlnx[rs babam ∂ ∂ γ+φ−φ−φ−+φ−= (7) once the free energy of mixing, gm and entropy of mixing, sm are obtained, the heat of mixing, hm can be readily calculated using the standard thermodynamic relation: mmm stgh += (8) , 2.2 microscopic functions the microscopic functions such as concentration fluctuation in long wavelength limit (scc(0)) and warren-cowley [6] short-range order parameter ( 1α ) are useful properties to obtain valuable information about structure of molten alloys. r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.11 (online publication: dec., 2013) 2.2.1 concentration fluctuation in long wavelength limit (scc(0)) the concentration fluctuation in long wavelength limit (scc(0)) indicates nature of local ordering of atoms in the liquid alloys. the standard relation for concentration fluctuation in long wavelength limit (scc(0)) for binary liquid alloys is given as: 1 p,t 2 am 2 cc )x/g(rt)0(s −∂∂= (9) eqs.(1) and (9) yield: ),,(1 )0( ωνµfxx xx s ba ba cc − = (10) where 3 22 )( )()1(2 ),,( ba ba xx xx rt w f γ γγγ ωνµ + +−− = (11) the value of (scc(0)) can also be determined using activity data in the following thermodynamic equations: 1 p,taaabcc )x/a(ax)0(s −∂∂= 1 p,tbbba )x/a(ax −∂∂= (12) which are usually considered as the experimental values. 2.2.2 warren-cowley short range order parameter ( 1α ) in order to quantify the degree of atomic order in the alloy, warren-cowley short range order parameter ( 1α ) for the first nearest neighbours can be estimated from the relation [7] 1 1 1 +β −β =α (13) where β is an auxiliary variable given by: 2/12 aa ])1()x1(x41[ −η−+=β (14) with )/(exp tzkw b=η (15) here z represents the number of nearest neighbours of an atom in the bulk, called co-ordination number and kb is boltzmann number. in terms of the variable β , an expression for scc(0)[7] is expressed as )1/1(z2/11 )c1(c )0(scc −β+ − = (16) by taking together eqs. (13) and (16), an expression for 1α can be derived in the following form 1)1z(s )1s( 1 +− − =α with )0(s )0(s s id cc cc= (17) where ba id cc xx)0(s = . the value of 1α can be computed from the knowledge of scc(0) using eq. (17). 2.2.3 diffusion the mixing behaviour of the alloys forming molten metals can also be studied at the microscopic level in terms of the diffusion coefficients. the scc(0) and diffusion coefficients can be related using darken thermodynamic equation for diffusion as [8] r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.12 (online publication: dec., 2013) )0(s )0(s d d cc id cc id m = (18a) where dm is the mutual diffusion coefficient and did is the intrinsic diffusion coefficient for an ideal mixture given as: abbam dxdxd += (18b) where da and db are the self-diffusivities of pure components a and b respectively. the ratio dm/did indicates the mixing behaviour of alloy; dm/did > 1 indicates the tendency for compound formation and dm/did < 1 indicates tendency of segregation. for random mixing, the ratio dm/did approaches 1. 2.3 surface properties the surface tension effects play vital role in the formation of solid alloys by solidification process of the melts. the knowledge of surface properties is required for understanding of the surface related phenomena such as wetting characteristics of solders, corrosion and kinetics of phase transformation. at high temperatures the surface tension is very sensitive to physical and chemical contamination. therefore, for understanding, description and metallurgical modeling as well as prediction of structure development during solidification in the binary system surface properties need to be known. the experimental determination of surface tension involves several difficulties in many cases. because of this, several theoretical models [9-13] have long been developed to determine surface tension data of metals and alloys. in the present paper we employ the following two statistical formulations for the comparative study of the concentration dependence of surface tension of the cd-ga liquid alloys at 700k. 2.3.1 butler’s approach butler’s formulation for surface tension (butler, 1932; koirala et al., 2013) is based on the assumption that the liquid binary mixture has monatomic layer at the surface. this layer is considered as a separate phase that is in thermodynamic equilibrium with the bulk. under this assumption, the surface tension, σ of a binary liquid solution in this approach can be expressed as: i b i s i bsbs aaa µµµµµµ σ − == − = − = ........... 2 22 1 11 (19) where b i s i µµ , and ia denote the chemical potential of component i in the hypothetical surface, and that in the bulk, and the molar surface area of pure component i respectively. the variation of the chemical potential with the composition of the surface layer in ideal solution can be expressed by the same equation in the surface and in the bulk as follows: s i s i s i xrt ln 0 +=µµ , b i b i b i xrt ln 0 +=µµ (20) where s ix and b ix are mole fraction of component i in the surface, and that in the bulk; r is the universal gas constant and t stands for absolute temperature. from eqs. (19) and (20), the expressions for the surface tension of the binary alloys can be derived in terms of partial excess free energy of mixing, b,e ig in the bulk and s,e ig at the surface, and surface concentrations, b ix in the bulk and s ix at the surface ( b,ai = ), in the following forms: )]x(ln)x(ln[ a rt )gg( a 1 b b s b 1 b,e a s,e a 1 1 −+−+=σσ (21) )]x(ln)x(ln[ a rt )gg( a 1 b a s a 2 b,e b s,e b 2 2 −+−+=σσ (22) r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.13 (online publication: dec., 2013) where 1σ and 2σ are surface tension of pure component 1 and 2 respectively. b,e ig and s,e ig ( 2,1i= ) are partial excess free energy of component i in the bulk and at the surface respectively. the area of monatomic surface layer for the component i is commonly calculated from the following relation: 3/2 i 3/1 i vnla = (23) where l= 1.091 is called geometrical factor for the closed packed atoms of the surface monolayer. n is avogadro’s constant and vi stands for the molar volume of the component i. the molar volume can be calculated from the atomic mass and density of the pure component. solving eq. (21) and (22) together, we can obtain surface concentration of the components in the liquid solution if the ratio of partial excess free energy in the surface and that in the bulk is known because all other quantities are either known or can be calculated using available data for pure components. assuming the partial excess gibbs energy in the bulk and that in the surface to have the same concentration dependence, they can be related to each other through a parameter λ as: b,e i s,e i g g =λ (24) the value of λ is assumed a fixed number in the calculations. in our calculations, we have taken the values of the partial excess free energy in the bulk from the reference [14] using of the value of surface concentration in either of eqs. (21) and (22), surface tension of the binary liquid solution can be computed. 2.3.2 quasi-chemical approach the surface tension of regular binary liquid alloys in which no complexes are formed can be examined by the application of quasi-lattice theory [12]. the following pair of equations are available for the theoretical investigation of the surface tension of the binary liquid alloys:       + +− − ++− ++− + − += a a s a s a s b a s ab 1 x)1( )x21( lnq )1()x21( )1()x21( nlp 2 tkz x x nl 2 )pz2(tk β β ββ ββ αα σσ (25a) s s s a a ab b 2 s a aa (2 pz) (1 x ) z ( 1 2x )(1 ) ( 1 2x )k t k t n p n qlnl l 2 (1 x ) 2 (1 )(1 x )( 1 2x )(1 )  − − β + − +β β + − σ=σ + + −  − + β −α α  β + − +β  (25b) here σ , 1σ and 2σ are surface tensions of alloy and those of pure components a and b respectively; kb stands for boltzmann constant; z is co-ordination number in the bulk; s ax is the mole concentration of the alloy component a at the surface. α is the mean atomic surface area given as ∑= iix αα )2,1( =i (26) where the atomic area of hypothetical surface for each component is calculated as: 3/23/2102.1 ii n ω= −α (27) where iω is the molar volume of species i and n stands for avogadro's number. p and q are surface coordination fractions which are defined as the fractions of the total number of nearest neighbours made by atom within its own layer and that in the adjoining layer. for p and q the following relation is available (prasad et al., 1994): 12 =+ qp (28) and for closed packed structures the values of these parameters are taken as 0.5 and 0.25 respectively. when the disordered structure and relaxation effect of the surface layer are taken into account, p and q must be treated as parameters. the concentration dependent auxiliary variable β is defined by the order energy term, w through the following equation [13] r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.14 (online publication: dec., 2013) 2/12 abaa ])x21()tkz/w2(exp)x1(x4[ −+−=β (29) the function sβ for surface is obtained from eq. (28) by replacing the bulk concentration xa by the surface concentration s ax and the coordination number z by coordination number of the surface atoms, s z . the value of s z is calculated from its relation with z given by [13] z)qp(z s += (30) 3. results and discussion 3.1 thermodynamic functions in qca the ratio of self-associates, γ and the interaction energy parameter, w are required for the computation of the thermodynamic and structural properties. these are estimated from eq. (1) by fitting them into the experimental values of the free energy of mixing and chemical activities at all concentrations [15]. the best fit values of these parameters cd-ga liquid alloys at 1023 k are found to be 99.0=γ and rt9.1w += . the free energy of mixing, gm computed from eq. (1) is found negative throughout the entire concentration range and is almost symmetric about equi-atomic composition. the computed values of free energy of mixing have been found in fairly good agreement with the observed values [15](fig. 1). fig. 1: free energy of mixing (gm) and heat of mixing (hm) vs bulk concentration of c d(xa) in cdga liquid alloys at 700k: theorysolid line ; experimentcircles. the interaction energy parameter is assumed to be temperature dependent in qca for the computation of the entropy of mixing, sm. the temperature dependence of energy parameter, dt/dw has been best estimated from eq. (7) for the cd-ga alloy system at 700k to be r18.0 dt dw −= and the calculated values of entropy of mixing have been found positive at all concentrations. this indicates that there is low ordering of atoms in the cd-ga system at the temperature of investigation. a good agreement is observed between theoretical and experimental values [15] (fig.2). next the heat of mixing of the cd-ga liquid alloy was calculated using the calculated values of free energy of mixing and entropy of mixing in eq. (8). the calculated values are in reasonable agreement with the observed values [15] (fig. 1) with small deviation from the experimental values. the deviation may r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.15 (online publication: dec., 2013) be due to the neglect of vibrational and electronic contributions on entropy of mixing. both calculated and observed values are all positive for the whole range of concentration. this indicates that the alloy system at 700k is segregating in nature which is consistent with the sign of ordering energy w. the enthalpic and entropic effects compete with each other to dictate the degree of segregation in the binary alloy systems. fig. 2: entropy of mixing (sm) vs bulk concentration of cd (xa) in cd-ga liquid alloys at 700k: theorysolid line; experimentcircles. the activity is another important thermodynamic function which is a measure of a component to leave the solution. the deviation from the ideal behaviour is incorporated into activity. activity is used to calculate the values of the concentration fluctuation at long wavelength limit, scc(0) which are considered as experimental values. the magnitude of the activity depends on the interaction among the constituent species of the system which in turn determine the bond energies. thus measurement of activity within a class of similar systems can be expected to provide at least a basis for correlation of the behaviour which can be used for the extrapolation of behaviour of more complex systems. in order to maintain the consistency in our calculations, we have used the same values of γ , w and the temperature derivative of w for the computation of activity. the values of the activities of the component metals calculated using equations (4) and (5) are found in good agreement with the experimental values 15] (fig. 3). 3.2 microscopic functions the concentration fluctuation in long wavelength limit (scc(0)) is an important microscopic function that can be used to understand the nature of atomic order in the binary liquid alloys. when the computed scc(0) is found to be greater than the ideal scc(0) ( i.e. )0(s)0(s id cccc < ) in a binary alloy, then ordering is expected and when )0(s)0(s id cccc > , tendency of segregation is observed in the alloy. in the present analysis we have found both computed and observed values of scc(0), calculated respectively from eqs. (9) and (11) greater than ideal values, )0(sid cc at all concentrations (fig. 4). this indicates that there is homo-coordination of atoms in the cd-ga molten alloys at 700k. this result is in well agreement with the result for the heat of mixing. r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.16 (online publication: dec., 2013) fig. 3: activities of cd and ga (aa and ab) bulk concentration of cd (xa) in cd-ga liquid alloys at 700k: theorysolid line: experimentaa -crosses; ab circles. fig. 4: concentration fluctuations in long wavelength limit (scc(0))) vs bulk concentration of cd (xa) in cd-ga liquid alloys at 700k: theorysolid line ; experimentcircles; ideal values broken line. the warren-cowley short range order parameter, 1α is another important microscopic function required to get better insight into the degree of local ordering of atoms in the liquid alloys. for a binary liquid alloy if 1α is negative, there is tendency of ordering and there is tendency of phase separation if 1α is positive. we have calculated the 1α using calculated values of scc(0) in the eq. (17). we have found 1α small positive for all concentrations which indicates that there is weak tendency of phase separation in the molten cd-ga alloy at 700k (fig. 5), as observed from the results of hm and scc(0). in our calculation we have taken z = 10. we note that varying the value of z does not have any r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.17 (online publication: dec., 2013) effect on the position of minima of 1α ; the effect is to vary the depth while the overall feature remains unchanged. the other important microscopic function which is required to understand the mixing properties is diffusion. chemical diffusion coefficient is one of the transport properties which in the present analysis has been calculated from eq. (18a) and has been found to be positive for the whole range of concentration. positive values of this ratio indicate that the cd-ga liquid alloy at 700k is segregating in nature (fig. 6). fig. 5: ratio of chemical and intrinsic diffusion coefficients (dm/ did) and short range order parameter ( 1α ) vs bulk concentration of cd (xa) in cd-ga liquid alloys at 700k. fig. 6: surface concentration ( s ax ) vs bulk concentration of cd (xa) in cd-ga liquid alloys at 700k: butler’s approachsolid line; quasi-chemical approachbroken line. 3.3 surface properties 3.3. 1 butler’s approach to study the surface properties (surface concentration and surface tension) of the binary liquid alloys from butler’s monolayer approach, we need experimental data of density, surface tension and partial r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.18 (online publication: dec., 2013) excess free energies of mixing of the components at the working temperature. we calculated the density and surface tension for the components cd and ga at the working temperature by using their temperature coefficients and the values at the melting temperature in the following equations [14] )tt( t )t( mm − ∂ ρ∂ +ρ=ρ (31) )tt( t )t( mm − ∂ σ∂ +σ=σ (32) where t and tm are respectively the temperature of investigation and melting temperature; and t∂ ρ∂ and t∂ σ∂ represent the temperature coefficient of density and temperature coefficient of surface tension for each component metal of the alloys. the partial excess free energies of mixing of the pure components of the cd-ga alloys at the temperature of investigation were taken from the ref. [14]. the mole fraction concentration of the cd-atoms at the surface was then computed at all concentrations by simultaneously solving eqs. (21) and (22) and then the surface tension of the alloy were worked out from either of these equations. the surface concentration of cd-atoms is found to have a linear/nonlinear increase with the bulk concentration. the surface tension of the cd-ga molten alloys on the other hand is found to decrease with the increasing bulk concentration of the cd-atoms. 3.3.2 quasi-chemical approach mixing properties namely the thermodynamic properties and the surface properties in quasi-chemical approach have an integral relation through the order energy parameter. the surface concentrations of the component metals have been obtained from the simultaneous solution of the eqs. (25a) and (25b) at all bulk compositions by using the values of the interaction energy parameter obtained from the application of quasi-chemical approximation to the alloys. surface tension and densities of the components calculated above from eqs. (31) and (32) were used in solving the equations for surface concentrations. the surface concentration of cd-atoms in cd-ga alloys at 700k has been found to be increase with the bulk concentration of the cd-atoms. when there is a larger difference in surface tension between the solvent and solute, the segregating behaviour of the component is more significant. having obtained the surface concentrations of cd-atoms, the surface tension was calculated from either of the eqs. (25a) or (25b). this approach predicts the surface tension values which are almost matching with those obtained from the previous approach (fig. 6 & fig. 7). fig. 7: surface tension (σ ) vs bulk concentration of cd (xa) in cd-ga liquid alloys at 700k: butler’s approach solid line; quasi-chemical approach-short broken line; ideal values long broken line. r.p. koirala et al / bibechana 10 (2014) 9-19 : bmhss, p.19 (online publication: dec., 2013) we do not have experimental values of surface tension of the cd-ga alloys at 700k to compare our computed result. it is worthwhile to mention that the approaches which we have employed in present work have been successfully used by several workers to compute the surface tension of metallic solution. 4. conclusions present theoretical analysis of the microscopic and thermodynamic properties of the cd-ga molten alloys at 700k reveals that the alloys represent a segregating system; homopairs (cd-cd and ga-ga) are preferred. the ordering energy is found to be temperature dependent. furthermore, the study shows that the cd-component with lower surface tension tends to segregate on the surface of molten alloy while the other component with higher surface tension tends to segregate in the bulk. acknowledgements we are grateful to prof. l.n. jha (head, central department of physics, t.u., kathamandu); prof. p. r. pradhan (post-graduate department of physics, m.m.a.m. campus, t.u., biratnagar) and dr. i. s. jha (post-graduate department of physics, m.m.a.m. campus, t.u., biratnagar) for fruitful suggestions and inspiring discussions. references 1. r.n. singh, i.k. mishra and v.n. singh. j.physics: condensed matter, 2(1990) 8457-8462. 2. r.n. singh and f. sommer, rep.prog. phys., 60 (1997)57-150. 3. b.c., anusionwu and c.a. madu, pramanaj. physics, 72 (2009) 951-967. 4. a.k. mishra and m. milanarun, high temperature materials and processes, 21 (2005) 47-56. 5. r. n. singh, can. j. phys., 65 (1987)309-325. 6. b.e. warren, x-ray diffraction. addison-wesley, reading, 1969. 7. a.b. bhatia, and r.n. singh, physics and chemistry of liquids, 13(1984) 177. 8. l.s., darken, and r.w. gurry, physical chemistry of metals. mcgraw hill, new york, 1953. 9. j.a. butler, proceedings of the royal society, a 1932, 135. 10. r.p. koirala, b.p. singh,i.s. jha, and d. adhikari, journal of molecular liquids, 179(2013) 60– 66. 11. n.h .march and j.a. alonso physics and chemistry of liquids, 46 (2008)52226. 12. r. novakovic, journal of non-crystalline solids, 356 (2010) 1593-1598. 13. l.c. prasad, r.n. singh and g.p. singh, physics and chemistry of liquids, 27(1994) 179185. 14. brandes, smithells, metals reference book ( sixth ed.) sec. 14-6, 1983. 15. r. hultgren, p. d., desai, d.t. hawkins, m. gleiser and k.k. kelley, selected values of the thermodynamic properties of binary alloys, asm, metal park, oh, 1973. microsoft word shree ram khadka shree ram khadka / bibechana 8 (2012) 53-58 : bmhss, p.53 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana bottlenecks to product rate variation problem with batching shree ram khadka central department mathematics,tribhuvan university, kathmandu, nepal p.o.box, 13143 e-mail: shreeramkhadka@gmail.com article history: received 25 may, 2011; accepted 8 june, 2011 abstract the product rate variation problem with batching minimizes the variation in the rate at which different models of a common base product are produced on the assembly lines with the assumption of significant setup and arbitrary processing times for each copy of each model. establishment of bottlenecks to the problem is important for the feasible and the optimal solution to the problem. in this paper, the lower and the upper bottlenecks to the problem are established. moreover, small bottlenecks that lead to optimality to some instances are investigated. keywords: product rate variation problem; batching; sequencing problem; nonlinear intege programming 1. introduction the product rate variation problem (prvp) with batching minimizes the variation in the rate at which different models of a common base product are produced in batches on the assembly lines [7,8]. the problem minimizes both the earliness and the tardiness penalties that respond to the customer demands for a variety of models without holding large inventories or incurring large shortages. this is a problem of finding a sequence of batches of different models distributed as evenly as possible on the assembly lines with the assumption of significant set up and arbitrary processing times. significant setup and arbitrary processing times can be undertaken when the planning horizon is partitioned into a finite number of time-buckets with equal length. the time length of a time-bucket is called a takt-time. a time-bucket consists of a setup and a batch (a copy or several copies) of a model. the assumption that allows significant setup and arbitrary processing times forces the product rate variation problem to be a two-phase problem [7,8]. we call this problem as the product rate variation problem with batching. the first phase is the batching problem that determines the batch size and the number of batches of the models. the second phase is the sequencing problem that sequences the batches. the problem that determines the size and the number of batches and minimizes the maximum variation in the rate at which batches of different models of a common base product are produced is called the bottleneck product rate variation with batching problem. shree ram khadka / bibechana 8 (2012) 53-58 : bmhss, p.54 the problem has been formulated as a non-linear integer programming with the objective of minimizing the deviation between the actual and the ideal production under the assumption that the system has sufficient capacity with significant set up and arbitrary processing times each batch of a model is produced in a unit time-bucket [7,8]. the problem has mathematically interesting base model with theoretical value and real world applications, see [3]. the problem has been extensively studied and solved in pseudo-polynomial time. the total prvp i.e. the problem with the objective of minimizing the total deviation has been solved in o(d�), [5] and the problem with the objective of minimizing the maximum deviation i.e. the bottleneck prvp in o(dlogd) time [4]. note that the solution to both cases of the problem is pareto optimal. establishment of bottlenecks is important to the optimization problem since the bottlenecks guaranty whether the optimal or feasible solution exists or not. it is clear that there exists no even feasible solution below the lower bottleneck and every instance has optimal solution below the upper one. in this paper, the lower and the upper bottlenecks to the problem are established. moreover, small bottlenecks that lead to optimality to some instances are investigated. the plan of the paper is as follows. section 2 reviews the mathematical model. in section 3, the lower and the upper bottlenecks are established. section 4 studies small bottlenecks that lead to optimality to some instances are investigated. the last section concludes the paper. 2. mathematical formulation let s and p be the setup and processing times of a model i, i = 1, . . . , n, respectively. the total demands d = ∑ d � �� are manufactured over the planning horizon t partitioned into � timebuckets i.e. the number of batches with the takt-time t = � �. there may exist batches with no models to be manufactured. such empty batches are potentially useful for the improvement of the system performance [5]. the takt-time satisfies t ≥ s + p ,i = 1, . . . , n. we denote x� , i = 0, 1, . . . , n; k = 1, . . . , � to be the actual cumulative number of batches for model i produced during the time-buckets 1 through k. the actual cumulative production of model i during the same time-buckets is γ x� , where γ = #$ #%$ is the average number of copies of model i per batch. the ideal cumulative production of model i during 1 through k timebuckets is γ kr� , where r� = #%$ � is the batch rate. the sequencing problem minimizes the deviation between the actual and the ideal productions. let m be a positive integer. the mathematical programming for the sequencing phase of the bottleneck product rate variation problem with batching is minimize [f* = max , (γ |x� − kr� | )*] (8) subject to ∑ x� = k� �� , k = 1, … , � (9) x� ( 0�) ≤ x� , i = 0,1, … , n; k = 2, … , � (10) x� � = d3 , x� 4 = 0, i = 0,1, … , n (11) x� ≥ 0 , integer i = 0,1, … , n; k = 1, … , � (12) constraint (9) ensures that exactly k batches are produced during the periods 1 through k. constraint (10) states that the total number of batches is a non decreasing function of k. constraint (11) guarantees that the batches are exactly met. constraints (9), (10) and (12) ensure that exactly one batch of a model is sequenced during a unit time-bucket. note that the formulation of the sequencing phase of the problem is similar to the formulation in [6] for the bottleneck product rate variation problem. shree ram khadka / bibechana 8 (2012) 53-58 : bmhss, p.55 we denote problem f* for the bottleneck product rate variation problem with batching with the objective function fm and the constraints (9) to (12). 3. bottlenecks establishment of bottlenecks is important to the optimization problem since the bottlenecks guaranty whether the optimal or feasible solution exists or not. it is clear that there exists no even feasible solution below the lower bottleneck and every instance has optimal solution below the upper one. let 5 be a bottleneck to the problem. theorem 1. the lower bottleneck to the problem is (67(1 − 8̃:;<)):. proof: a batch for some model i is sequenced at the first time-bucket. it holds min(67(1 − 8̃7)): ≤ 5. for any feasible solution, min(67(1 − 8̃7)): ≤ 5. ⟹ (67(1 − 8̃:;<)): ≤ 5. thus, the lower bottleneck is (67(1 − 8̃:;<)):. theorem 2. the upper bottleneck to the problem is (67 >1 − � �?):. proof: for 5 = (67 >1 − � �?):, @ab8̃7 + c de √gh i = jab8̃7 + 1 − c �k = ab8̃7, for ab8̃7 being integer. if ab8̃7 is not an integer, @ab8̃7 + c de √gh i = jab8̃7 + 1 − c �k ≥ lab8̃7m + 1, since ab8̃7 = lab8̃7m + (ab8̃7), where (ab8̃7) is the fractional part of ab8̃7. > ab8̃7. therefore, @ab8̃7 + c de √gh i ≥ ab8̃7. again, oab8̃7 − c de √gh p = qab8̃7 − 1 + c �r. = ab8̃7, for ab8̃7 being integer. if ab8̃7 is not an integer, oab8̃7 − c de √gh p ≤ slab8̃7mt, since (ab8̃7) ≤ 1 − c � < ab8̃7. therefore, oab8̃7 − c de √gh p ≤ ab8̃7 now, ∑ (@ab8̃7 + c de √gh i − o(a� − 1)8̃7 − c de √gh p)v 7�� ≥ ∑ ab8̃7 v 7�� − ∑ (a� − 1)8̃7 v 7�� ≥ ab − a� + 1. and ∑ (oab8̃7 − c de √gh p − @(a� − 1)8̃7 + c de √gh i)v 7�� shree ram khadka / bibechana 8 (2012) 53-58 : bmhss, p.56 ≤ ∑ ab8̃7 v 7�� − ∑ (a� − 1)8̃7 v 7�� ≤ ab − a� + 1. the bottleneck (67 >1 − � �?): is an upper bottleneck since it satisfies the hall’s theorem [4]. importance of upper bottleneck is that every instance has an optimal sequence when the given bottleneck is the upper bottleneck. however, it is not guaranteed for smaller value. the upper bottleneck for any instance with n = 1 is trivially 0. the lower bottleneck is important because a feasible sequence that exists for lower bottleneck is optimal. an optimizer always seeks instances that give rise to optimal sequence for smaller bottleneck. 4. small bottleneck every instance has optimal sequence when the given bottleneck is the upper bottleneck. however, it is not guaranteed for smaller value. a feasible solution with a minimum b is optimal. so, it is always interesting and important to seek small bottleneck. it has been established that there is no instance with a feasible sequence for the bottleneck 5 < (de w ):. theorem 3 no instance with x ≥ 2 of the problem has a feasible sequence for 5 < (de w ):. proof: the bottleneck (67(1 − 8̃:;<)): implies 1 − 8̃:;< ≤ c de √yh . for feasible sequence, z3:([, \) ≤ ]3:([, \), where z3:([, \) and ]3:([, \) are the earliest and the latest sequencing times, respectively. ⟹ ^_ c de √`h abe c d0�e c de √`h f̃e + 1 ⟹ 1 − 8̃7 ≤ b ge √5h for all [. ⟹ 1 − 8̃:7v ≤ b ge √5h ⟹ ∑ 8̃h́ v 7�� ≤ b ge √5h , 8̃h́ ≠ 8̃:7v ⟹ 8̃:;< ≤ ∑ 8̃h́ v 7�� ≤ b ge √5h ⟹ 1 − 8̃:;< ≥ 1 − b ge √5h . then, 1 − b ge √5h ≤ 1 − � ge √5h ⟹ de w ≤ √5h . this shows that any instance with the bottleneck less than (ge � ): does not yield any feasible sequence. for any feasible solution, (67|[kf̃e]0kf̃e|): ≤ (67|<�el0kf̃e|):, [ = 1, . . . , x, where [a8̃7] is the closest integer to a8̃7. it is observed that |[a8̃7] − a8̃7| = c m if � is even and |[a8̃7] − a8̃7| = �_c m� if � is odd [1]. this shows that any instance, x ≥ 2, with even � of the problem has lower bottleneck (de m ): and has lower bottleneck (de w ): for the instance, x ≥ 2, with odd �. for x ≥ 2, a standard instance (1, 2, 2b, . . . , 270�), [ = 1, . . . , x, has optimal sequence with bottleneck less than (de m ): [2]. theorem 4 the instance (1, 2, 2b, . . . , 270�), [ = 1, . . . , x, x ≥ 2 has an optimal sequence with 5 < (de m ): . shree ram khadka / bibechana 8 (2012) 53-58 : bmhss, p.57 proof: we consider the bottleneck 5 = (67(c m − c m�)): and assume that ([, \) be sequenced in the ideal position om^_c mabe p. for this instance, 5 = (67(mn_c_c mn_c )): < (de m ): and om^_c mabe p = 2v07(2\ − 1), [ = 1, . . . , x; \ = 1, . . . , pq7. we show that the instance has a feasible sequence with this bottleneck. consider, d0 c de √`h f̃e = ^_mn_c_c mn_c me_c mn_c = 2v07(2\ − 1) + c_(m^_c) me ≤ 2v07(2\ − 1) = d0�emn_c_c mn_c me_c mn_c + 1 = ^_cr c de √`h abe e� one can write z3:([, \) ≤ 2v07(2\ − 1) ≤ ]3:([, \), since 2v07(2\ − 1) is an integer. thus, the instance has a feasible sequence to the problem. now, we show that ([, \) does not compete with (ś, t́ ) with [ ≠ ś and j ≠ t́. assume that ([, \) and (ś, t́ ) be sequenced at the same position. ⟹ om^_c mabe p = omú_c mabv́ p ⟹ o(m^_c)(mn_c) me p = o(mú_c)(mn_c) mv́ p, for pq7 = 270�, [ = 1, . . . , x. ⟹ q(2\ − 1)2v07 − (2\ − 1)207r = q(2t́ − 1)2v0h́ − (2t́ − 1)20h́r . ⟹ mú_c mv́ = bẃ0� bv́ since both (2\ − 1) and (2t́ − 1) are odd, neither 27 divides (2\ − 1) nor 2h́ divides (2t́ − 1). this implies [ = ś and = t́ . thus, the copies do not compete one another for the position. a feasible sequence of which the copies do not compete one another for the position is optimal. 5. conclusion establishment of bottlenecks is important to the optimization problem since the bottlenecks guaranty whether the optimal or feasible solution exists or not. it is clear that there exists no even feasible solution below the lower bottleneck and every instance has optimal solution below the upper one. the lower and the upper bottlenecks to the problem has been established to be (67(1 − 8̃:;<)): and (67(1 − c �)):, respectively. it has been investigated that the only instance with optimality for the bottleneck less than (de m ): is (1, 2, 2b, . . . , 270�), [ = 1, . . . , x, x ≥ 2. further, there exists no such instance for the bottleneck less than (de w ): . references [1] n. brauner, and y. crama, discrete applied mathematics, 134 (2004), 25. [2] n. brauner, v. jost and w. kubiak, on symmetric fraenkel’s and small deviations conjecture, les cahiers du laboratoire leibniz-imag, 54, grenoble, france, 2004. [3] t. n. dhamala and s. r. khadka, iranian journal of optimization, 1, 3, (2009)266. [4] s. r. khadka and t. n. dhamala, iranian journal of optimization, 3 (2010) 477. [5] w. kubiak and m. yavuz, manufacturing and service operations management, 10, 3, (2008) 506. shree ram khadka / bibechana 8 (2012) 53-58 : bmhss, p.58 [6] g. steiner and j. s. yeomans, management science, 39, 6, (1993)728. [7] m. yavuz, e. akcali and s. tufekci, international journal of production research, 44, 15, (2006)3061. [8] m. yavuz and s. tufekci, international journal of production research, 45, 17, (2007) 389 microsoft word m.r. hassan and r.r. thapa _54-60_.doc m.r. hassan and r.r. thapa / bibechana 7 (2011) 54-60 : bmhss 54 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana applications of ks – variables in celestial mechanics m.r. hassana , r.r. thapab ∗∗∗∗ a dept. of mathematics, s.m. college, bhagalpur, india b dept. of mathematics, p.g. college, biratnagar, morang ,nepal article history: received 5 september 2010; revised 18 november 2010; accepted 29 november 2010 abstract this paper deals with the transformation of ks-variables and canonically conjugate variables from sideral (inertial) to synodic (rotating) form and their applications in “the circular restricted problem of three bodies in three-dimensional coordinate system” to form generating solutions. keywords : ks – transformation; ks – variables; orbital elements; generating solutions 1. introduction kustannheimo and steifel [1] presented a very convenient regularization method for the space motion of particles near an attracting centre. this mechanism leads to a transformation, called ks – transformation. the transformation is of the type xk = xk (uj), (k = 1, 2, ……… n), (j = 1, 2, 3 ,…….., n + 1) which increases the number of variables. in this regard schiefle [2] and steifel and schiefle [3] have considered the so – called generalized canonical transformation increasing the number of variables. as in physical space, ks – regularization is the most perfect regularization, so to solve all the problems easily of three dimensional synodic coordinate system by ks – variables; it is necessary to transform the ks – variables from sidereal to synodic form. in this paper, we attempted to present the ks – variables in synodic form and their simple application to the motion of an infinitesimal mass in the restricted problem of the three bodies in three dimensional synodic coordinate system have been shown. in earlier sections we just presented some important tools of ks – transformations in terms of orbital elements i, σω,,ω , t etc. in synodic coordinate system. some related and conjugate variables are also presented here in these sections. in later section, the synodic ks – variables are used to solve the equations of motion of infinitesimal mass in the circular restricted three – body problem in three dimensional synodic coordinate system in the form of generating solutions. the symbols used are as follows: i = inclination of the orbital plane with the plane of motion of the central body, ω = longitude of the ascending node, ω = argument of perihelion, φ = true anomaly, e = eccentric anomaly, t = physical time, ∗ corresponding author: raju ram thapa, post graduate campus, biratnagar, tribhuvan university, nepal, email:thaparajuram@yahoo.com m.r. hassan and r.r. thapa / bibechana 7 (2011) 54-60 : bmhss 55 s = psedo time, n = mean angular motion , . = , dt d / = , ds d σ = φ + ω 2. derivation of synodic ks – variables in 1965 kustaanheimo and steifel [1] defined an orthogonal matrix l (u), called ks – matrix, where l(u) =             −− −− −− 1234 2143 3412 4321 uuuu uuuu uuuu uuuu (1) lt (u) l (u) = l(u) lt (u) = (u, u) i. here lt(u) is the transpose of l(u), i is the 4 × 4 unit matrix and u = (u1, u2, u3, u4). if x = (x1, x2, x3) are three dimensional coordinates of a point, ks – transformation in sidereal frame is given by the single matrix equation: x = l(u) (u) (2) explicitly, x1 = u1 2 – u2 2 – u3 2 + u4 2 x2 = 2 (u1.u2 – u3.u4) (3) x3 = 2 (u1.u3 – u2.u3) in sidereal frame, the compact parametric representation of ks – variables in terms of orbital elements i, σ,ω in any plane curve having its orbital plane in general position, is given by [3] as : u1 = ] 2 )( sin[) 2 sin(] 2 )( cos[) 2 sin( 2 σσ −ω = −ω i u i (4) u3 = ] 2 )( cos[) 2 cos(] 2 )( sin[) 2 cos( 4 σσ +ω −= +ω i u i the sidereal parameters uj (j = 1, 2, 3, 4) of the particle itself are obtained by multiplying the square root of its distance ‘r’ from the central body. therefore, u1 = ] 2 )( cos[) 2 sin( σ−ωi r u2 = ] 2 )( sin[) 2 sin( σ−ωi r (5) u3 = ] 2 )( sin[) 2 cos( σ+ωi r u4 = ] 2 )( cos[) 2 cos( σ+ω − i r where r = (x1 2 + x2 2 + x3 2)½ = u1 2 + u2 2 + u3 2 + u4 2 = (u, u) (6) it may be noted that i & ω are fixed orbital elements whereas σ is only the variable orbital element. in terms of orbital elements i, ω & σ t he sidereal physical coordinates xi s of a point are given by x1 = )cos() 2 (cos)cos() 2 (sin 22 σσ +ω+−ω ii x2 = )sin() 2 (cos)sin() 2 (sin 22 σσ +ω+−ω ii (7) x3 = sin i. sinσ if x1 x2 plane rotates about x3 – axis with mean angular motion n, then at any time t, the synodic coordinates (y1, y2, y3) of the point, are given by y1 = x1cos nt + x2 sin nt, y2 = x1 sin nt + x2 cos nt, y3 = x3 (8) introduction of eqs. (7) in (8) yields m.r. hassan and r.r. thapa / bibechana 7 (2011) 54-60 : bmhss 56 y1 = )cos() 2 (cos)cos() 2 (sin 22 nt i nt i −+ω+−−ω σσ y2 = )sin() 2 (cos)sin() 2 (sin 22 nt i nt i −+ω+−−ω σσ (9) y3 = sin i. sinσ if q = (q1, q2, q3, q4) are the synodic ks – variables corresponding to physical synodic coordinates y = (y1, y2, y3), then y = l (q) q (10) explicitly: y1 = q1 2 – q2 2 – q3 2 + q4 2 , y2 = 2(q1q2 – q3q4) , y3 = 2(q1q3 + q2q4) (11) from eqs. (9) & (11) the parametric representation of a point in synodic ks – variables are given q1 = ] 2 )( cos[) 2 sin( nti −−ω σ q2 = ] 2 )( sin[) 2 sin( nti −−ω σ (12) q3 = ] 2 )( sin[) 2 cos( nti −+ω σ q4 = ] 2 )( cos[) 2 cos( nti −+ω − σ which satisfy all the eqs.(9) & (11) & properties of ks – transformations. the synodic parameters qj (j = 1, 2, 3, 4) of the particle itself can be obtained by multiplying by the square root of its distance ‘r’ from the central body. i.e. q1 = ] 2 )( cos[) 2 sin( nti r −−ω σ q2= ] 2 )( sin[) 2 sin( nti r −−ω σ (13) q3 = ] 2 )( sin[) 2 cos( nti r −+ω σ q4 = ] 2 )( cos[) 2 cos( nti r −+ω σ where r = (y1 2 + y2 2 + y3 2 ) ½ = q1 2 + q2 2 + q3 2 + x4 2 = (q, q) (14) from symbolic representations, we have φωσ += where ω is the constant orbital element. i.e. . . σ φ= 3. derivation of the generalized momenta corresponding to synodic ks – variables the set of synodic ks – variables given in eq.(13) acquire great importance, while studying the motion of an infinitesimal mass in synodic frame of reference. moreover, in hamiltonian dynamics, the generalized momenta corresponding to the generalized coordinates are also of great importance, so here we need to establish the generalized momenta corresponding to the synodic ks – variables in terms of orbital elements i, σ,ω etc. if x = (x1, x2, x3) are the momenta corresponding to sidereal physical coordinates x = (x1, x2, x3) and p = (p1, p2, p3, p4) are the generalized momenta corresponding to sidereal parametric coordinates u = (u1 u2 u3 u4), then momenta transformation is given by the single matrix equation: x = (1/2r) l(u) p (15) explicitly x1 = 2r )up + up up u(p 44332211 x2 = 2r )up up up u(p 34431221 + (16) x3 = 2r )up + up up u(p 24134231 ++ and t (p, u) = p1u4 – p2u3 + p3u2 p4u1 = 0 (17) the bilinear relation (16) plays an important key role in the above representations. the inverse transformation of (15) is given as : p = 2h (u) x (18) m.r. hassan and r.r. thapa / bibechana 7 (2011) 54-60 : bmhss 57 . . . . . . . . . . explicitly from eqs. (3) and (15) p1 = 2(x1u1 + x2u2 + x3u3) p2 = 2(-x1u2 + x2u1 + x3u4) (19) p3 = 2(-x1u3 + x2u4 + x3u1) p4 = 2(x1u4 x2u3 + x3u2) suppose that y = (y1, y2, y3) are the momenta is synodic system corresponding to y = (y1, y2, y3), then from the definition of momenta y1 = . 1 2y ny− , y2 = . 2 1y ny+ + ny1, y3 = . 3y (20) from eqs. (7) and (20) we get y1 = . 2 2[sin ( )sin( ) cos ( )sin( ) 2 2 i i nt ntσ σ σω − − − ω + − y2 = . σ 2 2[sin ( ) cos( ) cos ( ) cos( ) 2 2 i i nt ntσ σω − − + ω + − (21) y3 = . σ sin i cos σ if q = (q1, q2, q3, q4) are the generalized momenta in synodic system corresponding to q = (q1, q2, q3, q4), then with the help of eq.(18), the value of qj s may be represented as : q = 2h (q) y (22) therefore, q1 = 2(y1q1 + y2q2 + y3q3) = . ( ) 2 sin( )sin[ ] 2 2 i nt r σ σ ω − − = . 2σ q2 (23) therefore, q1 = . 2σ q2, q2 = . 2σ q1, q3 = . 2σ q4, q4 = σ2 q3 the set of variables qj s and qj s satisfy the bilinear relation t(q, q) = q1q4 – q2q3 + q3q2 – q4q1 = o (24) thus in both the systems t (p, u) and t (q, q) are invariant. also |q| 2 = (q, q) = 24 . 2 1 4j j q rσ = =∑ (25) 4. the equations of motion the regularized canonical equations of motion of the infinitesimal mass in synodic coordinate system given by kurcheeva [4] are : )4,3,2,1(, = ∂ ∂− = ∂ ∂ = j q k ds dq q k ds dq j j j j (26) where the hamiltonian k (regularized at r = 0 only) is given by : k = ½ 4)(2 034431221 2 4 1 2 −+−+−+∑ = cqqqqqqqqq j j ρ µ4+ [1 2ρ (q1 2 – q2 2 – q3 2 + q4 2 + 2 11 1 − r (c1+1)] (27) with r = q1 2 + q2 2 + q3 2 + q4 2 = 2ρ (28) = the distance of the infinitesimal mass from the first primary, r1 2 =1 + 2(q1 2 q2 2 q3 2 + q4 2) + 4ρ (29) = the square of the distance of the infinitesimal mass from the second pimary. c = ∑ ∞ =0i i ic µ , the jacobi’s constant, (30) the physical time ‘t’ and the pseudo time ‘s’ are connected by the differential equation 244)( ρ== r ds dt (31) m.r. hassan and r.r. thapa / bibechana 7 (2011) 54-60 : bmhss 58 5. generating solutions for generating solutions, taking 0=µ , the reduced hamiltonian, k0 = ½ 4)(2 034431221 2 4 1 2 −+−+−+∑ = cqqqqqqqqq j j ρ (32) the hamilton canonical equation of motion due to k0 are : )4,3,2,1(, 00 = ∂ ∂ = ∂ ∂ = j q k ds dq q k ds dq j j j j (33) thus the equations of motion of an infinitesimal mass in terms of synodic ks – variables can easily by derived from (30), (32) & (33) as : q1˝–4( 2ρ +q1 2 +q2 2 )q2΄+4(q1q4–q2q3)q3΄-4(q1q3+q2q4)q4΄=4q1(3 4ρ -c0) (34) q2˝+4( 2ρ +q1 2 +q2 2 )q1΄+4(q1q3+q2q4)q3΄+ 4(q1q4–q2q3)q4΄=4q2(3 4ρ -c0) (35) q3˝-4(q1q4-q2q3)q1΄-4(q1q3+q2q4)q2΄ 4( 2ρ +q3 2 +q4 2)q4΄ =4q3(3 4ρ -c0) (36) q4˝+4(q1q3+q2q4)q1΄-4(q1q4-q2q3)q2΄ +4( 2ρ +q3 2 +q4 2)q3΄ =4q4(3 4ρ -c0) (37) by multiplying eqs. (34) to (37) respectively by q1΄, q2΄, q3΄, q4΄ and integrating their sum, one has hcq j j ++−=∑ = 844' 2 0 6 4 1 2 ρρ (38) here, h is taken as the constant of integration. again multiplying (34) to (37) respectively by q2, q1, q4 & q3 and subtracting the sum of the second and fourth from the sum of the first and third and integrating we get q1΄q2 – q1 q2΄ + q3΄q4 – q3q4΄ = 2 4ρ + b (39) here b is the constant of integration to be determined by the initial conditions. it is well known that in the restricted three – body problem, mean angular motion is taken to be unity i.e. n = 1 (as the total mass of the primaries is 1 and separation = 1 ⇒ n = 1) and thus the synodic ks – variables qj s given in (13) will be of the form : q1 = ] 2 )( cos[) 2 sin( ti −−ω σ ρ q2 = ] 2 )( sin[) 2 sin( ti −−ω σ ρ (40) q3 = ] 2 )( sin[) 2 cos( ti −+ω σ ρ q4 = ] 2 )( cos[) 2 cos( ti −+ω − σ ρ from eqs. (27) and (40) one can easily find that )cos816(' '24'22' 4 1 2 iq j j σρρσρρ −++=∑ = (41) and q1΄q2 – q1q2΄ + q3΄q4 – q3q4΄ = 2 icos) 2 1 ( '24 σρρ − (42) the combinations eqs.(38, 41) and (39, 42) yield hci ++−=−++ 844)cos816() 4 1 ( 2 0 6'242'22' ρρσρρσρρ (43) and ( bi =cos) 2 1 '2σρ (44) following [4] and [5] at s = 0, ρ = 0 and which gives b = 0, consequently 'σ =0 i.e. σ = constant = 0σ (say) and the second degree differential equation reduces to m.r. hassan and r.r. thapa / bibechana 7 (2011) 54-60 : bmhss 59 2 0 2' 48 ρρ ch −+= (45) at h = 0, the generating solutions with generalized period s* = k 2 π , k∈n of the system of eqs. (34) to (37) are given by [6, 7] as : q1 = ] 2 )( cos[) 2 sin( 0 ti −−ω σ ρ q2 = ] 2 )( sin[) 2 sin( 0 ti −−ω σ ρ (46) q3 = ] 2 )( sin[) 2 cos( 0 ti −+ω σ ρ q4 = ] 2 )( cos[) 2 cos( 0 ti −+ω − σ ρ and q1 = ] 2 )( cos[) 2 sin( 0' ti −−ω σ ρ q2 = ] 2 )( sin[) 2 sin( 0' ti −−ω σ ρ (47) q3 = ] 2 )( sin[) 2 cos( 0' ti −+ω σ ρ q4 = ] 2 )( cos[) 2 cos( 0' ti −+ω − σ ρ where 00 ' 2sin(22 ssc −−=ρ ) (48) from (32) t = 10000 0 )]24sin(4)[ 1 ( ssscscc c +−+ (49) where s1 is the constant of integration. let us introduce two variables θ and ϕ , where θ = ( ) 2 (&) 2 00 tt −+ω = −−ω σ ϕ σ (50) introduction of (31) yield 2'' 2ρϕθ −== (51) q1 = θρ cos) 2 sin( i q2 = θρ sin) 2 sin( i (52) q3 = ϕρ cos) 2 cos( i q4 = ϕρ cos) 2 cos( i − and q1 = θρ cos) 2 sin(' i q2 = θρ sin) 2 sin(' i (53) q3 = ϕρ cos) 2 cos(' i q4 = ϕρ cos) 2 cos(' i − now from eq.(45) 2 0 2' 48 ρρ ch −+= (54) integrating eq.(54) with respect to s we get s = ∫ −+ ρ ρ ρ 0 2 048 ch d with the substitution αρ sin 4 )8( 0c h+= one can easily find sc02=α & sc c h 0 0 2sin 4 )8( +=ρ (55) using eqs. (58) in (35) and (55) one has t = )]24sin(4[8 )8( 00000 sscsccc h −− + (56) m.r. hassan and r.r. thapa / bibechana 7 (2011) 54-60 : bmhss 60 ), 2 ( 1 t −= ωθ ) 2 ( 2 t −= ωϕ (57) where 1ω and 2ω are the constants of integration. thus the solutions of the problem in question at 0=µ depend upon three arbitrary constants h, 1ω and 2ω . 6. discussion a system of differential equations may have infinitely many generating solutions so there are many possibilities of generating solutions of the differential eqs. (26). here in our case (50) represents one set of generating solution for the satellite motion. references [1] p. kustaanheimo and e. steifel, j. reine angew math. 218 (1965) 204. [2] g. scheifle, , cele. mech., 2 (1970)296. [3] e. stiefel, and g. scheifle, linear and regular celestial mechanics, berlin, heidelberg, new york,(1971). [4] i.v. kurcheeva, cele. mech, 15 (1977) 353. [5] a. ahmad, cele. mech & dynamical astronomy, 61 (1995)181. [6] g.a. krashinaski, bull., i.t.a , 9 (1963)205. [7] m.r. hassan, bull. astr. soc., india, 2001. 94-102 kumar p. dahal r c o s t n k.p. dahal et al. / bibechana 11(1) (2014) 94-102: (online publication: march, 2014) p.94 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana study on the soil corrosivity towards the buried water supply pipelines in madhyapur thimi municipality, bhaktapur kumar p. dahal, dinesh k. c., jagadeesh bhattarai* central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal *corresponding author: e-mail: bhattarai_05@yahoo.com. accepted for publication: february 16, 2014 abstract this research work is carried out to identify the corrosive nature of soils towards the buried-galvanized steel and cast iron pipelines buried in sanothimi areas of madhyapur thimi municipality, bhaktapur based on different soil parameters such as organic content, moisture content, ph, resistivity, oxidation-reduction potential, chloride and sulfate ions. the soil parameters of the collected soil samples from the study areas were analyzed using standard astm methods. concentrations of these soil parameters measured in this study were found as: organic content (0.97.9%), moisture content (8.0-36.7%), ph (6.8-7.7), resistivity (3900-16700 ohm.cm), oxidation-reduction potential (337-461 mv vs she), chloride (25-71 ppm) and sulfate (35-464 ppm) contents. these soil parameters gave an indication of “mildly corrosive” to “less corrosive” nature of soils on the galvanized steels and cast iron pipelines buried in the study areas. based on the findings of the present studies, it can be advised to the related authorities or local people that simple modification of the soils by using cheapest non-conducting materials like gravel or sand around the buried water supply pipelines before undergrounding them in the study areas is very beneficial from the corrosion point of view to increase their life time. © 2014 rcost: all rights reserved. keywords: chloride & sulfate; moisture; ph; resistivity; oxidation-reduction potential. 1. introduction the study of corrosion behavior of the buried metallic materials in soil is of major importance in corrosion studies, because millions of kilometers of the buried pipelines are used to supply the drinking water, petroleum products and other hazardous chemicals all over the world [1,2]. it was reported that about 0.6% of the water supply pipelines used in usa was replaced due to the corrosion damage by soil each year during 1990s [1]. the usa has over 3.7 million kilometer of pipelines crossing the country transporting natural gas and hazardous liquids from sources to consumers [2]. similarly, it was reported that about 150,000 km of ferrous pipelines used to supply the drinking water in australia were also affected by localized corrosion leading to leaking [3]. in gutenberg of sweden alone the water supply system for instance includes a total pipe length of 2000 km, valued at almost 700 million euro. the water supply pipelines are kept in repair at an annual cost of three million euro; almost 50% of the damage can be related directly or indirectly to soil corrosion [4]. there is a high degree of environmental and economic consequences of soil corrosivity due to a failure of the buried pipelines used to supply the drinking water, natural gas and crude oil all over the world. the corrosion of the buried materials in disturbed soil is mainly influenced by a number of soil parameters like moisture, ph, resistivity, oxidation-reduction potential (orp), chloride and sulfate contents k.p. dahal et al. / bibechana 11(1) (2014) 94-102: (online publication: march, 2014) p.95 in soil and so on [5-27], because the soil corrosivity towards the buried materials in an undisturbed soil is generally negligible as compared with that of the disturbed soils [5]. estimation of these parameters of the disturbed soils can give an indication of their corrosive nature towards the buried pipelines. it was studied the corrosion behavior of galvanized steels, bare steels and zinc metal in different soils of usa [9,10]. it was found that the corrosion of mild steel was increased when the soil moisture content was found more than 60 % [9,10,12,21]. the soil ph below 5 can lead to extreme corrosion of the buried materials by soil and hence soil showing ph 7 is most desirable to minimize the corrosion of the buried materials in soils [5,6]. therefore, the soil ph ranges from 5 to 8 is not usually considered to be a problem for the corrosion of galvanized steels, cast iron, zinc coatings and so on in soil environments [7,8]. the soil resistivity (reverse of soil conductivity) is historically used as one of the broad indicators for the soil corrosivity towards the buried metallic materials. there is found to be good correlation between the soil resistivity and the corrosion rate of the buried materials. it was reported that the soil resistivity decreased with increasing the moisture content [19]. hence, the corrosive nature of soil towards the buried materials is increased with increasing the moisture content or decreasing the soil resistivity [10,19]. consequently, sand and gravel are considered to be less corrosive towards the galvanized steels, because they showed a high resistivity of 6000 ohm.cm or more. on the other hand, clayey and silty soils with the resistivity less than 1000 ohm.cm are generally considered to be highly corrosive for the buried galvanized steels [5,6,28-30]. the measurement of soil orp is significant to explain the soil corrosivity towards the buried materials, because it determines partially the stability of the materials. on the other hand, soil is generally considered to be “mildly corrosive” if the sulfate and chloride ions are below 200 ppm and 100 ppm, respectively, for soil with ph range between 5–8 and the soil resistivity greater than 3,000 ohm.cm [5-6, 28-30]. in this context, it is meaningful to mention here that the supply of the drinking water from water reservoirs to distribution terminal in nepal is mostly through the buried-galvanized steels as well as cast iron pipelines, and the study of the corrosion behavior of these buried materials in soil of kathmandu valley is becoming one of the most importance topics of the underground corrosion [31-36]. the main objective of the present research work is to study the effects of different soil parameters for corrosivity towards the buried-galvanized steel and cast iron pipelines used to supply the drinking water in sanothimi area of madhyapur thimi municipality of bhaktapur, nepal. 2. materials and experimental methods total twenty soil samples were collected from sanothimi area of bhaktapur, nepal which is located within the latitude of 27o 40’ 45”-27o 41’ 10” north and the longitude of 85o 22’ 00”-85o 23’ 00” east as shown in fig. 1(a). eight soil samples were taken from the depth of about 1 meter from the ground level for the real location of the buried-pipelines used to supply the drinking water in the study area as shown in fig. 1(b). to study the effects of depths for soil corrosivity towards the buried metallic materials, twelve more soil samples were also taken from different depths of about 0.25, 0.50, 0.75 and 1.25 meters below the ground level from three sampling sites (i.e., st2, st3 & st8). the soil sample was taken in an air tight polyvinyl bag so that the moisture remained same for a period of moisture content analysis in the laboratory. organic content in the soil samples was estimated using hydrogen peroxide treatment method. moisture content in soil was determined using weight loss method in accordance with the astm d4959-07 standards [37]. a 1:2 soil-water suspension of each soil sample was used to determine the soil ph using a digital ph-meter in accordance with the astm g51-95 (2012) standards [38]. the conductivity bridge was used to determine the electrical conductivity of a 1:2 soil-water suspension in accordance with the astm g187-05 standards [39]. the soil resistivity was calculated from the conductivity. the orp of the k.p. dahal et al. / bibechana 11(1) (2014) 94-102: (online publication: march, 2014) p.96 (a) (b) figure 1: (a) location and (b) satellite maps of the sampling sites of sanothimi area of madhyapur thimi municipality, bhaktapur. k.p. dahal et al. / bibechana 11(1) (2014) 94-102: (online publication: march, 2014) p.97 soil sample was measured with the help of a digital potentiometer in accordance with the astm g200-09 standards [40]. the recorded orp values vs sce was converted to reference value of the saturated hydrogen electrode (she). a platinum wire and a saturated calomel electrode (sce) were used as working and reference electrode, respectively. argentometric titration was used to determine the chloride content in soil. the chloride content in a 1:2 soil-water suspension was determined by titrating the soil suspension against standard silver nitrate solution using potassium chromate as an indicator. gravimetric method was used to estimate the amounts of sulfate content in soil sample. the details of these methods are discussed elsewhere [31-36]. 3. results and discussion 3.1 analysis of parameters of soils collected from the depth of one meter below it was found that organic and moisture contents in the collected twenty soil samples ranges from 0.9-7.9% and 8-37%, respectively. among eight soil samples from sanothimi area of bhaktapur, the organic contained in five samples was less than 5% while reaming three contained more than 5% and the sample st-8 contained about 11% organic content as shown in fig. 2(a). similarly, one soil sample contained less than 10%, three samples contained 10-20% and remaining four samples contained 21-40% moisture content among eight soil samples collected from the depth of 1 m below the ground level as shown in fig. 2(b). these results revealed that 50% of the soil samples (4 out of 8 soil samples) are assumed to be "mildly corrosive", while eight samples containing less than 20% moisture content are classified to "less corrosive" for the galvanized steels and cast iron pipes based on the moisture content. ph is another an important soil parameter that determine the soil corrosivity towards the buriedgalvanized steel and cast irons pipelines. the ph value of all eight soil samples collected from study area was in near neutral ph range of 6.8-7.7 as shown in fig. 2(c). therefore, these eight soil samples are assumed to be "non corrosive" towards the buried-galvanized steel and cast iron pipelines. figure 2(d) shows the results of the soil resistivity of eight soil samples collected from sanothimi study area. among these eight soil samples, one has the soil resistivity less than 5000 ohm.cm, four samples have between 5,000-10,000 ohm.cm and remaining three samples showed the resistivity more than 20,000 ohm.cm. it is clearly observed that the soil resistivity is directly correlated with the moisture content in soil samples. the soil samples having high amount of moisture content showed lower value of the soil resistivity as shown in fig. 2(e). these results revealed that all most all soil samples, except st-2 are assumed to be "mildly corrosive" to "non-corrosive" nature towards the buriedgalvanized steel and castiron pipelines based on the classification of the astm and nace standards [28-30]. the st-2 soil is assumed to be "moderately corrosive" and is more corrosive than those other seven soils. the orp value of all eight soil samples of the study area was in the range of 337 to 451 mv vs she. among these soil samples, three samples have the orp value in the range of 200-400 mv vs she and remaining five soil samples have the orp value more than 400 mv vs she as shown in fig. 2(f). these results revealed that all the soil samples are belonged to "non-corrosive" for the buried-structural materials based on the johe's classification as shown in table 1 [13,41]. the chloride and sulfate contents in the collected eight soil samples from the study area were found to be in the ranges of 25-71 ppm and 35-229 ppm, respectively, which is shown in figs 2(g) and 1(h). it was found that all of the soil samples contained less than 100 ppm of chloride which is the upper limit of the chloride content in the soil for showing "mildly corrosive" nature towards the buried galvanized steel as well as the cast iron pipelines as shown in fig. 2(g). on the other hand, most of the soil samples collected from sanothimi area, except three samples (i.e., st-4, st-7 & st-8) contained less than 200 ppm sulfate ions which is upper limits of the sulfate content in the soil for showing "mildly corrosive" nature toward the buried-galvanized steel and cast iron pipelines used to supply the drinking water based on the sulfate content results from the present study. k.p. dahal et al. / bibechana 11(1) (2014) figure 2: (a) organic content, (b) moisture content, (c) soil ph, (d) soil resistivity, (e) moisture content & soil resistivity relationship (f) oxidation-reduction potential (g) chloride content and (h) sulfate content in each soil samples collected from sanothimi area of bhaktapur, nepal. / bibechana 11(1) (2014) 94-102: (online publication: march, 2014) p. (a) organic content, (b) moisture content, (c) soil ph, (d) soil resistivity, (e) moisture content & soil reduction potential (g) chloride content and (h) sulfate content in each soil area of bhaktapur, nepal. : (online publication: march, 2014) p.98 (a) organic content, (b) moisture content, (c) soil ph, (d) soil resistivity, (e) moisture content & soil reduction potential (g) chloride content and (h) sulfate content in each soil k.p. dahal et al. / bibechana 11(1) (2014) 94-102: (online publication: march, 2014) p.99 table 1: relationship between different soil parameters and soil corrosivity towards the buried materials. soil parameter soil corrosivity 1. soil resistivity (ohm.cm)[28-30] > 20,000 10,000-20,000 5,000-10,000 3,000-5,000 1,000-3,000 < 1,000 essentially noncorrosive mildly corrosive moderately corrosive corrosive highly corrosive extremely corrosive 2. chloride content (ppm)[28-30] < 100 mildly corrosive 3. sulfate content (ppm)[28-30] < 200 mildly corrosive 3.2 analysis of parameters of soils collected from different depths the effect of soil depths on the soil parameters was carried out to study the corrosive nature of soils of the different depths towards the buried galvanized steel and cast iron pipelines. fifteen soil samples were collected from different depths of 0.25, 0.50, 0.75, 1.00 and 1.25 meters below the ground level of three sampling sites (i.e., st-3, st-4 and st-8) as indicated in fig. 1(b). figures 3(a) to 3(f) summarized the results of organic content, moisture content, ph, orp, chloride and sulfate contents in soils. in general, the contents of organic matter and moisture in soil samples were increased with increasing the depth of soil sampling part. however, the amount of chloride content is decreased with increasing the soil depths mostly the upper parts of the soil level as shown in fig. 3(e), probably due to the contamination of some chloride containing pesticides or herbicides in the study areas. on the other hand, there is no effect of depths in soil ph and orp as shown in figs 3(c) and 3(d), respectively. but there is no regular pattern of changes of sulfate content with depths soil. details about such effects will be studied in more soil samples and discussed subsequently. 4. oxidation–reduction potential [13,41] (mv vs she) >400 201–400 100–200 <100 non–corrosive mildly corrosive moderately corrosive severe corrosive k.p. dahal et al. / bibechana 11(1) (2014) figure 3: (a) organic content, (b) moisture content, (c) soil ph, (d) soil resistivity, (e) moisture content & resistivity relationship (f) oxidation-reduction potential (g) chloride content and (h) sulfate content in each soil samples collected from sanothimi area of bhaktapur, nepal. / bibechana 11(1) (2014) 94-102: (online publication: march, 2014) p. (a) organic content, (b) moisture content, (c) soil ph, (d) soil resistivity, (e) moisture content & reduction potential (g) chloride content and (h) sulfate content in each soil samples collected from sanothimi area of bhaktapur, nepal. 2014) p.100 (a) organic content, (b) moisture content, (c) soil ph, (d) soil resistivity, (e) moisture content & soil reduction potential (g) chloride content and (h) sulfate content in each soil k.p. dahal et al. / bibechana 11(1) (2014) 94-102: (online publication: march, 2014) p.101 conclusion the following conclusions are drawn from the above results and discussion on the corrosive nature of the twenty soil samples collected from sanothimi area of madhyapur thimi municipality, bhaktapur. most of the soil samples of the study area are assumed to be “mildly corrosive” to “less corrosive” towards the galvanized steels and cast iron pipelines buried in the study areas based on the findings of some important soil parameters those affect the buried materials corrosion. consequently, it can be advised to the local people and government authorities that simple modification of the soils by mixing gravel or sand around the buried water supply pipelines before undergrounding them in the study areas is very beneficial from the corrosion point of view to increase their life time. references [1] g. j. kirmeyer, w. richards, c. d. smith. an assessment of the water distribution system and associated research needs. american water works research foundation, denver, 1994. [2] r. e. ricker, j. res. natl. inst. stand. technol., 115 (2010) 373. [3] wsaa. national performance report-urban water utilities-part c, water services association of australia, 2009. [4] m. norin, t.-g. vinka, mater. corros., 54 (2003) 641. [5] h. h. uhlig, r. w. revie, in corrosion and corrosion control; an introduction to corrosion science and engineering, fourth edition, john wiley and sons, new york, usa, 2008. [6] j. bhattarai, frontiers of corrosion science, 1st edition, kshitiz publication, kirtipur, kathmandu, nepal, 2010. [7] k. h. logan, in underground corrosion, circular of the bureau of standards c450, national bureau of standards, 1957. [8] t. r. jack, m. j. wilmott, corrosion by soils; uhlig’s corrosion handbook, third edition (ed. r. w. revie), john wiley & sons, inc. and the electrochemical society inc., n.j. pennington, 2011. [9] i. a. denison, m. romanoff, j. res. natl. bur. stnd., 49 (1952) 299. 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[31] j. bhattarai, investigation of soil parameters for their corrosivity on buried galvanized steel pipelines used in kathmandu valley. research report, submitted to nepal academy of science and technology-nast, khumaltar, lalitpur, nepal, 2013. [32] j. bhattarai, scientific world, 11 (2013) 43. [33] y. r. dhakal, k. p. dahal, j. bhattarai, bibechana, 10 (2014) 82. [34] p. p. bhandari, k. p. dahal, j. bhattarai, j. inst. sci. technol., 18 (2013) 71. [35] m. gautam, j. bhattarai, nepal j. sci. technol., 14 (2013) 65. [36] s. k. regmi, j. bhattarai, scientific world (in press). [37] astm d4959-07, “standard test method for determination of water (moisture) content of soil by direct heating”, annual book of astm standards, american society for testing and materials, 2007. [38] astm g51-95 (2012), “standard test method for measurement of ph of soil for use in corrosion testing”, annual book of astm standards, american society for testing and materials, 2012. 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[41] d. a. jones, in principles and prevention of corrosion, second edition, prentice hall, 1996. microsoft word sujit kumar shah et al.doc sujit kumar shah et al. / bibechana 8 (2012) 37-45 : bmhss, p.37 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana a comparative study of critical micelle concentration (cmc) and free energy of micellization (∆g o m) of cationic surfactant (dodecyltrimethylammonium bromide, dtab) and anionic surfactant (sodiumdodecyl sulphate, sds) in different composition of methanol-water mixed solvent media by conductometric method at 308.15 k sujit kumar shah, tulasi prasad niraula, ajaya bhattarai, sujeet kumar chatterjee* department of chemistry, mahendra morang adarsh multiple campus (tribhuvan university), biratnagar, nepal *corresponding author: sujeetkumarchatterjee@yahoo.com article history: received 14 june, 2011; accepted 10 july, 2011 abstract precise measurements on the specific conductivity of cationic surfactant (dodecyltrimethylammonium bromide) and anionic surfactant (sodiumdodecyl sulphate) in methanol-water mixed solvent media containing 0.1, 0.2 and 0.3 volume fractions of methanol are reported at 308.15 k. specific conductivities of dodecyltrimethylammonium bromide and sodiumdodecyl sulphate increase with increase in concentration and decrease with increase in the volume fractions of methanol. critical micelle concentration (cmc) increases with increase in volume fraction of methanol in case of both surfactants. free energy of micellization (∆gºm) has been calculated. increase in cmc with increase in volume fractions of methanol has been explained in terms of breaking of structure of water due to co-solvent effect. keywords: critical micelle concentration; methanol-water mixed solvent media; specific conductivity; dodecyltrimethylammonium bromide; sodiumdodecyl sulphate 1. introduction surfactants have various applications to different daily use products and in research fields [1]. zana and coworkers [2-6] have reported extensive studies on the effect of the linear alcohols ethanol to hexanol on the critical micelle concentration (cmc), micelle molecular weight and degree of ionisation. the behaviour of sodiumdodecyl sulphate micelles in the presence of n-alcohols has been extensively investigated [714]. according to rubio et al. [13] moderately hydrophobic alcohols in low concentration promote micellization probably by residing at the micellar surface and reducing unfavourable water hydrocarbon contacts. however, at higher concentrations these alcohols destabilize micelles by displacing water from the surface, therefore decreasing its effective dielectric constant, increasing head group repulsions, and disrupting surfactant packing. since water-alcoholsurfactant systems are frequently used as media in the studies of chemical equilibria and reaction rates, it is essential to investigate the effect of the nature of the alkyl groups in the alcohol on the cmc of the surfactants. addition of alcohols to aqueous solutions of sujit kumar shah et al. / bibechana 8 (2012) 37-45 : bmhss, p.38 surfactants has allowed the investigation of the effect of hydrophobic interactions on the micellar structure [15]. almgren et al. [16] investigated on the effect of formamide and other solvents, including dimethylsulfoxide and dimethylacetamide on the micelle formation of sodiumdodecyl sulphate. they observed the reduction of both critical micelle concentration (cmc) and mean aggregation number of sodiumdodecyl sulphate micelles upon the addition of formamide. the gradual replacement of water with other organic polar solvent allows one to explore a wide bulk phase polarity range and its influence on micellization. addition of small amount of an organic solvent has been known to produce marked changes, in the critical micelle concentration (cmc) of ionic surfactants due to tendency of added organic solvent either to break or make the water structure through solvation of hydrophobic tail of the surfactant by the hydrocarbon part of the organic solvent [17-18]. akbas et al. [19] carried out an investigation on the effect of ethanol and ethylene glycol on the cmc of cetyltrimethylammonium bromide. they observed that cmc decreases upon the addition of ethanol and ethylene glycol. the aim of the present work is to investigate the effect of methanol on the micellar behaviour of dodecyltrimethylammonium bromide and sodiumdodecyl sulphate at 308.15 k by conductance measurement. 2. experimental section methanol (merck, india) was distilled with phosphorous pentoxide and then redistilled over calcium hydride. the purified solvent had a density of 0.77723 ± 0.00004 g.cm -3 and a co-efficient of viscosity of 0.47424 ± 0.00005 mpa.s at 308.15 k; these values are in good agreement with the literature values [20]. triply distilled water with a specific conductance less than 10 -6 s.cm -1 at 308.15 k was used for the preparation of the mixed solvents. the physical properties of methanol-water mixed solvents used in this study at 308.15 k are shown in table 1 and those values are matched with the published works [21-23]. the relative permittivity of methanol-water mixtures at the experimental temperatures were obtained by regressing the relative permittivity data as function of solvent composition from the literature [24]. dodecyltrimethylammonium bromide (98% pure) and sodiumdodecyl sulphate (98% pure) were obtained from loba chemi, india and were dried in oven for one hour before use. solutions were prepared of dodecyltrimethylammonium bromide and sodiumdodecyl sulphate by weighing appropriate amount in an electronic balance, (afcoset-er120a) with a precision of 0.0001g. conductivities were measured using digital conductivity meter (306) of systronics which is a microcontroller based instrument for measuring specific conductivity of solutions. the accuracy in conductance measurements is ± 1%. the cell was calibrated by the method of lind and co-workers [25] using aqueous potassium chloride solution. measurements were carried out in a jacket containing conductivity cell of cell constant 1.002 cm –1 . water was circulated in the jacket from thermostat and the temperature was maintained within ± 0.1ºc. the details of the experimental procedure have been described earlier [26-27]. several independent solutions were prepared and runs were performed to ensure the reproducibility of the results. due correction was made for the specific conductance of the solvent by subtracting the specific conductance of the relevant solvent medium from those of the electrolyte solutions. in order to avoid moisture pickup, all solutions were prepared in a dehumidified room with utmost care. in all cases, the experiments were performed in three replicates. 3. result and discussion conductivity measurements are carried out in 0.1, 0.2 and 0.3 volume fractions of methanol in methanolwater mixed solvent media for dodecyltrimethylammonium bromide and sodiumdodecyl sulphate at 308.15 k in order to evaluate the cmc. the plots between specific conductance and concentration of surfactants solution in methanol-water mixed solvent media at 308.15 k is shown in fig. 1 to fig. 6. the critical micellar concentrations (cmc) of dodecyltrimethylammonium bromide and sodiumdodecyl sulphate are found very easily from conductometry. these are obtained from the inflections in the plots of 0 1 2 3 0 0.02 0.04 0.06 [s d s ] / mol l -1 κ / m s c m -1 sujit kumar shah et al. / bibechana 8 (2012) 37-45 : bmhss, p.39 specific conductivity versus surfactant concentration. the data points above and below the inflection are fitted to two linear equations, and the cmcs are obtained from the common intersection. this method is found to be reliable and convenient for the present system because of the significant variations of specific conductivity with surfactant concentration in the preand postmicellar regions which allowed us to draw two unambiguous straight lines above and below the cmc. temperature dependence values of cmc and α (degree of ionisation) can be used to obtain information about thermodynamics of micellization. degree of ionisations are calculated by taking ratio of slope of line after micelle and the slope of line before micelle. the standard gibbs free energy of micellization for ionic surfactant (∆gºm) are calculated from the relation derived for the charged phase separation model of micellization[28-29]. this relation is given by ∆gºm = (2-α) r t ln(χcmc) (1) χcmc represents cmc in mole fraction. the values of cmc and standard free energy of micellization of dodecyltrimethylammonium bromide and sodiumdodecyl sulphate are listed in table 2. with the increase in the volume fraction of methanol, values of cmc for both surfactants increases. this increase in values of cmc is also explained by the decrease in negative values of standard free energy change. fig. 7 shows the effect of volume fraction of methanol on the free energy change for the micellization of dodecyltrimethylammonium bromide at 308.15 k. it can be observed that the volume fraction of methanol in water increases the negative values of free energy of micellization (∆gºm) decreases thus making less favourable for the micelle to form. similar behaviour can be seen in case of sodiumdodecyl sulphate (fig. 8). it is well known that addition of solvents, which act as water structure breakers decrease the hydrophobic effect resulting into an increase in the cmc of ionic surfactants [30]. breaking of water structure by methanol would facilitate interactions between the hydrophobic tail of the surfactant molecules and the hydrophobic part (methyl group) of the methanol and consequently, the local concentration of methanol molecules around the surfactant monomers becomes larger than the average of the bulk. solvation of the surfactant molecules by the hydrophobic part of the organic solvent would, therefore, lead to delaying the aggregation of the surfactant monomers to form micelles and hence the increase in the cmc of the surfactant. fig. 1: variation of specific conductance with molar concentration of sodiumdodecyl sulphate (sds) in methanol water mixed solvent media containing 0.1 volume fraction of methanol at 308.15 k 0 1 2 3 0 0.02 0.04 0.06 [ s d s ] / mol l -1 κ / m s c m -1 0 1 2 3 0 0.02 0.04 0.06 [ s d s ] / mol l -1 κ / m s c m -1 sujit kumar shah et al. / bibechana 8 (2012) 37-45 : bmhss, p.40 fig. 2: variation of specific conductance with molar concentration of sodiumdodecyl sulphate (sds) in methanol water mixed solvent media containing 0.2 volume fraction of methanol at 308.15 k. fig. 3: variation of specific conductance with molar concentration of sodiumdodecyl sulphate (sds) in methanol water mixed solvent media containing 0.3 volume fraction of methanol at 308.15 k. 0 0.5 1.0 1.5 2.0 0 0.01 0.02 0.03 0.04 0.05 [dtab] / mol l -1 κ / m s c m -1 0 0.5 1.0 1.5 2.0 0 0.01 0.02 0.03 0.04 0.05 [dtab] / mol l -1 κ / m s c m -1 sujit kumar shah et al. / bibechana 8 (2012) 37-45 : bmhss, p.41 fig. 4: variation of specific conductance with molar concentration of dodecyltrimethylammonium bromide (dtab) in methanol water mixed solvent media containing 0.1 volume fraction of methanol at 308.15 k. fig. 5: variation of specific conductance with molar concentration of dodecyltrimethylammonium bromide (dtab) in methanol water mixed solvent media containing 0.2 volume fraction of methanol at 308.15 k. 0 0.5 1.0 1.5 2.0 0 0.01 0.02 0.03 0.04 0.05 [dtab] / mol l -1 κ / m s c m -1 15 20 25 30 35 40 0 0.1 0.2 0.3 0.4 volume fraction of methanol in water -∆ g 0 m / ( k j m o l-1 ) sujit kumar shah et al. / bibechana 8 (2012) 37-45 : bmhss, p.42 fig. 6: variation of specific conductance with molar concentration of dodecyltrimethylammonium bromide (dtab) in methanol water mixed solvent media containing 0.3 volume fraction of methanol at 308.15 k. fig. 7: variation of standard free energy change of micellization of dodecyltrimethylammonium bromide (dtab) with volume fractions of methanol in water. 15 20 25 30 35 40 0 0.1 0.2 0.3 0.4 volume fraction of methanol in water -∆ g o m / ( k j m o l-1 ) sujit kumar shah et al. / bibechana 8 (2012) 37-45 : bmhss, p.43 fig. 8: variation of standard free energy change of micellization of sodiumdodecyl sulphate (sds) with volume fraction of methanol in water. table 1: properties of methanol-water mixtures containing 0.1, 0.2, and 0.3 volume fractions of methanol at 308.15 k. t/k 0ρ /g.cm -3 0η / mpa.s d 0.1 volume fraction of methanol 308.15 0.9797 0.8665 71.57 0.2 volume fraction of methanol 308.15 0.9663 1.0217 68.14 0.3 volume fraction of methanol 308.15 0.9516 1.1418 64.25 sujit kumar shah et al. / bibechana 8 (2012) 37-45 : bmhss, p.44 table 2: values of cmc and free energy of micellization of sodiumdodecyl sulphate (sds) and dodecyltrimethylammonium bromide (dtab) in methanol water mixed solvent media containing 0.1, 0.2 and 0.3 volume fractions of methanol at 308.15 k volume fractions of methanol cmc (mm) degree of ionisation (α) -∆gºm ( kj mol -1 ) sds 0.0 8.7 * 0.1 9.31 0.493 33.28 0.2 10.04 0.473 32.97 0.3 10.75 0.466 32.83 dtab 0.0 15.6 ** 0.1 18.75 0.263 35.29 0.2 21.62 0.237 34.90 0.3 28.86 0.233 33.38 ref. no. [31] *, [32] ** 4. conclusion , effects of concentration and solvent composition on dodecyltrimethylammonium bromide and sodiumdodecyl sulphate in methanol–water mixed solvent media have been studied by measuring specific conductance through conductometric method. the following conclusions have been drawn from the above results and discussion. the conductance decreases with increase of alcohol content for the studied methanol-water mixed solvent system. the presence of methanol reduces the dielectric constant of the solvent phase and makes easier for the formation of ion-pairs in the solution phase. the cmc increases with the increase of methanol for dodecyltrimethylammonium bromide and sodiumdodecyl sulphate but dodecyltrimethylammonium bromide has higher cmc values in comparison with sodiumdodecyl sulphate in the measured ranges of methanol-water mixed solvent media. furthermore, the negative value of free energy of micellization decreases with the increase of methanol for dodecyltrimethylammonium bromide and sodiumdodecyl sulphate but dodecyltrimethylammonium bromide has higher values in comparison with sodiumdodecyl sulphate in the measured ranges of methanol-water mixed solvent media. acknowledgements the authors are grateful to mr. g. shrivastav (head of the department of chemistry), mahendra morang adarsh multiple campus for providing research facilities. one of the authors (s.k. shah) is thankful to university grants commission (ugc), nepal, for providing financial support to pursue the research. sujit kumar shah et al. / bibechana 8 (2012) 37-45 : bmhss, p.45 references [1] s. k. shah, a. bhattarai and s. k. chatterjee, bibechana 7(2011) 61. 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[32] d. lópez-díaz and m. m. velázquez, chem. educator 12 (2007) 5. microsoft word tilak gautam-f.doc t.n. mandal and t.p. gautam / bibechana 8 (2012) 131-138 : bmhss, p. 131 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana chemical analysis of fodder tree leaves found in sunsari district, nepal t.n. mandal 1 and t.p. gautam 2* 1 department of botany, post graduate campus (tribhuvan university), biratnagar 2 department of botany, mahendra morang a. m. campus (tribhuvan university), biratnagar * corresponding author: tilak prasad gautam, department of botany, m.m.a.m. campus (tribhuvan university), biratnagar, nepal, email:tilakg673@gmail.com article history: received 10 ocober, 2011; accepted 4 january, 2012 abstract altogether 55 fodder trees were collected with their local information from sunsari district, nepal. among them, the leaves of 19 fodder trees were analyzed for dry matter, crude protein, ether extract, crude fibre, n-free extract, total ash and mineral contents (k, ca, and p). regarding fodder quality, local information and chemical composition do not match for all plants. on the basis of chemical composition 12 fodder trees were recognized as good fodders. on the basis of both local information and chemical composition following trees were assessed as very good fodders: artocarpus heterophyllus, bauhinia variegata, ficus cunia, f. glomerata and f. lacor. keywords: tree fodders; farmers’ assessment; proximate analysis; nutrient contents 1. introduction fodder plants are the important source of green fodders for livestock. the grasses, herbs, shrubs, vines and trees may be the source of green fodders. in sunsari district fodder trees are the major source of such green fodders which are collected from the nearby forest in bhabar to hilly region. the fodder leaves of some tree species are almost as nutritious as that of the leguminous forage crops. several works on fodder plants have been done in nepal in connection with pasture and fodder development, livestock development and aforestation programme, cited by mandal [1]. stebler [2] reported the chemical composition of leaves of 13 fodder trees found in the jiri region. dutt [3] determined the nutritive values of 17 tree fodders from the annapurna region. the fodder trees from different hill forests of kathmandu valley have been identified and analyzed for their nutrient contents by bajracharya et al. [4 and 5]. pandey [6] reported the chemical composition and nutritive constituents of 49 tree fodder found in nepal. the information on the availability of fodder trees and nutrient contents in their leaves from sunsari district, nepal, has been documented. the work was carried with the following objectives: i) to identify the fodder trees along with local information ii) to analyze the chemical composition of the fodder leaves iii) to recognize the nutritive fodders on the basis of chemical composition and local information. t.n. mandal and t.p. gautam / bibechana 8 (2012) 131-138 : bmhss, p. 132 study area sunsari district, covering an area of 1265 km 2 , lies at the southern part of koshi zone of nepal. it is located between 26 0 23’26 0 55’ n and 87 0 05’87 0 21’ e. the topographical variations range from 152914 meters within the district. there are three distinct regions within the district. the northern part is covered by the hills; middle part is occupied by bhabar region, the south face of which is covered by charkoshe jungle. the southern plain part is terai. climate and vegetation the south terai and bhabar regions have tropical climate while the north hilly region has subtropical type of climate. the monsoon starts usually in may and lasts till october. the average annual rainfall is 2154.1mm. the minimum and maximum temperature is 14.2 0 c and 30.6 0 c. vegetational zone varies due to climatic and topographic variation. there are two vegetation zones namely tropical and subtropical. the representative tree species are dalbergia sissoo, terminalia bellerica in tropical and castanopsis indica, schima wallichii in subtropical zone. 2. materials and methods fodder tree leaves were collected from different regions namely terai, bhabar and hilly region of sunsari district. the collection of plant samples was done in different feeding seasons in which the farmers use to feed their livestock. plants were identified as fodder by applying them to the grazing animals in the field and by observation on farmers’ collection who regularly collect fodder from the forest. the information about local names, quality and availability of fodder plants were recorded with the help of local experienced farmers. fodder leaves were collected in polythene bags and kept air-tight till the fresh weight was taken. the plants were then allowed to air-dry. fodder tree leaves were kept in hot air oven at 60 0 70 0 c for 48 hours and then the dry samples were kept at 103 0 c temperature for 4 hours to determine dry matter content. oven dried fodder samples were powdered and packaged in airtight small polythene bags for further chemical analysis. chemical analysis chemical analysis was done on dry matter basis. for each analysis triplicate samples were used. crude protein content was estimated by multiplying the percentage of nitrogen by a factor 6.25. the percentage of nitrogen was determined by micro-kjeldahal technique [7]. ether extract (crude fat) was determined by the soxhlet apparatus. extraction was done in petroleum ether having boiling point 40 0 c60 0 c [8]. crude fibre content was estimated from the fat free oven dried samples following the method described by i.s.i. [8]. nitrogen free extract was estimated by substraction method. the sum of total crude protein, ether extract, crude fibre and total ash was substracted from 100 [9]. total ash content was determined by heating the ground material in a dry crucible on a low flame and then it was heated in muffle furnace at 600 0 c for 34 hours [7]. potassium, calcium and phosphorus contents were determined from the ash samples. potassium was estimated by flame photometric method and calcium was estimated by titration method as described by jackson [10]. estimation of phosphorus was done colorimetrically according to a.o.a.c. [11]. t.n. mandal and t.p. gautam / bibechana 8 (2012) 131-138 : bmhss, p. 133 3. results altogether 55 fodder trees were reported from different parts of sunsari district. they have been arranged alphabetically with their local names (nepali names) and respective families in table 1. all the fodder trees were belonged to 29 families and 40 genera. the highest number of fodder trees (12 species) was found under the family moraceae followed by 8 tree species of the family leguminosae (added number of its subfamilies). local information on fodder trees local information on fodder trees for their qualities, availability, feeding seasons, preference by livestock and distributions were collected during the field study with the help of local experienced farmers. the information is listed in table 2. the qualities are rated as fairly good, good and very good. leaves of fodder trees are fed to the ruminants mainly in the winter. the preference of fodder trees by the ruminants was surveyed. for this purpose the ruminants have been grouped as cowbuffalo group and goat group. many of the fodder species have been consumed by both of these groups with equal interest. however, few fodder species were consumed by the goats only. the distribution of fodder trees varies according to the locality. many fodder trees are distributed in the bhabar, siwalik and upper hills. fodder plants are fed at their different stages of growth. in case of trees, generally the tender twigs are given to the livestock. but some fodder species namely celties australis and eurya acuminata cause diarrhea and other ill effects if they are fed at immature stage. similarly, prunus cerasoides is not fed to lactating animals as it decreases the milk yield. in contrast, the fodder species namely artocarpus lakoocha, ficus glomerata and ficus nemoralis are generally fed to the lactating animals to increase the milk yield. chemical analysis of fodder tree leaves altogether, 19 fodder trees were selected on the basis of availability, preference by ruminants and local information. the leaves of these species were analyzed for their dry matter, crude protein, ether extract, crude fibre, n-free extract, total ash and mineral contents (potassium, calcium and phosphorus). the estimated values of these constituents are given in table 3 and 4. dry matter content ranged from 19.25-48.61%, which was in madhuca longifolia and maximum in albizia lebbek. nearly 63% fodder tree leaves contained more than 35% dry matter. crude protein content ranged from 9.7321.35%. lowest crude protein was observed in madhuca longifolia and highest in albizia lebbek. nearly 53% of the fodder tree leaves contained more than 14% crude protein. ether extract ranged from 2.32-6.45% among the fodder trees. the amount of ether extract was significantly lower. it was less than 5% in all fodder trees except morus alba (6.5%). crude fibre content ranged from 14.87-31.54% among the tree fodders, minimum in morus alba and maximum in albizia lebbek. almost 53% of the tree fodders contained more than 20% of crude fibre. nitrogenfree extract content ranged from 36.4757.71% with the lowest value in albizia lebbek and highest value in madhuca longifolia. total ash content among fodder trees ranged from 7.84 15.63%, minimum in schleichera oleosa and maximum in kydia calycina. potassium content ranged from 1.122.23%, with the lowest value in terminalia alata and highest value in artocarpus heterophyllus and morus alba. calcium content ranged from 1.614.21%. the highest value was observed in celtis australis. most of the trees had more than 2.0% calcium content in dry matter. phosphorus content ranged from 0.140.37% among the tree fodders. kydia calycina had highest phosphorus content t.n. mandal and t.p. gautam / bibechana 8 (2012) 131-138: bmhss, p. 134 table 1: fodder trees of sunsari district, their local names (nepali names) and families s. n. species local name family 1 acacia catechu (l. f.) willd. khayar mimosaceae 2 aegle marmelos (l.) correa bel rutaceae 3 albizia lebbek (l.) benth. siris mimosaceae 4 anthocephalus chinensis hassk. kadam rubiaceae 5 artocarpus heterophyllus lamk. katahar moraceae 6 artocarpus lokoocha roxb. badahar moaceae 7 bauhinia purpurea l. tanki caesalpinaceae 8 bauhinia variegata l. koiralo caesalpinaceae 9 bombax ceiba l. simal bombacaceae 10 castanopsis indica (roxb.) miq. dhalne katus fagaceae 11 castanopsis tribuloides (sm.)a.dc. musure kattus fagaceae 12 celtis australis l. khari ulmaceae 13 dalbergia sissoo roxb. sisau papilionaceae 14 dalbergia stipulacea roxb. tantebari papilionaceae 15 dillenia pentagyna roxb. tantari dilleniaceae 16 diploknema butyracea (roxb.) lam. chiuri sapotaceae 17 erythrina variegata l. phaledo papilionaceae 18 eurya acuminata dc. thulo jhigane theaceae 19 ficus auriculata lour. newaro moraceae 20 ficus bengalensis l. bar moraceae 21 ficus benjamina l. sami moraceae 22 ficus cunia buch.-ham ex roxb. khanyu moraceae 23 ficus glomerata roxb. gular moraceae 24 ficus hispida l. khasreto moraceae 25 ficus lacor buch.-ham. kabro moraceae 26 ficus nemoralis wall. ex miq. dudhilo moraceae 27 ficus religiosa l. pipal moraceae 28 garuga pinnata roxb. dabdabe burseraceae 29 grewia tiliaefolia vahl. syalphusro tiliaceae 30 kydia calycina roxb. kubinde malvaceae 31 lagerstroemia parviflora roxb. bot dhayero lythraceae 32 litsea polyantha juss. kutmiro lauraceae 33 madhuca longifolia (koeing) macbride mauwa sapotaceae 34 maesa chisia buch.-ham. ex d. don bilaune myrsinaceae 35 mallotus phillippinensis muell. arg. sindure (rohini) euphorbiaceae 36 melia azedarach l. bakaino meliaceae 37 moringa oleifera lamk. saijan moringaceae 38 morus alba l. kimbu moraceae 39 myrsine capitellata wall. seti kath myrsinaceae 40 persea odoratissima (nees) kosterm. seto kaulo lauraceae 41 premna bengalensis clarke gineri verbenaceae 42 prunus cerasoides d. don painyu rosaceae 43 schima wallichii (dc.) korth. chilaune theaceae 44 schleichera oleosa (laur.) oken kusum sapindaceae 45 shorea robusta gaertn. sal dipterocarpaceae 46 spondias pinnata (l.f.) kurz amaro anacardiaceae 47 syzygium cumini (l.) skeels jamun myrtaceae 48 tamarindus indica l. titri caesalpinaceae 49 terminalia alata heyne ex roth. sahaj combretaceae 50 terminalia bellirica c. b. clarke barro combretaceae 51 terminalia chebula retz. harro combretaceae 52 terminalia myriocarpa heurcken. pani sahaj combretaceae 53 trichilia connaroides (wt.& arn.) bentv. ankhataruwa meliaceae 54 woodfordia fruticosa (l.) s. kurz dhayero lythraceae 55 zizyphus mauratiana lamk. bayar rhamnaceae t.n. mandal and t.p. gautam / bibechana 8 (2012) 131-138: bmhss, p. 135 table 2: local information on fodder trees s. n. species quality feeding season preference of ruminants distribution 1 acacia catechu + + w xy tbs 2 aegle marmelos + w y tbs 3 albizia lebbek + s y tbs 4 anthocephalus chinensis + w xy t 5 artocarpus heterophyllus + + + w xy tbs 6 artocarpus lokoocha + + + w xy tsu 7 bauhinia purpurea + + + w xy bsu 8 bauhinia variegata + + + w xy tbsu 9 bombax ceiba + + w xy tbs 10 castanopsis indica + s y u 11 castanopsis tribuloides + + rw xy u 12 celtis australis + + + w xy su 13 dalbergia sissoo + + s xy tbs 14 dalbergia stipulacea + + w xy tb 15 dillenia pentagyna + w xy s 16 diploknema butyracea + + + w xy su 17 erythrina variegata + + rw xy tbs 18 eugenia jambolana + + w y tbs 19 eurya acuminate + w y su 20 ficus auriculata + + + w xy u 21 ficus bengalensis + + rw xy tbs 22 ficus benjamina + + + w xy tbs 23 ficus cunia + + + w xy su 24 ficus glomerata + + + sw xy tb 25 ficus hispida + + w xy su 26 ficus lacor + + + w xy su 27 ficus nemoralis + + + w xy u 28 ficus religisa + + sw xy tbs 29 garuga pinnata. + + w xy su 30 grewia tiliaefolia + + + w xy su 31 kydia calycina + + w xy bs 32 lagerstroemia parviflora + w xy bs 33 litsea polyantha + + + w xy bsu 34 madhuca longifolia + + w xy t 35 maesa chisia + w y su 36 mallotus phillippinensis + w xy su 37 melia azedarach + + w xy tsu 38 moringa oleifera + + w xy ts 39 morus alba + + w xy su 40 myrsine capitellata + s y su 41 persea odoratissima + + w xy su 42 premna bengalensis + + w xy su 43 prunus cerasoides + + w xy u 44 schima wallichii + + s xy su 45 schleichera oleosa + + w xy bs 46 shorea robusta + w xy bs 47 spondias pinnata + + w xy tbs 48 tamarindus indica + + s xy tbs 49 terminalia alata + + w xy su 50 terminalia belerica + + w xy bs 51 terminalia chebula + + w xy bs 52 terminalia myriocarpa + w xy bsu 53 trichilia connaroides + w xy u 54 woodfordia fruticosa + w xy bsu 55 zizyphus mauratiana + + rw xy tbs t.n. mandal and t.p. gautam / bibechana 8 (2012) 131-138 : bmhss, p. 136 quality of fodder: + + + very good, + + good, + fair. feeding season: s – summer, r – rainy, w – winter; preference by ruminants: x – cow and buffalo group, y – goat group; distribution: t – terai, b – bhabar, s – siwalik hills, u – upper hills. table 3: chemical composition and nutritive constituents of fodder tree leaves % in dry matter species dry matter % in fresh matter crude protein ether extract crude fibre n-free extract albizia lebbek 48.61 21.35 3.41 29.25 36.47 anthocephalus chinensis 20.24 17.51 3.21 28.72 39.70 artocarpus heterophyllus 31.32 12.56 3.13 21.74 51.33 bauhinia variegatas 38.43 16.54 2.32 28.81 43.12 celtis australis 36.51 14.82 3.75 21.28 45.80 dalbergia sissoo 36.62 17.86 3.52 20.24 48.71 ficus cunia 38.21 12.35 3.16 24.88 46.35 ficus glomerata 36.41 14.35 2.62 15.45 54.94 ficus lacor 29.00 14.62 3.35 22.46 49.70 garuga pinnata 34.00 11.76 4.24 18.63 52.55 kydia calycina 43.31 12.62 4.26 18.54 48.95 madhuca longifolia 19.25 9.73 3.63 19.26 57.71 melia azedarach 31.32 14.26 3.49 21.45 50.56 moringa oleifera 29.75 14.42 4.54 18.59 50.13 morus alba 36.57 20.65 6.45 14.87 43.62 schleichera oleosa 37.54 11.39 2.39 31.54 46.84 terminalia alata 37.62 11.57 3.75 18.84 54.57 terminalia belerica 43.21 13.65 4.35 17.27 55.11 terminalia chebula 45.43 12.24 3.84 18.35 56.92 table 4: mineral contents of fodder tree leaves % in dry matter species total ash potassium calcium phosphorus albizia lebbek 9.52 1.86 2.13 0.21 anthocephalus chinensis 10.86 1.76 2.45 0.24 artocarpus heterophyllus 11.24 2.23 1.92 0.23 bauhinia variegata 9.21 1.85 2.87 0.15 celtis australis 14.35 2.15 4.21 0.18 dalbergia sissoo 9.67 1.87 2.12 0.19 ficus cunia 13.86 1.91 3.16 0.14 ficus glomerata 12.64 1.36 2.21 0.28 ficus lacor 9.87 1.63 2.15 0.19 garuga pinnata 12.82 1.76 2.86 0.16 kydia calycina 15.63 1.46 3.75 0.37 madhuca longifolia 9.67 1.78 1.61 0.17 melia azedarach 10.24 1.45 2.87 0.25 moringa oleifera 12.32 1.16 3.23 0.23 morus alba 14.41 2.23 3.55 0.32 schleichera oleosa 7.84 1.45 1.85 0.29 terminalia alata 11.27 1.12 2.87 0.24 terminalia belerica 9.62 1.35 2.76 0.22 terminalia chebula 8.47 1.24 2.51 0.21 . t.n. mandal and t.p. gautam / bibechana 8 (2012) 131-138 : bmhss, p. 137 4. discussion in the present work, the proximate analysis of fodder tree leaves was done. chemical analysis can indicate the gross feeding potential of a feeding stuff [12]. in case of tree fodders also the chemical composition provides basic information about their feed value but how much nutrients of a fodder plant become available to the feeding animals are determined only after conducting a digestion trial. a fodder plant containing 30% dry matter, 50% organic matter digestibility and less than 10% total ash in the dry matter is generally considered as a good fodder [13]. on the basis of dry matter and total ash content most of the fodder trees could be considered as good fodder. all the analyzed fodder trees have at least more than 30% dry matter except anthocephalus chinensis and madhuca longifolia. the total ash content is also almost 10% or less in most of the fodder species. but few species like celtis australis, kydia calycina and morus alba have exceptionally higher amount of total ash. higher percentage of acid insoluble ash indicates the poor quality of feed [14]. higher amount of crude protein, ether extract, n-free extract and lower amount of crude fibre help to examine the quality of the fodders. the crude protein content was higher in all fodder trees except madhuca longifolia. crude fibre content was exceptionally high in schleichera oleosa, albizia lebbek, anthocephalus chinensis and bauhinia variegata. if the crude fibre content of a plant is high, the digestibility of the fodder may be lower as it contains lignin, a non-nutrient component. the nfree extract is the fraction of total carbohydrates excluding the crude fibre. thus it includes all the digestible carbohydrates and gives more energy to the animals. among the minerals, the potassium which plays an important role in nerveirritation and carbohydrate metabolism was found sufficient in all the fodder trees. the animals require 0.2-0.3% potassium in dry ration [9]. the ratio of calcium and phosphorus should be 2:1 in the feed for the better absorption in the animal body [14]. the calcium content was high in all the fodder trees. thus, the plants which are rich in dry matter, crude protein, ether extract, nfree extract, and poor in crude fibre and ash content are considered as good fodders. in the present investigation the quality of the fodders based on their chemical composition was compared with the quality based on farmers’ judgment. it was found similar for many fodder plants. however, differences were also seen for some important species. dalbergia sissoo and terminalia belerica were rated as simply “good” (medium quality) by the local people but these fodder plants have adequate nutritive constituents. albizia lebbek which is of lowest quality “fairly good” in farmer’s view contains high dry matter, crude protein, ether extract and crude fibre. it is more appropriate to use the chemical composition as primary criteria and farmers’ evaluation as secondary, to assess the quality of fodder plants. on the basis of chemical composition a compilation of good fodders has been made as follows: artocarpus heterophyllus, bauhinia variegata, dalbergia sissoo, ficus cunia, ficus glomerata, ficus lacor, garuga pinnata, kydia calycina, melia azedarach, moringa oleifera, morus alba and terminalia belerica. the fodder species like dalbergia sissoo, ficus glomerata, ficus lacor, melia azedarach, moringa oleifera and terminalia belerica have also been reported as good and nutritious by gupta et al. [15] and singh [16]. on the basis of local information and chemical composition following plants were assessed as “very good” fodders: artocarpus heterophyllus, bauhinia variegata, ficus cunia, ficus glomerata and ficus lacor. t.n. mandal and t.p. gautam / bibechana 8 (2012) 131-138 : bmhss, p. 138 acknowledgements the authors are grateful to the authorities of national academy of science and technology for financial support and institute of science and technology, tribhuvan university for research facilities. references [1] t.n. mandal, general survey and biochemical analysis of fodder herbs, shrubs and vines found in godawari hill-forest. m. sc. thesis, tribhuvan university, kathmandu, nepal (1980). [2] j. stebler, final report on jiri multipurpose development project and quaterly reports on forest and pasture section, swiss association for technical assistance, kathmandu, nepal (1970). [3] p. dutt, grazing and resources management and improvement, report submitted to the workshop on hill agriculture, dept. of agric., nepal (1978). [4] d. bajrachrya, s.j.b. rana and a.k. shrestha, general survey and biochemical analysis of fodder plants found in nagarjun hill forest of kathmandu valley, j. nat. hist. museum, 2 (14) (1978) 105-116. [5] d. bajracharya, t.b. bhattarai, m.r. dhakal, t.n. mandal, m.r. sharma, s. sitaula and b.k. vimal, some feed values for fodder plants from nepal, angew. botanik, 59 (1985) 357-365. [6] k.k. panday, fodder trees and tree fodder in nepal, swiss development cooperation, berue, switzerland and swiss federal institute of forestry research, birmensdorf, switzerland (1982). [7] k. peach and m.v. tracey, modern method of plant analysis, springerverlang 1 (1956) 468486. [8] i.s.i., specification for compound feeds for cattle is: 2052, indian standards institution, new delhi (1968). [9] l.a. maynard and j.k. loosli, animal nutrition , 6 th edn., mc graw hill book company, new york (1969). [10] m.l. jackson, soil chemical analysis, prentice hall of india, pvt. ltd., new delhi (1953). [11] a.o.a.c., methods of analysis, association of official and analytical chemist, u.s.d.awashington, d.c (1970). [12] t.r. narayan and p.m. dabadghao, forage crops of india, indian council of agric. res., new delhi (1972). [13] k.k. panday, importance of fodder trees and tree fodder in nepal, m. sc. thesis, institute of plant production, federal tech. univ., zurich, switzerland (1975). [14] s.k. ranjhan, animal nutrition in tropics, 2 nd edn., vikas publishing house pvt. ltd., new delhi (1981). [15] p.c gupta, randhir singh, d.c. sangwan and k. pradhan, chemical composition and in vitro nutrient digestibility of some of the tree leaves, indian forest, 101, 11 (1975) 674-680. [16] r.v. singh, fodder trees of india, oxford and ibh publishing co., new delhi (1982). 8-16 b.c. paul r c o s t n b.c. paul / bibechana 11(1) (2014) 8-16: (online publication: march, 2014) p.8 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana dark matter and dark energy in the universe b. c. paul*1 department of physics, university of north bengal, darjeeling, 734 013, india email: bcpaul@iucaa.ernet.in accepted for publication: february 02, 2014 abstract cosmological and astronomical observations predict that the present universe is passing through an accelerating phase of expansion. the universe emerged out of an exponential phase in the very early universe. the scalar field of the standard model of particle physics when used in cosmology admits such a phase of expansion known as inflation. the most favourable condition for inflation with scalar field to admit an inflationary scenario is that the potential energy must dominate over the kinetic energy which one obtains with a flat potential. thereafter the universe enters into a matter dominated phase when the field oscillates at the minimum of the potential. but it is not possible to accommodate the present accelerating phase in the einstein’s gravity. it is known from observational analysis that about 73 % matter is responsible for the late phase expansion and 23 % matter called dark matter is responsible for a stable galaxy. we discuss here the relevant fields and theories that are useful for describing the late universe. © 2014 rcost: all rights reserved. keywords: dark matter; dark energy; stable galaxy; late universe. 1. introduction in 1915, einstein proposed the general theory of relativity (gtr, henceforth) which is important in understanding the origin and evolution of the universe [14]. gtr is also important to understand highly massive objects where the strength of gravity is not weak. einstein applied his famous equation in 1917 to obtain a model of the universe which is static but failed to achieve a static model of the universe with the field equation. this is because of the limitation of the then astronomical instruments which could observe only upto the periphery of our galaxy (milkyway) i.e., up to a region which is almost not changing. einstein then modified his gtr field equation by introducing a term which corresponds to repulsive force called cosmological constant. in 1927, while studying spectra of galaxies hubble discovered that the universe is expanding. it may be pointed out here that existence of non-static solution of the einstein's field equation was noted by friedmann in 1917. but those solutions were of academic interest for more than ten years. hubble's discovery led einstein to give away the cosmological constant term from the gtr equation. hubble's discovery also supports the fact that the universe originated from a big-bang in the past from a cosmic egg. the universe was very hot after its birth in the big-bang model. as it * invited speaker international conference on emerging trends in science and technology (march 22-23, 2014) biratnagar, nepal b.c. paul / bibechana 11(1) (2014) 8-16: (online publication: march, 2014) p.9 evolved, the temperature of the universe decreased due to adiabatic expansion. the nucleosynthesis of the universe might have occurred in the first three minutes. subsequently stars, galaxies and the large scale structure of the universe came up. after the discovery of cosmic microwave background radiation [5] the big-bang model became the standard model of the universe which has a beginning of the universe at some finite past. however, big-bang model based on perfect fluid model failed to account some of the observed facts of the universe. while probing the early universe the problems that cropped up are the horizon problem, flatness problem, singularity problem. however, the above problems can be addressed in the framework of standard model of particle physics by invoking the concept of inflation [1-4, 6-12]. the matter is replaced by scalar fields and the necessary condition for inflation may be achieved successfully. the small quantum fluctuation of the fields that originated in the very early universe leads to the structure formation of the universe [3]. it is further known from the study of galaxy rotation curve that in addition to visible matter another form of matter known as dark matter exists in nature. recent astronomical and cosmological observations predict existence of a new form of energy hitherto unknown. the discovery of riess et al. in 1998 [13] and perlmutter et al. [15] in 1999 changed the landscape of vision of the observed universe in addition to other cosmological observations. it is suggested that the current universe is accelerating. in most of the investigations the origin of the acceleration is attributed to a mysterious component due to a source possessing negative pressure called dark energy (de). not only type ia supernova (sn ia) observations but also cosmic microwave background (cmb) and baryon acoustic oscillations (bao) have continued to confirm that about 73 % of the energy density of the present universe consists of dark energy. dark energy is a major outstanding issue in physics and cosmology today. in the literature the reported work mainly focused on theory, probes de and on cosmological constant [7,8,16] . the preferred candidate for de is a cosmological constant λ. consequently λ cold-dark-matter (cdm) model is constructed which plays the role of a model for alternative approaches to understand the de-problems. although λcdm fits most observational data well, it suffers from two main shortcomings: (i) the low value of the vacuum energy and (ii) the cosmic coincidence problem. in order to address the above issues a constant λ is replaced by a time varying λ resulting in a dynamical de models. from cosmological observations it is also understood that about 23 % matter in the universe is in the form of dark matter (dm). in most investigations dm and de are considered independent substance. but there is a possibility of existing coupling between dm and de. so far dm and de manifests only through their gravitational action. as a result the motivation for unified models of the cosmological substratum in which one single component plays the role of dm and de simultaneously is studied. recently, holographic principle [17] is incorporated in cosmology [18,19] to track the dark energy content of the universe following the work of cohen et al [20]. in this paper we discuss the origin of dark matter and dark energy in the universe and possible candidates in favour of dm and de. 1.1. dark matter in the galaxies in 1932, a dutch astronomer jan oort was the first to interpret evidence and infer the presence of dark matter. he found that the mass in the galactic plane must be more than the material that could be seen while studying stellar motions in the local galactic neighbourhood but this measurement was later determined to be essentially erroneous. in 1933, the swiss astrophysicist fritz zwicky, who studied clusters of galaxies made a similar inference. zwicky applied the virial theorem to the coma cluster of galaxies and obtained evidence of unseen mass. in fig.1, the observed galaxy rotation curve for m33 is shown. let us consider an object (say a planet) at a distance r from the gravitating centre (the sun). the gravitational force on it is proportional to the product of masses and inversely proportional to the square of the distance. for dynamical equilibrium we determine the velocity of rotation of the planet. in the box below we consider solar system to evaluate rotational velocity of the planets. b.c. paul / bibechana 11(1) (2014) 8-16: (online publication: march, 2014) p.10 as an example in the above, we consider earth and a distant planet neptune to estimate their rotational velocities. the values obtained using the newton’s formula is reliable. now in the case of objects in the galaxies, analogously consider a light emitting source at a distance r from the centre of the galaxy. for dynamical equilibrium the same velocity equation for the light emitting source will be valid and consequently velocity of rotation should fall as square root of the distance r: rr rgm rv 1)( )( ∝= (1) where m(r) represents the mass which is supposed to be constant as was found in the case of a star in the solar system. figure 2: rotation curve • for dynamical equilibrium d sun planet v )(/4.530 /3010150 6 2 2 formulareliableskmvrr skmvkmr r gm v r mv r gmm neptuneen earthe =⇒= =⇒×= =⇒ = figure 1: velocity of rotation b.c. paul / bibechana 11(1) (2014) 8-16: (online publication: march, 2014) p.11 now let us consider a galaxy consisting of about 1011 stars of mass equal to or more than the mass of the sun. compare to the centre of the galaxy the stars are like point objects. in the case of m33 galaxy the observed velocity rotation curve as shown in fig.(2), at first increases, it attains a maximum and thereafter its change in velocity is almost constant. but the expected velocity rotation curve from luminous disk after certain distance from the centre of the galaxy should decrease as shown. it is observed that • velocity at a distance r (denoted by v(r) ) rises towards a constant after about 2 kpc. • m(r) interior to r increases linearly with r thus the above confrontation with observation may be removed assuming that the disc galaxies are immersed in extended dark matter (dm) halos, at small distances this dm is only a small fraction of the galaxy mass inside; it becomes very large at large distances. let us estimate the dark matter from the following data: velocity of a luminous object at 10 kpc away is 120 km/s but its luminous velocity expected is 40 km/s. using eq. (1), we get where mtotal represents the total mass and mlum represents the luminous mass corresponding to rotational velocity vt and vlum respectively. we have the following data: thus a major composition of matter in the galaxies is dark matter. 1.2. dark energy and the dark matter in cosmology cosmology is the study of the cosmos consisting of galaxies, clusters, superclusters etc. einstein’s general theory of relativity (gtr) is useful to understand the dynamics of the universe. about 99 years back einstein obtained field equation connecting geometry in one side and matter in the other side. this is an intuitive concept to relate the effect of matter in the space time. the space time geometry is flat in the absence of matter, however, in the presence of matter flat geometry changes its shape and it becomes curved. this curvature and matter are interrelated. the famous einstein equation is (2) where rµν and r represent the ricci tensor and ricci scalar respectively, gµν represents the metric tensor, tµν represents the energy momentum tensor and g is the newton’s gravitational constant. according to cosmological principle the universe is isotropic and homogeneous and the most acceptable metric is the robertson-walker metric which is given by 2 2 lum t lum total v v m m = .%90 9 9 40 120 , /40,/120,10 2 2 2 . darkisgalaxiesinmassof mm v v m m thus skmvskmvkpcr lumtotal lum t lum total lum ⇒ ≈⇒ =     == === µνµνµν π−=− tg8rg 2 1 r b.c. paul / bibechana 11(1) (2014) 8-16: (online publication: march, 2014) p.12 (3) in the (t, r, θ, ϕ) coordinates, a(t) represents the scale factor of the universe. in the above k is the index which represents a closed universe for +1, open universe for – 1 and a flat universe for 0. in the case of perfect fluid the energy momentum is given by (4) where ρ and p represent the energy density and pressure respectively. using eqs. (3) and (4) in eq. (2) one obtains the field equations (5) (6) the famous raychaudhuri equation is obtained using eqs. (5) and (6) as in 1926, hubble discovered that the universe is expanding, for which one requires to have matter with negative pressure as which is not permitted classically in the framework of perfect fluid assumption. note that even 10-6 sec after big-bang, e(particle) > 1 gev. at this energy scale it is necessary to describe matter by quantum fields. for energies less than planck energy, classical description of space-time possible with scalar fields permitted by particle physics. as discussed above the concept of inflation in cosmology is therefore essential which is permitted if quantum fields are considered. in 1981 guth [6] proposed inflationary universe scenario using temperature dependent phase transition mechanism in order to get rid of the problems of the big-bang cosmology. in this scenario there was a phase of expansion of the universe when a small causally coherent region grows to a huge size to encompass the present universe. subsequently it is found that a graceful exit from inflation is not permitted in the scenario [7]. a new inflation is then proposed by linde [8], albrecht and steinhardt [9, 10] where the graceful exit is natural. the period of inflation was very short in which the universe grows rapidly so that at a later epoch it allows the different parts we see to come in casual contact with each other, thereby explaining the isotropy of the observed universe. eventually, the quantum vacuum state decays, dumping its energy into the form of thermal radiation and the big-bang friedmann model takes over. in 1983, linde [8] proposed a suitable inflationary universe model which does not require temperature dependent phase transition mechanism instead the universe can be realized from a chaotic distribution of a homogeneous scalar field. in this scenario sufficient inflation required to solve the problems of the big-bang model can be realized if a causally coherent region grow out with an initial scalar field which picks up values ϕ > 3 mp , where mp represents the planck mass. quantum gravity region is not important in this case as v(ϕ) ≥mp 4 . linde [8] has shown that a kinetic energy dominated region can pass on to an inflationary era afterwards as the potential energy domination sets in at a late epoch in scalar field cosmology. paul et al. [11] shown       ++ − +−= )sin( 1 )( 2222 2 2 222 ϕθθ ddr kr dr tadtds [ ]pppt −−−= ,,,ρµν ρπ g a k a a 83 22 . 2 =           + gp a k a a a a π82 22 . 2 .. −=           ++ ( )p g a a 3 3 4 .. +−= ρπ 3 ρ−〈p b.c. paul / bibechana 11(1) (2014) 8-16: (online publication: march, 2014) p.13 that chaotic scenario is more realistic as it can be accommodated even in the presence of an anisotropy. an inflationary universe model is important as it opens up new avenues not only in cosmology but also in particle physics. it can solve some of the outstanding conceptual issues in cosmology particle physics not understood before. in the last three decades a number of inflationary models of the universe proposed in the literature in the context of different theories e.g. • (1980-1989): r2 –inflation [12], old inflation [6], new inflation [16], chaotic inflation [8,21], power-law inflation [22], extended inflation [23], sugra inflation [24],double inflation [25]. • (1990-1999): hybrid inflation [26], susy d-term inflation [27], brane inflation [28], assisted inflation [29] . • (2000-2008): super-natural inflation [30], k-inflation [31], d3-d7 inflation [32], tachyon inflation [33], hill top inflation [34], dbi inflation [35]. till now it is not clear when and how the universe entered the inflationary phase in the past. a suitable model which can describe the entire evolution of the universe is yet to be constructed. a baby universe i.e., a tiny causally connected region grew into a huge size due to early inflation which engulfed the entire universe in a very short time. during the creation the universe was very hot as it expands its temperature decreases enhancing the formation of atoms from a soup of quark-gluon plasma. a photon thus emitted at very high temperature is the sole spectator of the phase which is commoving with the stratum. its temperature decreases and the present 2.73k black body radiation is due to this decoupled photon and expansion of the universe. the frequency range of this radiation lies in the microwave region at the present epoch which is showering isotropically in the universe. this is cosmic microwave background radiation (cmbr). thus it is important to encode the message hidden in cmbr. penzias and wilson discovered the presence of cmbr while scanning the entire sky for source emitting microwave. later they were awarded with nobel prize. in the inflationary theory the quantum fluctuations that developed in the early universe leads to large structure formation which was supported by cosmic background explorer (cobe). the present decade is witnessing a transition from speculative science to an experimental science because of a number of precision observational projects namely, cmb, sdss, wmap and planck. the analysis of the data from those missions are confronting with theoretical cosmology. when observational data are analyzed in the framework of big-bang cosmology it comes out that the present universe is composed of 73 % dark energy (darkshade), 23 % dark matter (violet) and only 4 % (red) are baryons that is visible around us. a pie chart reflects the energy budget of the universe. figure 3: energy distribution in the universe dark energy (darkshade), dark matter (violet) and only 4 % (red) observed matter. b.c. paul / bibechana 11(1) (2014) 8-16: (online publication: march, 2014) p.14 one of the most exciting observational discoveries of the past decade is that the universe is accelerating. the source responsible for cosmic acceleration is presently unknown and has been called dark energy. dark energy has large negative pressure and could account for up to 73 % of the total matter density in the universe!! using eq. (5) with a number of fluids and defining the density parameter (ω), and critical density (ρc ) which represents the energy density corresponding to a flat universe as below one obtains in the case of rapid expansion in a very short period called inflation, through which the universe emerged in the past, we get for a number of fluids, we can write as thus it is evident that the observation predicts existence of matter other than the matter we observe around us. it is predicted from supernova experiments that the universe is expanding at a rate much faster than that theoretically calculated. this result is amazing! in the large scale structure (lss) experiments dedicated telescope measured cosmological red shift of more than 2,50,000 galaxies! the derived galaxy-galaxy correlation function provides a tantalizing glimpse of the power spectrum of galaxy clustering and places powerful constraints on the density in clustered matter. it is also known from high red shift type i a supernova study that the universe is accelerating and its acceleration is fuelled by unknown form of dark energy having negative pressure. thus due to advancement of technology the present era is witnessing a transition of cosmology from speculative science to experimental science. a number of astronomical and cosmological observations in the recent past made it possible to visualize the universe which is different from what we understood a decade ago. riess et al. [13] and perlmutter et al. [14] found that the present universe is accelerating which they observed while analyzing data from large red shift survey of supernovae. this late acceleration cannot be realized in the framework of standard model of particle physics. it is one of the challenges in theoretical physics to develop a consistent theory to address the issue. it is found that old cosmological constant term of einstein again can help to obtain such late accelerating universe. however, origin of a cosmological constant term required at late epoch is not known. when observational results 22 222 2 1 3 8 1 8 3 ,, ha k h g ha k g h a a h i i c i c c =−ω⇒ ω=ω ω===+⇒ ==ω= ∑ ∑∑ ρ ρρπ π ρ ρ ρ& 8.02.0 1 101 ≈ω⇒≈ω ≈ω+ω∴ ≈ω=ω⇒→−ω ∑ nonlumobs nonlumlum i i ,...,2.0 1... 1 21 321 1 ω=ω =+ω+ω+ω⇒ =ω∑ = n i i b.c. paul / bibechana 11(1) (2014) 8-16: (online publication: march, 2014) p.15 are analyzed in the big-bang model, existence of a new kind of energy that fills the space is required which is termed as dark energy. it has a negative pressure and negative gravitational effect causing a gravitational repulsion. as the universe expands, dark energy stays at nearly constant energy density and, as the matter in the universe thins out, the dark energy begins to dominate. the repulsive effect of dark energy seems to guarantee that the universe might continue to expand forever. it is now a great challenge to theoretical physicists to give a consistent model for the dark energy in addition to dark matter. in the einstein field equation this may be achieved by a modification of the gravitational sector [36] or the matter sector [37]. the work in this direction is now in progress worldwide to unravel the mystery of the universe. emergent universe model in a flat universe is another interesting model of the universe which can be obtained with a non-linear equation of state [38]. in the emergent universe scenario the initial size of the universe was large enough so that quantum gravity effect is not important. the horizon and flatness problems do not arise. in the eu scenario, the universe evolves from a static phase in the infinite past into an inflationary phase at a later epoch. in the usual description with a scalar field it is shown that a universe starts expanding from the above phase, later on smoothly joins with a stage of exponential expansion followed by standard reheating and then approaches the classical thermal radiation dominated era of the conventional big-bang cosmology. the matter in the universe may be considered as a composition of three kinds of fluids depending on eos parameter. in the model one of the compositions of matter is dark energy. it permits an accelerating universe which is supported by observations. acknowledgment the author acknowledges the university grants commission, new delhi for awarding a major research project (grant no. f.42-783/2013 (sr)). references 1. s.w. weinberg, gravitation & cosmology, john wiley and sons, 2004. 2. j.v. narlikar, introduction to cosmology, cambridge university press, 1993. 3. t. padmanabhan, theoretical cosmology vol. iii, cambridge university press, 2002. 4. s. dodelson, modern cosmology, academic press, 2003. 5. a.a. penzias, r. w. wilson, astrophys. j., 142( 1965)419. 6. a.h. guth, phys. rev. d, 23 (1981)347. 7. k. sato, mon. not. roy. astron. soc., 195 (1981) 467. 8. a.d. linde, phys. lett. b, 108 (1982) 389. 9. a. albrecht, p. steinhardt, phys. rev. lett., 48 (1982) 1220. 10. a. albrecht, arxiv:astro-ph/0007247, 2000. 11. b.c. paul, d.p. datta, s. mukherjee, {\it mod. phys. letts. a} {\bf 1 }, 149 (1986). 12. a.a. starobinsky, jetp lett., 30 (1979) 682; 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s. mukherjee, b.c. paul, s.d. maharaj, a. beesham, arxive:gr-qc/0505103 (2005); b.c. paul, s. ghose, gen. rel. grav., 42 (2010) 795; a. banerjee, t. bandyopadhyay, s. chakraborty, gen. rel. grav. 40 (2008) 1603; a. banerjee, t. bandyopadhyay, s. chakraborty, grav. and cosmology 13 (2007) 290; u. debnath, class. quant. grav., 25 (2008) 205019; b.c. paul, p. thakur, s. ghose, mon. not. roy. astron. soc., 407 (2010) 415; b.c. paul, s. ghose, p. thakur, mon. not. roy. astron. soc., 413 (2011) 686; s. ghose, p. thakur, b.c. paul, mon. not. roy. astron. soc., 421 (2012) 20. microsoft word b singh _7-12_.doc b.k. singh and sudhir singh / bibechana 9 (2013) 7-12 : bmhss, p.7 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana temperature dependence of the helmholtz free energy of liquid alkali metals b. k. singh1*, sudhir singh2 1 university department of physics, t.m. bhagalpur university, bhagalpur 2 department of physics, r. d. college sheikhpura, t.m. bhag. univ., bhagalpur * corresponding author: e-mail : bijay.k.singh@gmail.com article history: received 12 february, 2012; accepted 5 july, 2012 abstract the gibbs-bogoliubov variational method has been considered to study the helmholtz free energy of liquid alkali metals (na, k, rb and cs) as a function of temperature, using heine abarenkov type model potential with hubbard-sham exchange and correlation function. the computed values are in very good agreement with experimental observations. keywords: helmholtz free energy; entropy; specific heat; boltzman constant; perturbation energy; madelung energy 1. introduction the variational prescription based on the gibbs-bogoliubov inequality [1] has provided a convenient computational tool for evaluating the free energy of liquid metals with the framework of a hard-sphere reference system and pseudopotential theory [2,3]. recently, many workers [4-8] have utilized successfully the gibbs bagoliubov (gb) variational technique to study the thermodynamic properties of liquid metals and alloys. in most of the cases the earlier studies are confined near the melting temperature (tm). the present work is an attempt in this direction to investigate the thermal effect on the helmholtz free energy of liquid metals for t > tm, which is least understood. this will help us to examine the utility of hard-sphere reference system for election-ion interaction energy. we consider the heine-abarenkov (ha) form of model potential [9] in conjunction with the hubbardsham [10-11] (hs) exchange and correlation function. for the present purpose we choose na, k, rb and cs because the pseudopotential perturbation can be applied without committing any appreciable error [12]. 2. theory the details of the variational method used for investigating the thermodynamic properties of liquid metals and alloys are available in the work of umar et al [13] and ashcroft and stroud [14]. in the framework of gb method the helmholtz free energy, f, per ion at fixed temperature t and volume ω can be expressed as b.k. sing and sudhir singh / bibechana 9 (2013) 7-12 : bmhss, p.8 (online publication: nov., 2012) f = fhs + fps (1) here fhs is the helmholtz free energy of the hard-sphere system, which can be expressed as fhs = (3/2) kbt ts (2) where (3/2) kbt is the mean kinetic energy and s, the entropy of the system can be written as s = sgas + sη (3) with sgas = (5/2)kb + kb ln{ω(mkbt/2πħ2)3/2} (4) sη = kb ln (1-η) + 3/2 kb{1-(1-η)2} (5) eq. (3) has further been improved by incorporating the low temperature specific heat contribution of electron gas. the resulting expression for the entropy becomes s = sgas + sη + selec (6) with 2 2 2/elec b fs k t kπ= (7) where kb is the boltzmann constant and kf stand for the fermi wave vector 3 2( 3 ,fk nzπ= n is the number density). fps = feg + f1 + f2 + fm (8) where feg is the free energy of the electron gas, f1 and f2 are, respectively, first and second order perturbation energies due to the electron-ion interaction. fm is the madelung contribution which takes into accounts for the ion-ion interaction. the expressions for these contributions for a metal have been worked out in detail by harrison [2]. 2[(3 /10) (3 / 4 ) 0.0474 0.0155ln ]eg f f ff nz k k kπ= − − − (9) 2 1 0 lim { ( ) 4 / } q f n z v q z qπ → = − (10) 3 2 4 2 0 (1/16 ) ( ) ( )[{1/ *( )} 1]f v q s q q q dqπ ∞ = − ∈ −∫ (11) 2 0 ( / ) { ( ) 1}mf z s q dqπ ∞ = −∫ (12) where q is the phonon wave vector v(q) stands for unscreened from factor, which can be obtained using the ha potential, 2 3( ) (4 / )cos (4 / )(sin cos )m m m mv q zn q qr an q qr qr qrπ π= − − − (13) b.k. singh and sudhir singh / bibechana 9 (2013) 7-12 : bmhss, p.9 (online publication: nov., 2012) here a is the well depth and rm is the model radius. these are obtained quantum mechanically by matching the wave function at *( )mr r q= ⋅∈ in eq. (11) is the modified hartree dielectric screening function which takes into account of the conducting electron interaction, ∈*(q) = 1 + {є(q) 1}{1 – g(q)} (14) ∈(q) is the hartree dielectric function and g(q) is the correction factor for the exchange and correlated motion of the conducting electron. presently we consider g(q) prescribed by hubbard and sham 2 2 31 ( ) /[ {2 /(0.153 )}] 2 f fg q q q k kπ π= + + (15) the structure factor, s(q), for liquid metals appearing in eq. (11) and (12) can be calculated from the parcus-yevick approximation for hard–sphere potential, which is characterized by the hard-sphere diameter(σ),or equivalently, by the packing fraction 3( /6)mη πσ= 3. results and discussion the general expression for the helmholtz free energy of pure liquid metals can be written as f = feg + f1 + f2 + fm + (3/2)kbt ts (16) the different terms occurring in eq. (16) are already defined in section 2. it is well known that hardsphere potential serves as an effective reference system for liquid metals. the best hard sphere reference system is obtained by selecting those diameters which minimize the helmholtz free energy, f, at the same temperature t and volume ω through , 0 t f σ ω ∂  = ∂  (17) the optimum values of the parameters used in the calculation of the helmholtz free energy of liquid alkali metals as a function of temperature are compiled in table 1. the volume of the liquid metals at different temperatures required in the calculation is determined from the relation provided in the work of huijben [17]. the experimental values of the entropies at appropriate temperature are obtained from tables found in hultgren et al [18-21]. using table 1, we can calculate easily the various terms of eq. (16). the computed values of feg, f1, f2, fm and fhs are listed in table 2. a perusal of table 2 show that the major contribution to the theoretical determined helmholtz free energies comes from the madelung terms fm, the other terms contribute a relatively small amount and in order of magnitude falls as f1, feg, fhs and f2. table 2 shows that the magnitude of f1 and fm decreases with the rise of temperature where as the magnitude of feg, f2, fhs increases. the computed values of f for liquid alkali metals are displayed in fig.1 as a function of temperature along with the experimental observation of hultgren et al [18]. the best agreement is obtained for cs followed by rb, k and na. it may be noted that the helmholtz free energy of liquid alkali metals depend sensitively on temperature above the melting point. the rise of temperature b.k. singh and sudhir singh / bibechana 9 (2013) 7-12 : bmhss, p.10 (online publication: nov., 2012) experiences a decrease in the helmholtz free energy. our results reveal that the decrease of magnitude of the helmholtz free energy due to first order energy and madelung energy is compensated due to increasing values of f2, feg and fhs as a result f only depends considerably on temperature above the melting point. table 1: input parameters in the calculation of the helmholtz free energy of na, k, rb and cs at different temperatures liquid metals t(°°°°k) ω(a.u) σ(a.u) s/kb 371.0 278.187 6.2579 7.1043 473.0 285.722 6.1659 8.0953 573.0 293.427 6.0922 8.8416 673.0 301.495 6.0293 9.4533 na 773.0 310.077 5.9741 9.9751 336.6 530.504 7.6633 8.7493 423.0 543.360 7.5449 9.6486 523.0 559.190 7.4313 10.4569 623.0 576.037 7.3349 11.1095 k 723.0 593.824 7.2502 11.6587 312.6 667.200 7.2179 10.1972 373.0 681.292 8.1174 10.9056 473.0 705.516 7.9788 11.8184 573.0 731.796 7.8625 12.5406 rb 673.0 759.994 7.7624 13.1400 301.8 804.117 8.7922 10.8790 373.0 824.402 3.6678 11.7315 473.0 852.587 8.5192 12.6487 573.0 884.556 8.3973 13.3825 cs 673.0 919.709 8.2915 13.9931 fig. 1 : helmholtz free energy of na, k, rb and cs as a function of temperature. full and broken curve refer to theoretical and experimental values respectively b.k. singh and sudhir singh. / bibechana 9 (2013) 7-12 : bmhss, p.11 (online publication: nov., 2012) table 2: contribution to helmholtz free energy of liquid alkali metals as function of temperature liquid metals t(°k) -feg f1 -f2 -fm -fhs 371.0 0.08162 0.07734 0.00479 0.21371 0.00656 473.0 0.08168 0.07530 0.00619 0.20968 0.00988 573.0 0.08175 0.07332 0.00761 0.20575 0.01333 673.0 0.08180 0.07136 0.00910 0.20181 0.01695 na 773.0 0.08185 0.06938 0.01066 0.19781 0.02075 336.6 0.07995 0.06419 0.00465 0.17144 0.00773 423.0 0.07982 0.06267 -0.00587 0.16825 0.01092 523.0 0.07966 0.06089 0.00737 0.16454 0.01434 623.0 0.07949 0.05912 0.00894 0.16079 0.01896 k 723.0 0.07933 0.05734 0.01057 0.15702 0.02326 312.6 0.07826 0.05782 0.00476 0.15837 0.00859 373.0 0.07841 0.05779 0.00543 0.15827 0.01111 473.0 0.07784 0.05467 0.00747 0.15172 0.01546 573.0 0.07757 0.05272 0.00929 0.14753 0.02004 rb 673.0 0.07720 0.05076 0.01122 0.14327 0.02481 301.8 0.07660 0.05795 0.00419 0.14917 0.00896 373.0 0.07638 0.05653 0.00521 0.14641 0.01209 473.0 0.07610 0.05466 0.00672 0.14265 0.01670 573.0 0.07578 0.05265 0.00835 0.13868 0.02157 ca 673.0 0.07545 0.05067 0.01009 0.13466 0.02663 acknowledgement we would like to thank prof. r. n. singh, department of physics, bhagalpur university for his useful suggestions and encouragement in this work. i am also thankful to the u.g.c., new delhi, for the financial support under grant no. f10-109/90(rbbii). references [1] a. isihare, j. phy a: gen. phys, 1 (1968) 53. [2] w.a. harrison, pseudopotential in the theory of metals ,w a benjamin inc., new york (1966). [3] t.e. feber, introduction to the theory of liquid metals ,cambridge: cup, (1972). [4] h. jones , j chem phys, 55(1971)2640, phys rev a, 133 (1973) 3215. [5] d. stroud and n.w. ashcroft, phys. rev. b, 5 (1972) 371. [6] i.h. umar and w.h. young, j phys f, 4 (1974) 525. [7] r.n. singh , j phys f, 10 (1980) 1411. [8] r.n. singh and s. singh, physica b, 128 (1985) 304. [9] v. heine and i.v. abarenkov, philos mag, 9 (1964) 451. [10] j. hubbard , proc. roy. soc. a, 240 (1957) 539. [11] l.j.sham, proc. roy soc. a, 283 (1965) 33. [12] v. heine and d.l weare, solid state physics, 24 (1970) 249. [13] i.a. umar , a. meyer, m. watabe and w.h. young, j. phys. f, 4(1974) 1691. [14] n.w. ashcroft and d. stroud, solid state physics, 33 (1978) 1. b.k. singh and sudhir singh / bibechana 9 (2013) 7-12 : bmhss, p.12 (online publication: nov., 2012) [15] o. ese and j.a. reissland , j phys f, 3 (1963) 2066. [16] n.w. ashcroft and j. lekner , phys rev, 145 (1966) 83. [17] m.j. huijben ph.d. thesis, university of groningen, the netherlands (1978). [18] r. hultgren,p.d. desai, d.t. hawkin and m. gleiser, kelley k k & wagmann d d, selected values of the thermodynamic properties of the elements ,american society of metals, metal park , ohio, (1973). [19] d. adhikari, b.p. singh, i.s. jha, and b.k. singh, j. non-cryst. solids, 357 (2011) 2892. [20] d. adhikari , i.s.jha, and b.p.singh, philos. mag. 90 (2010) 2687. [21] d. adhikari, b.p. singh , i.s. jha, and b.k. singh , j. mol. liq. 156 (2010) 115. microsoft word sitnshu s. chaudhary _18-20_.doc shitanshu shekhar choudhary and raju ram thapa / bibechana 7 (2011) 18-20 : bmhss 18 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana locally compact space and continuity shitanshu shekhar choudhary , raju ram thapa ∗∗∗∗ p.g. campus, biratnagar, tribhuvan university article history: received 27 september 2010; revised 1 november 2010; accepted 7 november 2010 abstract topological spaces for being t0, t1, t2 and regular space have been discussed. the conditions for a topological space to be locally compact have also been studied. we have found that a continuous function preserves locally compactness. keywords: topological spaces; compactness; regular space 1. introduction it has been seen that any product of compact spaces is compact. it has been also seen that most of the spaces turn out to be closed subspaces of products of compact spaces and such spaces are necessarily compact. the n-dimensional euclidean space r n is the most important type of topological space which has a great importance in modern analysis. a topological space is locally compact if each of it's point has a neighborhood with compact closure. as a result, r n is locally compact for any open sphere centred on any point, is the neighborhood of the point whose closure, being a closed and bounded subspace of r n is compact. it's application is in the field of geometry and analysis. 2. definitions 2.1 t0space a topological space (x, j) is called t0 space or kolmogorff space iff given any pair of points xy,x ∈ (distinct) there exists an open set containing one of them but not the other. 2.2 t1space a topological space (x, j) is called t1space or frechet space ∗ corresponding author: raju ram thapa, dept. of mathematics, post graduate campus, biratnagar, tribhuvan university, email: thaparajuram@yahoo.com shitanshu shekhar choudhary and raju ram thapa / bibechana 7 (2011) 18-20 : bmhss 19 iff given any pair of points xy,x ∈ there exist two open set, one containing x not y & other containing y not x. 2.3 t2space a topological space (x, j) is said to be t2-space or hausdroff space iff given any pair of points xy,x ∈ there exits two disjoint open sets one containing x and other y. regular space : a topological space x is called regular if for each closed subset f of x and xx ∈ such that fx ∉ , there exist disjoint open sets g and h such gf ⊆ and hx ∈ . 2.4 t3 space a regular t1-space is called t3-space. 2.5 locally compact space a top. space (x, j) is said to locally compact if given xx ∈ and any nbd. u of x, there is a compact set a such that .uaax 0 ⊂⊂∈ 0 a : it is union of all open sets contained in a called interior of a, obviously aa 0 ⊂ . 3. formalism proposition: let (x, j) be a t2-space then x is locally compact iff given xx ∈ , there is a compact set a such that 0 ax ∈ . proposition: any compact t2-space is locally compact. proposition: any locally compact t2-space x is t3. proposition: if a space x is t2 and locally compact then every open and closed subspace is also t2 space and locally compact. proposition: a substance y of a locally compact t2-space x is locally compact iff it is the intersection of an open set and a closed set. proposition: let f be a continuous and open function from one topological space (x, j) to another topological space (y, j') then x is locally compact y⇒ is locally compact. proof: let (x, j) and (y, j') be two topological spaces and f be a continuous and open mapping from x onto y. let x is locally compact. to show that y is also locally compact, let yy ∈ and n be the neighborhood of y then )x(fy = for some xx ∈ . since f is continuous so there exists a neighborhood v of x such that f(v) ⊂ n. since x is locally compact so there exists a compact set b such that 0 bx∈ nb ⊂⊂ . then .n)b(f)b(fy)x(f 0 ⊂⊂⊂= but )b(f 0 is open, being f is open mapping and also compactness is invariant under continuous mapping so f(b) is compact. thus n)b(f)b(fx 0 ⊂⊂∈ . which shows that y is locally compact. shitanshu shekhar choudhary and raju ram thapa / bibechana 7 (2011) 18-20 : bmhss 20 proposition: let iii }j,x{ ∈ be a countable families of non-empty spaces and ix∏ be the product spaces. then ix∏ is locally compact iff each component spaces is locally compact and all of the component spaces except atmost finitely many are compact. proof: let ip be the projection mapping i ii ii xx:p →∏ ∈ which is continuous onto and open so each ix is locally compact. let a be any compact subset of ix∏ such that some point y of ∏ ∈ii ix is in 0 a . then there is a basis neighborhood ∏ ∈ii iv of y such that ii xv = for all but at most finitely many i and ∏ ∈ ⊂ ii 0 i av . thus ii x)a(p = for all but at most finitely many i, since ip is continuous and a is compact so ix is compact for all but at most finitely many i. now we assume that each ix is locally compact and all but finitely many of ix are compact. let ∏ ∈ ∈ ii ixy,x and let iy be the i th co-ordinate of y. if u is any neighborhood of y then u contains a basis neighborhood of y of the form ∏ ∈ii iv , where iv is open in ix for each i and ii xv = for all ii∈ , except for at most finitely many say n21 i.,.........i,i . since each ix is locally compact so for each ii∈ there is a compact subset ia of ix . such that ii 0 ii vaay ⊂⊂∈ . there are at most finitely many more ii∈ , other than n21 i.,.........i,i say m2n1n i,.........i,i ++ such that m2n1n xi.........,,xi,xi ++ are not compact. for any i not in n21 i.,.........i,i , m2n1n i,.........i,i ++ we may let ii xa = then ∏∏ ∏∏ ∈∈ ∈∈ ⊂⊂⊂∈ ii i ii ii i 0 i ii i 0 va)a(ay . but ∏ ∈ii ia is product of compact sets and is therefore compact. hence ∏ ∈ii ix is locally compact. 4. conclusion locally compactness is not invariant under continuous mapping but in under certain assumptions which are openness, a continuous function preserves local compactness. references [1] g. a. quarw, point countable open covering in countable compact space; academic press, new york (1967). [2] r. arers, remark on concept of compactness; port maths (1950). [3] n. dykes, pac.j. maths(1970). [4] m. henrikse and j.r., isbell duke maths j. (1958). [5] h. wickle & j.m. worrel, proc. aurer, maths society (1976). 113-122 s. lamichhane-naraya adhikari r c o s t n s. lamichhane et al. / bibechana 11(1) (2014) 113-122: (online publication: march, 2014) p.113 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana hydrogen storage on platinum decorated graphene: a first-principles study s. lamichhane, n. pantha, n. p. adhikari central department of physics, tribhuvan university kirtipur, kathmandu, nepal e-mail : npadhikari@gmail.com, npadhikari@tucdp.edu.np accepted for publication: february 15, 2014 abstract adsorption of gaseous/molecular hydrogen on platinum (pt) decorated and pristine graphene have been studied systematically by using density functional theory (dft) level of calculations implemented by quantum espresso codes. the perdew-burke-ernzerhof (pbe) type generalized gradient approximation (gga) exchange-correlation functional and london dispersion forces have been incorporated in the dft-d2 level of algorithm for short and long range electron-electron interactions, respectively. with reference to the binding energy of pt on different symmetry sites of graphene supercells, the bridge (b) site has been predicted as the best adsorption site. in case of 3×3 supercell of graphene (used for detail calculations), the binding energy has been estimated as 2.02 ev. the band structure and density of states calculations of pt adatom graphene predict changes in electronic/magnetic properties caused by the atom (pt). the adatom (pt) also enhances the binding energy per hydrogen molecule in pt-graphene comparing to that in pristine graphene and records the values within the range of 1.84 ev to 0.13 ev for one to eight molecules, respectively. © 2014 rcost: all rights reserved. keywords: hydrogen adsorption; dft; geometrical stability; hydrogen storage; charge transfer. 1. introduction graphene, one atom thick sheet of sp2 bonded carbon atoms arranged laterally in a honeycomb crystal lattice, has been developed from theoretical model systems [1] to experimental reality [2]. because of the two-dimensional crystal structure, it shows many interesting properties like observable quantum hall effect even at the room temperature [3], an ambipolar electric field effect along with ballistic conduction of charge carriers [4], tunable band gap [5] and high elasticity [6]. after the experimental production of graphene in 2004 [7], considerable research interest has been shifted to explore its unique properties and various potential applications such as in energy storage [8,9], spintronics [10] and microelectronics [11]. various theoretical and experimental works have been performed focusing on the electronic and magnetic behaviours of different adatoms [12-15] adsorbed on graphene system, and have been found to yield many interesting results. in addition to fascinating intrinsic electronic and mechanical properties exhibited by pure graphene, the structure and properties of graphene can also be controlled and modified by adsorption and/or doping of foreign atoms [16]. very highly porous carbon materials offer a wide variety of chemical compositions that are suitable for the adsorption and storage of gaseous molecules like hydrogen, methane and carbon dioxide. currently, gas storage in solids is an important technology with potential applications ranging from energy, environment and all the way biology to medicine [17]. s. lamichhane et al. / bibechana 11(1) (2014) 113-122: (online publication: march, 2014) p.114 the development of the fuel cell technologies, based on hydrogen, holds the promise for producing renewable energy. the safe storage of hydrogen is also crucial for the development of hydrogen energy [18]. carbon nanomaterials are suitable for the hydrogen storage due to high surface to volume ratio. dillion et al. [19] were the first to study the hydrogen by assemblies of single walled carbon nano tubes (swcnt) and porous activated carbon [20]. later, many works focused on carbon based materials such as nanotubes [21,22] and fullerene c60 [23] have been performed. although the transition metal atoms such as pt and pd, can bind multiple h2 molecule and metal adatom carbon material can adsorb more hydrogen molecules, exceeding the minimum requirement of 6wt% for practical applications, a reliable and quantitative analysis of binding character is still insufficient. after the synthesization of graphene, its capacity of binding hydrogen molecule should be the great matter of interest. the remaining part of the paper is organized as follows. this section (introduction) is followed by the computational method in section 2 where we describe the systems, algorithm, and approximations for the whole calculations. the section 3 presents and discusses the results of the present work. the last section ‘conclusions and concluding remarks’ highlights the summary of the paper and also presents its possible extension in near future. 2. computational method the dft based first-principles calculations [26,27] are carried out to know the structural stability and electronic properties of adatom adsorption on graphene. further, we have studied the adsorption of hydrogen molecule/s on pt decorated graphene to investigate its hydrogen storage capacity. the long range dispersion forces are incorporated via london interaction [28] in dft-d2 level of approximations, implemented with the quantum espresso code [29]. the interaction between electrons and ion cores is described by ultrasoft pseudo potentials, and generalized gradient approximation (gga) formalism is adopted to treat the electronic exchange and correlation effects, as described by perdew-burke-ernzerhof (pbe) [30]. the plane wave basis set with the kinetic energy cut-off of 35 ry is used for the expansion of the ground state electronic wave functions. the plane waves are chosen to have a periodicity compatible with the periodic boundary conditions of the simulating cell. the supercell dimensions are kept fixed during the relaxation. we have used calculated value of the lattice constant ( o a46.2a = ), which overlaps with the experimental value [31], obtained from our convergence tests. the adatom graphene system is modeled using single adatom in 2×2, 3×3, and 4×4 supercells of graphene containing 8, 18 and 32 number of carbon atoms. in this work, the adsorption of single pt atom on graphene is performed at three different high symmetry sites, top (t), hollow (h) and bridge (b). for each adsorption site of the adatom-graphene system, the adatom is relaxed along the z-direction and the c atoms on graphene in all x, y, and z directions. to estimate the binding energy of adatom (pt), the calculations for the isolated pt, graphene and adatomgraphene are performed within the identical supercell of graphene. the optimized geometry is obtained with fully relaxed bfgs (broyden-fletcher-goldfarb-shanno) scheme [32] until the total energy change between two consecutive scf steps becomes less than 10-4ry and force acting goes below 10-3 ry. the brillioun zone of graphene is sampled in k-space using the monkhorst-pack scheme [33] with an appropriate number of k-points. different sized supercells are considered to see the size effect of the interaction between the isolated adatom and graphene. in order to avoid the interaction between the adatoms at adjacent supercells, vaccum length of supercell was made large enough, i.e. 20å along zaxis. the detail calculations to study the electronic properties, like density of states (dos) and electronic band structure of pure graphene and pt-adsorbed graphene are calculated in 3×3 supercell of graphene and 15×15×1 mesh in k-space. the adsorption properties of molecular hydrogen are observed on the most stable geometry of platinum decorated 3×3 supercell of graphene. at first, we optimized h2 molecule and found bond length of 0.75 å s. lamichhane et al. / bibechana 11(1) (2014) 113-122: (online publication: march, 2014) p.115 between two hydrogen atoms. the optimized molecule/s is then placed within the pt-adatom graphene supercell of height 20å, very large in comparison to the bond length of h2, which prevents interaction between two hydrogen molecules at adjacent supercells. the calculations for a large number of molecular hydrogen (up to eight), with in the limit of computational power, has been covered in this study to observe the desirable binding energy and hydrogen storage capacity. 3. results and discussion in the present work, we study the adsorption properties of single pt on different symmetry sites of 2×2, 3×3, and 4×4 supercells of pure graphene and also present the binding strength/geometry of a number of hydrogen molecules on its preferred geometry. a. binding energy and geometry the binding energy (∆e) of adatom on graphene is defined as, ∆e = ea+ egega where, ega, eg and ea are the values of energy of adatom-graphene, pure graphene and an isolated adatom in 3×3 supercell of graphene. out of the three adsorption sites (h, b and t) considered in present calculations, the configuration with the highest binding energy is defined as the most favored one. the adatom height (h) is defined as the difference in z coordinates of adatom and the average of the z coordinates of the carbon atoms in the graphene layer. we have also calculated the distance dac between the adatom and its nearest carbon atom. the adsorption of adatom on graphene produces a distortion (dz), which is quantified by computing the maximum deviation of c atoms along z-direction from their average positions in pristine graphene. the distortion of the graphene layer upon the adsorption of adatom is also calculated in terms of change in dihedral angles. table 1. the binding energy eb, adatom height h and the nearest carbon distance dac for adatom (pt) in 2×2, 3×3 and 4×4 supercells of graphene are noted. further, deformation produced in graphene layer due to adsorption of adatom is quantified in terms of distortion along z-direction (dz). size of graphene supercell adsorption site binding energy (eb,ev) height of pt atom (h, å ) distance of nearest carbon (dac, å ) distortion (dz, å ) 2×2 h b t 1.087 1.175 1.089 2.12 2.09 2.13 2.48 2.12 2.55 0.09 0.11 0.09 3×3 h b t 1.305 2.022 1.905 1.95 2.15 2.16 2.41 2.10 2.03 0.02 0.17 0.01 4×4 h b t 1.317 2.048 1.917 1.95 2.20 2.20 2.40 2.10 2.03 0.03 0.22 0.16 s. lamichhane et al. / bibechana 11(1) (2014) 113-122: (online publication: march, 2014) p.116 table (1) shows that the adsorption of platinum atom on different sites of pure graphene sheet is feasible. the table also reveals the most favored site for pt as bridge site with the highest binding energy (eb). the binding energy seems to increase on increasing the computed graphene size. however, the increment in eb is nominal for 4×4 supercell with reference to 3×3, and this helps to conclude that size effect of graphene beyond 3×3 does not alter the quality of calculations. taking care of size effect information and computational cost for bigger system, we consider 3×3 supercell for further calculations. the distortion in the graphene plane due to the adsorption of adatom is observed maximum at the bridge site. this correlates the direct relationship of distortion with binding energy. the distortion can also be measured in terms of change in bond length, bond angle and dihedral angle. in case of 3×3 graphene sheet, maximum change in bond length, bond angle and dihedral angle are observed as 0.02å, 0.9o and 12.07o from their initial values 1.42 å, 120o and 0o, respectively. b. electronic structures we have computed the electronic density of states (dos) and band structures of pure graphene and adatom graphene. the kohn-sham dos is computed for adatom at the most favorable (b) site of the 3×3 graphene supercell using 15×15×1 gamma centered brillouin zone-sampling. the energy eigen values are smeared by ‘marzari-vanderbilt’ smearing [35] of width 0.001 ry. fig.1 (a) fig.1 (b) figure 1: plot of density of states for pure graphene (a) and pt adsorbed graphene (b). the dos is plotted assuming fermi level as the reference. the spin up and spin down calculations of pure graphene are plotted by assuming fermi energy as reference level (fig. 1a). the dirac point, where dos is nearly equal to zero, lies at the fermi level, and approves that the valence and conduction band meet at that point with zero band gap. the identical density of states for spin up and spin down in the figure approves the non magnetic nature of pure graphene. from fig. (1b) it is seen that fermi level of adatom graphene again appears to remain at the dirac point. on the other hands, dos of adatom graphene system has been modified near the fermi level. the contribution of different pt orbitals in the dos of pt adatom system is shown in fig. 2. s. lamichhane et al. / bibechana 11(1) (2014) 113-122: (online publication: march, 2014) p.117 fig. 2 (a) fig. 2 (b) figure 2: the projected densityof states (pdos) for spin up and spin down of s (a), p (b), and d (c) orbitals of pt, an adatom on graphene. they show the different orbital’s contribution on the dos of pristine graphene. fig. 2(c) the band structure of pure graphene exhibits its unique feature showing zero band gap at fermi level. the bands meet at a point in fermi level (observed at -2.351 ev) and form a conical structure, which are known as dirac point and dirac cone respectively (fig. 3a). the interaction of the adatom with п and п* states of the carbon atoms in graphene, however, breaks the symmetry of graphene and band gap occurs at the fermi level. new bands originating from pt modify the band structure of pure graphene and disclose a band gap of 1.10 ev in adatom graphene. this change in band gap from zero in pure graphene to 1.10 ev in pt-added graphene shows the potential use of the material for practical applications. s. lamichhane et al. / bibechana 11(1) (2014) 113-122: (online publication: march, 2014) p.118 fig. 3(a) fig. 3(b) figure 3: band structure of 3×3×3 supercell of pure graphene (a) and pt-adsorbed graphene (b) along k γm-k path of irreducible brillouin zone. c. charge transfer charge transfer, an ambiguous quantity [16, 17], is an important feature of adatom-graphene interaction in which transfer of electronic charge takes place between the adatom and graphene. in this section, we discuss and quantify the charge transfer due to the adsorption of adatom on bridge site of 3×3 graphene supercell, which we believe an essential part to study the nature of bonding between the interactive materials. by keeping in mind that the magnitude of charge transfer is highly method dependent and difficult to quantify as an absolute value, we have used one of the algorithms followed by previous studies [15], where we integrate differences in electronic charge density in planer basis. with the help of optimized structures, the charge densities for pure graphene layer, isolated adatom, and adatom graphene are calculated. the difference in charge-density is then defined as ∆ρ(r) = ρag(r) – ρa(r) ρg(r) where ρag(r), ρa(r) and ρg(r) are the charge densities of the adatom-graphene, an isolated adatom, and graphene respectively, calculated in the same positions of the supercell as done for adatom-graphene calculations. figure 4: planner averaged electron charge difference for pt on graphene at b site as a function of position along z-direction. the vertical line at z=0 represents the position of graphene sheet and the line at z = 5.32 bohr indicates rcut. the integration between the region z=0 and z=5.32 bohr quantifies the charge transfer. s. lamichhane et al. / bibechana 11(1) (2014) 113-122: (online publication: march, 2014) p.119 figure (4) shows the planar averaged linear charge density difference as a function of z, along the height of supercell, for pt on b-site of graphene. the figure implies the position of planar graphene sheet and adatom (pt) at z = 0 and 5.32 bohr, respectively. positive difference in electron density towards the region of graphene sheet and negative towards the adatom illustrates the transfer of electronic charge from adatom to graphene. to calculate the charge transfer using the linear charge density difference, the region of the space belonging to graphene and/or adatom must be specified. as similar to the concept used by chan et al., [15], an adsorbate-substrate cutoff distance rcut is defined as the distance from the graphene plane to the point between the plane and the adatom at which charge accumulation changes to charge depletion. in the fig. (4) the region with z < rcut is assigned to the substrate and the region with z > rcut is assigned to the adatom. the charge transfer is obtained by the integral of linear charge density difference in the substrate region, and the quantity in case of pt adatom graphene has been found as 0.18e. higher the value of charge transfer may cause more impacts on the electronic structure and therefore on the catalytic activities of the system. d. adsorption of hydrogen molecule/s on pt adsorbed graphene we have also performed the first-principles calculations to study the adsorption of hydrogen molecule/s in pt decorated graphene. the system is modeled by allowing the adsorption of hydrogen molecule/s from one up to maximum eight in number on a single pt decorated 3×3 graphene supercell. the binding energy (∆e) of h2 molecule is then calculated using the formula, ∆e = eag + eh2 eagh where eagh is the energy of the system containing graphene, adatom and h2 molecules, eag is the energy of the pt-graphene system and eh2 is the energy of the h2 molecule. furthermore, binding energy/h2 molecule is calculated as, b.e/h2 = ∆e/n, with n as the number of the hydrogen molecules. figure (5) represents the optimized structures for the adsorption of hydrogen molecule/s on pt decorated graphene system. the figures show that two hydrogen molecules dissociate into atomic hydrogen and a complex, due to interaction with the adatom. most of the h2 molecules in the larger systems seem to be attracted by long-range dispersion forces. figure 5: optimized geometries for the adsorption of h2 in pt-decorated graphene system. s. lamichhane et al. / bibechana 11(1) (2014) 113-122: (online publication: march, 2014) p.120 the variation of the binding energy per h2 molecule with the number of h2 molecules adsorbed on ptdecorated graphene is shown in figure (6). table (2) presents the observed values of energy of total system, binding energy of h2 molecules and binding energy per h2 molecule. it can be seen that the observed binding energy per h2 molecule decreases with increasing the number of adsorbed hydrogen molecules. when a single hydrogen molecule is adsorbed in pt-graphene system, the binding energy for h2 molecule is found 1.84ev. the decreasing pattern of the binding energy per hydrogen molecule, as seen in fig. 6, for the adsorption of one to eight adsorbed h2 molecules goes through the range of 1.84 ev to 0.13 ev. the binding energy values per hydrogen molecule from this work meet the u.s. doe (department of energy) target (0.2ev-0.7ev) [36]. table 2: the binding energy of hydrogen molecules (eb) and binding energy per h2 molecule (eb/h2), for the adsorption of h2 molecules in pt decorated graphene are presented. figure 6: variation of binding energy per h2 molecule with the number of hydrogen molecule adsorbed in platinum adatom graphene. number of h2 molecule binding energy (ev) binding energy/h2 (ev) 1 0.415 1.847 2 0.914 0.957 3 1.957 0.652 4 1.937 0.484 5 1.985 0.397 6 2.076 0.346 7 1.137 0.162 8 0.904 0.134 s. lamichhane et al. / bibechana 11(1) (2014) 113-122: (online publication: march, 2014) p.121 one of the major purposes of this study (adsorption of hydrogen molecules on graphene) is to explore the possibility of the gaseous storage at operating conditions. if we compare the strength by which h2 are bound in pure and adatom graphene system, the maximum possible binding energy per h2 molecule is enhanced remarkably in adatom (pt) graphene (1.84ev) over the pure graphene (~ 0.07 ev). the hydrogen storage capacity of single pt decorated graphene for the adsorption of 8 h2 molecules is 3.74 wt % per substrate, comparing to the doe target (around 6 wt %) [9], for the practical applications. the estimated results display the potential application of pt decorated graphene in hydrogen gas storage material. 4. conclusion and concluding remarks we studied the structural and electronic properties of pure graphene and platinum adsorped graphene systems. using the estimated values of binding energies of platinum at three high symmetry sites (h, b and t) of 3×3×3 graphene supercell, it is found that the bridge site is energetically favourable with its magnitude 2.022 ev. the adsorption of adatoms on the bridge site of the graphene changes some of the graphene sp2 like orbital character to a more covalently reactive sp3 like character, which is accounted by calculating the deformation on graphene sheet. a small band gap of 1.10ev has been noticed in band structure calculations of pt-added graphene over the zero band gap pure graphene, which causes the breaking of symmetry of the graphene. we have also studied the adsorption of the hydrogen molecules on pt-decorated graphene in order to investigate its hydrogen storage capacity. the binding energy per h2 molecule due to adsorption of one to eight number of hydrogen molecules on pt adatom graphene ranges within 1.847 ev to 0.134 ev, where its value decreases on increasing the number of 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[36] j. g. zhou, q. l. willians, j. nano research, 15 (2011) 29. microsoft word ujjol.doc ujjal alok et al. / bibechana 8 (2012) 67-72 : bmhss, p.67 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana acoustoelectric effect in semiconductor superlattice ujjwal alok 1* , manoj kumar 1 , b.k.singh 1 , praveen kumar 2 1 univ. dept. of physics, t.m.b. university, bhagalpur (bihar) india 2 research scholar, s.k.m. university, dumka (jharkhand) india ∗ corresponding author, e-mail : okujjwal@rediffmail.com article history: received 8 july, 2011; accepted 7 august, 2011 abstract acoustoelectric effect in semiconductor superlattice (sl) in the region ql >>1 has been studied. the equation of motion of the lattice has been transformed into a simple form which becomes identical with the dynamic equation for the wave amplitude in the theory of plasma turbulence. a dispersion relation has been derived from the acoustoelectric current j on the constant electric field e. it is noted that when the electric field is negative the current j rises, reaches a peak and falls off. on the other hand, when the electric field is positive the current decreases, reaches a peak and then rises. a similar observation has been noted for an acoustoelectric interaction in a multilayered structure resulting from the analysis of the si/sio2 structure. keywords: acoustoelectric current; acoustomagnetothermal effect; quantum transparency 1. introduction the propagation of acoustic wave through a semiconductor has been discussed from many angles. blotekjaer and quate [1] have used the coupled mode approach in which one regards the acoustic wave as the lattice mode which are coupled piezo – electrically to the space charge modes of the electron distribution. in [2] thakur et al. observed the effect of a dc current on the drift of optically generated carriers in a quantum well. another interesting mechanism based on the transfer of energy and momentum is the interaction of acoustic phonons with carrier charges in semiconductor materials. this mechanism occurs not only during the scattering of quasimomentum carriers with lattice vibrations but also when acoustic waves propagate through the material. among the effects observed are the absorption ( amplification ) of acoustic waves [3-5], acoustoelectric effect (ae) [6-10], acoustomagnetoelectric effect (ame) [11-12], acoustothermal effect [13], and acoustomagnetothermal effect [13]. these phenomena have, however, received very little attention in (sl) even though they have immense device applications. acoustoelectric effect is the transfer of momentum from acoustic waves to the conduction electrons as a result of which may give rise to a current usually called the acoustoelectric current j or in the case of an open circuit, a constant electric field e. the study of this effect is vital because of the complimentary role it may play in the understanding of the properties of the sl which we believe should find an important place in the acoustoelectric devices. experimental evidence of the dependence of the acoustoelectric effect on the ujjal alok et al. / bibechana 8 (2012) 6772: bmhss, p.68 parameters of sl has been reported in [14]. in [15] experimental work on the acoustoelectric interaction of saw in gaasin gaas superlattice has been reported. a theoretical model for measuring transverse acoustoelectric voltage in multilayered structure resulting from the analysis of the si/sio2 has also been reported in [16]. 2. distribution function and threshold field assume the sound wave as collimated monochromatic phonons with all exactly in phase with one another, we write distribution function, as. f(k) = δ(k q) (1) where ‘k’ is the current phonon wave vector, in many semiconductors, such as gaas the conduction band has a minimum at zone centre and an indirect gap with higher energy at another minimum, at a critical point on the zone boundary. the sl has above other minimum on zone boundary. if the gaas quantum well width is small enough, the confined state of the zone centre can be pushed higher than the other zone boundary. in this case, electrons will fall from the zone centre into other minimum. the valence band holes will remain confined in this layers, however. this is called a type -ii sl. a structure in which both the electrons and the holes are in the same layer is called a type –i sl. sl have been used to demonstrate the basic effect of bloch oscillations [17] in which a d c electric field generates. it is assumed that the sound wave and the applied constant electric field e propagates along the z – axis of the sl. the problem will be solved in the quasi – classical case, i.e. 2∆ >>τ -1 (ћ = 1), eed << 2∆ ( d is the period of the sl, 2∆ is the width of the lowest energy miniband and e is the electron charge ). the current density associated with an acoustic wave may be obtained from the expression [18]. j = (2) where, u = (3) ‘ ’is the sound flux density, ωq and are the frequency and the group velocity of sound wave with the vector and is the solution of the boltzmann kinetic equation in the absence of a magnetic field. if we introduce a new term = p-q in the second term of the integrals in eq. (3) and take = . we can express eq. (3) in the form j = (4) where the vector as indicated in [19] is the mean free path li(p). thus the acoustoelectric current in eq. (4) in the direction of sl axis becomes jz= (5) where f( ) is the distribution function, p is the momentum of electrons, g(p2, ) is the matrix element of the electron-phonon interaction and for qd<<1 it is given as, ujjal alok et al. / bibechana 8 (2012) 6772: bmhss, p.69 (6) where c is the deformation potential constant. is the density of the sl in the τ approximation and further when τ is taken to be constant, lz = τ sz (7) sz = (8) inserting eqs. (6) and (7) into eq. (5) we obtain jz = (9) for superlattices the dispersion law is given by (10) where pt and pl are the transverse and longitudinal ( relative to the sl axis ) components of the quasi momentum respectively, ∆υ is the half width of the υth allowed miniband (11) are the sizequantized levels in an isolated conduction film, d = d0+d1 ( d0 is the width of the rectangular potential wells and d1 is the barrier width a non-zero quantum transparency) is the sl period. the distribution function in the presence of the applied constant field e is obtained by solving the boltzmann equation in the τ approximation, given by f(p) = (12) here, (13) where n is the electron density, t is the temperature in energy units and io(x) is the modified bessel function. we assume that electrons are confined to the lowest conduction miniband (υ=1) and omit the miniband indices. this is to say that the field does not induce transitions between the filled and empty minibands. the electron velocity is given by (14) we further assume that and write eq. (10) in the usual form as (15) substituting eqs. (12),(14) and (15) into eq. (4) and solving for a non-degenerate electron gas. ujjal alok et al. / bibechana 8 (2012) 6772: bmhss, p.70 jz= (16) where is the heaviside step function. b = x = sinh , and = we shall solve eq. (16) for two particular case, (i) in the absence of the applied constant field (e=0), from eq. (16) we obtain jz = (17) if , jz =0 i.e; there appears a transparency window. this is a consequence of the conservation law. (ii) in a weak constant electric field, eed , , from eq. (16) we obtain jz= (18) from eq. (18) it is observed that at e > e0 = ωq the acoustoelectric current changes sign. the value e0 can be interpreted as a threshold field. e0 is a function of the sl parameters d and , and temperature t, frequency and the wave number q. for example, at , , d= cm, , and . for these values we obtain the threshold field e0 = 8.65vcm -1 which is small and can be observed. 3. results and discussion the general solution of eq. (16) cannot be obtained analytically. we, therefore, obtained it numerically and the graph of jz on e have been plotted. it is noted that the acoustoelectric current has a peak at some values e. these peaks decrease with a corresponding decrease of . more interesting is the nature of the acoustoelectric current. it is observed that when the electric field is negative the current rises and reaches a maximum and then falls of in a manner similar to that ujjal alok et al. / bibechana 8 (2012) 6772: bmhss, p.71 observed during a negative differential conductivity. on the other hand, when the electric field is positive the current decreases and reaches a minimum then increases. this can be attributed to the bragg reflection at the band edge. it is further observed that the ratio of the height of the peak corresponding to absorption to that corresponding to amplification differ from one. this value also decreases with a decrease in . the threshold field e0 also increases with the decrease of . it is noteworthy to show that a similar relation was obtained for a transverse acoustoelectric voltage experiment on si/sio2 and this result agrees quite well with our result [15] fig : dependence of jz/jo on ------= 0.09 -------= 0.07 evv..... = 0.05 ev references [1] k. blotekjaer and c.f.quate, proc. ieee 52 (1964) 360 [2] r. y. thakur, b. k. singh. and anjula singh, semicond.sci. technol. uk 5 (1990) 405 [3] k.b.tolpygo and z.i.uritskii, zh. eksp. teor. fiz 30 (1956) 929 [4] g. weinreich, phys. rev. 104 (1956) 321 [5] a.r.hatson, j.h mcfee and d.l.white, phys. rev. lett. 7 (1961) 237 [6] r.h.parmenter, phys. rev. b 89 (1953) 990 [7] m. rotter, a.v.kalameitsev, a.o.govorov, w. ruile and a. wixforth, phys. rev. lett. 82 (1999) 2171 [8] j. m. shilton, d.r.mace, v.i. talyanskii, yu. galperin, m.y.simmons, m.pepper and d.a.ritchie, j.condens. matter 8 (1996) l 337 [9] v.l.gurevich and v.i. kozub, phys. rev. b 58 (1998) 13088 [10] v.v.afonin, yu. m. gal’perin, semiconductor 27 (1993) 61 [11] m.i.kaganov, sh. t. mevlyut and i.m. suslev, sov. phys jetp 51 (1980) 189 [12] a.d. margulis and v.a.margulis j.condens. matter 6 (1994)6139 [13] yu. v. gulyaev and e.m.epshlein sov. phys. solid state 9 (1967) 674 [14] v.a vyun, yu.o. kanter, s.m.kikkarin, v.v.pnev, a.a.fedorov, and yakovkin 1988, academy of science ussr 11 th all union conference on physics of semiconductors ( kishinev, 1988) vol 3 (kishinev academy) p118 ujjal alok et al. / bibechana 8 (2012) 6772: bmhss, p.72 [15] v.a vyun, yu.o.kanter, s.m. kikkarin, v.v.pnev, a. a.fedorov, and i.b.yakovkin, solid state communications 78 (1991) 823 [16] f. palma, j.appl. phys. 66 (1989) 292 [17] c. waschke, physical review letters 70, (1993) 3319 [18] m.i. kaganov. sh.t. mevlyut, and i.m.suslev, zh. eksp. teor. fiz 78 (1980) 376 [19] s.v. krychkov and n.p. mikheev, fiz. tekh. poluprov. 16 (1982) 169 microsoft word s.k. chakrabarti _92-96_.doc s.k. chakrabarti et al. / bibechana 9 (2013) 92-95: bmhss, p.92 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana electrical conductivity and knight shift of liquid alkali metals s. k. chakrabarti1*, i. s. jha1, r. n. yadav2, b. p. singh3 1department of physics, tribhuvan university, m. m. a. m. campus, biratnagar, nepal 2department of mathematics, tribhuvan university, m. m. a. m. campus, biratnagar, nepal 3department of physics, tilka manjhi bhagalpur university, bhagalpur, bihar, india *corresponding author: skc_2007@yahoo.com article history: received 22 october, 2012; accepted 12 november, 2012 abstract in the present work we have considered two alkali metals―sodium and potassium―at their molten stage near the melting point. for the purpose of this theoretical investigation we have used harrison’s first principle (hfp) pseudopotential technique which is basically an orthogonalised plane wave method. the electrical resistivity has been computed through ziman’s formula. then the electrical conductivity of the present metals is found out just by taking the reciprocal of the values so obtained. our computed results have been compared with the experimental data and a good agreement is obtained. a study of the existing literature reveals that the work with the magnetic property like knight shift of metals is scarce. this has encouraged us to apply the said hfp technique to study the knight shift of the present alkali metals. for this purpose we have used knight’s formula. our computed values of knight shift are in reasonable agreement for the metals under investigation. keywords: electrical conductivity; knight shift; pseudopotential; alkali metals. 1. introduction one of the important physical properties of a metal is its electrical conductivity. this electrical conductivity is found to vary gradually with the increase in temperature. it is really a matter of interest to study the electrical conductivity of a metal at its molten stage. a method to study the electrical conductivity of a liquid metal is faber-ziman’s electrical conduction theory based on the concept of model pseudopotential. in this approach a liquid metal is assumed to consist of a system of ions and electrons [1]. besides metals the electrical conductivity of some binary liquid alloys has also been studied in details by faber and ziman through such pseudopotential. however, a problem of model pseudopotential is its transferability because sometimes with the change of environment the change of parameters is also required to get a good agreement with the experimental results. in the present work harrison’s first principle (hfp) pseudopotential technique, based on the concept of orthogonalised plane waves (opw), has been applied to compute various electronic and core interactions in order to obtain the fourier transform of the crystal potentials termed as the form factor [2], w(k, q). the computed form factors have been consequently used to calculate the physical properties through formulas developed by various authors in the past few decades. s.k. chakrabarti et al. / bibechana 9 (2013) 92-95: bmhss, p.93 (online publication: nov., 2012) here for the computation of resistivity we have used ziman’s formula. knight shift has been computed by knight’s formula. and for this purpose the liquid alkali metals sodium and potassium have been considered near their melting points. 2. basic formalism ziman’s formula for resistivity is [3]   1 2 30 2 2 2 0 3 ( ) , , 4 f z a q w k q d h e v      (i) where ωo is the atomic volume of the metal, z its valency, vf the velocity of electron and . f q k   (ii) hence, electrical conductivity is given by 1 .   (iii) the knight shift has been computed through knight’s formula [4]     ' 1 0 2 0 0 3 2 , ln , 4 2 f f f f f f k p z q k a q w k q q dq k p e k q k      (iv) where pf denotes the cauchy principal value and ef the fermi energy. 3. results and discussion we have computed the form factors of the alkali metals sodium and potassium using various sets of eigenvalues and corresponding eigen functions of herman-skillman and clementi and also the xαexchange parameters as suggested by different authors viz. slater, kohn-sham and schwarz [5-9]. further, the experimental and theoretical structure factors [a(q)] measured by various authors have also been considered during the evaluation of the electrical conductivity and knight shift of the abovementioned monovalent metals [10, 11]. the results thus obtained have been presented in the table. the form factors are furnished in fig. 1 and fig. 2. table: electrical conductivity and knight shift electrical conductivity (ms/m) knight shift (%) metal eigenvalues due to theoretical experimental theoretical experimental na herman-skillman 10.7 10.36 0.075 0.116 k herman-skillman 7.6 7.58 0.301 0.253 -0.12 -0.08 -0.04 0 0.04 0.5 1 1.5 2 2.5 w (k , q ) i n ry d.   herman-skillman clementi  s.k. chakrabarti et al. / bibechana 9 (2013) 92-95: bmhss, p.94 (online publication: nov., 2012) fig. 1: form factor of na fig.2 : form factor of k it is observed that for sodium the eigenvalues of herman-skillman give better result than those of clementi. in case of potassium also it is found that instead of the eigenvalues of clementi those of herman-skillman present better picture. so, further investigation of knight shift has been carried with these form factors using xα-parameters as proposed by schwarz. the computed values of knight shift are in reasonable agreement for the metals under investigation. 4. summary and conclusion hfp pseudopotential technique has been applied to compute the electrical conductivity of the alkali metals sodium and potassium in liquid phase around melting point with the help of ziman’s formula. side by side the knight shift of them has also been calculated on using knight’s formula. in both the cases a reasonable agreement with the experimental results has been noticed. -0.2 -0.1 0 0.1 0.5 1 1.5 2 2.5  herman-skillman w (k , q ) i n ry d.   clementi s.k. chakrabarti et al. / bibechana 9 (2013) 92-95: bmhss, p.95 (online publication: nov., 2012) during our investigation it has been observed that unlike other properties such as resistivity, thermoelectric power, fermi energy, density of states etc., which involve square of the form factor, the knight shift, vide equation (iv), depends linearly upon w(k, q). hence, through the computation of knight shift one can assess the correctness of the magnitude as well as the sign of the form factor. the electrical conductivity depending upon the square of the form factor can be used to test the correctness of its magnitude only. however, it has been observed that the electrical conductivity having lower magnitude and more sensitiveness to the nature and magnitude of the form factor can serves the purpose quite satisfactorily. references [1] c. r. dasgupta, physics, book syndicate, kolkata (1972). [2] w. a. harrison, pseudopotential in the theory of metals, benjamin, new york (1966). [3] j. m. ziman, adv. phys., 16 (1967) 551. [4] w. d. knight, a. g. berger and v. heine, ann. phys., 8 (1959) 173. [5] f. herman and j. skillman, atomic structure calculation, prentice hall, new jersey (1963). [6] e. clementi, ibm j. res. and dev., 9 (1965) 2. [7] j. c. slater, phys. rev., 81 (1951) 385. [8] w. kohn and l. j. sham, phys. rev., a140 (1965) 1133. [9] k. schwarz, phys. rev., b5 (1972) 2466. [10] y. waseda, the structure of non-crystalline materials, mcgraw hill book co., new york (1980). [11] g. e. pake, solid state physics, academic press, new york (1966). microsoft word devesh pradhan _65-69_.doc devesh pradhan / bibechana 7 (2011) 65-69: bmhss 65 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana waste management devesh pradhan∗∗∗∗ dept. of chemistry, bhanu m.h.s.s. biratnagar, nepal article history: received 29 october 2010; revised 25 november 2010; accepted 2 december 2010 abstract waste management has become very challenging in our society. different types of wastes which are produced in our society have been investigated. special attention has been given in the management methods of waste. keywords: industrial waste, domestic waste, composting, recycling 1. introduction wastes are produced by all living things – exerted by an organism or thrown away by society because they are no longer useful. but the make up of waste means that once discarded by one body its constituents may become useful to another. in the natural world, a waste produced by an animal that urinates, is disposing of waste products its body does not need, but the water and nutrient can become resources for other organisms. similarly, sewage from a town or municipality can be used by bacteria (microbe) which break it down in a river, for example, an old shirt discarded by one person might be worn by another, often poorer individual. the term waste is therefore a label determined by ecology, economics or culture. much of the waste produced by human society is natural although we have created products not found in natural world, such as cfcs and plastics which can become wastes. the use of resources, by people, and hence production of waste has accelerated in the period since the industrial revolution, and this fact combined with the growing number of people on the planet has created increasing volumes of waste that need to be disposed off. this disposal requires are careful management since too much waste disposed off in a certain place at a certain time can contaminate or pollute the environment, creating a hazard to the health, safety or welfare of living things. the principal objective of waste management is to control, collect, treat, utilize and dispose off the wastes in an economical manner consistent with the protection of public health. 2. types of wastes wastes have different forms: solid, liquid, gas or energy in the form of heat or noise. the sources of wastes are following: 2.1 domestic and municipal wastes ∗ address for correspondence: devesh pradhan, dept. of chemistry, bhanu memorial higher secondary school, biratnagar-14, morang. email: deveshsmail@yahoo.com devesh pradhan / bibechana 7 (2011) 65-69: bmhss 66 these include wastes (garbage and rubbish) from households offices, hotels, markets, etc. and also the refuse such as street sweepings, dirt, leaves, etc. the term ‘garbage’ is generally used to denote bio-degradable food wastes. the term ‘rubbish’ is used to denote nonbio-degradable. 2.2 agricultural wastes these wastes result from farm, feed lots and live stock yards. the agricultural waste include paddy husk, baggage from sugar cane, tobacco and corn residue, slaughter house wastes, manure 2.3 industrial wastes these include non process wastes such as packing wastes, raw material wastes and process wastes which depend upon the type of product being manufactured such as tannery wastes, weaving and dyeing wastes, food processing wastes, plastic wastes, rubber wastes, metal scraps, etc. from the respective industrial establishment. 2.4 mining and construction wastes these include the waste produced in coal mining, gold mining, copper mining, china clay mining, etc. 2.5 special wastes the wastes that are toxic to humans, plants or animals, are inflammable, corrosive,exclosive or radioactive. such hazardous wastes include acids and alkalis, heavy metals, oils, solvents, pesticides, enzymes, antibiotics and various hospital wastes. 3. disposal of waste all wastes are disposal off into the environment, but some enter the environment in a more controlled manner than others. wastes produced from the combustion of fuel by vehicles are emitted directly into the atmosphere, while domestic sewage wastes are often collected by municipal authorities and disposed off into specific locations such as a river or ocean. the three major reservoirs (air, river & ocean) are publicly owned and this common ownership has facilitated unregulated emission of wastes. in many countries, however, the gradation of these common property resources by wastes have spawned numerous controls on their emission. wastes that are actively managed and a wide range of management options are available. the most commonly used options are: (a) sanitary land fills or controlled tipping (b) thermal process (e.g. incineration and pyrolysis) (c) composting (d) recycle and re-use (f) waste prevention, cleaner production 3.1 sanitary land fills land filling is the most common and economic method of solid waste disposal in many countries. the ‘municipal dump’ generally used to be in low-lying area near a water course. this unsanitary dumping of the waste used to result in water pollution, bad odours. blowing papers, rats or fermentation bacteria can generate methane and cause a fire hazard. these problems were mostly reduced by burial of waste after compacting the waste in layers and covering it with soil at the end of the disposal of the waste every day. this method of land fill is known as ‘sanitary land fill’. although compacting and covering still continue to be basic operations today, several further improvements in the process have taken place during recent years. these include careful and scientific site selection, controlled deposition, better devesh pradhan / bibechana 7 (2011) 65-69: bmhss 67 methods of compaction, reduced cover, leachate collection to avoid water pollution and site monitoring to ensure environmental protection. in sanitary land fill, complex organic wastes are slowly decomposed by the soil microorganisms. the aerobic bacteria decompose the organic solid waste by using whatever oxygen is present inside the land fill. then, decomposition by the anaerobic begins and this accounts for the degradation of most of the solid waste present in the landfill. the water soluble organic acids generated in this process enters the water media and diffuses through the landfill soil. the bacteria present in the soil aerobically metabolize these organic acids into co2 and water. in order to control the contamination of ground water by the leachate (contaminated liquid having high organic content, soluble salts and other constituents) certain regulations are prescribed for sanitary landfills. these include mandatory minimum distance of the location of landfills above the ground water level, minimum distance from the nearest point of water use of soil of low permeability, preventing the build up of the leachate within the landfill, drainage and ground water depth and movement etc., supplementary measures such as clay covers for the landfill, leachate collection, removal and treatment facility, installation of monitoring system are also suggested to ensure that the buried refuse remains as dry as possible and the leachate do not reach the ground water. in spite of these precautions, if some leakage of the leachate still occurs , the soil serves as an additional barrier by mechanism such as filtration, absorption, precipitation and biological activity. if properly designed and managed, landfill sites may do little harm to the environment and can eventually provide a surface for such land uses as playing fields or reforestation, although not usually for heavy structures such as housing. 3.2 thermal process the important thermal processes used in solid waste treatment are incineration and pyrolysis. 3.2.1 incineration in this process, the solid organic wastes are subjected to combustion so as to covert them into combustible residue and gaseous products. incineration is increasingly used in many countries to reduce the bulk of wastes and to break down hazardous compounds, so rendering them less dangerous. the incineration process is considered when suitable site for land filling is not available within the economic distances from the sources of solid wastes. incinerators do, however, release harmful emissions into the atmosphere, such as particulate matter, heavy metals and trace organics. such emissions can be limited with a range of approaches, such as improved combustion techniques, sorting of wastes prior to incineration and by fitting pollution control devices. ash produced in incinerators is commonly buried in landfills, although some attempts have been made to use this ash as a component of building materials. 3.2.2 pyrolysis the chemical constituents of some organic wastes can be recovered by destructive distillation (or pyrolysis) of solid waste. in this process, the combustible constituents of the solid waste are heated in a special retort retort like chamber known as pyrolysis reactor at 600 to 1000 0 c in a low oxygen or an oxygen free environment. this is an endothermic process and thus differs from the conventional incineration. pyrolysis of the solid yields the following components. (a) tan or oil containing methanol, acetone, acetic acid etc (b) gaseous phase containing h2, ch4, co, co2 etc (c) solid phase containing pure carbon char and inert materials like glass, rock, metal, etc., the advantages of pyrolysis process include: (a) volume reduction by about 90% (b) possibility of handling potentially hazardous plastics, e.g. p.v.c. in a safe way (c) absence of pollution problem. devesh pradhan / bibechana 7 (2011) 65-69: bmhss 68 3.3 composting it may be carried out naturally under controlled condition or in mechanized composting plants. in natural system, the solid waste is placed on slow moving conveyor belts. materials like glass, paper, metals are hand-picked and them the ferrous materials are removed by magnetic separation. the waste is then ground in hammer mills to the desired size range (0.6to2.5cm). then it is mixed with nutrient source (e.g. sewage sludge, animal manure or night soil), filler (e.g. wood chips or ground corn cobs) and water (to provide 50% moisture). this is known as waste preparation. the mixture or waste preparation is placed in the windows for 4 to 6 weeks, while turning it once or twice a week. the waste is decomposed by thermophilic micro-organism during this period. the materials are then allowed to stabilize for other 2 to 5 weeks, the temperature falls, the colour darkens and a musty odour develops. this indicates completion of the process. the filler may then be removed and the remaining humus like material is used as soil conditioner. with mechanical systems, the composting time is reduced to half of that required in natural systems, because of continuous aeration and mixing. in order to ensure quick and better marketing prospects, the product is sometimes upgraded by operations such as curing, grinding, and screening, pellestising and bagging. 3.4 recycling and reuse realization of the economic value of certain wastes promotes reuse, recovery and recycling. in many developing countries, informal scavenging of municipal wastes from city dumps is widely practiced and the materials recovered are put to a variety of uses. it provides employment for individuals who otherwise would have none, particularly important in those countries where social security systems are inadequate or non-existent. low cost buckets, charcoal stoves and lamps are all made from scavenged metals from city dumps and sold to people who live in squatter settlements in the city. in the more developed countries such informal waste recovery was also common more than 100 years ago, but more formalized recycling schemes have now sprung up. these schemes are more advanced for metals and some other materials such as glass, paper and broken polythene and collection points for such solid wastes have become a familiar sight in many cities in recent years. from the standpoint of energy conservation there is every justification for the recycling and reuse of ferrous metals, aluminium and some other non-ferrous metals because the mining of virgin material is energy intensive. as far as glass is concerned, it was found that the energy spent on reuse of old glass is more than that required to process new material. hence energy saving can be realized only by reuse of the glass containers than to reprocess them. paper constitutes nearly 50% by weight of the solid wastes. total recycling of paper has not been possible so far. unrecoverable paper is generally disposed by controlled incineration and the gaseous products obtained are co2 and water vapour which are non-polluting. paper has a high heat of combustion and hence is disposed by converting it to energy. refuse derived fuel (rdf) can be used as supplementary fuel for use in boilers or in other combustion processes. recycling of plastics received considerable attention primarily because of ever increasing use of plastics and also because of their non-biodegradable nature. for a satisfactory recycling of plastics the following two requirements are to be taken into account: (a) the plastic material should be made up of only on type, i.e. it should be homogeneous. (b) the plastic scrap or waste should be collected from the consumer. recycling of plastics may be carried out in any of the following ways: (a) primary recycling where the same plastic product is manufactured again. devesh pradhan / bibechana 7 (2011) 65-69: bmhss 69 (b) secondary recycling where the material the material is reprocessed to a new product with different composition of inferior quality. (c) tertiary recycling where the plastic material is completely processed to a new form as in pyrolysis. another waste product that is commonly reused or recycled in many countries is waste water from urban areas. it is often diverted to cropland for irrigation. the water itself is a valuable resource and sewage contains plant nutrients (phosphorous and nitrogen). in countries where sewage is treated, the sludge that remains after treatment is also reused as a fertilizer due to it’s high nutrient content. about half of the sewage sludge produced in the uk and a third of that in germany is reused in this way, but in these and other countries, further use is limited due to its high heavy metal (gold, platinum, and palladium) content. hence, sewage sludge not used as fertilizer is disposed off by ocean dumping, dumping in landfill or incineration. as population and industrialization continue to increase, however, and the treatment of water and sewage becomes more widely used in order to reduce the pollution impacts from untreated sewage outlet, so more sludge will need to be disposed off. an innovative approach to this increasing dilemma of disposal can turn a problem into a benefit by recovering the heavy metal from sewage and sludge. the global production of palladium from sewage and sludge could be of the same order of magnitude as that from mining production. the future disposal off sewage sludge should concentrate on the control of pollutants at source and extraction of metals, as approach which would yield numerous benefits, including. (a) more wide spread use of sludge as fertilizer (b) revenue from metals extracted (c) conservation of geological metal resources (d) saving on expensive waste depository space (e) prevention of environmental impacts on terrestrial and marine ecosystem 3.5 waste prevention, cleaner production there is no doubt that the best way to manage waste is to prevent it at source whenever this is possible. on the other hand cleaner production is a preventive approach to environmental protection. cleaner production is achieved by examining all phases of a product’s life cycle, from raw material extraction to its ultimate disposal, and reducing the wastefulness of any particular phase. cleaner production embodies the ideas both of environmental sustainability and of economic efficiency. in practice it involves improving the productivity of energy and material use to reduce consumption of resources and cut pollution per unit output. a number of companies go beyond legal requirements, however, and attempt to develop ‘closed loop’ proceeding cycles in which waste products are completely recycled and enter the environment to become pollutant. 4. conclusion this review presented here gives information about several sources and activities which produce waste in our society. these wasteproducing sources and activities can not be completely controlled. so the waste management methods should be discovered. the existing waste management methods should be improved. references [1] www.enpho.org [2] www.wateraid.org/nepal [3] d. pokhrel et al municipal solid waste management in nepal: practices and challenges, waste management, science direct, 25 (2005) 555. [4] www.wisegeek.com/ 157-160 r.n. yadav r c o s t n r.n. yadav / bibechana 11(1) (2014) 157-160: (online publication: march, 2014) p.157 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana signed graphs connected with the root lattice r.n. yadav department of mathematics m.m.a.m. campus, t.u., biratnagar, nepal e-mail: rajnarayanyadav29@yahoo.com accepted for publication: february 12, 2014 abstract for any base of the root lattice (an) we can construct a signed graph. a signed graph is one whose edges are signed by +1 or -1. a signed graph is balanced if and only if its vertex set can be divided into two sets-either of which may be empty–so that each edge between the sets is negative and each edge within a set is positive. for a given signed graph tsaranov, siedel and cameron constructed the corresponding root lattice. in the present work we have dealt with signed graphs corresponding to the root lattice an. a connected graph is called a fushimi tree if its all blocks are complete subgraphs. a fushimi tree is said to be simple when by deleting any cut vertex we have always two connected components. a signed fushimi tree is called a fushimi tree with standard sign if it can be transformed into a signed fushimi tree whose all edges are signed by +1 by switching. here we have proved that any signed graph corresponding to an is a simple fushimi tree with standard sign. our main result is that s simple fushimi tree with standard sign is contained in the cluster given by a line. © 2014 rcost: all rights reserved. keywords: signed graph; root lattice; fushimi tree. 1. introduction a signed graph is a graph in which each edge has a positive or negative sign. a signed graph is balanced if and only if its vertex set can be divided into two sets (either of which may be empty) x and y, so that each edge between the sets is negative and each edge within a set is positive. this is the first theorem of signed graphs (harary, 1953) a given signed graph, tsaranov, seidel and cameron instruct the corresponding root lattice. we treated with signed graphs corresponding to the root lattice an. a connected graph is called a fushimi tree if its all blocks are complete subgraphs. a fushimi, tree is said to be simple when by deleting any cut vertex, we have always two its connected components. switching and local switching of signed graphs are also introduced by cameron, seidel and tsaranov. a signed fushimi tree is said to be a fushimi tree with standard sign if it can be transformed to a signed fushimi tree whose all edges are signed by +1. by a switching we prove that any signed graph corresponding to an is a simple fushimi tree with standard sign. 2. some definitions (i) posets : let p be any set in which the partial order relation ≤ holds i.e. this relation is a. reflexive : ,xx ≤ ∀ px ∈ r.n. yadav / bibechana 11(1) (2014) 157-160: (online publication: march, 2014) p.158 b. anti-symmetric : yx ≤ and ,yxxy =⇒≤ ∀ pyx ∈, c. transitive : yx ≤ and ,zxzy ≤⇒≤ ∀ pzyx ∈,, for example: the se of natural number n={1,2,3,………..w} with maximal elements w is a poset with the usual ordering ≤ . (ii) lattice : a poset (p, ≤) in which every pair of elements has a supremum (v) or join and infimum (λ) or meet is called a lattice. it is noted by l. for example: it is a lattice, for avb = a or b ∈ n, according as ba ≤ or ab ≤ nboraba ∈=∧ , according as ba ≤ or ab ≤ (iii) the lattice an and signed fushimi trees a connected graph g = (v, e) is called fushimi tree if each block of g is a perfect graph. a fushimi tree g is said to be fushimi tree if g is divided exactly two connected components when each cut verdex in g is deleted. a signed simple fushimi tree is called a special fushimi tree with standard sign if we switch all signs of edges in to +1. the lattice an is spanned by vectors ji ee − , ,1+≤≠≤ njil where }.........,{ 12,1 +neee is the orthonormal base of the euclidean (n+1) space 1+nr there is the one to one correspondence between orderd root bases of an and connected signed graphs associated with an. (iv) local switching : let s be subset of vertices of a graph g then the graph h formed by vertices of s is called local switching of g generated by s. 3. theorem any connected signed graph is a signed graph associated with na if and only if it is a simple fushimi tree with standard sign. proof. let g be a singed graph corresponding to a ordered base },...,,{ 21 naaa . if we replace ia by ia , then the sign of g is switched with respect to {ia }. hence there is no problem whether we take ia or – ia . there is no cycle in g whose length is more than 3. in fact, if 3,,...,, 21 >maaa miii make a cycle, then we can assume that , 2211 jjji eeea =−= , 32 ji ea = ,,..., 1433 jjijji eeaeea mm −=−= but this implies that miii aaa ,...,, 21 are not linearly independent. if 321 ,, iii aaa make a cycle, then we can assume that , 11 jji eea −= ., 3322 jjijji eeaeea −=−= we have cycles of this type only in g. now take a block b of g consisting of vertices miii aaa ,..., 21 . two vertices all 1i a and 2i a must be on a cycle in b. we may r.n. yadav / bibechana 11(1) (2014) 157-160: (online publication: march, 2014) p.159 assume that 321 ,, iii aaa make a cycle, then we can put 332211 ,, jjijjijji eeaeeaeea −=−=−= . the vertices 1i a and 4i a are also on a cycle in b, which may be 541 ,, iii aaa . then we can put 44 jji eea −= , 55 jji eea −= or 515414 , jjijji eeaeea −=−= , where jj ≠4 . assume that 515414 , jjijji eeaeea −=−= . two vertices 2a and 4a are also on a cycle in .b then we have ,24 jj = a contradiction. hence, we get 5544 , jjijji eeaeea −=−= . by this way, we get kk jji eea −= , .1 mk ≤≤ hence any block of g is a perfect graph whose edges have sign+1. suppose that 11 jji eea −= of a block b is a cut vertex. if two vertex kj aa , which are not in b are adjacent with 1i a , then we can put 1111 , kjjkjjj eeaeea −=−= . hence kj iii aaa ,, 1 are contained in another block of g. hence we show that g 1i a has two connected components. thus g is a simple fushimi tree with standard sign. conversely: let g be a special fushimi tree with standard sign. assume that g has m blocks. if m = 1, it is evident that g is a connected signed graph associated with na . now suppose that the result is true for simple signed fushimi trees with m blocks. let g be a simple signed fushimi tree with m + 1 blocks. let g' be a simple fushimi tree with standard sign which is made from g by deleting one block b of g. then g' is a connected signed graph associated with na and corresponding to a ordered base },....,,{ 21 naaa . now assume that all l vertices of b are adjacement with a vertex 21 jji eea −= and that 2j e is not used in any other 2j a is not used in any otherja . then we can consider that the block b consists of ++++ −−− lnjnjni eeeeee 222 ,...,, 32 and 1a . hence we regard g as a connected signed graph associated with lna + . 3.1. local switching of simple fushimi trees let g be a simple fushimi tree with standard sign. take a block b of g. in the present work, g is said to be ( )kkn ,+ -type with respect to b if the order of b is n+k and the number of cut vertices in b is k. let a be a cut vertex in a block b. g/{a} has the two connected components. one is the component containing b/{a}. we call the other the branch with respect to (b, a). all such components are called branches with respect to b. a block of a simple fushimi tree is said to be pendant if it has only one cut vertex. we call a simple fushimi tree line-like if it has only one block or it has exactly two pendant blocks. a branch ab with respect to (b, a) is called line like if }{ auba i line-like. a simple fushimi tree is said to be a line fushimi tree if the order of its every block is 2. 3.2. lemma let g be a simple fushimi tree of (n+k, k) -type with respect to a block b. we can transform g into a simple fushimi tree of (k, k)-type, by a sequence of local switching. proof. let the block b consist of vertices knnn aaaaa ++ ....,,,....,, ,121 where knn aa ++ ,....,1 are cut vertices. set }{ 1+= naj and }.....,,,,( ,2121 knnn aaaaak ++−= by local switching with respect to ( )jan , , we obtain a simple fushimi tree of (n+k-1, k)-type with respect to block },.....,,,....,,{ 221 knnn aaaaa ++ , r.n. yadav / bibechana 11(1) (2014) 157-160: (online publication: march, 2014) p.160 where an and an+1 are cut vertices. denote by 1g this simple fushimi tree of (n+k-1, k)-type. applying the same procedure to ,1g we get a simple fushimi tree of (n+k-2,k)-type. repeating the same method, we get a simple fushimi tree of (k, k)-type at last. references [1] p. j. cameron, j. m. goethals, j. j. seidel, e. e. shult, j. algebra, 43 (1976) 305. [2] d. m. cvetkovic, m. doob, i. gutman, a. torgasev, annals of discrete mathematics 36, northroland, amsterdam, 1991. [3] p. j. cameron, j. j. seidel, s. v. tsaranov, j. algebra, 164 (1994) 173. [4] j. e. humphreys, reflection group and coxeter groups, cambridge staudies in advanced mathamatics 28, cambridge, 1989. [5] t. ishihara, j. math. univ. tokushim, 36 (2002) 1. microsoft word damodar thapa chhetry and joydeb pal.doc damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 105 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana physico-chemical parameters of seepage stream at kushaha area damodar thapa chhetry 1 and joydeb pal 2 1 department of zoology, post graduate campus, biratnagar 2 department of zoology, north bengal university , india article history: article history: received 22 november, 2011; accepted 17 december, 2011 abstract physico-chemical parameters of the seepage stream of kushaha area were studied for two years from july, 2002-june, 2004, once in every month at regular intervals. the monthly data were pooled in seasonal value. the maximum air temperature was recorded in rainy season during first year study period (july, 2002 to june, 2003) but in the second year study period (july, 2003 to june 2004) it was maximum in summer season. water temperature was maximum in summer and lowest in winter season. transparency, ph, dissolved oxygen, total alkalinity, total hardness, chloride were recorded maximum in winter season. free carbondioxide, and biological oxygen demand was maximum in summer season. the minimum transparency, total alkalinity, total hardness and chloride were recorded in rainy season. dissolved oxygen, and ph, were minimum in summer season. the minimum carbondioxide and bod were recorded in winter season. air temperature, water temperature, free carbondioxide, biological oxygen demand showed positive and significant correlation with each other. similarly, transparency, ph, total alkalinity, total hardness, chloride, showed positive and significant correlation with each other. dissolved oxygen showed positive and significant correlation with ph, total alkalinity, total hardness and chloride. keywords: physicochemical parameters; seepage system 1. introduction the physicochemical condition of a water body has a direct influence on the organisms. seasonal fluctuations of various physicochemical parameters have an important role in the distribution, periodicity, qualitative and quantitative composition of biota in aquatic ecosystem. the knowledge of all these parameters are essential for identifying the suitability and fertility of an aquatic ecosystem. several limnological studies have been done in the rivers and lakes of nepal. hickel [1], lohaman et al. [2], jones et.al [3], mceachern [4], aryal and lacoul [5], ormerod et al. [6] have contributed on limnological work. damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 105 study area the seepage stream is situated outside the koshi tappu wildlife reserve, east to the eastern embankment of sapta koshi river. it is a perennial water body flowing from kushaha village development committee (vdc) to south, bhantabari area. the study site kushaha vdc area, lies between 26°37' 10.6" n latitude and 87° 01' 38.2" e longitude (fig. 1). the seepage stream at kushaha area has 125 m to 250 m wide marshes on its fringe. the depth of water of seepage stream varies in different seasons. it is somewhat polluted due to human encroachment but rich in biodiversity. damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 106 2. materials and methods physico-chemical parameters of the seepage stream were studied for two years from july, 2002june, 2004. the water samples were collected from three sites between 8 a.m. and 11 p.m., once in every month. the air temperature and physicochemical parameters of water were analysed in the field. however, the bod test after 5 days incubation in the incubator was done in the laboratory of post graduate campus, biratnagar. transparency, air temperature and water temperature were recorded between 12 noon and 1 p.m. air and water temperatures were recorded by centigrade mercury thermometer and ph with the help of ph meter. the transparency was measured by secchi disc. other parameters such as dissolved oxygen, free carbon dioxide, alkalinity, hardness, chloride, and bod were measured according to michael (7) zobel et al. (8) and apha (9). 3. results 3.1 air temperature the minimum air temperature was 18.5 ±0.656 °c in the month of january and maximum 32.4± 0.421 °c in august during the first year study period. the air temperature increased from july to august and decreased from september to january. again it increased from february to may then a slight decrease was recorded in june during the first year study period (table 1). during the second year study period, the air temperature increased a little in august then decreased from september to january. again it increased from february to may then a slight decrease was recorded in june and july (table 2). the maximum air temperature was 33.2 ± 0.559 °c in may and minimum 19.3 ± 0.382 °c in january during the second year study period. air temperature showed positive and significant correlation with water temperature (r = 0.9794, p<0.01), free carbon dioxide (r = 0. 6677, p<0.01) and biological oxygen demand ( r = 0.6062, p<0.01) but it had inverse and significant correlation with transparency (r= 0.452, p<0.05), ph (r = -0 .908, p<0.01), dissolved oxygen ( r = 0.8994 p<0.01), total alkalinity (r = 0.6713, p<0.01), total hardness ( r = 0.6239, p<0.01) and chloride (r = 0.6759, p<0.01) (table 3 ). seasonally, the highest air temperature was recorded in rainy season and minimum in winter season during the first year study period but it was highest in summer during the second year study period (table 4). 3.2 water temperature the water temperature increased from july to august then decreased from september to january. again it increased from february to may and a slight decrease was recorded in june during the first year (table 1) and the second year study periods (table 2). the maximum water temperature was recorded in may and minimum in january during the whole study period. the water temperature showed positive and significant correlation with free carbon dioxide (r = 0.7319, p<0.01) and biological oxygen demand ( r = 0.6960 p<0.01) but it showed inverse and significant correlation with transparency (r = -3893, p<0.10), p h (r = 0.917, p <0.01), dissolved oxygen ( r = -0.9229, p<0.01), total alkalinity (r = -0.5613, p<0.01), total hardness ( r = 0.5167, p<0.01) and chloride (r = -0.6645, p<0.01) (table 3). seasonally, the maximum water temperature was in summer followed by rainy and winter seasons during the first and the second year study periods (table 4). damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 107 3.3 transparency the transparency increased from august to december then decreased a little in january. again it increased from february to march then decreased a little in april and again increased a little in may then decreased from june to july during the first year study period (table 1). the maximum transparency was 37.34 ± 0.650 cm in december and minimum 19.2 ± 0.419 cm in july during the first year study period. in the second year study period, the transparency increased from august to december then decreased a little in january. again it increased from february to march then decreased from april to july (table 2). the maximum transparency was 33.2 ± 1.001 cm in march and minimum 20.2 ± 0.986 cm in july during the second year study period. water transparency showed positive and significant correlation with ph (r = 0.5196, p <0.01), total alkalinity (r = 0.5621, p<0.01), total hardness (r = 0.8032, p<0.01) and chloride (r = 0.4667, p<0.05) (table 3). the maximum value of transparency was in winter season followed by summer and rainy seasons during the first and second year study periods (table 4). 3.4 ph the ph increased from july to december then decreased from january to may. again it increased a little in june during the first year study period (table 1). the maximum ph was 8.3±0.221 in december and minimum 7.2 ± 0.211 in may during the first year study period. during the second year study period, ph increased from july to january then decreased from february to april. again a slight increase was recorded in may then decreased a little in june (table 2). the maximum ph was 8.3 ± 0.205 in january and minimum 7.1mg/l ±0.163 and 7.1 ± 0.240 in april and june, respectively. ph showed positive and significant correlation with dissolved oxygen (r = 0.887, p<0.01), total alkalinity (r = 0.5583, p<0.01) total hardness (r = 0.6099, p<0.01) and chloride (r = 0. 6314, p<0.01) but inverse and significant correlation with free carbon dioxide (r = -0.712, p< 0.01) and biological oxygen demand (r = -0. 67, p<0.01) (table 3). the maximum ph was in winter and minimum in summer season during the first and the second year study period (table 4). 3.5 dissolved oxygen the dissolved oxygen decreased from july to september then increased from october to january. again it decreased from february to may and a slight increase was recorded in june during the first year study period (table 1). the maximum dissolved oxygen was 6.96 ± 0.268 mg/l in january and minimum 5.73 ± 0.287 mg/l in may during the first year study period. during the second year study period, the dissolved oxygen decreased from july to august then increased from september to january. again it decreased from february to may and a slight increase was recorded in june (table 2). the maximum dissolved oxygen was 7.3 ± 0.301 mg/l in january and minimum 5.92 ± 0.219 mg/l in may. the dissolved oxygen showed positive and significant correlation with total alkalinity (r = 0. 5241, p<0.01), total hardness (r = 0. 4430, p<0.05) and with chloride (r = 0.6643, p<0.01) but inverse and significant correlation with free carbon dioxide (r = 0.7342, p<0.01) and biological oxygen demand (r = -0.7237, p<0.0.01) (table 3). the maximum dissolved oxygen was in winter season followed by rainy and summer seasons during the first and the second year study periods (table 4). damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 108 table 1 air temperature and physico -chemical parameters of water of seepage stream at kuhasha area from july 2002 june 2003 (mean ± s.d., n = 9). months parameters jul. aug. sep. oct. nov. dec. jan. feb. march apr. may jun. 31.3 32.4 28.3 27.6 22.7 21.2 18.5 27.6 29.4 30.3 31.3 29.2 air temperature (°c ) +0.487 +0.421 +0.483 +0.609 +0.394 +0.397 +0.656 +0.586 +0.459 +0.385 +0.501 +0.294 27.3 28.2 24.2 23.3 19.2 18.1 16.2 25.4 27.4 28.3 29.3 25.3 water temperature (°c) +0.485 +0.283 +0.427 +0.616 +0.326 +0.569 +0.343 +0.416 +0.639 +0.464 +0.589 +0.383 19.2 22.3 24.2 25.4 31.6 37.34 25.3 31.5 34.3 22.7 23.4 22.3 transparency (cm). +0.419 +0.604 +0.721 +0.678 +0.548 +0.650 +0.512 +0.863 +0.818 +0.467 +0.705 +0.803 7.4 7.5 7.5 7.7 7.9 8.3 8.1 7.7 7.4 7.3 7.2 7.3 ph +0.176 +0.182 +0.216 +0.210 +0.194 +0.221 +0.188 +0.156 +0.216 +0.149 +0.211 +0.176 6.18 6.15 6.13 6.29 6.61 6.91 6.96 6.26 5.98 5.92 5.73 6.25 dissolved oxygen (do2), (mg/l) +0.236 +0.216 +0.231 +0.222 +0.223 +0.277 +0.268 +0.165 +0.260 +0.253 +0.287 +0.205 5.12 5.63 5.75 5.33 4.92 4.83 5.23 5.46 5.79 5.84 5.75 5.35 free carbon dioxide (co2), (mg/l) +0.215 +0.221 +0.222 +0.156 +0.154 +0.211 +0.188 +0.240 +0.214 +0.236 +0.170 +0.221 71.33 67.64 60.35 72.53 95.45 108.34 110.64 96.56 94.67 91.58 89.6 79.63 total alkalinity (mg/ l) +0.725 +0.634 +0.683 +0.812 +1.023 +1.107 +1.040 +0.820 +0.728 +1.014 +0.805 +0.783 50.52 56.34 61.25 63.52 75.56 76.33 78.65 79.34 81.22 63.65 53.34 52.56 total hardness (mg/ l) +0.539 +0.389 +0.437 +0.475 +0.405 +0.349 +0.391 +0.368 +0.535 +0.321 +0.585 +0.435 13.24 13.83 14.23 14.45 15.26 18.73 17.27 16.36 14.84 13.14 14.45 17.23 chloride (mg/ l) +0.142 +0.156 +0.149 +0.163 +0.169 +0.205 +0.196 +0.157 +0.171 +0.134 +0.188 +0.216 0.99 0.98 0.93 0.91 0.87 0.82 0.79 1.14 1.61 1.81 2.11 1.13 biological oxygen demand (bod), (mg/ l) +0.033 +0.036 +0.049 +0.041 +0.045 +0.056 +0.052 +0.058 +0.075 +0.030 +0.055 +0.057 damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 109 table 2 air temperature and physico-chemical parameters of water of seepage stream at kuhasha area from july 2003 june 2004 (mean ± s.d., n = 9). months parameters jul. aug. sep. oct. nov. dec. jan. feb. march apr. may jun. 30.3 31.4 29.3 28.3 23.5 22.4 19.3 28.4 30.3 31.4 33.2 30.3 air temperature (°c) +0.457 +0.416 +0.489 +0.410 +0.421 +0.402 +0.382 +0.571 +0.487 +0.405 +0.559 +0.485 27.2 28.2 25.4 24.6 19.4 18.2 16.5 25.6 28.6 29.1 29.3 26.4 water temperature (°c) +0.346 +0.437 +0.346 +0.336 +0.480 +0.391 +0.249 +0.461 +0.336 +0.294 +0.489 +0.489 20.2 23.4 26.5 27.4 28.6 32.3 24.2 29.4 33.2 24.5 23.4 22.3 transparency (cm). +0.986 +0.820 +0.890 +0.804 +0.909 +1.141 +0.653 +0.819 +1.001 +0.870 +0.857 +0.671 7.3 7.5 7.6 7.7 7.9 8.2 8.3 7.6 7.4 7.1 7.3 7.1 ph +0.176 +0.188 +0.163 +0.176 +0.176 +0.187 +0.205 +0.206 +0.230 +0.163 +0.226 +0.240 6.19 6.15 6.26 6.75 6.85 6.9 7.3 6.14 6.12 6.1 5.92 6.24 dissolved oxygen (do2), (mg/ l) +0.224 +0.286 +0.254 +0.197 +0.156 +0.240 +0.301 +0.216 +0.239 +0.274 +0.219 +0.206 5.23 5.57 5.92 5.14 5.1 4.73 5.23 5.9 6.2 5.93 5.89 5.87 free carbon dioxide (co2), (mg/ l) +0.230 +0.257 +0.261 +0.216 +0.258 +0.258 +0.230 +0.210 +0.194 +0.235 +0.207 +0.240 69.45 66.78 61.52 74.52 98.72 107.83 111.73 98.64 94.57 93.52 87.65 77.76 total alkalinity (mg/ l) +1.005 +0.931 +0.944 +0.929 +0.858 +1.003 +0.953 +0.916 +0.843 +1.098 +0.841 +0.810 51.45 54.35 60.65 63.52 65.34 69.89 77.65 78.34 82.49 56.34 54.11 53.54 total hardness (mg/ l) +0.434 +0.307 +0.343 +0.415 +0.449 +0.373 +0.623 +0.408 +0.430 +0.655 +0.395 +0.279 14.56 14.83 15.14 15.17 15.34 18.63 18.34 17.24 15.54 14.32 15.26 17.13 chloride (mg/ l) +0.221 +0.258 +0.206 +0.278 +0.283 +0.282 +0.236 +0.254 +0.240 +0.257 +0.233 +0.230 1 0.98 0.89 0.85 0.84 0.78 0.72 1.1 1.56 1.79 2.14 1.1 biological oxygen demand (bod), (mg/ l) +0.036 +0.048 +0.043 +0.042 +0.044 +0.048 +0.040 +0.042 +0.071 +0.055 +0.040 +0.048 damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 110 table 3 pearson's correlation coefficient (r) for air temperature and physico chemical parameters of water of seepage stream at kushaha area during july 2002 – june 2004. n = 24, d.f. = 22. parameters water temperatur e (°c ) transparenc y (cm). ph dissolve d oxygen (do2), (mg/l) free carbon dioxide (co2) (mg/l) total alkalinit y (mg/l) total hardnes s (mg/l) chloride (mg/l) biological oxygen demand (bod), (mg/l) air temperature (°c) 0.9794* -0.452** -0.908* -0.8994* 0.6677* 0.6713* -0.6239* -0.6759* 0.6062* water temperature (°c) -0.3893*** -0.917* -0.9229* 0.7319* 0.5613* -0.5167* -0.6645* 0.6960* transparenc y (cm). 0.5196 * 0.3216 -0.1971 0.5621* 0.8032* 0.4667** -0.1251 ph 0.887* -0.712* 0.5583* 0.6099* 0.6314* -0.67* dissolved oxygen (do2),(mg/ l) 0.7342* 0.5241* 0.4430** 0.6643* -0.7237* free carbon dioxide (co2) (mg/l) -0.2834 -0.1117 0.3789*** 0.6473* total alkalinity (mg/l) 0.6943* 0.6284* 0.0548 total hardness (mg/l) 0.4786** -0.2052 chloride (mg/l) 0.3984*** (i) * significant at 1% level (p<0. 01), ** significant at 5% level (p<0. 05), *** significant at 10% level (p<0. 10) (ii) values not marked denote non-significant correlation. table 4 seasonal variations in air temperature and physico-chemical parameters of water of seepage stream at kuhasha area during the first year (july 2002 june 2003) and the second year (july 2003 – june 2004) study periods. year i year ii parameters summer rainy winter summer rainy winter air temperature (°c) 29.65 30.3 22.5 30.83 30.33 23.38 water temperature( °c) 27.6 26.25 19.2 28.15 26.8 19.68 transparency (cm). 27.98 22 29.91 27.63 23.1 28.13 ph 7.4 7.43 8 7.35 7.38 8.03 dissolved oxygen (do2), (mg/l) 5.97 6.18 6.69 6.07 6.21 6.95 free carbon dioxide(co2) (mg/l) 5.71 5.46 5.08 5.98 5.65 5.05 total alkalinity (mg/l) 93.10 69.74 96.74 93.60 68.88 98.2 total hardness (mg/l) 69.39 55.17 73.52 67.82 55 69.1 chloride (mg/l) 14.70 14.63 16.43 15.59 15.42 16.87 biological oxygen demand (bod), (mg/l) 1.67 1.01 0.85 1.65 0.99 0.80 damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 111 3.6 free carbon dioxide the free carbon dioxide increased a little from august to september then decreased from october to december. again it increased from january to april then decreased from may to july during the first year study period (table 1). the maximum free carbon dioxide was recorded 5.84 ± 0.236 mg/l in april and minimum 4. 83 ± 0. 211 mg/l in december during the first year study period. during the second year study period, the free carbon dioxide increased from august to september then decreased from october to december. again it increased from january to march then decreased from april to july (table 2). the maximum free carbon dioxide was 6. 2 ± 0.194 mg/l in march and minimum 4.73 ± 0.258 mg/l in the month of december during the second year study period. free carbon dioxide showed positive and significant correlation with biological oxygen demand (r =0. 6473, p<0.01) and inverse and significant correlation with chloride (r = 0.3789, p<0.10) (table 3). the free carbon dioxide was maximum in summer season followed by rainy and winter seasons during the first and the second year study periods (table 4). 3.7 total alkalinity the total alkalinity decreased from july to september then increased from october to january. again it decreased from february to june during the first year (table 1) and the second year study periods (table 2). the maximum total alkalinity was recorded 110.64 ± 1.040 mg/l in january and minimum 60.35 ± 0.683 mg/l in september during the first year study period. during the second year study period, the maximum total alkalinity was recorded 111.73 ± 0.953 mg/l in january and minimum 61.52 ± 0.944 mg/l in september. the total alkalinity showed positive and significant correlation with total hardness (r = 0.6943, p<0.01) and chloride (r = 0.6284, p< 0.01) (table 3). the maximum value of total alkalinity was in winter season followed by summer and rainy seasons during the first and second year study periods (table 4). 3.8 total hardness the total hardness increased from august to march then decreased from april to july during the first year (table 1) and the second year study periods (table 2). the maximum hardness was 81.22 ± 0.535 mg/l in march and minimum 50.52 ±0.539 mg/l in july during the first year study period. during the second year study period, the maximum total hardness was 82.49 ± 0.430 mg/l in march and minimum was 51.45 ± 0.434 mg/l in july. total hardness showed positive and significant correlation with chloride (r = 0.4786, p<0.05) (table 3). the maximum value of total hardness was in winter season followed by summer and rainy seasons during the first and second year study periods (table 4). 3.9 chloride the chloride increased from august to december then decreased from january to april. again it increased from may to june then a slight decrease was recorded in july during the first year (table 2) and the second year study periods (table 2). the maximum chloride was 18.73 ± 0.205 mg/l in december and minimum 13.14 ± 0.134 mg/l in april during the first year study period. during the second year study period, the maximum chloride was 18.63 ± 0.282 mg/l in december and minimum 14.32 ± 0.257 mg/l in april. chloride showed inverse and significant correlation with biological oxygen demand (r = -0.3984, p< 0.10) (table 3). damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 112 the maximum value of chloride was in winter season followed by summer and rainy seasons during the first and second year study periods (table 4). 3.10 biological oxygen demand the biological oxygen demand decreased from july to january then increased from february to may. again it decreased a little in june during the first year (table 1) and the second year study periods (table 2). the maximum biological oxygen demand was 2.11 ±0.055 mg/ l in the month of may and minimum 0.79 ± 0.052 mg/l in the month of january during the first year study period. during the second year study period, the maximum biological oxygen demand was 2.14 ±0.040 mg/l in the month of may and minimum 0.72 ± 0.040 mg/l in the month of january. biological oxygen demand showed positive and significant correlation with air temperature (r = 0.6062 p<0.01), water temperature (r =0. 6960 p< 0.01) and free carbon dioxide (r = 0.6473 p < 0.01) but it had inverse and significant correlation with p h (r = 0. 67, p< 0.01), dissolved oxygen (r = 0.7237, p< 0.01), and chloride (r = 0.3984 p < 0.10) (table 3). seasonally, biological oxygen demand was maximum in summer season followed by rainy and winter seasons during the first and the second year study periods (table 4). 4. discussion the rainy season showed highest air temperature in the first year study period because gradual increase in air temperature was noticed during summer months (february, march, april and may). air temperature showed positive and significant correlation with water temperature. chakaraborty et al. (10), kant and anand (11) and rawat et al. (12) also obtained strong positive correlation between air and water temperatures. generally, water temperature is influenced by air temperature and intensity of solar radiation. it was highest in summer and lowest in winter. highest value was recorded in summer might be due to high air temperature and greater light penetration. though the high air temperature appeared in rainy season in the first year study period, a little lower water temperature was recorded at that time in comparison to that of summer season. it might be due to high turbidity, high volume of water and greater velocity of water in rainy season. the water temperature showed inverse and significant correlation with dissolved oxygen. bose and gorai (13) also reported inverse and significant correlation between water temperature and dissolved oxygen. welch (14) and munawar (15) have observed that shallower the water body more quickly it reacts to the change in the temperature. the maximum secchi disc transparency was recorded in winter followed by summer and rainy seasons. the maximum transparency was in winter due to lesser amount of suspended organic and inorganic materials and absence of rain. higher transparency during winter months was recorded by singh (16), rawat et al. (12), and mishra et al. (17). in this study minimum transparency was recorded in rainy season might be due to more sand particles and colloidal soil carried by the rain water. similar trends were observed by singh (18), rawat et al. (12), and mishra et al. (19). the maximum ph was in winter season may be attributed to algal blooms because hutchinson et al. (20) and roy (21) have shown that the higher ph is associated with the phytoplankton maxima. the minimum ph recorded in summer may be due to low photosynthesis. several workers have reported low ph during the low photosynthesis due to the formation of carbonic acid (hannan and yong (22) cabecadas and brogueira (23) bais et al.(24). damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 113 the maximum dissolved oxygen found in winter season may be due to low temperature. similar observation were made by moitra and bhattacharya (25). the minimum dissolved oxygen was found in summer due to high temperature, and higher microbial demand for oxygen in decomposition of suspended organic matter (bhowmick and singh (26) dissolved oxygen content showed inverse and significant correlation with water temperature. bose and gorai (13) also reported similar result. the maximum free carbon dioxide was recorded in summer, it may be due to high temperature, high rate of decomposition of organic matter, low volume of water etc. michael (27) stated that the concentration of carbon dioxide is directly correlated with the amount and nature of biological activity in water. the minimum free carbon dioxide was found in winter season. pahwa and mehrotra (28), ray et al. (29) also found minimum free carbon dioxide in winter season. the maximum total alkalinity was found in winter season due to high ph. chakraborty et al. (10), singh (16) and mishra et al. (19) also reported maximum total alkalinity during winter. jhingran (30) reported water bodies having total alkalinity from 40 to 90 mg/l as medium productive and above 90 mg/l as highly productive. this investigation showed that the study area is suitable for aquatic production. total alkalinity showed positive and significant correlation with total hardness. barat and jha, (31) also reported similar result. the maximum total hardness in winter season might be due to low volume of water and slow current of water. similar results were obtained by misra et al. (17). patralekh (32) pointed minimum quantity in rainy season may be due to more dilution of water. ruttner (33) also recorded similar relationship. maximum chloride recorded in winter season might be due to more contamination by organic matters. klein (34) pointed out a direct relationship between amount of chloride and level of pollution. the maximum bod obtained in summer may be due to low volume of water and high content of organic matter whereas minimum obtained in winter may be due to low temperature and retarded microbial activity for the decomposition of organic matters. similar observations were also made by singh (18). ray and devid (35) opined that high bod value indicates organic waste pollution. bod showed inverse and significant correlation with dissolved oxygen. ray and david (35) also reported similar relationship. references [1] b. hickel, limnological investigations in lakes of the pokhara valley, nepal. hydrobiol. 58 (1973) 659 – 672. [2] k. lohman, jones j.r., m.f. knowlton and d.b. swar m.a. pamperl and b.j. brazos, pre and post monsoon limnological characteristics of lakes in the pokhara and kathmandu valleys, nepal. verh. internat. verin. limnol. 23 (1988) 558-565. [3] j.r. jones, m.f. knowlton and d.b. swar, limnological reconnaissance of water bodies in central and southern nepal. hydrobiologia 184 (1989)171-189. [4] p. mceachern, limnology and the natural wetlands survey. in: safeguarding wetlands in nepal (eds.b. bhandari,t.b.shrestha and p. mceachern (1994) pp. 89-103. iucn, nepal. [5] s. aryal and p. lacoul (1996) water quality and diversity of diatoms in punyamati river, nepal. ecoprint 3 (1996) 45-49. [6] s.j. ormerod, s.t. buckton, p.a brewin, a. jenkins, r.c.johnson, u. juttner and a. suren, biodiversity, chemistry and structure in streams of the nepalese himalaya. in: proc. inter. confer. ecohydrol. high moun. 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[29] p. ray, s.b. singh and k.l. sehgal, a study on some aspects of the river ganga and jamuna at allahabad (u.p.) in 1958-59. proc. nat. acad. sci. 36b (1966) 235-272. [30] v.g. jhingran, fish and fisheries of india, 3rd edition. hindustan publ. corp, new delhi (1991) [31] s. barat and p. jha, changes in the water quality and total coliform bacterial load in a stretch of river mahananda at siliguri city ,west bengal. asian j. of microbiol. biotech. env. sc. 4 (2002) 571-575 damodar thapa chhetry and joydeb pal / bibechana 8 (2012) 105-115 : bmhss, p. 115 [32] l. n. patralekh comparative account of physico -chemical properties of three freshwater ecosystems. j .freshwater biol.6 (1994) 115-119. [33] f. ruttner, fundamentals of limnology. university of toronto press, toronto (1953). [34] l. .klein aspects of river pollution. butherworths scientific publication, london (1957). [35] p. ray and a. david, effect of industrial wastes and sewage upon the chemical and biological composition and fisheries of the river ganga at kanpur, up environ. health, 8(1966)307. microsoft word n.k. chaudhary _75-80_.doc n. k. chaudhary / bibechana 9 (2013) 75-80 : bmhss, p. 75 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana synthesis and medicinal use of metal complexes of schiff bases narendra kumar chaudhary pg department of chemistry, mahendra morang adarsh multiple campus, tribhuvan university, biratnagar, nepal e mail: chem._narendra@yahoo.com article history: received 10 july, 2011; accepted 7 novemer, 2012 abstract different schemes for the synthesis of schiff bases have been discussed. solvent free synthesis by microwave irradiation technique is observed to be rapid, more efficient and more economical and at the same time may play a pivotal role in the progress of schiff base synthesis. mechanism for the synthesis of schiff bases at controlled ph range has been studied. biological functions of metal complexes of schiff bases have found to be increased potentiality in presence of transition metal ions. keywords: metal complexes, schiff base, microwave irradiation, metallo-elements, azeotropic distillation, molecular sieve 1. introduction the chemistry of the carbon-nitrogen double bond plays a vital role in the progress of chemical science [1]. schiff bases are the condensation product of an amine and carbonyl compounds and are an important class of ligands that coordinate to metal ions via azomethine nitrogen. schiff bases are named in the owner of hugo schiff in 1864. solvent based synthesis of schiff bases through classical condensation of aldehydes (or ketones) and amines require ph control, however the yield of products is low. ph range for such synthesis should be 5 to 8 i.e. weak acid, neutral or weak alkaline medium depending upon the basicity of amines. microwave assisted synthesis of schiff base is rapid and efficient with no use of solvent. the yield of products is also high and purification is done by simple recrystallization technique [2]. schiff bases have active imine (c=n) linkage which provide binding site for the metal ions through nonbonding electrons of nitrogen. they have also many other hetero-elements like oxygen and sulphur which provide binding sites through nonbonding electrons. specially, d block transition metals having vacant d-orbitals are able to bind with such complexes. binding of metal ions with polydentate ligands form ring structure, where the metal ion is a part of the ring, is called chelation. extensive studies revealed that chelation makes the complex more stable and biologically more active in the presence of bio-metals. metal ions fix the complexes at the specific site of proteins and enzymes of the host and show their potentiality. metal based schiff bases have important applications in medicinal chemistry. medical science demands such and such types of drugs which are more potent, biologically active, easily absorbable, no toxicity and show fast action for the treatment of diseases. human body contains seven major and twenty-two cho oh + h2n h c n oh mw n n o + h2n oh h3c sncl2 grinding n n n oh h3c n. k. chaudhary / bibechana 9 (2013) 75-80 : bmhss, p. 76 (online publication: nov., 2012) trace elements which are called metallo-elements. they, in trace and ultra-trace amounts, are very essential for the normal functioning of human body and play vital role at the molecular level. the transition metal ions have binding capacity with the amino acids, proteins and enzymes and catalyze many biological reactions without which the life is impossible. metal ions provide stability of the complexes by delocalization of electrons of the ligands by chelation and enhance their activity [3]. if their concentration exceeds certain level then their toxic effects are evident. nitrogen containing bases such as schiff base, pyridine, pyrimidine, purine and pyrrole, amines such as histamines are well recognized bioligands. 2. synthesis of schiff bases scheme 1: solvent free synthesis by microwave irradiation the microwave –assisted synthesis of schiff base from salicyldehyde and different aryl amines is performed efficiently and get high yield of products in short time [2]. this is carried in an oven, midea pj21b-a 800w and is subjected to microwave for an optimized time on the "m-high" setting. the solvent free organic synthesis mediated by microwave irradiation performs several economies such as low risk of hazard, time economy and environmental friendship. purification by simple recrystallization technique offers less contamination. scheme 2: solvent free synthesis by using catalyst solvent free synthesis of schiff bases obtained from 4,5-diazafluuoren-9-one with substituted amines is done efficiently at room temperature by using sncl2 catalyst [4]. the reaction mixture is grinded in a mortar with the help of pestle and the progress reaction is monitored by tlc and column chromatography. schiff base scheme 3: solvent and catalyst free synthesis a mixture of substituted aromatic amines and substituted aromatic aldehydes is grinded in a mortar with a pestle made of porcelain and the progress of reaction is monitored by tlc. the crude product of schiff base is purified by column chromatography. the completion of reaction takes place within 2-3 minutes. however the synthesis of schiff bases from ketone requires acetic acid as a catalyst [5]. ohh3c h2n cl c h o + no solvent no catalyst cl c h n ohh3c r c o h + h2n r1 ethanol reflux r c n h r1 + h2o schiff base c o r1 r2 h protonation c oh r1 r2 n r h h c r1 n h ohr2 hr c r1 n h oh2r2 rconjugate base n c r r1 r2 h2o + n. k. chaudhary / bibechana 9 (2013) 75-80 : bmhss, p. 77 (online publication: nov., 2012) schiff base scheme 4: solvent based synthesis solvent based schiff base synthesis generally requires appropriate solvent like ethanol or methanol and mixture is refluxed under pressure by applying acidic, basic or neutral medium. the first preparation of schiff base was reported in the 19th century by schiff (1864). since then a variety of methods for the synthesis of schiff base have been described. the classical synthesis reported by schiff involves the condensation of a carbonyl compound with an amine under azeotropic distillation [6]. molecular sieves are then used to completely remove water formed in the system [7]. in the 1990s an in situ method for water elimination was developed, using dehydrating solvents such as tetramethyl orthosilicate or trimethyl orthoformate [8,9]. in 2004, chakraborti et al. [10] demonstrated that the efficiency of these methods is dependent on the use of highly electrophilic carbonyl compounds and strongly nucleophilic amines. presence of water may reverse the reaction by hydrolyzing the schiff base. 3. reaction mechanism 3.1 acidic medium c o r1 r2 n r h h c r1 n h r2 hr c r1 n h ohr2 r n c r r1 r2 h2o + + o ch3 ch2 o h c r1 nr h oh2r2 h3c h2 c o m(ii) salts + n n n n o o nh2 nh2 h h bis (2-aminobenzaldehyde) malonylhydrazone reflux 3 hrs. n n n n oo n h2 n h2 m x2metal complex of schiff base m = cu, ni, zn and (vo)2+ x = so4 n. k. chaudhary / bibechana 9 (2013) 75-80 : bmhss, p. 78 (online publication: nov., 2012) 3.2 neutral medium 3.3 basic medium mechanism will be similar to that of neutral medium, difference being only in the rate of reaction. the increased basicity of amines in basic medium speed up the nucleophilic attack and thus make rapid formation of schiff base. 4. synthesis of metal complexes of schiff bases the metal complex of schiff bases is prepared by stirring the mixture of metal salts with synthesized schiff base ligands using suitable solvent generally ethanol and then refluxing the mixture. the complexes obtained is washed with alcohol and dried. in 2008, rajavel et al. [11] prepared metal complexes of bis(2-aminobenzaldehyde) malonylhydrazone by refluxing the mixture for 3 hrs in alcoholic medium. n. k. chaudhary / bibechana 9 (2013) 75-80 : bmhss, p. 79 (online publication: nov., 2012) 5. medicinal use of metal complexes of schiff bases azomethine nitrogen in schiff base, not only provides binding site for metal ions but also make attachment with various substrate of bio-molecules like proteins and amino acids in biological systems and that of diseases causing germs. through the metabolic activities, our body generates schiff base complexes that show activities against various microbes. schiff bases in the form of enzymes catalyze many metabolic reactions. various researches in the field of schiff bases indicate that metal complexes of schiff bases have additional and improved bio-functions. they have antibacterial, antifungal, antiviral, antiulcer and anticancer activities depending upon the transition metal ions present in schiff bases. study of bismuth (v) complex of novel schiff base mixed ligand obtained from streptomycin and chloramphenicol have found to be better antibiotic activity than parent antibiotics alone [12]. 3dmetal complex of schiff base mixed ligands of streptomycin and oxime have also better antibacterial activity than precursor compounds [13]. similarly the metallo-elements [copper(ii), zinc(ii) and oxovanadium (iv)] complexes of schiff base have more enhanced biological activities than free ligands [14,15]. first row transition metal (ii) ion complexes of chromenyl schiff base are also associated with lots of biological activities such as antibacterial, antifungal and anticancer. for example, cu(ii), ni(ii) and co(ii) chelates of schiff base derived from aminoantipyrine and 3-formyl chromone exhibited good invitro antibacterial activity against s.aureus, e.coli and p. aeuriginosa, [16]. similarly, the cytotoxic study of cu(ii) schiff base complex shows that it has best in-vitro anticancer activity against both mcf-7 (human breast adenocarcinoma) and ht-29 (colon carcinoma) [17]. synthesis of metal [mn(ii), co(ii), ni(ii)and vo(ii)] complexes of the schiff bases 2-[(2,3-dihydro-1h-inden-4-ylimino)methyl]-5nitrophenol (hl 1 ) and 3-[2,4-dihydro-1h-inden-4-ylimino) methyl]napthalen-2-ol (hl 2 ) are found to have better effective antibiotic activity towards staphylococcus aureus, bacillus cereus, escherichia coli, proteus mirabilis, klebsiella oxytoca and pseudomonas aeruginosa [18] . schiff base ligand derived from 5-chlorosalicyldehyde and 2-(2-aminophenyl) 1h-benzamidazole and their derivative have wide biological activities like antitumor, antiamoebic, antihistaminic, anthelmintic and antihypertensive activity [19]. schiff base copper(ii) complexes of antibiotics: penicillin, streptomycin and tetracycline are reported to have higher antibacterial activity against the bacteria staphyloccus aureus, klebsiella pneumoniae, salmonella typhi etc. 6. conclusion the simple preparation procedures of schiff bases and their metal complexes make them versatile ligands in biological systems for the treatment of diseases that will open a new era in medicinal science. requirement of transition metal ions in trace and ultra trace amounts in the human body are supplemented by the use of metal complex of schiff bases in addition to their biological activities. acknowledgement author thanks to associate professor, dr. parashuram mishra of mahendra morang adarsh multiple campus, biratnagar for his continuous inspiration towards research. references [1] patai,s., the chemistry of carbon-nitrogrn double bonds; john willey and sons ltd (1970). [2] yang h. j., sun w. h., li z. l. and zhi m.a.; the rapid synthesis of schiff base without solvent under microwave irradiation, chinese chemical letters, 13 (2002) 3-6. [3] bukhari i.h., arif m., akbar j. and khan a.h.; preparation, characterization and biological evaluation of schiff base transition metal complexes with cephadrine; pakistan journal of biological sciences, 8 (2005) 614-617. n. k. chaudhary / bibechana 9 (2013) 75-80 : bmhss, p. 80 (online publication: nov., 2012) [4] shaikh k. a., patil v. a. and ahmed a.; an environmentally benign, solvent free synthesis and antibacterial activity of novel schiff bases derived from 4,5-diazafluoren-9-one, elixir org. chem., 45 (2012) 7881-7883. [5] shaikh k. a., patil v. a. and zamir a. m.; solid phase promoted greener synthesis and antibacterial activity of novel schiff base under catalytically free condition, elixir org. chem., 43 (2012) 6960-6963. [6] moffett r.b., rabjohn n, editor. organic synthesis, new york (usa); john willey and sons, inc; 4 (1963 ) 605-608. [7] taguchi k. and weitheimer f.h., catalysis by molecular sieves in the preparation of ketimines and enamines. j. org. chem., 36 (1971) 1570-1572. [8] love b.e. and ren j. , synthesis of sterically hindered imines; j org. chem.. 58(1993)5556-5557 [9] look g.c., murphy m.m., campbell d.a. and gallop m.a.; trimethylorthoformate: a mild and effective dehydrating reagent for solution and solid phase imine formation, tetrahedron lett., 36 (1995) 2937-2940. [10] chabraborti a.k., bhagat s. and rudrawar s.; magnesium perchlorate as an effective catalyst for the synthesis of imines and polyhydrazones, tetrahedron lett., 45 (2004) 7641-7644. [11] rajavel r., vadivu m.s. and anitha c.; synthesis, physical characterization and biological activity of some schiff base complexes. e journal of chemistry, 5 (2008) 620-626 [12] garg s., attri p., sharma k., ranjan r. and mishra p.; invitro cell viability and antibacterial activity of novel bismuth (v) complex; international journal of pharmtech research, 1 (2009) 1685-1691. [13] mishra, p.; synthesis, investigation, spectroscopic characterization and computational modeling of mixed ligand complexes of cu (ii),fe(ii),co(ii) and bi(v) using biological active streptomycin and oxime; elixir appl. chem., 48 (2012) 9361-9366. [14] sandhanamalar, d., vedanayaki, s. and rajavel, r.; synthesis and characterization of nfunctionalized macrocyclic binuclear cu(ii),ni(ii) and vo(ii) schiff base complexes and their antimicrobial activity; elixir appl. chem., 43 (2012) 6803-6808. [15] liu j., wu b., zhang b. and liu y.; synthesis and characterization of metal complexes of cu(ii), ni(ii), zn(ii), co(ii), mn(ii) and cd(ii) with tetradentate schiff bases; turk j chem., 30 (2006) 41-48. [16] rosu, t., pohuntu, e., maxim, c., georgescu r., stanica n., almajan g., gabriela l. and gulea a.; synthesis, characterization, antibacterial activity of some new complexes of cu(ii), ni(ii), vo(ii), mn(ii) with schiff base derived from 4-amino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one , polyhedron, 29 (2010) 757-766. [17] osowole, a.a. ;synthesis, characterization, in-vitro antibacterial and anticancer studies on some metal(ii) complexes of (methylsufanyl)chromenol schiff base; elixir appl.chem., 39 (2011) 48274831. [18] osowole a.a. and daramola a.o.; synthesis, spectroscopic characterization and in-vitro antibacterial properties of some metal(ii) complexes of schiff bases containing aminoindane moiety; elixir appl. chem., 47 (2012) 8662-8666. [19] sunitha m., jogi p., ushaiah and gyanakumari c.; synthesis¸ structural characterization, molecular modelling and antimicrobial studies of transition metal complexes of schiff base ligand derived from 5-chlorosalicylaldehyde and 2-(2-aminophenyl) 1h-benzimidazole; journal of chemical and pharmaceutical research, 4 (2012) 1553-1561 microsoft word bhawani datt joshi et al _73-79_.doc bhawani datt joshi et al./ bibechana 8 (2012) 73-80 : bmhss, p.73 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana molecular characterization of yohimbine hydrochloride using vibrational spectroscopy and quantum chemical calculations bhawani datt joshi 1,3 , poonam tandon 1,* and sudha jain 2 1department of physics, university of lucknow, lucknow-226007, india 2department of chemistry, university of lucknow, lucknow-226007, india 3department of physics, siddhanath sc. campus, mahendranagar, tribhuvan university, nepal *corresponding author. tel.: +91 522 2782653; fax: +91 522 2740840. e-mail address: poonam_tandon@yahoo.co.uk, poonam_tandon@hotmail.com (p. tandon) article history: received 22 june, 2011; accepted 20 august, 2011 abstract in this work, we have performed the extraction of yohimbine hydrochloride (c21h27cln2o3) (yhcl). the optimized geometry, total energy, potential energy surface and vibrational wavenumbers of yhcl have been determined by using ab initio hartree–fock (hf) and density functional theory (dft/b3lyp) method with 6-311++g(d,p) basis set. the calculated wavenumbers are scaled by a proper scaling factor. a selected number of vibrational assignment is provided for the observed raman and ir spectra. keywords: yhcl; vibrational spectroscopy; esp; ab initio and dft calculations 1. introduction yohimbine, an indole alkaloid is the active ingredient obtained from the bark of various tropical trees such as pausinystalia yohimbe (formarly corynanthe yohimbe), a tall evergreen tree indigenous to southern african countries, and from the indian snake root rauwolfia serpentina [1,2]. yohimbine hydrochloride (17α – hydroxy –yohimbane 16α – carboxylic acid methyl ester hydrochloride), a standard form belongs to an orthorhombic system, probable space group p212121 having lattice parameters, a = 11.54å, b = 24.88å, c = 7.00å and z = 4 [2]. it has been known as an aphrodisiac compound [2,3] and used traditionally since before the last century, even in the crude form by the african natives, and promoted for erectile dysfunction, weight loss (by releasing norepinephrine and blocking alpha-2 receptors) and depression (by blocking an enzyme called monoamine oxidase) [4-6]. it is used in tablets, capsule and tincture form for increased serumtesterone levels, muscle growth and strength, weight-loss, reduce fatigue in aids patients and libido enhancer [7]. also it has been reported as traditional medicine to treat high blood pressure, chest pain, agerelated cognitive disorders and obesity [8]. as the literature survey reveals neither raman and ir spectra nor quantum chemical calculations for yhcl molecule have been reported so far, hence the present work was undertaken to study the vibrational spectra with quantum chemical calculation with greater accuracy. although x-ray diffraction method is one of the most frequently applied techniques for structural characterization of pharmaceutical compounds but the use of vibrational spectroscopy is also gaining increasing attention. x-ray diffraction techniques are sensible to the long-range order while vibrational spectroscopy (ir [9] and raman [10]) is applicable to the short-range structure of molecular solids. bhawani datt joshi et al./ bibechana 8 (2012) 73-80 : bmhss, p.74 fig. 1: crystal structure of yhcl. fig. 2: optimized structure of yhcl. bhawani datt joshi et al./ bibechana 8 (2012) 73-80 : bmhss, p.75 furthermore, we interpreted the calculated spectra in terms of potential energy distributions (ped) and made the assignment of the experimental bands due to ped analysis results. information about the geometry and structure of the molecule with their electrostatic potential surfaces should help in understanding the structure-activity relationship. figure 1 shows the crystal structure of the yhcl molecule. 2. materials and methods 2.1 experimental methods the whole plants of rauwolfia serpentine benth. (apocynaceae) were collected from lucknow, uttar pradesh, india and identified by the botany division of central drug research institute, lucknow, india. the plant material (2.4 kg) was air-dried, powdered and percolated with ethyl alcohol (6 x 4 lt) at room temperature. the combined percolate was concentrated under reduced pressure below 40o to give the viscous mass. the material was partitioned between 2% tartaric acid and hexane. the aqueous solution was re-extracted with hexane (4 x 250 ml), basified with solid na2co3 (ph 7.5) and extracted with benzene (6 x 250 ml). the combined benzene layer was dried over anhydrous na2so4 and solvent removed under reduced pressure to give a residue i. the aqueous solution left after extraction with benzene was further extracted with methylene chloride (5 x 250 ml). the combined methylene chloride layer was dried over anhydrous na2so4 and solvent removed under reduced pressure to give a residue -ii. both the residues i and ii were mixed to afford crude alkaloidal mixture (4.0 g) which was subjected to column chromatography over neutral alumina. the column was successively eluted with hexane, hexane: benzene (20:80), benzene, benzene ethyl acetate, v/v (98:2), (95:5), (90:10), (85:15), (50:50), (25:75), ethyl acetate, ethyl acetate-methanol (95:5) and methanol. elution was monitored by thin layer chromatography (tlc). a total of 190 fractions, 100 ml each, were collected and mixed on the basis of tlc. the fractions 42 – 75 eluted from benzene-ethyl acetate (98:2), (95:5) and (90:10) were mixed and solvent removed. the crude product was subjected to preparative tlc (plates: sio2 gf254; solvent: chloroform – methanol, 95:5; double run). the major band on the plates was scraped, extracted with chloroform – methanol (3:1), the solvent removed under reduced pressure to give a pure compound (8.4 mg), converted to its hydrochloride, crystallized from methanol ether, m.p. 299.50 [3010][11,12]. the compound was identified as yohimbine by a direct comparison with an authentic sample procured from sigma chemical company, usa. an excitation laser of wavelength 514 nm was emitted from an argon ion laser source and a power of 12 mw was used to record the vibrational spectra using an efficient visible micro raman setup at room temperature. the scattered raman light was collected in a back scattering geometry using a microscope objective (ulw x50). the scattered light was dispersed using a monochromator with 1200 grooves/mm diffraction grating, and an entrance slit width of 200 micrometer. the raman signals were detected using liquid nitrogen cooled charged coupled device (ccd) with an optimal sensitivity in the visible range. the total exposure time for each sample was 5 sec and averaged over five accumulations. infrared spectra of yhcl were recorded on a bruker tensor 27 ft-ir spectrometer with a spectral resolution of 4 cm-1 in the region 300-4000 cm-1. the kbr pellets of solid samples were prepared from mixtures of kbr and the sample in 200:1 ratio using a hydraulic press. multi-tasking opus software was used for base line corrections. 2.2 computational methods geometry optimization was performed as the first task of computational work for the yhcl molecule. the experimental geometric parameters from x-ray diffraction data [2] of yhcl molecule were used as the initial parameters for the theoretical calculations. the electronic structure and optimized geometry of the molecule were computed by ab initio hartree-fock (hf) and dft (density functional bhawani datt joshi et al./ bibechana 8 (2012) 73-80 : bmhss, p.76 theory) using gaussian 09 [13] program package employing 6-311++g(d,p) basis set based on becke’s three-parameter (local, non-local, hartree-fock) hybrid exchange functional with lee-yangparr correlation functional (b3lyp) [14].the basis set 6-311++g(d,p) augmented by d polarization functions on heavy atoms and p polarization functions on hydrogen atoms as well as diffuse functions for both hydrogen and heavy atoms were used. the optimized structural parameters were used to calculate the absolute raman intensities and infrared absorption intensities in the harmonic approximation at the hf and dft levels. the positive values of all the obtained 156 wavenumbers confirm the stability of optimized geometry. for analyzing the normal a complete set of 156 internal co-ordinates was defined using pulay’s recommendations [15]. the vibrational assignments of the normal modes were proposed on the basis of the ped calculated using the program gar2ped [16]. raman and infrared spectra were simulated using a pure lorentzian band profile (fwhm = 8 cm-1) using indigenously developed software. visualization and confirmation of the calculated forms of the vibrations were done using the chemcraft program [17]. 3. geometry optimization and energies initial geometry taken from the x-ray diffraction data [2] of yhcl was minimized without any constraint to the potential energy surface and the optimized structural parameters were used in the vibrational frequency calculation to characterize all stationary points as minima. the equilibrium geometry has been determined by the energy minimization. the optimized structure of yhcl molecule is shown in figure 2. the relative energies of the molecule are calculated employing ab initio hf and dft functional (b3lyp). the dft includes some electron correlation effects and hence the calculations with this method are better than the hf approach. the energy calculated by dft (-1612.2632515 hartree) is lower than the one calculated by hf (-1612.2607923 hartree). the optimized structural parameters (bond lengths, bond angles, dihedral angles) of yhcl have been compared with the experimental one. the difference between experimental and calculated values of bond-lengths is not more than 0.04å, both in dft and hf methods. the bond angles differ by not more than 2.5o except the angles, c19-o2-c26 and o1-c13-c10 which differ by 4.82o/5.82o and 5.64o /5.64o in the dft/hf respectively. similarly the dihedral angles differ by not more than 4.9 o except the angles c6-c10-c19-o2 and c6-c10-c19-o3 differ by 6.83o/6.83o and 6.34o/6.34o in the dft/hf respectively. 4. results and discussion 4.1 molecular electrostatic potential the molecular electrostatic potential (esp) of a molecule at a point in space around it gives an indication of the net electrostatic effect produced by the total charge distribution (electrons + nuclei) of the molecule. the molecular esp of yhcl molecule is shown in figure 3. it correlates the total charge distribution with dipole moments, partial charges, electro-negativity and site of chemical reactivity of a molecule. esp provides a visual method to understand the relative polarity of a molecule and serves as a useful quantity to explain hydrogen bonding, reactivity and structure-activity relationship of molecules including biomolecules and drugs [18]. different colours represent the different values of the electrostatic potential at the surface of a molecule. in general, red colour represents the regions of most negative electrostatic potential (possess electrophilic property), blue represents the regions of most positive electrostatic potential (possess nucleophilic property) and green represents the regions of zero potential. potential increases in the order red < orange < yellow <green < blue. the electrostatic potential has been used primarily for predicting sites and relative reactivities towards electrophilic attack and in studies of biological recognition and hydrogen bonding interactions [19]. in order to predict the reactive sites for electrophilic and nucleophilic attacks of the title molecule, such electrostatic potential surfaces have been plotted for molecules in 6-311++g(d,p) basis set using the computer software gaussview ver.09 [14] as shown in figure 3. in yhcl molecule, the regions near bhawani datt joshi et al./ bibechana 8 (2012) 73-80 : bmhss, p.77 fig. 3. molecular electrostatic potential mapped on the isodensity surface in the range from -7.390*102 (red) to +7.390*10-2 (blue) for yhcl. the chlorine atom of hydrochloride groups as well as those of hydroxyl groups are most negative, while the regions near hydrogen of hydroxyl groups are the most positive regions. 4.2 vibrational assignments the total number of atoms in a molecule is 54, hence gives 156 (3n-6) normal modes of vibrations. all the 156 fundamental vibrations of the yhcl molecule are both raman and ir active. the vibrational spectrum is mainly determined by the modes of the free molecule observed at higher wavenumbers, together with the lattice (translational and vlibrational) modes in the low wavenumber region. all the vibrational bands have been assigned satisfactorily. the assigned wavenumbers of the selected vibrational modes calculated at the hf and b3lyp level with the basis set 6-311++g(d,p) along with their ped are given in table. since the vibrational wavenumbers obtained from the dft calculations are higher than the experimental wavenumbers, they were scaled down by the wavenumber linear scaling procedure (wls) [νobs/νcal = (1.0087 – 0.0000163 x νcal) cm-1] of yoshida et al. [20] and a comparison was made with the experimental values. however there are different scaling factors, but the vibrational wavenumbers calculated uniformly scaled with only one scaling factor [21] are often in good agreement the observed ones. all the calculated vibrational wavenumbers reported in this study are the scaled values. in the ring r1, the ch stretching of the ring is calculated in the region 3052-3027 cm-1 and match well with the values 3057, 3031 cm-1 in the raman and 3087 and 3066 cm-1 in the ir spectra. the in-plane deformations of ch group are calculated to be 1453, 1384 and 1238 cm-1 and reported at 1452, 1383 and 1245 cm-1 in the raman and at 1452 and 1234 cm-1 in the ir spectrum, respectively. in the ring r2, the n5h stretching vibration is calculated to be 3481 cm-1 and observed as high intense peak at 3514 cm-1 in the ir spectrum as shown in the figure 4. in the ring r3, weak asymmetric stretching mode of c11h2 is calculated at 2972 cm-1 and assigned to the peak at 2965 cm-1 in the raman and 2960 cm-1 in the ir spectrum. symmetric stretching vibration bhawani datt joshi et al./ bibechana 8 (2012) 73-80 : bmhss, p.78 table: some selected calculated and experimental wavenumbers (cm-1) of yhcl. unscaled scaled dft hf dft raman ir potential energy distribution 3838 3631 3631 3670 o1h stretching 3669 3481 3481 3514 n5h stretching 3190 3052 3052 3057 3087 ch stretching 3179 3042 3042 3066 ch stretching 3169 3033 3033 3031 ch stretching 3163 3027 3027 ch stretching 3158 3023 3023 3024 ch3 asym stretching 3125 2993 2993 2989 ch3 asym stretching 3102 2972 2972 2965 2960 c11h2 –asym stretching 3052 2927 2927 2935 ch3 sym stretching 3034 2910 2910 2911 c11h2 – sym stretching 3017 2895 2895 2894 2887 (c6h +c7h) stretching 3006 2885 2885 2876 2883 (c7h + c6h) stretching 1785 1748 1748 1754 1718 c=o stretching 1478 1455 1456 1453 1454 c18h2 deformation 1476 1453 1453 1452 1452 ch in-plane deformation 1424 1403 1403 1408 1408 hc13o1 deformation 1403 1384 1384 1383 ch in-plane deformation 1253 1238 1238 1245 1234 ch – in-plane deformation 1176 1163 1163 1165 c13o1h45 deformation fig. 4: experimental and calculated (scaled) ir absorption spectra of yhcl in the region 400-1800 and 2600-3800 cm-1 bhawani datt joshi et al./ bibechana 8 (2012) 73-80 : bmhss, p.79 of this mode is calculated to be 2910 cm-1 and reported at 2911 cm-1 in the raman spectrum. the mixed vibrations of c7h and c6h stretching modes are calculated to be 2885 / 2895 cm-1 and observed at 2876/2894 cm-1 in the raman and at 2883/2887 cm-1 in the ir spectrum, which match well with the experimental results. in the ring r4, the stretching vibration of alcoholic o1h group is calculated at 3631 cm-1 and observed to the weak band in the ir spectrum at 3670 cm-1. the o1h deformations are calculated to be 1403/1163 cm-1 and reported at 1408/1165 cm-1 with very weak band in the raman and at 1408 cm-1 with a strong band in the ir spectrum. the asymmetric stretches of ch3 group are calculated to be 3023 and 2993 cm-1 and reported at 2989 cm-1 with strong intensity in the raman and with weak intensity at 3024 cm-1 in the ir spectrum. the ch3 symmetric stretching is calculated to be 2927 cm-1 and reported at 2935 cm-1 with medium intensity in the ir spectrum. high contributions of c=o stretching band is calculated to be at 1748 cm1 and match nicely to the peak at 1719 cm-1 with weak intensity in the raman and with strong intensity at 1718 cm-1 in the ir spectrum. this multiple bonded group is highly polar, therefore, gives rise to an intense ir band. 5. conclusions in this work, we have performed the experimental and theoretical vibrational and electrostatic potential surface analysis of the yhcl. these assignments are important to understand the molecular structure and biological activity of the title molecule. the equilibrium geometries and harmonic vibrational wavenumbers of all the 156 normal modes of the molecule were determined and analyzed both at dft and hf levels of theory employing the 6-311++g(d,p) basis set. information about the size, shape, charge density distribution and structure-activity relationship of the yhcl molecule has been obtained by mapping electron density isosurface with esp. raman and infrared spectra were recorded, and the vibrational bands were assigned on the basis of the ped obtained from the dft calculations. acknowledgements the authors are grateful to the university grants commission, nepal and, alexander von humboltd foundation, germany for providing partial financial assistance. references [1] a.e. el gindy, m. farouk, l. abd el aziz and e.s. shokry, j. appl. sciences research 5 (2009) 693. 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[14] c.t. lee, w.t. yang and r. g. parr, phys. rev. b 37 (1998) 785. [15] p. pulay, g. fogarasi, f. pang and j.e. boggs, j. am. chem. soc. 101 (1979) 2550. [16] m.l. martin and c van aslenoy, gar2ped. university of antwerp. 1995. [17] e. scrocco and j. tomasi, adv. quantum chem., 11 (1978) 115. [18] t. ashida, r. repinsky and y. okaya, acta cryst. a.16 (1963) 48. [19] c. muñoz-caro, a. niño, m.l. sement, j.m. leal and s. ibeas, j. org. chem. 65 (2000) 405. [20] h. yoshida, k. takeda, j. okamura, a. ehara, and h. matsurra, j. phys. chem. a 106 (2002) 3580. [21] a.p. scott and l. radom, j. phys. chem. 100 (1996) 16502. microsoft word a. kumar _33-38_.doc a. kumar et al. / bibechana 7 (2011) 33-38 : bmhss 33 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana anomaly in energetic and structural properties of mgsn liquid alloys a. kumara∗∗∗∗, i. s. jhaa, b. p. singhb a dept. of physics, m.m.a.m campus tribhuvan university, biratnagar, nepal. b university department of physics ,t.m. bhagalpur university, bhagalpur, bihar, india article history: received 1 november 2010; revised 15 november 2010; accepted 18 november 2010 abstract the observed asymmetry in the properties of mixing of mgsn alloy in molten state is successfully explained on basis of the quasi-lattice model. it has been utilized to determine the free energy of mixing, entropy of mixing, heat of mixing, the concentrationconcentration structure factor in long wave-length limit [scc(0)] and the warren cowley short range order parameter (α1) of mgsn alloy in molten state at 1073 k. the analysis suggests that heterocordiantion leading to the formation of chemical complex mg2sn is likely to exist in the melt but is of a weakly interacting in nature. the interaction energies between the species of the melt are found to depend considerably on temperature and the alloy is more ordered towards mg rich region keywords: quasi-lattice model; binary alloys; short range order parameter; asymmetry 1. introduction a large number of binary alloys specially the compound forming alloys exhibit interesting behaviour as a function of concentration as regards the thermodynamic [1] and electric properties [2, 3]. the properties of mixing are not symmetrical about the equiatomic compositiondeviating maximally from those of ideal alloys. some of the alloys also depict metal non metal transition across narrow band of concentration. the liquidus lines are usually s-shaped and the heat of mixing and excess free energy of mixing are large negative quantities at one or other concentrations [46]. the anomalous behaviour of these liquid alloys still demands extensive theoretical investigation. the properties of mixing of mgsn alloy is of interest as various properties of it show anomalous behaviour as the function of concentration. the liquidus line is endowed with two eutectics in the terminal region of concentration with the bump around the stoichiometric ∗ corresponding author: ashok kumar, dept. of physics, m.m.a.m campus tribhuvan university, biratnagar, nepal, email :ashok_kumar601@yahoo.com a. kumar et al. / bibechana 7 (2011) 33-38 : bmhss 34 composition of mg2sn. the large value of viscosity [7] and the analysis of the radial distribution function [8] indicate that unlike atoms attract, with the interaction being greatest at the composition mg2sn.the properties of mixing show asymmetry around the equiatomic composition for mgsn alloy also. there are so many models such as pseudo potential theory [9, 10], hard sphere model [1114], the conformal solution model [15] etc. to study the alloying behaviour of liquid alloy. but in the present investigation we have used quasi-lattice model developed by bhatia and singh as it is successful in investigating both the thermodynamic properties and microscopic structure [16, 17]. on the basis of this model we have calculated the thermodynamic quantities such as free energy of mixing, excess entropy of mixing, and heat of mixing. to understand the microscope structure of the alloy we have calculated concentration-concentration fluctuation in the long wave-length limit [scc(0)] and the short range order parameter [α1]. the phenomena of compound formation and segregation can easily be interpreted through the study of scc(0) and α1 [18-26]. in section 2 the general formulation of quasi-lattice model are summarised to simple expressions. section 3 deals with the results and discussions. section 4 provides the conclusion. 2. theory the quasi-lattice chemical model envisages the existence of chemical complex [aµ bν] where a and b are constituent species and µ and ν are small integers, µa + νb aµbν. the grand partition function is solved by assuming that the energy of a given nearest bond is different if it belongs to the complex than if it does not. with this consideration the expression for excess free energy of mixing comes out to be dclntnkg c ob xs m γ= ∫ (1) where n is the total no. of atom in the alloy ‘c’ the concentration of atom a t the absolute scale temp., kb the boltzman constant and γ is the ratio of the activity co-efficient of atom a to b. the solution of equation (1) leads to [ ]bbbbaaaaabab xs m )c1(cng ω∆φ+ω∆φ+ω∆φ+ω−= (2) where ω's are ordering energy and φ is some constant given by kbt φµ, ν = ∆ωαβ[2β (µ+1, ν) – 2β (µ, ν+1) + β (2µ, 2ν–1) + β (2µ – 1, 2ν)] + ∆ωαα[β (2µ–2, 2ν + 1) – 2β (µ, ν+1) + ∆ωββ [2β (µ+1, ν) – β (2µ + 1, 2ν–2)] (3) for fe-si liquid alloy a = mg, b = sn, µ = 2, ν = 1 φab(c) =       +−+ 432 c 2 1 c 3 5 cc 6 1 (4) φaa(c) =       −+− 42 c 4 1 c 2 1 c 4 1 (5) φbb(c) = 0 (6) using eqn. (4), (5) and (6) in eqn. (2), xs 2 3 4 2 4 m ab aa 1 5 1 1 1 1 g n c(1 c) c c c c c c c 6 3 2 4 2 4      = ω − + ∆ω + − + + ∆ω − + −          (7) the free energy of mixing of complex forming binary alloy gm = [ ])c1ln()c1(clncrtgxs m −−++ (8) where r is universal gas constant. a. kumar et al. / bibechana 7 (2011) 33-38 : bmhss 35 the excess entropy of mixing is given by p xs mxs m ) dt dg (s −= )]c()( dt d )c()( dt d )c()( dt d )c( dt d [ns bbbbaaaaabab xs m φω∆+φω∆+φω∆+φ ω −= (9) where φ(c) = c(1–c). xs m ms s r[c ln c (c 1) ln(c 1)= − + − − (9a) from standard thermodynamic relations, the heat of mixing hm = xs m xs m tsg + (10) to understand the nature of atomic order in the binary liquid alloy it is instructive to study the behaviour of the long wave-length limit of the concentration-concentration structure factor [scc(0)] (16, 17) given as scc(o) = n,p,t 2 m 2 b c g tnk         ∂ ∂ (11) where gm is free energy of mixing. using eqn. (7), (8) and (11) scc(o) = [ ]bbbbaaaaabab b 2 tk )c1(c 1 )c1(c φ ′′ω∆+φ ′′ω∆+φ ′′ω∆+ω− − + − (12) where j,iφ ′′ = )b,aj,i( dc d 2 j,i 2 = φ the experimental determination of scc(0) poses more difficulty, but it can be determined from measured activity data and it is usually considered to be experimental values. the warrencowley short-range order parameter (α1) [26, 27]. can estimated from the knowledge of scc(0) as α1 = 1)1z(s )1s( +− − , s = )0(s )0(s id cc cc )0(sid cc = c (1– c) and z is co-ordination number z = 10 has been taken for our calculation. 3. results and discussions 3.1 free energy of mixing the energy parameters used for the calculations of the free energy of mixing for mgsn liquid alloys are has been determined from experimental values of gm (1) in the concentration range from 0.1 to 0.9 by the method of successive approximation. the coefficient (∆ωbb) = 0 since ν = 1. the remaining two parameters are found to be b 5.0, k t ω = − ab b 0.86 k t ∆ω = − and aa b 0.47 k t ∆ω = − thus equation (7) and (8) are used to compute free energy of mixing (gm/rt) of mgsn liquid alloy. the theoretical and experimental values of free energy of mixing for mgsn liquid alloy is shown in figure 1. the theoretical result is in good agreement with experimental values in the terminal regions of concentrations cmg = 0.1 to 0.3 and 0.8 to 0.9, in which the liquidus line is endowed with eutectics. but the theoretical results do not agree so well with experimental values in the intermediate region of concentration cmg = 0.3 to 0.7 in which the liquidus line shows sharp a. kumar et al. / bibechana 7 (2011) 33-38 : bmhss 36 rise with the bump at cmg = 0.66. the experimental value shows value of gm/rt= -2.316 at cmg = 0.6 but our theoretical result shows minimum gm/rt= -2.0714 at cmg = 0.51. the theoretical analysis of free energy of mixing shows that in liquid state mgsn is a weak interacting system. 3.2 entropy of mixing to determine the excess entropy mixing for mgsn liquid alloy we need the temperature derivatives of interaction parameters in eq. (9). the observed values of sx ms are used to obtained the temperature derivative by successive approximation method. it is notice that the temperature derivative of ωaa is negligibly small so we set the dt d (ωaa) = 0 and also dt d (ωbb) = 0. the remaining parameters are found to be 2.0 dt d k 1 b −= ω ab b d1 0.03 k dt ω = − the excess entropy of mixing is calculated using eqs.(9) and (9a) to evaluate sm. the theoretical and experimental values of r sm against cmg are plotted in figure 1. the theoretical and experimental values are in excellent agreement. both show minimum at cmg =0.6. 3.3. heat of mixing the heat of mixing for mgsn liquid alloy has been computed from eq. (10) using the same values of dt dω and dt d abω . the plot of rt hm versus cmg at 1073k is depicted in figure 1. the theoretical and experimental values are in good agreement. the theoretical and experimental figure: free energy of mixing ( )rt/g m , heat of mixing ( rt/h m ) and entropy of mixing ( r/sm )verses cmg (concentration of mg) for mgsn liquid alloy at 1073 k. [––––] theoretical, [oooo] , [ xxx] and [ ] experimental [1]. a. kumar et al. / bibechana 7 (2011) 33-38 : bmhss 37 results show almost the same nature as shown by the free energy of mixing. again the theoretical results are good agreement in terminal regions of concentration but do not agree so well in the intermediate region of concentration. 3.4. the concentration-concentration structure factor [scc(0)] and short range order parameter (αααα1) the theoretical values of scc(0) computed from eq.(12) using the same energy parameters and experimental values along with the ideal values are shown in figure 2. the theoretical values of scc(0) are in good agreement with the experimental values. scc(0) can be used to understand the nature of atomic order in binary alloys. at the given composition if scc(0) < ),0(sid cc ordering in liquid alloy is excepted and if scc(0) > ),0(sid cc there is tendency of segregation. we find that there is a clear dip at cmg = 0.7 showing that mg2sn is most ordered at this concentration. figure 2: upper part concentration fluctuation in long wave-length limit [scc(0)] for mgsn liquid alloy at 1073 k at different concentrations of mg. [––––] theoretical, [oooo] experimental. lower part short range order parameter (α1) versus cmg. the knowledge of α1 provides an immediate insight into the nature of the local arrangement of atoms in the mixture. the minimum possible value of α1 is –1 and it implies complete ordering of unlike atom paring at nearest atoms. on the other hand the maximum value of α1 is +1, which implies complete segregation leading to the phase separation and α1= 0 corresponds to a random distribution of atoms. figure 2 show that α1 is negative throughout showing that α1 mgsn is an ordered system of unlike atom pairing at all concentration. α1 is found to be minimum at cmg = 0.7. a. kumar et al. / bibechana 7 (2011) 33-38 : bmhss 38 4. conclusion in present work, we have used quasi-lattice model and calculated the pair wise interaction energy for mgsn liquid alloy at 1073 k. these were used to estimate the thermodynamic properties and concentration fluctuation in long wavelength limit of mgsn liquid alloy. computed values of scc(0) and α1 suggest that there is a tendency towards unlike atom pairing (mg-sn) over the whole range of concentration. our theoretical analysis shows that the complex mg 2 sn is present in the molten state of mgsn alloy. references [1] r. hultgren p. d. desai, d. t. hawkins, m. gleisser and k. k. kelley. selected values of the thermodynamic properties of binary alloys. asm, metal park ohio, 1973 (871). [2] g. busch, h. n. guntnerodt, in ehrenreich, f. seitz, d. turnball (eds) solid state physics, academic, new york ,29 (1974) 1235. [3] s. takeuchi, k. murakami, sci. rep. ritu, 25 (1974). [4] p. chiux and h. rupersberg, j. phys (les ulis. fr.) ,c8 (lam4) 41 (1980) 145. [5] p. lamperter, w. martin and s. steeb, j. non cryst. solids, 61 (1984) 279. [6] b. c. anusionwu, pramana, j. phys., 67 (2006) 319. [7] v.m. glazov, s.n. chizhevskaya and n.n. glagoleva, liqs. semicondutors (new york paenum), (1969)277. [8] s.steeb and h. entress, z. metallik, 57(1966)803. [9] w. a. harrison pseudo potential in the theory of metals, benjami new york, (1966). [10] v. hein, solid state physics ,academic new york, (1970). [11] e. theile, j. chem. phys, lett., 39 (1963) 474. [12] j. libowitz, phys. rev. a,133 (1964) 895. [13] t. e. faber, introduction to the theory of liquid metals cambridge university press, cambridge, (1972). [14] m. shimoji, liquid metals ,london academy london ,(1977). [15] h. c. longuet higgins, proc. roy. soc., a 205 (1951) 247. [16] a. b. bhatia and r. n. singh (phys. chem liqs., 11 (1982) 343. [17] a. b. bhatia and r. n. singh (phys. chem. liqs., 13 (1984) 177. [18] d. adhikari, i.s.jha and b.p.singh, physica b, 405(2010)1861. [19] a. b. bhatia, w. h. hargrove and n. h. march, j. phys. ,c6 (1973) 621. [20] j. a. alonso, and n. h. march physica b,114 (1982) 67. [21] e. a. guggenheim, mixtures, oxford university press, oxford, (1952). [22] n. k. p. singh, i. k. mishra and v. n. singh j. phys. conds. matter ,2 (1990) 8445. [23] r. n. singh and l. c. prasad phys. chem. liqs. ,22 (1990)1. [24] s. k. chatterjee and l. c. prasad, indian j. pure app. phys., 42 (2004), 279. [25] n. k. p. singh, r. n. singh and r. b. choudhary, j. phys. conds. matter, 3 (1991) 5345. [26] j. m. cowley, phys. rev. 77 (1950) 667. [27] b. e. warren x-ray diffraction, addison wesley, reading m. a. ,(1969)p. 227. microsoft word armila _1-6_.doc a. rajbhandari et al. / bibechana 9 (2013) 1-6 : bmhss, p.1 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana a study on the surface deterioration of home made halide sensors a. rajbhandari (nyachhyon)*, k. manandhar, r.r. pradhananga central department of chemistry, tribhuvan university, kathmandu, nepal *corresponding author: email: armila3@yahoo.com article history: received 25 november, 2011; accepted 2 july, 2012 abstract home made halide sensors based on silver sulphide-silver halide have been prepared and successfully employed for the determination of iodide, bromide and chlorides ions in solutions. these ion sensors showed a nernstian response in the concentration range of 10 -1 to 10 -7 m for iodide ions, 10 -6 m for bromide ions, and 10 -5 m for chloride ions. the response time of these sensors was < 1 min. we have found that the iodide ion sensor can selectively detect iodide ions in presence of chloride and bromide ions. however, sensing performance of the bromide and chloride sensors are largely interfered by the presence of iodide ions. surface study showed that surface deterioration of membrane was caused by the solutions containing interfering ions and its regular use, particularly in dilute solutions. keywords: electrochemical sensors; nernstian response; selectivity co-efficient, surface deterioration 1. introduction halide sensors are ion selective electrodes (ises) that provide a convenient and quick analytical procedure for the estimation of particular ions in solution. because of the simplicity, low cost of fabrication and operation, accuracy, applicability to extreme conditions and timeliness, they are renowned as novel analytical tools [1] and are suitable for diverse fields of analysis such as pharmaceutical analysis, plant and vegetable analysis, seawater analysis. ion selective electrodes of different types are reported in the literature [1]. silver sulphide-based all solid state ion selective electrodes [2-7] are one of the promising electrodes as these are free from the problem of leakage and evaporation of internal electrolytes and stable among other ises. but the nernstian response of electrode was affected after using prolonged period of time. the reproducibility and response time was adversely affected. in this study, a simple, low cost iodide, bromide and chloride ion sensors have been developed from polycrystalline silver sulphide-silver halide materials. the response behavior and selectivity of fabricated electrodes were studied. potentiometric titrations were performed to evaluate the applicability of electrodes. finally, the surface deterioration of the membrane was investigated to study the reproducibility and response time. 2. experimental section materials and methods all the reagents (agno3, ki, kbr, kcl, kno3) were of analytical grade. all the solutions were prepared in distilled water. all potentiometric measurements on electrodes were performed with osaw digital a. rajbhandari et al. / bibechana 9 (2013) 1-6 : bmhss, p.2 (online publication: nov., 2012) potentiometer, india. the silver/silver chloride electrode (sse) was used as a standard reference electrode. all the measurements were carried out in constant stirring conditions at 25 o c. fabrication of electrodes equi-molar mixture of aqueous solution of na2s and kx (x= i, br, cl) were taken in separately and silver nitrate solution was added. after shaking, co-precipitate of ag2s/agi, ag2s/agbr, ag2s/agcl were obtained and were filtered, dried, grinded into fine powders. then the pellets were prepared using kbr pellet making machine . details of preparation and characterization of pellets are given elsewhere [3]. thus prepared ag2s-agx pellets were connected with silver back having a copper wire and adhered into a polyethylene tube with araldite. the wire was about 6 inches long for electrical conduction. the detail procedure of fabrication of electrode is given elsewhere [3-5]. the electrodewas then abraded using silicon carbide paper from 1000-2000 grit size. the electrode was washed thoroughly with distilled water and then sonicated for 15 minutes. electrodes were immersed for 15 minutes in solution of respective ions before use. the response of the ag2s/agx electrodes for respective x (x= i, br, cl) ions was measured by standard addition technique at constant ionic strength (µ = 0.1m) using 0.1m kno3 as background electrolyte. dynamic response of electrodes was obtained by noting the cell emf at the interval of 30 seconds till equilibrium potential was obtained. selectivity coefficient values were obtained by fixed interference method [8]. potentiometric titrations of kx (x=i, br, cl) by silver nitrate were carried out. surface study of membrane pellets of ag2s-agi, ag2s-agbr and ag2s-agcl were studied by visual observation. a digital photo graphs were taken before and after immersion of electrode in solutions containing interfering ions and in dilute solutions. 3. results and discussion potentiometric response of the ag2s-agi to iodide ions the response of ag2s-agi electrode to iodide ion was investigated by measuring cell potential (emf) of the ag2s-agi electrode coupled with a saturated silver-silver chloride reference electrode. the emf was measured at 25°c at 10 -1 to 10 -7 m [i ] ion concentrations. the ionic strength was maintained by using 0.1 m kno3. the result is shown in fig 1 (curve c). the cell potential showed a linear decrease in the emf vs. -log[i ] plot over a wide concentration range of 10 -1 to 10 -7 m. symbols are the data points and dotted line represents the line of best fit. from the best fit in the linear region, the slope was calculated to be 58.7 mv, indicating that the electrode shows nernstian behavior. from fig.1 (curve c), the emf of cell can be expressed by the equation below for the concentration range 10 -1 m to 10 -7 m. e = -398 – 58.7 log [i ] ………… (1) potentiometric response of the ag2s-agbr to bromide ions the response of ag2s-agbr electrode to bromide ion was investigated by measuring cell potential (emf) of the ag2s-agbr electrode coupled with a saturated silver-silver chloride reference electrode. the emf of the cell was measured at 25°c at 10 -1 to 10 -6 m br ion concentrations while maintaining the ionic strength at 0.1 m using kno3. the result is shown in fig. 1 (curve b). a linear response with 58 mv per concentration decade was obtained in the concentration range from 10 -1 m to 10 -6 m (fig.1 curve b). from fig 1 (curve b), the emf of cell can be expressed by following equation. e = -175 58 log [br ] ………… (2) a. rajbhandari et al. / bibechana 9 (2013) 1-6 : bmhss, p.3 (online publication: nov., 2012) fig.1: plot of the cell emf against – log[x ]. symbols are the data poinst and dotted line represents the line of best fit. curve a indicates cell emf as a function of -log[cl-] , curve b indicates cell emf as a function of –log[br ] and curve c indicates cell emf as a function of –log[i ]. potentiometric response of the ag2s-agcl to chloride ions the emf of the cell in mv with ag2s-agcl membrane electrode coupled with a saturated silver-silver chloride reference electrode is plotted against -log[cl ] which is shown in fig. 1(curve a). a linear curve was obtained over a concentration range of 10 -1 m to 10 -5 m. from the best fit in the linear region, the slope was calculated to be 56 mv. this means the cell potential changes by 56 mv per decade change in cl ion concentration at 25 o c indicating the nernstian behavior of fabricated electrode. from fig. 1 (curve a), the emf of cell follows the following equation. e = -27 – 56 log [cl ] ………… (3) dynamic response the dynamic response of ag2s-agi, ag2s-agbr, ag2s-agcl electrodes were measured in 10 -3 m concentration of respective ions at 1 minute interval of time. the results are shown in fig 2. the stable potential was obtained within 1 minute indicating that the equilibrium was established very fast. in fig. 2 (curve c) shows the dynamic response curve for ag2s-agi , while fig. 2 (curve b) and fig. 1 (curve a) for ag2s-agbr, ag2s-agcl electrodes respectively. selectivity coefficient the potentiometric selectivity coefficient indicates the extent to which a foreign ion b interferes with the response of the electrode to its primary ion a. the potentiometric selectivity coefficients pot bak , for the suggested electrodes were measured by fixed solution method [8]. the value of k pot a,b is defined by the modified nickolsky–eisenman equation (eq.4) [8].the smaller the value of k pot a,b the greater the electrode’s preference for the principal ion, a. e = e 0 + (rt/n a f ) ln (aa+ σ k pot a,b (a b ) n a / n b)................... (4) a. rajbhandari et al. / bibechana 9 (2013) 1-6 : bmhss, p.4 (online publication: nov., 2012) fig. 2: dynamic response curve of (a) ag2s-agcl electrode, (b) ag2s-agbr electrode, (c) ag2s-agi electrode. where aa and ab are the activities of main and interfering ions having charges na and nb respectively, e 0 is standard potential of the electrode and k pot a,b is the selectivity coefficient which describes the relative sensitivity of determinant ion. in the present study, fixed solution method [8] was used to determine the selectivity of ag2s-agi electrode containing iodide ion with br , cl ions as interfering ions. in this method, the potential of cell comprising an ion selective electrode and reference electrode is measured with solutions of constant level of interfering ions, (br , cl ) and varying activity of primary ion (i ). similarly, selectivity of ag2s-agbr electrode towards i and cl ions and selectivity of ag2s-agcl electrode towards i and br ions were also studied using fixed solution method. the results obtained are tabulated in table 1. these results showed that iodide electrodes are not affected by bromide and chloride ions where as bromide and chloride electrodes are affected by iodide ions which is according to following surface reaction [9] c + a (s,membrane) + j (aq) = c + j (s,surface) + a + (aq) ………….. (5) ( where, c + is cation and a is anion in membrane and j is interfering ion) and the relative magnitude of the interference depend upon the relative solubilities of the solids. table 1: selectivity coefficient values of respective electrodes. electrode primary ion interfering ion k pot a,b br 7.94x10 -3 ag2s-agi i cl 1.77x10 -2 i 3.98 ag2s-agbr br cl 8x10 -2 i 48.9 ag2s-agcl cl br 10.0 10 -3 m [i ] 10 -3 m [br ] 10 -3 m [cl ] a. rajbhandari et al. / bibechana 9 (2013) 1-6 : bmhss, p.5 (online publication: nov., 2012) potentiometric titration to test the usefulness of laboratory prepared iodide, bromide and chloride electrodes as an indicator electrode, potentiometric titrations of ki with agno3, kbr with agno3 and kcl with agno3 were carried out by respective electrodes. a potentiometric titration curve of 1x10 -2 m potassium iodide with 1x10 -1 m silver nitrate solution is shown in fig. 3. similar titration curves of potassium bromide with silver nitrate and potassium chloride with silver nitrate were observed ( curves are not shown). a clear inflation point can be observed in the titration curve from which one can conclude that the present electrode can be utilized as an indicator electrode for respective ion. fig.3: potentiometric titration 20 ml of 1x10 -2 m potassium iodide with 1x10 -1 m silver nitrate. surface study of the membrane surface of membrane is one of the important parameter to study the better performance of electrode. in this study, surface deterioration of membrane of electrodes were investigated by visual observation of surface of membrane. a digital photograph of membrane were taken before and after immersing the electrode in solutions having interfering ions and in dilute solution of its determinant ion. in fig.4 (a,b,c) digital pictures of ag2s-agcl electrode are shown before and after immersing the electrode in 10 -3 m kcl solutions having interfering ions namely iodide and bromide at 10 -3 m concentration and storing the electrode in 10 -7 m kcl for 48 hours. then the response behavior was examined and found that results are not reproducible and increase of response time. fig. 4a showed that surface of the membrane is found to be smooth and fine. in fig. 4b, it was clearly observed that surface is tanned due to formation of surface film of precipitate of agi and agbr as agi and agbr has low solubility values of (8.3x10 -16 ) and (5x10 13 ) respectively. the selectivity coefficient values were also indicating the formation of agi and agbr as equilibrium of reaction lies to right side in equation (5). in fig. 4c, a pitted surface can be clearly seen when it was storing in dilute solution of 10 -7 m kcl for 48 hours. it is obvious that the dissolution of membrane surface was occurred. it may be due to the higher value of solubility of agcl (1.7x10 -10 ). it is unfortunate that dissolution of membrane is not uniform, then surface became very rough having small pitted holes. as increase in number of pitted holes occur, the reproducibility in response behavior was adversely affected. small volumes of solution may get trapped in the cavities and transferred from one a. rajbhandari et al. / bibechana 9 (2013) 1-6 : bmhss, p.6 (online publication: nov., 2012) sample to next sample during emf measurement. similar pictures were obtained in ag2s-agbr electrode whereas in ag2s-agi electrode, surface got tanned due to formation of kag[i]2 complex. fig. 4: (a) surface of ag2s-agcl membrane pellet before immersing in kcl solution, (b) surface of ag2s-agcl membrane pellet after immersing in 10 -3 m kcl having 10 -3 m [i ] and [br ] solution, (c) surface of ag2s-agcl membrane pellet after storing in 10 -7 m kcl for 48 hours. 4. conclusions home made halide sensors sensitive for iodide; bromide and chloride ions prepared and revealed a nernstian response over a wide concentration range, fast response time. the selectivity coefficient values showed that iodide electrodes are not interfered by chloride and bromide ions which is in agreement with solubility values. these sensors are found to be applicable as an indicator electrode for respective ions. the surface deterioration of electrode mainly depends upon the regular use in solutions having interfering ions and dilute solutions of determinant ion. acknowledgements we gratefully acknowledge the support of institute of science and technology, tribhuvan university, and nepal academy of science and technology, nepal for this research work. references [1] p.l. bailey, analysis with ion selective electrodes, heyden and son, london (1976). [2] r.r. pradhananga, and l.k. shrestha: trans mrs-j., 33(2008)345. [3] a. rajbhandari (nyachhyon), a.p. yadav, k. manandhar and r.r. pradhananga, talanta, 82 (2010) 1448. [4] r.r. pradhananga and a. rajbhandari (nyachhyon): scientific world, 6 (2008) 33. [5] a. rajbhandari (nyachhyon), a.p. yadav, k., manandhar and r.r. pradhananga, scientific world, 7 (2009) 19. [6] a. rajbhandari (nyachhyon), a.p. yadav, k., manandhar and r.r. pradhananga, advanced materials research, 117 (2010) 93. [7] a. rajbhandari (nyachhyon), a.p. yadav, k.. manandhar and r.r. pradhananga, advanced materials research, 17 (2010) 7. [8] y. umezawa , p. buhlmann, k. umezawa, k. tohda, and s. amemiya, pure appl. chem. 72 (2000) 1851. [9] a. m. james and a. evans, potentiometry and ion selective electrodes (analytical chemistry by open learning), john willey and sons inc. (1987). 46-52 r.p. koirala r c o s t n r. p. koirala et al. / bibechana 11(1) (2014) 46-52: (online publication: march, 2014) p.46 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana structural study of liquid sn-tl alloys r.p. koirala1, 2, i.s. jha2, b.p. singh1, d. adhikari2* 1university department of physics, t.m. bhagalpur university, bhagalpur, india 2department of physics, m.m.a.m. campus biratnagar, tribhuvan university, nepal *corresponding author: e-mail: adksbdev@yahoo.com accepted for publication: february 06, 2014 abstract the concentration fluctuations in long wavelength limit, scc(0) and the warren-cowley short range order parameter ( 1α ) are important microscopic functions which provide valuable information about the local arrangements of the constituent atoms in the alloy melts. in order to investigate the nature of atomic ordering in sn-tl alloy in the molten state at 723k, we have computed these functions using theoretical models. the models satisfactorily explain the small asymmetry observed in the experimental data of free energy of mixing of the alloy. the comparative study further reveals that the energy interaction parameters are temperature dependent and the sn-tl alloy is weakly interacting segregating system. © 2014 rcost: all rights reserved. keywords: free energy of mixing; concentration fluctuation; short range order; segregation. 1. introduction tin and thallium are two members among seven orphans, or metals that belong to a smaller family of elements. tin is well known metallic element which can be alloyed with many metals. thallium is less common metal. no large prospective applications for thallium have so far been reported. the unalloyed pure thallium is unsuitable for direct use, because of its unfavourable mechanical properties and marked tendency to oxidize. the isotope 204tl is radioactive (β emmiter, t1/2=3.5 years) while the isotope 205tl has most constant atomic vibrations (suitable for use in atomic clocks). thallium readily forms alloys with most other metals. it forms simple eutectic alloy with tin. thallium, like tin, lead, cadmium etc., possesses good wear resistance behaviour when used in bearings for steel shafts. as addition of thallium improves the deformation resistance, breaking strength, and hardness of lead and its alloys, metallic alloys with thallium are frequently recommended for bearings [1]. the alloys of tin with thallium are drawing attention of some authors for the past several years [2-6]. the activities of the metals in the sn-tl alloy at 723k show slight deviation from the raoultian behaviour along with a small asymmetry in the free energy of mixing [6]. the interatomic interactions in the alloy determine the nature of the liquid alloy. this has aroused our interest to undertake a theoretical assessment of the structural sn-tl system. as most of the commercial solid alloys derived from their corresponding liquid phase, it is important to have knowledge about the alloying behaviour of the alloys in the liquid state so that the nature of solid alloys can be understood properly. metallic alloys in the liquid phase lack long range atomic order r. p. koirala et al. / bibechana 11(1) (2014) 46-52: (online publication: march, 2014) p.47 and they are considered as disordered systems. the physics and chemistry of such systems are normally complex phenomena. the energetics of formation in such disordered systems may result in a variety of atomic arrangements [7]. on mixing the metals in the molten state, the atoms of the constituent metals may prefer to remain self coordinated (like atoms pairing) or hetero-coordinated (unlike atoms pairing). the alloys having structural arrangement of the former type are said to be segregating and those with latter type are termed as ordering. the segregating or ordering nature of an alloy has direct influence on its thermodynamic, transport and surface properties. the nature of atomic ordering in an alloy can be comprehended from knowledge of the microscopic functions namely the concentration fluctuations in long wavelength limit, scc(0) and the warren-cowley short range order parameter, 1α . the function scc(0) in particular is useful in ascertaining the segregation in binary liquid alloys. moreover it can be helpful to gain insight into the stability for the binary metallic solutions. the function 1α gives the degree of ordering or segregation in the binary liquid alloy. in the present work we intend to investigate the structural arrangement in the sn-tl alloy at 723k by computing scc(0) and 1α using two statistical mechanical methods namely the quasi-lattice theory (qlt) for weakly interacting system [8-9] and the quasi-chemical approximation (qca) [10-11]. for the computation of scc(0), we take into consideration the free energy of mixing of the alloy in both models. necessary expressions for the theoretical analysis are presented in the next section. section 3 deals with numerical results and discussion while conclusions are provided in section 4. 2. theoretical basis basic expressions of the statistical models we employ in current work are presented in the following subsections. 2.1. quasi-lattice theory for weakly interacting alloys we consider statistical model of complex formation on the basis of quasi-lattice theory for weakly interacting systems [8-9]. in this approach, an interaction between the constituents of the alloys is supposed to exist in the solution due to which chemical complexes, νµba ( where µ and ν are small integers) are formed. these complexes are given various names such as ‘pseudomolecules’, ‘associations’, ‘clusters’ etc. along with these associations of unlike atoms there are also self associations between like atoms in the solution. thus a binary alloy can be considered to be a ternary mixture of a atoms, b atoms and a number of complexes, νµba . bhatia and singh developed compound formation model assuming the energy of an aa, bb, or ab bond depends on whether that bond is part of the complex or not, i.e. the energy of a given nearest bond is different if it belongs to the complex than if it does not. in the sn-tl alloy at 723k, the observed value of scc(0), calculated directly from observed activity data [6], shows maximum deviation from the ideal value at 6.0csn = . thus we assume the existence of the complexes sn3tl2 in the molten state in order to understand the mixing behaviour of the sn-tl alloys in the framework of quasi-lattice model for weakly interacting alloys. in this model expressions for the free energy of mixing, gm; and for the microscopic functions scc(0) and 1α can be derived by constructing grand partition function for a cluster of two lattice sites in a binary metallic solution and solving it (a detail of the formulation is available in the ref. [8] ): considering nc mole of sn atoms and n(1-c) mole of tl atoms mixed in molten state of sn-tl alloy, expressions have been derived which are given as follows: (i) free energy of mixing the free energy of mixing, gm of a binary liquid solution at temperature t is expressed as [8]: r. p. koirala et al. / bibechana 11(1) (2014) 46-52: (online publication: march, 2014) p.48 xs mbm g)]c1ln()c1(clnc[tnkg +−−+= (1) where kb is boltzmann constant, c is the concentration of a-component of the alloy. xs mg is the excess free energy of mixing. in qlt, xs mg is given by: ] tktktktk )c1(c[tnkg b bb bb b aa aa b ab ab b b xs m ω∆φ+ω∆φ+ω∆φ+ω−= (2) here s'ω are the ordering energies and )b,aj,i(ij =φ are the simple polynomials in c depending on the values of µ andν . with 3=µ and 2=ν , the values of the s'ijφ are given as [8]: 876543 ab c 4 1 c 7 5 c 3 2 c 5 3 c 2 3 c 3 2 c 420 13 +−++−+=φ (3a) 876543 aa c 8 1 c 7 4 cc 5 6 c 4 5 c 3 2 c 840 53 −+−+−+−=φ (3b) 8754 bb c 8 1 c 7 1 c 5 2 c 2 1 c 280 23 −++−=φ (3c) (ii) concentration fluctuations in the long wavelength limit, scc(0): for the weakly interacting compound forming alloys, the qlt expression for scc(0) is expressed as [8]: ] tktktktk 2[)c1(c1 )c1(c )0(s " bb b bb" aa b aa" ab b ab b cc φω∆+φω∆+φω∆+ω−−+ −= (4) where, 2 ij 2 " ij c∂ φ∂ =φ , )b,aj,i( = with 3=µ and 2=ν , are given by 65432" ab c14c30c20c12c18c4 +−++−=φ (5a) 65432" aa c7c24c30c24c15c4 −+−+−=φ (5b) 6532" bb c7c6c8c6 −++−=φ (5c) (ii) short range order parameter, short range order parameter, 1α : in qlt, the short range order parameter, 1α is given by [8]: 1 1 1 +β −β=α (6) where 2/12 )]1()c1(c41[ −η−+=β (7) with ) tk ppp2 exp(.) tzk 2 exp( b bbbbaaaaabab b 2 ε∆−ε∆−ε∆ω=η (8) here, ijε∆ )b,aj,i( = represents the bond energy ( z ij ij ω∆ =ε∆ , =z coordination number) and ijp )b,aj,i( = represents the probability that the bond in the cluster is part of the complex, given by r. p. koirala et al. / bibechana 11(1) (2014) 46-52: (online publication: march, 2014) p.49 ])c1(c2[)c1(cp 1111 ab −ν−µ−ν−µ −−−= (9a) ])c1(c2[)c1(cp 22 aa ν−µν−µ −−−= ; 2≥µ (9b) ])c1(c2[)c1(cp 22 bb −νµ−νµ −−−= ; 2≥ν (9c) assuming weak interaction in compound forming alloys where 1 tzkb <<ω and 1 tkb ij << ε∆ (i.e. 1 tzkb ij << ω∆ ), we have )ppp22( tzk 1 1 bbbbaaaaabab b 2 ω∆−ω∆−ω∆+ω+=η (10) and )ppp22( tzk )c1(c2 1 bbbbaaaaabab b ω∆−ω∆−ω∆+ω−+=β (11) the short range order parameter can then be obtained from the expression x1 x 1 + =α (12) where )ppp22( tzk )c1(c x bbbbaaaaabab b ω∆−ω∆−ω∆+ω−= (13) 2.2. quasi-chemical approximation (qca) qca for binary liquid alloys assumes the homo-coordination of like atoms at equivalent sites that results in the formation of self-associates of types aµ and .bν in this approach the ratio of self associates µ≠νµν= ,/n and order energy parameter w are taken as the fitting parameters to study the thermodynamic and structural properties of a liquid alloy. (i) free energy of mixing: the qca expression for the free energy of mixing, gm for the binary liquid a-b alloy is given as [1011]: w)cnnc()1()]1(ln)c1(lnc[rtgm −+φ−φ+φ−−+φ= (14) where, r is universal gas constant. the auxiliary function φ is defined by ncnc c −+ =φ (15) (ii) concentration fluctuations in the long wavelength limit, scc(0): the microscopic structure, concentration fluctuation in long wavelength limit, scc(0) is obtained from the second composition derivative of the free energy of mixing: 1 n,p,t 2 m 2 cc )c/g(rt)0(s −∂∂= (16) using eqs. (14) and (16), we get )w,n(f)c1(c1 )c1(c )0(scc −− − = (17) where 3 22 )ncnc( )cnnc()1n()rt/w(n2 )w,n(f −+ −+−−= (18) r. p. koirala et al. / bibechana 11(1) (2014) 46-52: (online publication: march, 2014) p.50 the value of )0(scc indicates the nature of chemical ordering in the alloy. the values of )0(scc computed from the following relation are regarded as the experimental )0(scc [10]: )c1( a ac c a a)c1( )0(s b b a a cc −∂ ∂ = ∂ ∂ −= (19) (ii) short range order parameter, short range order parameter, 1α : warren-cowley short-range parameter, 1α which represents the degree of ordering in the melt, can be estimated from the knowledge of scc(0) using the following expression [10-13]: 1)1z(s 1s 1 +− −=α , with )c1(c )0(s s cc − = (20) where z is the coordination number. 3. results and discussion in the present work we have theoretically studied structural behaviour in the liquid sn-tl alloys at 723k by comparative method. for the computation of the microscopic functions from qlt, interatomic interaction energy parameters s'and ijω∆ω are required while in qca, the ratio of self associates n and order energy parameter w are needed. we have estimated the model fit parameters for the alloy using the experimental data of integral free energy of mixing [6], from eqs. (1) and (2) in qlt and from eq. (14) in qca. the best fit values of energy parameters for the computation of free energy of mixing of the alloy are found to be: qlt: 69.0 tkb +=ω ; 38.1 tkb ab +=ω∆ ; 0 tkb aa ≈ω∆ ; 85.0 tkb bb −=ω∆ qca: 23.1n = ; 70.0 rt w += obviously if ω˂ 0, pairing of unlike atoms is preferred over pairing of like atoms. on the other hand, if ω˃ 0, there is a tendency of like atom pairing (self-associations). 0=ω indicates random mixing of component atoms so that the mixture is perfectly disordered. we have found thatω˃ 0 for the sn-tl alloy at 723k. this shows that there is a tendency to form homo-pairs in the alloy. using the estimated parameters, we have worked out the theoretical values of excess free energy of mixing and integral free energy of mixing from both models over the whole range of concentration. the excess free energy of mixing has been found positive at all concentrations with maximum value at 1.16kjmol-1 (qlt) and 1.13kjmol-1 (qca) at the equi-atomic concentration. this is an indication of segregating tendency in the sn-tl alloy. the theoretical results for the integral free energy of mixing are found in good agreement with the experimental result [6] as depicted in fig. 1. the nature and degree of local ordering of atoms in the nearest cells in a binary liquid alloy can be effectively discussed in terms of the microscopic constructs scc(0) and 1α . here we have computed the concentration fluctuation in the long wavelength limit, scc(0) as function of concentration for the sn-tl alloy from eq. (4) of qlt and eq. (17) of qca. in order to maintain the consistency we have used the same parameters which were used in the computation of free energy of mixing. the experimental scc(0) values are obtained directly from the observed activity data [6] using eq. (19). the computed values of scc(0) are plotted against concentration of tl-component in fig. 2 along with the observed and ideal values. the scc(0) calculated from both approaches are found greater than the ideal values throughout the entire concentration range. this indicates that there is segregating nature in the sn-tl alloy. r. p. koirala et al. / bibechana 11(1) (2014) to gain a deeper understanding into the microscopic structure regarding the degree of atomic ordering in the liquid sn-tl alloy, we have next calculated the warren from eq. (12) for qlt and from eq. (20) for qca. it is observed that (fig. 3). the positive values of 1α between the unlike atoms in the sn energy of mixing. in this study asα alloy at 723k. it is clear from fig. (3) that there is larger segregation in the alloy towards sn the concentration. along with the study of the microscopic structure, we have also examined the validity of two statistical methods to explain the behaviour of the sn quasi-chemical approximation is found more appropriate approach for the sn theory in weak interaction indicating very we bibechana 11(1) (2014) 46-52: (online publication: march, 2014) p. to gain a deeper understanding into the microscopic structure regarding the degree of atomic ordering in tl alloy, we have next calculated the warren-cowley short range ordering parameter, from eq. (12) for qlt and from eq. (20) for qca. it is observed that 1α is positive at all concentrations figure 1: free energy of mixing of sn 723k versus concentration of tl thick dots – qlt squares – qca broken curve – experimental [6]. figure 2: concentration fluctuations in long wavelength limit of sn-tl alloy at 723 k versus concentration of tl thick dots – qlt squares – qca thick broken line – experimental thin broken line – ideal. 1 confirms the preference of self association over hetero between the unlike atoms in the sn-tl alloy as observed from the result of w, scc(0) and the excess free 11 <<α , there is weak interaction among the species of the liquid sn alloy at 723k. it is clear from fig. (3) that there is larger segregation in the alloy towards sn the concentration. along with the study of the microscopic structure, we have also examined the validity of two statistical methods to explain the behaviour of the sn-tl alloy in the molten state. in our analysis chemical approximation is found more appropriate approach for the sn-tl alloy than quasi theory in weak interaction indicating very weak complex sn3tl2 likely to exist in the alloy at 723k. : (online publication: march, 2014) p.51 to gain a deeper understanding into the microscopic structure regarding the degree of atomic ordering in rdering parameter,1α is positive at all concentrations free energy of mixing of sn-tl alloy at 723k versus concentration of tl-component: experimental [6]. concentration fluctuations in long tl alloy at 723 k -component: experimental confirms the preference of self association over hetero-coordination (0) and the excess free n among the species of the liquid sn-tl alloy at 723k. it is clear from fig. (3) that there is larger segregation in the alloy towards sn-rich side of the concentration. along with the study of the microscopic structure, we have also examined the validity tl alloy in the molten state. in our analysis tl alloy than quasi-lattice likely to exist in the alloy at 723k. r. p. koirala et al. / bibechana 11(1) (2014) 46-52: (online publication: march, 2014) p.52 figure 3: warren-cowley short range order parameter of sn-tl alloy at 723 k versus concentration of tl component: thick dots –qlt dashed line with squares – qca. 4. conclusion we have performed a theoretical study of the free energy of mixing and the microscopic structures of sntl alloy in the molten state using two approaches. our theoretical analysis suggests that the alloy is a weakly interacting segregating system. further the quasi-chemical approximation seems more appropriate than the quasi-lattice theory in explaining the thermodynamic behaviour of the sn-tl alloy at 723k. acknowledgments we are grateful to prof. dr. pradeep raj pradhan, post graduate department of physics, m.m.a.m. campus, biratnagar, tribhuvan university, nepal for inspiring discussion and encouragement. references [1] fathi habashi (editor), alloys: preparation, properties & applications, john wiley & sons, 2008. [2] p.e. berthou, r. tougas, metallurgical transactions, 3 (1972) 51. [3] e.yu.tonkov, i.l. aptekar', v.k. gartman, russian journal of physical chemistry, 44 (1970) 1490. [4] p.e. berthou , journal of the less-common metals, 16 (1968) 465. [5] ryoji suganuma, j. physical society of japan, 15 (1960) 1395. [6] r. hultgren, p.d. desai, d.t. hawkins, m. gleiser, and k.k. kelly, selected values of the thermodynamic properties of binary alloys, asm, metal park, 1973. [7] p.j. tumidajski, a. petric, t. takenaka, a.d. pelton, m.l. saboungi, j. phys.: cond. mat., 2 (1990) 209. [8] r.n. singh, can. j. physics, 65 (1987) 309. [9] b.p. singh, d. adhikari, i.s. jha, phys. and chem. of liq., 50 (2012) 697. [10] r.n. singh, f. sommer, rep. prog. phys., 60 (1997) 57. [11] b.c. anusionwu, c.a. madhu, c.e. orji, pramana: j. physics, 72 (2009) 951. [12] r. novakovic, j. non-cryst. solids, 356 (2010) 1593. [13] b.p. singh, d. adhikari, i.s. jha, b.c. kumar, s.k. chaudhary, s.k. jayaswal, r.p. koirala, bibechana, 7 (2011) 1. microsoft word editorial.doc editorial it is our pleasure to present a new volume of bibechana (volume 7) where we have interesting and educational research articles in physics, chemistry, biology, mathematics and related disciplines. it is believed that bibechana will provide major contributions to the field of science, technology and mathematics. we have had an excellent response from authors and readers. it is a very exciting experience to get an overwhelming response from scholars and colleagues. with this volume online version of bibechana will also be published in the homepage http://www.nepjol.info/index.php/bibichana . this will help us expand our presence in superior community of educationists, scientists and technologists. at this point, we sincerely thank mrs. sioux cumming for her cooperation. finally, we would like to thank all contributors who have supported this journal specially authors, referees and readers. devendra adhikari editorinchief 165-168 g.k. paleip.k. karn r c o s t n g.k. palei & p.k. karn / bibechana 11(1) (2014) 165-168: (online publication: march, 2014) p.165 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana some remarks on the definition of numbers g. k. palei1, p. k. karn2* 1 dept. of mathematics, b.n. college patna, patna university, patna, india 2 dept. of mathematics, m.m.a.m. campus, biratnagar, t.u. , nepal *corresponding author email: pawankarn12345@gmail.com accepted for publication: february 15, 2014 abstract in this paper some remarks have been given on the definition of number. it is clear that peano’s definition of a number and frege-russel definition of number are not satisfactory. number states some things about the concept and not about the counted things themselves. © 2014 rcost: all rights reserved. keywords: quotient number; polygamy; successor. 1. vaisesika definition of number the vaisesikas have attempted to define and characterized numbers unity, duality, triplicity etc and that they have accepted numbers as objectively real quantities inhering in all substances. for them unity, like god, inheres in all substances and is a basic number with which all higher numbers are formed by means of relative understanding modern western philosopher like hilbert and brouwer also agree with their view that the concept of one is fundamental in mathematics. but the vaisesikas have not defined zero, which has its use as a number in the indian mathematical literatures since about 200 b.c. [1] or even earlier in the vedic literature. it was brahmagupta (628 a.d.), the prince of indian mathematics, who correctly defined zero. he gave a relational rather than half-scientific and halfintuitive definition of zero. since zero is the number smaller than any one of the numbers unity, duality etc. which are used for counting purposes, it is desirable and proper to define zero first and then to define other numbers with the help of zero. the vaisesikas have no method to define zero first and then the numbers unity, duality etc. (or to define zero with the knowledge of unity, duality etc.) by means of relative understanding. it was frege-russel [2] definition of number which could enable one to define zero first and then other higher numbers. further we see that we can get only finite numbers, however large, in their system and as such the concept of infinity cannot be cognized. but cantor (1845-1918) has shown how to deal with the infinite, and hence it is both desirable and possible to deal with the fundamental properties of numbers in some way which is applicable to finite as well as infinite numbers. 2. peano’s definition of number guiseppe peano [3] believed like pythagoras that the whole of mathematics could be deducted from numbers. having reduced all traditional pure mathematics to the theory of natural numbers, the next step in the logical analysis was to reduce the theory itself to the minimum number of premises and undefined g.k. palei & p.k. karn / bibechana 11(1) (2014) 165-168: (online publication: march, 2014) p.166 terms from which it could be derived. peano showed that the entire theory of natural number could be derived from the three primitive ideas viz. ‘zero’, ‘successor’ and ‘number’ and the following five propositions. (i) zero is a number. (ii) successor of every number is also a number. (iii) no two number have the same successor. (iv) zero is not a successor. (v) if a property is possessed by zero and whenever it is possessed by any number. it is also possessed by its successor, then the property is possessed by all the numbers. at present we shall simply discuss how he has defined number and how his definition has been improved by russell [4]. peano [3] gave the definition of number by abstraction, accepting that numbers are applicable essentially to classes (i.e collection) he defined number as a ‘property of classes’. two classes have the same number when one-one relation exists between their numbers. two such classes are said to be ‘similar’ and the similarity relation has three properties viz reflexivity, symmetricity and transitivity. peano told that when similarity relation holds between two terms, the two terms have a common property called their number [4]. but this definition is not satisfactory. for, all similar classes have the same number as a common property, so there is a many one relation which every class has to its number and to nothing else, in other words, we have a set of entities such that any class, and all other classes similar to it, have a certain many one relation to one and only one of the entities of the set. but there may be many such sets of entities and the definition of peano by abstraction fails to define the number of class. the axioms of peano do not enable us to know whether there exists any set of terms verifying the axioms. we want our number to be such that can be used for counting and this requires that our numbers should have a definite meaning, not merely that they have certain formal properties only. this definite meaning is defined only by the logical theory of arithmetic. 3. frege-russell definition of number it was frege [2] who first of all attempted to give a logical definition of numbers but none paid any attention to his views until russell independently gave the same definition of number. in 1901. he did not define number by means of relative understanding (like the vaisesikas) but he used two concepts viz. the similarity of sets’ (which peano also used) and the class of classes to define all numbers including zero russell also introduced infinity through an axiom known as the ‘axiom of infinity’. one might confuse the concept of number of a collection with its plurality. but this is not proper. plurality is not a number but an instance of some particular number. for example, the trio of men, say, ram, shyam and hari is an example of the number three, but the latter is not identical with the trio consisting of ram, shyam and hari. according to frege and russell, number is an attribute (unlike colour, taste etc. as it is according to the vaisesikas)it is defining property of a collection. there are two ways of defining a collection. one way is by ‘extension’. i.e. enumeration and the other way is by ‘intension’, i.e. characterization. according to the extension method number of a collection is to be determined by counting the members of the collection. but this system suffers from two defects. the first defect is that counting is nothing else than labelling each member of a collection with a number and then it suffers from the defect of circularity. secondly, numbers themselves form an infinite class and hence it is not always possible to enumerate or count the member of an infinite collection. hence frege and russell attempted to define number by intension. russell defines it in two steps, first he defines the concept of similarity of two sets and then he formulates the concept of number in terms of this similarity concept. he defines the number of a set to be ‘the class of all sets similar to it [5]. similarity can be defined as in case of peano, without g.k. palei & p.k. karn / bibechana 11(1) (2014) 165-168: (online publication: march, 2014) p.167 the help of the concept of numbers. for example, in a country where polygamy is prohibited, one can say without counting that the set of husbands is similar to the set of wives, for every husband has a wife and every wife has a husband uniquely. we need not count the actual number of the husbands or the wives. the second part of this definition describes number as a ‘class of classes’ or more clearly, a ‘class of similar classes’ at the first sight it appears paradoxical to accept number as ‘class of classes’ and peano never accepted this definition. but if we treat class as a concept and not as a collection, then a number is really defined as a common property of a set of similar classes and nothing else. this view removes the appearance of the paradox to a great extent. further it may be seen that this definition allows the deduction of all the usual properties of numbers, finite as well as infinite, and is the only one which is possible in terms of the fundamental concept of general logic [4]. frege-russell definition too is far from being satisfactory. firstly, we find that like peano they too have based their definition on the concept of “similarity of sets.’ but it is not always easy to establish similarity between two collections. if we have two collections, say a collection of cups and another collection of saucers, we can verify the similarity between these collections by placing each cup on a saucer and finding that no saucer is left without cup. here one-one correspondence is established. but if the cups are closed in one box and saucers in another box, no such correspondence is visualized unless the boxes are opened and the cups are placed on saucers. the question arises whether similarity existed between the two collection before the cups were actually placed on the saucers obviously we feel that such similarity exists from before, so we see that it is possible to exhibit the correspondence between two sets only when similarity exists between them from before. hence we conclude that correspondence simply verifies similarity. it is not at all possible to establish a correspondence between these collections. hence the proposed definition of similarity gives only a sufficient but not necessary condition of similarity and restricts the meaning of similarity too narrowly. secondly, in order to determine similarity between two classes, we have to know the proper meaning of the word ‘class’. it has two meanings viz. ‘list’ and ‘concept’. if it means list i.e. a collection, then correspondence can be established between the members of two collectors only if they have equal number of members. but if class means concept, then two concepts can be put in one-one correspondence, even though one set is an extension of the other, i.e., even if two classes are not equi-numbered. according to frege two sets must either be similar or not similar from a purely logical basis. but if someone is asked to tell the number of stars twinkling in the sky in dark night at particulars moment, he has no method to determine the number; for while establishing correspondence with any other collection, say, a collection of mustard seeds, some stars will disappear and some new ones will appear without his notice. at best he can say that there are many stars. hence we find that sometimes we have to indicate the number of a collection by numerals ‘many’, ‘very many’ and ‘few’. but frege seems to pay no attention towards this aspect. from the second part of frege’s definition and the manner of description for the number zero, one, two, etc. it appears that number states something about the concept and not about the counted things themselves. but do we always remember this fact in our language or statements? in any command, say, ‘3 books’ the command does not say that the class of books to be asked for is ‘an element of the class three’. our command or language is unaware of this interpretation. it cannot be expressed in the subject predicate form. frege-russell definition unnecessarily restricts the concept of number to the subject predicate form of own preposition [6]. 4. concluding remarks the vaisesikas accepted number as a real quantity inhering in all substances. they realized that all higher numbers are formed by means of relative understanding of unit as a basic number, but they have not g.k. palei & p.k. karn / bibechana 11(1) (2014) 165-168: (online publication: march, 2014) p.168 defined zero. peano defined number as a property of classes, but this definition is not satisfactory, as number should have a definite logical meaning. frege and russell gave the logical definition of number. they have defined number as a common property of a set of similar classes and nothing else, but this definition too is far from being satisfactory, because it is not always easy to establish similarity between two collections. thus we conclude that the number states something about the concept and not about the counted things themselves. references [1] b.b. dutta, a.n. singh, hindu ganit shastra ka itihas, 1956. [2] g. frege, the basic laws of arithmetic, university of california press, 1967. [3] h. c. kennedy, peano: life and works of guiseppe peano, d. radial pub., 1980. [4] b. russell, the principle of mathematics, george allen and unwin london, 1956. [5] b. russell, introduction to mathematical philosophy, macmillan, new york, 1924. [4] f. waismann, introduction to mathematical thinking, harper & brother, new york, 1959. microsoft word a.k. khan _49-53_.doc a. k. khan / bibechana, 7 (2011) 49-53 : bmhss 49 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana thermal properties [compressibility and moelwynhughes parameter] of nacl crystals under high pressure a. k. khan∗∗∗∗ department of physics, r.m. college, saharsa,india article history: received 20 november 2010; accepted 29 november 2010 abstract many inter ionic potential functions have been proposed since the born and lande’s inverse function. an exponential function for the repulsive component of the potential has been proposed by born and lande’, none of the potential function proposed is successful. a new interionic function proposed by jha and thakur to study the properties of ionic crystal under high pressure. its repulsive component includes both an inverse power function due to born and lande’ and an exponential function due to born and mayer. jha has used it to study the thermal properties of nacl and cscl crystal under high pressure up to 100 kilo bar. keywords: nacl crystals; moelwyn-hughes parameter, isothermal compressibility 1. introduction in the early part of 20 th century there was a revolution in solid state physics. to study the theory of solid the born model of ionic solids [1] provides a method for calculating elastic and thermal properties of ionic crystal under high pressure. the calculations are based on an inter ionic potential function. an important component of the potential function is the repulsive term. born and lande’’s describe this term by inverse power function while born and mayer used an exponential function to describe this term. in accounting for the compression for the sodium halide crystals roberts and smith [2] have shown that neither of these functions is successful. 2. theory an inter ionic potential function has been proposed by jha and thakur [3]. its repulsive components includes both an inverse power function due to born and lande’ and an exponential function due to born and mayer. jha [4] has used it the thermal properties of nacl and cscl crystal under high pressure. in the present work i shall report the success of this potential in describing the elastic properties of nacl crystals under high pressure up to 100 kilo bar. the new inter ionic potential for the crystal under study using reduced units of equilibrium inter ionic distance r0 for distance and e 2 /r0 can be written as [3] . ∗ corresponding author: dr. a. k. khan, department of physics, r.m college, saharsa, india email: arunkumarkhan@gmail, ph. no.: +919431862819. a. k. khan / bibechana, 7 (2011) 49-53 : bmhss 50 86 n m r d r c r m )1r(bexp[ r a )r( −−−−−=ϕ (1) where r is the inter ionic distance, a , b , m & n are the potential parameters which are constants for a given crystal , m is the madeline constant , c & d are van dar walls constants for dipoledipole and dipole-quadruple interactions , respectively and e is the electronic charge. crystal properties have also been calculated using born-lande’’ and born mayer potential for the sake of comparison. these can be written as 861m 1 r d r c r m r a )r( −−−=ϕ (2) and 862 r d r c r m )/rexp(a)r( −−−ρ−=ϕ (3) 3. results and discussion potential parameters of the born – lande’ and born mayer potentials have been calculated in the usual manner. the parameters of the new potential have been calculated using a procedure described by jha & thakur [3] . m has been given integer values and n has been varied and n has been varied in steps of 0.1. input crystal data are taken from tosi [1] and ashcroft and mermin [5]. values of potential parameters for the crystal under study have been listed in table 1. at a given compression, the pressure have been calculate with the help of debye’s equation of state [6] p = ( ðe0/ ðv)+ γ ed/v (4) where e0 is the internal energy of the volume, p pressure at 0 kelvin, ed the debye energy of the crystal at the temperature at which the crystal properties are being studied, and γ the gruneisen parameter. table 1: potential parameters of nacl crystals in reduced (dimensionless) units parameter value parameter value c 0.0446 born lande’ potential d 0.0056 m1 7.81 new potential a1 0.264 m 4 born mayer potential n 3.1 1/ ρ 9.049 a 0.2142 a2 1978.83 b 1.8122 a. k. khan / bibechana, 7 (2011) 49-53 : bmhss 51 figure 1: variation of isothermal compressibility with pressure here we have taken in to account the variation of ed and  γ with pressure, but their temperature has been ignored. ed has been calculated by calculating the debye temperature. jha and thakur[3] explained the calculation of gruneisen parameter and debye temperature. the isothermal compressibility has been calculated with the relation kt = 1/v (ðv/ðp)t (5) the moelwyn-hughes parameters[7,8] is the pressure derivative of the isothermal bulk modelus bt. it is defined by c1 =(ðbt/ðp)t (6) the computed results have been displayed in fig. 1 and 2. fig. 1 shows the variation of kt with pressure at room temperature (298 k) . fig. 2 shows the variation of c1 with pressure at room temperature. curves marked l have been drawn using the born-lande’ potential , curves marked m using the born-mayer potential and curves marked n using the new potential. the open circles are estimates of kt and c1 obtained from the compression data of bridgman [9]using a modified murnaghan equation [10,11]. this equation helps us to express bt as a parabolic function of p, a. k. khan / bibechana, 7 (2011) 49-53 : bmhss 52 bt = b0+b1p+1/2b2p 2 (7) figure 2: variation of moelwyn-hughes parameter with pressure it follows from the definition of the moelwyn-hughes parameter that c1=b1+b2p (8) values of b0,b1 & b2 have been mentioned in figure 1. 4. conclusion it is seen that the inverse power law of born lande’ is not suitable for predicting the elastic properties of nacl crystal under high pressure, whereas the exponential laws is better for studying the elastic properties of crystal under high pressure. the new potential is most successful in explaining mechanical and thermal properties of nacl crystal under high pressure i.e, from 100 kilo bar study. a. k. khan / bibechana, 7 (2011) 49-53 : bmhss 53 references [1] m.p. tos, in solid state physics, , ed. f. seitz and d. turnbull, academic press, new york/london, 16(1964)pp. 1-42,44. [2] r. w. roberts and c. s. smith, j. phys. chem. solids, 31 (1970)619. [3] b. n. jha and k.p. thakur, physic b , 173 ( 1991)408. [4] b. n. jha physica b, 192(1993)253. [5] n. w. ashcroft and n. d. mermin, solid state physics, holt, rinehart and winston, new york, (1976) p.459. [6] c. kittel , introduction to solid state physics, john wiley and sons, inc., new york, (1996 ) p 182 184. [7] k. p. thakur, acta cryst. a, 32( 1976)363. [8] k. p. thakur, physics of the earth and planetary interiors, 27(1982)235. [9] p. w. bridgman, proc. amer. acad. arts sci., 76, 1(1945). [10] f. d. murnaghan, proc. nat. acad. sci. usa ,30,244(1944). [11] f. d. murnaghan, finite deformation of an elastic solid, john wiley and sons, inc., new york, (1951)chap. 4. further reading [12] z. hong, t. jin and c.xin-lu ,chinese physics letters, (2008). [13] a.y.u. kuznetsov, l.d. sky , a. kurnosov, m. m. lucchese, w. crichton and c.a. achete, advances in physical chemistry, 2009(2009), article id 180784. [14] a. tiwari, n. k. gaur and p singh, j. phys.,( 2010). microsoft word ab hamis ganie _97-102_ ab hamis ganie / bibechana 9 (2013) 97-101 : bmhss, p.97 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana almost boundedness and matrix transformation ab hamid ganie department of mathematics, national institute of technology, srinagar (india)190006. email: ashamidg@rediffmail.com article history: received 25 september, 2012; accepted 12 november, 2012 abstract the sequence space ��� have been defined and the various classes of infinite matrices have been characterized by aydin and başar, ( see, [1] ) , where 1 p≤ ≤ ∞ . in this paper we characterize the classes ( : )r c a f∞ , ( : )r c a f and 0 ( : )r c a f ,where ,f f∞ and 0 f denote respectively the spaces of almost bounded sequences , almost convergent sequences and almost convergent null sequences. keywords: sequence space of non-absolute type;, almost convergent sequences; β-duals and matrix transformations. 1. introduction, background and preliminaries a sequence space is defined to be a linear space with real or complex sequences. throughout the paper ℕ, ℝ and ℂ denotes the set of non-negative integers, the set of real numbers and the set of complex numbers, respectively. let denote the space of all sequences ( real or complex ). let and �be two non-empty subsets of . let � = ���� , �, � ∈ ℕ�, be an infinite matrix of real or complex numbers. we write ���� = �� �� = ∑ ����� � . then �� = ��� ��� is called the �-transform of �, whenever �� �� = ∑ ����� � < ∞ for all � ∈ ℕ. we write lim� �� = lim� �� ��. if � ∈ implies �� ∈ �, we say that �-defines a matrix transformations from into �, denoted by �: → �. by : ��, we mean the class of all matrices � such that �: → �. for a sequence space, the matrix domain of an infinite matrix � is defined as (1) = �� = ��� ∈ : �� ∈ � let ℓ" and # be the banach spaces of bounded and convergent sequences � = �� ����$%" with supremum norm ‖�‖ = '()�|� ��|. let + denote the shift operator on , that is , +� = �� ����$," , +-� = �� ����$-" and so on. a banach limit .is a non-negative linear functional ab hamis ganie / bibechana 9 (2013) 97-102: bmhss, p.98 (online publication: nov., 2012) on ℓ" such that . is invariant under the shift operator and . /� = 1, where / = 1,1, … � (see, [2]), that is, a functional .: ℓ" → ℝ is called a banach limit if (i) . is linear, (ii) . �� ≥ 0if�� ≥ 0 for all �. (iii) . �� = . +��where+ is shift operator on . (iv) . /� = 1, where / = 1, 1 , … �. since the hahn-banach norm preserving extension is not unique, there must be many banach limits in the dual space of ℓ", and usually different banach limits have different values at the same element in ℓ". however, there indeed exists sequences whose values of all banach limits are same. if � = �����$%" ∈ #, where # is a banach space of ℓ" consisting of convergent sequences, then . �� = lim� �� is a trivial example. besides this there also exists non-convergent sequences satisfying this property. for example � = �1, 0, 1, 0, … �the value of . �� = , is same for every banach limit. lorentz (see, [4]) called a sequence � = �����$," almost convergent if all banach limits of �, . �� , are same, and this unique banach limit is called 5-lim of �. in his paper lorentz proved the following criterion for almost convergent sequences. a � = �����$%" ∈ ℓ" is almost convergent with 5-limit . �� if and only if lim6→" 78� ��= . ��, where, 78� �� = , 6 ∑ +9��6:, 9$% , +% = 0�, uniformly in � ≥ 0. the above limit can be rewritten in detail as ∀< > 0�, ∃)%� ∀) > )%� ∀�� ?�� + ⋯ + ��b6:, ) − .? < <. we denote the set of almost convergent sequences by d. d = �� ∈ e" ∶ lim8 78� �� /�g'7' , (�gdhijek g� ��. nanda [6] has defined a new set of sequences f∞ as follows: d" = �� ∈ e" ∶ lim8|78� ��| < ∞�. we call d"the set of all almost bounded sequences. the approach of constructing a new sequence space by means of matrix domain of a particular limitation method has been studied by several authors viz., ( see, [1, 5, 7] ). following (see, [1], [7]), the sequence space r c a is defined as the set of all sequences whose ra -transform is in c , that is, 0 1 ( ) :lim ( 1 ) 1 n r k c k k n k a x x r x exists n ω =   = = ∈ +  +  ∑ ab hamis ganie / bibechana 9 (2013) 97-102 : bmhss, p.99 (online publication: nov., 2012) ; where , 1 , 0 , 1 0 , . k r nk r k n n a k n  + ≤ ≤ + =   >   with the notation of (1) that, ( ) r r c a a c= . 2. main results define the sequence ( ( )) k y y r= which will be used, by the ra -transform of a sequence ( ) k x x= , that is, (2) 0 1 ( ) ; 1 jk k j j r y r x k= + = +∑ for .k∈ℕ for brevity in notation, we write 0 1 ( ) ( ) ( , , ) 1 m mn n i k j k t ax a x a n k m x m + = = = + ∑ ∑ where , , 0 1 ( , , ) ; ( , , ) 1 m n j k j a n k m a n k m m + = = ∈ + ∑ ℕ also , 1 ( , , ) ( , , ) ( , 1, ) ( , , ) ( 1) ( 1) 1 1 1k k k a n k m a n k m a n k m a n k m k k r r r + +   =∆ + = − +   + + +    ɶ we denote by x β , the β − deal of a sequence space x and mean the set of all the sequences ( ) k x x= such that ( ) k k xy x y cs= ∈ for all ( ) k y y x= ∈ . now, we give the following lemmas which will be needed in proving the main theorems. lemma 2.1[1]: define the sets 1 ( )d p and 2 ( )d p as follows 1 ( ) : ( 1) 1 r k k k k a d a a k r ω     = = ∈ ∆ + < ∞  +    ∑ 2 ( ) : 1 r k k k a d a a cs r ω    = = ∈ ∈  +   where , 1 k k a r   ∆  +  = 1 k k a r+ 11 k k a r ++ then , 1 2 r r r c a d d β   =  ∩ lemma 2.2 [5]: f f∞⊂ theorem 2.1: ( : )r c a a f∞∈ if and only if ab hamis ganie / bibechana 9 (2013) 97-102 : bmhss, p.100 (online publication: nov., 2012) (3) , sup ( , , ) n m k a n k m ∈ < ∞∑ ℕ ɶ and (4) 1 nk k k a cs r ∈   ∈  +  ℕ , for all n∈ℕ proof: sufficiency: suppose the conditions (3) & (4) holds and .r c x a∈ then { },n k k a ∈ ∈ ℕ r c a β    for every n∈ℕ ,the a -transform of x exists. since r c x a∈ , by hypothesis, and r c a c≅ ( see,[1] ) , we have y c∈ . thus , we can find 0k > such that sup k k y k< . ( ) ( , , ) mn k k t ax a n k m x= ∑ ( , , ) k k a n k m y= ∑ ɶ ( , , ) k k a n k m y≤ ∑ ɶ ( , , ) k k a n k m≤ ∑ ɶ taking , sup m n on both sides, we get ax f∞∈ for every .r c x a∈ necessity: suppose that ( : )r c a a f∞∈ . then ax exists for every r c x a∈ and this implies that { },n k k a ∈ ∈ ℕ r c a β    for every n∈ℕ , the necessity of (4) is immediate. now, ( , , ) k k a n k m x∑ exists for each m , n and r c x a∈ , the sequences { ( , , )} k a n k m ∈ℕ define the continuous linear functionals ( ) mn xψ on r c a by ( ) ( , , ) mn k k x a n k m xψ =∑ ; ( , , )n k m∈ℕ . since r c a and c are norm isomorphic ( see [1] , ), it should follow with (2) that ( ) ( , , ) mn x a n k mψ = ɶ holds for every k∈ℕ . this implies that the functionals defined by mn ψ on r c a are point wise bounded, so by uniform bounded principle , there exists 0m > such that ( ) mn x mψ ≤ for every ,m n∈ℕ . thus we conclude that , , , sup ( ) sup ( , , ) sup ( , , ) mn k k m n m n m nk k x a n k m x a n k m y mψ = = <∑ ∑ ɶ this implies that , sup ( , , ) n m k a n k m ∈ < ∞∑ ℕ ɶ , which shows the necessity of the condition (3) and the proof of (i) is complete.□ theorem 2.2 : ( : )r c a a f∈ if and only if (3) ,(4) and (5) lim ( , , ) , k m a n k m β=ɶ uniformly in n , and for each k∈ℕ . (6) lim ( , , ) 0k m a n k m β− =∑ ɶ , uniformly in n . ab hamis ganie / bibechana 9 (2013) 97-102 : bmhss, p.101 (online publication: nov., 2012) proof: sufficiency: suppose that the conditions (3), (4), (5) and (6) hold and r c x a∈ . then ax exists and at this stage , we observe with the help of (5 ) & (6) that ,0 sup ( , , ) k j m nj j a n j mβ = = < ∞∑ ∑ ɶ holds for every k .this gives that ( ) 1k lβ ∈ .since r c x a∈ by hypothesis and r c a c≅ ( see,[1] ) , we have y c∈ .therefore , we can easily see that ( ) 1k k y lβ ∈ for each y c∈ and also there exists 0k > such that sup k k y k< . now for 0ε > , choose a fixed 0 k ∈ℕ ,there is some 0 m ∈ℕ such that 0 0 ( , , ) 2 k k k k a n k m y ε β = − <∑ ɶ for every 0 m m≥ and 0 k ∈ℕ . also by (6) , there is some 1 m ∈ℕ , such that 0 1 ( , , ) 2 k k k a n k m ε β ∞ = + − <∑ ɶ for every 1 m m≥ uniformly in n .thus , we have ( ) 0 1 ( , , ) 1 m k k k kn j j k k ax y a n k m y m β β + = − = − + ∑ ∑ ∑ ɶ 0 00 1 ( , , ) ( , , ) k k k k k k k k a n k m y a n k m yβ β ∞ = = + ≤ − + −∑ ∑ɶ ɶ 0 1 ( , , ) 2 k k k k a n k m y ε β ∞ = + < + −∑ ɶ 2 2 k k ε ε ε< + = for all sufficiently large m ,uniformly in n . hence, ax f∈ , which proves sufficiency. necessity: suppose that ( : )r c a a f∈ . then , since f f∞⊂ ( by lemma 2.2 ), the necessities of (3) and (4) are immediately obtained from theorem 2.1 . to prove the necessity of (5), consider the sequence ( )( ) ( )( ) ( )k k n b r b r= for every k∈ℕ , where ( ) 1 ( 1) , 1 ( ) 1 0 , 0 1 n k k k n k k n k b r r n k or n k − + − ≤ ≤ + = +  ≤ < > + since ax exists and is in f for each r c x a∈ , one can easily see that ab hamis ganie / bibechana 9 (2013) 97-102 : bmhss, p.102 (online publication: nov., 2012) ( ) ( ) ( 1) 1 k nk k n a ab r k f r ∈    = ∆ + ∈  +   ℕ for all k∈ℕ ,which proves the necessity of (6). similarly taking r c x e a= ∈ , we shall get ( 1) 1 nk k k n a ax k f r ∈    = ∆ + ∈  +   ∑ ℕ ,which proves the necessity of (5).this concludes the proof. note that if we replace f by 0 f , then theorem 2.2 is reduced to the following corollary: corollary: 0 ( : )r c a a f∈ if and only if (3) ,(4), (5) and (6) holds with 0 k β = for each k∈ℕ . references [1] c. aydinand f. başar, on the new sequence space of which include the spaces 0 c and c , hokkaido math. j., 33(2) (2004) 83-398. [2] s. banach, theỏries des operations linẻaries, warszawa, (1932). [3] c. g. lascarides and i. j. maddox, matrix transformations between some classes of sequences, proc. camb. phil. soc., 68 (1970) 99-104. [4] g. g. lorentz, a contribution to the theory of divergent series, acta math., 80(1948)167-190. [5] mursaleen, infinite matrices and almost convergent sequences, southeast asian bulletin of math. 19(1995) 45-48. [6] s. nanda, matrix transformations and almost boundedness, glasnik mat., 14(1979) 99-107. [7] n. a. sheikh, and a. h. ganie,on the λ-convergent sequence and almost convergence ( to be appeared in thai j. of math, vol.3 (2012). microsoft word bhawani datta _38-49_.doc bhawani datt joshi et al. / bibechana 9 (2013) 38-49 : bmhss, p.38 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana structure, mesp and homo-lumo study of 10-acetyl10h-phenothiazine 5-oxide using vibrational spectroscopy and quantum chemical methods bhawani datt joshi 1,2* , poonam tandon 1 , sudha jain 3 1department of physics, university of lucknow, lucknow-226007, up, india 2department of physics, siddhanath sc. campus, mahendranagar, tribhuvan university, nepal 3department of chemistry, university of lucknow, lucknow-226007, up, india *corresponding author: e-mail: bdjoshi_007@yahoo.com article history: received 5 october, 2012; accepted 7 november, 2012 abstract in this communication, we have presented the geometry optimization, complete vibrational study with potential energy distribution (ped) and frontier orbital energy gap for the 10-acetyl-10h-phenothiazine 5-oxide (aptz) molecule using ab initio hartree-fock (hf) and density functional theory (dft/b3lyp) method employing 6-311++g(d,p) basis set. the calculated ir and raman spectra with their intensities, molecular electrostatic potential (mesp) surface and highest occupied molecular orbital (homo) lowest unoccupied molecular orbital (lumo) plot have been given. keywords: aptz; ab initio; dft; ir; raman; mesp; homo lumo. 1. introduction phenothiazines, the heterocyclic organic compounds in which sulphur and nitrogen are incorporated in the tricyclic system, exhibit a wide range of pharmacological / biological activities [1-10]. their several derivatives have been found to possess clinical activities, such as: tranquilizers, antihistamines, diuretics, analgesics, neurolepitcs, anticancer activity [5,6] in vitro (cancer cell lines), antileukemic [5] antimutagenic [2], antitrypanosomal, antileishmanial [3], and inhibition of the growth of autoimmune deficiency syndrome (aids)-related lymphoma cells [4]. properties of 10-h-phenothiazine, such as: semiconductivity [11], electrical conductivities [12] and low thermal activation energies of charge transfer complexes [13], has opened new practical fields of investigation. alconea palafox et al. [14] had given a complete vibrational analysis of the fourier transform (ft) infrared (ir) and ft-raman spectra of both phenothiazine (ptz) and n-methylphenothiazine molecules using ab initio method as well as quantum chemical calculations. sharma et al. [15] found the better biological activity of 4-thiazolidinone derivatives of phenothiazine. dixit et al. [2] had synthesized some 10h-phenothiazine sulphone derivatives and characterized them with selected bands of ir and 1h nmr spectroscopic methods. bhawani datt joshi et al. / bibechana 9 (2013) 38-49: bmhss, p.39 (online publication: nov., 2012) fig. 1: optimized structure of aptz molecule. literature survey reveals that neither the vibrational assignments nor the highest molecular orbital (homo) lowest unoccupied molecular orbital (lumo) study of aptz derivative of phenothiazine has been studied so far. thus, a complete vibrational study along with molecular electrostatic potential (mesp) surface and homo lumo analysis has been carried in the present study using ab initio hartree-fock (hf) and density functional theory (dft) method. the vibrational spectroscopy, that deals the short range structure studies, has very keen applications in these days for the structure characterization of biologically active materials [16]. homo lumo analysis has been performed which helps elucidate charge transfer occurring in the molecule. 2. methodology computational geometry optimization, an important issue in molecular mechanics, was performed as the first task of the computational work for the aptz molecule taking the parameters from the x-ray diffraction data [17]. the optimized ground state molecular structure is shown in fig. 1. the molecular structure, vibrational frequencies and energy of the optimized geometry of aptz were computed employing the dft [18] and hf methods using gaussian 09 [19] program package employing 6-311++g(d,p) basis set based on becke’s three parameters (local, non-local and hartree-fock) hybrid exchange functional with lee-yangparr correlation functional (b3lyp) [20,21]. the basis set 6-311++g(d,p) augmented by ‘d’ polarization functions on heavy atoms and ‘p’ polarization functions on hydrogen atoms as well as diffuse functions for both hydrogen and heavy atoms were used [22,23]. the absolute raman intensities and ir absorption intensities were calculated in the harmonic approximation at the same level of theory as used for the optimized geometries associated with each normal mode, respectively. the normal mode analysis was performed and the ped was calculated along the internal coordinates using localized symmetry. for this purpose, a complete set of 84 internal coordinates were defined using pulay’s recommendations [24,25]. the vibrational assignments of the normal modes were made on the basis of the ped calculated by using the program gar2ped [26]. raman and ir spectra were simulated using a pure lorentzian band profile (fwhm = 8 cm-1) using indigenously developed software. visualization and confirmation of calculated data were done by using the chemcraft program [27]. bhawani datt joshi et al. / bibechana 9 (2013) 38-49: bmhss, p.40 (online publication: nov., 2012) 3. results and discussion 3.1. geometry optimization initial geometry taken from x-ray diffraction data [17] of aptz was minimized without any constraint to the potential energy surface and the optimized structural parameters were used in the vibrational frequency calculation to characterize all stationary points as minima. the molecular conformation from the crystalline structure, as well as yielded by geometry optimization, exhibits no special symmetries. hence, aptz molecule crystallizes in the monoclinic, p21/n form having lattice parameters a = 8.1244 (1) å, b = 14.1787 (2) å, c = 10.7576 (1) å, β = 100.963 (1)o and z = 4 in a unit cell [17]. the sulphoxide fig. 2: comparison of the experimental (from single crystal x-ray diffraction) and optimized structure (purple) of aptz (hydrogen atoms are excluded for clarity). oxygen atom is disordered over two sites with occupancies of 0.886 (4) and 0.114 (4), reflecting a partial inversion of the lone pair at the tetrahedral s-atom site. the optimized structure produced is very similar to the experimental one. both the optimized and experimental structures of the title molecule were compared by superimposing them using a least-squares algorithm that minimizes the distances between the corresponding non-hydrogen atoms as shown in fig. 2. 3.2. molecular electrostatic potential surface in this study, the electrostatic potential (esp), electron density (ed) and molecular electrostatic potential (mesp) maps for aptz are as shown in fig. 3. in esp, the negative potential is localized near the oxygen atoms and reflects by the yellowish blobs, while the positive potential is localized on the rest surface. however, the ed plot of the title molecule shows uniform distribution. the molecular electrostatic potential (mesp), the force acting on a positive test charge located at point through the electrical charge cloud generated through the net charge of molecule (electrons and nuclei), has been a widely used entity in the chemical literature, generally employed as a tool for probing electron rich regions [28-31]. the mesp at a point ‘r’ in a molecular framework with nuclear charges za located at ra and electron density ρ(r) is given by a relation: bhawani datt joshi et al./ bibechana 9 (2013) 38-49: bmhss, p.41 (online publication: nov., 2012) where n is the total number of nuclei in the molecule. the first term on the right hand side of the above equation represent the contribution due to nucleus and second due to electrons, respectively. when the latter contribution overrides the former one, the net mesp attains a negative value, providing information about electron-rich sites. fig. 3: (a) esp (b) electron density (c) molecular electrostatic potential mapped on the isodensity surface in the range -6.521x10-2 (red) to +6.521x10-2 (blue) for aptz. mesp correlates the total charge distribution with dipole moment, electronegativity, and partial charges and site of chemical reactivity of a molecule. the projection of molecular mesp of aptz along the molecular plane is given in fig. 3c. it provides a visual method to understand the relative polarity of a molecule and serves as a useful quantity to explain hydrogen bonding, reactivity and structure-activity relationship of molecules including biomolecules and drugs. it is the potential energy of a proton at a particular location near a molecule. different values of the electrostatic potential at the surface of a molecule appear with the different colours. in general the attractive (or negative) potential appears in red coloured regions and those of repulsive (or positive) potential appear in blue. in the title molecule the regions near oxygen atoms are most attractive and the regions near hydrogen of methyl group are positive. 3.3. homo-lumo analysis the homo is the outermost (highest energy) orbital containing electrons that could act as an electron donor. the lumo is the innermost (lowest energy) orbital that has room to accept electrons and can act as the electron acceptor. according to the frontier molecular orbital theory, the formation of a transition state is due to an interaction between the frontier orbitals (homo and lumo) of reactants [32]. the energy of the homo is directly related to the ionization potential and the energy of the lumo is directly related to the electron affinity. high value of homo energy is likely to indicate a tendency of the molecule to donate electrons to appropriate acceptor molecule of low empty molecular orbital energy. the lower values of lumo energy show more probability to accept electrons. so, the gap energy, i.e. the bhawani datt joshi et al. / bibechana 9 (2013) 38-49: bmhss, p.42 (online publication: nov., 2012) difference in energy between the homo and lumo, is an important stability index. it is a critical parameter in determining molecular electrical transport properties because it is a measure of electron conductivity. low gap value refers to the higher electronic transition and vice versa. the homo lumo plot with the frontier orbital energy gap for the title molecule is shown in fig. 4. fig. 4: homo-lumo plot of aptz molecule. in homo the main electronic transition is occurred at c=c bonds of all the rings, s atom of the rings r2 and carbonyl group (in small amounts), while in lumo the charge density is mainly accumulated at cc bond in rings. table 1. electronic transitions, absorption wavelength λmax (nm), excitation energy (ev), oscillator strengths (f), frontier orbital energies (ev) and dipole moment (debye) of aptz. calculated gas phase benzene solution excited states λmax (nm) transitions e(ev) oscillator strength (f) λmax (nm) transitions e(ev) oscillator strength (f) transition type/ assignments 1 278 h→l 4.4594 0.0549 280 h→l 4.4249 0.0838 π→π * 2 256 h-1→l 4.8445 0.0152 251 h→l+1 4.9486 0.0983 3 252 h→l+1 4.9107 0.0537 246 h-3→l 5.0408 0.0271 4 244 h→l+2 5.0754 0.0283 244 h→l+2 5.0852 0.0489 π→π * 5 236 h-3→l 5.2463 0.0081 235 h-5→l 5.2858 0.0160 6 231 h-5→l 5.3783 0.0091 225 h→l+3 5.4995 0.0215 7 226 h-7→l 5.4730 0.0122 222 h→l+4 5.5930 0.0434 8 221 h-1→l+2 5.154 0.0152 221 h6→l 5.6169 0.0224 ehomo (ev) elumo (ev) ∆e (ev) µ(d) gas -6.9067143 -1.7289234 5.1777909 6.1429 benzene -6.8639946 -1.7066112 5.1573834 7.0474 homo = 71, lumo = 72 bhawani datt joshi et al. / bibechana 9 (2013) 38-49. : bmhss, p.43 (online publication: nov., 2012) the calculated frontier orbital energies, absorption wavelengths (λmax), oscillator strengths (f), excitation energies (e) and dipole moments (µ) for gas phase and benzene solvent environment (integral equation formalism-polarizable continuum model, ief-pcm) using the td-dft/6-31g method are illustrated in table 1. this electronic absorption corresponds to the transition from the ground to the first excited state and is mainly described by one electron excitation from the homo to the lumo. the first alloweddipole transition in the gas phase was calculated about 278 nm with oscillator strength 0.0549. the next transitions were calculated about 252, 244 and 221 nm with oscillator strengths 0.0537, 0.0283 and 0.0152, respectively. the transitions π→π* are the main observed transitions. 3.4. vibrational assignment an aptz molecule has 30 atoms and hence gives 84 (3n-6) fundamental modes of vibration. all of them are both the raman and ir active. since the vibrational wavenumbers calculated by dft methods are higher than their precise values, so they were scaled down by the wavenumber linear scaling procedure (wls) [νobs/νcal = (1.0087 – 0.0000163 x νcal) cm-1] of yoshida et al. [33]. however, there are different scaling factors, but the vibrational wavenumbers calculated uniformly scaled with only one scaling factor [34,35] are often in good agreement to the observed ones. the raman scattering cross sections, ∂σj/∂ω, which are proportional to the raman intensities, may be calculated from the raman scattering amplitude and predicted wavenumbers for each normal modes using the relationship [36,37] j jj j j s c h kt hc                              − −       −       = ω∂ ∂ νπν νν πσ 2 4 044 8 exp1 45 2 where sj and υj are the calculated scattering activities and the predicted wavenumbers, respectively, of the jth normal mode, υo is the raman excitation wavenumber and h, c and k are the universal constants. assignments have been made on the basis of relative intensities, energies, line shape and potential energy distribution. all the vibrational bands have been assigned satisfactorily, together with the ir and the raman intensities. the assigned wavenumbers of the vibrational modes calculated at the hf and b3lyp level with the basis set 6-311++g(d,p) along with their ped are given in table 2. in the aptz molecule, there are three rings with different functional groups as shown in fig. 1. the vibrational assignments of these rings along with some functional groups have been discussed separately. the calculated ir and raman spectra are given in the figs. 5 and 6, respectively. 3.4.1. ch3 vibrations the title molecule has one methyl group associated with different types of vibrations: like symmetric and asymmetric stretching, deformations and rocking as listed in table 2. asymmetric stretching of ch3 is at 3039/3017 cm-1 in scaled dft having intensities of 5.43/3.53 a.u in the ir and 258.68/292.55 a.u in the raman spectra, respectively. the symmetric stretching is calculated at 2927 cm-1 (contribution 100%). this band is weak in ir band with intensity of 2.81 a.u. and strong intensity of 824.08 a.u. in the raman spectra. the asymmetric bending modes of this group are calculated at 1461 and 1447 cm-1, while the symmetric bending mode is calculated around 1380 cm-1. the rocking vibration is calculated at 1043 and 1017 cm-1 in the scaled dft, which is weaker in intensity in the ir spectrum in comparison to that in the raman spectrum. bhawani datt joshi et al. / bibechana 9 (2013) 38-49: bmhss, p.44 (online publication: nov., 2012) table 2. calculated wavenumbers (in cm -1 ), ir and raman intensities (in a.u.). unscaled scaled intensity dft hf dft ir raman peda (%) 3232 3228 3090 0.31 382.37 r1[υ(ch)](97) 3203 3213 3063 6.21 1517.81 r3[ υ(ch)](96) 3202 3212 3063 8.53 585.95 r1[υ(ch)](95) 3198 3205 3059 2.15 174.26 r3[υ(ch)](98) 3190 3197 3052 6.43 696.38 r1[υ(ch)](98) 3189 3196 3051 5.87 487.54 r3[υ(ch)](99) 3176 3182 3040 3.5 309.77 r1[υ(ch)](99) 3176 3181 3039 1.74 271.13 r3[υ(ch)](99) 3151 3152 3017 5.43 258.68 υa(ch3)(99) 3120 3123 2988 3.53 292.55 υa(ch3)(100) 3052 3061 2927 2.81 824.08 υs(ch3)(100) 1760 1906 1725 321.27 503.6 [υ(c=o)](78)+ρ[c=o](7)+[υ(cc)](5) 1636 1750 1607 18.47 370.17 r3[υ(cc)(32)+δin(ch)(6)]+r1[υ(cc)(22)+δa(5)] 1624 1742 1595 32.61 1411.67 r1[υ(cc)(35)+δin(ch)(11)+δa(6)]+r3[υ(cc)](27) 1619 1733 1591 13.48 527.92 r1[υ(cc)(35)+δ’a(5)]+r3[υ(cc)](27)+r2[υ(cc)]7) 1609 1719 1581 2.36 178.71 r1[υ(cc)](31)+r3[υ(cc)(27)+δin(ch)](8)]+r2[υ(cc)](9) 1507 1610 1483 52.39 7.75 r1[δin(ch)(25)+υ(cc)](11)]+r3[δin(ch)](24)+υ(cc)](6)+r2[υ(cc)] (8) 1492 1595 1468 90.55 105.5 r1[δin(ch)(25)+υ(cc)(19)]+r3[δin(ch)](20)+r2[υ(cc)(8)+υ(cn)(8 )] 1484 1578 1461 18.95 202.89 [δa(60)+δ’a(22)+ρ’(6)](ch3) 1481 1574 1458 13.74 21.16 r3[δin(ch)(33)+υ(cc)(21)]+r1[δin(ch)](14)+r2[δtrig](7) 1476 1572 1454 5.69 26.18 r1[δin(ch)(38)+υ(cc)(22)]+r3[δin(ch)](11)+υ(cc)(8)] 1469 1559 1447 7.43 128.29 [δ’a(61)+δa(19)+ρ(9)](ch3) 1399 1509 1380 40.71 79.17 δs[ch3](88)+[υ(cc)](7) 1340 1427 1323 12.27 376.6 r1[υ(cc)](49)+r3[υ(cc)](26)+r2[υ(cc)]6) 1332 1405 1315 62.21 319.78 r2[υ(cn)(26)+δin(nc21)(6)]+r3[υ(cc)(24)+δin(ch)(7)] 1326 1396 1309 10.69 307.35 r1[υ(cc)(36)+δin(ch)(8)]+r3[υ(cc)(25)+δin(ch)(9)]+r2[υ(cc)](9) 1309 1369 1293 61.86 190.42 r1[δin(ch)](25)+υ(nc21)(11)]+r3[δin(ch)(22)+υ(cc)(5)]+r2[δtrig]( 13) 1272 1345 1257 277.81 400.6 r2[υa(so2)](85) 1257 1308 1243 97.12 1261.13 r2[υ(nc21)(16)+δin(ch)(18)+υ(cc)(8)+υ(cn)(22)] 1256 1300 1241 134.26 625.29 r3[δin(ch)](26)+υ(cc)(11)]+r2[υ(cn)](17)+r1[υ(nc21)](13) 1213 1294 1200 64.05 1000.42 r2[υ(cn)(15)+υ(cc)(12)+δin(ch)(11)+υ(nc21)(7)+δtrig(6)]+[υ(cc)] (11)+δ[c=o](9)+[ρ[ch3](5) 1187 1251 1174 0.46 62.57 r1[δin(ch)(55)+υ(cc)(9)]+r3[δin(ch)(19)+δin(ch)(9)] 1186 1233 1173 0.71 356.79 r3[δin(ch)(54)+υ(cc)(10)]+r1[δin(ch)](23) 1159 1213 1147 41.18 654.94 r1[δin(ch)(22)+υ(cc)(20)]+r3[δin(ch)(15)+υ(cc)(11)]+r2[υ(cs)]( 13) 1153 1188 1142 3.5 123.02 r3[δin(ch)(23)+υ(cc)(21)]+r1[υ(cc)(15)+δin(ch)(15)]+r2[υ(cs)](10) 1124 1185 1113 123.48 1162.02 r2[υs(so2)(32)+υ(cs)(12)]+r1[δtrig](9)+r3[δtrig](9) 1083 1159 1073 26.3 29.9 r3[δtrig(18)+δin(ch)(8)+υ(cc)(7)]+r1[δtrig(19)+υ(cc)(6)]+r2[υ(cs)](1 3) 1058 1149 1049 37.24 1602.59 r1[υ(cc)](22)+δin(ch)(8)+[ρ’(13)+ρ(8)](ch3)+r2[υs(so2)](14)+ω[ c=o](5)+[r3[υ(cc)(5)+δtrig(5)] 1057 1144 1048 0.46 248.47 r3[υ(cc)(37) +δin(ch)(10)+δtrig(7)] +r1[υ(cc)(21)+δtrig(9)] bhawani datt joshi et al. / bibechana 9 (2013) 38-49: bmhss, p.45 (online publication: nov., 2012) 1052 1115 1043 0.59 839.1 [ρ’(43)+ρ(7)+δa(5)](ch3)+ω[c=o](12)+r1[υ(cc)](6) 1048 1113 1039 42.63 1154.47 r2[υs(so2)](31)+r3[δtrig(10)+υ(cc)(8)]+r1[δtrig(17)+υ(cc)(8)] 1026 1107 1017 32.89 197.49 [ρ(38)+ρ’(10)](ch3)+r1[δtrig(11)+υ(nc21)(7)]+ρ[c=o](5)+[υ(cc)]( 5)+δ’a[ch3](5) 1003 1106 996 0.05 6.51 r3[oop(ch)(81)+puck(12)] 1002 1103 994 0.09 6.74 r1[oop(ch)(83)+puck(11)] 991 1078 984 2.79 197.74 r3[δtrig](25)+r1[oop(ch)(12)]+r2[δtrig(6)+δin(nc21)(6)]+[υ(cc)](8) +ρ[c=o](6) 974 1076 967 0.87 13.73 r3[oop(ch)(88)+τ’(5)] 970 1057 963 0.85 43.24 r1[oop)ch)(84)+τ’(5)] 907 988 902 7.46 106.16 [υ(cc)](20)+r1[δtrig(15)+υ(cc)](7)+r3[oop(ch)](7)+r2[υ(cn)](6)+ ρ[ch3](5) 888 978 883 0.14 24.54 r3[oop(ch)(81)+puck(5)] 883 960 878 0.43 45.94 r1[oop(ch)(85)+puck(7)] 780 856 777 65.95 18.38 r3[oop(ch)(53)+puck(7)]+r1[oop(ch)](16)+r2[puck](6) 772 848 769 7.95 8.61 r1[oop(ch)](61)+r3[oop(ch)](22) 760 838 757 13.83 205.58 r3[puck(39)+oop(ch)(8)]+r1[puck](17)+r2[puck](17) 744 812 741 29.41 38.51 r1[puck(25)+oop(ch)(7)]+r3[δa(14)+puck(10)]+r2[υ(cs)]7) 740 808 737 2.75 49.1 r1[δa(16)+δ’a(5)+puck(12)+r3[δa(11)+δ’a(5)+puck(7)]+r2[υ(cs)(7) +υ(nc21)(5)] 732 795 730 41.02 52.37 r1[puck(24)+δ’a(6)]+r3[puck](21)+r2[ω(so2)(8)+υ(cs)(10)+τ(6)] 680 734 678 0.96 1560.6 r1[δ’a(24)+δa(5)]+r3[δ’a(17)+δa(10)+puck(5)]+r2[υ(cs)](8) 650 696 649 6.25 59.28 r3[δ’a](39)+r1[δa(15)+δ’a(8)]+ρ[c=o](7)+[υ(cc)](6) 618 667 618 24.55 111.18 [ω(29)+δ(10)](c=o)+r2[δtrig(11)+oop(nc21)(10)]+ρ[ch3](6)+r1[δa] (6) 592 646 591 26.66 239.37 [ω(13)+δ(9)](c=o)+r1[puck(12)+τ(7)]+r2[oop(nc21)(5)+puck(5)]+ ρ’[ch3](6) 581 638 581 45.4 58.91 r2[ω(so2)](27)+r3[puck(16)+τ(10)+δa(6)]+r1[δ’a](9) 561 630 561 53.14 590.6 r2[δ(so2)(26)+δtrig(8)+δ’a(7)]+r1[τ’](5)+r3[τ](5)+τ(c11c12)(5) 555 606 555 13.39 309.64 r2[puck(16)+δtrig(7)+ρ(so2)(5)]+ω[c=o](16)+r3[τ](10)+r1[τ](7)+ρ ’[ch3](5) 516 567 516 11.61 34.39 r1[τ](29)+r3[τ](22)+r2[τ](15) 502 553 502 7.58 81.73 r3[τ’](18)+δ[c=o](14)+r2[ρ(so2)(12)+τ’(6)]+τ(c1c10)(9)+r1[τ’(7 )+δa(6)]+τ(c11c12)(5) 464 519 464 8.81 249 r2[δ(so2)(23)+oop(nc21)(9)+δtrig(8)+τ’(7)]+r3[τ](16)+τ(c1c10)(1 3)+δ[c=o] (5) 458 505 458 1.63 301.3 r1[τ’](30)+r3[τ’(10)+τ(10)]+τ(c11c12)(13)+τ(c1c10)(8)+r2[γ(so 2)](6) 411 442 412 10.79 887.25 ρ[c=o](28)+r3[τ’(11)+τ(6)+δ’a(8)]+r2[υ(cn)](10) 397 436 398 8.74 409.44 r2[δa(36)+δ’a(16)+υ(cs)(10)]+r1[τ’](9) 381 414 382 2.12 727.17 r1[τ’](15)+[ρ(14)+δ(6)](c=o)+r2[ρ(so2)(11)+τ’(7)+υ(cs)(5)]+r3[ τ](5) 353 387 354 1.29 2098.6 r3[τ’(18)+τ(6)]+r1[τ’](15)+r2[υ(cs)(6)+υ(cn)(5)] 319 356 320 1.12 867.18 r2[δ’a(29)+δa(13)+υ(nc21)(5)]+[δ(11)+ρ(5)](so2)+r3[τ’](9) 312 347 313 4.36 268.87 r2[(γ(15)+ω(5))(so2)+υ(cs)(11)+δin(nc21)(8)]+r1[τ’(11)+τ(9)]+r3 [τ’](6)+ρ[c=o](6) 280 306 281 1.99 197.05 r3[τ](19)+r1[τ](11)+r2[oop(nc21)(6)+(ρ(6)+δ(5)(so2))+υ(cs)(7)+ δtrig(5)]+τ(c1c10)(10)+τ(c11c12)(5 ) bhawani datt joshi et al. / bibechana 9 (2013) 38-49: bmhss, p.46 (online publication: nov., 2012) 242 274 243 4.75 1023.84 r2[(ω(20)+γ(18))(so2)+υ(cs)(16)+δa(11)]+r3[δa](5) 205 224 206 1.75 636.7 r2[γ(so2)(23)+δin(nc21)(18)]+r3[τ](15)+τ(c1c10)(14)+r1[τ](6) 193 214 194 0.26 784.79 r2[oop(nc21)(13)+ρ(so2)(10)+υ(cs)(10)+δtrig(5)+τ’(5)]+r1[τ](12)+ r3[δa](6) 150 168 151 2.18 3124.11 τ(c11c12)(28)+τ(c1c10)(25)+r2[γ(so2)(14)+δin(nc21)(8)]+r3[τ’]( 5) 128 147 129 0.12 6552.24 τ(c21c22)(26)+r2[puck(25)+ρ(so2)(5)]+τ(c11c12)(10)+τ(c1c10)( 8)+ρ’[ch3](6)+r3[τ](6) 115 131 116 0.2 5116.14 τ(c21c22)(29)+τ(c11c12)(22)+r2[puck(11)+r2τ’(7)]+ρ’[ch3](8) 97 114 98 0.94 1060.01 r2[τ](26)+r2[τ’(12)+δin(nc21)(7)]+τ(c11c12)(18)+τ(c21c22 )(10)+τ(c1c10)(7) 75 81 76 0.59 19405.86 r2[oop(nc21)(45)+τ’(5)]+τ(c1c10)(16)+τ(c21c22)(10)+τ(c11c12) (6) 71 76 71 4.07 1737.43 τ(c21c26)(63)+r2[δin(nc21)](5)+τ(c1c10)(5) 51 50 52 4.64 23135.09 r2[τ’](24)+oop(nc21)(14)+τ(5)]+τ(c21c26)(18)+τ(c21c22)(14) proposed assignments and potential energy distribution (ped) for vibrational normal modes. types of vibration: ν, stretching; δ, deformation (bending), scissoring; oop, out-of-plane bending; ω, wagging; γ, twisting; ρ, rocking; τ, torsion. apotential energy distribution (contribution ≥ 5). 3.4.2. c= o vibrations a carbonyl (c=o) group is connected at the nitrogen atom of ring r2. regarding to this group; stretching, bending, rocking and wagging modes of vibrations are observed. the stretching of c=o is calculated at 1725 cm-1 (contribution 78%). the deformation and wagging calculated at 618 and 591 cm-1 are the mixed modes. the rocking vibration is calculated at 412 cm-1 (contribution 28%) with the intensities of 10.79 a.u. in the ir spectrum and 887.25 a.u. in the raman spectrum, respectively. 3.4.3. ring r1 vibrations ring r1 has four ch moieties; hence one can expect four stretching modes associated to this group. all these modes are pure in the range 3090-3040 cm-1 and have very weak in intensity in the ir spectrum. the mixed in-plane deformations are calculated at 183, 1468, 1454, 1293, 1174 and 1147 cm-1. the outof-plane bending modes are calculated at 994, 963, 878 and 769 cm-1. fig. 5. theoretical ir spectra between the ranges 0-3100 cm-1. bhawani datt joshi et al. / bibechana 9 (2013) 38-49: bmhss, p.47 (online publication: nov., 2012) the c-c stretching is stronger in intensity in the raman spectrum than in the ir spectrum. these modes are calculated below 1595 cm-1. around 741/730 cm-1 and 737/678 cm-1 are the puckering and deformation of the ring, respectively. the ring torsion is calculated at 516, 458 and 382 cm-1 in the mixed modes. 3.4.4. ring r2 vibrations two important functional groups so2 and –coch3 are connected with this ring r2. the six fundamental modes of vibrations are assigned with so2 group; namely symmetric, asymmetric stretch, deformation and rocking, which belong to polarized in-plane vibrations. in addition to that, so2 wagging and twisting modes would be expected to be depolarized out-of-plane symmetry species. the so2 asymmetric stretching having contribution of 85% in ped is calculated at 1257 cm-1. the symmetric stretching is calculated at 1113/1029 cm-1, which have strong raman intensities of 1162.02/1154.47 units. the deformations are calculated at 561 and 464 cm-1. the wagging and twisting vibrations are calculated at 581/243 cm-1 and 313/206 cm-1, respectively. highly mixed rocking mode with low contribution in ped is calculated below 555 cm-1. cn stretching is calculated at 1315 and 1200 cm-1. nc21 stretching is calculated at 1243 cm-1, which has weak ir and strong raman intensities as listed in table 2. fig. 6. theoretical raman spectra between the ranges 20-3200 cm-1. 3.4.5. ring r3 vibrations ring r3 has also four ch moieties; hence four ch stretching modes are assigned between the range 3063-3039 cm-1. the cc stretching of the ring is calculated at 1607/1048 cm-1. the trigonal ring deformation is calculated at 1073 cm-1 with weak intensities both in the ir and the raman spectra. the ring puckering, asymmetric deformation and the ring torsion are calculated at 757, 649 and 502 cm-1, respectively. 4. conclusion the equilibrium geometries and harmonic vibrational wavenumbers of all the 84 normal modes of the aptz molecule were determined and analyzed both at dft (b3lyp) and hf levels of theory employing the 6-311++g(d,p) basis set. these theoretical vibrational assignments along with the electronic transitions are important to understand the molecular structure and biological activity of the title bhawani datt joshi et al. / bibechana 9 (2013): 38-49: bmhss, p.48 (online publication: nov., 2012) molecule. the ir and the raman spectra were presented, and the 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[37] p.l. polavarapu, j. phys. chem., 94 (1990) 8106. microsoft word j. bhattarai _69-74_.doc j. bhattarai / bibechana 9 (2013) 69-74: bmhss, p.69 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana the durability of mn–mo–sn–w–sb–o/ir1–x–ysnxsbyo2+0.5y /ti oxygen evolution anode for hydrogen production from seawater electrolysis jagadeesh bhattarai central department of chemistry, tribhuvan university, kathmandu, nepal. e-mail : bhattarai_05@yahoo.com article history: received 22 august, 2012; accepted 7 november, 2012 abstract new types of electrodeposited nanocrystalline mn–mo–sn–w–sb–o/ir1–x–ysnxsbyo2+0.5y/ti anode is successfully tailored for hydrogen production from seawater electrolysis. simultaneous additions of tungsten and antimony in an electrodeposited mn–mo–sn–w–sb–o/ir1–x–ysnxsbyo2+0.5y/ti anode are found to be more effective for better durability than that of the electrodeposited mn–mo–sn–o/ir1–x– ysnxsbyo2+0.5y/ti anode for long period seawater electrolysis. the examined mn–mo–sn–w–sb–o/ir1–x– ysnxsbyo2+0.5y/ti anode showed nearly 100% oxygen evolution efficiency at the current density of 1000 a.m -2 in 0.5 m nacl solution of ph 1 at 25°c and it is guaranteed the stable anode performance with 99.7–99.8% oxygen evolution efficiency for more than five months in seawater electrolysis for hydrogen production. keywords: global warming; co2 recycling; electrodeposition; hydrogen production; seawater electrolysis 1. introduction koji hashimoto and his research groups of japan have been proposed global co2 recycling project to prevent global warming and to supply abundant energy converted from solar energy for last twenty years [1–10] considering the facts that a continuous increase in primary energy consumption results in continuous increase in co2 emissions [11,12] and such a huge co2 emissions resulting from complete exhaustion of fossil fuel reserves will induce intolerable global warming. key materials necessary for the global co2 recycling project are anode and cathode for seawater electrolysis, and catalyst for co2 conversion into ch4 from the reaction between co2 and h2. in general, for large–scale seawater electrolysis to produce hydrogen at cathode for the co2 recycle project, environmentally harmful chlorine release is not allowed. therefore, oxygen production is prerequisite without forming environmentally harmful chlorine for safety production of hydrogen from seawater electrolysis. one of the most difficult subjects in tailoring key materials for the global co2 recycling project was the development of stable and more efficient anodes for seawater electrolysis, because for ch4 production a large quantity of chlorine emissions are not allow and hence the anode should evolve only oxygen with very high efficiency and durability even in seawater electrolysis at very high current density of 1000 a.m -2 . varieties anodes composed of γ–mno2 type double, triple or quadrate oxides were prepared by anodic deposition on the ir1–x–ysnxsbyo2+0.5y/ti electrode and these anodes showed about 99.50−99.85% oxygen j. bhattarai / bibechana 9 (2013) 69-74 : bmhss, p.70 (online publication: nov., 2012) evolution efficiency (oee) after electrolysis for about 4200 h in 0.5 m nacl solution of ph 1 at current density of 1000 a.m -2 [13–22]. the intermediate ir1–x–ysnxsbyo2+0.5y layer was prepared using the mixture of coating solutions (butanolic) containing 0.024 m ir 4+ , 0.0676 m sn 4+ and 0.0084 m sb 5+ on titanium substrate in which the sum of the metallic cations in the intermediate oxide layer was kept at 0.1 m as described elsewhere [13,14,16]. it has been reported that γ–mno2 type mn–mo–sn–o/ir1–x– ysnxsbyo2+y/ti anode showed about 99.6% oxygen evolution efficiency (oee) after electrolysis for about 4200 h in 0.5 m nacl solution of ph 1 at 1000 a.m –2 [16,17]. in this context, present work is aimed to develop a more stable, efficient and nanocrystalline mn–mo–sn–w–sb–o/ir1–x–ysnxsbyo2+y/ti oxygen evolution anode for hydrogen production from seawater electrolysis. 2. materials and experimental methods punched titanium metal substrate was treated in 0.5 m hf solution to remove air–formed oxide film, rinsed with de–ionized water and then subjected for surface roughening by etching in 11.5 m h2so4 solution at 80°c. the treated–titanium metal was used as a substrate for coating of the intermediate ir1–x– ysnxsbyo2+0.5y layer. it is noteworthy to mention here that iridium, tin and antimony oxides on the titanium substrate were identified as iro2, sno2 and sb2o5, respectively, from xps analysis [13]. the intermediate ir1–x–ysnxsbyo2+0.5y layer, coated on the titanium is called as ir1–x–ysnxsbyo2+0.5y/ti electrode, was degreased by anodic polarization at 1000 a.m –2 for 5 minutes in 10 m naoh solution and then electro−analytically rinsed at 1000 a.m –2 for 5 minutes in 1 m h2so4 solution. the mn–mo–sn–w– sb–o electrocatalyst for oxygen evolution was anodically deposited on the clean and activated ir1–x– ysnxsbyo2+0.5y/ti electrode at 600 a.m –2 in 0.2 m mnso4.5h2o + 0.003 m na2moo4.2h2o + 0.006 m sncl.5h2o + 0.0045 m na2wo4.2h2o + 0.003 m sbcl5 solutions at ph –0.1 and 90°c for 90 minutes. the electrodeposition of the mn–mo–sn–w–sb–o electrocatalysts was carried out by exchanging electrolyte for every 30 minutes. the performance of the electrodeposited mn–mo–sn–w–sb–o}/ir1–x– ysnxsbyo2+0.5y/ti anode was examined by oxygen evolution and galvanostatic polarization measurements. the oxygen evolution efficiency of the electrodeposited anode was measured by electrolysis at a constant current density of 1000 a.m -2 in 0.5 m nacl solution of ph 1 until the amount of charges of 300 coulombs was passed. the amount of oxygen evolved was determined as the difference between the total charge passed and the charge for chlorine formation during electrolysis as described elsewhere [13,14]. the amount of chlorine formed was analyzed by iodimetric titration of chlorine and hypochlorite. galvanostatic polarization measurement of the electrodeposited mn–mo–sn–x(x=w & sb)–o electrocatalysts on the ir1–x–ysnxsbyo2+0.5y/ti electrode was carried out in 0.5 m nacl solution of ph 1 at room temperature. the ohmic drop was corrected using a current interruption method. the potential written in this paper hereafter is the overpotential and relative to ag/agcl reference electrode with saturated kcl solution. the surface morphology and structure of the anodically deposited mn–mo–sn– w–sb−o/ir1–x–ysnxsbyo2+0.5y/ti anode were observed using confocal scanning laser microscopy (cslm) and x–ray diffraction (xrd) patterns, respectively. 3. results and discussion figure 1 shows the result of the durability of the mn–mo–sn–w−sb–o/ir1–x–ysnxsbyo2+0.5y/ti anode in 0.5 m nacl solution of ph 1 at 25°c. the durability result of the mn–mo–sn–o/ir1–x–ysnxsbyo2+0.5y/ti anode is also shown for comparison. the mn–mo–sn–w–sb–o/ir1–x–ysnxsbyo2+0.5y/ti anode shows about 99.7 to 99.8% oxygen evolution efficiency after electrolysis for about 500−3650 h in 0.5 m nacl of ph 1 at 25°c, which is slightly higher oee than that of the mn–mo–sn–o/ir1–x–ysnxsbyo2+0.5y/ti anode, although initial oxygen evolution efficiency of it was about 99.0% only. consequently, the simultaneous additions of tungsten and antimony are more effective for better durability of the electrodeposited mn– j. bhattarai / bibechana 9 (2013) 69-74: bmhss, p.71 (online publication: nov., 2012) mo–sn–w−sb–o/ir1–x–ysnxsbyo2+0.5y/ti anode than that of the mn–mo–sn–o/ir1–x–ysnxsbyo2+0.5y/ti anode for long period electrolysis of seawater for hydrogen production. fig.1: changes in the oxygen evolution efficiency of the mn–mo–sn–w–sb–o/ir1–x–ysnxsbyo2+0.5y/ti and mn– mo–sn–o/ir1–x–ysnxsbyo2+0.5y/ti anodes in 0.5 m nacl of ph 1 at the current density of 1000 a.m -2 , as a function of electrolysis time. figure 2 shows ir−corrected galvanostatic polarization curves measured in 0.5 m nacl solution of ph 1 at 25°c for the anodically deposited {mn–mo–sn–w−sb–o, mn–mo–sn or mn–o}/ir1–x– ysnxsbyo2+0.5y/ti anodes to study the effects of tungsten and antimony oxides in the anodes. all the examined double, triple or more oxide electrocatalysts deposited on the ir1–x–ysnxsbyo2+0.5y /ti electrode showed almost same and lower oxygen overpotential (i.e., about 1.6 v vs ag/agcl) than that of mn–o/ ir1–x–ysnxsbyo2+0.5y /ti anode in 0.5 m nacl of ph 1 at 1000 a.m -2 . it is noteworthy for mentioning here that the observed oxygen overpotential value of 1.60 v vs ag/agcl at 1000 a.m -2 in the present study is almost same as that was reported for the anodically deposited mn–mo–x(x=w,sn)–o/iro2/ti anodes [3– 11]. however, the amount of iridium content in the ir1–x–ysnxsbyo2+0.5y /ti electrode is only about 1/22 of the iro2/ti electrode. these results revealed that the simultaneous additions of molybdenum, tin, tungsten and antimony in the mn–based oxide electrocatalyst are more effective for high electronic conductivity of the mno2/ ir1–x–ysnxsbyo2+0.5y /ti anode. j. bhattarai / bibechana 9 (2013) 69-74: bmhss, p.72 (online publication: nov., 2012) fig.2: galvanostatic polarization curves for {mn–o,mn–mo–sn–o and mn–mo–sn–w–sb–o}/ir ir1–x– ysnxsbyo2+0.5y /ti anodes after electrolysis in 0.5 m nacl. figure 3 shows the changes of the surface morphology of the electrodeposited mn–mo–sn–w−sb–o/ ir1–x–ysnxsbyo2+0.5y /ti anode before and after electrolysis for 1545 h in 0.5 m nacl solution of ph 1 at 1000 a.m −2 . numbers of cracks and pores on the surface of anode are decreased to form a smooth surface after electrolysis for about 1545 h. this revealed that the filling of cracks and pores by the beneficial ions (e.g., mn 2+ , mo 6+ , sn 4+ , w 6+ or sb 5+ ) in the electrocatalyst was clearly observed after electrolysis for about one week or more time. in accordance of the changes in the surface morphology, the durability of the oxygen evolution efficiency of the mn–mo–sn–w−sb–o/ ir1–x–ysnxsbyo2+0.5y /ti anode increased with increasing the electrolysis times and became steady state after electrolysis for about 500 hours as shown in fig. 1 above. it is meaningful to mention here that there is no separate peaks for manganese, molybdenum, tin, tungsten and antimony oxides on the anodically deposited mn–mo–sn–w–sb–o/ ir1–x–ysnxsbyo2+0.5y /ti anode and was shown only the reflections of γ–mno2 from the analysis of the x−ray diffraction patterns of the anode which is not presented here. furthermore, the apparent grain size of the anodically deposited mn– mo–sn–w–sb–o/ir ir1–x–ysnxsbyo2+0.5y /ti anode was estimated from full width at half maximum (fwhm) of the most intense xrd reflection using scherrer’s equation [23] and the apparent grain size of the anode was found about 8 nm. these results revealed that the anodically deposited mn–mo–sn– j. bhattarai / bibechana 9 (2013) 69-74: bmhss, p.73 (online publication: nov., 2012) w−sb–o/ ir1–x–ysnxsbyo2+0.5y /ti anode consisted of a nanocrystalline γ–mno2–type oxides consisting of mn 2+ , mo 6+ , sn 4+ , w 6+ and sb 5+ ions. fig.3: changes in the surface morphology of the mn–mo–sn–w–sb–o/ir ir1–x–ysnxsbyo2+0.5y /ti anode (a) before and (b) after electrolysis for 1545 h in 0.5 m nacl solution of ph 1 at the current density of 1000 a.m -2. 4. conclusion the ir1–x–ysnxsbyo2+0.5y /ti supported γ–mno2 type nanocrystalline mn–mo–sn–w–sb–o/ ir1–x– ysnxsbyo2+0.5y /ti anode guaranteed the stable anode performance showing 99.7–99.8 % oxygen evolution efficiency from seawater electrolysis for more than five months to produce hydrogen gas necessary for the prototype co2 recycling project. acknowledgements the author would like to express his sincere gratitude to emeritus professor koji hashimoto and dr. zenta kato of tohoku institute of technology, sendai, japan for providing the research facilities of xrd and an opportunity to visit tohoku institute of technology, japan as a visiting research fellow. author is very thankful to dr. himendra jha of hokkaido university, japan for taking cslm images. j. bhattarai / bibechana 9 (2013) 69-74: bmhss, p.74 (online publication: nov., 2012) references [1] k. hashimoto, mater. sci. eng. a, 179/a180 (1994) 27. 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[23] b. d. cullity, elements of x–ray diffraction, 2 nd edition, addison−wesley publ. co, inc., (1977) 101. microsoft word harihar paudyal.doc harihar paudyal / bibechana 7 (2011) 76-82: bmhss 76 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana anomalous seismic activity associated with 1988 udayapur earthquake harihar paudyal∗∗∗∗ dept. of physics, birendra multiple campus, (tribhuvan university) bharatpur, chitwan, nepal article history: accepted 5 december 2010 abstract the udayapur earthquake of august 20, 1988 (mb 6.4, ms 6.6, origin time: 23:09:10, epicenter at 26.8 o n 86.6 o e and focal depth 57 km) occurred in the himalayan front arc which caused severe damage in the region will loss of 1100 lives. in the same epicentral region, a strong event of mb 5.4 has occurred on 20 april 1988. anomalous seismic activity associated with these earthquake in eastern nepal and its adjoining region in an area bounded by 26.0 o -29.0 o n and 84.6 o -88.4 o e have been studied using seismicity data from 1975-1988. the preparatory zone is delineated using the temporal and the spatial distribution of earthquakes, considering the events with cutoff magnitude mb ≥ 4.3. based on daily number of events as well as cumulative number of earthquake with time within the preparatory zone anomalous seismicity is recognized. accordingly four anomalous episodes: normal/ background (n); anomalous/ swarm (a); precursory gap (g) and mainshock sequence (m) are identified. it is observed that the first mainshock (mb 5.4) was related to the second mainshock (mb 6.4) which was preceded by well defined patterns of anomalous seismicity/ precursory swarm which commenced about ten years and six months prior to mainshock. keywords: anomalous seismicity; central himalaya; south eastern nepal; precursory swarm 1. introduction four great earthquakes and a large number of major earthquakes have occurred in the himalayan region since 1897. the seismic activity in the region is directly related to the collision between indian and tibetan plate. three northward dipping thrusts, i.e. main central thrust (mct), main boundary thrust (mbt) and main frontal thrust (mft), are the continuous structure throughout the himalayan range having offset at many places by nearly n-s transverse fault. seismic activity within the region is due to release of stress along the major faults and lineaments. a number of seismic precursors are known to precede medium to large earthquakes [1, 2]. anomalous seismicity is the first to take place as compared to other precursory phenomena due to ∗ corresponding author: dr. harihar paudyal, dept. of physics, birendra multiple campus, (tribhuvan university) bharatpur, chitwan, nepal, email: hariharpaudyal@gmail.com harihar paudyal / bibechana 7 (2011) 76-82: bmhss 77 formation of various ruptures where considerable strain energy is accumulated [3]. noticeable fluctuations in seismicity, mostly prior to significant earthquakes, have been observed in various regions of the world. hence it may be an important parameter for the prediction of long-range earthquake related hazards in a region. the phenomenon of seismic quiescence, in which seismic activity drops to almost zero, has often been observed prior to the mainshock. the quiescence is often broken by stress buildup resulting in an increase in the number of earthquakes, known as pre-shocks. such seismic quiescence often ends with foreshock activity that takes place just before the mainshock. the seismicity level drops to a low background level after the completion of a mainshock sequence. anomalous seismicity pattern has some kind of casual relationship with the time of occurrence and magnitude of the mainshock. such patterns follow episodes of relatively very low seismic activity, which is an important finding to visualize that an area might be preparing for the forthcoming mainshock. the patterns of anomalous seismicity/ earthquake swarms can be considered as an important parameter for the forecasting of long-range earthquake hazards in the region. if any region is observed in which anomalously low precursory quiescence period is continuing, efforts have been made to search for other short term premonitory phenomena. a burst of seismic activity reflects the onset of the precursory sequence that follows a period of abnormal quiescence which continues till the occurrence of the major event [4, 5]. the entire preparatory period may be classified into four episodes as: normal (or background) seismicity sequence (measured till the onset of swarm activity); anomalous seismicity (or precursory swarm) sequence (period from the onset to end of swarm activity); precursory gap (or seismic quiescence) sequence (from the date of termination of swarm activity to the onset of the mainshock sequence); and the mainshock sequence (duration of mainshock and its associated aftershocks) [4]. within the preparatory area, the episodes of normal (n), anomalous (a), gap (g) and mainshock (m) sequences represent anomalously low, high, low and high seismic activities, respectively. a precursory earthquake swarm occurs in and around the focal region of a major earthquake several years before its occurrence [4, 5]. evison [6] proposed a generalized precursory swarm hypothesis for the occurrence of multiple earthquake swarms, precursory gap and multiple mainshock events. the hypothesis was tested in japan and new zealand [7, 8, 9] and updated accordingly. following a similar methodology, several cases of the earthquake swarm pattern were reported in different parts of himalaya and its adjoining region, such as: singh et al. for burma szechwan region [10]; singh and singh [11, 12] for pamir and its adjoining region; gupta and singh [13, 14] for eastern himalaya and recently singh et al. [15] for western nepal in central himalaya. in the present study, the existence of anomalous seismicity patterns in the region prior to the occurrence of 1988 udayapur earthquake is examined. the earthquake database compiled for central himalaya region by paudyal [16] using existing catalogues of neic, national seismological center (nsc) and international seismological center (isc) has been used for the identification of seismicity patterns. in the central himalaya regions, the cutoff magnitude for the period 1963-2006 is estimated to be mb ≥ 4.3 using b-value method [16]. hence only earthquakes with mb ≥ 4.3 have been considered for identifying seismic anomalies. 2. udayapur earthquakes of 20 aug. 1988 (mb 6.4) and 20 april 1988 (mb 5.4) the udayapur earthquake of 20 august 1988 is the largest one in the recent time that occurred in the southeastern nepal and caused widespread devastation in the adjoining areas of the nepal and india. prior to this, an earthquake of mb 5.4 has occurred ~30 km to the north of the epicenter of the udayapur earthquake on 20 april 1988. these two earthquakes have occurred in the epicentral tract of 1934 great earthquake. in order to investigate anomalous seismic patterns associated with these two recent earthquakes, the seismicity data for the period 1975 to 1988 harihar paudyal / bibechana 7 (2011) 76-82: bmhss 78 falling within an area bounded by 26 o -29 o n and 84.6 o -88.4 o e is considered. the spatial distribution of events during the considered period is located in the northwest-southeast direction including both the mainshocks. an elliptical area oriented in the same direction is delineated as the preparatory area (~4.7 x 10 4 km 2 ) for the 1988 udayapur earthquake which encloses most of the events during the period (fig. 1). the temporal pattern, shown in fig. 2a, clearly shows a significant increase in the seismic activity during the two periods i.e. from 10 february 1978 to 19 june 1979 (495 days) and 23 december 1985 to 02 february 1986 (52 days) (tables 1 and 2). the first high active phase is found to be related with 20 august 1988 mainshock and the second one with the 20 april 1988 mainshock. the second anomalous high activity, both in the space and time, occurred well within the preparatory area of the 20 august 1988 mainshock during its gap episode. four anomalous episodes associated with 20 august 1988 mainshock identified as normal seismicity, anomalous/ swarm, gap and mainshock sequence based on critical examination of the spatial and the temporal distributions of events are furnished in table 1. the temporal pattern of events and their magnitude relationship within the preparation area is depicted in fig. 2a show that the seismicity preceding mainshock fluctuated in the order as low-high-low in the ratio 1:4:1 during the normal, anomalous and gap episodes, respectively. the anomalous seismic activity (swarm sequence) initiated about ten and half years prior to the mainshock that lasted for 495 days. though the number of seismic events in the anomalous episode within the delineated preparatory area is not very large but it is characterized by the four fold higher seismicity over the preceding normal and the following gap episodes. figure 1: spatial distribution of events (mb ≥ 4.3) for the period 1975-1988 associated with the mainshock of 20 april 1988 (mb 5.4) and 20 august 1988 (mb 6.4) in udayapur region, eastern nepal. the smaller (shaded) and larger dotted elliptical region are the preparatory areas for the mainshocks of 20 april 1988 and 20 august 1988 respectively delineated based on spatial distribution of normal (n), swarm/ anomalous seismicity (a), gap (g) and the mainshock sequences(m) on the surface. harihar paudyal / bibechana 7 (2011) 76-82: bmhss 79 leaving a seismic gap in the southeastern part of the preparatory area, the seismic events in all the episodes are widely distributed but mostly concentrated in the northwestern portion. the magnitude of events in the swarm sequence range from 4.3 to 5.2; whereas an event with m 5.4 (which is the second mainshock) has occurred on 20 april 1988 during the gap period which itself was found to be preceded by the anomalous swarm activity some 26 ½ months prior to the mainshock. four out of five events in the swarm sequence are located in between 84.5 o to 86 o e at about 33 km depth, whereas the remaining one is located far away within the preparatory area around 87.5 o e at a depth of 24 km. the mainshock occurred on 20 august 1988 after a precursory gap period of 3,349 days in the southern part of the preparatory area at a depth of 57 km close to the mft and to the south of largest gap event. aftershocks are confined in the depth range of 30-45 km around the mainshock (fig. 2b). based on these information, it is inferred that the mainshock of 20 august 1988 was preceded by the anomalous seismic activity/ earthquake swarms which commenced about 10 ½ years before the mainshock. the aftershocks and the anomalous seismic events occupy the eastern and the western parts of the preparatory area, respectively. the seismicity data from 1984 to 1988 is considered here to study the earthquake swarm/ anomalous seismic activity associated with the mainshock of 20 april 1988. this event occurred close to the surface trace of the mct at 27 o n and 86.7 o e (fig. 1). it is observed here that this earthquake was preceded by a swarm sequence which occurred within the continuing precursory gap period associated with 20 august 1988 udaypur mainshock. this is a clear case of an earthquake swarm in which another swarm sequence occurs at a later stage, principally in the continuing gap episode of the first one. all the characteristic events (table 2) related with the 20 april 1988 mainshock are the gap events of 20 august 1988 mainshock as shown in figs. 2a and 3a. the delineated preparatory area (~2 x 10 4 km 2 ) for this earthquake falls completely within the preparatory area of 20 august 1988 mainshock, and has similar orientation along the northwestsoutheast (fig. 1). the temporal pattern of events and their magnitude relationships within the preparation area depicted in fig. 3a show that the seismicity preceding mainshock in the normal, swarm and gap episodes fluctuated in the order as low-high-low in the ratio of 1:41:2, respectively as normalized on annual basis. the precursory swarm events are distributed in the western part of the preparatory area and their magnitude range from 4.5 to 4.6. the mainshock has occurred in the southeast portion of the preparatory area after a quiescence of 807 days from the termination of the anomalous phase. the swarm and the gap events are clustered in the depth figure 2: temporal (a) and focal depth (b) distribution of events (mb ≥ 4.3) for the period 1975-1988 associated with the mainshock of 20 august 1988 (mb 6.4) in udayapur region, eastern nepal. four identified anomalous sequences are: normal/ background seismicity (n); precursory swarm (a); precursory gap or quiescence (g); and mainshock and its associated aftershocks (m). harihar paudyal / bibechana 7 (2011) 76-82: bmhss 80 range 30–45 km; whereas the mainshock has occurred at deeper level at 54 km (fig. 3b). only one aftershock is reported to occur at deeper focal depth (66 km) to the south of mainshock and very close to mainshock of 20 august 1988. the above observations suggest that the mainshock of 20 april 1988 was preceded by an earthquake swarms/ anomalous seismic activity which commenced about two years and four months before the mainshock. seismic episodes duration d a y s t ot al ev en ts level of activity normal/ background (n) 01 jan. 1975-09 feb.1978 1 1 3 6 3 moderately low anomalous/ swarm (a) 10 feb.1978-19 jun. 1979 4 9 5 5 moderately high precursory gap (g) 20 jun.1979-19 aug.1988 3 3 4 9 11 moderately low mainshock sequence (m) 20 aug.1988-27 dec.1988 1 3 0 7 table 1: seismic characteristics in the identified episodes within the preparatory area of mainshock of 20 august 1988 in udayapur region, nepal. figure 3: temporal (a) and focal depth (b) distribution of events (mb ≥ 4.3) for the period 1984-1988 associated with the mainshock of 20 april 1988 (mb 5.4) in udayapur region, eastern nepal. four identified anomalous sequences are: normal/ background seismicity (n); precursory swarm (a); precursory gap or quiescence (g); and mainshock and its associated aftershocks (m). harihar paudyal / bibechana 7 (2011) 76-82: bmhss 81 seismic episodes duration d a y s t ot al ev en ts level of activity normal/ background (n) 01 jan.1984-22 dec.1985 7 1 2 1 extremely low anomalous/ swarm (a) 23 dec.1985-02 feb.1986 5 2 3 extremely high precursory gap (g) 03 feb.1986-19 apr.1988 8 0 7 2 extremely low mainshock sequence (m) 20 apr.1988-25 apr.1988 6 2 there have been several marked similarities in the occurrence pattern of anomalous seismic activity preceding the mainshocks of 20 april 1988 and 20 august 1988 as: 1) preparatory areas have similar orientation along the northwest-southeast; 2) almost all events in the preceding episodes occurred in the northwest side whereas both the mainshocks occurred opposite side in the southeast part of the preparatory areas; 3) the majority of the preceding events occurred at shallower levels as compared to the mainshocks which occurred at a greater focal depths (54 and 57 km). considering the above similarities, it may be concluded that both the mainshocks were preceded by the different swarm sequences at two different times within the larger preparatory area. further, it demonstrates that the entire preceding seismic activities, including the second swarm sequence and the associated mainshock, are related to the 20 august 1988 mainshock and appears to be caused by the same triggering mechanism. 3. conclusion the spatial and temporal changes in seismic activity may be causally related to the time of occurrence and the magnitude of the mainshocks. in view of this, an attempt has been made here to search for the pattern of the seismicity changes in space and time domains prior to udayapur earthquake. the earthquake was found to be associated with a well defined anomalous seismic activity both in space and time during 11.02.1978 to 19.06.1979 some three years and four months prior to the mainshock. the seismicity fluctuated in the order of low-high-low-high in the characteristics four phases from 1975 to 1988. the anomalous seismic phase within the preparatory zone was characterized by considerably high seismicity as compared to its preceding background seismicity phase and the following precursory gap phase. table 2: seismic characteristics in the identified episodes within the preparatory area of mainshock of 20 april 1988 (mb 5.4) in udayapur region, nepal. harihar paudyal / bibechana 7 (2011) 76-82: bmhss 82 acknowledgement the author is grateful to associate prof. dr. hn singh, department of geophysics, banaras hindu university india for offering useful comments and suggestions. references [1] t. rikitake, earthquake prediction, elsevier, amsterdam,(1976)357 [2] t. rikitake, earthquake forecasting and warning., center for academic publications, japan,(1982)402. [3] h. sekiya, j. phys. earth, 25(1977) s85-s93. [4] f. f. evison, nature ,266 (1977a) 710. [5] f. f. evison, the precursory earthquake swarm, physics of the earth and planetary interiors, 15(1977b) 19. [6] f. f. evison, j. physics of the earth, 30 (1982) 155. [7] f. f evison and d. a. rhoades, earth planets space, 51 (1999) 1267. [8] f. f. evison and d. a. rhoades, j. geology and geophysics, 40 (1997) 537. [9] f. f. evison and d. a. rhoades, j. geology and geophysics, 36 (1993) 51. [10] v. p. singh, h. n. singh and j. singh, tectonophysics, 85(1982) t21-t29. [11] v. p. singh and h. n. singh, tectonophysics, 113 (1985 )295. [12] v. p. singh and h. n. singh, earthquake prediction research, 4(1986) 83. [13] h. k. gupta and h. n. singh, j. geol. soc. india , 28 (1986) 367. [14] h. k. gupta and h. n. singh, tectonophysics, 167 (1989) 285. [15] h. n. singh, h. paudyal, d. shankar, a. panthi and a. kumar, pure and applied geophysics, 167 ( 2010)667. [16] h. paudyal, seismicity and seismotectonics of nepal and its adjoining region ph. d. thesis, department of geophysics, faculty of science, banaras hindu university, varanasi, india( 2008). microsoft word shobha kanta lamichhane-final 59-66.doc shobha kanta lamichhane / bibechana 8 (2012) 59-66 : bmhss, p.59 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana experimental investigation on anisotropic surface properties of crystalline silicon shobha kanta lamichhane department of physics, prithvi narayan campus, pokhara, nepal e-mail: sklamichhane@hotmail.com article history: received 31 may, 2011; accepted 25 july, 2011 abstract anisotropic etching of silicon has been studied by wet potassium hydroxide (koh) etchant with its variation of temperature and concentration. results presented here are temperature dependent etch rate along the crystallographic orientations. the etching rate of the (111) surface family is of prime importance for microfabrication. however, the experimental values of the corresponding etch rate are often scattered and the etching mechanism of (111) remains unclear. etching and activation energy are found to be consistently favorable with the thermal agitation for a given crystal plane. study demonstrate that the contribution of microscopic activation energy that effectively controls the etching process. such a strong anisotropy in koh allows us a precious control of lateral dimensions of the silicon microstructure. keywords: microfabrication; activation energy; concentration; anisotropy; crystal plane 1. introduction anisotropic etching of silicon is used to obtain varied microstructures [1–3], and anisotropic etchants extensively used are koh, edp (ethylene diamine, pyrocatechol), tmh (tetryl methylammonium hydroxide), etc. the mechanisms of anisotropic etching of silicon and the etching processes that occur in the crystalline surfaces are not well known. many authors have suggested a different sort of mechanism for the reactions to explain the anisotropic behaviour of etching of silicon in alkaline solutions [4, 5]. seidel et al [6] has proposed an electro-chemical model which involves the transfer of the electrons from ions in the solution to the crystal surface. in this model, the rate determining step is the transfer of electrons from the surface state, which lies in the forbidden gap, to the conduction band. this process is thermally activated. seidel states that the difference in energy between final and initial state contributes significantly to the macroscopic activation energy. anisotropy can be accounted for by the fact that the energy level of the surface state depends on the surface orientation. thus the (111) surface which exhibits the highest activation energy when etched with koh, has the lowest level energy state. the (110) and (100) planes present roughly the same level below that corresponding to (111) surface state. in other words, they have approximately the same activation energy. on the other hand, elwenspoek [7] puts forward a model inspired from the crystal growth theories in which the etch rate should be governed by a nucleation barrier of one atomic layer deep cavities and the activation energy depends on the step-free energy and under saturation. shobha kanta lamichhane / bibechana 8 (2012) 59-65 : bmhss, p.60 micro-electro mechanical structure (mems) devices are the output of either an etching process (or micromachining) from larger structures or are built up atom by atom through material deposition processes. maintaining dimensional control and retaining consistent mechanical property is considerably difficult because feature sizes are in the micrometer range. silicon mems offer these challenges. formation of a functional mems structure on a substrate, it is necessary to etch the thin films previously deposited or the substrate itself. in general there are two type of etching process: wet etching, where the material is dissolved when immersed in a chemical solution and, dry etching, where the material is sputtered or dissolved using reactive ions. in the following we briefly discuss the most popular technology, wet etching, is a simplest etching technology. all it requires is a container with a liquid solution that will dissolve the material. unfortunately, there are complications since a mask is desired to selectively etch the material. one must find a mask that will not dissolve or at least etch much slower then the material to be patterned. anisotropic is contrast to isotropic etching means different etch rates in different plane surfaces. the classic example of this is the (111) crystal plane sidewalls that appears when etching a hole in (100) silicon wafer in a chemical such as koh. the result is a pyramid shaped whole instead of a hole with round sidewalls with an isotropic etchant. etching technologies in thin film processes play an important role in the semiconductor industry. wet chemical etching techniques are used extensively in semiconductor processing because of their low cost, high throughput, and excellent selectivity. important progress in the fabrication of microelectrical structure with integrated circuits has been achieved. though detailed kinetic and electrochemical measurements have not been made, koh solutions are extensively used for the etching of single crystal silicon [8, 9]. fabrication of umos transistors on silicon (111) wafers for high power and high current densities has been achieved by applying koh anisotropic wet etching to the silicon substrate. other applications of koh wet etching include the fabrication of vmosfets, radio frequency amplifiers, power supplies, and microcomputers [10]. using its selective and anisotropic etching properties, koh wet etching has also been applied to yield such devices as field emission devices, optical waveguides, pressure sensors and ink nozzles [11]. koh wet etching is one of the old anisotropic orientation dependent wet etching techniques. etching of (100) oriented silicon using aqueous koh creates v-shaped grooves with (111) planes at an angle of 54.74° from the (100) surface. koh solution can also be used to produce mesa structures. there are several models proposed for the silicon etching mechanism in aqueous koh. bean and runyan found that the slow etch rate in the (111) direction is a consequence of the diamond lattice structure because the (111) plane is a double layer bound together by more atomic bonds than that of other planes. glembocki et al. proposed an electrochemical reaction mechanism that exists in the rate determining step for koh etching. a compromise model was proposed by seidel et al. in 1990, assuming that electrochemical reactions dominate during etching and that anisotropic etching was caused by the orientation-dependent number of dangling bonds available per surface area. the (100) silicon surface etches faster than the (111) because the free surface of (100) silicon is attacked by one oh per silicon atom, whereas the (111) silicon surface is attacked by two oh per silicon atoms [12]. although the mechanisms are not clear and need to be answer all these questions. the approach followed so as to determine the significant factor in a given electrochemical process and their quantification are prime importance from technological point of view. such proposed quires are being addressed in this work. if we have answer of all these quires in hand, then there is no doubt of etching silicon in aqueous koh is of both technological and fundamental importance. etching of (100) oriented silicon using aqueous koh creates v-shaped grooves with (111) planes at an angle of 54.74° from the (100) surface. koh solution can also be used to produce mesa structures. there are several models proposed for the silicon etching mechanism in aqueous koh. bean and runyan found that the slow etch rate in the (111) direction is a consequence of shobha kanta lamichhane / bibechana 8 (2012) 59-65 : bmhss, p.61 the diamond lattice structure because the (111) plane is a double layer bound together by more atomic bonds than that of other planes [10]. a compromise model was proposed by assuming electrochemical reactions dominate during etching and that anisotropic etching was caused by the orientation-dependent number of dangling bonds available per surface area. the (100) si surface etches faster than the (111) because the free surface of (100) si is attacked by one oh per si atom, whereas the (111) si surface is attacked by two oh per si atoms. although the mechanisms are not clear, it is known that electrochemical reactions play an important role in this process. 2. methodology the design of the present work was lab based experimental work. the procedure followed during this study was mentioned herewith sequentially. the wafers used in this study were thermally bonded silicon on insulator (soi) wafers with (100) orientation. the thickness of the top silicon, buried sio2 layer and bottom silicon were 2 and 450 mm respectively. the wafers were of p-type silicon with a resistivity of 4 – 631022 v-cm for the top silicon and 12–15 v cm for the bottom silicon. only the top silicon layer was etched by the koh solution. first, the soi wafers were prepared with standard rca cleaning. a 450 å layer of si3n4, which acts as a koh etching mask, was deposited on each wafer using low pressure chemical vapor deposition (lpcvd). oxide can be used as an etch mask for short periods in the koh solution, but for long periods, nitride is a better etch mask as it etches more slowly. the soi wafer was then cut into 10 mm×10 mm pieces. with the diced pieces held on a vacuum chuck, positive photoresist, ocg 825 [sutter et al, 2003; pp 4] was used to pattern the si3n4 for the koh etching mask. the nitride was etched with cf4 plasma and then the exposed portion of the top silicon on each soi wafer was etched in koh solutions of varying temperature and concentration. to assure the samples were free of particulate and other airborne contaminants. the experiments were conducted in a clean room environment. 3. results and discussion koh etch is a bulk silicon etch whose etch rate is depends on the orientation of the crystal plane can be exploited to create specific geometries (for example, v-grooves sown below). formation of such geometrical structure on silicon crystal depends on various factors: temperature, concentration, activation energy, surface finish and its cleaning process etc. we have performed on crystalline silicon with aqueous koh for the temperature ranging from 70°c to 90°c and its concentration was 30%. our results shows that the optimum etch rate with the minimum surface roughness, indicates low activation energy at 800c. with this one can easily understand that a single result is the outcome of various factors including koh concentration. the etch rate versus temperature as well as etch rate versus koh concentration are displayed in figure 2. figure 2 (a) and (b) shows that etch rate increases with increasing reaction temperature, regardless about koh concentration. within the working range investigated, the etch rate exhibits a maximum at approximately 20% koh and 90°c. below 70°c, little dependence of etch rate with the koh concentration is observed. without considering the effect of etching, we conclude that the highest etch rate can be achieved with a high temperature reaction. figure 2 (d) demonstrate the effect of changing koh concentration with the etch rate. as we conclude from figure. 2 that er depends on concentration are less significant than reaction temperature. dimensional control of a microstructure is strongly related to mems performance. etching technique allows control of the dimension. working in micromachining we need to both add and shobha kanta lamichhane / bibechana 8 (2012) 59-65 : bmhss, p.62 remove the material in a controlled way. adding material on a silicon wafer can be done by chemical vapor deposition (cvd). removing material is done almost by chemical etching, where a material is removed atom by atom [13]. this can be done either in a liquid (wet etching) or in plasma (dry etching). still the most simple and versatile anisotropic wet chemical etching for silicon is in koh. generally, etch anisotropy is given by, ea= 1(erl/erv), where erl and erv are the lateral and vertical etch rates. a process is said to be purely anisotropic (ea=1) if lateral etch rate is zero. on the other hand, if ea=0, lateral and vertical etch rates are identical and etching is said to be isotropic. the geometry what we got is shown in fig.1 below. fig.1: schematic showing anisotropic etches of silicon the final shape of the etched wafer depends highly on relative etching speed along crystallographic planes. the (111) plane is comparatively inert to alkaline etchants, while the relative etching speed of other planes depends on nature of etchant, temperature, concentration etc. in our experiment, we have taken 33 % koh by weight as an etchant for silicon (111) and (100) planes ambient conditions, unless otherwise specified. 3.1 surface finish of etched silicon contaminants are attached to the wafer surface physically or chemically. chemical cleaning is necessary in many steps during fabrication. the process that is widely used is so called “rca cleaning” consist of two consecutive cleaning solutions including h2o-h2o2-nh4oh (standard clean1, i.e. sc1 clean) and h2o-h2o2-hcl (standard clean 2, i.e. sc2). the sc1 cleaning with volume ratios typically 5:1:1 is to remove organic contaminants. the sc1 can remove particles physically attached to a wafer surface by etching with nh4oh that detaches the particles from the wafer surface and prevents re-deposition. the sc2 clean, with typical volume ratios of 6:1:1 removes metals from wafer surface and prevents re-deposition [13]. a modified rca clean (i.e., dilute hf after sc1) is designed to eliminate the thin oxide layer grown on silicon surface. modification of rca clean exists on the volume ratios. as for example, in order to reduce silicon surface roughness one needs to greatly reduce the volume fraction of nh4oh in sc1 from the original composition. surface taken by afm is depicted in fig. 3 below. other cleaning processes, such as piranha (h2so4 -h2o2-h2o), ozonized water etc. are also effective. however, rca clean have been most popular cleaning process, is adopted in this work. shobha kanta lamichhane / bibechana 8 (2012) 59-65 : bmhss, p.63 70 75 80 85 90 0.0 0.1 0.2 0.3 0.4 e tc h r a te ( µµ µµ m /m in ) temperature ( 0 c) 20 40 60 80 100 0 1 2 3 4 5 6 e tc h r a te ( µµ µµ m /m in ) temperature ( 0 c) 100 110 111 (a) (b) 0.0027 0.0030 0.0033 -24 -22 -20 -18 -16 ln (e r m /s ) 1/t (k -1 ) 100 110 111 10 20 30 40 50 60 70 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 e tc h r a te ( m ic ro n /m in ) koh concentration (wt % ) 100 110 111 (c) (d) fig. 2: behaviors of etching of crystalline silicon: (a) variation of er along (111) plane with temperature (b) variation of er along (111, 110, 100) plane with temperature (c) arrhenius plot of er for primary crystal planes (d) variation of er along (111, 110, 100) plane with koh concentration 3.2 association between etch rate and activation energy the macroscopic activation energy of er is explained by the sum of two terms. one corresponds to the average of the microscopic activation energies and other accounts for the existence of fluctuation in the fraction of particles at a fixed temperature. er depends on pi and t. in order to understand this point, we define er as ∑ ∆ ∆ = ∆ ∆ = i iimc mc pz tt z er ... .. )( 1 (1) where, ..mcz∆ is the distance traveled by the center of mass of the surface, pi, is the removal probability of the surface atom i, and is given by tk e ii b ia epp − = 0 (2) shobha kanta lamichhane / bibechana 8 (2012) 59-65 : bmhss, p.64 where t is the temperature, kb is the boltzmann constant, eai is the microscopic activation energy for removal of site i and poi is a prefactor. hence, macroscopic and microscopic activation energy and temperature are interrelated. thus, er is the distance traveled by the moving surface per unit time. when the etching process has reached steady state, er is simply the ratio of the distance traveled by the center of mass (cm) of the surface (zcm) to the period of time elapsed (t). i.e. er = zcm/t. during a modeling, zcm can be determined as the sum of all individual shifts (zcm)i of the surface following each successful event, i.e. the sum over all successful particle removal is occurring during ‘t’. although (zcm)i is typically positive, occasionally it may be negative if the removal of site i involves a reduction in the total number of surface sites [14]. in particular, certain sitetypes of our formula for wet chemical etching, typically contribute to the motion of the cm with a negative shift on average. alternatively, we may consider the sum over all events, independently of whether the event is a successful removal or not. note that the positive/negative shift of the cm of the surface due to the removal of atom i, (zcm)i, may be calculated independently, whether the atom is removed or not. equation suggests that the etch rate is composed of two factors: one purely geometrical (the cm-shifts) and one purely numerical. indeed, er is proportional to the average number of surface atoms removed from the surface per unit time. here, proportionality constant (z) is precisely a measure of the average shifts in the cm of the surface per removed atom. z is an exclusively geometrical feature of the er. in particular, it is independent of temperature. although z may take different values for different surface orientations, z does not depend on temperature for a specified orientation. this is an important observation because the appearance of negative cm-shifts (zcm)i may be accepted as the interpretation of the relative importance (weight) of the different particle types for the calculation of an average. actually, the interpretation becomes meaningless if some of the weights are negative. however, the use of i is free of these artifacts and allows unambiguous interpretation, as shown in this study. there are three alternate ways to determine the rate of removal of particles [15]: (i) as in the case of the er, of the removal of particles can be determined using only successful events. note that the averages of the number of surface atoms n are not constant. (ii) the rate of removal of particles can be written in terms of a sum over the different types of surface sites. the rate of removal of particles may also be expressed in terms of the average fraction of particles removed per unit time. here we have defined as the average fraction of particles. activation energy, in relation to the er, the activation energy (ea) is, by definition, the slope of the curve. 3.3 etched crystallographic planes it is essential to monitor the evolution of the surface configuration and roughness during etching. although we are dealing with ideal conditions, this gives us an idea of the difference in etching between the different planes. it is thought that all faces that are rough in the atomic scale etch in the same manner. this is supported by the afm micrograph representation of one plane viz. (111). this is a characteristic feature of rough faces at the atomic level when etched with an alkaline solution. shobha kanta lamichhane / bibechana 8 (2012) 59-65 : bmhss, p.65 fig.3: structure of (111) silicon plane as seen from the top and its afm micrograph. seidel et al [6] has carried out precise experiments to determine the values of the er of the three silicon orientations (100), (110) and (111). in their experiments, the concentration of koh was also modified. the result shows that the anisotropic ratio (110)/(100) has a small dependence on the concentrations (from 10–60%), and the value is on the order of 1.55 at 800c. the macroscopic activation energies were found to be similar for (100) and (110) planes [16], being approximately 0.6 ev. we found an anisotropic ratio (110)/(100) of the same order as above (1.5). for activation energies, we found approximately 0.6 ev for (100) and (110) planes. 4. conclusion the etching mechanism is ‘layer-by-layer’ removal. this mechanism leads to a particular evolution of the roughness which shows an alternation of peaks. anisotropic etching of silicon with koh is a well-known method of forming grooves in the silicon-surface. etching of (100) silicon on silicon on insulator wafers was carried out over a wide range of temperatures and concentrations. using statistical methods, we show that the factors important in the silicon er are reaction temperature, koh concentration, and interaction between them. the activation energy belongs to etching at different koh concentration was calculated from arrhenius plots. in addition, in this work we report a qualitative study of the surface roughness formed in koh etching. the smoothness increases with temperature to a critical point and then decreases at very high temperature and concentration. results presented here are temperature dependent er along the crystallographic orientations. based on this work, temperature is a crucial factor, which control er. activation and cohesive energies along the crystallographic planes are thus microscopic quantities that determine er. er is slow for (111) face and fast in (110). strong er anisotropy allows us a precious control of lateral dimension of the microstructure bound by the (111) surface and activation energy depends on the step-free energy and undersaturation. references [1] k. e. petersen ieee proc. 70 (1982) 420. [2] d. l. kendall, annual rev. mater. sci. vol 9, ed r a huggins (1979) 373. [3] h. namatsu, m. nagase, k. kurihara, k. iwadate and k.murase, microelectron. eng. 27 (1995) 7. shobha kanta lamichhane / bibechana 8 (2012) 59-65 : bmhss, p.66 [4] o. j. glembocki, e d palik, g r de guel and d l kendall, j. electrochem. soc. 138 (1991) 1055. [5] e. d. palik, v m bermudez and o j glembocki, j. electrochem. soc. 132 (1985) 871. [6] h. seidel, l. csepregi, a heuberger and h baumgartel, j. electrochem. soc 137 (1990) 3612. [7] e. vazonyi and t. szkufcik, journal of micromechanics and microengineering 13 (2003) 165. [8] n. p. krivorotov, y. g. svinolupov, t. i izaak, v. v. bychkov, sensors and actuatiors a 113(2004) 350. [9] k.. mylvaganam and c. l. zhang, key engineering materials 233 (2003) 615. [10] p. sutter, e. sutter and m. g. lagally, surface science 30 (2003)1. [11] p. waish, r. omeitchenko, r. k. kalla, a. nakano and p. vashishta, applied physics letters 82 (2003) 118. [12] x. yan, t. xu, g. chen, s. yang, and huiwenliu, journal of physics d: applied physics 37 (2004) 907. [13] p. j.french and a. g. r. evans, solid state electronics 32 (1989) 1. [14] p. j french. and a.g.r evans, journal of physics e: scientific instruments 19 (1986) 1055. [15] j. duck lee, b. chang shim, h. soo and b. gook, electron device letters 20 (1999) 215. [16] k. e. bean and w. r. runyan, semiconductor integrated circuit processing technology, addisionwesley, new york 1990. microsoft word khadka and joshi _40-52_.doc r c o s t n publisher: research council of science and technology, biratnagar, nepal p.40 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana molecular electrostatic potential, homo-lumo and vibrational study of aristolochic acid ii using density functional theory jang bahadur khadka 1 , bhawani datt joshi 2* 1department of chemistry, siddhanath sc. campus, mahendranagar, tribhuvan university, nepal 2department of physics, siddhanath sc. campus, mahendranagar, tribhuvan university, nepal * e-mail: bdjoshi_007@yahoo.com accepted for publication: december 12, 2014 abstract because of their wide applications in human or animal medicine, the natural products have been the subject of investigation. aristolochic acids (aas) (aristolochiaceae), however toxic, are reported for many medicinal uses. in this work, computational study on the molecular properties of aa ii is presented using density functional theory (dft), b3lyp functional along with hartree-fock (hf) theory at 6-311++g(d,p) level. a complete vibrational assignment has been done for the observed ft-ir and raman wavenumbers with the results of quantum chemical calculations. the structure– activity relationship has been interpreted by mapping electrostatic potential surface (mep). graphical representation of frontier molecular orbitals with their energy gap has been analyzed theoretically for both the gaseous and solvent environment employing td-dft using ief-pcm model. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11702 © 2014 rcost: all rights reserved. keywords: mep; homo-lumo; vibrational spectroscopy; dft. 1. introduction medicinal plants play a fundamental role in the world health, since they are sources of several pharmacologically active compounds such as flavonoids and tannins. many of these molecular structures are similar to those of our molecules and this is the basis for their physiological action [1]. the use of medicinal plants has been an elected practice throughout human history. it is important to point out that the plants, in addition to their therapeutic use in folk medicine, have contributed to the obtention of many drugs which are still in use, such as morphine, the main anesthetic alkaloid in opium, vincristine etc. aristolochic acids (aas), found in aristolochia spp, are structurally related nitrophenanthrene carboxylic acids. drugs derived from aristolochia plants have been used as medicine in obstetrics and in the treatment of snake bites [2]. the plant extracts have also been used for the therapy of arthritis, gout, rheumatism, and festering wounds [3,4]. however, aristolochic acid is an established human carcinogen [5,6], increase risk of developing urothelial carcinoma [7-11] in the patients with endemic nephropathy and chronic renal failure with some herbal medicines [12]. khadka and joshi / bibechana 12 (2015) 40-52: p. 41 in this communication, we have presented molecular electrostatic potential surface (mep), highest occupied molecular orbitals (homo)lowest unoccupied molecular orbital (lumo), and the vibrational spectra of the molecule aristolochic acid ii (aa ii) using ab initio hartreefock (hf) and density functional theory (dft). with the help of specific scaling procedures, the observed vibrational wavenumbers were analyzed and accurately assigned to different normal modes of the molecule; and using ped’s the contributions of the different modes to each wavenumber were determined. 2. methodology 2.1 experimental infrared spectra were recorded on a bruker tensor 27 ft-ir spectrometer with a spectral resolution of 4 cm-1 in the region 400-4000 cm-1. kbr pellets of solid samples were prepared from mixtures of kbr and the sample in 200:1 ratio using a hydraulic press. multi-tasking opus software was used for base line corrections. the ft-raman spectra were recorded on a perkin-elmer 2000r spectrometer as powder sealed in a capillary tube in the region 100-3500 cm-1. the 1064 nm line of an elforlight model l04-2000s nd: yag laser was used as the exciting source with an output power of about 100 mw at the sample position. all spectra were accumulated for 100 scans with a resolution of 4 cm-1. 2.2 computational geometry optimization has been performed as the first task of the computational work. the geometric parameters available from the pubchem data base [13] have been used as the basis for the optimization. the molecular structure, vibrational frequencies and energies of the aa ii were computed employing the dft [14] method using gaussian 09 program [15] package and becke’s three parameter (local, non-local, hartree–fock) hybrid exchange functional with lee–yang–parr correlation functional (b3lyp) [16–18]. the split valence basis set 6-311++g(d,p), augmented by ‘d’ polarization functions on heavy atoms and ‘p’ polarization functions on hydrogen atoms as well as diffuse functions for both hydrogen and heavy atoms were used [19,20]. the ir absorption intensities and absolute raman intensities were calculated in the same level of theory as used for the optimized geometry. the normal mode analysis was performed and the ped was calculated, employing gar2ped program [21], along the internal coordinates using localized symmetry. for this purpose, a complete set of 90 internal coordinates were defined using pulay’s recommendations [22,23]. the vibrational assignments of the normal modes were done on the basis of the band profile, intensity and ped. gauss-view program [24] was used for graphical presentation of the calculated raman and ir spectra. to elucidate the differences of first excitation energies and oscillator strengths in gas and solution, the solvent effects were taken into account by means of integral equation formalism polarizable continuum model (ief-pcm) [25-27]. 3. results and discussion 3.1 geometry optimization geometry optimization has been performed as the first task in the ab initio calculations, using the molecular conformation obtained from pubchem data base [13]. the ground state optimized structure (in gas phase) of the molecule is presented in fig. 1. the optimized parameters have been used for the other calculations. some of the calculated bond parameters are listed below in the table 1. khadka and joshi / bibechana 12 (2015) 40-52: p. 42 table 1. some calculated (dft) bond parameters of aa ii. bond length (å) bond angle (o) dihedral angle (o) c23-o4 = 1.2079 c13-c23-o3 = 112.74992 c17-c13-c23-o3 = 35.36312 o4-o6 = 2.87273 c12-c23-o4 = 124.70005 16-c13-c23-o4 = 30.81523 o4-o5 3.17938 c14-n7-o6 = 116.97323 c9-c14-n7-o6 = 34.44447 o6-h32 2.27952 c14-n7-o5 = 117.98883 c16-c14-n7-o5 = 38.83665 o1-h26 2.13096 o6-n7-o5 = 124.87079 c13-c23-o3-h32 = 176.71139 fig. 1. opitmized structure of aa ii. the equilibrium geometry has been determined by the energy minimization. the energy calculated by dft (-1121.42720029 hartree) is lower than the one calculated by hf (-1114.91828124 hartree) as it should be. similarly, the dipole moment calculated by dft (6.6567 debye) is higher than that calculated by hf (6.4607 debye). 3.2 molecular electrostatic potential molecular electrostatic potential surface is a good tool for assessing the reactive sites towards positively or negatively charged reactants to explain hydrogen bonding and structure-activity of the molecule; however, the molecular charge distribution remains unperturbed through the external test charge [28]. by quantum chemical calculations it is observed that there is a strong correlation between the dipole moment, electro-negativity, and partial charges with electrostatic potential [29]. it provides a visual method to understand the relative polarity of a molecule through mapping total density surface on electrostatic potential energy surface, which depict the size, shape, charge density, and site of chemical reactivity of the molecules. khadka and joshi / bibechana 12 (2015) 40-52: p. 43 . fig. 2. (a & b) mep (molecular electrostatic potential) (c) esp (electrostatic potential), and (d) ed (electron density) mapped on the isodensity surface from -5.5982 e-2 to +5.5982 e-2. the mep plots of aa ii, shown in the fig. 2, was based on the calculations performed with b3lyp/6-311++g(d,p) level of theory visualized with gauss view program 5.0 [30]. in this molecule, regions near the oxygen atoms of methyl group are most negative (red regions) due the concentrated electron density. the regions near the hydrogen atoms of the same group are the most positive regions (blue regions) which correspond to the repulsion of proton by low electron density. the ed (electron density) plots of the investigated molecule show uniform charge distribution. however, yellowish blob from the esp (electrostatic potential), in the fig 2(c), reflects that the negative esp is localized more over the oxygen atoms and the positive esp is localized on the rest of the molecule. this result is expected, because esp correlates with electro negativity and partial charges. 3.3 frontier molecular orbitals and electronic absorption the electronic transition corresponds from homo (characterizes of electron giving) to the lumo (characterizes of electron accepting) orbital. both the frontier molecular orbitals (fmos), highest occupied molecular orbital (homo) and lowest unoccupied molecular orbital (lumo) are the main orbitals taking part in chemical reaction. the electron delocalization between these orbitals is a principal factor in determining the easiness of a chemical reaction and the stereo-selective path, irrespective of intra and intermolecular processes. the energy gap between the homo and lumo molecular orbitals characterizes the chemical reactivity and kinetic stability along with spectroscopic properties [31]. the electronic transitions of high oscillatory strength (f) along with their absorption wavelength (λmax) and excitation energies (ev), obtained from the time dependent dft (td-dft) calculation employing 6-31g(d,p) level of theory [32,33], have been listed in the table 2. khadka and joshi / bibechana 12 (2015) 40-52: p. 44 the negative values of all the fmo energies indicate the stability of the title molecule. the calculation in the gas phase shows that the bands at 389.22, 269.69, 208.29 and 206.13 nm originate due to h→l, h-1→l+1, h-4→l+2 and h-7→l+1 transitions, respectively. however, the electronic transitions between these fmos occur with some different values of λ and the oscillatory strengths. this discripancy is due to the solvent effect on the molecular orbitals. the homo-lumo plot is shown below in the fig. 3. fig. 3. homo-lumo plot of aa ii in the gas phase. 3.4 vibrational wavenumbers the total number of atoms in aa ii molecule is 32 and gives 90 (3n-6; nthe number of atoms) normal modes of vibrations. all the fundamental modes of vibrations are both ft-ir and raman active. as dft calculation yields raman scattering amplitude but not the raman intensities, so the raman scattering amplitudes can be predicted for each wavenumber using a relation [34,35]; j jj j j s c h kt hc                               − −       −       = ω∂ ∂ νπν νν πσ 2 4 044 8 exp1 45 2 where sj and υj are the calculated scattering activities and the predicted wavenumbers, respectively, of the jth normal mode, υ0 is the raman excitation wavenumber and h, c and k are the universal constants. khadka and joshi / bibechana 12 (2015) 40-52: p. 45 table 2. electronic transitions, absorption wavelength λmax (nm), excitation energy (ev), oscillator strengths (f), frontier orbital energies (ev) and dipole moment (debye). excited states gas phase solvent phase transition types transition states λmax e (ev) oscilator strength (f) transition states λmax e (ev) oscilator strength (f) 1 h→l 389.22 3.1855 0.0538 h→l 428.20 2.8955 0.0559 π→π * 2 h-1→l 337.82 3.6701 0.0028 h-1→l 355.67 3.4859 0.0046 π→π * 3 h-2→l 331.52 3.7399 0.0104 h→l+1 340.88 3.6372 0.1354 π→π * 4 h→l+1 325.78 3.8058 0.0939 h-2→l 321.46 3.8569 0.1008 π→π * 5 h→l+2 304.96 4.0656 0.0894 h→l+2 318.42 3.8937 0.0732 π→π * 6 h-1→l+1 269.69 4.5973 0.1155 h-1→l+1 281.14 4.4101 0.0905 π→π * 7 h-3→l+1 261.71 4.7374 0.1583 h-1→l+1 275.03 4.5081 0.1723 π→π * 8 h-1→l+1 252.87 4.9031 0.1294 h-2→l+1 265.17 4.6756 0.0637 π→π * 9 h→l+3 245.47 5.0509 0.0615 h-1→l+2 259.49 4.7780 0.2527 π→π * 10 h-4→l+1 237.32 5.2244 0.1899 h-1→l+2 242.99 5.1024 0.3188 π→π * 11 h→l+5 222.51 5.5721 0.1024 h→l+4 229.71 5.3974 0.0620 π→π * 12 h-8→l 217.15 5.7097 0.0719 h-4→l+1 221.30 5.6025 0.2128 σ→π * 13 h-4→l+2 208.21 5.9548 0.2432 h-1→l+3 215.89 5.7429 0.2100 σ →π * 14 h-7→l+1 206.13 6.0149 0.2034 h-3→l+2 212.62 5.8313 0.057 σ →π * 15 h-8→l+1 200.22 6.1923 0.0838 h-2→l+3 201.04 6.1672 0.1219 σ→π * ehomo (ev) elumo (ev) ∆e (ev) µ (d) gas 5.90364486 2.44626063 3.45738423 6.9762 ethanol 5.90359044 2.44103631 3.46255413 8.1606 the calculated raman and ir intensities were used to convolute each predicted vibrational mode with a lorentzian line shape (fwhm = 8 cm-1) to produce simulated spectra. since, the dft and hf vibrational wavenumbers are known to be higher than the experimental wavenumbers due to neglect of anharmonicity effects, they were scaled down by the wavenumber linear scaling procedure (wls) [υobs = (1.0087–0.0000163 υcalc) υcalc cm-1] of yoshida et al. [36]. comparison of the wavenumbers, calculated with the hf and dft method with experimental values, reveals that the dft method shows very good agreement with experimental observation than the hf due to inclusion of electron correlation, approximate treatment of basis set deficiencies and for the anharmonicity. the detailed comparison of observed and scaled wavenumbers along with the potential energy distribution is presented in table 3. the comparison of observed and calculated ft-ir and raman spectra of aa ii molecule is presented in figs. 4 and 5, respectively. the description of vibrational assignments of the 4 rings and the functional groups has been given below: 3.4.1 o-h vibrations in this molecule, there is one hydroxyl group (o-h) attached at the ring r2 through carbonyl. the hydroxyl group vibrations are the most sensitive to the environment, so the hydrogen bonded species show pronounced variation in the observables of a spectral band, such as band intensity and shape, frequency position of band maxima. the free hydroxyl group absorbs strongly in the region 3600– 3550 cm-1, whereas the existence of hydrogen bond can khadka and joshi / bibechana 12 (2015) 40-52: p. 46 lower the o-h stretching wavenumber to the 3550–3200 cm-1 region with an increase in ir intensity and breadth [37]. in our study, the o-h stretching is calculated at 3566/3875 cm-1 in scaled dft/hf and match with very weak band at 3477 cm-1 in the ir spectrum, which indicates the group involvement in intermolecular hydrogen bonding. the o-h deformation is calculated at 1164/1245 cm-1 in the dft/hf and assigned to the observed peaks at 1149/1148 cm-1 in the ir/raman spectra. 3.4.2 c=o vibrations most of the characteristic features of the carboxylic group are observed usually 1750–1600 cm-1 region [38]. c=o bonds being highly polar show intense peak in the ir and weak peak the raman spectra. the c=o stretching vibration is calculated at 1749 cm-1, which match with the observed strong peak at 1687 cm-1 in the ir and weak peak at 1740 cm-1 in the raman spectra, respectively. the wagging, deformation and rocking of c=o are calculated at 800/889, 665/721 and 431/464 cm-1 in the dft/hf showing good agreements with the observed wavenumbers at 791/797, 650/672 and 420/430 cm-1 in the ir/raman spectra. table 3. observed and calculated ft-ir and raman wavenumbers (cm-1) of aa ii. unscaled dft scaled observed ped % dft hf ir raman 3765 3566 3875 3477 υ(oh)(100) 3250 3106 3269 3097 3096 r4[υ(ch)](98) 3229 3087 3233 3078 3083 r2[υ(ch)](99) 3204 3065 3223 3072 r3[υ(ch)](99) 3192 3054 3199 3020 3042 r4[υ(ch)](99) 3177 3040 3184 3018 3032 r4[υ(ch)](99) 3169 3032 3175 3016 3028 r4[υ(ch)](99) 3131 2998 3160 2999 2997 r1[υa(ch2)](99) 3012 2890 3061 2852 2880 r1[υs(ch2)](100) 1785 1749 1933 1687 1740 υ(c=o)(77)+r2[υ(c13c23)](6) 1660 1630 1804 1685 1624 r3[υ(cc)(40)+δa(10)+δin(ch)(5)]+r2[υ(cc)](9)+r1[υ(cc)](7) 1648 1618 1761 1626 1609 r4[υ(cc)(51)+δa(8)+δin(ch)(12)] 1630 1600 1755 1595 1593 r2[υ(cc)(26)+δa(6)]+r1[υ(cc)](21)+r4[υ(cc)](12)+r3[υ(cc)](7) 1620 1591 1740 1593 1591 r2[υ(cc)(46)+δ’a(9)+δin(ch)(6)]+r1[δ’ring](6)+r3[υ(cc)](5) 1589 1562 1734 1539 1543 υa(no2)(78)+ρ(no2)(6) 1569 1543 1678 1525 1541 r4[υ(cc)(30)+δin(ch)(10)]+r3[υ(cc)](22)+r2[υ(cc)](6) 1539 1514 1648 1523 1508 r1[δ(ch2)](77) 1529 1504 1630 1506 1507 r4[δin(ch)(23)+υ(cc)(5)]+r3[υ(cc)](23+r1[δ(ch2)](17) 1480 1458 1603 1452 1451 r4[δin(ch)(31)+υ(cc)(16)]+r3[υ(cc)(8)+δtrig](7)]+r2[υ(cc)](14) 1473 1450 1581 1450 1449 r2[υ(cc)(20)+δin(ch)(7)]+r4[δin(ch)](15)+υ(cc)(8)]+r3[υ(cc)](15)+ r1[υ(co)](7) 1436 1415 1569 1417 1406 r1[ω(ch2)](42)+r3[υ(cc)](11)+δin(ch)(5)]+r2[δtrig](8) 1422 1401 1543 1391 r1[ω(ch2)](30)+r3[υ(cc)(16)+δin(ch)(11)]+r4[δin(ch)](10) 1400 1380 1516 1373 1372 r2[υ(cc)(33)+υ(c13c23)(12)]+r1[υ(co)](14) 1377 1358 1502 1350 1350 r2[υ(cc)(21)+δin(c13c23)(6)]+r3[υ(cc)](25) 1371 1353 1473 1348 1348 υs(no2)(57)+δ(no2)(14)+r3[υ(cn)](12) 1360 1342 1416 1347 r4[υ(cc)](44)+r3[υ(cc)](11)+r3[δin(ch)](9) 1350 1332 1387 1331 1331 r2[υ(cc)](37)+r1[υ(cc)](10)+r3[υ(cc)](8)+δ(cho)(5) 1321 1304 1376 r4[δin(ch)](17)+υ(cc)(5)]+r3[υ(cc)](11)+δtrig(6)]+δ(cho)(14)+r2[υ(cc)](8) 1287 1271 1344 1273 1271 r4[δin(ch)(19)+υ(cc)(10)]+r2[υ(cc)(16)+δin(ch)(9)]+r3[υ(cc)(11)+δtrig(5)] 1269 1253 1328 1348 1246 r4[υ(cc)(14)+δtrig)(10)+δin(ch)(9)]+r3[υ(cc)](27)+r1[υ(co)](8) 1231 1217 1322 1213 r1[γ(ch2)(9)+υ(co)(9)]+r3[δin(ch)](17)+r2[δtrig(9)+δin(ch)(7)]+r4[υ(cc)](9)+δ(cho)(5) 1220 1206 1302 1205 1194 r1[γ(ch2)](77) 1202 1189 1282 1171 1173 r2[δin(ch)(29)+υ(cc)(13)]+r3[δin(ch)(12)+υ(cc)(10)]+r4[δin(ch)](7) 1195 1182 1266 1169 1171 r4[δin(ch)(49)+υ(cc)(8)]+δ(cho)(8)+r2[δin(ch)](6) 1177 1165 1244 1149 1148 δ(oh)(20)+υ(co)(18)+r4[δin(ch)](14)+r2[υ(c13c23)](7) 1160 1148 1234 1147 1142 r4[δin(ch)(30)+υ(cc)(17)]+r3[δtrig](9)+r4[δtrig)](7) 1146 1134 1223 1126 1115 r1[ρ(ch2)](85) 1122 1111 1175 1080 1113 υ(co)(20)+r2[δtrig](18)+r1[υ(co)](17)+δ(cho)(5) 1076 1067 1171 1066 1067 r1[υ(co)](33)+r3[υ(cn)(7)+δtrig(5)]+r4[δtrig)](7) 1065 1056 1149 1065 1065 r4[υ(cc)(52)+δin(ch)(9)]+r1[υ(co)](16) 1053 1044 1109 1043 1040 r1[υ(co)](32)]+r4[υ(cc)](10)+r2[υ(cc)](9)+r3[υ(cn)](8) 1005 997 1107 999 1001 r4[oop(ch)(86)+puck(11)] 987 980 1104 982 980 r1[υ(co)](25)+r2[δ’a(10)+υ(c13c23)(7)+δtrig(5)]+r3[δtrig(14)+υ(cn)(7)]+r4[δtrig)](11) 980 973 1084 962 9961 r4[oop(ch)](89)+r4[τ’a](5) 952 946 1065 943 947 r1[υ(co)](68)+r1[δ’ring](8) 933 927 1043 920 928 r3[oop(ch)](63)+ puck(12)+oop(cn)(7)] 925 919 1011 903 915 r4[δtrig)](30)+r1[ν(co)](14)+r3[υ(cn)](8)+δ(no2)(7)+r2[δa](6) 905 899 997 901 897 r2[oop(ch)(73)+oop(c13c23)(6)+puck(7)+τa(6)] 881 876 970 877 872 r4[oop(ch)(81)+puck(5)] 870 865 934 856 862 r3[υ(cc)(23)+δ’a(6)]+r4[υ(cc)](10)+δtrig)(5)]+r1[υ(co)(10)+υ(cc)(5)]+r2[δa](8) 846 842 915 841 839 δ(no2)(30)+r3[υ(cc)(6)+δa(5)]+r2[υ(c13c23)](9)+r4[δtrig)](8) 804 800 889 791 797 ω(c=o)(30)+r2[oop(15)+δin)(6)](c13c23)(6)+puck(5)]+r1[δring](6 790 787 880 789 780 r3[puck](16)+r2[puck(14)+oop(c13c23)(11)]+r1[δring](12)+ω(c=o)(7) 787 784 860 777 778 r3[oop(cn)(15)+puck(15)]+ω(no2)(15)+r4[oop(ch)](15)+r2[puck](13) 775 772 856 766 770 r4[puck](37)+r3[puck](22)+ω(no2)(7)+r2[τa](5) 766 763 840 754 756 r4[oop(ch)](51)+r3[puck(11)+oop(cn)(7)]+r2[puck](7) 751 748 818 729 745 r1[δ’ring(31)+δring(24)]+r1[υ(co)](7) 735 733 806 727 726 r2[puck(24)+τa(8)]+r4[puck](16)+r3[δ’a](6) 721 719 784 714 r2[puck](36)+r4[puck](6)+r1[δ’ring](5) 702 700 765 700 702 r2[τ’a(10)+oop(c13c23)(7)+δin(c13c23)(7)+ω(no2)(7) 687 685 750 675 683 r2[τ’a](25)+r3[oop(cn)(9)+puck(7)]+τ(c8c9)(9)+r1[τ](5) 667 665 721 650 672 r4[δa)](32)+δ[(c=o)](22) 623 622 672 621 619 r4[δ’a)(30)+δa)(8)]+δ(c=o)](16)+r2[δa](8) 617 616 662 619 618 τ(o3c23)(23)+r2[oop(c13c23)(17)+τa(6)+puck(5)]+r3[puck(7) 609 608 659 607 600 r4[puck](12)+r4[δ’a)](12)+δa(8)]+r2[τa](11)+r3[puck](10) 584 583 628 592 589 τ(o3c23)(16)+r3[δa(11)+oop(cn)(5)]+r2[τ’a](11)+τ(c10c12)(5) 543 543 587 550 537 r2[τ’a(20)+τa(10)]+r3[oop(cn)(11)+puck(11)]+r4[τ’a](12) 536 536 580 530 531 r2[τ’a(10)+δ’a(9)+puck(5)+r3[δa](10)+ρ(no2)(9)+τ(c8c9)(7)+τ(c10c12)(6)+ρ(c=o)(6) 512 512 557 507 504 r2[τa(24)+oop(c13c23)(9)]+r3[oop(cn)](11)+r4[τa(10)+τ’a(8)] 450 450 493 447 447 r4[τ’a(24)+τa(18)]+r2[τa](16)+τ(c10c12)(11)+τ(c11c15)(6) 431 431 464 420 430 r2[δ’a(13)+τa(9)]+r3[oop(cn)(6)+δ’a(6)]+ρ(c=o)(10)+τ(c11c15)(7)+r2[puck](7) 401 402 436 402 r3[δa](14)+ρ(no2)(13)+r4[τ’a](13)+r2[δa](10)+τ(c11c15)(5) 375 376 409 378 r2[τ’a(15)+δ’a(10)]+τ(c11c15)(14)+r4[τ’a](13)+ρ(n=o)(8) 353 354 376 346 r2[δa(15)+δ’a(14)+υ(cc)(7)]+r3[δ’a(25)+δa(5)]+r1[υ(co)](5) 339 340 366 344 r3[υ(cn)(21)+υ(cc)(13)+δ’a(11)]+r2[υ(cc)(10)+υ(c13c23)(7)]+δ[(c=o)](5) 328 329 361 r2[oop(c13c23)(13)+τ’a(9)+τa(8)]+τ(c8c9)(12)+r1[τ](11+τ(c11c15)(9)+r2[puck](5) +ρ[(c=o)](5) 302 303 330 308 τ(c11c15)(33)+r2[τa(6)+τ’a(6)]+r4[τa](9)+r1[τ’](7)+r3[puck](6) 274 275 299 288 τ(c11c15)(13)+r3[δa](9)+τ(c8c9)(6)+r4[τ’a](8) 257 259 283 255 r3[oop(cn)](30)+r4[τ’a](16)+r2[τa](11)+τ(c8c9)(5) 203 204 222 201 r2[τ’a(16)+oop(c13c23)(8)]+r3[δin(cn)](15)+r1[τ](13)+τ(c10c12)(12)+r4[τa](7) 198 199 213 199 r2[δin(c13c23)(17)+oop(c13c23)(7)+τ’a(6)]+r1[τ](11) 185 186 204 r2[oop(c13c23)(17)+τ’a(15)]+τ(c10c12)(14)+r4[τa](9)+r1[τ](6)+r3[oop(cn)](5) +τ(c11c15)(5) 173 174 188 r2[δin(c13c23)(19)+τ’a(7)]+r3[δin(cn)](17)+τ(c10c12)(13)+r4[τa](7)+r1[τ’](5) 154 155 164 151 r1[τ’(50)+τ(27)] 109 109 124 τ(nc)(37)+r2[δin(c13c23)(14)+τ’a(5)]+r3[δin(cn)](9) 100 101 111 r2[τ’a(25)+τa(12)]+τ(c11c15)(13)+r1[τ](10)+τ(nc)(9)+τ(c10c12)(8) 92 93 100 85 r2[oop(c13c23)](19)+τ(c8c9)(16)+r3[oop(cn)](14)+r1[τ’](12)+τ(c10c12)(9)+r1[τ](7) 80 81 90 83 τ(nc)(31)+τ(c13c23)(30)+r2[τa(11)+τ’a(5)]+τ(c10c12)(8) 69 69 76 r2[τ’a(39)+τa(10)]+τ(c13c23)(12)+τ(c8c9)(10)+τ(c10c12)(8)+r4[τa](8) 38 38 41 41 r2[τa(27)+τ’a(11)]+τ(c13c23)(20)+τ(c8c9)(20)+τ(nc)(7) proposed assignments and potential energy distribution (ped) for vibrational normal modes. types of vibration: ν, stretching; δ, deformation (bending), scissoring; oop, out-of-plane bending; ω, wagging; γ, twisting; ρ, rocking; τ, torsion. apotential energy distribution (contribution ≥ 5). 3.4.3 c-no2 vibrations there is one nitro (no2) group connected with the ring r3 as a functional group in this molecule. generally, the asymmetric no2 stretching modes are expected in the interval 1600-1500 cm-1 and symmetric stretching modes in the interval 1400–1300 cm-1 in the ir absorption bands [39]. in this study, the asymmetric n=o vibration is calculated at 1562/1734 cm-1 in the dft/hf, which matches well with a weak band at 1539 cm-1 in the ir and the medium intensity band at 1534 cm-1 in the raman spectrum. khadka and joshi / bibechana 12 (2015) 40-52: p. 48 cm-1 in the raman spectrum. the symmetric n=o vibration is calculated at 1353/1473 cm-1 in the dft/hf, which is observed with the weak intensity at 1348 cm-1 in the ir spectrum and the strong peak at 1348 cm-1 in the raman spectrum. this mode is mixed with no2 deformation and c-n stretching vibration of the ring. the deformation (or scissoring) of no2 vibration is calculated at 842/915 cm-1 in the dft/hf and observed at 841/839 cm-1 in the ir/raman spectra. the no2 wagging vibration is calculated at 784/860 in dft/hf, which is observed at 777 cm-1 in the ir spectrum and 778 cm-1 in the raman spectrum. the mixed rocking mode vibration of no2 is calculated at 536/580 cm-1 in dft/hf. fig. 4. observed and calculated ft-ir spectra between the ranges 400-3600 cm -1 . 3.4.4 ring r1 vibrations there is one ch2 moiety in this five membered planer ring. basically, one can expect six fundamental modes associated with each ch2 group vibrations namely: symmetric, asymmetric stretch, deformation and rocking modes which belong to polarized in-plane vibrations. in addition to that, ch2 wagging and twisting modes would be expected to be depolarized out-of-plane symmetry species. the asymmetric ch2 stretching vibrations are generally observed in the range 3000–2900 cm-1, while the symmetric stretch appears in the region 2900–2800 cm-1 [40,41]. in this study, the pure ch2 asymmetric stretching vibration is calculated at 2998/3160 cm-1 in the dft/hf, which is observed at 2999 cm-1 in the ir spectrum and 2995 cm-1 in the raman spectrum. symmetric stretching vibrarion of this group is calculated at 2830/3061 cm-1 in the dft/hf and assigned at 2852 cm-1 in the ir and 2880 cm-1 in the raman spectra, respectively. the ch2 deformation calculated at 1514/1648 cm-1 in the dft/hf is observed with good agreements with strong band at 1523 cm-1 in the ir and with weak band at 1508 cm-1 in the raman spectra, respectively. the mixed ch2 wagging vibration is calculated at 1415/1569 cm-1 in the dft/hf, which is assigned at 1417 cm-1 in the ir spectrum and at 1406 cm-1 in the raman spectrum. the pure ch2 rocking mode is calculated at 1134/1223 cm-1 in the dft/hf. this mode is observed at 1126 cm-1 in the ir and at 1115 cm-1 in the raman spectra, respectively. the twisting vibration of ch2 is calculated at 1206/1302 cm-1 in the dft/hf. khadka and joshi / bibechana 12 (2015) 40-52: p. 49 3.4.5 ring r2 vibrations an aromatic six membered ring r2 lying between r1 and r3 have a methine (ch) and a carboxyl (cooh) moiety as functional groups. the characteristic region for the identification of c-h stretching in the heteroaromatic structures is 3100–3000 cm-1 [42,43]. in this study, the c-h stretching vibration is calculated at 3087/3233 cm-1 in the dft/hf as a pure mode. the observed ir/raman peaks are at 3038/3083 cm-1. the mixed in-plane deformation is calculated at 1189 in dft and at 1282 cm-1 in hf, respectively. the observed wavenumbers of this mode are 1171 cm-1 in the ir spectrum and at 1173 cm-1 in the raman spectrum. the c-h out-of-plane deformation is calculated at 899/997 cm-1 in the dft/hf, which is observed at the peaks 901 cm-1 in the ir and at 897 cm-1 in the raman spectra, respectively. fig. 5. observed and calculated ft-raman spectra between the range 0-3700 cm -1 . 3.4.6 ring r3 vibrations the six membered ring r3 has a ch and one no2 moiety. the c-h stretching vibration is calculated at 3065/3223 cm-1 in the dft/hf and observed at 3072 cm-1 in the raman spectrum. the c-h inplane deformation is calculated at 1217/1322 cm-1 in dft/hf and observed at the very weak band in raman spectrum. the out-of-plane deformation is calculated at 927/1043 cm-1 in the dft/hf, which is observed in the bands at 920 cm-1 in the ir and at 928 cm-1 in the raman spectrum, respectively. the mixed c-c ring stretching vibrations are calculated below 772/856 cm-1 in the dft/hf calculations. the highly mixed c-n stretching vibrations are calculated below 1380 cm-1 in dft with low contributions. the dft calculation yields c-n out-of plane deformations below 950 cm-1 as mixed modes and with low contributions. similarly, the c-n and in-plane deformations are calculated below 500 cm-1. khadka and joshi / bibechana 12 (2015) 40-52: p. 50 3.4.7 ring r4 vibrations ring r4 is also a phenyl ring having four methine moieties and connected with the other ring r3 as shown in the fig. 1. the c-h stretching vibrations are calculated as the pure modes in the ranges 3106-3032 in the dft and 3269-3175 cm-1 in the hf, respectively. the mixed c-h in-plane deformations are calculated at 1504, 1528, 1271, 1182 and 1148 cm-1 in the dft, which have good agreements with the observed ir and raman bands. similarly, these wavenumbers are calculated at 1630, 1603, 1344, 1266 and 1264 cm-1 in the hf method. the c-h out-of-plane deformations are calculated below 1000 cm-1 in the dft. these mixed modes of vibration are calculated below 1110 cm-1 in the hf. in the dft, the c-c ring stretching vibrations are calculated at 1618 and 1543 cm-1, which match with the strong peak at 1626, 1525 cm-1 in the ir spectrum and with the weak peaks at 1609, 1541 cm-1 in the raman spectrum. the trigonal deformation, puckering, asymmetric deformation and asymmetric torsion of this ring are calculated at 919, 772, 622 and 450 cm-1 in the dft method. 4 conclusion in the present study, the frequency assignments of the normal modes of aa ii using the spectroscopic intuition as well as the quantum chemical calculations were performed. the comparison of the results of experimental and theoretical study has given a full description of the geometry, vibrational wavenumbers and electronic properties of this molecule. the scaled wavenumbers obtained using dft/hf methods for aa ii, showed good correlation with the observed raman and ft-ir spectra. any discrepancies noted between the observed and the calculated wavenumbers was observed due to the fact that the calculations have been actually performed on single (or isolated) molecule in the gaseous state. by mapping molecular electrostatic potential surface (mep) on the electron density isosurface helps in assessing information regarding the size, shape, charge density distribution 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[38] j.p. abraham, spectrochim. acta a, 71 (2008) 355. http://dx.doi.org/10.1016/j.saa.2008.01.010 [39] s.n. terekhov, v.s. chirvonyi, p.y. turpin, j. appl. spectrosc., 67(5) (2006) 796. http://dx.doi.org/10.1023/a:1004199313485 [40] d. sajan, j. binoy, b. pradeep, k. venkata krishna, v.b. kartha, i. hubart joe and v.s. jaykumar, spectrochim. acta a, 60 (2004) 173. http://dx.doi.org/10.1016/s1386-1425(03)00193-8 [41] k. furic, v. muhacek and m. bonifacic, i. stefanic, j. mol. struct., 267 (1992) 39. http://dx.doi.org/10.1016/0022-2860(92)87006-h [42] v.k. rastogi, m.a. palafox, r.p. tanwar and l. mittal, spectrochim. acta a, 58(9) (2002) 1987. http://dx.doi.org/10.1016/s1386-1425(01)00650-3 [43] m. silverstein, g.c. basseler and c. morill, spectrometric identification of organic compounds, wiley, new york, 1981. 169-174 mahendra sahi r c o s t n m. sahi / bibechana 11(1) (2014) 169-174: (online publication: march, 2014) p.169 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana some special characterisations of fredholm operators in banach space mahendra shahi department. of mathematics, m.m.a.m. campus, biratnagar tribhuvan university, nepal e-mail: mshahi11@hotmail.com accepted for publication: february 06, 2014 abstract a bounded linear operator which has a finite index and which is defined on a banach space is often referred to in the literature as a fredholm operator. fredholm operators are important for a variety of reasons, one being the role that their index plays in global analysis. the aim of this paper is to prove the spectral theorem for compact operators in refined form and to describe some properties of the essential spectrum of general bounded operators by the use of the theorem of fredholm operators. for this, we have analysed the fredholm operator which is defined in a banach space for some special characterisations. © 2014 rcost: all rights reserved. keywords: bounded linear operator; compact operator; fredholm operator; banach space. 1. introduction an operator k defined by a kernel k is called a fredholm type operator. the name goes back to swede, e. ivar fredholm who developed a comprehensive theory for integral equations of second kind at the beginning of the twentieth century [4]. let x = y = c[a,b] be a banach space.let k(s,t) be defined for a≤s≤band a≤t≤b. then for each xϵx the riemann integral � k�s, t�x�t�dt �1� � exists and defines a continuous function of s on [a,b]. the integral (1) defines a linear operator k on x into x. if we take kx = y to mean y�s� = � k�s, t�x�t�dt �2� � the equation(2) is known as fredholm type integral equation of the first kind [7]. another operator t is obtained by defining tx = y to mean m. sahi / bibechana 11(1) (2014) 169-174: (online publication: march, 2014) p.170 y�s� = x�s� − � k�s, t�x�t�dt �3� � here k(s,t) is a continuous function on [a,b]×[a,b] and is called the kernel of the integral equation. y(s) is continuous on [a,b] and therefore yϵc[a,b]. the equation(3) is known as fredholm type integral equation of the second kind [5]. equations of this sort are of great importance. the application of this operator plays a vital role in the theory of boundary value problems in differential equations. fredholm studied fredholm type integral equations of the second kind, which gave rise to such operators. in view of the development of the theory of fredholm operators the following definitions are frequently used. definitions fredholm operator (i) a closed linear operator which has a finite index is called a fredholm operator. (ii) let x and y are banach spaces. a linear operator t from x to y is called a fredholmoperator if i. t is closed. ii. the domain of t is dense in x. iii. α(t), the dimension of the null space n(t) of t is finite. iv. the range of t is closed in y v. b(t), the co-dimension of r(t) in y is finite. the terminology stems from the classical theory of integral equations. special types of fredholm operators were considered by many authors since that time but systematic treatment were not given until the work of atkimon [1], gohberg [4] and yood [9]. a general account of the history of the theory is given by [a]gohberg krein [3] and (b) kato [5]. for a good general account of the theory can be found in the book written by gohberg [4]. definition(3) let b & c be two banach spaces. a bounded linear operator a: b → c is defined to be a linear map for which the norm ∥ a ∥∶= sup�∥ af ∥∶ ∥ f ∥≤ 1 � is finite. definition(4) let x and y be normed linear spaces. suppose t is a linear operator with domain x and range in y. we say that t is compact if for each bounded sequence {xn} in x, the sequence {t xn} contains a sub sequence converging to some limit in y. a compact operator is also called completely continuous. lemma (1) if a is a compact operator on b, then (λia) is fredholm for all λ ≠ 0. proof: we first prove that ℒ≔ker(λi a) is finite dimensional by contradiction. if this were not the case there would exist an infinite sequence xnєℒ such that ∥ x� ∥ = 1 and ∥ x − x� ∥ ≥ 1/2 for all distinct m and n. since axn = λxn and λ ≠ 0, we could conclude that axn has no convergent subsequence. we can write b=ℒ + m, where ℒ ∩ m = {0}and m is a closed linear subspace on which (λi a) is one-one. we next prove that ℛ≔ran(λi-a) is closed. if gnє ℛand ∥ #$ − # ∥ →0, then there exist fn є m such that gn= (λia)fn. if ∥ f� ∥ is not a bounded sequence then by passing to a subsequence (without m. sahi / bibechana 11(1) (2014) 169-174: (online publication: march, 2014) p.171 change of notation) we may assume that ∥ f� ∥ → ∞ as n → ∞. putting hn≔ fn/∥ %$ ∥we have∥ ℎ$ ∥ =1 and kn≔ (λi a)hn → 0. the compactness of a implies that h n = λ-1(ahn + kn) has a convergent subsequence. passing to this subsequence we have hn → hwhere ∥ ℎ ∥ = 1, h є m, andh = λ-1ah. we conclude that h є m ∩ ℒ. the contradiction implies that ∥ %$ ∥ is a bounded sequence. given this fact the compactness of a implies that the sequence fn = λ-1(afn + gn) has a convergent subsequence. passing to this subsequence we obtain fn→fas n → ∞, sof = λ-1(af + g), and g = (λi a)f. therefore ℛ is closed. since ran(λi a) is closed, an application of the hahn-banach theorem implies that its codimension equals the dimension of ker(λi a*) in b*. but a* is compact, so this is finite by the first paragraph. our next theorem provides a second characterization of fredholm operators. theorem (1) every fredholm operator has closed range. the bounded operator a : b → c is fredholm if and only if there is a bounded operator b : c → b such that both (ab i) and (ba i) are compact. proof: if a is fredholm then b1≔ ker(a) is finite-dimensional and so has a complementary closed subspace b0 in b. moreover a maps b0one-one onto co ≔ ran(a). if c1 is a complementary finite-dimensional subspace of c0 in c then the operatorx : b0⨁ c1 → c defined by (�% ⨁ )� ≔ *% + ) is bounded and invertible. we deduce by the inverse mapping theorem that c0≔x(b0) is closed. this completes the proof of the first statement of the theorem. still assuming that a is fredholm, put b(g⨁v) ≔(a 0) -1g for all g є c0 and v є c1, where a0 : b0 → c0is the restriction of a to b0. then bis a bounded operator from c to band both of ,≔ *. − /, ,0 ≔ .* − / �1� are finite rank and hence compact. conversely suppose that a, bare bounded, k1, k2are compact and (1) hold. then ,12�*� ⊆ ,12�/ + ,0�, 456�*� ⊇ 456�/ + ,-�. since (i + k1) and (i + k2) are both fredholm by lemma (7.1), it follows that amust be fredholm. the proof of theorem (1) provides an important structure theorem for fredholm operators. theorem (2) if a is a fredholm operator then there exist decompositions b = b0⨁ b1 and c = c0⨁ c1 such that (i) b0and c0 are closed subspaces; m. sahi / bibechana 11(1) (2014) 169-174: (online publication: march, 2014) p.172 (ii) b1and c1 are finite-dimensional subspaces; (iii) b1 = ker(a) and c0= ran(a); (iv) index(a) = dim(b1) dim(c1); (v) a has the matrix representation * = 9*: 0 0 0< �2� where a0 : b0 → c0 is one-one onto. example (1) let a be a fredholm operator on the banach space b. prove that if ker(a) = {0} then ker(a i) = {0} for all small enough . it can be proved that if ran(a) = bthen ran(a i) = b for all small enough . before stating our next theorem we make some definitions. we say that λ lies in the essential spectrum essspec(a) of a bounded operator a if (λi a) is not a fredholm operator. since the set κ (b) of all compact operators is a norm closed two-sided ideal in the banach algebra ℒ(b) of all bounded operators on b, the quotient algebra c := ℒ(b)/ κ(b) is a banach algebra with respect to the quotient norm ∥ >�*� ∥≔ inf �∥ * + , ∥∶ , ∈ κ�.�� where π : ℒ(b) → cis the quotient map. the calkin algebra c enables us to rewrite theorem (1) is particularly in a simple form. theorem (3) the bounded operator a on b is fredholm if and only if π(a) is invertible in the calkin algebra c. if a є ℒ(b) then bccde1f�*� = de1f�>�*��. proof : both statements of the theorem are elementary consequences of theorem (1). corollary: if a : b → b is a fredholm operator and b ≔ a + k where k is compact, then b is a fredholm operator and bccde1f�*� = bccde1f�.�. theorem (4) if a is a fredholm operator on b then a* is fredholm. proof : suppose that ab = i + k1 and ba = i + k2 where k1, k2 are compact. then b*a* = i + k1* and a*b* = i + k2*. we deduce that a* is fredholm by applying theorem (1). m. sahi / bibechana 11(1) (2014) 169-174: (online publication: march, 2014) p.173 example (2): prove directly from the definition that if a1 and a2 are both fredholm operators then so is a1a2. note: if b1 = b2 then this is an obvious consequence of theorem (7.3), but there is an elementary direct proof. theorem (5) if a:b → c is a fredholm operator, then there exists є >0 such that every bounded operator x satisfying ∥ ( − * ∥<∈ is also fredholm with h6i1j�(� = h6i1j�*�. proof: we make use of the matrix representation of theorem (2). if ( = 9. k l b< and ∥ ( − * ∥<є then ∥ . − *: ∥< cϵ, so b is invertible provided ϵ > 0 is small enough. if f ϵ boand g ϵ b1then x(f ⨁g) = 0 if and only if .% + k# = 0, l% + b# = 0. this reduces to �b – l.n-k�# = 0, where (e – db-1 c)g : b1 → c1, both of these spaces being finite-dimensional. we deduce that iho�,12�(�� = iho�,12�b – l.n-k�� for all small enough є > 0. by applying a similar argument to (∗ = 9.∗ l∗ k∗ b∗< we obtain iho�kqr12�(�� = iho�kqr12�b − l.n-k�� for all small enough ε > 0. problem now implies that h6i1j�(� = h6i1j�b − l.n-k�� = iho�ℬ-� − iho�k-�. this formula establishes that index(x) does not depend on x, provided ∥ ( − * ∥is small enough. theorem (5) establishes that the index is a homotopy invariant: if t → a t is a norm continuous family of fredholm operators then index(at) does not depend on t. in a hilbert space context one can even identify the homotopy classes. m. sahi / bibechana 11(1) (2014) 169-174: (online publication: march, 2014) p.174 conclusion thus, we see that fredholm operators are important for variety of reasons, one being the role that their index plays in global analysis. the dimension of null space n(t) and the co-dimension of r(t) of the operator t are finite and it is closed and range of the operator is also closed. the application of this operator plays a vital role in the theory of boundary value problems in differential equations. references [1] f-v atkinson, acta sci. math., 15 (1953) 38. [2] bovenbek boss, j. phillips, canada. j. math., 57 (2005) 225. [3] i.c. gohberb, m. g. krein, amer. math. soc. transl., 13 (1960)185. [4] s. goldberg, unbounded linear operators, mc graw hill, new york, 1966. [5] t kato, perturbation theory for linear operators, springer, 1996. [6] g. kothe, topological vector spaces, vol. 1.and vol. ii, 1979. [7] a.e. taylor, d. c. lay, introduction functional analysis, 2nd ed. wiley, new york, 1980. [8] a.e. taylor, theorems on ascent, descent, nullity and defect of linear operators, math. ann., 163 (1966) 18. [9] b. yood, properties of linear transformations: preserved under addition of a completely continuous trans. duke math., j. 18. m.a. lone et al. / bibechana 13 (2016) 72-76 : rcost p.72 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal fuzzy linear mathematical programming in agriculture m a. lone 1, m. s. pukhta1* s. a. mir1 division of agri-statistics, sher-e-kashmir university of agricultural sciences and technology of kashmir, india 190025 *e-mail: mspukhta_67@yahoo.co.in article history: received 08 august, 2015; accepted 13 september, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13363 abstract in this paper we present a fuzzy linear mathematical programming approach for optimal allocation of land under cultivation. fuzzy mathematical programming approach is more realistic and flexible optimal solution for the agricultural land cultivation problem. in this study we have discussed how to deal with decision making problems that are described by fuzzy linear programming (flp) models and formulated with the elements of uncertainty. this form of approximation can be convenient and sufficient for making good decisions. ©rcost: all rights reserved. keywords: fuzzy linear programming; trapezoidal membership function; maximizing income; and crop combination. 1. introduction many problems in agriculture planning, science and engineering are important from both social as well as economic point of view. there is always a need of more production to meet the increasing demands of the population. farmers usually encountered large number of problems related to allocate the optimum number of plants in their farms in order to get the best possible result. there are number of ways of achieving high productivity is to increase the area under cultivation. the production of crops can be increased by proper utilization of resources. the most crucial factor in agriculture is planning; several operations research techniques have been used in agricultural planning. the most commonly used technique in agricultural planning is linear programming (lp). in reality, a manufacturer may start a production process with budget i.e. a minimum amount for investment. but in course of time the manufacture may have to invest a little more than the initial proposed budget in the interest of his production process. in this situation fuzzy set theory can be used to formulate the model with the help of membership functions. again in real life situations, a linear programming model involves parameters m.a. lone et al. / bibechana 13 (2016) 72-76 : rcost p.73 (online publication: dec., 2015) whose values are not known but assigned by experts. these assigned values are not exact and the decision maker has to deal with uncertainties that are described by manufacture. we will study fuzzy linear programming (flp) models in which the parameters are known only partially to some degree of precision. the first mathematical formulation of fuzziness was pioneered by zadeh [1]. orlovsky [2] made a numerous attempts to explore the ability of fuzzy set theory to become a useful tool for adequate mathematical analysis of real world problems. several authors use different methods to solve the various types of flp problems. fuzzy methods have been developed in virtually all branches of decision making problems can be found in tamiz [3], zimmermann [4] and ross [5]. senthilkumar and g.rajendran [6] solve the flpp with fuzzy variables in parametric form. the comparisons between fuzzy numbers using ranking functions can be found in campos and verdegay [7] and maleki et al [8] where crisp model is defined. in this paper a methodology to solve the fuzzy linear programming (flp) problem with trapezoidal membership is considered. 2. model formulation consider the following linear programming model: maximize z = cx subject to ax ≤ b (1) x ≥ 0 where c = 1˟ n vector of components, a = m × n matrix of coefficients, b = n ×1 vector of all crisp parameters and x = is a decision variable vector. definitions:1) a fuzzy vector x is a basic solution of the flpp if it satisfies set of constraints (ax ≤ b). 2) a fuzzy vector x is a feasible solution of the flpp if it satisfies set of constraints (ax ≤ b) non-negativity condition x ≥ 0. 3) a feasible solution of fuzzy vector x that optimizes the objective function z = cx is the optimal solution to the flpp. 4) the value of the objective function provided by the optimal solution is called an optimal value. the characteristic function 5) the characteristic function a of crisp set xa assigns a value 0 or 1 to each member in x .this function can be generalized to a function ~a such that the value assigned to the element of the universal set a : ]1,0[x and indicates the membership grade of the element in the set. the function )(xa is called membership function of set x. a generalized fuzzy number a is said to be a generalized trapezoidal fuzzy number denoted by (a, b, c, d; w) if its membership is given by m.a. lone et al. / bibechana 13 (2016) 72-76 : rcost p. 74 (online publication: dec., 2015) elesewhere dxc cd xdw cxbwx bxa ab axw a 0 , )( ,)( , )(         (2) a fuzzy number a is said to be a trapezoidal fuzzy number denoted by (a1, a2, a3, a4; w) if its membership is given by elesewhere axa aa xa axax axa aa ax a 0 , )( ,1)( , )( 43 34 4 32 21 12 1         (3) the parametric form of a fuzzy number a can be written in terms of ordered pair of functions (amin( ) and amax( )), 0≤ ≤1.,where amin( ) and amax( ) are bounded left non decreasing and bounded right non increasing functions over [0,1].in our case , the parametric form of a trapezoidal fuzzy number b= (b1, b2,b3,b4) can be written as b= ( (b2b1)+ b1, b4- ( b4b3)) the system (1) can be written in parametric form as maximize z= c1(x1 l, x1 r) + . . . + cn(xn l, xn r) subject to (4) ah1(x1 l, x1 r)+ . . . + ahn(xn l, xn r) ≤(bh l, bh r) xj l, xj r ≥0. for all h = 1,2, . . . ,m and j = 1,2, . . ., n. numerical example a farmer has around 15 hectares farm on which he plants three crops: corn and rice and maize. each crop has certain requirements for capital($) and labor (hrs) as given in table (1) below. table 1 crop(per acre) capital($) labor(hrs) rice 42 8 maize 24 6 oats 19 2 m.a. lone et al. / bibechana 13 (2016) 72-76 : rcost p.75 (online publication: dec., 2015) in this example the profit per acre of rice crop is $30, per acre of maize crop is $25 and per acre of oats crop is $20.the total capital and time available for working these crops are about $400 and around 45 hours respectively. now, it is required to determine how many hectares of each crop should be planted in order to maximize the farmer’s profit. let x1 be the planted area with rice, x2 be the planted area with maize and x3 be the planted area with oats. each vague data are represented by a trapezoidal fuzzy number as: 15 hectares = (12, 15, 17, 18); about $400 = (370, 400, 430, 450); around 45 hours = (40, 45, 50, 55). now the fuzzy linear programming problem (flpp) can be written as maximize z=30 x1 +25 x2+20 x3 subject to 42 x1 + 24 x2 + 19 x3 ≤ (370, 400, 430, 450) 8 x1 + 6 x2 + 2 x3 ≤ (40, 45, 50, 55) x1 + x2 + x3 ≤ (12, 15, 17, 18) x1 , x2, x3 ≥ 0 crisp multi objective linear programming problem of above flpp can be written as maximize z1 = 30 x1 l +25 x2 l+20 x3 l and maximize z2 = 30 x1 r +25 x2 r+20 x3 r subject to 0≤ ≤1 42 x1 l + 24 x2 l + 19 x3 l ≤ 30 +370 42 x1 r + 24 x2 r + 19 x3 r ≤ 450-20 8 x1 l + 6 x2 l+ 2 x3 l ≤ 5 +40 8 x1 r + 6 x2 r + 2 x3 r ≤ 55-10 x1 l + x2 l + x3 l ≤ 3 +12 x1 r + x2 r + x3 r ≤ 18- x1 l, x2 l, x3 l, x1 r , x2 r, x3 r ≥ 0 the results can be obtained through lingo 13.0 [9] for different values of as given in table (2) below. table (2) represents the results of crisp linear programming problem. the optimal solution of the original problem is x1= (2, 2, 2.54, 2), x2= (0, 0, 0, 0), x3 = (9.33, 10.91, 11.70, 12.50) and the optimal value is z = (246.6, 278.20, 294, 310).also it can be seen from table (2) which cropping combination provides us best optimal solution. m.a. lone et al. / bibechana 13 (2016) 72-76 : rcost p.76 (online publication: dec., 2015) table 2  0 0.50 0.75 1 x1 l 2 2 2.54 2 x2 l 0 0 0 0 x3 l 9.33 10.91 11.70 12.50 x1 r 3.16 2.50 2 1.83 x2 r 0 0 0 0 x3 r 14.83 15.0 15.08 15.16 maximize z1 266.66 295.83 310.41 325.0 maximize z2 391.66 375.00 366.66 358.33 . 3. conclusion this paper has discussed the use of fuzzy linear programming for solving a production planning problem in agriculture. it concludes that how the farmer gets best possible result with the use of limited resources and how flpp is converted into crisp multi objective linear programming problems. in this paper only trapezoidal membership function is considered. in the future various membership functions will be considered like logistic, s-curve, z-shaped function, pi function etc. references [1] l. a zadeh, inform. contr., 8 (1965) 338-353. [2] s. a orlovsky, fuzzy sets and systems, 3 (1980)311-321. [3] m. tamiz, multi-objective programming and goal programming theories and applications, germany : springerverlag, 1996. [4] h.j. zimmermann, fuzzy set theory and its applications, (2nd rev .ed). boston: kulwer, 1991. [5] t.j. ross, fuzzy logic with engineering applications, new york: mcgraw-hill, 1995. [6] p. senthilkumar and g. rajendran, on the solution of fuzzy linear programming problem, international journal of computational cognition, 8(3) (2010)45-47. [7] l. campos and j. l. verdegay, fuzzy sets and systems, 32 (1989)1-11. [8] h.r. maleki, m. tata, m. mashinchi, fuzzy sets and systems, 9 (2000)21-33. [9] lingo 13.0, lindo inc. ltd. microsoft word mohan k. shrestha _70-75_.doc mohan k. shrestha / bibechana 7 (2011) 70-75: bmhss 70 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana effect of sewage and industrial effluents on flowering behavior and yield of pea (pisum sativum l. var. arkel) mohan kumar shrestha∗∗∗∗ dept. of biology, bhanu memorial higher secondary school, biratnagar, nepal article history: received 25 november 2010; accepted 5 december 2010 abstract municipality sewage and effluents from shah udyog and dairy farming were taken to assess the flowering behavior and yield of pea. the effluents from dairy farming initiated flowering earlier than the other effluents while effluents of shah udyog retarded comparatively. the same trend was followed for anthesis, withering and pod appearance. duration of anthesis was found increasing in the order: dairy farming, municipality sewage, control and shah udyog respectively. on the other hand, number of seed per plant and dry weight per seed was found in decreasing order from dairy farming to shah udyog through municipality sewage. key words: effluents; flowering; yield; inhibition and promotion 1. introduction discharge of waste unscientifically is a major problem in the large cities and industrial area like biratnagar (lat n 26 0 29’, long e 87 0 16’, altitude 72m).the industries viz. textile , sugar, leather, soap, plastic, iron rod, stainless steel, liquors, biscuits, dairy, oil seed extraction mills etc. discharge their untreated waste directly into the natural environments thereby polluting them [1-5]. the liquid waste of this city is discharged mainly to the singhia river through municipal sewage. the industrial effluents are discharged directly into the neighbouring water bodies or into the agricultural land. the polluted water thus produced is being used by the farmers to irrigate their crop land that adds plant nutrients to some extent and increases fertility of soil but also includes toxicants that change soil fertility and micro-flora [6]. as it needs to investigate the effects of effluents on the different parameters before using them in irrigation, an attempt has been made to find out effect of effluents from municipality sewage, dairy farming and shah udyog on flowering behavior and yield of pea (pisum sativum l. var. arkel). 2. materials and methods the seeds of pea were obtained from siwani seeds selling centre, biratnagar and were stored in air tight plastic bottle in dark room under ambient conditions. the municipality sewage ∗ corresponding author: mohan k. shrestha, dept. of biology, bhanu memorial higher secondary school, biratnagar, email:stha.mohan@yahoo.com mohan k. shrestha / bibechana 7 (2011) 70-75: bmhss 71 was collected from the discharge point of the sewer of biratnagar municipality, located at the bank of singhia river. the effluents were collected directly from the outlet of the factories and were stored inside the air tight polythene containers in dark room under ambient conditions. the colour (visual appearance), ph (ph meter method), dissolved oxygen (winkler’s method), solute particles [7]and organic matter [8] were recorded within three days of effluent collection(table 1). the concrete pots (diameter 44.5cm, depth 23.4cm) were filled with mixture of garden soil, compost manure and sand in the ratio of 2:1:1 by volume. ¾ parts of them were buried in the field. the seeds were sown in the pots and were irrigated daily with tap water. each treatment was carried out in triplicates. the effluent treatment was started when the seedlings were 30 days old. each pot for particular effluent/control was irrigated with 500ml of 100% effluent/tap water at the interval of 10 days. the seedlings were irrigated with tap water daily except the day of treatment. when the plants entered in reproductive phase, flowering behavior was observed daily for each treatment/control, the number of plants having floral buds, number of flowers, withered flowers and pods were recorded separately. the former two observations were recorded daily and the rest were recorded at the intervals of twelve hours. for the observation of anthesis, withering of flowers and pod appearance, 40 plants from each treatment were tagged randomly. for each treatment/control, the smallest visible bud was tagged and the time taken for anthesis was recorded. three independent observations were carried out to calculate the mean value. after harvesting, the number of pod(s) per plant and number of seeds per pod were recorded separately. the seeds from each treatment/control were oven dried at 80 0 c for 24 hours and the dry weight per seed was calculated. the experiments were conducted in 1999. 3. results and discussion the observation revealed that dairy farming and municipality sewage effluents initiated reproductive phase earlier (fig.1). the rate of increase in number of flowering plants was initially high in municipality sewage effluent but was leaded by dairy farming effluent in final days. the shah udyog effluent delayed the initiation of reproductive phase and the rate was also low. comparatively, the dairy farming and municipality sewage effluents correlated in other flowering and yield parameters i.e.; anthesis (fig.2, table 2), withering (fig.3 ), pod appearance (fig.4 ), number of pods, seed set and dry weight of seed (table 3 ). the shah udyog effluent on the other hand delayed all the parameters than the other effluents. the municipality sewage receives the discharge of liquid waste of colleges, hospitals, hotels, nursing homes and large number of household by-products that may contain high amount of organic and inorganic toxicants and stimulants for plant growth and development. the dairy farming effluent on the other hand may have less amount of inorganic toxicants but more organic ones as it involves more biological action on the milk and its products. similarly, shah udyog effluent contains different classes of dyes including naphthol, sulphur, chromate, basic and direct dyes used in cotton fabric production. some of these contain toxic chemicals e. g; chromium [9]. shrestha and niroula [10] reported that municipality sewage and dairy farming effluents are inhibitory for seed germination while shah udyog effluent stimulated this parameter. the inhibitory effect of the former two effluents on seed germination and stimulatory effect in flowering and yield suggests that these effluents are not suitable for the earlier developmental stages of pea but can be used to increase the yield after some chemical treatment. the shah udyog effluent on the other hand, though stimulatory in earlier stages of development, proved that it is not useful to get good yield of pea plant as it not only delayed the yield but the seeds set inside the pods were not fully developed. plants show different degree of responses with effluents at different stages and also the magnitude of toxicity depends upon species [2,5,11]. the present study also has shown that the mohan k. shrestha / bibechana 7 (2011) 70-75: bmhss 72 inhibitory effect of the effluents on the same plant in earlier stages of development has changed to stimulatory effect. to understand the exact nature and causes of different effluents/ sewage on the tested plants, it still awaits detail physico-chemical analysis and further research in different growth parameters. though the industrial and municipal sewage effluents may contain some useful organic and inorganic nutrients required for plants, their more toxic nature than useful property suggests not bringing them in use for irrigation without proper treatment. it is also indispensable to treat the effluent chemically before discharge to the surrounding water bodies to minimize water pollution and to save the quality of soil and surrounding air. table 1: physico-chemical characteristics of effluents and tap water (control) s.n. effluents /tap water parameters color solute (g/l) d.o.(mg/l) organic matter ph 1. dairy farming silvery white 1.4 3 only small amount 7.4 2. municipality sewage blackish turbid 1.5 2.5 high 7.1 3. shah udyog violet 1.7 3.6 moderate 7.1 4. tap water ---------0.4 4.15 negligible 6.9 mohan k. shrestha / bibechana 7 (2011) 70-75: bmhss 73 mohan k. shrestha / bibechana 7 (2011) 70-75: bmhss 74 table 2. effect of effluents on duration of anthesis of p. sativum. s.n. effluents/tap water time (in hours) 1. control 74.5 2. dairy farming 73.4 3. municipality sewage 73.6 4. shah udyog 76.1 table 3. effect of effluents on yield of p. sativum. seed s.n. effluents/tap water pod number / plant number/pod dry weight seed (mg) 1. control 1 1.2 66.7 2. dairy farming 1.2 1.4 87.1 3. municipality sewage 1.2 1.4 76.9 4. shah udyog 1.1 1.1 65.0 acknowledgement author is grateful to p. g. campus, biratnagar, nepal for providing laboratory facilities. mohan k. shrestha / bibechana 7 (2011) 70-75: bmhss 75 references [1] a. p. sharma and a. rijal, impact of industrial effluent on pollution of river and adjoining land, project report, national committee for man and biosphere (mab), kathmandu, nepal, (1988). [2] b. niroula, evaluation of some effluents on germination and growth of oryza sativa l.. cv. “chaite 4” and vigna mungo (linn) hepper. m. sc. thesis, dept. of botany, p. g. campus, biratnagar, nepal, (1996). [3] m. dahal, m. d. kafle and d. rijal, environmental impact assessment of rani, biratnagar, ( fieldwork report), department of botany, post graduate campus, t. u., biratnagar, nepal, (1997). [4] s. jha and b. niroula, t.u. journal, xxi(1)(1998) 63. [5] m. shrestha, effect of industrial and municipality sewage effluents on germination, growth and yield of pea (pisum sativum l. var. arkel ), m.sc. thesis, department of botany, post graduate campus, t. u., biratnagar, nepal, (2000). [6] p. k. goel and s. m. kulkarni, effects of sugar factory waste on germination of gram seed ( cicer arietinum l.) j. of environ. pollution, 1(1994) 35. [7] d. b. zobel, p. k. jha, m. j. benan and u. k. r. yadav, a practical manual for ecology, ratna book distributor, kathmandu ,(1987). [8] p. michael, ecological methods for field and laboratory investigations, tata mc graw hill publishing co. ltd., new delhi ,(1984). [9] npc/ iucn implementation project, balaju industrial district pollution control study, jeevan printing press, kathmandu, nepal, (1992). [10] m. shrestha and b. niroula, our nature, 1(2003) 33. [11] n. chapagain, physiological impact of dhobikhola (katmandu) water pollution on persicaria perfoliata l. leaves and germination of some vegetable seeds, m. sc. thesis, central department of botany, t.u., kathmandu, nepal, (1991). . microsoft word mohd yusuf yasin.doc mohd yusuf yasin / bibechana 8 (2012) 31-36 : bmhss, p. 31 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana scientific calculators and the skill of efficient computation mohd yusuf yasin ece department, integral university, lucknow, up, india e-mail: mmyasin@rediffmail.com article history: received 12 may 2011; accepted 21 june 2011 abstract calculators are part and parcel of modern education. involvement of science and engineering in different fields of knowledge is increasing with each bit of time is passed by, and they are playing a role in description and characterization of the delicate phenomena of nature arising day by day. these fields of knowledge and mathematics in particular, are influencing even those distant branches of knowledge, which were so far imagined to be free of mathematics. even art is not free of mathematics and there exists mathematical art. computations are getting lengthy and complex specially in design and analysis of engineering systems. scientific calculators are handy tools. but an efficient computation is a skill that can be developed. keywords: scientific calculators; calculator techniques; efficient computation; efficient use of calculators, computation skills; numerical techniques 1. introduction today’s world is of science and technology. science has pervaded in other branches of knowledge, it has become difficult to think a subject thoroughly explained without inviting science to help. more insight into the natural phenomena are required and as a way, they demand computations. subjects specifically related to engineering and technology, are heavily computational. fortunately, powerful computing devices are readily available and in every body’s reach. it has been observed that usually students buy scientific calculators. but it is a pity that most of these students usually imagine the operations of multiplying and dividing, and computations of functions like sine and cosine is the all a scientific calculator can do. today’s scientific calculators are highly powerful and if their operation is properly understood, a little innovative imagination can do wonders. long calculations are a normal part of design and analysis, where students spend time like anything, and conclude the computational procedure in distaste. in this short paper efforts are made to point out that this attitude needs a rethinking on the process afresh to settle down the matters favorably. mohd yusuf yasin / bibechana 8 (2012) 31-36 : bmhss, p. 32 2. preliminaries a little knowledge is required before one should start working with a calculator. every calculator is complemented with a manual, which delineates the calculator capabilities. it needs proper attention to go through the manual. scientific calculators are highly capable and therefore are complex entities. their functioning is grouped. therefore a calculator needs to be prepared for a proper functioning. a very common mistake usually observed in this context is the computation performed on functions containing ‘circular functions’ without a care of the proper mode of their arguments or computations on functions containing a ‘log’ without an idea of the natural log or log on base 10. such improper modes lead to wrong results and may cause a failure to maintain interest in the process of design and analysis both. 3. calculator techniques almost all scientific calculators posses a temporary register under the key ans, which automatically modifies after each computation, and holds the current result. in design or analysis, this result is usually needed by the next step. still there are examples where recursive computations are necessary to ascertain the final results. normally, calculators have a few more variable like a, b, c, ;, but presently a description is restricted on some simple tricks based upon the ans key only. in fig.1 the general scheme adopted here is presented. figure 1: general flow graph of the computational procedure mohd yusuf yasin / bibechana 8 (2012) 31-36 : bmhss, p. 33 in the following sections, two examples are considered for the purpose of description on how the calculator tricks are applicable to ease the process of approaching final accurate result recursively. in both these examples, due to their simplicity and excellent bidirectional approach to the final accurate solution, the simple newton – raphson method is employed. 3.1 calculators referred in this article, scientific calculators referred to as the casio make only, like fx-82ms, fx-991ms or later versions. all these calculators have a distinct feature of displaying full scientific equations before and after the calculation is done. a ‘scientific calculator’ afterwards refers to a calculator possessing these specific features. other brands of calculators with similar features can also be used for the purpose of this article, possibly with a little or no modification in the computational scheme depending upon their operating principles [1,2]. 3.2 example – 1: square root of a given number in the first example, computation of the square root of a given number ‘a‘ is considered. let x be the square root of the number a thus mathematically this can be represented as ax =2 , and the corresponding functional equation is axxf −= 2 )( . according to the ordinary newton – raphson method, the square root is approached by the equation )( )( '1 n n nn xf xf xx −=+ , where nx is the first approximation, 1+nx is the new improved approximation and )(' nxf is the first derivative of the function )( nxf . when applied to the required square root of the given number, this approximating equation can be expressed as [3]:       +=+ n nn x a xx 2 1 1 (1) this method is particularly important as it is quite fast in approaching the final reasonable result in just a few iterations. further, the final result is possible even when an absurd initial approximation is adopted, of course, in such a case, total number of iterations may be increased. for applying a scientific calculator, the above root approximating equation is considered for determining a square root of the given number 3, with an initial approximation, say, 1. the procedure can be as follows. 1. type the initial approximation, (say, ‘1’ for this example) and press ‘=’ (enter through the key ‘=’ in casio calculators, refer, fx-82ms, fx-991ms). this step stores the ‘1’ in the register associated with the key ‘ans’. as every result is automatically stored under the key ‘ans’, therefore this key can be used as a variable. hence, the square root determining equation can be re written with ‘ans’ as variable,       += ans a ansans 2 1 (2) here in equation (2), the ‘ans’ inside the braces refers to nx and contain the last result, whereas the ‘ans’ outside refers to 1+nx and automatically modifies to the latest result. as mohd yusuf yasin / bibechana 8 (2012) 31-36 : bmhss, p. 34 per the data handling scheme of the calculators, the equation (2) is read as       +← ans a ansans 2 1 , where the calculation results on the right hand side are transferred to the register attached to the ‘ans’ key, 2. second step is to type the equation in accordance with the right hand side of the above equation assuming the variable key ans and do the required computation by just pressing the ‘=’ key as many number of times as required. the sequence of keys pressed on a calculator may be as follows: 1 =; ( ans + a / ans ) / 2 = = = (3) in this construct, each key is separated by multiple spaces for the sake of clarity only, the spaces are not a part of the equation. as is evident from the calculation of the examples below, for three iterations, the total number of key presses are just 14 in each case. convergence of 3 to it’s final numerical value is as follows: ans ← 1.0 ans ← 2.0 ans ← 1.75 ans ← 1.732142857 ans ← 1.73205081 ans ← 1.732050808. (4) the value calculated from the calculator is 732050808.13 = , thereby showing no error in the two results. however, 732.13 = is normally the accepted approximate value, and is available within third iteration. 3.3 root of an equation again, consider to find the intersection of the curves [4] xy cos= and xy = . (5) it is a single root problem. a solution exists as shown in fig. 2. analytically, the solution is obtained as follows. applying the ordinary newton raphson method, equation for solution is obtained as xxxf cos)( −= from eq. (5) above. the corresponding approximation equation to it’s root is n nn nn x xx xx sin1 cos 1 + − −=+ n nnn x xxx sin1 cossin + + = . (6) mohd yusuf yasin / bibechana 8 (2012) 31-36 : bmhss, p. 35 the computational equation for a calculator is written as given in equation (7) ans ansansans ans sin1 cossin + + = (7) convergence pattern of the root of the above equation with 1.0 as initial approximation, and for ‘radians’ as the mode of calculation, is figure 2: graphical solution of the equations of section 3.3 [4] ans ← 1 ans ← 0.750363867 ans ← 0.73911289 ans ← 0.739085133 ans ← 0.739085133 (8) a root of third decimal place accuracy is again achieved just within three iterations. it is important to consider that the concerned equations contain circular function, and therefore the selection of the mode radian becomes important. the results presented above are obtained in radian mode. purpose of the problem in equation (5) is to bring out the importance of consideration as mentioned earlier. in the solution of equation (6), ‘deg’ mode selection will produce a look alike root, 0.999847784, which unfortunately is not a root but merely an approximation of the equation (5) for the argument of the circular function tending 0 ( 0;cos →xx ). this situation arises due to an inappropriate mode selection. 4. discussions the above examples are common yet simple and are readily available in text books on advanced mathematics for engineers and scientists, numerical techniques etc. here the point of emphasis is how to make the computation effectively. the effective computational process for example in section 3.2 for a single digit number as per the flow graph, needs, all in all, 14 judicial key presses mohd yusuf yasin / bibechana 8 (2012) 31-36 : bmhss, p. 36 on an already on calculator. however, the engineering students have often been observed haggling for hours over solving such problems and with absurd or at least, inaccurate come outs. 5. conclusion for fields like numerical methods, where usually computations are huge but are iterative in nature, it is important to optimize computational efforts. such efforts are based on computational skills. these are some of the calculator tricks presented here which can be found quite useful. scientific calculators are quite powerful, but their real power remains untapped. a little practice can help develop the capability to perform computations in technical manner. references [1] users’ guide, fx-82ms/83ms/85ms/270ms/300ms/350ms, http://support.casio.com [2] users’ guide, fx-95ms/100ms/115ms/(912ms)/570ms/991ms, http://support.casio.com [3] erwin kreyszig, advanced engineering mathematics, 5 th edition, wiley eastern limited, 1989, pp 764 [4] http://www.sosmath.com/calculus/diff/der07/der07.html; graphical solution for the equations given in eq. (5) microsoft word arun kumar khan _88-91_.doc a. k. khan / bibechana 9 (2013) 88-91 : bmhss, p.88 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana compressibility and moelwyn-hughes parameter of nai crystals under high pressure, as the function of thermal properties arun kumar khan department of physics, r.m college, saharsa, india e-mail : arunkumarkhan@gmail.com article history: received 8 october, 2012; accepted 7 november, 2012 abstract the credit for the commencement of inter ionic potential function goes to born and lande, one of whose milestone has been their expression into inverse function. similarly, born and mayer also proposed the exponential function of the potential for the repulsive component. however none of them could get the desired success. subsequently, many more prominent scientists devoted their effort towards these thermal properties of the crystals, among which the endeavour of jha and thakur cannot be overlooked, who proposed a new interionic function to observe the properties of ionic crystal under high pressure. during its formulation they included both an inverse power function due to born and lande and an exponential function due to to born and mayer. appreciably, jha and khan used it for studying the hyped thermal properties of nai and csi crystal under high pressure up to 100 kilo bar. keywords: moelwyn-hughes parameter; isothermal compressibility; nai crystals; debye temperature 1. introduction solid state physics went through a roller coaster ride in the begining of the last century. riding on the same momentum, born model of ionic solids [1] provided a substantial method to calculate the elastic and thermal properties of ionic crystal under high pressure, whose calculations are based on an inter ionic potential function. repulsive term being an important component of the potential function, has been described by born and lande by an inverse power function, whereas, the same has been described as an exponential function by born and mayer. in contrary, roberts and smith [2] found none of these functions to be successful, if the compression of sodium halide crystals are concerned. 2. formalism the new inter ionic potential function as proposed by jha and thakur [3] has included both an inverse power function due to born and lande and an exponential function due to born and mayer as it repulsive component. after which, jha [4] used it for studying the thermal properties of nai and csi crystal under a. k. khan / bibechana 9 (2013) 88-91 : bmhss, p. 89 (online publication: nov., 2012) high pressure. to our happiness, we disclose the thunderous success of this potential to describe the elastic properties of nai crystals under high pressure up to 100 kbar. using reduced units of equilibrium inter ionic distance r0 for distance and e2/r0 for energy, the new interionic potential for the crystal under study can be written as [3] where r is the inter ionic distance, a , b , m & n are the potential parameters which are constants for a given cnrystal , m is the madelung constant , c & d are van der walls costants for dipole-dipole and dipole-quadruple interactions , respectively and e is the electronic charge.crystal properties have also been calculated using born-lande’ and born mayer potential for the sake of comparison. these can be written as: 3. results and discussion jha and thakur [3] have described a procedure, using which the parameters of the new potential have been calculated. m obtains only integral values, whereas n has been varied in steps of 0.1. the data for input crystal has been taken from tosi [1] and ashcroft and mermin [5]. potential parameters of the born – mayer potentials have been calculated in the usual manner. values of potential parameters for the crystal under study have been listed in table 1. table 1: potential parameters of nai crystals in reduced (dimensionless) units parameter value parameter value c 0.0595 born lande’ potential d 0.0075 8.3678 new potential 0.25868 m 4 born mayer potential n 2.9 1/ee 9.3678 a 0.213852 2704.6774 b 2.110957 at a given compression, the pressure has been calculated with the help of debye’s equation of state [6], p = -( ðeo/ ðv) + γ ed/v (4) here eo is the internal energy of the volume, p pressure at 0 kelvin, ed the debye energy of the crystalat the temperature at which the crystal properties are being studied, and γ the gruneisen parameter. here we a. k. khan / bibechana 9 (2013) 88-91 : bmhss, p.90 (online publication: nov., 2012) have taken in to account the variation of ed and γ with pressure, but their temperature has been ignored. ed has been calculated by calculating the debye temperature. jha and thakur[3] explained the calculation fig. 1. variation of isothermal compressibility with pressure of gruneisen parameter and debye temperature. the isothermal compressibility has been calculated with the relation kt = 1/v (ðv/ðp)t (5) the moelwyn-hughes parameters[7,8] is the pressure derivative of the isothermal bulk modelus bt. it is defined by c1 = (ðbt/ðp)t (6) the computed results have been displayed in fig. 1 and 2. fig. 1 shows the variation of kt with pressure at room temperature (298 k) . fig. 2 shows the variation of c1 with pressure at room temperature. curves marked l have been drawn using the born-lande’ potential, curves marked m using the born-mayer potential and curves marked n using the new potential. the open circles are estimates of kt and c1 obtained from the compression data of bridgman [9] using a modified murnaghan equation [10, 11]. this equation helps us to express bt as a parabolic function of p, bt= b0+b1p+1/2b2p 2 (7) it follows from the definition of the moelwyn-hughes parameter that c1=b1+b2p (8) values of b0, b1 & b2 have been mentioned in figure 1. a. k. khan / bibechana 9 (2013) 88-91 : bmhss, p.91 (online publication: nov., 2012) fig. 2. variation of moelwyn-hughes parameter with pressure 4. conclusion however, the observation cannot be overlooked that the inverse power law of born lande’ is not apposite for predicting the elastic properties of nai crystal under high pressure, whereas the exponential laws is better for studying the elastic properties of crystal under high pressure. the new potential is most successful in explaining mechanical and thermal properties of nai crystal under high pressure i.e, from 100 kilo bar study. references [1] m.p. tos, solid state physics, ed. f. seitz and d. turnbull, academic press, 16 (1964) 1. [2] r. w. roberts and c. s. smith, j. phys. chem. solids, 31(1970) 619. [3] b. n. jha and k. p. thakur, physics, 173b (1991) 408. [4] b. n. jha, physica, 192b (1993) 253. [5] n. w. ashcroft and n. d. mermin, solid state physics, holt, rinehart and winston, new york (1976) 459. [6] c. kittel, introduction to solid state physics, john wiley and sons, inc., new york (1996) 182. [7] k. p. thakur, acta cryst., a32 (1976) 363. [8] k. p. thakur, physics of the earth and planetary interiors, 27 (1982) 235. [9] p. w. bridgman, proc. amer. acad. arts sci., 76 (1945) 1. [10] f. d. murnaghan, proc. nat. acad. sci. usa, 30 (1944) 244. [11] f. d. murnaghan, finite deformation of an elastic solid, john wiley and sons, inc., new york (1951). further readings [12] zhang hong tangjin and cheng xin-lu, chinese physics letters (2008). [13] ayu.. kuznetsov, l. dubrovimin sky, a kurnosov, m. m. lucchese, w. crichton and c.a. achete, advances in physical chemistry, (2009)article id 180784. [14] alapana tiwari, n. k. gaur and p singh, journal of physics (2010). [15] a.k. khan, bibechana, 7 (2011) 49. microsoft word s.r.b. _13-17_.doc s.r.b. thapa / bibechana 9 (2013) 13-17 : bmhss, p.13 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana study of lattice dynamics of silicon s. r. b. thapa birendra multiple campus, bharatpur,chitwan, nepal article history: received 25 november, 2011; accepted 14 july, 2012 abstract lattice dynamics of si has been investigated by using a urey-bradley valence force field (uvff) model which is a phenomenological model. in this model following interactions are taken into account: (i) the central force due to bond-stretching (ii) the angular force due to bond bending (iii) central force between non-bonded atoms (iv) the force due to interaction of one internal co-ordinate to adjacent internal coordinate. calculated results of phonon dispersion curves, debye characteristic temperature, microscopic elastic constants and bulk modulus of si are compared with experimental results giving fairly good agreement. keywords: phenomenological model; phonon frequencies; debye characteristic temperature; microscopic elastic constants; urey bradley valence force field (uvff) approximations 1. introduction yin and cohen [1] investigated theoretically lattice dynamical properties of diamond crystal si using ab initio pseudopotential theory within the local density functional formalism. inter-planar and inter-atomic force constants in si has been investigated using adiabatic bond-charge model by fleszar and resta [2]. bose et al.[3] investigated phonon dispersion curves of si in three symmetry directions of brillouin zone using the angular forces of type employed by delaunay and clark, gazis and wallis. phonon frequencies, elastic constants, specific heat and debye temperature of diamond structure crystal si has been investigated by zdetsis and wang [4] using born von-karman (bvk) model. lattice dynamical calculations of phonon scattering at ideal si-ge interfaces has been done by zhao and freund [5]. dispersive elastic constants of si has been determined by jakata and every [6].maranganti and sharma [7] incorporated third and fourth order spatial derivatives of the displacement field in the elastic wave equation to calculate elastic constants of si. urey-bradley valence force field (uvvf) model which is successfully used to investigate the lattice dynamics of diamond by thapa [8] is extended to study the lattice dynamics of diamond like crystals si. in this paper urey-bradley valence force field (uvvf) is assumed to describe the forces operating inside the solids which crystallize in diamond structure. urey-bradley valence force field is the combination of the simple valence force field and the central interaction between the non-bonded atoms. thus forces considered are those which resist the extension or compression of valence bonds together with those which oppose the bending or torsion of bonds and central interaction between the non-bonded atoms. contribution to potential energy from other neighbours except first and second neighbours has been neglected because of the short range character of the force field. the coulomb electrostatic interactions are not considered since atomic charges are either zero or very small. s.r.b. thapa / bibechana 9 (2013) 13-17 : bmhss, p.14 (online publication: nov., 2012) 2. theoretical models theoretical model used in this paper is reported by thapa [8].the secular determinant for the normal modes of vibration of the atoms in the crystal is given by 0 ),( 2 = −′ ′kkkkd δδω αβαβ q (1) dαβ (q,kk ′ ) represents the elements of the dynamical matrix d(q) and ω is the angular frequency of the normal modes of the vibration of the crystal. δαβ and δkk′ are the usual kronecker delta functions. solving the secular determinant for long wavelength limit, following expressions for the three elastic constants for the diamond structure crystal are obtained in terms of model parameters kr , krr , kr1 and ϒ/r0 2 . c11 = 1/2a[(1/3)kr – (1/6)krr + 4kr1 + 4(ϒ/r0 2 )] (2) c12 = 1/2a[(1/3)kr – (1/6)krr + 2kr1 2(ϒ/r0 2 )] (3) c44 = 1/2a[(1/3)kr – (1/6)krr + 2kr1 + (2/3)(ϒ/r0 2 ) – a 2 /b] (4) where a = [(2/3) kr – (1/3)krr – (8/3)(ϒ/r0 2 )], b = [(4/3) kr – (2/3)krr + (32/3)(ϒ/r0 2 )] solving the secular determinant along [100] direction one gets (i) at zone centre ( γ ) (ωlo) 2 ( γ ) = 2/m[(4/3) kr – (2/3)krr + (32/3)(ϒ/r0 2 )] (5) (ii) at zone boundary ( x ) (ωlo) 2 ( x ) = 1/m[(4/3)kr – (2/3)krr + 8kr1 +(40/3)(ϒ/r0 2 )] (6) (ωto) 2 ( x ) = 1/m[(4/3)kr – (2/3)krr + 4kr1 +(20/3)(ϒ/r0 2 ) + {(4/3)kr – (2/3)krr (16/3)(ϒ/r0 2 )}] (7) numerical computation with the help of equations (5), (6) and (7) along with equilibrium condition of the lattice model parameters are evaluated. input data for evaluating model parameters kr, kr1 , krr and (ϒ/r0 2 ) are given in table 1 & 2 while evaluated values of model parameters are given in table 3. table-1:zone boundary phonon frequencies of si crystal zone boundary and zone centre phonon frequencies(10 12 hz) reference νlo(x) νto(x) νlo(γ) si 12.32 13.90 15.53 nilsson and nelin [9] table-2: lattice constant and mass of si crystal lattice constant (2a) mass(m) si 5.4307 × 10 -8 cm 46.629 × 10 -24 gm table-3:evaluated values of model parameters of si using the evaluated values of model parameters elastic constants c11, c12, c44 and bulk modulus are evaluated using equations (2),(3)&(4). crystal f orce constants (10 4 dyne cm -1 ) (ϒ/r0 2 ) kr kr1 krr si -2.141340 0.535335 -28.824330 0.548956 s.r.b. thapa / bibechana 9 (2013) 13-17 : bmhss, p.15 (online publication: nov., 2012) table 4: elastic cnstants and bulk modulus in units of 1012 dyne cm-2 calculated values of others experimental values jakata and every [6] present calculated values sokel and harrison [10] chadi and martin [11] baraff et al [12] c11 1.775 1.552 1.207 c12 0.745 0.748 0.860 c44 0.807 0.789 0.717 0.943 0.317 bulk mod. 1.088 2.000 2.00 the calculated values of model parameters are used to obtain phonon dispersion curves of si along [100],[11 0] and [111] directions. lattice specific heats at different temperatures is ( )∑       = ν ν ν tk h eg r c b v 6000 3 (8) ( )2 2 1− = x x x e ex e where x = hυ/kbt. h = plank’s constant, υ = frequency, kb is botzmann constant, t = temperature of crystal, r = universal gas constant. the computed values of cv are used to find debye characteristic temperatures from standard table of ( cv θd/t ) from saha and srivastava [13]. 3. results and discussion elastic constants the calculated values of elastic constants c11,c12 and c44 and bulk modulus of si in the present work along with their experimental values and calculated values of by other workers are shown in the table 4 for comparison. calculated result of c44 differs slightly with the experimental value but superior to the calculated value of baraff et al [12]. calculated values for c11 and c12 are in satisfactory agreement with their experimental results. the bulk modulus calculated in the present work is found to be nearly twice the experimental value. surprisingly the calculated value of bulk modulus is almost equal to the value obtained by harrison and sokel [14] calculated on the basis of linear combination of atomic orbitals (lcao). phonon frequencies propagation of acoustic phonons in si on the basis of two lattice dynamical models: a bond-charge model and effective force constant model consisting of only short range forces have been investigated by tamura et al. [15]. mazur and pollman [16] investigated lattice dynamics of si with semi empirical approach using tight binding green functions and dynamical matrix of the system has been set up. elastic constants and normal mode frequencies of si has been computed with empirical many-body potentials s.r.b. thapa / bibechana 9 (2013) 13-17 : bmhss, p.16 (online publication: nov., 2012) and compared with experimental results by cowley [17]. none of the models tested is completely satisfactory. the results of phonon dispersion curves in present work are shown in fig.1. along three symmetry directions [100], [110] and [111].the agreement of the results with the experimental values of dolling [18] and nilsson and nelin [9] shown in the figures is fairly satisfactory. our results are comparable with those of tubino et al. [19] and superior over the results of martin [20], soma and marita [21] and sinha et al. [22]. fig.1: phonon dispersion curves of si along symmetry direction [100],[110] and [111]. solid circles (••••) represent the experimental results due to dolling [18], nilsson and nelin [9]. solid lines represent calculated curve. debye temperature calculated debye temperatures of si are plotted against temperature in fig.5 along with experimental points of flubacher and leadbetter [23] giving fairly satisfactory agreement. the calculated values deviate from experimental values at higher temperature. divergence of the calculated result with experimental results is almost same as that of 16 parameter bvk model of zdetsis and wang (1979). thus only four parameter present harmonic model provides satisfactory result of debye temperature. fig.2: ( θθθθd – t ) curve for si. experimental points (0) are due to flubacher and leadbetter [23]. s.r.b. thapa / bibechana 9 (2013) 13-17 : bmhss, p.17 (online publication: nov., 2012) 4. conclusion the present lattice dynamical model having four disposable parameters which is successful in explaining the phonon dispersion relations, elastic constants and debye temperature of diamond, when extended for another diamond structure crystal si is capable to explain its lattice dynamic propertiesphonon frequencies, elastic constants and debye temperature. this model which does not require the employment of elastic constants for the evaluation of its model parameters very satisfactorily reproduces the values of elastic constants and bulk modulus of si. the results for these quantities obtained on theoretical considerations based on pseudopotential and lcao theories are found not superior and in some cases far inferior to the present results. this gives an emphasis on the suitability of the application of valence force fields to the covalent crystals which gave highly directional bonds resulting from the well defined orbital hybridization. introduction of interaction terms for changes in bond length and bond angles in the present formulation may improve the features of the present results. references [1] m.t. yin and marvin l. cohen, phys. rev.b,26 (1982) 3259. [2] a. fleszar and r. resta, phys. rev.b, 34 (1986) 7140. [3] g. bose, b.b.tripathi and h.c. gupta, j. phys. chem. solids, 34 (1973) 1867. [4] a. d. zdetsis and c. s. wang, phys. rev.b, 19 (1979) 2999. [5] h. zhao and j. b. freund, j. appl. phys. 97 (2005) 024903. [6] k. jakata and a.g. every, phys. rev.b, 77 (2008) 174301. [7] r. maranganti and p. sharma, phys. rev. letters ,98 (2007) 195504. [8] s. r. b. thapa j. purvanchal acad. sc.,17 (2011) (accepted paper). [9] g. nilsson and g. nelin, phys. rev.b, 6 (1972) 3777. [10] r. sokel and w.a. harrison, phys. rev. letters, 36 (1976) 212. [11] d.j. chadi and r. m. martin, solid state commun.,19 (1976) 193. [12] g.a. baraff, e.o. kane and m. schuluter, phys. rev.b, 21 (1980) 5662. [13] m. n. saha and b. n. srivastava, a treatise on heat,5 th ed., indian press , alllahabad (1965). [14] w.a. harrison and r. sokel, j.chem. phys.,65 (1976) 379. [15] s. tamura, j.a. shields and j.p. wolfe, phys. rev.b ,44 (1991) 3011. [16] a. mazur and j. pollman, phys. rev.b, 39 (1989) 5261. [17] e. roger cowley, phys. rev.lett. ,60 (1988) 2379. [18] g. dolling, inelastic scattering of neutrons, iaea(vienna) vol.ii, (1965) p-249. [19] r. tubino, l. poseri and c. zebri, j. chem. phys.,56 (1972) 1022. [20] r.m. martin, phys. rev., 186 (1959) 871. [21] t. soma and a. marita, j. phys. soc. japan, 32 (1972) 38. [22] s. k. sinha r.p. gupta and d.l. price, phys. rev.b, 9 (1974 )2564. [23] p. flubacher and a.j. leadbetter, philos. mag.,4 (1959) 273. microsoft word n.k. chaudhary pages _44-48_.doc n.k.chaudhary / bibechana 7 (2011) 44-48: bmhss 44 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana rotaxane: a switching element in molecular electronics n. k. chaudhary∗∗∗∗ dept. of chemistry, m.m.a.m. campus biratnagar, nepal article history: received 5 october 2010; revised 15 november 2010; accepted 22 november 2010 abstract the switching in materials is the most interesting phenomenon discovered in materials, both organic and inorganic. the switching materials opened a large class of applications in electronics and informatics. rotaxane is one such type of molecule which shows switching ability by the action of external stimuli either chemical or physical. reversible structural change occurring in rotaxane due to external stimulus is described and its application in nanorecording is also studied. keywords: cbpqt (cyclobis(paraquat-p-phenylene); ttf (tetrathiafulvalene); dnp (1,5dioxynaphthalene} 1. introduction rotaxanes have novel characteristics as a switching element in the molecular electronics. with the development of supramolecular chemistry, it has become possible to synthesize rotaxanes by template directed synthesis method developed by leigh et al. switching action of rotaxanes is due to movement of macrocycle over the axis of dumbbell shaped molecules. this opened a large class of applications in electronics and informatics. the use of switching in computer memories, in information recording and the application in automation and robotics are due to polyfunctional activities of rotaxanes. 2. structure of rotaxane a rotaxane is a mechanically interlocked molecular architecture consisting of a dumbbell shaped molecule, that is threaded through a macrocycle or ring-like molecule. its key structure contains a pie (π ) electron deficient macrocycle that is locked around a pie (π ) electron rich component along the molecular thread with two bulky stoppers .the macrocycle can move between different pie(π ) electron rich components of dumb bell shaped molecule by the action of external stimuli either chemical or physical, resulting in switching of electronic configuration [1]. this creates new configuration of molecules with different functions and acts as molecular ∗ corresponding author: n.k. chaudhary, department of chemistry, m.m.a.m. campus, tribhuvan university, biratnagar, email: chem_narendra@yahoo.com n.k.chaudhary / bibechana 7 (2011) 44-48: bmhss 45 switch. the binding site of macrocycle can be reversed back to its original position by another stimulus. such a molecule constitutes molecular shuttle. graphical representation of a rotaxane cyclobis(paraquat-p-phenylene) a rotaxane molecule firure: 1 external stimulus applied to affect in switching motion of rotaxane weakens the binding forces between the macrocycle and dumbbell shaped molecule. macroscopic machine uses power for intercomponental relative position changes while a switchable rotaxane performs shuttling motion in response to external stimulus. so molecular shuttle is also called molecular machine. 2.1 applications a. in molecular electronics as a memory device due to ability of rotaxanes to exist between two different co-conformations, they can store high density mass data irreversibly and show nonvolatile memory effect [2, 3]. controlling switching motion of rotaxane in solid state could be used to store information by encoding the two different states into binary digits. figure 2: graphical representation of a molecular memory based on [2] rotaxane. n.k.chaudhary / bibechana 7 (2011) 44-48: bmhss 46 in a nanorecording application, a certain rotaxane is deposited as a langmuir –blodgett film on ito coated glass. when a +ve voltage is applied with a tip of scanning tunneling microscope probe, the rotaxane rings in the tip area switch to a different part of dumbbell and the resulting new conformation makes the molecules stick out from the surface by 0.3 nm [4] and this height difference turns out to be sufficient for a memory dot. the dots could encode data into binary digits and such a film has capacity to store data up to 100 gbits per square inch. figure 3: the switchable [2] rotaxane used for nonorecording. in the bistable rotaxane[2] shown above that consists of a pie-acceptor tetracationic ring (cbpqt 4+ ) and two pie-donor stations (ttf and dnp), switching is originated due to reversible mechanical movement of the cbpqt 4+ macrocycle between ttf and dnp component triggered by chemical stimuli or electrical stimulus. in the ground state of the switch [5], the paraquat ring is located around a tetrathiafulvalene (ttf) unit but it moves to the dioxynapthyl unit (dnp) when the fulvalene unit is oxidized by application of a current. b. as a molecular transistor another use of switchable rotaxanes is for the fabrication of molecular transistors. a molecular shuttle can serve as a molecular switch, in that it can be triggered to switch between two different co-conformations. in the following scheme present an example of single molecule devices which contains molecular transistors based on a bistable [2] rotaxane. ttf cbpqt 4+ dnp ttf cbpqt 4+ dnp ttf cbpqt 4+ dnp ttf cbpqt 4+ dnp n.k.chaudhary / bibechana 7 (2011) 44-48: bmhss 47 (a) (b) (c) (d) figure 4: (a) sem pictures of single molecular devices fabricated on a si substrate. the centre metal electrode, where the break junction is made of 7 nm thick pt, followed by 100 nm thick gold wires and pads for wire bonding. (b) the sem image after the break junction is made. the gap between the two metal electrodes is around 4 nm. (c) a cross section through a single molecule transistor. (d) rotaxane which the molecular transistor is based on [2]. 3. conclusion exploring the physical properties of different types of rotaxanes on solid surfaces provides versatile and valuable information for the development of atomic and molecular devices and will open new future world in molecular electronics. it is inspiring that more fantastic properties have been found for nanometer scale materials, and more novel methods have been developed for fabricating nanometer scale functional materials. however, towards practical n.k.chaudhary / bibechana 7 (2011) 44-48: bmhss 48 application, there are still many challenges. we expect that these goals can be achieved by the collaboration of specialists in different areas and by the successful integration of various techniques into the challenging research on atomic scale engineering. references [1] m. feng, x. guo, x. lin, x. he, w. ji, s. du, d. zhang, d. zhu, and h.gao j. am. chem. soc., 127 (2005)15338. [2] h. tian and q. c. wang, recent progress on switchable rotaxanes, chem. soc. rev., 35 (2006)361. [3] j. p. miron (phd thesis-2008), universitat autonoma de barcelona -molecular modeling of switchable[2] rotaxanes. [4] m. popescu, a. velea, a. lőrinczi, f. sava, j. ovonic research 5 (2009) 27. [5] h. j. gao, li gao, progress in surface science, 85 (2010) 28. microsoft word reviewers.doc thanks to reviewers we greatly appreciate the voluntary contribution that each reviewer gives to the journal. we hope that our reviewers will help us by reviewing the articles submitted to bibechana in future also. prof. devendra adhikari editor-in-chief bibechana http://nepjol.info/index.php/bibechana/index reviewers dr. alev dogan, gazi university, ankara 6100, turkey. dr. xilian jin, college of physics, jilin university, china. dr. mohd nazri idris, universiti sains malaysia, engineering campus, malaysia. dr. aditya mahabhai vora, b. v. shah science college, gujarat, india. dr. b.p. singh, t.m. bhagalpur university, bhagalpur, india. dr. nicola seriani, ictp, strada costeera 11, 34151 trieste, italy. prof. ramazan sever, middle east technical university, turkey. dr. martin lopez corredira, instituto de astrofísica de canarias, tenerife, spain. prof. r.n. joarder, jadavpur university, kolkata-700 032, india. dr. g.s. shivaprasanna, amruta institute of eng. and manag. sc., bangalore. dr. b.c. paul, university of north bengal, india. prof. md. haider biswas, khulna university, khulna-9208, bangladesh. prof. r.b. chaudhary, bra, bihar university, muzafffarpur, india. prof. badiadka narayana, mangalore university, india. prof. b.k. singh, t.m. bhagalpur university, bhagalpur. dr. basant giri, university of wyoming, wyoming, usa. microsoft word b.p.singh _1-5_.doc b.p. singh et al. / bibichana 7 (2011) 1-5 : bmhss 1 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibichana complex formation in liquid potassium-lead alloy b.p. singha∗∗∗∗, d. adhikaria, i. s. jhab , b.k. singha a univ. dept. of physics, t. m. bhag. university, bhagalpur, bihar, india b dept. of physics, m.m.a.m. campus (tribhuvan university), biratnagar, nepal article history: received 24 september 2010; accepted 25 october 2010 abstract regular associated solution model has been used to study the mixing properties of kpb liquid alloy at 848 k. the values of different thermodynamic parameters obtained from this model are compared with corresponding experimental values. most of the computed values are in good agreement with the observed values. keywords: compound forming alloy; pairwise interaction energy; equilibrium constant 1. introduction liquid alloys, which are disordered systems in the sense of having no long-range atomic or magnetic order, display a remarkable variety of local chemical order. the free energy of mixing, heat of mixing and entropy of mixing of several liquid alloys are asymmetric with respect to concentration. the knowledge of thermodynamic and microscopic properties of binary liquid alloys is necessary for the design and development of reliable materials for high temperature application. the purpose of present investigation is to study energetic and structural properties of potassium lead alloy in molten state. potassium lead alloy in molten state is strongly compound forming alloy [1]. the phase diagram of kpb [2] lists kpb and kpb2 intermediate compounds in solid state. the formation of compound in solid state led many theoreticians to believe the existence of strong associations present in the alloy in molten state near melting temperature [4-13]. in this paper, we have calculated the equilibrium concentration of complex assuming kpb2 complex present in liquid state of kpb alloy at 848 k on the basis of regular associated solution model. we have then used these concentrations to calculate free energy of mixing (∆g) , heat of mixing (∆h) , entropy of mixing (∆s) and activities of pure species in liquid kpb alloy. 2. model basis suppose type a (=pb) and type b (=k) metals are mixed in the melt to form alloy ab (=pbk). according to regular associated solution model, the melt consists of three species namely unassociated a-atoms, unassociated b-atoms and complex ab. considering a solution of 1n ∗ corresponding author: dr. b.p. singh, univ. department of physics, t. m. bhagalpur university, bhag. india, email: bhrigunandan@gmail.com b.p. singh et al. / bibichana 7 (2011) 1-5 : bmhss 2 atoms of a and 2n atoms of b, the formation of apbn complex requires apba1 pnnn += and apbb2 nnn += for conservation of mass in the partially associated solution, where ,n,n ba and apbn are concentration of unassociated a-atoms, batoms and complex respectively where p is small integer. when there is association, the thermodynamic behaviour of complexes a and b components is governed by their true mole fractions ax , bx and apbx rather than their gross mole fraction 1x and 2x , where 21 1 1 nn n x + = , 21 2 2 nn n x + = apbba a a nnn n x ++ = , apbba b b nnn n x ++ = and apbba apb apb nnn n x ++ = (1) the free energy of mixing in regular associated solution model of given by [14] )xlnxxlnxxlnx(rt)xxxxxx[( )x21( 1 g bababbaa23bab13baa12ba ba 2222 2 +++ω+ω+ω + =∆ ]klnxrt ba2 + (2) where 12ω , 13ω and 23ω are pairwise interaction energies for the species a, b ; a, a2b and b, a2b respectively, k is equilibrium constant, t the temperature and r stands for the universal gas constant. the pairwise interaction energies and equilibrium constant are determined using the methods employed by lele and ramchandrarao [14]. once the expressions for g∆ is obtained, other thermodynamic and microscopic functions follow readily. heat of mixing and entropy of mixing are related to g∆ through standard thermodynamic relations p,t t g∆ tg∆h∆         ∂ ∂ −= (3) t g∆h∆ s∆ − = (4) following jordan [15] the activity coefficients aγ , bγ and ba2 γ of monomers and complex can be expressed in terms of pairwise interaction energies through )(xxxxlnrt 132312bab13 2 ba12 2 ba 22 ω+ω−ω+ω+ω=γ (5a) )(xxxxlnrt 121323baa12 2 a23 2 bab 22 ω+ω−ω+ω+ω=γ (5b) )(xxxxlnrt 231213bab23 2 b13 2 aba 22 ω+ω−ω+ω+ω=γ (5c) and ]x)x21(x[ rt ]x)x1(x2[ rt ]x)x1(x2[ rtx xx lnkln bbba 23 aaba 13 abb 12 ba b 2 a 22 2 −− ω +−− ω ++− ω +         = (6) 3. results and discussion the compositional dependence of various species (figure 1) shows that the maximum association occurs at 60 at. pct. of pb. at this composition and 848 k, about 52 mol pct. of the liquid alloy is associated. the equilibrium constant and interaction energies for the alloy pbk in liquid state are found to be k = 0.009, 12ω = -32523 j mol -1 , 13ω = -14110 j mol -1 and 23ω = -50596 j mol -1 b.p. singh et al. / bibichana 7 (2011) 1-5 : bmhss 3 all the interaction energies are found to be negative and show that left over pb and k atoms are attracted to each other and to the complex. theoretical calculation of free energy of mixing for pbk liquid alloy shows that the minimum value of free energy of mixing for pbk is -18.0 kjmol -1 at xag = 0.5. figure 1 : compositional dependence of mole fractions xa (a=pb), xb (b=k) and apbx (ab= pb2k) versus xpb (concentration of pb in the liquid pbk solution (848k) figure 2 : free energy of mixing (∆g) versus xpb (concentration of pb) in the liquid pbk solution (848 k); (––––) theory, (000) experiment [2] and heat of mixing (∆h) versus xpb (concentration of pb) in the liquid pbk solution (848 k) (………) theory, ( ××× ) experiment [2]. b.p. singh et al. / bibichana 7 (2011) 1-5 : bmhss 4 this minimum value of free energy of mixing of this alloy shows that pbk alloy in molten state is strongly interacting system. the agreement between calculated and observed value of free energy of mixing is good. it is found from the analysis that the interaction energy parameters are temperature dependent. the best fit values of temperature dependent interaction energy parameters and heat of dissociation are found to be 1112 kjmol20 t −−+= ∂ ω∂ , 1113 kjmol40 t −−+= ∂ ω∂ , 1123 kjmol45 t −−+= ∂ ω∂ and = ∂ ∂ t kln tr 2 35500 ± 1500 j mol -1 it is found from the analysis that the heat of mixing is negative at all concentration which is in agreement with experimental result. there is reasonable agreement between calculated and observed value of heat of mixing of pbk alloy in molten state. figure 2 shows the comparison between the experimental and calculated values of free energy of mixing and heat of mixing. the calculated value and observed value of entropy of mixing are furnished in figure 3. the calculated values of entropy of mixing do not always match in sign with experimental values. the deviation of calculated value of entropy of mixing is more below the concentration xpb = 0.6. the discrepancy could be due to errors in enthalpy data or neglect of vibrational and electronic contributions on entropy. the deviations in entropy are, however, not significant enough to influence the agreement between other calculated and observed thermodynamic functions as shown in figure 2. figure 3 : entropy of mixing (sm) versus xpb(concentration of pb) in the liquid pbk solution (848k); (––––) theory, (000) experiment [2]. the deviations from ideal behaviour of the alloy can be incorporated into activities. the calculated and experimental activities are compared in figure 4. there is a good agreement between the calculated and experimental values. b.p. singh et al. / bibichana 7 (2011) 1-5 : bmhss 5 figure 4: activity (a) of pb and k in liquid kpb solution (848 k) versus xmg ; (––––) theory, (○○○) and (xxxx) experiment [2]. 4. conclusion the analysis based on regular associated solution model shows that the kpb system is strongly interacting heterocoordination system and the pairwise interaction energies of this system depend strongly on temperature. our theoretical analysis also shows that there exist complexes pb2k in pbk alloy in molten state. acknowledgement d. adhikari gratefully acknowledges ugc, nepal for the financial support to conduct the research. references [1] p. p. nath and r. n. joarder, indian j. phys. ,84 (2010) 125. [2] r. hultgren, p. d desai, d.t hawkins, m. gleser and k.k. kelley, selected values of the thermodynamic properties of binary alloys (metals park, ohio: american society for metals (1973). [3] d. adhikari, b.p. singh, i.s. jha and b.k. singh, j. mol. liqs., 156 (2010) 155. [4] d. adhikari, i.s. jha and b.p. singh, phil. mag. 90 (2010) 2687. [5] a.b. bhatia and d.e. thornton, phys. rev., b 2 (1970) 3004. [6] r.n. singh, can. j. phys., 65(1987)309. [7] k. hoshino and w.h. young, j. phys. f. 10(1980) 1365. [8] s.p. mcalister and e.d. crozier, j. of phys., c7 (1974) 3509. [9] m. b. yang, y. l. ma and f. s. pan, trans. nonferrous met. soc. china, 19 (2009)1087. [10] a.r miedema, p.f de chatel and f.r. boer, physica b, 100 (1980) 1. [11] p. chieux and h. rupperesberg, j. phys. coll., 41(c8)(1980). [12] d. adhikari , i.s. jha and b.p. singh, physica b, 405(2010) 1861. [13] b.p. singh, d. adhikari and i.s. jha, j. non-crystalline solids, 356(2010) 1730. [14] s. lele and p. ramchandrarao, metall. trans. b, 12 (1981) 659. [15] a.s. jordan, metall. trans., 1 (1970) 239. microsoft word sanju dahal _113-120_.doc sanju dahal and d. thapa chhetry / bibechana 9 (2013) 113-120 : bmhss, p.113 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana anthropogenic impact on wetland bird diversity in and around of budhi and tengra rivers of itahari municipality sanju dahal , damodar thapa chhetry * department of zoology, post graduate campus, t.u. biratnagar, nepal corresponding author email: thp_damodar@rediffmail.com article history: received 25 september, 2012; accepted 15 november, 2012 abstract the diversity and population of birds was studied from january, 2011 to december, 2011, once a week regularly. altogether fifteen species of wetland birds were recorded from tengra and budhi rivers. maximum species were recorded in january and minimum in july and august. out of total bird species 40% were migratory, 46.67 % were resident, and 13.33 % were winter visitors. on the basis of abundance, there were 46.67% scarce, 33.33% fairly common and 20% common. on the basis of their population status, maximum number belonged to ardeola grayii species and minimum in leptoptilos javanicus species. maximum species of the birds belonged to family ardeidae. according to statistical analysis, the resident bird were more diversed then migrant and winter visitor respectively. similarly, resident birds were much evenly distributed then winter visitors and migrant respectively. the study revealed decreasing trend of bird species from previous period. the conversion of wetland into agricultural land and plotting programmes were the main causes to decline the bird species. keywords: budhi and tengra river; bird diversity; anthropogenic impact. 1. introduction birds are the beautiful creatures of nature. nepal is rich in bird diversity. there are 865 species of birds in nepal [1]. according to iucn category [2] list, 27 birds species are as threatened, 31 as critical, 44 as endangered, 54 as vulnerable, 1 having insufficient data and 9 as species needing more ecological information [3]. but the bird diversity threats are increased by human interference, direct and indirect resulting in habitat destruction and fragmentation. anthropogenic activities like mass bathing in holy ponds, cutting of emergent and fringed vegetation, draining of water, release of sewage, throwing of domestic garbage, weeds, developmental activities like construction of roads and retaining walls are some major threats to the birds. nepal's wetlands face threats from drainage, diversion, siltation, over enrichment, pollution and poisons used to kill the fish. sanju dahal and d. thapa chhetry / bibechana 9 (2013) 113-120 : bmhss, p.114 (online publication: nov., 2012) the mounting pressure of population explosion in the world including nepal indicates increasing food shortage. so, anthropogenic impact being a burning issue which is extending day by day. study area in and around of budhi and tengra rivers of itahari, municipality, sunsari (fig. 1) were chosen for the study of wetland birds. budhi river budhi river is one of the most important river of sunsari district which is originated from foot hill of mahabharat range. it flows eastern boarder of sunsari district and separates sunsari district from morang district. it passes through dharan-biratnagar highway at duhabi. this river flows with a definite course from its origin from nepal to india boarder. this river passes through charkoshe jhadee situated east of dharan-biratnagar highway. in this river, water remains throughout the year. sunsari-morang irrigational canal crosses this river near sisbani badahara village of morang, and number of outlet of this canal finally meets budhi river and it also acts as a escape drainage for sunsari-morang irrigation project. at the rainy season, the water of sunsari morang irrigation canal contains maximum amount of silt and clay which enters into the river through different outlet so that the water of this river becomes highly silty and turbid. the water of budhi river is clear in dry season. the sediment load in this season is zero. the sediment load is highest during the rainy season. in this season, the strong current also causes soil erosion and silting. the water level during the winter and summer decreases to considerable amount but doesn't dry up. hence, the rivers is potentially important for aquatic life as well as for the irrigation. tengra river tengra river is one of the most important river of sunsari district. it originates from the north of pindeswor and flows eastern side of sunsari district. it passes through dharan-biratnagar highway at south of itahari. this river also passes through charkoshe jhadee situated south of dharan upto tarahara. in this river water generally remains throughout the year. sunsari-morang irrigation canal crosses the river at khanar village. and number of outlet of this canal finally meets the tengra river and it also acts as a escape drainage for sunsari-morang irrigation project. at the rainy season the water of sunsari morang irrigation canal contains maximum amount of silt and clay which enters into the river through different outlet of this canal. so, that the water of this river becomes highly silty and turbid. this river finally meets with budhi river at south-east of sonapur. sanju dahal and d. thapa chhetry / bibechana 9 (2013) 113-120 : bmhss, p.115 (online publication: nov., 2012) 2. materials and methods the diversity and population of birds was studied from january, 2011 to december, 2011, once a week regularly. birds were counted by the direct observation and also collected informations from the local people. for the study of birds, binoculars (tasco, 8x21 magnification), camera (cannon 10 megapixel), field dairy were used. similarly, for the identification of the bird species, the main field books of fleming et.al.[4], inskipp and inskipp [5], shrestha [3], (grimmett et al.[1], were used. the list of observed bird was prepared. for the statistical analysis, species diversity of birds and evenness of species were calculated by using following methods: a. shannon weaver diversity index (h ) = ʃ pi log2 pi [6] where, pi = proportion of individuals b. evenness index (e) = ][ max 7 h h sh 2logmax = where s = number of species. anthropogenic impacts were studied through direct field visit and informations were collected by informal interview with local people. 3. results altogether fifteen species of wetland birds were recorded from tengra and budhi rivers. thirteen species were recorded in january and only four in july and august. total numbers of individuals counted during study period were 350. on the basis of their population status, maximum (sixty five) belonged to ardeola grayii species and the least, (two) belonged to leptoptilos javanicus species. on the basis of abundance, 46.67% birds were scarce, 33.33% were fairly common and 20% were common birds in study area. maximum species of the birds belonged to family ardeidae (table 1). variation of bird species and total number of individuals of the bird species on monthly basis have been shown in fig. 2 and fig. 3 respectively. seasonal status and abundance of birds on percentage basis have been shown in fig. 4 and fig. 5 respectively. sanju dahal and d. thapa chhetry / bibechana 9 (2013) 113-120 : bmhss, p.116 (online publication: nov., 2012) table 1 : list of observed bird species of study areas ss = seasonal satus ab = abundance r = resident c = common w = winter visitor fc = fairly common m = migrant sc = scarce s. no. common name scientific name family jan feb mar apr may june july aug sep oct nov dec total ss ab 1 little grebe podiceps ruficollis podicipedidae 6 2 1 9 w sc 2 little cormorant phalacrocorax niger phalacrocoracidae 3 4 15 1 2 1 3 2 3 34 w fc 3 pond heron ardeola grayii ardeidae 9 12 7 4 2 8 7 6 10 65 r fc 4 night heron nycticorax nycticorax ardeidae 2 2 3 2 9 m sc 5 cattle egret bubulcus ibis ardeidae 2 6 20 4 1 4 1 1 10 4 10 63 r fc 6 little egret egretta garzetta ardeidae 3 1 4 2 1 3 1 6 2 6 29 r c 7 intermediate egret egretta intermedia ardeidae 2 3 2 2 10 1 1 4 2 5 8 40 r fc 8 open-billed stork anastomus oscitans ciconiidae 4 3 1 5 4 2 1 1 8 4 4 37 r fc 9 lesser adjutant stork leptoptilos javanicus ciconiidae 2 2 m sc 10 black ibis pseudibis papillosa threskiornithidae 5 3 1 1 2 4 2 1 7 26 r c 11 white breasted kingfisher halcyon smyrnensis alcedinidae 1 2 2 5 m sc 12 eurasian kingfisher alcedo atthis alcedinidae 1 2 1 1 5 m sc 13 blueeared kingfisher alcedo meninting alcedinidae 1 2 3 m sc 14 lesser-pied kingfisher ceryle rudis alcedinidae 1 2 2 2 1 8 r sc 15 red-wattled lapwing vanellus indicus charadriidae charadriidae 2 1 1 1 2 1 1 total 36 36 55 28 30 18 7 6 26 43 21 44 no. of species 13 9 9 10 11 6 4 4 10 10 5 8 sanju dahal and d. thapa chhetry / bibechana 9 (2013) 113-120 : bmhss, p.117 (online publication: nov., 2012) fig. 2: variation of the bird species on monthly basis fig. 3: variation of total no. of individuals on monthly basis sanju dahal and d. thapa chhetry / bibechana 9 (2013) 113-120 : bmhss, p.118 (online publication: nov., 2012) piediagrams fig. 4: seasonal status of birds on percentage basis fig. 5: abundance of birds on percentage basis sanju dahal and d. thapa chhetry / bibechana 9 (2013) 113-120 : bmhss, p.119 (online publication: nov., 2012) according to statistical analysis, the resident birds were more diversed then migrant and winter visitor birds respectively (table 2, 3 and 4). similarly, resident birds were much evenly distributed then winter visitors and migrant birds respectively (table 5 ). table 2: analysis of species diversity of resident birds s.n. name of species n pi logpi log2pi pi log2pi 1 ardeola grayii 65 0.2416 -0.6169 -2.0493 -0.4951 2 bubulcus ibis 63 0.2342 -0.6304 -2.0941 -0.4904 3 egretta garzetta 29 0.1078 -0.9673 -3.2133 -0.3464 4 egretta intermedia 40 0.1487 -0.8277 -2.7495 -0.4088 5 anastomus oscitans 37 0.1375 -0.8617 -2.8625 -0.3966 6 pseudibis papillosa 26 0.0966 -1.0150 -3.3717 -0.3257 7 ceryle rudis 9 0.0334 -1.4762 -4.9038 -0.1638 total 269 -2.6238 table 3: analysis of species diversity of migrant birds s.n. name of species n pi logpi log2pi pi log2pi 1 nycticorax nycticorax 9 0.2368 -0.6256 -2.0782 -0.4921 2 leptoptilos javanicus 2 0.0526 -1.2790 -4.2487 -0.2235 3 halcyon smyrnensis 5 0.0131 -1.8827 -6.2541 -0.0819 4 alcedo atthis 4 0.0153 -1.8153 -6.0302 -0.0923 5 alcedo meninting 3 0.0789 -1.1029 -3.6637 -0.2890 6 vanellus indicus 15 0.0395 -1.4034 -4.6619 0.1841 total 38 -1.3629 table 4: analysis of species diversity of winter visitor birds s.n. name of species n pi logpi log2pi pi log2pi 1 podiceps ruficollis 9 0.2093 -0.6792 -2.2562 -0.4722 2 phalacrocorax niger 34 0.7907 -0.1019 -0.3388 -0.2679 total 43 -0.7401 4. discussion birds are suffering at the hands of human in different ways. they hunt them, take their eggs and graze domestic animals or introduce exotic predators into their habitats. habitat alteration, destruction or loss are the major threats to survival of birds [8]. in koshi tappu wildlife reserve, 461 species of birds representing 58 families were recorded. at least 176 species breed in the reserve and 180 species are passage migrant or visitors [9] in the present study fifteen species of water birds belonging to seven families were recorded. maximum number of species recorded during the study period of twelve months was thirteen in the month of january. least number of birds, four species was recorded on july and august. this may be due to local migration of resident bird, departure of winter visitors and commencement of monsoon season and this may also be caused due to habitat destruction of birds. the number of wetlands birds species recorded during this study period was compared with earlier records given by different researchers of various places. subba [10] recorded 86 birds in biratnagar. pandey [11] recorded 104 species of birds in itahari, out of which 22 were wetland birds. surana [12] sanju dahal and d. thapa chhetry / bibechana 9 (2013) 113-120 : bmhss, p.120 (online publication: nov., 2012) recorded 109 species of bird from chimdi lake of sunsari district, out of which fifty four species were wetland birds. similarly, thapa chhetry [13] reported hundred species of wetland birds from the wetlands of koshi tappu wildlife reserve and its surroundings. comparatively, the present study recorded less number of bird species. the present study showed decreasing trend of bird species from previous record, this may be due to different kinds of human activities. the feeding habit of bird has been highly affected by the urbanization and industrialization of the city. human beings are playing a destructive role to unbalance the system of nature. the main anthropogenic impacts were observed to decline the wetland birds are conversion of most of the wetlands around taltalaiya area of itahari into agricultural land, urbanization, pesticides, increment of human population by immigration from hills and mountains, cultivable lands have been changed into plotted area for construction and lands are left unfarmed etc. 5. conclusions the declining of bird species is mainly due to the anthropogenic factors. the anthropogenic factors include establishment of industry, urbanization, agriculture, mining, transportation, construction, waste disposal practices, vehicular air pollution, concentration of sewage and debris, habitat loss, encroachment on wetlands, loss of feeding ground, use of insecticide, lack of awareness about importance of birds. so, the study can be concluded that for the restoration of wetland bird species proper management, conservation planning and infrastructure development are essential. references [1] r. grimmett, c. inskipp, t. inskipp, birds of nepal, christopher helm. london (2009). [2] iucn, an inventory of nepal's wetlands, iucn-nepal kathmandu (1996). [3] t.k. shrestha, birds of nepal, field ecology, natural history and conservation, vol. i. r.k. printers. kathmandu (2000). [4] sr. r.l. fleming, jr. r.j. fleming, and l.s. bangdel birds of nepal. second edition, avalok, kathmandu (1979). [5] c. inskipp, and j. inskipp a guide to the birds of nepal, christopher helm. london (1985). [6] c.e. shannon and w. weaver the mathmatical theory of communication, university of illinois press, urbana (1963). [7] e.c. pielou the measurement of diversity in different types of biological collection, j. theoret diol, 1-3 (1966) 131-144. [8] h.s. baral,, c. inskipp, t. inskipp and u.r. regmi threatened birds of nepal, bird conservation nepal and department of national park and wild life conservation, kathmandu (1996). [9] iucn an interpretation and education system for koshi tappu wildlife reserve and its buffer zones, iucn nepal (1998). [10] subba, b.r. checklist of birds of biratnagar, newsletter for bird watchers, 34 (6) (1994) 128 129 [11] m.r. pandey birds of itahari, j. our nature, nature conservation and health care council, biratnagar, nepal, 1 (1) (2003) 64 67. [12] r. surana, wetland ecology of chimdi lake (birju tal), sunsari district, eastern nepal, department of zoology, post-graduate campus, biratnagar, tribhuwan university (m.sc. dissertation) (2005). [13] d. thapa chhetry studies on physico-chemical parameters and macrobiota with special reference to fishes in the wetland of koshi tappu wildlife reserve and its surroundings, nepal, ph. d. thesis, north bengal university, india (2006). microsoft word r.r.thapa _92-99_.doc r. r. thapa and m.r. hassan / bibechana 10 (2014) 92-99 : bmhss, p.92 (online publication: dec., 2013) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana solutions of the sitnikov's circular restricted three body problems when primaries are oblate spheroid r.r.thapa 1* , m.r. hassan 2 1dept. of mathematics, p.g.campus, biratnagar, morang, nepal. 2 dept. of mathematics, s.m. college, bhagalpur, under t.m.b.university, bhagalpur * email: email: thaparajuram@yahoo.com article history: received 25 september, 2013; accepted 26 november, 2013 abstract the solutions of sitnikov's circular restricted three body problem has been tried to obtain by using lindstedt poincare method if the primaries are oblate spheroid. keywords: lindstedt poincare method, oblate spheroid, perturbation, primaries, sitnikov's circular restricted three body problem. 1. introduction macmillan [1] has studied an integrable case in restricted problem of three bodies by imposing further restrictions on the restricted three body problem by supposing the two finite bodies of equal masses and an infinitesimal body be moving in their common axis of revolution. sitnikov [2] motion in three body problem has two primaries of equal masses and these two moving in (i) circular orbits and (ii) elliptic orbits around their center of mass. the third body (infinitesimal mass) is moving along a line which is perpendicular to the plane of primaries and passing through the center of mass of the primaries. further hagel [3] have studied a higher order perturbation analysis of the sitnikov problem and investigated the low amplitude bounded oscillatory solutions in full range of primary eccentricities – 0.99 < e < 0.99. they have found that near integrals in a polynomial form can be obtained for sufficiently small oscillation amplitudes in the entire interval of eccentricities. in addition they derived a relation for the non-linear frequency of the oscillatory solution as function of e and t0. faruque [4] has studied a new analytic expression for the position of the infinitesimal body in the elliptic sitnikov problem. this solution is valid for small bounded oscillations in cases of moderate primary eccentricities. the final solution to the equation with non-linear force included is obtained through first the use of a courant and synder transformation followed by lindstedt-poincare perturbation method and again an application of courant and synder transformation. we have studied the sitnikov’s circular restricted problem of the bodies when both the primaries are oblate spheroids and moving in circular orbits around their centre of mass. the sitnikov’s problem is a special case of the restricted three body problem when both the primaries are of equal masses (m1 = m2 = 1/2) moving in circular orbits or elliptic orbits under newtonion force of attraction and the third r. r. thapa and m.r. hassan / bibechana 10 (2014) 92-99 : bmhss, p.93 (online publication: dec., 2013) body of mass m3 (m3 is much less then the primaries) moves along the line perpendicular to the plane of motion of the primaries and passes through the center of mass of the primaries. 2. equations of motion here the system consists of two oblate primaries with equal masses (m1 = m2 = 1/2). the third body of mass m3 is much less than the masses of the primaries. we know that both the primaries in the sitnikov’s problem move on the circumference of the same circle if the primaries are spheroid in shape. but if the primaries are oblate spheroid in shape then due to their oblateness the primaries will not be equidistant from their center of mass. to keep the primaries equidistant from the centre of mass of the primaries, the following conditions are to be imposed : (i) principal axes of the oblate bodies should be parallel to the synodic axes. (ii) the masses of both the primaries should be equal. let ai, bi, ci (i = 1, 2) be the semi axes of the primaries. when ai = bi, as the primaries are oblate, then the moment of inertia of the oblate spheroid m1 and m2 about the principal axes of body are m1 a/2 a/2 k̂ î ĵ x p (0, 0, z) p1(a/2, 0, 0) p2(-a/2, 0, 0) m2 r2 r1 y z o(0, 0, 0) r. r. thapa and m.r. hassan / bibechana 10 (2014) 92-99 : bmhss, p.94 (online publication: dec., 2013) 2 2 2 2 1 2 2 2 1 2 2 2 2 1 2 5 5 5 2 5 5 b c a c a a a c b b a b a c c + + = = =   +  = =   + = = =   (1) thus the potential between two bodies m1 and m2 is given by ( ) ( ) 2 2 21 2 1 1 1 1 1 1 1 1 1 13 2 2 22 2 2 2 2 2 2 2 2 23 3 2 2 3 2 2 + + − = + − + +   + + + − + +   gmm gm a b c v al b m c n r r gm a b c a l b m c n r (2) 1 2 1 2 3 ( )gm m ga m m v r r + ⇒ − = + (3) where 2 2 10 a c a − = = oblatenless of the primaries if op1 = r1 and op2 = r2 and 1̂u and 2û are the unit vectors along r1 and r2, then the equation of motion of m1 can be written as 2 1 1 2 23 5 3 5 1 4 1 4 ˆ ˆ 0 2 2 a a n ru r u r r r r    ⇒ − + + − + =        (4) similarly from equation of motion of m2, we get 2 1 1 2 23 5 3 5 1 4 1 4 ˆ ˆ 0 2 2 a a ru n r u r r r r    − + + − + + =        (5) 1 1 2 2 ˆ ˆ 0ru r u⇒ + = (6) as mccuskey [5] the equations (4), (5) and (6) have the non-trivial solutions if the 2 × 2 determinant obtained from any two of the above three equations is zero. i.e. 2 3 5 1 8a n r r ⇒ = + (7) now following suraj et.al.[6], we can find the equation of motion of the third body as 2 2 2 2 2 3/ 2 2 2 5/ 2 2 2 7 / 2 9 15 ( ) ( ) ( ) d z z az az dt z r z r z r − = − + + + + 2 8 16 1 1 3 3 a a b  ⇒ + = + =    , say r. r. thapa and m.r. hassan / bibechana 10 (2014) 92-99 : bmhss, p.95 (online publication: dec., 2013) 2 2 2 2 3/ 2 2 5/ 2 2 7 / 2 9 15 0 ( ) ( ) ( ) d z z az az dt z b z b z b ⇒ + + − = + + + (8) 3. solutions by lindsted-poincare method the equation of motion of third body is ( ) ( ) ( ) 2 2 3/ 2 5/ 2 7 / 22 2 2 2 9 15 0+ + − = + + + d z z az az dt z b z b z b 2 2 3 2 3/ 2 5/ 2 7 / 2 5/ 2 7 / 2 4 5 9/ 2 7 / 2 9/ 2 1 9 15 3 45 2 2 105 15 315 ... 0 2 8 8    ⇒ + + − − +         + + + − =    d z a a a z z z dt b b b b b az z b b b ( ) 2 2 3 2 4 5 3 5 1 15 1 2 3 105 15 784 11 ... 0 2 4 3 d z a a z az z dt a a z z  ⇒ + + − − +     + + − + =    (9) since, there is no effect of independent perturbating terms i.e. 15az 2 , 4105 2 az and hence they may be omitted from the equation (9) we get, ( ) 2 3 2 3 5 1 1 ... 0 2 3 d z a a z z dt  + + − + + =    2 2 3 02 0 d z z z dt η ε⇒ + − = (10) where, 2 0 3 5 1 and (1 ) 2 3 a aη ε= + = + let us write, 2 3 0 1 2 3( ) ( ) ( ) ( ) ( ) ... & , where is some parameter z t z t z t z t z t t d dt ε ε ε τ η η τ η = + + + + = = let us write 2 3 0 1 2 3 ...η η εη ε η ε η= + + + + from (10) r. r. thapa and m.r. hassan / bibechana 10 (2014) 92-99 : bmhss, p.96 (online publication: dec., 2013) ( ) ( ) ( ) ( ) 2 2 2 3 02 2 2 2 3 2 3 0 1 2 3 0 1 2 32 3 2 2 3 2 3 0 0 1 2 3 0 1 2 3 2 22 2 2 20 01 0 0 0 0 1 1 0 02 2 2 2 2 2 22 0 0 2 12 0 ... ... ... ... 0 2 2 + − = ⇒ + + + + + + + + + + + + + − + + + + =     ⇒ + + + + −        + + − + d z z z d d z z z z d z z z z z z z z d z d zd z z z d d d d z z d η η ε τ η εη ε η ε η ε ε ε τ η ε ε ε ε ε ε ε η ε η η ηη α τ τ τ ε η η α η τ ( ) ( ) ( ) 22 2 01 1 0 1 2 02 2 2 2 2 3 2 2 23 2 1 0 0 3 2 1 0 1 2 02 2 2 2 0 1 2 3 0 2 2 2 2 2 ... 0 (11)   + +     + + − + + +   + + + =  d zd z d d d z d z d z z d d d d z d η η η η τ τ ε η η α ηη η η η τ τ τ ηη η η τ hence (11) is identity in ε so the coefficients of 2 3 4, , , ,...ε ε ε ε must be zero. 2 0 02 0 d z z dτ ∴ + = (12) 22 2 301 0 1 1 0 02 2 2 0 d zd z z z d d η ηη τ τ   + + − =    (13) ( ) 22 2 2 2 202 1 0 2 1 2 0 1 0 0 12 2 2 2 2 3 0 d zd z d z z z z d d d η η η η ηη τ τ τ   + + + + − =    (14) ( ) ( ) ( ) 2 2 2 2 23 0 1 0 3 1 2 3 0 1 2 02 2 2 2 2 22 1 0 0 2 0 12 2 2 2 3 0 (15)   + + + + +    + − + = d z d z d z z d d d d z z z z z d η ηη η η η η η τ τ τ ηη τ the general solution of the equation (12) is z0 = c1 cos τ + c2 sin τ z0 = c cos τ (16) from (16), 22 2 301 0 1 1 0 02 2 2 0   + + − =    d zd z z z d d η ηη τ τ r. r. thapa and m.r. hassan / bibechana 10 (2014) 92-99 : bmhss, p.97 (online publication: dec., 2013) to avoid the secular terms, equating the coefficient of cos τ to zero, we get ( ) 2 1 3 8 1 c a η − = + (17) 2 3 1 12 2 0 cos3 4 d z c z d τ τ η + = (18) the general solution of the equation (18) is 3 1 3 4 2 0 0 1 3 3 4 2 0 3 3 4 2 0 cos sin cos3 32 cos cos sin cos3 32 3 sin sin cos sin 3 32 = + − ∴ = + = + + − = − − + +ɺ c z c c z z z c z c c c c z c c c τ τ τ η ε ε τ ε τ ε τ τ η ε τ ε τ ε τ τ η 3 3 2 2 0 0 cos cos cos3 32 32 c c z c ε τ ε τ τ η η ∴ = + − (19) or, ( ) 3 1 2 0 cos cos3 32 c z τ τ η = − (20) ( ) ( ) 3 1 cos cos3 32 1 c z a τ τ= − + (21) ( ) ( ) 2 3 1 2 9cos3 cos 32 1 = − + d z c d a τ τ τ now from (14) ( ) 22 2 2 2 202 1 0 2 1 2 0 1 0 0 12 2 2 4 2 3/ 2 2 2 3 0 21 256(1 ) d zd z d z z z z d d d c a η η η η ηη τ τ τ η   + + + + − =    − = + r. r. thapa and m.r. hassan / bibechana 10 (2014) 92-99 : bmhss, p.98 (online publication: dec., 2013) ( ) 5 5 2 5 6 4 4 0 0 2 0 1 2 3 2 0 5 5 2 5 6 4 4 0 0 3 and cos sin cos 3 cos 5 128 1024 since, cos cos cos 3 32 3 cos 5 cos sin cos 3 128 1024 = + − + = + + = + −   + + − +    c c z c c z z z z c z c c c c c τ τ τ τ η η ε ε ε τ τ τ η τ ε τ τ τ η η , ( ) ( ) ( ) 3 5 5 2 5 2 2 2 4 4 0 0 3 2 5 2 4 0 0 cos cos cos3 32(1 ) 23 3 cos5 cos cos3 1024(1 ) 128 1024 cos cos 3cos3 23cos 24cos3 cos5 32 1024 c z c a c c c a c c z c ε τ τ τ ε ε τ ε τ τ η η ε ε τ τ τ τ τ τ η η ∴ = + − + + − + + = + − + − + now following, raju ram thapa et.al.[6], ( ) ( ) 3 2 5 2 4 0 0 7 7 3 6 6 0 0 cos cos cos3 23cos 24cos3 cos5 32 1024 547 297 1 cos cos3 3cos5 cos7 32768 2048 8 16 c c z c c c ε ε τ τ τ τ τ τ η η ε τ τ τ τ η η = + − + − +  − + + + −      2 0 3 5 but, 1 and 1 2 3 a aη ε  = + = +    ( ) ( ) ( ) 3 2 5 2 3 7 3 7 3 3 5 1 2 3 cos cos cos3 32(1 ) 9 5 1 4 3 23cos 24 cos3 cos5 1024(1 ) 27 5 547 1 cos 8 3 32768 1 297 1 cos3 3cos5 cos 7 8 165 2048 1 3 a c z c a a c a c a a c a τ τ τ τ τ τ τ τ τ τ  +   = + − +  +   + − + +  + +     +  − + + −   +      r. r. thapa and m.r. hassan / bibechana 10 (2014) 92-99 : bmhss, p.99 (online publication: dec., 2013) ( ) ( ) ( ) ( ) 5 3 7 3 5 3 9 cos cos cos 3 23cos 24 cos 3 cos 5 64 4096 27 547 297 3 1 cos cos 3 cos 5 cos 7 8 32768 16384 2048 32768 1 3 cos cos 3 23cos 24 cos 3 cos 5 32 1024 27 547 297 cos 4 32768 1638 c z c t t t c t t t c t t t t a t t c t t t c t η η η η η η η η η η η η η η η η = + − + − +  + − + −   + − + − + + − 73 1 cos 3 cos 5 cos 7 ... 4 2048 32768 t t t cη η η  + − +     4. conclusion the solution z of sitnikov's circular restricted three body problem depends on constant 'c', independent variable τ & oblateness parameter a. the third body moves around the equilibrium point. acknowledgement we are thankful to prof. dr. jaishanker jha, professor and former head, university department of mathematics, t.m.b. university bhagalpur, india, for his kind co-operation and help during the research. reference 1. w.d. macmillan, astronomical journal, 27(1913) 11. 2. k.a. stinikov, dokl.akad.nauk, ussr, 133(1960) 303-306. 3. j. a. hagel, celestial mechanics and dynamical astronomy, 56 (1993) 81. 4. s.b. faraque, celes. mech & dyn. astron., 87(2003) 353-369. 5. s.w. mccuskey, introduction to cel. mechanics, addison-wesley publishing company, inc., 1963 6. m.s. suraj, and m.r. hassan, solution of sitnikov restricted four body problem when all the primaries are oblate bodies: circular case, proceeding of pas, 50 (1)(2013) 61-79. 7. r.r. thapa and m.r. hassan, solutions of sitnikov's restricted three body problem when the primaries are sources of radiation. modern trends in science and technology devendra adhikari, shiva kumar rai and kul prasad limbu (editors). nepal physical society (eastern chapter) and research council of science and technology (publishers), (2013)97-111. puspa raj adhikari et al./ bibechana 16 (2019) 7-14 : rcost p.7 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal abstract nanowires are the one-dimensional nanostructures with the diameter order of one to few hundred nanometres. these structures show unique properties other than their bulk structures. in this article, a qualitative first principle discussion of tic nanowire is reported, indicating the impact of dft based gga relativistic corrections on its electronic properties. here, we analyse the titanium carbide (tic) nanowire of hexagonal structure periodic in z-direction with the density functional theory (dft). the gga with rbbe correlation analysis of this material shows the metallic characteristics in its bulk but the electronic density of state shows that the hybridization states are different from their bulk when the material is analysed in nanostructure form. three structures of hexagonal tic nanowire directed in (1,1,1) plane were analysed to explore diameter (4-18) å dependent comparative study of electronic, stabilizing and optical property which shows unique different result counterparts to its bulk. hexagonal tic nanowire were found to be semiconducting with narrow band gap (0.21-0.34) ev in small diameter while metallic in higher diameter. they are comparable stables as their bulk for higher structure. similarly, for the same investigation, the structures are cross checked by surface atom passivation to verify the reliability of the result that we found. keywords: nanowire, dft; dos; band structure; binding energy; density of state; hydrogen passivation. 1. introduction depending upon the structures, nanowires forms different periodic linear shape, so that they can be taken as 1-dimensional nano-structure. they show many interesting properties that makes them a https://creativecommons.org/licenses/by-nc/4.0/ this work is licensed under the creative commons cc by-nc license. doi: https://doi.org/10.3126/bibechana.v16i0.20865 article history: received 3 february, 2018; accepted 23 august, 2018 *e-mail: gck223@gmail.com 5hydra research and policy center, kathmandu, nepal 4department of physics, tribhuwan university, kirtipur, nepal. 3abvindian institute of information technology and management, gwalior, m.p – 474010, india. 2central department of physics tribhuvan university, kirtipur, nepal 1patan multiple campus, tribhuwan university, lalitpur, nepal puspa raj adhikari1,3, om prakash upadhyay1, gopi chandra kaphle1,2,4,*, anurag srivastava3 initio study electronic and structural study of hexagonal tic nanowires: ab http://nepjol.info/index.php/bibechana https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v16i0.20865 mailto:gck223@gmail.com puspa raj adhikari et al./ bibechana 16 (2019) 7-14 : rcost p.8 (online publication: dec., 2018) potential candidate in wide variety of application [1] in nanotechnology, electrooptical, mechanical and many more fields of academic to industry[2-3]. the research of nanotechnology is not much older than other but the acceleration on this field is 10 times over for this recent decades. the eco-friendly behaviour and clean energy application of the nanomaterial are the great attraction to researchers that makes the efficient and durability to this field. to develop a fundamental understanding and application to excellent properties shown by the nanostructures are the main goals of nanostructure investigation[4]. the first discovery of the 1-d nanotube by iijima 1991 blow stream to research on nanostructure [5] and spread much excitement to the researchers due to demonstration of extraordinary properties. the reduction on the dimensional and size of the material enable the quantum confinement due to which material shows unusual behaviour [5,6] to its bulk counter parts. such effects in nanostructure’s are called quantum mechanical effect. the variety of nanowires (semiconducting nanowire (si) [7], magnetic nanowire (ni, pt) [6,8], dielectric nanowire (sio2, tio2)[9] and other inorganic molecular nanowire (mo6s9-x7x) [10] are successfully investigated and analysed till the date. these show the drastic change on nano sized electronic application such as nanoscale quantum device, biomolecular nonsense and optoelectronic device over the old fashion material device. tic bulk is a face cantered cubic (fcc) crystal with rocksalt type structure. the lattice parameter (a) of this crystal is 4.3186 angstrom with space group of 225 [11]. the pearson symmetry notation is cfn but often represented by fm3m in hermann-mauguin notation. basically it is found in back powder form [12] but referred as the strong reinforcement material [13]. this material has unique property that it is corrosion resistance material so that its application is high for thermal shock wear, cutting tool and hard military application [13-14]. it is metallic in nature in its bulk with no spin polarization and referred as paramagnetic material. due to high hardness, titanium carbide is taken as the excellent mechanical material. on addition, due to high melting and boiling point of this material, its demand for the wear equipment is high. recently andrey et. al. [16] theoretical dftb study shows that onedimensional tic nanotubes are semiconducting and electronic properties are diameter dependent. similarly, kaifu et. al. [17] synthesis the tic nanowire of 20-30 å with good emission stability. in these nano-sized structure, the quantum mechanical effect come to play to show different unexpected properties. these properties demands more study and investigation of nanoscale structure to explore more important properties in the recent technological application. here we also aspect that the one dimensional tic nanowire must show some unique property rather than its bulk. 2. structure and computational details first, the stable onedimensional nanowire of tic material is constructed by the program atkvnl provided by quantumwise. out of different shape, we have selected hexagonal nanowire periodic in z direction for our study which is oriented in (1,1,1) plane. for the detail analysis of electric and optical property of tic nanowire, all the calculation are performed using density functional theory with generalized gradient approximate(gga). this entire calculation is done with room temp 300k and fine density mesh cutoff energy 75 hartree. the revised-pardew–burke–ernzerhof (rpbe) type parameterization with gga exchange correction is used at k-point sampling 1×1×30. monk horstpack scheme using a k-point grid of 6×6×6 was chosen for bulk structure calculation of total energy and density of state. double zeta double polarized basis set is chosen for each structure to account the valence electron effect. each structure were freely relaxed before the calculation to get the minimum https://www.researchgate.net/profile/andrey_enyashin puspa raj adhikari et al./ bibechana 16 (2019) 7-14 : rcost p.9 (online publication: dec., 2018) energy structure to calculate the nobel property at ground state. the force tolerance and stress tolerance are kept 0.05 ev/å and 0.1 gpa during the self-consistent force optimization. the energy range 0 ev to 5 ev is taken to observe the optical spectrum where 10 band below the fermi level and 20 bands above the fermi level are taken into consideration. for the next part of comparative study, the dangling bonds of surface atoms are passivated by hydrogen to analyze the significant effect on electronic and optical property. (a) (b) (c) fig. 1: systematic structures of (a) bulk tic crystal at 2*2*2 repetition (b) hexagonal tic nanowire (111) plane and (c) h-passivated hexagonal tic nanowire. 3. results and discussions in order to investigate the stability of formation of tic nanowire, first we calculate the total energy of the whole structure and each free atom. with these data, the stability of the nanowire in increasing diameter has been calculated. to observe the electric behaviour of each nanowire the electron base structure and density of state has been computed taking same functional. 3.1. structural stability in order to study the structural stability of the nanowire, the total binding energy for each structure is calculated. the structures with low total energy with high binding energy are said to be stable in the structural form and possess low energy system. the total energy of each freely optimised structure is calculated and the free energy of each individual atom ti and c are calculated separately. the free energy of individual ti atom is found to be et(titanium)= -174.083 ev and individual c atom is found to be et(carbon)=-148.182ev. then by using the binding energy formula, 𝐸𝐵 = [𝑝 ∗ 𝐸𝑇(𝑇𝑖𝑡𝑎𝑛𝑖𝑢𝑚) + 𝑞 ∗ 𝐸𝑇(𝐶𝑎𝑟𝑏𝑜𝑛)–𝐸𝑇(𝑇𝑖𝐶)] 𝑝 + 𝑞 where, p and q represents the number of ti and c atom in the structure. similarly et (tic) represents the total calculated energy of the structure. but for the hydrogen passivated structure, the additional term et (hydrogen) is included where r represents the number of hydrogen atoms attached to the structure during passivation. puspa raj adhikari et al./ bibechana 16 (2019) 7-4 : rcost p. 10 (online publication: dec., 2018) 𝐸𝐵 = [𝑝 ∗ 𝐸𝑇(𝑇𝑖𝑡𝑎𝑛𝑖𝑢𝑚) + 𝑞 ∗ 𝐸𝑇(𝐶𝑎𝑟𝑏𝑜𝑛) + 𝑟 ∗ 𝐸𝑇(𝐻𝑦𝑑𝑟𝑜𝑔𝑒𝑛)–𝐸𝑇(𝑇𝑖𝐶)] 𝑝 + 𝑞 + 𝑟 the stability calculated for each structure determines its probability to obtain during synthesis as the major product on applying some appropriate external parameter. these principles suggest that the higher diameter tic nanowire can be synthesized more extent due to their more stability than the lower diameter nanowire. the graphical representation of stability of nanowire with varying its diameter is as shown in figure. fig. 2: systematic graph plot of binding energy variation with number of atoms of tic nanowire. from graph of stability vs. diameter of structure shows that when the number of atoms on structure increases, the binding energy of each atoms also observed to be increases. this suggests that the structure containing more atom, binding energy between atoms also increases and stability tends to approximately to its bulk structure. naturally, the intrinsic bulk structure are most stable form in nature. finally, the higher structures leads to the most stable nws among the considered surface configurations with binding energies that are even close to the bulk limit. but, unfortunately the passivated structure become distorted during their optimization calculation. this theoretical investigation upon h-passivated tic nanowire suggest that passivation doesn’t account the dangling bonds of nanowire [18]. the molecular dynamics picture over the optimization shows that the passivated hydrogen atoms try to takes the position at the interior vacant part of nanowire and then bonded between interior atoms and edge of exterior dangling bonds. the observed total energy of the structure is decreases in some extent nut the shape and size of the structure are much more distorted in higher diameter nanotube. 3.2. electronic properties the electronic properties of the tic nanowire is analysed on the basis of density of states and electronic band gap. both properties of tic nanowire is calculated on the background of gga based dft calculation. puspa raj adhikari et al./ bibechana 16 (2019) 7-14 : rcost p. 11 (online publication: dec., 2018) 3.2.1 electronic band gap fig. 3: band structure plot and partial density of states plot of titanium carbide bulk. the band gap calculation of tic nanowire found to be interesting. the smallest structure of nanowire under my calculation shows that its electronic behaviour lies on semiconducting while its bulk counterpart is pure metallic in nature. on increasing diameter of nanowire, the band gap of structure decreases gradually decreases and all structures of tic nanowire become metallic when their diameter exceeds the size of 8.5 å which suggest that the smaller diameter nanowire are semiconductor having direct band gap while higher diameter nanowire are metallic in nature along (1,1,1) crystallographic plane. the plot of observed band gap of structure vs. diameter are represented as below. the observed semiconducting nanowire of titanium carbide have very narrow bandgap about (0.20.35)ev which are also direct bandgap in nature. the narrow band gap structure with direct nature semiconducting material are supposed to be very important for the choice of many applications in the infrared region. because in wide band gap semiconductors (band gap greater than si) are not desirable for bipolar devices due to higher difference in mobility of electrons and hole for power application. the narrow band gap semiconducting materials are building block for novel tunnel devices and infrared super lattices [19]. simple k-p theory suggest that the small gap materials basically means small effective mass which are obvious candidates to observe quantum confinement effects at larger dimensions[20]. the small masses with dual high conductivities and unique band offsets are the interesting part of narrow band gap materials for quantum application. 3.2.2 density of states. dos (ev-1) the electronic properties with conductivity of the material can be discussed with the help of density of states. measuring the electrical and optical properties of nanowires are considered as important for future electronic, optical devices and nanoelectromechanical devices however a difficult task is due to their small dimensions. here we have plotted 2-dimensional density of states for tic nanowire using dft calculation which also confirms the result of structures band gap. for the smaller structure, the carrier density separates at fermi level leaving some gap. but on increasing size of the nanowire. puspa raj adhikari et al./ bibechana 16 (2019) 7-14 : rcost p. 12 (online publication: dec., 2018) (a) (b) (c) fig. 4: band structure plot of (a) hexagonal tic nw r=2 (b) hexagonal tic nw r=3 and (c) hexagonal tic nw r=4. the energy per state decreased on conduction band and the states shrink towards the fermi level. the valence band which is mainly composed of c-2p state and partially ti-3p and ti-4s state remains same proportion on increasing size of nanowire but the conduction band which is mainly composed of ti-3d state and ti-4s state begin to flat over the conduction band to valence band. the decreasing band gap on increasing size contributes to gaining more metallic property is cause of decreasing density per states on higher energy range band (conduction band). for the higher size structure, the bond length between the atoms also observed to be decreasing due to compact geometry and the effect of each atom to its dangling bond may also deserve the flatten of the conduction band over low energy range to high energy range. the effective mass become much more negligible to addressed the changed metallic property from semiconducting property of nanowire on increasing diameter size. from this dos analysis, a particular emphasis is stressed about the metal-semiconductor transition is observed on changing the diameter of nanowire. this is interesting result of this research article. the changing properties of the material under study, leading sometimes to an electronic phase transition without change of the crystal symmetry are well established results of many classical to quantum semiconductor nanowire family by various studies like sm-sc transition in silicon and nickel nanowires. puspa raj adhikari et al./ bibechana 16 (2019) 7-14 : rcost p. 13 (online publication: dec., 2018) 4. conclusions to study the comprehensive structural and electronic characterization of tic nanowire, we have calculated the total energy of each freely relaxed structure of tic nanowire using quantum mechanical dft calculation with gga functional. from which we estimate the binding energy of geometry due to number of atoms present on unit cell. this provides the formation probability of the nanowire as the major product during synthesis. the low diameter structures are less stable than the higher diameter geometry is observed from out binding energy calculation. the semiconducting electronic behavior fot the smaller diameter hexagonal tic nanowire to metallic transition shows that the nanowire is promising candidate for optical to mechanical purposes. the observed electronic band structure are narrow which again adds the field of application in infrared region. the nanowire in 111 plane deserves its metallic property gaining transition phase from semiconducting state at small geometry shape. this property addressed the states per unit higher energy range become lower for larger structure on going from less number of atom containing geometry. the overall analysis of hexagonal tic nanowire shows higher stability for higher diameter geometries and the transition of electronic property from semiconducting to metallic on increasing wire diameter is observed. furthermore the results presented in this article demonstrates that the ability to manipulate different geometry properties in 1-d semiconductor to metallic nanowires offering future experimental insight into mechanical, optical and electric (i-v) property and their noble application that has not been widely investigated to the date. acknowledgements the authors are thankful to abv-iiitm gwalior for providing the infrastructural support to perform the present computation at the computational nanoscience and technology lab (cntl). we 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[20] n. luo, g. liao and h.q. xu. k.p, theory of freestanding narrow band gap semiconductor nanowires. aip advances 6 (12) (2016) 125109. doi.org/10.1063/1.4972987. http://pubs.acs.org/doi/abs/10.1021/nl903868w http://onlinelibrary.wiley.com/doi/10.1002/1521-3765(20021004)8:19%3c4354::aid-chem4354%3e3.0.co;2-1/full http://onlinelibrary.wiley.com/doi/10.1002/1521-3765(20021004)8:19%3c4354::aid-chem4354%3e3.0.co;2-1/full http://pubs.acs.org/doi/abs/10.1021/nl0613858 http://onlinelibrary.wiley.com/doi/10.1002/adfm.200700846/full http://iopscience.iop.org/article/10.1088/0957-4484/15/9/028/meta https://www.nature.com/articles/ncomms8731?wt.ec_id=ncomms-20150708&spjobid=720950074&spmailingid=49050995&spreportid=nziwotuwmdc0s0&spuserid=odkwmtm2njqyngs2 https://link.springer.com/article/10.1007/bf00351548#citeas https://www.sciencedirect.com/science/article/pii/s0043164899000307 https://www.sciencedirect.com/science/article/pii/s0043164899000307 https://doi.org/10.1299/jsmec.49.11 https://doi.org/10.1016/j.physe.2005.08.004 http://iopscience.iop.org/article/10.1088/0957-4484/18/14/145615/meta https://doi.org/10.1166/jnn.2008.n03 https://doi.org/10.1109/tpel.2003.810840 https://doi.org/10.1063/1.4972987 m.a.a. khan et al./ bibechana 13 (2016) 18-22 : rcost p.18 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal study of the stability of the perturbed solutions of the restricted three body problem m.a.a. khan1, m.r. hassan2, r.r.thapa3* 1teacher of maths, muslim higher school, bhagalpur-812002, india 2dept. of mathematics, s.m. college, bhagalpur, t.m.b. university, bhagalpur – 812007, india 3dept. of mathematics, p.g. campus, tribhuvan university, biratnagar, nepal *e-mail: thaparajuram@yahoo.com article history: received 14 august, 2015; accepted 04 september, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13321 abstract in this paper we have been examined the stability of the perturbed solutions of the restricted three body problem. we have been restricted ourselves only to the first order variational equations. our variational equations depend on the periodic solutions. here the applications of the method of fuchs and floquet proves to be complicated and hence we have been preferred poincare's method of determination of the characteristic exponents. with the determination of the characteristic exponents we have been abled to conclude regarding the stability of the generating solution. we have obtained that the motions are unstable in all the cases. by poincare's implicit function theorem we have concluded that the stability would remain the same for small value of the parameter  and in all types of motion of the restricted three-body problem. ©rcost: all rights reserved. keywords: characteristic equations; characteristic exponents; complex plane; poincare's implicit function. 1. introduction according to poincare [1] there are three kinds of periodic solutions of the restricted three body problem. planer case of three body problem depends on first and second kind solutions of the three body problem. eccentricity is reduced to zero for solution of first kind but it does not reduced to zero for solution of second kind. poincare observed the first kind solution in details. kurcheeva [2] considered the second kind solution. hassan et al. [3] also studied the effect of perturbation due to coriolis and centrifugal force on the periodic solution of the collision orbits of the restricted three body problem. m.a.a. khan et al./ bibechana 13 (2016) 18-22 : rcost p.19 (online publication: dec., 2015) in this paper we have examined the stability of the perturbed solutions of the restricted three body problem. for these characteristic equations of the periodic solutions are used to study. 2. characteristic equations of the periodic solutions the stability of a periodic solution depends on the variational system with periodic coefficients; and poincare's characteristic equation become (minorsky, [4]) 0 s1 s1 s1 s1 4 4 3 4 2 4 1 4 4 3 3 2 2 3 1 3 4 2 3 2 2 2 1 2 4 1 3 1 2 1 1 1                                      ……(1) where, in our case .4,3,2,1),,,,,(),,,,( 4141  icoxcsx iii oc4 k *s   substituting corresponding values in (1), we get j i   0)1( * 44 * 41 * 14 * 11 2     saa asa s …….(2) therefore, we get two values of s to be unity which implies that two characteristic exponents are zero; and 0)()( * 41 * 14 * 44 * 11 * 44 * 11 2  aaaaaass …….(3) if ,1s  then the solutions will be stable otherwise they will be unstable. 3. proof of stability of the solutions: case i: ( )2/w,0o  (i) k-even, m-odd, s*= oc4 k m.a.a. khan et al./ bibechana 13 (2016) 18-22 : rcost p.20 (online publication: dec., 2015) m)1(a 2/)1mk(* 11   m)1(a 2/)1mk(* 44   o 2/)1mk(* 14 cn2 m )1(a    0a* 41  substituting these values in (3), we get 0m)1(ms2)1(s 221mk2/)1mk(2   m)1(s 2/)1mk(   m let us change s by   1 1 . this maps the interior of the unit circle onto the left half of the complex plane, so that the condition /s/<1 is equivalent to re .0 applying this transformation, we get 1m 1m or 1m 1m      which are positive as  m>1. therefore, the solutions are unstable. (ii) k-odd, m-even, s* = oc4 k n m2/)1mk(* 44 * 11 )1(a,0a    o 2/)1mk(* 41c2 m2/)1mk(* 14 c2)1(a,)1(a o substituting these values in (3), we get 0mss 22 n m2   whose roots are real. applying s=   1 1 and taking +ve sign, we get 0)n/m1m()1m(2)n/m1m( 2222222    n/m1m )n/14(m1m n/m1m n/)m(m41m 22 222 22 2222222       hence at least one value of  is positive as )m/kn(,01)k/1(mn/m1m 222  therefore, the solutions are unstable. and taking negative sign, we get 0) n m 1m()1m(2) n m 1m( 2222222      m.a.a. khan et al./ bibechana 13 (2016) 18-22 : rcost p.21 (online publication: dec., 2015)   n/m1m n/)mm41m 22 2222222    .01)k/1(m2  therefore, the solutions are unstable. (iii) kodd, m – odd, s* oc4 k 2/)mk( o * 41 2/)mk( c2 1* 14 2/)mk(* 44 * 11 )1(c2a )1(a,)1(n/2a,0a o     substituting these values in equation (3), we get 0ns2ns2  whose roots are real. applying s=   1 1 , we get )}1n(n{)1n(n 01n2 22 2   therefore, one value of  is positive and consequently the solutions are unstable. case ii: for ,........)2,1,0i(iw,2/o  i) k-even, m-odd, s*= oc4 k n pt l3a,0a,am)1(a * 0 * 0ii 41 * 41 * 14 * 44 2/)1mk(* 11   substituting these values in equation (3), we get 0)1(m)1s2s 2/)1mk(2/)1mk(2   and hence by case i (i), the solutions are unstable. ii) k-odd, m-even, s*= oc4 k o 2/)1mk(* 41 o 2/)1mk(* 14 * 44 2/)1mk(* 11 cm2)1(a, c2 m )1(a 0a,2/m)1(a       substituting these values in (3), we get 0ms n m s 222    and hence by case i (ii) the solutions are unstable. iii) k-odd, m-odd, s*= oc4 k o 2/)mk(* 41 o 2/)mk(* 14 * 44 2/)mk(* 11 c2)1(a , c2 1 )1(a,0a, n 2 )1(a     substituting these values in (3), we get ns2  2s – n = 0 m.a.a. khan et al./ bibechana 13 (2016) 18-22 : rcost p.22 (online publication: dec., 2015) and hence by case i (iii), the solutions are unstable. 4. conclusion we have examined the stability of motion of the restricted three-body problem for the generating solutions applying direct method. we obtained that motions are unstable in all the cases. by virtue of poincare's implicit function theorem we concluded that the stability would remain the same for small values of the parameters. references [1] poincare, h. los method nonvelles de la machanique celeste, gauthier-villars, pairs, 1992. [2] i.v. kurcheeve, bull. inst. of theo. astron. (1968)149. [3] m. a. a. khan, m. r. hassan, r.r. thapa, a research journal in mathematics, m0 1, 2 (2015) 48-58. [4] n. minorsky, non-linear oscillations d. van nonstand company, inc. toronto, new york, london, 1962. narayan p. chapagain/ bibechana 13 (2016) 9-17 : rcost p.9 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal variability of the atmospheric ozone over kathmandu using ground-based measurements narayan p. chapagain department of physics, patan multiple campus, tribhuvan university, lalitpur, nepal e-mail: npchapagain@gmail.com article history: received 21 july, 2015; accepted 30 august, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13311 abstract measurement of the atmospheric total ozone over kathmandu (27.670n, 85.290e) was carried out with a brewer spectrophotometer from february 2001 through february 2002. the total ozone data obtained from brewer instrument are analyzed to study the daily variations of total ozone over kathmandu on different seasons. the results reveal that day-to-day variations of the total ozone over kathmandu are seasonal dependent. total ozone values are relatively high in summer and spring seasons (up to 327 du) and low (~213 du) during the winter season. the low ozone concentration would be due to chemical and dynamic destruction processes related to the low temperature and less active photochemical reaction as less intense solar radiations are received during winter season. ©rcost: all rights reserved. keywords: brewer spectrophotometer; dobson unit; ozone depletion; stratosphere; total ozone. 1. introduction a useful general measure of ozone in the atmosphere is the column ozone or total ozone. the total ozone is defined as being equal to the amount of ozone contained in a vertical column with a base of 1 cm2. a convenient measure of total ozone is the dobson unit (du). it is the thickness of the total ozone layer in milli atmosphere centimeter if all the ozone molecules are brought to surface at normal pressure and temperature. one du represents an average atmospheric concentration of approximately one part per billion by volume (ppbv) of o3. the ozone is not distributed uniformly over the globe. typical amount of ozone vary 230 to 480 du with a world average of about 300 du [1]. a level of 260 du or below this is considered critical and if measurements decline below this, ozone depletion is considered serious at high latitudes. stratospheric ozone depletion in the atmosphere, particularly in the polar regions, has wide spread concern to the health hazards on earth's surface [2, 3, 4, 5]. the downward trend in the total ozone column narayan p. chapagain/ bibechana 13 (2016) 9-17 : rcost p.10 (online publication: dec., 2015) has been well documented for the regions inside and outside of antarctica after the detection of the antarctica ozone hole by ferman and shanklin [6]. here total ozone signifies the columnar ozone measurements from surface of the earth to the top of the stratospheric region. the decrease of total ozone in mid – latitudes in both the southern and northern hemispheres over most of the globe has been detected from the groundand satellite-based observations [7, 8, 9, 10]. several studies were carried out for the comparison of groundand satellitebased observations of total ozone [e.g., 11, 12; 13]. the ground-based ozone measurements can be used to determine the climatological characteristics of the ozone distribution. the variability in the total ozone over thumba india (80n, 760e), was measured with brewer spectrophotometer [14] and they have presented the climatological study of atmospheric total ozone. similarly, zou has reported the seasonal trends of toms ozone over tibet, china, using the logterm data during 1979 – 1991 [15]. in nepal a few studies have been carried out during the past years using the groundand space-based observations and have first reported the variability of atmospheric total ozone over kathmandu using ground-based measurement by a brewer spectrophotometer and space-based observations by total ozone mapping spectrometer (toms) satellite [16, 17]. the results reported that the total atmospheric ozone over kathmandu occurred low in winter and large in summer and spring seasons. in this paper, we present the daily total ozone variations over kathmandu measured by the brewer spectrophotometer on different seasons during one-year period from february 2001 to february 2002. 2. methodology the ozone data used in this study were obtained by using brewer spectrophotometer. the brewer spectrophotometer, mkii # 176 has been operating since january 2000 at the central department of physics, tribhuvan university, kirtipur, kathmandu, nepal (27.670n, 83.290e). the brewer instrument is an improved optical scheme for observations of total ozone. kerr and mcelory [11] reported operating systems and about the automation of brewer spectrophotometer. it has also the ability to perform spectral scans to quantify the uv radiation that passes through the atmosphere [18, 19]. there are six exit slits. one is used for wavelength calibration against the 302 nm groups of mercury lines. the other five are for intensity measurements and are normally set at 306.3, 310.1, 313.5, 316.7, and 320.1 nm. the band pass of each is 0.6 nm [20]. these spectral intensity measurements are used to determine atmospheric total ozone column and so2 . the accuracy of ozone measurements is estimated to be 1% [16]. the data recorded by brewer instrument are direct sun (ds) ozone measurements and zenith sky (zs) ozone measurements (17]. the measurements are in dobson units (du). the ozone is measured on every 2 narayan p. chapagain/ bibechana 13 (2016) 9-17 : rcost p.11 (online publication: dec., 2015) minutes. in this study, we use the daily average value of ozone data measured by the brewer instrument. ozone data are averaged from data collected symmetrically around the daytime. 3. results and discussion total ozone variations associated with solar radiation have been observed using brewer data. daily averages of total ozone over kathmandu have been plotted in figures 1 to 4 for different seasons. the vertical error bars in the plot indicate the standard deviation of the daily ozone mean. fig. 1: daily variations of average value of total ozone over kathmandu during spring season (marchmay). figure 1 shows the daily averages of brewer ozone in the spring season (march – may, 2001). in the plot, x-axis represents the days (month/day) of the year, while y-axis represent total ozone measurements in the dobson unit (du). the data are direct sun (ds) and zenith sky (zs) measurements. the gap in plot shows the data are missing due to either improper operation of instruments or due to bad weather conditions (cloudy sky or rainy days). the result clearly shows that there is a significant day-to-day variation of total ozone over kathmandu. the ozone value is minimum (~270 du) in early march and increases up to 327 du in middle of march and early may. we do not have much data available during the month of april. the amplitude of oscillation of ozone data is asymmetric and becomes large in the first week of march and may. narayan p. chapagain/ bibechana 13 (2016) 9-17 : rcost p.12 (online publication: dec., 2015) figures 2, 3 and 4 are the plot of daily averages of total ozone data in summer (june – august), autumn (september–november) and winter (december–february) seasons respectively. figure 2 shows that ozone value is large (up to 300 du) in first week of june and then slightly decreases during july and august. however, the ozone values are almost remaining same during july and august (~270-290 du). similarly, figure 3 plots the daily variations of ozone over kathmandu during the autumn season, which shows the maximum value up to 290 du and particularly, high ozone concentration during september and october that decrease at the end of october. during this season, ozone value becomes minimum on november (230 du). moreover, the ozone data plotted during the winter season (in figure 4) shows the low value of ozone data with the range of ~213-275 du with lowest values on december and january. to summarize one-year period of measurements, all data of daily mean total ozone is plotted in figure 5. the plot illustrates the seasonal variations of total ozone over kathmandu from february 2001 to february 2002. figure illustrates the expected trend of total ozone variations. ozone measurements are low in early february and steeply rise in march and become maxima in spring season. then ozone value gradually decreases at the end of the summer through autumn and becomes minimum in winter. the highest value of total ozone recorded by the brewer spectrophotometer is 327 du on march 8 and the lowest value is 213 du on december 20. it can be inferred from the figure that the total ozone over kathmandu decreases faster during november, december and january than that during other months. the figure for minima and maxima agree to expectations for atmospheric total ozone levels in the change of seasons. the expected anomalies in the monsoon did not show in the measurements. from the plots, it is evident that the ozone level mostly decline after the first week of may. in the figures, the steep jumps at the beginning of march and the end of april indicate how total ozone level in spring soared. in the beginning of monsoon in mid june, the total ozone value rises slightly. the pattern of the variation of ozone is similar to either side of the peak. the average total ozone of entire period is 273 du, which is sufficient higher compared to the critical value of atmospheric ozone required to filter the uv radiation, which is considered to be 220 du. however, the total ozone over kathmandu in a few days is recorded below the critical value. it clearly illustrates the importance of consistent measurements and study atmospheric ozone over this region. figure 6 illustrates the variation of monthly average values of toms total ozone and brewer total ozone over kathmandu for the period of february 2001 through february 2002. the minimum value of monthly average of toms total ozone is 243 du and 244 du in november and december, respectively, while the maximum ozone value is 299 du in may 2001. the amplitude of variations of toms ozone is 56 du in narayan p. chapagain/ bibechana 13 (2016) 9-17 : rcost p.13 (online publication: dec., 2015) absolute units and 22% in terms of the percentage of the mean. the minimum value of monthly average brewer total ozone is 244 du in december 2001 and the maximum value is 302 du in may 2001. the amplitude of variation of total ozone is 58 du in absolute units and 21 % in terms of percentage of the mean. the average of entire period is 271 du for the toms ozone, 274 du for the brewer ozone. the results show that the variations of toms total ozone and brewer total ozone are symmetric. hence, from the figure 6 illustrating the monthly trends, it can be seen that the total ozone over kathmandu decreases faster during november, december and january than that during other months. fig. 2: daily variations of average values of total ozone over kathmandu during summer (june-august) season. fig. 3: daily variations of average values of total ozone over kathmandu during autumn season (september-november). narayan p. chapagain/ bibechana 13 (2016) 9-17 : rcost p.14 (online publication: dec., 2015) fig. 4: daily variations of average values of total ozone over kathmandu during winter season (december– february). fig. 5: daily average values of total ozone measured over kathmandu during february 2001 – february 2002. the monthly or seasonal variation of total ozone over kathmandu is similar to those in other studies [21, 22]. for instance, seasonal variation of total ozone over tibet [15] varies between 273 du and 315 du with minimum in october and maximum in march. similarly, the total ozone over thumba, india, is narayan p. chapagain/ bibechana 13 (2016) 9-17 : rcost p.15 (online publication: dec., 2015) minimum in winter (december-january) and maximum in spring (april – may) [23]. in tropical region, the total ozone value is higher in summer and smaller in winter. the low ozone concentrations over kathmandu, particularly during winter season, would be caused by chemical dynamic destruction processes related to the low temperature and less active photochemical reaction due to less intense solar radiation. more research is needed to delineate the relative contributions of dynamic, chemical and catalytic processes that cause ozone decrease. it is important to determine how clouds and other climate factors affect the measurements of ozone. fig. 6: monthly averages of total ozone over kathmandu measured by brewer spectrophotometer and toms satellite observations during february 2001 february 2002. 4. conclusions in this study, we report the atmospheric total ozone over kathmandu measured with a brewer spectrophotometer during one-year period from february 2001 to february 2002. the result reveals a significant day-to-day variation of total ozone over kathmandu. the variation of total ozone is also the functions of seasons, meteorological condition, clouds and solar zenith sky angle. the result illustrates that seasonal variations of atmospheric ozone are significant with maximum in spring (up to 327 du) and minimum (go down to 213 du) in winter season. this implies that ozone values in sunny days or cloud free days are large as the photochemical reaction is predominant for the ozone formation. while total ozone values are low on days having less solar intensity or cloudy days. the low ozone perturbations are stronger in summer than in winter. diurnal and annual study in ozone level would also provide deeper narayan p. chapagain/ bibechana 13 (2016) 9-17 : rcost p.16 (online publication: dec., 2015) insight into the changes in ozone taking place in this region. the study of seasonal variation of ozone levels can be backed by using the long-term groundand satellite-based measurements. acknowledgement author would like to thank prof. dr. shekhar gurung, central department of physics, tribhuvan university, nepal for providing the ozone data over kathmandu measured by brewer spectrophotometer. references [1] world meteorological organization (wmo)/united nations environment programme (unep): scientific assessment of ozone depletion: 2006, world meteorological organization, global ozone research and monitoring project, report n 50 (geneva, 2007). [2] a.p. alshuller, fapca, 37, 12 (1987) 1409 – 1417. [3] a. jayaraman, s. lal, b.h. subbaraya, ozone in the atmosphere, proc. quadrennial ozone symposium, 1988. [4] f. li stolarski, r. s., and p. a. newman, atmos. chem. phys. 9, 16 (2009) 2207–2213. [5] d. w. waugh, l. oman, s. r. kawa, r. s. stolarski, s. pawson, a. r. douglass, p. a. newman and j. e. nielsen, geophys. rev. lett. 36 (2009) l03805. [6] j. g. ferman and j. d. shanklin, nature, 315(1985) 207 – 210. [7] c.e. jung, tellux xiv, 4, (1962) 336-337. [8] r. d. bojkov, v. e. fioletov and s. b. diaz, geophysical research letters, 22, 10 (1995) 1249 – 1252. [9] p. m. banks and g. kockerts, aeronomy, part a, academic press new york london, 1973. [10] r. s. solarski, science, 256 (1992) 342 – 349. [11] j. b. kerr and c. t. mcelory, the automated brewer spectrophotometer, atmospheric ozone, proceedings of quadrennial ozone symposium, greece, international ozone commission, 1984, p. 396. [12] u. kohler, u.r. hartmanns gruber, and w. attmanspacher, atmospheric ozone proceedings of quadrennial ozone symposium, international ozone commission (iamap),1984, 402. [13] m. a. bondarenko, o. e. bazhenov, and m. v. grishaev, atmos. ocean. opt. 19, 9 (2006) 699–702. [14] b. h. subbaraya and s. lal, journal of atmospheric and terrestrial physics, 56, 12 (1999a) 1557 – 1561. [15] h. zou, j. geophys, res. 90, 10 (1996) 463. [16] n. p. chapagain, total ozone measurements over kathmandu using brewer spectrophotometer, thesis, master of technology, andhra university, india, 2003. [17] n. p. chapagain, quest-journal of kathmandu bernhardt college, 1, 1 (2013) 1-6 [18] s. bairs, geophysical research letters, 23, 8(1994) 833 – 836. [19] w. a. mathews, atmospheric ozone: natural and manmade variations, ozone depletion, edited by mohammed ilyas and published by university of science of malayasia and unep, 1991. [20] wmo, report of the international ozone trends panel, global ozone research monitoring project report no. 18, published nasa, noaa, faa and unep, 1988. [21] a. m. zvyagintsev, l. b. anan’ev, and a. a. artamonova, opt. atmos. okeana, 23, 3 (2010) 190–195. narayan p. chapagain/ bibechana 13 (2016) 9-17 : rcost p.17 (online publication: dec., 2015) [22] o. e. bazhenov, atmospheric and oceanic optics, 25, 2 (2012)142-146. [23]b.h. subbaraya and s. lal, space research in india: accomplishments and prospects, prl alumni association, ahmedabad, 1999. microsoft word bhanu final (41-46) jyoti rauniyar et al./ bibechana 16 (2019) 41-46: rcost p.41 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal morphological study on particulate matter of kathmandu valley jyoti rauniyaar1, girja mani aryal2, bhanu bhakta neupane3, 4,* 1amrit campus, tribhuvan university, kathmandu, nepal 2research center for applied science and technology, t. u., kathmandu, nepal 3central department of chemistry, tribhuvan university, kathmandu, nepal 4kathmandu institute of applied sciences, kathmandu, nepal *email: newbhanu@gmail.com article history: received 13 may, 2018; accepted 06 september, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.19190 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract air borne particulate matter (pm) depending on size, shape, concentration, and chemical composition can cause multitude of health issues. in this study, we report the morphological study of dust samples obtained from twenty different locations of kathmandu valley by imaging the sample directly by a bright field optical microscope. we find that the average size of particles in all the samples examined below 10 micrometer. individual examination of particles revealed that significant number of particles asymmetric. the observation of asymmetric particles having aspect ratio as high as 20 may suggest that asbestiform particles exist in all the dust samples examined. keywords: particulate matter; bright field optical microscopy; dust samples; aspect ratio. 1. introduction air pollution is one of the leading causes of death thorough out the world. the major contributors to air pollution are particulate matter (pm) and volatile organic compounds (vocs). particulate matter having size smaller or equal to ten micrometers (pm10), that contains fine pm2.5 and course particles, contribute significantly to overall ambient air pollution. the pm10, contains inhalable particles which can penetrate to the thoracic region, and can deposit to the conducting zone of the respiratory system and even in alveoli inducing many pulmonary, cardiovascular, and other health problems. many epidemiological and toxicological studies have suggested that pms are linked with lung inflammation, respiratory cancer, vascular dysfunction, systemic inflammation, myocardial infarction, and exacerbation of existing conditions (like asthma, diabetes mellitus etc.). world health organization (who) estimates that around 0.8 million people die annually from pm exposure; with asia alone contributing around 65% of total global burden [1-2] jyoti rauniyar et al./ bibechana 16 (2019) 41-46: rcost p.42 (online publication: dec., 2018) kathmandu valley, with population of around 3 million, is one of the most densely populated, fastest-growing, and polluted metropolitan areas in south asia. it is reported that in kathmandu valley pm alone contributes around 50-60% of total pollution burden [3-6]. the recent environment performances index (epi), shows that air quality of urban areas of nepal is very poor (ranked 177th out of 180) [7]. the ambient annual-average pm10 concentration levels in core urban areas is reported to be in the range of 80-200 μg/m3 [3, 4, 6]; which is roughly 2-5 times higher than the who standard of 40 μg/m3 [1]. it is also reported that the number of cardiovascular and pulmonary outdoor patients, and morbidity and morbidity rates of indoor patients are increasing [5, 8, 9]. the main sources of pm in kathmandu city are industrial gases, photochemical oxidants, vehicular exhaust, burning of agriculture waste, smokes from brick kiln and industries, dust from construction sites etc. health effects caused by pm and vocs depends both on concentration (or dose) and chemical and morphological composition. studies made in cities of developed countries reported that cardiovascular and pulmonary related morbidity and mortality rates positively correlate with heavy metals (like lead, nickel, cadmium, mercury, and vanadium) enriched pms and several volatile carcinogenic compounds [10,11]. such studies are very scarce for the cities of developing countries. in this study, we examined the dust samples of different locations of kathmandu valley by using a bright field optical microscopic technique. by using direct image analysis, we report the size and asymmetry of pm particles in the all dust samples collected. variation of size and asymmetry of particles in the samples collected at same location but at different height is also reported. 2. materials and experimental methods dust samples were collected from twenty different locations of kathmandu valley in the month of april. the sample collection site map is shown in figure 1. all samples were collected in dry sunny days in the time window 10 am-4 pm. to collect the sample a pre-cleaned glass petri disc was used. the petri disc was placed at height of around 20 meter from the surface. fig. 1: a portion of goggle map of kathmandu valley that shows approximate location of sample collection site. in the map, the collection sites are indicated by a donut shaped structures. jyoti rauniyar et al./ bibechana 16 (2019) 41-46: rcost p.43 (online publication: dec., 2018) a small amount of dust sample was transferred in a microscopic cover slide. the sample was imaged by using a amscope bright field microscope (amscope, usa) equipped with a software controlled cmos camera. around 6-20 images were collected for each sample and the number of particles per field of view was in the range of 200-400. the field of view was measured by using high precision glass slide having 10 micrometer spaced linear lines. the collected images were imported to imagej (nih, usa) software and analyzed to get size and asymmetry information. 3. results and discussion the measured particle size for all twenty samples is shown in figure 2. it is obvious form the figure that for all samples particle size is below 10μm with average particle size in the range of 3.5-4.8μm. the lateral resolution of the optical microscope system used in this study was around 0.5μm, so limited resolution gives a small uncertainty in measurement in particle size. although many optical microscopic approaches that can provide better resolution than a bight field microscope are in use [13-15] microscope having resolution around 500 nm will help to resolve objects that have size of few micrometer. the lateral resolution (dxy) of the microscope system used in this work can be calculated on the basis of following equation [13]. nadxy 2λ= for the microscopic system used in this study the peak wavelength (λ) of light source used is around 500 and numerical aperture of light (na) is 0.5. using these parameters, above equation results dxy of 500 nm. form figure 2, it is evident that particle size for all samples is below 10μm. on the basis of this, we can say that all samples examined contain pm10. the source of pm10, as suggested in many studies could be vehicular exhaust, construction sites, burning of agricultural and organic wastages, brick kiln etc. fig. 2: the measured particle size for the samples 1-20. in the figure, error bars are shown as vertical lines. for each sample, error bar is reported as mean± standard deviation. 01234567 sample 1 sample 2 sample 3 sample 4 sample 5 sample 6 sample 7 sample 8 sample 9 sample 10 sample 11 sample 12 sample 13 sample 14 sample 15 sample 16 sample 17 sample 18 sample 19 sample 20particle size(µm) jyoti rauniyar et al./ bibechana 16 (2019) 41-46: rcost p.44 (online publication: dec., 2018) we also measured the number of symmetric and asymmetric particles in each samples and the data are reported in figure 3. we chose aspect ratio as a parameter to classify a particle as symmetric and asymmetric. here, as in literature, aspect ratio is defined as ratio of length of longest axis to length of shortest axis of a particle. if this ratio is below two we assigned the particle as symmetric and asymmetric if the aspect is higher than two. fig. 3: measurement on % of symmetric and asymmetric particles for the samples 1-20. during measurement we found around 1 % of the particles having aspect ratio as high as 20. these high aspect ratio particles most likely are of asbestiform type. although scientific study on source of these particles is not clear, it can be inferred that the materials used in construction such as cement, concrete etc. could be their origin. we also examined the samples collected at different heights. the measured particle size for samples collected in three different heights (20m, 30m, and 40m) is reported in figure 4. interestingly, for the heights selected the particle size is similar within the standard deviation. although we did not study the number density variation of particle with height, suggests that particles are homogeneously distributed in terms of morphology. we also measured the number of symmetric and asymmetric particles for the samples collected at different height and data are reported in figure 5. as in previous case, we chose aspect ratio as a parameter to classify a particle as symmetric and asymmetric. if this ratio is below two we assigned the particle as symmetric and asymmetric if the aspect is higher than two. as reported previously, for the samples collected at different height, we found around 1-2 % of the particles having aspect ratio as high as 20. 0102030405060708090 sample1 sample2 sample3 sample4 sample5 sample6 sample7 sample8 sample9 sample10 sample11 sample12 sample13 sample14 sample15 sample16 sample17 sample18 sample19 sample20% symmetry %symmetry%assymetry jyoti rauniyar et al./ bibechana 16 (2019) 41-46: rcost p.45 (online publication: dec., 2018) fig. 4: particulate matter size measured at three different heights; height 1 at 20m, height 2 at 30m, and height 3 at 40m from the surface. in the figure, error bars are shown as vertical lines. for each sample, error bar is reported as mean± standard deviation. fig. 5: measurement on % of symmetric and asymmetric particles for the samples collected at different height; height 1 at 20m, height 2 at 30m, and height 3 at 40m from the surface. 4. conclusion we examined the particulate matter size and shape in the dust samples collected from twenty different sites of kathmandu valley using bright field microscopic system. we found that all samples contained particulate matter of size at or below ten micrometer. in all the samples examined, we report that significant number of particles asymmetric and out of them around 1-2 % with aspect ratio as high as 20. existence of high aspect ratio particles could tell the existence of asbestiform type particles. 0123456 1 2 3particle size (µm) height 1 height 2 height 301020304050607080 height 1 height 2 height 3% symmetry %symmetry%assymetry jyoti rauniyar et al./ bibechana 16 (2019) 41-46: rcost p.46 (online publication: dec., 2018) examination of samples collected at different height revealed that particles are homogenously distributed in terms of morphology. acknowledgements we acknowledge kathmandu institute of applied science, kathmandu, nepal for providing optical microscopic system for data collection. references [1] who, air quality guidelines: global updates, who regional office copenhagen, denmark, 2005. [2] health effects of outdoor air pollution in developing countries in asia, health effects institute, boston, ma, 2004. [3] d. giri, k. v. murthy, p. r. adhikary, and s. n. khanal, ambient air quality of kathmandu valley as reflected by atmospheric particulate matter concentrations (pm10), int. j. environ. sci. technol. 3 (2006) 403. [4] r. k. aryal, b. –k. lee, r. karki, a. gurung, j. kandasamy, b. k. pathak, s. sharma, and n. giri, seasonal pm10 dynamics in kathmandu valley. atmospheric environment, atmospheric environment 42 (2008) 8623. [5] a. gurung, and m. l. bell, bell exposure to airborne particulate matter in kathmandu valley, nepal. j. expos sci. environ. epidemiol. 22 (2012) 235. [6] b. b. pradhan, p. m. dangol, r. m. bhaunju, and s. pradhan, international centre for integrated mountain development, kathmandu (2012). [7] epi report, air quality, 2018, https://epi.envirocenter.yale.edu/2018-epi-report/air-quality, sept 5 2018. [8] h. s. shrestha, o. nepal, k. khanal, and b. k. kapoor, a cross-sectional study of lung functions in traffic police personnel at work in kathmandu valley, nepal, annals of clinical chemistry and laboratory medicine 1 (2015) 42. [9] a. gurung, and m. l. bell, the state of scientific evidence on air pollution and human health in nepal environmental research (2013) 124, 54. [10] n. s. thomaidis, e. b. bakeas, and p. a. siskos, characterization of lead, cadmium, arsenic and nickel in pm(2.5) particles in the athens atmosphere, greece, chemosphere 52 (2003) 959. [11] m. lippmann, k. ito, j.-s. hwang, p. maciejczyk, and l.-c. chen, cardiovascular effects of nickel in ambient air, environmental health perspectives 114 (2006) 1662. [12] m. franklin, p. koutrakis, and j. schwartz, epidemiology (cambridge, mass.) 19 (2008) 680. [13] a. s. stender , k. marchuk, c. liu, s. sander, m. w. meyer, e. a. smith, b. neupane, g. wang, j. li, j.-x. cheng, b. huang, n. fang, single cell optical imaging and spectroscopy, chemical reviews 113 (2013) 2469. [14] s. w. hell, far-field optical nanoscopy, science 316 (2006) 1153. [15] b. neupane, f. chen, w. sun, d. t. chiu, g. wang, tuning donut profile for spatial resolution in stimulated emission depletion microscopy, review of scientific instruments 84 (2013) 043701. jamshad ahmed and faizan hussain/ bibechana 13 (2016) 77-86: rcost p.77 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal analytical solution of system of differential equations by variational iteration method jamshad ahmed1*, faizan hussain2, 3 1department of mathematics, faculty of sciences, university of gujrat, pakistan 2department of mathematics, university of gujrat, (sialkot campus) pakistan 3department of mathematics, ncba&e, gujrat (sub-campus) pakistan *email: jamshadahmadm@gmail.com article history: received 11 march, 2015; accepted 17 september, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13394 abstract in this paper, varitational iteration method using he’s polynomials is used to construct the exact as well as approximate solutions of differential equations. from the obtained numerical results, it has been observed that this proposed technique is very efficient and reliable for the solution of the linear and nonlinear system of differential equations. numerical results and graphical representation reflect the accuracy and effectiveness of the proposed modification. ©rcost: all rights reserved. keywords: variational interation method; he’s polynomials; system of linear and non-linear differential equations. 1. introduction in recent years considerable interest in system of ordinary differential equations has been stimulated due to their numerous applications in the fields of physics and engineering. a huge number of research and investigations have been invested in these directions. in this paper we consider a very efficient and power full technique he’s variational iteration method for finding approximate solutions of systems of differential equations. this technique was first time introduce by the chinese mathematician he [1]. the variational interaion method is used to investigate autonomous ordinary differential systems [2], helmholtz equation [3], burger’s and coupled burger’s equation [4], coupled schrodinger-kdv equations and shallow water equations [4]. also the application of the present technique to linear fractional partial differential equations arising from fluid mechanics is presented in [5]. the variational iteration method is investigated in [6-10] to solve parabolic integro-differential equations. this method is jamshad ahmed and faizan hussain/ bibechana 13 (2016) 77-86: rcost p.78 (online publication: dec., 2015) applied to find the solution of various classes of variational problem [11]. some recent research works in this field are [12-20]. 2. analysis of vim for system of differential equations in case of m equations, we rewrite equations in the form ,,2,1,)()()( 21 mixfyyynyl imiii   (1) where il is a linear with respect to iy and in is the nonlinear part of ith equation. in this case the correct functional are obtained as                    ,~,,~,~, 0 ,,2,1,1,   x nmnniiiinini dfyyynylxxyxy   (2) and the optimal values of ,,,2,1, mii  are obtained by taking the variation from both sides of the functional and finding stationary condition using .,,2,1,01, miy ni  our goal in the paper is the use of the following system of sequences instead of the system which results from the variational iteration method:                    ,,,,, 0 ,,2,1,1,   x nmnniiiinini dfyyynylxxyxy   (3) for .,,2 mi  in fact the updated values     ,,,, 1,12,21,1  ninn yyy  are used for finding  .1, niy this technique accelerates the convergence of the system of sequences. therefore, using just few terms of the sequences, an accurate solution can be obtained for a large domain of the problem. 3. analysis of vim using he’s polynomials variational iteration method using he’s polynomials [21] is a modified form of vim. this modification is obtained by coupling the correction functional of vim with he's polynomials and is given by                   midfynpylpxpxyxyp inini n n nii n n x ii n ni n ,,2,1,~, ,, 0 , 00 0, 0 1,                 by comparing the like powers of p, give solution of various order. 4. numerical applications example 4.1 consider the system of first order differential equations, ,cos31 xyy  (4) ,32 xeyy  (5) jamshad ahmed and faizan hussain/ bibechana 13 (2016) 77-86: rcost p.79 (online publication: dec., 2015) ,213 yyy  (6) subjected to the initial conditions   ,101 y   ,002 y   .203 y according to vim, correction functional for eq. (4), (5) & (6) can be writ ten as,                                                   ,~~,)()( ,~~,)()( ,~cos~, ,2,1 ,3 0 3,31,3 0 ,3 ,2 2,21,2 0 ,3 ,1 1,11,1            dyy d yd xxyxy dey d yd xxyxy dy d yd xxyxy nn n x nn x n n nn x n n nn (7) the lagrange multiplier   3,2,1,, ixi  can be identified via variational theory; i.e. the multiplier should be chosen in such a way that the correction functional equation is stationary i.e.       .0&0,0 1,31,21,1   xyxyxy nnn  from eq. (7)   ,1,1  x   ,1,2  x and   ,1,3  x thus eq. (7) becomes           , 1)()( 1)()( cos)1( ,2,1 ,3 0 ,31,3 0 ,3 ,2 ,21,2 0 ,3 ,1 ,11,1                                               dyy d yd xyxy dey d yd xyxy dy d yd xyxy nn n x nn x n n nn x n n nn (8) for ,0n eq. (8) gives,              ,2 ,1 ,sin1 0,3 0,2 0,1 xy exy xxy x for ,1n eq. (8) gives, jamshad ahmed and faizan hussain/ bibechana 13 (2016) 77-86: rcost p.80 (online publication: dec., 2015)                                              ,1)()( ,1)()( ,cos)1( 0,20,1 0,3 0 0,31,3 0 0,3 0,2 0,21,2 0 0,3 0,1 0,11,1         dyy d yd xyxy dey d yd xyxy dy d yd xyxy x x x (9)               , ,sin 2,3 2,2 2,1 x x excosxy xxy exy therefore, we get the result as,              , ,sin 3 2 1 x x excosxy xxy exy this is the same result obtained by adm in [22]. example 4.2 consider the non-linear system of differential equations, ,2 2 2 1 y xd yd  (10) ,1 2 ye xd yd x (11) ,32 3 yy xd yd  (12) subjected to the initial conditions   ,101 y   ,102 y   .003 y the exact solution is given, ,2 1 xey  ,2 xey  and .3 xexy  according to vim, the correction functional for the eq. (10), (11) & (12) can be writ ten as jamshad ahmed and faizan hussain/ bibechana 13 (2016) 77-86: rcost p.81 (online publication: dec., 2015)                                                    ,~~,)()( ,~,)()( ,~2, ,3,2 ,3 0 3,31,3 0 ,1 ,2 2,21,2 0 2 ,2 ,1 1,11,1            dyy d yd xxyxy dye d yd xxyxy dy d yd xxyxy nn n x nn x n n nn x n n nn (13) the lagrange multiplier   3,2,1,, ixi  can be identified via variational theory; i.e. the multiplier should be chosen in such a way that the correction functional equation is stationary i.e.       0&0,0 1,31,21,1   xyxyxy nnn  so from eq. (13), we get   ,1,1  x   ,1,2  x and   ,1,3  x thus eq. (13) becomes                                                      ,1)()( ,1)()( ,21 ,3,2 ,3 0 ,31,3 0 ,1 ,2 ,21,2 0 2 ,2 ,1 ,11,1         dyy d yd xyxy dye d yd xyxy dy d yd xyxy nn n x nn x n n nn x n n nn (14) according to vimhp, eq. (14) can be writ ten as                                                                         ,1)()( ,1)()( ,21 0 ,3 0 ,2 0 ,3 0 0,3 0 ,3 0 0 ,1 0 ,2 0,2 0 ,2 0 0 2 ,2 0 ,1 0,1 0 ,1         dypyp d yd ppxyxyp dype d yd ppxyxyp dyp d yd ppxyxyp n n n n n n n nn x n n n x n n n n nn n n n x n n n n nn n n n                                                                     ,1)( ,11)( ,211 0 ,3 0 ,2 0 ,3 00 ,3 0 0 ,1 0 ,2 0 ,2 0 0 2 ,2 0 ,1 0 ,1         dypyp d yd ppxyp dype d yd ppxyp dyp d yd ppxyp n n n n n n n nn x n n n x n n n n nn n n n x n n n n nn n n n (15) jamshad ahmed and faizan hussain/ bibechana 13 (2016) 77-86: rcost p.82 (online publication: dec., 2015) now, comparing the co-efficient of like powers of p,         , 0 1 1 : 0,3 0,2 0,1 0         xy xy xy p               , )1( 1 21 : 0 0,30,2 0,3 1,3 0 0,1 0,2 1,2 0 2 0,2 0,1 1,1 1                                            dyy d yd xy dye d yd xy dy d yd xy p x x x       ,1 2 : 1,3 1,2 1,1          xxy exy xxy x         , 2 1 222 444 : 2 2,3 2 2,2 2,1 2               x xexy exexy exxy p x xx x         , 62 222 422 83121015 : 32 2 3,3 2 3,2 2 3,1 3               xx xeexexxy exexy exeexxy p xxx xx xxx therefore, approximations to the solutions with the five terms are as follows:                               3888.106666.40083333.0111111.05.72312 ,5555.111312111111.0528784 888.1346666.5811111.3156431264 2532 3 32 2 322 1 xxxeexexxy exexexxy xeexxexxy xxx xxx xxx this is same as obtain by adm in [22]. jamshad ahmed and faizan hussain/ bibechana 13 (2016) 77-86: rcost p.83 (online publication: dec., 2015) table1. numerical values of these solution. ix  ixy1  ixye 1  ixy2  ixye 2  ixy3  ixye 3 0 1.00008 0 1 0 0 0 0.1 1.22132 1.6535e-5 1.10516 2.9323e-6 0.110517 0 0.2 1.49186 5.3375e-5 1.22139 1.1211e-5 0.244275 0 0.3 1.82161 5.9740e-4 1.34974 1.1407e-4 0.404906 5.1165e-5 0.4 2.22249 3.1315e-3 1.49125 5.7298e-4 0.594560 2.7328e-4 0.5 2.70702 1.1341e-2 1.64676 1.9591e-3 0.823372 9.8853e-4 0.6 3.28813 3.2068e-2 1.81686 5.2497e-3 1.090460 2.8076e-3 0.7 3.97860 7.6660e-2 2.00184 1.1909e-2 1.402860 6.7609e-3 0.8 4.79050 6.6253e-1 2.20161 2.3929e-2 1.766030 1.1440e-2 0.9 5.73528 3.1445e-1 2.41576 4.3841e-2 2.185680 2.7962e-2 graphical representation: fig. 1: comparison of exact and approximate solution of ,1y fig. 2: comparison of exact and approximate solution of ,2y exact ______ y1 _ _ _ _ _ 0.0 0.2 0.4 0.6 0.8 1 2 3 4 5 exact ______ y2 _ _ _ _ 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 jamshad ahmed and faizan hussain/ bibechana 13 (2016) 77-86: rcost p.84 (online publication: dec., 2015) fig. 3: comparison of exact and approximate solution of y3. example 4.3 consider a non-linear ordinary differential equation , 1 3 3 xd yd y xxd yd  (16) subject to the boundary conditions   ,00 y   ,10 y   .20 y considering    ,1 xyxy     ,2 xyxy  and    ,3 xyxy  we convert eq. (16) in the system of nonlinear of three differential equation of order one, i.e.     ,21 xyxy  (17)    ,32 xyxy  (18)      ,1 313 xyxy x xy  (19) according to vim, the correction functional for the eq. (17), (18) & (19) can be writ ten as,                                                   ,~~1 ,)()( ,~,)()( ,~, ,3,1 ,3 0 ,31,3 0 ,3 ,2 ,21,2 0 ,2 ,1 ,11,1           dyy d yd xxyxy dy d yd xxyxy dy d yd xxyxy nn n x nn x n n nn x n n nn (20) exact: ______ y3 : 0.0 0.2 0.4 0.6 0.8 0.0 0.5 1.0 1.5 2.0 jamshad ahmed and faizan hussain/ bibechana 13 (2016) 77-86: rcost p.85 (online publication: dec., 2015) the lagrange multiplier   3,2,1,, ixi  can be identified via variational theory. i.e. the multiplier should be chosen in such a way that the correction functional equation is stationary i.e.       0&0,0 1,31,21,1   xyxyxy nnn  so from eq. (20), we get   ,1,1  x   ,1,2  x and   ,1,3  x thus eq. (20) becomes                                                   ,~~1 1)()( ,~1)()( ,~1 ,3,1 ,3 0 ,31,3 0 ,3 ,2 ,21,2 0 ,2 ,1 ,11,1        dyy d yd xyxy dy d yd xyxy dy d yd xyxy nn n x nn x n n nn x n n nn (21) therefore, we get,              ,2 ,1 ,0 0,3 0,2 0,1 xy xy xy let r r yyyyy ,12,11,10,1   is a notation for an approximation to the solution with p+1 term. therefore, some computed approximations are as follows , 3 1 2 3        x xxy , 122 1 32 4        xx xxy , 6062 1 432 5        xxx xxy . , 360180 7 62 1 5432 6         xxxx xxy the closed form solution is   .xexxy  (22) this is the exact solution. jamshad ahmed and faizan hussain/ bibechana 13 (2016) 77-86: rcost p.86 (online publication: dec., 2015) 4. conclusion in this paper, variational iteration method using he’s polynomials has been implemented successfully to find exact and approximate solutions of linear and nonlinear system of ordinary differential equations. three numerical examples have been presented to show that this technique is promising. all the calculations are performed easily. therefore, this method can be applied to many other complicated nonlinear systems of odes and pdes. references [1] j. h. he, international journal of modern physics b, 20 (10) (2006) 1141–1199. 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[21] s. t. mohyud-din and m. a. noor, j. appl. math. comp., (2008) doi: 10.1007/s12190-008-0212-7 [22] j. biazar, e. babolian, r. islam, appl. math. comp., 147 (2004) 713-719. md. tariqul islam et al./ bibechana 15 (2018) 121-130: rcost p.121 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal effect of position of irregularity in concrete frame on response to seismic forces md. tariqul islam1,md. samdani azad2*, md. fahim atif3 , gazi md. sharfaraz imam azad1 1department of civil engineering, rajshahi university of engineering & technology (ruet). 2department of civil and environmental engineering, faculty of engineering, mahidol university, thailand. 3dhaka mass rapid transit development-metro rail project. *email: samdani.civil.ruet@gmail.com article history: received 08 december, 2017; accepted 17 december, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18718 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract this paper deals with the irregular profile of concrete frame building along vertical direction comprising of mass discontinuity and overhanging mass. the underlying fact of the paper is the effect of seismic force in concrete frames with different types of irregularities including mass discontinuity and overhanging mass. for each successive model, the position of overhanging mass and mass discontinuity is kept variable to make the study effective. this study delineates the vulnerable effect of mass discontinuity and overhanging mass in concrete frame buildings. to attain the nonlinear property of each element of frame, pushover analysis method along with the equivalent static force method has been adopted for the present study. ubc97 code has been used here for linear static analysis while the parameters for nonlinear static analysis are arrogated from fema356 and atc40. investigations on different frames exhibit that the location of mass discontinuity and overhanging mass can be a key matter to avoid risks due to earthquake. while considering the design of such frames which have irregularities, designer must think about the position of irregularity. basically, vulnerability increases in case of mass discontinuity if the irregularity is in lower stories. moreover, vulnerability increases in case of overhanging masses if the irregularity is in higher stories. keywords: concrete frame; pushover analysis; mass discontinuity; overhanging mass. 1. introduction most notable events of major earthquakes took place in bangladesh since 1762 to 2015 jolted large part of the country [1]. the frequent earthquakes have made the engineering community aware of the need of seismic evaluation and retrofitting of existing structures. recent progress in the development of new architectural forms of buildings and high strength materials coupled with more pioneering computational methods and design procedures have led to a new generation of high-rise rc buildings drastically. based on the technology advancement and knowledge gained after earthquake occurrences, the seismic code is usually revised by including new clauses and updating old provisions. primary goal of seismic provisions in building codes is to protect life safety through the http://nepjol.info/index.php/bibechana mailto:samdani.civil.ruet@gmail.com http://dx.doi.org/10.3126/bibechana.v15i0.18 https://creativecommons.org/licenses/by-nc/4.0/ md. tariqul islam et al./ bibechana 15 (2018) 121-130: rcost p.122 prevention of structural collapse. the failure of structure starts at points of weakness. this weakness arises due to discontinuity in mass, stiffness and geometry of structure. the structures having different discontinuities are termed as irregular structures. mass irregularity by reducing the mass in the upper part of the structure or by providing overhanging mass in concrete frame is commonly done in practice to meet client’s requirements or architectural requirements. this type of irregularity, which is due to asymmetric distributions of mass, is one of the most frequent sources of severe damage, since it results in floor rotations (torsion response) in addition to floor translations. different building codes provided seismic provisions for different irregularities. the paper presents an overview of the progress in research regarding seismic response of building structures with mass discontinuity or overhanging mass in different story levels. stefano & pintucchi [2] presented a review of the research on the seismic behavior of both plan and vertically irregular building structures. tremblay and poncet [3] examined the influence of mass irregularity for several eight-story structures with different mass discontinuity patterns. they made both the static analysis approach and dynamic analysis method for the presentation. mass irregularity was found to have limited effects on the level of protection against structural collapse when static analysis was used. dynamic analysis method did not seem to provide marked benefit on the response of the buildings with mass discontinuity. nonlinear dynamic behavior of a set of five-story asymmetric buildings with different strength distribution was studied by aziminejad and moghadam [4] to investigate the effect of different strength distribution strategies. the results showed that for inter-story drift and plastic rotation parameters, models with lower diaphragm rotation perform better. but for the ductility demand parameter this situation is not valid. in torsionally stiff buildings, each of the models similar trends of responses was observed for life safety (ls) and collapse preventation (cp) limit states. in lower limit states such as io, the effect of strength distribution on improvement of building performance decreases and in higher limit states such as cp, the effect of strength distribution increases. an approximate seismic analysis was presented by georgoussis et al. [5] for multistory setback buildings with mass and stiffness irregularities subjected to strong ground motions. the method predicted the structural configuration of minimum torsion, which signified that the building elastic response during a ground motion is more or less translational. this response was preserved in the inelastic phase when the strength assignment of the lateral load resisting bents was derived from a planar static analysis, as a consequence of the almost concurrent yielding of these bents. chintanapakdee & chopra [6] deliberated about the seismic response of vertically irregular frames. they investigated the effects of stiffness, strength, and combined stiffness and strength irregularity on seismic demands of strong column weak beam frames using response history analysis and modal pushover analysis. the three types of irregularities similarly influence the height wise variation of story drifts, with the effects of strength irregularity being larger than stiffness irregularity, and the effects of combined stiffness and strength irregularity being the largest among the three. drift demands in the upper stories are much more sensitive to irregularities in the lower stories than the response of lower stories is affected by irregularities in the upper stories. effects of the structural irregularity developed by the discontinuity of a column in a plane frame subjected to seismic loads including the gravity loads were investigated by kara and celep [7]. the results of the nonlinear static and dynamic analyses gave much more useful information regarding the irregularity than the linear analysis. the nonlinear story drift demand was found significantly large, when the column discontinuity was in the lower stories of the frame. seismic response of building frames with vertical structural irregularities was discussed by valmundsson and nau [8]. in this paper, the mass, strength, and stiffness limits for regular buildings as specified by the uniform building code (ubc) were evaluated. conclusions were derived regarding the effects of the irregularities on shear forces and maximum ductility demands. it was found that the mass and stiffness criteria of ubc result in moderate increases in response quantities of irregular structures compared to regular structures. the strength criterion results in large increases in response quantities and was not consistent with the mass and stiffness requirements. hosseini et al. [14] discussed on pushover analysis of rcc frames with bracings. they emphasized on the using of shear links in bracings and found positive affectivity of shear links. six incompatible frames limited to six story were taken into consideration in this study to md. tariqul islam et al./ bibechana 15 (2018) 121-130: rcost p.123 obtain the effect of mass irregularity. the aim of this research includes the effect of location of mass discontinuity and overhanging mass along vertical direction. there are some important points of this research which represents it bit different from the previous. previous studies delineated on the analysis methods, stiffness, mass irregularities, comparison of drifts ratios. this research also deals with irregularity but the most noticeable point is their position. this paper deals with the position of mass discontinuity as well as overhanging mass. to investigate the nonlinear behavior along with the linear performance of selected frames, push over analysis is carried out. pushover analysis has become the preferred method for performance based seismic performance evaluation of structures by the rehabilitation guidelines and codes because it is conceptually and computationally simple. pushover analysis allows tracing the sequence of yielding and failure on member and structural level as well as the progress of overall capacity curve of the structure. the research output suggests maintaining overhanging mass in lower story and mass discontinuity in higher story according to the response of considered frames. 2. materials and methods 2.1 materials specifications of materials used in the numerical analysis are detailed in table 1. the loading conditions were adopted from ubc97 [9]. the interpretation was performed as per the guidelines of fema 356 [10]. the adopted properties of frame can be observed in table 1 and in all frames; the beams and columns of same sizes were provided. all the properties in table are kept constant. table 1: details of members used. members configuration beam size 30 cm *40 cm column size 30 cm * 30 cm total story 6 bay width 5m story height 3 m 2.2 frame types six concrete frames having vertical discontinuity in column and overhanging mass along height have been considered for the present study. all the considered 6 story frames are assumed to be fixed at ground level, floor to floor heights are taken as 3m and bay width is taken as 5m as described in table 1.constant beam and columns sizes were taken at all floors levels for each considered frame so that the numerical results can be interpreted easily, however number of columns and beams vary with respect to model. fig. 1a (model-1) depicts the frame has vertically discontinuity after third floor. fig. 1b (model-2) depicts a frame that has mass irregularity after second floor but has symmetry along the vertical axis. fig. 1c (model-3) depicts a frame that has mass discontinuity at second floor. fig. 1d (model-4), on the other hand, depicts an overhanging mass at 5th story. fig. 1e (model-5) depicts a frame that has an overhanging mass at 4th story. fig. 1f (model-6) depicts an overhanging mass at 3rd story. it is noted that the locations of mass discontinuity and overhanging mass is variable. 2.3 methodology to understand the variations of nonlinear properties of different frames, pushover analysis has been conducted. assessments of the certain frames can be done by conducting nonlinear static or pushover analysis. pushover analysis method is mainly adopted in case of existing structures and to find out the nonlinear properties of frames. assessment of effective stiffness, secant stiffness and ductility and target displacements along a certain direction can be determined by means of pushover analysis. the steel frames are assumed as ordinary moment resisting frames and ordinary braced frames. pushover parameters have been taken from fema 356 prestandard [10]. the behavior of structures can be comprehended from the force-displacement curve which is recognized as capacity curve. from fig.2, the behavior of force displacement curve can be observed. as per the notations in the fig. 2, point md. tariqul islam et al./ bibechana 15 (2018) 121-130: rcost p.124 “a” represents the origin while point “b” represents the yield point. after point d, the element responds with substantially reduced strength to point e. the boundaries required for pushover analysis have been conveyed from fema 356 [10]. the parameters from ubc97 [9] have been listed in table 2 while the pushover criteria is shown in table 3. a. model-1 b. model-2 c. model-3 d. model-4 e. model-5 f. model-6 fig. 1: selected concrete frames. the base shears which have been applied for pushover analysis was derived from the following equations. w rt ic v v (1) where, 4/3 nt )h(ct  (2) the computed base shear (v) from equation (1) must be less than that calculated by equation (3) and must be greater than that calculated by equation (4). in equation (1), w indicates the self-weight of the frame. w r ic5.2 v a (3) iwc11.0v a (4) md. tariqul islam et al./ bibechana 15 (2018) 121-130: rcost p.125 fig. 2: force vs. deformation/deformation ratio curve. reviewing the aspects adjudging pushover analysis, a number of facts are entailed to be adopted from fema356. the nonlinear behavior of certain structure can be assessed by dint of conjuring a nonlinear static analysis or pushover analysis. staad.pro v8i has been utilized for pushover analysis. the assumptions through which the pushover analysis has been followed are listed below: i) the frames are special moment resisting frames. ii) the geometric nonlinearity with p-δ is considered. iii) the nonlinear hinges are presumed as per fema356. iv) deduction of the damping ratio is 5% and the site class is sc v) mapped spectral acceleration factor, fa= 1.2 and fv=1.7 vi) ca=0.09and cv =0.13 was adopted as per atc40 [11] vii) a certain value of displacement has been entered to terminate the pushover analysis. both linear and nonlinear static analysis following equations (1-4) and maintaining the assumptions were also performed for each consecutive case to record the maximum deflection, story drift, capacity curve, ductility of frames, performance points. table-2 illustrates the seismic parameters considered in the study. seismic zone-i is considered for why the value of z is taken as 0.075. the frames adopted for analysis are of special moment resisting type and the response modification factor is taken 8.5, seismic coefficients ca and cv are related to soil profile sc and values are taken according to ubc97. moreover, the value of near source factors are also taken from ubc97. table-3 describes the pushover parameters that are applied for the analysis. the values of mapped spectral acceleration fa and fv are taken as per fema356. site category class c as per fema356 and it is similar to the soil profile type sc as per ubc97. table 2: values considered from ubc97 [9]. parameters values/ standards zone factor, z 0.075 soil profile type sc seismic importance factor, i 1 response modification factor, r 8.5 seismic coefficient, ca 0.09 seismic coefficient, cv 0.13 near-source factor, na 1 near-source factor, nv 1 ct 0.073 md. tariqul islam et al./ bibechana 15 (2018) 121-130: rcost p.126 table 3 pushover parameters. parameter input value/system frame type moment resisting frame geometric nonlinearity and p-δ effects included hinge type as per fema356 damping 5% site category class c mapped spectral acceleration, fa 1.2 mapped spectral acceleration, fv 1.7 3. analysis and results the analysis of all the frames has been carried out following ubc97 [9] and fema356 [10] for linear static and nonlinear static/pushover analysis sequentially. the analyses depict inherent illustrations about the behavior of the frames of this research. the main intent of the research includes the computation of displacement under linear and nonlinear analysis with observing the nonlinear hinge formation in the members. the formation of nonlinear hinges at a certain load-step defines the load capacity of the certain member/element. fig. 3 presents the different lateral displacements of different frames obtained from linear static analysis. it can be observed that model-3 is susceptible to largest lateral displacements due to seismic forces. fig. 3: maximum roof displacements. the reason behind this is that the discontinuous portion of the frame carries largest mass among model [1-3]. on the contrary, this mass discontinuity decreases the total stiffness of the certain story level. this discontinuity decreased the stiffness of that portion of the frame. in model-3, the mass discontinuity is in lower story level. that causes less stiffness in that story. this story carries higher loads of upper stories comparing the other two models. the second maximum displacement is observed in the model-4. the overhanging mass is located in higher story. there is a reason behind it. if the overhanging mass is in higher story, it causes more overturning moment in the base. the effect of this extra overturning moment is added to the lateral forces and cause larger displacements. that is this graph represents a typical behavior of the frames which delineates that mass discontinuity in lower story and overhanging mass in higher story is liable to higher lateral displacements due to seismic forces. the value of lateral displacement of model-1 is around 7.58 mm which is the lowest among all the frames and highest value for model-3 is about 8.45mm. for the rest of the models this value ranges around 8mm. fig. 4 deliberates the relation between story height and percentage of story drift ratio. it can be observed that the drift ratio at first, is increasing gradually in case of all the models and after a certain point it starts decreasing with height. but it doesn’t continue upto the peak 7 7.2 7.4 7.6 7.8 8 8.2 8.4 8.6 model 1 model 2 model 3 model 4 model 5 model 6 d is p la ce m en ts ( m m ) models md. tariqul islam et al./ bibechana 15 (2018) 121-130: rcost p.127 height rather it shows a different behavior in case of models-(1,2&3). for model-1, it can be noted that the drift suddenly increases at 12m to 15 m height. same issue can be observed for models (2 and 3). for model-2, the sudden increase occures at at 9m to 12m height and 6m to 9m height for model-3. moreover, it is also subtantial that the mass discontinuity of models (1, 2 and 3) starts at 12m, 9m and 6m subssequently. the value of drift ratio abruptly changes in that story containing the mass discontinuety. furthermore, fig. 4 delineates one more thing. the peak story drift occurs at 6m for model (4, 5, and 6). but it is already explained that the peak drift occurs at different height for models (1, 2, and 3) which illustrates that the story drift has the dependency of mass discontinuity. fig. 4: story drift. the location of peak story drift is same for the models with overhanging mass but not same for the models with mass discontinuity. it shifts with the change of the location of mass discontinuity. the formation of nonlinear hinges can be observed from fig. 5. the location is same for all models and the first nonlinear hinge is generated in the beam of level-1. but there is an important thing which should be discussed in this matter. it is observed from table 4 that formation of nonlinear hinge occurs at least base shear is in model-4 while the value of base shear is highest in model-1. there is a tendency of formation such hinges in less base shears in the models containing overhanging mass. this phenomenon depicts that the overhanging mass affects the nonlinear resistance of a frame. this effect is higher when the location of overhanging mass is in higher story levels. fig. 6 depicts the capacity curve of all models. the maximum value is for the model-1 while the minimum stands for model-4. it is substantial from the chart that discontinuity in lower story and overhanging mass in higher story delineate less value of base shear in capacity curve. fig. 7 and fig. 8 illustrate the performance points of the models as per atc-40. fig. 7 shows the relationship between sa-sd. it can be observed that model-1 can sustain at the earthquake with maximum acceleration while model-4 is with the minimum acceleration among these models. from the following figure, it is obtained that the maximum v/w value is for model-1 while the minimum is for model-4. table 5 depicts that the maximum value of ductility is for model-3 and the minimum value stands for model-6. the ductility was determined using fema440 [12]. 0 2 4 6 8 10 12 14 16 18 20 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 h ei g h t (m ) story drift (%) model 1 model 2 model 3 model 4 model 5 model 6 md. tariqul islam et al./ bibechana 15 (2018) 121-130: rcost p.128 model-1 model-2 model-3 model-4 model-5 model-6 fig. 5: formation of hinges in beams for different models. table 4 nonlinear hinge formation. models io (w) ls (w) cp (w) model 1 0.122491 0.134992 0.140245 model 2 0.12132 0.133516 0.138596 model 3 0.12028 0.12871 0.132497 model 4 0.108504 0.118185 0.123462 model 5 0.109203 0.120828 0.127135 model 6 0.110118 0.121678 0.126049 md. tariqul islam et al./ bibechana 15 (2018) 121-130: rcost p.129 fig. 6: capacity curve of all specimens. fig. 7: performance point (sa-sd) as per atc40. fig. 8 performance point (v/w-d) as per atc40. table 5: ductility in different models. models ductility model 1 1.33 model 2 1.332 model 3 1.395 model 4 1.36 model 5 1.34 model 6 1.325 4. conclusion the numerical investigation mainly indicates that the story drift and lateral displacements has dependency based on the pattern of vertical geometric irregularity. from the numerical evaluation, a number of conclusions can be obtained as below: 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0 50 100 150 200 250 b as e s h ea r/ w displacements (mm) 1 2 3 4 5 6 0.1 0.102 0.104 0.106 0.108 0.11 0.112 0.114 0.116 27 28 29 30 31 s a (g ) sd (mm) model 1 model 2 model 3 model 4 model 5 model 6 0.09 0.091 0.092 0.093 0.094 0.095 0.096 0.097 0.098 0.099 34 36 38 40 v /w displacement (mm) model 1 model 2 model 3 model 4 model 5 model 6 md. tariqul islam et al./ bibechana 15 (2018) 121-130: rcost p.130 1. vulnerability increases if the mass discontinuity locates at the lower story and overhanging mass in the higher story. 2. mass discontinuity has effects on the peak story drift of a frame. the story drift suddenly increases where discontinuity of mass exists. 3. overhanging mass doesn’t affect the peak story drift locations. 4. overhanging mass in higher story decreases the performance point to a good extent. from the above discussion, it is evident that determining the position of overhanging mass and mass discontinuity should be descent to ensure better performance and stiffness of multistory building frames. references [1] major earthquakes in bangladesh (2016). the daily observer. http://www.observerbd.com/2016/01/05/129456.php. accessed 5 january 2016. [2] m. d. stefano and b. pintucchi, a review of research on seismic behaviour of irregular building structures since 2002. bull earthquake eng 6 (2008) 285–308. doi.org/10.1007/s10518-007-9052-3. [3] r. tremblay and l. poncet, seismic performance of concentrically braced steel frames in multistory buildings with mass irregularity, j. struct. eng. 131 (2005) 1363-1375. doi.org/10.1061/(asce)07339445(2005)131:9(1363). [4] a. aziminejad and a.s. moghadam, performance of asymmetric multistory shear buildings with different strength distributions, j. applied sci. 9 (2009) 1082-1089. http://dx.doi.org/10.3923/jas.2009.1082.1089. [5] g. georgoussisa, a. tsompanosa and t. makarios, approximate seismic analysis of multi-story buildings with mass and stiffness irregularities, procedia engineering 125 (2015) 959 – 966. doi.org/10.1016/j.proeng.2015.11.147. [6] c. chintanapakdee and a.k. chopra, seismic response of vertically irregular frames: response history and modal pushover analyses, j. struct. eng.130 (2004) 1177-1185. doi.org/10.1061/(asce)07339445(2004)130:8(1177) . [7] n. kara n and z. celep, nonlinear seismic response of structural systems having vertical irregularities due to discontinuities in columns. proceedings of fifteen world conference of earthquake engineering (2012). http://www.iitk.ac.in/nicee/wcee/article/wcee2012_2685.pdf . [8] e.v. valmundsson and j. m. nau, seismic response of building frames with vertical structural irregularities, j. struct. eng. 123 (1997) 30-41. https://ascelibrary.org/doi/abs/10.1061/%28asce%290733-9445%281997%29123%3a1%2830%29 [9] uniform building code 1997. [10] fema 356, prestandard and commentary for the seismic rehabilitation of buildings (2000). [11] atc40, seismic evaluation and retrofit of concrete buildings vol. 1 (1996). [12] fema440, improvement of nonlinear static seismic analysis procedures, 2005. [13] a. prabhu t., seismic evaluation of 4-story reinforced concrete structure by non-linear static pushover analysis, national institute of technology rourkela, 2013. [14] s.h. hosseini, s.a. bakar, k. bagherinejad and e. hosseinpour, pushover analysis of reinforced concrete building with vertical shear link steel braces, malaysian journal of civil engineering 27 (2015) 169-179 http://civil.utm.my/mjce/files/2015/08/vol-27-no-2-paper-1.pdf [15] bangladesh national building code, 2006 http://www.observerbd.com/2016/01/05/129456.php.%20accessed%205%20january%202016 http://doi.org/10.1007/s10518-007-9052-3 http://doi.org/10.1061/(asce)0733-9445(2005)131:9(1363) http://doi.org/10.1061/(asce)0733-9445(2005)131:9(1363) http://dx.doi.org/10.3923/jas.2009.1082.1089 https://doi.org/10.1016/j.proeng.2015.11.147 http://doi.org/10.1061/(asce)0733-9445(2004)130:8(1177) http://doi.org/10.1061/(asce)0733-9445(2004)130:8(1177) http://www.iitk.ac.in/nicee/wcee/article/wcee2012_2685.pdf https://ascelibrary.org/doi/abs/10.1061/%28asce%290733-9445%281997%29123%3a1%2830%29 http://civil.utm.my/mjce/files/2015/08/vol-27-no-2-paper-1.pdf microsoft word jbhattarai _1-12_.doc r c o s t n publisher: research council of science and technology, biratnagar, nepal p. 1 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana study the effect of sodium nitrite as a green corrosion inhibitor for the sputter-deposited tungsten-based ternary alloys in 0.5 m nacl solution durga bhakta pokharel 1 , dhruba babu subedi 1 , jagadeesh bhattarai 2,* 1 department of chemistry, tri-chandra m. campus, tribhuvan university, kathmandu 2 central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal *e-mail:bhattarai_05@yahoo.com accepted for publication: december 4, 2014 abstract effects of sodium nitrite on the corrosion resistance and mechanism of the sputter-deposited w-80cr10zr and w-42cr-5ni alloys were studied using corrosion tests and open circuit potential (ocp) measurements in 0.5 m nacl solution, open to air at 25ºc. the corrosion resistance property of the w-80cr-10zr and w-42cr-5ni alloys was enhanced by the use of environmental friendly corrosion inhibitor of sodium nitrite. higher corrosion resistance property and passivation behavior was observed for the w-42cr-5ni alloy than that for the w-80cr-10zr alloy based on the corrosion rate and ocp measurements. adsorption process obeyed langmuir adsorption isotherm to explain the corrosion inhibition mechanism of the alloys by sodium nitrite solution. the standard free energy change of adsorption of sodium nitrite on the w-80cr-10zr and w-42cr-5ni alloys was found to be 23.70 kj/mole and -23.38 kj/mole, respectively which suggested that sodium nitrite is strongly adsorbed on the surfaces of the alloy surfaces by physical adsorption, not by the chemisorption. as a result the corrosion resistance property of the alloys was significantly increased with increasing the sodium nitrite concentration. from the ocp measurement, it is concluded that sodium nitrite acts as an anodic corrosion inhibitor, because the ocps of the alloys in presences of the corrosion inhibitors were shifted to more positive direction with increasing the concentration of sodium nitrite in 0.5 m nacl solution open to air at 25ºc. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11670 © 2014 rcost: all rights reserved. keywords: green inhibitor; corrosion; tungsten-based alloys; 0.5 m nacl solution; inhibition mechanism. 1. introduction corrosion is an undesirable phenomenon which destroys the properties of metallic materials and shortens life of the materials [1, 2]. it is mainly due to the spontaneous instability of the metallic substances that results from the charge−transfer reactions at interfaces between the metallic materials and their environments [3]. the corrosion is one of the major industrial, scientif ic and technological pokharel et al. / bibechana 12 (2015) 1-12 : p. 2 problems. a small careless regarding to the corrosion at the beginning of implementation of any system plants and processes can cause major economic loss during their operation. corrosion science and engineering is interrelated each other which is a multidisciplinary subject, probably unique in crossing the borders of almost all branches of science and technology. engineering materials are generally developed based on their corrosion resistance properties. the lack of information about the corrosion resistance properties of the engineering materials may be one of the causes of wastages of much money, labor as well as destroy the quality of the materials in a short time. hence, the works of engineers and technologists become unreliable without testimony of corrosion properties of the engineering materials. early in the past, engineers and technologists did not take into consideration the importance of the corrosion study during the initial stage of the designing of materials with the thought that the corrosion problems could be avoided later by additional surface treatments at the time of problems (corrosion) observe [1]. in general, two things should be significantly taken into mind of engineers and technologists before the engineering materials are subjected for applications in any fields. firstly, under what conditions it is used and secondly, how it is processed. nowadays, the engineers as well as the technologists have realized that corrosion behavior of the materials used in the system plants and processes should be solved at early stage of installations. the control of such unwanted corrosion phenomena is a subject of tremendous technological and industrial significances. the corrosion can be controlled using different techniques. nowadays, the corrosion control method of metallic materials using various types of eco-friendly green corrosion inhibitors is becoming a fundamental academic and research concerns of corrosion scientists, engineers and technologists [1, 2]. the corrosion inhibitor is a chemical substance that when added in small amounts to a corrosive environment, effectively decreases the corrosion rate of the metallic materials exposed to that environment [1]. very low concentrations of chemical species with special characteristics, that can intervene the corrosion kinetics and thereby control the corrosion is generally term as corrosion inhibitor. there are several types of such inhibitors designated are inorganic, organic, vapor−phase inhibitors and so on. the use of such inhibitor to retard the corrosion rate of the materials is becoming one of the widely used corrosion control methods. practical criteria for the selection of corrosion inhibitors from the variety of inorganic and organic compounds with inhibiting properties are not only their inhibition efficiency but also safety of use, economic constraints and compatibility with other chemicals in the system as well as the environmental concerns. in recent years, many alternative eco-friendly green inorganic [4-7] and organic [7-12] corrosion inhibitors are developed. in the past, a lot of chemical compounds were used as the corrosion inhibitors to control the corrosion kinetics of different metals and alloys in aggressive environments [8-17]. however, all of these corrosion inhibitors were not eco-friendly green inhibitors. for example, chromate (vi) is reported as one of the most effective inhibitors, but it is toxic to human beings [18, 19]. therefore, nowadays cr(vi) is not generally practiced as a corrosion inhibitor. there is great interest in replacing chromates with effective and non-hazardous alternatives eco-friendly green corrosion inhibitors. nitrites, molybdate, tungstate are now being increasingly used as eco-friendly green inorganic corrosion inhibitors due to their low order of toxicity [20-30]. it was reported that the sputter-deposited amorphous/nanocrystalline w-xzr-ycr [31-37] and w-xcryni [31, 38-41] alloys were spontaneously passivated showing higher corrosion resistance properties than those of their alloy-constituting elements in different aggressive acidic to alkaline solutions. in pokharel et al. / bibechana 12 (2015) 1-12: p. 3 this context, the present work is focused to study the effects of the eco-friendly green corrosion inhibitor of sodium nitrite on the corrosion behavior and inhibition mechanism of two sputterdeposited w-80cr-10zr and w-42cr-5ni alloys in 0.5 m nacl solution, open to air at 25ºc using corrosion tests and open circuit potential measurement. 2. materials and experimental methods 2.1 ternary w-80cr-10zr and w-42cr-5ni alloys the instrument used and conditions subjected for sputter deposition of these two sputter-deposited ternary alloys were same as those described elsewhere [32, 33, 38, 41]. x–ray diffractometer with cukα radiation at θ−θ 2 mode and electron probe microanalysis were used to determine the composition and structure of the sputter-deposited w-80cr-10zr [32, 33] and w-42cr-5ni [38, 41] alloys, respectively. apparent grain size of the alloys was estimated using scherrer’s formula from the most intense xrd peak [42]. 2.2 corrosion rate measurement the corrosion test of the w-80cr-10zr and w-42cr-5ni alloys was carried out in 0.5 m nacl solution with different concentrations (i.e. 200, 400, 800, 1200, 1600 and 2400 ppm) of sodium nitrite. before each corrosion test, the alloy specimens were polished mechanically using silicon carbide paper having grit number 1500 in cyclohexane. the polished alloy specimens were rinsed with acetone and dried in air to obtain reproducible result. the weight loss method was used to estimate the average corrosion rate of the alloys using the equation 1 [2]. the estimation of the average corrosion rate was carried out two times or more so as to obtained delimited results. (1) tad 108760w /y)(mm rateorrosion c ×× ××∆ = where, ∆w is the weight loss of the alloy specimen in gram (g), d is the density of the alloy specimen in g/cm3, a is area of the alloy specimen in cm2 and t is the time of immersion in hour. 2.3 corrosion inhibition efficiency and mechanism studies in order to explain the corrosion inhibition mechanism based on the corrosion rate for the corrosion control of the sputter-deposited w-80cr-10zr and w-42cr-5ni alloys in 0.5 m nacl and 1 m naoh solutions open to air at 25ºc in presence of sodium nitrite concentrations, the inhibition efficiency (iecr) and the degree of surface coverage (θ) of the inhibitor molecule adsorbed on the alloy surface [43, 44] were estimated using equations (2) and (3), respectively, where, cr(unhib.) and cr(inhib.) are the corrosion rates of the alloys in absence and presence of the corrosion inhibitor of sodium nitrite, respectively. the langmuir adsorption isothermal equation (4) was used to study the corrosion inhibition mechanism. the adsorptive equilibrium constant (kads) value was estimated from the intercept of a straight line obtained by plotting cinhib./θ vs cinhib.. furthermore, the kads value was used to estimate the standard free energy change of adsorption ( o adsg∆ ) using equations (5) and (6) [43, 44]. pokharel et al. / bibechana 12 (2015) 1-12: p. 4 (2) 100 cr crcr (%) ei .)unhibit( .)inhib(.)unhib( cr × − = (3) cr crcr .)unhib( .)inhib(.)unhib( − =θ (4) c k 1 c inhib. ads .inhib +      = θ (5) rt g exp 55.5 1 k o ads ads         ∆ = ( ) (6) k5.55ln rt g ads o ads ×=∆ where, cinhib. is the inhibitor concentration, r is gas constant, t is absolute temperature and the value of 55.5 is the molar concentration of water in solution. 2.4 open circuit potential measurement the open circuit potential (ocp) of the sputtered w-80cr-10zr and w-42cr-5ni alloys was measured in 0.5 m nacl solution open to air at 25 o c containing different concentrations (i.e. 200, 400, 800, 1200, 1600 and 2400 ppm) of sodium nitrite as a green corrosion inhibitor. the test specimens of the alloys were first mechanically polished by silicon carbide paper (grit number 1500) in cyclohexane, rinsed with acetone and dried in air to obtain reproducible results. then, the test specimens of the alloys were clipped by a sample holder that was made by welding the crocodile pin with a titanium rod. the readings were taken immediately after immersion of the alloy specimen in the electrolytic solution until 72 hours at different time intervals. the ocp measurement was repeated two times or more. all the electrolytic solutions used in the present work were prepared using ar grade chemicals in distilled water. a saturated calomel electrode (sce) and the sputter-deposited alloy specimens were used as reference and working electrodes, respectively. 3. results and discussion 3.1 effects of sodium nitrite inhibitor in the corrosion rate of alloys the effect of different concentrations (i.e., 200, 400, 800, 1200, 1600 and 2400 ppm) of sodium nitrite in the corrosion rate of the sputter-deposited w-80cr-10zr and w-42cr-5ni alloys was estimated after immersion for 240 h in 0.5 m nacl solution open to air at 25ºc. the corrosion rate of both the alloys was decreased with increasing the concentrations of sodium nitrite between 200 to 2400 ppm in 0.5 m nacl solution as depicted in fig. 1. the corrosion rate of both alloys was found to be lowest in 2400 ppm of sodium nitrite in 0.5 m nacl solution and it is about one order of magnitude lower than in 0.5 m nacl solution in addition of 2400 ppm sodium nitrite concentration. these results revealed that the use of sodium nitrite as an eco-friendly green corrosion inhibitor enhanced to increase the corrosion resistance properties of the sputter-deposited ternary w-80cr-10zr and w-42cr-5ni alloys in near neutral 0.5 m nacl solution at 25ºc. it is meaningful for mentioning here that the corrosion rate of the w-42cr-5ni alloy in absence and presence of sodium nitrite is lower than that for w-80cr10zr alloy as shown fig. 1. pokharel et al. / bibechana 12 (2015) 1-12: p. 5 fig. 1: changes in the corrosion rates of the sputter-deposited w-80cr-10zr and w-42cr-5ni alloys after immersion for 240 hours in 0.5 m nacl solution, open to air at 25ºc, as a function of the concentration of sodium nitrite. 3.2 efficiency and mechanism of corrosion inhibition on alloys by sodium nitrite the inhibition efficiency of sodium nitrite in 0.5 m nacl solution for the w-80cr-10zr and w-42cr5ni alloys is increased with increasing sodium nitrite concentrations as shown in fig 2. the maximum inhibition efficiency of about 81-92 % was obtained between 1200 to 2400 ppm of sodium nitrite in 0.5 m nacl solution for the w-80cr-10zr alloy whereas it was found to be between 80 to 85 % for the w-42cr-5ni alloy as shown in fig. 2 (a). it is found that the most efficient corrosion inhibitor concentration of sodium nitrite is found to be at 2400 ppm for both the alloys in 0.5 m nacl solution, open to air at 25ºc. the inhibition action of the corrosion inhibitor of sodium nitrite was found to obey the langmuir isotherm model of adsorption. consequently, the increase in the percentage corrosion inhibition efficiency with increasing inhibitor concentrations indicated that the sodium nitrite acting as adsorption inhibitor to decrease the corrosion rate of the sputter-deposited w80cr-10zr and w-42cr-5ni alloys in 0.5 m nacl solution at 25ºc. the langmuir adsorption isotherm model was performed to have more insights into the mechanism of corrosion inhibition of sodium nitrite on the sputter-deposited w-80cr-10zr and w-42cr-5ni alloys in 0.5 m nacl solution at 25ºc. in order to obtain adsorption isotherm to explain the corrosion inhibition mechanism of sodium nitrite for the w-80cr-10zr and w-42cr-5ni alloys, the θ value was estimated from the weight loss measurement at different concentrations of sodium nitrite. the process of inhibitor adsorption on the surface of the alloys can be described by different isotherms, from which langmuir model is simplest and based on the assumption that all adsorption sites are equivalent pokharel et al. / bibechana 12 (2015) 1-12: p. 6 and the particle binding occurs independently from nearby sites being occupied or not as expressed in equation (4). figure 2 (b) show the relationship between cinhib ./ θ and concentration of sodium nitrite (cinhib.) for the w-80cr-10zr and w-42cr-5ni alloys in 0.5 m nacl solution. the linear correlation coefficient (r2) and the slope of the straight line for both the alloys were found to almost unity. these results indicated that the adsorption process obeyed langmuir adsorption isotherm to explain the corrosion inhibition mechanism on the surface of the alloys by sodium nitrite in 0.5 m nacl solution. it is meaningful for mentioning here that there is no interaction between the adsorbed corrosion inhibitor molecules, the energy of adsorption is independent with θ, the alloy surfaces contain a fixed number of adsorption sites and each site holds one adsorbed species according to the langmuir isotherm model [23]. in literature, it was reported that the high kads value (greater than 100 mol/g) attributes to stronger and more stable adsorbed layer formation on the metals or/and alloys surfaces [45, 46]. it was reported that the o adsg∆ values of metals or alloys around -20 kj/mole or lower indicate adsorption of inhibitors onto material surface with electrostatic interaction is due to physical adsorption, while those around or higher (more negative) than -40 kj/mole involve charge sharing between inhibitor molecules and material surfaces is of chemisorption [47]. negative values of o adsg∆ ensure the spontaneity of the adsorption process and stability of the adsorbed layer of the corrosion inhibitors on the materials surfaces. in the present study, the o adsg∆ values for sodium nitrite as corrosion inhibitor in 0.5 m nacl solution at 25ºc for the sputter-deposited w-80cr-10zr and w42cr-5ni alloys were found to be -23.70 and -23.38 kj/mole, respectively, that are consistent with literatures for physical type of adsorption. hence authenticates physical adsorption of the inhibitors on the surface of w-80cr-10zr and w-42cr-5ni alloys. this implies that the corrosion inhibitor of sodium nitrite adhere on the surfaces of the sputter-deposited alloys and so give more efficient inhibition effects to decrease the corrosion rate of the alloys in 0.5 m nacl solution, open to air at 25ºc. 3.3 open circuit potential the open circuit potential (ocp) or corrosion potential (ϕcorr.) measurement was carried out for a better understanding of the corrosion behavior of the w-80cr-10zr and w-42cr-5ni alloys in 0.5 m nacl solution open to air at 25ºc in absence and presence of sodium nitrite as the corrosion inhibitor. figure 3 shows the changes in the open circuit potential for the alloy specimens after immersion for 72 hours in 0.5 m nacl solution at 25ºc in absence and presence of different concentrations of sodium nitrite. it is clearly showed that ocp of the alloys in 0.5 m nacl solution with different concentrations of sodium nitrite is shifted to more positive or noble direction with increasing the concentrations of sodium nitrite after immersion for 72 hours as shown in fig. 3. these results revealed that the eco-friendly green corrosion inhibitor of sodium nitrite used in the present study acts as the anodic inhibitor for the sputter-deposited ternary w-80cr-10zr and w-42cr-5ni alloys in near neutral 0.5 m nacl solution, because the ocp of the alloy is shifted to more positive direction in all concentrations in both the alloys. in particular, the shifting of the ocp towards the more positive direction with increasing the concentration of the sodium nitrite is more clearly observed for the w42cr-5ni alloy than for the w-80cr-10zr alloy which is consistent with the corrosion rate result as shown above in fig. 1. pokharel et al. / bibechana 12 (2015) 1-12: p. 7 fig. 2: (a) changes in corrosion inhibition efficiency and (b) langmuir plot for the sputterdeposited ternary (a) w-42cr-5ni and (b) w-80cr-10zr alloys after immersion for 240 hours in 0.5 m nacl solution open to air at 25ºc. pokharel et al. / bibechana 12 (2015) 1-12: p. 8 fig. 3: changes in open circuit potential of the sputter-deposited (a) w-80cr-10zr and (b) w42cr-5ni alloys in 0.5 m nacl solution open to air at 25ºc in absence and presence of different concentrations of sodium nitrite, as a function of immersion time. pokharel et al. / bibechana 12 (2015) 1-12: p. 9 fig. 4: comparison of the change in open circuit potential of the sputtered w-80cr-10zr and w-42cr-5ni alloys in 0.5 m nacl solution open to air at 25ºc in absence and presence of different concentrations of sodium nitrite. pokharel et al. / bibechana 12 (2015) 1-12: p. 10 figure 4 shows the comparative changes in ocp of the sputter-deposited w-80cr-10zr and w-42cr5ni alloys in 0.5 m nacl solution in absence and presence of 200 ppm, 400 ppm, 800 ppm, 1200 ppm, 1600 ppm and 2400 ppm concentrations of sodium nitrite. it is clearly observed that the open circuit potential of the w-42cr-5ni alloy is particularly shifted to more positive or noble than that of the w-80cr-10zr alloy. consequently, it can be said that the more effective anodic inhibition effect is observed on the w-42cr-5ni alloy than w-80cr-10zr alloy. this behavior is also supported the results of showing higher corrosion rate by w-42cr-5ni alloy than by w-80cr-10zr alloy as shown above in fig. 1. 4. conclusions the effect of sodium nitrite as an environmental friendly green corrosion inhibitor on the corrosion behavior of the sputter-deposited ternary w-80cr-10zr and w-42cr-5ni alloys in 0.5 m nacl solution open to air at 25ºc was studied using corrosion tests and open circuit potential measurements. from the results and discussion following conclusions are drawn. sodium nitrite use as a green corrosion inhibitor in 0.5 m nacl solution was found to be effective to decrease the corrosion rate (nearly one order of magnitude) of the tungsten-based alloys with increasing the concentration of the inhibitor. the corrosion inhibition efficiency was increased with increasing the concentration of sodium nitrite in 0.5 m nacl solution and follows the langmuir adsorption model of which indicates that sodium nitrite adsorbed onto the alloy surfaces in 0.5 m nacl solution as a result the corrosion rate of the alloys is significantly decreased with addition of the inhibitor. experimentally obtained values of the standard free energy change ( o adsg∆ ) of adsorption of sodium nitrite onto w-80cr-10zr and w-42cr-5ni alloys were found to be -23.70 kj/mole and -23.38 kj/mole, respectively, suggested that the adsorption of inhibitor onto alloy surfaces is due to physical adsorption, not by the chemical adsorption. the open circuit potential of the alloys 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[47] k. f. khaled, corros. sci., 52 (2010) 2905. http://dx.doi.org/10.1016/j.corsci.2010.05.001 microsoft word j giri & r adhikari _81-87_.doc jyoti giri and rameshwar adhikari / bibechana 9 (2013) 81-87 : bmhss, p.81 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana a brief review on extraction of nanocellulose and its application jyoti giri 1 , rameshwar adhikari 2,* 1 department of chemistry, tri-chandra campus, tribhuvan university, kathmandu, nepal 2 central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal * corresponding author: e mail: nepalpolymer@yahoo.com article history: received 22 october, 2012; accepted 7 november, 2012 abstract cellulose is one of the most abundant renewable natural resources. with the advent of nanotechnology, the interests of cellulose scientists have diverted towards the extraction of nanocellulose from various plant sources and utilize them in technical applications. the reason behind the rapid progress in the nanocellulose chemistry and engineering lies in the promising properties of the nanocellulose and the products thereof. in fact, nanocelluloses combine the important properties of cellulose with amazing features of nanoscale materials. with the perspective of potential of cellulosic materials production in nepal basically from agricultural wastes and uses in several applications such as in the preparation of biomaterials, this paper reviews the current knowledge in research and development of nanocelluloses in particular for biomedical applications. after the introduction to the chemical constitution and microfibrillar arrangement of nanocellulose in the cellulose bundles together with other constituents, the ways of preparation of nanocellulose and its functionalization approaches will be discussed. finally, the application of nanocellulose for preparing biomaterials scaffolds will be introduced keywords: nanocellulose; tissue engineering; functionalization; biopolymer 1. introduction cellulose is main lignocellulosic component of cell wall in plants along with hemicellulose, lignin, pectin, wax and constitutes 25 -50% of the plants [1]. cellulose can be replenished by photosynthesis and its estimated biosynthesis is 10 11 tons per year [2]. the simple molecular structure of cellulose is given in fig. 1. o h h oh h h oh h o ch 2 oh h oh h h oh h h o h oh h h oh h o o ch 2 oh ch 2 oh oh oh n-2-d-glucose h 1 2 3 4 5 6 ß fig. 1: structure of cellulose macromolecule. jyoti giri and rameshwar adhikari / bibechana 9 (2013) 81-87 : bmhss, p.82 (online publication: nov., 2012) cellulose is linear polymer of β-anhydroglucopyranoside with 1, 4 β-glycosidic linkage. the structure is supported by the free secondary oh groups at c-2, c-3 position and primary oh group at c-6 position [1,3,4]. its general molecular formula is (c6h10o5)n and density is 1.50 g/cm 3 . about several hundred to10 millions of glucose units condense to form a straight chain of a polysaccharide unit in the term of cellulose nanofiber. the free oh groups in one polysaccharide thread have higher possibilities to form hydrogen bonds with another thread. therefore a number of nanofibers bind through intermolecular hydrogen-bonding with each other to form microfibers and then to microscopic cellulose fibers. the cellulose macromolecule assembled in semicrystalline filament is expressed in term of microfibers and nanofibers. the oh groups are also the active sites for the chemical modifications [5]. hemicellulose is amorphous polysaccharide which is a mixture of carbohydrates comprising 36 membered units [1,6]. lignin is complex dendridic network of phenyl propene which acts as binder in cellulose fiber to give the exact morphology for plant cell wall [1,6]. similarly pectin is heteropolysaccharide of 1-4 linked galacturonic acid with methyl esters of different sugar units [1,6]. wax has various composition of esters obtained from fatty acids and long chain alcohols. e.g. rice bran wax, soy wax etc. [2,6]. cellulose occurs in 4 major polymorphic forms: cellulose i, ii, iii and iv. cellulose fibrils are either manmade (regenerated also called fibers) or natural. cellulose with these two origins has predominantly structures i and ii 2 . in cellulose i crystal structure has parallel unit cell whereas in cellulose ii unit cells of crystals are antiparallel 2 . cellulose iii is obtained on treating cellulose i and ii with ammonia. likewise cellulose iv can be prepared by heating cellulose iii [7]. although native cellulose has i structure, it can be converted into other forms by different treatments. cellulose fibrils are partly crystalline with cellulose iα and iβ. cellulose iα has a single chain triclinic structure and iβ has two chain monoclinic structures 2 . these special arrangements provide the cellulose nanofibers with remarkably interesting mechanical properties [8]. lignin, hemicellulose and wax matrix bind the cellulose fibers in plant cell wall. in a single fiber, a number of threads like microfibrils are bound together which are called microfibers. their size varies from 10 to 40 µm in diameter depending upon the types of plants; see table 1 [9]. table 1: average fiber dimensions of some cellulose raw materials [9]. cellulose material fiber length (µm) fiber width (µm) spruce 3400 31 pine 3100 25 beech 1200 21 eucalypt 850 20 bamboo 2700 14 cotton linters 9000 19 wheat straw 1410 15 baggage 1700 20 each microfiber is a bundle of individual nanosize thread, called as nanofiber or nanofibril which consists of a number of filamental cellulose chain passing through numerous crystallites in thread like fashion. the elementary nanofibril has diameter of 3-15 nm and length with an average aspect ratio of 20-200 [10]. these nanofibrils contain ordered nanocrystallites and disordered amorphous domains placed in definite intervals [11]. cellulose fibers being most abundant, constantly replenished in nature by photosynthesis [2,12] and being stronger than steel, glass fiber etc, has attracted new trends of development in material science [13,14]. jyoti giri and rameshwar adhikari / bibechana 9 (2013) 81-87 : bmhss, p.83 (online publication: nov., 2012) high mechanical strength, stiffness, large surface area and biodegradability are the properties often referred to nanocellulose which make it as tempting raw material for new biobased composites. around 1990, their strong hydrophilic nature, resistant to many chemicals, safety to life, reproducibility and recyclability, brought nanocellulose in many intense applications compared to cellulose and microcellulose [15]. additionally the recent advances in nanocellulose supports medical fields in different aspect as implant materials (artificial organs), biodegradable tissue scaffolds, drug delivery vehicles, etc. further nanofiber composites are used for making flexible circuits, solar panels and other electronics devices. many more applications in paints, pigment, inks, screens, coatings, packaging materials, optical appliances, cosmetics etc. also make use of cellulosic materials [15,16]. the aim of this paper is to review the extraction methods of nanocellulose from renewable natural resources and give an overview of various applications as novel biomaterials. 2. extraction microand nanocellulose with the beginning of civilization cellulose is being used for many purpose; such as for making clothes, ropes, housing materials and paper from fiber. time passed by and new ideas with novel developments started. in late 1970s, turbak, snyder and samberg introduced the new material microfibrillated (mfc) and nanofibrillated cellulose (nfc) [17]. cotton [11,12], ramie [11], jute [11,18], bamboo [19,22], sisal [9], rice [19], starch [21] etc have been used to extract nanocellulose. there are various procedures for the preparation of micro and nanofibrillated cellulose. deshpande & coworkers had extracted microfibrillated cellulose by compression and roller mechanical techniques and blended with polyesters to prepare high strength composite materials [19]. rajan & co-workers microfibrillated bamboo fibers by chemical treatment with naocl / naoh and acetic acid in an autoclave which were then compounded with polyhydroxybutyrate (phb) matrix [22]. similarly, okubo, fujii & yamashita extracted microfibers by steam explosion process and developed composites with polylactic acid (pla) matrix, whose bending, fracture properties were improved [18]. in nature even the waste materials could be of high value as they could be one of the sources for raw material to isolate micro-nanocellulose. sun & co-workes and mandal & co-workers isolated cellulose microfibers from the waste sugarcane dewaxed bagasse by chemical treatments followed by ultasonication process and oxidation with hydrogen peroxide (h2o2) and sodium hydroxide (naoh) [2,12]. liu, yuan & bhattacharyya extracted suspension of nanocellulose fiber from flax yarns. mercerized flax yarns on acid treatment and neutralization with alkali yielded nanocellulose. the pla composites with these nanofibers showed significant increase in tensile strength and modulus whereas elongation at break was decreased with fiber content [23]. cherian & co-workers used pineapple leaf fiber (palf) to extract nanocellulose by chemical as well as mechanical process. fibers on delignification, bleaching and steam explosion gives nanocellulose width in the range of 5-60 nm [24]. kukle & co-workers optimized the percentage of naoh, temperature, time and pressure for nanoscaled disintegration of hemp fibers after steam explosion to isolate the nanocellulose [8]. likewise, luduena and co-workers obtained nanocellulose from rice husk by chemical process [25]. in the survey it is found that there are many different methods for the extraction / preparations of cellulose, cellulose micro and nanofibrils which can be summarized as chemical and mechanical processes [13]. 3. chemical process the chemical process comprises the treatment of raw cellulosic mass with required amount of alkali for delignification, organosolvation (with acetic acid, aqueous methanol or ethanol), and acid treatment jyoti giri and rameshwar adhikari / bibechana 9 (2013) 81-87 : bmhss, p.84 (online publication: nov., 2012) for the hydrolysis. chemical process also involves oxidation with oxidizing agent hydrogen peroxide (h2o2), sodium hypochlorite (naocl) for bleaching the coloured materials. fig. 2: sem images of chemical treated hemp fiber: [a] washed, [ b] delignified [10]. 4. mechanical process mechanical process can be carried out in different ways: roller mechanical technique, compression mechanical technique, cryocrushing, sonication, homogenization and wet cooking process (steam explosion). 4.1 compression (cmt) and roller mechanical (rmt) techniques in cmt delignified fibers of cellulosic materials are placed in a bed of stripes placed between the two plates and subjected to a constant load of 10 tons for 10 seconds. in contrast, rmt delignified stripes are forced between the two rollers, one of which is fixed while the other is rotating [3]. fig. 3: sem images of mechanical and chemical treated delignified hemp fiber for micro, nanofibrillation: [a] steam exploded, [b] acid hydrolysed steam exploded fibers [8]. 4.2 homogenization in this process fibers (either crude one or delignified ones) are passed through a valve at high pressure and exposed to a pressure drop to atmospheric condition when the valve is released resulting in high shear force on the fiber surface [3,21]. jyoti giri and rameshwar adhikari / bibechana 9 (2013) 81-87 : bmhss, p.85 (online publication: nov., 2012) 4.3 cryocrushing the fibers are first frozen in liquid nitrogen. the embrittled glassy fibers are then subjected to high speed crushing. the high shear and impact forces acting on the fibers turn them to powder comprising microfibrils. the cryocrushed fibers may then be dispersed uniformly into water suspension using a disintegrator [21]. 4.4 steam explosion it is a thermomechanical process to breakdown the structural components of cellulose. the process is accompanied with heat carried by steam. steam at high pressure penetrates the lignocellulosic biomass through diffusion. the sudden release of pressure generates shear force which hydrolyze the glycosidic bond and hydrogen bonds between the glucose chains, leading to the formation of nanofibers [24]. fig. 4: scheme for nanofibers extraction from lignocellulosic materials using chemical and mechanical treatments. it is convenient method and common practice both chemical and mechanical processes to prepare nanocellulose from lignocellulosic materials. the unified chemical /mechanical scheme is presented in fig. 4. 5. applications the nanofibers obtained have several potential applications in the field of electronics, used to prepare flexible circuits, flexible solar panels, optical applications, etc [5]. for instance, the acetate functional derivatives of sisal cellulose have been found to be applicable in textile (clothing and fabric), high absorbency products (diapers, cigarettefilters and other filters), thermoplastic products (films and plastic instruments), nourishing (food packaging), cosmetics and pharmaceuticals (extended capsule, tablet release agents and encapsulating agents), medicinal (hypoallergenic surgical products) and others [16]. jyoti giri and rameshwar adhikari / bibechana 9 (2013) 81-87 : bmhss, p.86 (online publication: nov., 2012) cellulose nanocrystals with defined dimension formulate the cellulose based nano composites for different coating applications and in packaging materials. cellulose bears high capacity to hold water, and therefore has higher compatibility with human body. thus nanocellulose can be used to fabricate tissue scaffolds and implants, wound dressing, biocompatible coatings and drug release formulations. 6. concluding remarks nanocellulose is an interesting material with amazing properties and can be applied for many useful purposes such as in textile industries, nanomedicine, food packaging, cosmetics and pharmacy. other potential applications are use as polymer nanocomposites in combination with other polymers, hydrogels and technical materials. the research works envisioned in our laboratory are focusing on the extraction, chemical modification and applications of nanocellulose especially in the preparation of composite materials, biomedical and tissue engineering devices with the aid of electrospinning. in the frame of a university grants commission (ugc) supported project, we are working to develop standard protocols to extract the nanocellulose from some agricultural wastes and prepare useful devices for biomedical applications. acknowledgements the authors would like to thank the university grants commission (ugc), nepal for providing us with the faculty research grant 2068/2069 (project: extraction of microand nanofibers from renewable resources to develop completely biodegradable plastics composites). references [1] t.t. teeri , h. brumer-iii, g. daniel and p. gatenholm trends in biotechnology, 25 (2007) 299-306. 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[15] y.h. han, s.o. han, d. cho and h. kim-ii, macromolecular research, 16 (2008) 253-260. [16] m.p.d. paula, t.m. lacerda and e. frollini, express polymer letters, 2 (2008) 423-428. jyoti giri and rameshwar adhikari / bibechana 9 (2013) 81-87 : bmhss, p.87 (online publication: nov.,( 2012) [17] a.f. turbak, f.w. snyder and k.r. sandberg, journal of applied polymer science, applied polymer symposia, 37 (1983) 815-827. [18] k. okubo, t. fujii and n. yamashita, jsme international journal, 48 (2005) 199-204. [19] a.p. deshpande, m.b. rao and c. l. rao, journal of applied polymer science., 76 (2000) 83-92. [20] k.p. rajan, n.r. veena, h.j. maria, r. rajan, m. skrifvars and k. joseph, journal of polymers and environment, 17 (2009) 109-114. [21] i. siro and d. plackett, cellulose., 17 (2010) 459-494. [22] k.p. rajan, n.r. veena, h.j. maria, r. rajan, journal of composite materials, 45 (2010) 1325-1329. [23] d.y. liu, x.w. yuan, d. bhattacharyya and a.j. easteal, express polymer letters, 4 (2010) 26-31. [24] b.m. cherian, a.l. leao, s.f. de-souza, s. thomas, l.a. pothan and m. kottaisamy, carbohydrate polymers, 81 (2010) 720-725. [25] l. luduena, d. fasce, v.a. alvarez and p. m. stefani, bioresoources, 6 (2011) 1440-1453. bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal physical properties of dust particles around white dwarf in far infrared sky at 12.80 galactic latitude b. b. sapkota1*, b. aryal2, r. weinberger3 1mahendra ratna campus, tahachal, tribhuvan university, kathmandu, nepal. 2center department of physics, tribhuvan university, kirtipur, nepal. 3 institute of astro-particle physics, insbruck university, austria. *email: bhanusapkota45@gmail.com article history: received 15 october, 2017; accepted 12 november, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18488 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract we study the active region in the interstellar medium in which the process of cavity formation is expected. the interaction between wind and its surroundings in the interstellar medium (ism) provides a laboratory to study the behavior of dust particles. the information obtained from the dust colour temperature and dust mass of wd2116+675 will be presented. it is found that the dust colour temperature and dust mass lie in the range 20 k to 22.3 k and 2.1×1023 kg to 2.9×1023 kg respectively. with the help of number density, flux density, dust colour temperature and dust mass maps, the variation of temperature and mass in different position of dust will be presented and discussed. keywords: white dwarfs; flux density; cavity. . 1. introduction white dwarf are hot (~10,000k) low luminosity stars composed mostly of carbon, oxygen and helium. their luminosity is low because their surface is small. the electrons in the white dwarf are degenerate. the largest possible white dwarf is 1.4 of msun. this is called chandrasekhar limit, and is the most mass that the electron degenerate core can support without collapsing under its own gravity. no white dwarf with masses less than 0.6msun have been observed yet. the matter and radiation that exists in the space between the star system in galaxy is called interstellar medium (ism). the ism is the dust and gas between the stars. 99%of ism is gas, and only 1% of the mass is dust. about 20% of the galaxies mass is ism [1]. the interstellar dust consists of particles of silicates or carbon. the gas is mostly hydrogen gas, atomic and molecular gas. dust emits in the infrared but blocks visible light. the reduction in amount of light or other radiation received from star as a result of absorption and scattering of the radiation by intervening dust grains in space is called extinction. the extinction decreases with increase of wavelength of the radiation and increases with the path length through the absorbing medium and .b. b sapkota et al. / bibechana 15 (2018) 43-49: rcost p.43 http://nepjol.info/index.php/bibechana mailto:bhanusapkota45@gmail.com http://dx.doi.org/10.3126/bibechana.v15i0.18488 https://creativecommons.org/licenses/by-nc/4.0/ with the density of the medium. blue light is scattered and absorbed more than red in interstellar medium. this effect is called reddening of light. in other words, the extinction of blue light by dust is greater than red light [2]. in the present work we intend to study a new cavitylike structure around white dwarf. 2. region of interest and methods we have compiled a database of 1978 number of white dwarfs which are listed in the catalogue of holberg et. al.[3]. out of which we have studied wd2116+675 here. we have carried out a systematic search of iras maps available in the sky view virtual observatory (http://skyview.gsfc.nasa.gov). this sample white dwarf has the right ascension of 20h 17m 17s and declination of +670 44m 44s in equatorial coordinate system. the following input parameters were used for the search: (1) coordinate: j2000, (2) projection: gnomonic (tan), (3) image size (pixel): 500×500 (4) image size (degrees) : 0.50×0.50 (5) brightness scaling: histogram equilization (histeq) (6) colour table: stern special. we have downloaded flexible image transport system (fits) v3 image of the selected region. we selected fits format of 0.50×0.50 at 60 and 100µm for the image processing. using aladin v2.5 software the fits image carries the information concerning the flux density, position, etc for each pixels. aladin v2.5 is an interactive sky atlas developed and maintained by the center de donne's astronomiques de strasbourg (cds) for the identification of astronomical sources through visual analysis of reference sky images. aladin v2.5 allows the user to visualize digitized images of any part of the sky, to superimpose entries from the cds astronomical catalogues and tables, and to interactively access related data and information from simbad, ned or other archives of all known objects in the field. in ordered to separate the region of minimum flux density region, contours are drawn at 60 and 100 μm respectively. because we are interested to study temperature and mass profile of the region. we intend to study the cavity like structure at 60 µm and 100 µm. measured flux density is subtracted with the background values. background flux is the flux emitted by other sources lying nearby the region of interest (not from the region of interest). the average value of the background flux is obtained by noting and summing up of the minimum flux densities around the region of interest and dividing the sum by total number of pixel with this minimum flux density. when this background flux is subtracted from the obtained flux density of each pixels in the region of interest, it is said to be background flux density. 3. dust color temperature estimation we use data base from the iras 60 µm and 100 µm flux densities is similar to that of schnee et. al.[4]. by knowing the flux densities at 60µm and 100 µm, the temperature contribution due to dust color can be calculated. the dust temperature 𝑇𝑑 in each pixel of a fits image can be obtained by assuming that the dust in a single beam is isothermal and that the observed ratio of 60 µm to 100 µm emission is due to black body radiation from dust grains at 𝑇𝑑, modified by a power law of spectral emissivity index. the flux density of emission at awavelength 𝜆𝑖is given by 𝐹𝑖 = [ 2ℎ𝑐 𝜆𝑖 3(𝑒 ℎ𝑐 𝑘𝑇𝑑−1) ] 𝑁𝑑𝛼𝜆𝑖 −𝛽 𝛺𝑖) (1) b. b sapkota et al. / bibechana 15 (2018) 43-49: rcost p.44 where, 𝑁𝑑 is the column density of dust grains, is a constant which relates the flux withthe optical depth of the dust, β is the spectral emissivity index, and 𝛺𝑖 is the solid angle subtended at 𝜆𝑖 by the detector. following [6], we use the equation 𝛽 = 1 𝛿+𝜔𝑇𝑑 (2) to describe the observed inverse relationship between temperature and emissivity spectral index. here, 𝛿 and 𝜔 are free parameters found that the temperature dependence of the emissivity index fits very well with the hyperbolic approximating function. considering temperature as an independent variable, the best fit gives 𝛿 = 0.40 ± 0.02 and 𝜔= 0.0079 ±0.0005 𝐾−1, with the 𝜒2/degree of freedom = 120/120. with the assumptions that the dust emission is optically thin at 60 𝜇m and 100 𝜇m and that 𝛺𝜔 ≅ 𝛺100 (true for iras image), we can write the ratio “r” of the flux densities at 60 𝜇m and 100 𝜇m as 𝑅 = 0.6−(3+ 𝛽) 𝑒 144 𝑇𝑑 – 1 𝑒 240 𝑇𝑑 – 1 ) (3) the value of 𝛽 depends on dust grain properties as composition, size, and compactness. for reference, a pure blackbody would have 𝛽 = 0, the amorphous layer-lattice matter has 𝛽~1, and the metals and crystalline dielectrics have 𝛽~ 2. for a smaller value of 𝑇𝑑, 1 can be dropped from both numerator and denominator of equation and it takes the form 𝑅 = 0.6−(3+ 𝛽) 𝑒 144 𝑇𝑑 𝑒 240 𝑇𝑑 (4) taking natural logarithm on both sides of equation (4) we find the expression for the temperature as 𝑇𝑑 = −96 1 𝑙𝑛{𝑅×0.6(3+𝛽)} (5) where r is given by r = f(60 𝜇m) f(100 𝜇m) (6) f(60 𝜇m)and f(100 𝜇m) are the flux densities at 60 𝜇m and 100 𝜇m, respectively. in this way we can use equation (5) for the determination of the dust grain temperature [6]. 4. mass estimation since the longer wavelength measurements give us more precise dust masses due to the characteristics of the planck curve, the far infrared emission which is used for the derivation of the dust mass is measured from the 100 𝜇𝑚 iras images. the dust masses are estimated from the ir flux densities. in order to estimate the dust masses from the infrared flux densities at 100 𝜇𝑚, followingthe calculation of young et. al.[7]. we need the background correction of flux and convert the relative flux into absolute flux. the background correction is done by subtracting the average flux emitted by the external sources other than the object of interest. the blackbody intensity can be calculated using the basic expression as given in equation (2). the resulting dust mass depends on the physical and chemical properties of the dust grains, the adopted dust temperature td and the distance d to the object. 𝑀𝑑𝑢𝑠𝑡 = 4 3 𝑎𝜌 𝑄𝜈 [ 𝑆𝜈𝐷2 𝐵(𝜈,𝑇) ] (7) where a, ρ,qvand sv represent weighted grain size, grain density ,grain emissivity and flux density of the region of interest, respectively. here, sν = f × 5.288 × 10−9 mjy s the distance (d) to the cavity is 205 pc, known from odenwald et .al.[5]. the planck’s function is given by, b(ν, t) = 2hν3 c2 [ 1 e hν kt−1 ] (8) b. b sapkota et al. / bibechana 15 (2018) 43-49: rcost p.45 where h,c,ν ,and t represent planck's constant, velocity, frequency of light, and average temperature of region respectively. by using, a=0.1 µm [5], ρ=3000 kgm-3, and qν =0.0010 for 100 µm and 0.0046 for 60 µm respectively [6] ,the expression (7) takes the form : mdust=0.4 [ sνd2 b(ν,t) ] (9) we use the equation (9) for the calculation of the dust mass it is clear from the expression (8) that the value of planck function 𝐵 (𝜈, 𝑇) for longer wavelength is higher than that of the shorter wavelength. consequently, the range of 𝐵 (𝜈, 𝑇) for fixed temperature (say∆t) goes narrower if wave-length of the images increases. 5. results and discussion fig. 1: 0.5 0 ×0.50 image of the region centered at r.a.(j2000)=21h 17m 17s,dec. (j2000)=+67 044'44" at 60µm (left) and 100µm (right) of wd 2116+675. fig 2 fig.3 60micron 60micron 100micron b. b sapkota et al. / bibechana 15 (2018) 43-49: rcost p.46 fig. 2: cavity with contour and major diameter (ab) and minor diameter (cd). the size of image is 0.50×0.50 at 100 µm iras maps. fig. 3:showing different flux density inside the different contour level outside whole region of wd2116+675 centered at r.a.= 21h 17 m 17 s and dec. = +67 044' 44". + sign represents position of white dwarf and a, b, c, and d represents four contour level drawn at 2, 40, 69, and 255 respectively. figure (1) represents 60 and 100 µm iras image of the region of interest. the region of minimum and maximum flux is represented by black and white colors respectively. diameters are drawn passing through minimum flux inside the cavity as shown in figure (2). figure (3) shows four contour level a, b, c, and d that surround flux density 23.86,25.75, 25.02 and 30.57 mjysr-1 respectively. contour a encloses minimum flux density and b encloses maximum flux density inside the cavity. similarly, contour level c , and d encloses minimum and maximum flux density including whole region of the region. the flux density obtained inside the contour level c helps to determine background count. similarly, the flux density of other required region can be obtained with the help of aladin software. by comparing figures (1), (2) ,and (3), we get same result. fig. 4 fig. 5 b. b sapkota et al. / bibechana 15 (2018) 43-49: rcost p.47 fig 4 : contour map of mass distribution. the map is centered at r.a.(j2000)=21h 17m 17s, dec. (j2000)=+67 044'44". fig. 5: dust colour temperature contour plot. the map is centered at r.a.(j2000)=21h 17m 17s, dec. (j2000)=+67 044'44".the contour levels are shown. in figure (4), different colour counter represents the different range of mass. from above plot mass is higher at centre and decreases across the outward region. figure (5) shows the different colour map of temperature. from above plot temperature is lower at centre and increases across the outward region. by comparing figure (4) and figure (5) we get those region at which mass is minimum, greater the value of temperature of dust. fig. 6 fig. 7 fig. 6: the flux density at 60m versus 100m plot. the best fit can be seen. fig. 7: dust mass distribution. the gaussian fit and the ±1σ statistical error bars can be seen. here σ = √n. figure (6) is the plot of relative flux density of 60 µm versus 100 µm. the solid line represents linear fit. the slope of the line has been used to find average dust color temperature of the region of interest. figure(7) shows the gaussian plot of mass distribution. the solid curve represents gaussian fit of mass with error bar. the dust mass is very well fitted. the gaussian parameter i.e. gaussian centre is 2.37×1023 kg and offset mass is -0.11 kg. fig. 8: distribution of dust color temperature. the gaussian fit and the ±1σ statistical error bars can be seen. here σ = √n. b. b sapkota et al. / bibechana 15 (2018) 43-49: rcost p.48 the maximum and minimum dust color temperature of structure wd2116+675 is found to be 22.34k and 20.02k respectively. total mass of dust structure is found to be 7.42×1024kg. the dust mass and dust colour temperature is found to be well fitted by gaussian distribution. the size of cavity is 0.78 pc × 0.329 pc. the cavity is found to be formed due to presence of nearby white dwarf. the white dwarf evolves from the planetary nebula stage by ejecting its outer envelopes. acknowledgements we thank editor and referee for the constructive comments and suggestion. one of the authors (bbs) thanks university grants commission of nepal for providing research fund and acknowledge central department of physics, tribhuvan university , nepal for various kinds of support during ph.d. in addition, we acknowledge sky view virtual observatory ( http://skyview.gsfc.nasa.gov ) simbad ( http://skyview.gsfc.nasa.gov ) for providing database and software. references [1] s. palen, schaum's outlines astronomy, mc graw hill, usa, 2004. [2] h. karttunen, p. kroeoger, h. oja, m. poutanen, k.j. donner, fundamental astronomy, springer berlin heidelberg, fifth edition. usa, 2007.doi.org/10.1007/978-3-540-34144-4. [3] j. b. holberg, terry d. oswalt,and e. m. sion., a determination of the local density of white dwarf stars astrophysical journal 571 (2002) 512-518. doi.org/10.1086/339842. [4] s. l.schnee, n. a. ridge, n.a., goodman, a.a, jason, g. l. , a complete look at the use of iras emission maps to estimate extinction and dust temperature, astrophysical journal 634 (2005) 442450. doi.org/10.1086/491729. [5] s. f. odenwald and l. j. richard, hydrodynamical process in the draco, astrophysical journal 318 (1987) 702-711. [6] x. dupac, j.p. bernard, n boudet, m. giard, j.m. lamarre, c meny, f. pajot, i. ristorcell., g. serra, b. stepnik, j.p. torre, inverse temperature dependence of the dust submillimeter spectral index astronomy & astrophysics 404 (2000) l11-l15. doi.org/10.1051/0004-6361:20030575. [7] k. young., t.g. philip., & g.r. knapp, circumstellar shells resolved in iras survey data. ii – analysis, astrophysical journal, 409, (1993) 725-738. doi.org/10.1086/172702 b. b sapkota et al. / bibechana 15 (2018) 43-49: rcost p.49 figure(8) shows the gaussian plot of dust color temperature the solid curve represents gaussian distribution. the dust color temperature is well fitted as gaussian distribution. the offset temperature is 0.28k and gaussian centre is 20.77k. this suggest that the cavity is in thermal equilibrium and not effected by external cause. there is less deviation in temperature. 6. conclusions http://skyview.gsfc.nasa.gov/ http://skyview.gsfc.nasa.gov/ https://doi.org/10.1007/978-3-540-34144-4 https://doi.org/10.1086/339842 https://doi.org/10.1086/491729 https://doi.org/10.1051/0004-6361:20030575 https://doi.org/10.1086/172702 microsoft word reviewers of bibechana i reviewers of bibechana2018 prof. iosif galanakis prof. raju khanal prof. narayan prasad adhikari kul prasad limbu prof. a. weiss dr. dil kumar limbu dr. gulshan singh prof d. adhikari dr. cut tian prof. o. c. jones prof. xuefang dai prof r.n. jordar prof. b.p. singh prof. p.r. pradhan dr. anant babu marahatta dr. j. kumar prof. b.k. singh r c o s t n chom nath adhikari et al./ bibechana 14 (2017) 77-85 : rcost p.77 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana micellization behavior of cetyltrimethylammonium bromide in presence and absence of na2so4 and mgso4 in aqueous media chom nath adhikari, g.s. shrivastav, ajaya bhattarai* *department of chemistry, m.m.a.m.c., tribhuvan university, biratnagar, nepal * e-mail: bkajaya@yahoo.com article history: received 1 april, 2016; accepted 1 october, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15871 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract viscosity and surface tension measurements of cetyltrimethylammonium bromide (ctab) in presence and absence of na2so4 and mgso4 in aqueous media are reported. the results showed an increase in viscosity with increase in concentration of cetyltrimethylammonium bromide in presence and absence of salts where as the decrease in surface tension with increase in concentration of cetyltrimethylammonium bromide in presence and absence of salts. the viscosity of ctab was observed lowest in pure water and increases in presence of mgso4 and then more increases in presence of na2so4 where as the surface tension of ctab was observed highest in pure water and decreases in presence of na2so4 and then more decreases in presence of mgso4.the critical micelle concentration (cmc) of ctab decreases in presence of salts in both viscosity and surface tension measurements. the decreasing cmc of ctab are found to be more in the presence of na2so4 in comparison with the presence of mgso4 for both measurements. the graphs of viscosity versus log[c] and the surface tension versus log[c] are used in determining the critical micelle concentration (cmc). keywords: critical micelle concentration; cetyltrimethylammonium bromide; viscosity; surface tension. 1. introduction cationic surfactants do show antibacterial properties and are used as cationic softeners, lubricants, retarding agents and antistatic agents and in some cases consumer use also. hence, cationic surfactants offer some additional advantages over other class of surfactants [1-4]. like all other surfactants ctab also shows a rapid change in viscosity when the physical and chemical compositions of the solution are changed [5]. in viscometric determination of cmc of pure surfactant in presence and absence of na2so4, mgso4, the viscosities (η) are plotted as a function of the logarithm of the surfactant. the surface tension of a solution is lowered when surfactants are present [6]. the limiting value of surfactant concentration that produces a surface tension decrease is the critical micelle chom nath adhikari et al./ bibechana 14 (2017) 77-85 : rcost p.78 (online publication: dec., 2016) concentration [7]. in tensiometric determination of the cmc of pure surfactants, the surface tensions (γ ) are plotted as a function of logarithm of the surfactant concentration. the two fitted lines meet in the curve at the particular point. that point of intersection is known as cmc of the solution.the effective factors, such as the addition of electrolytes, buffer ph, temperature, addition of organic modifiers, ionic strength of the aqueous solution, and presence of additives can change the cmc value from that determined in pure water[8-10]. addition of electrolyte in the surfactant solution decreases the cmc value [11]. in this paper, we report a study of the aggregation process of ctab at room temperature in the absence and in the presence of na2so4 and mgso4 in aqueous media at room temperature by viscometric and surface tension method. 2. experimental cetyltrimethylammonium bromide (ctab), na2so4 and mgso4 were used as purchased from loba chemical, india. the water used in the solutions prepared at room temperature experiments was doubly distilled. the viscometric measurements were performed at room temperature using an ostwald viscometer. several independent solutions were prepared, and runs were performed to ensure the reproducibility of the results. to check whether the reduced viscosities depend on the shear rate in the concentration range investigated. this did not lead to different values of the reduced viscosity. solvent medium from those of the surfactant solutions in presence and absence of salt was taken. the viscometer was always suspended vertically at room temperature. the viscometer was cleaned and dried every time before each measurement. the flow time for constant volume of solution through the capillary was measured with a calibrated stop watch. the coefficient of viscosity of a given liquid can be calculated according to the following equation: 2 2 1 2 1 1 t t d d              (1) 1 = coefficient of viscosity of the solution 2 = coefficient of viscosity of the solvent t1 = time flow of the solution t2 = time flow of the solvent d1 = density of the solution d2 = density of the solvent the density of any one solution must be known which is calculated by using the expression: 2 2 1 1 d w w d        (2) d1 = density of liquid d2 = density of water w1= weight of liquid w2= weight of water before using the stalagmometer was first carefully washed with a solution of chromic acid and then with doubled distilled water. finally it was washed with acetone and water and dried. the surface tension of ctab in absence and presence of na2so4 and mgso4 was measured by drop count method using a stalagmometer. in this process, first the stalagmometer was filled with chom nath adhikari et al./ bibechana 14 (2017) 77-85 : rcost p.79 (online publication: dec., 2016) distilled water as above without changing the pressure. then the drop count was started. by following the same process all the solutions of varied strength of ctab in presence and absence of salts (na2so4 and mgso4) was measured. the following equation is used to calculate the surface tension of required solution: solv solv lnso lnso solv lnso d d n n              (3) where, γ soln = surface tension of solution γ solv = surface tension of solvent nsoln = number of drops of solution nsolv = number of drops of solvent dsoln = density of solution dsolv = density of solvent if the surface tension of one of the liquids is known then that of the other can be easily calculated from the equation (3). 3. results and discussion the specific viscosity decreases with decrease of concentration of ctab and there is a pronounced break and then remains constant. the breaking point is known as critical micelle concentration, cmc (fig. 1-3). our results indicate that there is increase in viscosity with increase in concentration of salt added. the viscosity of ctab in presence of na2so4 is more than in presence of mgso4 (table1), this is because while mgso4 is absorbed on the surface of the micelle, na2so4 remains in the bulk of the solution. addition of salt is known to decrease cmc of the solution [12]. increasing the salt concentration reduces the electrostatic debye screening length around the surfactant, which encourages the formation of longer micelles at equilibrium. this, in turn contributes to the changes in cmc. fujio (1998) [13] found that spherical micelles associated to form into rod-like micelles when salt concentration exceeded a threshold concentration. salts decrease the cmc in the order: mgso4< na2so4. here mg+ + is least effective in decreasing the cmc due to small size and large hydrated radius and would act as a water-structure promoter decreasing the availability of water to the micelles. therefore, upon addition of mgso4 and na2so4 in ctab, na2so4 is more effective in reducing the cmc of ctab. hence in our case na2so4 decreases the cmc of ctab more than mgso4 (table 2). the surface tension of ctab in the presence and absence of na2so4 and mgso4 were calculated from equation (3) and were tabulated in table 3. the graphical representations of the surface tension of ctab in the presence and absence of na2so4 and mgso4 with log [ctab] are shown in figs. 46. since, there was sharp decrease of surface tension on increase of surfactant concentrations. according to the experimental calculations and determinations, the surface tension was found to be decreased in presence of salts .i.e. na2so4 and mgso4.the surface tension value was high in case of water because of absence of externally added salts. since, on the addition of inorganic salts, affect surfactant aggregation mainly through reducing the electrostatic interaction among the surfactant head groups and consequently decrease the surface tension of the surfactant molecules. chom nath adhikari et al./ bibechana 14 (2017) 77-85 : rcost p.80 (online publication: dec., 2016) table 1: viscosity of ctab in absence and presence of mgso4 and na2so4 at room temperature solvent concentration(mol/l) viscosity(cp) distilled water 0.00315 0.91643 0.00271 0.90422 0.00235 0.89231 0.00204 0.88256 0.00176 0.87561 0.00153 0.86825 0.00133 0.85967 0.00116 0.85272 0.00103 0.84782 0.00086 0.84921 0.00074 0.84920 0.00065 0.84919 0.00056 0.84919 0.00048 0.84918 solvent concentration(mol/l) viscosity(cp) mgso4-water 0.00210 0.89079 0.00181 0.88780 0.00157 0.88380 0.00136 0.88050 0.00118 0.87800 0.00100 0.87500 0.00085 0.86900 0.00077 0.86500 0.00066 0.85100 0.00057 0.85100 0.00050 0.85100 0.00043 0.85100 solvent concentration(mol/l) viscosity(cp) na2so4-water 0.00170 0.92019 0.00156 0.91475 0.00135 0.90722 0.00118 0.89900 0.00104 0.89433 0.00074 0.88079 0.00052 0.86689 0.00040 0.86025 0.00031 0.85300 0.00025 0.85300 0.00020 0.85300 0.83 0.85 0.87 0.89 0.91 0.93 0.0001 0.001 0.01 cmc=1.0mm log[ctab] v is c o s it y (c p ) 0.87 0.91 0.0001 0.001 0.01 cmc=0.63m m log[ctab] v is c o s it y (c p ) 0.85 0.87 0.89 0.91 0.93 0.0001 0.001 0.01 cmc=0.31m m log[ctab] vi sc o si ty (c p ) 30 35 40 45 50 -3.208 -3.108 -3.008 -2.908 -2.808 -2.708 -2.608 -2.508 cmc = 1.04 mm log[ctab] su rf a ce te n si o n ( , d yn e /c m ) chom nath adhikari et al./ bibechana 14 (2017) 77-85 : rcost p.81 (online publication: dec., 2016) fig. 1: variation of viscosity with log[ctab] in distilled water at room temperature. fig. 2: variation of viscosity with log[ctab] in mgso4-water at room temperature. fig.3: variation of viscosity with log[ctab] in na2so4-water at room temperature. fig. 4: variation of surface tension with log[ctab] in distilled water at room temperature. 30 35 40 45 50 55 -3.4 -3.2 -3.0 -2.8 -2.6 -2.4 cmc = 0. 4 m m log[ctab] s u rf a c e te n s io n ( , d y n e /c m ) 33 35 37 39 41 -3.408 -3.308 -3.208 -3.108 -3.008 -2.908 -2.808 -2.708 cmc = 0.64 mm log[ctab] s u rf a c e te n s io n ( , d y n e /c m ) chom nath adhikari et al./ bibechana 14 (2017) 77-85 : rcost p.82 (online publication: dec., 2016) fig. 5 : variation of surface tension with log[ctab] in na2so4-water at room temperature. fig. 6: variation of surface tension with log[ctab] in mgso4water at room temperature. table 2. critical micellar concentration (cmc) obtained from viscometry of ctab in presence and in absence of na2so4 and mgso4 in aqueous media at room temperature distilled water cmc (mm) na2so4-water cmc (mm) mgso4-water cmc (mm) 1.08 0.31 0.63 in the case of na2so4 and mgso4, the sodium ion (na+) is larger than the magnesium ion (mg2+) because the magnesium cation, mg2+ has a greater cationic charge than the na+ cation. the surface tension of ctab in presence of na2so4 is more than in presence of mgso4 because the smaller ions are strongly hydrated, so they need to pull more water molecules with them which make them less mobile. thus, due to magnesium ions (mg2+) .i.e. counter ions reduced largely the electrostatic interaction among the surfactant molecules and decreased surface tension largely. when surface tension of a solution is plotted against log[c], where c is the concentration of surfactant. the results showed a sharp decrease in surface tension with increase in concentration of cetyltrimethylammonium bromide in presence and absence of na2so4 and mgso4 and then minimum surface tension has been observed and again the small increase in surface tension has been noticed and finally the almost flat curves were obtained. the intersection between two curves gives the critical chom nath adhikari et al./ bibechana 14 (2017) 77-85 : rcost p.83 (online publication: dec., 2016) micelle concentration. the critical micelle concentration of the surfactant decreased in presence of na2so4 and mgso4, the decrease in cmc depended upon the concentration of added salts. our calculation of cmc of ctab in distilled water at room temperature found to be 1.04 mm which is almost matching with 1.102 mm by surface tension method [14]. when surfactant and salt are mixed in solution, salting-out phenomenon often happens [15-18]. according to hydration theory [19] salting-out is the result of preferential movement of water molecules, which immobilize and quench their role as solvents, from coordination shells of surfactant molecules to those of salts. the effects of halide salts on the growth of micelles in ionic surfactant solutions have been systematically studied [20-21]. with the addition of inorganic salts, the reduced electrostatic repulsion among the surfactant head groups is a key factor to influence the morphology of aggregates in ionic surfactant solutions. for conventional single-chain cationic surfactants, micelles may change from global to rod like or wormlike with the addition of inorganic salts [22-23 ]. salts decrease the cmc in the order: mgso4< na2so4 as like viscosity measurements. (table 4). table 3: the surface tension of ctab in presence and absence of na2so4 and mgso4 . solvent concentration(mol/l) surface tension(dyne/cm) distilled water 0.00253 33.43 0.00203 33.77 0.00162 34.11 0.00130 34.47 0.00104 34.83 0.00095 37.79 0.00087 40.52 0.00078 43.73 0.00070 46.46 0.00066 48.31 0.00063 49.40 na2so4-water 0.00073 40.70 0.00066 40.70 0.00060 40.60 0.00040 40.10 0.00030 41.00 0.00020 42.00 0.00010 43.00 0.00009 43.50 mgso4-water 0.00161 33.55 0.00127 33.54 0.00091 33.78 0.00077 34.03 0.00064 33.44 0.00057 38.02 0.00053 39.11 0.00050 39.38 0.00047 39.55 0.00044 40.14 chom nath adhikari et al./ bibechana 14 (2017) 77-85 : rcost p.84 (online publication: dec., 2016) table 4: critical micellar concentration (cmc) obtained from tensiometry of ctab in presence and in absence of na2so4 and mgso4 distilled water na2so4-water mgso4-water cmc cmc cmc (mm) (mm) (mm) 1.04 0.40 0.64 4. conclusions the following conclusions have been drawn from above results and discussion. the results showed an increase in viscosity of cetyltrimethylammonium bromide with addition of salts where as decrease in surface tension of cetyltrimethylammonium bromide with addition of salts. the viscosity of cetyltrimethylammonium bromide is found more in presence of na2so4 than mgso4 in aqueous media whereas the surface tension of cetyltrimethylammonium bromide is found less in presence of mgso4 than na2so4 in aqueous media. in the presence of na2so4, the cmc of cetyltrimethylammonium bromide decreases more in comparison with presence of mgso4 for both viscosity and surface tension measurements. the calculations of cmc from both systems seem to be equal. references [1] e. jungerman, cationic surfactants, marcel dekker, new york, (1969). 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received 11 july, 2015; accepted 10 august, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13344 abstract the study assessed the perception of fish farmers to wildlife predators’ attack of fish ponds in borgu local government area of niger state, nigeria. the study covered three wards; bussa, karabonde and rafi which were purposively sampled. questionnaire, personal interview and physical observation were employed to collect necessary data. a face to face questionnaire survey was carried out on a total of thirty-two (32) fish farmers and pond managers to elicit information on extent of predator’s activities by wildlife, and frequency of occurrence and period or season of predation. the result revealed that predation occurred both day and night. most respondents (65.63%) attested to the predator attack in the fish farm. the most preferred prey size appeared to be fish fingerlings which were consumed wholly. five (5) wildlife species include frog (rana sp) 16.66%, wildcat (felis silvestris) 8.3%, water snake (grayia smithii) 11.66%, monitor lizard (varanus niloticus) and birds like kingfisher( alcedo sp) 26.66% were identified as the predators of fish. from the wildlife species identified, birds mostly attack fish in ponds in the study area. wildlife predators including reptiles and amphibians are some of the numerous challenges to culture fisheries in the study area. however, the preventive measures and controls of wild animals attacked fish in farms are netting (59.38%) which is the best method to prevent predators from fish ponds, fencing (28.13%) and security guards (12.50%). in control measure, 68.75% confirmed that the physical method usually works better than biological and chemical control measures. hence, its adoption for the management of the pest and predators is essential for sustainable culture fisheries in the study area. ©rcost: all rights reserved. keywords: fisheries; perception, predator; ponds, prey; wildlife. k.m. adelakun et al. / bibechana 13 (2016) 29-37: rcost p.30 (online publication: dec., 2015) 1. introduction wildlife species prey on fish ponds and the predators are significant causes of reduction in fish population in ponds, resulting to low output [1]. wildlife occurring at aquaculture sites can ignite conflicts over resources managed by humans [2]. fish predators are attracted to farm ponds by abundant food supplies and specific habitats hence many generate human-wildlife conflicts by causing stock losses and physical destruction at aquaculture facilities [3, 4]. predation describes a biological interaction, where a predator feed on its prey [5]. predators may or may not kill their prey prior to feeding on them, but the act of predation often results in the death of its prey and the eventual absorption of the prey’s tissue through consumption [6]. the act of predation can be broken down into a maximum of three (3) stages: detection of prey, attack or capture and finally consumption. the relationship between predator and prey is one which is typically beneficial to the predator, detrimental to the prey species. sometime however, predation has indirect benefits to the prey species though the individuals preyed upon do not benefit. this means that, at each applicable stage predator and prey species are in an evolutionary superiority to maximize their respective abilities to obtain food or avoid being eaten [7]. predation eliminates a prey species and many studies have shown predations to be an important factor in maintaining species diversity and ecological balance in a community [8]. although predation may not always limit prey population, the availability of prey constitutes a major component of the carrying capacity of predator population; this is evident in relatively simple situations, such as when bloom of phytoplankton resulting from an upwelling of nutrients due to ocean currents and this is followed by a corresponding increase in zooplankton [8]. culture fisheries like every other agricultural practice encounter problems; this destroy fish or hinder the production of target fish species [9], these predators can be grouped into birds, mammals, amphibian and reptiles which can retards fish product. a true predator can commonly be known as one which kills and eats another organism. whereas other types of predators all harm their prey in some way or certainly kills them e.g hippopotamus. predators may hunt actively for prey, or sit and wait for prey to approach within striking distance, as in ambush predators. some predators kill large prey and dismember or chew it prior to eating it, such as a alligator or a human; others may eat their (usually much smaller) prey whole, as does a bottlenose dolphin swallowing a fish, or a snake, duck or stork swallowing a frog. some animals that kill both large and small prey for their size may do either depending upon the circumstances; either would devour a large insect whole but dismember a fish. some predation entails venom which subdues a prey creature before the predator ingests the prey by killing, which k.m. adelakun et al. / bibechana 13 (2016) 29-37: rcost p.31 (online publication: dec., 2015) the box jellyfish does, or disabling it, found in the behaviour of the cone shell. in some cases, the venom, as in rattlesnakes contributes to the digestion of the prey item even before the predator begins eating. in other cases, the prey organism may die in the mouth or digestive system of the predator. increases in some wildlife populations and their spread into human -dominated landscapes are a growing concern [10; 11]. wildlife predation on fish ponds have serious consequences both for the profitability of aquaculture enterprise, due to loss of production and costs of implementing damage control or prevention methods [10] and for wildlife population, due to the cumulative adverse impact of human-mediated mortality of wildlife (kloskowski, 2010). monitoring wildlife predators on fish farm may yield a substantial amount of population data on wildlife interacting with fisheries which may be especially valuable in the area of animal conservation and economic interest. therefore, this work assessed the occurrence, distribution and perception of wildlife species that may adversely affect fisheries yield in the context of the potential impact on pond culture in the study area. 2. materials and method study area borgu local government area lies between latitude 900n and 110n and longitude 20e and 40e, covering a land mass of about 16,200km providing both natural and acquired materials of attraction to business and economic activities [12]. a reconnaissance survey of major pond sites within purposively selected wards of borgu local government area in niger state was carried out in september, 2012 to determine our sample size for data collection in october, 2012 to april 2013.sites were selected based on strategic and level of fish culture production i.e grow-out fish farmer were considered. 3. methodology study population borgu local government area consists of ten (10) political wards namely: babanna, bussa, duga, kabe, karabonde, konkoso, malale, rafi, shagunu and wawa. this survey cut across fish farmer who have fish farms and direct link of responsibility to the issue being investigated in three major wards of bussa, karabonde, and rafi because preliminary survey has shown that the wards have considerable number of fish farms (at least 4) sample size and sample techniques from the reconnaissance survey of the study area, population census of the farms comprising the study populations are: bussa ward-30 fish farms; karabonde ward (including monai)-6 fish farms; rafi ward6 fish farms n [sample population] = 42; simple random sampling were used in order to select between 75 to100% sample size from each selected ward to have thirty –two (32) respondents i.e (20+6+6) = 32; n=32 (85.7%) k.m. adelakun et al. / bibechana 13 (2016) 29-37: rcost p.32 (online publication: dec., 2015) where n =sample size. data collection data were collected from two main sources, on site data collection and social survey through structured questionnaire which was administered to fish farmers and fish pond managers (onadeko et al., 2000). each pond site was visited and wildlife predators activities were observed around their boundary and within pond. physical appearance and behavioural activity pattern of various kinds of animals visiting the ponds were noted. observations were made at different periods of the day (morning, afternoon and evening). physical examination was conducted where fish carcasses were found. face to face questionnaire survey were administered to a total of thirty –two (32) fish farmers and pond managers to elicit information on extent of predators activities by wildlife, and include frequency of occurrence of predators and time of season. data analysis all data collected were interpreted using descriptive statistics of frequency tables and simple percentage. 4. results table 1: demographic characteristic of respondents. variables frequency percentage (%) age 20-30 15 46.88 31-40 12 37.50 41 above 5 15.63 sex male 31 98.88 female 1 3.13 marital status single 19 59.38 married 13 40.63 occupation fish farming 21 65.63 civil servant 7 21.88 student 4 12.5 educational qualification primary secondary 6 18.75 tertiary 25 78.13 others[informal] 1 3.13 table 1 revealed the demographic characteristic of respondents. majority age of respondent is within the 20 and 30 (46.88%), while the least respondents are aged 41 and above. however, most respondents are k.m. adelakun et al. / bibechana 13 (2016) 29-37: rcost p.33 (online publication: dec., 2015) male (96.88%), single respondents are 59.39% in comparison to 40.63% married. major occupation of the respondents is fish farming (65.63%), while 21.88% and12.5% are civil servants and students respectively. respondents with formal education are (78.13%). table 2: management practice of respondents. variables frequency percentage culture system (rearing methods) extensive 5 15.63 intensive 12 37.50 semi intensive 15 46.88 scale of operation (based on production capacity) commercial 30 68.18 subsistence 14 31.81 both 1 3.13 species of fish culture catfish 29 90.63 tilapia 2 6.25 both 1 3.13 sorting of fish stock yes 27 84,38 no 2 6.25 no response 3 9.38 from table 2, semi-intensive farming is mostly practiced in the study area (46.88%) while extensive was least practiced (15.63%). however, in fish farming, respondents that based production on commercial level are more (68.18%) when compared to subsistence farming (31.81%). similarly, the species of fish culture is mostly catfish (90.63%). 87.57% do stock taking/counting of fish while those that do not and no response were 6.25% and 3.13% respectively. result also show that 84.38% of the respondents do sort fish stock while only 6.25% do not, though 34.38% do the sorting monthly while only 3.13% sort occasionally. prevalent wildlife attacking fish farms in the study area figure 1 revealed that monitor lizard mostly attack fish in the pond in the study area compare to other species of animals. k.m. adelakun et al. / bibechana 13 (2016) 29-37: rcost p.34 (online publication: dec., 2015) fig. 1: response to pond predators prevalent in the study area. table 3: wildlife predation perception of respondents. variables frequency percentage occurrence of predation on farm yes 21 65.63 no 10 31.25 no response 1 3.13 respondent preference for predator attack yes no 30 93.75 no response 2 6.26 daily time of attack morning 4 12.5 afternoon night 7 21.88 both day and night 21 65.63 frequency of the attack occasionally 9 28.13 weekly 2 6.25 season of attack dry season 16 50.0 rainy season 9 28.13 all year round 7 21.88 stage of fish predators mostly attack fry 3 9.38 fingerling 19 59.38 juvenile 6 18.75 grow-out 5 15.63 0 2 4 6 8 10 12 14 16 18 monitor lizard bird snake wildcat frog no of respondent pr ed at or s a tt ac ki ng p on ds k.m. adelakun et al. / bibechana 13 (2016) 29-37: rcost p.35 (online publication: dec., 2015) from table 3, 65.63% admitted to predator attack on their pond while 31.25% did not. most respondents (93.74%) do not wish for predator attack, while 6.26% did not respond to the question.the result further revealed that, predator mostly attack pond during day and night (65.63%). 50% of the respondents reported that predatory activities are more pronounced during the dry season than in rainy season (28.13%) while 21.88% report that it was all year round. it was also reported that, predator mostly attack fish fingerling (59.38%) compare to other growing stages of fish. table 4: wildlife attack prevention and controls measures in fish farms. variables frequency percentage preventive measures fencing 9 28.13 security 4 12.5 covering pond with net 19 59.38 control measures chemical (e.g lime) 1 3.13 biological (e.g use of hunting animals like trained dog) 9 28.13 physical 22 68.5 from table 4, most respondents (59.38%) reported that netting is the best method to prevent predator from fish pond than fencing (28.13%) and use of security personnel (12.5%). 68.75% confirmed that they used physical method, while 28.13% and 3.13% preferred biological and chemical methods respectively. 5. discussion from the finding it is strongly agreed that, occurrence, distribution and perceptions of wildlife species at pond fisheries were not desirable probably due to the fact it could leads to loss of fish stocked. this has been reported by kloskowski [2] that serious damage of pond fisheries is caused by wildlife in eastern poland. the present results show that presence of birds and reptiles in pond could pose a serious economic problem to fish farmer. these wildlife species observed in the study area had earlier been reported as fish predators by bellairs, [3]; brown, [14]; landan, [15]. the high response to the existence of birds’ predator in this study area is in conformity with shitote et al., [16] who reported birds as the highest predator of fish in western kenya. wild animals dominated the aquaculture damage; they were widely reported and believed to be responsible for severe stock losses at over a half the sites where they k.m. adelakun et al. / bibechana 13 (2016) 29-37: rcost p.36 (online publication: dec., 2015) were observed. the present survey shows that monitoring fish farms may yield a substantial amount of data on wildlife interacting with fisheries. this may be especially valuable in the case of mammals, for which monitoring schemes are less developed than those for birds [17]. wildlife observations from fish farms may be useful for atlas data and assessment of population dynamics. therefore, confirmation on the regular occurrence of these species at fish farms should justify the preventive measure and control measure of wildlife attack in fish farms to avert human-wildlife conflict. a related problem is adequate assistance in managing wildlife damage at fish farms suffering costs from multiple problem species. financial burdens on this group of farms may be particularly heavy, due to the different types of production losses to species with differing impact on farm resources and because protective measures against different groups of nuisance species require greater expenditures. 6. conclusion farmers that engaged vigorously on this fish farming business are often faced with various challenges among which are the fish predators; which could drastically affected fish production in recent years. wildlife predators which include aquatic birds, reptiles, mammal (including man as poacher) and amphibians such as frog are some of the challenges to culture fisheries in the study area. these predators destroy fish or hinder the production of target fish species. hence, the management of the predators is essential for the sustaining culture fisheries as wildlife predatory activities may constitute an economic problem to fish pond management in the study area. uncontrolled predation on fish is inimical to the survival of fish culture business. it is of great importance therefore, to keep fish predation at its lowest. references [1] s.a onadeko, g.n.o.ezeri and a.l.a. shotuyo, aquafield, 1 (1) (2000) 45-52. [2] j. kloskowski, european journal of wildlife research, 57(2) (2010)295-304. [3] r. billard (eds.), carp: biology and culture. springer, berlin, 1999. [4] k. dobrowolski, (eds.), environmental-economic evaluation of fish ponds in poland. iucn, warszawa, 1995. [5] m. begon, c. townsend and j. harper, ecology: individuals, populations and communities (third edition) blackwell science, london, 1996. [6] encyclopedia britannica, predation, www.britannica.com: predation, 2013. [7] m. homing and j.e. mellish, plots one 7 (1) (2012). [8] h. curtis, biology of fishes (2nd eds) john wiley and sons, inc (publ), 1993 pp 5-11. [9] niger delta environmental survey (ndes), final report of phase 1, vol. 1, 1997. [10] z. adámek, h. klinger, e. staub, suppl. ric. biol. selvag, 26 (1997) 347–353. [11] a. kranz, mammalia, 64 (2000) 357 -368. [12] f.o. amobode, influence of human activities on the conservation of flora and fauna resources of kainji lake national park, 1989 pp 245-256. [13] a. a. bellairs, the encyclopedia of wildlife introduction to reptiles and tortoise: alligators and crocodiles, lizards and snakes. longman london, 1974 (publl.) pp 980. k.m. adelakun et al. / bibechana 13 (2016) 29-37: rcost p.37 (online publication: dec., 2015) [14] l.h. brown, birds of african waterside. macmillan company, london, new york. 1979 (publl) p 230. [15] m. landan introduction to agricultural john wiley and sons, inc. , 1992 (publ) p127. [16] z. shitote, j. wakhungu, and s. china, challenges facing fish farming development in western kenya. greener journal of agricultural sciences, 3(5) (2013) 305-311. [17] j. e. battersby and j.d. greenwood mammal rev., 34 (2004) 3–29. microsoft word shah _80-88_.docx r c o s t n publisher: research council of science and technology, biratnagar, nepal: p. 80 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana on contact conformal curvature tensor in trans-sasakian manifolds riddhi jung shah department of mathematics, janata campus nepal sanskrit university, dang e-mail: shahrjgeo@gmail.com accepted for publication: december 18, 2014 abstract the purpose of this paper is to study some results on contact conformal curvature tensor in trans-sasakian manifolds. contact conformally flat trans-sasakian manifold, ξ -contact conformally flat trans-sasakian manifold and curvature conditions ( )0 , . 0c x sξ = and ( )0 0, . 0c x cξ = are studied with some interesting results. finally, we study an example of 3dimensional trans-sasakian manifold. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11783 © 2014 rcost: all rights reserved. keywords: contact conformal curvature tensor; trans-sasakian manifold; hermitian manifolds. 1. introduction in 1978, gray and hervella [1] studied on the sixteen classes of almost hermitian manifolds and their linear invariants. they considered unitary group ( )u n on a certain space w and studied that the representation of ( )u n on w has four irreducible components, 1 2 3 4.w w w w w= ⊕ ⊕ ⊕ from these four components sixteen different invariants subspaces were obtained. among four components 3 4w w⊕ corresponds to the class of hermitian manifolds. oubina [2] studied a new class of almost contact metric structure, called trans-sasakian which is an analogue of a locally conformal kaehler structure on an almost hermitian manifold. an almost contact metric structure ( ), , , gϕ ξ η (where ϕ is a (1, 1) tensor field, ξ is a vector field, η is a 1-form and g is a compatible rimannian metric) on m is trans-sasakian [2] if ( ), ,m j g×ℝ belongs to the class 4 ,w where j is the almost complex structure on m ×ℝ defined by (1.1) ( ), , , d d j x f x f x dt dt ϕ ξ η   = −        shah/bibechana 12 (2015) 80-88 : p. 81 for any vector field x on ,m where g is the product metric on .m ×ℝ trans-sasakian manifold is the trans-sasakian structure of type ( ), ,α β where α and β are smooth functions on .m transsasakian manifolds of type ( ) ( )0,0 , ,0α and ( )0,β are cosympletic [3],α -sasakian [4] and β kenmotsu manifold [4,5] respectively. trans-sasakian manifolds have been studied in [6,7] and by many others. on the other hand, contact conformal curvature tensor field was introduced and defined by jeong et al. [8] in a ( )2 1n+ -dimensional sasakian manifold which was constructed from the conformal curvature tensor field defined by kitahara et al. [9] in a kaehler manifold by using the boothbywang’s fibration. contact conformal curvature tensor has also been studied in [10] and [11]. 2. preliminaries let m be a ( )2 1n+ -dimensional almost contact metric manifold equipped with an almost contact metric structure ( ), , , ,gϕ ξ η where ϕ is a (1, 1) tensor field, ξ is a vector field, η -is a 1-form and g is a compatible riemannian metric such that [3] (2.1) ( ) ( ) ( ) ( )2 , 1, =0, 0,x x x xϕ η ξ η ξ ϕξ η ϕ= − + = = (2.2) ( ) ( ) ( ) ( ), , ,g x y g x y x yϕ ϕ η η= − (2.3) ( ) ( ) ( ) ( ), , , , ,g x y g x y g x xϕ ϕ ξ η= − = for all , .x y tm∈ the fundamental 2-form φ of the almost contact metric structure ( ), , , gϕ ξ η is defined as (2.4) ( ) ( ) ( ), , , ,x y g x y g x yϕ ϕφ = = − since ϕ is a skew-symmetric with respect to .g an almost contact metric manifold m is called trans-sasakian manifold if [2] (2.5) ( ) ( ) ( ){ } ( ) ( ){ }, , ,x y g x y y x g x y y xϕ α ξ η β ϕ ξ η ϕ∇ = − + − where ∇ is levi-civita connection of riemannian metric g and ,α β are smooth functions on .m from (2.5) it follows that (2.6) ( ){ },x x x xξ αϕ β η ξ∇ = − + − (2.7) ( ) ( ) ( ), , .x y g x y g x yη α ϕ β ϕ ϕ∇ = − + in a ( )2 1n+ -dimensional trans-sasakian manifold ,m the following relations hold [6] (2.8) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 2 2 2 , [ ] 2 [ ] , r x y y x x y x y x y y x x y y x y x ξ α β η η α ϕ β ϕ αβ η ϕ η ϕ α ϕ β ϕ = − − − − + − + + (2.9) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 2, [ , ] 2 [ , ] , [ ] , , r x y g x y y x g y x y x y x g y x grad y x x g x y grad ξ α β ξ η αβ ϕ ξ η ϕ α ϕ ϕ α β η ξ ϕ ϕ β = − − + − + + + − − shah/bibechana 12 (2015) 80-88 : p. 82 (2.10) ( )2 0,αβ ξα+ = (2.11) ( ) ( ) ( ) ( ) ( )( ) ( )( )2 2 , [2 ] 2 1 ,s x n x x n xξ α β ξβ η ϕ α β= − − − − − (2.12) ( )( ) ( )( ), , , ,r x y z g r x y zη ξ= − (2.13) ( )( ) ( )( ) ( )( ), , , 0,r x y r x r xη ξ η ξ ξ η ξ ξ= = = (2.14) ( )( ) ( )( ) ( )2 2 , , .r x y g x yη ξ α β ξβ ϕ ϕ= − − in a ( )2 1n+ -dimensional trans-sasakian manifold if we put ( ) ( )2 1 ,grad n gradϕ α β= − then we have (2.15) ( ) 0,ξβ = (2.16) ( ) ( ) ( )2 2 , 2 ,s x n xξ α β η= − (2.17) ( )( ) ( ) ( )2 2 , , ,r x y g x yη ξ α β ϕ ϕ= − (2.18) ( ) ( ) ( ){ }2 2 , ,r x x xξ ξ α β η ξ= − − (2.19) ( ) ( ), , .r x r xξ ξ ξ ξ= − throughout the paper we consider the trans-sasakian manifold under the condition ( ) ( )2 1 .grad n gradϕ α β= − in a ( )2 1n+ -dimensional trans-sasakian manifold the contact conformal curvature tensor field 0c of type (1, 3) which is defined by [8] can be written as (2.20) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 0 1 , , { , , , 2 , , , , , , , 2 , 2 , c x y z r x y z s y z x s x z y g y z qx n g x z qy s x z y s y z x x z qy y z qx s x z y s y z x g x z q y g y z q x g x y q z s x η ξ η ξ η η η η ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ = + − + − + − + − + − + − + + ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) } 21 2 {2 2 }{ , 2 1 2 , 2 , } 3 21 { 2 }{ , , } 2 1 2 y z n r n n g y z x n n n g x z y g x y z n r n g y z x g x z y n n n ϕ ϕ ϕ ϕ ϕ ϕ ϕ + + − − + + − − + + + − − + ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 3 21 2 {4 5 2 }{ 2 1 2 , , }, n r n n y z x n n n x z y g y z x g x z y η η η η η ξ η ξ + − + + − + − + − where , ,r s q and r denote the curvature tensor, the ricci tensor, the ricci operator and the scalar curvature respectively. from (2.20), we also have shah/bibechana 12 (2015) 80-88 : p. 83 (2.21) ( ) ( ) ( ) ( ) ( ){ }2 2 0 , , 2 ,c x y r x y y x x yξ ξ α β η η= + − − − (2.22) ( ) ( ) ( ) ( ) ( ){ }2 2 0 , , 2 , ,c x y r x y g x y y xξ ξ α β ξ η= + − − − (2.23) ( )( ) ( )( ) ( ) ( ) ( ) ( ) ( ){ } 0 2 2 , , 2 , , , c x y z r x y z g y z x g x z y η η α β η η = + − − − (2.24) ( )( )0 , 0,c x yη ξ = (2.25) ( )( ) ( ) ( ) ( ) ( ){ }2 2 0 , 2 1 , .c x y g x y x yη ξ α β η η= − − − definition. a ( )2 1n+ -dimensional trans-sasakian manifold m is said to be an η -einstein manifold if its ricci tensor s of type (0, 2) is of the form (2.26) ( ) ( ) ( ) ( ), , ,s x y ag x y b x yη η= + where ,a b are smooth functions on .m if 0,b = then the manifold m becomes an einstein manifold. 3. contact conformally flat trans-sasakian manifold definition. a ( )2 1n+ -dimensional trans-sasakian manifold is said to be contact conformally flat if it satisfies the condition (3.1) ( )0 , 0.c x y z = now, we prove the following result: theorem 3.1. if a ( )2 1n+ -dimensional trans-sasakian manifold m is contact conformally flat, then 2 2 1.α β= + proof. let m be a ( )2 1n+ -dimensional trans-sasakian manifold. suppose m is contact conformally flat then the condition ( )0 , 0c x y z = holds. now, using (3.1) in (2.20) and taking inner product on both sides by ,ξ we get (3.2) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1 , [ , , , , 2 , , ] 2[ , , ]. r x y z g x z s y g y z s x n x z s y y z s x g y z x g x z y η ξ ξ η η ξ η η ξ η η = − − + + − in view of (2.12), (2.16) and (3.2), we get (3.3) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 20 2 1 [ , , ] 2 [ , , ] , , , . g y z x g x z y g y z x g x z y x g y z y g x z x g y z α β η η αβ ϕ η ϕ η α ϕ α ϕ β ϕ ϕ = − − − + − + − − putting x ξ= in (3.3) and using (2.1), (2.10) and (2.15), we obtain (3.4) ( ) ( ) ( ) ( )2 2 1 [ , ] 0.g y z y zα β η η− − − = since ( ) ( ) ( ), 0,g y z y zη η− ≠ we have ( )2 2 1 0.α β− − = this implies that shah/bibechana 12 (2015) 80-88 : p. 84 (3.5) 2 2 1.α β= + this completes the proof of the theorem. 4. ξ -contact conformally flat trans-sasakian manifold definition. a trans-sasakian manifold of dimension ( )2 1n+ is said to be ξ -contact conformally flat if the condition (4.1) ( )0 , 0c x y ξ = holds. theorem 4.1. let m be a ( )2 1n+ -dimensional trans-sasakian manifold satisfying the condition ( )0 , 0,c x y ξ = then 2 2 1.α β= + proof. let us consider a ( )2 1n+ -dimensional trans-sasakian manifold m which satisfies the condition ( )0 , 0.c x y ξ = then by virtue of (2.1), (2.3), (2.8), (2.16) and (4.1) in (2.20), we get (4.2) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 20 2 1 { } 2 [ ] . y x x y x y x y x y y x x y y x y x y x α β η η α ϕ β β η ξ αβ η ϕ η ϕ α ϕ β β η ξ = − − − − + − + − + − + putting x ξ= in (4.2) and using (2.1), (2.10) and (2.15), we obtain (4.3) ( ) ( ){ }2 2 1 0.y yα β η ξ− − − = since ( ) ( )2 0,y y yη ξ ϕ− = ≠ we have ( )2 2 1 0.α β− − = this yields (4.4) 2 2 1.α β= + thus the theorem is proved. from theorem 3.1 and theorem 4.1, we can state the following result: theorem 4.2. trans-sasakian manifolds of dimension ( )2 1n+ which satisfy the conditions ( )0 , 0c x y z = and ( )0 , 0c x y ξ = are equivalent. 5. trans-sasakian manifold satisfying ( )0c ξ,x .s=0 consider a trans-sasakian manifold m of dimension ( )2 1 .n+ let s be the ricci tensor of type (0, 2). we prove the following result: theorem 5.1. let m be a ( )2 1n+ -dimensional trans-sasakian manifold. if m satisfies the condition ( )0 , . 0,c x sξ = then it is an einstein manifold with scalar curvature ( )( )2 22 2 1 .r n n α β= + − proof. let m be a ( )2 1n+ -dimensional trans-sasakian manifold which satisfies the condition shah/bibechana 12 (2015) 80-88 : p. 85 (5.1) ( ) ( )0 , . , 0.c x s u vξ = this condition implies that (5.2) ( )( ) ( )( )0 0, , , , 0.s c x u v s u c x vξ ξ+ = putting v ξ= in (5.2) and using (2.16) and (2.22), we obtain (5.3) ( ) ( ) ( )2 2, 2 , .s x u n g x uα β= − taking an orthonormal frame field at any point of the manifold and contracting over x and u in (5.3), we get (5.4) ( )( )2 22 2 1 .r n n α β= + − from (5.3) and (5.4) it follows that the manifold m is an einstein manifold with scalar curvature ( )( )2 22 2 1 .r n n α β= + − this completes the proof of the result. 6. trans-sasakian manifold satisfying ( )0 0c ξ,x .c =0 let m be a ( )2 1n+ -dimensional trans-sasakian manifold. suppose the condition ( )( )( )0 0, . , 0c x c u v zξ = holds in .m then we have theorem 6.1. a ( )2 1n+ -dimensional trans-sasakian manifold satisfying the condition ( )0 0, . 0c x cξ = is contact conformally semi-symmetric if ( ) ( ) ( ) ( ){ } ( )( ) ( ) 2 20 2 , , , , , , . g v z x g x v z g x z v g r v z x r x v z α β ξ ξ = − − − − − proof. let us consider a ( )2 1n+ -dimensional trans-sasakian manifold which satisfies the condition ( ) ( )0 0, . , 0,c x c u v zξ = then by definition we have (6.1) ( ) ( ) ( )( ) ( )( ) ( ) ( ) 0 0 0 0 0 0 0 0 0 , , , , , , , , . c x c u v z c c x u v z c u c x v z c u v c x z ξ ξ ξ ξ = − − − using (2.22) in (6.1) we get (6.2) ( ) ( ) ( ) ( )( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 2 0 0 0 0 0 0 0 0 0 0 , . , 2 [ , , , , , , , , , , , , ]. r x c u v z g x c u v z c u v z x g x u c v z u c x v z g x v c u z v c u x z g x z c u v z c u v x ξ α β ξ η ξ η ξ η ξ η = + − − − − + − + − + taking inner product on both sides of (6.2) by ξ and using (2.24), we obtain shah/bibechana 12 (2015) 80-88 : p. 86 (6.3) ( ) ( )( ) ( ) ( )( ) ( ) ( )( ) ( ) ( )( ) ( ) ( )( ) ( ) ( )( ) ( ) ( )( ) ( ) ( )( ) 2 2 0 0 0 0 0 0 0 0 , . , , 2 [ , , , , , , , , , , ]. og r x c u v z g x c u v z x c u v z g x u c v z u c x v z g x v c u z v c u x z z c u v x ξ ξ α β η η η ξ η η η ξ η η η η = + − − − − + − + − putting u ξ= in (6.3) and using (2.22), (2.23) and (2.25), we get (6.4) ( ) ( )( ) ( ) ( )( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 0 2 2 2 2 0 , . , , 2 [ , , , { , 2 , , }]. g r x c v z g r v z x r x v z z g x v x g v z v g x z ξ ξ ξ α β ξ η α β η η η = + − − + + − − + this implies that (6.5) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( ) ( ) 0 2 2 2 2 , . , 2 [ {2 , , , } , , , ]. r x c v z g v z x g x v z g x z v g r v z x r x v z ξ ξ α β α β ξ ξ = − − − − − − − from this it follows that the manifold is contact conformally semi-symmetric if the right hand side of (6.5) vanishes, i. e., if ( ) ( ) ( ) ( ){ } ( )( ) ( ) 2 20 2 , , , , , , . g v z x g x v z g x z v g r v z x r x v z α β ξ ξ = − − − − − this completes the proof of the theorem. 7. an example of a 3-dimensional trans-sasakian manifold let us consider a 3-dimensional manifold ( ) ( ){ }3, , : , , , 0,m x y z x y z z= ∈ ≠ℝ where ( ), ,x y z are the standard coordinates in 3.ℝ we choose the vector fields (7.1) 1 2, ,z ze e y e e x z y ∂ ∂ ∂ = + = ∂ ∂ ∂  3 ,e z ∂ = ∂ which are linearly independent at each point of .m now we define a semi-riemannian metric g on m as (7.2) ( ) ( ) ( )1 3 2 3 1 2, , , 0,g e e g e e g e e= = = (7.3) ( ) ( ) ( )1 1 2 2 3 3, , , 1.g e e g e e g e e= = = let η be a 1-form defined by ( ) ( )3,z g z eη = for any vector field z m∈ and ϕ be a (1, 1) tensor field defined by shah/bibechana 12 (2015) 80-88 : p. 87 (7.4) ( ) ( ) ( )1 2 2 1 3, , 0.e e e e eϕ ϕ ϕ= = − = the linearity property of ϕ and g yields that (7.5) ( ) ( ) ( ) ( ) ( ) ( ) ( )2 3 31, , , ,e z z z e g z u g z u z uη ϕ η ϕ ϕ η η= = − + = − for any , .z u m∈ if we take 3e ξ= in (7.5), ( ), , , gϕ ξ η defines an almost contact metric structure on .m by the definition of lie bracket and (7.1) we have [ ]1 2 1 2 2 1 2 2 3 , . z z z z z z z e e e e e e e y e e e ye x z y y x z ye e e e ∂ ∂ ∂ ∂ ∂ ∂   = − = + − +   ∂ ∂ ∂ ∂ ∂ ∂    = − proceeding same way we obtain [ ]2 3 2,e e e= − and [ ]1 3 1, .e e e= − thus we have (7.6) [ ] [ ] [ ]2 1 2 2 3 2 3 2 1 3 1, , , , , . z ze e ye e e e e e e e e e= − = − = − let ∇ be the levi-civita connection with respect to g then we have the koszul's formula (7.7) ( ) ( ) ( ) ( ) [ ]( ) [ ]( ) [ ]( ) 2 , , , , , , , , , , . xg y z xg y z yg z x zg x y g x y z g y z x g z x y ∇ = + − + − + by the use of (7.2), (7.3) and (7.6), (7.7) yields (7.8) 1 1 1 2 2 2 3 3 3 2 2 3 1 2 2 3 1 3 2 2 3 2 1 2 3 1 1 2 3 2 2 3 2 1 1 2 1 1 , , , 2 2 1 1 , , , 2 2 1 1 0, , , 2 2 z z z z z z z z e e e e e e e e e e e e e e e e e e e e e e e e ye e e ye e e e e e e e e e e ∇ = − + ∇ = ∇ =   ∇ = − − ∇ = + ∇ = − +   ∇ = ∇ = − ∇ = in view of (2.6), (7.2), (7.3) and (7.4) we have 1 2 1 2 1 2, e ee e e eξ β α ξ α β∇ = − ∇ = + and 3 0e ξ∇ = for 3 .e ξ= comparing these equations with (7.8) (first column), we get 21 2 zeα = − and 1.β = − again, by virtue of (2.7) and ( ) ( ) ( )x x xy y yη η η∇ = ∇ − ∇ we obtain ( ) ( ) ( ) 1 2 3 2 1 1 1 1 1, , 0. 2 z e e ee e e eη β η α η∇ = = − ∇ = = − ∇ == thus from above calculation the conditions (2.6) and (2.7) are satisfied and the structure ( ), , , gϕ ξ η is a trans-sasakian structure of type ( ),α β where 21 2 zeα = − and 1.β = − consequently ( )3 , , ,m gϕ ξ η is a trans-sasakian manifold. shah/bibechana 12 (2015) 80-88 : p. 88 references [1] a. gray, and l. m. harvella, ann. mat. pura. appl., 123(4)(1980) 35-58. http://dx.doi.org/10.1007/bf01796539 [2] j. a. oubina, publ. math. debrecen, 32(1985) 187-193. [3] d. e. blair, contact manifolds in riemannian geometry, lecture notes in math., vol. 509, springer-verlag, berlin, (1976). [4] d. e. blair, riemannian geometry of contact and sympletic manifolds, birkhauser boston, 2002. http://dx.doi.org/10.1007/978-1-4757-3604-5 [5] k. kenmotsu, tohoku math. j., 24(1972) 93-103. [6] u. c. de and m. m. tripathi, kyungpook math. j., 43(2003) 247-255. http://dx.doi.org/10.2748/tmj/1178241594 [7] r. j. shah, kathmandu univ. j. of sci., eng. and tech., 8(1)(2012) 81-87. [8] j. c. jeong, j. d. lee, g. h. oh. and j. s. pak, bull. korean math. soc., 27(1990) 133-142. [9] h. kitahara, k. matsuo and j. s. pak, bull. korean math. soc., 27(1990) 27-30. [10] j. c. jeong and j. k. park, comm. korean math. soc., 8(1993) 689-697. [11] j. s. pak, j. c. jeong and w. t. kim, j. korean math. soc. 28(1991) 267-274. microsoft word r.p. koirala _128-137_.docx r c o s t n publisher: research council of science and technology, biratnagar, nepal p.135 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana viscosity of liquid na-k alloy r. p. koirala 1, 2* , b. p. singh 1 , i.s. jha 2 , d. adhikari 2 1 university department of physics, t.m. bhagalpur university, bhagalpur, india 2 department of physics, m.m.a.m. campus, biratnagar, tribhuvan university, nepal * e-mail: rpphysics@gmail.com accepted for publication: december 20, 2014 abstract the present work reports a theoretical assessment of the composition dependence of mixing properties of liquid na-k alloy at 384k at fixed pressure, most likely, at the atmospheric pressure. in this work we have estimated the interaction energy in the alloy at the mentioned temperature on the basis of quasi-chemical approximation for regular alloy and employed it to work out basic thermodynamic properties of mixing such as free energy of mixing, entropy of mixing and enthalpy of mixing as function of composition of the alloy. to understand the dynamic behaviour in the liquid na-k alloy, we have carried out theoretical investigation of viscosity under consideration of moelwyn-hughes equation by using data for enthalpy of mixing obtained from quasi-chemical approximation. due to scanty of experimental data on viscosity of na-k alloy at 384k, we have performed computation of viscosity also from kaptay equation for comparison. the calculations have shown that there is a good match between theoretically computed thermodynamic functions and the available corresponding experimental data. the sets of viscosity values obtained against composition from the two equations show deviations from the ideality and themselves are reasonably comparable to each other. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11797 © 2014 rcost: all rights reserved. keywords: order energy; moelwyn-hughes equation; kaptay equation; viscosity. 1. introduction sodium and potassium occupy large proportion of the mass of the earth. they are respectively the sixth and seventh most abundant elements on the earth’s crust. these metals are one of the most reactive and electropositive classes of all metals. potassium and sodium can be alloyed to form na-k alloy. industrially, na-k is produced in a reactive distillation [1]. na-k is highly reactive with water and on exposure to air it ignites instantly, so it is stored under hexane or other hydrocarbons or an inert gas such as dry argon or dry nitrogen, for safety reasons [2]. na-k is low melting eutectic alloy (eutectic composition: 22% na & 78% k, by mass; eutectic temperature =−12.8°c) [3] and the alloy containing 40% to 90% potassium by weight is usually liquid at room temperature. as the eutectic composition of na-k has wide liquid temperature range at atmospheric pressure ( −12.8°c to 785 °c) and has properties such as melting point, density, vapor pressure, viscosity all low but thermal conductivity higher, it has got wide range applications. it is identified as an ideal htf (heat transfer fluid) candidate in a storage system such as concentrating koirala et al./bibechana 12 (2015) 135-144: p. 136 solar power (csp) that uses latent heat storage materials or pcms (phase changing materials) for storing relatively large amounts of energy in small volumes [3]. the alloy is used as the coolant in experimental fast neutron nuclear reactors; the soviet rorsat radar satellites were powered by a na-k cooled reactor [4]. in the past the na-k system has been the subject of several other research studies too in different aspects [5-13]. such potential applications of na-k alloy are drawing the attention of many researchers towards the investigation of its properties. here in this work the purpose of this article is to discuss the role of enthalpic and viscous properties in the mixing behaviour of liquid na-k alloy at 384k. it is known that most binary alloys are far from ideal solutions and reveal a micro-inhomogeneous atomic distribution and are less easy to understand as compared to crystals. the solubility in a homogeneous metallic mixture is basically governed by the size factor, electrochemical effect and electron concentration [14]. experience shows that these factors alone cannot be used effectively to understand the alloying of metals in the liquid phase and hence other properties of mixing should be incorporated. the properties of mixing are attributed to short range atomic interactions at the state of disorder in the alloy. based on the nature of atomic interaction in a liquid alloy, they are generally categorized into two generic types of ordering or phase separating alloys. the phase behaviour of a binary a-b alloy is determined by a balance between the atomic interactions eaa, ebb and eab. broadly, the properties of liquid alloys can be studied mainly under two distinct groups of theoretical models, the statistical mechanical model and electronic models. all the statistical theoretical models developed for the alloys are based on some sort of inter-atomic interactions which plays an important role in the formation of an alloy. the accurate determination of the interaction energy terms among species of a disordered system like a liquid alloy is actually a complex problem as compared to those of crystals. thus there always exists an opportunity for the investigation of the true nature of atomic interaction in a liquid alloy so that the alloying properties could be comprehended on the basis of theoretical analysis. over the past years, several theoretical models have been developed to assess the properties of liquid alloys and efforts have been on the move for future investigations. na-k alloy has an interesting feature that some of its equilibrium properties of mixing, such as free energy of mixing, entropy of mixing and enthalpy of mixing of this alloy at 384 k, are nearly symmetrical [15] about equiatomic composition despite the large atomic size mismatch of k and na ( %2.21r/r =∆ ), where r is the mean of the atomic radii of potassium and sodium. the experimental enthalpy of mixing for na-k is positive, the maximum being 762 j/mole [15] and concentration structure factors computed from the activity data indicate weaker tendency of phase separation in the alloy over whole range of concentration although both sodium and potassium have simple electronic structures and are soluble with each other [11]. from the analysis of the size difference of the constituent atoms as well as the strength of the interatomic interactions, alblas et al. have considered the na-k system as a borderline case for treatment as a regular solution [12]. in this analysis we aim to review the concentration dependence of the enthalpy of mixing, hm of na-k alloy at 384k by computing free energy of mixing, gm and entropy of mixing, sm in the framework of quasi-chemical approximation (qca) for regular alloy [16,17]. in compound formation model (cfm) for a metallic liquid a-b alloy, appropriate privileged groups or chemical complexes νµba ( νµ, small integers) are assumed to exist in the melt and the energy of an ab, aa or bb bound depend on whether that bond is part of the complex or not. when no complexes are formed, the cfm model reduces to the qca for regular alloys [16-18]. application of the approximation to a segregating alloy in particular makes it koirala et al./bibechana 12 (2015) 135-144: p. 137 possible to reproduce closely the observed thermodynamic properties. over time a great deal of attempt has been devoted on this basis of this approximation to the investigation the mixing properties of liquid alloys [19-23]. viscosity of molten metals and alloys, on the other hand is a very important atomic transport property in metallurgical science which reflects their liquid structure [24]. the viscosity of molten metals and alloys is a structurally sensitive dynamic property which indeed depends on the interactions between cohesive energies of the components giving the cohesive energy of the solution by the arrangement of the solute atoms in the solution. the cohesive interactions in condensed phase, whether liquid or solid, can be approximated by the bonding that occurs between atoms and their nearest neighbors. in order to investigate the dynamic behaviour in the liquid alloys several theoretical methods have been suggested [24-29]. in the current study, we intend to study the viscosity of the liquid na-k alloy at 384k against concentration by correlating it with the enthalpy of mixing through available theoretical equations, moelwyn-hughes equation [29] and the kaptay equation [29]. due to scanty of viscosity data of na-k alloy at hand, we have performed a comparative study in reference to the ideal viscous behaviour by using enthalpy of mixing, deduced theoretically from qca and those available in the literature. the layout of this paper is as follows. in section 2, we present the basic theoretical expressions for thermodynamic functions and viscosity of liquid binary alloys used in this work. section 3 deals with the result and a general discussion of the work. we conclude the paper with a summary of the work in section 4. 2. formalism we present the theoretical expressions that we have used in the present analysis for determining the enthalpy of mixing and the viscosity of a metallic binary separately in the following sub-sections. 2.1. qca for enthalpy of mixing the qca, which is an approximation of compound formation model, in essence, is appropriate for studying liquid alloys having phase separating tendencies. according to this approximation, a binary liquid alloy is assumed to consist of n1 atoms of component a and n2 atoms of component b situated at equivalent sites. there is short ranged atomic interaction between the nearest neighbours that forms a polyatomic matrix leading to the formation of like atom clusters or self-associates of the type ia and jb, where i and j are the number of atoms in the clusters of elements a and b respectively. under the assumption of qca, working expressions for thermodynamic and microscopic functions of binary liquid alloys have been derived [20]. the enthalpy of mixing, hm of a liquid binary mixture at a given temperature, t can be calculated theoretically from the knowledge of two important thermodynamic quantities namely the free energy of mixing, gm and the entropy of mixing, sm using the standard thermodynamic relation: mmm stgh += (1) for one mole of a binary liquid alloy a-b consisting of n1 ( xn= ) atoms of a-component and n2 ( n)x1( −= ) atoms of b-component in the bulk phase, n being the total number of atoms and x the mole fraction of a-component, an expression for the free energy of mixing, gm of a binary liquid alloy at temperature t in qca can be obtained as [20]: koirala et al./bibechana 12 (2015) 135-144: p. 138 w )x1(x )x1(x )x1(x )x1( ln)x1( )x1(x x lnxrtgm −γ+ −γ +      −γ+ −γ −+ −γ+ = (2) where, kb is boltzmann constant; w is ordering energy parameter and i/j=γ is the ratio of the self associates. in order to estimate qca fitting parameters w and i/j=γ , the value of the energy parameter w, we also recall the following standard thermodynamic relations for the chemical activities, ai [20]: rt w )x1(x )x1( )x1(x 1 )x1(x x ln1aln 2 a       −γ+ −γ + −γ+ − −γ+ += (3a) rt w )x1(x x )x1(x x)1( )x1(x )x1( lnaln 2 b       −γ+ γ+ −γ+ γ− + −γ+ −γ = (3b) the entropy of mixing (sm) of mixture, defined through the standard thermodynamic relation p m m t g s       ∂ ∂ −= (4) is obtained in qca for regular alloy as follows: t w )x1(x )x1(x )x1(x )x1( ln)x1( )x1(x x lnxrsm ∂ ∂ −γ+ −γ +      −γ+ −γ −+ −γ+ −= (5) 2.2. viscosity 2.2.1. the moelwyn-hughes equation the viscous flow of a liquid mixture depends on the cohesive interactions in liquid phase. cohesive interactions arise due to the bonding that develops between atoms/or molecules and their nearest neighbours and they give rise to the enthalpic effect. in a liquid metal, the variations in the cohesive energies may result from coupling of geometric and electronic shell effects [30]. the moelwynhughes equation for viscosity of liquid mixture has been formulated to incorporate the cohesion energy in terms of enthalpic effect in order to account for viscous flow in a liquid binary alloy and at a temperature t, it is given as [29]: ] rt h )x2x21[(])x1(x[ m2 21 +−η−+η=η (6) where η and kη represent respectively the viscosity of the liquid alloy a-b and of pure component metal k )2,1k( = ; x the mole fraction of component a, hm the enthalpy of mixing of the alloy and r is the universal gas constant. for most metals the variation of viscosity, kη with temperature t may be expressed as [31]: )rt/e(expokk η=η (7) where, okη and e are constants for pure metal, in units of viscosity and energy per mole respectively. koirala et al./bibechana 12 (2015) 135-144: p. 139 2.2.2. the kaptay equation in an attempt to give better insight into the viscous nature of a binary liquid alloy, kaptay unified various thermodynamic models into a single equation. the unified equation, termed as kaptay equation for viscosity, is in a qualitative conformity with the majority of the thermodynamic models [29]. it takes into account of the theoretical relationship between the cohesion energy of the alloy and the activation energy of viscous flow, stating that in alloys with stronger cohesion energy the viscosity will increase, and not decrease. this equation reads as:         α−−+ +−+ =η tr h.g)x1(gx exp vv)x1(xv nh m * 2 * 1 e 21 a (8) where * kg is the gibbs energy of activation of the viscous flow in pure component metal k given by: ) nh v (lnrtg a kk* k η = ; ( 2,1k = ) (9) here, hm is enthalpy of mixing of the alloy; na is avogadro number; vk represents the molar volume of the component k; e v is the excess molar volume upon alloy formation which can be neglected for simplicity [29]; kη is the viscosity of the component at temperature t as given by eq. (7) and α is a constant whose value is taken to be )015.0155.0( ± [29]. 3. results and discussion 3.1. enthalpy of mixing the formation of a metallic solution depends on the inter-atomic interactions that can take place between atoms of the pure components and also between the two different components. the interactions of atoms in solutions give rise to two thermodynamic effects such as enthalpic and entropic. the fundamentals of mixing of liquid metals forming binary alloys are generally discussed in terms of the enthalpic and entropic constructs as they are required to understand the nature and strength of the atomic bonding and the phase stability in the alloy. to determine these functions in the framework of qca for regular alloy, the fitting parameters namely, the interaction energy parameter, w and the ratio of self-associates γ are needed. in the present work the parameters w and γ for the na-k alloy at 384k were estimated over the whole range of concentration from the method of iterative procedure by fitting them into the available literature data of free energy of mixing (gm) and chemical activities (ai) [15] respectively in eqs. (2) and (3a & 3b). we have obtained the best fit values of these parameters for the alloy to be rt106.1w += and 795.0=γ . the positive sign of w is an indication of like atom pairing (homo-coordination) in the liquid na-k alloy. the estimated value of γ implies that the mixing of the molten metals na and k is energetically favoured forming like atom clusters of na atoms and k atoms in the ratio of about 4:5 so that the short range interaction between the nearest atoms results in the equilibrium properties of na-k liquid alloy at the temperature of investigation. chemical activity on the other hand is a measure of the tendency of the component to leave the solution. the deviations in the nature of a solution from ideal behaviour can be incorporated into activity. the calculated values of the free energy of mixing (fig.1) and the chemical activities have found to agree quite satisfactorily with the available literature data [15] over the whole range of concentration. koirala et al./bibechana 12 (2015) 135-144: p. 140 entropy of mixing is a measure of disorderness in the local arrangement of atoms in the system. basically the term entropy represents the sharing of energy between the atoms in the neighbourhood. for the liquid na-k alloy at 384k, we have computed the entropy of mixing, sm from eq. (5) by estimating the temperature dependence of the energy parameter to be 416.0 t w += ∂ ∂ jmol -1 k -1 . a reasonably good agreement is noticed in the computed values of the entropy of mixing and the corresponding experimental values [15] (fig. 2). at a given temperature, the atoms in a liquid alloy are assumed to interact only with the limited nearest neighbours (short range interaction). if the temperature of the alloy is increased, the bonding interaction between the atoms is found to increase. the positive value of the temperature derivative of order energy for the na-k alloy indicates that the interaction strengthens by about 0.42 jmol -1 k -1 with the increase in temperature of the alloy. using the calculated values of the free energy of mixing and the entropy of mixing, we have computed the heat of mixing, hm throughout the whole concentration range from eq. (6). the values of hm predicted from quasi-chemical approximation agree quite satisfactorily with the available experimental data [15], with a small departure (fig. 3). this disparity may be due to the role of the entropic effect as the behaviour of entropy is often complicated for many of the binary liquid alloys. as segregating systems are generally endowed with positive heat of mixing, the small positive values of hm for na-k liquid alloy also suggest that the alloy belongs to a weakly segregating system. 3.2. viscosity the local atomic ordering in a liquid a-b alloy is non-periodic, unlike crystals, as the solute atoms in the homogeneous solution can arrange in many ways by diffusion which contrasts with the pure metals a and b, in each of which the atoms can arrange only in a particular way. in the state of disorder in the atomic arrangements, some sort of short range atomic bonding (metallic, ionic, or covalent, or even secondary bonds, such as hydrogen bonding or vander waals forces as in the case of molecular crystals or liquids) can be assumed to exist between the nearest neighbours to present cohesive energy of solution. the cohesive energy of solution depends on the size difference of the atomic species and entirely to the size-dependent variations in the latent heats [30]. the cohesive energy may be thought to be responsible for the enthalpic effect and the viscous nature of the liquid alloys. viscosity of liquid metals/alloys is one of the technologically important transport properties, needed to develop and optimize metallurgical technologies. the analysis of the viscosity gives some insight into the alloying behaviour in the liquid alloys. in order to study the viscous property of liquid na-k alloy, we have computed it as function of concentration from the m-h equation, eqs. (6) and the kaptay equation, eq. (8) separately using the viscosities of the component metals at the temperature of investigation, calculated from eq. (9) and the heat of mixing, hm of the alloy, calculated from the quasi-chemical approximation. here the values of the constants k0η and e for the metals na and k were taken from the reference [31]. due to unavailability of the experimental data of viscosity for the na-k alloy at 384k, we could not compare our theoretical result. alternatively, as a reference for comparison we have computed the viscosity of the alloy at all concentrations from the same equations, eqs. (6) and (8) but using the experimental data for the enthalpy of mixing [15]. calculations done from m-h equation shows that the viscosity of na-k alloy first increases with addition of the na atoms up to about concentration 1.0x = and then decreases slowly up to the concentration 4.0x = , and again increases rapidly for the rest of the concentration (fig. 4). the kaptay equation first shows a small decrease in viscosity and then a rapid increase. in both of these cases the viscosity calculated from experimental value of hm and that from theoretical value of hm are found to be almost matching (fig. 4). koirala et al./bi in our calculation, the value of v e mentioned that the excess molar volume can be neglected for simplicity in the calculation of viscosity [29]. this can be done as this term has comparison to the mean molar volume of the metallic solution, determining the viscosity. the two sets of the results computed using the theoretical values of h satisfactorily comparable to the calculations based on experimental values of h the ideal values 21id )x1(x η−+η=η fig. 1 fig. 3 fig. 1: free energy of mixing (gm) solid curve; experiment – circles. fig. 2: entropy of mixing (sm) of liquid na curve ; experiment – circles. fig. 3: enthalpy of mixing (hm) of liquid na solid curve; experiment – circles. fig. 4: viscosity (η) of liquid na-k alloy versus concentration (x) at 384k: (i) m with theoretical hm – solid line; (b) with experimental h with theoretical hm – broken line; (b) with experimental h koirala et al./bibechana 12 (2015) 135-144: p. 141 e was taken as zero, due to lack of experimental data. it has been mentioned that the excess molar volume can be neglected for simplicity in the calculation of viscosity [29]. this can be done as this term has too small contribution )mol/m10( 37−≈ , often not significant, in comparison to the mean molar volume of the metallic solution, v)x1(xv( 21 ≈−+ determining the viscosity. the two sets of the results computed using the theoretical values of h satisfactorily comparable to the calculations based on experimental values of hm with deviation from (fig. 4). fig. 2 fig. 4 ) of liquid na-k alloy versus concentration (x) at 384k: theory ) of liquid na-k alloy versus concentration (x) at 384k: theory ) of liquid na-k alloy versus concentration (x) at 384k: theory k alloy versus concentration (x) at 384k: (i) m-h equation: (a) solid line; (b) with experimental hm – solid circles (ii) kaptay equation: (a) broken line; (b) with experimental hm – crosses. was taken as zero, due to lack of experimental data. it has been mentioned that the excess molar volume can be neglected for simplicity in the calculation of viscosity , often not significant, in )mol/m10 35−≈ in determining the viscosity. the two sets of the results computed using the theoretical values of hm are with deviation from k alloy versus concentration (x) at 384k: theory – k alloy versus concentration (x) at 384k: theory – solid k alloy versus concentration (x) at 384k: theory – h equation: (a) (ii) kaptay equation: (a) koirala et al./bibechana 12 (2015) 135-144: p. 142 5. conclusion calculations of the enthalpy of mixing and the viscosity in liquid na-k alloy are presented. our calculations based on moelwyn-hughes equation and kaptay equation predict that liquid na-k alloy at 384k is non-ideal with respect to the viscosity. there is negative deviation of viscosity from ideal behaviour. acknowledgements one of the author, r.p. koirala, is grateful to retired professor dr. l.n. jha and prof. dr. pradeep raj pradhan (post-graduate department of physics, m.m.a.m. campus, t.u., biratnagar, nepal) for fruitful suggestions and inspiring discussions. references [1] c. b. jackson, r. c. werner, advances in chemistry, 19 (1957) 169–173. http://dx.doi.org/10.1021/ba-1957-0019.ch018 [2] strem chemical, "msds" 2012. 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s. lamichhane et al. / bibechana 13 (2016) 94-99: rcost p. 94 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal structural and electronic properties of perovskite hydrides acah3 (a=cs and rb) s. lamichhane1, b. aryal1, g. c. kaphle1,2, 3, n. p. adhikari1* 1central department of physics, tribhuvan university, kathmandu, nepal 2tri-chandra multiple campus, ghantaghar, kathmandu, nepal 3condensed matter physics research center, butwal, rupandehi, nepal *e-mail: npadhikari@tucdp.edu.np article history: received 31 july, 2015; accepted 20 september, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13437 abstract we have performed structural properties, electronic properties, charge density and potential distribution of cscah3 and rbcah3 using tb-lmto-asa approach under local density approximation. our findings show that both cscah3 and rbcah3 are non-magnetic and then insulators with estimated direct band gaps (m-m) of 3.15 ev and 3.17 ev respectively. our estimated values of band gap suggest to both materials as better candidate for the high frequency ultra-violet devices. furthermore, role of corner atoms in perovskite hydrides are also presented in this study. present calculations agree well with the previous work. ©rcost: all rights reserved. keywords: projected density of states; perovskite; charge density and tb-lmto-asa. 1. introduction binary alloys of transition and post-transition elements, and also graphene related work have been studied with high effort by many researchers [1-6] but have no band gap. however, various potential applications in optics need significant band gap. the perovskite structure of ternary chlorides is applicable in optics due to their wide band gap [7, 8]. perovskite compounds and its derivatives are the most popular field owing to their diverse physical properties while going to binary alloy to ternary alloy to perovskite material. besides this, anomalous dielectric properties of perovskite and phase transition with increasing temperature have made fundamental interest in physics [9-11]. perovskite hydride compounds belong to perovskite family, symbolized as abh3 (a and b represent lighter metals) are well characterized with their optical properties. perovskite hydrides have become a source of attraction to experimentalists due to presence of lightweight elements, low production cost and s. lamichhane et al. / bibechana 13 (2016) 94-99: rcost p. 95 (online publication: dec., 2015) wide range of applications in the industrial area. alkali and alkaline earth-based complex hydrides are expected to have application for the hydrogen gas storage at certain temperature and pressure [12, 13]. the complexity in structural arrangement of perovskite hydrides and difficulties in establishing proper hydrogen position by x-ray diffraction method in previous attempt [14] motivated us to enter in this burning area of research. as increase in ca-h distance, narrower the density of states (dos) on moving from licah3 to cscah3, predicted in previous work [15] is insufficient to address the factors for dos variation and also the compound nacah3 has shown absurd behaviour than others in regards to m-h and ca-h distance. hence, in the present work efforts have been taken to study the structural, electronic and charge distribution to explore the origin of band gap, contribution of orbitals and role of potentials to bands separation. moreover, the crystal structure, shape, size, and surface composition of materials plays vital role to control the hydrogen sorption properties for energy storage applications. for the efficient energy carrier, hydrogen should be absorbed and desorbed in materials easily in sufficient quantities in cheaper price. the complex compound based on alkaliand alkalineearth hydrides are expected to have potential candidates for storing hydrogen at moderate temperatures and pressures [16-17]. this is another motivation of present work to study the electronic behavior of such materials. the paper is organized as follows: in section ii, the computational details of the present study are included. results and discussion are presented in section iii whereas section iv provides the conclusions of the present study and finally references are listed at the end of the paper. 2. computational details the unit cell of the perovskites hydrides cscah3 and rbcah3 crystallize in to the cubic structure with space group pm-3m. the atomic positions in the elementary cell are at cs(0.0,0.0,0.0), rb(0.0,0.0,0.0), ca (0.5,0.5,0.5) and three hydrogen atoms are at three different positions as h1(0.5,0.5,0.0) , h2(0.5,0.0,0.5) and h3(0.0,0.5,0.5) [8]. with reference to experimental lattice parameter of 4.609 å for cscah3 [18] and 4.547 å for rbcah3 [19] unit cell structures thus obtained with the help of xcrysden visualization are shown in figures 1(a) and (b). fig. 1: (a) unit cell of cscah3 and (b) unit cell of rbcah3. s. lamichhane et al. / bibechana 13 (2016) 94-99: rcost p. 96 (online publication: dec., 2015) all the calculations are done based on the density functional theory implemented with tb-lmto-asa code to carry out comprehensive analysis of structures along with electronic and magnetic properties. the standard local density approximation (lda) is used to address exchange correlation potential. the concept of wigner-seitz spheres for each atom in the unit cell is taken into account to determine the potential of the crystal [20]. we have only included the energetically higher-lying valence states in the self-consistent calculations of the effective crystal potential [21] according to the norms of the tblmto-asa approach. the core states are treated fully relativistically while the semi-core and valence states as treated semi-relativistically. all the calculations were iterated to self-consistency along with accuracy of 10-6 rydberg. 3. results and discussion the new findings from the calculations of band structures, dos, charge density and potential distributions are described as follows. a. band structures the calculated energy bands of perovskites cscah3 and rbcah3 along the high symmetry lines in the brillouin zone are shown in fig (2). fig. 2: band structures of cscah3 (left) and rbcah3 (right). the horizontal dotted line in the above figures represents the fermi level. we have found 10 different energy bands in both cscah3 and rbcah3. zero energy is chosen to coincide with the cbm and vbm both occur at same m point results the direct band gap in both of these perovskite hydrides which indicates that both cscah3 and rbcah3 bear the non-metallic behaviour. our estimated band gaps of cscah3 and rbcah3 are 3.15 ev and 3.17 ev which indicates that cscah3 and rbcah3 are insulators. our results of band gap well agree with previous generalized-gradient approximation based theoretical calculations [8]. resulting band gap of these perovskites meet the requirement for the applications in high frequency ultra-violet device [22]. s. lamichhane et al. / bibechana 13 (2016) 94-99: rcost p. 97 (online publication: dec., 2015) b. density of states to observe the density of states, we have taken same value of the lattice parameter as in band structures calculations. the total dos and pdos of cscah3 and rbcah3 are shown below. the total density of states are categorized into four different parts and the contributions of different states can easily be seen from the pdos analysis. fig. 3: total dos and pdos of cscah3(left) and rbcah3(right). the fermi energy line is in the valence band which supports the non-metallic behaviour. in both cscah3 and rbcah3 ca-p and h-s states are located in the vicinity of the fermi level at the valence band. in cscah3 ca-s and −p states are well-separated where as in rbcah3 ca-s and −p states are not wellseparated. the symmetric nature of spin up and spin down dos indicate the non-magnetic behavior of cscah3 and rbcah3. the contribution to the valance band is maximum by s states of hydrogen and less contributions is seen from ca and cs. the contribution of ca and h atoms to the dos is major in the valence bands while cs/s, cs/p are responsible for that in the conduction band. further, one valance electron of cs (or rb) in cscah3 ( or rbcah3) fill the partially occupied s-orbital of one hydrogen and remaining two partially filled orbitals of hydrogen is filled by two valence electrons of calcium. since the valence electrons are completely filled, cscah3 and rbcah3 both acts as an insulating materials. c. charge density and potential distribution the charge density distribution and chemical bonding behaviour of mcah3 is important to check the stability of these materials for hydrogen storage. the charge density plot of cscah3 and rbcah3 obtained by using the same lattice parameters as in dos and band structures calculations are shown in figure (4). s. lamichhane et al. / bibechana 13 (2016) 94-99: rcost p. 98 (online publication: dec., 2015) fig. 4: the charge density distribution of cscah3 and rbcah3. from figure 4, we have found that there are five peaks along the corners and faces which shows the maximum distribution of the charges at the corners and faces. about 10-40 % of total charge occur along the corners and faces which has been shown by a high peaks lines while the distribution of the charges is negligible at other interstitial sites. this is the site at which adsorption and desorption of hydrogen takes place, indicating that such materials can be used for hydrogen storage purposes. the potential distribution plot of cscah3 and rbcah3 are shown in figure (5) . fig. 5: potential distribution in cscah3 (left) and rbcah3 (right). from figure 5, we can find that the potential is maximum in the vicinity of core whereas at the interstitial region the potential is found to be constant (flat). our results agree well with the muffin-tin potential in which the potential is maximum near the core electrons and almost flat in the interstitial space. this kind s. lamichhane et al. / bibechana 13 (2016) 94-99: rcost p. 99 (online publication: dec., 2015) of potential distribution fully supports the maximum distribution of charge near the corner of crystal structure. 4. conclusions in this present work, we studied the band structures, density of states, charge density and potential distribution of perovskite hydrides cscah3 and rbcah3 by using tb-lmto-asa. taking the experimental lattice parameters, we calculated the electronic and magnetic properties of cscah3 and rbcah3. the calculated dos shows that cscah3 and rbcah3 are non-magnetic. the direct band gap of 3.15 ev found in cscah3 and 3.17 ev in rbcah3 meet the requirement for the application in high frequency ultra-violet device. the charge density plot of cscah3 and rbcah3 indicate that the corner atom contributes mainly to increase charge density which also support from the potential distribution curve. from potential distribution of cscah3 and rbcah3, we found that potential is maximum at core whereas flat at interstitial region. this may be the vital site to store the hydrogen and hence system acts as hydrogen storage materials. finally we can conclude that tb-lmto-asa method can be used as a convenient method for studying the band structures and density of states of different solids. our results may be useful to study the other various types of elemental solids and perovskites in future. acknowledgments we are grateful to ictp/oea net-56 program of trieste, italy for the partial support. references [1] b. i. min, t. oguchi, h. j. f. jawsen, a. j. freeman, phy. rev. b, 12 (2003) 1091. 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[22] m. maqbool, b. amin, i. ahmad, j. opt. soc. am., b, 26 (2009) 2181. microsoft word ahmad _59-69_.docx r c o s t n publisher: research council of science and technology, biratnagar, nepal p.59 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana on some nonlinear fractional pdes in physics jamshad ahmad * , syed tauseef mohyud-din department of mathematics, faculty of sciences, hitec university taxila, pakistan * email: jamshadahmadm@gmail.com accepted for publication: december 12, 2014 abstract in this paper, we applied relatively new fractional complex transform (fct) to convert the given fractional partial differential equations (fpdes) into corresponding partial differential equations (pdes) and variational iteration method (vim) is to find approximate solution of timefractional fornberg-whitham and time-fractional wu-zhang equations. the results so obtained are re-stated by making use of inverse transformation which yields it in terms of original variables. it is observed that the proposed algorithm is highly efficient and appropriate for fractional pdes arising in mathematical physics and hence can be extended to other problems of diversified nonlinear nature. numerical results coupled with graphical representations explicitly reveal the complete reliability and efficiency of the proposed algorithm. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11687 © 2014 rcost: all rights reserved. keywords: jumarie’s fractional derivatve; fractional fornberg-whitham equation; fractional wuzhang equations; variational iteration method; fractional complex transform. . 1. introduction the nonlinear partial differential equations (npdes) are encountered in various disciplines, such as physics, mechanics, chemistry, biology, mathematics and engineering. nonlinear partial differential equations [1-29] are of extreme importance. recently, scientists have observed that number of real time problems is modeled by fractional nonlinear differential equations [4-5,7,10,19,21-25] which are very hard to tackle. transform is an important method to solve mathematical problems. recently the fractional complex transform [20-23] was suggested to convert fractional order differential equations with modified riemann-liouville derivatives [24-25] into integer order differential equations, and the resultant equations can be solved by different methods. this paper is devoted to the study of time-fractional fornberg-whitham equation, modified time fractional fornberg-whitham equation [6-12], time-fractional wu-zhang equation [24, 25]. the fornberg–whitham equation was first proposed for studying the qualitative behavior of wave breaking. the time fractional fornberg–whitham equation can be written as ���� − ���� + �� = ����� − ��� + 3����� , � > 0 , 0 < � ≤ 1, (1) subject to the initial conditions ahmad and mohyud-din/ bibechana 12 (2015) 59-69: p. 60 ���, 0� = ����, and modifying the nonlinear term ��� in eq. (1) by ����, he et al. proposed in [12] the modified time fractional fornberg-whitham equation ���� − ���� + �� = ����� − ���� + 3����� , � > 0 , 0 < � ≤ 1, (2) and time-fractional wu-zhang equation ���� + ��� + ��� + �� = 0 , ����+��� + ��� + �� = 0, 0 < � ≤ 1 (3) ���� + ����� + ����� + �� ����� + ���� + ���� + ����� = 0 with initial conditions ���, �, 0� = ����, ��, ���, �, 0� = ����, ��, ���, �, 0� = ����, ��. where w is the elevation of the water, u is the surface velocity of water along x -direction, and v is the surface velocity of water along y-direction. wu and zhang derived three sets of model equations for modeling nonlinear and dispersive long gravity waves travelling in two horizontal directions on shallow waters of uniform depth. eq. (3) is one of these equations, wu-zhang equation (which describes (2+1)-dimensional dispersive long wave). the fractional derivatives are considered in the jumarie sense. the basic motivation of this paper is the extension of a very reliable and efficient technique namely variational iteration method using complex transform (vimct) to find approximate solutions of time-fractional fornberg-whitham and system of time-fractional wu-zhang equations. the convergence of the proposed variational iteration method using fractional derivative is addressed in [28-29]. it is observed that the proposed algorithms is fully synchronized with the complexity of fractional differential equations, numerical results coupled with graphical representations explicitly reveal the complete reliability and efficiency of the proposed algorithm. 2. definitions definition 2.1 jumarie’s fractional derivative [24-25] is a modified riemann-liouville derivative defied as ������� = &'( ') � γ�*α� + �x − t�*α*��f�t� − f�0��dt, α < 0 /0 , � γ��*α� 11/ + �x − t�*α�f�t� − f�0��dt, 0 < α < 1,/0�f α*2�x��2 n ≤ α < 4 + 1, 4 ≥ 1. 6 (4) where �: 8 → 8, � → ���� denotes a continous (but not necessarily differentiable) function. some useful formulas and results of jumarie’s modified riemann-liouville derivatives are as follows: ���: = 0 , � > 0, : = :;4<�=4�. (5) ���>: ����? = : �������, � > 0, : = :;<4�=4�. (6) ahmad and mohyud-din/ bibechana 12 (2015) 59-69: p. 61 ��� �@ = γ��a���bcd γ��a@*�� , e > � > 0. (7) ���>����f���? = >�������? f��� + ���� >���f���?. (8) ���� ������ = ��̀���. �����. (9) 3. variational iteration method (vim) using complex transform the nonlinear differential equations [13-16] can be expressed in the operator form as �������, ��� + 8����, ��� + h����, ��� = 0. (10) where ��� is the time-fractional jumarie’s fractional derivative , h���is the nonlinear operator and 8��� is some linear operator. the complex transform requires i = �� using the basic properties of the fractional derivative [20], we can convert the fractional derivative into classical derivative. jdkj�d = jkjl jld j�d = σ jkjl, (11) where σ, is defined [20], eq. (10) becomes σ �m�u��, ��� + 8�u��, ��� + h�u��, ��� = 0, (12) where �m = jkjm nm����, ���� + 8����, ���� + h����, ����=0, (13) where nm is the linear differential operator. according to variational iteration method, we construct a correction functional as follows: �oa���, �� = �o��, �� + + p��, q�>nr�o�x, q��0 + 8�so�x, q� + h�so��, ��?tq, (14) where p is the general lagrangian multiplier which can be indentified optimally by the variational theory ,the subscript 4 denotes the nth order approximation, and �so is considered as a restricted variation, i.e. u�so = 0. its stationary conditions can be obtained as follows: p/�x, q� = 0, 1 + p�x, q� = 0. the lagrange multiplier, therefore, can be obtained as p = −1, and the following variational iteration formula can be obtained as �oa���, �� = �o��, �� − + nr�o��, q��0 + 8��o� + h��o�tq. (15) considering �0��, 0� = ���, 0�, we can easily find the components of the iterative formula defined in (15). applying backward substitution to the computed components i = �� , we get ahmad and mohyud-din/ bibechana 12 (2015) 59-69: p. 62 ���, �� = limo→∞ �o��, ��. (16) 4. numerical applications example 4.1 consider the following timefractional fornberg-whitham equation defined in eq. (1) ���� − ���� + �� = ����� − ��� + 3����� , � > 0 , 0 < � ≤ 1, (17) subject to the initial conditions ���, 0� = z[\. applying procedure defined in (11-15), u0 = e\̂, u��x, s� = − ��σ e\̂�−2 + s�, u��x, s� = �aσ e\̂�8 − 5s + s��, u��x, s� = − �deσ e\̂�−96 + 63s − 18s� + 2s��, ⋮. applying backward substitution u��x, t� = − ��σ e\̂�−2 + tα�, u��x, t� = �aσ e\̂�8 − 5tα + t�α�, u��x, t� = − �deσ e\̂�−96 + 63tα − 18t�α + 2t�α�, (18) ⋮. and so on. the exact solution of the timefractional fornberg-whitham equation is obtained [6]. u�x, t� = e�\̂*\jk �. (19) graphical representation of exact solution (19) and the approximate solutions (18) for ∝= 0.3,0.6,1. (a) α = 0.3 (b) α = 0.6 ahmad and mohyud-din/ bibechana 12 (2015) 59-69: p. 63 (c) α = 1 (d) exact solution example 4.2 consider the following time-fractional modified fornberg-whitham equation defined in eq. (2) ���� − ���� + �� = ����� − ���� + 3����� , � > 0 , 0 < � ≤ 1, (20) subject to the initial conditions ���, 0� = = sech��:��, where = = �q �√15 − 5�, : = ��0 �s10�5 − √15��. applying procedure defined in (11-15) �0 = = sech��:��, u��x, s� = aσ coshw�cx� >coshx�cx�2c sinh�cx� coshq�cx�s + 2a�c sinh�cx� s32c�a sinh�cx� cosh��cx� + 60ac� sinh�cx� s, ⋮, and so on. applying backward substitution u0 = a sech 2�cx�, u1�x, t� = a σcosh 7�cx� >cosh 5�cx� 2c sinh�cx� cosh 4�cx�tα + 2a2c sinh�cx� tα − 32c3a sinh�cx� cosh 2�cx� + 60ac3 sinh�cx� tα, (21) ⋮, and so on. the exact solution of the timefractional modified fornberg-whitham equation is obtained [6]. u�x, t� = asech 2�c yx − �5 − z15�t�{ . (22) graphical representation of exact solution (22) and the approximate solutions (21) for ∝= 0.3,0.6,1. ahmad and mohyud-din/ bibechana 12 (2015) 59-69: p. 64 (a) � = 0.3 (b) � = 0.6 (c) � = 1 (d) exact solution example 4.3 consider timefractional wu-zhang equation, dt αu + uux + vuy + wx = 0, dt αv+uvx + vvy + wy = 0, (23) dt αw + �uw�x + �vw�y + 1 3 �uxxx + uxyy + vxxy + vyyy� = 0, with initial conditions u�x, y, 0� = − k3ak2b0 k1 + 2√3 3 k1 tanh�k1x + k2y�, v�x, y, 0� = b0 + 2√3 3 k2 tanh�k1x + k2y�, w�x, y, 0� = 2 3 �k1 2 + k2 2� sech 2�k1x + k2y�, where |0, }�, }� and }� are arbitrary constants. applying the procedure defined above (10-15), we get u0�x, y, s� = − ~ka~\��~� + �√�� k� tanh�k�x + k�y�, v0�x, y, s� = b0 + �√�� k� tanh�k�x + k�y�, u0�x, y, s� = �� �k�� + k��� sech��k�x + k�y�, ahmad and mohyud-din/ bibechana 12 (2015) 59-69: p. 65 u1�x, y, s� = 1 3 σcosh 2�k1xak2y� �−3k3 cosh 2�k1x + k2y�2 − 3k2 c cosh 2�k1x + k2y�2 + 2√3k1 2 sinh�k1x + k2y� cosh�k1x + k2y� + 2√3k1 2 sk3�, v1�x, y, s� = 1 3σ cosh 2�k1xak2y� �3c cosh 2�k1x + k2y�2 + 2√3 k2sinh�k1x + k2y� cosh�k1x + k2y� + 2√3k2sk3�, w1�x, y, s� = − 2 3σ cosh 3�k1xak2y� �2 sinh�k1x + k2y� sk3k1 2 + 2 sinh�k1x + k2y� sk3k2 2 − k1 2 cosh�k1x + k2y��, ⋮, and so on. applying backward transformation u1�x, y, t� = 1 3σ cosh 2�k1xak2y� �−3k3 cosh 2�k1x + k2y�2 − 3k2 c cosh 2�k1x + k2y�2 + 2√3k1 2 sinh�k1x + k2y� cosh�k1x + k2y� + 2√3k1 2 tαk3�, (24) v1�x, y, t� = 1 3σ cosh 2�k1xak2y� �3c cosh 2�k1x + k2y�2 + 2√3 k2sinh�k1x + k2y� cosh�k1x + k2y� + 2√3k2tαk3�, (25) w��x, y, t� = − ��� ����k�~�/a~\�� �2 sinh�k�x + k�y� t�k�k�� + 2 sinh�k�x + k�y� t�k�k�� − k�� cosh�k�x + k�y��, (26) ⋮, and so on. finally, we have u�x, y, t� = limn→∞ un�x, y, t�, v�x, y, t� = limn→∞ vn�x, y, t�, w�x, y, t� = limn→∞ wn�x, y, t�. the exact solution of time-fractional wu-zhang equations [26], is given by u�x, y, t� = − k3ak2b0 k1 + 2√3 3 k1 tanh�k1x + k2y + k3t�. (27) v�x, y, t� = b0 + 2√3 3 k2 tanh�k1x + k2y + k3t�. (28) w�x, y, t� = 2 3 �k1 2 + k2 2� sech 2�k1x + k2y + k3t�. (29) graphical representation of exact solution (27) and the approximate solution (24) for ∝= 0.3,0.6,1. ahmad and mohyud-din/ bibechana 12 (2015) 59-69: p. 66 (a) α = 0.3 (b) α = 0.6 (c) α = 1 (d) exact solution graphical representation of the exact solution (28) and the approximate solution (25) for ∝= 0.3,0.6,1. (a) α = 0.3 (b) α = 0.6 (c) α = 1 (d) exact solution ahmad and mohyud-din/ bibechana 12 (2015) 59-69: p. 67 graphical representation of exact solution (29) and the approximate solution (26) for ∝= 0.3,0.6,1. (a) α = 0.3 (b) α = 0.6 (c) α = 1 (d) exact solution 5. conclusions applied fractional complex transform (fct) proved very effective to convert the given partial differential equations (pdes) into corresponding partial differential equations (pdes) and the same is true for its subsequent effect in variational iteration method (vim) which was implemented on the transformed pdes. computational work fully re-confirms the reliability and efficacy of the proposed algorithm and hence it may be concluded that presented scheme may be applied to a wide range of complex physical problems. references [1] g. b. whitham, variational methods and applications to water wave. proc. r. soc. lond. ser. a, 229 (1967) 6-25. [2] j. zhou and l. tian, j. math. anal. appl,. 346 (2008) 255–261. http://dx.doi.org/10.1016/j.jmaa.2008.05.055 [3] i. podlubny, fractional differential equations. new york: academic press, (1999). 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[29] b. ghazanfari and a. sepahvandzadeh, solving fractional bratu-type equations by modified variational iteration method, selcuk journal of applied mathematics, article in press ( 2014). 17-24 saroj nepal r c o s t n s. nepal / bibechana 11(1) (2014) 17-24: (online publication: march, 2014) p.17 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana relativity in cosmologically preferred frame and the uhecr paradox saroj nepal post graduate department of physics m. m. a. m. campus, biratnagar, nepal email: saroj.paradox@gmail.com accepted for publication: february 02, 2014 abstract the greisen-zatsepin-kuzmin (gzk) cutoff (5 × 1019ev) of special relativity in the observed ultra high energy cosmic rays (uhecr) spectrum is one of the most puzzling paradoxes in physics. experimentally a number of cosmic ray events have been detected above this gzk limit which is known as uhecr paradox. we propose a resolution of this paradox through a modification of the relativistic kinematics keeping in mind that it should not lead to predictions different from those of special relativity in the well tested domains. it is shown that theoretical limit in uhecr spectrum can be explained in the framework of lorentz invariance violation (liv) theories which assume the existence of a preferred frame. the present paper proposes that the velocity of the solar system with respect to the rest frame of the universe plays a role in explaining the paradox. © 2014 rcost: all rights reserved. keywords: special relativity (sr); gzk limit; lorentz invariance violation; lorentz transformation; einstein synchrony. 1. introduction the possibility that lorentz invariance can be violated in nature has currently become a subject of interest. people often doubt if the special relativity (sr) is only an approximate symmetry of nature [1, 2]. to give a quantitative measure of lorentz invariance violation (liv), one can build up a test theory where the lagrangian of electrodynamics can be slightly deformed by adding to it a tiny lorentz violating term. one such deformation considered by the authors of ref. [1] (see also [3]) following standard practice causes the speed of light c to differ from the maximum attainable speed c0 (which hereafter, unless stated otherwise, will be assumed to be equal to 1) by a small velocity parameter ε of the theory. the obvious consequence of this consideration is the existence of a preferred inertial frame of reference. it is a common practice and also reasonable to assume this preferred frame to be “the rest frame of the universe” (σ0) with respect to which the cosmic microwave background radiation (cmbr) is isotropic. let us call it the rest frame of the cosmic substratum (rfcs). precision tests for anisotropies in velocity of light due to the motion of the solar system relative to the cmbr frame have set a limit on this ε [1, 4], |1 − c| = | ε | < 3 × 10−22. (1) s. nepal / bibechana 11(1) (2014) 17-24: (online publication: march, 2014) p.18 however it has been argued [1-3] that stronger constraints on ε can be obtained, not from precision tests, but from observations on ultra high energy cosmic rays (uhecr). for example, if c < 1 it has been shown that the mere detection of primary proton energy up to 100 eev set the bound on ε more than one order of magnitude stronger: | ε | < 5 × 10−24. (2) the physical basis for obtaining such a bound is that a particle can be super luminal in vacuum (if c < 1) in which case, a proton being a charged particle will in its passage, quickly lose energy through the so called “vacuum cerenkov radiation” and will therefore fail to be detected with the super luminal speed. the last bound on | ε | is obtained by equating the speed of proton at 100 eev with the speed of light c, then subtracting it from unity, the latter being the limiting speed of sr. the limit on ε thus obtained does not require (unlike the way it is obtained through precision test mentioned before) any assumption regarding the motion of the laboratory frame with respect to σ0. liv is also much discussed in connection with one of the most puzzling paradoxes in physics concerning uhecrs. one quite robust predictions of special relativity is the existence of the so called greisen-zatsepin-kuzmin (gzk) phenomenon, which tells us that cosmic ray protons coming from cosmological distances with energies above certain limiting value (gzk cutoff), should not be observed on earth. the predicted value for this catastrophic cutoff is 5 × 1019 ev . this value corresponds to the threshold energy for photo-pion production by cosmic ray protons interacting with soft cmbr photons which pervade the universe. however some recent experiments have shown that this relativistically calculated threshold energy seems to be too low. indeed recently ground based detectors have detected over about a hundred events near and above the gzk cutoff and a double digit number of events with energies at or above 1020ev. the highest energy cosmic ray so far has been the 3.2×1020ev detected by the fly’s eye air shower detector in utah [5]. however if the sources of uhecrs are really extragalactic (there are ample reasons to believe so[6]) and since the calculation of gzk limit is so robust that even one event at 1020ev “appears surprising” [7]. the arrival of uhecr on earth with energies above the gzk threshold is known as the uhecr paradox [8-10] mentioned in the beginning of this paragraph. there have been exotic proposals in the literature which try to explain the trans gzk cosmic ray events in the framework of liv theories which assume the existence of a preferred frame [2, 9, 11]. let us call them preferred frame theories. as an example, according to one most popular scenarios [12], existence of different maximal speeds for different particle species is assumed and they are also assumed in general to differ from the speed of light in vacuo [see ref.[2] and references therein]. in this way, introduction of small liv has been shown to have effects that increase rapidly with energy in such a manner that ultimately inelastic collisions with cmbr photons become kinematically forbidden [2]. the present paper proposes that the velocity of the solar system with respect to the rest frame of the universe might play a role in explaining the paradox. in an effort to look for new physics, when one considers theories involving liv one still believes that behavior of moving rods and clocks is still governed by the lorentz transformation (lt). however, other laws of physics might not strictly remain covariant under lt. for example one may consider the possibility that causal cone need not coincide with the light cone [13], i.e the speed of light may not be the same as the invariant speed c of lt. however if one is prepared to do away with the principle of relativity, or in other words if one believes in the existence of a preferred inertial frame, there is no point in holding on to the belief that standard rods and clocks of different inertial frames behave strictly according to lt. note that after all lt is a consequence of the relativity principle. hence in search for a new physics one may consider the possibility of a deformed lt (not just a deformed dispersion relation) to relate observations performed by different inertial observers. once such a transformation is guessed, other aspects of kinematics such as expressions for momentum p and energy e of a particle or the dispersion relation can be obtained through s. nepal / bibechana 11(1) (2014) 17-24: (online publication: march, 2014) p.19 a kind of 4-vector formulation (see below). clearly the predictions of the deformed lt will be different from those of the relativity theory. however the difference in the predictions must be undetectable in the domain where special relativity has been tested beyond doubt. in the following we shall look for such a transformation that will be capable to explain the uhecr paradox and at the same time will be able to reproduce the standard relativistic results. we know that einstein obtained his transformations deductively from his relativity and the “constancy of velocity of light” (cvl) postulates. if the relativity postulate is sacrificed what guidelines should one follow in order to guess the transformation equation? the next section will provide an answer to this question. 2. transformation equations although the kinematics of relativity theory was obtained by einstein from a general principle like the relativity of motion and a principle concerning the speed of light, the operative aspects of these postulates used in the derivation can be laid down in more concrete terms. indeed if one consults a standard text book on relativity, one finds that the derivation of lt starts from the assumption of a linear transformation with unknown coefficients which are determined using essentially the following operative inputs: (1) the coordinate clocks in any inertial frame are assumed to be synchronized by light signal following the einstein synchrony or the standard synchrony, according to which the one-way-speed (ows) of light is assumed to be the same as its two-way-speed (tws) in any direction [14-16]. (2) the speed of light is the (i) same and (ii) isotropic with respect to all inertial observers. (3) measuring rods placed perpendicular to its direction of motion do not undergo any contraction or elongation with respect to its rest length. the first of the above is just a synchronization convention but the other two items are the consequences of the relativity principle. a little amplification of this statement in respect of item (2) may be in order. one might think that (2) is equivalent to einstein’s cvl postulate. this is indeed a misconception [17]. the cvl postulate of einstein refers to constancy with respect to change in the velocity of light source. in effect this postulate emphasizes the wave character of light. once wave is launched it is no longer linked to the source. indeed einstein’s second postulate concerning the speed of light in conjunction with the principle of relativity only imply the constancy with respect to the change of the inertial observer as well [17]. in a preferred frame theory where the principle of relativity is expected to be violated, the transformation equations cannot be obtained with item (2) as an input which, as explained, depends on the relativity principle although cvl can be used in the stationary frame. as regards input (1) however there is no difficulty but there is no special advantage in synchronizing coordinate clocks using light signal. one may then ask what if the clocks were synchronized by some other signal say an “acoustic signal” for example. one may consider a substratum which can support such a signal and through which different inertial frames are supposed to move. to effect the synchronization, like the standard synchrony we shall stipulate the ows of the signal along a straight line be equal to its tws along the line in any frame σk. it has been shown elsewhere[14] that if input (2) is withheld, and the coordinate clocks of any inertial frame is synchronized by “acoustic signal”, the transformation equation between a preferred frame σ0 and an arbitrary inertial frame σk can be obtained as, xk = (akx/aky)(1 − u0k 2 /a0 2)−1/2(x0 − u0kt0), (3) tk = (a0/aky)(1 − u0k 2/a0 2)−1/2(t0 − u0kx0/a0 2 ), (4) where (x0,t0) and (xk,tk) refer to space-time coordinates as measured with respect to the stationary (σ0) and moving frame (σk) respectively. the relative velocity of σk with respect to σ0 has been denoted by u0k. as regards other terms, a0 denotes the isotropic “acoustic speed” (two way or one way) in the stationary s. nepal / bibechana 11(1) (2014) 17-24: (online publication: march, 2014) p.20 substratum, whereas akx and aky are the tws’ of the synchronizing signal in σk parallel (along the xdirection) and perpendicular (along the y-direction) to its direction of motion respectively. note that in general akx and aky are expected to be functions of u0k and hence the above equations are only formal and not usable unless some phenomenological assumptions are made regarding these functions. for optical signal synchronization we replace the terms akx, aky and a0 in eqs.(3) and (4) by ckx, cky and c0 respectively where the latter three terms represent the respective speeds of the light signal. in the relativistic world, by input (2), one finds in any σk ckx(u0k) = cky(u0k) = c0, (5) and the above equations (eqs.(3) and (4)) turns out to be lt under optical synchronization. we now ask what if eq.(5) is approximately valid, so that the speed of light is almost and not quite independent of the speed of the reference frame with respect to a “preferred” one. note that the transformation equations (3) and (4) are now most appropriate to deal with such questions. we now wish to use input (2) in these equations by modifying the former minimally. we try this by preserving the isotropy component (2(ii)) and relaxing the constancy component (2(i)) of the said input. thus tws of light is assumed to be isotropic in any frame σk and now we conjecture that this isotropic speed depends on u0k in following way, ckx = cky = ck = c0(1 + αu0k 2/c0 2 )1/2, (6) where we have introduced a dimensionless constant α which is assumed to have such a small value that the proposed theory does not differ in its predictions from that so far tested relativistically. clearly eq.(5) is now replaced by eq.(6) which approximately reduces to eq.(5) for αu0k 2/c0 2 << 1. note that, depending on the smallness of α, u0k can be very close to c0 and yet the last condition can still remain valid. we shall show below that if the phenomenological assumption described by eq.(6) is believed to be true, the uhecr paradox can be explained in terms of the motion of the solar system with respect to the rfcs. we conclude this section by quoting the relevant transformation equations which are obtained by plugging in eq.(6) in eqs.(3) and (4): xk = (1 − u0k 2/c0 2)−1/2(x0 − u0kt0), (7) tk = (1 + αu0k 2/c0 2 )−1/2(1 − u0k 2/c0 2 )−1/2(t0 − u0kx0/c0 2). (8) 3. metric and 4-vectors in sr classical expressions for momentum and energy had to be altered in order for the conservation principles to be lorentz covariant. these expressions can easily be obtained by writing the energy momentum conservation in terms of a 4-vector relation. the energy momentum 4-vectors are obtained in terms of the invariant interval of sr. in the present situation, such a thing cannot be obtained easily since one recalls that the notion of invariant interval of sr is an outcome of the existence of an invariant speed c (c0) of the theory. in the present context in absence of such a speed the invariant interval does not exist in the way it existed in sr. besides, since there should exist a preferred frame, in order to obtain the correct conservation principle (or to obtain definition of energy and momentum) an appeal to covariance of physical laws cannot be made. in the following we suggest a way out. from the transformations (3) and (4) together with yk = y0, zk = z0, (9) it is evident that (cky/ckx) 2xk 2 + yk 2 + zk 2 − cky 2tk 2 = x0 2+ y0 2 + z0 2 – c0 2t0 2 . (10) recalling eq. (6) the above relation reads xk 2 + yk 2 + zk 2 − ck 2tk 2 = x0 2+ y0 2 + z0 2 – c0 2t0 2, (11) and in terms of the differential intervals one obtains the following invariant interval s. nepal / bibechana 11(1) (2014) 17-24: (online publication: march, 2014) p.21 dτ 2 = d tk 2 − (1/ ck 2)(d xk 2 + d yk 2 + d zk 2), (12) and by analogy with sr we call dτ as the proper time interval. note that the expression for the above invariant interval is frame dependent unlike the case in sr because of the presence of ck(u0k) in the last expression. however one can easily develop a 4-vector formulation like that in sr by defining the 4-momentum of a particle of mass m as p = (mγk,mγk(vk)i), (13) with γk = (1 − vk 2/ck 2)−1/2, (14) where (vk)i represents the ith component of the three velocity vk of the particle in σk. imposing p.p = p2 = ηµνpµpν = invariant, (15) where ηµν = (1,−1/ck 2,−1/ck 2,−1/ck 2), (16) one obtain the dispersion relation for the particle in any frame σk as ek 2 = pk 2ck 2 + m2ck 4, (17) where pk = mvk/(1 − vk 2/ck 2)1/2= mγkvk, (18) and ek = mγkck 2. (19) although eqs.(17), (18) and (19) look like the corresponding equations in sr, they are different since the relations are dependent on the frame considered, since now ck = ck(u0k). note that expressions for energy, momentum and the dispersion relation reduce to the usual relativistic ones in the preferred frame σ0. 4. velocity transformations our theory therefore does not predict outcomes which are different from those in sr in σ0. the question now arises as to whether it is possible to predict a result significantly different from that of sr in a frame of reference (solar system) which is moving with a non-relativistic speed (u0k ≈ 10−3), with respect to rfcs (σ0). the answer seems to be affirmative and we suspect that the resolution of the cosmic ray paradox lies in such a non-preferred frame effect of the theory. to understand this question let us first quote the velocity transformation laws that follow from the transformation relations. we first consider a particle (say a proton) travelling along the x-direction with speed v0 with respect to σ0. the corresponding speed in σk will be obtained from the transformations (7) and (8) as vk = (1 + αuk 2/c0 2)1/2(v0 ± uk)/(1 ± v0uk/c0 2 ), (20) where we have put uk for u0k for brevity. we shall consider the speeds of the cosmic ray protons in σ0 to be very close to unity, v0 = 1 − ε0, (21) where ε0 is of the order of 10−22 (see below). with this range of values for v0 and recalling uk ≈ 10−3, the velocity transformation formula (eq.(20)) can be approximated as vk = (1 + αuk 2)1/2v0, (22) s. nepal / bibechana 11(1) (2014) 17-24: (online publication: march, 2014) p.22 where the terms of the order of ε0 2 and ε0uk have been neglected in comparison to unity. although in obtaining eq.(22) we have assumed the motion of the particles to be along the x-direction, interestingly it can be shown that the above relation holds even for particle travelling along any direction under the above mentioned approximation. 5. velocity threshold and the resolution of the paradox using the usual relativistic energy formula valid in σ0 e0 = m/(1 − v0 2)1/2, (23) the velocity threshold for proton in σ0 corresponding to the gzk threshold energy e0th = 5 × 1019ev speed can be calculated as v0th = 1 − 1.76 × 10−22. (24) now we will provide a possible explanation for the apparent detection of the trans-gzk events in terms of the motion of the solar system with respect to the cmbr frame. a surprisingly small value of the parameter α of the theory will be found to do this job. in order to demonstrate this we first anticipate (see below) this value for α: α = 3.42 × 10−16. (25) from eq.(6) the speed of light in the laboratory frame σk (for which uk ≈ 10−3) can approximately be written as ck = 1 + ηk ≈ (1 + αuk 2/2), (26) where ηk measures the departure of the light speed value in σk from unity. clearly ηk ≈ αuk 2/2 = 1.71 × 10−22. (27) however this term is absent in the preferred frame and as we have seen, the special relativistic results (formulas for energy, momentum, dispersion relation etc) hold in σ0 and hence gzk cut off value for proton energy obtained from sr is still valid in the cmbr frame. we shall see how this threshold value may appear to be about 3 × 1020ev in σk as detected by fly’s eye air shower detector. without going into the details of the experimental analysis we now speculate that the observed energy of a cosmic ray particle is its relativistic energy. we denote it by ek rel which is given by, ek rel = mc0 2/(1 − vk 2/c0 2)1/2, (28) where we have explicitly retained c0 for clarity. returning to the energy formula for a particle in our frame σk one notes that its value in the solar system (laboratory) practically does not differ from its relativistic value in σ0, as ek = mck 2/(1 − vk 2/ck 2)1/2 ≈ mc0 2/(1 – v0 2/c0 2)1/2= e0, (29) where we have used vk 2/ck 2 = v0 2/c0 2, (30) that follows from eqs. (6) and (22).we have also assumed in eq.(29), ck 2 ≈ c0 2, since the error involved in such an approximation is only about 1 part in 1022, which can be disregarded since ultimately we will have to explain a discrepancy much bigger than this error (3×1020ev against 5×1019ev ). the above energy formula (eq. (29)) can also be expressed as ek = mck 2/[1 − vk 2/ c0 2 (1 + αuk 2/ c0 2 )]1/2 ≈ m/[(1 − vk 2)1/2(1 + αuk 2/2εk) 1/2], (31) where in arriving at the last approximate expression we have put c0 = 1 again and defined, εk = 1 − vk. (32) s. nepal / bibechana 11(1) (2014) 17-24: (online publication: march, 2014) p.23 using eq.(28), one obtains from eq.(31) ek rel = ek(1 + αuk 2/2 εk) 1/2, (33) which by eq.(6.29) can be written as ek rel ≈ e0(1 + αuk 2/2 εk) 1/2. (34) note that this is the relativistic energy of a particle moving with speed vk. we now calculate this relativistic value of energy for a proton having the gzk threshold energy e0th. using the transformation (22) and assuming v0 = v0th, where the later is given by eq.(24), one obtains the corresponding vk as vk = 1 − εk = 1 − 5 × 10−24, (35) giving εk = 5 × 10−24. (36) using this value for εk and assumed value for α (eq.( 25)) and finally putting e0 = e0th, we find from eq.(34) ek rel ≈ 3 × 1020ev, (37) which is nothing but the energy of the 300 eev event detected by the fly’s eye. therefore we conclude that the value of the parameter α ≈ 3.42 × 10−16 can explain the apparent detection of trans-gzk events. note that the above calculation (or the choice of the value for α) depends on the assumption that the 300 eev event corresponds to the cut off value. however, it may not be so, indeed in future, a bit higher energy event may be detected, in which case the value of α will slightly go up. but this will not pose much problem since the assumed value of α is so small, it has enough flexibility to increase even substantially without contradicting sr in the tested domain. 6. discussions in this paper we have shown that the uhecr paradox can be explained in terms of a non-preferred frame effect of the laboratory frame which is moving with velocity ≈ 300 km/sec with respect to the preferred one, assumed to be at rest with cmbr frame. unlike some earlier efforts (the coleman glashow scheme for example) which consider liv but assume that the physical kinematics is still lorentzian, we propose to modify the transformation equation itself. deformed lt are generally discussed in connection with test theories like that of robertson [18] or mansouri and sexl [19] on which improved tests of sr are often based (see for example [20]). but they are not usually considered to represent a new physics that may provide a solution for the uhecr paradox. some authors find it troublesome giving up the principle of relativity. in the so called “doubly special relativistic” [21,22] theories, the particle dispersion relation is modified but the introduction of an invariant length or energy scale in addition to the invariant velocity scale of sr, the “relativity of inertial frames” is still maintained. such theories, often motivated by quantum-gravity considerations are interesting but are unable to resolve the uhecr paradox quantitatively at the moment. we here attempt to deform the relativistic kinematics using heuristic means. we do it first by identifying the objective contents of the relativity principle and then go in for modifying these contents minimally to obtain a new transformation that relates space-time of an arbitrary frame of reference with that of the universal rest frame of the cosmic substratum. the only phenomenological assumption regarding the speed of light in σk, ck = c0(1 + αuk 2/ c0 2)1/2 (in contrast to the assumption, ck = c0 in sr) for which ck − c0 = ηk ≈ 1.71 × 10−22 in the laboratory frame (uk ≈ 300 km/sec), is the only speculative aspect that has been used to derive the new kinematics. since the isotropy ingredient of the second relativity postulates has not been disturbed, michelson-morley type experiments cannot distinguish the proposed kinematics with that of the relativistic one. also the limit on ε given in eq. (1) as s. nepal / bibechana 11(1) (2014) 17-24: (online publication: march, 2014) p.24 a result of precision test becomes inconsequential, since the expected result in the present case would be zero. the recent improved test of time dilation in sr using laser spectroscopy sets a new limit of 2.2 × 10−7 for deviation of time dilation factor [20]. this even does not match with the smallness of ηk which is also the measure of this deviation according to the new kinematics. hence the precision tests possibly will be unable to discern any deviation from sr in the near future, yet one may find an explanation of the cosmic ray paradox in the proposed deformed relativistic kinematics. acknowledgment the author expresses sincere gratitude to prof. s. k. ghosal, department of physics, north bengal university, india. references [1] s. coleman, s.l. glashow, phys. letts. b, 405 (1997) 249. [2] s. coleman, s. glashow, phys. rev. d, 59 (1999) 116008. [3] h. sato, arxiv: astro-ph/0005218 v1, 2000. [4] s .k. lamoreaux, j.p. jacobs, b.r. heckel, f.j. raab, e.n. fortson, phys. rev. lett., 57 (1986) 3125. [5] d. j. bird et.al, astrophys. j., 441 (1995) 144. [6] f. w. stecker, s.t. scully, arxiv: astro-ph/0412495 v3, 2005. [7] k. greisen, phys. rev. lett., 16 (17) (1996) 748. [8] g. amelino-camelia, nature, 408 (2000) 661. [9] g. amelino-camelia, t. piran, phys. rev. d 64, (2001) 036005-1-12. [10] g. amelino-camelia, nature, 418 (2002) 34. [11] t. kifune, astrophys. j., 518 (1999) l21-l24. [12] s. kovesi-domoskos, g. domoskos, arxiv: hep-ph/0501281 v1, 2005. [13] george f.r. ellis, jean-philippe uzan, am. j. phys., 73 (2005) 240. [14] s.k. ghosal, d. mukhopadhyay, p. chakraborty, eur. j. phys., 15 (1994) 21. [15] s.k. ghosal, b. raychaudhuri, a. k. chowdhury, minakshi sarker, found. phys. lett., 17 (2004) 457. [16] c. kacser, introduction to the special theory of relativity, (edgewood cliffs, nj: prentice-hall), 1967. [17] r. baierlein, am. j. phys., 74 (2006) 193. [18] h. p. robertson, rev. mod. phys., 21 (1949) 378. [19] r. mansouri, r. u. sexl, gen. rel. grav., 8 (1977) 497. [20] g. saathoff et.al, phys. rev. lett., 91 (2003) 190403-1-4. [21] g. amelino-camelia, int. j. mod. phys. d, 11 (2002) 35. [22] j. magueijo, l. smolin, phys. rev. lett., 88 (2002) 190403-1-4. bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal design and development of shovel type-spring steel furrow opener for cultivator mounted seed metering mechanism ajay verma1, ankitesh shrivastava2* 1farm machinery & power engineering, indira gandhi agricultural university, raipur (c.g.), india. 2production engineering, bhilai institute of technology, durg (c.g.), india. #email: ankiteshrivastava@gmail.com article history: received 20 october, 2017; accepted 24 november, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18455 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the cultivator mounted seed metering mechanism consists of cultivator frame, tines, seed box, seed tubes, metering mechanism, power transmission unit, furrow opener and hitching attachments. the drawings of the developed machine were generated using cad software and the machine was fabricated in the workshop of faculty of agricultural engineering, igau, raipur. power was transmitted from ground wheel through sprocket-chain drive to the main shaft. at the average working speed of 3.8 km/h of tractor drawn cultivator, depth of operation was found 129 mm, average weed efficiency was found 76.42 %,effective field capacity was found 0.826 ha/h with field efficiency of 87.40 %. the cost of operation and energy requirement of cultivator was found to be rs 387 per ha and 241 mj/ha. the energy requirement for cultivator-cum-seed drill was found to be 454.18 mj/ha. keywords: furrow opener, cultivator; metering device; fluted roller; seed tubes. 1. introduction in the trend of growth of power operated machinery, cultivators and seed drill are the equipment mostly used by farmers. most of the farmers are having cultivators keeping in this mind the shape to this idea is given of a seed metering attachments to cultivator will be developed in workshop of faculty of agricultural engineering. it will perform both tillage as well as sowing operation. this developed attachment will easily be attached to the existing cultivator, and consequently will minimise the energy and cost of operation. baker (1976) investigated the performances of furrow openers including disc, chisel and hoe types in the lab. it was noted that germination was significantly higher by chisel (77%) than hoe (26%) and disc (27%) that was mainly due to remaining moisture in the furrows. the developed machine could also be adopted as cultivator for secondary tillage operations and inter-culture operations by simply removing seed box with the help of nuts and bolts on the cultivator frame. ajaya verma and ankitesh shrivastava / bibechana 15 (2018) 79-84: rcost p.79 http://nepjol.info/index.php/bibechana http://dx.doi.org/10.3126/bibechana.v15i0.18 https://creativecommons.org/licenses/by-nc/4.0/ iqbal (1994) reported that the draft requirement of tillage implement has a great influence in design of tillage implements and deciding suitable tractor size and also concluded that draft of implement increases with increase in depth of ploughing. damora (1995) observed that more compaction of furrow bottom and less seed scatter occurred with shoe type openers as compared to shovel and hoe type openers. the type and purpose of presowing tillage implement is many ranging in operations from breaking of soil to finishing the surface which consumes considerable time and energy resulting in delayed sowing with higher cost of cultivation. laurel (1995) reported that at 150 mm working depth, the v-shaped sweep with pitch angle of 10 degree and the blade swept back at angle of 70 degrees performed good control of weeds. at this configuration, the sweep did not invert the soil. there was minimum soil disturbance, which was found adequate to drill the crop in the same operation. sharma (2001) reported the performance of tractor drawn multi-crop ridge-furrow and flatbed seeding machine. it was capable of sowing 5-6 ha/day depending on type of crop sown. there was 30-40 % saving of irrigation water with its use as ridge-seeder. 2. materials & methods furrow openers reversible shovel type furrow openers were provided on the machine to help in sowing of crop. the furrow opener comprises of shovel, tine, boot and boot pipe to attach delivery tubes. the boot of opener was made out of 1.5 mm thick ms sheet it was welded to the tine and shovel assembly. two holes each 10 mm diameter at a spacing of 50 mm were provided to fix the boot and opener using nuts and bolts (fig. 1). one ms boot pipe of 25 mm external diameter and 150 mm length for seed was welded in the boot. seed are received from the respective tubes and conveyed to deposits in to furrow. the developed furrow opener is shown in fig. 3. fig. 1: design developed for furrow opener. ajaya verma and ankitesh shrivastava / bibechana 15 (2018) 79-84: rcost p.80 fluted roller type seed metering devices the metering mechanism for seed consisted of standard die cast aluminum fluted roller (bis: 6816 part i, ii, iii, iv) seed metering unit with 12 flute were used for seed metering. one square shaft of 16mm size, and 2100 mm made up of mild steel were passed through fluted roller for rotating the roller. rotation of fluted roller in housing, filled with seeds causes the seeds to flow out from roller housing in a continuous stream. the seed rate can be adjusted by controlling exposed length of flutes, which is in contact with seed .fairly accurate seed rate can be achieved for a variety of medium size seeds like paddy wheat and sunflower etc. seed tubes seed tubes were made of transparent plastic pipe according to distance between different fluted roller and furrow opener boot pipes. each seed tube was attached to the seed distributor at one end the other end was attached to the boot at furrow opener. the length of the pipe has been taken according to the distance between different fluted rollers and furrow opener boot pipes. the time of fall of the seed through a tube is affected by the size and type of tube by the striking and bouncing of seeds against the wall of the seed tube. transparent plastic tubes of 22 mm diameter and 2 mm thick were selected. drive mechanism the chain and sprocket drive was used to transmit power from ground wheel to the metering device, where power is supplied to a number of rows. selection of motorcycle chain of 0.5 inch (16 mm) pitch is adequate. a mild steel ground wheel provided with 12 spikes on the periphery of the wheel of 450 mm diameter has been used. on ground wheel shaft a 10 teeth sprocket is mounted and in another intermediate shaft 18 teeth sprocket is mounted. on the same shaft a 10 teeth sprocket is mounted which is connected to the seed metering fluted roller shaft through 18 teeth sprocket with chain. an idler was provided to adjust tension developed in chain (fig. 2). 3. results & discussion design of shank of furrow opener considering available draft of 345.6 kg exerted on the tip of furrow opener bending moment = draft x ground clearance = 345.6 x 50 cm = 17280 kg-cm bending stress, f = mc/ i … (1) where, m = bending stress, kg/cm2. i = moment of inertia, cm4. c = distance from the neutral axis to the point at which stress is determined. the section modulus of axis computed by using formula, z = i/c … (2) from (1) and (2) z = m/f … (3) assuming bending stress equal to 1000 kg/cm2, z = 17280/1000 z = 17.28 cm3 section modulus of furrow opener is, z = bh2/6 … (4) the most assumed ratio of thickness to the width of shank is b: h = 1: 2 to 1: 4 assuming b: h = 1: 2 17.28 = bh2/6 b = 29.59 mm considering availability of material of standard size the thickness of shank selected is 32 mm. exposed length of fluted roller ajaya verma and ankitesh shrivastava / bibechana 15 (2018) 79-84: rcost p.81 the volume of seed dropped per meter length of the row is given by vs = (s x r)/ (10 ρ) … (5) where, s = seed rate for crop in kg/ha ρ = bulk density of seed in g/cm3 r = row spacing m the area of semi-circular flute is given by, af = ρ df 2 / 8 … (6) where df = diameter of flute in cm. the delivered volume per revolution of the roller is given by, vd = af x nf x if … (7) where, af = area of semi-circular flute in cm2 nf = number of flute if = exposed length of flute in cm. the number of revolutions of a fluted roller, nf is given by nf = i x ng … (8) where, i = transmission ratio ng = number of revolutions of ground wheel. fig. 2: drive mechanism for the cultivator. the distance, dg covered by the ground wheel per revolution is given by, dg = п x dg … (9) where, dg = diameter of ground wheel in m. the volume of seed per meter traveled by the ground wheel is given by vs = vd i / п dg ... (10) ajaya verma and ankitesh shrivastava / bibechana 15 (2018) 79-84: rcost p.82 the exposed length of the fluted roller is derived by combining equations (4) up to (8) as follows if = (8 x s x r x dg) / (10 x  x df 2 x nf x i) … (11) fig. 3: developed furrow opener. fig. 4: developed seed-drill in operation. ajaya verma and ankitesh shrivastava / bibechana 15 (2018) 79-84: rcost p.83 4. conclusion the seed rate of cultivator-cum-seed drill was found to be 80.87 kg/ha when seed drill was half filled and flute exposure was 14.9 mm and that of conventional seed drill was found to be 80.26 kg/ha. when seed drill was half filled and flute exposure was 13.8 mm. the variation in dropping the seeds between the rows of cultivator-cum-seed drill was -3.05 to + 3.1 for paddy and that of conventional seed drill was -2.02 to + 2.02 respectively. the standard deviation for inter row variation for sowing paddy with cultivator-cum-seed drill was 0.46 with cv of 1.8 % and for conventional seed drill was 0.41 and 1.5 % respectively. the average speed of operation of cultivator-cum-seed drill was found 3.09 km/h and that of conventional seed drill was 3.5 km/h. the average depth of seed placement with cultivator-cum-seed drill was found to be 57.8 mm and that of conventional seed drill was 60.6 mm. the effective field capacity of the cultivator-cum seed drill was 0.537 ha/h with field efficiency 82.8 % as compared to conventional seed drill which was 0.596 ha/h and 82.32 %. references [2] d. p. darmora, k.p. pandey, evaluation of performance of furrow openers of combined seed and fertilizer drills. soil & tillage research 34 (1995) 127-139. [3] m. iqbal, m.s. sabir, md. younis, a. h. azhar, draft requirements of selected tillage implements. ama 25(1) (1994) 13-15. [4] h. laural ortiz, an agricultural implement for non-inversion tillage in semiarid regions. ama 26(4) (1994) 22-24. [5] d.n. sharma, d.p. kataria, v.p. bahl, on farm trials of tractor drawn multicrop ridge-furrow and flat bed seeding machine for rain fed and irrigated conditions. journal of agricultural engineering 38(1) (2001) 24-33. ajaya verma and ankitesh shrivastava / bibechana 15 (2018) 79-84: rcost p.84 [1] c.j. baker, experiments relating to techniques for direct drilling of seeds into untilled dead turf, j. of agricultural engineering research 21(1976) 133-144. doi.org/10.1016/0021-8634(76)90068-8. https://doi.org/10.1016/0021-8634(76)90068-8 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal a study of far infrared loop at -5o galactic latitude around pulsar j1627-5547 a.k. jha, b. aryal central department of physics, tribhuvan university, nepal. email: astroajay123@gmail.com article history: received 14 october, 2017; accepted 22 november, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18443 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract we present physical properties of the core region of infrared loop g329-05 which is found to be located within 1o from the pulsar psr j1627-5547. the loop has 3-fold reduced flux density than its surroundings. in the 100 micron infrared map, a new cavity-like isolated far infrared dust structure of core region (size ~0.750 x 0.230 ) is found at r.a. (j2000)= 16h 27m 19.9s & dec. (j2000) = -56035’14”. this loop is believed to be formed because of high pressure events occurred in the past. the dust color temperature of the core region is found to lie in the range 25.26 ± 0.09 k to 27.91 ± 0.09 k, whereas the value of dust color temperature increased to 36.72 ± 0.18 k for the outer region. the dust color temperature and dust mass distribution maps showed that the low temperature region has greater density as expected. the dust mass of the core region of the loop is found to be 1.67 x 1027 kg i.e. about 0.00835 mʘ. the core region of the loop is found to be edge-on (i ˃780) whereas the larger structure is faced-on (i =00). possible explanation of results will be presented. keywords: ism; far infrared loops; dust color temperature and dust mass; inclination angle. 1. introduction the large scale structure of the interstellar medium (ism) in the galaxy is diverse, with a complex distribution of cavities, filaments, arcs, loops, lobes and shells [1]. the most studied galactic shells were formed by supernova explosions and winds of massive stars [2]. however, high velocity clouds may also form large cavities when in falling from the galactic halo and colliding with the ism of the disc. a remarkable example of high velocity cloud – galactic disc interaction is the north celestial pole loop [3]. the evolution of bubbles and super bubbles produced by supernovae explosions and stellar winds of association are the primary processes that determine the structure and energetic of all components of the diffused interstellar medium. kiss et al. (2004) & koenyves et al. (2007) [4, 5] identified 462 far infrared loops using 100 and 60 µm iras maps. they studied their size, luminosity, distributions and concluded that these structures are formed and governed by supernovae and stellar winds at the low galactic latitude. at high galactic latitude fractal structures of loops suggest the probability of super-sonic turbulence. on 100 and 60 µm iras maps [6] found two giant (2.1 pc, 0.9pc) bipolar dust emission structures centered on pn ngc 1514 representing one of the very few none cases where the preserved history of all main mass-loss phases of a star of intermediate a.k. jha and b. aryal / bibechana 15 (2018) 70-76: rcost p.70 http://nepjol.info/index.php/bibechana mailto:astroajay123@gmail.com http://dx.doi.org/10.3126/bibechana.v15i0.18 https://creativecommons.org/licenses/by-nc/4.0/ initial mass. we intend to find the physical properties of infrared loop (kiss et al., 2004 & koenyves et al., 2007; kk loop here after) near to atnf pulsar. in the present work, we intend to find an isolated far infrared cavity nearby pulsar and kk-loop and study its physical properties (dust color temperatures, dust mass, inclination angle, etc). finally we are interested to understand its formation and evolution. the role of the pulsar in the structure formation will be discussed. 2. region of interest by performing systematic search using the catalogue reported by kiss et al. [4] and koenyves et al.[5], we have selected a new cavity-like region close to far infrared cavity girl g329-05 for the study. following are the selection criteria of the loop: a) the core region of the loop should have flux minima at 100µm iras maps, b) the major diameter should be greater than 0.50, c) should be located within 10 of atnf pulsar, d) should lie in the galactic plane (-200 ˂b˂200), and e) no diffuse optical emission the loop is centered at r.a. (j2000) = 16h 27m 19.9s & dec. (j2000) = -56035’14” prominent cavity is seen in both bands 60µm and 100µm. the pixel size of the image is 0.80 x 0.80 as shown in fig 1. fig. 1: 0.80 x 0.80 iras image of our region of interest at 100 micron (a) and 60 micron (b) jpeg images of g329-05 kk-loop having cavity. the ‘x’ sign in the north-east corner represents the position of pulsar j1627-5547. (source: sky view virtual observatory, 2017) 3. methods 3.1 dust color temperature estimation: we adopt the method developed by schnee [7] to calculate the dust color temperature from the iras 60μm and 100μm flux densities. for dust color temperature estimation we use the expression as 𝑇𝑑 = −96 1 𝑙𝑛{𝑅× 0.6(3+𝛽)} (1) the value of the spectral emissivity index (𝛽) depends on dust grain properties as composition, size, and compactness. for reference, a pure blackbody would have 𝛽 = 0, the amorphous layer-lattice matter has 𝛽 ~1, and the metals and crystalline dielectrics have 𝛽 ~ 2 [8]. a.k. jha and b. aryal / bibechana 15 (2018) 70-76: rcost p.71 where r is given r = f(60 𝜇m) f(100 𝜇m) (2) f (60 micron) and f (100 micron) are the flux densities at 60 𝜇m and 100 𝜇m, respectively. in this way we can use equation (1) for the determination of the dust grain temperature (dupac et al. 2003). 3.1 dust mass estimation the dust masses are estimated from the ir flux densities. the resulting dust mass depends on the physical and chemical properties of the dust grains, the adopted dust temperature td and the distance d to the object [9]. 𝑀𝑑𝑢𝑠𝑡 = 4 3 𝑎𝜌 𝑄𝜈 [ 𝑆𝜈𝐷2 𝐵(𝜈,𝑇) ] (3) where, 𝑎 = weighted grain size = 0.1 μm 𝜌 = grain density = 3000 kg m−3 𝑄𝜈= grain emissivity = 0 .0010 for 100μm and 0.0046 for 60μm respectively [10]. 𝑆𝜈= total flux density of the region whose mass is to be determined 𝑆𝜈 = 𝑓 × 5.288 × 10−9 mjy/sr 𝐷 = distance of the structure 𝐵(𝜈, 𝑇) = planck’s function given by, 𝐵(𝜈, 𝑇) = 2ℎ𝜈3 𝑐2 [ 1 𝑒 ℎ𝜈 𝑘𝑇−1 ] (4) where, ℎ = planck’s constant, 𝑐 = velocity of light, 𝜈 = frequency at which the emission is observed & 𝑇 = the average temperatures of the region. using these values the equation (3) takes the form: 𝑀𝑑𝑢𝑠𝑡 = 0.4 [ 𝑆𝜈𝐷2 𝐵(𝜈,𝑇) ] (5) we use the equation (5) for the calculation of the dust mass. it is clear from the expression (4) that the value of planck function 𝐵(𝜈, 𝑇) for longer wavelength is higher than that of the shorter wavelength. consequently, the range of 𝐵(𝜈, 𝑇) for fixed temperature (says ∆t) goes narrower if wavelength of the images increases [11]. inclination angle is the angle between the line of sight and normal to the plane of the structure. the inclination angle i of the structure can be determined by the method [12] given by equation (6) below 𝑐𝑜𝑠2𝑖 = [(𝑏 𝑎⁄ ) 2 −(𝑞∗)2] 1−(𝑞∗)2 (6) where 𝑏 𝑎⁄ is the axial ratio and q* is the intrinsic flatness. holmberg used the value of q* to be 0.23 for oblate spheroid. 4. results and discussion here we present physical properties of a look-like structure that we found at -50 galactic latitude in the far infrared iras maps. figure (2) shows image of the cavity. in the image, the dark and bright color represents the minimum and maximum values of flux densities, respectively. iras 100µm fits image for ra/dec(j2000) = 16h27m19.9s /-56035’14” is shown in figure (2), here fig (a) represents core region of the cavity surrounded by contour & fig (b) represents lines ab represent major diameter and cd minor diameter passing through minimum flux pixel respectively. the value of minimum flux at the center of the cavity is found to be 23.36 mjy/sr. the maximum flux of the contour levels of the core region of the loop is found to be 27.92 mjy/sr. a.k. jha and b. aryal / bibechana 15 (2018) 70-76: rcost p.72 fig. 2: dust structures of the at 100 micron. (a) the contour levels are drawn. the appropriate isocontour is found at 27.92 mjy/sr corresponding to level 82. (b) the lines ab & cd represent the major and minor diameters passing through minimum flux density (flux-minima). 4.1 dust color temperature, dust mass and inclination angle we calculated dust color temperature of all pixels of the loop. for the calculation of dust color temperature, we adopt the method developed [7] and [8]. the region with minimum and maximum temperature is found to lie in the range of 25.26 ± 0.09 k at r.a. (j2000) = 16h30m17.77s & dec (j2000) = -56o 03’51.10” to 27.91 ± 0.09 k at r.a. (j2000) = 16h 31m 12.48s & dec (j2000) = -56o 29’ 19”. an offset of about 2 k suggest that the core of the loop is stable. the average dust temperature calculated using the slope of f(100) and f(60) plot (figure 3b), is found to be 25.85 k. the minimum temperature region is found to be elongated along east-west direction (figure 3c). the distribution of dust color temperature fits well with gaussian (fig.3e) with gaussian centre 25.70 k. the value of td of the larger structure is found to be 36.72 k. therefore the cavity is cold (low density) enough at the core region than that of the outer region. an offset of 16 k temperature suggest that the cavity is dynamically active. the dust mass contours (figure 3d) seems to follow the expected trend: higher density at low temperature region (fig.3 c, d) the distribution of td (dust color temperature) is well fitted by a gaussian plot (figure 3e). the value of δtd of the core region is small which indicates that the dust is mostly in thermal equilibrium whereas, in outer region the temperature offset is 16k which suggests that the cavity is not in thermal equilibrium. we used [12] method, equation (6), to calculate the inclination angle of the core and whole loop. the inclination angle of the core and whole loop are found to be 780 and 00 respectively. it means the core region is edge-on where as outer region of this loop is completely faced-on. the size of the large structure of the kkloop is 1.40x1.40 [5] where as of the core region is found to be 0.750 x 0.230. therefore, the size of the core region of this loop is only about 9 % of the whole loop. using the distance of the loop to be 200 pc [13], the dust mass of the cavity is found to be 1.67 x 1027kg i.e. about 0.00835 mʘ by using equation (5). the outflow nature in the core region along major diameter (north-south direction) has been observed. this is probably due to wind of pulsar j1627-5547 which is situated at a distance of 0.790 from the kk-loop g329-05. besides this, we found 3, 22 and 76 number of pulsars within 3o, 6o and 9o radii respectively from the kk-loop. the a.k. jha and b. aryal / bibechana 15 (2018) 70-76: rcost p.73 age and dispersion measure of the nearby pulsar j1627-5547 is found to be 7.57 x 106 years and 1666.2 cm-3 pc respectively (atnf pulsar catalogue). fig.3 (a): iras 100µm far infrared images of the core region of kk-loop g329-05 centered at r.a. (j2000) = 16h27m19.9s, dec. (j2000) = -560 35’14”.the flux contours are shown which represents 23.36, 24.51, 25.65, 26.80 and 27.94 mjy/sr. (b) flux at 100 µm versus 60 µm plot. the dust color temperature (c) and dust mass (d) contour maps. the contour levels are shown. the distribution of a.k. jha and b. aryal / bibechana 15 (2018) 70-76: rcost p.74 dust color temperature (e) and dust mass (f). the solid curve represents gaussian fits. the gaussian parameters are given. 5. conclusions we present physical properties of g329-05 dusty loops at far infrared (60 µm and 100 µm) iras maps located around atnf pulsar within 10 radius. the dust color temperature, dust mass, inclination angle and the size of the core region of the kkloop are studied and are compared with its larger structures [4, 5] in iras maps. we conclude our results as follow: a) dust color temperature and dust mass distributions show a very good agreement with gaussian. however the outer region show relatively higher temperature with an offset of about 16 k than that of its core region, suggesting the loop is dynamically unstable. b) the inclination angle of the core region is found to be 780, suggesting edge-on appearance. at the outer region, the inclination angle is found to be 00, i.e. faced-on. c) the dust mass of the core region is estimated to be 1.67 x 1027 kg, i.e. about 0.00835mʘ at a distance 200 pc. acknowledgement we acknowledge our collaborator r. weinberg, innsbruck university, innsbruck, austria for critical suggestions, university grant commission, nepal to assist financial support for ph.d. simbad database, sky view virtual observatory, atnf pulsar catalog, iras surveys and girl catalog. one of the authors (akj) acknowledges central department of physics, tribhuvan university, nepal for all kinds of support for his ph.d. work. references [1] p.w.j.l. brand, w.j zealey, cloud structure in the galactic plane-a cosmic bubble bath, astronomy & astrophysics 38 (1975) 363. [2] tenorio – tagle, bodenheimer, supernova explosions inside pre-existing wind driven cavities, spherically symmetric models, springer & verlag, newyork & berlin (1988) 77-87. [3] h. meyerdierks, a. heithausen, m. grashoff, the north celestial pole loop, astronomy & astrophysics 245 (1991) 247-256. [4] cs. kiss, a. mor, l.v. tth, far-infrared loops in the 2nd galactic quadrant, astronomy & astrophysics 418 (2004) 131. doi.org/10.1051/0004-6361:20034530. [5] v. koenyves, cs. kiss, a. mor, z.t. kiss, l.v.tth, ,catalogue of far-infrared loops in the galaxy, astronomy & astrophysics 463 (2007) 1227. doi.org/10.1051/0004-6361:20065438. [6] b. aryal, c. rajbahak, r. weinberger, , a giant dusty bipolar structure around the planetary nebula ngc 1514, monthly notices royal astron. soc. 402 (2010) 1307. doi.org/10.1111/j.1365-2966.2009.15966.x. [7] s. l. schnee, , n.a. ridge, a.a. goodman, g.l. jason, , a complete look at the use of iras emission maps to estimate extinction and dust temperature. astrophysical journal 634 (2005) 442-450. [8] x. dupac, j.p. bernard, n. boudet, m. giard, j.m. lamarre, c. mny, f. pajot, , i. ristorcelli, g. serra, b. stepnik, j.p. torre, ,inverse temperature dependence of the dust sub millimeter spectral index, astronomy & astrophysics 404 (2003) l11-l15. doi.org/10.1051/0004-6361:20030575. [9] r. h. hildebrand, the determination of cloud masses and dust characteristics from sub millimeter thermal emission, q. journal of royal astronomical society 24 (1983) 267-282. [10] k.young, t.g. philips, g.r. knapp, circumstellar shells resolved in iras survey data ii-analysis, astrophysical journal 409 (1993) 725. doi.org/10.1086/172702 a.k. jha and b. aryal / bibechana 15 (2018) 70-76: rcost p.75 http://dx.doi.org/10.1051/0004-6361:20034530 http://dx.doi.org/10.1051/0004-6361:20065438 http://dx.doi.org/10.1111/j.1365-2966.2009.15966.x http://dx.doi.org/10.1051/0004-6361:20030575 http://dx.doi.org/10.1086/172702 [11] c. a. beichman, g. neugebauer, h. j. habing, p. e. clegg, t. j chester, infrared astronomical satellite (iras) catalogues and atlases i: explanatory supplement. us government printing office, washington (1988). [12] e. holmberg, on the apparent diameters and the orientation in space of extragalactic nebulae, medd. lund astron. obs. ser. vi, (1946) 117. [13] sten f. odenwald, comet like clouds at far infrared and optical wavelength, astrophysical journal 325 (1988) 320-341. doi.org/10.1086/166006. a.k. jha and b. aryal / bibechana 15 (2018) 70-76: rcost p.76 http://dx.doi.org/10.1086/166006 microsoft word mohd yusuf yasin _18-27_.doc mohd yusuf yasin / bibechana 9 (2013) 18-27 : bmhss, p.18 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana complex roots of polynomials and their computation with the help of scientific calculators mohd yusuf yasin ece department, integral university, lucknow, up, india phone: (office)091-522-2890812, (mobile)091-9335924865, email: mmyasin@rediffmail.com article history: received 10 march, 2012; accepted 2 august, 2012 abstract real numbers are something which are associated with the practical life. this number system is one dimensional. situations arise when the real numbers fail to provide a solution. perhaps the italian mathematician gerolamo cardano is the first known mathematician who pointed out the necessity of imaginary and complex numbers. complex numbers are now a vital part of sciences and are used in various branches of engineering, technology, electromagnetism, quantum theory, chaos theory etc. a complex number constitutes a real number along with an imaginary number that lies on the quadrature axis and gives an additional dimension to the number system. therefore any computation based on complex numbers, is usually complex because both the real and imaginary parts of the number are to be simultaneously dealt with. modern scientific calculators are capable of performing on a wide range of functions on complex numbers in their comp and cmplx modes with an equal ease as with the real numbers. in this work, the use of scientific calculators (casio brand) for efficient determination of complex roots of various types of equations is discussed. keywords: scientific calculators; calculator techniques; complex roots; complex domain computation skills, numerical techniques 1. introduction the complex number is a great reality of modern sciences, of which one can never get rid off. there are real examples that can never yield to real solutions. 1)( 2 += xxf (1) eq.1 is such a polynomial, which has real coefficients, but never intersects with the real axis. according to the fundamental theorem of algebra [1], this equation has two roots. the content of two roots and no intersection with real axis of the eq.1 can only be satisfied in complex domain. mohd yusuf yasin / bibechana 9 (2013) 18-27: bmhss, p.19 (online publication: nov., 2012) a complex number contains a real part accompanied with an imaginary part, and therefore can only be expressed in a two dimensional plane. real part lies in the usual real plane, but the imaginary part needs be placed in the second direction. the complex numbers can be expressed in any system of representation like rectilinear, polar, spherical etc., but will always need two components to handle. this renders complexity to any computational procedure involving complex numbers. )()())(( 21212121221121 yxyxiyyxxiyxiyxzz ++−=++= (2) 2 2 2 2 2112 2 2 2 2 2121 22 11 2 1 )()( )( )( yx yxyx i yx yyxx iyx iyx z z + − + + + = + + = (3) 1−≡i or 12 −≡i (4) eq.2 and eq.3 show the additional complexity of computation in case of dealing with complex numbers [2], z being a complex number. 2. calculator techniques casio brand scientific calculators usually posses a temporary register under the key “ans”. this register automatically modifies after each computation, and holds the current result. the same key also holds the real and imaginary parts of a result under “cmplx” mode, which is directly accessible through “ imre↔ ” key. while handling complex numbers recursively, this “ans” key is quite useful same as it is in case of problems handling with real numbers [3]. “ans” key can be used as variable in both recursive and non recursive procedures. 3. complex number handling in scientific calculators in this work, calculators of casio fx-991/570 series (fx-991w/115w, fx-991w/115w, fx-991ms, fx991es etc.) are under consideration [4,5]. these calculators offer help to tackle with complex number in different ways. in normal computing mode “comp”, conversion function rrectangulapolar⇔ is operational. this function stores the result under memory “e” and “f”. this function is helpful for conversion among rectangular and polar coordinates, since for complex numbers, multiplication and division are easier in polar form whereas addition and subtraction are simpler in rectangular form. rrectangulapolar⇔ transformation function swaps a number from one form to the other. a calculator can set in complex domain by selecting the mode “cmplx”. under this mode, the complex number can be directly treated in rectangular form with imaginary operator “i”. complex number )32( i+ is fed to calculator as “2”, “3”,”i”. here “ξ” is a key, pressed or needs to be pressed on the calculator, or is an entity under a key. a press “=” will store this complex number under the key “ans”. this result can be checked by pressing “ imre↔ ” key through “shift”. this “ans” key and the storage style is extremely helpful in computations involving complex numbers. calculations in complex mode can be performed with an equal ease as is in the real mode [3]. here in this work, calculation techniques with respect to roots of polynomials are considered. it may be pointed out here that some calculators like fx991ms can solve third order equations in one variable and with real coefficients [5]. higher order polynomials, polynomials with complex or imaginary coefficients and other non-polynomials can not be directly solved. therefore tricks and methods for such computation are highly sought forth. mohd yusuf yasin / bibechana 9 (2013) 18-27: bmhss, p.20 (online publication: nov., 2012) 4. complex roots the fundamental theorem of algebra states a polynomial 0f(x) = of order “n” and with complex coefficients, will have exactly “n” complex roots, complex number is being the more general number [1], a real number is a complex number that contains no imaginary part. from above it is simple to deduce various cases like (a) a polynomial with only real coefficients can have real, complex or imaginary roots, (b) a polynomial with some complex or imaginary coefficients must have one or more complex or imaginary roots, (c) if the polynomial 0f(x) = tends to have imaginary roots, and all of its coefficients are only real, then the complex roots shall appear in complex conjugate pairs. imaginary number is a complex number with imaginary coefficient, a real number is with only real coefficient, and a complex number is one which contains both real and imaginary coefficients. complex roots arise due to the nature of functions which do not have any intersection with the real axis. fig. 1: imaginary roots of eq.1 mohd yusuf yasin / bibechana 9 (2013) 18-27: bmhss, p.21 (online publication: nov., 2012) eq.1 does not yield to a real solution. however, it can be solved for imaginary roots, ix ±= . these roots can be represented as intersection of the eq.1 with imaginary axis or the intersection of the flipped plot of eq.1 with real axis 5. calculation of complex roots it is suggested by the fundamental theorem of algebra that both the real and complex roots of a given polynomial are possible [1]. these roots can be determined by using a root finding method of general nature. one possible method is newton – raphson, which is found quite reasonable in such analyses [2]. this method has a reasonably high convergence rate to estimate a root, and generally yields even to the less meaningful initial approximations. this method is found suitable for the analyses of the complex polynomials, functions and for real and complex roots. according to the newton – raphson method, the root of a polynomial 0)( =xf is approached by using eq.5. )( )( '1 n n nn xf xf xx −=+ (5) where nx is a previous estimate of the root, 1+nx is the new improved approximation and )(' nxf is the first derivative of )( nxf [2]. 6. complex root determination with calculator the calculator is set to “cmplx” mode. initial approximation iba + is suitably chosen to determine a root and is fed to be in the register under the “ans” key. using eq.5, a similar equation is developed for the problem and is fed to the calculator in terms of the “ans” as variable. the solution is converged after a few clicks of the “=” key. this scheme is shown by the flow graph of fig.2. in the following sections, two examples are considered to demonstrate how easy it is to approach the final accurate result recursively in case of complex root. in both these examples, due to their simplicity and excellent bidirectional approach to the final accurate solution, the simple newton – raphson method is employed. 7.1 calculators referred in this article, scientific calculators referred are casio models like fx-991w, fx-991w, fx-115w, fx991ms, fx-991es etc. or later versions which can work on and display scientific equations [4,5]. 7.2 equations with real coefficients and imaginary roots eq.1 or similar equations can be considered here, which contain roots in conjugate pairs. solving eq.1 the roots are found to be mohd yusuf yasin / bibechana 9 (2013) 18-27: bmhss, p.22 (online publication: nov., 2012) ix ±= (6) the procedure for determining a root of eq.1 can be obtained using eq.5. thus       −=+ n nn x xx 1 2 1 1 (7) using a calculator, the eq.7 can be rewritten as ( )1 2 1 −−= ansansans (8) various possibilities on the basis of the initial approximation are as follows. 1. ians ±←1 (complex initial approximation) ans ← 0.25+0.75i ans ← -0.075+0.975i ans ← -1.7157e -3 +0.9973i ans ← -4.642e -6 +1.00000216i fig. 2: general flow graph of the computational procedure mohd yusuf yasin / bibechana 9 (2013) 18-27: bmhss, p.23 (online publication: nov., 2012) ans ← 1.002866e -11 + i ans ←←←← i the root smoothly converges to the solution and answer is available after the fifth press of the “=” key. 2. ians 5.0← (imaginary initial approximation) ans ← 1.25i ans ← 1.025i ans ← 1.00030i ans ← 1.000000046i ans ←←←← i 3. 0.1←ans (real initial approximation) in this option, the root either oscillates or prematurely terminates. 7.3 equations with real coefficients and complex roots let )1()( 2 ++= xxxf (9) both roots of this equation are complex and are )866.50000.0)(866.05000.0()1()( 2 ixixxxxf +++=++= (10) using the method described here, the root approximating equation for eq.9 is written as ( ) )12/(1 2 +−= ansansans (11) table 1: solution details of eq.9 initial approximation xn final roots of eq.9 iterations x=1.0 no convergence root oscillates (no real root) x=1+i x=1-i -0.5+0.8660i -0.5-0.8660i 05 iterations x=±i -0.5±0.8660i 03 iterations mohd yusuf yasin / bibechana 9 (2013) 18-27: bmhss, p.24 (online publication: nov., 2012) 7.4 equations with real coefficients and mixed roots let an arbitrary equation, and it’s roots are )1)(5.0()( 2 ++−= xxxxf (12) ;866.05.0;5.0 ixx ±−== (13) applying the above algorithm, the convergence detail to the roots are as follows. table 2: solution details of eq.12 xn final roots of eq.12 iterations x=1.0 0.5000 04 iterations x=1± i -0.5000±0.0000i 06 iterations x=±i -0.5000 ± 0.8660i 05 iterations 7.5 equations with one imaginary coefficient let an arbitrary equation be 1)( 2 ++= xixxf (14) this equation must have at least one complex root because of the imaginary coefficient. calculator analysis results are summarized in table 3. table 3: solution details of eq.14 xn final roots of eq.14 iterations x=1+i 0.0000 + 0.6180i 04 iterations x=1i 0.0000 1.6180i 06 iterations x=i 0.0000 + 0.6180i 03 iterations x=-i 0.0000 1.6180i 04 iterations analysis for finding real roots is futile, since the two consistent roots are already found from above, and the eq.14 is rewritten as below. )6180.0)(6180.1(1)( 2 ixixxixxf −+=++= (15) 7.6 equations with complex coefficients consider an equation with a complex coefficient 1)3.01()( 2 +++= xixxxf (16) root convergence details of this equation are summarized in table 4. mohd yusuf yasin / bibechana 9 (2013) 18-27: bmhss, p.25 (online publication: nov., 2012) table 4: solution details of eq.16 xn final roots of eq.16 iterations x=1+i -0.4151 + 0.7330i 05 iterations x=1i -0.5849 1.0330i 06 iterations x=i -0.4151 + 0.7330i 03 iterations x=-i -0.5849 1.0330i 04 iterations x=0 -0.4151 + 0.7330i 05 iterations )1.0330i 0.5849)(0.7330i 0.4151(1)3.01()( 2 +++=+++= xxixxxf (17) 7.7 analysis of an arbitrary equation with complex coefficients for all of it’s roots let the equation given be ixiixxf −−+= 23 )1()( (18) coefficients of this equation are all complex. analysis using the usual newton – raphson method to determine it’s possible roots, shows the following pattern of roots convergence given in table 5 below. table 5: solution details of eq.18 xn final roots of eq.18 iterations x=1 1.3002 + 0.6248i 07 iterations x=2 1.3002 + 0.6248i 05 iterations x=-1 -0.3002 0.6248i 10 iterations x=i 0 + 1.0000i 02 iterations x=2i 0.0000 + 1.0000i 06 iterations x=-i -0.3002 0.6248i 04 iterations from table 5, the roots of the equation are 1.3002 + 0.6248i, -0.3002 0.6248i and i. hence, the resulting )6248.03002.0)(6248.03002.1)(( ixixix ++−−− ixiixixxix −−+=−−−= 232 )1())(( analysis is simple, every approximation converges to the nearest root. therefore it as advisable to use fewer approximations than one in the vicinity of every root to ascertain it’s validity in the case of an unknown equation. geometrically locating the roots and applying the above given mechanism can also be helpful. 8. discussion the above examples are arbitrarily considered, with known or partially known roots (eq.1, 9 and 12) and others (eq.14 and 16). the lower order of equations is considered for the following reasons; (a) simple to handle on calculators, because a calculator can allow a limited number of characters in the equation, e.g. mohd yusuf yasin / bibechana 9 (2013) 18-27: bmhss, p.26 (online publication: nov., 2012) casio calculators can allow only 71 characters + 08 extended characters in a function, the “ans” key is treated as one character, i.e. the character “ans” can be typed 79 time; (b) lower order equations are more probable in applications, higher order equations usually turn up systematic, and therefore can be handled with considerations specific to the problem, e.g. poles of butterworth filter are equally spaced on a unit radius circle; (c) purpose here is to delineate the methodology. above equations are analyzed with the help of calculators as per the scheme outlined above. the following remarkable observations are as follows. 1. order of an equation suggests the number of roots, real or complex. 2. in presence of a complex/imaginary root, root determination may face convergence problem, as above in eq.12. root approximation tries to converge to the nearest root. therefore if the initial approximation is in the middle of the two roots, it will oscillate. for example, 3)( 2 += xxf has two roots at x=±√3i. if it is estimated with an initial approximation (±b), and |b| lies in the middle, the root oscillates. this is because the initial approximation is equidistant from the roots. 3. if coefficients of the equation are real, and the equation seems to contain roots complex or imaginary, it may be tried by assuming initial approximations of the form (a±bi) or (±bi), usually the later is better. 4. conjugate initial approximation determines the conjugate roots, usually without any added advantage of process or time. similarly the equation with conjugate coefficients will have conjugate roots. 5. if the equation posses one or more imaginary coefficients, it will have all its roots complex, whereas the equation with one or more complex coefficients may have one or more real roots. for all such analysis, the well known newton raphson method is found extremely suitable and easy to apply in the fields of sciences, engineering and technology for problems of design and analysis where accuracy and reliability are a major concern. this method gives the better convergence to a root, and also because many brands of casio calculator can operate on (a±bi) p , p being an integer, rather than (a±bi)1/p . 9. conclusion in the fields of engineering and technology where numerical methods are extensively involved and usually demand huge computations along with the requirements to maintain reliability and accuracy of the computations, to meet the targets of designs, it is important to optimize computational efforts. many a times equations do appear with complex roots, whose determination is not easy. for such problems these efforts are aimed at facilitating the complex computation and optimizing the exercises and the goals. the calculator tricks presented here can be found useful. also, this effort aims at making things easier for design people who may not always be found willing to write software programs to solve such equations with complex roots. only lower order polynomials are treated here to facilitate the use of calculators with their obvious limits. the manner of analysis remains the same as described here in this work. these tricks can also be adapted to software calculators, being on-line or off-line, for example, web2.0calc [6]. this calculator is quite powerful and can help calculate a lot more complex functions. mohd yusuf yasin / bibechana 9 (2013) 18-27: bmhss, p.27 (online publication: nov., 2012) references [1] richard courant,an elementary approach to ideas and methods, revised by ian stewart, [paperback], oxford university press, new york (1996). [2] erwin kreyszig, advanced engineering mathematics, 5 th edition, wiley eastern limited (1989). [3] mohd yusuf yasin, scientific calculators and the skill of efficient computation, bibechana, 8 (2012) 31-36. [4] users’ guide, fx-82ms/83ms/85ms/270ms/300ms/350ms, http://support.casio.com [5] users’ guide, fx-95ms/100ms/115ms/(912ms)/570ms/991ms/991es, http://support.casio.com [6] web2.0calc, a ready to use software calculator, available online, http://web2.0calc.com/ microsoft word gopi et al(50-59) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal first-principles study of structural, electronic and magnetic properties of co-based quaternary heusler compounds: cofecral, cofetias, cofecrga and comnvas bikram pandey1, ram babu ray2,5, gopi chandra kaphle 3, 4, 5,* 1patan multiple campus, tribhuwan university, lalitpur, nepal 2department of physics, amrit science campus, tribhuwan university, kathmandu, nepal 3central department of physics tribhuvan university, kirtipur, nepal 4condensed matter physics research center, butwal, nepal 5hydra research and policy center, kathmandu, nepal *email: gck223@gmail.com article history: received 21 september, 2017; accepted 13 november, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18344 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract we study the structural, electronic and magnetic properties of co-based limgpdsn-types of quaternary heusler compounds (cofecral, cofetias, cofecrga, and comnvas) using density functional theory (dft) implemented on tight binding linear muffin-tin orbital within atomic sphere approximation (tb-lmto-asa) code. the optimized value of lattice parameter for cofecral, cofetias, cofecrga and comnvas are found to be 5.61a˚, 5.76 a˚, 5.61a˚ and 5.71a˚ , respectively. from the calculation of electronic band structure and spin polarized total density of states (dos), we found that cofecral and cofecrga are spin-gapless semiconductors with half-metallic gap of 0.82ev and 0.25ev respectively. cofetias half-metal (nearly spin-gapless semiconductor) with half-metallic gap of 0.38 ev, and comnvas is found to be nearly gapless half-metal. magnetic moment of these compounds almost obey the slater-pauling rules. all these compounds expected to have high curie temperature which makes them significant for spintroincs/magnetoelectroincs applications. keywords: spintronics; quaternary heusler compounds; spin-gapless semiconductor; gapless-half metal, dft. 1. introduction the major concern of material science is the search of materials and their properties that can be used to enhance the functionality of electronic devices. conventionally electronic devices are based on the transformation of charge of electrons whereas in spintronics, the spin degree of freedom of electrons are added to the conventional charged based electronic devices to make them more enhanced. spintronics is the recently burgeoning field, based on spin-polarized electron transport. it is believed that device based on spintronics can meet the necessities of higher aptitude of data storage, faster data transfer and faster data processing, through assemble of spins, and connection of electron spin to bikram pandey et al. / bibechana 15 (2018) 50-59: rcost p.50 optics for future development of information and communication technology [1, 2]. spin-gapless semiconductors (sgs) and half-metallic (hm) materials are the new classes of materials that are characterized by 100% spin polarization. in spin-gapless semiconductor, up spin band shows zero gap (gap-less) behavior at fermi-level, and down spin band exhibits semiconducting behavior with significant gap at fermi level. in sgss, no energy is required to excite electrons from the valence band to the conduction band. in the case of half-metallic materials, one spin band shows metallic, while semiconducting for the other spin band. both in sgs and hm, electrons as well as holes can be completely spin-polarized, which results in exceptional transport properties. therefore, these materials utilize spin along with the charge of electrons to transmit current. density of states n(e) as the function of energy (e) for spin gap-less semiconductors, half-metallic materials and gap-less half-metals are shown in figure (1) [3, 4, 5]. fig. 1: (color online) schematic representation of density of states n(e) as the function of energy (e) showing half metal (left), spin-gapless semiconductor (center) and spin-gapless half metal (right). red shaded area represents spin up states and blue shaded area represents spin down states. spintronics/magnetoelectronics make some heusler compounds momentous in the scientific research because, not only they bear spin-gapless semiconductor (sgs) and half-metalic properties but also the fundamental properties such as high curie temperature, spin polarization, generalized slater-pauling rule atomic substitution etc.. due to above mentioned reasons we are motivated to go more insight into the quaternary heusler compounds. generally, quaternary heusler compounds have the chemical formula xx'yz, where x, x © and y are different transition metal atoms and z is main group element. the valence of y is lower than the valence of the x' element, and the valence of the x' is lower than the valence of x element. the sequence of the atoms along the face centered cubic (fcc) cube’s diagonal is x-y-x'-z which is energetically the most stable [6, 7]. the concept of spin-gap less semiconductor was first proposed by wang [3] in 2008, that doping of pbpdo2, gap-less semiconductor with transition metal atoms would lead to a sgs based on band-structure calculations. later, kim et al. and choo et al. confirmed this experimentally the electronic structure of mn and co doped pbpdo2 polycrystalline films[8]. several heusler compounds have been reported to be a spin-gap less semiconductor. among the quaternary heusler (limgpdsn-type) compounds that were studied several have been reported as the half-metal and spin-gap less semiconductors. bainsla et al. studied the equiatomic quaternary heusler compound cofecrga, from first-principles calculation, and confirmed its sgs nature experimentally [9]. in 2013, xu et al. examined the band structure of the quaternary heusler compound cofemnsi from of first-principles calculation and predicted as the sgs, which was confirmed experimentally by bainsla et al. in 2015 [9, 10]. the connection between magnetic and electronic properties of half-metallic heusler compounds are given by slater-pauling rule. for the half-metallic full-heusler compounds slater-pauling rule is bikram pandey et al. / bibechana 15 (2018) 50-59: rcost p.51 given by mt = zt 24, where mt is the total spin magnetic moment of unit cell in µb and zt is the total valence electrons [11]. most of the limgpdsn-type quaternary heusler compounds which obey same slater-pauling rule for full-heusler compounds were half metals. in order to explain the origin of half metallic gap and slater-pauling behavior of full-heusler compounds, there have been detailed analysis of hybridization scheme, which is same for the quaternary heusler compounds [12]. in this communication, we are focusing towards some co-based quaternary limgpdsn-types heusler compounds having 26 valence electrons in the search of sgs and to go more insight into their properties using tb-lmto-asa. this is because co based compounds show comparatively high curie temperature and high spin polarization basicaly used for gmr , tmr etc. and modern technological devices. in addition, some earlier researcher reported a semi-empirical rule of valence electrons being 26 or 28 for the sake of searching for sgs among heusler compounds from the comprehensive study of atomic and orbital hybridization scheme. we believe that present work will assist to guide the scope of finding sgs, among limgpdsn-type quaternary heusler compounds having 26 (or 28) valence electrons in the future. number of works have been carried out using tblmto-asa approach in ordered binary alloys [13-14], disordered alloys [15], perovskites [16-17] and heusler alloys [18]. the other motivation or aim is to use tblmto-asa approach on quaternary alloys. this article is organized as follows, section 2 discusses the method and computational details, followed by results and discussion. section 3 contains conclusions followed by the references listed at the end of section after the acknowledgments. 2. methodology and computational details we performed all the calculation using first principles based density functional theory (dft) implemented on tight binding linear muffin-tin orbital within atomic sphere approximation (tblmto-asa) code [19-20]. the partial-potential linearized augmented plane wave is used within atomic spheres which ultimately gives total potential through tail cancellation process [21-22]. minimal basis set parameter is used throughout the calculations. the electronic exchange-correlation function we used is the local density approximation (lda). the lda+u is also implemented whenever we required [23-25] for the calculations. the 8x8x8 numbers of k points meshes are considered for the brillouin zone integration. the core states are taken relativistic where as valence states are taken as semi relativistic nature. the self-consistency calculations are considered to be succeeded when the total energy difference between consecutive iterations is less than 10-6 ryd. per formula unit. 3. results and discussion 3.1 structural stability analysis depending upon the possible site of occupation of y on x, x', y, and z, quaternary heusler alloys with space group f-43 (no. 216) have categorized into y1, y2 and y3-types of structures (collectively named as y-types of structures) [26]. the energy minimization process is carried out, from the spin-polarized energies as the function of lattice parameter, for the all possible y-type of structures to find out most stable structure. we found, from the calculation that the most stable equilibrium structure is y1-type, with atom x, x', y and z locate the position at (0.75 0.75 075), (0.25 0.25 0.25), (0.5 0.5 0.5) and (0 0 0) respectively, shown in figure (1). the spin polarized total energies as the function of lattice parameters for the different possible y-type structure of cofecral are shown in figure (2), which indicate that y1-type crystal structure is most stable and similar results are obtained for cofetias, cofecrga and comnvas respectively. the optimized value of lattice parameter for cofecral, cofetias, cofecrga and comnvas are found to be 5.61 a˚, 5.76 a˚, 5.61 a˚ and 5.71 a˚ respectively. 3.2 electronic band structure and density of states the spin polarized density of states (dos) for cofecral, cofecrga cofetias and comnvas at their most stable equilibrium lattice constant are shown in figure (3). figures show that cofecral and bikram pandey et al. / bibechana 15 (2018) 50-59: rcost p.52 cofecrga are spin-gap less semiconductors. since, these compounds exhibit the finite energy gap at fermi level in spin-down channel, while the fermi level falls within a zero-energy gap in the spin-up channel. furthermore, the extensive studied of the band structure also confirmed it. in the band structure of cofecral for spin up channel, it is seen that bands just touches the fermi-level at symmetric points x and between k and γ in conduction band, while band touches fermi level at symmetric points l and w in valence band, and no bands crossing the fermi level. in spin down channel there is 0.82ev band gap between conduction band and valence band near the fermi level as shown in figure. this confirmed the sgs nature of cofecral. the gap less behavior in spin up band and semiconducting behavior in spin down band, clearly indicates that cofecral is sgs material. present calculations also support the results obtained by xu et al. and k. ozdogan et al. [10, 12] they predicted cofecral as sgs material. in case of cofecrga, band just touches the fermi-level at symmetric points w and k in the conduction band while band touches the fermi-level at symmetric points l in the valence band for spin up band structure and in the spin down band structure, there is 0.25ev band gap, indicating that cofecrga is sgs material as shown in figure. this calculation also support the results obtained by bainsla et al. who predicted cofecrga as sgs from first-principles calculations, and verified experimentally [9, 10]. . fig. 2.: (color online) (a) y1-type of structure for xx'yz heusler compound, red, blue, yellow and green color represents x, x', y and z atom respectively. (b) the spin polarized energies as a function of lattice parameter for the different possible y-types of structure for cofecral. the spin polarized density of states (dos) indicates that cofetias, is half-metal, since the continuous but low dos at the fermi level of spin up channel shows the usual metallic behavior, meanwhile the spin down channel exhibits a semiconducting nature with a gap of 0.38 ev at the fermi level. k. ozdogan et al. [12] also studied the cofetias using fplo method and reported as sgs. the half-metallic nature of cofetias has also been considered by l. xiong et al. [27]. although, semiconducting gap reported by them is 0.18ev. it is believed that the contrast arises from the different electronic band structure calculation methods used in the two studies. the study of spin band structure in detail reveals that a small overlap of band around the fermi level although bands does not cross with each other as shown figure (4c), thus we can conclude that cofetias, is half-metal also possible candidate for sgs i.e. nearly spin-gap less semiconductor. the spin polarized total density of states (dos) indicate that comnvas is a gap less-metallic nature since it shows that almost vanishing of dos at fermi level in spin up channel and continuous dos at fermi level in spin down channel. on the other hand, the study of spin up band structure of comnvas in detail shows that there is a small overlay of band at fermi level in conduction band but bikram pandey et al. / bibechana 15 (2018) 50-59: rcost p.53 do not crossing with valence band which is shown in figure (4d), on this base we can say that comnvas is nearly gap less-half metal. present system consists of three transition metals and one main group element (sp element). the study of atom resolved and orbital resolved partial density of states (pdos) shows that the major contribution in dos is due to the d-orbital of transition metals and the contribution of main group element is almost negligible as shown in figure (3c and 3d). fig (3a): (color online) density of states (dos) of cofecral (left) and cofecrga (right). fig. (3b): (color online) density of states (dos) of cofetias (left) and comnvas (right) . fig. (3c): (color online) atom resolved (left) and orbital resolved (right) partial dos of cofecrga. bikram pandey et al. / bibechana 15 (2018) 50-59: rcost p.54 fig. (3d): (color online) atom resolved (left) and orbital resolved (right) partial dos of cofetias. fig.(4a): (color online) spin up (left) and spin down (right) band structure of cofecral. fig. (4b): (color online) spin up (left) and spin down (right) band structure of cofecrga. bikram pandey et al. / bibechana 15 (2018) 50-59: rcost p.55 fig. (4c): (color online) spin up (left) and spin down (right) band structure of cofetias. fig. (4d): (color online) spin up (left) and spin down (right) band structure of comnvas. 3.3 magnetic moments the unsymmetrical density of states (dos) for spin up and spin down channel clearly indicate that systems under the present study are magnetic materials. the total magnetic moment(mt) of limgsnpd-type quaternary heusler compounds (cofecral, cofetias, cofecrga and comnvas) at their optimized lattice parameter that we calculated are shown in table (1). all the compounds have 26 total number of valence electrons (zt) and calculated magnetic moments almost follow the slater pauling rule mt = zt -24. in order to explain the origin of half metallic gap and slater-pauling behavior of full-heusler compounds, there have been detailed analysis of hybridization scheme, which is same for the quaternary heusler (limgpdsn-type) compounds. the spin-gapless semiconductor, having 26 total number of valence electrons, schematic representation of the energy levels of the spin up and spin down electronic band structure done by k. ozdogan et al. [12] is shown figure (5). table [1]: the calculated equilibrium lattice constant (a), the total spin magnetic moment (mt) in µb and atom resolved magnetic moment with total number of valence electron (zt) of limgsnpd-type heusler compounds (cofecral, cofetias cofecrga and comnvas). xx'yz a(a˚) mx mx' my mz mt (µb) zt cofecral 5.61 0.885 -0.076 1.233 -0.049 1.993 26 cofetias 5.76 1.048 1.031 -0.121 0.040 1.999 26 cofecrga 5.61 0.841 -0.132 1.331 -0.039 2.002 26 comnvas 5.71 1.151 0.444 0.376 0.019 1.986 26 bikram pandey et al. / bibechana 15 (2018) 50-59: rcost p.56 fig. (5): (color online) schematic representation of the energy levels of the up and down spin electronic band structure for the 26 valence-electrons spin-gapless semiconductors. 3.4 charge distribution and hartree potential we plot the hartree potential of cofecral, cofetias cofecrga and comnvas using their space group f-43m (no. 216) at their optimized value of lattice parameter, which support the theory that considered the muffin-tin potential in which the potential is maximum near the core of the atom and almost flat in the interstitial space region as shown in figure (6). this indicates that potential is sharp where the charge distribution is maximum and flat at the interstitial regions. the charge density distribution plot also supports the same. fig. ( 6): (color online) hartree potential (left) and charge density distribution (right) of cofetias. 4. conclusions in conclusion, we study the structural, electronic and magnetic properties of cofecral, cofetias, cofecrga and comnvas, using tblmto-asa based on density functional theory. first, we have found that y1-type structure is most stable structure among the possible y-types of structures through energy minimization process. next, from the detailed study of electronic band structure and spin polarized dos, we have found that cofecral, cofecrga are sgs, with half-metallic band gap of bikram pandey et al. / bibechana 15 (2018) 50-59: rcost p.57 0.82ev and 0. 25 ev, respectively. the cofetias is found to be nearly spin-gapless semiconductor, with half-metallic gap 0.38ev, also possible candidate for sgs, and comnvas is nearly gapless-half-metal. we have also calculated the magnetic moment and found that all the compounds under present study almost follow the slater-pauling rule. finally, we can conclude that all the heusler compound having 26 valence electrons are not sgs. the semi-empirical rule with 26 valence electrons can play a supportive for the possibility of finding sgs in future, which is one of the necessary but not sufficient conditions. acknowledgments this work is partially supported by hrpcn. the authors would like to express gratitude to prof. n. p. adhikari, cdp, tu, kirtipur, kathmandu, nepal and prof. a. mookerjee, snbncbs, kolkota, india for providing tb-lmto-asa package. one of the author b. pandey would like to thank physics for curious brain nepal, a research group, for the valuable discussions during this work. references [1] a. hirohata and k. tankanashi, future perspectives for spintronic devices, j. phys. d: applied. phys. 47(19) (2014) 193001-40. doi.org/10.1088/0022-3727/47/19/193001. 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[27] l. xiong, l. yi, g. y. gao,search for half-metallic magnets with large half-metallic gaps in the quaternary heusler alloys cofetiz and cofevz (z=al, ga, si, ge, sb), j. magn. magn. mater. 360,(2014) 98-103. doi.org/10.1016/j.jmmm.2014.02.050. bikram pandey et al. / bibechana 15 (2018) 50-59: rcost p.59 microsoft word nurapati _70-79_.docx r c o s t n publisher: research council of science and technology, biratnagar, nepal: p. 70 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana first-principles study of solid methane at high pressure nurapati pantha, jagaran acharya, narayan prasad adhikari ** central department of physics, tribhuvan university, kathmandu, nepal *e-mail: mrnurapati@gmail.com **e-mail: npadhikari@gmail.com accepted for publication: december 17, 2014 abstract we study the structural and electronic properties of solid methane of space group p212121 at high pressure. the density-functional theory (dft) based first-principles calculations within the generalized gradient approximations (gga) have been performed by using quantum espresso package. our findings show that the solid methane in orthorhombic structure compresses fast at the first, and then slowly as a function of elevated hydrostatic pressure. the pressure-volume diagram agrees with the available previously reported data up to pressure of around 200 gpa. in orthorhombic structure, solid methane is a wide band gap insulator at low pressures (tens of gpa). the band gap decreases with increase in the pressure. at high pressure (around 900 gpa), the band gap decreases to semi-conductor range (1.78 ev). our results reveal that methane to be metallic above the pressure coverage of the present study which is consistent to the interior of the giant planets. the band gap as a function of pressure (from the present work) agrees well with the previously reported data. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11779 © 2014 rcost: all rights reserved. keywords: density-functional theory; solid methane; high pressure; band gap. 1. introduction methane is an important energy source with a great abundance in nature. it plays a significant role in a planetary physics, being one of the major constituents of giant planets uranus and neptune, and also pluto [1, 2] where it is subjected to high pressure and thousand degrees of temperature [3, 4]. it is anticipated that, methane in both the liquid and solid phases is also present in different outer planets and satellites. methane is also present in earth's mantle and crust at high pressure and temperature, where it is mainly found in the hydrated form forming a methane clathrate structure. thus, the knowledge of h2o-ch4 fluid mixtures throughout the wide range of temperature and pressure can help in understanding thermodynamic models at relevant geothermal conditions [5]. pantha et al./bibechana 12 (2015) 70-79: p.71 methane is the simplest alkane, the main component of natural gas, and is probably the most abundant organic compound on the earth, which makes it an attractive natural gas fuel. it is important from the view of petrology also. in addition, it is also used in industrial chemical processes and may be transported as a refrigerated liquid. gas pipelines, that distribute large amount of natural gas, have methane as principal component. however, being gaseous at normal conditions, methane is difficult to transport from its sources. for the transportation and storage, economical ways, safety and feasibility are always the prime concern. as an alternative technique, adsorption of gases like ch4 and h2o in modified carbon nano-structures have been studied through dft calculations [6-9] in recent time. methane is also a potent greenhouse gas. the biological aspect of methane is also important as its concentration is increasing day by day [10]. we know methane is released in atmosphere during methanogenesis process. furthermore, the knowledge of properties of methane is also important in understanding the abiogenic formation of methane [11, 12]. this increasing concentration of methane has made it necessary and urgent to study its both biological and physical aspects. methane concentration affects tropospheric ozone chemistry, carbon monoxide concentration, and climatic variations, which ultimately affect the human activities and hence, measures should be taken to reduce its concentration. methane is the simplest of all the saturated hydrocarbon compounds. it is tetrahedral molecule with c-h bond 1.09 å and h-c-h bond angle 109.5o in phase without orientational ordering. in spite of the simplicity of its molecular structure, it has a complex and poorly understood phase diagram [1324]. furthermore, depending on the pressure and temperature, different phases are produced due to the degree of freedom of orientations. solid methane also exhibits a wide variety of phases due to orientational ordering. recently hirai et al. [25] has reported wide variety of structures due to difference in orientational ordering ranging from fcc structure at 1.7 gpa to phase a (rhombohedral or tetragonal structure) at 5.2 gpa, and transforms to phase b(cubic or hcp) at 10-18 gpa and further transforms to (cubic or hcp) at 25 gpa. zhao et al. [26] suggested a new monoclinic structure p21/b, with four molecules of methane in a unit cell. this structure is reported to be stable at above 10 gpa upto 90 gpa. also, their calculations show that it is not metallic until 90 gpa. there is more controversy regarding the phase transition of solid methane which has complex phase diagram. the phase diagram of methane is both rich and intricate, and is poorly understood, which needs a careful investigation. as a first step to understanding the rich and poorly understood phase diagram of solid methane we focus on the one of its stable structures, of space group p212121, in the order of gpa of pressures. the structure has been searched by ab-initio calculations, which has also been supported by neutron experiment (at low temperature) for the similar compounds, as mentioned in [27] and references thereby. in the present work, we present first-principles simulations to determine structural changes and electronic properties of solid methane in p212121 space group. the calculations cover a wide range of pressure values (10 gpa to 900 gpa) and reveal the change in cell-dimensions/molecular-volume as well as the band structure of solid methane. the remaining part of this paper is organized as follows. we discuss computational details in section ii, present the results and discussion in section iii, and finally mention conclusions in section iv, before the acknowledgements and references. pantha et al./bibechana 12 (2015) 70-79: p.72 2. computational details we have used plane wave self consistent field (pwscf) implementation of density functional theory (dft) calculations [28, 29] in quantum espresso package [30]. the interaction between the ion-cores and the valence electrons are accounted by the ultrasoft pseudo-potentials. the plane wave basis set with cut off values of 40 ry and 520 ry for wave-functions and charge density respectively, is used through-out the calculations. the exchange and correlations parts of electron-electron interactions are treated by generalized gradient approximation (gga) as suggested by perdew-burke-ernzerhof (pbe) [31]. both the internal (atomic co-ordinates) and external (cell dimensions) parameters of solid methane in orthorhombic unit cell, as described by gao et al., [27] are relaxed for geometrical optimization. the calculations are performed over the first brillouin zone by using the monkhorst-pack scheme with 4× 5 × 8 mesh of k-points. the convergence threshold for self-consistency is considered as 10-7 ry. the structural optimization, within the limitations of standard dft calculations (which assumes zero temperature), has been performed at different pressure values starting from 10 gpa and up to 900 gpa, in the steps of 10 gpa. the structural parameters, like cell dimensions and volume of the unit cell are noted, and compared with the available literature. similarly, band structure calculations at some of the representative pressures are included to specify their electronic properties. 3. results and discussion we have performed variable-cell relaxation of solid methane (in space group p212121) within the dft levels of calculation using gga exchange-correlation functional in quantum espresso package. the unit cell contains four methane molecules in orthorhombic structure, as shown in figure 1. the unit cell of solid methane is compressed through a number of steps (of interval 10 gpa) of hydrostatic pressure up to 900 gpa. the (unit) cell sides of solid methane compress almost by one-third of their original (uncompressed) values a = 7.81 å, b = 7.46 å and c = 5.35 å until reaching up to 50 gpa of pressure (not shown in figure). this implies the high rate of hardening of the structure at low pressures values. at moderate pressures, just above 50 gpa, the rate of compression decreases comparing to that at lower pressures, however, has sufficient space for further compression. within the range of pressure covered in figure 2 (50-900 gpa), we can notice that the cell-sides compress a bit faster at the moderate pressures and become harder and harder for further compression at higher pressures. with pressure, the sides of the unit cell decrease. percentage decrease on the cell sides at the pressure of 200 gpa, with respect to the values at 50 gpa, are found to be 12.84 %, 13.90 % and 12.94 % for sides a, b and c respectively. similarly, the percentage decrease on the cell sides at the pressure of 900 gpa, with respect to the values at 50 gpa, are found to be 30.70 %, 27.73 % and 27.70 % for the sides in same order. at high pressures ( > 200 gpa), the decrease in the cell dimensions is correlated to the length of the sides. as seen from above data, the side with longer length compresses more than the side with shorter ones. due to reduction of the cell-size in all the directions, the original (uncompressed) volume of the unit cell ( 275.75 å3 ) compresses to less than one third of its initial volume (73.17 å3) at 50 gpa. pantha et al fig. 1.: solid methane in orthorhombic structure molecules, and the structure is compressed by hydrostatic (homogeneous) pressure (p). the figure contains two unit cells in every direction (2 fig. 2: compression of cell-dimensions with the elevated pressure. the cell parameters are compressed monotonically in all the directions. pantha et al./bibechana 12 (2015) 70-79: p.73 thane in orthorhombic structure [27]. every unit cell has four methane molecules, and the structure is compressed by hydrostatic (homogeneous) pressure (p). the figure contains two unit cells in every direction (2× 2 × 2 supercell) for the clear illustration. dimensions with the elevated pressure. the cell parameters are compressed monotonically in all the directions. every unit cell has four methane molecules, and the structure is compressed by hydrostatic (homogeneous) pressure (p). the 2 supercell) for the clear illustration. dimensions with the elevated pressure. the cell parameters are pantha et al./bibechana 12 (2015) 70-79: p.74 fig. 3: compression of molecular volume of methane with elevated pressure. the volume decreases faster at lower pressures where as compression becomes slower while moving up towards higher pressures. the black line with open circles represent the values from the present calculations where as red up-triangles represent those taken from the experimental equation of state [32]. to check the pressure-volume relation of the compressed system, we compare the p-v diagram of the present work with that obtained from brich-murnaghan equation of state (eos) [32], ( )                 −      −+               −      = −−− 14 4 3 1 2 3 3/2 0 ' 3/5 0 3/7 0 0 v v b v v v v bp o (1) in eq. (1), b0 is the isothermal bulk modulus at zero pressure, b'0 is the pressure derivative of b0 at zero pressure and (v/v0) is the ratio of the volume at high pressure to that at zero pressure. on comparing our data for pressure-volume values to that obtained in [32] by using experimental eos mentioned in eq. (1), we notice that our calculations agree very well with the reported values (figure 3). to study the effect of elevated pressure on the electronic structure of solid methane, we performed the band structure calculations at various pressure values. the band structures at representative pressures (20 gpa, 200 gpa and 550 gpa) are shown in figure 4. the figures illustrate that solid methane has indirect type of band gap and the magnitude decreases as a function of increasing pressure. to understand the dependence of band gap on pressure, we have estimated the band gap of solid methane at various pressures and presented in figure 5. from figure 5, it is seen that the band gap decreases pantha et al with pressure. due to compression, the distance between different atoms decreases and hence the probability of overlapping of different molecular orbitals increases. the estimated band gap values agree with the previously reported (simulated) values within 20% understood on the difference between the methods used. fig. 4: the band gap decreases with the elevated pressure. figures from left to right represent the band structure calculations at 20, 200 and 550 gpa pantha et al./bibechana 12 (2015) 70-79: p.75 pressure. due to compression, the distance between different atoms decreases and hence the probability of overlapping of different molecular orbitals increases. the estimated band gap values agree with the previously reported (simulated) values within 20%. the slight difference can be understood on the difference between the methods used. the band gap decreases with the elevated pressure. figures from left to right represent the band structure calculations at 20, 200 and 550 gpa respectively. pressure. due to compression, the distance between different atoms decreases and hence the probability of overlapping of different molecular orbitals increases. the estimated band gap values . the slight difference can be the band gap decreases with the elevated pressure. figures from left to right represent pantha et al./bibechana 12 (2015) 70-79: p.76 fig. 5: the band gap decreases with the elevated pressure. the band gap form the present calculations at low pressure agree well with the references and where as deviation increases on increasing pressure. the computed reference values are within 20 % of the present calculations (up to 400 gpa) [27]. 4. conclusions and concluding remarks the structural and electronic properties of solid methane have been studied by using dft levels of calculations in quantum espresso package. the structural analysis shows that the cell parameters of the unit cell compress fast at the first and then a bit slowly as a function of pressure. at higher pressures ( > 200 gpa), the longest cell-side compresses more than the others. also the molecular volume of methane decreases fast at low pressures and slowly at higher pressures. the molecular volumes from the present calculations agree well with the available range of 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9 (2013) 50-58 : bmhss, p.50 (online publication: nov., 2012) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana synthesis and design of laboratory device from proton conducting block copolymer membrane shankar p. khatiwada 1 , amar p. yadav 1 , werner lebek 2 , jean marc saiter 3 , rameshwar adhikari 1,* 1 central department of chemistry, tribhuvan university, kathmandu, nepal 2 institute of physics, martin luther university halle-wittenberg, halle/saale, germany 3 amme-lecap international laboratory ea 4528, université de rouen, 76801 saint etienne du rouvray cedex, france * corresponding author: e-mail : nepalpolymer@yahoo.com article history: received 22 october, 2012; accepted 7 november, 2012 abstract the butadiene units of polystyrene-block-polybutadiene-block-polystyrene (sbs) triblock copolymer were subjected to epoxidation and subsequent sulphonation in order to prepare proton conducting ionomer membrane. the products were characterized by different techniques such as atomic force microscopy, fourier transform infrared (ftir) spectroscopy and electron microscopy. a simple laboratory device was developed to carry out the tests on proton conductance ability of the prepared ionomer membrane. the experiments demonstrated that the prepared membrane excellently performed as proton conducting membrane. keywords: block copolymer; idation; sulphonation; ftir spectroscopy; electron microscopy; proton conducting membrane 1. introduction block copolymer molecules self-assemble in the melt as well as in the solid state into a large variety of periodic nanostructures through intra-molecular phase separation. the periodicity of these structures lies between the 10-100 nm which enables precise control of their mechanical properties over the wide range [1,2]. styrenic copolymers, such as polystyrene-block-polybutadiene-block-polystyrene (sbs) and polystyreneblock-polyisoprene-block-polystyrene (sis) triblock copolymers constitute an important class of thermoplastic elastomers [1-3]. both sbs and sis are non-polar and nonconducting polymers. however, sometimes it is useful to increase their molecular polarity by inserting some functional groups for several specific applications. also the functionalization of the copolymer matrix with epoxy group and s. p. khatiwada et al. / bibechana 9 (2013) 50-58 : bmhss, p.51 (online publication: nov., 2012) fabricating the blends with metal compounds leads to the formation of a novel conducting materials [4]. further, the unique properties arise in such nanostructured polymers by incorporating functional groups into polymers via sulfonation. these features have led to an exploration of different applications for sulfonated block copolymers, such as in ion exchange resins, batteries, sensors etc. [5-7]. the aim of present work is to chemically modify an sbs triblock copolymer in such a way that it performs as a flexible conducting ionomer membrane that may be useful in sustainable fuel cell applications. it is further aimed at developing a simple laboratory tool to demonstrate the ability of the prepared ionomer film for ion conductivity. 2. experimental section materials the polymer used in this work was polystyrene-block-polybutadiene-block-polystyrene (sbs) triblock copolymer (commercial name: kraton d1184 cs) with 70 wt. % polybutadiene and having weight average molecular weight (mw) of 310,000 g/mol. toluene (99%), formic acid (85%), polyethylene glycol (peg-400) and hydrogen peroxide (30%-w/v), methanol (99.5%), sodium bisulphite (nahso3), sodium bicarbonate (nahco3), tetraethyl-ammonium bromide (teab), n-n dimethyl aniline (dma) and different inorganic compounds were purchased from local market and used as received. synthesis of epoxidized block copolymer (esbs) the sbs block copolymer was epoxidized to different degrees following the standard procedures discussed in literature [8-10]. the epoxidation reaction is described in scheme 1. h c o oh h2o2 h c o o o h h2o formic acid hydrogen peroxide performic acid hcooh/h2o2 o butadiene unit epoxide unit scheme 1. scheme of epoxidation reaction of styrene/butadiene block copolymer; the butadiene block undergoes chemical modification resulting in epoxide groups. the mass fraction of epoxy groups of epoxidized polystyrene-block-polybutadiene-block-polystyrene (esbs) block copolymer was determined by directly titrating the hcl-acetone (1:80 ratios by volume) solution of the polymer by standardized methanolic caustic soda solution [10]. preparation of sulphonated block copolymer (sbcp) ionomer esbs sample having 80% epoxidation level was dissolved in toluene to prepare 10% (mass by volume) solution and subsequently sulphonated using tetraethyl ammonium bromide (teab) as phase transfer catalyst and dimethyl aniline (dma) as ring-opening catalyst in presence of nahso3 and na2so3 solutions 11. the synthetic procedure is illustrated in scheme 2. the specimen of each sample was prepared by solution casting using toluene as solvent. the sample was dissolved in the solvent to make its 5 % solution and poured into a petri dish. the solvent was allowed to evaporate slowly at room temperature (approximately 25 ºc) to form a uniformly thick films. the resulting film was dried to constant weight. additionally, nanocomposite film with 5 wt.-% organically modified layered silicate s. p. khatiwada et al. / bibechana 9 (2013) 50-58 : bmhss, p.52 (online publication: nov., 2012) e poxide unit o c c o h o s o n a + o sulphonic group na2so3/nahso3 scheme 2. scheme showing the formation of ionomer from esbs through ring opening reaction (nanofil 5, südchemie, munich) was also prepared using the same procedure for polymer/filler mixture. test of ionomer as proton conducting membrane in order to perform the laboratory test for proton conductivity through the ionomer film, a simple cell having two compartments was designed, those being separated by the ionomer membrane. during the experiment, the ionomer membrane having 25% sulphonation of available epoxy groups was taken to separate the two half cells. both the cells were provided with sulphuric acid solution (2m h2so4 in 20 ml of distilled water). the h+ concentration of one of the compartments was varied by the progressive addition of concentrated sulphuric acid into it and keeping the concentration of another compartment constant. the solution was thoroughly mixed and the overall cell potential was measured by completing the circuit and recording the change in potential caused by variation in concentration of h+ ion in the half cells with the aid of a digital multimeter. the device thus constructed represents a concentration cell whose total electromotive force (emf) changes with the variation in electrolyte concentration of the half cells. the cell emf, which depends upon the acid concentration difference in the half cells, will be given by the corresponding nernst equation: b a cell ][h ][h ln f rt e + + = (1) where the symbols have usual meanings. characterization techniques the morphological details of the sbs copolymer was inspected by means of tapping mode atomic force microscopy (afm, multimode, digital instruments, santa barbara, ca) using the surface of a thin film. scanning electron microscopy (sem) (jsm 6300, jeol) was used to visualize the structural details of the ionomer samples using freshly cryo-fractured surfaces. the fracture surface was sputtered coated with thin gold film to avoid charging and irradiation damage during the sem inspection. fourier transform infrared (ftir) spectroscopy and transmission electron microscopy (tem) were used for the characterization of the structure and morphology of the sample. ftir spectra were collected by a perkin elmer ftir 2000 spectrophotometer in atr mode by collecting and averaging 32 scans over a range of 400 cm-1 4000 cm-1 at a resolution of 4 cm-1. thermal studies were performed by means of thermogravimetric analysis (tga) using tga 209 balance (netzsch, germany) in nitrogen atmosphere from 10 to 250 °c at a heating rate of 10 °c/min. s. p. khatiwada et al. / bibechana 9 (2013) 50-58 : bmhss, p.53 (online publication: nov., 2012) 3. results and discussion characterization of block copolymers morphology and degree of epoxidation fig. 1 presents the afm phase image of thin film of the block copolymer used in this study. the film was prepared by dip coating technique following by vacuum annealing at 120 °c for 24 hours. fig. 1: lower (left) and higher (right) tapping mode afm phase image of sbs triblock copolymer used in this work. the morphology of the pristine copolymer comprises ordered cylindrical domains of polystyrene (bright appearing in the phase image) dispersed in the matrix of polybutadiene (dark appearing in fig. 1), the latter being the majority component of the block copolymer. the chemical modification intended in the present work will take place in the polybutadiene matrix. hence, it may be expected that, in particular, the matrix property of the copolymer may be modified. the degree of epoxidation is defined as the percentage of repeating units of the block copolymer that has been epoxidised. epoxidation process was conducted several times by varying the reaction times at room temperature (about 25 ºc) and the extent of epoxidation was determined. the results are presented in fig. 2. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.0 0.2 0.4 0.6 0.8 1.0 e p o x y v a lu e , e t im e, t (h r) fig. 2: plot of epoxy level of the block copolymer as a function of time. s. p. khatiwada et al. / bibechana 9 (2013) 50-58 : bmhss, p. 54 (online publication: nov., 2012) initially, the epoxy level remains zero, as expected. after half an hour, the epoxy level reaches over 0.2 (i.e., 0.2 equivalent mole of sbs is converted to esbs). the sbs to esbs conversion increases rapidly under given condition and reaches maximum of about 90% conversion after 2 hours after which epoxidation content practically levels off. the attempts were also made to carry out the epoxidation reactions at higher temperatures up to 50 ºc. however, the output was not satisfactory as the solvent evaporated rapidly making it difficult to handle the polymer solution towards favorable yield. the ftir spectra of bcp, esbs and ssbs (ionomer) are compared in fig. 3(a,b). a part of the spectrum of interest in fig.3a has been magnified in fig. 3b. the peak at 910 cm-1 is characteristic of the c=c linkages present in the butadiene units of the block copolymer and corresponds to the trans -c=c double bonds vibrations of 1,4-polybutadiene [11,12]. 4000 3500 3000 2500 2000 1500 1000 500 esb s ion om er t ra n s m it ta n c e ( a .u .) w avenu m b er (cm -1 ) s b s a 1800 1500 1200 900 600 1158 1218 1072 734 1450 esb s ionom er t ra n s m it ta n c e ( a .u .) w avenum ber (cm -1 ) sbs 910 b fig. 3: ftir spectra of different specimens (sbs, esbs and ionomer) investigated in present work; a part of spectrum given in top has been magnified at the bottom figure. s. p. khatiwada et al. / bibechana 9 (2013) 50-58 : bmhss, p.55 (online publication: nov., 2012) in the spectrum of esbs, additional peaks, not present in the sbs copolymer, appear. among them, the peaks centered at 734 cm-1, 1072 cm-1 and 1158 cm-1 can be assigned to the epoxy ring stretching [8,11] and attest the insertion of epoxy groups in the block copolymer leading to the formation of epoxidized esbs. in case of ionomer film, those peaks disappear and a distinct peak centered at 1218 cm-1 appears indicating the sulfonation of the esbs into its sulphonated version (i.e., ssbs). 4 µm 20 µm a b fig. 4: lower (top) and higher (bottom) magnifications of scanning electron micrographs of the sulphonated sbs ionomer. unlike literature reports in similar systems, no remarkable absorption peak was found around 1,725 cm-1 implying the absence of the side reactions leading to the formation of carbonyl (–co) group. however, peaks around 3,500 cm-1, indicates the presence of hydroxyl (–oh) groups, which might have resulted from moisture and residual methanol used in the coagulation of the epoxidised products [13]. scanning electron micrographs of different magnification of the ssbs ionomer is presented in fig. 4. the micrographs depict a characteristic morphology of an elastomeric material (or rubber) with flat areas over a wide range. however, on the fracture surface, small islands of irregular shapes appear to be embedded suggesting that there is a sort of phase separation in the ionomer sample. let us recall the fact that only approximately 25% of the butadiene units of the sbs were converted into the epoxidized units which were later sulphonated. the possible reason for segregation of different components as indicated in fig. 4 could be the incompatibility of the sulphonated copolymer with the neat matrix. similar behavior was also observed in acrylated styrene/isoprene based triblock copolymer [13]. s. p. khatiwada et al. / bibechana 9 (2013) 50-58 : bmhss, p .56 (online publication: nov., 2012) 100 200 300 400 500 600 0 10 20 30 40 50 60 70 80 90 100 ionomer nanocomposite ionomer sbs m a s s ( % ) temperature (°c) esbs fig. 5: thermogravimetric plots of different specimens studied in this work compared with a nanocomposite of the ionomer with 5 wt.-% layered silicate. thermal characterization by thermogravimetric analysis the thermal stability is an important property of materials which primarily depends on the nature of the materials, chemistry of the constituents and the processing history. most of the organic compounds degrade at lower temperatures compared to the inorganic compound. thermogravimetric analyses (tga) show that sbs and esbs polymers are not much different with respect to the thermal stability, both of them showing mass loss process beginning at 300 ºc. fig. 5 shows that sbs and esbs undergo complete degradation at 500 °c. the tga curves show one step decrease in their mass, fig. 5. in ionomer, there is over 20% residual mass due to the presence of ionic –so3na groups which form the tiny ionic aggregates attached to the organic mass, possibly responsible for the stability of the ionomer. similarly, upon addition of 5 wt.-% nanofiller such as nanofil-5 to the ionomer, the residual mass again increased. the reasons of these enhancements in residual masses are not well understood; and more experiments are required to clarify these issues. laboratory test of ionomer films as proton conducting membrane as mentioned in the experimental section, a simple device was constructed to test the ability of the ionomer film as proton conducting membrane. the results are shown in fig. 6, in which the variation of the cell emf as a function of h+ ion concentration in one of the cell compartments is plotted. the emf increases gradually (shown by filled symbols in fig. 6) with the increase in the h+ ion concentration, as may be expected to the concentration cell. in order to evaluate the reproducibility of the results, similar sets of experiments were performed using the polymer membrane with 50 and 100% sulphonation (results not shown here). for all the experiments, nearly identical results were observed on using agar-agar gel based salt bridge (see the data shown by open symbols in fig. 6) instead of the membrane. these observations demonstrate s. p. khatiwada et al. / bibechana 9 (2013) 50-58 : bmhss, p.57 (online publication: nov., 2012) 0.0 0.4 0.8 1.2 1.6 2.0 140 160 180 200 220 240 260 c e ll e m f ( m v ) volume of h2so4 added (ml) fig. 6: variation in total cell potential due to change in the concentration of h+ ions in cell b presented in fig. 3; the full symbols stand for the potential measured with ionomer membrane while open symbols represent the values measured with salt bridge. that there is an unhindered flow of the h+ ions from one compartment of the cell to another through the ssbs ionomer membrane thus confirms its proton conducting ability of the ssbs ionomer film. 4. concluding remarks the commercially available polystyrene-block-polybutadiene-block-polystyrene (sbs) triblock copolymer was subjected to epoxidation reaction using performic acid generated in situ as a result of reaction between formic acid and hydrogen peroxide. the products were characterized by different techniques such as ftir spectroscopy, electron microscopy. the esbs was successfully modified into different ionomers. the formation of ionomer was characterized by proton conductivity measurement. the conductive ionomer was formed due to the presence of -so3h group on which passage of ions through ionomer films took place. ionic conductivity was found to increase with the increase of degree of sulfonation in the ionomer. acknowledgements the authors are thankful to kraton polymers, houston, tx for the supply of block copolymer used in this work. mr. netra lal bhandari, mr. santosh khanal, mr. rajesh pandit and dr. megh raj pokharel are thanked for fruitful discussions and various experimental supports. references [1] i. hamley, the physics of block copolymers, oxford publishers, london (1998). [2] r. adhikari and g. h. michler, progress in polymer science, 29 (2004) 949. [3] g. holden, understanding thermoplastic elastomers,hanser, munich (2000). [4] e. dalas, s.n. koklas, e. vitoratos, s. sakkopoulos, j. materials science letters, 12 (1993) 497. [5] j. p. gouin, c. e. williams, a. eisenberg, macromolecules, 22 (1989) 4573. s. p. khatiwada et al. / bibechana 9 (2013) 50-58: bmhss, p. 58 (online publication: nov., 2012) [6] r. a. weiss, a. sen, c. l. willis, l. a. pottick, polymer, 32 (1991) 1867. [7] t. schultz, s. zhou, k. sundmacher, chemical engineering and technology, 24 (2001) 1223. [8] r. pandit, j. giri, r. lach, w. grellmann, g. h. michler, b. youssef, j. m. saiter, r. adhikari, macromolecular symposia, 315 (2012) 152. [9] j. m. dean, p. m. lipic, r. b. grubbs, r. f. cook, f. s. bates, j. polymer science part b: polymer physics, 39 (2011) 2996. [10] h. li, x. zeng, and w. wu, j. of elastomers and plastics, 40 (2008) 317. [11] b. c. johnson, i. yilgor, c. tran, m. iqbal, j. p. wightman, d. r. lloyd, j. e. mcgarth, j. polymer science: part a: polymer chemistry, 22 (1984) 721. [12] r. pandit, a. berkessel, r. lach, r. adhikari, nepal journal of science and technology, 13 ( 2012) 81. [13] r. adhikari, s. khanal, a. shakya, g. h. michler, b. youssef, j. m. saiter, materials research and innovation, 16 (2012) 356. k. k. mishra et al./ bibechana 14 (2017) 54-65 : rcost p.54 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal thermodynamic, structural, surface and transport properties of zncd liquid alloy at 800 k k. k. mishra1*, h . k. limbu1, b. yadav1, a. k. khan2, i. s. jha1, d. adhikari1 department of physics, mahendra morang aadarsh multiple campus, t. u., biratnagar, nepal 2department of physics, r.m. college, saharsa, india *email address: mailkaushalko@yahoo.com article history: received 25july, 2016; accepted 18 september, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15715 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the mixing thermodynamic and structural properties of zn-cd liquid at 800k has been studied using flory’s model. to explain the mixing properties of binary liquid alloys, size factor (ф) and ordering energy (ω) are taken into account. thermodynamic properties like free energy of mixing (gm), activity (a), heat of mixing (hm) and entropy of mixing (sm) and the microscopic properties like concentration fluctuation in the long wave length limit (scc(0)) and chemical short range order parameter (α1) have been calculated. surface property has also been studied with the help of buttler’s model. the viscosity of the melt has been computed from kaptay equation and bbk models. both the viscosity and surface tension of the alloy increase with addition of zinccomponent. keywords: thermodynamic properties; structural properties; surface properties; transport properties 1. introduction zn-cd alloy is a simple eutectic system which has been widely studied due to its low melting point and regular lamellar structure. since cadmium is highly reactive element it has limited applications in its pure state. but the alloys of cadmium have several useful properties for industrial applications. when cadmium is alloyed with zinc, the properties of hardness, wear resistance, mechanical strength and fatigue strength are significantly improved. cadmium and cadmium based alloys is the subject of both theoretical and experimental research studies [1-6]. zinc–cadmium alloys are used as solders at medium temperature which provide excellent corrosion resistance joints on most metals. devices with such superior strength joints can work in high vibration http://nepjol.info/index.php/bibechana mailto:mailkaushalko@yahoo.com http://dx.doi.org/10.3126/bibechana.v14i0.15715 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ k. k. mishra et al./ bibechana 14 (2017) 54-65 : rcost p.55 (online publication: dec., 2016) and high stress applications in electronics, lighting and electrical products. moreover, use of cadmium in electroplating as in cyanide bath poses problems of environmental concern because cadmium is toxic. zncd alloys can be used in dry electroplating and can be a safer potential substitute for cadmium. in metallurgical science, the study of mixing properties of liquid alloys is important because a good knowledge of their mixing properties in the liquid state is necessary for preparation of desired materials. surface properties are required to understand the surface related phenomena such as corrosion, wetting characteristics of solders and kinetics of phase transformation. transport properties such as viscosity and diffusivity of metals in the liquid state are required for many metallurgical processes and heterogeneous chemical reactions. many researchers [7-12] have been working with several models to explain the mixing properties of binary liquid alloys. the alloying behavior of binary liquid alloys can be studied theoretically by computing thermodynamic, structural, transport and surface properties of alloys in the liquid state. the mixing behavior of binary liquid has been explained by several theoreticians of the basis of several models [13-19]. in this work we have used flory’s model [19, 20] to explain the thermodynamic and structural behavior of zn-cd liquid alloy at 800 k. in flory’s model the interaction energy parameter is considered as temperature dependent and is determined by fitting experimental values of thermodynamic functions at different concentrations. 2. formalism 2.1 thermodynamic function 2.1.1 free energy of mixing flory’s model [19] is found to be the best applicable for the determination of thermodynamic and microscopic properties of those alloys which has greater size mismatch. homogenous solution of binary liquid alloy a-b consists of ca (≡ c) mole of a and cb {≡ c(1-c)} mole of b respectively, where ca and cb are the mole fractions of a (≡ zn) and b (≡ sn) in the binary liquid solution of a and b. thus free energy of mixing of those alloys whose constituent atoms differ widely in sizes can be expressed as [19] 𝐺𝑀 = 𝐺(𝑖𝑑𝑒𝑎𝑙) + 𝐺(𝑠𝑖𝑧𝑒) + 𝑐(1 − 𝑐)𝐺(𝜔) (1) where, 𝐺(𝑖𝑑) = [𝑐𝑙𝑛𝑐 + (1 − 𝑐)ln⁡(1 − 𝑐)]𝑅𝑇 (2) g (size) and g (ω) are contributions due to the size effect and the interchange energy (ω) respectively. from flory’s model [19], we have 𝐺(𝑠𝑖𝑧𝑒) = 𝑅𝑇[𝑐𝑙𝑛(1 − 𝛽) − ln⁡(1 − 𝛽𝑐)] (3) 𝐺(𝜔) = 𝑐(1 − 𝑐)𝜔 (1 − 𝛽𝑐)⁄ (4) 𝛽 = 1 − 1/𝛷 (5) with𝛷 = 𝜗𝐵/𝜗𝐴 where⁡𝜗𝐴and 𝜗𝐵are atomic volumes of the pure species a and b respectively [20] here ϑzn =ϑm [1+𝛼p (t-tm)] and ϑcd = ϑm [1+𝛼p (t-tm)] (6) where, ϑm = atomic volume at melting point k. k. mishra et al./ bibechana 14 (2017) 54-65 : rcost p.56 (online publication: dec., 2016) tm = melting temperature and 𝛼p = volume coefficient at constant temperature then the expression for free energy of mixing is given by gm = ⁡rt⁡[c⁡ln⁡c + (1 − c)ln(1 − c) + ⁡c⁡ln(1⁡– ⁡β) − ⁡ln(1⁡– ⁡βc)] + 𝜔𝑐(1−𝑐)⁡ (1−𝛽𝑐) (7) 2.1.2 chemical activity (a) the activity (aa) of the element a in the binary liquid alloy is given as 𝑅𝑇𝑙𝑛𝑎𝐴 = 𝐺𝑀 + (1 − 𝑐) 𝜕𝐺𝑀 𝜕𝑐 (8) from equation (1) and (8), we get 𝑙𝑛𝑎𝐴 ⁡⁡= ⁡𝑙𝑛⁡[𝑐⁡(1 − 𝛽)⁡𝜂(𝑐)] ⁡⁡+ 𝛽(1 − 𝑐)⁡𝜂(𝑐) ⁡+⁡(1 − 𝑐)2𝜂2(𝑐)𝜔/𝑅𝑇 (9) where, 𝜂(𝑐) = 1 (1 − 𝛽𝑐)⁄ 2.1.3 entropy of mixing (sm) the temperature derivative of gm provides an expression for integral entropy of mixing 𝑆𝑀 = −𝑅𝐺(𝑖𝑑) − 𝑅𝐺(𝑠𝑖𝑧𝑒) − 𝑐(1 − 𝑐)𝜂(𝑐)𝜕𝜔 𝜕𝑇 + 𝑅𝑇𝑐(1 − 𝑐)𝜂(𝑐) ⁡⁡×⁡ [𝛽/(1 − 𝛽) − 𝑐𝜂(𝑐)𝜔/𝑅𝑇] ∂𝛽/ ∂𝑇 (10) where, 𝜕β/𝜕t =(𝛼b –𝛼a).𝜗𝐴/𝜗𝐵and𝜂(𝑐) = 1 (1 − 𝛽𝑐)⁄ where, 𝛼a and 𝛼b are the coefficients of thermal expansion of pure species a and b respectively. 2.1.4 heat of mixing (hm) the heat of mixing can be obtained from equation (1) and (10) from standard thermodynamic relation, 𝐻𝑀 𝑅𝑇 = 𝑆𝑀 𝑅 + 𝐺𝑀 𝑅𝑇 (11) 𝐻𝑀 𝑅𝑇 = ⁡cln⁡c⁡ +⁡(1 − c)ln⁡(1 − c) + ⁡c⁡ln(1⁡– ⁡β) − ⁡ln(1⁡– ⁡βc) +⁡ 𝑐(1−𝑐)⁡ (1−𝛽𝑐) ⁡ . 𝜔 𝑅𝑇⁡ ⁡⁡− ⁡α(c)⁡– ⁡φ⁡(c) − ⁡⁡ 1 𝑅⁡⁡ 𝑐(1−𝑐)⁡ (1−𝛽𝑐) . 𝜕𝜔 𝜕𝑇 +⁡ 𝑇𝑐(1−𝑐)⁡ (1−𝛽𝑐) . [⁡⁡ 𝛽 (1−𝛽) ⁡− ⁡ 𝑐 (1−𝛽𝑐) 𝜔 𝑅𝑇⁡ ]⁡. 𝜕𝛽 𝜕𝑇 (12) where, 𝛼(𝑐) = [𝑐𝑙𝑛𝑐 + (1 − 𝑐)ln⁡(1 − 𝑐)]andф(𝑐) = [𝑐𝑙𝑛(1 − 𝛽) − ln⁡(1 − 𝛽𝑐)] 2.2 microscopic functions 2.2.1 concentration fluctuation in the long wavelength limit (scc(0)) to study the atomic order of binary liquid alloy it is important to understand the behavior of the long wavelength limit of the concentrationconcentration structure factor (scc(0)) and is given as [10,17,18] 𝑆𝐶𝐶(0) = 𝑅𝑇 ( 𝜕2𝐺𝑀 𝜕𝑐2 )t,p,n (13) the expression for concentration fluctuation in the long wavelength limit is obtained using equation (1) and (13) and is expressed as k. k. mishra et al./ bibechana 14 (2017) 54-65 : rcost p.57 (online publication: dec., 2016) 𝑆𝑐𝑐(0) = 𝑐𝐴𝑐𝐵 [1− 𝑐𝐴𝑐𝐵 (1−𝛽𝑐)3 ⁡{2(1−𝛽) 𝜔 𝑅𝑇 −𝛽2(1−𝛽𝑐)}] (14) the experimental values of concentration fluctuation in the long wavelength limit scc(0) derived from experimental data of the activities of the constituent species of the binary liquid alloys from the relation 1 ,, 1 ,, )1()0(                   npt b b npt a a c a ca c a acscc where aa and ab are the activities of the component of a and b respectively. 2.2.2 short range order parameter (α1) the warren-cowley short range order parameter 𝛼1 can be estimated from the knowledge of scc(0) as 𝛼1 = 𝑠−1 𝑠(𝑍−1)+1 (15) where z= coordination number and 𝑆 = 𝑆𝑐𝑐(0) 𝑆𝑐𝑐 𝑖𝑑(0) 2.3 surface tension buttler assumed the existence of surface monolayer at the surface of a liquid as a separate phase that is in thermodynamic equilibrium with the bulk phase and derived an equation, known as buttler equation [7, 21, 22]. buttler equation for the surface tension, σ of a binary a-b solution at temperature t reads as [7, 21, 22] 𝛤 = 𝛤1 + 1 𝐴1 (𝐺1 𝐸,𝑠 − 𝐺1 𝐸,𝑏) + 𝑅𝑇 𝐴1 [ln(1 − 𝑋2 𝑠) − ln(1 − 𝑋2 𝑏)] = ⁡𝛤2 + 1 𝐴2 (𝐺2 𝐸,𝑠 − 𝐺2 𝐸,𝑏) +⁡⁡⁡⁡ 𝑅𝑇 𝐴2 [ln(𝑋2 𝑠) − ln(𝑋2 𝑏)] (16) where, γ1 and γ2 are the surface tension of the pure component 1 and 2 respectively. 𝐺𝑖 𝐸,𝑠 and𝐺𝑖 𝐸,𝑏 (i = 1,2) are partial excess free energy of component i in the surface and the bulk respectively. the molar surface area of the component i can be computed by using the relation 𝐴𝑖 = 𝐾.𝑁𝐴 1/3 . 𝑉𝑖 2/3 (17) where, k (= 1.091) is geometrical factor for the liquid alloy [23, 24] na is avogadro’s number and vi is the molar volume of the component i. for binary mixture𝑋1 𝑏 + 𝑋2 𝑏 = 𝑋1 𝑠 + 𝑋2 𝑠 = 1, where 𝑋𝑖 𝑠⁡𝑎𝑛𝑑⁡𝑋𝑖 𝑏 are mole fractions of component i in the surface and bulk respectively. r is universal gas constant and t stands for absolute temperature. 2.4 viscosity to study the atomic transport behavior in zn-cd alloys, we have computed its viscosity at 800 k by using kaptay equation and bbk model [24, 25]. 2.4.1 kaptay equation kaptay [24] equation for the viscosity of the binary liquid alloys at temperature t is given as 𝜂 = ℎ𝑁𝐴 ∑ 𝐶𝐾ω𝐾+ω 𝐸 𝐾 ⁡⁡exp⁡[ ∑ 𝐶𝐾𝐺𝐾 ∗ ⁡−⁡𝜃.𝐻𝑀𝐾 𝑅𝑇 ] (18) k. k. mishra et al./ bibechana 14 (2017) 54-65 : rcost p.58 (online publication: dec., 2016) where, h = plank’s constant, na is avogadro’s number, r is the ideal gas constant, ωeis the excess molar volume upon alloy formation, hm is enthalpy of mixing of the alloy, ck (=a,b) represents concentration,ωk represents the molar volume and 𝐺𝐾 ∗ is the gibb’s energy of activation of the viscous flow in pure component k and 𝜃 is a constant whose value is taken to be 0.155±0.015 [25]. 𝐺𝐾 ∗of component k can be calculated from the equation [25] 𝐺𝐾 ∗ = 𝑅𝑇 ln ( 𝜂𝐾ω𝐾 ℎ𝑁𝐴 ) (19) where, 𝜂k is the viscosity of pure component k; is the planks constant. 𝜂k at temperature t can be evaluated by 𝜂𝐾 =⁡𝜂𝑂𝐾⁡ exp [ 𝐸𝑛 𝑅𝑇 ] (20) where, 𝜂𝑂𝐾⁡ is constant (in unit of viscosity) and en is the energy of activation of viscous flow for pure metal (in unit of energy per mole). 2.4.2 budai-benkokaptay (bbk) model the expression for estimation of the viscosity of a multicomponent alloy from bbk model is given by [25] 𝜂 = 𝐴(𝑇∑ 𝑐𝐾𝑀𝐾⁡𝐾 )1/2. (∑ 𝑐𝐾ω𝐾 +ω𝐸 ⁡)⁡𝐾 − 2 3 . exp[(∑ 𝑐𝐾𝑇𝑚,𝑘 − 𝐻𝑀 𝑞𝑅𝐾 ) . 𝐵 𝑇 ]⁡ (21) where, a and b are fitting parameter equal to (1.80±0.39)x10-8 (j-kmol-1/3)1/2 and (2.34±0.20) respectively; ck is the concentration , and mk is the atomic mass of the given component k, q is the semi – empirical parameter equal to q≡25.4±2; ωk is the molar volume of the alloy, and tm,kis the effective melting temperature of the component k given by 𝑇𝑚,𝑘 =⁡ 𝑇 𝐵 ⁡𝑙𝑛 ( 𝜂𝐾ω𝐾 2 3 𝐴𝑀𝐾 1 2𝑇 1 2 ) (22) where ,𝜂k is viscosity of the pure component k. 3. result and discussion 3.1 free energy of mixing to compute the free energy of mixing gm/rt of molten zn-cd as a function of concentration at 800 k, size factor (ф) and energy parameter are required. the interchange energy ω has been calculated from equation (7) with the help of experimental values of gm [26] in the concentration range of czn=0.1 to 0.9 by the method of successive approximation and the value of size factor ф is evaluated by equation (5) and (6) in alloying temperature. in the present work the best fit value of ordering energy (ω) has been found to be 1.085rt. the size ratio (i.e. ф = vcd/vzn) where v stands for atomic volume for the constituent atom in zn-cd alloys at 800k is determined by using equation (5). the value of size ratio is found to be 1.43. using these two input parameters the free energy of mixing gm of zn-cd liquid alloys at 800 k has been computed using equation (7) for concentration range czn =0.1 to 0.9. the experimental values of free energy of mixing are taken from the ref. [26]. k. k. mishra et al./ bibechana 14 (2017) 54-65 : rcost p.59 (online publication: dec., 2016) the plot of computed and experimental values of free energy of mixing with respect to concentration is depicted in fig 3.1. the computed and experimental values of free energy of mixing are in good agreement in entire concentration range. the disagreement between the computed and experimental values is within 6%. the theoretical values is minimum around czn = 0.4 (i.e. gm/rt = -0.3919) while the experimental values is minimum around czn = 0.5 (i.e. gm/rt = -0.3927). the minimum value suggests that zn-cd alloy in liquid state at 800 k is weekly interacting system. 3.2 activity by putting the input parameters interchange energy (ω) and size factor (ф) in equation (8) and (9), we have computed the activity of zn and cd of zn-cd alloys in molten state at 800 fig. 3. 1: free energy of mixing of zn-cd liquid alloys at 800 k. the solid line represents theoretical values and circle represents experimental values fig.3. 2: activities azn and acd of zn-cd liquid alloys at 800 k. the solid line represents theoretical values and circle represents experimental values. the computed values of activity of both the components of zn-cd alloys at 800 k are in good agreement with the experimental values for whole range of concentration with some discrepancies. for zinc the maximum departure from experimental value [26] of lnazn from experimental value is 9.4% around czn = 0.4 as shown in figure 3.2. 3.3 heat of mixing the heat of mixing of zn-cd liquid alloy at 800 k has been determined by using equation (10). both of the computed and experimental values of heat of mixing are positive in whole range of concentrations. the computed and experimental values of heat of mixing are in reasonable agreement in all compositions. k. k. mishra et al./ bibechana 14 (2017) 54-65 : rcost p.60 (online publication: dec., 2016) there is small negative deviation of computed values from experimental values in the region czn>0.4 whereas small positive deviation has been observed in the region czn<0.4 at czn=0.4. the computed and experimental values are almost same. the graphical comparison between computed and experimental values [26] of heat of mixing with respect to concentration is displayed in fig 3.3. 3.4 entropy of mixing following equation (11) the entropy of mixing of zn-cd alloy in molten state at 800 k has computed. for the computation of entropy of mixing the basic input parameters are interchange energy (ω), size factor (ф) and temperature derivative of ordering energy (dω/dt). for the consistency we have used the same values of these parameters as used in the calculation of free energy of mixing, activity and heat of mixing. the computed and experimental values are found to be in excellent agreement. the disagreement between computed and experimental values is within 1%. the computed entropy of mixing is minimum (i.e.sm/r = 0.7050) at czn =0.5. the computed values of entropy of mixing together with experimental values are plotted as a function of concentration as shown in fig 3.4. fig. 3. 3: heat of mixing of zn-cd liquid alloys at 800 k. the solid line represents theoretical values and circle represents experimental values. fig. 3. 4: entropy of mixing of zn-cd liquid alloys at 800 k. the solid line represents theoretical values and circle represents experimental values. 3.5 concentration – concentration structure factor in long wavelength limit scc(0) the theoretical value of scc(0) of zn-cd liquid alloys at 800 k computed from equation (12) using the same energy parameter ω and size factor ф for the full range of concentration (i.e. czn= 0.1 to 0.9) as used for the computation of free energy of mixing, activity, heat of mixing and entropy of mixing. k. k. mishra et al./ bibechana 14 (2017) 54-65 : rcost p.61 (online publication: dec., 2016) both the computed and experimental values of scc(0)>scc id(0). the plot of computed and experimental values of scc(0) along with the ideal values with respect to concentration are also depicted in figure 3.5. the computed values of scc(0) are in good agreement with the experimental values in entire range. the disagreement between the computed and experimental values is within 12%. the theoretical value is maximum at czn= 0.6 (=0.6407), but the experimental value is maximum at czn = 0.5 (=0.5522). the scc(0) is used to understand the nature of atomic order in binary alloys. any deviation of scc(0) from ideal value is of interest in reflecting the extent of interactions in the mixture. at the given composition if scc(0)<scc id(0), ordering of liquid alloy is expected and if scc(0)>scc id(0), there is tendency of segregation or phase separation. in present case scc(0)>scc id(0) which indicates that zn-cd liquid alloys is segregating in nature. 3.6 chemical short range order parameter (α1) the chemical short range parameter has been computed by using equation (13) as a function of concentration of zn-cd liquid alloys at 800 k for full range of concentrations. in our present work we have computed the value of short range order parameters for different values of coordination numbers (i.e. z= 7,8,10). fig. 3. 5: concentration fluctuation of zn-cd liquid alloys at 800 k. the solid line represents theoretical values, dotted line represents ideal values and circle represents experimental values. fig.3 . 6: chemical short range parameter (𝛼1) of zn-cd liquid alloys at 800 k for different coordination number z= 7, 8 and 10. dotted line represents ideal scc(0). the values of short range order parameter have been found positive in all concentration ranges. the value of short range order parameter has been found maximum at czn = 0.6 in all three coordination numbers. the plot of computed values of zn-cd liquid alloy at 800 k is depicted in fig3.6. k. k. mishra et al./ bibechana 14 (2017) 54-65 : rcost p.62 (online publication: dec., 2016) the knowledge of short range order parameter (α1) provides an immediate insight into the nature of the local arrangement of atoms in the mixture. the minimum possible value of α1 is -1 and it implies complete ordering of unlike atoms pairing at nearest atoms. on the other hand the maximum value of α1 is +1 which implies complete segregation leading to the phase separation and α1=0 corresponding to the random distribution of atoms. figure 3.6 shows that α1 is positive in the entire concentration range (i.e. czn= 0.1 to 0.9) showing that α1 in zn-cd is segregating system of like atoms pairing (i.e. zn-zn and cdcd ) as nearest neighbours. 3.7 surface tension the surface tension of the liquid alloys can be computed using equation (14). the ratio of partial excess gibbs energy in the bulk and that in the surface can be expressed as 𝛽 =⁡ 𝐺𝑖 𝐸,𝑠 𝐺𝑖 𝐸,𝑏 where⁡𝐺𝑖 𝐸,𝑠 and 𝐺𝑖 𝐸,𝑏 are the partial excess free energy in the surface and that in the bulk. the values of excess mixing of the pure componenst are taken from ref. [26]. the value of parameter β has been taken as 0.83 as suggested by different researchers to compute surface tension of liquid alloys [27-29]. we have taken the surface tension of zn-cd and temperature coefficients for pure zn and cd components from the ref. [30]. the surface tension of the pure component at the temperature of study have been computed by the equation 𝛤(𝑇) = ⁡𝛤𝑚 + 𝜕𝛤 𝜕𝑇 (𝑇 − 𝑇𝑚) t=800 k; tm= melting temperature (tm= 692.5 k for zn, and 594 k for cd); 𝜕𝛤 𝜕𝑇 (= -0.17mnm-1k-1 for zn, and -0.26 mnm-1k-1 for cadmium) is the temperature coefficient of surface tension. fig 3. 7: surface tension of zn-cd liquid alloy at 800 k. solid line is calculated surface tension and dotted line is ideal surface tension. fig 3. 8 : viscosity (𝜂) of zn-cd liquid alloy at 800k versus concentration of zn. dotted line represents ideal viscosity, solid line represents bbk and solid with circle represents kaptay. k. k. mishra et al./ bibechana 14 (2017) 54-65 : rcost p.63 (online publication: dec., 2016) the graph shows that the computed surface tension for zn-cd system at 800 k is less than ideal value (= c1γ1 + c2γ2) at all the concentration of zn as shown in figure 3.7 i.e. there is negative departure of surface tension from ideality. it is found that surface tension of zn in zn-cd alloy is increased on increasing the bulk concentration of zn. 3.8 viscosity to compute viscosity of zn-cd alloy at 800 k, the viscosities of the pure components zn and cd at 800 k are required. the viscosity of pure component can be obtained with the help of constants 𝜂ok and e for the metals [31]. we have used kaptay equation (15) and bbk model (16) to evaluate viscosity of the alloy and compared the results as shown in figure 3.8. to calculate the viscosity by kaptay equation enthalpy of mixing (hm), the gibbs free energy of activation of various viscous flow of the pure components (g*) and excess molar volume of the alloy (ωe) are required. the enthalpy of mixing is taken from flory’s model calculations. the value of g* for each component was calculated from equation (17) with knowing the viscosity and molar volumes of pure components. due to lack of experimental data we have taken the volume of ωe to be zero in our calculations for simplicity. 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[31] e. a. brandes and g. b. brook, smithells, metals reference book, reed educational and professional publishing ltd., oxford (1992). http://dx.doi.org/10.1007/bf02655927 http://dx.doi.org/10.1007/bf02655927 microsoft word md yasin _13-19_.doc r c o s t n publisher: research council of science and technology, biratnagar, nepal p. 13 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana simplified approach to dft computation for nonprogrammable scientific calculators mohd yusuf yasin ece department, integral university, kursi road, lucknow, uttar pradesh, india, pin 226026, email: mmyasin@rediffmail.com accepted for publication: december 6, 2014 abstract fourier analysis is an important tool used as it is or it’s different variants in many fields of sciences and engineering. it’s importance is due to it’s simplicity with which it expands a given function in terms of circular or complex exponents. further it is quite versatile to handle many functions of practical interest, specifically, the functions with several mathematical disabilities that are hard to be handled with tools like taylor series. discrete fourier transform (dft) is a form of fourier analysis where the discrete function and it’s transform are both of finite length. this processing requires lot many computations. here in this work a simplified and non programmable calculator based scheme is presented with which one can easily determine the dft of the given function by feeding in the dft equation once and a few presses of the calculator keys. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11681 © 2014 rcost: all rights reserved. keywords: fourier analysis; dft computation; scientific calculator. 1. introduction engineering is so heavily endowed with the mathematics that it may be hard to find out a single topic of mathematics that is never used in any application; engineering and mathematics run side by side and are naturally inseparable from one another. more sophisticated engineering applications usually involve advanced mathematics. engineering point of view is to achieve the solution with a certain tolerances. this is a necessary design parameter that involves a compromise between the efforts required to obtain the final solution and the total time spent in achieving it. bode’s plotting is a popular example, where error at a corner frequency is substantially high (3db maximum), accuracy of the function is sacrificed at the corner, but it pays off by enhancing the speed in estimating the characteristics of a system containing several distinguished poles and zeros, of different types, in just a few steps [1]. optimization of speed and efforts seem to occupy the central place in design and analysis. however, the accuracy is all important and may not be sacrificed every time. non programmable scientific calculators are a handy tool the engineering students usually are equipped with. but it is observed that unskil lful use of the calculator leads to the adoption of yasin./ bibechana 12 (2015) 13-19: p. 14 cumbersome computational procedures, which unfortunately leads to the failure in maintaining interest in computation [2]. here in this work, the discrete fourier transform (dft) computation is presented, which normally demands a good some of mathematical calculations, usually involving complex numbers. computation with complex numbers is as easy a task as the computation with real numbers [3], and hence the dft of a function can also be easily computed. 2. fourier analysis fourier analysis expands a periodic function in terms of the sum of simple circular functions. it finds applications in engineering systems analysis, mathematical analysis, mechanics, audio and video signal processing. it is considered more versatile than taylor series, as it can expand many discontinuous functions of practical interest [4]. different versions of fourier analysis practically exist, for periodic and non periodic functions, which may be continuous or discrete. fourier series is used for periodic functions whereas fourier transforms are used for aperiodic functions. it is of particular importance that when a discrete function of finite sample length is analyzed, the corresponding fourier transform is also discrete. such a function has both the fourier series and fourier transforms similar [5]. let {x[n]}be an aperiodic finite energy sequence of sample length n, x[n] being a discrete function, ‘n’ being integer and is uniformly spaced in time. actually the independent variable n being ‘nt’, t is the time period of sampling function, though t is dropped for the sake of simplicity. a periodic representation of the function x[n] is defined by ∑ −= ∞ −∞=l p lnnxnx )()( (1) fourier series representation of (1) over n samples can be given by the following synthesis – analysis pair. ∑ −≤≤= − = −1 0 2 10)( 1 n n nk n j pk nkenx n c π (2) ∑ ∞<<−∞= − = 1 0 2 )( n k nk n j kp necnx π (3) similarly the fourier transform pair for the finite sequence {x(n)} can be given by. ∑ −≤≤= − = −1 0 2 10)()( n n nk n j nkenxkx π (4) ∑ −≤≤= − = 1 0 2 10)( 1 )( n k nk n j nnekx n nx π (5) comparing the pairs of equations (2) – (3) and (4) – (5), it is evident that the fourier transform of the aperiodic sequence {x(n)} of length n, and its periodically expressed sequence {xp(n)}can be defined by one another, as below: yasin./ bibechana 12 (2015) 13-19: p. 15 knckx =)( (6) this type of analysis requires a set of cumbersome computations as it involves complex numbers. the equations (2 – 5) are in fact n equations each one containing n terms with a weight nk n j e π2 ± but in practical computations, a little manipulation can lead to simpler computations for the above analysis, which can be run on a simple non-programmable calculator. here it is demonstrated through an example, how this can be accomplished with affordable simple equation(s). 6 point analysis of an arbitrary sequence x(n) = {2, 1, -3, 4} can be performed by using equation (4). ∑=∑= = −− = − 5 0 3 1 0 2 )()()( n nkjn n nk n j enxenxkx ππ (7) 5,4,3,2,1,0;4312)( 3 3 2 33 =+−+= −−− keeekx kjkjkj πππ (8) the exponent of (7), could be expressed in calculator syntax. ( )nk nknk jnkj ee 601 3 133 −∠=      −∠=        = −− πππ (9) ( ) 16013 =−∠= − nk nk j e π (10) ( ) ( )m m 601601 −∠=−∠ (11) using equations (9) and (11), equation (8) can be rewritten as fig. 1: points of dft computation uniformly placed on the unit circle, alongwith the points of data of the function x(n) mapped to the circle. ( ) ( ) ( ) kkk kx kkk 1801*41201*3601*12 141201360112)( −∠+−∠−−∠+= −+−∠−−∠+= (12) o601 −∠ o2401 −∠ o1801 −∠ o1201 −∠ o3001 −∠ o01∠ )0(x )1(x)2(x )3(x )4(x )5(x yasin./ bibechana 12 (2015) 13-19: p. 16 equation (12) can be implemented directly on a calculator, k replaced by a memory, say a, and with modes be set cmplx and deg. once the equation (12) is fed, the press of the key calc asks for the value of “a” and offers the corresponding dft component at a consecutive press of the = key. the result is presented below. { }732.1,464.37,6,464.37,732.1,4)( jjjjkx −+−−= (13) the process to approach equation (12) is still simple and can also be written by considering the fact that the computation points are uniformly distributed over the circle of unit radius by a phase n π2 radians in the π2 phase space. with the help of figure 1, dft equation can be written directly. kkk xxxkx )3001)(5(...)601)(1()01)(0()( ��� −∠++−∠+∠= (14) similarly, the inverse dft (idft) computation is also as simple, and can again be directly written with the help of figure 2, keeping in mind that the weights in the idft equation as follows. fig. 2: idft computation scheme. idft computation points uniformly placed on the unit circle, alongwith the dft mapped on the circle. ( )nnn xxx n nx )3001)(5(...)601)(1()01)(0( 1 )( ��� ∠++∠+∠= (15) perhaps, the equations (14) and (15) are in their simplest possible form. other forms are also possible involving conjugate weights, as the weights corresponding to �60∠ is conjugate to �300∠ and vice versa, and may be incorporated if needed. generalized equations based on the representations of equations (14) and (15) can thus be given as follows. ( ) kn n n nnxkx ∑ −∠= − = 1 0 21)()( π (16) o3001∠ o1201∠ o1801∠ o2401∠ o601∠ o01∠ )0(x )5(x)4(x )3(x )2(x )1(x yasin./ bibechana 12 (2015) 13-19: p. 17 ( ) nn k n kkx n nx ∑ ∠= − = 1 0 3601)( 1 )( � (17) 3. dft computation – schemes and results the procedure of dft computation on casio calculators like fx 991es plus natural v.p.a./m., can be summarized as follows. use of equation (12) or (14) can facilitates to write an equation in calculator syntax for the discrete sequence x(n)={2, 1, -3, 4}. the computation is done in a bit interactive manner as presented in table 1 below. in bold and italic, are the calculator key presses required right from the basic equation and the components of the results are in normal text. aaa ��� 180412036012 −∠+−∠−−∠+ (18) table 1:implementation of equation (18) calc a=? 0 = 4 shift reim j0 calc a=? 1 = 0 shift reim j1.732 calc a=? 2 = 7 shift reim -j3.464 calc a=? 3 = -6 shift reim j0 calc a=? 4 = 7 shift reim j3.464 calc a=? 5 = 0 shift reim -j1.732 hence the result is { }732.1,464.37,6,464.37,732.1,4)( jjjjkx −+−−= . similarly the idft computation can also be done through a similar procedure. thus ( +∠−∠−+∠+ aajaj ��� 180611201)464.37(601*17324 6 1 )ajaj �� 3007321.12401)464.37( ∠−∠+ (19) hence the result of idft computation is x(n) = {2, 1, -3, 4, 0, 0} = {2, 1, -3, 4}. this method is extremely simple, but is not suitable for ordinary scientific calculators. all common calculators do not permit complex computations like those advised in equations (14) (15) or equations (18) (19) for yasin./ bibechana 12 (2015) 13-19: p. 18 powers higher than 3. for example, in casio fx-991w s-v.p.a.m., one can adopt another simple yet elegant method. let n j ea π2 − = , equation (4) can be rearranged as follows. table 2:implementation of equation (19) calc a=? 0 = 2 shift reim j0 calc a=? 1 = 1 shift reim j0 calc a=? 2 = -3 shift reim j0 calc a=? 3 = 4 shift reim j0 calc a=? 4 = 0 shift reim j0 calc a=? 5 = 0 shift reim j0 ))))1()2((...)3(()2(()1(()0()( −+−++++= nxanxaxaxaxaxkx kkkkk (20) use of equation (20) can facilitate to overcome the complex power limitation of a calculator. considering the use of calculator memories a and b, and the cmplx mode, a simple algorithm can be suggested as follows. ba n j n e n j →→−= − ) 2 sin() 2 cos( 2 πππ { ))))1()2((...)3(()2(()1(()0()( −+−++++= kaxkxaxaxaxaxkx baa *= )(kxcalc repeat if 1−≤ nk . } (21) this simple algorithm may be demonstrated on casio calculators like fx-100ms svpam. for 7 point dft computation of the data x(n) = {1, 2, 3, 4}. select the cmplx mode. step by step procedure is as follows. yasin./ bibechana 12 (2015) 13-19: p. 19 initialize bajje j →→−=−= − 78183.062349.0) 7 2 sin() 7 2 cos(7 2 πππ . feed ))43(2(1 aaa +++ = x(1)= -2.0245 j6.2240 rcl a rcl b = ajab →−−= 974928.022252.0 . display ))43(2(1 aaa +++ , = x(2) = 0.3460 + j2.4791 display aab → = -0.9010 j0.4339 display ))43(2(1 aaa +++ , = x(3)= 0.1784 -j2.4220. repeat this and obtain x(4)= 0.1784 + j2.4220, x(5)= 0.3460 j2.4791, and x(6)= -2.0245 + j6.2240. the method is so simple that the dft computation is merely a matter of a minute. idft computation is similar except the initialization of memories for n j e π2 + and each x(k) must be divided by n. unfortunately, stacking in cmplx mode is limited to level 2 only. moreover, the power of complex number is up to only 3, the built-in function. the power may be resolved like 235 .aaa = . combining the stacking and power resolving, the range for dft/idft computation can be easily raised. 4. conclusion the scheme presented above can be applied to real or complex functions both, with the same ease. radix – 2 algorithms popular for dft/idft computation, but these algorithms also get more and more complicated for radix >3. however, the scheme presented here is simple and is radix independent and can be considered as a tool as far as the textual length of the equations (16) or (17) is permissible by a calculator display. for educational purpose, usually small order computations are considered, therefore, the scheme presented here can be a useful method. references [1] j. millman, a. grabel, microelectronics, 2 nd edition, 25 th reprint, india edition,tata mcgrawhill. (2010). [2] m. y. yasin, bibechana 8 (2012) 31-36. http://dx.doi.org/10.3126/bibechana.v8i0.4702 [3] m. y. yasin, bibechana 9 (2013) 18-27. http://dx.doi.org/10.3126/bibechana.v9i0.7148 [4] e. kreyszig, advanced engineering mathematics, 5th edition, john wiley & sons. inc., 5th wiley eastern reprint (1989). [5] john g. proakis, dimitris g. manolakis, digital signal processing: principles, algorithms and applications, 4th edition, pearson education (2007). microsoft word carvaja-gamezl _30-34_.doc r c o s t n publisher: research council of science and technology, biratnagar, nepal p.30 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana quaternions, 2x2 complex matrices and lorentz transformations b. e. carvajal-gámez 1 , i. j. guerrero-moreno 2 , j. lópez-bonilla 2* 1 sepi-escom, instituto politécnico nacional (ipn), av. bátiz, 07738 méxico df, 2 esime-zacatenco, ipn, edif. 5, lindavista, cp 07738 méxico df; *email: jlopezb@ipn.mx accepted for publication: december 9, 2014 abstract we show that the matrix method to construct lorentz transformations permit to deduce the corresponding quaternionic procedure. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11671 © 2014 rcost: all rights reserved. keywords: unitary quaternions; 2x2 complex matrices; lorentz’s matrix. 1. introduction in spacetime an event is represented by ( ) ( )zyxctx j ,,,= , ,3,...,0=j with the metric ( ) ( )1,1,1,1 diag −−−=jrg . if it is necessary to employ another frame of reference, then the new coordinates rx~ are connected with jx via the linear transformation: ,~ r r jj xlx = (1) where the lorentz’s matrix l~ verifies the restriction: ,abb r rja j glgl = (2) because the minkowskian line element must remain invariant under l~ , that is, r r r r xxxx =~~ from (2) we see that l~ has six degrees of freedom, which permits to work with four complex numbers δγβα ,,, such that 1=− βγαδ , then the components of homogeneous lorentz transformation l~ can be written in the form [1-5] (i = √-1): ( ) ( ) , c.c. 2 1 , 2 1 ** 1 0**** 0 0 ++=+++= δγβαδδγγββαα ll carvajal-gámez et al. / bibechana (2015) 30-34: p. 31 ( ) ( ) , 2 1 ,c.c. 2 **** 3 0** 2 0 δδγγββααδγβα −+−=++= l i l ( ) ( ) ,c.c. 2 1 ,c.c. 2 1 ** 1 1** 0 1 ++=++= βγδαδβγα ll ( ) ( ) (3) c.c. 2 1 ,c.c. 2 ** 3 1** 2 1 +−=++= δβγαβγδα l i l ( ) ( ) , c.c. 2 ,c.c. 2 ** 1 2** 0 2 ++=+−= βγαδδβαγ i l i l ( ) ( ) ,c.c. 2 ,c.c. 2 1 ** 3 2** 2 2 ++=+−= δβαγγβδα i ll ( ) ( ) , 2 1 ,c.c. 2 **** 3 3** 2 3 δδγγββααδγβα +−−=+−= l i l where c.c. means the complex conjugate of all the previous terms. therefore, any complex 2x2 matrix: ,1~ det,~ =−=      = βγαδ δγ βα ∪∪ (4) generates one lorentz matrix through (3), or via the expression [6-8]: =         + −+ 3~~2~1~ 2~1~3~~ xxixx xixxx o o ,~ ~ † 321 213 ∪∪         −+ −+ xxixx xixxx o o (5) where: ( ) ,1~ det~det ,~ *† ** ** † ==      = ∪∪∪ δβ γα (6) thus the determinant of (5) implies the invariance of the line element: ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) . 232221223~22~21~2~ xxxxxxxx oo −−−=−−− (7) in the next section, from (5) we shall deduce a quaternionic expression to produce lorentz transformations. 2. lorentz’s matrix via quaternions the matrix (4) can be written in the form [9, 10]: ( ) ( ) ,c.c. 2 1 , 2 1 ** 1 3**** 0 3 +−=−−+= δγβαδδγγββαα ll carvajal-gámez et al. / bibechana (2015) 30-34: p.32 ,~i~ 3322110 σσσ iaiaiaa −−−=∪ (8) being jσ the cayley [11]-sylvester [12]-pauli matrices [13]: , 1-0 01 , 0i i-0 , 01 10 321       =      =      = σσσ (9) with the euler-olinde rodrigues parameters [14]: ( ) ( ) ( ) ( ) , 2 , 2 1 , 2 , 2 1 32 10 δαβγ βγδα −=−= +=+= i aa i aa (10) if we employ the following formal association with the quaternionic units [15]: , iσ , iσ, iσ,~i kji →−→−→−→ 3211 (11) then the properties of the jσ give us the rules of multiplication : ,, ,1 ,ji kikj kj ikji 222 ===−=== (12) besides from (8) it appears the relationship: , ~ 3210 kjia aaaa +++=→∪ (13) where a is a unitary quaternion because the condition 1=βγαδ and (10) imply: , 12 3 2 2 2 1 2 0 =+++= aaaaaa (14) with . 3210 kjia aaaa −−−= (15) therefore, any 2x2 complex matrix (4) has associated a unitary quaternion via (10) and (13). now we shall apply this procedure to each matrix appearing in (5) to obtain its quaternionic version: r→      −+ −+ 321 213 xxixx xixxx o o (16) , ct , 3210 kji kji iziyix ixixixx +++= +++= , ~ , ~ 321 * 0 † kjiaa **** aaaa −−−=→→ ∪∪ thus (5) implies [16-21]: carvajal-gámez et al. / bibechana (2015) 30-34: p.33 ,~ *aarr = (17) which generates the linear mapping (1) and reproduces all the components (3) because (10) gives the link: ;, ,, 3012 1230 iaaiaa iaaiaa +=−= −−=−= δγ βα (18) then (17) is a quaternionic factory to elaborate lorentz transformations. references [1] j. aharoni, the special theory of relativity, clarendon press, oxford (1959). [2] j. l. synge, relativity: the special theory, north-holland pub., amsterdam, chap. 4, sec. 11. (1965) [3] p. j. greenberg and j. p. knauer, stud. appl. math. 53 (1974) 165. [4] j. lópez-bonilla, j. morales and g. ovando, bull. allahabad math. soc. 17 (2002) 53-58. [5] z. ahsan, j. lópez-bonilla and b. man tuladhar, j. of advances in natural sciences 2, no. 1 (2014) 49-51. [6] e. cartan, bull. soc. math. de france 41 (1913) 53-96. [7] o. veblen, proc. nat. acad. sci. usa 19 (1933) 462-474. [8] w. rindler, am. j. phys. 34, no. 10 (1966) 937-942. http://dx.doi.org/10.1119/1.1972301 [9] e. piña g., am. j. phys. 51, no. 4 (1983) 375-379. http://dx.doi.org/10.1119/1.13253 [10] g. f. torres del castillo, 3-d spinors, spin-weighted functions and their applications, birkhäuser, boston (2003) p. 10. http://dx.doi.org/10.1007/978-0-8176-8146-3 [11] a. cayley, london phil. trans. 148 (1858) 17-37. [12] j. sylvester, johns hopkins circ. 3 (1884) 7-9. [13] w. pauli, zeits. für physik 43 (1927) 601-623. http://dx.doi.org/10.1007/bf01397326 [14] r. e. roberson, aiaa journal 6 (1968) 5-71. [15] j. kronsbein, am. j. phys. 35, no. 4 (1967) 335-342. http://dx.doi.org/10.1119/1.1974074 [16] l. silberstein, phil. mag. 23, no. 137 (1912) 790-809. http://dx.doi.org/10.1080/14786440508637276 carvajal-gámez et al. / bibechana (2015) 30-34: p.34 [17] c. lanczos, zeits. für physik 57 (1929) 447-473. http://dx.doi.org/10.1007/bf01340274 [18] c. lanczos, the variational principles of mechanics, university of toronto press, chap. 9, sec. 4 (1970). [19] j. l. synge, comm. dublin inst. adv. stud. ser. a, no. 21 (1972) p. 19. [20] r. penrose and w. rindler, spinors and space-time, vol. 1, cambridge university press, chap. 1, sec. 2 (1984). [21] r. penrose, the road to reality, ed. jonathan cape, london, chap. 24, sec. 6 (2004). i thanks to reviewers we greatly appreciate the voluntary contribution that each reviewer gives to the journal. we hope that our reviewers will co-operate us by reviewing the articles submitted to bibechana in future also. reviewers for volume 13 (2016) shohail murad nicola seriani alev doğan subrata kr. mandal b.p. singh robert gardner m.s. pukhta martin lopez corredoira yongde d. meng aditya m. vora y. kimura daniel s. simson e. a. salehpoor binod bhattarai m. y. ukirmizi jagadish bhattarai p. r. vajeeston nirajan sharma a. firoozabadi p.r. pradhan t. bartels-rausch shobha kant lamichhane damodar thapa chheti microsoft word aryal _114-127_.docx r c o s t n publisher: research council of science and technology, biratnagar, nepal p.114 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana a study of co-existence between the hubble flow and the random alignments of spin vectors of sdss galaxies shiv narayan yadav et al. 1 , walter saurer 2 , binil aryal 1* 1 central department of physics, tribhuvan university, kirtipur 2institute of astrophysics, innsbruck university, innsbruck, austria *e-mail: binil.aryal@uibk.ac.at accepted for publication: december 19, 2014 abstract we present a study of spin vector orientation of 14,118 sdss (sloan digital sky survey) galaxies having redshift in the range 0.19 to 0.20 (radial velocity 57,000 km/s to 60,000 km/s) with respect to galactic coordinate system using 7th data release (2008, october). these galaxies were observed through sdss telescope of apache point observatory located at new mexico, usa. the photometric database is made available through our collaboration with institute of astro-particle physics, innsbruck university, austria. we used the `godlowskian' method to convert two dimensional data to three dimensional galaxy rotation axes. our intension is to find out non-random effects in the spatial orientation of galaxies and to check redshift dependence. the expected isotropy distribution curves are obtained by removing the selection effects and performing a random simulation method. the observed and expected polar and azimuthal angle distributions are compared by using three statistical testschi-square, auto-correlation and the fourier. it is found that the spatial orientation of galaxies tend to be oriented randomly with respect to the galactic coordinate system, supporting hierarchy model of galaxy evolution. in few cases we noticed a preference, probably due to the gravitational shearing or tidal effects in the large scale structure. in general, redshift is found to be independent of orientation. hence, a very good correlation between the hubble flow (redshift) and the random alignments of spin vectors of sdss galaxies is noticed. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11787 © 2014 rcost: all rights reserved. keywords: supercluster – galaxies; evolution – galaxies; statistics – galaxies; general -astronomical databases. 1. introduction evolution and distribution of galaxies is closely related to the physics of the early universe. the universe was very violent in its early epochs, and galaxies grew quickly, evolving by accretion of smaller mass galaxies. the result of this process is left imprinted on the distribution of galaxies in the nearby universe. galaxies are not isolated objects in space; rather, galaxies are distributed in great cosmic waves of filaments throughout the universe [1]. we can study galaxy evolution by observing yadav et al./bibechana 12 (2015) 114-127: p. 115 the galaxy population at different redshifts since the light from high-redshift galaxies was emitted when the universe was younger. actually, high-redshift galaxies are the progenitors of present-day galaxies, and any changes in the number density or intrinsic properties of galaxies with redshift give us a direct window on the formation and evolution of the galaxy population. these days with the help of large telescope we can observe galaxies out to redshift beyond six, making possible for us to probe the galaxy population back to a time when the universe was only 10% of its current age. the spin vector distribution is a property of galaxies in clusters for which theories make different predictions. the `pancake model' [2,3], predicts that the spin vectors of galaxies tend to lie within the cluster plane. according to the `hierarchy model' [4], the directions of the spin vectors should be distributed randomly. the `primordial vorticity theory' [5,6] predicts that the spin vectors of galaxies are distributed primarily perpendicular to the cluster plane. these three theories are contradictory as their predictions are completely as different from each other. true spatial orientation of angular momentum of galaxies in the large scale structure is one of the most effective ways of testing the galaxy formation scenarios. li (1998) model predicts that the global rotation of the universe provide angular momentum to the large scale structure [7]. according to this model, galaxies form in a rotating universe, and acquire angular momentum through global rotation. godlowski et al. (2003) showed that li model predicts the existence of a vanishing angular momentum [8]. their prediction was observationally tested by several authors [9-18] and found the vanishing angular momenta for less massive structures (galaxy groups, poor galaxy clusters, etc) and non-vanshing angular momenta for larger structures (compact groups, rich galaxy clusters, etc). therefore, it is essential to probe the angular momenta of galaxy clusters directly based on dynamical analysis. study of the evolution of galaxies in the large scale structure is vague and fascinating. so, in order to accomplish our work we have made certain objectives, which are: (a) to test homogeneity and isotropic nature of the universe. (b) to study the preferred alignment of the spin vectors of sdss galaxies using `position angle inclination' method [19]. (c) to test the galaxy evolution models, namely primordial vorticity theory, pancake theory and hierarchy theory. (d) to study the reliability of galactic co-ordinate system while studying the orientation of distant galaxies. (e) to perform numerical simulation by generating 107 virtual galaxies in order to find the expected distribution of angular momentum vectors of galaxies. in the present work we are interested to work on sdss (7th data release) database of galaxies that have radial velocity in the range 57,000 km/s to 60,000 km/s (0.19 < z(redshift) < 0.20). we are interested to check whether redshift dependence exist concerning galaxy orientation or not. 2. data compilation the first redshift survey was the cfa redshift survey, started in 1977 with the initial data collection completed in 1982. more recently, the 2df (two degree field) galaxy redshift survey determined the large-scale structure of one section of the universe, measuring redshifts for over 220,000 galaxies; data collection was completed in 2002, and the final data set was released 30 june 2003. the sloan digital sky survey (sdss), is ongoing as of 2015 and aims to measure the redshifts of around 3 million objects. sdss has recorded redshifts for galaxies as high as 0.8, and has been involved in the detection of quasars beyond z = 6 [21]. yadav et al./bibechana 12 (2015) 114-127: p. 116 fig. 1: all sky distribution of galaxies having redshift in the range 0.19 to 0.20 covered by sdss 7 th data release in the galactic co-ordinate system (left). the redshift distribution of galaxies in our database is shown in the right panel. the solid and dashed lines represent expected (average / homogeneous and isotropic) and observed (linear fit / deviation from isotropy) distribution. we use the database of sdss galaxies that have redshift in the range 0.19 to 0.20. these database were downloaded from sloan digital sky survey (sdss) data release 7[20]. there are 14,118 galaxies in the region of interest. figure 1 shows the all sky distribution of galaxies of our database. the apparent distribution of the galaxies is because of the nature of the survey. the redshift distribution of galaxies can be seen in figure 2 (right). the number of galaxies is found to decrease with the redshift. a systematic deviation from the average distribution suggests that the preferred alignments of angular momentum vectors of galaxies are not random. we plotted bin size versus standard error of the database and use basic statistic and obtained the appropriate bin size in order to classify subsamples. we classified total sample into 11 subsamples in order to check deviation from isotropy. 3. godlowskian transformation the angular momentum vectors (or spin vectors) of a galaxy is characterized by two angles: the polar angle (θ) between the angular momentum vectors and a reference plane (here equatorial plane), and the azimuthal angle (φ) between the projection of a angular momentum vectors on to this reference plane and the x-axis within this plane. the detail derivations of the expressions of the angles θ and φ are given in flin & godłowski (1986). when using galactic coordinate system as reference, then θ and φ can be obtained from measurable quantities as follows: bpili cossinsinsincossin ±−=θ (1) ( )[ ]lplbpilbi coscossinsinsinsinsincoscos)(cossin 1 ∓∓+−= −θφ (2) where i is the inclination angle, the angle between the normal to the galaxy plane and the observer’s line-of-sight. the inclination angle can be computed from the formula yadav et al./bibechana 12 (2015) 114-127: p. 117 )*1( )*( cos 2 22 2 q qq i − − = (3) this expression can be used for oblate spheroids [22], suitable for the disk galaxies [23]. here, q and q* represent the measured axial ratio (b/a) and the intrinsic flatness of the galaxy, respectively. the intrinsic flatness of a disk galaxy depends on the morphological type and is taken from heidmann et al. (1971) [24]. hiedmann et al. (1971) showed that the values of q* range from 0.083 for sd spirals to 0.33 for ellipticals. for the galaxies with unknown morphology q*=0.20 is assumed. in the equations (1) and (2) the galactic longitude, latitude and the position angle is represented by l, b and p. 4. numerical simulation we briefly explain the procedure by which selection effects can be removed and obtain the expected isotropic distributions for both θ and φ as recommended by aryal & saurer (2000) [25]. theoretically, the isotropic distribution curve for polar angle is cosine and that for azimuthal angle is the average distribution curve, with the restriction that the database is free from se lection effect. aryal & saurer (2000) suggested that any selections imposed on the database may cause severe changes in the shapes of the expected isotropic distribution curves. in their method, a true spatial distribution of the galaxy rotation axis is assumed to be isotropic. then, due to the projection effects, i can be distributed as ~ sin i, b can be distributed ~ cosb, the variables l and p can be distributed randomly, and the equation (1,2) can be used to calculate the corresponding values of polar (θ) and azimuthal (φ). we run simulations in order to define expected isotropic distribution curves for both the θ and φ distributions. the isotropic distribution curves are based on simulations including 107 virtual galaxies. at first we observed the distributions of l, b, p and i for the galaxies in our samples and distributed by creating 107 virtual galaxies for respective parameters. we use these numbers to make input file and the expected distribution by running simulation in matlab 7.0. the program file is as follows: name of the program _le: polar1 clear all; % making the work place free of memory t=cputime; input(type the name of your input _le: ); delta1 = asin(_cos(i).*sin(b)+ sin(i).*sin(p).*cos(b)); %polar angle delta2 = asin(_cos(i).*sin(b)_ sin(i).*sin(p).*cos(b)); %polar angle eta1 = asin ((_cos(i).*cos(b).*sin(l) + sin(i).*(_sin(p).*sin(b).*sin(l)_ cos(p).*cos(l)))./cos(theta1)); %azimuthal angle eta2 = asin ((_cos(i).*cos(b).*sin(l) + sin(i).*(+sin(p).*sin(b).*sin(l)+ cos(p).*cos(l)))./cos(theta2)); %azimuthal angle delta1 = delta1.*180/pi; % changing to degrees delta2 = delta2.*180/pi; eta1 = eta1.*180/pi; eta2 = eta2.*180/pi; delta=[delta1; delta2]; %polar angle eta=[eta1; eta2]; %azimuthal angle vec=[-90:5:90]; %making 36 bins of 5_ interval (delta n, dx) = hist(delta, vec); %histogram showing polar angle distribution (eta n,dx) = hist(eta, vec); %histogram showing azimuthal angle distributiion delta n = delta n' %placing theta in column matrix eta n = eta n' %placing phi in column matrix sprintf('calculation time: %f seconds ',cputime-t) yadav et al./bibechana 12 (2015) 114-127: p. 118 5. method of analysis the sdss dataset of galaxies having redshift in the range 0.19 to 0.20 (real observed dataset) are compared with the isotropic distribution curves (obtained from simulation) in both θ and φ distributions. we use three different statistical tests: chi-square-, fourier-, and auto correlation-test in order to check any deviation from isotropy. 6.1 chi-square test the chi-square χ2 test is an objective way to examine whether the observational distribution deviates from the expected distribution (in our case, to the isotropic distribution), which is based on the reduced χ2 value given by, ν χ χν 2 2 = (4) ∑ = − = n i ei eii n nn 1 2 02 )( χ (5) here, n represents the number of bins, n0i and nei represent the observed and expected isotropic distributions and ν is the degree of freedom (ν = n−1). for an isotropic distribution, the χ2 value is expected to be nearly zero. the quantity p(>χ2) gives the probability that the observed χ2 value is realised by the isotropic distribution. the observed distribution is more consistent with the expected isotropic distribution when p(>χ2) is larger. we set p(>χ2) =0.050 as the critical value to discriminate isotropy from anisotropy, it corresponds to the deviation from the isotropy at 2σ level. 6.2 fourier test fourier test can be applied only if the deviation from isotropy is only slowly varying with θ or φ. a method of expanding a function by expressing it as an infinite series of periodic functions (sines and cosines) is called fourier series. the frequencies of the sines and cosines are increased by a constant factor with each successive term. the general mathematical form of the fourier series is: ⋅⋅⋅⋅+++++= )2sin2cos()sincos( 2 )( 2211 0 xbxaxbxa a xf (6) the constants a0, a1, b1,…….. etc., called fourier coefficients, are obtained by the formulae: ∫ ∫ ∫ − − − = = = π π π π π π π π π nxdxxfb nxdxxfa dxxfa n n sin)( 1 cos)( 1 )( 1 0 (7) we compare the observed distributions of the polar and azimuthal angle (θ and φ) of the galaxy rotation axis with the expected isotropic distributions. if the deviation from isotropy is a slowly varying function of the angle θ (or φ), one can use the fourier test. let n denote the total number of solutions for galaxies in the sample, nk the number of solutions in the k th bin, n0 the mean number of solutions per bin, and n0k the expected number of solutions in the k th bin. then the fourier series becomes yadav et al./bibechana 12 (2015) 114-127: p. 119 )4sin4cos2sin2cos1( 221221110 ⋯+∆+∆+∆+∆+= kkkkk nn θθθθ here the angle θk represents the polar angle in the kth bin. taking first order fourier mode, )2sin2cos1( 21110 kkk nn θθ ∆+∆+= (8) here the fourier coefficients ∆11 and ∆21 are the parameters of the distributions. we obtain the following expressions for the fourier coefficients ∆11 and ∆21 ∑ ∑ ∑ ∑ = = = = − =∆ − =∆ n k kk n k kkk n k kk n k kkk n nn n nn 1 2 0 1 0 21 1 2 0 1 0 11 2sin 2sin)( 2cos 2cos)( θ θ θ θ (9) the standard deviations σ(∆11) and σ(∆21) can be obtained using the expressions 2/1 2 1 021 2/1 2 1 011 2sin)( 2cos)( − = − =       =∆       =∆ ∑ ∑ k n k k k n k k n n θσ θσ (10) the probability that the amplitude ( ) 2/12 21 2 111 ∆+∆=∆ (11) is greater than a certain chosen value is given by the formula       ∆−=∆> 2 101 4 exp)( n n p , (12) with standard deviation 2/1 0 1 2 )(       =∆ nn σ (13) the first order fourier coefficient ∆11 is extremely useful because it provides the direction of departure from isotropy. in the polar angle (θ) distribution, if ∆11< 0 an excess of galaxies with rotation axis parallel to the reference plane is present, whereas for ∆11> 0 the rotation axis tend to be perpendicular to that plane. in the analysis of the azimuthal angle (φ), if ∆11<0 an excess of galaxies with rotation axis projections perpendicular to the direction of the virgo cluster center, whereas with ∆11>0 the projections tend to be parallel to that direction. the first order fourier probability function p(>∆1) explains the depth of the preferred orientation. we set p(>∆11) = 0.150 as a critical value as suggested by godlowski (1994) [26]. 6.3 auto correlation test auto correlation test is a measure of a degree to which there is a linear relationship between two variables. in our case, it takes account the correlation between the number of galaxies in adjoining angular bins. the correlation function is ( )( ) ∑ + ++ −− = n kk kkkk nn nnnn c 1 2/1 100 1010 )( (14) yadav et al./bibechana 12 (2015) 114-127: p. 120 with the standard deviation ( ) 2/1 )( nc =σ . in an isotropic distribution any correlation vanishes, so we expect to have c→0 7. results and discussion we describe the ways through which polar and azimuthal angle distributions are tested. for this, we use four statistical parameters, namely chi-square probability (p >χ2), autocorrelation coefficient (c/c(σ)), first order fourier coefficient (∆11/σ(∆11)) and first order fourier probability (p >∆1). for anisotropy, the limit of chi-square probability p(>χ2) is < 0.050, auto correlation coefficient (c/c(σ)) is > 1.0, first order fourier coefficient (∆11/σ(∆11)) is > 1.5 and fourier probability p(> ∆1) is < 0.150 respectively. the statistics for the polar and azimuthal angle distributions is given in table 1 and table 2 respectively. in the statistics of θ, a negative value of first order fourier coefficient suggests that the spin vectors of galaxies tend to be oriented perpendicular with respect to the equatorial coordinate system. similarly, a positive value of first order fourier coefficient suggests that the spin vectors of galaxies tend to be oriented parallel with respect to the equatorial coordinate system. whereas, in the statistics of φ, a positive (∆11/σ(∆11) with significant value suggests that the spin vector projections of galaxies tend to point radially with respect to the center of the equatorial coordinate system. similarly, a significant negative value of (∆11/σ(∆11) implies that the spin vector projection of galaxies tend to orient tangentially with respect to the equatorial coordinate system. in addition to the statistical tests, we also study the `humps' (bins with more solutions than the expected) and `dips' (bins with less solutions than the expected) in the polar and azimuthal angle distributions. the solid curve, in the histogram of the θ-distribution, represents the expected isotropic distribution whereas dashed curve is the cosine distribution. the solid circles with ±1σ error bars represent the observed distribution. the shaded portion represents the range 0 o < θ < 45o. a hump (or dip) in the smaller θ suggests that the spin vectors of galaxies tend to orient parallel (or perpendicular) with respect to the equatorial coordinate system. table 1: statistics of the polar (left) and azimuthal angle (right) distributions of sdss galaxies having redshift in the range 0.19 to 0.20 in the subsamples. the z01 to z11 represents the subsamples as discussed in section 3. the p(>χ2 ) represents the chi-square probability (second column). similarly, c/c(σ) represents the auto-correlation coefficient (third column). the last two columns give the first order fourier coefficient (∆11/σ(∆11) and first order fourier probability p(>∆1). sample polar angle (θ) azimuthal angle (φ) p(>χ2 ) c/c(σ) ∆11/σ(∆11) p(>∆1) p(>χ2) c/c(σ) ∆11/σ(∆11) p(>∆1) z01 0.628 -0.6 -0.4 0.920 0.694 -0.5 +0.7 0.381 z02 0.881 +0.0 +0.2 0.900 0.550 +0.2 +0.3 0.924 z03 0.781 +0.1 +0.0 0.834 0.661 -0.1 +0.2 0.367 z04 0.783 +0.4 -0.4 0.900 0.334 -1.3 +0.3 0.827 z05 0.486 -0.6 -0.7 0.735 0.195 +1.8 +2.2 0.079 z06 0.310 -1.7 +0.1 0.921 0.224 +0.5 +0.6 0.768 z07 0.073 +0.8 +0.9 0.473 0.066 -0.9 +0.7 0.263 z08 0.322 +1.1 +1.3 0.357 0.213 -1.3 +0.1 0.130 z09 0.266 -0.6 +0.5 0.764 0.606 +0.6 +1.7 0.096 z10 0.769 -0.2 -0.5 0.826 0.638 -3.4 +1.0 0.613 z11 0.184 -0.2 +1.1 0.448 0.020 +2.8 +1.5 0.032 yadav et al./bibechana 12 (2015) 114-127: p. 121 similarly, a hump (or dip) in the larger φ indicates that the spin vectors of galaxies tend to be oriented perpendicular with respect to the equatorial coordinate system. in the histogram of the φ-distribution, solid curve represents the expected isotropic distribution whereas dashed curve is the average distribution. the solid circles with ±1σ error bars represent the observed distribution. the shaded portion represents the range -45 o < φ < +45o. the humps and dips in the histograms of φ-distribution are not so easy to interpret as compared to φ-distributions. it is because the range of φ is -90o to +90o. in the histogram of the φ-distribution, φ = 0o means spin vector projections tend to point radially towards the center of the equatorial coordinate system. a hump in the middle (central eight bins) of the histogram suggests that the spin vector projections of galaxies tend to point towards the center of the chosen co-ordinate system. similarly, a hump at first four and last four bins indicates that the spin vectors projections of galaxies tend to be oriented tangentially with respect to the chosen reference coordinate system. 7.1 anisotropy in the polar angle distribution table 1 shows the statistics of the polar angle distribution of galaxies in the samples with respect to galactic coordinate system. figure 2 shows the observed (solid circles with error bars) and expected (solid curves) polar angle distributions. the statistics for the polar angle distribution in the sample z01 shows the value of chi-square probability (p(>χ2)) to be 0.628 i.e. 62.8% (greater than the significant level 0.050 i.e. 5.0%). the auto-correlation coefficient (c/c(σ)) is found to be -0.6 (less than the limit 1σ). the first order fourier coefficient (∆11/σ(∆11)) is found to be -0.4 (less than the limit 1.5σ). the first order fourier probability (p(>∆1)) is found to be 0.921 i.e., 92.1% (more than 15% limit). all these statistics suggest isotropy. the polar angle distribution of galaxies in the sample z01 is shown in the fig. 2a. the number of observed and expected solutions for small angle (<45 o ) is 1685 and 1679 respectively which suggests that the observed solutions is greater than expected solutions by 6. there is a significant dip at an angle 12.5o with > 2σ error limit and no hump is notice at all. at bimodal region (θ ~ 45o), the observed solution is less than expected solution by 2 and the observed and expected distribution agree within ±1σ. for the large angles (>45o), the expected solution is greater than observed solution by 6 and no humps and dips were seen there. in general, no preferred alignments of spin vectors of galaxies that have redshift in the lower limit is found. this results supports hierarchy model. fig. 2b shows the θ distribution for the galaxies of in the sample z02. a dip can be seen at 37.5o with slightly greater than ~ 1σ error limit. the number of observed solutions for θ < 45o is 1728 and expected solutions is 1723. thus the number of observed distribution of galaxies is more by 5 than that of the expected. at bimodal region (θ ~ 45o), the observed solutions is less than the expected solutions by 26. for larger angles (> 45o), no humps and dips were observed. the number of observed solutions lag the expected solutions by 5 at θ > 45o. statistical parameters for the polar angle distribution of sample z02 indicate isotropy. thus, a random distribution of angular momentum vectors of galaxies is noticed. the statistics for polar angle distribution for sample z03 (table 1) suggest strong isotropy. the polar angle distribution of galaxies in the sample z03 is shown in the fig. 2c. the number of observed and expected solutions for small angle (θ < 45o) is 1583 and 1584 respectively which indicates 1 less solution in observed than the expected distribution. there is dip at yadav et al./bibechana 12 (2015) 114-127: p. 122 an angle 7.5o with equal to 1σ error limit and one hump at an angle 47.5o with slightly > 1σ error limit. at bimodal region (θ ~ 45o), the number of expected solutions is 394 and the number of observed solutions is 418 which shows that the expected solutions is less than the observed solutions by 24. for the large angles (> 45 o ), the number of observed solution is more by 1 than expected. all statistical tests suggest strong isotropy for z04 (fig. 2d). a very good agreement between the observed and expected distributions can be seen. at bimodal region (θ ~ 45o), the observed distribution is less than the expected distribution by 21. for the θ less than 45o, the observed distribution is 5 less than the expected whereas for the θ greater than 45o the observed distribution is 5 more than the expected. fig. 2: the polar (θθθθ) angle distribution of sdss galaxies in 11 subsamples having redshift in the range 0.19 to 0.20. the solid line represents the expected isotropic distributions. the cosine distribution (dashed) is shown for the comparison. the statistical error (±1σσσσ) bars are shown for the observed counts. similar to the subsample z04, the statistical parameters for z05 suggest strong isotropy. the polar angle distribution of galaxies in the sample z05 is shown in fig. 2e. there is a dip at an angle 2.5 o with ~ 2σ error and a hump is at an angle 27.5o with ~ 1.4σ error. at bimodal region (θ ~ 45o, the yadav et al./bibechana 12 (2015) 114-127: p. 123 observed is 21 less than the expected distribution. for the large angles (>45o), the observed distribution is more by 6 than the expected. the statistics for polar angle distribution of sample z06 is given in table 1. a strong isotropy is suggested by the all four statistical parameters. the θdistribution of galaxies is shown in fig. 2f. for less than 45 o , the number of solutions for observed distribution exceeds the expected distribution by 8. at 7.5 o , a hump is seen with ~ 2σ error limit whereas a dip is seen at 27.5o with ~ 2σ error limit. at bimodal region (θ ~ 45o), the observed solutions is 10 more than the expected solutions. the number of observes solutions is less than the expected solutions for large angle (>45o) by 7. similar to the samples z01 to z05, a very good agreement between the observed and expected isotropic distribution of galaxies in other samples (z06 to z11) is noticed in the polar angle distribution. this suggests that the spatial orientation of galaxies in the large scale structure prefers hierarchy model as suggested by peebles (1969) [4]. 7.2 anisotropy in the azimuthal angle distribution table 1 gives the statistics of the azimuthal angle distribution of galaxies in the samples with respect to galactic coordinate system. figure 3 shows the observed (solid circles with error bars) and expected (solid curves) azimuthal angle distributions. fig. 3: the azimuthal angle (φφφφ) distributions of sdss galaxies in 11 subsamples having redshift in the range 0.19 to 0.20. the solid line represents the expected isotropic distributions. the cosine and average distribution (dashed) is shown for the comparison. the statistical error (±1σσσσ) bars are shown for the observed counts. yadav et al./bibechana 12 (2015) 114-127: p. 124 the statistics for the azimuthal angle distribution (table 1) in the sample z01 shows the value of chisquare probability (p(> χ2)) to be 0.694 (greater than the significant level 0.050). the auto-correlation coefficient c/c(σ) is found to be -0.5 (< 1σ). the first order fourier coefficient (∆11/σ(∆11)) is found to be 0.7 (less than the limit 1.5σ). the first order fourier probability p(>∆1) is found to be 38.1% (greater than 15% limit). here, all the statistics show isotropy. fig. 3a shows the φ-distribution for the galaxies in the sample z01. a dip is seen at an angle -85o and hump is notice at an angle 65o, with nearly 2σ error limit. the numbers of observed and expected solutions are 1343 and 1325 respectively for central eight bins. these numbers suggests that the observed distribution exceeds the expected distribution by 18. overall distributions for the first four bins and last four bins suggest that the observed distribution lags the expected distribution by 10. all the statistics suggest isotropy for z02. fig. 3b shows the φ-distribution for the galaxies of this sample z02. at angles -55o with ~ 1.1σ error limit, 15 o with ~ 1.1σ error limit and 65o with > 2σ error limit, significant dips are seen and at angle 45 o , a significant hump with ~ 1.1σ error limit is seen. for the central eight bins, the observed distribution leads the expected distribution of galaxies by 12. overall statistics for first four bins and last four bins show the expected distribution leads the observed distribution by 41. similar to the subsample z02, all the statistics suggest strong isotropy for z03. from the fig. 3c, a dip at an angle 25o with > 1σ error is seen. whereas at an angle 15o, a significant hump is seen (>2σ) and the next hump is seen at an angle 65 o with >1σ error. statistics for center eight bins indicates that the observed solutions are 6 more than the expected solutions. in the first four bins the expected distributions exceeds the observed distributions by 2 whereas in the last four bins the observed distributions exceeds the expected distributions by 2. a strong isotropy is suggested by the statistical parameters for z04 in the azimuthal angle distribution (fig. 3d). significance hump is notice at an angle -65 o with ~ 3σ error limit and at an angle 35 o with ~ 1.1σ error limit. hump is notice at an angle 15 o with equal to 1σ error limit and next significance hump is notice at an angle 15 o with ~ 2σ error limit. statistics reveal 5 less observed solutions than the expected solutions for the center eight bins. for first four and last four bins, the expected distribution leads the observed distribution by 25. as given in table 1, statistical parameters for azimuthal angle for sample z05 inferred the value of chi-square probability (p(> χ2)) is to be 19.5% (> 5.0%). the auto-correlation coefficient c/c(σ) is found to be 1.8 (>1σ). the first order fourier coefficient (∆11/σ(∆11)) is found to be 2.2 (> 1.5σ). the first order fourier probability p(>∆1) is found to be 7.9% (<15% limit). hence, all the statistics except chi-square probability suggest anisotropy. fig. 3e shows the φ-distribution for the galaxies of this sample z05. at angles 45o with ~ 1.1σ error limit, 65o with ~ 1.2σ error limit, 75 o with ~ 1.2σ error limit and 85o with error limit ~ 1σ, significant dips are seen. at an angle -15 o with error ~ 2σ and at an angle 45 o with error > 2σ, significant humps are seen. for the central eight bins, the observed distribution leads the expected distribution of galaxies by 44. in the first four bins the expected distribution is 7 more than the observed and in the last four bins the expected distribution is 52 more than the observed. in this sample, isotropy in the polar angle and anisotropy in the azimuthal angle is seen which shows that our reference galactic coordinate system is inappropriate. except in the samples z05 and z09, a random orientation of spin vector projections of galaxies is found in all subsamples. this suggests that the spatial orientation of galaxies in the large scale structure prefers hierarchy model as suggested by peebles (1969) [4]. yadav et al./bibechana 12 (2015) 114-127: p. 125 8. conclusion we studied the spatial orientation of 14,118 galaxies surveyed by sdss having redshift in the range 0.19 to 0.20 with respect to the galactic coordinate system. the two dimensional measured parameters are transformed into three dimensional galaxy rotation axes using `position angle inclination' method as proposed by flin & godlowski (1986) [19]. in order to remove various selection effects we use a random simulation as proposed by aryal & saurer (2000) [25]. the expected isotropic distribution curves for the total samples are deduced by performing a numerical simulation based on the godlowskian transformation. total galaxies are classified into 11 samples on the basis of redshift. to check for anisotropy or isotropy we have carried out three statistical tests: chi-square, auto-correlation and the fourier. the main goal of this thesis is to examine non-random effects in the galaxy and to find out the appropriateness of choice of coordinate system in order to explain true orientation scenario of distant galaxies. in our work, we have found that, except for samples z05 and z09, our reference galactic coordinate system to explain true orientation scenario was correct. also our results support hierarchy model of galaxy evolution scenario as suggested by peebles (1969). we intend to address following issues in our future works. 1. we have studied the galaxy orientation with respect to the galactic coordinate system. we wish to define a local reference system within the galaxies and study the preferred alignments of galaxies in association with it. 2. the results of the statistical analysis have been noticed to have a strong dependence on the sample classification criteria. a straight mathematical computation method instead of statistical method would be essential. acknowledgements this research has made use of the sdss database. we acknowledge prof. ronald weinberger for critical discussions. one author (sny) acknowledges central department of physics, tribhuvan university, kirtipur, for providing various forms of support for his doctoral thesis. we thank mr. rajesh kumar bachchan for his help during data compilation. references [1] t. padmanabhan, an invitation to astrophysics, world scientific publishing co. pvt. ltd. 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[26] w. godlowski, monthly notices royal astron. soc, 271 (1994) 19. http://dx.doi.org/10.1093/mnras/271.1.19 i. koirala et al./ bibechana 13 (2016) 87-93 : rcost p.87 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal thermodynamic and structural investigations on mixing behavior of hetero-coordinated al-based alloys in the fusion state i. koirala1, 2*, b. p. singh1, i. s. jha3 1university department of physics, t.m. bhagalpur university, india 2central department of physics, t.u. kirtipur, kathmandu, nepal 3m.m.a.m. campus, biratnagar, tribhuvan university, nepal *e-mail: ikphysicstu@gmail.com article history: received 07 september 2015; accepted 19 september, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13416 abstract we have used simple statistical model to report the hetero-coordination of two albased liquid alloys, i.e. al-ge and al-fe at temperatures 2000k and 1873k respectively. through thermodynamic functions such as free energy of mixing and ratio of activity of the component atoms of the alloys, we have reported the information on the interaction, stability and bonding strength among the constituent atoms in the alloys. at the microscopic level, concentration fluctuation in the long wavelength limit and warren-cowely short range order parameter help to obtain the microscopic information on structure of molten alloys. our theoretical analysis is based on interchange or ordering energy parameter which is found to be negative and temperature dependent. negative deviation from raoultian behaviour is observed in the computed thermodynamic and structural parameters of the alloys. the computed results are in good agreement with experimental data. the analysis concluded that both alloys are of weakly interacting and chemically ordered system. ©rcost: all rights reserved. keywords: simple statistical model; negative deviation; chemically ordered system; activity ratio. 1. introduction aluminium in pure state is ductile and relatively soft. to overcome this, the metal can be alloyed with other metals. aluminium alloys with a wide range of properties are used in various engineering applications such as electrical conductors, transport, packaging, building, architecture etc. selecting a right alloy for a given application entails considerations of strength, ductility, formability, weldability and corrosion resistance, to maintain a few. to obtain aluminium alloys which have the advantages of highly improved properties, the rapid solidification processing of aluminium alloys is being increasingly i. koirala et al./ bibechana 13 (2016) 87-93 : rcost p.88 (online publication: dec., 2015) employed for their manufacture [1, 2]. it is well known that during rapid solidification of alloys the arrangement or ordering alloys components in the liquid state have a considerable influence on the properties of the resulting solid. al-ge and al-fe are interesting aluminium based alloys. they exhibit phase diagram that show the system to behave as simple binary eutectic with mutual solubility [3, 4]. this suggests a tendency to regular alloys formation. al-ge alloys have been of interest in fundamental studies of nucleation in solid [5, 6] and in principle of precipitation reactions. the primary application of al-fe alloys is electrical distribution in the buildings with potential in automobiles, aerospace, telephone lines magnet winding [7-9]. therefore theoretical investigation giving mixing properties of both alloys are highly desirable for the material preparation of the metal alloys. several theoretical models [10-15] have long been proposed to understand mixing properties of binary liquid alloys. in present work, we study the concentration dependent mixing properties of liquid al-ge and al-fe at 2000k and 1873k respectively by the simple statistical model [16, 17]. the layout of this paper is arranged as follows: we present theoretical formalism in section 2, which is followed by results and discussions in section 3 and finally, we end the paper with a summary of concluding remarks in section 4. 2. theoretical formalism the excess free energy of mixing for binary alloys is obtained by solving the grand partition function in the framework of simple statistical model [16,17]. for regular solution which is given as   xxs z m a b 0 g rt in dx rt xin (1 x)in       (1) where   b2x 1 exp( / zk t) / 2x    (1a)   2/z a )1(x/)x21(  (1b)   2/z b )1)(x1/()x21(  (1c)    2/1 b 1)tzk/2exp()x1(x41  (1d) where r is universal molar constant; t, absolute temperature; x, concentration of the component; ω, interchange energy; z, coordination number and kb, boltzmann constant. for the ideal solution, the interaction between constituent atoms are identical (ω = 0). therefore the expression (1) becomes as  id mg rt xinx (1 x)in(1 x)    (2) free energy of mixing is an important thermodynamic function which gives the knowledge about stability and interaction information of the constituent atoms in the alloys. through standard thermodynamic relation as given below, we obtain the expression for free energy of mixing [17] as xs m id mm ggg   a brt{x ln x (1 x) ln(1 x)} rt xin (1 x)in         (3) i. koirala et al./ bibechana 13 (2016) 87-93 : rcost p.89 (online publication: dec., 2015) for the equi-atomic composition ( 2 1 x  ), relation (1) reduces to 2/z b 2/z xs m )]tzk/exp(1[2ln rt g  (4) the activity of binary liquid alloys is another fortune thermodynamic parameter which gives the nature and magnitude of interaction or bonding strength of the species of the alloys system. it can be evaluated from the free energy of mixing by the relation  m m i m i i in,p,t n,p,t g g rtln a g 1 x n x                    (5) guggenheim zeroth approximation [18] yields the expression of activity of component atoms a and b from eq.(3) and (5).which are respectively,  2a b a x exp 1 x k t         (6)    2b b a 1 x exp x k t          (7) the ratio of activity of the component atoms (a) is given by   b x a exp 1 2x 1 x k t          (8) concentration fluctuations in the long-wavelength limit (scc(0)) is an essential structural function which has been widely used to study the nature of atomic order in binary liquid alloys [19,20]. scc(0) is thermodynamically related to free energy of mixing(gm) [19]. it is given as   12 m cc 2 t,p,n g s 0 rt x         (9) equations (3) and (9) gives the theoretical value of scc(0): 1 cc bs (0) x(1 x)[1 x(1 x) 2 / k t]     (10) the ideal value of concentration-concentration fluctuations, when the ordering energy is zero, is usually computed from: id ccs (0) x(1 x)  (11) the warren-cowley [21, 22] short-range order parameter (α1) is another useful structural parameter to quantify the degree of chemical order in the alloy melt. it provides insight into the local arrangement of the atoms in the molten alloys. although it is difficult to obtain the experimental values of α1, theoretical values of this parameter are easily obtain via conditional probability [a/b] which defines the probability of finding an a-atom as a nearest neighbor of a given b-atom. it can be evaluated theoretically [21,22]: i. koirala et al./ bibechana 13 (2016) 87-93 : rcost p. 90 (online publication: dec., 2015) id 1 cc cc(s 1) /{s (z 1) 1}, s s (0) / s (0)      (12) where z is the coordination number, which is taken as 10 for our purposes. 3. results and discussion for the computation of thermodynamic and structural functions of binary alloys, the basic input parameter is interchange energy (ω), which is concentration independent but dependent of temperature [23]. the interchange energy used for the calculation for al-ge and al-fe liquid alloys at respective temperature 1200k and 1873k has been determined from eq. (3) or (4) by the method of successive approximation and comparing the results with the experimental value [24] of gm or xs mg till the best fit value is obtained for the given alloys. the best fit values of the parameters for both alloys are given in table (1). table1: basic parameter for the calculation. alloys t(k) z ω (ev) al-ge al-fe 1200k 1873k 10 10 0.183 0.507 the implications of ω in the table 1 being negative for both alloys considered for the study are chemically ordered. the value of inter change energy suggests that there is higher tendency for unlike atoms to pair in the alloys which implies that both are of hetero-coordination system. however, the tendency of pairing is weak since energy parameter is small. the free energy of mixing for al-ge and al-fe liquid alloys have been computed from equation (3).the plot of gm/rt for both alloys with computed and experimental values against concentration of aluminium (xal) are depicted in figure 1. the computed values of gm/rt for the both alloys systems, are in good agreement with the experimental data [24] in the whole range of concentration, xal = 0.1 to 0.9. the minimum value of gm /rt for al-ge is – 1.1357 at xal = 0.5 which almost matches with the experimental value at the same concentration. but for al-fe system at the same concentration gm/rt is found to minimum (1.4782) which also matches with the observed data [24].from the analysis it is clear that both alloys systems are symmetric about equi-atomic composition. further, the negative small values of free energy of mixing throughout the entire compositions indicate that the proposed alloys in molten state are weakly interacting system. i. koirala et al./ bibechana 13 (2016) 87-93 : rcost p.91 (online publication: dec., 2015) fig.1: free energy of mixing (gm/rt) as a function of concentration (xal) for al-ge and alfe liquid alloys at 2000k and 1873k respectively. fig.2: activity ratio (a) as a function of concentration (xal) for al-ge and al-fe liquid alloys at 2000k and 1873k respectively. with respect to magnitude of gm/rt, we concluded that al-fe is more interacting system. the activity is one of the important thermodynamic functions which are obtained directly from experiment. the deviation from ideal behavior is incorporated into activity. following the eq.(8), we have computed the ratio of chemical activities of the components of the alloys by using the same value of the interchange energy which have been already used in free energy of mixing. the computed values of ratio of activities of the components of the alloys are plotted along with the experimental values against concentration is given in figure 2. there is reasonable agreement between calculated and experimental values of ratio of activities of the components of the alloys. high activity ratio of al-fe suggests that ordering state of it is more as compared to al-ge system. there are difficulties in diffraction experiment, therefore theoretical determination of scc(0) is of great importance when nature of interactions in the melt has to be analyzed. the mixing behavior of liquid alloys can be deduced from the deviation of scc(0) from id ccs (0) . at a given composition if  )0(s)0(s id cccc negative, ordering in liquid alloy is expected while  )0(s)0(s id cccc positive; it gives the indication of tendency of segregation [19]. we have used eq.(10) to compute the scc(0) for the alloys. it can also be obtained directly from the measured activity [24] data as 11 m m cc a b g g s (1 x)a xa x (1 x)                (13) -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 g m /r t xal experimental theoretical 0.2 0.4 0.6 0.8 1.0 fig.1 al-fe al-ge [24] 0.2 0.4 0.6 0.8 1.0 -20 0 20 40 60 80 100 120 140 160 a xal experimental theoretical al fe al ge fig.2 [24] i. koirala et al./ bibechana 13 (2016) 87-93 : rcost p.92 (online publication: dec., 2015) fig.3: concentration-concentration fluctuation in long wavelength limit (scc(0)) and chemical short range order parameter (α1) as a function of concentration (xal) for al-ge and al-fe liquid alloys at 2000k and 1873k respectively. where aa and ab are the observed chemical activities of a and b respectively of the alloys a-b. the scc(0), obtained from eq. (13) are taken as experimental values. figure 3 shows a plot of the computed and experimental values of scc(0) along with the ideal values as a function of concentration. the computed values of scc(0) are in remarkable agreement with the experimental values of scc(0) with little discrepancies. in the region xal ˂ 0.3, discrepancy is observed between the computed and experimental values, which are due to size mismatch in the mixture. the result  )0(s)0(s id cccc negative, clearly described both systems as compound forming. as scc(0) for al-fe system is smaller than that of al-ge system, it confirms that al-ge is less ordered than al-fe system. the local ordering in the binary liquid alloys has been quantitatively described in terms of warren-cowley short range order parameter (α1). for the equi-atomic composition, the chemical short range order parameter is found to be -1 ≤ α1 ≤ 1. negative values of α1 indicate ordering in the melt, which is complete if α1= -1. on the other hand, positive values of α1indicate segregation, leading to complete only if α1 = 1. but α1 = 0, corresponds to random distribution of the atoms in the mixture. figure 3 also shows the plots of α1 against chemical composition of aluminium, obtained from eq. (12). it is observed that the plots are symmetrical about equi-atomic composition and negative throughout the whole concentration range of aluminium. the negative values of α1 (minimum at xal = 0.5) throughout whole concentration range are the signatures of hetero-coordination system in the both alloys al-ge and al-fe. the magnitude of α1 (more negative) indicates that al-fe system is more ordering than al-ge alloys system. 4. conclusions our theoretical analysis reveals that both alloys al-ge and al-fe systems respectively at 2000k and 1873k are chemically ordered. the free energy of mixing and concentration fluctuation in long 0.2 0.4 0.6 0.8 1.0 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 s cc (0 ) xal experimental theoretical ideal  1 al-ge al-fe al-ge al-fe fig.3 [24] i. koirala et al./ bibechana 13 (2016) 87-93 : rcost p.93 (online publication: dec., 2015) wavelength limit deviates negatively from their ideality. in the overall calculation, interchange energy takes important role which is concentration independent but always dependent of temperature. from the nature and magnitude of free energy of mixing, concentration fluctuation in long wavelength limit, warren-cowley short range order parameter and activity ratio of the components of the respective alloys we concluded that both alloys are of weakly interacting system and comparatively liquid al-fe alloys is more chemically ordered than al-ge alloys. acknowledgment one of the authors (i. koirala) acknowledges dr. devendra adhikari (professor, m.m.a.m. campus biratnagar, tribhuvan university, nepal); and dr. lok narayan jha and dr. shekhar gurung (retired professors, tribhuvan university, nepal) for fruitful suggestions and inspiring discussions. references [1] i. i. tashlykova-bushkevich, v. g. shepelevich, j. alloys compd., 299(2009)205. 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[24] r. hultgren, p.d. desai, d.t. hawkins, m. gleiser, k.k. kelley, selected values the of thermodynamic properties of binary alloys. asm metals park, ohio., 1973. microsoft word thapa _53-58_.doc r c o s t n publisher: research council of science and technology, biratnagar, nepal p. 53 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana energy of sitnikov's restricted three body problem if the primaries are source of radiation and triaxial rigid bodies r.r.thapa 1,2* 1 university department of mathematics., t.m. bhagalpur university, bhagalpur, india 2p.g. department of mathematics., p.g. campus, biratnagar, t.u., nepal. *e-mail: thaparajuram@yahoo.com accepted for publication: december 13, 2014 abstract in this paper the joint effect of source of radiation and triaxial rigid body has been studied. the energy of sitnikov's restricted three body problem when primaries are sources of radiation and energy of sitnikov's restricted problem of three bodies when primaries are triaxial rigid bodies have been studied to calculate the joint effect. equation of motion of the third body of infitesimal mass, if primaries are sources of radiation and triaxial rigid bodies, are calculated. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11707 © 2014 rcost: all rights reserved. keywords: dimensional distance; oscillatory motion; periodicity; radiation parameter. 1. introduction sitnikov [1] problem can be integrated in case of restricted problem if primaries are taken to be equal masses. if primaries are triaxial rigid bodies then distance between them will be changed. then third body can move along z axis. but if primaries are sources of radiation then the third body moves along the line perpendicular through the centre of mass of the primaries and is perpendicular to the plane of motion. thapa et al. [2] obtained the periodicity of sitnikov's restricted three body problem when the primaries are sources of radiation. they found the equations of motion of the third body and total energy of the system. r.r. thapa et al. [3] also obtained the equations of motion of the sitnikov's restricted problem of three bodies when primaries are triaxial rigid bodies. they got the equations of motion in dimensionless variables and cartesian form as 2 2 x y z x ny y nx z − = ω + = ω = ω ɺɺ ɺ ɺɺ ɺ ɺɺ thapa/ bibechana 12 (2015) 53-58: p. 54 2 2 2 1 2 3 1 2 1 2 1 2 1 2 3 5 2 1 2 2 2 1 2 1 1 5 5 5 2 1 2 (1 )(2 )1 where ( ) 2 2 (2 ) 3(1 )( ) 2 2 3 ( ) 3(1 ) 3 2 2 2 − −− ω = + + + + ′ ′− − − + − ′ ′ ′− − − − − n x y r r r y r r y z z r r r µ σ σµ µ µ σ σ µ σ σ µ σ σ µ σ µσ in present work we have proposed to get the energy of restricted three body problem if the primaries are source of radiation and triaxial rigid bodies. 2. equation of motion we will adopt the notation and terminology of szehebely [4]. we have the equation of motion of the third body of infinitesimal mass is 3 1 2 1 2 1 1 3 5 7 2 2 22 2 2 2 2 2 3(2 2 ) 15( )(1 ) 4 4 4 4 4 σ σ σ σ σ σ′ ′ ′− + − +∂ω − − = = − + ∂       + + +            ɺɺ z zp z z z a a a z z z 32 1 1 3 5 72 2 2 22 2 2 2 2 2 ( )(1 ) 3 15 4 4 4 4 4 σ σα ′+− − = − +       + + +            zd z p z z dt a a a z z z (1) where 1 2 1 22 2α σ σ σ σ′ ′= − + − equation (1) is non-linear equation. it can be integrated by linearizing it. 3. energy of the third body if we multiply (1) by2 dz dt we get, 32 1 1 3 5 72 2 2 22 2 2 2 2 2 15( )2(1 ) 3 2 2 2 4 4 4 4 4 ′+− = − − × +       + + +            zdz d z p z dz dz dz z dt dt dt dt dt a a a z z z σ σα or, 2 2 2 2 1 1 3 5 7 2 2 22 2 2 2 2 2 4 415( )1 (1 ) 3 2 4 4 4 4 4   + − ′+−   = − − × +          + + +            a a z z d dz p z dz z dz dz dt dt dt dt dt a a a z z z σ σα thapa/ bibechana 12 (2015) 53-58: p. 55 2 1 1 3 5 5 7 2 2 2 22 2 2 2 2 2 2 2 15( )(1 ) 3 4 4 4 4 4 4 4      ′+− − − + −           + + + +                   p z dz z dz z dz a z dz dt dt dt dt a a a a z z z z σ σα (2) if we substitute du dz u z dt dt = and 2 2 2 4 a u z= + we get, ( ) ( ) ( ) ( ) 2 2 1 1 3 5 5 7 2 2 2 22 2 2 2 21 1 2 4 4 6 1 1 1 12 4 4 15( )1 (1 ) 3 1 1 2 4 4 4 15( )(1 ) 3 1 1 1 4 4 4 1 3 15 1 15 ( ) ( 4 4 4   ′+−    = − − + −        ′+−  = − − + −   ′ ′= − − + + − + d dz p du du du a du u u u u dt dt dt dt dt dt u u u u p du du du du a u dt u dt u dt u dt du du du u dt u dt u dt σ σα σ σα α σ σ σ σ ( ) 2 6 21 3 3 51 1 1 1 1 ) 4 5( ) 3( )(1 ) 4 4 16 − − − − ⋅ ′ ′+ +− = + − + a du u dt ap du du du d u dt dt dt dt σ σ σ σα 2 21 3 3 5 1 1 1 1 2 2 1 3 3 51 1 1 1 2 1 1 1 1 3 3 5( ) 3( )1 (1 ) 2 4 4 16 3( )1 5 (1 ) ( ) 2 4 4 16 5( ) 3( )1 (1 ) 2 4 4 − − − − − − − − ′ ′+ +  = − + −    ′+  ′⇒ = − + − + + +    ′ ′+ +− ⇒ = + − +    ∫ ∫ ∫ ∫ ∫ ad dz du du du du dt p dt dt dt dt dt dt dt dt dt dt adz p u u u u c dt adz p dt u u u σ σ σ σα σ σα σ σ σ σ σ σα 2 5 2 2 1 1 1 1 3 3 52 2 2 22 2 22 2 2 2 2 2 1 1 1 1 3 32 2 2 22 22 2 2 2 1 16 5( ) 3( )1 (1 ) 2 4 4 164 4 4 4 5( ) 3( )1 (1 ) 2 4 4 164 4 4 4 + ′ ′+ +− ⇒ = + − + +         + + + +            ′ ′+ +− ⇒ − − + −         + + + +            c u adz p c dt a a a az z z z adz p dt a a a az z z z σ σ σ σα σ σ σ σα 5 2 = c ( )2 2 1 1 1 2 1 2 1 1 3 52 2 22 22 2 2 5 5 2 2 3( )1 (1 ) 2 4 164 4 4 ′ ′ ′+ − + − + ′+− ⇒ − + − =       + + +        adz p c dt a a az z z σ σ σ σ σ σ σ σ thapa/ bibechana 12 (2015) 53-58: p. 56 ( )2 2 1 2 1 2 1 1 3 52 2 22 22 2 2 3 3 3( )1 (1 ) 2 4 164 4 4 ′ ′+ + + ′+− ⇒ − + − =       + + +        adz p c dt a a az z z σ σ σ σ σ σ 2 2 1 1 1 3 5 2 2 22 2 2 2 2 2 3( )1 (1 ) constant 2 4 16 4 4 4 σ σ ′+− ⇒ − + − =          + + +            adz p p dt a a a z z z 2 2 1 1 1 3 5 2 2 22 2 2 2 2 2 2 1 1 3 52 2 22 22 2 2 3( )1 (1 ) constant. 2 4 16 4 4 4 3( )1 (1 ) constant. 2 4 164 4 4 σ σ σ σ ′+− = − + − =          + + +            ′+− = − + − =       + + +        adz p p e dt a a a z z z dz p p e dt a a az z z now from equation (1) 2 31 1 3 5 72 2 2 22 2 2 2 2 2 2 31 1 3 5 72 3 5 72 2 22 2 2 2 2 2 2 2 3 15( )(1 ) 3 0 4 4 4 4 4 15( )(1 ) 3 0 4 4 4 1 4 1 4 1 2 2 2 (1 )8 σ σα σ σα ′+− + + − =       + + +            ′+− ⇒ + + − =           + + +                      − ⇒ + d z p z z z dt a a a z z z d z p z z z dt a z a z a z a a a d z p z dt a 3 5 2 22 2 2 5 2 7 3 2 2 1 1 7 2 4 24 4 1 1 15( ) 32 4 1 0 (as so 1) α σ σ − − −     + + +        ′  + × − + =     << <<<    z z z a a a z z a a z z a a 2 2 22 3 1 12 3 5 7 (1 )8 3 2 24 5 2 15 32 7 2 1 ... 1 ... ( ) 1 ... 0 2 2 2      − ×     ′⇒ + − + + − + − + − + =                          d z p z z z z z z dt a a a a a a α σ σ neglecting higher order term of (z/a) above the third order, we get, thapa/ bibechana 12 (2015) 53-58: p. 57 ( ) 22 2 31 1 2 3 3 5 5 2 7 2 31 1 7 2 2 31 1 2 3 5 5 7 7 2 2 2 2 5 7 480( )(1 )8 8 12 24 24 5 4 2 2 480( ) 7 4 0 2 480( )(1 )8 24 48 240 ... 0 8(1 ) 48 3 5 1 d z p z z z z z z z dt a a a a a a a z z a a d z p z z dt a a a a a d z p a z a dt a a σ σα α σ σ σ σα α α α ′+− × + − ⋅ + − × −    ′+ + × = ′+−   + + − + + + =        − + + − + +( ) 3 1 1 0( ) 0zσ σ ′+ = 2 2 3 0 0 d z z z dt η ε+ − = (4) ( ) 2 2 2 0 5 5 2 1 17 8(1 ) 8 ( 3 ) where 3 48 and 5 10( ) p q a a a a a a α η α ε α σ σ − + = + =   ′ = + + +   the equations (3), (4) represent energy of sitnikov's restricted three body problem if the primaries are source of radiation and triaxial rigid bodies. 4. result and discussion the energy of third body depends on variable z, radiation parameter p, (parameter) α = 1 2 1 121 22 σ−σ+σ−σ , distance between the primaries a; where 2 2 1 3 1 2 a a , 5r − σ = 2 2 2 2 2 2 2 12 3 1 3 2 3 2 1 22 2 2 a a b b b b , , 5r 5r 5r − − − σ = σ = σ = ; r is dimensional distance between the primaries and 321 a,a,a ; 321 b,b,b are lengths of semi-axes of two primaries parallel to axes respectively. the kinetic energy of the third body depends on variable z but potential energy depends on 0 andη ε . where 5 2 2 0 a )3a( q8 α+ =η and )](105a[( a 48 12 7 σ+σ+α+=ε . hence the third body will perform oscillatory motion. acknowledgement i want to acknowledge with thanks my supervisor dr. m.r. hassan, department of mathematics, s.m. college, bhagalpur, t.m.b.u. bghagalpur, 812007, india for his meticulous guidance during the work. (3) thapa/ bibechana 12 (2015) 53-58: p. 58 references [1] k.a. sitnikov, dokl. akad, nauk, ussr 132(2) (1960) 303. [2] r.r. thapa, and m.r. hassan, journal of the bihar mathematical society 27(2013) 99105. [3] r.r. thapa and m.r. hassan, a research journal in mathematics "m0" 1(2014) 37-39. [4] v. szebehely, theory of orbits, academic press, new york (1967). r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.60 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal energetics and local order in in-based liquid alloys r. p. koirala1, 2*, b. p. singh1, i.s. jha2, d. adhikari2 1university department of physics, t.m. bhagalpur university, bhagalpur, india 2department of physics, m.m.a.m. campus, biratnagar, tribhuvan university, nepal *e-mail: rpphysics@gmail.com article history: received 05 june, 2015; accepted 20 august, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13359 abstract a comparative study has been carried out to understand the concentration dependence of thermodynamic properties such as, free energy of mixing (δgm), heat of mixing (δhm), entropy of mixing (δsm), activity (ai) and microscopic properties, such as concentration fluctuation in long wavelength limit (scc(0)) and warren-cowley short range order parameter (α1) of in-based three liquid alloys (in-pb , in-tl and in-zn) on the basis of self-association model. the analysis reveals that self-association model successfully explains the observed properties of the liquid alloys. positive deviation of the thermodynamic properties of the alloys from the raoultian solution behaviour indicates that the alloys are weakly segregating in nature. the comparative assessment of the interaction energy and the microscopic properties suggests that the degree of segregation is greatest in in-zn alloy and comparable in in-pb and in-tl alloys. ©rcost: all rights reserved. keywords: liquid alloys; self association model; order energy; segregation. 1. introduction preliminary ideas about the mixing of metals in a binary alloy can be deduced from hume-rothery rules for metallic solution which describe condition for forming substitutional and interstitial solutions. experience shows that the hume-rothery factors, such as the valence difference, electro-negativity difference and atomic size mismatch are not sufficient to provide detail information for understanding the alloying of metals in the liquid phase, and for this reason, properties of mixing are considered. the properties of mixing in a liquid alloy at a given temperature and pressure are ascribed to the role of some sort of short range microscopic interactions which are assumed to exist in a micro-inhomogeneous atomic distribution giving rise to the equilibrium properties of the alloy. the accurate determination of the interaction energy terms in liquid alloy is usually a difficult task as compared to those in ordered systems r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.61 (online publication: dec., 2015) like crystals. thus there always remains an opportunity for the prediction of the true character of atomic interaction in a liquid alloy so that the observed properties of mixing could be explained adequately. the mixing behaviour of binary liquid alloys is described as ordering or segregating depending on the nature of arrangement of atoms of the constituent metals in the alloys. alloys of ordering nature are characterized by the pairing of unlike atoms leading to the formation of chemical complexes. segregating alloys, on the other hand, have pairing of like atoms at equivalent sites. it is known that many binary liquid alloys exhibit non-regular solution behaviour. the alloys of a versatile metal indium, such as in-pb (673 k), in-tl (723 k) and in-zn (700k) in particular are interesting in that the observed thermodynamic properties of mixing like free energy of mixing and entropy of mixing are asymmetrical to some extent about the equiatomic composition [1]. the positive sign of observed heat of mixing for these alloys and the concentration fluctuation in long wavelength limit (scc(0)) of the alloys calculated from the observed activity data indicate that the alloys show positive deviations from the additive rule of mixing. since long, many studies have been carried out to understand the alloying behaviour of various liquid alloys in different concerns [2-21]. of the models the self-association model [4, 8, 12] is considered appropriate for the study of the equilibrium thermodynamic and structural properties of binary liquid alloys endowed with segregating nature. this model is the approximation over the compound formation model when no chemical complex is assumed to exist in the binary alloy melt [2, 14]. over times, various studies have been carried out for the study of the mixing properties of in-pb, in-tl and in-zn alloys in different concerns [22-31]. in this paper we aim to review alloying behaviour in the three in-based liquid alloys, in-pb (673 k), in-tl (723 k) and in-zn (700k) by computing the concentration dependence of thermodynamic properties such as, free energy of mixing (δgm), heat of mixing (δhm), entropy of mixing (δsm), activity (ai) and microscopic functions, such as the concentration fluctuation in long wavelength limit and the short range order parameter, as function of concentration in the light of this self-association model. in the following section, we present the necessary theoretical expressions required for the computation of thermodynamic and the microscopic functions of binary liquid alloys, which is followed by result and a discussion of the work in section 3 and conclusions in section 4. 2. theoretical basis the self-association model is a simple scheme for demixing binary liquid alloys [8, 12]. it assumes pairing of like atoms at equivalent sites that have short-ranged interaction between nearest neighbours. such homo-coordination of atoms leads to the formation of self-associates in the alloys. let a liquid binary a-b alloy consist of cnna  atoms of element a and n)c1(nb  atoms of element b which form like atom clusters or self-associates of type a and b , where  and  are the number of atoms in the clusters of type a and b matrices respectively. on the basis of this assumption the expressions for thermodynamic and microscopic functions are derived for binary liquid alloy. r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.62 (online publication: dec., 2015) 2.1 thermodynamic properties in the self-association model, the free energy of mixing, δgm for binary liquid alloys at temperature t can be obtained using the following expression [12]: w)c1(c]ln)1(lnc)c1(ln)c1(clnc[rtg m  (1) where, r is universal gas constant, c is concentration of a-atoms in the alloy and w is order energy parameter. the auxiliary functions  and  are defined as  /11 , )c1/(1  where  / (  ) is called the ratio of self-associates. at a given temperature  and w are the model parameters of self-association model which are estimated for a liquid alloy by fitting them into experimental thermodynamic data of the alloy to estimate the thermodynamic and structural properties of a binary liquid alloy. in order to obtain the expression for the activity, ai of constituent element in a binary liquid alloy the following standard thermodynamic relation, which relates activity, ai to the free energy of mixing, gm is used: c )g( )c1(galnrt m mi    (where i = a, b) (2) from eqs. (1) and (2), we get rt w )c1()c1()]1(cln[aln 22 a  (3) and rt w )1(nc)1()1(c)cln(aln 22 b  (4) the entropy of mixing, δsm for binary alloys can be obtained using the thermodynamic relation t )g( s m m    (5) by the differentiation of the expression for δgm in eqn. (1) is obtained as t w )c1(c]ln)1(lnc)c1(ln)c1(clnc[rsm    (6) r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.63 (online publication: dec., 2015) the heat of mixing, δhm can be calculated from the knowledge of the free energy of mixing and the entropy of mixing, using the standard thermodynamic relation mmm stgh  (7) 2.2 microscopic properties the microscopic functions such as concentration fluctuation in long wavelength limit, scc(0) and warrencowley short-range order parameter, 1α are useful properties to obtain valuable information about structure of binary liquid alloys [2,8]. scc(0) indicates the nature of local arrangement of atoms and 1α represents the degree of atomic ordering in the melt. the standard relation for concentration fluctuation in long wavelength limit (scc(0)) for binary liquid alloys is given as 1 n,p,t2 m 2 cc ] c )g( [rt)0(s     (8) the analytical expression for concentration fluctuation in long wavelength limit, scc(0) in self-association model is obtained from eq. (8) by taking the second composition derivative of the expression for δgm, from eqs. (1) and it can be put in the following form [12]: )w,(f)c1(c1 )c1(c )0(scc    (9) where 3 22 )]c1(c[ )]c1(c[)1()rt/w(2 )w,(f    (10) the value of scc(0) can also be obtained by taking the first composition derivative of the activity as given below [8]: 1 p,tbb 1 p,taacc ))c1(/a(ac)c/a(a)c1()0(s   (11) in the literature, the scc(0) determined by using the measured activity data in eq. (11) is usually referred to as an experimental scc(0) [8]. in order to ascertain the degree of local ordering of atoms in the alloy, warren-cowley short range order parameter, 1α can be estimated from the knowledge of the interchange energy parameter, w. for this parameter, the following expression is available [2, 8]: 1 1 1    , (12) r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.64 (online publication: dec., 2015) where  is an auxiliary variable and is a function of composition defined by: ]1)tzk/w2)[exp(c1(c41 b  (13) here z represents the co-ordination number. in terms of the function  , the concentration fluctuation in long wavelength, scc(0) can be expressed as [2, 8]: )1/1(z2/11 )c1(c )0(scc    (14) from eqs. (12) and (14), the short range order parameter, 1 can be expressed in the following form: )0(s)0(s)1z( )0(s)0(s id cccc id cccc 1    , with )c1(c)0(sid cc  (15) 3. results and discussion 3.1 thermodynamic properties a significant amount of information on the mixing of liquid metals forming a binary alloy can be obtained from the analysis of the energetics in the alloy. in order to study the composition dependence of the energetics in a binary liquid alloy in the framework of self-association model, as stated before, the ratio of self-associates  and the order energy parameter w are required. in the present work, these parameters have been determined for the liquid in-pb alloy at 673 k, in-tl alloy at 723 k and in-zn alloy at 700 from the method of successive approximation by fitting them into the experimental data of the free energy of mixing, δgm [1] in eqs. (1) and the activities, ai [1] in eqs. (3) and (4) simultaneously, over the whole range of composition. in in-zn alloy the calculations have been done taking the concentration ‘c’ for zn-component for getting better results. for the computation of the entropy of mixing, δsm, in addition to the ratio of self-associates  , the temperature derivative of the order energy parameter, t w   is also needed. this has been estimated using the experimental data of the entropy of mixing, δsm [1]. the best estimated values of the parameters for the liquid alloys have been listed as follows: alloy temperature  w t w   in-pb 673 k 1.66 0.44 -0.69 in-tl 723 k 1.45 0.49 +1.58 in-zn 700 k 1.68 1.44 +2.99 the calculated values of δgm of the alloys are compared with the corresponding experimental values [1] by plotting them against the concentration of in-component in fig.1. the plot shows there is excellent agreement between the theoretical values and the experimental values for in-pb and in-tl alloys while in in-zn alloy the two sets of the δgm agree well in the whole range of concentration. r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.65 (online publication: dec., 2015) like the experimental values, the theoretical values of δgm have been found to be the minimum at the equi-atomic composition in in-pb and in-tl alloys. however, in in-zn alloy our analysis predicts the minimum value around 70% atomic composition of in-component. this is slightly different from the minimum experimental value which is reported to occur at 60% atomic composition of in-component. of the three binary liquid alloys of indium, the calculations of the free energy of mixing suggest that there is weakest tendency of spontaneous mixing of the metals in the in-zn alloy at 700 k and it is found to increase in the direction of in-pb alloy at 673 k and in-tl alloy at 723 k. the order energy parameter has been found to be positive in all the three alloys, which indicates that the atoms of the components in the alloys prefer to remain self-associated and the alloys are segregating in nature. the observed asymmetry in the free energy of mixing, δgm of the alloys is well explained by the self-association model. fig. 1: free energy of mixing, δgm of liquid in-pb (673 k), in-tl (723 k) and in-zn (700 k) alloys versus concentration, cin of in-component: theorycurves: solid [in-pb]; dotted [in-tl]; dash [in-zn] experiment-symbols: circles [in-pb]; sold circles [in-tl]; squares [in-zn]. the behaviour of the atoms in a binary liquid mixture can be accounted in terms of the chemical activity. the chemical activity is a measure of the tendency of the component to leave the solution. the deviations in the nature of a solution from ideal behaviour can be incorporated into activity. as in the case of free energy of mixing, the computed values of the chemical activities have been found to agree very well with the observed data [1] in the two alloys, in-pb at 673 k and in-tl at 723 k at all concentrations and small discrepancies are observed in in-zn alloy at 700 k (fig. 2). it is clear from the plot that the activities, i.e. tendency of in-atoms to leave the metallic solution, are very comparable in the in-pb and in-tl alloys, with small positive deviation from the ideality. the in-zn alloy is found to have large values for the r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.66 (online publication: dec., 2015) activities of in-atoms, indicating that the alloy has the smallest tendency of mixing of the atoms in the alloy. fig. 2: chemical activity, ain of in-component in liquid in-pb (673 k), in-tl (723 k) and in-zn (700 k) alloys versus concentration, cin of in-component: theorycurves: solid [in-pb]; dotted [in-tl]; dash [in-zn] experiment-symbols: circles [in-pb]; sold circles [in-tl]; squares [in-zn]. fig. 3: entropy of mixing, δsm of liquid in-pb (673 k), in-tl (723 k) and in-zn (700 k) alloys versus concentration, cin of in-component: theorycurves: solid [in-pb]; dotted [in-tl]; dash [inzn]experiment-symbols: circles [in-pb]; sold circles [in-tl]; squares [in-zn]. r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.67 (online publication: dec., 2015) the inter-atomic interactions in a binary liquid alloy can also be described in terms of the enthalpic and entropic effects. the entropy of mixing which is a measure of disorderness in the local arrangement of atoms in the system indeed represents the sharing of energy between the atoms in the neighbourhood. the concentration dependence of the entropy of mixing, δsm of the three alloys has been computed from eq. (6) by estimating the temperature dependence of the energy parameter. the theoretical results for the alloys are compared in fig. (3), along with the parallel experimental results [1]. fig. 4: entropy of mixing, δhm of liquid in-pb (673 k), in-tl (723 k) and in-zn (700 k) alloys versus concentration, cin of in-component: theorycurves: solid [in-pb]; dotted [in-tl]; dash [in-zn] experiment-symbols: circles [in-pb]; sold circles [in-tl]; squares [in-zn]. the plot shows that the computed values of the entropy of mixing are in good agreement with the corresponding experimental values. the maximum in the calculated entropy of mixing of all the alloys have been found to occur at the equiatomic composition. this is in agreement with the observed results for the alloys. using the calculated values of the free energy of mixing and the entropy of mixing, we have computed the heat of mixing, δhm for the alloys throughout the whole concentration range from eq. (7). the computed results for δhm in the alloys have been found to agree well with the corresponding experimental results [1], with a little deviation (fig. 4). the small positive values of δhm of the alloys suggest that each of the alloys belongs to system with the weak strength of the interatomic interactions showing a tendency of phase separation. r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.68 (online publication: dec., 2015) 3.2. microscopic properties in order to investigate the nature of local atomic ordering in the in-pb, in-tl and in-zn liquid alloys in more detail, we have computed microscopic functions, the concentration fluctuations in long wavelength limit, scc(0) from eqs. (9) and (10). the computed and experimental values of scc(0) along with the ideal values are compared by plotting them as function of concentration in fig. 5. in our analysis, both the theoretical and experimental values of scc(0) have been found to be greater than the corresponding ideal values in all liquid alloys at all concentrations (fig. 5). this clearly suggests that the indium based alloys under study have preference of like atom pairing over hetero-pairing of atoms. fig. 5: concentration fluctuation in long wavelength limit, scc(0) of liquid in-pb (673 k), in-tl (723 k) and in-zn (700 k) alloys versus concentration, cin of in-component: theorycurves: thin solid [inpb]; dotted [in-tl]; thick solid [in-zn]; dash [ideal] experiment-symbols: circles [in-pb]; solid circles [in-tl]; squares [in-zn]. the structure regarding the atomic ordering in the liquid alloys has been additionally accessed by computing the warren-cowely short range ordering parameter, 1 using eq. (15) throughout the composition range. the short range parameter has been found to be positive at all concentrations for the alloys (fig. 6). in our calculation we have taken z = 10. we note that on varying the value of z, the peak value in c1  curve changes but the nature of variation and position of the peak in the value of 1 against concentration remain unchanged. r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.69 (online publication: dec., 2015) fig. 6: warren-cowley short range order parameter, 1 of liquid in-pb (673 k), in-tl (723 k) and inzn (700 k) alloys versus concentration, cin of in-component: solid curve [in-pb]; thin dotted curve [in-tl]; dashed curve [in-zn] it is interesting to note that both sign and the order of magnitude of 1 in all the three alloys are in conformity with the same in the order energy parameter, w, indicating the segregating nature of the alloys. it is clear from small positive values of 1 that the in-pb, in-tl and in-zn liquid alloys have weak tendency of segregation, the degree of segregation being comparable in in-pb and in-tl alloys and relatively much larger in the in-zn alloy. 4. conclusion the theoretical analysis reveals that quasi-chemical analysis successfully explains the observed properties of the in-pb, in-tl and in-zn liquid alloys. positive deviation of the thermodynamic properties of the alloys from the raoultian solution behaviour indicates that the alloys are weakly segregating in nature. the comparative assessment of the interaction energy and the microscopic properties suggests that the degree of segregation is greatest in in-zn alloy and comparable in in-pb and in-tl alloys. acknowledgements one of the authors, r.p. koirala, is grateful to retired prof. dr. l.n. jha and prof. dr. pradeep raj pradhan (post-graduate department of physics, m.m.a.m. campus, t.u., biratnagar, nepal) and prof. dr. ashok kumar (post-graduate department of physics, m.m.a.m. campus, t.u., biratnagar, nepal) for their fruitful suggestions and inspiring discussions. r.p. koirala et al./ bibechana 13 (2016) 60-71 : rcost p.70 (online publication: dec., 2015) references [1] r. hultgren, p.d. desai, d.t. hawkins, m. gleiser, k.k. kelly, selected values of the thermodynamic properties of binary alloys (asm, metal park, oh), 1973. 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[26] o. e. awe, o. akinlade, and l. a. hussain, z. metallkd., 96 (2005) 89. http://dx.doi.org/10.3139/146.018076 [27] e. o. ilo-okekea, b. c. anusionwua and o. popoola, phys. chem. liq., 43( 2005) 333. http://dx.doi.org/10.1080/00319100500087964 [28] j.-e. lee, k.-s. kim, k. suganuma, m. inoue and g. izuta, mater. trans. jim, 48 (2007) 584. http://dx.doi.org/10.2320/matertrans.48.584 [29] i. koirala, i. s. jha, b. p. singh and d. adhikari, physica b: condens. matter, 423 (2013) 49. http://dx.doi.org/10.1016/j.physb.2013.04.051 [30] j. pstrus, z. moser, w. gasior, appl. surf. sci., 257 (2011) 3867. http://dx.doi.org/10.1016/j.apsusc.2010.11.076 [31] i. koirala · b.p. singh · i.s. jha, j. non-cryst. solids, 398-399 (2014) 26. http://dx.doi.org/10.1016/j.jnoncrysol.2014.04.018 microsoft word koirala _96-103_.docx r c o s t n publisher: research council of science and technology, biratnagar, nepal p. 96 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana study of size mismatches effect on transport properties in cu-sb and cu-sn liquid alloys b. p. singh 1 , b. k. singh 1 , i. s. jha 3 , g. k. shrestha 1,4 , i. koirala 1,2* 1 university department of physics, t.m. bhagalpur university, bhagalpur, india 2 central department of physics, tribhuvan university, kirtipur, nepal 3 m.m.a.m. campus, biratnagar, tribhuvan university, nepal 4 pulchok engineering college, pulchok, ,lalitpur,nepal * e-mail : ikphysicstu@gmail.com accepted for publication: december 17, 2014 abstract we report a formalism that connects thermodynamics and transport properties such as viscosity and diffusion coefficient which has been used to calculate the concentration dependence of free energy of mixing, concentration-concentration fluctuations in the long wavelength limit and concentration dependence of diffusion and viscosity in cu-sb and cu-sn binary liquid alloys at 1190k and 1400k respectively with aid of size effect and no size effect. our calculations show that a reasonable degree of chemical order exists in both alloys system. it can be concluded that size mismatch has more effects on the transport properties of cu-sb hetero-coordinated system with greater size ratio than cusn hetero-coordinated system. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11781 © 2014 rcost: all rights reserved. keywords: hetero-coordinated alloys; size mismatch; diffusivity; viscosity. 1. introduction various empirical models have been used to study the structure and thermodynamics of the liquid binary alloys since midway of last century. however, it has been observed that establishing an empirical model that will link thermodynamics and transport properties of binary liquid alloys was a difficult task. to the best of our knowledge the empirical model of singh and sommer in ref. [1] was about the first pioneer work in providing the aforementioned essential link. in this model, they were able to link two transport quantities: viscosity (ɳ) and diffusion coefficient (d) for binary liquid alloys with thermodynamic quantities like the gibb’s free energy of mixing (gm) and the concentration fluctuation in the long wavelength limit (scc(0)). in essence, they related these four quantities by using enthalpic (i.e. energetics) and entropic (i.e. size) contributions to gm. this model has been singh et al./bibechana 12 (2015) 96-103: p. 97 applied at first by akinlade et al [2] to two segregating alloys, bi-zn and cu-bi and later o. e. awe applied it for four liquid alloys [3]. in the present paper, we employed the same empirical model of singh and sommer and darken thermodynamic equation of diffusion to investigate the effect of size on the transport properties of two copper based alloys (i.e.cu-sb and cu-sn). our choice of these two alloys was based on the fact that they are examples of alloys where size mismatch between atom-a and atom-b in each of the alloys is considered to be significant [4]. that is the volume or size difference between atom-a and atom-b does not lies within 50 percent and, hence, the difference is not negligible, i.e.at the melting points, in cu-sb, sb atom is 2.56 times bigger than the cu-atom and in cu-sn, sn atom is 2.29 times bigger than cu-atom [5]. in addition we are also aware that the two alloys represent the distinct classes of binary liquid alloys, namely, class of alloys that exhibit negative deviation from raoult’s law of linearity, known as hetero-coordinated or short-ranged ordered alloys. another reason for choosing to work on these alloys is that each of the two alloys has either an interesting features or is industrially relevant. the next section focuses on formalism for each of the transport properties of interest. we present the results of our calculations and their discussion in section 3. in the last section, we round off with concluding remarks. 2. formalism 2.1. transport properties: diffusion and viscosity essentially, viscosity and diffusion measurements are employed by theoreticians as well as experimentalists to extract information about alloying or atomic association in liquids as they shed light on the understanding of the mixing behavior and can be used to ascertain the stoichiometric composition of associates that are formed [6, 5]. also, from the point of view of ordering, diffusivity seems to be a more sufficient parameter than the warren–cowley short-range order, α1 on the ground that its calculation does not require any need of z as an input, and thus, the problems associated with its estimated value are overcame [6]. with a view to investigate the effect of size on the transport properties of the two alloys of present interest we have attempted to calculate their ratio of the mutual and self diffusion coefficients, dm/ds (or dm/did) as well as their viscosities using darken’s thermodynamic equation of diffusion as in ref. [6] and the model of singh and sommer as in ref. [1], respectively. 2.1.1. diffusion the relationship between darken’s thermodynamic equation of diffusion and concentrationconcentration fluctuation in long wavelength limits is given by ref.[4] as )0(s )0(s d d cc id cc id m = (1) where dm is the mutual or chemical diffusion coefficient and did is the self or intrinsic coefficients for ideal mixture while )0(s id cc is the ideal concentration-concentration fluctuations. the ratio dm / did indicates the mixing nature of molten alloys; dm / did < 1 indicates the tendency of homocoordination while dm / did > 1 indicates the tendency of hetero-coordination and dm / did approaches 1 for ideal mixing. consequently, the highest peak on the diffusivity curve (i.e. plot of dm/did against singh et al./bibechana 12 (2015) 96-103: p. 98 concentration of the species) suggest the presence of maximum chemical order in the liquid alloy system and the composition of the most probable associates to be formed in the liquid phase [6]. 2.1.2. viscosity the relationship between the viscosity (ɳ) and chemical diffusion coefficient (dm) is given by ref.[1,6,7] as b a b m b a k t c c d m m   η = + ψ     (2) where mi (i= a or b) is a parameter that depends on the size and shape of the particle i.e. ; kb and t are the respectively boltzmann’s constant and absolute temperature; ca and cb are the concentrations for a and b atom respectively. eq.(2) can be re-written as ɳ = ɳ 0 ψ (3) where ɳ 0 = b a b m b a k t c c d m m   +     (4) the expression of ψ that incorporates both enthalpic and entropic effect is given by ref.[1] as a b1 c c f ( ,w)ψ= − γ (5) with 2 2 a b 3 a b 2 w ( 1) (c c ) f ( ,w) (c c ) γ − γ − + γ γ = + γ (6) from eq.(2) and (5),one obtains the expression for viscosity a bc c f ( ,w) ∆η = − γ η (7) where ∆ɳ = ɳ ɳ o , deviation in ɳ. according to ref.[1],when only enthalpic effect is considered, the expression for ψ is given as a b b 2 1 c c k t  ω ψ = −      (8) where ω is the ordering energy. when eq.(2) and (8) are combined, we obtain an expression as a b b 2 c c k t  ∆η ω =−   η   (9) in the light of conformal solution it has been reported in ref.[1] that eq.(9) can be re-written in term of enthalpy of mixing, hm as singh et al./bibechana 12 (2015) 96-103: p. 99 mh rt ∆η =− η (10) where r is the molar gas constant. we have used eq.(9) to calculate the viscosity for each alloys when size mismatch is not taken into consideration and on the basis of eq.(10) considered the negative value of experimental enthalpy of mixing for each alloy as the corresponding experimental values of viscosity. eq.(7) is used to obtained the calculated values of viscosity when size mismatch is taken into consideration for each alloy. we shall employ the expressions for gm and scc(0) which incorporate the two fitting parameters( w and γ), are needed to calculate the transport properties. these expressions are based on guggenheim’s theory of mixture and quasi-lattice theory [9]. the equations which are used to compute gm and scc(0) for each of two alloys when size mismatch is taken into consideration(i.e.wse) are given as [9] wse m a b a g c ln(1 ) c ln c w rt = −β + β + β (11) where b a a b b c , w c c k t  γ ω β= =ω   + γ   wse a b cc a b c c s (0) 1 c c f ( ,w) = − γ (12) where γ = ωb/ ωa , size ratio of the constituent atoms. however, for the purpose of completeness we have as well computed the gm and scc(0) for each of the two alloys where size mismatch are immaterial (i.e.nse) using the following equations in simple statistical model[10] nse m a a b b a b b g c ln c c ln c c c rt k t ω = + + (13) nse a b cc a b b c c s (0) 2 1 c c k t =  ω −     (14) in order to investigate the effect of size mismatch on the diffusivity of each of the two alloys we put eq.(12) and (14) in turns in eq.(1) so as to obtain the following two equations which respectively represent the diffusivity when the size mismatch is taken into consideration (i.e.wse) and the diffusivity when size mismatch is immaterial (i.e.nse): wse m a b id d 1 c c f ( , w) d = − γ (15) nse m a b id b d 2 1 c c d k t  ω = −      (16) singh et al./bibechana 12 (2015) 96-103: p. 100 3. result and discussions although, the emphasis in this paper is on transport properties, we nevertheless need to calculate two of the bulk properties (gm and scc(0) ) so that we can obtain the two fitting parameters(i.e.w,γ ). we have no information on the experimental values of the transport properties while we have experimental data on gm and scc(0). in this light we shall employ the expressions for gm and scc(0) which incorporate the two fitting parameters. eqs.(11) and (12) have been used simultaneously to obtain the fitting parameters that give a good overall fit for gm and scc(0). the values obtained are shown in table 1.experimental values of gm for the two alloys obtained directly from hultgren et al [11]. the values of scc(0) are obtained via the values of experimental activity [11] as given by 1 1 a b cc b a a b a b a a s (0) c a c a c c − −    ∂ ∂ = =    ∂ ∂    where aa and ab are the observed chemical activities of atom a and b respectively. the values of fitting parameters obtained as shown in table 1 are quite reliable since figs. 1 and 2 indicate that we have a good fits for gm and scc(0) two alloys of current interest. a comparison of the plots of wse and nse in each of the figures show that the degree of asymmetry in cu-sb (γ=2.56) is more than that of cu-sn(γ=2.29). this implies that the effect of size mismatch on hetero-coordinated alloys is directly proportional to the size ratio. in addition, we observe that in these figures the plot of wse shows that in the hetero-coordinated alloys there is crossover from a decrease in the degree of heterocoordination to an increase in the degree of hetero-coordination. table 1 essential parameters for the calculation of transport properties for cu-sb and cu-sn at 1190k and 1400k respectively. alloys (ω / kbt)wse or (ω / kbt)nse γ cu-sb -0.211 2.56 cu-sn -0.169 2.29 ______________________________________________________________________________ the plots of graph of ratio of diffusion coefficients against concentration for each of the two alloys are shown in figs.3 and 4. in both alloys, dm/did is greater than one, indicates that alloys are heterocoordinated, as earlier confirmed in the bulk properties calculations. a comparison of the plots wse and nse reveals that the effect of size mismatch on cu-sb and cu-sn is to reduce the degree of hetero-coordination in the range of composition 0≤ ccu< 0.32 and increase the degree of heterocoordination in the rest of the composition. we also observe that the effect of size mismatch on the diffusivity of cu-sb is more than that on cu-sn, since the asymmetry caused by size mismatch is more pronounced in cu-sb than in cu-sn. also, in view of fact that size ratio of cu-sb is greater than cu-sn, we infer that there is direct relationship between size mismatch and diffusivity of heterocoordinated alloys. 0.2 0.4 0.6 0.8 1.0 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 ∆ η /η c cu 1 wse 2 wse 1 nse 2 nse fig.4 1= cu-sb 2= cu-sn 0.0 0.2 0.4 0.6 0.8 1.0 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 g m / r t c cu 1 wse 2 wse 1 nse 2 nse fig.1 1= cu-sb 2= cu-sn 0.2 0.4 0.6 0.8 1.0 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 d m / d id c cu 1 wse 2 wse 1 nse 2 nse fig.3 1= cu-sb 2= cu-sn 0.2 0.4 0.6 0.8 1.0 0.00 0.05 0.10 0.15 0.20 0.25 s c c (0 ) c cu 1 wse 2 wse 2 nse 1 nse fig.2 1= cu-sb 2= cu-sn singh et al./bibechana 12 (2015) 96-103: p. 101 fig. 1: free energy of mixing (gm/rt) vs concentration of copper(ccu) for cu-sb and cu-sn liquid alloys at 1190k and 1400k respectively; circles and stars represent experimental values[11] for cu-sb and cusn respectively;wse means with size effect and nse means no size effect. fig. 2: concentration-concentration fluctuation (scc(0)) vs concentration of copper(ccu) for cu-sb and cu-sn liquid alloys at 1190k and 1400k respectively; circles and stars represent experimental values[11] for cu-sb and cu-sn respectively;wse means with size effect and nse means no size effect. fig. 3: diffusion coefficient ratio (dm/did) vs concentration of copper(ccu) for cu-sb and cu-sn liquid alloys at 1190k and 1400k respectively; wse means with size effect and nse means no size effect. fig. 4: deviation of viscosity from ideal values (∆ɳ/ɳ 0 ) vs concentration of copper(ccu) for cu-sb and cu-sn liquid alloys at 1190k and 1400k respectively; circles and stars represent experimental values(-hm/rt) taken from ref.[11] for cusb and cu-sn respectively;wse means with size effect and nse means no size effect. singh et al./bibechana 12 (2015) 96-103: p. 102 a perusal of the plots in figs.3 and 4 for the two alloys shoes that the plots nse are symmetrical about equi-atomic composition while there is significant asymmetry in wse plots due to size mismatch. in addition, we observe that asymmetry in cu-sb is more than in cu-sn. this is in agreement with the statement that asymmetry in ∆ɳ about equi-atomic composition is induced by size factors [1]. 4. conclusions our studies of size mismatch effects on the transport properties of cu-sb at 1190k and cu-sn at 1400k have led to the following submissions: the size mismatch is either solely or at least majorly responsible for the asymmetry and shaping of the asymmetry in each of the two alloys. the degree of asymmetry of transport properties caused by size mismatch is directly proportional to the magnitude of size mismatch in the hetero-coordinated alloys. size mismatch has a crossover effect on the transport properties of the alloys studied: it reduces the degree of hetero-coordination in cu-sb and cu-sn in the range of composition 0≤ ccu< 0.32 and the increases the degree of hetero-coordination in the rest of composition. this work has confirmed that the presented model and formulation can be used to study the size mismatch effects on the transport properties of binary liquid alloys on the basis thermodynamic data. references [1] r.n.singh, f.sommer, phys.chem.liq.36 (1998)17. http://dx.doi.org/10.1080/00319109808035917 [2] o.akinlade, r.n.singh, f. sommer, j. alloys and compd. 267(1998)195. http://dx.doi.org/10.1016/s0925-8388(97)00547-1 [3] o.e.awe, physica b 405(2010)2545. http://dx.doi.org/10.1016/j.physb.2010.03.028 [4] r.n.singh, can.j.phys.65 (1987)309. http://dx.doi.org/10.1139/p87-038 [5] t. iida, r.i.l. guthrie, the physical properties of liquid metals. clarendon press; oxford.(1988). [6] r.novakovic, m.l.muolo, a.passerone, surf.sci. 549 (2004)281. http://dx.doi.org/10.1016/j.susc.2003.12.006 [7] b.c. anusionwu, o. akinlade, l.a. hussain, j.alloys compounds, 175 ( 1998) 278. singh et al./bibechana 12 (2015) 96-103: p. 103 [8] r.n.singh, n.h.march, intermettalic compounds, john wiley and sons, new work (1995). [9] e.a.gaggenheim, mixture,oxford university press, oxpord(1952). [10] i. koirala, b.p. singh, i.s. jha j. non-cryst.solids 398-399(2014)26-31. http://dx.doi.org/10.1016/j.jnoncrysol.2014.04.018 [11] r.hultgren,p.d. desai, d.t. hawkins, m. gleiser, and k.k. kelly, selected values of the thermodynamic properties of binary alloys, asm ,metal park,ohio, (1973). microsoft word shrestha et al(11-23) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal theoretical investigations on temperature dependence of thermodynamic properties and concentration fluctuations of in-tl binary liquid alloys by optimization method g. k. shrestha1, 2,* b. k. singh1, i. s. jha3 1university department of physics, t.m. bhagalpur university, bhagalpur, india. 2pulchowk campus, ioe, lalitpur, tribhuvan university, nepal. 3m.m.a.m. campus, biratnagar, tribhuvan university, nepal. *email: ganeshphy50@gmail.com article history: received 01 october, 2017; accepted 21 october , 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18470 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the thermodynamic properties, i.e. free energy of mixing (gm), heat of mixing (hm), entropy of mixing (sm) and activity (ai) of the component i (i ≡ in; tl�, and structural property i.e. concentration fluctuations in long wave-length limit [scc(0)] of in-tl binary liquid alloy at a specified temperature have been investigated in the framework of quasi-lattice model on assuming the coupled effect of size ratio and entropic (or energetic) as well as enthalpic effect. these properties of in-tl liquid alloy at 723 k have been computed theoretically by estimating the best fit value of order energy parameter (w) and size ratio (ω) over the entire range of concentration in order to match their experimental values. the best fit value of w at 723 k has been used to determine the values of w at different temperatures with the help of temperature derivative of w which are then used for the optimization procedure in order to calculate the corresponding values of excess free energy of mixing, partial excess free energy of mixing and activity of the components involved in the alloy at different temperatures. these parameters have been used to investigate the concentration fluctuations in long wavelength limit {scc(0)} of in-tl binary liquid alloy at different temperatures over the entire range of concentration which have been used to predict the various other structural properties like excess stability function (exs), diffusion coefficient ratio (dm/did), short range order parameter (α1) at different temperatures. keywords: order energy parameter; concentration fluctuations; free energy of mixing; optimization procedure. 1. introduction a binary alloy is a mixture of two elemental metals. in present days, various binary alloys have wide applications in many industries than their component element because of dramatic improvement in various useful properties like hardness, corrosion resistance, wear resistance, mechanical strength, fatigue strength, etc. as regards mixing of two metals, it is widely known that most metals dissolve in one another readily once they are in liquid phase but the same is not true for solid alloys. the g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.11 solubility of homogeneous solid phase is governed by size mismatch, electro-negativity difference and electron concentrations (i.e. electron per atom ratio). experience shows that these factors cannot be used effectively to interpret the alloying behaviour of liquid alloys to a great deal. the characteristic behaviour may be regarded as to the coupled effect of the energetic and structural arrangement of the constituent elemental metals. from the metallurgical standpoint, they are very important because many binary solid alloys are formed by cooling from a liquid phase. it is suggested that the energetic of the formation of solid alloys can be understood by the knowledge of the corresponding liquid phase. from the theory of liquid state, the liquid alloys are supposed to be simple liquids where structure is usually determined by two body central interactions. the liquid alloys are considered as disordered systems because they do not have long range order or magnetic order in them. the physical properties like thermodynamic, structural, surface, transport, electrical, etc. of liquid alloys show interesting behaviour as a function of concentration. thus the mixing behaviour of liquid alloys generates manifold interest for physicists, chemists and metallurgists. the anomaly in the properties of mixing of liquid alloys is least understood. hence, extensive theoretical investigations are required for the study of the mixing properties of binary liquid alloys. since long, the theoreticians have been working on various models [1-22] to interpret the physical properties of liquid alloys matching with available experimental results so that the mixing behaviour could adequately be understood. in the present research work, we have applied quasi-lattice model on assuming the coupled effect of size ratio and energetic (or enthalpic) contribution along with entropic effect to derive the analytical expressions for the thermodynamic properties like free energy of mixing (gm), activity (ai), entropy of mixing (sm), heat of mixing (hm) and concentration fluctuations in long wavelength limit (s (0�) of in-tl binary liquid alloys as discussed in section-2. the analytical expression for free energy of mixing (gm) contains two input parameters i.e. the size ratio (ω) and order energy parameter (w). the input parameters w and ω have been estimated by the method of successive approximation on using the experimental values of gm of in-tl binary liquid alloys at 723k and temperature derivative of w i.e. � � has been estimated by the same process on using the experimental values of sm of in-tl binary liquid alloys at 723 k. the computed values of free energy of mixing (gm), activity (ai), entropy of mixing (sm), heat of mixing (hm) and concentration fluctuations in long wavelength limit (s (0�) of in-tl binary liquid alloys at 723 k are compared with the corresponding experimental values in all the concentration ranging from 0.1 to 0.9 in section-3. further, the temperature dependence of the concentration fluctuations in the long wavelength limit, s (0� of in-tl binary liquid alloy has been computed by the optimization procedure [23] on taking into account of the thermodynamic data, theoretically obtained. the optimized coefficients set of excess free energy of mixing (g���) have been used to compute partial excess free energy of mixing of each component ( g� �,��� ), excess free energy of mixing (g���), activity (a�) of the component i (i≡in; tl�, and concentration fluctuations in long wavelength limit, s (0� in the entire range of concentration for the in-tl binary liquid alloy at four different temperatures i.e. 723 k, 1123 k, 1223 k and 1323 k in section-4. these values of concentration fluctuations in long wavelength limit (scc(0)) of in-tl binary liquid alloy at above mentoined temperatures as a function of concentration have been used to determine the various other structural properties like excess stability function (exs), diffusion coefficient ratio (dm/did), short range order parameter (α1) at corresponding temperatures. 2. formalism let us assume one mole binary liquid mixture of constituent x (≡in) and constituent y (≡tl) in which the constituent atoms x and y of the binary mixture are different in shape and size from each other. we consider the constituent x has concentration cx = c and the constituent y has concentration cy = (1-c) so that cn = nx (no. of constituent x) and (1-c)n=ny (no. of constituent y) where n represents avogadro's number. as explained by guggenheim [24] in the limit z (the coordination number) → ∞ on considering the coupled effect of size ratio and entropic (or energetic) as well as g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.12 enthalpic effect of the binary mixture (so that hm ≠ 0), the quasilattice theory (qlt) of liquid mixture gives an expression for free energy of mixing (gm) at a temperature (t) which is represented by �� = ��[(1 − #� ln ψ + c ln(1 − ψ� + cψw] (1) where the first two terms on right hand side appear due to entropic contribution and last term appears due to enthalpic contribution. here, r is the molar gas constant, and ) = *(+,�-.*(+,-� (2) where ω (= */*0 ; 12 > 14) is the size ratio of the alloy. also, w = γ� 6 ⍵89�: (3) which represents order energy parameter here, ;x is the number of a group of lattice sites, occupying by nx atoms of the constituent x, kb is the boltzmann constant and ω is the interchange energy, given by <=6∈42− ∈00. ∈//> : (4) where ∈�? (i; j ≡ in; tl) is i-j bond strength. 2.2 activity (ai) of constituent i from the standard thermodynamic relation, the activity of a constituent i of the binary liquid alloy, is given by �� @a bc = �� + #d 6e f ge h : (5) where ai and cj are the activity and concentration of component i and j ( i; j ≡in; tl) respectively. on solving equation (5) by using equation (1), we obtain @a b4 = @a(1 − )� + ) i(*,+�* j + )>k (6) also, @a b2 = @a ) − (1 − )�(1 − 1� + k1(1 − )�> (7) where ax and ay are the activities of the constituent x and y respectively. 2.3 concentration fluctuations in long wave-length limit (scc(0)) as explained by bhatia and thornton [25], the concentration fluctuations in long wavelength limit {sc c(0)} of binary liquid alloy at a temperature (t) is given by l--(0� = mn opq r sp tq uv ,w ,x (8) on solving equation (8) by using equation (1), we obtain l--(0� = ( +,�+ – (+,� {[(*,\�} (9) with ^(1, k� = >*q \,(*,+ �q{-. * (+,-�}{-.*(+,-�}_ (10) in the other hand, the experimental value of concentration fluctuations in long wavelength limit can also be determined from the activity (which is measured directly in experiment) as explained by singh [26] on using the relation l--(0� = c�a? o ` a au� , b,+ (11) where ci and aj are the concentration and activity of component i and j (i; j ≡ in; tl ) respectively. also, the ideal value of concentration fluctuations is obtained from the relation c--c d(0� = #(1 − c� (12) the concentration fluctuations in long wavelength limit (scc (0)) is the structural property of binary liquid alloys which gives the idea to understand the nature of liquid alloys. the mixing behaviour, i.e. g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.13 the nature of interaction of constituent atoms of binary liquid alloys can be analyzed with the help of deviation of scc(0) from c--c d (0). for the given composition, the binary liquid alloys is of ordering nature, if l--(0� < c--c d(0), but segregating nature, if scc (0) > c--c d(0). further, various properties of binary liquid alloys like excess stability function (exs), diffusion coefficient ratio (dm/did), short range order parameter (α1) can be computed by using the concept of concentration fluctuations in long wavelength limit. 2.4 entropy of mixing (sm) from the standard thermodynamic relation, the entropy of mixing for a binary liquid alloys is given by l� = − e(fg�en on solving this equation by using equation (1), we obtain f gm = −[(1 − #� ln ) + # ln(1 − )� + #)(k + � e\en �] (13) 2.5 heat of mixing (hm) from the standard thermodynamic relation, the heat of mixing for a binary liquid alloys is given by g gmn = fgmn + fgm = −#)�(e\en � (14) 3. results and discussion the free energy of mixing (gm) and activity (ai) of the constituent i (i ≡ in; tl ) of binary liquid alloys at a specified temperature have two input parameters i.e. size ratio (ω) and order energy parameter (w) so that they are needed to compute them. the size ratio (ω) for a binary liquid alloy has been estimated by knowing the atomic volumes of the constituent i at the specified temperature, t from the relation 1c(n� = 1c(nh�[1 + ijc(� − �k�] (15) where 1c(nh� is the atomic volume of the constituent i at the melting temperature (tm) and ijc is the coefficient of thermal expansion of the constituent i. on taking the values of αpi and 1c(nh� for in and tl from shimoji [27], the value of size ratio (ω) for in-tl binary liquid alloy at 723k is found to be 1.0973. however, this value of size ratio (ω) and order energy parameter (w) for in-tl binary liquid alloy at 723k have been adjusted to obtain the theoretical values for thermodynamic properties and concentration fluctuations of in-tl binary liquid alloys at 723k in the entire concentration range, matching with their corresponding experimental values. the values of size ratio (ω) and order energy parameter (w) have been estimated from equation (1), (6), (7), and (9) to reproduce simultaneously an overall fit for the experimental values of free energy of mixing (gm), activity (ai) of the component i (i=≡in; tl) and concentration fluctuations in long wavelength limit {sc c(0)} of in-tl liquid alloys at 723k as obtained from hultgren et. al. [28] in the entire concentration ranging from 0.1 to 0.9. in this process, we have determined the best fit value of size ratio (ω) and order energy parameter (w) for in-tl binary liquid alloys at 723k, which are found to be 1.15 and 0.48 respectively. the theoretical values of gm/rt on taking the values of ω = 1.15 and w = 0.48, as computed by using equation (1) and experimental values of gm /rt of in-tl liquid alloys at 723k in the entire concentration ranging from 0.1 to 0.9 [28] are shown in fig-1, which are in excellent agreement. the theoretical value of gm/rt at 723 k is minimum at the concentration, c = 0.5, which is found to be -0.567125 and the experimental value of gm/rt at 723 k is minimum at the same concentration, c = 0.5 which is found to be -0.566600. g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.14 0.0 0.2 0.4 0.6 0.8 1.0-2.0-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.0 intlfig-2:graph for lna i versus cin of in-tl liquid alloys at 723k (i=in;tl) lna i (i=in;tl) concentration of in (cin ) (lnain) th (lnatl) th (lnain) exp (lnatl) exp0.0 0.2 0.4 0.6 0.8 1.0-0.6-0.5-0.4-0.3-0.2-0.10.0 intlfig-1: graph for (gm / rt) versus cin of in-tl liquid alloys at 723kg m / rt concentration of in (cin ) (gm / rt)th (gm / rt)exp the theoretical values of ln bc (i ≡ in; tl) as computed by using equation (6) and (7) (on taking ω = 1.15 and w = 0.48), and experimental values of ln bc (i = x; y) of in-tl liquid alloys at 723 k [28] in the entire concentration range are shown in fig-2, which are in excellent agreement. the theoretical values of scc(0) for in-tl binary liquid alloys at 723k in the entire concentration range have been calculated by using the equation (9) (on taking 1 = 1.15 and w = 0.48) while the experimental values of concentration fluctuations in long wave-length limit (scc (0)) have been calculated by using the experimental values of activity in equation (11). the theoretical and experimental values of scc(0) in in-tl liquid alloys at 723k in the entire concentration range are shown in fig-3, which are in reasonable agreement with some discrepancies in the concentration range 0.4 < #lm < 0.7. the theoretical value of scc(0) is maximum at the concentration, c = 0.5 which is found to be 0.333612 while the experimental value of scc(0) is maximum at the same concentration, c = 0.5 which is found to be 0.318222. it is obvious that the concentration fluctuations in long wave-length limit {scc(0)} of in-tl liquid alloy at 723k is greater than the ideal value of concentration fluctuations { l--c d(0) } at each concentration which confirms that the in-tl liquid alloy has segregating nature. the value of temperature derivative of order energy parameter, i.e. e\en , for in-tl binary liquid alloy has been estimated from equation (13) or (14) to reproduce simultaneously an overall fit for the experimental values of entropy of mixing (sm) or heat of mixing (hm) of in-tl liquid alloy at 723k in the entire concentration ranging from 0.1 to 0.9. the best fit value of e\en for in-tl liquid alloy is found to be – 0.00048k-1. the theoretical values of sm/r as computed by using equation (13) and the corresponding experimental values of in-tl liquid alloys at 723k in the entire concentration range are shown in fig-4, which are in excellent agreement. the theoretical value of sm/r at 723k is maximum at the concentration, c = 0.5 which is found to be 0.660028 while the experimental value of sm/r at 723k is maximum at the same concentration, c = 0.5, which is found to be 0.659200. again, the theoretical values of hm/rt (on taking e\en = 0.00048k-1) as computed by using equation (14) and experimental values of hm /rt of in-tl liquid alloys at 723k in the entire concentration range are shown in fig-5, which are in reasonable agreement. the theoretical value of hm/rt at 723k is maximum at the concentration, c = 0.5 which is found to be 0.092813 but the experimental value of hm/rt at 723k is maximum at the concentration, c = 0.6 which is found to be 0.094700. g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.15 0.0 0.2 0.4 0.6 0.8 1.00.00.20.40.60.8 intlfig-4:graph for sm / r versus cin of in-tl liquid alloys at 723ks m / r concentration of in (cin) (sm / r)th (sm / r)exp0.0 0.2 0.4 0.6 0.8 1.00.000.050.100.150.20 intlfig-5:graph for (hm / rt) versus cin of in-tl liquid alloys at 723kh m / rt concentration of in (cin ) (hm / rt)th (hm / rt)exp0.0 0.2 0.4 0.6 0.8 1.00.00.10.20.30.40.5 intlfig-3:graph for scc(0) versus cin of in-tl liquid alloys at 723ks c c(0) concentration of in (cin ) sc c(0) th sc c(0) exp sc c(0) id this result reveals that the theoretical values of free energy of mixing (gm), entropy of mixing (sm), heat of mixing (hm), activity (ai) of both the constituents and concentration fluctuations in long wave-length limit {scc(0)} of in-tl binary liquid alloy at 723k and their corresponding experimental values are in good agreement so that the theoretical model mentioned in this research work successfully explain the various thermodynamic properties and concentration fluctuations of in-tl liquid alloy. thus, this estimated values of ω =1.15, w=0.48 and e\en = –0.00048k-1 for in-tl liquid alloy at 723k have been used in next section for optimization procedure to predict the thermodynamic properties and concentration fluctuations in long wave-length limit of in-tl liquid alloys at different temperatures. 4. optimization of free energy of mixing, activity, concentration fluctuations optimization procedure is the thermodynamic explanation in which statistical thermodynamics and polynomial expressions are used. it has good potential to obtain a consistent set of model parameters analytically which gives the idea to extrapolate into temperature and concentration region in which the direct experimental observation is not available. the adjustable coefficients, used in this process, are estimated by least-square method. the various thermodynamic properties, described by a power-series law whose coefficients are a, b, c, d, e, …….(say), are determined by least-square method [23]. the heat capacity at a temperature (t) can be expressed as pj = −p − 2r� − 2s�,> − … … … … .. (16) from the thermodynamic relation, the enthalpy is given by u = u(�v� + w cydt�v g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.16 = { − p� − r�> + 2s�,+ − … … … … … … (17) also, the entropy is given by l = l(�v� + w | }� dt�v = −~ − p(1 + ln �� − 2r� + s�,> − … … … … . . (18) on using equations (17) and (18), the standard thermodynamic relation, g = h – ts, provides the temperature (t) dependent free energy as � = { + ~� + p� ln � + r�> + s�,+ + … … … … . . (19) the concentration dependence of excess free energy of mixing is given by redlich-kister polynomial equation as ��4f(#, �� = #(1 − #� ∑ ��k��v (��[2# − 1]� (20) with ��(�� = {� + ~�� + p�� ln � + r��> + … … … … (21) the coefficients �� depend upon the temperature like g in equation (19). the least-square method has been used to obtain the unknown parameters involved in equation (20). so, we need the excess free energy of mixing (��4f) of the binary liquid alloys at different temperatures which can be determined by the relation ��4f = �� − ��cd = �� − ��[# ln # + (1 − #� ln(1 − c�] (22) thus, we require the values of free energy of mixing (gm) of binary liquid alloys at different temperatures which can be computed from equation (1) by knowing the values of order energy parameter (w) at different temperatures from the relation k(��� = k(�� + e\en (t8 − t� (23) where w(t) is the order energy parameter at the given temperature t, w(tk) is order energy parameter at required temperature tk and e\en represents temperature derivative of order energy parameter for the given liquid alloy. by using the best fit value of e\en and w(t) at the given temperature t= 723k (as obtained in section-3) in equation (23), the values of w(tk) at temperatures tk = 1123k, 1223k, 1323k are estimated and listed in table-1. table-1: estimated values of order energy parameter (w) at different temperatures in in-tl liquid alloys. it is also noted that the change in temperature may change the size ratio (1) of in-tl liquid alloy but the consequent change in the values of various thermodynamic properties of the alloys is obtained in negligible amount only. thus, for entire calculation of thermodynamic and other properties, the value of size ratio is taken as constant (i.e. ω = 1.15 for in-tl liquid alloy at all temperatures). the values of free energy of mixing (gm) of in-tl liquid alloys at different temperatures (i.e. at 723k,1123k, 1223k and 1323k) have been calculated by using the corresponding values of w in equation (1) in the entire range of concentration and then they are used to calculate the corresponding excess free energy of mixing (��4f) of in-tl liquid alloys at different temperatures (i.e. at 723k, 1123k, 1223k and 1323k) by using equation (22). the least-square method has been used to calculate the parameters involved in equation (20) and then the optimized coefficients for in-tl liquid alloys are computed which are listed in the table-2. temperature (tk) in k order energy parameter, w(tk) 723 0.480 1123 0.288 1223 0.240 1323 0.192 g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.17 0.0 0.2 0.4 0.6 0.8 1.002004006008001000 intlfig-6:graph for gmxs at different temperatures versus cin of in-tl liquid alloysg mxs (in j mol -1 ) concentration of in (cin ) (gmxs)723 (gmxs)1123 (gmxs)1223 (gmxs)1323 table-2: calculated values of optimized coefficients a l , b l , c l , d l (l = 0 to 3) for in-tl liquid alloy. values of l a l (j mol -1) b l (j mol -1 k 1) c l (j mol-1k-1) d l (jmol-1k2) 0 -0.0000000034 7.2745953781 0.0000000000 -0.0042691409 1 -0.0000000010 0.5094149143 0.0000000000 -0.0002978470 2 0.0000000025 0.0356759527 0.0000000000 -0.0000208206 3 -0.0000000047 0.0024917775 0.0000000000 -0.0000014526 further, the optimized value of partial excess free energy of mixing of the constituent x(≡ in) and y(≡tl) in in-tl liquid alloys are respectively given by ���,44f (#, �� = (1 − #�> ∑ ��k� � v (��[2#(@ + 1� − 1] (2c − 1 ��,+ (24) and ���,24f (#, �� = #> ∑ ��k� � v (��[2c(@ + 1� − 2@ − 1] (2c − 1��,+ (25) the partial excess free energy of mixing of both the components in and tl of in-tl liquid alloys at different temperatures (i.e. 723 k,1123 k, 1223 k and 1323 k) have been calculated separately over the entire concentration range by equations (24) and (25) with the help of optimized coefficients. these optimized values of partial excess free energy of mixing of both the components involved in the alloy have also been used to obtain the corresponding excess free energy of mixing for in-tl liquid alloys at different temperatures in the entire concentration range from the relation ��4f(#, �� = # ����,44f (#, ��� + (1 − #�{���,24f (#, ��} the optimized values of excess free energy of mixing for in-tl liquid alloys at different temperatures, t= 723k, 1123k, 1223k and 1323k in the entire concentration range are shown in fig-6. again, the optimized values of activity coefficients (γi ) in the entire concentration range of the component i, (i ≡ in ; tl) at corresponding temperature have been computed from the relation ���,c4f = �� ln ;c (26) with ;c = `� � (27) where ai and ci be the activity and concentration of the component i (i ≡in; tl) respectively of in-tl liquid alloys at corresponding temperature. the optimized values of partial excess free energy of mixing, the corresponding activity coefficients and hence activity of both the components involved in in-tl liquid alloys in the entire concentration range at the temperatures t= 723k,1123k, 1223k and 1323k are noted in table-3, table-4, table-5 and table-6 respectively. g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.18 table-3: optimized values of partial excess free energy of mixing, activity coefficients and activity of both the components involved in in-tl liquid alloys at 723k. #lm incomponent tl-component ���,lm4� ln ;lm = ���,lm4��� ;lm blm ln blm ���,n�4� ln ;n� = ���,n�4��� ; n� bn� ln bn� 0.1 2353.049 0.391 1.479 0.148 -1.911 25.235 0.004 1.004 0.904 -0.101 0.2 1909.659 0.318 1.374 0.275 -1.292 103.686 0.017 1.017 0.814 -0.206 0.3 1502.298 0.250 1.284 0.385 -0.954 239.719 0.040 1.041 0.728 -0.317 0.4 1134.509 0.189 1.208 0.483 -0.728 438.058 0.073 1.076 0.645 -0.438 0.5 810.136 0.135 1.144 0.572 -0.558 703.829 0.117 1.124 0.562 -0.576 0.6 533.360 0.089 1.093 0.656 -0.422 1042.594 0.173 1.189 0.476 -0.743 0.7 308.744 0.051 1.053 0.737 -0.305 1460.397 0.243 1.275 0.383 -0.961 0.8 141.268 0.024 1.024 0.819 -0.200 1963.800 0.327 1.386 0.277 -1.283 0.9 36.373 0.006 1.006 0.905 -0.099 2559.925 0.426 1.531 0.153 -1.877 table-4: optimized values of partial excess free energy of mixing, activity coefficients and activity of both the components involved in in-tl liquid alloys at 1123k. #lm incomponent tl-component ���,lm4� ln ;lm= ���,lm4��� ;lm blm ln blm ���,n�4� ln ;n� = ���,n�4��� ; n� bn� ln bn� 0.1 2164.205 0.232 1.261 0.126 -2.071 23.194 0.002 1.002 0.902 -0.103 0.2 1756.605 0.188 1.207 0.241 -1.421 95.314 0.010 1.010 0.808 -0.213 0.3 1382.056 0.148 1.160 0.348 -1.056 220.391 0.024 1.024 0.717 -0.333 0.4 1043.828 0.112 1.118 0.447 -0.804 402.790 0.043 1.044 0.626 -0.468 0.5 745.471 0.080 1.083 0.542 -0.613 647.246 0.069 1.072 0.536 -0.624 0.6 490.846 0.053 1.054 0.632 -0.458 958.901 0.103 1.108 0.443 -0.814 0.7 284.168 0.030 1.031 0.722 -0.326 1343.339 0.144 1.155 0.346 -1.060 0.8 130.039 0.014 1.014 0.811 -0.209 1806.629 0.193 1.213 0.243 -1.416 0.9 33.486 0.004 1.004 0.903 -0.102 2355.354 0.252 1.287 0.129 -2.050 table-5: optimized values of partial excess free energy of mixing, activity coefficients and activity of both the components involved in in-tl liquid alloys at 1223k. #lm incomponent tl-component ���,lm4� ln ;lm = ���,lm4��� ;lm blm ln blm ���,n�4� ln ;n� = ���,n�4��� ; n� bn� ln bn� 0.1 1951.069 0.192 1.212 0.121 -2.111 20.903 0.002 1.002 0.902 -0.103 0.2 1583.705 0.156 1.169 0.234 -1.454 85.904 0.008 1.008 0.807 -0.215 0.3 1246.097 0.123 1.130 0.339 -1.081 198.645 0.020 1.020 0.714 -0.337 0.4 941.199 0.093 1.097 0.439 -0.824 363.071 0.036 1.036 0.622 -0.475 0.5 672.217 0.066 1.068 0.534 -0.627 583.459 0.057 1.059 0.530 -0.636 0.6 442.640 0.044 1.044 0.627 -0.467 864.457 0.085 1.089 0.435 -0.831 0.7 256.276 0.025 1.026 0.718 -0.331 1211.112 0.119 1.126 0.338 -1.085 0.8 117.283 0.012 1.012 0.809 -0.212 1628.907 0.160 1.174 0.235 -1.449 0.9 30.203 0.003 1.003 0.903 -0.102 2123.796 0.209 1.232 0.123 -2.094 table-6: optimized values of partial excess free energy of mixing, activity coefficients and activity of both the components present in in-tl liquid alloys at 1323k. #lm incomponent tl-component ���,lm4� ln ;lm = ���,lm4��� ;lm blm ln blm ���,n�4� ln ;n� = ���,n�4��� ; n� bn� ln bn� 0.1 1671.564 0.152 1.164 0.116 -2.151 17.899 0.002 1.002 0.901 -0.104 0.2 1356.951 0.123 1.131 0.226 -1.486 73.567 0.007 1.007 0.805 -0.216 0.3 1067.779 0.097 1.102 0.331 -1.107 170.134 0.015 1.016 0.711 -0.341 0.4 806.587 0.073 1.076 0.430 -0.843 310.991 0.028 1.029 0.617 -0.483 0.5 576.129 0.052 1.054 0.527 -0.641 499.816 0.045 1.046 0.523 -0.648 0.6 379.404 0.034 1.035 0.621 -0.476 740.605 0.067 1.070 0.428 -0.849 0.7 219.684 0.020 1.020 0.714 -0.337 1037.699 0.094 1.099 0.330 -1.110 0.8 100.546 0.009 1.009 0.807 -0.214 1395.814 0.127 1.135 0.227 -1.483 0.9 25.896 0.002 1.002 0.902 -0.103 1820.072 0.165 1.180 0.118 -2.137 g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.19 0.0 0.2 0.4 0.6 0.8 1.00.000.050.100.150.200.250.300.35 intl fig-8:graph for optimized values of s cc (0 ) versus c in of in-tl liquid alloys at different temp. s cc(0) at different temp. concentration of in (cin) (scc(0)id) (scc(0)723) (scc(0)1123) (scc(0)1223) (scc(0)1323)0.0 0.2 0.4 0.6 0.8 1.0-2.0-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.0 intlfig-7:graph for optimized lnai versus cin of in-tl liquid alloys (i=in;tl) at different temp.lna i (i=zn;sn) concentration of zn (czn ) (lnain )723 (lnatl )723 (lnain )1123 (lnatl )1123 (lnain )1223 (lnatl )1223 (lnain )1323 the natural logarithms of optimized values of activities of both the components of in-tl liquid alloys at different temperatures t= 723k,1123k, 1223k and 1323k in the entire concentration range are shown in fig-7. again, the concentration fluctuations in long wave-length limit {scc(0)} of in-tl liquid alloys at different temperatures t= 723k,1123k, 1223k and 1323k in entire concentration range have been computed by using equation (11) with the help of the corresponding optimized values of the activities of both the components which are shown in fig.-8. from this result, it is concluded that the concentration fluctuations in long wavelength limit of in-tl liquid alloys at the temperatures between 723k and 1323k decreases as the temperature increases and shift towards the ideal value of concentration fluctuations (s � �(0�) at each concentration on increasing the temperature but remains greater than the ideal value of concentration fluctuations which indicates that the in-tl liquid alloy has segregating nature in the entire concentration range but the segregating nature decreases as the temperature increases. from the relation for excess stability function(s4 f � = oeqfg0 �e�q u = �� � +f��(v� −+f�� h� (v�� [23], the excess stability function at the temperature t = 723k, 1123k, 1223k and 1323k in the entire concentration range have been calculated from optimized data which are shown in fig-9 and they give the idea to predict stability of in-tl liquid alloys at different temperatures. this result suggests that the excess stability function of in-tl liquid alloy becomes less and less negative as the temperature increases more and more which indicates that the stability of in-tl liquid alloy increases as the temperature increases i.e. the bond strength between unlike atoms of the alloy increases as the temperature increases. 0.0 0.2 0.4 0.6 0.8 1.0-10 intl fig-9:graph for opt. exs/rt versus cinof in-tl liquid alloys at different temperaturesexs /rt (at different temp.) concentration of in (cin) opt. (exs/rt)723 opt. (exs/rt)1123 opt. (exs/rt)1223 opt. (exs/rt)1323 g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.20 0.0 0.2 0.4 0.6 0.8 1.00.0000.0050.0100.0150.0200.0250.030fig-11:graph for optimized sro(a1) versus cin of in-tl liquid alloys at different temp.sro(a 1) at different temp. concentration of in (cin) opt. (a1)723 opt. (a1)1123 opt. (a1)1223 opt. (a1)1323 again, the diffusion coefficients (�h�h� � of in-tl liquid alloy at different temperatures in the entire concentration range can also be computed by using the optimized data from the relation �h�h� = f��h� (v�f�� (v� [23], which are shown in fig-10. this result reveals that the diffusion coefficient for in-tl liquid alloys increases as the temperature increases in the entire concentration range. in order to determine the extreme condition of segregation, i.e. phase separation, we can use the knowledge of warren-cowley short range order parameter (sro), i+, for the first neighbour shell (l=1) which is directly related to l--(0� and represented by the relation [23] i+ = f∗,+f∗(�,+�.+ where z is the co-ordination number and l∗ = f��(v�f��h�(v� the optimized values of i+ (computed from the above relation on taking z = 10) of in-tl liquid alloys at different temperature is shown in fig-11, which exhibits the temperature dependence of sro (i+) in the entire concentration range. our result reveals that the values of sro (i+) are positive at all the temperatures such that the value of i+increases on decreasing the temperature. its value is far lower than the required value for phase separation, i.e. ik�� = +1, even at the lowest temperature under consideration. at all the temperatures under consideration, the magnitude of i+ is though positive but much less than unity which indicates that the in-tl binary liquid alloy is weak homo-coordinated alloy. 5. conclusions the following conclusions may be drawn from the study of this theoretical investigation in in-tl liquid alloys: • the size ratio (ω) plays vital role in determining the mixing properties of the in-tl liquid alloys at a specified temperature but its effect in the values of other thermodynamic and structural properties of the alloy due to temperature change is only negligible and hence it is taken as constant at all above temperatures. • the order energy parameter (w) plays important role in determining the mixing properties of the in-tl liquid alloys which has a fixed value at a particular temperature and it is temperature dependent. the values of w between temperature range 723k and 1323k in in-tl liquid alloys are + ve and its value decreases as the temperature increases which indicates that the segregating nature of the alloy decreases as the temperature increases. 0.0 0.2 0.4 0.6 0.8 1.00.00.10.20.30.40.50.60.70.80.91.0 intlfig-10:graph for opt. dm/did versus cin of in-tl liquid alloys at different temp.d m/d id at different temp. concentration of in (cin ) opt. (dm/did)723 opt. (dm/did)1123 opt. (dm/did)1223 opt. (dm/did)1323g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.21 • the values of concentration fluctuations in long wavelength limit between temperature range 723k and 1323k in in-tl liquid alloys are always greater than the ideal value of concentration fluctuations at each concentration so that this alloy is of segregating nature in this range of temperature. • the concentration fluctuations in long wavelength limit of in-tl liquid alloy decreases as the temperature increases at each concentration and shifts towards the ideal value of concentration fluctuation as the temperature increases which indicates that the segregating nature of the alloy decreases as the temperature increases. • the free energy of mixing (gm), entropy of mixing (sm), heat of mixing (hm) and the concentration fluctuations (scc(0)) in long wavelength limit of in-tl liquid alloys are symmetrical at the equiatomic composition of its constituents (i.e. c = 0.5) so that it is symmetric alloy. • the excess free energy of mixing in in-tl liquid alloy decreases as the temperature of the alloy increases which indicates that the bonding strength between unlike atoms present in the alloys increases as temperature increases. • the excess stability function of in-tl liquid alloy becomes less and less negative as the temperature increases more and more which indicates that the stability of in-tl liquid alloy increases as the temperature increases. • the diffusion coefficient for in-tl liquid alloys in the entire concentration range increases as the temperature increases. • the values of sro (i+) are positive at all the temperatures under consideration such that the value of i+increases on decreasing the temperature which is far lower than the required value for phase separation, i.e. ik�� = +1, even at the lowest temperature under consideration so that the in-tl binary liquid alloy is weak homo-coordinated alloy. references [1] i. koirala, b. p. singh, i. s. jha, theoretical assessment on segregating nature of liquid in–tl alloys, j. non. cryst. solids 398–399 (2014) 26–31. doi.org/10.1016/j.jnoncrysol.2014.04.018. 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[26] r. n. singh, short-range order and concentration fluctuations in binary molten alloys, can. j. phys. 65 (1987) 309–325. doi.org/10.1139/p87-038 [27] m. shimoji, liquid metals. academic press, 1977. [28] r. hultgren, p. d. desai, d. t. hawkins, m. gleiser k. k. kelley, selected values of thermodynamic properties of binary alloys. metal park, asm international, ohio, 1973. g.k. shrestha et al. / bibechana 15 (2018) 11-23: rcost p.23 r.n. yadav et al. / bibechana 13 (2016) 132-136: rcost p.132 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal finite partially ordered set and some of its properties r. n. yadav1, s. k. chakrabarti2*, i. s. jha2 and u. p. yadav1 1department of mathematics, m. m. a. m. campus, tribhuvan university, biratnagar, nepal 2department of physics, m. m. a. m. campus, tribhuvan university, biratnagar, nepal *e-mail: skc_2007@yahoo.com article history: received 21 july, 2015; accepted 29 november, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13985 abstract this paper focuses on some main properties of the finite partially ordered sets. these properties are furnished in the form of theorems. here we have presented three such theorems. the first theorem is called as ‘duality theorem’. this fundamental theorem was first obtained by greene. few years later it was rediscovered and given an alternative proof by fomin. the second theorem bestows the functionality property. the proof of this was also done by greene. however, gansner gave an alternative proof of the theorem taking advantage of a connection between poset and linear algebra. the proof of the third theorem is fully due to us. this theorem gives rise to a recursive computation of the shape. in the present paper we have discussed the first two properties through suitable illustrations only whereas a complete proof is furnished for the last one. ©rcost: all rights reserved. keywords: poset; ferrers shape; duality theorem; functionality; recursive computation. 1. introduction a set is a well-defined collection of objects called as elements [1]. an ordered set is a sequence of elements that is distinguished from the other sequences of the same element by the order of the elements. a partially ordered set (or poset) is a set in which a relation as ‘less than or equal to’ holds for some pairs of elements of the set but not for all. formally, a poset is defined as an ordered pair p = (x, ≤), where x is called the ground set of p and ≤ is the partial order of p. an element u in a partially ordered set (x, ≤) is said to be an upper bound for a subset s of x if for every s  s, we have s ≤ u. similarly, a lower bound for a subset s is an element l such that for every s  s, l ≤ s. if there are an upper bound and a lower bound for x, then the poset (x, ≤) is said to be finite. here we bring together some main properties of finite posets in the form of theorems. in this spirit, we r.n. yadav et al. / bibechana 13 (2016) 132-136: rcost p.133 (online publication: dec., 2015) begin our presentation by stating greene’s fundamental theorem that introduces the map p  (p). the next theorem asserts that the shape (p) grows as new maximal elements added to the poset p. the third theorem, representing a recursive computational property, is furnished with our proof of the same. 2. properties 2.1. theorem 1 let p be a finite partially ordered set of cardinality n. a chain is a totally ordered subset of p. an antichain is a subset of p in which no two elements are comparable. according to dilworth, the maximal size of an antichain in p is equal to the minimal number of chain into which p can be partitioned [2]. this has an easy ‘dual’ counterpart in which the words ‘chain’ and ‘antichain’ can be interchanged. such duality has a beautiful and powerful common generalisation due to greene. for k = 0, 1, 2, 3, ..., let ak (resp. ck) denotes the maximal cardinality of a union of k antichains (resp. chains) in p. let k = ck – ck-1 and = ak – ak-1 for all k ≥ 1. theorem : for any finite partially ordered set p the sequences  = (1, 2, …) and = ( , , …) are weakly decreasing and form conjugate partitions of the number n = [p]. for posets this is the fundamental theorem called as ‘duality theorem’. this theorem was first obtained by greene as a corollary of another result due to greene and kleitman [3, 4]. few years later fomin gave an alternative proof of it [5]. other proofs appeared as well [6–8]. the duality theorem associates to every finite poset having ferrers shape whose row lengths are 1, 2,  … and column lengths , , … . we have identified this shape with the partition  and denoted it by p(). (a) p (b) (p) fig. 1 : duality theorem. to illustrate, let us consider the poset p in fig. 1. for this poset we have c0 = 0, c1 = 4, c2 = c3 = … = 6 f d e b c a r.n. yadav et al. / bibechana 13 (2016) 132-136: rcost p.134 (online publication: dec., 2015) implying  = (4, 2) while a0 = 0, a1 = 2, a2 = 4, a3 = 5, a4 = a5 = … = 6 imply that = (2, 2, 1, 1), a shape conjugate to . various attempts have been made to generalise theorem 1 to directed graphs [9–11]. the following ‘functionality’ result shows that the shape of a poset contains the shape of its arbitrary order ideal. 2.2. theorem 2 theorem : if p be a maximal (or minimal) element of a finite partially ordered set p, then (p – {p})  (p). for example, the poset p in fig. 1 has maximal elements e and f. the shapes (p–{e}) and (p–{f}) are shown in fig. 2; both are contained in (p). (a) (p – {e}) (b) (p – {f}) fig. 2 : theorem 2. in theorem 2 the restriction for p  p to be an extremal element cannot be dropped. a counter-example is given in fig. 3. fig. 3 : a counter-example : (p – {p})  (p). fig. 4 : a linear extension and the associated standard tableau. p 6 4 5 2 3 1 1 2 3 5 4 6 r.n. yadav et al. / bibechana 13 (2016) 132-136: rcost p.135 (online publication: dec., 2015) this theorem implies that any linear extension  : p [n] = {1, 2, 3, …, n} of p gives rise to a standard young tableau t of shape (p) defined by the condition that the entries 1, 2, 3, …, k of t form [12] the shape ( [1, k]). as an example, let us consider the poset in fig. 1 and its linear extension given by (a) = 1, (b) = 2, …, (f) = 6. the resulting standard tableau is given in fig. 4. it is also greene who deduced this theorem. however, gansner gave an alternative proof of it by the connection of poset with linear algebra. a generalisation of the theorem to path families in acyclic directed graphs was also given by gansner [13]. 2.3. theorem 3 let p1 p2 be the fall list of maximal elements in p. then the shape  = (p) is uniquely determined by the shapes (p–{p1}), (p–{p2}), (p–{p3}), …, (p–{pk}). theorem : if (p – {p1}) = (p – {p2}) = (p – {p3}) = … = (p – {pk}) = , then  is obtained by adding a box into the kth row of . theorem 3 represents a recursive computational property. we furnish below a proof of this theorem. the proof is fully due to us. 3. proof in order to prove theorem 3 let us recall the lemma : if c = {c1, c2, c3, ..., cl} and a = {a1, a2, a3, …, ak} are the chain and antichain respectively, then c and a are orthogonal if and only if : (i) c is a maximal chain l-family, (ii) a is a maximal antichain k-family and (iii) the point (k, l) lies on the outer boundary of the shape (p). it will be convenient to assume that p1, p2, p3, …, pk is the complete list or minimal (rather than maximal) elements of p. the resulting statement is equivalent to theorem 3 if we pass to the dual poset. let us assume that (p – {p1}) = (p – {pk}) = . the shape (p) is obtained by adding a box to . say, this box lies in row r and column s. we need to show that r = k. the number of elements covered by a maximal chain r-family decreases by 1 if any of the pi is removed from p. hence, any maximal chain r-family in p covers all the pi, implying r  k. let a = {a1, a2, a3, …} be a maximal antichain s-family in p and, furthermore, assume that a is of canonical form. since the number of elements covered by such a family decreases if any of the pi is removed, we conclude that all the pi are covered by a and, therefore, contained in a1. since any element of p is comparable to some of the pi, the antichain a1 may not contain any other elements. and its cardinality is equal to k. on the other hand, by the above lemma, a is orthogonal to any maximal chain rfamily. therefore, any antichain a (inducting a1) must contain at least r elements. thus k  r and we are done. 4. conclusion the correspondence p  (p) is intimately related to at least three areas of discrete mathematics : combinatorial optimisation, lattice theory and combinatorics of tableaux. the theorems enumerated here r.n. yadav et al. / bibechana 13 (2016) 132-136: rcost p.136 (online publication: dec., 2015) furnish some main properties of finite partially ordered sets. theorem 3, which we have proved above from a poset-theoretic viewpoint, describes a simple recursive algorithm for computing the shapes λ(p') for all order ideals p' of a given finite poset p. such ideals form a distributive lattice. references [1] h.s. sharma and s.s. seth, modern algebra, ram prasad and sons, agra, (1981. [2] r.p. dilworth, ann. math., 102 (1956) 161. [3] c. greene, j. combin, th. ser., a 20 (1976) 69. [4] c. greene and d.j. kleitman, j. combin. th. ser., a 20 (1976) 41. [5] s.v. fomin, soviet math., d 19 (1978) 1510. [6] a. frank, j. combin. th. ser., b 29 (1980) 176. [7] s. felsner, j. combin. th. ser., b 57 (1993) 309. [8] k. engel, spencer theory, cambridge university press, cambridge, 1997. [9] n. linial, j. combin. th. ser., a 30 (1981) 331. [10] d.b. west, graphs and order, reidel, boston, 1985. [11] i.b.a. hartman, f. saleh and d. hershkowitz, j. graph th., 18 (1994) 169. [12] r.p. stanley, enumerative combinatories, cambridge university press, cambridge, 1999. [13] e.r. gansner, siam j. algebra disc. methods, 2 (1981) 429. j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.37 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal the socio economic effect of cancer on patients’ livelihoods in kenyan house holds j. mutuma*, j. wakhungu, c. mutai centre for disaster management and humanitarian assistance, masinde muliro university of science and technology, p.o.box 190, kakamega, kenya *email: mutumajg2@gmail.com article history: received 24 july, 2016; accepted 5 august, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15412 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the study assessed the socio economic effect of cancer on patients’ livelihoods in kenyan households. in kenya, cancer is ranked third among the main causes of death after infectious and cardiovascular diseases. in recent years, cases of cancer in kenya have increased creating a burden on many households. this has negatively impacted on poverty alleviation and sustainable development in the long run. a sample of 245 patients seeking treatment in the three major oncology centers in the country namely kenyatta national and referal hospital, moi teaching and referal hospital and agakhan university hospital was used. . data was collected through self-administered questionares, focus groups discussions and key informant interviews. a triangulation approach involving in-depth interview using questionnaires as the main collection instrument for key informants were carried out. secondary data was collected through case study, review of documents, reports and publications related to the topic and online journals. chi square was used to test the independence of variables. the result revealed poverty, late and poor cancer diagnosis and lack of medical cover were found to be the top ranking serious challenges facing cancer patients in the country. cross-sectional survey, correlational and evaluation research designs were adopted for the study. both non-probability sampling and probabilistic sampling methods were used in selecting subjects seeking treatment at the three main oncology centers in kenya. keywords: vulnerability; cancer; household; livelihoods; poverty. http://nepjol.info/index.php/bibechana mailto:mutumajg2@gmail.com http://dx.doi.org/10.3126/bibechana.v14i0.15405 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.38 (online publication: dec., 2016) 1. introduction in kenya, cancer is ranked third among the main causes of death after infectious and cardiovascular diseases [1]. in recent years, cases of cancer in kenya have increased creating a burden on many households. this has negatively impacted on poverty alleviation and sustainable development in the long run [1]. the rapid increase in the number of cancer cases has increased public health crisis with a critical and direct negative impact on the first three millennium development goals (mdgs) namely; poverty, education, and gender equity especially in the developing countries, where 58% of all cancer deaths occur [2]. although population based data does not exist in the country, it is estimated that the annual incidence of cancer is about 28,000 cases and the annual mortality to be over 22,000. over 60% of those affected are below the age of 70 years [3]. the treatment and management of cancer is expensive to a poor economy like kenya and the most recommended treatment regimens including chemotherapy, surgery and radiation are unaffordable to most of the patients and their families. the few who are able to afford the treatment are often forced to a lifestyle change as the treatment and management of the disease eats into finances and investments[1]. additionally, cancer patients experience psycho socio and economic issues including worry, social stigma, lowered self-esteem, employment factors, impact on family and relationships, an increased sense of vulnerability, uncertainty about the future, and fear of death [4]. though research has been carried on the occurrence, awareness, causes, prevention, and treatment of cancer in kenya [1] there’s hardly any research that has been conducted to study the socio economic impact of cancer to sustainable livelihood. the rising medical costs associated with cancer have led to considerable financial hardship for patients and their families. a study by who in america concludes that approximately onethird of the cancer survivors had gone into debt and 3 percent had filed for bankruptcy, of those who had gone into debt, 55 percent incurred obligations of $10,000 or more, it further observes that cancer survivors who were younger, had lower incomes, and had public health insurance were more likely to go into debt or file for bankruptcy, compared to those who were older, had higher incomes, and had private insurance, respectively [5]. in kenya due to the economic status of most patients there is likelihood that more cancer patients will fall into debts. there are several causes of societal and economic impact of cancer health disparities. this statement attempts to quantify three types of costs: the cost of premature death, the cost of medical care to cancer patients, and the indirect cost of cancer on economic productivity through lost wages and hours worked [6]. in a study done by arrossi et al (2007) on socio economic impact of cancer, he found out that the impact of cervical cancer is considerable and can have negative consequences on treatment compliance [7]. j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.39 (online publication: dec., 2016) mulemi (2010) observes that cancer impacts negatively on the livelihood of people of low socioeconomic status because it leads to more poverty [8]. the economic costs of cancer are high for both the person with cancer and for society as a whole. the agency for healthcare research and quality (ahrq) estimates that the direct medical costs (total of all health care costs) for cancer in the us in 2011 were $88.7 billion. 50% of this cost is for hospital outpatient and doctor office visits, 35% of this cost is for inpatient hospital stays while 11% of this cost was for prescription drugs [9]. according to cancer facts & figures 2015, uninsured patients and those from ethnic minorities are substantially more likely to be diagnosed with cancer at a later stage, when treatment can be more extensive, more costly, and less successful. the diagnosis of a cancer has far reaching economic and social consequences on the individual, his family and the society. the economic consequences are the direct and indirect costs incurred upon the individual over the course of the disease. direct costs include cost of medicines, physician consultation charges, hospital admission charges, investigation charges and cost of medical durables like wheel chairs, wound care supplies or respirators especially when hospital stay becomes prolonged and expensive requiring a shift to home care [10]. the indirect costs include loss of productivity of both the patient and a close family member who has to take the role of the care giver [10]. the social impact of cancer is far reaching and often not quantifiable. it involves a huge amount of suffering and pain, both physical and psychological, for the patient and his family. often the patient has limitation in performing everyday tasks like bathing, dressing or eating; deteriorating his quality of life further [10]. according to merletti et al., (2011), cancer has adverse social effects on the livelihood of patients. they say that prolonged cancer hospitalization usually alienates cancer patients from their livelihood and social relationships. they acknowledge that cancer hospitalization usually takes six consecutive months, and this makes victim’s lives to oscillate around medication and therapy. according to them, cancer patients lose their social identity in the process of seeking medical attention. these authors agree that most cancer patients usually lose employment in the course of seeking medical attention. they posit that those who find themselves in such a situation end up depending on handouts from relatives, and this demeans their social standing [11]. taylor et al. [12] believe that hospitalization and management of cancer is usually an additional threat to the fragile life of patients. they argue that the lengthy hospitalization associated with cancer treatment exhausts the patient’s capacity to cope with illness. by derailing the patient emotionally, the author believes that it affects his/her social wellbeing [12]. these sentiments are shared by mulemi [8], who considers the case of a caretaker, who experienced the frustrations of cancer patients who were working with a certain company in nairobi kenya. the author narrates how patients who receive lengthy cancer treatment are forced to retire early because of becoming less productive. http://www.addresshealth.com/thought_leadership/living-with-epilepsy-fits/ http://www.addresshealth.com/thought_leadership/living-with-epilepsy-fits/ j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.40 (online publication: dec., 2016) 2. methods and materials study area the study was conducted in kenya. kenya lies across the equator in east-central africa, on the coast of the indian ocean (figure 3.1). kenya has a total area of 224,962 square miles. kenya borders somalia to the east, ethiopia to the north, tanzania to the south, uganda to the west, and sudan to the northwest. the population of kenya is approximately 44.6 million (knbs, 2015). 44 % of the country population lives below the poverty line of 1.25 us dollars per day (world bank, 2014). kenya current per capita income is about us $1,700 according to international monetary fund which places kenya as number 154 out of 183 world countries. a study by the institute of security studies (iss) has found that 18.4 million kenyans, out of 46.3 million, live in extreme poverty. 3. methodology study population the study targeted patients seeking treatment in the three referral hospitals and members of affected households (caregivers) having a surviving family member and key informants (oncologists and nurses). caregiver’s were members of a house hold or the main person responsible for the social wellbeing of the patient. it included close relatives such as spouses, adult children of the patient, brothers, sisters, uncles and aunts who were actively involved in the patients care. others target were major stakeholders involved in cancer care including oncologist and nurses who are also actively involved in patient care during their stay in the hospital. sample size and sample techniques the sample was determined using the formula by fisher et al. (1998). the sample size of 245 was arrived at using the following formula. in total 245 cancer patients were selected for the study. a large sample was required to produce salient characteristics of the population to an acceptable degree and also reduce sampling errors [15]. the respondents who formed the sample were from kenyatta national hospital, agha khan university hospital and moi teaching and referral hospital. reconnaissance visits were made to the study sites. the information obtained formed the basis for selection of patients for the survey. during the same period, the questionnaires were pre-tested (to 25 patients) and necessary corrections were made on the questionnaire before a full-scale survey was undertaken. this process utilized convenience sampling method, muilti stage sampling method, purposive and quota sampling methods. data collection data gathering was through multiple methods; primary data was collected using self and researcher administered structured quesionnaires. key informant interview schedule and focused groups discussion j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.41 (online publication: dec., 2016) (fgds) were employed to obtain data from the patients’ medical personnel and caregivers. fgds consisted of two groups from each healthcare facility i.e. the patients and the caregivers. a total of 7 fgds were conducted at knh, mtrh, and akuh. in each of the hospitals, one fgds were conducted for nurses. data analysis the statistical package for social sciences (spss-version 17) computer programme was used to analyse the data. two analyses were made: descriptive analyses (by use of means, modes, standard deviations, variance, percentages, and frequencies) and the inferential analyses (by use of chi-square, correlation analyses). the former provided the descriptive and documentation of the state of affairs as they were, while the latter indicated statistically significant relationships between the variables and in the testing of the specific objectives. means, standard deviation and chi square test were used to test differences that existed. all this were tested at the probability level of p=0.05 or p=0.01 level of significance. 4. results demographic characteristics of the respondents fig. 1: age of patients seeking cancer treatment in kenya. the results indicated that 47.0% of the respondents were aged between 40 and 50 years, 24.9% of the respondents indicated that they were aged between 51 and 60 years, 13.5% of the respondents indicated that they were aged between 31 and 39years, 11.4% of the respondents indicated that they were aged between 60 years and above and 3.2% of the respondents indicated that they were aged between 18 and 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 18-30 years 30-45 years 45-56 years 56-60 years 60 years > 3.20% 13.50% 47% 24.90% 11.40%p e rc e n t age bracket n=245 j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.42 (online publication: dec., 2016) 30 years (fig. 1). a chisquare test conducted on the respondents age distribution indicated that there was a highly significant (<0.01) variation in the responses 𝜒4.001 2 = 163.613 in the distribution of age. it emerged from the fgds and secondary data that most of the patients admitted at the cancer hospital were in the working age bracket of between 18 years and 60 years. the key informant interview revealed that most cancer patients are in their early 40’s and 50’. type of cancer patients were diagnosed with fig. 2: type of cancer diagnosed. 51.4% of the respondents indicated that they were having breast cancer, 20.0% of the respondents indicated that they were diagnosed with prostate, 15.7% of the respondents indicated that they were diagnosed with esophageal and 13.0% of the respondents indicated that they were diagnosed with cervical cancer (fig. 2). this implies that most of the respondents who participated in the study were women. focused group discussion and key informants observed most patients seeking cancer treatment in their health facilities were diagnosed with both prostate and esophageal cancer for men and breast and cervical cancer for women. they observed that breast cancer was the most common for patients admitted in their facilities which they attributed to better diagnosis. table 1: occupation of cancer patients seeking treatment in kenya frequency percent agriculture sector 78 31.8 formal sector 35 14.2 informal sector 48 19.5 student 27 11.3 unemployed 57 23.2 total 245 100 15.70% 13.00% 51.40% 20.00% 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% esophageal cervical breast prostate p e rc e n t type of cancer n=245 j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.43 (online publication: dec., 2016) most cancer patients were employed in the agricultural sector 31.8%, , 19.5% of the respondents indicated that they were in the informal sector, 23.2 % of the respondents indicated that they were unemployed while 14.2% indicated that they were in the formal sector employment while 11.3% of the respondents indicated that they were students (table 1). a chi square test carried out and the results indicated that there was a significant (p < 0.01) variation 𝜒3,0.01 2 = 360.733) in the distribution of primary occupations of cancer patients seeking treatment in kenya referral hospitals.. information obtained from fgds indicated that most patients were in the agricultural sector which is the largest employer in kenya. most of the patients seeking treatment in the government hospitals comprised of informal and agriculture sector. in private hospitals majority of the patients were in the formal sector. fig 3: cancer patients’ monthly income. according to the findings, 44.6% of the respondents indicated that they earned between 200 and 500 us dollars, 28.4% of the respondents indicated that they earned between 100 and 200 us dollars, 23.8.% of the respondents indicated that they earned less than 100 us dollars while only 6.2% of the respondents indicated that they earned more than 501 us dollars per month (fig. 3). this depicts that most of the respondents earned between 200 and 500 us dollars per month. from the fgds it emerged that most of the cancer patients earned less than 200 us dollars and were not able to meet medical cost for cancer treatment. key informants observed that more than 95% 0f cancer patients in kenya are unable to afford cancer treatment comfortably. a chi square test carried out on patients income levels indicated that there was a highly significant (p<0.01) variation (𝜒3,0.01 2 = 890.796) in the distribution of patients income. 23.80% 28.40% 44.60% 6.20% 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% less than us $100 $101-$200 $201-$500 more than $501 p er c en t patient income n=245 j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.44 (online publication: dec., 2016) fig.4: source of financing expenditures. a chi square test carried out on responses indicated that there was a significant (p<0.01) variation in the responses (𝜒5,0.01 2 = 298.490). results from questionnaires indicated that, 29.0% of the respondents indicated that the expenses were financed from self-income, 23.8% of the respondents indicated that expenses were financed by savings, 16.6% of the respondents indicated that the expenses were financed through insurance, 22.4% of the respondents indicated that the financing was through borrowing and 8.1% of the respondents indicated that they sold assets to finance both medical and non-medical expenditures due to cancer (fig. 4). this shows that most of the patients were financing their expenditures through self-income. focus group discussion and key informants observed that most of the patients had incurred a form of debt while seeking treatment. relationship between the time patient took to visit health facility and income status the study sought to determine whether there was an association between time taken by a patient to visit a health facility and their income status. the results were as shown in table 5. table 2: relationship between times took to visit the health facility and income status. duration income status low income medium income high income five days 0.00% 4.50% 1.70% ten days 12.50% 8.20% 5.10% twenty days 0.00% 7.30% 6.80% one month 6.20% 9.10% 6.80% two month 31.20% 30.00% 25.40% three month 31.20% 6.40% 10.20% four month 6.20% 14.50% 18.60% six months 6.20% 14.50% 13.60% more than six months 0.00% 1.80% 6.80% total 100 100 100 0.00% 20.00% 40.00% 29.00% 23.80% 16.60% 22.40% 8.10% p e rc e n t medical financing source n=245 j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.45 (online publication: dec., 2016) as indicated in the table 2 above, there is a statistically significant relationship between time it took to get to the health facility and income status. this is because the calculated x2 (19.159) is greater than the critical x2 which is 15.507. in addition, the p-value (0.003) is less than the significant level (0.05). this shows that the higher the income the lesser the time took to go to the health facility and the lower the income the more the time took to get to the health facility. fgds findings indicated that low income earners were less likely to seek treatment on time due to financial constraints. they observed that some low income patients took as much as two years to seek treatment in their health facilities. they also observed that some patients diagnosed with the disease never came back for treatment due to financial constraints. the study sought to determine the number of patients who have incurred debts while seeking treatment in kenya oncology centers. 81% of cancer patients incurred debts while seeking treatment while 19% did not incur debts while seeking treatment (fig. 5). fig 5: cancer patients who incurred debts while seeking treatment in kenya. a chi square test carried out on the responses indicated that there was a highly significant (p<0.01) variation in the responses (𝜒1,0.05 2 = 156.960). according to the findings, 81% of the respondents indicated that they incurred debt when seeking treatment for cancer while 19% of the respondents indicated otherwise. this shows that most of the respondents were not in a position to finance their medication process. from fgds finding it emerged that most cancer patients had borrowed cash from relatives, from savings and credit societies and others from banks. other patients observed that they had to call upon friends and families to contribute to their medical expenses. amount incurred by patients while seeking cancer treatment further, the respondents were asked to indicate the amount they incurred as a debt while seeking treatment. yes, 81% no, 19% n=245 j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.46 (online publication: dec., 2016) table 3: amount incurred by patients while seeking cancer treatment n mean std. deviation amount incurred 245 $5533.37 $10845.21 source: field data (2015) according to the findings, the respondents indicated that they had relatively incurred a debt of 5533.37 us dollars as indicated by the mean in the table 3 above (tab. the focus group discussion and key informant interviews observed that debts accrual was the most common economic effect of cancer on the affected households. they observed that most families had accrued debts to pay for cancer treatment. pamuk, (2009) found that although cancer patients are willing to invest huge resources into the treatment of cancer, diseases often find them ill prepared for emergencies, and this is the reason as to why they solicit for funds elsewhere. this is in consideration of the fact that most of the resources are committed in other areas e.g. businesses, fees, agriculture etc (pamuk, 2009). 5. discussions the study established that majority of the cancer patients admitted in the hospitals were female and were diagnosed with breast and cervical cancer. men admitted in the oncology centers were diagnosed with prostate and esophageal cancer. the study established that most of the patients were also found to have reached tertiary level of education. also, most of the respondents were found to working in the informal sector contrary to those who were in the formal sector. majority of the patients were found to be residing in rented houses. the study established that most of the cancer patients were of low socio economic group. from the study findings most respondents spent between us dollars 5000 to us dollars,10000 on cancer treatment a year which is unaffordable for most kenyans. the study established that the socio and economic impact of cancer on patient livelihoods was high, and patients have to dispose their assets to finance cancer treatment. from the fgds it was established that most patients had either disposed their assets or borrowed money from financial institutions to pay for the medical bills when they depleted their savings. the study established that cancer stigma is still rampant in the country. 6. conclusions and recommendations the study established that most households in kenya cannot afford cancer treatment and that families have to dispose assets, borrow from financial institutions, call for fundraising (harambees) after depleting all their family savings to pay for cancer treatment. the study established that households resource base were negatively affected, it further established that loss of wages, under employment/unemployment, immature death, stigma and lose of autonomy due to protracted cancer illness was prevalent and increased household vulnerabilities. the study concluded that cancer patients and their families j. mutuma, j. wakhungu, c. mutai/ bibechana 14 (2017) 30-36 : rcost p.47 (online publication: dec., 2016) experienced socio and economic vulnerabilities including human, financial and social capital, owing to the fact that cancer impacts on household demographic structure. references [1] ministry of health report ‘cancer burden in the country, (2010) nairobi kenya. [2] world health organization,the global burden of disease: 2004 update. geneva: world health organization, (2008). [3] c. d.mathers & l. dejan, projections of global mortality and burden of disease from 2002 to 2030, (2006). [4] m.t. hegel, c.p. moore, e.d.collins, s. kearing , k.l. gillock, r.l. riggs, k.f. clay, t.a. ahles, cancer, 107(12) (2006) 2924–2931. http://dx.doi.org/10.1002/cncr.22335 [5] world health organization. ten statistical highlights in global public health. world health statistics, geneva: world health organization (2007). [6] kenya medical research institute (kemri) cancer incidence report, (2010). [7] s. arrossi. , n. bhagwan , j. kasturi , determinants of women participation in cervical cancer screening in maharashtra, india, (2007). [8] b.a. mulemi, coping with cancer and adversity:hospital ethonograpy in kenya, (2010). [9] american cancer society, cancer facts and figures, atlanta: american cancer, (2011). [10] p. kanavos, the rising burden of cancer in the developing world. annals of oncology,17(8) (2006) viii15-viii23. [11] f. merletti , c. galassi , t. spadea, the socioeconomic determinants of cancer, (2011). [12] e. a. taylor, economic costs of cancer health disparities summary of meeting proceedings, center to reduce cancer health disparities. us department of health and human services national institutes of health, (2005). [13] g. danaei, s. vander-hoorn, a .d. lopez, c.j. murray, & m. ezzati, causes of cancer in the world: comparative assessment of nine behavioral and environmental risk factors.lancet, (2006) 1784-1793. [14] p. b. gichangi, b. wayo, b. estambale, yust h de, s. b. o ojwang, r. abwao, & m. termmerman, east afr med j., 17 (2003) 1-6. [15] o. mugenda ,& g. mugenda, research methods: qualitative and quantitative approaches. nairobi: laba graphics services, (1999). http://dx.doi.org/10.1002/cncr.22335 http://dx.doi.org/10.1002/cncr.22335 http://www.ncbi.nlm.nih.gov/pubmed/?term=arrossi%20s%5bauth%5d http://www.ncbi.nlm.nih.gov/pubmed/?term=nene%20b%5bauth%5d http://www.ncbi.nlm.nih.gov/pubmed/?term=jayant%20k%5bauth%5d http://www.ncbi.nlm.nih.gov/pubmed/?term=merletti%20f%5bauthor%5d&cauthor=true&cauthor_uid=21489217 http://www.ncbi.nlm.nih.gov/pubmed/?term=galassi%20c%5bauthor%5d&cauthor=true&cauthor_uid=21489217 http://www.ncbi.nlm.nih.gov/pubmed/?term=spadea%20t%5bauthor%5d&cauthor=true&cauthor_uid=21489217 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal design and development of low-range frequency modulated signal (f.m.) transmitter abhishek shrivastava electronics and communication engineering, jaypee institute of information technology, noida, uttar pradesh, india. *email: abhi6191995@gmail.com article history: received 20 september, 2017; accepted 28 october, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18279 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract frequency modulated (fm) signal transmitter is a small device that can transmit frequency modulated signal over short range. [1] this document consists of most simple and economical technique for building a fm transmitter using basic electronic components like resistor, capacitor, inductor etc. the fm transmitter receives human voice signals though microphone. it further amplifies it, modulate it over carrier and finally transmit it. assuming favorable conditions, output of transmitter can be received by anyone who tunes it in frequency of our transmitter. here, i have described circuit diagram, its working, components required, uses of various components in our circuit, its practical applicability. the design is simulated using ni multisim and is further implemented on bread-board. this design is capable of transmitting signal for distance of radius 20m, tuned at 97.1 mhz one could clearly hear sound produced at microphone of transmitter. keywords: inductor; lc oscillator; telescopic antenna; 2n3904 bipolar transistor. 1. introduction fm transmitter is an electronic device, which produces frequency-modulated waves with the help of an antenna. a transmitter generates fm waves for various purposes such as communication, broadcasting a message etc. furthermore, fm signals are less prone to interference as compared to am signals due to higher bandwidth. also, it is less susceptible to noise [1,2]. the signal transmitted has a limited range for its reception, as we increase our distance from source, the signal received is merged with noise and further more noise component dominates signal transmitted and hence message cannot be received successfully after certain distance due to obstacles. the source of power is 9v dc battery, which starts discharging after constant power supply for around 6 hours [3]. the information that is provided to the transmitter is in the form of an electronic signal. this includes audio from a microphone. the transmitter combines the information signal that is to be carried with the rf signal (the carrier). this is called modulation. in an fm transmitter, the information is added to the radio signal by slightly varying the radio signal's frequency. 2. materials & methods the components used in our design are easy to find and easy to implement. the circuit designing and implementing part can also be done using breadboard but as it is not suitable high frequency circuits. further components are shown in table 1. abhishek shrivastava/ bibechana 15 (2018) 30-36: rcost p.30 http://nepjol.info/index.php/bibechana mailto:abhi6191995@gmail.com http://dx.doi.org/10.3126/bibechana.v15i0.18279 https://creativecommons.org/licenses/by-nc/4.0/ table 1: microphone: microphone is a transducer, which converts sound energy to electric energy. the microphone used in our design is ‘electret condenser microphone’[4] it consists of parallel plate capacitor which has one plate as fixed and other plate being movable. the movable plate is called diaphragm. when sound strikes diaphragm it starts moving, thus in turn changing capacitance of capacitor, which in turn results in flow of variable current. transistor (2n3904): transistor 2n3904 is a medium gain general-purpose transistor. it is widely used for low power amplification. it has transition frequency of around 300 mhz with a minimum current gain of 100. the circuit diagram is shown in figure 1, which was stimulated in ni multisim 10. fig.1: circuit diagram. discription of circuit the circuit basically operates in 4 steps. firstly a condenser microphone takes input, then amplifier does amplification, the amplified signal is modulated with frequency being generated by lc oscillator and finally antenna transmits the signal. the inductor l1 and capacitor c3 forms an oscillating tank circuit along with the transistor 2n3904. as long as the current exists across the inductor coil l1 and the capacitor c3, the tank circuit will oscillate at the resonant carrier frequency for fm modulation. whereas capacitor c1 acts as a negative feedback to the oscillating tank circuit. the modulated signal from the antenna is radiated as radio waves at fm frequency band. antenna is nothing but a simple copper wire of 20 cm or more long. part name quantity value description m1 1 12-3 db microphone r1 1 470ω resistor r2 1 4.7kω resistor c1 1 4.7pf capacitor c2 1 20nf capacitor c3 1 50pf capacitor c4 1 0.01uf capacitor c5 1 0.1uf capacitor l1 1 0.05uh inductor q1 1 2n3904 general purpose transistor v1 1 9v dc power supply abhishek shrivastava/ bibechana 15 (2018) 30-36: rcost p.31 input stage: inside the microphone, a capacitive sensor diaphragm is present. it vibrates according to the air pressure changes and generates ac signals. the capacitor c4 and c5 can be thought of as a frequency-dependent resistor (called reactance). the capacitor c5 separates microphone from transistor. speech consists of different frequencies and the capacitor impedes them. the net effect is that c4 modulates the current going into the transistor. using a large value for c4 reinforces bass (low frequencies) while smaller values boost treble (high frequencies). the input stage of multisim circuit is shown in figure 2. here we used an a.c. voltage source instead of microphone for simulation purpose. amplification stage: the sound signal converted by microphone to alternating signal has very low power, hence if we modulate it directly over the carrier and transmit it, it would not be possible to demodulate it and retrieve the original signal from it. the resistance r1 and r2 are used to bias the bjt, it is being illustrated in figure 3. fig.2: input stage. fig. 3: amplification stage. tank circuit: the inductor and capacitor together form an oscillating tank circuit or a resonant circuit oscillating at frequency given by, f = 1 √2∗𝜋∗𝐿∗𝐶 where, l & c are values of inductor and capacitor forming tank circuit respectively. here l1 and c3 forms an oscillating tank circuit with frequency = 97.1 mhz. it is further displayed in figure 4. final transmission of fm signal now, the signal after amplification by bjt is further modulated with carrier signal generated by tank circuit. after successful modulation the wave is transmitted using antenna. it is displayed in figure 5. abhishek shrivastava/ bibechana 15 (2018) 30-36: rcost p.32 fig. 4: tank circuit. fig. 5: transmission using antenna. 3. results and discussion simulation using ni multisim 10 fm transmitter can be simulated using tools from multisim. this circuit is simulated using ni multisim 10. firstly, circuit is created using multisim, using the tools and parts from library, dedicated for circuit designing. the main purpose of using multisim to simulate the design is to affirm that values of inductor capacitor, etc. are under the bounds. after the circuit is designed it is further simulated and analyzed using spectrum analyzer and virtual oscilloscope present in multisim. also, applying probes at antenna shows the values of various parameters at output of circuit. the results of simulation are illustrated in figure 6. fig. 6: results of simulation. abhishek shrivastava/ bibechana 15 (2018) 30-36: rcost p.33 interpretation by oscilloscope as it can be seen in figure 6, the oscilloscope displays the output waveform of fm signal that is transmitted through antenna. the output wave can be clearly seen through oscilloscope. as our design is very basic, the effect of noise can be seen in output as well. clearly it can be noted that the output waveform has time period of 10.4 ns which is approx. 97 mhz. slight variations are observed due to effect of noise. interpretation by spectrum analyzer the spectrum of output waveform can be analyzed using spectrum analyzer. it can be clearly observed from the graph of spectrum analyzer of figure 6, the peak of spectrum (bandwidth) is at 96.663 mhz, approximately 97 mhz. also the effect of noise can be observed as the spectrum is not idle as it is expected to be of a sinusoidal wave. interpretation by probe marker using the probe marker placed at output during simulation, the frequency of output signal can be clearly seen from figure 6 as 97.0 mhz., along with various other parameters such as current, voltage etc. implementation and testing implementation further after all the simulation results are achieved as per desired, we further implement circuit designed on breadboard first. all the components listed in table-1 are further arranged and assembled in circuit as per design requirement of our fm transmitter. implemented circuit on bread board is shown in figure-7, along with battery source. fig. 7: practical implementation. testing the implemented circuit is further tested. to test the transmitter, the tank circuit is tuned properly so that frequency generated can be easily modulated with message signal. now, both fm transmitter and receiver are switched on. the receiver is tuned to 97.1 mhz and voice signal is being transmitted. instantly the voice signal is heard clearly at the receiver. furthermore, to check the range of transmitter, a constant voice signal is applied at input and receiver is moved away from the transmitter slowly. as distance increased, the impact of noise started dominating our message signal. also, as our transmitter is producing a low power signal, output can be obtained clearly in a radius of 20m around abhishek shrivastava/ bibechana 15 (2018) 30-36: rcost p.34 transmitter. the figure 8 shows output of our design being verified using digital storage oscilloscope (dso). fig. 8(a) fig. 8(b) 4. conclusion the human voice transmitted, was received at output on 97.1 mhz frequency, provided conditions are favorable for wireless transmission. for extending the range and power of fm transmitter, one can apply another level of amplification after second stage, that would in turn further amplify the signal and then it can be transmitted, the more the power of signal transmitted, greater is its range and more noise immune it becomes. also, to improve efficiency one may check the voltage of source applied abhishek shrivastava/ bibechana 15 (2018) 30-36: rcost p.35 and assure it is 9 v for above circuit. furthermore, one should implement the design on pcb board as bread-board is not preferred for high frequency circuits. references [1] r.l. boylestad, introductory circuit analysis, eleventh edition, prentice hall, 2007. [2] n. braga, pirate radio and video: experimental transmitter projects, newnes butterworth-heinemann publishing, 2001.. [3] b.p. lathi., modern analog and digital communication systems, third edition, oxford university press. 1998. [4] t. l. floyd, principles of electric circuits, eighth edition, upper saddle river, nj: prentice hall, 2007. abhishek shrivastava/ bibechana 15 (2018) 30-36: rcost p.36 microsoft word joshi(113-121) bhawani d. joshi, manoj k. chaudhary/ bibechana 15 (2018) 131-139: rcost p.131 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal nbo, nonlinear optical and thermodynamic properties of 10-acetyl-10h-phenothiazine 5-oxide bhawani datt joshi1,2*, manoj kumar chaudhary3 1department of physics, siddhanath sc. campus, tribhuvan university, nepal 2departamento de física, universidade federal do ceará, fortaleza, ce, brazil. 3department of physics, amrit sc. campus, tribhuvan university, nepal *email: pbdjoshi@gmail.com article history: received 11 october, 2017; 11 december, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18385 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract in this paper, natural bond orbital (nbo) analysis, nonlinear optical and the thermodynamic properties of 10-acetyl-10h-phenothiazine 5-oxide have been analyzed by employing density functional theory level employing 6-311++g(d,p) basis set. nbo analysis reveals that the intraintermolecular charge transfer occurs within the molecule leading to the stabilization. the predicted nonlinear optical properties (nlo) like; polarizability and first hyperpolarizabiliy support that the molecule could attract the interests for future investigation. keywords: aptz; dft; nbo, nonlinear optical and thermodynamic properties. 1. introduction the heterocyclic organic compounds in which sulphur and nitrogen are incorporated in the tricyclic system; exhibit a wide range of pharmacological / biological activities [1-5]. different derivatives of phnothiozene are kwon for their clinical activities. antihistamines, diuretics, analgesics, neurolepitcs, antileukemic, antimutagenic, antileishmanial etc. are some of their main potential applications [2-7] of the drugs that containing phenothiozenes. pallafox et. al. [6] studied the infrared, raman and 13c-nmr spectroscopic studies of n-methyl phenothiazine. sharma et. al. [7] reported various remarkable biological activities of thiazolidines. previously, we have revealed vibrational analysis of 10-acetyl-10h-phenothiazine5-oxide [aptz] using quantum chemical calculations [8]. the aim of the present study is to communicate some additional investigations on structure activity relation of the molecule on the aptz molecule. in this study, we have presented the nonlinear optical and thermodynamic properties together with the natural bond orbital (nbo) analysis of the title compound by employing density functional theory [dft] [9] 6-311++g(d,p) basis set [10] using gaussian 09 program package [11]. 2. materials and methods 2.1. theoretical method using the data available in pubchem data base [12] geometry optimization has been performed bhawani d. joshi, manoj k. chaudhary/ bibechana 15 (2018) 131-139: rcost p.132 without using any constraints. the optimized ground state structure of the molecule obtained by dft method visualized in gauss view program [13] is shown in figure 1. we have utilized the dft based on becke’s three-parameter (local, non-local, hf) hybrid exchange functional with lee–yang–parr correlation functional (b3lyp) [10]. fig. 1: optimized structure of aptz molecule (sulphur: yellow, nitrogen: blue, oxygen: red, carbon: gray and hydrogen: white in colours). the basis set 6-311++g(d,p) augmented by ‘d’ polarization functions on heavy atoms (nitrogen, sulphur etc.) and ‘p’ polarization functions on hydrogen atoms as well as diffuse functions for both hydrogen and heavy atoms. 3. results and discussion 3.1. natural bond orbital (nbo) analysis nbo analysis is one of the efficient methods for studying hybridization, conjugative interactions, covalence effects and charge transfer in polyatomic wave functions into localized form, corresponding to one center (lone pairs) and two centers (bonds) of lewis structure picture [14]. here, by utilizing the second-order micro-disturbance theory analysis we have reported some of the electron donor orbital, acceptor orbital and the interacting stabilization energy. the intensity of the interaction between electron donors and electron acceptors, i.e. the more donating tendency from electron donors to electron acceptors depends on the e(2) value. the hyperconjugative interaction energy was deduced from the second-order perturbation approach [15, 16]. e��� � �n� σ|f|σ�� e�∗ � e�⁄ � � �n��f��� ∆e⁄ � wheref��� is the fock matrix element between i and j nbo orbital, e�and e�∗are the energies of �and �*nbo’s, and n� is the population of the donor orbital. the larger the e(2) value the more intensive is interaction between electron donors and electron acceptors , the greater the extent of conjugation of the whole system [14]. hyperconjugation is a stabilizing effect that arises from overlap between an occupied orbital with another neighboring electron deficient orbital when these orbitals are properly oriented. the most important interaction between ‘‘filled’’ (donor) lewis type nbos and ‘‘empty’’ (acceptor) non-lewis nbos are reported in table 1. a strong intramolecular hyperconjugative interaction of � electrons occurs from c1-c10 to the �*(c2 – c4) and �*(c6 – c8) bonds of the ring r1 which increase the electron densities (eds) (0.31e and 0.32e) leading to the stabilizations of 20.07 and 16.82 kcal/mol, respectively. another intermolecular bhawani d. joshi, manoj k. chaudhary/ bibechana 15 (2018) 131-139: rcost p.133 hyperconjugative interaction of � electrons occurs from c17-c19 to the �*(c11 – c12) and �*(c13 – c15) bonds of the ring r3 which increase the eds (0.43e and 0.31e) leading to the stabilizations 23.89 kcal/mol and 18.92 kcal/mol, respectively. the enhanced interaction table 1. second order perturbation theory analysis of fock matrix in nbo basis. donor nbo (i) ed/e acceptor nbo (j) ed/e e(2) kcal/mol e(j)-e(i) a.u. f(i,j)a.u. �(c13-h14) 1.97771 �*(c11-c12) 0.03212 5.08 1.06 0.065 �(c19-h20) 1.97695 �*(c11-c12) 0.03212 5.03 1.05 40.065 �*(s28-o29) 0.13706 �*(s28-o30) 0.15311 58.58 0.01 0.069 π(c1-c10) 1.67702 π*(c2-c4) 0.30670 20.07 0.30 0.070 π*(c6-c8) 0.32028 16.82 0.30 0.063 π(c2-c4) 1.64157 π*(c1-c10) 0.43019 20.47 0.26 0.067 π*(c6-c8) 0.32028 21.67 0.28 0.070 π(c6-c8) 1.65806 π*(c1-c10) 0.43019 23.09 0.27 0.072 π*(c2-c4) 0.30670 18.10 0.29 0.065 π(c11-c12) 1.68646 π*(c13-c15) 0.30962 20.12 0.30 0.070 π*(c17-c19) 0.30712 16.33 0.31 0.063 π(c13-c15) 1.64879 π*(c11-c12) 0.43279 20.21 0.26 0.066 π*(c17-c19) 0.30712 20.51 0.29 0.069 π(c17-c19) 1.64130 π*(c11-c12) 0.43279 23.89 0.26 0.072 π*(c13-c15) 0.30962 18.92 0.28 0.066 lp(1)n26 1.68652 π*(c1-c10) 0.43019 14.67 0.27 0.058 π*(c11-c12) 0.43279 14.63 0.27 0.058 π*(c21-o27) 0.01587 41.57 0.30 0.102 lp(2)o27 1.85623 �*(c21-c22) 0.05125 18.85 0.62 0.099 �*(c21-n26) 0.10121 30.04 0.64 0.126 lp(2)o29 1.80719 �*(c1-s28) 0.20940 12.01 0.45 0.066 �*(c12-s28) 0.20601 17.58 0.45 0.079 lp(3)o29 1.79804 �*(s28-o30) 0.15311 21.15 0.57 0.100 lp(2)o30 1.81031 �*(c1-s28) 0.20940 14.23 0.44 0.071 �*(c12-s28) 0.20601 14.70 0.44 0.072 lp(3)o30 1.77862 �*(s28-o29) 0.13706 21.63 0.55 0.100 π*(c1-c10) 0.43019 π*(c2-c4) 0.30670 149.22 0.02 0.081 π*(c6-c8) 0.32028 195.11 0.02 0.083 π*(c11-c12) 0.43279 π*(c13-c15) 0.30962 138.07 0.02 0.080 π*(c17-c19) 0.30712 135.91 0.02 0.084 e(2) means energy of hyper conjugative interaction (stabilization energy). e(i)-e(j) is the energy difference between donor (i) and acceptor ( j) nbo orbitals. f(i,j) is the fock matrix element between i and j nbo orbitals. π*(c1-c10) further conjugate with the nbos π*(c2-c4) and π*(c6-c8) resulting to high stabilizations 149.22 and 195.11 kcal/mol. similarly, the enhanced interaction π*(c11-c12) further conjugates with the nbos π*(c13-c15) and π*(c17-c19) leading to the high stabilizations 138.07 and 135.91 kcal/mole, respectively. further, the other significant hyperconjugative interactions of π electrons in the molecular system are from π(c2-c4) to π*(c1-c10) / π*(c6-c8) leading energies 20.47 / 21.67 kcal/mol, and from π(c13-c15) to π*(c11-c12) /π*(c17-c19) leading energies 20.21 / 20.51 kcal/mol, respectively. delocalization of lone pair electron is otherwise related to the resonance interaction in a molecular system. in this molecule, the main lone pair electron donation are from lp(1) n26 to the antibonding acceptor π*(c21-o27) (41.57 kcal/mol), from lp(2)o27 to the antibonding acceptor �*(c21-n26) (30.04 kcal/mol). similarly, another lone pair electron donations are from lp(3) o29 to the antibonding acceptors �*(s28-o30) with stabilization energy 21.15 kcal/mol and from lp(3)o30 to the antibonding acceptor �*(s28-o29) with stabilization 21.63 kcal/mol. the interactions mainly include within the rings r1 and r3, and the nitrogen and sulphur atoms of the ring r2. the nbo analysis also describes the bonding in terms of the natural hybrid orbital lp(2) o27, which occupy a higher energy orbital (-0.27030 a.u.) with considerable p-character (99.92%) and low bhawani d. joshi, manoj k. chaudhary/ bibechana 15 (2018) 131-139: rcost p.134 occupation number (1.85623) and the other lp(1)o27 occupy a lower energy orbital (-0.70715 a.u.) with p-character (41.40%) and high occupation number (1.98474). another natural hybrid orbital lp(2) o29, which occupy a higher energy orbital (-0.30236a.u.) with considerable p-character (99.91%) and low occupation number (1.80719) and the other lp(1)o29 occupy a lower energy orbital (-0.29619 a.u.) with p-character (24.15%) and high occupation number (1.98263). similarly, the other nbo analysis describes in terms of the natural hybrid orbital lp(2)o2, which occupy a higher energy orbital (0.29619 a.u.) with p-character (99.92%) and low energy occupation (1.81031) and other lp(1)o30 occupy a lower energy orbital (-0.81342 a.u.) with p-character (23.45%) and high occupation number (1.98110).thus, pure p-type lone pair orbital participates in the electron donation interactions in the compound. the results are tabulated in table 2. table 2.selected lewis orbitals (occupied bond or lone pair) with the valence hybrids corresponding to the various interactions in (3): a-donor, b-acceptor and(ed)-electron density. bond(a–b) eda–b eda (%) edb (%) nbo hybrid orbitals s (%) p (%) σ (c1–s28) 1.96350 54.34 45.66 0.7372(sp3.21)c+ 23.73 76.23 -0.69894 0.6757(sp3.34)s 22.74 75.92 σ (c10–n26) 1.97989 38.37 61.63 0.6194(sp2.69)c+ 27.04 72.86 -0.80968 0.7850(sp1.98)n 33.54 66.42 σ (c11–n26) 1.97750 37.98 62.02 0.6163(sp2.74)c+ 26.70 73.20 -0.79572 0.7875(sp2.06)n 32.64 67.32 σ (c12–s28) 1.96303 53.74 46.26 0.7330(sp3.24)c+ 23.59 76.36 -0.69859 0.6802(sp3.26)s 23.17 75.52 σ (c21–n26) 1.98018 35.37 64.63 0.5947(sp2.39)c+ 29.50 70.37 -0.81385 0.8039(sp1.98)n 33.50 66.47 σ (c21–o27) 1.99417 35.16 64.84 0.5930(sp2.08)c+ 32.42 67.40 -1.09153 0.8052(sp1.44)o 40.97 58.92 σ (s21–o29) 1.98590 35.28 64.72 0.5939(sp2.61)s+ 27.25 71.24 -0.98985 0.8045(sp3.15)o 24.08 75.80 σ (s21–o30) 1.98233 35.24 64.76 0.5937(sp2.62)s+ 27.22 71.24 -0.97802 0.8047(sp3.25)o 23.48 76.41 lp(1)n26 1.68652 (sp99.99) 0.30 99.69 -0.28427 lp(1) o27 1.97547 (sp0.71) 58.58 41.40 -0.70715 lp(2) o27 1.85623) p 99.92 -0.27030 lp(1) o29 1.98263 (sp0.32) 75.84 24.15 -0.81174 lp(2) o29 1.80719 p 99.91 -0.30236 lp(3) o29 1.79804 (sp99.99) 0.12 99.79 -0.29967 lp(1) o30 1.98110 (sp0.31) 76.54 23.45 -0.81342 lp(2) o30 1.81031 p 99.92 -0.29619 lp(3) o30 1.77862 (sp99.99) 0.04 99.87 -0.29196 the mulliken charges provide partial atomic charges. they are explicitly sensitive to the choice of basis set used for theoretical calculation. they give qualitative results of the charge distribution to the related atoms. the nbo charges operate the electron density and are more reliable. localized natural atomic orbitals can be used to describe electron density. the polarization bonds are considered in this method while no polarization is considered in the mulliken system. the mulliken and nbo charges obtained by b3lyp/6-311++g(d,p) basis have been listed in the table 3. their graphical comparison is shown in the figure 2. bhawani d. joshi, manoj k. chaudhary/ bibechana 15 (2018) 131-139: rcost p.135 table 3. comparison of nbo and mulliken charges by b3lyp/6-311++g(d,p) basis. atom no. mulliken charges (esu) nbo charges (esu) atom no. mulliken charges (esu) nbo charges (esu) 1 c -0.801065 -0.32909 16 h 0.072371 0.24827 2 c 0.338536 -0.18010 17 c 0.065647 -0.20784 3 h 0.138707 0.27189 18 h 0.077403 0.24719 4 c -0.174436 -0.23767 19 c -0.128778 -0.21207 5h 0.073405 0.25036 20 h 0.109145 0.26802 6 c 0.018242 -0.20909 21 c 0.159322 0.70133 7 h 0.090411 0.24828 22 c -0.308930 -0.74808 8 c 0.056851 -0.23514 23 h 0.163485 0.27063 9 h 0.065658 0.25055 24 h 0.141922 0.25093 10 c -0.394878 0.16009 25 h 0.146591 0.24921 11 c -0.003160 0.16753 26 n 0.352297 -0.49404 12 c -0.554110 -0.32425 27 o -0.278885 -0.57932 13 c 0.203503 -0.20626 28 s 0.861219 2.17709 14 h 0.133208 0.26962 29 o -0.340694 -0.92582 15 c -0.033144 -0.23002 30 o -0.249846 -0.91217 fig. 2: graphical representation of mulliken and nbo charges. 3.2. nonlinear optical (nlo) properties nlo phenomena have attractive attention because of their potential applications in optical communication, optical sensing, data storage, computing etc. [17, 18]. the first hyperpolarizability (β0) of the molecular system, and the related properties; mean polarizability (α0) and anisotropy of polarizability (∆α) have been calculated using b3lyp/6-311++g(d,p) basis set. first order hyperpolarizability is a third rank tensor that can be described by 3x3x3 matrix. the 27 components of 3d-matrix can be reduced to 10 components by kleinman symmetry [19]. it can be given in the lower tetrahedral format. energy of a system during weak and homogeneous electric field can be given as: e � e� ��μ�f�� � 12�α��f�f� � 16�β��"f�f�f"……��"�� where e0 is the energy of unperturbed molecule, fi is the field at the origin μi, αij and βijk are the components of dipole moment, polarizability and first hyperpolarizability, respectively. the components of hyperpolarizability tensor are listed in the table 4. bhawani d. joshi, manoj k. chaudhary/ bibechana 15 (2018) 131-139: rcost p.136 table 4.dipolemoment (µ; debye), polarizability (α x10-24 esu) and first hyperpolarizability (β0 x10-31 esu) by b3lyp/6-311++ g(d,p) method. dipole moment polarizability hyperpolarizability μ$ -2.5505 α$$ -95.1487 β$$$ 6.4396 μ% 1.8587 α%% -125.1014 β%%% 9.9021 μ& -4.6646 α&& -124.3313 β&&& 4.3677 μ' 5.6319 4.2 (urea) α$% -6.6784 β$%% -28.9734 α$& -2.1461 β$$% -19.6156 α%& 0.6211 β$$& -36.0926 α0 17.0223 β$&& -5.6695 ∆α 35.0921 β%&& 16.7140 β%%& -15.6364 β$%& -10.6509 β0 4.8308 1.947 (urea) the total static dipole moment (μ�), mean polarizability (∆α�, anisotropy of polarizability (|α�|� and first hyperpolarizability (β�� can be expressed as [20]: μ� � (μ$� + μ%� + μ&�*+ �⁄ |α�| � 13 (α$$ + α%% + α&&* ∆α � 12 -(α$$ � α%%*� + (α%% � α&&*� + �α&& � α$$�� + 6α$$� .+ �⁄ β� � -(β$$$ + β$%% + β$&&*� + (β%%% + β$$% + β%&&*� + (β&&& + β$$& + β%%&*�.+ �⁄ the dipole moment, mean polarizability, anisotropy of polarizability and first hyperpolarizability of the title compound have been calculated and listed in the table 4. these values are found to be higher than that of the standard nlo material urea [21]. in this study the first hyperpolarizability has been calculated nearly 2 times that of urea. hence, the higher value of βo shows that the investigated compound has good nonlinear property. 3.3 thermodynamic properties computation of thermodynamic properties of molecules is important for both thermochemistry and chemical equilibrium. statistical thermodynamics with the two key ideas, boltzmann distribution and the partition function leads to the derivation of the equations utilized for computing thermochemical data in gaussian programs. the total energy, zero-point energy, heat capacity (c0� ), entropy (s2,0� ), enthalpy (h0� ), dipole moment and the rotational constants of the molecular system were obtained directly from the output of gaussian calculation employing b3lyp/6-311g(d.p) basis set and are listed in the tables 5 (a & b). table 5(a). variation of different thermodynamic parameters with temperature. temp (k) enthalpy (kcal/mol) specific heat (cal/mol-k) entropy (cal/mol-k) 100 141.533 23.442 79.872 200 144.808 42.245 103.205 300 150.005 61.648 124.810 400 157.087 79.568 145.639 500 165.817 94.504 165.501 600 175.887 106.439 184.190 700 187.024 115.953 201.647 800 198.963 123.673 218.447 bhawani d. joshi, manoj k. chaudhary/ bibechana 15 (2018) 131-139: rcost p.137 the correlation between temperature and these thermodynamic properties are given in figure3. the correlation equations are as follows: h0� � 138.660893 + 0.01732 t + 7.32786 x10<=t��r� � 0.99966� s0� � 55.97127 + 0.24566 t � 5.33423 x10<=t��r� � 0.9999� c2,0� � �1.05686 + 0.24515 t � 1.11082 x10<at��r� � 0.9995� table 5(b). different thermodynamic parameters at room temperature. parameters dft/6-311++g(d,p) total energy (hartree) -1218.8951192 zero-point vibrational energy (kcal/mol) 140.14841 rotational constants (ghz) 0.48096 0.37617 0.27138 enthalpy (kcal/mol) 149.891 specific heat (cal/mol-k) 61.295 entropy (cal/mol-k) 124.424 fig. 3: correlation between different thermodynamic properties with the temperature. it is observed that the parameters increase from 100 to 800 k due to the increase in the molecular vibrational intensities with the temperature. 4. conclusion using nbo studies stability of the molecule arising from hyperconjugative interaction and charge delocalization has been predicted by b3lyp/6-311++g(d,p) method. the � → �* interactions are responsible for the conjugation of respective �-bonds within aromatic rings r1 and r3 with maximum energy ~ 195, and 135 kcal/mol, respectively. the calculated data suggest an extended π-electron delocalization in the system is responsible for the nonlinearity of the title compound. due to 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[20] s.p. karna, p.n. prasad and m. dupuis, nonlinear optical properties of p‐nitroaniline: an ab initio time‐dependent coupled perturbed hartree–fock study, j. chem. phys. 94(2) (1991) 1171. doi.org/10.1063/1.460024 [21] c.y. panicker, h.t. varghese, p.s. manjula, b.k. sarojini, b. narayana, j.a. war, s.k. srivastava, c. van alsenoy and a.a. al-saadi, ft-ir, homo–lumo, nbo, mep analysis and molecular docking study of 3-methyl-4-{(e)-[4-(methylsulfanyl)-benzylidene]amino}1h-1,2,4-triazole-5(4h)-thione, spectrochim. acta a 151 (2015) 198. doi.org/10.1016/j.saa.2015.06.076. bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal theoretical investigation of mixing properties of sb-sn binary liquid alloy at 905 k h. k. limbu, k. k. mishra*, a. k. sah, i. s. jha, d. adhikari department of physics mahendra morang aadarsh multiple campus tribhuvan university, biratnagar, nepal. *email: mailkaushalko@yahoo.com article history: received 05 february, 2017; accepted 21 august, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18306 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the thermodynamic, microscopic, surface and transport properties of sb-sn liquid alloy at 905k have been studied using regular solution model. in thermodynamic properties, free energy of mixing(gm) , activity(a), entropy of mixing(sm), heat of mixing (hm) have been studied. to understand structural behavior of the liquid alloys concentration fluctuations in the long wavelength limit i.e. (scc(0)) and short range order parameter (α1) have been computed. surface property is studied with the help of butler’s model while transport property is computed from moelwyn-hughes equation. the theoretical and experimental values of thermodynamic and microscopic properties of sb-sn liquid alloy at 905k have been compared. in present work the value of interchange energy (ω) is found to be negative suggesting that there is a tendency of unlike atoms pairing (i.e. sb-sn) as the nearest neighbor indicating the ordering behavior in sb-sn liquid alloy. the symmetric behavior of concentration fluctuations of the liquid alloy has been well explained by the model. the temperature dependence of interchange energy (ω) has been found during the computation of entropy of mixing (sm) and heat of mixing (hm) of the liquid alloy. keywords: thermodynamic properties; structural properties; surface properties; transport properties. 1. introduction alloys of sn are likely to be very promising as an alternative solder in the electronic industry[1] .the commonly used solder consists of lead which is known to be toxic to the human body and causes serious environmental problems. antimony compounds have been known since ancient times and were used for cosmetics. alloying lead and tin with antimony improves the properties of the alloys which are used in solders, bullets and plain bearings. this is the motivation of our theoretical work on sb-sn system. the sb-sn alloy is of practical importance in view of their use, mainly in optoelectronic devices. the in-sb compound (diamond type a = 0.6478nm) can be used as a stabilizer for the sb-sn phase[2]. the mixing behavior of two elemental metals forming a binary alloy has always been a subject of considerable interest to many researchers[3–11]. the study of mixing properties of liquid alloys is h.k. limbu et al. / bibechana 15 (2018) 1-10: rcost p.1 http://nepjol.info/index.php/bibechana mailto:mailkaushalko@yahoo.com http://dx.doi.org/10.3126/bibechana.v15i0.18306 https://creativecommons.org/licenses/by-nc/4.0/ important because a good knowledge of their mixing properties in the liquid state is necessary for preparation of desired materials. surface properties are required to understand the surface related phenomenon such as corrosion, wetting characteristics of solders and kinetics of phase transformation. transport properties are required for many metallurgical process and heterogeneous chemical reactions. the thermodynamic properties are important to understand the behavior of alloys which is studied with the knowledge of free energy of mixing (gm), activity (a), entropy of mixing (sm), heat of mixing (hm). structural behavior is interpreted by the concentration fluctuation in long wave limit (scc(0)) and chemical short range order parameters (α1). surface tension is computed using buttler’s model[12] and viscosity is calculated with the help of moelwyn-hughes equation[13]. since the atoms sb and sn are identical in shape and size (i.e. atomic volume of sb / atomic volume of sn =18.703/17.741 ~1), the sb-sn liquid alloy is suitable candidate for our investigation on using regular solution model[14]. the theoretical formulation of regular solution model has been presented in section (2), result and discussion in section (3) and conclusion in section (4). 2. formalism regular solution model is based on the approximation that the constituent atoms a and b are sufficiently similar in size and shape so that they are interchangeable on the lattice or quasi-lattice, and the configuration is no longer independent of the mutual disposition of the two or more kinds of molecules. homogenous solution of binary liquid alloy a-b consists of ca (≡c) mole of a and cb {≡c(1-c)} mole of b respectively, where ca and cb are the mole fractions of a (≡sb) and b (≡sn) in the binary liquid alloy a-b. 2.1. thermodynamic properties in the frame work of regular solution model, the expression for the free energy of mixing (𝐺𝑀)of binary liquid alloy is 𝐺𝑀 = 𝐺𝑀 𝑖𝑑 + 𝐻𝑀 (1) where, heat of mixing (𝐻𝑀) and ideal free energy of mixing (𝐺𝑀 𝑖𝑑) are given by 𝐻𝑀 = 𝜔𝑐𝐴𝑐𝐵 (2) gm = rt [c ln c + (1 − c)ln(1 − c)] + 𝑐(1 − 𝑐). 𝜔 (3) here 𝜔 is interaction energy. the expression for activities aa of the elements a in the binary liquid alloy can be derived from the standard relation, that is 𝑅𝑇𝑙𝑛𝑎𝐴 = 𝐺𝑀 + (1 − 𝑐) 𝜕𝐺𝑀 𝜕𝑐 (4) 𝜕𝐺𝑀 𝜕𝐶 = 𝑅𝑇[𝑙𝑛𝑐 − ln(1 − 𝑐)] + (1 − 2𝑐). 𝜔 (5) using equation (3) and (5) in equation (4), we get 𝑙𝑛𝑎𝐴 = 𝑙𝑛𝑐 + 𝜔 𝑅𝑇 (1 − 𝑐)2 (6) and the activity of the element b (𝑎𝐵) is given by 𝑙𝑛𝑎𝐵 = ln (1 − 𝑐) + 𝜔 𝑅𝑇 𝑐 (7) the temperature derivative of gm provides an expression for integral entropy of mixing (𝑆𝑀) which is given by 𝑆𝑀 = 𝜕𝐺𝑀 𝜕𝑇 (8) from equation (3) and (8), we get 𝑆𝑀 𝑅 = [c ln c + (1 − c)ln(1 − c)] − 𝑐(1 − 𝑐). 1 𝑅 𝜕𝜔 𝜕𝑇 (9) h.k. limbu et al. / bibechana 15 (2018) 1-10: rcost p.2 the first term in the r.h.s of equation (9) is usual ideal of mixing. the last term represents the contributions from the temperature derivatives of the interchange energy. the necessity of taking 𝜔 as temperature dependent has been noticed by bhatia et. al[15], ratti and bhatia[7] ,alblas et. al[6]. the relation between free energy of mixing (gm), entropy of mixing (sm), and heat of mixing (hm) is given as, 𝐻𝑀 𝑅𝑇 = 𝑆𝑀 𝑅 + 𝐺𝑀 𝑅𝑇 (10) using equation (3), (9) and (10), we get 𝐻𝑀 𝑅𝑇 = c(1 − c). 𝜔 𝑅𝑇 + 𝑐(1 − 𝑐) 1 𝑅 . 𝜕𝜔 𝜕𝑇 (11) 2.2 structural properties the regular solution model has been successfully used to evaluate the value of concentration structure factor or concentration fluctuation in the long wavelength limit (scc(0)) which has been used to study the nature of atomic order in binary liquid alloy [17] by using relation, 𝑆𝐶𝐶(0) = 𝑅𝑇 ( 𝜕2𝐺𝑀 𝜕𝑐2 )t,p,n (12) from equation (3) and (12), we get 𝑠𝑐𝑐(0) = 𝑐𝐴𝑐𝐵 1− 2𝑐𝐴 𝑐𝐵 . 𝜔 𝑅𝑇 (13) the experimental determination of concentration fluctuation in the long wavelength limit scc(0) is derived from experimental data of the activities of the constituent species of the binary liquid alloys from the relation 𝑠𝑐𝑐(0) = (1 − 𝑐)𝑎𝐴 ( 𝜕𝑎𝐴 𝜕𝑐 ) 𝑇,𝑃,𝑁 −1 = 𝑐𝑎𝐵 ( 𝜕𝑎𝐵 𝜕𝑐 ) 𝑇,𝑃,𝑁 −1 (14) where, aa and ab are the activities of the component of a and b respectively. the warren-cowley[15,16] short range order parameter (α1) is useful parameter to quantify the degree of chemical order in the alloy melt. it provides insight into the local arrangement of the atoms in the molten alloys. although it is difficult to obtain the experimental values of α1, theoretical values of this parameters can be evaluated 𝛼1 = 𝑠−1 𝑠(𝑍−1)+1 (15) where, 𝑠 = 𝑆𝑐𝑐(0) 𝑆𝑐𝑐 𝑖𝑑(0) , 𝑠𝑐𝑐 𝑖𝑑(0) = 𝑐𝐴𝑐𝐵 and z is the coordination number, which is taken z = 6,8 and 10 for our purpose. 2.3 surface property butler assumed the existence of mono atomic layer at the surface of a liquid solution, called surface monolayer, as a separate phase that is in thermodynamic equilibrium with the bulk phase and derived an equation[7,18,19]. butler equation for the surface tension, γ of a binary a-b solution at temperature t is expressed as 𝛤 = 𝛤1 + 1 𝐴1 (𝐺1 𝐸,𝑠 − 𝐺1 𝐸,𝑏) + 𝑅𝑇 𝐴1 [ln(1 − 𝑐2 𝑠) − ln(1 − 𝑐2 𝑏)] = 𝛤2 + 1 𝐴2 (𝐺2 𝐸,𝑠 − 𝐺2 𝐸,𝑏) + 𝑅𝑇 𝐴2 [ln(𝑐2 𝑠) − ln(𝑐2 𝑏)] (16) where, r is universal gas constant. 𝑐𝑖 𝑠and 𝑐𝑖 𝑏 are mole fraction of component ‘i’ in the surface and bulk respectively. γ1 and γ2 are the surface tension of the pure component 1 and 2 respectively. 𝐺𝑖 𝐸,𝑠 and 𝐺𝑖 𝐸,𝑏 (i = 1,2) are partial excess free energy of component ‘i’ in the surface and the bulk respectively. the molar surface area of the component ‘i’ can be computed by using the relation 𝐴𝑖 = 𝐾. 𝑁𝐴 1/3 . 𝑉𝑖 2/3 (17) where, k(= 1.091) is geometrical factor for the liquid alloy, na is avogadro’s number, vi is the molar volume of the component i. h.k. limbu et al. / bibechana 15 (2018) 1-10: rcost p.3 2.4 transport properties the mixing behavior of an alloy in microscopic level can also be studied by diffusion coefficient. singh and sommer[18] have derived a relation between diffusion coefficient and concentration fluctuation as 𝐷𝑀 𝐷𝑖𝑑 = 𝑆𝐶𝐶 𝑖𝑑 (0) 𝑆𝐶𝐶(0) (19) where, dm is the mutual diffusion coefficient and did is the intrinsic diffusion coefficient for an ideal mixture given as 𝐷𝑀 = 𝑐1𝐷2 + 𝑐2𝐷1 (20) where, d1 and d2 are the self-diffusivities of pure components a and b respectively. in term of energy order parameter ω, the diffusion coefficient can be expressed as[18] 𝐷𝑀 𝐷𝑖𝑑 = [1 − 2𝜔 𝑅𝑇 𝑆𝑐𝑐 𝑖𝑑(0)] (21) the ration 𝐷𝑀/𝐷𝑖𝑑 indicates the mixing behavior of the alloys i.e. 𝐷𝑀/𝐷𝑖𝑑> 1 indicates compound formation and if 𝐷𝑀/𝐷𝑖𝑑< 1 then there is tendency of phase separation. for ideal mixing, 𝐷𝑀/𝐷𝑖𝑑 approaches 1 viscosity is one of the transport properties of binary liquid alloy. the moelwyn-hughes equation[13] for viscosity of liquid mixture is given as 𝜂 = (𝑐1𝜂1 + 𝑐2𝜂2 )(1 − 2𝑐1𝑐2. 𝐻𝑀 𝑅𝑇 ) (22) where, 𝜂k is the viscosity of pure component k(k= 1, 2), c is the mole fraction of the component k and hm is the enthalpy of mixing. for most liquid metals, 𝜂𝐾 can be calculated at temperature t from arrhenius type equation[20] 𝜂𝐾 = 𝜂𝑂𝐾 exp [ 𝐸𝑛 𝑅𝑇 ] (23) where, 𝜂𝑂𝐾 is constant (in units of viscosity) and en is the energy of activation of viscous flow for pure metal (in unit of energy per mole). 3. results and discussion 3.1. thermodynamic properties: free energy of mixing, activity, heat of mixing and entropy of mixing the value of energy parameter i.e. interchange energy (ω) used for the calculation of thermodynamic properties of sb-sn liquid alloy at 905 k has been estimated from equation (3) by the method of successive approximation, using the observed data of free energy of mixing, gm [21] over the entire range of concentration. the best fit value is found to be 𝜔 𝑅𝑇 = −0.8925 . the sign and size of the energy parameter governs the general character, phase separation or complex formation of the alloys system. the negative sign of energy parameter suggests that there is a general tendency for unlike atoms to pair in the sb-sn liquid alloy at 905 k. however, the tendency of pairing is weak as the energy parameter is small. the same value of the energy parameter has been used throughout the calculations in order to maintain the consistency for the other properties of mixing of the liquid alloy at 905 k. the plot of experimental and computed values of free energy of mixing (gm) of sb-sn liquid alloy with respect to the concentration of sb is shown in fig.1. h.k. limbu et al. / bibechana 15 (2018) 1-10: rcost p.4 where, vsb = vm [1+𝛼p (t-tm)] and vsn = vm [1+𝛼p (t-tm)] (18) vm = atomic volume at melting point tm = melting temperature and 𝛼p = volume coefficient at constant temperature. we have computed the activities of sb and sn in the liquid sb-sn alloy using the same energy parameter (ω) in equation (6) and (7), and then compared them with experimental values as depicted in fig. 2. fig. 1: free energy of mixing of sb-sn liquid alloy at 905 k. the solid line represents theoretical values and circle represents experimental values. fig. 2: activities azn and acd of sb-sn liquid alloy at 905k.the solid line theoretical values and circle represents experimental values. the plot shows that there is a good agreement between the sets of computed and experimental results. activity coefficient represents the measure of tendency of a component to leave the solution. the magnitude of activities depends on the bound energies. activity is very important quantity which can be associated to the free energy of mixing gm and concentration fluctuation scc(0). measurement of activities provides correlation of the behavior of the system. the heat of mixing and entropy of mixing of the sb-sn binary liquid alloy at 905 k has been calculated from equation (11) and (9) respectively .to determine heat of mixing (hm) and entropy of mixing (sm) we need temperature derivative of energy parameters. the observed values of heat of mixing[21] were utilized to obtain the temperature derivatives by the method of successive approximation. the best fit value has found to be 1 𝑅 𝜕𝜔 𝜕𝑇 = −0.18. both computed and experimental values of heat of mixing and entropy of mixing are in good agreement at all compositions as shown in figures 3 and 4. the observed symmetry in the heat of mixing and entropy of mixing about equiatomic composition of sb-sn liquid alloy at 905 k is well explained by the present theoretical analysis. the negative value of hm indicates the ordering nature of the liquid alloy in the entire range of concentration. the theoretical understanding of heat of mixing as a function of concentration is very useful as it directly h.k. limbu et al. / bibechana 15 (2018) 1-10: rcost p.5 the computed and experimental values[21] of free energy of mixing are in good agreement in the entire concentration range. the computed value of gm/rt (= -0.9163) is minimum at csb=0.5 while, experimental value of gm/rt(= -0.9163) at csb=0.5. the negative small values of free energy of mixing throughout the entire concentration range indicate that the sb-sn alloy at 905 k in liquid state is a weak interacting system. the entropy of mixing sm is helpful to draw important structural information for binary liquid alloys. it represents the sharing of energy among the atoms of the constituent metals forming the alloys and hence the disorder in the equilibrium state of the alloys. the role of entropy is often complicated for most of the binary liquid alloys. the computed and experimental values[21] of entropy of mixing in sb-sn binary liquid alloy are positive in the entire range of concentration. fig. 3: heat of mixing of sb-sn liquid alloy at 905k. the solid line represents theoretical values and circle represents experimental values. fig. 4: entropy of mixing of sb-sn liquid alloy at 905k.the solid line represents theoretical values and circle represents experimental values. 3.2 structural properties: concentration fluctuation in the long wavelength limit and chemical short range order parameter the scc(0) computed from equation (14) is referred as to the experimental value. the computed and experimental values of scc(0) are depicted in figure 5 along with the ideal values i.e. scc id(0) = c(1 − c). liquid alloys. at a given composition, if scc(0) < scc id(0) then, ordering in liquid alloys is expected, while scc(0) > scc id(0) is the indication of a tendency of phase separation. figure-5 shows that scc(0) < scc id(0)throughout the entire concentration range which indicates that heterocoordination is favored in the sb-sn alloy at 905 k. the calculated values of scc(0) are in good agreement with the experimental values[21]. the calculated values of scc(0)(= 0.1729) and experimental values of scc(0) (= 0.1729) are maximum about equiatomic composition. the result can be used to understand the nature of atomic order in binary the warren-cowley chemical short-range order parameter α1 is an important microscopic function which is used to predict the degree of local arrangement of atoms in the mixture. the chemical short-range order parameter has been computed from equation (15) on using the theoretical value of scc(0). the value of coordination number (z) is taken to be 6,8 and 10. for equiatomic composition the parameter α1 is found to be −1 ≤ 𝛼1 ≤ +1.the value of 𝛼1 min = -1 indicates complete ordering and the value of 𝛼1 max = 1 indicates complete segregation leading to phase separation and α1=0 corresponds to a h.k. limbu et al. / bibechana 15 (2018) 1-10: rcost p.6 leads to the nature of interaction among the constituent’s species of the alloys. though such information is available from free energy of mixing we may emphasize that heat of mixing has some added significance. from the definition of hm (hm= gm + tsm) it is obvious that hm has greater significance than gm, as the physical significance of sm is also locked up in the heat of mixing. fig. 5: concentration fluctuation of sb-sn liquid alloy at 905k. the solid line represents theoretical values, circle represents experimental values and dotted line represents ideal values. fig. 6: chemical short range order parameter (α1) of sb-sn liquid alloy at 905k for different coordination number z= 6,8and 10.the solid line represents z=10, dotted line represents z=8 and solid line with hollow circle represents z=6. 3.3. surface property the surface tension of a liquid sb-sn has been computed by using equation (16). we have used the experimental value of bulk partial excess free energy 𝐺𝑖 𝐸,𝑏 [21] of the monomers of the liquid alloy at 905 k. 𝛽 = 𝐺𝑖 𝐸,𝑠 𝐺𝑖 𝐸,𝑏 (24) the value of parameter β has been taken as 0.83 as suggested by different researchers to compute surface tension of liquid alloys[20,22]. for computation of surface tension of sn-sn at 905k equation (16) in conjugation with equation (17) and (18) are used. we have calculated the surface tension of pure components (i.e. sb and sn) using equation 𝛤(𝑇) = 𝛤𝑚 + 𝜕𝛤 𝜕𝑇 (𝑇 − 𝑇𝑚) (25) where, t = 905 k, tm = melting temperature (tm= 903.5k for sb, and 505k for sn) ; 𝜕𝛤 𝜕𝑇 is temperature coefficient of surface tension (= -0.05 x 10-3 nm-1k-1 for sb, and -0.07x 10-3 nm-1k-1 for sn). the partial excess free energy of mixing of the pure components for the systems sb-sn at 905 k are taken from the reference[20]. the surface concentration of a component with respect to the bulk concentrations has been calculated from equation (16). the variation of surface concentration with the bulk concentration of sb component has been shown in fig. 7. it is to be noted that the components to the alloy do not mix completely with each other in the bulk because of the difference in the values of surface tension of constituent metals. the calculated values of surface concentration have been used to compute the surface tension of sb-sn liquid alloy at 905 k. from fig. 7 it is clear that the surface concentration of sb increases with increasing bulk concentration of sb (i.e. csb). this shows that sb atoms (having lower value of surface tension relative h.k. limbu et al. / bibechana 15 (2018) 1-10: rcost p.7 random mixing of atoms. the values of short range order parameter α1 are negative in the entire concentration range and the minimum value (i.e. α1= -0.0692 at z=6,α1= -0.0528 at z=8,α1= -0.0427 at z=10) is at equiatomic composition as shown in figure 6,which indicates the ordering nature of the alloy as evident from the scc(0). to snatoms in sb-sn system) segregate at the surface of sb-sn liquid alloy throughout the entire concentrations. the computed values of surface tension of sb-sn liquid alloys at 905 k are depicted in fig. 8. fig. 7: surface concentration of sb versus bulk concentration of sb in molten sb-sn liquid alloy at 905k.the solid line represents theoretical values and the dotted line represents ideal values. fig. 8: surface tension of sb-sn liquid alloy at 905k.the solid line represents calculated surface tension and dotted line represents ideal surface tension. it is obvious from figure 8 that the computed values of surface tension of sb-sn liquid alloy at 905 k shows deviation from the ideal values (𝛤 = 𝑐1γ1 + c2γ2) i.e. the computed values of surface tension are slightly more than the ideal values at csb=0.1 to 0.9 compositions. it is also found that the surface tension of sb-sn liquid alloy decreases with the increase in the concentration of sb atoms in the alloy as the surface tension of pure component of sb atom is less than pure component of sn atom at the temperature of study. 3.4 transport properties: chemical diffusion and viscosity the calculated values of scc(0) are used in equation (20) to evaluate the ratio of mutual and selfdiffusivities, 𝐷𝑀/𝐷𝑖𝑑 for cd-mg liquid alloy at 923 k. for the consistency of the estimated order energy parameter ω, we have also calculated 𝐷𝑀/𝐷𝑖𝑑 using equation (21) which predicts 𝐷𝑀 𝐷𝑖𝑑 = 1 at csb=0 and csb=1. fig. 9 shows plot of 𝐷𝑀/𝐷𝑖𝑑 against the concentration of sb calculated from equation (21). from the figure it is clear that the value of 𝐷𝑀 𝐷𝑖𝑑 > 1 in the entire range of concentration which is indicative for the presence of chemical order in the alloy. the maximum value of 𝐷𝑀/𝐷𝑖𝑑 is 1.4459 at csb = 0.5, confirms the ordering tendency of the atoms in sb-sn liquid alloys is greater about equiatomic composition. we have used moelwyn-hughes equation (22) in conjugation with equation (23). to compute fig. 9: ratio of mutual and self-diffusivities, 𝐷𝑀/𝐷𝑖𝑑 for sb-sn liquid alloy at 905k versus concentration of sb. h.k. limbu et al. / bibechana 15 (2018) 1-10: rcost p.8 viscosity of sb-sn alloy at 905 k, the viscosities of pure components sb and sn at 905 k are required which is computed using equation (23). the viscosity of pure component can be obtained with the help of constants 𝜂ok and e for the metals[20] and is as shown in the fig.10. the plot shows that viscosity of the alloy is slightly deviated at the concentration csb=0.1 to 0.9.the viscosity of pure component of sb atom is more than the viscosity of pure component sn which results increase in the viscosity as the concentration of sb atom increases in the alloy as shown in the fig. 10. fig. 10: viscosity of sb-sn liquid alloy at 905k versus concentration of sb.the solid line represents calculated viscosity and dotted line represents ideal values. 4. conclusion the negative interchange energy (ω) suggests that there is a tendency of unlike atoms pairing (sb-sn) of the alloy at 905 k. it is a weak interacting system. the interchange energy is found to be temperature dependent and plays important role to explain the alloying behavior of the alloy. all the thermodynamic and microscopic properties of this alloy are symmetric at equi-atomic composition as a function of concentration. the computed values of surface tension show small positive deviations from ideality and surface tension 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[22] k.s. yeum, r. speiser, d.r. poirier, estimation of the surface tensions of binary liquid alloys, met. trans. b. b20 (1989) 693–703. h.k. limbu et al. / bibechana 15 (2018) 1-10 : rcost p.10 http://www.sciencedirect.com/science/article/pii/s0022309312001706?via%3dihub http://www.sciencedirect.com/science/article/pii/s0167732211004120?via%3dihub http://www.tandfonline.com/doi/abs/10.1080/00319109008036406 http://rspa.royalsocietypublishing.org/content/135/827/348 file:///d:/bibechana-2016/accepted%20paper/doi.org/10.1103/physrev.77.669 http://www.tandfonline.com/doi/abs/10.1080/00319108208080755 http://iopscience.iop.org/article/10.1088/0034-4885/60/1/003/pdf http://www.sciencedirect.com/science/article/pii/s0022309310002942?via%3dihub r. p. koirala et al. / bibechana 15 (2018) 113-120: rcost p.113 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal energetics of mixing and transport phenomena in cd-x (x=pb, sn) melts r.p. koirala1*, i. koirala2, d. adhikari1 1department of physics, m.m.a.m. campus, tribhuvan university, biratnagar, nepal. 2central department of physics, tribhuvan university, kirtipur, nepal. *email: rpphysics@gmail.com article history: received 21 september, 2017; accepted 17 december, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18751 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract we report a quasi-chemical study of the thermodynamic and transport properties of mixing of liquid cd-pb and cd-sn alloys at 773k. the interaction energy in the alloys is found to be positive which suggests homo-coordination of atoms in the alloys. the viscosities of the alloys at 773k computed from two different approaches exhibit non-linear concentration dependence with the results for cd-sn alloy being in very good agreement and satisfactory agreement for cd-pb alloy. in lower concentrations of cd-component, cd-pb alloy has larger viscosity and on the other side of concentration, cd-sn alloy has larger value. the calculations of inter-diffusion coefficients result in concave diffusion isotherms for the alloys. the higher values of inter-diffusion coefficients for cd-sn suggest that cd and sn metals tend to mix more readily than cd and pb metals do in cd-pb alloy. the correlation between viscosity and diffusion implies that the inter-diffusion coefficient is large for low viscous liquid alloy and vice-versa. keywords: mixing properties; transport properties, diffusion; free energy of mixing. 1. introduction of various traditionally classified materials such as metals, semiconductors, alloys, ceramics and polymers in use today, metal alloys make up a large proportion both by quantity and commercial value.the major building materials of the industrial revolution are indeed metals and alloys. among a vast number of metallic alloys so far produced, those with cadmium metal have received much attention from both experimental and theoretical researchers and in the context two liquid alloys namely cd-pb and cd-sn in particular have become the subject of various research studies over several decades [1-9]. this is due to interest in these alloys for the substantial variation in their observed properties [10] and wide range electrical, mechanical, coating, and especially hightemperature structural applications [11]. in metallurgical science the determination of the mixing properties of liquid alloys is prerequisite for the preparation of desired materials for commercial use. growing technological interest to the nonperiodicity in the atomic arrangement of liquid alloys has led metallurgists to emphasize understanding of the high temperature dynamics of the alloys in the liquid state for the description of http://nepjol.info/index.php/bibechana mailto:rpphysics@gmail.com http://dx.doi.org/10.3126/bibechana.v15i0.183 https://creativecommons.org/licenses/by-nc/4.0/ r. p. koirala et al. / bibechana 15 (2018) 113-120: rcost p.114 the behaviour and performance of the commercial alloys in the solid state. the dynamics in fluids is governed by two intimately related transport phenomena namely viscosity and atomic diffusion. the viscosity and diffusion of metals and the alloys are technologically important properties which are required for the interpretation of the kinetics of the reactions and modelling of metallurgical processes. while the first describes the macroscopic transport of momentum by the collective motion of the particles, the latter describes single-particle diffusive transport. the interest for the study of the transport phenomena in liquid alloys thus stems from the significance of these properties in both the technology and theory of the liquid alloys. as the variation in the elemental composition in the metallic mixture produces alloys with different properties, it is logical to examine the alloying behavior by computing the properties of mixing as function of concentration. in the current work we have focused our attention towards the review of the thermodynamics of the formation of liquid cd-pb and cd-sn alloys at 773k and the transport phenomena in them. for the review of the thermodynamics of mixing in the liquid alloys as function of composition we employ self-association model based on the formation of like atom clusters [12, 13]. the self-association model is assumed to be good for regular alloys [14], and to our interest we intend to apply it to the alloys, which are not strictly regular solutions but have their behaviour close to that of regular solution. due to unavailability of reference experimental data of viscosity at hand, we cannot compare the results which can be obtained from a model and for this reason we have carried out a comparative study using quasi-chemical analysis [15] and moelwyn-hughes (m-h) equation [12]. in order to study of transport behaviour in the liquid alloys in further detail we have also assessed inter-diffusion coefficients of the alloys from the quasi-chemical approach [16]. the outline of the paper is as follows: theoretical basis of the work is presented in section 2. sections 3 and 4 deal with the results and discussions respectively and conclusions are outlined in section 5. 2. theoretical basis 2.1 thermodynamic properties let us assume that a liquid binary alloy contains altogether n atoms, of which nca are atoms of element a and ncb are atoms of element b. in self-association model for regular alloy [5] the atoms of the elements a and b are assumed to be located at equivalent sites with short range interactions effective only between nearest neighbours in polyatomic matrices. this leads to the formation of like atom clusters or self-associates of type ia and jb , where i and j are the numbers of atoms in the clusters of type a and b matrices respectively. on the basis of such assumption, expressions for thermodynamic functions are derived for liquid binary alloys [12, 13]. the free energy of mixing, gm is obtained using the following analytical expression [12, 13]: w)cnc()()](lnclnc[rtg babam   11 (1) with ba a cnc c   (2) here, r is molar gas constant; t is the temperature; ca and cb are concentrations of components a and b respectively; w is ordering energy parameter and ijn / is the ratio of the self-associates. in order to estimate the value of the energy parameter w, we also recall the following standard thermodynamic relations for the chemical activities, ak [12, 13]: rt w )( c lnaln a a 2 11     (3a) rt w n)n()(lnaln b 2 11   (3b) an analytical expression for the entropy of mixing, sm can be obtained, from eq. (1), in the following form: r. p. koirala et al. / bibechana 15 (2018) 113-120: rcost p.115 t w )cnc()()](lnclnc[rs babam     11 (4) the enthalpy of mixing hm is calculated from the following standard thermodynamic relation: mmm stgh  (5) 2.2 transport properties 2.2.1 viscosity unlike equilibrium properties, for which more or less accurate expressions have been derived on the basis of statistical mechanical theory, the derivation of computable, exact expressions for the dynamic properties of the liquid alloys is a complex task as it is hard to describe atomic motions precisely in the liquid phase. the scientific literature provides a number of semi-empirical equations or approximate expressions for the computation of the viscosity of the metals and the alloys [15, 17-20]. for want of the experimental results for the viscosities of the alloys in this work, we have performed comparative study using the following two different approaches for the computation of viscosities of liquid cd-pb and cd-sn alloys. (i) quasi-chemical approach the concentration dependence of the viscosity of metal alloy at a given temperature can be computed from the following expression [15]: ]),(1[)( wngcccc babbaa   (6) where 3 22 )( )()1()/(2 ),( ba ba cnc cncnrtwn wng    (7) with n and w/rt being the fitting parameters appearing in the self-association model, eq. (1). the viscosities, k (k=a, b) of pure metals can be calculated from the knowledge of their viscosities at their respective melting temperatures using the iida-guthrie equation for temperature dependence as follows [20]: )rt/t.(exp . i,moii 291 322  (8) with )t.(exp)rt/t.(exp . i,m i,m i,m . i,m i,m oi 290291 2790322    (9) the performance of the equations for the temperature dependences of the above equations have been analysed by computing the results for different metals and comparing with the corresponding experimental results [20, 21]. (ii) moelwyn-hughes (m-h) equation the viscous flow of a liquid mixture depends on the cohesive interactions in liquid phase. cohesive interactions arise due to the bonding that develops between atoms/or molecules and their nearest neighbours and they give rise to the enthalpic effect. in order to account for viscous flow in a binary liquid mixture, a simple equation, called moelwyn-hughes (m-h) equation [12], has been suggested which is based on fact that the viscous flow becomes more difficult when the cohesion energy of the alloy is increased. the m-h equation for the viscosity,  of binary solution at temperature t as function of mole fraction concentration, ci ),( bai  reads as r. p. koirala et al. / bibechana 15 (2018) 113-120: rcost p.116 )]/2(1[)( rtwcccc babbaa   , (10) where w is the interaction energy which can be estimated from self-association model, eq. (1) and a and b being the viscosities of the components at temperature t. the sign of deviation of viscosity from linearity depends only on the sign of w. for segregating systems, 0w and, therefore, id  , i.e. negative deviation of viscosity is expected for these systems. for ordering systems on the other hand, id  is expected. 2.2.2 diffusion atomic diffusions in metals and alloys are important transport phenomena in metallurgical science. to study atomic diffusion theoretically, several models/equations have been suggested. an equation for the self diffusivity or intrinsic diffusion coefficients, i,md of liquid metals at their melting points, i,mt has been derived through a combination of the modified stokes-einstein relation and the andrade formula for melting-point viscosity [22], as well as the hard-sphere model [23] and the correspondingstates principle [22] in the form [24]: 31219 10321 / i,m / ii,mi,m v)m/t(.d   (11) where im is the atomic mass and i,mv is the atomic volume. the temperature dependence of self-diffusivity of liquid metals can be expressed by the arrhenius equation [24] as follows: )/(exp ,, rtedd idioi  (12) where the pre-exponential constant, do,i and the apparent activation energy of self-diffusivity for metal, ed,i are called arrhenius parameters. the parameter ed,i, is related to its melting temperature, i,mt as 111 imid t612e . ,, . (13) the parameter do,i is obtained by substituting i,mtt  and imi dd , in eq. (12) )/.(exp . ,,, rt612dd 110 imimio  (14) for a binary system of constant molar volume, the inter-diffusion coefficient, dm can be expressed as follows [16]: ) ln ln ()( a a baabm cd d 1dcdcd   (15) where a is the activity coefficient of a, da and db are the self-diffusivities of the components a and b respectively. in quasi-chemical analysis a workable expression for the factor )clnd/lnd( aa1 can be derived from eq. (3), in terms of the fitting parameters n and w of self-association model in the form rt w nccn ccn nccn nc nccn n cd d a a 3 2 2 )( )1(2 )( )1( ln ln 1          (16) having known the parameters n and w, the inter-diffusion coefficient, dm of the binary liquid alloys can then be computed. 3. results the thermodynamics of mixing in metallic alloys can be regarded as the interplay between enthalpic and entropic effects which gives rise to the nature of nature of alloy, either ordering or segregating. at r. p. koirala et al. / bibechana 15 (2018) 113-120: rcost p.117 a given temperature and fixed pressure, equilibrium mixing properties of a binary liquid alloy vary with the composition of the alloy. to begin with we have fitted the parameters of the self-association model into eqs. (1-3) separately to be respectively (n=1.31, w/rt=1.212) and (n=1.225, w/rt=0.545) for cd-pb and cd-sn alloys at 773k, so as to reproduce closely the corresponding experimental values of the free energy of mixing, gm and activities, ak over the entire range of concentration [10]. we have next computed the entropy of mixing, sm taking dw/dt= -2.25 and 4.45 in eq. (4) respectively for cd-pb and cd-sn alloys and then the enthalpy of mixing, hm for the alloys from eq. (5). numerical results of the thermodynamic functions gm, sm and hm along with the corresponding reference values [10] are depicted in the isotherms of fig.1(a) for cd-pb alloy and those for cd-sn alloy in fig. 1(b). fig. 1: thermodynamic functions gm, sm and hm versus concentration of cd-component of (a) cdpb alloy at 773k and (b) cd-sn alloy at 773k [solid linetheory; crossesexperiment]. the dynamic mixing behaviour of the alloys is studied in terms of the atomic transport coefficients namely viscosity and diffusion coefficients. the knowledge of viscosity helps to understand the bonding strengths among various species in the liquid alloys. for calculations of the viscosity of the alloys, the viscosities of the pure metals cd, pb and sn at the temperature of investigation are required which are calculated from eq. (8) using the values of their viscosities at the respective melting temperatures [20]. we have then computed the concentration dependence of the viscosity of liquid alloys using separately the values of the interaction energy w as thermodynamic input for each alloy. due to scanty of reference data of the alloys for comparison, we have carried out comparative analysis by computing the viscosities from the quasi-chemical approach, eq. (10) over the full range of concentration. the results for viscosity of alloys calculated from m-h equation and quasichemical approach are found to be reasonably in good agreement with negative deviation from the additive rule of mixing [fig. 2 (a)]. in order to examine the dynamic behaviour in the alloys at 773k in some more detail, we have also computed inter-diffusion coefficients as function of concentration using eq. (15) in conjunction with eq. (16). the inter-diffusion isotherms for both the alloys are found concave with a minimum value at 60% atomic composition of cd-content for cd-pb alloy and at 50% for cd-sn alloy [fig. 2 (b). the higher values of inter-diffusion coefficients for cd-sn suggest that cd and sn metals tend to mix more readily than cd and pb metals do. this is in conformity with smaller segregating tendency in cd-sn alloy. r. p. koirala et al. / bibechana 15 (2018) 113-120: rcost p.118 fig. 2: (a)viscosity of cd-pb and cd-sn alloys at 773k versus concentration of cd-component [solid curvequasi-chemical approach; circles and crossesm-h equation; dotsideal values (b) inter-diffusion coefficient (dm) of cd-pb and cd-sn alloys at 773k [solid line-theory; dotsideal values]. 4. discussion the interaction energy parameters estimated in our study are model specific and the prediction of the properties of the alloys using the energy parameters is a success of the model. the positive sign of the energy parameters in both the alloys suggests a general tendency of repulsive interaction between corresponding species in that results in homo-coordination of the atoms in the alloys showing positive deviation from raoult’s law. for either alloy the temperature derivative of order energy has been found to be a non-zero quantity. this suggests that the interaction energy in an alloy is temperature dependent. in our comparative study, the viscosities of the alloy are found to have non-linear (concave) concentration dependence with the results from the two approaches for cd-sn alloy being in very good agreement and it is also reasonably good enough to accept the departure in the results for cd-pb alloy. it is apparent from the viscosity isotherms that cd-pb has larger viscosity in lower concentration of cd-component while cd-sn alloy has larger value in cd-rich side of the composition. the local atomic ordering in a liquid a-b alloy is non-periodic, unlike crystals, as the solute atoms in the homogeneous solution can arrange in many ways by diffusion which contrasts with the pure metals a and b, in each of which the atoms can arrange only in a particular way. in the state of disorder in the atomic arrangements, some sort of short range atomic bonding (metallic, ionic, or covalent, or even secondary bonds, such as hydrogen bonding or vander waals forces as in the case of molecular crystals or liquids) can be assumed to exist between the nearest neighbours to present cohesive energy of solution. the cohesive energy of solution depends on the size difference of the atomic species and entirely to the size-dependent variations in the latent heats [25]. the cohesive energy may be thought to be responsible for the enthalpic effect and the viscous nature of the liquid alloys. in general larger viscosity values of a liquid alloy indicate stronger cohesive interactions in it suggesting a slow viscous flow of the melt. it is noted that the agreement in the results from different equations for viscosity of alloys casts considerable doubt on the reliability of the results and hence suggests the limitations to the validity of r. p. koirala et al. / bibechana 15 (2018) 113-120: rcost p.119 the equations. indeed, it is very difficult to judge the reliability of such work without a clearer understanding of the controlling factors involved. at this point it would be proper to mention that the equations, which we have employed in this work for computing viscosities of binary liquid alloys, have already been applied in several other studies. it is apparent that the mutual diffusion of liquid metals in forming a binary liquid alloy depends on sizes of the atomic species; it is found to be preferably large when the atomic volumes of the component metals are nearly equal and it decreases as the size ratio deviates from unity. it is found to be preferably large when the atomic volumes of the component metals are nearly equal and it decreases as the size ratio deviates from unity. moreover, it is mentioned that diffusion coefficient varies inversely with viscosity when the ratio of solute to solvent exceeds five and in extremely high viscosity materials, diffusion becomes independent of viscosity [22]. 5. conclusion our theoretical analysis of mixing properties of cd-pb and cd-sn alloys at 773k shows that selfassociation model successfully explains the observed thermodynamics of mixing in the alloys showing positive deviation from raoult’s law. the analysis of viscosity calculations reveals nonlinear concentration dependence of viscosity for both the alloys. in lower concentrations of cdcomponent, cd-pb alloy has been found to have larger viscosity and on the other side of concentration, cd-sn alloy has larger value. the calculations of inter-diffusion coefficients result in concave diffusion isotherms for the alloys. the higher values of inter-diffusion coefficients for cd-sn suggest that cd and sn metals tend to mix more readily than cd and pb metals do in cd-pb alloy. the correlation between viscosity and diffusion is remarkable which simply suggests that the diffusion coefficient is large for low viscous liquid alloy and vice-versa. acknowledgements we are grateful to prof. b.p. singh (retired from t.m. bhagalpur university, bhagalpur, india) and dr. indu shekhar jha (post graduate department of physics, m.m.a.m. campus biratnagar, tribhuvan university, nepal) for their valuable suggestions and inspiring discussions. references [1] a. qin, r. wang, y. wang, j. wang, s. liu, k. cheng, y. du, b. sundman, thermodynamic assessment of the cd-x (x=sn, mn, fe) systems, calphad. 47 (2014) 83-91. doi.org/10.1016/j.calphad.2014.06.006. 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[25] a.k. starace, c.m. neal, b. cao, m.f. jarrold, a. aguado, j.m. lopez, correlation between the latent heats and cohesive energies of metal clusters, j. chem. phys. 129 (2008) 144702-(1-10). doi.org/10.1063/1.2987720. http://www.cadmium.org/ http://dx.doi.org/10.1088/0034-4885/60/1/003 http://dx.doi.org/10.1007/s12043-009-0088-6 http://dx.doi.org/10.1139/p87-038 https://doi.org/10.1080/00319109808035917 https://doi.org/10.1088/0957-0233/16/2/005 https://doi.org/10.1063/1.2987720 hari paudyal et al. / bibechana 13 (2016) 50-59 : rcost p.50 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal first-principles study of a molecular adsorption of fluorine on monolayer mos2 hari paudyal1, nurapati pantha2, narayan prasad adhikari2* 1golden gate international college, kathmandu, nepal 2central department of physics, tribhuvan university, kathmandu, nepal. *email: npadhikari@tucdp.edu.np article history: received 05 august, 2015; accepted 12 september, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13356 abstract we have performed density functional theory (dft) based first-principles calculations to study the stability, geometrical structures and electronic properties of pure monolayer molybdenum disulphide (mos2) and fluorine (f2) adsorbed monolayer mos2 within the dft-d2 level of approximations. present study shows that a f2 molecule adsorbed mos2 monolayer system is stable. from the geometry and information of adsorption energy of f2 molecule on the different occupation sites of mos2 monolayer, it has been found that fluorine prefers atomic adsorption above sulphur (s) atom. the binding energy per equivalent molecular fluorine above the sulfur (s) atom is found to be 1.83 ev. the electronic structure calculations of mos2 and f2 adsorbed mos2 monolayer shows that there is a band gap of 1.14 ev and 1.01 ev respectively, at the fermi level. further, the symmetry of total dos for up and down spin calculations reveals that the f2 adsorbed mos2 monolayer is non-magnetic as similar to that of pure mos2 monolayer. the projected density of states (pdos) of a f2 adsorbed mos2 monolayer is studied to understand the weighted contributions of different orbitals. ©rcost: all rights reserved. keywords: density functional theory; mos2 monolayer; band structure properties. 1. introduction after the discovery of graphene [1], atomic crystals of two-dimensional materials, consisting of single sheets, extracted from bulk materials are gaining considerable attention with a wide range of electronic properties and potential practical applications [2]. the study on low dimensional hexagonal structure based materials have become of great interest to many researchers for nanoscience and consequent nanotechnology. molybdenum disulfide mos2, is a two dimensional transition metal dichalcogenide honeycomb structure with certain gap in its electronic bands, consistent with a semiconductor [3]. it is formed by weakly bonded three layers of sulphur, hari paudyal et al. / bibechana 13 (2016) 50-59 : rcost p.51 (online publication: dec., 2015) molybdenum and sulphur (s-mo-s). it means that two planes of s atoms and an intercalated plane of mo atoms are bound together in a trigonal prismatic arrangement [3, 4] of mos2. currently, mos2 is attracting the most valuable researches because of its availability in the form of a natural mineral, molybdenite [5]. adsorption of foreign atom/s and molecule/s on twodimensional materials is a promising approach to suitably modify their properties [6]. the functionalization of mos2 has also occupied an important domain in the research activities to study electronic, magnetic and band structure properties [7]. a number of theoretical and experimental works have been carried out to study these important behaviors of different elements adsorbed mos2 monolayer, and have found to yield many interesting results [8]. in the halogen group (vii), fluorine is the most electronegative and highly reactive element in our periodic table. the primary reason why we choose fluorine in our calculation is that the adsorption of fluorine molecule may have significant potential to modify the electronic properties of mos2 monolayer, which can be used in many desired electronic practical applications. further, it may be a useful effort to synthesize chemically modified mos2 monolayer and present new directions in two dimensional materials. these purpose require the atomistic level of understanding, and in our best knowledge, it is yet to be understood for halogen adsorbed mos2. the remaining part of this work is organized in following way. we first discuss the computational details and the systems under our study. we then go into the results section and describe our findings for structural and binding properties of f2 adsorbed on mos2 monolayer. the section is followed by the discussion of adsorption properties of f2 on pure mos2 monolayer. the post-processing analysis, e.g. density of states is incorporated in the section. the last section, conclusions, summarizes the major findings and possible extension of ongoing research work. 2. computational details in the present work, we study the geometrical and electronic properties of monolayer mos2 and fluorine molecule adsorbed monolayer mos2. to perform the calculations, we have used density functional theory (dft) [9, 10] implemented in the quantum espresso [11] code. the perdewburke-ernzerhof (pbe) variant of the generalized gradient approximation (gga) [12], incorporating van der walls interaction via grimme’s model [13, 14] is used to treat electronelectron interaction. the algorithm has used rappe-rabe-kaxiras-joannopoulos (rrkj) model of ultrasoft pseudo-pot ent i a l s to account the interaction between the ion cores and valence electrons. the plane wave expansion with kinetic energy cut-off values of magnitudes 35 ry, and 350 ry, respectively, are used for wave-function and charge density. a mesh of 10×10×1 k-points is used for unit cell of mos2 monolayer for brillouin-zone integration and a mesh of 4×4×1 k-points is taken for 3×3 supercell of monolayer mos2. further, in order to minimize the interactions between two adjacent mos2 layers, a vaccum distance of 12 å is maintained in the calculations. all the structures are optimized using the bfgs (broyden-fletcher-goldfarb-shanno) [15] scheme until the total energy hari paudyal et al. / bibechana 13 (2016) 50-59 : rcost p.52 (online publication: dec., 2015) change is less than 10 −4 ry between two consecutive scf steps and force acting is less than 10 -3 ry/bohrs. the ‘marzarri-vanderbilt’ [16] smearing or cold smearing with a small broadening width of 0.001 ry is used. furthermore, diagonalization method is chosen as ‘david’, with mixing factor 0.6 for selfconsistency. spin polarized calculations are accommodated to study the magnetic properties of the systems. for the density of states (dos) calculations of pure monolayer mos2 and f2 adsorbed monolayer mos2 systems, we have used 3×3 supercell of monolayer mos2 with a denser mesh of (8×8×1) k-points. 3. results and discussion a hexagonal unit cell of monolayer mos2 with the basis of three (1-mo and 2-s) atoms in honeycomb lattice structure is initially constructed by using experimental value [17]. it is build up by single layers of s-mo-s atoms as shown in figure 1. it consists of two planes of sulphur (s) atoms and an intercalated plane of molybdenum (mo) atoms bound with the sulphur atoms in a trigonal prismatic arrangement. each mo atom is surrounded by six first-nearest neighbouring s atoms, while each s atom is connected to three first-nearest neighbouring mo atoms [3, 5] as shown in figure 1. (a) (b) fig. 1: unit cell of monolayer mos2 (shown by dotted parallelogram), (a) top-view and (b) sideview. the unit-cell consists of a single mo atom intercalated between two s atoms at a bond length of 2.42 å and s-mo-s angle of 80.80o. propagation of mos2 unit-cell along xand y-directions to form 3×3 supercell of monolayer mos2. single mo-atom is covalently bonded with 6 s-atoms to form hexagonal honey-comb structure. after the construction of the unit-cell, the structure is optimized with respect to latticeparameter ‘a’, kinetic energy cutoff (ecut−off) for plane wave and the number of k-points along xand y-axes respectively. based on these convergence tests, we obtained that the lattice constant ‘a’ for the unit cell of monolayer mos2 is 3.18 å, which agrees with the previous results [3, 5]. for the 3×3 supercell of monolayer mos2 the lattice constant is three times that of the unit cell. further, the plot of the total energy verses the number of k-points shows that the energy of the unitcell of monolayer mos2 is almost constant when the number of k points (nk x = nk y ) crosses 10. a a mesh of 10×10×1 k-points is, therefore, used for brillouin-zone integration of unit cells and a mesh of 4×4×1 k-points are taken for 3×3 supercell. a plane wave basis set with energy cutoff values of hari paudyal et al. / bibechana 13 (2016) 50-59 : rcost p.53 (online publication: dec., 2015) 35 ry for the wave-function and 350 ry for the charge density is used for the expansion of the ground state electronic wave functions. (a) (b) (c) fig. 2: initial structures of mos2 and f2 added mos2. (a) different possible adsorption sites, (b) horizontal (parallel) configuration of molecular f2 and (c) vertical (perpendicular ) configuration of molecular f2 for the adsorption of molecular f2 on monolayer mos2. a molecular fluorine (f2) is adsorbed on monolayer mos2 of size 3×3 supercell. the adsorption is carried out at different possible sites of mos2 (figure 2(a)), with different orientations/configurations of f2 molecule. we have taken three different occupation sites for the adsorption, which are: the hollow (h) site at the center of the hexagonal ring, the top of the mo atom (mo-top) site, and the top of the s atom (s-top). further, two configurations of molecular f2 for its adsorption, i.e., the vertical (perpendicular) to the mos2 plane and the horizontal (parallel) to the mos2 plane, are considered. all together we have studied six different possible ways for its adsorption. for each of the sites and the configurations, the total energy and hence the binding energy (b.e) of the adsorbed molecule is calculated. the most suitable site with the suitable configuration is determined by using the information of total energy (minimum) or the binding energy (maximum). hari paudyal et al. / bibechana 13 (2016) 50-59 : rcost p.54 (online publication: dec., 2015) (b) (a) .(b) (c) (d) . (e) (f) . fig. 3: optimized geometries of f2 molecule adsorbed monolayer mos2 with topand side-view respectively, (a) f2 molecule perpendicular to mos2 plane at h-site (hperpendicular), (b) f2 molecule parallel to mos2 plane at h site (h-parallel), (c) f2 molecule perpendicular to mos2 plane at mo-t site (mo-t-perpendicular), (d) f2 molecule parallel to mos2 plane at mot site (mo-t-parallel), (e) f2 molecule perpendicular to mos2 plane at s-t site (s-tperpendicular) and (f) f2 molecule parallel to mos2 plane at s-t site (s-t-parallel) the binding energy (b.e)/adsorption energy (∆e) of a molecular fluorine on monolayer mos2 is calculated using the relation, ∆e= ef2 + emos2 −emos2+f2 (1) where, ef2 , emos2 and emos2+f2 are the total energies of the isolated f2 molecule, monolayer mos2, and the f2 adsorbed monolayer mos2 system respectively. of the three adsorption sites (h, mo-t and s-t), with two possible configurations taken, the site with the largest adsorption energy is referred as the suitable site for adsorption. the optimized structures of f2 adsorbed monolayer mos2 systems are shown in the figure 3. hari paudyal et al. / bibechana 13 (2016) 50-59 : rcost p.55 (online publication: dec., 2015) table 1: the table lists the adsorption energy of molecular fluorine (∆e), it’s height from the average of upper sulphur plane (h), optimized f-f distance in f2 molecule (df −f ) after adsorption, the distance of the atomic f from it’s nearest s-atom (ds−f ) and the distortion observed in 3×3 supercell of monolayer mos2 (dmos2 ) due to adsorption of f2. adsorption site configuration of f2 ∆e (ev) h (å) df–f (å) ds−f (å) ˚ dmos2 (10-1å) hollow (h) perpendicular parallel 0.1788 1.4661 3.187 1.634 1.486 4.487 3.031 1.791 -0.823 -0.139 mo-top perpendicular parallel 0.1455 0.9916 3.358 1.582 1.464 2.979 3.191 1.764 -0.943 -0.135 s-top perpendicular parallel 0.6327 1.8304 2.657 1.396 1.827 2.159 1.827 1.729 -0.039 0.366 table 1 represents the adsorption/binding energy values (∆e), the relaxed distance ofcenter of mass of molecular f2 from s-plane of monolayer mos2 (h), the separation between the two f atoms in f2 (df −f ), the distance of a f atom from nearest s-atom (ds−f ) and the distortion observed in 3 × 3 supercell of monolayer mos2 (dmos2 ) due to adsorption of f2. the table shows that a f2 molecule is bound to all the adsorption sites considered and the parallel configuration on the top of the s atom is the most stable one among them. there is a large variation in the binding energy values of molecular fluorine, which is due the different configurations of f2 molecule towards the varying sites of substrate. during the optimization of the adsorbed system it is found that the molecular fluorine, in some of the cases, breaks it’s bond and each of the isolated f atom gets bonded with the nearest s atom. the geometries with the atomic adsorption of f are seen more stable (see table 1). the table also reveals that the system having maximum b.e has the minimum planer distance from the s-plane. in addition, the distance between two f atoms increases when it is bound more strongly to monolayer mos2. the results imply that the boding of f/f2 with the substrate happens on the cost of weakening of f-f interaction. the density of states (dos) of up and down spin for pure and f2 adsorbed mos2, with reference to fermi level (represented by vertical dotted line), are shown in the figures 4(a) and 4(b). present calculations show that the fermi energy for the pure and f2 adsorbedmonolayer mos2 are 0.5647 ev and -0.0461 ev, respectively. the values (of fermi energy) imply that there is a shift in fermi level by 0.6108 ev after the adsorption of f2. the density of states for pure monolayer mos2 can also reveal that there is a gap (between valence and conduction bands) of about 1.14 ev near in the fermi level. since the pbe type gga calculations underestimate the band gap near by hari paudyal et al. / bibechana 13 (2016) 50-59 : rcost p.56 (online publication: dec., 2015) the fermi level [18, 19], the value of the band gap obtained from the present calculations is smaller than the previously reported values [3, 4]. however, the electronic band structure (figure is not shown) reveals that the material is direct band gap semiconductor, which is consistent with the core concept of the band structure reported in the references. further, the symmetry in the upand down-dos supports the fact that the monolayer mos2 is non-magnetic material. (a) (b) fig. 4: density of states (dos) of (a) monolayer mos2, and (b) f2 adsorbed monolayer mos2. on the other hand, the band gap near the fermi level of f2 adsorbed monolayer mos2 is found to be 1.01 ev. it means that the band gap has decreased by 0.13 ev due to adsorption of f2. it may be due to the fact that fluorine is highly reactive and most electronegative element in the nature, and certain bands at valence/conduction band are occupied by the addition of f2 electrons. the high peaks which are seen in total dos of pure monolayer mos2 are found to be decreasing after the adsorption of f2. the symmetry of dos (for upand down-dos) of f2 adsorbed monolayer mos2 shows that the system remains non-magnetic after the adsorption of f2 as well. to get t h e better understanding of the sharp energy bands on total dos of the f2 molecule adsorbed monolayer mos2, we have performed the partial dos analysis (pdos). the contributions of different orbitals of mo, s and f atoms on the f2 molecule adsorbed mos2 are presented in the figures 5, 6 and 7. in the figures the fermi energy is taken as reference, and represented by the vertical dotted line. the figures reveal that 4d, 3p and 2p orbitals of mo, s and f atoms respectively, are the dominant contributions on the sharp energy bands of total dos. hari paudyal et al. / bibechana 13 (2016) 50-59 : rcost p.57 (online publication: dec., 2015) fig. 5: pdos of 4s, 5s, 4p, 5p and 4d orbitals of mo atom respectively. pdos due to 4d-orbitals is seen dominan t over the o ther s . fig. 6: pdos of 3s and 3p orbitals of s atom, respectively. pdos due to 3p-orbitals, poisoned nearby fermi level, is seen dominant. fig. 7: pdos of 2s and 2p orbitals of f atoms respectively. the pdos due to 2p-orbitals is seen dominant over the 2s-orbitals. hari paudyal et al. / bibechana 13 (2016) 50-59 : rcost p.58 (online publication: dec., 2015) 4. conclusions the structural and electronic properties of pure and f2 adsorbed monolayer mos2 systems are studied. the binding energy values of f2 at different sites suggest that f2 can be adsorbed on monolayer mos2 and the parallel configuration of f2 above sulphur (s) atom is found to be the most stable with the binding energy of 1.83 ev. the geometry reveals that the molecular f2 dissociates and each atom of f is adsorbed to nearby s in the structure. the dos calculations of the pure monolayer mos2 find a band gap of 1.14 ev and reiterates that the system is nonmagnetic. in case of f2 adsorbed monolayer mos2, the band gap decreases to 1.03 ev. upand down-dos are again symmetrical, and indicate that the f2 adsorbed monolayer mos2 is also non-magnetic. acknowledgements we acknowledge the partial support from the abdus salam international center for theoretical physics (ictp) through office of external activities within net-56 project. also, we extend our gratitude to the world academy of science and technology (twas) research grants for providing computational facilities. references [1] 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biomedical engineering, university of north carolina at chapel hill and north carolina state university, raleigh, nc 27599-7115 2department of chemistry, north carolina state university, raleigh, nc 27695-8204 3current affiliation: central department of chemistry, tribhuvan university, kathmandu, nepal *email: newbhanu@gmail.com article history: received 6 september, 2018; accepted 22 september, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21103 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract we investigated toxicological effects of two of the most common polybrominated diphenyl ether (pbde) flame retardants, bde-47 and bde-209, in model pc12 cell line under two environmentally relevant exposure conditions: long term exposure to microgram-per-liter levels of pbdes and acute exposure to high concentrations of pbdes. cells treated under both long term and acute exposure conditions showed significantly perturbed cell growth and differentiation. importantly, even when the cells were exposed to microgram-per-liter concentration of pbdes over an extended period, both the fraction of differentiated cells and the axonal growth were affected. the calcium release assay showed that pbdes perturbed intracellular calcium release in a concentration dependent manner, indicating that intracellular ca++ homeostasis and signaling was involved in the neurotoxicity. more interestingly, depending on pbde concentration and exposure conditions, cytoskeleton f-actin distribution was altered. keywords: actin, axons; brominated flame retardants; calcium signaling; neurons. 1. introduction fire safety regulations require the use of flame retarding additives in a wide variety of industrial and commercial products. brominated flame retardants are most commonly used because of their excellent fire quenching efficiency. brominated flame retardants are available in different forms including compounds such as polybrominated diphenyl ethers (pbdes), hexabromocyclododacane, and tetrabromobisphenol-a. like other brominated flame retardants, pbdes have been used in a http://nepjol.info/index.php/bibechana mailto:newbhanu@gmail.com http://dx.doi.org/10.3126/bibechana.v16i0.21103 https://creativecommons.org/licenses/by-nc/4.0/ bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.65 (online publication: dec., 2018) broad range of products including plastics, textiles, building and filling materials, furnishings, electronics, airplanes, and motor vehicles, etc. these chemicals disseminate into the environment and degrade slowly, making them persistent organic pollutants [1]. living beings are exposed to these chemicals via several routes including ingestion and inhalation [2-4]. infants are more easily exposed because of more frequent hand-to-mouth and ground-contact activities, as well as breast feeding and placental transfer. the absorbed pbdes will accumulate in blood, breast milk, and fat tissues [3-5]. partially metabolized forms of these pollutants such as methoxylatedand hydroxylated-pbdes are also found in human bodies [6, 7]. in recent years, toxicological effects of pdbes raised serious concerns. all forms of pbdes, depending upon the dose and growth phase of a living species, pose mild to acute health hazards. recently, it was found in animal models that pbdes are responsible for neurodevelopmental disorders [8, 9]. the environmental protection agency (epa) has set a safe dose of 7 micrograms per kilogram of body weight, which is "believed to be without appreciable effects" [10]. note that although some pbdes are banned (including bde-47) and most of them are being phased out voluntarily in developed countries [11,12] the banned pbdes still exist in environment, and there is a real potential for continued exposure and absorption by humans. how pbdes cause neurotoxicity is still unclear but may involve multiple pathways. it has been found that pbdes disrupt endocrine systems and ca++ intracellular signaling pathways [13-15] pbdes and the hydroxylated derivative oh-pbdes structurally resemble thyroxin a thyroid hormone and may cause hypothyroidism due to direct binding. thyroid hormone levels directly impact proper functioning of brain and other body processes [16-18]. it was also reported that several brominated flame retardants including pbdes and their derivatives bind to estrogen, progesterone, and androgen hormone receptors and perturb their normal activity, which can lead to reproductive and developmental disorders [18]. toxicological studies at the cellular level showed that exposure to 1-50 µm (equivalent to ~1-50 mg/l) pbdes perturbs calcium homeostasis and signaling and can cause neurotoxicity. the neurotoxic effect of pbde exposure can be observed using multiple end points [19-20]. for example, the pbde exposure reduced long-term potentiation (which relates to decreased memory) and postsynaptic protein levels [21-23] in mouse hippocampus and caused abnormal motor behavior in developing zebra fish [24]. even more disturbing was the observation that the metabolized pbdes generated more severe health effects than parent pbdes [22, 25]. many of above mentioned in vivo and in vitro pbde toxicological studies were performed in the µm (equivalent to ~mg/l) to few mm (~g/l) pbde concentration range. neuronal growth disruption under high pbde concentrations, e.g., shorter axons, was observed, which resulted in functional deficits of neuron cells [24]. however, recent studies also showed that preand postnatal exposures to low concentrations of pbdes caused significant neurobehavioral alterations in fish and rodent models [26, 27]. the possibility that low concentrations of pbdes interfered with axonal growth was rarely explored. this study investigates the effect of low concentrations of pdbes on neuronal cell growth and differentiation using cell model obtained from pheochromocytoma of the rat adrenal medulla (pc12). using direct cell imaging, we studied the toxicity of two of the most common pbdes: bde-47 and bde-209. bde-47 was one of the most widely distributed brominated flame retardants and bde-209 was one of the most used flame retardants in electronics. to mimic the natural exposure conditions, low concentration of pbdes (µg/l range) were provided throughout the cell growth and differentiation (condition i). as a comparison to the epa’s safe limit of 7 µg/kg body weight, a 50 kg human could take in 350 µg of bde-47 per day. this amount in a bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.66 (online publication: dec., 2018) liter of drinking water would be present at a total pbde concentration of 350 µg/l. further postintake dilution as the pbde circulated through the body would be offset to an unknown extent by intracellular accumulation over time [28]. given the limits of predicting the in vivo concentrations, the concentrations used in condition i were selected to be in the µg/l range and lower mg/l range. scheme 1: molecular structures of brominated flame retardants bde-47 and bde-209. to provide a high-dose comparison and exposure conditions more like those generally used in the literature, we also tested the pbde toxicity by exposing the cells to spiked pbde concentrations in the mg/l range for short period of time before inducing cell differentiation (condition ii). cell morphology and the structure and localization of the cytoskeleton protein f-actin were examined. actin plays a vital role in plasma membrane morphology, cell growth, differentiation, locomotion, and transportation [29]. in neurons, actin mediates dynamics of spine morphology, the organization of the postsynaptic density, and anchoring and trafficking of postsynaptic receptors [30-32]. extensive changes of cell morphology are required in neuron functioning: (1) the formation of axonal and dendritic morphologies is a central feature in information processing in the central nervous system; and (2) actin filament formation at delegated sites at the cell cortex is the driving force for the induction of different protrusive structures of neurons, e.g., neurites, branches within the neuritic arbor, and dendritic spines. we found that pc12 cell growth, differentiation and axon growth were negatively affected at pbde concentrations as low as several to several 10s of µg/l. we also observed abnormal actin expression for cells exposed to low concentrations of pbdes. f-actin distribution was perturbed by high bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.67 (online publication: dec., 2018) concentrations of pbdes, but not in low concentrations, indicating different pathways may be involved for axon growth inhibition at low and high exposures of pbdes. 2. materials and methods 2.1. cell culture pc12 cells were purchased from atcc (atcc® crl-1721.1™). first, cells were grown in a collagen iv coated 25 cm2 cell culture flask (bde biosciences) in a complete base medium (atcc, rpmi-1640 medium) supplemented with 5% fetal bovine serum (atcc® 30-2020™)), 10% horse serum (atcc® 30-2040™)), and 1% penicillin streptomycin incubated under 370c, 95% humidity, and 5% co2 conditions. after a week of growth in the culture flask, cells were subcultured in sterilized 2 cm2 petri dishes (greiner bio-one international) for 12 hours on poly-l-lysine-coated microscope coverslips (corning, 1.5 and 22×22 mm2). next, cells were treated with pbdes under two different conditions. in condition i, cells were further grown for seven days in low serum medium supplemented with 50 nm neural growth factor (ngf 2.5s native mouse protein, life technologies) and microgram-per-liter concentration of bde-47 (5-2500 μg/l) or bde-209 (10-5000 μg/l). in condition ii, cells were grown for 12 hours in high serum medium supplemented with a total pbde concentration in the milligram-per-liter range: 0.5-10 mg/l bde-47, or 1-20 mg/l bde-209, after which the media was replaced with low serum medium supplemented with 50 nm nerve growth factor (ngf, life technologies #13257-019) to encourage differentiation over the following 6.5 days. the pbdes used in the study were purchased from accustandard inc. in solid phase and dissolved in 100% dimethyl sulfoxide (dmso) (bde-47: fw 485.8 g/mol; bde-209: fw 959.22 g/mol). the concentration of dmso in cell culture medium was maintained less than 1%. for long-term growth, culture medium containing all required supplements was changed every 48 hours. 2.2. cell fixation and actin staining cells were washed in 1x phosphate buffer three times and fixed with 4% formaldehyde for 10 minutes. cells were again washed three times with 1x phosphate buffer and incubated for six hours with a 10 μm solution of phalloidin (a bicyclic peptide isolated from the poisonous amanita phalloides "death cap" mushroom) conjugated with green fluorescent dye fluorescin isothiocyante (fitc) (molecular probes®, f432). cells were again washed with 1x phosphate buffer three times to remove unbound phalloidin-fitc. 2.3. optical imaging and cell viability analysis optical imaging of live cells in bright field and differentiation interference contrast modes was performed by using a commercial carl zeiss microscope (observer. z1) equipped with an axiocam ccd camera. fluorescence imaging was done in a nikon (eclipse 80i) microscope equipped with an andor ixon 897 camera. for the determination of cell viability in bfr treatment, number of adherent cells per field of view were counted and compared with untreated ones. the concentration of bfr at which 50% cell viability was observed was assigned as lethal concentration-50 (lc-50). 2.4. intracellular ca++ imaging the intracellular calcium release in live cells was measured using abcam’s fluo-8 calcium assay kit (catalog #ab112159) using the recommended protocol. the complete assay kit was prepared just before the experiments. cells were grown overnight in a 2 cm2 petri disc on poly-l-lysine coated microscope coverslips in complete base medium supplemented with 0.5 % fetal bovine serum. cells were washed two times in 1x hhbs buffer (1x hank’s balanced salt solution with 20mm hepes buffer, ph 7.3). the dye loading buffer was made by mixing hhbs buffer with 10x pluoronic® f127 bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.68 (online publication: dec., 2018) plus (a nonionic surfactant) in 9:1 ratio. the fluo-8 stock solution was made in 20 μl of 100% dmso. the final fluo-8-dye loading solution was prepared by adding 20 μl of fluro-8 stock solution in 10 ml of dye loading buffer. finally, 1.5-ml of fluro-8-dye loading solution was added to each petri disc containing cells and incubated 30 min in dark at 37 oc. the required concentration of pbde solution (prepared in hhbs buffer) was added to the cells and green fluorescent image were collected. 3. results and discussion 3.1. long term exposure to low concentration of pbdes (condition i) to mimic the long term exposure scenario, low concentrations of pbdes were provided throughout the pc12 cell growth and differentiation conditions, i.e. condition i. the differential interference contrast (dic) images of pc12 cells after differentiation in the presence of 0 to 500 μg/l bde-209 are shown in figure 1a. during the differentiation period, the low serum growth medium was supplemented with nerve growth factor (ngf).(greene, 1978) as expected, cells grown for a week without pbde differentiated and grew long axons (figure 1a control). the percentage of differentiated cells (as indicated by the presence of axons) was ~95 ± 5% as determined by counting cells on five cell slides. since the majority of dead cells were washed off the substrate when changing the cell culture medium during the growth and differentiation, the density of cells per slide also gave information on cell viability. to quantify, we counted the total number of cells in the control slides right before differentiation period as 100%. the cell density dropped gradually as the concentration of pbde increased (figure 2a and table 1). the number of surviving cells dropped to 50% for cultures including 500 μg/l bde-209. thus, even the presence of low mass concentrations of bde-209 during long term culture can intoxicate the pc12 cells. for the surviving cells, the cell differentiation and axon growth were apparently perturbed. as the pbde concentration increased, the percentage of cells with axons dropped (figure 2b); only 50% of cells culture with 50 μg/l bde-209 displayed axons even though most of the cells were still alive. also, the length of axons in the differentiated cells became shorter (figure 2c). at 100 μg/l bde209, the axons were 65 ± 15 μm as compared to the length of 125 ± 15 μm measured for those from untreated pc12 cells. a similar study for bde-47 exposures produced the representative images shown in figure 1b. a simple comparison of images in figures 1a and 1b showed that bde-47 was more toxic than bde209, which is consistent with the literature [33]. the lethal concentration lc50, at which the cell viability decreased to 50%, was ~50 μg/l bde-47. it is consistent that, in these low exposure studies, the fraction of differentiated cells dropped to 50% at the even lower concentration of ~15 μg/l bde47. note the concentrations in which the cells showed decreased viability or disrupted differentiation were significantly lower than the reported toxic concentrations. for example, the neuro-toxicological study of bde-47 was reported for growing zebra fish embryos in water containing 1-20 μm (equivalent to ~0.5-10 mg/l) [24]. at ~1 μm bde-47, depending on the growth phase of embryos and the dorsal/ventral position of axons, ~50-70% shorter axons were reported. in contrast, in the in vitro experiments, we observed that a large portion of pc12 cells did not differentiate even in μg/l concentrations of pbdes. for the surviving differentiated cells, large variations in axon lengths were observed. on average, 60 ± 20 μm long axons were found in cells treated with ~50 μg/l bde-47, which is ~50% of the length of the controls (125 ± 15 μm). this study clearly showed that bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.69 (online publication: dec., 2018) mammalian cell differentiation (fraction of cells producing axons) and axon growth (length) were disrupted at even lower concentrations of pbdes than previously reported in the literature for studies of fish embryos. fig. 1: dic images of live differentiated pc12 cells treated with different concentrations of (a-e) bde-209 and (f-i) bde-47. exposure condition i – long term exposure. scale bar: 100 μm. bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.70 (online publication: dec., 2018) fig. 2: pc12 cell growth and differentiation affected by pbdes under long term exposure condition (condition i). (a-c) cells exposed to bde-209; (d-e) cells exposed to bde-47. (a) and (d) viability. (b) and (e) fraction of differentiated cells. (c) and (f) length of axons. table 1: pc12 cell growth and differentiation affected by pbdes under long term exposure condition (condition i). bde-209 (µg/l) bde-47 (µg/l) 50% cell viability 500 50 50% cells having axons 50 15 axon growing to 50% of norm length 100 50 3.2. acute exposure to high concentration pbdes (condition ii). for comparison to the low dose exposure studies, we also mimicked the acute exposure conditions that living species may encounter. the cells were grown under normal conditions. before differentiation, the cells were exposed to cell culture media containing a high total pbde concentration: bde-47 (50 μg/l to 10 mg/l) or bde-209 bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.71 (online publication: dec., 2018) (100 μg/l to 20 mg/l), for 12 hours. the cells were then washed off pbdes and treated with ngf for differentiation. a complete viability and cell differentiation analysis for both pbdes is reported in figure 3. after acute exposure, the lc50 concentration was estimated to be ~5 mg/l for bde-209 and ~1 mg/l for bde-47, respectively. however, for the surviving cells, the cell differentiation and growth were significantly interfered. the fraction of cells having axons dropped to 27 ± 3% and 10 ± 4% (n ≥ 5, n is the number of images of multiple cells) for 0.1 mg/l bde-209 and 0.05 mg/lbde-47, respectively. compared to the length of axons in the control cells (120 ± 25 μm), the length of pbdetreated cells dropped to 65 ± 20 μm and 30 ± 5 μm for bde-209 and bde-47, respectively. these studies showed that the cell differentiation and growth of pc12 cells are very sensitive to high concentration pbde shocks, and bde-47 was more toxic than bde-209. fig. 3: pc12 cell growth and differentiation affected by pbdes under acute exposure condition (condition ii). (a-c) cells exposed to bde-209; (d-e) cells exposed to bde-47. (a) and (d) viability. (b) and (e) fraction of differentiated cells. (c) and (f) length of axons. 3.3. calcium release upon exposure to pbdes as discussed earlier, brominated flame retardants may affect several neurotoxicity pathways in animal models but in the cell model, perturbation of calcium homeostasis and signaling may be the most probable mechanism [22, 34, 35]. in general, calcium homeostasis and signaling control a number of cellular processes starting from the genetic level to cell growth, differentiation, and bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.72 (online publication: dec., 2018) apoptosis. in neural cells, changes in intracellular calcium levels affect various stages of neuronal development and processes including neurotransmitter uptake and release [36]. environmentally regulated, high frequency ca++ transients have been documented to be responsible for growth-cone stalling and axon retraction [37]. thus, undifferentiated pc12 cells and short axon length observed in pbde treated cells in figure 1 may be a result of pbde-induced changes in intracellular calcium levels and perturbed calcium signaling pathways. to confirm that calcium signaling was involved in pbde-disrupted cell differentiation and axon growth, we measured calcium release of live, undifferentiated pc12 cells exposed to different concentrations of bde-47 and bde-209 using fluro-8 calcium detection assays. when fluro-8 enters the cell, the esterase enzyme in live cells cleaves the lipophilic blocking groups in fluo-8, resulting in negatively charged fluorescent dye fluo-8-. in the presence of stimulants, calcium sensing receptors are activated, releasing calcium ions from intracellular calcium stores into the cytoplasm. the transiently released free calcium ions bind to fluo-8dye, resulting in significant increase in fluorescence. the representative epifluorescent images of live, undifferentiated pc12 cells collected shortly (1 min) after bde-47 or bde-209 exposures are shown in figure 4. compared to untreated cells (figure 4a), cells exposed to pbde were significantly brighter, with the cell brightness increasing with the increase in pbde concentration. thus pbde induced intracellular ca++ release and perturbed normal ca++ balance in the pc12 cells. figure 4e shows the concentration-dependent analysis of average cell brightness. at low pbde concentrations, a linear relationship was identified. under current experimental settings, the lowest detectable ca++ signal, according to the background plus three times of the standard deviation rule, was generated by the exposure of 250 μg/l pbde-47. the correlation between pbde concentration-dependent calcium release and the perturbation of axon growth suggests that disrupted calcium signaling is involved in the perturbed pc12 differentiation. as reported by almousa and michelangeli [38]. pbde-induced calcium release is most likely due to the perturbation of active of ca++ receptors. figure 4e also showed that, at the same concentration, bde-47 exposure triggered more calcium release than exposure to bde-209. this was consistent with the observation that bde-47 had more impact on cell differentiation and survival than bde-209. 3.4. perturbation of cytoskeleton protein f-actin to study the possible perturbation of brominated flame retardants on actin cytoskeleton as a factor directly related to the axon growth, treated cells were fixed and stained with phalloidin-fitc. phalloidin is a protein that specifically binds to f-actins with high affinity (ka/kd~40 μm-1) [39]. the fluorescent images of differentiated pc12 cells grown in the presence of bde-209 and bde-47 under condition i are shown in figure 5. since phalloidin specifically binds to f-actin, the brightness in the image correlates with the f-actin distribution. under long term exposure to low concentrations of pbdes, the actin distribution did not have obvious observable changes. however, the cells became brighter continuously as the pbde concentration increased from 0 to 500 μg/l for bde-209, or 0 to 250 μg/l for bde-47. the quantitative fluorescence intensity (average over twenty cells) as a function of pbde concentration is shown in figure 6. both bde-209 and bde-47 treated cells showed higher fluorescence intensity as pbde concentration increased. further increasing pbde concentration above 500 μg/l for bde-209 or 250 bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.73 (online publication: dec., 2018) μg/l for bde-47 showed a decrease of the abnormally high fluorescence level, possibly indicating the abnormal actin expressing activity was hampered. fig. 4: calcium release as a function of pbde concentration. representative epifluorescent images of (a) untreated live pc12 cells; (b) and (c) pc12 cells treated with different concentrations of bde47; and (d) and (e) bde-209. (f) fluorescence intensity as a function of pbde concentration. exposure condition ii. scale bar: 100 μm. no increased fluorescence intensity was evident in cells treated with high concentrations of pbdes under condition ii. however, the f-actin morphology was significantly different in treated cells than the control cells, showing bright patches localized at the cell periphery after exposure to both types of pbde (figure 7). in addition, the cells treated with high concentrations of pbdes showed shorter axons, with hairy fibers at the periphery of the cells. prior reports using other types of cells document increases in actin concentration after exposure to pbdes. for example, from the biochemical analysis of microsomal pellets sedimented from homogenized mussel tissues exposed to ~10 nm (equivalent to 5 μg/l) concentration of bde-47, jonsson et al. found ~two fold increase in actin [40]. similarly, alm et al. reported that actin proteins in microsomal and cytosol pellets of developing cerebral cortex tissue of mouse treated with bde-99 increased by a factor of ~1.5 [41]. these findings showed that pbdes increased the total actin expression, which may explain the observed increased amount of f-actins. our studies showed there was a correlation between the over expression of actin and the perturbed pc12 cell differentiation and suppressed axon growth. however, it was unclear how pbdes affected actin expression and whether actin overexpression was the direct cause of the perturbed cell differentiation and suppressed axon growth. bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.74 (online publication: dec., 2018) at high pbde concentrations, the over-expression of actin was not observed, possibly due to the lower activity of the cells in a toxic environment. however, the phalloidin-fitc-tagged f-actin showed different localization in live cells. this may be caused by other negative effects of short term exposure to the high pbde concentrations. for example, it has been reported that few hours after exposure of human neuroblastoma cells to ~1 μm (~0.5 mg/l) bde-47, reactive oxygen species (ros) were produced in significant amount [42]. thus, it was very likely that high concentration of bde-47 or bde-209 can cause ros-induced f-actin re-distribution [43]. as the actin organization is essential in axon growth and extension, the disruption of spatial distribution of actin may further disrupt the axon growth under high pbde concentrations. fig. 5: epifluorescent images of differentiated, phalloidin-fitc stained pc12 cells treated with different concentrations of (a-f) bde-209 and (g-k) bde-47. exposure condition i – long term exposure. scale bar: 100 μm. bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.75 (online publication: dec., 2018) fig. 6: fluorescence intensity analysis of phalloidin-fitc stained pc12 cells treated with different concentrations of (a) bde-209 and (b) bde-47. exposure condition i. fig. 7: epifluorescent images of differentiated, phalloidin-fitc stained pc12 cells treated with different concentrations of (a-d) bde-209 and (e-g) bde-47. exposure condition ii – acute exposure. scale bar: 20 μm. bhanu b. neupane et al./ bibechana 16 (2019) 64-78: rcost p.76 (online publication: dec., 2018) 4. conclusion in summary, even at low concentrations (microgram per liter) of bde-47 and bde-209, neurotoxic effects were observed for pc12 neurons. cells treated with these brominated flame retardants showed lower viability. both the fraction of differentiated cells and the axon growth length decreased. pbdes perturbed intracellular calcium release in a concentration-dependent manner, indicating intracellular ca++ homeostasis and signaling was involved in the neurotoxicity. interestingly, depending on pbde concentration and exposure conditions, cytoskeleton f-actin expression or distribution were perturbed. long term exposure to low pbde concentrations (< 500 μg/l) showed increased f-actin content in pc12 cells. under acute exposure to high concentrations (> 0.5 mg/l) of pbdes, increased f-actin content was not observed but f-actin showed localized distribution at cell periphery. these indicated that pbdes at may interrupt the cell growth and differentiation through different pathways, depending on toxicant concentration and duration of exposure. the potential neurotoxic impact of extended exposure to low concentrations of pbdes, particularly for infants and other developing animals is a major concern. acknowledgments this work is supported by a grant from the research innovation seed fund at north carolina state university and funds from the lampe endowed professorship in biomedical engineering (fsl). references [1] k. hooper, and t. a. mcdonald, the pbdes: an emerging environmental challenge and another reason for breast-milk monitoring programs, environmental health perspectives 108 (2000) 387. 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lampblack prepared by using a traditional mustard oil lamp was mixed with printer toner in the ratio of 1:1 by weight and the composite was used as a lowcost catalyst for the reduction of tri-iodide ions in dye-sensitized solar cells (dscs). the x-ray diffraction (xrd) of the lampblack showed that the lampblack contains a carbonaceous material of graphitic form. the scanning electron microscope (sem) images of the lampblack and printer toner revealed that the lampblack consists of a few tens of nanometer to 100 nanometer sized particles (or nanosheet) whereas the toner powder consists of micron sized particles. the adhesion test of the composite film on the counter electrode (ce) of the dsc showed that the composite film is firmly attached on the ce. the dscs based on the composite yielded the overall light to electricity conversion efficiency of 3.20 % (jsc = 7.90 ma/cm 2 , voc = 0.667 v and ff = 0.607) compared with 4.18 % efficiency (jsc = 8.56 ma/cm 2 , voc = 0.748 v and ff = 0.654) of the dsc based on platinum when the solar cells were tested in the simulated light of 100 mw/cm 2 . 1. introduction dye-sensitized solar cells (dscs), developed by o’regan and gratzel, have been attracting researchers as these photovoltaic devices can generate low-cost solar electricity compared with crystalline silicon solar cells [1-3]. a dsc is an electrochemical solar cell with a liquid electrolyte enclosed between two electrodes named photoanode and counter electrode [1]. generally, the electrolyte is a solution of chemicals in organic solvents comprising iodide and tri-iodide ions [46]. similarly, the photoanode is a few microns thick film of interconnected titanium-dioxide (tio2) nano-particles coated onto a transparent conducting oxide (tco)-glass substrate like fluorine-doped tin-oxide (fto)-glass substrate. furthermore, a mono-layer of light sensitive dye molecules is chemically attached onto the surface of the nanoparticles of the tio2 film [2,5,7]. the counter electrode (ce) is a tco (like fto-glass substrate) coated with a thin film of catalyst like platinum [4,8-10]. when the photoanode is irradiated with this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.25598 http://nepjol.info/index.php/bibechana mailto:joship7@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.25598 prakash joshi et al. / bibechana 17 (2020) 58-66 59 sunlight, the dye-molecules on the photoanode emit electrons and they enter in the conduction band of the tio2. the photoelectrons diffuse in the tio2 film and they flow up to the ce through an external circuit. the oxidized dye-molecules obtain electrons from the iodide ions in the electrolyte and the dye molecules are regenerated [5,11,12]. on the other hand, the iodide ions are converted into triiodide ions after losing the electrons and the triiodide ions diffuse towards the ce. the tri-iodide ions capture the photoelectrons arrived at the ce and the tri-iodide ions are converted into iodide ions [1,5]. the thin film of platinum coated onto the ce serves a catalyst to accelerate the flow of the electrons from the ce to the electrolyte [6,10]. because of excellent catalytic property for the reduction of tri-iodide ions, platinum is widely used in the fabrication of ces of dscs [1,13]. however, platinum is an expensive metal [6]. thus, the use of platinum as a ce material can increase the fabrication cost of dscs. besides, the instability of platinum in the corrosive electrolyte used in dscs is another concern among researchers [11,14,15]. thus, researchers have used various types of carbon such as graphite, carbon black, carbon nanotubes, carbon nanofibers and activated carbon instead of platinum while fabricating the ces [1,10,11,13,15-19]. similarly, wu et al. reported discarded toner of a printer as a catalyst for the reduction of tri-iodide ions of dscs [20]. in this research, the composite of mustard oil based lampblack and printer toner was adopted as a novel low-cost ce material for dscs; the printer toner (in the composite) was used as a binder (rather than a catalyst) to adhere the lampblack powder of the composite on the ces of dscs. the dscs with ces based on the composite of the lampblack and printer toner yielded comparable light to electricity conversion efficiency as the dscs with ces based on platinum. 2. experimental method preparation of lampblack and its characterization mustard oil was purchased from a local market (in nepal). the lampblack of the mustard oil was prepared as described below. the flame of a traditional mustard oil lamp with cotton wicks was covered with a porcelain mortar (bowl) so that the lamp soot is deposited onto the inner surface of the bowl and the lampblack was collected from the porcelain mortar. the structural composition of the lampblack was analyzed by using x-ray powder diffractometer (d2 phaser, bruker) at nepal academy of science and technology (nast), nepal. similarly, the xrd (x-ray diffraction) of the printer toner powder (available in the local market for refilling of brother printer toner) was also obtained. in order to explore size and shape of the mustard oil-based lampblack and printer toner, their scanning electron microscope (sem) images were obtained. similarly, the carbon film was prepared by doctorblading the paste of mustard lampblack and printer toner (the ratio of the two materials was 1:1 by weight in ethanol) onto a glass substrate and the sem images of the film were also obtained after sintering the film. similarly, thin film of printer toner was obtained by doctorblading the paste of the printer toner (in ethanol) on a glass substrate and the sem image of the sintered film of the toner was obtained. the sem images of all the samples were taken using leo 435vp sem at the indian institute of technology (iit), roorkee, india. adhesion test of lampblack film without and with printer toner as adhesion of the carbon film on the ces of carbon-based dscs may affect stability of the solar cells; adhesion test of lampblack film without and with printer toner was carried out. procedures for the adhesion test adopted here are similar to those described by joshi [21]. the procedures of the adhesion test adopted here are briefly described below. the paste of the lampblack without the printer toner and the paste of the lampblack with the printer toner were prepared in ethanol and the prakash joshi et al. / bibechana 17 (2020) 58-66 60 two types of pastes were doctobladed onto two separate fto-glass substrates. the fto-glass substrates with doctorbladed paste were sintered at ~100ºc. the ftos having the sintered films of the lampblack (without and with printer toner) were covered with pieces of a transparent tape. then the pieces of the transparent tape were removed from the ftos to check adhesion of the carbon films on the ftos. fabrication of dscs and their characterization in order to fabricate dscs, counter electrodes (ces) and photoanodes were prepared. the ces of the dscs were prepared as described below. first of all, fto-glass substrates were cleaned with soap water, acetone, ethanol and distilled water successively. then the paste of the composite of mustard oil lampblack and printer toner was doctorbladed onto the fto. the fto-glass substrates with the doctorbladed film of the composite were heated on a hot plate first at ~50˚c and then at ~100°c for several hours. similarly, the photoanodes of the dscs were prepared following similar procedures described by joshi [21]. brief description of the method is given below. the paste of nano-crystalline tio2 (tinanoxide t/sp, solaronix, switzerland) was doctorbladed onto the clean fto-glass substrates. the fto-glass substrate with the doctorbladed tio2 film was sintered at temperature of ~100°c for ~30 minutes and then at ~450°c for ~45 minutes. the fto-glass substrates with sintered tio2 film were allowed to cool down to room temperature in air. in order to sensitize the sintered tio2, the fto-glass substrates with the sintered tio2 film were heated at ~80 °c for few minutes in air and then they were immersed into ~0.25 mm ruthenizer 535-bistba (solaronix, switzerland) dye solution in anhydrous ethanol at least for 12 hours. just before assembling the photoanodes and the ces, the photoanodes (fto-glass substrates with dye-sensitized tio2 film) were removed from the dye solution and they were washed with anhydrous ethanol to remove unanchored dye on the tio2 film. then they were dried with a hot air drier to evaporate ethanol from the tio2 film. similarly, the ces with the composite film were dried to remove the adsorbed water vapour on the carbon film. the two electrodes were assembled with a piece of parafilm sheet; the parafilm served both as a sealant and a spacer (to separate the electrodes). the space between the two electrodes was filed with a liquid electrolyte containing iodide/tri-iodide ions (solaronix) and the dsc was further sealed with hot-glue [21]. in addition to the fabrication of dscs with the ces based on the composite film, the dscs with the ces based on platinum, printer toner and only fto (without any catalyst) were also fabricated to use them as reference cells. the photoanodes and electrolyte of these reference cells were similar with those of the dscs with ces based on the composite, however, the catalyst used in the reference cells were different from the previous ones (composite based dscs). the ces of the platinum based solar cells were prepared by coating the conducting part of fto-glass substrates with platisol t solution (precursor of platinum purchased from solaronix) and sintering the ftoglass substrates at ~450°c for 30 minutes. similarly, the ces of the toner based dscs were prepared by simply doctorblading the paste of the toner powder (in ethanol) onto the fto-glass substrates, then sintering the paste at temperature ~80°c to ~100°c. in case of the dscs without catalyst, simply the fto-glass substrates (without any catalyst) were used as ces. the photovoltaic performances of the solar cells were tested in the simulated light of ~100 mw/cm 2 (abet sunlite solar stimulator 11002 available at kathmandu university, nepal). 3. results and discussion fig.1 is the x-ray diffraction (xrd) pattern of the lampblack of a mustard oil lamp. the diffraction peak centered at 2θ~25° shows that the lampblack contains graphitic form of carbon [1]. joshi et al. prakash joshi et al. / bibechana 17 (2020) 58-66 61 have demonstrated that electrospun carbon nanofibers having graphitic structure of carbon possess good catalytic property for the reduction of tri-iodide ions in dscs [1]. thus, the lampblack with graphitic form of carbon can also be employed as the catalyst in dcss. fig. 2 shows the sem images of the lampblack powder, the printer toner powder, the film of printer toner powder and the film of lampblack/printer toner composite. fig. 2a is the sem image of the lampblack powder, the image shows that the lampblack consists of particles (or sheets) of a few tens of nanometer to ~100 nm. similarly, fig. 2b is the sem image of the printer toner powder and the sem image shows that the particles of the toner are irregular in shape and they are several microns in size. fig. 2c is the sem image of the film of the printer toner and the image reveals that the micron sized particles of the toner powder were glued together after sintering the film. similarly, fig. 2d is the sem image of the film of the lampblack and printer toner composite. the size of the particles seen in this sem image is comparable (several microns) with the size of the particles seen in the sem image of the printer toner powder (fig. 2c). however, the surface of the micron-sized particles seen in the sem image of the composite (fig. 2d) is different from the surface of toner powder seen in the sem image of film of the toner power only (fig 2c). the surface of the particles seen in fig. 2d is rougher compared with that seen in fig. 2c. the rough surface of the particles (seen in fig. 2d compared with those seen in fig. 2c) can be due to the adherence of the lampblack onto the toner particles. this indicates that when the composite of the lampblack and the printer toner is used in the fabrication of ces, the printer toner powder acts as a binder to hold the particles of the lampblack on the ces. fig. 3 is the photographs of the adhesion test of the lampblack without and with printer toner powder. fig. 3a is the photograph of the carbon film of the lampblack only (without printer toner) coated onto an fto-glass substrate; the carbon film was covered with a transparent tape. fig. 3b is the photograph of the carbon film (without printer toner) after removal of the transparent tape. similarly, fig. 3c is the photograph of the carbon film of lampblack with the printer toner coated onto an fto-glass substrate; the carbon film (with printer toner) was covered with a transparent tape. fig. 3d is the photograph of the film of the lampblack and the printer toner after removal of the transparent tape. fig. 3 shows that the carbon film of the lampblack without the printer toner detached from the fto (fig. 3b) whereas the carbon film of the lampblack with the printer toner remained on the fto (fig. 3d) after removal of the tapes. this experiment indicates that the carbon film of the composite of the lampblack and the printer toner strongly adhered on the fto compared with the carbon film of the lampblack without the printer toner. moreover, it implies that the printer toner in the composite is required to enhance adhesion of the particles of the lampblack on the fto of ces. fig. 4 shows current densityvoltage (j-v) curves of dscs. fig. 4a, fig. 4b and fig. 4c are j-v curves of dscs with ces based on fto (without catalyst), toner powder and platinum, respectively. similarly, fig. 4d is the j-v curve of the dsc with ce containing the composite of the lampblack of mustard oil lamp and the toner powder as a catalyst. the photovoltaic parameters of the dscs calculated from the j-v curves are enlisted in table 1. the overall light to electricity conversion efficiency (η) of dscs with ces without catalyst (fto only), printer toner, platinum and the composite of lampblack and printer toner composite were 0.16%, 0.05%, 4.18% and 3.20%, respectively. as η (3.20 %) of the dsc with ce based on the composite is significantly greater that η (0.16%) of the dsc with ce based on fto only (without catalyst), it can be concluded that the composite of mustard oil lampblack and printer toner has excellent catalytic property for the prakash joshi et al. / bibechana 17 (2020) 58-66 62 0 1000 2000 3000 4000 15 35 55 75 in te n si ty (a .u .) 2θ reduction of tri-iodide ions in dscs. however, the 𝜂(0.05%) of the dsc with ce based on the printer toner was much smaller than the η (3.20%) of the dsc with ce prepared from the lampblack and printer toner composite. similarly, the values of the other photovoltaic parameters: short circuit current density (jsc), open circuit voltage (voc) and fillfactor (ff) of the toner based dsc were much smaller than those of the dsc based on the composite. this indicates that the printer toner in the composite does not play significant role of the catalyst for the reduction of the tri-iodide ions, rather it (the printer toner) plays the role of a binder to adhere the lampblack powder onto the fto-glass substrate of the ces, and better performance of the composite based dscs was attributed to the catalytic ability of the lampblack. on the other hand, the comparable photovoltaic parameters of the dsc based on the composite with those of the dsc based on the platinum indicate that the catalytic ability of the composite is comparable with that of the platinum, and the composite can be employed as a low-cost catalyst for the reduction of tri-iodide ions instead of expensive platinum metal in dscs. however, the composite based solar cell yielded slightly lower value of the η (3.20%) compared with the η (4.18%) of the platinum based solar cell. one of the causes of lower efficiency of the composite based solar cell can be its lower ff compared with that of the platinum based solar cell. in a previous paper, joshi et al. [1] have revealed that higher value of series resistance (rs) of a dsc can cause lower value of ff and η of the device. the researchers have reported that the dsc with ce based on electrospun carbon nanofibers (ecn) yielded η of 5.5 % compared with 6.97 % efficiency from the dsc with ce based on sputtered platinum. the ff of the ecn based dsc was 0.57 and that of the platinum based dsc was 0.71. similarly, the rs of the ecn based device was 15.5 ω cm 2 and that of the platinum based device was 4.8 ω cm 2 ; they concluded that the lower value η of the ecn based solar cell was mainly due to the larger value of the rs of the ecn based device compared with that of the platinum based device [1]. in this research, the values of the rs of the dscs based on composite and thermally deposited platinum were found to be equal to 49.410 ω and 38.430 ω, respectively. thus, slightly lower value of the efficiency of the composite based dsc compared with that of the thermally deposited platinum based dsc can be due to the higher value of rs of the composite based solar cell. hence, the rs of the composite based dscs should be minimized to improve ff and η of the device. optimization of the ratio of the lampblack and printer toner powder in the composite film may improve the ff and η of the composite based dscs. fig. 1: the xrd of mustard oil based lampblack. prakash joshi et al. / bibechana 17 (2020) 58-66 63 fig. 2: sem images of a) mustard oil based lampblack powder, b) printer toner powder, c) film of sintered printer toner and d) film of mustard oil based lampblack and printer toner composite. fig. 3: photographs of adhesion test of lampblack a) & b) without printer toner and c) & d) with printer toner. prakash joshi et al. / bibechana 17 (2020) 58-66 64 fig. 4: current density-voltage (j-v) curves of dscs with ces based on a) fto only (without catalyst), b) printer toner, c) platinum and d) the composite of lampblack of mustard oil lamp and printer toner. table 1: photovoltaic parameters of the dsc with the composite of mustard oil based lampblack and printer toner and reference dscs. dscs with ce based on jsc (ma/cm 2 ) voc (v) ff η (%) fto only 3.98 0.505 0.078 0.16 printer toner 0.89 0.414 0.132 0.05 platinum 8.56 0.748 0.654 4.18 composite 7.90 0.667 0.607 3.20 4. conclusions the composite of lampblack of mustard oil lamp and printer toner was used as a novel counter electrode material of dscs. the printer toner used in the composite served as a binder to hold the lampblack (of the composite) on the counter electrode and the composite film showed good adhesion on fto-glass substrates. the film of lampblack and printer toner composite exhibited rough and porous surface morphology. though the series resistance of the dscs with ces based on the composite of the lampblack of mustard oil lamp and printer toner was higher than that of the dscs with ces based on thermally deposited platinum, the dscs based on the composite yielded 3.20 % light to electricity conversion efficiency which was comparable to the 4.18 % efficiency of the dscs with ces based on platinum. the composite film used in the ce of dscs exhibited good catalytic ability for the reduction of tri-iodide ions, hence, it can be used as a low-cost counter electrode material to replace expensive platinum used in the fabrication of dscs. prakash joshi et al. / bibechana 17 (2020) 58-66 65 acknowledgements this research was carried out with the research grant awarded by university grants commission (ugc)-nepal (award no. srdi-73/74-s&t-01). thus, authors are thankful to ugc-nepal. the solar cells prepared under this project were tested using the standard solar cell testing system available at the kathmandu university (k.u.) and the authors would like to acknowledge k.u. and dr. bhim kafle (k.u.) for providing the facility of testing the solar cells. similarly, the authors are thankful to bhaktapur multiple campus (bmc), t.u., associate prof. dr. krishna prasad pokharel (campus chief, bmc), associate prof. sudarshana shakya ( assistant campus chief, science, bmc), dr. suresh kumar dhungel (nepal academy of science and technology), indian institute of technology (iit)roorkee, prof. dr. tika katuwal (physics department, tri-chandra multiple campus, t.u.) and associate prof. dr. mimlal nakarmi (chairperson, physics department, the graduate centre, brooklyn college, the city university of new york, usa) for their support. references [1] p. joshi, l. zhang, q. chen, d. galipeau, h. fong, q. qiao, electrospun carbon nanofibers as lowcost counter electrode for dye-sensitized solar cells, acs applied materials & interfaces 2 (2010) 3572-3577. https://doi.org/10.1021/am100742s. 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[21] p. joshi, electrospun carbon nanofibers and composites as low cost counter electrodes for dye-sensitized solar cells, ph.d. diss, south dakota state university, 2012. https://doi.org/10.1016/s0927-0248(03)00021-7 https://doi.org/10.1021/am800249k https://doi.org/10.1016/j.solener.2018.04.002. https://doi.org/10.1016/j.solener.2017.01.030. https://pubs.rsc.org/en/content/articlelanding/2011/ee/c1ee01059j https://pubs.rsc.org/en/content/articlelanding/2011/ee/c1ee01059j vinod kumar mahaseth/ bibechana 14 (2017) 98-102 : rcost p.98 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal primary productivity of phytoplankton of mahakali river, nepal vinod kumar mahaseth department of zoology, mmam campus, tribhuvan university, biratnagar, nepal e-mail: vkmahaseth1962@gmail.com article history: received 11 august, 2016; accepted 4 november, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15988 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract present paper describes primary productivity of mahakali river at four stations. the two years mean of net primary production was 96.80 mgc/m3/day. the net primary production value of mahakali river was less due to the low water temperature and less phytoplanktonic growth. two years mean value of gross primary production of mahakali river was 176.29 mgc/m3/day, which is less than lentic water. it shows that the river is oligotrophic but developing a tendency as going towards mesotrophic. keywords: mahakali river; productivity; phytoplankton. 1. introduction phytoplankton, the minute chlorophyll bearing organisms, constitutes the most important component of the plankton and account for almost all the primary production in the water body. plankton forms the base of food chain in most of the aquatic ecosystem, thus playing a vital role in fisheries. the productivity of a water body is characterized by the presence of living organisms in the natural environment. among the biotic components of an aquatic ecosystem, plankton community plays a significant role in the productivity and the trophic balance of the system. plankton constitutes the major source of energy in the food web of aquatic systems. their population fluctuates, depending on the hydrological regime and saprobiotic condition of the water. because of their short life cycles, plankton responds quickly to environmental changes. water temperature, light intensity, velocity and discharge of water, turbidity and alkalinity have widely been reported to affect plankton density in flowing waters [1, 2]. some extensive investigation on various aspects of productivity has been made by dash et al. [3], jabde and rokade [4] and sharma [5]. planktonic fauna was abundant during the post-monsoon period, when the water temperature was moderate to low, current strength was feeble and the water was calm without turbidity. plankton, particularly phytoplankton, has been used as indicators of water quality. phytoplankton http://nepjol.info/index.php/bibechana mailto:vkmahaseth1962@gmail.com http://dx.doi.org/10.3126/bibechana.v14i0.15 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ vinod kumar mahaseth/ bibechana 14 (2017) 98-102 : rcost p.99 (online publication: dec., 2016) productivity and biomass of river are dependent on several interrelated physical, chemical and biological factors. during the study period the mahakali river was rapidly surveyed to evaluate their productivity in the context of plankton population. study area mahakali river originates from indo-nepalese glaciers, milan glacier of india and lipu-lekh of nepal. the river leaves the mountains near tanakpur and is now known as sarada in india. later, it reaches sharada barrage, where it is considerably wider. mahakali then enters into nepal at chandani and flows through nepal upto dodhara, after which it enters into indian territory, finally confluencing with the ghaghara. the present studies were conducted at the chandani and dodhara v.d.c. (village development committee). they are the v.d.c. of kanchanpur district near the bank of mahakali river. the study area lies between longitude 80025’ east and latitude 28035’ north. four stations (a, b, c and d) were selected. first station ‘a’ is an upper station, which is near at purnagiri temple of syavle bajar. second station ‘b’ is 4 kilometres from station a. third station ‘c’, which is 4 kilometres from station b. fourth station ‘d’ is a lower station, which is 4 kilometres from station c. 2. materials and methods the present study was carried out for a period of two years from september 2003 to august 2005. this period was used to collect the quantitative data on various aspects of river ecology. in the present investigations, samples were collected from the study area, every month at 15 days interval. phytoplankton primary productivity was measured by “light and dark bottle” method [6]. duplicate light bottles and a single dark bottle were used to determine productivity. water from surface level was collected and filled in duplicate light and dark bottles. another water sample (in light bottle) was also collected simultaneously for determination of initial oxygen concentration. bottles were kept suspended into the water. after 4 5 hours, oxygen was determined with the help of changes in oxygen concentration in light and dark bottles, gross and net primary productivity and community respiration were determined. oxygen values were converted to carbon values (mg c/m3/d) by multiplying the values with 0.375 [7]. the productivity values were calculated using following equations: (i) gross primary productivity (mg c/m3/d) 𝑃𝑔 = 𝐿𝑂 − 𝐷𝑂 × 0.375 𝑇 × 𝑃𝑄 × 1000 (ii) net primary productivity (mg c/m3/d) 𝑃𝑛 = 𝐿𝑂 − 𝐼𝑂 × 0.375 𝑇 × 𝑃𝑄 × 1000 vinod kumar mahaseth/ bibechana 14 (2017) 98-102 : rcost p.100 (online publication: dec., 2016) (iii) community respiration (mg c/m3/d) 𝑅 = 𝐼𝑂 − 𝐷𝑂 × 0.375 𝑇 × 𝑃𝑄 × 1000 where, io = initial oxygen concentration, lo and do = concentrations of oxygen in light and dark bottle, respectively after incubation; t= time, pq and rq = photosynthetic and respiratory quotients, respectively, which were assumed to be 1.2 [8]. 3. results and discussion the values of primary productivity of phytoplankton were observed during the whole study period (september 2003 – august 2005). it was noticed that the net primary productivity values varied from month to month (table 1). the net primary productivity of mahakali river was 96.80 mgc/m3/day on the basis of two years mean. the maximum value was recorded in april while lowest value was recorded in july in both years. seasonally, the minimum and maximum values ranged from 10.93 – 164.00 mgc/m3 /day during the first year and from 15.62 – 209.37 mgc/m3/day during second year. the community respiration values also varied from month to month. the value of community respiration was observed to be 79.49 mgc/m3/day on the basis of two years mean. community respiration values fluctuated from 18.75 – 321.87 mgc/m3/day during first year while from 29.62 – 128.12 mgc/m3/day during second year of investigation. the highest values were recorded in the month of february 2004 and april 2005 during the first and second years of investigation, respectively. the values of gross primary productivity also varied from month to month as like net primary productivity and community respiration. the two years mean value of gross primary productivity was observed 176.29 mgc/m3/day. the minimum and maximum values recorded from 78.11 – 356.24 mgc/m3/day during first year while from 45.24 – 337.49 mgc/m3/day during second year of study. the highest value was noticed in the month of february 2004 and april 2005 while lowest values were observed in the month of september 2003 and july 2005 during the first and second year of study. among the biotic components of an aquatic ecosystem, plankton community plays an important role in the productivity of any water body. the water temperature is one of the most important factor which influences the production of phytoplankton in a river system. das and srivastava [9] pointed out the role of temperature as limiting factor for phytoplanktonic production. khanna et al. [2]and joshi et al. [10]are of the same view that the planktonic production was mainly influenced by temperature. during the present investigation, maximum phytoplankton was observed during summers. during the present investigation, the two years mean of net primary production was 96.80 mgc/m3/day which was less than value of net primary production of lentic water. the net primary production value of lotic water (mahakali river ) is less due to the low water temperature and less phytoplanktonic growth. baduni [11] and pathani [12] also recorded low rates of productivity in alaknanda river in garhwal himalayas and sarju river in kumaun himalayas, respectively. vinod kumar mahaseth/ bibechana 14 (2017) 98-102 : rcost p.101 (online publication: dec., 2016) two years mean value of gross primary production of mahakali river was 176.29 mgc/m3/day, which is less than lentic water. this result is confirmed by other workers like baduni (11) and pathani (12). the monthly values of gross primary production varied from 78.11 mgc/m3/day to 356.24 mgc/m3/day and 45.24 mgc/m3/day to 337.49 mgc/m3/day during first and second year of investigations. table 1: primary productivity of phytoplankton of mahakali river. (2003/04) month net primary production mgc/m3/day community respiration mgc/m3/day gross primary production mgc/m3/day sep. 2003 42.18 35.93 78.11 oct. 75.00 18.75 93.75 nov. 75.00 59.37 134.37 dec. 89.06 67.18 156.24 jan.2004 98.43 82.81 181.24 feb. 34.37 321.87 356.24 mar. 121.87 220.31 342.18 apr. 164.00 179.68 343.68 may 101.56 114.06 215.62 jun. 89.06 18.75 107.81 jul. 10.93 93.75 104.68 aug. 35.93 57.98 93.91 mean 78.11 s.d. 42.65 105.87 91.43 183.98 106.17 (2004/05) sep. 2004 62.50 29.68 92.18 oct. 81.25 31.25 112.5 nov. 121.87 42.18 164.05 dec. 117.18 100.00 217.18 jan.2005 187.50 40.62 228.12 feb. 178.12 54.68 232.8 mar. 189.06 62.50 251.56 apr. 209.37 128.12 337.49 may 132.81 40.62 173.43 jun. 62.50 32.84 95.34 jul. 15.62 29.62 45.24 aug. 28.12 45.31 73.43 mean 115.49 53.11 168.61 s.d. 66.11 30.74 87.44 vinod kumar mahaseth/ bibechana 14 (2017) 98-102 : rcost p.102 (online publication: dec., 2016) vollenweider [13] classified the fresh water bodies as oligotrophic (gpp, 65 300 mgc/m3/day) mesotrophic (gpp, 250 1000 mgc/m3/day ) and eutrophic (gpp, 10008000 mgc/m3/day). the gross primary production value of mahakali river shows that the river is oligotrophic but developing a tendency as going towards mesotrophic. acknowledgements thanks are due to the campus chief of s.n. science campus, mahendranagar for providing the necessary facilities to present work. the author is thankful also to dr. (mrs.) manju lata bisht, department of zoology, d.s.b. campus, kumaun university, nainital for her valuable guidance. references [1] k. l.bisht, advances in limnology. narendra publishing house, delhi (1993). [2] d. r.khanna, s. p. badola and a. k.dobriyal, advances in limnology. narendra publishing house, delhi (1993). [3] s. dash, a. k. patra and s adhikary, j. ecophysiol 11(2011) 219. [4] p. v. jabde and p. b. rokade, an international peer–reviewed journal, 3 (2014) 1. [5] j. sharma, imperial journal of interdisciplinary research 2 (2016) 460. [6] t. garder, and h. h. gran, et. proc. – verb., cons. int. explor. 42 (1927) 1. [7] d. f. westlake, biol. rev. 38 (1963) 385. http://dx.doi.org/10.1111/j.1469-185x.1963.tb00788.x [8] g. e. fogg, british phycological bulletin. 2 (1963) 195. [9] s. m. das and v. k. srivastava, proc. nat. acad. sci. india. 29 (1959) 174. [10] b. d. joshi, r. c. s. bisht and namita joshi, him, j. env. zool. 10 (1996) 31. [11] veena baduni, advances in limnology. narendra publishing house, delhi (1993). [12] s. s.pathani, report ministry of environment and forest poryavaran bhawan c.g.o. complex, lodi road delhi (1995). [13] r. a.vollenweider, i.b.p. handbook 12, blackwells, oxford 12 (1974). http://dx.doi.org/10.1111/j.1469-185x.1963.tb00788.x http://dx.doi.org/10.1111/j.1469-185x.1963.tb00788.x shankar p. khatiwada et al./ bibechana 16 (2019) 196-203: rcost p.196 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal mechanical and thermal properties of triblock copolymer modified epoxy resins shankar p. khatiwada1, 2, sabu thomas3, jean marc saiter4, ralf lach5, rameshwar adhikari1, 6 1research center for applied science and technology, tribhuvan university, kirtipur, kathmandu, nepal 2nepal polymer institute (npi), p. o. box 24411, kathmandu, nepal 3school of chemical sciences, mahatma gandhi university, kottayam, kerala, india 4université de normandie rouen laboratoire sms faculté des sciences and onyx developpment, groupe-nutriset, rouen, france 5polymer service gmbh merseburg (psm), merseburg, germany 6central department of chemistry, tribhuvan university, kirtipur, katmandu, nepal *email: nepalpolymer@yahoo.com article history: accepted 06 november, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21651 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract we investigate the ways of improving thermal and mechanical properties of diglycidyl ether of bisphenol-a (dgeba) based thermoset resin using diaminodiphenylsulphone (dds) as hardener and using epoxidized polystyrene/polybutadiene-based triblock copolymers as modifier. the epoxidation was performed. the targeted chemical modification using meta-chloroperoxybenzoic acid (m-cpba) of the copolymer was performed whereby the epoxidation of the butadiene chains mainly took place at 1,4 linkages. the modification copolymer was found to contribute in enhancing the mechanical performance of the blends with epoxy resin. the results indicated the formation of nanostructured morphology in the blends attributable to their enhanced impact strength. keywords: block copolymers, epoxy resins, toughness, mechanical properties. 1. introduction epoxy thermoset have found uses in diverse applications ranging from adhesives to bulk components, widely used in industry as protective coatings and for structural applications, such as laminates and composites, tooling, molding, casting and others [1]. epoxy resins are having at least two epoxy groups which react to form a highly crosslinked networks that are stiff, chemically and environmentally resistant, have good mechanical and thermal properties for high temperature applications as well as outstanding adhesion to various substrates, low shrinkage. however, these benefits are limited by the fact that the crosslinked resins are typically brittle possessing relatively poor fracture toughness and ductility [2]. http://nepjol.info/index.php/bibechana mailto:nepalpolymer@yahoo.com http://dx.doi.org/10.3126/bibechana.v16i0.2 https://creativecommons.org/licenses/by-nc/4.0/ diglycidyl ether of bisphenol-a (dgeba) diphenyl diamine sulphone (dds) diglycidyl ether of bisphenol-a (dgeba) diaminodiphenylsulphone (dds) shankar p. khatiwada et al./ bibechana 16 (2019) 196-203: rcost p.197 (online publication: dec., 2018) to amplify the area of commercial applications available to epoxy materials, strategy for improving the fracture toughness with little or no loss of the desired stiffness and thermal stability must be developed. for this purpose, a common toughening mechanism such as an addition of the phase separating additives to the epoxy system can be followed. for example, the addition of thermoplastic elastomer has been shown to offer effective toughening of epoxy resin materials [3]. however, the addition of more rubber into the epoxy resin can give rise to processing difficulties and the drop-in glass transition temperature (tg) and elastic modulus of the thermoset [4]. thus, the use of block copolymer as toughening agent has been explored quite comprehensibly [5–10]. in most cases, the formation of nanostructures was reported by incorporating ab-type diblock copolymers into thermosets [5–13]. also, the ordered nanostructures formed by abc triblock copolymers and hydrogenated systems were investigated [14–18]. however, the structural effect of block copolymers on the formation of nanostructures in thermosets was occasionally investigated. this work is aimed at the study of thermal and mechanical properties of the epoxy resins modified by styrene-rich styrenic triblock copolymer having linear asymmetric architectures. 2. experimental section 2.1 materials the diglycidyl ether of bisphenol-a (dgeba) resin was supplied by araldite ly556 huntsman and had an average epoxy equivalent of 186 g/equiv. the curing agent used was diaminodiphenylsulphone (dds) supplied by fluka. other chemicals like meta-chloroperoxybenzoic acid (m-cpba), sodium bicarbonate (nahco3) and sodium sulphate (na2so4) were purchased from the local market and used without further purification. the chemical structure of dgeba and dds are shown in fig. 1. fig. 1: chemical structures of diglycidyl ether of bisphenol-a (dgeba) (left) and 4,4 diaminodiphenylmethane (ddm) (right); the components used to prepare epoxy resin systems. the polystyrene–polybutadiene-based triblock copolymer (which has been named as ln3 in this and previous publications) was supplied by basf se, ludwigshafen, germany. the triblock copolymer has 74 % by volume of styrene, number average molecular weight (mn) 127 kg/mol and polydispersity index (mw/mn, where mw is the weight average molecular weight) of 1.1. more studies on this block copolymer can be found elsewhere [19]. 2.2 epoxidation of block copolymer the epoxidation of the styrene/butadiene-based triblock copolymer was accomplished following the standard method by using m-cpba [20-21]. in a typical experiment, 10 g of ln3 and 200 ml of dichloromethane were poured into a three-necked round bottomed flask and stirred gently by magnetic stirrer until the polymer dissolved. to achieve a degree of epoxidation (doe) of 80 mol%; shankar p. khatiwada et al./ bibechana 16 (2019) 196-203: rcost p.198 (online publication: dec., 2018) calculated amount of m-cpba were charged to the polymer solution. the chemical modification reaction is presented in schematically in fig. 2. fig. 2: schematic of chemical reaction involved in epoxidation of the block copolymer. the mixture was then vigorously agitated for two hours under dry n2 gas atmosphere at 0 °c. after the reaction was complete, the polymer solution was filtered. the excess m-cpba was removed by extracting with a saturated aqueous nahco3 solution and the mixture was further dried by the na2so4 solution. the final polymer solution was recovered using a separating funnel and a vacuum suction pump. the solvent was evaporated to recover the solid residue which was vacuum dried at 23 °c. the name epln3 is used for the epoxidized sample. 2.3 synthesis of blends with epoxy resin pure epoxy thermoset was prepared by the reaction of stoichiometric amount of dgeba with dds (ep: dds= 3:1). the mixture was pre-cured at 180 °c for 3 hours followed by post curing at 200ºc for 2 hours. epoxidized epln3 was dissolved in dichloromethane and blended with 5, 10 and 15 by weight % of the epln3. the mixture was heated up to 100°c to completely evaporate the solvent. then, the temperature was increased to 180°c and stoichiometric amount of dds hardener was added. the resultant mixture was stirred until the complete dissolution of the dds leading to the homogenous mixture. as in the case of pure thermoset resin, the mixture containing epln3 was cured. each cured blend was cooled gradually down to room temperature. thus, the prepared blends were named as ep, ep/epln3-5, ep/epln3-10 and ep/epln3-15 for those blends containing 0, 5, 10 and 15 wt.-% of epln3. 2.4. experimental techniques fourier transform infrared (ftir) spectroscopy was used to record the infrared spectra of the polymers using jasco ftir 615 instrument using atr transmission mode in the wavenumber range 4000 cm–1 to 600 cm–1. the impact strength of the blends was measured using izod impact tester according to astm d256 method. the sample dimensions were 100 mm × 12 mm × 3 mm and a notch of 1.5 mm in depth was introduced in to each specimen at a distance of 20 mm from one end. the hammer speed was 2.9 m/s with working capacity 4 j. at least five successive measurements were performed for each sample and the results were averaged. scanning electron microscopy (sem) was used to study the morphologies of cryo-fractured surfaces of the samples. the specimens were sputter coated with a thin layer of platinum (~3 nm) in order to avoid surface charging. thermogravimetric analysis (tga) was performed by of thermogravimetric analysis using netzsch tga 209 balance under n2 atmosphere from 20°c to 700°c at a heating rate of 10°c/min. the pressure of 1 bar was maintained with flow rate 15 ml/min in this analysis. m-cpba shankar p. khatiwada et al./ bibechana 16 (2019) 196-203: rcost p.199 (online publication: dec., 2018) dynamic mechanical analysis (dma) measurements was carried out on specimens with dimensions of 30 mm × 10 mm × 1 mm using an ares g2 rheometer in torsion mode to characterize the glass transition behavior of the sample using standard oscillatory temperature sweeps between 0°c and 250 °c at a frequency of 1 rad/s. 3. results and discussion 3.1 structural characterization the ftir spectra of the virgin ln3 and its epoxidized version (epln3) are presented in fig. 3. the peaks located at 910 cm–1 and 965 cm–1 for the virgin ln3 correspond to c–h bending vibration of vinyl side chains (–ch=ch2–) and trans 1,4 polybutadiene chains (–ch2–ch=ch–ch2–), respectively. the epoxidation of the 1,4 butadiene parts of the block copolymer is confirmed by the appearance of new peaks located around 890 cm–1 and 810 cm–1 for transand cis1,4 epoxidized copolymer respectively. after epoxidation, the peak corresponding to 1,4 butadiene decreases but that corresponding to 1,2 butadiene remains unchanged implying that the chemical modification of the butadiene chains mainly takes place at 1,4 linkages. thus, on the basis of the spectroscopic results, the targeted chemical modification of the copolymer can be confirmed. so far, the extent of the chemical modification cannot be ascertained by the spectroscopic methods. these results are in consistence with the previous works reported in similar system [22]. 3.2 mechanical behavior the notched izod impact strength of pure epoxy thermoset (ep) compared with epoxy blends with 5, 10 and 15 wt.-% of epln3 are presented in fig. 4. one can see that the value of impact strength increases insignificantly for the blend containing 5 wt.-% of epln3. in case of blends with the higher amount of epln3, however, the impact strength increases. among all the blends, ep/epln3-15 shows much better impact strength (6 kj/m2) compared to pure epoxy thermoset (3.7 kj/m2). the reason behind this observation is the proper miscibility of the epln3 with the ep and leading to larger plastic deformation of the material dissipation higher amount of energy delaying the crack propagation [23]. in summary, the epln3 contributes to quite significantly enhance the mechanical performance of the blends. the results thus give indication of the evolution of morphologies in the blends which might be responsible for enhancing their observed impact strength at higher epln3 contents. the exact morphologies must be, however, further investigated for precise structure-properties correlations. sem images of the cured samples after fracture toughness test are shown in fig. 5. the fracture surface of the single-phase neat epoxy resin (fig. 5a) appears typically, smooth with the cracks rippled freely and orienting in the loading direction representative of brittle failure and resulting in poor resistance to crack initiation and uninterrupted crack propagation [23]. owing to the better compatibility of epln3 in the ep matrix chain, the dispersed phase could be epln3 were distributed throughout the thermoset material. thus, the fractured surface has been changed significantly at higher loading of epln3. as a result, an irregular fracture patch with stretched fibrils appearing stress whitened edges were observed in case of blend containing 5 wt.-% of epln3 as shown in fig. 5b. the result provided an evidence of plastic deformation. numerous fibrillar fracture patches were observed in the blends containing large amount of epln3. 3.3 thermal behaviors thermal properties of the epoxy-based materials analyzed by thermogravimetric analysis (tga), are presented in fig. 6 and 7 as well in table 1. typical tga curves of mass loss as a function of temperature of ep is compared with that of blends are presented in fig. 6. at the first glance, similar 1800 1600 1400 1200 1000 800 890 a b s o rb a n c e ( a .u ) wavenumber (cm -1 ) ln3 epln3 810 0 5 10 15 0 2 4 6 e p /e p l n 3 -1 5 e p /e p l n 3 -1 0 e p /e p l n 3 -5 e p n o tc h e d i z o d i m p a c t s tr e n g th ( k j /m 2 ) epln3 content (wt.-%) shankar p. khatiwada et al./ bibechana 16 (2019) 196-203: rcost p.200 (online publication: dec., 2018) tga curves are shown by all materials. however, some changes can observe if the curves are carefully analyzed. the weight loss of the materials containing different amount of epln3 occurs mainly between 340 °c and 500 °c, and the temperatures of initial degradation for the blends with 5 % mass loss (td5) are apparently higher than that of the pure thermoset resin. fig. 3: ftir spectra of ln3 and epln3. . fig. 4: notched impact strength of the ep/epln3 blends with variation of epln3 content. fig. 5: sem image showing the fracture surface morphology of neat epoxy resin (ep) (a) and ep/epln3-10. the first derivative peak temperature (not shown here) indicates the point of the greatest rate of mass loss during degradation. here all materials show same first derivative peak at 418 °c. that indicates the all materials have usually similar thermal behavior. the char yield of ep thermoset at 600 °c is 17.6 % of original mass while the yield slightly increases up to 18.9 % after blending with increasing amount of epln3. this might be because of the contribution of different amount of epln3 making the stable network by some interaction. 10 µm a 10 µm b 0 200 400 600 800 0 20 40 60 80 100 ep ep/epln3-5 ep/epln3-10 ep/epln3-15 600 620 640 660 680 700 17 18 19 20 21 370 375 380 385 390 395 94 95 96 97 98 95 389387 391td5 381 m a s s l o s s ( % ) temperature ( °c) 418 td5 char yield -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 2,5 1.561.52 ln (d  d t) 1/t (10 -3 ) 1.48 y = -38283x +59,066 r 2 = 0.9929 shankar p. khatiwada et al./ bibechana 16 (2019) 196-203: rcost p.201 (online publication: dec., 2018) in order to analyze the activation energy of thermal degradation during the curing process, detailed analysis of the tga data obtaining through temperature scanning procedures was carried out using kinetic model. for degradation process, the rate of reaction can be expressed as a function of curing degree [24]. the rate constant of the curing reaction is generally expressed by arrhenius equation as in eqn. 1. dα dt = f(α). k(t) = a. e− ea rt f. (α) (1) where a is a pre-exponential factor (1/min), ea is the apparent activation energy in j/mol, t is the absolute temperature (k) and r is the gas constant (8.3136 j/mol k–1). for each sample, the sudden mass loss was observed and the ea values can thus be calculated from the slope of the linear part of ln (dα/dt) versus 1/t curves as shown in fig. 7. in similar manner the ea values for the blends were calculated from the slop of the curves in fig. 7 the values of ea was calculate calculated (see table 1). table 1: activation energy obtained from slope of ln(dα/dt) versus 1/t curves. sample activation energy (ea) kj/mol ep 318 ep/epln3-5 350 ep/epln3-10 354 ep/epln3-15 446 for the given temperature range, the ea value of neat epoxy resin is found to be 318 kj/mol. similarly, the ea values of blends were found to be in increasing order with increase in epln3 composition. the reason behind this phenomenon needs further investigations. fig. 6: tga curves for neat ep compared with ep/epln3 blends modified with different amount of epln3. fig.7: ln(da/dt) versus 1/t plots for calculation of activation energy of neat epoxy resin (ep). shankar p. khatiwada et al./ bibechana 16 (2019) 196-203: rcost p.202 (online publication: dec., 2018) 4. conclusions the results presented in this paper can be summarized as follows: (a) on the basis of the spectroscopic results, the targeted chemical modification of the copolymer can be confirmed. it was further observed that the chemical modification of the butadiene chains mainly took place at 1,4 linkages. (b) the modified block copolymer contributes to quite significantly enhance the mechanical performance of the blends with epoxy resin. the results thus give an indication of the formation of nanostructured morphology in the blends which might be responsible for enhancing their impact strength at higher epln3 content. (c) based on the thermogravimetric analyses, the enhanced stability of the blends can be correlated with the formation of nanostructured morphology of the blends. acknowledgements spk thanks german academic exchange service (daad) ((57129430) for providing the ph.d. scholarship and further acknowledges prof. gert heinrich (ipf, dresden, germany) for experimental support and fruitful discussions. references [1] l.v. mcadams, j.a. gannon, in: high performance polymer and composites, j.i. kroschwitz, ed., john wiley and sons, hoboken (1991) 258–318. 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[24] a. arbelaiz, b. fernandez, j.a. ramos, i. mondragon, thermal and crystallization studies of short flax fibre reinforced polypropylene matrix composites: effect of treatments, thermochimica acta 440 (2006) 111–121. doi.org/10.1016/j.tca.2005.10.016. https://doi.org/10.1021/ma001559m https://doi.org/10.1021/ma0490754 https://doi.org/10.1016/j.polymer.2005.02.012 https://doi.org/10.1002/marc.200500131 https://doi.org/10.1088/1367-2630/6/1/028 https://doi.org/10.1016/j.matpr.2017.06.038 https://doi.org/10.1002/masy.201400001 https://doi.org/10.1016/0032-3861(77)90016-7 https://doi.org/10.1016/j.tca.2005.10.016 m. bhandari/ bibechana 14 (2017) 103-109 : rcost p.103 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal anxiety and depression among adolescent students at higher secondary school m. bhandari faculty of child health nursing, tribhuwan university, institute of medicine, nursing campus biratnagar, nepal *e-mail: menukamenu@gmail.com article history: received 6 november, 2016; accepted 15 november, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.16019 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract this study was conducted to assess the association of depression and anxiety with selected variables; low academic performance and poor parent adolescent relationship among the adolescent students at arniko higher secondary school at biratnagar. beck depression inventory (bdi) and beck anxiety inventory (bai) tools were used for data collection. spearman’s rank correlation coefficient and chi square test were applied to assess the significant variables. the findings of the study revealed that there was significant correlation between total depression and total anxiety score i.e. spearman’s rank correlation coefficient value was 0.554 (p = 0.000). the study also found that the depression and anxiety were significantly associated with type of family (p =0.005 & p = 0.015). the depression was significantly associated with academic performance of adolescent students (p = 0.030) and major accident in the family (p =0.009). similarly, the anxiety was significantly associated with parental fight (p = 0.007), conflict with father (p = 0.019), and death of family member (p = 0.016). it can be concluded that adolescent anxiety and depression are significant mental health problems so further studies are needed to validate the findings. keywords: depression; anxiety; adolescent student; correlation; higher secondary school. 1. introduction the term “adolescence” comes from the latin word adolescence, which means, “to grow into adulthood”. it has illustrated it begins with the onset of puberty and ends with the assumption of adult responsibilities; as one philosopher remarked, adolescence begins in biology and ends in culture as stated by laufer [1]. adolescence has been defined by world health organization (who) as the period of life spanning the m. bhandari/ bibechana 14 (2017) 103-109 : rcost p.104 (online publication: dec., 2016) ages between 10 and 19 years. adolescence is a crucial phase in life and the presence of conditions like depression and anxiety at this stage of life is a matter of concern. a study conducted by mayne r.g. has highlighted that mental health problems can develop at any point in life and may be influenced by a variety of factors, including genetics or family history of a disorder, chemical imbalances in the brain, or stressors in the environment [2]. world health organization [3] reported the increase in mental health problems such as depression, anxiety and suicide rate may reflect the difficulties that some adolescents face as they encounter the cognitive, physical, psychological and spiritual changes that accompany during puberty. epidemiological studies suggest that the comorbidity is much higher, thus suggesting an intimate connection between them where the presence of one increases the likelihood of the other occurring. anxiety disorders typically onset in childhood and adolescence and run a chronic course well into adulthood according to a study conducted by albano, chorpita & barlow [4]. in the united states, prevalence studies of childhood and adolescent anxiety disorders in the general population have yielded overall rates of between 17 and 21% as reported by kashani & orvaschel [5]. essau et al. [6] concluded that anxiety is associated with substantial negative effects on children’s social, emotional and academic success. in the same way major depressive disorder (mdd) often has an onset in adolescence, across diverse countries, and is associated with substantial psychosocial impairment and risk of suicide, weiss & last’s study suggested [7]. the incidence of major depressive disorder is estimated to be approximately 5-8% in adolescents. one of the study conducted by hughes showed that adolescent girls are twice as likely as adolescent boys to experience depression [8]. objectives of the study general objective: the general objective of this research was to assess the association of depression and anxiety with selected variables. specific objectives: o to assess the depression level of adolescents students. o to assess the anxiety level of adolescents students. o to correlate the depression and anxiety scores of adolescents students. o to assess the association of depression and anxiety scores with selected variables. hypotheses o there is a positive relationship between depression and anxiety scores of adolescent students. o there is a significant association between depression and anxiety level of adolescent students with low academic performance. o the depression and anxiety level of adolescent students are significantly associated with poor parent adolescent relationship. m. bhandari/ bibechana 14 (2017) 103-109 : rcost p.105 (online publication: dec., 2016) 2. methods the study adopted descriptive correlational research design to find out the degree of association between depression and anxiety of adolescent and the association of selected variables with depression and anxiety level during the same period of time. the study was conducted at arniko higher secondary school which is located in biratnagar municipality of morang district. the study period was from july, 2014 to january, 2015. formal permission for the study was taken from the ethical committee and written permission was obtained from arniko higher secondary school. informed consent was taken from the respondents verbally. objectives of the study were clearly explained to the respondents before data collection.the study population was all the adolescent students who were studying in class 12 in science faculty at arniko higher secondary school at biratnagar. there were 300 students in class twelve. the study adopted probability sampling technique, sample was selected following simple random, lottery method; required number 100 was selected among male and female students (50/50). confidentiality of all the collected information was maintained throughout the study. in keeping objectives of the study in mind, the following tools were selected: part i: semistructured bio-demographic performa with selected variables, part ii: beck anxiety inventory (bai), part iii: beck depression inventory (bdi). the selected variables were academic performance of students, parentadolescent relationship and adverse events in family in the last one year. beck anxiety inventory (bai) was developed by aaron t. beck and his colleagues is a 21 item self-rated questionnaire that describes common symptoms of anxiety. the subject has to rate how much he/she has been bothered by each symptom during the past one week on a 4 point scale ranging from 0-3. this scale has a reliability value of 0.92 & a validity that ranges from 0.820.87. since the scale is considered as a standard tool to measure anxiety symptoms. scores will have implications for both in measuring severity and assessing changes in symptoms due to intervention [9]. beck depression inventory (bdi) developed by aaron t.beck and his colleagues, is a 21 item self-rated questionnaire that describes common symptoms of depression. the subject has to rate according to how much he/she has been feeling during the past two weeks on a 4 point scale ranging from 0-3. the tool is considered as a standard scale for measuring severity of the depressive symptoms & assessing the changes in the symptoms due to intervention. this scale has a reliability value ranging from 0.76 to 0.95 in psychiatric samples & 0.73 to 0.92 in non psychiatric samples [10]. for descriptive analysis, mean, standard deviation, and median was calculated. to find out the correlation between depression and anxiety scores, spearman’s rank correlation coefficient was calculated and to find out the association with selected variables, chi square test was applied. the beck anxiety inventory score of students was categorized as no anxiety (0-21), mild anxiety (22-32), moderate anxiety (33-48) & severe anxiety (49-63). similarly beck depression inventory scored and cases were categorized as no depression (0-9), mild depression (10-19), moderate depression (20-29) & severe depression (30-63). 3. results the age group was homogeneous, the caste distribution showed the representation of brahmin was high i.e. 40% then others, the overall representation of hindus and others were 98% and 2% respectively. m. bhandari/ bibechana 14 (2017) 103-109 : rcost p.106 (online publication: dec., 2016) most of the respondents’ father’s educational status was graduation above i.e. 51% and mother’s educational status was intermediate level i.e. 38%. the thirty six percentage respondents were from the higher family income group and 11% from low family income group. the major occupation of fathers of respondents was government job and the most of the respondents’ mothers were housewife. the 64% of the students were hail from nuclear families shows the growing trend away from joint families, especially in urban areas. regarding the socio-demographic variables, it was found significant association between type of family and anxiety and depression of respondents (p = 0.015) and (p = 0.005) at 95% of confidence interval i.e. the anxiety and depression level of respondent was high in single parent family then joint and nuclear family. table 1: anxiety level of respondents. n = 100 anxiety level respondents none 90 mild anxiety 10 this study showed the 90% respondents had no anxiety and only 10% respondents had mild anxiety out of 100 respondents (table 1) table 2: depression level of respondents. n =100 this study showed the 59% respondents had mild depression, 14% respondents had moderate depression, 3% had severe depression & only 24% had no depression out of 100 respondents. (table 2) table 3: association between depression and academic performance. chi square test *significant at p < 0.05 depression level respondents none 24 mild moderate severe 59 14 3 academic score depression no yes chi value pvalue less than 70% 3 26 4.730 0.030* 70% 80% 14 38 80 90% 7 12 m. bhandari/ bibechana 14 (2017) 103-109 : rcost p.107 (online publication: dec., 2016) it was found significant association between depression and academic performance of students. therefore it can be concluded that the research hypothesis was accepted (table 3) table 4:total score analysis of anxiety and depression of respondents. n = 100 iqr = interquartile range the study depicted that the total score analysis of anxiety and depression in which mean (± sd) of anxiety was 13.15 (± 6.06), median was 12.50 and range was 31 whereas the mean (± sd) of depression was 13.82(± 6.88), median was 13.00 and range was 34. we can conclude that the mean and median score of anxiety and depression were not equal. so the scores were not normally distributed (table 4). table 5: relationship between total depression and total anxiety scores of respondents. n = 100 relationship of scores spearman’s rank correlation 0.554 p-value 0.000 this study revealed the positive relationship between total depression and total anxiety score of respondents. it was found to be correlated with each other i.e. spearman’s rank correlation value was 0.554 (p = <0.05) (table 5). 4. discussion the present study found anxiety among 10% of adolescent students. the study also found 59% respondents had mild depression, 14% respondents had moderate depression, and 3% had severe depression which is comparable with the study carried out in iran, it has reported the prevalence of depression among high school students as follows: mild depression in 18%, moderate depression in 9%, and severe depression in 7%, hence, a total rate of 34%, jafar et al [11]. the research hypothesis was that depression and anxiety would be significantly associated with low academic performance. the present study showed anxiety was not significantly associated with academic performance but depression was significantly associated with low academic performance (p = 0.030) at 95% confidence interval which means those who have lower academic performance have higher level of statistics anxiety depression mean (± sd) 13.15 (± 6.06) 13.82( ± 6.88) median (iqr) 12.50 (9.00 – 15.00) 13.00 (10.00 – 17.00) range(maximum – minimum) 32.00 – 1.00 35.00 – 1.00 m. bhandari/ bibechana 14 (2017) 103-109 : rcost p.108 (online publication: dec., 2016) depression. research has indicated that depressed mood is negatively related to academic achievement carried out by moosavi & fallahi [12]. it was also found consistent with literature. the research hypothesis was that depression and anxiety would be significantly associated with low academic performance. the present study showed anxiety was not significantly associated with academic performance but depression was significantly associated with low academic performance (p = 0.030) at 95% confidence interval which means those who have lower academic performance have higher level of depression. maccoby & martin’s study has indicated that depressed mood is negatively related to academic achievement [13]. the next hypothesis was depression and anxiety would be significantly associated with poor parent – adolescent relationship. parentadolescent relationship is a strong bulwark for the adolescent during this delicate period of major changes in life. among the variables conflict with father was significantly associated with the high level of anxiety of adolescents’ i.e. p value was 0.019. these variables were not significantly associated with depression of adolescents. research has proved that warmth and control are thought to be the most important ways in which parents influence the development of their offspring or children as suggested by lewinsohn et al. [14]. depression in adolescence is often associated with the absence of supportive and positive interactions with parents and is characterized by elevated levels of conflictual, critical and angry interactions, brady & kendall reported [15]. the most important part of this study was to test the correlation between depression and anxiety score. the hypothesis was, there would be positive relationship between depression & anxiety score. the present study revealed that the relationship between total depression and total anxiety score of respondents was found to be remarkably correlated to each other i.e. spearman’s rank coefficient value was 0.554 which indicated that when anxiety was more, the depression level was also going up. it was founded that when degree of depression was more, the anxiety must be present which was coincide with the research findings indicates that there is considerable overlap between anxiety and depressive symptoms in youth, as measured by commonly used self-report questionnaires by seligman & ollendick [16]. 5. conclusion it can be concluded that adolescent depression and anxiety are significant mental health problems. many depressed and anxious students fail in school, develop interpersonal difficulties, and get in troubles with parent adolescent relationship. these also decrease motivation towards the ability for attention and concentration. depression is an under-recognized yet a prevalent health problem among adolescents. it does not only cause suffering and loss of functional ability, but it also serves as a risk factor for suicidal attempts and numerous negative behaviors such as smoking, alcohol and drug use. prevention and control activities focus on modifying and improving the psychosocial factors. acknowledgement the author would like to express her gratitude to tribhuvan university, institute of medicine, and nursing campus maharajgunj. the author would like to express her heartfelt gratitude to nhrc for m. bhandari/ bibechana 14 (2017) 103-109 : rcost p.109 (online publication: dec., 2016) providing financial support which is the golden opportunity for post graduate student researcher. the author would like to thank principal of arniko higher secondary school at biratnagar for giving permission and cooperation for this study. the author would like to express her heartfelt thanks to professor dr. vidya dev sharma, head of the department, psychiatry for providing guidance for selection of topic and giving permission to use tool for data collection. the author would ever indebted to all adolescent students who consented and cooperated to become the part of this study. references [1] m. laufer, assessment of adolescent disturbances, the application of anne freud’s diagnostic profile, psychoanalytic study of children, 20 (1965) 99-123. [2[ r.g. mayne, an expository lexicon of the terms, ancient and modern, in medical and general science, london, churchill livingston (1860). [3] world health organization, strategies for adolescent health and development, (1998). [4] a. m. albano, b.f. chorpita, and d. h. barlow, journal of abnormal psychology 107 (1998) 74−85. https:/doi.org/10.1037/0021-843x.107.1.74 [5] j. h. kashani, h. orvaschel, american journal of psychiatry 147 (1990) 313–318. https:/doi.org/10.1176/ajp.147.3.313 [6] c. a. essau, j. conrad , f. petermann, journal of anxiety disorders 14 (2000) 263-279. https:/doi.org/10.1016/s0887-6185(99)00039-0 [7] d. d. weiss, c.g. las, developmental variations in the prevalence and manifestations of anxiety disorders, the developmental psychopathology of anxiety: oxford university press (2001) pp.27-42. [8] n. hughes, cognitive behavior, therapy of children in schools, new york: pergamon press, (1988) pp. 172 – 174. 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[15] e.u. brady, p. c. kendall, psychological bulletin 111 (1992) 244−255. https:/doi.org/10.1037/0033-2909.111.2.244 [16] l. d. seligma, t. h. ollendick, clinical child and family psychology review 1 (1998) 125−144. https:/doi.org/10.1023/a:1021887712873 gabriel james tambunga / bibechana 14 (2017) 9-15 : rcost p.9 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal general relativity, quantum behavior and doppler factor basics in laser-driven light sailing and solar sailing gabriel james tambunga 916 s. delhi street, philadelphia, pa, u.s.a. e-mail: mexicanengineer911@gmail.com article history: received 12 may, 2016; accepted 2 august, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15407 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract basic concepts of the quantum behavior of atoms and molecules, modified concepts of general relativity and the doppler factor were applied to a reflection associated with solar sailing and laserdriven light sailing, which provides the motion in the sailing due to energy and momentum transfer of the photons to the sail. the result of this application is the energy and momentum being conserved, for the first time, from the perspective of the reflector and the source. the magnitude and the direction of the reflector, after a reflection, are not consistent with current beliefs of the reflection of a photon, which is a consequence of the conservation proposed in this paper. an experimental test to verify the actual energy and momentum transfer from a photon to a reflector is also proposed. keywords: general relativity; quantum behavior; doppler factor; laser-driven light sailing; solar sailing. . 1. introduction quantum electrodynamics (qed) and the doppler factor were previously applied to laser-driven light sailing [1], where these applications indicated the laser source used to propel the reflector needed to decrease the wavelength of the photons as the sail increased in velocity. this is because the atoms or molecules associated with the reflection would observe a larger wavelength due to the doppler factor when the reflectors velocity increases away from the source, where the atoms or molecules would absorb and emit photons, a reflection, at discrete energies. however, in the paper the conservation of energy from the reflectors perspective indicated the reflector should not be in motion, as the photon energy would enter and exit the reflector at the same value. that is, according to current viewpoints [2, 3], the http://nepjol.info/index.php/bibechana mailto:mexicanengineer911@gmail.com http://dx.doi.org/10.3126/bibechana.v14i0.15407 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ gabriel james tambunga / bibechana 14 (2017) 9-15 : rcost p.10 (online publication: dec., 2016) reflector should be in motion, a kinetic energy, after a reflection, but the paper indicated the reflector should not be in motion as kinetic energy cannot be gained per the conservation of energy. the current paper will continue the research and show how energy and momentum is conserved, from both a reflector and sources perspective, by using the quantum behavior of atoms and molecules and modified concepts of general relativity (gr), while maintaining the use of the doppler factor. the results of this current paper will indicate changes to current beliefs of a reflection and will suggest an experimental apparatus that can used to confirm or challenge current beliefs. only parallel vectors will be used in this paper, for simplicity. as the current paper is only an introduction of the quantum behavior of atoms and molecules and modified concepts of gr to a reflection, performing the suggested experiment is beyond the scope of the current paper. emitted energy and the einstein field equations when a source emits a photon, the photon has an energy hfs, a momentum h/λs, and a space-time geometry gμν, where gμν is calculated from the energy-momentum tensor, tμν [4]. that is, 𝐺𝜇𝜈 = 8𝜋𝐺 𝑐4 𝑇𝜇𝜈 (1) this space-time geometry would also be observed by a reflector, when both source and reflector are in the same reference frame. however, if a reflector is in motion and requires the photon to be at an energy hfr, for a reflection, then the source would need to emit a photon energy of √1+𝛽 √1−𝛽 ℎ𝑓𝑟, (2) due to the doppler factor, where β is the velocity of the reflector from the sources perspective divided by the speed of light. as a result, per equation (1), the space-time geometry of the photon, from the sources perspective, would also change. that is, the emitted photon from the sources perspective would have a space-time geometry of rμν, and the space-time geometry from the reflectors perspective would be gμν. however, for this paper, the space-time geometry observed by the reflector will be the same space-time geometry the source observes, rμν, as this will be necessary, as will be shown, for balancing the conservation of energy and momentum. reflector physical description to facilitate the discussion in this paper the physical characteristics of a reflector may be necessary. a reflector is composed of atoms and molecules, where one side of a reflector absorbs then emits photons, a reflection, in the opposite direction of the original photon. the other side of the reflector does not absorb or emit photons. gabriel james tambunga / bibechana 14 (2017) 9-15 : rcost p.11 (online publication: dec., 2016) , energy and momentum of a non-moving source according to quantum theory [5], when an atom or molecule within the reflector absorbs a photon the atom or molecule is in an excited state, where the electron is at a higher energy level and is equal to the energy of the photon. for the atom or molecule to be in motion both momentum and energy must be conserved. as there is no excess energy for the atom or molecule to be in motion after absorption, then the momentum of the photon must be changed to momentum within the atom or molecule, similar to the way a photons energy changes to an electrons excited energy state within an atom or molecule. further, the direction of the momentum, prior to absorption, does not affect the excited state after absorption. for this paper, there is no excess momentum to cause motion of the atom or molecule, as the momentum from the photon is absorbed into the atom or molecule. after a photon is absorbed, the photon energy and momentum remains in the atom or molecule for time τ, the decay time. that is; the time it takes for the atom or molecule to be in this excited state; from absorption to emission. during this time, the side of the reflector that absorbs and emits the photon is in a higher energy state, where there is a small increase of the space-time geometry according to the einstein field equations. as a result, a small acceleration occurs for time τ for each atom or molecule that absorbs a photon. energy and momentum of a moving source if a moving source emits a photon energy as indicated in equation (2), but the reflector observes a spacetime geometry of rμν, the space-time geometry observed by the source, this would indicate to the reflector there will be more or less energy and momentum associated with the photon than what will be absorbed. for a source moving away from a reflector, the enlarged space-time geometry, from the reflectors perspective, indicates there is an excess energy of √1+𝛽 √1−𝛽 ℎ𝑓𝑟 − ℎ𝑓𝑟 (3) and an excess momentum of √1+𝛽 √1−𝛽 ℎ 𝜆𝑟 − ℎ 𝜆𝑟 , (4) pointing toward the reflector. for a source moving toward a reflector the β values would be negative, so the energy value would be less than what is required to excite the atom or molecule. from the reflectors perspective, equations (3) and (4) are still used but the energy would be negative with the momentum pointing in the direction of the incoming photon. gabriel james tambunga / bibechana 14 (2017) 9-15 : rcost p.12 (online publication: dec., 2016) as in a non-moving source, after absorption, there would be an enlarged energy state on the reflection side of the reflector for time τ, resulting in an acceleration for the atoms or molecules that absorbed a photon. emission for a non-moving and moving source after emission, the energy state and momentum within the atom or molecule are return to its state prior to absorption. the momentum of the photon contains a direction; however, this direction has no effect on the energy state and momentum within the atom or molecule after emission. as the emitted photon has the same energy and momentum as the excited state of the atom or molecule, there would be no excess for motion. further, as there is no more excited state, the space-time geometry of the atom or molecule returns to the geometry prior to absorption. after the emission, the reflector emits and observes a photon with an energy, momentum, and space-time geometry of hfr, h/λr and gμν, respectively, where the momentum is pointing toward the source. the source would observe an energy and momentum of √1+𝛽’ √1−𝛽’ ℎ𝑓𝑟 and √1+𝛽’ √1−𝛽’ ℎ 𝜆𝑟 respectively, where β’ is the velocity of the reflector from the sources perspective divided by the speed of light. however, by maintaining the space-time geometry from the reflectors prespective, gμν, there is more or less energy and momentum associated with the photon than what is observed. this being an energy and momentum of hfr and h/λr, respectively. taking the difference of what was emitted by the source and what was observed by the source, after the reflectors emission, through gμν determination, results in an energy difference of ( √1+𝛽 √1−𝛽 ℎ𝑓𝑟 − ℎ𝑓𝑟), and a momentum of ( √1+𝛽 √1−𝛽 ℎ 𝜆𝑟 − ℎ 𝜆𝑟 ), this energy value and this scalar value of the momentum are the same values as the energy and momentum applied to the reflector that are not associated with what was absorbed into the atom or gabriel james tambunga / bibechana 14 (2017) 9-15 : rcost p.13 (online publication: dec., 2016) molecule, equations (3) and (4). equations (3) and (4) apply to a moving source and a non-moving source, as the results of a non-moving source would be zero. necessities for energy and momentum conservation the reasoning and analysis provided in his paper shows energy and momentum as conserved. however, for the conservations to uphold the following was used and, to the author’s knowledge, has not been considered in laser-driven light sailing or solar sailing. (a) the space-time geometry associated with the photon at the source is maintained with the photon despite observers or reflectors relative motion. (b) the energy and momentum of an absorbed photon becomes the energy and momentum within the atom or molecule, leaving no excess of energy and momentum. (c) the direction of the photon’s momentum, when absorbed in an atom or molecule, does not impact the excited state of the atom or molecule. (d) the energy and momentum of an emitted photon originates from the energy and momentum within the atom or molecule, leaving no excess of energy and momentum. (e) the direction of the photon’s momentum, when emitted from an atom or molecule, does not impact the state of the atom or molecule after emission. (f) despite absorbed energy and momentum of a photon, the space-time geometry of the photon determines the excess or deficiency of the actual energy and momentum of a photon. for (e) above, the direction of the photon is engineered, via the reflector, to emit in a certain direction. however, only the state of the careful placement of molecules, after an emission, is affected. that is, the molecule decreases to a lower state only. 2. discussion current beliefs for motion of a reflector in laser-driven light sailing and solar sailing do not consider individual events, such as a photons energy and momentum changing to energy and momentum within an atom or molecule, and energy and momentum within an atom or molecule changing to a photons energy and momentum. by not considering the individual events, the conservation laws were not satisfied for both the source and reflector. however, by considering the individual events, as what was done in this paper, the conservation laws are satisfied between each event. in a previous paper [1], it was determined motion due to a reflection was a result of the doppler shift. however, the balancing of the energy and momentum in the current paper indicates limitations in the energy of a reflector. gabriel james tambunga / bibechana 14 (2017) 9-15 : rcost p.14 (online publication: dec., 2016) fig. 1: a plot of β (x-axis), and the excess energy, in hfr, of a single atom or molecule applied to a reflector (y-axis), when a source is moving away from a reflector. this plot indicates that the velocity of the source must be at approximately 0.8 times the speed of light for the reflector to be twice the energy of a single photon. current beliefs indicate that twice the momentum of a photon [6, 7], at minimum, will be applied to reflector despite the speed or direction of the source. a proposed experimental test for verification though the conservation of energy and momentum are balanced, the direction of motion of the atom or molecule, during absorption, is inconsistent with current beliefs and practices. that is, when a source and reflector are moving towards each other, this result in a reflector increasing its velocity towards the source, according to the viewpoint presented in this paper. however, current beliefs, such as doppler cooling [8], indicate the atom or molecule would slow down in this same situation. a test to determine the actual direction of a reflector due to a reflection, from a moving or non-moving source, can be performed as follows: engineered molecule: a molecule would need to be engineered that can align in a magnetic field in a way that will cause a photon to emit vertically, where the location on the molecule where the photon emits from will contain an unoccupied energy state in the environment where the molecule will be used, unless stimulated by the experimental setup. gabriel james tambunga / bibechana 14 (2017) 9-15 : rcost p.15 (online publication: dec., 2016) magnetic field: a magnetic field will cause the molecule to orbit an apparatus, where sensors to detect the molecule and photon will be above and below the path the molecule follows. the magnetic field will need to be designed to not be strong enough to maintain the molecule in the magnetic field if a vertical momentum of the molecule is above a threshold. source: the path of the photons from the source, which is either moving away or towards the molecule, to the molecule must be unperturbed. this is because, for example, funneling, reflecting or re-directing of the photons will cause the space-time geometry of the photons to change to the space-time geometry of a non-moving source. this will cause the molecule to not move from the magnetic field. further, this experimental setup may also determine the effect of the increased space-time geometry on the molecule for a non-moving source during the time the photons energy and momentum are in the molecule. this can be done by decreasing the threshold that holds the molecule in the magnetic field. references [1] g. j. tambunga, international letters of chemistry, physics and astronomy, 19 (2013) 10-14. [2] g. vulpetti, l. johnson, g. l. matlof, solar sails: a novel approach to interplanetary travel, second ed., springer-praxis, chichester, uk, (2015). http://dx.doi.org/10.1007/978-1-4939-0941-4 [3] y. k. bae, physics procedia, 38 (2012) 253-279. http://dx.doi.org/10.1016/j.phpro.2012.08.026 [4] c. w. misner, k. s. thorne, j. a. wheeler, gravitation, w. h. freeman and company, new york, (1973). [5] information on http://www.feynmanlectures.caltech.edu/iii_02.html [6] m. guthrie, solar sails – a discussion ( 2011). https://web2.ph.utexas.edu/~mwguthrie/p.solarsails.pdf [7] information on http://www.feynmanlectures.caltech.edu/i_39.html [8] d. j. wineland, w. m. itano, physical review a, 20 (1979) 1521-1540. http://dx.doi.org/10.1103/physreva.20.1521 http://dx.doi.org/10.1007/978-1-4939-0941-4 http://dx.doi.org/10.1007/978-1-4939-0941-4 http://dx.doi.org/10.1016/j.phpro.2012.08.026 http://dx.doi.org/10.1016/j.phpro.2012.08.026 http://www.feynmanlectures.caltech.edu/iii_02.html https://web2.ph.utexas.edu/~mwguthrie/p.solarsails.pdf http://www.feynmanlectures.caltech.edu/i_39.html http://dx.doi.org/10.1103/physreva.20.1521 http://dx.doi.org/10.1103/physreva.20.1521 microsoft word nakarmi _89-95_.docx r c o s t n publisher: research council of science and technology, biratnagar, nepal p. 89 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana significance of neutrino-neutrino interaction in neutrino oscillation in core-collapse supernova prabandha nakarmi 1* , jeevan jyoti nakarmi 2** 1 department of physics, patan multiple campus, patandhoka, nepal 2central department of physics, tribhuvan university, kirtipur, nepal *e-mail: nakarmipra@gmail.com **e-mail: nakarmijj@tu.cdp.edu.np accepted for publication: december 19, 2014 abstract we study the possibility of neutrino-neutrino interaction inside the neutrino core of supernova (� ≥ 10�� �/ ) and outside the neutrinosphere. the angular dependence of the neutrino-neutrino interaction hamiltonian causes multi-angle effects that can lead either to oscillation or free streaming of neutrinos. if the angle between interactions is � 2⁄ , the neutrinos are trapped inside neutrino core and chances of oscillation increases due to interaction. as the angle gradually changes, the chance of oscillation decreases and free streaming of neutrino can be observed out of core of supernova as shock waves. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11780 © 2014 rcost: all rights reserved. keywords: neutrino-neutrino interaction; supernova; hamiltonian. 1. introduction since the discovery of neutrinos, there have been series of tremendous successful works carried out in the study of neutrinos. neutrinos are very elusive in nature. because of this nature, neutrinos rarely interact with matter and therefore very difficult to detect. the interaction of neutrino with matter is studied with great interest and the effect is known as msw effect [1, 2]. msw effect is mostly popular in solution of solar neutrino problem. since the discovery of msw effect, the study of neutrino oscillation has been accelerated. after the supernova explosion in 1987, the detail study of neutrino oscillation in core collapse supernova revealed surprising facts of neutrino oscillation. the huge amount of neutrinos produced in sn 1987a showed that the neutrinos gets trapped inside the core of supernova. hence the study of neutrino-neutrino interaction must be accounted in the region where density of neutrino is very high such as core of supernova (� ≥ 10�� �/ ). several works have investigated the conditions for the � − � effects to be triggered. neutrino-neutrino interaction may be one of the strong causes of neutrino oscillations. the no. of neutrinos formed during r-process nucleo-synthesis in core of supernova is very high; hence the probability of � − �effects inside core increases. the interaction of neutrino with other leptons and with neutrino itself is studied in a series of papers [1-7]. also the neutrino oscillation in dense neutrino gases such as core of supernova is studied in paper [8], which showed the self-induced msw effect. also paper [9] shows that the angular nakarmi and nakarmi/ bibechana 12 (2015) 89-95: p. 90 dependence of the neutrino-neutrino interaction potential causes multi-angle effects that can lead either to complete kinematical decoherence in flavor space or only to small differences between different trajectories. this nonlinear system switches abruptly between “self-maintained coherence” and “self-induced decoherence” among the angular modes, depending on the strength of the deleptonization flux. the present work is to study about the multi-angle effects of � − �interaction in core collapse supernova. the variation of interaction length due to angle variation is estimated through the angle dependent term of the hamiltonian of � − �interaction. 2. formalism the � − � interaction hamiltonian can be written as [10], ��� =��√�� � ��������� !"#$�%!"$�%!"#$�%!"$�% + !'#$�%!'$�%!'#$�%!'$�% + !'#$�%!"$�%!"#$�%!'$�% +!"#$�%!'$�%!'#$�%!"$�%( (1) where, we defined ��� = )1 − cos -��. (2) !"#$�%and!'#$�% are the creation operators for the left-handed �" and �' with momentum �, respectively, and !"$�% and !'$�% are the corresponding annihilation operators [10-12]. here, -�� is the angle between the momentum directions of the neutrinos with momenta p and q and box quantization conditions for a box with volume v is used in above equation. the interaction between � − � can also be written in the form, [7] ��� = √2/0 1 2 ��3)4′.5 )1 − 46. 46′.�893 ��′ − √2/0 1 2 ��3)4′.5 )1 − 46. 46′.�893 ��′ (3) where �893 :�893 ; are the differential neutrino (anti-neutrino) number densities and ��3 :��3; is the density matrix for neutrinos (anti-neutrinos), encoding neutrino flavor conversion, whose expression is, for neutrinos ��3 ≡ =|�"|� �"�?∗ �"�a∗�"∗�? b�?b� �?�a∗�"∗�a �?∗�a |�a|�c (4) and similarly for ��3 for anti-neutrinos. in above equation, the neutrino flavor might have changed is indicated with a flavor underlined (�5). in eq. 3, 4, 4′are different momenta of neutrinos and antineutrinos, also46 = 4 |4|⁄ .the fact that their flavor might change in the interaction is encoded in the neutrino density matrix. nakarmi and nakarmi/ bibechana 12 (2015) 89-95: p. 91 3. application to the neutrino-neutrino interaction let us apply the formalism and the results of the previous section to the hamiltonian eq. (3) describing neutrino propagation in a core-collapse supernova with the neutrino-neutrino interaction contribution. here we treat the neutrino-neutrino contribution in the single-angle approximation. from now, the time (t) is replaced with distance(x). if we calculate the derivative of h necessary to determine the diagonal and off-diagonal terms of the hamiltonian in the ‘matter’ basis, we find two contribution, �e = �e fgh + �e �� (5) for the single-angle approximation, ��� in eq. 3 becomes, [7] ���i.g. = j$k%i.g./$�%i.g. (6) with the geometrical factor, j$k%i.g. = √����lm9n �� o1 − p1 − :m9' ;�q� (7) where �� is the radius of the neutrinosphere. the non-linear contribution is given by, /$�%i.g. = ∑ � s��3)�′.t�3 )�′. − ��3)�′.t�3)�′.u5 ��′ (8) with t�3, the neutrino flux at the same location for a neutrino of a flavor v. the corresponding derivative �e�� includes contributions from both the derivative of the geometrical factor and the density matrices, i.e. �e ��i.g. = je $k%i.g./$�%i.g. + j$k%i.g./e $�%i.g. (9) where the calculation of je $k% is straight forward and the non-linear term is obtained using of the liouville von-neumann equation which gives, /e $�%i.g. = −w ∑ � sx�, ��3)�′.y t�3)�′. + x�, ��3)�′.y∗ t�3)�′.u5 ��′ (10) where � indicates the hamiltonian for anti-neutrinos. in the case of anti-neutrinos, eq. (10) holds by replacing � ↔ � and � ↔ �. from the derived relations, we can identify two interesting conditions to be fulfilled: (i) for the neutrino-neutrino interaction effects to occur (ii) for the onset of bipolar oscillations. 4. multi-angle approximation in the multi-angle approximation, assuming spherical geometry for the neutrino sphere, ��� of eq. (3) reads as ���f.g. = √2/02���� 1 2 2 ��′ � [\] ^_`a ∞ �5 � cos b ′ )1 − cos b cos b ′. nakarmi and nakarmi/ bibechana 12 (2015) 89-95: p. 92 x��3)�′, b ′.t�3)�′. − ��3∗ )�′, b ′.t�3)�′.y (11) with, cos bfg' = c1 − $�� k⁄ %� (12) using leibniz integral rule: dde � f$g, h%�ij$e%g$e% = � dk$l,e%dej$e%g$e% �i + f$m$h%, n% dj$e%de − f$!$h%, h% dg$e%de (13) the derivative for eq. (11) is �e ��f.g. = √����lm9n ∑ � ��′)�)b ′, �′. − o$k%p$�′%.∞�5 (14) with, �)b ′, �′. = � � cos b ′�[\] ^_`a q−w)1 − cos b cos b ′. sx�, ��3)�′, b ′.y t�3)�′. + x�, ��3 )�′, b ′.y∗ t�3)�′.ur (15) o$k% = $m9 '⁄ %n'c�s$m9 '⁄ %n (16) p)�′. = $1 − cos b cos bfg'% x��3 )�′, bfg'.t�3 )�′. − ��3∗ )�′, bfg'.t�3)�′.y (17) 5. numerical results and discussion here we present results of multi-angle variation in neutrino oscillation due to � − � interaction and the probability of neutrino oscillation in core collapse supernova due to � − � interaction by using eq. (12), (16), and (18). in this calculation, spherical symmetry is assumed. the distance (k) is taken in km and the value ofcos bfg' ranges between -1 to +1. the radius of neutrino sphere (��) is taken as 10km. figure 1 and 2 shows the variation of distance k with interaction angle. this variation shows the � −oscillation probabilities, as a function of the distance in supernova. the graphs obtained clearly indicate strong � − � interaction atcos bfg' = 0 i.e. bfg' = � 2⁄ where the length of interaction is equals to ��. the possibility of � − � interaction in the range k → ��shows the probability of � −oscillation in the dense core of sn. if the value ofcos bfg' is altered, then we see the length of interaction increases exponentially, and hence the � −oscillation due to � − � interaction will be rare. also when the angle of interaction is about 25˚ or 155˚, the graph indicates free streaming of neutrinos in the form of shock waves. some of the recent study of core collapse supernovae justifies the above conclusion. substituting equation (12) in equation (16) and using simple algebra we obtain, o$k% = ]uvw ^_`am9 [\] ^_`a (18) nakarmi and nakarmi/ bibechana 12 (2015) 89-95: p. 93 when we plot o$k% against kandbfg' , figure 3 and 4 are obtained respectively. the graph thus obtained resembles with the result obtained from figure 1 and 2. the value of o$k% is also varied with varying length and angle. fig. 1: graph between xyz {|}~ along x-axis and distance ~(in km) along y-axis. fig.2: graph between {|}~ $�}���z � �y ��% along x-axis and ~ (in km) along y-axis. fig. 3: graph between ~(in km) along x-axis and �$~% along y-axis. -1 -0.5 0.5 1 20 40 60 80 100 0 1 2 3 4 5 6 0 100 200 300 400 20 40 60 80 100 0.1 0.2 0.3 0.4 nakarmi and nakarmi/ bibechana 12 (2015) 89-95: p. 94 figure 3 shows that at k → �� , neutrinos are trapped due to interaction and the possibility of � −oscillation is high at core of sn. also figure 4 supports the idea of multi-angle effects in � −oscillation due to interaction. as the angle is � 2⁄ , the probability of � −oscillation is maximum, and outside the neutrino core, probability falls exponentially. fig. 4: graph between {|}~ along x-axis and �$~% along y-axis. 6. conclusion a neutrino gas is a highly nonlinear system in which unexpected phenomenon may occur. in core collapse supernova we have observed two types of behavior. there is a self-induced msw effect due to neutrino-neutrino interaction inside the core of supernova (� ≥ 10�� �/ ) and free streaming of neutrinos outside core of supernova in the form of shock waves. the matter induced mixing angle evolved from a value around � 2⁄ to a value near zero. we found that neutrino-neutrino interactions caused the oscillations to remain in phase and decoherence did not occur. this phenomenon took place for a relatively dense system and arouse due to the nonlinear nature of the problem. references [1] l. wolfenstein, phys. rev. d 17 (1978) 2369; 20 (1979) 2634. http://dx.doi.org/10.1103/physrevd.45.1782 [2] s. p. mikheev and a. yu. smirnov, yad. fiz. 42, (1985) 1441. [3] g. raffelt, g. sigl and l. stodolsky phys. rev. d 45 (1992) 1782. [4] a. b. balantekin and g. m. fuller, phys. lett. b 471 (1999) 195 [5] s. p. mikheev and a. y. smirnov, nuovo cimento c (1976) 917. [6] a. b. balantekin and g. m. fuller, j. phys. g: nucl. part. phys. 29 (2003) 2513. [7] sébastien galais, james keneller, and cristina volpe [astro-ph.sr] 26 aug, 2011. 0 1 2 3 4 5 6 -1 -0.5 0 0.5 1 nakarmi and nakarmi/ bibechana 12 (2015) 89-95: p. 95 [8] stuart samuel, phys. rev. d, 48 (1993) 1462-1477. http://dx.doi.org/10.1103/physrevd.48.1462 [9] a. esteban-pertel, s pastor, r. tomas, g. g raffelt, g. sigl, journal of phys. conference series 120 (2008) 052021. [10] a.b. balantekin and y. pehlivan, j. phys. g: nucl. part. phys., 34 (2007) 47-65. http://dx.doi.org/10.1088/0954-3899/34/3/n01 [11] g. raffelt, g. sigl and l. stodolsky, phys. rev. d 45 (1992) 1782. http://dx.doi.org/10.1103/physrevd.45.1782 [12] a. b. balantekin and g.m. fuller, phys. lett. b, 471 (195). piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.38 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal traction and drawbar performance characteristics of power tiller attached cage wheel piyush pradhan1*, ajay verma2, rajesh naik3, prabhat guru4 department of farm machinery and power engineering svcaet & rs faculty of agricultural engineering igkv raipur-492012 chhattisgarh, india *e-mail: piyushpradhan202@gmail.com article history: received 28 july, 2015; accepted 11 august, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13351 abstract the study was carried out in the research farm of indira gandhi agricultural university raipur chhattisgarh in june 2014. to evaluate drawbar and tractive power of 4.85kw of power tiller cultivator attached with two different types of cage wheel of half width (c1) and angle type wheels (c2) for a small power tiller operated in clay soil of wet land and flood condition. it was found that the maximum draft values of c1 and c2 were 1192n and 1039n in flood condition and 1318n and 1225n in wet condition. the results showed that maximum tractive efficiency was for cage wheel c1 and c2 values were 72.91% and 69.86% in puddle soil. the maximum field capacity was 0.084 ha/h for cage wheel c2 in puddle soil. ©rcost: all rights reserved. keywords: draft; tractive efficiency; field capacity; fuel consumption; wheel slippage; cage wheel. 1. introduction power tiller is walking tractor mostly used for rotary cultivation in puddle soil. cage wheel have proved one of the important traction devices for wetland cultivation. physical conditions of the soil in poorly drained paddy fields were also defined to distinguish it from the general wetlands. the efficiency with which a power tiller converts energy into pull is extremely poor when operating on wet soil. the top layer of wet soil has low shear strength so that sufficient thrust cannot be developed [1]. due to the slippage, stickiness and sinkage limit in driving wheel affect the available pull and forward speed of a power tiller. in such situations the middle layer of the soil bears the traffic load of agricultural machinery. studies conducted to test a 7.46 kw power tiller for drawbar pull, fuel consumption and wheel slip by alvi and pandya [2], have revealed low drawbar pull and power and high specific fuel consumption. the testing of http://nepjol.info/index.php/bibechana mailto:piyushpradhan202@gmail.com http://dx.doi.org/10.3126/bibechana.v13i0.13351 piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.39 (online publication: dec., 2015) a 4.10 kw power tiller for drawbar performance with three-bottom mouldboard plough and 5-tyne cultivator, revealed that use of 60 kg ballast weight could develop a maximum pull of 1333.75 n with cage wheels under field conditions [3]. in wet fields, with a hard pan at considerable depth, the utility of agricultural machines is limited due to their bogging down in the soil. verma [4] revealed that cage wheel exerted 3 times more pull in comparison with tyres in flooded soil conditions. in agricultural operations, the effect of the vehicle on the soil is more important than the maximum traction that can be developed. a tractor that develops the desired pull at high efficiency may not be useful if it makes ruts in the soil so severe that subsequent cultural operations are adversely affected. application of a drawbar load improves the performance of lighter tractors on wet soil because it increases the driving axle load by the effect of weight transfer [5]. traction problems in the saturated paddy soils have a major limitation to the adaptation of agricultural mechanization in rice producing asian countries. sinkage of agricultural machinery has been the topic of intensive research in the past and will continue to be in the future. the main problem in mechanizing paddy cultivation is the development of a suitable traction device for operation in the saturated soils. soft soils with low trafficability have resulted in excessive sinkage of agricultural machinery. considerable time and energy are lost in attempting to cultivate in soft soils. because of the extra time necessary to remove sunken machinery from the fields. 2. material and method the experiments were conducted in the indira gandhi krishi vishwavidyalaya research farm raipur in clay soil. two replications were taken for testing each set of cage wheel in wet and puddle soil condition. the average values of soil properties are shown in (table 1). small power tiller of greaves ltd. of 4.85kw engine power were used to test both cage wheels of c1 and c2 (fig.1) attached with five tynes cultivator in wet and puddle soil to comparing the performance of power tiller in terms of tractive efficiency and drawbar pull. the field was prepared by cultivator and rotavator for creating a puddled soil conditions. specification of both cage wheels for testing is given in table 2. for evaluating performance of both cage wheel following points are taken. effective field capacity it is the actual average rate of area covered by the implement. the total time required to complete the operation was recorded and effective field capacity was calculated as follows, actual field capacity (ha⁄h) = a/t where, a = actual area covered, ha. t = total time required to cover an area, hr. piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.40 (online publication: dec., 2015) field efficiency this gives an indication of the time lost in the field and the failure to utilize the full working width of the machine. it is calculated as follows, field efficiency (%) = (effective field capacity) / (theoretical field capacity) ×100 fuel consumption it was measured with fuel fill top-up method. before operating, the tank of power tiller was filled completely with fuel and after the operation was performed, the fuel tank refilled up to same level. the total quantity of fuel needed to refill the fuel tank up to the same mark was recorded and total time was taken in test plot. fig. 1: half width c1 and angle type c2 cage wheel. measurement of draft a loading car was used to measurement of draft of the power tiller. a commercially available proving ring type of load cell with strain gauges (novatech, uk model tr150) with a capacity of 0-4900 n, was used in the loading device for measurement of draft. the two ends of the load cell were mounted through articulated eye joints. the loads on the power tiller were varied by moisture content and were taken in load and no load conditions. the output of the load cell was connected to the digital indicator unit [6]. the indicator unit directly indicated the draft of the power tiller fig 2. piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.41 (online publication: dec., 2015) measurement of drawbar power: for measuring drawbar power is calculated by the following formula. 𝐷𝑝 = 𝑃 × 𝑉 1000 where, dp is a drawbar power (kw) v is the actual forward speed (with load) (m/s), and p is the pull generated (n). tractive efficiency (te) tractive efficiency is defined as output power / input power. it can also be expressed as the product of pull ratio and velocity ratio. from a power tiller drawbar power standpoint, tractive efficiency (te) is the most important of the traction parameters. it measure efficiency, with which the traction device transmit torque, acting on the axle to the linear drawbar pull. t. e. = driving force tractive force = drawbar power axle power fig. 2: measurement of draft of both cage wheel c1 and c2 by load cell. piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.42 (online publication: dec., 2015) axle power = 2ᴫnt 6o × linear speed wheel slip the distance of the power tiller moves in a given number of revolutions of the drive wheel decreases when wheel slip. a simple method of determining the amount of wheel slip is to make a mark on the power tiller drive cage wheel with coloured tapes and the distance of power tiller covered at load and no load. following formula are used to compute wheel slip wheel slip, s = n1 − n2 n1 where, n1 = speed at no load m/s n2 = speed at load m/s puddling index soil water suspension samples volume of 500 ml were collected during puddling from different spots behind the puddling equipment with the help of 1.25 cm diameter steel pipe. the soil water suspension was allowed to settle for 48 hours and the volume of soil settled was recorded. puddling index was determined by the following relationship [7]. puddling index (pi) = vs v x 100 where, vs = volume of settled soil, ml v = total volume of the sample, ml soil sticking it was measured with suitable scale on lug surface of cage wheel during operation in wet and puddle soil fig 3. piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.43 (online publication: dec., 2015) table 1: experimental setup and soil condition. rpm of cage wheel c1 17 rev/min linear speed 0.62 m/s rpm of cage wheel c2 20 rev/min linear speed 0.87m/s clay soil 53% silt 32% sand 15% soil moisture 47% internal friction angle 26.14º fig. 3: sticking of soil on lug surface in puddle and wet soil condition. piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.44 (online publication: dec., 2015) table 2: parameter of cage wheels s.n. angle type c1 half width c2 wheel diameter 600 mm 700 mm wheel width 240 mm 120 mm no of lug 20 8 lug width 200 mm 210mm lug length 50 mm 130 mm lug angle 30º 45º lug thickness 5mm 4mm lug height 50 mm 30 mm 3. result and discussion the experiment was carried out in igkv raipur farm in two replications, where cage wheel c1 and c2 were used to evaluate field performance and tractive performance in wet and puddle soil condition. cage wheels were tested by power tiller attached with five tines of cultivator in the field were investigated for wheel slippage, effective field capacity, and fuel consumption, sinkage, sticking and puddling index. the obtained results are given in table 3. table 3: performance of half width and angle type cage wheel. s. no operation wet condition puddle condition c1 73 cm c2 68 cm c1 73 cm c2 68 cm 1 time of operation (h/ha) 16.66 14.49 13.88 11.90 2 effective width of implement (mm) 1500 1500 1500 1500 3 field capacity (ha/h) 0.06 0.069 0.072 0.084 4 field efficiency % 72 86 68 77 5 working speed 1.04 1.22 1.33 1.58 6 fuel consumption lit/ha 15.36 13.62 11.57 09.83 7 puddling index 23.47 30.91 8 soil sticking in cage wheel (cm) 6.2 4.8 2.92 1. 79 9 sinkage (cm) 9.12 7.29 8.56 6.31 10 wheel slip % 22.37 18.56 16.95 13.43 from the table 3 it was observed that field performance of angle type cage wheel c2 was highest than half width cage wheel c1. maximum time of operation required in wet lad operation in half width cage wheel of 16.66 h for per ha. piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.45 (online publication: dec., 2015) 1. effect of draft on tractive performance and drawbar power of the half width and angle type cage wheel in wet soil the maximum tractive efficiency with minimum wheel slip of the angle type cage wheel (lug size: 200×50 mm2, 30º lug angle and 20 lugs on a wheel) in clay soils were relatively good as compared with the results obtained by half width cage wheel (lug size 210×130 mm2,45º lug angle and 8 lugs). due to 20 lugs and 240 mm wheel width greater interaction of soil and wheel caused more tractive efficiency of angle type cage wheel c2 in wet land was maximum 66.96,62.60, and 60.82 % at 18.56 % wheel slip as compare c1 of attached 8 lugs and wheel width 120 mm produce tractive efficiency with 63.41,59.32 and 56.26 at 22.37% slippage. from this study, it was also revealed that, half width cage wheel c1 of tractive and drawbar performance was poor as compare with angle type cage wheel c2. fig. 4: effect of draft on drawbar power on wet soil. from the fig.4 it was found that as draft and slippage increase the drawbar power also increases. maximum drawbar power was 710.56 w for angle type cage wheel at 1225 n while minimum 635 w at 1270 n draft as given in table 3. 500 550 600 650 700 750 800 1220 1240 1260 1280 1300 1320 1340 d ra w b ar p o w e r (w ) draft (n) half width c1 angle type c2 piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.46 (online publication: dec., 2015) fig 5: effect of draft on tractive efficiency on wet soil. from the fig 5 it was resulted that as the draft increases tractive power increases till a maximum point than further decreases. the maximum tractive efficiency was observed 66.96% with draft 1188 n at 18.56 % slippage for angle type cage wheel c1. it was also revealed from the study that as draft increases, working speed reduced due to increase in sinkage and slippage. the maximum tractive efficiency 63.41 % for half width cage wheel c2 at 1296 n whereas minimum tractive efficiency was observed 53.74% at 1318n draft (table 3). table 3: performance of cage wheel in wet soil. s.no half width cage wheel c1 angle type cage wheel c2 draft (n) drawbar power (w) tractive efficiency (%) draft (n) drawbar power (w) tractive efficiency (%) 1 1270 635 56.26 1162 673.96 60.82 2 1286 643 59.32 1176 682.08 62.60 3 1296 648 63.41 1188 689.04 66.96 4 1310 655 56.02 1207 700.06 58.31 5 1318 659 53.74 1225 710.56 55.44 40 50 60 70 1200 1220 1240 1260 1280 1300 1320 1340 tr ac ti ve e ff ic ie n cy ( % ) draft (n) half width c1 angle type c2 piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.47 (online publication: dec., 2015) table 4: performance of cage wheel in puddle soil. s.no half width cage wheel c1 angle type cage wheel c2 draft (n) drawbar power (w) tractive efficiency (%) draft (n) drawbar power (w) tractive efficiency (%) 1 1130 565 62.12 987 651.42 65.76 2 1148 574 64.53 996 657.36 68.59 3 1166 583 69.86 1011 667.26 72.91 4 1181 590.5 61.29 1024 675.84 63.33 5 1192 596 54.17 1039 664.96 60.73 2. effect of draft on tractive efficiency and drawbar power in puddle soil the increase in soil moisture content caused a decrease in the peak values of pull and lift forces. the peak values of pull and lift forces at 24% soil moisture content were much higher than those at 30, 35 and 44% soil moisture contents [8] from study it was found that increasing moisture content in field drawbar pull decrease but drawbar power efficiency increases because greater interaction of soil and wheel. as increasing of draft up to 1166 n in cage wheel tractive efficiency increases maximum at 69.86% and then further decreases but draft increases continuous increases to 1192 n fig (6&7). minimum tractive efficiency obtained 29.24% at 136 n. keuther [9] concluded in soil bin that the continuous use of machines in flooded field conditions increased the hard pan depth and bogging problems become so serious from the fifth crop season. salokhe [10] studied soil wedge formation on a single lug by conducting experiments in a laboratory soil bin in bangkok clay soil. fig. 6: effect of draft on drawbar power in puddle soil. 400 450 500 550 600 650 700 750 1080 1100 1120 1140 1160 1180 1200 d ra w b ar p o w e r (w ) draft (n) angle type c2 half width c1 piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.48 (online publication: dec., 2015) maximum drawbar 675.84 w was obtained at 1024n draft where tractive efficiency was 63.33%.maximum tractive efficiency was 72.91% at 1011n for angle type cage wheel c2. increasing draft, tractive efficiency increases, but with the increase draft it again falls, fig 7. fig. 7: effect of draft on tractive efficiency on puddle soil. 4. conclusions it was concluded that as increasing the pull of power tiller drawbar power increases in both cage wheel and tractive efficiency increases at point than further decreases. this study showed that increasing the moisture strongly affects the wedge formation over the lug plates of the cage wheel operated on clay soil. references [1] m.s. abubakar, d. ahmad, j. othman, and s. sulaiman, research journal of agriculture and biological sciences, 5(4) (2009) 489-497. [2] s. a. a. alvi and a. c. pandya, the harvester, iit, kharagpur, india, 10 (1) (1968) 51-61. [3] j. s. panwar, s. k. tondan and n. p. s. sirohi, performance evaluation of power machine systems for tillage and traction, annual report, division of agricultural engineering, indian agricultural research institute, new delhi, india, 1984. [4] s. verma, development and testing of refractive lugged cage wheels, asian institute of technology, m. eng thesis no. ae-84–12, 1984 (unpublished). 50 55 60 65 70 75 1080 1100 1120 1140 1160 1180 1200 tr ac ti ve e ff ic ie n cy ( % ) draft (n) half width c1 angle type c2 piyush pradhan et al./ bibechana 13 (2016) 38-49 : rcost p.49 (online publication: dec., 2015) [5] m. j. baloch, b.a. mirani and s. bukhari, agricultural mechanization in asia, africa and latin america, 22(4) (1991) 21-24. [6] suresh narang and a. c. varshney, journal of terramechanics, ( 32) (2) (1995) 91-97. [7] b. baboo, effect of lug angle of cage wheel on traction and puddling performance of dual wheels, m. tech. diss., dept. of farm machinery and power engineering, g. b. pant univ. of agriculture and technology. pantnagar, india, 1976. [8] wawan hermawan, journal of terramechanics, (33) (2) (1996) 91-101. [9] d.o. keuther, soil compaction and wetland rice tillage system, am soc. agric. engrs. paper no. 77-1021, 1977. [10] v. m. salokhe and d.gee-clough j. agric. engg res., 38 (1987) 113-125. jamshad ahamad and ghulam mohiuddin/ bibechana 14 (2017) 30-36 : rcost p.30 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal analytical exact solution of telegraph equation using hpm jamshad ahmad*1 and ghulam mohiuddin2 1department of mathematics, faculty of sciences, university of gujrat, pakistan 2department of mathematics, ncba & e, pakistan *email: jamshadahmadm@gmail.com article history: received 1 march, 2016; accepted 4 august, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15411 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract in this paper, exact solutions of different variants of second order hyperbolic telegraph equation are investigated with homotopy perturbation method (hpm). the results determined by the proposed method are quite satisfactory and shows that hpm technique is very effective and useful for solving the nonlinear partial differential equations (pdes) with given initial or boundary conditions. the proposed iterative scheme finds the solution without any discretization, linearization or restrictive assumptions. keywords: telegraph equation; homotopy perturbation method. 1. introduction hyperbolic pdes are the area of interest of many mathematicians because of their applications in many applied sciences for example wave equation and telegraph equation. the telegraph equation was first introduced by kirchoff in 1857. but it was first examined by poincare in 1893. the telegraph equation has both wave motion and diffusion properties. telegraph equation describes various phenomena in many appliedfields, for example in fluid dynamics it shows the random motion of the particle, travelling of electromagnetic waves in superconducting media and propagation of pressure waves occurring in pulsatile blood flow in arteries [1]. in the last few years, many techniques have been introduced for the exact and numerical solutions of the nonlinear pdes, such as the adm [2], exponential function method [3,4], homotopy analysis method (ham)[5-7] and variational iteration method (vim)[8-10]. http://nepjol.info/index.php/bibechana mailto:jamshadahmadm@gmail.com http://dx.doi.org/10.3126/bibechana.v14i0.154 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ jamshad ahamad and ghulam mohiuddin/ bibechana 14 (2017) 30-36 : rcost p.31 (online publication: dec., 2016) in this work, we use homotopy perturbation method (hpm) for solving hyperbolic telegraph equation. besides from the other techniques, the nonlinear pdes are solved easily and efficiently without transforming or linearizing the equation by using the homotopy perturbation method (hpm) [10]. it gives the solution with great accuracy, less calculations and avoiding of unnecessary assumptions. the hpm was first proposed by he and it is applied to solve a wide class of nonlinear pdes and odes effectively, more easily and much accurately with approximations converging rapidly to accurate solutions. 2. basic idea of homotopy perturbation method (hpm) consider the following non-linear differential equation ,0)()(  rrfua (1) with the boundary conditions of ,0),(    r n u ub (2) where a, b, f(r) and γ are differential operator, boundary operator, known analytic function and the boundary of the domain ω, respectively. the operator a(u) can be divided into a linear part l(u) and a non-linear part n(u). therefore eq.(1) can be rewritten as .0)()()(  rfunul (3) in case the nonlinear eq. (1) has no small parameter, we can construct the following homotopy, .0)]()([)()()(),( 00  rfvnpuplulvlpvh (4) here p is homotopy parameter. according to the homotopy perturbation method, the approximate solution of eq. (4) can be expressed as a series of the power p i.e. u = 𝑙𝑖𝑚 𝑝→1 (uo+pu1+p2u2+p3u3+…). (5) when eq. (4) corresponds to eq. (1), (5) becomes the approximate solution of eq. (1). 3. numerical examples in this section we give some numerical examples to check the efficiency and accuracy of the proposed method by solving some hyperbolic telegraph equation. example 3.1 consider the following hyperbolic telegraph equation ,xxttt uuuu  (6) with the initial conditions .)0,(,)0,( x t x exuexu  (7) according to the above defined procedure, we have ][),( 1 txx xx uuulteetxu   (8) jamshad ahamad and ghulam mohiuddin/ bibechana 14 (2017) 30-36 : rcost p.32 (online publication: dec., 2016)                t xx xx upuppuu upuppuu upuppuu plteeupuppuu ...)( ...)( ...)( ... 3 3 2 2 10 3 3 2 2 10 3 3 2 2 10 1 3 3 2 2 10 equating powers of p xx teetxup ),(, 0 0   x txx e t txu uuultxup !2 ),( )()(),(, 2 1 000 1 1 1      x txx e t txu uuultxup !3 ),( )()(),(, 3 2 111 1 2 2      , !4 ),( )()(),(, 4 3 222 1 3 3  x txx e t txu uuultxup    and so on. the closed form solution is .),( ... !4!3!2 ),( 432 tx xxxxx etxu e t e t e t teetxu   (9) this is the exact solution of the eq. (6) as given by [11]. example 3.2 consider the following telegraph eq. ,2,4     xxttt uuuu (10) with the initial conditions .sin)0,(,sin)0,( xxuxxu t  according to the above defined procedure, we have ],42[sinsin),( 1 txx uuulxtxtxu   (11)                t xx upuppuu upuppuu upuppuu plxtxupuppuu ...)(4 ...)(2 ...)( sinsin... 3 3 2 2 10 3 3 2 2 10 3 3 2 2 10 1 3 3 2 2 10 consequently, xtxtxup sinsin),(, 0 0  jamshad ahamad and ghulam mohiuddin/ bibechana 14 (2017) 30-36 : rcost p.33 (online publication: dec., 2016)            !3 3 !2 sin),( )(42)(),(, 32 1 000 1 1 1 tt xtxu uuultxup txx             !5 9 !4 15 !3 4 sin),( )(42)(),(, 543 2 111 1 2 2 ttt xtxu uuultxup txx and so on. the closed form solution is                     ... !3!2 1sin),( ... !5 9 !4 15 !3 4 sin !3 3 !2 sinsinsin),( 32 54332 tt txtxu ttt x tt xxtxtxu ..sin),( textxu  (12) this is exact solution [11]. example 3.3 consider the following telegraph equations ),,( txfuuuu xxttt   (13) ,1),(,1 2  txtxf with the initial conditions .1),(,),( 2  txuxtxu t (14) according to the above defined procedure, we have  )( !3!2!2 1),( 1 322 2 txx uuull tt t t xtxu         (15)                      tupuppuu upuppuu upuppuu pl tt t t xupuppuu ...)( ...)( ...)( !3!2!2 1... 3 3 2 2 10 3 3 2 2 10 3 3 2 2 10 1 322 2 3 3 2 2 10 equating powers of p jamshad ahamad and ghulam mohiuddin/ bibechana 14 (2017) 30-36 : rcost p.34 (online publication: dec., 2016)        !9!7 3 !6 5 !5 4 !4!8!7 3 !6 4 !5 3 !4 ),( )()(),(, !7!6 3 !5 4 !4 3 !3!6!5 2 !4 2 !3 ),( )()(),(, !5!4 2 !2!4!3!2 ),( )()(),(, !3!2!2 1),(, 9765487654 2 3 222 1 3 3 765436543 2 2 111 1 2 2 542432 2 1 000 1 1 1 322 2 0 0 tttttttttt xtxu uuultxup ttttttttt xtxu uuultxup tttttt xtxu uuultxup tt t t xtxup txx txx txx                                   and so on. the series solution is ... !7!6 3 !5 4 !4 3 !3!5!4 2 !2!3!2!8!7 3 !6 4 !5 3 !4 !6!5 2 !4 2 !3!4!3!2!2 1),( 765435423287654 2 6543 2 432 2 2 2                           tttttttttt t ttttt x tttt x ttt x t xtxu the closed form solution is .),( 2 txtxu  (16) this is the exact solution as given by [11]. example 3.4 consider the following telegraph equation txxtt uuuu 2 (17) with the initial conditions .1)0,(,1)cosh()0,(  xuxxu t (18) according to the above defined procedure, we have  ,21)cosh(),( 1 txx uuultxtxu   (17)                t xx upuppuu upuppuu upuppuu pltxupuppuu ...)( ...)( ...)( 1)cosh(... 3 3 2 2 10 3 3 2 2 10 3 3 2 2 10 1 3 3 2 2 10 consequently, we have jamshad ahamad and ghulam mohiuddin/ bibechana 14 (2017) 30-36 : rcost p.35 (online publication: dec., 2016)   !3!2 ),( )(2)(),(, 1)cosh(),(, 32 1 000 1 1 1 0 0 tt txu uuultxup txtxup txx       !5!4 3 !3 2 ),( )(2)(),(, 543 2 111 1 2 2 ttt txu uuultxup txx      , !7!6 5 !5 8 !4 4 ),( )(2)(),(, 7654 3 222 1 3 3  tttt txu uuultxup txx    and so on. the series solution is        ... !4!3!2 1)cosh(),( 432 ttt txtxu .)cosh(),( textxu  this is exact solution as was found in [12]. 4. conclusion we have applied hpm for calculating the exact solution of second order hyperbolic telegraph equation. the results obtained by this method are quite satisfactory and are in accordance with the other techniques. the results gained through hpm prove that this is a powerful method for finding the exact. references [1] s. y. lai, j. appl. math.. mech. 43(7) (1997) 657-662 [2] g. adomian, solving frontier problems of physics, the decomposition method, kluwer academic publishers, dordrecht, (1994) pp. 372. http://dx.doi.org/10.1007/978-94-015-8289-6 [3] j. he and m. abdou, new periodic solutions for nonlinear evolution equations using exp -function method, chaos, solutions and fractals, 34 (2007) 1421-1429 http://dx.doi.org/10.1016/j.chaos.2006.05.072 [4] q. m. hassan s. t. mohyud-din, exp-function method using modified riemann-liouville derivative for burger's equations of fractional-order. qscience connect: (2013). 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[6] a. molabahrami, f. khani, real world applications 10 (2009) 589-600. http://dx.doi.org/10.1016/j.nonrwa.2007.10.014 http://dx.doi.org/10.1007/978-94-015-8289-6 http://dx.doi.org/10.1007/978-94-015-8289-6 http://dx.doi.org/10.1016/j.chaos.2006.05.072 http://dx.doi.org/10.1016/j.chaos.2006.05.072 http://dx.doi.org/10.1016/j.nonrwa.2007.10.014 jamshad ahamad and ghulam mohiuddin/ bibechana 14 (2017) 30-36 : rcost p.36 (online publication: dec., 2016) [7] a. mastroberardino, common nonlinear science and numerical simulations 16 (2011) 2730-2736. http://dx.doi.org/10.1016/j.cnsns.2010.10.004 [8] j. he, applied mathematics and computations,114 (2000) 115-123. http://dx.doi.org/10.1016/s0096-3003(99)00104-6 [9] l. xu, (guest editors) j. h. he and a.m. wazwaz, journal of computational and applied mathematics,207 (2007) 1-2. http://dx.doi.org/10.1016/j.cam.2006.07.021 [10] m. dehghani et.al, international journal of numerical methods and biomedical engineering, 27 (2011) 219-231. http://dx.doi.org/10.1002/cnm.1293 [11] j. he, international journal of non-linear science and numerical simulation, 135 (2003) 73-79. 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[13] m. rawashdeh, n. a. obeidat, an international journal of applied mathematics & information sciences, 8( 5) (2014) 2171-2176. http://dx.doi.org/10.1016/j.cnsns.2010.10.004 http://dx.doi.org/10.1016/j.cnsns.2010.10.004 http://dx.doi.org/10.1016/s0096-3003(99)00104-6 http://dx.doi.org/10.1016/s0096-3003(99)00104-6 http://dx.doi.org/10.1016/j.cam.2006.07.021 http://dx.doi.org/10.1016/j.cam.2006.07.021 http://dx.doi.org/10.1002/cnm.1293 http://dx.doi.org/10.1002/cnm.1293 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal micellisation behavior on the dodecyltrimethylammonium bromide in the presence of brij-35 in pure water by conductivity measurement neelam shahi, ajaya bhattarai* department of chemistry, m.m.a.m.c., tribhuvan university, biratnagar, nepal. *e-mail: bkajaya@yahoo.com article history: accepted 28 november, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18443 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/bync/4.0/ abstract conductivity measurement of dodecyltrimethylammonium bromide in the presence of brij-35 in aqueous media at 289.15 k is performed. the result showed a sharp increase in conductivity with increase in the concentration of dodecyltrimethylammonium bromide in the presence of brij-35. the graph of specific conductivity versus concentration is used in determining the critical micelle concentration (cmc). there is the decrease in cmc of dodecyltrimethylammonium bromide in the presence of brij-35 in comparison with the cmc of dodecyltrimethyl ammonium bromide [dtab]. gibbs free energy of micellisation has also been evaluated. keywords: dodecyltrimethylammonium bromide; brij-35; conductivity; critical micelle concentration. 1. introduction critical micelle concentrations have been experimentally determined using a number of different methodologies [1,2]. the critical micellar concentration of surfactant in pure water is determined by conductometry method by plotting specific conductance versus surfactant concentration. the data points above and below the inflation were fitted to two linear equation and the curves were obtained from the common intersection. the resolution of cmc indicates self-aggregation of amphiphilic molecules in aqueous media. the idea of cmc plays the significant role during scientific research [3-5]. dtab is a quaternary ammonium cationic surfactant. it has been used in a study assess the distribution of binary mixed counter ions in surfactant adsorbed films. brij-35 is a non-ionic surfactant which is beneficial in uv monitoring of solubilized proteins due to their low uv absorbance. it is a polyglycol ether which functions as a detergent for the isolation of functional cell membrane complexes. different investigation clarifies that brij-35 acts as a surfactant in micellar electrokinetic chromatography(mekc). neelam shahi and ajaya bhattarai / bibechana 15 (2018) 85-89: rcost p.85 http://nepjol.info/index.php/bibechana mailto:bkajaya@yahoo.com http://dx.doi.org/10.3126/bibechana.v15i0.18 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ it is beneficial in slowing down electroosmotic pump which allows users to change ph values without drastically altering the flow rate. the optimization of mixtures of surfactants in aqueous solution is an important part of the formulation of many commercial cleaning products [6]. the mixture of ionic and non-ionic surfactants in pure water exhibit the highly non-ideal behaviour and their behaviour can be complementary to the mixed micelle causing the cmc to decrease [7]. there are many examples in the literature showing that binary mixtures of different types of surfactant are non-ideal in such a way that important properties of the mixture are quite different from those of the individual species [10-12]. in the literature, it is possible to find data concerning the anionic/non-ionic mixtures of two surfaces rather than those of cationic/non-ionic surfactants [2]. 2. experimental thus, the graph was plotted taking specific conductance vs concentration of the surfactant so that cmc was determined. 3. results and discussion the cmc determined using conductivity method is the most reliable and easy method for the investigation. the cmc value obtained for the mixed surfactant (cationic and non-ionic surfactant) in pure water has the significant influence on the cmc value in contrast to the single cationic surfactant. the size and type of structure of the polar head region of the surfactant molecule play a significant role in surfactant’s cmc under different conditions. small ionic heads typically form micelles at higher molar concentrations than surfactants with large nonionic compounds. thus the mixed cationic and non-ionic surfactant have decreased cmc value than single cationic surfactant due to their non-ideal behaviour. thus, the cmc of mixed surfactants in pure water was determined using conductivity method at temperature 289.15 k. the cmc determined is 12.42 mmol/lt obtained from the break in the conductance-concentration profile (fig.1). there is the intersection of two lines having different slopes is identified as cmc. the ratio of slopes i.e., post-micellar slope (s2) to the pre-micellar slope (s1) gives the degree of ionization (α). α = s2/ s1 (1) neelam shahi and ajaya bhattarai / bibechana 15 (2018) 85-89: rcost p.86 further reading of specific conductance was measured by the process of internal dilution [25 ml dtab – 2 ml dtab = 23 ml dtab and adding 2 ml brij-35 solution making 25 ml dtab + brij-35 solution] repeating a process no. of times till the constant reading appeared. the specific conductance of dtab in the presence of brij -35 solution at different concentrations was mentioned in table 1. dtab and brij-35 (merck specialties pvt. ltd., mumbai, india) were dried in an electric oven below their melting points for 1 h and 0.00124 m brij-35 solution was prepared by dissolving 0.3715 gm in 250 ml volumetric flask. 0.0748 m dtab solution was prepared by dissolving 2.3051 gm in 100 ml volumetric flask by using brij 35 solution and 25 ml dtab solution in the presence of brij-35 was taken in a small beaker and specific conductance was measured using conductivity meter (lt-17 e.i. an iso 9001-2000 certified company). cationic surfactants are used as antifungal, antibacterial and antiseptic agents and have attracted recently more attention with reference to their dna and lipids whereas non-ionic surfactants are useful as detergents, solubilizers and emulsifiers [8,9]. s.no. volume of (dtab+brij 35) ml specific conductance(ms/cm) concentration(mol/lt) 1 25 1.46 0.0322 2 25 1.39 0.0298 3 25 1.32 0.0274 4 25 1.26 0.0254 5 25 1.20 0.0234 6 25 1.14 0.0213 7 25 1.08 0.0197 8 25 1.04 0.0181 9 25 1.00 0.0167 10 25 0.97 0.0153 11 25 0.93 0.0141 12 25 0.89 0.0130 13 25 0.85 0.0119 14 25 0.81 0.0110 15 25 0.77 0.0101 16 25 0.73 0.0092 17 25 0.67 0.0081 18 25 0.63 0.0072 19 25 0.57 0.0060 20 25 0.53 0.0052 the cmc value has been calculated for dtab in pure water is 12.68 mmol/lt. it is seen that the cmc value has been decreased in the mixture of cationic and non-ionic surfactant in pure water than the cmc value of cationic surfactant in pure water. on the basis of pseudo-phase separation model [13], standard gibb’s free energy of micellization (∆𝐺m o ) is calculated from the relation ∆𝐺m o = (2 − 𝛼)𝑅𝑇 ln𝑋cmc (2) where r is universal gas constant, t is the temperature and 𝑋cmc is mole fraction of surfactant at cmc. the critical micelle concentration (cmc) of a surfactant is an important physical parameter. when surfactants are present at the concentration above the cmc they can act as emulsifiers, allowing normally immiscible compounds to dissolve in the solvent [1]. neelam shahi and ajaya bhattarai / bibechana 15 (2018) 85-89: rcost p.87 fig1:variation of specific conductivity versus concentration of dtab in the presence of brij-35. table 1: variation of specific conductance versus concentration of dtab in the presence of brij-35. the normally insoluble compound is sequestered in the micelle core, while the head group interacts with the solvent. the cmc value of the mixed surfactants is significantly necessary for further utilization in different modern methods. among them, conductometry method has been adopted for cmc determination for the mixed surfactants. this method is found to be reliable and convenient for the present system because of the significant variations of specific conductivity with surfactant concentration in the preand post-micellar regions which allowed us to draw two unambiguous straight lines above and below the cmc. it is the matter of great concern for further investigation under such mixed surfactant in characterized solvent media for better utilization. the gibbs free energy of micellisation of dodecyltrimethylammonium bromide in the presence of brij-35 is found to be -28.96 kj/mol. according to sharma et.al [2], ∆𝐺m 4. conclusion acknowledgment one of the authors (neelam shahi) is very grateful to associate prof. sitaram gupta (head of the department of chemistry), mahendra morang adarsh multiple campus for providing research facilities. references [1] m. prasad, r. palepu, s. p. moulik, interaction between sodium dodecyl sulfate (sds) and polyvinylpyrrolidone (pvp) investigated with forward and reverse component addition protocols employing tensiometric, conductometric, microcalorimetric, electrokinetic, and dls techniques. colloid polym. sci. 284 (2006 ) 871-878. doi.org/10.1007/s00396-005-1453-8. 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[10] m. bourrel, d. bernard, a. gracra, properties of binary mixtures of anionic and cationic surfactants: micellization and microemulsions. tenside deterg. 21(1984) 311-318. [11] h. hoffmann, g. possneeker, the mixing behavior of surfactants. langmuir 10 (1994) 381-389. doi.org/10.1021/la00014a009. [12] p.m. holland, d. n. rubingh, nonideal multicomponent mixed micelle model. j. phys. chem. 87 (1983)1984-1990. doi.org/10.1021/j100234a030. [13] t. perger, m. bester-rogac, thermodynamics of micelle formation of alkyltrimethylammonium chlorides from high performance electric conductivity measurements. j. colloid interface sci. 313 (2007) 288-295. doi.org/10.1016/j.jcis.2007.04.043. [14] h. maeda, a simple thermodynamic analysis of the stability of ionic/nonionic mixed micelles. colloid interface sci. 172 (1995) 98-105. doi.org/10.1006/jcis.1995.1230. [15] p. mukerjee, fluorocarbon-hydrocarbon interactions in micelles and other lipid assemblies, at interfaces, and in solutions. colloids surf. a 84 (1994) 1-10. doi.org/10.1016/0927-7757(93)02682-5. neelam shahi and ajaya bhattarai / bibechana 15 (2018) 85-89: rcost p.89 http://www.sciencedirect.com/science/article/pii/0927775795032870#! http://www.sciencedirect.com/science/article/pii/0927775795032870#! http://www.sciencedirect.com/science/article/pii/0927775795032870#! http://www.sciencedirect.com/science/article/pii/0927775795032870#! http://www.sciencedirect.com/science/journal/09277757 http://www.sciencedirect.com/science/journal/09277757 https://doi.org/10.1016/0927-7757(95)03287-0 http://www.sciencedirect.com/science/article/pii/s0021979785712301 https://doi.org/10.1006/jcis.1995.1230 https://doi.org/10.1016/0927-7757(93)02682-5 narayan p. chapagain/ bibechana 14 (2017) 1-8 : rcost p.1 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal equatorial ionospheric plasma drifts velocities using radar observations narayan p. chapagain department of physics, patan multiple campus, tribhuvan university, lalitpur, nepal e-mail: npchapagain@gmail.com article history: received 21 may, 2016; accepted 2 august, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15405 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract this study presents the experimental results of the equatorial ionospheric plasma drift zonal velocity obtained from incoherent scatter radar (isr) observations for 6 selective days in 2011 from jicamarca, peru. our results indicate that the daytime drifts are westward with peak values mostly below ~50 m/s, while the night time drifts velocities are eastward, with a maximum value up to 120 m/s at around local midnight hours. the drift velocity decreases during post-midnight hours and starts to reverse westward in early morning hours. our plasma drifts results are in good agreement with results from previous radar studies and other measurement techniques. keywords: equatorial ionosphere, plasma drift, f-region plasma, incoherent scatter radar. 1. introduction the climatology and characteristics of low-latitude f-region plasma drift have been extensively studied over the past few decades using ground-based radar observations, optical measurements, ionosonde, and satellite observations [1, 2, 3, 4, 5, 6, 7, 8]. the previous studies have shown that the night-time zonal plasma drifts in geomagnetically quiet days were eastward while plasma drift during the geomagnetic disturbance days are westward. many of these studies have reported on the geomagnetic zonal motion of large-scale ionospheric depletions, or equatorial plasma bubbles (epbs), and the small-scale irregularities [9, 10, 11, 12]. fejer et al. [12] reported the model results of zonal plasma drift velocity obtained from jicamarca incoherent scatter (isr) radar observations and they investigated that the zonal drifts velocities were westward during the day and eastward during the night-time period. the majority of the information about plasma drifts at equatorial latitudes has come from observations at the jicamarca radio observatory near lima, peru using incoherent scatter radar (isr) at 50 mhz [1, 3, narayan p. chapagain/ bibechana 14 (2017) 1-8 : rcost p.2 (online publication: dec., 2016) 12]. the primary goal of this on-going study is to address the zonal plasma drift velocity using the database available from jicamarca isr observations from the data recorded in 2011. incoherent scatter radar (isr) radar techniques have been used since the beginning of the space age in the 1950s to study the ionosphere [13]. incoherent scatter radar is a very powerful ground-based remote sensing technique that can be used to measure many ionospheric parameters including density and temperature of the electrons and ions and line-of-sight ion flow velocity, as well as some of the properties and behaviour of the neutral atmosphere. it can also observe both sides of the peak electron density region simultaneously. it has a larger antenna relative to the radio wavelength and hence, it produces a narrow beam and achieves far better resolution. as incoherent radar scatter has to work with very weak signals, which requires a high power transmitter, a large antenna and the most sensitive receiver and sophisticated data processing available. this can be observed in very powerful radars such as jicamarca radio observatory in peru and arecibo observatory in puerto rico. the physical basis of the incoherent radar technique is thomson scattering in which the echo is the result of the scattering of electromagnetic energy radiated by the radar and reflected by electrons in the ionospheric plasma. incoherent radars transmit a radar signal and receive a reflected echo from the ionosphere. isrs’ usually emit at a frequency of a few hundred mhz up to ~1200 mhz [14], which is much higher than the peak plasma frequency. since the frequencies used by isr are much higher than the plasma frequency, almost the entire transmitted signal passes through the ionosphere and out into space. therefore, isr can probe the ionosphere above the f-region peak. the transmitted signals are emitted in pulses so the distance of the echoing region (altitude) can be calculated from the delay time and the speed of light. however, there is a very small amount of the transmitted signal that gets reflected by the ionosphere and is received back to the radar. it is the spectrum of this received signal that contains the information about the ionospheric region being investigated. overviews of this technique have been presented by several authors [14]. thermal backscatter level is the source of the isr echoes often used to determine ionospheric parameters. this method requires a minimum plasma density in the scattering volume determined by the system noise, antenna size, transmitter power, integration time etc. for the jicamarca radio observatory, this minimum is ~104 cm-3. this limitation usually prohibits measurements at night in the altitude range below the f peak. 2. measurement techniques the jicamarca radio observatory (jro) is in the equatorial region of the western hemisphere and was established in 1961 at lima, peru (12˚s, 76.9˚w, dip latitude ~1˚n). the basic procedure for measuring f region drifts at jicamarca was described in detail by woodman [1]. here we have explained briefly that jicamarca september 14, 2005 narayan p. chapagain/ bibechana 14 (2017) 1-8 : rcost p.3 (online publication: dec., 2016) the large 50 mhz antenna is split into two beams perpendicular to the geomagnetic field and pointed about 2.5° to the east and 4.3° to the west of vertical, giving a net split of about 6.8°. these line-of-sight drifts are combined to give the vertical and zonal drift components. the measurements were usually made from about 200 to 900 km with a resolution of about 15 km, and an integration time of about 5 min. the data used in this study correspond to averages near the f region peak (typically between about 300 and 500 km), where they do not change much with altitude, and the signal-to-noise ratios are highest. reliable drift measurements are not possible during periods of spread f occurrence over a large range of altitudes. figure 1 shows an example of radar echo measured by isr from jicamarca on september 14, 2005. the figure indicates three nicely developed plumes with quasi-periodic equatorial spread f (esf) structure on its bottom. the altitudinal resolution was 25-40 km with an integration time of 5 min. in this paper, we use extensive f-region isr data from jicamarca to investigate the night-time zonal drift velocities. these velocities were calculated at altitude range of ~ 300-400 km, where signal-to-noise ratio is large. fig. 1: an example of radar echo obtained from jicamarca incoherent scatter radar observation on september 14, 2005. in this study, we use selected days from data recorded by the jicamarca incoherent scatter radar observations in 2011. since the isr requires high power transmitter, its running cost is very expensive. so the observations from isr are recorded for a few days. the data presented in this paper are for 6 selective days from many observations, which give the overall trends of the plasma drifts velocity obtained over this region. 3. results and discussion we have studied the diurnal variations of plasma drifts zonal velocities from jicamarca isr observations. figure 1 shows the zonal plasma drift velocity as a function of local time (lt) over jicamarca, peru on narayan p. chapagain/ bibechana 14 (2017) 1-8 : rcost p.4 (online publication: dec., 2016) 01-02 and 03-04 august 2011. the solid curves represent the plasma drifts zonal velocities, while vertical bars denote the standard deviations in the measurement uncertainty at that time. fig. 2: plasma drift zonal velocities using incoherent scatter radar observations obtained from jicamarca radar observatory on 01-02 and 03-04 august 2011. in the plot, positive values correspond to eastward drifts, while negative values denote the westward motions of the plasma drifts. in the first plot (august 01-02), initially, the drift velocity is almost zero at about 09:00 lt (day time) and then the drift motion is in westward, which increases as time progresses and then peaks to about 50 m/s at around 12:00-13:00 lt. the drift velocity gradually decreases in magnitude and finally reverses eastward at ~16:00 and ~19:00 lt, around the sunset time. the eastward velocity gradually increases as the night progresses and finally becomes maximum value of about 120 m/s at around local midnight (00:00 lt). the velocity then decreases in the post midnight hours and again starts to reverse westward in early morning (at around 07:00 lt). on the second plot of figure 2, the daytime plasma drift velocity is westward, which reverse eastward at around 15:00-16:00 lt. however, the data are discontinuous between 20:00 lt and local midnight, which does not represent actual trend of the plasma drift velocity. in the post midnight period, the results also show similar trends of variations of plasma drifts as plotted on august 01-02. in this case, the peak drift velocity is also ~120 m/s at just right after the local midnight. the drift velocity again reverses westward in the early morning hours at ~07:00 lt with similar trends to the first plot. figure 3 also shows the local time variations of the average zonal drifts velocity on august 04-05 and 0708. similar to previous plots, the daytime plasma drift velocity is westward, while the nighttime drift velocity is eastward. the magnitude of westward velocity is about 50 m/s in the first plot and it is quiet narayan p. chapagain/ bibechana 14 (2017) 1-8 : rcost p.5 (online publication: dec., 2016) large in the second plot increasing up to ~100 m/s. in both plots, the magnitudes of eastward drifts velocities are larger than that of westward drifts. the trends of plasma drifts zonal velocities are similar to the other previous results reported by fejer et al. and chapagain et al. [3,4]. fig. 3: plasma drifts zonal velocities using incoherent scatter radar observations obtained from jicamarca radar observatory on 04-05 and 07-08 august 2011. fig. 4: plasma drift velocities using incoherent scatter radar observations obtained from jicamarca radar observatory on 10-11 june and 30 november 01 december 2011. similarly, figure 4 shows the plasma drifts zonal velocities on june 10-11 and november 30december 01, 2011. both plots show the westward motions during the day and eastward during night -time period in which the magnitudes of eastward motions are larger than that of the westward motions. in first plot, narayan p. chapagain/ bibechana 14 (2017) 1-8 : rcost p.6 (online publication: dec., 2016) the data are not available after ~ 22:00 lt, while in the second plot, the data are discontinuous around 19:00 lt to midnight hours. similar trend of variations of the plasma drift velocities as a function of local time has been observed as in other plots. the results presented above reveal a significant day-to-day variability in magnitudes of the plasma drift zonal velocities, however, the trends of the variations with the local time is similar. the plots as explained above (figure 24), show that daytime plasma drifts are westward, while the night-time drifts are eastward, which is consistent with the previous results [3, 4, 12, 15]. similarly, increase in the plasma drifts has been seen shortly after sunset (see in figures 2-4) as the drift reverses from westward to eastward from the day to night transition. it is also noted that the eastward zonal drifts are much larger than the westward drifts. these results are good consistent with the previous experimental results [3] and the model results as well [12]. the zonal drifts have a large eastward peak (up to 120 m/s) near local midnight, and then gradually decrease during the post-midnight period. fejer et al. [3] reported that jicamarca plasma zonal drifts are westward during the day with typical values of about 40 m/s, and they do not change much with altitude, season, and solar activity. they also found that the night-time zonal drifts are eastward near the f –region peak with maximum values of about 100 and 150 m/s near solar minimum and maximum, respectively. these drifts are largest at about 2100–2200 local time, and they decrease toward dawn. our results are in moderate solar flux conditions, which is very good consist with the results reported by fejer et al. [3] and sobral et al. [16]. the daytime westward and night-time eastward zonal drifts are due to the upward vertical electric fields during the day and the downward fields during the night-time period, respectively [17, 18, 19]. 4. summary we have studied the trends of equatorial ionospheric plasma drifts zonal velocities using jicamarca incoherent scatter observations for selective 6 days from many observations recorded in 2011. our results indicate that the daytime drifts are westward with peak values mostly below ~50 m/s. on the other hand, the night time drifts velocities are eastward, which gradually increases with the night progresses and finally becomes maximum value of about 120 m/s at around local midnight hours. the velocity then decreases during post-midnight hours and again starts to reverse westward in dawn. our plasma drifts results are in good agreement with results from previous radar studies and other measurement techniques. the day-time westward and night-time eastward zonal drifts are due to the development of upward vertical electric fields during the day time and the downward fields during the night-time period, respectively. the more research work needs to be done to investigate the actual physical process involved on these phenomena. acknowledgement i would like to thank the team of the jicamarca radio observatory, peru for providing the data for this study. narayan p. chapagain/ bibechana 14 (2017) 1-8 : rcost p.7 (online publication: dec., 2016) references [1] r. f. woodman and c. lahoz, j. geophys. res., 81 (1976) 5447–5466. http://dx.doi.org/10.1029/ja081i031p05447 [2] m. mendillo and j. baumgardner, j. geophys. res., 87 (1982) 7641–7652. http://dx.doi.org/10.1029/ja087ia09p07641 [3] b. g. fejer, e. r. de paula, s. a. gonzalez, and r. f. woodman, j. geophys. res., 96 (a8) 13 (1991). 901–13,906. http://dx.doi.org/10.1029/91ja01171 [4] n. p. chapagain, m. j. taylor, and j. v. eccles, j. geophys. res., 116 (2011) a02301. http://dx.doi.org/10.1029/2010ja015958 [5] n. p. chapagain journal of institute of science and technology, tribhuvan university, 20(2) (2015) 84-89. 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[15] t. j. immel, h. u. frey, s. b. mende, and e. sagawa, ann. geophys., 22 (2004) 30993107. http://dx.doi.org/10.5194/angeo-22-3099-2004 [16] j. h. a. sobral et al., j. geophys. res., 114 (2009) a04309. http://dx.doi.org/10.1029/2008ja013896 narayan p. chapagain/ bibechana 14 (2017) 1-8 : rcost p.8 (online publication: dec., 2016) [17] j. v. eccles, j. geophys. res., 103 (a11) (1998) 26699-26708. http://dx.doi.org/10.1029/98ja02657 [18] j. v eccles, n. maynard, and g. wilson, j. geophys. res.,104 (a12(1999) 28133-28143. [19] h. rishbeth, journal of atmospheric and solar-terrestrial physics, 59 (1997) 1873–1880. http://dx.doi.org/10.1016/s1364-6826(97)00005-9 ajaya bhattarai et al. / bibechana 13 (2016) 114-120: rcost p. 114 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal micellization behavior of mixed surfactants in pure water and methanol-water mixed solvent media by density methods ajaya bhattarai*, kavita pathak, bikash dev department of chemistry, m.m.a.m.c., tribhuvan university, biratnagar, nepal * e-mail: bkajaya@yahoo.com article history: received 11 september, 2015; accepted 20 november, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13887 abstract the properties of anionic-rich and cationic-rich mixtures of dodecyltrimethylammonium bromide (dtab) and sodium dodecylsulfate (sds) in pure water and methanol-water mixed solvent media were studied using density measurements at room temperature. the results showed that density increases with increasing concentration of surfactant mixture over the entire concentration range investigated in pure water and in the given mixed solvent media and which are found to decrease with an increase in the volume fraction of methanol in the solvent composition. the critical micelle concentration increases with the increase in volume fraction of methanol for both the anionic-rich (sds-dtab) and cationic-rich (dtab-sds) systems. k ©rcost: all rights reserved. keywords: mixed solvent; dodecyltrimethylammonium bromide; sodium dodecylsulfate; density; critical micelle concentration. 1. introduction mixed surfactant systems are much favored from the view point of economy and performance. they are less expensive than isomerically pure surfactants. the latter often arises from the deliberate formulation of mixtures of different surfactant type to exploit the synergistic behavior in mixed systems or to provide qualitatively different types of performance in a single formulation. the performance of mixed surfactant systems is often superior to that of a single surfactant system. the practical formulations often require the addition of surfactant additives to help control the physical properties of the product or improve its stability. different surfactants are often deliberately mixed to provide enhanced performance [1]. the optimization of mixtures of surfactants in aqueous solution is an important part of the formulation of many commercial cleaning products [2]. hence, it is essential to understand how surfactants interact in mixtures [3]. the mixed surfactant systems often show synergistic behavior, resulting in reduction of the ajaya bhattarai et al. / bibechana 13 (2016) 114-120: rcost p. 115 (online publication: dec., 2015) total amount of surfactant used in a particular application, which in turn reduces both cost and environmental impact. it was reported that the physical properties of the mixed surfactant systems such as critical micelle concentration (cmc) are often substantially lower than that expected based on the properties of pure components due to the synergistic behavior [4]. especially mixing of the two surfactant ions of opposite charge, cationic/anionic surfactant mixtures exhibits largest synergistic effects while it seems to be negligible for mixtures of nonionic surfactants. there is physically simple explanation for enhanced synergism in such mixed charge systems. the basic idea is the hydrophobicity of the salts formed by the strong interactions between two different surfactants with opposite charge [5-6]. since the properties of surfactant solutions change markedly when micelle formation occurs, many investigations have been focused on determining the values of the cmc in various systems and many studies have been carried out to elucidate the factors that determine the cmc value at which micelle formation becomes significant, especially in aqueous media. the most important factor known to affect the cmc in aqueous solution is the structure of the surfactant [7]. there is little work in the literature dealing with the solution properties of binary mixtures of anionic (sodium dodceylsulfate) and cationic (dodecyltrimethylammonium bromide) surfactants and few works has been done on the effect of medium [8-9]. among various physical parameters, densities have been recognized as the quantities that are sensitive to structural changes occurring in solution [10]. in this article, the results are reported for density measurements and critical micelle concentration have been calculated for anionic-rich (sds in the presence of dtab) and cationic-rich (dtab in the presence of sds) mixtures in pure water and methanol-water mixed solvent media at room temperature (20 0c). the aim of this research work is to analyze the influence of concentration and solvent composition on the micellization behavior of mixed surfactants in pure water and methanol-water mixed solvent media. 2. experimental methanol (e. merck, india, 99% pure) was first distilled with phosphorous pentoxide and then redistilled over calcium hydride. the purified solvent had a density of 0.7772 g.cm-3 and a coefficient of viscosity of 0.4742 mpa.s at 308.15 k. these values are in good agreement with those found in the literature [11].triply distilled water with a specific conductance lower than 10-6 s.cm-1 at 308.15 k was used for the preparation of the mixed solvents. dtab was purchased from loba chemie private limited, mumbai, india. dtab was recrystallized several times until no minimum in the surface tension-concentration plot was observed and its critical micellar concentration (cmc) agreed with the literature value [12]. sodium dodecylsulfate was purchased from merck specialties private limited, india. it was recrystallized several times for purification. a minimum in the surface tension-concentration plot was observed. the aqueous solutions of the purified and unpurified samples of sodium dodecylsulfate exhibited a minimum in the surface tension versus log c plot (where c is the concentration of sodium dodecylsulfate). the ajaya bhattarai et al. / bibechana 13 (2016) 114-120: rcost p. 116 (online publication: dec., 2015) minimum in the γ versus log c plot for sodium dodecylsulfate is considered to be due to the presence of highly surface-active dodecyl alcohol molecules [13]. dodecyl alcohol may be present as an impurity in the supplied sample of sodium dodecylsulfate or may be produced in the sodium dodecylsulfate solution by hydrolysis. the cmc of sodium dodecylsulfate is taken to be the concentration of sodium dodecylsulfate corresponding to the minimum in the γ versus log c plot and is equal to 8.10 mmol.kg−1 in the absence of any added electrolyte at 25 °c. this value is in good agreement with the cmc of sodium dodecylsulfate obtained from conductance measurements (8.10 mmol.kg−1) previously [14]. for the measurement of density in cases of both anionic-rich (sds-dtab) and cationic-rich (dtabsds) solution, was performed using a kruss k20s force tensiometer purchased from germany, which was funded by third world academy of sciences(twas), italy at room temperature (20 °c). the tensiometer was calibrated against distilled water, the holder for the density probe and the probe itself was thoroughly cleaned with distilled water, acetone and kept for a while to natural dry before each measurement. to measure the density, holder was hung vertically; the clean density body (i.e. probe) was attached to the holder and waited until the holder along with the density body no longer moved. the weight of the density body was determined in air, immediately after that the density body was removed from the holder. again, the vertically hung holder was dipped into the solution up to the yoke and pressed the tare to tare the weight of the holder in the liquid. the sample stage was moved downward and the weight to the holder was attached with the help of tweezers. then the holder with the density body was dipped in the solution to exactly the same depth as during the taring process and the liquid had come to rest. finally, the density of the solution was measured and noted. for every measurement, sample solution was stirred with a magnetic stirrer and then the stirring of the sample was continued for 3 minutes in order to make the homogenous solution. similar procedures were followed for the measurement of densities for both anionic and cationic rich mixtures having different concentrations and several readings were noted. 3. results and discussion the densities for anionic-rich (sds in the presence of dtab) and cationic-rich (dtab in the presence of sds) mixtures in pure water and in three different methanol-water mixtures (containing 0.10, 0.20 and 0.30 volume fraction of methanol) at room temperature (20 °c) are depicted in figures 1-2. it is evident that density exhibits almost increase with increasing concentration of anionic-rich (sds-dtab) and cationic-rich (dtab-sds) solutions as shown in figs 1a and 1b. in fact, the variation of density with mixed surfactant concentrations is always found to be linear in higher concentration range and such trend was also observed previously [9] whereas in the lower concentration range, a break can be seen with the decreasing pattern in densities. it is also observed that densities decreases gradually with the increase of methanol content for the studied methanol-water mixed solvent system. ajaya bhattarai et al. / bibechana 13 (2016) 114-120: rcost p. 117 (online publication: dec., 2015) fig. 1a: concentration dependence of density for anionic-rich mixtures (sds in the presence of dtab) at room temperature, in pure water (open circles) and different methanol-water mixtures (closed squares, 0.10 volume fraction of methanol; open triangles, 0.20 volume fraction of methanol; open squares, 0.30 volume fraction of methanol). fig. 1b: concentration dependence of density for cationic-rich mixtures (dtab in the presence of sds) at room temperature, in pure water (open circles) and different methanolwater mixtures (closed squares, 0.10 volume fraction of methanol; open triangles, 0.20 volume fraction of methanol; open squares, 0.30 volume fraction of methanol). estimation of the slope leads to an important insight as to the solution behavior of anionic-rich (sdsdtab) and cationic-rich (dtab-sds) mixtures. however, below the cmc, concentration of the mixed surfactants decreases along with the density having slopes, intercepts and correlation coefficients as shown in tables 1 and 2: table 1: the experimental slopes, intercepts and correlation coefficients of fits (as r2) of anionic-rich system (sds in the presence of dtab) from figure (1a) in pure water and methanol-water mixtures. volume fraction of methanol slope intercept r2 0 1.45 0.990 1.00 0.1 1.37 0.977 1.00 0.2 1.25 0.965 1.00 0.3 1.06 0.952 1.00 0.95 0.96 0.97 0.98 0.99 1.00 0.01 cs (mol.lt-1)  (g /m l) 0.95 0.96 0.97 0.98 0.99 1.00 0.008 0.018 0.028 cs(mol.lt-1)  (g /m l) ajaya bhattarai et al. / bibechana 13 (2016) 114-120: rcost p. 118 (online publication: dec., 2015) table 2: the experimental slopes, intercepts and correlation coefficients of fits (as r2) of cationic-rich system (dtab in the presence of sds) from figure (1b) in pure water and methanol-water mixtures. volume fraction of methanol slope intercept r2 0 0.601 0.989 1.00 0.1 0.537 0.976 1.00 0.2 0.412 0.966 1.00 0.3 0.316 0.955 1.00 the possible explanation for the positive slopes in the present mixed solvent media may be that the counterion binding would become quite appreciable in these media as the concentration of the surfactant is increased, thereby weaker ion-solvent interactions. as a consequence, contraction of the solvent would be gradually lowered with increasing concentration of the surfactant, resulting in a net positive volume change per mole of the added surfactant. there are several methods to obtain the critical micelle concentration. we found very less literature [7, 15-16] regarding the calculation of the cmc from the density measurement. the intersection between the two straight lines gives the cmc. bhattarai et. al [9] only measured densities at a higher concentration range of ctab and sds system in pure water and methanol water mixed solvent media but the cmc has not been calculated. while here, in our case new improvement has been done by measuring density in both higher and lower concentration range of mixed surfactants and the cmc has been calculated (fig 2) and the cmcs are found to be increased for both the anionic-rich and cationic-rich mixtures by the addition of methanol in pure water. harkot and janczuk [7] carried out density measurement and calculated the cmc of two cationic surfactants: (dodecylethyldimethylammonium bromide and benzyldimethyldodecylammonium bromide) in aqueous solutions. gonzalez-perez et. al [16] studied the micellar properties of octyldimethylbenzylammonium bromide in aqueous solution by density measurement at different temperatures. as alcohol is added to a surfactant mixture solution, the dielectric constant and degree of structuring of the solvent is lowered. as more alcohol is added, this process continues and the micelles expand, hence leading to an increased cmc. it can also be seen that cmc increases with the increasing methanol content for both the anionic-rich and cationic-rich mixtures of water and methanol-water mixed solvent media as tabulated in table 3. ajaya bhattarai et al. / bibechana 13 (2016) 114-120: rcost p. 119 (online publication: dec., 2015) fig. 2a : representative figure of concentration dependence of density for anionic-rich surfactant mixture (sds in the presence of dtab) in 0.20 volume fraction of methanol at room temperature: for critical micelle concentration (cmc) calculation. fig. 2b: representative figure of concentration dependence of density for cationic-rich surfactant mixture (dtab in the presence of sds) in 0.20 volume fraction of methanol at room temperature: for critical micelle concentration (cmc) calculation. table 3: the critical micelle concentration (cmc) for both the anionic-rich (sds-dtab) system and cationic-rich (dtab-sds) system obtained from density measurements in pure water and in methanolwater mixed solvent media containing 0.10, 0.20 and 0.30 volume fractions of methanol. anionic-rich (sds in the presence of dtab) cationic-rich (dtab in the presence of sds) volume fraction of methanol cmc(mmol/lt) cmc(mmol/lt) 0 5.79 13.31 0.1 6.63 14.89 0.2 6.80 16.21 0.3 7.24 17.34 0.95 0.96 0.97 0.98 0.99 1.00 0.01 cmc = 6.80mmol/lt cs(mol.lt-1)  (g /m l) 0.95 0.96 0.97 0.98 0.99 1.00 0.008 0.018 0.028 cmc = 16.21mmol/lt  cs(mol/lt-1)  (g /m l) ajaya bhattarai et al. / bibechana 13 (2016) 114-120: rcost p. 120 (online publication: dec., 2015) 4. conclusions the experimental results of the density of anionic-rich (sds in the presence of dtab) and cationic-rich (dtab in the presence of sds) mixtures of pure water and methanol-water mixed solvent media have been presented as a function of the concentration of surfactants. the densities are found to be almost linear in higher concentration range while, a break is seen in the lower concentration range which results decrease in densities. also, densities gradually decrease with an increase in the volume fraction of methanol for both the anionic-rich and cationic-rich mixtures in a given mixed solvent medium. after cmc, visible slopes were observed and they followed the decreasing trend for both the sds/dtab and dtab/sds systems. estimation of slopes and intercepts provides a pertinent view regarding the solution behavior of mixed surfactants in methanol-water mixtures. the cmcs are found to be increased with the increase in volume fraction of methanol for both the anionic-rich (sds-dtab) and cationic-rich (dtabsds) systems. acknowledgments authors are thankful for the twas research grants program for third world academy of sciences (twas), italy in providing funds for purchasing kruss k20s force tensiometer, germany which helps to measure the density on this work. references [1] j. penfold, e. staples, i. tucker, j. phys. chem. b., 106 (2002) 8891. [2] j.d. hines, r.k. thomas, p.r. garrett, g.k. rennie, j. penfold, j. phys. chem. b., 101 (1997) 9215. [3] p.m. holland, d.n.roubingh, mixed surfactant systems, am. chem. soc., washington, dc 1992. [4] p.parekh, d.varade, j. parikh, p. bahadur, colloids and surfaces a: physicochemical and engineering aspects., 385 (2011) 111. [5] m.j. rosen, x.y. hua, j. am. oil. chem. soc., 59 (1982) 582. [6] e.h. lucassen-reynders, j. lucassen, d. giles, j. colloid interface sci., 81 (1981) 150. [7] j. harkot, b. janczuk, j. colloid interface sci., 330 (2009) 467. [8] v.tomasic, i. stefanic, n. filipovic-vincekovic, colloid. polym.sci., 277 (1999) 153. [9] a. bhattarai, s.k. chatterjee, t.p. niraula, springerplus., 2 (2013) 280. [10] m.f. hossain, t.k. biswas, m.n. islam, m.e. huque, monatsh chem., 141 (2010) 1297. [11] a.bhattarai, p. nandi, b. das, j. polym. res., 13 (2006) 475. [12] m.l.moya, a. rodriguez,m.d.m.graciani, g. fernandez, j. colloid interface sci.,316 (2007) 787. [13] s.lin, y. lin, e. chen, c. hsu, c. kwan,langmuir., 15 (1999) 4370. [14] i.m. umlong, k. ismail,colloids & surf. a. phy. chem. eng. aspects., 299(2007) 8. [15] m. usman, a. khan, m. siddiq, j. chem. soc. pak., 31 (2009) 221. [16] a. gonzalez-perez, j. czapkiewicz, j. l. del castillo, j. r. rodriguez., colloid. polym. sci., 281 (2003) 556. bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal on contact conformal curvature tensor in lp-sasakian manifolds riddhi jung shah department of mathematics, janata campus, nepal sanskrit university, dang, nepal. *email: shahrjgeo@gmail.com article history: received 01 february, 2017; accepted 27 october , 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.16507 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the purpose of the present paper is to study the contact conformal curvature tensor in lp-sasakian manifolds. some properties of contact conformally flat,  -contact conformally flat and contact conformally semi-symmetric lp-sasakian manifolds are obtained. keywords: contact conformal curvature tensor; lp-sasakian manifold;  -einstein manifold. 1. introduction the contact conformal curvature tensor is a curvature like tensor defined on a contact metric manifold which is constructed from the conformal curvature tensor by using the boothby-wang's fibration [1]. jeong, lee and pak [2] defined the contact conformal curvature tensor on  12 n -dimensional sasakian manifolds and proved that it is invariant under d-homothetic deformation. they also proved that a sasakian manifold  212  nm n with vanishing contact conformal curvature tensor field is of constant  -homothetic sectional curvature    .1/]13[  nnnnr pak and shin [3] gave a geometric characterization of a contact metric manifold with vanishing contact conformal curvature tensor by showing that for ,2n every  12 n -dimensional contact metric manifold with vanishing contact conformal curvature tensor is a sasakian space form. bang and kye [4] studied contact conformal curvature tensor on 3-dimensional sasakian manifolds and gave a partial extension of pak and shin's result to 3-dimensional locally  -symmetric contact metric manifold and also showed that the contact conformal curvature tensor on 3-dimensional sasakian manifold always vanishes. on the other hand, matsumoto [5] introduced the notion of lorentzian para-sasakian manifold. then mihai and rosca [6] introduced the same notion independently and obtained many results on this manifold. lorentzian para-sasakian manifolds have also been studied by matsumoto and mihai [7], de et al. [8], shaikh and biswas [9] and bagewadi et al. [10]. 2. preliminaries a differentiable manifold of dimension  12 n is called lorentzian para-sasakian manifold (briefly, lpsasakian manifold) if it admits a (1, 1) tensor field , a contravariant vector field , a 1-form  and a lorentzian metric g which satisfy riddhi jung shah / bibechana 15 (2018) 24-29: rcost p.24 http://nepjol.info/index.php/bibechana mailto:shahrjgeo@gmail.com http://dx.doi.org/10.3126/bibechana.v15i0.16507 https://creativecommons.org/licenses/by-nc/4.0/ (2.1)       ,,1 2  xxx  (2.2)        ,,, yxyxgyxg   (2.3)    ,, xxg   (2.4) ,x x   (2.5)           ,2,  yxxyyxgy x  where  denotes the covariant differentiation with respect to the lorentzian metric g [5,7]. in an lp-sasakian manifold it can be easily seen that; (2.6) .2rank,0,0 n   if we put (2.7)    ,,, yxgyx  for any vector fields x and ,y then the tensor field  yx , is a symmetric (0, 2) tensor field [5]. also since the 1-form  is closed in an lp-sasakian manifold we have (2.8)            ,0,,,,,   xyxgyxgyxy x for any vector fields x and y [5,9]. an lp-sasakian manifold m is said to be  -einstein if its ricci tensor s of type (0, 2) is of the form (2.9)        ,,, yxbyxagyxs  for any vector fields x and ,y where ba, are smooth functions on the manifold. in particular, if ,0b then the manifold is said to be an einstein manifold. in a  12 n -dimensional lp-sasakian manifold the following relations hold: (2.10)           ,,,, yzxgxzygzyxr   (2.11)       ,,, xyyxgyxr   (2.12)       ,, yxxyyxr   (2.13)     ,,  xxxr  (2.14)    ,2, xnxs   (2.15)        ,2,, yxnyxsyxs   for any vector fields yx , and ,z where r and s are the riemannian curvature tensor and ricci tensor of the manifold, respectively [8, 9]. in a  12 n -dimensional lp-sasakian manifold the contact conformal curvature tensor 0 c of type (1, 3) is defined by [2] can be written as (2.16)                                                                                     },,, }{ 2 23 254{ 12 1 }, ,}{ 2 23 2{ 12 1 },2 ,,}{ 2 2 22{ 12 1 },2,2, ,,, ,,, ,,,{ 2 1 ,, 2 2 0        zxgyzygxyzx xzy n rn nn nn yzxg xzyg n rn n nn zyxg yzxgxzyg n rn nn nn zyxszqyxgxqzyg yqzxgxzysyzxsqxzy qyzxzysxzxsyqyzxg qxzygyzxsxzys n zyxrzyxc                   riddhi jung shah / bibechana 15 (2018) 24-29: rcost p.25 where qsr ,, and r denote the curvature tensor, the ricci tensor, the ricci operator and the scalar curvature, respectively. definition 2.1 a  12 n -dimensional lp-sasakian manifold m is said to be contact conformally flat if the condition (2.17)   0, 0 zyxc holds. definition 2.2 a  12 n -dimensional lp-sasakian manifold m is said to be  -contact conformally flat if (2.18)   .0, 0 yxc definition 2.3 a riemannian or pseudo-riemannian manifold is said to be semi-symmetric if the condition (2.19)   0., ryxr holds, where  yxr , denotes the derivation in the tensor algebra at each point of the manifold. definition 2.4 a  12 n -dimensional lp-sasakian manifold m is said to be contact conformally semi-symmetric if (2.20)   .0., 0 cyxr 3. results and discussion we prove the following results which are related with above definitions theorem 3.1 a contact conformally flat lp-sasakian manifold m of dimension  12 n is an  einstein manifold. proof: let us consider a contact conformally flat lp-sasakian manifold ,m then (2.17) holds and from (2.16) we have (3.1)                                                                                   }.,, }{ 2 23 254{ 12 1 }, ,}{ 2 23 2{ 12 1 },2 ,,}{ 2 2 22{ 12 1 },2,2, ,,, ,,, ,,,{ 2 1 ,0 2 2        zxgyzygxyzx xzy n rn nn nn yzxg xzyg n rn n nn zyxg yzxgxzyg n rn nn nn zyxszqyxgxqzyg yqzxgxzysyzxsqxzy qyzxzysxzxsyqyzxg qxzygyzxsxzys n zyxr                   taking inner product on both sides of (3.1) by ,w we get riddhi jung shah / bibechana 15 (2018) 24-29: rcost p.26 (3.2)                                                                              wygzxgwxgzyg n rn nn nn wzgyxswzsyxgwxszyg wyszxgwxgzyswygzxswxszy wyszxwzysxwzxsywyszxg wxszygwygzxswxgzys n wzyxr ,,,,}{ 2 2 22{ 12 1 },,2,,2,, ,,,,,,, ,,,,, ,,,,,,{ 2 1 ,,, ~ 0 2                                                         },,,, ,}{ 2 23 254{ 12 1 },, ,,}{ 2 23 2{ 12 1 },,2 2 wzxgywzygxwygzx wxgzy n rn nn nn wygzxg wxgzyg n rn n nn wzgyxg             where     .,,,,, ~ wzyxrgwzyxr  setting w in (3.2) and using (2.1), (2.3), (2.6), (2.10), (2.14) and then further simplifying yields (3.3)                     .,, ,, 122 234108 0 23 yzxsxzys yzxgxzyg nn rnnnn              in (3.3) replacing x by  and using (2.1), (2.3) and (2.14), we get (3.4)                    . 12 232762 , 12 232542 , 2 2 zy nn rnnnn zyg nn rnnnn zys                    equation (3.4) implies that (3.5)        ,,, zyzygzys   where      12 232542 2    nn rnnnn  and       . 12 232762 2    nn rnnnn  the relation (3.5) implies that the manifold is an  -einstein manifold. this completes the proof of the theorem. theorem 3.2 let m be a  12 n -dimensional lp-sasakian manifold. if the condition   0, 0 yxc holds in ,m then the manifold is an  -einstein manifold. proof: let us consider a  12 n -dimensional lp-sasakian manifold m which is  -contact conformally flat, then we have   .0, 0 yxc now, replacing z by  in (2.16) and using (2.1), (2.3), (2.6), (2.12), (2.14) and (2.18), we get (3.6)                . 12 232542 0 2 qyxqxy yxxy nn rnnnn              taking inner product on both sides of (3.6) by ,w we obtain riddhi jung shah / bibechana 15 (2018) 24-29: rcost p.27 (3.7)                       ., ,, 12 232542 , 2 ywxs xwygywxg nn rnnnn xwys              putting x in (3.7) and using (2.1), (2.3) and (2.14), we get (3.8)                    . 12 232762 , 12 232542 , 2 2 wy nn rnnnn wyg nn rnnnn wys                    from (3.8), we have (3.9)        ,,, wybwyagwys  where                12 232542 2 nn rnnnn a and     . 12 )23(2762 2          nn rnnnn b hence the manifold is an  -einstein manifold. this completes the proof of the theorem. theorem 3.3 a contact conformally semi-symmetric lp-sasakian manifold  gm n ,12  is an einstein manifold and a manifold of constant curvature  .122  nnr proof: let us consider an lp-sasakian manifold  gm n ,12  satisfying the condition   .0., 0 cyxr now, we have (3.10)                   .,,,, ,,,,,., 00 000 zyxrvuczvyxruc zvuyxrczvucyxrzvucyxr   in view of (2.20) and (3.10), we get (3.11)               .,,,, ,,,,0 00 00 zyxrvuczvyxruc zvuyxrczvucyxr   taking x in (3.11) and using (2.11), we obtain (3.12)                               .,,, ,,,, ,,,,,0 00 000 000 yvuczvuczyg zyucvzucvygzvycu zvcuygyzvucyzvucg       taking inner product on both sides of (3.12) by , we get (3.13)                                      .,,, ,,,, ,,,,,0 00 000 000 yvuczvuczyg zyucvzucvygzvycu zvcuygyzvucyzvucg       putting uy  in (3.13) we obtain (3.14)                            .,,,, ,,,,,,0 000 000 uvuczvuczugzuucv zucvugzvcuuguzvucg     now, from (2.16) we have (3.15)    ,0, 0  vuc riddhi jung shah / bibechana 15 (2018) 24-29: rcost p.28 (3.16)                       zv nn rnnnn zvg nn rnnnn zvs n zvc   12 232762 , 12 232542 , 1 , 2 2 2 2 0       and (3.17)    .0, 0 zuuc by virtue of (3.15) and (3.17), (3.14) reduces to (3.18)                  .,,, ,,,,0 00 00 uvuczzucvug zvcuuguzvucg     let  12,..,2,1:  nie i be an orthonormal basis of the tangent space at any point of the manifold. putting i eu  in (3.18) and taking summation over ,121,  nii we get (3.19)                  12 1 12 1 000 ,0,,2,, n i n i iiii eveczzvcnezvecg  since            12 1 00 .,,, n i ii zvczecveg  again, from (2.16) it follows (3.20)                         zv nn rnnnnnn zvg nn rnnnnn zvs n n ezvecg n i ii                        12 4222524 , 12 22242 , 12 ,, 2 223 2 22 12 1 0 under the condition   0..  qtrtr  and by the use of (2.2), (2.8) and (2.15). from the definition of contact conformal curvature tensor, we also have (3.21)                      12 1 0 . 1 12212 , n i ii zv nn nnrn evecz  in view of (3.16), (3.20) and (3.21), (3.21) takes the form (3.22)        ,,, 21 zvzvgzvs   where      14 234231482 223 1    nn rnnnnnn  and      . 1221 2 n rnnn   taking an orthonormal frame field at any point of the manifold and contracting over v and z in (3.22) we get (3.23)  .122  nnr using (3.23) in (3.22) we obtain (3.24)    .,2, zvngzvs  in view of (3.23) and (3.24), the theorem is proved. 4. conclusions in this paper, we have studied on contact conformal curvature tensor in a  12 n -dimensional lorentzian para-sasakian manifold (briefly, lp-sasakian manifold). we have investigated that riddhi jung shah / bibechana 15 (2018) 24-29: rcost p.28 contact conformally flat and  -contact conformally flat lp-sasakian manifold is an  -einstein manifold. it is also proved that a contact conformally semi-symmetric lp-sasakian manifold is an einstein manifold. acknowledgement the author is grateful to worthy referee for his/her valuable suggestions and comments for the improvement of this paper. references [1] w. m. boothby, h. c. wang, on contact manifolds, ann. of math. 68 (1958) 721-734. doi.org/10.2307/1970165. [2] j .c. jeong, j.d. lee, g.h. oh, j.s. pak, on the contact conformal curvature tensor, bull. korean math. soc. 27 (1990) 133-142. [3] j.s. pak, y.j. shin, a note on contact conformal curvature tensor, comm. korean math. soc. 13(2) (1998) 337-343. [4] k. bang, j.y. kye, vanishing of contact conformal curvature tensor on 3-dimensional sasakian manifolds, kangweon-kyngki math. j. 10 (2) (2002) 157-166. [5] k. matsumoto, on lorentzian paracontact manifolds, bull. of yamagata univ. nat. sci. 12 (1989) 151 156. [6] i. mihai, r. rosca, on lorentzian p-sasakian manifolds, classical analysis, world. scientific publi. (1992) 155-169. [7] k. matsumoto, i. mihai, on a certain transformation in a lorentzian para-sasakian manifold, tensor n. s. 47 (1988), 189-197. [8] u. c. de, k. matsumoto, a. a. shaikh, on lorentzian para-sasakian manifolds, rendiconti del seminario matematico di mesina, serrie ii, supplemento al n. 3 (1999) 149-158. [9] a. a. shaikh, s. biswas, on lp-sasakian manifolds, bull. malaysian sci. soc. 27 (2007) 17-26. [10] c. s. bagewadi, venkatesha, n.s. basavarajappa, on lp-sasakian manifolds, scientia series a, mathematical sciences 16 (2008) 1-8. [11] z. i. szabo, structures theorems on riemannian spaces satisfying, i, j. diiff. geom. 17 (1982) 531-582. riddhi jung shah / bibechana 15 (2018) 24-29: rcost p.29 https://doi.org/10.2307/1970165 microsoft word ajaya final (131-136) kuber limbu et al. / bibechana 16 (2019) 131-136: rcost p.131 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal density and partial molar volume of sodium dodecyl sulfate in presence and absence of sodium sulfate and zinc sulfate in distilled water kuber limbu, sujit kumar shah, ajaya bhattarai* department of chemistry, m.m.a.m.c., tribhuvan university, biratnagar, nepal *e-mail: bkajaya@yahoo.com article history: received 09 september, 2018; accepted 27 october, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21515 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the precise measurements of density of sodium dodecyl sulfate (sds) in distilled water and in presence of 0.01m na2so4 and 0.01m znso4 at room temperature were measured by ostwald-sprengel type pycnometer. the density of sds in distilled water was found lower than the density of sds in na2so4 and znso4 solutions whereas the density of sds in the presence of znso4 is higher than the density of sds in the presence of na2so4. the partial molar volume of sds in distilled water was obtained higher than in presence of na2so4 and znso4 solutions. keywords: sodiumdodecyl sulfate; na2so4; znso4.; density; partial molar volume(pmv). . 1. introduction in physical chemistry research, the density of surfactant solution is very important. it can be observed that the density of the system increases with the addition of surfactant [1]. such behavior has been noticed for the density of surfactants in the various literature [2, 3]. the density of surfactant solutions is used to calculate the critical micelle concentration [4, 5, 6] and the partial molar volume [1]. the partial molar volume is the thermodynamic quantity of the surfactant and is very useful to elucidating the interactions occurring in solutions and to examine the behaviours of surfactant solutions [7]. particularly, detailed definitions and explanations of the partial molar volume have been provided in several papers [8, 9]. the density and partial molar volume,v , is defined by the following equation[10]; ptnvv ,)/( ∂∂= (1) where, v∂ represent change in total volume and n as the number of moles. the partial molar volume is often provided in units of partial molar volume cm3/mol. the concentration dependence of the kuber limbu et al. / bibechana 16 (2019) 131-136: rcost p.132 (online publication: dec., 2018) partial molar volume is accounted by using the following equation which calculate the apparent molar volume at the finite concentrations c[8]. )1(10 030 −−= ρ ρ ρ cmv (2) where, m is the molecular weight of the sds , 0ρ is the density of the solvent, ρ is the density of the solution and c is having the unit as equivalent concentration in mol/l. our aim is to determine of densities and pmv of different solutions of sds and their comparison with the solutions of sds in the presence of salts. 2. experimental sodium dodecyl sulfate (sds) of molecular weight 288.38 g/mol was purchased from merck specialities pvt. ltd., mumbai, india whereas sodium sulfate and zinc sulfate was purchased from ranbaxy pvt. ltd., mumbai, india. single distilled water was used as primary solvents for the preparation of different experimental solutions of different concentrations of sds in absence and presence of sodium sulfate and zinc sulfate. electronic balance was used for weighing the different concentrations of sds, sodium sulfate and zinc sulfate. ostwald-sprengel type pycnometer was used to measure density. for this purpose, the cleaned ostwald-sprengel type pycnometer was taken and was first filled with air-free distilled water in it, then the stopper was inserted into its mouth so that the small amount of water flowed out the capillary then the outer surface of it was wiped out with a tissue paper ensuring that outer surface was completely dried. finally the ostwald-sprengel type pycnometer was weighed and then contents after allowing them to stand for a short time. the ostwald-sprengel type pycnometer was then emptied and dried. then the same process was repeated for every type of solutions under investigations. after collecting the weights, densities of related solutions were calculated and tabulated with reference to the standard density of water at 30oc i.e. 0.99571 g/cm3. the pmv values were also calculated and tabulated along with densities. the calculated densities and pmv values of sds in aqueous and in presence of salts with different concentrations were plotted in the graph with the help of easy plot software. 3. results and discussion the densities of sds in distilled water, na2so4 and znso4 solution have been calculated and compared with a wide range of concentrations of sds (table 1). density has been found to be increased significantly on going from distilled water to na2so4 and znso4. the density increased with the increase of molecular weight of the added salts. in our case the molecular weight of sodium sulfate is 142.04 g/mol whereas for zinc sulfate is 161.47 g/mol. so, the density of sds in the presence of zinc sulfate is high than the density of sds in the presence of sodium sulfate (figure 1). it is not possible to calculate the critical micelle concentration of sds in distilled water and in the presence of salts because the investigated concentrations of sds in higher concentration are in regular trends whereas the lower concentration below the critical micelle concentration is in irregular trends and hence there will not possible to see the accurate intersection point between the pre and post micellar slope of the surfactant solutions. this is may be due to the presence of the impurities and the fluctuations of the temperature while measuring the density of the solutions. kuber limbu et al. / bibechana 16 (2019) 131-136: rcost p.133 (online publication: dec., 2018) the calculation of the partial molar volume of sds in distilled water and in presence of salts is the good option to see the solute and solvent interactions. partial molar volume (pmv) of sds has been found to be higher in distilled water and gradually decreased in other salts (table 2 and figure 2). table 1: density of sds in distilled water, na2so4 and znso4 at 30oc. solvent concentration (mol/lt) density (g/cm-3) pure distilled water 0.100076 0.080061 0.060046 0.04003 0.024018 0.018014 0.012009 0.007205 0.005404 0.999567 0.997363 0.996733 0.996064 0.995749 0.995671 0.995395 0.995316 0.995238 na2so4 0.10008 0.080061 0.060046 0.04003 0.024018 0.018014 0.012009 0.007205 0.005404 1.000000 0.999685 0.999056 0.99819 0.997678 0.997599 0.997284 0.997166 0.997088 znso4 0.100284 0.080227 0.060171 0.040114 0.024007 0.018051 0.012034 0.00722 0.005415 1.000788 0.999922 0.999213 0.998426 0.997757 0.997678 0.997481 0.997363 0.997206 kuber limbu et al. / bibechana 16 (2019) 131-136: rcost p.134 (online publication: dec., 2018) table2: partial molar volume of sds in distilled water, na2so4 and znso4 at 30oc. solvents concentration (mol/lt) pmv (cm3/mol) distilled water 0.100076 0.080061 0.060046 0.04003 0.024018 0.018014 0.012009 0.007205 0.005404 250.9122 268.8848 272.5057 280.7349 287.9766 291.8169 315.956 344.4908 377.4008 na2so4 0.10008 0.080061 0.060046 0.04003 0.024018 0.018014 0.012009 0.007205 0.005404 251.1895 245.562 241.4493 239.146 226.9728 210.5221 197.3616 152.3965 121.3232 znso4 0.100284 0.080227 0.060171 0.040114 0.024007 0.018051 0.012034 0.00722 0.005415 251.0638 252.3419 251.8475 252.8272 256.3429 249.8579 246.562 234.5024 245.4129 100200300400 0 0.04 0.08 0.12concentration (mol/lt)pmv (cm3 /mol) kuber limbu et al. / bibechana 16 (2019) 131-136: rcost p.135 (online publication: dec., 2018) fig.1: density of sds in distilled water (circles), na2so4 (opposite triangles) and znso4 (squares). . fig. 2: partial molar volumes of sds in distilled water (circles), znso4 (opposite triangles) and na2so4 (squares). 0.9950.9960.9970.9980.9991.000 0 0.04 0.08 0.12concentration(mol/lt)density(gm.cm-3 ) kuber limbu et al. / bibechana 16 (2019) 131-136: rcost p.136 (online publication: dec., 2018) 4. conclusion the following conclusion has been drawn from the above results and discussion. the density of sds in distilled water is found to be low as compared to sds solution in the presence of na2so4 and znso4. the molecular weight of the substance is related with the density. the molecular weight of znso4 is higher than the molecular weight of na2so4. hence the density of sds in the presence of znso4 is higher than the density of sds in the presence of na2so4 . the values of the partial molar volumes are found to be higher of sds in distilled water in comparison with the values of the partial molar volumes of sds in the presence of na2so4 and znso4. acknowledgments one of the authors (kuber limbu) is thankful to the university grants commission (ugc), nepal, for providing grants for m. sc.dissertation work. authors are also grateful to associate professor ghanashyam shrivastav, head of department of chemistry, m.m.a.m.c., biratnagar, nepal for providing the available research facilities to conduct this research work. references [1] a. bhattarai, s.k. chatterjee, t. k. deo, t. p. niraula, effects of concentration, temperature, and solvent composition on the partial molar volumes of sodium lauryl sulfate in methanol (1) + water (2) mixed solvent media, j. chem. eng. data, 56(2011) 3400-3405. https://pubs.acs.org/doi/abs/10.1021/je2003622. 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[10] c. wandrey, a. bartkowiak, d. hunkeler, partial molar and specific volumes of polyelectrolytes:  comparison of experimental and predicted values in salt-free solutions, langmuir 15 (1999) 4062-4068. https://pubs.acs.org/doi/abs/10.1021/la981089d. m. h. gulzar and a. w. manzoor/ bibechana 13 (2016) 1-8 : rcost p.1 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal generalizations of some enestrom-kakeya type results m.h. gulzar*, a.w. manzoor department of mathematics, university of kashmir, srinager-190006, jammu and kashmir, india. *e-mail: gulzarmh@gmail.com article history: received 05 june, 2015; accepted 20 august, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13309 abstract in this paper we give interesting generalizations of some well-known enestrom-kakeya type results on the location of zeros of a complex polynomial under less restrictive conditions on the coefficients of the polynomial. ©rcost: all rights reserved. keywords: bound; coefficient; polynomial; zeros. 1. introduction regarding the zeros of a polynomial with real and positive coefficients, we have the following result known as the enestrom-kakeya theorem [1, 2, 3]. theorem a: let    n j j j zazp 0 )( be a polynomial of degree n such that 0...... 011   aaaa nn . then all the zeros of )(zp lie in 1z . various extensions and generalizations of this result are available in the literature. joyal et al [4] proved the following generalization of theorem a: theorem b: let    n j j j zazp 0 )( be a polynomial of degree n such that 011 ...... aaaa nn   . then )(zp has all its zeros in the disk n n a aaa z 00   . as a generalization of theorems a and b, aziz and zargar [5] proved the following: theorem c: let    n j j j zazp 0 )( be a polynomial of degree n such that for some 1k 011 ...... aaaka nn   . m. h. gulzar and a. w. manzoor/ bibechana 13 (2016) 1-8 : rcost p.2 (online publication: dec., 2015) then )(zp has all its zeros in the disk n n a aaka kz 001   . shah et al [6] extended theorem b to polynomials with complex coefficients and proved the following result: theorem d: let    n j j j zazp 0 )( be a complex polynomial of degree n with jja )re( and jja )im( for ,,......,2,1,0 nj  such that for some 1k .0...... ...... 011 011       nn nnk . then )(zp has all its zeros in the disk n nn n n a k k a z    00)1( . liman et al [7] proved the following generalization of theorem d: theorem e: let    n j j j zazp 0 )( be a complex polynomial of degree n with jja )re( and jja )im( for 0,,......,2,1,0  nanj . if for some positive integer n and 1k ,............ 0111 2 2 1 1 1         kkkkk n n n n n n 0....... 011    nn , then all the zeros of )(zp lie in n n n j njjn n n a k k a z              )()1( )1( 00 . in the same paper they proved the following result also. theorem f: let    n j j j zazp 0 )( be a complex polynomial of degree n with jja )re( and jja )im( for 0,,......,2,1,0  nanj . if for some positive integer n , 1k and 1 , ,............ 0111 2 2 1 1 1         kkkkk n n n n n n 0....... 011    nn , then all the zeros of )(zp lie in n n n j njjn n nn a k a ik z                )()1( 1 00 . recently gulshan singh [8] proved the following generalization of theorems e and f: m. h. gulzar and a. w. manzoor/ bibechana 13 (2016) 1-8 : rcost p.3 (online publication: dec., 2015) theorem g: let    n j j j zazp 0 )( be a complex polynomial of degree n with njia jjj ,......,2,1,0,   , where j and j are real numbers. if for some positive integers n, and for some real numbers 1,10,10 21  k , ,............ ,............ 02111 2 2 1 1 1 01111 2 2 1 1 1                 kkkkk kkkkk n n n n n n n n n n n n then all the zeros of )(zp lie in  )()1()1()()( 1 1 0002010201   nn na kz nn n j jj n j jjk      )()()1( . in this paper we prove the following result which not only generalizes the above results but also gives many other results for different values of the parameters. 2. theorems and proofs theorem 1. let    n j j j zazp 0 )( be a complex polynomial of degree n with njia jjj ,......,2,1,0,   , where j and j are real numbers. if for some positive integers n, and for some real numbers 1,1,10,10 2121  kk , ,............ ,............ 021121 2 22 1 212 1 2 011111 2 12 1 111 1 1                 kkkbkk kkkkk n n n n n n n n n n n n then all the zeros of )(zp lie in  010201 21 )1()()( 1)1()1(      nn nn nn aa kik z )()1( 0002   ||)1()()1( 1 n n j jj kk            n n j jj kk   )1(()1( 22          . taking ,, 2121   kkk in theorem 1 we get theorem g. taking 0,1,1, 02121   andkkk in theorem 1, we get theorem e. taking 01,,, 02121   andnkkk in theorem 1 we get theorem f of liman et al.taking   n in theorem 1,we get a theorem of gulzar [9,theorem 1]. taking 2121 1  kk in theorem 1 we get the following interesting result: m. h. gulzar and a. w. manzoor/ bibechana 13 (2016) 1-8 : rcost p.4 (online publication: dec., 2015) corollary 1. let    n j j j zazp 0 )( be a complex polynomial of degree n with ,,......,2,1,0)im(.)re( njforaa jjjj   such that ....... ,...... 011 011       nn nn . then )(zp has all its zeros in the disk  nn na z   1 taking ja real, that is j =0 for j=0,1,2,……..,n and 00  ,corollary 1 reduces to enestrom-kakeya theorem. taking   in theorem 1, we get the following result:. corollary 2. let    n j j j zazp 0 )( be a complex polynomial of degree n with 0,,......,2,1,0)im(.)re(  njjjj anjforaa  . if for some positive integer ,1,1,10,10, 2121  kkn  ,............ ,............ 021121 2 22 1 212 1 2 011111 2 12 1 111 1 1                 kkkkk kkkkk n n n n n n n n n n n n then all the zeros of )(zp lie in  010201 21 )1()()( 1)1()1(      nn nn nn aa kik z )()1( 0002   ||)1()()1( 1 n n j jj kk            n n j jj kk   )1(()1( 22          . many other results may be deduced from theorem 1 for different values of parameters. proof of theorem 1: consider the polynomial m. h. gulzar and a. w. manzoor/ bibechana 13 (2016) 1-8 : rcost p.5 (online publication: dec., 2015)         }]........)1( )1()()(........)( )()()( .......)()()1({ ........)1()1()()( .......)()()()( .......)()()1( ........... )(..........)( )(..........)( )...........)(1( )()1()( 1 1 1 12 002021 2 12 2 32 1 2112 1 12 1 212122 1 1 1 11001011 2 12 2 32 1 2111 1 11 1 211111 1 0011 0011 1 0011 1 01 1 1                                  zzzk zzzz zzkzk zkzkzki zzzkzzz zzzkzk zkzkzkza zzi zzza azaazaaza azazazaz zpzzf n n n nn n nn n n n n n nn n nn n n n n n nn n nn n n n nn n n n n n n                                             }] 1 ........ 1 )1( 1 )1( 1 )( 1 )(........ 1 )( 1 )( 1 )( 1 )( ....... 1 )(){( 1 ........ 1 )1( 11 )1( 1 )( 1 )(....... 1 )( 1 )( 1 )( 1 )( .......... 1 )()()1()1([ 12 0 102 1021212232 12112112 21212 110101 1011212232 12111111 2111121                                             nnnn nnn nnn nnnn nnnn nnn nnn nnnnnnn n zz k zz zzz zz k z k z kki zz k zz zzz zz k z k z kkkikzaz for |z|>1 so that nj z jn ,,.........2,1,0,1 || 1  .we have by using the hypothesis, m. h. gulzar and a. w. manzoor/ bibechana 13 (2016) 1-8 : rcost p.6 (online publication: dec., 2015)  }] || 1 ||........ || 1 ||)1( || || || 1 |||1| || 1 || || 1 ||........ || 1 || || 1 || || 1 || || 1 || ....... || 1 |||| || 1 ||........ || 1 ||)1( || 1 || || 1 ||1 || 1 || || 1 || ....... || 1 || || 1 || || 1 || || 1 )1()1(||)( 12 0 102 1021212232 12112112 2121211 101011011212 23212111 2111121                                         nnnn nnn nnn nnnnnn nnnn nnn nnnnnnn n zz k zz zzz zz k z k z kk zz k zzzz zzz k z kkkikzazzf     ||........||)1(||||)1( ........ .......||........||)1( ||||)1( ....... )1()1(|| 12002 0211232 211212 2121211 001011 322111 2111121                          n nnnnn nnnnnnn n k kk kkk k kkkikzaz      0 )1(()1()1()()1(|||| ||)1(||)1()1()1(|| 221100 0201020121                  n n j jjn n j jj nnnnn n kkkk kikzaz    if   n n j jj n n j jj nnnnn kk kk kikza      )1(()1( )1(()1(|||| ||)1(||)1()()1()1( 22 1100 0201020121                    that is, if m. h. gulzar and a. w. manzoor/ bibechana 13 (2016) 1-8 : rcost p.7 (online publication: dec., 2015)  )()1()1()()( 1)1()1( 0002010201 21      nn nn nn aa kik z n n j jj n n j jj kk kk     )1(()1( ||)1()()1( 22 1                   this shows that those zeros of f(z) whose modulus is greater than 1 lie in  )()1()1()()( 1)1()1( 0002010201 21      nn nn nn aa kik z n n j jj n n j jj kk kk     )1(()1( ||)1()()1( 22 1                   since those zeros of f(z) whose modulus is less than or equal to 1 already satisfy the above inequality, it follows that all the zeros of f(z) and hence of p(z) lie in  )()1()1()()( 1)1()1( 0002010201 21      nn nn nn aa kik z n n j jj n n j jj kk kk     )1(()1( ||)1()()1( 22 1                   this completes the proof of theorem 1. references [1] m. marden, geometry of polynomials, math. surveys no.3, amer. math. soc. providence r.i. 1996. [2] g.v. milovanovic, d.s. mitrinovic and t.m. rassias, topics in polynomials, extremal problems, inequalities, zeros. world scientific publishing co. river edge, nj, 1994. [3] q. i. rahman and g. schmeisser, analytic theory of polynomials, oxford university press, 2002. [4] a. joyal, g. labelle and q.i. rahman, canad. math. bull. 10 (1967) 53-63. [5] a. aziz and b. a. zargar, mathematiki, 31(1996) 239-244. m. h. gulzar and a. w. manzoor/ bibechana 13 (2016) 1-8 : rcost p.8 (online publication: dec., 2015) [6] w. m. shah and a. liman, on enestrom-kakeya theorem and related analytic functions, proc. indian acad. sci (math sci) 17 ( 3) (2007)359-370. [7] a. liman, tawheeda rasool and w.m. shah, bibechana, 10(2014) 71-81. [8] gulshan singh, american journal of mathematical analysis, 2 (1) (2014) 1518. [9] m. h. gulzar, international journal of innovative research in engineering and science, 4( 3 )(2014) 33-36. microsoft word chakrabari et al _35-39_.docx r c o s t n publisher: research council of science and technology, biratnagar, nepal p.35 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana impact of eigenvalues on the electron-phonon coupling strength of aluminium and its binary alloys b. k. kanth 1 , s. k. chakrabarti 2* , i. s. jha 2 , b. p. singh 3 1 department of chemistry, m. m. a. m. campus, tribhuvan university, biratnagar, nepal 2department of physics, m. m. a. m. campus, tribhuvan university, biratnagar, nepal 3department of physics, t. m. bhagalpur university, bhagalpur, bihar, india *e-mail: skc_2007@yahoo.com accepted for publication: december 10, 2014 abstract aluminium is a third group element according to the periodic table. chemically it is a reactive metal often forming complexes within its binary alloys. in the present work we have dealt with the impact of eigenvalues on the superconducting state parameter viz. the electron-phonon coupling strength of this metal. we have also dealt with the same for two binary alloys of it viz. aluminium-magnesium and aluminium-zinc. for this purpose we have computed the non-local screened form factor for each of them. initially the orthogonalised plane wave parameter has been taken as unity. thereafter vashishta-singwi form of exchange and correlation is employed. the core energy eigenvalues of herman-skillman have been used. our results are quite satisfactory for the metal as well as its present alloys. our computation reveals that the superconducting state parameter can be reasonably reproduced by harrison’s first principle pseudopotential technique along with mcmillan’s formalism provided a proper choice of the core energy eigenvalues is made. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11699 © 2014 rcost: all rights reserved. keywords: superconducting state parameter; orthogonalised plane wave parameter; eigenvalue; form factor. 1. introduction the electron-phonon coupling strength gives us the superconducting state parameter. the basis of a general quantum theory of superconductivity was given in the year 1957 by bardeen, cooper and schrieffer [1]. after a decade mcmillan developed this bcs theory by the concept of pseudopotential [2]. few years later the theory was developed further by allen and dynes for application on binary alloys [3]. in the present theoretical work we have used harrison's first principle (hfp) pseudopotential technique to study the impact of eigenvalues on the electron-phonon coupling strength of the trivalent metal aluminium and its binary alloys i.e. aluminium-magnesium and aluminium-zinc [4]. in section 2 the necessary formula for computation is furnished. the results of our computation have been discussed in section 3 which is followed by a brief conclusion in section 4. kantha et al./ bibechana 12 (2015) 35-39: p. 36 2. formulation the electron-phonon coupling strength is given by 2 23 2 0 12 ( , ) , mz w k q d m λ η η ω = < > ∫ where m is the atomic mass, z the valency, m the mass of electron, <ω2> the average phonon frequency, w(k, q) the non-local screened form factor and . f q k η = 3. results and discussion 3.1 metal aluminium we have computed the form factors of aluminium using the core energy eigenvalues of hermanskillman and considering the orthogonalised plane wave parameter to be unity [5]. due to small core in case of aluminium the xα-exchange parameter has been taken as α=αvt satisfying virial theorem. then the vashishta-singwi form of exchange and correlation has been used [6]. the nature of the form factors is furnished in figure–1. 0.4 0.8 1.2 1.6 0.2 2 – 0.4 – 0.2 0 η fig. 1 : form factors of aluminium. the computed value of λ is given in the table below. our result is quite satisfactory. the impact of eigenvalues on the electron-phonon coupling strength of aluminium can be realized from this table. kantha et al./ bibechana 12 (2015) 35-39: p. 37 table: electron-phonon coupling strength matter computed λλλλ λλλλ desired λλλλ due to others nature name value ev of value researcher metal al 0.43 hs * 0.43 0.43 rg ** alloy al-mg 0.40 hs-hs 0.37 0.42 yrk*** alloy al-zn 0.36 hs-hs 0.35 0.37 allendynes *hs≡herman-skillman **rg≡rajput-gupta [7] *** yrk≡yadav-rafique-kumar [8] 3.2 alloys of aluminium in case of the alloy aluminium-magnesium the herman-skillman eigenvalues have been considered for aluminium [9]. for magnesium also we have taken the eigenvalues of herman-skillman. the nature of the form factors is shown in figure–2. 0.4 0.2 0.8 1.2 1.6 2 0 – 0.2 – 0.4 – 0.6 η fig. 2 : form factors of aluminium-magnesium alloy. the nature of the form factors of aluminium-zinc alloy is depicted in figure–3. herman-skillman eigenvalues have been used for aluminium. for zinc also the eigenvalues of herman-skillman have been considered to have better result. kantha et al./ bibechana 12 (2015) 35-39: p. 38 0.4 0.2 0.8 1.2 1.6 2 0 – 0.2 – 0.4 η fig. 3 : form factors of aluminium-zinc alloy. the computed values of the electron-phonon coupling strength of the present alloys are furnished in the said table along with the respective values provided by previous researchers. the desired value of λ for al-mg alloy is 0.37 and our computed value is 0.40. for al-zn alloy our computed value of λ is 0.36 whereas the desired value is 0.35. 4. summary and conclusion hfp pseudopotential technique based on bcs theory and mcmillan's formalism has been used to compute the electron-phonon coupling strength (λ) of aluminium. besides this the values of λ have been computed for two binary alloys of it―al-mg and al-zn. our results are quite satisfactory as compared to the values obtained by previous researchers. our computation reveals that the superconducting state parameter is reasonably reproducible by hfp pseudopotential technique if the core energy eigenvalues can be chosen properly. references [1] b.s. saxena, r.c. gupta and p.n. saxena, solid state physics, pragati prakashan, meerut (1975). [2] w.l. mcmillan, phys. rev., 167 (1968) 331. http://dx.doi.org/10.1103/physrev.167.331 [3] p.b. allen and r.c. dynes, phys. rev., b 12 (1975) 905. http://dx.doi.org/10.1103/physrevb.12.905 [4] w.a. harrison, pseudopotential in the theory of metals, benjamin, new york (1966). kantha et al./ bibechana 12 (2015) 35-39: p. 39 [5] s.k. chakrabarti, i.s. jha, r.n. yadav and m. shahi, acta cien. indica, xxxviii m (2012) 751. [6] p. vashishta and k.s. singwi, phys. rev., b 6 (1972) 875. http://dx.doi.org/10.1103/physrevb.6.875 [7] j.s. rajput and a.k. gupta, phys. rev., 181 (1968) 743. http://dx.doi.org/10.1103/physrev.181.743 [8] j.p. yadav, s.m. rafique and a. kumar, acta cien. indica, xxxv p (2009) 155. [9] f. herman and j. skillman, atomic structure calculation, prentice hall, new jersey (1963). b .a. zargar and a . w. manzoo / bibechana 14 (2017) 48-53 : rcost p.48 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal on zero-free regions for the derivative of a polynomial b .a. zargar* and a . w. manzoor department of mathematics, university of kashmir hazratbal srinagar 190006, india *email: bazargar@gmail.com article history: received 27 june, 2016; accepted 17 august, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15521 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract let pn denote the set of all polynomials of the form      1 1 )( n j jzzzzp with .11,1  njz j in this paper we shall obtain some zero-free regions for the derivative of a polynomial. keywords: zero-free regions; critical points; sendov’s conjecture. 1. introduction let us suppose that p(z) is an nth degree polynomial which has all its zeros in the unit disk 1z , then all the critical points of p(z) also lie in the same disk 1z .this is in fact the wellknown theorem which was implied in a note of gauss dated 1836 and proved explicitly by lucas dated 1874 (see also marden [1]. now instead of considering the relative position of all the zeros and critical points of p(z), let us choose any one zero zo of p(z) and ask: at most how far from zo does the nearest critical point lie ? a possible answer to this question is given by the following :conjecture: “ if p(z) is an nth degree polynomial having all its zeros in the unit disk 1z and if zo is any one such zero, then at least one critical point of p(z) lie in the disk .10  zz ” this conjecture was included in the collection of research problems in function theory published in 1967 by professor hayman [2], (see also [3]). since it had been brought to hayman’s attention by professor ilyeff. it became b .a. zargar and a . w. manzoo / bibechana 14 (2017) 48-53 : rcost p.49 (online publication: dec., 2016) known as “ilyeff’s conjecture”. actually conjecture was due to a bulgarian mathematician b. sendov. in connection with this conjecture brown [4] posed the following problem. let nq denote the set of all complex polynomials of the form      1 1 )( n j jzzzzp with .11,1  njz j find the best constant cn such that )(zp does not vanish in ncz  for all nqp . brown observed that if 1)1()(  nzzzp then 0 1       n p and conjectured that . 1 n cn  recently aziz and zargar [5] settled this conjecture. theorem1.1. let      1 1 )( n k kzzzzp be a polynomial of degree n with ,11,1  nkzk then )(zp does not vanish in the disk . 1 n z  the result is best possible for the polynomial  20,)()( 1  niezzzp . first we shall prove the following interesting result which provides the zero free regions for the second derivative of polynomial      mn k j m zzzzp 1 )( theorem 1.2. if      mn j j m zzzzp 1 )( where ,.,.........2,1,1 mnjz j  then the polynomial )(zp  does not vanish in . )1( )1( 0    nn mm z taking m = 2 we get corollary 1.if      2 1 2)( n j jzzzzp where ,2.,.........2,1,1  njz j then the polynomial )(zp  does not vanish in . )1( 2 0   nn z it is clearly of interest to known that a zero free region for the polynomial )(zpm where      mn j j m zzzzp 1 )( in this direction, we prove the following interesting results: b .a. zargar and a . w. manzoo / bibechana 14 (2017) 48-53 : rcost p.50 (online publication: dec., 2016) theorem1.3. let      mn j j m zzzzp 1 )( be a polynomial of degree n, with ,.,.........2,1,1 mnjz j  then the polynomial )(zpm does not vanish in the disk . )1)....(1( !   mnnn m z remark 1. if m=1,then we get theorem 1.1. for the proofs of these theorems we need the following result which is due to aziz and zagar [5]. lemma: let      mn j j m zzzzp 1 )( where ,1,1 mnjz j  then )(zp does not vanish in .0 n m z  2. proofs of theorems proof of theorem 1.2. we write, )()( zqzzp m where   .,......2,1,1,)( 1 mnjzzzzq j mn j j    by above lemma, the polynomial )()()( 1 zqmzzqzzp mm  )(1 zrzm , where ),()()( zmqzqzzr  does not vanish in .0 n m z  replacing zby ,z n m it follows that the polynomial,       z n m pzs )(               z n m rz n m m m 1 1 does not vanish in 10  z ,so that all the zeros of       z n m r lie in .1z b .a. zargar and a . w. manzoo / bibechana 14 (2017) 48-53 : rcost p.51 (online publication: dec., 2016) using the above lemma again and noting that s(z) is a polynomial of degree n-1, it follows that )(zs  does not vanish in . 1 1 0    n m z or equivalently,       z n m p does not vanish in 1 1 0    n m z replacing z by ,z n m it follows that     )(1)( 21 zrzmzrzzp mm    )()1()(2 zrmzrzzm   )(2 ztzm where     )(1)( zzrmzrzzt  does not vanish in 1 1 0    n m z . this completes the proof of theorem 1.2. proof of theorem 1.3. by hypothesis, )()( zqzzp m where   mnjzzzzq j mn j j    ,......2,1,1,)( 1 . by the above lemma, the polynomial )(zp does not vanish in .0 n m z  therefore theorem 1.2 yeilds that   )(2 ztzzp n , where     )(1)( zzrmzrzzt  does not vanish in . )1( )1( 0    nn mm z replacing z by , it follows that z nn mm )1( )1(   b .a. zargar and a . w. manzoo / bibechana 14 (2017) 48-53 : rcost p.52 (online publication: dec., 2016)         z nn mm pzu )1( )1( )(                   z nn mm tz nn mm n )1( )1( )1( )1( 2 does not vanish in ,10  z so that all the zeros of         z nn mm t )1( )1( lie in 1z .applying the above lemma again and noting that u(z) is a polynomial of degree n-2, thus it implies that )(zu  does not vanish in . 2 2 0    n m z or equivalently,         z nn mm p )1( )1( does not vanish in . 2 2 0    n m z replacing z by z mm nn )1( )1(   it follows that, )()2()()( 32 ztznztzzp nn    )()2()(3 ztnztzz n   )(3 zvz n , where )()2()()( ztnztzzv  does not vanish in . )2)(1( )2)(1( 0    nnn mmm z in a similar way we see that the polynomial )()3()3()()( 43 zvznnzvzzp nniv   )(4 zwz n where, )()3()()( zvnzvzzw  does not vanish in . )3)(2)(1( )3)(2)(1( 0    nnnn mmmm z proceeding in this way and noting that m and n are positive integers it follows that the polynomial does not vanish in )1).....(1( ! )1)....(1( 1.2).......1(      mnnn m mnnn mm z which proves theorem 1.3. b .a. zargar and a . w. manzoo / bibechana 14 (2017) 48-53 : rcost p.53 (online publication: dec., 2016) references [1] m. marden, geometry of polynomials, math. survey’s no.3, american math.soc. (1966). [2] w. k. hayman, research problems in function theory, london (1967) pp. 1-25. [3] q. i. rahman and g. schmesser’s analytic theory of polynomials, oxford university press,new york (2002). [4] j. e. brown, on theilief-sendov conjecture, pacific j.math.135 (1988) 223-232. http://dx.doi.org/10.2140/pjm.1988.135.223 [5] a. aziz and b.a. zargar, on the critical points of a polynomial, bull. austral. math. soc.57 (1998) 173-174. http://dx.doi.org/10.1017/s000497270003152x microsoft word arjun final (23-30) a.k. gautam and b. aryal/ bibechana 16 (2019) 23-30: rcost p.23 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal study of far infrared cavity around a post agb star under iras survey at galactic latitude -30 a. k. gautam*, b. aryal** central department of physics, t.u., kirtipur,nepal email: arjungautamnpj@gmail.com*, baryal@tucdp.edu.np** article history: received 20 february, 2018; accepted 3 september, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.20960 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract a systematic search of dust structure in the far infrared (100 μm and 60 μm) under infrared astronomical satellite (iras) survey was performed using sky view virtual observatory. in order to find the possible candidate of cavity structure not yet studied, we used simbad database to locate discrete sources in the region. a new relatively symmetric spherical cavity like structure (size: 44.4 pc x 19.4 pc) at r.a.(j2000) =08h 03m 01.65s, dec.(j2000) = -360 35' 47.9" was found at the distance of about 2800 pc. in this article, we have calculated dust color temperature, dust mass and size. we also studied the flux density variation and then calculated temperature and mass profile of the dust of p-agb star using data reduction software aladin2.5 and aladin8.0. we have studied a cavity like structure centered at r.a.(j2000) = 08h 04m 07.21s, dec.(j2000) = -370 11' 48.0". the dust color temperature is found to lie in the range 21.6 ± 0.09 k to 22.5 ± 0.05 k with an offset of 0.9 k. such low off set suggests that the post agb is in local thermodynamic equilibrium. the total mass of the dust in the cavity structure is found about 5.93 x 1025 kg (0.00003m⊙) keywords: agb stars; dust color temperature; dust mass; post agb star; inclination angle. 1. introduction low-to-intermediate mass stars end their life on the asymptotic giant branch (agb) star. agb stars are the main distributors of dust into the interstellar medium due to their high mass loss rates in combination with an effective dust condensation. it is therefore important to understand the dust formation process and sequence in their extended atmosphere [1]. an evolutionary phase in which the star sheds most of its mantle into the circumstellar environment through a stellar wind. this stellar wind expands at relatively low velocities and enriches the interstellar medium with elements newly made in the stellar interior. the physical processes controlling the gas and dust chemistry in the outflow, as well as the driving mechanism of the wind itself, are poorly understood and constitute the broader context. when helium in the core is used up, energy production shifts to helium burning in a a.k. gautam and b. aryal/ bibechana 16 (2019) 23-30: rcost p.24 (online publication: dec., 2018) shell. the outer layers of the star expand. the star evolves towards the early-asymptotic giant branch (agb) and becomes a red-giant for the second time. the expansion of the outer layer extinguishes the hydrogen-burning shell in the intermediate-mass stars, which causes the convective envelope to move inward for a second time. this second dredge-up brings the hydrogen burning products, mainly helium and nitrogen, to the surface but it does not occur in low mass stars since the hydrogen-burning shell is not extinguished. following the helium exhaustion in the shell, the hydrogen-burning shell takes over until enough helium has been produced. when the helium shell is sufficiently massive, it will re-ignite and new helium-burning will control the evolution. the helium-burning shell is known to be thermally unstable and it undergoes thermal pulses recurrently. this is the thermally-pulsing agb (tp-agb) phase, characterised by two nuclear burning shells surrounding an electron-degenerate carbon-oxygen core and a deep convective envelope. according to [1], thermal pulses may occur in both lowand intermediate mass stars and huge amounts of energy are released. this allows envelope convection to penetrate to the inter-shell region and mix carbon and oxygen enriched material to the surface (third dredge-up). it is important to note that mixing events occurring during these thermal pulses are responsible for the transport of carbon and s-process elements to the surface [2]. it is also equally important to note that observed abundances of post-agb stars are mostly determined during this stage of mixing episodes driven by consecutive thermal pulses. during agb evolution, the helium-burning shell is thermally unstable and causes energy bursts called thermal pulses or flashes repeating apparently every 105 years leading to the development of a convective zone in the shell (3). the phase where hydrogen-shell burning dominates is known as the “inter-pulse phase” which is interrupted by the helium-shell instabilities. the thermal pulse drives a convection zone between the helium and hydrogen burning shells. the fusion products of the helium-burning shell including 12c and some 16o are mixed throughout this region. once a thermal pulse has occurred, a huge amount of energy is released. low to intermediate-mass stars cross the hr diagram horizontally from the tip of the asymptotic giant branch (agb) to the planetary nebula (pn) region after they terminate a rapid mass-loss phase. this transition phase is called post-agb phase of evolution. from an analysis of the iras point source catalog, several post-agb stars have been identified [4, 5]. the spectral energy distribution (sed) of post-agb stars is double peaked. one peak is at far-infrared wavelengths due to the cold dust shell (100-200 k) and the other peak is at shorter wavelengths, optical or near-infrared, from the obscured central star. the cold dust-shell was observed by iras. most of the post-agb stars, proto-planetary nebulae (ppne) and pne were found within the iras color box defined by f(12 μm)/f(25 μm) < 0.3 and f(25 μm)/f(60 μm) > 0.3 [6]. in this paper, we study the physical properties of a far infrared cavity, that we investigated during a systematic search on iras maps, located close to a carbon-rich post agb star (pagb 08-36) at -3o galactic latitude. in section 2, we describe methods of calculation. a brief description of the result and discussion will be given in the section 3. finally, we conclude our results in the section 4. 2. methods we investigated a cavity-like structure in both 60 and 100 micron iras maps around a p-agb star. fig.1(a), and 1(b) are cavity images at 60 and 100 μm whereas 1(c) is its contour map. we briefly a.k. gautam and b. aryal/ bibechana 16 (2019) 23-30: rcost p.25 (online publication: dec., 2018) describe a method for calculation of dust color temperature and dust mass of the dusty environment around carbon-rich post asymptotic giant branch named p-agb08-36[7]. 2.1 dust color temperature for the calculation of dust color temperature, we adopt the method proposed by schnee et al. (2005) [8] and dupac et al. (2003)[9]. according to schnee et al. (2005)[8], dust color temperature of the emission at a wavelength λi is given by �� � ��� � ��.�����)� (1) where , r = f(60 μm)f(100 μm) fig. 1: (a) & (b) iras 60 μm and 100 μm far infrared image of the core region of agb 08-36 centered at r.a. (j2000)= 08h 04m 07.21s and dec.(j2000) = -370 11' 48.0", and (c) contour map of the cavity where contour level is 1-50. f(60 µm) and f(100 µm) are the flux densities in 60 µm and 100 µm respectively and eq. (1) is used for calculation of the dust color temperature. the spectral emissivity index (β) depends on dust grain properties like composition, size, and compactness. for a pure blackbody would have β = 0, the amorphous layer-lattice matter has β ~ 1, and the metals and crystalline dielectrics have β ~ 2 which is used in our calculations. 2.2 planck's function the value of planck's function depends on the wavelength (frequency), and hence the temperature. finally it is used to calculate dust mass. in 1900, planck proposed a relation which is named as planck's function. according to him, the planck's function is given by ���, �) � ����� � � !"#$%��& (2) where, h = planck’s constant, c = velocity of light, ν = frequency at which the emission is observed, λ = wavelength of the radiation and t = temperature of each pixel. 2.3 dust mass for the calculation of dust mass, first we need the value of flux density (fν) at 100 μm maps and we use the expression given by hildebrand (1983)[10], (b) iras 100 micron (a) 1.00x1.00 (c) a.k. gautam and b. aryal/ bibechana 16 (2019) 23-30: rcost p.26 (online publication: dec., 2018) '�()* � +,-./0 1 20345�6,7)1 (3) where, weighted grain size (a) = 0.1 μm, grain density (ρ) = 3000 kg m-3, grain emissivity (qν) = 0.0010 (for 100 μm) [11]. so the equation (3) reduces to '�()* � 0.4 1 20345�6,7)1 (4) we use equation (4) to calculate dust mass of the cavity. 2.4. inclination angle the long axis of kk-loops can be assumed to be inclined by a certain angle with respect to the plane of the sky. the inclination angle i (angle between the line-of-sight and the normal vector of the plane of the loops) can be estimated using holmberg (1946) [12] formula: :;<�= � >4?4�@4��@4 (5) where b/a is the measured axial ratio and q is the intrinsic flatness of the cavity. we use the value of intrinsic flatness q = 0.33 as suggested by holmberg (1946) for oblate spheroid structure. 3. results and discussion 3.1 structure: contour maps while going through the systematic search on iras maps, we found an isolated cavity in the 100 µm and 60 µm at r.a. (j2000)= 08h 04m 07.21s and dec.(j2000) = -370 11' 48.0". with the help of the software aladin2.5, we have studied physical properties (size, dust color temperature, dust mass, etc) of the cavity. we selected contour level in such a way that it circles the cavity. the contour map in the contour level 1-50 is shown in the fig.1(c). 3.2 flux density and its variation by using aladin 2.5 software, the values of flux densities at 60μm and 100μm have measured. the flux density distribution within the contour of the region of interest has studied. we plotted a graph between flux at 100μm and 60μm with the help of origin 5.0 which is shown in fig.2(a). from the linear fit, slope of the line was 0.2. the linear equation of the fitted line is, y= -1.9 + 0.2x. using the slope of best fitted plot, dust color temperature is found as 23 k which is slightly more than our calculated value. again distribution of flux at 100μm of the pixels within the contour level with right ascension (r.a.) and declination (dec.) are plotted by using origin 8.0 and the graph is shown in fig.2(b). graph shows that all the fluxes from minimum to maximum lie within the contour level. most of the maximum flux regions lie at the boundary. 3.3. dust color temperature and its variation using the method of [8], we calculated dust color temperature of each pixel inner the outer isocontour in the region of interest. we use the iras 100 µm and 60 µm fits images downloaded from the iras server. for the calculation of temperature we choose the value of β = 2 following the explanation given by [9]. variation of temperature with corresponding r.a.(j2000) and dec.(j2000) are plotted by using origin 8.0 and the graph is shown in figure 3(a). graph shows that temperature distributions are in separate cluster but minimum temperature region is little bit shifted from minimum flux density which is unusual behaviour. such type of nature is obtained due to external factors. graph 3(b) is the gaussian fit between dust color temperature and number of pixels with . a.k. gautam and b. aryal/ bibechana 16 (2019) 23-30: rcost p.27 (online publication: dec., 2018) offset temperature 0.98 k. this gaussian fit more or less follow the gaussian distribution with positive skewness. 28.5 30.0 31.5 33.0 34.54.44.85.25.66.06.4 f(60) f(100) 121.4 121.2 121.0 120.8-36.8-37.0-37.2-37.4dec.(j2000) r.a.(j2000)28.5230.1431.7533.3734.98 contour map of flux density fig.2(a): the 100μm verses 60μm flux density in the region of interest and 2(b) contour map at 100μm flux density where the agb star is located at the center r.a. (j2000)= 08h 04m 07.21s and dec.(j2000) = -370 11' 48.0". 121.4 121.2 121.0 120.8-36.8-37.0-37.2-37.4dec.9j2000) r.a.(j2000)21.5921.8222.0622.2922.52 contour map of temperature 21.6 21.8 22.0 22.2020406080100 gaussian center = 21.83 knumber td (k) fig. 3: (a) contour map of dust color temperature and (b) gaussian fit between dust color temperature and number of pixels. the field is centered at r.a. (j2000)= 08h 04m 07.21s and dec.(j2000) = -370 11' 48.0". the region in which minimum and maximum temperature is found in the range of 21.6 k to 22.5 k with an offset temperature of dust 0.9 k. it suggests that particles are independently vibrating . the cavity may be in thermally pulsating phase. when this result is compared with the result obtained in [13] where temperature variation is 20k to 22 k so our result is also comparable with that result. in the contour map, minimum flux and minimum temperature region are shifted which is due to some pagb 08-36 1.00x1.00 pagb 081.00x1.00 (a) (b) a.k. gautam and b. aryal/ bibechana 16 (2019) 23-30: rcost p.28 (online publication: dec., 2018) external factors possibly due to agb wind. there is good agreement in case of temperature in the gaussian fit with offset 0.98 k. 3.4. size of the structure major and minor diameter of the structure can be easily calculated by using a simple expression i.e., l = r × θ, where r = 2.8 kpc is the distance of the structure [7 ] and θ = pixel size (in radian). after calculation the major and minor diameter of the cavity region are found to be 44.4 pc and 19.4 pc respectively. thus, the size of the structure is 44.4 pc × 19.4 pc. 3.5. dust mass estimation and its variation for the calculation of dust mass, we need the distance to the region of interest. the distance of the structure is 2.8 kpc [7]. by using the temperature of each pixel and corresponding distance of the structure, we calculated mass of each pixel. average mass of each pixel is 8.7 x 1027 kg and total mass of the structure is 4.3 x 1030 kg i.e 2.16 m⊙.. but mass of dust obtained around white dwarf wd 1003-44 in [12] is 0.08 m⊙.. it means mass of dust around agb star is less than white dwarf. 121.4 121.2 121.0 120.8-36.8-37.0-37.2-37.4dec.(j2000) r.a.(j2000)7.250e277.785e278.320e278.855e279.390e27 contour map of dust mass 8.00e+027 8.50e+027 9.00e+027 9.50e+02710203040506070 gaussian center = 8.7 x 1027 (kg) number md (kg) fig.4: (a) contour map of dust mass and (b) gaussian fit between mass and number of pixels. the field is centered at r.a. (j2000)= 08h 04m 07.21s and dec.(j2000) = -370 11' 48.0". distribution of dust mass of the pixels within the selected contour level with r.a. (j2000) and dec.(j2000) are plotted in contour map by using origin 8.0. graph obtained is shown in fig.4(a) which shows that minimum temperature region is massive which suggests that it follows cosmological principle means distribution of dust mass is homogeneous and isotropy. graph 4(b) is the gaussian fit between mass and number of pixels with standard error ±σ. fitted gaussian fit of dust mass follow the gaussian distribution and suggests symmetric behaviour. 4. conclusion the physical properties of the cavity-like structure that we investigated while searching an effect of agb wind around carbon-rich agb stars. a study of flux density and dust color temperature maps, mass of dust, size of the cavity and inclination angle was calculated. our conclusions are as follows: • the major and minor diameter of the cavity like structure was found to be 44.4 pc and 19.4 pc respectively so size of the cavity is 44.4 pc x 19.4 pc. pagb 08-36 1.00x1.00 (b) (a) a.k. gautam and b. aryal/ bibechana 16 (2019) 23-30: rcost p.29 (online publication: dec., 2018) • the maximum temperature 22.5±0.05k was found at r.a.(j2000) = 121.040 & dec.(j2000) = -36.940 and minimum temperature 21.6±0.09 k was found at r.a.(j2000) = 121.290 & dec.(j2000) = -36.980 with offset of 0.9k. the small value of dust color temperature in the cavity suggests a continuous process by which cavity is supposed to be formed. low offset in the temperature hints that there is symmetric outflow or symmetric distribution of density and temperature. • in general, minimum flux and minimum temperature lie at same point in the pixel and in this case nearly normal condition is achieved. similarly maximum temperature and minimum mass region lie nearly at same region which is normal behavior. it means their distribution follow cosmological principle • average mass of each pixel is 8.7 x 1027 kg and total mass of the cavity is 4.3 x 1030 kg. • the inclination angle (i) of the cavity is found to be and 840 suggesting that the cavity will be in face-on (i = 0◦) when it is rotated through 60 from northern to southern direction (it is assumed that the cavity is in the sky plane). we intend to study the role of cabon-rich pagb star to form the far-infrared cavity in the future. acknowledgements we are grateful to the department of astro-particle physics, innsbrck university, specially to prof. r. weinberger for invoking us to work on dusty environments around agb stars. this research has made use of skyview virtual observatory, aladin v2.5 and nasa/ipac extragalactic database (ned). one of the authors (akg) acknowledges central department of physics, t.u., nepal for providing various support of ph.d. references [1] f. herwig, evolution of asymptotic giant branch stars. araa 43 (2005) 435. doi.org/10.1146/annurev.astro.43.072103.150600. [2] jr. icko iben and a.renzini, asymptotic giant branch evolution and beyond, annual review of astronomy and astrophysics 21 (983) 271. [3] a. i. karakas, j. c. lattanzio and o. r. pols, parameterising the third dredgeup in asymptotic giant branch stars, astron. soc. aust. 19 (2002) 515. [4] m. pathasarathy & s. r. pottasch, the infrared (iras) excess in hd161796 and related stars, a & a 154 (1986) l16. [5] s. r. pottasch, c. bignell, r. olling & zijlstra, planetary nebula near the galactic plane, a & a 225 (1989) 521. [6] w.e.c.j. van der veen & h.j. habing, the iras two color diagram as a tool for studying late stages of stellar evolution, a & a 194 (1988) 125. [7] r. szczerba, n. siodmiak, g. stasinska and j.borkowski, an evolutionary catalogue of galactic post-agb and related objects, astronomy and astrophysics 469 (2007) 799. doi.org / 10.1051/0004-6361:20067035. [8] s. l. schnee, n. a. ridge, a. a. goodman, g. l. jason, a complete look at the use of iras emission maps to estimate extinction and dust temperature, apj 634 (2005) 442. doi.org/10.1086/511054. [9] x. dupac, j. p. bernard, n. boudet, m. giard, j. m. lamarre, c. meny, f. pajot, i. ristorcelli, g. serra, b. stepnik, j. p. torre, inverse temperature dependance of the dust submillimeter spectral index, a&a, .404 (2003) l11. doi.org/10.1051/0004-6361:200030575. [10] r. h. hildebrand, the determination of cloud mass and dust characteristics from sub millimeter thermal emission, q.jl.r.astr. obs.ser 24 (1983) 267. a.k. gautam and b. aryal/ bibechana 16 (2019) 23-30: rcost p.30 (online publication: dec., 2018) [11] k. young, t. g. phillips, g. r. knapp, circumstellar shells resolved in iras survey data ii analysis, apj 409 (1993) 725. [12] erik holmberg, investigations of the systematic errors in the apparent diameters of the nebulae, melus, 117 (1946) 3h. [13] b. aryal, r. weinberger, dust structure around white dwarf wd 1003-44 in 60 and 100 μm iras survey, the himalayan physics ii (2011) 5. bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal far infrared cavity of a post c-rich agb star under iras survey a.k. gautam*, b. aryal central department of physics, t.u., kirtipur,nepal *email: arjungautamnpj@gmail.com article history: received 26 october, 2017; accepted 03 december, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18506 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/bync/4.0/ abstract in this paper, we discuss about the physical properties of the dusty environment around the mass losing carbon rich post agb star located at r.a. (j2000) =06 h 53m 01s and dec (j2000) =-02o 16’ 00”, in the far infrared iras maps. a cavity like structure (major diameter ∼ 103.3 pc & minor diameter ∼33.1 pc) is found to lie at r.a. (j2000)= 06 h 51 m 54.02 s and dec (j2000) = -01o 35’ 43”, located at a distance ∼ 6.11 kpc from the star. we studied the distribution of flux density, dust color temperature, dust mass in the cavity. the dust color temperature is found to lie in the range 18.7 k to 20.5 k which shows the cavity is isolated and independently evolved. such a low offset temperature variation shows that there is symmetric outflow or symmetric distribution of density and temperature. it further suggests that our structure is bigger in size and is far away from the far infrared loops(kk loops). the cavity may be in thermally pulsating phase. a possible explanation of the results will be discussed. keywords: agb stars; post agb stars; dust color temperature; dust mass. 1. introduction asymptotic giant branch (agb) stars are the final nuclear burning stage of lowand intermediate-mass stars driven by nuclear burning. this phase of evolution is characterized by two nuclear burning shell of hydrogen and helium where hydrogen burning shell lies below the convective envelope and helium burning shell lies above the electron-degenerate core of carbon and oxygen, or for the most massive agb stars a core of oxygen, neon, and magnesium [1]. this agb stage is characterized by low surface effective temperatures (below 3000k) and intense mass loss (from10−7 to 10−4 m⊙yr−1) [2]. when the gas temperature drops to the sublimation temperature range, heavy elements in the mass outflow from a central star will condense to form dust . dusty circumstellar envelopes will format the distance of several stellar radii. dust grains in the envelopes absorb stellar radiation and re-emit infrared radiation so agb stars are important infrared sources . the mass loss process plays an important role in the evolution of agb stars . it affects the lifetime of the agb phase and the core-mass of the subsequent post-agb stars. statistics of a large sample of agb stars would help to constrain the evolution of dust envelope. a.k. gautam and b. aryal. / bibechana 15 (2018) 90-96: rcost p.90 http://nepjol.info/index.php/bibechana mailto:arjungautamnpj@gmail.com http://dx.doi.org/10.3126/bibechana.v15i0.18 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ there are two main types of agb stars: the o-rich with c/o < 1 and mainly silicate-type grains in the outflow, and c-rich with c/o > 1 and mainly carbonaceous grains in the envelopes. due to different dust compositions of these two types of agb stars, different infrared spectral features are obtained which can be used to distinguish the two groups of the stellar objects . most of the carbon compounds such as aromatic hydrocarbon, benzene, methane, etc. are responsible for biological life so carbonrich agb stars are preferred in our research work. he-core burning phase is about 10 times shorter than the h-core burning shell so that the he-core burning leaves a c/o core behind that is surrounded by both a hydrogen and helium burning shell. for low and intermediate mass stars, carbon doesn't ignite and c/o core contracts and becomes electron degenerate. during the early agb phase, the abundance of he in the centre goes to zero where he-burning continues in a shell around a degenerate c-o core. in the meantime, the hlayer around the helium shell expands and cools sufficiently so that hydrogen burning shell is extinguished. convective envelope sets in and moves inwards and second dredge-up takes place. he shell is the main source for nuclear production so that it burns outward and reaches the hydrogen shell. in case of thermally pulsating agb phase, helium shell becomes thin and remains thermally unstable as a result thermal pulses are produced. in each thermal pulse, luminosity of helium shell nearly approaches 108l⊙[3].the production of such high luminosity in helium shell is called he shell flash or thermal pulse which is used to expand the outer layers. such strong expansion drives the h shell cooler and less dense as a result h shell is extinguished. the inner edge of deep convective envelope can then move inward and mix to the surface products of internal nucleosynthesis. this mixing process which occurs periodically after each tp is known as third dredge-up which is the mechanism for producing carbon stars. during tp-agb phase, main dominant source of nuclear energy is the hydrogen shell. thermally pulsating agb phase is the phase after the first thermal pulse to the time when the star ejects its envelope. at the end of the tp-agb, the envelope mass is strongly reduced down to 0.05 m⊙ due to the strong mass loss. the star now evolves towards high temperatures at an almost constant luminosity . this is because the surface layer is gradually heating up due to the proximity of the stable burning thin h-shell which produces the luminosity. the star has now entered the post-asymptotic giant branch (post-agb) phase. the material expelled away from the system during the agb stage forms a slowly expanding circumstellar shell [4]. when the mass of the hydrogen-rich envelope drops to ≈10−3m⊙, it starts to contract at a constant luminosity. this contraction phase causes an increase in effective temperature and at the same time leads to a radiatively driven wind which can compress the circumstellar shell and may result in ionization of the circumstellar material. in other words, the star may become hot enough to ionize its circumstellar material, observable as a planetary nebula (pn), in a few hundred years [5]. the star at this stage is known as a post-agb star. these have luminosity classes ranging from i (supergiant) to iii (giant) with spectral types from b to k. typical post-agb stars are expected to have luminosities around 103–104 l⊙ [6]. masses of these objects are in the range 0.6m⊙ – 1 m⊙. the star leaves the agb with teff< 5000 k . when it reaches teff> 30,000, it may ionize the remnant nebula. in this paper, we study the physical properties of a far infrared cavity, that we investigated during a systematic search on iras maps, located close to a carbon-rich post agb star (pagb 06-02) at -1.3o latitude. in section 2, we describe methods of calculation. a brief description of the result and discussion will be given in the section 3. finally, we conclude our results in the section 4. 2. methods we investigated a cavity-like structure in both 60 and 100 micron iras maps around a pagb star. fig.1(a), and 1(b) are cavity images at 60 and 100 μm whereas 1(c) is its contour map. we briefly describe a method for calculation of dust color temperature and dust mass of the dusty environment around carbon-rich post asymptotic giant branch named pagb06-02. a.k. gautam and b. aryal. / bibechana 15 (2018) 90-96: rcost p.91 fig. 1: (a) and (b) iras 60 μm and 100 μm far infrared image of the core region of agb 06-02 centered at r.a. (j2000) = 06h 51m 54.02s, dec. (j2000) = -010 35' 43” and (c) contour map of the cavity where major diameter (ab) and minor diameter (cd) passing through minimum flux. 2.1. dust color temperature estimation by using the iras 60 µm and 100 µm flux densities, schnee et al.[7] calculated dust color temperature. the flux density of emission at a wavelength λi is given by fi =                        1 2 3 dikt hc i e hc  nd α λi -β i (1) where β is the spectral emissivity index, nd is the column density of dust grains, α is a constant i.e. free parameter which relates the flux with the optical depth of the dust, and ωi is the solid angle subtended at λi by the detector. in dupac et al. [8], there is an inverse relationship between temperature and emissivity spectral index. we have with the assumptions that the dust emission is optically thin at 60 µm and 100 µm and that ωω∼ ω100 (true for iras image), we can write the ratio, r, of the flux densities at 60 µm and 100 µm as r = 0.6−(3+β) 1 1 240 144   d d t t e e (2) the spectral emissivity index (β) depends on dust grain properties like composition, size, and compactness. for a pure blackbody would have β = 0, the amorphous layer-lattice matter has β ∼ 1, and the metals and crystalline dielectrics have β ∼ 2 which is used in our calculations. for a smaller value of td, 1 can be dropped from both numerator and denominator of eq. (2) and it takes the form r == 0.6−(3+β) d d t t e e 240 144 (3) where , r = f(60µm) f(100µm) taking natural logarithm on both sides of eq. (3) and solving it, we find the expression for the temperature as ln(r)=ln 0.6−(3+β) [144/td-240/td] = ln 0.6−(3+β)[-96/td] td = −96 ln{r × 0.6(3+β)} (4) (b) iras 100 micron (a) 1.80x1.80 (c) a.k. gautam and b. aryal. / bibechana 15 (2018) 90-96: rcost p.92 f(60 µm) and f(100 µm) are the flux densities in 60 µm and 100 µm respectively and eq. (5) can be used for calculation of the dust grain temperature. 2.2. dust mass estimation dust mass is another important physical quantity which is useful to analysis the cavity structure. we need the known distance of the loops to calculate its dust mass which was provided in catalog of far infrared loops in the galaxy [9]. for the calculation of dust mass, we first obtained the value of flux density (sν) at 100 μm maps. the dust mass is estimated using [10], mdust = 4𝑎𝜌 3𝑄𝑛    snd2 b(n t) (5) where, weighted grain size (a) = 0.1 μm, grain density (ρ) = 3000 kg m-3, grain emissivity (qν) = 0.0010 (for 100 μm) [11]. the planck’s function b(ν, t), which is the function of temperature and frequency and is given by the expression: b(ν, t )= 2ℎ𝑐 𝜆3        1 hc elkt – 1 (6) where, h = planck’s constant, c = velocity of light, ν = frequency at which the emission is observed, t = the average temperature of the region. for 100 μm wavelength, the expression for the dust mass (5) reduces to, mdust =0.4[ 𝑆𝜗𝐷 2 𝐵(𝜗,𝑇) ] (7) we use equation (7) to calculate dust mass of the cavity. 3. result and discussion 3.1 structure: contour maps while going through the systematic search on iras maps, we discovered an isolated cavity in the 100 µm and 60 µm at r.a. (j2000) = 06h 51m 54.02s and dec. (j2000) = -01o 35’ 43”. with the help of the software aladin2.5, we have studied physical properties (size, dust color temperature, dust mass, etc) of the cavity. we selected contour level in such a way that it circles the cavity. the major axis, minor axis and line passing through minimum temperature and minimum flux are shown in the fig.1(b). 3.2 flux density and its variation by using aladin 2.5 software, the values of flux densities at 60μm and 100μm have measured. the flux density distribution within the contour of the region of interest has studied. we plotted a graph between flux at 100μm and 60μm with the help of origin 5.0 which is shown in fig.2(a). from the linear fit, slope of the line was 0.25. the linear equation of the fitted line is, y=-2.87+0.25x. using the slope of best fitted plot, dust color temperature is found as 24.4 k which is slightly more than our calculated value. again distribution of flux at 100μm of the pixels within the contour level with right ascension (r.a.) and declination (dec.) are plotted by using origin 8.0 and the graph is shown in fig.2(b). graph shows that all the fluxes from minimum to maximum lie within the contour level. most of the maximum flux regions lie at the boundary. 3.3. dust color temperature and its variation using the method of [7], we calculated dust color temperature of each pixel inner the outer isocontour in the region of interest. we use the iras 100 µm and 60 µm fits images downloaded from the iras a.k. gautam and b. aryal. / bibechana 15 (2018) 90-96: rcost p.93 server. for the calculation of temperature we choose the value of β = 2 following the explanation given by [8]. variation of temperature with corresponding r.a.(j2000) and dec.(j2000) are plotted by using origin 8.0 and the graph is shown in fig. 3(a). graph shows that temperature distributions are in separate cluster but minimum temperature region is little bit shifted from minimum flux density which is unusual behaviour. such type of nature is obtained due to external factors. 16.5 17.0 17.5 18.0 18.5 19.0 19.5 1.2 1.4 1.6 1.8 2.0 2.2 2.4 f (6 0 ) f(100) equation y = a + b* adj. r-squar 0.61449 value standard err b intercept -2.8675 0.17518 b slope 0.24983 0.00945 103.20 103.05 102.90 102.75 -1.2 -1.4 -1.6 -1.8 d e c. (j 2 0 0 0 ) r.a.(j2000) 16.7417.0917.4417.7918.1418.4918.8419.1919.54 flux density variation (a) fig.2: (a) the 100μm verses 60μm flux density in the region of interest and 2(b) contour map at 100μm flux density where the agb star is located at the center r.a. (j2000) = 06h 51m 54.02s, dec. (j2000) = -010 35' 43". 103.2 103.1 103.0 102.9 102.8 -1.2 -1.4 -1.6 -1.8 d e c .( j 2 0 0 0 ) r.a.(j2000) 18.7219.1619.6120.0520.50 distribution of temp. (a) 18.6 18.9 19.2 19.5 19.8 20.1 20.4 0 12 24 36 48 60 72 gaussian center = 19.43 k n u m b e r t d (k) fig. 3: (a) contour map of dust color temperature and (b) gaussian fit between dust color temperature and number of pixels. the field is centered at r.a.(j2000)= 06h 51m 54.02s and dec. (j2000) = -01o 35’ 43”. the region in which minimum and maximum temperature is found in the range of 18.7k to 20.5k with an offset temperature of dust 1.8k. such a low offset temperature variation shows that there is symmetric outflow or symmetric distribution of density and temperature. it further suggests that particles are independently vibrating . the cavity may be in thermally pulsating phase. when this result is compared with the result obtained in [12] where temperature variation is 20k to 22k so our result is also agb 09-52 agb 06-02 (a) 1.80x1.80 1.80x1.80 (b) a.k. gautam and b. aryal. / bibechana 15 (2018) 90-96: rcost p.94 comparable with that result. in the contour map, minimum flux and minimum temperature region are shifted which is due to some external factors possibly due to agb wind. there is no good agreement in case of temperature in the gaussian fit (fig. 3b) with offset 12.69 k. 3.4 size of the structure major and minor diameter of the structure can be easily calculated by using a simple expression i.e., l = r × θ, where r = 6.11kpc is the distance of the structure [9 ] and θ = pixel size (in radian). after calculation the major and minor diameter of the cavity region are found to be 103.3 pc and 33.1 pc respectively. thus, the size of the structure is 103.3 pc × 33.1 pc. 3.5 dust mass estimation and its variation for the calculation of dust mass, we need the distance to the region of interest. the distance of the structure is 6.11kpc [9]. by using the temperature of each pixel and corresponding distance of the structure, we calculated mass of each pixel. average mass of each pixel is 5.6x1028 kg and total mass of the structure is 2.5 x 1031 kg i.e 12.6m⊙. but mass of dust obtained around white dwarf wd 1003-44 in [12, 5] is 0.08m⊙. it means mass of dust around agb star is less than white dwarf. 103.20 103.05 102.90 102.75 -1.2 -1.4 -1.6 -1.8 d e c .( j 2 0 0 0 ) r.a.(j2000) 4.080e284.863e285.645e286.428e287.210e28 distribution of mass (a) 4.00e+028 5.00e+028 6.00e+028 7.00e+028 8.00e+028 0 30 60 90 120 150 gaussian center = 5.7x10 28 kg n u m b e r m d (kg) fig.4: (a) contour map of dust mass and (b)gaussian fit between mass and number of pixels. the field is centered at r.a.(j2000)= 06h 51m 54.02s and dec. (j2000) = -010 35’ 43”. distribution of dust mass of the pixels within the selected contour level with r.a. (j2000) and dec.(j2000) are plotted in contour map by using origin 8.0. graph obtained is shown in fig.4(a) which shows that minimum mass region didn't lie at the maximum temperature region in the selected contour which is unusual trend and is possibly due to agb wind. there is around good agreement in case of dust mass where offset mass is 1.6 kg. graph 4(b) is the gaussian fit between mass and number of pixels where offset mass is 1.6 kg. 4. conclusion the physical properties of the cavity-like structure that we investigated while searching an effect of agb wind around carbon-rich agb stars. a study of flux density and dust color temperature maps mass of dust was calculated. our conclusions are as follows: • the major and minor diameter of the cavity like structure was found to be 103.3 pc and 33.1 pc respectively. agb 06-02 1.80x1.8 0 (b) (a) a.k. gautam and b. aryal. / bibechana 15 (2018) 90-96: rcost p.95 • the maximum temperature 20.5k was found at r.a.(j2000) = 102.850 & dec.(j2000) = -1.360 and minimum temperature 18.7k was found at r.a.(j2000) = 102.980 & dec.(j2000) = -1.550 with offset of 1.8k. the small value of dust color temperature in the cavity suggests a continuous process by which cavity is supposed to be formed. low offset in the temperature hints that there is symmetric outflow or symmetric distribution of density and temperature. • in general, minimum flux and minimum temperature lie at same point in the pixel and in this case nearly normal condition is achieved. similarly maximum temperature and minimum mass region lie nearly at same region which is normal behavior. • average mass of each pixel is 5.6x1028kg and total mass of the cavity is 2.5x1031kg. we intend to study the role of cabon-rich pagb star to form the far-infrared cavity in the future. acknowledgements we are grateful to the department of astro-particle physics, innsbrck university, specially to prof. r. weinberger for invoking us to work on dusty environments around agb stars. this research has made use of skyview virtual observatory, aladin v2.5 and nasa/ipac extragalactic database (ned). one of the authors (akg) acknowledges central department of physics, t.u., nepal for providing various support of ph.d. references [1] f. herwig, evolution of asymptotic giant branch stars, araa, 43 ( 2005) 435. doi.org/10.1146/annurev.astro.43.072103.150600. [2] kyung-won suh, astrophysics of dusty stellar winds from agb stars, journal of the korean astrophysical society 47(2014) 219-233. doi.org/10.5303/jkas.2014.47.6.219. [3] a.i. karakas, j.c. lattanzio and o.r. pols, parameterising the third dredgeup in asymptotic giant branch stars, astron. soc. aust. 19 ( 200 ) 515. [4] jr. icko iben and a.renzini, asymptotic giant branch evolution and beyond, annual review of astronomy and astrophysics 21(1983) 271. [5] r.d. oudmaizer, a search for hotpost agb stars in the iras point source catalog, astronomy and astrophysics 306 (1996) 823. [6] t. blocker, stellar evolution of low-and intermediate mass stars ii. post agb evolution, astronomy and astrophysics 299 (1995) 755. [7] s.l. schnee, n. a. ridge, a.a. goodman, g. l. jason, a complete look at the use of iras emission maps to estimate extinction and dust temperature, apj .634 (2005) 442. doi.org/10.1086/511054. [8] x. dupac, j.p. bernard, n. boudet, m. giard, j.m. lamarre, c. meny, f. pajot, i. ristorcelli, g. serra, b. stepnik, j.p. torre,inverse temperature dependance of the dust submillimeter spectral index, a&a, 404 (2003) l11. doi.org/10.1051/0004-6361:200030575. [9] r. szczerba, n. siodmiak, g. stasinska and j.borkowski, an evolutionary catalogue of galactic post-agb and related objects, astronomy and astrophysics 469 (2007) 799. doi.org / 10.1051/0004-6361:20067035. [10] r.h. hildebrand, the determination of cloud mass and dust characteristics from sub millimeter thermal emission, q.jl.r.astr. obs.ser 24 (1983) 267. [11] k. young, t.g. phillips, g.r. knapp, circumstellar shells resolved in iras survey data ii. analysis, apj, 409 (1993) 725. [12] b. aryal, r. weinbergerr., dust structure around white dwarf wd 1003-44 in 60 and 100 μm iras survey". the himalayan physics ii (2011) 5. a.k. gautam and b. aryal. / bibechana 15 (2018) 90-96: rcost p.96 jyoti giri et al./ bibechana 16 (2019) 177-186: rcost p.177 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal structural and thermal characterization of different types of cellulosic fibers jyoti giri 1,2,3, ralf lach 4, janak sapkota 5, md. abu bin hasan susan 6, jean-marc saiter 7, sven henning 8, vimal katiyar 9, rameshwar adhikari 1,3,10 1central department of chemistry, tribhuvan university, kathmandu, nepal 2department of chemistry, tri-chandra campus, tribhuvan university, kathmandu, nepal 3nepal polymer institute (npi),p. o. box 24411, kathmandu, nepal 4polymer service gmbh merseburg (psm), merseburg, germany 5institute of polymer processing, department of polymer engineering and science, montanuniversitaet leoben, otto-glockel-strasse 2, 800 leoben, austria 6department of chemistry, dhaka university, dhaka, bangladesh 7université de normandie rouen laboratoire sms faculté des sciences and onyx developpment, groupe-nutriset, rouen, france 8fraunhofer institute for microstructure of materials and systems (imws), halle/s, germany 9department of chemical engineering, indian institute of technology (iit), guwahati, india 10research centre of applied science and technology (recast), tribhuvan university,kathmandu, nepal *email: nepalpolymer@yahoo.com article history: accepted 14 november, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21650 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract microand nanocrystalline cellulose were extracted from wheat stalk (ws) using different thermomechanical and chemical treatments and characterized by spectroscopic, microscopic and diffraction techniques. the virgin ws fibers were found to be structurally quite similar to the commercial microcrystalline cellulose (mcc). similar to the commercial one, the mcc extracted from the ws possessed intense infrared (ir) peaks whereas those peaks became more broader in the nanocrystalline cellulose (ncc) of the same origin, which can be attributed to possible breakdown of interand intramolecular h-bonding due to strong acid treatment of the mcc. microscopic results revealed characteristic textures of the mcc and the ncc, the mcc being irregular bundles of the primary crystals bound together with the amorphous phase. the latter was found to disintegrate upon acid hydrolysis giving rise to the rod-shaped nanocrystals having much larger surface area and thus possessing more intense hydrophilic character. the mcc was found to be more stable than the ncc which can be attributed to the presence of protective and binding coating provided by the amorphous cellulosic matter. keywords: natural fibers, morphology, electron microscopy, ftir spectroscopy, cellulose. http://nepjol.info/index.php/bibechana mailto:nepalpolymer@yahoo.com http://dx.doi.org/10.3126/bibechana.v16i0.20998 https://creativecommons.org/licenses/by-nc/4.0/ jyoti giri et al./ bibechana 16 (2019) 177-186: rcost p.178 (online publication: dec., 2018) 1. introduction polymers and fibers from renewable resources as well as their combinations in different forms have become attractive alternatives to conventional plastics, blends and composites for different practical applications [1, 2]. cellulose is one of the most abundant renewable natural resources. with the advancement in nanotechnology, the interests of polymer scientists have been attracted by microand nanocellulose of microbial as well as plants origin [1, 2]. among the natural fibers, cellulosics of various types and dimensionalities have special position in technical applications such as biodegradable tissue scaffolds, drug delivery vehicles and implantable biomaterials, aerospace engineering, functional devices and electronics. the applications of such materials include not only in paints, inks, cosmetics, and coatings but also in textiles, flexible electronics, packaging materials, and optical appliances [3–6]. nanocellulose composites have high mechanical properties and are non-toxic in nature and hence can be used in wide application areas. it has been recognized that the natural fibers are being progressively introduced in nanocomposite materials sectors as reinforcing agents for the fabrication of lightweight materials. these fibers not only enhance the mechanical and thermal properties but can also induce ease of degradation in the composites with other polymers [7–9]. biodegradation can also be observed based on the water absorption capacity of the composites, which is one of the criteria required to be easily attacked by microbes [8, 9]. in view of the potential opportunities of developing nanocellulose based enterprises based on agricultural wastes, a review on the extraction of microand nanocellulose was published a few years ago [10]. the objective of this paper is to discuss the structural and thermal properties of the micro and nanocellulose materials that can be used for the fabrication of the degradable composite materials targeted for packaging applications. 2. experimental 2.1 chemicals and sample preparation chemicals such as absolute alcohol, naoh, naocl, nahso3, and conc. h2so4 used in this work were purchased from qualigen fisher scientific, mumbai, india and were used without further purification. dry straw of the wheat (triticum aestivum) was collected from kathmandu and chopped into about 1 mm long fragments and then powdered properly with the help of a laboratory grinder. the wheat stalk (ws) powder was turned into micro crystalline cellulose (mcc) and nanocrystalline cellulose (ncc) using the procedures explained elsewhere [10]. 2.2 characterization methods fourier transform infrared (ftir) spectroscopy was performed on perkin elmer ftir2000) in attenuated total reflectance (atr) mode within the wavenumber range of 4000 to 700 cm–1 with resolution of 20 cm–1 in the atr mode. scanning electron microscope (sem, joel 6300) and field emission scanning electron microscope (fesem; zeiss gemin fesem) were used to visualize the morphology of the fibers. the specimen surface was coated with a thin film of gold for sem investigations. additionally, transmission electron microscope (fetem, joel, jem-2100f) was used to study the crystalline structure of the jyoti giri et al./ bibechana 16 (2019) 177-186: rcost p.179 (online publication: dec., 2018) fibers. the specimens were prepared by dropping dilute solution of ncc powder in deionized water onto carbon coated copper grid followed by oven drying at 40 °c for 24 h. thermogravimetric analysis (tga) of the samples was carried out using mettler-toledo, tga/sdta 851 equipment, under the inert atmosphere of dry nitrogen from 30 °c to 600 °c with the heating rate of 20° c/min. x-ray diffraction (xrd) was performed on x-ray diffractometer (rigaku, ttrax iii 18kw and bruker, germany) running on the cu-kα radiation (λ = 1.5406 å) at a scan rate of 0.05° per 0.5 s for 2ɵ range 5–50°. 3. results and discussion 3.1 spectroscopic characterization fig. 1(a) presents the ftir spectra of commercial mcc (named as mcc-com, hm400x) and the wheat stalk powder. the ftir spectra are similar; only a few peaks of the mcc are found to be sharper and distinct. both the spectra have broad absorption bands between 3600 cm–1 to 3000 cm–1 representing the o-h stretching vibration and the strong intraand intermolecular hydrogen bonds present in cellulose [11–14]. the ftir peak located at 1593 cm–1 represents the small bending vibration of oh bond. the axial c-h stretching of cellulose can be seen at 2894 cm–1 which is more intense and sharper in mcc-com than in the ws. the c–h stretching and ch2 wagging vibrations of cellulose are signature by correlated by the peaks located at 1369 cm–1 and 1315 cm–1, respectively [11]. likewise, the characteristic anti-symmetric bridge stretching of c–o and c–o–c pyranose ring vibration of cellulose is represented by the peak located at 1157 cm–1 [11]. similar type of c–o stretching and c–o–c glycosidic bond stretching are attested by strong band at 1023 cm–1 [15, 16]. the absorption peak at 890 cm–1 represents the typical structure of cellulose showing c–o–c stretching vibration for β, 1,4-glycosidic linkages [13, 17]. in ws fibers, a few peaks (such as around 1300 cm–1) are quite different than commercial mcc (mcc-com), such as phenolic c–o stretching which the signatures of presence of lignin and similar natural polymers in the neat ws. ws fibers further bear quite sharp peak corresponding to aromatic rings centered at 1604 cm–1 for lignin in comparison to mcc-com [18, 19]. fig. 1(b) compares the ftir spectra of mcc with that of ncc obtained from the ws fibers. the mcc and ncc both have almost identical ftir spectra as also reported by satyamurthy and vigneshwaran in cotton fibers [20]. the ftir peaks of the ncc are weaker and less intense than the mcc, due to the reduction in crystallinity value and breakdown of numerous and intraand intermolecular h-bonding between in the former [13, 19]. the prominent cellulose peaks appear more intense in the mcc as compared to the ws due to the exposure of the mcc crystallites resulting from the dissolution of lignin binder and hemicellulose during chemical treatments. few more cellulosic peaks are observed, in the mcc and ncc, such as at 1642 cm–1 representing carbonyl c=o stretching of a saturated hydrocarbon [21]. it can be summarized that similar to the commercial one, the mcc extracted from the ws possessed intense peaks centered at 3329 cm–1, whereas these peaks became broad and diffuse in the ncc of the same origin, which can be attributed to possible breakdown of interand intramolecular hbonding due to strong acid treatment. 3500 3000 2500 2000 1500 1000 500 mcc-com 1604 cm -12894 cm -1 3600-3000 cm -1 792 cm -1 1023 cm -1 a b so rb a n ce ( a .u .) wavenumber (cm -1 ) ws fiber a 3500 3000 2500 2000 1500 1000 500 ncc mcc 886cm -1 3732-2992cm -1 1650cm -1 1318cm -1 1062cm -1 a b so rb a n ce ( a .u .) wavenumber (cm-1) 2904cm -1 b a b 100 μm 20 μm jyoti giri et al./ bibechana 16 (2019) 177-186: rcost p.180 (online publication: dec., 2018) 3.2 morphological characterization the microscopic techniques provide direct evidence of morphological details of the materials at different length scales. the electron micrographs give fiber surface morphology, including their size and dimensionality as well as their overall surface texture. the scanning electron micrograph of the mcc derived from the ws fiber is shown in fig. 2 (a). the mcc fibers are semi-crystalline in nature with length of approximately 25 μm and width of 5 μm. in nature, the mcc has amorphous cellulose residing in between the micro-crystallites to form a long cylindrical structure with aspect ratio of approximately 5:1. the higher magnification sem image in fig. 2 (b) shows that the mcc bundles are made up of fine nanofibrillar texture. the dissolution of amorphous region of the ws fibers by different chemicals such as naoh, naocl and h2so4 can be attributed to the development of this texture. the results reported on commercial mcc in an earlier work were also quite similar with respect to fibrillation and surface texture evolution, as well as shape and size of the mcc crystals [22-27]. fig. 1: ftir spectra of different forms of natural fibers studied in this work: (a) pure wheat stalk (ws) powder compared to commercial mcc, and (b) the mcc and the ncc extracted from the ws powder. fig. 2: lower (top) and higher (bottom) magnifications of the sem images of the mcc extracted from ws. jyoti giri et al./ bibechana 16 (2019) 177-186: rcost p.181 (online publication: dec., 2018) fesem technique is very useful for morphological studies of mcc and ncc under almost environmental condition. in this work, ncc powder was observed by fesem, fig. 3. the synthesized bulk ncc powder in the dry form seems to have course, porous surface with large agglomeration. only few ncc crystallites are projecting outside from the agglomerate, fig. 3 (a). the shape of the ncc is more distinct in fig. 3 (b), showing its rod shaped texture. the largest ncc aggregates observed has the dimension approximately 1 µm long and 80 nm width, whereas the smallest one is about 200 nm long and 50 nm wide. these results are consistent with that reported in the literature [29–33]. the transmission electron micrographs presented in fig. 4 (a) manifest that ncc fibers are in a bundle before nano-fibrillation out of the mcc, which are then exposed out on acid hydrolysis followed by the dissolution of amorphous region present between the nano-fibrils. these ncc get dispersed as rod-like crystals as shown in fig. 4 (b). these crystals, being very hydrophilic in nature due to the presence of free –oh groups on their surfaces, can easily absorb water droplets or moisture, as demonstrated by cellular structures on the ncc crystals surfaces. the dimension of ncc from ws produced in this work is found to be approximately, 50 nm wide and 300 nm long. the results, in general, agree with the literature works [31–33]. from the microscopic results, it can be concluded that the mcc and ncc obtained from the ws fibers possess characteristic textures, the mcc being irregular bundles of the primary crystals bound together by the amorphous phase. the latter disintegrates upon acid hydrolysis giving rise to sharp rod-shaped nanocrystals which have much larger surface areas and thus possess strongly hydrophilic character. the mcc and ncc fibers were studied also using xrd whereby the diffractograms were utilized to calculate the degree of crystallinity and d-spacing of the crystallites. in the first glance, the mcc spectrum shows a clear amorphous halo and a crystalline structure which the ncc spectrum has practically no amorphous halo showing the lack of amorphous phase. the ncc have quasi no amorphous halo showing the lack of amorphous phase. the diffraction patterns of the mcc are shown in fig. 5 (a). the xrd plot of the mcc shows two feeble 2ɵ peaks in between 12 – 17° as well as two sharp peaks at 20.04° and 22.02° which have been assigned to the cellulose i [15, 35–38]. the high intensity of the peaks at 2ɵ positions further indicates the highly crystalline nature of the cellulosic fibers. the degree of crystallinity (χc) values for the ncc (50 %) was found to be much higher than for the mcc (31 %) which has been attributed as the result of strong acid hydrolysis induced dissolution of the amorphous zone embedding the crystalline fibrils [39, 40]. 3.3 thermal behavior the plot in fig. 6 illustrates of thermogravimetric analysis of mcc and ncc. both show two-step degradation. the mcc shows initial weight loss up to 7 % at around 120 °c which corresponds to the removal of water and other volatile substances. the mcc itself starts to degrade at 225 °c, the major degradation occurs at tmax of 373 °c, which can be observed from the accompanying differential curve. the complete thermal degradation occurred at around 400 °c with the char yield of 1.33 % at 600 °c which is consistent with the values reported for the cellulosic materials of different origins [17]. the char yield limits the production of combustible gases and can even decrease the exothermic pyrolytic reaction inhibiting the thermal conductivity of the burning materials. a b 4 μm 400 nm a b 200 nm 500 nm jyoti giri et al./ bibechana 16 (2019) 177-186: rcost p.182 (online publication: dec., 2018) similarly, ncc also losses its weight by 10 % due to removal of water and volatiles at around 120 °c while its degradation starts at 231 °c followed by the major degradation occurring at tmax of 300 °c. the complete degradation of the ncc occurs at 408 °c leaving the residual mass of 22.16 % in the form of char after combustion at 600 °c. thus, on comparing thermal behavior, on can observe that the mcc is found to be more thermally stable than the ncc. fig. 3: lower (a) and higher (b) magnifications of fesem images showing nano-sized cellulose particles extracted from ws. fig. 4: tem images of ncc extracted from mcc; (a) bundle showing ncc fibers in mcc, and (b) a single ncc crystallite dispersed from mcc. 0 10 20 30 40 50 in te n si ty ( a . u .) 2q (°) 22.02 20.04 12-17 0 10 20 30 40 50 in te n si ty ( a .u .) 2 () 22.2 19.63 12.14 a). mcc b). ncc 100 200 300 400 500 600 700 0 20 40 60 80 100 d m /d t ( % /o c ) temperature (oc) m a s s ( % ) mcc ncc -24 -22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 jyoti giri et al./ bibechana 16 (2019) 177-186: rcost p.183 (online publication: dec., 2018) fig. 6: tga thermograms of mcc and ncc extracted from ws. 4. conclusions microand nanocrystalline cellulose was extracted from wheat stalk using different thermomechanical and chemical treatments and characterized by spectroscopic, microscopic and diffraction techniques. the results presented in this paper can be concluded as follows: fig. 5: xrd patterns of mcc and ncc extracted from ws fibers. (a) the spectroscopic analyses conclude that the virgin ws fibers are structurally quite similar to the commercial mcc. similar to the commercial one, the mcc extracted from the ws possessed intense peaks centered at 3329 cm–1, whereas these peak became broad and diffuse in the ncc of the same origin, which can be attributed to possible breakdown of interand intramolecular hbonding due to strong acid treatment. (b) from the microscopic evidences obtained from sem and tem, it is concluded that the mcc and ncc obtained from ws fibers are characterized by definite textures, the mcc being irregular bundles of the primary crystals bound together with the amorphous phase. the latter disintegrates upon acid hydrolysis to give rise to the rod-shaped sharp nanocrystals which have much larger surface area and thus intense hydrophilic character. (c) the xrd results revealed that the natural fibers extracted from the ws predominantly contained cellulose i form of the crystals whereby the nanofibrillation increased the degree of crystallinity by about two folds. (d) the mcc and ncc thus prepared were found to be generally thermally stable while the ncc was found to be slightly less stable. the thermal stability of the mcc can be attributed to the security coating provided by the amorphous part of the cellulose which gets eliminated due to treatment with the strong acids. 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[29] w. gauitua, a. ballerini, j. zhang, polymer nanocomposites: synthetic and natural fillers a review. maderas clencia y technologia 7 (2005) 159–178. doi.org/10.4067/s0718-221x2005000300002. s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.100 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal thermodynamic, structural, transport and surface properties of pbtl liquid alloy s.k. yadav1, 2*, l.n. jha2, d. adhikari1** 1department of physics, mahendra morang adarsh multiple campus,tribhuvan university, biratnagar, nepal 2central department of physics, tribhuvan university, kirtipur, kathmandu, nepal **e-mail: adksbdev@yahoo.com *email: yadavshashit@yahoo.com article history: received 07 september, 2015; accepted 22 september, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13443 abstract thermodynamic properties, such as free energy of mixing, heat of mixing, entropy of mixing, activities and the microscopic structural properties, such as concentration fluctuation in long-wavelength limit and chemical short-range order parameter of pb-tl liquid alloy at 773 k have been studied on the basis of regular associated solution model. we have estimated the mole fractions of the complex and the unassociated atoms assuming the existence of pbtl3 complex as energetically favoured in the liquid state. the compositional contributions of the heat of mixing of the species pb and tl and the heat of formation of the compound to the net enthalpy change have also been studied. the transport properties such as, viscosity and the ratio of mutual and intrinsic coefficients have been studied using different approaches. the surface concentration of tl atoms has been computed and it has been employed to calculate the surface tension of pb-tl liquid alloy. both the theoretical and the experimental values of the concentration fluctuation in long-wavelength limit are found to be less than the ideal value, revealing that the concerned system is hetero-coordinating in nature. the interaction energies are found to be temperature dependent and respective alloy is found to be weakly interacting system. ©rcost: all rights reserved. keywords: structural properties; compositional contributions; hetero-coordinating; transport properties, surface tension; weakly interacting. 1. introduction though the direct intake thallium (tl) is harmful to human due to its toxicity but it has wide range of uses when quenched with other atoms. it is used in the manufacture of electronic components, optical lenses, semiconductor materials, alloys, gamma radiation detector equipment, imitation jewelry, artist's paints, http://nepjol.info/index.php/bibechana mailto:adksbdev@yahoo.com mailto:yadavshashit@yahoo.com http://dx.doi.org/10.3126/bibechana.v13i0.13443 s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.101 (online publication: dec., 2015) low temperature thermometers and green fireworks [1-3]. it is also used as a contrast agent in the visualization of cardiac function and tumors in small amounts. thallium forms simple eutectic alloys with tin, lead, cadmium, magnesium, etc. these alloys are resistance to wear and tear characteristics when used in bearing for steel shafts. thallium when alloyed with lead and tin increases mechanical strain of the materials by improving the resistance against deformation, breaking strength and hardness leading to preferable uses in bearings of machine parts [4]. these multidisciplinary uses of tl have attracted considerable attentions of the modern day researchers to predict the thermodynamic and structural properties of tl based alloys. as the alloys are generally grown from their liquid state at temperatures near to their melting point, the properties of the initial melt have great reflection on the characteristics of alloying materials. thus enormous work has been done by several theoreticians leading to the development of different theoretical models [5-16] for the investigations of the thermodynamic and microscopic structural behaviour of liquid binary alloys. this work is focused on the study of the thermodynamic and microscopic structural behaviour of pb-tl liquid alloy at 773 k on the basis of regular associated solution model [17-21]. according to the regular associated solution model, it is assumed that the liquid solution consist of an ideal mixture of free monomers and the complex in tranquility. further there appear strong associations among the constituent species in liquid phase close to their melting points. these associations are given different names such as, 'complexes', 'pseudomolecules', 'clusters' or simply 'associations'. the initial melt thus can be considered as the ternary mixture of the associated atoms and the free monomers. the expressions for the different thermodynamic and the microscopic functions are derived on these considerations. in the microscopic structural functions, the concentration fluctuation in long wavelength limit (scc(0)) has become an important parameter to predict the structure of the liquid alloys. bhatia et al, [16] has shown that the concentration fluctuation in the long wavelength limit can be obtained from the model parameters even if the data from the low angle x-ray and neutron diffraction experiments are not available. the expressions for scc(0) and the thermodynamic functions of compound forming liquid binary alloys were later derived by bhatia and hargrove [16], however, this procedure was significantly simplified by lele and ramchandrarao [18] which involves the estimation of the pairwise interaction energy parameters and the equilibrium constant from the activity coefficients of the components at infinite dilution and the activity data at one another intermediate compositions.the phase diagrams of the pb-tl alloy [22] shows that there exhibit three different phases such as, pbtl2, pbtl3 and pbtl7 . among these phases, we have assumed the existence of pbtl3 complex and estimated its thermodynamic and structural properties. the theoretical estimation shows that there is significant asymmetry in structural properties (short range order parameters) of this alloy. the size factor and the difference in the electronegativity of the alloying materials are also the influencing parameters resulting to asymmetry. the size factors of pb-tl alloy (ωtl/ωpb= 0.943) is quite small for this behaviour. also, the greater is the difference in the electronegativity of the alloying atoms, greater is the change in the metallic behaviour to s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.102 (online publication: dec., 2015) the ionic behaviour resulting into the asymmetry. the difference in the electronegativity of pb-tl liquid system (etl – epb = -0.29) is also too small for this anomalous behaviour. the viscosity of the pb-tl liquid alloy at 773 k has been computed using moelwyn-hughes theory [23], kozlov theory [24] and kaptay theory [25]. the ratio of mutual to intrinsic diffusion coefficients has also been estimated to explain the nature of local arrangements of atoms in the liquid state. the surface tension of the liquid alloy has also computed using butler's approach of mono-atomic surface layer [26]. the theory containing the methodology of this work is presented in the section 2, the results and discussion is presented in the section 3 and the conclusions are presented in the section 4. 2. theory 2.1 thermodynamic and structural properties let the binary liquid solution consists of 𝑛1 and 𝑛2 atoms of the monomers a (=tl) and b (=pb) respectively. then from the conservation of mass, the formation of the complex aμb (aμb ⟺ μa + b) in the partially associated solution requires n1 = na + μnaμb and n2 = nb + naμb, where na, nb and naμb are respectively the concentrations of the unassociated monomers a and b and the complex aμb [18] and μ is a small integer whose value is determined from the complex forming concentration (= μ / (μ +1)) in the solid state. due to the formation of the complexes, the thermodynamic and the microscopic functions are governed by their true mole fractions xa, xb and xaμb than their gross mole fractions x1 and x2, where xa = na na+ nb+naμb , xb = nb na+ nb+naμb and xaμb = naμb na+ nb+naμb (1a) x1 = n1 n1+ n2 , x2 = n2 n1+ n2 (1b) on solving above two equations, the true mole fractions can be expressed as xa = x1 − px2xaμb and xb = x2 − (1 − px2)xaμb (2) according to prigonine and defay [27], in the associated solution the gross chemical potentials of the components 1 and 2 are equal to the chemical potentials of the free monomers a and b. following jordan [20], the activity coefficients of monomers γa, γb and γaμb can be represented in terms of pairwise interaction energies as rt lnγa = xb 2 ω12 + xaμb 2 ω13 + xb xaμb (ω12‒ ω23 + ω13) (3a) rt lnγb = xaμb 2 ω23 + xa 2 ω12 + xa xaμb(ω23 − ω13 + ω12) (3b) rt lnγaμb = xa 2 ω13 + xb 2 ω23 + xaxb(ω13 − ω12 + ω23) (3c) s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.103 (online publication: dec., 2015) where ω12, ω13 and ω23 represents the pairwise interaction energies for the species a, b; a, aμb and b, aμb respectively. t and r represent temperature and universal real gas constant respectively. the relation for the equilibrium constant is expressed as [18] lnk = ln ( xa μ xb xaμb ) + ω12 rt + ω12 rt [ μxb (1 ‒ xa) + xa ] + ω13 rt [ μxaμb (1 ‒ xa) ‒ xa ] + ω23 rt [ xaμb (1‒ μxb) ‒ xb] (4) and the free energy of mixing (gm) is given as gm = 1 1+μxaμb rt [( xaxb ω12 rt + xaxaμb ω13 rt + xbxaμb ω23 rt ) + (xalnxa + xblnxb + xaμblnxaμb) + xaμblnk] (5) the other thermodynamic functions such as heat of mixing (hm), entropy of mixing (sm) and the microscopic structural function, concentration fluctuation in the long wavelength limit ( scc (0) ) are corelated with free energy of mixing (gm) by the following standard thermodynamic relations hm = gmt ( ∂gm ∂t )p (6a) sm = hm− gm t (6b) scc (0) = rt ( ∂2gm ∂x1 2 ) t,p −1 (6c) scc (0) = x2 α1( ∂α1 ∂x1 ) t,p −1 = x1 α2( ∂α2 ∂x2 ) t,p −1 (6d) the expression for the enthalpy of mixing can be obtained solving equations (5) and (6a) as hm = 1 1+μxaμb [( xaxb ω12 rt + xaxaμb ω13 rt + xbxaμb ω23 rt ) – t ( xaxb ∂ω12 ∂t + xaxaμb ∂ω13 ∂t + xbxaμb ∂ω23 ∂t ) − rt2 dlnk dt ] (7) the expression for the concentration fluctuation in the long wavelength limit (scc(0)) can be obtained by using equation (5) in equations (6c) as scc(0) = 1/ [ ( 1 1+μxaμb ) { 2 rt (xa ′ xb ′ w12 + xa ′ xaμb ′ w13 + xb ′ xaμb ′ w23) + ( xa ′2 xa + xb ′2 xb + xaμb ′2 xaμb )} ] (8) here, ∂2gm ∂x1 2 > 0 for ∂gm ∂x1 = 0. the prime denotes the differentiations with respect to concentrations, and xa ′ and xb ′ are obtained by using equation (2). xaμb ′ is obtained using equation (5) by using the condition dlnk dx1 = 0 [28,29]. the factor ( 1+ pxaμb )-1, which appears as a coefficient of all terms containing xa, xb s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.104 (online publication: dec., 2015) and xaμb in equations (5), (7) and (8), is a result of change in the basis for expressing mole fractions of species a, b and aμb from that used for x1 and x2. at a given concentration, if scc (0) < scc id (0) then ordering (unlike atoms pairing) is expected and if scc (0) > scc id (0), then segregation (like atoms pairing) is expected, where scc id (0) =x1x2. the experimental values of scc (0) can be obtained from equation (6d) using the observed avlues of activities [22]. the degree of local ordering in such liquid systems can be studied by estimating warren-cowley short range order parameter (α1) with the knowledge of (scc(0)) [16,17]. the expression for α1 in terms of scc(0) is given as α1 = s −1 s (z −1) + 1 where, s = scc (0) scc id (0) and scc id (0) =x1x2 (9) where z is the coordination number and z = 10 is taken for our calculation. the methodology for the estimation of the equilibrium constant and the interaction energy parameters: the unknown interaction energy parameters (ω12, ω13 and ω23), the equilibrium constant (k) and the complex concentrations can be obtained by the consideration of the activity coefficients at infinite dilution and adoption of the iterative procedure [18]. in regular associated solution model, x1γ1 = xaγa and x2γ2 = xbγb, where γ1 and γ2 are the gross activity coefficients of components 1 and 2 respectively. lnγ1 = lnγa + ln ( xa x1 ) (12a) and, lnγ2 = lnγb + ln ( xb x2 ) (12b) on solving equations (12a) and (12b), we obtain ω13 rt = xb ln( α2 xb )+( 1− xb ) ln( α1 xa )− xb (1− xb ) ω12 rt xaμb 2 (13a) ω23 rt = xa ln( α1 xa ) +( 1−xa ) ln( α2 xb ) − xa( 1− xa ) ω12 rt xaμb 2 (13b) where α1 and α2 are activities of components 1 and 2 respectively. the pairwise interaction energies, the equilibrium constants and the activity coefficients at infinite dilution can be related as [18] ln γ1 0 = ω12 rt (14a) k exp ( ω13 rt ) = ( γ1 0 γ2 0 γ1 0 − γ2 0) (14b) on solving equations (4), (13a) and ( 13b), we obtain s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.105 (online publication: dec., 2015) lnk + ω13 rt = ( 1+xa xaμb ) ln ( α1 xa ) + xb xaμb [ln ( α1 xa ) − ω12 rt ] + ln ( a1 μ a2 xaμb ) (15) after estimating the mole fraction of the complex xaμb, the mole fractions of the unassociated monomers (xa and xb) will follow readily from equation (2). 2.2 transport properties the study of the transport properties, such as viscosity, diffusion coefficients, etc helps to understand the mixing behaviour of binary liquid alloys at the microscopic level. in this work, we have employed the following three different theoretical approaches to compute the viscosity of the pb-tl liquid alloy at 773 k. the moelwyn-hughes equation [23] for viscosity of liquid mixture assumes that the viscous flow becomes more difficult when the cohesion energy of the alloy is increased is given as η = (x1η1 + x2η2)(1 − 2x1x2. hm rt ) (16) where η is the viscosity of the alloy, ηi ( i = 1,2) is the viscosity of the pure components tl and pb respectively. the variation of viscosity, ηi with temperature t may be expressed as [30] ηi = η0i exp( e rt ) (17) where η0iand e are constants for pure metal, in units of viscosity and energy per mole respectively. the kozlov equation [24] for the viscosity of binary mixture has been derived in a theoretical way with the correlation in semi-logarithmic coordinates as lnη = x1η1 + x2η2 − hm 3rt (18) where the symbols have the same meanings as those in eq. (16). the kaptay equation [25] for the viscosity of binary mixture has been derived taking into account the theoretical relationship between the cohesion energy of the alloy and the activation energy of viscous flow assuming that in the alloys with stronger cohesion energy the viscosity will increase, and not decrease η = ( h na x1v1+x2v2+ve) exp ( x1g1 ∗ +x2g2 ∗ −(0.155±0.015)hm rt ) (19) where gi ∗ is the gibb's energy of activation of the viscous flow in pure components i given by gi ∗ = rt ln ( ηi vi h na ) (20) where na is avogadro's number, vi are the molar volumes of components i (i = 1,2), h is the planck's constant and ve is the excess volume upon alloy formation which can be neglected. s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.106 (online publication: dec., 2015) the greater insight of microscopic structural properties can be done by evaluating diffusion coefficient which is expressed in terms of scc (0) by using darken thermodynamic equation [31, 32] as dm did = x1 x2 scc (0) (21) where, dm stands for the chemical or mutual diffusion coefficient and did stands for the intrinsic diffusion coefficient for an ideal mixture which are related as dm = did ∂lnaa ∂x1 , with dm = x1db + x2da (22) where, da and db are the self-diffusion coefficient of pure components a and b respectively. 2.3 surface properties the surface tension of the initial melt has great influence on the formation of solid alloys by the solidification process. the metallurgical phenomenons, such as crystal growth, welding, gas absorption, nucleation of gas bubbles are minutely associated with the surface tension. the surface properties help in understanding, description and metallurgical modeling as well as prediction of structure development during solidification in the binary alloys. the butler’s method [26] has been employed to determine the surface tension of pb-tl alloys in liquid state at 773 k. butler’s model considers the existence of monoatomic layer at the surface as a separate phase that is in thermodynamic equilibrium with the bulk phase. the surface tension (τ) of a binary liquid solution at temperature t in this model can be expressed as τ = τ1 + 1 a1 (g1 e,s − g1 e,b) + rt a1 (lnx1 s − lnx1) (23) τ = τ2 + 1 a2 (g2 e,s − g2 e,b) + rt a2 (lnx2 s − lnx2) (24) where τ1 and τ2 are surface tensions, and a1 and a2 are the areas of the hypothetical layer at the surface of the components a and b respectively at temperature t. gi e,s andgi e,b , (i =1,2), are partial excess free energies xi and xi s and are mole fractions of component i in the bulk and that in the surface respectively. the area of monatomic surface layer for the component i is obtained from the following relation ai = 1.091 na 1/3 vi 2/3 (25) where na is avogadro’s constant and vi represents the molar volume of the component i. the molar volume can be calculated from the atomic mass and density of the pure component at the temperature of investigation. on solving eqs. (23) and (24) together for the surface concentration, we can compute surface tension of a liquid alloy system if the ratio of partial excess free energy in the surface and that in the bulk is known because all other quantities are either known or can be calculated using available data for pure components. assuming the partial excess gibbs energy in the bulk and that in the surface to have the same concentration dependence, they can be related to each other through a parameter 𝝺 as s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.107 (online publication: dec., 2015) λ = gi e,s/gi e,b (26) the value of 𝝺 is considered to be 0.83 for the calculations. 3. results and discussion 3.1 thermodynamic and structural properties the model parameters are determined from equation (14) with the knowledge of the observed activity coefficients [22]. the mole fraction xtl−pb of the complex pbtl3 is then estimated using equation (15) by iterative procedure. the compositional dependence of mole fractions various species shows the maximum association of about 4.84 mole % at xtl = 0.5 (figure 1). the other model parameters are determined from equations (4) and (13). these values are slightly adjusted by the successive approximation to explain the experimental values of the free energy of mixing [22] using equation (5). the best fit values of so obtained are found to be k = 0.623, ω12 rt = 0. 228, ω13 rt = + 2.41 and ω23 rt = -1.46 the negative values of ω12/rt and ω23/rt indicates that there exists attraction between the monomers tl and pb, and pb and the complex pbtl3 whereas the positive value of ω13/rt indicates the repulsion between the monomer tl and the complex pbtl3 in the initial melt. the theoretical values of the free energy of mixing (gm/rt ) are calculated using equation (5). the theoretical investigation shows that the minimum values of gm/rt are found to be at xtl = 0.5 (the theoretical value of gm/rt = 0.79434 and the experimental value of gm/rt = 0.79090). both the theoretical and the experimental values of gm/rt are in well agreement (figure 2). the other temperature dependent model parameters are estimated using equation (7) to explain the experimental values of the enthalpy of mixing (hm/rt) [23]. the best fit values are found to be ∂ω12 ∂t = + 2.39 j mol-1k-1, ∂ω13 ∂t = + 4.98 j mol-1 k-1, ∂ω23 ∂t = + 6.01 j mol-1 k-1 and rt2 dlnk dt = 12900 ± 2700 j mol-1 the theoretical values of the enthalpy of mixing (hm/rt) are obtained from equation (7) with the aid of above determined parameters. both the calculated and the observed values [22] of the enthalpy have small negative values revealing the fact that the system under consideration is weakly interacting system. the minimum values hm/rt are found to at xtl = 0.5 (the theoretical value of hm/rt = 0.18366 and the experimental value of hm/rt = 0.18101). figure 2 shows that both the calculated and the experimental values are in well agreement. s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.108 (online publication: dec., 2015) fig. 1: mole fractions of pb (xpb), tl (xtl) and pbtl3 (xtl−pb) vs concentrations of tl (xtl) of pb-tl liquid alloy at 773 k. fig. 2: free energy of mixing (gm/rt), heat of mixing (hm/rt) and entropy of mixing (sm/r) vs concentrations of tl (xtl) of pb-tl liquid alloy at 773 k. the compositional contributions of the heat of mixing of the species xa, xb and xaμb and the heat associated with the formation of the complexes to the net enthalpy change can be obtained from equation (7) [33]. the complex formation term contributes the maximum at 69.49 % of tl and the mixing term contributes the maximum at 40.68 % of tl as a result of which the net enthalpy change shows the maximum at 50.85 % of tl (figure 3). the theoretical values of the entropy of mixing (sm/r) are obtained using equation (6b) with the help of theoretically determined values of gm/rt and hm/rt. both the experimental and the theoretical values of entropy of mixing are in well agreement (figure 2). the theoretical activities values for both of the unassociated species aa and ab (a = tl and b = pb) were computed using equations (12a) and (12b). both the theoretical and experimental values of activities [23] are in well agreement (figure 4). it can thus be concluded that the model parameters have not only explained the thermodynamic properties of the pb-tl liquid alloy at 773 k but also have successfully reproduced the activities. to peep into the microscopic behaviour of the liquid alloy, the concentration fluctuation in the long wavelength limit (scc(0)) was calculated. the theoretical and the experimental values are respectively obtained from equations (8) and (6d), and the ideal values are obtained from equation (9). both the theoretical and the observed values of scc(0)) are less than the ideal value at all concentrations thereby predicting the ordering (hetero-coordinating) nature of the pb-tl melt at 773 k. s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.109 (online publication: dec., 2015) there is reasonable match between the theoretical and the experimental values of the concentration fluctuation in the long wavelength (figure 5). fig. 3: contributions of heat associated with the formation of compound and mixing of free monomers to total enthalpy change vs concentrations of tl (xtl) of pb-tl liquid alloy at 773 k. fig. 4: the activities of tl (atl) and pb (apb) vs the concentration of tl (xtl) of pb-tl liquid alloy at 773 k. the nature and the strength of local ordering of the melt can be greater understood by estimating the short-range order parameter (α1). at equiatomic composition, the values of α1 lies between -1 to +1. if α1 = −1, indicates the complete ordering of unlike atoms at nearest neighbours, if α1 = +1, indicates the complete segregation or paring of like atoms in the nearest neighbours and if α1 = 0, indicates the complete randomness of the atoms in the liquid state. theoretical values of α1 are obtained from equation (9). the compositional dependence of α1 is shown in figure 6. it can be seen that the values of α1 are found to be negative at all compositions which further verifies the ordering nature of the pb-tl liquid alloy at 773 k. 3.2 transport properties at first, the viscosities of the component metals at the temperature of investigation are computed from eq. (17) with the aid of the values of constants η0i and e which are taken from the reference [30]. the comparative study of the viscosity of the liquid alloy is then done by computing the viscosity from eqs. s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.110 (online publication: dec., 2015) (16), (18) and (19) separately. the compositional depemdence of the viscosity along with the ideal value is shown in figure 7. with the increase in the concentration of tl, the viscosity obtained from all the three models are greater than the ideal value but sharply decreases below the ideal value at about xtl = 0.6. with the further increase in the concentration of tl, the viscosity values obtained from different model again rises above the ideal values. the values obtained from all the models are comparable with each other. fig. 5: the concentration fluctuation in long wavelength limit (scc(0)) vs the concentration of tl (xtl) of pb-tl liquid alloy at 773 k. fig. 6: the short-range ordering parameter (α1) and the ratio of mutual and intrinsic coefficients (dm/did) vs the concentration of tl (xtl) of pbtl liquid alloy at 773 k. the mixing tendency of the liquid alloy can be studied at the microscopic level by computing the ratio of the mutual and intrinsic-diffusion coefficients (dm/did). if dm/did > 1, indicates the tendency of compound formation; if dm/did < 1, indicates the separation of phase and dm/did = 1, for the ideal mixing of the liquid alloy. the values of dm/did are obtained from eq. (21) and are found to be positive and greater than one in the entire compositions (figure 6). this further clarify the theoretical analysis of the presence of the chemical order in the liquid state of pb-tl alloy at 773 k. 3.3 surface properties the surface concentration of tl has been computed by simultaneously solving eqs.(23) and (24). the surface tension of the pb-tl liquid alloy at 773 k is then calculated using the determined values of surface s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.111 (online publication: dec., 2015) concentrations. the density and surface tension of the pure components at the temperature of investigation have been computed from the following expressions [30] ρ(t) = ρm + ∂ρ ∂t (t − tm) (26) 𝜏(𝑇) = 𝜏𝑚 + 𝜕𝜏 𝜕𝑇 (t − tm) (27) where ∂ρ ∂t , 𝜕𝜏 𝜕𝑇 ,t and tm are temperature coefficient of density, temperature coefficient of surface tension, temperature of investigation and melting temperature respectively. the density, surface tension and temperature coefficients for pure tl and pb components are taken from the ref. [30]. theeoretical values of surface concentrations are almost equal to the ideal values at all concentrations (figure 8). the value of surface tension obtained from the butler's model is lose to the ideal values (figure 9). fig. 7: viscosity vs concentration of tl (xtl) of pb-tl liquid alloy at 773 k. fig. 8: surface concentration of tl vs concentration of tl (xtl) of pb-tl liquid alloy at 773 k. s.k.yadav et al. / bibechana 13 (2016) 100-113 : rcost p.112 (online publication: dec., 2015) fig. 9: surface tension vs concentration of tl (xtl) of pb-tl liquid alloy at 773k. 4. conclusions the regular associated solution model has been useful in understanding and predicting the thermodynamic as well as the microscopic structural properties of pb-tl liquid alloy at 773 k. the theoretical analysis reveals that the pb-tl melt is complete ordering (unlike atoms pairing) in nature. the liquid system under consideration is found to be weakly interacting and the interaction energy parameters are found to be temperature dependent. references [1] la dou, j. metals. in., (1997) 429 [2] c. wang, y. chen, j. liu , j. wang, x. li, y. zhang, ecotoxicol environ saf. ; 90 (2013) 76-81. http://dx.doi.org/10.1016/j.ecoenv.2012.12.014 [3] a. turner, o. furniss, mar pollut bull, 64(2012) 2720-2724. http://dx.doi.org/10.1016/j.marpolbul.2012.09.023 [4] f. habashi , alloys: preparation, properties and applications, john wiley and sons (2008). 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publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal spatial orientation of galaxies in supercluster s[227+006+0078] janak ratna malla 1* , walter saurer 2 , binil aryal 3** 1 amrit campus, t.u., kathmandu 2 institute of astro-particle physics, innsbruck university, austria 2 3 central department of physics, kirtipur ,kathmandu email: * janak_malla@yahoo.com, ** aryalbinil@gmail.com article information: received: august 21, 2019 accepted: december 07, 2019 keywords: sdss supercluser redshift galaxy abstract we present a study of spin vector orientation of 1218 sdss (sloan digital sky survey) galaxies in supercluster s [227+006+0078] having redshift 0.07 to 0.09. the database of these galaxies is taken from sdss (sloan digital sky survey) 7 th and 9 th data release. we have converted two dimensional data to three dimensional by godlowskian transformation using position angle-inclination angle method. we intend to find non-random effects in the spatial orientation of galaxies in the supercluster. no preferred alignment of angular momentum vectors is noticed, supporting hierarchy model of galaxy formation. 1. introduction modern cosmology is based on two fundamental assumptions: first, the dominant interaction on cosmological scales is gravity, and second, the cosmological principle is a good approximation to the universe. the cosmological principle states that the universe, smoothed over large enough scales, is essentially homogeneous and isotropic. ‘homogeneity’ has the intuitive meaning that at a given time the universe looks the same everywhere, and ‘isotropy’ refers to the fact that for any observer moving with the local matter the universe looks (locally) the same in all directions. von weizsacker and gamow (1951 & 1952) verified that the observed rotation of the galaxies is important for cosmology: the fact that the galaxies rotate may be clue to the physical conditions under which these systems formed. in the instability picture, one imagines that large irregularity like galaxies grew under the in influence of gravity from small imperfections in the early universe [1, 2]. in this picture one must abandon the idea that the angular momentum of the galaxies was given as the initial value, or developed in some sort of primeval turbulence (as was proposed by von weizsaker [3] and gamow [4] , for otherwise the galaxies would have formed too soon [2]. on the other hand, huge low red shift galaxy surveys such as the 2-degree field galaxy red shift survey and the sloan digital sky survey (sdss) [5] have convinced most cosmologists that not only isotropy but also homogeneity is in fact a reasonable assumption for the universe. the universe is homogeneous and isotropic on scales larger than this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.26582 http://nepjol.info/index.php/bibechana mailto:janak_malla@yahoo.com mailto:aryalbinil@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.26582 janak ratna malla / bibechana 17 (2020) 117-122 118 100 mpc, but on smaller scales we observe huge deviations from the mean density in the form of galaxies, galaxy clusters, and the cosmic web being made of sheets and filaments of galaxies. how do structures grow in the universe and how can we describe them? the most accepted view on the formation and evolution of large scale structure is that it was formed as a consequence of the growth of primordial fluctuations by gravitational instability [6]. in the current favored model, smaller structures collapse first and are later incorporated in larger collapsing structures in a bottom-up scenario that provides a natural explanation for the formation of galaxies, clusters, filaments and superclusters [7] . there are three predictions about the spatial orientation of spin vectors of galaxies. these are the `pancake model', the `hierarchy model,' and the `primordial vorticity theory.' the `pancake model' [8, 9] predicts that the angular momentum vectors of galaxies tend to lie within the cluster plane. according to the `hierarchy model' [2], the directions of the angular momentum vectors should be distributed randomly. the `primordial vorticity theory' [10,11] predicts that the spin vectors of galaxies are distributed primarily perpendicular to the cluster plane. in this paper, we analyze spatial orientation of angular momentum vectors of 1218 galaxies in the sdss supercluster s [227+006+0078]. the methods and results are described in the following chapters. godlowskian transformation the three dimensional orientation of the angular momentum vectors of a galaxy is characterized by two angles: the polar angle (between the galactic sv and a reference plane (here equatorial plane), and the azimuthal angle  between the projection of a galactic sv on to this reference plane and the x-axis within this plane. the detail derivations of the expressions of the angles  and  are given in flin & godłowski [12] . when using equatorial coordinate system as reference, then  and can be obtained from measurable quantities as follows:  cossinsinsincossin pii  (1)    coscossinsinsinsinsincoscos)(cossin 1 ppii   (2) where , i is the inclination angle, the angle between the normal to the galaxy plane and the observer’s line-of-sight, αis right ascension, δ is declination and p is position angle. the inclination angle can be computed from the formula )*1( )*( cos 2 22 2 q qq i    (3) this expression is valid for oblate spheroids [13]. here, q and q* represent the measured axial ratio (b/a) and the intrinsic flatness of the galaxy, respectively. hiedmann et al.[14] showed that the values of q* range from 0.083 for sd spirals to 0.33 for ellipticals. for the galaxies with unknown morphology q*= 0.20 is assumed holmberg [13]. 2. method of analysis here we describe the procedure for the removal the selection effects to obtain the isotropic distributions for both and as given by aryal & saurer [15]. theoretically, the isotropic distribution curve for polar angle is cosine and that for azimuthal angle is the average distribution curve, with the restriction that the database is free from selection effect. aryal & saurer [15] concluded that any selections imposed on the database may cause severe changes in the shapes of the expected isotropic distribution curves. in their method, a true spatial distribution of the galaxy rotation axis is assumed to be isotropic. then, due to the projection effects, i can be distributed as sin i, b can be distributed cosb, the variables α and p can be distributed randomly, and the equation (1,2) can be used to calculate the corresponding values of polar () and azimuthal (). we run simulations in order to define expected isotropic distribution curves for both the and distributions. the isotropic distribution curves are based on simulations including 10 7 virtual galaxies. at first we observed the distributions of α, δ, p and i for the galaxies in our samples and janak ratna malla / bibechana 17 (2020) 117-122 119 distributed by creating 10 7 virtual galaxies for respective parameters. we use these numbers to make input file and the expected distribution by running simulation in matlab 15.0. our observations (real observed data set) are compared with the isotropic distribution curves (obtained from simulation) in both and  distributions. for this comparison we use four different statistical tests: chi-square probability, first order fourier coefficient (11/(11)), fourier probability (p >1) and auto correlation-test (c/c()). 3. results and discussion figure 1(a) shows all sky distribution of galaxies in the superclusters s [227+006+0078] several groups of galaxies can be seen. these groups can form a substructure, ultimately a cluster of galaxies. figure 1(b) shows redshift distribution of galaxy in this supercluster where we can see low redshifted galaxies in the substructure region. high redshifted galaxies are found to be distributed randomly. any deviation from expected isotropic distribution will be tested using four statistical parameters, namely chi-square probability (p>2), autocorrelation coefficient (c/c()), first order fourier coefficient (11/(11)) and first order fourier probability (p >1). for anisotropy, the limit of chi-square probability p(>2) is <0.050, auto correlation coefficient (c/c()) is >1.0, first order fourier coefficient (11/(11)) is >1.5 and fourier probability p(>1) is <0.150 respectively. any `hump' (more solutions than the expected) or `dip' ( less solutions than the expected) in the histogram will be discussed as a local effect in the samples. the statistics for the polar and azimuthal angle distributions is given in table 1 . in the statistics of , a negative value of first order fourier coefficient suggests that the spin vectors of galaxies tend to be oriented perpendicular with respect to the equatorial coordinate system. similarly, a positive value of first order fourier coefficient suggests that the spin vectors of galaxies tend to be oriented parallel with respect to the 234 232 230 228 226 2 3 4 5 6 7 8 9 10 11 (a) d e c . (j 2 0 0 0 ) (d e g ) r.a. (j2000) (deg) 233 232 231 230 229 228 227 226 3 4 5 6 7 8 9 10 11 d e c (j 2 0 0 0 ) ra(j2000) 0.070.080.080.080.09 (b) fig. 1 : (a) all sky distribution of galaxies and (b) red shift distribution map. equatorial coordinate system. whereas, in the statistics of , a positive (11/(11) with significant value suggests that the spin vector projections of galaxies tend to point radially with respect to the center of the equatorial coordinate system. similarly, a significant negative value of (11/(11) implies that the spin vector projection of galaxies tend to orient tangentially with respect to the equatorial coordinate system. (b) janak ratna malla / bibechana 17 (2020) 117-122 120 in addition to the statistical tests, we also study the `humps' and `dips' in the polar and azimuthal angle distributions. the solid curve, in the histogram of the -distribution, represents the expected isotropic distribution whereas dashed curve is the cosine distribution. the solid circles with ±1error bars represent the observed distribution. the shaded portion represents the range 0o<<45o . a hump (or dip) in the smaller suggests that the spin vectors of galaxies tend to orient parallel (or perpendicular) with respect to the equatorial coordinate system. similarly, a hump (or dip) in the larger 45osuggests that the spin vectors of galaxies tend to orient perpendicular with respect to the equatorial coordinate system. in figure 2, there is a hump on polar angle distribution at θ = 46.this hump is due to 13 more expected solution than observed solutions in the range 45o . similarly, a hump (or dip) in the larger indicates that the spin vectors of galaxies tend to be oriented perpendicular with respect to the equatorial coordinate system .in the histogram of the distribution, solid curve represents the expected isotropic distribution whereas dashed curve is the average distribution. the solid circles with ±±1 error bars represent the observed distribution. the shaded portion represents the range --45o<<+45o. the humps and dips in the histograms of distribution are not so easy to interpret as compared to -distributions. it is because the range of is 90 o to +90 o . in the histogram of the -distribution, = 0 o means spin vector projections tend to point radially towards the center of the equatorial coordinate system. a hump in the middle (central eight bins) of the histogram suggests that the spin vector projections of galaxies tend to point towards the center of the chosen co-ordinate system. similarly, a hump at first four and last four bins indicates that the spin vectors projections of galaxies tend to be oriented tangentially with respect to the chosen reference co-ordinate system. a hump in the middle (central eight bins) of the plot suggests that the spin vector projections of galaxies tend to point towards the center of the chosen co-ordinate system. table 1: statistics of the polar and azimuthal angle distributions of galaxies in the supercluster s(227+006+0078). the first column represents the statistics used, p(>2) represents the chi-square probability (second row). similarly, c/c() represents the auto-correlation coefficient(third row). the last two rows give the first order fourier coefficient (11/(11) and first order fourier probability p(>1). the statistics for the θ-distribution of galaxies of supercluster s [227+006+0078] is shown in the table 1. the statistics for the polar angle distribution in this sample shows that the value of chi-square probability (p(>χ 2 ) to be 0.045 (smaller than the significant level 0.050 i.e., 5.0%). the auto-correlation coefficient (c/c(σ))is found to be 0.688 (smaller than 1σ limit). the first order fourier coefficient (δ11/σ(δ11)) is found to be 0.0823 (smaller than 1.5σ the limit). the first order fourier probability (p>( δ1)) is found to be 0 (smaller than 0.15 i.e.,15%). except first order fourier coefficient and chi-square probability, other statistical tests suggest anisotropy. isotropy in the first order fourier coefficient test suggests that the direction of departure from isotropy. the statistics of the φ-distribution of galaxies of supercluster s [227+006+0078] is shown in the table 1. the statistics for the azimuthal angle distribution in this sample shows that the value of chi-square probability (p(>χ 2 )) to be 0.0 i.e., 0(smaller than the significant level 0.050 i.e., 5.0%). the auto-correlation coefficient (c/c(σ)) is found to be 5.681 (greater than 1σ limit). the first statistics polar angle(θ) azimuthal angle () p(>χ2) 0.045 0.000 c/c(σ) 0.688 5.681 11/(11) 0.823 -1.894 p(>1) 0 0.000 janak ratna malla / bibechana 17 (2020) 117-122 121 order fourier coefficient (δ11/σ(δ11))is found to be -1.894 (smaller than 1.5σ the limit). the first order fourier probability (p>( δ1)) is found to be 0.0 (smaller than 0.15 i.e., 15%). except first order fourier coefficient, other statistical tests suggest anisotropy. isotropy in the first order fourier coefficient test suggests that the direction of departure from isotropy. 0 20 40 60 80 100 -10 0 10 20 30 40 50 60 observed expected cosine n u m b e r o f g a la x ie s polar angle() -100 -80 -60 -40 -20 0 20 40 60 80 100 -20 0 20 40 60 80 100 120 140 160 observed expected average n u m b e r o f g a la x ie s azimuthal angle() fig. 2: the polar () and azimuthal () angle distributions of galaxies in the supercluster s[227+006+0078]. the solid line represents the expected isotropic distributions. the dash lines represent the cosine and average distributions respectively. the solid circles with ±1 error bars are represent the observed distribution. 4. conclusion we have studied the preferred alignment of spin vector orientation of 1218 sdss galaxies of supercluster s [227+006+0078] that have redshift in the range 0.07 to 0.09. we used the method proposed by flin & godlowski [12] in order to compute two-dimensional data to three dimensional galaxy rotation axis (polar & azimuthal angles). we have carried out random simulation by creating 10 7 virtual galaxies and adopting the method proposed by aryal & saurer [15] in order to find theoretical distribution of galaxy rotation axes. we have compared the differences between theoretical distributions and observed distributions using three statistics, namely chi-square, auto-correlation and the fourier. the distribution of spin vector and spin vector projections of total sdss galaxies that have redshift in the range 0.07 to 0.09 are found to be random in all samples, our results support hierarchy model [2]. however, a local 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[15] b. aryal, w. saurer, comments on the expected isotropic distribution curves in the galaxy orientation studies, astronom. astrophys. lett. 364 (2000)l97-l100. http://articles.adsabs.harvard.edu/pdf/2000a%26a. .364l..97a. https://academic.oup.com/mnras/articleabstract/481/4/4753/5104417redirected https://academic.oup.com/mnras/articleabstract/481/4/4753/5104417redirected https://doi/10.1093/mnras/184.3.643 https://adsabs.harvard.edu/full/1974.26%20a..35..175 https://doi.org/10.1093/mnras/222.3.525 http://articles.adsabs.harvard.edu/pdf/2000a%26a..364l..97a http://articles.adsabs.harvard.edu/pdf/2000a%26a..364l..97a b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.16 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal temperature dependence of entropy of mixing of liquid alkali alloys b. k. singh1*, sudhir singh2, golak kumar mandal1, dhiraj kumar jha1 1 university department of physics, t.m. bhagalpur university, bhagalpur 2 department of physics, r. d. college sheikhpura, t.m. bhag. univ., bhagalpur *e-mail : bijay.k.singh@gmail.com article history: received 21 may, 2016; accepted 3 august, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15410 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract a semi-empirical approach has been considered to study the temperature dependence of entropy of mixing, (δsm), for various alkai-alkali alloys using hard-sphere model. the most important physical parameters occurring here is the hard-sphere diameter (σ) and the packing fraction (η). for pure liquid metals, this is usually determined empirically from the observed entropy as a function of temperature which in turn are utilised to compute δsm for na-k, k-rb, na-rb, nacs, rb-cs and k-cs alloys as a function of concentration at five different temperature ranging from 400k-800k. the study reveals that entropy of mixing for na-k, na-rb and k-rb systems decreases with increasing temperature. but the result for cs-based alloys exhibit a mixed behaviour. keywords: alkali alloys; semi-empirical approach; entropy; helmholtz free energy, boltzmann constant; packing fraction. 1. introduction though enormous experimental data exist on entropy of pure liquid metals and alloys [1], the theoretical works lag behind. recently the hard-sphere (hs) model has been widely used to remedy this lack. the theoretical study of the entropy of mixing is of current interest to unlock the secrets of the structure of liquid alloys on the basis of experimental observations. the most important and basic ingredients are the hard sphere diameter (σ) and the packing fraction (η). several workers [2-5] have computed the hs parameters by minimising the free energy of the system through first principle estimation. in the present work, a semi-empirical technique, without undergoing a rigorous first principle calculation attempt has b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.17 (online publication: dec., 2016) been made to determine the hs parameters from the observed entropy of pure liquid metals[6], which in turn are utilised to compute the entropy of mixing for na-k, na-rb, k-rb, na-cs, rb-cs, and k-cs alloys [7] as a function of concentration and temperature. these systems are preferred as their densities as a function of composition are experimentally available [8] and also there are typical representation of simple system where the sizes of constituent atoms differ from a factor of 1 to 3. out of these, cs-based binary molten of alloys are of particular interest for both theoretical [9-12] and experimental workers [1315]. 2. theory we consider a simple binary liquid alloy with components of atomic concentration c1 and c2 comprising c1n hard spheres with diameter 1 of species 1 and c2n with diameter 2 of species 2. following umar et. al., the expression for the entropy of hard sphere mixture can be expressed as s = sgas + sc + sη + sσ (1) where sgas is the ideal gas entropy, sc represents the ideal entropy of mixing, s corresponds to the packing density η and sσ is the entropy contribution due to mismatch of the hard sphere diameters σ1 and σ2. explicit expression for the various contributions are 1 2 3/ 2 1 2 2 5 2 2 c c gas b n b s m m k t k               (2) 1 1 2 2( )c b s c nc c nc k     (3) ( 1)( ) b s k        (4) 2 1 2 2 2( )c b s a c c k     (5) the expressions used for sη and sσ which are derived by umar et. al.[16] from the helmholtz free energy formulae of mansoori et. al.]17], the latter work itself providing an accurate analytical fit to the computer simulation data. here α = (1-η)-1 and 3 3 1 1 2 2( ) 6        is the packing fraction. ω is the atomic volume of an alloy for given concentration c1 and c2, (c1 + c2 = 1). m1 and m2 are atomic masses of the constituent species n1(= c1/ω) and n2(= c2/ω) are partial number densities. kb is the boltzmann constant.in eq. (5), a = [(-1) n](y1 + y2) + 3(-1)y1 (6) where y1 = (1 + 2) -3 (7) b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.18 (online publication: dec., 2016) y2 = 12(c11 + c22) -6 (8) where 3 3 1/3 1 1 2 2( )c c    is the hard-sphere diameter of the alloy. following eq.(1), the entropy of mixing for a binary alloy can be written as. sm = sgas + sη + sσ + sc (9) with (1) (2) 1 2 alloy gas gas gas gass s c s c s    (10) (1) (2) 1 2 alloys s c s c s       (11) superscript 1 and 2 in eqs. (10) and (11) refer to pure species 1 and 2 respectively. it is clear that for a given composition and volume of alloy, the entropy expressions contain two unknown parameters namely, hard sphere diameter σ1 and σ2. the packing fraction η is easily derivable from the value of σ. in order to evaluate the value of σ at different temperatures, we reduce the expression (2) to (5) to pure elements. for the corresponding pure liquid metals, we merely use c1 = 1, c2 = 0 and c2 = 1, c1 = 0 above. the formalism is much simplified and, in particular, sc = 0 and sσ = 0 in eq.(1). thus ( 1,2)i i i gass s s i   (12) with 3/ 2 2 5 2 2 ii b n i b m k ts k                (13) 2(1 ) {1 (1 ) } i n i i b s k        (14) where 22 i i         is the packing fraction of pure liquid materials. it may be mentioned that the well-known carnahan and starling [18-22] formula for the entropy of pure element can be obtained from eq. (14) by expanding in (1-ηi) and retaining only the terms up to 2 i . the packing fraction and hence the hard sphere the hence the hard sphere diameter has been determind at a given temperature by using eq. (12) and taking the observed values of entropy from hultgren et. al., the appropriate density of liquid metals required at a given temperature have been taken from literature [8]. b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.19 (online publication: dec., 2016) 3. results and discussion in table 1. we have listed the computed values of σ and η for na, k, rb and cs at temperatures 400k, 500k, 600k, 700k and 800k along with the available experimental values of entropy and density. the result shows that the values of η vary from metal to metal. the maximum value is obtained for na and the minimum value is for cs. the values of η also depend on temperature. as the temperature increases, η decreases. the values of (dη/dt) for different alkali metals are of the order of: (dη/dt)na = -2.4*10-4(k)-1, (dη/dt)k = -2.7*10-4(k)-1, (dη/dt)rb = -2.9*10-4(k)-1 and (dη/dt)cs = -2.9*104(k)-1. though, these coefficients are very small, but they may affect the properties which are sensitive to temperature. the entropies of the pure alkali metals, s, are determind by adding ideal gas term (sgas) and the packing density term sη through eq. (12). the former is two to four times greater in magnitude and opposite in sign to sη for all the metals under consideration. the basic parameters required in the calculation are taken from table 1. hard sphere parameters for pure elements as reported in table 1, have also been utilised to compute the various contribution i.e. sgas, sc, sη and sη and sσ respectively from eqs. (2) to (5) for alloys of interest. the relevant data for the various contribution to the entropy for alloys are listed in tables 2 to 7 and hence δsm can easily be evaluated through eq. (9) for these systems. the computation of the various contribution to entropy are very important to understand the gross behaviour of alkali-alkali alloys. first we note that the absolute value of sgas are much larger than sη but after alloying δsη becomes effective in comparison to δsgas. this shows that in alloying the packing of constituent atoms are more important than the behaviour of individual atom in a given volume element. for investigating the effect of temperature on δsm for all the six systems, the values of entropy of mixing are displayed in figs. (1) to (6). a perusal of figs: (1) to (3) reveals that δsm of na-k, na-rb and k-rb alloys decreases with increasing temperature. but the result of na-cs, rb-cs and k-cs systems exhibit a mixed behaviour. near the melting point i.e. between 400k to 600k for na-cs δsm increases with increasing temperature and above 600k it starts falling towards the ideal entropy of mixing. but, δsm for rb-cs and k-cs alloys, increases with increasing temperature between 400 to 500 and above 500k it starts falling similarly to na-cs. though the experimental values of temperature dependence of δsm for the above mentioned systems are not available in literature for an effective comparison, yet good accord with experiment for na-k and nacs at melting point confirms the validity of results obtained for these system at different temperatures. thus, our work provides an additional confidence in the hard sphere formalism for calculating the entropies of liquid metals and alloys. this is the most valuable contribution of semi-empirical approach to study δsm of alkali-alkali alloys as a function of concentration and temperature. this is not easily accessible from any other source and such investigation to the best of our knowledge are completely lacking. b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.20 (online publication: dec., 2016) in conclusion it may be asserted that this paper outlines the general theory of δsm and the numerical values obtained for alloys form a good set of reliable data. table 1: the hard sphere parameters () entropy (s/kb) and density of liquid alkali metals at different temperatures. pure liquid metals temp. (k) hard-sphere parameter entropy (s/kb) expt. density (a.u) expt.hard-sphere diameter () packing factor() sodium 400 6.052 0.4143 8.061 0.92038 500 5.954 0.3835 8.895 0.89438 600 5.872 0.3572 9.557 0.86838 700 5.804 0.3346 10.103 0.83238 800 5.725 0.3111 10.606 0.81638 potassium 400 7.460 0.4027 9.724 0.812155 500 7.330 0.3710 10.556 0.788655 600 7.216 0.3434 11.226 0.765155 700 7.118 0.3194 11.782 0.741655 800 7.030 0.2980 12.261 0.718155 rubidium 400 7.919 0.3928 11.259 1.447653 500 7.760 0.3578 12.119 1.401553 600 7.628 0.3287 12.796 1.355453 700 7.519 0.3041 13.351 1.309353 800 7.432 0.2833 13.821 1.263253 caesium 400 8.416 0.3725 12.452 1.77885 500 8.185 0.3322 13.340 1.72385 600 8.042 0.3049 13.969 1.6685 700 7.954 0.2853 14.460 1.61385 800 7.886 0.2686 14.884 1.55885 b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.21 (online publication: dec., 2016) table 2 : relevant data for sgas/kb, sη/kb and sσ/kb used in the calculation. alloys temp (k) cna sgas/kb -s/kb s/kb na-k 400 0.8 11.6540 3.3480 0.0520 0.7017 11.8033 3.3445 0.0632 0.5001 12.1004 3.3064 0.0650 0.2997 12.3844 3.2459 0.0475 0.1999 12.5214 3.2153 0.0339 500 0.8 12.0158 2.8909 0.0434 0.7017 12.1649 2.8862 0.0523 0.5001 12.4624 2.8477 0.0542 0.2997 12.7471 2.7914 0.0396 0.1999 12.8842 2.7647 0.0283 600 0.8 12.3171 2.5463 0.0369 0.7017 12.4659 2.5406 0.0449 0.5001 12.7639 2.5015 0.0461 0.2997 13.0494 2.4478 0.0336 0.1999 13.1866 2.4237 0.0240 700 0.8 12.5769 2.2765 0.0318 0.7017 12.7255 2.2697 0.0387 0.5001 13.0240 2.2294 0.0398 0.2997 13.3103 2.1770 0.0289 0.1999 13.4476 2.1546 0.0207 800 0.8 12.8066 2.0320 0.0284 0.7017 13.0347 2.0281 0.0326 0.5001 13.2541 1.9951 0.0356 0.2997 13.4632 1.9648 0.0289 0.1999 13.6786 1.9307 0.0186 b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.22 (online publication: dec., 2016) table 3: relevant data for sgas/kb, sη/kb and sσ/kb used in the calculation. alloys temp (k) crb sgas/kb -sη/kb sσ/kb na-rb 400 0.2 13.649 3.036 0.04926 0.3 13.385 3.054 0.06952 0.5 12.841 3.099 0.09743 0.7 12.270 3.163 0.09944 0.8 11.971 3.206 0.08489 500 0.2 14.016 2.570 0.03864 0.3 13.751 2.589 0.0563 0.5 13.207 2.636 0.0789 0.7 12.635 2.702 0.0808 0.8 12.336 2.746 0.0690 600 0.2 14.322 2.229 0.0347 0.3 14.058 2.248 0.0471 0.5 13.512 2.294 0.0661 0.7 12.940 2.359 0.0676 0.8 12.640 2.404 0.0578 700 0.2 14.588 1.968 0.0271 0.3 14.323 1.987 0.0394 0.5 13.777 2.031 0.0566 0.7 13.204 2.059 0.0580 0.8 12.903 2.138 0.0496 800 0.2 14.824 1.762 0.0256 0.3 14.559 1.777 0.0342 0.5 14.012 1.815 0.0472 0.7 13.438 1.868 0.0519 0.8 13.137 1.904 0.0444 b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.23 (online publication: dec., 2016) table 4: relevant data for sgas/kb, sη/kb and sσ/kb used in the calculation. alloys temp (k) ck sgas/kb sη/kb sσ/kb k-rb 400 0.2022 13.8886 3.0419 0.00307 0.3998 13.6177 3.0711 0.00478 0.5004 13.4793 3.0864 0.00510 0.6005 13.3418 3.0980 0.00501 0.8514 12.9946 3.1353 0.00281 500 0.2022 14.2519 2.5910 0.00236 0.3998 13.9817 2.6177 0.00367 0.5004 13.8431 2.6342 0.00392 0.6005 13.7068 2.6415 0.01079 0.8514 13.3579 2.6883 0.00216 600 0.2022 14.5549 2.2586 0.00191 0.3998 14.2853 2.2817 0.00297 0.5004 14.1465 2.2979 0.00317 0.6005 14.0115 2.3011 0.00310 0.8514 13.6610 2.3516 0.00175 700 0.2022 14.8166 2.0044 0.00163 0.3998 14.5476 2.0229 0.00256 0.5004 14.4086 2.0380 0.00271 0.6005 14.2749 2.0369 0.00265 0.8514 13.9227 2.0873 0.00149 800 0.2022 15.0483 1.8047 0.00148 0.3998 14.7800 1.8177 0.00231 0.5004 14.6408 1.8309 0.00246 0.6005 14.5086 1.8254 0.00239 0.8514 14.1544 1.8728 0.00136 b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.24 (online publication: dec., 2016) table 5: relevant data for sgas/kb, sη/kb and sσ/kb used in the calculation. alloys temp (k) cna sgas/kb sη/kb sσ/kb na-cs 400 0.1518 14.5366 2.8643 0.0503 0.3 14.0109 3.0122 0.0969 0.5023 13.2769 3.1965 0.1470 0.7014 12.5326 3.3140 0.1579 0.8 12.1507 3.3468 0.1378 500 0.1578 14.9034 2.3469 0.0380 0.3 14.3783 2.4667 0.0731 0.5023 13.6410 2.6420 0.1113 0.7014 12.8960 2.7679 0.1201 0.8 12.5133 2.8206 0.1053 600 0.1518 15.2099 2.0384 0.0391 0.3 14.6855 2.1377 0.0611 0.5023 13.9448 2.3007 0.0933 0.7014 13.1990 2.4167 0.1006 0.8 12.8115 2.4703 0.0884 700 0.1518 15.4754 1.8332 0.0285 0.3 14.9517 1.9164 0.0543 0.5023 14.2072 2.0680 0.0832 0.7014 13.4607 2.1692 0.0896 0.8 13.0763 2.2176 0.0787 800 0.1578 15.7112 1.6674 0.0263 0.3 15.1882 1.7355 0.0501 0.5023 14.4397 1.8732 0.0768 0.7014 13.6923 1.9547 0.0825 0.8 13.3070 1.9932 0.0724 b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.25 (online publication: dec., 2016) table 6: relevant data for sgas/kb, sη/kb and sσ/kb used in the calculation. alloys temp (k) crb sgas/kb sη/kb sσ/kb rb-cs 400 0.2 14.888 2.775 0.0028 0.3 14.799 2.795 0.0038 0.5 14.621 2.848 0.0048 0.7 14.441 2.906 0.0043 0.8 14.350 2.936 0.0032 500 0.2 15.254 2.285 0.00177 0.3 15.166 2.311 0.00232 0.5 14.988 2.367 0.00303 0.7 14.808 2.429 0.00271 0.8 14.717 2.464 0.00213 600 0.2 15.560 1.987 0.0015 0.3 15.472 2.009 0.0021 0.5 15.294 2.056 0.0025 0.7 15.114 2.108 0.0023 0.8 15.023 2.137 0.0018 700 0.2 15.825 1.785 0.00149 0.3 15.737 1.802 0.00201 0.5 15.559 1.836 0.00253 0.7 15.379 1.874 0.00225 0.8 15.289 1.894 0.00169 800 0.2 16.061 1.626 0.00149 0.3 15.973 1.637 0.00201 0.5 15.795 1.662 0.00252 0.7 15.615 1.689 0.00225 0.8 15.525 1.705 0.00176 b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.26 (online publication: dec., 2016) table 7. relevant data for sgas/kb, sη/kb and sσ/kb used in the calculation. alloys temp (k) ck sgas/kb sη/kb sσ/kb k-cs 400 0.2 14.632 2.783 0.0106 0.3 14.400 2.815 0.0105 0.5 13.951 2.887 0.0191 0.7 13.493 2.975 0.0179 0.8 13.261 3.027 0.0145 500 0.2 14.988 2.298 0.00721 0.3 14.766 2.333 0.00993 0.5 14.315 2.413 0.01311 0.7 13.857 2.511 0.01234 0.8 13.625 2.568 0.01001 600 0.2 15.294 2.002 0.00598 0.3 15.071 2.032 0.00822 0.5 14.620 2.104 0.01085 0.7 14.162 2.191 0.01021 0.8 13.929 2.242 0.00827 700 0.2 15.558 1.801 0.00557 0.3 15.335 1.827 0.00767 0.5 14.884 1.884 0.01009 0.7 14.425 1.955 0.00950 0.8 14.193 1.997 0.00766 800 0.2 15.793 1.640 0.00536 0.3 15.570 1.660 0.00736 0.5 15.118 1.708 0.00967 0.7 14.659 1.765 0.01552 0.8 14.426 1.799 0.00732 b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.27 (online publication: dec., 2016) fig. 1: entropy of mixing (sm/kb) of na-k as a as a function of concentration and temperature. fig. 2: entropy of mixing of (sm/kb) na-rb alloys function of concentration and temperature. fig. 3: temperature dependence of the entropy of mixing (sm/kb) for liquid k-rb alloys. fig. 4: temperature dependence of the entropy of mixing (sm/kb) for liquid na-cs alloys. corresponds to the experimental value at 380k of neale & caoack (1982). b.k. singh et al./ bibechana 14 (2017) 16-29 : rcost p.28 (online publication: dec., 2016) fig. : entropy of mixing (sm/kb) of (rb-cs) alloys as a function of temperature. fig. 6: entropy of mixing (sm/kb) for liquid (k-cs) alloys as a function of temperature & 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http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal spatial orientations of angular momentum vectors of galaxies in supercluster s [173+014+0082] janak ratna malla1*, walter saurer2, binil aryal1 1central department of physics, kirtipur, kathmandu 2institute of astro-particle physics, innsbruck university, austria *email: janak_malla@yahoo.com article information: received: may 28, 2020 accepted: june 16, 2020 keywords: sdss supercluser galaxy redshift intrinsic flatness abstract the spin vector orientation of 1302 sdss (sloan digital sky survey) galaxies in supercluster s[173+014+0082] having redshift 0.076 to 0.091 has been analysed. the positions, position angles and inclination angles of galaxies are used to convert two-dimensional observed parameters into three-dimensional angular momentum vectors of the galaxy using the `position angle-inclination' method. the expected isotropic distribution curves are determined performing numerical simulation by generating 107 virtual galaxies. the observed distribution is compared with the expected isotropic distribution curves using three statistical tools namely chi-square test, auto-correlation test and fourier test. redshift map is studied and found that the distributions fit with the gaussian. no preferred alignment of angular momentum vectors is noticed, supporting hierarchy model of galaxy formation. doi: https://doi.org/10.3126/bibechana.v18i1.29165 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction during the path of history different ideas had been recommended describing the starting place of the universe. the most persuasive model is the standard big bang model, which remains valid. this model shows the creation technique of the universe began with an enlargement 20 billion years ago. nowadays, the big bang model is believed to be the beginning of space and time. the tiny, hot (1012k) universe started out to cool and fundamental symmetry damaged down. the breaking of this symmetry results in the inflation of the universe exponentially. within a fraction of second, after the big bang, the procedure of nucleosynthesis, baryongenesis & leptogenesis took place. after this procedure the universe entered into the matter dominated era. during dark epoch, the stars and galaxies are assumed to be formed. today, how matter is distributed in the universe is the crucial field of study in cosmology and astronomy. the mutual attraction between the galaxies due to the gravitational force leads to the formation of clusters. depending upon the number of galaxies http://nepjol.info/index.php/bibechana mailto:janak_malla@yahoo.com https://doi.org/10.3126/bibechana.v18i1.29165 https://creativecommons.org/licenses/by-nc/4.0/ janak ratna malla et al. / bibechana 18 (1) (2021) 26-32 27 inside the cluster, they're labeled as poor and rich clusters. in case of poor clusters the force of gravity is weak to keep them tightly due to lower mass of the galaxy. thus they seem irregular in shape. our milky way is part of a poor cluster referred to as a local group which includes 54 galaxies [1]. the virgo cluster is an example of a moderately rich cluster that is closest to us and the coma cluster is a rich cluster, has thousands of spiral and elliptical galaxies. the clustering technique of galaxy clusters lead to the formation of large scale structures known as superclusters. thus they're collections of galaxy clusters, with 20-100h-1mpc [2]. the scientist assumed that the variety of superclusters in the universe is set 10 million and it occupies the 10% area of the universe. as it contains organizations and clusters of galaxies, it provides the strong proof that galaxies inside the universe are not distributed uniformly. abell catalogue is the pioneer work in the study of superclusters. it was proposed by george abell in 1958 and he called them second order cluster or clusters of clusters [3]. the study of superclusters highly benefited from the 2df galaxy redshift survey (2dfgrs) and the sloan digital sky survey (sdss) [4]. currently sloan digital sky survey (sdss) is taking data from the deep sky. our work is based totally on the data provided by sdss-dr7. as suggested by weizscker & gamow [5, 6], the observe of origin of angular momentum of galaxies might be the clue for the physical properties of the initial situations of galaxies. thus, the observed rotation of galaxy is critical to the cosmology and subsequently it is essential to recognize how they obtained their angular momentum. pebbles [7] put forward detail calculations of the acquisition of angular momentum in early stage of proto-galactic evolution. he argued that, the gravitational interplay of quadrapole moment of the system with tidal field of the matter causes transformation of angular momentum to the developing proto-galaxy. the transformation of angular momentum between rotation and orbital motion is a outcome of the gravitational instability [8]. peebles assumed that, as soon as the primeval plasma has recombined and decoupled from the primeval fireball radiation, gravitation appears to be the dominant force transferring the angular momentum to a developing proto-galaxy. on the basis of orientation of angular momentum vectors of galaxies one can determine the evolution of large scale structure, i.e., supercluster. the alignment of rotational axes of galaxies in the supercluster provides us information about the formation process of galaxies in early epoch [9]. there had been contradictory theoretical models predicting various galaxy cluster formation. the hierarchy model [7] predicts random orientation of angular momentum vectors. the pancake model [10] predicts the parallel orientation whereas the primordial vorticity model [11] says angular momentum vector distributed perpendicular to the cluster plane. we are interested to study the evolution of galaxies in the supercluster by analyzing their preferred alignments. 2. materials and method database the analyzed data set has been recorded by sloan digital sky survey (sdss). with the collaboration of prof. walter saurer's group at the institute of astro-particle physics, innsbruck university, austria, we obtained the set of sdss (7th data release) data. this supercluster s [173 + 014 + 0082] contains a total number of 1302 galaxies having redshift ranges from 0.076 to 0.091. in this work, r-filter is used to study the spin vector orientation of the galaxies. in order to calculate inclination angle first of all we used intrinsic flatness (q*) = 0.2 (holmberg, [12]) and, then 0.13 for those galaxies whose inclination angle was undetermined from the previous value of q*. in this process nine galaxies were excluded whose intrinsic flatness is less than 0.13. hence, finally there are 1293 galaxies in the data set whose position (right ascension and declination), position angle and inclination are known. janak ratna malla et al. / bibechana 18 (1) (2021) 26-32 28 godlowskian transformation the two dimensional parameters such as position, position angle and diameter can be transformed into 3 dimensional parameters using the method proposed by flin and godlowski [13] and polar (𝜃) and azimuthal (𝜙) angle can be calculated for each galaxy. the polar angle (𝜃) is the angle between galactic spin vector (sv) and reference plane, and azimuthal angle (𝜙) is the angle between projection of a galactic spin vector to the reference plane and x-axis. these angles are given below. sin𝜃 = −cos𝑖 sin𝛼 ± sin𝑖 sin𝑝 cos𝛿 (1) sin𝜙 = (cos𝜃)−1[−cos𝑖 cos𝛿sin𝛼 + sin𝑖(∓sin𝑝 sin𝛿 sin𝛼 ∓ cos𝑝cos𝛼)] (2) here, i, δ, α, and 𝜌 represent the inclination angle, declination, right ascension and position angles respectively and ∓ and ± indicate the two possible solution. the inclination angle (i) defined the angle between normal to the galaxy plane and line of sight of the observer. this is given by following relation: 𝑐𝑜𝑠2𝑖 = ( 𝑏 𝑎 ) 2 −𝑞∗2 1−𝑞∗2 (3) here b/a is axial ratio and q*represents the intrinsic flatness factor of the galaxy. for the disk galaxies its value depends upon the morphological type. holmberg [12] showed that the values of q*varies from 0.083 for sd spirals to 0.3 for elliptical. at first, q*= 0.20 for morphologically unidentified galaxies which leads to the removal of a certain number of galaxies that have axial ratio (b/a) is less than 0.20. then, we used q*= 0.13 for those galaxies that have b/a < 0.20. method of analysis aryal & saurer [14], proposed a method for the removal the selection effects and the expected isotropic distribution curves (θ and ϕ) are determined using the numerical simulation. for this, a true spatial distribution of the galaxy rotation axis is assumed to be isotropic. then, due to the projection effects, i can be distributed ∝sin i, latitude can be distributed ∝cos b, the variables longitude () and position angle (p) can be distributed randomly and formulae (1) and (2) can be used to simulate (numerically) the corresponding distribution of θ and ϕ. at first, the isotropic distribution curves are based on simulations including 107 virtual galaxies aryal & saurer [14]. we use these numbers to make an input file and the predicted distribution by using a running simulation in matlab 15.0. finally, the observed and expected distributions are compared with the help of appropriate statistical tests. in order to use origin 5.0 to determine the all sky distribution of galaxies where as origin 8.0 used for the redshift distribution of galaxy. 3. results and discussion all sky distribution is the pictorial representation of distribution of galaxies within a certain range of right ascension and declination in the sky. the all sky distribution plot for our supercluster s [173++014+0082] is shown in fig. 1. the diagram shows that galaxies are distributed within the range of right ascension from 1700 to 1810 and declination from 60 to 180. figure 1 shows that galaxies are distributed inhomogenously. to study the preferred alignment of each galaxy, we plotted the various parameters of galaxies. for each parameter the proper bin size is calculated using origin 5.0. these plots are presented in following fig. 2. from these histogram plots of galaxies it is seen that the distribution of observed numbers of galaxies are clearly inhomogeneous. figure 3 shows redshift distribution of the galaxy in the supercluster s [173 + 014 + 0082] [15]. in the map, low redshift galaxies are found in the substructure region. high redshifted galaxies are found to be distributed randomly [16]. the color map shows that the velocity dispersion is minimum in the region where the number density of the janak ratna malla et al. / bibechana 18 (1) (2021) 26-32 29 galaxy is minimum. in the substructure region, at 80 declination, the redshift dispersion is found to be δz = 0.084, whereas the lower substructure shows δz= 0.076 and 0.080, respectively. it seems that there is gaussian distribution between redshift dispersion and number density of galaxies in the substructures. it shows that the superclusters evolve naturally. fig. 1: all sky distribution of galaxies in the sdss supercluster s[173 + 014 + 0082] in equatorial coordinate system. right ascension (r.a.) and declination (dec.) are given in degree. in order to identify the preferred alignment of the spin vector of galaxies we have performed three different statistical tests [17]. for anisotropy, the limit of chi-square probability p (> 𝜒2) is < 0.050, auto correlation coefficient (c/c (𝜎)) is > 1.0, first order fourier coefficient (δ11/𝜎(δ11)) is >1.5 and fourier probability p( >δ11) is < 0.150 respectively. for θ distribution (table 1), the result of these tests is found as: the chi square probability p (> χ2) is 0.653 which is greater than critical value (0.05) for anisotropy. in addition to this, the autocorrelation coefficient c/c (σ)) is 0.410 which is less than critical value; this result is in favor of isotropic distribution. similarly, the first order fourier coefficient (δ11/σ(δ11)) and fourier probability (p >∆1) found to be 0.860 and 0.643 respectively. these two results also support the isotropic distribution of 𝜃. hence, all three statistical tests show isotropic distribution of supercluster s[173 + 014 + 0082] indicating random orientation of spin vectors of galaxies. from this result we can conclude that the galaxy formation model of supercluster s [173 + 014 + 0082] follows the hierarchy model. according to this model galaxies are believed to be formed from the clustering. fig. 4(a) shows the polar (𝜃) distribution of galaxies of the supercluster s[173 + 014 + 0082]. in the figure, solid and dotted curves represent expected isotropic and cosine distribution. in the small angle (𝜃< 450) angle region i.e. shaded region no significant hump and dip are observed. while, in a larger angle (𝜃 > 450) a significant dip is observed at an angle 750 with 1𝜎 error limit. in the shaded region the observed number of solutions is 1674 and expected number of solutions is 1652. thus the observed number of solutions exceeds the expected solution by 22. this means that there are 11 more galaxies observed. on the other hand, in a larger angle region the observed solution is less than expected solution by 24. this causes deficiency of 12 galaxies in that region. furthermore, at the bimodal region one extra galaxy is observed. thus these humps at small angle regions are totally nullified by the dip at the larger angle. the excess number of galaxies in the smaller angle can be regarded as transfer of the galaxies from the larger angle region. this may happen due to the gravitational tidal effect. in 𝜙 distribution, the statistics (table 1) support the isotropic distribution. the chi square probability ( p > 𝜒2) and auto-correlation coefficient (c/c(𝜎) found to be 0.610 (greater than 0.05) and -0.481 (less than 1𝜎). similarly, the value of first order fourier coefficient (∆11/𝜎 (∆11)) and first order fourier probability (p > ∆1) is -0.358 (less than 1.5𝜎) and 0.883 (greater than 0.15). these results are strong evidence to advocate the hierarchy model of galaxy evolution in the supercluster s[173 + 014 + 0082]. janak ratna malla et al. / bibechana 18 (1) (2021) 26-32 30 fig. 2: the distribution of right ascension (𝛼), declination (𝛿), position angle (p) and inclination angle (i) of galaxies in the supercluster s [173 + 014 + 0082]. the y-axis represents the number of observed galaxies. the inhomogeneous distribution of galaxies can be seen. fig. 3: (a) red shift map and (b) the distribution of galaxies in the supercluster region. solid curves represent gaussian fit. the statistical error bars are shown. janak ratna malla et al. / bibechana 18 (1) (2021) 26-32 31 fig. 4(b) represents the distribution of azimuthal angle of supercluster s[173 + 014 + 0082]. the solid and dotted line indicate the expected and average distribution. the observed number of solutions in the small angle region (-900 < 𝜙 < -450) is 19 more than expected solution; however, no significant humps are observed in the distribution curve. similar result is obtained at a larger angle region (450 < 𝜙 < 900) also. the shaded region represents the bimodal region (-450 < 𝜙 < 450). in this region the expected and observed numbers of solutions are 1405 and 1396 respectively. from the figure, two crystal clear humps are observed at -50 and 50and dip is observed at -150within error limit 1𝜎. table 1: statistics of the polar and azimuthal angle distributions of galaxies in the supercluster s[173+014+0082]. the first column represents the statistics used, p ( > 𝜒2) represents the chi-square probability (second row). similarly, c/c(𝜎) represents the auto-correlation coefficient(third row). the last two rows give the first order fourier coefficient (∆11/𝜎 (∆11)) and first order fourier probability p (>δ1). fig. 4: (a) the polar (𝜃) and (b) azimuthal (𝜑) angle distributions of galaxies in the supercluster s[173+014+0082]. the solid line represents the expected isotropic distributions. the dash lines represent the cosine and average distributions respectively. the solid circles with ±1 error bars are represent the observed distribution. 4. conclusions the supercluster s[173+014+0082] consists of 1302galaxies of which position angles, right ascension, declination, and axial ratio are known. these are obtained from two dimensional projections on the celestial sphere by sdss dr 12 survey. the conversion of two dimensional observed parameters into three dimensional is carried out by using `position angleinclination' method. in order to find out the theoretical distribution of galaxy rotation axes we ran random simulation by generating 107 virtual galaxies as proposed by aryal & saurer. here we assumed cosmological principle: distribution of galaxies in the large scale structure is homogeneous and isotropic. the simulated results were compared with the observed distribution using the statistical tools namely chi-square test, auto-correlation test and fourier test. the distribution of spin vector and spin vector projections of total sdss galaxies that have redshift in the range 0.076 to 0.091 are found to be random in all samples. we conclude our results as follows: statistics polar angle (θ) azimuthal angle () p ( > 𝜒2) 0.653 0.610 c/c(𝜎) 0.410 -0.481 (∆11/𝜎 (∆11)) 0.860 -0.358 p (>δ1). 0.643 0.883 janak ratna malla et al. / bibechana 18 (1) (2021) 26-32 32 (a) the polar and azimuthal angles of supercluster galaxies shows isotropic isotropic distribution suggesting no preferred alignment of angular momentum vectors as well as its projection. in other words we observed vanishing angular momentum in the supercluster. this result advocates the hierarchy model of galaxy evolution as suggested by peebles. (b) the redshift distribution of galaxies in supercluster showed gaussian-like nature, suggesting the distribution of galaxies’ hubble recessional velocity is isotropic, satisfying cosmological principle. acknowledgements one of the authors (j.r.malla) is thankful to the department of astro-particle physics, innsbruck university, austria, for providing data access . one of them (j.r.malla ) is grateful to the authorities of the sdss for providing the database. references [1] s. colids, jindal a jindal., n. e. chisari, d. vibert, y. dubois, c. pichon, j. devriendt. galaxy orientation with the cosmic web across cosmic time, monthly notice of the royal astronomical society 481(2018) 4753-4774. https://doi.org/10.1093/mnras/sty2567. 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[9] s. djorgovski, nearly normal galaxies, edited by s. m .faber, springer (1987) [10] a. g. doroshkevich, s. f. shandarin, e. saar, spatial structure of protoclusters and the formation of galaxies, monthly notices royal astron. soc. 184 (1978) 643 – 660. https://doi.org/10.1093/mnras/184.3. [11] l. m .ozernoy, sov.astron, whirl theory of the origin and clusters of galaxiex, 15 (1972) 923. [12] e. holmberg, on the apparent diameters and the orientation in space of extragalactic nebulae, medd. lund. astron. obs. 117 (1946) 3-82. [13] p. flin, w. godlowski, the orientation of galaxy groups and formation of the local supercluster, monthly notices royal astron. soc. 222 (1986) 525. [14] b. aryal , w. saurer , comments on the expected i so tropic di s tr ibution curves in the ga laxyor ien tat ion stud ies, astronom. astrophys. le t t . 364 (2000) l97-l100. http://articles.adsabs.harvard.edu/pdf/2000a%26 a..364l..97a. [15] c. m. casey ,d.narayanan, a.cooray, dusty starforming galaxies at high redshift, physics reports elsevier science direct. 541 (2014) 45-161. [16] s. n yadav, b. aryal, a study of r-and umagnitude dependence in the spatial orientation of spin vectors of sdss galaxies having redshift 0.10 < z < 0.11. himalayan physics 5 (2015) 111. https://doi.org/10.3126/hj.v5io.12814. [17] s. n yadav, b. aryal , w. saurer , preferred alignments of angular momentum vectors of six galaxies in six dynamically unstable abell clusters. research in astronomy and astrophysics, 17 (2017) 7. https://doi.org/10.1088/1674–4527/17/7/64 https://doi.org/10.1051/0004-6361/201016288 http://articles.adsabs.harvard.edu/pdf/2000a%26a..364l..97a http://articles.adsabs.harvard.edu/pdf/2000a%26a..364l..97a https://doi.org/10.3126/hj.v5io.12814 https://doi.org/10.1088/1674–4527/17/7/64 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal analytical approximate solution of higher order boundary value problems via variational iteration method zobia hamid, jamshad ahmad* department of mathematics, faculty of science, university of gujrat, pakistan. *email: jamshadahmadm@gmail.com article history: received 09 october, 2017; accepted 31 october, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18347 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract in this paper, application of variational iteration method has been successfully extended to obtain approximate solutions of some higher order boundary value problems. we emphasize the power of the method by testing three different mathematical models of distinct orders. the results are obtained by using only little iteration. keywords: nonlinear bvp; variational iteration method; approximate solution. 1. introduction the ordinary differential equations (ode) with variable coefficients appear in many areas of applied sciences. examples of these equations are euler equation, bessel equation and legendre equation. moreover, the nonlinear ordinary differential equations with variable coefficients, such as the doffing equation, the thomas-fermi equation, and the van der pole equation, have been investigated in the literature. linear and nonlinear odes with variable coefficients play a significant role in applied mathematics, physics, and engineering [1-5]. researchers were aiming to establish reliable methods capable for solving a large class of linear or nonlinear differential and integral equations without the tangible restrictive assumptions or discretization of the variables. recently, there has been great development of new powerful methods capable of handling linear and nonlinear equations that overcome most of the classical methods. the adomian decomposition method, the variational iteration method, and the homotopy perturbation method are examples of the newly developed methods. the variational iteration method, now used by many researchers is capable for handling a large class of linear or nonlinear differential equations. the flexibility and adaptation provided by the method have made it readily applicable to cases where the solution is unknown in advance as is often the case in the applied sciences and engineering. the vim provides efficient algorithm for analytic approximate solutions and numeric simulations for real-world applications in sciences [6–18]. unlike the adomian decomposition method, where computational algorithms are normally used to deal with the nonlinear terms, the vim does not require the use of restrictive as-assumptions for the nonlinear terms which would complicate the analytic calculations. the vim approaches linear and nonlinear problems directly in a like manner. the aim of this work is reconfirm the potential and applicability of the proposed method on higher order boundary value problems. zobia hamid, jamshad ahmad / bibechana 15 (2018) 37-42: rcost p.37 http://nepjol.info/index.php/bibechana http://dx.doi.org/10.3126/bibechana.v15i0.18347 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ 2. the analysis of variational iteration method consider the general differential equation lu+nu = g(x) (1) where l and n are linear and nonlinear operators respectively, and g(x) is the source inhomogeneous term. the variational iteration method admits the use of a correction functional for equation (1) in the form ,dt))t(g)t(un)t(lu()t()x(u)x(u nn x 0 n1n    (2) where  is a general lagrange’s multiplier, which can be identified optimally via the variational theory, and 𝑢𝑛̅̅̅̅ as a restricted variation which means 𝛿𝑢𝑛̅̅̅̅ =0. the lagrange multiplier  is crucial and critical in the method, and it can be a constant or a function. having  determined, an iteration formula should be used for the determination of the successive approximations 0;)(1  nxun of the solution u(x). the zeroth approximation u0 can be any selective function. however, using the initial values u(0); );0(u and )0(u  are preferably used for the selective zeroth approximation 0u as will be seen later. consequently, the solution is given by )x(ulim)x(u n n   (3) 3. numerical applications problem 3.1 consider a fifth order non-linear bvp ( ) ( )( ) ( ),v x iiu x e u x (4) with boundary conditions (0) (0) (0) 1 , (1) (1) 1.u u u u u       (5) the correctional functional is given as ,dt)}t(ue)t(u{)x(u)x(u x 0 )ii( n t)v( nn1n     (6) where ‘λ’ is langrage multiplier, which is identified as 1( 1) ( ) . ( 1) m mt x m         (7) and the initial approximation is ,)(0 xexu  for n=0,the equation (6) gives, ,dt)}t(ue)t(u{)xt( 24 1 )x(u)x(u )ii( 0 t)5( 0 x 0 4 01   ,dt)1e()xt( 24 1 e t x 0 4x   120 x 24 x 6 x 2 x x1 5432  for n=1, ,dt)}t(ue)t(u{)xt( 24 1 )x(u)x(u )ii( 1 t)5( 1 x 0 4 12    ,x 2 21 e56xe21ex3e 6 x x34 2 x3 24 x5 57 2xxx2x 334   zobia hamid, jamshad ahmad / bibechana 15 (2018) 37-42: rcost p.38 the approximate solution is 14111310129 118 10 96 8 765 43 2 n x105587471470745608.1x103331866059043833.1x10867510876756987.2 x10441725052108385.2 2628800 x x1099667557319236.2 x0000248016.0 5040 x 720 x 120 x x0416667.0x166667.0 2 x x1)x(u      fig 1: comparison of exact and approximate solution. problem 3.2 consider a non-linear bvp ( ) 2( ) ( ),vi xu x e u x (8) 1 1 1(0) 1, (0) 1, (0) 1, (1) , (1) , (1) .u u u u e u e u e             (9) the correctional functional is given as ( ) ( ) 1 0 ( ) ( ) { ( ) ( )} , x v x ii n n n nu x u x u t e u t dt      (10) where ‘λ’ is langrage multiplier ,which is calculated by 1 5( 1) ( ) ( ) , ( 1) 5 m mt x t x m             (11) and the initial approximation is ,e)x(u x 0  (12) for n=0, the equation (10) becomes, dt))}t(u(e)t(u{)xt( 120 1 )x(u)x(u )ii( 0 t)vi( o x 0 5 01   , dt)}e(ee{)xt( 120 1 e ttt x 0 5x    ,          5 x 4 x 3 x 2 x x1 5432 , closed approximate 2 2 4 6 8 100 200 300 400 500 600 700 zobia hamid, jamshad ahmad / bibechana 15 (2018) 37-42: rcost p.39 dt))}t(u(e)t(u{)xt( 120 1 )x(u)x(u )ii( 1 t)vi( 1 x 0 5 12   , 209 20 x x 12 7 x6x 2 69 xe84 24 ex ex 6 7 ex14x127e210 5 432x x4 x3x2x        14111310 129118107 876 543 2 x107297251470745597.1x106059043836.1 x108681750876756987.2x10565052108667.2x10760537557319336.2 40320 x 5040 x 720 x x0083333.0x0416667.0x166667.0 2 x x1)x(u the closed solution of this problem is e-x . fig.2: comparison of closed and approximate solution. problem 3.3 consider a six order non-linear bvp )x(ueu )ii(x)vi(  (13) with boundary conditions 1)0(u)0(u)0(u )iv(  (14) e)1(u)1(u)1(u )iv(  (15) the correctional functional is given as ,dt)}t(ue)t(u{)x(u)x(u x 0 )ii( n t)vi( nn1n     (16) where ‘λ’ is langrage multiplier, which is identified as ; 5 )xt( )1m( )xt()1( 51mm         (17) and the initial approximation is ,)(0 xexu  (18) for n=0,the equation (17) becomes, ,dt)}e(ee{)xt( 120 1 e)x(u ttt x 0 5x 1   6 4 2 2 4 50 100 150 closed approximate zobia hamid, jamshad ahmad / bibechana 15 (2018) 37-42: rcost p.40            6 x 5 x 4 x 3 x 2 x x1 65432 ,dt)}t(ue)t(u{)xt( 120 1 )x(u)x(u 1 t)vi( 1 x 0 5 12     4 2 3 2 3 4 5 7 69 127 210 84 14 6 6 24 2 7 1 12 20 x x x x x x e x e xe x e x e x x x x               14111310129 11810796 87 6 5 4 3 2 x101470745597.1x106059043867.1x100876756988.2 x105052109648.2x107557319224.2x107557318996.2 x0000248016.0x000198413.0 720 x x00833333.0 24 x x166667.0 2 x x1)x(u      fig.3: comparison of exact and approximate solution. 4. conclusion in this work, the variational iteration method has been successfully employed on higher order boundary value problems by converting into corresponding system of first order differential equations. the obtained results are good agreement with the existing results in literature. references [1] a. m. wazwaz, the variational iteration method for analytic treatment for linear and nonlinear odes, appl. math. comput. 212 (2009) 120–134. doi.org/10.1016/j.amc.2009.02.003. 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[18] s. s. sadiqqi, m. iftikhar, variational iteration method for the solution of seventh order boundary value problems using he’s polynomials, j. assoc. arab univ. basic appl. sci. 18 (2015) 60–65. doi.org/10.1016/j.jaubas.2014.03.001. zobia hamid, jamshad ahmad / bibechana 15 (2018) 37-42: rcost p.42 https://doi.org/10.1016/s0096-3003%2899%2900104-6 https://doi.org/10.1016/s0096-3003%2899%2900104-6 https://doi.org/10.1016/j.cam.2006.07.009 https://doi.org/10.1016/j.cam.2006.07.009 doi.org/10.2478/s13531-013-0141-6.uropean%20journal%20of%20engineering. doi.org/10.2478/s13531-013-0141-6.uropean%20journal%20of%20engineering. http://www.sciencedirect.com/science/article/pii/s1877705815038308 http://www.sciencedirect.com/science/journal/18777058 http://www.sciencedirect.com/science/journal/18777058/127/supp/c https://doi.org/10.1016/j.proeng.2015.11.470 doi.org/10.1142/s0219876212400269 https://doi.org/10.1016/s0893-9659%2899%2900052-x https://doi.org/10.1016/s0377-0427%2800%2900618-x https://doi.org/10.1016/s0377-0427%2800%2900618-x doi.org/%2010.1098/rspa.1990.0142. doi.org/%2010.1098/rspa.1990.0142. https://doi.org/10.1016/s0096-3003%2899%2900224-6 https://doi.org/10.1016/s0096-3003%2899%2900224-6 http://www.sciencedirect.com/science/journal/18153852/18/supp/c doi.org/10.1016/j.jaubas.2014.03.001. 175-180 ajaya bhattarai r c o s t n a. bhattarai / bibechana 11(1) (2014) 175-180: (online publication: march, 2014) p.175 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana investigation on solution properties of surfactants in mixed solvent media: landmark towards surface chemistry in eastern nepal ajaya bhattarai department of chemistry, m.m.a.m.c., tribhuvan university, biratnagar, nepal * e-mail: bkajaya@yahoo.com accepted for publication: february 16, 2014 abstract surfactants are amphiphilic molecules having a hydrophilic or water soluble moiety (head group) and a hydrophobic, or water insoluble moiety (tail group). surfactants are not only related to soaps and detergents, they are also in heavy demand for industrial processes requiring colloid stability, metal treatments, mineral flotation, pesticides, oil production, pharmaceutical formulation, emulsion polymerization, particle growth and many more. that is why surfactants have been and continue to be a very active area of scientific research and commercial growth for several decades. one interesting property of surfactants is that at low concentrations, they exist solely as monomers. the formation of micelles, begins at a specific surfactant concentration termed the critical micelle concentration (cmc), where the physical properties of the solution, such as interfacial tension, electrical conductivity, and light scattering behaviour, often changes abruptly due to the existence of micelles. the formation of micelles will be able to calculate various thermodynamic parameters. these parameters make surfactants not only an interesting and rich area for the exploration of novel phenomena but also an area of research which can lead to new applications in a variety of fields. however, most of the previous studies on surfactants are limited to aqueous media only. studies in mixed solvent media are very natural one as one can modulate the conformations of surfactants and their interactions easily by simply varying the composition of the media. with this concept, the research team of eastern nepal has started to work the solution properties of surfactants in different mixed solvent media in presence and absence of salts and has also investigated cationic and anionic surfactant interaction in mixed solvent media. © 2014 rcost: all rights reserved. keywords: surfactants; mixed solvent media; critical micelle concentration. 1. introduction surfactants are amphiphilic materials containing both a polar long-chain hydrocarbon “tail” and polar, usually ionic, “head” groups. in polar solvents, for example water, this dual character of the amphiphile leads to self-association or micellization, the surfactant molecules arrange themselves into organized molecular assemblies known as micelles. in colloidal and surface chemistry, the critical micelle concentration (cmc) is defined as the concentration of surfactants above which micelles form and almost all additional surfactants added to the system go to micelles [1]. the properties of surfactants in mixed solvent media are an interesting subject. however, very less work has been done for solution properties of surfactants in mixed solvent media. the following popular methods were used in the eastern part of nepal for scientific investigations on the solution properties of surfactants in mixed solvent media: a. bhattarai / bibechana 11(1) (2014) 175-180: (online publication: march, 2014) p.176 1.1. electrical conductivity in the case of ionic surfactants, the utilization of electrochemical measurement is much more convenient, especially the measurements of the electrical conductivity of their solutions with varying concentration. the conductometric method is based on the finding of a breaking point on the curves, which describe the concentration dependence of conductivity [2]. to investigate the solution properties of surfactants, the electrical conductivity method is very promising one as one can study the various thermodynamic parameters. shah et al. [3] measured the specific conductivity of cationic surfactant (dodecyltrimethylammonium bromide) and anionic surfactant (sodiumdodecyl sulphate) in methanol-water mixed solvent media containing 0.1, 0.2 and 0.3 volume fractions of methanol at 308.15 k. the specific conductivities of dodecyltrimethylammonium bromide and sodiumdodecyl sulphate were increased with increment in concentration and decreased with increment in the volume fractions of methanol. also, the critical micelle concentration (cmc) was increased with increment in volume fraction of methanol in case of both surfactants. the free energy of micellization (∆gom) was calculated. bhattarai [4] studied the solution behavior of a surfactant in methanol water mixed solvent media by electrical conductivity methods. cetyltrimethylammonium bromide (ctab) as the surfactant used in this investigation. the micelle behaviour of cetyltrimethylammonium bromide in methanol-water mixed solvent media containing 0.10 volume fractions of methanol at 308.15 k was observed by the value of critical micelle concentration (cmc) obtained from conductivity and found to be 1.13 mm which was higher than that of cmc of cetyltrimethylammonium bromide in water. in water, the cmc of ctab was reported [5] to be 1.007 mm from conductometry. bhattarai et al. [6] measured the specific conductivity of cetylpyridinium chloride in pure water and ethanol-water mixed solvent media containing 0.10, 0.20, 0.30 and 0.40 volume fraction of ethanol at room temperature. it was found that the conductivity of cetylpyridinium chloride decreases with the increase in the volume fraction of ethanol. the critical micelle concentration of cetylpyridinium chloride was found to be increased with the increment in the volume fraction of ethanol. niraula et al. [7] studied the conductance of sodium dodecyl sulphate in presence and in absence of kcl and nabr in methanol-water mixed solvent media containing 0.1, 0.2, 0.3, and 0.4 volume fractions of methanol at 308.15 k. the results showed a sharp increase in conductivity with increase in concentration of sodium dodecyl sulphate. also, the conductivity of sodium dodecyl sulphate was increased with addition of salts. the conductivity of sodium dodecyl sulphate was decreased with increment in amount of methanol. the conductance of sodium dodecyl sulphate was found more in presence of kcl than nabr in methanol-water mixed solvent media containing 0.1, 0.2, 0.3, and 0.4 volume fractions of methanol. bhattarai et al. [8] measured the specific conductivity of sodium deoxycholate in pure water and ethanolwater mixed solvent media containing 0.10 and 0.20 volume fraction of ethanol at 303.15 k.the conductivity of sodium deoxycholate was found to be decreased with the increase in the volume fraction of ethanol. the critical micelle concentration of sodium deoxycholate was found to be increase with increase in the volume fraction of ethanol. niraula et al. [9] studied conductivity of sodium dodecyl sulphate in presence and in absence of kbr and nacl in methanol-water mixed solvent media containing 0.1, 0.2 and 0.4 volume fractions of methanol at 308.15k. the results showed a sharp increase in conductivity with increase in concentration of sodium a. bhattarai / bibechana 11(1) (2014) 175-180: (online publication: march, 2014) p.177 dodecyl sulphate. also, the conductivity of sodium dodecyl sulphate was increased with addition of salts. the conductivity of sodium dodecyl sulphate was found to be decreased with increment in amount of methanol. the conductance of sodium dodecyl sulphate was found more in presence of kbr than nacl in methanol-water mixed solvent media containing 0.1, 0.2 and 0.4 volume fractions of methanol. also, niraula et al. [10] studied conductometric studies on the effect of nabr on the micellization of sodium dodecyl sulphate in pure water and methanol water mixed solvent media at different temperatures containing 0.1, 0.2, 0.3 and 0.4 volume fractions of methanol at 308.15 and 318.15 k.the conductance was decreased with addition of methanol. it was observed that the conductance of sodium dodecyl sulphate was found to be increased with increment in concentration as well as with addition of salt (nabr). the result showed that critical micelle concentration increased with addition of methanol and with rise of temperature and decreased with addition of sodium bromide. shah et al. [11] measured the specific conductivity of solutions of cetyltrimethylammonium bromide in absence and in the presence of potassium chloride in methanol-water mixed solvent media containing 0.10, 0.20, 0.30 and 0.40 volume fractions of methanol at 308.15, 318.15 and 323.15 k. the conductance of cetyltrimethylammonium bromide decreased with addition of methanol. it was observed that the conductance of cetyltrimethylammonium bromide increased with increase in concentration as well as with addition of salt (kcl). the concentrations of kcl were taken 0.0001, 0.001 and 0.01 m during the experiments. the result showed that critical micelle concentration of cetyltrimethylammonium bromide increased with addition of methanol and with rise of temperature. also, the critical micelle concentration of cetyltrimethylammonium bromide decreased with addition of potassium chloride. yadav et al. [12] investigated the comparative study of conductance of sodium dodecyl sulphate in different percentage of ethanol water mixed solvent media at 318. 15 k and found the conductance decreased with increase of ethanol. shah et al. [13] studied the effect of kcl on conductivity of dodecyltrimethylammouium bromide (dtab) in presence and absence of methanol at 298.15 k and found the cmc increases with increase of methanol whereas decreases with the addition of kcl. the above findings were supported by other works. for example, the effect of kcl and alcohol on the cmc of cetylpyridinium chloride (cpc) was studied by chung et al.[14]. they observed the decrease in cmc with the addition of electrolyte and vice versa. akbas and kartal [15] carried out an investigation on the effect of ethanol and ethylene glycol on the critical micelle concentration (cmc) of ctab. they observed that cmc decreases upon the addition of ethanol and ethylene glycol. the value of cmc increased with increase in temperature, such behavior was also observed by dubey[16]. 1.2. density the density is very important parameter for the thermodynamic studies of surfactant [17]. the thermodynamic quantity known as the partial molar volume has proved to be very useful tool in elucidating the interactions occurring in solutions. studies of partial molar volume of surfactants have been used to examine the behavior of surfactant solutions [18-23]. shah et al. [24] measured the density of cetyltrimethylammonium bromide solutions in pure water and in methanol-water mixed solvent media containing 0.10, 0.20 and 0.30 volume fractions of methanol at 308.15, 318.15 and 323.15 k and then calculated the partial molar volumes. the results showed almost constant on the partial molar volumes with increasing surfactant concentration. also, the partial molar a. bhattarai / bibechana 11(1) (2014) 175-180: (online publication: march, 2014) p.178 volumes were found to increase with increasing temperature over the entire concentration range investigated in a given mixed solvent medium and these values were found to decrease with increasing methanol content in the solvent composition. bhattarai et al. [25] measured the density of sodium lauryl sulfate in pure water and in methanol –water mixed solvent media containing (0.10, 0.20, 0.30, and 0.40) volume fractions of methanol at (298.15, 308.15, 318.15, and 323.15) k .the results were almost constant on the partial molar volumes with increasing surfactant concentration. also, the partial molar volumes were found to increase with increasing temperature over the entire concentration range investigated in a given mixed solvent medium and were found to decrease with increasing methanol content in the solvent composition. bhattarai and chatterjee [26] determined the densities of cetyltrimethylammonium bromide in methanolwater mixed solvent media at 308.15, 318.15, and 323.15 k and found the densities increase with increase of concentration of surfactant. also, the densities decreased with increment of temperature and also decreased with solvent composition. bhattarai et al. [27] measured the density of the binary mixtures of cetyltrimethylammonium bromide and sodium dodecyl sulphate in pure water and in methanol-water mixed solvent media containing (0.10, 0.20, and 0.30) volume fractions of methanol at 308.15, 318.15, and 323.15 k. the concentrations were varied from (0.03 to 0.12) mol.l-1 of sodium dodecyl sulphate in the presence of ~ 5.0×10-4 mol.l-1 cetyltrimethylammonium bromide. the results showed almost increase in the densities with increasing the concentration of surfactant mixture. also, the densities were found to decrease with increasing temperature over the entire concentration range investigated in a given mixed solvent medium and these values were found to decrease with increasing methanol content in the solvent composition. the concentration dependence of the apparent molar volumes appeared to be negligible over the entire concentration range, investigated in a given mixed solvent medium and the apparent molar volumes increase with increasing temperature and were found to decrease with increasing methanol content in the solvent composition. shah et al. [13] measured the density of dodecyltrimethylammouium bromide (dtab) in presence and absence of methanol at 298.15 k and found the partial molar volume. the results showed almost constant on the partial molar volumes with increasing surfactant concentration and the partial molar volumes were found to decrease with increasing methanol content in the solvent composition. the above findings were supported by other works. for example, iqbal and siddiquah[28] measured the partial molar volume of the surfactant and found the partial molar volume increased significantly with temperature. with regard to the partial molar volume in a mixed solvent, lee and hyne[29] have been determined the partial molar volumes of tetraalkylammonium chlorides in ethanol-water mixtures. they found the partial molar volumes decreased with increasing ethanol content in the solvent composition. 1.3. surface tension surfactants reduce the amount of work necessary to create unit surface area i .e. surface tension of a solution is lowered when surfactants are present [30]. the following are a few generalizations regarding surface tension and surfactants, followed by a discussion of surfactants and dynamic surface tension. a. bhattarai / bibechana 11(1) (2014) 175-180: (online publication: march, 2014) p.179 higher concentrations of surfactants lower the surface tension in comparison to the pure solvent state. the limiting value of surfactant concentration that produces a surface tension decrease is the critical micelle concentration [31]. bhattarai [4] measured the surface tension of cetyltrimethylammonium bromide in methanol water mixed solvent media by ring method. the critical micelle concentration of cetyltrimethylammonium bromide in methanol-water mixed solvent media containing 0.10 volume fractions of methanol at 308.15 k was obtained 1.11mm but in water, the cmc of ctab was reported [5] to be 1.102 mm from tensiometry at 308.15 k which was less than the cmc of cetyltrimethylammonium bromide in methanol water mixed solvent media. jha et al. [32] measured surface tension of cetyltrimethylammonium bromide in presence and in the absence of kcl and nacl in aqueous media. the results showed a sharp decrease in surface tension with increase in concentration of cetyltrimethylammonium bromide and then almost constant value of surface tension was observed. also, the surface tension was found to decrease with addition of salts. in presence of monovalent salts, the critical micelle concentration of surfactant was found to decrease. shah et al. [13] measured the surface tension of dodecyltrimethylammouium bromide (dtab) in presence and absence of kcl in methanol-water mixed solvent medai at 298.15 k and found the critical micelle concentration increasing with solvent composition and decreasing with presence of salt. the above findings were supported by other works. for example, bhattarai [33] measured the surface tension of cetyltrimethylammonium bromide and found the increase in the value of cmc with increasing methanol and temperature. with the addition of inorganic salts, the reduced electrostatic repulsion among the surfactant head groups is a key factor to influence the morphology of aggregates in ionic surfactant solutions. for conventional single-chain cationic surfactants, micelles may change from global to rod like or wormlike with the addition of inorganic salts. hence the cmc of surfactant found to decrease with addition of inorganic salts [34, 35]. 1.4. viscosity like all other surfactants, cetyltrimethylammonium bromide also shows a rapid change in viscosity when the physical and chemical compositions of the solution are changed. this rise in viscosity has been mainly attributed to the change in the structure of the cetyltrimethylammonium bromide micelles depending upon the ambient condition to which it has been subjected. a similar phenomenon happens on dodecyltrimethylammonium bromide. viscosities of solutions increase with increase in the concentrations. the increase in the concentration of the surfactants, make the micelles larger. there is slightly breakage at certain concentration, called cmc. it is also observed that there is increase in the viscosity with the addition of salt. by adding salt to a surfactant, the solution becomes thicker. the electrolyte increases the size of the micelles in the surfactants. hence the addition of electrolyte to the surfactant solution induces the growth of micelle or change in morphology of micelle due to which viscosity is increased and hence cmc of the surfactant decreases [36]. in the presence of 0.1 mol.l-1kbr salt, the relative viscosity of 0.01 mol.l-1 ctab systems increases with increasing amount of benzyl alcohol to a value of approximate 1.9 for a benzyl alcohol content of 0.6% (v/v). if more benzyl alcohol is added, the viscosity is decreased. in the absence of kbr salt, the viscosity of 0.01 mol.l-1ctab solution increases slightly with addition of alcohol due to the increase of volume fraction of mixed micelles [37]. the above findings of other works were supported by the work of research team of eastern nepal. for example, shah et al. [13] studied the effect of kcl on viscosity of dodecyltrimethylammouium bromide (dtab) in the presence and absence of methanol at 298.15 k and found the cmc increases with increase of methanol whereas decreases with the addition of kcl. a. bhattarai / bibechana 11(1) (2014) 175-180: (online publication: march, 2014) p.180 references [1] a. d. mcnaught, a. wilkinson, compendium of chemical terminology, second edition, blackwell scientific publications, oxford, iupac, 1997. [2] a. bhattarai, s.k. shah, a. k. yadav, nepal j. sci. and tech., 13 (2012) 89. [3] s. k. shah, t. p. niraula, a. bhattarai, s.k. chatterjee, bibechana, 8 (2012) 37. [4] a. bhattarai, sonsik journal, 4 (2012) 52. [5] t. chakraborty, i. chakraborty and s. ghosh, langmuir, 22(2006)9905. [6] a. bhattarai, s. k. shah, a. k. yadav, nepal j. sci. & tech., 13 (2012) 89. [7] t.p. niraula, s. k. chatterjee, a. bhattarai, j. nepal chem. soc., 29 (2012) 5. 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[ 37] w. zhang, g. li, j. mu, l. zheng, j. disp. sci. & tech., 21 (2000)605. l. khanal et al./ bibechana 16 (2019) 31-40: rcost p.31 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal study of ambient environment around asymptotic giant branch carbon star: iras 01142+6306 l. khanal1, d. r. upadhyay1*, a.k. jha2, b. aryal2 1amrit campus, tribhuvan university, thamel, kathmandu nepal. 2central department of physics, tribhuvan university, kirtipur, kathmandu, nepal. *email: mnadphy03@gmail.com* article history: received 01 may, 2018; accepted 04 september, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.20998 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract we studied dust environment such as flux, temperature, mass and inclination angle of the cavity structure around the c-rich asymptotic giant branch star in 60 μm and 100 μm wavelengths band using infrared astronomical survey. we observed the data of agb star having iras name 01142+6306 corresponding to r.a.(j2000)= 01h 17m 33.504s and dec.(j2000)= 630 22’ 4.98’. flexible image transport system image was downloaded from sky view observatory; we obtained the surrounding flux density using software aladinv2.5. the dust color average temperature and mass are found to be 25.08 k and 4.73×1026 kg (0.00024 mʘ) respectively. the dust color temperature ranges from 18.76 ± 3.16 k to 33.21 ± 4.07 k. the isolated cavity like structure around agb star has extension 45.67 parsec and contraction 17.02 parsec was observed using detailed calculation. the core region is found to be edge-on having inclination angle 79.46o. keywords: ism; agb star; dust color temperature; dust mass; inclination angle. 1. introduction the interstellar medium (ism) is the low density matter space between star and surrounding. the ism contains gas in molecular, atomic or ionic form as well as cosmic rays and dust particles. by mass, 99% is gas and 1 % is dust particle [1]. the percentage of gas particle is 91 % hydrogen, 9 % are helium and 0.1 % are the atoms of elements heavier than hydrogen and helium [2]. the most abundant component in ism is hydrogen and its various forms: molecular form (h2), neutral form(hi) and ionized form (hii) [3]. ism environment is slightly different around the asymptotic giant branch (agb) star as compared to main sequence stars. stellar wind of agb, supergiant interactions with ism, supernova explosion and releasing matter of planetary nebulae have major roles for the formation of dilute ism. this thermally unstable star burns vigorously and certainly extinguishes. during thermal pulse he shell performs 107lʘ for short period and forms convective zones with releasing excessive mass and tremendous amount of energy. this approximate http://nepjol.info/index.php/bibechana mailto:mnadphy03@gmail.com* http://dx.doi.org/10.3126/bibechana.v16i0.20998 https://creativecommons.org/licenses/by-nc/4.0/ l. khanal et al./ bibechana 16 (2019) 31-40: rcost p.32 (online publication: dec., 2018) composition of this zone is 25 % carbon and 75% helium. out of this, agb wind and supergiant interaction plays prominent role for the formation and interaction between ambient ism and agb star. during the stellar evolution, when the normal star terminates from the main sequence of hr diagram, star becomes more luminous and red in color. this stage is late stage of stellar evolution, which is generated by finishing hydrogen (h) fuel and abundant central helium(he) ash. the asymptotic star evolves when the mass of the star is (1-8) mʘ and is located at the right and upper part of hr diagram [4]. in this research work we discussed how mass is distributed around agb star, dust color temperature distribution and cavity like structure gives wide range of area for studying the interaction between ism and agb star. low and intermediate mass star (lims) evolve and become asymptotic giant branch stars: luminous (lstar=104lʘ), cool (teff =3000k) giants (rstar =1 au), which lose mass at high rates (10-7 to a few times 10-4mʘ/yr) [5]. aryal & weinberger (2006) discovered a new isolated interstellar nebula (ra = 08h27m (j2000), dec = +25°54’ (j2000)) found at 60 m and 100 m on iras maps. it has dimensions of ~140’ × 70’ and a cone-like shape, suggesting interaction with ambient interstellar matter or external radiation field [6]. they used similar method for as we have using calculating dust color temperature and found that the southern nucleus is about 34±4 k temperature of its northern counterpart 32±4 k. the eastern filamentary structures are slightly cooler (20±2 k) than the western filamentary structures (26±3 k) [6]. again similar work done by jha et al.(2017) in kk loops and pulsar coordinates [7]. here we have presented work related to asymptotic giant branch star by using similar methods. agb stars are generally classified as oxygen-rich (m-type) or carbon-rich (c-type) based on the chemistry and composition of the photosphere and/or the outer envelope [5]. we have investigate the surrounding temperature, mass and cavity around the c-rich agb star cgcs201 at a distance 4.49 kpc[8] and lies at galactic latitude 0.6450 using iras survey [9]. we have uses method developed by henning et. al. (1990) and hildebrand et al.(1983) [10] data are obtained and cross checked from skyview virtual observatory [10] and simbad [11] respectively. 2. material and methods infrared astronomical satellite survey (iras) mission performed very precise, sensitive of sky survey at 12 μm, 25 μm, 60 μm and 100 μm. the infrared astronomical satellite (iras) mission was a combined effort and joint project by the united states (nasa), the netherlands (nivr), and the united kingdom (serc) [6]. this satellite configuration and survey were optimized for maximally reliable captures of point sources for ten months in 1983, iras captured more than 95%. here most of the sky survey and images has been taken from skyview virtual observatory [9]. we scanned 12 μm, 25 μm, 60 μm, 100 μm iras survey using virtual sky view observatory[10] to get the flexible image transport system (fits) image. when we enter the coordinate ra(01h17m33:504s) and dec. (+630 22’ 4:98’’), (galactic longitude/latitude:125.85o/0.6450) [8]. the fits image is capable of carrying the physical information (flux density) at our region of interest. we tagged 225 pixels at 60 micron and 100 micron to get the relative flux density. the nature of contour depends upon whether the formation of cavity is isolated or not. also the ambient pixels and tagging depends upon the probable location of our agb star. l. khanal et al./ bibechana 16 (2019) 31-40: rcost p.33 (online publication: dec., 2018) 3. theory 3. 1 dust color temperature estimation the flux density of emission at a wavelength λi is given by schnee et al. (2005) [12]. fi = [ 2hc λi 3 (e hc λiktd−1) ] ndαλi −β ωi (1) where nd represents column density of dust grains, α is a constant that relates the flux to the optical depth of the dust, β is the emissivity spectral index and ωi is the solid angle subtended at λi by the detector. following [13], we use the equation β = 1 δ+𝜔td (2) to describe the observed inverse relationship between termperature and emissivity spectral index. here δ and 𝜔 are free parameters. dupace et al. (2003)[13] found that the temperature dependence of the emissivity spectral index fits very well with the hyperbolic approximating function. considering temperature as an independent variable, the best fit gives δ = 0.40 ± 0.02 and 𝜔 = 0.0079±0.0005k-1, with the χ2/degree of freedom=120/120. with the assumption that the dust emission is optically thin at 60 μm and 100 μm and ω60 ≅ ω100, we can write the ratio, r, of the flux densities at 60 μm and 100 μm as r = 0.6−(3+β) [ e 144 td −1 e 240 td −1 ] (3) once the approximate value of β is known , one can use equation (3) to derive td. the value of β depends on such dust grain properties as composition, size and compactness. for reference, a pure blackbody would have β=0, the amorphous layer-lattice matter has β ~ 1 and the metals and crystalline dielectrics have β ~ 2[13]. fig. 1 : (a) and (b) iras 60 μm and 100 μm far infrared image around agb star centered at r.a. (j2000) = 06h 51m 54.02s, dec. (j2000) = -010 35' 43”[9] . l. khanal et al./ bibechana 16 (2019) 31-40: rcost p.34 (online publication: dec., 2018) for a smaller value of td, 1 can be dropped form both numerator and denominator of equation (3) and it takes the form r = 0.6−(3+β) e 144 td e 240 td (4) to determine the dust color temperature we required the flux densities at 60 μm to 100 μm. the dust temperature td in each pixel of a fits image can be obtained by assuming that the dust in a single beam is isothermal and that the observed ratio of 60 μm to 100 μm emission is due to black body radiation from dust grains at td, modified by a power law of spectral emissivity index. taking natural logarithm on both sides of equation (4), we find the expression used for the dust temperature estimation as [13], t 𝐝= −96 ln[r×.063+β] (5) where r = f(60μm) f(100μm) (6) here f(60µm) and f(100µm) are the flux densities in 60 µm and 100 µm respectively [13]. 3.2 dust mass estimation the dust masses are estimated from the ir flux densities. the resulting dust mass depends on the physical and chemical properties of the dust grains. the dust masses are estimated using (hildebrand 1983)[10]; 𝑀𝑑𝑢𝑠𝑡 = 4 3 𝑎𝜌 𝑄𝜈 [ 𝐹𝜈𝐷2 𝐵(𝜈,𝑇) ] (7) where, 𝑎 = weighted grain size = 0.1 μm 𝜌 = grain density= 3000 𝑘𝑔𝑚−3 𝑄𝜈= grain emissivity = 0 .0010 for 100μm and 0.0046 for 60μm respectively [15]. f𝜈 = total flux density of the region whose mass is to be determined, f𝜈 = 𝑓 × 5.288 × 10−9𝑀𝐽𝑦/ 𝑠𝑟 𝐷 = distance of the structure 𝐵(𝜈, 𝑇)= planck’s function [10]. where, ℎ = planck’s constant, 𝑐 = velocity of light, 𝜈 = frequency at which the emission is observed & 𝑇= the average temperatures of the region. using values of different parameters equation (7) takes the form. m𝑑𝑢𝑠𝑡 = 0.4 [ f𝜈𝐷2 𝐵(𝜈,𝑇) ] (8) the distance d and co-ordinate was taken from the source of catalogue paper [8]. we use the equation (8) for the calculation of the dust mass. 3.3 inclination inclination angle is the angle between line of sight and the plane of celestial object projected in the sphere. holmberg (1946) [16] established a simple model to find the inclination angle of celestial objects. holmberg equation is the relation between the axial ratio ( b/a ) and the inclination angle (i), the angle between the line of sight and normal to the galactic plane. the flatness factor (q*) = 0.33 is assumed by considering oblate spheroid. in this case, the equation of the ellipse can be written as 𝑥2 𝑎2 + 𝑦2 𝑎2𝑞∗2 = 1 (9) the equation of the tangent at point p is 𝑦 = 𝑘𝑥 + 𝑦0 (10) where, 𝑘 = 𝑡𝑎𝑛(90 − 𝑖) = 𝑐𝑜𝑡 𝑖 and y-intercept oq = yo solving above equations, we get l. khanal et al./ bibechana 16 (2019) 31-40: rcost p.35 (online publication: dec., 2018) fig. 2: a schematic representation of inclination angle. here ‘a’ and ‘q*a’ represent the semi major and minor axes of ellipse. 𝑥 = −2𝑦0 𝑘 ±√{(2𝑦𝑜𝑘)2−4(𝑞∗2+𝑘2)(𝑦𝑜 2−𝑞∗2𝑎2)} 2(𝑞∗2+𝑘2) (11) the line touches the ellipse at only one point p, if 𝑎2𝑘2 + 𝑎2𝑞 ∗2 from above figure, 𝑠𝑖𝑛 𝑖 = 𝑏 𝑦𝑜 using 𝑦𝑜 = 𝑏 𝑠𝑖𝑛𝑖 𝑎𝑛𝑑 𝑘 = 𝑐𝑜𝑡 𝑖, we get, cos2 𝑖 = 𝑏2 𝑎2−𝑞∗2 1−𝑞∗2 (12) is called ‘holmberg formula’ for inclination angle [16]. ∴ angle of inclination (𝑖) = cos−1 (√ 𝑏2 𝑎2−𝑞∗2 1−𝑞∗2 ) (13) 4. result and discussion 4. 1 flux density variation the best fit line between f60 and f100 with error 0.02, slope of the linear fitted line is 0.28 whereas the coefficient of determination is 0.68. it gives average value of temperature nearly 25.08 k. again coefficient of determination shows the square of the correlation between 100 μm flux density and 60 μm as shown in fig. 3. it indicates inside the cavity region flux density data follows best fit condition nearly 68%. the slope of flux at 60 μm and 100 μm is calculated in equation (6). the nonlinear phenomenon is due to the rapid increase in flux at intersecting point between extension (ab) and contraction (cd) as shown in fig.6. we studied the contour map of flux density with respect to right ascension and declination as shown in fig.4(b). the violet color represents the minimum flux and red color represents higher flux density region around agb star. it has been observed that two cavity was formed by the central and dense flux region around carbon star : iras 01142+6306. l. khanal et al./ bibechana 16 (2019) 31-40: rcost p.36 (online publication: dec., 2018) fig. 3:(a) flux at 60 m (f60) versus flux at 100 m (f100) scattered plot which suggest that the linearity between f60 and f100, the slope of the given distribution found to be with 0.28 error 0.02 and coefficient of determination nearly 0.68. fig. (b) the flux density contour map of the inner region of the cavity at 100 m. the contour levels and the color bars are shown. 4.2 gaussian plot of temperature and mass we have plotted the gaussian plot of dust color temperature and dust mass. the gaussian center is found to be 23.76 k which is near to the average value of temperature the region i.e. 25.08 k. here number of pixels corresponding to average value of temperature is maximum. the relatively lower value of temperature leads low value of error suggest that uniformity and consistency in temperature. the sharpness in curve represents dust color temperature of the pixels in the cavity region are found to be near to the average temperature. the graph between the number of the pixels and temperature is slightly positively skewed. similarly we obtained the information about dust mass distribution. the gaussian area of dust mass was found to be 2.10×1028 kg, whereas gaussian center 4.06×1026 kg. the gaussian average represents the most abundant pixel dust mass around the star cgcs201. the non-uniform (right skewed) distribution of dust mass shows that there is fluctuation in density which implies that the ism grains are in the form of inhomogeneous distribution of ism matter within region of interest. 4.3 contour plot of mass and temperature the distribution of the right ascension and declination with the dust color temperature and dust mass has been plotted as shown in fig. 5. the contour plot of fig. 5 (a) and (b) shows the nearly inverse relationship between the mass and temperature. the average dust mass inside the structure is found to be (0.00024)mʘ. we found the minimum mass at the high temperature region. and mass is highly concentrated at the right side of the neck of the cavity structure. l. khanal et al./ bibechana 16 (2019) 31-40: rcost p.37 (online publication: dec., 2018) the continuous distribution of the temperature with at given right ascension and declination is shown in the fig. 5 (b). by using origin 8.0 the three dimensional plot has displayed. there is rise in temperature from violet to red color. the temperature has lies within the range 18.76 ± 3.16 k to 33.21 ± 4.07 k. there is nearly inverse relation between the mass distribution and temperature distribution at different pixel coordinate. we found the temperature is high at the intersecting points of cavity, which have high flux density. fig. 4: (a), (b) the solid curve with error bar represents gaussian plot of dust color temperature and mass respectively. here error bar represents root square error in number of pixel corresponding calculated parameters. fig. 5: (a)r.a./dec.(j2000): 01h 17m 33:504s +630 22’ 4.98’’ the contour plot of mass with respect to right ascension and declination and (b) the contour plot of temperature with respect to right ascension and declination. l. khanal et al./ bibechana 16 (2019) 31-40: rcost p.38 (online publication: dec., 2018) fig. 6: representation of extension (ab) and contraction (cd) of dust structure around iras 01142+6306. 4.4 isolated cavity structure & inclination angle we proceed a systematic search using fits image from which we discovered two differently isolated cavity in 60 μm and 100 μm iras map around agb star named as iras 01142+6306 or cgcs 201 having r.a./dec.(j2000): 01h 17m 33:504s +630 22’ 4.98’’. we have used aladinv2.5 to find the closed loop for region of interest. the closed loop having extension i.e. we called major diameter 34.96'(45.67 parsec) and contraction i.e. minor diameter 13.03'(17.02 parsec) was found using aladinv2.5. the region of interest or ambient medium is sketched. the shape and contour of the loop depends upon the flux distribution around agb star and contour level. different color flux density shows variation physical parameters around the region of interest. here diameter ab representing major diameter and cd is minor diameter interestingly maximum flux is found at their intersecting point. hence from this observation we have major axis (a) = 45.67 pc, minor axis (b) = 17.02 pc and the value of intrinsic flatness q = 0.33 as suggested by holmberg (1946) for oblate spheroid structure then using equation (13) inclination angle found to be 79.46o. the inclination angle of the core region greater than 70o suggesting edge-on appearance. 5. conclusion this work contributed following understanding. • we studied (100 μm and 60 μm) iras survey using virtual skyview observatory, simbad and other platform. the maximum at r.a./dec.j(2000): 01h 17m 28.69s/630 21’32.6’’, minimum at r.a./dec. j(2000): 01h 16m 36.08s/630 26’ 5.5” average temperature of ambient ism around agb star is 33.21± 4.06 k, 18.76 ± 3.16 k, 25.08 k respectively. maximum at j(2000) r.a./dec.: 01h 16m 38.29sec/ 630, 24’, 10.3’’), minimum at j(2000)r.a./dec: 01h 18m 25.69s / 630 30’ 24.8” and average mass of the surrounding pixels are 1.89×1027 kg (0.00094 mʘ), 9.16×1025 kg (0.00005 mʘ) and 4.73×1026 kg (0.00024mʘ) respectively. due to more temperature difference, we realized that star is in late agb phase. l. khanal et al./ bibechana 16 (2019) 31-40: rcost p.39 (online publication: dec., 2018) • environment around iras 01142+6306 shows dust color temperature and dust mass of the structure which indicates a very good agreement with gaussian distribution, and contour maps follows as expected trend slightly variation due to region affected by surrounding high pressure events. by using linear fitting between 60 μm and 100 μm we found slope 0.28(with error 0.02) which gives average temperature and coefficient of determination 0.68 which is nearly 1 gives 68% best fit. this suggests that there is linearly change in flux density. the data scattered above the line is due to the rapid increase in flux at intersecting points of two diameters inside the contour map. • the inclination angle of the core region of iras 01142+6306 was found to be79.46o, suggesting edge-on appearance and size of the structure found to be 45.67 pc ×17.02 pc. acknowledgement we acknowledge strasbourg astronomical data center (cds) and sky view virtual observatory. one of the authors (lk) acknowledges department of physics amrit campus, tribhuvan university, nepal for all kinds of supports during this research work. references [1] d. p. cox, the three-phase interstellar medium revisited, annu. rev. astron. astrophys. 43 (2005, september) 337-385. doi.org/10.1146/annurev.astro.43.072103.150615. [2] k. m. ferriere, the interstellar environment of our galaxy, reviews of modern physics 73(4) (2001) 1031. [3] h. p. gail, s. v. zhukovska, p. hoppe & m.trieloff, stardust from asymptotic giant branch stars, the astrophysical journal 698(2) (2009) 1136. doi.org/10.1088/0004-637x/698/2/1136. [4] t. r. bedding, a. j. boothm & j. m. davis, (eds.). (2013), fundamental stellar properties: the interaction between observation and theory: proceedings of the 189th symposium of the international astronomical union, held at the women’s college, university of sydney, australia, 13–17 january 1997 (vol. 189), springer science & business media. [5] i. iben, & a. renzini,, asymptotic giant branch evolution and beyond, annual review of astronomy and astrophysics 21(1) (1983) 271-342. [6] b. aryal, & r. weinberger, a new large high latitude cone-like far-ir nebula, astronomy & astrophysics 448(1) (2006) 213. doi.org/10.1051/0004-6361:20042440. [7] a. k. jha, b. aryal, & r. weinberger, a study of dust color temperature and dust mass distributions of four far infrared loops. revista mexicana de astronomía astrofísica 53(2) (2017) 467-476. [8] r. guandalini, m. busso, s. ciprini, g. silvestro, & p. persi, infrared photometry and evolution of masslosing agb stars-i. carbon stars revisited. astronomy & astrophysics 445(3) (2006) 1069-1080. doi.org/10.1051/0004-6361:20053208. [9] http://skyview.gsfc.nasa.gov/current/cgi/query.pl (2017). [10] r. h. hildebrand, the determination of cloud masses and dust characteristics from sub millimeter thermal emission, journal of royal astronomical society 24 (1983) 267-282. [11] http://simbad.u-strasbg.fr/simbad/sim-fcoo (2017). [12] s. l. schnee, , n.a. ridge, a. a. goodman, g. l. jason, a complete look at the use of iras emission maps to estimate extinction and dust temperature, astrophysical journal 634 (2005) 442450. [13] x. dupac, j. p. bernard, n. boudet, m. giard, j. m. lamarre, c. mny, f. pajot, , i. ristorcelli, g. serra, b. stepnik, j.p. torre, inverse temperature dependence of the dust sub millimeter spectral index, astronomy & astrophysics 404 (2003) l11-l15. doi.org/10.1051/0004-6361:20030575. l. khanal et al./ bibechana 16 (2019) 31-40: rcost p.40 (online publication: dec., 2018) [14] k.young, t.g. philips, g. r. knapp, circumstellar shells resolved in iras survey data ii-analysis, astrophysical journal 409 (1993) 725. doi.org/10.1086/172702. [15] c. a. beichman, g. neugebauer, h. j. habing, p. e. clegg, t. j. chester, infrared astronomical satellite (iras) catalogues and atlases i: explanatory supplement. us government printing office, washington (1988). [16] e. holmberg, on the apparent diameters and the orientation in space of extragalactic nebulae medd. lund astron. obs. ser. vi, (1946) 117. 3. 1 dust color temperature estimation 3.2 dust mass estimation 4. 1 flux density variation 4.2 gaussian plot of temperature and mass 4.4 isolated cavity structure & inclination angle microsoft word abhattarai.docx r c o s t n publisher: research council of science and technology, biratnagar, nepal p. 128 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (online) journal homepage: http://nepjol.info/index.php/bibechana conductometric study of nickel chloride in ethanol-water mixed solvent media at various temperatures nabin basnet 1 , ajaya bhattarai 2* 1 department of chemistry, damak multiple campus,tribhuvan university, damak, nepal 2 department of chemistry, m.m.a.m.c., tribhuvan university, biratnagar, nepal * e-mail: bkajaya@yahoo.com accepted for publication: december 20, 2014 abstract the conductivity measurement of nickel chloride has been done in binary solvent of the ethanol-water system. the different percentage of ethanol including 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 (v/v) has been chosen as binary solvents. the concentration of the electrolyte in the prepared solutions varies from 0.008 to 0.1 mol.l -1 for temperatures 298.15 k, 303.15 k and 308.15 k. the conductivity of the electrolyte decreases with increase in ethanol content in the solvent at a particular temperature, which is due to the decrease in dielectric constant of the medium. the conductivity increases with increase in temperature and concentration, due to increase in mobility of ions and number of ions from observed electrolyte respectively. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11789 © 2014 rcost: all rights reserved. keywords: binary solvent; nickel chloride; ethanol-water mixed solvent media; conductivity. 1. introduction an electrolyte is the substance which can conduct electric current in aqueous solution, non-aqueous solution or in molten state. in electrolytes, freely movable ions are the charge carriers, so that these substances are electrically conductive. the electrical conductivity provides useful information in the area of engineering and in corrosions area provides useful information for assessing the corrosively of aqueous media and for the design of cathodic protection system. also, it is used to gain insight into the properties of electrolyte solutions and evaluate characteristic quantities such as dissociation constants [1]. the conductance measurements provide valuable information regarding the ion-ion, ion-solvent interaction and solvent structure for both aqueous and binary solvent systems. the conductance in different electrolytes in aqueous solution have been extensively reported in literature, but in mixed solvent media including ethanol-water binary solvent is rare[2], also the conductivity measurement of transition metal salts is very rarely found in literature, so we have been selected nicl2 for our study. moreover, it is interesting that the nicl2 .6h2o is moderately soluble even in the absolute ethanol. in recent, several studies have reported that the nature of the spherical ions, having a large variation in size in aqueous mixtures of the alcohols, has received considerable attention [3]. it was reported in the previous work [4] that potassium halides are structured breakers in ethanol-water basnet and bhattarai/ bibechana 12 (2015) 128-134: p.129 mixtures and the maximum in breaking power occurs at 0.1 mole fraction of ethanol. the conductance of sodium nitrate in ethanol water mixtures were measured at 308.15 k in 1979 [5]. the measurement of conductance of sodium chloride, potassium bromide, sodium bromide, potassium chloride, and also potassium nitrate in pure water and ethanol-water mixed solvent media has been done [6, 7, 8, 9, 10]. this paper deals with the conductance behavior of nickel chloride in ethanolwater mixed solvents covering a range of dielectric constant values at temperature 298.15, 303.15 and 308.15 k. 2. experimental the ethanol is purchased from merck, india which was then distilled with phosphorous pentoxide and again redistilled over calcium hydride. the purified ethanol had a density of 0.78097gcm -3 at 303.15 k. the density of ethanol was measured by the use of an ostwald-sprengel type pycnometer of about 25 cm3 capacity. the pycnometer was then tightly fixed in a thermostat at the experimental temperatures within 0.005 k for at least 15 minutes to have thermal equilibrium with thermostat. after thermal equilibrium was attained, the mass of the pycnometer was measured with an electronic balance having 0.0001 gm sensitivity, made by kern company, germany and the density was calculated. the water used in preparation of binary solvent was obtained by triply distillation of ordinary water using potassium permanganate and sodium hydroxide. the purified water has a specific conductance less than 10-6 s.cm-1 at 303.15 k. the dielectric constant of the binary solvent of ethanol-water mixtures at the experimental temperatures were obtained by regressing the relative permittivity data as a function of solvent composition from the literature [3]. the nicl2 . 6h2o employed in these investigations was purchased from sd fine chem limited, mumbai, india. conductance measurements were carried out on a pye-unicam pw 9509 conductivity meter at a frequency of 2000 hz using a dip-type cell with a cell constant of 1.15 cm-1 and having an uncertainty of 0.01%. the cell was calibrated by the method of lind and co-workers[11 ], 1959 using the aqueous potassium chloride solution. the measurements were made in a water bath maintained within ± 0.005 k of the desired temperature. the details of the experimental procedure have been described earlier [12, 13]. to ensure the reproducibility of the results, several independent solutions were prepared and runs were performed. due correction was made for the specific conductance of the solvent by subtracting the specific conductance of the relevant solvent medium from those of the electrolyte solutions. in order to avoid moisture pickup, all solutions were prepared in a dehumidified room with utmost care. in all cases, the experiments were performed three times. 3. results and discussion the water and alcohol have different structures; the structure of alcohol is much simpler than that of water. the water and alcohol molecules associate much less strongly, and form polymeric h-bonded chains, rather than large cluster, which rarely contain 5 to 7 molecules for sterically hindered alcohols [14]. the hydrogen bonding network strengthening and tetrahedral like water network changes to zigzag chain structure of the system with increase in alcohol concentration in the ethanol-water system [15]. the hydrogen bonding and a closer packing of the molecules by the attraction allows a larger number of molecules of the hydrated ethanol to fit into the same space, thus decreasing the overall volume. the density of the binary solvent decreased with the increase of ethanol content for the basnet and bhattarai/ bibechana 12 (2015) 128-134: p.130 ethanol-water mixed solvent system [10, 16, 17]. in ethanol-water mixtures, solvent-solvent interactions play a considerable part and properties of these mixtures cannot always be interpreted on the basis of the continuous miscibility of the components in all mixtures. these mixtures possess also pronounced structures which vary with temperature and ethanol content. the relative permittivity of the medium (fig. 1) decreased at a given temperature with increasing in the ethanol content [3, 6, 7, 8, 10] in the binary solvent system. the specific conductance data taken during the study were given below in the tables 1-3, in the electrolyte concentration ranges from 0.008 mol.l-1 to 0.1 mol.l-1. table 1: concentration and sp. conductance (κ, ms/cm) of nicl2 in various % (v/v) of ethanol at 298.15 k s.n. conc. specific conductance of nicl2 in various % (v/v) of ethanol at 298.15 k (mol/l) 10 20 30 40 50 60 70 80 90 100 1 0.100 12.89 10.13 8.14 6.70 5.66 4.75 3.99 3.15 2.27 1.07 2 0.080 10.85 8.54 6.82 5.62 4.62 3.95 3.35 2.67 1.95 0.91 3 0.060 8.30 6.54 5.26 4.31 3.35 3.07 2.59 2.07 1.52 0.71 4 0.040 5.70 4.43 3.59 2.95 2.47 2.07 1.79 1.43 1.03 0.51 5 0.020 3.07 2.39 1.99 1.63 1.39 1.15 0.99 0.83 0.68 0.31 6 0.010 1.87 1.47 1.27 1.07 0.91 0.83 0.75 0.63 0.47 0.23 7 0.008 1.51 1.23 1.15 1.03 0.83 0.71 0.63 0.55 0.35 0.19 table 2: concentration and sp. conductance (κ, ms/cm) of nicl2 in various % (v/v) of ethanol at 303.15 k s.n. conc. specific conductance of nicl2 in various % (v/v) of ethanol at 303.15 k (mol/l) 10 20 30 40 50 60 70 80 90 100 1 0.100 14.65 11.73 9.50 7.82 6.50 5.54 4.35 3.59 2.55 1.21 2 0.080 12.45 9.90 7.98 6.54 5.54 4.60 3.79 3.03 2.15 0.95 3 0.060 9.58 7.62 6.14 5.02 4.23 3.59 2.91 2.39 1.71 0.79 4 0.040 6.54 5.22 4.27 3.51 2.87 2.47 2.03 1.63 1.23 0.55 5 0.020 3.55 2.95 2.35 1.91 1.51 1.35 1.19 0.99 0.75 0.35 6 0.010 1.91 1.71 1.43 1.15 0.95 0.83 0.75 0.67 0.55 0.31 7 0.008 1.63 1.51 1.27 1.03 0.87 0.75 0.67 0.55 0.43 0.27 table 3: concentration and sp. conductance (κ, ms/cm) of nicl2 in various % (v/v) of ethanol at 308.15 k s.n. conc. specific conductance of nicl2 in various % (v/v) of ethanol at 308.15 k (mol/l) 10 20 30 40 50 60 70 80 90 100 1 0.100 17.20 13.73 10.89 9.14 7.66 6.18 5.14 3.91 2.71 1.23 2 0.080 14.49 11.57 9.14 7.62 6.42 5.14 4.35 3.31 2.31 1.03 3 0.060 11.25 8.98 7.06 5.9 4.95 4.07 3.39 2.67 1.83 0.83 4 0.040 7.94 6.30 5.02 4.11 3.35 2.87 2.39 1.91 1.31 0.59 5 0.020 4.35 3.47 2.79 2.31 1.91 1.63 1.35 1.07 0.75 0.35 6 0.010 2.59 2.03 1.63 1.27 1.15 1.03 0.87 0.75 0.51 0.23 7 0.008 2.27 1.71 1.43 1.19 0.95 0.83 0.78 0.59 0.47 0.19 basnet and bhattarai/ bibechana 12 (2015) 128-134: p.131 table 4: experimental slopes, correlation coefficients of fits (as r 2 ) of nickel chloride and dielectric constant of ethanol-water mixtures at different temperatures % of ethanol (v/v) 298.15 k 303.15 k 308.15 k slope r 2 εsolvent slope r 2 εsolvent slope r 2 εsolvent 10 125 0.999 74.49 145 0.998 72.00 166 0.998 71.00 20 98.4 0.999 69.58 114 0.999 67.32 133 0.998 66.37 30 77.6 0.999 64.31 91.4 0.999 62.07 104 0.999 61.33 40 63.5 0.999 58.56 75.3 0.999 56.89 87.7 0.999 56.29 50 52.5 0.999 52.81 63.2 0.998 51.48 73.6 0.999 50.70 60 44.5 0.999 46.82 53 0.999 45.77 58.5 0.999 44.98 70 37.1 0.999 41.07 41.4 0.997 40.08 48.8 0.998 39.26 80 28.9 0.999 35.21 33.7 0.998 34.61 36.8 0.996 33.89 90 21 0.997 30.29 23.4 0.999 29.46 25.1 0.998 28.74 100 9.75 0.998 24.30 10.2 0.993 23.54 11.4 0.997 22.63 it is a known fact that the ionic conductance increases with temperature and decreases with concentration. the highest or the limit equivalent conductance can only be achieved with the extrapolation of conductance to the zero concentration. this is the result which can be obtained with all ions. here, we calculated the limiting molar conductance in table 5 from our investigated system with the help of table 1-3. table 5: limiting molar conductance (ms cm 2 mol -1 ) of nicl2 in ethanol –water system at different temperatures % of ethanol (v/v) 298.15 k 303.15 k 308.15 k limiting molar conductance limiting molar conductance limiting molar conductance 10 245 262 277 20 176 207 215 30 144 170 185 40 124 132 154 50 98.6 117 132 60 83.4 100 116 70 73.8 88.1 95.9 80 62.3 76.8 84.6 90 51.7 55.2 56.5 100 29.5 31.3 33.8 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 90 100 110 at 308.15 k at 303.15 k at 298.15 k % of ethanol(v/v) d ie le c tr ic c o n s ta n t (ε ) 0 4 8 12 16 20 0 0.02 0.04 0.06 0.08 0.10 0.12 in 100% ethanol in 90% ethanol in 80% ethanol in 70% ethanol in 60% ethanol in 50% ethanol in 40% ethanol in 30% ethanol in 20% ethanol in 10% ethanol concentration (moll -1 ) κ ( m s c m -1 ) basnet and bhattarai/ bibechana 12 (2015) 128-134: p.132 the experimental specific conductivities of nickel chloride as a function of the salt concentration at 298.15 k, 303.15 k and 308.15 k of ten different ethanol-water binary mixtures containing 10, 20, 30, 40 50, 60, 70, 80, 90 and 100 % (v/v) ethanol are depicted in figs. 2-4. these figures show that the specific conductivities linearly increase with increasing concentration within the concentration range investigated here. the increase in the conductance with concentration is due to an increase in the ionic density in the solution. the conductivity is also the function of temperature, so it is well known fact that specific conductance of an electrolyte increases with increase in temperature. in this study, also the specific conductance of nicl2 increases with increasing temperatures in ethanol water mixed solvent media which was also reported in the same solvent system for electrolyte kno3 [10] and also in methanol-water system for electrolytes nabr and nai [18]. the increase in specific conductance with temperature is mainly due to the increase in thermal energy of the ions which responsible for the mobility of ions, decrease in the viscosity of the solvent, and also an increase in the degree of ionization. there is the linear relationship between specific conductance and the electrolyte concentrations for all concentrations and solvent composition investigated. but, it has been studied earlier that the conductivity value decreases with increase of ethanol in the system [10, 19]. the specific conductance of the electrolyte nickel chloride also shows the same pattern as reported earlier in the literature, i.e. decreases with increase of ethanol content for the studied ethanol-water mixed solvent system (shown in figs. 2, 3 and 4). the presence of ethanol reduces the dielectric constant of the binary solvent phase (shown in table 4 and fig.1) by breaking the structure of water, disturbed the original orientations of water molecules. the decrease in dielectric constant of binary solvent makes easier for the formation of ion-pairs in the solution phase. the decrease in specific conductance can also be explained in terms of having the small ionizing effect of the solvent on electrolytes, so the electrostatic forces between oppositely charged ions would be appreciable and will have the small value of the specific conductance. figure 1: dielectric constant as a function of the volume fractions of ethanol at different temperatures. figure 2: sp. conductance of nicl2 as a function of concentration at 298.15 k (solid lines – fitted graphs). 0 4 8 12 16 20 0 0.02 0.04 0.06 0.08 0.10 0.12 in 100% ethanol in 90% ethanol in 80% ethanol in 70% ethanol in 60% ethanol in 50% ethanol in 40% ethanol in 30% ethanol in 20% ethanol in 10% ethanol concentration (moll -1 ) κ ( m s c m -1 ) 0 4 8 12 16 20 0 0.02 0.04 0.06 0.08 0.10 0.12 in 100% ethanol in 90% ethanol in 80% ethanol in 70% ethanol in 60% ethanol in 50% ethanol in 40% ethanol in 30% ethanol in 20% ethanol in 10% ethanol concentration (moll -1 ) κ ( m s c m -1 ) basnet and bhattarai/ bibechana 12 (2015) 128-134: p.133 figure 3: sp. conductance of nicl2 as a function of concentration at 303.15 k (solid lines – fitted graphs). figure 4: sp. conductance of nicl2 as a function of concentration at 308.15 k (solid lines – fitted graphs). 4. conclusion the conductometric data have been obtained to study the variation of specific conductance of nickel chloride with the concentration, temperature, and solvent composition in ethanolwater mixed solvent media. on the basis of results and discussion of the experimental study, it is found that the specific conductance increases with increasing concentration and temperature of the electrolytic solutions over the entire concentration range investigated whereas the specific conductance of the same electrolyte in same binary mixed solvent media decreases with decreasing dielectric constant of solvent composition. acknowledgments the authors are grateful 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[17]v. k. syal, s.k. thakur, s. chauhan, p.sharma, int. j. thermophys. 26(2005) 807. http://dx.doi.org/10.1007/s10765-005-5579-1 [18] s. zhang, h. li, s. dai, t. wang, s. han, j. chem. eng. data, 42 (1997) 651. http://dx.doi.org/10.1021/je960235j [19] s. zhang, s. han, y. jin, acta physicochemica sinica, 12 ( 1996) 75. microsoft word srivastava et. al _104-113_.doc r c o s t n publisher: research council of science and technology, biratnagar, nepal p. 104 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana implementation of designed jigs and fixtures for hand operated press in production of mainframe for paddy-weeder ankitesh shrivastava 1* , s.k. ganguly 2 , ajay verma 3 1 production engineering, bhilai institute of technology, durg (c.g.), india. 2 mechanical engineering department, bhilai institute of technology, durg (c.g.), india. 3 farm machinery & power engineering, indira gandhi agricultural university, raipur (c.g.), india. *email: ankiteshrivastava@gmail.com accepted for publication: december 18, 2014 abstract the main purpose of paddy weeder is to dislocate the weeds present in paddy fields. the operation, when done manually causes drudgery in workers, which in turn reduces their efficiency in fields. paddy weeder proved to be efficient enough to perform the work manually with less efforts & time consumed. the product was being manufactured by traditional methods, i.e. without implementation of jigs & fixtures. the paper presents a procedure for inclusion of designed & developed jigs and fixtures in the production of paddy weeder, and hence fulfills the need of mass production. the designed jigs proved quite efficient & were helpful in reduction of 50 % in welding operations performed. hence, it is helpful in enabling mass production. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11672 © 2014 rcost: all rights reserved. keywords: designed jigs & fixtures; hand operated press; production; paddy-weeder. 1. introduction weeds are the plants which grow, in a region where they are not desired. paddy weeder is agricultural equipment used to remove weeds from a desired area. one of the major laborious and time consuming operations in rice cultivation is weeding. the concept of weed control is as old as agriculture itself. the global figure for crop yield loss is accepted as 10% of actual yield [1]. to get the full benefit of mechanization it is very necessary to use proper weeding implements, which will reduce drudgery and cost of cultivation [2]. study was conducted by [3] to evaluate and compare the inputs of manual energy only and manual-cum-mechanical energy in the production of ground-nuts. study revealed that weeding had the most energy requirement (45% and 52% of the mean total energy inputs) in groundnut cultivation. the human labour output capacity is increased by 8 – 10 times in weeding by the use of mechanical weeder [4]. jig is a special tool used for locating and firmly holding work piece in the proper position during the manufacturing or assembly operation. it also guides the tool or work piece during the operation. jig is designed to increase the productivity of operation assisting worker to do job easier, faster and more comfortable [5]. fixtures are mechanism used to rapidly, accurately, and securely position workpiece shrivastava et al./ bibechana 12 (2015) 104-113: p. 105 during machining such that all machined parts fall within the design specifications. this accuracy facilitates the interchangeability of parts. the goal of research was to find appropriate systematic approach to quality improvement in the production preparation, within the frame of metal production. starting from the main principles and methodologies of manufacturing process quality improvement, in the paper are identified possibilities of integration of methods and tools in an operational model of quality improvement in the process of production preparation [6]. the implementation of power press into the production operation was not a feasible alternative, as the pressure developed by it would be way too much. as the desired outcome was just to get a bend of 900 on ms plates of 6mm thickness, its implementation would lead towards more time consumption in the process, with added quantity of scrap. 2. problem statement keeping an eye on the huge demand of the paddy weeder in the present scenario, and on the other hand workers presently operating without jigs and fixtures, the parts were welded using visual observations which resulted in in-accuracy in dimensions, and poor workmanship & lack of interchangeability. jigs to serve for the sole purpose has been designed and developed at faculty of agricultural engineering workshop. mass production aims at high productivity to reduce unit cost and interchangeability to facilitate easy assembly. this necessitates production devices to increase the rate of manufacture and inspection device to speed-up inspection procedure. nowadays new machine tools, high-performance cutting tools, and modern manufacturing processes enable industries to produce parts faster and better than ever before. to counterbalance the need and production, implementation of jigs and fixtures in the production line is extremely important to produce good parts with low cost and high quality. when changes in a manufacturing method are proposed, it is first necessary to assess the extent of the change. similarly, in consideration of paddy weeder the change should be within the limits defined for the parameters of manufacturing process. in this case, since the whole process had been demonstrated to yield product that meets the design intent, change within the process can be allowed with no further process validation. based on this evaluation, it was found that there were processes that need upgrading for enabling mass-production with less time consumed and material wastage with higher accuracy. since there were a lot of parameters that needed the attention, hence the need to design the jigs for the processes emerged. jig is one of the most important components in the processes for manufacturing precision parts in mass production. both the material costs and manufacturing time will be decreased in many of the process involved in manufacturing steps, this means the cost of these steps would be reduced as a result as well. 3. materials and methods considerations while designing jigs and fixtures designing of jigs and fixtures depends upon so many factors. these factors are analyzed to get design inputs for jigs and fixtures. the list of such factors is mentioned below (a) study of work piece and finished component size and geometry. shrivastava et al./ bibechana 12 (2015) 104-113: p. 106 (b) type and capacity of the machine, its extent of automation. (c) provision of locating devices in the machine. (d) available clamping arrangements in the machine. (e) available indexing devices, their accuracy. (f) evaluation of variability in the performance results of the machine. (g) rigidity and of the machine tool under consideration. (h) study of ejecting devices, safety devices, etc. (i) required level of the accuracy in the work and quality to be produced. main-frame the main frame of the paddy weeder consists of two metal plates of 205mm each, one plate of 125mm, are weld together at 900 (fig. 1). fig. 1: frame manufactured traditionally. a different metal plate is taken with dimensions 405mm, and was bent with the help of a handmade fixture (fig.2). the part is called float, as it skids over the fields so as to facilitate proper working of equipment. shrivastava et al./ bibechana 12 (2015) 104-113: p. 107 fig. 2 hand-made jig for bending float table 1 shows the amount of welding operations being performed, while manufacturing the equipment’s frame traditionally. table 1: welding operation for traditional method s. no. name of part no. of welding operations 1 weeder frame 02 2 joining frame with float 02 total 04 shrivastava et al./ bibechana 12 (2015) 104-113: p. 108 design of jigs & fixtures to facilitate the fast manufacturing process for the production, jigs and fixtures were designed on designing software solid works 2012. fig.3(a) fixture be fixed on bending machine fig. 3 (b) jig for bending float shrivastava et al./ bibechana 12 (2015) 104-113: p. 109 for bending float, set of jigs & fixtures were developed to facilitate the bending of float, the ms plates cut after the marking operation were placed on the elevated corners (fig. 3(a)) and the other fixture was made to be fixed on the bending machine (fig. 3(b)), with the help of nuts and bolts. fig. 4: designed jig for bending at right angles. a solution was needed for replacing welding with the bending operation and hence a jig was designed to serve for this purpose. the plates were bent with the help of a set of jigs and fixtures, plates were placed on the elevated surface (fig. 4), and were pressed with the help of bending machine and hence creating a bend of 90 0 , and eliminating the need of welding operation to remarkable extent. 4. results and discussion hand operated press the jigs and fixtures designed for the weeder were developed and were made to serve the sole purpose of reducing the time consumed in the production with less efforts to be laid for operations (fig. 5). hand operated press was used instead of power press, to reduce the complexity of operation and to ensure the mobility of operation. shrivastava et al./ bibechana 12 (2015) 104-113: p. 110 fig. 5 hand operated press developed jigs & fixtures the purpose of designing a jig for paddy weeder was to eliminate the time consumption in process and increase the quality of the product. the jig and fixture designed for bending the float was hence developed (fig.6 & 7) in accordance with the design produced. fig. 6 developed fixture for bending the float shrivastava et al./ bibechana 12 (2015) 104-113: p. 111 fig. 7 developed jig for bending float. the jig and fixture developed for producing frame (fig.8) with minimum number of welding operations involved, desired the plates to be bent at an angle of 90 0 . fig. 8 developed jig for bending plates shrivastava et al./ bibechana 12 (2015) 104-113: p. 112 fig.9 shows the jig and fixture setup on the bending machine, which uses mechanical force to create bends. the jigs were designed so as to reduce the welding operation. fig. 9 set of jig &fixture for manufacturing frame the new developed jigs and equipments helped in reducing the number of welding operations to half, i.e. two (fig.10) fig. 10 frame manufactured by jigs & fixtures shrivastava et al./ bibechana 12 (2015) 104-113: p. 113 5. conclusion the developed jigs & fixtures according to the designs generated, proved helpful in reducing the time elapsed in manufacturing by reducing the number of times an operation was being performed to achieve the goal. the reduction in operations to half, proved helpful in reducing the time consumed in manufacturing operation. hence, the goal of enabling mass-production was achieved. references [1] w.w. fletcher, recent advances in weed science. introductory chapter.(ed w.wfletcher) commonwealth agricultural bureaux. the gresham press: surrey, uk, (1983) pp1–3. [2] r. remesan, m.s. roopesh, n. remya, p.s. preman, wet land paddy weedinga comprehensive comparative study from south india. agricultural engineering international: the cigr journal, 9 (2007). [3] b. umar, agricultural engineering international: the cigr journal of scientific research and development, (2003) 1-11. [4] b.p. mishra, v.k. panday, d.k. dwivedi, effect of different weeding methods on energy and economic management under khura rice cultivation system. all india seminar of agril. engineers, institution of engineers, india (1993). [5] a. saptari, w.s. lai, m.r. salleh, jordan journal of mechanical and industrial engineering, 5(1) (2011) 9-16. [6] d. pavletic, m. sokovic, international journal for quality research, 3(4) (2009) 309-315. devendra sir cover page copy.jpg bibechana 17 (2020) 28-33 28 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal natural dyes as photo-sensitizer in solar cells surendra bikram silwal 1,2,3 , rameshwar adhikari 2 , prakash lamichhane 3 , netra lal bhandari 1, 2* 1 department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal 2 research centre for applied science and technology (recast), tribhuvan university, kirtipur kathmandu, nepal 3 department of chemical science and engineering, school of engineering, kathmandu university, dhulikhel kavre, nepal *email: netra.tu.edu@gmail.com article information: received: june 07, 2019 accepted: september 14, 2019 keywords: natural dyes dye-sensitized solar cell thin film spray pyrolysis zno abstract the objective of this research is to employ the natural dyes in dye-sensitized solar cell (dssc). on account of eco-friendly, renewable, and non-hazardous properties of natural dyes over silicon, a semiconductor, photo-sensitizer in conventional solar cells, cyclohexane extract of terminalia alata, a natural dye, was employed as photo-sensitizer. the photoanodes zno and 5% al-doped zno for dsscs were developed by spray pyrolysis. the x-ray diffraction (xrd) has shown hexagonal wurtzite structure of zno with lattice constants a = 3.2487 å and b = 5.1518 å having particle size 25.85 nm for zno and 33.17 nm for aldoped zno. the dssc properties such as solar conversion efficiency (η), shortcircuit current density (jsc), open-circuit voltage (voc), and fill factor (ff) were found to be 0.31%, 2.10 ma/cm 2 , 0.73v, and 45% for zno photoanode and 0.37%, 2.25ma/cm 2 , 0.70 v, and 52.10% for 5% al-doped photoanode 1. introduction the global energy demand is rocketing, it was 12.7 tw (terawatt, 1 tw = 1012 w) in 1998 but is expected to be 26.4 to 32.9 tw in 2050 and 46.3 to 58.7 tw in 2100 [1]. since the fossil fuels are nonrenewable and will suffice for merely few decades, solar energy, best option so far, is one of the major viable, eco-friendly, and renewable, alternative source of energy. as it is said, “more energy from sunlight strikes earth in 1 hour than all of the energy consumed by humans in an entire year.” [2], solar energy can sustainably be harvested for human civilization. a solar cell is an electrical device that converts sunlight directly into electricity by photovoltaic effect whose production has been exponentially increasing [3]. this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.25599 respectively. http://nepjol.info/index.php/bibechana mailto:netra.tu.edu@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.25599 surendra bikram silwal, rameshwar adhikari et al / bibechana 17 (2020) 28-33 29 a dye-sensitized solar cell (dssc), first developed by gratzel et al. in 1991 [4], is an electrical device which converts light photons into electricity by photovoltaic effect, incorporating oxide semiconductor like tio2, zno, nb2o5, etc. with wide band gap ≥3 ev as photoelectrode and dye molecules as photo-sensitizer. since natural dyes are more economical, easily attainable, abundant in supply, non-hazardous, eco-friendly, and renewable, fabricating an environment friendly dssc, more precisely natural dye-sensitized solar cell (ndssc), are both technically and economically credible alternative to p-n junction silicon solar cells [1]. the objective of this research is to strive n-type doping of zno, a semiconductor, with aluminum and observe its optical, structural properties; and their effect on dssc properties employing natural dye as photo-sensitizer. 2. materials and method a natural red dye from the bark of terminalia alata (local name: saaj), a photo-sensitizer for dssc, was extracted on both polar solvent, water as shown in figure 1, and non-polar solvent, cyclohexane, to compare their uv-visible absorption spectra obtained by using uv-1800 spectrophotometer of shimadzu corp. (05103). fig. 1: flow chart showing different steps in aqueous extraction of natural dye. for dye-sensitized solar cell (dssc), zno and 5% al-doped zno photoanodes were fabricated by spray pyrolysis of precursors on fluorine doped tin oxide (fto) glass sheets with 8 ω/sq. surface resistivity. the spray pyrolysis is a technique in which chemical precursors are atomized into aerosol droplets and sprayed over a highly heated substrate so that the solution of undesired compounds get evaporated leaving behind the ultrafine particles of required compound which on sintering at above 400 o c forms a thin film. the precursor for zno fabrication, 100 ml 0.3 m zn(ch3co2)2 (zinc acetate) solution, was prepared by dissolving 6.7125 g of merck 98% zinc acetate in 100 ml solvent of propan-2-ol and distilled water in the ratio 3:1. to make a clear solution, the solution was continuously stirred keeping over magnetic stirrer with hot plate for 30 minutes and remaining little white turbidity of zinc acetate was dissociated by adding few drops of acetic acid. and for 5% al-doped zno, 0.2 g of alcl3 (aluminum chloride) was dissolved in 100 ml of 0.3 m zinc acetate solution. during spray pyrolysis, the aerosol of zinc acetate was created by using an ultrasonic nebulizer which was sprayed vertically through a spray nozzle on the heated fto substrate, 25 × 25 mm 2 , placed on a heating block of temperature 400 o c. the fto substrate was maintained to move in a 2×2 matrix pathway at a fixed frequency by an electronically controlled motor keeping the spray nozzle to fto’s height 6 cm and spraying rate 40 ml/hr. the fto substrate was sprayed over with precursor for 10 minutes and sintered at 500 o c for 30 minutes in muffle furnace. after 30 minutes of sintering, the substrate was sprayed over again for 5 minutes and then sintered for 2 hours facilitating the deposition of zno particles on fto. and for the 5% al-doped zno fabrication, the fto substrate was sprayed over with zinc acetate solution for 10 minutes, sintered at 500 o c for 30 minutes, after again soaking 80 g of crude dye sample in 800 ml water in 1000 ml heating the soaked sample in electric heater at 800c for 2 hours filtering the dye sample through whatman no.1 filter paper under suction filtrate of aqueous dye extract keeping the concentrated dye extract in hot air oven to get powder dye dried aqueous extracts of all six dye samples surendra bikram silwal, rameshwar adhikari et al / bibechana 17 (2020) 28-33 30 sprayed over with 5% al-doped zinc acetate for 5 minutes, and then sintered for 2 hours. the transmittance of those fabricated thin films was measured by using optical profilometer (spectroscopic reflectometer, srm 300, angstrom sun technology) and that of crystallographic structures by x-ray diffraction (xrd) using broker d2 phaser (cu kαl, λ = 1.54060 å). fig.2: a typical dye-sensitized solar cell. the redox electrolyte i-/i3couple was made by mixing 25 ml 0.05 m i2 (aldrich iodine) and 25 ml of 0.1m ki (potassium iodide) in acetonitrile with 20 ml of peg (polyethylene glycol) as a binder. the counter electrode, cathode, was made by rubbing pencil graphite in the middle 25 × 25 mm 2 conducting side of the fto glass sheet. the zno and 5% al-doped zno fabricated fto substrates, photoanodes, were dipped in cyclohexane extract of natural red dye from the bark of terminalia alata for 12 hours, then taken out, dried, and reduced to 15 × 15 mm 2 leaving each side 0.5 mm using forceps with conc. hcl. the opposite two sides of each fto substrate were masked with plastic tape, few drops of redox electrolyte was poured and allowed to spread all over. then the counter electrode, cathode, was gently placed over the photoanode and tightly sealed using alligator clips as shown in figure 2. the photovoltaic parameters of such fabricated dssc were measured by using kiethley source meter (a tektronix company) maintaining 1000 w/m 2 incident light intensity. 3. results and discussion the uv-visible spectra of cyclohexane extract, cs, from the bark of terminalia alata, were found to be comparatively better than of aqueous extract, s, as shown in figure 3(a) so cs was used as photosensitizer in dssc. the absorbance peaks of employed sensitizer dye sample, s, has shown peaks in 675 nm and 415nm which are similar to the peaks of both zno and 5% al-doped zno thin films as shown in figure 3(b). the optical transmittance of fto was above 80% and it has reduced to 50% after coating zno for 15 minutes, but for the same duration of coating, the transmittance of 5% al-doped zno thin film is found to be 55% as shown in figure 4(a). the 5% more transparency of al-doped zno may be due to the formation of more porous thin film by aldoping. the xrd peaks, as shown in figure 4(b), have been identified to (100), (002), (101), (102), (103) and (112) plane of reflections which are in agreement with the joint committee on powder diffraction standards (jcpds) data for a single phase wurtzite structure of zno. the xrd of undoped zno has shown preferential orientation of grains along the c-axis, perpendicular to the film surface (002), whereas, the aluminum doping has resulted random orientation of peaks. the rest unmarked major peaks oriented to (200), (211) etc. seen in the xrd spectra are contributed by the fto. the mean crystalline size of the zno particles is calculated by using scherrer formula [5], d = 0.9λ βcosθ , and found to be 25.85 nm for undoped zno and 33.17 nm for al-doped zno. similarly, the lattice constants of deposited zno particles are calculated, found to be a = 3.2487 å and b = 5.1518 å which are in agreement with jcpds data values for zno lattice constants, a = 3.24982 å and c = 5.20661 å. surendra bikram silwal, rameshwar adhikari et al / bibechana 17 (2020) 28-33 31 current-voltage curve analysis a current-voltage (iv) curve is obtained by plotting short-circuit current density (jsc) against opencircuit voltage (voc) [6] as shown in figure 5. the values of voc, vmax, jsc and jmax are obtained from iv curve. the fill factor (ff) and solar conversion efficiency (η) have calculated using the formulae ff = jmax×vmax jsc×voc , and, η = jsc×voc×ff is , and obtained values are tabulated in table 2. the efficiency of saaj-sensitized solar cell based on al-doped zno photoanode, 0.37%, is found to be slightly greater than that of zno photoanode, 0.31%, possibly due to increase in the particle size of zno from 25.85 nm to 33.17 nm with aldoping. the increased particle size enhances the porosity and transparency of thin film which facilitates the more light intensity to the dye molecules (sensitizers) to generate more electrons. thus by generating more electrons, al-doping has increased the cell’s efficiency. however, the overall poor efficiency of natural dye-sensitized solar cell may be attributed to the poor transmittance, ≤ 55%, and improper thickness of the fabricated oxide film, insufficient adsorption of dye molecules, poor absorbance of dye molecules in visible region, or may be because of poor performance of redox electrolyte and counter electrode. those limitations, nevertheless, can be overcome by tailoring optoelectronic properties of dyes and modifying the cell’s components, for example, incorporation of nanoparticles or quantum dots into photoelectrodes, molecular engineering of the natural dye molecules, etc. fig. 3: uv-visible spectra of (a) aqueous extract (s) and cyclohexane extract (cs) of natural dye sample and (b) fto, zno, 5% al-doped zno thin film and natural dye sample. fig. 4: plots of (a) transmittance of fto, zno and 5% al-doped zno thin film and (b) xrd pattern of al-doped and undoped zno nanoparticles along with fluorine doped tin oxide (fto). surendra bikram silwal, rameshwar adhikari et al / bibechana 17 (2020) 28-33 32 table 1: interplanar spacing (dhkl) from xrd spectra of zno particles. 2θ (degree) miller indices (hkl) calculated dhkl (å) jcpds dhkl (å) 31.78 100 2.8135 2.81179 34.80 002 2.5759 2.6049 36.33 101 2.4709 2.4786 47.54 102 1.9111 1.9128 57.52 110 1.6005 1.6269 64.21 103 1.4494 1.4784 68.02 112 1.3772 1.3799 a fig. 5: iv curve of saaj-sensitized solar cell based on (a) undoped zno and (b) 5% al-doped zno photoanode. table 2: photovoltaic parameters of saaj-sensitized solar cell sample jsc (ma/cm 2 ) voc (v) pmax ff (%) efficiency (η) saaj (undoped zno) 2.10 0.73 0.69 45.00 0.31 saaj (al-doped zno) 2.25 0.70 0.82 52.10 0.37 4. conclusions the cyclohexane extract of red dye from the bark of terminalia alata gave relatively better absorbance than aqueous extract, so, employed as photo-sensitizer. the zno and 5% al-doped zno thin films developed by spray pyrolysis technique have shown transmittance 50% and 55% respectively. the xrd of zno has shown hexagonal wurtzite structure with lattice constants a = 3.2487 å and b = 5.1518 å having particle size 25.85 nm for undoped zno and 33.17 nm for aldoped zno. thus, natural red dye-sensitized solar cell has given 0.31% solar conversion efficiency (η) incorporating zno photoanode with 2.10 ma/cm 2 short-circuit current density (jsc), 0.73 v open-circuit voltage (voc) and 45% fill factor (ff), and 0.37% efficiency incorporating 5% al-doped zno photoanode with 2.25ma/cm 2 jsc, 0.70 v voc and 52.10% ff. acknowledgements authors sincerely thank university grants commission (ugc), nepal for financial support. thanks also goes to department of chemical science and engineering, school of engineering, kathmandu university, dhulikhel, kavre, nepal for providing laboratory facilities and nepal surendra bikram silwal, rameshwar adhikari et al / bibechana 17 (2020) 28-33 33 academy of science and technology (nast), khumaltar, lalitpur, nepal for xrd analysis. references [1] a. n. b. zulkifili, t. kento, m. daiki, and a. fujiki, the basic research on the dye-sensitized solar cells (dssc), journal of clean energy technologies 3 (5) (2015) 382-386. 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[17] y. e. morales, j. reyes, b. hermosin, and j. a. a. barrios, characterization of a natural dye by spectroscopic and chromatographic techniques, materials research society, 1374 (2012) 1-10. https://doi.org/10.1557/opl.2012.1377. microsoft word villikodi final (15-22) m. vallikkodi and s. sudhahar/ bibechana 16 (2019) 15-22: rcost p.15 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal the non-linear optical crystal growth and characterization of piperizantum paminobentzone m. vallikkodi*, s. sudhahar department of physics, alagappa university, karaikudi630 004, india. *email: vallikkodi.10@gmail.com article history: received 09 february, 2018; accepted 3 august, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.20875 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the nonlinear optical properties of piperizanium p – aminobenzoate (pzpab) crystal were successfully grown with the help of temperature gradient (slow evaporation) method. the good quality of pzpab single crystal is formed. the pzpab is characterized with the help of x-ray diffraction (xrd), fourier transform infrared (ftir) measurement, photoluminescence (pl), raman spectroscopy, ultra violet visible spectroscopy (uv) and finally etching analysis was done. keywords: piperizanium p – aminobenzoate; nonlinear optical crystal; slow evaporation method. . 1. introduction a material that has good crystalline nature is also having good optical and electrical properties [1-3]. many organic and inorganic crystal materials had high polarization ability and are good candidates for nonlinear optical (nlo) studies [4]. however, the net polarization depends on the material symmetry properties, with respect to the impinging fields. so far, there are many organic crystals which is used for nlo yet, piperizanium paminobenzoate having the adorable nature of nonlinear properties. in the present article, gives the advancement of new nlo material (piperizanium paminobenzoate); which is being characterized with the help of xrd, ftir, uv, raman and pl. 2. materials and methods piperazinium p-aminobenzoate crystal was prepared in the room temperature by slow evaporation growth method [5] by using as a methanol solvent. the precursor’s materials of piperazine (98%) and p-aminobenzoic acid (99%) were taken in the equimolar ratio of 1:1 for the synthesis process is shown in figure 1. the p-aminobenzoic acid was first dissolved in the solvent of methonal, after m. vallikkodi and s. sudhahar/ bibechana 16 (2019) 15-22: rcost p.16 (online publication: dec., 2018) complete dissolved acid material and then the base compound of piperazine was added little by little with the acid solution. the solution is allowed to get a homogenous mixture by continuously stirring for 8 hours using the temperature control magnetic stirrer in the room temperature circumstances [5]. after attaining the homogenous saturated state the solution was filtered using the whatman filter paper which is having the fine holes in the range of 110 µm and the filtered solution was covered with the perforated sheet having the fine holes for the evaporation and it was kept at the room temperature without disturbance. after 2 successive recrystallization process the good quality pzpab crystal was harvested with in the span of 60 days. the figure 2 shows the crystal of pzpab. nhhnpiperazine oho nh2p aminobenzoic acid nh2+hn piperazinium p aminobenzoateo-o nh2 fig. 1: synthesis scheme of piperazinium p-aminobenzoate. fig. 2: grown crystal of piperazinium p-aminobenzoate. 3. results and discussion xrd analysis (i) the single crystal x-ray diffraction analysis is the powerful tool for determination of the structure of the crystal. the piperazinium p-aminobenzoate crystal belongs to orthorhombic crystal system with noncentrosymmetric space group pna21. this space group satisfies one of the basic essential requirements of nlo material. the lattice parameters of the piperazinium p-aminobenzoate is found m. vallikkodi and s. sudhahar/ bibechana 16 (2019) 15-22: rcost p.17 (online publication: dec., 2018) to be a = 18.2964 å, b = 7.1388 å, c = 10.3574 å, α = 90°, β = 90°, γ = 90° and volume v = 1352.83 å3. the structural parameters of the piperazinium p-aminobenzoate crystal were listed in the table 1. table 1: pzpab crystal. crystal property piperazinium p-aminobenzoate empirical formula c4h11n2+•c7h6no2−•h2o crystal system orthorhombic spacegroup pna21 unit cell parameters a = 18.2964 å, b =7.1388 å, c =10.3574 å, α = 90°, β = 90°, γ = 90° volume of the unit cell v = 1352.83 å3 radiation wavelength λ = 0.71073 å the crystalline nature of the piperazinium p-aminobenzoic crystal was characterized by powder x-ray diffraction analysis to reveal crystalline perfection of the compound. the x-ray diffraction spectrum of pzpab was recorded using the x’pert pro powder diffractometer with cukα radiation having the wavelength of λ = 1.5406 å. the sample was scanned from the range of 10° to 80° at the rate of 2°/minute. the recorded powder x-ray diffraction spectrum is shown in figure 3. the presence of sharp and well defined peaks confirms the good crystalline nature of piperazinium p-aminobenzoate crystal and the corresponding peaks were indexed. the sharp intense peaks are shown in the table 2. ftir analysis the ftir spectrum was recorded to understand the chemical bonding and it provides useful information regarding the molecular structure of the compound. the kbr pellet technique was used to analyze the sample. ftir spectrum was taken for the powdered sample in the wavelength range 4000-400 cm-1 using 380 ftir spectrophotometer having the resolution of 0.5 cm-1 and the spectrum of ftir is shown in figure 4.the observed ftir is summarized in table 3. raman analysis laser raman spectrum was taken for the powdered sample in the wavelength range 4000-400 cm-1 using str 500 mm focal length laser raman spectrometer and the raman spectrum is shown in the figure 5. raman bands along with their vibrational assignments are summarized in table 4. uv-visible optical absorption spectral analysis the optical absorption spectral analysis of the grown pzpab crystal was carried out using perkin elmer lambda35 spectrometer between 250 and 800 nm. the absorption & transmittance spectrum of the as grown pzpab crystal is shown in the figure 6. the uv cut off wavelength of the crystal was found to be at 317 nm. the absence of absorption in the visible region suggests that the crystal possess the good nonlinear optical property. m. vallikkodi and s. sudhahar/ bibechana 16 (2019) 15-22: rcost p.18 (online publication: dec., 2018) table 2: peaks of xrd. pos. [°2th.] height [cts] fwhm left [°2th.] d-spacing [å] rel. int. [%] 10.4002 121.43 0.1476 8.50603 3.53 13.5267 439.65 0.1476 6.54617 12.78 14.1626 173.47 0.1476 6.25365 5.04 15.1903 641.65 0.1476 5.83283 18.65 15.5192 252.21 0.0984 5.70992 7.33 17.0567 1184.78 0.1476 5.19854 34.44 19.5580 551.63 0.1476 4.53897 16.04 21.0129 470.57 0.1476 4.22787 13.68 21.5337 3439.78 0.1476 4.12679 100.00 23.8882 2086.44 0.1476 3.72510 60.66 24.8055 1168.61 0.1476 3.58939 33.97 26.3194 821.87 0.1476 3.38626 23.89 26.8804 317.96 0.1476 3.31685 9.24 27.4870 740.96 0.1476 3.24502 21.54 28.3924 145.42 0.1476 3.14356 4.23 29.4507 256.36 0.1476 3.03297 7.45 30.5232 719.77 0.1968 2.92879 20.92 31.3467 721.21 0.1476 2.85371 20.97 31.9957 276.41 0.1476 2.79729 8.04 32.4648 201.46 0.1968 2.75793 5.86 33.7596 164.56 0.1476 2.65506 4.78 34.3585 209.28 0.2952 2.61014 6.08 35.1350 131.82 0.1968 2.55421 3.83 35.6070 134.51 0.1476 2.52143 3.91 36.3967 554.72 0.1968 2.46852 16.13 37.9391 177.68 0.1476 2.37163 5.17 39.0984 130.54 0.2460 2.30395 3.80 39.5630 76.17 0.1476 2.27795 2.21 41.2584 89.98 0.3936 2.18818 2.62 41.8669 81.48 0.1476 2.15778 2.37 43.3737 77.32 0.1476 2.08624 2.25 43.8176 84.64 0.1476 2.06613 2.46 44.3690 117.18 0.1476 2.04173 3.41 45.0060 82.97 0.1968 2.01430 2.41 46.4121 73.75 0.1476 1.95650 2.14 48.0597 46.94 0.1968 1.89320 1.36 49.2598 48.17 0.1968 1.84985 1.40 50.7274 282.97 0.2460 1.79973 8.23 51.2972 67.33 0.1476 1.78107 1.96 52.5555 50.83 0.2460 1.74135 1.48 53.4279 22.86 0.2952 1.71496 0.66 54.1358 19.44 0.2952 1.69420 0.57 55.2169 25.97 0.3936 1.66356 0.76 56.6958 36.33 0.2952 1.62363 1.06 57.8343 32.12 0.5904 1.59435 0.93 60.7458 28.30 0.5904 1.52472 0.82 m. vallikkodi and s. sudhahar/ bibechana 16 (2019) 15-22: rcost p.19 (online publication: dec., 2018) fig. 3: powder xrd pattern of pzpab crystal. table 3: ftir frequency assignments of pzpab compound. functional groups theoretical value ftir experimental value assignments amine 1200 – 1025 1089 c-n stretching alkyl amine 3500 – 3300 3327 n-h stretching alcohols 1200 – 1000 1123 c-o stretching carboxyl 1320 – 1210 1224 c-o stretching aromatics 3020 – 3000 3009 ch stretching aromatics ~1600 1609 c=c stretching fig. 4: ftir spectrum of pzpab. m. vallikkodi and s. sudhahar/ bibechana 16 (2019) 15-22: rcost p.20 (online publication: dec., 2018) table 4: raman frequency assignments of pzpab compound. functional groups theoretical value laser raman experimental values assignments amine 1200 – 1025 1150 c-n stretching alkyl amine 3500 – 3300 3331 n-h stretching alcohols 1200 – 1000 1150 c-o stretching carboxyl 1320 – 1210 ----c-o stretching aromatics 3020 – 3000 3077 ch stretching aromatics ~1600 1605 c=c stretching fig. 5: laser raman spectrum of pzpab. uv-visible optical absorption spectral analysis the optical absorption spectral analysis of the grown pzpab crystal was carried out using perkin elmer lambda35 spectrometer between 250 and 800 nm. the absorption & transmittance spectrum of the as grown pzpab crystal is shown in the figure 6. the uv cut off wavelength of the crystal was found to be at 317 nm. the absence of absorption in the visible region suggests that the crystal possess the good nonlinear optical property. photoluminescence studies photo luminescence spectroscopy is a non -destructive method for finding out the electronic structure and optical behavior. the photoluminescence spectrum of the grown pzpab was recorded in the wavelength region between 300 nm and 550 nm using rf-5301 spectrophotometer. the pl spectrum (figure 7) of pzpab grown crystal is excited at 350 nm. from the pl spectrum, one high intensity blue emission peak and one medium intensity violet emission peak was observed at 455 nm, 384 nm m. vallikkodi and s. sudhahar/ bibechana 16 (2019) 15-22: rcost p.21 (online publication: dec., 2018) respectively, and it attributes to shallow defects in the band gap and more ordered structure. the sharp high intensity caused because of the similar transition occurring at the various energy levels within the band gap. fig. 6: uv-visible absorption & transmittance spectrum of pzpab. fig. 7: photoluminescence spectrum of pzpab. 4. conclusion the piperazinium p-aminobenzoate crystal was successfully grown and characterized. the xrd pattern confirms the properties of nlo and the raman and ftir confirm all the functional groups. the uv and pl show the optical properties. thus, a good nlo crystal was successfully formed for laser applications. m. vallikkodi and s. sudhahar/ bibechana 16 (2019) 15-22: rcost p.22 (online publication: dec., 2018) references [1] g. u. sankar, a survey on wavelength based application of ultraviolet led computing, 2007. [2] c. g. moorthy, g. u. sankar, and g. raj kumar, a design for charging section of electrostatic precipitators by applying a law for electric field waves. imperial journal of interdisciplinary research 3(6) (2017) 842. [3] g. u. sankar, climate change challenge – photosynthesis vs. hydro-electrolysis principle. climate change 3 (2016) 128-131. [4] y.r. shen, the principles of nonlinear optics, new york, wiley-inter-science, 1984, p.575. [5] h. g. bhamidi, s. r. wilson, r.b. tan, p.j. kenis, and c. f. zukoski, direct growth of γ-glycine from neutral aqueous solutions by slow, evaporation-driven crystallization, crystal growth & design 6(8) (2006) 1746-1749. milan kharel/ bibechana 16 (2019) 154-164: rcost p.154 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal general survey on avifaunal composition of betana wetland, morang, province number 1, eastern nepal milan kharel department of zoology, central campus of technology, tribhuvan university, dharan e-mail id: milankharel2000@gmail.com article history: received 22 september, 2018; accepted 2 november, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21570 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/bync/4.0/ abstract the present study conducted in betana wetland, morang, province number 1, nepal. the study based on the field survey in order to find out the avifaunal composition. in the present study, total 320 individuals of birds belonging 49 species, 30 families and 15 orders reported from betana wetland based on field observation. the highest proportions of individuals recorded from the sampling station f1 forest area was 35% (n=112). the highest number of species (n= 15) recorded belong to the order passeriformes with nine families, followed by coraciformes with three families and four species then pelicaniformes with two families and six species. of them, two species viz. grey-headed fish eagle (icthyophaga humilis) and lesser adjutant stork (leptoptilos javanicus ) are kept under near threatened (nt) and vulnerable (vu) category of iucn red list of threatened species. about 70 % of total bird recorded was resident type and about 35% of total recorded bird species common in abundance. the species richness and abundance of avifauna found higher in winter season than summer. compared to the previous study, birds belonging to four more families and five more orders recorded this time. the shannon–weiner diversity index and species evenness of avifauna from the study area found 1.332 and 0.789 respectively. keywords: betana; avifauna; wetland; icthyophaga humilis; leptoptilos javanicus. . 1. introduction after forest, more than a quarter (27%) of nepal’s nationally threatened birds inhabits in wetlands [1]. out of 886 species of bird species recorded so far in nepal, about 42 species recorded in nepal are listed in iucn red list of globally threatened birds, 35 globally near threatened and 167 species are nationally threatened [2]. more than 230 species of birds found to be wetland-dependent in nepal [3]. wetlands are among the most productive ecosystem in the world. the wetlands of nepal well known for their unusually http://nepjol.info/index.php/bibechana mailto:milankharel2000@gmail.com http://dx.doi.org/10.3126/bibechana.v16i0.20960 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ milan kharel/ bibechana 16 (2019) 154-164: rcost p.155 (online publication: dec., 2018) rich biodiversity. they occupy approximately five percent of the total area of nepal in the form of rivers, stream, lakes, reservoirs, village ponds, paddy fields, marsh and swampland. there are over 405 wetland areas in nepal from the terai to the himalayas. the loss of diversity of the water birds reduces the natural resource base of the country. wetlands are one of the most threatened habitats because of their vulnerability and attractiveness for development [4]. betana wetland is an important recreational destination with great potential of wildlife including bird diversity. now this area has established as a picnic spot and other recreational activities that have created lots of problem on habitat, breeding and feeding activities of birds. firewood collection and grazing are the prominent human-induced disturbances of this area. the forest area of wetland dominated by sal (shorea robusta) followed by khair-sissoo (acacia catechudalbergia sissoo) and mixed forest. grassland flora consisted of a combination of wetland herbs and moist grass species that are commonly composed of imperata cylindrica, cyperus papyrus, digitariya ciliaris, bulbostylis barabata, erasgrostis tentella, cyperus totundus, polygonum spp.etc [5]. data on the avifaunal composition of this area is not adequate to assess conservation needs. only a little information from records of bird watchers, nature guides etc. are available. hence, the present study was essential to provide baseline data on avifaunal composition for the proper conservation and management initiatives. study area betana wetland is a freshwater pond situated between 26.659106° n to 87.428814° e and 26.662894° n to 87.434018° e at an elevation of 123 m msl, covering 5.5 ha area in belbari municipality of morang district. it is one kilometer far from the belbari bazar in the east. the wetland area remains surrounded by sal forest from east, north and west sides whereas mahendra highway lies adjacent on its south. the depth of the pond varies from 0.5 to 1.5 m in the dry season and 1 to 2.5 m in monsoon season [6]. the study area experiences a tropical monsoon climate with winter, summer and rainy seasons in a year. the soil is alluvial type and the average annual temperature of 24.6 °c. the average rainfall is 2256 mm per year and about 90% of rainfall occurs within three months of monsoon seasons (june-august) [7]. fig.1: map of study the site. milan kharel/ bibechana 16 (2019) 154-164: rcost p.156 (online publication: dec., 2018) 2. material and methods study of the avifaunal composition of betana wetland carried out for six months from february 2017 to july 2017. therefore, the birds of summer, winter and monsoon season observed within a short field visit period. regular visits of the study site done almost once a week on every saturday morning between 7 -10 am and 4-6 pm in the evening in order to know the avifaunal composition. the bird census was done by applying the point count survey method within the radius of 50m [8]. in the direct count method, counts performed in the four sampling stations (f1, f2, w1 and w2) repeatedly. to prevent overlapping, the total number of individuals counted only for every two or three species during the first sightings of field visits. some birds photographed with the help of canon powershot sx520 hs 42x 24-1008mm 16 mp optical zoom digital camera. the primary data collected by direct observation of species with the help of bushnell h2o waterproof/fogproof prism binocular 10 x42 mm. while secondary data collected by the help of a questionnaire, reviewing literature such as journals, articles, proceedings and books. the geographical coordinates were taken by using garmin etrex 10 worldwide handheld gps navigator. the identification of birds done by direct observation method. birds were observed within transect of 100m and identified with the help of field guide books of ali and ripley [9], fleming et al. [10], shrestha [3] and grimmett [1], grimmett et.,al.[11] and pradhan [12]. photograph of unidentified species identified with the help of subject expertise of post-graduate campus, biratnagar. for the birds, which are shy and not observed directly, the call count method employed for their identification. the study area divided into four pockets (map1). bird observation done at these four pockets viz. the forest area f1 (west) and forest area f2 (east), wetland area w1 (east) and wetland area w2 (west) of betana wetland area. four line transects were set along the two forests sampling areas (f1 and f2) and two wetland areas (w1 and w2). each pocket used as the reference points for the point count method. observations of birds carried out on each 50 m radius of each pocket. the collected data represented in the tabular form by using microsoft excel. shannon-weiner diversity index and species evenness calculated by using by using spss software version v23. shannon-weiner diversity index (h) is an index that commonly used to characterize species diversity in a community. it calculated by the following function: 𝐻 = −∑[(𝑝𝑖) × 𝑙𝑛⁡(𝑝𝑖)] where, pi = proportion⁡of⁡total⁡sample⁡represented⁡by⁡species⁡i s = species⁡richness⁡or⁡number⁡of⁡different⁡species⁡in⁡a⁡given⁡area e = evenness = h ln⁡(s) 3. results in the present study, 49 species of birds belonging to 30 families and 15 orders reported from betana wetland based on field observation (table 1). the highest number of species (n= 15) recorded belong to the order passeriformes with nine families. the total number of individuals of birds in all four sampling stations were 320. the highest number of individuals recorded from the sampling station f1 forest area was 35% (n=112). similarly, 27% (n=89) from w1, 23% (n=76) from f2 and 13% (n=43) from w2. the shannon-weiner diversity index of avifauna at four sampling stations found 1.334 and that of species evenness found to be 0.789. similarly, the rest of the orders in terms of species richness recorded as coraciiformes (3 families and 4 species). pelicaniformes (2 families and 6 species), accipitriformes (2 families and 4 species). piciformes milan kharel/ bibechana 16 (2019) 154-164: rcost p.157 (online publication: dec., 2018) (2 families and 2 species), charadriformes (2 families and 2 species), anseriformes (2 families and 2 species), strigiformes (one family and 3 species), columbiformes (one family and 3 species), cululiformes (one family and 2 species), ciconiformes (one family and 2 species) and the orders representing one family and one species were suliformes, gruiformes and psittaciformes. out of 49 total species, 34 species (69.38%) of birds were of the resident type, 9 species (18.36%) were winter visitor and 6 species (12.24%) were summer visitors (fig 3). of them, 34.69% species (n= 17) were common, 24.48 % species (n=12) of birds were common, 22.44% (n=11) species were occasional and 18.36% (n=9) species were uncommon (fig 4). the number of bird species were recorded from the sampling area were f1 = 32.65% (n=17), f2= 34.69% (17), w1= 20.40% (n=10) and w2 = 12.24% (n=06) respectively (fig 5). table 1: avifaunal composition of betana wetland. sn family common name scientific name local name ss ab iucn hl orderaccipitriformes 1 accipitridae black kite milvus migrans (boddaert,1783) kalocheel wv uc lc f1 2 accipitridae grey-headed fish eagle icthyophaga humilis a (muller, s & schlegel, 1841) machhakul r o vu w2 3 pandionidae osprey pandion haliaetus (linnaeus,1758) malaha cheel wv uc lc f2 4 accipitridae crested serpent eagle spilornis cheela (latham,1790) kakakul r uc lc w1 anseriformes 5 anatidae commonteal anas crecca (linnaeus,1758) vijula gairi wv c lc f2 6 dendroygnida e lesser whistling duck dendrocygna javanica (horsfield, 1821) silsile wv uc lc w1 bucerotiformes 7 upupidae common hoopoe upupa epops (linnaeus,1758) fafre chara r fc lc f2 charadriiformes 8 charadriidae redwattled lapwig vanellus indicus (boddaert,1783) huttityaun r c lc w2 9 jacanidae bronze-winged jacana metopidius indicus (latham, 1790) lama aunle r fc lc w1 sn family common name scientific name local name ss ab iucn hl ciconiiformes 10 ciconiidae lesser adjutant leptoptilos javanicus b (horsfield,1821) bhundifor garud r o vu w1 11 ciconiidae asian openbill anastomus oscitans (boddaert,1783) ghungifor garud sv uc lc w1 columbiformes 12 columbidae rock pigeon columba livia (gmelin, 1789 parewa r fc lc f1 13 columbidae spotted dove streptopelia chinensis (scopoli, 1786) kurle dhukur r fc f1 14 columbidae eurasian collared dove streptopelia decaocto (frivaldszky, 1838) kanthe dhukur r fc lc f1 coraciiformes 15 alcedinidae stork-billed kingfisher halcyon capinsis (linnaeus,1766) thulomatik ore r o lc f1 16 coraciidae dollarbird eurystomus orientalis (linnaeus, 1766) lal chuche theuwa sv o lc f2 17 alcedinidae white-throated kingfisher halcyon smyrnensis (linnaeus, 1758) setokanthe matikore r o lc w2 18 meropidae chestnut-headed bee-eater merops leschenaultia (linnaeus,1758) katus tauke murali chara sv uc lc f2 cuculiformes 19 cuculidae indian cuckoo cuculus micropterus (gould, 1838) kaphal pakyo sv o lc f2 20 cuculidae greater couckal centropus sinensis (stephens, 1815) dhade gokul wv c lc f2 gruiformes 21 rallidae white-brested waterhen amaurornis phoenicurus (pennant, 1769) sim kukhura r fc lc w2 https://en.wikipedia.org/wiki/carl_linnaeus https://en.wikipedia.org/wiki/10th_edition_of_systema_naturae https://en.wikipedia.org/wiki/thomas_pennant sn family common name scientific name local name ss ab iucn hl passeriformes 22 corvidae large-billed crow corvus macrorhynchos (wagler,1827) kalokag r c lc f1 23 corvidae rufous treepie dendrocitta vagabunda (latham,1790) kokale r o lc f1 24 corvidae house crow corvus splendens (vieillot, 1817) gharkag r fc lc f1 25 dicuridae black drongo dicrurus macrocercus (vieillot, 1817) kalochibe r fc lc f2 26 dicuridae crow billed drongo dicrurus annectans (hodgson,1838) kagthude chibe sv fc lc f1 27 dicuridae geater rackettailed drongo dicrurus paradiseus (linnaeus, 1766) bhimraj chibe r c lc f2 28 oriolidae golden oriole oriolus oriolus (linnaeus,1758) gajale sunchari sv uc lc f2 29 oriolidae blackheaded oriole oriolus xanthornus (linnaeus, 1758) kalotauke sunchari r uc lc f2 30 sturnidae common myna acridotheres tristis (linnaeus, 1766) dangrerupi r fc lc f1 31 sturnidae asian pied starling gracupica contra (linnaeus, 1758) danger saraun r fc lc f1 32 laniidae long-tailed shrike lanius schach (linnaeus, 1758) bhadrai wv uc lc f2 33 passeridae house sparrow passer domesticus (linnaeus,1758) bhagera r fc lc f1 34 pycnonotidae red-vented bulbul pycnonotus cafer (linnaeus, 1766) jureli r fc lc f1 35 muscicapidae oriental magpie robin copsychus saularis (linnaeus, 1758) dhobi chara r fc lc f1 36 leiothrichidae jungle babbler turdoides striata (dumont, 1823) bagale vyakur r c lc f2 https://en.wikipedia.org/wiki/louis_jean_pierre_vieillot https://en.wikipedia.org/wiki/leiothrichidae ss = seasonal status, ab = abundance, r = resident, wv = winter visitor, sv = summer visitor, c = common, fc = fairly common, o = occasional, uc = uncommon, a near threatened, b vulnerable, sn family common name scientific name local name ss ab iucn hl pelicaniformes 37 ardeidae indian pond heron ardeola grayii (sykes,1832) askote bakulla r fc lc w2 38 ardeidae purple heron ardea purpurea (linnaeus,1766) dhyani bakulla wv o lc w1 39 ardeidae great egret ardea alba (linnaeus,1758) thulo seto bakulla r c lc w1 40 ardeidae cattle egret bubulcus ibis (linnaeus, 1758) bastu bakulla r c lc w1 41 ardeidae intermediate egret ardea intermedia (wagler, 1827) sano bakulla r c lc w1 42 threskiornithi dae black ibis pseudibus papillosa (temminck,1824) karra sawari wv o lc w2 piciformes 43 megalaimidae blue-throated barbet megalaima asiatica (latham, 1790) kuthukre r o lc f1 44 picidae fulvous-brested woodpecker dendrocopos macei (vieillot, 1818) kastha kut r c lc f2 psittaciformes 45 psittacidae rose-ringed parakeet psittacula krameri (scopoli, 1769) kanthe suga r c lc f2 strigiformes 46 strigidae spotted owlet athene brama (temminck, 1821) laatkosero r c lc f2 47 strigidae jungle owlet glaucidium radiatum (tickell, 1833) dundul r c lc f1 48 strigidae brawn hawk owl ninox scutulata (raffles, 1822) kaal pechak r o lc f2 suliformes 49 phalacrocoraci dae little cormorant phalacrocorax niger (vieillot, 1817) saano jalewa wv fc lc w1 https://en.wikipedia.org/wiki/carl_linnaeus https://en.wikipedia.org/wiki/10th_edition_of_systema_naturae https://en.wikipedia.org/wiki/johann_georg_wagler https://en.wikipedia.org/wiki/coenraad_jacob_temminck https://en.wikipedia.org/wiki/samuel_tickell milan kharel/ bibechana 16 (2019) 154-164: rcost p.161 (online publication: dec., 2018) iucn= iucn status of threatened species 2018, lc = least concern, vu = vulnerable, hl= habitat location, f1= forest area (west), f2= forest area (east), w1= wetland area (east), w2= wetland area (west), hl= habitat location. fig. 2: avifaunal composition of betana wetland (order-wise). fig 3: pie showing seasonal status of avifauna on percentage basis. 0 2 4 6 8 10 12 14 16 family species order s resident ® 70% winter visitor (wv) 18% summer visitor (sv) 12% 34.69 24.48 22.44 18.36 0 5 10 15 20 25 30 35 40 fairy common common occasional uncommon p er ce n ta g e milan kharel/ bibechana 16 (2019) 154-164: rcost p.162 (online publication: dec., 2018) fig 4: species dispersal of avifauna. table 2: habitat wise composition of avifauna. source: field survey, 2018. (n= number of species, n= number of individuals, sv= summer visitor, wv= winter visitor, r=resident). table 3: shannon weiner diversity index (h) and species evenness (e). sampling stations no. of individuals (n) pi (= n/n) lnpi pi* lnpi h (= -∑pi*lnpi) e (= h/logs) w1 89 0.278125 -1.27968 -0.35591 1.33448 0.789 (for s=49) w2 43 0.134375 -2.00712 -0.26971 f1 112 0.35 -1.04982 -0.36744 f2 76 0.2375 -1.43759 -0.34143 total n= 320 ∑ pi =1 ∑lnpi= -5.77422 ∑pi*lnpi= -1.33448 habitat location n % n % sv wv r wetland area w1 10 20.40 89 27.81 01 03 06 wetland area w2 06 12.24 43 13.43 -01 05 forest area f1 16 32.65 112 35.00 01 01 14 forest area f2 17 34.69 76 23.75 04 04 09 total 49 320 06 09 34 milan kharel/ bibechana 16 (2019) 154-164: rcost p.163 (online publication: dec., 2018) fig 5: habitat wise composition of birds. 4. discussion in the present study most of the birds were found belong to the order passeriformes including nine families and 15 species, followed by coraciformes with three families and four species then pelicaniformes with two families and six species. of them, two species grey-headed fish eagle (icthyophaga humilis) and lesser adjutant stork (leptoptilos javanicus ) are kept under near threatened (nt) and vulnerable (vu) categories of iucn red list status of threatened species respectively [13]. surana [14] reported 109 species of birds from chimdi lake. they belong to 34 families where 28 species were resident, 27 species were winter visitor, 17 species were summer visitor 37 species were migratory. of them, 16 species were common, 23 species were fairly common, 25 species were occasional and 45 species were scarce. pokharel [15] recorded 295 individuals belonging to 55 species of birds from 26 families and 10 orders from the betana wetland area but in the present study, altogether 320 individuals belonging to 49 species of birds with 30 families and 15 orders were recorded. black kite (milvus migrans), indian roller (coracius benghalensis) and whitethroated kingfisher (halcyon smyrnensis) as very common species in the betana wetland. but this time these species were occasionally seen. this may be due to limitation of survey period or due to shortage of food resources (?). however, red-vented bulbul (pycnonotus cafer), rose-ringed parakeet (psittacula krameri), black drongo (dicrurus macrocercus), oriental magpie robin (copsychuss aularis), common myna (acridotherestristis), great egret (casmerodius albus), house sparrow (passer domesticus), spotted dove (streptopelia chinensis) etc. were recorded as high population especially in winter season. in the previous study, out of 55 species, 44 species were resident, five species were winter visitor and six species were summer visitor but this time, out of 49 species, 34 species were resident (70%) , nine species (18%) were winter visitor and six species (12%) were summer visitor. four more species of winter visitor birds were recorded this time. the maximum number of summer visitor (8.16%) and winter visitor (8.16%) were recorded from sampling station f2 forest area while maximum number of resident types of birds (28.57%) were recorded from the sampling stations f1 forest area. the total number species of birds were recorded from the both sampling areas of forest f1 and f2 was 67.34% (n= 33) and that of from the both sampling areas of wetland w1 and w2 was 32.64% (n=16). pokharel (2015) calculated shannon – 0 20 40 60 80 100 120 wetland area w1 wetland area w2 forest area f1 forest area f2 number of species summer visitor winter visitor resident no of individuals milan kharel/ bibechana 16 (2019) 154-164: rcost p.164 (online publication: dec., 2018) weiner diversity index and evenness index 1.27 and 0.82 respectively. in the present study, it was found to be 1.332 and 0.789 respectively. this indicates the study area now has higher diversity and species evenness. 5. conclusions compared to the previous work, birds belonging to four more families and five more orders were recorded this time. however, total numbers of species were recorded less during the present study. the species richness was found higher in winter season than summer. this may be due to easy availability of food, suitable climate, temperature and migration of species. during the present survey, 320 individuals belonging to 49 species of birds under 30 families and 15 orders have been recorded from the betana wetland, which proves that the study area is one of the suitable habitats for avifaunal abundance. about 70 % of total bird recorded was found to be the resident type and about 35% of total recorded bird species were found common. the maximum species of birds were recorded from the forest area 67.34% (n= 33) where the maximum number of individuals were found 35% (n=112). of them maximum number of species 69.38% (n=34) species of birds were resident type. the major threats to the avifauna in the study site were found to be deforestation, overgrazing, bird killing by using catapult and pollution due to recreational activities. acknowledgements i am thankful to the local people who helped during field visits. i would like to acknowledge the head, department of zoology, central campus of technology, dharan (tu) for providing the concerned literatures. thanks are due to idea wild org., usa for donating field gears. references [1] r. grimmet, c. inskipp, t. inskipp, birds of nepal. helm field guide. prakash books, new delhi. 2000. [2] birdlife nepal, http://www.birdlifenepal.org/status-of-birds.php accessed 20th aug 2018. [3] t. k. shrestha, birds of nepal. field ecology, j. nat. his. and con. 1 (2000) 287. [4] g. e. hollis, m. m. holland, j. s. larson, wise use of wetlands, j. nature and resource 24 (1998) 213. doi: http://dx.doi.org/10.3126/on.v2i1.323 [5] b. r. subba, d. c. chhetri, study of fauna of betana village development committee, morang, nepal. (2005), a report submitted to apec, biratnagar. [6] s. k. rai, algal flora of betana wetland, morang, nepal. j. nepalese journal of biosciences 1 (2011) 104-113. doi: http://dx.doi.org/10.3126/njbs.v1i0.7477 [7] webpage https://en.climate-data.org/location/47719/ [8] r. l. hutto, s. m. pletscher, p. hendricks, a fixedradius point count method for nonbreeding and breeding season use. j. auk 103 (1986) 593-602. [9] s. ali, s. d. ripley, handbook of the birds of india and pakistan, vol. v, oxford university press. 1986. doi: https://www.jstor.org/stable/4086054 / 10.2307/4086054 [10] r. l (sr) fleming, r. l. (jr.) fleming, l.s. bangdel, birds of nepal with reference to kashmir and sikkim. first adarsh impression, gaurav offset, delhi. 2000. [11] r. grimmet, c. inskipp, t. inskipp, h. s. baral, birds of nepal, helm field guide. revised edition, christopher helm, london. 2016. doi: https://doi.org/10.1017/s0959270901240170. [12] p. pradhan, a pocket photo guide to the birds of nepal. falcon publication, singapore. 2016. [13] webpage https://www.iucnredlist.org. accessed on 20 august 2018. [14] r. surana, b.r subba, k. p. limbu, avian diversity during rehabilitation stage of chimdi lake, sunsari, nepal. our nature 5 (2007) 75-80. doi: http://dx.doi.org/10.3126/on.v5i1.802. [15] u. pokharel, diversity and conservation status of birds of betana wetland area, belbari, morang, nepal. m.sc. unpublished thesis. central department of zoology, tribhuvan university, kathmandu, nepal. 2015. http://dx.doi.org/10.3126/on.v2i1.323 http://dx.doi.org/10.3126/njbs.v1i0.7477 https://en.climate-data.org/location/47719/ https://www.jstor.org/stable/4086054%20/%2010.2307/4086054 https://doi.org/10.1017/s0959270901240170 https://www.iucnredlist.org/ http://dx.doi.org/10.3126/on.v5i1.802 leela pradhan joshi/ bibechana 13 (2016) 23-28 : rcost p.23 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal prunus domestica dye extraction for fabrication of zinc oxide based dye-sensitized solar cells leela pradhan joshi department of physics, amrit campus, tribhuvan university, kathmandu, nepal e-mail: leela.pradhan@gmail.com article history: received 19 august, 2015; accepted 09 september, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13341 abstract aluminium doped zinc oxide (azo) seed layers were deposited on fluorine doped tin oxide (fto) substrates using a spin coating technique. these were then immersed in growth solutions of zinc nitrate, hexamethylenetetramine and distilled water to develop nanoplates of zinc oxide (zno). the nanostructures of zno grown on fto were studied using x-ray diffraction techniques. dye-sensitized solar cells (dssc) were fabricated using two prepared electrodes, one of dye-loaded zinc oxide and another that was platinum coated. the electrolyte used was potassium iodide iodine solution. the performance of the assembled dsccs was tested by drawing an iv curve. the results showed that the short circuit current and open circuit voltages were about 10 microamperes and 270 millivolts respectively. ©rcost: all rights reserved. keywords: zinc oxide; seed layers; spin coating; hydrothermal; solar cells. 1. introduction in recent years a wide band semiconducting material zno has been an attractive and efficient material to be utilized in fabrication of dye-sensitized solar cells [1-5]. zno can be prepared using several methods, spin coating [6], spray pyrolysis [7], chemical bath deposition [8], dip coating [9]. its morphology, electronic as well as optical properties depend on method of preparation. zno is a very versatile material because it's electrical and optical properties can be tailored by doping with different elements such as aluminium, boron, fluorine [10-12]. the fabrication of dssc with various types of zno nanostructures such as nanowires, nanoflowers, nanoribbons has been reported [1]. another vital component which affects the performance of dssc is the type of dye extraction used to sensitize high band zno. because of low cost and environmentally friendly material the different types of natural dyes from fruits and leela pradhan joshi/ bibechana 13 (2016) 23-28 : rcost p.24 (online publication: dec., 2015) flowers can be used to fabricate solar cells [13-14]. this work reports the measurement on performance of dssc fabricated with nanoplates of zno and prunus domestica dye extraction. 2. experimental zno nanostructured films were grown by using a two-step spin coating and hydrothermal process on glass as well as fto substrates. a precursor solution was made using zinc acetate, diethanolamine, and ethanol solution for spin coating [6]. before coating the solution substrates were ultrasonically cleaned using acetone and rinsed with distilled water several times. the growth solutions were prepared by mixing equal molar concentrations of zinc nitrate and hexamethylenetetramine in distilled water at room temperature. the azo coated substrates were dipped into the growth solution at the constant temperature of 905oc for 2 hours for the zno nanostructures to grow [15]. after taking out from the solution these were rinsed with distilled water and dried in air at 4005oc for 30 minutes. investigation on effect of thickness of seed layer on optical property of zno has also been made in this work. dye extraction from the bark of prunus domestica is used to sensitize the zno layer. to extract the dye from prunus domestica locally called as plums, we first collected few pieces of bark of prunus domestica. it is then cleaned and dried in air. a 50gm of this is then dropped into ethanol and heated at constant temperature of 60±5oc for 2 hours which gives the nice red color solution. as-prepared zno films were characterized by using x-ray diffraction, and ultra-violet visible spectrophotometer. we have measured the short circuit current and open circuit voltage of assembled dssc using digital fluke multimeters. the absorbance spectrum of dye extraction is measured using spectrophotometer. above developed zno films were then dipped into the dye solution at constant temperature of 60±5oc for 6 hours for dye loading. finally, we assembled the dye loaded zno electrodes and platinum coated counter electrode prepared by spin coating method using 5mm potassium iodide iodine liquid electrolyte solution [16]. the i-v curve of assembled dsscs was measured using two digital fluke multimeters model 179. 3. results and discussion 3.1 structural properties figure 1 shows the x-ray diffraction pattern of zno film deposited on fto substrate. the peaks observed at 2θ = 35.38o (d = 2.53ǻ), 37.84 o (d= 2.37ǻ) and 48.65 o (d=1.86 ǻ) corresponds to zno peaks orientating along (002), (101) and (102) planes respectively when comparison was made with standard spectrum of joint committee on power diffraction standards (jcpds) values from pdf card # 361451 [6]. the xrd pattern also shows other low intensity zno peaks at 2θ = 56.14 o, 63.19 o, 64.38 o and 67.17o which corresponds to (110), (103), (200), and (112) planes respectively. the d spacing values were found to be slightly shifted from standard values which may be due to either al doping in zinc acetate solution or stress produced in the film. the fto peaks were also significantly observed in the diffraction pattern at 2θ = 28.16o (d = 3.16å), 39.46o (d = 2.28å), 53.16o (d = 1.72å) respectively. we calculated the average crystallite size of zno film by measuring the full width half maximum of peaks using the debye leela pradhan joshi/ bibechana 13 (2016) 23-28 : rcost p.25 (online publication: dec., 2015) scherrer's formula, d= 0.9 λ/β cosθ [6-7]. the symbol λ, β, and θ represent the wavelength of x-ray ( 1.54å), width of peak, and bragg's angle respectively. the average value of crystallite size was calculated by measuring the full width half maximum (fwhm) of first two zno peaks of (002) and (101) orientations and it was found to be of 239å. fig. 1: x-ray diffraction pattern of zno film grown on fto substrate at 90±5oc (sample a5). 3.2 scanning electron microscope the previous report on study of morphology of the zno film prepared on glass substrate from 0.3m al doped zinc acetate precursor solution and 25mm growth solution is shown in figure 2 below. it shows the formation of nano-plate like structures. the average thickness and breadth of zno plates are of 96nm and 480nm respectively [17]. fig. 2: a scanning electron microscope image of zno film grown on glass substrate. leela pradhan joshi/ bibechana 13 (2016) 23-28 : rcost p.26 (online publication: dec., 2015) 3.3 optical properties the optical transmittance curves as a function of wavelength for hydrothermally grown zno films on fto substrates at 90±5oc were shown in figure 3a (sample a1) and 4a (samplea5) respectively. the transmittances (t %) of all films were about 60% in the visible region. the band gap values were estimated by the manifacier method for the deposited zno films [6-10].to calculate band gap of zno the graphs of ( h )2 versus photon energy hn (ev) for films a1 and a5 were plotted where a represents the absorption coefficient of zno. these graphs were shown in figure 3b and 4b respectively. by extrapolating the linear portion of energy curves on hν axis gives the band gap of zno. the calculated values of band gap of a1 and a5 are found to be 3.04ev to 3.08ev respectively. it is inferred that no significant change in transmittance ( t%) as well as band gap on increasing azo thickness from 1 coat to 2 coats while depositing zno films on fto substrate in hydrothermal process. fig. 3: (a) transmittance versus wavelength (b) (αhν)2 versus hν of zno film grown on fto substrate (sample a1). fig. 4: (a) transmittance versus wavelength (b) (αhν)2 versus hν of zno film grown on fto substrate (sample a5). leela pradhan joshi/ bibechana 13 (2016) 23-28 : rcost p.27 (online publication: dec., 2015) in this paper we have used the prunus domestica dye extraction to assemble dssc. the captured absorption spectrum of dye extraction is shown in figure 5a. the spectrum shows the absorption peak at 365nm. the zno nanostructured films dipped into the dye solution for 6 hours at 60oc for sufficient amount to be adsorbed. finally, the solar cell is assembled using as prepared zno photoanode, platinum coated counter electrode of fto and potassium iodide iodine redox electrolyte [16]. the performance of encapsulated dssc is tested by measurement of current voltage characteristic curve shown in figure 5b. it clearly shows the same behavior of i-v curves for two different light intensities. black colored filled squares symbol in the figure represent the power generation from assembled dye-sensitized solar cell with and 500w halogen light source and red filled circles represent the dark light of room only respectively. the result showed the maximum short circuit current of about 10 microampere and open circuit voltage of 270 millivolts respectively. fig.5: (a) the absorption spectrum of prunus dye extraction solution.(b) current voltage characteristic curve of fabricated dye sensitized solar cell. 4. conclusions zno films were successfully deposited on glass and fto substrates using an economic two step spin coating followed by hydrothermal method. x-ray diffraction analysis confirms that the zno deposited was of polycrystalline wurtzite structure. the average crystallite size of zno was 239ǻ. an optical analysis showed that band gap of zno film was only slightly increased from 3.04ev to 3.08ev as the thickness of seed layer was increased from 1 coat to 2 coats. the measurement on current voltage curve of assembled zno based solar cell using prunus domestica dye extraction shows the short circuit current of 10 microampere and open circuit voltage of about 270millivolts respectively. leela pradhan joshi/ bibechana 13 (2016) 23-28 : rcost p.28 (online publication: dec., 2015) references [1] j. b. baxter, and e. s. aydil, solar energy materials & solar cells, 90 (2006) 607. [2] m. grätzel, journal of photochemistry and photobiology, 4 (2003) 145. [3] m. krunks, t. dedova, and i. o. acik, thin solid films, 515 (2006) 1157. [4] s. -h. lee, s. -h. han, h. s. jung, h. shin, j. lee, j.-h noh, s. lee, i. -s. cho, j. –k. lee, j. kim, and h. shin, journal of physical chemistry c, 114 (2010) 7185. [5] b. o’regan, and m. grätzel, nature, 335 (1991) 737. [6] s. p. shrestha, s. r. ghimire, j. j. nakarmi, y.-s. kim, s. shrestha, c.-y. park, and j.-h. boo, bull korean chemistry society, 31 (2010) 1. [7] u. alver, t. kılınç, e. bacaksız, t. küçükömeroģlu, s. nezir, i. h. mutlu, and f. aslan, thin solid films, 515 (2007) 3448. [8] b. cao, and w. cai, journal of physical chemistry c, 112(2008) 680. [9] d. djouadi, a. chelouche, a. aksas, and m. sebais, physics procedia, 2 (2009) 701. [10] b. joseph, p. k. manoj, and v. k. vaidyan, ceramics international, 32 (2006) 487. [11] b. n. pawar, s. r. jadkar, and m. g. takwale, journal of physics and chemistry of solids, 66 (2005) 1779. [12] s. tiradoguerra, m. de la l. olvera, a. maldonado, and l. castañeda, solar energy materials & solar cells, 90 (2006) 2346. [13] b. pradhan, s. k. batabyal, and a. j. pal, solar energy materials and solar cells, 91(2007) 769. [14] n. m. gómez-ortíz, i. a. vázquez-maldonado, a. r. pérez-espadas, g.j. mena-rejón, j. a. azamarbarrios, and g. oskam, solar energy materials & solar cells, 94 (2010) 40. [15] n. j. nicholas, g. v. franks, and w. a. ducker, crystengcomm, 14 (2012) 1232. [16] s. s. kanmani, k. ramachandran, and s. umapathy, international journal of photoenergy, 2012, article id 267824 (2012) 1. [17] l. p. joshi, p. s. shrestha, a. shakya, l. dangol, k. p. subedi, and s. p. shrestha, university grants commission nepal report, 2014. microsoft word yadv _20-29_.docx r c o s t n publisher: research council of science and technology, biratnagar, nepal p.20 bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana thermodynamic and structural behaviour of tl-na liquid alloy s. k. yadav 1* , l.n. jha 2 , d. adhikari 1** 1department of physics, mahendra morang adarsh multiple campus (tribhuvan university) biratnagar, nepal 2 central department of physics, tribhuvan university, kirtipur, kathmandu, nepal ** e-mail: adksbdev@yahoo.com *e-mail: yadavshashit@yahoo.com accepted for publication: december 8, 2014 abstract in this work we intend to study the thermodynamic and microscopic structural properties of tl-na liquid alloy at 673 k on the basis of regular associated solution model. we have estimated the mole fractions of the complex and the free monomers assuming the complex ���� as energetically favoured in the initial melt. in thermodynamic properties, we have computed free energy of mixing (��), enthalpy of mixing (��), entropy of mixing (��) and activities of the monomers (� and ���). the compositional contributions of the heat of mixing and the heat of formation of the complex to the net enthalpy change have also been studied. the microscopic structural properties of the alloy have been studied by computing concentration fluctuation in the long wavelength limit (� (0)), chemical short range order parameter (��) and the ratio of mutual to intrinsic diffusion coefficients (��/���). both the theoretical and the experimental values of � (0) are found to be less than the ideal values at all compositions which indicates the ordering nature of tl-na liquid alloy at 673 k. all the interaction energy parameters are found to be negative and temperature dependent. the liquid system is found to be moderately interacting. doi: http://dx.doi.org/10.3126/bibechana.v12i0.11784 © 2014 rcost: all rights reserved. keywords: tl-na liquid alloy; energetically favoured; interaction energy parameters; temperature dependent; moderately interacting. 1. introduction the multidimensional uses and the dynamical properties of binary liquid alloys have drawn considerable attentions of the present day researches. most of the researches are confined to develop new alloys and to investigate their thermodynamic and structural behaviors to meet the greater demands of the today's world. generally, the alloys are grown from their liquid state and hence the study of thermodynamic and structural properties of the initial melt play important role for their uses in the solid state. several theoretical models till now have been proposed to study the thermodynamic and structural properties of the liquid alloys [1-12]. there also exist immense interest in developing and devising the tl-based alloys because of their involvements in the manufacture of electronic components, optical lenses, semiconductor materials, gamma radiation detectors, jewelry, green fireworks and wear and tear resistant shafts [13-16]. in this work, we intend to study and predict the yadav et al./bibechana 12 (2015) 20-29: p. 21 thermodynamic and microscopic structural properties of tl-na liquid alloy at 673 k on the basis of regular associated solution model [17-22]. the regular associated solution model is based on the assumption of the presence of the complexes in the liquid state. when the atoms of types a and b are mixed in the liquid state, there are associations among a, b; a, a and b, b called 'complexes', 'pseudomolecules', 'clusters' or simply 'associations' [6]. the expressions for the different thermodynamic and structural function are derived on the basis of the existence of unequal interactions among complex and the unassociated atoms. prigogine and defay [23] proposed that the interaction energies and the concentrations of the two free monomers and the complex would determine the ternary activity coefficients. jordan [21] further elaborated that the activities of the free monomers and the complexes can be estimated by considering the liquid solution as the ternary system and attributing the deviations from the ideal behaviour to the short range neighborhood of interactions. he named the solution as regular associated solution and applied this concept in the congruently melting semiconductors zn-te and cd-te. this concept was employed by osamura and predel [24] to the in-sb system but derived the necessary equations by neglecting the higher order terms. later, lele and ramchandrarao [19] further extended this model and verified its utility for the determination of the thermodynamic properties and the activities for mg-sn and in-sb liquid alloys. the phase diagram of the tl-na alloys, [25] shows the existence of two phases, such as �, "����" (with fcc protopype structure and �, "�����" (with end centered-orthorhombic structure). in this work we have assumed the presence of ���� complex as energetically favoured in the liquid state of tl-na alloy at 673 k and studied its thermodynamic and microscopic structural properties. the expressions for the various thermodynamic and structural functions are presented in the section 2, the results and discussion are presented in section 3 and the conclusions of this work are presented in the section 4. 2. theory when the atoms of the type a (= tl) and b (= na) are mixed at a temperature near to their melting point, there is formation of the complex of the form ab (����). let one mole of the binary liquid contain �� atoms of monomer a (= in) and �� atoms of monomer b (= bi).following lele and ramchandrarao [19], the chemical complexes of the form ��� (��� ⟺ !� + �) is assumed to exists in the initial melt, where ! is a small integer whose value is determined from the compound forming concentration (= ! / (! +1)) in the solid state. the liquid mixture is thus the ternary mixtures of unassociated atoms a (= tl) and b (= na) and the complex ��� (=����), where ! = 1. if �#, �$ and �#%$ moles are the concentrations of a, b and ��� in the melt then according to the conservation of mass, in the partially associated solution the formation of the complex ��� requires �� = �# +!�#%$ and �� = �$ + �#%$. but the thermodynamic and microscopic structural behaviours of the complexes in the melt are governed by their true mole fractions '#, '$ and '#%$ in spite of their gross mole fractions '� and '�, where '�= ��/�� + �� , '� = ��/�� + �� , '# = �#/�# + �$ + �#%$ , '$ = �$/�# + �$ + �#%$ and '#%$ = �#%$ /�# + �$ + �#%$. using above expressions, the equations for the true mole fractions can be derived as '# = '� − !'�'#%$ and '$ = '� − (1 − !'�)'#%$ (1) yadav et al./bibechana 12 (2015) 20-29: p. 22 following prigogine and defay [23], in the regular associated liquid solution the gross chemical potentials of the components 1 and 2 are equal to the chemical potentials of the free monomers a and b. according to jordan, [21] the activity coefficients of monomers �#, �$ and complex �#%$ can be represented in terms of pairwise interaction energies as rt ln�# = '$� .�� + '#%$� .�/ + '$ '#%$ (.��‒ .�/ + .�/) (2a) rt ln�$ = '#%$� .�/ + '#�.�� + '# '#%$(.�/ − .�/ + .��) (2b) rt ln�#%$ = '#�.�/ + '$�.�/ + '#'$(.�/ − .�� + .�/) (2c) where .��, .�/ and .�/ represents the pairwise interaction energies for the species a, b; a, ��� and b, ��� respectively. t and r represent temperature and universal real gas constant respectively.following lele and ramchandrarao,[19] the equilibrium constant for the reaction ��� ⟺ !� + � can given by following equation 1 = 23% 24 53 % 542 3%4 5 3%4 (3) solving equations (2) and (3), the relation for the equilibrium constant can be obtained as lnk = ln 7 23% 2423%4 8 + 9:;< + 9:;< [ !'$ (1 ‒ '#) + '# ] + 9:?< [ !'#%$ (1 ‒ '#) ‒ '# ] + 9;?< [ '#%$ (1‒ !'$) ‒ '$] (4) the expression for free energy of mixing (��) is given as [19] �� =� �@�23%4 a� bc '#'$ 9:;< + '#'#%$ 9:?< + '$'#%$ 9;?< d + c'#lne# + '$lne$ + '#%$lne#%$d + '#%$lnkf (5) the other thermodynamic functions, such as heat of mixing (��), entropy of mixing (��) and concentration fluctuation in the long wavelength limit ( � (0) ) are related with free energy of mixing ( ��) by the following standard thermodynamic relations �� = ��t ( ghi g )j (6a) �� = kil mi (6b) � (0) = rt ( g;hig2:; ) ,jn� (6c) � (0) = '� ��( go:g2: ) ,jn� = '� ��( go;g2; ) ,jn� (6d) using equation (5) in equation (6a), the expression for the enthalpy of mixing can be obtained as �� = � �@�23%4 bc '#'$ 9:;< + '#'#%$ 9:?< + '$'#%$ 9;?< d – t c '#'$ g9:;g + '#'#%$ g9:?g + '$'#%$ g9;?g d − '#%$ a�� � qr � f (7) the expression for the concentration fluction in the long-wavelength limit (� (0)) can be obtained by using equation (5) in equations (6c) and (6d) as yadav et al./bibechana 12 (2015) 20-29: p. 23 � (0) = 1/ s 7 � �@�23%4 8 t � uv c'# ′ '$ ′ w�� + '# ′ '#%$′ w�/ + '$ ′ '#%$′ w�/d + x23′;23 + 24′; 24 + 23%4′ ; 23%4 yz [ (8) here, g;hig2:; > 0 for ghig2: = 0. the prime denotes the differentiations with respect to concentrations, and '# ′ and '$ ′ are obtained by using equation (1). '#%$′ is obtained using equation (4) by using the condition � qr �2: = 0. [5,6,17] the factor ( 1+ p'#%$ )-1, which appears as a coefficient of all terms containing '#, '$ and '#%$ in equations (5), (7) and (8), is a result of change in the basis for expressing mole fractions of species a, b and ��� from that used for '� and '�. the concentration fluctuation in long wavelength limit (� (0)) has been developed as an important tool to understand the nature of atomic ordering in the binary liquid alloys. at a given concentration, if � (0) < � �� (0) then ordering (unlike atoms pairing) is expected and if � (0) > � �� (0) then segregation (like atoms pairing) is expected, where � �� (0) = '�'�. the experimental values of � (0) can be obtained from equation (6d).[26,27] the degree of local ordering in such liquid systems can be studied by estimating warren-cowley short range order parameter (��) with the knowledge of (� (0)).[12, 27, 28] the expression for �� in terms of � (0) is given as �� = \ n� \ (] n�) @ � where, � = \^^ (_) \^^`a (_) and � �� (0) ='�'� (9) where z is the coordination number and z= 10 is taken for our calculation. we note that varying the value of z doesn't have any effect on the position of the minima of ��; the effect is to vary the depth while the overall features remains unchanged. the greater insight of microscopic structural properties can be done by evaluating diffusion coefficient which is expressed in terms of � (0) by using darken thermodynamic equation [29, 30] as bib`a = 2: 2;\^^ (_) (10) where, �� stands for the chemical or mutual diffusion coefficient and ��� stands for the intrinsic diffusion coefficient for an ideal mixture which are related as �� = ��� g q�3g2: , with �� = '��$ + '��# (11) where, �# and �$ are the self-diffusion coefficient of pure components a and b respectively. the pairwise interaction energy parameters and the equilibrium constant are determined by the following procedures: according to the regular associated solution model '��� = '#�# and '��� = '$�$, where �� and �� are the gross activity coefficients of components 1 and 2 respectively. they can thus be related as follows ���� = ���# + ln ( 232: ) (12a) and, ���� = ���$ + ln ( 242; ) (12b) on solving equations (2a) and (2b), we obtain 9:?< = 24 q7 c;d4 8@( �n 24 ) ef7 c:d3 8n 24 (�n 24 )g:;hi 23%4; (13) yadav et al./bibechana 12 (2015) 20-29: p. 24 9;?< = 23 ef7 c: d3 8 @( �n23 ) ef7 c;d4 8 n 23( �n 23 )g:;hi 23%4; (14) where �� = '��� and �� = '��� are activities of components 1 and 2 respectively. the pairwise interaction energies, the equilibrium constants and the activity coefficients at infinite dilution for ! = 1 can be related as [19] ln ��_ = 9:;< + j1 − c1 + 1 k'l 9;?lg:;< dn�m (15a) ln ��_ = 9:;< + j1 − c1 + 1 k'l 9:?lg:;< dn�m (15b) where ��_ and ��_ are the activity coefficients at zero concentrations of the free monomers a and b respectively. on solving equations (4), (11) and ( 12), we obtain ��1 + 9:?< = 7 �@2323%4 8 ln c o:23 d + 2423%4 bln c o:23 d − 9:;< f + ln 7 �:%�;23%4 8 (16a) = ln ��_ − ln[1 − ��_ exp(−.��/a�)] (16b) the expression for the complex at equiatomic composition i.e., at '� = '� = 0.5; '# = '$ can be written as '#%$ = ef(5;/5:)d:sd;st.u efvw:tw;t∗ :lw;t yz{ (lg:;hi ) :lw:t yz{(lg:;hi ) | (17) the mole fraction of the complex and the interaction energy .�� are simultaneously obtained by solving equations (16) and (17) by an iterative procedure. 3. results and discussion the mole fraction of the complex ���� at eqiatomic composition and the model parameters .��/a� and ��1 + .�//a� are first determine simultaneously by solving the equations (16) and (17) with the help of observed values of activity coefficient [25] at equiatomic and zero compositions. then the mole fractions of the complexes and the unassociated atoms are obtained from equations (1) and (16a) with the aid of above determined parameters by iterative process. figure 1 shows the compositional dependence of the mole fractions of the complex and the unassociated atoms. it is found that the maximum association occurs at 53.88 at pct. of tl and at this composition about 50.85 mol pct. of the liquid alloy is associated. the pairwise interaction energies and the equilibrium constant are calculated from equations (5), (13) and (14) by the successive approximation to explain the observed values of free energy of mixing [25]. the best fit values so obtained for tl-na liquid alloy at 673 k are found to be 9:;< = −1.68, 9:?< = −2.31, 9;?< = −0.986 and 1 = 0.0347. figure 2 shows the well agreements between the theoretical values (equation (5)) and the observed values of the free energy of mixing. both the theoretical and the observed values of hi< are found to be minimum at ' = 0.5 ( theoretical values of hi< = −2.1569 and the observed value of hi< = −2.2008 ± 0.07472 [25]). the observed values of excess free energy of mixing of tl-na liquid alloy at 673 k are moderately high indicating that this system is moderately interacting system. yadav et al./bibechana 12 (2015) 20-29: p. 25 fig. 1: mole fractions of the complex (����), unassociated atoms (tl and na) vs concentrations of in (���) of tl-na liquid alloy at 673 k. fig. 2: free energy of mixing (��/��), heat of mixing (��/��) and entropy of mixing (��/�) vs concentrations of tl (���) of tlna liquid alloy at 673 k. according to this model, all the interaction energy parameters are considered to be temperature dependent. however, if they are assumed independent of temperature then the expression for the enthalpy of mixing can be simply expressed as �� = � �@�23%4 bc'#'$.�� + '#'#%$.�/ + '$'#%$d − '#%$a�� � qr � f then �� can be obtained with the knowledge of the interaction energy parameters between the unassociated species and to the complex and a�� � qr � . the �� so obtained differ far from the observed values. this supports the importance of the temperature dependence of interaction energy parameters. the temperature dependent model parameters are obtained using equation (7) to explain the observed values of �� [25] by successive approximations. the best fit values of such parameters are found to be g9:;g = 8.00 , g9:?g = 13.67 , g9;?g = 7.00 and a�� � qr � = 20500 ± 4500. both the theoretical (equation (7)) and the observed values of �� are in well agreements (figure 2). the minimum values of both of �� are found to be at ' = 0.5 ( theoretical value of ki< = −1.9975 and the observed value of ki< = −2.0432 ± 0.01868 [25]). the theoretical values of the entropy of mixing(��) are obtained from the equation (6b) with the knowledge of �� and ��. both the theoretical and the observed values of �� are in well agreements (figure 2). the compositional contributions of the heat of mixing of the species x�, x� and x��� and the heat associated with the formation of the complexes to the total enthalpy change are obtained from equation (7). the contribution from the complex formation term is maximum at 47.46 at. pct. of tl and the mixing term contributes the maximum at 67.79 at. pct. of tl due to which the net enthalpy yadav et al./bibechana 12 (2015) 20-29: p. 26 change shows absolute maximum at around 50.85 at. pct. of tl. figure 3 shows the compositional dependance of the heat of mixing, heat associated with the formation of the complexes and the total enthalpy change. the theoretical values of the activities of the unassociated atoms of the liquid alloys are estimated using equations (12). the model parameters obtained above for the present system must not only explain the thermodunamic properties but also must reproduce the activity. it is an important parameter having great influence on the thermodynamic as well as the structural properties of the liquid alloys. any deviation from the ideality can be incorporated into the activity. figure 4 shows the well greements between the theoretical and the observed values [25] of the activities. the microscopic structural behaviour of the liquid alloys can be studied by estimating concentration fluctuation in long wavelength limit (� (0)). the theoretical and the experimental values of � (0) are respectively obtained from equations (8) and (6d). both the theoretical and the experimental values of � (0) are found to be less than the ideal values throughout the entire concentrations. the theoretical analysis thus suggest that there is unlike atoms pairing (ordering) in tl-na liquid alloy at 673 k. both the theoretical and the experimental values of � (0) are in reasonable agreements (figure 5). the degree of local ordering of atoms in the liquid state can be studied by estimating the warrencowley short range order parameter (��). at the equiatomic composition, the values of �� lies between -1 to +1. if �� = −1, indicates the complete ordering of unlike atoms at nearest neighbours, if �� = +1, indicates the complete segregation or paring of like atoms in the nearest neighbours and if �� = 0, indicates the complete randomness of the atoms in the liquid state. the compositional dependence of �� is shown in figure 6. it can be seen that the values of �� are found to be negative at all compositions which further verifies the ordering nature of the liquid system . fig. 3: contributions of the heat of compound formation and heat of mixing to total enthalpy change vs concentrations of tl (���) of tl-na liquid alloy at 673 k. fig. 4: activities of tl (���) and na (���) vs the concentration of tl (���) of tl-na liquid alloy at 673 k. yadav et al./bibechana 12 (2015) 20-29: p. 27 the mixing tendency of the liquid alloy can be studied at the microscopic level by computing the ratio of the mutual and intrinsic-diffusion coefficients (��/���). if ��/��� > 1, indicates the tendency of compound formation; if ��/��� < 1, indicates the separation of phase and ��/���= 1, for the ideal mixing of the liquid alloy. the values of ��/��� are obtained from equation (10) and found to be positive and greater than one in the entire compositions. this further strengthen the theoretical analysis of the presence of the chemical order in the liquid state of tl-na liquid alloy at 673 k. fig. 5: concentration fluctuation in long wavelength limit (���(�)) vs the concentration of tl (���) of tl-na liquid alloy at 673 k. fig. 6: short-range order parameter (��) and the ratio of mutual and intrinsic coefficients (��/���) vs the concentration of tl (���) of tl-na liquid alloy at 673 k. 4. conclusions the theoretical analysis of the tl-na liquid alloy at 673 k indicates that the interaction energy parameters are temperature dependent and there is tendency of chemical ordering in this system. the system under consideration is found to be moderately interacting. references [1] f. sommer, j. non-cryst. solids, 117 (1990) 505. http://dx.doi.org/10.1016/0022-3093(90)90580-f [2] k. hoshino, j. phys. f: met. phys., 13 (1983) 1981. http://dx.doi.org/10.1016/0022-3093(90)90580-f [3] r.n. singh, f. sommer, j. phys. condens. matter., 4 (1992) 5345. http://dx.doi.org/10.1088/0953-8984/4/24/004 yadav et al./bibechana 12 (2015) 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[26] t.s. yih, j.c. thompson, j. phys. f. met. phys., 12 (1982) 1625. http://dx.doi.org/10.1088/0305-4608/12/8/009 [27] r.n. singh, can. j. phys., 65 (1987) 309. http://dx.doi.org/10.1139/p87-038 [28] r. novakovic, j. non-cryst. solids, 356 (2010) 1593. http://dx.doi.org/10.1016/j.jnoncrysol.2010.05.055 [29] r. singh, f. sommer, phys. chem. liq., 36 (1998) 17. http://dx.doi.org/10.1080/00319109808035917 [30] l. darken, r. gurry, physical chemistry of metals, new york: mcgraw hill (1953). bibechana 19 (1-2) (2022) 195-200 195 micellization of sodium dodecyl sulphate in the presence and absence of potassium sulphate and nickel sulphate jay narayan mitruka1, keshab ojha1, arush bhattarai2, sadiksha nepal2, ajaya bhattarai*2 1mechi multiple campus,tribhuvan university, bhadrapur, jhapa, nepal 2mahendra morang adarsh multiple campus, tribhuvan university, biratnagar, nepal email: ajaya.bhattarai@mmamc.tu.edu.np article information: received: may 07, 2022 accepted: june 17, 2022 keywords: surfactant cmc electrolyte sds abstract the effect of addition of salts on the micellization of anionic surfactant sodium dodecyl sulphate (sds) in aqueous medium has been studied by conductance measurement at 298.15 k. the critical micelle concentration (cmc) as well as thermodynamic properties was evaluated. from the premicellar and postmicellar slopes, the degree of dissociation (α) of sds was also calculated. on adding the salts, cmc decreased whereas degree of dissociation increased. employing these cmc and α values, the standard free energy of micellization was also evaluated. the negative values of ∆gm o was decreased when k2so4 was added but increased when niso4 was added. doi: https://doi.org/10.3126/bibechana.v19i1-2.46830 this work is licensed under the creative commons ccby-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction surfactants are surface-active molecules which possess both hydrophobic tail and hydrophilic head and are therefore amphiphilic in nature [1]. due to amphiphilic nature, they exhibit various unique properties such as adsorption at interfaces, self-association and solubilization of hydrophobic molecules, so widely used in pharmaceutical, food, cosmetic, textile, paint and coating industries [2]. the narrow concentration range above which micelles are formed is called critical micelle concentration [3]. from the cmc value of a surfactant, fundamental information about the surfacebibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal https://doi.org/10.3126/bibechana.v19i1-2.46830 https://creativecommons.org/licenses/by-nc/4.0/ mitruka et al / bibechana 19 (1-2) (2022) 195-200 196 active properties can be known. micelle formation plays a model role in biological, chemical and industrial processes [4]. the physicochemical properties of aqueous surfactants can be changed by external means, such as, concentration of reactants, type of additives, nature of the solvent and temperature [5]. in the present scenario, due to the increasing demand for novel materials with unique and enhanced properties has given priorities to the investigation of surfactant-additives system [6]. the aggregation behaviour of surfactants in aqueous solutions can be changed by altering the temperature of solution and also by changing the solvent. the addition of salts can also affect the aggregation behavior of anionic surfactants in aqueous solutions, which is crucial to different applications in detergency and emulsification [7]. when salts are added to surfactants, their properties change, which plays an influential role in many research fields. conductivity measurements in aqueous and ethanol-water systems at 298.15 k, niraula et al. investigated the influence of solvent permittivity and salt on sodium dodecyl sulphate micellization behavior [8]. ren studied the mechanism of salt effect on micellization of sodiumdodecyl diamino sulphonate amphoteric surfactant in aqueous medium by tensiometry using the wilhelmy plate method at 298.15 k [9]. miyagishi et al. studied the salt effect on critical micelle concentration of nonionic surfactants, n-acyl-n-methylglucamides using surface tension or a fluorescent probe method at 298.15 k [10]. no studies have been conducted on the effect of salts (k2so4, niso4) on sds surfactant. conductivity measurements have been used in the present study to determine sodium dodecyl sulphate's thermodynamic properties. the measurement was performed in aqueous system at room temperature. additionally, salts have been studied for their effect on sds, which is quite different from the previous studies. 2. materials and method materials the materials that were used for the determination of cmc are conductivity meter, cotton, beaker, measuring cylinder, pipette, potassium sulfate, nickel sulfate and distilled water. conductance measurements was carried out on 601/602/611 digital conductivity meter purchased from esico international having cell constant of 1.0 cm-1 from india. various independent solutions were prepared and were carried out to check the reproducibility of the outcome. sodium dodecyl sulfate [sds] and nickel (ii) sulfate heptahydrate [niso4.7h2o] was purchased from merck life science private limited, mumbai, india. k2so4 was purchased from glaxo india limited, mumbai. distilled water was used in the experiments. the solutions were prepared at room temperature. methods determination of cmc of sodium dodecyl sulfate with and without salts since conductivity measurement is very simple to do in the lab, it is a very convenient way to determine cmc. at first sodium dodecyl sulfate of 0.05m was prepared by mixing 1.442gm of sds in 100 ml of distilled water. it was kept for whole night to make homogenous solution. about 30 ml sds was taken in one beaker. the conductivity meter was standardized at 298.15 k and the conductance of sds solution was first measured. 2ml of sds was pipetted out and 2 ml of distilled water was added each time and the conductance of diluted sds solution was noted. again100 ml of 0.05m sds solution was prepared in 0.001m k2so4 aqueous solution. 30 ml of the mixture was taken and its conductance was measured. 2ml of the mixture was pipette out and 2ml k2so4 was added in the beaker and conductance was measured each time after addition. similarly, 100 ml of 0.05m sds solution was prepared in 0.001m niso4.7h2o in distilled water. mitruka et al / bibechana 19 (1-2) (2022) 195-200 197 30 ml of the mixture was taken and its conductance was measured. 2 ml of mixture was pipette out and 2 ml niso4 solution was added followed by measurement of conductance each time. about 35 readings were taken for sds in aqueous medium in absence and in presence of each salt. the graph of specific conductance versus concentration of sds in aqueous medium was plotted by using easy plot program to get two straight lines with different slopes. the breaking point of these two lines was the cmc of the surfactant, the value of which is determined by solving two equations. 3. results and discussion the conductivities of sodium dodecyl sulphate in pure water and in presence of k2so4 and niso4 at room temperature is presented in figure 1. sds is more conductive when salts are added because salts have a higher mobility (figure 1). sds in the presence of k2so4 has less conductance than sds in the presence of niso4. since conductivity and resistivity have an inverse relationship. small ions, therefore, have a high charge density. because of this, smaller ions have more conductivity than larger ones. atomic size of ni is 163 pm which has the equivalent value 1.63 å appears on p. 449 in the literature [11] whereas atomic size of k seems 275 pm which has the equivalent value 2.75 å appears on p. 113 in the literature [12]. in other words, as ion size increases, ion mobility decreases and conductivity decreases. fig. 1: specific conductance of sds as a function of concentration in aqueous system (circles) and in the presence of k2so4 (opposite triangles) and niso4 (closed squares) fig. 2: plot of conductivity of sds in water versus concentration of sds fig. 3: plot of conductivity of sds in presence of k2so4 fig. 4: plot of conductivity of sds in presence of niso4 0 0.25 0.50 0.75 1.00 0 0.005 0.010 0.015 0.020 c[m]  ( m s /c m ) 0 0.2 0.4 0.6 0.8 1.0 -0.005 0 0.005 0.010 0.015 0.020 c[m]  ( m s /c m ) 0 0.25 0.50 0.75 1.00 -0.005 0 0.005 0.010 0.015 0.020 c[m]  ( m s /c m ) 0 0.4 0.8 1.2 -0.005 0 0.005 0.010 0.015 0.020 c[m]  ( m s /c m ) mitruka et al / bibechana 19 (1-2) (2022) 195-200 198 there is the calculation of gibbs free energy of micellization (∆𝐺m o ) [8] as ∆𝐺m o = (2 − α)𝑅𝑇 ln𝑋cmc (1) here, r is the universal gas constant, t is the absolute temperature and 𝑋cmc is the mole fraction of surfactant at cmc. the critical micelle concentration (cmc), degree of micelle ionization (α) and standard free energy of micellization (∆𝐺m o ) of sds in the absence and presence of salts in water are given in table 1. table 1: table for cmc, degree of dissociation, gibbs free energy of micellization, premicellar and postmicellar slopes table 1 shows the decrease in the cmc values with the addition of salts (k2so4, niso4). the variation of the cmc of sds in presence and absence of salts are in the order: sds > k2so4 > niso4. ni and k have ionic radii of 69 pm [13]and 133 pm [14], respectively, and the cmc increases as the ionic radii of counterions increase [15]. cmc of sds decreases in the presence of salts (figures 3 & 4) because salt ions interact with the surfactant's head group. as salts are added, the electrostatic repulsive force between polar head groups of sds molecules is reduced by shielding micelle charge, resulting in more tightly packed spherical micelles, which reduces the cmc [16]. the increase in degree of dissociation after the addition of salts may be due to the increased in the number of unbound counterions in sds solution [17]. in regard to standard free energy of micellization of sds in the presence of salts, the standard free energy of micellization becomes less negative in presence of k2so4 and more negative in presence of niso4, indicating that micelle formation becomes less spontaneous in case of k2so4 and more favourable in case of niso4. such type of behaviour infers that micellization becomes less favourable in presence of k2so4 and more favourable in presence of niso4 [18]. table 1 also shows the values of premicellar (s1) and postmicellar slopes (s2) drawn from the graphs of specific conductance with the concentration of sds with salts (k2so4, niso4) in aqueous system. with the addition of salts, these two slopes are changed which leads to difference in physicochemical properties of solution [19]. conclusion the micellization behaviour of sodium dodecyl sulphate in aqueous solution in presence and absence of salts was investigated conductometrically. the critical micelle concentration decreased when salts were added. this decreased in the values of the cmc is due to the interaction of salt ions with the head group of the surfactant. it was also found that degree of dissociation of sds increased when salts were added. also, ∆gm o was found less negative in presence of k2so4 and more negative in presence of niso4. references [1] a. aliet et al., critical micelle concentration and self_aggregation of hexadecyltrimethylammonium bromide in aqueous glycine and glycylglycine solutions at different temperatures, russ. j. phys. chem. a.86 (2012)1923-1929. https://doi.org/10.1134/s0036024412130031 [2] m. c. celia et al., mixed micelle formation between an amino acid-based anionic gemini surfactant and bile salts, ind. eng. chem. res. 53(2014)10112−10118. https://doi.org/10.1021/ie5003735 sur fac tan t salts cm c (m m) α ∆gm o (kj/mol ) s1 s2 k2s o4 5.1 0.55 -33.40 51.2 28. 4 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acetone-water mixtures at different temperatures, sn appl. sci.2(2020)1295. https://doi.org/10.1007/s42452-020-3036-1 [19] s. k. shah et al., micellization of cationic surfactants in alcohol-water mixed solvent media, j. mol. liq. 222 (2016) 906-914. https://doi.org/10.1016/j.molliq.2016.07.098 https://doi.org/10.1007/s42452-020-3036-1 https://doi.org/10.1016/j.molliq.2016.07.098 bibechana 18 (2) (2021) 61-67 61 radon study around earthquake affected areas of nepal bipin rijal1, nigam s. silwal1, govinda chaudhary2, pitamber shrestha2, buddha r. shah1,* 1physical science laboratory, faculty of science, nepal academy of science and technology (nast), khumaltar, lalitpur, gpo 3323 kathmandu, nepal 2department of physics, amrit science campus, thamel, kathmandu, nepal *e-mail: buddharshah25@gmail.com article information: received: july 3, 2020 accepted: march 13, 2021 keywords: indoor radon annual effective dose earthquake lr 115 ssntd abstract indoor radon concentrations were measured in dwellings of the earthquake affected areas of kathmandu valley, gorkha and sindhupalchowk districts of nepal using passive radon dosimeter lr115, a solid-state nuclear track detector, ssntd. the radon concentrations in dwellings of kathmndu valley ranged from 11±6 bq/m3 to 135±26 bq/m3 with mean of 67.63 bq/m3. for gorkha it ranged from 18±7 bq/m3 to 363±65 bq /m3with an average of 104.64 bq/m3while minimum, maximum and average radon concentrations for sindhupalchowk were 14±6 bq/m3, 397±71 bq/m3and 78.46 bq/m3 respectively. the average annual effective dose to the inhabitants of kathmandu valley, gorkha and sindhupalchowk districts were calculated as 1.46 msv/y, 2.26 msv/y and 1.69 msv/y respectively. these annual doses were well below the action level of 10 msv/y recommended by international commission on radiological protection (icrp) which implies no significant radiological health hazards. also, excess lifetime cancer risk and lungs cancer cases per year per million people were determined. doi: https://doi.org/10.3126/bibechana.v18i2.29840 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction radon rn-222 is a radioactive gas derived from uranium-238 decay series. uranium is a ubiquitous radioactive element present in varying amount in rock, soil and air. radon has a half-life of 3.8 days that is sufficient for it to migrate through pore space in the soil and rock into dwellings. despite being a member of noble gases, it spontaneously decays into very high alpha emitters such as polonium-218 and polonium-214. radon and its progenies represent more than 50% of the total natural radiation of human exposure to ionizing radiation [1]. radon is considered as carcinogenic to human [2]. it stands second to cause lungs cancer after tobacco smoking in general population [3]. apart from lungs cancer, mailto:buddharshah25@gmail.com https://doi.org/10.3126/bibechana.v18i2.29840 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana bipin rijal et al. / bibechana 18 (2) (2021) 61-67 62 radon exposure is also responsible for various noncancerous diseases like stroke, heart disease and diseases related to respiratory and digestive system [1,4]. studies on risk assessment of radon, both in mines and dwellings, have shown several health effects [5,6] and the regulatory requirement has been advised to control public exposure due to radon indoors [7]. an earthquake of magnitude 7.6 struck on 25th april 2015 in nepal and was followed by several aftershocks [8]. gorkha district, kathmandu valley and sindhupalchowk district were the most affected by this earthquake. the cracks and fissures developed on soil due to earthquake or landslides are supposed to enhance radon exhalation from soil [9-12]. as nepal is prone to earthquake, the assessment of radon concentration has become necessary as a baseline study for future investigation. therefore, assessment of the indoor radon concentrations has been carried out starting from those most affected areas. in addition, the annual effective dose along with any cancerous risk associated with this radon exposure has been estimated around the earthquake-affected areas of nepal. 2. materials and methods 2.1. study area kathmandu valley, gorkha and sindhupalchowk were selected for this study. kathmandu valley is comprised of three districts kathmandu, lalitpur and bhaktapur and is the capital city of nepal located at 27o 42' n and 85o 18' e with an average altitude of 1292 m. gorkha district, the other location is about 80 km northwest of kathmandu valley with an average altitude of 1900 m from sea level having coordinates 28o12' n and 84o44' e. the epicenter of 2015 earthquake was in gorkha. sindhupalchowk, the third location, is 60 km east from kathmandu with an average elevation of 1450 m located at 27o46' n and 85o43' e. 2.2. methodology solid state nuclear track detector, a passive radon detector (lr-115 type ii, dosirad, france) was employed for radon concentration measurement. each detector consists of 12 µm thick cellulose nitrate film coated on a 100 µm polyester base. the film of the detector can record alpha particles of energy range 0.1 mev to 4.8 mev [13]. fig.1:map of study areas. a total of 90 dosimeters were fixed in the dwellings of study area out of which 68 detectors were retrieved. the detectors were placed on ground floor approximately 1.5 m above the ground level and were exposed for about 100 days (may to august, 2017). the detectors were read at dosirad, france. exposed films were etched on 10 % analytical grade naoh bath for about 75 to 100 minutes at constant bath temperature of 60oc. after this, films were washed by acidified water (hcl upto ph 3) for 30 minutes and final rinse of around 2 minutes at 20oc by distilled water was done. the etched tracks were counted using a binocular optical research microscope at magnification 400x. the radon concentrations were used to calculate annual effective dose (aed) using the unscear, 2000 model [1]. bipin rijal et al. / bibechana 18 (2) (2021) 61-67 63 aed msv/yr = crn × e × t × d where, crnradon concentration (bq/m3). e-indoor equilibrium factor (0.4; [1,7]) t-time in hours per year spent indoor d-dose conversion factor (9nsv/bq.h.m3; [1]) 6000 hours per year was considered to be total time spent indoors by the inhabitants following a questionnaire. excess lifetime cancer risk (elcr) was calculated as [14]. elcr = aed×dl×rf where, dlduration of life (70.2 years; [15]) rffatal cancer risk per sievert (5.5×10-2; [16] ) lung’s cancer cases per year per million people (lcc) were calculated as [17]. lcc = aed×18×10-6 3. results and discussions 3.1. radon concentrations the indoor radon concentrations were measured in dwellings of different places of kathmandu valley, gorkha and sindhupalchowk districts, which are shown in figure 2, 3 and 4 respectively. as radon concentrations generally follow a log normal distribution [14] the measured radon concentrations also were log-normally distributed (at 0.05 level, shapiro-wilk test). fig.2: radon concentrations in dwellings of kathmandu valley. radon concentrations varied in different dwellings in kathmandu valley with the lowest concentration of 11±6 bq/ m3 to highest of 135±26 bq/ m3. the arithmetic average, geometric average and median value for the concentrations were 67.63 bq/m3, 57.26 bq/ m3and 66 bq/ m3 respectively. out of studied 16 dwellings of kathmandu valley 81% of dwellings had radon concentration below 100 bq/ m3 and remaining 19% had in between 100-150 bq/ m3. fig.3: radon concentrations in dwellings of gorkha. the minimum, maximum and average radon concentrations in gorkha districts were 18±7 bq/m3, 363±65 bq/m3 and 104.64 bq/m3 respectively with geometric mean of 80.63 bq/m3 and median value 76 bq/m3. in gorkha, 61% of the dwellings had concentrations below 100 bq/m3, 36% have concentrations in between 100-300 bq/m3 and remaining 3% had concentrations above 300 bq/m3. the indoor radon concentration in sindhupalchowk ranged from 14±6 bq/m3 to 397±71 bq/m3 with an arithmetic mean of 78.46 bq/m3, geometric mean of 60.78 bq/m3 and the median value of 65.5 bq/m3. in this district, 79% of dwellings had concentrations below 100 bq/m3, 17% were in between 100-300 bq/m3 while only 4% were above 300 bq/m3. bipin rijal et al. / bibechana 18 (2) (2021) 61-67 64 a comparative representation of radon concentrations in gorkha, kathmandu and sindhupalchowk has been shown in the figure 5. it is observed that radon concentrations in gorkha and sindhupalchowk were comparatively higher than those of kathmandu valley. the variation in radon concentrations might be due to difference in topography of locations, ventilation systems and building materials used in the dwellings [9, 10]. the permissible limit for radon concentration is 300 bq/m3[18] and in this study only two of the measurements, 397±71 bq/m3 (sindhupalchowk) and 363±65 bq/m3 (gorkha), were observed above the limit. both the dwellings were old aged, made from mud with several cracks, fissures and fractures due to devastating earthquake. furthermore, poor ventilation system was also observed in both cases. fig.4: radon concentrations in dwellings of sindhupalchowk. the overall average radon concentration of study locations was 83.57 bq/m3 which is lower than those reported in the dwellings of hemavathi river basin, karnatak, india (99.35 bq/m3;[9]), lahore and islamabad, pakistan (135.25 bq/m3 and 112.5 bq/m3 respectively; [19, 20] ), shenyan and gansu, china (115.7 and 222.9 bq/m3respectively; [21] ), nationwide average of korea (102 bq/m3; [22] ), nationwide average of u.k. (101 bq/m3; [23] ), fredicton and halifax of canada (138 bq/m3and 259bq/m3 respectively; [24] ). however, the average of this study was higher than those calculated in the dwellings of kathmandu valley, nepal (80 bq/m3; [25, 26]), nationwide average of japan (14.3 bq/m3; [27]) and indoor radon of meghalaya, india (59.9 bq/m3; [10]) . in addition this average was slightly more than double the world average indoor radon concentration of 40 bq/m3[1]. the higher radon concentrations in some dwellings might be due to following reasons.  cracks, fissures and fractures in the basement and wall of the house due to earthquake  higher uranium content in the soil  high permeability and porosity of bedrock  some old houses built from mud and wood  poor ventilation condition in some houses  some houses built on old landslide deposits fig.5: box plot of radon concentrations. bipin rijal et al. / bibechana 18 (2) (2021) 61-67 65 3.2. annual effective dose the radon concentrations obtained in the study of kathmandu valley, gorkha and sindhupalchowk districts were used to estimate the annual effective dose (aed) to the inhabitants using unscear, 2000 model. the aed due to radon received by residents of kathmandu valley, gorkha and sindhupalchowk districts are shown in figure 6, 7 and 8 respectively. fig.6: annual effective dose for kathmandu valley. fig.7: annual effective dose for gorkha. the dose in dwellings of kathmandu valley varied from 0.24 msv/y to 2.92 msv/y with an arithmetic average of 1.46 msv/y. for gorkha dose were reported to lie between 0.39 msv/y and 7.84 msv/y with an average of 2.26 msv/y. similarly, for sindhupalchowk, the dose ranged from 0.30 msv/y to 8.58 msv/y with an average of 1.69 msv/y. relatively higher doses were observed in gorkha which might be attributed to geological variations and nearness to the epicenter of 2015 earthquake. the average doses of all three study locations were higher than the world mean dose from environmental radon of 1.15 msv/y [1]. however the average doses were below the action level of 3 to 10 msv/y [7,16]. fig.8: annual effective dose for sindhupalchowk. the average aed was used to determine excess lifetime cancer risk (elcr), which was calculated as 0.56%, 0.87% and 0.65% for kathmandu valley, gorkha and sindhupalchowk respectively. the conversion factor of 18 10-6 /msv [17] was used to determine indoor radon induced lungs cancer risk. the lungs cancer cases per year per million persons were 26.28, 40.68 and 30.51 for kathmandu valley, gorkha and sindhupalchowk respectively. 4. conclusion the radon concentrations in kathmandu valley, gorkha and sindhupalchowk districts were measured and aed of the study areas were calculated. relatively higher dose were observed in gorkha. the annual doses due to radon were below icrp recommended action level of 10 msv/y. thus, bipin rijal et al. / bibechana 18 (2) (2021) 61-67 66 there are no significant radiological health hazards to the population and the immediate counter measures are not necessary. however increased ventilation system of houses can be suggested to further reduce the radon concentrations in the dwellings. all the study areas lie in mid hilly region of nepal where it is very cold during november to march. as the present study was carried out during summer, it is recommended to have indoor radon measurements in winter season when poor ventilation system is expected which might attribute to higher radon concentrations. acknowledgments the authors gratefully acknowledge nepal academy of science and technology (nast) in funding the research work. we are also thankful to the dosirad laboratory, france for track analysis. owners of the dwellings of study area are also highly appreciated. references [1] united nations scientific committee onthe effects of atomic radiation, sources and effects of ionizing radiation. unscear 2000 report to the general assembly, with scientific annexes, unscear, new york, (2000). 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[27] g. suzuki et al., a nation-wide survey on indoor radon from 2007 to 2010 in japan, journal of radiation research 51(6) (2010) 683–689. https://doi.org/10.1269/jrr.10083 https://doi.org/10.1177/1420326x15588567 https://doi.org/10.1002/ijc.11683 https://doi.org/10.1093/rpd/ncq567 https://doi.org/10.1269/jrr.10083 devendra sir cover page copy.jpg bibechana 17 (2020) 1-12 1 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal hydrophobicity of small alkane molecules (propane dimer) in solvents: a classical molecular dynamics study bikash panthi, nurapati pantha * central department of physics, tribhuvan university, kirtipur, kathmandu, nepal * email: npantha@tucdp.edu.np article information received: july 17, 2019 accepted: august 29, 2019 keywords: hydrophobicity potential of mean force propane dimer abstract molecular dynamics (md) simulations of propane dimer in different solvents (water, acetonitrile and methanol) were performed by using charmm platform for modeling the solute and solvents. a series of umbrella sampling md simulations were carried out in each solvent separately and potential of mean force (pmfs) were calculated by using weighted histogram analysis method. results show that two minima (contact minima and solvent separated minima) characterize the pmf of propane dimer in all three solvent environments. the contact minima are deeper and less sensitive to solvent environment for its position. however, significant effect in the position of second minima, solvent separated minima, was observed. our study reveals that the interaction between propane dimer is softer in methanol and acetonitrile than in water. 1. introduction the organic compounds were once considered to be obtained from living organisms only. it was believed that only a special force, existing in living organisms, called vital force could produce the organic compounds. however, urea and many other compounds found in living organisms were later on synthesized in lab without vital force. this led to the synthesis of organic compounds as hydrocarbons: compounds with basic components hydrogen and carbon [1]. propane is a saturated hydrocarbon with three carbon atoms bonded together with single covalent bonds along with eight hydrogen atoms. the molecular formula of propane is c3h8. the angle between two c-c bonds is 112 0 . the separation of carbon atoms is 153 pm and the bond length between carbon and hydrogen atoms is 111 pm [2]. hydrophobicity the exclusion of water molecules due to the aggregation of non-polar substances in aqueous solution is called hydrophobic effect [3]. hydrophobic hydration and hydrophobic interactions are indicated by the term hydrophobic effect. hydrophobic interactions refer to the solvent induced interactions between the apolar this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.25504 http://nepjol.info/index.php/bibechana mailto:npantha@tucdp.edu.np https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.25504 bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 2 solutes whereas hydrophobic hydration deals with the change in water structure in presence of non polar solute[4]. when the highly dynamic hydrogen bonds get disrupted, hydrophobic interactions are originated [5]. the hydrophobic effect is responsible for effects related to biology including cell membranes and vesicles formation, protein folding, insertion of membrane proteins into the non-polar lipid environment and protein [6]. for the proteins that have hydrophobic amino acids, hydrophobic effect is important to understand their structure. proteins try to minimize the number of hydrophobic side chains exposed to water by forming a hydrophobic core covered by hydrophilic components. this tendency to reduce the number of side chains that are in contact with water provides a major contribution for folding process [7]. md simulations of propane dimer in water have shown a deeper contact minima and a shallower solvent separated minima in the potential of mean force (pmf) curve [8]. potential of mean force hydrophobic interactions are described in terms of potential of mean force (pmf). this potential is useful to get the average force acting over all the configurations of the given system [9]. basically, pmf is the free energy profile along a reaction coordinate and is determined through the boltzmannweighted average over all degrees of freedom other than the reaction coordinate [10]. in other words pmf enables us to observe free energy changes with respect to some particular coordinates like solute-solute separation. the shape of pmf curve in the presence and absence of solvent environments is different. this difference in the pmf profile enables the use of pmf curve to analyze the solvent effect in solute-solute interactions. if distance between two particles r is taken as reaction coordinate then pmf w(r) is related to the radial distribution function g(r) as: w(r) = −kbt ln g(r) + const. (1) the constant is chosen such that the most probable distribution corresponds to a free energy of zero magnitude. if w (r) denotes the free energy change of the system then the relation between pmf and free energy is given by, w(r) = w (r) + 2kbt ln r + const. (2) this equation shows that the free energy change of the system is not equal to the change in pmf. distinction between them is very important while comparing with experiments and relating various approaches used for the study. 2. computational details modeling of system molecular dynamics is computer simulation method for studying the physical movement of atoms and molecules. the inadequacy of the crystallographic images to provide information on dynamic features, lack of technique to provide high resolution in time and space, and the tedious experimental method require a new approach to follow the movement of individual molecules [11]. method of computer simulation aims to fulfill this need. molecular dynamics simulations are used to compute the equilibrium and transport properties by using process similar to the real experiments. we prepare the sample by selecting a model system with n particles and solve newton’s equation of motion for this system until we are assured that the properties of the system no longer change with time [12]. we have for the i th particle with mass mi, position ri experiencing force fi, newton’s equation of motion is: 𝑚𝑖 𝜕2𝑟𝑖 𝜕𝑡2 = −∇𝑖𝑈(𝑟) = 𝐹𝑖 . (3) equation (3) provides us with the relation between potential energy and the rate of change in position. thus with the model of potential energy u(r) of the system under study, integration of this equation yields trajectory of the system describing the positions, velocities and accelerations of particles with time. the total potential energy of a system is sum of bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 3 − − all interaction potential energy: 𝑈𝑡𝑜𝑡𝑎𝑙 = 𝑈𝑏𝑜𝑛𝑑 + 𝑈𝑎𝑛𝑔𝑙𝑒 + 𝑈𝑝𝑟𝑜𝑝𝑒𝑟 + 𝑈𝐿𝐽 + 𝑈𝐶𝑜𝑢𝑙𝑜𝑚𝑏 (4) where the terms in right hand side represent potentials due to bond, angle, proper dihedral, lennard-jones and coulomb interaction respectively. simulation set up molecular dynamics simulations were performed for three different systems (water-propane, acetonitrile propane and methanol-propane). propane has three carbon atoms covalently bonded with each other. the carbon atoms complete their valence shell by sharing electrons with hydrogen atoms. there are two methyl groups (ch3) and one methylene group (ch2) in propane. all bonded and non-bonded interactions were taken into account to make our system as real as possible. we also use lj parameters to consider the van der waals interaction. all the interactions were parameterized by using charmm force field parameters. detail information about the solvents used for the simulations is presented in table 1. fig.1: sample of system under study (waterpropane). table i: partial charge and mass of each atom in solvents. solvents atoms partial charge mass ow -0.8476 15.9994 water hw 0.4328 1.008 hw 0.4328 1.008 c1 -0.17 12.011 h11 0.09 1.008 acetonitrile h12 0.09 1.008 h13 0.09 1.008 c2 0.36 12.011 n3 -0.46 14.007 cb -0.04 12.011 hb1 0.09 1.008 methanol hb2 0.09 1.008 hb3 0.09 1.008 og -0.65 15.9994 hg1 -0.42 1.008 a cubic box of size 4 nm was taken in each of the three cases and was filled with the system (propane and solvent).our system for simulation is ready after adding the solute and solvent in the box. figure 1 is the sample of our system after adding the solute and solvent in the box. however, the forces acting on molecules might be large and may result failure in md simulation. to avoid this, we bring the system into equilibrium by performing energy minimization. after achieving energy minimization for the system, we bring the system to the state of thermo dynamical equilibrium. this is done because the dynamical variables that we intend to study change along with parameters like pressure, density, temperature and so on. suitable thermostats are used to obtain thermal equilibrium. a process called temperature coupling is used to do so. similarly, pressure coupling is done by using suitable barostat in order to obtain constant pressure [13]. we did equilibration in two steps. at first equilibration was done in nvt ensemble to attain thermal equilibrium and was followed by equilibration in npt ensemble to maintain bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 4 constant pressure (density). this equilibration was done by using md integrator. the simulation was done for 200 ps by taking step size of 0.001 for 200000 steps. the output control parameters specify when to write the position, velocity, energy and force in trajectory file. for coulomb interaction we used particle mesh ewald (pme) with 0.12 fourier spacing along with cut-off distance of 1 nm. the simulations were intended for 298 k so the reference temperature is specified as 298 k for all simulations. to perform temperature coupling we use v-scale thermostat. in nvt equilibration pressure coupling was kept off. lincs was used as constraint algorithm. nvt equilibration was followed by equilibration in npt ensemble. this equilibration was done for 1 ns. the parameters were specified as in nvt equilibration however pressure coupling was done in addition using berendsen barostat. after equilibration of the system, a series of configuration were generated along the reaction coordinates. these configurations were then run in independent simulations. for generating configuration, we performed a pulling simulation for different windows. we then selected the frames based on their spacing and prepared for umbrella sampling. a short equilibration was then performed on the configuration of sampling windows. umbrella sampling and production run for every window were performed by following the procedure of molecular dynamics simulation. the data collected from umbrella sampling was subjected to analysis by extracting potential of mean force using wham (weighted histogram analysis method). 3. results and discussion the propane dimer modeled by specifying the parameters was kept inside a cubic box along with solvents water, acetonitrile and methanol respectively. the simulations were carried out for time period of 10 ns. in this section we discuss the structural properties of the system by analyzing the radial distribution function and the hydrophobic interactions in terms of potential of mean force. propane dimer in water the simulation has been carried out with 2160 water molecules and 2 propane molecules in the box size of 4 nm. after performing umbrella sampling, potential of mean effective force (pmef) was determined by using wham. we then applied volume entropy correction to obtain potential of mean force (pmf). the system is shown in figure 2 and the potential of mean effective force between the solutes in water is shown in figure3. fig. 2: propane-water system. fig 3: the potential of mean effective force calculated by means of umbrella sampling for water-propane system. the first minima seen at 0.49 nm represents the minimum energy distance. this distance is the equilibrium distance between the molecules in the absence of solvent environment. this minima bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 5 resembles the lj potential minima and is also regarded as contact minima. the contact minima is the position of minimum energy where the solute (propane) molecules come in contact with each other. similarly the position of desolvation barrier represents the position when the solvent molecules are just about to penetrate the solute. likewise, the position of solvent separated minimum resembles a layer of solvent in between the solutes. the contact minima is followed by a hump representing the desolvation barrier which ends at 0.84 nm, i.e the position of second minima. the decreasing nature of pmef has caused the second minima to be indistinct in absence of volume entropy contributions. for larger separations, the system becomes unstable as shown by the decreasing slope of pmef curve. we apply volume entropy correction in pmef to obtain pmf. the volume entropy correction is given by 2kbtln(r) and is shown in figure 4. the boltzmann’s constant is taken to be 0.002 kcalmol −1 k −1 and temperature (t) is 298 k. when the volume-entropy correction was done for the same system, we obtained the graph for potential of mean force with correction as in figure 5. fig. 4: the volume entropy correction term and pmef shown together. as discussed before, the observed contact minima at position 0.49 nm is followed by the hump. further, second minima is seen at 0.84 nm just at the end of hump. the addition of volume entropy correction term 2kbtln(r) with the pmef (figure 3) line gives the potential of mean force. the pmf line has distinct second minima at 0.83 nm. fig. 5: the potential of mean effective force calculated by means of umbrella sampling for propane dimer in water. this minima is also called solvent separated minima as it is the distance between the propane molecules separated by a layer of water between them. in other words, the second minima is the effect of solvent environment. the depth of contact minima is -0.58 kcal/mol and the solvent separated minima is -0.14 kcal/mol. structure of system radial distribution function is used to analyze the structure of solvent. the rdf of solvent describes the equilibrium structure of the water molecules in simulation box. since, we have used spc/e model for water in our simulation, the hydrogen atoms in water do not take part in lj interaction with any other atoms. rdf of central carbon of propane and oxygen of water (c2-ow) figure 6 shows the rdf gc2−ow (r) at 298 k temperature. oxygen atom of water is taken as reference and is allotted a position at origin. the position of carbon atom with reference to this oxygen atom is studied with the help of figure 6. bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 6 rdf shows first peak at 0.48 nm which is the most probable position of the closest carbon atom with respect to the reference propane molecule. similarly, the second peak at 0.758 nm represents the position for second solvation shell. beyond the second peak the rdf is a straight line with unit fig. 6: rdf gc2−ow (r) for central carbon atom of propane with oxygen of water as reference. value. the region up-to the distance of 0.294 nm is the exclusion region. this is the region around the reference atom without the possibility of presence of another atom. the value of sigma (σ) for the atoms (ow-c2) is 0.327 nm and the van der waals radius corresponding to this value of σ is 0.367 nm. the value of excluded region is less than the van der waals radius, which is in agreement with the theory that no particle can be found in the excluded region. the dashed line in the graph is the line fitted for tenth order polynomial. rdf of oxygen of water and oxygen of water (ow-ow) figure 7 depicts the rdf gow −ow (r) at 298 k. this rdf represents the probability of finding the oxygen atoms at a distance (r) around the reference oxygen atom. in figure the reference oxygen atom is at zero (origin) and first peak represents the oxygen atoms closest to the reference oxygen atom. the radial distribution function is essentially zero between origin (zero) and the molecular separation. the second peak is the position of the second closest atom and so on. fig 7: the rdf gow−ow, oxygen atom of water with another oxygen atom from reference water molecule. as seen in figure 7, three distinct peaks of height 3.088, 1.110, and 1.051 are obtained at distances 0.274 nm, 0.446 nm, and 0.684 nm respectively at 298 k. this implies that the oxygen atom is at a distance 0.274 nm from the reference atom. beyond the third peak the rdf is straight line with average value 1.the zero value of rdf from origin to the distance of 0.240 nm is the exclusion region. this is the minimum distance between the oxygen atoms and represents the intermolecular separation. the value of sigma (σ) for the atoms (owow) is 0.315 nm and the van der waals radius corresponding to this value of σ is 0.353 nm. here, the value of excluded region is less than the van der waals radius. rdf of oxygen of water and terminal carbon of propane (ow-c1) bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 7 to study the arrangement of terminal carbon atoms of propane around the oxygen atoms of water, we analyze the rdf gow −c1. figure 8 shows gow −c1. fig. 8: the rdf gow −c1, terminal carbon of propane with oxygen atom of water as reference. two distinct peaks are seen at 0.374 nm and 0.646 nm with height of 1.471 and 1.084 respectively. the first peak represents the position of terminal carbon closest to the reference oxygen. likewise, second peak represents the second closest atom. after, the second peak we can see a straight line with value 1. in this case, the exclusion region is seen up-to the distance of 0.290 nm. this implies that the terminal carbon of propane maintains at least this distance with the oxygen atom of water. the value of sigma (σ) for the atoms (ow-c1) is 0.327 nm and the van der waals radius corresponding to this value of σ is 0.367 nm. propane dimer in acetonitrile we took acetonitrile as solvent medium and per formed similar simulations and procedures just like in water. the following figure 9 shows our system and figure (10) shows the pmef and pmf of the system. the system was prepared by adding propane dimer in solvent environment of 676 acetonitrile molecules. whole process of simulation was repeated for this system just like in water to obtain the pmef and pmf curve depicting the contact minima along with solvent separated minima. fig. 9: propane-acetonitrile system. fig 10: the potential of mean effective force calculated by means of umbrella sampling for propane dimer in acetonitrile. in this case, the contact minima was seen at 0.50 nm followed by dissolvation barrier and solvent separated minima at 0.90 nm. these minima are seen to have shifted to a larger distance than water. the depth of contact minima and solvent separated minima are -0.47 kcal/mol and -0.10 kcal/mol respectively. structure of system as in water the structure of system was analyzed with the help of rdf. rdfs were used to bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 8 understand the radial distribution of molecules around a reference molecule. rdf of carbon (of -cn group) of acetonitrile with reference carbon atom (of -cn group) the figure 11 shows the radial distribution function of carbon atom (c2) of cyanide group of acetonitrile molecule with respect to the similar carbon atom (c2) taken as reference. the rdf represents the probability of finding the carbon atom at certain distance from the reference atom. fig. 11: the rdf gc2−c2, carbon of cyanide group with carbon of another cyanide group as reference molecule. in figure11 first, second and third peaks are seen at the distance of 0.492 nm, 0.834 nm and 1.196 nm respectively. the first peak represents the most probable position for the closest cyanide carbon with respect to the reference carbon atom. we thus can expect the first solvation shell at 0.492 nm, second at 0.834 nm and so on. after the third peak, the rdf is seen to be a straight line with unit value. the exclusion region is observed up-to 0.294 nm from the reference atom. from this rdf, it can be assumed that the atoms maintain a minimum distance of 0.294 nm between them. further, the value of sigma (σ) for the atoms (c2-c2) is 0.336 nm and the van der waals radius corresponding to this value of σ is 0.377 nm. the value of excluded region is less than the van der waals radius, which agrees with the theory that no particle can be found in the excluded region. rdf of carbon atom (of methyl group) of acetonitrile and terminal carbon of propane (c1-c1) the figure 12 shows the radial distribution function of terminal carbon of propane with reference to carbon atom of acetonitrile. the peaks represent the most probable positions for carbon of solute with another carbon of solvent as reference. fig. 12: the rdf gc1−c1, terminal carbon of propane with methyl carbon of acetonitrile as reference molecule. the rdf figure 12 shows the first and second peak positions at distances 0.406 nm and 0.834 nm with corresponding heights 1.761 and 1.140. after the second peak position rdf is a straight line with value unity. it means that the most probable position of terminal carbon of propane is at distance 0.406 nm from the reference atom. similarly, the second most probable position is at 0.834 nm. since there are only two propane molecules, it is logical to get two peaks only. as in other rdfs, exclusion region up-to 0.322 nm represents the region without any possibility of • bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 9 finding carbon atom of propane around the methyl carbon of reference molecule. the value of sigma (σ) for the atoms (c1-c1) is 0.339 nm and the van der waals radius corresponding to this value of σ is 0.380 nm. rdf of central carbon of propane and nitrogen of acetonitrile (c2-n3) following graph 13 depicts the position of nitrogen atom of cyanide group of acetonitrile with reference to the central carbon atom of propane. the reference carbon atom is considered to be at the origin and the corresponding probable positions of nitrogen are shown in graph. fig. 13: the rdf gc2−n3, nitrogen of acetonitrile with central carbon of propane as reference molecule. the first peak position at 0.454 nm is the most probable position of finding propane molecule with the peak height of 1.501 followed by second peak at distance 0.834 nm with height 1.180. the third peak is observed at position 1.064 nm and the rdf curve gains value of unity thereafter. the exclusion region shows that the atoms are maintaining a distance of at least 0.3 nm between them. the value of sigma (σ) for the atoms (c2-n3) is 0.334 nm and the van der waals radius corresponding to this value of σ is 0.375 nm. the dashed line in the graph is the line fitted for tenth order polynomial. propane dimer in methanol methanol was also considered as a solvent media for the same solute dimer of propane. figure 14 shows our system of methanol and propane dimer. this system was prepared by adding propane dimer in 943 methanol molecules. the calculations were performed as in case of water and acetonitrile to obtain the graph for pmf. the resulting graph for pmef and pmf after volume fig .14: propane-methanol system. entropy correction is demonstrated in figure (15). the pmf curve shows the first minima at 0.53 nm and second minima at 0.96 nm. these minima have shifted towards larger distances than in water and acetonitrile. similarly, the depth of contact minima and solvent separated minima are fig. 15: the potential of mean effective force (pmef) and potential of mean force (pmf) calculated by means of umbrella sampling for propane dimer in methanol. • bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 10 -0.55 kcal/mol and -0.01 kcal/mol respectively. structure of system the structure for this system was also analyzed with the help of rdf curve. the positions of the peaks were used to estimate the position of molecules around each other. rdf of carbon and carbon of methanol (cb-cb) the rdf of carbon atom present in methyl group of methanol with carbon from another methanol molecule, represented by figure 16 has the peak positions at 0.404 nm, 0.786 nm and 1.160 nm representing the position of first, second and third solvation shell respectively. the distance of 0.306 nm is the distance between the atoms as represented by exclusion region of rdf. the rdf in this region has a zero value because it is the distance around the reference atom that has no possibility of finding another atom under observation. the value of sigma (σ) for the atoms (cb-cb) is 0.339 nm and the van der waals radius corresponding to this value of σ is 0.380 nm. the value of excluded region is less than the van der waals radius, which agrees with the theory that no particle can be found in the excluded region. the peak positions are seen at distances 0.508 nm, 0.87 nm and 1.314 nm representing the first shell, second shell and so on. the exclusion region with zero value of rdf is observed up-to 0.322 nm, representing the minimum distance that the atoms maintain between them. the value of sigma (σ) for the atoms (cb-c2) is 0.339 nm and the van der waals radius corresponding to this value of σ is 0.380 nm. the value of excluded region is less than the van der waals radius. the dashed line in the graph is the line fitted for tenth order polynomial. the obtained results for all the solvent environment are tabulated in table ii. e1 and e2 are in kcal/mol and represent the depth of contact minima and solvent separated minima respectively. comparison of pmf in water, acetonitrile and methanol fig. 16: the rdf gcb−cb, carbon of methanol with carbon of reference methanol molecule. fig. 17: the rdf gcb−c2, central carbon atom of propane with carbon of methanol as reference atom. comparing structures of pmfs and their contact minimum, it is seen that contact minimum is stiffer in water rather than that in methanol and acetonitrile. the presence of methyl group in both solute and solvent (in case of methanol and acetonitrile) might have caused competitive interaction between similar groups. • bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 11 this results wider (shallower) contact minima in such cases. further investigations are to be done to have better understanding of this result. table ii: details of pmf curve for propane dimer in different solvents. figure 18 shows that the addition of solvent does not have greater effect on position of contact minima but it shows distinct effect on the solvent separated minima. the pmf curve shows a characteristic shape with deep minima at about 0.49 nm, 0.50 nm and 0.53 nm for water, acetonitrile and methanol respectively. the comparison of the obtained results for propane dimer in water with the previous works shows good agreement. in the reference [5] the position of contact minima and solvent separated minima are 0.49 nm and 0.82 nm respectively. our result for position of contact minima (0.49 nm) corresponds with the reference and the result for position of second minima (0.84 nm) shows a discrepancy of 2.4% [8]. this discrepancy might be due to the difference in the model of solvent used in the reference and in our work. in contrast to the tip3p model of water and amber force field used in reference we used spce model of water in charmm force field. conclusions and concluding remarks molecular dynamics simulations of systems containing a propane dimer and different solvents (water, acetonitrile and methanol) were carried out. classical md simulations were done using gromacs and charmm force fields. umbrella sampling was done for biased sampling and wham was used for unbiasing the potential. we obtained the pmf curve for each system and observed its characteristic shape. the pmf curve possessed its characteristic shape with two distinct minima along with dissolvation barrier. the results for propane-water system were compared with previous works. comparison shows a good agreement in the position of contact minima (at 0.49 nm) and a small fig. 18: the potential of mean effective force calculated by means of umbrella sampling for propane dimer in water (solid line), acetonitrile (dotted dash line) methanol (dotted line). discrepancy (of 2.4%) in the position of solvent separated minima (at 0.82 nm in reference and 0.84 nm in our work). with satisfactory results in water medium we conclude that the results for other two mediums are also reliable. further, we observed the shifting of solvent separated minima towards larger distance for acetonitrile and methanol than in water, as in the reference works. in this study, we observed the solvent perturbation on non-polar solute-solute interactions and the results were compared with previous works to study the size effect of hydrophobic interactions. in future, this work can be further extended to study the effect of temperature, shape of solvent environment or solvents contact minima (nm) e1 kcal/mol solvent separated minima (nm) e2 kcal/mol water 0.49 -0.58 0.84 -0.14 acetonitrile 0.50 -0.47 0.90 -0.10 methanol 0.53 -0.55 0.96 -0.01 bikash panthi and nurapati pantha/bibechana 17 (2020) 1-12 12 solvents other than water, acetonitrile and methanol. similar studies can also be done in alkanes like butane, pentane. acknowledgements this work was supported by university grants commission (ugc), nepal. references [1] fromm j. richard: introduction to the alkanes, revised may 1998. http://www.3rd1000.com/chem301/chem301j.htm [2] f. a. carey, carey: organic chemistry, 5 th ed., the mcgraw-hill companies, new york, 2004. [3] v. gold, k. l.loening, a. d. mcnaught, and p. shemi, iupac compendium of chemical terminology, blackwell science, protein chem. oxford, 1997. [4] d. paschek, heat capacity effects associated with the hydrophobic hydration and interaction of simple solutes: a detailed structural and energetical analysis based on molecular dynamics simulations, j. phys. chem. 120(22) (2004) 10605-10617. https://aip.scitation.org/doi/abs/10.1063/1.1737294 [5] t. p. silverstein, the real reason why oil and water don't mix, j. chem. educ.75 (1) (1998) 116-118. https://pubs.acs.org/doi/abs/10.1021/ed075p116 [6] w. kauzmann, some factors in the interpretation of protein denaturation, adv. 14 (1959) 1-63. https://www.sciencedirect.com/science/article/abs/ pii/s0065323308606087 [7] k. a. dill, dominant forces in protein folding, biochem. 29(31) (1990) 7133-7155. https://pubs.acs.org/doi/10.1021/bi00483a001 [8] m. makowski, c. czaplewski, a. liwo, and h. a. scheraga, potential of mean force of hydrophobic association:  dependence on solute size, j. phys. chem. b. 111 (2007) 1076510774. https://pubs.acs.org/doi/abs/10.1021/jp070594t [9] http://www.gromacs.org/documentation/how tos/potential-of-meanforce [10] s. park and k. schulten, calculating potentials of mean force from steered molecular dynamics simulations, j. chem. phys. 120 (13) (2004) 5946-5961. https://aip.scitation.org/doi/10.1063/1.1651473 [11] a. hazel and j. c. gumbart methods for calculating potentials of mean force, 2015. https://www.ks.uiuc.edu/training/tutorials/scienc e/channel/channel-tut_old.pdf [12] d. frenkel, b. smit, understanding molecular simulations from algorithms to applications, academic press, new york, 2002. [13] m. j. abraham, d. van der spoel, e. lindahl, b. hess, and the gromacs development team, gromacs user manual version 5.0beta 1, www.gromacs.org, 2013. http://www.3rd1000.com/chem301/chem301j.htm https://aip.scitation.org/doi/abs/10.1063/1.1737294 https://pubs.acs.org/doi/abs/10.1021/ed075p116 https://www.sciencedirect.com/science/article/abs/pii/s0065323308606087 https://www.sciencedirect.com/science/article/abs/pii/s0065323308606087 https://pubs.acs.org/doi/10.1021/bi00483a001 https://pubs.acs.org/doi/abs/10.1021/jp070594t http://www.gromacs.org/documentation/howhttps://aip.scitation.org/doi/10.1063/1.1651473 https://www.ks.uiuc.edu/training/tutorials/science/channel/channel-tut_old.pdf https://www.ks.uiuc.edu/training/tutorials/science/channel/channel-tut_old.pdf http://www.gromacs.org/ vinod kumar mahaseth / bibechana 13 (2016) 121-131: rcost p. 121 (online publication: dec., 2015) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal food and feeding habit of tor putitora of mahakali river, nepal vinod kumar mahaseth department of zoology, mmam campus, tribhuvan university, biratnagar, nepal email: vkmahaseth1962@gmail.com article history: received 07 november, 2015; accepted 29 november, 2015 doi: http://dx.doi.org/10.3126/bibechana.v13i0.13983 abstract t.putitora is a sight feeder and can be categorized as column feeder, which at some stage resorts to bottom feeding as well. depending upon the availability of food, the fish consumes a wide spectrum of dietary items varying from microscopic organisms and macrophytes to large number of insects and even small fishes. the feeding activities of t. putitora appeared to be good during pre-spawning (pre-monsoon) and postspawning season while poor during monsoon or spawning season, which is directly related to the availability of food and maturation of gonads. the estimation of gsi (gastro-somatic index) also supported this fact. ©rcost: all rights reserved. keywords: mahakali river; tor putitora; gut. 1. introduction: tor putitora which is commonly known as mahseer or sahar or golden mahseer. in nepal mahseer is known as ‘sahar’, which means a big fish. it has large scales. it is a superior game fish. live adult mahseer is olive green at the top of the head and back. its lateral line is generally silvery golden. the scales on the lateral line are marked with dark colour at their bases. the fins are generally yellow and rimmed with orange red. the lips of the adult mahseer are thick and are beset with horny tubercles. its barbels are quite short. only four barbels are present ones being the maxillary longer than the rostral ones. feeding is one of the most important functions of an organism. the basic functions of an organism, like growth, development, reproduction all take place at the expense of the energy, which enters the organism in the form of its food. feeding activity influences the growth and productivity of fishes. therefore, the study of food and feeding habits of a fish is very important. important contributions on food and feeding habits of the different fishes have been made by hynes [1], alikunhi [2], das and moitra [3], menon and chacko [4], vashist [5], george [6], kamal [7], agrawal and tyagi [8] jan and das [9], majkowski and waiwood [10], bahuguna and singh [11]. some work on food and feeding habits has also been done by pathani [12], nautiyal [13], sundar et al.[14], sharma [15], dasgupta [16], bhanja et al. [17], hossain et al. [18], basade and kohli [19], joadder and hossain [20], vinod kumar mahaseth / bibechana 13 (2016) 121-131: rcost p. 122 (online publication: dec., 2015) dadebo [21], shinkafi et al. [22], manon and hossain [23], kanwal and pathani [24], omondi et al.[25], and sharma et al.[26]. but there is no relevant literature on food and feeding habits of mahseer inhabiting mahakali river. the present investigation is the first attempt to study the feeding habit of mahseer in its habitat. during the study period qualitative and quantitative food analysis, seasonal variations in the food items, gastrosomatic index (gsi), feeding intensity and relative length of the gut (rlg) of mahseer were observed. study area mahakali river originates from indo-nepalese glaciers, milan glacier of india and lipu-lekh of nepal. the river leaves the mountains near tanakpur and is now known as sarada in india. later, it reaches sharada barrage, where it is considerably wider. mahakali then enters into nepal at chandani and flows through nepal upto dodhara, after which it enters into indian territory, finally confluencing with the ghaghara. the present studies were conducted at the chandani and dodhara v. d. c. (village development committee). they are the v. d. c. of kanchanpur district near the bank of mahakali river. the study area lies between longitude 80025’ east and latitude 28035’ north. four stations (a, b, c and d) were selected. first station ‘a’ is an upper station, which is near at purnagiri temple of syavle bajar. second station ‘b’ is 4 kilometres from station a. third station ‘c’, which is 4 kilometres from station b. fourth station ‘d’ is a lower station, which is 4 kilometres from station c. 2. materials and methods the present study was carried out for a period of two years. the period from september 2003 to august 2005 was used to collect the fishes. gut analysis: the samples were collected fortnightly; total length was recorded up to the nearest centimetre and the weight up to gram. the gut of each fish was removed, the weight of the gut and gut contents were also recorded and preserved in 5 % formaldehyde for analysis. the gut content of each fish was transferred in to a petridish and examined under a microscope. each food item was sorted out and identified. the food item per fish was examined by the frequency of occurrence method and point’s method of hynes [1]. qualitative analysis and food volume: in this method food items were sorted out and were identified up to genus level only. food volume was measured in partially filled graduated cylinder. the entire gut content was kept in 10-125 ml graduated measuring cylinder. the settling was done for 24 hours, after which the volume was read and recorded for each fish, in the catches of each fortnight. the fullness of stomach was classified as very full, ¾ full, ½ full, ¼ full and empty. the points were awarded for each category as 20, 15, 10, 5 and 0, respectively. the resultant fullness index was based on mean number of points, which was calculated by the total number of the awarded points divided by the number of stomachs examined in each fortnight. this vinod kumar mahaseth / bibechana 13 (2016) 121-131: rcost p. 123 (online publication: dec., 2015) depends on eye estimation of distension of intestinal bulb confirmed by ratio of the capacity of the intestinal bulb to total food. quantitative analysis quantitative study of fish food in each intestinal bulb was measured by hynes [1] method. for quantitative accuracy only the intestinal bulb content was considered as gut content. the sedgwick rafter method was used for counting each food item and was given a point, according to their size as seen in sedgwick rafter slide, using a research microscope. gsi (gastro somatic index) was calculated by following formula: total weight of the alimentary canal of fish gsi = x100 total weight of fish length of entire alimentary canal rlg = length of fish in fresh condition 3. results qualitative monthly fluctuation in food items the identified food items are listed in tabl 1. the identified food items were grouped under 12 categories, chlorophyceae, cyanophyceae, bacillariophyceae, xanthophyceae, protozoa, rotifera, crustacea, fish parts, insects, unidentified plant matter, unidentified animal matter and sand and debris.the chlorophyceae, cyanophyceae, bacillariophyceae were found throughout the year during entire study period and are considered as preferred food. xanthophyceae was found only in three months during the first year and two months in second year from the gut of tor putitora. protozoan, rotifers, crustaceans, fish parts and insects were found in low amount in few months of both years (table 2 & 3). quantitative monthly fluctuation in food items: chlorophyceae the group chlorophyceae consisted of chlorella, ankistrodesmus, gonatozygon, scenedesmus, mougeotia, chlamydomonas, periastrum, spirogyra, desmidium, coelastrum, cylindocystis, coefastrum, dictyosphaerium, ulothrix and cladophora. this group occurred throughout the investigation in the gut of t. putitora. during the first year, it varied from a minimum of 12.40 % (september 2003) and maximum of 43.10 % (february 2004). in second year, this alga varied from minimum 19.23 in december 2004 and maximum 39.13 % in the month of may 2005 (table 4 & 5). the important constituents of this alga were chlorella, spirogyra, and gonatozygon. the annual mean percentages of these algae were 28.58 and 25.94 during first and second year, respectively (table 4 & 5). cyanophyceae the maximum contribution of cyanophyceae was recorded during the month of october 18.62 % and minimum 4.31 % in the month of february during the first year while in second year, the maximum value was recorded 17.47 % in the month of march and minimum 7.24 %in the month of september (table 4 & 5). microcystis was the most prevalent form of this group. the annual mean percentage of this group was vinod kumar mahaseth / bibechana 13 (2016) 121-131: rcost p. 124 (online publication: dec., 2015) 11.55 % and 12.54 % during first and second year, respectively (table 4 & 5). cyanophyceae was recorded throughout the study period. bacillariophyceae bacillariophyceae was the second most important alga which was found throughout the twenty four months of the study period, in the gut of t. putitora. the percentage value of bacillariophyceae varied from 5.78 % (june 2004) to 33.61 % (april 2004) during the first year while in second year, it varied from 9.63 % (august 2005) to 32.29 % (february 2005). the important diatoms were diatoma and synedra which were found almost throughout the study period. the annual mean percentages of this group were 20.92 % and 22.39 % during first and second year, respectively (table 4 & 5). xanthophyceae this group of alga was rarely found in the gut of t. putitora. xanthophyceae was found only in the months of april, may and july during the first year while in september and january in second year of investigation. tribonema and tetraedriella were important forms of this group. the annual mean percentages of this group were 0.84 and 0.24 % during first and second year, respectively (table 4 & 5). protozoa this group of food item was found during several months in the entire study period, but in little amount. the peak of this group was observed in the month of july 6.29 % and february 12.50 % during first and second year, respectively. this group was represented by paramecium, spirostomum and verticella. the annual mean percentages of this group were 2.67 and 3.17 during first and second year, respectively (table 4 & 5). rotifers this group was represented by keretella, nothalca, rotaria, brachionus, philodina, mytilina and dinobryon but kiretella was the important form of this group. rotifers were observed throughout the year during first year while they have absent from january 2005 to march 2005 during the second year. the peak of this group was observed in the month of june (15.70 %) and september (10.14 %) during first and second year, respectively. the annual mean percentages of this group were 8.01 in first and 5.40 % during second year (table 4 & 5). crustaceans crustaceans were observed in several months, during the period of investigation. daphnia and cyclops were main form of this group. the peak of this group were observed in the month of june (10.74 %) and december (16.34 %) during the first and second year, respectively. the annual mean percentages of this group were 5.23 and 4.40 during respective year (table 4 & 5). fish remains only in the month of september, some parts of fish were observed in the gut of t. putitora, during the first year. in second year of observations, they were found in various months (september. october, january, april, june) while absent in the remaining seven months of the year. the annual mean percentage of fish parts was very low (0.55 %) during the first year while 2.85 % during the second year (table 4 & 5). insects some parts of insects were found in the gut of t. putitora in few months (december, january and august) of first year. in second year, they were present in the month of september, december, january, march, vinod kumar mahaseth / bibechana 13 (2016) 121-131: rcost p. 125 (online publication: dec., 2015) may and august. the peak of this group was observed in the month of august in both years. the annual mean percentages were 1.27 and 3.57 during first and second years, respectively (table 4 & 5). unidentified plant matter this group of food item was observed in decayed or semi decayed state. it was found in appreciable quantities throughout the year during whole study period. its percentage of occurrence was highest in the month of october (11.76 % and 10.52 %) during both years of investigation. the lowest value of this group was 3.14 % in the month of july 2004 and 1.94 % in the month of march 2005 during respective years. the annual mean percentages were observed 6.41 and 6.33 during first and second year, respectively (table 4 & 5). unidentified animal matter this group of food item was observed in a decayed or semi decayed state like unidentified plant matter. it was also found throughout the year during investigation. its percentage of occurrence was highest in the month of february (8.62) and lowest in the month of april (3.36) during the first year while in second year, the highest value was observed in the month of may (6.52 %) and lowest in the month of april (1.98 %). the annual mean percentages were 5.72 and 3.62 during first and second years of observations (table 4 & 5). sand and debris the sand and debris were observed within the gut content throughout the year. their percentage varied from 3.42 (january 2004) to 18.69 (august 2004) and 2.98 (january 2005) to 26.50 (august 2005) during the first and second years of investigation, respectively (table 4 & 5). the peak was observed in the month of august (monsoon) during whole study period, when turbidity was as its peak. gastro-somatic index the gastro-somatic index (gsi) is a relationship between weight of alimentary canal and weight of fish, which helps in determining the feeding condition in different months and seasons. the average gastrosomatic index of t. putitora ranged from 1.33 to 4.59 during the first year while 1.65 to 4.73 in second year of the study. the peak of gastro-somatic index was observed during the pre monsoon season (april 2004 and march 2005) when the plankton was as its peak during the entire study period (fig 1). gastro-somatic index was as high as 3.44 and 3.08 during post-spawning season in the month of november and december during the first year of study. in the second year of observation, the gastro somatic index was as high as 3.69 and 3.90 in the same month during postspawning season like first year (fig 1). the general picture emerges that voracious feeding takes place during post spawning season and whenever plenty of food items were available in the river. relative length of gut the length of intestine varies from fish to fish, but for a particular species, it has a definite relation with length of fish which helps to determine the feeding habits of the fish species. relative length of gut (rlg) differs in different stages of life history of fish. the relative length of gut values of t. putitora varied from 1.48 to 2.18 during the first year while in second year its value ranged between 1.32 to 2.07 (fig 2). the maximum values were obtained in the months of january (2004) and may (2005) during the first and second year of study, respectively. the minimum values were obtained in the months of may (2004) and july (2005) during the respective years of study period. the quantitative food and study of the vinod kumar mahaseth / bibechana 13 (2016) 121-131: rcost p. 126 (online publication: dec., 2015) alimentary canal show, this fish to be more of a herbivore than an omnivore. therefore, t. putitora has been categorized to be of herbi-omnivorous nature. 4. discussion nikolsky [27] classified the food of fish into four categories basic, secondary, accidental and obligatory food. the basic food of t. putitora constitutes phytoplankton specially chlorophyceae (28.58 % during first year and 25.94 % in second year), bacillariophyceae (20.92 % in first year and 22.39 % in second year), cyanophyceae (11.55 and 12.54 % during first and second year, respectively). the rotifers, protozoans, crustaceans and insects comprise the secondary food, which were found frequently in the gut but in small amounts. fish parts and xanthophyceae group of phytoplankton were observed as accidental food in the gut of t. putitora. the sand and debris were also present throughout the year but in small amount. the food and feeding habits and adaptations of the gut have been worked out by many authors. it is a fact that the vegetable matter requires more time for digestion, hence herbivorous fishes have higher rlg (relative length of gut) value than omnivorous fishes. in the present study, two years mean of rlg value of t. putitora was 1.73. on this basis, t. putitora may be kept in the category of herbi omnivorous fishes. this observation is in conformation with the observations made by das and pathani [28], who have considered t. putitora to be a herbi-omnivore on the basis of rlg value, percentage of food items and position of the bile duct. the herbi-omnivorous nature of t. putitora has been considered to be a peculiar example of evolutionary transition from herbivorous to omnivorous nature (das and pathani, [28]). however, the result of present study differs from the opinion of badola and singh [29], who have categorized t. putitora to be a carni omnivorous fish. in the present study, the maximum feeding intensity in t. putitora was recorded during pre-monsoon as well as pre-spawning season (april 2004 and march 2005), during which the planktons were plenty in number. during the post spawning season also (november and december), the feeding intensity was high (3.44, 3.08 and 3.69, 3.90 during first and second year, respectively). high feeding intensity during prespawning is due to maturation and enlargement of the gonads while during post-spawning it may be due to spent and starved condition of the fishes. feeding intensity is correlated with the postspawning period and the availability of food in the river mahakali, which confirms the view of malhotra [30], jyoti and malhotra [31], and jyoti [32]. during monsoon season (july and august) shortage of food items in the mahakali river and the abdomen being filled with mature gonads may be the reason for lowering of feeding intensity. in general, the gsi is maximum during the post spawning period when plenty of food items are available and minimum during the breeding season when food materials become less. therefore, it may be concluded that t. putitora of mahakali river feeds voraciously during pre-spawning when plenty of food items are available followed by the post-spawning season when its abdomen becomes empty due to spent phase. vinod kumar mahaseth / bibechana 13 (2016) 121-131: rcost p. 127 (online publication: dec., 2015) acknowledgements thanks are due to the campus chief of s.n.science campus, mahendranagar for providing the necessary facilities to present work. the author is thankful also to dr. (mrs.) manju lata bisht, department of zoology, d.s.b. campus, kumaun university, nainital for her valuable guidance. table 1: list of food items found in the gut of t. putitora during 2003/05. species chlorophyce chlorella sp. ankistrodesmus sp. gonatozygon sp. scenedesmus sp. mougeotia sp. chlamydomonas sp. pediastrum sp. spirogyra sp. desmidium sp. coelastrum sp. cylindrocystis sp. dictyosphaerium sp. ulothrix sp. cladophora sp. cyanophyceae microcystis sp. chroococcus sp. aphanizomenon sp. spirulina sp. anabaena sp. bacillariophyceae diatoma sp. asterionella sp. synedra sp. gomphonema sp. gyrosigma sp. tabellaria sp. navicula sp. fragilaria sp. cymbella sp. xanthophyceae tribonema sp. tetraedriella sp. chrysoamphitrema sp. protozoa paramecium sp. spirostomum sp. vorticella sp. rotifera keratella sp. notholca sp. rotaria sp. brachionus sp. philodina sp. mytilina sp. crustacea daphnia sp. cyclops sp. chirocephalus sp. orchestia sp. fish parts insects unidentified plant matter unidentified animal matter sand and debris vinod kumar mahaseth / bibechana 13 (2016) 121-131: rcost p. 128 (online publication: dec., 2015) table 2: monthly average no. of different food items (groups) in gut of t.putitora during 2003/04. month sep . oct. nov. dec. jan. feb. mar. apr. may jun. jul. aug. totalfood groups chlorophyceae 15 22 39 47 49 50 33 35 27 29 32 27 405 cyanophyceae 19 19 14 08 13 05 11 12 13 17 15 15 161 bacillariophyceae 30 14 21 25 43 26 36 40 23 07 21 12 298 xanthophyceae 05 03 04 012 protozoa 03 04 02 04 03 07 08 06 037 rotifera 11 08 06 05 06 08 10 12 08 19 09 10 112 crustacea 07 08 06 11 09 10 13 11 075 fish parts 08 008 insect 04 08 07 019 unidentified plant matter 10 12 09 08 07 08 07 05 06 07 04 06 089 unidentified animal matter 08 07 08 09 06 10 06 04 07 06 05 04 080 sand & debris 10 08 07 06 05 05 06 06 07 16 18 20 114 total 121 102 112 123 146 116 109 119 107 121 127 107 1410 table 3: monthly average no. of different food items (groups) in gut of t.putitora during 2004/05. month sep. oct. nov. dec. jan. feb. mar. apr. may jun. jul. aug. totalfood groups chlorophyceae 32 22 28 20 35 26 33 29 36 23 21 16 321 cyanophyceae 10 08 13 12 21 15 18 14 08 09 13 14 155 bacillariophyceae 32 21 23 27 31 31 29 26 14 21 18 08 281 xanthophyceae 02 02 004 protozoa 02 03 02 12 03 12 04 038 rotifera 14 09 09 02 08 09 02 09 05 067 crustacea 08 07 06 17 13 02 06 059 fish parts 07 06 08 09 07 037 insect 07 08 10 08 06 07 046 unidentified plant matter 08 10 09 07 05 03 02 07 06 09 06 05 077 unidentified animal matter 04 03 05 06 05 04 03 02 06 02 03 02 045 sand & debris 12 06 07 05 04 05 07 06 05 15 18 22 112 total 138 95 102 104 134 96 103 101 92 88 106 83 1242 vinod kumar mahaseth / bibechana 13 (2016) 121-131: rcost p. 129 (online publication: dec., 2015) table 4: monthly average percentage of different food items (groups) in gut of t.putitora during 2003/04. month food groups sep. oct. nov. dec. jan. feb. mar. apr. may jun. jul. aug. average chlorophyceae 12.40 21.56 34.82 38.21 33.56 43.10 30.27 29.41 25.23 23.96 25.19 25.23 28.58 cyanophyceae 15.70 18.62 12.50 6.50 8.90 4.31 10.09 10.08 12.14 14.04 11.81 14.01 11.55 bacillariophyceae 24.79 13.72 18.75 20.32 29.45 22.41 33.02 33.61 21.50 5.78 16.53 11.21 20.92 xanthophyceae 4.20 2.80 3.14 0.84 protozoa 2.47 3.92 1.78 3.45 2.80 5.78 6.29 5.60 2.67 rotifera 9.09 7.84 5.35 4.06 4.10 6.89 9.17 10.08 7.47 15.70 7.08 9.34 8.01 crustacea 5.78 7.84 5.35 8.94 6.16 9.34 10.74 8.66 5.23 fish parts 6.61 0.55 insect 3.25 5.47 6.54 1.27 unidentified plant matter 8.26 11.76 8.03 6.50 4.79 6.89 6.42 4.20 5.60 5.78 3.14 5.60 6.41 unidentified animal matter 6.61 6.86 7.14 7.31 4.10 8.62 5.50 3.36 6.54 4.95 3.93 3.73 5.72 sand & debris 8.26 7.84 6.25 4.87 3.42 4.31 5.50 5.04 6.54 13.22 14.17 18.69 8.17 vinod kumar mahaseth / bibechana 13 (2016) 121-131: rcost p. 130 (online publication: dec., 2015) table 5: monthly average percentage of different food items (groups) in gut of t.putitora during 2004/05. month food groups sep. oct. nov. dec. jan. feb. mar. apr. may jun. jul. aug. average chlorophyceae 23.18 23.15 27.45 19.23 26.11 27.08 32.03 28.71 39.13 26.13 19.81 19.27 25.94 cyanophyceae 7.24 8.42 12.74 11.53 15.67 15.62 17.47 13.86 8.70 10.22 12.26 16.86 12.54 bacillariophyceae 23.18 22.10 22.54 25.96 23.13 32.29 28.15 25.74 15.21 23.86 16.98 9.63 22.39 xanthophyceae 1.45 1.49 0.24 protozoa 1.45 3.15 1.96 12.50 2.91 11.32 4.81 3.17 rotifera 10.14 9.47 8.82 1.92 7.92 9.78 2.27 8.49 6.02 5.40 crustacea 5.79 7.36 5.88 16.34 9.70 2.17 5.66 4.40 fish parts 5.07 6.31 5.97 8.91 7.95 2.85 insect 5.07 7.69 7.46 7.76 6.52 8.43 3.57 unidentified plant matter 5.79 10.52 8.82 6.73 3.73 3.12 1.94 6.93 6.52 10.22 5.66 6.02 6.33 unidentified animal matter 2.89 3.15 4.90 5.76 3.73 4.16 2.91 1.98 6.52 2.27 2.83 2.40 3.62 sand & debris 8.69 6.31 6.86 4.80 2.98 5.20 6.79 5.94 5.43 17.04 16.98 26.50 9.79 fig. 1: gastro-somatic index of t. putitor. vinod kumar mahaseth / bibechana 13 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[32] m. a. jyoti, j. inland fish. res. soc. india, 8 (1976) 24. bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal bibechana 19 (1-2) (2022) 127-132 electronic structure and magnetic properties of double perovskites ca2mniro6 shalika ram bhandari1,2, sarita lawaju1, santosh kc3, gopi chandra kaphle1 and madhav prasad ghimire1 * 1central department of physics, tribhuvan university, kirtipur, 44613, kathmandu, nepal 2leibniz ifw dresden, helmholtzstr. 20, 01069 dresden, germany 3chemical and materials engineering, san josé state university, california, usa * email: madhav.ghimire@cdp.tu.edu.np article information: received: january 30, 2022 accepted: february 26, 2022 keywords: density functional theory double perovskites electronic structure half metals spin-exchange coupling abstract using the density functional theory formalism, electronic and magnetic properties of double perovskites ca2mniro6 are investigated. we found ferrimagnetic ground state with half-metallic nature in ca2mniro6. the electron-correlation, crystal distortion, and spin-orbit coupling (soc) plays significant role in dictating the electronic properties in this system. from the density of states calculations, a strong hybridization were noted between o-2p, ir-5d and mn-3d states resulting ca2mniro6 to half-metal (hm) with metallic state in spin up channel and insulating state in spin-down channel. the hm state persists even when soc is taken into account, though the spin-polarization reduces slightly. we thus predict ca2mniro6 as a new hm ferrimagnet which can be useful for modern technological applications. we further investigated the curie temperature of ca2mniro6 by calculating the spin-exchange coupling parameters. our results are found to be comparable with other perovskites. doi: https://doi.org/10.3126/bibechana.v19i1-2.46404 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction the interest in double perovskite (dps) with chemical formula a2bb'o6 (where a = rare earth elements and b & b'= 3d and 4d/5d transition metals (tm)) are increasing due to their novel properties such as crystal field splitting, half-metallicity (hm), ferromagnetism (fm), ferrimagnetism (fim), mott insulating, multiferroicity, etc. [1-8]. these properties are found useful in device fabrication for technological applications. when chemical substitution is done to the b or b' site, they show additional properties relevant for spintronic devices [9-15]. among many, hm is one of the important property found in dps where one spin channel is metallic and the other one is insulating. one such application of hm gives rise to ultra-high density suitable for magnetic recordings. specifically, dp family containing tm oxides are found to attract researchers because of their unconventional phases [16-18]. for instance, iridate dps such as ln2mgiro6 shows magnetic transition from fm to 127 http://nepjol.info/index.php/bibechana mailto:madhav.ghimire@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v19i1-2.46404 https://creativecommons.org/licenses/by-nc/4.0/ bhandari et al. / bibechana 19 (1-2) (2022) 127-132 128 afm state [19,20], magnetic ordering in la2miro6 [21]. likewise, layered perovskites sr4co3o10 and sr4rh3o10 shows hm-fm state [22] while fim to hm-fim and hm-afm were observed in pr2 xsrxmgiro6 (x = 0 to 2) [23]. many dps are reported to have high curie temperature (tc) [24-26]. one such example is sr2croso6 whose tc is found to be 725 k [27]. in some of the dps such as ca2mwo6, sr2mwo6 and ba2mreo6, where m= co, ni, magnetic atoms at the b/b’ sites are 3d/5d and are found to carry opposite spin orientations. this is found to result in octahedral connection exhibiting large crystal distortion [28-30]. likewise, magnetic phase transition from afm to fim takes place when the a site element ca was substituted partly by la3+ [31]. in this work, we report the electronic, magnetic and exchange coupling in the new yet un-synthesized ca2mniro6. we provide the possibility that the material can be synthesized experimentally and suitable for spintronic applications due to sizable tc. crystal structure and computational details figure 1 shows the crystal structure of ca2mniro6 with space group p21/n and its monoclinic structure is maintained by mno6 and iro6 octahedra. the crystal parameters used for our calculations are a =5.351 å, b = 5.456 å, c = 7.620 å and β= 90.092 [32]. the symmetrized structure of ca2mniro6 with one atom each of ca, mn, ir and three oxygen was transformed to p1 space group consisting of 4 ca, two each of mn and ir and 12 oxygen atoms resulting to 20 in-equivalent atoms within a unit cell. the density functional theory (dft) calculations is performed using the full-potential linearized augmented planewave (flapw) method as implemented in the wien2k code [33]. the standard generalized gradient approximation (gga) within the parametrization of pbe scheme was used for the exchange-correlation energy [34]. in order to consider the electron-electron correlations in tms, the hubbard potential u of 6 ev and 1.5 ev were used for mn and ir, respectively [35, 36]. spin orbit coupling (soc) is also taken into account to compute the magnetic anisotropy energy (mae). the atomic sphere radii (rmt) used for elements ca, mn, ir and o, were 2.14, 1.94, 2.01 and 1.64 bohr respectively. calculations are done with 8 x 8 x 6 k-mesh with energy and charge convergent criteria set to 10-8 ry and 10-5e. fig. 1: crystal structure (left) and ferrimagnetic ground state spin structure (right) of ca2mniro6. the grey, purple, gold and red spheres corresponds to ca, mn, ir and o atoms, respectively. 2. results and discussion we start first by calculating the total energies for the four magnetic configurations (i.e., fm-uuuu, fim uudd, afm1-udud, and afm2-uddu; where u represents up spin and d represents down spin alignment of magnetic ions). note that we have two atoms each of mn and ir whose magnetic configurations are arranged as mn1, mn2, ir1 and ir2, respectively. the magnetic arrangement, say fim-uudd implies the alignment of mn1-up, mn2 up, ir1-down, and ir2-down spins in fim configuration. from the above calculation, we found fim as the magnetic ground state. the discussion below is therefore focused for the fim configuration of ca2mniro6. in ca2mniro6, mn atom carries a charge state +3 with 3d3 configuration in which three electrons are distributed in the t2g state in spin up channel and lie in the valence region close to the fermi level (ef) while eg state being empty lies in the conduction region in both spin channel. on the other hand, ir with charge state +3 and 5d5 configuration has five outermost electrons. due to low-spin state, the five electron are found to occupy only the t2g states while eg states being empty lies in the conduction region for both spin channel. as can be seen in the partial dos of ir in fig. 2, the spin-up channel is metallic while spin down remains insulating. this is found consistent with the electron number count of five. this implies that 3 electrons in spin-down channel are fully occupied generating a band gap while two bhandari et al. / bibechana 19 (1-2) (2022) 127-132 129 out of three are occupied in spin up, and thus partially occupied dictating the metallic state. the spin resolved partial and total dos of ca2mniro6 within gga, gga+u and gga+u+soc are shown in fig 2 and fig 3. the role of partial dos near ef (fig. 2 (a) (left)) are contributed by mn-3d, ir-5d and o-2p states. here, ir-t2g states are in high spin state as shown in spin down channel while spin up channels are found to be in conduction region. the ir-5d states are found to hybridize strongly with o-2p states in the valence region. due to this hybridization, charge transfer effect was observed where charge is transferred from ir-5d to o-2p states giving rise to finite moments in oxygen atoms (see table 1). fig. 2: the dos of ca2mniro6 within gga and gga+u. the vertical dotted line indicates ef = 0. the combined effect of electron correlation and soc is found to generate a psuedo band gap (or a semi-metallic state) in the band structure as shown in fig. 3 (right). despite the strong soc strength of ir, crystal distortion seems to dominate resulting in the metallic state in spin up channel. soc effect is found prominent in ir as it belongs to heavier element. the ir-5d bands splits significantly as shown in fig 3 which can be well compared with gga+u results shown in fig. 2 (right). thus, with up spin channel being metallic and down spin channel being insulating, ca2mniro6 shows hm fim state which can be confirmed both from dos and band structure. focusing now on magnetic moment within effective magnetic moment of 4.15 µb per unit cell in the fim configurations. this difference in the magnetic moment is due to finite transfer of charges from mn and ir to oxygens. as a result, oxygen gain small moment (~0.06 µb) and get polarized. the orbital moment of ir is sizable as compared to mn while the spin magnetic moment is reduced on ir because of the ir-o hybridization. mae is also calculated and the obtained value is ~9 mev per unit cell with magnetic easy axis along [001] direction (c-axis). fig. 3: the dos and band structures of ca2mniro6 within gga+u+soc. table 1: calculated spin magnetic moments (in µb) of mn, ir, 3 oxygens and band gap eg (ev). the calculated orbital moments at mn and ir sites are shown within parentheses for ca2mniro6 compound. site gga gga+u ga+u+soc mn 2.84 2.93 3.06/-0.03 ir -0.57 -0.61 -0.62/ -0.24 o1 -0.05 -0.04 -0.06 o2 -0.05 -0.04 -0.06 o3 -0.05 -0.04 -0.06 net 3.25 4 4.15 eg metallic hm hm gga+u+soc (see table 1 for details), the individual magnetic moment of mn, and ir are calculated to be 3.06 µb, and -0.62 µb with an bhandari et al. / bibechana 19 (1-2) (2022) 127-132 130 fig. 4: magnetic exchange interactions in ca2mniro6. we also estimated the curie temperature (tc) of the material by utilizing the exchange parameters based on the heisenberg model of the mean-field approximation. the hamiltonian for the interaction of spins is given by, 𝐻 = − ∑ 𝐽𝑖𝑗𝑆𝑖 𝑆𝑗 𝑖𝑗 where, jij is the exchange coupling constant between spins at atomic sites i and j in the crystal, as shown in fig. 4. si and sj are the spin quantum number at i, and j sub-lattices. the tc of the proposed materials using the mean field theory is given by, 𝑇 = 𝑆 𝑆 2 ∑ 𝐽𝑖𝑗 . suggesting that this material as a suitable for application in the room-temperature regime. acknowledgments srb acknowledges nepal academy of science and technology, nepal for the phd fellowship. mpg thanks the avh foundation, germany for equipment grants and ifw-dresden, germany for providing equipment for scientific computations to tribhuvan university. srb and mpg thanks 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http://susi.theochem.tuwien.ac.at/ https://doi.org/10.1103/physrev.136.b864 doi: https://doi.org/10.3126/bibechana.v19i1-2.46404 1. introduction 127 2. results and discussion acknowledgments references conclusions microsoft word narayan final (91-104 ) sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p. 92 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal solvation free energy of light alkanes in polar and amphiphilic environments sunil pokharel, shyam prakash khanal, n. p. adhikari* central department of physics, tribhuvan university, kirtipur, nepal *email: npadhikari@gmail.com article history: received 3 may, 2018; accepted 22 september, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21136 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract computer simulations of molecular models are powerful technique that have improved the understanding of many biochemical phenomena. the method is frequently applied to study the motions of biological macromolecules such as protein and nucleic acids, which can be useful for interpreting the results of certain biophysical experiments. in this work, we have estimated the solvation free energy for light alkane (methane, ethane, propane and n-butane) dissolved in water and methanol respectively over a broad range of temperatures, from 275 k to 375 k, using molecular dynamics simulations. the alkane (methane, ethane, propane and n-butane), and methanol molecules are described by the opls-aa (optimized potentials for liquid simulations-all atom) potential, while water is modeled by tip3p (transferable intermolecular potential with 3-points) model. we have used the free energy perturbation method (bennett acceptance ratio (bar) method) for the calculation of free energy of solvation. the estimated values of solvation free energy of alkane in the corresponding solvents agree well with the available experimental data. keywords: alkane; free energy; molecular dynamics; bar. 1. introduction solubility, lack of solubility and other solvation properties of atoms, molecules and ions in aqueous solutions play a crucial role in biological processes and industrial applications. the free energy of solvation (specifically, hydration) is one of the most important properties in the study of solvent effects which determines solubilities, partition coefficients, association, dissociation, and binding constants, phase equilibria, and for transition states, reaction rates in many bio-chemical and physical processes [1]. for instance, protein folding occurs spontaneously because of a favorable change in the interactions between the protein and the surrounding water molecules. the folded proteins, caused by combined sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p. 93 (online publication: dec., 2018) effects of solvent and hydrogen bonding, are stable by 5-10 kcal/mol. the solvation is driven by minimizing the number of side-chains, exposed to water and hydrophobic in nature, covered by the folded protein at its centre [2]. the host-guest complexes, whose binding constant depends on solvent polarity, caused by hydrophobic pores present in host molecules also act as driving force for solvation [3]. furthermore, the interactions can be used in biological system to deliver the hydophobic drugs. hydration has effects on electronic and vibrational properties of biomolecule [4, 5]. computer simulation and modeling is performed in order to comprehend the properties of assemblies of molecules in terms of their structure and the microscopic interactions between them. in a classical framework, the main computational methods are molecular dynamics (md) and monte carlo (mc) simulations. molecular dynamics (md) simulation is a powerful approach for predicting and knowing the structure, function, dynamics, and interactions of atoms and molecules starting from a simple to complex systems in biophysical phenomenon of materials science study. these techniques are complement to conventional experiments, enabling us to learn something new, something that cannot be found out in other ways [6-11]. alkanes are saturated hydrocarbons that consist only of the elements carbon (c) and hydrogen (h), where each of these atoms are linked together exclusively by single bonds. alkanes belong to a homologous series of organic compounds in which the members differ by a constant molecular mass of 14 that is ch2 [12]. first four members (lighter alkanes) of alkane series are methane, ethane, propane, and butane with molecular formula ch4, c2h6, c3h8, and c4h10 respectively. the most important sources of alkanes are natural gas and crude oil. alkanes are non-polar solvents as only c and h atoms are present. methane, ethane, propane and n-butane are hydrophobic molecules, and as such its solubility in water is rather low, and they tend to aggregate when solvated in water, but freely soluble in non-polar solvent like ether and benzene. this behavior is more clearly exhibited by longer n-alkane chains, which may be considered as polymers of methane. the complicated organic compounds that once made up living plants or animals have transformed into a mixture of alkanes [12-16]. furthermore, the first four members of alkanes are also neutral analogs of amino acid side chain. amino acid side chain analogs represent a natural test case for biomolecular interaction [17, 18]. transport properties such as diffusion, viscosity and thermodynamic properties like free energy of hydration/solvation of hydrocarbons (alkanes) in aqueous environment is a basic consideration in many processes like processing of natural gases and petroleum, understanding the tertiary structure of proteins, as well as the important role it plays as a driving force in a number of processes occurring within living cells [19-21]. the free energy of hydration of light alkanes (a polar molecule) for a few temperatures and pressures have been repeatedly measured by computer simulations but the experimental values are rare. on the other hand, there is no literature data for the free energy of solvation of light alkanes in methanol (an amphiphilic molecule). so, we are motivated to calculate the free energy of hydration/solvation of light alkanes in water and ethanol molecules. our findings from the numerical simulation can also be used as a crude reference for any further studies of hydrophobicity and solubility of organic and inorganic substances in different solvent environments. the outline of the paper is as follows: in sec. ii, we discuss the theoretical background of the free energy of solvation and method of calculation. computational details of our work are stated in sec. iii. results of the work are presented in secs. iv. our conclusions are collected in sec. v. sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p. 94 (online publication: dec., 2018) 2. theoretical background a thermodynamic quantity equivalent to the capacity of a system to do work, the difference between internal energy of the system and the amount of energy that cannot be used to perform work, is known as free energy of the system. mathematically, the helmholtz free energy a�n, v, t� and the gibbs free energy g�n, p, t� are defined as: a = u − ts (1) g = a + pv = u − ts + pv = μn (2) where, u, s and µ are internal energy, entropy and chemical potential of the system respectively. the helmholtz free energy a�n, v, t� describes a closed, isochoric, isothermal assembly, so it is a function of temperature �t�, volume �v�, and number of molecules �n�. the gibbs free energy g�n, p, t� describes a closed isobaric, isothermal assembly, so it is a function of temperature �t�, pressure�p�, and number of molecules �n� [22, 23]. the chemical potential is given by μ = �������,� = �������,� (3) two ensembles are particularly useful for the calculations of free energy: the canonical �nvt� ensemble and the isobaric-isothermal �npt� ensemble. the helmholtz free energy and gibbs free energy are determined by the corresponding partition functions q defined by [22, 23]: a�n, v, t� = k� t ln q� �v, t� = �!"#$ ×% e'()*�+,,� dp dq (4) and g�n, p, t� = k� t ln q� �p, t� = �!"#$ ×% e'( � � q��v, t� dv (5) where β = 1/k� t, h4 is the unperturbed hamiltonian of the system and v is the volume. in simulation, the direct measurement of the free energy is not possible but difference in free energy can be calculated. for any other system differing in the hamiltonian by a perturbation of the potential energy�u�, h+ = h4 + u, the dfference in helmholtz free energy is, ∆a = a+ − a4 = −k� t ln �676*� (6) free energy calculations have a number of practical applications, of which some of the more common ones include free energies of solvation/hydration and free energy of binding for a small molecule to some larger receptor biomolecule (usually a protein). equilibrium free energy methodologies share the common strategy of generating equilibrium ensembles of configurations at multiple values of the scaling parameter λ. the commonly used methods are thermodynamic integration [24], adaptive integration [25], multistage free energy perturbation [26], and multistage equilibrium bennett analysis [27]. in gromacs, different approaches, including “slow-growth” can be used to calculate the free energy differences. in the “slow-growth” method, the hamiltonian of system, that changes slowly to remain in equilibrium from one system a to other system b, is modified by making the hamiltonian as function of coupling parameter λ as h�p, q; λ� such that h�p, q ; 0� = h��p, q� and h�p, q ; 1� =h��p, q�. the helmholtz free energy ;�n, v, t� in terms of partition function q is defined as [22, 23, 36]: a�λ� = −k�t ln q��v, t� = �!"#$ × % e'()*�+, ,; =� dp dq (7) where β= 1/k�t , h�p, q; λ� is the hamiltonian of the system. in order to calculate free energy difference, we define potential energy function which linearly depends on coupling parameters λ i.e. u� λ� such that, for λ = 0, u�� λ = 0� represents the potential energy of system a and u�� λ = 1�represents the potential energy of system b, then u�λ� = �1 − λ� u� + λu� = u� + λ� u� − u�� (8) sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p. 95 (online publication: dec., 2018) also, the derivative of helmoltz free energy eq. (7) with respect to coupling parameter λ and using eq. (8), we get the relation as: >�>= = % �?@?λ � abβ @�c,d;λ� >+ >,% abβ @�c,d;λ� >+ >, = 〈�)�=〉���;= = 〈�g�=��= 〉���;= (9) the 〈… 〉 brackets represent the ensemble average. after integrating the eq.(9) from λ = 0 to λ = 1 using thermodynamic integration (ti) method, we can evaluate the free energy difference between the system a and b as ∆a = a��v, t� − a��v, t� = % 〈�)�=〉���;= 4 dλ = % 〈�g�=��= 〉���;= 4 dλ (10) according to the bennett acceptance ratio (bar) [27] method, the ratio of partition function q0 for λ=0 and q1 for λ=1 is given by: 6*6i = 6* % j�k$� abβ�l*mli� >k$6i % j�k$� abβ�l*mli� >k$ = 〈j abnl*〉i〈j abnli〉* (11) where ‘w’ is an arbitrary weight function. in terms of ‘w’, the helmoltz free energy difference is given by β ∆a = ln〈w e'(g*〉 − ln〈w e'(gi〉4 (12) it is also possible to use bennetts method to combine the information normally used for forward and reverse free energy perturbations. in this approach, we compute the free energy difference between successive λ values δa according to the relation 〈p1 + e(�gqrmi�sr�'gqr�sr� – u�r�v' 〉=r = 〈p1 + e(�gqrmi�srmi�'gqr�srmi� w u�r�v' 〉=rw (13) then the sum of these δa i is the total helmholtz free energy difference [27], ∆a = ∑ δaz[' z\4 (14) 3. computational model a. molecular models the tip3p (transferable intermolecular potential with 3-points) model [28] is used in all the simulation for water as a solvent. the oplss-aa (optimized potentials for liquid simulations-all atom) potential model [29] is used for alkanes (methane, ethane, propane, n-butane) and methanol. the all atom model of the studied alkane system is shown in figure (1). the system under study consists of 1 alkane (methane, ethane, propane, n-butane) molecule and 596 water, and 1 alkane (methane, ethane, propane, n-butane) molecule and 354 methanol, a separate system separately. in classical force fields like opls-aa, the potential functions are derived empirically to describe the atomic interactions. the atoms are treated as spherically symmetric particles and are considered to be connected through covalent bonds to form molecules. each and every atom experiences a force resulting from its pairwise additive interactions with the rest of the system. the total potential energy u tot includes contributions from both bonded and non-bonded interactions [36]. the bonded interactions are bond stretching (2-body), bond angle (3body) and dihedral angle (4-body) interactions. a special type of dihedral interaction (called improper dihedrals) is used to force atoms to remain in a plane or to prevent transition to a configuration of opposite chirality (a mirror image). the non-bonded interactions are represented by the lennard-jones potential and coulomb potential. therefore, the total potential energy function of a system can be written as [36]: u]^] = u_^[>a> + u[^['_^[>a> = u_^[> + u`[aba + u>z"a>k`b + ucd + ue^fb (15) sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p. 96 (online publication: dec., 2018) fig. 1: pymol snapshots of light alkanes (a) methane, (b) ethane, (c) propane and (d) n-butane model used in this work. the bond stretching between two covalently bonded atoms i and j is represented by harmonic potential [36] u_^[>jrzlm = n kzl_jrzl − bzlmn (16) where kzl_ is the force constant andbzl is the equilibrium bond length between two atoms i and j. the bond angle vibration between a triplet of atoms i − j − k is also represented by a harmonic potential on the angle ɵzlq [ 36] u`[abajɵzlqm = n kzlqɵ jɵzlq − ɵzlq4 mn (17) where kzlqɵ is the force constant and ɵzlq4 is the equilibrium bond angle. the proper dihedral angle is defined as the angle between the ijk and jkl planes. in this study, we have used thefollowing dihedral potential (ryckaert-bellmans potential) [36] for alkanes: ur� = c4 + c �1 + cosφ� + cn�1 − cos2φ� + cx�1 + cos3φ� (18) where φ is the dihedral angle and c4, c , cn, cx are constants. the bonded parameters for water and alkanes are given in the table (i). sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p. 97 (online publication: dec., 2018) table i: force-field (bonded) parameters for tip3p water and opls-aa alkanes and methanol. the units of equilibrium bond length (b) and equilibrium bond angle (θ0) are nanometer (nm) and degrees (o) respectively. similarly, the units of k_, kɵ and cz �c4, c , cn, cx� are kjmol−1nm−2, kjmol−1rad−2 and kjmol−1 respectively. tip3p water kz)_ k)z)ɵ 502415.0 628.02 bz) ɵ)z)4 0.09572 104.52 opls-aa alkanes ke)_ kee_ k)e)ɵ k)eeɵ keeeɵ 284512.0 224262.4 276.144 313.800 488.273 be) bee ɵ)e)4 ɵ)ee4 ɵeee4 0.1090 0.1529 109.47 109.47 109.47 dihedral potential (alkanes) h-c-c-h h-c-c-c c-c-c-c c0 c2 c0 c2 c0 c2 0.62760 0.00000 0.62760 0.00000 2.92880 0.20920 c0 c2 c0 c2 c0 c2 1.88280 -2.51040 1.88280 -2.51040 -1.46440 -1.67360 dihedral potential (methanol) h-c-oh-ho h-c-c-c c-c-c-c c0 c2 c0 c2 c0 c2 0.94140 0.00000 0.62760 0.00000 2.92880 0.20920 c0 c2 c0 c2 c0 c2 2.82420 -3.76560 1.88280 -2.51040 -1.46440 -1.67360 the non-bonded inter-atomic interaction is the sum of lennard-jones interaction (ulj) and coulomb interaction (ucoul), that can be written as: u{((rzl� = 4ϵ{([���nkr� � n − ���nkr� �� ] + ,r� ,�n���*kr� (19) where rij is the cartesian distance between the two atoms i and j; α and β indicate the type of the atoms. the non-bonded parameters for alkanes and water is given in the table (ii). table ii: force-field (non-bonded) parameters for tip3p water and opls-aa alkanes and methanol. atoms σ�nm� ϵ(kj/mol) charge (q) tip3p water ow hw 0.315061 0.000000 0.636386 0.000000 -0.834 e +0.417 e opls-aa alkanes c(ch4) c(ch3) c(ch2) h 0.35000 0.35000 0.35000 0.25000 0.276144 0.276144 0.276144 0.125520 0.000 e 0.000 e 0.000 e 0.000 e opls-aa methanol c(ch3) c(ch2) oh ho 0.35000 0.25000 0.312000 0.00000 0.276144 0.125520 0.711280 0.000000 + 0.145 e + 0.040 e 0.683 e + 0.418 e sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p. 98 (online publication: dec., 2018) here ow and hw represent the oxygen and hydrogen atoms of the water molecules respectively and c(ch4), c(ch3) and c(ch2) are the methane, methyl and methylene carbon atoms of the alkane molecules respectively. similarly, oh and ho are oxygen and hydrogen atoms of hydroxyl group of methanol respectively. the parameters for the non-bonded lennard-jones interaction between two different atoms for opls-aa force field are written as [36]: σ{( = �σ{{ × σ((�i� (20) ϵ{( = �ϵ{{ × ϵ((�i� (21) b. simulation procedure molecular dynamics simulation was carried out in a cubic box with periodic boundary conditions [7] using gromacs 5.1.1 [37, 38, 47 ]. the distance to the edge of the box from the solute (alkane) is an important parameter for defining the size of the box. since we are using periodic boundary conditions, we must satisfy the minimum image convention. that is alkane (solute) should never see its periodic image, otherwise the forces calculated will be spurious. the size of the box defined here is sufficient for just about any cutoffi scheme commonly used in simulations. our system consists of, 596 water and 1 alkane molecule, 354 ethanol and 1 alkane molecule a separate system. after defining a system in a simulation box, energy minimization is carried out for each values of λ from 0 to 1, for 21 diffierent values to avoid unphysical van der waals contact caused by the atoms that are too close [36]. energy minimization brings the system to equilibrium configuration, removes all the kinetic energy from the system, reduces thermal noise in structure and brings the system to one of the local minimum. steepest descent algorithm followed by l-bfgs (limitedmemorybroyden-fletcher-goldfarb-shanno quasinewtonian-mimimizer) [30, 31] algorithm has been used for energy minimization [36]. this combination (steepest descent and l-bfgs) yields a thoroughly-minimized structure suitable for starting equilibration and subsequent data collection. the energy (potential) of the system after energy minimization is shown in figure (2). fig. 2: plot of potential energy as a function of time after energy minimization for methane-methanol system at λ=0 sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p. 99 (online publication: dec., 2018) after energy minimization, nvt equilibration of 5 × 105steps for 1 ns and isobaric-isothermal (npt) equilibration of 2.5 × 106 of 5 ns was carried out at different temperature, from 275k to 375 k and a pressure of 105 nm−2 by using velocity-rescaling thermostat [32] and berendsen barostat [33] at a coupling time τt = 1.0 ps and τp = 0.5 ps respectively. integration of the equations of motion were performed using an accurate leap-frog stochastic dynamics (sd) algorithm [34], and all bonds were constrained using linc algorithm [35]. during equilibration, the long range coulomb interaction is handled via the pme (particle mesh ewald) algorithm [39, 40] with fourier spacing 0.12 with a real space cutoffi of 1.2 nm and a pme order of 6. we monitored the temperature, pressure, density, and energy of each studied system to bring it in thermodynamic equilibrium. after equilibration run we performed the production run to calculate the equilibrium properties of the system, that is free energy of solvation for each values of λ by fixing the number of particles, volume and temperature i.e. nvt ensemble. we use velocity-rescale thermostat for this case. we don’t couple the system to a fixed pressure and use the structure obtained after equilibration run by which we fix the volume of the system. the production run was carried out for 1 ns with the time step of 2fs. 4. results and discussion using the computational details described above, free energy of solvation calculations were carried out in a cubic box in infinite dilution for two separate systems: (i) 596 tip3p water molecules and 1 opls-aa alkane (methane, ethane, propane and n-butane) molecule (ii) 354 opls-aa methanol and 1 opls-aa alkane (methane, ethane, propane and n-butane) molecule. the free energy of solvation of alkanes in diffierent solvent environments, water and methanol were estimated by eq.(14). the extent to which hamiltonian of the system has been perturbed is measured by the free energy change of transforming a system from state a (λ = 0) to state b (λ = 1), ∆a, as a function of a coupling parameter, λ. for decoupling van der waals interactions, we used an equidistant λ spacing of 21 diffierent λ’s from 0 to 1. thus, the free energy change from λ = 0 to λ = 1 is simply the sum of the free energy changes of each pair of neighboring λ simulations. the free energy changes of each pair of neighboring λ and the cumulative free energy change which is negative of free energy of solvation of butane in water is shown in figure (3). fig. 3: difference in free energy (∆a) and cumulative free energy diffierence (∆a) for diffierent λ points for simulation of butane in water at t = 300 k. sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p100 (online publication: dec., 2018) the calculated values of solvation free energy of alkane (methane, ethane, propane, n-butane) in water and methanol along with the references (if available) at different temperatures are presented in table (iii). there is good agreement between experimental values at 298 k and calculated values at 300 k of the solvation free energy of alkanes in water within 15 % error, but at higher temperatures there is no available experimental results. and there is no experimental available result for solvation free energy of alkanes in methanol. table iii: calculated and available experimental solvation free energies (kjmol−1) at different temperature of light alkanes in water and methanol. water methanol molecule t(k) calculated expt.[41] (298.15k) calculted ref. methane 275 300 325 350 375 8.33±0.05 9.08±0.12 10.01±0.14 10.32±0.09 10.63±0.07 -8.08 ---2.94±0.02 3.05±0.10 3.36±0.01 3.58±0.03 3.79±0.05 ----- ethane 275 300 325 350 375 8.22±0.14 9.02±0.19 11.12±0.07 11.20±0.10 11.52±0.10 -7.41 ---0.20±0.15 0.70±0.12 0.90±0.10 0.99±0.10 1.01±0.07 ----- propane 275 300 325 350 375 8.77±0.14 9.61±0.21 11.27±0.08 11.80±0.06 12.70±0.20 -8.28 ----2.73±0.21 -1.28±0.30 -0.93±0.16 ------- n-butane 275 300 325 350 375 9.10±0.13 10.99±0.18 11.82±0.11 12.95±0.20 13.93±0.11 -9.03 ----4.92±0.19 -3.77±0.18 -3.60±0.19 -2.75±0.16 ------ fig. 4: solvation free energy of alkanes in tip3p water at t=300 k. sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p101 (online publication: dec., 2018) fig. 5: comparision of calculated and literature values (reference (1) [42, 43], reference (2) [44] of solvation free energy of methane in water at different temperature. the comparison between the calculated values with error bars of solvation free energy of alkane in water at 300 k and the corresponding experimental values at 298 k is shown in figure (4). similarly, the comparison of calculated and literature values of free energy of solvation of methane in water at diffierent temperature in shown in figure (5) and tabulated in table (iv). the free energy of solvation of alkanes (methane, ethane, propane and n-butane) in methanol as a fuction of temperature is plotted in figure (6). table iv: calculated and reference (experimental and literature) values of solvation free energies (kj/mol) at different temperature of methane in water. molecule t(k) calculated ref.(1)[42, 43] ref.(2) [44] methane 275 300 325 350 375 8.33±0.05 9.08±0.12 10.01±0.14 10.32±0.09 10.63±0.07 6.95 8.21 9.58 -11.13 8.09 9.45 10.54 -11.78 the solvation process is considered to consist of two steps, (i) the formation of a repulsive cavity of appropriate size, and (ii) the introduction of the soa lute into this cavity. the positive values of calculated free energies of solvation (∆a) in tip3p water for all of the alkanes (methane, ethane, propane and n-butane) indicate their low solubilities in water that means alkanes are hydrophobic in nature. the simulations also show, in accordance with experiment, that ∆a decreases from methane to ethane, but then increases with increasing carbon number for longer up to butane at 300 k. this shows that the methyl group of alkane molecules have a preferential tendency to be dissolved in the vicinity of water molecules and that this tendency decreases with chain length. sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p102 (online publication: dec., 2018) fig. 6: solvation free energy of alkane in methanol at different temperature from t = 275 k to t = 375k. the increase in free energy of solvation with increase in temperature describes that the formation of repulsive cavity in water is perturbed by the thermal agitation of the water molecules. that means when temperature is incresed we dont have new interactions that are strong enough to introduce some important change in enthalpy and change in helmoltz free energy a is mostly connected with entropy or reordering of hydrogen bonds. by placing alkane in water we are perturbing the hydrogen bond network so that water molecules need to reorganize themselves around the solvent in a particular way that makes possible for average number of bonds for one molecule to remain constant. since hydrogen bonds are directional this leads to a smaller configurational space for water molecules and change in entropy will be negative 45, 46]. again , we have calculated free energy of solvation of alkanes in methanol at diffierent temperature. from table (iii) and figure (6), free energy of solvation ∆a in methanol becomes more negative as the alkane chain increases. the positive values of solvation free energy of methane and ethane shows that they are insoluble in methanol but the negative values of it for propane and butane indicates they are soluble in the methanol. methanol is amphiphilic organic substance. there is a competition between hybrophobic group (methyl-ch3) and a hydrophilic group (hydroxyl-oh). amphiphilic nature makes methanol interesting solvent because alkanes should show greater solubility in it than in water. for methane and ethane the hydrophobic groups dominates over the hydrophilic group, on the other hand for propane and butane the reverse situation occurs. 4. conclusions and concluding remarks in this work, we have computed free energy of solvation (helmholtz free energy a ) of alkane (methane, ethane, propane, n-butane) molecules in different solvent environments water as a polar and methanol as an amphiphilic solvent, for various temperatures 275 k, 300 k, 325 k, 350 k, 375 k, using molecular dynamics simulation technique. the transferable intermolecular potential with 3-points (tip3p) model of water and the optimized potential for liquid simulationsall atom (opls-aa) model of alkane and methanol were used. here alkane (methane, ethane, propane and n-butane) acts as a solute and water and methanol act as a polar and an amphiphilic solvent respectively. the free energy of solvation or hydration sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p103 (online publication: dec., 2018) of alkane in water is positive, and this values increases with increase in change length of alkanes. the calculated values of the free energy are in agreement with the available literature values. the free energy of solvation of alkanes in methanol shows different trends, it is negative for propane and butane but positive for methane and ethane. this shows that methane and ethane are insoluble whereas propane and butane are soluble in methanol. this study reports the first complete description of the solution thermodynamics calculating solvation free energy of alkanes in water and methanol by computer simulations, using bennet acceptance ratio (bar) method. this study could be the basis for understanding the biomolecular interactions and calculation of free energy of binding for a small molecule to some larger receptor biomolecule (usually a protein). in the near future, we also plan to study the solvation/hydration of a larger series of solutes and calculation free energy of binding between a ligand and a receptor in diffierent aqueous environment. acknowledgements s. pokharel acknowledges the receipt of the grant from the abdus salam international centre for theoretical physics, trieste, italy through the office of external activities (oea) for the phd studies. n.p. adhikari acknowledges the ugc award no. crg-73/74-s&t-01. s.p. khanal acknowledges the partical financial support from nepal academy of science and technology (nast), nepal. we further acknowledge the computing facilities by icq-13. references [1] t. p. straatsma, h. j. c. berendsen, and j. p. m. postma, free energy of hydrophobic hydration: a molecular dynamics study of noble gases in water, j. chem. phys. 85 (1986) 6720. 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[42] d. paschek, temperature dependence of the hydrophobic hydration and interaction of simple solutes: an examination of five popular water models, j. chem. phys. 120 (2004) 6674. sunil pokharel et al../ bibechana 16 (2019) 92-105 rcost p105 (online publication: dec., 2018) [43] r. f. prini and r. crovetto, j. phys. chem. ref. data, 18 (1998) 1231. [44] h. docherty, a. galindo, c. vega and e. sanz, a potential model for methane in water describing correctly the solubility of the gas and the properties of the methane hydrate, j. chem. phys. 125 (2006) 074510. [45] jianzhong wu and john m. prausnitz, pairwise-additive hydrophobic effect for alkanes in water, pnas 105 (2008) 9515. [46] michael h. abraham and enrico matteoli, the temperature variation of the hydrophobic effect, j. chem. soc., faraday trans. 1, 84 (1988) 1985-2000. [47] s. pokharel, n. pantha and n. p. adhikari, diffusion coefficients of nitric oxide in water: a molecular dynamics study, international journal of modern physics b 30 (2016) 1650205 bibechana 18 (1) (2021) 100-107 100 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal a spectroscopic study of the low redshift dwarf galaxy sdss j134326.99+431118.7 to calculate star formation rate daya nidhi chhatkuli1*, sanjaya paudel2, binil aryal1** 1central department of physics, tribhuvan university, nepal. 2centre for galaxy evolution research, department of astronomy, yonsei university, seoul, south korea. *email: chhatkulidn@gmail.com **email: binil.aryal@cdp.tu.edu.np article information: received: june 15, 2020 accepted: july 10, 2020 keywords: dwarf galaxy star formation rate characteristic peaks 𝐻𝛼 line abstract we present a spectroscopic study of an interacting emission-line dwarf galaxy sdss j134326.99+431118.7. we analyzed eight-strong emission lines of wavelength in a range of 3902.1å to 6619.1å. among them, the strongest emission line is oiii, with an intensity of 1043.6 x 10-17 erg/s/cm2/å. these characteristic lines show a perfect gaussian fit with a coefficient of regression greater than 98%, where the derived full width half maximum (fwhm) is less than 3.8 å. the line ratio between h and h (h h) is 2.73. this suggests that the galaxy is a starburst galaxy. star formation rate (sfr) of the galaxy derived from h emission line flux is 0.019 m⊙year−1 and emission line metallicity derived from flux ratio between nii and h is 7.85 dex. these morphological and physical properties of sdssj134326.99+431118.7 are very similar to those of a typical blue compact dwarf (bcd) galaxy. we conclude that we have presented another evidence of forming a bcd-type galaxy through a merger. doi: https://doi.org/10.3126/bibechana.v18i1.29466 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction a galaxy whose gravitational fields interact with another and produce a disturbance in their morphological and dynamical properties are called interacting galaxies [1]. there are many observational pieces of evidence that link galaxies' morphological and physical evolution with interactions and mergers. starburst activities are frequent among the interacting galaxies, particularly in low mass cases where a vast amount of gas reservoir is present. the gravitational tidal force of the interacting system destroys the regular http://nepjol.info/index.php/bibechana https://doi.org/10.3126/bibechana.v18i1.29466 https://creativecommons.org/licenses/by-nc/4.0/ daya nidhi chhatkuli et al. / bibechana 18 (1) (2021) 100-107 101 morphology of the participating galaxies and produces bridges and tails between them [2]. this also destabilizes gaseous disk leading to an inflow of star-forming gas toward the central region, which creates a nuclear starburst [3, 4]. according to lambda cold dark matter (λcdm) cosmology, dwarf galaxies are the building blocks of the universe, and all large-scale structures are build up progressively later with the hierarchical coalescence of these building blocks. they dominate the number distribution at any epoch of the universe, and there should be a more frequent merger between dwarf galaxies than between massive galaxies. however, the dwarf-dwarf interactions are not explored in detail, as in the case of massive galaxies' interactions. on the other hand, dwarf galaxies are inherently low-surface brightness in nature, and it is challenging to detect them. because of this, it is not trivial to detect tidal features in dwarf galaxies, which are even fainter than host galaxies. there is a great deal of the study of the interacting massive galaxies, but it is less known about the interaction and mergers of the dwarf galaxies to date [5]. it is also true that the merging probability of dwarf galaxies is low at low redshift universe as most of them are bound within the gravity of large scale structures, where dispersion velocities are high [6]. because of this, dwarf-dwarf interactions are more frequent in the field environment than in the group environment where galaxies are more gas-rich compare to dwarf galaxies located in the group environment [7]. furthermore, dwarf galaxies merge frequently and assemble due to collision to make bigger galaxies. the growth and evolution of the galaxies is based on the merger of dwarf galaxies [8]. therefore, it is interesting to study the dwarf-dwarf merger at a low redshift regime and understand the effect of the merger in gas removal and star-formation in these low-mass systems. it is not conclusively understood how important a merger is in dwarf galaxy evolution. stierwalt et al. (2015) [9] is the first to perform a statistical study of interacting dwarf galaxy pairs and found that star formation is more intensified in paired dwarfs than that in unpaired galaxies. they found that star-formation rates of interacting dwarf galaxies are anti-correlated with their pair separation. moreover, a significant fraction of starburst in dwarf galaxies are contributed by the interaction. lelli et al. (2018) suggest that the activity of the starburst galaxies such as blue compact dwarfs (bcds) strongly depends on the inner shape of the potential well and the central gas surface density [10]. in this work, we present the spectroscopic study of a star-forming interacting dwarf galaxy sdss j134326.99+431118.7, a morphologically blue and edge-on dwarf galaxy. this galaxy is located in a nearly isolated environment where we find no massive galaxies within a 500 kpc radius around it. 2. sample selection sdss j134326.99+431118.7 is listed in the catalog of interacting dwarf galaxies by paudel et al. (2018) [11]. it is located in the sky position ra= 13h 43m 26.9s and dec = 43d 11m 18.78s with a line-ofsight radial velocity 2511 (z = 0.00837) km/s. it has g and r band magnitude 16.18 mag and 15.98 mag respectively, and total absolute b-band magnitude is -15.34 mag. in figure 1, we show the g-r-i combined tri-color image obtained from the legacy survey. we can see a shell feature morphology at the lower side with an extended arclike feature at the sky projected distance of 5 kpc from the center. the central part is significantly blue compare to the outer extended low-surface brightness region. a red cross mark identifies an off-centered star-burst region, where the sdss has positioned its fiber to take the optical spectrum. in figure 2, we show the sdss optical spectrum of the wavelength range of 4000 to 6600 a. we can see several characteristic lines in the spectrum and highlighted some of the prominent emission lines, mainly balmer lines. the strongest emission line is oiii, and h is the strongest among the balmer lines. daya nidhi chhatkuli et al. / bibechana 18 (1) (2021) 100-107 102 fig. 1: optical view of sdss j134326.99+431118.7. the image is obtained from the sdss sky-server. fig. 2: optical spectrum of sdss j134326.99+431118.7. positon of the emission lines h, h, h, h, oiii, hei and nii are identified. the x-axis is rest-frame wavelength and y-axis is flux. 3. data analysis in this work, we extensively use the sdss archival data to measure morphological and chemical parameters of the galaxy. we obtained the sdss g and r band images and optical fiber-spectrum from the sdss data archive server (das). the images and spectrum are already well-calibrated, and we further do not perform any operation in this regard. both images and spectrum data are in the fits file format. the sdss fiber has a diameter of 3 arc seconds. hence, the observed spectrum only covers a small portion of the galaxy area. the sdss optical spectrum has coverage of 3650 to 10,400 å, which includes primary emission and absorption lines that are frequently used to investigate the chemical properties of stars or galaxies. the spectral resolution of the sdss spectrum is 1500 at 3800 å. the spectrum of the galaxy was analyzed by using the origin software of the 18th version. we first identified 21 different emission lines in the spectrum as shown in figure 2. we performed gaussian fits in each emission line and measured their parameters such as full width half maximum (fwhm), total flux, and best-fit coefficient. before modeling each emission line, we subtracted the continuum flux taking a median of flux value of spectrum range  100 from the center of the emission line. emission line profile of the extragalactic object is dominated by doppler broadening. the atoms/molecules in a gas, which emits the radiation, will have a distribution of velocities. the photon emitted by transition will be either red or blue-shifted by the doppler effect, depending on the atom's velocity relative to the observer. since the spectral line is a combination of all of the emitted radiation, the line profile is considered a gaussian in nature. the center is zero shift or an average shift of the system. mathematically gaussian distribution function is defined as [12] fg(x) = 1 √2πσ2 e −(x−μ)2 2σ2 (1) where, x is a normal random variable,  is the mean deviation and  is the standard deviation of the distribution. the fwhm is a width at which maximum amplitude drops to the half. we selected eight emission lines based on a higher intensity, which will be presented in this paper, along with their gaussian parameters. the gaussian parameters will be enlisted in a separate table and the corresponding elements will be identified. moreover, we calculate the star formation rate (sfr) and the hydrogen line ratio. we will use the gaussian area of h emission line to calculate the star formation rate of the galaxy. we calculate star daya nidhi chhatkuli et al. / bibechana 18 (1) (2021) 100-107 103 formation rate adopting the empirical formula proposed by kennicutt (1998) [13] as follows: sfr (m☉year-1) = 7.9× 10-42 ∑ l (h) (ergs s-1) (2) where ∑ l(hα) is the total luminosity of hα line which will be calculated by using gaussian fits. ∑ l(hα) = area of gaussian fit × 10-17 × 4𝜋r2(ergs s-1). r is the radius of the sphere which is calculated as r = d × 3.08 × 1024 cm. here, d is luminosity distance of the galaxy in mpc. we derive emission line metallicity using a line ratio between h and nii. we use a calibration provided by marino et al.(2013) [14]. 12 + log(o/h) = 8.743 + 0.462 × log(nii/ h) (3) 4. results in this work we have analyzed eight main emission lines, i.e., hei, h h h oiii, oiii, h and nii which are identified in figure 2. the oiii is a doublet. therefore, it has two different emission lines. the h h h and h are balmer lines and they are sensitive to the galaxies' gas-mass and star-formation rate. the h, principally, is a well-known tracer of star-formation and widely used to calculate the star-formation rate of the gas-rich galaxies. heavier elements oiii and nii emission fluxes are used to calculate the star-forming galaxies' emission line metallicity. in figure 3, we show a few examples of the gaussian fitting procedure. here, we selected four main examples of emission lines of the spectra of interacting dwarf galaxy sdss j134326.99+431118.7. we list peaks’ position and the central wavelength value of all eight emission lines in table 1. the solid line represents the gaussian distribution. the error bars are also shown in the gaussian curves. we can see that there is the almost perfect agreement of the observed data with the gaussian distribution. we list all eight strongest emission lines in the spectrum of the galaxy sdss j134326.99+431118.7 that we have studied in this work in table 1. their maximum intensity, the wavelength corresponding to maximum intensity, and corresponding elements are also provided. from the table, we can see that the doubly ionized oxygen oiii has a maximum intensity of 1043.6 x 10-17 erg/s/cm2/å, which has a central wavelength 5050.1 å. the second strongest intensity (391.8 x 10-17 erg/s/cm2/å) is found corresponding to the wavelength 6619.1 å, which is h line. the weakest intensity (31.34 x 10-17 erg/s/cm2/å) among the eight emission lines corresponds to the wavelength 6634.23 å for the nii. the gaussian parameters of all eight gaussian distributions are listed in table 2. the gaussian height is given in the unit of intensity. gaussian offset is the positional difference between the gaussian peak and the observed peak in the spectra. the coefficient of regression represented by rsquare is found to be more than 0.980. this suggests a perfect gaussian fit with the characteristic lines. calculation star formation rate can be calculated by using equation (2). here, we take d = 35.27 mpc from the catalogue prepared by paudel et al. (2018) for this particular galaxy. now, r = d × 3.08 × 1024 cm = 35.27 × 3.08 × 1024 cm = 108.63 × 1024 cm star formation rate due to h line is sfr(m⊙year−1) = 7.9 × 10−42 × area of gaussian fit × 10-17 × 4𝜋r = 7.9 × 10−42 × 1661.01× 10-17 × 4𝜋 ×(108.63 × 1024)2 = 0.019 m⊙year−1 line ratio h h = 2.73. this is slightly lower than the theoretical value of h h = 2.8. we suspect that this discrepancy between the theoretical and observed value is due to the inaccurate subtraction of continuum in the region of daya nidhi chhatkuli et al. / bibechana 18 (1) (2021) 100-107 104 fig. 3: we show four main examples of gaussian fitting procedure. they are four balmer lines: h. hδ, hγ, and h. solid curves represent gaussian fits. we show a conservative estimate of the flux error in the plot, i.e., 10 % of the observed flux provided by sdss webpage (https://www.sdss.org/dr15/spectro/caveats/). the major cause of broadening of characteristic line is due to the doppler broadening. the wavelengths given in the x-axis are not redshift corrected. table 1: the selected characteristic emission lines of spectra of dwarf galaxy sdss j134326.99+431118.7 shown in figure 3 are described along with their physical parameters listed in the table. the first column represents the name of the selected emission lines. second and third columns represent the wavelength ((p) corresponding to the peak intensity, the value of peak intensity (ip). responsible elements for emission lines wavelength corresponding to peak intensity p (å) peak intensity ip (10-17 erg/sec/cm2/å) hei 3921.9 64.8 h 4137.1 76.8 h 4378.2 114.6 h 4903.4 209.8 oiii 5001.5 349.7 oiii 5050.1 1043.6 h 6619.1 391.8 nii 6634.23 31.34 https://l.facebook.com/l.php?u=https%3a%2f%2fwww.sdss.org%2fdr15%2fspectro%2fcaveats%2f%3ffbclid%3diwar3jfnnofffdjqff8uxkcgwwvutylx5qodlzrdreoqeucvvd1-6yjxmu10a&h=at3vnpkq0gg3i7r58adgvtq_glpy-ysfiwljz1xkkohgqltu2wjr0ncsbnkhv-3veuzi2hoo1rpfkd6zhhzlkomvmvuzvfj6v145aunhg5h2nxhtu6mtdza4meoe-iwd_4q daya nidhi chhatkuli et al. / bibechana 18 (1) (2021) 100-107 105 table 2: full width half maximum, area of the curve, height of the gaussian curve, offset and coefficient of regression of the data corresponding to each selected spectral lines are enlisted in the table in second, third, fourth, fifth and sixth column respectively corresponding to the responsible elements. h, where we can see absorption feature is also present. the ratio between h and h are also used to check the presence of internal dust reddening in the galaxies. the observed line ratio is near to the theoretical value or less. this imply that sdssj134326.99+431118.7 is a nearly dust free galaxy. line ratio nii/ h = 0.011. we calculate emission line metallicity for this galaxy using equation (3), 12 + log(o/h) = 7.85 dex. logarithmic value is represented by dex. it is especially suitable while talking about metallicity. metallicity is measured logarithmically in connection with the plenty of metals in the galaxy. 5. discussion table 2 shows that the selected gaussian distributions of hei, h, oiii doublet and h have a negative value of the offset. these curves have negative skewness. this means that the left-hand tail is longer than that on the right-hand side, and the mode is more than the mean. similarly, the distributions of h h and nii have a positive offset. the curves have positive skewness. this means that the right-hand tail is longer than that of the left-hand side, and the mode is less than the mean. the value of fwhm is maximum (3.80 å), corresponding to the curve of h. this indicates that the observed data is in excellent agreement with the gaussian fit. the gaussian area is maximum (2982.67 x 10-17 erg/s/cm2/å) for the line oiii. normal galaxies follow scaling relations of b-band absolute magnitude (mb) versus star-formation rate and mb versus emission-line metallicity. the position of sdssj134326.99+431118.7 in these relations is shown in figure 4. in this figure, we have taken the sdss star-forming galaxies as a comparative sample for the magnitude-metallicity relationship and the local volume star-forming galaxies studied by lee et al. (2009) [15] for the magnitude-star-formation rate relation. interestingly, we find that sdssj134326.99+431118.7 is a significant outlier. it is significantly metal-poor compare to the normal sdss star-forming galaxies. similarly, the starformation activity in this galaxies is notably higher than that of normal star-forming galaxies of local volume. the catalog value of the star-formation rate of sdssj134326.99+431118.7 is 0.0083m⊙ year−1, which is derived by using the far-ultraviolet (fuv) flux of the galaxy. this shows that our element fwhm (å) area (10-17 erg/s/cm2/å) height (10-17 erg/s/cm2/å) offset r-square hei 2.23 117.49 49.39 -0.253 0.980 h 2.35 150.05 59.92 -0.008 0.984 h 2.57 292.96 107.25 +0.376 0.995 h 2.82 606.93 202.38 +0.099 0.997 oiii 2.69 1003.65 350.56 -0.252 0.998 oiii 2.68 2982.67 1045.33 -0.001 0.999 h 3.80 1661.01 411.18 -0.558 0.999 nii 3.80 19.30 32.40 +0.023 0.999 daya nidhi chhatkuli et al. / bibechana 18 (1) (2021) 100-107 106 fig. 4: magnitude-metallicity relation of star-forming galaxies, left, where the sdss star-forming galaxies as a comparative sample are shown in gray symbol. the figure is reproduced from paudel et al. (2018). in right, we show a relation between star-formation rate and b-band absolute magnitude, where the comparative sample galaxies taken from lee et al. derived value of the star-formation rate is significantly lower than the fuv value. this is because, area coverage of fuv is substantially more extensive compared to the sdss 3” central region. this implies that, only a fraction of starformation happens in the center of the galaxy. the emission line metallicity of sdssj134326.99+431118.7 is 7.85 dex, which is a typical for metal-poor the vigorously star-forming galaxies, called blue-compact dwarf galaxies (bcds) [15]. as their name indicates, they are significantly blue and gas-rich compact galaxies, mainly found in a very low-density environment. comparing morphological and physical properties of sdssj134326.99+431118.7 with that of bcds, it is clear that sdssj134326.99+431118.7 is a typical bcds type galaxy formed by the merger in an isolated environment. 6. conclusion the emission-line spectrum of a system of interacting dwarf galaxy sdss j134326.99+431118.7 is studied. we noticed 21 spectral lines in the spectrum. among them, only eight most robust emission-lines are analyzed in this work by using gaussian fits. the following results are concluded from the observations and calculations. a) we fitted the observed emission lines on the optical spectrum of sdss j134326.99+431118.7 and found that there is an excellent agreement of all eight characteristic lines with gaussian fits with more than 98% coefficient of regression. b) we derived star-formation rate and emission line metallicity of sdss j134326.99+431118.7, and found that the galaxy does not follow the scaling relation of mb versus sfr and mb versus 12 + log(o/h). c) the morphological and physical properties of sdssj134326.99+431118.7 are very similar to those of a typical bcd galaxy. we conclude that we have presented another evidence of forming a bcd-type galaxy through a merger. acknowledgements daya nidhi chhatkuli acknowledge the university grants commission of nepal, for financial support daya nidhi chhatkuli et al. / bibechana 18 (1) (2021) 100-107 107 by providing phd fellowship and research support grant (award no.: phd-75/76-s & t-13) to carry out this research. this study is based on the archival images and spectra from the sloan digital sky survey (http://www:sdss.org/collaboration/credits.html). references [1] f. schweizer, colliding and merging galaxies. science 231 (1986) 227-234. https://science.sciencemag.org/content/231/4735/227 [2] s. pearson, g. besla, m. e. putman, k. a. lutz, x. fernández, s. stierwalt, ... & e. c. sung, local volume tiny titans: gaseous dwarf–dwarf interactions in the local universe, monthly notices of the royal astronomical society 459 (2016) 1827-1846. https://doi.org/10.1093/mnras/stw757 [3] j. e. barnes, & l. hernquist, transformations of galaxies, ii. gasdynamics in merging disk galaxies. the astrophysical journal, 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[15] lee, j.c., kennicutt, r.c., jr., funes, s.j.j.g., sakai, s., akiyama, s.. dwarf galaxy starburst statistics in the local volume, the astrophysical journal 692 (2009) 1305–1320. https://doi.org/10.1088/0004-637x/692/2/1305 . http://www:sdss.org/collaboration/credits.html https://science.sciencemag.org/content/231/4735/227 https://doi.org/10.1093/mnras/stw757 https://doi.org/10.3847/1538-3881/aadb8d microsoft word nkc final(47-54) s. chaudhary et al./ bibechana 16 (2019) 47-54: rcost p.47 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal antibiotic susceptibility pattern of biofilm forming uropathogenic escherichia coli isolated from uti infected patients of koshi zonal hospital in biratnagar, nepal s. chaudhary1, b. khatiwada1, n. k. chaudhary2*, 1department of microbiology, mahendra morang adarsh multiple campus, biratnagar, nepal 2department of chemistry, mahendra morang adarsh multiple campus, biratnagar, nepal tribhuvan university *email: chem_narendra@yahoo.com article history: received 3 september, 2018; accepted 13 september, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.19192 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract objectives: to investigate the prevalence and antibiotic resistance pattern of biofilm-forming uropathogenic escherichia coli (upec) from urine samples isolated from uti infected patients of koshi zonal hospital, biratnagar. methods: a total of 51 urine samples from urinary tract infected patients were collected from koshi zonal hospital, biratnagar in the period of july to august 2017. following the isolation and identification of biofilm-forming uropathogenic escherichia coli, antibiotic susceptibility test was performed by a modified kirby-bauer disc diffusion technique. the biofilm detection was done by congo red agar method. results: in the present study, 45% of the urine samples showed a predominant growth of e. coli, among which 70% of isolates exhibited positive biofilm formation. biofilm forming isolates revealed 100%, 87.5%, 75%, 63% and 12.5% resistant to erythromycin, amoxicillin, cefotaxime, levofloxacin, and nitrofurantoin respectively. approximately 87.5% of biofilm-forming isolates were found multi-drug resistant. conclusion: the study revealed the major issue of uti by e. coli which may be due to poor sanitation, not the proper cleanliness of genitals and unsafe sexual intercourse. nitrofurantoin and levofloxacin were examined the most effective antibiotics for upec. keywords: biofilm; urinary tract infection; antibiotic susceptibility; e. coli; multidrug resistance. 1. introduction urinary tract infections have become a major public health concern in the medical science and represent one of the most common infectious disease ranking next to upper respiratory tract infection. they contribute to the nosocomial infection in many hospitals and account for approximately 35% of s. chaudhary et al./ bibechana 16 (2019) 47-54: rcost p.48 (online publication: dec., 2018) all hospital-acquired infections [1]. unhygienic sexual intercourse and not washing the genitals properly have made the urinary tract infection prevalence in the urban areas of nepal. infection by uropathogenic escherichia coli has made a worldwide problem mostly affecting the women in both developed and underdeveloped countries [2]. it is the most important pathogen associated with uti and the primary etiological agent among both outpatients and inpatients. common pathogens that have been implicated in utis are primarily gram-negative organisms with e. coli having a more prevalence than others including k. pneumoniae, enterobacter spp., p. mirabilis, p. aeruginosa and citrobacter spp. the organism is therefore of clinical importance and can be isolated from various clinical specimens [3, 4]. it is one of the organisms most frequently isolated from urine. in addition to urinary tract infection, e. coli is the most frequent pathogen associated with intra-abdominal infection. the biofilm forming upec has made much more difficulties in the eradication and elimination of the urinary tract infection [5]. the resistance of bacteria to antimicrobials may pose a serious threat in both developing and developed countries. patients with infections by resistant organisms are at an increased risk of treatment failure [6]. bacterial biofilms generally provide a protective environment for their constituent bacteria, shielding them from antibiotics and host immune effects, and it seems quite likely that biofilms in the bladder may account for the recalcitrance of upec to treatment and clearance from the urinary tract [7, 8]. in the present investigation, we aimed to detect the biofilm forming uropathogenic e. coli isolated from utis infected patients of koshi zonal hospital, biratnagar and evaluated their antibiotic susceptibility pattern. we have also examined the isolates that showed drug resistance. 2. materials and methods 2.1 sample collection and processing urine samples were collected from koshi zonal hospital, biratnagar from july to august 2017. a total of 51 freshly voided midstream urine samples (10-20 ml) were collected aseptically from uti suspected patients in the wide-mouthed sterile plastic vial. the collected urine samples were kept in the icebox at 4 °c during transportation and analyzed in microbiology laboratory of mahendra morang adarsh multiple campus, biratnagar, on the same day immediately after their delivery within 6 hours of collection. 2.2 isolation and identification of e.coli from urine samples 0.1 µl of each urine sample received from the patients were spread on eosine methylene blue (emb) agar by spread plate method for the growth of bacteria and the culture plates were incubated in an inverted position at 37 °c under the aerobic condition for 24-48 hours [9]. after growth of organisms, the pink greenish metallic sheen was inoculated on nutrient agar medium for each discrete colony presented in the specimen to obtain wellisolated pure colonies incubated at 37 °c for 24 hours. isolated colonies were subjected to biochemical tests such as catalase, oxidase, mr, vp, urease, citrate, indole, tsi to identify the e. coli based on the bergey’s manual of determination of bacteriology [10]. the figure (4 a-d) presents isolation and identification of biofilm-forming upec and ast pattern performed by e. coli. 2.3 identification of biofilm-forming upec the well identified e. coli were subjected to biofilm formation by congo red agar method [11]. the isolated colony was streaked on the congo red agar (cra) and incubated for 24 hours at 37 °c. after the incubation, the biofilm forming upec showed black colonies with dry crystalline consistency. s. chaudhary et al./ bibechana 16 (2019) 47-54: rcost p.49 (online publication: dec., 2018) red or pink colonies are considered as nonbiofilm producers and the pink colony with black centered is considered as moderate biofilm producer [12]. 2.4 ast pattern of biofilm-forming upec antibiotic susceptibility test of the biofilm forming upec towards various antimicrobial discs such as nitrofurantoin (300 mcg/disc), levofloxacin (5 mcg/disc), cefotaxime (30 mcg/disc), erythromycin (15 mcg/disc) and amoxicillin (10 mcg/disc) was done by modified kirby-bauer disk diffusion method on mueller hilton agar [13]. organisms were classified as sensitive or resistant to an antibiotic according to the diameter of the zone of inhibition surrounding each antibiotic disc based on the clinical and laboratory standards institute guidelines [14]. based on the sensitive pattern, isolates resistant to three or more antibiotics were considered as multidrug-resistant bacteria. 3. results fifty-one urine samples of urinary tract infected patients were processed, among which 15 (29.41%) samples gave significant growth, 8 (15.69%) samples gave mixed growth and 7 (13.73%) samples (figure 1) gave nonsignificant growth while remaining samples showed no growth. e. coli was found to be the most predominant isolate in 23 (45.09%) samples. the distribution of e. coli was found to be the most frequent in age groups 13-55 years in both sexes i.e. 3 in male and 20 in the female. the sex wise distribution (figure 2) showed that females (86.97%) were more susceptible than males (13.04%). out of 51 samples, 23 samples showed the growth of e. coli which were subjected to biofilm productions by congo red agar method among which 16 (70%) isolates showed the formation of biofilms [15]. all the biofilm producing upec were subjected to antibiotic susceptibility test [16, 17] which showed maximum resistant towards erythromycin (100%) followed by amoxicillin (87.5%), cefotaxime (75%), levofloxacin (63%) and nitrofurantoin (12.5%). thus, maximum susceptibility was shown by nitrofurantoin (87.5%) and the least effective drug was erythromycin (0%). the bar graph analysis for antibiotic susceptibility pattern of biofilm-forming upec is given in figure 3 and the growth inhibition data is reported in table 1. table 1: antimicrobial susceptibility pattern of biofilm-forming upec (%). antibiotics sensitive resistant amoxicillin 12.5 87.5 cefotaxime 25 75 erythromycin 0 100 levofloxacin 37 63 nitrofurantoin 87.5 12.5 multidrug resistance is defined as the resistance to more than three antibiotics or more. taking resistant to two or more classes of antibiotics as mdr, it was detected that 14 (87.5%) isolates were resistant to more than three antibiotics. the mdr data for biofilm-forming upec is reported in table 2. 4. discussion the antibiotic-resistant pathogens have resulted in an increment of health care cost worldwide. not only the resistant to antibiotics, the biofilm production by an organism has made it more difficult for curing. the availability of antibiotics seems to be inadequate in the context of increasing resistant problems. antibiotic resistance is a common phenomenon in the developing country where antibiotics are available freely without the prescription [18, 19]. the antibiotic susceptibility pattern varies no growth 44% significant growth 29% mixed growth 16% non-significant growth 14% females 87% males 13% s. chaudhary et al./ bibechana 16 (2019) 47-54: rcost p.50 (online publication: dec., 2018) among the hospitals and nations from one country to another and also depends upon the variation of geographical regions. therefore therapeutic success against upec depends upon the local susceptibility profiles [20]. this study was done to screen the resistance pattern of antibiotics among the biofilm producing uropathogenic escherichia coli. fig. 1: pie-chart distribution of bacteria. fig. 2: pie-chart distribution of e. coli according to sex. fig. 3: antibiotic susceptibility bar graph of biofilm-forming upec. table 2: multidrug-resistant pattern of biofilm-forming upec . bacterial isolates no. of biofilm isolates mdr strain total % 0 drug 1 drug 2 drug >2 drug e. coli 16 0 2 0 14 14 87.5% 0%20%40%60%80%100%antibiotic susceptibility pattern in % sensitiveresistant s. chaudhary et al./ bibechana 16 (2019) 47-54: rcost p.51 (online publication: dec., 2018) fig. 4: (a) e. coli on eosin methylene blue (emb) agar media. (b) biofilm forming upec (high growth). (c) biofilm forming upec (moderate growth) (d) ast of e. coli performed on mha. biofilm formation is closely related with the resistance of upec towards the beta-lactam antibiotics; amoxicillin and cefotaxime, and the macrolides; erythromycin. they are hardly effective antimicrobial drugs and also increase the chronicity of urinary tract infection. the high resistance of biofilms towards β-lactam antibiotics and macrolides may be due to restricted penetration of antimicrobial agents into biofilms, nutrients limitation, gene expression in the stress response and further, due to the more space in the biofilm rather than that of planktonic cells. the genetic exchange takes place between the resistance and nonresistance strains and finally increase the emergence of multidrug-resistant strains of upec [21–23]. antibiotics resistance in biofilm forming upec is further aided by the irrational exposure of several antibiotics without precise prescription which is very common in the developing country like nepal. our study was conducted among outpatients suspected of uti, attending koshi zonal hospital of biratnagar. in this research, the analytical data presented in the result section in response to the growth of biofilm-forming e. coli are in good agreement with other investigators. in our study, 23 (45.09%) e. coli isolated from 8 significant and 7 mixed growth urine samples was found the commonest organism isolated. almost similar results were observed in the literature [24, 25] and e. coli is considered as the predominant pathogen for biofilm-forming upec. uropathogenic e. coli was isolated most commonly from female patients compared to male patients. the study showed that 87% female were susceptible to uti in comparison to male 13%. the increased rate of uti in the female is due to anatomic factors, urodynamic disturbance, and hormonal changes. biofilm producing upec played a significant role in the antibiotic resistance and incurable stages leading to high morbidity and mortality. among 23 e. coli isolates, 16 (70%) isolates showed biofilm formation dividing it into high, moderate and low biofilm formation. the results are in good agreement with the literature [26–29]. a b c d s. chaudhary et al./ bibechana 16 (2019) 47-54: rcost p.52 (online publication: dec., 2018) the investigation revealed that the biofilm forming upec were mostly resistant to erythromycin (100%) followed by amoxicillin (86%) which resembles other studies [7,26,27,29]. on the basis of our findings, antibiotic such as erythromycin and amoxicillin should be no longer recommended for initial therapeutics for urinary tract infections caused by biofilm-forming upec. our study also showed that only 2 (12.5%) biofilm forming upec were resistant to nitrofurantoin which is similar to the findings of other researchers. in the context of nepal, nitrofurantoin is the best antibiotic prescribed for the case of uti and biofilm forming upec [7]. however resistant to quinolones and fluoroquinolones has been increasing day by day. the major consequences being the use of the antibiotics at the poultry and the resistant strain being transmitted from animal to the human beings [30, 31]. 5. conclusion in nepalese context, the biofilm forming upec and the mdr strains of e. coli, being more prevalence of urinary tract infection, are an alarming signal of health hazard which will be very difficult to control in the future. in conclusion, the major issue of uti infection is due to e. coli which were about 45.09 %. the poor sanitary condition, lack of health education, careless in the cleanliness of genitals and unsafe sexual intercourse are playing the leading role in uti infection. according to the antibiotic sensitivity test, nitrofurantoin and levofloxacin are the most effective antibiotics for the treatment of uti. erythromycin and amoxicillin are not active against the uti infections due to drug resistance and these should not be used. the biofilm forming capability of the upec poses a great challenge to clinicians and microbiologist and therefore, the major focus should be on drug resistance, so that we can minimize the mortality and morbidity. declaration of interest the authors declare no conflicts of interest. the content and writing of the paper are all under the author's responsibility. references [1] a. l. flores-mireles, j. .n. walker, m. caparon, s.j. hultgren, urinary tract infections: epidemiology, mechanisms of infection and treatment options, nature rev. microbiol. 13 (2015) 269–284. doi:10.1038/nrmicro3432. 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[31] k. dhama, v. verma, p.m. sawant, r. tiwari, r.k. vaid, r.s. chauhan, applications of probiotics in poultry: enhancing immunity and beneficial effects on production performances and health a review, j. immunol. immunopathol. 13 (2011). bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal modeling equations to predict the mixing behaviour of al−fe liquid alloy at different temperatures s. k. yadav1, 2*, l. n. jha2, d. adhikari3* 1department of physics, suryanarayan satyanarayan morbaita yadav multiple campus, tribhuvan university, siraha, nepal. 2central department of physics, tribhuvan university, kirtipur, nepal. 3department of physics, mahendra morang adarsh multiple campus, tribhuvan university, biratnagar, nepal. *e-mail: yadavshashit@yahoo.com article history: received 05 october, 2017; accepted 20 november, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18624 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/bync/4.0/ abstract redlich−kister (r−k) polynomials have been associated with the extended regular associated solution model to predict and explain the thermodynamic properties and structural properties of al−fe liquid alloy at 1873 k, 1973 k, 2073 k and 2173 k; 1873 k being its melting temperature. the thermodynamic properties, such as free energy of mixing (gm) and activities of free monomers (aal and afe) and structural properties, such as concentration fluctuation in long wave length limit (scc(0)), chemical short range order parameter (α1) and ratio of diffusion coefficients (dm/did) have been predicted at above stated temperatures. renovated butler model has been employed to predict the surface tension (σ) and surface segregation (xs) of the alloy at stated temperatures with the help of thermodynamic properties. theoretical findings prevail that the tendency towards compound formation of the liquid alloy decreases with increase in its temperature beyond melting temperature. eventually, its surface tension decreases and there is gradual exchange of atoms between the surface and bulk regions to maintain equilibrium at elevated temperatures. the liquid alloy under investigation thus shows ideal behaviours at higher temperatures. keywords: r−k polynomials; thermodynamic properties; surface segregation; ideal behaviour. 1. introduction alloying phenomena have been developed as one of the robust tool to achieve desired materials with required characteristics. though alloys have profound utilizations in the solid state, they are fabricated near to the melting temperatures of the constituent atoms. the comprehensive knowledge of the thermodynamics of the initial melt is thus imperative to explain the mixing behavious of the subsystems. this information cannot be solely achieved from experiments as being cumbersome facing adversities associated with the high reactivity of metals at elevated temperatures. in this limelight, the devising of theoretical models to explain the mixing behaviours of the alloy melts at a s.k. yadav et al. / bibechana 15 (2018) 60-69: rcost p.60 http://nepjol.info/index.php/bibechana mailto:yadavshashit@yahoo.com http://dx.doi.org/10.3126/bibechana.v15i0.18 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ temperature and extrapolating at different temperatures are mandatory. several theoretical models [1−9] so far have been tooled to understand and explain the energetic of the liquid alloys. in this work, we intend to predict the thermodynamic and structural properties of al−fe liquid alloy at different temperatures by extending regular associated solution model [5, 7, 9−12]. moreover, the thermodynamic properties at different temperatures have been correlated with renovated butler model [13−15] to predict the surface properties of the liquid alloy at different temperatures. when the atoms of type a (=al) and b (=fe) are mixed near to their melting temperature, there are preferable associations of the types aa, bb and ab in the framework of regular associated solution model. it is assumed that there exist unequal interactions among the associated and unassociated atoms. the expressions for the thermodynamic and structural properties of the liquid melt are derived on this fundamental. the details about the model can be found from references 5, 7 and 9 (also see ref. 15). the model parameters of most of the theoretical models are just fitting parameters to establish the equivalence between the computed and observed thermodynamic properties. but the model fit parameters of the preferred model (regular associated solution model) are determined from the experimental values of the activity coefficients of the monomers of the liquid alloys at infinite dilutions. also the mole fractions of the associated complex and unassociated atoms can be computed in the preferred model regardless of other models. with this regard, the regular associated model has been extended to predict the thermodynamic and structural properties of the considered system at different temperatures. accordingly, r−k polynomials [16, 17] have been associated with these procedures to determine the fitting coefficients. moreover, the importance of the al−fe liquid alloys is mentioned in ref. 16. among the different stable chemical complexes, we have assumed al3fe as one of the most energetically favoured complex at 1873 k and have considered for further study [18, 19]. the details of the methodology containing basic formulations are mentioned in the section 2, results and discussion are amended in the section 3 and the section 4 contains the conclusions of the present work. 2. methodology 2.1 thermodynamic properties assume the chemical complex of type aμbν (aμbνμa + νb) exists in a mole of binary solution, where a (=al), b (=fe) and μ (=3) and ν (=1) are small integers whose values are determined from the compound forming concentration in the solid state. the true mole fractions of free monomers a (xa) and b (xb) are then given as [5, 11, 18] xa = x1 − μx2xaμb and xb = x2 − (1 − μx2) xaμb (1) where x1 and x2 are the gross mole fractions of atoms a and b respectively and xaμbν is the true mole fraction of the complex. the activity coefficients of monomers (γ a and γ b ) and complex (γ aμb ) can be expressed in terms of pairwise interaction energies as rt lnγa = xb 2 ω12 + xaμb 2 ω13 + xb xaμb ( ω12 − ω23 + ω13 ) (2a) rt lnγb = xaμb 2 ω23 + xa 2 ω12 + xa xaμb ( ω23 − ω13 + ω12) (2b) rtln γaμb = xa 2 ω13 + xb 2 ω23 + xaxb (ω13 − ω12 + ω23) (2c) where t is temperature in absolute scale and r is the universal gas constant. the terms ω12, ω13 and ω23 represent the pairwise interaction energies for the species a, b; a, aμb and b, aμb respectively. ω12and ω13 in terms with activity coefficients at infinite dilution (γ1 0, 1=a and γ2 0, 2=b) can be correlated as follows [11, 15] s.k. yadav et al. / bibechana 15 (2018) 60-69: rcost p.61 lnγ1 0 = ω12 rt (3a) k exp ( ω13 rt ) = γ1 0 γ2 0 γ1 0 − γ2 0 (3b) where k is the equlibrium constant for the above mentioned chemical reaction and is given as lnk = ln ( xa μ xb xaμb ) + ω12 rt [μxb(1 − xa) + xa] + ω13 rt [μxaμb(1 ‒ xa) ‒ xa] + ω23 rt [ xaμb (1‒ μxb) ‒ xb] (4) in regular associated solution model, it is assumed that x1 γ1= xa γa and x2 γ2= xb γb where γ1 and γ2 are the respective gross activity coefficients of monomers 1 and 2 respectively. one can, therefore, obtain the following relations [11, 20] lnγ1 = lnγa + ln( xa x1 ) and lnγ2 = lnγb + ln( xb x2 ) (5) on solving equations (2a) and (2b), yields ω13 rt = xb ln( α2 xb )+( 1− xb ) ln( α1 xa )− xb (1− xb ) ω12 rt xaμb 2 (6a) ω23 rt = xa ln( α1 xa ) +( 1−xa ) ln( α2 xb ) − xa( 1− xa ) ω12 rt xaμb 2 (6b) where α1 and α2 are the activities of a and b respectively. using equations (4) and (6), the mole fraction of the complex and the unassociated atoms can be expressed by the relation [5, 7] lnk + ω13 rt = ( 1+xa xaμb ) ln ( α1 xa ) + xb xaμb [ln ( α1 xa ) − ω12 rt ] + ln ( a1 μ a2 xaμb ) (7) using above relations, the expression for the free energy of mixing ( gm rt ) can be obtained as [11] gm rt = 1 1+μxaμb rt [( xaxb ω12 rt + xaxaμb ω13 rt + xbxaμb ω23 rt ) + (xalnxa + xlnxb + xaμblnxaμb) + xaμblnk] (8) 2.2 structural properties concentration fluctuation in the long wavelength limit (scc (0)) in terms of free energy of mixing ( gm) can be given by the standard thermodynamic relation as [5, 15] scc(0) = rt ( ∂2gm ∂x1 2 ) t,p −1 (9a) using equation (8) in equation (9a); the expression for (scc(0)) can be obtained as scc(0) = 1/[ 1 1+μxaμb { 2 rt (xa ′ xb ′ w12 + xa ′ xaμb ′ w13 + xb ′ xaμb ′ w23) + ( xa ′2 xa + xb ′2 xb + xaμb ′2 xμb )}] (9b) where the prime denotes the differentiations with respect to concentrations and ∂2gm ∂x1 2 > 0 for ∂gm ∂x1 = 0. xa ′ and xb ′ are obtained by using equation (1) and xaμb ′ is obtained using equation (4) by using the condition dlnk dx1 = 0. the factor ( 1 + μxaμb )-1, which appears as a coefficient of all terms containing xa, xb and xaμb in equations (8) and (9b) is a result of change in the basis for expressing mole fractions of species a, b and aμb from that used for x1 and x2. further, the degree of local ordering in the liquid binary alloy can be understood by estimating chemical short range order parameter (α1) and in terms of scc(0) is expressed as [7, 21] s.k. yadav et al. / bibechana 15 (2018) 60-69: rcost p.62 α1 = s −1 s (z −1) + 1 , where s = scc (0) scc id (0) (10) where z is the coordination number and z= 10 is taken for our calculation [16]. it is seen that varying the value of z does not have any effect in on the position of the minima of α1 but it helps to vary the depth keeping the other features unchanged. the microscopic structural properties of binary liquid alloy can be further understood in terms of ratio of coefficients of diffusion. the ratio of diffusion coefficients (dm/did) can be expressed in terms of scc(0) by using darken thermodynamic equation as [22] dm did = x1 x2 scc (0) (11) where dm = did ∂lnaa/ ∂x1 represents the chemical or mutual diffusion coefficient and did represents the intrinsic diffusion coefficient for an ideal mixture. 2.3 surface properties according to renovated butler model, the surface tension (σ) for the a−b type liquid alloys can be given as [13-15] σ = σi 0 + rt λi ln ( xs,i xi ) + ∆gs,i e −∆gi e λi = σj 0 + rt λj ln ( xs,j xj ) + ∆gs,j e −∆gj e λj (12a) where σi 0 represents the surface tension of the pure components, λi represents the molar surface area of component i in the liquid solution and i=a, b. ∆gs,i e stands for the surface partial excess free energy of the components, ∆gi e stands for the bulk partial free energy of the components, xi represents the bulk mole fraction of the components and xs,i represents the surface mole fraction of the components and xs,i + xs,j = 1. the molar surface area of a pure liquid metal i is computed by the relation λi = f(vi 0)2/3(nav)1/3 (12b) where nav(=6.022 × 1023 mol−1) is the avogadro's number, vi 0 is the molar volume of pure metal i at the melting temperature and f is the geometrical constant which is given as f = ( 3fb 4 )2/3 π1/3 fs (12c) where fb and fs are the volume and surface packing fractions. the values of fb and fs depends upon the type of crystal structure of the pure components of the liquid alloys. 3. results and discussion 3.1 thermodynamic properties the model fit parameters (ω12, ω13, ω23, xa=al, xb=fe, xaμb=al3fe and k) for al−fe melt at 1873 k are evaluated using equations (1), (3), (4), (6) and (7) with the aid of observed essential ingredients [19]. the initial values of these input parameters as well as the temperature derivative terms of pairwise interaction energies (∂ω12/ ∂t, ∂ω13/ ∂t and ∂ω23/ ∂t) are taken from ref. 18. the extension of the regular associated solution model has been made by considering that the parameters, such as xa, xb, xaμb, k, ∂ω12/ ∂t, ∂ω13/ ∂t and ∂ω23/ ∂t remain constant with increase in the temperature of the system above its melting temperature. we have computed the mixing behaviors of the alloy at 1873 k, 1973 k, 2073 k and 2173 k, 1873 k being its melting temperature. the parameters ω12, ω13and ω23 in the preferred model are assumed to be temperature dependent only and they are computed using the following relations [15, 23] s.k. yadav et al. / bibechana 15 (2018) 60-69: rcost p.63 d[ωi,j(t)] xp = (∂ωi,j/ ∂t)dt and ωi,j(tk) = ωi,j(t) + (∂ωi,j/ ∂t)dt (13) where i , j = 1, 2 and 3 for i ≠ j, xp is the bulk mole fraction of a or b such that p = 1 or 2 and dt = tk − t; t (=1873 k) is the melting temperature and tk (=1973 k, 2073 k and 2173 k) are the temperature of interests for the alloy. the activity coefficients as a function of concentration for the unassociated atoms of al and fe of the liquid alloy are then computed at different temperatures using equations (2a) and (2b). eventually, the compositional dependence of excess free energy of mixing (gm xs) of the liquid alloy are predicted at such temperatures on the floor of which r−k polynomials are fitted. the excess free energy of mixing as a function of concentration is given by a polynomial, such as r−k polynomial [16, 17] as gm xs(x, t) = x1x2 ∑ k𝑙(t)(x1 − x2)𝑙m 𝑙=0 (14a) with k𝑙(t) = a𝑙 + b𝑙t + c𝑙t ln t + d𝑙t2 + -; where k𝑙 has the same temperature dependence as gm xs and a, b, c and d are the coefficients to be determined. the partial excess free energies of components of the alloy are given as ga xs(x, t) = x2 2 ∑ k𝑙(t)[(1 + 2𝑙)x1 − x2](x1 − x2)𝑙−1m 𝑙=0 (14b) gb xs(x, t) = x1 2 ∑ k𝑙(t)[x1 − x2(1 + 2𝑙)](x1 − x2)𝑙−1m 𝑙=0 (14c) the optimized coefficients are obtained by the method of least square fitting using programming in computer software microsoft excel 2007 and are tabulated in the table 1. table 1: optimized coefficient set of gm xs for al−fe liquid alloy l a𝑙(j mol-1) b𝑙(j mol-1k-1) c𝑙(j mol-1k-1) d𝑙(j mol-1k-2) 0 -65932.40 0.7591290 1.225507 -0.0003400 1 -140.5359 -6.861770 7.28x10-12 -5.00x10-6 2 -342.6730 -9.319690 -0.4085 9.86x10-5 3 -486.8970 -4.731690 -0.4085 9.86x10-5 the compositional dependence of excess free energy of mixing at different temperatures computed from equation (14a) using the values in table 1 are plotted in figure 1. it can be observed that gm xs gradually decreases at elevated temperatures. it can, therefore, be forecasted that the complex formation tendency of the liquid alloy is the maximum at its melting temperature and gradually decreases at elevated temperatures. once the partial excess free energies of a and b are obtained, the activity coefficients at different temperatures are computed using the relation gp xs = rt ∑ ln γp, where the terms carry their usual meanings. the compositional dependence of the activities of a (aal) and b (afe) are then computed from equation (5) and are plotted in figure 2. it can be observed that the activities of the free monomers gradually increase with increase in the temperature of the alloy predicting the similar tendency as by gm above. similar results are predicted and explained by other researches [17, 23−25] for different alloy systems employing different techniques. 3.2 structural properties the tendency towards complex formation and the local arrangements of atoms in the initial melt of the liquid systems can be further analyzed in terms of scc(0), α1 and dm/did. at a temperature and a concentration if scc(0) < scc id (0) for which α1 < 0 and dm/did > 1, then there is favourable association s.k. yadav et al. / bibechana 15 (2018) 60-69: rcost p.64 between the unlike atoms of the form a−b called ordering. additionally, at such conditions if scc(0) > scc id (0) for which α1 > 0 and dm/did < 1, then the association between the like atoms of form a−a or b−b is favoured in the melt called segregating. fig. 1: excess free energy of mixing (gm xs) as a function of concentration of al (x1) for al−fe liquid alloy at different temperatures. fig. 2: activities of al (ln(aal)) and fe (ln(afe)) as a function of concentration of al (x1) for al−fe liquid alloy at different temperatures. figure 3 shows the compositional dependence of scc(0) for the alloy at different temperatures computed from equation (9) with the aid of above determined model parameters. the predicted theoretical values of scc(0) gradually increases and get closure to their corresponding ideal values at elevated temperatures. the deviation between the ideal and theoretical values of scc(0) at complex formation concentration (xcc = x1 = 0.75) are 0.1121, 0.1093, 0.1065 and 0.1038 at temperatures 1873 k, 1973 k, 2073 k and 2173 k respectively forecasting that the tendency towards the complex formation is the most at 1873 k which is its melting temperature and the least at 2173 k. theoretical investigations thus predict that the preferred system is the most interacting at 1873 k and the least at 2173 k. the compositional dependence of α1 and dm/did at different temperatures are computed from equations (10) and (11) and are portrayed in figure 4. it can be observed that the plots of α1 gradually shallows with increase in the temperature of the alloy predicting the decrease in the compound forming tendency at elevated temperatures. the computed values of α1 at compound forming concentration are -0.1298, 0.1228, -0.1164 and -0.1103 at 1873 k, 1973 k, 2073 k and 2173 k respectively. the perusal of figure 5 indicates that computed values of dm/did gradually decreases at higher temperatures indicating the similar results as discussed above. 3.3 surface properties the study of surface properties, such as surface tension (σ) and surface segregation (xal s and xfe s ) provides information about the wettability, catalytic activities of alloy catalysts and other mechanical properties of liquid alloys. the surface properties of al−fe liquid alloy at 1873 k have been computed using equation (12a) in the framework of renovated butler model. the molar surface areas of the components of the liquid alloy (λi; i = a = al and b = fe) are calculated from equations (12b) and (12c) by putting s.k. yadav et al. / bibechana 15 (2018) 60-69: rcost p.65 f = 1.06 [14, 15, 23]. the molar volume (vi 0) of the pure component is estimated from the ratio of its atomic mass to density (m/ρ). the densities and the surface tension (σi 0) of the pure components of the liquid alloy are taken from table 2. fig. 3: the computed values of scc(0) versus concentration of al (x1) for al−fe liquid alloy at different temperatures. fig. 4: the computed values of α1 versus concentration of al (x1) for al−fe liquid alloy at different temperatures. table 2: densities and surface tensions of pure metals [26] metal melting temp. density surface tension t0(k) ρ(kg m-3) σi 0(n m-1) al 933 2385-0.280(t-t0) 0.914-0.35x10-3(t-t0) fe 1809 7015-0.880(t-t0) 1.872-0.49x10-3(t-t0) the computed values of σ as a function of concentration for al−fe liquid alloy at 1873 k are plotted in figure 6. it can be observed that the theoretical value of σ is less than its ideal value at all concentrations. the perusal of figure 7 communicates that the surface concentration of al (xal s ) is greater whereas that of fe (xfe s ) is less than their corresponding ideal values revealing that al atoms segregates on the surface region and fe atoms remains in the bulk region of the liquid mixture at 1873 k. it has been already mentioned that the thermodynamic properties have been correlated with the renovated butler model to predict the surface properties of the preferred liquid alloys at different temperatures. the compositional dependence of σ, xal s and xfe s are computed at afore mentioned temperatures from equation (12) with the aid of values from tables 1 and 2. figure 8 portrays the compositional dependence of σ of the system at different temperatures. the predicted value of surface tensions decreases at elevated temperatures which may due to decrease in cohesive force of the liquid mixture as forecasted by the thermodynamic and structural properties earlier. s.k. yadav et al. / bibechana 15 (2018) 60-69: rcost p.66 figure 9 shows the compositional dependence of xal s and xfe s for the alloy at different temperature. the computed values of xal s gradually decreases whereas that of xfe s gradually increases with increase in the temperatures of the melt above 1873 k. both of these values get closure to their respective ideal values at elevated temperatures. it can be thus predicted that the al atoms move from surface region to the bulk region whereas the fe atoms move from bulk region to the surface region with increase in temperature of the alloy to maintain equilibrium in the liquid phase. fig. 5: the computed values of dm/did) versus concentration of al (x1) for al−fe liquid alloy at different temperatures. figure 6: surface tension (σ) versus concentration of al (x1) for al−fe liquid alloy at 1873 k. fig. 7: the computed values of surface concentration of al (xal s ) and fe (xfe s ) versus concentration of al (x1) for al−fe liquid alloy at 1873 k. fig. 8: the computed values of surface tension (σ) versus concentration of al (x1) for al−fe liquid alloy at different temperatures. s.k. yadav et al. / bibechana 15 (2018) 60-69: rcost p.67 fig. 9: the computed values of xal s and xfe s versus concentration of al (x1) for al−fe liquid alloy at different temperatures. 4. conclusions the theoretical investigations forecast that the compound forming tendency of the preferred liquid alloy gradually decreases at higher temperatures. the alloy is found to be the most reactive at its melting temperature and this nature gradually declines at elevated temperature. the surface concentrations of al decreases whereas that of fe increases with increase in temperature of the alloy indicating the movement of former atoms from the surface to bulk region and that of later atoms from bulk to surface region. additionally, the system shows ideal behaviour at higher temperatures. references [1] a.b. bhatia, w.h. hargrove, concentration fluctuations and thermodynamic properties of some compound forming binary molten systems, phys. rev. b 10 (1974) 3186. doi.org/10.1103/physrevb.10.3186. 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[26] e.a. brandes, g.b. brook, smithells metals reference book, jordanhill, oxford: butterwarth−heinemann (1992). s.k. yadav et al. / bibechana 15 (2018) 60-69: rcost p.69 https://doi.org/10.1080/00319104.2011.569887 https://doi.org/10.1021/acs.langmuir.5b00217 https://doi.org/10.1007/s10853-015-9533-8 https://doi.org/10.1080/14786435.2016.1181281 https://doi.org/10.1021/ie50458a035 https://doi.org/10.1088/0034-4885/60/1/003 https://doi.org/10.1080/22243682.2014.928603 https://doi.org/10.1063/1.555788 https://doi.org/10.1103/physrev.77.669 https://doi.org/10.1016/j.tca.2011.02.028 https://doi.org/10.1007/s11661-011-0902-x devendra sir cover page copy.jpg bibechana 17 (2020) 146-153 146 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal reassessments of thermo-physical properties of si-ti melt at different temperatures s. k. yadav 1* , u. mehta 1, 2 , r. k. gohivar 1, 2 , a. dhungana 1, 2 , r. p. koirala 1 , d. adhikari 1 1 department of physics, mahendra morang adarsh multiple campus, t. u., biratnagar, nepal 2 central department of physics, tribhuvan university, kirtipur, kathmandu, nepal *e-mail: yadavshashit@yahoo.com article information: received: july 06, 2019 accepted: december 26, 2019 keywords: si-ti system surface segregation reassessment ideal behaviours abstract the compositional dependence of thermo-physical properties of si-ti liquid alloy has been reassessed using different modeling equations at temperatures 2000 k, 2400 k and 2473 k. the thermodynamic and structural properties of the system have been computed in the frame work of quasi-lattice test. the extent of surface segregation and surface tension of the liquid mixture have been computed using butler’s equations at afore mentioned temperatures. the results so obtained have been compared with the available literature database. theoretical investigations show that the compound forming tendency of the system gradually decreases at elevated temperatures and hence it shows ideal behaviours, as expected. 1. introduction the assessment of the thermo-physical properties of metallic solutions are of fundamental importance in the field of metallurgy to characterize, design and fabricate new materials with desired properties. the micro-granules along with the temperature, pressure and atmospheric conditions of the initial melts determine the physical strength, wettability, stability, ductility, electrical resistivity, etc. of the metallic complexes [1]. therefore, the comprehensive knowledge of the energetic of the liquid mixtures is mandatory. this information cannot be solely obtained from the experimental measurements as they are tedious, expensive and often encounter difficulties to be handled at high temperatures. with these regards, the development of modeling equations to explain and predict the thermo-physical properties of liquid alloys serve as robotic tool in material science and engineering. several theoretical models [1-8] so far have been developed to access these properties to develop thermodynamic database. in present work, we intend to apply quasi-lattice test [5, 9, 10] to study and predict the thermodynamic, structural and surface properties of si-ti liquid alloys at different temperatures. this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.26877 http://nepjol.info/index.php/bibechana mailto:yadavshashit@yahoo.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.26877 s.k. yadav et al. / bibechana 17 (2020) 146-153 147 alloys of titanium have light weight, high ductility, low thermal conductivity, high melting temperature and high strength due to which they are used as functional materials in aerospace, automotive industries and various high temperature applications [11, 12]. among which si-ti alloy provides useful dispersive strength and improves microstructure stability [11]. these desirable properties have drawn considerable attentions of the researchers [11, 13-17] working in this field to study the thermodynamic properties of liquid si-ti alloy. topor and kleppa (1986) studied the standard enthalpy of formation of si2ti complex by high temperature calorimetric measurements and have presented the results for the solid state at 298 k. tabaian et al. (2000) presented the results for the thermodynamic properties of the concerned system by the langmuir effusion method for the alloy containing 0-58.7 mass% of ti. their results constitute the partial enthalpy and entropy of si and activity coefficient of ti in the alloy at 1873 k in the above mentioned concentration range. further, they presented the expression for the integral excess free energy of mixing (gm xs) in the form of redlich-kister (r-k) [18, 19] polynomials and computed the activity of si (asi) and gm xs. later tokunaga et al. (2004) used regular solution approximation based on the sub-lattice model to comprehend the gibbs free for the individual phases in the binary and ternary systems of ni-siti alloy on the basis of calphad method and recalculated the phase diagram of si-ti alloy. in 2007, kostov et al. calculated the activities of si and ti, partial and integral fee energy of mixing for the alloy at 2000 k, 2400 k and 2473 k using factsage thermo-chemical, a computer based software. taking this database as reference, awe et al. in 2011 computed the thermodynamic and structural properties of the system at aforementioned temperatures on the basis of statistical mechanical model. recently, safarian et al. in 2012 used a quasi-regular solution model to determine the thermodynamic activity of si in si-ti liquid alloy and presented the results so obtained in graphical form. as per the available literatures, the complete dataset of thermo-physical properties of si-ti liquid alloy is not yet available till date. in this work, therefore, we have employed the modeling equations of quasi-lattice test to compute the thermodynamic properties, such as excess free energy of mixing (gm xs) and activity (ati and asi) and structural properties, such as concentration fluctuation in long wavelength limit (scc(0)), chemical short-range order parameter (α1) and ratio of diffusion coefficients (dm/did) of the alloy at different temperatures. further, the surface properties, such as surface tension (σ) and the extent of surface segregation (xi s; i = ti and si) have been computed using equations of butler model [20]. the results so obtained have been compared with the available literature database. we have assumed the metallic complex ti3si as a stable phase [11, 14, 15, 21] and computed the herein required model parameters. the details of the modeling equations are presented in the section 2, the results along with the necessary discussions are presented in the section 3 and the conclusions of the present findings are summarized in the section 4. 2. formulations thermodynamic properties let one mole of the binary liquid solution consisting of x1(= c) atoms of a (=ti) and x2(= 1 − c) atoms of b (=si). the quasi-lattice test can explain the thermodynamic properties of binary liquid alloys. according to quasi-lattice test, the expression for the thermodynamic functions having suitable chemical complex of the form aμ bϑ (where μ = 3 and ϑ = 1) can be given as [5, 9, 10, 22] gm xs = nkb t [ϕ ω kb t + ϕab ∆ωab kb t + ϕaa ∆ωaa kb t ] (1) where n is avogardo's number, kb is boltzmann constant, t is the temperature and ω's are the ordering energies. c1(= cti) is the concentration of a, c2(= 1 − c = csi) is concentration of b, and ϕij (i, j = a, b) are the simple polynomials in c s.k. yadav et al. / bibechana 17 (2020) 146-153 148 depending upon μ. the ordering energy coefficient ∆ωaa = 0, if μ = 1 and ordering energy coefficent ∆ωbb = 0, if ϑ = 1 for the ti3si liquid binary alloy (present case), the values of ϕ's are expressed as [9, 10] ϕ = c(1 − c) (2) ϕab = ( c 5 + 2c3 3 − c4 − c5 5 + c6 3 ) (3) ϕaa = (− 3c 20 + 2c3 3 − 3c4 4 + 2c5 5 − c6 6 ) (4) the free energy of mixing (gm) then can be expressed as gm = gm xs + rt[(c ln c + (1 − c) ln(1 − c)] (5) activity is one of the thermodynamic functions which are obtained directly from experiment and can be interpreted to describe the stability of the metallic complex of the liquid mixture. activity depends upon temperature, pressure and concentration of mixture. although its value depends upon customary choices of standard state for the species, activity is treated as dimensionless quantity. it can be given as [5, 9, 10, 22] ln aa= gm rt +(1-c)[ ω kbt ϕ′ + ∆ωab kbt ϕ′ ab + ∆ωaa kbt ϕ′ aa + ln c 1−c ] (6) where ϕ′ = 𝜕ϕ 𝜕𝑐 . in similar manner, the activity of b (ab) can be obtained from equation (6) by substituting ϕ′ = 𝜕ϕ 𝜕(1−𝑐) and making the necessary adjustments. structural properties the alloys are grown from the liquid state near to the melting temperatures of individual ingredients and hence are assumed to be disorder state exhibiting only short-range order interactions. the study of the structural properties, such as concentration fluctuation in long wavelength limit (scc(0)), warren-cowley short-range order parameter (𝛼1) and ratio of mutual to intrinsic diffusion coefficients (dm/did) helps to understand the arrangement of atoms of the liquid mixture in the nearest neighbourhood. according to quasilattice model, the expression for scc(0) can be given as [5, 9, 10] scc(0) = c(1−c) 1+ c(1−c) kbt [ωϕ′′ +∆ωabϕ′′ ab+∆ωaaϕ′′ aa] (7) where ϕ′′ = ∂2ϕ ∂c2 . 𝛼1 and dm/did can then be expressed in terms scc(0) by the following relations [1, 6, 7] α1 = s−1 s(z−1)+1 with s = scc(0) scc id(0) ; and scc id(0) = x1x2 (8) and dm did = scc id (0 scc(0) (9) where z is the coordination number and is takes 10 in present work calculation. surface properties the surface properties of the liquid mixture help to understand the metallurgical phenomenon, such as crystal growth, welding, gas absorption, nucleation of gas bubbles. as mentioned earlier, the butler’s model has been used to compute the surface tension of the concerned alloy. according to this model, the surface tension (σ) of a binary liquid solution at temperature t can be expressed as [20, 23] σ = σ1 + 1 τ1 (g1 e,s − g1 e,b) + rt τ1 (lnx1 s − lnx1) (10) σ = σ2 + 1 τ2 (g2 e,s − g2 e,b) + rt τ2 (lnx2 s − lnx2) (11) where σ1 and σ2 are surface tensions, and τ 1 and τ 2 are the areas of the hypothetical layer at the surface of the pure components a and b respectively at temperature t. gi e,s andgi e,b , (i =1,2), are partial excess free energies xi and xi s and are mole fractions of component i in the bulk and that in the surface respectively. the area of monatomic surface layer for the component i is obtained from the following relation τi = 1.091 na 1/3 vi 2/3 (12) where na is avogadro’s constant and vi represents the molar volume of the component i. the molar volume can be calculated from the atomic mass and density of the pure component at the temperature of investigation. the partial excess gibbs energy in the bulk and that in the surface are assumed to have s.k. yadav et al. / bibechana 17 (2020) 146-153 149 the same concentration dependence, they can be related to each other through a parameter λ as λ = gi e,s/gi e,b (13) the value of λ is considered to be 0.83 for the calculations. 3. results and discussion the model parameters herein required are optimized using equations (1-4) with the aid of reference values of gm xs [11] at temperatures 2000 k, 2400 k and 2473 k. the values so optimized are presented in table 1. in order to provide validation of the present theoretical reassessment, the computed values of gm xs/rt were compared with the available literature datasets [11, 14, 16, 21, 24]. awe et al. [16] obtained the thermodynamic and structural properties of the system considering the dataset of ref. [11] as experimental value, meanwhile, gm xs is expressed in the form of r-k polynomials [18] in the literatures of ref. [14, 21, 24]. in terms of such polynomials, the integral excess free energy (gm xs) of the liquid alloy is expressed as gm xs(x, t) = c1c1 ∑ kz(t)(c1 − c2)zn z=0 (14) withkz(t) = az + bzt + cz ln t + dzt2 + − −; where a, b, c and d are the coefficient to be determined and kz has the same temperature dependence as gm xs. the partial excess free energies of granules of the alloy then can be expressed as ga xs(x, t) = c2 2 ∑ kz(t)n z=0 [(1 + 2z)c1 − c2](c1 − c2)z−1 (15) and gb xs(x, t) = c1 2 ∑ kz(t)n z=0 [c1 − c2(1 + 2z)](c1 − c2)z−1 (16) table 1: optimized model parameters (present work). t (k) ∆ω/kbt ∆ωab/kbt ∆ωaa/kbt 2000 0.67311 0.80990 0.82940 2400 -18.461 -15.383 -14.928 2473 37.609 31.333 30.403 the values of gm xs/rt have been obtained using equation (14) with the help of coefficients presented in the above mentioned references. the compositional dependence of the different values of gm xs/rt at above mentioned temperatures are plotted in figures 1(a-c). the computed values of the present work is in well agreement with the reference dataset of kostov et al. [11] and cost 507 [21] throughout the entire concentration range at preferred temperatures. these values slightly deviate with those of awe at al. [16] and tokunuga et al. [24] in the concentration range 0.41 < cti < 0.86 whereas that of tabaian et al. [14] in the concentration range cti < 0.56. even though, the reference thermodynamic data is same in the present work and that in ref. 16, the computed values deviate. this may be due the modeling equations used in the present work have three model parameters whereas those used in ref. 16 has only one. moreover, the values calculated from ref. 14 shows miscibility gap above 2000 k and hence are excluded. further, the plots of computed values of gm xs/rt as a function of concentration (cti) gradually shallows with increase in temperature of the alloy (figs. 1(ac)). it corresponds that the compound forming tendency of the liquid alloy gradually decreases at higher temperatures and is found to be most interacting at its melting temperature (2000 k). the similar tendency has been predicted by several researchers in different alloy systems [1, 11, 16, 19, 25, 26]. the extent of compound forming tendency can further be interpreted in terms of activities of the free monomers (ati and asi) of the liquid alloys. these values for the present work at different temperatures are obtained using equations (5 and 6) with the help of the parameters from table 1. to compute these values for the ref. 14, 21 and 24, at first the partial excess free energies of the monomers (gti xs and gsi xs) are obtained using the equations (15 and 16) and the necessary parameters are taken from the respective references. the values so obtained are plotted as function of cti in figs. 2 (a-c). s.k. yadav et al. / bibechana 17 (2020) 146-153 150 1(a) 1(b) 1(c) figs. 1(a-c): gm xs/rt versus cti for si-ti liquid alloy at different temperatures. 2(a) 2(b) 2(c) figs. 2(a-c): ati and asi versus cti for si-ti liquid alloy at different temperatures. s.k. yadav et al. / bibechana 17 (2020) 146-153 151 the computed value of activity of the system for present work are in well agreement with those obtained from the ref. 11 and 21 and is in good agreement with those of ref. 16 and 24. meanwhile, the activity computed using ref. 14 data are in poor agreement. therefore, the reassessment of the thermodynamic data in present work is comparatively more reliable. further, the activity curves show negative deviation from raoult’s law but this deviation gradually decreases with increase in the temperature of the alloy. these findings further strengthen the results obtained from the free energy of mixing as mentioned above. to understand the local arrangement of atoms in the liquid alloy, its structural properties (scc(0), α1 and dm/did) have been computed using equations (7-9) and values from table 1. the compositional dependence of the values so obtained is plotted in figs. 3(a-c). the computed values of scc(0) gradually increases and ascends towards ideal values with raise in temperature above 2000 k (fig. 3(a)). the curve of α1 gradually shallows up and that of dm/did shallows down predicting the similar trends as above (fig. 3(b and c)). these results are in accordance with those of other researchers [1, 16, 26]. as per the available literatures, the surface properties of si-ti liquid alloy have been computed for the first time in present work. for this purpose, we have used equations (10-13), herein required parameters have been taken from table 2 (with tq= 2000 k, 2400 k and 2473 k) and ref. 11, 21 and 24. the values of σ, xti s and xsi s for the concerned liquid alloy are plotted in figs. 4(a and b). it can be observed that xti s > xsi s which corresponds that ti atoms segregate on the surface phase whereas si atoms remain in the bulk phase of the liquid mixture. with the increase in the temperature of the mixture, ti atoms gradually move towards the bulk phase and si atoms move gradually move towards the surface phase in order to maintain equilibrium [1, 16, 25] (fig. 4(a)). the surface tension of the mixture computed from above mentioned reference data gradually decreases with increase in its temperature (fig. 4(b)). these findings further stand in favour to the conclusions drawn from the computations of thermodynamic and structural properties of the alloy. due to unavailability of the experimental and literature data, the present findings of surface properties could not be compared. but the theoretical investigations of the present work are in accordance with that of earlier researches [1, 16, 25]. 3(a) 3(b) figs. 3(a-c): scc(0), α1 and dm/didversus cti for si-ti liquid alloy at different temperatures. s.k. yadav et al. / bibechana 17 (2020) 146-153 152 table 2: input parameters for surface tension [27]. 4(a) 4(b) figs. 4(a, b): surface tension (σ) and surface concentration (xti s and xsi s ) for si-ti liquid alloy at different temperatures. 4. conclusions a complete dataset of thermo-physical properties for si-ti liquid alloy at different temperatures have been presented in the present work. theoretical investigations show that the alloy is most interacting and shows greatest mixing tendency at its melting temperature. this tendency, 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(section 14.2), butterwarth−heinemann, 1992. https://doi.org/10.2298/jmmb0701029k https://doi.org/10.1007/bf02665321 https://doi.org/10.1515/htmp.2000.19.3-4.257 https://doi.org/10.2320/matertrans.45.1507 https://doi.org/10.1016/j.tca.2011.02.028 https://doi.org/10.1007/s10853-012-6449-4 https://doi.org/10.1021/ie50458a036 https://doi.org/10.4236/msa.2018.910058 https://doi.org/10.1016/j.apsusc.2011.04.019 https://doi.org/10.3126/bibechana.v13i0.13443 https://doi.org/10.1007/s11661-011-0902-x bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.86 (online publication: dec., 2016) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal nbo, chemical reactivity, thermodynamic properties and hyperpolarizability analysis of aristolochic acid ii bhawani datt joshi department of physics, tribhuvan university, siddhanath sc. campus, mahendranagar, nepal * email bdjoshi_007@yahoo.com, pbdjoshi@gmail.com article history: received 3 september, 2016; accepted 8 october, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15892 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract alkaloids are a group of naturally occurring chemical compounds and show immense potential of medicinal uses in traditional systems. in this work, a computational study on an alkaloid aristolochc acidid ii (aa ii) is presented using density functional theory, b3lyp functional employing 6-311g (d,p) basis set. natural bond orbital analysis has been carried out to investigate the various conjugative and hyperconjugative interactions within the molecule and their second-order stabilisation energy (e(2)). the local nucleophilic reactivity descriptors such as fukui functions (𝑓𝑘 +, 𝑓𝑘 −), local softness (𝑠𝑘 +, 𝑠𝑘 −) and electrophilicity indices (ω𝑘, + , ω𝑘 −) analyses have been carried out to determine the reactive sites within the molecule. the non-linear optical properties have been calculated using the same basis set. the calculated value of the first order hyperpolarisability (β0), suggests that the investigated molecule is an attractive object in future for non-linear optical properties. keywords: aa ii; dft; nbo; chemical reactivity; hyperpolarizability. . 1. introduction majority of drugs in use today are natural products, natural product mimics or semi synthetic derivatives. therefore in recent times, focus on plant research has increased all over the world and large body of evidence has been collected to show immense potential of medicinal plants used in various traditional systems. plants are sources of natural antioxidants, and some of the compounds have significant antioxidative properties and health benefits. aristolochic acids (aas) which mainly include aristolochic acid i (aa i), aristolochic acid ii (aa ii) and aristolochic acid iii (aa iii) are normally present in aristolochia and asarum of aristolochiaceae [1]. in oriental medicine the fruit of aristolochia is given for cough and dyspnea. their roots have biological functions including treatment of stomach-ache, http://nepjol.info/index.php/bibechana mailto:bdjoshi_007@yahoo.com mailto:pbdjoshi@gmail.com http://dx.doi.org/10.3126/bibechana.v14i0.15 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ https://en.wikipedia.org/wiki/natural_product https://en.wikipedia.org/wiki/chemical_compound https://creativecommons.org/licenses/by-nc/4.0/ bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.87 (online publication: dec., 2016) toothache, eczema, hypertension relief, rheumatism relief, leukocyte enhancement, edema therapy, poisonous snake bites as well as analgesic and diuretic effects [2,3]. in the family of natural products, the alkaloids occupy a unique place and provide challenging problems for structural elucidation, synthetic and biosynthetic studies. because of their very complex structure and unique places the determination of their constitution and the discovery of the methods producing them synthetically offer attractive problems to the chemist and though a great deal has been accomplished much still remains to be done in this field. vibrational spectroscopy is a very valuable method for studying the dynamical behavior and to gain insight into the electronic structures of alkaloids at microscopic level [4]. however, both the raman and ir are the best traditional methods for the vibrational analysis and particularly for the non-destructive characterization of the substances [5], but in the recent years there has been interest in the application of ab initio calculations to the alkaloids as it provide the additional vibrational spectroscopic data [3-6]. in the present work the chemical reactivity descriptors, thermodynamic properties and the natural bond orbitals (nbos) analysis of an alkaloid aristolochic acid ii have been communicated. the aim of this study was to determine the stabilization energy when the system acquires an additional charge from the environment and the direction of the charge transfer. similarly, the variation of the thermodynamic properties with the temperature and, hybridization, conjugation and charge transfer in the polyatomic wave functions theoretically using ab initio hf and density functional theory (dft) [7]. we had presented some spectroscopic analysis on the title molecule in our previous work [8]. the crystal structure and optimized structure of aa ii are as shown in the figure 1a and b. fig. 1(a): crystal structure of aa ii. fig. 1(b): optimized structure of aa ii. 2. materials and methods 2.1 computational details geometry optimization has been performed as the first task of the computational work. the geometric parameters available from the pubchem data base [9] have been used as the basis for the optimization. these optimized parameters were computed by ab intio hf and the dft using gaussian 09 [10] program package employing b3lyp/6-311g (d,p) basis set. the dft calculations were mainly carried out in the bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.88 (online publication: dec., 2016) frame-work of the becke–lee-yang-parr [b3lyp] functional, in which the exchange functional is a local spin density exchange with becke gradient correction [11] and the correlation functional is that of lee, yang and parr with both local and nonlocal terms [12,13]. 3. results and discussion 3.1 natural bond orbital (nbo) analysis nbo analysis is one of the efficient methods for studying hybridization, conjugative interactions, covalence effects and charge transfer in polyatomic wave functions [4]. in the present work, utilizing the second-order micro-disturbance theory analysis, we have reported some of the electron donor orbital, acceptor orbital and the interacting stabilization energy. higher the value of stabilization energy e(2) more is the intensity of the interaction between electron donors and electron acceptors, i.e. the more donating tendency from electron donors to electron acceptors. the hyperconjugative interaction energy was deduced from the second-order perturbation approach [14-16]. 𝐸(2) = − 𝑛𝜎⟨𝜎|𝐹|𝜎⟩ 2 𝐸𝜎∗−𝐸𝜎 = −𝑛𝜎 | 𝐹𝑖𝑗 2 ∆𝐸 | where ⟨𝜎|𝐹|𝜎⟩2, or 𝐹𝑖𝑗 2 is the fock matrix element between i and j nbo orbital, 𝐸𝜎 and 𝐸𝜎∗ are the energies of 𝜎 and 𝜎* nbo’s, and 𝑛𝜎 is the population of the donor orbital. the larger the e(2) value the more intensive is interaction, the greater the extent of conjugation of the whole system [16]. hyperconjugation may be given as a stabilizing effect that arises from overlap between an occupied orbital with another neighboring electron deficient orbital when these orbitals are properly oriented. the most important interaction between ‘‘filled’’ (donor) lewis type nbos and ‘‘empty’’ (acceptor) nonlewis nbos are reported in table 1. there occurs a strong intramolecular hyperconjugative interactions of 𝜋 electrons of the rings r2 and r3 from c11 c15, c13 c17, c10 c12 and c14 c16 to the 𝜋*(c8 c9) bond of which increases the electron density 0.474e leading to the stabilization. this enhanced the further conjugation of the 𝜋*(c8 c9) nbo mainly with 𝜋*(c10 – c12) and 𝜋*(c14 – c16) resulting to the high stabilization of 236.16 and 134.76 kcal/mol, respectively. also, there occur some another hypercinjugative interactions of 𝜋 electrons from c13 – c17 → 𝜋*(c11 – c15) with ed 0.40135e, c14 – c16 → 𝜋*(o5 – n7) with ed 0.60349e, c18 – c21 → 𝜋*(c10 – c12) with ed 0.44633e and c20 – c22 → 𝜋*(c18 – c21) with ed 0.27488e leading to the stabilization energies 21.06, 16.48, 18.62 and 18.77 kcal/mol, respectively. similarly, the enhanced nbos 𝜋*(c11 – c15) conjugate with 𝜋*(c13 – c17) in ring r2 which further conjugates with 𝜋*(o4 – c23) of the carboxyl group leading to the corresponding stabilization energies 276.35 and 112.33 kcal/mol, respectively. the electron donation related to the resonance in the molecule is from lp(2) o3 to antibonding acceptor 𝜋*(o4 – c23) of carboxyl group (41.00 kcal/mol) and from lp(2) o6 to 𝜋*(o5 – n7) of no2 group (168.74 kcal/mol). the interactions are mainly confined between the rings and the lone pair electron groups. these charge transfer in the system lead to the structure activity of the molecule. a comparison of the nbo and mullikan charges is given in the table 2. bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.89 (online publication: dec., 2016) table 1: second order perturbation theory analysis of fock matrix in nbo basis for aa ii. donor nbio(i) ed (i)/e acceptor nbo(j) ed (j)/e e(2)a (kcl/mol) [e(j) –e(i)]b f(i,j)c lp(2)o1 1.85366 𝜋* (c11 – c15) 0.40135 23.22 0.35 0.087 lp(2)o2 1.85651 𝜋* (c11 – c15) 0.40135 23.59 0.35 0.086 lp(2)o3 1.82127 𝜋* (o4 – c23) 0.24140 41.00 0.36 0.111 lp(2)o4 1.83912 𝜎*(o3 c23) 0.09844 32.38 0.61 0.128 𝜎*(c13 c23) 0.06750 18.44 0.68 0.102 lp(2)o5 1.89423 𝜎*(o6 – n7) 0.07135 19.19 0.71 0.105 𝜎*(n7 – c14) 0.10978 14.26 0.55 0.079 lp(2)o6 1.89355 𝜎*(o6 – n7) 0.07135 18.60 0.73 0.105 𝜋*(o5 – n7) 0.60349 168.74 0.15 0.144 𝜎(c11 c15) 1.97681 𝜎*(c8 c11) 0.02801 6.07 1.27 0.079 𝜎(c14 c16) 1.97140 𝜎*(c9 c14) 0.03163 5.49 1.24 0.074 𝜎(c16 – h24) 1.97338 𝜎*(c9 c14) 0.03163 6.26 1.02 0.072 𝜋(c8 c9) 1.58253 𝜎*(o1 c11) 0.02832 6.00 0.99 0.069 𝜋(c10 – c12) 1.56437 𝜋* (c8 – c9) 0.47400 16.91 0.26 0.060 𝜋* (c14 – c16) 0.22748 16.78 0.28 0.065 𝜋* (c18 – c21) 0.27488 17.31 0.28 0.065 𝜋* (c20 – c22) 0.27301 17.26 0.28 0.065 𝜋(c11 – c15) 1.63802 𝜋* (c8 – c9) 0.47400 17.68 0.30 0.067 𝜋* (c13 – c17) 0.36737 20.25 0.31 0.071 𝜋(c13 – c17) 1.68334 𝜋* (o4 – c23) 0.24140 17.24 0.30 0.065 𝜋* (c8 – c9) 0.47400 18.48 0.28 0.067 𝜋* (c11 – c15) 0.40135 21.06 0.27 0.069 𝜋(c14 – c16) 1.77190 𝜋* (o5 – n7) 0.60349 16.48 0.17 0.052 𝜋* (c8 – c9) 0.47400 13.55 0.30 0.061 𝜋* (c10 – c12) 0.44633 12.99 0.31 0.060 𝜋(c18 – c21) 1.68756 𝜋* (c10 – c12) 0.44633 18.62 0.28 0.067 𝜋* (c20 – c22) 0.27301 18.46 0.29 0.066 𝜋(c20 – c22) 1.69812 𝜋* (c10 – c12) 0.44633 18.47 0.29 0.067 𝜋* (c18 – c21) 0.27488 18.77 0.29 0.067 𝜋*(c8 c9) 0.47400 𝜋* (c10 – c12) 0.44633 16.36 0.28 0.061 𝜋* (c11 – c15) 0.40135 23.40 0.26 0.070 𝜋* (c13 – c17) 0.36737 18.20 0.28 0.064 𝜋*(c10 – c12) 0.44633 236.16 0.01 0.074 𝜋*(c14 – c16) 0.22748 134.76 0.02 0.072 𝜋*(c11 – c15) 0.40135 𝜋*(c13 – c17) 0.36737 276.35 0.01 0.084 𝜋*(c13 – c17) 0.36737 𝜋*(o4 – c23) 0.24140 112.33 0.01 0.063 a e(2) means energy of hyper conjugative interaction (stabilization energy). b energy difference between donor (i) and acceptor ( j) nbo orbitals. c f(i,j) is the fock matrix element between i and j nbo orbitals. bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.90 (online publication: dec., 2016) table 2: comparison between nbo and mullikan charges (esu) of aa ii. atom no nbo charges mulliken charges atom no nbo charges mulliken charges 1 o -0.541 -0.364 2 o -0.523 -0.339 3 o -0.688 -0.064 14 c 0.108 0.067 4 o -0.595 -0.333 15 c 0.269 0.189 5 o -0.367 -0.245 16 c -0.147 0.172 6 o -0.384 -0.271 17 c -0.201 0.122 7 n 0.522 0.156 18 c -0.180 0.080 8 c -0.061 -0.045 19 c 0.318 0.429 9 c -0.032 0.103 20 c -0.165 0.032 10 c -0.026 0.016 21 c -0.179 0.014 11 c 0.298 0.078 22 c -0.189 0.027 12 c -0.054 -0.084 23 c 0.820 0.328 13 c -0.124 -0.067 fig. 2: correlation between nbo and mulliken charges. 3.2 chemical reactivity 3.2 (a) global reactivity descriptors electrophilicity and hardness are two important molecular properties, which are useful for interpreting and understanding the stability and reactivity of molecular system [17]. according to the hohenberg and kohn (hk), theorems [7], the energy of the basic state of an electronic system is a functional of electron density. on the basis of koopman’s theorem [17], global reactivity descriptors: electronegativity (χ), bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.91 (online publication: dec., 2016) chemical potential (μ), global hardness (η), global softness (s) and global electrophilicity index (ω) were calculated using the energies of frontier molecular orbitals ehomo, elumo and given by relations (1) (5) [18-20]. χ = − 1 2 [ 𝐸𝐻𝑂𝑀𝑂 + 𝐸𝐿𝑈𝑀𝑂] (1) μ = − χ = 1 2 [ 𝐸𝐻𝑂𝑀𝑂 + 𝐸𝐿𝑈𝑀𝑂] (2) η = 1 2 [𝐸𝐿𝑈𝑀𝑂 − 𝐸𝐻𝑂𝑀𝑂] (3) s = 1 2 η (4) ω = μ2 2η (5) ∆𝑁𝑚𝑎𝑥 = − μ η (6) according to parr et al., electrophilicity index (ω), a positive and finite quantity, is a global reactivity index similar to the chemical hardness (a measure of the resistance of a system to transfer charge), and chemical potential. this new reactivity index measures the stabilization in energy when the system acquires an additional electronic charge (∆n) from the environment up to saturation. the direction of the charge transfer is completely determined by the electronic chemical potential of the molecule because an electrophile is a chemical species capable of accepting electrons from the environments. therefore its energy must decrease upon accepting electronic charge and its electronic chemical potential must be negative. the energies of frontier energy levels (ehomo, elumo), energy band gap (δe), electronegativity (χ) that representing the tendency of atoms or molecules to attract electrons; chemical potential (μ), global hardness (η), global softness (s), global electrophilicity index (ω), and additional electronic charge (δn) for aa ii are listed in the table 3. the calculated high value of electrofilicity index (ω) shows that the molecule behaves as a strong electrophile. table 3: calculated ehomo, elumo, energy band gap (δe), electronegativity (χ), chemical potential (μ), global hardness (η), global softness (s), global electrophilicity index (ω) and additional electronic charge (δnmax) (in ev) for aa ii , using b3lyp/6-31g (d,p). ehomo elumo ∆e μ η s ω ∆nmax -6.113904 2.396963 3.716941 -4.267835 1.858471 0.269038 4.900378 2.296299 3.2 (b) local reactivity descriptors using hirshfeld population analysis of neutral, cation and anion state of molecule, fukui functions (𝑓𝑘 +, 𝑓𝑘 −, 𝑓𝑘 0) [20, 21], are calculated at same calculation method b3lyp/6-31 g (d,p) using following relations (7-9): 𝑓𝑘 + = [q(n+1) – q(n)] for nucleophilic attack (7) 𝑓𝑘 − = [q(n) – q(n-1)] for electrophilic attack (8) 𝑓𝑘 0 = ½[q(n+1) –q(n-1)] for radical attack (9) where n, n-1 and n+1 are total electrons present in neutral, cation and anion state of molecule, respectively. local softnesses (𝑠𝑘 +, 𝑠𝑘 −, 𝑠𝑘 0) and local electrophilicity indices (ω𝑘 +, ω𝑘 −, ω𝑘 0), also used to describe the reactivity of atoms in molecule, are calculated using the following equations (10) and (11): 𝑠𝑘 + = s𝑓𝑘 +, 𝑠𝑘 − = s𝑓𝑘 −, 𝑠𝑘 0 = s𝑓𝑘 0 (10) ω𝑘 + = ω𝑓𝑘 +, ω𝑘 − = ω𝑓𝑘 −, ω𝑘 0 = ω𝑓𝑘 0 (11) where +, −, 0 signs show nucleophilic, electrophilic and radical attack, respectively. bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.92 (online publication: dec., 2016) table 4: hirshfelf atomic charges (in esu), fukui functions (𝑓𝑘 +, 𝑓𝑘 −); local softness (𝑠𝑘 +, 𝑠𝑘 −); and local electrophilicity indices (ω𝑘 +, ω𝑘 −); in ev for atomic sites of aa ii, using hirshfeld population analysis at b3lyp/6-31g (d,p) level. atom no. hirshfeld atomic charges fukui functions local softness local electrophilicity indices qn qn+1 qn-1 𝑓𝑘 + 𝑓𝑘 − 𝑠𝑘 + 𝑠𝑘 − ω𝑘 + ω𝑘 − 1 o -0.137056 -0.082403 -0.154852 0.05465 0.01779 0.0147 0.0048 0.2678 0.0872 2 o -0.154125 -0.084260 -0.180316 0.06986 0.02619 0.0188 0.0070 0.3424 0.1283 3 o 0.014549 0.054444 -0.024939 0.03989 0.03948 0.0107 0.0106 0.1955 0.1935 4 o -0.285351 -0.247806 -0.310391 0.03754 0.02504 0.0101 0.0067 0.1840 0.1227 5 o -0.188738 -0.146976 -0.272371 0.04176 0.08363 0.0112 0.0225 0.2046 0.4098 6 o -0.197151 -0.168658 -0.278778 0.02849 0.08162 0.0077 0.0220 0.1396 0.4000 7 n 0.235014 0.239420 0.193255 0.00440 0.04175 0.0012 0.0112 0.0216 0.2046 8 c -0.004447 0.007625 -0.015539 0.01207 0.01109 0.0032 0.0030 0.0592 0.0544 9 c -0.001680 0.024782 -0.005068 0.02646 0.00338 0.0071 0.0009 0.1297 0.0166 10 c 0.002314 0.017857 -0.029614 0.01554 0.03192 0.0042 0.0086 0.0762 0.1565 11 c 0.067660 0.115375 0.035707 0.04771 0.03195 0.0128 0.0086 0.2338 0.1566 12 c -0.003587 0.019794 -0.024961 0.02338 0.02137 0.0063 0.0058 0.1146 0.1047 13 c -0.019426 0.041108 -0.050936 0.06053 0.03151 0.0163 0.0085 0.2966 0.1544 14 c 0.037710 0.073211 -0.007816 0.03550 0.04552 0.0096 0.0122 0.1740 0.2231 15 c 0.060119 0.117917 0.026964 0.05779 0.03315 0.0155 0.0089 0.2832 0.1625 16 c 0.032000 0.105890 -0.068122 0.07389 0.10012 0.0199 0.0269 0.3621 0.4906 17 c 0.027244 0.077415 -0.035180 0.05017 0.06242 0.0135 0.0168 0.2459 0.3059 18 c 0.001778 0.029849 -0.037889 0.02807 0.03966 0.0076 0.0107 0.1376 0.1944 19 c 0.252942 0.342971 0.204487 0.09002 0.04845 0.0242 0.0130 0.4412 0.2374 20 c 0.019442 0.075432 -0.037948 0.05599 0.05739 0.0151 0.0154 0.2744 0.2812 21 c 0.016208 0.092320 -0.075592 0.07611 0.0918 0.0205 0.0247 0.3730 0.4499 22 c 0.014773 0.073505 -0.047009 0.05873 0.06178 0.0158 0.0166 0.2878 0.3028 23 c 0.209756 0.221156 0.196862 0.0114 0.01289 0.0031 0.0035 0.0559 0.0632 bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.93 (online publication: dec., 2016) 3.3 thermodynamic properties computation of thermodynamic properties of molecules is important for both thermochemistry and chemical equilibrium. statistical thermodynamics with the two key ideas, boltzmann distribution and the partition function leads to the derivation of the equations utilized for computing thermochemical data in gaussian programs. the standard thermodynamic functions: heat capacity (𝐶𝑝,𝑚 𝑜 ), entropy (𝑆𝑚 𝑜 ) and enthalpy (𝐻𝑚 𝑜 ) together with the total energy, zero point energy, rotational constants, dipole moment were obtained directly from the output of dft calculation employing 6-311g (d,p) basis set and listed in tables 5a and b. as observed from the table, the values of 𝐶𝑝,𝑚 𝑜 , 𝑆𝑚 𝑜 and 𝐻𝑚 𝑜 increase with the increase of temperature from 100 k to 900 k which is attributed to the enhancement of molecular vibration while the temperature increases. the correlation between temperature and these thermodynamic properties are given in fig. 3. table 5(a): theoretically calculated thermodynamic properties at different temperatures using 6-311g (d,p) basis set. temperature (k) enthalpy (kj/mol) specific heat (j/mol-k) entropy (j/mol-k) 100 600.0808 109.4366 349.5692 200 615.3002 195.5655 457.4258 300 639.3226 284.6956 556.9808 400 671.9977 366.7323 652.7906 500 712.2009 434.9499 744.0818 600 758.5195 489.2314 829.8888 700 809.6702 532.1265 909.9358 800 864.6581 566.3607 984.4193 900 922.7266 594.0700 1053.757 the correlation equations are as follows: 𝐻𝑚 𝑜 = 583.65002 + 0.10323 t + 3.07745 x10-4t2 (r2 = 0.99952) (12) 𝐶𝑝,𝑚 𝑜 = -2.98254 + 1.12581 t – 5.14425 x10-4 t2 (r2 = 0.99957) (13) 𝑆𝑚 𝑜 = 238.13449 + 1.14381 – 2.63687 x10-4 t2 (r2 = 0.99999) (14) these thermodynamic relations would provide useful information for the study of thermodynamic energies and estimate directions of chemical reactions according to the second law of thermodynamics in thermochemical field. further, these equations could be utilized in predicting the gibbs free energy, which would help in the judgment of spontaneity of the reactions. [22]. 3.4 nonlinear optical properties (nlo) nonlinear optics (nlo) deals with the interactions of applied magnetic fields in various materials to generate new magnetic field altered in phase, frequency, amplitude or other physical properties [23]. some organic substances with 𝜋 electronic system exhibit the largest known nonlinear coefficients and show promise for thin fabrication, allowing the enormous function and cost integrated electronic circuitry. bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.94 (online publication: dec., 2016) fig. 3: correlation between the thermodynamic parameters with the temperature. table 5(b): theoretically calculated thermodynamic properties at room temperature using 6-311g (d,p) basis set. thermodynamic properties dft (b3lyp) hf total energy (ev) -30513.38103 -30336.08362 zero-point energy (kj/mol) 142.05075 151.82499 rotational constants (ghz) 0.33647 0.33647 0.27097 0.27097 0.15671 0.15671 dipole moment (d) 6.2937 6.8561 entropy (j/mol-k) 555.17088 498.49426 enthalpy (kj/mol) 638.80014 673.31022 specific heat (j/mol-k) 283.07796 256.55586 first hyperpolarizability is a third rank tensor that can be described by a 3×3×3 matrix. the 27 components of the 3d-matrix can be reduced to 10 components due to the kleinmann symmetry [21]. it can be given in the lower tetrahedral format. it is obvious that the lower part of the 3×3×3 matrix is a tetrahedral. the components of β0 are defined as the coefficients in the taylor series expansion of the bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.95 (online publication: dec., 2016) energy in the external electric field. when the external electric field is weak and homogeneous this expansion becomes: 𝐸 = 𝐸0 − μ𝑖𝐹𝑖 − 1 2 α𝑖𝑗𝐹𝑖𝐹𝑗 − 1 6 β𝑖𝑗𝑘𝐹𝑖𝐹𝑗𝐹𝑘 … .. where 𝐸0 is the energy of the unperturbed molecules, 𝐹𝑖 is the field at the origin and μ𝑖, α𝑖𝑗, β𝑖𝑗𝑘 are the components of dipole moment, polarizability, and first hyperpolarizability respectively. the total dipole moment (μ0), the mean polarizability (|α0|), the anisotropy of the polarizability (∆α) and the total first hyperpolarizability (β0) using x, y, z components are defined as [24]: 𝜇 = (𝜇𝑥 2 + 𝜇𝑦 2 + 𝜇𝑧 2) 1 2⁄ (15) |α0| = 1 3 (α𝑥𝑥 + α𝑦𝑦 + α𝑧𝑧) (16) ∆α = 2−1/2 [(α𝑥𝑥 − α𝑦𝑦) 2 + (α𝑦𝑦 − α𝑧𝑧) 2 + (α𝑧𝑧 − α𝑥𝑥)2 + 6α𝑥𝑥 2 ] 1/2 (17) β0 = ( β𝑥 2 + β𝑦 2 + βz 2) 1/2 (18) where β𝑥 = β𝑥𝑥𝑥 + β𝑥𝑦𝑦 + β𝑥𝑧𝑧 β𝑦 = β𝑦𝑦𝑦 + β𝑥𝑥𝑦 + β𝑦𝑧𝑧 β𝑧 = β𝑧𝑧𝑧 + β𝑥𝑥𝑧 + β𝑦𝑦𝑧 since the x, y, z components of |α0|, ∆α and β0 of gaussian 09 output are reported in a atomic mass unit (a.u.), the calculated values have been converted into electrostatic unit (esu) (for |α0|: 1 a.u. = 0.1482 × 10−24 esu; for β0: 1 a.u. = 0.086393 × 10−31 esu) and listed in the table 6. the high value of β0, one of the key factors in an nlo system, supports that the investigated molecule will show good nlo response. table 6: dipolemoment (µ debye), polarizability (α x10-24esu) and first order hyperpolarizability (β0 x10-31esu). dipole moment polarizability hyperpolarizability dft hf dft hf dft hf μ𝑥 -5.2839 -5.2243 α𝑥𝑥 -119.1408 -118.3740 β𝑥𝑥𝑥 27.3548 31.7449 μ𝑦 4.0465 3.7945 α𝑦𝑦 -121.7131 -122.2665 β𝑦𝑦𝑦 53.8593 47.8559 μ𝑧 0.1350 0.2183 α𝑧𝑧 -136.8908 -138.6496 β𝑧𝑧𝑧 5.8486 6.4994 μ0 6.6567 6.4607 α𝑥𝑦 10.6612 12.0501 β𝑥𝑦𝑦 -71.5489 -71.1348 α𝑥𝑧 -2.7854 -2.4720 β𝑥𝑥𝑦 37.2794 38.8391 α𝑦𝑧 0.7627 0.7135 β𝑥𝑥𝑧 -17.6840 -16.7678 |α0| -125.9149 -126.4300 β𝑥𝑧𝑧 7.6975 8.5779 ∆α 207.6443 206.4903 β𝑦𝑧𝑧 16.6563 18.0840 30.7314 30.5606 β𝑦𝑦𝑧 8.8145 9.7722 β𝑥𝑦𝑧 -9.5344 -10.3423 β0 9.8355 9.4355 4. conclusion computational study proves that nbo analysis and nlo properties of the investigated molecule are successfully predicted by the b3lyp/6-311g (d,p) method. the 𝜋 → 𝜋* interactions are responsible for bhawani dutt joshi / bibechana 14 (2017) 86-97 : rcost p.96 (online publication: dec., 2016) the conjugation of respective 𝜋-bonds within aromatic rings, rings and c=o, no2 groups, which stabilized the molecule with maximum energy ~ 21.06, 17.24 and 16.48 kcal/mol, respectively. the electron donation related to the resonance interaction in the molecule is mainly confined between the rings and the lone pair groups leading to the maximum energy 168.74 kcal/mol. the calculated high value of electrofilicity index (ω) is in agreement that the molecule behaves as a global electrophile. the compound exhibits strong effective ict due to the movement of the 𝜋-electron cloud from donor to acceptor and shows second-order nonlinearity. the value of first order hyperpolarisability (β0) shows that the title molecule can be used as an attractive material for nlo applications. acknowledgements we acknowledge to prof. poonam tandon, macromolecular research laboratory, university of lucknow, india for providing facility of the gaussian 09 calculations. also, thanks are to cnpq-twas fellowship program for financial support to pursue post-doc study in universidate federal do ceara, fortaleza, brazil. references [1] a.a. pozdzik, i.j. salmon, f.d. debelle, c. decaestecker, c, van den branden, j.l. vanherweghem, d. verbeelen, m.m. deschodt-lankman, j.l. nortier, kidney international 73 (2008) 595-607. http://dx.doi.org/10.1038/sj.ki.5002714 [2] w. tang and g. eisenbrand, chinese drugs of plant origin-chemistry, pharmacology and use in traditional and modern medicine, springer-verlag, berlin, germany, (1992) pp.145. 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http://dx.doi.org/0002-7863/83/1505-7512$01.50/0 http://dx.doi.org/10.1021/ja983494x http://dx.doi.org/10.1021/jp0760758 http://www.hindawi.com/24593503/ http://www.hindawi.com/65672832/ http://www.hindawi.com/94654659/ http://dx.doi.org/10.1155/2013/258519 http://dx.doi.org/10.1002/anie.198406901 http://dx.doi.org/10.1016/j.molstruc.2006.11.066 devendra sir cover page copy.jpg review article bibechana 17 (2020) 139-145 139 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal conventional to slow muon microscopy – a review amba datt pant1,2 1institute of quantum beam science, graduate school of science and engineering, ibaraki university, 21-1 bunkyo, mito 310-8512, japan 2institute of materials structure science, high energy accelerator research organization (kek), 1-1 oho, tsukuba, ibaraki 305-0801, japan email: amba.datt.pant.phys@vc.ibaraki.ac.jp article information: received: september 27, 2019 accepted: december 04, 2019 keywords: muon muonium sr technique abstract because of special characteristics (fully spin polarized and asymmetric decay to positron), muon acts as sensitive probe to study the local electronic and dynamics of materials. the muon of energy mev or high, conventional muon, are used to study bulk properties of the materials. for the study of nanoscience, slow muon (20 ev 30 kev) muon with low energy spread are essential that leads to development of slow muon microscopy. introduction to muon microscopy, application of conventional muons and need of slow muon beam along with future prospects are briefly discussed. ultra-slow muon 1. introduction muon is an elementary particle of lepton family of 2nd generation of standard model of particles (table 1). its mass is about 207 times of electron mass and 1/9 times of proton mass as shown in table 2. the gyromagnetic ratio of muon is around three times higher than that of proton which makes it more sensitive in materials. muons are available from two ways naturally, it is available in cosmic ray with 1 event per square cm per min with relatively higher energy (~gev) [1], and another is from accelerators with high intensity (e.g., ~ 106 muons per sec in japan proton accelerator research complex, j-parc) and tunable energy. muon born from decay of pion. in accelerators, high energy proton are bombarded to pion production target (usually graphite) and pions are produced (p + p → π+ + p + n). when the pion at rest decays (two body decay, fig. 1) to muon and a neutrino (+ → + + ), due to conservation of momentum, muon and neutrino have equal and opposite momentum [2]. the pion is the zero spin particle and the spin of neutrino is antiparallel to momentum (negative helicity) which suggests that the spin of muon must be opposite to its momentum (fig. 1). thus muon has 100% spin polarization. this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.26867 http://nepjol.info/index.php/bibechana mailto:amba.datt.pant.phys@vc.ibaraki.ac.jp https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.26867 amba datt p / bibechana 17 (2020) 139-145 140 muon decays to positron and two neutrinos ( 𝜇+ → 𝑒+ + 𝜈𝑒 + 𝜈𝜇̅̅̅ ) with life time 2.2 s. due to violation of parity in weak interaction, positrons are produced asymmetrically along the spin direction of muon at the time of decay. with these characteristics – fully spin polarized and asymmetric decay to positron, it works as sensitive magnetic (spin) probe to study the materials. since it is sensitive even less than a gauss magnetic field, it acts as sensitive probe to study the local electronic and spin states of materials through muon spin rotation and relaxation (sr) method [1, 3]. conserving the momentum, muon is 100% spin polarized. here, pi and si are used for momentum and spin of corresponding particles, respectively. table 1. standard model of particles. table 2: properties of electron, muon and proton. fig. 1: decay of pion (𝜋+ → 𝜇+ + 𝜈𝝁) at rest. when the muons are produced from the pions at rest on the surface of pion production target (like graphite), such muons are called as surface muon. energy of such surface muons is ~ 4.1 mev (momentum ~ 29 mev/c). and when the muons are produced from the pion in-flight and captured by strong magnets, then such muons are called as decay muons (momentum > 40 mev/c). in this article conventional term is used for both surface and decays muons having energy of mev order. on the other hand, slow muon are refereed as sloweddown surface muon to low energy (20 ev – 30 kev). such slow muons can be stopped in the thin films of some nm depth from surface of sample however conventional muons needs thicker (~mm) samples to stop. in addition to positive muons, negative muons are also being popular for study of elemental analysis [4]. when a negative muon incident in materials, it is attracted by atomic nuclei. since its mass is much greater than that of an electron, it readily displaces an electron from an atom and rapidly drops down to the 1s state. consequently, emission of muonic x-ray can be observed [4, 5]. analysis of such muonic x-ray provides the information about the elemental composition of materials as a nondestructive analysis method. in this review, we concentrate on only positive muon and its applications. 2. advantages of muon microscopy muon acts as spin polarized probe so it behaves as a magnetic needle in materials. it can be applied at any temperature and without perturbation (without external field) of system. its time window (10-11 – 10-5 s) is wider than other techniques (nmr, neutron and mossbaur) [6] as shown in fig. 2. unlike electron and proton, when high energy muon incident into materials there are no braking radiation, pair production and nuclear reactions happened. it can approach to higher depth in the materials than other particles. it stops interstitial sites in near the high electron density. its bound state with an electron known as muonium which is like a light isotope of hydrogen. it is an exotic atom amba datt p / bibechana 17 (2020) 139-145 141 made up of two lepton particles. it can predict/mimic the behavior of h in the materials. it also used to test the quantum electrodynamics (qed) fig. 2: comparison of time window of different techniques. the sr technique has wider time (~ 10-11 to 10-5 s) window than other methods. 3. sr techniques initially in 1981, the term μsr was coined [8] as “μsr stands for muon spin relaxation, rotation, resonance, research, or what have you. the intention of the mnemonic acronym is to draw attention to the analogy with nmr and esr, the range of whose applications is well known. any study of the interactions of the muon spin by virtue of the asymmetric decay is considered μsr, but this definition is not intended to exclude any peripherally related phenomena, especially if relevant to the use of the muon's magnetic moment as a delicate probe of matter.” in sr technique, the spin polarization of muon is 100%. however in nmr and esr, the polarization of the nuclear or electron spins is very far from 100%, so that a radio frequency or microwave photon is required to resonantly perturb the system and obtain a signal. when muons are incident on material, decayed positrons are collected by detectors around the sample (fig. 3(a)). time evolution of those positron provides the information about the material [3]. suppose, f is positron events collected by forward counter and b is that by backward counter, then asymmetry = (f b) / (f + b) = a0 g(t), where  is alpha factor that depends on efficiency of detectors and sample positions, a0 is initial asymmetry, and g(t) is polarization function. the collections of some of g(t) are presented in musrfit program [9, 10]. in general, there are two geometrical set-ups for sr measurements – transverse and longitudinal field sr measurement (namely tf and lf measurement). when momentum of incident muon spin is parallel to external applied magnetic field it is known as longitudinal field measurement and when muon spin is perpendicular to applied field it is known as transverse field measurement (fig. 3 (a,b,c)). muon precesses around the field according to the larmor precession. fig. 3: schematic diagram for sr set-ups and spectrum. (a) experimental set-up for transverse field (tf) and longitudinal field (lf) measurement, (note that the both measurements set up performed separately) (b) counts collected by forward and backward detectors at tf measurement, and (c) the muon time evolution spectra, asymmetry, at tf measurement. 4. applications of conventional muons when muon implanted into materials, it thermalizes very quickly (within ns) and its spin is not affected during thermalization. however the spin of muon is affected by the magnetic properties of environment of specimen. depending on nature of materials and environment of stopping site of muon, it captures electron and form muonium or remained in same amba datt p / bibechana 17 (2020) 139-145 142 diamagnetic state. the polarization function, g(t), provides important information about the materials. thus the muons are used to study the magnetism, superconductivity, molecular dynamics, particle physics, life science, new physics beyond standard model, etc. researches in physics, chemistry and biology have been widened using conventional muons. for example, study of energy storage materials [11], semiconductor [12], semiconductor and insulators [13], life science [2, 14-17], polymer [18], particle physics [19, 20], and many more. with the use of high intensity muons, there are some experiments like g-2/edm, muon to electron conversion, etc. are being carrying out. the g-2 experiment is being carrying out by two independent groups one in j-parc [21] and another in fermi national lab [22] to achieve the higher precision on the value of anomalous magnetic moment of muon than the previous experiment in brookhaven national laboratory group [19] and to discover the new physics beyond the standard model [19, 23]. because of functional and dynamic complexity of biosamples, few literatures are available on use of muon for study of life phenomena. to the best knowledge of author, nagamine et al [2] initiated the use of muon in biomaterials and explained the behavior based on muon labelled electron method [1]. recently sr method pointed out its application for cancer research [14] and diagnosis of disease [24]. electron transfer in protein [17, 25] and photosynthesis processes have been studying intensively through experimentally and theoretically [26, 27]. besides accelerator produced muon, cosmic muons are also useful for the study of non-destructive analysis of large scale architectures [28] and characterization of materials like study of trapped radioactive materials [29]. 5. need and development of slow muon beam the conventional muon (~mev energy or high) are stopped in a thick sample with broad stopping depth. with such high energy spread and incident energy, it can only be used to study the bulk properties of materials (schematic diagram presented in fig. 4). for the study of thin film, layered material, surface/interface and nanoscience study, slow muon beam is required. k. nagamine pointed out three methods for production of slow muons [30]. the generation of low energy muon through the cryogenic moderation method using van der waals solids such as solid ar or n2, which has been initiated at triumf and is developed at psi, switzerland [31]. second one is the laser resonant ionization of muonium produced from muonium generation materials [30]. this method was developed at kek and then at riken/ral pulsed muon facilities [30] and now adopting in jparc, japan [32-34]. third one is the beam cooling method by using electromagnetic confinement as well as acceleration or deceleration after detecting the phase space of each injected conventional muon. at psi, using continuous muon beam, the slow muon microscopy has been applied in different materials through user programs [35]. using pulsed muon beam in j-parc, the development of ultra slow muon beamline which is dedicated to slow muon microscopy is still in progress [33, 34]. the slow muons are successfully generated and transported to sample position [36]. now we are struggling to enhance the intensity and optimize the beam parameters. for the study of nanoscience and three dimensional visualization of materials, ultra slow muons are considered as promising tool. for this purpose, ultra slow muon microscope, an innovative instrumentation, is being developed in japan proton accelerator research complex (j-parc), japan [37]. there are two beams – ultra slow muon beam (energy 20ev – 30kev, beam size < 10mm) for surface and interface study of materials with nm depth and muon microbeam (energy 200 kev – 1 mev, beam size tens of micrometer). after reacceleration of slow muon (to prepare coherent beam), another instrumentation transmission muon microscope is also under development in jparc [38]. main goal of this instrument is to prove amba datt p / bibechana 17 (2020) 139-145 143 the dual nature of muon (wave and particle) and to provide three dimensional imaging of small alive samples. it will fulfil the gap between optical microscope and transmission electron microscope. fig. 4: schematic diagram for effect of energy spread of muon beams (left figure) – need of slow muon for nanoscience. slow muon can be controlled within nm depth however wide spread stopping depth for conventional muons (right figure). 6. future perspectives ultra slow muon is promising tool to study the nanoscience. it can be used for both materials and life study. the use of slow muon to study the surface, interface and grain boundary of materials will help to advance the development of functional materials for devices and understanding the basic and advanced sciences. there are still some challenges regarding to development of high intensity and low tunable energy slow muon beam. furthermore the application of slow muon to solution form or real biosample is another challenge because of need of high vacuum environment. without using the sample cell (window), we can use slow muon on single crystal samples but it is still difficult to 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[37] http://slowmuon.jp/english/head.html [38] http://slowmuon.kek.jp/muonmicroscopy_e.html [39] k. nagamine, past, present and future of ultra-slow muons, jps conf. proc. 2 (2014) 010001. doi: https://doi.org/10.7566/jpscp.2.010001. https://doi.org/10.1016/s0969-806x(00)00398-4 https://doi.org/10.1016/s0969-806x(00)00398-4 https://www.psi.ch/en/smus/lem http://slowmuon.jp/english/head.html http://slowmuon.kek.jp/muonmicroscopy_e.html https://doi.org/10.7566/jpscp.2.010001 bibechana 18 (2) (2021) 26-31 26 study of two-photon absorption and optical limiting bal ram ghimire central department of physics, tribhuvan university, kirtipur email: balram.ghimire@cdp.tu.edu.np article information: received: october 20, 2020 accepted: february 9, 2021 keywords: photon absorption optical limiters irradiance semiconductors abstract simultaneous absorption of two photons of identical or different frequencies to excite a system that is atom or molecule from ground state to excited state has great importance. it has important role as a spectroscopic tool for determining the positions of energy levels that are not connected to the atomic ground state by the one photon transition. in this work experimental study of two photon absorption of fused silica, quartz crystal and metal halides and optical limiters based on the semiconductors are studied. it was investigated that two photons absorption depletes the transmitted beam but carrier defocusing spreads the beam in space and hence density is reduced. it was realized that limiters with thin sample have low dynamic range and fluency is high on the damage prone surface and irreversible damage occurs. some semiconductors with high nonlinearity are found to be useful materials for optical limiters to protect devices like sensors. doi: https://doi.org/10.3126/bibechana.v18i2.34838 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction the process of simultaneous absorption of two photons of identical or different frequencies to excite a system that is atom or molecule from ground state to excited state is called two-photon absorption. in other words, in the process of two photon absorption (tpa) the transition between two states of the atom takes place by simultaneous absorption of two photon. this process was first reported experimentally by kaiser and garrett in 1961 [1]. two photon absorption is useful to spectroscopic tools for determining the positions of energy levels that are not connected to the atomic ground state by a one photon transition. the absorption cross section describing this process increases linearly with laser intensity according to the relation [1]. i)2( = [1] where )2( is a coefficient that describes twophoton absorption. the atomic transition rate due to two photon absorption scales as the square of the laser intensity [1], r =    2)2( i [2] devices designed to have high transmittance for low level inputs while blocking the transmittance for high intensity laser beams, are optical limiters. the bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:balram.ghimire@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v18i2.34838 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana bal ram ghimire / bibechana 18 (2) (2021) 26-31 27 first optical limiters for cw laser were based on the thermal lensing in absorbing liquid that is heating reduced the index causing thermal blooming resulting in a beam that was no longer focused in an imaging system. it is desirable for a limiter to keep its transmitted focusable energy below about 1mj even for inputs up to many milli joules, while maintaining a linear transmittance of approximately 50%. two photon absorption, self-focusing in kerr liquids, nonlinear scattering from carbon particle suspensions and among other processes have been suggested for pulsed laser sources. the focusable energy depends on the particular type of system the limiter is to protect. for example, for the human eye, a good measure of the focusable energy is that which falls within a 1.5 mrad diameter in the final focal plane. the device must have a high damage threshold. basic requirement for a material to be good optical limiter are: (1) high damage threshold, (2) fast response, (3) an excited state absorption cross-section that exceeds the good state absorption cross-section. to meet all these demanding specifications research has progressed on two fronts. the first is to synthesize and characterize new limiting materials and second is to design new optical geometries that maximize the range of protection using available materials. for a limiter it must have a high linear transmission for low input energy or power and large dynamic range at which device damage to the limiting input. the ideal optical limiter has the characteristics as shown in the figure-1. main application of the optical limiter is for sensor protection and damage to detectors is almost always determined by fluence that is irradiance, these are the quantity of interest for the output of the limiter. for high transmission at low input, we must have low linear absorption. these criteria lead to the use of two-photon absorption process is shown in fig-2. in 1964-1967 leite et al. described nonlinear refraction as a means to measure low absorption in liquids and demonstrated an optical limiter that used thermal blooming in nitrobenzene and along with a spatial filter, regulated the output power of a cw argon laser to 30mw. in 1966 reickhoff reported irradiance dependent self-defocusing in liquids. in 1969 geusic et al. reported limiting behavior in si attributed to stepwise nonlinear absorption with 1.06 micrometer radiation. bogges et al. shoed fluence limiting in si that was due to combination of nonlinear absorption with a refractive contribution induced by the photoexcitation of free carriers. ralston and chang described the use of two photon absorption for optical limiting and conducted power limiting experiments in a series of semiconductors like gaas, cdse, and cds. in 1980 cs2 was tested as a limiting medium. an apparent advantage of liquid-based limiters is that they self-heal, permitting high dynamic ranges limited only by damage to cell windows. the response time has been shown to be 2 p sec in the visible. the limiting power can be varied by adjusting the concentration of cs2 in solvents. soileau et al. described that when picoseconds pulses were used in a comparative study of limiting in seven liquid crystals, two photon absorption was responsible for the limiting behavior. bjorkholm et al. built advice that uses the selffocusing in sodium vapor that is due to near-resonant excitation at a wavelength of 590 nm. some of the largest nonlinearities exhibited to date are in semiconductors. fig. 1: irradiance output of an ideal optical limiter as a function of input power of energy [2]. bal ram ghimire / bibechana 18 (2) (2021) 26-31 28 in this work description of the experimental determination of two-photon absorption coefficient in fused silica, crystalline quartz and some alkali halides are given on the basis of stephen a. slattery and co-workers. report of the detailed operational characteristics and a theoretical description of optical limiters based on two-photon absorption and the subsequent photo-generated free-carrier defocusing in semiconductors are given. fig. 2: two photon absorption. 2. theory and methodology experimental determination of two-photon absorption coefficient in 2020 nugroho et al. realized that for many applications potential can be hold by two photon absorption and predicted that two-photon absorption occur coherent and incoherent biexcitation transition [3]. stephen a. slattery and d. n. nikogasyan described two photon absorption properties of some common uv materials like fused silica, quartz, caf2, and baf2, using the fifth harmonic of nd-glass laser radiation at 211nm. they determined tpa coefficient with the help of following experimental set up as shown in the fig-3. the pulses at fundamental frequency at 1055nm, 800 j , with repetition rate 27 hz and fourth harmonic at 264nm, 400 j , with repetition rate 27 hz were directed into the 0.2 mm thick betabarium-borate (  -bab2o4) crystal cut for first type nonlinear sum-frequency mixing such that the angle between two pulses was about 7 0 in vertical plane. the energy stability of 211nm radiation was 100 j [ 5, 6,7,8, 9]. to achieve the time coincidence between the interacting pulses inside the nonlinear crystal the manually optical delay was used. to control the energy incident on the energy detector small part of uv pulse was reflected to the energy detector by a selected suprasil fused silica plate at near normal incidence. there is a plane-convex caf2 lens to change the cross-sectional area of the laser beam. the samples were placed on a mountable table along the axis of uv beam behind the lens. there is another detector placed 10 cm in front of the focal point which restrict the movement of sample towards the beam focus in order to protect it from damage [5]. similarly, hagen et al. calculated two photon absorption coefficients of ten different semiconductors using the following model [11]. ( ) 32 2 /2 g g p en ef ek    = (3) where n is linear refractive index ep and eg are in electron volts, constant k is was found to be 2600 to 3600. fig. 3: experimental set up for determination of two photon absorption coefficient [3]. bal ram ghimire / bibechana 18 (2) (2021) 26-31 29 optical limiting with semiconductors e. w. van stryland and coworkers described the optical limiting with semiconductors. in 2020 qian et al. demonstrated reflection-mode pulse limiters using nano-scale refractory films of aluminium based metallic quantum well and investigated that such a device could provide large and ultra-fast kerr-type optical non-linarites [4]. when the thick samples of semiconductor like znse, gaas were used, the large nonlinearities of semiconductor could be used to prevent damage [5, 6, 10, 11]. when the light was focused tightly into the bulk of the materials, the nonlinear absorption combines with nonlinear refraction and keeps the irradiance within the semiconductor below the damage threshold and becomes self-protecting. if low input limiting threshold is maintained the irradiance reduces on the surface, at high inputs the two photon absorption and defocusing reduce the irradiance in the bulk preventing damage. such situation cannot be explained quantitatively, though it can be explained qualitatively [2]. schematic drawing of the thick limiter geometry has been shown in the figure 5. the solid lines show linear beam propagation for low inputs and the dashed lines show the beam for high inputs. two photons absorption depletes the transmitted beam but carrier defocusing spreads the beam in space and hence density is reduced. it was noted that limiters with thin sample have low dynamic range and fluence is high on the damage prone surface and irreversible damage occurs within 1 or 2 orders of magnitude of limiting. to reduce this problem is to use thick samples having large thickness than depth of the focus and to focus into the bulk of the materials reducing the irradiance on the damage prone -surface. at low inputs the thick limiter acts linearly as thin limiter. but at thin limiter’s threshold thick limiter does not act as linear at the region within the focal volume. because at that region the irradiance become high enough to have significant two photon absorption along with carrier defocusing. monolithic optical limiter optical limiters for the visible based on znse and zns were built by the process of combination of absorption and refraction. these limiters work well for picoseconds inputs [11]. the geometrical arrangement of a monolithic optical limiter has been given in the figure 7. the solid lines show the optical path for inputs and dashed lines represent the optical paths for high inputs. this device acts as a unity power inverting lens for the low inputs. the design of the monolithic optical limiter takes the damageprone surface as far from focus as is possible to maintain high irradiance within the bulk, so that there would be maximum dynamic range. the out of the mode locked nd: yag laser was collimated to a spot size of 1mm and directed into the device. for znse device limiting energy was found to be 10nj with 300w, 30ps and fwhm into 0.53  m pulse and dynamic range 10 4 . the optical damage to the bulk of the material was prevented by combining the effect of depletion due to tpa and carrier defocusing before the focal position determined by linear optics. thus monolithic limiter is self-protecting against high irradiance nano and picoseconds pulses. when they focused nanoseconds pulses less tightly into plane parallel to znse and zns samples, they found that the devices suffered bulk damage. but when they focused tightly the focus volume become small and the thermal nonlinearity. caused damage. however, problem can be overcome by using materials with a negative thermal nonlinearity. fig. 4: schematic diagram of thick limiter geometry. bal ram ghimire / bibechana 18 (2) (2021) 26-31 30 fig. 5: monolithic optical limiter [2]. 3. result and discussion the uv beam irradiance was varied in the range 2-40gw/cm 2 at room temperature incident and transmitted pulse energies were measured by using photo electric detector pe10 connected to laser star energy meter system. here the position of the sample is so adjusted that allowed them to avoid selffocusing. when these conditions were fulfilled there would be no break-up and filamentation of beam. they recorded the transmittance irradiance dependencies and fitted them with the theoretical curve using mathematica package that has been shown in fig-4. the beam diameter was measured by measuring the energy transmittance through an aperture placed at the center of the beam symmetrically around the optical axis. the average value for the beam diameter at fwhm was 2.2 0.1 mm and pulse duration value at 211nm was 250 20 fs and 220 10 fs at 264 at 1/e level. by measuring the beam diameter and pulse duration they calculated the values of two photon absorption coefficients of samples at different wavelengths which are given in the table-1. van stryland and co-workers observed that at the aperture 30cm behind the second lens, of the thick znse optical limiter the transmitted energy varies with incident energy as shown in the figure 6. where (a) represent the linear transmission, (b) represents the effect of two photon absorption showing all energy collected and (c) indicates the transmitted energy through an aperture as a function of the input 0.53 m picoseconds pulses. fig. 6: transmittance as a function of incident laser intensity for fused silica [2]. table-1: two photon absorption coefficients of samples at different wavelengths. materials )(nm )/10( 11 wcm− fused silica crystalline quartz barium fluoride calcium fluoride 211 248 264 211 264 211 258 211 248 50 8 4.5 2.9 1.7 0.2 59 8 1.2 0.2 58 9 11 7 26 5 0.8 0.5 this shows that the limiting is weakly dependent on the focal length of the second lens and distance to the aperture. with the help of limiter at this configuration using picoseconds 0.5  m pulses and tight focusing they obtained limiting energies down to 14 nj corresponding to a peak power of 400w with dynamic range1000. bal ram ghimire / bibechana 18 (2) (2021) 26-31 31 fig. 7: transmitted energy as a function of incident energy [2] 4. conclusion process of two-photon absorption and experimental determination of two photon absorption coefficients of fused silica, quartz crystal and metal halides are discussed, on the basis of model given by stephen a. slattery and coworkers. working of optical limiters based on the semiconductors with the help of the model given by van stryland and co-workers was studied. it is investigated that two photons absorption depletes the transmitted beam but carrier defocusing spreads the beam in space and hence density is reduced. it was noted that limiters with thin sample have low dynamic range and fluency is high on the damage prone surface and irreversible damage occurs. optical limiters based on the process of two photon absorption are better and cheaper devices to protect the expensive and sensitive devices like sensor. references [1] r. w. boyd, academic press, 2003, pp. 528-530. [2] s. eric, y. y. wu, d. j. hagan, m. j. soileau, and k. mansour j. opt. soc. b 5 (9) (1988) 1228-1235. [3] b. s. nugroho, a. a. iskandar, v. a. mallyshev and j. knoester, phy rev. b 102 (2020) 045405 [4] h. qian, s. li, y. li, c. f. chen, w. chen, s. e. bopp, y. u. lee, w. xiong and z. liu, science advances 6 (2020) 3456 . https://doi.org/10.1126/sciadv.aay3456. [5] s. a. slattery and d. nikogosyan, optics communications 228 (2003) 127-131. [6] j. m. hales, d. hagan, and s. eric, journal of chemical physics 121 (2004) 1101-1106. [7] m. balu, j. hales, d. hagan, and s. eric, optical society of america 9 12(2004) 3820. [8] r. a. negres, j. hales j, a. kobyakob, d. hagan, and s. eric, optics letters 27 (2002) 1980-1088 [9] i. k. dmitriy, s. yang, d. hagan, and s. eric applied optics 38 (1999) 5168-5180 [10] k. delfield, l. yong, r. negres, f. meigong,and h. florencio, chem. mater. 14 (2002) 3663-3667. [11] d. j. hagan, e. w. van stryland, m. j. soileau, and y. y. wu, j. opt. soc. am a 3(13) (1986) 105. bibechana 18 (1) (2021) 19-25 19 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal surface modification of polyamide by 50 hz dielectric barrier discharge (dbd) produced in air at atmospheric pressure rajesh prakash guragain1*, hom bahadur baniya1,2, santosh dhungana1, bishnu prasad pandey3 ujjwal man joshi1, deepak prasad subedi1 1department of physics, school of science, kathmandu university, dhulikhel, nepal 2department of physics, tri-chandra college, tribhuvan university, kathmandu, nepal 3department of chemical science and engineering, kathmandu university, dhulikhel, nepal *email: rayessprakash@gmail.com article information: received: february 14, 2020 accepted: june 15, 2020 keywords: polyamide (pa) contact angle surface free energy hydrophilicity optical characterization abstract industrial applications of the dielectric barrier discharge (dbd) have a long tradition. however, lack of understanding in some of its fundamental issues, such as the stochastic behaviors, is still a challenge for dbd researchers. the work was carried out at line frequency, 15 kv and at atmospheric pressure. this work focuses on the study of the electrical and optical characteristics of dbd at atmospheric pressure to determine a suitable condition for utilization of the device for surface modification of polyamides (pa) (nylon 6/6). in this work, films were treated by dielectric barrier discharge and the effects on the morphology and chemistry of the material was studied. surface characteristics were examined via contact angle measurements and sem. the wettability tests revealed the improvement of the hydrophilic character of the surface of polyamide films as the water contact angle measured after the plasma treatments significantly decreased. the corresponding changes of the total surface energy revealed a significant increase in its polar component. the improvement of the wettability of pa strongly depends on the treatment time. the outcomes of the experiments proved that the modification of surface properties via plasma treatment reach to its saturation point after certain treatment time thus reducing the necessity of further treatment. doi: https://doi.org/10.3126/bibechana.v18i1.27650 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction discharge characterization of dielectric barrier discharge (dbd) are often done using both numerical and experimental methods [1,2]. the scientific method includes techniques like optical and electrical means. the high electron temperature in nonthermal plasma causes changes on the surface properties of treated sample while its bulk properties remaining unaffected because of the low http://nepjol.info/index.php/bibechana mailto:rayessprakash@gmail.com https://doi.org/10.3126/bibechana.v18i1.27650 https://creativecommons.org/licenses/by-nc/4.0/ rajesh prakash guragain et al. / bibechana 18 (1) (2021) 19-25 20 ion temperature [3,4]. most of the polymers treated industrially are heat sensitive, so treating them with hot plasma doesn't yield good results [5]. here we discuss about the characterization of dbd and its application on the surface modification of polyamide at gas pressure condition. the surface modification of polymer includes change in wettability and adhesion as well as the enhancement or reduction of friction on the polymer surface [6]. the surface energy of the polymer can be either increased or decreased according to the need of the experiment and the functional groups can be either added or wiped out from the surface. surface energy is a very important property for applications of polymers. the low surface energy of polyamide causes that its adhesive properties are insufficient for bonding and printing. the poor adhesion of polyamide to more polar polymers and other substrates represents a controversy, which might be solved with modification of the polymer [7]. for this reason, the securing of fine adhesion of printing inks or adhesives to pa surface necessitates to boost its surface energy by a convenient method of modification. so, industrial plasma treatment involves continuous and rapid treatment of huge quantity of polymeric sample every day. reduction of treatment time of such polymeric samples by a few milliseconds can finally result out to the reduction of the treatment of thousands of samples by few minutes. so, determining optimal treatment time of the polymers sample is therefore, very important for industries which is the primary objective of the research. 2. materials and method the experimental setup of the research is as shown as in fig. 1. a cylindrical polycarbonate tube is used as the plasma chamber. the pc chamber is preferred due to its transparent nature allowing the experimentalist to see what actually is happening inside the discharge chamber. two circular brass electrodes, each diameter 5 cm and thickness 1 cm are 3.5 mm apart and a polycarbonate sheet of thickness 2mm is used as dielectric. the working voltage for the entire experiment is set to be 15000 v. current and voltage waveform are obtained using the digital oscilloscope (tektronix tds2000). a high voltage probe (pintek hvp28hf) is used for the determination of voltage across the electrodes. similarly, optical characterization of dbd at both the conditions is carried using ocean optics (usb2000+). the samples of polyamides (nylon 6/6) are cut into (3 cm × 1.5 cm) rectangular pieces. they are then washed by isopropanol and put into an ultrasonic bath for further cleaning. samples are placed on the polycarbonate sheet between the electrodes. thus, treated sample are taken for surface characterization. contact angle was measured using a contact angle goniometer (rame-hart model 200). in this work, leo (500) /zeiss fieldemission scanning electron microscope (sem) was used to examine surface morphology. fig. 1: schematic diagram of the experimental setup. 3. results and discussion electrical characterization the value of electron density (𝑛𝑒) has been calculated by using power balance method [8,9]. rajesh prakash guragain et al. / bibechana 18 (1) (2021) 19-25 21 this method is based upon the principle that the energy lost by the plasma parameters is equal to the power delivered by the source. the balance between the input power from high voltage power supply (p) and power lost in the plasma leads to. ............(1) 2 ab e b lost p n av e = fig. 2: electrical characterization of dbd at atmospheric condition. fig.2 shows the current and voltage waveform as a function of time of the dielectric barrier discharge generated using line frequency. the calculation was made by using the values given below: applied voltage = 15000 𝑉, discharge current = 0.0386 𝑚𝐴, interelectrode separation = 3.5 𝑚𝑚, applied frequency = 50 𝐻𝑧, area of each electrode = 20.43 𝑐𝑚2, bohm velocity (𝑣𝑏) = 2 × 105 𝑐𝑚/𝑠, 𝐸𝑙𝑜𝑠𝑡 = 50 𝑒𝑉 (in our condition) and 𝑃𝑎𝑏 is the total power absorbed by the capacitively coupled plasma. using these values, the electron density (𝑛𝑒) was found to be 2.52 × 1013𝑐𝑚−3 at atmospheric condition. optical characterization for optical characterization of dbd, a small hole is made on the cylindrical polycarbonate tube and, an optical fiber is inserted there. the discharge of the dbd is made to pass through the optical fibre and the spectra is recorded by the ocean optics (usb2000+) at atmospheric conditions. fig. 3 shows the spectra of the discharge and their corresponding intensities, and wavelength at an atmospheric pressure condition. fig. 3: spectra of the discharge at atmospheric pressure. in this method four suitable lines; two for nii (204.02 nm, 655.85 nm) and two for n iii (245.21nm, 378.57 nm) were chosen from spectral lines of nitrogen obtained from the discharge. the optical characterization is carried out using line intensity ratio method [10,11]. 𝑅1 𝑅2 = 𝐼1 𝐼2⁄ 𝐼3 𝐼4⁄ = ( 𝐴𝑝𝑞 𝐴𝑥𝑦 ) ( 𝑔𝑝 𝑔𝑥 ) ( 𝜆𝑥𝑦 𝜆𝑝𝑞 ) ( 𝐴𝑢𝑣 𝐴𝑟𝑠 ) ( 𝑔𝑢 𝑔𝑟 ) ( 𝜆𝑟𝑠 𝜆𝑢𝑣 ) 𝑒𝑥𝑝 [− 𝐸𝑝−𝐸𝑥−𝐸𝑟+𝐸𝑢 𝐾𝐵𝑇𝑒 ]………... (2) here, in equation (2), 𝑅 is the ratio of the intensity of two lines, 𝐼 is the intensity of the spectral line, 𝐴𝑖𝑗 is the transition probability of the transition 𝑖 ⟶ 𝑗, 𝑔𝑖 is the statistical weight of the upper level, 𝜆 is the wavelength of the line radiation, 𝐸𝑖 is the energy of the upper level, 𝐾𝐵 is boltzmann constant and 𝑇𝑒 is the electron temperature. the values of 𝜆 and 𝐼 are obtained from the observation, and the values of 𝐴𝑖𝑗 , 𝑔𝑖 and 𝐸𝑖 are obtained rajesh prakash guragain et al. / bibechana 18 (1) (2021) 19-25 22 from the national institute of standards and technology (nist) atomic spectra database [12]. table 1: shows the values of transition probability (𝐴𝑗𝑖), statistical weight of upper level (𝑔𝑖) and energy of the upper level (𝐸𝑖) for nii and niii lines obtained from nist database. nitrogen lines (𝝀) transition probability (𝑨𝒋𝒊) (𝑺−𝟏) statistical weight of upper level (𝒈𝒊) energy of upper level (𝑬𝒊) (ev) nii (204.02nm) 2.11×107 5 21.62 nii (655.85nm) 1.43×106 5 41.73 niii (245.21nm) 1.21×107 6 23.26 niii (378.57nm) 2.40×106 5 40.59 using the above data in equation (3.6) mentioned above, we obtain, 𝑅1 𝑅2 = 0.506𝑒𝑥𝑝 [ 2.78 𝐾𝐵𝑇𝑒 ] taking 𝑇𝑒 = 0.5 𝑒𝑉 , corresponding intensity ratio 𝑅1 𝑅2 = 131.4. similarly, the other values of 𝑇𝑒 and their corresponding intensity ratio 𝑅1 𝑅2 are listed in table 2. table 2: value of 𝑅1 𝑅2 for different 𝑇𝑒. electron temperature (ev) intensity ratio 𝑹𝟏 𝑹𝟐 0.5 131.47 0.6 52.04 0.7 26.84 0.8 16.34 0.9 11.10 1 8.15 1.1 6.33 1.2 5.13 1.3 4.29 1.4 3.68 1.5 3.22 1.6 2.87 1.7 2.59 1.8 2.37 fig. 4: optical characterization of dbd at atmospheric condition. fig.4 is the graph plotted between electron temperature 𝑇𝑒 and corresponding intensity ratio 𝑅1 𝑅2 . this graph is used to determine the electron temperature using the value of 𝑅1 𝑅2 obtained from the intensity ratio. from the oes spectra, the value of the ratio of the intensity of spectral lines is found to be 8.58 which corresponds to the electron temperature of 0.97 ev. rajesh prakash guragain et al. / bibechana 18 (1) (2021) 19-25 23 contact angle and surface free energy measurements the static contact angle measurements are made before the treatment and immediately after the treatment by dropping 4 𝜇𝑙 of distilled water (h2o) and glycerol (c3h8o3) on the surface of the pa samples. for smooth and homogeneous surface, the water contact angle and surface free energy is measured at the equilibrium according to the young's equation, and owens wendt kaeble methods respectively [13,14]. cos ..........(3)sv sl lv     − = where, sv is the surface free energy of the solid substrate, sl is the interfacial tension between the solid and the liquid and lv is the surface tension of the liquid. for two liquids i and j , ( ) ( ) 1 1 2 2(1 cos ) 2 2 ......(4)d d p p li i li s li s     + = + ( ) ( ) 1 1 2 2(1 cos ) 2 2 ......(5)d d p p lj j lj s lj s     + = + surface free energy (γ) was calculated in terms of polar p s and dispersive d s components. the addition of these two components eventually gives the total surface free energy of the solid. fig. [5, 6] show the variation of water contact angle and surface free energy of pa surface as the function of treatment time. the contact angle is found to decrease with the increase in treatment time. after few minutes it finally saturates. treatment of pa by atmospheric pressure dielectric barrier discharge is able to change its contact angle from 57.510 (control) to a minimum value of 29.010 after 30 seconds. when the treatment time exceeds 30 seconds, the measured water contact angle nearly seems to reach a saturation state suggesting that the physical and chemical changes induced fig. 5: contact angle measurement at atmospheric pressure. fig. 6: surface energy measurement of polyamide at atmospheric pressure. by the plasma is also in saturation state [15]. also, the treatment of pa by atmospheric plasma is able to change its surface energy from 49.84 mj/m2 (control) to about 64.91 mj/ m2. similar trend is also observed for the polar component and it is mainly due to the incorporation of the polar species such as carbonyl (c=o) and carboxyl (-cooh) groups on the treated pa surface. the dispersive rajesh prakash guragain et al. / bibechana 18 (1) (2021) 19-25 24 component does not have any contribution to increase the wettability of the pa surface [16]. it is found that the further treatment of pa also does not cause any significant changes in the surface free energy reducing the requirement of further treatment. sem analysis fig. [7-8] show the sem micrographs of control and plasma treated pa films at atmospheric pressure. as can be seen in the micrograph, the untreated polymer surfaces is characterized by organized lamellae. this texture of the untreated sample of the polymer pertains to the process of the polymer film production (which is possibly induced by the film blow procedure during production) and not due to plasma treatment. it can be seen that the surfaces of the air plasma treated polymer is changed with slightly increased non-uniform roughness compared to the untreated polymers. the gradual increase in the particle grain size with the image scan area can be attributed to the etching of the polymer surface by plasma treatment [17]. fig. 7: sem micrograph of control sample of polyamide. fig. 8: sem micrograph of plasma treated sample of polyamide at 1 minute. 4. conclusions the results of this research showed that a relatively homogeneous discharge can be achieved at an atmospheric pressure condition. treatment of pa using dielectric barrier resulted in improvement on hydrophilicity of the polymeric material. the improvement of wettability of pa strongly depends on the treatment time. during the experiment, contact angle of polymers after plasma treatment was found to decrease effectively whereas, corresponding surface free energy was increased. sem micrographs of the plasma treated pa samples revealed the change in the surface morphology of the film. it was also seen that the change in surface properties of the treated sample reached its saturation point, eliminating the requirement of further treatment. so, the polymer industries can therefore save the energy by calculating the optimal treatment time for the sample over which there is noticeable change on the surface properties. rajesh prakash guragain et al. / bibechana 18 (1) (2021) 19-25 25 references [1] m. petit, n. jidenko, a. goldman, m. goldman & j.p. borra, electrical characterization of gas discharges using a numerical treatment. application to dielectric barrier discharges, review of scientific instruments. 73 (2002) 2705-2712. https://doi.org/10.1063/1.1484236 [2] g. nersisyan and w. g. graham, characterization of a dielectric barrier discharge operating in an open reactor with flowing helium, iop publishing ltd, plasma sources science and technology. 13 (2004) 582-587. https://doi.org/10.1088/0963-0252/13/4/005 [3] m. kuzuya, t. izumi, y. sasai, & s. kondo, sodium carboxylate effect of non-cross-linked hydrogel on plasma-induced radical formation as studied by electron spin resonance, thin solid films. 457 (2004)12–19. https://doi.org/10.1016/j.tsf.2003.12.032 [4] h. b. baniya, r. shrestha, r. p. guragain, m. b. kshetri, b. p. pandey, & d. p. subedi, generation and characterization of an atmospheric-pressure plasma jet (appj) and its application in the surface modification of polyethylene terephthalate, international journal of polymer science. 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https://doi.org/10.1016/j.apsusc.2009.04.137 https://doi.org/10.1063/1.1484236 https://iopscience.iop.org/journal/0963-0252 https://doi.org/10.1088/0963-0252/13/4/005 https://doi.org/10.1016/j.tsf.2003.12.032 https://doi.org/10.1016/c2014-0-02434-3 https://doi.org/10.1016/s0168-583x(03)00644-x https://doi.org/10.1080/1023666x.2014.850907 https://doi.org/10.1088/0963-0252/16/2/002 https://doi.org/10.3126/bibechana.v17i0.26869 https://doi.org/10.18434/t4w30f https://doi.org/10.1007/978-3-642-34243-1_1 https://doi.org/10.1016/j.surfcoat.2006.08.068 https://doi.org/10.1016/j.apsusc.2011.01.132 https://doi.org/10.1016/j.apsusc.2009.04.137 bibechana 18 (1) (2021) 67-74 67 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal molecular dynamics study of structural properties of γ-aminobutyric acid (gaba) shyam p. khanal, rajendra prasad koirala, esha mishra, narayan p. adhikari* central department of physics, tribhuvan university, kirtipur, nepal *email: narayan.adhikari@cdp.tu.edu.np article information: received: june 13, 2020 accepted: june 25, 2020 keywords: molecular dynamics gaba radial distribution function van der waals radius abstract the study of structural conformation of gamma-aminobutyric acid (gaba) exhibits its biological and chemical activities. the gaba molecule is responsible in neurotransmission from one neuron to another neuron and activates the ion channels to pass the chlorine and sodium ions in nerve cells. its conformation in solid state and gas state are extremely different and it also shows five different conformations in aqueous solution. the study of its structure in such environment can reveal its activity in cellular environment. we have performed the classical molecular dynamics study of this system of gaba in aqueous medium to deal its structure. radial distribution function (rdf) has been used to study the structural properties of the system. doi: https://doi.org/10.3126/bibechana.v18i1.29442 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction gamma-aminobutyric acid (gaba), a chief inhibitory neurotransmitter, plays major role in reducing the neuronal excitability throughout the central nervous system [1-3]. it is mostly found in nervous system of highly developed brain of mammals. it is, in fact, a chemical messenger that transmits the signals across chemical synapses from one neuron to another neuron, gland cells or to the muscles [4]. it is also used to treat high blood pressure, stress and anxiety; and to stimulate the secretion of natural growth hormone of body. the disorder of gaba in the body may cause the neurologic and psychiatric conditions. in addition, gaba is also detected in the other part from central nervous system like intestines, kidneys, uterus, ovaries, lungs etc. so, it has several functions in body mechanisms [5]. gaba is synthesized from anion of glutamic acid, called glutamate, via the enzyme glutamate decarboxylase with pyridoxal phosphate as a cofactor [6]. its chemical formula is c4h9no2 and molar mass 103.120 g/mol. it is a white microcrystalline powder with density 1.11 g/ml. it is soluble in water with solubility value 130 g/100 ml. the temperature difference between solid state http://nepjol.info/index.php/bibechana mailto:narayan.adhikari@cdp.tu.edu. https://doi.org/10.3126/bibechana.v18i1.29442 https://creativecommons.org/licenses/by-nc/4.0/ shyam p. khanal et al. / bibechana 18 (1) (2021) 67-74 68 and the gas state is quite narrow, with melting point 203.7oc and boiling point 247.9oc [7,8]. it contains a primary amine group and a carboxylic acid functional group, due to which it is categorized in amino acid group; however, the amino group (nh2) does not link to the alpha carbon as the ordinary amino acid contains. that is why, the gaba is not incorporated into the protein molecule. it is mostly found in zwitterion form [9, 10]. the interesting characteristic of gaba is its nature of conformation with its surroundings. it is mostly found highly folded configuration in gas phase and extended form in solid phase. its character is surprising in solvent. it has high solvent effect with five different conformation [11]. the biochemical functions of biomolecules are greatly influenced by their structural conformation. since the gaba can be at different conformations in various phases and also in the surrounding conditions, its structural study makes the great sense to understand the neurotransmission in nervous system, the spinal cord and hyperpolarization condition in ion exchange process in nerve cells [12]. several researches have been carried out to deal the structural conformations of gaba in aqueous solution; however its structural variations in the living body are still unclear. solvation of gaba molecule in water resembles real body. ashby et al. studied about different interactions with binding site that involved in gaba binding in molecular level; and zafar and jabeen studied the structure and function of gaba transporters (gats) using computational method [13, 14]. also, many experimental studies about transport properties of gaba have been already performed. umecky et al. and yui et al. measured the binary diffusion coefficient of gaba in infinitesimal aqueous medium at different temperature using taylor dispersion method [15,16]. also, viscosity of aqueous solution of gaba was estimated by romero and beltron [17]. molecular dynamics (md) study can be considered as an alternative technique to study about many properties including structural analysis [18]. md also provides guideline for experimental study. to our best knowledge, the structural properties of gaba in water have not been studied using molecular dynamics. we expect that this study will help to learn the structural conformation of the molecule in water environment. in this paper, we have discussed methods and methodology in section 2. the results of the work are presented and discussed in section 3; and finally conclusions and concluding remarks are presented in section 4. fig. 1: snapshot of gaba molecule. 2. methods and methodology modeling of system we performed classical molecular dynamics simulations of the system of aqueous solution of gaba. gromacs 5.1.1 software package was used for the simulations [19]. the opls-aa (optimized potentials for liquid simulations – all atom) force field for modeling the gaba molecule and three point spc/e [20] water model were used during the simulations. in the classical molecular dynamics simulations, we solve the newton’s equation of motion [21]. to account the intramolecular interactions, the bonded interaction i.e. bond stretching, bond angle and dihedral potentials are considered. and, the non-bonded coulomb and lennard-jones (lj) interactions contribute to the inter-molecular interactions. the coulomb interaction arises due to partial charges of the shyam p. khanal et al. / bibechana 18 (1) (2021) 67-74 69 atoms in gaba and water molecules. for spc/e water model, the partial charges of hydrogen and oxygen atoms are +0.4238e and -0.8476e respectively where e is elementary charge; and lennard-jones (lj) parameters are 0.316 nm and 78.2kb. now, the inter-molecular interaction is caused due to non-bonded interactions which can be expressed as 𝑉(𝑟𝑖𝑗) = 4𝜀 [( 𝜎 𝑟 ) 12 − ( 𝜎 𝑟 ) 6 ] + 𝑞𝑖𝑞𝑗 4𝜋𝜖𝑚𝑟𝑖𝑗 where 𝑟𝑖𝑗 is the distance between 𝑖𝑡ℎ & 𝑗𝑡ℎ atoms of charges 𝑞𝑖 & 𝑞𝑗 respectively, 𝜀 & 𝜎 are lj parameters and 𝜖𝑚 is permittivity of medium between the charge. computational details we performed the simulations of the system of 3 γaminobutyric acid (gaba) as solute and 1035 water molecules as solvent at 1 atm pressure at five different temperature: 298.2 k, 303.2 k, 313.2 k, 323.2 k and 333.2. the simulations were carried out in cubic simulation box under periodic boundary conditions (pbc). at first, to remove van der waals bad contact and to obtain the minimum potential energy state, energy minimization of the system was carried out using steepest-descent method taking 50 kj/mole-nm force tolerance [22, 23]. many properties of the system under study depend upon the parameters like temperature, pressure etc. so, the system must be in thermodynamics equilibrium. for this, the system was equilibrated at each temperature for 200 ns time taking time step of 0.002 ps using isothermal-isobaric (npt) ensemble. during equilibration run, velocity rescaling thermostat with 0.01 ps coupling time was used to control temperature and beresdsen barostat with coupling time of 0.8 ps was used to keep constant pressure [24]. lincs algorithm and maxwell-boltzmann distribution were taken to constraint all bonds and to assign initial velocities for each particle respectively [24]. also, particle mesh ewald (pme) method was chosen to account the long range coulomb interaction; and cut off parameters of 1 nm was taken for both short range coulomb & lennard-jones (lj) interactions. in order to solve the equations of motion, leap-frog algorithm was used [24]. figure 2 represents the temperature and density profiles of the system after equilibration run at temperature of 303.2 k. also, the simulated values of temperature and density are presented in the table 1. fig. 2: temperature (left) and density (right) profiles of the system after equilibration run at 303.2 k temperature. shyam p. khanal et al. / bibechana 18 (1) (2021) 67-74 70 table 1: simulated values of temperature and density at five different coupling temperature. coupling temperature (k) simulated temperature (k) simulated density (kg/m3) experimental density (kg/m3)[25] 298.2 298.20±0.01 990.07±0.02 997.03 303.2 303.19±0.00 987.49±0.02 995.63 313.2 313.19±0.04 981.46±0.03 992.19 323.2 323.19±0.01 974.45±0.02 988.19 333.2 333.19±0.02 967.19±0.02 983.17 from the table , it is seen that the simulated values of densities at different coupling temperature agree within 2% with previously reported experimental values. after the equilibrating the system, the production run was done at each temperature using canonical (nvt) ensemble. during the production run, velocity rescaling thermostat with coupling time of 0.01 ps was used to control temperature. the velocities of final step of equilibration run were taken as initial velocities for production run. each production was performed for 100 ns with time step 0.002 ps. 3. results and discussion in this section, we present the rdf between different atoms of gaba and water molecules. radial distribution function (rdf) structural properties of the system has been studied by using radial distribution function (rdf). rdf, that provides the idea of distribution of molecules around another molecule which is taken as reference, gives the probability of finding a pair of atoms located at distance `r' [26]. for liquid, rdf shows an oscillation up to certain distance and becomes unity which means that there is no correlation between molecules after the distance [27, 28]. the gaba molecule contains the functional groups amide (-nh2) and carboxyl (-cooh). thus, to find the structural properties of the system under study, we have calculated the rdf of oxygen of water & oxygen of water (g owow(r)), oxygen of water & nitrogen of amide ( nh2) group of gaba (g ow-n1(r)), and oxygen of water & oxygen of carboxylic group (-cooh) of gaba (g ow-o2(r)). figures 3, 4 and 5 represent the g ow-ow(r), g ow-n1(r) and g ow-o2(r) at five different temperature 298.2 k, 303.2 k, 313.2 k, 323.2 k and 333.2 k respectively. in the rdf plots, there is a region from the reference atom up to which the value of rdf is zero. in this region, the probability of finding another atom is zero. such region is known as excluded region (er). beyond the zero probability region, some peaks are observed and the value of rdf becomes unity beyond certain distance from reference atom. the unity value of rdf indicates that no correlation between atoms at that region i.e. correlation between atoms takes place up to certain distance from reference position [23]. three peaks are observed between excluded and unity regions. the peaks indicate the favorable position of the atoms/molecules from reference. the first peak means the most favorable position of the atoms from reference. the values of excluded region (er), first peak position (fpp), first peak value (fpv) ), second peak position (spp), second peak value (spv) ), third peak position (tpp) and third peak value (fpv) for g ow-ow(r), g ow-n1(r) and g ow-o2(r) are presented in tables 2, 3,and 4 respectively. shyam p. khanal et al. / bibechana 18 (1) (2021) 67-74 71 fig. 3: rdf between oxygen atoms of water (g ow-ow(r)) at different temperature. fig. 4: rdf between nitrogen of gaba and oxygen of water (g ow-n1(r)) at different temperature. . fig. 5: rdf between oxygen of gaba and oxygen of water (g ow-o2(r)) at different temperature. shyam p. khanal et al. / bibechana 18 (1) (2021) 67-74 72 table 2: simulated data for radial distribution function (rdf) between water molecules (g ow-ow(r)) at different temperature. temperature(k) er(nm) fpp(nm) fpv spp(nm) spv tpp(nm) tpv 298.2 0.240 0.274 3.141 0.450 1.126 0.686 1.046 303.2 0.240 0.276 3.104 0.450 1.120 0.690 1.040 313.2 0.240 0.276 3.018 0.450 1.103 0.688 1.037 323.2 0.240 0.276 2.936 0.450 1.087 0.694 1.036 333.2 0.240 0.276 2.874 0.450 1.075 0.686 1.034 table 3: simulated data for radial distribution function (rdf) between nitrogen (n1) of gaba and water molecules (g ow-n1(r)) at different temperature. temperature(k) er(nm) fpp(nm) fpv spp(nm) spv tpp(nm) tpv 298.2 0.248 0.284 1.379 0.466 1.016 0.726 1.047 303.2 0.248 0.286 1.352 0.452 1.017 0.712 1.047 313.2 0.246 0.284 1.359 0.470 1.004 0.730 1.048 323.2 0.248 0.286 1.344 0.468 0.997 0.724 1.045 333.2 0.248 0.290 1.321 0.458 0.985 0.726 1.040 table 4: simulated data for radial distribution function (rdf) between oxygen (o2) of gaba and water molecules (g ow-o2(r)) at different temperature. temperature(k) er(nm) fpp(nm) fpv spp(nm) spv tpp(nm) tpv 298.2 0.234 0.266 1.258 0.494 1.003 0.700 1.039 303.2 0.236 0.266 1.231 0.494 1.008 0.700 1.039 313.2 0.234 0.266 1.242 0.490 1.006 0.684 1.034 323.2 0.234 0.266 1.228 0.494 0.999 0.690 1.037 333.2 0.234 0.266 1.188 0.488 0.991 0.684 1.031 the values of lennard-jones parameter (σ) for ow-ow, ow-n1 and ow-o2 are 0.316 nm, 0.323 nm and 0.308 nm respectively. and, the calculated values of van der waals radius (21/6 σ) for ow-ow, ow-n1 and ow-o2 are 0.355 nm, 0.363 nm and 0.346 nm respectively. from the tables 2-4, it is clearly observed that the values of first peak position (fpp) are smaller than the respective van der waals radius, which indicates that other potentials along with lennard-jones (lj) also contribute for stability of the system. on the other hand, coulomb interactions arise in the system due to partial charges of hydrogen and oxygen of spc/e water model, and of n1 from -nh2 & o2 from -cooh group of gaba molecule. thus, both coulomb as well as lj including many body effects are responsible for structural properties of the system [19, 20]. from the table, it is also observed that the values of excluded region (er) are less than corresponding values of the van der waals radius. 4. conclusions and concluding remarks we performed classical molecular dynamics of a system of 3 γ-aminobutyric acid (gaba) as solute and 1035 water as solvent at five different shyam p. khanal et al. / bibechana 18 (1) (2021) 67-74 73 temperature: 298.2 k, 303.2 k, 313.2 k, 323.2 k and 333.2 k using gromacs 5.1.1 package. during the simulations, spc/e water model and opls-aa force field parameters were used. radial distribution function (rdf) was taken to analyze the structural properties of the system. for this, we plotted the rdf between different atoms at five different temperature 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[27] s. pokharel, n. pantha, and n. p. adhikari, diffusion coefficients of nitric oxide in water: a molecular dynamics study, international journal of modern physics b 30 (2016) 1650205. https://doi.org/10.1142/s0217979216502052 [28] k. sharma and n. p. adhikari, temperature dependence of diffusion coefficient of nitrogen gas in water: a molecular dynamics study, international journal of modern physics b 28 (2014) 1450084. https://doi.org/10.1142/s0217979214500842 https://doi.org/10.1021/je3012698 https://doi.org/10.1021/je301370s https://doi.org/10.1002/jcc.20291 https://doi.org/10.1063/1.5099069 https://doi.org/10.1063/1.5132777 https://doi.org/10.1142/s0217979216502052 https://doi.org/10.1142/s0217979214500842 sources and causes of water pollution in bangladesh: a technical overview md. arman arefin, avijjit mallik* department of mechanical engineering, rajshahi university of engineering and technology, rajshahi-6204, bangladesh *email: avijitme13@gmail.com article history: received 01 december, 2017; accepted 09 december, 2017 doi: http://dx.doi.org/10.3126/bibechana.v15i0.18688 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract water pollution is one of the significant dangers to general wellbeing of bangladesh. drinking water quality is inadequately overseen and checked. bangladesh positions at number 86 among 142 countries with respect to drinking water quality. drinking water sources, both surface and groundwater are debased with coliforms, harmful metals and pesticides all through the nation. different drinking water quality parameters set by who are every now and again damaged. human wastes, transfer of civil and mechanical wastes and aimless use of agrochemicals in agribusiness are the principle factors affecting the water quality. microbial and substance contaminations are the primary elements work solely or in mix for different general medical issues. this paper presents a detailed layout of water quality in bangladesh with unique inflection on significant poisons, sources and causes of pollution. the information introduced in this paper are extracted from different surveys and reports distributed in national and global journals; likewise reports discharged by the government and ngo associations are incorporated. keywords: water pollution; causes of pollution; sources of pollution; bangladesh. 1. introduction water they say is life, and to be sure they are correct. with around 70% of the world is covered by water, it certainly winds up plainly one of our most noteworthy assets. water is used practically in every vital human tasks and procedures. it is a vital component in both household and additionally mechanical and industrial purposes. however a nearer investigation of our water assets today, gives us an impolite result. invaded with waste running from drifting plastic packs to synthetic waste, our water bodies have transformed into a pool of toxin. the defilement of water bodies in least complex word implies water pollution. consequently the mishandle of lakes, seas, rivers, repositories and so on are water bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.97 mailto:avijitme13@gmail.com http://dx.doi.org/10.3126/bibechana.v15i0.18 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana pollution. pollution of water occurs when substances that will adjust the water in negative mold are released in it. this release of poisons can be immediate and additionally backhanded [1]. poison inputs have expanded in late decades and have corrupted water nature of numerous waterways, lakes, and seaside seas. humiliation of these crucial water assets can be measured as the loss of normal frameworks, their segment species, and the comforts that they give [2-4]. water deficiencies are progressively normal and liable to end up plainly more extreme later on [5-6]. water lack and poor water quality are connected, in light of the fact that pollution lessens the supply of water and builds the expenses of treating water for utilization. prevention pollution is among the most financially savvy methods for expanding water supplies. just a little rate (0.01%) of this crisp water is accessible for human use [7]. water pollution is surpassing the breaking point in the greater part of the water sources, and has turned into a tremendous risk to the survival of water species. in the year 2011 in 'the daily star', most of the news (added 38+ news) were related to water pollution and were distributed in the months january and june. detectable number of news likewise distributed in the month may and july. 2. previous work fariha binte amin [8] published an article about the water pollution caused by oil and marine pollution. the article mainly focused on this causes of water pollution. g. kibria et al [9] published a research article about the buriganga river water pollution causes and consequences. the author mainly focused on the river water pollution due to waste disposal and industrial pollution. k. n. mukti [10] worked on the water pollution effects on human life. authors made a case study report on bansi river, savar, dhaka. muhammad rezaul kabir [11] discussed about the social impact of water pollution. author mainly focused on how water pollution affects our social and economic life. g. j. alam [12] discussed about the environmental pollution of bangladesh and its effects. author focused on several reasons of environmental pollution in bangladesh. m. a. bhuiyan [13] investigated the possible sources of heavy metal contamination in central and lagoon water in the tannery industrial area of dhaka. m. ahmad et al [14] investigated water pollution due to heavy metals and sediment in buriganga river. nasema tanvir chowdhury [15] investigated about the water management of bangladesh. the paper identified various geographic, socioeconomic factors that shape the water management. m. a. bhuiyan et al. [16] evaluated the hazardous metal pollution in irrigation and drinking water system near the coal mind area. the paper mainly focused on the coal mine water pollution. from the literature it is seen that all the previous work were based on one or two causes of water pollution. no literature found which discussed the sources of water pollution in bangladesh. this paper focused on the causes and sources of water pollution in a broad sense. moreover, water pollution due to boating, wetland, and road construction are not found in literature. the discussions based on these topics are also conducted in this paper. 3. methodology a detailed evaluation of different sectors of water pollution is present in this paper. first, the sources of water pollution are divided into two sectors (point and non-point).point sources are not major reasons of water pollution in bangladesh. non-point sources are described in details including urban land use and heavy rainfall, agricultural land and forestry land use, abandoned mines, hydro modification and habitant alteration, marines and boating, roads, highways and wetland areas. a detailed study about all these mentioned sectors are conducted is this paper. then an elaborated study on the causes of water pollution in bangladesh is present considering sewage and solid waste, industrial waste and effluents, inadequate sanitary facilities, arsenic contamination, oil pollution and global warming. all the data presented in this paper are collected from different government and nongovernment surveys, reports and reliable sources. 4. sources of water pollution water pollution occurs regularly because of human exercises [17]. the significant ones are unpredictable transfer of mechanical, civil and household wastes in water channels, waterways, rivers and lakes, and so on [18]. an assessed 2 million tons of sewage and different effluents are released md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.98 into the worlds waters each day. in creating nations the circumstance is more regrettable where more than 90% of crude sewage and 70% of untreated mechanical wastages are dumped into surface water sources [19]. the two main wellsprings of water pollution can be viewed as point and non-point sources. point sources are moderately simple to recognize, measure and control. point sources of water pollution incorporate release from metropolitan sewage treatment plant and modern plant [20]. while non-point implies poisons radiated from different sources .the pollution can't be followed to a solitary purpose of release, hard to screen and control [2]. non-point source pollution is water pollution that influences a water body from diffuse sources, for example, human land utilize and dirty spillover from rural regions depleting into a river [21, 22] contaminated water after downpours that has gone through a few locales may likewise be considered as a non-point wellspring of pollution. utilization of concentrated mineral composts related with tainting of rural groundwater prompts expanding level of supplements in ground and surface waters, particularly from non-point sources and hard to anticipate contrasted with point sources. horticultural movement is major non-point sources pollution including utilization of nitrogen composts, use of domesticated animals excrement, vegetable obsession and mineralization of soil nitrogen [17]. 4.1 point sources "point source water pollution is characterized as emanations which enter water from a sample single source, for example, a pipe from a production line or the outfall from a sewage works" [23]. this kind of pollution affects the condition of water. the released waste from firms can influence water groups of any size. poisons can change the synthetic cosmetics of the water. they can influence oxygen levels, sharpness levels, green growth and micro-organisms development and even change water temperature. these things extraordinarily influence the sea life existence of these water bodies. pollution of this kind turns into a hazard and along these lines a market disappointment when there is a negative effect on people notwithstanding the earth. with fish and shellfish being an essential nourishment source, gaming and recreational exercises happening on water bodies and with tap water giving a water source to savoring, pollution of the water can without much of a stretch convert into enormous issues for individuals a genuine outer cost. figure 1 shows the sources of water pollution. table-1: common point and non-point sources of water pollution point source  waste water effluent (municipal and industrial).  runoff and leachate from waste disposal site.  runoff and inflation from animal feedlots.  runoff from mines, oil fields, unsowed industrial sites.  storm sewer outfall from cities of population < 100000.  overflow of combined storms and sanitary sewers.  runoff of construction sites > 2ha. non-point source  runoff from agriculture (including return flow from irrigated agriculture).  runoff from pasture and range.  urban runoff of un-drained and drained areas of population <100000.  septic tank leachate and runoff from septic system.  runoff from construction sites <2 ha.  run off from abandoned mines  atmospheric deposition over a water surface  activities of land that generate contaminates such as logging, wetland conversion, construction and development of land and water ways. md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.99 fig. 1: sources of water pollution [24]. in bangladesh the main sources of water pollution are non-point sources of pollution, though point sources have adverse effects on water pollution. table-1 shows common point and non-point sources of water pollution of bangladesh. 4.2 non-point sources 4.2.1 urban land use & heavy rainfall in our urban territories, precipitation run-off as storm water is one of the major non-point source of pollution affecting the nature of our waterways and water inlets. storm water from road surfaces is frequently degraded with auto oil and the fasces of creatures and soil and residue run-off from development destinations and in mechanical ranges regularly contains more toxicants and chemicals. figure 2 shows the average monthly rainfall of bangladesh (1901-2015) and table-2 shows rainfall in bangladesh from year 2011-2015. 600 average monthly rainfall of bangladesh (1901-2015) 500 400 300 200 100 0 jan feb mar apr may jun jul aug sep oct nov dec fig. 2: average monthly rainfall of bangladesh (1901-2015) (source: world bank). r ai n fa ll (m m ) md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.100 table-2: rainfall in bangladesh from year 2011-2015 [25]. rainfall(mm) year month 3.38142 2011 1 17.2459 2011 2 15.7637 2011 3 65.5495 2011 4 248.726 2011 5 656.316 2011 6 382.637 2011 7 834.379 2011 8 188.915 2011 9 22.2288 2011 10 7.44226 2011 11 0.32617 2011 12 17.4969 2012 1 2.54444 2012 2 29.6885 2012 3 196.192 2012 4 273.627 2012 5 260.061 2012 6 487.52 2012 7 354.074 2012 8 256.22 2012 9 176.708 2012 10 23.0077 2012 11 20.4967 2012 12 1.04773 2013 1 11.4669 2013 2 8.60079 2013 3 111.975 2013 4 276.491 2013 5 347.167 2013 6 458.96 2013 7 423.581 2013 8 219.738 2013 9 254.105 2013 10 0.73076 2013 11 0.90544 2013 12 0.69295 2014 1 35.6462 2014 2 13.9601 2014 3 61.5042 2014 4 173.85 2014 5 333.012 2014 6 385.073 2014 7 474.12 2014 8 335.726 2014 9 57.8275 2014 10 0.85865 2014 11 0.53106 2014 12 10.4185 2015 1 22.3004 2015 2 22.3094 2015 3 245.063 2015 4 179.614 2015 5 878.927 2015 6 566.637 2015 7 493.387 2015 8 321.713 2015 9 86.5896 2015 10 5.06601 2015 11 5.94112 2015 12 md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.101 in some outer-urban and urban fringe areas, a reticulated sewerage system is not available. so sewage is discharged to onsite wastewater systems and septic tanks. seepage and surface run-off of septic tank effluents may also be considered as non-point source of pollution of rivers in these areas. 4.2.2 agricultural land use in cultivating zones non-point sources of pollution incorporate pesticides, composts, creature excrement and soil washed into rivers in precipitation run-off. where stocks are offered access to riverbanks they may pollute the water and quicken disintegration. horticulture annihilates are common free frameworks. it clears characteristic vegetation and substitutes, for the common supplement and soil protection instruments, defective frameworks in which supplement misfortunes to expelled crops and by washout from bothered soils must be consistently removed by compost. it expels the supply of woody debris and jetsam, dispenses with top predators like bears and deceivers of securing household stock and may totally change the complex physical and natural structures of surge plain frameworks to advance discharge and water system. it might support the expansion of specific fish species through supplement advancement and cause significant disturbances in food products through modified predator– prey connections. it presents novel and outsider substances, for example, biocides to which there has been little time for advancement of cautious instruments. basically despite the nearby cases of support of biodiversity by conventional farming frameworks in keeping up lakes, wet knolls and fens, agribusiness has not a positive net impact on the natural working or biodiversity of getting water. land utilization change for farming has been notable as the real danger to oceanic biodiversity [26-29]. farming here means change of the scene for creation of goods that are utilized for sustenance or market, regardless of whether eaten or utilized as a part of different routes by settled human social orders. it along these lines incorporates ranger service, trim culture, biomass creation for fuel and creature farming. effects on freshwater and marine frameworks may incorporate consequences for water science [30-36] with resulting eutrophication and nourishment web adjustment [37-39], biocide filtering [40-45], suspended burdens from soil disintegration [46], change of the hydrological cycles [47], impacts of unusual species utilized, especially in fish and shellfish culture, and physical alteration of the living space (channelization, station change, bank and seepage) [48]. it is difficult to isolate impacts of horticulture from those of urbanization. nitrogen and phosphorus filtered from fields or creature waste have very same impacts as those delivered by road seepage and human excrement. 4.2.3 forestry land use forestry operations may contribute to non-point source pollution of rivers by increasing soil erosion and sediment run-off. figure 3 and figure 4 show the total forestry area and a statistical graph denoting reduction of it from 2005-2016 of bangladesh respectively. the data of figure 4 were collected from various government and non-governmental sources. fig. 3: forestry lands of bangladesh [49]. md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.102 percentage of forestry land 11.2 11.15 11.1 11.05 11 10.95 10.9 10.85 10.8 2005 2007 2009 2011 2013 2015 year percentage of forestry land fig. 4: forestry land of bangladesh (2005-2016). 4.2.4 abandoned mines (i) barapukuria coal mine: barapukuria coal mine is controlled by the barapukuria coal mining company limited [50]. barapukuria coal mining company limited is a supporting project of petrobangla [51]. the mine is situated in dinajpur, this is the main dynamic mine in bangladesh [52]. local people close to the mine have announced harms to their homes. the water close to the mine is being polluted for various point and non-point reasons [53]. the u.s. geographical survey reports that "the coal mine had a generation limit of 1 mt/yr of coal [54]. (ii) jamalganj coal: the aggregate hold of coal in the field is evaluated at 1,053 million tons. jamalganj coal has a high unstable bituminous coal and has a normal calorific estimation of 12,100 btu/lb. it is a decent quality gondwana coal with little sulfur content. proximate investigation demonstrates that it has 33-54% (normal 47%) settled carbon, 30-40% unpredictable issue, 10-60% (normal 22%) fiery debris and a normal of 0.65% sulfur. the coal usually contains a variable number of non-dirt partings, fundamentally carbonaceous mudstone. mining jamalganj coal was deserted after the disclosure of coal in much shallower profundities in the dinajpur-rangpur area (source: banglapedia, wikipedia, world bank, unesco) [55]. (iii) phulbari coal mine: the undertaking undermines has affected the homes, terrains, and water sources of upwards of 220,000 individuals. add up to coal extraction: 572 million tons; 16 million tons every year at crest generation. (source: global responsibility venture) [56]. (iv) khalashpir mine: in 2003, china national machinery import and export corporation (cmc) proposed to the state minister for energy, a. k. m. mosharraf hossain to lead a specialized review of the newfound coal mine in the northern area of rangpur district. shan wei, director of cmc, expressed that cmc was set up to stretch out money related and specialized help to build up the khalashpir mine. a review was directed, in spite of the fact that it is unclear who led it. the hold would meet fuel prerequisites of the nation for no less than one hundred years; 2 million tons of coal can be separated from the coal mine each year a 400 to 500 mw coal-based power era plant can be set up at the mine site. the mine f o re st ry l an d ( % ) md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.103 site is not experiencing any type of movement, because of absence of assets. (source: help information association) [57]. 4.2.5 hydro-modification & habitat alteration ‘hydro-modification’ alludes to alterations in normal watershed hydrology. hydro-modification incorporates channelization and channel alteration, dams, river banks and shorelines disintegration. in bangladesh because of channelization and direct adjustment exercises in various waterways like buriganga, padma, jamuna reducing rationality of river and riverside habitat for fish and wild life. they are additionally adjusting with river water temperature and residue sort, and in addition the rates and ways of sediment disintegration, transport and testimony. md. saiful islam [55] demonstrated that the estimation of various organization of water because of hydro-modification has changed. in his research the water tests were gathered from the buriganga, shitalakkhya and turag river [58]. 4.2.6 marinas and boating marinas and recreational boat-races are extremely famous employments of beach front waters. the development of recreational sailing, alongside the development of seaside improvement has prompted an expanded consciousness of the need to secure the ecological nature of our waterways. since marinas are found comfortable water's edge, there is a solid potential for marina waters to wind up noticeably defiled with contaminations produced from the different activities that happen at marinas, for example, watercraft cleaning, filling operations and marine head release or from the passage of tempest water spillover from parking garages and body upkeep and repair zones into marina bowls. there are a lot of marinas and boating club in bangladesh (table 3) which causes water pollution tremendously. table 3: marines and boating of bangladesh. marina & boating location 1. leisure marina sports village serene banks of river sitalakhya, sripur, gazipur, bangladesh 2. chittagong boat club kaptai/rangamati, bangladesh 3. sher-e-bangla club narsingdi, bangladesh. 4. cafe & boat club ecb square zia colony road, dhaka-1206, bangladesh 5. dhaka boat club mirpur road, dhaka-1216, bangladesh 6. meghna village boat club gazaria, bangladesh 7. kalir bazar boat pier kalir bazar, bangladesh 8. boat club, jessore jessore, bangladesh 4.2.7 roads, highways and bridges development of streets, parkways and spans result in the production of waste that can cover sea-going habitat and stop waterways. figure 5 shows road construction near dhaka, bangladesh. substantial metals, oils, other harmful substances and debris and jetsam from development movement and spillage can be consumed by soil at development destinations and conveyed with overflow water to lakes, rivers and bayous. md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.104 fig. 5: road construction near dhaka, bangladesh. 4.2.8 wetland/riparian areas wetlands and riparian regions commonly build as characteristic cushions amongst uplands and adjoining water bodies. they go about as regular channels of nonpoint source poisons, including residue, supplements, pathogens and metals, to water bodies, for example, waterways, rivers, lakes and waterfront waters. figure 6 shows state and management of wetlands in bangladesh. wetland and riparian zones give an assortment of natural administrations that add to biological community capacities at nearby, watershed, and territorial scales [59-62] wetlands can viably limit waste adversity, control overflow volume and decontaminate surface water [63, 64]. the shape, size, and conveyance of wetland and riparian zones are to a great extent dictated by geologic, topographic, and hydrologic conditions [65, 66]. fig. 6: state and management of wetlands in bangladesh. (source: amaderprani). md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.105 in bangladesh because of absence of appropriate care and control of wetland, water pollution occurs. study shows that the wetlands of dhaka city are changing rapidly. in 1960, the aggregate region of water bodies and swamps were 2952.02 and 13527.58 ha, individually. while in 1988, the aggregate range of the same diminished to 2103.62 and 12717.73 ha, individually [67]. this decayed further, possessing a territory of 1990.71 ha in 2008, which shows that the marshes kept on diminishing. consequently the water bodies and marshes diminished by 32.57% and 52.58%, separately in the middle of 1960 and 2008. these changing patterns of wetlands make the waste arrangement of dhaka city defenseless, making water logging issues and their outcomes. land filling and violation were perceived to be the primary explanations behind changing wetlands in the city [67]. 5. causes of water pollution in bangladesh water pollution is caused due to several reasons. here are the few major causes of water pollution in bangladesh. 5.1 sewage and solid waste sewage, junk and water misuse of family units, horticultural grounds and processing plants are released into lakes and rivers. these wastes contain unsafe chemicals and poisons which make the water toxic for oceanic creatures and plants. the unpredictable release of strong waste, local and healing facility sewage are the real causes of water pollution in bangladesh. around 4,000 to 4,500 tons of strong wastes are created every day and just 50% of the produced wastes are discarded in low lying ranges or into river water. these strong wastes are related with the issues of littering on streets, spilling around the containers, stopping up of channels, aimless dumping on empty plots and cause genuine natural pollution. more than 500 hospitals in dhaka city create and discharge risky and harmful wasters without treatment [68]. the created strong misuse of six well known healing facilities/centers of dhaka city is demonstrated as follows (table-4). table 4: the generated solid waste of six famous hospitals / clinics of dhaka city [69]. name of hospital/clinic generated waste(kg/bed/day) non hazardous waste hazardous waste qty % of total waste qty % of total waste dmch 1.19 1.07 90 0.12 10 ssmch 1.23 1.09 89 0.14 11 rihd 1.20 .91 76 0.29 24 hfrch 1.59 1.29 81 0.30 19 dnmch .80 .70 88 0.10 12 sahl .83 .72 87 0.11 13 5.2 industrial waste and effluent the principle mechanical activity regions of bangladesh are at dhaka, chittagong, khulna and bogra. the main industries that cause water pollution are paper, pharmaceuticals, metal industries, sustenance industry, manure, pesticides, coloring and painting, material, tannery and so on. more than 200 rivers of bangladesh specifically or in a roundabout get a substantial amount of untreated mechanical wastes. regular roughly 700 tanneries of dhaka city are releasing around 16,000 cubic md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.106 p o ll u ti o n ( % ) meters of harmful waste. the department of environment (doe) has recorded 1,176 processing plants that create pollution all through the nation. water pollution level of most five modern segments of bangladesh in the year 2001 is shown in figure 7. 100000 90000 80000 70000 60000 50000 40000 30000 20000 10000 0 80 70 60 50 emission (t 40 ons/yr) pollution 30 (%) 20 10 0 fig. 7: industrial emission and percentage pollution of bangladesh (2001). 5.3 inadequate sanitary facilities lacking sanitation represent a genuine natural risk of water pollution in bangladesh. dhaka water and sewerage authority (dwasa) can serve just for 15 to 20% of city population. without the sanitation and infrastructural administrations, 40% having septic tank and douse pit, 15% utilizing pit latrines and 30% utilizing open toilets. the sewage is for the most part discharged into low-lying territories and the untreated water causing incredible natural risks [70]. 5.4 arsenic contamination of ground water arsenic in ground water imposes a genuine natural threat for bangladesh. around ninety-seven percent (97%) of bangladeshi individuals have been utilizing ground water as the primary source of drinking water yet the water has been undermined by arsenic sullying. the greater part (52%) of the considered population drink well-water containing >50ug/l of arsenic and more than 66% (70%) drink well-water containing > 10ug/l of arsenic. the satisfactory level of arsenic in drinking water is 0.05 mg/l for bangladesh yet in few regions, it is discovered more than 70 times higher than that standard. around 80 million individuals are at a danger of arsenic defilement. table-5 shows percentage of ground waters surveyed in 1998 by the british geological survey team with arsenic levels over the limit. the arsenic level of ground water more than 0.05 mg/l reviewed in 1998 by the british geological survey group is as follows ( table-5) [source : world bank, unicef, who]. e m is si o n s (t o n s/ y r) md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.107 table-5: percentage of ground waters surveyed in 1998by the british geological survey team with arsenic levels over the limit [71]. district % of ground water surveyed district % of ground water surveyed bagherhat 66 madaripur 93 barishal 63 magura 19 brahmanbaria 38 manikganj 15 chadpur 96 meherpur 60 chittagong 20 moulovibazar 12 chuadanga 44 munshiganj 83 comilla 65 narail 43 cox’s bazar 3 narayanganj 24 dhaka 37 nowabganj 4 faridpur 66 noakhali 75 feni 39 pabna 17 gopalganj 94 pirojpur 24 jessore 51 rajbari 24 jhalakathi 14 rajshahi 6 jhenaidah 26 satkhira 73 khulna 32 shariatpur 80 kushtia 28 sylhet 19 lakshmipur 68 fig. 8: arsenic prone zone of bangladesh. 5.5 oil pollution river water gets contaminated because of oil spilled from boats and tankers while traveling around. the spilled oil does not break up in water and structures. in bangladesh, mixing of oil in the river water is the main reason of river water pollution. md. arman arefin and avijjit mallik / bibechana 15 (2018) 97-112: rcost p.108 5.6 global warming in bangladesh due to an abrupt weather change, there is an increase in water temperature. this expansion in temperature brings about death of amphibian plants and creatures. this likewise brings about fading of coral reefs in water. since the worldwide normal air and sea temperatures are steadily increasing, this influences the eventual fate of bangladesh to be at a higher danger of more disastrous events. an abrupt weather change will trigger a chain of awful occasions. at first, an abrupt weather change will cause the ocean level to rise because of warm extension and the melting of land-based ice. notwithstanding bangladesh being profoundly populated with a poor economy and a low-lying land, the blend of these variables will put bangladesh in danger to an exceptionally 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https://assets.publishing.service.gov.uk/media/57a08cba40f0b652dd0014f8/r8161-diseases.pdf https://assets.publishing.service.gov.uk/media/57a08cba40f0b652dd0014f8/r8161-diseases.pdf http://cdrwww.who.int/entity/bulletin/archives/78(9)1093.pdf http://cdrwww.who.int/entity/bulletin/archives/78(9)1093.pdf devendra sir cover page copy.jpg bibechana 17 (2020) 123-132 123 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal variation of total electron content (tec) in the quiet and disturbed days and their correlation with geomagnetic parameters of lamjung station in the year of 2015 basu dev ghimire 1,2,5* , narayan prasad chapagain 3 , vardhan basnet 2 , karan bhatta 4,5 , balaram khadka 2,5 1 central department of physics, tribhuvan university, nepal 2 st.xavier’s college, maitighar, kathmandu, nepal 3 amrit campus (ascol), lainchaur, nepal 4 national academic of science and technology, khumaltar, nepal 5 nepalese center for research in physical sciences, kathmandu, nepal * email: basu.ghimire99@gmail.com article information: received: november 06, 2019 accepted: december 14, 2019 keywords: total electron content geomagnetic parameters gps abstract total electron content (tec) is measured using a dual frequency gps receiver in lamgung (lmjg) station located at 84.57° longitude and 28.17° latitude of the year 2015 as it is considered as geo-magnetically active year. in this study, diurnal variation of vtec has been studied separately for quiet and disturbed days and, for the effective study of the case the prn wise data of vtec have been also used. the maximum vtec is seen from 0700 lt to 1100 lt (lt=ut+5.45). prn wise vtec is studied taking the lower bound (lb) and upper bound (ub). the correlation of vtec with dst index, kp index and solar flux have been studied. positive correlation has been found in disturbed days with kp index and solar flux but negative correlation with dst index. dst index shows positive correlation in quiet days but kp index shows negative correlation. 1. introduction total electron content (tec) is one of the important tools to study ionosphere which holds many unsolved mysteries of our planet. nowadays, global positioning system (gps) has become a great aid to study the characteristics of ionosphere [1-4]. the gps-tec is the total number of electrons in a vertical column of 1 𝑚2 cross-section from the height of the gps satellite (~ 20,000 km) to the receiver on the ground. it is measured in tec unit (tecu) and 1 tecu is equal to 1×1016 el 𝑚−2 [5, 6]. the ionospheric delay which is proportional to tec is the highest contributor of gps positional errors [7, 8]. since, the use of gps based devices are increased, the importance of tec is also increased. this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.26249 http://nepjol.info/index.php/bibechana mailto:basu.ghimire99@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.26249 basu dev ghimire et al. / bibechana 17 (2020) 123-132 124 the delay in radio signals produced by gps satellite occurs in the atmosphere [2, 9]. gps satellite has 32 prn (pseudo random noise). a gps receiver receives 32 different waves of data or signals released from gps satellite. normally, the value of vtec is taken as average of the values of vtec received by 32 prn but for precise analysis value of each prn is taken. it basically helps to learn about scintillation of tec [10-12]. tec is important tool to indicate the changes in the atmosphere [3, 13, 14]. study on both quiet and disturbed days is important. so, many studies on disturbed days [15-19] and study on quiet day since shuster (1889) have been performed. retrieval of data to process the data obtained from gps satellite, chauhan et al., [5] and arikan et al., 2003 have given different methods for calculation of tec. in our study, the method given by chauhan et al. [5] is followed. using a dual frequency receiver having l1=1575.42mhz and l2=1227.60mhz in one station which include l1/l2 gps antenna, the tec measurements have been carried out through combined frequencies of pseudorange and carrier phase measurements. the formula for calculation of tec given by [5] is: tec = [9.483*(prl2-prl1 ∆c/a-p, prn) + tecrx + teccal] tecu where, prl2, is the l2 pseudo-range in meters; prl1, the l1 pseudo-range in meters; and ∆c/a-p, prn, the input bias between sv c/aand p-code chip transition in meters. there are 32 offset values (one for each satellite) which added to the c/a code pseudo-range measurements. tecrx is the tec result due to internal receiver l1/l2 delay and teccal is the user defined tec offset [5, 8]. as slant tec depends upon ray path geometry through the ionosphere, an independent and equivalent vtec of elevation angle is calculated [3]. the above-mentioned gps equipment provide slant tec data at a sampling rate of 60 s. from this data, vertical tec (vtec) values are obtained at different ionospheric pierce point (ipp) locations by using a mapping function, i.e. 𝑆(𝐸) = 1 cos(𝑍) = {1 − (𝑅𝐸 ∗ cos(𝐸) 𝑅𝐸 + ℎ𝑠 ) ∧ 2} ∧ −0.5 fig: conversion of stec to vtec where, 𝑅𝐸, is the mean radius of the earth in km; ℎ𝑠, the ionosphere (effective) height above the earth’s surface; z, the zenith angle; and e, the elevation angle in degrees [5]. rama rao et al. (2006) observed that the ipp (ionospheric pierce point) altitude of 350 km is valid for the satellite elevation angle greater than 50°. 2. method of study unavco provided the data of tec obtained from gps satellite. the gps data is available the form of rinex (receiver independent exchange format) which are further processed into ascii files. data of every 60 sec of tec has been converted into hourly data. average value of vtec has been taken into study in both cases, average vtec of 32 prn and vtec of each prn. the value of kp index provided from nasa's omniweb data explorer was given in the multiple of 10. so, in this paper, the value of kp index's value is given in multiple of 10 and is represented as kp*10. data of values of dst index, kp index and solar flux were obtained from nasa’s omniweb data explorer (https://omniweb.gsfc.nasa.gov/vitmo/iri2012_vitmo. html). basu dev ghimire et al. / bibechana 17 (2020) 123-132 125 the station taken into study is lmjg (lamjung). the details of the station is satellite lmjg location lamjung latitude (degree) 28.17 longitude (degree) 84.57 elevation (m) 2025.2 fig: map of nepal showing gps station taken in our study source: www.unavco.org/highlights/nepalfield 3. results and discussions in this paper, vtec variation of lmjg has been studied on daily basis. the study has been performed separately for quiet and disturbed days. furthermore, the vtec value of each prn has also been studied on daily basis. data of vtec of all months were not available due to the technical problems at the station. data of may to july was available with few missing days. diurnal variation of vtec diurnal variation of tec has been studied separately for quiet and disturbed days of three stations of the year 2015. graphs of each quiet and disturbed days are presented for each month showing daily change. generally, the diurnal variation of tec is minimum a pre-dawn, a steady increase in the early morning followed by afternoon maximum then gradual decrease after the sunset. http://www.unavco.org/highlights/nepalfield basu dev ghimire et al. / bibechana 17 (2020) 123-132 126 the variation for peak value of tec differs each and every day and also the time of the peak value. the value of tec was greater for quiet days than disturbed days which is opposite to the general result i.e. the higher value of vtec in disturbed days than quiet days. there were many geomagnetic events that took place on 2015 which affected the value of tec like solar flare, st.patrick's day and high euv. quiet day variation fig. 1 (a) and fig (b) show the daily variation of average vtec and the variation of vtec with prn of may of quiet days of the year 2015 respectively. data of each day of this month have been plotted. considering the variation of average vtec, the trend of diurnal variation of minimum a pre-dawn, a steady increase in the early morning followed by afternoon maximum then gradual decrease after the sunset seems to be followed. the highest value of vtec has been found to be 49.17 tecu at 1000lt. in case of prn wise variation, all the values of vtec seems to lie between upper bound (ub) and lower bound (lb). however, prn 9 recedes the value of lower bound (lb). this shows that there has been abnormal event in the values of vtec received by the prn 9. it has been found that the prn 9 was exactly below the gps satellite which resulted in abnormal value of vtec. fig. 1: (a) (b) fig. 2 (a) and (b) show the daily variation of average vtec and the variation of vtec with prn of june of quiet days of the year 2015 respectively. in the study of variation of average vtec, the trend of diurnal variation of minimum a pre-dawn, a steady increase in the early morning followed by afternoon maximum then gradual decrease after the sunset seems to be followed. the highest value of vtec has been found to be 58.34 tecu at 0900lt. in case of prn wise variation, all the values of vtec seems to lie between upper bound (ub) and lower bound (lb). this shows that there has not been any abnormal event in quiet days of june. fig. 2 (a) and (b) show the daily variation of average vtec and the variation of vtec with prn of july of quiet days of the year 2015 respectively. in the study of variation of average vtec, the trend of diurnal variation of minimum a pre-dawn, a steady increase in the early morning followed by afternoon maximum then gradual decrease after the sunset seems to be followed. the highest value of vtec has been found to be 57.63 tecu at 0900lt. basu dev ghimire et al. / bibechana 17 (2020) 123-132 127 in case of prn wise variation, all the values of vtec seems to lie between upper bound (ub) and lower bound (lb). this shows that there has not been any abnormal event in quiet days of july. fig. 2: (a) (b) fig. 3: (a) (b) disturbed day variation fig. 4 (a) and (b) show the daily variation of average vtec and the variation of vtec with prn of may of disturbed days of the year 2015 respectively. data of each day of this month have been plotted. the graphs similar to quiet days has been observed. in the study of the variation of average vtec, the trend of diurnal variation of minimum a pre-dawn, a steady increase in the early morning followed by afternoon maximum then gradual decrease after the sunset seems to be followed. the highest value of vtec has been found to be 27.02 tecu at 0900 lt. in case of prn wise variation, all the values of vtec seems to lie between upper bound (ub) and lower bound (lb). this shows that there has not been any abnormal event in disturbed days of may. basu dev ghimire et al. / bibechana 17 (2020) 123-132 128 fig. 4 (a) (b) fig. 5 (a) and (b) show the daily variation of average vtec and the variation of vtec with prn of june of disturbed days of the year 2015 respectively. data of each day of this month have been plotted. the graphs similar to quiet days has been observed. in the study of the variation of average vtec, the trend of diurnal variation of minimum a pre-dawn, a steady increase in the early morning followed by afternoon maximum then gradual decrease after the sunset seems to be followed. the highest value of vtec has been found to be 44.22 tecu at 1100 lt. in case of prn wise variation, all the values of vtec seems to lie between upper bound (ub) and lower bound (lb). this shows that there has not been any abnormal event in disturbed days of june. fig. 5: (a) (b) fig. 6 (a) and (b) show the daily variation of average vtec and the variation of vtec with prn of july of disturbed days of the year 2015 respectively. data of each day of this month have been plotted. the graphs similar to quiet days has been observed. in the study of the variation of average vtec, the trend of diurnal variation of minimum a pre-dawn, a steady increase in the early morning followed by afternoon maximum then gradual decrease after the sunset seems to be followed. the highest value of vtec has been found to be 44.91 tecu at 0800 lt. basu dev ghimire et al. / bibechana 17 (2020) 123-132 129 in case of prn wise variation, all the values of vtec seems to lie between upper bound (ub) and lower bound (lb). however, prn 31 recedes the lower bound (lb) value of vtec. this shows that there has been abnormal event in the values of vtec received by the prn 31. prn 31 position has been found just below the gpssatellite which resulted in abnormal value of vtec. fig. 6: (a) (b) solar activity dependence of tec solar activity greatly affects tec. mainly, solar radiations are the cause of solar activity. solar indices like f10.7, sunspot number (ssn), euv flux and many more are parameters that are used to represent solar activity. in our study, dst index, kp index and 10.7 cm solar radio flux (sfu) are taken into study the effect where kp index's value is given in the multiple of 10. since, one parameter may not be enough to find the correlation between different seasons of lmjg; so, dst and kp were taken into study for both quiet and disturbed days. the correlation has been calculated from the average gpstec data of all seasons in a combined manner. quiet day variation fig.7 (a) and (b) show the correlation of gpstec with dst index and kp index respectively of lmjg station of quiet days of the year 2015. the correlation with dst index has been found to be 0.143 nt whereas the correlation with kp index has been found to be -0.128. it shows that dst index correlates well but kp index doesn't correlate with gpstec of lmjg station. disturbed day variation fig. 8 (a), (b) and (c) show the correlation of gps tec with dst index, kp index and 10.7 cm solar radio flux (sfu) of lmjg station of disturbed days of the year 2015. the correlation with dst index has been found to be -0.109 nt, 0.454 with kp index and 0.096 with solar flux. this shows that kp and solar flux correlate well with gpstec of lmjg station but dst doesn't correlate with dst index. soalr flux and kp index support the occurrence of disturbed days as the correlation is positive whereas f10.7 was taken for disturbed days only as it has no significance in quiet days. basu dev ghimire et al. / bibechana 17 (2020) 123-132 130 fig. 7: (a) (b) fig. 8: (a) (b) (c) 4. conclusion variation of average vtec and prn wise vtec have been studied on daily basis separately for quiet and disturbed days of lmjg station of the year 2015. although, the data available was limited but the variation has been found positive. average tec varies from 0100 lt to maximum tec from basu dev ghimire et al. / bibechana 17 (2020) 123-132 131 0900 lt to 1000 lt on quiet days and from 0800lt to 1100 lt on disturbed days showing pre dawn minimum and steep rise in the morning and peak value around 1000lt and then gradual decrease after sunset. in case of prn wise tec variation, average vtec has been found to lie between upper and lower bound except in two cases in may of quiet day and in july of disturbed day; this showed the geomagnetic event in prn 9 and prn 31 in the latter case. 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[18] r. warnant. the increase of ionospheric activity as measured by gps, earth planets space 52 (2000) 1055–1060. https://link.springer.com/article/10.1186/bf033523 30 [19] w. chin-chun, k. liou, s. shao-ju, and c. l. tseng. variation of ionospheric total electron content in taiwan region of the equator ial anomaly f rom 1994–2003, adv. space res. 41 (2008) 611–616. https://doi.org/10.1016/j.asr.2007.06.013 https://doi.org/10.1016/j.asr.2007.09.043 https://doi.org/10.1016/s1364-6826(01)00036-0 https://link.springer.com/article/10.1186/bf03352330 https://link.springer.com/article/10.1186/bf03352330 https://doi.org/10.1016/j.asr.2007.06.013 devendra sir cover page copy.jpg bibechana 17 (2020) 133-138 133 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal improvement of hydrophilicity of polyamide using atmospheric pressure plasma jet h. b. baniya 1,2, * , r. p. guragain 1 , b. baniya 3 g. , qin 4 , d. p. subedi 1 1 department of physics, school of science, kathmandu university, dhulikhel, nepal 2 department of physics, tri-chandra college, tribhuvan university, kathmandu, nepal 3 institute of geographic sciences and natural resources research, cas, beijing, china 4 herbin institute of science and technology, school of science, shenzhen, china * email: hombaniya@gmail.com article information: received: october 17, 2019 accepted: december 26, 2019 keywords: electron temperature electron density surface modification surface energy abstract atmospheric pressure plasma jet (appj) has many applications in material processing such as surface modification and biomedical material processing. appj has been generated by a high voltage power supply (0-20 kv) at an operating frequency of (20-30) 23 khz. this paper reports the generation and characterization of appj in argon environment and its application in the surface modification of polymeric materials. the discharge has been characterized by optical and electrical methods. in order to characterize the plasma jet, its electron temperature and electron density has been determined by optical emissions spectroscopy. the surface properties of the untreated and plasma treated polyamide (pa) samples were characterized by contact angle measurement and surface energy analysis. 1. introduction atmospheric pressure plasma technology offers an attractive perspective in today’s industrial processes due to the elimination of expensive vacuum equipment, easier handling of the samples. therefore, in recent years a lot of effort has been invested in the development of non-thermal plasma reactors working at atmospheric pressure [1]. the plasma technology is gaining a reputation as one of the most effective tools for a wide range of applications. plasma is produced and sustained usually to a high voltage power supply at different pressures. the theoretical measurement of various plasma parameters is possible for the accuracy of the experiment. plasma parameters such as electron temperature and density have to be calculated [2]. different pressure plasma sources have been used for polymer surface treatment [3]. plasma consists of ions, free electrons, free radicals, excited species, photons, and neutrals. one of the important areas of application of atmospheric pressure plasma is in the surface treatment of polymers to improve their hydrophilicity [4]. the simplest definition of a this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.26869 http://nepjol.info/index.php/bibechana mailto:hombaniya@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.26869 h. b. baniya et al. / bibechana 17 (2020) 133-138 134 polymer is a useful chemical made of many repeating units. a polymer can be a threedimensional network or a two-dimensional network or a one-dimensional network [5]. atmospheric pressure plasma jet treatment of polymers brings an effective and versatile surface modification by removing volatile impurities, increasing surface roughness, breaking of c c and c h bonds to form the stable linking surface structure and producing particular functional groups[6]. polymer surface modification by discharge plasma such as plasma jet is of great industrial application and drastically enhanced wettability of polymer surface by introducing special functional groups like the carbonyl (-c=o), carboxyl (-cooh), hydroxyl (oh) on the polymer surface after treatment [7,8]. because of high strength to weight ratio, good resistance to corrosion, good transparency, their relatively low cost, polymers have been used to replace traditional engineering materials. however, polyamides are somewhat hydrophobic, lowsurface energy materials, and thus do not adhere well to other materials. due to its low hardness, low scratch resistance and degradation by uv radiation made surface modification possible without changing the bulk properties [9]. 2. experimental setup fig.1: schematic diagram of the experimental setup to produce plasma jet. fig. 1: shows the schematic diagram of the experimental setup to produce plasma jet. the experimental setup consists of capacitively coupled electrode system made of aluminum foil of 3 mm diameter wrapped around two ordinary glass tube of outer diameter 4 mm and inner diameter 3 mm. the aluminum electrode is connected to high voltage power supply and the glass tube is coupled with nylon coupler of length 50 mm which has fine bore of 5 mm. the distance between two electrodes is fixed at 80 mm and the distance between the tip of the nozzle and lower electrode is 3 mm. the system consists of one additional inlet with a third tube connected with nylon coupler horizontally in the middle as shown in fig.1. this third inlet can be used to introduce additional gas into the system. argon is used as a main working gas in the experiment. the flow rate for argon gas is 2.5 ltr/min and the voltage and the frequency were maintained at 3.5 kv and 23 khz respectively. the samples were provided by u.k. before treatment, removal of organic contaminants from the surface of the specimens were done by rinsing in isopropyl alcohol for 10 minutes. the samples were then ultrasonically cleaned in distilled water for 20 minutes and after that dried at room temperature. in this work, to check the homogeneity of treatment, the contact angle measurement was made at least five different locations of the samples. the average value of the contact angle thus obtained was used for the surface energy calculation. 3. results and discussions optical characterization of appj fig. 2: shows the spectra of the discharge and their corresponding intensities and wavelength using argon as a working gas. the optical characterization of the discharge was carried out by using the line intensity ratio method. in this method four suitable lines (two for ar i and two for ar ii) were chosen from spectral lines of argon obtain from the discharge. the working formula used to calculate the electron temperature is as follows: [10]. h. b. baniya et al. / bibechana 17 (2020) 133-138 135 1 1 2 2 3 4 / exp / pq p xy p r x vrs uv u rs r pq xy x uv b e a g e e e er i i a g r i i a g a g k t                                         (1) here, in equation (1), r is the ratio of the intensity of two lines, i is the intensity of the spectral line, jia is the transition probability of the transition i j , ig is the statistical weight of the upper level,  is the wavelength of the line radiation, ie is the energy of the upper level, bk is boltzmann constant and et is the electron temperature. the values of  and i are obtained from the observation, and the values of jia , ig and ie are obtained from the national institute of standards and technology (nist) atomic spectra database. fig.2: spectra of the discharge at 3.5 kv with frequency 23 khz. the corresponding values of the transition probability, statistical weight and energy levels for the argon i and ii lines were obtained through nist database. table 1: electron temperature and their corresponding intensity ratio. table 1: shows the values of intensity ratio of spectral lines at various electron temperature. fig.3: graph of ratio of intensities(r1/r2)as the function of electron temperature(te) fig.3: shows the graph of ratio of intensities of spectral lines with the corresponding electron temperatures. from the graph, the electron temperature (te) was found to be 0.59 ev.similarly, the electron density was calculated by using the formula expressed in equation (2). electron temperature (te) (ev) ratio of the intensity of spectral lines (r1/r2) 0.5 1.57256 0.6 1.27136 0.7 0.98976 0.8 0.64225 0.9 0.31240 0.95 0.14225 h. b. baniya et al. / bibechana 17 (2020) 133-138 136 3 2 1 21 1 2 2 2 2 2 1 1 2 2 expe e i e e m kt e e ei a g n i a g h kt                             (2) the electron density was found to be ne = 2.1 × 10 16 cm -3 . surface modification of polyamide (pa) contact angle and surface energy measurements the water contact angle and surface free energy are measured at the equilibrium condition according to the young's equation and owens wendt kaeble methods respectively [11]. cos sv sl lv       (3) where, sv is the surface free energy of the solid substrate, sl is the interfacial tension between the solid and the liquid and lv is the surface tension of the liquid. for two liquids model i and j ,     1 1 2 2(1 cos ) 2 2d d p p li i li s li s        (4)     1 1 2 2(1 cos ) 2 2d d p p lj j lj s lj s        (5) substituting the known values of the surface tension and its polar and dispersion components of the test liquids, components of surface free energy of the solid, p s and d s can be determined. the sum of these two quantities gives the total surface energy of the solid. the treatment of the pa sample was performed for various exposure times from 5sec to 120 sec. the influence of this parameter on the hydrophilicity was investigated by contact angle measurement using a rame-hart contact angle goniometer taking two test liquids (water and glycerol) on the surface of the pa. initially contact angle of the untreated pa for water and glycerol was 51.270and 47.40but after plasma treatment contact angle was effectively reduced to 150 and 240 respectively and become saturated after the treatment time 30 sec as shown in fig.4 [12]. the reduction in contact angle might be due to increase roughness on the surface of pa [13]. fig.4: variation of contact angle with the fuction of treatment time. fig. 5: variation of surface energy with the fuction of treatment time the variation of surface energy with treatment time is shown in fig.5. total surface energy increases from 47.8 mj/m 2 to 72.5 mj/m 2 during 120 sec treatment time. similar trend is also observed for the polar component and it is mainly due to the incorporation of the polar species such as carbonyl (c=o) and carboxyl (-cooh) groups on the treated h. b. baniya et al. / bibechana 17 (2020) 133-138 137 pa surface. the dispersive component does not have any contribution to increase the wettability of the pa surface [14, 15]. 4. conclusion atmospheric pressure argon plasma jet has been produced and characterized by optical method. electron density (ne) and electron temperature (te) were found to be of the order of 2.1 ×1016cm−3and 0.59 ev respectively using intensity ratio method. treatment of pa using atmospheric pressure plasma jet resulted in improvement on hydrophilicity. it is mainly due to the increase in the polar component of the surface free energy after plasma treatment which indicates the formation of polar functional groups on the surface. during the experiment, contact angle of polymers after plasma jet treatment was found to decrease effectively whereas corresponding surface free energy was increased. this system is suitable for the treatment of various polymeric materials. acknowledgement the corresponding author was supported by nepal academy of science and technology (nast), nepal, providing phd fellowship through grant no: 11/073/074. the authors would like to acknowledge kathmandu university plasma physics laboratory for getting chance to handle related equipment's. the corresponding author also would like to acknowledge institute of science and technology (iost) and tri-chandra college, tribhuvan university, nepal for their invaluable support with providing study leave. references [1] a. v. deynse, r. morent, n. d. geyter, surface modification of polymers using atmospheric pressure cold plasma technology, polymer science : research advances, practical applications and educational aspects, (2016) 506–516, http: 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[15] a. akşit, b. kutlu, m. mutlu, surface modification of polyester and polyamide fabrics by low frequency plasma polymerization of acrylic acid, journal of applied polymer science 104 (2007) 2318 – 2322. https: //doi.org/10.1002/app.25701. microsoft word lamichhane final (79-91) tika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.79 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal molecular dynamics approach to the i431v mutational impact on thyroid hormone receptor-beta tika ram lamichhane1, sharma paudel2, binod kumar yadav2, hari prasad lamichhane1* 1central department of physics, tribhuvan university, kirtipur, kathmandu, nepal 2institute of medicine, tribhuvan university, teaching hospital, maharajgunj, kathmandu, nepal *email: hlamichhane1@gmail.com article history: received 15 march, 2018; accepted 16 september, 2018 doi: http://dx.doi.org/10.3126/bibechana.v13i0.21109 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the point mutations like i431v on thyroid hormone receptor-beta (thr-β) gene cause resistance to thyroid hormones (rth) with the clinical diagnosis of elevated free triiodothyronine (t3) and free thyroxin (t4) but not suppressed thyroid stimulating hormone (tsh) on the blood serum. some ultrasonographic (usg) reports of the patients with rth show thyroid gland disorder with goiter or nodule(s) or cyst(s) and some usg reports even with rth are normal. i431v-mutant causes more steric hindrance while binding t3 into thr-β than the native wild type thrt3. the residue on the 431-codon is dynamic in nature showing its flexibility over the course of entry and release of t3-hormone into/from the ligand binding pocket. the more increased solvent accessible surface area of i431v-mutant than that of native i431-residue makes the partial unfolding of the globular thr-β protein. the smaller height of radial distribution function between i431-mutant and t3 shows the decrease in probability of finding the atomic particles nearby t3-hormone in thrt3-mt than in thrt3-wt. the electrostatic interaction energy between native i431 and t3 is negative, but it is positive between i431v and t3. moreover, the internal energy of i431v-mutant has been found smaller than that of native i431-residue in thrt3 systems. keywords: thyroid hormone receptor; resistance to thyroid hormones; point mutation; interaction energy; internal energy. 1. introduction thyroid hormone receptors (thrs) are the nuclear receptor proteins that actively bind triiodothyronine (t3: hormone secreted by thyroid gland) to mediate the biological activities associated with gene transcription. thrs regulate gene expressions upon binding to the dna sequences called as thyroid response elements (tres). thrs have two isoforms thr-α and thr-β that are in hetero-diversity in the different organs. t3 has the higher affinity to bind into both isoforms than thyroxin (t4). while t3 tika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.80 (online publication: dec., 2018) binds to the ligand binding domain (lbd) of hydrophobicity, thr shows its structural change [1-4]. the carboxy-terminal activation domain forms an amphi-pathic helix[2, 3] as a part of cavity or lbd. the dynamic nature of helix-12 (h12 in fig. 2-c) of thr is is important for the hormone binding, ligand dissociation, activation mechanism and regulation of transcription activity [5]. the mutational impact on thr reduces the hormone binding affinity and gene expression activity. ultimately, the mutations leading to the resistance to thyroid hormone (rth) cause the endocrine disorder. the inactivated thr-β gene by means of homozygous mutant (thrb-/-) in mice results in a goiter and elevated levels of thyroid hormones [6]. the mutant t327i found in thr-β gene shows the paucity of symptoms and signs of thyroid dysfunction suggesting rth despite the increased serum levels of t3, t4 and thyroid stimulating hormone (tsh) [7]. a rare mutation a268g found in axon 9 of thr-β gene results rth with elevated serum t3 and t4, tsh in the normal range and the episodic palpitations associated with mild dizziness [8]. a heterogeneous mutation g344r is identified in axon 10 of thr-β gene of 10-month-old-female resulting in paucity of symptoms of rth with normal t3, t4 and tsh levels [9]. also, r383h mutation is found in thr-β gene of a woman with inappropriate central secretion of tsh despite of elevated t3 and t4 [10]. the rth patients are clinically euthyroid or hypothyroid depending on severity of mutation. a point mutation r429q found in mice has the elevated serum thyroid hormones but the inappropriate tsh consistent with hypothalamic-pituitary rth [11]. the active sites of these point mutations along with the site of i431v-mutant [12] in the thr-β gene are indicated in fig. (2-c). the helix-12 serves as a selective gatekeeper which is responsible for corepressor specificity by the wild type receptor (thr-wt). the point mutations in thr are all positioned to impact the gatekeeper functions and then to change corepressor specificity by the mutated receptor (thr-mt) [13, 14]. thr-wts regulate normal physiological and developmental pathways, but thr-mts result neoplastic and endocrine diseases. (a) (b) (c) fig. 1: chemical structures of (a) triiodothyronine (t3): c15h12i3no4 with molar mass = 650.98 g/mol, (b) isoleucine (ile): c6h13no2 with molar mass = 131.17 g/mol and (c) valine (val): c5h11no2 with molar mass = 117.15 g/mol[prepared from pymol molecular graphics system]. the i431v point mutation is detected experimentally in thr-β gene of a 14-year-old brazilian girl with elevated t3 and t4 but unsuppressed tsh showing rth with goiter [12]. this mutation occurs tika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.81 (online publication: dec., 2018) by replacing isoleucine (ile) amino acid residue by valine (val) in 431 codon of thr-β gene. i431v mutation exerts impairment of ligand-dependent release of corepressor, silencing mediator for retinoid and thyroid receptors (smrt) with dominant negative effects on thr-wt and reducing potency. the chemical structures of t3, ile and val are shown in fig. 1. ile is heavier and larger in size than val. t3 binding assay [12] shows that the hormone binding affinity of i431v-mutant thr-β is 2.6 times lower than that in wild type thr-β. thr-wt, thrt3-wt and thrt3-mt show the distinct features reflecting in terms of root mean square deviation (rmsd), radius of gyration (rg), root mean square fluctuation (rmsf), ir spectra, radial distribution functions, solvent accessible surface area (sasa), interaction energy, internal energy, etc. the structural and physical properties of the wild type and the mutated protein-hormone systems can be studied by using molecular dynamics simulations (mds). (a) (b) (c) fig.2: (a) wild type thr-β highlighting with i431 codon and t3 hormone, (b) i431v-mutant on thr-β gene and (c) experimentally observed mutational sites on thr-β gene [7-12]. the images are prepared from pymol molecular graphics system. 2. methodology the structure of wild type thrt3 was taken from the x-ray crystallographic data of protein data bank code-3gws [15]. the charmm force field topologies and parameters [16, 17, 18, 19] were used for mds of the protein-hormone systems. the hetero-atomic t3-hormone was parameterized first to describe its molecular geometry, atomic masses, charges and torsion barriers [19]. the generation of the complete systems of thr-wt, thrt3-wt and thrt3-mt starting from their protein structure files to the solvation in neutral water-ion environment, equilibration, production runs and analysis of the results were performed by using the interfaces of visual molecular dynamics (vmd) [20] and nanoscale molecular dynamics (namd) [21] computational packages. from the wild type native structure of thrt3, the mutated thrt3 was made after the point mutation on 431-codon replacing ile by val with the help of vmd-mutagenesis. unliganded thr-wt, t3-liganded thrt3-wt and i431v-mutant thrt3-mt were solvated separately in the tip3p water-box tika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.82 (online publication: dec., 2018) which was neutralized with na+ & clions in the concentration of 0.15 mol/l. each water-box has the periodic cell basis vectors 50.35, 61.92 and 74.78 å along x, y and z-axes, respectively. configuration files were prepared by writing tcl-scripts to simulate the systems for which langevin piston temperature, pressure and damping coefficient are 310 k, 1 bar and 1 ps-1, respectively. oscillation period of the piston was 100 fs with decay time of 50 fs and periodic cell fluctuation was isotropic. the langevin dynamics [22, 23] was applied for all atoms except hydrogens of the systems. particle mesh ewald (pme) was active with the grid dimensions of (54, 64, 80å) and the pme coefficient of 0.258 for the electrostatic force evaluation [24]. in adjusting the force field parameters used in mds, 1-4 scaling was 1.0; cut-off, switching and pair-list distances for the electrostatic and van der waals interactions were 12, 10 and 14 å, respectively. finally, each system was geometrically optimized with 3000 conjugate gradient steps and then it was equilibrated up to 2ns at 310 k. to calculate the trajectory of atomic particles, the velocity verlet algorithm [25] was used during mds of the systems. all the simulations were performed adjusting integrator parameters of 2 fs/step constrained with rigid bonds of h-atoms. conformational stability of the protein-hormone systems was tested by plotting rmsd, rg, rmsf and sasa of protein backbone, t3-hormone and residues of interest: i431 and i431v of thr-wt, thrt3-wt and thrt3-mt. the dihedral angle distributions were analyzed from ramachandran plots to test the steric hindrance among α-helices, β-sheets and side chains and residues of the systems. the electrostatic and van der waals interactions were observed between the native or mutated residue on 431-codon and t3-hormone by using namd-energy-gui. also, number of h-bonding, probability density from radial distribution functions, ir spectral densities, internal energies of the native wild type and mutated systems were calculated, analyzed and compared by plotting the corresponding results over the simulation time. 3. result and discussion thr-β nuclear receptor isoform consists of a chain length of 259 amino acid residues. the protein structure of wild type thr-β that we take for the simulation has total mass of 27640 amu and 3895 atoms. the active ligand bound to the lbd of thr-β is the thyroid hormone (t3) which has mass of 651 amu and 35 atoms. the plots of dihedral angles (φ,ψ), i. e. ramachandran plots for thr-wt, thrt3-wt and i431v mutant thrt3-mt are shown in fig. 3. in these plots, most of the amino acid residues of parallel, anti-parallel and right twisted β-sheets lie in the blue region of i-quadrant; that of right handed α-helix lie in the blue region of ii-quadrant and left handed α-helix lie in the green region of iii-quadrant [26, 27]. the residue gly has no side chain so that it has no steric hindrance and it is allowed in the white region. the white region is sterically disallowed for all other amino acids except gly. the blue regions are the most allowed regions for α-helices and β-sheets. the green area is allowed for the shorter van der waal radii of atoms and the related amino acids. by comparing three plots of fig. 2, we observe that smaller number of amino acid residues lies in the disallowed region for thrt3-wt than for thr-wt and thrt3-i431v. thus, the larger steric hindrances occur for the unliganded and mutated thr-β. the clinical analysis shows that thrt3-wt is related to euthyroid or normal thyroid functions, thr-wt is related to overt thyroidism and thrt3-mt is related to rth [6-14]. 012345678 0 1000 2000 3000 4000rmsd (å) time frame (0.5ps/frame)i431 thr-protein t3024681012 0 1000 2000 3000 4000rmsd(å) time frame (0.5ps/frame)thr-protein i431 0123456789 0 1000 2000 3000 4000rmsd (å) time frame (0.5ps/frame)thr-protein i431v t3 tika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.83 (online publication: dec., 2018) fig. 3:ramachandran plots for (a) wild type thr-β, (b) t3-liganded wild type thr-β and (c) i431v-mutant thrt3. the constancy of root mean square deviation (rmsd) and radius of gyration (rg) of the molecules thr-β protein and t3-hormone over the time frames of equilibration run (fig. 4, 5) show the conformational stability and validity of force field topology and parameters used for mds of wild type and mutated nuclear receptors. the more fluctuating rmsd and rg of residue id-431 show its dynamic property. this dynamic property of the residues is significantly important while trapping t3 in and releasing t3 from the lbd of thyroid hormone receptors. (a) (b) (c) fig.4: rmsd-plots of 431 residue, thr-protein and t3-hormone during equilibration of (a) wild type thr, (b) wild type thrt3 and (c) i431v-mutant thrt3. the values of rmsd and rg of the molecules with the standard deviations of the data are listed in the table 1. during their 2 ns equilibration run in neutral water-ion environment, rg of 431-residue of thr-wt is being smaller with larger rmsd, i.e. it is bending more towards the center of mass of the system than that of thrt3-wt and thrt3-mt. in other words, the nature of rmsd of 431-residue change from unliganded to liganded as well as wild type to mutated thr-β. the rmsd or rg of the protein is almost same with small fluctuations for these three cases. the protein rmsd is about 2 å and the protein rg is about 19 å for the wild type and the mutated thr-β systems. the rmsd 0510152025 0 1000 2000 3000 4000rg(å) time frame (0.5ps/frame)thr-protein i431v t30510152025 0 1000 2000 3000 4000rg(å) time frame (0.5ps/frame)thr-protein i4310510152025 0 1000 2000 3000 4000rg(å) time frame (0.5ps/frame)thr-protein i431 t3tika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.84 (online publication: dec., 2018) and rg of t3-hormone while bounded in the lbd of nuclear receptors are 0.7 å and 4.3 å respectively. (a) (b) (c) fig. 5: rg-plots of 431 residue, thr-protein and t3-hormone during equilibration of (a) wild type thr, (b) wild type thrt3 and (c) i431v-mutant thrt3. table 1: average values of root mean square deviation (rmsd) and radius of gyration (rg) of unliganded wild type and t3-liganded wild type and i431v-mutant thr-β including with the standard deviation of the data obtained after mds by their equilibration runs. molecule thr-wt thrt3-wt thrt3-mt i431 protein i431 t3 protein i431v t3 protein rmsd(å) 4.6 ± 2.4 2.0 ± 0.2 3.6 ± 1.6 0.7 ± 0.1 2.0 ± 0.3 3.5 ± 1.5 0.7 ± 0.1 2.3 ± 0.4 rg(å) 10.3 ± 3.7 18.8 ± 0.1 12.1 ± 3.1 4.3 ± 0.1 19.2 ± 0.2 12.8 ± 3.6 4.3 ± 0.1 19.1 ± 0.1 in this study, the root mean square fluctuations (rmsf) of most of the residues of thrt3-wt are observed to be a little bit larger than that of thr-wt and thrt3-mt as shown in fig. 6. in the i431v mutational site, the values of rmsf are 3.2 å for ile of thr-wt, 4.1 å for ile of thrt3-wt and 3.0 å for val of thrt3-mt. the residues in helix-1 have the highest rmsf so that the helix-1in thrt3-wt is more flexible. fig. 6: rmsf of amino acid residues of thr-wt, thrt3-wt and i431v-mutant thrt3-mt during their 2 ns equilibration run. 024681012 200 220 240 260 280 300 320 340 360 380 400 420 440 460rmsf (å) amino acid residuesthr-wt thrt3-wt thrt3-mt i431v mutational site tika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.85 (online publication: dec., 2018) solvent accessible surface area (sasa) of thr-wt, thrt3-wt and thrt3-mt are observed to be slightly different in the extension radius of 1.4 å. after 500 frames of energy minimization and equilibration, the sasa with the standard deviation of the data from frame to frame simulation up to 2 ns is 13620.1 ± 253.07 å2 for thr-wt, 13952.4 ± 130.9 å2 for thrt3-wt and 13721.0 ± 147.9 å2 for thrt3-mt. in this way, the sasa of 431-residue is 14.8 ± 9.0 å2 for thr-wt, 12.6 ± 10.1 å2 for thrt3-wt and 17.4 ± 8.1 å2 for thrt3-mt. the lower sasa indicates the higher thermodynamic stability of the protein. the sasa of t3-hormone is observed to be zero indicating the hydrophobicity of lbd of thr-β. the mutation on the solvent accessible residue causes the conformational change by partial unfolding of the protein with increasing sasa [28]. such effect is more intensive if the mutation occurs on the surface residue than on the interior of the protein. the i431v mutation is the interior one so that no significant change in sasa of wild type and mutated thr-β has been observed after their 2 ns equilibration. however, the total sasa of thr-wt and thrt3-mt are more fluctuating than that of thrt3-wt up to 3000 frames of the equilibration runs (fig. 7-a). furthermore, sasa of i431v-mutant is higher and less fluctuating than that of native and wild type i431-rsidue of thr-β (fig.7-b). (a) (b) fig. 7: (a) sasa of protein in wild type thr, thrt3 and mutated-thrt3, (b) sasa of i431 residue in thrt3-wt and i431v mutant in thrt3-mt during their equilibration runs. the distributions of number of h-bonds along with the frame order of the simulations up to 2 ns equilibrations are shown in fig. 8. here, the average values of h-bond number with the standard deviation of the data after 500 frames with the donor-acceptor distance 4.0 å and cut-off angle 40o among n and o atoms are 5 ± 2 for i431-thr(wt), 16 ± 4 for t3-thr(wt), 4 ± 2 for i431-thr(mt) and 15 ± 4 for t3-thr(mt). during mds of the wild type and mutated thr-β systems, the distance between i431 and t3 in thrt3-wt varies as 10.2 ± 2.6 å and the distance between i431v and t3 in thrt3-mt varies as 13.1 ± 2.0 å as shown in fig. 9-b. such distance is smaller and more fluctuating in thrt3-wt than in thrt3-mt. this is one of the indicators of t3 resistant features of mutated nuclear receptor proteins that cause rth. radial distribution function [29] or pair auto-correlation function g(r) in a system of particles measures probability of finding a particle at r distance away from the reference particle. the distribution function g(r) between i431-residue and t3-hormone has the higher value than that between i431v and t3 12000125001300013500140001450015000 0 1000 2000 3000 4000sasa (å2 ) frame order (0.5ps/frame)thr-wt thrt3-wt thrt3-mt 020406080 0 1000 2000 3000 4000sasa(å2 ) frame order (0.5ps/frame)i431 i431v 05101520 0 5 10 15 20 25g (r) r (å) i431v-t3i431-t305101520 0 1000 2000 3000 4000distance(å) frame order (0.5ps/frame)i431-t3 i431v-t3tika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.86 (online publication: dec., 2018) and it lies in the range of 5 å and 18 å as shown in fig. 9-c. in other words, the number density of mutated residue is less than that of the native wild type residue to respond for t3-hormone and tres. (a) (b) fig. 8: variation of number of h-bonds between 431-residue and protein vs. simulation time in case of (a) wild type and (b) i431v-mutant thrt3 systems. (a) (b) (c) fig. 9: (a) positions of i431v-mutant and t3-hormone in thrt3-mt, (b) changing distance between 431-codon and t3 while equilibrating thrt3-wt and thrt3-mt systems and (c) radial distribution functions between 431-residue and t3-hormone in case of wild type and mutated thrt3. ir spectral densities using total dipole moment of the atoms in 431-residue and t3 are calculated in the frequency range of 0 to 2000 cm-1 and their plots are different for thrt3-wt and thrt3-mt as shown in fig. 10. the maximum ir-intensity of t3 in the wild type receptor is 0.041 at 1837.42 cm-1 and that of i431 (wild type) is 0.027 at 1637.88 cm-1. again, the maximum ir-intensity of t3 in the mutated receptor is 0.037 at 1313.63 cm-1 and that for i431v-mutant is 0.029 at 1571.37 cm-1. the distribution has larger number of high intensity peaks for t3 and i431v in thrt3-mt than in thrt3-wt. total non-bonding interaction energy is the sum of electrostatic and van der waal’s interaction energy. the changing values of interaction energy between 431-residue and t3-hormone in wild type and mutated thr-β systems are plotted with respect to the frame order in fig. 11 and these are averaged 05101520253035 0 1000 2000 3000 4000no. of h-bonds frame order (0.5ps/frame)i431-thr(wt) t3-thr(wt) 05101520253035 0 1000 2000 3000 4000no.of h-bonds frame order (0.5ps/frame)i431v-thr(mt) t3-thr(mt) -1.5-1-0.500.5 0 1000 2000 3000 4000energy (kcal/mol) frame order (0.5ps/frame)elec vdw -1-0.500.51 0 1000 2000 3000 4000energy (kcal/mole) frame order (0.5ps/frame)elec vdwtika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.87 (online publication: dec., 2018) over the time frames from 500 to 4013. the average values of electrostatic and van der waals interaction energy (from namd-energy-gui using switching and cut-off distances of 10 å and 12 å, respectively) with their standard deviations are -0.25 ± 0.17 kcal/mol and -0.18 ± 0.07 kcal/mol between i431 and t3 of thrt3-wt and 0.21 ± 0.08 kcal/mol and -0.07 ± 0.05 kcal/mol between i431v and t3 of thrt3-mt, respectively. thus, the electrostatic energy between i431 and t3 in thrt3-wt is negative and more fluctuating and that between i431v and t3 in thrt3-mt is positive and less fluctuating over the simulation time. (a) (b) fig. 10: ir spectra of (a) i431 residue and t3-hormone in wild type thrt3 and (b) i431v-mutant and t3-hormone in mutated thrt3. (a) (b) fig. 11: electrostatic and van der waals interaction energies (a) between i431 and t3 in wild type thrt3 and (b) between i431v and t3 in mutated thrt3. internal energy of the biomolecular system is the sum of bonding and non-bonding potentials. coulomb energy is the largest and its fluctuation during smd makes the total internal energy fluctuate about its mean value. using namd-energy-gui with switching and cut-off distances of 10 å and 12 å, the internal energy of 431-residue, bounded t3-hormone and protein of thr-wt, thrt3-wt and thrt3-mt are calculated and the average values for the corresponding systems are listed in the table 2. the variations of the related internal energy with respect to the simulation time are plotted in the fig. 12. the plots for the individual potential terms show that the major contributor of fluctuations in the internal energy is the electrostatic energy of the related system. 204060801001201403500 3600 3700 3800 3900 4000int. energy (kcal/mol) time frame (0.5ps/frame) i431_thr-wti431_thrt3-wtt3_thrt3-wti431v_thrt3-mtt3_thrt3-mt -1500-1200-900-600-30003500 3600 3700 3800 3900 4000int. energy (kcal/mol) time frame (0.5ps/frame)protein_thr-wt protein_thrt3-wt protein_thrt3-mttika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.88 (online publication: dec., 2018) table 2: internal energy of the components of unliganded wild type, t3-liganded wild type and i431v-mutant thr-β systems averaged over the values from the last 0.25 ns of their equilibrations where the including error represents standard deviation of the data. molecule thr-wt thrt3-wt thrt3-mt i431 protein i431 t3 protein i431v t3 protein int. energy (kcal/mol) 42.82 ± 3.21 -822.38 ± 67.67 42.88 ± 3.18 128.73 ± 4.52 -644.21 ± 109.87 36.13 ± 3.07 124.41 ± 4.63 -756.54 ± 104.22 (a) (b) fig. 12: fluctuating total internal energy along the frame order of (a) i431-residue and t3, and (b) thr-proteins for unliganded as well as t3-liganded wild type and i431v-muatant thr-β systems in the last 0.25 ns of their equilibrations. 4. conclusion conformational properties and interactions of mutational residues and t3-hormone of unliganded and t3-liganded thyroid hormone receptor-beta (thr-β) can be studied by means of molecular dynamics simulations (mds). the almost constant values of root mean square deviation (rmsd ≈ 2 å) and radius of gyration (rg ≈ 19 å) of native and i431-mutant thr-β proteins show their conformational stability during mds. the native i431-residue has largely fluctuating rmsd and rg showing its dynamic property in adapting and releasing t3-hormone. the experimentally verified i431v mutation on thr-β gene (ferreira et al., 2010) is the subject of this computational study. this mutation causes resistance to thyroid hormones [12]. solvent accessible surface area (sasa) is larger for the i431v-mutant indicating partial unfolding of the globular protein. however, the root mean square fluctuation of i431v-mutant is smaller in comparison with that of native wild type i431. the sasa of t3 is zero verifying the hydrophobicity upon binding to the ligand binding domain (lbd) of thr-β. comparing the radial distribution functions g(r) for the atomic particles between i431 and t3 as well as i431v and t3, the probability density is higher in the former wild type than the latter mutated type for which g(r) covers the distance of 5 å to 18 å. ir spectral density calculations for i431-residue and t3-hormone in the frequency range of 0-2000 cm-1 imply that greater number of intensity maxima is found in thrt3-mt than in thrt3-wt. this signifies higher dipole moment distributions by supporting less globular stability of the mutated thr-β than that of the wild type thr-β. furthermore, electrostatic interaction energy between i431v-mutant and t3 is positive whereas it is negative between tika ram lamichhane et al./ bibechana 16 (2019) 79-91 : rcost p.89 (online publication: dec., 2018) native i431-residue and t3. in this study, internal energy of the native i431-residue is 42.88 ± 3.18 kcal/mol and that of wild type i431v-mutant is 36.13 ± 3.07 kcal/mol in thrt3 systems. the major contributor of such change in the internal energy is the electrostatic energy. acknowledgement this work was partially supported by nepal academy of science and technology (nast) as the ph. d. fellowship grant to the first author. the computing facility was provided by central department of physics, tribhuvan university, kathmandu, nepal. references [1] l. martínez, i. polikarpov, m. s. skaf, only subtle protein conformational adaptations are required for ligand binding to thyroid hormone receptors: simulations using a novel multipoint steered molecular dynamics approach,j. phys. chem. b 112 (2008) 10741–10751. doi.org/10.1021/jp803403c. 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effect of additional side groups on the vibrational frequencies of benzoquinone molecules nabin kumar raut, hari prasad lamichhane* central department of physics tribhuvan university, kirtipur, kathmandu, nepal *e-mail:hlamichhane1@gmail.com article history: received 30 may, 2016; accepted 29 september, 2016 doi: http://dx.doi.org/10.3126/bibechana.v14i0.15860 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the present work enumerates detailed computational investigation into the ir spectra in gas phase and in solvent of 1, 4benzoquinone family (benzoquinone (bq), duroquinone (dq), plastoquinone (pq), ubiquinone (uq), and dimethoxy dimethyl benzoquinone (mqo)). in the spectra of bq, pq, and dq, we observed separate intense carbonyl (c=o) and c=c bands respectively around 1730 cm-1 (intense), 1645 cm-1 (weak). on the other hand, for uq and mqo, three prominent bands around 1652, 1703, and 1733 cm-1 were observed, where two c=o modes were uncoupled but one of the carbonyl is strongly coupled with c=c vibrations. the additional methyl groups downshift the intense carbonyl bands and upshift c=c mode frequencies. the carbonyl modes further downshifted in the solvent phase calculation. keywords: photosynthesis; reaction center; benzoquinone; ir spectra; qa, qb . 1. introduction quinone serves as a coupler of electron and proton transfers in vivo in energy-transducing membrane for respiration and photosynthesis [1-4]. based on nature of work, not on types, quinones in the reaction center (rc) are classified as qa (primary quinone) and qb (secondary quinone). they can be chemically identical or different depending upon rc. for example, ubiquinone in rb. sphaeroids and menaquinone in cf. aurantiacus rc works as both qa and qb, in contrast in chromatium or rp. viridis rc menaquinone is qa and ubiquinone is qb. however, each of them has to complete significantly different task. here, qa works as transporter of electron and undergoes only single redox steps, while qb works like recipient and has to go through two redox steps. indeed, their mutual working leads to the proton-coupled electron transport reaction. the former can transport an electron to latter at a time until it gets two nabin kumar raut, hari prasad lamichhane / bibechana 14 (2017) 66-76 : rcost p.67 (online publication: dec., 2016) electrons. eventually after receiving two electrons, qb gets two protons from protein membrane forming qbh2 i.e. quinol which then leaves the reaction center. qb + 2e+ 2h+ qbh2 qbh2 leaves the binding site and a new qb occupies the vacant space. the quinol (qbh2) releases two hydrogen atoms whenever it reaches the place of higher redox potential [3]. thus, this process creates a potential gradient across the photosynthetic membrane which drives atp synthesis reaction [3]. moreover, in purple bacteria rc, the electron transfer from qa to qb spans a distance of 15 å (edge to edge) and are linked by h-bonds through a his-fe2+-his complex [4]. on the other hand, the process of proton and electron transfer by a quinone is in reverse direction in respiration to that of photosynthesis [3]. hence, study of quinones is so important for the understanding of reaction center and eventually about photosynthesis and respiration, which is essential for the survival of living things. 2. materials and methods by using hybrid density functional theory (dft) method we have done geometrical optimization and vibrational frequency calculations, employing b3lyp functional and the 6-31g+(d) basis within gaussian 03 [5]. the solvent phase calculation employs iefpcm method in carbon tetrachloride (ccl4) solvent. 3. results and discussions 1, 4-benzoquinone family here, we have studied ir spectra and solvent effect of 1, 4-benzoquinone family by dividing it into the two classes, which are benzoquinone with and without methoxy side group. a. benzoquinone without methoxy side group i. structure and numbering of bq, pq, and dq fig. 1: structure and numbering for (a) benzoquinone (bq), (b) duroquinone (dq), (c) plastoquinone (pq). for the sake of simplicity the hydrogen atoms have been removed. nabin kumar raut, hari prasad lamichhane / bibechana 14 (2017) 66-76 : rcost p.68 (online publication: dec., 2016) figure (1) shows structure and numbering scheme for benzoquinone without methoxy side groups (bq, pq, and dq). they have a quinone ring and differ from one another by particular functional group. out of three, benzoquinone (bq) has simplest structure and by replacing all of its hydrogen atom by methyl side group we can get duroquinone (dq). similarly, by replacing hydrogen atoms at the positions c2 and c3 by methyl groups and at c6 by isoprene unit we can get plastoquinone (pq). the information of fuctional groups is summarized in table (1). table 1: summary side groups in bq, pq, and dq. 1, 4-bq side groups c2 c3 c5 c6 bq h h h h dq ch3 ch3 ch3 ch3 pq ch3 ch3 h isoprene unit ii. the ir spectra of bq, pq, and dq calculated ir spectra of bq, dq, and pq are shown in the figure (2) and (3). figure (2) shows these three quinones and their corresponding spectra. on the other hand, figure (3) shows comparative spectra of all three of them. we have chosen spectra in the region 1800-1600 cm-1 because experimentally detectable carbonyl (c=o) and c=c vibrations lie in this region. from figure (2) we observed that, in the ir spectra respectively of bq/dq/pq, the weak band is at 1651/1675/1663 cm-1 and are due to an out-ofphase vibration of the c=cr groups (c2=c3 and c5=c6) of the quinone ring. given the antisymmetric nature of vibration it is very weakly raman active (data not included). in addition to that, a highly intense ir band respectively of them is found at 1735/1707/1714 cm-1 and are due to out-of-phase c=o vibration. these modes also have asymmetric nature of vibration again they have weak raman activities. although not always true, as a general rule, band that are weak in raman spectra are often strong in ir spectra [6]. by analyzing figure (3), we can conclude that bq, dq, and pq have similar nature of spectra. indeed, all of them have one intense and one weak band. which means, addition of methyl and isoprene side group, respectively, in bq to get dq and pq does not really change the nature of the spectra. however, addition of methyl side groups lowered the band positions carbonyl vibrations in proportion to the number of methyl groups. iii. the solvent effect table (2) shows bond length of carbonyl group and c=cr (c2= c3 and c5= c6) of optimized quinone structure in gas phase and ccl4. the 1aij crystal structure [7] indicates that the c1=o bond is marginally longer than the c4=o bond (1.234 versus 1.232 å). the c1=o and c4=o bond length of bq, dq, and pq were found shorter in the gas phase than that of the corresponding length in the ccl4. among all three, bq got maximum elongation (0.003 å) in both c1=o and c4=o bond in solvent phase calculation. in nabin kumar raut, hari prasad lamichhane / bibechana 14 (2017) 66-76 : rcost p.69 (online publication: dec., 2016) opposite, they got minimum elongation (0.001 å) in case of pq. this change in length is due to increase in value of dielectric constant. fig. 2: structure and gas phase calculated ir spectra in the c=o and c=c vibrating region for the (a) benzoquinone, (b) plastoquinone, and (c) duroquinone. for the sake of simplicity r is written instead of ch3. nabin kumar raut, hari prasad lamichhane / bibechana 14 (2017) 66-76 : rcost p.70 (online publication: dec., 2016) fig. 3: calculated ir absorption spectra of bq, dq, and pq in gas phase. the spectra are generated from the calculated stick spectra by convolving with gaussian function of wavenumber 4 cm-1. furthermore, 1aij crystal structure [7] indicates that the c2=c3 bond is shorter than the c5=c6 bond (1.404 versus 1.419 å). in contrast, for the case of bq, dq, and pq, in both ccl4 and gas phase calculation c2=c3 and c5=c6 are equal. since, in the gas phase or in ccl4 there is no effect of hydrogen bonding but in the protein environment i.e. in the crystal structure there is effect of hydrogen atom neighbor molecules which is difference of the bond length observed here with the bond length c=c and c=o group in crystal structure. so, it can be concluded that calculation of quinone in solvent does effect in carbonyl group but effect is almost negligible for c=c bond of quinone ring. which suggested that the solvent not much constrain the quinone ring. table 2: bond length of carbonyl group and c=cr in (å) unit of optimized structure of bq, dq, and pq in gas phase (gp), ccl4, and crystal structure (cs). types c1=o c4=o c2=c3 c5=c6 gp ccl4 cs gp ccl4 cs gp ccl4 cs gp ccl4 cs bq 1.227 1.230 1.234 1.227 1.230 1.232 1.345 1.345 1.404 1.345 1.345 1.419 dq 1.230 1.232 1.234 1.230 1.232 1.232 1.356 1.356 1.404 1.356 1.356 1.419 pq 1.229 1.230 1.234 1.230 1.233 1.232 1.358 1.358 1.404 1.347 1.347 1.419 nabin kumar raut, hari prasad lamichhane / bibechana 14 (2017) 66-76 : rcost p.71 (online publication: dec., 2016) figure (4) shows comparative ir spectra of bq, dq, and pq in gas phase and ccl4. from the figure it is obvious that frequency decreases in solvent (ccl4) than that of in the gas phase calculation. in fact, there is general trend of lowering of frequency in intense band but case is not true for weak band. the cause of the intense band is due to asymmetric c=o vibration, while that of weak band is due to asymmetric c=cr, c2=c3 and c5=c6, vibration. the force constant is inversely proportional to the bond length and directly proportional to the frequency i.e. frequency (f) α force constant (k) α {1/ bond length (l)} [8]. thus, increase in bond length in c1=o and c4=o that calculated in solvent than in gas phase results decrease in frequency for intense band {figure (4) and table (2)}. our results also indicate frequencies shift and bond lengths shift are inversely proportional under calculation in solvent than in gas phase. fig. 4: comparative spectra of bq, dq, and pq in gas phase and ccl4. the spectra are generated from the calculated stick spectra by convolving with gaussian function of wavenumber 4 cm-1. b. benzoquinone with methoxy side group i. structure and numbering of uq and mqo the structure and numbering scheme for benzoquinone with methoxy side group (mqo and uq) is shown in figure (5). both of them have methoxy group at c2 and c3 and methyl at c5. the key component that distinguishes both of them is the functional group at c5. uq has isoprene unit at that position, while mqo has methyl side group. nabin kumar raut, hari prasad lamichhane / bibechana 14 (2017) 66-76 : rcost p.72 (online publication: dec., 2016) fig. 5: structure and numbering for (a) 2, 3-dimethoxy-5, 6-dimethyl benzoquinone (mqo) and (b) ubiquinone (uq). for the sake of simplicity the hydrogen atoms have been removed. ii. the ir spectra of uq and mqo here, ir spectra of two methoxy containing benzoquinones (mqo and uq) are shown in figure (6) and (7) in the region of 1800-1600 cm-1. actually, figure (6) shows structure of mqo and uq and their corresponding ir spectra with different modes of vibration. on the other hand, figure (7) shows the comparative spectra between them. fig. 6: structure and gas phase calculated ir spectra in the uncoupled and coupled c=o and c=c vibrating region for the (a) mqo and (b) uq. for the sake of simplicity r is written instead of ch3. nabin kumar raut, hari prasad lamichhane / bibechana 14 (2017) 66-76 : rcost p.73 (online publication: dec., 2016) fig. 7: calculated ir absorption spectra of uq and mqo in gas phase. the spectra are generated from the calculated stick spectra by convolving with gaussian function of wavenumber 4 cm-1. the ir spectra of uq and mqo had shown three prominent bands in the 1800-1600 cm-1 region. for both quinones (uq/mqo) bands are observed, respectively, at 1652/1653, 1702/1705, and 1733/1733 cm-1. the first two bands are occurred due to coupled vibration, whereas cause of the last band is due to single mode vibration. in fact, band at 1652/1653 cm-1 of uq/ mqo are predominantly due to antisymmetric c=cr (c2=c3 and c5=c6) vibration coupled to the c4=o vibration and band at 1702/1705 cm-1 is predominantly due to c4=o vibration mixed with c2=c3 vibration. however, uncoupled c1=o vibration produced band at 1733 cm-1 for both of them. in mqo presence of two methyl side groups contributed more to the band at 1653 cm-1 and hence it is more intense. but, in uq due to single methyl side group the intensity of bands at 1653 and 1702 cm-1 are same. the observation of uq is in closer agreement with the work done by lamichhane and hastings [9]. in figure (7), we observed the similar nature of spectra for both uq and mqo. the band due to single mode vibrations are not shifted. in addition to that, the coupled vibrations are slightly deviated and deviation is less than 3 cm-1. it further strengthens our conclusion that the addition of side group does not bring change in the nature of the spectra. nabin kumar raut, hari prasad lamichhane / bibechana 14 (2017) 66-76 : rcost p.74 (online publication: dec., 2016) iii. the solvent effect table 3: bond length of carbonyl group and c=cr in (å) unit of optimized structure of uq, and mqo in gas phase (gp), ccl4, and crystal structure (cs). types c1=o c4=o c2=c3 c5=c6 gp ccl4 cs gp ccl4 cs gp ccl4 cs gp ccl4 cs mqo 1.223 1.225 1.234 1.231 1.232 1.232 1.364 1.364 1.404 1.354 1.354 1.419 uq 1.223 1.225 1.234 1.231 1.232 1.232 1.364 1.364 1.404 1.354 1.355 1.419 by analyzing table (3) and figure (8), we came to the conclusion that frequency of both uq and mqo decreased in the solvent phase calculation than that of in the gas phase in the 1800-1600 cm-1 region. as a matter of fact, amount of decrement of particular ir band depend upon amount of change in bond length of the functional group that contributes to that specific band and they follows inverse relation. for example, bond length of c=c remains almost same for both types of quinones in both phase calculations. hence, very slight decrement in the band at 1653 cm-1, that is occurred predominantly due to antisymmetric c=cr (c2=c3 and c5=c6) vibration coupled to the c4=o vibration, is observed. on the other hand, c1=o mode shifted down nearly by 11 cm-1 and hence corresponding bond length increases by 0.002 å. similarly, lengthing of c4=o (of uq and mqo) by 0.001 å leads to the lowering of bands at 1702 cm-1 (uq) and 1705 cm-1 (mqo) to 1695 cm-1 (uq) and 1696 cm-1 (mqo). fig. 8: comparative spectra of uq and mqo in gas phase and ccl4. the spectra are generated from the calculated stick spectra by convolving with gaussian function of wavenumber 4 cm-1. nabin kumar raut, hari prasad lamichhane / bibechana 14 (2017) 66-76 : rcost p.75 (online publication: dec., 2016) 4. conclusions by studding ir spectra in gas phase and ccl4 of two different benzoquinones (with and without methoxy side group), we reach to the following conclusions. for the benzoquinones without methoxy side group (benzoquinone, duroquinone, and plastoquinone) two prominent ir bands are observed. the highly intense band is due to asymmetric c=o (c1=o and c4=o) vibration, while weak one is due to asymmetric c=cr (c2=c3 and c5=c6) vibration. but, for the benzoquinones with methoxy side groups (ubiquinone, dimethoxy dimethyl benzoquinone) three prominent ir bands in different (high/intermediate/low) frequency is observed. here, high/intermediate/low frequency bands are due to c1=o/coupled c4=o and c2=c3/ coupled asymmetric c=cr and c4=o vibration. moreover, addition of methyl side groups lowered the band positions carbonyl vibrations in proportion to the number of methyl groups. furthermore, upon solvent phase calculation prominent lowering in the intense carbonyl band is seen. acknowledgement for providing gaussian 03 and computational facilities we want to acknowledge central department of physics. references [1] s. patai, the chemistry of quinonoid compounds, john willey & sons, new york, (1974). 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[9] h. p. lamichhane, calculated vibrational properties of quinones in photosynthetic reaction centers, phd thesis, georgia state university, usa, (2011). bibechana 18 (2) (2021) 95-104 95 surface air temperature trends in kathmandu valley for 2011-2017 a. thapa1, a. silwal1 *, p. sharma1, s. p. gautam2, c. k. nepal1, s. bhattarai1, d. timsina1 1patan multiple campus, tribhuvan university, lalitpur, nepal 2central department of physics, tribhuvan university, kirtipur, nepal email: ashoksilwal0@gmail.com article information: received: june 17, 2020 accepted: may 7, 2021 keywords: air temperature kathmandu dhm climate change precipitation rainfall abstract in this study, we reviewed the maximum and minimum temperature trends of the kathmandu valley over the period of 2011-2017. in addition, the average monthly temperature trends were studied annually for the same period, with the data made available from the department of hydrology and meteorology (dhm) of nepal. the annual temperature trended in the same direction, with winter temperatures being lower and summer temperatures being higher. the annual average minimum and maximum air temperature trends were found to be slightly rising at 0.097˚c/year and 0.04˚c/year, respectively. the mean air temperature in kathmandu valley is increasing at a rate of 0.06 degrees celsius per year, with 2016 being the warmest year and 2012 being the least warm, with annual mean temperatures of 19.82˚c and 19.32˚c, respectively. the temperature difference is much smaller in the summer (less than ~12˚c) than in the winter. doi: https://doi.org/10.3126/bibechana.v18i2.29495 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction climate is a statistical description of surface variables like temperature, humidity, wind, atmospheric pressure over a long period of time [1]. climate change is generally described as a statistically detectable change in climate that lasts for a long time, typically decades or longer [1]. the earth's climate is primarily influenced by latitude, altitude, the tilt of the earth's axis, temperature differences between land and sea, and topography [1]. several lines of scientific evidence indicate that the earth's atmosphere has changed over time, implying that the planet is warming [2]. natural variability, on the other hand, cannot account for the recent observed warming. over the last 200 years, the atmosphere has changed dramatically, and the explanation for this is the industrial revolution, which has resulted in a gradual rise in co2 and other greenhouse gases due to the burning of fossil fuels. this fact is best supported by the intergovernmental panel on climate change (ipcc) report of 2014, where it is mentioned that more than 95% of the scientists were certain that we mailto:ashoksilwal0@gmail.com https://doi.org/10.3126/bibechana.v18i2.29495 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana a. thapa et al. / bibechana 18 (2) (2021) 95-104 96 humans are primarily responsible for the climate change, mainly increasing concentrations of greenhouse gases such as carbon dioxide (co2) [2]. according to the royal society and the us national academy of sciences, the earth’s global average temperature has risen by about 0.8˚c since 1900 [3], which thus motivates us to look for the air temperature trend in these recent years since that rate of increase in temperature has not been evidenced before that in the earth’s history. this transition is challenging for both the developing and developed worlds. because of urbanization, there is less greenery and more impervious surfaces, resulting in changes in land cover, land use, and land surface characteristics, which modify the local climate, moisture exchange, and ecosystem services, favoring heat-trapping and storage [4, 5]. changes in land use and land cover affect air temperature by affecting the sensible and latent heat partitioning of usable resources [6, 7]. understanding the climate change caused by different factors requires a thorough examination of historical climate changes. air temperature is thought to be a significant predictor of climate among these variables. the broad knowledge and information gathered over a long period of time from continuous research and forecasts of climatic phenomena have guided us in understanding current weather conditions and predicting future fluctuations [4, 6]. as a result, climatic change has a major impact on people's lives and the environment [8]. local weather conditions, on the other hand are the most readily accessible data source since they can be aggregated over time to detect potential climate changes at the local scale [9]. research on local climate knowledge has allowed people to detect and respond to the fluctuations in the climate [10]. the air temperature influences nearly every other weather parameter, including dew point temperature, precipitation, humidity, clouds, and air pressure, and is, therefore, a commonly measured variable that directly impacts n weather change [11]. nepal is located between the latitudes of 26°22' and 30°27'n, and the longitudes of 80°04' and 88°12'e. the nation is 885 kilometers long from east to west, with a north-south distance ranging from 130 to 260 kilometers. from the southern plain (terai) to mount everest in the northeast, the altitudinal variation varies between 60 and 8848 meters above mean sea level [12]. altitude, prevailing winds, topography, and seasonal atmospheric circulations are all factors that influence nepal's climate [13]. the present work aims to extend the analysis of kathmandu, nepal's monthly average air temperature from 2011 to 2017. this research will provide crucial information on the climatic variations in nepal over the last seven years. we conclude that the findings of this study will serve as a baseline for predicting long-term climate trends by analyzing data at the local scale. as shown by the recurring scientific and political discourse on these issues, scientists from all over the world show a high degree of uncertainty when analyzing and cross-referencing past and future records associated with climate change. this emphasizes the importance of accurate data, accurate research, and better science in order to improve our understanding of climate change based on local scale parameters [14]. climate change analysis and forecasts in nepal are still based on a literature review and some scattered data. there is still no strategy in place to collect long-term, highquality data that can be used to make accurate analyses and forecasts. a lot of research has been done in nepal over the last few years as well. shrestha et al. (1999) [15] studied the temperature trends of nepal for the 18 years period (1977-1994) and found that the annual maximum temperature was increasing at the rate of 0.06˚c /year. they further added that a significant increase in warming trends in the higher altitude regions of the middle mountain and the high himalaya than in the terai and siwalik regions was observed [15]. later on, in 2008 you et al. [16] investigated changes of eastern and central tibetan plateau for the period of 19612005 and found that both minimum and maximum temperature showed a warming trend, while the a. thapa et al. / bibechana 18 (2) (2021) 95-104 97 diurnal temperature range (dtr) was found to be decreasing for the studied period [16]. marahatta et al., (2009) [17] also analyzed the temperature trends all over nepal based on data from 1976 – 2005 and found that the maximum temperature was found to be increasing at a greater rate (0.05˚c/year) than the minimum temperature (0.03˚c/year). in 2015, dhm of nepal (www.dhm.gov.np/) [13] conducted a study based on the trend analysis of air temperature and precipitation for the period of 1971-2012 and hence identified an increasing trend on both minimum and maximum temperature in almost all the seasons. the average trend of mean annual minimum and maximum temperature over nepal was only 0.01˚c/year and 0.04˚c/year, respectively. another noteworthy finding of this report was that the mean annual temperature trend was found lower in the high altitude region while higher in the low altitude terai and siwalik range. at the same time, the reverse trend pattern was observed for mean annual maximum temperature with higher in high altitude region and lower in low altitude terai. +++++++++ in particular, this study for air temperature trend during seven years period (2011-2017) has benefited from several early research work by dhm (2017) [18], shrestha et al. (2010, 2016) [19, 20], hazo et al. (2020) [21]. such type of research works promotes future researches to be done on climatic variability based on different climatic parameters in account to local communities. the paper is organized as follows. first, in section ii we discuss few related works that are performed on various years regarding air temperature and climate change. in section iii, the methodology and device used in this work are best described with the necessary explanation. based on this methodology, various graphs are produced in section iv along with statistical analysis. these graphs help to get a better understanding of air temperature trends for seven consecutive years. section v concludes the work and gives a future perspective. 2. methodology kathmandu valley is situated in the middle part of nepal. it lies between the latitude of 27˚ 32’ 13” and 27˚ 49’ 10” north and longitude of 85˚ 11’ 31” and 85˚ 31’ 38” east with the mean elevation of about 1300 meters (4265 feet) above sea level [17]. the east-west and north-south axis of this valley are about 30-20 km, respectively [22]. for this study, we have taken the data of the tribhuvan international airport (tia) station located in the kathmandu valley, where various sensors are attached to detect various climatic parameters. air temperature and relative humidity sensors are used to determine the temperature and relative humidity. it was a digital sensor in which the temperature ranges from -40 to 124.2˚c with ±0.1˚c at 6 to 40˚c and incorporates a resolution of 0.01˚c typical [23]. a data logger is connected to the sensor to capture real time automatically. the analog signals from these sensors are converted to a digitally readable format by the microcontroller. [23]. fig. 1: location map of kathmandu valley. a. thapa et al. / bibechana 18 (2) (2021) 95-104 98 data for the respective stations were collected and published by the dhm of nepal. the collected data were based on a day-wise maximum and minimum air temperature for each year. the mean monthly maximum and minimum temperature are calculated for 12 months of every year from 2011 to 2017, and the necessary analysis and interpretation of the data for the related study was done by using pandas and matplotlib data visualization of python. 3. result and discussion based on the methodology discussed in the previous section, the monthly variation of an average minimum and maximum air temperature of kathmandu valley for 7 consecutive years i.e., from 2011 to 2017 is depicted in fig. 2. a. thapa et al. / bibechana 18 (2) (2021) 95-104 99 fig. 2: monthly variation of average minimum and maximum temperature during 2011-2017. fig. 3: monthly variation of mean air temperature during 2011-2017. 4. discussion the comparative study shows that january and december, which falls on the winter season, is found to be the coldest month of the year with an average temperature of ~ 10˚c 11˚c while june, july, and august (summer season) are found to be the warmest month of the year with an average temperature of ~ 24˚c 25˚c. this is due to the fact that the winter season has the shortest day lengths while the summer season has the longest day lengths. the longer that a day lasts, the earth will get more time to absorb energy from the sun. thus, longer days result in warmer days and shorter days in cooler days. another noteworthy finding of this study is the average air temperature trend in the coldest and hottest month. the average temperature during the coldest month rises to 2015 and then it falls back again whereas this trend is significantly different in the hottest month. the average temperature during the warmest month for each year is fluctuating as shown in fig 3. the reason behind the fluctuation in average air temperature is the gradual increase in minimum temperature (0.097˚c/year) than the maximum temperature (0.06˚c/year) as it slowly surpasses the maximum air temperature while taking the average. thapa et al. / bibechana 18 (2) (2021) 95-104 100 the reason behind the fluctuation in average air temperature is the gradual increase in minimum temperature (0.097˚c/year) than the maximum temperature (0.06˚c/year) as it slowly surpasses the maximum air temperature while taking the average. (a) (b) fig. 3: average air temperature trend during (a) the coldest month and (b) the hottest month during 2011-2017. fig. 4: average air temperature trend during (a) the coldest month and (b) the hottest month during 2011-2017. the air temperature usually rises and drops faster just after the sunrise and just before the sunset. but, again, the air temperature takes around 8 hours to rise from the lowest to the highest point, whereas it takes more than ~15 hours to fall from the highest to the lowest. it relies on the fact that the earth's surface absorbs the light easily and converts it into heat energy, but the heat, once generated, is not easily escaped from the atmosphere because the atmosphere acts as a blanket and blocks the outgoing radiation [23]. surface solar radiation is a factor that drives the diurnal cycle of surface air temperatures. this is due to the fact that clouds significantly modulate solar radiation. as a result, clouds have the greatest impact on the maximum temperature (tmax) and diurnal temperature range (dtr) [24]. in addition, the atmospheric water vapor has a smaller effect on dtr and it also increases both tmax and minimum temperature (tmin) because its greenhouse warming effect has little diurnal variation. wind speed and the direct evaporative cooling of precipitation seem to have small effects on dtr [24]. wind speed, relative humidity, rainfall, solar radiation, and other factors can all contribute to temperature fluctuations. the annual average minimum and maximum temperature, along with the mean annual temperature, are listed in table 1. the data is then analyzed, and the results are processed to obtain figures 4, 5, and 6. table 1: descriptive statistics of the air temperature trends rate for seven years. figs. 4 and 5 show the annual average minimum temperature and annual average maximum temperature with their corresponding linear fit. what we observed is that the dependency of average minimum air temperature on subsequent years was significant (high r2 of 0.756). on the other hand, it became insignificant for the case of year average min. temperature [˚c] average max. temperature [˚c] mean temperature [˚c] 2011 12.61 26.11 19.36 2012 12.40 26.25 19.32 2013 12.97 26.40 19.69 2014 13.04 25.92 19.48 2015 13.05 26.10 19.58 2016 13.35 26.29 19.82 2017 13.19 26.16 19.68 thapa et al. / bibechana 18 (2) (2021) 95-104 101 average maximum air temperature (very low r2 of 0.001). also, fig. 6 shows the annual mean air temperature with its linear fit. comprising all the data, i.e., for the entire period of 2011 2017, the correlations were higher (r2 of 0.601). the slopes of the trend lines for average minimum air temperature were found to be much higher than those for average maximum air temperature. fig. 4: best fit line for average minimum temperature trend for the period 2011-2017. fig. 5: best fit line for average maximum temperature trend for the period 2011-2017 fig. 6: annual mean air temperature trends of the kathmandu valley during 2011-2017. thapa et al. / bibechana 18 (2) (2021) 95-104 102 regarding the air temperature, annual average minimum, maximum by mean air temperature shows increasing trends based on the data of the year 2011-2017. the annual average minimum and maximum air temperature trends were found to be increasing significantly at the rate of 0.097˚c/year and 0.04˚c/year respectively, while the mean annual maximum temperature was found to be increasing with the rate of 0.06˚c/year. the anthropogenic activities, local and regional climate have triggered to increase in the air temperature in the kathmandu valley of nepal. the majority of the agricultural land of kathmandu valley has been turned to an impervious surface layer, drastically altering the valley's landscape [25]. the climatic and weather conditions of the kathmandu valley have changed dramatically over the last few decades as a result of rapid urbanization [26,27]. prior to the early detection of the greenhouse effect, comprehensive and timely studies of the effects of urbanization on long-term temperature trends are also needed. 5. conclusion the present study was keenly focused on analysis of recent air temperature trends in the kathmandu valley, the capital city of nepal. although, the main focus of the study is to estimate the recent temperature trends on the annual minimum and maximum air temperature, the monthly average variation of air temperature for 2011-2017 was also analyzed with the necessary explanation. the monthly variation pattern of air temperature every year demonstrates that they have the highest value in summer while (june, july, and august) and lowest in winter (january and december). the year 2016 was found to be the warmest year among all the other years with an annual mean temperature of 19.82˚c and 2012 with the least warm with an annual mean temperature of 19.32˚c. although the average monthly air temperature shows a similar pattern, the average temperature during the coldest and hottest month of every year shows a slightly different pattern. we witnessed a steep increase in the minimum temperature trends (0.097˚c/year), and a slight increase in maximum temperature trends (0.04˚c /year), and it affects the average air temperatures of every month and season. the annual mean temperature of kathmandu valley was found to be increasing at the rate of 0.06˚c /year. for the studied period, it has been witnessed that the average temperature during the coldest month varies from 10.09 ˚c 12.27 ˚c, while 24.76 ˚c 25.68 ˚c during the hottest months, which suggests a relative change in the frequency of warmer days or cold nights. without this sort of environmental information coming from research work, plans for dealing with climate change would be scientifically baseless. we believe that the study of such climatic variables helps to understand, analyze and predict the impact of climate change, and contributes to a more precise estimation of global climate change required by policymakers to formulate effective strategies along the lines of mitigation and adaptation of the climate change. to our understanding, the influence of urban warming has only been researched superficially, but we agree that a rigorous investigation of this issue should be prioritized to raise awareness of the negative effects of climate change. due to rapid urbanization, fluctuations or changes in climatic parameters are a recurring phenomenon in the kathmandu valley. as a result, the concerned organization should concentrate on developing a climate change adaptation plan to deal with potential climate variability extremes, which could reduce the magnitude of economic, social, and human losses. acknowledgment the dhm of nepal is highly acknowledged for providing data of air temperature. we are also thankful to dr. indra bahadur karki for rendering valuable comments for improving this paper. author contributions this work is conducted with group efforts of all the 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on some curvature tensors in n(k)-contact metric manifolds riddhi jung shah department of mathematics, janata campus, nepal sanskrit university, dang, nepal email: shahrjgeo@gmail.com article history: received 25 april, 2018; accepted 14 september, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.19674 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the purpose of this paper is to study 7w and 9w -curvature tensors on )(kn -contact metric manifolds. we prove that a )(kn -contact metric manifold satisfying the condition 0).,( 97 =wxw ξis η -einstein manifold. we also obtain the ricci tensor s of type (0, 2) for 9w−ϕ flat and 09 =divw conditions on )(kn -contact metric manifolds. finally, we give an example of 3-dimensional )(kn -contact metric manifold. keywords: contact manifold; )(kn -contact metric manifold; η -einstein manifold. 1. introduction in 1988, tanno [1] introduced the notion of k -nullity distribution of a contact metric manifold as a distribution such that the characteristic vector field or reeb vector field (reeb 1952) [2] ξ of the contact metric manifold belongs to the distribution. a contact metric manifold with ξ belonging to the k -nullity distribution is called )(kn -contact metric manifold. generalizing this notion blair, koufogiorgos and popantoniou [3] introduced the notion of a contact metric manifold with ξ belonging to the ),( µk -nullity distribution, where k and µ are real constants. in particular, if ,0=µ then the notion of ),( µk -nullity distribution reduces to the notion of k -nullity distribution. on the other hand, in 1982, pokhariyal [4] defined ,7w 8w and 9w -curvature tensors with the help of the weyl's projective curvature tensor defined by eisenhart [5]. in [4] it is studied that distribution of vector field over the metric potentials and matter tensors plays an important role in shaping the various physical and geometrical properties of a tensor. in the same paper it is proved that 9w -curvature tensor satisfies the cyclic property. in this paper, we study some curvature conditions of 7w and 9w -curvature tensors in )(kn -contact metric manifolds and obtain some results. riddhi jung shah./ bibechana 16 (2019) 55-63: rcost p.56 (online publication: dec., 2018) 2. preliminaries a )12( +n -dimensional smooth manifold m is said to be a contact manifold, if it carries a global 1-form η such that 0)( ≠∧ ndηη everywhere. given a contact form η , it is well known that there exists a unique vector field ξ , called the characteristic vector field or reeb vector field (reeb 1952) [2] of η , satisfying ,1)( =ξη 0),( =xd ξη (2.1) for all vector fields .x a riemannian metric g is said to be an associated metric if there exists a tensor field ϕ of type (1, 1) such that ),,(),( yxgyxd ϕη = ),,()( ξη xgx = ξηϕ )()(2 xxx +−= (2.2) for all vector fields yx , on .12 +nm from above conditions one can easily obtain ,0=ϕξ ,0=ϕη o ).()(),(),( yxyxgyxg ηηϕϕ −= (2.3) the structure ),,,( gηξϕ is called a contact metric structure and a manifold 12 +nm with a contact metric structure ),,,( gηξϕ is said to be a contact metric manifold [6]. now, we define the operators l and h by ,),( ξξxrlx = h = 21 ëξ ϕ (2.4) where r and ë denote the curvature tensor and lie differentiation respectively. the (1, 1)-type tensors h and l are symmetric and satisfy ,0=ξh ,0=ξl ,0. =htr 0. =ϕhtr and .hh ϕϕ −= (2.5) we also have the following relations for a contact metric manifold: hxxx ϕϕξ −−=∇ (2.6) 0=∇ ϕ ξ (2.7) 2.2),(. htrnqgltr −== ξξ (2.8) )(2 22 hll +=− ϕϕϕ (2.9) 2hlh ϕϕϕ ξ −−=∇ (2.10) where q is the ricci operator defined by ),,(),( yxsyqxg = ∇ is the levi-civita connection of the riemannian metric g and s the ricci tensor [6,7]. an almost contact metric manifold is an odd dimensional smooth manifold 12 +nm equipped with an almost contact metric structure ),,,( gηξϕ satisfying the conditions (2.1) (2.3) except the condition ),(),( yxgyxd ϕη = or .0),( =xd ξη sasaki and hatakeyama [8] defined an almost complex structure j on rm n ×+12 by       −=      dtdxfxdtdfxj )(,, ηξϕ (2.11) where f is a smooth real valued function on .12 rm n ×+ an almost contact metric structure is said to be normal if j is integrable. an almost contact metric manifold is sasakian if and only if ( ) .)(),()( xyyxgyx ηξϕ −=∇ (2.12) a contact metric manifold is sasakian if and only if yxxyyxr )()(),( ηηξ −= (2.13) for all vector fields x and y [6]. riddhi jung shah./ bibechana 16 (2019) 55-63: rcost p.57 (online publication: dec., 2018) a contact metric manifold for which ξ is a killing vector is called a k -contact manifold. it is well known that a contact manifold is k -contact if and only if .0=h we note that a sasakian manifold is k -contact, but the converse holds only if dim .3=m the k -nullity distribution [1] of a riemannian manifold ),( gm for a real number k is a distribution ]}),(),([),(:)({)(:)( yzxgxzygkzyxrmtzknpkn pp −=∈=→ (2.14) for any ).(, mtyx p∈ if the characteristic vector field ),(kn∈ξ then the relation ])()([),( yxxykyxr ηηξ −= (2.15) hods. a contact metric manifold satisfying the relation (2.15) is called a )(kn -contact metric manifold. from (2.13) and (2.15) it follows that a )(kn -contact metric manifold is a sasakian manifold if and only if .1=k if 0=k i.e., ,0),( =ξyxr then )(kn -contact metric manifold is locally isometric to the riemannian product )4()0(1 nn se ×+ for 1>n and flat for .1=n if ,1<k the scalar curvature is }.)1(2{2 knnr +−= in a )12( +n -dimensional )(kn -contact metric manifold ,m the following relations hold: ,)1( 22 ϕ−= kh 1≤k (2.16) )(2),(,2 xnkxsnkq ηξξξ == (2.17) ])(),([),( xyyxgkyxr ηξξ −= (2.18) ( ) ))((),()( hxxyyhxxgyx +−+=∇ ηξϕ (2.19) )1(2. 2 knhtr −= (2.20) ϕϕϕ hnqq )1(4 −=− (2.21) ),()1(4)()(2),(),( yhxgnyxnkyxsyxs −−−= ηηϕϕ (2.22) ),()1(4),(),( hyxgnyxsyxs ϕϕϕ −=+ (2.23) )](),()(),([)),(( yzxgxzygkzyxr ηηη −= (2.24) ( ) ),()( yhxxgyx ϕη +=∇ (2.25) for any vector fields yx , on 12 +nm [1, 3]. in n -dimensional space nv pokhariyal [4] defined the 7w and 9w curvature tensors as follows )],(),(),(),([11),,,(),,,(7 zyrictxgtxriczygntzyxrtzyxw − − += and )],(),(),(),([11),,,(),,,(9 txriczygyxrictzgntzyxrtzyxw − − += respectively. in )12( +n -dimensional )(kn -contact metric manifold above two tensors can be written as ]),(),([21),(),(7 xzysqxzygnzyxrzyxw −+= (2.26) and ]),(),([21),(),(9 qxzygzyxsnzyxrzyxw −+= (2.27) respectively, where ),,,(),),(( tzyxrtzyxrg = for any vector fields tzyx ,,, on .12 +nm now, using (2.17) and (2.18) in (2.26) and (2.27) we obtain ξηξξ ),(21])(),(2[),(7 yxsnxyyxgkyxw −−= (2.28) riddhi jung shah./ bibechana 16 (2019) 55-63: rcost p.58 (online publication: dec., 2018) and ])()([),(9 xyyxkyxw ηηξ −= (2.29) respectively. from (2.27) we also have )(),()(),(21)),(( 9 yzxkgzyxsnzyxw ηηη −= (2.30) ( ) 0),(9 =yxw ξη (2.31) ( ) )],()()([),(9 yxgyxkyxw −= ηηξη (2.32) ( ) ).()(),(21),(9 yxkyxsnyxw ηηξη −= (2.33) definition 2.1. a )(kn -contact metric manifold is said to be η -einstein if its ricci tensor s of type (0, 2) is of the form )()(),(),( 21 yxyxgyxs ηηµµ += (2.34) where 21 ,µµ are smooth functions on the manifold. definition 2.2. a )(kn -contact metric manifold is said to be ϕ 9w flat if the condition ( ) 0,),(9 =wzyxwg ϕϕϕϕ holds for any vector fields ).(,,, mtwzyx p∈ 3. results and discussion in this section we obtain some results on 7w and 9w curvature tensors in )(kn -contact metric manifolds. theorem 3.1. let m be a )12( +n -dimensional )(kn -contact metric manifold satisfying the curvature condition ,0).,( 97 =wxw ξ then either m is locally isometric to the riemannian product )4()0(1 nn se ×+ for 1>n or m is η -einstein manifold. proof. let us consider a )12( +n -dimensional )(kn -contact metric manifold m which satisfies the curvature condition ( ) 0),().,( 97 =zvuwxw ξ for any vector fields zvux ,,, on .12 +nm by definition we have ( ) ( ) ( ) zxwvuwzvxwuw zvuxwwzvuwxwzvuwxw ),(),(),(, ,),(),(),(),().,( 7979 799797 ξξ ξξξ −− −= ( ) ( ) .),(),(),(, ,),(),(),(0 or, 7979 7997 zxwvuwzvxwuw zvuxwwzvuwxw ξξ ξξ −− −= (3.1) in view of (2.28) and (3.1) we get ( ) ( ) ( ) .),(),(21),()(),(),(2 ),(),(21),()(),(),(2 ),(),(21),()(),(),(2 ),(,21),(),(,20 999 999 999 999 ξηξ ξηξ ξηξ ξηξ vuwzxsnxvuwzkvuwzxkg zuwvxsnzxuwvkzuwvxkg zvwuxsnzvxwukzvwuxkg zvuwxsnxzvuwkzvuwxkg ++− ++− ++− −−= (3.2) taking inner product on both sides of (3.2) by ξ and using (2.1) and (2.2) we obtain riddhi jung shah./ bibechana 16 (2019) 55-63: rcost p.59 (online publication: dec., 2018) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ).),(),(21),()(),(),(2 ),(),(21),()(),(),(2 ),(),(21),()(),(),(2 ),(,21)(),(),(,20 999 999 999 999 ξηηηξη ξηηηξη ξηηηξη ηη vuwzxsnxvuwzkvuwzxkg zuwvxsnzxuwvkzuwvxkg zvwuxsnzvxwukzvwuxkg zvuwxsnxzvuwkzvuwxkg ++− ++− ++− −−= (3.3) by the use of (2.30) (2.33), (3.3) reduces to ).()(),(2),(),(41)()()},( ),({)}()(),(){,(2 )},(1 )()(){,()},(21)()(){,( )),(,(21)),(,(20 22 99 vuzxsnkvuszxsnzvuxkg uxskzuzugvxgkvusn vukzxkgzugzuvxsnk zvuwxsnzvuwxkg ηηηη ηη ηηηη −+− +−+− +−+ −= (3.4) putting ξ=u in (3.4) and using (2.1), (2.2), (2.17) and (2.29) we get )].()()()12()(),(1 )(),(21)(),(2)(),([0 zxvknzvxsn vzxsnzvxkgvzxkgk ηηηη ηηη −++ −−= (3.5) from (3.5) it follows that either 0=k or .0)]()()()12()(),(1 )(),(21)(),(2)(),([ =−++ −− zxvknzvxsn vzxsnzvxkgvzxkg ηηηη ηηη if ,0=k then we know that )(kn -contact metric manifold is locally isometric to the riemannian product )4()0(1 nn se ×+ for 1>n [9]. if ,0)]()()()12()(),(1 )(),(21)(),(2)(),([ =−++ −− zxvknzvxsn vzxsnzvxkgvzxkg ηηηη ηηη then replacing z by ξ we get ).()()12(),(2),( vxknnvxnkgvxs ηη−−= (3.6) from (3.6) we obtain ).()(),(),( 21 vxvxgvxs ηηλλ += (3.7) where nk21 =λ and .)12(2 knn −−=λ in view of (2.34) and (3.7) we conclude that )(kn -contact metric manifold 12 +nm is η -einstein manifold. this completes the proof of the theorem. theorem 3.2. in a ϕ 9w flat )(kn -contact metric manifold 12 +nm the ricci tensor s and the scalar curvature r are given by ),()1(4)()(})12(2{),()4(),( 2 zhygnzyrknnzygknrzys −+−++−= ηη riddhi jung shah./ bibechana 16 (2019) 55-63: rcost p.60 (online publication: dec., 2018) and knnr )12(2 += respectively. proof. let us consider a )12( +n -dimensional )(kn -contact metric manifold m which is ϕ 9wflat. then we have ( ) 0,),(9 =wzyxwg ϕϕϕϕ (3.8) for any vector fields ).(,,, mtwzyx p∈ in view of (2.27) we have ( ) ( ) )].,(),( ),(),([21,),(,),(9 zygwxs wzgyxsnwzyxrgwzyxwg ϕϕϕϕ ϕϕϕϕϕϕϕϕϕϕϕϕ − += (3.9) using (2.3), (2.14), (2.22) and (3.8) in (3.9) we obtain )}]()(),()}{,()1(4)()(2),({ )}()(),()}{,()1(4)()(2),([{21 ),(),(),(),(0 zyzygwhxgnwxnkwxs zwzwgyhxgnyxnkyxsn wygzxkgwxgzykg ηηηη ηηηη ϕϕϕϕϕϕϕϕ −−−−− −−−−+ −= ),(),()1(2),(),(21 )()(),()1(2)()(),(21 ),(),()1(2)()(),( ),(),(21)()(),()()(),( ),(),()()(),(),(),(0 or, whxgzygnnzygwxsn zwyhxgnnzwyxsn yhxgzwgnnyxzwkg zwgyxsnwyzxkgzxwykg wygzxkgzywxkgwxgzykg − +− − +− − −− +++ −−= ηηηη ηη ηηηη ηη (3.10) ).()(),()1(2)()(),(21 zywhxgnnzywxsn ηηηη − −+ let 12,...,2,1},{ += niei be an orthonormal basis of the tangent space at any point of the manifold. putting iewx == in (3.10) and taking summation over ,121 , +≤≤ nii we get ),()1(4)()(})12(2{),()4(),( 2 zhygnzyrknnzygknrzys −+−++−= ηη (3.11) by the use of (2.5) and symmetry property of .h again, taking an orthonormal frame field at any point of the manifold and contracting over y and z in (3.11) we obtain .)12(2 knnr += (3.12) in view of (3.11) and (3.12), the theorem is proved. theorem 3.3. if a )12( +n -dimensional )(kn -contact metric manifold m satisfies the condition ,09 =divw then the ricci tensor s is of the form ).,(),(12 )12(2),(2),( yhzshzygn knnzynkgzys + + − += proof. let us consider a )12( +n -dimensional )(kn -contact metric manifold m which satisfies the condition 0),)(( 9 =zyxdivw (3.13) where 'div' denotes the divergence. taking inner product on both sides of (2.27) with v we get riddhi jung shah./ bibechana 16 (2019) 55-63: rcost p.61 (online publication: dec., 2018) ( ) ( ) )].,(),(),(),([21,),(,),(9 zygvxsvzgyxsnvzyxrgvzyxwg −+= (3.14) differentiating (3.14) covariantly along u we have )],(),)((),(),)([(21),,,)(~( ),,,)(~( 9 zygvxsvzgyxsnvzyxr vzyxw uuuu ∇−∇+∇= ∇ (3.15) where ),,,(~),),(( vzyxrvzyxrg = for all .,,, vzyx let 12,...,2,1},{ += niei be an orthonormal basis of the tangent space at any point of the manifold. putting ievu == in (3.15) and taking summation over ,121 , +≤≤ nii we get )].,(2 )(),)([(21),)((),)(( 9 zygxdryxsnzyxdivrzyxdivw z −∇+= (3.16) from bianchi second identity we also know that ).,)((),)((),)(( zxszyszyxdivr yx ∇−∇= (3.17) in view of (3.13), (3.16) and (3.17) we have ).(),(41),)((21),)((),)((0 xdrzygnyxsnzxszys zyx −∇+∇−∇= (3.18) replacing x by ξ in (3.18) we obtain 0),)((21),)((),)(( =∇+∇−∇ ysnzszys zy ξξξ (3.19) since .0)( =ξdr from ëξ 0=s we get ),(),(),()1(4 ),(),(),)(( yhzszhyshzygn yszszys zy ϕϕϕ ξξ ξ ++−= ∇−∇−=∇ by the use of (2.6) and (2.23). again, ( ) ).,(),(),(2),(2 ),(),()(2 ),(),(),(),)(( zhyszyszhynkgzynkg zhyszysznk zszszszs y yyyy ϕϕϕϕ ϕϕη ξξξξ +++= ++∇= ∇−∇−∇=∇ by the use of (2.6), (2.17) and (2.25). similarly, ).,(),(),(2),(2),)(( yhzsyzsyhznkgyznkgysz ϕϕϕϕξ +++=∇ using above relations in (3.19) we get ).,(21),(),(),(2 ),(2),(2 )12(),(})1(4{0 yzsnyzkgzyszhynkg zynkgyhzsnnhzygkn ϕϕϕϕ ϕϕϕ ++−− − + ++−= (3.20) replacing z by zϕ in (3.20) and using (2.2), (2.3), (2.5), (2.17), (2.22) and symmetry property of h we obtain ),(21),(),(),(2 ),(2),(2 )12(),(})1(4{0 22 2yzsnzykgzyszhynkg zynkgyzhsnnzhygkn ϕϕϕϕϕϕ ϕϕϕϕϕ ++−− − + ++−= or, ).,(),(12 )12(2),(2),( yhzshzygn knnzynkgzys + + − += (3.21) riddhi jung shah./ bibechana 16 (2019) 55-63: rcost p.62 (online publication: dec., 2018) this completes the proof of the theorem. 4. example of 3-dimensional )(kn -contact metric manifold consider a 3-dimensional manifold }0:),,{( 3 ≠∈= xrzyxm where ),,( zyx are the standard coordinates in .3r let },,{ 321 eee be linearly independent global frame on m defined by zxyyxzxeyxe ∂ ∂ + ∂ ∂ − ∂ ∂ = ∂ ∂ = 42 ,2 21 and .3 ze ∂ ∂ = let g be the riemannian metric defined by ,0),(),(),( 213231 === eegeegeeg .1),(),(),( 332211 === eegeegeeg let η be the 1-form defined by ),()( 3evgv =η for any ),(mv χ∈ the set of vector fields. let ϕ be the (1, 1) tensor field defined by .0,, 31221 =−== eeeee ϕϕϕ then using the linearity of ϕ and g we have 323 )( ,1)( evvve ηϕη +−== and )()(),(),( vuvugvug ηηϕϕ −= for any ).(, mvu χ∈ moreover, .0 , , 32211 ==−= heeheehe thus for ,3 ξ=e the structure ),,,( gηξϕ defines a contact metric structure on .m now, from definition of lie bracket we have .22 24 242422],[ 31221 eex zyx yxzxyyxzxzxyyxzxyxee += ∂ ∂ + ∂ ∂ =       ∂ ∂       ∂ ∂ + ∂ ∂ − ∂ ∂ −      ∂ ∂ + ∂ ∂ − ∂ ∂ ∂ ∂ = similarly, we obtain 0],[ 31 =ee and .2],[ 132 eee = now, we have koszul's formula ( ) ( ) ( ) ( ).],[,],[, ],[,),(),(),(,2 yxzgzxyg zyxgyxzgxzygzyxgzyg x +− −−+=∇ taking ξ=3e and using koszul formula we obtain ( ) ),,(4,2 11121 eegxeeg e =∇ ( ) ),(40,2 21221 eegxeeg e ==∇ and ( ) ).,(40,2 31321 eegxeeg e ==∇ from above it follows that ( ) ).,(2, 121 xegxxeg e =∇ hence .2 121 exee =∇ similarly we obtain other results and finally we have ,2 211 exee −=∇ ,2 121 exee =∇ ,2 312 eee −=∇ ,2 132 eee =∇ .03323132231 =∇=∇=∇=∇=∇ eeeee eeeee from above one can easily seen that the conditions for )(kn -contact metric manifold are satisfied for ξ=3e and .0,4 ≠−= xxk riddhi jung shah./ bibechana 16 (2019) 55-63: rcost p.63 (online publication: dec., 2018) 5. conclusion in this paper we have studied 7w and 9w curvature tensors on )(kn -contact metric manifolds. it is proved that a )12( +n -dimensional )(kn -contact metric manifold satisfying the condition 0).,( 97 =wxw ξ is either locally isometric to the riemannian product )4()0(1 nn se ×+ or is η -einstein. it is also investigated that a )(kn -contact metric manifold satisfying the conditions 9w−ϕ flat and 09 =divw has the ricci tensor s of different forms. 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[2] g. reeb, sur certaines proprietes topologiques des trajectoires des systemes dynamiques, memoires de 1acad. roy. de beligique, sci. ser. 2 (1952) 1-62. [3] d. e. blair, t. koufogiorgos, b. j. papantoniou, contact metric manifolds satisfying a nullity condition, israel j. of math. 19 (1995) 189-214. [4] g. p. pokhariyal, relativistic significance of curvature tensors, internat. j. math. and math. sci. 5(1) (1982) 133-139. [5] l. p. eisenhart, riemannian geometry, princeton university press, 1950. [6] d. e. blair, contact manifolds in riemannian geometry, lecture notes in mathematics, 509, springer-verlag, berlin, 1976. [7] d. e. blair, j. n. patnaik, contact manifolds with characteristic vector field annihilated by the curvature, bull. inst. math. acad. sinica 9 (1981) 533-545. [8] s. sasaki, y. hatakeyama, on differentiable manifolds with certain structures which are closely related to almost contact structure ii, tohoku math. j. 13 (1961) 281-294. [9] c. baikoussis, t. koufogiorgos, on a type of contact manifolds, j. of geometry 46 (1993) 1-9. devendra sir cover page copy.jpg bibechana 17 (2020) 13-19 13 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal bio-synthesis of copper nanoparticles (cunps) using garlic extract to investigate antibacterial activity sharmila pradhan amatya1*, leela pradhan joshi2 1chemistry department, amrit campus, tribhuvan university, kathmandu, nepal 2 physics department, amrit campus, tribhuvan university, kathmandu, nepal * email: amatyasharmila@yahoo.com article information received: april 5, 2019 accepted: september 7, 2019 keywords: allium sativum copper nanoparticles edx ftir abstract bio-synthesis of metal nanoparticles is regarded as one of the recently developed environmentally benign method. in the present investigation, copper nanoparticles were synthesized reacting garlic (allium sativum) extract with copper sulphate (cuso4∙5h2o) solution over magnetic stirrer at 80 °c for 1 hour. so-prepared cunps were studied by observing the color change at various time intervals. further, the nanoparticles were characterized using uv-visible spectroscopy, energy dispersive x-ray spectroscopy (edx) and fourier transform infrared spectroscopy (ftir). the results of uv-vis spectroscopy clearly showed presence of absorption peak at 595 nm which confirmed the formation of copper nanoparticles. likewise, the edx spectrum depicts the presence of optical band at 8 ev which is the characteristic peak of copper consisting of 38.747 % by weight and ftir spectra revealed presence of various phytochemicals possessing characteristic functional groups such as carbonyl and phenolic at the surface of cunps. thus, natural products available in the garlic extract help in reduction and stabilization of copper nanoparticles. the antibacterial activity of copper nanoparticles was investigated against gram +ve (staphylococcus aureus) and gram –ve bacteria (escherichia coli) using agarwell diffusion method. the results of antibacterial test showed that cunps were found to be much sensitive towards gram –ve bacteria compared to gram +ve bacteria. 1. introduction in the current era, most of the research activities belong to nanotechnology as it can be applied in innumerous fields such as textile, pharmaceuticals, electronics, food industries, biomedical science, drug and gene delivery, engineering, environmental science, automobiles, mechanics and space industries. nanotechnology is mainly concerned with synthesis of nanoparticles of various sizes, shapes, chemical compositions and controlled disparity and their potential use for human benefits [1-4]. nanomaterials depict the class of materials with at least one of their dimensions in the range of 1-100 nm i.e this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.23485 http://nepjol.info/index.php/bibechana mailto:amatyasharmila@yahoo.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.23485 sharmila pradhan amatya, leela pradhan joshi/ bibechana 17 (2020) 13-19 14 nanoscopic range. these nanomaterials are significant for possessing improved properties different from bulk materials simply by virtue of their small size, larger surface to volume ratio, distribution and morphology. nanomaterials are of varied types such as metallic, insulating, semiconducting, and hybrid type [5-7]. among the various kinds of nanomaterials, bio-synthesized metallic nanoparticles is increasing commercial demand for their unique properties such as physical, catalytic, chemical, electrical, electronic and antibacterial properties. because of these various properties, metallic nanoparticles have been used in many applications such as catalysis, photonics, electronics, medicine, electric and many more [8-10]. copper nanoparticles have been found to be extensively studied by many researchers for their excellent electrical, optical, catalytic, biomedical, antifungal, and antibacterial properties. as a consequence of possessing excellent electrical property, cunps play major role for making future low cost nanodevices [11]. at the same time, inclusion of cunps at different matrixes could be potential materials for synthesizing thin film optical devices. their efficient toxic property is considered to be an effective anti-bactericidal agent. likewise, they have been found employed in drug delivery, textiles, electronics, biosensing, food industry, cosmetics, medical devices, catalytic process, high temperature superconductors and solar cells etc. [9-12]. consequently, cunps act as low cost effective and good alternative material for noble metals such as au, ag, pt, pd [12]. in nanotechnology, various methods are known to prepare nanoparticles with controlled size and shape. these include metal vapor deposition, radiolytic reduction, thermal decomposition, thermal reduction [4, 5], electrochemical reduction [7], mechano-chemical process [8], chemical reduction etc. [710]. chemical reduction method is one of the most convenient methods for the synthesis of metallic nanoparticles as one can simply synthesize shape and size-controlled nanoparticles by this process [12-16]. while talking about synthesis of cunps, the process is quite challenging due to its high tendency for oxidation. it is extremely sensitive to air, and the oxide phases are thermodynamically more stable. the high oxidation state of copper nanoparticle may limit their applications. to avoid oxidation, these methods were usually performed in non-aqueous media, at low precursor concentration, and under an inert atmosphere (argon, nitrogen) [6-9]. the nanoparticles are also found encapsulated using different capping agent to prevent it from oxidation during synthesis. garlic (allium sativum), perennial plant of the family alliaceae, belongs to the order of plant liliales, grown for its flavourful bulbs. the plant is native to central asia and is a classic ingredient in many national cuisines. chiefly, garlic possesses antibacterial, antifungal, antiparasitic, antiviral, antioxidant, anti cancerous and vasodilators characteristics which motivate to carry research over this vegetable. the medicinal values of garlic has been attributed due to presence of many significant phytochemicals such as allicin, allinin, ajoene, diallylsulfide, enzymes, b-vitamins, proteins, minerals, saponins, and flavonoids etc. [17-19 ]. many of the research have been focused on exploring the bactericidal effect of cunps as many of bacteria have been found resistant towards popular antibiotics. hence, aim of the current investigation is to synthesize copper nanoparticles using easily available garlic extract and its characterization. in addition to this, it will also explore the antibacterial property of synthesized nanoparticles. 2. experimental chemicals analytical grade copper (ii) sulphate pentahydrate (cuso4∙5h2o), hydrazine hydrate, nutrient agar media, dimethyl sulphoxide (dmso) were used. bulbs of garlic were purchased from local market. sharmila pradhan amatya, leela pradhan joshi/ bibechana 17 (2020) 13-19 15 test organisms antibacterial activity of the as-synthesized copper nanoparticles was investigated against gram +ve bacteria (staphylococcus aureus), and gram –ve bacteria (escherichia coli). biosynthesis of copper nanoparticles 10 ml of freshly prepared garlic extract was treated with 80 ml of 0.01m copper sulphate solution and 10ml of hydrazine hydrate [2]. then after, the resulting solution was incubated for 24 hours at room temperature and centrifuged for 20 minutes at 3000 rpm. centrifugationdecantation-washing processes were repeatedly done three times to remove impurities. the obtained precipitate was dried in an oven at 50 °c for 5 hours. so prepared, cunps were subjected to various characterizations techniques. characterization techniques visual observation bio-reduction of the copper sulphate using aqueous garlic extract was monitored by observing the gradual color change at different time intervals. uv-visible spectroscopic studies uv-visible spectrum of the solution containing cunps was carried by using double beam uvvisible spectrophotometer (labrotonic, model lt-2802) in wavelength range of 300-700 nm, at resolution of 1 nm. the measurements were recorded at every 15 minutes of time interval. energy dispersive x-ray (edx) spectroscopic studies energy dispersive x-ray (edx) spectroscopy (edx) is used for quantitative elemental analysis which was carried out by using edx-8000 instrument. for edx analysis, about 3 ml of the solution containing cunps was used to observe the energy absorption pattern of different elements. fourier transforms infrared (ftir) spectroscopic studies fourier transform infrared (ftir) spectroscopy is well known method for determining different types of bonding associated with characteristic functional groups present in the sample. ftir measurements were done in attenuated total reflectance (atr) mode in the wavenumber range 4000 to 750 cm-1 at the resolution of 8 cm-1. antibacterial activity antibacterial assay was performed by agar well diffusion method using muller hilton agar (mha) in the petri dish [20]. three mha agar plates were loaded with corresponding sterile bacteria, garlic extracts, positive control (ofloxacin 50 µg/ml), and negative control (dmso) at their respective well. it was allowed to diffuse for about 30 minutes at room temperature and incubated for 24 hours. after incubation the clear zone formed around the well were measured. 3. results and discussion visual observation preliminarily, the formation of cunps was studied by visual observation of the reacting solutions at different intervals of time. initially, the color of the precursor solution and garlic extract was dark green (fig. 1a). the color of the reaction solution gradually started to change to light green (fig. 1b), reddish brown (fig. 1c and 1d) with increase in stirring time. finally, the deposition of the shiny reddish-brown precipitate was observed on the inner wall of the vessel after 1 hour stirring indicating the formation of copper nanoparticles. the change in coloration attributed to the bio reduction of cu 2+ ions to nanoparticles (i.e cu 0 , cunps) [5, 10]. hence, visual observation provides the preliminary information for the formation of nanoparticles. variations of color observed at different time intervals are shown in fig. 1. uv-visible absorption spectroscopic studies uv-visible absorption spectroscopy is important tool for characterizing metal nanoparticle as the maximum absorbance corresponds to the particle sharmila pradhan amatya, leela pradhan joshi/ bibechana 17 (2020) 13-19 16 size [17]. the result of uv-visible spectroscopy of the as synthesized nanoparticle is presented in the fig. 2. it shows a broad absorption peak of at around 595 nm which is due to the surface plasmon resonance (spr) of electrons present at the surface of metal nanoparticles. hence, this result signifies the formation of cunps which is supported by the result presented by eman et al and suresh et al. [20, 21]. similarly, the wavelength of maximum absorption peaks of samples recorded at every 15 minutes of time intervals are presented in the table 1. it depicts that the wavelength of maximum absorbance (λmax) of reacting solutions shift towards higher wavelength with increase of time. the absorption peaks of the reacting solutions at 30, 45 and 60 minutes were observed at 495 nm, 545 nm and 595 nm, respectively. the maximum absorption peak of copper nanoparticles appeared at 595 nm (fig. 2) after 60 minutes indicates the formation of separated copper nanoparticles which is quite similar to the maximum absorption peak at 560-570 nm as reported by suresh et al. and suramwar et al. [21, 22]. it clearly revealed that formation of nanoparticles take place after stirring the solution for 60 minutes while the absorption peaks at 495 and 545 nm attributes for the agglomerated particles. energy dispersive x-ray (edx) spectroscopic study elemental analysis of the sample was determined from edx spectrum which is presented in fig. 3. the edx pattern shows the existence of copper along with some other elements like silicon, sulphur, phosphorous, oxygen etc. as impurities. the edx peak position is consistent with copper hence it confirmed the formation of copper nanoparticles as reported in the literature [7]. further, the edx signal at 8 ev indicates presence of copper of about 24.6% by weight which may be due to presence of other impurities. fourier transform infrared spectroscopic studies the ftir spectrum of biosynthesized cunps is presented in fig. 4. which shows the existence of various biomolecules at around the cunps. broad bands at around 3200-3600 cm-1, 1600-1800 cm-1 and 2400 cm-1 attribute for the presence of (oh) stretching of phenolic group, (>c=o) and (>nh) stretching. hence, ftir spectra of copper nanoparticles confirmed the presence of various biomolecules such as saponins, tannins, flavonoids, alkaloids and polyphenols etc. surrounding copper nanoparticles which are responsible for reduction as well as in the stabilization of nanoparticles [8, 23]. antibacterial activity of copper nanoparticles result of antibacterial test of as synthesized copper nanoparticles against gram negative bacteria (escherichia coli), and gram positive bacteria (staphylococcus aureus) are shown in table 2. the result showed that the bactericidal effect of copper nanoparticles was found to be satisfactory. the zone of inhibition (zoi) for gram negative bacteria was observed to be more than that of gram positive bacteria. the zoi of gram negative bacteria (escherchia coli) and that of gram positive bacteria are found to be 20 mm, and 13 mm, respectively. the difference in activity against these two types of bacteria is attributed to the difference of structure of cell membrane. gram positive bacteria have thicker peptidoglycan cell membranes compared to the gram negative bacteria, hence, it is harder for cunps to penetrate it resulting lower zoi [18]. these recorded (zoi) values of corresponding bacteria seemed to be lower than that of standard antibiotic ofloxacin, (positive control) may be due to weak solution of copper nanoparticle. further, the photographs of antibacterial test are presented in fig. 5. which clearly depict differences in the zone of inhibitions for two different types of bacteria as reported by padil et al. and kartik et al. [24, 25]. figure 5: photographs showing zone of inhibition formed by bio-synthesized copper nanoparticles using garlic extract against: a) gram +ve, bacteria, staphylococus aureus and b) gram –ve, bacteria, escheria coli. sharmila pradhan amatya, leela pradhan joshi/ bibechana 17 (2020) 13-19 17 a b c d fig. 1: variation of colour of the garlic extract and cuso4 solution at different time intervals a) after 15 minutes b) 30 minutes c) 45 minutes and d) 60 minutes table 1: color observed and maximum absorption peak of bio-synthesized cunps at different time intervals. color time λmax(nm) dark green immediately after mixing light green 30 min 495 greenish brown 45 min 545 reddish brown 60 min 595 fig. 2: uv-visible spectrum of bio-synthesized copper nanoparticles using copper sulphate and garlic extract in presence of hydrazine hydrate (hh). fig. 3: energy dispersive x-ray (edx) spectrum of as synthesized cu nps using garlic extract (allium sativum) and copper sulphate solution. fig. 4: fourier transform infrared spectrum of as synthesized cu nps using garlic extract. sharmila pradhan amatya, leela pradhan joshi/ bibechana 17 (2020) 13-19 18 b staphylococc us aureus escheria coli a table 2: measured inhibition zone of bio-synthesized copper nanoparticles using allium sativum and positive control, of loxacin. fig. 5: photographs showing zone of inhibition formed by bio-synthesized copper nanoparticles using garlic extract against: a) gram +ve, bacteria, staphylococus aureus and b) gram –ve, bacteria, escheria coli 4. conclusion bio-synthesis of copper nanoparticles using allium sativum (garlic) extract was successfully carried out at room temperature. during the synthesis, biomolecules present in the garlic extract are mainly responsible for the reduction and stabilization of the nanoparticles. optical properties, compositional analysis and functional group content of as-synthesized copper nanoparticles were studied using uv-vis spectrophotometer, energy dispersive x-ray spectroscopy (edx) and fourier transform infrared spectroscopy (ftir) respectively. the absorption spectrum of cunps prepared with 15 mins of stirring showed maximum peak at 495 nm. this was found to be shifted towards higher wavelength for increase in stirring time indicates the formation of cunps. ftir analysis illustrated the presence of chief functional groups; phenol, carbonyl and amide groups at the surface of cunps which are responsible for reducing and stabilizing the nanoparticlees. similarly, edx result depicts the presence of copper of 24 wt % at 8 ev along with traces of si, s, p etc. as impurities. as-synthesized cunps are quite stable and have antibacterial action towards both types of bacteria though its power of killing the different bacteria is slightly different. hence, we conclude that bio-synthesized cunps could be used as alternative antibiotics. acknowledgement authors gratefully acknowledge to university grant commission, frg 13, bhaktapur for financial support to carry out this research. references [1] v. d. kulkarni, p. s. kulkarni, green synthesis of copper nanoparticles using ocimum sanctum leaf extract, international journal of chemical studies, 1 (3) (2013) 4. 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http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal study of electronic transport parameters on the heterojunction of algan/gan, grown on sapphire: two layer model s. shrestha1*, ambika shakya1, c. k. sarkar2 1central department of physics, tribhuvan university, kathmandu, nepal 2dept. of etce, jadavpur university, kolkata-700032, india *email: sanju12np@yahoo.com article history: received 17 august , 2018; accepted 11 september, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21072 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract in spatially confined system such as heterojunction of high and low band gap material, carriers are transferred from higher band gap to the lower band gap. it causes the band bending and the formation of a triangular quantum well at the junction. such system behaves as quantum-two dimension (q2d) system because the carriers are free to move on a plane, perpendicular to the junction. mobility of such quantized system is very high as compare to the bulk system due to the reduction of various scattering mechanisms. gan is a very useful material. however, a non availability of single crystalline form of gan and perfectly matched substrates are always problems for gan. hence gan, grown on a substrate such as sapphire is having a very large dislocations at the interface. such interfacial layer significantly affects the transport parameters of the material, where the transport properties are highly dominated by scattering due to dislocations. the authors have calculated the mobilities of algan/gan, a heterojunction considering the gan, grown on sapphire with reference to the two layer model of look, in which the 2nd layer is the dislocation layer of gan and the 1st layer is the junction of algan/gan where carriers are in the form of two dimensional electron gas (2d eg). the obtained calculated results are also compared with the experimental results as obtained by sibel gokden et al. it is observed that the nature of the curve is found to be in agreement with the experimental curve when the ratio of the thicknesses is taken to be 1:1. keywords: heterojunction; quantum well; two layer model; algan/gan. 1. introduction in the present and in the upcoming generation, there is very high demand of high speed electronic devices. hence, the study of electron transport in low dimensional semiconductor system has been very important. the low dimensional devices can be made either by external perturbation or by spatial confinement. the development of various growth techniques such as molecular beam epitaxy (mbe) http://nepjol.info/index.php/bibechana mailto:sanju12np@yahoo.com http://dx.doi.org/10.3126/bibechana.v16i0.21072 https://creativecommons.org/licenses/by-nc/4.0/ s. shrestha et al./ bibechana 16 (2019) 137-144: rcost p.138 (online publication: dec., 2018) and molecular oxide vapor chemical deposition (movcd) has opened the door for the spatially confined structures like quantum wells (qws), quantum well wires (qwws) and quantum dots (qds). heterojunction: the idea of heterojunction was forwarded by anderson[1]. heterojunction is the junction between the low and high band gap materials as shown in fig. 1 (a), in which the electrons from higher band gap fall to the lower band gap. the accumulated electrons in the lower band gap create space charges in the higher band gap region and the band bending takes place due to coulomb interaction between positive charges left on donor side and the electrons in the interface. as a result, a triangular well is formed at the junction. here, the electrons get trapped into the well and quantized in the various energy levels shown by fig. 1(b). such quantized electrons can move only in the plane of the quantized level or perpendicular to the surface of the junction. these quantized electrons are called two dimensional electron gas (2d eg). in the present work the authors have used the heterojunction of algan/gan in which from doped and has higher band gap algan electron get transferred to the undoped and lower band gap gan. these electrons are quantized in various levels forming 2d eg as described above. however, the authors have taken account of the extreme quantum limit (eql) condition i.e. only the electrons in the lowest energy level take part in the various electronic transport phenomena. in compound semiconductors, the scattering of the electrons by ionized impurities limits the mobility of the sample [2]. hence, the ionized impurity (ii) is also included for the heterojunction. at the same time due to the presence of interface between gan and algan surface roughness scattering mechanism (sr) plays an important and dominating role in limiting the mobility at low temperatures and high carrier densities. the acoustic phonon (ac) via deformation potential scattering mechanism is caused by the perturbing potential arising from the strain produced in the crystal lattice by the acoustic vibrations. in crystals lacking inversion symmetry, other than the deformation potential interactions, piezoelectric coupling occurs with acoustic modes. the displacements of the ionized atoms associated with the acoustic vibrations in these crystals produce an electrical polarization giving rise to piezoelectric scattering (pz) of the carries. piezoelectric scattering (pz) is important for weak-field transport at low temperatures[3]. at high fields however, the important of this type of scattering deceases since the corresponding scattering rate diminishes with increasing electron energy. hence, various low temperature scatterings mechanisms such as acoustic phonon (ac), piezoelectric (pz), surface roughness (sr) and ionize impurity (ii) scattering etc are included to the heterojunction of algan/gan. two layer model: gan is not available in single crystalline form. therefore, it is normally grown on sapphire (al2o3) or sic substrate with a large lattice mismatch. the gan grown on substrate sapphire having 14% lattice size mismatch and 34% mismatch in the thermal expansion coefficient4 has been selected for the present work. hence, the whole material algan/gan grown on sapphire substrate system can be considered to be made up of two layers5 formulated by look et al. the first layer is the junction between algan/gan and the second layer is the dislocation layer between gan and the sapphire substrate as shown in the fig.2. according to the model, current passing through the whole system can be divided into two layers as if two resistors are kept in parallel. the combined current will be the sum of the currents due to two individual layers, as shown in the fig. 2. the model has been used to calculate different transport parameters such as ac and dc mobilities and conductivities. + e2 a lg an e1 a lg an ef a lg an g an sa pp hi re a lg an + + in te rf ac ia l l ay er s. shrestha et al./ bibechana 16 (2019) 137-144: rcost p.139 (online publication: dec., 2018) fig. 1 (a) heterojuction of higher and lower fig. 1 (b): quantized energy levels at heterojunction. band gap semiconductor. fig. 2(a) fig. 2(a) fig. 2 (a) and fig 2 (b) represent the schematic representation of the two layer model of the algan/gan grown on sapphire. the top or the first layer represents the junction of algan/gan heterojunction while the second layer represents the interfacial layer of gan and the sapphire. the bottom most layer is the substrate of sapphire which is an insulator layer and does not take part in any electronic transport phenomena. due to the high density of dislocations in the interfacial layer, transport properties in the layer are highly affected by scattering due to the dislocation. hence scattering due to dislocation will be dominant in the interfacial layer whereas various other types of scattering mechanisms are included for the heterojunction such as ionized impurity (ii), piezoelectric (pz) acoustic phonon (ac) and surface roughness (sr) scatterings as mentioned above[6]. the influence of dislocation scattering (dis) in the heterojunction layer has not been considered because of the negligible density of dislocations as compared to that of the interfacial layer. 2. theory transport parameters based on two layer model: due to the mismatch between the gan and the sapphire, very large number of dislocations is present in the interfacial layer. the transport parameters are highly affected by these dense dislocations. however, in the heterojunction, the transport interfacial layer heterojunction layer sapphire substrate s. shrestha et al./ bibechana 16 (2019) 137-144: rcost p.140 (online publication: dec., 2018) parameters are affected by various other phonon and nonphonon scattering mechanisms as described above. according to the twolayer model, the combined current will be the sum of the currents through two individual layers. hence it is given as: 𝐼𝑐𝑜𝑚 = 𝐼1 + 𝐼2 (1) where, i1, i2 and icom are current in the heterojunction, the interfacial layer and the total current respectively. the subscripts 1 and 2 are used for the heterojunction or the first layer and the interfacial layer or the second layers respectively in the rest of the work. combined mobility: we have, current density, 𝐽 = 𝐼/𝐴 or 𝐽 = 𝜎𝐸j, 𝐴 = 𝑏 × 𝑊, 𝐸 = 𝑉/𝑙, 𝜎 = 𝑛𝑒𝜇 and 𝜇 = 𝑣𝑒 𝐸 . therefore 𝐼 = 𝑛𝑒𝜇𝑉𝐴/𝑙 now, substituting the values of currents for the heterojunction, the interfacial layer and the combined two layer with their respective parameters from equation in eq.1, we get the combined mobility 𝜇𝑐𝑜𝑚 as 𝑛𝑒𝜇𝑐𝑜𝑚 𝑉 𝑙 𝑏𝑊 = 𝑛1𝑒𝜇1 𝑉 𝑙 𝑏𝑊1 + 𝑛2𝑒𝜇2 𝑉 𝑙 𝑏𝑊2 or 𝜇𝑐𝑜𝑚 = 𝑛1𝑎𝜇1+ 𝑛2𝜇2 𝑛1𝑎+𝑛2 (2) where, a = (w1/w2): the ratio of the thickness of the heterojunction w1 to the interfacial layer w2. for the heterojunction, as the first layer the mobility is given as: 𝜇1 = 𝑒 𝑚∗ 〈𝜏〉 (3) where 〈𝜏〉 is the average of the total relaxation time, it is the sum of individual scattering mechanism due to ionized impurity (ii), piezoelectric (pz) acoustic phonon (ac) and surface roughness (sr) scatterings as mentioned above[6]. for the, dislocation layer i.e. the 2nd layer 〈𝜏〉 in the eq. 3 displaced by 〈𝜏𝑑𝑖𝑠〉 and obtained the mobility for the layer. where 𝜏𝑑𝑖𝑠 is the relaxation time for dislocation scattering mechanism [7]. in the presence of a weak ac field with frequency, , the scattering time or relaxation time becomes complex, i.e 𝜔−1 changes to (𝜏 + 𝑖𝜔)−1 leading to the real and the imaginary parts of the mobility 𝜇𝑟 and 𝜇𝑖𝑚 respectively. these are given as[8]: 𝜇 = 𝜇𝑟 + 𝜇𝑖𝑚 𝜇𝑟 = ( 𝑒 𝑚∗) 〈 𝜏 1+𝜔2𝜏2 〉 (4) 𝜇𝑖𝑚 = ( 𝑒 𝑚∗) 𝜔 〈 𝜏 1+𝜔2𝜏2 〉 (5) where ω is the angular frequency and τ is the scattering mechanisms as described above. the real and imaginary parts of ac mobility given by eqs. 4 and 5 have been evaluated for the heterojunction and the interfacial layers separately by assuming their respective dominant scattering mechanisms as explained earlier and, the combined real part (𝜇𝑟𝑐𝑜𝑚) and the combined imaginary part (𝜇𝑖𝑚𝑐𝑜𝑚) of the ac mobility are obtained as it has been carried out in the case of dc mobility i.e. by using eq. 2 with the real part of the respective mobilities and the imaginary part of the respective mobilities respectively. s. shrestha et al./ bibechana 16 (2019) 137-144: rcost p.141 (online publication: dec., 2018) 3. results and discussion the alloy composition x for alxga(1-x)n is taken to be 0.33. the dislocation density in the interfacial layer (ndis), carrier concentration in the triangular well (n2d) and the interfacial layer (ns) are taken as 7x1014 m-2[4], 1014 m-2 and 1016 m-2[9] respectively. fig.3 represents the variation of dc mobility with temperature in the heterojunction of algan/gan for various scattering mechanisms such as acoustic phonon via deformation potential (ac), surface roughness (sr), ionized impurity (ii) , piezoelectric (pz) scattering [6] and dislocation (dis) scattering mechanisms [7] individually. in the fig. 3, it is seen that the mobility increases significantly with rise in temperature for non phonon scattering mechanisms like ionize impurity (ii) and surface roughness scatterings (sr), shown by curves indicated by ‘ii’ and ‘sr’ respectively in the fig. the figure shows that at low temperature below 30 k the ionize impurity scattering mechanism dominates all other scattering mechanisms. that means the non phonon scattering mechanism is dominant at low temperature as compared to that of the phonon scattering mechanisms. at temperature above 30 k, the piezoelectric scattering mechanism (pz) is dominant. this indicates that the phonon scattering dominates the other non phonon scattering mechanisms at temperature above 30 k. the mobility due to dislocation scattering in the junction between gan and sapphire is constant with temperature, shown by the curve indicated as (dis) in the fig. fig. 3 shows the variation of 2d eg dc mobility versus temperature in the heterojunction of algan/gan including the total effect of all scattering mechanisms. the total mobility μ2d eg in the heterojunction initially rises with temperature, reaches maximum at 41.8 k and then decreases with the increase of temperature. the maximum value of such mobililty is obtained to be 0.57516 m2/vs. the curve μdis shows the variation of the interfacial layer mobility with temperature for dislocation layer or the interfacial layer of gan and the sapphire substrate. the interfacial layer mobility due to dislocation scattering is constant of temperature. also, the magnitude of the dislocation scattering mechanism is dominant at all temperature as compared to all other scattering mechanisms in the heterojunction. the curves indicated as μ24:1 and μ1:1 is shown in the fig.4 are combined mobilities taking the ratios of the thickness of the heterojunction and the dislocation layer to be 24:1 and 1:1 respectively. both the mobility curves are observed to be increased with temperature, reaches maximum value at about 42k and then decreases with the increase of temperature. however, the slope of the mobility μ1:1 decreases gradually with the increase of temperature in the higher temperature region. comparison of theoretical mobility curves such as μ24:1, μ1:1 and μ hetero with experimental mobility curve μexp [10] is shown in fig 5. considering the heterojunction as a single layer, in which all the scattering mechanism such as ionized impurities (ii), surface roughness (sr), acoustic phonon via potential deformation (ac), piezoelectric (pz) and the dislocation scattering (dis) are obtained individually and the total of which is obtained by using matthiessen’s rule for the heterojunction of algan/gan. the author gokden [10] has compared his experimental hall mobility of a 2d eg formed at algan/gan heterointerface with the theory. in which the author has also considered all standard scattering mechanisms including dislocation scattering (dis), acoustic deformation via potential scattering (ac), piezoelectric (pz), polar optical phonon (pop), background and remote impurities (ii) in the heterojunction of algan/gan. s. shrestha et al./ bibechana 16 (2019) 137-144: rcost p.142 (online publication: dec., 2018) in the fig. 6 the magnitude of the curves μ1:1 and μ24:1 at low temperature range is comparable with that of the curve μexp through the temperature range. the curves μ1:1 and μ24:1 initially increase to certain value then gradually decrease, whereas where as the curve μexp decreases rather steeply with the increase of temperature. the curve μ24:1 has hump like nature at temperature around 40k that doesn’t match with μexp exactly. hence the curve μ1:1 is much comparable with μexp though at high temperature its magnitude is slightly different. the reason behind the difference of magnitudes at high temperature is expected due to that in the present work, the optical phonon scattering mechanism (pop) is not considered. at high temperature, polar optical scattering (pop) is much effective due to which the mobility decreases with temperature. hence at present work, the variation of mobility is taken for temperature range limited up to 140k only. further inclusion of polar optical phonon (pop) scattering mechanism is expected to get the theoretical result more closed to the experimental result. however, the figure shows that the two layer model gives the results closer to the experimental value rather than the single layer concept. moreover, the experimental mobility curve agrees with the combined mobility for the junction to the dislocation layer thickness ratio 1:1 rather than that of the ratio 24:1. this signifies that the consideration of dislocation layer as a separate layer which has thickness equal to that of the junction in the two layer model is more effective and the results obtained is convincing with the experimental data also. the variation of the temperature dependent two layer ac mobility at constant frequency 60 ghz for the junction to interfacial layer thickness in the ratio 1:1 with various scattering mechanisms in the heterojunction as mentioned above and the dislocation scattering only in the interfacial layer is shown in fig 6. the combined real part of ac mobility indicated by the curve μr first increases to the highest at temperature 42k and then decreases gradually with the increase of the temperature. the highest value of the real part is nearly equal to that of the combined dc mobility for the ratio 1:1 as shown in the fig 5. in eq. (4), when ω is taken as zero, the real part of the ac mobility determines the dc mobility term which is true in low frequency region. similarly the combined imaginary part of the ac mobility indicated by the curve μim in the fig 6 first increases at about temperature 42k then it decreases gradually as temperature increases. 0 40 80 120 160 0.01 0.1 1 10 100 n s =10 16 m -2 n 2d =10 14 m -2 n dis =7x10 14 m -2 dc m ob ili ty m 2 /v s temperature k ii sr ac dis total pz fig. 3: variation of dc mobility with temperature in the heterojunction of algan/gan for various scattering mechanisms such as acoustic phonon (ac),piezoelectric (pz), surface roughness (sr), ionized impurity (ii): and only the dislocation (dis) scatterings for interfacial layer separately and also the resultant of above all scattering mechanisms(total) in the heterojunction layer considering it as a single layer. s. shrestha et al./ bibechana 16 (2019) 137-144: rcost p.143 (online publication: dec., 2018) 0 40 80 120 160 0.1 0.2 0.3 0.4 0.5 0.6 n s =10 16 m -2 n 2d =10 14 m -2 n dis =7x10 14 m -2  1:1  dis  24:1  2d eg d c m o b il it y  m 2 /v s temperature k fig. 4: variation of 2d eg mobility μ2deg versus temperature in which curves shown by μ24:1 , μ1:1 μ2d eg μdis are for the resultant taking the ration of thickness of heterojunction to the interfacial layer 24:, 1:1, the heterojunction mobility alone and the interfacial mobility alone respectively. 0 40 80 120 160 0.01 0.1 1  r  im =60 ghz ratio=1:1 n s =10 16 m -2 n 2d =10 14 m -2 n dis =7x10 14 m -2 temperature k a c m o b il it y m 2 /v s fig. 5 fig. 6 fig. 5: variation of dc mobility versus temperature. here μhetero is the mobility of 2d eg in the heterojunction taking it as a single layer, μ1:1 and μ24:1 are the combined two layer mobilities with the junction to the dislocation layer thickness ratio to be 1:1 and 24:1 respectively. whereas μexp is the experimental result of gokden [10]. fig. 6: variation of two layer ac mobility versus temperature, taking the ratio of the junction to the dislocation layer thickness to be 1:1 at constant frequency 60ghz. the curves indicated by μr and μim show the combined real and imaginary parts of the ac mobility respectively. 4. conclusions the electronic transport parameters such as dc and ac mobilities on heterojunction of algan/gan, grown on sapphire is calculated on the basis of two-layer model, formulated by look is calculated. s. shrestha et al./ bibechana 16 (2019) 137-144: rcost p.144 (online publication: dec., 2018) the various scattering mechanisms such as acoustic phonon (ac), piezoelectric (pz), surface roughness (sr) and ionize impurity (ii) scatterings are taken into consideration in the heterojunction layer whereas only the dislocation (dis) scattering is taken into account in the interfacial layer between gan and the sapphire. < the two layer combined mobility curve for the thickness of the heterojunction layer equal to the interfacial layer in the low temperature range is found comparable to the experimental result[10]. at high temperature range, on the inclusion of the polar optical scattering (pop) becomes dominant but in the present work, it is not taken into account. however, the presence of the interfacial or dislocation layer can’t be ignored. on the basis of the results obtained for the thickness ratio 1:1, it can be concluded that the two layer model as suggested by d.c look supports the experimental results. acknowledgement one of the authors s. shrestha is grateful to indian national science academy (insa), new delhi, india for providing the insa-jrd-tata fellowship to carry out the above research work. references [1] r.l. anderson, germanium-gallium arsenide heterojunctions, ibm.j. res. dev. 4 (1960) 283-287. doi.org/10.1147/rd.43.0283 [2] f. stern, w.e. howard, properties of semiconductor surface inversion layers in the electric quantum limit, phys. rev. 163 (1987) 816. doi.org/10.1103/physrev.163.816. [3] j. d. zook, piezoelectric scattering in semiconductors, phy. rev. 136 (1964) a869. doi.org/10.1103/physrev.136.a869. [4] d.c. look, j.r. sizelove, dislocation scattering in gan, phys. rev. lett. 82 (1999) 1237. doi.org/10.1103/physrevlett.82.1237. [5] d.c. look, r.j. molnar, degenerate layer at gan/sapphire interface: influence on hall-effect, appl. phys. lett. 70 (1997) 3377. doi.org/10.1063/1.119176. [6] c.k. sarkar, p. banerji, estimation of the alloy scattering potential in . wiley online library, phys. stat. sol. (b), 156 (1989) k145. doi.org/10.1002/pssb.2221560248. [7] d.c. look, electrical characterization of gaas materials and devices, johan and sons ltd., ny, 1989. [8] b.r. nag, electron transport in compound semiconductors vol. ii, edited by h.j. queisser, springer berlin, 1980. [9] d. jena, a.c. gossard, u.k. mishra, dislocation scattering in a two-dimensional electron gas. department of electrical and computer engineering. university of california. santa barbara, california, 93106, 2000. [10] s. gokden, dislocation scattering effect on two-dimensional electron gas transport in gan/algan modulation-doped heterostructures. elsevier. physica e 23 (2003) 19 – 25. https://doi.org/10.1147/rd.43.0283 https://doi.org/10.1103/physrev.163.816 https://doi.org/10.1103/physrev.136.a869 https://doi.org/10.1103/physrevlett.82.1237 https://aip.scitation.org/doi/10.1063/1.119176 microsoft word jha et all final (1-6) vijay kumar jha et al. / bibechana 16 (2019) 1-6: rcost p.1 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal experimental set up for the study of plasma parameters in seeded arc plasma using langmuir probes inside low-cost vacuum chamber vijay kumar jha1*, lekha nath mishra2, bijoyendra narayan3 1central department of physics, kirtipur (tribhuvan university, kathmandu), nepal *permanent address1:amrit campus, thamel (tribhuvan university, kathmandu), nepal 2patan multiple campus, patandhoka, lalitpur(tribhuvan university, kathmandu), nepal 3dr. s. k. sinha women’s college, motihari (b. r. a. bihar university, muzaffarpur), india *email: jhav7050@gmail.com1 article history: received 20 february, 2018; accepted 04 august, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.20839 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract in this piece of study, the design and development of a low cost vacuum chamber with different ports are mentioned. i-v characteristic of langmuir probe is obtained using the primary data of the experimental set up for ‘single probe method’ in nitrogen seeded arc plasma at atmospheric pressure the floating potential was found to be 36v and the electron density to be 1.24 × 104 k. variation in electron density of the arc plasma with probe potential is also studied at low pressure range from 10 nm−2 (0.10 mbar) to 20 nm−2. keywords: arc plasma; vacuum chamber; plasma parameters; operational constraints; langmuir probe; floating potential; electron density. 1. introduction the mechanical design of a vacuum chamber requires defining the boundary conditions. the conceptual design is followed by a detailed design, which is actually associated with the development of the device. methodology & methods [1] of development of the device are given in this study together with a schematic diagram of a low cost vacuum chamber. in the cold plasma, unlike in low density plasma [2], plasma parameters such as floating potential and electron density are calculated. i-v characteristic for langmuir probe [3-5] is obtained using ‘single probe method’ from the experimental set up. variation in electron density of the arc plasma due to variation in pressure is also also observed using ‘double probe method’ for low pressure range from 0.1mbar to 0.2mbar. 2. boundary conditions environment determination of the environment in which the vacuum chamber is to be operated is the first step in its design and development. the sub-sections are given below deals with the important points of environment. vijay kumar jha et al. / bibechana 16 (2019) 1-6: rcost p.2 (online publication: dec., 2018) the situation should not be very difficult when it is located inside a large building if the external envelope is simply the volume where the chamber is situated at adequate space for supports simplifies the design of the chamber. in addition, space and access to the pumping ports. the envelope is the main parameter for the vacuum chamber of an accelerator, but the conductance is another one in case of lumped pumps; the pressure distribution between two pumping ports is parabolic, and the maximum value of this parabola defines the operating pressure. the inner piping and its insulation layers define the inner envelope, but an extra space is included to allow for the movements resulting from pressure and temperature variations. operating temperature is room temperature, bake-out temperature between 150ºc and 300ºc. the different effects of temperature include dilatations, stresses and changes of material properties, which have destructive effects if nod mastered properly. electrical impedance is reduced with a good electrical conductivity, but on the other hand, non-conducting material is required for electric insulation. the parameters such as the radiation length (x0), and the collision length are considered. materials the material parameters for the design of a vacuum chamber in terms of mechanics could be many, but there are only three main parameters. they are young’s modulus (e), the elastic limit (σ 0.2) and rupture limit (σ r). these parameters are usually easily available for materials. figure 1 shows a typical shape of traction curves [1] of materials. it shows how to define the yield or elastic limit. the modulus of rigidity is obtained through the value of the slope of the quasilinear part of the curve. (i) steel except austenitic stainless steel (ii) austenitic stainless steel, aluminium alloys fig. 1: traction curves of metals [1]. selecting materials for specific cases is a multi-parameter problem. it is eased by the use of non-dimensional parameters [6]. these have been used for the specific types of vacuum chambers such as the beam pipes, for the experiments installed in colliders [7]. they should be transparent to particles. the material selection is based on the non-dimensional parameter (x0e1/3) that gives a figure of merit for the materials (table 1) and, for this specific case of beam pipes, beryllium and carbon fibre composite outrun by a large factor aluminium, titanium, and steel. vijay kumar jha et al. / bibechana 16 (2019) 1-6: rcost p.3 (online publication: dec., 2018) table 1: figures of merit of materials. be cfc al-be al ti fe e(gpa) 290 200 193 70 110 210 x0 (m) 0.353 0.271 0,253 0.089 0.036 0.018 x0e1/3 2.34 1.58 1.46 0.37 0.17 0.11 leak tightness of a vacuum chamber is a must, but is difficult to obtain if the weldability of the material is poor. cost is the final criterion behind it. the most common materials are austenitic stainless steel. design stresses generated by the loads enumerated before should usually remain in the elastic range. this means that the equivalent stress should not exceed the elastic limit (σ0.2) anywhere in the structure. the membrane strain energy can be converted to bending strain energy, leading to instability and a bifurcation point on the behavioral curve, a potential buckling (figure 2). buckling is a non-linear phenomenon, and is strongly influenced by the defects inherent in the manufacturing. fig. 2: buckling behaviours [1]. the use of structural analysis, usually based on the finite-element method, is necessary for the detailed design of vacuum vessels. in the shell elements [figure 3], the through thickness stresses are assumed linear and integrated in membrane (constant term) and bending (linear term). bellows are either mechanically formed from thin tubes, or assembled by welding a series of individual annular rings. bellows are designed to withstand a given number of cycles of axial expansion/compression over the expected life of the system. assembly materials for manufacturing are available in various states; raw products like blanks or sheets, or semi-finished products like extruded elements (aluminium, copper), moulded, forged, or sintered. the choice is usually based on cost but the final quality in terms of vacuum may be disturbed by the vijay kumar jha et al. / bibechana 16 (2019) 1-6: rcost p.4 (online publication: dec., 2018) manufacturing techniques. defects due to impurities internal to the material should not provoke a leak-through, and elaboration techniques properly handled is of help in this connection. fig. 3: shell element: a bellow [1]. the main parameters for their design are the strength of the material to withstand high forces for bolting or clamping, and the quality and hardness of the surface where the seal is positioned. the first point is the weldability of the material. to fulfill their role of mechanical resistance, the welds are designed. grooves help minimize heat propagation along the walls and can be useful in case of subsequent cutting and re-welding. the surfaces are etched before the brazing, and also a high-quality cleaning after brazing is important to increase the lifespan [8] of the vacuum chamber. 3. results and discussion figure 4 shows the schematic diagram of the vacuum chamber with quartz windows figure 5 shows the variation of probe current(ln i) with probe voltage(v) for single probe method, using the data obtained from the experimental set up. from the figure, the floating potential is 36v, and electron temperature is calculated to be 1.24 × 104 k. variation of electron density at different pressure is shown in figure 6. figure 6 shows that the low cost vacuum chamber is suitable for the measurement of plasma parameters in a seeded arc plasma. fig. 4: a schematic diagram for vacuum chamber. 2 ¯ + 7 6 5 4 31 1. vacuum chamber 2. poly carbonate flange 3. arc plasma 4. langmuir probe 5. pressure gauge 6. rotary pump 7. metal flange vijay kumar jha et al. / bibechana 16 (2018) 1-6: rcost p.5 (online publication: dec., 2018) fig. 5: i-v characteristics of langmuir probe (single probe method) from data obtained from experimental set up. fig. 6: variation of electron density in arc plasma at low pressure. 440 460 480 500 520 540 560 5803.23.43.63.84.04.24.44.64.85.0electron density x1015 (m-3 ) applied voltage(v) 0.10mbar 0.15mbar 0.20mbar vijay kumar jha et al. / bibechana 16 (2019) 1-6: rcost p.6 (online publication: dec., 2018) 4. conclusions a low-cost vacuum chamber of stainless steel has been developed in the laboratory by adopting a systematic approach for the study of plasma parameters in seeded arc plasma. the nature of i-v characteristic plotted using data obtained from the single probe method. the results are in good agreement with the characteristics of the langmuir probe obtained by other researchers [9]. the electron density of the low pressure plasma increases as pressure increases. results show that the experimental set up is suitable for measuring plasma parameters. acknowledgement the financial support of university grants commission (ugc), nepal for the present study is heartily acknowledged. references [1] c. hauviller, design of vacuum chambers, cern, geneva, switzerland (2007). [2] v. k. jha, study on compression of icf fuel in rocket model, american journal of physics and applications, 5 (2017) 95-98. doi.org/10.11648/j.ajpa.20170506. [3] a. brockhaus, c. borchardt and j. engemann, langmuir probe measurements in plasma sources sci. technol., 3 (1994) 539-544. [4] b. l. robert and e. b. brian, recommended practice for use of langmuir probes in electric propulsion testing, journal of propulsion and power, 33 (2017) 566-581. doi.org/10.2514/1.b35531. [5] t. h. chung, y. m. shin &amp; d. c. seo, comparision of two methods of interpretation of langmuir probe data for an inductively coupled oxygen plasma, contrib. plasma phys, 46 (2006) 348-353. doi.org/ 10.1002/ctpp. 200610013. [6] m. f. ashby, materials selection and process in mechanical design, butterworth heinemann, oxford, (1999). [7] c. hauviller, design of vacuum chambers for experimental regions of colliding beam machines, ieee particle accelerator conference (1993). [8] h. fujimoto, t. suekane, k. imanishi, s. yukiwaki, h. wei, k. nagayoshi, m. yahiro, and c. adachi, impurities on oled degradation, sid symposium digest of technical papers, 48 (2017) 9-12. [9] r.p. sinha, b.m.k. prasaad, m. bhagat and b. narayan, a study of cu arc plasma using a moving langmuir probe, indian journal of pure & applied physics, 26 (1988) 720-721. bibechana 18 (1) (2021) 91-99 91 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal study of tunneling and oscillation in a 𝑮𝒂𝑨𝒔/𝑨𝒍𝟎.𝟑𝑮𝒂𝟎.𝟕𝑨𝒔 superlattice: using transfer matrix method s. shrestha1,*, n. bhusal1, s. byahut1, c. k. sarkar2 1central department of physics, tribhuvan university, kathmandu, nepal 2 dept. of electronics and tele-communication engineering, jadavpur university, kolkata 700 032, india *email: sanju12np@yahoo.com article information: received: january 28, 2020 accepted: july 7, 2020 keywords: gaas/al0.3ga0.7as superlattice quantum tunneling high frequency oscillation abstract the study of superlattice (sl) system in lower dimensions, which shows tunneling and oscillation of particles, is very interesting from the point of view of fundamental physics and is important for devices. here, we present results of our calculations related to tunneling/oscillations in a general sl system using a symmetrical quadruple well (sqw) potential. this class of problems is handled using a transfer matrix (t-matrix), which is obtained by taking the solution of schroedinger equation with appropriate boundary conditions on either side of sqw and then repeatedly applying it for the sl system. the electron wave functions in the system are found to be either in a symmetric or an anti-symmetric state with a very small energy difference between the two, leading to oscillations between these states. in this study, probability density and period of oscillation of the particle in sqw is calculated. the result is useful for high frequency operations in devices using sl. doi: https://doi.org/10.3126/bibechana.v18i1.27450 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction a superlattice (sl) can be modeled by a set of quantum wells, spaced sufficiently close, in which electrons can tunnel between the wells. the potential profile of the sl is analogous to the kronig-penney model [1,2]. the sl system has a variety of applications in devices such as resonant tunneling structure and far-infrared detector. if the quantum wells are periodically coupled, new phenomena may arise because carriers from one quantum well may tunnel though an intervening layer to the next well. by varying the number of wells and controlling the strength of interaction between wells there is a possibility of making semiconductor devices with tailored band gap. this will enable devices sensitive to and operating at energies in the range of our interest. http://nepjol.info/index.php/bibechana mailto:sanju12np@yahoo.com https://doi.org/10.3126/bibechana.v18i1.27450 https://creativecommons.org/licenses/by-nc/4.0/ s. shrestha et al. / bibechana 18 (1) (2021) 91-99 92 the idea of semiconductor sl was first proposed by esaki and tsu in 1970 [3]. semiconductor sl is formed by layered fabrication of two or more semiconductors of different band gaps (e.g. 𝐺𝑎𝐴𝑠 and𝐴𝑙0.3𝐺𝑎0.7𝐴𝑠) in a nanometer scale. it has been studied for different applications by several groups for their optical and transport properties [4-6]. photoluminescence measurement was performed in sl with parabolic bands, such as 𝐺𝑎𝐴𝑠/ 𝐴𝑙𝐺𝑎𝐴𝑠[7]. 𝐴𝑙𝐺𝑎𝐴𝑠/𝐺𝑎𝐴𝑠 sl mini-band detectors, which operate at very low or zero bias voltage, have been discussed and their peak spectral response in the range from 4 to 10 pm has also been reported [8,9]. blotch oscillations in algaas/gaas sl in terahertz region using monte carlo method have also been studied [10], in which, the effective mass approximation was used in two dimensional model and studied electron miniband transport. renk et al. [11] have done experimental study on semiconductor sl oscillator in the frequency range of 60ghz. high frequency devices have been an important research area for many years. the application of resonant tunneling diode (rtd) in 1980’s was not very successful in the terahertz (thz) region due to the extrinsic design manner, which relied on external circuit elements to induce oscillation. a new theory for the origin of intrinsic oscillation due to inter sub-band coupling in a multi sub-band system in the terahertz frequency region has been developed (for example, current oscillation in a double barrier quantum well structure [dbqws] based oscillators) [12,13]. the relationship between oscillation frequency and sub-band structure can be used as design criteria for new types of intrinsic oscillators. the tunneling calculations on sawtooth and rectangular sl of algaas/gaas using transfer matrix was previously done [14]. hence, the concept of the transfer matrix on sl of algaas/gaas, as done by forrest et al. [14] is used to study tunneling, oscillatory behavior and the frequency of oscillation. in the present work a sl of 𝐺𝑎𝐴𝑠 and 𝐴𝑙0.3𝐺𝑎0.7𝐴𝑠 is studied. an accurate form of solution is offered by transfer matrix method [15]. we first solve a symmetric quadruple wells (sqw) (with three barriers in between) problem exactly and find the matrix which associates the wave function in the first well with the wave function of the fourth well. this matrix is then used to develop the transfer matrix (t-matrix) which relates the wave function in the first well of the sl with the wave function of the last well. in this paper, we derive a theoretical formalism for a general sl, utilizing the methods of t-matrix. first we find the solution of the schrödinger equation as applied to an sqw with suitable boundary conditions and then repeating the obtained result for the whole sl system. in the first part of section 2 we develop a general theory of a sl and derive t-matrix by finding first the solution of the schroedinger equation as applied to a sqw with suitable boundary conditions and then repeating the obtained result for the whole sl system. in the second part, we use the t-matrix method to find solution in the sqw. a sqw is a four well structure bounded by vacuum levels at the either ends in the growth directions. due to spatial symmetry the electron wave function in the system is either symmetric or anti-symmetric with a small energy difference between the levels [16]. to simplify the problem, time evolution of combined symmetric and anti-symmetric lowest lying state is taken which gives the frequency of oscillation in the sqw. the probability density of finding a particle in the sqw is also calculated and shown graphically. 2. theoretical formulation 2.1 a general superlattice (sl) consider a general sl system of (𝑛 + 1) layers having 𝑛/2 barriers and (𝑛/2 + 1) wells, fig. 1(a). we explore the tunneling of electrons through a single barrier to find the transfer coefficient. s. shrestha et al. / bibechana 18 (1) (2021) 91-99 93 schrodinger equations for an electron with energy𝐸 < 𝑉0, (v0 being the height of the barrier) and effective masses 𝑚𝑤and 𝑚𝑏in the well and in the barrier regions respectively of the sl are: for the well region, d 2𝜓𝑤(z) dz2 + 2𝑚𝑤e ℏ2 𝜓𝑤(z)=0 (1a) for the barrier region, d 2𝜓𝑏(z) dz2 − 2𝑚𝑏(𝑉0−𝐸) ℏ2 𝜓𝑏(z)=0 (1b) the corresponding wave vectors are: 𝑘𝑤 = √2𝑚𝑤𝐸 ℏ2⁄ , and𝑘𝑏 = √2𝑚𝑏(𝑉0 − 𝐸) ℏ2⁄ . the solutions of the equations above are: for the well region: 𝜓𝑤(z = 𝐴𝑤sin(𝑘𝑤𝑧) + 𝐵𝑤cos(𝑘𝑤𝑧) (2a) for the barrier region: 𝜓𝑏(z) = 𝐴𝑏sinh(𝑘𝑏𝑧) + 𝐵𝑏cosh(𝑘𝑏𝑧) (2b) the applicable boundary conditions are continuity of the wave function and equality of the effective mass-weighted slope of the wave functions (ben daniel duke condition) at the interface [17]. applying this for the (p-1)th well, pth barrier and (p+1)th well we get ( 𝐴𝑝+1 𝐵𝑝+1 ) = 𝑀𝑤 −1(𝑧)|𝑧=𝑧𝑝 𝑀𝑏(𝑧)|𝑧=𝑧𝑝 𝑀𝑏 −1(𝑧)| 𝑧=𝑧𝑝−1 𝑀𝑤(𝑧)|𝑧=𝑧𝑝−1 ( 𝐴𝑝−1 𝐵𝑝−1 ) = 𝑇𝑝+1←𝑝−1 ( 𝐴𝑝−1 𝐵𝑝−1 ) (3) where, 𝑀𝑤(𝑧)|𝑧=𝑧𝑝 = [ sin(𝑘𝑤𝑧𝑝) cos(𝑘𝑤𝑧𝑝) ( 𝑘𝑤 𝑚𝑤 ) cos(𝑘𝑤𝑧𝑝) (− 𝑘𝑤 𝑚𝑤 ) sin(𝑘𝑤𝑧𝑝) ] (4a) 𝑀𝑏(𝑧)|𝑧=𝑧𝑝 = [ sinh(𝑘𝑏𝑧𝑝) cosh(𝑘𝑏𝑧𝑝) ( 𝑘𝑏 𝑚𝑏 ) cosh(𝑘𝑏𝑧𝑝) ( 𝑘𝑏 𝑚𝑏 ) sinh(𝑘𝑏𝑧𝑝) ] (4b) and 𝑇𝑝+1←𝑝−1 = 𝑀𝑤 −1(𝑧)|𝑧=𝑧𝑝 𝑀𝑏(𝑧)|𝑧=𝑧𝑝 𝑀𝑏 −1(𝑧)|𝑧=𝑧𝑝−1 𝑀𝑤(𝑧)|𝑧=𝑧𝑝−1 (5) 𝑇𝑝+1←𝑝−1 is the transfer matrix, which is a product of four matrices and connects the coefficients of the wave functions of the (𝑝 + 1)𝑡ℎand (𝑝 − 1)𝑡ℎwell. the idea of transfer matrix can be extended to envelope the whole sl system. therefore, ( 𝐴2𝑛+1 𝐵2𝑛+1 ) = 𝑇(2𝑛+1)←1 ( 𝐴1 𝐵1 ) (6) 2.2 symmetric quadruple well (sqw) consider a sqw, a system formed by four alternate wells and three barriers between them using, for example, alternating layers of gaas and al0.3ga0.7as in such a way that the central barrier divides the system into symmetric left and right halves as shown in fig. 1(b). r and l in the fig. 1(b) are the extreme right and extreme left high potential barriers going into vacuum level. the wave functions in r and l regions have a single exponentially decreasing term. the width of the barrier and the wells are taken to be 𝑙𝑏and 𝑙𝑤 respectively. the odd greek numerals as subscript on 𝜓 represent, from right, the four wells and even numbered subscripts give the three barriers. since the potential is symmetric, the solutions of the schroedinger equations 2(a) and 2(b) separate into symmetric and anti-symmetric wave functions. symmetric solutions are given by 𝜓𝑅(𝑧) = 𝐷𝑅𝑒−𝑘𝐷𝑧 𝜓𝑉𝐼𝐼 𝑠 (𝑧) = 𝐴7 𝑠 sin(𝑘𝑤𝑧) + 𝐵7 𝑠 cos(𝑘𝑤𝑧) 𝜓𝑉𝐼 𝑠 (𝑧) = 𝐴6 𝑠 sinh(𝑘𝑏𝑧) + 𝐵6 𝑠 cosh(𝑘𝑏𝑧) (7) 𝜓𝑉 𝑠 (𝑧) = 𝐴5 𝑠 sin(𝑘𝑤𝑧) + 𝐵5 𝑠 cos(𝑘𝑤𝑧) 𝜓𝐼𝑉 𝑠 (𝑧) = 𝐶𝑠 cosh(𝑘𝑏𝑧) here, 𝑘𝑤and 𝑘𝑏were defined earlier and 𝑘𝐷 = √2𝑚𝑤(𝑉𝐷 − 𝐸) ℏ2⁄ , where 𝑉𝐷is the vacuum level. the symmetric solutions 𝜓𝐼𝐼𝐼 𝑠 (𝑧), 𝜓𝐼𝐼 𝑠 (𝑧),𝜓𝐼 𝑠(𝑧) and 𝜓𝐿 𝑠(𝑧)are obtained by changing 𝑧 to – 𝑧 in 𝜓𝑉 𝑠 (𝑧), 𝜓𝑉𝐼 𝑠 (𝑧), 𝜓𝑉𝐼𝐼 𝑠 (𝑧)and 𝜓𝑅 𝑠 (𝑧) respectively and without changing the sign of 𝜓(𝑧). the anti-symmetric solutions are obtained in an analogous manner and are denoted by superscript ‘a’. the solution in the central barrier is given by a sinh rather than a cosh. change of sign of 𝑧 is accompanied by simultaneous change in the sign of the corresponding 𝜓. s. shrestha et al. / bibechana 18 (1) (2021) 91-99 94 fig. 1: (a) rectangular superlattice of equal barrier height vo. (b) spatially symmetric quadruple well (sqw) with a barrier in the center. the boundary conditions are applied at each point separating a barrier and a well and also at r and at l to obtain expressions for the energy levels corresponding to the symmetric and antisymmetric states. all the coefficients in different regions can be related to the coefficient 𝐶𝑠or𝐶𝑎 in the central region (barrier region iv). after some tedious algebra we get tan(𝑘𝑤 𝑠 𝑧4) = (− 𝐵1 𝑠 𝐴1 𝑠 )[1+( 𝑘𝑤 𝑠 𝑘𝐷 )( 𝑚𝑏 𝑚𝑤 ) 𝐴1 𝑠 𝐵1 𝑠 ] [1−( 𝑘𝑤 𝑠 𝑘𝐷 )( 𝑚𝑏 𝑚𝑤 ) 𝐵1 𝑠 𝐴1 𝑠 ] = (− 𝐵1 𝑠 𝐴1 𝑠) 𝐹 (𝐴1 𝑠 , 𝐵1 𝑠 , 𝑘𝑤 𝑠 𝑘𝐷 ), which gives, 𝑘𝑤 𝑠 𝑧4 = 𝑛𝜋 + tan−1 [(− 𝐵1 𝑠 𝐴1 𝑠 ) 𝐹 (𝐴1 𝑠 , 𝐵1 𝑠 , 𝑘𝑤 𝑠 𝑘𝐷 )] (8) since vd is very large in comparison to v0, the wave vector ratio 𝑘𝑤 𝑠 𝑘𝐷 is small. this leads the function 𝐹 (𝐴1 𝑠 , 𝐵1 𝑠, 𝑘𝑤 𝑠 𝑘𝐷 ) to converge to 1[14]. the final relation is, 𝑘𝑤 𝑠 ( 3 2 𝑙𝑏 + 2 𝑙𝑤) = 𝑛𝜋 + tan−1 (− 𝐵1 𝑠 𝐴1 𝑠) = 𝑛𝜋 + tan−1 (− 𝛽1 𝑠 𝛼1 𝑠) (9) where 𝐵𝑛 𝑠 𝐴𝑛 𝑠 = 𝛽𝑛 𝑠 𝛼𝑛 𝑠 left hand side relation in (9) is a function of energy assuming the barrier parameters are known and the right hand side is accessible in terms of energy. thus, by plotting left hand and right hand side functions with energy the intersecting points would give the symmetric energy eigen values. the evaluation of the right hand side function can be done using the value of 𝐵1 𝑠 𝐴1 𝑠 in (8). let t be the transfer matrix that connects the wave function coefficients of region i to region iii. ( a3 s b3 s) = [ t11 t12 t21 t22 ] ( a1 s b1 s) on solving and rearranging the terms we arrive at the following relation, ( 𝐵1 𝑠 𝐴1 𝑠 ) = [𝑇11−𝑇21 𝐴3 𝑠 𝐵3 𝑠 ] [𝑇22 𝐴3 𝑠 𝐵3 𝑠 −𝑇12] (10) furthermore, the evaluation of 𝐶𝑆 can be done by normalization condition for the system as, |𝐶𝑠|2 {∫ |−𝛼1 𝑠sin(𝑘𝑤𝑧) + 𝛽1 𝑠cos(𝑘𝑤𝑧)|2𝑑𝑧 −𝑧3 −𝑧4 + ∫ |−𝛼2 𝑠sinh(𝑘𝑏𝑧) + 𝛽2 𝑠cosh(𝑘𝑏𝑧)|2𝑑𝑧 −𝑧2 −𝑧3 + ∫ |−𝛼3 𝑠sin(𝑘𝑤𝑧) + 𝛽3 𝑠cos(𝑘𝑤𝑧)|2𝑑𝑧 −𝑧1 −𝑧2 + ∫ |cosh(𝑘𝑏𝑧)|2𝑑𝑧 𝑧1 −𝑧1 + ∫ |𝛼3 𝑠sin(𝑘𝑤𝑧) + 𝑧2 𝑧1 𝛽3 𝑠cos(𝑘𝑤𝑧)|2𝑑𝑧 + ∫ |𝛼2 𝑠sinh(𝑘𝑏𝑧) + 𝑧3 𝑧2 𝛽2 𝑠cosh(𝑘𝑏𝑧)|2𝑑𝑧 + ∫ |𝛼1 𝑠sin(𝑘𝑤𝑧) + 𝑧4 𝑧3 𝛽1 𝑠cos(𝑘𝑤𝑧)|2𝑑𝑧} = 1 (11) the replication of similar technique for antisymmetric states leads to the solution of energy value and wave function coefficient 𝐶𝑎for the particles in this state. calculations on concrete systems, detailed later, show that consecutive symmetric and anti-symmetric energy levels are very close, resulting in oscillations between the levels. the total travelling wave solution in the sqw is 𝜓(𝑧, 𝑡) = 1 √2 [𝜓s exp (−𝑖 2𝜋 ℎ 𝐸𝑠𝑡) + 𝜓a exp (−i 2π h eat)] (12) s. shrestha et al. / bibechana 18 (1) (2021) 91-99 95 where 𝐸𝑠 and 𝐸𝑎 are nearby symmetric and antisymmetric energy values. the probability to find particle at any time 𝑡 is given by: 𝑃(𝑧, 𝑡) = |𝜓(𝑧, 𝑡)|2 𝑃(𝑧, 𝑡) = 1 2 [𝜓𝑠2 + 𝜓𝑎2 + 𝜓s𝜓a (exp (−𝑖 2𝜋 ℎ (𝐸𝑎 − 𝐸𝑠)𝑡) + exp (𝑖 2𝜋 ℎ (𝐸𝑎 − 𝐸𝑠)𝑡))] 𝑃(𝑧, 𝑡) = 1 2 [𝜓𝑠2 + 𝜓𝑎2 + {𝜓s𝜓a (exp (−𝑖 2𝜋 ℎ ∆𝐸𝑡) + exp (𝑖 2𝜋 ℎ ∆𝐸𝑡))}] therefore, 𝑃(𝑧, 𝑡) = 1 2 [𝜓𝑠2 + 𝜓𝑎2 + 2𝜓s𝜓acos ( 2𝜋 ℎ ∆𝐸𝑡)] this equation gives the probability to find the particle at time ‘t’ in the neighborhood of spatial region z and can be used to study the time evolution of system including its tunneling behavior in sqw. 3. results and discussion we consider 𝐺𝑎𝐴𝑠 and 𝐴𝑙𝑥𝐺𝑎(1−𝑥)𝐴𝑠 sl system with sqw potential in which the width of the well and barrierare 4 nm and 5 nm respectively. the height of barrier depends on the concentration of 𝐴𝑙 in 𝐴𝑙𝑥𝐺𝑎(1−𝑥)𝐴𝑠 and is given by 0.067 + 0.083𝑥. with 𝑥 = 0.3,the height of barrier is taken to be 228 𝑚𝑒𝑉[17]. effective masses of electrons in the well (𝑚𝑤) and in the barrier (𝑚𝑏) regions are taken as 0.067𝑚𝑒 and 0.091𝑚𝑒 [18] respectively. fig. 2(a) shows the graphical solution for energy levels in symmetric state corresponding to the value of the right and of the left sides of the eq. (9). the plot of𝑌1 = 𝑘𝑤 𝑠 ( 3 2 𝑙𝑏 + 2 𝑙𝑤) is in solid (black) line and𝑌2 = 𝑛𝜋 + tan−1 [(− 𝐵1 𝑠 𝐴1 𝑠 )] is plotted in dash (red), dot (blue),dash dot(magenta) and short dash dot (navy) styles color (color online) for n=1, 2, 3 and 4 respectively. the eigen values of energy for the symmetric states for n=1, 2 and 3, in ev, are 0.0147000839, 0.136077023 and 0.156888216 respectively. fig. 2(b) shows similar plots of 𝑌1 and 𝑌2 in the same colors and styles for n=1 to 4 for anti-symmetric states. the anti-symmetric energy eigen values are 0.0147488590, 0.137090183 and 0.15718252 in ev the states n=1,2 and 3 respectively. for simplicity, only the lowest symmetric and antisymmetric state for n=1 are considered in the calculation. the energy of the lowest antisymmetric state is slightly higher as compared to the symmetric state, which is clearly seen in inset of the fig. 2(c). the difference ∆𝐸 is 0.0000487751 𝑒𝑉 and is also referred as ‘energy ting’[16]. fig. 3 shows the variation of the lowest (𝑛 = 1) lying anti-symmetric dash (red) and symmetric dot (blue) wave functions as a function of the width of the sqw. it shows the amplitude of the two waves, which are in phase in the right half and amplitude peaks in this region. they are out of phase in the left hand side and cancel each other. the time evolution of the combined wave function is displayed in fig. 4.(a), (b) and (c), which show the probability of finding a particle with position within the sqw at different instants of time. at t=0, fig. 4(a) shows higher probability in the right half of the system. it gradually decreases and becomes nearly equal in both half at t = t/4, as shown in fig. 4(b). then, the peak starts to increase in the left half of the sqw. t= t/2, the probability of finding the particle in the left half of the system s. shrestha et al. / bibechana 18 (1) (2021) 91-99 96 0.0 0.1 0.2 0 4 8 12 l b =5 nm m w =0.067 m e m b =0.091 m e (a) v o =228 mev l w =4 nm f u n c ti o n y 1 a n d y 2 energy in ev . fig. 2: (a) plot ofy1 = kw s ( 3 2 lb + 2 lw)in solid (black) line andy2 = nπ + tan−1 [(− b1 s a1 s)] in dash (red), dot (blue), dash dot (magenta) and short dash dot(navy) styles color (color online) for n=1, 2, 3 and 4 respectively for symmetric states. the intersecting values of abscissa give the energy of symmetric states. (b) similar plot of y1 in solid (black) line and y2 in different style and color line showing the energy of anti-symmetric states. (c) expanded view of the lowest symmetric in dash (red) and anti-symmetric in solid (blue) states (online) of the curvesare shown in the inset view. 0.0 0.1 0.2 0 4 8 12 l b =5 nm m w =0.067 m e m b =0.091 m e v o =228 mev l w =4 nm (b) f u n c ti o n y 1 a n d y 2 energy in ev 0.0147000 0.0147001 2.49950 2.49975 2.50000 0.00 0.05 0.10 0.15 0 2 4 6 f u n c ti o n y 1 a n d y 2 energy in ev (c) symmetric antisymmetric energy in ev e s. shrestha et al. / bibechana 18 (1) (2021) 91-99 97 fig. 3: the lowest symmetric and anti-symmetric wave functions, shown by solid (blue) and dash (red) line (color online)respectively versus the net width of the sqw. here, v0=228 mev, width of each barrier region (lb)=5 nm and width of each well region (lw)=4 nm. fig. 4: probability distribution of finding a charged particle in different spatial region within the sqw with height of barrier region v0= 228 mev, width of barrier region lb=5nm at time(t)=0, t= t/4 and t=t/2 shown by solid (black), dash (red) and dash-dot (blue) (color online) line respectively. -10 0 10 -40 -20 0 20 40 lowest anti-symmetric  a lowest symmetric  s w a v e a m p li tu d e  position (z) in nm -10 0 10 0.0 0.5 1.0 0.0 0.5 1.0 time (t)=51 time (t)=0time (t)=102 p ro b a b il it y a m p li tu d e p (z ,t ) position (z) in nm s. shrestha et al. / bibechana 18 (1) (2021) 91-99 98 becomes the largest, as shown in fig. 4(c). thus, the particle which initially was in the left region of system tunneled through all the barriers to reach to the right part of the system, giving rise to tunneling-oscillation phenomenon. the time taken by particle to tunnel through the barrier is found to be 102 units of time, which is half of the time period of oscillation measured in the units of ( ℎ 𝑒∗10−2). the total time period of oscillation is 𝑇 = 2 ∗ 102 ∗ ( ℎ 𝑒∗10−2) i.e. 8.479 ∗ 10−11 𝑠. it corresponds to the tunneling frequency equal to11.79 𝐺𝐻𝑧. the tunneling behavior of electron in symmetric double well has been studied by e.p. lopez 2006 [16] with the barrier height(𝑉0) as 108 𝑚𝑒𝑉 and barrier width (𝑙𝑏) as 0.2 a0 and the width of the well(𝑙𝑤) as0.6 𝐴0also. the authors have calculated the frequency of oscillations to be 25.356 𝐺𝐻𝑧. it is found that as the barrier height is increased, the difference in energy values decreases. this increases the time period and the time taken by the particle to tunnel through it. for sufficiently high barriers the particle may not tunnel through, because the frequency of tunneling decays to a very small value. in case of very high barrier quantum well structures in which the frequency of oscillation is almost zero. this model of tunneling oscillation is expected to be useful for the study of the strength of the barrier and oscillation behavior of electron in symmetric quantum well/barrier systems. in addition, the fast switching semiconductor devices and high frequency oscillators can be studied by the proposed method and using the related results. 4. conclusion a method of exact solution for energy level and wave function of the particle in sl is studied using t-matrix. the tunneling behavior of the electron in sqw is described with the help of time evolution. the value of energy ting and tunneling frequency for the electron described in sqw are estimated to be∇𝐸1 = 0.0000487751𝑒𝑉 and 𝜈𝑇 = 11.79 𝐺𝐻𝑧 respectively. the method can be extended for larger number of wells as well for fast switching semiconductor devices in 𝐺𝐻𝑧 region. references [1] c. kittle, introduction to solid state physics, 7th edition, john wiley &sons (asia) pvt ltd, singapore, 2002. 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[18] g. bastard , wave mechanics applied to semiconductorheterostructure, france: les edition de physique, 1988 https://www.researchgate.net/scientific-contributions/73112268_helena_moravcova?_sg%5b0%5d=atervgbhksh271z-loxkejdnu2dkqlpgmrggt_kafgxsi0h4czorhcsrprthrp6uim5y4zs.8hhkys3-6oudp7aju5fhnm7e-tzhbvbdy4e_0de_kjflp_v4dh1p9jwcj6lu7bbgapmqagngi3cpiphsr4blsa&_sg%5b1%5d=qd8deaff67pwuwtasmpz3-xf14k0jgn1cu475bnlo2ykxcw2k2tumwgv4b_qiffex9_zrla.z9umpsvaer_gcx3h709tqhcjgybf0r_ejic815ed76eoxb4d-a9xv-ievu4pb4mtzplds4rynzcxt6chete6hg https://www.researchgate.net/profile/jan_voves?_sg%5b0%5d=atervgbhksh271z-loxkejdnu2dkqlpgmrggt_kafgxsi0h4czorhcsrprthrp6uim5y4zs.8hhkys3-6oudp7aju5fhnm7e-tzhbvbdy4e_0de_kjflp_v4dh1p9jwcj6lu7bbgapmqagngi3cpiphsr4blsa&_sg%5b1%5d=qd8deaff67pwuwtasmpz3-xf14k0jgn1cu475bnlo2ykxcw2k2tumwgv4b_qiffex9_zrla.z9umpsvaer_gcx3h709tqhcjgybf0r_ejic815ed76eoxb4d-a9xv-ievu4pb4mtzplds4rynzcxt6chete6hg https://www.researchgate.net/deref/http%3a%2f%2fdx.doi.org%2f10.1109%2fasdam.2002.1088492?_sg%5b0%5d=ck1kqko8ubs02oinxelpu8ylea1eilnlzgk378xk3kyi8fjfkcsxevrrvyoihayqu28npk6eyygfq6jwtcgsgms9aa.w70bfdhagumls-havfac3q1q3dvxpb1czdol4ovphyysgpeiv1d7ac2mibm7f0yjp5ntdck_5lzxjgtywbbt-a https://www.researchgate.net/profile/kf_renk?_sg%5b0%5d=xpvv87s-cgkh5opaduozfr5vhwhyd79rrcudsperwfodtuzxo1bxavczcp4kgs7ub9ccboo.xb7izt2svggvrqvrhdulcqtl0ixovgowqb-iv1cvbnfm-5frbqukjif_00sisnigvfvnsy7ylvwrxg2-r7gyrg&_sg%5b1%5d=ylyi8pfi3lfp0m8t3uhplpvvfplsttvpplu1c8vjitsazeuyxy2ixt7ciwqvwlognekr4zu.n85--td_puxm_lzfh4nl-otdm4_crgm2hu__4qlxr3u5jsw9yml5zhxkfva_-wq6oq9zigfwrnonazwcfwfwpa https://www.researchgate.net/scientific-contributions/11904743_b_i_stahl?_sg%5b0%5d=xpvv87s-cgkh5opaduozfr5vhwhyd79rrcudsperwfodtuzxo1bxavczcp4kgs7ub9ccboo.xb7izt2svggvrqvrhdulcqtl0ixovgowqb-iv1cvbnfm-5frbqukjif_00sisnigvfvnsy7ylvwrxg2-r7gyrg&_sg%5b1%5d=ylyi8pfi3lfp0m8t3uhplpvvfplsttvpplu1c8vjitsazeuyxy2ixt7ciwqvwlognekr4zu.n85--td_puxm_lzfh4nl-otdm4_crgm2hu__4qlxr3u5jsw9yml5zhxkfva_-wq6oq9zigfwrnonazwcfwfwpa https://www.researchgate.net/deref/http%3a%2f%2fdx.doi.org%2f10.1016%2fj.physleta.2011.05.038?_sg%5b0%5d=38pdxok6vbjyoqbdgnjwbnza9pkwdzx03ndxmaa2f14rwyn12gl3axteecodu9a5he0i7ymy0w3ffho5ttsua8s4wg.reecrw78b4g019jdglmolfmwaxf39ql3ehamflgnxnrenkmax4e1_ac-sgsedhufp6irkcnbefzrmf8ltvtfjg https://doi.org/10.1103/physrevb.63.075302 https://www.researchgate.net/deref/http%3a%2f%2fdx.doi.org%2f10.1103%2fphysrevb.67.085312#_blank http://avs.scitation.org/author/yoo%2c+k+h http://avs.scitation.org/author/aggarwal%2c+r+l https://doi.org/10.1103/physrevb.33.2941#_blank devendra sir cover page copy.jpg bibechana 17 (2020) 42-49 42 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal study of dust color temperature and visual extinction distribution of a far infrared cavity at 60 and 100 µm iras map around the agb star at galactic latitude 8.6⁰ a. k. gautam * , b. aryal ** central department of physics, t.u., kirtipur, nepal email: arjungautamnpj@gmail.com * , ** baryal@tucdp.edu.np article information received: july 02, 2019 accepted: september 14, 2019 keywords: far infrared cavity far infrared loops agb stars dust color temperature dust mass abstract the dust-grain structure in the far infrared region under iras (infrared astronomical satellite) survey was studied using sky view virtual observatory. in order to find the possible far infrared cavity, we used simbad database. in this paper, we discuss about the dusty environment of a far infrared cavity around the agb star located at r.a. (j2000) =01 h 41 m 01 s and dec (j2000) = 71 o 04’ 00” lying within far infrared loop g125+09 in the far infrared iras maps. a cavity like structure (major diameter ∼ 2.55 pc & minor diameter ∼ 0.77 pc) is found to lie at r.a. (j2000)= 01 h 46 m 57.2 s and dec (j2000)= 71 o 24’ 57.1”, located at a distance ∼ 220 pc from the star. we studied the distribution of flux density, dust color temperature, dust mass, inclination angle, visual extinction and fir spectral distribution of the cavity. we further studied the distribution of planck function along extension and compression. the dust color temperature is found to lie in the range (19.7±0.65) k to 21.1±0.35) k which shows the cavity is isolated and stable. product of visual extinction and dust color temperature is found to be less than one. a possible explanation of the results will be discussed. 1. introduction there are three types of stars according to their mass. they are low mass stars, intermediate mass stars and massive stars. their proportion in existence is 1: 10: 1000. most of the stars spend their half-life in main sequence. when fusion of hydrogen is exhausted in the main sequence, the star leaves the main sequence and rises up towards right side. this stage of evolution is called red giant branch (rgb) phase. during this phase, the star expands but core contracts as a result luminosity increases. as the luminosity reaches nearly 10 3 l⊙, inert he core burns means he shell flash takes place and the star moves horizontally with almost constant luminosity. this stage of stellar evolution is called horizontal branch (hb). after around 10 8 years, he core exhausts. at this condition, he core leaves its space and two burning shells i.e. h-burning shell and hethis work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.25839 http://nepjol.info/index.php/bibechana mailto:baryal@tucdp.edu.np https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.25839 a.k. gautam, b. aryal / bibechana 17 (2020) 42-49 43 burning shell are produced leaving c/o core as a result the star moves up parallel to rgb which is called asymptotic giant branch (agb) herwig [1]. for low mass stars having masses < 0.8m⊙, there is not sufficient temperature for fusion of hydrogen so that they can't change in to asymptotic giant branch (agb) stars. actually low and intermediate mass stars in the range (0.8m⊙ < m > 8.0m⊙) are the agb stars which is the final nuclear burning stage. this phase of evolution is characterized by two nuclear burning shell of hydrogen and helium where hydrogen burning shell lies below the convective envelope and helium burning shell lies above the electron-degenerate core of carbon and oxygen, or for the most massive agb stars a core of oxygen, neon, and magnesium [1]. this agb stage is characterized by low surface effective temperatures (below 3500k) and intense mass loss (from10 −7 to 10 −4 m⊙yr −1 ) [2]. interstellar medium consists of matter and field. matter contains gas and dust. first evidence of dust in the ism was first justified by interstellar extinction curve. dusty circumstellar envelopes will form at the distance of several stellar radii. dust grains in the envelopes absorb stellar radiation say uv radiation and re-emit infrared radiation so agb stars are important infrared sources. the mass loss process plays an important role in the evolution of agb stars. statistics of a large sample of agb stars would help to constrain the evolution of dust envelope. there are mainly three types of agb stars: the o-rich with c/o < 1 and mainly silicate-type grains in the outflow, c-rich with c/o > 1 and mainly carbonaceous grains in the envelopes and stype with c/o ~ 1. due to different dust compositions of these agb stars, different infrared spectral features are obtained which can be used to distinguish the groups of the stellar objects . he-core burning phase is about 10 times shorter than the h-core burning shell so that the he-core burning leaves a c/o core behind that is surrounded by both a hydrogen and helium burning shell. for low and intermediate mass stars, carbon doesn't ignite and c/o core contracts and becomes electron degenerate. during the early agb phase, the abundance of he in the center goes to zero where he-burning continues in a shell around a degenerate c-o core. in the meantime, the hlayer around the helium shell expands and cools sufficiently so that hydrogen burning shell is extinguished. convective envelope sets in and moves inwards and second dredge-up takes place. he shell is the main source for nuclear production so that it burns outward and reaches the hydrogen shell. in case of thermally pulsating agb phase, helium shell becomes thin and remains thermally unstable as a result thermal pulses are produced. in each thermal pulse, luminosity of helium shell nearly approaches 10 8 l⊙[3].the production of such high luminosity in helium shell is called he shell flash or thermal pulse which is used to expand the outer layers. such strong expansion drives the h shell cooler and less dense as a result h shell is extinguished. the inner edge of deep convective envelope can then move inward and mix to the surface products of internal nucleosynthesis. this mixing process which occurs periodically after each tp is known as third dredge-up which is the mechanism for producing carbon stars. during tpagb phase, main dominant source of nuclear energy is the hydrogen shell. thermally pulsating agb phase is the phase after the first thermal pulse to the time when the star ejects its envelope. in this paper, we study the physical properties of far infrared cavity, that we investigated during a systematic search on iras maps, located close to a carbon-rich agb star named agb01+71 at 8.6 o galactic latitude. in section 2, we describe methods of calculation. a brief description of the result and discussion will be given in the section 3. finally, we conclude our results in the section 4. 2. methods we found a far infrared cavity at 60 and 100 micron iras maps around an asymptotic giant branch star named agb 01+71. we briefly describe a method for calculation of dust color temperature, dust mass and visual extinction of the far infrared cavity around the agb star. additionally far infrared spectral distribution of the cavity is also described. a.k. gautam, b. aryal / bibechana 17 (2020) 42-49 44 fig. 1: (a) and (b) are the jpeg images of the far infrared cavity at 60 μm and 100 μm iras maps around the agb 01+71 centered at r.a. (j2000) = 01 h 46 m 57.2 s , dec. (j2000) = 71 0 24' 57.1”, located within far infrared loop g125+09. dust color temperature for the calculation of dust color temperature, we adopt the method proposed by schnee et al. [4] and dupac et al. [5]. according to schnee et al. [4], dust color temperature of the emission at a wavelength λi is given by td = −96 in{r+(0.6)(3+β)} (1) where , r = f(60 μm) f(100 μm) f(60 µm) and f(100 µm) are the flux densities in 60 µm and 100 µm respectively and eq. (1) is used for calculation of the dust color temperature. the spectral emissivity index (β) depends on dust grain properties like composition, size, and compactness. for a pure blackbody would have β = 0, the amorphous layer-lattice matter has β ∼1, and the metals and crystalline dielectrics have β∼2 which is used in our calculations. planck function the value of planck's function depends on the wavelength (frequency), and hence the temperature. finally it is used to calculate dust mass. in 1900, planck proposed a relation which is named as planck's function. according to him, the planck's function is given by 𝐵(𝜈, 𝑇) = 2ℎ𝜈3 𝑐2 [ 1 𝑒 ( ℎ𝜈 𝑘𝑇 ) −1 ] (2) where, h = planck’s constant, c = velocity of light, ν = frequency at which the emission is observed, λ = wavelength of the radiation and t = temperature of each pixel. dust mass for the calculation of dust mass, first we need the value of flux density (fν) at 100 μm maps and we use the expression given by [6], md = 4aρ 3q(ν) f(ν)d2 b(ν,t) (3) where, weighted grain size (a) = 0.1 μm, grain density (ρ) = 3000 kg m -3 , grain emissivity (qν) = 0.0010 (for 100 μm) [7]. so the equation (3) reduces to mdust = 0.4      sd2 b( t) (4) we use equation (4) to calculate dust mass of the cavity. inclination angle the inclination angle (i) is the angle between the line-of-sight and the normal vector of the plane of the loops. here, the long axis of kk-loops can be assumed to be inclined by a certain angle with respect to the plane of the sky. in such case, the inclination angle can be estimated using holmberg [8] formula: cos2i = b2 a2 -q2 1-q2 (5) (b) iras 100 micron (a) 1.00x1.00 iras 60 µm 1.0 0 x1.0 0 a.k. gautam, b. aryal / bibechana 17 (2020) 42-49 45 where b/a is the axial ratio measured and q is the intrinsic flatness of the cavity. as suggested by holmberg [8] for oblate spheroid structure, we used the value of intrinsic flatness q = 0.33. estimation of visual extinction for estimation of visual extinction, wood et al. [9] has provided an empirical formula using optical depth at 100 µm. according to them, we have 𝐴𝑣(𝑚𝑎𝑔) = 15.078 (1 − 𝑒− 𝜏100 641.3) (6) where 𝜏100 = 𝐹λ(100𝜇𝑚) 𝐵λ(100𝜇𝑚,𝑇𝑑) (7) is optical depth at 100 µm wavelength. here fλ is flux density and bλ is planck function at 100 µm wavelength. 3. result and discussion structure: contour maps using sky view virtual observatory and its jpeg and fits images in the far infrared region, we found an isolated far infrared cavity in the 100 µm and 60 µm iras maps at r.a. (j2000) = 01 h 46 m 57.2 s , dec. (j2000) = 71 0 24' 57.1”, located within far infrared loop g125+09. we used aladin2.5 software in fits image of sky view virtual observatory of the cavity and have studied size, dust color temperature, dust mass, inclination angle, visual extinction and spectral distribution of the fir cavity. we selected contour level 1-85 in such a way that it circles the cavity. jpeg images of the cavity at 60 µm and 100 µm iras map are shown in the fig.1 (a) and (b) respectively. distribution of flux density flux densities at 60μm and 100μm have been measured by using aladin 2.5 software. distribution of flux density within the core region of the cavity has been studied. we have plotted a graph between (100) and f(60) with the help of origin 5.0 which is shown in figure 2(a) to calculate average dust color temperature. from the linear fit, slope of the line was 0.17, correlation coefficient (r)= 0.68. the linear equation of the fitted line is, y = -1.01+0.17x. using the slope of best fitted plot, average dust color temperature has been found as 22.2 k which is used to calculate error in calculated dust color temperature. again distribution of flux density at 100 μm flux density within the contour level with right ascension (r.a.) and declination (dec.) are plotted in contour map by using origin 8.0 and is shown in figure 2(b). graph shows that all the fluxes from minimum to maximum lie within the contour level. most of the maximum flux regions lie at the boundary. dust color temperature and its variation schnee at. al.[4] has derived an expression for calculation of dust color temperature. gautam and fig.2: (a) the 100μm verses 60μm flux density in the region of interest and (b) contour map at 100μm flux density where the agb star is located at the center r.a. = 01h 46m 57.2s, dec. (j2000) = 710 24' 57.1”. agb 01+71 1.00x1.00 a.k. gautam, b. aryal / bibechana 17 (2020) 42-49 46 aryal [10] used the formula for calculation of dust color temperature. we also adopted similar method for calculation of dust color temperature in the core region of our interest. for the calculation of temperature we choose the value of β = 2 following the explanation given by dupac at.al. [5]. variation of temperature with corresponding r.a.(j2000) and dec.(j2000) are plotted by using origin 8.0 and the graph is shown in figure 3(a). graph shows that temperature distributions are in separate cluster but minimum temperature region is little bit shifted from minimum flux density which is unusual behavior. such type of nature is obtained due to external factors. the region in which minimum and maximum temperature is found in the range (19.7±1.25) k to (21.1±0.55) k with low offset temperature. such low offset temperature variation shows that there is fig. 3: (a) contour map of dust color temperature and (b) gaussian fit of dust color temperature. the far infrared cavity is centered at r.a. = 01 h 46 m 57.2 s , dec. (j2000) = 71 0 24' 57.1”. symmetric outflow or symmetric distribution of density and temperature. it further suggests that particles are independently vibrating. gaussian fit of dust color temperature is gaussian like with positive skewness shown in figure 3(b). when this result is compared with the result obtained in jha et al. [11] where temperature variation is 19.4 k to 25.3 k so our result is also comparable with that result. in the contour map, minimum flux and minimum temperature region are shifted which is due to some external factors possibly due to agb wind. size of the structure major and minor diameter of the structure can be easily calculated by using a simple expression i.e., l = r × θ, where r = 220 pc is the distance of the structure and θ = pixel size (in radian). after calculation the major and minor diameter of the cavity are found to be 2.55 pc and 0.77 pc respectively. thus, the size of the structure is 2.55 pc × 0.77 pc . dust mass estimation and its variation for the calculation of dust mass, we need the distance of the structure (cavity) from earth. the distance of the structure is 220 pc [3]. after calculation of dust color temperature and planck function, we have calculated mass of the cavity. average mass of each pixel has found to be 4.91 x 10 25 kg and total mass of the structure is 1.86 x 10 28 kg i.e 0.0094m⊙. but mass of dust obtained around white dwarf wd 1003-44 in aryal et al. [12] is 0.08m⊙. it means mass of dust around agb star is less than white dwarf. distribution of dust mass in the contour map is shown in figure 4(a) which shows that minimum temperature region is denser and lie at the maximum mass region in the selected contour which is usual trend means distribution of mass follows cosmological principle. it means distribution of dust mass follow cosmological principle i.e their distribution is homogeneous and isotropy. figure 4(b) is the gaussian fit where the agb 01+71 1.00x1.00 (a) a.k. gautam, b. aryal / bibechana 17 (2020) 42-49 47 data more or less follow gaussian distribution with negative skewness. distribution of planck function with diameters figure 5(a) and (b) show the distribution of planck function along major and minor diameters where the dust particles are oscillating non-uniformly with very low correlation coefficient (r). there is no systematic trend of their distribution in both cases so that the dust particles about the diameters are not in thermal equilibrium means they are oscillating in order to get dynamical equilibrium [10]. variation of visual extinction figure 6 (a) is contour map of visual extinction and 6(b) is a linear fit of the scattered plot between visual extinction and dust color temperature. from figure 3(a) and 6(a), it is found that higher the temperature, lower the visual extinction and viceversa. the figure 6(b) shows a systematic trend with high correlation coefficient i.e., -0.92, which shows that there is best correlation between the data. from the linear fit , we found a relation between visual extinction and dust color temperature. the relation is (av x td) < 1 which also supports our result. fir spectral distribution a graph between wavelength and flux density is called spectral distribution. we studied spectral distribution of the far infrared cavity around the agb star named agb01+71 where we found positive slope in transition from 12 µm to 25 µm and 60 µm to 100 µm but there is negative slope in transition from 25 µm to 60 µm which is one finding of this work shown in figure 7. 4. conclusion the physical properties of the far infrared cavity around the agb01+71 star located within far infrared loop g125+09 are measured and analyzed. from the calculated value, distribution of flux density, dust color temperature, planck function, dust mass and visual extinction of the cavity were studied. following are the conclusions: fig.4: (a) contour map of dust mass and (b) gaussian fit of dust mass. the far infrared cavity is centered at r.a. = 01 h 46 m 57.2 s , dec. (j2000) = 71 0 24' 57.1”.  the major and minor diameter of the far infrared cavity was found to be 2.55 pc and 0.77 pc respectively.  the maximum temperature (21.1 ± 0.25) k was found at r.a.(j2000) = 27.820 & dec.(j2000) = 71.310 27.80 and minimum temperature (19.7 ± 0.65) k was found at r.a.(j2000) = 26.780 & dec.(j2000) = 71.26026.80, with low offset temperature which suggests that the cavity is isolated and stable.  inclination angle is found to be 910 i.e., edgeon.  in general, minimum flux and minimum temperature lie at same point in the pixel but in this case minimum temperature is shifted which may be due to external factors, possibly wind emitted from the agb star. similarly maximum temperature region is the densest region which is normal behavior. it means distribution of dust mass follow cosmological agb 01+71 1.0 0 x1.0 0 (a) a.k. gautam, b. aryal / bibechana 17 (2020) 42-49 48 principle.  total mass of the cavity was found to be 1.86 x 1028 kg and that of average mass was 4.91 x 1025 kg.  linear fit of scattered plot between visual extinction and dust color temperature shows that there is a systematic trend and visual extinction decreases with increase in dust color temperature and vice-versa.  distribution of planck function along extension and compression is non-uniform so that dust particles are not in thermal equilibrium along the diameters. fig.(5):(a) linear fit of scattered plot between major diameter and planck function and (b) linear fit of scattered plot between minor diameter and planck function of the cavity centered at r.a. = 01h 46m 57.2s, dec. (j2000) = 710 24' 57.1”.  fir spectral distributions of the cavity showed similar nature in transition from 12 µm to 25 µm and 60 µm to 100 µm. negative slope in transition from 25 µm to 60 µm is our finding regarding fir spectral distribution in cavities. this suggests that the number density of dust particles are found to be less (than expected) in 60 µm region. we intend to study the role of cabon-rich agb star to form the far-infrared cavity in the future. fig. 6: (a) contour map of visual extinction and (b) a linear fit of the scattered plot between visual extinction and dust color temperature of the far infrared cavity centered at r.a. = 01 h 46 m 57.2 s , dec. (j2000) = 71 0 24' 57.1”. (a) (b) (a) (b) a.k. gautam, b. aryal / bibechana 17 (2020) 42-49 49 . fig. 7: far infrared spectral distributions of the cavity located nearby agb star agb01+71. acknowledgements we are grateful to the department of astro-particle physics, innsbrck university, specially to prof. r. weinberger for invoking us to work on dusty environments around agb stars. this research has made use of sky view virtual observatory, aladin v2.5 and nasa/ipac extragalactic database (ned). references [1] f. herwig, evolution of asymptotic giant branch stars, annu. rev. astron. astrophysics 43 (2005) 435-479. https://doi.org/10.1146/annurev.astro.43.072103.15 0600 [2] l. seiss, m. l. pumo, evolutionary properties of massive agb stars, memorie della societa astronomica italiana 77 (2006) 822-827. [3] a. l. karakas, j. c. lattanzio, o. r. pols, parameterising the third dredgeup in asymptotic giant branch stars, astron. soc. aust. 19 (2002) 515-38. https://doi.org/10.1071/as02013 [4] s.l. schnee, n.a. ridge, a. a. goodman, g. l. jason, a complete look at the use of iras emission maps to estimate extinction and dust temperature, the astrophysical journal 634 (2005) 442-450. https://doi.org/10.1086/491729 [5] x. dupac, j. p. bernard, n. boudet, m. giard, j. m. lamarre, c. meny, f. pajot, i. ristorcelli, g. serra, stepnik, j. p. torre, inverse temperature dependence of the dust submillimeter spectral index, astronomy & astrophysics 404 (2003) l11l15. https://doi.org/10.1051/0004-6361:20030575 [6] r. h. hildebrand, the determination of cloud mass and dust characteristics from sub millimeter thermal emission, royal astronomical society, 24 (1983) 267-282. [7] k. young, t. g. phillips, g. r. knapp, circumstellar shells resolved in iras survey data ii analysis, astrophysical journal 409 (1993) 725-738. https://doi.org/10.1086/172702 [8] erik holmberg, investigations of the systematic errors in the apparent diameters of the nebulae, melus, 117 (1946) 3h. [9] d. o. s. wood, p. c. myers, d. a. daugherty, iras images of nearby dark clouds, the astrophysical journal supplement 95 (1994) 457501. https://doi.org/10.1086/192107 [10] a. k. gautam, b. aryal, a study of four low latitude (|l| < 100) far-infrared cavities, journal of astrophysics and astronomy 40 (2019)16. 10.1007/s12036-019-9578-1. https://doi.org/10.1007/s12036-019-9578-1 [11] a. k jha, b. aryal, r. weinberger a study of dust color temperature and dust mass distributions of four far infrared loops, north america astronomical society, mexico 53 (2017) 467-476. [12] b. aryal, and r. weinberger, dust structure around white dwarf wd 1003-44 in 60 and 100μm iras survey, the himalayan physics ii (2011) 5-10. https://doi.org/10.3126/hj.v2i2.5202 https://doi.org/10.1146/annurev.astro.43.072103.150600 https://doi.org/10.1146/annurev.astro.43.072103.150600 https://doi.org/10.1071/as02013 https://doi.org/10.1086/491729 https://doi.org/10.1051/0004-6361:20030575 https://doi.org/10.1086/172702 https://doi.org/10.1086/192107 https://doi.org/10.1007/s12036-019-9578-1 https://doi.org/10.3126/hj.v2i2.5202 bibechana 18 (1) (2021) 48-57 48 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal simulated spectra (ir and raman), nlo, aim and molecular docking of carisoprodol from dft approach manoj kumar chaudhary1,2, tarun chaudhary1, bhawani datt joshi3* 1central department of physics, tribhuvan university, kirtipur, kathmandu, nepal 2department of physics, university of lucknow, lucknow-226007, india 3department of physics, siddhanath science campus, tribhuvan university, mahendranagar, 10406, nepal * email: pbdjoshi@gmail.com article information: received: may 20, 2020 accepted: june 20, 2020 keywords: carisoprodol vibrational spectroscopy (ir and raman) molecular docking abstract the aim of this study to explore the spectroscopic behavior of carisoprodol in terms of simulated spectra (ir and raman). the intramolecular h-bond of the molecule has been inspected from the atoms in molecule (aim) approach which infers that there exist partial covalent h-bond in nature. the protein-ligand binding activity of the drug molecule has been analyzed theoretically from the molecular docking approach with the predicted targets in terms of binding energy and conventional h-bond with residue. the molecular docking analysis of the title molecule explores that the binding energy with the protein acetylcholinesterase is more than the protein epoxide hydrolase1. the nonlinear optical (nlo) behavior of title molecule has been scrutinized which motivates that the potent use of the molecule as nlo material. doi: https://doi.org/10.3126/bibechana.v18i1.29036 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction carisoprodol, (rs)-2-{[(amino carbonyl) oxy] methyl}-2methyl pentyl isopropyl carbamate, with the molecular formula (c12h24n2o4) is a centrally acting skeletal muscle relaxant belonging to the bcs class ii drug [1-3]. carisoprodol is generally prescribed for the treatment of various muscular problems, mainly for lower back pain [2]. further, it is used in the treatment of muscular spasm related to the craniomandibular disorder, lumbago, sciatica, and other lower back syndromes [4]. the anticholinergic, antipyretic, and analgesic property behavior of carisoprodol has been studied regarding the treatment of distress associated with painful musculoskeletal conditions in adults [4,5]. it is triclinic in the crystalline structure lies in p1 space group with the cell dimensions a = 5.334(3), b = 10.831(5), c = 13.114(5)å, α =92.66(4), β = 96.03(4), γ = 92.70 (4)º and it is fully in extended conformations due to intramolecular c-h∙∙∙o hydrogen bonding [6]. to enhance the potential of drugs many pharmacological and drug behavior of http://nepjol.info/index.php/bibechana mailto:pbdjoshi@gmail.com mailto:pbdjoshi@gmail.com https://doi.org/10.3126/bibechana.v18i1.29036 https://creativecommons.org/licenses/by-nc/4.0/ https://pubchem.ncbi.nlm.nih.gov/search/#query=c12h24n2o4 manoj kumar chaudhary et al. / bibechana 18 (1) (2021) 48-57 49 carisoprodol has been carried out [7-9]. the structural and spectroscopic properties of this molecule at the atomic level have not been conducted so far. therefore, in present work, an endeavor has been made to investigate the employments of the quantum computational method (applying dft) to explore the vibrational spectra (ft-ir and ft-raman), nonlinear optical (nlo) properties and atoms in molecule (aim) of the molecule. furthermore, molecular docking is performed to study hydrogen bonding and the biological activity of carisoprodol with different proteins. ultimately, the study of different molecular properties might have great importance in designing and developing new efficient drugs in the coming days on the basis of protine ligand binding interaction [10-12]. fig. 1: chemical structure of carisoprodol. fig. 2: optimized structure atom numbering scheme of carisoprodol. the chemical structure of carisoprodol is shown in fig. 1. the optimized structure of the title molecule using functional b3lyp/6-31g(d,p) with the atom numbering system used in this study is shown in fig. 2. the minimum energy position of the molecule has been predicted based on geometry optimization with dft calculation by using the functional b3lyp/6-31g(d,p) which gives better agreement with the x-ray crystal structure [13]. the optimization energy of the title compound was calculated at room temperature is 553413.0830 kcal/mol which is less than the value of kt. this gives support towards the stability of the molecule at room temperature. 2. computational and theoretical details the geometry optimization of carisoprodol was performed with the gaussian-09 software package [14]. the density functional theory (dft) study has been performed by using the functional b3lyp/631g(d,p) basis set [15,16]. the hybrid exchange functional becke’s three parameters contain local, non-local, and hf (hartree-fock) with lee-yangpar correlation functional. the literature survey reveals that the result of the functional b3lyp is closer to the experimental values [17,18]. so, we have considered the functional b3lyp for the calculation. it is one of the most frequently used functional for quantum computing procedure to investigate theoretical results as supporting tools to the experimental results. the output data of gaussian-09 has been visualized with gauss view 05 software. the raman intensity, infrared absorption, and first-order hyperpolarizability were calculated at the same level of theory as optimization. the atom in the molecule (aim) of the title molecule has been studied with aim 2000 and aim all software, employing quantum theory of atoms in molecule (qtaim) [19,20]. the molecular docking of carisoprodol has been carried out with autodock software and ligand-protein interaction has been visualized with bio visualizer software [21,22]. manoj kumar chaudhary et al. / bibechana 18 (1) (2021) 48-57 50 the raman intensity for vibration is obtained in terms of raman scattering cross-section, 𝜕𝜎𝑗 𝜕ω , which depend on raman amplitude and is given by the expression [23,24] 𝜕𝜎𝑗 𝜕ω = ( 24𝜋4 45 ) ( (𝜈0−𝜈𝑗) 4 1−𝑒𝑥𝑝[ −ℎ𝑐𝜈𝑗 𝑘𝑇 ] ) ( ℎ 8𝜋2𝑐𝜈𝑗 ) 𝑆𝑗 (1) where sj= scattering activities, νj = predicted wavenumbers for jth normal mode, ν0 = wavenumber of raman excited state and h, c and k are universal constants. the lorentzian line shape (fwhm= 8 cm-1) is used to produce simulated spectra from the calculated raman and ir intensities to convolute each predicted vibrational mode. total static dipole moment (µ0), the first hyperpolarizability (β0), mean polarizability (∆α0) and anisotropy of polarizability |𝛼0| of the molecular system were calculated by using dft at b3lyp/6-31g(d, p) level of theory and are given by the equations [25,26]. 𝜇0 = (𝜇𝑥 2 + 𝜇𝑦 2 + 𝜇𝑧 2) 1/2 (2) |𝛼0| = 1 3 (𝛼𝑥𝑥 + 𝛼𝑦𝑦 + 𝛼𝑧𝑧) (3) ∆𝛼 = 2−1/2 [(𝛼𝑥𝑥 − 𝛼𝑦𝑦) 2 + (𝛼𝑦𝑦 − 𝛼𝑧𝑧) 2 + (𝛼𝑧𝑧 − 𝛼𝑥𝑥)2 + 6𝛼𝑥𝑥 2 ] 1/2 (4) 𝛽0 = [(𝛽𝑥𝑥𝑥 + 𝛽𝑥𝑦𝑦 + 𝛽𝑥𝑧𝑧) 2 + (𝛽𝑦𝑦𝑦 + 𝛽𝑥𝑥𝑦 + 𝛽𝑦𝑧𝑧) 2 + (𝛽𝑧𝑧𝑧 + 𝛽𝑥𝑥𝑧 + 𝛽𝑦𝑦𝑧) 2 ] 1/2 (5) 3. results and discussion 3.1 vibrational spectra the carisoprodol molecule has 42 atoms so it has 120 (3n-6) modes of vibration including stretching and bending. all the normal modes of vibration are both ir and raman active. in the calculated spectra with b3lyp, the overestimated wavenumber is obtained due to anharmonicity present in a real system. so, the wavenumber is lowered down by wavenumber linear scaling (wls) factor [27] which gives better resonance with experimental data. the graph of calculated ir absorbance and raman intensity of the title molecule with scaled wavenumber is plotted as shown in fig. 3. 3.1.1 amine group (nh2) vibration from the literature survey, the stretching of an amine group (nh2) lies in the range between 32003500 cm−1 [28]. in this study, the asymmetric stretching of nh2 was calculated at 3534 cm−1 in both ir and raman spectrum. and the symmetric stretching was calculated at 3420 cm−1 but the inplane bending is calculated at 1603 cm−1. the intense peak for n-h stretching was at 3441 cm−1 in both ir and raman spectrum. the c-n stretching is seen in ir and raman spectra at 1233 cm−1 in the scaled dft. the increase in wave number of asymmetric stretching of the amine group infers that the amine group take part in intermolecular hbonding with neighboring molecules in the crystalline structure. in this study, we have taken a single molecule in the gaseous state that shows some differences in the vibrational frequencies. 3.1.2 carbonyl group (c=o) vibration the stretching for carbonyl group was calculated at 1793 cm−1 in the ir and 1770 cm−1 in raman band. from the literature, the range for stretching of the carbonyl group is 1670-1820 cm−1 [29]. the out of plane bending was calculated at 773 cm−1 and 757 cm−1 in ir and raman spectra, respectively. 3.1.3 ch2 and ch3 vibration a literature survey reveals that the range of symmetric stretching for ch2 is 3000-3100 cm−1 [30]. in this study, the intense peaks for symmetric stretching are calculated at 2894 cm−1, 2930 cm−1, and 2944 cm−1 but another intense peak for asymmetric stretching for ch2 is obtained in both ir and raman spectra at 2981 cm−1. the distinct peak for symmetric stretching of ch3 in the title molecule is obtained at 2915 cm−1. manoj kumar chaudhary et al. / bibechana 18 (1) (2021) 48-57 51 fig. 3. simulation of calculated ir and raman spectra of carisoprodol. 3.2 nonlinear optical (nlo) properties the attractive potential application of nlo properties of the material is in optical communication, optical sensing, and data storage. the nlo properties of the material are explained in terms of static dipole moment (µ0), the mean polarizability (∆α), the first hyperpolarizability (β0) and the anisotropy of polarizability (|𝛼0|). these values of carisoprodol are calculated from b3lyp/6-31g(d,p) and their values are presented in table 1. table 1: the calculated dipole moment (µ0), mean polarizability|𝛼0|, anisotropy of polarizability (∆α) and first hyperpolarizability (β0) of carisoprodol at b3lyp/6-31g(d,p). dipole moment (debye) polarizability (*10–24esu ) hyperpolarizability (*10–30esu) µx −0.8384 αxx 12.5980 βxxx 0.9424 µy −1.0866 αxy 0.5476 βxxy 0.3385 µz 0.6195 αyy 21.9204 βxyy −0.5901 µ0 1.5058 αxz −0.6665 βyyy −0.4011 µ0(urea) 1.3732 αyz 1.6162 βxxz 0.0089 αzz 19.0427 βxyz 0.2270 |𝛼0| 17.8537 βyyz −0.0855 ∆α 23.3704 βxzz −0.6754 ∆α(urea) 9.7710 βyzz −0.2433 βzzz 0.1166 β0 0.4467 β0(urea) 0.3728 manoj kumar chaudhary et al. / bibechana 18 (1) (2021) 48-57 52 the significant delocalization of charge in a particular direction is mentioned by the component of polarizability in that direction. the dipole moment (µ0), the anisotropy of polarizability (∆α), and the first hyperpolarizability (β0) of carisoprodol obtained as 1.5058 debye, 23.3704x10–24esu, and 0.4467x10–30esu respectively. these values are more than the experimental values of urea, so carisoprodol can be used as nlo material. 3.3 atoms in molecule (aim) atoms in molecules’ (aim) is the proper way to evaluate the inter and intramolecular h-bonding. the quantum theory of atoms in molecules (qtaim) has wide application for identification and classification of h-bonding in terms of electron density (ρ) and laplacian of electron density (∇2ρ) at the bond critical point (bcp). the molecular graph of carisoprodol by using the functional b3lyp/6-31g(d,p) with aim 2000 and aim all software is presented in fig. 4. the topological parameters: ed (ρbcp), laplacian of ed (∇2ρbcp), electron kinetic energy density (gbcp), electron potential energy density (vbcp), total electron energy density (hbcp), interaction energy (eint) at bcp; in carisoprodol is presented in table 2. the geometrical parameters, bond length, bond angle, and the sum of van der waal radii of interacting atoms (rh + ra) is visualized in table 3. in the carisoprodol molecule, four intramolecular h-bond has been observed and they have the electron density (ρ) between proton (h) and acceptor (a) in the order 0.002−0.040 a.u. and the laplacian (∇2ρbcp) of electron density lies in the order 0.024−0.139 a.u. these values are in the range proposed by koch and popelier [31] for the existence of h-bond. for the investigated molecule it has been identified that (∇2ρbcp) > 0 and (hbcp) < 0, so the h-bond is partially covalent as given by rosa et al. criteria [32]. but for strong h-bond and weak h-bond, the criteria given by rosa et al. are (∇2ρbcp) < 0 and (hbcp) < 0, and (∇2ρbcp) > 0 and (hbcp) > 0 respectively. out of the four h-bond, the interaction c9-h21…o3 has the highest values of electron density, laplacian of electron density, and interaction energy as presented in table 2, so it is the strongest interaction. this interaction is similar as explained by horio et al. [6]. table 2: topological parameters for intramolecular interaction in carisoprodol: ed (ρbcp), laplacian of ed (∇2ρbcp), electron kinetic energy density (gbcp), electron potential energy density (vbcp), total electron energy density (hbcp), interaction energy (eint) at bcp. interactions bond length (å) ρbcp (a.u) ∇2ρbcp (a.u) gbcp (a.u) vbcp (a.u) hbcp (a.u) eint (kcal/mol) h36…o4 2.5062 0.0085 0.0276 −0.0006 −0.0056 −0.0063 −1.4828 h21…o3 2.2215 0.0203 0.0850 −0.0024 −0.0164 −0.0189 −4.3367 c16…o3 3.1270 0.0059 0.0239 −0.0012 −0.0036 −0.0048 −0.9414 h28…h22 2.2443 0.0084 0.0347 −0.0021 −0.0044 −0.0066 −1.1719 table 3: geometrical parameters for intramolecular hydrogen bonds in carisoprodol: bond length(å), bond angle (°), and the sum of van der waal radii of interacting atoms (rh + ra) in å. d-h...a d-h (å) h...a (å) d-h...a (°) (rh+ ra) (å) c17-h36…o4 1.0931 2.5062 159.1608 2.72 c9-h21…o3 1.0905 2.2215 105.8896 2.72 n6-c16…o3 1.3684 3.1270 90.2495 3.22 c12-h28…h22 1.0971 2.2443 113.4188 2.40 manoj kumar chaudhary et al. / bibechana 18 (1) (2021) 48-57 53 fig. 4. molecular graph of carisoprodol obtained by aim. 3.4 molecular docking molecular docking is a fundamental tool, which predicts the non-covalent binding of a receptor. it is used to study the protean-ligand binding affinity of bound conformations. to predict the active binding sites of carisoprodol, a docking study was performed using autodock-vina software [21]. the proteins epoxide hydralase1 and acetylcholinesterase were predicted with online swiss target prediction as shown in fig. 5. the crystal structure of epoxide hydrolase with pdb code; 4xdv, 4xdw, and acetylcholinesterase with pdb code; 2ace, 2v96 were downloaded from rscb pdb website. epoxide hydralase1 is an enzyme that is mainly found in the endoplasmic reticulum. it has curative behavior to metabolize reactive epoxide to less toxic water-soluble diols [33,34]. protein acetylcholinesterase is mainly found in the central nervous system having curative behavior to terminate nerve impulse and prevents nerve firing at the nerve ending and assists in the normal functioning of the central and peripheral nervous system [35]. the protein was prepared by removing water molecules and crystallized ligand from it. further, polar hydrogen and kollman charges were added to the protein using autodock tools. the active site of protein was confined in the grid box of size 60å×60å×60å with the spacing of 0.347 å. biovia discovery studio 2020 was used for visualization of autodock-vina result. the protein-ligand interaction of docked conformers is presented in fig. 6. the calculated value of binding energy, the number of hydrogen bonds, and active binding residues are tabulated in table 4. out of four docked conformations, 2v96 showed the best binding energy −6.6 kcal/mol which binds with residue ser b:286 (2.77å and 2.82 å). similarly, the conformer 2ace of acetylcholinesterase bind with carisoprodol and gives three hydrogen bond (2.54 å, asp a:72, and 3.02/2.71 å, tyra:121) with the binding energy −6.5 kcal/mol. from this study, it is observed that the amine group and carbonyl group behave as active binding sites which is also explored in the section 3.1.1. manoj kumar chaudhary et al. / bibechana 18 (1) (2021) 48-57 54 table 4: bond length, and binding energy of carisoprodol against two protein targets. ligand protein pdb code binding energy (kcal/mol) bond length (å) amino acid no. of hydrogen bond carisoprodol epoxide hydrolase1 4xdv − 6.1 3.08(o3) asn g:92 5 3.09(o3) ser g:91 2.09(h41) ser g:90 2.74(h42) glu g:25 2.37(h42) ser h:91 4xdw −5.7 2.81(h42) tyr b:53 4 2.83(h41) pro b:59 3.13(o4) asn b:55 2.99(o3) thr b:70 acetylcholinesterase 2ace − 6.5 2.54(h42) asp a:72 3 3.02(04) tyra:121 2.71(o1) tyra:121 2v96 −6.6 2.77(h42) serb:286 2 2.82(h34) serb:286 fig. 5: swiss target prediction of carisoprodol. manoj kumar chaudhary et al. / bibechana 18 (1) (2021) 48-57 55 fig. 6: molecular docking of carisoprodol. 4. conclusions from the simulated ir and raman spectra of the title molecule, it is observed that functional groups: carbonyl (c=o), amine (nh2), ch2, and ch3 vibrations are in the range given by the literature survey. the dipole moment (µ0), polarizability (∆α), and first hyperpolarizability (β0) of carisoprodol are 1.5058 d, 23.3704x10–24esu, and 0.4467x10–30esu, respectively. these values are more than the experimental values of urea (taken as a standard nlo material), so this material can be treated as nlo material besides the medicinal properties. the outcome of the aim study of investigated molecule showed four intermolecular h-bonds which are partially covalent. among them, the interaction c9-h21…o3 is the strongest due to the highest interaction energy (eint = − 4.3367) at bcp. the molecular docking studies reveal good binding with acetylcholinesterase protein, pdb code: 2v96 with a binding energy of − 6.6 kcal/mol. references [1] r.r. reeves, o.s. carter, h.b. pinkofsky, f.a. struve, d.m. bennett, carisoprodol (soma) abuse poten tia l and physic ian unawareness , j. addict. dis. 18 (1999) 51-56. https://doi.org/10.1300/j069v18n02_05 https://doi.org/10.1300/j069v18n02_05 manoj kumar chaudhary et al. / bibechana 18 (1) (2021) 48-57 56 [2] j.g. bramness, s. skurtveit, j. mørland, impairment due to intake of carisoprodol, drug alcohol depend, 74 (2004) 311 -318. https://doi.org/10.1016/j.drugalcdep.2004.01.007 [3] v.g. rajurkar, s.k. somware, a. aher, v. pansare, tablet formulation and enhancement of aqueous solubility of carisoprodol by solvent evaporation cocrystal technique, anal. chem. lett. 5 (2015) 364-376. https://doi.org/10.1080/22297928.2015.1129288 [4] k. a. kumar, v.s. lakshmipathi, s. meenakshi, m.h. balakrishnan, synthesis and characterization of potential impurity of muscle relaxant drug carisoprodol, j. chem. sci. 7 (4) (2017) 352-360. www.chemistry-journal.org [5] m.b. bolattin, s.t. nandibewoor, s.d. joshi, s.r. dixit, s.a. chimatadar, interaction between carisoprodol and bovine serum albumin and effect of β-cyclodextrin on binding: insights from molecular docking and spectroscopic techniques, rsc adv. 6 (2016) 63463-63471. https://doi.org/10.1039/c6ra08063d [6] k. horio, r. tanaka, h. akama, m. haramura, a. tanaka, t. akimoto, n. hirayama, crystal structure of carisoprodol, anal. sci.: x-ray structure analysis online, 20 (2004) x43-x44. https://doi.org/10.2116/analscix.20.x43 [7] s. niemi, muscle relaxants and antispasticity drugs , in : abd-elsayed a. 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(2013). http://dx.doi.org/10.1155/2013/321213 https://doi.org/10.1039/c6ra13035f http://www.accelrys.com/ https://doi.org/10.1002/jrs.989 https://doi.org/10.1021/j100384a024 https://doi.org/10.3126/bibechana.v15i0.18385 https://doi.org/10.1021/jp013084m https://doi.org/10.1016/j.saa.2012.09.014 https://doi.org/10.1002/0471238961.0914061810151405.a01.pub2 https://doi.org/10.1002/0471238961.0914061810151405.a01.pub2 https://doi.org/10.1021/j100024a016 https://doi.org/10.1021/ja0017864 https://doi.org/10.1093/hmg/3.3.421 https://doi.org/10.1016/j.gene.2015.07.071 giri et al. / bibechana 19 (1-2) (2022) 34-39 34 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal application of absorption of infra-red radiation and reflection spectra to distinguish different inks of same color in alteration roshan giri1, shanker prasad chimouriya2, bal ram ghimire3 1national forensic science laboratory, khumaltar, lalitpur, nepal 2deprtment of natural sciences (physics), kathmandu university, kavre, nepal 3central department of physics, tribhuvan university, kirtipur, kathmandu, nepal email: balramghimire@gmail.com article information: received: may 7, 2022 accepted: june 17, 2022 keywords: non-destructive absorption spectra alteration abstract the main aim of this study is to introduce non-destructive method to distinguish different types of ink of same color. in our daily life, we face many problems of alteration of genuine documents. such alteration is done by using same color of ink as used in the document. it is not possible to differentiate the altered part by our naked eyes. there are many methods, destructive as well as non-destructive methods, to solve the problem of alteration. we have discussed the non-destructive method using video spectral comparator (vsc)-6000. analysis is carried out with application of infra-red (ir) radiation of different wavelength and reflection spectra to reach the conclusion. absorption of infra-red (ir) radiation is found very effective whereas use of reflection spectra is totally failed in this experiment. doi: https://doi.org/10.3126/bibechana.v19i1-2.46380 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction genuineness and authentication of documents like bank cheque, power of attorney, property paper, school college certificates, medical bills etc. depend upon the ink and material used to make the documents. ink is colored liquid used to produce colored surface in different fields http://nepjol.info/index.php/bibechana mailto:surendra.gautam@trc.tu.edu.np https://doi.org/10.3126/bibechana.v19i1-2.46380 https://creativecommons.org/licenses/by-nc/4.0/ bibechana 19 (1-2) (2022) 34-39 35 like painting image, text or any kind of design. major raw materials used for ink production are pigments, binders, solvents and additives. pigment is chief constituent of ink and contributes 50% of its cost. a pigment is essentially any particulate solid-colored, black, white or fluorescent which alters the appearance of object by selective absorption or scattering of light. as the particle size reduces, the color intensity of pigment increases. resins bind the ingredients of ink together [1]. documents are also made with stamp, embossing, watermark and so on to prevent from forgery. but sometime genuine document is altered by using another ink of same color for personal benefit. such alteration can be done on any part of document like date, amount, name, signature etc. to hide originality of documents. destructive method like thin layer chromatography (tlc), destroys some parts of document. so, it is better to carry out non-destructive methods at first as much as possible. non-destructive methods does not change document physically and involves use of different light sources and interaction of light with ink in different ways like absorption, reflection, luminescence etc [2]. s.r. khairkar et al. [3] studied fraud cases and questioned documents of india based on alteration. they analyzed 6 different types of blue ballpoint pen inks (reynolds, parker, lexis, cello gripper and local pen found in india) by using vsc-5000. h.k. bamburde et al. [4] studied about obliterated writing on questioned documents by the application of vsc-6000. similarly, r.k. pandey et al. [5] did work on alteration, erasures and obliteration on suspected documents. also, t.n. moorthy et al. [6] studied to enhance handwriting on charred documents by the application of vsc-6000. but still we do not find any research work on the alteration from various inks found in the local market of nepal. so, we have decided to carry out this work. this work is very useful to questioned document examiners and forensic researchers. this method is convening, lucid, illustrative and easy to perform by document examiners. 2. theory different materials have different tendency of absorption and reflection. so, this work is basically based on the absorption of infra-red radiation and fundamental laws of reflection of light. 2.1 absorption of infra-red radiation infra-red (ir) spectroscopy simply deals with absorption measurement of ir radiation of different wavelength by a sample placed in the path of ir beam. infrared radiation covers section of electromagnetic spectrum having wavelength roughly from 700 nm to 1 mm. ir absorption positions are generally represented in terms of either wavenumber or wavelength. wavenumber is the number of waves per unit length. if frequency of ir radiation is matched with the vibrational frequency of molecule, then molecule absorbs ir radiation [7]. hence, ir spectroscopy is based on hook’s law. according to hook’s law, frequency of vibration of two atoms or masses connected through spring (bond) is given as ν = 1 2𝜋 √ 𝑘 𝜇 (1) 'k' is force constant of the bond and 'μ' is reduced mass. if m1 and m2 are masses of two atoms, then reduced mass is given as μ = 𝑚1.𝑚2 (𝑚1+𝑚2) (2) absorption of ir radiation by molecules results in the excitation of vibrational, rotational and bending modes while molecules remain in its electronic ground state. ir analysis involves the characterization of a materials with respect to presence or absence of a specific group frequency associated with one or more fundamental modes of vibration. absorbance or co-efficient of absorption (a) is the giri et al. / bibechana 19 (1-2) (2022) 34-39 36 logarithm to the base 10 of reciprocal of transmittance (t) i. e. a = log10[ 1 𝑇 ] = -log10t (3) here, transmittance (t) is the ration of radiant power transmitted by the sample (i) to the radiant power incident on the sample (io). 2.2 laws of reflection when beam of light falls on any surface, part of it is reflected, a part of it is transmitted and rest of it is absorbed. according to first law of reflection: the incident ray, reflected ray and normal to the surface lie in the same plane. this law implies that reflection is surface phenomenon i.e. reflected ray essentially characterize the surface from which it is reflected [8]. when we write above any surface, there is a deposition of thin layer of ink. hence, reflection spectra from the ink layer of genuine and altered part may be different. fig. 1: phenomena of reflection, transmission and absorption when an incident rays falls on a surface 3. materials and method we prepared some samples of alteration by ourselves using different black ink pen (black pilot pen, black cello techno tip pen, black maxriter pen and black cello pointec pen) found in our market now days in white photocopy paper. we choose black ink pen because in most of the documents black pen is used. in our sample, digit one ‘1’ is altered to make digit four ‘4’ as shown in figure 3 and figure 6 by using different black ink pens. such samples can be prepared in number of ways. for this study, we use video spectral comparator (vsc)-6000 which works on the principle of interaction of light of different wavelength with matter. 3.1 video spectral comparator-6000 video spectral comparator (vsc) is very useful tool in document examination which allows an examiner to analyze ink [9], visualize hidden security features [10,11], crossing stroke examination [12,13] and reveal alteration in document. it is an automated device that uses different light sources for examination of document. at first power of vsc is switch on and appropriate setting is done before working. the position of document to be checked is adjusted by viewing on the monitor. after placing the document, infra-red light of various wavelengths is passed and absorption of ir light by ink is studied. also reflection spectra from different points of genuine and altered part is observed. once the required result is obtained, the image is saved. fig. 2: video spectral comparator-6000 at first, we observed our prepared sample under normal light and then into spot light with ir radiation of different wave length. finally, both results with normal light and ir radiation are analyzed. for the study of reflection spectra, spectra form three to five different points of strokes produced by each pen is taken by using spectrometer available in vsc-6000 with reference to white back ground of photocopy paper. then, average of thus produced spectra is taken with the help of software available in equipment. finally, nature and characteristics of average of spectra of two strokes produced bibechana 19 (1-2) (2022) 34-39 37 by different pens are studied and compared to come to conclusion. 4. results and discussion though, we see the same color of ink but their composition may be different. if their composition is different, then absorption and reflection properties also will be different. this concept is useful to this work. in all samples, we altered digit one into digit four. we obtained good results in all cases but only results of two of them are discussed here. 4.1 alteration from black cello techno tip pen and black cello maxriter pen under visible light digit four ‘4’ is seen as shown in figure 3 which is written by using two different black pens cello techno tip and cello maxriter. but under spot light with ir radiation of wave length 645 nm altered part made by using cello maxriter is absorbed more as shown in figure 4. so, from these two results, two different black colored inks are differentiated. in figure 5, we have an average of reflection spectra obtained from these two inks. from this graph, we find similar nature of both spectral lines indicating negative result against our basic assumption because we expect difference in nature and peak character between these two spectra. fig 3: prepared sample of alteration under visible light where at first digit one (1) is written with black cello techno tip pen which is altered into digit four (4) using cello maxriter pen fig. 4: prepared sample of alteration under spot light with ir radiation of wave length 645 nm where at first digit one ‘1’ is written with black cello techno tip pen which is altered into digit four ‘4’ using cello maxriter pen giri et al. / bibechana 19 (1-2) (2022) 34-39 38 fig. 5: average of reflection spectra from three different points of strokes made by black cello techno tip pen (red line) and black cello maxriter pen (black line) 4.2 alteration from black cello pointec pen and black pilot pen similarly, in the next sample prepared from black pilot pen and black cello pointec pen, under visible light digit four ‘4’ is seen as shown in figure 6. fig 6: prepared sample of alteration under visible light where at first digit one (1) is written with black cello pointec pen which is altered into digit four (4) using black pilot pen under flood light with ir radiation of wavelength 780 nm, altered part made by using black pilot pen is absorbed more as shown in figure 7. in figure 8, we have an average of obtained reflection spectra. here, also we do not get difference in nature and peak character between these two spectral lines in graph which means application of reflection spectra to study alteration is failed. fig. 7: prepared sample of alteration under spot light with ir radiation of wave length 780 nm where at first digit one ‘1’ is written with black cello pointec pen which is altered into digit four ‘4’ using black pilot pen bibechana 19 (1-2) (2022) 34-39 39 fig. 8: average of reflection spectra from five different points of strokes made by black pilot pen (red dot line) and black pointec pen (black solid line) 5. conclusion in this work, we took very simple case of alteration where digit one ‘1’ is altered into digit four ‘4’ by using four different black color pens. we successfully differentiated altered parts by analyzing absorption of infrared (ir) radiation but reflection spectra is not found effective. so, we can suggest to use concept of absorption of ir radiation not reflection spectra to solve problem of alteration to document examiners. references [1] b. r. sharma. forensic science in criminal investigation & trails, universal law publishing co. pvt. ltd. (2014). [2] a. s. osborn. questioned documents, boyd printing company, second edition, (1929). [3] s. r. khairkar, s. v. gaikawad, r.n. kokare and b.b. daundkar. forensic discrimination potential of video spectral comparator and micro spectrometer in analyzing question document and fraud cases in india, j. forensic res. 7(2016) 1-4. [4] h. k. bamburde and m. p. goutam. questioned documents analysis for decipherment of obliterated writing, int. j. sci. res. 9(2020). [5] r. k. pandey, m. s. sankhla and r. kumar. forensic investigation of suspected document for alteration, erasures & obliteration, galore int. j. appl. sci. hum. 2(2018). [6] t. n. moorthy and k. narayanan. enhancement of handwriting on selected charred documents using video spectral comparator (vsc), arab j. forensic sci. & forensic med. (2016). [7] d. l. pvia, g. m. lampman, g. s. criz and j. r. vyvyan. introduction to spectroscopy, cengage learning, fifth edition, (2015). [8] b. a. vaid, r. s. rana and c. dhawan. determination of sequence of strokes through reflection spectra, prob. forensic sci. vol-lxxxvii, (2011). [9] a. e. manal, and e. abd. different types of ink having certain medicolegal importance: deciphering the faded and physically erased handwriting, egyptian j. forensic sci. 4(2014)39-44. . [10] n. k. kanwal, d. jat, m. malhotra. spectral analysis of various security features in the indian currency note of highest denomination using video spectral comparator-40, int.j.innov. sci. eng. technol.1(2015)823-841. [11] r. giri, p. bhattarai, s. p. chimouriya, and b. r. ghimire. examination of security features in nepali currency of denomination rs. 500 and rs. 1000 using video spectral comparator-6000, j. nepal phys. soc. 7(2021)36-42. [12] r. kaur, k. saini and n. c. sood. application of video spectral comparator (absorption spectra) for establishing chronological order of intersecting printed strokes and writing pen strokes, sci. just. 53(2013)212-219 . [13] r. giri, s. p. chimouriya and b. r. ghimire. study of chronological order in intersecting printed and pen strokes with the help of chromaticity diagram, acta scientifica malaysia, 6(2022)38-42. doi: https://doi.org/10.3126/bibechana.v19i1-2.46380 mamata kadel and menuka bhandari/ bibechana 16 (2019) 213-220: rcost p.213 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal factors intended to brain drain among nurses working at private hospitals of biratnagar, nepal mamata kadel1, menuka bhandari2* 1department of nursing, neuro health college, biratnagar, nepal 2department of child health nursing, nursing campus, biratnagar, nepal *e-mail: menukamenu@gmail.com article history: received 12 august 2018; accepted 6 november, 2018 http://dx.doi.org/10.3126/bibechana.v16i0.21642 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract introduction:the migration of health worker is a complex and multifaceted phenomena. emigration of highly skilled and competent nurses to other countries seems to have negative impact on the delivery of excellent health care services. objective:the objective of this study was to assess factors intend to brain drain among nurses working at private hospitals of biratnagar. methodology: a cross sectional study was conducted on staff nurses of selected hospitals of biratnagar, nepal from 2017 february to 2018 february; non-probability purposive sampling technique was used. required information was collected using self-administered semi structured questionnaire related to demographic and factors intending to brain drain from 99 nurses. results: majority (78.8%) of nurses were below 25 years of age. most (81.8%) of them had completed pcl nursing, more than half (55.6%) wanted to migrate abroad to pursue further work and study. australia (56.4%) and usa (25.5%) emerged as the top destination of choice, while only (5.5%) of them wanted to migrate united kingdom. lack of career opportunities, low salary and poor working condition were main pull factors and push factors intending to brain drain among nurses. this study also found that majority (96%) of nurses were not satisfied with their salary. conclusion:more than half of nurses working in private hospitals would like to migrate abroad. the major push factors for migration was lack of career development and low salary. keywords:brain drain; private hospitals; pull factors and push factors. 1. introduction the term brain drain was first coined by the british royal society to refer to the exodus of scientists and technologists from the united kingdom and canada in the 1950s and 1960s to the united states. it is regarded as the international transfer of resources in the form of human capital and mainly applies to the migration of relatively highly educated individuals from developing to develop countries [1]. http://nepjol.info/index.php/bibechana mailto:menukamenu@gmail.com http://dx.doi.org/10.3126/bibechana.v16i0.20960 https://creativecommons.org/licenses/by-nc/4.0/ mamata kadel and menuka bhandari/ bibechana 16 (2019) 213-220: rcost p.214 (online publication: dec., 2018) throughout the 20th century, there have been a substantial number of highly skilled and educated professionals emigrating from their home countries in search of better economic and social opportunities in other countries. in the 1960s the term “brain drain” was coined in response to the large number of trained scientists, physicians and university teachers leaving developing countries [2].migration of health workers ‘brain drain’ is defined as the movement of health personnel in search of the better standard of living and life quality, higher salaries, access to advanced technology and more stable political conditions in different places worldwide. the migration of highly skilled workers from less-developed nations to industrialized nations is an inevitable part of the process of globalization and has positive and negative aspects. trained health professionals are needed in every part of the world. however, better standards of living and quality of life, higher salaries, access to advanced technology and more stable political conditions in the developed countries attract talent from less developed areas. the majority of migration is from developing to developed countries. this is of growing concern worldwide because of its impact on the health systems in developing countries [3].an increasing number of nurses trained in nepal, growing number of colleges with nurses at private sector have a strong desire to migrate, study and work abroad. twenty years ago few nurse in nepal had global aspiration and plan to migrate and settle in the west. this has completely changed. at present, new generation of nurses in nepal are choosing nursing as a vehicle to migrate to the west and fulfill their modern aspiration [4].the large proportion of nepal’s health workforce is in the health management and support workforce that comprise of 38%. the nursing council estimates registering over 4000 new nurses in 2013. yet, shortage of nurse persists in the public sector, district hospitals and primary health care center (phc) is particular. there is mismatch between numbers of nursing professionals working in nepal and annual registration of nursing professionals in nepal nursing council (nnc).study suggest a significant numbers of nursing professionals are working outside the country and nonhealth sectors [5].there is an abundance of human resources for health (hrh) production, especially doctors and nurses, in nepal but when it comes about employing they are underpaid and had to work laboriously often involving with harmful practices without compensation that demotivates them. unlike other developing countries, “brain drain” of health workers has been identified as a major health concern in nepal. previous research has identified that professional councils are being approached for letters of good standing by staff wanting to work abroad and data suggests approximately 16% of registered doctors are outside the country. the uneven distribution of health workers has been a major concern in the health sector and the deployment of health personnel to the rural and remote areas of the country is a challenge. although, nepal produces an adequate number of doctors and nurses there are still huge shortage of qualified nurse midwife [6].similar study done in nepal showed that 52.22% of respondent were not satisfied with their job in nepal. it was found that beside provision of modern facilities, age and personal ambition were also a motivating factor for nursing personnel migration [7].emigration of highly skilled and competent nurses to other countries seems to have negative impact on the delivery of excellent health care services. brain drain of nepalese nurses is increasing day by day and shortage of health workforce is the burning issue of nepal health care system. therefore, researcher aims to study different factors intended to brain drain among the nurses of selected private hospitals of biratnagar, nepal. 2. methodology a cross-sectional study was conducted to identify the factors intended to brain drain among nurses of selected private hospitals of biratnagar metropolitan of morang district. biratnagar is the second largest city of nepal, which consists of approximately 16 private registered hospitals. the study mamata kadel and menuka bhandari/ bibechana 16 (2019) 213-220: rcost p.215 (online publication: dec., 2018) duration was 2017 february to 2018 february. formal permission for the study was taken from the ethical committee of institute and written permission was obtained from selected hospitals. informed consent was taken from the participants. purposive sampling was used to select 99 registered nurses working in different private hospitals. self-administered questionnaire was administered. data was entered in microsoft excel and analyzed by statistical package for social sciences (spss). mean, frequency, percentage and standard deviation was calculated. 3. results table 1 shows the sociodemographic information of the study populations, in which mean age of participant was22.34 years with standard deviation of 2.94 years. majority (78.8%) of them were unmarried. most of them (81.8%) had completed pcl nursing and 9.2% had completed bachelor level nursing respectively. more than half of the participants (57.6%) immediate family members studied/worked/ permanently settled in abroad. according to table 2, most of the participants (96.96%) were not satisfied with their salary while only (3.03%) were satisfied. table 3 states that majority (39.4%) of respondents want to pursue further study in abroad while only (28.3%) of them planning to do further study in nepal. similarly respondent’s intention to work in nepal and abroad is equal (16.2%). among those who wanted to migrate abroad to pursue further study and work, australia (56.4%) and usa (25.5%) emerged as the top destination of choice, while only (5.5%) of them wanted to migrate to united kingdom. table 4 indicates a multiple response question in which individuals were asked to rank each item. this table reveals those push and pull factors as ranked by participants as not important, less important and very important. the most important push factors were lack of career development (92.9%), low salary (90.9%) and poor working environment (71.7%) and least important factors were political conflict (35.4%) and family/friend influence (44.4%). similarly most important pull factors were better career development (87.9%), high salary (86.9%), better working environment (81.8%) and better education (77.8%) and least important pull factors were family/friend influence (42.4%) and political stability (36.4%). table 5 depicts respondents processing for migration, majority 76.8% have not precede any steps for migration while 6% have submitted college application, 8.1% have registered for country specific license examination and 9.1% have registered for language test. table 1: socio-demographic characteristics of participants (n=99). variables frequency percentage age in years below 25 above 25 78 21 78.8 21.2 mean ± sd 22.34±2.942 ethnicity brahmin chettri madhesi muslim dalit janajati 38 24 20 3 7 7 38.6 24.2 20.2 3 7 7 marital status married unmarried 21 78 21.2 78.8 mamata kadel and menuka bhandari/ bibechana 16 (2019) 213-220: rcost p.216 (online publication: dec., 2018) table 2: participant’s satisfaction with paid salary (n=99). response frequency percentage satisfied 3 3.03 unsatisfied 96 96.96 table 3: distribution of participants according to future plan (n=99). response frequency percentage future plan further study in nepal work in nepal further study in abroad work in abroad 28 16 39 16 28.3 16.2 39.4 16.2 country selected for further study/work australia usa canada uk 31 14 7 3 56.4 25.5 12.7 5.5 table 4: distribution of pull and push factors according to response (n=99). factors not important (%) less important(%) very important(%) push factors lack of career development low salary poor working environment unsatisfactory living condition family/friends influence poor quality of education personal ambition political conflict 3 3 2.0 11.1 25.3 15.2 15.2 33.3 4 6.1 26.3 38.4 30.3 31.3 25.3 31.3 92.9 90.9 71.7 50.5 44.4 53.5 59.6 35.4 pull factors better career development high salary better working environment higher living standard family/friends influence better education personal ambition political stability 6.1 1.0 5.1 7.1 25.3 11.1 17.2 32.3 5.1 12.1 13.1 28.3 32.3 11.1 19.2 31.3 87.9 86.9 81.8 64.6 42.4 77.8 63.6 36.4 table 5: participant’s processing for abroad (n=99). response frequency percentage submitted college application registered for country specific examination registered for language nothing done 6 8 9 76 6 8.1 9.1 76.8 mamata kadel and menuka bhandari/ bibechana 16 (2019) 213-220: rcost p.217 (online publication: dec., 2018) the table 6 depicts respondent’s response to consequences of brain drain. majority 63.6% of respondents were known about consequences of brain drain. multiple response questions was asked for consequences, 37% of respondents recognized shortage of skilled manpower as consequences, while 20% and 17% respondents recognized increased remittance and increased dependency in foreign technical assistance as consequences respectively. majority, 81.8% of respondent’s think that brain drain should be controlled. table 6: distribution of participants according to consequences of brain drain (n=99). response frequency percentage known about consequences not known about consequences consequences shortage of skilled manpower increased remittance increased dependency in foreign technical assistance controlling brain drain yes no 63 36 37 20 17 81 18 63.6 36.4 37.4 20.2 17.2 81.8 18.2 figure 1 reveals that 68.7% of respondents have planned to come back to nepal once they are migrated. fig. 1: participants plan to come back to nepal (n=99). 4. discussion this study revealed that majority (96%) of respondents were not satisfied with their salary, whereas it compared by study conducted among migrated nurses from nepal revealed that 55.22% of respondents were not satisfied with their salary and job in nepal [7].in addition, research published by connel states that the economic factors and the better working environment with more technological facilities in foreign countries are the main pulling factors of migration among doctors and nurses which is lacking in nepal [8].this study found most of the (55.6%) nurses wanted to 68.70% 31.30% yes no mamata kadel and menuka bhandari/ bibechana 16 (2019) 213-220: rcost p.218 (online publication: dec., 2018) migrate abroad to pursue study and work. similar study conducted on “factors driving nepali health workers to seek employment opportunities in abroad among medical and nursing students in kathmandu” has shown that more than half of them planned to migrate abroad, to pursue further studies (39%) and work (11.7%) after completion of their degree program in nepal [9].this study shows that most important push factors were lack of career development (92.9%), low salary (90.9%) and poor working environment (71.7%) and least important push factors were political conflict (35.4%) and family/friends influence (44.4%). similarly, most important pull factors were better career development (87.9%), high salary (86.9%), better working environment (87.8%) and better education (77.8%) and least important pull factors were family/friends influence (42.4%) and political stability (36.4%), whereas it is further supported by a study conducted on health workers migration to uk, showed major push factors includes low pay condition, political instability and poor workplace security and the pull factors include increasing access to global market, better pay opportunities, living standard[10] .the world health report summarized a number of reasons why health workers moved to richer countries are lack of promotion prospects, poor management, heavy workload, lack of facilities, declining health service, inadequate living conditions and high levels of violence and crime. these factors are closely related to nepalese situation [11].according to world health organization, the insufficient number of health workers in less developed countries leads to delays in providing care, the closure of services, a lack of services in remote areas, excessive workload, demoralization, burn out, an inability to meet health goals and loss of life. these problems are further worsened by migration of health workers. health workers, like workers in all sectors, tend to go where the working conditions are best. income is an important motivation for migration, but not the only one. other reasons include: greater job satisfaction, career opportunities, the quality of management and governance, moving away from political conflicts, war, and the threat of violence in the workplace [12].majority 76% had not preceded any steps for migration while 6% had submitted college application, 8.1% had registered for country specific license examination and 9.1% had registered for language test. according to a study every year 250000 youth are reported to leave nepal for higher living standards, employment, better income, education, a luring western lifestyle, stability and security, as our country seemed incapable to provide those to the youths. according to nepal nursing council records, a total number of 3461 nurses migrated abroad between 2002 and 2011. the number further increased to 4155 from 2011 to 2013 [13].majority 63.6% of participants were known about consequences of brain drain. about 37% of respondents recognized shortage of skilled manpower as consequences, while 20% and 17% respondents recognized increased remittance and increased dependency in foreign technical assistance as consequences respectively. majority, 81.8% of respondent’s think that brain drain should be controlled. many researches revealed that young, well-educated, healthy individuals are most likely to migrate, especially in pursuit of higher education and economic improvement [14, 15]. the distinction between ‘push’ and ‘pull’ factors has been recognized. continuing disparities in working conditions between richer and poorer countries offer a greater ‘pull’ towards the more developed countries [16]. 5. conclusion more than half of nurses working in private hospitals would like to migrate abroad. the major push factors for migration were lack of career development and low salary. recommendations career development opportunities, salary and working environment should be improved in nepal which could be the strong and good motivating factors for nepalese nurses to control them migrate mamata kadel and menuka bhandari/ bibechana 16 (2019) 213-220: rcost p.219 (online publication: dec., 2018) abroad. the study can be replicated in large scale. a similar type of study can be conducted in different settings to increase representativeness of findings. further research focused on various aspects of this complex phenomenon needs to be conducted to inform policies and programming dealing with it. limitation of the study this study was conducted only in private hospitals of biratnagar. the findings were based on individual perception of the participants at private hospitals. the study could not cover all private hospitals of biratnagar so the research findings would not be generalized. acknowledgements the authors would like to acknowledge tribhuvan university, institute of medicine, biratnagar nursing campus for providing an opportunity to carry out this research. the researchers are ever indebted to the concerned private hospitals for permission and all nurses who consented and cooperated for study. conflict of interest the authors declare that no competing interest exists. financial disclosure no specific funding received for the study. total expenditure was beard by authors themselves. references [1] a. chimenya, b. qi, investigating determinants of brain drain of health care professionals in developing countries, net journal of business management 3(2) (2015)27-35. [2] j. william, carrington and enrica detragiache, “how big is the brain drain?" imf working paper 98/102 (washington), finance and development 36 (2) (1999). [3] m.k. bimal, r. kaur, factors intend to brain drain among staff nurse,int. j. adv. nur. management; 4(4) (2016) 327-330.doi: 10.5958/2454-2652.2016.00073. [4] r. adhikari, the dream trap: brokering, ‘study abroad’ and nurse migration from nepal to uk. european bulletin of himalayan research30(3) (2009-2010) 122-138. [5] mohp & nhssp, human resource for health: nepal country profile, kathmandu: ministry of health and population,2014, retrieved from http://www.searo.who.int/entity/human_resources/data/hrh-profilenepal. [6] j.b. sherchand, human resources for health (hrh) and challenges in nepal, journal of institute of medicine 35(2013) 1. [7] r. baral, s. sapkota, factors influencing migration among nepalese nurses, journal of chitwan medical college 5(12) (2015) 25-29. [8] j. connell, migration of health workers in the asia-pacific region, human resources for health knowledge hub, university of new south wales, sydney (2010) 1-28. [9] b. sijapati, j. baniya, n. choudhary, a. bhtattarai, migration of health workers from nepal, international labour organization, retrieved from www.ceslam.org/index.php. [10] t.n. sapkota, e. teijlingen, p. simkhada, nepalese health workers migration to uk. health science journal, 8(1) (2104) 57-58. [11] the world health report, migration of health workers: who code of practice and the global economic crisis, 2006. [12] world health organization (who), migration of health workers, fact sheet, july 2010, available from: http://www. who.int/mesiacentre/factsheets/fs301/en/index.html [13] s. manandhar, who pays the price for nepal’s brain drain? the himalayan times (nepal), september 2010; 18:3. http://www.searo.who.int/entity/human_resources/data/hrh-profile-nepal http://www.searo.who.int/entity/human_resources/data/hrh-profile-nepal mamata kadel and menuka bhandari/ bibechana 16 (2019) 213-220: rcost p.220 (online publication: dec., 2018) [14] a. mejía, h. pizurki, e. royston, physician and nurse migration: analysis and policy implications. geneva: world health organization, 1979. [15] m. awases, a.gbary, j. nyoni, r. chatora, migration of health professionals in six countries: report. brazzaville: who regional office for africa, 2003. [16] s. bach, international migration of health workers: labour and social issues, geneva: internationallabour office, 2003 (www.ilo.org/public/english/dialogue/sector/papers/health/wp209.pdf). http://www.ilo.org/public/english/dialogue/sector/papers/health/wp209.pdf bibechana 18 (1) (2021) 184-192 184 thermodynamic, structural, surface and transport properties of au-ni liquid alloy at 1150 k s. k. yadav, n. chaudhary, d. adhikari* department of physics, mahendra morang adarsh multiple campus, tribhuvan university, biratnagar, nepal. *email: adksbdev@yahoo.com article information: received: july 14, 2020 accepted: november 8, 2020 keywords: thermodynamic properties surface properties transport properties au-ni alloy abstract thermodynamic, structural, surface and transport properties of au-ni liquid alloy at 1150 k were computed using different theoretical approaches. the thermodynamic properties, such as excess gibbs free energy of mixing, enthalpy of mixing, activity and excess entropy of mixing and structural properties, such as concentration fluctuation in long wavelength limit and warren-cowley short range order parameter were computed in the frame work of flory’s model. the effect of positive and negative values of the interchange energy parameter on the excess gibbs free energy of mixing and concentration fluctuation in long wave length limit was also observed. the surface tension and surface concentration of the system were calculated using butler’s model. in transport property, the viscosity of the system was calculated using kaptay and budai-benko-kaptay (bbk) models. doi: https://doi.org/10.3126/bibechana.v18i1.30546 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction the comprehensive knowledge of the mixing behaviours of binary and multi-component liquid alloys are mandatory in order to develop new materials with desired characteristics. the study and explanation of the hetero-coordinating and homocoordinating tendencies of the liquid alloys leading to different phase stabilities in the solid states are the most promising research directions in the metallurgical science and engineering. several researchers [1-16] working in this field have long been attempting to reveal these behaviours by developing different modelling equations or by correlating them. therefore, an attempt has been made in this work to study and explain the mixing and demixing behaviours of au-ni liquid alloy at 1150 k using different theoretical approaches. the thermodynamics of au-ni system have been studied by different authors [17–26]. but the complete set of mixing properties of the system is lacking till date. in this regard, the mixing behaviours of au-ni liquid alloy at 1150 k have been explained in terms of the thermodynamic, structural, surface and transport properties. the bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:adksbdev@yahoo.com https://doi.org/10.3126/bibechana.v18i1.30546 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana s.k. yadav et al. / bibechana 18 (1) (2021) 184-192 185 thermodynamic and structural properties of the system were computed on the basis of flory’s model [11, 27]. the mixing and demixing behaviours of the binary liquid alloys are generally explained in terms of the thermodynamic and structural properties. the compound forming liquid alloys are characterised by high negative values of excess free energy of mixing (∆𝐺𝑀 𝑥𝑠) and enthalpy of mixing (∆𝐻𝑀). the activities (𝑎) of such systems show negative deviation from the raoult’s law. meanwhile, the liquid alloys showing demixing behaviours have positive or very low negative values of ∆𝐺𝑀 𝑥𝑠 and ∆𝐻𝑀, and their activities show positive deviation from the raoul’ts law [4, 28, 29]. likewise, the study of structural properties has been developed as an important tool to explain and predict the nature of the local arrangements of liquid alloys. if the computed values of concentration fluctuation in long wavelength limit (𝑆𝐶𝐶(0)) is less than the ideal value (𝑆𝐶𝐶 𝑖𝑑 (0)), i.e., if 𝑆𝐶𝐶(0) < 𝑆𝐶𝐶 𝑖𝑑 (0), then heterocoordinating or ordering nature of the system is expected and if 𝑆𝐶𝐶(0) > 𝑆𝐶𝐶 𝑖𝑑 (0), then homocoordinating or segregating nature of the system is expected. consequently, the value of warrencowley short range order parameter (𝛼1) is found to be non-zero and negative (𝛼1 < 0) for ordering system, 𝛼1 > 0 is found for segregating system and 𝛼1 = 0 represents random mixing. the surface properties and the viscosity of the liquid alloys are the direct consequences of their thermodynamic properties. hence the surface properties, such as surface tension (𝜎) and the extent of surface segregation (𝑥𝑖 𝑠) of the system were computed using butler’s model [30-34]. the viscosity (𝜂) of the system was computed on the basis of kaptay [34, 35] and budai-benko-kaptay (bbk) [36] models. the necessary theoretical formulations of the work are presented in the section 2, the results and discussion are presented in the section 3 and the conclusions are outlined in the section 4. 2. modeling equations thermodynamic properties in thermodynamic properties, excess free energy of mixing (∆𝐺𝑀 𝑥𝑠), activities of monomers al (𝑎𝐴𝑙) and ni (𝑎𝑁𝑖), enthalpy of mixing (∆𝐻𝑀) and excess entropy of mixing (∆𝑆𝑀 𝑥𝑠) have been analysed using flory’s model [11, 22]. this model is fundamentally used to explain the properties of alloys showing likeatoms clusters or self-associates. the preferred liquid alloy, au-ni at 1100 k also show the same behaviour. if 𝜇 atoms of 𝐴 (=al) and 𝑣 atoms of 𝐵 (=ni) are mixed near to their melting temperatures, then there are preferable associations among the like atoms in the metallic mixture of the types 𝜇𝐴 ⇋ 𝐴𝜇 and 𝑣𝐵 ⇋ 𝐵𝑣, called self-associates. the expression for ∆𝐺𝑀 𝑥𝑠 on the basis of the selected model can be given as ∆𝐺𝑀 𝑥𝑠 = 𝑅𝑇 [ln (1−𝛽)𝑥 (1−𝛽𝑥) + 𝑥(1−𝑥) (1−𝛽𝑥) 𝜔] (1) where 𝑅 is the real gas constant, 𝑇 is the absolute temperature, 𝑥 is the composition of al and 𝜔 is the interchange energy. the term 𝛽 is the size factor and is given as 𝛽 = (𝜙−1) 𝜙 with 𝜙 = ωni ωau (2) where ω is the atomic size of the atom. the free energy of mixing (∆𝐺𝑀) and excess free energy of the mixing (∆𝐺𝑀 𝑥𝑠) are related as ∆𝐺𝑀 = ∆𝐺𝑀 𝑥𝑠 + 𝑅𝑇[𝑥 ln 𝑥 + (1 − 𝑥) ln(1 − 𝑥)] (3) the activity (𝑎𝑖; 𝑖 = 1,2) of the ith component of the binary liquid alloy in terms of ∆𝐺𝑀 is expressed as 𝑅𝑇 ln(𝑎𝑖) = ∆𝐺𝑀 + (1 − 𝑥) ( 𝜕∆𝐺𝑀 𝜕𝑥 ) (4) using equations (1) and (3) in equation (4), the expression for 𝑎𝑖 can be obtained as ln 𝑎𝑖 = ln[(1 − 𝛽)(1 − 𝑥)𝛾(𝑥)] + 𝛽(1 − 𝑥)𝛾(𝑥) + 𝜔 𝑅𝑇 (1 − 𝑥)2[𝛾(𝑥)]2 (5) where 𝛾(𝑥) = 1/(1 − 𝛽𝑥). the standard thermodynamic relation relating enthalpy of mixing, excess entropy of mixing and free energy of mixing are given as ∆𝐻𝑀 = ∆𝐺𝑀 − 𝑇 ( 𝜕∆𝐺𝑀 𝜕𝑇 ) (6) and ∆𝑆𝑀 𝑥𝑠 = − ( 𝜕∆𝐺𝑀 𝑥𝑠 𝜕𝑇 ) (7) s.k. yadav et al. / bibechana 18 (1) (2021) 184-192 186 using equations (1) and (3) in equation (7), one can yield the respective expressions for ∆𝐻𝑀 and ∆𝑆𝑀 𝑥𝑠 as ∆𝐻𝑀 = 𝑥(1−𝑥)𝜔 (1−𝛽𝑥) − 𝑇 𝑥(1−𝑥) (1−𝛽𝑥) 𝜕𝜔 𝜕𝑇 + 𝑅𝑇2 𝑥(1−𝑥) (1−𝛽𝑥) [ 𝛽 (1−𝛽) − 𝑥 (1−𝛽𝑥) 𝜔 𝑅𝑇 ] 𝜕𝛽 𝜕𝑇 (8) ∆𝑆𝑀 𝑥𝑠 = 𝑅𝑇𝑥(1−𝑥) (1−𝛽𝑥) [ 𝛽 (1−𝛽) − 𝜔𝑥 𝑅𝑇(1−𝛽𝑥) ] 𝜕𝛽 𝜕𝑇 − 𝑥(1 − 𝑥) 1 (1−𝛽𝑥) 𝜕𝜔 𝜕𝑇 − 𝑅[𝑥 ln(1 − 𝛽) − ln(1 − 𝛽𝑥) (9) where 𝜕𝜔 𝜕𝑇 and 𝜕𝛽 𝜕𝑇 are the temperature derivative terms of interchange energy and size factor respectively. structural properties to analyse the local arrangements of atoms in the metallic mixture, the concentration fluctuation in long wavelength limit (𝑆𝐶𝐶(0)) and warren-cowley short range order parameter (wcsrop), 𝛼1, were calculated. 𝑆𝐶𝐶(0) in terms of ∆𝐺𝑀 can be expressed by standard thermodynamic relation as [37, 38] 𝑆𝐶𝐶(0) = 𝑅𝑇 ( 𝜕2𝐺𝑀 𝜕𝑥2 ) −1 (10) using equations (1) and (3), the relation for 𝑆𝐶𝐶(0) can be obtained as 𝑆𝐶𝐶(0) = 𝑥(1−𝑥) 1−𝑥(1−𝑥)𝑓(𝛽,𝜔) (11) where 𝑓(𝛽, 𝜔) = [ 2𝜔 𝑅𝑇 (1−𝛽) (1−𝛽𝑥)3 − 𝛽2 (1−𝛽𝑥)2] (12) putting 𝑓(𝛽, 𝜔) = 0 in equations (11) and (12), the expression for ideal value of 𝑆𝐶𝐶(0) can be obtained as 𝑆𝐶𝐶 𝑖𝑑 (0) = 𝑥(1 − 𝑥) (13) the experimental value of 𝑆𝐶𝐶(0) can be calculated by the following relation 𝑆𝐶𝐶(0) = (1 − 𝑥) 𝑎𝑖 ( 𝜕𝑎𝑖 𝜕𝑥 ) = 𝑥 𝑎𝑗 ( 𝜕𝑎𝑗 𝜕(1−𝑥) ) (14) herein, 𝑎𝑖 and 𝑎𝑗 are the experimental values of the activity of ith (𝑎𝐴𝑢) and jth (𝑎𝑁𝑖) respectively. the warren-cowley short range order parameter (𝛼1) for binary liquid alloys can be given as [37, 38] 𝛼1 = (𝑆−1) [𝑆(𝑍−1)+1] (15) where 𝑍 is the coordination number and its value is taken to be 10 in present work and 𝑆 = 𝑆𝐶𝐶 𝑖𝑑 (0) 𝑆𝐶𝐶(0) . surface properties according to the butler model, the surface tension (𝜎) of the binary liquid alloy in the initial melt can be expressed as [30-32] 𝜎 = 𝜎1 0 + 𝑅𝑇 𝜑1 [ln 𝑥1 𝑆 − ln 𝑥1] + ∆𝐺𝑠,1 𝑥𝑠−∆𝐺1 𝑥𝑠 𝜑1 (16) 𝜎 = 𝜎2 0 + 𝑅𝑇 𝜑2 [ln 𝑥2 𝑆 − ln 𝑥2] + ∆𝐺𝑠,2 𝑥𝑠−∆𝐺2 𝑥𝑠 𝜑2 (17) where 𝜎𝑖 0 (𝑖 = 1, 2) is the surface tension of the pure atom 𝑖, 𝜑𝑖 is the molar surface area of pure atom 𝑖 and 𝑥𝑖 𝑆 and 𝑥𝑖 are the surface and bulk concentrations of atoms 𝑖 in the surface phase and bulk phase of the liquid alloy respectively. ∆𝐺𝑠,𝑖 𝑥𝑠 is the surface partial excess free energy of atom 𝑖 and ∆𝐺𝑖 𝑥𝑠 is the bulk partial excess free energy of atom 𝑖 and they are related as ∆𝐺𝑠,𝑖 𝑥𝑠 = 𝛽∆𝐺𝑖 𝑥𝑠, where 𝛽 is constant and 𝛽 = 0.83 [28, 32, 34, 39] is taken for calculations in the present work. the molar surface area of ith atom is expressed as 𝜑𝑖 = 1.091 (𝑉𝑖 0) 2/3 (𝑁𝐴)1/3 (18) where 𝑉𝑖 0 is the molar volume of ith atom and 𝑁𝐴 = 𝑁 is the avogadro’s number. the molar volume (𝑉𝑖 0) of ith atom is calculated by taking the ratio of its mass (𝑚𝑖) and density (𝜌𝑖 0) at the required temperature (𝑇𝐾). the temperature dependent expressions of 𝜎𝑖 0 and 𝜌𝑖 0 can be given as [40] 𝜎𝑖 0 = 𝜎0 + (𝑇𝐾 − 𝑇0) 𝑑𝜎 𝑑𝑇 and 𝜌𝑖 0 = 𝜌0 + (𝑇𝐾 − 𝑇0) 𝑑𝜌 𝑑𝑇 (19) herein, 𝜎0 and 𝜌0 are the surface tension and density of the pure atom at its melting temperature, 𝑇0 is the melting temperature of the pure atom and 𝑑𝜎 𝑑𝑇 and 𝑑𝜌 𝑑𝑇 are the temperature derivative terms of surface tension and density respectively. transport property in transport property, the viscosity (𝜂) of the system was calculated using kaptay equation [34,35] and s.k. yadav et al. / bibechana 18 (1) (2021) 184-192 187 budai-benko-kaptay (bbk) model [36]. according to the kaptay model, the expression for the viscosity of the binary liquid alloys can be given by 𝜂 = ( ℎ 𝑁𝐴 ∑ 𝑥𝑖𝑉𝑖 0 𝑖 +𝑉𝐸) exp ( ∑ 𝑥𝑖𝐺𝑖 ∗ 𝑖 −(0.155±0.015)𝐻𝑀 𝑅𝑇 ) (20) where ℎ is planck’s constant and 𝑉𝐸 is the excess volume of alloy formation which can be neglected. the term 𝐺𝑖 ∗ stands for the gibb’s energy of activation of the viscous flow of ith component and is expressed as 𝐺𝑖 ∗ = 𝑅𝑇 ln ( 𝜂𝑖 0 𝑉𝑖 0 ℎ𝑁𝐴 ) (21) where 𝜂𝑖 0 is the viscosity of the pure component of the metallic mixture and can be given as [40] 𝜂𝑖 0 = 𝜂0 exp( 𝐸 𝑅𝑇 ) (22) where 𝜂0 is the viscosity of the pure atom at its melting temperature and 𝐸 is the activation energy. the ideal value of the viscosity of the liquid mixture can be expressed as 𝜂𝑖𝑑 = ∑ 𝑥𝑖𝑖 𝜂𝑖 0 (23) following budai-benko-kaptay [36], the expression for the viscosity of binary liquid alloy can be given as 𝜂 = 𝐴. (∑ 𝑥𝑖𝑀𝑖𝑖 )1/2 (∑ 𝑥𝑖𝑉𝑖+𝑉𝐸 𝑖 )2/3 𝑇1/2 exp [ 𝐵 𝑇 (∑ 𝑥𝑖𝑇𝑚,𝑖 ∗ −𝑖 ∆𝐻𝑀 𝑞.𝑅 )] (24) where 𝑞 = 25.4 is the semi-empirical parameter which is related to the cohesion energy of the pure liquid metal and 𝑇𝑚,𝑖 ∗ is defined as effective melting point of the pure component. the values of the coefficients 𝐴 and 𝐵 can be taken as (1.8 ± 0.39) × 108 and (2.34 ± 0.2) respectively 3. results and discussion the value of 𝜙 = 1.63 was first calculated using equation (2) and then the effect of interchange energy (𝜔) on free energy of mixing (∆𝐺𝑀) was observed. for this purpose, the values of ∆𝐺𝑀 were computed using equations (1-3) for different values of 𝜔, such as ±3𝑅𝑇, ±2𝑅𝑇 and ±1𝑅𝑇. the plot of the isotherms of the compositional dependence of ∆𝐺𝑀 for aforementioned values of 𝜔 at 1150 k is portrayed in fig. 1(a). it can be observed that the negative values ∆𝐺𝑀 gradually increases with the increase in the negative values of 𝜔 and decreases with increase in the positive values of 𝜔. the value of ∆𝐺𝑀 is found to be positive for 𝑥𝐴𝑢 = 𝑥 < 0.8 for 𝜔 = +3𝑅𝑇. the optimised value of 𝜔 = 15400 and 𝛽 = 0.32886 were then obtained using equations (1-3) and the experimental value of ∆𝐺𝑀 𝑥𝑠 [29] employing the method of successive approximation. the experimental and the calculated values of ∆𝐺𝑀 𝑥𝑠 were found to be in well agreement (fig. 1(b)). both of these values are found to be positive which correspond that the au-ni liquid alloy at 1150 k is a homo-coordinating or segregating system. hence, the system shows demixing tendency with respect to the thermodynamic functions. the like-atoms clusters or self-associates are favourable in the liquid state and the system exhibit liquid miscibility gaps [4]. the activity of the system was computed using equations (5) and above determined model parameters. the experimental [29] as well as the theoretical values of activities of the monomers au (𝑎𝐴𝑢) and ni (𝑎𝑁𝑖) were found to be in well agreement (fig. 1(c)). both of these values show positive deviation from raoult’s law indicating that the preferred system is segregating in nature. theoretical investigations show that the model parameters have successfully reproduced excess free energy of mixing and activity of the system. the temperature derivative terms of model parameters ( 𝜕𝜔 𝜕𝑇 = −7.2000 and 𝜕𝛽 𝜕𝑇 = −0.00001) were optimised using equation (8) and the experimental value of the enthalpy of mixing (∆𝐻𝑀) [29]. the enthalpy of mixing (∆𝐻𝑀) and the excess entropy of mixing (∆𝑆𝑀 𝑥𝑠) were then computed using equations (8) and (9) respectively with the aid of abovementioned model parameters. both of these values are found to be in good agreement with their respective experimental values (fig. 1 (b)). moreover, the positive value of ∆𝐻𝑀 reveals the demixing tendency of the system. s.k. yadav et al. / bibechana 18 (1) (2021) 184-192 188 (a) (b) (c) fig. 1(a-c): plots of the compositional dependence of thermodynamic functions for au-ni liquid alloys at 1150 k. (a) effect of positive and negative values of 𝜔 𝑅𝑇⁄ on ∆𝐺𝑀, (b) ∆𝐺𝑀 𝑥𝑠, ∆𝐻𝑀 and ∆𝑆𝑀 and (c) 𝑎𝐴𝑢 and 𝑎𝑁𝑖. the greater insight of the homo-coordinating and hetero-coordinating nature of the liquid alloys can be obtained by computing and analysing the structural functions. for this purpose, the theoretical, ideal and experimental values of the concentration fluctuation in long wavelength limit (𝑆𝐶𝐶(0)) were computed using equations (11-14) with the help of abovementioned model parameters and the experimental value of activity [29]. the effect of the positive and the negative values of 𝜔 on 𝑆𝐶𝐶(0) were studied by arbitrarily varying the values of as 𝜔 = ±4𝑅𝑇, ±3𝑅𝑇, ±2𝑅𝑇 and ±1𝑅𝑇. it can be observed that with gradual increase in the negative values of 𝜔, the deviation between the ideal and the theoretical values of 𝑆𝐶𝐶(0) gradually increases (fig. 2(a)). these results predict that the preferred system would turn into segregating to ordering nature with increase in the negative value of 𝜔. likewise, the effect of positive values of 𝜔 on 𝑆𝐶𝐶(0) as a function of concentration is presented in fig. 2(b). it indicates that the computed values of 𝑆𝐶𝐶(0) gradually increases and reaches the peak value at 𝑥 = 0.4 for 𝜔 = +1𝑅𝑇. for 𝜔 = +2𝑅𝑇, 𝑆𝐶𝐶(0) is found to have negative value in the range 0.1 < 𝑥 < 0.53. likewise, for 𝜔 = +3𝑅𝑇, 𝑆𝐶𝐶(0) is found to be negative in the range 𝑥 < 0.9 and for 𝜔 = +4𝑅𝑇, it is found to be negative in the range 0.1 < 𝑥 < 0.62, 0.69 < 𝑥 < 0.9. as 𝑆𝐶𝐶(0) cannot have negative values, the value of interchange energy should be in between 1 and 2, i.e., +1𝑅𝑇 < 𝜔 < +2𝑅𝑇. the same result (𝜔 = +1.6107𝑅𝑇) was found during the investigation of the thermodynamic properties. the theoretical as well experimental computed values of 𝑆𝐶𝐶(0) are in excellent agreement and are found to be grater than the ideal value at all concentrations (fig. 2(c)). therefore, it can be concluded that the liquid au-ni at 1150 k shows complete homo-coordinating tendency. the theoretical values of wcsrop (𝛼1) were computed using equation (15) and plotted in fig. 2(d). the value of 𝛼1 > 1 at all compositions revealing the similar nature as by 𝑆𝐶𝐶(0). thus, the theoretical findings of thermodynamic and structural properties are in accordance and suggest the demixing behaviour of the system at selected temperature. s.k. yadav et al. / bibechana 18 (1) (2021) 184-192 189 the surface tension (𝜎) and the surface concentrations of the monomers au (𝑥𝐴𝑢 𝑠 ) and ni (𝑥𝑁𝑖 𝑠 ) were computed using butler’s model [30]. the surface tensions and densities of the pure components of the system were computed using equation (19) and the parameters in table 1. the values of 𝜎, 𝑥𝐴𝑢 𝑠 and 𝑥𝑁𝑖 𝑠 were then computed using equations (17) and (18). the ideal value of the surface tension (𝜎𝑖𝑑) of the liquid alloy is obtained as the additive sum of the surface tension of the pure atoms in it using the relation 𝜎𝑖𝑑 = ∑ 𝑥𝑖𝑖 𝜎𝑖 0. the surface concentration of au atom is found to be higher whereas that of ni is found to be lower than their respective ideal values (fig. 3(a)). therefore, au atoms segregates on the surface phase and ni atoms remains in the bulk phase in the initial melt. the computed values of the surface tension of the system is found to be less than the ideal value at all compositions (fig. 3(b)). in transport property, the viscosity (𝜂) of the system was computed using kaptay model [34,35] and budai-benko-kaptay (bbk) model [36]. the viscosity is directly related to the enthalpy of mixing of the system and is the measure of the cohesion energy of the metallic solution. the viscosity (𝜂) and its necessary ingredients for the system was computed using equations (20-24) with the help of the input parameters from table 1. the computed values of the viscosity of the system from both of the preferred models are found to be less than the ideal value at all compositions (fig. 4). (a) (b) (c) (d) fig. 2(a-d): plots of the compositional dependence of structural functions for au-ni liquid alloy at 1150 k. (a) effect of negative values of 𝜔 𝑅𝑇⁄ on 𝑆𝐶𝐶(0), (b) effect of positive values of 𝜔 𝑅𝑇⁄ on 𝑆𝐶𝐶(0), (c) 𝑆𝐶𝐶(0) and (d) wcsrop. s.k. yadav et al. / bibechana 18 (1) (2021) 184-192 190 (a) (a) (b) 3(a, b): plots of the compositional dependence of the surface tension (𝜎) and surface concentrations (𝑥𝐴𝑢 𝑠 and 𝑥𝑁𝑖 𝑠 ) for au-ni liquid alloy at 1150 k. 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1992. bibechana 19 (1-2) (2022) 170-183 170 remediation of bagmati river water using activated carbon from macrotyloma uniflorum (gram horse) seed mandira pradhananga adhikari! and janak raj bhatt central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal !email: mandira43@hotmail.com article information: received: january 23, 2022 accepted: february 02, 2022 keywords: activated carbon gram horse seed remediation water pollution abstract remediation is a technique that facilitates the removable of pollutants from contaminated water. activated carbons were prepared from indigenous macrotyloma uniflorum (gram horse) seed using orthophosphoric acid as an activating agent. the chemically activated gram horse seed powder was carbonized using muffle furnace and characterized using thermo-gravimetric analysis (tga), x-ray diffraction (xrd), fourier-transform infrared spectroscopy (ftir), boehm titration, methylene blue and iodine numbers. xrd and ftir spectra indicated that the surface of amorphous activated carbon consisted of acidic and basic functional groups which efficiently adsorb pollutants from the polluted river water. the observed methylene blue and iodine numbers suggested that an impregnation ratio of 1.26:1, three hours of carbonization duration and carbonization temperature of 300 oc were the optimum conditions for the development of micro and mesopores on the surface of the activated carbon prepared from gram horse powder. the maximum adsorption capacity of methylene blue was 312.5 mg/g and that of iodine was 1006.2 mg/g and specific surface area was 1160.44 m2/g. the both langmuir and freundlich model fit well in the methylene blue adsorption. a simple column filtration was used for the purification of river water. most of the observed water quality parameters of the sample collected from the bagmati river exceeded the limit recommended by who. however, after treatment with gram horse activated carbon, concentrations of measured parameters were reduced to who recommended value. more than 60% of the hardness, sulphate and phosphate concentrations were removed and more than 40% of alkalinity and chlorine demand were reduced by activated carbon. based on the results it is considered that activated carbon from gram horse seed can be an effectively used as bio-adsorbent for the remediation of highly polluted river water. doi: https://doi.org/10.3126/bibechana.v19i1-2.46435 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/bync/4.0/ bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:mandira43@hotmail.com https://doi.org/10.3126/bibechana.v19i1-2.46435 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ adhikari & bhatta. / bibechana 19 (1-2) (2022) 170-183 171 1. introduction water is the most essential compound for the survival of all living organisms. therefore, the accessibility of safe and palatable water is of permanent importance to human health. the ideal water should be pleasant to taste, free from harmful chemicals and pathogens and noncorrosive for domestic purposes. it is considered to be polluted if it possesses high turbidity, bad taste and odor and contains microorganisms and unwanted chemicals in quantities that can put the health at risk [1]. the water sources are getting polluted day by day due to the discharge of household, domestic, sewage, agricultural, and industrial wastes without any treatment. these pollutants create a huge problem rendering water no longer fit for drinking, domestic, industrial, and agriculture, use as well as for aquatic life [2-5]. the bagmati river is an important source of water for cultural, religious, domestic, irrigational and industrial uses in nepal. it is a principal river in the kathmandu valley river system. the river flows through the heart of kathmandu valley and continues downward through the southern plain to join the holy ganga in india [6]. until the last three decades, bagmati and its tributaries were able to fulfil the drinking, irrigation, and various other need of the valley. however, unmanaged but speedy urbanization and lacks of well manage disposing system for the household and industrial waste and untreated sewage have led to water quality deterioration which harms the river ecosystem and the health of communities living along the riverside in the kathmandu valley [3-5]. although, there are a few small and large scale bagmati clean up campaigns that were started in the kathmandu valley, effective results have not been observed yet [7]. further, the lack of efficient water treatment facilities throughout the urban and rural regions is forcing people to use polluted water for domestic, industrial and agricultural purposes. as a result, people in nepal are facing water-borne diseases such as diarrhea, dysentery, cholera, gastroenteritis, and skin diseases. almost 44,000 children are dying every year in nepal from these diseases [8]. the generation of water-borne disease suggested that water should be treated before its use for drinking water production as well as for other domestic purposes. various conventional methods were developed like filtration, chemical precipitation, ion exchange, chlorination, chemical oxidation and reduction for the treatment of water. however, these methods have certain limitations like expensive, inefficient, or generating large amounts of waste products that require further disposal [9,10]. therefore, it is necessary to conduct research on sustainable and efficient solutions especially investigating natural sources [10]. recently, the adsorption techniques using activated carbon becoming popular in the treatment of domestic and industrial water [11]. activated carbon is a powerful adsorbent used regularly throughout water purification to remove contaminants and undesirable components. it is a critical and popular tool used throughout municipal and industrial water treatment facilities [11,12]. activated carbon is carbonaceous material with different pore sizes resulting from the physical and chemical activations of raw materials at high-temperature reactions. its specific surface area varies typically from 800 m2/g to 1500 m2/g [13]. a precursor is carbonized at high temperature (800-1100 oc) and activated using steam, carbon dioxide, air etc. in physical activation. at low temperature, diffusion dominates the activation resulting in poor development of the pore structure but at high temperature diffusion process is dominated by activation leading to well develop pores [14]. in chemical activation, precursors are impregnated with different activating agents such as phosphoric acid, zinc chloride, sodium hydroxide etc. and carbonized at low bibechana 19 (1-2) (2022) 170-183 172 temperature (300600 oc). in this process, carbonization and activation occur simultaneously, hence, the decomposition of lignocellulosic material and dehydration and volatilization of impurities occur at the same time leading to well-developed pores. a maximum pore on the activated carbon depends upon the activation temperature, activating agent, impregnation ratio and carbonization time [14-18]. the porous structure of activated carbon adsorbs materials from the water. recently, studies were directed to develop activated carbon using locally available materials namely rice husk [15], corn-corb [16], lapsi seed [17], barro seed [18] etc. the efficiency of activated carbon depends upon the large number of functional groups namely hydroxyl, carboxyl acid group etc. in addition to pore structure. the lignocellulosic materials consist of hemicellulose, cellulose, lignin, protein and pectin which are responsible to develop the required functional groups on the surface of activated carbon during activation and carbonization [19]. locally available macrotyloma uniflorum (gram horse) seed contains carbohydrates, protein, dietary fiber, fat, calcium, phosphorus, iron, thiamine, riboflavin niacin etc. it is a trypsin inhibitor and source of natural phenols, such as 4hydroxybenzoic, 3,4-dihydroxybenzoic, coumaric, caffeic, ferulic, vanillic, syringic, and sinapic acids [20]. it is one of the calcium reached pulses that has many medicinal applications. it is popular in the treatment/breakdown of kidney stones [21], for the antimicrobial activities [22], as antioxidants [23] etc. therefore, in this study activated carbons were prepared from phenolic acidcontaining gram horse seed using phosphoric acid as activating agent. 2. material and method the macrotyloma uniflorum (gram horse) seeds, brought from the local market of darchula, were ground to a fine powder and sieved to 420 µm particle size. the fine powder was dried in an air oven after washing several times with distilled water. thermogravimetric analysis (tga) of the precursor was done by using a muffle furnace. 1 gram of dried powder was taken in silica crucible and subjected to pyrolysis for half an hour at each temperature in a muffle furnace and the remaining weight of the precursor was measured at different temperatures such as 100, 150, 200, 250, 300, 400, 450, 500, 550, and 600 ºc [24]. the precursor was chemically activated using 65% orthophosphoric acid as an activating agent. the optimum condition for the activation was find out by subjecting precursor at different ratios (0.16:1, 0.32:1, 0.63:1, 1.26:1 and 1.58:1, phosphorus: precursor) and carbonized at different temperatures (300, 400 500 and 600 oc) for different durations (2, 3, 4 and 5 hours) in a muffle furnace. the carbonized activated carbon was cooled, washed with1 % nahco3 and with distilled water till neutral ph was obtained then dried in an air oven at 110 oc for 24 hours. the dried activated carbon was sieved to 212 µm in size and kept in an airtight container for further analysis [25]. the activated carbons thus obtained were characterized by adsorption of methylene blue and iodine. the boehm titration was used for the determination of surface functional groups present on the surface of the activated carbon [26]. the methylene blue and iodine adsorptions were used to determine the porosity of the activated carbon. iodine number was calculated by astm d4607-94 method. the mixture of 5 ml of 5% hcl and 0.1 gram of activated carbon was boiled and cooled to room temperature. the mixture was shaken vigorously after adding 10 ml of 0.1 n iodine solution. the solution was then filtrated and titrated with 0.05 n sodium thiosulphate solution. the iodine number was calculated from the following equation [27]. 𝐼𝑜𝑑𝑖𝑛𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 = 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑖𝑜𝑑𝑖𝑛𝑒 𝑎𝑑𝑠𝑜𝑟𝑏𝑒𝑑 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑐𝑎𝑟𝑏𝑜𝑛 (𝑔) (1) methylene blue number was calculated from the single point adsorption method. the activated carbon (0.1 gram) was mixed with 100 ml of different concentrations of methylene blue adhikari & bhatta. / bibechana 19 (1-2) (2022) 170-183 173 solution such as 50, 100, 150, 200, 250, and 300 ppm and was agitated for 24 hours in a shaker at 190 rpm. the equilibrium methylene blue concentration was determined spectrophotometrically (max = 665 nm, ssi uv 2110 spectrophotometer) [28]. the amount of methylene blue adsorbed per unit mass of the adsorbent was calculated from the following equation: 𝑀𝐵𝑛 = (𝐶𝑜 − 𝐶𝑡)𝑉 𝑀 (2) where, co is the initial concentration of methylene blue and ct is the concentration at time t, in mg/l. mbn represents the amount of methylene blue adsorbed (mg/g), v and m are the volume of methylene blue and mass of activated carbon in gram, respectively. specific surface area (m2/g), was calculated using multipoint adsorption isotherm of methylene blue using langmuir model. the qe was determined from the linearized langmuir isotherm and the specific surface area calculated from the equation below [29]. s𝑀𝐵 = 𝑞𝑒 x 𝑎𝑀𝐵 x 𝑁𝐴 x 10−20 𝑀𝑀𝐵 (3) where, smb represents a specific surface area (10-3 m2/g), qe is the number of molecules of methylene blue adsorbed (mg/g), amb represents the occupied surface area of one molecule of methylene blue (197.2 å), na is the avogadro’s number and mmb represents the molecular weight of the methylene blue (319.85 g/mol) the adsorption efficiency of methylene blue was analyzed using langmuir and freundlich adsorption models [30]. the linearized langmuir adsorption isotherm is defined as 𝐶𝑒 𝑞 𝑒 = 1 𝑞 𝑚𝑎𝑥 𝑏 + ( 1 𝑞 𝑚𝑎𝑥 ) 𝐶𝑒 (4) where, ce defines the equilibrium concentration of the solution (mg/l), qe defines the amount of adsorbate adsorbed (mg/g), qmax represents a maximum amount adsorbed (mg/g), b is the langmuir constant (l/mg). the plot of ce/qe against ce gives the straight line. qmax and b were calculated from slope and intercept, respectively. the linearized freundlich adsorption isotherm is expressed as 𝑙𝑜𝑔𝑞𝑒 = 𝑙𝑜𝑔𝐾𝐹 + ( 1 𝑛 ) 𝑙𝑜𝑔𝐶𝑒 (5) where, qe = x/m, where, x is mass of substance adsorbed (mg), m is the mass of activated carbon (g), the freundlich adsorption parameters n is the adsorption intensity, and kf is the adsorption capacity of the adsorbent (mg/g). activated carbon prepared from gram horse seeds was used for the remediation of the highly polluted water from bagmati river. the water sample was collected from the balkhu region, one of the most polluted sites inside the kathmandu valley [31]. the water quality parameters such as ph, conductivity, alkalinity, hardness, sulphate, ammonia and phosphate were determined before and after the treatment of water using activated carbon. in the treatment process, 2g activated carbon was taken in a column having a diameter of 2 cm and polluted water was added slowly into the column. the rate was adjusted in 100 ml per hour and thus obtained purified sample water was analyzed subsequently. 3. results and discussion 3.1 thermogravimetric analysis a thermal behavior of lignocellulosic material can be qualitatively determined from thermogravimetry analysis. weight losses observed in the thermogravimetric analysis is found to be relevant to the composition of hemicellulose, cellulose and lignin fractions in gram horse powder [18, 24]. figure 1 shows the thermogravimetric (tg) curve of macrotyloma uniflorum (gram horse) seed powder with a diameter of less than 425 µm. the thermogravimetric analysis curve shows that the weight of gram horse seed powder decreased bibechana 19 (1-2) (2022) 170-183 174 slightly until 200ºc, and then drastically after 250 °c. above 300 °c the weight loss was insignificant which indicates completion of pyrolysis at 300 °c [24]. fig 1: thermogravimetric analysis of gram horse powder. the derivative thermogravimetric analysis (dtga) curve shows two peaks, a small peak in between 100 and 150 oc and another a large peak in between 200 and 300 °c and peak was not observed beyond 400 °c. weight loss before 200 °c was considered as evaporation of moisture and highly volatile compounds. the major weight loss between 200 and 300 °c depicts as the decomposition of hemicellulose and the degradation of lignin and cellulose [24, 32]. above 300 °c temperature residue consists of almost carbon. based on the tga curve 300 °c is considered as the optimum temperature to develop porous structure in the activated carbon. 3.2 iodine and methylene blue adsorption the adsorption capacity of gram horse activated carbon was more efficiently determined by activating precursor with different amounts of phosphoric acid and carbonized at different temperatures with various time duration. thus, obtained gram horse activated carbons were characterized using methylene blue and iodine adsorption. iodine number gives information about the presence of micropores on the surface of activated carbon. iodine numbers of different activated carbons prepared by using different amounts (ratios) of the activating agent were plotted in figure 2a. the iodine numbers of activated carbons ranged from 805 to 1006 mg/g. figure 2a shows that initially the iodine number was about 805 mg/g and it increased almost linearly till the impregnation ratio of 0.9:1 and becomes a maximum at the ratio of 1.26:1. the iodine number is decreased further increasing the activating agent. this may be attributed to a more extensive and complete reaction of phosphoric acid and surface of carbon at 1.26:1 impregnation ratio [33]. the methylene blue number was about 200 mg/g at an impregnation ratio of 0.3:1 and remained almost constant on increasing the impregnation ratio till 0.9:1 but drastically increased to 312 mg/g at the ratio of 1.26:1 and decreased with further increased in activating agent. at less amount of activating agent, reaction between phosphoric acid and carbon was not complete, however, increasing the activating agent enhanced the reaction and increased iodine and methylene blue numbers but further increasing activating agent destroyed the pore structure and decreased in iodine as well as methylene blue numbers [33, 34]. the effect of carbonization temperature was analyzed by using figure 2b, the curve reveals that iodine and methylene blue numbers were maximum, 1006.5 and 312.5 mg/g, respectively at 300 °c carbonization temperature. both iodine and methylene blue adsorptions were decreased linearly with further increase in temperature. the tga curve (figure 1) also support the results hence it was considered that pore structure was significantly developed by degradation of more volatile cellulose, hemicellulose materials at 300 oc but pores were destroyed further increase in temperature due to excess burn off carbon and coalescence of micro and mesopores or expansion of pore sizes [33]. in addition to carbonization temperature, carbonization time also effects the pore density of activated carbon. figure 2c shows that the iodine and methylene blue numbers ranged from 899 to 1006 mg/g and from 222 to 312 mg/g, 0 0.2 0.4 0.6 0.8 1 1.2 0 20 40 60 80 100 0 100 200 300 400 500 600 d t g a ( % / °c ) w ei g h t ( % ) temperature (°c) adhikari & bhatta. / bibechana 19 (1-2) (2022) 170-183 175 respectively for activated carbon carbonized for 2 to 6 hours. the values were maximum at 3hour carbonization time. fig 2: iodine and methylene blue (mb) number at different (a)impregnation ratio (b)carbonization temperature and (c)carbonization time. among the all, the activated carbon prepared by using the ratio of phosphoric acid (phosphorus) and precursor 1.26:1.0 and carbonized at 300 °c for 3 hours duration had maximum iodine (1006.5 mg/g) and methylene blue (312.50 mg/g) numbers which were almost comparable to those (1035 mg/g and 324.7 mg/g) of tea seed shells activated carbon [29].the high iodine and methylene blue numbers attributed that activated carbon consists a large density of pore hence have a great probability of a large specific surface area of gram horse activated carbon [33]. the observed iodine and methylene blue numbers of different precursors activated with phosphoric acid were tabulated in table 1. the iodine number of gram horse seed activated carbon was higher than that observed for the other precursors. it was more than 4 times higher than that of bamboo. the methylene blue number was higher than that of other precursors except for areca nut and wood. the results suggested that phosphoric acid develops numerous micropores on the surface of activated carbon which can efficiently adsorb small ions from the aqueous solutions table 1: iodine and methylene blue numbers of activated carbon prepared using different precursors precursor iodine number methylene blue number bamboo [35] 243 156 barro seed stone [18] 357 173 rice husk [36] 367 196 amaro seed stone [32] 371 256.42 sugarcane bagasse [37] 814.67 198 areca nut[38] 888 369 wood(thevetia peruviana) [39] 798 532 gram horse [this study] 1006.5 312.5 3.3 specific surface area the adsorption efficiency of activated carbon is directly related to its surface area and pore size. the iodine and methylene blue numbers depict pore structure whereas specific surface area implies available surface area for adsorption of the adsorbate. the adsorbent has a high extent of adsorption was considered to have a large specific surface area and having a low extent of adsorption have a small specific area. the specific surface area of activated carbons was plotted in figure 3. figures 3a, 3b and 3c depict 0 100 200 300 400 500 600 700 800 900 1000 1100 0 0.3 0.6 0.9 1.2 1.5 1.8 m b n u m b er (m g /g ) io d in e n u m b er ( m g /g ) impregnation ratio (a) 0 100 200 300 400 500 600 700 800 900 1000 1100 200 300 400 500 600 700 m b n u m b er ( m g /g ) io d in e n u m b er ( m g /g ) carbonization temperature (oc) (b) 0 100 200 300 400 500 600 700 800 900 1000 1100 1 2 3 4 5 6 m b n u m b er ( m g /g ) io d in e n u m b er ( m g /g ) carbonization time (hour) (c) iodine numbers (mg/g) methylene blue number(mg/g) bibechana 19 (1-2) (2022) 170-183 176 the effect of activating agent, carbonization temperature and carbonization time, respectively. fig. 3: specific surface observed at different (a) impregnation ratio (b) carbonization temperature and (c) carbonization time prepared sample the specific surface area was a maximum (1160 m2/g) at an activation ratio of 1.26:1 which was nearly 1.5 times higher than that at other activation ratios. similarly, specific surface area was a maximum at carbonization temperature of 300 oc, that was linearly decreased with further increase in temperature indicating high temperature caused coalescence of micro and mesopores. figure 3c attributed that three hour of carbonization time was appropriate for the development of a maximum surface area on the surface of gram horse activated carbon [40]. a small carbonization time caused incomplete burn off which developed a low number of pores hence a low surface area. the decrease in a specific surface area after the optimum carbonization time attributed that excess burning destroyed the micro and mesopores structure. the observed specific surface area (1160 m2/g) is higher than that reported for activated carbon from barro seed stone (537 m2/g) [18] and amaro seed stone (581.69 m2/g) [32] prepared using a similar technique. 3.3 physical and chemical characterization of activated carbon the adsorption phenomena occur on the surface of a material by which ions, metals, or substances interact with the functional group present on the surface. the seed of gram horse is rich in polyphenols flavonoids and proteins [20-22]. these functional groups can absorb ions, metals, or substances through exchange or complexation phenomena. therefore, characterization of surface properties i.e., functional group present on the surface of a precursor is essential to understand the adsorption efficiency. infrared spectroscopy is widely implied to explicate the functional groups present in the sample, particularly for the availability of main functional groups involved in adsorption phenomena. figure 4a shows the ftir spectrum of gram horse powder. the spectrum shows a broad peak in the range 32003600 cm-1 which was due to stretching vibrations of the hydroxyl group into intermolecular hydrogen bonding. the peak at 2922.70 cm-1 was considered as asymmetrical c-h stretching mode and the peak at 2841.32 cm-1 was attributed to symmetrical c-h stretching. the olefinic, c=c, stretching vibration in disubstituted (cis-) alkene caused the emergence of a peak at 1632.36 cm-1. the strong peak observed at 1537.39 cm-1 represents the n-h bending of amine. the peaks at 1394.55 600 750 900 1050 1200 0 0.3 0.6 0.9 1.2 1.5 1.8 s p . su rf ac e ar ea ( m 2 /g ) impregnation ratio (a) 600 750 900 1050 1200 0 150 300 450 600 750 s p . s u rf ac e ar ea ( m 2 /g ) carbonization temperature (oc) (b) 600 750 900 1050 1200 0 1 2 3 4 5 6 s p . s u rf ac e ar ea ( m 2 /g ) carbonization time (hour) (c) adhikari & bhatta. / bibechana 19 (1-2) (2022) 170-183 177 cm-1 and 1231.76 cm-1 were due to (-oh) bending vibration and c-o stretching vibration of the carboxylate group. the strong peak at 994.45 cm-1 was attributed to strong (c=c) bending in an alkene [41]. fig 4: ftir spectrum of (a) precursor and (b) prepared activated carbon sample figure 4b shows the ftir spectrum of activated carbon. ftir spectrum activated carbon showed a peak at 3352.39 cm-1 which was due to (o-h) stretching vibrations of the hydroxyl group. the stretching of hydrogen bonding of alcohol and phenols was located in the range of 3200 – 3600 cm-1. the peak 2137.34 cm-1 was due to (c≡c) stretching vibration in alkyne. the intense peak at 1627.90 cm-1 is attributed to (c=c) stretching vibration in an alkene. the peak at 1054.90 is attributed to the stretching vibration of c-o group. definite changes were observed in the ftir spectra of activation after activation with orthophosphoric acid. several peaks of functional groups such as carboxylic, amine disappeared which indicated that the weak bonds present in the precursor were broken during the activation process. also, the extent of the remaining functional groups was decreased in activated carbon. this was because most of the oxygenated functional groups of precursors were lost in the form of water during activation and carbonization [41]. table 2: surface properties of activated carbon. boehm’s titration is another simple method used for the determination of the acidic and basic functional groups present in the activated carbon. the amount of acidic and basic functional groups of the activated carbon analyzed from boehm’s titration were shown in table 2. the table shows that the surface of activated carbon consists of carboxylic and phenolic groups and a small amount of lactonic group. the presence of an almost equal amount of acidic and basic functional groups suggested that gram horse activated carbon may be capable to adsorb cation and anion from an aqueous solution. the phpzc implies the acidity/basicity of the surface of the adsorbent. the phpzc value of activated carbon was 5.7. this indicated that the surface of activated carbon is positively charged when the solution ph is lower and negatively charged when the solution ph is higher than phpzc. the surface of activated carbon will be protonated at low ph so negatively charge anions can electrostatically adsorb and at high ph, the surface becomes negatively charged hence can adsorb positively charged cations. the microstructure of the activated carbon was analyzed by using x-ray diffraction (xrd). figure 5 shows two broad diffraction peaks detected at 2𝜽 = 27º and 44º . the broad large peak detected at around 27º is due to the reflection from (002) plane and the small broad peak detected at around 44º is due to the reflection from (101) plane. the diffraction peaks at 2𝜽 = 27º and 44º signify that 4000 3500 3000 2500 2000 1500 1000 500 75 80 85 90 95 100 t ra ns m itt an ce wavenumber cm -1 32 75 .4 2 29 22 .7 0 22 58 .8 2 16 32 .3 5 15 37 .3 9 13 94 .5 5 99 4. 45 28 41 .3 2 12 31 .7 6 4000 3500 3000 2500 2000 1500 1000 500 91 92 93 94 95 96 97 98 99 100 t ra ns m itt an ce ( a. u. ) wavenumber cm-1 33 52 .3 9 10 54 .9 0 16 27 .9 021 37 .3 4 the concentration of functional groups, meq/g carboxyl lactone phenol acidic basic phpzc 0.85 0.019 0.39 1.259 1.19 5.7 bibechana 19 (1-2) (2022) 170-183 178 activated carbon consists of carbonaceous material [42]. the results attributed that the activated carbon prepared from gram horse seed consists of amorphous carbonaceous particles. fig. 5: xrd diagram of activated carbon 3.5 adsorption isotherms the adsorption efficiency of gram horse activated carbon was carried out by using the commonly used langmuir and freundlich adsorption model for methylene blue adsorption. figures 6a and 6b represent the linearized curves of the langmuir and freundlich isotherms, respectively. figure 6a shows a linear relation between ce and ce/qe with a coefficient of determination, r2 of 0.975 (table 3). the maximum adsorption capacity calculated from langmuir model was 312.5 mg/g and langmuir constant was 0.325 (table 3). the good correlation between the parameters depicts that there is homogeneous monolayer adsorption of methylene blue on the surface of activated carbon. the plot between log qe and logce represents the freundlich adsorption model. figure 6b shows the linear relationship between the parameters with a coefficient of determination of 0.997 (table 3). this value is higher than that for the langmuir model, which suggests that the gram horse activated carbon was more suitable for the freundlich isotherm model i.e., there is the presence of ionic bonding between negative charge surface of activated carbon and positively charge methylene blue [31]. the plot between log qe and logce represents the freundlich adsorption model. figure 6b shows the linear relationship between the parameters with a coefficient of determination of 0.997 (table 3). this value is higher than that for the langmuir model, which suggests that the gram horse activated carbon was more suitable for the freundlich isotherm model i.e., there is the presence of ionic bonding between negative charge surface of activated carbon and positively charge methylene blue [31]. fig. 6: (a) langmuir adsorption isotherm and (b) freundlich adsorption isotherm table 3: langmuir and freundlich adsorption parameters langmuir parameters freundlich parameters qmax = 312.5 mg/g b = 0.325 r2 = 0.975 kf = 87.09 n = 2.48 1/n = 0.40 r2 = 0.997 15 20 25 30 35 40 45 50 0 500 1000 1500 2000 in te n s it y (a .u ) 2theta(degrees) 002 101 0 0.5 1 1.5 2 2.5 3 -1 0 1 2 lo g q e log ce (a) 0 0.02 0.04 0.06 0.08 0 5 10 15 20 25 c e/ q e (g /l ) ce(mg/l) (b) adhikari & bhatta. / bibechana 19 (1-2) (2022) 170-183 179 3.5 remediation of bagmati river water bagmati river is prestigious for hindu people because it is used for different rituals. however previous studies reported that river water is highly polluted and most of the water quality parameters exceeded the standard who limit. it was also reported that the river water cannot be used without treatment for a domestic, industrial and agricultural purposes [2-5, 31] ]. in this study activated carbon prepared from gram horse seed was subjected for the remediation of river water. a water sample was collected from balkhu one of the most polluted regions of the bagmati river inside the kathmandu valley [31]. the physicochemical parameters of river water before and after treatment were tabulated in table 4 table 4: physicochemical parameters of river water before and after treatment with activated carbon. measured parameters before treatm ent after treatm ent who limits[43] remova l (%) ph 7.96 8.3 6.5-8.5 -4.27 conductivity (µs/cm) 520 558 1500 -7.31 total hardness (ppm) 1000 250 500 75.00 alkalinity (ppm) 420.6 220.14 200 47.66 sulphate (ppm) 45 13.5 300 70.00 phosphate (ppm) 0.36 0.126 0.1 65.00 ammonia (ppm) 0.443 0.325 0.2532.5 26.64 chlorine demand (ppm) 37.70 22.14 0.2-5 41.27 table 4 shows that the value of most of the observed water quality parameters such as hardness, alkalinity, phosphate, ammonia and chlorine demand was very high and exceeded the standard value of who [43]. based on the observed water quality parameter the river water cannot be used for domestic, agricultural and industrial without treatment. the ph of the river water was slightly alkaline (7.9) and it was increased slightly after treatment with activated carbon. although the ph of the water before and after treatment was slightly alkaline it was within the range recommended by who (6.58.5) for the drinking water. similarly, the conductivity of the river water was slightly increased after treatment however, it was also within the who limit. the slight increase in ph of treated water may be due to ion exchange interactions with surface groups on activated carbon which generate hydroxide (oh-) ions that raise the ph of water. the discharge of unbound hydroxide ions increased the conductivity of treated water [11]. because the conductivity of water is the ability of water to pass current and increase in the concentration of ions enhance the conductivity. total hardness measures the concentration of calcium and magnesium present in the water in the form of bicarbonates, chloride, and sulfate and alkalinity is measures the concentration of carbonate, bicarbonate, and hydroxide ions. the total hardness and alkalinity of the river water were 1000 and 420 ppm, respectively. both the parameters were 2 times higher than that of the value recommended by who (table 4). after treatment, the total hardness reduced by four times to 250 ppm which is within the limit of the who value. similarly, alkalinity reduced by two times to 220 ppm, which is slightly higher than who recommended value. this enormous reduction in the concentration will reduce the pollutant loading of the rivers. the result suggested that alkalinity and hardness can be removed efficiently from the polluted river water using activated carbon [44, 45]. sulphate, phosphate and ammonia concentrations are the water quality parameter that indicates water pollution. the sulfate concentration in the river water was within the who limit however, the concentration of ammonia and phosphate exceeded the who limits. the gram horse activated carbon reduced more than 65% of phosphate and sulphate and about 26% of ammonia concentration (table 4). as indicated by boehm titration the surface of activated bibechana 19 (1-2) (2022) 170-183 180 carbon consists of acidic and basic functional groups which are responsible to adsorb negatively charged sulphate and phosphate ions and positively charged ammonium ions [46]. the activated carbon adsorbed sulfate ion efficiently and reduced its concentration of it to 13.5 mg/l. other common water pollutants are pathogenic microorganisms and organic compounds. chlorine demand indicates the amount of the pathogenic microorganisms and organic pollutants present in water. table 4 shows that the chlorine demand of river water was 37.70 ppm indicating that the river water was highly contaminated with pathogenic microorganisms and organic pollutants. it was observed that after treatment the chlorine demand of the water sample decreased to 22.14 ppm. the decrease in total chlorine demand for treated water indicated that activated carbon also removed organic compounds [47] and may be pathogenic microorganisms from the water. these results suggested that gram horse activated carbon can be used efficiently for the purification of river water and possibly treated river water can be used for agricultural, industrial, irrigation and livestock drinking purpose provided that all other pollutants of concern are also within the recommended standard value. 4. conclusions activated carbons were prepared from m. uniflorum (gram horse) seeds by chemical activation with orthophosphoric acid in a muffle furnace. the activated carbons were prepared using different impregnation ratios, different carbonization temperatures and times for the optimum condition determination. the surface morphology and functional group present on the surface of activated carbon were determined by using x-ray diffraction (xrd), boehm’s titration and fourier-transform infrared spectroscopy (ftir). iodine and methylene blue numbers and specific surface area were used for the characterization of pore size and density. the methylene blue adsorption capacity of activated carbon was determined by langmuir and freundlich adsorption models. the boehm titration and ftir spectrum of activated carbon show that the surface of activated carbon contents almost equal amounts of acidic and basic functional groups with the point of zero charges is at ph 5.6. the broad two peaks in the xrd spectrum suggested that the activated carbon is amorphous. the activated carbon prepared by using different impregnation ratios, carbonization times and temperatures adsorbed 204 to 312 mg/g of methylene blue and 805 to 1006 mg/g of iodine. the maximum specific surface area (1160 m2/g) was observed for the activated carbon prepared using phosphoric acid (phosphorus) to precursor impregnation ratio of 1.26:1 and carbonization at 300 oc. both the langmuir and freundlich models suggested that the gram horse activated carbon could adsorb methylene blue efficiently. as expected, the physicochemical parameters of bagmati river water revealed that the river water was highly polluted. it was observed that the total alkalinity and hardness content of the bagmati river water were 2 times higher than the limit recommended by who, whereas phosphate content was 3 times higher than that of who standards. the results indicate 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[47] k. urano et al., adsorption of chlorinated organic compounds on activated carbon from water. water res. 25 (1991) 1459–1464. https://doi.org/10.1016/0043-1354(91)90175p. devendra sir cover page copy.jpg bibechana 17 (2020) 34-41 34 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal comparative studies on the electronic transport in magnetically quantized low band gap semiconductor system s. shrestha 1* , c. k. sarkar 2 1 central department of physics, tribhuvan university, kathmandu, nepal 2 department of etce, jadavpur university, kolkata, india * email: sanju12np@yahoo.com article information received: november 19, 2018 accepted: september 28, 2019 keywords: high magnetic field figure of merit mercury cadmium telluride electron transport abstract the q1d system formed by magnetically confined system is attracting attention of researchers in device application because it is capable of over-looking the various techniques of fabrication difficulties and defects created by such fabrication techniques. in the presence of a high magnetic field, the transverse component of the energy dispersion relation gets quantized into various equally spaced energy levels called landau levels and the motion of the carriers is completely restricted. however, the longitudinal component along the field is still free to move. the mobility of such system is enhanced when a low effective mass semiconductors n-hgcdte (mercury cadmium telluride) is used. the band structure of n-hgcdte is found to be nonparabolic due to its low band gap according to kane [phadke and sharma, 1975]. recent publications, based on experimental verifications of transport coefficient of n-hgcdte of chen and sher [chen and sher, 1982] show that the band structure of mercury cadmium telluride (mct) is more hyperbolic in nature rather than nonparabolic. the author has compared the effect of band structures on the various transport properties of mct such as mobility, seebeck coefficient, thermal conductivity, figure of merit (z) etc. the figure of merit is a very important property of a material to be used in thermoelectric devices, such as cooler, refrigerator etc. the product of z and temperature i.e. (zt), a dimensionless quantity is found to be maximum for parabolic band structure and is followed by nonparabolic and hyperbolic band structures for all ranges of variation of temperature as well as magnetic field. taking the hyperbolic band structure of mct, the effect of high and low temperature scattering mechanisms on zt is also observed. 1. introduction the quasi-one dimensional (q1d) system formed by magnetically confined system is attracting attention of researchers in device application because it is capable of over-looking the various techniques of fabrication difficulties and defects created by such fabrication techniques. in the presence of high magnetic field, the electrons in sample move into a helical path due to the lorentz force in the direction transverse to the this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.21741 http://nepjol.info/index.php/bibechana mailto:sanju12np@yahoo.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.21741 s. shrestha, c.k. sarkar / bibechana 17 (2020) 34-41 35 magnetic field. the energy of such electrons are quantized into various energy levels called the landau levels [1]. however, the motion of the electrons in the longitudinal direction i.e. along the direction of the magnetic field is still free to move, such a system behaves as a quasi-one dimensional (q1d) system. at a reasonable high magnetic field, electrons would occupy only the lowest landau level and the condition is called the extreme quantum limit (eql). to simplify our calculations we have considered the case eql in our work. the thermal transport property of semiconductors characterized by figure of merit of thermoelectric is defined as [2-4], where , and are the electrical conductivity, seebeck coefficient and the thermal conductivity respectively. has the dimension of inverse temperature. if we are trying to pump heat from cooler region to hotter one, we need high pumping efficiency (high ), low backward conduction of heat (low ) and low production of heat through joule heating (high ) [5]. high mobility is inherently important to facilitate electron transport in the thermoelectric materials to reduce the joule heating [6]. hg0.8cd0.2te (mct) is a narrow-direct band gap and alloy semiconductor useful for various electronics and optoelectronic devices for different applications such as infrared detectors [6], thermoelectric devices such as cooler (7), refrigerator etc. due to the narrow band gap, mct has very low effective mass. hence mct has a very high conductivity, is necessary to optimize the performance of thermoelectric devices. also, due to the narrow band gap, the band structure of mct is highly nonparabolic and the nonparabolicity has been calculated based on kane’s model [8]. the study of chen and sher [9], shows that the band structure of mct is more hyperbolic in nature rather than nonparabolic, as described by kane in order to explain the transport parameters of mct. in the present paper, we have calculated the thermoelectric figure of merit  z of magnetically confined q1d system of mct. the effect of the band structures on z is also studied. the effect of various low temperature scattering mechanisms such as ionized impurity (in), alloy disorder (all), acoustic phonon via deformation potential (ac) and piezoelectric (pz) scattering mechanisms and high temperature scattering mechanism such as polar optical phonon (pop) scattering mechanism [8,10,11] on the figure of merit z is also examined assuming nondegenerate carrier distributions for electrons. 2. theoretical formulation band structures of mct we consider a semiconductor with nonparabolic spherically symmetric conduction band subjected to a large longitudinal quantizing magnetic field b along -axis which causes the electrons to occupy the lowest landau level i.e. extreme quantum limit (eql). a temperature gradient ∆𝑇 is also applied along the z-axis. the boltzmann transport equation can be used for the longitudinal configuration since the magnetic quantization does not produce any effect on the longitudinal motion of charge carriers. the energy dispersion relation for electrons is given below for nonparabolic band based on kane’s model [8],  ...1ae 2 1 n am2 k e og o * 2 z 2 np         (1) where, the 1st term in the equation (1), ℏ2kz 2/ 2m∗a0 gives the longitudinal component of energy (eoz) along z-axis. in the expression kz be the z-component of the wave vector. m∗ and ℏ are the effective mass and planck’s constant divided by 2π respectively. the second term of the equation (1), gives transverse component of quantized energy along xy-plane due to the presence of magnetic field, where, eg is the band gap energy. n is landau subband index and ao being the nonparabolicity factor is given as, ...e m2 m g121a 2 1 g o * co                   (2)  /2sz   s  z s  z s. shrestha, c.k. sarkar / bibechana 17 (2020) 34-41 36 in the equation (2), |𝑔| and ωc = (be/m∗) be the lande’s g-factor and the cyclotron frequency respectively; where e, mo and b are the charge of an electron, free electron mass and magnetic flux density respectively. the wide band gap parabolic semiconductor material means eg to be large i.e. eg → ∞. in such condition ao → 1. hence, nonparabolicity factor (ao) reduces to unity. the energy dispersion relation given by equation (1) for nonparabolic band structure reduces to parabolic relation and is given as below, ... m m g1 2 1 n *m2 k e o * c 2 z 2 p                  (3) for the sake of interpretation of the experimental transport results, krishnamurthy and sher [12] suggested the hyperbolic band relation for narrow band gap semiconductors such as mct, and is given in the following form,   ...ccke 2 1 22h  (4) where, ...k eb2 2 1 nk 2 z 2         (5) the terms  and c in equation (4) are adjustable parameters to fit the experimental data[13]. the hyperbolic band structure of equation (4) is simplified in a form to make a comparative study with parabolic and nonparabolic band structures. the hyperbolic band relation given by equation (4) reduces to the simple forms similar to the equations (1) and (3) as for nonparabolic and parabolic respectively and given as, ...cc be am2 k e 2 h 0 * 2 z 2 h            (6) the nonparabolicity factor ao h for hyperbolic band structure is, ...c be m a 2 * 2 h o             (7) figure of merit the figure of merit z is expressed as [2-4], ...sz 2          (8) where, s and κ (= κe + κ1) are seebeck coefficient and thermal conductivity respectively. the electronic conductivity (σ) is given by,  ne … (9) where n is the concentration of carriers per unit volume and 𝜇 is the mobility. the mobility of electrons in the eql [14] can be expressed as,    o *am e2 (10) the symbol 〈𝜏〉 in equations (10) indicates the average over the carrier distribution function. for a nondegenerate semiconductor, the mobility relation given by equation (10) in the case of eql [14] becomes,   ...dxexpxx am e2 )x( 0 2 1 o *       (11) where, χ = eoz/kbt with , kb the boltzmann’s constant and t being the electron temperature in kelvin. for a degenerate semiconductor the mobility relation is given as [15],     ... dxfx dxf1fxx am e2 o 2 1 0 oo 2 1 0 *       (12) knowing the mobility, from equations (11) and (12) for nondegenerate and degenerate cases, one can obtain the electrical conductivity (𝜎) also, using equation (9). τ(x) in equations (11) and (12) is the total momentum relaxation time for nonphonon scattering mechanisms such as ionized impurity (in) and alloy disorder (all) scattering, found to be dominant in alloy semiconductor such as mct at low temperatures and phonon scattering mechanisms such as acoustic phonon via deformation potential (ac), piezoelectric (pz) scattering mechanism dominant at low temperatures and polar optical phonon (pop) scattering mechanism, dominant at high temperatures. the total momentum relaxation time s. shrestha, c.k. sarkar / bibechana 17 (2020) 34-41 37 due to all the scattering mechanisms is obtained by combining them using matthiessen’s rule [16]. seebeck coefficient also gives an idea of scattering processes operative and the nature of the band structures. in the presence of a temperature gradient parallel to the applied high magnetic field along zdirection, the seebeck coefficient is given [17] as,   ... tktk be e k t s bb fb z               (13) the 1st term in the equation (13) gives the magnetic field dependent fermi level term and the 2nd term is the scattering term in the form of ratio. the equation (13) is applicable for both degenerate and nondegenerate cases. the fermi energy term (ef(b)) and the average scattering term 〈𝜏〉 with proper carriers distributions are taken according to the condition of degeneracy i.e. for nondegenerate and degenerate cases separately. for a semiconductor, there are two separate contributions to the thermal conduction. the conduction due to the vibration of the atoms about their position of the thermal equilibrium (lattice vibrations for crystals) and that due to the mobile charge carriers electrons or holes. the electronic thermal conductivity, κe [18] can be expressed as, ...le  (14) the lorentz ratio l =ℒ  22 b ek , where ℒ= ... k 222 22    (15) the expression 2e is also calculated in the similar way mentioned earlier. the lattice thermal conductivity  l calculation is based on callaway’s phenomenological theory [19]. in callaway’s formula the lattice thermal conductivity is given as,   '...dx 1e e'x t 2 kk t t 0 2'x 'x l 4 3 2 b 3 b l d             (16) where, is the debye temperature. tk'x b  , where is the phonon frequency. the phonon relaxation time  l is determined by the phonon boundary scattering [20] i.e.  'll , 'l is the shortest dimension of the sample. the phonon once strike the boundary of the sample loses all it coherence. hence l is defined for the shortest length of the sample  'l along with velocity of sound   ,  is taken separately for acoustic sound velocity  acu and the piezoelectric sound velocity  pzu . 3. results and discussions the material parameters for mct are taken from the references [13,21]. for hyperbolic band structure the constants are taken as, 𝛾 = 48.3 × 10−20𝑒2 and c = 0.058e[12]. the calculations have been done with the carrier concentrations of 1 × 1020𝑚−3 for nondegenerate mct, with different nonphonon scattering mechanisms such as ionized impurity (in) and alloy disorder (all) scattering, and phonon scattering mechanisms such as acoustic phonon (ac) via deformation potential, piezoelectric (pz) and polar optical phonon (pop) scattering mechanisms [8,10,11]. the total scattering mechanism is obtained by using the matthiessen’s rule. total thermal conductivity is taken as a sum of the thermal conductivity due to electron and the lattice. for the lattice part of the thermal conductivity the boundary scatterings due to acoustic phonon (ac) and piezoelectric (pz) phonons are taken. the debye temperature td has been taken as 300k [22]. incorporating the low and high temperature scattering mechanisms such as ionized impurity (in), alloy disorder (all), acoustic phonon via deformation potential (ac), piezoelectric (pz) and polar optical phonon (pop) scattering mechanisms, dt  s. shrestha, c.k. sarkar / bibechana 17 (2020) 34-41 38 the variations of with temperature at a constant magnetic field 4.0t for nondegenerate mct, considering parabolic, nonparabolic and hyperbolic band structures are calculated and is shown in fig. 1. with the same scattering mechanisms as described above for fig.1, the variation of with magnetic field at a constant temperature 77 k for nondegenerate mct, with all three types of band structures is also shown in the fig. 2. it is observed from figs. 1-2, that the value of be maximum for parabolic band structure and is followed by the nonparabolic and then hyperbolic band structures. it is expected because is a function of conductivity (𝜎), seebeck coefficient (s), temperature (t) and the thermal conductivity (κ). the thermal conductivity (κ) is a combination of thermal conductivity due to electron (κe) and due to lattice (κ1). the lattice thermal conductivity (κ1), highly dominates the electronic thermal conductivity (κe) and hence the total thermal conductivity (κ). is found to be decreasing with temperature. however, the lattice thermal conductivity is independent of the magnetic field, is also not effected by the band structures. s for hyperbolic band structure is found to be maximum and is followed by the nonparabolic and then the parabolic band structures. however, the mobility for the parabolic band structure is found to be maximum and is followed by nonparabolic and then hyperbolic band structures [15]. hence, the overall effect causes the zt for parabolic band structure to be maximum. the variation of zt with temperature at a constant magnetic field 4t for nondegenerate mct, considering only hyperbolic band structure with the same low and high temperature scattering mechanisms used in the fig. 1 and polar optical phonon (pop) scattering mechanism, a high temperature scattering mechanism separately is shown in fig. 3. whereas the fig. 4 shows the variation of zt with magnetic field at a constant temperature 77k for nondegenerate mct, considering only hyperbolic band structure with the same combination of scattering mechanisms used in the fig. 3. both figs. 3 and 4 shows that the magnitude of zt for the curve due to polar optical phonon (pop) scattering mechanism be higher compared to the curve given by the total scattering mechanisms. it shows that the polar optical phonon (pop) scattering mechanism highly dominates over the other scattering mechanisms. it is also observed that the difference in the values of zt between two curves be significant at high temperatures and low magnetic fields. the variation of zt with temperature at a constant magnetic field 4t for nondegenerate mct, considering only hyperbolic band structure for low temperature nonphonon and phonon scattering mechanisms separately is shown in the fig. 5. whereas, fig. 6 shows the variation of zt with magnetic field at a constant temperature 77k for nondegenerate mct, considering only hyperbolic band structure with the same combination of low temperature scattering mechanisms as that used in the fig. 5. from both fig. 5 and 6 it is observed that the zt due to phonon scattering mechanisms highly dominates the zt due to nonphonon scattering mechanisms. in addition it is also found the difference in the value of zt be more prominent at high temperatures and low magnetic fields. the use of novel mct superlattices was also done for the purpose [24-26] i.e. superlattice of hg0.2cd0.8 te/hg0.8cd0.2 te [26]. according to the author, the reason for the low value of zt in mct bulk is due to its very low effective mass and a single conduction band [26]. both the properties of mct are considered by authors in the present calculation also. hagelstein and kucherov [27] examined the thermally induced open circuit voltage for hg0.86cd0.14 te thermal diode (500 μm) using inge eleuteric to make contact on both the emitters and collector sides. however, the figure of merit have been measured in hg0.86cd0.14 te [27] is without the magnetic field. we have zt zt zt zt s. shrestha, c.k. sarkar / bibechana 17 (2020) 34-41 39 compared our results for the sake of quali tat ive understanding. the results show that the value of z increases with temperature reaches maximum around about 90k and then decreases. a similar variation of dependences of z for degenerate hg0.8cd0.2 te is also found in our calculation. fig. 1: variation of zt with temperature at a constant magnetic field 4t for nondegenerate nhg0.8cd0.2te, considering parabolic (para), nonparabolic (nonp) and hyperbolic (hyper) band structures with various scattering mechanisms such as ionized impurity (in), alloy disorder (all), acoustic phonon via deformation potential (ac), piezoelectric (pz) and polar optical phonon (pop) scattering mechanisms. boundary scatterings due to acoustic phonon (ac) and piezoelectric (pz) are included for lattice thermal conductivity. fig. 2: variation of with magnetic field at a constant temperature 77k for nondegenerate nhg0.8cd0.2te, considering all the band structures and with the same scattering mechanisms used in the fig. 1. fig. 3: variation of with temperature at a constant magnetic field 4t for nondegenerate nhg0.8cd0.2te, considering only hyperbolic (hyper) band structure with the same scattering mechanisms used in the fig. 1 and only polar optical phonon (pop) scattering mechanism separately. zt zt 0 50 100 150 200 250 300 0 2000 4000 6000 8000 b=4t in+all+ac+pz+pop n=10 20 m -3 ac+pz hyper nonp para z t x 1 0 -6 temperature k 0 5 10 15 20 0 40 80 120 160 hyper nonp para t=77k in+all+ac+pz+pop n=10 20 m -3 ac+pz z t x 1 0 -6 magnetic field t 0 50 100 150 200 250 300 0 1x10 4 2x10 4 3x10 4 4x10 4 in+all+ac+pz+pop pop hyper b=4t n=10 20 m -3 ac+pz z t x 1 0 -6 temperature k s. shrestha, c.k. sarkar / bibechana 17 (2020) 34-41 40 fig. 4: variation of with magnetic field at a constant temperature 77k for nondegenerate n hg0.8cd0.2te, considering only hyperbolic (hyper) band structure with the same scattering mechanisms used in the fig. 1 and only polar optical phonon (pop) scattering mechanism separately. fig. 5: variation of zt with temperature at a constant magnetic field 4t for nondegenerate n hg0.8cd0.2te, considering only hyperbolic (hyper) band structure with low temperature phonon (ac+pz) and nonphonon (in+all) scattering mechanisms. fig. 6: variation of with magnetic field at a constant temperature 77k for nondegenerate nhg0.8cd0.2te with low temperature phonon (ac+pz) and nonphonon (in+all) scattering mechanisms. 4. conclusions the magnitude and variation of zt is found to be maximum for mct with parabolic band structure is followed by nonparabolic and hyperbolic band structures for all ranges of variation of temperature as well as magnetic field. zt due to polar optical phonon scattering mechanism dominates the total zt given by all the low and high temperature scattering mechanisms for the overall ranges of temperatures as well as for all magnetic fields. but the higher difference in the value of zt is observed at high temperatures and low magnetic fields for nondegenerate mct. in the low temperatures, zt due to phonon scattering mechanisms dominates the values of zt due to nonphonon scattering mechanisms for all temperatures and magnetic fields. acknowledgements cks wishes to thank ugc, government of india zt zt 0 5 10 15 20 0.0 2.0x10 3 4.0x10 3 6.0x10 3 in+all+ac+pz+pop pop hyper t=77k n=10 20 m -3 ac+pz z t x 1 0 -6 magnetic field t 20 40 60 80 100 0.0 2.0x10 3 4.0x10 3 6.0x10 3 in+all ac+pz hyper b=4t n=10 20 m -3 ac+pz z t x 1 0 -6 temperature k 0 5 10 15 20 0 200 400 600 hyper t=30k n=10 20 m -3 ac+pz in+all ac+pz z t x 1 0 -6 magnetic field t s. shrestha, c.k. sarkar / bibechana 17 (2020) 34-41 41 and nanotechnology and science centre ju, kolkata for financial support. s. shrestha sincerely thanks twas for providing her twows fellowship to carry out the research work. references [1] l. d. landau, diamagnetism of metals, s. physik 64 (1930) 629. 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https://journals.aps.org/prb/abstract/10.1103/physrevb.13.4457 https://doi.org/10.1002/pssb.2220940138 https://link.springer.com/article/10.1007/bf02653063 https://doi.org/10.1063/1.356576doi:10.1007/978-3-642-81416-7 https://iopscience.iop.org/article/10.1088/0022-3719/9/16/015/meta https://iopscience.iop.org/article/10.1088/0022-3719/9/16/015/meta https://doi.org/10.1063/1.356576doi:10.1007/978-3-642-81416-7 https://doi.org/10.1103/physrev.113.1046 https://link.springer.com/chapter/10.1007/bfb0044921 https://link.springer.com/chapter/10.1007/bfb0044921 https://doi.org/10.1103 https://doi.org/10.1063/1.1635992 https://doi.org/10.1063/1.371188 https://doi.org/10.1063/1.1493224 bibechana 18 (2) (2021) 18-25 18 phytochemical analysis, antioxidant and antibacterial efficacy of methanol and hexane extract of centella asiatica shanta pokhrel*, prabha neupane department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal *e-mail: shantabhattarai2014@gmail.com article information: received: august 22, 2020 accepted: november 08, 2020 keywords: antibacterial antioxidant dpp ic50 phytochemical screening abstract centella asiatica is well known for its anti-inflammatory, anticancer, antioxidant, antimicrobial, analgesic, diuretic properties. its hexane and methanol extracts were screened for the presence of phytoconstituents as well as their antibacterial and antioxidant activity. the phytochemical screening showed the presence of carbohydrate, glycosides, flavonoids, phenolic compound, alkaloids, and saponins. the methanol extract showed more effective antibacterial activity against salmonella typhi. antioxidant activity of methanol extract was evaluated by 2, 2diphenyl-1-picrylhydrazyl (dpph) free radical scavenging activity showed potent antioxidant activities with ic50 value 2.57 μg/ml slightly higher than standard ascorbic acid (ic50 = 3.74 μg/ml). the present study indicates that the tested plant can be an important source of antibacterial agents and recommends that the active phytoconstituents be isolated, identified, and screened individually for activities and also subjected further for in vivo and toxicological studies. doi: https://doi.org/10.3126/bibechana.v18i2.30760 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction centella asiatica (family umbelliferae) commonly referred to as water pennywort or indian pennywort or asiatic pennywort or ghodtapre in nepal. it is a common perennial herbaceous creeper flourishing abundantly in moist areas and distributing widely in tropical and subtropical countries including bangladesh, nepal, south africa, india etc [1]. the plant of centella asiatica is a quite aromatic, prostrate, perennial, stoloniferous, creeper herb, which height up to 15 cm. stem is striated, glabrous, rooting at the nodes. several pharmaceutical companies are utilizing such plant based formulations in treatment of various diseases and disorders world around [2]. a large number of people in developing countries depend on medicinal plants as their primary source of medication [3]. centella asiatica has been used by ayurvedic medical practitioners for almost 3000 years [4] to treat wounds, mental and neurological disorders, atherosclerosis, microbial infections, and cancer [5]. traditionally it is used to treat a broad range of diseases such as diarrhea, hepatitis, measles, toothache, syphilis, leucorrhoea etc [6]. it also possesses ulcer-preventive [7, 8a, b], bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal https://doi.org/10.3126/bibechana.v18i2.30760 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana shanta pokhrel and prabha neupane / bibechana 18 (2) (2021) 18-25 19 antioxidant, and antidepressive effects and improves venous insufficiency [9, 10]. pittella reported that centella asiatica prevents the oxidative damage that takes place in neuropathological disorders including stroke, parkinson’s disease and alzheimer’s disease by increasing the antioxidant neurological state related to aging [11]. therefore, this study was conducted to investigate the bioactive compounds of methanol and hexane extracts, their antioxidant and antibacterial activities against different strains of bacteria. 2. materials and methods 2.1 plant materials the plants (centella asiatica) were collected from hamsapur, gorkha district, western development region of nepal in june, 2018 and authenticated by central department of botany, tribhuvan university, kathmandu, nepal. the collected plants were washed, air dried in shade for about a month then ground to powder and stored in clean plastic bag. 2.2 chemicals and equipment dpph, ascorbic acid and ofloxacin were purchased from merck, darmstadt, germany. dmso, methanol, n-hexane etc. are of analytical grade reagent were brought from thermo fisher scientific india pvt. ltd. (india). spectrophotometer [sl177] was used for the absorption for dpph assay. 2.3 extraction the dried and powdered form of whole plant (65 g) were extracted successively with hexane (300 ml, 8 h), methane (300 ml, 8 h) by soxhlet extraction. the extracts were concentrated by rotary evaporator and solid and semi-solid mass obtained was kept in freezer for further analysis. 2.4 phytochemical screening the freshly prepared crude extracts were subjected to analyze the presence of main classes of phytoconstituents in hexane and methanol extract using standard protocol [12]. 2.5 antibacterial screening the antibacterial assay of the crude extract of centella asiatica was carried out by agar well diffusion method. effectiveness of antibacterial substance was evaluated by determination of zone of inhibition (zoi) as given in ref [13, 14]. the microbial strains staphylococcus aureus cocci atcc 25923 (gram-positive) and escherichia coli atcc 25922 and salmonella typhi (gram-negative) bacteria were obtained from med-micro nepal lab, kathmandu. the 50 μl of the working solution of the plant extract, dmso as negative control (nc) and 25 μl of ofloxacin (antibioticear and eye drop) as positive control (pc) at the same time in separated well (6 mm) were loaded into the respective wells with the help of micropipette. the plates were incubated overnight at 37 ℃. after 24 hours of incubation, the plates were observed for the presence of inhibition of bacterial growth that indicated by a clear zone around the wells. the size of the zone of inhibition was measured and the antibacterial activity expressed in term of the average diameter of zone of inhibition in millimeters. 2.6 antioxidant activity antioxidant activity of the methanol extract was assessed using dpph free radical [15, 16]. initially, 10 mg of the sample to be tested was dissolved in 10 ml methanol to get the stock solution of concentration of 1 mg/ml (1000 µg/ml). different concentrations of test samples of 20, 40, 60, 80 and 100 µ/ml were made from stock solutions. then 2 ml of all the concentration of test solution were mixed with 2 ml of dpph solution. the test tubes were shaken vigorously for the uniform mixing then the solutions was kept for 30 minutes in dark place at room temperature. the control was prepared as above but without the plant extracts (methanol + dpph). after 30 minutes, absorbance of the entire sample was measured at 517 nm using a uv-visible spectrophotometer. ascorbic acid of same concentration was prepared as a standard and its absorbance was also taken at 517 nm and calibration curve was constructed. percent radical scavenging shanta pokhrel and prabha neupane / bibechana 18 (2) (2021) 18-25 20 activity by sample treatment was determine by comparison with methanol treated control group, ascorbic acid was used as positive control. the radical scavenging activity was expressed as the radical scavenging percentage using the equation (1) [16]: 𝑅𝑎𝑑𝑖𝑐𝑎𝑙 𝑆𝑐𝑎𝑣𝑒𝑛𝑔𝑖𝑛𝑔 (%) = 𝐴0−𝐴𝑠 𝐴0 × 100 (1) where, a0 = absorbance of the control as = absorbance of test sample the ic50 value is the concentration of sample required to scavenge 50% of dpph free radical and was calculated from the plotted graph of radical scavenging activity against the concentration of extracts. 3. results and discussion 3.1 phytochemical screening results of the phytochemical screening are summarized in below table 1. the phytochemical screening of methanol extract of centella asiatica leaves revealed that carbohydrate, glycosides, phenols, flavonoids, and saponin were present but alkaloids, protein and xanthoprotein were absent. except alkaloid, carbohydrate, glycosides, other tested phytochemicals were found to be absent in hexane extract. the most important bioactive compounds (phytochemicals) such as alkaloids, saponins, flavonoids, tannins, sterols and phenolic compounds [17, 18] are plant derived metabolites naturally occurring in medicinal plant leaves, stem and roots where they are used as defense mechanism to protect the plant from various diseases. the presence of these phytochemicals in centella asiatica is an indication of its medicinal potential. the results presented in the above table are slightly different than the data present in the literature of plants. flory shobana et al. reported that the plant part contains most of the important secondary metabolites like carboxylic acid, flavanoids, saponin, steroids, resins, xanthoprotein, coumarins etc [17]. saranya et al. reported the presence of carbohydrates, tannins, steroids, terpenoids, alkaloids, flavanoids, cardiac glycosides, saponins etc [18]. the outputs of this study are consistent with saranya et al. and flory shobana et al. with slight different results. these slight differences are due to variation in altitude of plants, different environmental conditions. 3.2 antibacterial susceptibility assay results obtained from the antibacterial assay of methanol and hexane extracts of centella asiatica are tabulated as table 2. hexane extracts against escherichia coli, staphylococcus aureus and salmonella typhi gives zoi value 13 mm, 0 mm, and 10 mm respectively in 10% concentration. hence, the hexane extracts showed more effective towards e. coli. figure 1 (a, b, c) show the results of antibacterial activity of methanol and hexane extract. hexane extracts against escherichia coli, staphylococcus aureus and salmonella typhi showed zoi value 13, 0, and 10 mm respectively in 10% concentration. however that of 1% hexane extracts against escherichia coli, staphylococcus aureus and salmonella typhi was found 11 mm, 0 mm, and 12 mm respectively. thus hexane extracts was found more effective against escherichia coli and salmonella typhi. on the other hand hexane extract did not show any antibacterial activity against staphylococcus aureus. methanol (10% concentration) extracts showed moderately effective against escherichia coli, staphylococcus aureus and salmonella typhi with zoi 11, 10, and 14 mm respectively whereas 1% methanol extracts proved more effective against salmonella typhi with 16 mm zone of inhibition (zoi). flory shobana et al. reported that the methanol leaf extract showed maximum inhibition against staphylococcus aureus 16 mm and the 50% and 75% methanol extract also showed inhibition zone 10 and 11 mm respectively [17]. zaidan et al. explored in vitro antibacterial activity of the plant extract against staphylococcus aureus showed a zone of inhibition of 5 mm [19]. therefore, the result of antibacterial assay was also supported by other study [17, 19]. staphylococcus aureus causes infections including shanta pokhrel and prabha neupane / bibechana 18 (2) (2021) 18-25 21 superficial skin lesion, localized abscesses, and food poisoning [19]. centella asiatica has traditional claims for antibacterial activity and this finding is in line with table 1: phytochemical screening of different extracts of centella asiatica s.n phytochemical hexane methanol 1 alkaloids + 2 carbohydrate + + 3 glycosides + + 4 phenol + 5 flavanoids + 6 proteins 7 xanthoproteins 8 saponins + (+) indicates present and (–) indicates absent table 2: antibacterial analysis results of methanol and hexane extracts of centella asiatica s.n. plant extract bacteria zoi (mm) of crude extract zoi (mm) of positive control 1. hexane 10% 1% e. coli 13 11 28 s. aureus 0 0 30 s. typhi 10 12 28 2. methanol e. coli 11 0 28 s. aureus 10 0 30 s. typhi 14 16 28 table 3: percentage of radical scavenging with different concentration % of radical scavenging concentration (µg/ml ) sample 20 40 60 80 100 methanol extract 26.68 34.25 61.98 74.44 88.94 ascorbic acid 13.21 19.38 27.50 58.66 72.59 shanta pokhrel and prabha neupane / bibechana 18 (2) (2021) 18-25 22 fig. 1: antibacterial screening of methanol and hexane extract of (a) centella asiatica against (b) escherichia coli, staphylococcus aureus and (c) salmonella typhi. their indication as curative properties for antibacterial as claims. the result of this study can form the basis for further studies to evaluate against a wider range of bacteria strains. figure 1 (a, b, c) show the results of antibacterial activity of methanol and hexane extract. 3.3 antioxidant activity the antioxidant activity of extract was calculated as their capacity to scavenge free radicals of dpph, which has been widely used to evaluate the antioxidant activity of natural products from plant and microbial sources [20]. the dpph radical assay was carried out for the methanol extract of centella asiatica by using ascorbic acid as standard. the absorbance values were measured at 517 nm for different concentrations of extracts and the control. these values were used to calculate the percentage inhibitions of dpph radicals against the samples. ic50 value was calculated from the calibration curve constructed by measuring the absorbance of ascorbic acid (table 3). the absorbance with the different concentration of ascorbic acid was taken as the reference from our previous paper [14]. the comparison of percentage radical scavenging at different concentration between plant extract and ascorbic acid as standard was shown in fig 2. a b c shanta pokhrel and prabha neupane / bibechana 18 (2) (2021) 18-25 23 fig. 2: a plot of percentage radical scavenging activity vs. concentration of methanol extract and ascorbic acid. table 4: ic50 values of methanol extract and ascorbic acid s.n. sample ic50 (µg/ ml) 1. standard ascorbic acid 3.74 2. methanol extract 2.576 the ic50 value of methanol extract and ascorbic acid was observed 2.576 µg/ml and 3.74 µg/ml respectively supported by ref [14]. the antioxidant potential is in an inverse relation with ic50 value, lower value of ic50 indicates high antioxidant potential. anand et al. reported 0.07 mg/ml and 500 μg/ml ic50 values of dpph and hydroxyl radical scavenging activity of methanol extract respectively [21]. since the phytochemical screening of methanol extract showed the presence of phenol and flavonoids which are responsible for the antioxidant activity. singh et al. mentioned antioxidant activity of methanol extracts ranged from 72.0 to 85.7% and proved that there is a significantly positive correlation with anthocyanin, total phenol, flavonoids, and tannin [22]. phenolic contents are very important constituents because they act as reducing agent, hydrogen donors and metal chelator. they also act as radical scavenger due to their hydroxyl groups. funde reported that flavonoids can show their antioxidant action through scavenging or chelating process [23]. alkaloids have been associated with medicinal uses for centuries and one of their common biological properties is their cytotoxicity [23]. y = 15.803x 9.145 y = 16.471x + 7.845 0 20 40 60 80 100 20 40 60 80 100 % r a d ic a l sc a n v en in g concentration (µg/ml) shanta pokhrel and prabha neupane / bibechana 18 (2) (2021) 18-25 24 4. conclusions the results of this study revealed that the methanol extract of centella asiatica possesses pharmacologically active substances like carbohydrate, glycosides, phenols, flavonoids, saponins. the antibacterial assay of hexane extract showed moderate activity against salmonella typhi and escherichia coli but methanol extract has proved most effective against salmonella typhi. similarly, antioxidant activity of methanol extract showed potent antioxidant activities with ic50 value 2.57 μg/ml slightly higher than standard ascorbic acid (ic50 = 3.74 μg/ml). it is concluded that centella asiatica extract possess pronounced antioxidant and antibacterial biological properties and recommends that active phytoconstituents can be isolated, identified, and screened individually for activities and also subjected further for in vivo and toxicological studies. acknowledgements the authors are grateful to department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal for providing laboratory facilities to conduct experimental work. we are thankful to med-micro nepal lab, thapathali, kathmandu, nepal for antibacterial tests. references [1] g.e. trease, w.c. evans. pharmacognosy, 13th edition; elbs oxford university. press, london, uk, (1989) 245-263. 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[7] k. zahara, y. bibi, and s. tabassum, clinical and therapeutic benefits of centella asiatica. pure appl biology 3 (2014) 152-159. [8] c.l. cheng, j.s. guo, j. luk, and m.w.l. koo, the healing effects of centella extract and asiaticoside on acetic acid induced gastric ulcers in rats. life sci. 74(18) (2004) 2237-2249. [9] a) s.a. polash, t. saha, hossain m.s., and s.r. sarker, phytochemical contents, antioxidant and antibacterial activity of the ethanolic extracts of centella asiatica (l.) urb. leaf and stem, jahangirnagar university j. biol. sci. 6 (2017) 5157. b) s.a. polash, t. saha, m.s. hossain, and s.r. sarker, investigation of the phytochemicals, antioxidant, and antimicrobial activity of the andrographis paniculata leaf and stem extracts, advances in biosci. biotechnol. 8 (2017) 149-162. 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[23] d. chaudhuri, n.b. ghate, r. sarkar, and n. mandal, phytochemical analysis and evaluation of antioxidant and free radical scavenging activity of root. asian j. pharmaceut. clin. res. 5 (2012) 193-199. devendra sir cover page copy.jpg bibechana 17 (2020) 104-109 104 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal phytoconstituents and biological analysis of acorus calamus rhizome of sindhupalchowk district, nepal shanta pokhrel * , kalpana chaulagain department of chemistry, tri-chandra multiple campus, tribhuvan university, nepal ∗e-mail: shantabhattarai2014@gmail.com article information received: october 25, 2019 accepted: december 2, 2019 keywords: acoruscalamus rhizome, antibacterial activity, antioxidant activity abstract phytochemical and biological activities of methanolic and hexane extract of acorus calamus rhizome were carried out. phytochemical analysis showed the presence of flavonoid, glycoside, saponin, resin and carbohydrates which are responsible for the antibacterial activities. the antibacterial potential was studied against staphylococcus aureus (gram positive bacteria) and escherichia coli, salmonella typhi (gram negative bacteria) using agar well diffusion method. the activity was shown by both methanolic and hexane extract of acorus calamus rhizome against both gram positive and gram negative bacteria. antioxidant activity of methanolic extract was evaluated by 2, 2-diphenyl-1-picrylhydrazyl (dpph) free radical scavenging activity showed potent antioxidant activities with ic50 value 3.74 μg/ml slightly higher than standard ascorbic acid (ic50 = 3.56 μg/ml). 1. introduction acorus calamus linn. (familyaraceae) commonly referred to as calamus or sweet flag, bojho in nepali, is a well-known medicinal plant.the rhizomes were utilized extensively by the chinese, indians and american indians as well as by other cultures, and many of these uses continue to this day [1] including in nepali traditional medicine [2]. people of far western region (baitadi and darchula) of nepal utilize the juice of the acorus calamus l. rhizome as an anthelmintic and it is chewed to treat coughs, cold and sore throat [3,5]. medicinal plants, possessing secondary metabolites, are potential sources of curative drugs with the very long list of chemicals and its curative nature. plant products are used as main source of medicine throughout the world for treating various human ailments [6]. the interest to study the plants is because of their medicinally and pharmacologically important active ingredients. plant produces a plethora of natural products, such as alkaloids, flavonoid, glycoside, steroid, saponin and resin which has often been correlated with medicinal and pharmacological properties of the plants. the this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.24674 http://nepjol.info/index.php/bibechana mailto:shantabhattarai2014@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.24674 shanta pokhrel, kalpana chaulagain / bibechana 17 (2020) 104-109 105 rhizome, roots and essential oil distilled from have been reported to possess several important biological activities including antimicrobial [7-10], anticellular and immunosuppressive [11]. the aim of present study was to investigate the phytochemical constituents of extracts with methanol and hexane solvents, their antioxidant activity and antibacterial activities of extract acorus calamus rhizomes against different strains of bacteria. 2. experimental collection and preparation of plants extracts the acorus calamus rhizome was collected from the sindhupalchowk, nepal. the collected rhizomes were washed by fresh water to remove other contamination like dust, soil, insect larvae, eggs etc. then clean plant were air dried in shade for about a month, then obtained dried leaves were grinded to power and store in clean plastic bag. the powdered form (60 g) of plants rhizomes was extracted by soxhlet method in n-hexane, and methanol solvents (250 ml) at room temperature. the solvent used for soxhlet extraction, which has undergone several cycle for about 8-10 hours was collected and obtained solvents were individually concentrated by rotary evaporator under reduced pressure, maintaining temperature lower than the boiling point of respective solvents used. these extracts were stored in the refrigerator until use in vile tubes. phytochemical screening analysis of crude methanolic and hexane extracts of acorus calamus rhizome for various phytochemical constituents were carried out using standard protocols [12]. the analysis of the presence of main group of natural constituents present in the different plant extract was done by the color reaction using different specific reagents. antibacterial activity antibacterial activity of the plant extract was performed by agar well diffusion method. effectiveness of antimicrobial substance was evaluated by determination of zone of inhibition (zoi) [13]. the microbial strains staphylococcus aureus cocci atcc 25923 (gram-positive) and escherichia coli atcc 25922 and salmonella typhi (gram-negative) bacteria were obtained from medmicro nepal lab, kathmandu. the 50 µl of the working solution of the plant extract, dmso as negative control (nc) and 25 µl of ofloxacin (antibioticear and eye drop) as positive control (pc) at the same time in separated well (6 mm) were loaded into the respective wells with the help of micropipette. the plates were then left for half an hour with the lid closed so that the extract diffused into media. the plates were incubated overnight at 37 ℃. after 24 hours of incubation, the plates were observed for the presence of inhibition of bacterial growth that indicated by a clear zone around the wells. the size of the zone of inhibition was measured and the antibacterial activity expressed in term of the average diameter of zone of inhibition in millimeters. the zoi were measured with the help of millimeter ruler and mean was recorded. antioxidant activity the free radical scavenging activity of samples and standard ascorbic acid solution in methanol was determined based on their ability to react with stable 1, 1-diphenyl-2-picrylhyrazyl (dpph) free radical [14]. the ic50 (50% inhibitor concentration) value is indicated as the effective concentration of the sample that is required to scavenge 50% of the dpph free radicals. ic50 values were calculated using the inhibition curve by plotting extract concentration vs the corresponding scavenging effect. different concentrations of test samples of 20, 40, 60, 80 and 100 µ/ml were made from stock solutions. then 2 ml of all the concentration of test solution were mixed 2 ml of 2 mm dpph solution. the test tubes were shaken vigorously for the uniform mixing then the solutions was kept for 30 minutes in dark place at room temperature. the control was prepared as above but without the plant extracts (methanol + dpph). after 30 minutes absorbance of the entire sample was measured at 517 nm using a uv-visible spectrophotometer. the antioxidant activity of the samples was expressed as ic50 (inhibitory concentration), which was defined as the concentration (in μg/ml) of sample required to inhibit the formation of dpph radicals by 50%. ascorbic acid was used as positive control. free shanta pokhrel, kalpana chaulagain / bibechana 17 (2020) 104-109 106 radical scavenging activity was calculated by using following equation (1): radical scavenging (%) = a0 − as a0 ∗ 100 (1) where, ao = absorbance of the control (dpph solution + methanol) as = absorbance of test sample the % scavenging was then plotted against concentrations used and from the graph ic50 was calculated. 3. results and discussion phytochemical screening the different phytochemicals in the crude methanol and n-hexane extracts were identified by the color reaction with different reagents. the results obtained for methanolic and n-hexane extract of the plant is tabulated below (table 1). a preliminary study has reported the rhizome extracts contains large number of bioactive secondary molecules like alkaloids, tannins, carbohydrates, flavonoids, glycoside (table-1). the presence of these components in this species is an indication that it may have some medicinal potential. the rhizome of acorus calamus are used traditionally for treatment of emetic, stomachic, dyspepsia, colic, remittent fevers, nerve tonic, in bronchitis, dysentery in children, insectifying and in snake bite [6]. these results are consistent with reported in the literature [6] with slight difference. this is due to the variation in altitude of plants and different environmental conditions. table 1: phytochemical screening of various extracts of acorus calamus. s.n. phytochemicals n-hexane extracts methanol extracts 1. alkaloids + 2. flavonoids + + 3. steroids + 4. glycosides + 5. tannins + + 6. carbohydrates 7. phenol (+) sign indicated the presence of phytochemicals whereas (-) sign indicated the absence of phytochemicals antibacterial assay the diameter of zone of inhibition (zoi) produced by the plant extracts on particular bacteria was measured for the estimation of their antibacterial activity. the methanol and hexane extracts of rhizome of acorus calamus were studied. results obtained from the antibacterial analysis of different extracts are tabulated (table 2). figure 1 (a, b, c) show the results of antibacterial activity of methanolic and hexane extract of acorus calamus rhizome. it is clear that the extract shows higher antibacterial activity against s. aureus than the salmonella typhi and e. coli. hexane extracts shows higher antibacterial activity against s. aureus than the salmonella typhi and e. coli gives zoi value 15 mm, 11 mm and 11 mm respectively in 50% concentration. but in crude hexane extract of acorus calamus only show antibacterial activity against s. aureus gives zoi value 14 mm and others do not show antibacterial activity. table 2: antibacterial analysis of methanol and hexane extracts of acorus calamus rhizome. s.n. plant extract (solid) bacteria zoi (mm) of extracts at concentration 100 mg/ ml zoi (mm) of description ofloxacin as control at 100 mg/ml 1. hexane 50% crude e. coli 11 0 30 s. aureus 15 14 28 s. typhi 11 0 26 2. methanol 10% 1% e. coli 10 0 30 s. aureus 12 10 28 s. typhi 0 12 26 methanol extracts of acorus calamus against staphylococcus aureus and salmonella typhi gives zoi value 10 mm and 12 mm respectively in 1% concentration. but in 10% concentration of methanol extracts against staphylococcus aureus and shanta pokhrel, kalpana chaulagain / bibechana 17 (2020) 104-109 107 escherichia coli gives zoi value 10 mm and 12 mm and other are inactive. hexane extract shows highest zone of inhibition against staphylococcus aureus 15 mm in 50% concentration than that in methanol (12 mm in 10% concentration). according to chhatopadhyay et al. the rhizome of a. calamus exhibited 16 mm zone of inhibition, which support the present finding [16]. fig. 1: antibacterial screening of methanol and hexane extract of acorus calamus rhizome against (a) escherichia coli, (b) staphylococcus aureus, (c) salmonella typhi. antioxidant activity the antioxidant activity of the methanolic solution of different samples were explored by using 2,2diphenyl-1-picrylhydrazyl (dpph) radical scavenging assay. dpph assay antioxidants are the compounds which terminate the attack of reactive species and reduce the risk of disease [16]. most of the plants have antioxidant property. in this study, the antioxidant activity of each plant extract was measured by using 1,1diphenyl-2-picrylhydrazyl radical (dpph), is a very stable free radical with purple color. it is scavenging by antioxidants through the donation of proton forming the reduced dpph. the dpph radical assay was performed for methanol extract of acorus calamus rhizome by using ascorbic acid as standard. in this assay the mixture of dpph with different concentration of extract solution and ascorbic acid were separately incubated at room temperature and absorbance was recorded at 517 nm by spectrophotometer. calibration curve was constructed by measuring the absorbance of ascorbic acid in order to calculate ic50 value. the value obtained from plant extract was compared with ascorbic acid. the observed absorbance with the different concentration of ascorbic acid was plotted in the graph as shown below. the comparison of percentage radical scavenging at different concentration between plant extract and ascorbic acid as standard was shown in table (3) and figure (2). the comparison of percentage radical scavenging at different concentration between plant extract and ascorbic acid as standard was shown in graph. the antioxidant potential is in an inverse relation with ic50value, lower value of ic50 indicates high antioxidant potential. the ic50 values of the plant extracts along with the standard ascorbic acid is tabulated below. it is found that the ic50 value of acorus calamus rhizome in methanol extract is 3.74 μg/ml and that of standard ascorbic acid is 3.56 μg/ml. by comparing the reference standard ascorbic acid, the methanol extract showed less a b c shanta pokhrel, kalpana chaulagain / bibechana 17 (2020) 104-109 108 antioxidant activity. kumar reported that the chloroform extract of acorus calamus showed more antioxidant property and is potent dpph free radical scavenger [17]. world health organization (who) mentioned that medicinal plants would be the best source to a variety of drugs. about 80% of individuals from developed countries use natural medicine. alkaloids and tannin have antioxidant capacities because they have been found to possess antioxidant and free radical scavenging effect [17]. fig. 2: graph of absorbance vs concentration of ascorbic acid. table 3: percentage of radical scavenging with different concentrations radical scavenging (%) sample concentration (µg/ml) 20 40 60 80 100 mr 13.21 19.38 27.50 58.66 72.59 ascorbic acid 13.12 23.75 31.87 42.58 52.05 where, mr =methanol rhizome extract fig. 3: a plot of percentage radical scavenging activity vs concentration of methanol extract and ascorbic acid table 4: comparison of ic50 values of methanol extract and ascorbic acid. s. no sample ic50(µg/ml) 1. standard ascorbic acid 3.56 2. methanol rhizome extract 3.74 0 0.2 0.4 0.6 0.8 1 1.2 0 20 40 60 80 100 120 a b so rb an ce concentration absorbance absorbance y = 15.804x 9.144 y = 9.669x + 3.667 0 20 40 60 80 20 40 60 80 100% r ad ic al s ca v en g in g concentration (µg/ml) methanol ascorbic acid shanta pokhrel, kalpana chaulagain / bibechana 17 (2020) 104-109 109 4. conclusion phytochemical screening of different rhizome extract of acorus calamus showed the flavonoids and tannins were present in both the extracts while alkaloids, glycosides and steroids were only in methanol extract. the phytochemical screening and antibacterial assay of the plants indicated positive application of these plant extracts for medicinal use wherein their antioxidant property is an added advantage. more studies on this plants help to study the use of the plant. acknowledgements authors are thankful to department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal for providing laboratory facilities to conduct experimental work. we are thankful to med-micro nepal lab, thapathali, kathmandu, nepal for antibacterial tests. references [1] t. j. motley, the ethnobotany of sweet flag, acorus calamus (araceae), 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[2] anonymous, thai herbal pharmacopoeia volume ii, department of medical sciences, ministry of public health, thailand, prachachon co., ltd., bangkok, 2000. [3] p. satyal, p. poudel, a. poudel, n. s. dosoky, d. m. moriarity, b. vogler, and w.n. setzer. chemical compositions, phytotoxicity and biological activities of acorus calamus essential oils from nepal, nat prod commun. 8 (2013) 1179-1181. [4] r. c. uprety, h. asselin, e. k. boon, s. yadav, k. k. shrestha, indigenous use and bio-efficacy of medicinal plants in the rasuwa district, central nepal, j ethnobiol ethnomed. 13 (2011) 463-492. [5] s. joshi, bashyal s, study on the chemical constituents and antibacterial activity of essential oil of acorus calamus l. rhizomes of rupendehi district (nepal), j inst sci technol 23 (2018) 57-60 [6] r. balakumbahan, k. rajamani and k. kumanan, acorus calamus: an overview, j med plant res 4 (2010) 2740-2745, [7] l. j. mcgaw, a. k. jager, j. vanstaden, isolation of β-asarone, an antibacterial and anthelmintic compound, from acorus calamus in south africa, south african j. bot. 68 (2002) 31-35 [8] h. s. lee. pesticidal constituents derived from piperaceae fruit, agric chem biotechnol, 48 (2005) 65-74 [9] j. y. lee, j. y. lee, b. s. yun, b. k. hwang, antifungal activity of β-asarone from rhizome of acorus gramineus, j. agric. food chem. 52 (2004) 777-780. [10] s. phongpaichit, n. pujenjob, v. rukachaisirkul, m. ongsakul, antimicrobial activities of the crude methanol extract of acorus calamus linn., songklanakarin j. sci. technol. 27 (2005) 517-523. [11] s. mehrotra, k. p. mishra, r. maurya, r.c. srimal, v.s. yadav, r. pandey, v. k. singh, anticellular and immunosuppressive properties of ethanolic extract of acorus calamus rhizome, int. immunopharmacol. 3 (2003) 53-61. [12] i. culie, methology for analysis of vegetable drugs, practical manuals on industrial utilization of medicinal and aromatic plant, bucharest, phytochemistry 63 (1982) 97-104. [13] m. valko, d. leibfritz, j. moncol, m. t. d. cronin, m. mazur, and j. telser, free radicals and antioxidants in normal physiological functions and human disease, int. j. biochem. cell biol. 39 (2007) 44-84. [14] g. funde, phytochemicals evaluation, anticancer, antioxidant and antimicrobial activity of acorus calamus different solvent extracts, j chem pharm res 7 (2015) 495-504. [15] m. saxena, j. saxena, phytochemical screening of acorus calamus and lantana camara, int res j pharm 3 (2012) 324-326. [16] m. chhatopadhyay, s. r. ali and s. aboud, antimicrobial activities of aqueous and methanolic extracts from acorus calamus used in the treatment of wound infection isolates. int j infect 2 (2010) 18-25. [17] s. kumar, studies on antioxidant and antimicrobial activity of acorus calamus and myristica fragrans. int. j. appl. res. 2 (2016) 292-297. bibechana vol. 20, no. 1, april 2023, 36-45 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar the fatalities and injuries due to avalanche effect in the himalayan region, nepal pitri bhakta adhikari∗, sapana dawadi, shanta nepal department of physics, tri-chandra multiple campus kathmandu, nepal ∗corresponding author. email: pbadhikari09@gmail.com abstract snow avalanches present the major natural hazard in himalayan region of nepal. the loss of human life is the main effect of avalanche. the records and casualties compared with european countries which help to analyze the hazard in the mountain region and can be recommend to the public people of this area about the avalanche condition, prevention from it and dissemination of information. on analyzing the statistics of avalanche fatality in the high mountain of asia from 1895 to 2022, the fatality number was 59 at annapurna and dhaulagiri mountain peaks. different highest peak of mountains attract tourist and the massive amount of snow create an avalanche, which is one of the most devastating hazards in himalayan. this fatality events, and fatality rates of nepal and european countries from 1971 to 2022 analyzes the collected data from the des-inventor data-set, disaster risk reduction (drr) portal of the government of nepal. the european avalanche warning system is used in the government of europe using the geographic information system (arcgis) tools. this study recommends the establishment of an avalanche warning system with proper tools in the western himalayan to save the life of humans and property. keywords nepal, disaster, snow avalanche, arc gis tool, high mountain of asia. article information manuscript received: october 09, 2022; accepted: march 31, 2023 doi https://doi.org/10.3126/bibechana.v20i1.42206 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction nepal is one of the asian countries having latitude in the northern hemisphere from 26° 22’ n to 30° 27’ n and elongated along east-west with a longitude 80° 4’ e to 88° 12’ e. there are three regions: himalayan, hilly, and terai. nepal contains eight of the ten top highest mountain peaks, including mount everest, annapurna, etc. the naturally beautiful country with full of wonderful peaks of the mountain range, scenery of glorious nature, and lakes, there are ample amazing snowfalls that attract many tourists to visit. along with the glorious scenario, nepal is also susceptible to different natural hazards such as landslides, floods, thunderstorms, lightning, avalanche, earthquakes, and so on. nepal is facing several types of disaster which has damage human life and community. koenig and schultz’s (2016) state that, a large number of the mass casualties with wounded and dead peo36 http://nepjol.info/index.php/bibechana pbadhikari09@gmail.com https://doi.org/10.3126/bibechana.v20i1.42206 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ pitri bhakta adhikari et al./ bibechana 20 (2023) 36-45 37 ple within a short period [1]. they also reported that it is very difficult to give medical service because it is associated with the sudden rush of mass casualties and associated with mass panic and usually large-scale movement of the population. disaster disrupts the normal life of people, organizations, community [2]. it brings great loss in the people health which immediately poses stressful circumstance in people to handle situation for which it is not usually fully prepared. the growth of world population has increased the concentration in hazardous surroundings which focus on severity of disasters. national snow and ice data center, (2021) reported that avalanche is a natural disaster which is unpredictable and causes many injuries, loss of life, and social and economic destruction [3]. avalanche is a mass of snow, ice, and rock that collapses sliding down a mountain which harms the traveler, mountain dwellers, their work, transport, vegetation, and timber. it plays a vital role in forming sculptures and weathering the world’s most wondrous peaks. avalanches, earthquakes, tornadoes, tidal waves, tsunamis, hurricanes, volcanic eruptions, landslides, are natural disaster [4]. nepal, due to its unique geographical character, faces natural disasters every year which cause massive harm to lives and property [5]. schweizer et al., (2003) reported that the result of a complex interaction between snowpack, terrain, and meteorological weather condition creating the avalanche [6]. it can be classified into two models using the complex interaction between terrain, snowpack, and meteorological condition and from the physical and mechanical mechanisms of avalanche formation. most avalanches that cause injury to people are caused by the victims themselves. they also added that there are many ways to determine the snow avalanche. the avalanches occur on the slopes of 35 to 40 degrees because the force of gravity is generally insufficient to cause an avalanche beyond this value. it is influenced by the weather and can be prevented by vegetation on the slope. after heavy snowfall and the additional snow adds the stress and forms the avalanche and forms its different types [7]. singh and ganju, (2002) explained about calamity present in the western himalayan of india, and how snow avalanches initiate and its effects on the lives of civil and military people in the winter season [8]. they found that potential near avalanche sites got triggered due to snow metrological factors. reuter and schweizer (2009) reviewed avalanche triggering through the sound wave citeref9. they performed that some myths believed that avalanches can be triggered by noise. dixon et al., (2013) studied avalanche destruction around glacier national park (gnp), montana, on the united states at canadian border [10]. they examined the damage to transportation, property with injured and dead people from avalanches from 1949 to 1997. mcclung (2016) considered avalanche activity in the high mountain in asia and analyzed and reviewed the statistics of avalanche fatalities [11]. he concluded that the reduction of the fatal avalanche in the high mountains of asia can be governed by human action and their decision. chabot and kaba (2016) studied avalanche hazards in afghanistan, pakistan, and tajikistan and made a strong plan to reduce fatalities from avalanche hazards including in remote areas too [12]. fujita et al., (2017) considered snow amplified by an earthquake which was occurred in 2015 causing induced calamity of torrential slides in langtang region in nepal [13]. they studied the co-seismic avalanches and rock falls along with their cause and destruction which occurred in the 2015 gorkha earthquake destroying the langtang village. amanambu (2018) reported about avalanche activity in the western tianshan mountains of china and studied on the features of its triggering factors. they found that snow avalanches pose a major danger to road safety in mountainous places [14]. thakuri & koirala (2019) studied mountaineering in nepal with its effects and challenges including avalanches caused [15]. they considered the climate change occurring through the different types of natural hazards emerging in the mountain region. they got that snow avalanches had caused many deaths in the himalayan region which harmed the ascents in mountaineering. schweizer et al., (2020) considered avalanche occurrence and avalanche danger level. they got that in the snow covered mountain range of many countries, warning alerts are imminent in avalanche danger employing a five-level danger scale [16]. they found that their data were inherently incomplete got results referring to a lower limit, and consider using other similarly comprehensive data sets. thakuri et al., (2020) studied an avalanche in the high mountain of nepal [17]. they underlined avalanche as well as glacial hazards and reflect the condition of a mountain in nepal. in this article, the nature is to understand the various avalanche data and casualty of nepal present in snow covering area of nepal and in different highest mountains of asia. it helps us to compare various avalanche fatality of us, colorado and european country with nepal which helps us to reduce the damage and human loss from avalanche. 2 methodology and instrumentation the data is collected from united national disaster risk reduction (undrr) from 1971 to 2021 that includes all the disasters available in the world and the nepal disaster risk reduction portal; government of nepal (http:// drrportal.gov.np) from 2012 to 2022.the data is also collected from minpitri bhakta adhikari et al./ bibechana 20 (2023) 36-45 38 istry of home affairs (moha) compared with united national disaster risk reduction. the data include death, missing, and injured people along with economic loss of all affected areas out of 77 districts of nepal from 1971 to 2022. the collected data were analyzed using graphical design was done by aeronautical reconnaissance coverage geographic information system (arcgis) software tools. statistical package for social science (spss) is one of the statistical analyzed packages used to calculate sampled data. geographic information system (gis) is the software used to visualize, analyze and explore geographically referenced information. this software is used to map the different data and used to map the avalanche data district-wise of all the disasters compared with the avalanche. study area: nepal is an asian country that lies between india and china having 147,516 km2 in the surface area. it has been characterized into three major regions namely terai, hill, and himalayan. the altitude varies from 59 m above sea level to 8848.86 m; the height of mount everest, within the range of 160 km. the whole region of the nepal as well as other himalayan region are study area. 3 results and discussion 3.1 analysis of disaster of nepal and avalanche fatality rate of highest mountain peak of asia there are several natural hazards such as avalanche, earthquake, landslide, flood, etc. in the study area. due to this disaster, there are so many people lost their life, injured and missing. the data observed and recorded from 1971 to 2022, is shown in the table 1 in which the number of death people, injured and missing people with the estimated loss due to different disaster in nepal. figure 1: avalanche causality of nepal from 1971-2022. figure 2: avalanche fatality in 8000ers above high mountain peak, source:www.earthobservatory. nasa.gov. www.earthobservatory.nasa.gov www.earthobservatory.nasa.gov pitri bhakta adhikari et al./ bibechana 20 (2023) 36-45 39 table 1: the data of deaths, injured and missing people caused by several hazards in the nepal during 1971-01-01 to 2022-06-30. s.n. name of incidents number of death people number of missing people number of injured people 1 animal incidents 138 0 638 2 snake bite 85 0 60 3 flash fllod 43 32 0 4 accident 1675 286 646 5 panic 89 0 121 6 explosion 36 0 99 7 strong wind 184 0 497 8 forest fire 74 7 48 9 snow storm 98 31 45 10 heat wave 45 0 20 11 plague 11 0 0 12 hail storm 65 0 104 13 structure collapse 417 8 668 14 breaking tuin 0 2 0 15 bridge collapse 2 1 12 16 air crash 56 0 38 17 avalanche 281 65 138 18 cold wave 870 0 83 19 boat capsize 334 586 181 20 high altitude 80 0 22 21 heavy rainfall 186 4 285 22 wind storm 84 1 1449 23 hailstone 0 0 0 24 epidemic 7684 0 32709 25 storm 90 8 303 26 thunderbolt 1718 0 4485 27 fire 1304 0 2964 28 landslide 3520 660 2068 29 flood 2089 702 622 30 earthquake 8969 195 22311 31 other 201 20 268 total 30428 2608 70884 pitri bhakta adhikari et al./ bibechana 20 (2023) 36-45 40 table 2: fatality number, fatality rate and deaths to total number due to avalanche on the 8000 m peaks during the period of 1922 to august 2022, respectively. district average population (millions) fatalities number of missing people number of injured people fatalities density (per km2) panchthar 0.191 2 12 0 0 0.00161 solukhumbu 0.105 76 1 15 25 0.00051 taplejung 0.127 13 7 3 0 0.00357 dhading 0.33 2 12 0 0 0.0010 makwanpur 0.42 1 13 0 0 0.0004 nuwakot 0.27 1 13 4 0 0.00008 rasuwa 0.04 13 7 1 0 0.00841 gorkha 0.27 20 4 7 18 0.0055 kaski 0.49 18 5 12 6 0.0089 shankhuwasabha 1.58 2 12 1 0 0.00057 manang 0.006 59 2 1 7 0.02600 mustang 0.01 16 6 0 26 0.00447 myagdi 0.11 6 10 3 4 0.00261 rukum east 0.05 0 14 0 1 0 dolpa 0.03 32 3 2 3 0.00405 humla 0.05 7 9 6 4 0.00159 jumla 0.10 9 8 9 6 0.00316 rukum west 0.15 1 13 0 0 0.00034 bajhang 0.19 0 14 7 0 0 darchula 0.13 3 11 0 35 0.00129 table 3: the data of deaths, injured and missing people caused by several hazards in the nepal during 1971-01-01 to 2022-06-30 source(www.8000ers.com;www.earthobservatory.nasa.gov/ 8000meterpeaks;www.wikipedia/wiki/list_of_deaths_on_eightthousanders.com). s.n. peak(altitude) height(m) fatality number avalanche fatality rate (%) total number of death 1 everest(nepal-tibet) 8848 10 26.77 83 2 k2(pakistan-china) 8611 95 16.84 16 3 kanchenjunga(nepalindia) 8586 54 9.25 5 4 lhotse(nepal) 8516 32 40.62 13 5 makalu( nepal-tibet) 8463 40 7.5 3 6 cho oyu(nepal-tibet) 8201 52 17.30 9 7 dhaulagiri(nepal) 8167 82 51.21 42 8 manaslu (nepal) 8163 89 44.94 40 9 nanga parbat(pakistan) 8125 82 40.24 33 10 annapurna(nepal) 8091 73 54.79 40 11 gasherbrum i (pakistanchina) 8068 34 26.47 9 12 broad peak(pakistan) 8047 37 13.51 13 gasherbrum ii(pakistanchina) 8035 24 16.67 4 14 shisha pangma (tibet) 8013 31 35.48 11 www.8000ers.com; www.earthobservatory.nasa.gov/8000 meterpeaks; www.wikipedia/wiki/list_of_deaths_on_eightthousanders.com www.8000ers.com; www.earthobservatory.nasa.gov/8000 meterpeaks; www.wikipedia/wiki/list_of_deaths_on_eightthousanders.com pitri bhakta adhikari et al./ bibechana 20 (2023) 36-45 41 table 4: avalanche occurred in nepal himalaya and human casualties due to avalanche for the year 1990 to 2022. s. n. year location no. of death people 1 1990 mount everest 6 2 1991 mount everest 8 3 1992 khumbu 2 4 1994 mount everest 2 5 1995 khumbu region, near mt.kanchanjunga base camp 48 6 1996 mount everest 9 7 1997 mount everest 19 8 1998 mount everest 6 9 1999 mount everest; chunchet 6 10 2005 french expedition base camp 21 11 2006 khumbu icefall at mount everest 3 12 2007 mount everest 6 13 2009 khumbu icefall 2 14 2010 mount baruntse 2 15 2012 manaslu peak 9 16 2013 mount everest 8 17 2014 annapurna and dhaulagiri 59 18 2015 mount everest 23 19 2017 dolpa 1 20 2018 dhaulagiri 9 21 2019 dhading 8 table 5: total numbers of annual fatalities with 5 year average of us, colorado and european countries. year fatalities in united states colorado european 1950-1960 38 13 854 19601970 53 21 627 1970 – 1980 120 27 1158 1980 -1990 143 51 1177 1990 2000 220 62 1015 2000 -2010 279 52 990 2010 -2020 256 61 938 2020 – 60 18 182 total 1169 305 6941 pitri bhakta adhikari et al./ bibechana 20 (2023) 36-45 42 figure 3: us avalanche fatalities data in combination chart. figure 4: colorado avalanche fatalities data in combination chart. nepal is affected by different disaster as shown in table 1. the earthquake, epidemic, landslide, flood, thunderbolt, accident, fire, cold wave, avalanche, boat capsize, are the main disaster during the time of fifty-two years. nepal is mostly harmed by earthquake which was totally damaged in 2015 gorkha epicenter earthquake. in this earthquake 8969 lost their life and so many were injured with many loss of property. similarly, 7684 people lost their life due to epidemic, 3520 due to landslide, 2089 due to flood, 1718 due to thunder-bold lightning, 281 due to avalanche during the mentioned period. nepal had been facing economic problems from the natural disaster which created lots of losses the property. not only the loss of human life, animals, but also many physical properties. among 77 district of nepal, only 20 districts area affected from avalanche. the total number of fatalities was divided by the total number of population is the fatality density as per millions to obtain fatality rate per million for each district of nepal as shown in table 2. the total population of nepal was obpitri bhakta adhikari et al./ bibechana 20 (2023) 36-45 43 figure 5: europe avalanche fatalities data in bar graph. tained from the nepal census 2021 and the data of fatalities, missing, and injured people in different district occurred from avalanche during the period of 52 years. in the table 2, we mentioned districts, average populations of these districts, fatalities numbers with ranks and fatality density per area (km2). there are only 20 district’s data among 77 districts because no loss of lives and properties in this area caused due to avalanche. the fatality density on this table is calculated by dividing fatality number by area (per square kilometer) where the highest one is 0.00051 of district solukhumbu and lowest are bajhang, rukum east and lamjung. the highest fatality occurred, 76 in solukhumbu district followed by manang with 58.4. fatalities and dolpa as a third ranked has 32 deaths due to avalanche. himalaya lies in nepal are mostly triggered by avalanche. the highest peak mount everest having height 8848.86 meter have two base camps. many tourists or mountaineers come there to climb the peak and they can be affected mostly. the figure 1 represents the injured and missing people from avalanche effect. in this pie diagram, the size of the circle represents the affected area which is highest in solukhumbu, then manang, dolpa and so on. hence, in the himalayan part avalanche condition is more than in hilly and terai region. in the himalayan area, it is covered by snow and mountain peaks so avalanche triggering area is more. in the world, northern hemisphere is covered by snow and ice. in table 3, there is the data of avalanche fatality with different incident event recorded by european avalanche warning services from 2020 to 2022. fatality number of 14 mountain peaks due to avalanche up to august 2021 is shown in table 3. the data consist of documented cases and summary data from the websites of (www.8000ers.com) for the information of 8000 m peaks since 1979. the proliferation of expedition containing the database cannot be comprehensively represented over the past 30 years and has grown rapidly since 1990. the data were stratified according to type of accidents, climate change and so on. the table is the lists of avalanche fatality with its characteristics and risks occurred in this sets of peaks. these peaks are very challenging having highest risks to reach the summits. the high mountain of asia having 8000 m peaks are the best recorded for fatal accidents. the table 3 suggests that the highest peaks of central himalayas exhibit very high risk area of avalanche for climbers. the highest number of fatality was happened in peak mount everest and the lowest number in shisha pangma in comparison to world’s peaks but in the context of nepal, the highest mountain in the world. mount everest which have height 8848.86 m have highest number of fatality and successful ascents per death and the lowest one is in the peak makalu having deaths of 40 people. k2 peak located in pakistan to china and nanga parbat located in pakistan are the second and third in rank for fatality number 91 and 85 respectively. there are four peaks which have the same number of fatality case due to avalanche. broad peak located in pakistan and gasherbrum i located in pakistan to china are pitri bhakta adhikari et al./ bibechana 20 (2023) 36-45 44 figure 6: us, colorado and european avalanche fatalities data in combination chart. two peaks which have the same number of fatality 34, similarly, peak manaslu and lhotse both from nepal felt same number of fatalities 84. in shisha pangma, the deaths appear from a mix of routes having fairly simple snow climbs prone for the formation of avalanche. the most deadly disaster in the history in mt. everest was from avalanche. there are eight mountain peaks which touch the outline of nepal and four peaks are near and at pakistan area. avalanche data occurred in nepal himalayan is been listed in table 4. here is the description of avalanche statistical data based on different literature, article, moha, on different location occurred on different ice land area and snow area. the years 1995, 1997, 2005, 2014 and 2015 have the top deaths rate respectively 48, 19, 21, 59 and 23 caused due to avalanche. the most affected area for the avalanche is mount everest where every year certain people died from avalanche. the area is also most triggering place where tourist has been killed in an avalanche as well as snow storm. the description of these all fatality rate in the 8000ers mountain peaks is virtually shown in figure 2. the most affected region from avalanche is in mount everest. 3.2 comparing the avalanche data of us, colorado and europe in the table 5, the total number of dead people from avalanche in europe country is listed. the data is from 1951 to 2021 in which 5 year average fatalities of us, colorado and european countries are also illustrated. the europe continent contains 16 country. the data is taken from european avalanche warning services. the bar diagram and line graph of us avalanche fatalities is shown in figure 3, colorado fatalities is shown in figure 4, and european avalanche fatalities is shown in figure 5 during the years of 1951 to 2021. the data is collected from colorado avalanche information center and european avalanche warning service from 1951 to 2021. bar diagram represent here in year wise avalanche and the red line denote the five year fatalities in the respective figures. here, in us annual fatality rate from 1951 to 2022 is 1169. in the table 5 total annual fatality rate of colorado is 305. the five year average annual fatality rate of avalanche from 1951 to 2021 is 284.6. it is shown that most affected area from avalanche is european continent. there are sixteen countries in a european continent. mostly there is highest number of the european country is covered by snow which is most affected for avalanche. all the annual fatality rate of different years is represented in the given figure. total number of fatalities with incident event from january 2020 to april 2022 occurred in european country** recorded by european avalanche warning services. the fatality rate is going on increasing from the data which indicates that the avalanche problem going on the danger level. here the fatality rate of three countries is shown i.e. us, colorado and european of fatality is shown in table 5. the table described about avalanche problem in different year with forecasted regional danger level. here comparing the fatality rate of three countries which is shown in figure 6, i.e. us, colorado and european. 4 conclusion the avalanche is less studied in nepal, on comparing to other disasters even its fatality rate is pitri bhakta adhikari et al./ bibechana 20 (2023) 36-45 45 high. especially, people suffered from avalanche in the mountainous area and its dwellers area. the avalanche activity also depends on elevation of mountain. there is an estimated loss of lives through disaster in different region of nepal. the total deaths, missing and injured people due to avalanche is found to almost 100. the fatality rate due to avalanche activity in the himalayan region varies from place to place. the solukhumbu is the most affected area due to avalanche, covered from snow due to high altitude. mt. everest, dhaulagiri, annapurna, manaslu, have higher mortality rate than kanchenjunga, lotse, cho-you, and makalu. the death rate is high in nepal than other due to avalanche. european countries are most harmed and hampered than united states and colorado. switzerland is mostly effected among the different countries of europe. references [1] k. l. koenig and c. h. schultz. koenig and schultz’s disaster medicine. cambridge university press, usa, 2016. [2] c. b. lavinia javier cueto. pandemic and typhoon: positive impacts of a double disaster on mental health of female students in the philippines. behaviour sciences, 11(5):64, 2021. [3] national snow and ice data center. national snow and ice data center. retrieved from https://nsidc.org/, 2021. [4] international federation of red cross and red crescent societies. international federation of red cross and red crescent societies. retrieved 2022, from https: //www.ifrc.org/: https://www.ifrc.org/ what-disaster, 2022. [5] k. neupane, u. dhakal, and s. h. acharya. nepal disaster report. ministry of home affairs, government of nepal, nepal, 2017. [6] j. schweizer, j. b. jamieson, and m. schneebe. snow avalanche formation. reviews of geophysics, 41, 2003. [7] types of avalanches. retrieved from https:// www.americanavalancheassociation.org/, 2021. [8] a. singh and a. ganju. earthquakes and avalanches in western himalaya. in proceedings of the 12th symposium on earthquake engineering, 16:18, 2002. [9] b. reuter and j. schweizer. avalanche triggering by sound: myth and truth. in proceedings of the international snow science workshop, pages 330–333, 2009. [10] r. w. dixon, b. r. david, l. m. dechano, and j. a. henry. avalanche hazard in glacier national park: an el nino connection. physical geography, 20:461–467, 2013. [11] d. mcclung. avalanche character and fatalities in the high mountains of asia. annals of glaciology, pages 114–118, 2016. [12] d. chabot and a. kaba. avalanche forecasting in the central asian countries of afghanistan, pakistan and tajikistan. proc. (2016) intl. snow sci. wksp., breckenridge, co, 2016. [13] h. i. fujita koji and k. fujita. anomalous winter-snow-amplified earthquake-induced disaster. natural hazards earth sysem sciences, pages 749–764, 2017. [14] a. amanambu. avalanche activity and characteristics of its triggering factors in the western tianshan mountains,china. the jounal of mountain science, 2018. [15] s. thakuri and s. koirala. climate change and mountaineering in nepal: issues and challenges. nepal mountain academy, 1(1):137– 152, 2019. [16] j. schweizer, c. mitterer, f. techel, a. stoffel, and b. reuter. on the relation between avalanche occurrence and avalanche danger level. the cryosphere, pages 737–750, 2020. [17] s. thakuri, r. chauhan, and p. baskota. glacial hazards and avalanches in high mountains of nepal himalaya. journal of tourism and himalayan adventures, 2:2738– 9642, 2020. https://nsidc.org/ https://www.ifrc.org/ https://www.ifrc.org/ https://www.ifrc.org/what-disaster https://www.ifrc.org/what-disaster https://www.americanavalancheassociation.org/ https://www.americanavalancheassociation.org/ introduction methodology and instrumentation results and discussion analysis of disaster of nepal and avalanche fatality rate of highest mountain peak of asia comparing the avalanche data of us, colorado and europe conclusion bibechana 18 (1) (2021) 193-200 193 empirical model for estimation of global solar radiation at lowland region biratnagar using satellite data ganesh k. shrestha1, binod pandey1*, usha joshi2, khem n. poudyal1 1 institute of engineering, tribhuvan university, kathmandu, nepal 2department of physics, patan multiple campus, tu, kathmandu, nepal *email: pandeybinod@ioe.edu.np article information: received: june 26, 2020 accepted: december 7, 2020 keywords: sunshine duration satellite data of gsr regression coefficient linear model statistical test abstract this study proposes to find the regression coefficient of modified angstrom type model for the estimation of global solar radiation (gsr) in lowland biratnagar (lat. 26.5º n, long. 87.3º e and alt. 72m) using relative sunshine duration and satellite data of gsr. using the regression technique, the empirical constants 0.29 and 0.56 are found in modified angstrom model. furthermore, modified angstrom model along with other linear models such as glover and mcculloch model, page model, rietveld model and turton's model are statistically assessed to evaluate the significance of models. statistical test like mpe, mbe, rmse and cc reveal that all these models are statistically significant. these findings can be utilized for other locations with high confidence level at the similar climatic locations of nepal. doi: https://doi.org/10.3126/bibechana.v18i1.29689 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction energy is a fundamental driving tool in global change. fossil fuel has been playing a key role in global energy systems as well as technological, social and economic progress. however, use of fossil fuel increase by leaps and bounds since 20th century has been releasing carbon on alarming rate. this leads to various repercussions like climate change which may wipe out the human civilization from the earth. so it is high time to explore and promote renewable energy technology for the sustainable development on low carbon trajectory [1, 2, 3, 4]. solar energy is the energy from the sun which is emitted in the form of electromagnetic radiation. solar energy, an ultimate source of all form of energy, is also a promising source of energy for the sustainable future. solar radiation data are crucial in agriculture, evapotranspiration, architectural design, meteorology, hydrology, and the designing and sizing of solar energy systems. the development of bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:pandeybinod@ioe.edu.np https://doi.org/10.3126/bibechana.v18i1.29689 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana ganesh k. shrestha et al. / bibechana 18 (1) (2021) 193-200 194 database on the long term solar radiation is essential for evaluation of solar energy potential and other modelling applications. indeed, efficient design, sizing, and performance of solar energy devices depend on the accuracy of the available insolation data of the site. this information is utilized in the design, cost analysis, and calculation of the efficiency of a project. apart from this, assessment of various meteorological parameters like humidity, temperature, clearness index as well as sunshine hours for specific period is essential in the viability of solar related project [3, 4, 5, 6, 7, 8]. ground measurement at site of interest by installing a thermopile sensor such as pyranometer or pyroheliometer is considered as most accurate and reliable way of obtaining global solar radiation data for solar energy system design. however, continuous and long-term ground measurements is daunting because of high acquisition and maintenance costs, susceptibility of soiling as well as high power demand for operation of pyranometer[3,4]. for country like nepal, it is difficult to setup good network of measuring station for long term measurement. although, different study shows that the average gsr is about 4.23 kwh/m2/day and the sun shines for about 300 days in a year .the national average sunshine duration is about 6.8 hrs/day. this study indicates that nepal is rich in solar energy. but, to confirm this statement long term continuous solar energy data are required [8, 9]. in order to overcome these difficulties we can develop an empirical models based on radiation data derived from satellite database and meteorological parameters. it is an alternative way to get solar database for research and development of solar energy systems. there are various empirical models for estimating gsr using several meteorological data. the most commonly used model which relates the gsr to sunshine duration was first time developed by angstrom [10]. subsequently, other more models are introduced using sunshine duration, maximum and minimum temperature, relative humidity, rainfall, wind speed and so on [8, 11]. the main purpose of this paper is to determine the coefficients 'a' and 'b' from angstrom’s model as well as statistically assess the appropriateness of existing linear model like glover and mcculloch model, page model, rietveld model and turton's model for estimation of gsr in horizontal surface based on satellites data for biratnagar, nepal. climatic properties biratnagar is the capital city of province no 1, nepal, lies at 26.5 0n and 87.30 e at mean elevation of about 72m from sea level. it is characterized by humid subtropical warm temperate climate where temperature normally varies from a minimum of 10.50c for december to maximum of 33.9 0c for april with annual average of mean temperature normal of 24.20c. the annual average of precipitation is normally 1891.8mm, most of which falls during monsoon. july has the most rainfall, with an average of 530.8 mm and november is the driest month, with an average rainfall of 5.9 mm [12]. 2. method methods of instrumentation in the present study, the data of the bright sunshine hours for the biratnagar were supplied from the dept. of hydrology and meteorology. the monthly average data of global solar radiation on horizontal surface over the period of 22 years (1983-2005) was obtained from surface meteorological and solar energy (sse) web portal supported by nasa larc [13]. there are various equations relating solar radiation as function of meteorological parameters like relative humidity, ambient temperature and sunshine hours. the first correlation proposed for estimating the monthly mean daily global solar radiation on a horizontal surface using the sunshine duration data is due to angstrom [10] and prescott [14] have put ganesh k. shrestha et al. / bibechana 18 (1) (2021) 193-200 195 the angstrom correlation in more convenient form as h̅g h̅o = a + b ( n̅ n̅ ) …(1) where, constants 'a' and 'b' are empirical constants estimated using regression analysis. the physical significance of the regression constants is that ‘a’ represents the case of overall atmospheric transmission for an overcast sky condition. it means that n̅/n̅ is nearly equal to zero. in other hands, ‘b’ is the rate of increase of h̅g/h̅o with mean of n/n. the sum of 'a' and 'b' significantly represents the overall transmission under clear sky index. n is the day length (hours), n is bright sunshine hours, h̅g is the monthly average of daily global solar radiation, measured on horizontal surface, h̅o is the monthly average of extra-terrestrial solar radiation,n ̅ is the monthly average daily sunshine hours and n̅ is monthly average day length in hours. the monthly average daily extra-terrestrial solar radiation h̅o is calculated using h̅o = 1 n2−n1 ∑ ho n2 n1 ….(2) where n1 and n2 are the day numbers at beginning and end of the month respectively and, ho is given by ho = 24 π isc (1 + 0.033 cos 360 365 n) (ω π 180 sin∅ sinδ + cos∅ cosδ sinω) …(3) δ = 23.45 sin ( 360 365 (284 + n)) …(4) n = 2 15 cos−1(−tan∅ tanδ) …(5) ω = cos−1(−tan∅ tanδ) …(6) whereisc is the solar constant ,∅ is the latitude of the site ,δ is the solar declination, ωis the hours angle ,n is the day length, n is the day of the year starting from 1st of january [15, 16]. the angstrom-prescott regression equation is commonly used simplest model to estimate the average global solar radiation on horizontal surface that is used to estimate the monthly average daily global solar radiation on a horizontal surface in biratnagar. the solar radiation reaching the earth’s surface can be estimated by empirical model when measured data are available. the result of our model is compared with four other previously reported linear models. the models are: turton’s model, which developed an average regression constants for the humid tropical climate as: h̅g h̅o = 0.34 + 0.4 ( n̅ n̅ ) …(7) rietveld’s model is believed to be universal in nature given by: h̅g h̅o = 0.18 + 0.62 ( n̅ n̅ ) …(8) mcculloch’s model takes into account the latitude effect and is valid for ∅ < 60° given by h̅g h̅o = 0.29cos∅ + 0.52 ( n̅ n̅ ) …(9) page model is as follows: h̅g h̅o = 0.23 + 0.48 ( n̅ n̅ ) ….(10) these models are applied to the sunshine data at biratnagar. the estimated and measured value of average daily global radiation on the horizontal surface is compared to find the best correlation with the measured global solar radiation. the results are as shown in table2 [15, 16]. method of statistical comparison the results of these models were assessed by the statistical tests like mean percentage error (mpe), root mean square error (rmse), mean bias error (mbe), and correlation coefficient (cc). mpe, mbe, rmse and cc are the statistical gauges with which one can compare the models. the result of statistical assessment is shown in table-3. the mpe can be defined as the percentage deviation of the monthly average daily radiation values estimated by the model used from the measured values. the signs of errors are neglected and percentage errors are added up to obtain the mean. mpe = ( 1 n ) ∑ [ hest−hmes hmes ] ….(11) ganesh k. shrestha et al. / bibechana 18 (1) (2021) 193-200 196 the mean bias error gives an idea of the difference between the monthly average daily radiation values estimated by the model used and the measured value. a positive value shows over estimation and a negative value is under estimation. over estimation of an individual observation will cancel under estimation in a separate observation. mbe = ( 1 n ) ∑[hest − hmes] ….(12) it gives the long term performance of the correlation by allowing a comparison of the actual deviation between calculated and measured values term by term. the root mean square error yields the same idea of the divergence between the monthly average daily radiation values estimated by the model used and the measured values as given by mbe. however the information is relevant to the short-term performance. rmse = √ ∑(hest−hmes)2 n …(13) the correlation coefficient (cc) is the measure of linear relationship between the estimated and measured values. it is given by the correlation coefficient (cc) is the measure of linear relationship between the estimated and measured values. it is given by cc = ∑(hest−h̅est)(hmes−h̅mes) √[∑(hest−h̅est)2][∑(hmes−h̅mes)2] …(14) where hest is calculated value and table -1: meteorological data and solar radiation at lowland biratnagar. month h̅o (mj/m2/day) h̅g (mj/m2/day) kt (h̅g h̅o⁄ ) n̅ (hours) n̅ (hours) n̅/n̅ jan 23.37 15.12 0.65 10.54 6.15 0.58 feb 27.61 18.68 0.68 11.11 7.72 0.70 mar 32.95 22.32 0.68 11.87 7.26 0.61 apr 37.42 23.98 0.64 12.66 8.61 0.68 may 39.90 23.47 0.59 13.32 6.83 0.51 jun 40.66 19.48 0.48 13.63 3.96 0.29 jul 40.09 15.88 0.40 13.46 3.35 0.25 aug 37.99 16.31 0.43 12.88 3.58 0.28 sep 34.05 15.62 0.46 12.11 5.44 0.45 oct 28.81 17.78 0.62 11.31 8.00 0.71 nov 24.11 17.06 0.71 10.66 7.44 0.70 dec 22.00 14.90 0.68 10.36 5.33 0.51 hmes is the measured value of the average daily global solar radiation and n is the number of observations. h̅est and h̅mes are the mean estimated and measured values of global solar radiation on horizontal surface. the ideal value for mpe, mbe and rmse would be zero. however, ideal value of cc should be 1. rmse can never be negative and the lower the value the more accurate the estimate [15]. 3. results and discussion the input parameters used for the estimation of monthly average global solar radiation at lowland region, biratnagar are given in table-1. data of table-2 shows the results of statistical test along with the models. data of table-3 depicts the estimated values of monthly average global solar radiation by using these linear models. figure-1 shows that the sunshine duration (ssd) varies as rotation of earth and local weather condition. its maximum and minimum values, i.e. 8.61 hours and 3.35 hours are found on april and ganesh k. shrestha et al. / bibechana 18 (1) (2021) 193-200 197 july. data of table-1 shows that the sunshine duration is more than 6 hours per day except in june, july, august and september. in those months the sunshine hour and gsr is comparatively lower due to clouds and rainfall. figure.-2 shows the monthly variation of relative sunshine hours (n̅/n̅) and clearness index (kt) at biratnagar. the poor sky condition due to high relative humidity and rainfall cause depression in the month of july and august. where n̅/n̅ goes as low as 0.25 and kt reaches a minimum value of 0.40 for july and 0.43 for august. figure-3 shows that both measured and estimated values of gsr are strongly correlated as the correlation coefficient is greater than 0.85 for ever model. the value of mbe is slightly positive for ap model which indicates overestimation than measured value. for rest of the models, the mbe is negative which show underestimation than measured value. the rmse for a-p model is least and greatest for the page model. table-2: summary of empiricals models with statistical indicators. model name empirical model mpe (%) mbe rmse cc angstrom-prescott model h̅g/h̅o=0.29+0.56(n̅/n̅) 1.50 0.25 1.50 0.89 glover and mcculloch model h̅g/h̅o=0.29cos(φ)+0.52(n̅/n̅) 7.50 -1.40 1.99 0.90 page model h̅g/h̅o=0.23+0.48(n̅/n̅) 16.34 -3.02 3.32 0.90 rietveld model h̅g/h̅o=0.18+0.62(n̅/n̅) 12.94 -2.36 2.81 0.88 turton's model h̅g/h̅o=0.34+0.4(n̅/n̅) 3.67 -0.74 1.81 0.85 table-3: estimated value of global solar radiation (mj/m2/day) by differnt models. month a-p model g m model page model rietveld model turton's model jan 14.48 13.21 11.97 12.72 13.46 feb 18.92 17.30 15.70 17.02 17.22 mar 20.97 19.15 17.36 18.54 19.38 apr 25.17 23.00 20.87 22.57 22.96 may 23.04 21.01 19.01 19.88 21.76 jun 18.43 16.72 15.04 14.66 18.58 jul 17.24 15.61 14.03 13.42 17.64 aug 16.99 15.41 13.85 13.43 17.20 sep 18.66 16.99 15.35 15.80 17.90 oct 20.20 18.47 16.77 18.22 18.34 nov 16.72 15.28 13.87 15.04 15.20 dec 12.74 11.61 10.51 10.99 12.02 ganesh k. shrestha et al. / bibechana 18 (1) (2021) 193-200 198 jan feb m ar apr m ay jun jul aug sep o ct nov dec -1 2 3 4 5 6 7 8 9 s u n sh in e h o u r (h r) month n monthly variation of sunshine hour for biratnagar fig.1: monthly variation of sunshine hours. jan feb m ar apr m ay jun jul aug sep o ct nov dec -0.2 0.4 0.6 0.8 n/n monthly variation of relative ssh and clearness index for biratnagar r el at iv e su ns hi ne h ou r (n /n ) month 0.4 0.5 0.6 0.7 kt c le ar ne ss in de x( k t) fig. 2: monthly variation of clearness index and relative sunshine hour. ganesh k. shrestha et al. / bibechana 18 (1) (2021) 193-200 199 fig.3: comparison of estimated global solar radiation using different models with measured value. 4. conclusion by the regression analysis of gsr satellite data with sunshine hour we found the correlation equation based on angstrom-prescott model and statistically compare existing linear models. statistical assessment shows that all these linear models are significant for the estimation of global solar radiation. however, overall performance parameter mpe (%), mbe, rmse and cc of a-p model are found to be 1.50, 0.25, 1.50 and 0.89 respectively which show superiority of a-p models over rest of the models. furthermore, among the existing linear models turton's model is best so it could be preferred for estimation of global solar radiation in location with similar climatic condition in absence of reliable data for development of new model. acknowledgement authors are grateful to express their sincere thanks to department of hydrology and meteorology (dhm), government of nepal for providing the meteorological data and nasa langley research centre (lcr) power project funded through the nasa earth science/applied science program for providing data on monthly average daily global solar radiation. we would like to special thanks to faculty members and staffs of department of applied sciences and chemical engineering, ioe, pulchowk campus, tribhuvan university. references [1] https://ourworldindata.org/fossil-fuels [2] b. pandey et al., prediction of global solar radiation using meteorological parameters on empirical model at mountain region jumla, nepal, research journal of chemical sciences. 8(2018) 23-29. [3] j. l. chen et al., empirical models for estimating monthly global solar radiation: a most comprehensive review and comparative case study in china, renewable and sustainable energy reviews. 108 (2019) 91 -111. https://doi.org/10.1016/j.rser.2019.03.033. [4] f. besharat et al., empirical models for estimating global solar radiation: a review and case study, renewable and sustainable energy reviews. 21(2013)789-821. http://dx.doi.org/10.1016/j.rser.2012.12.043. https://ourworldindata.org/fossil-fuels http://dx.doi.org/10.1016/j.rser.2012.12.043 ganesh k. shrestha et al. / bibechana 18 (1) (2021) 193-200 200 [5] b. pandey et al., estimation of monthly average daily diffuse solar radiation using empirical models for kathmandu nepal, journal of nepal physical society. 5(2019) 6-13. https://doi.org/10.3126/jnphyssoc.v5i1.26875. 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[11] k. n. poudyal et al., estimation of the daily global solar radiation, nepal experience, measurement. 46(2013)1807–1817. http://dx.doi.org/10.1016/j.measurement.2013.0 1.012. [12] climate. retrieved from department of hydrology and meterology: (2020) www.dhm.gov.np [13] data access retrieved from nasa prediction of worldwide energy resources: (2020) https://power.larc.nasa.gov [14] j.a. prescott, evaporation from a water surface in relation to solar radiation, tran roy soc south aust. 64 (1940) 114-118. [15] m. iqbal, an introduction to solar radiation, academic press, new york (1983). [16] j.a. duffie and w.a. beckman, solar engineering of thermal processes, 2nd edition, johnwiley and sons, new york (1991). https://doi.org/10.1016/j.csite.2020.100591 https://doi.org/10.1155/2016/8197389 https://doi.org/10.3126/jie.v8i3.5944 https://doi.org/10.3126/jie.v9i1.10675 http://www.dhm.gov.np/ https://power.larc.nasa.gov/ bibechana 18 (1) (2021) 149-158 149 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal investigation on thermo-physical properties of liquid in-tl alloy i. b. bhandari1,2, n. panthi1,3 , i. koirala1* 1central department of physics, tribhuvan university, kirtipur, nepal 2department of applied sciences, purwanchal campus, tribhuvan university, dharan, nepal 3department of physics, patan multiple campus, tribhuvan university, lalitpur, nepal *e-mail: ikphysicstu@gmail.com article information: received: june 29, 2020 accepted: august 8, 2020 keywords: mixing properties ordering energy complex formation model segregation abstract this research explores mixing behaviour of liquid in – tl system through thermodynamic and the structural properties on the basis of complex formation model. the properties like surface tension and viscosity have been analyzed through simple statistical model and moelwyn – hughes equation. the interaction parameters are found to be positive, concentration independent and temperature dependent. theoretical results are in a good agreement with the corresponding literature data which support homo-coordinating tendency in the liquid in-tl alloy. doi: https://doi.org/10.3126/bibechana.v18i1.29531 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction indium is a substance which is used in solder alloys which are applied in electronics for assembling semiconductor chips to a base and hybrid integrated circuits and to seal glass to metal in vacuum tubes. fusible indium alloys are used to bend thin walled tubes without wrinkling the wall or changing the original cross-section. these alloys are not only used in fire control system, restraining links that hold alarm, water valve and door operating mechanism but also used as temperature indicators in situations where other methods of temperature measurements are impracticable and infeasible [1]. indium is also used in nuclear reactor control rod alloys, low pressure sodium lamps and alkaline batteries. additions of indium to lead–tin bearings are utilized in piston type aircraft engines, high performance automobile engines and in turbo– diesel truck engines. the addition of indium to gold dental alloys recuperates their mechanical properties and increases resistance to discoloring. small amount of indium is used to improve the machinability of gold alloys for jewelry [1].the indium–thallium alloy is a classic type of shape memory alloy with a low melting temperature. it has wide range of practical applications in the field of metallurgy which includes the use in http://nepjol.info/index.php/bibechana mailto:ikphysicstu@gmail.com https://doi.org/10.3126/bibechana.v18i1.29531 https://creativecommons.org/licenses/by-nc/4.0/ i. b. bhandari et al. / bibechana 18 (1) (2021) 149-158 150 thermostats, hydraulic lines and electrical circuits [2]. thallium alone is improper for direct use because of its properties of toxicity, unfavorable mechanical properties and significant tendency to oxidize. thallium contains the most constant atomic vibration so far experimented. this property of tl preceded it to be used in atomic clocks. thallium immediately forms alloys with most other metals. there is incomplete mutual insolubility with iron and limited solubility in the liquid state with copper, aluminum, zinc, arsenic, manganese and nickel. gold, silver, cadmium and tin formulate simple eutectic point with thallium. thallium also forms binary alloys with antimony, barium, calcium, cerium, cobalt, germanium, lanthanum, lithium, magnesium, strontium, tellurium, bismuth and indium. the ternary alloys of thallium tl–pb– bi, tl–al–ag, in–hg–tl, sn–cd–tl, bi–sn–tl and bi–cd–tl are used as semiconductors in ceramic compounds. thallium has good wear resistance when it is used in bearing shafts. thallium containing alloys are frequently recommended for bearings, electronics industry such as in solid state rectifiers, electrical fuses and soldering materials [1]. the study of in-tl alloy is also useful to investigate the corresponding higher order alloy through different approaches [3]. there is difficulty in studying the properties of alloys in liquid state due to lack of long range atomic order. therefore, theoreticians have exercised different models to understand the properties of various binary liquid alloys [4–22]. the different properties were studied at fixed temperature of 723 k through different models. in present work, we have explored the energetic of in – tl alloy at a temperature of 723k using complex formation model [23]. the outcomes are analyzed and compared with literature data [24] to explicate the accuracy of this method in thermodynamic and structural description of the presented binary system. 2. theory thermodynamic properties if a binary alloy contains na = x number of a atoms and nb = (1-x) number of b atoms, so that total number of atoms is n = na + nb. when components a and b are amalgamated together to form a binary a-b solution, thermodynamic properties are changed. the liquid alloy is considered to be ternary mixture of three species; a atom, b atom and chemical complex aubv, is also called conformal solution. the number of free atoms will be reduced due to compound formation in the melt. now for n1g atoms of a, n2g atoms of b and n3g atoms of aubv, 𝑛1 = 𝑥 − 𝑢𝑛3 and 𝑛2 = (1 − 𝑥) − 𝑣𝑛3 (1) the total number of atoms after mixing can be given as 𝑛 = 𝑛1 + 𝑛2 + 𝑛3 = 1 − (𝑢 + 𝑣 − 1)𝑛3 (2) the free energy of mixing of the binary a-b mixture can be written as [23], 𝐺𝑀 = −𝑛3𝑔 + 𝐺′ (3) here,−𝑛3𝑔 stands for lowering of free energy due to compound formation, g is the formation energy of complex. 𝐺′ is the free energy of mixing of the ternary mixture of a, b and aubv. if the ternary mixture is an ideal solution, 𝐺′ = 𝑅𝑇 ∑ 𝑛𝑖𝑙𝑛 ( 𝑛𝑖 𝑛 ) (4) if the effects of differences in sizes of the various constituents in the mixture cannot be ignored and the interaction 𝜔𝑖𝑗 are small but not zero, the theory of regular solutions in the zeroth approximation [25] or the conformal solution approximation [26] is valid. for regular solution 𝐺′ = 𝑅𝑇 ∑ 𝑛𝑖𝑙𝑛 ( 𝑛𝑖 𝑛 ) + ∑ 𝜔𝑖𝑗 ( 𝑛𝑖𝑛𝑗 𝑛 ) (5) this equation is concerned to conformal solution approximation. where 𝜔𝑖𝑗= 0 (for i = j) are termed as the interaction energies and by definition are independent of concentration, although they are depended upon temperature and pressure. now the expression for free energy of mixing gm for the compound forming binary alloy is 𝐺𝑀 = −𝑛3𝑔 + 𝑅𝑇 ∑ 𝑛𝑖𝑙𝑛 ( 𝑛𝑖 𝑛 )3 𝑖=1 + ∑ ∑ ( 𝑛𝑖𝑛𝑖 𝑛 )𝑖<𝑗 𝜔𝑖𝑗 (6) i. b. bhandari et al. / bibechana 18 (1) (2021) 149-158 151 the expression for heat of mixing hm is given by[23] 𝐻𝑀 = 𝐺𝑀 − 𝑇 ( 𝜕𝐺𝑀 𝜕𝑇 ) 𝑃 (7) substituting for gm, 𝐻𝑀 = −𝑛3𝑔 + 𝑅𝑇 ∑ 𝑛𝑖𝑙𝑛 ( 𝑛𝑖 𝑛 ) 3 1 + ∑ ∑ ( 𝑛𝑖𝑛𝑗 𝑛 ) 𝜔𝑖𝑗 𝑖<𝑗 − 𝑇 𝜕 𝜕𝑇 [−𝑛3𝑔 + 𝑅𝑇 ∑ 𝑛𝑖 3 𝑖=1 𝑙𝑛 ( 𝑛𝑖 𝑛 ) + ∑ ∑ ( 𝑛𝑖𝑛𝑗 𝑛 ) 𝜔𝑖𝑗 𝑖<𝑗 ] 𝐻𝑀 = −𝑛3 [𝑔 − 𝑇 ( 𝜕𝑔 𝜕𝑇 ) 𝑃 ] + 1 𝑛 ∑ ∑(𝑛𝑖𝑛𝑗)𝑖<𝑗 [𝜔𝑖𝑗 − 𝑇 ( 𝜕𝜔𝑖𝑗 𝜕𝑇 ) 𝑃 ] (8) the expression for entropy of mixing sm can be obtained as [23] 𝑆𝑀 = 𝑛3 𝜕𝑔 𝜕𝑇 − 𝑅 ∑ 𝑛𝑖𝑙𝑛 𝑛𝑖 𝑛 − ∑ ∑ 𝑛𝑖𝑛𝑗 𝑛 𝜕𝜔𝑖𝑗 𝜕𝑇𝑖<𝑗 3 𝑖=1 (9) the equilibrium value of 𝑛3 at a given pressure and temperature is given by[23] ( 𝜕𝐺𝑀 𝜕𝑛3 ) 𝑇,𝑃,𝑁,𝐶 = 0 (10) substituting the value of gm from equation (6) and after some algebraic calculation 𝑙𝑛(𝑛3𝑛𝑢+𝑣−1𝑛1 −𝑢𝑛2 −𝑣) + 𝑌 = 𝑔 𝑅𝑇 (11) the equation (11) is called equilibrium equation, where 𝑌 = [ 𝑛1𝑛2 𝑛2 (𝑢 + 𝑣 − 1) − 𝑢 𝑛2 𝑛 − 𝑣 𝑛1 𝑛 ] 𝜔12 𝑅𝑇 + [ 𝑛2𝑛3 𝑛2 (𝑢 + 𝑣 − 1) − 𝑣 𝑛3 𝑛 + 𝑛2 𝑛 ] 𝜔23 𝑅𝑇 + [ 𝑛1𝑛3 𝑛2 (𝑢 + 𝑣 − 1) − 𝑢 𝑛3 𝑛 + 𝑛1 𝑛 ] 𝜔13 𝑅𝑇 (12) structural properties the concentration fluctuation at long wavelength limit is of good interest because any deviation from ideal value 𝑆𝑐𝑐 𝑖𝑑 (0) is significant in describing the nature of ordering and phase segregation in molten alloys. this has been used to investigate the nature of atomic order. the concentration fluctuation at long wavelength limit is related with free energy of mixing by the expression [27], 𝑆𝑐𝑐(0) = 𝑅𝑇 𝜕2𝐺𝑀 𝜕𝑐2 (13) 𝑆𝑐𝑐(0) = 𝑅𝑇 𝑅𝑇 ∑ ( (𝑛𝑖 ′) 2 𝑛𝑖 − (𝑛′) 2 𝑛 )3 𝑖=1 +2𝑛 ∑ ∑ 𝜔𝑖𝑗( 𝑛𝑖 𝑛 ) ′ ( 𝑛𝑗 𝑛 ) ′ 𝑖<𝑗 (14) theoretically computed values of 𝑆𝑐𝑐(0) can be compared with the observed values computed from activity data by the expression, 𝑆𝑐𝑐(0) = (1 − 𝑥)𝑎𝐴 ( 𝜕𝑎𝐴 𝜕𝑐 ) 𝑇,𝑃,𝑁 −1 = 𝑥𝑎𝐵 ( 𝜕𝑎𝐵 𝜕𝑐 ) 𝑇,𝑃,𝑁 −1 (15) the ideal value of scc(0) can be expressed as, 𝑆𝑐𝑐 𝑖𝑑(0) = 𝑥(1 − 𝑥) (16) the warren–cowley short range order parameter quantify the degree of local order in the binary alloy [28,29]. the theoretical values of this parameter can be calculated as α1 = (s−1) s(z−1)+1 ,s = scc(0) scc id(0) (17) where z is coordination number, which is taken as 10 for our calculation. transport properties the mixing behaviour of the alloys forming molten alloy can also be studied at the microscopic level in terms of coefficient of diffusion. the mutual diffusion coefficient (dm) of binary liquid alloys can be expressed in terms of activity (ai) and self diffusion coefficient (did) of pure component with the help of darken’s equation [30] 𝐷𝑀 = 𝐷𝑖𝑑𝑥 𝑑𝑙𝑛𝑎𝑖 𝑑𝑥 (18) with 𝐷𝑀 = 𝑐𝐴𝐷𝐵 + 𝑐𝐵𝐷𝐴 where da and db are the self – diffusion coefficients of pure components a and b respectively, the expression for dm in terms of scc(0) can be given as 𝐷𝑀 𝐷𝑖𝑑 = 𝑆𝑐𝑐 𝑖𝑑(0) 𝑆𝑐𝑐(0) (19) i. b. bhandari et al. / bibechana 18 (1) (2021) 149-158 152 the mixing behaviour of liquid alloys at microscopic level can also be understood in terms of viscosity. the moelwyn – hughes equation for viscosity of liquid alloy [31] is 𝜂 = 𝜂𝑖𝑑 [1 − 𝑥𝐴𝑥𝐵 ( 2𝑔 𝑅𝑇 )] (20) with 𝜂𝑖𝑑 = 𝑥𝜂𝐴 + (1 − 𝑥)𝜂𝐵 where 𝜂𝑖 is the viscosity of pure component i. at temperature t, it is given by [32] 𝜂𝑖 = 𝜂𝑖0exp ( 𝐸 𝑅𝑇 ) (21) here 𝜂𝑖0 a constant in the unit of viscosity and e is the activation energy. surface properties the surface properties of the liquid mixture give insight into the metallurgical phenomenon, such as crystal growth, wielding, gas absorption and nucleation of gas bubbles [33]. the expressions for surface tension proposed by prasad et al., [34,35], has been reduced in the simple form using zeroth approximation as 𝜏 = 𝜏𝐴 + 𝑘𝐵𝑇 𝜉 𝑙𝑛 𝑥𝑠 𝑥 + 𝑔 𝜉 [𝑝(1 − 𝑥𝑠)2 + (𝑞 − 1)(1 − 𝑥)2] (22) 𝜏 = 𝜏𝐵 + 𝑘𝐵𝑇 𝜉 𝑙𝑛 (1−𝑥𝑠) (1−𝑥) + 𝑔 𝜉 [𝑝(𝑥𝑠)2 + (𝑞 − 1)(𝑥)2] (23) where 𝜏𝐴 and 𝜏𝐵 are the surface tensions of pure components a and b respectively, 𝑥 and 𝑥𝑠 are the bulk and surface concentration of the components of alloy, p and q are called coordination fractions, which are defined as the fraction of the total number of nearest neighbors made by atom within its own layer and that in the adjoining layer. the coordination fractions p and q are related to each other by the relation 𝑝 + 2𝑞 = 1, for closed packed structure, 𝑝 = 0.5 and 𝑞 = 0.25 the expression for the mean atomic surface area 𝜉 is 𝜉 = ∑ 𝑐𝑖𝜉𝑖 (24) the atomic surface are for each component is 𝜉𝑖 = 1.102 ( 𝛺𝑖 𝑁𝐴 ) 2/3 (25) where 𝛺𝑖is the molar volume of the component i and 𝑁𝐴represents avogadro number. equating equations (22) and (23), we can solve it for 𝑥𝑠 as the function of x and hence compositional dependence of surface tension can be evaluated. where 𝜏𝐴 and 𝜏𝐵 are the surface tensions of pure components a and b respectively, 𝑥 and 𝑥𝑠 are the bulk and surface concentration of the components of alloy, p and q are called coordination fractions, which are defined as the fraction of the total number of nearest neighbors made by atom within its own layer and that in the adjoining layer. the coordination fractions p and q are related to each other by the relation 𝑝 + 2𝑞 = 1, for closed packed structure, 𝑝 = 0.5 and 𝑞 = 0.25 the expression for the mean atomic surface area 𝜉 is 𝜉 = ∑ 𝑐𝑖𝜉𝑖 (24) the atomic surface are for each component is 𝜉𝑖 = 1.102 ( 𝛺𝑖 𝑁𝐴 ) 2/3 (25) where 𝛺𝑖is the molar volume of the component i and 𝑁𝐴represents avogadro number. equating equations (22) and (23), we can solve it for 𝑥𝑠 as the function of x and hence compositional dependence of surface tension can be evaluated. 3. results and discussion thermodynamic properties the experimental data on the thermodynamic properties as well as phase diagram information [24] have been used for the calculation of order energy parameters for liquid phase in–tl system. the data set of the gibbs energy of mixing (gm) were taken as input data to calculate by the cfm the interaction energy parameters, i.e. g, ω12, ω13, ω23. the starting values of g/rt and ωij/rt were obtained as suggested in ref. [23]. equilibrium equation (11) along with equations (1) and (2) were applied to compute the number of complexes, i. b. bhandari et al. / bibechana 18 (1) (2021) 149-158 153 n3, as a function of concentration. the values of interaction energy parameters were adjusted to give the concentration dependence of free energy of mixing which fits well with the corresponding thermodynamic data. from the phase diagram [24] in-tl alloy is expected to aggregate with stoichiometry in-tl ( u = 1, v = 1).the calculations were done at temperature of 723 k. the interaction energy parameters for in–tl liquid alloys are found to be g = 0.755 rt, ω12 =0.476 rt, ω13=1.610 rt and ω23= 1.481 rt. the positive interaction energies imply the repulsion between the corresponding species. the concentration dependence of the equilibrium values of chemical complexes, n3, (fig. 1) displays the symmetry with the maximum value of 0.4178 at equiatomic composition. the curve describing the gibbs free energy of mixing of the in–tl liquid phase is symmetric with respect to the equiatomic composition (fig. 2). theoretical calculation of free energy of mixing for in-tl liquid alloy shows that in tl alloy in liquid state is weakly interacting or homo-coordinating system. there is an excellent agreement between the experimental and calculated integral free energies. very poor agreement of calculated values of hm and sm with experimental simply indicates the importance of the dependence of interaction energies on temperature. to account this, we have used equations (8) and (9) to determine the variation in energy parameters with respect to temperature from experimental values of hm and sm [24]. the temperature dependent interaction energies at t=723k are found to be 1 𝑅 𝜕𝑔 𝜕𝑡 = 0.845, 1 𝑅 𝜕𝜔12 𝜕𝑡 = 0.383, 1 𝑅 𝜕𝜔13 𝜕𝑡 = 1.493, 1 𝑅 𝜕𝜔23 𝜕𝑡 = 1.430 it is found from the present analysis that the heat of mixing and entropy of mixing both are positive at all concentrations. our theoretical calculation shows that the maximum value of the heat of mixing is 0.0512 rt at xin = 0.6 (fig.3) and the maximum value of entropy of mixing is 0.6107 at xin = 0.5 (fig.4). there is excellent agreement between experimental and calculated values of hm. the calculated values of sm deviates from experimental values by maximum percentage of 8.31 at xin = 0.8 and by minimum percentage of 5.56 at xin = 0.4. this deviation is because of the propagation of error from previous calculation. 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 n 1 , n 2 , n 3 xin n3 n1n2 fig.1 fig.1: number of complexes (n1, n2, n3) vs. concentration xin of liquid in tl alloy at 723k. -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 g m / r t experimental theoretical fig.2 0.0 0.2 0.4 0.6 0.8 1.0 xin fig. 2: free energy of mixing (gm/rt) vs. concentration (xin) of liquid in tl alloy at 723k. structural properties it has been reported that when scc(0) < scc id(0), the existence of chemical ordering leading to complex i. b. bhandari et al. / bibechana 18 (1) (2021) 149-158 154 formation is expected while scc(0) > scc id(0), is an indication of segregation. the same interaction parameters used in the calculation of the thermodynamic properties were employed in the calculations of scc(0) using equation (14) while the experimental values of scc(0) were obtained from equation (15) using the experimental activity data. the results obtained from the above computations are plotted in fig. (5). it is found that scc(0) > scc id(0) throughout the entire concentration range, this also confirms the presence of chemical segregation or a preference for like atoms to pair. the value of short range order parameter is positive through the whole concentration range which indicates that the alloy is segregating at all compositions. the value of short range order parameter has been found maximum (= 0.02438) at xin = 0.5 at 723 k (fig. (6)). 0.0 0.2 0.4 0.6 0.8 1.0 0.00 0.01 0.02 0.03 0.04 0.05 0.06 h m / r t xin experimental theoretical fig.3 fig. 3: heat of mixing (hm) vs. concentration of indium (xin) in the liquid in tl alloy at 723k. transport properties the calculated values of scc(0)) by equation (17) can be applied to evaluate the ratio of the mutual and intrinsic-diffusion coefficients (dm/did) using equation (19), against the concentration of indium. we note that the ratio of diffusivities can also be used to indicate levels of order in the liquid binary alloys. the presence of chemical order is indicated by dm/did>1. similarly, dm/did<1 suggests the tendency for segregation. fig. (7) shows the plots dm/did against concentration of indium. it can be observed that the ratio dm/did is less than 1 throughout the whole concentration range. this indicates the homo – coordinating tendency in in– tl alloys at the temperature of investigation. it is also noticed that dm/did exhibits maximum peak at around the equi-atomic composition. the result predicted by dm/did is in agreement with the results obtained from the free energy of mixing, concentration fluctuations and csro parameter. the viscosity of the in–tl liquid alloy has been calculated numerically using equation (20). from the plot of η verses bulk concentration of indium (fig. 8) small negative deviation from the linear law (raoult's law) in viscosity isotherms η(x) has been inspected. surface properties the surface concentrations and surface tension of in–tl alloy have been computed numerically using equations (22) and (23). the values of densities and surface tension at melting temperature (t0) of pure atoms are taken from ref. [32]. these values have been optimized at required temperature (t) by using the expressions 𝜌𝑖(𝑇) = 𝜌𝑖 0 + (𝑇 − 𝑇𝑖 0) 𝑑𝜌𝑖 𝑑𝑡⁄ (26) 𝜏𝑖(𝑇) = 𝜏𝑖 0 + (𝑇 − 𝑇𝑖 0) 𝑑𝜏𝑖 𝑑𝑡⁄ (27) where 𝑑𝜌𝑖 𝑑𝑡⁄ and 𝑑𝜏𝑖 𝑑𝑡⁄ represent temperature coefficients of density and surface tension respectively for the components of the metal alloys. the computed values of surface concentration for molten in–tl alloys at 723 k are depicted in fig. (9). surface concentration of indium in in–tl alloys is found to increase with the increase of bulk concentration of in. the computed surface tension for in–tl alloys at 723 k is less than ideal values at all concentrations of indium; i.e., there is negative departure of surface tension from ideality (τ = τax+τb(1−x)) throughout the bulk concentrations of indium in in–tl alloys (fig. 10). for the in-tl melt, the surface tension of tl is smaller than that of in atom. therefore, tl atoms having lower surface tension segregates on the surface phase but in i. b. bhandari et al. / bibechana 18 (1) (2021) 149-158 155 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 s m / r xin experimental theoretical fig.4 atoms remains in the bulk phase throughout the entire composition. fig. 4: entropy of mixing (sm) vs. concentration of indium (xin) in the liquid in tl alloy at 723k. experimental theoretical ideal 0.0 0.2 0.4 0.6 0.8 1.0 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 s c c (0 ) xinfig.5 fig. 5: concentration fluctuation at long wavelength limit (scc(0)) vs. concentration of indium (xin) in the liquid in tl alloy at 723k. 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.005 0.010 0.015 0.020 0.025 a 1 xinfig.6 fig. 6: chemical short range order (α1) vs. concentration of indium (xin) in the liquid in tl alloy at 723k. 0.0 0.2 0.4 0.6 0.8 1.0 0.76 0.80 0.84 0.88 0.92 d m / d id xinfig.7 fig. 7: ratio of mutual and intrinsic diffusion coefficients (dm/did) vs. concentration of indium (xin) in the liquid in tl alloy at 723k. i. b. bhandari et al. / bibechana 18 (1) (2021) 149-158 156 0.0 0.2 0.4 0.6 0.8 1.0 0.0008 0.0010 0.0012 0.0014 0.0016 h n s m -2 xin theoretical alues ideal values fig.8 fig. 8: viscosity (η) vs. concentration of indium (xin) in the liquid in tl alloy at 723k. 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 x s in xin theoretical values ideal values fig.9 fig. 9: surface concentration of indium ( xin s ) vs. bulk concentration of indium (xin) in the liquid in tl alloy at 723k. 4. conclusions the theoretical analysis of the thermodynamic properties reveals that there is a tendency of like atom pairing in the liquid in–tl alloys at all concentrations. the ordering energy is found to be positive and temperature dependent. the study of concentration fluctuation in long wavelength limit and csro show that there is tendency of phase separation in in –tl liquid alloy. negative deviation of viscosity isotherms from raoult law is observed. viscosity of the alloys decreases with increase in the concentrations of indium. the ratio of diffusion coefficients (dm/did) is found to be greater than one at all compositions which also indicates segregating tendency of the system. at the temperature of investigation, the surface tension increases with the increase in the bulk concentration of in. the surface tension of the liquid in–tl alloy is found to be smaller than ideal values. 0.0 0.2 0.4 0.6 0.8 1.0 0.46 0.48 0.50 0.52 t n m -1 xin theoretical ideal fig.10 fig. 10: surface tension (τ) vs. bulk concentration of indium (xin) in the liquid in tl alloy at 723k. references [1] f. habashi, ed., alloys preparation, properties, applications, first, wiley-vch (1998). 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nepse index along with the prediction of indices through python programming platform. python simulation was carried out to check the consistency by implying it to the stable market timeline 2003/2004. and after the verification of the model proposed in the stable market year, the model (gbm) is employed to the unstable timeline; pandemic situation by covid-19 in 2020. mapping of nepal stock market through gbm was found to be consistent with the standard forecasting accuracy making gbm one of the flexible and consistent to predict stock market scenario of nepal accounting the random nature. doi: https://doi.org/10.3126/bibechana.v18i2.31180 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction stock market stock generally referred as equities or equity securities of any company or corporation determines the share in the ownership of esteemed company or corporation. stocks are mainly divided into two: public stock in which public are allowed taking certain portion of corporation securities or ownership through investment and private stock which is owned by private companies and sold only to investors. and the market facilitating the sales and purchase of this ownership among individuals, companies and investors is share market [1]. there are many indicators to measure the status of stock market, one of them is the stock index; in the context of nepal, nepal stock exchange (nepse) index which indicates the increase or decrease of total market capitalization of companies’ transactions that are enlisted in nepal stock exchange. this bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:physicpract@gmail.com https://doi.org/10.3126/bibechana.v18i2.31180 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana prabinthapa and binil aryal / bibechana 18 (2) (2021) 50-60 51 indicates the increase or decrease of overall market; therefore, it has significant importance to investors. factors affecting stock market the attractiveness of stock price is affected by several factors that results in the inconsistency or the randomness in the stock index. some of them are: • the after-hours trading (aht) where the trading between the closing bell of present day and opening bell of next day fluctuates the value of stock price. • sudden news about companies listed in share market during non-trading period. • political condition, natural calamities, epidemic and pandemic and many others. from above it can be said that figuratively stock market has the random nature inherent in it [1, 2]. so, modeling of such random nature of stock market needs to be accounted that is where stochastic process comes into play which shows the connection between physics and economics [3]. stochastic process stochastic process is a process where there are observations at the certain times and the outcomes or the observed values at each time has the randomness inherent in them; random variable. in terms of probability concept, there is a certain probability to acquire certain outcome and that probability depends upon the previously obtained observations [4]. this means that more the observations, more accuracy the stochastic process addresses to the outcome. but generally, such processes are cumbersome and become difficult to treat in long run. so, different simplified stochastic processes are proposed over time in the field of econophysics like markov process, step process. levy process, random walk, weiner process, brownian motion etc. [4, 5]. brownian motion brownian motion generally referred as the motion defined by a particle (brownian particle) suspended in a liquid where the particle is small enough to be influenced by the underlying molecular motion. such types of motion of small particles in liquid demonstrate dissipation and fluctuation. moreover, the motion is governed by two kinds of force; the systematic force which is responsible for damping by an exchange of energy and momentum between brownian particle and molecules of liquid, providing dissipation and the force by the irregular interactions from the collision between brownian particles and molecules of liquid may change the direction and velocity of brownian particles providing fluctuation in the system. in spite of dissipation and fluctuation, diffusion; an irregular way brownian particle is spread out in the system gives the concept of diffusion constant [4]. the brownian particle can also be influenced by external factors like presence of charged ions, presence of electric fields, temperature, pressure etc. geometric brownian motion (gbm) geometric brownian motion is continuous-time stochastic process also referred as wiener process with drift. it is the most used model for mathematical finance in modeling stock prices [4]. for stochastic process x (t) to follow gbm, it satisfies stochastic differential equation (sde) as [58] 𝑑𝑋(𝑡) = 𝜇𝑋(𝑡)𝑑𝑡 + 𝜎𝑋(𝑡)𝑑𝐵(𝑡) (1) where 𝐵(𝑡) represents the wiener process or brownian motion 𝜇 represents drift accounting for deterministic trend 𝜎 represents volatility accounting for unpredictable events under itô's interpretation [5], for arbitrary initial value x0 the equation has the analytic solution 𝑋𝑇 = 𝑋0𝑒 (𝜇− 1 2 𝜎2)𝑇+𝐵𝑇 (2) with the incorporation of such deterministic trend and unpredictable events in geometric brownian motion [9], it is well suited for modeling of stock market. 2. materials and methods modeling of stock market the prediction of nepal stock market scenario on the basis of nepse index using brownian notion is python simulation-based work. so, to use brownian prabinthapa and binil aryal / bibechana 18 (2) (2021) 50-60 52 motion in stock market we make appropriate analogy between brownian motion and stock market parameters. 𝑋0 = initial nepse index which in our case is the last date nepse index of our historical data. 𝑑𝑡 = increment in time (for our case one day) as the nepse index of the day is published in every one day. dt =1day. 𝑇 = length of our prediction horizon, in our case it is 22 days as trading days is only 22 days with the exclusion of weekend. 𝑁 = number of time points in the prediction time horizon = 𝑇/𝑑𝑡 𝜇 = mean return of nepse index i.e. 𝜇 = 1 𝑇𝑜𝑡𝑎𝑙 𝐷𝑎𝑦𝑠(𝑁) ∑ 𝑋𝑘−𝑋𝑘−1 𝑋𝑘 𝑁 𝑘=1 (3) 𝜎 = standard deviation of historical daily returnindex 𝜎 = √ 1 𝑁 ∑ (𝑋𝑘 − 𝜇)2𝑁 𝑘=1 (4) 𝐵 = brownian increment which follows normal distribution with mean zero and variance equal to interval of time in our case it is one as dt = 1day. drift: drift reflects the longer-term trend in stock index. they have constant value calculated from the historical data set. 𝐷𝑟𝑖𝑓𝑡 = 𝜇 − 1 2 𝜎2 (5) note: if we keep applying drift without any random shock the stock price smoothly goes up for positive drift and smoothly goes down for negative drift. so, the stock price is non-zero due to drift. diffusion: diffusion consists of the short-term fluctuations so it consists of the variable bk which contains random shock information. 𝐷𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 = 𝜎𝐵𝑘 (6) algorithm step 1: select the historical data set when the market is pretty stable. step 2: calculate drift and diffusion coefficient from the historical data set. step 3: predict nepse index for certain period using the simulation model. step 4: compare actual index and predicted one; is it consistent with mape (mean absolute percentage error) table. step 5: if the prediction is consistent with mape then apply the simulation model for prediction when the market is not stable enough. step 6: if the prediction is inconsistent with mape then search for the parameterization of the model for making it consistent and goto step 1. simulation set up stock market scenario was simulated for two different scenarios. first, for the stable market year which in our case is the year 2003/2004 where there is no sudden change in the political situation of nepal, less closing of market in business days and less external factors to affect market. we took historical nepse index data from july 17 2003 to june 15 2004 for the prediction of scenario of market from june 16 2004 to july 15 2004. we simulated one thousand possible market scenarios for this prediction time and tabulated them for percentile calculation. calculating the percentile for k values: 0.01 (predicted decreasing index), 0.50 (predicted stable index) and 0.99 (predicted increasing index), the three scenarios were deducted from the thousand simulated scenarios. considering all the scenario of that time line of nepal, out of three, one scenario was selected and made comparison with the standard table of forecasting. table i: a scale of judgment of forecast accuracy [8]. absolute percentage error judgment of forecasting accuracy < 10% highly accurate 11% to 20% good accurate 21% to 50% reasonable forecast > 51% inaccurate forecast prabinthapa and binil aryal / bibechana 18 (2) (2021) 50-60 53 on the comparison with the standard table for forecasting, the simulation outcome yielded error less than 10 percentages. so, we adopted that the simulation must be sufficient to predict the scenarios for unstable market year. moreover, best fit for the stable year along with r-squared value was calculated as it also should be consistent with the next simulation which in our case is for the year 2020. 3. results and discussion for the stable year 2003/2004 in order to simulate 1000 scenarios for the year 2003/2004 we took into account nepse index from july 17, 2003 to june 15, 2004. the simulation yielded 1000 scenarios from june 16, 2004 to july 15, 2004 as shown in fig. 1. fig. 1: thousand possible scenarios of stock market for 2003/2004. after the percentile calculation, deductions to three scenarios of market from thousand scenarios are able ii table ii: comparison between predicted indices and actual nepse index for year 2004 date (d/m) predicted indices actual nepse index decreasing stable increasing 6/15 211.31 211.31 211.31 211.31 6/16 208.64 211.34 214.18 211.45 6/21 204.54 211.47 218.62 211.51 6/22 203.57 211.24 219.13 213.25 6/23 203.61 211.37 220.02 215.10 6/24 202.62 211.36 220.32 216.51 6/25 202.88 211.48 220.24 217.46 6/28 201.85 211.61 221.60 217.41 6/29 201.40 211.63 222.24 217.72 6/30 201.54 211.65 222.39 218.65 7/1 201.18 211.73 222.86 219.41 7/2 200.83 211.78 222.66 220.75 7/5 200.76 212.08 223.63 225.15 7/6 200.17 212.02 223.68 227.83 7/8 199.69 212.08 225.12 226.88 7/9 199.28 212.19 225.57 226.30 7/12 198.75 212.60 227.34 226.16 7/13 198.57 212.64 227.49 226.42 7/14 198.29 212.66 227.80 226.61 7/15 198.18 212.65 228.12 222.04 we refer the situation of the market in order to select preferred index to represent market. as year 2003/2004 was selected as the stable market period with less inconsistency, we predict that the indices should either increase or remain stable which can also be seen through bar plot. from fig 2 and table ii we can say that out of three predicted indices the increasing predicted index is found to have the close resemblance to actual nepse index for the respective prediction days. now on selecting the increasing predicted index as our final index we calculate percentage error for the respective days as shown in able iii. prabinthapa and binil aryal / bibechana 18 (2) (2021) 50-60 54 fig 2: bar plot of three different scenarios for market year 2004 taking first five dates. table iii: error analysis between selected predicted index and actual nepse index for 2004 date (d/m) increasing predicted index actual nepse index percentage error 6/15 211.31 211.31 0.00 6/16 214.18 211.45 -1.29 6/21 218.62 211.51 -3.36 6/22 219.13 213.25 -2.76 6/23 220.02 215.10 -2.29 6/24 220.32 216.51 -1.76 6/25 220.24 217.46 -1.28 6/28 221.60 217.41 -1.93 6/29 222.24 217.72 -2.08 6/30 222.39 218.65 -1.71 7/1 222.86 219.41 -1.57 7/2 222.66 220.75 -0.86 7/5 223.63 225.15 0.67 7/6 223.68 227.83 1.82 7/8 225.12 226.88 0.78 7/9 225.57 226.30 0.32 7/12 227.34 226.16 -0.52 7/13 227.49 226.42 -0.47 7/14 227.80 226.61 -0.53 7/15 228.12 222.04 -2.74 on comparison with the standard table for forecasting accuracy table i, we found that our prediction of indices is quite accurate as the error lies below 10%. so, for further discussions we infer bestfit analysis along with r-squared value as in fig 3. fig 3: line plot of selected predicted index and actual index for market year 2004 along with best fit and r-squared value from the fig 3 above, it is clear that our model of prediction is consistent and can be applied to other fiscal year of stock market as the r-squared value 0.921 is nearly equal to 1 and the best fit to two degree polynomial shows that the model is capable of including the varying nature of stock market. moreover, the consistency with the forecast accuracy allows us to imply this model to other market years. for the year 2020 for the prediction of the current running year, we have taken account of all the historical data i.e. from 200 205 210 215 220 225 6/16 6/21 6/22 6/23 6/24 n e p s e i n d ex prediction days (d/m) decreasing predicted index stable predicted index increasing predicted index actual nepse index y = -0.0093x2 + 710.74x 1e+07 r² = 0.9615 210 212 214 216 218 220 222 224 226 228 230 6 /1 5 6 /2 2 6 /2 9 7 /6 7 /1 3 n e p s e i n d ex prediction days (d/m) increasing predicted index actual nepse index poly. (increasing predicted index) prabinthapa and binil aryal / bibechana 18 (2) (2021) 50-60 55 2003 to till available date for simulating thousand possible scenarios of market as shown in fig. 4. fig 4: thousand possible scenarios of stock market for year 2020. after the percentile calculation, deductions to three scenarios of market from thousand scenarios are shown in table iv. for the selection among the predicted three indices, we select the decreasing predicted indices due to scenario of year 2020 (pandemic of covid-19) which can be also seen through bar plot in fig 5. on the analysis of fig 5, we can say that the decreasing predicted index is more convenient to select for representing actual nepse index. table iv: comparison between predicted indices and actual nepse index for year 2020. date (d/m) predicted indices actual nepse index decreasing stable increasing 3/11 1423.09 1423.09 1423.09 1423.09 3/12 1384.84 1423.82 1464.31 1377.18 3/15 1348.07 1426.78 1509.26 1313.04 3/16 1346.43 1428.30 1522.36 1316.40 3/17 1342.36 1429.80 1532.88 1272.07 3/18 1337.62 1429.18 1539.36 1255.80 3/19 1332.03 1430.25 1554.57 1269.31 3/22 1314.95 1437.10 1570.07 1251.46 5/12 1208.81 1471.64 1827.46 1226.16 fig. 5: bar plot of three different scenarios for market year 2020 taking first five dates. comparison with the standard table for forecast accuracy table i, we can see that absolute percentage error is less than 10% which means our prediction is acceptable. the error greater than 4 percentages in table v can be accounted by the following reasoning: 1200 1250 1300 1350 1400 1450 1500 1550 1600 3/12 3/15 3/16 3/17 3/18 n e p s e i n d ex prediction days (d/m) decreasing predicted index stable predicted index increasing predicted index actual nepse index prabinthapa and binil aryal / bibechana 18 (2) (2021) 50-60 56 table v: comparison between predicted indices and actual nepse index for year 2020. dates (d/m) decreasing predicted index actual nepse index percentage error 3/11 1423.09 1423.09 0.00 3/12 1384.84 1377.18 -0.56 3/15 1348.07 1313.04 -2.67 3/16 1346.43 1316.40 -2.28 3/17 1342.36 1272.07 -5.53 3/18 1337.62 1255.80 -6.52 3/19 1332.03 1269.31 -4.94 3/22 1314.95 1251.46 -5.07 5/12 1208.81 1226.16 1.41 1. the opening of the market in weekend (in our case mainly sunday). 2. the pandemic of covid-19 worldwide which is responsible for the harsh irregularities in market strategy and situation. 3. opening of market after 50 days of gap (from march 22 to may 12) made the high impact in prediction as our simulation model is unknown of the sudden close of market. then the line plot for the predicted index and actual nepse index along with best-fit as shown in fig. 6. although the plot has the bestfit to second degree polynomial, the r-squared value is not as close as that in the year 2003/2004 which can be accounted by the fact the market remained closed for about 50 days which has affected the consistency of having r-squared value nearly equals to one as seen previously in 2003/2004. complete scenario of market in 2020 from fig 4, we can plot the complete scenario of nepse index up to 12 may 2020 including also the weekend. as we already know that decreasing predicted index is conveying the actual nepse index we can have all the decreasing predicted indices to represent the gap of 50 days when the market was closed. the predicted indices from the date 22 march 2020 to 12 may 2020 is represented table vi along with line plot in fig 6. fig 6: comparison between selected predicted index and actual index along with best-fit now for reliability of prediction we take a look at rsquared value and best fit to two degree polynomial fig 7 as done for stable market prediction. from the fig 7 it is clear that the model we have proposed for the stable market scenario is also applicable for other aspects when the market is random. the r-squared value which is 0.936 is nearly equals to 1 meaning the consistency of the model to adopt in stable and non–stable market year. so far as the part of result and discussion, we have taken two scenarios for stock market analysis; one being the stable stock market (year 2003/2004) and another being the present stock market (year 2020). y = -1.434x2 4.1213x + 1403.6 r² = 0.7843 1200 1250 1300 1350 1400 1450 3 /1 1 3 /1 2 3 /1 5 3 /1 6 3 /1 7 3 /1 8 3 /1 9 3 /2 2 5 /1 2 n e p s e i n d ex prediction days (d/m) decreasing predicted index actual nepse index prabinthapa and binil aryal / bibechana 18 (2) (2021) 50-60 57 table vi: predicted index for 50 days gap in 2020. prediction days predicted decreasing index sunday, march 22, 2020 1314.952 monday, march 23, 2020 1312.675 tuesday, march 24, 2020 1311.187 wednesday, march 25, 2020 1292.008 thursday, march 26, 2020 1294.899 friday, march 27, 2020 1287.029 saturday, march 28, 2020 1287.194 sunday, march 29, 2020 1289.939 monday, march 30, 2020 1286.990 tuesday, march 31, 2020 1281.568 wednesday, april 1, 2020 1275.187 thursday, april 2, 2020 1277.795 friday, april 3, 2020 1267.111 saturday, april 4, 2020 1269.603 sunday, april 5, 2020 1264.057 monday, april 6, 2020 1256.732 tuesday, april 7, 2020 1246.317 wednesday, april 8, 2020 1247.575 thursday, april 9, 2020 1251.434 friday, april 10, 2020 1249.477 saturday, april 11, 2020 1250.117 sunday, april 12, 2020 1245.852 monday, april 13, 2020 1236.393 tuesday, april 14, 2020 1238.411 wednesday, april 15, 2020 1240.697 thursday, april 16, 2020 1239.029 friday, april 17, 2020 1239.146 saturday, april 18, 2020 1233.699 sunday, april 19, 2020 1233.995 monday, april 20, 2020 1225.443 tuesday, april 21, 2020 1214.978 wednesday, april 22, 2020 1220.616 thursday, april 23, 2020 1222.788 friday, april 24, 2020 1217.785 saturday, april 25, 2020 1223.197 sunday, april 26, 2020 1226.043 monday, april 27, 2020 1225.471 tuesday, april 28, 2020 1239.949 wednesday, april 29, 2020 1232.231 thursday, april 30, 2020 1234.737 friday, may 1, 2020 1232.025 saturday, may 2, 2020 1223.204 sunday, may 3, 2020 1217.290 monday, may 4, 2020 1207.588 tuesday, may 5, 2020 1198.191 wednesday, may 6, 2020 1188.459 thursday, may 7, 2020 1205.884 friday, may 8, 2020 1209.662 saturday, may 9, 2020 1201.972 sunday, may 10, 2020 1193.005 monday, may 11, 2020 1209.513 tuesday, may 12, 2020 1208.813 fig 7: line plot for predicted (decreasing index) for 50 days gap in 2020 along with best-fit we tested our brownian motion model for the stable market at first and after checking its viability shifted to its application in the present date. on doing so we found that the model is applicable to all the scenarios with less than 10% error in each prediction which makes our model more accurate and consistent. the error greater than 3% is accounted by the ununiformed opening of the stock market like someday y = 0.0334x2 3.8005x + 1314 r² = 0.9362 1180 1200 1220 1240 1260 1280 1300 1320 3 /2 2 3 /2 9 4 /5 4 /1 2 4 /1 9 4 /2 6 5 /3 5 /1 0 n e p s e i n d ex prediction days (d/m) predicted decreasing index poly. (predicted decreasing index) prabinthapa and binil aryal / bibechana 18 (2) (2021) 50-60 58 the market has opened in sunday which is globally one of the weekdays when the market should be closed. moreover, the error in the year 2020 is by the un-uniformity as well as due to the pandemic scenario by covid-19. daily return index analysis fig 8: histogram plot of daily returns in terms of nepse index for year 2020 using 10 bins. table vii: table for the daily return calculation of predicted and actual nepse index for year 2020. (refer table v). nepse index daily return of nepse index predicted actual predicted actual 1423.09 1423.09 1384.84 1377.18 -0.03 -0.03 1348.07 1313.04 -0.03 -0.05 1346.43 1316.40 0.00 0.00 1342.36 1272.07 0.00 -0.03 1337.62 1255.80 0.00 -0.01 1332.03 1269.31 0.00 0.01 1314.95 1251.46 -0.01 -0.01 from table vii it can be annotated that the trend for the daily return between the predicted nepse index and actual nepse index for the year 2020 is merely the same indicating better viability of our simulation. moreover, from fig 7 it can be seen that the plotting of relative frequencies of daily return of index making 10 bins, the gaussian distribution is followed. the histogram for predicted index has half gaussian as we are selecting only the decreasing predicted index for the year 2020. quartile risk analysis or value at risk (var) table viii: table for the calculation of var or quartile risk. days daily return of predicted nepse index variance standard deviation (b) 3/11 0.18 0.42 3/12 -0.03 3/15 -0.03 3/16 0.00 3/17 0.00 3/18 0.00 3/19 0.00 3/22 -0.01 5/12 -0.08 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 -0 .0 8 1 -0 .0 7 2 -0 .0 6 3 -0 .0 5 4 -0 .0 4 5 -0 .0 3 7 -0 .0 2 8 -0 .0 1 9 -0 .0 1 0 -0 .0 0 1 r el at iv e f re q u en cy daily return ( predicted nepse index) 0 0.05 0.1 0.15 0.2 0.25 0.3 -0 .0 4 7 -0 .0 4 0 -0 .0 3 4 -0 .0 2 7 -0 .0 2 1 -0 .0 1 5 -0 .0 0 8 -0 .0 0 2 0 .0 0 4 0 .0 1 1 r el at iv e f re q u en cy daily return (actual nepse index) prabinthapa and binil aryal / bibechana 18 (2) (2021) 50-60 59 from table viii it can be seen that the predicted nepse index for the year 2020 has the volatility of 0.42. table ix: table for calculation of var at different confidence level. for initial nepse index (a)= 1423.09 standard deviation (b) = 0.42 trading days (c) = 8 (at may 12,2020) confidence level stress event (d) var (a*b*d*sqrt(c/252) 0.99 2.33 250.02 0.95 1.64 176.78 0.90 1.28 137.73 from table vii the value at risk (var) at different confidence level can be seen. at 0.99 confidence level the initial index has the risk of 265.19 giving out (1423.09-250.02) = 1173.07 nepse index (at may 12, 2020) which on comparison to actual nepse index gives an error percentage of 4.33% which is again consistent with the table of forecast table i. 4. conclusion the simulation of thousands possible scenarios of stock market on the basis of nepse index has been carried out using python simulation. on doing so the proposed model is found to be consistent for the analysis and prediction of nepal stock market scenario with error persistent with standard table of forecasting. the conclusions that can be drawn from the results encountered are enlisted as: 1. the predicted model for the stable period of market (2003/2004) shows two degree polynomial fit with r-squared value nearly equals to one. from this it can be known that the proposed model incorporates the changing nature of stock market. 2. comparison of predicted indices and actual indices shows the error less than 10 percentages which define the accuracy (highly accurate) of proposed model for the year 2003/2004 and year 2020. 3. as for the error analysis, errors greater than 3 percentage in the year 2020 is due to the irregularities in market like opening of the market in weekends and closing in business days, dealing a greater number of trades due to pandemic situation which is merely the case in the year 2003/2004. 4. the prediction of indices for 50 days gap in the year 2020 shows the trend of stock market if it was opened during that period of time resulting to latest published index at 11 may 2020 (actual nepse index 1226.16, predicted nepse index 1208.81 with error of 1.415%); the positive error representing presence of randomness in market. 5. brownian motion model is found to be more accurate than other stochastic processes like random walk, wiener process, levy process etc. as it incorporates the diffusion and drift along with the properties of wiener process incorporating both the deterministic parameter from historic data and the randomness by generating diffusion σbk. acknowledgements i would like to acknowledge nepse database center for conveying data needed. moreover, i would like to thank central department of physics (cdp) for all the support. references [1]. w.j. o’neil, how to make money in stocks, 4th ed., the mcgraw-hill companies, new york, 2009. [2]. d. owen and r. griffiths, mapping the markets: a guide to stock market analysis, the economist, london, 2006. [3]. g. sãvoiu, econophysics: background and applications in economics, finance, and sociophysics, academic press, waltham, 2012. [4]. c. blomberg, 1st ed., physics of life: the physicist’s road to biology, elsevier, netherlands, 2007. prabinthapa and binil aryal / bibechana 18 (2) (2021) 50-60 60 [5]. i. karatzas and s. e. shreve, 1st ed., brownian motion and stochastic calculus, springer, new york, 1987. [6]. k. f. vajargah and m. shoghi, simulation of stochastic differential equation of geometric brownian motion by quasi-monte carlo method and its application in prediction of total index of stock market and value at risk, math sci. 9 (2015) 115-125 https://doi.org/10.1007/s40096-015-0158-5 [7]. g. dhesi et al., modified brownian motion approach to modeling returns distribution, wilmott. 82 (2016) 74-77. https://doi.org/10.1002/wilm.10494 [8]. s. n. z. abidin and m. m. jaffar, a review on geometric brownian motion in forecasting the share prices in bursa malaysia, world applied sciences journal. 17 (2012) 87-93. https://www.researchgate.net/publication/325986 792 [9]. v. singal, beyond the random walk: a guide to stock market anomalies, oxford university press, usa, 2003. https://doi.org/10.1007/s40096-015-0158-5 https://doi.org/10.1002/wilm.10494 https://www.researchgate.net/publication/325986792 https://www.researchgate.net/publication/325986792 bibechana 18 (1) (2021) 134-139 134 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal modulation frequency and velocity variation of ions in a magnetized plasma sheath for different obliqueness of the field bhesha raj adhikari 1,2,*, hari prasad lamichhane1, raju khanal1 1 central department of physics, tribhuvan university, kirtipur, kathmandu, nepal 2 department of physics, bhaktapur multiple campus, tribhuvan university, bhaktapur, nepal * email: b.r.adhikari@hotmail.com article information: received: may 29, 2020 accepted: august 1, 2020 keywords: bohm criterion kinetic theory sheath presheath modulation frequency damping constant abstract the understanding of ion dynamics in magnetized plasma sheath is crucial for all applications of plasma. the velocity variation as well as modulation frequency of ions in a magnetized plasma sheath has been studied for different obliqueness of magnetic field. the governing lorentz force equation has been solved numerically for the given boundary conditions as applicable in kinetic simulation of the sheath. for different obliqueness of the magnetic field, the average values, maximum amplitude, damping factor as well as frequency of oscillation are studied. the oscillating velocity components change at different rates depending on their orientation with respect to the field direction. significant changes in the damping factor and modulation frequency has been observed for all components of velocity; however, the frequency of oscillation remains same. as the obliqueness increases, shoulder natures in the components of velocity are observed. doi: https://doi.org/10.3126/bibechana.v18i1.29171 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction the formation of non-neutral region in the vicinity of material wall is a ubiquitous feature of bounded plasma and it has wide range of growing applications in diverse fields (e.g. plasma confinement for fusion, sputtering, etching, surface treatment etc.) [1]. in plasma, the thermal velocity of electrons is higher as compared to that of the ions. due to this, the wall is charged up negatively with respect to the core plasma. therefore, negative potential attracts the ions and repels electrons forming a thin positive space charge region near to the wall. this positive space charge region, known as the ‘sheath’ separates the negatively charged material wall from the quasineutral ‘presheath’ plasma. the in-streaming ions have to satisfy the bohm criterion to ensure the stability of the overall plasma [2, 3]. the problem related to sheath is one of the oldest problems in plasma physics [3, 4] and once the plasma-wall interaction is well understood it will be possible to control heat loading, energy transfer and particle flow towards the wall and overall bulk plasma behavior [5 7]. http://nepjol.info/index.php/bibechana mailto:b.r.adhikari@hotmail.com https://doi.org/10.3126/bibechana.v18i1.29171 https://creativecommons.org/licenses/by-nc/4.0/ bhesha raj adhikari et al. / bibechana 18 (1) (2021) 134-139 135 the problem of sheath formation whenever it faces a material surface, its nature and evolution with time is significant for all plasma applications. this is a topic of interest and various works are reported recently as well; however, the study of modulation frequency as well as the time evolution of the ion velocity profile in a magnetized plasma sheath for varying obliqueness is still lacking [8-10]. this work focuses in the time variation of ion velocity, which shows oscillating nature, and its modulation frequency in a magnetized plasma sheath for different obliqueness of the field. the governing lorentz force equation are formulated and solved numerically for the given boundary conditions as applicable in kinetic trajectory simulation (kts) method of the sheath region [8, 11, 12]. in typical boundary layer problems, the sheath region is of several electron-debye lengths which is much smaller than the characteristic extension of the plasma. such a sheath can only be formed, if the bohm criterion [2, 5] is satisfied which demands that the ions enter the sheath region with a high velocity, which cannot be generated by thermal ion motion alone [5]. in the presence of a magnetic field, in kinetic form, the bohm criterion reads 22 || 11 scv  (1) where, i e ps ei ps i s m ttk c )(  + = is the ion-acoustic velocity defined at the presheath side of the sheath edge, with k is boltzmann constant, i and e the ion and electron polytropic constants, respectively, i pst and e pst the ion and electron temperatures at the presheath side of the sheath edge, respectively and mi is the mass of ion species. 2. model and basic equations the 1d3v model of magnetized plasma sheath is shown schematically in fig. 1. the region of interest is bounded by two parallel planes at 0=x and lx = , and the plasma consists of only electrons and singly charged ions. the plane at lx = represents the “sheath entrance” that faces the plasma side and 0=x is the material wall, assumed to be non-emitting in the present case. the uniform magnetic field b  acts on the xy-plane which makes an angle  with the normal to the wall. in the presence of oblique magnetic field, the presheath consist of two distinct regions: collisional presheath and magnetic presheath [3, 13]. the general schematic diagram of magnetized plasma-wall transition region is shown in fig. 2 [11]. as the sheath region is characterized by sharp gradients in a small scale of the order of electrondebye lengths, it is usually treated kinetically, where the particle distribution are governed by the boltzmann equation [1] c v t f f m f fv t f         =++   ..   (2) where f  is the macroscopic force acting on the particles, and ct f         is the time rate of change of distribution function ),,( tvrf  due to collisions. the symbol  represents the usual space-gradient operator whereas the symbol v represents the gradient in velocity space. for collisionless cases, suitable for sheath region as their dimension are much less than the mean free path, the equation (2) changes to so called vlasov equation: 0).(. =+++   →→→→ fbve m q fv t f v (3) in the kts method, the kinetic equations are solved along with other basic equations describing the plasma for given boundary and initial conditions. the distribution function at any point along the trajectory can be obtained if its value at one point (i.e., at the boundary) is known. density of the species ‘s’ is then given by bhesha raj adhikari et al. / bibechana 18 (1) (2021) 134-139 136 wall plasma  y o z x l → e → b x ( ) ( ) + − = vxvfdxn ss  ,3 , (4) which then yields the space charge density as ( ) ( )= s ss xnqx   . (5) thus obtained space charge density is then used in the poisson’s equation to obtain the electrostatic potential ( )x ( ) ( ) , 0 2 2   x dx xd  −= (6) and the electric field is given by ( ) ( ) dx xd xe    −= (7) the kinetic equations (3)-(7) are solved along the collisionless trajectories for given boundary conditions. the ion velocity in the plasma sheath are computed using the lorentz force equation ( ) bveq dt vd m  += (8) where q is the charge of ion species whose mass is m. the components of equation (8) are m qbv m qe dt dv zx sin −= (9) m qbv dt dv zy cos = (10) m qbv m qbv dt dv yxz  cossin −= (11) since the magnetic field is dominating near the sheath entrance over the electric field, which is almost zero, the ions gyrate as they move slowly forward towards the wall. as the ions move towards the wall from the sheath entrance the electric field starts dominating, and hence the gyration decreases, and the equation of the damped harmonic oscillator can be is written as [14] ( ) )(sin  ++= − taevtv tk m (12) where k, a,  and  are damping constant, amplitude, frequency of oscillation and phase angle, respectively. the damping constant of oscillating velocity components defined by equation (9) can be expressed as [14] 12 2 1ln tt vv vv k m m −         − − = (13) where 1v and 2v are the resultant velocity at time 1t and 2t , respectively and mv is the mean value of oscillating parts of velocity. fig. 1: schematic geometry of the plasma-wall interaction model. fig. 2: schematic diagram of magnetized plasmawall transition region. 3. results and discussion in order to study the temporal variation of velocity, the equations (9)-(11) are solved by using rungekutta method for the given boundary conditions. bhesha raj adhikari et al. / bibechana 18 (1) (2021) 134-139 137 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 -1 -0.5 0 0.5 1 1.5 x 10 4 time (s) v el o ci ty ( m /s ) v x v y v z furthermore, the amplitude of oscillation, damping factor, oscillation frequency and mean value are obtained by solving the equations (12) and (13) numerically. the temporal dependence of all three components of ion velocity have been calculated at constant magnetic field of 6 mt and for three different obliqueness of the field (30°, 60° and 75°), shown in figs. 3, 4, and 5, respectively. for the obliqueness of 30°, the x, y and z-component of velocity varies about the mean value of 0.007 m/s, 6661 m/s and 11600 m/s respectively with same frequency of oscillation 100 hz (fig. 3). also these components show damping nature of oscillation with damping factor 13.8 s-1, 13.1 s-1 and 13.0 s-1, respectively. likewise, these component of velocity varies with maximum amplitude of 9794 m/s, 3138 m/s and 1550 m/s, respectively. it also shows that the modulation frequency of x, y and z-component of velocity is same which is equal to 15.4 hz. fig. 4 shows that at obliqueness 60°, the x, y and zcomponent of velocity varies about the average values of -0.008 m/s, 11570 m/s and 6718 m/s, respectively with same frequency of oscillation, 100 hz. also these components show damping nature of oscillation with damping factor of 15.2 s1, 13.7 s-1 and 12.3 s-1 respectively. likewise, these components of velocity vary with maximum amplitude of 9794 m/s, 2650 m/s and 4632 m/s, respectively. the modulation frequency of x, y and z-component of velocity for this case is 16.2 hz, 15.8 hz and 16.2 hz, respectively. at obliqueness of 75°, the x, y and z-component of velocity varies about the average values of 0.0058 m/s, 11580 m/s and 3137 m/s respectively, with same frequency of oscillation 100 hz as shown in fig. 5. also these components show damping nature of oscillation with the damping factor as 12.9 s-1, 14.9 s-1, and 14.1 s-1, respectively. likewise, these component of velocity varies with the maximum amplitude of 9794 m/s, 1690 m/s and 6657 m/s, respectively. the modulation frequency of x, y and z-components of velocity are 15.8 hz, 16.0 hz and 15.4 hz, respectively. in this case, of obliqueness 75°, shoulder nature in the velocity components are observed around 0.05 second which was not the case when the angles were smaller. the obtained results are summarized in table 1, where the average value, maximum amplitude, damping factor, frequency of oscillation and modulation frequency of all three component of ion velocity at obliqueness of 30°, 60° and 75°. the ycomponent of mean value (11580 m/s) is maximum at 75° compared to other angles. the amplitude is maximum (9793.99 m/s) of the x-component in two cases, when the angles are 30° and 75°, whereas amplitude is minimum (1550 m/s) for z-component at 30°. the damping factor of the z-component is minimum (13.0 s-1) when the angle is 30°, on the other hand it is maximum for y-component (14.9 s1) at 75°. similarly, modulation frequency in the xcomponent and z-component is maximum (16.2 hz) at angle 60°, whereas frequency of oscillation remained same for all components of velocity for each cases considered. fig. 3: temporal variation of velocity of ions for a magnetic field of 6 mt at angle 30°. bhesha raj adhikari et al. / bibechana 18 (1) (2021) 134-139 138 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 -1 -0.5 0 0.5 1 1.5 x 10 4 time (s) v el o ci ty ( m /s ) v x v y v z 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 -1 -0.5 0 0.5 1 1.5 x 10 4 time (s) v el o ci ty ( m /s ) v x v y v z fig. 4: temporal variation of velocity of ions for a magnetic field of 6 mt at angle 60°. fig. 5: temporal variation of velocity of ions for a magnetic field of 6 mt at angle 75°. table 1: the average value, maximum amplitude, damping factor, frequency of oscillation and modulation frequency of ion velocity 4. conclusions velocity variation as well as modulation frequency of ions in a magnetized plasma sheath has been studied for different obliqueness of magnetic field. it has been observed that the ion velocity at presheath-sheath boundary is affected by varying the obliqueness of the field. various parameters like average ion velocity, amplitude, modulation frequency, and the damping factor can be controlled by varying the obliqueness. however, the frequency of oscillation is independent of obliqueness of magnetic field. the changes in these parameters results due to the change in contribution of the magnetic field with obliqueness. present work is useful in understanding the time evolution of the particles velocities, and hence, exact particle behavior in magnetized plasma sheath region which is important in diverse plasma applications: material processing, surface treatment, plasma etching, confinement of plasma in fusion devices, and many more. acknowledgement b. r. adhikari would like to acknowledge the university grants commission, nepal for the ph. d.  average value (m/s) maximum amplitude (m/s) damping factor (s-1) frequency of oscillation (hz) modulation frequency (hz) vxm vym vzm vxa vya vza vx vy vz vx vy vz vx vy vz 30° 0.007 6661 11600 9793.99 3138 1550 13.8 13.1 13.0 100 100 100 15.4 15.4 15.4 60° -0.008 11570 6718 9794 2650 4632 15.2 13.7 13.3 100 100 100 16.2 15.8 16.2 75° 0.0058 11580 3137 9793.99 1690 6657 12.9 14.9 14.1 100 100 100 15.8 16 15.4 bhesha raj adhikari et al. / bibechana 18 (1) (2021) 134-139 139 fellowship. the authors warmly thank mr. suresh basnet for fruitful discussions. references [1] r. chalise and r. khanal, a kinetic trajectory simulation model for magnetized plasma sheath, plasma phys, control. fusion 54 (2012) 095006 (5pp). https://doi.org/10.1088/0741-3335/54/9/095006 [2] d. bohm, the characteristics of electrical discharges in magnetic fields, edited by a. guthry and p.k. wakerling, mc-graw hill, 1949. [3] r. chodura, plasma wall transition in an oblique magnetic field, phys. fluids 25 (1982) 1628-1633. https://doi.org/10.1063/1.863955 [4] i. langmuir, oscillations in ionized gases, proc. national academy of sciences 14 (1928) 627637. [5] k. u. riemann, the bohm criterion and sheath formation, j. phys. d: appl. phys. 24 (1991) 493518. https://doi.org/10.1088/0022-3727/24/4/001 [6] k. u. riemann, theory of the plasma-sheath transition, j. tech. phys. 41 (2000) 89-121. [7] m. m. hatami, a. r. niknam, b. shokri and h. ghomi, magnetized plasma sheath with two species of positive ions, phys. plasmas 15 (2008) 053058 (5pp). https://doi.org/10.1063/1.2918319 [8] b. r. adhikari, s. basnet, h. p. lamichhane and r. khanal, presheath-sheath coupling for kinetic trajectory simulation of a magnetized plasma sheath, aip advances 9 (2019) 055123 (10pp). https://doi.org/10.1063/1.5088107 [9] r. moulick, s. adhikari and k. s. goswami, sheath formation in collisional, low pressure, and magnetized plasma, phys. plasmas 26 (2019) 043512 (10pp). https://doi.org/10.1063/1.5090537 [10] s. basnet, a. sarma and r. khanal, effect of presheath electron temperature on magnetized plasma-wall transition and wall sputtering by plasma having two species of positive ions, physica scripta 95(2020) 065601 (11pp). https://doi.org/10.1088/1402-4896/ab7b89 [11] r. khanal, a kinetic trajectory simulation model for bounded plasma, ph. d. thesis. innsbruck university, austria (2003). [12] r. chalise and r. khanal, self consistent one dimension in space and three dimension in velocity kinetic trajectory simulation model of magnet ized plasma wal l t ransi t ion , phys . plasmas 22 (2015) 113505 (5pp) . https://doi.org/10.1063/1.4934601 [13] p. c. stangeby, the plasma boundary of magnetic fusion devices, iop publishing ltd ( 2000). [14] g. f. simmons, differential equations with applications and historical notes, tata mcgraw hill, new delhi (1991). bibechana 18 (2) (2021)105-116 105 wavelet and cross correlation analysis on some climatology parameters of nepal babu ram tiwari1*, jiyao xu1, binod adhikari2, narayan p. chapagain3 1state key laboratory of space weather, national space science center, chinese academy of sciences, beijing, china100190 2department of physics, st. xavier’s college, maitighar , kathmandu, nepal 3department of physics, amrit campus, tribhuvan university, kathmandu, nepal email: tiwari.baburam@gmail.com article information: received:december 27, 2020 accepted: may 28, 2021 keywords: climate variability wavelet transform cross-correlation analysis abstract this study has been performed to understand the relationship between sunspot numbers (ssn) with climatology related parameters like temperature and rainfall from 1901 to 2016. the spectral characteristics of sunspot numbers, temperature and rainfall have been observed using continuous wavelet transform. crosscorrelation analyses were also performed to find any relation among temperature, rainfall, and sunspot numbers. the 9–11 year periodicity of sunspot numbers confirmed by wavelet transform in annual scale. the periodicity of highfrequency signals is identified between 4 to 11 years whereas the low frequencies signal is found throughout the periods of observation for temperature. similarly, it is clear that there is more concentration of power between 8–16 years for rainfall. cross-correlation analysis shows that the sunspot numbers is highly correlated with rainfall and temperature (correlation coefficient ~ 0.8054). the time lag relationship resulted in the almost simultaneous linear relationship between the temperature, rainfall, and the ssn tendency. development of convective motions over the subtropics might be affected by the time rate of change of ssn combined with the surface temperature changes of diverse time scales. the convective motions were mostly controlled by the available amount of water vapor and the stability of the atmosphere that had a strong connection with the heat capacity of the concerned region. to produce more authentic findings for policy implications, further comprehensive and appropriate research can be undertaken and implemented in this very important field. doi: https://doi.org/10.3126/bibechana.v18i2.33805 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ mailto:tiwari.baburam@gmail.com https://doi.org/10.3126/bibechana.v18i2.33805 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana babu ram tiwari et al. / bibechana 18 (2) (2021) 105-116 106 1. introduction the weather can be defined as the daily chaotic, non-linear dynamic system of the atmosphere, while the climate is the average state of the weather. the climate is fairly stable and predictable. the change in the state of climate that can be identified by changes in mean or variability of its properties and that persists for extended periods, typically decades or longer refers climate change [1]. although there is no particular time frame to define climate, scientists have however been taking variety of weather parameters, such as temperature or rainfall based on data from weather stations in the area of concern or interest. climate fluctuates annually above or below a long-term mean value. this fluctuation is called climate variability. the climate system shows high natural variability on different time scales. nepal is located in subtropical latitude constituting for its variations in climates. the climates of different regions vary according to the altitude and seasons throughout the year.it lies in the temperate region of the world when sun's rays are moderate so it have tropical monsoon climate.summer seasons are becoming hotter; more heavy rainfalls are being reported. analysis of history of disasters in south asia reveals that nepal is the country that experience different types of flood every year with negative impacts on their economies. the plains of the foothills of nepal mostly traversed by the rivers and tributaries mainly originated from the himalayas. it falls under the indian monsoon region with heavy precipitation during the wet monsoon that frequently causes severe floods destroying infrastructures, crops, and vegetations and displacing thousands of people [2]. climate change is a very important and widely discussed subject in recent years. climate change manifests in many respects apart from increase in rainfall, resulting into flood and the rising sea level. these include increased frequencies of extreme climatic events like above average daily minimum and maximum temperature. the most common parameters of climate change are increase in average global temperatures and precipitations. thus, increase in average global temperature and average global precipitation is indicators of climate change. a common method for the assessment of climatic changes is the analysis of historical climatic data, in which trend detection and analysis play important roles [3, 4, 5]. climatic elements and phenomena such as temperature, precipitation, humidity, and hurricanes are the results of various complex and often periodic processes in the atmosphere [6, 7, 8, 9]. the evaluation of the trend and periodic components of climatic time series separately provides more valuable information than those that can be obtained from direct trend analysis. signal processing methods have become widely used in atmospheric and hydrological sciences. the wavelet analysis technique analyzes data for local and global climate changes and reveals active frequencies in time series and their changes over time [10-13]. the time series are non stationary in meteorology and climatology so that it is necessary to apply an advanced transformation to decompose a series into the time-frequency domain. at present, the wavelet transform seems to be one of the most appropriate methods for such analyses. annual and seasonal scales variations of temperature and rainfall with sunspot numbers were considered in the present study. during this eleven-year cycle of sunspots, the sunspot number increases -solar maximum and decreasessolar minimum. in addition, the solar magnetic field, ultraviolet radiation, and other features that may affect climate are found to rise and fall along with the sunspot number. the main purpose of this research is to investigate how some climatological parameters (temperature and rainfall) vary periodically and temporally over nepal. the details of the data and data analysis methods adopted herein are briefly explained in next section. section 3 presents the results and https://www.sciencedirect.com/science/article/pii/s2468227618301388 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/weather-stations https://www.sciencedirect.com/topics/earth-and-planetary-sciences/rising-sea-level https://www.sciencedirect.com/science/article/pii/s2468227618301388 https://www.sciencedirect.com/science/article/pii/s2468227618301388 https://www.sciencedirect.com/science/article/pii/s2468227618301388 babu ram tiwari et al. / bibechana 18 (2) (2021) 105-116 107 discussion followed by conclusions in section 4. the results indicate the variations of temperature and rainfall with sunspot numbers in a long terms data over nepal. dataset the climate of nepal is diverse as the country’s topography, which encompasses eight of the ten highest mountains in the world and extends to the rim of the gangetic plains that have elevations below 300 meters above mean sea level basically subtropical; exhibiting two climatic sessions (dry and wet) annually. monthly average temperature as well as monthly total rainfall data of nepal, spanning 116 years; from 1901 to 2016 were collected from world bank data group (https://climateknowledgeportal.worldbank.org/). the annual temperature in nepal is defined as the mean of the temperature over all the months (january to december) of the year while the annual average rainfall accounted for the sum of all the total monthly rainfall divided by total number. sunspot data where obtain from the sunspot index and long-term solar observations (http://www.sidc.be/silso/datafiles). sunspot number is the longest solar activity index available and it is a representative of the general state of solar activity [14]. 2. methodology to achieve the objective of detecting the responses and significant periodicities of the temperature and the rainfall to ssn, the continuous wavelet transforms and cross-correlation analysis were employed. wavelet transform the wavelet transform (wt) is a strong mathematical tool that provides a time-frequency representation of an analyzed signal in the time domain [15]. wavelet transform has advantages over classical spectral analysis, because it allows the analysis of different scales of temporal variability and it does not need a stationary series [16]. thus, it is appropriate to analyze irregular distributed events and time series that contain non-stationary power at many different frequencies. wavelet analysis maintains time and frequency localization in a signal analysis by decomposing or transforming a one-dimensional (1-d) time series into a diffuse 2-d time-frequency image simultaneously. then, it is possible to get information on both the amplitude of any periodic signals within the series, and how this amplitude varies with time. for instance, in comparison with the fourier transformation, it is possible to differentiate not only values of particular frequencies in non-stationary series, but also their location in time can be determined [17]. on the other hand, the possibility of time-frequency representation relates to a problem of resolution. another advantage of wavelet analysis is that this method, contrary to the other types of transformation providing time-frequency presentation, like the windowed fourier transformation, solves the dilemma of resolution to a certain extent [18]. continuous wavelet transform the continuous wavelet transform (cwt) is the mathematical tool able to analyze any non stationary time-series, showing the temporal variability of the power spectral density. the “wavelet” word indicates a set of functions with the form of small waves created by dilations, ( ) (2 )t t  , and translations, ( ) ( 1)t t   applied on a simple generator function, ( )t , which is called mother wavelet.mathematically, the wavelet function is given by , 1( )s tt ss         (1) where s represents the scale associated to the dilation and contraction of the wavelet, and  is the temporal location, which relates to the translation in time. for each value of the s and  coefficients, we obtain a set of wavelet functions, called daughter wavelets [19].the wavelet transforms, w is then defined as a convolution integral of the time series with the wavelet function: http://www.sidc.be/silso/datafiles https://www.sciencedirect.com/science/article/pii/s2468227618301388 https://www.sciencedirect.com/topics/medicine-and-dentistry/spectroscopy https://www.sciencedirect.com/science/article/pii/s2468227618301388 https://www.sciencedirect.com/topics/earth-and-planetary-sciences/fourier-transformation https://www.sciencedirect.com/science/article/pii/s2468227618301388 https://www.sciencedirect.com/science/article/pii/s2468227618301388 babu ram tiwari et al. / bibechana 18 (2) (2021) 105-116 108 ( , ) 1( , ) ( ) ( )x s tw s x t dt x t dt ss            (2) where ( )x t is the time series, , ( )s t is the wavelet function and * represents the complex conjugate. here, s and  are real and s > 0. we used the morlet wavelet, a continuous and complex wavelet adapted to wavelike signals that allows identifying the main periodicities [10], [20]. it is a plane wave modulated by a gaussian envelope and can be described by equation 3: 2 01/ 4 /2( ) ti tt e e   (3) where 0 represents the dimensionless frequency. in this work this value of parameter was set up as 6.0, since its shape gives good localization in time [10], which is a monochromatic wave modulated by a gaussian of unit width. wavelet power spectrum the wavelet power spectrum (wps) is defined as 2 ( , )xw s  and represents the squared absolute value of the wavelet transform coefficients. the wps (which is sometimes also referred as local wavelet power spectrum (lwps)) is plotted as a function of time and period in a 2-dimensional graph. concerning the fact that the wavelet power spectrum gives more information in one picture, it is often practical to show the information as the averaged value of the result in the range of scale or time.the parameters used for the wavelet analysis of the yearly temperature and rainfall data in this study were: δt = 1year and s0 = 2 δt, δj = 0.25 to do 4 sub-octaves per octave, j1 = 7/ δj to do 7 powersof-two with δj sub-octaves each. information on the relative power of a particular scale and a particular time is provided by power of the yearly temperature and rainfall data. it reveals the magnitudes of the scaled and shifted version of the mother wavelet in addition to their actual oscillations. global wavelet power spectrum the average wavelet power (also known as global wavelet power spectrum (gws)) showed the average variations of the whole time series on every scale which is defined as [10] 2 ( , )xg w s w s d   (4) the scales are a series of fractional powers of 2 and are defined as: sj=s02kδjk=0, 1,…,j, where s0 is the least resolvable scale and j determines the highest scale. moreover, the scale δj= 0.25 is used, which will do 4 sub octaves per octave. the smaller values of δj give a finer resolution [10]. cone of influence the cone of influence (coi) is the errors occur at the beginning and at the end of wave power spectrum when considering a time series of finite length. the edge effects are reduced when number of the elements of the time series is equal to a power of 2. thus, there is need to pad the time series with zeros to bring the length of the time series to the next higher power of 2 before calculating wavelet transform [10]. the padding reduced the amplitude at the edges, as more zeros were involved in the analysis. the region of the wavelet spectrum in which edge effects become important is referred to as the cone of influence (coi). and it is defined as the e-folding time for the autocorrelation of wavelet power at each scale [10]. cross-correlation analysis the cross-correlation analysis (cca) is a wellknown method used to find where two signals match. several authors have used this method [2125]. the classical correlation is calculated by the displacement of one series relative to the other by units of time (t), which provides the lag of the correlation [25]. we calculated the crosscorrelation coefficients for the leading and lagging shifts between ssn with temperature and rainfall. the correlation coefficient also defines how well correlated the two series are, varying from -1 to 1. 3. results and discussion we plotted time series of yearly average sunspot number (ssn), yearly average temperature of nepal and yearly average rainfall of nepal during https://www.sciencedirect.com/topics/earth-and-planetary-sciences/power-spectra https://www.sciencedirect.com/science/article/pii/s2468227618301388 https://www.sciencedirect.com/science/article/pii/s2468227618301388 https://www.sciencedirect.com/science/article/pii/s2468227618301388 https://www.sciencedirect.com/topics/earth-and-planetary-sciences/autocorrelation https://www.sciencedirect.com/science/article/pii/s2468227618301388 babu ram tiwari et al. / bibechana 18 (2) (2021) 105-116 109 1901-2016. this time series for yearly average sunspot numbers, temperature and rainfall of nepal (19012016) as shown in figure 1. it is evident from figure 1 that both temperature and rainfall data appear irregular and random, while sunspot numbers have a clear cyclic character. this variability might be suggestive of coupled global ocean–atmospheric dynamics or some other factors, such as deforestation, anthropogenic, high latitudinal influence etc. [27]. figures 2(b), 3(b) and 4(b) show the power (absolute value squared) of the wavelet transform for the yearly sunspot numbers, temperature and rainfall for 116 years in nepal presented in figures 1(a)-(c). the (absolute value) 2 gives information on the relative power at a certain scale and a certain time. these figures show the actual oscillations of the individual wavelets, rather than just their magnitude. observing these figures, the concentration of power can be easily identified in the frequency or time domain.wavelet power decreases according to the following order: red, orange, yellow and blue.the cross-hatched regions in these figures are the cone of influence, where zero padding has reduced the variance. because we are dealing with finite-length time series, errors will occur at the beginning and end of the wavelet power spectrum [27]. the black contours in the same figures are the 5% significance level, using a red-noise background spectrum. as declared before, the absolute value squared offers info on the relative power at an explicit scale and an explicit time that shows the particular oscillations of the individual wavelets, instead of simply their magnitude. observing the global wavelet spectrum in figures 2(b)-4(b), it is clear that there is more concentration of power between the 8 – 16 years band. wavelet power spectrum at 95% significant level presents an important peak for sunspot numbers, temperature and rainfall episodes with characteristic scale of 9 11-years. the wavelet spectrum of sunspot numbers shows strong periods between 9 to 11 years [28-30] for the entire time span. contour lines delimit the periods significant at 95% confidence level. the parabolic curve delimits the cone of influence region. from this figure 2a the signal near 11-year is the strongest feature and is persistent during the entire series indicating the non-stationary behavior of the sunspot time series. the wavelet spectrum of temperature (figure 3a) shows strong amplitudes in the interval of 2–8 years. the signal is nonstationary with the periodicities alternating i.e., present at sometimes and absent in others. the wavelet power spectrum of rainfall variability (figure 4a) reveals significant power concentration at time scales of 8–16 years and at 11 years solar time scales [31]. a dominant amplitude mode is also seen in the low frequency range at around 1920-1940 years (at periods 30–35). the power in 8 16-year band in rainfall shows the dry and wet years which means when the power decreases substantially it means a dry year similarly for the maximum of power it is a wet year. in the years 1920 and between the years 1985 to 2010 an extreme increase in power can be found which corresponds nepal has a wet year. since 1960 to 1980 a dry period that contains certain reductions can be identified. also, there are intense periods around 16–32 years both in temperature and rainfall. higher order periods are also observed around 43 years, but they are insignificant as it lies under the hatched region. periods around 16 years also shows weak signal. like the sunspot numbers, the wavelet results of annual rainfall show periods around 11 years from 1910– 1920. shorter periods like 3–5 years are also visible in the beginning of the time series. there are periods greater than 32 years and lies above coi from 1910–1950. this annual rainfall of nepal shows shorter periods between 2 and 6 years. the power is intense at the beginning. more intense power is visible but lies near coi, so neglected. the brief discussion of the results of wavelet transform implies that oscillations of annual temperature and rainfall are likely driven, at least partly, by solar variability. the general correspondence of prominent rainfall changes with variations in solar activity implies a solar influence on area-scale rainfall oscillations during the past babu ram tiwari et al. / bibechana 18 (2) (2021) 105-116 110 fig. 1 :. figure from top to bottom a) yearly average sunspot number (1901-2016), b) yearly average temperature of nepal (1901-2016), and c) yearly average rainfall of nepal (1901-2016). fig. 2 : a) wavelet power spectrum of sunspot numbers (ssn) (1901-2016); cross-hatched regions on either end indicate the ‘cone of influence’ where edge effects become important. b) the global wavelet power spectrum. the dashed line indicates 5% significance level for the global wavelet spectrum. babu ram tiwari et al. / bibechana 18 (2) (2021) 105-116 111 fig. 3: a) wavelet power spectrum of temperature (1901-2016); cross-hatched regions on either end indicate the ‘cone of influence’ where edge effects become important. b) the global wavelet power spectrum. the dashed line indicates 5% significance level for the global wavelet spectrum. fig. 4: a) wavelet power spectrum of rainfall (1901-2016); cross-hatched regions on either end indicate the ‘cone of influence’ where edge effects become important. b) the global wavelet power spectrum. the dashed line indicates 5% significance level for the global wavelet spectrum. babu ram tiwari et al. / bibechana 18 (2) (2021) 105-116 112 fig. 5: temperature contour of nepal 1901–2016. 116 years. so, in this paper an attempt was made to study the relationship between temperature, rainfall, and solar activity [32-35]. figure 4(b) showed the significant peaks around the years of 1928, 1940, 1970 and 1990. the average yearly total rainfall of nepal from the year 1901 to 2016 is shown in 4(a). figure 4(b) revealed multilevel power peaks on the global wavelet spectrum, with the maximum of 600 occurring around the 32yearperiod but which lies above coi. however, the power peak of about 2 occurring around the 11yearperiod is the most significant at the 5% significance level. figure 5 depicts the detail information of temperature throughout the months of the given years. the range of temperature varies from 2 °c to 10°c. the result reveal that the temperature increases gradually from 18 °c to 20 °c in the month of may and then around 19 °c to 20 °c (brown color) in the month of jun (the hottest month). thereafter the temperature begins to decrease until a minimum around 2 °c to 4 °c in the month of december whereas another maximum turning point was observed in the month of october (light-olive green color). finally, the temperature decreases to around 3 °c in the month of december. it has been noticed that the intense temperature of 20 °c (dark brown color) was recorded in the months of april to august of the years. figure 6 illustrates the annually season variation of rainfall from 1901 to 2016 in nepal. it has been noticed that the rainfall picks up its momentum gradually, becoming more intense from july and reaching its maximum around august; and thereafter begins to decrease. we have also analyzed the correlative analysis of 116 years data of the sunspot, temperature, and rainfall. it has been found that the effect of the 22year solar cycle with a 0-year lag on global temperature is more significant rather than that of 11-year cycle. thus, the 22-year magnetic field solar cycle plays a greater role than that of 11-year sunspot cycle in global climate change. additionally, we notice that solar activity cannot explain the upward trend of global temperatures after 1970. this shows that positive correlation coefficient exists between rainfall and solar activity during the investigation. the positive value may be due to low temperature regions or months. the correlation of sunspot numbers with rainfall should have high correlation coefficient value [36] and the https://www.sciencedirect.com/science/article/pii/s2468227618301388 https://www.sciencedirect.com/science/article/pii/s2468227618301388 babu ram tiwari et al. / bibechana 18 (2) (2021) 105-116 113 present study shows similar result. the calculation of correlation between the datasets of sunspot numbers, temperature, and rainfall, found maximum positive correlation coefficient approximately 0.8054. the time lag relationship resulted in the almost simultaneous linear relationship between the temperature, rainfall, and the ssn tendency. development of convective motions over the subtropics might be affected by the time rate of change of ssn combined with the surface temperature changes of diverse time scales. the changes came from an annual cycle, the diurnal variation, and other various mechanisms. the convective motions were mostly controlled by the available amount of water vapor and the stability of the atmosphere that had a strong connection with the heat capacity of the concerned region. fig. 6: rainfall contour of nepal 1901–2016. fig. 7: cross-correlation between sunspot numbers (ssn) with temperature and rainfall. babu ram tiwari et al. / bibechana 18 (2) (2021) 105-116 114 4. conclusions the present paper is an attempt to quantify the relation between sunspot numbers and climatic related parameters. we applied waveletand crosscorrelation analysis to analyze the 116-year time series of temperature and rainfall of nepal with sunspot numbers. with spectral wavelet analysis, the time-frequency characteristics of the analyzed data were estimated. this analysis provides an insight into the dynamic behavior of the observed average temperature and rainfall over time. for both the yearly average temperature and rainfall of the analyzed time series, several local maximums were identified in the gws graphs, where the largest is that in a 9–11-yearperiod, showing that these time series have strong relations with sunspot numbers. change in climate is attributed to natural variability and anthropological activities. variation of solar activity reaching the earth is thought to influence rainfall, but we are still searching for better physics to understand how the periodic variation of the solar activity influences the variation of the rainfall of land. the wavelet analysis shows almost all kinds of periodicities on one time or other ranging from 2 to 11 years and more. therefore, it should be further studied to investigate any quantitative effect of solar activity on other parameters. the calculated correlation coefficient values arehigh. climate change in nepal got tremendous momentum since the advent of 90’s in terms of rainfall. the adverse impact of this climate change in nepal has become the most vulnerable and this process continues at an increasing rate. the findings of this study show that nepal is a vulnerable country to climate change in terms of rainfall. to produce more authentic findings for policy implications, further comprehensive 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http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal constant velocity pulling and unfolding of thyroid hormone receptor by steered molecular dynamics tika ram lamichhane, hari prasad lamichhane* central department of physics, tribhuvan university, kirtipur, kathmandu, nepal *email: tikaramlamichh@gmail.com article information: received: july 06, 2019 accepted: october 7, 2019 keywords: dynamicsmolecularsteered receptorhormonethyroid triiodothyronine ligand binding domain; protein unfolding abstract unfolding pathways of t3 liganded thyroid hormone receptor (thrt3) can be studied by using the protocols of steered molecular dynamics (smd). theory of constant velocity pulling has been implemented to the structure of thrt3 in a neutral water-ion solution equilibrated up to 20 ns. the globular form of thrt3 is completely unfolded extending n-c termini from 38 å to 876 å at a constant speed of 0.1 å/ps by means of 8.5 ns long smd simulations. the peak force measured in the intermediate conformations is related to a burst of backbone hbonds among -helices and -hairpins. with decrease in h-bonds, electrostatic energy increases by losing gradually the secondary structure and separating  and -strands in solution. the force at the end (t > 8.5 ns) increases steeply with the large increase in bond-angle and bond-length potentials when the system becomes completely unfolded. the hydrophobic ligand binding domain (lbd) of thr- with load bearing h-bonds protects t3 from water attack. even after complete unfolding of thr- lbd, the position of t3 is not deviated more than 2.5 å and a large number of water molecules remain in the surrounding of this domain area. this is a strong evidence for the mechanochemical stability of a receptor protein’s lbd towards hormone activated gene expressions followed by ligand binding and dissociation. 1. introduction steered molecular dynamics (smd) is used to unfold the proteins and to study their elastic properties visualizing the different unfolding pathways [1]. the biophysical phenomena behind ligand binding, dissociation and conformational changes of thyroid hormone receptors (thr) are important in triiodothyronine (t3) stimulated gene expressions [2]. the physical properties such as echo dephasing, heat capacity, thermal diffusivity and thermal conductivity of liganded and/or unliganded thr-subtypes in folding states are previously studied [3, 4] by using md simulations. this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.25870 http://nepjol.info/index.php/bibechana mailto:tikaramlamichh@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.25870 tika ram lamichhane, hari prasad lamichhane / bibechana 17 (2020) 50-57 51 a point mutation in thr- gene causes resistance to thyroid hormones. the mutational impacts are observed distinctly on the protein-hormone systems by analyzing conformations and interaction energies through molecular dynamics approach [5]. smd is a technique to know the structure-function relationships of the protein-hormone complex through unbinding of hormone or unfolding of protein under the application of time-dependent external forces. the elastic properties of the biomolecular systems subjected to deformations by smd are in close agreement with the experimental results obtained from atomic force microscopy (afm) and optical tweezers [6-8]. the mechanical stability of thyroid hormone like heavy ligand receptors is governed by protein’s secondary structure and pulling geometry [9]. thyroid hormone dissociation or unfolding of thr strands proceeds a frictional path with constant velocity along x-direction defined by langevin’s equation [1] 𝜇�̇� = − 𝑑𝑈 𝑑𝑥 + 𝐹(𝑥, 𝑡) + 𝜎𝑓(𝑡) (1) where  is time dependent frictional coefficient having dimension of [mt -1 ], f(x, t) is deforming force, 𝑈(𝑥) is potential governing ligand dissociation or protein unfolding pathways and 𝑓(𝑡) is the stochastic or fluctuating force term having coupling coefficient 𝜎. in smd simulation, the smd atom is attached to a dummy atom through a virtual spring. in one dimensional pulling, the dummy atom moves with constant velocity (�⃗� = 𝑑�⃗�/𝑑𝑡) so that the smd atom experiences the force vector �⃗�(𝑥, 𝑡) = 𝑘(�⃗�𝑡 − ∆�⃗�) depending on the linear distance between these atoms [10]. so, the external potential energy [11] is given by 𝑈(𝑥, 𝑡) = 1 2 𝑘[(�⃗�𝑡 − ∆�⃗�). �⃗⃗�]2 (2) where 𝑘 is spring constant that specifies the stiffness of the applied harmonic restraining force, ∆�⃗�(𝑡) = �⃗�(𝑡) − �⃗�0 is tagged group displacement with �⃗�(𝑡) and �⃗�0 being actual and initial positions of the smd atom and �⃗⃗� is the direction of pulling. 2. methodology the initial structure of t3-liganded thr- isoform of nuclear receptor super family was taken from the protein data bank code 3gws [12]. the thr- ligand binding domain (lbd) complex has the chain length of -helices and -forms with 259 amino acids and 3895 atoms. in the folding state or the globular form, end to end distance of thr- lbd is 38 å. the thr- lbd actively binds t3 hormones having 35 atoms including 3 iodine atoms. the simulation packages such as protein structure file (psf) generation and solvation with water (tip3p model) and ions providing cellular environment were prepared and structural and graphical analysis were performed by using visual molecular dynamics (vmd-1.9.3) [13]. in accordance with nanoscale molecular dynamics (namd-2.12) protocols [14], the topologies and parameters required for md simulations of the thr- lbd complex were obtained from charmm force fields for proteins [15, 16]. the t3-hormone was parameterized with the help of zoete’s force field generation tool [17]. the t3-liganded thr- lbd (thrt3) was fully solvated into a water droplet of radius 37.5 å consisting of 17245 water molecules neutralized with 26 na + and 16 cl ions in the concentrations of 0.15 mol/l. the system’s energy was minimized up to 3000 conjugate gradient steps and it was equilibrated up to 20 ns with namd protocols. velocity verlet algorithm [18] was used for the equilibration simulations with the integrator parameter of 2 fs/step, langevin thermostat at 310 k and barostat at 1-atm and damping coefficient of 1 ps -1 . for the lenard-jones interactions, a 12 å cut-off with smooth switching function starting at 10 å was applied with 1-4 scaling 1.0. the final coordinates of the solvated thrt3 were extracted from the equilibrated droplet in order to perform smd simulations. the smd simulation was conducted setting the c atom of the last residue-460 as the smd atom and the c atom of the first residue-202 as the fixed tika ram lamichhane, hari prasad lamichhane / bibechana 17 (2020) 50-57 52 atom. the virtual spring between the smd atom and the dummy atom was 7 kcal/mol/ å 2 . the one dimensional pulling was performed at constant velocity of 0.1 å/ps in the direction along a vector connecting the fixed atom and the smd atom. the thrt3 complex became completely unfolded at the simulation time of about 8.5 ns and the smd was conducted up to 10 ns. the intermediate conformational states of the thrt3 structures were visualized and the images were generated by using the vmd software. the related physical parameters such as radius of gyration (rg), root mean square deviation (rmsd), extension or endto-end distance (x), forces and energies were noted down and the graphical analysis was performed with the plotting program xmgrace. the smd simulation was repeated three times to check the accuracy of the obtained results. 3. results and discussion in the folding state or completely stable globular form, n-c termini or end to end length of the thrt3 system is 38 å. the receptor protein is unfolded smoothly with simulation time by breaking h-bonds among -helices or -sheets during the constant velocity (0.1 å/ps) pulling of the smd atom. the changing extension and rg of thrt3 over the course of simulation are shown in figures 1-a & 1-b, respectively. the system becomes completely unfolded after the simulation time of 8.5 ns. at t = 8.5 ns, the end-to-end length is 876 å and rg of about 258 å. the thrt3 conformations responsible for the peak force are b, c and d as indicated in force vs extension graph (figure 2). the structure a is the initial folding state in equilibrated form whereas e is the final unfolding state extended to 1023 å. the force at the end (t > 8.5 ns) of the simulation increases when thrt3 becomes completely unfolded due to stretching of the protein single strand. the structures (a, b, c, d and e) formed by sequential unzipping of h-bonds are shown in figure 3 and the related physical parameters such as time, length, rg, rmsd, number of h-bonds (at 3 å internal distance and 20 o angle), force, kinetic energy (ke), potential energy (pe) and electrostatic energy are reported in table 1. the resistance of hbonds ruptures simultaneously causing the structural change and rapid extension of thrt3 lbd. unfolding of native structures needs the maximum pulling force as they represent the bottom of the steep free energy well [19]. (a) (b) fig. 1: end-to-end distance or extension and radius of gyration (rg) of thrt3 over the course of smd simulation. the t3 binding domain formed by -helices and hairpins has been verified to be the most stable region, i.e. the hormone binds strongly in the lbd of thr- because this region surrounded by a large mass of water remains almost unchanged (figure 3-c) even up to 533 å extension and 5 ns smd simulation. even after the t3 binding pocket is completely unfolded and the protein rmsd is raised up to 300 å (figure 4-a), the position of t3 does not shift more from its actual position as indicated by its rmsd (< 2.5 å shown in figure 4tika ram lamichhane, hari prasad lamichhane / bibechana 17 (2020) 50-57 53 b). abrupt breaking of hydrophobic contacts between helices 8 and 12 is required for the dissociation of t3 hormone from thr- lbd. the ligand binding and dissociation pathways observed in thr-isoforms by using smd simulations have been explained in the previous studies [10, 20, 21]. rmsd of t3 gets small step-up jump, i.e. the ligand/hormone becomes slightly unstable in the unfolding states of thrt3 responsible for the peak force generation as shown in the figure 4-b. along with the elongating system, h-bonds decrease in number (figure 5-a) whereas electrostatic energy increases up to the complete unfolding state of thrt3 (figure 5-b). at the time of complete unfolding (t  8.5 ns), h-bonds reduce to 10 and the ranges of ke, pe and electrostatic energy are 13345, -5900 and -69000 kcal/mol, respectively. the actual data are reported in table 1. after the complete unfolding state (t > 8.5 ns), h-bonds in a small number and electrostatic energy both remain almost constant as shown in figure 5. fig. 2: force vs extension plot showing initial folding state (a), intermediate states (b, c) having greater force associated with the breaking of h-bonds among -helices or -sheets and completely unfolding states (d, e). the force at the end (t > 8.5 ns) increases when thrt3 becomes completely unfolded. table 1: physical parameters at different unfolding states of thrt3 protein responsible for peak force unfolding states time (ps) end-to-end distance (å) force (kcal/mol-å) no. of hbonds rg (å) rmsd (å) ke (kcal/mol) pe (kcal/mol) elect. energy (kcal/mol) a 0 38.00 0.00 60 18.86 0.61 13809.01 -65680.75 -75115.80 b 1673 203.64 15.40 54 34.06 23.75 13832.59 -64576.79 -74093.63 c 4964 532.87 17.17 31 125.17 121.28 13446.59 -61668.09 -71620.80 d 8404 875.90 17.10 10 257.22 254.02 13343.50 -58944.43 -69681.59 e 10000 1023.29 98.21 9 300.66 297.56 13273.46 -50967.98 -69695.32 c d tika ram lamichhane, hari prasad lamichhane / bibechana 17 (2020) 50-57 54 (a) t = 0 ps, x = 38.00 å (c) t = 4964 ps, x = 532.87 å (d) t = 8404 ps, x = 875.90 å (e) t =10000ps, x = 1023.29 å (b) t = 1673 ps, x = 203.64 å fig. 3: different unfolding states responsible for peak force provided with the simulation time (t) and end-to-end distance (x) during the constant velocity (0.1 å/ps) stretching of thrt3. fig. 4: root mean square deviation (rmsd) of (a) receptor protein and (b) t3-hormone during unfolding of thrt3. tika ram lamichhane, hari prasad lamichhane / bibechana 17 (2020) 50-57 55 fig. 5: variation of (a) h-bonds and (b) electrostatic energy over the course of 10 ns smd simulation at constant velocity (0.1 å/ps) pulling of thrt3. fig. 6: energy profile diagram during unfolding of thrt3 by smd at constant velocity (0.1 å/ps ) pulling. (a) (b) fig. 7: variation of (a) kinetic and (b) internal potential energies over the course of 10 ns smd simulation at constant velocity (0.1 å/ps) pulling of energy. tika ram lamichhane, hari prasad lamichhane / bibechana 17 (2020) 50-57 56 the linard jones potential is getting raised linearly with small slope and the energy terms: dihedral and improper remain almost constant throughout the smd simulation. bond-angle and bond-length energies are almost constant before 8.5 ns and they rise up steeply after 8.5 ns when thrt3 is completely unfolded as shown in figure 6. figures 7-a & 7-b show that ke decreases slowly and linearly throughout the simulation, and conversely, pe increases slightly up to the state of complete unfolding of thrt3. when the system is completely unfolded (t > 8.5 ns), pe increases steeply. the cause behind the steeply changed pe is the fast increasing force generated after unwinding the molecular system. the load bearing strands are shielded by water and it interacts with bond-breaking events between such strands [9]. even if the strand is fully dissociated, water makes h-bonding to the exposed sites as in figure 3. the hydrophobic lbd of thr- with load bearing h-bonds is protected from water attack so that t3 is not dragged away from its pocket position even if the system is completely unfolded. in order to employ the reversible work comparable to afm experiments, very low speed pulling is to be implemented while unwinding the molecular system which is practically difficult due to computational limits. however, higher pulling velocities do not influence the reliability of the smd results [22]. continuous breaking of h-bonds up to the complete unfolding of thrt3 (figure 5-a) and force vs extension graph (figure 2) are comparable to afm results even at this pulling speed of 0.1 å/ps. the smd technique of crack propagation allows the identification of intermediate conformations of thrt3 responsible for the gene transcriptional activities. 4. conclusion triiodothyronine nuclear receptor (thrt3) is completely unfolded resulting end-to-end length of 876 å by 8.5 ns long smd simulations performed at constant velocity of 0.1 å/ps. the peak force associated with the intermediate conformations is due to breaking of h-bonds among -helices and hairpins. though rmsd of t3 does not exceed 2.5 å throughout the simulation, t3 is deviated more from its mean position in the conformational states of peak force generation. hydrophobic lbd, i.e. t3 binding pocket of the receptor that gets surrounded by water is unfolded only in the last of the simulation. it is an evidence for the stability of thr- lbd towards ligand (t3) binding and dissociation. even after complete stretching of the protein strand lbd, the position of t3 remains almost constant surrounded by water molecules. along with decrease in h-bonds, electrostatic energy increases gently during unfolding. there are linear changes with slightly decreased kinetic energy and slightly increased van der waals energy at this constant velocity pulling. however, force or net potential of the system increases rapidly at the end (t > 8.5 ns) of the simulation. dihedral and improper energies remain almost unchanged throughout the smd simulations, but bond-angle and bond-length energies increase steeply after complete unfolding (t > 8.5 ns) of the system. thus, one dimensional mechanical pulling at constant velocity is important technique to better understand the unfolding pathways of thrt3 like nuclear receptors. acknowledgements we would like to acknowledge the computing resources provided by prof. dr. raju khanal at his plasma lab, central department of physics, tribhuvan university, kathmandu, nepal. the partial financial support for this research has been provided by nepal academy of science and technology as the phd fellowship to the first author. references [1] s. izrailev, s. stepaniants, b. isralewitz, d. kosztin, h. lu, f. molnar, w. wriggers, k. schulten, steered molecular dynamics, computational molecular dynamics: challenges, methods, ideas, (1999) 39-65, springer, berlin, heidelberg. 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doi.org/10.1016/j.cplett.2009.12.022 https://doi.org/10.1007/s10867-018-9518-3 https://doi.org/10.3934/biophy.2018.4.245 https://doi.org/10.3126/bibechana.v16i0.21109 https://doi.org/10.1021/acs.jpcb.5b11519 https://doi.org/10.1002/pro.3117 https://doi.org/10.1016/j.jmb.2016.09.006 https://doi.org/10.1073/pnas.0905796107 https://doi.org/10.1021/jp803403c https://doi.org/10.1006/jcph.1999.6218 https://doi.org/10.1021/acs.jpcb.5b11519 https://doi.org/10.1016/s0006-3495(99)77188-2 https://doi.org/10.1021/jm050805n devendra sir cover page copy.jpg bibechana 17 (2020) 96-103 96 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal study of damage profiles and energy calculation of arsenic ions during ion implantation on germanium k. giri * , b. kandel department of physics, tri-chandra multiple campus, kathmandu * email: karangiri575@gmail.com article information received: july 17, 2019 accepted: december 2, 2019 keywords: implantation doping ionization phonons abstract computational calculation of energy loss and damage profiles when implanted by arsenic ions on amorphous germanium during ion implantation had been carried out. the required energies for doping of arsenic ion on germanium, in order to obtain maximum damage at 600 å, were calculated using srim. these ions when implanted on germanium causes the production of germanium recoils, vacancy-interstitial pairs, and phonons during the collision process. for 140 kev arsenic ion, the energy consumption for ionization, phonon production and vacancies creation are 39.634 kev (28.31% of incident energy), 90.888 kev (64.92% of incident energy) and 9.478 kev (6.77% of incident energy), respectively. the amount of target displacement, replacement collisions and vacancies were also evaluated. doping of arsenic ions on germanium also revealed that the energy loss due to nuclear stopping was greater than electronic stopping. significantly, surface hardness and electrical conductivity on germanium cannot be improved with calculated energies. 1. introduction ion implantation ion implantation is the process in which an accelerated ion allowed to enter the surface of the target material. ion implantation method is used in semiconductor device fabrication and in metal finishing, as well as various applications in materials science research [1]. ion implantation in semiconductors is currently receiving attention in several rather different contexts. semiconductor physicists and device engineers are interested in the implantation process because it provides a new doping technique with several potential advantages over more conventional doping methods. material scientists are interested in the electrical properties of ion-implanted semiconductors because they provide an important tool for studying solubility problems, diffusion processes, and radiation damage effects. and nuclear physicists are interested in the ion distribution profile in an implanted semiconductor because, among other things, it yields important information on the nature of the physical processes that occur when an energetic particle interacts with a crystalline or amorphous target [2]. this technology also has its this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.26521 http://nepjol.info/index.php/bibechana mailto:karangiri575@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.26521 k. giri, k. kandel / bibechana 17 (2020) 96-103 97 very strong application in medical physics for treatment of cancer using radiations e.g. proton therapy [3]. most importantly, ion implantation requires an understanding of the fundamental physics and chemistry that dictate the interaction of the ion beam and the target. the ions alter the elemental composition of the target (if the ions differ in composition from the target), stopping in the target and staying there. they also cause many chemical and physical changes in the target by transferring their energy and momentum to the electrons and atomic nuclei of the target material [4]. this causes a structural change, in that the amorphous structure of the target can be damaged or even destroyed by the energetic collision cascades. nowadays this has been easier to a great extent by various simulations and programming. srim is one of the simulation programs based on monte carlo mathematical framework of quantum collision that predicts the various damages during ion implantation experiments [5]. since ion implantation is a low temperature process, thermal effects are not considered in srim for calculation of damage profiles on germanium, so the damage which is calculated is that which would happen for an implantation at 0 k. also, this paper doesn't take account of the dynamic composition changes in the material and there is no description of defect clustering and irradiation-induced amorphization that severely limits its usefulness in some cases. germanium as a substrate for ion implantation the development of the germanium transistor in 1948 opened the door to countless applications of solid state electronics. from 1950 through the early 1970s, this area provided an increasing market for germanium [6]. development in quantum physics in turn allowed the development of the integrated circuits in 1958 [7] and the transistor in 1947 [8]. meanwhile, the demand for germanium for fiber optic communication networks, infrared night vision systems, and polymerization catalysts increased dramatically. solar panels are a major use of germanium. germanium is the substrate of the wafers for highefficiency multi junction photovoltaic cells for space applications. high-brightness leds, used for automobile headlights and to backlight lcd screens, are an important application. because germanium and gallium arsenide have very similar lattice constants, germanium substrates can be used to make gallium arsenide solar cells. germaniumon-insulator substrates are seen as a potential replacement for silicon on miniaturized chips [9]. the mars exploration rovers and several satellites use triple junction gallium arsenide on germanium cells [10]. other uses in electronics include phosphors in fluorescent lamps and solidstate light-emitting diodes (leds) [11]. germanium transistors are still used in some effects pedals by musicians who wish to reproduce the distinctive tonal character of the "fuzz"-tone from the early rock and roll era, most notably the dallas arbiter fuzz face [12]. presently, the major end uses are fibreoptic systems, infrared optics, solar cell applications, and light-emitting diodes (leds). germanium compounds are also used for polymerization catalysts and have most recently found use in the production of nanowires. properties of germanium can be altered in useful ways by the deliberate, controlled introduction of impurities ("doping") into the crystal or amorphous structure and we take the amorphous structure as a target. where two differently-doped regions exist in the same layer, a p-n junction is created. the behavior of charge carriers which include electrons, ions and holes at these junctions is the basis of diodes, transistors and all modern electronics [13]. stopping power the stopping power is an essential parameter when ions penetrate matter. it defines how much energy per unit path length an ion loses when penetrating a crystal, thus the stopping power is usually measured in units of evcm -1 but here we will measure the stopping power in ev/å. the stopping power depends primarily on the type of material which is penetrated and on the ion energy. when energetic ions are allowed to penetrate through target surface, a series of screened coulomb collision occur where the ion's energy gets divided into two stopping parameters, one is nuclear stopping and another is electronic stopping. k. giri, k. kandel / bibechana 17 (2020) 96-103 98 mathematically, the total stopping power can be given as: s = ( 𝑑𝐸 𝑑𝑥 )nuclear + ( 𝑑𝐸 𝑑𝑥 )electronic ………….. (1) where, s = total stopping power and defined as the energy loss (e) per unit path length (x) of the ion is the sum of these two factors; nuclear stopping and electronic stopping. nuclear stopping is the energy loss by ion to the target nuclei per unit path length of the ion. it is an elastic collision between two atoms and can be described by classical kinematics. electronic stopping is the energy loss by ion to the electrons of target atoms per unit path. it is an inelastic collision and the theoretical model is quite complex. the stopping is similar to a viscous drag force and is proportional to the ion velocity. the energy loss by incident ions is dissipated through the electron cloud into thermal vibrations of the target. the energy loss by electronic energy loses are more important than nuclear energy loses for improving hardness at the near-surface region. the electrical conductivity and hardness increases with the increase in electronic energy loss while, conductivity and hardness increases with the decrease in nuclear energy loss. this remarkable improvement in hardness and electrical conductivity is related to the degree of radiationinduced changes in microstructure and composition. in particular, determination of the electronic stopping power becomes crucial for studies of ion ranges and radiation damage in semiconductors. range distribution and collision events the range distribution depends primarily on the energy, mass, and atomic number of the incoming ions, the mass and atomic number of target atoms, the density of the target. the total distance that the ion travels in coming to rest is called its range and the projection of this distance onto the direction of incidence is called the projected range. total target displacements are the number of atoms knocked off their target lattice site. a vacancy is the hole left behind when a recoil atom moves from its original site. if a moving atom strikes a stationary target atom and transfers more than its displacement energy to it, and the initial atom, after the collision, does not have enough energy to move onwards, and it is the same element as the atom it struck, then it just replaces that atom in the target and there is no vacancy created. these are termed as replacement collisions. displacements = vacancies + replacement collisions .………….. (2) when a recoil atom stops, and is not a replacement atom, then it becomes an interstitial. these may be summed as: vacancies = interstitials + atoms which leave the target volume …………. (3) if a cascade atom leaves the target volume, it is no longer followed. 2. methods the doping of impurities on semiconducting elements can be processed by two ways: diffusion and implantation [14]. diffusion is limiting process due to saturation limit and so, we can't make high concentrated carriers. to overcome the diffusion issues of dopants and activation of dopants in materialion implantation or ion irradiation is the best. in general, using particle accelerators to shoot energetic ion on a material is the basic process of implantation and irradiation. among some trending techniques we employed srim to study the damage profiles of target atom when doped with different ions. because of less error in srim data and availability of different updated version of this program motivates me to use srim for the study of damages in germanium. simulation methodology we use the simulation software srim and matlab for the ion implantation germanium. the core of srim is a program transport of ions in matter (trim). when an ion penetrates the target, it undergoes a series of screened coulomb collisions displacing target atoms along the way. basically, srim calculates the interactions of energetic ions with amorphous targets and presents those interactions statistically and graphically which make the implantation process easier to understand. it can also create three-dimensional plots of the ion distribution when penetrating matter, including the k. giri, k. kandel / bibechana 17 (2020) 96-103 99 trace of defects created by the ion beam and its socalled straggle and all resulting cascades which can occur when atoms are kicked out of their lattice position, becoming an interstitial atom which can subsequently hit other lattice atoms [6]. the text data of damage profiles in exponential form as calculated by trim are eventually converted to numerical values using microsoft excel and thus obtained numeric values were used in matlab to obtain schematic graphs of related values. 3. results and discussion energy calculations the energy needed to implant gallium and arsenic ions independently on germanium in order to obtain peak dopants concentration at range of 600 å were tabulated using srim. arsenic in germanium target density = 5.350 g/cm 3 = 4.4371 × 10 22 atoms/cm 3 table 2: energy calculation for arsenic ion. ion energy (kev) de/dx electrical de/dx nuclear projected range (å) 80.00 17.98 159.0 366 90.00 19.07 159.4 405 100.00 20.10 159.4 444 110.00 21.08 159.2 483 120.00 22.02 158.8 522 130.00 22.92 158.2 561 140.00 23.79 157.5 600 150.00 24.64 156.7 640 160.00 26.58 155.9 680 170.00 28.28 155.0 719 180.00 29.80 154.0 759 200.00 32.45 152.0 838 225.00 35.28 149.5 938 the table 2 demonstrates that the exact energy required for n-type arsenic dopants to obtain maximum defects at 600 å is 140 kev. therefore, we can now implant 10,000 arsenic ions accelerated by applying 140 kev energy in germanium monolayer target in order to obtain maximum defects concentration at 600 å. stopping power fig.1 demonstrates the nature of stopping power for as ions bombarded on germanium. on increasing ions energy nuclear stopping goes on increasing upto 100 kev and starts decreasing gradually, while, electronic stopping goes on gradual increase and starts dominating nuclear energy loss above 1000 kev i.e.1 mev. fig. 1: comparison of electronic energy loss and nuclear energy loss. the point of intersection of the two curves represents the corresponding ion energy where the electronic and nuclear energy losses are equal. in addition, we can conclude that there is no improvement in surface hardening and electrical conductivity of germanium upto 1 mev but implanting both ions above 1 mev increases the surface hardening and electrical conductivity because of dominance of electronic stopping power and decreasing nuclear stopping power. for 130 kev gallium ions, 24.27 ev/å and 142.60 ev/å are the value of electronic stopping and nuclear stopping respectively. these values indicate that averagely each gallium ion lose 24.27 ev/å to target electrons for every unit path of ion, whereas, to the target atoms, each gallium ion lose 142.60 ev/å for every unit path of ion. since for gallium ion accelerated at 130 kev have greater nuclear stopping so there is no improvement in surface hardness and electrical conductivity. similarly, the value of electronic stopping is 23.79 ev/å and nuclear stopping is 157.5 ev/å, for 140 kev k. giri, k. kandel / bibechana 17 (2020) 96-103 100 arsenic ions. since for arsenic ion accelerated at 140 kev have nuclear stopping, as a dominant process so desired surface hardening and electrical conductivity could not be achieved at 140 kev and similar will be for gallium ions. the reason behind dominance of nuclear stopping is mass of ions that are comparable with germanium. comparatively, ions energy should be increased to energy above 1 mev for both ions in order to obtain dominance of electronic stopping power over nuclear stopping power that eventually improve the surface hardening and electrical conductivity. energy loss during ionization the fig.2 reveals the energy imparted to the target fig.2: energy loss distribution during ionization. electrons during ionization process. the plot shows ionization from the incident ions and from recoiling target atoms. for both collisions, the energy loss to the target electrons by recoil atoms is greater than energy loss by ions. maximum ionization by ions begins from the surface of the target material and then gradually falls down. energy loss by arsenic ions and recoil atoms during ionization process is 14.126 kev 25.508 kev respectively. and the total energy loss during ionization process during arsenic-germanium interaction is 39.634 kev. energy loss to phonons when a germanium atom is knocked out of its lattice site, its binding energy, fig. 3: curve showing distribution of energy loss to phonons. elatt = 2 ev, is deposited into phonons produced by the recoils. vacancies/ion for arsenic is 4371.9, therefore for each arsenic ion, displacements by the ion or recoil cascades cause 4371.9 × 2 ev= 9463.8 ev of phonons. in fig.3, we can barely see the energy loss to phonons from the ions (red line at the bottom of the plot), and the phonons are produced almost exclusively by the recoiling target atoms. the energy loss for phonon production is high around the range of 400 å and then the gradual fall in energy loss for phonon production occurred as we increase the target depth. for arsenic, the ions generate phonon with 0.29% of their incident energy and the recoiling atoms contribute an additional 64.63 %. it means that 0.406 kev energy is lost by ions and 90.482 kev energy is lost by recoil ge atoms. total energy loss to phonons arsenic-germanium interaction is 90.888 kev. actually, phonons do not have contribution in improving electrical conductivity but do have contribution in increasing temperature of target material during implantation process. energy to recoil distribution of energy to recoil gives us the information about the amount of energy loss by ions to the recoiling atoms. overlapping of black and yellow curves demonstrates that energy losses by ions are very absorbed by target atoms, for both ions. in fig.4, we find that 160 ev/ion was absorbed by germanium at the surface of the target k. giri, k. kandel / bibechana 17 (2020) 96-103 101 atom followed by increase in energy loss to near 180 ev/ion at 500å. fig. 4: energy to recoil. ion range fig.5 is the curve of range distributions of ions building up in germanium target. the higher moments of the distribution (straggle, skewness, and kurtosis) are also given in the plot. both plots have ordinate unit: “(atoms/cm 3 ) / (atoms/cm 2 ). although these units appear strange, when we multiply by an implantation dose (ions/cm 2 ), we will end with the impurity concentration (atoms/cm 3 ) vs. depth. plot is the distribution of arsenic fig. 5: ion range distribution curve. ions (140 kev) over germanium monolayer surface. target depth is taken upto 1500 å in order to catch maximum number of ion in the plot. according to table 3, the mean ranges of implanted ions were found to be 622 å for arsenic ion. this value show little discrepancy with the value given by srim. however, 600 å was the mean ion range table 3: mean range and moments. arsenic ion range 622 å straggle 294 å skewness 0.63705 kurtosis -25.5672 value tabulated by srim and as per trim; the value was 622 å, for arsenic ion. this difference in mean ion range value was found as error. therefore, the percentage error for arsenicgermanium interaction was found to be 3.67%. these discrepancies were responsible for skewness. also, this value indicates that the peak concentrations of defects are formed at range of 622 å for 140 kev accelerated arsenic ion. < recoil distribution in fig.6, it can be seen that the concentration of recoil atoms at the surface of the target is fig. 6: germanium recoil distribution curve. 1.8 × 10 8 atoms/cm 2 for arsenic-germanium collision, followed by increase in maximum concentration of recoil atoms to 7.2 × 10 8 atoms/cm 2 at 400 å. k. giri, k. kandel / bibechana 17 (2020) 96-103 102 table 4: longitudinal, radial and lateral projection range for as ions range (å) longitudinal 622 lateral projection 201 radial 314 from the table 4, the average value of lateral projected for as ion is 201 å. the radial range is 314 å which is the mean radial displacements range from the x-axis assuming cylindrical symmetry. collision events target displacement the results for the collision events of the as ions with ge target give the total target displacements as shown in fig.7. the area under the curve gives the values for total displacements of 5116/ion arsenic. fig. 7: curve showing target displacement. target vacancies fig.8 shows the vacancy-target depth distribution curve which is the result of removal of ge atoms from their equilibrium positions because of the collision process. the general feature of the curves is also similar to those of the recoil distributions in peak positions except that their magnitudes are different. each displacement collision will lead to a displacement of a ge atom, that resides at the end as an interstitial, and creation of a vacancy (frenkel pair). fig. 8: curve showing vacancies per ion. therefore, it is expected that the number of vacancies and interstitials produced per ion are the same. the total number of vacancies amounted to 4738/ion for as ions. replacement collision the results indicate that replacement collisions of 378/ion are calculated from the collision of as ions with ge atoms. the replacement collisions amount to 7.98% for as ions. a summary of the collision events is shown in table 6. fig. 9: replacement collision curve. table 6: defects produced during ion implantation of as in ge. arsenic target displacements/ion 5116 vacancies/ion 4738 interstitials/ion 4738 replacement collisions/ion 378 k. giri, k. kandel / bibechana 17 (2020) 96-103 103 for arsenic-germanium collision, sum of vacancies/ion and replacement/ion is equal to target displacement/ion which shows a fair agreement with equation (2). i.e. 5116/ion = 4738/ion + 378/ion the results presented in the figures belonging to energy loss by ionization, recoil collisions, displacement collisions, and vacancies are similar by nature of graph but are characterized by difference in their numerical values. 4. conclusion doping of arsenic ions on germanium reveals that most of the energy loss is due to ionization and phonons production. for 140 kev arsenic ion, the energy loss for ionization, phonon production and vacancies creation are 39.634 kev (28.31% of incident energy), 90.89 kev (64.92% of incident energy) and 9.478 kev (6.77% of incident energy), respectively. almost three fold amount of energy was lost during phonon production when as ions are implanted on germanium. the collision events revealed the formation of interstitial vacancy pairs 4738, target displacements of 5116/ion and replacement collisions of 378/ion. another important finding of this work is that we cannot improve electrical conductivity and hardness of germanium by implanting 140 kev arsenic ions. to improve these properties by implanting arsenic ions we need to accelerate these ions above 1 mev of energy. references [1] a. u. mac rae, device fabrication by ion implantation, radiation effects. 1971 jan 1; 7(12):59-63. [2] j. f. gibbons, ion implantation in semiconductors—part i: range distribution theory and experiments, proceedings of the ieee, 56(3) (1968) 295-319. [3] e. a. schroeppel, m. w. kroll, inventors; oncostim, a minnesota corporation, assignee. implantable device and method for the electrical treatment of cancer, united states patent us 6,738( 2004) 663. [4] m. nastasi, j. mayer, j. k. hirvonen, ion-solid interactions: fundamentals and applications. cambridge university press; 1996. [5] j. f. ziegler, j. biersack,u. littmark, ‘‘the stopping and range of ions in matter’’, pergamon press, 1985. [6] "electronics history 4 – transistors". national academy of engineering, 2008, retrieved 200808-22. [7] j. s. kilby, invention of the integrated circuit. ieee transactions on electron devices. 23 (7) (1976) 648-54. [8] r. g. arns, the other transistor: early history of the metal-oxide semiconductor field-effect transistor, engineering science & education journal 7 (5) (1998) 233-40. [9] u. s. geological survey, "germanium—statistics and information", u.s. geological survey, mineral commodity summaries, 2008. retrieved 2008-0828. [10] d. crisp, a. pathare, r. c. well,"the performance of gallium arsenide/germanium solar cells at the martian surface", acta astronautica press, 2004. [11] p. e. schmidt and j. vedde, "high resistivity ntd production and applications", electrochemical society proceedings, 1998. [12] szweda, roy, "germanium phoenix", iii-vs review, (2005). [13] j. harold, j. r. leibowitz, a. p. ramsa , inventors. formation of junctions in semiconductors, united states patent us 2, 803 (1957) 569. [14] m. bruel, m. floccari, inventors; commissariat an l'energie atomique, assignee, process for doping semiconductors. united states patent us 4, 368 (1983) 083, 1983. microsoft word shashit final (--) s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 106 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal mixing properties of ni-al liquid alloys at different temperatures s. k. yadav1*, p. sharma2, r. p. koirala2, a. dhungana2, d. adhikari2 1department of physics, suryanarayan satyanarayan morbaita yadav multiple campus, tribhuvan university, siraha, nepal. 2department of physics, mahendra morang adarsh multiple campus, tribhuvan university, biratnagar, nepal. *e-mail: yadavshashit@yahoo.com article history: received 6 september, 2018; accepted 25 september, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21138 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the validity of simple statistical model or simple theory of mixing has been first established by explaining the experimental values of the thermodynamic and structural properties of ni-al melt at 1873 k. secondly, the linear temperature dependence of ordering energy parameter has been assumed to extend the model for predicting the mixing behaviours of the melt at different temperatures in correlation with r-k polynomials. the surface tension of the system has been explained and predicted with the help of renovated butler model. theoretical investigations correspond that alloy is found to be strongly interacting or hetero-coordinating at its melting temperature. this tendency, however, gradually decreases at higher temperatures. being more specific, the system shows ideal behaviours with respect to mixing properties at elevated temperatures. keywords: mixing behaviours, renovated butler model, hetero-coordinating, surface tension. 1. introduction alloying phenomenon has been evolved as a robust tool in the field of material science and engineering in order to develop new materials with predetermined characteristics. as a result, the alloys have numerous uses in household, industrial, medicinal, military and commercial fields. similarly, ni-al being super alloy has high thermal conductivity, high melting temperature, low density, offers good resistance to oxidation and corrosion and accessible costs. due to which they have profound utilizations in the modern day technological devices [1, 2]. the details of the uses of the alloy can be found from references 1 and 2. moreover, the thermal processing routes together with the governing parameters, such as pressure, s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 107 (online publication: dec., 2018) temperature and micro-granules determine the microstructure of an alloy. the in-depth understanding of the mixing properties of the initial melts of alloy is thus mandatory in this field. this information cannot be exclusively obtained from the experimental measurements only as being expensive, time consuming, tedious and often face difficulties with regard to the reactivity of the walls of the container at high temperatures [3]. even to perform experimental measurements, most of the governing parameters are computed by theoretical approximations. with due regards, several theoretical models [1, 3-18] so far have been developed to explain and predict the mixing properties of binary liquid alloys at a temperature or different temperatures. we, therefore, intend to study and explain thermodynamic, structural and transport properties of ni-al liquid alloy at 1873 k on the basis of simple theory of mixing (stm) in this work. the surface tension and surface segregation of the alloy have been explained using renovated butler model (rbm) [3, 14, 19]. the desirable properties and multi-disciplinary uses of ni-al alloy, as stated earlier, have drawn considerable attentions of the several researchers [1, 2, 20-27] working in the field of material science. ansara et al. (1988) compared the different thermodynamic model to compute the different phases of ni-al alloy and concluded that the results obtained from sub-lattice model are more close to experimental predictions. maret et al. (1990) have determined the bhatia-thornton and faber-ziman structure factors by neutron diffraction method for al80ni20 liquid alloy. their work further corresponds that the chemical short-range order is quite more prominent in al80ni20 than in al80[mnx(fecr)1-x]20 phase. pasturel et al. (1992) have shown that the phase diagram of the alloy computed using ab initio approximations are in agreement with experimental information. after reviewing the available phase equilibrium and thermodynamic data from different literatures for ni-al, two thermodynamic models were devised by huang and chang (1998) which have fewer and more reasonable model parameters as compared to others. they well explained the phase equilibrium and defect concentration of disordered fcc phase γ(-ni, al) are modeled by substitutional solution model and the ordered fcc γ' (-ni3al) are modeled with two-sublattice model. asta et al. (2001) studied the atomic and electronic structure and diffusion coefficients in liquid ni-al alloys by ab initio molecular dynamics simulations. moreover, adamiec (2007) determined the brittleness temperature range for the examined ni3al alloy to be 1340 0c both for the liquidus heating stage and cooling stage. the thermodynamic database for the mixing properties of the considered system at different temperatures throughout the entire concentration range, however, is lacking in the literatures. even though, grigorovitch and krylov (1998) used a new hightemperature calorimeter method to study the enthalpies of mixing of nickel-rich al-ni melts at 1823 k only in the concentration range al< 0.22. they computed the other thermodynamic properties, such as integral enthalpy of mixing and activities of al and ni at very few temperatures on the basis of quasi-ideal solution model. their results are in accordance with the findings of the present work. recently, yadav et al. (2016) have explained the thermodynamic and structural properties of ni-al liquid alloy at 1873 k using regular associated solution model and quasi-lattice model. ahmed et al. (20018) presented self-consistent results of molecular dynamics simulations for the temperature and concentration dependence of the self-diffusion and interdiffusion coefficients, thermodynamic factor, manning factor and the reduced heat of transport of the ni-al liquid alloy. but the phase determining mixing properties at different temperatures for the preferred system are unavailable in the literatures. eventually, we have extended stm by considering the linear temperature dependence of the interaction energy parameter to predict thermodynamic, structural and transport properties of the liquid alloy at s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 108 (online publication: dec., 2018) temperatures 1873 k, 1973 k, 2073 k and 2173 k, 1873 k being the melting temperature of the system. redlich-kister (r-k) polynomials [28, 29] have been associated with this approximation to determine the modeling parameters at different temperatures. the thermodynamic properties at different temperatures so computed have been correlated with rbm to predict the surface properties of the liquid alloy at above mentioned temperatures. the brief procedures to obtain the theoretical modeling equations are presented in the section 2, the results and discussion are outlined in the section 3 and the conclusions of the work are highlighted in the section 4. 2. theoretical modeling equations 2.1 thermodynamic properties simple statistical model is based upon pairwise interaction and conditional probabilities of occupation of neighbouring sites by the atoms of constituent elements which can be expressed in terms of interchange energy or interaction energy or ordering energy by applying grand partition function for binary alloys [30-32]. according to simple statistical method, the partition function for binary alloy of type a-b consisting of na and nb atoms type of a and b element under the criteria na+nb = n, where n=total number of each type atoms, is given by ξ=∑ q����t� q ���t�exp ����������� ��� � (1) where μi represents the chemical potential of ith component and qini represents atomic partition functions for ith components provided i = a or b. kb and t are boltzmann constant and absolute temperature, e is the configurational energy of alloy. the thermodynamic relation between free energy of mixing (gm) and excess free energy of mixing (g���) can be written as g� = g��� + rt ∑ x� log x�� (2) where x� is the concentration of each component. the excess free energy of mixing is also given as [30-32] !"#$� = % log σ'dx = x� log γ� + x log γ *+ (3) where σ is expressed as σ = �β + 2x� − 1� exp 0 �12���3 /2x� (4a) γ� = [�β − 1 + 2x�� x��1 + β�]⁄ 89 (4b) γ = [�β + 1 − 2x�� x �1 + β�]⁄ 89 (4c) β = 1 + 4x�x [exp�2ω zk t⁄ � − 1]> '⁄ (4d) at equiatomic concentration (x� = x = 0.5), the expression for g���/rt can be written as !"#$� = ln {2d 'e [1 + exp �−ω zk t�]⁄ �d '⁄ } (5) we have used “ω” notation for ordering energy of alloy and “z” for co-ordination number. then following equation (2), the expression for free energy of mixing can be written as g� = nk t[x�x 1��� + x� ln x� + x ln x ] (6) the standard thermodynamic for heat of mixing (h�) in terms of g� can be expressed as h� = g� − t 0i !i� 3 (7) s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 109 (online publication: dec., 2018) using equation (5) in equation (6), we get the expression for the heat of mixing as h� = nk t jx�x 1��� − >�� x�x i1i�k (8) the activity (a�) of the monomers of the binary liquid alloys in terms g� of is given as [30] nk t ln a� = g� + �1 − x�� 0m !mno 3�,q,� (9) for each of the component (a and b) the expressions for activity are ln a� = ln x� + x ' 1��� (10) ln a = ln x + x�' 1��� (11) 2.2 structural properties the atomic arrangement of constituents of the liquid alloys can be investigated by using the parameters like concentration fluctuation in the long wave length limit (scc(0)) and warren-cowley short range order parameter (α1) [17, 15, 33]. scc(0) can be related with the two thermodynamic parameters namely, free energy of mixing (g�) and activity (ai) [15] as s**�0� = k t 0m9 !mn9 3�>�,q,� (12a) = x a� 0ms�mn�3�> = x�a� 0ms�mn�3�> (12b) using the equation (5) in equation (12a) yields s**�0� = x�x j1 + d't �1 − β�k�> (13) where z represents the coordination number and we have taken it to be 10 for our work. moreover, the expression for the ideal value of s**�0� can be given as [10, 15] s**�i = x�x (14) warren-cowley short range order parameter (α1) in terms of s**�0� can be expressed as [10, 15] α> = ���>�[��d�>��>] (15) where s = s**�0�/x�x = s**�0�/s**�i �0� (16) 2.3 surface properties following kaptay (2015), according to renovated butler model, the surface tension (σ) of the binary liquid alloy of the type a-b can be given as [3, 14] σ = σ�+ v�wv� + $�v� ln xn�#n�y + ∆ #,�"# �∆ �"#v� = σ + v�wv� + $�v� ln xn�#n�y + ∆ #,�"# �∆ �"#v� (17a) where σ�+ is the surface tension of the pure ith component of the liquid mixture. λ�+ and λ� are the molar surface areas of ith component in the pure liquid and in the liquid solution respectively. ∆g�,��� and ∆g ��� are the surface partial excess free energy and bulk partial free energy of ith component; and x�� and x� surface mole fraction and bulk mole fraction of the same component respectively in the liquid mixture such that x�� + x� = 1. but the molar surface area of component in the pure liquid is equal to the molar surface area of the component in the liquid solution, i.e. λ�+ = λ� [3, 14]. the molar surface area of a pure liquid metal i is expressed as λ� = f ]v�+_'/`�n�a�>/` (17b) s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 110 (online publication: dec., 2018) where n�a = 6.022 × 10'`mol> is the avogadro's number, v�+ is the molar volume of pure metal i at its melting temperature and f is the geometrical constant which is expressed as f = 0` efg 3'/` hi/jek (17c) where fl and fm are the volume and surface packing fractions and their values depend upon the type of crystal structure of the pure components of the liquid alloys. the value of f is taken to be 1.06 for this work [3, 14, 34]. 2.4 transport properties the transport properties of liquid alloys can be interpreted by using two parameters namely, viscosity (η) and ratio of mutual to intrinsic diffusion coefficients (d�/d�i). according to simple statistical approach, viscosity (η) for liquid alloy can be expressed as [30, 31] η = η�i j1 − x�x 0 '1���3k (18) where η�i is ideal viscosity which is given by η�i = �x�η�+ + x η + �; η�+ stand for the viscosity of pure component in the liquid mixture. the mutual diffusion coefficient (d�� in terms of intrinsic diffusion coefficient (d�i) can be expressed as [35]. d� = d�i i pq soino (19a) where the terms carry their meanings as mentioned earlier. above equation can also be written as [10, 15, 29] r!ros=t�uuos �+��uu�+�v (19b) where d� = x�d + x d�; and d� and d are self-diffusion coefficients of pure component. further, the expression for d�/d�i can be expressed in term of ordering energy (ω) as d� = d�i j1 − x�x 0 '1���3k (20) 3 results and discussion 3.1 thermodynamic properties the thermodynamic model fit parameter, ω, called ordering energy for ni-al liquid alloy at 1875 k is computed using equations (2-5) in order to explain the observed excess free energy of mixing (g���) [36]. the optimized value of ordering energy so obtained is ω = −7.03 rt. the negative value of ω corresponds that the liquid system is found to be complete ordering in nature at least at its melting temperature, which is 1873 k. the compositional dependence of isotherm plots of the computed and observed g���/rt is portrayed in figure 1. it can be observed that both of these values are in excellent agreement throughout the entire concentration range (figure 1). the extremum values of g���/rt (=−2.0602, theoretical and = −2.0584, experimental [36]) at equiatomic concentration (x> = x' = 0.5) which corresponds that the system is strongly interacting and symmetric in nature at near to its melting temperature. the similar results were also obtained by yadav et al. (2016) [1]. the ordering energy is assumed to be only temperature dependent in simple theory of mixing. the temperature dependent model parameter (dω/dt) is obtained from equation (8) with the aid of above determined ω and experimental value of h� [36] by successive approximation method. the best fit value s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 111 (online publication: dec., 2018) dω/dt is found to be 47.25 for the system at 1873 k. eventually, the theoretical value of h� is computed from equation (8) using the determined values of model parameters. figure 1 displays the isotherm plots of experimental as well as theoretical values of h�/rt as a function of concentration for the system. this figure further corresponds that both of these values are in good agreement. the minimum values of h�/rt (=−3.1780, theoretical and −3.2111, experimental [36]) are found to be at x> = x' = 0.5. the theoretical findings thus communicates that the preferred system is symmetric with respect to h� and there appears strong bonding between the constituent atoms of the complex at 1873 k. activity (a) is an important thermodynamic property which is directly measured from the experiments. the strength of compound formation tendency can also be interpreted on the basis of activity. moreover, any observed deviation in the thermodynamic properties of the system can incorporated into the activity. the activities (a�� and a�p) of both the monomers (ni and al) of the liquid system are computed using equations (10 and 11) with the help of above determined model parameter. the isotherm plots of both the theoretical and experimental [36] values of a�� and a�p as a function of concentration are presented in figure 1. it can be observed that both the computed and observed values of a�� and a�p are in excellent agreement at all concentrations of ni (x�� = 0.1 − 0.9). the modeling equations and model fit parameter have not only explained g��� and h� but also have reproduced activity successfully. this establishes the validity of the simple theory of mixing. to predict the mixing behaviours of the liquid system at different temperatures, above stated thermodynamic properties of the liquid system have been computed at 1873 k, 1973 k, 2073 k and 2173 k; 1873 k being its melting temperature. as the model parameter ω depends on temperature, their values at different temperatures have been computed assuming dω/dt to be constant and using the following equations [3, 29] d[ω�t�]no = 0i1i�3 dt (21a) and, ω]tz_ = ω�t� + 0i1i�3 dt (21b) where tz (= 1973 k, 2073 k and 2173 k) are the temperatures of interests and t (=1873 k) is the melting temperature of the alloy. the ordering energies determined from equation (21) at different temperatures are presented in table 1. it can be observed that the negative values of ω gradually decreases with increase in temperature of the liquid alloy which indicates that the compound forming tendency gradually decreases at elevated temperatures. table 1: ordering energies (ω) at different temperatures temperature (k) ω �jmol�>� 1873 −109472 1973 −104747 2073 −100022 2173 −95296.9 the compositional dependence of activities of the free monomers ni (a��) and al (a�p) of the liquid alloy at different temperatures are then predicted using equations (10 and 11) with the help of ω (determined from equation (21)) and are plotted in figure 2. it can be observed that the activities of the monomers of the liquid alloy increases with increase in its temperature indicating the decrease in the compound. forming tendency at elevated temperatures. the theoretical findings of this work are in accordance with that of others [3, 29, 37-39, 40]. s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 112 (online publication: dec., 2018) fig. 1: isotherm plots of excess free energy of mixing (g���), heat of mixing (h�) and activities of ni (a��) and al (a�p) versus concentration of ni (x��) for ni-al liquid alloy at 1873 k. fig. 2: the plots of activities of ni (ln� |}~�) and al (ln� |���) versus concentration of ni (x��) at different temperatures for ni-al liquid alloy. to predict the excess free energy of mixing at the above mentioned different temperatures, r-k polynomials are fitted. on the fundamentals of r-k polynomials, excess free energy of mixing (g���) as a function of concentration and temperature is expressed as [28, 29, 40, 41] g����x, t� = x� ∑ kp�t��x> − x'�p�p�+ (22) where kp�t� = ap + bpt + cptln t + dpt' + and kp has the same temperature dependence as g���. a, b, c and d are the fitting coefficients. the partial excess free energies of each monomers of the liquid system are expressed as g����x, t� = x'' ∑ kp�t�[�1 + 2l�x> − x']�x> − x'�p�>�p�� (23a) g ���x, t� = x>' ∑ kp�t�[x> − x'�1 + 2l�]�x> − x'�p�>�p�� (23b) the optimized coefficients set of g��� for ni-al liquid alloy are tabulated in the table 2. these coefficients are obtained by the method of least square fitting. table 2: optimized coefficient set of g��� for ni-al liquid alloy l a��10�jmol�>� b��10gjmol�>k�>� c��10`jmol�>k�>� d��jmol�>k�'� 0 -80.3198 59.1000 -77.3906 18.6736 1 -1.92735 1.42178 -1.86200 0.449363 2 136.606 -100.755 131.948 -31.8373 3 59.3994 -43.8099 57.3728 -13.8431 s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 113 (online publication: dec., 2018) fig. 3: the predicted values of g��� versus concentration of ni (x��) for ni-al liquid alloy at different temperatures. fig. 4: the predicted values of h�/rt versus concentration of ni (x��) for ni-al liquid alloy at different temperatures. the excess free energy of mixing of the liquid alloy at above mentioned temperatures are then computed using equation (22) with the help of the fitting coefficients in table 1 and its compositional plots are displayed in figure 3. it can be observed that the plots of g��� gradually shallows up with the increase in the temperature of the system indicating the decrease in the values of g���. at x> = x' = 0.5, the computed values of g��� are −32.0820, −30.2981, −28.5837 and −26.9302 kjmol-1 respectively at 1873 k, 1973 k, 2073 k and 2173 k. g��� thus gradually decreases at higher temperature and is maximum at 1873 k which is the melting temperature of the system. the compound forming tendency, therefore, decreases at elevated temperatures and the system is found to be most interacting at its melting temperature. these results further strengthen the previous predictions of activity at different temperatures. the heat of mixing (h�/rt) of the system at different temperatures are computed using equations (7 and 8) with the aid of above determined values of g���. figure 4 represents the compositional dependence of h�/rt of the liquid alloy at different temperatures. like g���, the plots of h�/rt too gradually shallow up with the increase in the temperature of the system above 1873 k (figure 4) which corresponds the decrease in h�/rt. at x> = x' = 0.5, the computed values of h���/rt are −3.17830, −3.01721, −2.87166 and −2.73951 respectively at 1873 k, 1973 k, 2073 k and 2173 k. theoretical predictions thus indicate that the strength of bonding between the atoms of the complex gradually decreases at elevated temperatures. 3.2 structural properties to have greater insight of the atomic arrangements in the disordered liquid mixture, we have computed concentration fluctuation in long wavelength limit ]s**�0�_ and warren-cowley short range order parameter (alpha1= α>) in the frame work of stm at 1873 k. the ordering or compound forming s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 114 (online publication: dec., 2018) tendency and segregating or demixing tendency of the atoms of liquid mixture can also be interpreted on the basis of s**�0� and α>. at a given concentration and temperature, if s**�0� < s**�i �0� for which α> < 0, then the system shows ordering (hetero-coordinating) tendency and if s**�0� > s**�i �0� for which α> > 0, then it shows segregating (homo-coordinating) tendency. theoretical and ideal values of s**�0� are computed using equations (13 and 14) with the help of determined values of model parameters. the experimental values of s**�0� are computed using equation (12) and observed values of activity [36]. the theoretical values of α1 are computed using equations (15 and 16) with the help of determined values of essential ingredients. the isotherm plots of s**�0� and α> as a function of concentration are portrayed in figure 5. it can be observed that both the theoretical and experimental values of are less than ideal values, i.e. s**�0� < s**�i �0� and α> < 0 which correspond that the system is complete ordering in nature at its melting temperature. moreover, both the theoretical and experimental values of s**�0� are in good agreement which proves the validity of the theoretical modeling equations. it has been already mentioned that we have also computed theoretical values of s**�0� and α> at different temperatures within the constrained curtained of stm. these values are obtained using equations (13-16) with the help of above determined parameters at different temperatures. the compositional and temperature dependence of s**�0� and α> for the liquid alloy are presented in figures 6 and 7. the values of s**�0� < s**�i �0� and α> < 0 at all concentrations and temperatures indicating that the ordering tendency still prevail in the liquid system. at x> = x' = 0.5, the deviation between s**�0� and s**�i �0� are found to be 0.209010, 0.204286, 0.199324 and 0.194113 at 1873 k, 1973 k, 2073 k and 2173 k respectively which predicts the decrease in the compound forming tendency of liquid alloys at elevated temperatures. however, this tendency is the maximum at 1873 k, the melting temperature of the alloy. additionally, computed values of s**�0� gradually gets closure to the ideal values at elevated temperatures. the perusal of figure 7 communicates that the curves of α> gradually shallows up at elevated temperatures which indicates the decrease in compound forming tendency. likewise, the values of α> at equiatomic composition are found to be -0.337710, -0.308860, -0.282290 and -0.257790 at 1873 k, 1973 k, 2073 k and 2173 k respectively predicting the similar nature as above. 3.3 surface properties the surface properties (surface tension (σ) and surface segregation (x��� and x�p� ))give the information about various mechanical properties such as, the catalytic activity of alloy catalysts and wettability. the surface properties of the preferred liquid alloy at 1873 k have been studied in the frame work of renovated butler model (rbm) [8, 14, 19, 29, 34]. the theoretical values of σ, x��� and x�p� are computed using equation (17). the surface partial excess free energy (∆g�,���) required herein is computed using the expression ∆g�,��� = β�∆g ���� (24) where the values of ∆g ��� are taken from table 2 and the value of β is taken to be 0.8181 [8, 14, 19, 29, 34]. the molar surface areas of the monomers of the liquid alloy (λ�) are computed using equations (17b and 17c) by substituting f = 1.06 [3, 19]. the surface tensions of the pure components (σ�+) at the melting temperature (t=1873 k) of the liquid alloy are using the values from table 3 and the following expression [42] s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 115 (online publication: dec., 2018) σ�+ = σ+ + �t − t+� i�i� (25) fig. 5: the isotherm plots of computed values of s**�0� and α> versus concentration of ni (x��) for ni-al liquid alloy at 1873 k. fig. 6: the computed values of s**�0� versus concentration of ni (x��) for ni-al liquid alloy at different temperatures. where σ+ is the surface tension of the pure component at its melting temperature, t+ is its melting temperature in absolute scale and dσ/dt is the temperature derivative of the surface tension. the molar volumes of the pure components (v�+) are determined from the ratio of their atomic masses to respective densities (m/ρ). the density of each component of the liquid mixture at t=1873 k is computed using the parameters from table 3 and the expression [42] ρ = ρ+ + �t − t+� i�i� (26) where ρ+ is the density of the pure component at its melting temperature (t+) and dρ/dt is the temperature derivative of the density. table 3: input parameters for surface tension (σ) and viscosity (η� [42] density surface tension viscosity metal t+ ρ+ dρ/dt σ+ dσ/dt η+ e (k) (kg m-3) (kg m-3k-1) (mnm-1) (mnm-1k-1) (mnsm-2) (kjmol-1) ni 1727 7905 −1.160 1778 −0.38 0.1663 50.2 al 933 2385 −0.280 914 −0.35 0.1492 16.5 s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 116 (online publication: dec., 2018) fig. 7: the computed values of α> versus concentration of ni (x��) for ni-al liquid alloy at different temperatures fig. 8: the computed values of σ versus concentration of ni (x��) for ni-al liquid alloy at 1873 k. the isotherm graphical representations of surface tension (σ) and surface concentrations (x��� and x�p� ) as a function of concentration for the system at 1873 k are portrayed in figures 8 and 9 respectively. the surface tension of the system is found to be less than ideal value throughout the entire concentrations (figure 8). the perusal of figure 9 corresponds that the surface concentration of al is greater than its ideal value and that of ni is less than that of its ideal value indicating that al atoms segregate on the surface region whereas ni atoms remain in the bulk phase of the liquid mixture at 1873 k. fig. 9: the compositional dependence of isotherm plots of x��� and x�p� for ni-al liquid alloy at 1873 k. fig. 10: the compositional dependence of computed values of σ for ni-al liquid alloy at different temperatures. s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 117 (online publication: dec., 2018) the theoretical values of σ, x��� and x�p� for the preferred liquid alloys at above mentioned different temperatures are computed using equations (17, 24-26) with the help of ingredients from tables 2 and 3. the compositional and temperature dependence of σ, x��� and x�p� are plotted in figures 10, 11 and 12 respectively. figure 10 predicts that σ of the system gradually decreases with increase in its temperature which further strengthen the earlier findings of thermodynamic and structural properties. it can be observed that the predicted values of x��� gradually increases (figure 11) whereas that of x�p� gradually decreases with increase in the temperature of the system. more precisely, ni atoms gradually move from the bulk phase to the surface whereas al atoms gradually move from surface phase to the bulk in order to maintain equilibrium. moreover, the predicted values of x��� and x�p� gradually approaches their ideal values at elevated temperatures; and are accordance with findings of others [3, 29, 37-39, 40]. fig. 11: the compositional dependence of computed values of x��� for ni-al liquid alloy at different temperatures. fig. 12: the compositional dependence of computed values of x�p� for ni-al liquid alloy at different temperatures3.4transport properties in transport properties, we have computed viscosity (η) and ratio of mutual to intrinsic diffusion coefficients (d�/d�i) for the preferred system at 1873 k and also at above mentioned different temperatures on the floor of stm. theoretical values of η for the system at 1873 k and different temperatures are computed using equations (18) with the help of essential parameters from tables 1 and 3. the plots of η as a function of concentration and temperature are portrayed in figures 13 and 14. the perusal of figure 13 indicates that the viscosity of the liquid alloy at its melting temperature (1873 k) is less than its ideal value at all concentrations. it increases rapidly with increase in the concentration of ni till about x�� = 0.75 and then decreases. the viscosity of the system decreases gradually with increase s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 118 (online publication: dec., 2018) in its temperature as one expects. as viscosity depends upon h� of the liquid alloy, similar trends are followed by their plots at elevated temperatures. fig. 13: the compositional dependence of isotherm plot of viscosity (η) for ni-al liquid alloy at 1873 k. fig. 14: the compositional dependence of predicted values of η for ni-al liquid alloy at different temperatures. theoretical values of d�/d�i at 1873 k and also at higher temperatures are obtained using equation (20) and the values of parameters from table 1. the graphical representations of values so computed are displayed in figures 15 and 16. fig. 15: the computed values of d�/d�i versus concentration of ni (x��) for ni-al liquid alloy at 1873 k. fig. 16: the computed values of d�/d�i versus concentration of ni (x��) for ni-al liquid alloy at different temperatures. s.k. yadav et al../ bibechana 16 (2019) 106-121 rcost p. 119 (online publication: dec., 2018) the study of d�/d�i helps to understand the compound forming or ordering tendency of the liquid alloy. at given temperature and concentration, if r!ros > 1, then the liquid alloy shows ordering nature and if r!ros < 1, then it shows segregating nature. the perusal of figure 15 notifies that r!ros > 1 throughout the entire concentrations at the melting temperature of the system indicating that there is strong tendency towards compound formation at this temperature. however, it can be observed that the predicted values of d�/d�i gradually decreases with increase in the temperature of the system which corresponds that the compound forming tendency gradually declines at elevated temperatures. 4. conclusions the mixing behaviours of the preferred liquid alloy have been successfully explained and predicted at its melting and higher temperatures on the basis of theoretical modeling equations. theoretical investigations forecast that the system shows strong tendency towards compound formation at least at its melting 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[41] e.a. brandes, g.b. brook, smithells metals reference brook, jordanhill, oxford:butter warth-heinemann (1992). i table of contents research articles • insight of precursor concentration, particle size and band gap of zirconia nanoparticles synthesized by co-precipitation method arun bhujel, bibek sapkota, ram lochan aryal, bhoj raj poudel, sitaram bhattarai, surendra k. gautam 1-9 • fabrication of open type carbonizer for the preparation of activated carbon from rice husk a rajbhandari (nyachhyon), a kumari dhami 10-18 • surface modification of polyamide by 50 hz dielectric barrier discharge (dbd) produced in air at atmospheric pressure rajesh prakash guragain, hom bahadur baniya, santosh dhungana, bishnu prasad pandey, ujjwal man joshi, deepak prasad subedi 19-25 • spatial orientations of angular momentum vectors of galaxies in supercluster s [173+014+0082]astrophysics janak ratna malla, walter saurer, b aryal 26-32 • phonon dynamics of zr67ni33 and fe80b20 binary glassy alloysphonon dynamics aditya m vora, alkesh l gandhi 33-47 • simulated spectra (ir and raman), nlo, aim and molecular docking of carisoprodol from dft approachphysics manoj kumar chaudhary, tarun chaudhary, bhawani datt joshi 48-57 • effect of electron temperature in a magnetized plasma sheath using kinetic trajectory simulation r chalise, s k pandit, g thakur, r khanal 58-66 • molecular dynamics study of structural properties of γ-aminobutyric acid (gaba) shyam p khanal, rajendra p koirala, esha mishra, narayan prasad adhikari 67-74 • modeling and parameter analysis of deflection of a beam puskar raj pokhrel, bhabani lamsal 75-82 • facile methods of preparing pure hydroxyapatite nanoparticles in ordinary laboratories gokarna pandey, kedar nath dhakal, ajaya kumar singh, suresh kumar dhungel, rameshwar adhikari 96-103 • study of tunneling and oscillation in a gaas/〖al〗_(0.3) 〖ga〗_(0.7) as superlattice: using transfer matrix method s shrestha, n bhusal, s. byahut, c. k. sarkar 104-112 https://www.nepjol.info/index.php/bibechana/article/view/28958 https://www.nepjol.info/index.php/bibechana/article/view/28958 https://www.nepjol.info/index.php/bibechana/article/view/28918 https://www.nepjol.info/index.php/bibechana/article/view/27650 https://www.nepjol.info/index.php/bibechana/article/view/27650 https://www.nepjol.info/index.php/bibechana/article/view/29165 https://www.nepjol.info/index.php/bibechana/article/view/29165 https://www.nepjol.info/index.php/bibechana/article/view/28760 https://www.nepjol.info/index.php/bibechana/article/view/29036 https://www.nepjol.info/index.php/bibechana/article/view/29036 https://www.nepjol.info/index.php/bibechana/article/view/29204 https://www.nepjol.info/index.php/bibechana/article/view/29204 https://www.nepjol.info/index.php/bibechana/article/view/29442 https://www.nepjol.info/index.php/bibechana/article/view/29359 https://www.nepjol.info/index.php/bibechana/article/view/29600 https://www.nepjol.info/index.php/bibechana/article/view/27450 https://www.nepjol.info/index.php/bibechana/article/view/27450 ii • a spectroscopic study of the low redshift dwarf galaxy sdss j134326.99+431118.7 to calculate star formation rate daya nidhi chhatkuli, sanjaya paudel, binil aryal 113-120 • diffusion of oxytocin in water: a molecular dynamics study khimananda acharya, rajendra prasad koirala, nurapati pantha 121-130 • analysis of aerosol optical depth and angstrom exponents over an aeronet site at pokhara, nepal jeevan regmi, khem n poudyal, amod pokhrel, madhu gyawali, anthony barinelli, rudra aryal 131-140 • structural analysis of cu substituted ni\zn in ni-zn ferrite deependra parajuli, k samatha 141-146 • modulation frequency and velocity variation of ions in a magnetized plasma sheath for different obliqueness of the field bhesha raj adhikari, hari prasad lamichhane, raju khanal 147-152 • thermal properties of normal and sickled hemoglobin protein jhulan powrel, narayan p adhikari 153-161 • investigation on thermo-physical properties of liquid in-tl alloy i b bhandari, n panthi, i koirala 179-187 • prediction of daily global solar radiation using different empirical models on the basis of meteorological parameters at trans himalaya region, nepal usha joshi, i b karki, n p chapagain, k n poudyal 188-198 • study of aerosol optical properties at different tourist places of nepal rejeena jha, binod adhikari, dharmendra singh 199-212 • thermodynamic, structural, surface and transport properties of au-ni liquid alloy at 1150 k s k yadav, n chaudhary, d adhikari 236-244 • empirical model for estimation of global solar radiation at lowland region biratnagar using satellite data ganesh kumar shrestha, binod pandey, usha joshi, khem n. poudyal 245-252 review articles • an overview on the non-destructive in-depth surface analysis of corrosion-resistant films: a case study of w-xcr deposits in 12 m hcl solution jagadish bhattarai 83-95 • schiff base metal complex as a potential therapeutic drug in medical science: a critical review narendra kumar chaudhary, biswash guragain, siyanand kumar chaudhary, parashuram mishra 162-178 https://www.nepjol.info/index.php/bibechana/article/view/29466 https://www.nepjol.info/index.php/bibechana/article/view/29466 https://www.nepjol.info/index.php/bibechana/article/view/29316 https://www.nepjol.info/index.php/bibechana/article/view/29448 https://www.nepjol.info/index.php/bibechana/article/view/29448 https://www.nepjol.info/index.php/bibechana/article/view/29475 https://www.nepjol.info/index.php/bibechana/article/view/29171 https://www.nepjol.info/index.php/bibechana/article/view/29171 https://www.nepjol.info/index.php/bibechana/article/view/29750 https://www.nepjol.info/index.php/bibechana/article/view/29531 https://www.nepjol.info/index.php/bibechana/article/view/29203 https://www.nepjol.info/index.php/bibechana/article/view/29203 https://www.nepjol.info/index.php/bibechana/article/view/29906 https://www.nepjol.info/index.php/bibechana/article/view/30546 https://www.nepjol.info/index.php/bibechana/article/view/29689 https://www.nepjol.info/index.php/bibechana/article/view/29689 https://www.nepjol.info/index.php/bibechana/article/view/29222 https://www.nepjol.info/index.php/bibechana/article/view/29222 https://www.nepjol.info/index.php/bibechana/article/view/29841 iii • pyrolyzed human hair: a review on synthesis, characterization and applications tika ram bhandari, bidit lamsal, rameshwar adhikari 213-221 • degradation of fundamental polymers/plastics used in daily life: a review netra lal bhandari, ganesh bhandari, sunita bista, basant pokhrel, kabita bist, kedar nath dhakal 222-235 https://www.nepjol.info/index.php/bibechana/article/view/29601 https://www.nepjol.info/index.php/bibechana/article/view/29619 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal bibechana 19 (1-2) (2022) 119-126 development of construction materials from the geopolymerization of red clay and coal fly ash arvind pathak*, arpana ranjit and bijaya dhakal department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu-44600, nepal *email: apathak2070@gmail.com article information: received: november 29, 2021 accepted: december 4, 2021 keywords: alkaline activator, compressive strength, construction material, geopolymer abstract red clay contains solid aluminosilicate has been shown to be reactive in the presence of an alkaline activator. the addition of coal fly ash and lime has shown improvements in their mechanical and physical properties of the geopolymer products. ftir analysis and sem images of the product have shown the formation of aluminosilicate gel in the geopolymeric product. the maximum compressive strength of the geopolymer products gp-rfl was achieved to be 15.92 n/mm2 having water absorption of 10.47 % and bulk density 2.81 g/cm3. these results indicated that geopolymer mortars made from red clay, coal fly ash and lime could be used as an alternative construction material. doi: https://doi.org/10.3126/bibechana.v19i1-2.46403 this work is licensed under the creative commons ccby-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction red clay is found in banepa, beltar, chidika, gaighat, gultar, guttu, lamasure, manna buddhuk, panchkhal, salghari and sunkada areas of nepal. red clay is widely used in house painting in the rural areas of nepal. the presence of high alumina and iron content in red clay has been proved suitable as an additive material to produce cement. 10300.1 m3 of red clay in the fiscal year 2015/16 have been utilized in the cement industries [1]. in the construction industry, portland cement is the leading material for concrete. the cement industry contributes about 8 % of the global co2 gas emissions and it also produces about 5 % of greenhouse gas emissions [2]. this causes several environmental issues due to the high carbon foot print during cement production. due to environmental concerns, readily available commercial byproducts as a source of aluminosilicate such as fly ash, blast furnace slag and red mud have been used rather than 119 http://nepjol.info/index.php/bibechana mailto:apathak2070@gmail.com https://doi.org/10.3126/bibechana.v19i1-2.46403 https://creativecommons.org/licenses/by-nc/4.0/ pathak et al. / bibechana 19 (1-2) (2022) 119-126 120 naturally available materials such as metakaolin, red soil to meet these demands. geopolymer concrete is one of the building materials that have become popular since it is environmentally friendly [3, 4]. the formation of geopolymer at low temperature generally below than 100 ºc, consists of chains of mineral molecules joined with covalently with a three dimensional polymeric chain consisting of si-o-al-o bonds [5, 6]. the high strength development is considered due to the presence of chemical charge-balancing species located in the tetrahedral sites, i.e. the part of the structural network. mössbauer spectroscopy demonstrates that fe3+ is included in the geopolymer structure, i.e., fe3+ is the equivalent of al3+ in the alumino-silicate network, yielding a ferro-silico-aluminate sequence (-fe-o-si-o-al-o-), i.e, ferro sialate[7]. the tetrahedrons of silicon and aluminum are connected by oxygen bridges to form the high connectivity chain or ring network structures. such high-connectivity molecular structures of the products perform excellent in terms of strength and durability [8]. geopolymers are characterized by higher durability and greenness relative to conventional opc. these products have distinct cementitious and ceramic like formulation with good mechanical strength and chemical properties and have gained much attentions recently as a promising partial substitute to opc [6, 9, 10]. light weight geopolymer concretes are found as good insulators and fire-resistant and therefore applicable for high-rise buildings and in the areas of high earthquake risk [11]. global warming concerns will inevitably lead to the decrease of coal burning for the production of electricity and consequently to the exhaustion of this ultimate waste, which have been utilizing largely for the production of geopolymer and ppc cement [12]. the recent discovery of ancient red geopolymer sandstone monuments in south america (tiwanaku/ pumapunku, bolivia) have shown the extraordinary long-term durability of this [fe-o-si-o-al-o-] geopolymer molecule withstood at least 1400 years of archaeological burial. these artificial red sandstone megaliths contains in the form of ferro-sialate matrix [13]. the aim of this study was to optimize the condition of geopolymerisation behavior of red clay and coal fly ash in the presence of lime. 2. material and methods materials the red clay (rc) was collected from banepa and coal fly ash (cfa) was collected from brick factory of satungal, kathmandu. it was then grounded into a powder and dried at 120 ºc for 2 hours to remove the moisture content. calcium oxide was prepared by heating calcium hydroxide at 580 ºc for 2 hours. the powder form of sample was weight and mixing was done in different proportion. activator solution laboratory grade of naoh (97 %), liquid sodium silicate (na2o: 8.6 %, sio2: 28.0 % and h2o: 63.4 % lobe chemme, india) were used. 4 m naoh was prepared 24 h before mixing with liquid sodium silicate to prepare 1:1 activator solution. the use of 4 m naoh solution was found to develop higher compressive strength [14]. synthesis of geopolymer the red clay and coal fly ash (0 20 %) were dry mixed in different composition and then mixed with activator solution to prepare the geopolymer product. after the selection of cfa %, the amount of cao was varied to prepare the geopolymer product. finally two geopolymer products gp-rf (90 % red clay, 10 % coal fly ash and activator solution) and pathak et al. / bibechana 19 (1-2) (2022) 119-126 121 gp-rfl (mixture of 90 % red clay and 10 % coal fly ash was mixed with of 2 % of lime and activator solution) were considered for study. thus prepared clay paste was then casted in a wooden mould (2.5 cm × 2.5 cm × 2.5 cm) and cured at 60 ºc in oven for 2 hours followed by curing at room temperature for 7 – 28 days, schematically represented as: fig. 1. schematic diagram of geopolymer synthesis. curing at temperature at 60 ºc was found dominant compared to higher temperature and requires less energy consumption [15, 16]. characterization of the raw materials and geopolymer products chemical composition of the raw materials was obtained by using edx spectrophotometer (edx-8000, shimadzu) available at department of custom, tripureshwor, kathmandu. phase analysis of the powdered raw materials and the geopolymer products were carried out by x-ray diffractometer (d2 phaser diffractometer, bruker, germany) using cukα radiation available at nepal academy of science and technology (nast), khumaltar, lalitpur. fourier transform infrared spectrophotometer (ir tracer 100, shimadzu, japan) was used for structural characterization mechanical and physical properties compressive strength values were taken as the average of three consecutive measurements of geopolymer products and were measured using slf 9 load frame machine at central material testing laboratory, institute of engineering pulchowk campus, tribhuvan university. physical properties: apparent specific gravity, and bulk density, porosity and water absorption were measured as per astm c373 [17]. 3. results and discussion chemical composition of raw materials the chemical compositions of the raw materials red clay (rc) and coal fly ash (cfa) were analyzed and are shown in the following table 1: table 1. chemical composition (mass %) of the raw materials oxides (%) rc cfa sio2 42.39 39.14 fe2o3 28.72 24.95 al2o3 17.85 1.27 k2o 7.34 0.80 cao 0.94 tio2 1.11 so3 28.54 others 3.69 3.25 of geopolymers. ftir spectra were obtained in the frequency range of 4000 to 400 cm-1 by mixing the samples with kbr, available at the central department of chemistry, tibhuvan university, kirtipur. morphological characterization of the fractured samples was carried out by sem (s4800 10.0kv 7.9 mm × 2.5k sem, lao) at nims, japan. characterization of raw materials and the geopolymer products xray diffraction patterns pathak et al. / bibechana 19 (1-2) (2022) 119-126 122 x-ray diffraction patterns of red clay, coal fly ash and its geopolymer product are shown in the following figure 2: fig. 2. xrd pattern of raw materials and the geopolymeric product major peaks of the sample at 2θ values equal to 20.06, 26.85, 34.16, 36.72, 42.64, 45.63, 50.36 and 60.12 º mainly represents quartz (silica). these entire peaks are present in the both raw materials and its geopolymer products. ftir analysis ftir spectra of the raw materials red clay, coal fly ash and its geopolymer product gp-rfl are shown in the figure 3. the main absorption bands in rc and cfa were observed at 2361.5, 1025.9, 1001.2, 908.9, 793.7, 747.7, 524.4 and 1047.4, 592.9 cm-1 whereas the spectra for gp-rfl: 1001.2, 910.7, 529.5 cm-1 wavenumbers. absorption band at 2361 cm-1 could be attributed to bending vibration of h-o-h group associated with weakly bond water molecules [18]. the bands in the range of 950 to 1100 cm−1 assigned to the asymmetric stretching vibrations of si–o–si and/or si–o–al. the absorption bands at 910.7 cm-1 is due to al (oh) vibrations [19]. fig. 3. ftir spectra of red clay, coal fly ash and its geopolymeric product gp-rfl. the spectra in the frequencies between 800 cm 1 and 480 cm-1 correspond to the symmetry of the si-o-si stretching vibration [20]. in the geoplymeric product the entire main characteristics band gets broadened shows the substitution of si with al forming the geopolymeric network. sem analysis the scanning electron micrograph of the fractured surface of geopolymerization product gp-rfl is shown in the following figure 4: fig. 4. sem image of gp-rfl (g-gel, p porous site, a-aggregate) representing gel formation. the solid aluminosilicate material present in the powdered mixture are converted into a porous, hydrate gel and are bound through networking channel supported by the high pathak et al. / bibechana 19 (1-2) (2022) 119-126 123 compressive strength value of the geopolymerization product (gp-rfl). variation of the amount of rc and cfa the geopolymer products were prepared from the mixture of rc and cfa (5 – 20%) and mixing with the activator solution. the products were then cured at 60 °c for 2 hours followed by curing at room temperature for 7 days. the compressive strength values of the geopolymer products were found to be 0.60, 1.13, 1.75, 0.65 and 0.64 n/mm2 for 0, 5, 10, 15 and 20 % of cfa respectively and are shown in the following figure 5: 2.0 1.5 1.0 0.5 0.0 0 5 10 15 20 fly ash, % fig. 5. compressive strength of the geopolymer products with the variation of fly ash the compressive strength value increased with increasing with increase in amount of coal fly ash up to 10 %. the increase in compressive strength value may be due to the pozzolanic pozzo1anic activity of coal fly ash [21]. as the increases of % of coal fly ash some cracks was observed in the geopolymeric sample, thus compressive strength was decreased. variation of the amount of cao 90 % red clay and 10 % coal fly ash was mixed and then the amounts of cao were varied. at first these were dry mixed and then mixed with the activator solution. the geopolymer products were then cured at 60 °c for 2 hours followed by curing at room temperature for 7 days. the compressive strength of geopolymer products were found to be 5.78, 7.73, 5.66, and 4.64 n/mm2 for 1, 2, 3 and 4 % of cao respectively and are shown in the following figure 6: 10 8 6 4 2 0 0 1 2 3 4 5 cao, % fig. 6: compressive strength of the geopolymer product with cao % the compressive strength value of the geopolymer product was found maximum at 2 % of addition of cao. in ceramics, mechanical strength usually increases with decreases in porosity. similar trend of increase in strength was also observed in case of metakaolin based geoploymer on the addition of small amount of ca(oh)2 [22]. effect of curing time the geopolymer products gp-rf and gp-rfl were then cured at 60 °c for 2 hours followed by curing at room temperature up to 28 days. the compressive strength values of the geopolymer products were measured and are shown in the figure 7. the compressive strength value of the geopolymer products were found increasing with curing time. c o m p r e s s iv e s tr e n g th , n /m m 2 c o m p r e ss iv e s tr e n g th , n /m m 2 pathak et al. / bibechana 19 (1-2) (2022) 119-126 124 20 16 12 8 4 0 0 7 14 21 28 curing time, d fig. 7. compressive strength of the geopolymer products with curing time the curing for longer period of time at low temperature is preferable for the synthesis of geopolymer as the condensation and evaporation of water molecules takes place simultaneously preventing the formation of voids and cracks inside the materials thus increasing the compressive strength. the adequate curing time accelerates the extent of chemical reaction [23, 24]. physical properties of the geopolymer products the lower the value of water absorption indicates good quality and has higher resistance to water infiltration and to environmental damage. the water absorption value less than the 17 % are applicable in masonry units. the physical properties of the geopolymeric product measured at 28 days as per astm c373 standards are mentioned in the following table 2: table 2. physical properties of the geopolymer products measured at 28 days. apparent specific gravity, bulk density, porosity and water absorption and compressive strength value indicates these masonary unit can be used as an alternative construction material. conclusions the geopolymerisation behavior of red clay and fly ash was studied. the compressive strength values of the geopolymer gp-rf using rc (90%) and cfa (10%) using 1:1 solution of 4m naoh and liquid sodium silicate was found to be 8.80 n/mm2 at 28 days of curing. use of 2 % lime as additives enhanced the compressive strength of 15.92 n/mm2 at 28 days of curing. microstructural study of the geopolymeric product has shown the formation of aluminosilicate gel. the mechanical and physical properties of the geopolymer product were studies. these results indicated that geopolymer mortars made from red clay, coal fly ash and lime are suitable for construction activities and can be used as an alternative construction material. acknowledgments the authors are thankful to university grants commission (ugc), bhaktapur, nepal, for providing small rdi grant (srdig-74 75/s&t-05). we are grateful to the central material testing laboratory, pulchowk, lalitpur for compressive strength measurement, department of customs, ministry of finance, tripureshor, kathmandu for providing edx of the samples, nepal academy of science and technology (nast) for xrd measurements of the samples, central gp-rf gp-rfl c o m p r e ss iv e s tr e n g th , n /m m 2 physical properties gp-rfl absorption of water (%) 10.47 porosity (%) 27.56 apparent specific gravity 3.63 bulk density (g/cm3) 2.81 compressive strength (n/mm2) 15.92 pathak et al. / bibechana 19 (1-2) (2022) 119-126 125 department of chemistry, tribhuvan university, kirtipur for ftir spectra of the samples, dr. lok kumar shrestha, scientist, mana, nims, japan for providing sem image of the sample. references [1] ministry of industry, department of mines and geology, kathmandu. mineral resources of nepal. 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[24] j. davidovits, geopolymers: man-made rock geosynthesis and the resulting development of very early high strength, j. mater. educ. 16(2) (1994) 91-137. http://dx.doi.org/10.1590/1980-5373 1. introduction 2. material and methods 3. results and discussion conclusions acknowledgments references devendra sir cover page copy.jpg bibechana 17 (2020) 75-79 75 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal effective action approach to the leggett's mode in two-gap superconductors bal ram ghimire 1* , shanker p chimouriya 2 , basant gyawali 2 1 central department of physics, tribhuvan university, kirtipur, nepal 2 department of natural sciences (physics), katmandu university, kavre, nepal email: balramghimire@gmail.com article information: received: july 01, 2019 accepted: november 30, 2019 keywords: superconductor bcs theory collective excitation effective action leggett’s mode abstract when electrons of two electronic bands participate in superconducting phenomena, it is said to be two gap superconductor. there are two set of cooper pairs in different energy gap with different energy. the observation of leggett’s mode in two band superconductor provides an additional information about superconductor. by using the effective action, the thermodynamic potential in the case of neutral and charged two gap superconductor are calculated. using phase dependent action, we investigate a collective excitation (leggett’s mode) corresponding to small fluctuations of the relative phase of two condensates in two band superconductor. we consider the possibility of observing leggett’s mode in mgb2 superconductor and conclude that for the known values of two band model parameters for mgb2, leggett’s mode rises above the two particle threshold. 1. introduction superconductivity was first discovered by dutch physicist h .kamerlingh onnes , three years after he liquefied helium. he found that the resistance of mercury dropped to almost zero when the sample was sufficiently cooled to low temperature. cooper pairs are responsible for the phenomenon of superconductivity. the electrons with opposite momentum and spin undergo bose-einstein condensation to form cooper pair. exchange of phonon between electrons seems to have an attraction between electrons thus forming cooper pairs [1]. in the presence of weak uniform magnetic field, number of cooper pairs and their internal structure is unaltered. it leads to the vanishing of magnetic field in the interior of bulk superconductor. a superconductor in an external magnetic field carries an electric current near its surface. this current is of magnitude such that it cancels the external magnetic field. thus there is no field inside superconductor [2]. this is called meissner effect. if the electrons of single electronic band are participating for superconducting state, material is said to be one gap superconductor. energy required to break cooper pairs is same if all the pairs are this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.26503 http://nepjol.info/index.php/bibechana mailto:balramghimire@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.26503 bal ram ghimire et al / bibechana 17 (2020) 75-79 76 formed with same energy and hence shows only one gap. if the electrons of two electronic bands are participating for the superconducting state, material is said to be two gap superconductor. there are two set of cooper pairs in different energy bands and energy required to break the pairs is also different. interestingly cooper pairs of both bands are created at same critical temperature. the josephson effect occurs if two superconductors are separated by a thin insulator. the tunneling of cooper pairs through the insulator was first introduced by josephson [3, 4, 5]. the study of multiband superconductors started from the works of moskalenko, suhl, peretti and kando, as a generalization of bardeen-cooperschrieffer (bcs) theory to a multi gap superconductors. in the case of multi gap superconductors, coulomb repulsive interaction turns the one plasma mode into a gapped plasma mode. these modes are massive due to josephson interactions. there is a possibility that some of these modes become massless nambu-goldstone modes when the josephson couplings are frustrated. the josephson couplings between different bands will bring about attractive phenomena: they are time reversal symmetry breaking and existence of gapless modes. the phase difference mode between two gaps is called leggett’s mode [6].this mode yields new excitation modes in multi-gap superconductors. the leggett’s mode is realized as a josephson plasma oscillation in layered superconductors. the fluctuation of the inter band phase difference in the multi-gap superconductor is leggett‘s mode. this fluctuation can elevate the superconducting transition temperature. according to conventional superconducting microscopic bcs theory, the leggett’s mode is not implemented and their entropy is not taken into account. the formation of pair means the loosing of entropy. the competition between the gain of the energy due to gap evolution and the cost due to missing entropy determines if bcs gap opens or not. if the pair still has entropy after the formation, the cost due to missing entropy is reduced. this reduction assists the evolution of gap. the entropy, which leggett’s mode has corresponds to entropy of the pair [7]. 2. theory microscopic bcs theory for development of hamiltonian of the system we consider two electron system in fermi sea which aren’t interacting with each other. the electrons have equal and opposite spin so that the lowest energy state have total momentum zero [4]. the hamiltonian gives the total energy of the system. hamiltonian can be expressed as ĥ = ∑ t(xk) + 1 2 n k=1 ∑ v(xk, xl) n k=l=1 where t is kinetic energy and v is potential energy of interaction between particles , xk describes the coordinate of kth particle. similarly, xl denotes the co-ordinate of lth particle. in case of two gap superconductor, hamiltonian is , ĥ = ∑ĥtb,l + ĥt l where, ĥtb,l is hamiltonian for two band superconductor in ith layer and hamiltonian ĥt describes the electron tunneling between two adjacent s layers through the insulator. this can be expressed as, ĥt = ∑(tijcσ,1 i† cσ,2 j + h. c. ) i,j,σ where, tij is the tunneling matrix element for an electron from i to j band. also, cσ,l i† and cσ,l i denote the operator which create and destroy an electron with spin σ in the i-band. in the absence of magnetic field, ĥtb,l = ∑ eicσ,l i† cσ,l i + ĥl pair i=s,d where, ei is the energy of electron in i-band (i = s or d band) about fermi energy. hl pair is hamiltonian for interaction between electrons. according to leggett, bcs wave function in terms of pairing operator can be expressed as, bal ram ghimire et al / bibechana 17 (2020) 75-79 77 ψl i = c↑,l i†c↓,l i† by using this concept, pairing hamiltonian can be written as ĥl pair = −vssc↑,l s†c↓,l s†c↓,l s c↑,l s − vddc↑,l d†c↓,l d†c↓,l d c↑,l d − vsd(c↑,l s†c↓,l s†c↓,l d c↑,l d + h. c. ) here, vij is the strength of pairing interaction potential. interband pairing interaction between two electrons in s and d band is described by the hamiltonian hinter,l pair which is the last term of the above relation. this can be expressed as, ĥinter,l pair = −vsd ∑ck↑,l i† c−k↓,l i† c −k′↓,l j c k′↑,l j k,k′ here, i and j can take same value. by using this leggett concept, total hamiltonian for our system [5, 9] will be ĥ = ∑ek sck,σ † k,σ ck,σ + ∑ek dck,σ † k,σ ck,σ − ∑vk,k′ ss ck↑ † c−k↓ † c−k′↓ck′↑ k,k′ − ∑vk,k′ dd dk↑ † d−k↓ † d−k′↓dk′↑ k,k′ − ∑vk,k′ sd (ck↑ † c−k↓ † d−k′↓dk′↑ k,k′ + dk↑ † d−k↓ † d−k′↓dk′↑ ) collective excitation bogolyubov and anderson discovered that density oscillation can couple for oscillation of the phase of superconducting order parameter through pairing action. in neutral system, these collective sound like oscillation are known as bogolyubov anderson goldstone (bag mode). in charged system, the frequency of the mode is pushed into plasma frequency due to coulomb interaction [8]. a main idea beyond this approach is rather simple since the collective modes present low energy degree of freedom. physically, leggett’s mode is a collective excitation corresponding to a small fluctuation of the relative phase of two band superconductor. leggett’s mode is obtained using the modulus of phase variables in the path integral formalism. the action integral is given by, s = ∫ dτ[ ∑ ck,σ i ∂tck,σ i +i,σ,k β 0 ĥ(c)] the effective action can be written as, s = spair + scoulomb using hubbard stratonovich transformation and nambu notation, the effective action becomes, s = ∫ {∑[ ϕ k⃗⃗ s†ϕ k′⃗⃗⃗⃗ s gss + ϕ k⃗⃗ d†ϕ k′⃗⃗⃗⃗ d gdd k⃗⃗ k′⃗⃗⃗⃗ β 0 − gsd gssgdd (ϕ k⃗⃗ s†ϕ k′⃗⃗⃗⃗ s ) ] − trlngs −1 − trlngd −1} now, the thermodynamic potential can be written as, ω = 1 β ∫ dτ [ |δks|2 gss + |δkd|2 gdd β 0 − 2 gsd gssgdd |δks||δkd|cos (θs − θd)] − 1 β (trlngs −1 − trlngd −1) here, ω can be written as the sum of ωkin and ωpot as, ω(δi, θi,ϕ) = ωkin(δi, θi, ϕ) + ωpot(δi, θi, ϕ) where, ωkin is the sum of energies of phase fluctuations in each band and ωkin is responsible for the appearance of leggett’s mode term in the josephson coupling energy of the condensates in two bands. this term explicitly depends on relative phase ( θ1 − θ2 ) of two condensates. if we minimize ω with respect to θs − θd, we get dω d(θs − θd) = 1 β ∫ dτ β 0 ∑ 2gsd gssgdd |δks||δkd| sin(θs − θd) = 0 from this we obtain, bal ram ghimire et al / bibechana 17 (2020) 75-79 78 δs − gsd gdd δd − gssδ sn1f(δ1) = 0 and, δd − gsd gss δs − gddδ dn2f(δ2) = 0. where, ni = mipfi 2π2 is the density of states in ith band. in case of neutral superconductor, the terms with electric potential disappear from the equations above, and we can get ω2 = ω0 2 + v2k2 for positive solution and ω2 = c2k2 for negative solution where c2 = n1c1 2+ n2c2 2 n1+n2 and v2 = n1c2 2+ n2c1 2 n1+n2 . the positive solution corresponds to leggett’s mode whereas negative solution corresponds to bag mode. the collective mode is only possible if ω0 2 > 0 since v12 > 0 (h. goldstein et al. 2011). this implies that leggett’s mode exists for v11v22 – v12 2 > 0. but in case of charged superconductor, long distance coulomb interaction has a drastic influence on bag mode transforming in the plasma mode. here we get, ω2 = ω0 2 + v2k2 where, v = (n1+n2)c1 2c2 2 n1c1 2+ n2c2 2 this represents that the equation for collective mode has only solution describing leggett’s mode. 3. results and discussion recently discovered mgb2 superconductor can be described by the classical two gap model which convincingly fits the specific heat and penetration depth measurement. to be observed experimentally, leggett’s mode should have the value of ω0 in a well separated from two particle threshold given by smallest gap δ1. here we estimate the value of ω0 using recently suggested values of the coupling constants, introducing the dimensionless coupling constants, λij = nivij that are often used for description of two band model. we may rewrite equation of ω in the form as, ω2 = 4(λ12+ λ21)δ1δ2 λ11λ22− λ12λ21 for specific value of coupling constants λ11 = 0.96, λ22 = 0.28, λ12 = 0.16, λ21 = 0.22 making δ1 = 1.8 mev fixed we get, ω0 = 3.42√δ2 fig. 1: variation of ω as a function of gap parameter ∆2 for λ11 = 0.96 λ22 = 0.28, λ12 = 0.16, λ21 = 0.22 and varying ∆2 from 1.11 mev the fig. 2 represents a parabola with vertex at origin. here, ∆1= 1.8 mev so 2∆1= 3.6 mev. if ∆2= 1 mev, ω0 = 3.42 hz, which in turn implies that the ratio ω0 2∆1 > 1. this is the reason why we exclude ∆2= 1 mev and leggett’s mode is unlikely to be observed in mgb2. making ∆2= 8 mev, we get ω0 = 4.26√∆1 and the graph is plotted as, fig. 3: variation of frequency ω as a function of gap parameter ∆1 for λ11 = 2 λ22 = 2, λ12 = 1, λ12 = 1 and varying ∆1 from 8 mev. 2 3 4 5 6 2 4 5 6 7 8 9 o 8.5 9.0 9.5 10.0 1 12.5 13.0 13.5 o bal ram ghimire et al / bibechana 17 (2020) 75-79 79 here we fix ∆2= 8 mev, the nature of the curve is a straight line. if ∆1= 8 mev, ω0 = 13.07 hz, which implies ω0 2∆1 < 1 and explains that leggett’s mode is likely to be observed in mgb2. the results suggest that for the values of two band model parameters known at present for the two band model of mgb2, leggett’s mode arises above the two particle threshold and unlikely to be observed. we don’t exclude however, that leggett’s mode can be observed in mgb2 if the values of coupling constants λ12 and λ21 would become smaller. the observation of leggett’s mode provides an additional insight to the underlying physics of such a superconductor. 4. conclusion leggett’s mode is a collective excitation corresponding to a small fluctuation of the relative phase of two band superconductor. leggett’s mode is obtained using the modulus of phase variables in the path integral formalism. this work presents the study of validity of leggett’s mode in the twogap superconductor like magnesium-diboride. starting from the microscopic bcs hamiltonian of the system we derived effective action of the system and thermodynamic potential. we obtained the condition if the ratio ω0 2∆1 < 1 leggett’s mode is likely to be observed on the other hand when ω0 2∆1 > 1 leggett’s mode is unlikely to be observed in mgb2. references [1] c. kittel, introduction to solid state physics, 7th ed,, willey student edition, 2004, p. 335. [2] b. seeber, handbook of applied superconductivity, institute of physics, vol 1, publishing ltd, 1998, p. 24 [3] m. tinkam, introduction to superconductivity, 2nd ed, mcgraw hill, inc., 1996, p.12. [4] a .l. fetter and j. h. walecka, quantum theory of many particle system, 1st ed, mcgraw hill inc., 1971, p.4 [5] j. bardeen, l. n. cooper and schrieffer, theory of superconductivity, j. r. phys rev, 108 (1957) 1175. [6] h. goldstein, c. p. poole and j. safko, classical mechanics, 3rd ed, dorling kindersley pvt. ltd., 2011, p. 458. [7] k. wuang, statistical mechanics, 2 nd ed, john willey sons, 2003, p. 177. [8] s. fujita and s. godey, quantum statistical theory of superconductivity, kluwer academic publication, 2002, p. 2. [9] j .h. kim, b. r. ghimire, and h. y., tsai, fluxon dynamics of a long josephson junction with twogap superconductors phys. rev. b 85 (2012) 134511. 133 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal bibechana 19 (1-2) (2022) 133-141 antibacterial and antioxidant activity of biosynthesized silver nanoparticles from the high-altitude medicinal plants rhododendron anthopogen, neopicrorhiza scrophulariiflora and rheum australe of nepal rachana regmi,1 mitesh shrestha, 2 dilip karki, 1, 3 ram chandra poudel, 1 megh raj banjara,4 deegendra khadka 1 ⃰ 1 nepal academy of science and technology, khumaltar, lalitpur, nepal 2 research institute for bioscience and biotechnology, ekantakuna, lalitpur, nepal 3 department of physics, patan multiple campus, patandhoka, lalitpur, nepal 4 central department of microbiology, tribhuvan university, kirtipur, kathamandu, nepal email: deegendrakhadka@gmail.com article information: received: october 31, 2021 accepted: january 01, 2022 keywords: antibacterial antioxidant green synthesized agnps medicinal plant high altitude abstract silver nanoparticles have been massively applied in the medical field including microbial population controls. green synthesis of agnps is more intriguing domain due to possessing environmentally and economically friendly properties. for this experiment, we prepared agnps taking the methanolic extract of high altitude medicinal plants namely rhododendron anthopogen, neopicrorhiza scrophulariiflora and rheum australe and antibacterial and antioxidant activity were observed. the biosynthesized agnps was confirmed using techniques uv vis spectroscopy, ftir and xrd. thus, prepared agnps demonstrated surface plasmon peak at wavelength nearly 430 nm in uv-vis spectroscopy. ftir spectroscopy date explained the role of functional groups in forming stable agnps and xrd pattern revealed that the silver nanoparticles were face-centered, cubic and crystalline in nature. the green synthesis of agnps working as an antibacterial agent was assessed by zone of inhibition against four readily available bacterial strain staphylococcus aureus, escherichia coli, klebsiella pneumonia and pseudomonas aeruginosa and dpph method is used to calculate antioxidant activity. taken all together, the highest antioxidant activity ic50 69.84±0.03 μg/ml was exhibited by the silver nanoparticles of r. australe and the highest inhibition zone measuring16 mm was calculated by n. scrophulariiflora against s. aureus. doi: https://doi.org/10.3126/bibechana.v19i1-2.46406 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana mailto:deegendrakhadka@gmail.com https://doi.org/10.3126/bibechana.v19i1-2.46406 https://creativecommons.org/licenses/by-nc/4.0/ regmi et al / bibechana 19 (1-2) (2022) 133-141 133 1. introduction silver nanoparticles (agnps) have become a potential therapeutic tool for the healing of several malaises and parasites because of exhibiting potent anti-plasmodial, anti-bacterial and anti-fungal activities [1]. using antibiotics haphazardly consequences developing multidrug resistant pathogens and the several contagious ailments which is a crucial reason of rocketing mortality rate globally [2]. infections caused by multidrug resistant bacteria may create various impacts including suppression in mortality and morbidity rate, monetary problem along with hospitalization for a longer period [3]. there are different kinds of physical, chemical and biological methods established for the synthesis of nanoparticles. synthesizing nanomaterials using chemical process generates an immense quantity of hazardous by-products and the physical method requires high amount of energy, high pressure and high temperature. so, the green chemistry is today’s requirement because it corporates pollution free technologies. biological processes are assumed as sound safe and environmentally friendly. biological methods employ either microorganisms or plant extracts and these methods have been popular in the present time due to being cost effective, simple and a viable alternative to the chemical and physical synthetic methods [4]. microorganisms like fungi and bacteria have been used widely in the synthesis of agnps [5]. the effectiveness of antibiotics seems weaker than the earlier time due to increasing microbial resistivity, that is possible by either deteriorating immunity power of human or evolving a noble microbial strain by a mutation. hence, a new antibacterial drug molecule is always demanding. the green synthesis of agnps among other metals could be a promising agent because they are notable for their action towards both gram-positive and negative bacterial and fungal species [6, 7]. much studies have been done on the synthesis of green agnps using several medicinal plants [8, 9]. nevertheless, there is still a lack of synthesizing high altitude medicinal plant based agnps by adopting environmentally clean, economically stable and commercially viable protocols [10]. a large number of medicinal plants are being consumed industrially for making various herbal medicine and nutritional products using their bioactive ingredients. high-altitude medicinal plants are the rich sources of bioactive compounds due to their life cycle completed in the harsh climatic conditions [11]. in this study, we selected locally used three high altitude medicinal plants r. anthopogen, n. scrophulariiflora and r. australe considering their potent bioactive ingredients. r. anthopogen is a store house of camphene, thujene, pinene, δ-cadinene and α cadinol etc that are involved in anti flammatory, anti-microbial, anti-fungal and anti-proliferative activities [12]. n. scrophulariiflora contains many chemical constituents which include jatamansinone, jatamansic acid, volatile oil and supercritical fluid [13]. r. australe is rich in biologically (piceatannol, resveratrol). the root of r. australe is generally applied as an expectorant and appetizer and also practiced for healing cuts, wounds, muscular swellings, tonsillitis and mumps and as anti-bacterial, anti-cancer, anti-diabetic, anti-fungal and anti-oxidant agent [14]. thus, we selected these three medicinal plants whose anti-bacterial and anti oxidant activities are not reported using plant based agnps and their biological activities would be a new approach reporting from nepal originated plants. 2. material and methods fresh and healthy plant materials were collected from the low base camp, mardi himal, kashi district of nepal in october, 2018. details are shown in table 1. plants identification and authentication was done by dr. ram chandra poudel, taxonomist, molecular biotechnology unit, nepal academy of science and technology. chemicals and reagents utilized in the experiment are of molecular grade. the bacterial strains were brought from central department of microbiology, tribhuvan university, kathmandu, nepal. milli-q water potent secondary metabolite anthraquinones (emodin, chrysophanol, physcion, aloe emodin and rhein) and stilbenoids regmi et al / bibechana 19 (1-2) (2022) 133-141 134 (pcr grade; conductivity = 0.056 μs/cm, 25 oc) was used throughout the experiment. table 1: description of collected plants species for the study taxon ic name indige nous name collec ted sites eleva tion use d plan t part s yield in perce ntage neopi crorhi za scroph ulariif lora kutki low camp, mardi himal 3650 m lea ves 26. 5 rheu m austra l pada mchal low camp, mardi himal 3500 m lea ves and ste m 7.1 rhodo dendr on. antho pogen sunpa ti low camp, mardi himal 3300 m lea ves and ste m 9.7 taxon ic name indige nous name collec ted sites eleva tion use d plan t part s yield in perce ntage neopi crorhi za scroph ulariif lora kutki low camp, mardi himal 3650 m lea ves 26. 5 rheu m austra l pada mchal low camp, mardi himal 3500 m lea ves and ste m 7.1 rhodo dendr on. antho pogen sunpa ti low camp, mardi himal 3300 m lea ves and ste m 9.7 2.1 silver nanoparticle synthesis 100 mg of the dried methanolic extract was mixed in 1mm silver nitrate solution up to 100 ml volume. thus prepared solution was incubated at room temperature for 24 hours and observed for changing colors from brown to yellow. spectrophotometer (agilent technologies, cary-60, singapore) was used to analyze conversion of ag+ to ag(0). the sample was scanned in the absorbance ranging 350-700 nm at minimum scanning rate. baseline correction of the spectrometer was carried out using distilled water as a blank reference. the fully reduced solution that shows the peak in the absorbance 400-450 nm on uv-vis spectrophotometer. twenty-four hours later, the mixture was centrifuged (9000 rpm, 20 min, 25 oc). the pellet was redispersed in milli q filtered water (conductivity = 0.056 μs/cm, 25 oc). thus, synthesized agnps were oven dried at 25-26 oc. after cooling, the samples were stored in a vial at 4 oc till further usage [15]. 2.2 characterization technique 2.2.1 uv-vis spectra analysis the solution of agnps in deionized water were characterized in uv-vis spectrophotometer (agilent technologies, cary-60, singapore). the spectrograph of the agnps was observed in a quartz cuvette where baseline correction was taken with water as a reference [16]. absorbance was obtained at the range of 400-450 nm wavelengths. 2.2.2 ftir spectra analysis from ftir data confirms several functional groups found in the sample. for this purpose, prepared agnps dispersed in distilled water was registered in ftir spectrometer. at first, potassium bromide (kbr) sample was scanned as a background. a few drops of agnps dispersed in the distilled water were dribbled on the kbr and scanning was carried out. the spectra obtained from ftir demonstrating many frequencies at different wavelength were compared with standard infrared and raman spectroscopy table. ftir (ir tracer-100, shimadzu, japan) in the absorbance ranging 4000–400 cm-1 at a resolution of 4 cm-1 was used for the analysis. 2.2.3 xrd spectral analysis regmi et al / bibechana 19 (1-2) (2022) 133-141 135 agnps pellet was prepared by centrifuging the sample at 10,000 rpm for 15 min. thus made pellets were dehydrated completely in an oven at 50 oc and xrd was performed to find out the particles size. during the experiment, bruker d2 phaser diffractometer (germany) with 2θ angles ranging from 20° to 80° and monochromatic cu kα radiation source (λ = 0.15418 nm) generated by applying 30 kv and 10 ma to examine the particles nature. 2.3 antioxidant activity dpph assay ascorbic acid with the concentration 10, 20, 60, 80, 100, 120 and 150 μg/ml was taken as a reference. crude extract and agnps having 2000, 1500, 1000, 500, 250, 125 and 62.5 μg/ml solution were dissolved in dimethyl sulphoxide (dmso). 0.01 mm concentration of dpph was prepared in 100% methanol. thus, prepared 100 ml of dpph was mixed to the equal volume of different sample concentration and ascorbic acid solution. total 200 ml of each solution was prepared in an elisa plate. the plate was hold for 30 minutes under dark environment. similarly, 0.1 mm dpph measuring 200 μl was taken as a control. the absorbance was measured at the wavelength 517 nm after 30 minutes. the following equation was applied to calculate the scavenging capacity in percentage: activities using both synthesized agnps and plant extract. 2.4.2 inoculation a single colony of a bacterial strain was scratched and inoculated in a 5 ml inoculated bottle containing nutrient broth. the inoculation was allowed until the growth noted similar to the mac-farland (0.5%) as the standard suggested by who. then the bacterial growth was further incubated (37 °c, 3-4 h). the cloudiness of bacterial suspension was set at 0.5 mcfarland standards. the mcfarland standards was prepared the day before antibacterial tests. antimicrobial effect was observed after swabbing inoculums on mha plate. 2.4.3 agar well diffusion method antibacterial activity of different extracts was determined by well diffusion method on muller hinton agar (mha) medium. required wells were built on mha medium surface with a cork borer (6 mm diameter). inoculums with 106 cfu/ml of bacteria were scattered on the mha medium coated plates with a sterile swab moistened. 20 µl extract having the concentration of 100, 50, 25 and 12.5 mg/ml and same volume of extraction solvents (meoh and dmso) was taken as a negative and streptomycin (1mg/ml) as a positive control. likewise, biosynthesized agnps measuring 20 µl was added into the wells containing negative and scavenging capacity = a0 at a0 * 100 positive controls. the plates were left and allowed to disperse the sample on mha where, a0 = the absorbance of the control and at = the absorbance of the extractives/standard the scavenging capacity was determined by calculating ic50 value. a plot is designed taking concentration versus regression equation for ic50 determination [17]. 2.4 antibacterial properties 2.4.1 bacterial strains active cultures of four standard bacterial strain namely s. aureus (atcc 25923), e. coli (atcc 25922), k. pneumoniae (atcc 700603) and p. aeruginosa (atcc 27853) were used to know the antibacterial solution. the plate was covered and incubation was performed (37 °c, 24 h). in the next day, sample inhibited zone against microbial was calculated by measuring the diameter in mm [18]. the agnps showing the zone of inhibition above or equal to 8 mm were validated as the sample working effectively. in the study, plants with significant medicinal values were chosen from the high altitude of nepal regarding their importance in local areas. plants found in high altitude are rich sources of bioactive compounds because they have to battle with the harsh climatic conditions for survival. climatic condition, plants component used, extraction time and regmi et al / bibechana 19 (1-2) (2022) 133-141 136 a b so rb an ce procedure, solvent types and temperature play a pivotal role in separating biologically potent compounds [19]. 3.1.1 uv-vis spectra analysis 100 %t 80 60 40 the agnps of selected plants namely r. anthopogen, n. scrophulariiflora and r. australe extracts observed absorption peaks at the wavelenght 400-450 nm. r. australe exhibited the peak at 420 nm, r. anthopogen at 430 nm and n. scrophulariflora at 450 nm in 20 0 -20 4000 powder 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400 cm-1 this analysis. the occurrence of the peak in these range indicates the formation of agnps [20, 21, 33]. figure 1 shows uv-vis spectra of the plants based agnps. fig 2: ftir spectrum of the silver nanoparticle using n. scrophulariiflora. 80 rheum australe abs %t 0.4 0.2 0 0 100 200 300 400 500 600 700 800 900 wave length(nm) 60 40 20 0 -20 fig. 1: uv-vis spectra of agnps from r. austral, r. anthopgen and n. scrophulariflora. -40 4000 powder 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400 cm-1 3.1.2 ftir spectroscopic analysis in ftir spectroscopy, the absorption of agnps was carried out in the wavelenth between 4000 to 500 cm-1. the sample showed the peak at various wavelengths. the peak detected in between 3400 to 3700 cm-1 predicted the formation of hydroxyl group (o h) and the next observable peak at 1690-1630 cm-1 informs carbonyl group (c=o). presence of these two functional groups indicates the formation of nanoparticle by the reduction of silver nitrate. the ftir spectrum of n. scrophulariiflora synthesized agnps (fig 2) observes the primary peak at 3442 cm-1 which is possible having o-h stretching vibration occurs in alcoholic and phenolic groups and the peak at 1635 cm-1 indicates the formation fig 3: ftir spectrum of the silver nanoparticle using r. anthopogen. 80 %t 60 40 20 0 -20 -40 of carboxy groups [22]. similar peaks of r. anthopogen (fig 3) and r. australe (fig 4) 4000 powder 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400 cm-1 were appeared in the ftir spectra. fig 4: ftir spectrum of the silver nanoparticle using r. australe. kutki sunpat i rheun 3 4 4 4 . 8 7 3 4 4 4 . 8 7 3 4 4 2 .9 4 2 3 6 0 . 8 7 2 3 2 6 . 1 5 2 3 5 7 . 0 1 2 3 2 4 . 2 2 2 3 5 7 .0 1 2 0 6 3 . 8 3 2 0 6 1 . 9 0 2 0 6 7 .6 9 1 6 3 5 . 6 4 1 6 3 5 . 6 4 1 6 3 5 .6 4 6 6 7 . 3 7 6 6 7 . 3 7 6 6 7 .3 7 5 9 9 .8 6 4 1 8 . 5 5 4 2 0 . 4 8 regmi et al / bibechana 19 (1-2) (2022) 133-141 137 3.1.3 x-ray diffraction analysis xrd was used to examine crystallize size and structure of the biosynthesized agnps was examined by xrd. agnps of n. scrophulariiflora (fig 5c) showed the diffraction peak at 2𝜃 = 30.5, 37.8, 44.0, 64.3 and 77.7, r. anthopogen (fig 5a) showed at 30.3, 37.7, 43.9, 64.14 and 77.12 and r. australe (fig 5b) demonstrated at 32.08, 37.9, 44.3, 64.4 and 77.2. these peaks formation in xrd supported agnps having nanocrystal and crystalline shape which were compared with the standard. the observed peaks can be assigned to the planes (122), (111), (200), (220) and (311) facet of silver crystal [23]. spectra showing such a few peaks which were cumbersome to specify because of the bioorganic compounds/protein(s) contamination [24, 25]. the crystalline size was calculated by analyzing peak intensity, position and full width at half maximum (fwhm). the size of crystalline particles was determined by debye–scherrer’s equation. d = 0.9 λ/ β cosθ where, λ = x-ray wavelength, β= diffraction line broadening measured as half of its maximum intensity in radians and θ = diffraction angle the crystal size of the sample was estimated taking the line width of the peak (111) of all three samples. the size of agnps prepared from r. anthopogon (fig. 5a), r. austral (fig. 5b) and n. scrophulariiflora (fig. 5c) was found 9, 11 and 16 nm respectively. 3000 2500 2000 1500 1000 500 0 3.2 antioxidant activity of agnps among three medicinal plants, agnps synthesized using r. australe showed significant antioxidant potential having ic50 69.84±0.03 μg/ml but crude methanolic extract exhibited 100±0.54 μg/ml. similarly, the agnps of r. anthopogen and n. scrophulariflora had antioxidant activity ic50 98.17±0.02 and 74.56±0.05 µg/ml respectively. while comparing antioxidant activity between crude extract and their agnps, the former showed remarkably less potent with higher ic50 (table 2). several articles have reported significant antioxidant properties of biologically prepared agnps using p. pinnate plant [26] and e. suberosa [27, 33] than their crude and so on. the results suggested that biosynthesized silver nanoparticle is more beneficial than its crude extract using as an organic antioxidant. antioxidant compounds protects our health from various oxidative stresses which is connected to degenerative diseases. agnps can be taken into another screening test on animal models and then clinical trials to validate its effectiveness. table 2: antioxidant properties (ic50) of crude extract and agnps s.n . plant name extract in methano l ic50 (µg/ml) methanoli c agnps ic50 (μg/ml) 1. r. australe 100±0.5 4 69.84±0.0 3 2. r. anthopogen 140±0.3 9 98.17±0.0 2 3. n. scrophulariiflor a 120±0.7 8 74.56±0.0 5 20 30 40 50 60 70 80 2 (degree) fig 5: xrd diffraction pattern of agnps synthesized from (a) r. anthopogon, (b) r. austral and n. scrophulariiflora. 3.3 antimicrobial activity of silver nanoparticles agnps have been using several important fields like medicine, cosmetics and environment and so on [28]. the r. anthopogon r. australe n. scrophulariiflora 122 111 200 220 311 122 a 111 200 220 311 111 b 220 311 122 200 c in te n si ty regmi et al / bibechana 19 (1-2) (2022) 133-141 138 biosynthesized agnps of the medicinal plants were examined their antibacterial properties by measuring diameter of inhibition area with different bacterial strain (fig. 6 and table 3). the maximum inhibitory zone measuring 16 mm was exhibited by n. scrophulariflora silver nanoparticles against s. aureus in fig 6(e) and the minimum inhibition below 6 mm was showed by the agnps of r. australe against k. pneumoniae depicted in fig 6(k). from the studies, it is cleared that the agnps synthesized biologically has shown higher potential than its extract because of having wide surface region increases interaction to the cell wall of a bacterium [29]. several similar findings were cited describing effectiveness of agnps testing on e. coli with mentha piperita [30], acalypha indica [16] and berberis asiatica (33). the mysterious working principle between agnps and its effective microbial activity is developing an electrostatic force of the positively charged ag+ ion and negative charges generated on phospholipids bilayers of bacterial cell wall [31, 32]. fig 6: crude extract and agnps in several concentrations showing antibacterial properties of r. australe (a) s. aureus, (b) k. pneumoniae, (c) p. aeruginoa and (d) e. coli, n. scrophulariflora (e) s. aureus, (f) k. pneumoniae, (g) p. aeruginoa and (h) e. coli and r. anthopogon (i) s. aureus, (j) k. pneumoniae, and (k) p. aeruginoa and (l) e. ceoli. table 3: crude extract and agnps exhibiting zone of inhibition (in mm) against bacteria. plants concen tration mg/ml zone of inhibition (mm) s. aur eus k. pne umo niae p. aeru gino a e. coli r. australe crude (50) 6 10 12 6 agnps (12.5) 11 11 10 9 n. scrophul ariflora crude (50) 14 6 14 9 agnps (12.5) 16 9 12 13 r. anthopo gon crude( 50) 6 8 6 12 agnps (12.5) 15 12 6 12 conclusions methanolic extract of agnps was synthesized using high altitude medically profound plants namely r. australe, n. scrophulariflora and r. anthopogon. biosynthetic agnps formation was confirmed by using uv-vis spectrophotometer where the sample showed the peaks in the wavelength ranging 400-450 nm. ftir data added more evidences for the formation of agnps in the context to the functional groups by providing the peaks at 3400-3700 cm-1 and for 1690 1630 cm-1 wavelength for hydroxyl group (o regmi et al / bibechana 19 (1-2) (2022) 133-141 139 h) and carbonyl group (c=o) respectively. additionally, obtained xrd spectral peaks corresponding to the standard provided the synthetic sample in nanocrystal and crystalline in shape. r. australe agnps exhibited the highest antioxiant propertis (ic50 69.84±0.03 µg/ml) among the samples. the most effective antimicrobial activity was calculated from the agnps of n. scrophulariiflora showing zone of inhibition 16 mm against s. aureus. regarding our studies, it is cleared that the importance of biosynthesized agnps to their extracts is high. these biosynthesized agnps might be useful in the several domains in the coming times after performing additional experiments acknowledgement the authors are immensely thankful to dr. rosa ranjit, dr. deependra das mulmi, mr. hari ram shrestha and ms. bima maharjan for the supports. authors are equally grateful to 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[33]d. khadka et al, green synthesis of silver nanoparticles using medicinal plants berberis asiatica and cassia fistula and evaluation of antioxidant and anti-bacterial activities. nepal j. sci. technol. 19 (2020) 25-32. http://doi.org/10.3126/njst.v20i1.39384 http://doi.org/10.1016/j.colsurfb.2011.03.009 http://doi.org/10.1016/j.colsurfb.2011.03.009 http://doi.org/10.5101/nml.v2i2.p106-113 http://doi.org/10.5101/nml.v2i2.p106-113 https://doi.org/10.1078/0944-5013-00069 https://doi.org/10.1078/0944-5013-00069 http://doi.org/10.3126/njst.v20i1.39384 1. introduction 2. material and methods 2.1 silver nanoparticle synthesis 2.2 characterization technique 2.3 antioxidant activity 2.4 antibacterial properties 3.1.2 ftir spectroscopic analysis 3.1.3 x-ray diffraction analysis 3.2 antioxidant activity of agnps 3.3 antimicrobial activity of silver nanoparticles conclusions acknowledgement references [1]a. a. ashour et al, green synthesis of silver nanoparticles using cranberry powder aqueous extract: characterization and antimicrobial properties. int. j. nanomedicine. 10 (2015)7202-7221. bibechana 19 (1-2) (2022) 111-118 111 he2+ impact single ionization cross sections of cu atom 1s. p. gupta, 1k. yadav and 2l. k. jha 1patan multiple campus, lalitpur, tribhuvan university, nepal 2 university department of physics, bra bihar university, muzaffarpur 842001, bihar, india *email: suresh.gupta@pmc.edu.np article information: received: april 04, 2021 accepted: february 26, 2022 keywords: alpha particle impact single ionization cross section binary encounter approximation hartree-fock velocity distribution )(tf vrien’s cross section ( e ) abstract semi-classical binary encounter approximation has been used for theoretical calculations of single ionization cross sections of cu atom at ground state by alpha particle impact in energy range varying from threshold 35 kev/amu to 425 kev/amu. an accurate expression of cross section for energy transfer e ( e ) as given by vriens and quantum mechanical hartree-fock velocity distributions for target electrons have been used in the calculation. major contribution to the total single ionization cross sections of cu are from 4s and 3d subshells. the ionization cross sections decrease with the increase of impact energy same as experimental data reported. the theoretical and experimental results of single ionization cross sections have same trends against the increase of impact energy. the ratio factor falls within 2, varying from 1.26 to 1.86, for given energy range. theoretical results are under valid range. about 50% of total theoretical results of single ionization cross sections have ratio factor (r) 5.1 . major contribution to total ionization cross section is from 3d and 4s subshells-electrons whose contributions varies from 62 to 71% and 41.7% to 23.8% respectively. the higher value of linear correlation coefficient (=0.9647) and lower value of standard deviation (=0.822) shows that results calculated are close to the experimental data in the intermediate and high energy range. doi: https://doi.org/10.3126/bibechana.v19i1-2.46401 this work is licensed under the creative commons ccby-nc license. https://creativecommons.org/licenses/by-nc/4.0/ bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal https://doi.org/10.3126/bibechana.v19i1-2.46401 https://creativecommons.org/licenses/by-nc/4.0/ gupta et al / bibechana 19 (1-2) (2022) 111-118 112 1. introduction single and multiple ionizations of atoms and molecules by ionizing particles like electrons and ions is one of the fundamental processes in atomic physics. collision between heavy charged particles (h+ or he2+) with target atoms may results pure ionization, excitation, excitation-auto-ionization, electron capture, charge transfer and transfer ionization. molecular dissociation is a widespread phenomenon that can produce ions, atoms and molecular radicals which are far more reactive than the original molecules. molecular dissociation comprises a molecular medium and some kind of ionizing radiation. continuous data of ionization cross sections of respective processes have great importance in different fields of science. some important and quite distinct examples of this combination are (i) planetary atmospheres that are constantly irradiated by electrons, cosmic rays and fast ions affecting their molecular inventory [1-4]. a large number of elements both in natural and ionic forms exist in the upper atmosphere and the capture processes are relevant to upper atmosphere research. from astrophysical point of view, the charge exchange in alpha particleatom collision is important because the emission spectrum of solar chromosphere contains spectral line λ= 4686 a0 whose origin has been attributed to the presence of ionized helium formed due to the process of electron capture by fast alpha particles produced in nuclear reaction [5] (ii) cancer therapy [6,7] where the fragmentation of water molecules present in the human body by some ionizing agent can lead to several reactive radicals that can produce local biological damages near the tumor and help in the treatment. monte carlo simulations track structure is usually used in micro and nano-dosimetry to find radiation transport index in medical science. better the results of cross sections used as simulation codes better is the treatment in medical science. projectile particles of ions like protons (h+) and helium (he2+) deposit a large amount of their energy in a volume of a few micrometers or even nanometers and cause extensive damage to the microscopic structure of biological matter and results cell death in the dna and (iii) plasma physics, where the environment of ions reacting with each other have many applications, such as plasma etching of microchips [8]. indirectly the plasma-supplemented techniques are used to treat surfaces, materials and some devices to realize specific qualities. physical plasma has an application in the human or animal body to realize therapeutic effects [9,10]. therefore, a set of continuous and precise data of single and multiple ionization cross sections of different atoms are of great importance in the study of different fields of science as mentioned above. so, the theoretical results of ionization cross sections of different atoms have their own importance in physics. multiple-ionization is a complex many-electron process where direct and indirect ionization contribute to the final charge state. pindzola et al.[11] time-dependent close-coupling method in spherical polar coordinates is developed to calculate the electron-impact double ionization of the h2 molecule. montanan et al. [12] investigated multiple ionization of ar by impact of alpha particle using quantum mechanical model of continuum distorted wave ekonal initial state (cdweis). the theoretical results investigated were quite reasonable with experimental data at high energies range. despite these successes, difficulties still exist in the mathematical formulation for the calculation of single and multiple ionization cross sections of heavy atoms under quantal approximations. since the beginning of nineteenth century semiclassical theory is being used successfully along with its gradual modification. heavy charged particles (h+, he2+) impact direct single and double ionization cross sections of different atoms have been investigated theoretically using modified binary encounter approximation by singh et al [13], minakshi et al. [14] tan et al 1981, kumari et al. [16] and gupta et al. [17] to calculate direct single and double ionization cross sections of several light and heavy atoms/ions by the impact of heavy charged particles. 2. methods and theoretical details thomson first used the binary encounter theory for calculating cross section for ionization of atom by electrons. according to thomson consider a situation of collision where the energy transfer in coulomb collision between a particle of mass 1m gupta et al / bibechana 19 (1-2) (2022) 111-118 113 and charge ez 1 with initial kinetic energy 1e and a particle of mass 2m and ez2 with initial kinetic energy 02 =e (rest). in the case of binary encounter theory, it has been assumed that during the period of interaction between projectile and an orbital electron the other atomic electrons and the nucleus play no role. the thomson’s energy transfer )( ionization cross section for electron –electron collision is [18]       −= 11 4 11)( eue ne d dq    (1) for ionization 1eu  ; where n is the effective number of electrons in the atom and u is ionization potential energy. thomas and william (1927) modified the formulation for more general case where 02 e (considered symmetrical distribution of velocity of target electrons), m1 ˃˃m2 and z1≠ z2 which is relevant to proton and alpha particle –atom collision. energy transfer ionization cross section for this case has been given as [18]       += 1 3 2 2 12 1 2 2 2 1 4 3 41)(     e em mzze d dq (2) these classical theories remained dormant for three decade till the pioneering work of gryziniski [19]. in the literature. new progress was made by gryziniski. he obtained classical relations for coulomb collision of two moving charged particles and applied them for theoretical studies of a varity of charged particle-atom collision processes. gryzinski solved problem of collision using scattering angle insteed of momentum transfer as a variable. variens [20] gave a set of quantum mechanical formula for scattering of one electron beam by another interms of momentum transfer as a variable. he incorporated symmetrical properties in the formulation that includes exchange and interference effects and obtained differential cross section for momentum and energy transfer. we carry out theoretical calculations of alpha particle (he2+) impact single ionization cross sections of cu atom using the modified bea. the theoretical approach used in bea is based on independent particle model (ipm). the model is based on the hypothesis that the probability of ionizations is directly related to the energy deposited by the projectile on the target. the energy deposited is statistically distributed among all atomic electrons and one or more of which eventually auto ionize to the final state. an accurate expression of e (cross section for energy transfer e ) for proton impact given by vriens [21] and quantum mechanical hartree –fock velocity distribution functions for bound electrons of the target atoms or ions have been used to calculate total single ionization cross section of iron. following mcdowell [22], catlow and mcdowell [23] gave an expression of single ionization cross section of an atom by an electron and proton impact in terms of dimensionless variables s and t . the variables are related to kinetic energies of incoming and orbiting electrons and defined as 2 0 2 1 2 / vvs = and 2 0 2 2 2 / vvt = , where 1v and 2v are the velocities of incident particle and target orbiting electron in atomic units respectively and 0v is root mean square velocity of orbital electron. the ionization potential energy of bound electron u is defined as 2 0vu = . atomic electrons are taken to have a momentum distribution and can be given by fourier transformation of the hartree fock density distribution that includes quantum-mechanical velocity distribution for the bound electrons. following catlow and mcdowell, the expression of total single ionization cross section for heavy charged particle impact having energy of usm 2 1 with an orbital electron of a particular shell having energy ut 2 is given by (3) where q(s) is total single ionization cross section, en is the number of electrons in the shell under consideration, z is the charge on the projectile (for proton and electron z = 1 and 2 for alpha particle), )(tf is hartree-fock momentum distribution gupta et al / bibechana 19 (1-2) (2022) 111-118 114 function and 0a is bohr’s radius. in the present calculations, ),( tsqi is calculated using an accurate expressions of differential cross section e (cross section for energy transfer e ) under three different limits of energy transfer as given by vriens [21] (4) where                +  = 3 2 2 )(3 414 e ut eus a and       −+ −  = 2/32 2/12/12 3 ])[( 8 )(3 2 us tuute s et b integration over differential cross section in the above three cases of energy transfer gives ),( tsqi for the impact of unit heavy charged particle in terms of dimensionless variables as (5) the numerical integration of ),( tsqi carried out over hartree-fock momentum distribution function )(tf of the bound electron that yields total ionization cross section )(sqi [equation (3). the momentum distribution function )(tf is defined as, (6) where )( 12 1 1 1 2  + −+ = x l nlmnl  (7) and = drerr rik nlmnlm . 2 1 )( )2( 1 )(    is the fourier transform of the one electron orbital. the complete wave function is given by (8) where nln and )(rrnl are the normalization constant and analytical hartree-fock radial function, respectively. the empirical relations for nln & )(rrnl are (9) and (10) here  is orbital exponent of basis function. the spherical harmonic )(lmy have different forms depending upon the value of orbital and magnetic quantum numbers l and m respectively. it is well known that velocity of orbital electrons increases with the decrease in shell number and hence electron of inner shell possess relativistic in nature. here we have ignored the relativistic nature of orbiting electron. in the present work, ionization from valence shells and few inner shells have only been considered since rest inner orbitals have negligible contribution to the ionization cross sections. in the mathematical formulation of bea there used nonrelativistic wave functions. gupta et al / bibechana 19 (1-2) (2022) 111-118 115 3. results and discussion computational calculation of equation (3) finally gives results of sics for a particular orbital under different selective constants of the respective subshell. the expression of ),( tsqi and )(tf are taken from equation (5) and (6) respectively. the momentum distribution function )(tf has been constructed from equations (7-10) for particular orbital electron of the target atom as discussed above. for shell radii and binding energies of electrons, quantum mechanical value of radial distance of maximum probability given by desclanx [24] and quantum mechanical value of orbital energies given by clementi and roetti [25] have respectively been used in the calculations. we have considered contributions only from 4s, 3d and 3p subshells as inner shells have negligible effect. theoretical investigation of direct single ionization has been carried out in the energy range of 35 kev/amu to 425 kev/amu (patton et al.[26]) using bea. we compared the theoretical result of sics with the experimental data of single ionization cross sections for corresponding impact energy. the computational calculation includes contribution of 4s, 3d and 3p orbitals. theoretical results of sics of these orbitals and experimental data against corresponding impact energies have been presented in table 1 and fig. 1. table1: alpha particle impact sics of cu atom for different impact energies. e (kev/amu) contribution of total sics (10-16 cm2) 4s 3d 3p theory expt. [26] 35 6.02 7.6 2 0.06 13.70 22.7±1.5 0± 40 5.45 7.6 6 0.07 13.18 24.0±2.0 0 47 4.81 7.6 7 0.09 12.57 20.1±1.2 1.20 54 4.34 7.6 2 0.10 12.06 21.5 ±1.3 62 3.92 7.7 5 0.12 11.79 18.5 ±1.0 75 3.42 7.2 1 0.14 10.77 15.8 ±1.2 88 3.04 6.9 3 0.16 10.13 15.0 ±1.3 108 2.67 6.5 4 0.18 9.39 13.7 ±1.0 125 2.34 6.0 6 0.20 8.60 11.5 ±0.2 150 2.03 5.4 9 0.22 7.74 9.8 ±0.6 180 2.75 4.9 6 0.24 7.95 10.3 ±0.5 213 1.52 4.3 9 0.25 6.16 8.5 ±0.4 250 1.32 3.8 8 0.25 5.45 8.2 ±0.4 300 1.12 3.2 8 0.25 4.65 7.2 ±0.3 360 0.94 2.7 4 0.24 3.92 6.9 ±0.3 425 0.80 2.3 2 0.23 3.35 6.2 ±0.4 v the theoretical and experimental results of ionization cross section have the same trend against increase of impact energy. the experimental observations overestimate the theoretical results of sics of cu for all given energies. the variation of the results in both cases is almost four times. the theoretical results decrease very slowly with the increase of impact energy. except 54 and 180 kev/amu, values of experimental data calculated and experimental results of sics of cross sections decreases with impact energies. from a number of theoretical works done by percival (1966), vriens (1966) and rudge (1968), binary encounter model gives reasonable formula that estimates ionization cross sections over a significant range of energies if the ratio factor (theoretical result to the corresponding experimental value) is less or equal to 2. here, in our case our results have ratio factors (r) gupta et al / bibechana 19 (1-2) (2022) 111-118 116 falls within 2 for all given energy values. it varies from 1.26 to 1.86. this shows that all the results are within valid range. about 50% of theoretical results of sics have ratio factor (r) 5.1 as shown in the table 1 major contribution to the total theoretical results are from 3d shell which varies from 62 to 71% . in the same way 4s has contributions varying from 41.7% to 23.8% and 3p has very small contribution varying from 0.51% to 6.8% for entire energy range. also, the variations of theoretical and experimental values of sics at low to high impact energies are 4 and 3.66 respectively. we observed that the contribution of 3p is very small compared to the 4s and 3d subshells. it is found that 3p electrons have lower energy compared to 3d and 4s subshells in the electronic configuration of cu. only those electrons take part in pure ionization whose energies are high. here subshells 4s and 3d have greater energies compared to 3p and nest lower subshells. according to aufbau principle 4s is filled first if 3d has no electron. as 3d get populated with electrons, the relative energy of 4s and 3d fluctuate relative to one another and 4s ends up with higher energy state and ionization results from 3d and 4s of cu. the nature of variation observed in theoretical results is nearly same as that of variation in experimental data and all the theoretical results have ratio factor less than 2. this shows that these theoretical results are close to the corresponding experimental data. 50 100 150 200 250 300 350 400 450 0 5 10 15 20 25 c ro ss s ec ti o n s o f io n iz at io n (x 1 0 -1 6 cm 2 ) energy (kev/amu) contribution of 4s contribution of 3d contribution of 3p total theoretical expt. fig.1: alpha particle impact sics of cu atom in the given energy range the model does not include all physical insight of ionization at low energy range. the sharp fall in single ionization cross sections of 4s in threshold energy range is due to lack of suitability of our semiclassical model of binary encounter approximation. 50 100 150 200 250 300 350 400 450 2 4 6 8 10 12 14 16 18 20 22 24 26 c ro ss se ct io n s o f io n iz at io n (x 1 0 -1 6 cm 2 ) energy (kev/amu) theoretical experimental fig. 2: error bars associated to the theoretical results relative to the experimental data. the variation of error associated with theoretical results in comparison with corresponding experimental values has been shown in fig. 2. the errors associated with theoretical results have relatively high values at low energies and decreases with the increase of impact energies. 2 4 6 8 10 12 14 4 6 8 10 12 14 16 18 20 22 24 26 e x p e ri m e n ta l s ic s ( x 1 0 -1 6 c m 2 ) theortical sics of cu (x10 -16 cm 2 ) fig.3: linear fit for the theoretical results with the experimental data along with error-bars. fig.3 shows that linear correlation coefficient is 0.9647 and standard deviation (sd) is 0.822. this shows that about 96% of theoretical data are in close agreement to the line of best fit. in threshold energy range the theoretical results are more apart from corresponding experimental data and possess relatively more error compared to higher energy region. smaller value of standard deviation shows that the theoretical results are close to the experimental values in intermediate and high energies. gupta et al / bibechana 19 (1-2) (2022) 111-118 117 conclusion there observed that he2+ impact single ionization cross sections of cu are well 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revised: april 15, 2024; accepted: april 17, 2024 doi https://doi.org/10.3126/bibechana.v21i3.60796 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 171 http://nepjol.info/index.php/bibechana sagarkafle@ioepc.edu.np https://doi.org/10.3126/bibechana.v21i3.60796 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ aastha gautam et al./ bibechana 21 (2024) 171-179 172 1 introduction with the rise in urbanization, the urban population and consumption of materials are increasing, which has increased in waste generation [1]. the urban waste is called municipal solid waste (msw), which contains waste mostly from households, public spaces, and institutions [2]. the management of such waste is a complex issue for the municipality. due to proper knowledge and resources, most of the municipalities in nepal collect, transport, dump, and burn the waste [3]. most municipalities in nepal dump the msw far from the core areas of the cities, either in the forest or near the river, and burn the waste. this open dumping and burning practice has deteriorated the surrounding environment, especially the air, water, and soil, emitting harmful substances and posing severe risks to overall biodiversity, including human health [4]. investigating the risk associated with such poor practices of swm management is necessary to understand the consequences and be aware of the related to be aware of the related stakeholders. several studies in nepal and other developing countries have assessed the impacts of open dumping on nearby environments. khanal et al. 2021 [5] analyzed leachate discharge from the pokhara landfill site and found significant effects on the seti river's water quality. a study was carried out by shrestha et al. 2015 [6] and evaluated the water quality of the kolpu river near the sisdol landfill area in the district of nuwakot. six water samples and leachate were taken from upstream to downstream of the river, and their physical and chemical characteristics were examined. the study showed that leachate was highly contaminated, with the highest physicochemical characteristics. the river’s water was unhealthy for aquatic ecosystems and animal drinking. while several studies have analyzed the impacts of open dumping in nepal, there remains a gap in biratnagar metropolitan city’s dumping site. no such research has been reported that has investigated the air, soil, and water pollution arising from the dumping and burning of msw in biratnagar metropolitan city’s dumping site. given biratnagar’s large population, understanding the effects of such poor practices is vital, and the study’s findings could help compel the local government to establish waste management facilities and make the public aware. 2 research methodology 2.1 study area the study area is biratnagar metropolitan city (bmc)'s dumping site (figure 1). bmc is the capital city of koshi province and has a population of 243,927, 56,919 households, and a population density of 3,168 per km2. the city transports the msw to the dumping site and openly burns it, which has degraded the surrounding environment. the dumping site is on the bank of the keshaliya river and is roughly 0.01 km2 in area. 2.2 sampling method in this study, nine points are chosen, three for each, for the investigation (figure 2). the air test (pm 2.5 and pm10) was conducted using equipment named open seneca, at a height of 1.5m from ground level to indicate the breathing zone. it helps to expose significant human health risks that impact communities near dump sites. the first sampling point was taken as a center point (at0) (26°27’5.04” n, 87°14’47.98” e) at the dumpsite based on prevailing wind direction and the remaining two points were taken upstream (at1) (26°27’4.79” n, 87°14’51.4” e) and downstream (at-2) (26°27’5.47” n, 87°14’44.77” e) of the wind direction at 100m each from the reference point to assess particulate transport from the site. three pieces of equipment were used simultaneously, being held in position for 2 hours to obtain reliable data. the parameters were then evaluated from each testing point and were averaged to pull out the graph of the average value. for the water sample, we took three sample stations; one is the leachate outgo point (sw-0) (26°27’6.60” n, 87 14’47.70” e), and the other two are 100m upstream (sw-1) (26°27’10.11” n, 87 14’49.35” e) and downstream (sw-2) (26°27’1.7” n, 87 14’43.6” e) from the leachate outgoing point to analyzed the water quality impact on different conditions and determine the effect of surface water bodies. the sampling bottles and mineral water are cleaned properly with distilled water. we had chosen the sample station with a laminar flow and running water area. then sampling is sent to the nepal batawaraniya sewa kendra, biratnagar, for testing. total hardness, sulphate, nitrate, nitrite, ammonia, magnesium, calcium, chromium, nickel, lead, zinc, copper, cadmium, manganese, and cobalt tests were conducted. water testing includes physicochemical properties, nutrients, organic matter, and heavy metals that elevate due to the leaching of dump waste, affecting drinkability and ecosystem health. in this study, we chose the right-hand side of the landfill area because the soil on the left side is siltier and dryer. the surrounding area is cultivated with cash crops like sugarcane, cucumber, etc. we took the center point with the help of google earth software; the first sample (ss-0) (26°27’4.3” n, 87 14’49” e) is approximately 10 m distance aastha gautam et al./ bibechana 21 (2024) 171-179 173 from the center of the landfill for the analysis of most impacted soil. the second sample (ss-1) (26°27’3.4” n, 87 14’48.2” e) is taken approximately 25m from the first sample. the last sample (ss2) (26°27’1.5” n, 87 14’46.4” e) is taken approximately 60m from sample second with varying degrees of impact for testing the contamination gradients in the surroundings. we used a helical type of auger as a sampling instrument. it consists of a head, about 1 m long rod, tee pieces, and a handle. with the help of an auger, we bore holes to the desired sampling depth and the core is then withdrawn, and a sample is collected. we took around 1 kg of soil samples from each station in a plastic bag. for testing parameters, such as ph, electrical conductivity, coliform, moisture, total hardness, chloride, sulphate, nitrate, ammonia, magnesium, calcium, manganese, chromium, nickel, iron, lead, zinc, cadmium, total coliform, e-coli, toc, samples were sent to nepal batawaraniya sewa kendra, biratnagar. these physicochemical parameters, heavy metals, and microbes are tested in soil samples to analyze nutrients, salinization, toxicity levels, and pathogenic contamination associated with leakage from the accumulated waste. figure 1: map of nepal showing the study area, the dumping site (26°27’5.04” n, 87°14’47.98” e) of biratnagar metropolitan city, located near the keshalya river. figure 2: map showing air, soil, and water sampling points. at: air test, sw: surface water, and ss: soil sample. 3 results and discussion 3.1 impacts of open dumping on air quality based on the average values of air tests obtained during the study, the center point had the highest concentration of pm2.5 (2,428.443 µg/m³) and pm10 (2,689.667 µg/m³) (figure 3). the downstream particulate matter concentration was higher than the upstream, showing the transport from the dumping site to the downstream. the central point was on the dumping site, where the movement of waste collecting vehicles and dust generated during the unloading of the wastes, and open burning of the wastes, could be the possible reason for higher concentration levels. the pm2.5 and pm10 at the center and downstream points were far higher than the safe limits. the transfer of these particles can easily enter the human respiratory system and affect our lungs, heart, and liver, and it is even responsible for reducing visibility. waste collectors and disposal personnel were seen working without using protective equipment, such as masks, gloves, etc., with their bare hands. this directly harms the health of the workers. the nearby settlements also suffer a lot from this pollution. exposure to higher concentration particulate matter may lead to cardiovascular death and various respiratory symptoms like regular cough and breathlessness. [7]. aastha gautam et al./ bibechana 21 (2024) 171-179 174 figure 3: variation of particulate matter (pm2.5 and pm10) in different air testing points. the high pm2.5 and pm10 levels measured at the landfill site and downstream locations greatly exceeded who guidelines. this suggests significant health risks for site workers and nearby communities from particulate inhalation. open waste burning produces dangerous fine particulates that can penetrate the lungs. 3.2 impacts of open dumping on soil quality 3.2.1 physio-chemical parameters of soil samples the highest values of moisture (22.76 %), conductivity (1431 µs/cm), total hardness (2 mg/l), chloride (8.2 mg/l), sulphide (10 mg/100gm), calcium (1.69 mg/l), and total organic carbon (0.96 %) were found to be in soil samples taken near the landfill site (ss-0). the highest values of ph (7.76) and magnesium (0.4 mg/l) were found in the 3rd sample of the soil (ss-2), while nitrate (<0.05 mg/100gm) and temperature (25.10 c) were found to be the same for all samples. reciprocally, ss0 had the lowest ph value (7.59), 2nd soil sample (ss-1) had the lowest values of conductivity (53.5 s/cm), sulphide (2.8 mg100gm), magnesium (0.1 mg/l) and total organic carbon (0.82 %), ss-2 had the lowest values of chloride (0.65 mg/l), calcium (0.6 mg/l) and moisture (8.03 %), and total hardness (1 mg/l) was lowest on both ss-1 and ss-2. obtained values of conductivity (for ss-0), total hardness, chloride, magnesium, calcium, and total organic carbon were above the reference limit, whereas conductivity (for ss-1, ss-2), sulfide, and nitrate had values lower than the reference limit, and values of ph and temperature were within the limit. the ph value was found to be in increasing order (table 1) from the nearest point towards the farthest sample point, but the values did not vary much with each other and were within the guided limit. the reason behind the highest ph value at ss-2 (at the agricultural land/cropland) may be due to the use of fertilizers like nitrogen and sulfur, soil minerals removal during crop harvesting, or loss of organic matter [8]. if the soil is too alkaline, plant productivity is affected as it causes nutrient imbalances, reduced nutrient uptake, altered soil microbial activity, and plant-specific sensitivity. interestingly, the temperature of the soil samples at all the locations was found to be the same, 25 0c. an electrometric method was deployed to measure it. a 0 to 30 °c temperature range is often needed for seed germination [9]. temperature ranges are ideal for growth, and maximum yields during the day or night vary depending on the crop. crop enzyme activity and chemical reaction rates increase with temperature [10]. however, abnormally high temperatures restrict crops’ ability to grow and develop. the electrical conductivity was the highest at ss-0 and lowest at ss-1 (table 1). the decomposition of organic waste and the addition of minerals and salts from the waste dumping site to the nearest sampling point [11] is supposed to be the reason behind this. in addition, conductivity at ss-0 was found to be above the reference limit, indicating the availability of a high amount of calcium cations. the moisture content value was found to be in reducing order from ss-0 to ss-2 (table 1). leakage from liquid waste and decay of organic waste could have contributed to the highest moisture content in the first sample (ss-0). the total hardness of the soil was found to be the highest at the nearest soil sample ss-0 (table 1). the study [12] suggests that soil hardness is affected by soil moisture, as he aastha gautam et al./ bibechana 21 (2024) 171-179 175 hardness is an indicator of soil compaction. hard or compacted soil creates suffocation for the plant to survive as the roots cannot take the water and nutrients required. the chloride level is found to be the highest at ss-0 and lowest at ss-2 (table 1). cl anion is challenging to be absorbed by soil particles in neutral and alkaline soil [13]. this could be the reason for the lowest chloride measurement at ss2, implying it is the most alkaline among the three samples. although chloride is an essential nutrient for crops, its excessive presence can cause problems like extreme leaf separation, reduced crop growth, curling leaf margins, etc. the results showed that sulfide was the highest at ss-0 and lowest at ss-1 (table 1), yet the results are below the limits. in the case of nitrate, all the samples were reported to have an amount less than 0.05 mg/100 gm. this low presence of nitrate may be because, like other particles of soil that are negatively charged, it leaches into the underground. this also implies the absence of decomposed plant residues and animal compost. furthermore, magnesium is maximum at the farthest soil sample (ss-2) (table 1). since all three values of magnesium amount exceed the reference limit it is indicated that there is the possibility of prohibition to plant growth [14] even more calcium does. the result shows that calcium dropped as we approached ss-2 from ss-0 (table 1). municipal solid wastes like phosphate fertilizers, lime, and gypsum are the sources of calcium, and the figure below indicates the transfer of calcium from ss-0 to ss2. ca is essential to soil and plant health, but the values are above the considered limit, and too much calcium affects the plants’s mineral composition and ionic balance [14]. table 1: physiochemical parameters of soil samples. s.n parameters units results method reference limit ss-0 ss-1 ss-2 1 ph 7.59 7.63 7.76 ph metric 6-9 2 temperature ◦c 25.1 25.1 25.1 electrometric <40 3 conductivity µs/cm 1431 53.5 64.9 electrometric 1000 4 moisture % 22.8 9.2 8.03 oven not stated 5 total hardness (caco3) mg/l 2 1 1 trimetric 0.2 6 chloride mg/l 8.24 0.7 0.65 trimetric 0.25 7 sulphide mg/100gm 10 2.8 6.79 trimetric 250 8 nitrate (no− 3 ) mg/100gm <0.05 <0.05 <0.05 uv-spectrophotometer 200 9 magnesium mg/l 0.3 0.1 0.4 trimetric 0.05 10 calcium mg/l 1.69 0.9 0.6 trimetric 0.15 11 total organic carbon % 0.96 0.82 0.91 walkey-black 0.2 the total organic carbon was the highest at ss0 and lowest at ss-1 (table 1). the highest value at ss-0 might be due to the burning of waste materials on the landfill, as this point is near the landfill [15]. higher soil organic carbon means greater soil structure and a stable carbon cycle, enhancing crop productivity. based on figure 2, ss-2, which lies on agricultural land, shows low possible productivity as compared to other points [16]. deteriorated soil quality with heavy metal accumulations was observed within 10-60m of the dumping site. lead, iron and zinc exceeded permissible limits for agricultural soil. this indicates likely contamination of nearby crops, presenting another exposure route to residents. remediation of affected farm areas should be undertaken to restrict absorption in the food chain. 3.2.2 heavy metals analysis of soil samples for heavy metals analysis of soil samples, it was found that ss-0 possessed the highest values of pb (34.63 mg/100gm) and zn (8.08 mg/100gm), ss-1 possessed the highest values of fe (332.13 mg/100gm) and ni (0.28 mg/100gm) while cd value was identical for all soil samples. similarly, ss-2 had all the lowest values of fe (296.87 mg/100gm), pb (21.28 mg/100gm), zn (2.53 mg/100gm), and ni (0.25 mg/100gm). obtained values of fe and pb exceeded the reference limit, values of zn and cd were below the reference limit, and ni value was within the limit. the result showed the iron variations and provided a maximum value of iron at ss-1 and a minimum at ss-2 (table 2). as suggested by the study [17], the concentration of iron elements is low for aastha gautam et al./ bibechana 21 (2024) 171-179 176 alkaline soil solution, and the same might be the reason for the lowest value at ss-2, which has a peak ph among the three samples. however, the iron level exceeds the prescribed limit at all points. although iron is an essential nutrient contributing to the metabolism process, it can be toxic in an excessive amount by generating fe-catalyzed reactive oxygen species [18]. table 2: heavy metals analysis of soil samples. s.n. parameters units results method reference limit ss-0 ss-1 ss-2 1 iron (fe) mg/100gm 319.8 332.1 296.8 aas 15 2 lead (pb) mg/100gm 34.63 30.83 21.28 aas 10 3 zinc (zn) mg/100gm 8.08 3.14 2.53 aas 60 4 cadmium (cd) mg/100gm <0.003 <0.003 <0.003 aas 0.1 5 nickel (ni) mg/100gm 0.26 0.28 0.25 aas <10 table 2 has shown the descending lead level toward ss-2, which is more than the prescribed limit for all samples. the presence of lead-containing municipal solid wastes in dumping sites like batteries, paints, and plastic and their leakage into the soil may have caused a peak value of the lead-heavy metal at the nearest point. excess lead hinders the photosynthesis process, disturbs the water and mineral uptake, and affects the structure and growth of plants [19]. zinc levels decreased from ss-0 to ss-2 (table 2). the highest value of zinc at the point closest to the site might be due to the waste, slag discharge, and the presence of fertilizers and wood preservatives containing zinc on the dumping site. the maximum amount of zinc is toxic and may threaten the environment and ecosystem [20]. the highest quantity of nickel is found at ss1 and the lowest at ss-2 (table 2). however, the nickel quantities are not contrasting and are within the limit, indicating the acceptable state of one of the essential elements. 3.2.3 impacts of open dumping on water quality 3.3 physio-chemical parameters of water samples from the results obtained for the physio-chemical parameters test, a sample from leachate point (ss0) had the highest values of ph (7.9), conductivity (6640 µs/cm), total suspended solids (tss) (1270 mg/l), total dissolved solids (tds) (3340 mg/l),chemical oxygen demand (cod) (1860 ppm), biological oxygen demand (bod) (228 ppm) and calcium (61.72 mg/l). the upstream sample (ss-1) had the highest value of magnesium (15.56 mg/l).downstream sample (ss-2) had the highest values of total hardness (450 mg/l), sulphate (44 mg/l), and ammonia (3.04 mg/l) while both, nitrate and nitrite nitrogen had values of <0.05 mg/l for all water samples. on the other hand, sw-0 had the lowest value of total hardness (207 mg/l), sw-1 had the lowest values of tss (104 mg/l), cod (72 ppm), bod (36.6 ppm), ammonia (0.17 mg/l) and sulphate (33 mg/l) and sw-2 had the lowest values of ph (7.5), conductivity (502 µs/cm), tds (256 mg/l), calcium (21.64 mg/l) and magnesium (8.75 mg/l). the obtained values of conductivity (for sw0), tss (for sw-0, sw-2), tds (for sw-0), cod, bod, total hardness, and ammonia were recorded above the reference limit. values of conductivity (for sw-1, sw-2), tss (for sw-1), tds (for sw-1, sw-2), nitrate, nitrite nitrogen, sulphate, calcium, and magnesium were recorded below the reference limit, and ph value was within the limit followed. table 3 indicates ph variation in different sampling points. it is maximum at leachate, which might be due to the burning of wood and agricultural waste resulting in ash and slag, which increase the ph value [21]. however, the observed value is slightly alkaline and within the considered limit. aastha gautam et al./ bibechana 21 (2024) 171-179 177 table 3: physio-chemical parameters of water samples. s.n. parameters unit methods samples who limits sw-0 sw-1 sw-2 1 ph ph meter 7.9 7.7 7.5 6.5-8.5 2 conductivity µs/cm electrical conductivity meter 6640 520 502 1400 3 tss mg/l apha 1270 104 262 250 4 tds mg/l tds meter 3340 257 256 500 5 cod ppm apha 1860 72 152 <5 6 bod ppm apha 228 36.6 40.8 <5 7 total hardness (caco3) mg/l apha-2340 207 214 450 120-170 8 ammonia (nh4n) mg/l apha-4500 0.19 0.17 3.04 0.001 9 nitrate (no3) mg/l apha-4500 <0.05 <0.05 <0.05 45 furthermore, the descending conductivity level is found (table 3). a high quantity of inorganic dissolved solids like anions of sulphate and cations of iron on leachate could be the reason for the peak conductivity value on the leachate [22]. high conductivity means the existence of unwanted pollutant levels and can cause deterioration and harm to animals, humans, and plants if consumed for a long time. the amount of tss is lowest upstream, followed by downstream, and then leachate. this could be due to the accumulation of solid waste and leachate following from the dumping site towards downstream. tss is the carrier of toxic heavy metals and other pollutants, resulting in water impurity and turbidity, making plants difficult to grow [22]. tds is proportionally related to the conductivity of the water, which can also be seen in table 3 at top [21]in conclusion, high tds is an indicator of toxic minerals that are harmful to animal and plant health. tds is proportionally related to the conductivity of the water, as shown in table 3. in conclusion, high tds is an indicator of toxic minerals that are harmful to animal and plant health [23]. cod is highest at leachate, followed by downstream (table 3). it is observed that cod has risen with the rise in organic matter content, and leachate water flowing from landfills may have raised the cod level downstream. high cod is an indicator of the high demand for oxygen with low dissolved oxygen [24]. similarly, in table 3, bod is shown to be proportionally related to cod. this shows less oxygen is available for aquatic life at the leachate point [25]. the total hardness variation of water samples is minimum at upstream and highest at leachate. water’s hardness is mainly due to the presence of calcium and magnesium rather than iron and other heavy metals dissolved in water [24]. however, the obtained result does not match the data on calcium and magnesium, which could be due to sampling error. the amount of ammonia in water samples is in diminishing order form from ss-0 to ss-2 (table 3). this condition is in constant order with the ph value [22]. a high ammonia level is unsuitable for aquatic life; however, it can lead to eutrophication and heavy plant growth in water. the amount of nitrate was found to be below 0.05 mg/l in all the sample cases. this finding suggests that nitrate is negatively charged, like other soil particles, and is underground. this supports the low availability of decomposed plant residues and animal remains. the leachate and downstream water samples displayed excess iron, manganese, and other indices above drinking water standards, negatively impacting aquatic habitats. such leachate discharge could have caused algal blooms and biodiversity loss downstream. 3.4 heavy metals analysis of water samples heavy metals analysis for water samples showed sw-0 had the highest values of fe (11.67 mg/l), mn (0.79 mg/l), zn (2.18 mg/l), and pb (0.13 mg/l) (table 4). t-cr, ni,and co were found to be lower than <0.05 mg/l and cd <0.003 mg/l for all water samples. on the other hand, sw-2 had the lowest value of fe (0.45 mg/l) while sw-1 and sw-2 had the lowest value of <0.005 mg/l for zn, t-cr, mn, ni, and the lowest value of <0.001 mg/l for pb and cd. obtained values of fe, mn (for sw0), zn (for sw-0), and pb (for sw-0) were recorded aastha gautam et al./ bibechana 21 (2024) 171-179 178 above the reference limit, and values of mn (for sw-1, sw-2), zn (for sw-1, sw-2), pb (for sw1, sw-2), t-cr, cd, co were recorded to be below reference limit. leakage of rusted ferrous municipal waste, like construction waste, furniture, automobiles, etc., could be the reason for the leachate's high iron level. an excessive amount of iron may take the place of other essential nutrients and thus may lead to nutrient deficiency [26]. table 4: heavy metals analysis of water samples using apha-3111b method. sn parameters units results who limits sw-0 sw-1 sw-2 1 iron (fe) mg/l 11.67 0.7 0.45 0.3 2 manganese (mn) mg/l 0.79 <0.05 <0.05 0.1 3 zinc (zn) mg/l 2.18 <0.05 <0.05 0.05 4 lead (pb) mg/l 0.13 <0.01 <0.01 0.05 5 t-chromium (t-cr) mg/l <0.05 <0.05 <0.05 0.05 6 cadmium (cd) mg/l <0.003 <0.003 <0.003 0.003 7 nickel (ni) mg/l <0.05 <0.05 <0.05 0.02 8 cobalt (co) mg/l <0.05 <0.05 <0.05 0.11 the positive fact is that the manganese (mn) amount is below the who limit (i.e.) in all cases. this will support smooth photosynthesis, chlorophyll production, carotene synthesis, ascorbic acid, and riboflavin. the leachate sample contained the highest zinc (above who’s recommended limit). furthermore, excessive lead, a toxic heavy metal, should be controlled before it enters the water bodies. the consumption of water containing lead causes toxic effects on humans and livestock. the amounts of t-chromium, cadmium (cd), nickel (ni), and cobalt (co) were found to be much below the who’s limit (table 4). this shows that their respective contributions to environmental pollution are very low, which is preferable. 4 conclusion and recommendation the study concludes that open dumping near rivers and burning practices have impacted the 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[22] e.o. nyandwaro. the impacts of solid waste on ground and surface water quality in kisii municipality, kenya, 2017. [23] s. thirumalini and k. joseph. correlation between electrical conductivity and total dissolved solids in natural waters. malaysian journal of science, 28:55–61, 2009. [24] priyanka sharma et al. study of amount of oxygen (bod, od, cod) in water and their effect on fishes, 2014. [25] g. samudro and s. mangkoedihardjo. review on bod, cod and bod/cod ratio: a triangle zone for toxic, biodegradable and stable levels, 2010. [26] g. sorghum. irrigation water chemistry management. in proceedings of the 29th annual central plains irrigation conference, burlington, colorado, 2017. https://eos.com/blog/soil-temperature/ https://eos.com/blog/soil-temperature/ introduction research methodology study area sampling method results and discussion impacts of open dumping on air quality impacts of open dumping on soil quality physio-chemical parameters of soil samples heavy metals analysis of soil samples impacts of open dumping on water quality physio-chemical parameters of water samples heavy metals analysis of water samples conclusion and recommendation bibechana 18 (2) (2021) 117-129 117 effects of lightning as a disaster in himalayan region p. b. adhikari1*, a. adhikari2, a.k. tiwari3 1department of physics, tri chandra m. campus, tribhuvan university, kathmandu, nepal. 2department of electronics and computer engineering, pulchowk campus, tribhuvan university, kathmandu, nepal. 3department of physics, patan m. campus, tribhuvan university, kathmandu, nepal email: pitribhakta_adhikari@hotmail.com article information: received: may 28, 2020 accepted: may 29, 2021 keywords: disaster in himalayan region lightning as a major disaster awareness program lightning hazard potentially hazard areas abstract in nepal, the main disasters are flood, lightning, fire, epidemics, and landslides. among the several disasters in the himalayan region, lightning is an important one. because of the short distance (about 160 km) between the low land and peak mount everest from south to north, there is a variation of about 950c temperature in these regions. the topographical features of the southern slopes and variation of temperature within this short distance influences the features of lightning and in this scenario, we get positive cloud to ground lightning frequently which is more dangerous for human beings, animals and property. in the himalayan region, thunderstorms occur near the mountains due to which more positive charge can easily transfer from cloud to ground. hence positive lightning occurs in the himalayan region. majority of the lightning affected people are unaware of lightning safety and they should know the measures to protect life and property from lightning hazards. hence on conducting awareness program for the people of potentially hazard areas, the number of injured people can be reduced as well as electrical, medical, militarily equipment can be somewhat protected from lightning. doi: https://doi.org/10.3126/bibechana.v18i2.29168 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction nepal is a himalayan country which lies in the northern hemisphere within the latitude 26° 22’ n to 30° 27’ n and elongated along east west with longitude 80° 4’ e to 88° 12’ e. the altitude of the low land is 59 m in the terai region to the maximum height of 8848 m, the height of mount everest. another interesting fact about nepal is the air distance between the low land and the highest mountain of the world mount everest, which is about 160 km due to which there are different environments and climates in different regions. the temperature at the lowlands reaches maximum of about 45° c whereas the minimum temperature at the top of mount everest is about -50° c [1, 2]. hence the temperature difference between the short ranges of about 160 km is 95° c which is the main mailto:pitribhakta_adhikari@hotmail.com https://doi.org/10.3126/bibechana.v18i2.29168 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 118 cause of the diversity of weather and climate. this variety of topography within a short distance produces different types of lightning. as we know, water always flows from higher to lower lands and due to the short distance, the flow of water should be high. this scenario can be seen in the east to the west all over the country. due to this, other disasters such as landslides, floods, etc. can be seen in rainy season frequently which causes loss of human lives and animals along with destruction of physical properties of billions of dollars each year [3]. nepal is mainly divided into three regions: the terai lowlands, the himalayan region in the north with the hilly mountainous region in between. the main disasters in the terai region are flood in rainy season, fire in dry season, epidemics in summer season and lightning in pre-monsoon period. similarly, in the mountainous region, epidemics, flood, landslides, forest fires, hailstorms, soil erosion, lightning are the main disasters while in the himalayan region, glacier lakes outburst, floods, avalanche, etc. are added to this list. according to the disaster report 2015, it mentioned that earthquake, epidemics and lightning are the main disasters all over the country. the data reported during the period of 48 years is mentioned in the following table below. the data presented in this table consists of the death of people due to epidemics, earthquakes, landslides, flood, lightning and fire which are the main disasters of nepal in respective order [4]. lightning is a common natural activity that occurs in the atmosphere. during this process, high energy is released in different forms of energy such as light energy, heat energy, sound energy and other electromagnetic radiations [5, 6]. the cumulonimbus, the primary source of lightning produces the lightning discharge which is called thunder cloud or thunderstorm. thunderstorms produce more than 100 lightning flashes within a minute as mentioned by rakov and uman (2003), and it can generate power in the order of hundred megawatts. they also reported that about 20,000 people are affected by lightning globally and about the same number are injured [7]. besides these people, many animals are affected by the lightning. atmospheric structure and hydrometerological process on the south slopes of the himalayan region in nepal are not well documented as mentioned by barros and lang [8]. the signature of waveform of the lightning electromagnetic field of the mountainous country nepal are of very much interest to the scientific community of the world. because of the geological scenario of the mountainous country nepal, lightning is also taken as one of the largest disasters. the recorded data mentioned in the following tables are not accurately reported as lightning strikes individuals and not to large groups of people, because of which information is scattered and cannot be easily counted [9]. lightning occurs between two surfaces, either cloud and cloud or cloud and ground or cloud and air. among them, if the discharge occurs from a charge center of cloud to the charge center of another cloud, it is called intra cloud discharge. if the charge moves from one center to another center within the same cloud, it is called inter cloud discharge. similarly, if the charge moves from cloud to air it is cloud to air discharge and the discharge that occurs and reaches the ground is called cloud to ground discharge. hence, the lightning may be categorized mainly into two types: a) ground flash b) cloud flash ground flash is the electrical discharge phenomena between the cloud-to-ground whereas the cloud flash includes the inter-cloud, intra-cloud and cloud to air discharge [10, 11]. williams et al. reported that there is a tripole charge structure in the thunderstorm cloud, the negative charge which lies at the center of the cloud, an equal amount of positive charge above the negative charge center, which are called main positive and main negative charges, and some positive charge as a pocket charge on the bottom part of the cloud [12]. the diagram of this charge structure is shown in fig. 1 below. p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 119 fig. 1: tri-pole charge structure of the cloud, negative at the centre part of the cloud, positive at the top part of the cloud and some positive charge at the bottom part of the cloud as a pocket charge. in the cloud to ground discharge, if the positive charge transfers from cloud to ground it is called positive lightning whereas if the negative charge of the cloud transfers to ground, it is called negative lightning. these types of lightning can be seen in fig. 2 below. the lightning current in the strike reaches a peak value of about 30ka in average but the maximum current reaches up to 200ka in negative lightning with the temperature of the stroke during lightning about 30,000 k [7, 13, 14]. they also reported that the positive lightning is stronger than the negative one due to more charge transfer from cloud to ground occurring in the positive lightning. in this case, the current during the lightning process reaches a maximum of 400 ka. due to this high current up to 400 ka and the temperature 30,000 k, which is five times the surface temperature of the sun, lightning is considered a major disaster. baral and mackerras reported that in mountainous country nepal, 28% of total cloud to ground lightning is positive lightning [15]. hence in a himalayan country such as nepal, lightning is a major disaster which can damage not only lives of human beings and animals but also cause fire on buildings, electrical equipment, etc. hence, in this paper, the disaster due to the lightning since 2015, is examined and it has been clearly noticed that the lightning affects human life, animals, buildings, electrical equipment, electrical lines, telecommunication lines, etc. in the himalayan region. fig. 2: different types of the cloud, a represents intra-cloud lightning, b represents negative cloud to ground lightning, c represents positive cloud to ground lightning and d represents cloud to air discharge. 2. instrumentation and methodology in the phenomena of lightning discharge, there are electromagnetic radiations of different wavelengths and frequencies. these radiations travel in all possible directions from discharge channel. these vertical electric field is captured by the horizontal parallel plate antenna [16]. the waveforms were sensed by the antenna fixed on a 1.5 m high post p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 120 which is shown in the fig. 3 below. this antenna is placed on the rooftop of a building at height 12 m above from ground. the signal given by the antenna passing through buffer circuit, which is shown in the fig. 4 below, and is connected to the pico-scope 6404d through a 20 m long rg 58 coaxial cable. the diagram of the picoscope 6404d is shown in the fig. 5. there are mainly positive lightning events, unusual lightning events and cloud events of different flashes recorded from the himalayan region. the electronic circuit which was used in present work for the himalayan region was also used by other several researchers [17-21]. fig. 3: the elevated parallel-plate antenna installed in kathmandu. fig. 4: the electronic circuit inside the buffer amplifier. fig. 5: the diagram of the picoscope 6404d and is connected through rg 58 co-axial cable. 3. observation and discussion nepal is one of the highest risk countries in the world because of its geographical structure in the context of lightning. the northern part of nepal is covered by the high himalayas and the lower southern part consists of plain terai lands and in between are the rugged mountainous region with steep slopes. due to this geographical structure, disasters such as landslides, floods, thunderstorms, thunderbolts, etc. occur very frequently. landslide is the main disaster among these. in the terai region, the main disaster is fire as this region has vast jungles and animal terror is also very common. many people lose their lives as a direct result of natural as well as human induced incidents. there is a great challenge to protect the people, animals and property in the structures from these disasters. the scenario of the incidents along with the data of casualties, lost property and affected families is shown in table 1 below. p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 121 table 1:multi hazard scenario of himalayan region, nepal in 1978 – 2018* types of disaster number of incidents human loss houses damageddeath missing injured affected family fire 12694 1755 2176 265962 90044 lightning 2143 1780 129 3235 7758 1000 landslide 3729 5141 191 2053 559347 34094 windstorm 298 21 95 1718 1279 flood 4368 4628 87 615 3726261 230900 epidemics 3574 16598 44992 513409 0 avalanche 3 17 4 7 1 0 snow storm 7 97 7 0 10 0 hailstones 134 9 24 3407 157 earthquake 175 9771 29142 890995 982855 cold waves 438 563 83 2441 0 others** 1134 626 13 919 3214 2461 total 28597 41006 431 83341 5974523 1342790 *national emergency operation center, ministry of home affairs (neoc, moha) **structure collapse, drowning, boat capsize, animal attack, snake bite and others. as the report given in national emergency operation center, ministry of home affairs (neoc, moha), the multi hazard scenario of nepal by its socio-economic loss during the period of 1971 to 2018, i.e. in 48 years’ period, landslide, flood, epidemic, earthquake, lightning and fire are the main disasters of nepal. in this period, more than 41,000 people lost their lives in the 28,597 incidents of these disasters and 83,341 people were injured. 431 people were missing and 5,974,523 families were affected altogether with 1,342,790 houses being damaged. these scenarios are presented in table 1, which represents the incidents on human beings only but the effects on animals and other beings are not shown. neoc, moha published a report that during the two years 2017 and 2018 only, the estimated loss of npr 6,838,828,320 occurred which is very high in the context of nepal. during this period, 968 people died, 3639 people were injured and 27,255 families were affected by disasters. these numbers are quite high even when no major earthquakes occurred but 4433 houses were completely destroyed whereas 16308 houses were partially destroyed. these data are presented in table 2 below and the bar diagram of these disaster data are represented in fig. 6. since the number of casualties due to epidemics is very high, it is not presented in the bar diagram because of scaling issues. p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 122 table 2: damages and losses of disaster incidents in 2017 and 2018 disasters no. of incidents death injured affected family houses distroyed estimated loss (npr) partial complete flood 418 183 61 16196 14424 286 60,944,400 lightning 432 160 551 618 23 14 14,687,000 landslide 483 161 182 1083 149 328 191,662,000 fire 3973 150 557 6027 549 3234 6,422, 638,013 windstorm 254 19 84 1527 763 301 51,447,998 heavy rainfall 342 30 84 538 193 252 89,415,160 animal terror 141 22 69 280 136 8 4,390,150 epidemics 22 15 1881 420 0 0 high altitude 45 41 6 46 0 0 boat capsize 10 16 9 27 0 0 snake bite 18 14 5 18 0 0 snow storm 2 10 0 10 0 0 hailstones 3 0 0 127 2 0 457,000 cold waves 48 48 0 48 0 0 others** 189 99 150 289 69 10 3,181,599 total 6381 968 3639 27255 16308 4433 6,838,823,320 *source: national emergency operation center, ministry of home affairs (neoc, moha) ** structure collapse, drowning, avalanche and others. among the various disasters of nepal, lightning is a dangerous one not only because of the loss of lives but also to animals, fires in jungle and incident of injuries to living beings, buildings and electrical equipment. nowadays, lightning unknowingly damages various equipment such as television, radio, refrigerator, computer, phone and other electrical components. due to high voltage of lightning, it damages buildings and electrical components. it may cause fire in a building as well. we have observed and recorded the waveforms produced by lightning through the instrument picoscope 6404d in himalayan region of nepal measured from kathmandu, nepal. some of the examples of waveforms observed in the himalayan region recorded from kathmandu are presented in the following figs. (7-9). as we know, nepal has the variation of altitude from about 59m to 8848m within the air distance of 160 km in the cloud which can be seen near the mountains as shown in fig. 10 below. there are various types of lightning are mentioned already, but cloud to ground lightning and cloud to cloud lightning are common. in nepal, we often get unusual lightning activities of unique type and cloud to ground lightning also occurs frequently because of which lightning is more dangerous in nepal. an example of the unusual type of lightning is shown in fig. 7 and one example of positive cloud to ground lightning is presented in fig. 8 below. generally, in positive lightning, the stroke occurs without the stepped leaders but here in the himalayan region, we observed and recorded the stepped leaders with the stroke [22]. the example of the stepped leader with the stroke is shown in the fig. 9. p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 123 fig. 6: the diagram of the data of number of people injured and death due to disaster incidents in 2017 and 2018. as already mentioned, that lightning is one of the major disasters of nepal, we found that more than 100 people lost their lives in each year and more than 300 people were injured annually with more than 6 million npr being lost. the data is presented in the following table 3, in which the casualty of the human lives and human injured are mentioned since 2015ad. p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 124 fig. 7: one example of the unusual waveform and expanded the waveform is presented in incent [23]. fig. 8: one example of the positive lightning waveform recorded in the himalayan region. fig. 9: one example of the positive lightning of return stroke waveform with the stepped leaders recorded in the himalayan region [24]. p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 125 fig. 10: the example of the cloud of tripole charge structure just near the mountain and the positive lightning occurs frequently due to the shorter distances table 3: the data recorded due to lightning in the himalayan region as a disaster year death of the people no. of incidents no. of injured people total estimated cost rs affected family 2015 103 148 187 1000000 60 2016 118 206 240 3321000 259 2017 85 188 251 9125000 258 2018 75 244 300 5562000 360 2019 94 383 451 12208000 529 2020* 34 173 191 6931500 392 total 509 1342 1620 38147500 1858 *up to may 15. 4. effect of lighting there are many impacts of lightning including human casualties and death of animals, the secondary major impacts and effects are on power and tele-communication lines. lightning is not only the death of the people but also its hazardous effects. if there is direct strike of lightning to a person or animal, it causes death but besides the direct strike there may be death or injury depending upon the various factors such as striking distance, magnitudes of the current, step potential etc. people are prone to effects of lightning when they take shelter under tall trees and also in open agricultural fields [25]. the data of the death of the people, injured people etc. are presented here in table 3 and some examples of hazardous effect are shown in fig. 11. the effects of lightning in animals are ten times more dangerous than that of human beings due to step potential and the current flowing inside p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 126 the body through the main organs. we can see just the examples of jajarkoat on 2nd september, 2019 that 233 sheep were killed and 252 sheep were lost due to a single lightning stroke reported by the himalayan times daily newspaper published on 3rd september, 2019. similarly, 250 sheep in sudi village of tila rural municipality-6 in jumla district were killed due to lightning of single stroke just 3 days before on 29th august, 2019, while in the adjacent mountainous region of himachal pradesh in india, more than 200 met the same fate on august 29th. this scenario of that event is also presented in fig. 12 below. they also reported that snowfalls and lightning have been causing a huge loss to the sheep farmers for the past few years. in winter last year, hundreds of sheep were killed due to heavy snowfall. fig. 11: some examples of hazardous effects in the lightning. fig. 12: the example of the loss of animals due to the single lightning stroke in the himalayan region. p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 127 5. results and conclusions most important effect of lightning is the human casualties. it ignites fire on the buildings which converts them into ashes. the lightning current which is very high may destroy electrical, electronic and communication equipment beyond repair. the secondary effects of lightning are not only identified as to cause or mechanism. the sophisticated parts of electronic equipment, military equipment, medical equipment, such as mri, ecg equipment etc. can be destroyed by electromagnetic radiation produced due to lightning. similarly, the electrical power line and communication lines get affected by the radiation due to lightning. the main scope of the study is to conduct awareness program to the general people to spread the information to protect their life, electrical equipment, etc. the lightning hazard map for the stakeholders is to make plan to protect from lightning activities in the potential hazard areas, and for researchers and scientists to continue further research about lightning activities with various factors. mitigation of lightning hazards in the himalayan region is primarily based on the awareness program conducted to the general public and students of school level as well as higher level. even though awareness program conducted about the lightning mitigates the effects and aware people, the number of victims due to lightning strike has considerably increased throughout the years, which can be seen from the table 3. the bar diagram of the number of injured people and number of deaths since 2015 ad are presented in fig. 13. fig. 13: the bar diagram of the data of number of injured and death of people due to lightning disaster since 2015. p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 128 from the above bar diagram, it can be concluded that the number of injuries caused to people is far more than the number of deaths. the ratio of injured people to dead people is also increasing which can be seen in the same diagram. the lightning hazards frequently occurred and the areas of potential hazards are presented in the map of the country given in fig. 14. this information can be used for the preventive purpose to protect from this hazards and to avoid damages to their properties in such areas. this information also can be used in awareness program for the people of hazards area and give suitable instructions to prevent the after effects of lightning. fig. 14: the fatalities due to lightning represented from 13 april 2012 to 11 april 2019 [adopted from nepal disaster risk reduction portal]. acknowledgement we would like to thank for providing the instruments necessary for this research to the international science program (isp), uppsala university, sweden. we would like to express our sincere gratitude to the university grants commission (ugc) sanothimi, bhaktapur, nepal, for sdi research grant of number“srdi – 75/76 s & t – 8”. we would like to thank the trichandra college, tribhuvan university also. references [1] `p. b. adhikari, variation of atmospheric temperature with height in the phenomena of lightning waveforms,world j. ap. phys. 4 (2019) 46. https://doi.org/10.11648/j.wjap.20190404.11. p,b. adhikari e al. / bibechana 18 (2) (2021) 117-129 129 [2] t. wu, d. wang, and n. takagi, intra-cloud lightning flashes initiated at high altitudes and dominated by downward positive leaders, journal of geophysical research: atmospheres 124 (13) (2019) 6982-98. https://doi.org/10.1029/2018jd029907 [3] nepal disaster report, national emergency operation center, ministry of home affairs, government of nepal (2019). [4] nepal disaster report, national emergency operation center, ministry of home affairs, government of nepal (2015). [5] d. j. malan, physics of lightning. english universities press ltd (1963). [6] d. r. macgorman, and w. d. rust, the electrical nature of storms, new york: oxford univeristy press (1998). [7] v. a. rakov, and m. a. uman, lightning: physics and effects, cambridge university press, uk (2003). [8] a. barros, and t. lang, monitoring the monsoon in the himalayas: observation in central nepal, june 2001, monthly weather review 131 (2003) 14081427. [9] c. gomes, lightning, hazard profiles of sri lanka, (2013) pp. 104-23. [10] k. berger, the earth flash. in lightning, physics of lightning, academic press, new york (1977). [11] p. r. krehbiel, the electrical structure of thunderstorm, the earth’s electrical environment, national academy press, washington d. c. (1986). [12] e. williams, the tri-pole structure of thunderstorms, journal of geophysical research 94 (1989) 1315167. [13] m. a. uman, the lightning discharge, dover edition, new york (2001). [14] v. cooray, an introduction to lightning, springer netherlands (2015). [15] k. baral, and d. mackerras, positive cloud-toground lightning discharges in kathmandu thunderstorms, journal of geophysical research, 98 (1993) 10331-10340. [16] p. b. adhikari, measurement of electric fields due to lightning radiation, springer nature switzerland ag, aisc 905 (2020) pp. 38 43. https://doi.org/10.1007/978-3-030-14680-1_5 [17] p. b. adhikari, and s. r. sharma, characteristic features of electric fields radiated by cloud flashes in himalayan region. international journal of antennas and propagation, (2020). https://doi.org/10.1155/2020/6187635. 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[22] p. b. adhikari, s. r. sharma and k. n. baral, features of positive ground flashes observed in kathmandu nepal, journal of atmospheric and solar-terrestrial physics 145 (2016) 106-113. https://dx.doi.org/10.1016/j.jastp.2016.04016 [23] p. b. adhikari, s.r. sharma, k. n. baral, and v. a. rakov, unusual lightning electric field waveforms observed in kathmandu, nepal, and uppsala, sweden, journal of atmospheric and solarterrestrial physics 164 (2017) 172-184. https://dx.doi.org/10.1016/j.jastp.2017.08.028 [24] p. b. adhikari,, investigation of the features of electromagnetic fields due to lightning measured in kathmandu, phd thesis, tribhuvan university, kathmandu, nepal (2019 b). [25] c. gomes, m. ahmed, f. hussain, and k. r. abeysinghe, lightning accidents and awareness in south asia: experience in sri lanka and bangladesh, 28th international conference on lightning protection, iclp (2006). bibechana 17 (2020) 89-95 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal chemical profiling and antioxidant activities of essential oil from the rhizomes of acorus calamus l. sumnath khanal 1 , devi prasad bhandari 2 , laxman bhandari 2 , sabita dangol 1 , achyut adhikari 1 1 central department of chemistry, tribhuvan university, nepal 2 natural products research laboratory, thapathali, kathmandu, nepal * e-mail: achyutraj05@gmail.com article information received: august 10, 2019 accepted: december 01, 2019 keywords: acorus calamus l. dpph assay essential oil ic50 abstract acorus calamus l. is an indigenous herb in nepal. it belongs to family acoraceae and grows in wetland with scented rhizomes. it is also known as sweet flag in english and commonly as bojho in nepal. the present investigation reveals the chemical compositions and antioxidant activity of rhizome essential oil of a. calamus. the essential oil of rhizomes of acorus calamus l. from kaski district, nepal was extracted by hydrodistillation method and volatile constituents were analyzed using gas chromatography-mass spectrometry technique. the antioxidant potential of essential oil was analyzed by 1,1-diphenyl-2picrylhydrazyl (dpph) scavenging assay. a gc-ms analysis revealed the presence of β-asarone (22.38%), α-asarone (14.97%), 1-(4,6-dimethoxy-2,3dimethylphenylethanone (14.24%), isoelemicin (5.68%), cis-methylisoeugenol (4.26%), α-calacorene (4.16%), and other 20 minor components. from dpph assay, half-maximal inhibitory concentration (ic50) value of essential oil was found to be 109.83 µg/ml. these findings have strengthened the a. calamus is good source of compounds like β-asarone, α-asarone and can be used as potential antioxidants. 1. introduction acorus calamus l. belongs to the acoraceae family, is an important medicinal plant of south asia commonly recognized as bojho (in nepali), sweet flag (in english). it is a well-known herbal drug usually used in conventional medicines [1]. it grows as an herb with thick rhizomes in wetlands, mainly marshes [2]. it is widely distributed in south asia along with some countries of europe. the calamus species are used in the treatment of mental ailments, dysentery, chronic diarrhea, bronchial catarrh and abdominal tumors [3]. more specifically, a. calamus is an indigenous herb used in the treatment of fever, cough, bronchitis, inflammation, tumor, skin diseases and some other bacterial and fungal infections [4,5]. as an analgesic, it is used for relief of toothache, this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.25201 http://nepjol.info/index.php/bibechana mailto:achyutraj05@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.25201 bibechana 17 (2020) 89-95 headache, cough, asthma, and bronchitis and as a sedative [6]. additionally, it has significant antibacterial and antifungal properties [7]. the essential oil from the rhizome of a. calamus has been reported to have several biological activities such as antifungal, antibacterial [8] and its ethanolic extract has anti-cellular immunosuppressive properties [9]. monoterpene hydrocarbons, sequestrine ketones, αasarone (2,4,5-trimethoxy-1-propenyl benzene) and β-asarone are the major compounds of rhizome essential oil from a. calamus [10]. β-asarone (42.4% 60.7%) as the major constituents followed by α-asarone (2.6% 7.9%) have been reported from india [1]. however, β-asarone (40.59% 76.33%) as the major constituent, α-asarone (1.29% 10.48%) and some other minor compounds have been reported from nepal [10]. the chemical constituents, yield, and activities are influenced by weather, soil conditions, time of harvest and some other minor factors [11]. indian origin a. calamus has ic50 value 475.48 ± 0.08 µg/ml whereas 11.72 ± 0.03 µg/ml for standard [1]. the essential oil of a. calamus from different markets of nepal exhibited the ic50value 312.64±1.14 µg/ml [12]. antioxidants are the compounds that can slow or retard the oxidation of an oxidizable material, even when used in a small amount (commonly 1−1000 mg/ml) as compared to the amount of material they must protect [13]. the dpph (2,2-diphenyl-1picrylhydrazyl) is a well-known radical and by dpph assay antioxidant potential can be determined. because of a strong absorption band centered at about 517 nm, the dpph radical has a deep violet color in solution, and it becomes colorless or pale yellow when neutralized. this property allows visual monitoring of the reaction. to the best of our knowledge, the chemical profile and antioxidant potential of rhizome essential oil of a. calamus from kaski, nepal has not been investigated yet. so, the objectives of this research are to find its volatile constituents by gc-ms and its role as an antioxidant. dpph, purple antioxidants dpph-h yellow fig. 1: mechanism of antioxidants with dpph radical. 2. materials and methods plant materials rhizomes of a. calamus l. were collected from the togi village of kaski district, nepal in september 2018. the plant species was authenticated at national herbarium and plant laboratories, godavari, nepal. extraction of essential oils the rhizomes of a. calamus l. are washed with clean water and 200 g of it was subjected to .sumnath khanal et al./ hydrodistillation using the clevenger apparatus with 600 ml of distilled water. the extraction of essential oil was continued for 6 hours. the vapors of water along with volatile oils were condensed into a liquid by a condenser which was fitted with clevenger. the essential oil was collected in the bclevenger.oftubemeasuring ofecause immiscible nature, essential oil was separated from water and its volume was noted from which the percentage yield could be calculated. the oil was collected on a small glass bottle and a pinch of anhydrous sodium sulfate was added to remove moisture. finally, the bottle was sealed, labeled and stored in the refrigerator until further analysis. gas chromatography-mass spectrometry (gcms) analysis the chemical composition of essential oil was analyzed by gas chromatography (shimadzu gc 2010) having an rtx-5 ms column (60 m×0.32 mm×25µm) and using helium as the carrier gas. the sample (100 µl) diluted with spectroscopic grade hexane in a ratio 1:10 was injected into the gc inlet maintaining constant flow rate of 0.68 ml min -1 and purge flow 3 ml min -1 in split mode. the initial column temperature was set at 40 o c. the qualitative analysis of oil was further continued in a shimadzu gcms-qp 2010 plus. the ms library used for comparison was ffnsc 1.3, nist 2017. oil components were identified based on their retention indices (ri) and by comparison of their mass spectral fragmentation patterns. dpph assay this is a quick and easy method to analyze the scavenging potential of antioxidants. free radical scavenging activity of essential oil was measured by using 2, 2-diphenyl-1-picrylhydrazyl (dpph) radical, as previously described by jamuna et al. [14]. for this, 100 ml solution of 0.1 mm concentration of dpph was prepared and a stock solution of essential oil of 1 mg/ml.from the sample stock solution 50, 100, 150, 200, 250 μg/ml solutions were prepared. then, to the sample solutions of different concentrations, 1ml dpph solution was added. finally, the absorbance at 517 nm was taken after incubation at room temperature for 30 minutes. ascorbic acid was used as the standard for antioxidants. the percentage of inhibition was calculated by using formula, % i = ac−ao ac × 100% where, ac = absorbance value of the control (1 ml methanol+1 ml dpph solution), ao = absorbance value of the sample solution, and i % = percentage of inhibition the radical scavenging activities of essential oil were expressed in terms of their ic50 values. 3. results and discussion chemical profile the yellow-colored essential oil was obtained and the percentage yield of oil was 0.9 %. the percentage yield of essential oil in this study somewhat different from the previously published reports from india and nepal. the gas chromatogram of oil showed a total of 29 peaks corresponding to total 29 compounds. the oil was further continued in a shimadzu gcms-qp 2010 plus for the qualitative analysis. the ms library used for comparison was ffnsc 1.3, nist 2017, and from it, the 26 oil components were identified based on their retention indices (ri) and by comparison of their mass spectral fragmentation patterns. β-asarone (22.38%), α-asarone (14.97%), 1-(4,6-dimethoxy-2,3-dimethylphenylethanone (14.24%), isoelemicin(5.68%), cismethylisoeugenol (4.26%), α-calacorene (4.16%), are major components and other are minor constituents (less than 3%), shown in table 1. the major components of oil of indian origin were reported to be βasarone (43.4-60.7%), α-asarone (2.6-7.9%), shyobunone (3.4-6.3%) and β isoelemicin (3.2-5.4%) [1]. in the same way, nepalese origin a. calamus has major constituents βasarone and α-asarone are found 40.59% and 1.29% respectively from banke, 76.33% and 10.41% respectively from salyan [10]. this deviation in percentage yield and chemical constituents can be explained in terms of sumnath khanal et al./ bibechana 17 (2020) 89-95 contribution from several factors including age, vegetative cycle stage, climate, seasons, soil composition, altitude, etc. fig. 2: gas chromatogram of rhizome essential oil of a. calamus. the abundant constituents β-asarone (1,2,4trimethoxy-5-[(z)-prop-1-enyl] benzene) and αasarone(1,2,4-trimethoxy-5-[(e)-prop-1-enyl] benzene) are used in killing pests and bacteria [15]. asarone is not metabolized to trimethoxyamphetamine, which has been reported by online vendors [16]. the council of europe committee of experts on flavoring substances concluded that β-asarone is clearly carcinogenic and has proposed limits for its concentration in flavorings such as bitters made from a. calamus [17]. β-asarone exhibits antifungal activity by inhibiting ergosterol biosynthesis in aspergillus niger [18]. antioxidant activity dpph assay is fundamentally based on the capability of dpph free radical which is discolored in the presence of antioxidants present its sample. the results of the antioxidant activity of this study are demonstrated below. the ic50 values of ascorbic acid and essential oil of a. calamus was calculated and shown below in table 2. the half inhibitory concentration (ic50) of a. calamus oil was found to be 109.83 µg/ml whereas that of standard ascorbic acid is 25.38 µg/ml. this implies that a. calamus oil has 0.231 times antioxidant potential than that of ascorbic acid. these results are in close agreement with the previous report suggested by bhandari et. al., [12] which revealed that the antioxidant property of a. calamus oil is 0.277 times than that of ascorbic acid. in the same way, this result also correlated with the report suggested by parki et al. [1]. abundance retention time (minutes) sumnath khanal et al./bibechana 17 (2020) 89-95 https://en.wikipedia.org/wiki/pest_(organism) https://en.wikipedia.org/wiki/carcinogen https://en.wikipedia.org/wiki/bitters https://en.wikipedia.org/wiki/acorus_calamus table 1. the chemical composition of rhizome essential oil of a. calamus. peak retention time retention index area % name of the compounds identification methods 1 9.397 831 0.36 furfural ri, ms 2 18.02 1046 0.41 β-ocimene ri, ms 3 34.158 1375 0.54 1,3-dimethyl-8-propan-2-yltricyclo [4.4.0.02,7] dec-3-ene ri, ms 4 34.794 1398 0.38 1-ethenyl-1-methyl-2,4-bis(prop-1-en-2-yl) cyclohexane ri, ms 5 36.138 1419 0.52 isoledene ri, ms 6 36.707 1434 0.68 calarene ri, ms 7 37.42 1455 4.26 cis-methylisoeugenol ri, ms 8 37.12 1463 1.59 2,3-5,6-bis(1,5-octanediyl)-2,5-dibora-1,4dioxane ri, ms 9 39.282 1491 0.73 viridiflorene ri, ms 10 39.389 1497 0.40 α-muurolene ri, ms 11 40.323 1543 2.91 cedrol ri, ms 12 40.617 2.01 δ-cadinene ms 13 40.323 1537 2.21 9cedranone ri, ms 14 40.617 1538 1.18 (2s,3s,6s)-6-isopropyl-3-methyl-2-(prop-1-en2-yl)-3-vinylcyclohexanone ri, ms 15 40.676 1544 4.16 α-calacorene ri, ms 16 41.203 1550 0.97 elemicin ri, ms 17 41.409 1565 5.68 isoelemicin ri, ms 18 42.144 1614 2.30 acorenone b ri, ms 19 43.755 1617 22.38 β-asarone ri, ms 20 44.101 8.19 21 45.182 1634 14.24 1-(4,6-dimethoxy-2,3-dimethylphenyl) ethanone ri, ms 22 44.284 1635 2.48 isolongifolol ri, ms 23 44.747 1659 0.76 24 45.097 1659 0.59 cadin-4-en-10-ol ri, ms 25 45.933 1663 1.1 6-methyl-2-(4-methylcyclohex-3-en-1-yl) hepta-1,5-dien-4-ol ri, ms 26 46.301 1679 14.97 α-asarone ri, ms 27 46.442 1683 0.91 (5-methyl-8-propan-2-yl-3,4,4a,7,8,8ahexahydronaphthalen-2-yl) methanol ri, ms 28 47.723 0.9 29 48.981 1771 2.18 4α-hydroperoxy-2,5,5,8α-tetramethyl-4methylidene-7,8-dihydro-6h-chromene ri, ms sumnath khanal et al./bibechana 17 (2020) 89-95 0 10 20 30 40 50 60 70 80 90 100 0 20 40 60 80 100 120 % in h ib it io n concentration(µg/ml) ascorbic acid a. calamus fig. 3: percentage inhibition vs concentration plot of ascorbic acid and a. calamus esssential oil table 2: ic50 values of standard ascorbic acid and a. calamus essential oil. s.n name ic50 (µg/ml) 1. standard ascorbic acid 25.38 2. the essential oil of a. calamus 109.83 4. conclusions the rhizome essential oil of a. calamus from kaski, nepal was analyzed by gc and gc-ms and was found to be rich of β-asarone, α-asarone, asarone, α-calacorene and cis-methylisoeugenol. furthermore, essential oil of rhizome of a. calamus is a good source of antioxidants. acknowledgment we would like to express our sincere gratitude to department of plant resources for providing lab facilities to conduct this research work. financial support (award no. mrs/74_75/s&t-24) to mr. sumnath khanal from university grant commission (ugc) is heartily acknowledged. references [1] a. parki, p. chaubey, o. prakash, r. kumar, and a. k. pant, seasonal variation in essential oil compositions and antioxidant properties of acorus calamus l. accession, medicines 4(2017) 81.doi:10.3390/medicines4040081 [2] p. a keddy, wetland ecology: principles and conservation, 2 nd edition, cambridge university press: cambridge, uk, 2010; chapter 1. [3] v. v. paithankar, s. l. belsare, r. m. charde, and j. v. vyas, acoruscalamus: an overview. int. j. biomed. res. 2(2011) 518-529. sumnath khanal et al./bibechana 17 (2020) 89-95 [4] r. s. parab, and s. a. mengi, hypolipidemic activity of acoruscalamus l. in rats.fitoterapia 73(2002) 451–455. [5] r. shukla, a. kumar, c. s. prasad, b. srivastava, and n. k. dubey, efficacy of acoruscalamus l. leaves and rhizome on mortality and reproduction (coleoptera:schinensisbruchucallosoof bruchidae), appl. entomol. zool. 44(2009) 241– 247. [6] m.b. bajracharya, ayurvedic medicinal plants and piyusavarsikathmandu,treatmentgeneral ausadhalaya, 1979. [7] p. m. davidson, methods for testing the efficacy of foodantimicrobials,food technology 43(1989)148-155. [8] p. w. grosvenor, a. supriono, and d. o. gray, anti-bacterial and anti-fungal activity of medicinal plants from riau province sumatra indonesia, journal of ethnopharmacology 45(1995) 97-111. [9] s. mehrotra, k. p. mishra, r. maurya, r. c. srimal, v. s. yadav, r. pandey, and v. k. singh, anti-cellular and immunosuppressive properties of ethanolic extract of acorus calamus rhizome, international immunopharmacology 3(2013) 5361. [10] t. d. bhatt, p. yadav, a. dhungana, j. joshi, and c. basyal, 2018. study of the variation of major chemical constituents of essential oil extracted from rhizome and leaf of acoruscalamus l. (bojho) from nepal, journal of plant resources16(2018) 96-99. [11] h. boira, and a. blanquer, environmental factors affecting chemical variability of essential oils in thymus piperella l. biochemical systematics and ecology26(1998) 811-822. [12] d. p. bhandari, r. ranjitkar, and l. bhandari, antioxidantsofdeterminationquantitative potential of five selected essential oils of origin,nepalese plantofjournal resources16(2018) 84-89. [13] r. amorati, m. c. foti, and l. valgimigli, antioxidant activity of essential oils, journal of agricultural and food chemistry 61(2013) 1083510847. [14] s. jamuna, s. paulsamy, and k. karthika, screening of in vitro antioxidant activity of methanolic leaf and root extracts of hypochaerisradicata l. (asteraceae), journal of applied pharmaceutical science 2(2012) 149-154. [15] d. s. asha, and d. ganjewala, antimicrobial activity of acoruscalamus rhizome and leaf extract, acta biol. szeg. 53(2009) 45–49. [16] k. björnstad, a. helander, p. hultén, and o. beck, bioanalytical investigation of asarone in connection with acoruscalamus oil intoxications, journal of analytical toxicology 33(2009) 604-609. [17] p. k. mukherjee, v. kumar, m. mal, and p. j. houghton. in vitro acetylcholinesterase inhibitory the activity of the essential oil from acoruscalamus and its main constituents, plantamedica 73(2007) 283-285. [18] r. venkatesan, p. s. karuppiah, g. arumugam, and k. balamuthu, β-asarone exhibits antifungal activity by inhibiting ergosterol biosynthesis in aspergillus niger atcc 16888, proceedings of the national academy of sciences, india, section b: biological sciences, 2017, 1-12. sumnath khanal et al./bibechana 17 (2020) 89-95 microsoft word bohara et al (122-130)-corrected narendra bahadur bohara et al./ bibechana 16 (2019) 122-130: rcost p.122 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal investigation of the firing temperature effects on clay bricks of kathmandu valley (nepal); part-i: mineralogical phase characterization narendra bahadur bohara1, lal bahadur bhat1, dol bahadur ghale1, nirjan duwal2, jagadeesh bhattarai1* 1central department of chemistry, tribhuvan university, gpo box 2040, kathmandu 2st. xavier college, thapathali, kathmandu, nepal *e-mail: bhattarai_05@yahoo.com article history: received 25 august, 2018; accepted 9 october, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21319 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract present research work was focused to investigate the firing temperature effects on mineralogical phase composition of nine clay bricks collected from the brick factory of kathmandu valley using x-ray diffraction (xrd) patterns and fourier transform infrared (ftir) spectra analyses. main mineralogical phases of quartz, feldspars, spinel, mullite and hematite in the brick specimens fired at different firing temperatures including muscovite type of mica mineral in the sun-dried brick specimen are identified from xrd and ftir analyses. disappearance of the muscovite type of mica clay mineral with feldspars enhanced to form alumina rich spinel phase at firing 900° to 1000° c, and finally the primary mullite phase in the fired clay brick samples is clearly observed at 1100° c firing temperature. keywords: brick; firing temperature; phase composition; clay minerals; xrd; ftir. 1. introduction the clay brick is one of oldest building materials yet known and its widespread use is mainly due to the availability of clay minerals used for the production and durability in both load bearing and non-load bearing structures. it was a fundamental building material in the mesopotamian, egyptian and roman periods and the use of clay brick was increased and became specialized in order to maximize its benefits during the roman period [1].the durability of the bricks is its ability to withstand an applied load without failures [2]. the clay brick is used extensively in the construction industry all over the world. the global brick production is estimated about 1.5 trillion annually [3] and asian countries only accounts about 89-90 % of the global production, i. e., about 1.35 trillion bricks [4]. the clay brick production in kathmandu valley is estimated more than 3.3 billion units and with increasing demands of the clay bricks for construction industry, bricks quality and cost become more important nowadays [5]. narendra bahadur bohara et al./ bibechana 16 (2019) 122-130: rcost p.123 (online publication: dec., 2018) there are different types of clay bricks and are divided into various groups based on their mineralogical compositions, uses [6] and quality and appearance [7]. the main factor to manufacture these bricks is the clay raw material types used and the firing temperature during their production, because both of these affect the quality and durability of bricks [8-11]. the firing of clay bricks at high temperature is generally practiced to obtain coherent clay bricks with controlled microstructures, because the presence of pore in the fired bricks at low firing temperature is generally one of the causes for showing their low mechanical strength [12]. depending on the degree of firing, the porosity and water absorption capacity of the clay brick samples may vary. the fired clay brick is extremely durable and is perhaps one of the man-made building materials so far. it is said that the durability (i. e., mechanical) properties of the clay bricks depend mainly on their mineralogical and physico-sintering properties. furthermore, the physico-sintering properties of the clay brick depend on the mineralogical composition of the clay minerals used to manufacture it, the manufacturing process and firing temperature [13]. the mineralogical, physico-sintering and mechanical properties of clay bricks are varied depending on the degree of firing at high temperature and these properties are interrelated to each other. the physico-sintering and mechanical properties of different clay bricks were investigated at different firing temperatures and the brick sample fired at 1100 °c showed the best mechanical properties [12, 14-17]. it was reported that the firing temperature was the key factor to modulate the physico-sintering and mechanical properties of clay bricks, not so much affected by firing time [18].similarly, it was reported that the apparent porosity and water absorption capacity of the fired clay bodies were decreased with increasing their firing temperature, while the bulk density and young’s modulus of elasticity of the bodies were increased with increasing the temperature [14, 17]. the quality assessment of different types of clay bricks is based on their mineralogical, physico-sintering and mechanical properties. however, such technical properties of the clay bricks [19, 20] and ceramic tiles [21, 22] of nepal were studied by very few research groups in nepal. considering these facts, the present research work is focused to carry out an investigation of the firing temperature effect on the mineralogical phases of the fired clay brick samples by xrd and ftir analysis. 2. materials and methods nine pieces of sun-dried clay brick sample specimens and one piece of fired clay brick sample from factory of shiddi vinayak chimney vatta udhyog of lalitpur (nepal) were collected in this study. among these nine pieces of the sun-dried clay brick samples, eight pieces were fired at 700o, 750o, 800o, 850o, 900o, 950o, 1000o and 1100o c using muffle furnace maintaining two hours as a soaking period and remaining one piece of the sun-dried clay brick sample was used to identify their mineralogical compositions using xrd and ftir spectroscopic techniques. among these nine brick samples, only four samples of nb-0 (sun-dried), nb-900 (fired at 900° c), nb-1000 (fired at 1000° c) and nb-1100 (fired at 1100° c) were selected to carry out present research work. a small broken piece of each brick sample specimens was thoroughly hand grounded in agate mortarto make a fine powder for xrd and ftir analyses. mineralogical phase characterization of the clay brick samples was carried out at nepal academy of science and technology (nast), khumaltar, lalitpur using xrd analysis on a d8 advanced diffractometer (bruker, germany) with cukα radiation (λ = 0.15418 nm) at a scanning rate of 2o/minute in 2θ mode between 10° and 70°. major and minor phases present in all the brick powder samples used to record for the xrd measurement were identified from their basal spacing (d-spacing) in accordance with corresponding jcpds database files [23]. the brick powder sample was loaded in an xrd sample holder in a randomly orientated way to minimize preferred orientations of clay minerals. furthermore, identification of the mineralogical phase present in three fired clay brick samples at 900°, 1000° and 1100° c and one sun narendra bahadur bohara et al./ bibechana 16 (2019) 122-130: rcost p.124 (online publication: dec., 2018) dried sample used in this study were qualitatively analyzed with the help of their recorded ftir spectra using ir-tracer-100 (shimadzu, japan). 3. results and discussion mineralogical phases present in the powder form of the sun-dried brick collected from the local factory of kathmandu valley and its fired clay brick samples at three different firing temperatures of 900°, 1000° and 1100 °c raw materials were identified with the help of the xrd patterns as shown in figs 1-4. the mineralogical phases identified in the powder sample of the sun-dried clay brick (i.e., nb-0) are mainly of muscovite type of mica mineral with feldspars, quartz and hematite as shown in fig. 1. however, the mineralogical phases existed in other three fired brick samples of nb-900, nb-1000 and nb-1100 fired at the temperature of 900°, 1000° and 1100 °c, respectively, are found to be almost same phases, i.e., quartz, feldspars, alumina rich spinel and hematite including mullite as shown in figs 2-4.in particular, the fired clay brick sample of nb-1100 shows the xrd peaks of mullite including quartz, feldspars, spinel and hematite as shown in fig. 4. this result revealed that the muscovite type of mica mineral present in the sun-dried brick sample is found to be disappeared in the range of 900° -1100° c firing temperature. on the other hand, the mullite phase is not observed for the sun-dried and fired clay brick samples of nb-0, nb-900 and nb-1000 as shown in figs 1, 2 and 3, respectively. consequently, it can be said that the mineralogical phases developed in the fired clay brick samples produced by firing at different temperatures are different and hence their physico-sintering and mechanical properties should be different. these results show that the disappearance of the muscovite type of mica clay mineral with decreasing the intensity of feldspars diffraction peak and appearance of spinel phase and finally the mullite peaks in the fired clay brick samples is clearly observed with increasing the firing temperature from 900° to 1100 °c. fig. 1: xrd patterns of the sun-dried brick sample of nb-0. narendra bahadur bohara et al./ bibechana 16 (2019) 122-130: rcost p.125 (online publication: dec., 2018) it was reported that alumina-rich spinel phase was appeared in the ceramic bodies after fired at above 900° c and the spinel phase was lost and mullite crystals begin to develop at about 1050°-1200° c and the spinel phase completely disappeared with increasing firing at 1200 °c and the mullite phase becomes very pronounced [24]. this type of research results of the effect of firing temperature on the development of phases in the ceramic bodies could be helpful to identify the firing temperature of the locally available clay brick samples. it is generally assumed that the physico-sintering and mechanical properties of the fired ceramic bodies depend on the mineralogical composition, defects or faults developed during the firing of the ceramic bodies at high sintering temperatures and impurities [25-28]. for example, the presence of hematite, calcite and dolomite, as impurities of the ceramics raw materials was reported to be one of the causes for low mechanical strength of the fired ceramic bricks at high temperature [29]. in this study, the fired brick samples show the presence of hematite phases, although no indication of the presence of calcite and dolomite phase as impurity. fig. 2: xrd patterns of the brick sample of nb-900 fired at 900° c. ftir spectra analysis of four clay brick samples of nb-0, nb-900, nb-1000 and nb-1100 prepared by sun-dried, fired at 900°, 1000° and 1100° c, respectively, was carried out for the mineralogical phase identification and the results are depicted in fig. 5. the two absorption peaks at 3725 and 3600 cm–1 are almost diminished for all brick samples used in this study which is attributed to oh stretching vibration of hydroxide in the brick samples. this absorption band region should be accompanied by an absorption band in the region of 1620-1650 cm-1 assigned to h-o-h bending of adsorbed water molecules [30, 31], although there is not clearly observed the ftir peak is in this region for all four different clay bricks. the ftir absorption peak at 2975 cm-1 particularly for the brick samples of nb-900 and nb-1000 as depicted in figs 5(b) and 5(c), respectively, indicated that these brick samples should contained small amount of organic matters which is diminished by firing at about 1100 °c for nb-1100 as sown in fig. 5(d). the similar observation was reported in previous researchers also [32]. narendra bahadur bohara et al./ bibechana 16 (2019) 122-130: rcost p.126 (online publication: dec., 2018) fig. 3: xrd patterns of the brick sample of nb-1000 fired at 1000° c. fig. 4: xrd patterns of the brick sample of nb-1100 fired at 1100° c. the ftir absorption bands for clay minerals show si–o stretching and bending as well as oh bending absorptions in 1300–400 cm–1 range. the si–o stretching vibrations of clay minerals give several well resolved strong bands in the 1100–1000 cm–1 region [33]. the ftir spectra of the sun-dried clay brick sample and the fired brick samples show the absorption band at 1033 cm–1 attributed to the si–o stretching vibrations and the absorption bands at 515 and 445 cm–1 assigned to si–o–al narendra bahadur bohara et al./ bibechana 16 (2019) 122-130: rcost p.127 (online publication: dec., 2018) (octahedral al) and si–o–si bending vibrations, respectively. a very broad absorption band in the range at 515 cm-1 in all the clay bricks used to analyze in this study indicated that the fired clay brick bodies available in kathmandu valley contain a trace amounts of hematite. the ftir absorption peak at 1033 cm–1 attributed to the si–o vibrations of the tetrahedral sheet of the clay raw minerals of the fired brick sample and a new absorption peak at 1050–1040 cm–1 assigned to si–o vibrations of amorphous silica with a three dimensional framework originated from firing treatment [34]. fig. 3: ftir spectra of four brick sample specimens of the (a) sun-dried and fired at the temperature of (c) 900°, (c) 1000° and (d) 1100° c. the ftir spectra of all these sun-dried and fired clay brick samples showed that they are mainly composed of quartz (1050, 1033, 1015, 796, 725, 650 and 445 cm–1). it is meaningful for mentioning here that the previous research work was reported a ftir absorption peak chosen at around 796 cm–1 to be more suitable for quantitative amounts of quartz in clay bodies [35]. on the other hand, the presence of feldspar can be explained by si–o–al compounded vibrations at 775–780 cm–1. these assignments are in good agreement with that previously reported for quartz and feldspar [36]. the presence of quartz in the clay brick samples can be explained by si–o asymmetric bending vibration at 445 cm–1 and si–o symmetric bending vibration at 693 cm–1. on the other hand, the presence of feldspar can be explained by si–o–al compounded vibration at 775 cm–1 and symmetrical bending vibrations at 570-556 cm–1. these assignments are in good agreement with that previously reported for quartz and feldspars ftir absorption peak value [37]. the absorption band at 775–780 cm–1, which is a complementary peak of 796 cm–1 band, is attributed to the presence of quartz [38]. in the narendra bahadur bohara et al./ bibechana 16 (2019) 122-130: rcost p.128 (online publication: dec., 2018) present work, quartz is identified as predominant and makes the clay self-tempered during firing of clay raw materials at high temperature to produce the clay brick samples. these ftir analysis results are in agreement with the results obtained from xrd analysis as shown above in figs 1-4. 4. conclusions the investigation of the firing temperature effect on the mineralogical phase developed in the clay brick samples of kathmandu valley was studied using xrd and ftir techniques. following conclusions are drawn from the above results and discussion. i. mineralogy phases in the brick samples used in present study are found to be composed mainly of quartz, feldspars, spinel, hematite including muscovite type of mica mineral based on the xrd patterns and ftir spectra analyses. ii. the decreased in the intensity of the diffraction peaks of feldspars and appearance of the alumina-rich spinel phase in the brick samples fired at the range of 900°-1000° c is clearly observed. iii. the alumina-rich spinel phase formed on the fired brick samples enhanced to form the primary mullite phase at 1100° c firing temperature. acknowledgement the university grants commission-nepal (ugc-nepal) is highly appreciated for awarding the faculty research grant-2072/073 to conduct this research work in central department of chemistry, tribhuvan university. references [1]. f.m. fernandes, p.b. lourenço and f. castro, ancient clay bricks: manufactureand properties, inmaterials, technologies and practice in historic heritage structures. chapter-3 (eds dan, m.b., přikryl, r. & török, á.), springer, dordrecht (2010) 29–48. 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[38]. m.m. jordan, a. boix, t. sanfeliua and c. de la fuenteb, firing transformations of cretaceous clays used in the manufacturing of ceramic tiles. applied clay science 14(4) (1999)225–234. https://doi.org/10.1016/s0169-1317(98)00052-0. bibechana 18 (1) (2021) 231-239 231 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal pyrolyzed human hair: a review on synthesis, characterization and applications tika ram bhandari 1,2, bidit lamsal 2,3, rameshwar adhikari 2,3* 1tribhuvan university, central department of physics, kathmandu, nepal 2tribhuvan university, research center for applied science and technology, kathmandu, nepal 3tribhuvan university, central department of chemistry, kathmandu, nepal *email: ram.adhikari.tu@gmail.com, r_adhikari@recast.edu.np article information: received: june 23, 2020 accepted: september 3, 2020 keywords: hair, pyrolysis, biomedicine sensors microscopy spectroscopy abstract human hair, a common biowaste, can be pyrolyzed to prepare many kinds of functional materials. pyrolyzed hair has been used as in various forms of traditional medicine, sensor, ink and electrolytes. this review highlights the major structural characteristics of human hair and its pyrolyzed form. it also addresses the characterization techniques used for the structure elucidation of pyrolyzed human hair as well as its potential applications.. doi: https://doi.org/10.3126/bibechana.v18i1.29601 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction hair is the collection of the pigmented filaments of keratin growing from the skin of the humans and mammals. it forms a covering for a part of the head and/or for other parts or the whole body. each filament is divided into three major compartments: cuticle, cortex and medulla. depending upon types of origin, diameter of hair varies from 50 µm to 100 µm. hair filament is composed of keratinized dead cells [1] and has alpha keratin, beta keratin and matrix proteins and low sulphur. generally, the hair fiber contains 50-60% α-keratins, 20-30% matrix proteins and different pigments like melanin, water (up to 30%), lipids (structural and free), and trace elements [2]. toughness of hair is due to the accumulation of the α-keratin which forms a micro fibrous structure called as intermediate filaments (kifs). helical protein with 20 to 50 amino acids is found in human hair which includes amino acids such as; glycine, alanine, valine, isoleucine, leucine, phenylalanine, tyrosine, lysine, arginine, ornithine, histidine, citruline, glutamic acid, threonine, serine, cystine, methionine, cystiene, cysteic acid, proline, and tryptophan. however, aspartic acid and glutamic acid exist as the primary amides and free acids respectively in human hair. among them, cystine is the major form of amino acid. a very strong crosslinked sulphide bond, called disulphide linkage, is found between two cystine amino acid groups in two neighboring helical chains. the http://nepjol.info/index.php/bibechana mailto:ram.adhikari.tu@gmail.com https://doi.org/10.3126/bibechana.v18i1.29601 https://creativecommons.org/licenses/by-nc/4.0/ tika ram bhandari et al. / bibechana 18 (1) (2021) 231-239 232 matrix protein which impart such disulphide linkage and glue the two chains together are termed as keratin associated proteins (kaps) [3]. morphology of human hair of different people of different origins was studied with the help of scanning electron microscopy (sem). the sem investigations on three different kinds of hairs are presented in figure 1. sem micrographs reveal that, people of different origins have dissimilar hair structures. the observed variations in the structure are associated with keratin genes and keratin associated proteins (kaps). there are altogether 17 human hair keratin genes and more than 85 kaps genes have been recognized [4]. fig. 1: lower (left) and higher (right) magnifications sem images of caucasian (a), asian (b), and african (c) hair [5] sem images (figure 1) at lower magnification show that caucasian hair has much smaller (50 µm) diameter than the african (80 µm) and the asian (100 µm) hairs. highly magnified micrographs of the hair at the scalp region reveal that the cuticle of each type of hair has scaled laminar structure. however, the asian hair has more folded structure than the others. similarly, sem on a single hair filament of caucasian was used to study the morphological variation at three different parts of human hair by wei g. et al [5]. sem images of the hair at low resolution show the diameter of hair at scalp and middle region is almost same but slightly smaller diameter is observed towards the tip region. sem images at higher magnification further reveal that cuticle is fully developed and organized towards the bottom region of the hair. fig. 2: sem images of single strand of the human hair near scalp (a), at the middle (b) and near the tip (c) at different magnifications showing the cuticle is gradually lost from bottom to the tip region [5] cuticle deposition gradually decreases from middle to tip region. it was reported that the tip region of the human hair has no outer covering cuticle. cuticle content on different parts of hair depends upon the mechanical damage faced by hair such as friction and combing. therefore, it can be deduced that the tip region has no cuticle due to high mechanical stress, middle region has intermediate and bottom or near scalp region has no any mechanical damage [5]. additionally, chemical composition of hair makes it very slow degradable. deposition of the chemicals such as like cystine, cysteic acid, proline, serine, isoleucine, leucine, methionine, theorine, throsine, phenylalanine and arginine, is more in cuticle than other part of the hair [6] which reduces tika ram bhandari et al. / bibechana 18 (1) (2021) 231-239 233 the degradability of hair. therefore, human hair is generally considered as useless waste in the society. this waste produces a foul smell and burning of hair in the open surrounding produces an unpleasant odor along with harmful gases such as ammonia, carbonyl sulphides, hydrogen sulphides, sulphur dioxide, phenols, nitriles, pyrroles and pyridines [7, 8]. nowadays, it has become challenge to control this biological waste. alternately, hair can be used for various purposes in modified and unmodified forms. systematic reduction and reuse of this waste may improve our periphery as well as contribute our economy. hair fibers are made up of strong filaments which can be used as scaffold for tissue engineering application because of human origin and cytocompatibility [9]. many studies on human hair have demonstrated that keratin can be used to develop the biomaterials for biomedical applications, for making keratin films, keratins sponges, and scaffolds and also used in the tissue engineering and regenerative medicine. due to the high sulphur content, ability of selfassembly and intrinsic cellular identification, keratinized biomaterials has several distinct merits over pre-existing biomolecules [2, 10]. in past days, researches were conducted to extract the keratin at wet condition and many research papers, as well as patents have been published. however, there is only handful of publications on the study of pyrolyzed human hair. first use of the pyrolyzed human hair was documented by a chinese herbalist li shi-zhen in his book ben cao gang in 16th century [11]. the main emphasis of this review is to collect information from previous work in one paper and to find out some gaps on it for possible future research. 2. pyrolysis of organic matter and hair dense efforts have been conducted for minimizing the problem of the municipal waste like hair fiber. |hair fiber as composite material, pest controlling agent and some biomedical applications has been minimizing the risk due to the hair fiber [8]. another way to control this organic waste is pyrolysis. it is the process to change any organic matter in the absence of oxygen to obtain an array of solid, liquid and gas products. pyrolysis is widely used for production of a wide range of solvents, chemicals, fuels and other products from biomass. pyrolysis can be done into three ways; low temperature (< 550 ºc), moderate temperature (550 ºc to 800 ºc) and high temperature (>800ºc). slow conventional pyrolysis includes irreversible thermal decomposition of the organic matter for the production of biomass as well as charcoal. solid after the pyrolysis contain char, ash and unchanged biomass. heating rates, temperature and quenching phenomenon determine the nature of product like fraction occupied by the organic ashes in char after pyrolysis. when the char has appropriate pore structure and surface area, it can be used in the preparation of active carbon [12, 13, 14]. the liquid produced from pyrolysis can be used as fuel and raw materials for synthesis of fine chemicals, fertilizers, and adhesives etc. [15, 16]. pyrolysis of the human hair at moderate temperature yields a black, shiny solid product. pyrolyzed human hair has several significant applications. pyrolysis transforms the nondegradable hair as a degradable one. the char after pyrolysis of human hair can be used as medicine [8]. it contains pore structure and has high surface area so that they are highly applicable for the electrode in the supercapacitors. study carried on it reveals, the pyrolyzed hair contain heteroatom doped carbon and heteroatom doped carbon has higher performance on the oxygen redox reaction in electrochemical catalytic system. few studies were carried on the pyrolyzed human hair in order to investigate its conductive properties, capacitive properties and production of quantum dots [2, 17, 18]. details about the past studies are involved in the application part of this paper. 3. applications of pyrolyzed human hair some important application of the pyrolyzed human hair includes; medicine, electrodes, art and paintings, sensor and others are described below: tika ram bhandari et al. / bibechana 18 (1) (2021) 231-239 234 biomedicine in ancient period, pyrolyzed hair was taken as an important medicine. the first use of the pyrolyzed hair for medical application was mentioned by the chinese herbalist by the name of ‘xue yu tan’. he described more than 11,000 therapeutic medicines. carbonized hair, which is referred to as crinis carbonisatus, is one of them, which was used to increase blood clotting and wound healing [2, 11]. ash of organic matter is also reported as an important natural biomedicine. ash of wood chip, buffalo dung has been used for wound healing [19] and the smoke from the pyrolysis of the keratinized materials like hair, feather have been reported for anesthesia of the honey bees. hydrogen sulphide produced during pyrolysis was found as a main agent for anesthesia of honey bees on that study [20]. rural communities of south asian countries still use pyrolyzed hair for long term recovery and fast pain relief on the open wound [21]. but the systematic study of the pyrolyzed human hair as biomedicine has not been reported yet. moreover, the chemical agents present in pyrolyzed human hair and responsible for the blood clotting and wound healing still remain a mystery. art and painting in 2014, the straits times published an article about the use of human hair as art and its carbonized material as ink. chinese artist gu wenda worked on his different formulations for painting in which he used paper made from green tea and the ink made of the carbonized hair [22]. hence, use of pyrolyzed hair in production of ink and use of the hair as art provides a new path for reducing waste through traditional method and also innovation on ink making quantum dots for sensor quantum dots are the particle which is form due to the excessive size reduction; so that the three dimension structure reaches the nanometer range [23]. the production cost of the nanoparticles is generally high. however, the recent research shows a highly fluorescent carbon quantum dots can be obtained from the thermal treatment of the hair. black solid product obtained after thermal treatment of the human hair at 200 ºc for about 24 hours which after dissolution and centrifugation change into carbon quantum dots solution. direct thermal treatment yield more carbon quantum dots (cqds) than hydrothermal treatment of hair. these carbon quantum dots are highly useful in sensory of various metal ions like hg2+, ag+, cu2+and fe3+ and also very useful for testing of water purification. guo et. al reported that cqds can detect the minimum level up to 10 nm of hg2+ as shown in figure 3(b)[24, 25, 26]. fig. 3: fluorescence emission spectra of cqds showing peak at 415 nm which decreases with the concentration of hg2+ (a); and relative intensity plot i/i0 versus concentration of hg2+ (b) [24] energy application fuel cells are the energy storing devices. they provide clean energy. in fuel cell, pt and pt based tika ram bhandari et al. / bibechana 18 (1) (2021) 231-239 235 electrocatalysts are used to accelerate the oxygen reduction reaction (orr). high cost, low long term stability of the pt and pt based electrocatalysts interfere for the commercialization of fuel cells [27, 28, 29]. however, it has been found that heteroatom doped carbons from the pyrolyzed hair intensify the orr reaction than pt and pt based catalysts. for orr performance, peroxide species (ho2 -) yield and electron-transfer number during the phenomenon was monitored. sample with temperature 900 ºc showed low yield of ho2 and high electron transfer number as compared to other sample (800 ºc, 1000 ºc, 1100 ºc). further to confirmed sample as better electrocatalyst for orr methanol tolerance and stability test was performed on heteroatom doped carbon of 900 ºc , the obtained result was far good as compared to pt/c catalysts at constant potential of -0.3 v for 14h in an o2saturated 0.1 m koh solution. heteroatom doped carbon obtained from hair char have nitrogen and sulphur in carbon structure and also has graphite like stack form. this structure of carbon with hetero atoms increases the activity of the oxygen in oxygen reduction reaction. resistance of the pyrolyzed char was found very low and decrease with increase in temperature. researchers have reported the development of a superior and stable metal free catalyst having excellent electrochemical properties from pyrolyzed hair sample [18]. it may provide alternative catalysts for fuel cells in replace of pt and pt based catalysts. moreover, it is also highly applicable in supercapacitors. capacitors are the electric devices that are used to store the energy. supercapacitors are fast-charging energy storage devices having intermediate specific energy. they are designed to solve the gap between batteries and capacitors. super capacitor has high capacitance than congenital capacitors which highly depend upon the surface area of the electrode used [30]. the capacitance value of carbonized human hair in argon atmosphere at 800 °c was found 340 fg-1 at a current density of 1 ag-1 in 6m koh and also good stability over 20 000 cycles while evaluating electrochemical performance in a fully assembled two electrode cell with the 1 m lipf6 ec/dec electrolyte [17]. the high capacitance is the result of hydrophilicity and polarity of electrode which is induced due to doping of heteroatoms and porous structure in the carbon materials. it was demonstrated that the pyrolysis transfer human hair into highly porous, conductive heteroatom doped carbon char having high surface area. thus, electrode from the carbonized human hair has high energy and power density which can be a good candidate for energy applications [18]. excellent electrocatalytic properties of transformed hair (pyrolyzed) reveal that it could be used as promising catalyst, co2 adsorption, hydrogen storage and also in the supercapacitors. 4. characterization techniques several characterization technique such as; scanning electron microscope (sem), transmission electron microscope (tem) , x-ray diffraction (xrd), raman spectroscopy and xray photoelectron spectroscopy (xps), fourier transform-infrared spectroscopy (ftir) has been found on the pyrolyzed hair sample by the different researchers in order to study morphology, structure and the chemical composition. chemical composition x-ray photoelectron spectroscopy (xps) technique is used to probes the elemental composition of a material. xps spectra are obtained by irradiating a material with a beam of energetic photons while measuring the kinetic energy and the number of electron that escape [31]. xps spectrum of carbonized hair of 200 ºc over 24 hrs. reveals three major peaks at about 284.6 ev, 399.5 ev and 531.0 ev that confirms presence of carbon (c), nitrogen (n) and oxygen (o), but at high resolution c and o xps spectrum shows presence of c-c/c=c, cn/c-o and c=o bonds, whereas high resolution of n, xps spectrum shows presence of pyridinic n and pyrrolic n as shown in figure 4(a) [24]. tika ram bhandari et al. / bibechana 18 (1) (2021) 231-239 236 quaternary or graphine n peak and sulphur (s) peak above the graphene n at 164 ev can be seen in figure 4(b) [18]. moreover, the content of carbon decreases with increase in temperature which was confirmed by energy-assisted x-ray spectroscopy (eds) system based on sem [32]. fig. 4: xps spectra of pyrolyzed hair showing the presence of oxygen, nitrogen and carbon (a) [24] and c-s-c type of sulphur (b) [18] ftir spectrum of human hair char shows the presence of various functional groups in pyrolyzed form. absorption band at 2930 cm-1, 1410 cm-1, and 1330 cm-1 associated with the vibration of c-h, c=c and c-c functional groups where broad band at 3300 cm-1 reveals the presence of n-h and o-h group respectively. the peak about 1690 cm-1 and 1515 cm-1 in ftir spectrum conforms the bending vibration and stretching vibration of the c=o and n-h functional groups [24]. further, additional peak corresponding to the c-n groups of aliphatic and aromatic amines and h-o-h (bending band) were found at 1365-1370 cm-1 and 1600 cm-1 respectively [32] as shown in figure 5. this confirmed the presence of carboxylic, alkyl, aryl and amino functional groups in the pyrolyzed hair. microscopic studies scanning electron microscope (sem) is used to study the morphological structure of the given sample. sem micrograph of the pyrolyzed hair (300 ºc and 800 ºc) shows the existence of the lamellar shaped carbon flakes. these arrangement is similar to the sem image of the hair cuticle in figure 2, that means these structure were retain and unaltered during carbonization process [17] but porosity of the samples intensify with increase in temperature [32]. these carbon flakes are usually formed by randomly piled graphite like plane with high level of disorder, which consequence the high surface area and porosity which is shown in figure 6(a) [18]. fig. 5: ftir spectra of carbonized hair samples prepared at different temperatures (activated by zncl2) showing presence of different functional group [32] the pyrolyzed sample were further analyzed with transmission electron microscope (tem), this technique is generally used to know the particle size and the internal structure. in tem, a parallel beam of electrons is focused on to sample and allowed to penetrate through the sample. some electrons are scattered and energy loss by tika ram bhandari et al. / bibechana 18 (1) (2021) 231-239 237 inelastically scattered electron is recorded by tem and displayed in micrograph [33]. tem images of the hydrothermal treatment of human hair at 200 ºc for 24 hours revealed the presence of quantum dots in well scattered manner having diameter and structure in nanoscale range (2-10 nm) which is shown in figure 6(b) [24]. however, tem performed on the active carbon containing flakes graph shows thin pile of carbon sheets contain micro/meso-porous structure having channel like texture. these channels facilitate for penetration and the movement of the electrolytic ion in supercapacitors [17, 18]. fig. 6: sem micrograph of hair carbonized at 300 ºc (a) and 800 ºc (b) [17], tem image of hair carbonized at 800 ºc (c) [17] and tem image with size distribution of cqds (d) [24] optical characterization x-ray diffraction (xrd) of the pyrolyzed sample was used to know the crystal nature of sample. xrd graph is plotted with intensity versus 2θ. peaks were observed at about 22.3º and 43.8º on spectra of the material which show the graphite like structure, these graphitic stacks are responsible for electrical conductivity and nature of graph shows degree of the crystalline increase in temperature [17] but altuntaş et. al reported the degree of crystalline decreases with increases in temperature [32]. it can be assumed that crystalline behavior depends on nature of treatments/activations of sample which can be seen in figure 7. fig. 7: xrd patterns showing crystalline nature of koh activated (a) [17] and zncl2 activated (b) [32] pyrolyzed hair raman spectroscopy is a nondestructive, ambient probing instrument to characterize the detail bonding structure of carbon materials. mostly structures are analyzed in context of diamond (d) band versus graphite (g) band. for pure diamond a tika ram bhandari et al. / bibechana 18 (1) (2021) 231-239 238 raman active mode appear at 1332 cm-1 and for graphite active line appear at 1575 cm-1 [33]. crystal structure can also be studied through diffraction pattern using raman spectroscopy. the graphite like structure was determined by ratio of defects (d) to graphitic (g) bands of the sample i.e. d/g ratio. in figure 8 peaks were found around 1320 cm-1 and 1590 cm-1 in raman spectra that represents diamond and the graphitic band respectively. d/g ratio decreases with the increase in the temperature which means deformation decreases with carbonization temperature [17,18], similar result was reported by altuntaş et. al [32] fig. 8: raman spectra of the carbon materials obtained from hair showing d and g bands [17] 5. conclusions hair a keratinized filament has very strong crosslinked disulphide linkage and covered by thick cuticle. these two disulphide linkage and cuticle is responsible for the toughness of the hair. microstructure is different in asian, african and caucasian hair. hair on low temperature pyrolysis yields a black shiny char. this char on spectroscopic analysis shows the presence of carboxylic, alkyl, aryl and amino functional groups and also contains hetero atom like n, s and o. however, xrd shows degree of crystalline nature may found to be in reverse order under different treatment condition with increase in temperature. electron microscopic analysis shows the presence of randomly oriented flakes like structure having nanoscale dimension. these nanostructures have channels like texture, high surface area and porosity.. these property of the pyrolyzed sample helps to enhance the electrochemical properties. the channels intensify the movements of electrolyte in supercapacitor so acts as an electrode. as better my knowledge no any systematic study of the biomedical application has been reported yet though its uses was reported in the 16th century as a biomedicine. it may have many significant hidden scientific properties. investigations of such properties in the pyrolyzed hair contribute to the science for better innovation. commercialization of the use of pyrolyzed hair may help to control waste produced by the hair fibers. references [1] b. bhushan, biophysics of the human hair: structural, nanomechanical, and nanotribological studeies, springer, berlin (2010) 1-50 [2] j.r rouse, m.e.v. dyke, a review of the keratin based biomaterials for 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[31] t. susi, p. ayala. doping carbon nanomaterials with heteroatoms. carbon nanomaterials for advanced energy systems., john weily and sons, (2015) 133-161. https://doi.org/10.1002/9781118980989.ch4 [32] d. b. altuntaş, v. nevruzoglu, m. dokumaci, s. cam. synthesis and characterization of activated carbon produced from waste human hair mass using chemical activation, carbon letters. 30 (2019) 301-313. http://doi.org/10.1007/s42823-019-00099-9 [33] p. k. chu, l. li. characterization of amorphous and nanocrystalline carbon films, materials chemistry and physic s .96(2006)253-277 . http://doi.org/10.1016/j.matchemphys.2005.07.048 https://doi.org/10.1002/9781118980989.ch4 devendra sir cover page copy.jpg bibechana 17 (2020) 110-116 110 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal ricci solitons on lorentzian para-sasakian manifolds riddhi jung shah department of mathematics, janata campus, nepal sanskrit university, dang, nepal email: shahrjgeo@gmail.com article information received: june 5, 2019 accepted: december 5, 2019 keywords: ricci soliton lp-sasakian manifold 2 w -curvature tensor 4 w -curvature tensor abstract in this paper we study ricci solitons in lorentzian para-sasakian manifolds. it is proved that the ricci soliton in a  12 n -dimensinal lp-sasakian manifold is shrinking. it is also shown that ricci solitons in an lp-sasakian manifold satisfying the derivation conditions     0.,,0., 422  wxwwxr  and   0., 24 wxw  are shrinking but are steady for the condition   .0., 2 sxw  finally, we give an example of 3-dimensional lp-sasakian manifold and prove that the ricci soliton is expanding and shrinking in this manifold. 1. introduction a ricci soliton is a natural generalization of an einstein metric and is defined on a riemannian manifold  ., gm a ricci soliton is a triple  ,,vg with g a riemannian metric, v a vector field and  a real scalar such that ,022  gsgl v  (1.1) where s is the ricci tensor and gl v denotes the lie derivative of g along a vector field v [1]. the ricci soliton is said to be shrinking, steady and expanding according as 0,0   and 0 respectively. compact ricci solitons are the fixed points of the ricci flow s t g 2   projected from the space of metrics onto its quotient modulo diffeomorphism and scalings and often arise as blow-up limits for the ricci flow on compact manifolds. metrics satisfying (1.1) are interesting and useful in physics and often are referred as quasi-einstein (eg, see [2], [3]). the ricci flow was used by perelman to prove the poincare's conjecture theorem and the thurston's geometrization conjecture theorem in topology [4]. ricci solitons have also been studied by [5], [6], [7], [8] and others. on the other hand, the notion of a lorentzian para-sasakian manifold was introduced by https://creativecommons.org/licenses/bync/4.0/ this work is licensed under the creative commons ccby-nc license. doi: https://doi.org/10.3126/bibechana.v17i0.24341 http://nepjol.info/index.php/bibechana mailto:shahrjgeo@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.24341 riddhi jung shah / bibechana 17 (2020) 110-116 111 matsumoto [9]. mihai and rosca defined the same notion independently and obtain several results on this manifold [10]. lp-sasakian manifolds have also been studied by [11], [12], [13] and others. in this paper, we prove some derivation conditions for ricci solitons in lpsasakian manifolds. we investigate shrinking property of ricci soliton in a lp-sasakin manifold when a vector field v is collinear with . we obtain some results of ricci solitons on lp-sasakian manifolds satisfying the conditions   ,0., 2 wxr    ,0., 2 sxw    0., 42 wxw  and   0., 24 wxw  respectively. finally, we give an example of 3dimensional lp-sasakian manifold which is expanding and shrinking ricci soliton. 2. preliminaries let m be a  12 n -dimensional differentiable manifold. then m is said to be a lorentzian para-sasakian manifold (briefly lp-sasakian manifold), if it admits a (1, 1) tensor field , a contravariant vector field , a 1-form  and a lorentzian metric g which satisfy         ,0 ,0 , ,1 2   x xxx   (2.1)        ,,, yxyxgyxg   (2.2)    ,, xxg   (2.3) ,x x   (2.4)           ,2,  yxxyyxgy x  (2.5) for all ,, tmyx  where  denotes the covariant differentiation with respect to the lorentzian metric g [9, 10]. if we put,    ,,, yxgyx  then  is a symmetric (0,2) tensor field [9]. since the 1-form  is closed in an lp-sasakian manifold we have [12], [9]        .,,, yxgyxgyxy x   (2.6) in a  12 n -dimensional lp-sasakian manifold the following relations hold           ,,, , yzxgxzyg zyxr    (2.7)       ,,, xyyxgyxr   (2.8)       ,, yxxyyxr   (2.9)    ,2, xnxs   (2.10)        ,2,, yxnyxsyxs   (2.11) for any vector fields ,,, zyx where r and s are the riemannian curvature tensor and the ricci tensor of the manifold, respectively [11]. let  ,,vg be a ricci soliton in a  12 n dimensional lp-sasakian manifold .m then we have       .,,, xgygyxgl yx    using (2.4) and (2.6) in this equation we get     .,2, yxgyxgl    (2.12) from (1.1) and (2.12) we obtain      },,,{, yxgyxgyxs   (2.13)   ,12  nr provided .0. tr (2.14) in view of (2.1), (2.3) and (2.13) we get    ., xxs   (2.15) 3. results and discussion now, we have the following results and their proofs theorem 3.1: if in a  12 n -dimensional lpsasakian manifold the metric g is a ricci soliton and v is pointwise collinear with , then v is a constant multiple of  and g is shrinking. proof: let m be a  12 n -dimensional lpsasakian manifold with lorentzian metric .g a ricci soliton is a generalization of an einstein metric and defined on a riemannian manifold  gm , by (1.1). let v be pointwise collinear with  i.e., cv  where c is a function on a  12 n -dimensional lp-sasakian mani-fold. then from (1.1), we have riddhi jung shah / bibechana 17 (2020) 110-116 112        .0,2,2,  yxgyxsyxgl c   (3.1) further simplification and use of (2.4) in (3.1) yields                 .0,2,2 ,,   yxgyxsxyc xycgyxcyxcg   (3.2) by virtue of (2.6) and (3.2) we obtain               .0,2,2 ,2   yxgyxs xycyxcyxcg   (3.3) putting y in (3.3) and using (2.1), (2.3) and (2.10) we get        .024  xcxnc  (3.4) taking x in (3.4) gives  .2   nc (3.5) in view of (3.4) and (3.5) we obtain    ,2 xnxc  which implies   .2  ndc (3.6) taking exterior derivative on both sides of (3.6) we get   ,02   dn (3.7) since ,0d we have .02  n hence c is constant from (3.6). consequently, the equation (3.3) reduces to       .,,, yxcgyxgyxs   (3.8) comparing (2.13) and (3.8) we get .1c again, 02  n implies that 02  n for .1n thus the ricci soliton is shrinking. this proves the theorem. theorem 3.2: a ricci soliton in a 2 w -semisymmetric lp-sasakian manifold of dimension  12 n is shrinking. proof: let m be a  12 n -dimensional lpsasakian manifold admitting a ricci soliton  .,, vg the 2 w -curvature tensor in m is defined by [14]            ],,, ,,[ 2 1 ,,,,,, 2 txriczyg tyriczxg n tzyxrtzyxw   this can be written as         ]., ,[ 2 1 ,, 2 qxzyg qyzxg n zyxrzyxw   (3.9) putting x in (3.9) and using (2.3) and (2.8) we get           ].,[ 2 1 ,, 2   qzygqyz n yzzygzyw   (3.10) taking inner product on both sides of (3.9) with  and using (2.7) and (2.15) we obtain           ]. [ 2 1, , , 2 yzxg xzyg n zyxw             (3.11) suppose that the condition     0,., 2 uzywxr  holds in .m then by definition we have               0 ,,,, ,,,, 22 22    uxrzywuzxryw uzyxrwuzywxr   (3.12) for all vector fields uzyx ,,, on .m in view of (2.8) and (3.12) we get                               .0 ,,, ,,, ,,, ,,, 22 22 22 22      xzywuzywuxg uxywzuywzxg uzxwyuzwyxg xuzywuzywxg     (3.13) taking inner product on both sides of (3.13) with  and using (2.1) we obtain                                       .0 ,,, ,,, ,,, ,,, 22 22 22 22      xzywuzywuxg uxywzuywzxg uzxwyuzwyxg xuzywxuzywg     (314) in view of (3.9), (3.11) and (3.14), we get                                                                    .0}],,{ },,{ },{, },,{ },{,}, ,{[ 2 1],, ,,[ 2 1 ,,              zyxgyzxgu xuygyuxgz uyuygzxg zuxgxuzgy zuuzgyxgzuyg yzugx n yxsuzg zxsuyg n xuzyrg        (3.15) let  12,...,2,1:  nie i be an orthonormal basis of the tangent space at any point of the manifold. putting i eyx  in (3.15) and taking summation over ,121 ,  nii we get riddhi jung shah / bibechana 17 (2020) 110-116 113      ., 12 22 , uzg n nnr uzs     (3.16) again taking an orthonormal frame field at any point of the manifold and contracting over z and u in (3.16) we have ,02  n for .1n hence the ricci soliton is shrinking. this completes the proof of the theorem. theorem 3.3: let m be a  12 n -dimensional lp-sasakian manifold and  ,,vg be a ricci soliton satisfying the condition   0., 2 sxw  in ,m then the ricci soliton is steady. proof: let m be a  12 n -dimensional lpsasakian manifold and  ,,vg be a ricci soliton in .m suppose that the condition     0,., 2 zysxw  holds in ,m then we have       .0,,,, 22  zxwyszyxws  (3.17) in view of (3.10), (2.15) and (3.17) we obtain                                  .0,,,, ,,} { 2 1 ,, , ,     yqszxgzqsyxg zyxsyzxs n yzxgzyxg zyqxs yzqxs      (3.18) putting z in (3.18) and using (2.1), (2.3) and (2.15) we get                 .],, } 2 ,1{[2 , yqsxyxs yx n yxgn yqxs       (3.19) again taking y in (3.19) and using (2.1), (2.3) and (2.15) we obtain     ,012 2  xn  (3.20) since   ,0x (3.20) implies that .0 thus the ricci soliton is steady. this proves the theorem. theorem 3.4: a ricci soliton in a  12 n dimensional lp-sasakian manifold satisfying the condition   0., 42 wxw  is shrinking under the condition .0. tr proof: let m be a  12 n -dimensional lpsasakian manifold and  ,,vg be a ricci soliton in .m the 4 w -curvature tensor in m is defined by [15]            ] [ 2 1 ,,, ,,, ,, ,, 4 tzricyxg tyriczxg n tzyxr tzyxw   which can be written as         ]. [ 2 1 , , , , 4 qzyxg qyzxg n zyxr zyxw   (3.21) putting x in (3.21) and using (2.3) and (2.8) we obtain           . 2 1 ,, 4 qzyqyz n yzzygzyw     (3.22) taking inner product on both sides of (3.21) with  and using (2.7) and (2.15) we get               ., 2 1 , 2 , , 4 yzxg n zyxg n xzyg zyxw               (3.23) now, we assume that the condition     0,., 42 uzywxw  holds in ,m then we have               .0,, ,, ,, ,, 24 24 24 42    uxwzyw uzxwyw uzyxww uzywxw     (3.24) in view of (3.10) and (3.24) we get                                                             .0, ,,, ,,, ,,],, ,,, ,,, ,,, ,[ 2 1 ,,, 4 44 44 44 44 44 44 4 44          xzywu zywuxguxywz uywzxguzxwy uzwyxgqzywuxg qxzywuuqywzxg uqxywzuzqwyxg uzqxwyqxuzywg qxuzyw n xuzywxuzywg          (3.25) taking inner product on both sides of (3.25) with  and using (2.1), (2.3) and (2.15) we obtain riddhi jung shah / bibechana 17 (2020) 110-116 114                                                              .0,,, ,,, ,,, },,, ,,, )),((),()),(({ 2 1 ,,, 2 1 1 44 44 44 44 44 44 44              xzywuzywuxg uxywzuywzxg uzxwyuzwyxg qzywuxgqxzywu uqywzxguqxywz uzqwyxguzqxwy n uzywxxuzywg n        (3.26) in view of (3.21), (3.23), (3.26) and (2.15) we get                                                 .0)()(,, 2 1 },,{ 4 ],, 2 1},, ,, ,,,,{ 2 1 ,,,,[ 2 1 2                   zuyxsyxg n zyuxguxs n uygzxg n uxgzyg yuzxgyuzxs uxszygzxsuyg n uzgyxgxuzyrg n        (3.27) let  12,...,2,1: ne i be an orthonormal basis of the tangent space at any point of the manifold. putting i eyx  in (3.27) and summing over ,121 ,  nii we get          . 2 12 ,2, zu n rn zungzus              (3.28) again taking  zu and using (2.1), (2.3), (2.14) and (2.15) we get .02  n thus  is negative. this concludes that the ricci soliton is shrinking. this completes the proof of the theorem. theorem 3.5: let m be a  12 n -dimensional lp-sasakian manifold and  ,,vg be a ricci soliton in .m if g satisfies the condition   ,0., 24 wxw  then g is shrinking under the condition .0. tr proof: let m be a  12 n -dimensional lpsasakian manifold and  ,,vg be a ricci soliton in .m suppose that the condition     0,., 24 uzywxw  holds in ,m then by definition we have               .,,,, ,,,,0 4242 4224 uxwzywuzxwyw uzyxwwuzywxw     (3.29) by virtue of (3.22) and (3.29) we have                                                              .0 ,,, ,,, ,,, ],, ,, ,, ,,[ 2 1 ,,, 22 22 22 22 22 22 22 22          xzywuzywuxg uxywzuywzxg uzxwyuzwyxg quzywxqxzywu uqzywxuqxywz uzqywxuzqxwy uzyqwxqxuzyw n xuzywxuzywg         (3.30) taking inner product on both sides of (3.30) with  and using (2.1), (2.3) and (2.15) we obtain                                                                               .0,,, ,,, ,,, ],, ,, ,, ,,,[ 2 1 ,,, 22 22 22 22 22 22 22 22         xzywuzywuxg uxywzuywzxg uzxwyuzwyxg quzywxqxzywu uqzywxuqxywz uzqywxuzqxwy uzyqwgxuzywx n uzywxxuzywg         (3.31) in view of (3.9) and (3.11), (3.31) yields                          .0)}]()(),( 2 1 )()(),( 2 1 )()(),( ,{ 1 ,, ,,[ 2 1} { 2 1 ,, ,, ,,             zuyxs uyzxsyxuzs zxuys n uzgyxg zxguyg n n xuzyrg yxsuzg zxsuyg     (3.32) let  12,...,2,1:  nie i be an orthonormal basis of the tangent space at any point of the manifold. putting i eyx  in (3.32) and summing over ,121 ,  nii we get        . 264 326 , 264 248 , 2 2 2 23 zu nn rnrn zug nn nrnn uzs                        (3.33) again, putting uz in (3.33) and using (2.1), (2.3) and (2.15) we get .044 22  nn (3.34) riddhi jung shah / bibechana 17 (2020) 110-116 115 this equation gives nn 2,2  . hence  is negative. this concludes that the ricci soliton is shrinking. thus the theorem is proved. from theorem 3.4 and theorem 3.5 we can state next theorem theorem 3.6: ricci solitons in a  12 n dimensional lp-sasakian manifold satisfying the derivation conditions   0., 42 wxw  and   0., 24 wxw  are equivalent. now we give an example of lp-sasakian manifold. 4. example for 3-dimensional lp-sasakian manifold let us consider a 3-dimensional manifold     ,,,:,, 3rzyxzyxm  where  zyx ,, are standard coordinates in . 3 r we choose the vector fields , , , 321 x e yz ee y ee xx                   (4.1 which are linearly independent at each point of .m let g be the lorentzian metric defined by       ,0,,, 313221  eegeegeeg (4.2)       .1,,, 332211  eegeegeeg (4.3) let  be a 1-form defined by     3 , ezgz  for any vector field z on .m let  be a (1, 1) tensor field defined by       0., , 32211  eeeee  (4.4) the linearity property of  and g yields that       , ,1 3 2 3 euuue   (4.5)        ,,, uzuzguzg   (4.6) for any vector fields uz , on .m thus for  ge ,,, , 3  defines a lorentzian paracontact structure on .m by the definition of lie bracket and (4.1) we have       ., ,0, ,, 23221131 eeeeeeee  (4.7) let  be the levi-civita connection with respect to the lorentzian metric ,g the koszul formula is defined as                 .,, ,,,, ,,, ,2 yxzg xzygzyxg yxzgxzygzyxg zyg x     (4.8) in view of (4.2), (4.3), (4.7) and (4.8) we get                   .,2 ,,,,,, ,,, ,2 11 311113131 311113131 131 eeg eeegeeegeeeg eegeeegeeege eeg e     similarly, we can obtain     21231 ,20,2 eegeeg e  and    .,20,2 31331 eegeeg e  from above we can write    xegxeg e ,2,2 131  for all  .mx  thus . 131 ee e  proceeding same way we obtain .0 ,0 , ,, ,0 , 132333 12322 232311e 21131          eee eee eeee eee eee ee e ee (4.9) now, we have     . 3 311 111111 e ee eee e eee      again, from definition and by the use of (2.5) we obtain           . 2, 3 31111311 11 e eeeeeeeeg e e      similarly, we obtain other relations. thus we have                              .0 ,0,0 ,, ,0, ,0, 33 2313 232322 12131 21311 e ee eeee eee eee e ee ee ee ee      (4.10) from (4.5), (4.6), (4.9) and (4.10), we see that the equations (2.1) (2.5) are satisfied by the manifold ,m for . 3 e hence  g,,,  is an lp-sasakian structure in .m consequently  gm ,,, 3  is an lp-sasakian manifold. now, the riemannian curvature tensor is defined by     ., , zzzzyxr yx xyyx  (4.11) by virtue of (4.7), (4.9) and (4.11) we obtain riddhi jung shah / bibechana 17 (2020) 110-116 116     .0 , 1221 32,1312321321   ee eeeeeer ee eeeeee similarly, we obtain                                     .0,, 0,,, ,0,,, ,0,,, ,,,, ,,,0, 333222 1113131 1322121 2313232 12211331 2332321 eeereeer eeereeeer eeereeeer eeereeeer eeeereeeer eeeereeer (4.12) by the use of (4.12) we get                .0 ,, ,,,, , 1111 1331 3 1 122111 11 ,,        eegeeg eeeergeeeerg ees eeeerg i ii similarly, we obtain   0, 22 ees and   .2, 33 ees thus we have           .2, ,0,, 33 2211 ees eesees (4.13) from (2.13) we have       .,,, iiiiii eegeegees   this equation yields      ,1,, 2211  eesees by the use of (4.3), (4.4) and (4.13) for .2 ,1i this implies ,01  for .2,1i and   ,, 33 ees for .3i this yields .02  since 01 for 2,1i and 02  for ,3i this is an example of expanding and shrinking ricci soliton in 3-dimensional lp-sasakian manifold. 5. conclusions in this paper, we have investigated that the ricci soliton in a  12 n -dimensinal lpsasakian manifold is shrinking. it is also proved that ricci solitons in an lp-sasakian manifold satisfying the derivation conditions   ,0., 2 wxr    0., 42 wxw  and   0., 24 wxw  are shrinking but are steady for the condition   .0., 2 sxw  references [1] r. s. hamilton, the ricci flow on surfaces, mathematical and general relativity (santa cruz. ca. 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[10]i. mihai, r. rosca, on lorentzian p-sasakian manifolds, classical analysis, world scientific publ. 1992, 155-169. [11]u.c. de, k. matsumoto, a.a. shaikh, on lorentzian para-sasakian manifolds, rendicontidel seminaro matemetico di messina, serie ii, supplemento al. 3 (1990) 149-158. [12]k. matsumoto, i. mihai, on a certain transformation in lorentzian para-sasakian manifold, tensor n. s. 47 (1988) 189-197. [13] a.a. shaikh, s. biswas, on lp-sasakian manifolds, bull. malaysian math. sci. soc. 27 (2004) 17-26. [14] g.p. pokhariyal, r.s. mishra, curvature tensors and their relativistics significance,yokohama math. j. 18 (2) (1970), 105-108. [15]g.p. pokhariyal, curvature tensors and their relativistics significance iii, yokohama math. j. 21 (1973) 115-119. bibechana 18 (1) (2021) 33-47 33 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal phonon dynamics of zr67ni33 and fe80b20 binary glassy alloys aditya m. vora1*, alkesh l. gandhi2** 1department of physics, university school of sciences, gujarat university, ahmedabad, 380 009, gujarat, india. 2department of physics, b. v. shah (vadi vihar) science college, c. u. shah university, wadhwan, 363 002, gujarat, india. *email: amvora@gujaratuniversity.ac.in, voraam@gmail.com **email: gandhi.alkesh.jain@gmail.com article information: received: may 4, 2020 accepted: june 17, 2020 keywords: bulk metallic glass model potential interatomic pair potential phonon dispersion curve (pdc) thermodynamic properties abstract binary amorphous alloys are the primary bulk metallic glasses (bmgs). two binary bmgs zr67ni33 and fe80b20 have been studied in the present work using the pseudoalloy-atom (paa) model based on the pseudopotential theory. some important thermodynamic properties like debye temperature and elastic properties like elasticity moduli and poisson’s ratio at room temperature are theoretically computed with the help of pseudopotential theory from the elastic limit of the phonon dispersion curves (pdcs). the collective dynamics of longitudinal and transverse phonon modes are investigated in terms of eigenfrequencies of the localized collective modes. the presently computed results are compared with the other such data including theoretically generated results from the molecular dynamics at different temperatures as available in the literature and an acceptable agreement is found. doi: https://doi.org/10.3126/bibechana.v18i1.28760 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction generally, the bulk metallic glasses (bmgs), which are non-crystalline metallic alloys, can be made-up with low cooling rates in many alloy systems. a metallic material is formed by the basic units of well-arranged metallic microstructures designed by the single-crystal grains of varying sizes. an alloy is produced by melting the constituent metal elements in predefined proportions followed by the solidification process. the solidification process of an amorphous alloy has a deep impact on its properties and structure at the corresponding temperature. so, the data of the physical properties of the molten alloys, before its solidification, is necessary for the development of a bmg with predefined characteristics. the properties of an alloy are fully dependent on the crystallization procedure and the final metallic microstructure, where both are determined by the selection of cooling pattern and the adopted thermal treatments. unlike conventional crystalline alloys, a bmgs is http://nepjol.info/index.php/bibechana mailto:amvora@gujaratuniversity.ac.in mailto:voraam@gmail.com mailto:gandhi.alkesh.jain@gmail.com https://doi.org/10.3126/bibechana.v18i1.28760 https://creativecommons.org/licenses/by-nc/4.0/ https://www.sciencedirect.com/topics/engineering/alloy-system aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 34 produced by quenching the alloy melt below its crystalline temperature by preventing the regular long-range arrangement with crystallization. the quickly frozen alloy-melt keeps the precursor liquid structure. thus, the bmgs are said to be solids with liquid-like non-crystalline structure at the atomic or molecular level, which makes them highly resistant to permanent distortion and makes them more than twice tougher to its crystalline counterpart. in recent decades, the neutron scattering data from short-wavelength phonons in many bmgconfigurations have been increasingly available. there are found an interesting similarity between the scattered neutron spectra of liquids and that of amorphous or crystalline solids near their melting point. further, the theory of lattice dynamics is equally and successfully applied to the ordered crystalline as well as amorphous materials [1-32] 1.1 𝐙𝐫𝟔𝟕𝐍𝐢𝟑𝟑 bmg in the binary transition metal-metal alloy systems i.e. zr-ni bmg is a unique one and its crystallization temperature is higher than the glass transition temperature (652k) under the heating conditions. suck et al. [33] have studied longitudinal phonon dispersion mode of zr67ni33 glass by neutron inelastic scattering (nis) method. while, gupta et al. [13] have theoretically studied the phonon dispersion curves (pdcs) of such glass using hubbard-beeby (hb) [30] and bhatia-singh (bs) ([28] computational approaches and compared their outcomes with the results achieved through molecular dynamics (md) simulation by aihara et al. [15,16] . also, they have found that there is a good agreement between the experimentally observed and theoretically computed data. otomo et al. [17] have studied the dynamical structure factors and collective excitations of 𝑍𝑟67𝑁𝑖33 glass with nis method. similarly, lad and pratap [18] have theoretically investigated the pdc of zr-ni bmg with model potential formalism using tg [31,32] and bs [28] approaches and got the results very close to the experimental and theoretical data available in the literature. while, vora and coworkers [1-12] have evaluated the collective dynamics of some bmgs using ashcroft’s empty core model pseudopotential [34] singh et al. [19] have examined zr-ni bmg with hb [30], tg [31,32] and bs [28] approaches using a newly constructed free model potential, which is, in fact, the alteration of the ashcroft's model potential [34] only. the electronic structure, bonding and 3d atomic structure of zr67ni33 bmg were studied by sugita et al. [20]. very recently, gandhi and vora [6-10] have reported vibrational dynamics of some binary to hexanary bmgs using model pseudopotential theory. the interest in the zr-based bmgs has been growing due to their superior mechanical properties like high fracture resistance, good corrosion resistance and micro-formability, which make them a favorable choice for various applications including high field superconducting magnets and the place where brittle alloys are not used [19,20]. 1.2 fe80b20 bmg the metal-metalloid type fe80b20 bmg, mainly referred to be as metglas-2605, is produced by the rapid solidification process. it is a ferromagnetic with the good soft magnetic property having a high yield strength of ~3630 mpa, high elastic stiffness, and thermal stability, which all together make it superior to many other commercial binary bmgs. though a little plasticity is its minor drawback, the low-cost fe80b20 bmg is preferable for structural applications [21]. in the early 80's, devis et al. [35] have experimentally studied properties of fe80b20 bmg. dimitrov et al. [22] and agarwal et al. [23, 24] have carried out a limited study of this bmg. while, vora [3] has theoretically studied fe80b20 using all three theoretical approaches of pdcs. considering the multilevel applications of the bmgs, the vibrational dynamics of two binary bmgs zr67ni33 and fe80b20 are reported in the current work. the well-behaved shaw’s optimized constant-core model pseudopotential [36] is employed using a self-consistent phonon scheme by relating multiple scattering and phonon eigenfrequencies. such phonon frequencies aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 35 represent many-body correlation functions of atoms and concerned interatomic potential. to study the screening dependency on the aforesaid properties, the most effectively used five different local field correction (correlation) functions namely hartree (h) [37], taylor (t) [38] ichimaru-utsumi (iu) [39] and sarkar et al. (s) [40] have been adopted to determine the effect of exchange and correlation on the bare ion potential. these screening functions help us to investigate the screening influence on the vibrational dynamics of the selected binary bmgs. three independent computational approaches viz. hubbard-beeby (hb) [30], takeno-goda (tg) [31, 32], bhatia-singh (bs) [28] and shukla and campnha [29] have been employed to generate pdcs of said binary bmgs. the important thermodynamic and elastic properties viz. longitudinal sound velocity (𝜐𝐿), transverse sound velocity (𝜐𝑇), young’s modulus (𝑌), isothermal bulk modulus (𝐵𝑇), rigidity modulus (k), poisson’s ratio (𝜎) and debye temperature (𝜃𝐷) have been computed using the long wavelength limits of pdcs. 2. computational methodology the pseudopotential perturbation theory is an accepted tool for determining properties of amorphous alloys. as far as analytical calculations are concerned, many approximations based on model approaches are available to study the bmgs [1-11]. shaw’s optimized constant-core model pseudopotential [36] along with five different local field correction functions viz. h, t, iu, f and s have used for studying the screening influence on the said properties of the selected bmgs. here, the three theoretical approaches, namely hb [30], tg [31,32] and bs [28] have been extensively employed to study the phonon dispersion and collective excitations in binary bmgs. however, hubbard and beeby (hb) [30] have derived expressions for the longitudinal and transverse phonon eigenfrequencies by examining collective motion in the amorphous liquid system as a generalization of the phonon theory of solids using a random phase approximation. in which, the product of the static pair correlation function and the second order derivative of the interatomic potential is peaked near the hard-core radius. while, takeno and goda (tg) [31, 32] have expressed longitudinal and transverse phonon eigenfrequencies in terms of many-body correlation functions of atoms and interatomic potentials in amorphous solids. bhatia and singh (bs) [28, 29] have proposed a phenomenological model to determine the longitudinal and transverse phonon eigenfrequencies in amorphous solids. in most of such studies, the pseudopotential parameters are evaluated in such a way that it can generate the comparable results of the pair correlation function (pcf) (g(r)) and pdcs, which are found to be in good agreement with experimental data. mostly, vegard’s law is used to explain electron-ion interactions for binary bmgs. however, the well suitable pseudo-alloy-atom (paa) model explains such interactions vary precisely. hence, in the present article, the paa model is used to investigate the phonon dynamics of 𝐴𝑥𝐵100−𝑥 binary bmg systems [1-11]. considering these binary combinations of amorphous alloys to be mono-component fluids, the effective ion-ion interactions are given by [111], 𝑉 (𝑟) = 𝑍2𝑒2 𝑟 + 2 𝜋 ∫ 𝐹(𝑞) 𝑒−𝑖𝑞𝑟 𝑑𝑞 (1) where, 𝐹(𝑞) is the characteristics wave number, 𝑞 is the space vector. the first and second terms in the above equation represent coulombic interactions between ions and indirect interactions between conduction electrons, respectively. the pseudopotential perturbation along with the linear screening theory provides the basis of interatomic pair potential. the free-electron theory of metals has been extended to introduce the effects of amorphous structure. the presently computed interatomic pair potential (v(r)), based on the aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 36 extended theory of wills-harrison model [41] for the bmgs is given by, 𝑉(𝑟)= 𝑉𝑠(𝑟) + 𝑉𝑏(𝑟) + 𝑉𝑟(𝑟) 𝑉(𝑟) = { 𝑍𝑠 2𝑒2 𝑟 + 𝛺0 𝜋2 ∫ 𝐹(𝑞) [ sin(𝑞𝑟) (𝑞𝑟) ] 𝑞2 dq } + {− 𝑍𝑑 [1 − 𝑍𝑑 10 ] ( 12 𝑁𝑐 ) 1 2 ( 28.6 𝜋 ) ( 2 𝑟𝑑 3 𝑟5 )} + {𝑍𝑑 ( 450 π2 ) 2 ( 𝑟𝑑 6 𝑟8 ) } (2) where 𝑉𝑠(𝑟) is the 𝑠-electron contribution. the term 𝑉𝑏(𝑟) considers the friedel-model band broadening contribution to the transition metal cohesion and 𝑉𝑟(𝑟) came from the repulsion of the d-electron muffin-tin orbital on different sites owing to their non-orthogonality. also, the z is the valence and 𝛺0 the atomic volume of the bmgs, respectively. the self-consistent band structure calculation can provide the partials-density of states which can be used to obtain 𝑍𝑠. the characteristics energy wave number term 𝐹(𝑞), with 𝑞 as the 𝑞-space vector, under integration in the above equations, can be written as [1-11], 𝐹(𝑞) = −𝛺0𝑞 2 16𝜋 |𝑊𝐵(𝑞)| 2 [ 𝐻(𝑞)−1] {1+[ 𝐻(𝑞)−1][1−𝑓(𝑞)] } , (3) where 𝑊𝐵(𝑞), 휀𝐻(𝑞) and 𝑓(𝑞) are the bare ion potential, the hartree dielectric response screening function [37] and the local field correction functions needed to introduce the exchange and correlation effects, respectively. shaw’s model potential used in the present work is of the form [36] 𝑊𝐵(𝑞) = − 8𝜋𝑍 𝛺0𝑞 2 [ sin𝑞𝑟𝑐 𝑞𝑟𝑐 ] (4) where, the potential parameter is computed by 𝑟𝑐 = (0.51) 𝑟𝑆 z −1/3 [1-2]. here, wigner-seitz radius of the bmg is given by 𝑟𝑠 = ( 3𝛺0 4𝜋𝑍⁄ ) 1/3 for bmgs, the pcf (g(r)) discloses much useful information about the inter-particle radial correlation, structure and further, that predicts the electrical, elastic, thermodynamic and other physical properties. either it is obtained by using x-ray diffraction or by neutron scattering experimentally [25-27,42] theoretically [1-12, 2324, 43] from interatomic pair potentials. the vibrational dynamics of the aforementioned binary bmgs are studied by computing the longitudinal and transverse phonon eigenfrequencies, where the derivative of the interatomic pair potential (v(r)) in combination with pcf (g(r)) are used to compute the pdcs. the product of the static pair correlation function (g(r)) and the second order derivative (v′′(r)) of the interatomic potential is peaked at the hardsphere diameter. the rapid atomic motions of a disordered amorphous systems are very important because their structural, thermodynamic and transport properties are described by collective atomic motions. according to hb [30]-approach, the expressions for the two components of the phonon frequencies i.e. longitudinal and transverse are computed from [30], 𝜔𝐿 2(𝑞) = 𝜔𝐸 2 [1 − sin(𝑞𝜎) 𝑞𝜎 − 6 cos(𝑞𝜎) (𝑞𝜎)2 + 6 sin(𝑞𝜎) (𝑞𝜎)3 ] (5) 𝜔𝑇 2(𝑞) = 𝜔𝐸 2 [1 + 3 cos(𝑞𝜎) (𝑞𝜎)2 − 3 sin(𝑞𝜎) (𝑞𝜎)3 ] (6) with the maximum phonon frequency, 𝜔𝐸 2(𝑞) = ( 4𝜋𝜌 3𝑀 ) ∫ 𝑔(𝑟)𝑉′′(𝑟)𝑟2𝑑𝑟 ∞ 0 (7) < where 𝑀 is the atomic mass, 𝜌 the number density and 𝑉′′(𝑟) the second derivative of the interatomic pair potential, respectively. while, takeno and goda [31, 32] have derived the following expressions for wave vector (q) dependent longitudinal and transverse phonon eigenfrequencies as follows, 𝜔𝐿 2(𝑞) = ( 4𝜋𝜌 𝑀 ) ∫ 𝑑𝑟 𝑔(𝑟) { [𝑟 𝑉′(𝑟) (1 − sin(𝑞𝑟) 𝑞𝑟 )] + [𝑟2𝑉′′(𝑟) − 𝑟𝑉′(𝑟)] ( 1 3 − sin(𝑞𝑟) 𝑞𝑟 − 2 cos(𝑞𝑟) (𝑞𝑟)2 + 2 sin(𝑞𝑟) (𝑞𝑟)3 ) } ∞ 0 (8) and, aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 37 𝜔𝑇 2(𝑞) =( 4𝜋𝜌 𝑀 )∫ 𝑑𝑟 𝑔(𝑟) { [𝑟 𝑉′(𝑟) (1 − sin(𝑞𝑟) 𝑞𝑟 )] + [𝑟2𝑉′′(𝑟) − 𝑟𝑉′(𝑟)] ( 1 3 + 2 cos(𝑞𝑟) (𝑞𝑟)2 + 2 sin(𝑞𝑟) (𝑞𝑟)3 ) } ∞ 0 (9) according to improved bs model, the phonon frequencies of two branches are represented by [28, 29] 𝜔𝐿 2(𝑞) = 2𝑁𝐶 𝜌𝑞2 (𝛽𝐼0 + 𝛿𝐼2) + 𝑘𝑒𝑘𝑇𝐹 2 𝑞2|𝐺(𝑞𝑟𝑆)| 2 𝑞2+𝑘𝑇𝐹 2 (𝑞) (10) and, 𝜔𝑇 2(𝑞) = 2𝑁𝐶 𝜌𝑞2 (𝛽𝐼0 + 1 2 𝛿(𝐼0 − 𝐼2)) (11) with, 𝛽 = 𝜌𝑎2 2𝑀 [ 1 𝑟 𝑑𝑉(𝑟) 𝑑𝑟 ] 𝑟=𝑎 (12) 𝛿 = 𝜌𝑎3 2𝑀 [ 𝑑 𝑑𝑟 ( 1 𝑟 𝑑𝑉(𝑟) 𝑑𝑟 )] 𝑟=𝑎 (13) the notations of 𝐼0and 𝐼2 are, with 𝑥 = 𝑞𝑎, 𝐼0 = 1 − 𝑠𝑖𝑛(𝑥) 𝑥 (14) and, 𝐼2 = 1 3 − 𝑠𝑖𝑛(𝑥) [ 1 𝑥 − 2 𝑥3 ] − 2 𝑐𝑜𝑠(𝑥) 𝑥2 (15) here, 𝑀, 𝜌 and 𝑁𝐶 are the atomic mass, the number density and the coordination number of the said bmgs while 𝑉′(𝑟) and 𝑉″(𝑟) be the first and second derivatives of the interatomic pair potential, respectively. for the long-wavelength limit of the phonon frequency spectrum, the longitudinal and transverse frequencies are proportional to the wave vectors as follows [1-14, 18, 19, 23, 24, 28-32] . 𝜔𝐿 = 𝐿 𝑞 and 𝜔𝑇 = 𝑇 𝑞 (16) for hb [30], tg [31, 32] and bs [28] approaches respectively, the formulations of longitudinal sound velocity(𝑣𝐿), and transverse sound velocity(𝑣𝑇 ) are given by the following equations, 𝑣𝐿 (𝐻𝐵) = 𝜔𝐸 ( 3 10 𝜎2) 1/2 = (0.5477)𝜔𝐸 𝜎 (17) 𝑣𝑇 (𝐻𝐵) = 𝜔𝐸 ( 1 10 𝜎2) 1/2 = (0.3162)𝜔𝐸 𝜎 (18) 𝑣𝐿 (𝑇𝐺) = {( 4𝜋𝜌 30𝑀 ) ∫ 𝑑𝑟 𝑔(𝑟) 𝑟3 ∞ 0 [𝑟 𝑉′′(𝑟) − 4𝑉′(𝑟)]} 1 2 (19) 𝑣𝑇(𝑇𝐺) = {( 4𝜋𝜌 30𝑀 ) ∫ 𝑑𝑟 𝑔(𝑟) 𝑟3 ∞ 0 [3𝑟 𝑉′ (𝑟) − 4𝑉′(𝑟)]} 1 2(20) 𝑣𝐿 (𝐵𝑆) = {( 𝑁𝑐 𝜌𝑎 ) [ 𝛽 3 + 𝛿 5 ] + 𝑘𝑒 3 } 1 2 (21) 𝑣𝑇(𝐵𝑆) = {( 𝑁𝑐 𝜌𝑎 ) [ 𝛽 3 + 𝛿 15 ]} 1 2 (22) for the selected bmgs, some of the important properties viz. isothermal bulk modulus (𝐵𝑇), rigidity modulus (g), poisson’s ratio (σ ), young’s modulus (𝑌) and debye temperature 𝜃𝐷 are computed using the expressions as given below [114, 18, 19, 23, 24, 28-32]. isothermal bulk modulus 𝐵𝑇 = 𝜌𝑀 (𝑣𝐿 2 − 4 3 𝑣𝑇 2) (23) modulus of rigidity 𝐺 = 𝜌𝑀𝑣𝑇 2 (24) poisson’s ratio 𝜎 = 1 2 [ 1−2 ( 𝑣𝑇 2 𝑣𝐿 2⁄ ) 1− ( 𝑣𝑇 2 𝑣𝐿 2⁄ ) ] (25) young’s modulus 𝑌 = 2𝐺(𝜎 + 1) (26) debye temperature 𝜃𝐷 = ħ 𝜔𝐷 𝑘𝐵 = ħ 𝐾𝐵 2𝜋 ( 9𝜌 4𝜋 ) 1 3 ( 1 𝑣𝐿 3 + 2 𝑣𝑇 3) − 1 3 (27) the input parameters used for present computational work are tabulated in table 1, which are calculated from using paa model [1-11] by adopting pure standard data of constituent element of bmgs [41]. aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 38 table 1: input parameters and constants used in present work. bmg 𝒁 𝒁𝑺 𝒁𝒅 𝑹𝒅(𝐚𝐮) 𝑹𝒔(𝐚𝐮) 𝜴𝟎(𝐚𝐮) 𝟑 𝑵𝑪 m (amu) 𝒓𝒄 (𝐚𝐮) zr67ni33 3.00 1.50 5.20 1.21 1.96 95.02 6.40 46.84 0.6941 fe80b20 3.34 1.50 4.48 2.23 2.10 129.48 12.00 80.49 0.7163 3. results and discussion the discussion and comparison of our present results with available outcomes either theoretical or experimental in the literature are narrated in this section briefly. 3.1 interatomic pair potential the pair potentials 𝑉(𝑟) (in ryd.) versus interatomic distance 𝑟(au) are displayed in figs. 1(a) and 1(b) of both bmgs and compared with available theoretical data [12-14]. also, some theoretical observations from interatomic pair potential curves are presented in tables 2-3. though the shape and nature of the interatomic pair potentials appear similar type while the potential well depths related to different bmgs are appeared differently. it is observed that the location of the well-depth of computed pair potentials 𝑉(𝑟) moves towards the left for both bmgs as compared to that of reported theoretical data [12-14], which show higher results than the computed one. the first minima position is significantly affected by the types of screening i.e. the similarity is seen in the pair potential nature by changing the local field correction functions except at or near the dip position. under the exchange and correlation effect, inclusion in the static h-dielectric screening changes the width and depth of the interatomic pair potential curves. the well-depth impact due to hcorrection function is slightly less than that due to the rest of the screening functions. the first zero in the pair potential arises at 𝑟 = 𝑟0 = 1.94 au and 3.76 au for the 𝐹𝑒80𝐵20 and 𝑍𝑟67𝑁𝑖33 bmgs respectively. thus, the effect of exchange and correlation function is not found significantly, but the potential well is more in case of other correlation functions than that of the h-function. various screening functions influence to increase the well-depth slightly. the maximum and minimum well-depth for 𝐹𝑒80𝐵20 is seen due to s and t-functions, respectively, while the same for the rest of three are lying between them. similarly, in the case of 𝑍𝑟67𝑁𝑖33, the maximum and minimum well-depths are found for iuand hscreening functions and the rest of three are lying between them. the interatomic pair potential welldepth deepens with increasing atomic volume and hence here, well-depth of 𝐹𝑒80𝐵20 is more than that of 𝑍𝑟67𝑁𝑖33. the potential energy remains negative within the large 𝑟-region. the flat type negligible and gradually vanishing oscillations after 𝑟 =7.31 au and 𝑟 = 9.61 au in 𝐹𝑒80𝐵20 and 𝑍𝑟67𝑁𝑖33 bmgs are observed due to the interaction between electrons and ions because of colombian repulsion of the potential. however, we have not shown these features correctly from the graph. for the small values of interatomic distances 𝑟, the interatomic pair potentials 𝑉(𝑟) are strongly repulsive and with the increase of distances, less oscillating nature are observed as expected, which is directly related to the friedel oscillations due to log-singularity in electron susceptibility function. moreover, the interatomic pair potentials after the first minima or dip, show minor oscillations of very small amplitude and converges to zero at some larger interatomic distances. in the attractive part, the interatomic pair potentials converge to a limited and fixed value rather than being zero. while, bretonnet and derouiche [44] showed that the repulsive part of 𝑉(𝑟) is drawn lower and its appealing part is deeper because of the 𝑑-electron impact where the 𝑉(𝑟) is moved towards the lower 𝑟-values and supports the 𝑑-electron effect. all pair-potential graphs show the combined effect of 𝑠-and 𝑑-electrons. aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 39 table 2 : observations of interatomic pair potentials for fe80b20 bmg. screening function h t iu f s first zero r (au) 1.94 1.94 1.94 1.94 1.94 maximum depth r (au) 2.27 2.25 2.23 2.25 2.25 maximum dip (ryd.) −0.56 −0.56 −0.57 −0.57 −0.62 oscillatory behaviour starts from r (au) 7.92 6.18 6.34 6.07 6.75 table 3 : observations of interatomic pair potentials for zr67ni33 bmg. screening function h t iu f s first zero r (au) 3.76 3.76 3.76 3.76 3.76 maximum depth r (au) 4.44 4.46 4.52 4.51 4.41 maximum dip (ryd.) −0.10 −0.10 −0.12 −0.11 −0.11 oscillatory behaviour starts from r (au) 10.50 12.54 10.43 9.43 10.10 3.2 phonon dispersion curves figures 2-4 show the pdcs of the both bmgs under investigation generated from the interatomic pair potential and pair correlation functions using hb [30]-, tg[31,32]and bs [28]approaches with the five screening functions viz. h, t, iu, f and s, respectively. in these pdcs, the longitudinal and transverse modes of phonon eigenfrequencies have been plotted in the form of 𝜔𝐿 and 𝜔𝑇 (× 1013𝑠−1) versus 𝑞 (å−1) graphs. table 4 shows a comparative observational analysis from the pdcs of both bmgs. the presently computed outcomes are compared with available either theoretical [1416] or experimental data considered by gupta et al. [13]. the presently obtained results of pdcs are found qualitative agreement with them. also, the md result of the aihara et al. [15,16] of 𝑍𝑟67𝑁𝑖33 bmg at two different temperatures 100k and 500k indicates the low and high amorphous states respectively, which are also shown in the same figure. for 𝐹𝑒80𝐵20 bmg, the first and second 𝜔𝐿 𝜔𝑇 crossover positions for the hb [30], tg [31,32] and bs [28] approaches are seen at 2.5 (å−1) and 3.9; 1.3 (å−1) and 2.2 (å−1); 2.3 (å−1) and 2.6 (å−1), respectively. for 𝑍𝑟67𝑁𝑖33 bmg, the first and second 𝜔𝐿𝜔𝑇 crossover positions for the hb [30], tg [31,32] and bs [28] approaches are seen at 2.3 (å−1) and 3.6(å−1); 1.3(å−1) and 2.1(å−1); 2.2(å−1) and 2.6 (å−1), respectively. actually, here model potential parameter 𝑟𝐶 is calculated from the well-known formula, which shows significant difference than the reported data. moreover, the present outcomes of pdcs due to tg [31,32] approach is higher than those due to hb [30] and bs [28] approaches. from the pdcs, the frequency increases with the wave aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 40 (a) (b) fig. 1: pair potentials for (a) fe80b20 and (b) zr67ni33 bmgs. (a) (b) fig, 2: phonon dispersion curves for (a) fe80b20 and (b) zr67ni33 bmgs using hb approach. aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 41 (a) (b) fig. 3: phonon dispersion curves for (a) fe80b20 and (b) zr67ni33 bmgs using tg approach. (a) (b) fig. 4: phonon dispersion curves for (a) fe80b20 and (b) zr67ni33 bmgs using bs approach. aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 42 table 4 : comparison of the pdcs for the selected binary bmgs. bmg freq. order maxima 𝒒(å−𝟏) minima 𝒒(å−𝟏) [30] [31,32] [28] [30] [31,32] [28] f e 8 0 b 2 0 𝝎𝑳 first 1.7 0.7 0.9 3.2 1.7 2.4 second 4.7 2.5 3.0 --3.3 3.7 third --4.0 4.2 --4.7 4.7 𝝎𝑻 first 2.5 1.3 0.9 4 2.1 2.6 second --2.9 3.1 --3.6 3.7 third --4.3 4.2 ----4.7 z r 6 7 n i 3 3 𝝎𝑳 first 1.5 0.7 0.8 2.9 1.6 2.4 second 4.2 2.4 2.9 4.8 3.1 3.5 third --3.7 4.0 --4.4 4.6 𝝎𝑻 first 2.3 1.2 0.9 3.6 2.0 2.5 second 4.8 2.6 3.0 --3.2 3.5 third --3.9 4.1 --4.5 4.6 vector and then saturates after a certain level suggesting that the selected bmgs contain finite liquid clusters, which confirms the thorpe theory [45]. the transverse phonons are absorbed for such frequencies as they are larger than the smallest eigenfrequencies of the largest cluster. these pdcs reveal that the oscillations are more prominent in longitudinal phonon modes than those in the transverse phonon modes in the large wave vector transfer region, which corresponds to the fluctuations in the particle density of these bmgs and therefore, approves the presence of the shortwavelength collective excitations. the instability in the transverse mode oscillations is due to the anharmonicity of the atomic vibrations, which suggests the transverse phonons undergo a large thermal modulation. the fluctuations in the transverse phonon mode decrease out rapidly, which connects to the damping transverse phonon modes in bmgs. in the lower wave vector transfer region, the pdcs are linear due to the characteristics of the elastic waves; but for the higher wave vector region, this linear relationship does not hold, as the sound velocity is different for different wave vectors. the collective excitations at larger wave vector transfer are due to the eminence of the longitudinal mode excitations only. the longitudinal part of pdc shows that the bmgs are screening sensitive in the low momentum region. the difference in the 𝜔𝐿 or 𝜔𝑇 (𝑠−1) versus 𝑞 (å−1) exists from the beginning, becomes maximum at the peak point and again decreases till the dip point. the peak height is dependent on the screening function as well as on the applied pseudopotential approach. the longitudinal pdcs display oscillatory behavior for larger 𝑞 values, which is absent in case of transverse phonons. a longitudinal phonon curve reaches maxima at a higher 𝑞 value than the transverse one. comparatively, the longitudinal frequency bears higher numerical value than the transverse frequency for a particular 𝑞 value, which is reflected by the distance between their peak or deep positions. for all three approaches, the transverse phonon frequencies grow with wave number and aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 43 become saturated at the first peak with small variations. though the first peak position is independent of the screening functions, the peakheight is fairly dependent on the screening function used in this computational work. from the second and third ordered minima and maxima for any screening functions in the hb [30]-approach do not appear clearly. the selected bmgs are screening sensitive in the low-momentum region. furthermore, the phonons are detected as sound waves in the macroscopic frequency limits of the spectrum. hence, the longitudinal sound velocity (𝑣𝐿) and transverse sound velocity (𝑣𝑇) have been estimated from the linear part of their curves. 3.3 computed properties the computed elastic and thermodynamic properties of fe80b20 and zr67ni33 bmgs with the available reference data are presented by tables 5 and 6 respectively, from which, it appears that the calculated values of different properties nearly agree to each other for different screening functions for a particular approach but considerably differs for different approaches i.e. a property holds nearly the same value for all screening functions for a particular approach, but the same property holds different values for the same screening function in another approach. for the selected binary glasses, our presently computed outcomes from hb and bs approaches are found in fair qualitative agreement with available results [2, 5, 13-16, 19, 21]. our results are over estimated with them. it is quite tough to judge that which of the three approaches adopted here is the best suitable for computation of vibrational dynamics of aforesaid binary bmgs, because each approach has its own identity, importance and limitations too. the hb approach is an older one but simple enough to need a minimum number of parameters to produce consistent results of the phonon data. while, the tg [31,32] approach is established upon the quasicrystalline approximation, where effective force constant depends upon the correlation function for the displacement of atoms, which further depends on the phonon frequencies. similarly, the bs approach retains interatomic interactions effectively between the first nearest neighbours only. therefore, the atomic disorderedness in the formation of metallic glasses is more which show a deviation in the magnitude of pdcs and their concerned properties. the dielectric function plays an significant role in the estimation of potential due to the screening of the electron gas. for this determination, in the present study, the local filed correction function due to h, t, iu, f and s are taken. motive for choosing them is that, the h-function does not include exchange and correlation effect and signifies only static dielectric function, whereas the t-function cover the overall features of the numerous local field correction functions projected before 1972. the iu, f and s functions are newer one amongst the existing functions and not exploited thoroughly in current study. this helps us to study the comparative effects of exchange and correlation in the aforementioned properties. therefore, the present outcomes found from five dissimilar local field correction functions may be as in contract with each other, as different order of magnitude in the figures 1-4. aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 44 table 5: thermodynamic and elastic properties of fe80b20 bmg. a p p ro a ch s cr . f u n . 𝐯𝐋 × 𝟏𝟎 𝟓 (𝐜𝐦/𝐬) 𝐯𝐓 × 𝟏𝟎 𝟓 (𝐜𝐦/𝐬) 𝐁𝐓 × 𝟏𝟎 𝟏𝟏 𝐝(𝐲𝐧𝐞/𝒔𝟐) 𝐆 × 𝟏𝟎𝟏𝟏 (𝐝𝐲𝐧𝐞/𝒔𝟐) σ 𝐘 × 𝟏𝟎𝟏𝟏 (𝐝𝐲𝐧𝐞 /𝒔𝟐) 𝛉𝐃 k [3 0 ] h 8.23 4.75 20.78 12.47 0.25 31.17 650.71 t 8.44 4.87 21.84 13.10 0.25 32.76 667.12 iu 8.19 4.73 20.60 12.36 0.25 30.90 647.89 f 8.09 4.67 20.10 12.06 0.25 30.15 639.96 s 8.23 4.75 20.76 12.46 0.25 31.14 650.37 [3 1 , 3 2 ] h 28.70 16.71 249.04 154.27 0.24 383.59 2287.08 t 35.81 20.86 387.68 240.19 0.24 597.23 2853.78 iu 36.94 21.52 412.74 255.72 0.24 635.84 2944.58 f 36.94 21.52 412.69 255.68 0.24 635.75 2944.39 s 33.32 19.41 335.73 208.00 0.24 517.19 2655.68 [2 8 ] h 8.14 2.53 31.84 3.53 0.45 10.22 355.28 t 8.16 2.57 31.92 3.66 0.44 10.57 361.53 iu 8.16 2.61 31.80 3.76 0.44 10.85 366.48 f 8.17 2.62 31.83 3.80 0.44 10.97 368.47 s 8.26 2.70 32.25 4.04 0.44 11.63 379.60 o th er s[3 0 ] v o ra [ 5 ] h 3.86 2.23 5.98 3.59 0.25 8.98 333.79 t 3.39 1.96 4.61 2.77 0.25 6.92 293.04 iu 3.67 2.12 5.43 3.26 0.25 8.15 318.01 f 3.66 2.11 5.39 3.23 0.25 8.09 316.78 s 1.66 0.96 1.11 0.67 0.25 1.67 143.82 o th er st [3 1 ,3 2 ] v o ra [ 5 ] h 4.85 2.08 12.87 3.14 0.39 8.72 317.80 t 4.69 2.26 11.04 3.69 0.35 9.96 342.58 iu 4.91 2.27 12.47 3.75 0.36 10.22 345.93 f 4.94 2.31 12.55 3.86 3.36 10.50 350.98 s 3.30 1.89 4.42 2.59 0.25 6.50 283.61 o th er s[2 8 ] v o ra [ 5 ] h 9.49 3.56 53.06 9.16 0.42 25.99 545.01 t 9.61 3.71 53.64 9.95 0.41 28.11 567.51 iu 9.58 3.67 53.41 9.74 0.41 27.53 561.47 f 9.57 3.67 53.38 9.73 0.41 27.53 561.41 h 9.65 3.74 53.86 10.13 0.41 28.60 572.69 others [21] ----13.80 17.40 7.60 5.00 ----169.00 169.30 expt. [21] ----14.10 6.50 ------ aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 45 table 6 : thermodynamic and elastic properties of zr67ni33 bmg. a p p ro a ch s cr . f u n . 𝒗𝑳 × 𝟏𝟎 𝟓 (𝐜𝐦/𝐬) 𝒗𝑻 × 𝟏𝟎 𝟓 (𝐜𝐦/𝐬) 𝑩𝑻 × 𝟏𝟎 𝟏𝟏 (𝐝𝐲𝐧𝐞/𝒔𝟐) 𝑮 × 𝟏𝟎𝟏𝟏 (𝐝𝐲𝐧𝐞/𝒔𝟐) σ 𝒀 × 𝟏𝟎𝟏𝟏 (𝐝𝐲𝐧𝐞/𝒔𝟐) 𝜽𝑫 k [3 0 ] h 5.49 3.17 11.67 7.00 0.25 17.51 391.75 t 5.50 3.18 11.70 7.02 0.25 17.55 392.25 iu 5.47 3.16 11.59 6.95 0.25 17.38 390.34 f 5.55 3.20 11.91 7.15 0.25 17.87 395.71 s 5.49 3.17 11.66 7.00 0.25 17.49 391.51 [3 1 ,3 2 ] h 19.61 11.51 144.94 92.21 0.24 228.22 1419.31 t 25.51 14.99 244.58 156.50 0.24 386.96 1848.80 iu 26.60 15.63 265.81 170.20 0.24 420.78 1927.97 f 26.61 15.64 265.92 170.26 0.24 420.95 1928.35 s 23.36 13.72 205.16 131.07 0.24 324.18 1692.01 [2 8 ] h 7.61 3.65 27.93 9.29 0.35 25.09 456.96 t 7.65 3.69 28.09 9.50 0.35 25.61 461.92 iu 7.68 3.74 28.09 9.74 0.34 26.20 467.54 f 7.70 3.75 28.17 9.82 0.34 26.38 469.27 s 7.72 3.76 28.40 9.85 0.34 26.48 470.03 others [14] 4.46 1.88 10.40 2.43 ----236.00 others-md [15,16] 4.10 4.75 1.95 2.02 7.80 11.72 2.80 ----217.00 254±11 others-[14,30] 5.00 2.50 11.76 ------311.00 others [14, 28] 4.19 2.05 8.46 ------256.00 others [19] 3.53 2.04 4.94 2.96 --7.40 -- o th er s[3 0 ] v o ra [ 2 ,3 ] h 1.79 1.03 1.25 0.75 0.25 1.87 127.87 t 1.81 1.04 1.27 0.76 0.25 1.91 129.23 iu 0.87 0.50 0.29 0.18 0.25 0.44 62.10 f 0.85 0.49 0.28 0.17 0.25 0.42 60.80 s 1.59 0.92 0.99 0.59 0.25 1.48 113.73 o th er s[3 1 ,3 2 ] v o ra [ 2 ,3 ] h 2.41 1.37 2.34 1.31 0.26 3.30 169.30 t 2.80 1.61 3.06 1.83 0.25 4.57 199.80 iu 2.72 1.70 2.49 2.03 0.17 5.02 214.60 f 2.78 1.75 2.55 2.14 0.17 5.02 214.60 s 2.40 1.48 2.01 1.53 0.20 3.66 181.70 o th er s[2 8 ] v o ra [ 2 ,3 ] h 7.18 3.44 25.02 8.32 0.35 22.46 431.84 t 7.30 3.57 25.45 8.93 0.34 23.97 446.91 iu 7.25 3.52 25.28 8.69 0.35 23.38 441.08 f 7.23 3.50 25.14 8.60 0.35 23.16 438.94 s 7.36 3.62 25.75 9.21 0.34 24.68 453.72 aditya m. vora, alkesh l. gandhi / bibechana 18 (1) (2021) 33-47 46 4. conclusion lastly, the computed pdcs of the bmgs have satisfactorily reproduced the general characteristic features of a broad range of collective excitations. the presently computed pdcs and their concerned properties through hb, tg and bs approaches have shown consistent results with the successful application of the shaw’s model pseudopotential, where screening effects are also observed by various local field correction functions, which supports the paa model and pseudopotential concept. the screening effect plays a significant role in the estimation of the thermodynamic and elastic properties of said bmgs. the relative exchange and correlation effects in the selected properties are successfully examined by h-, t-, iu, fand slocal filed correction functions, which show variations according to the vibrational properties. the calculated properties observed at room temperature are found in qualitative agreement with acceptable differences with the data available in the literature. the pdc generated from the three approaches are satisfactorily reproduced general characteristics of dispersion curves. the thermodynamic and elastic properties obtained due to tg [31, 32]-approach are higher than those due to hb [30] or bs [31, 32]-approaches. hence, the pseudopotential theory is remarkably helpful for the framework of computation of theoretical data for a specific bmg. references [1] a. m. vora, vibrational dynamics of noncrystalline glassy alloys, front mater sci china 1(4) (2007) 366-378. https://doi.org/10.1007/s11706-007-0068-z [2] a. m. vora, vibrational dynamics of ni-glassy alloys, front mater sci china 3 (2009) 285-300. https://doi.org/10.1007/s11706-009-0045-9 [3] a. m. vora, vibrational dynamics of bulk metallic glasses studied by pseudopotential theory, in: oster wu (ed) computational materials, nova science publishers, inc., new york, 2009, pp 119-176. 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[6, 7] using both improved reprocessing of iras(iris) and akari survey they obtained the nearly inverse relationship between dust mass and temperature. the environment around planetary nebulae: ngc 1514, ngc 6826, ngc 2899, and cone like mailto:devendra.upadhyaya@ac.tu.edu.np https://doi.org/10.3126/bibechana.v18i2.35394 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana devendra raj upadhyay and trishna subedi/bibechana 18 (2) (2021) 154-163 155 asymmetrical dust structure studied by using iras 12, 25, 60, and 100 can not be visible by the necked eye, but their heating effect can felt. here, we have present our work related to cavities regions around agb stars by comparing two survey: iris and akari . so it is new work to understand far infrared features around agb stars. this work based on revised catalog of c-rich agb stars categorized by suh & hong(2017) [16] and it includes a comparative study of dust features. this work present in four sections first introduction, second methods, third results and discussion, and the fourth one is the conclusion. 2. methodology we have taken data of agb stars using a catalog of agb stars in our galaxy (http://web.chungbuk.ac.kr/~kwsuh/agb.html) presented by shu et al. [16-19]. his group presented a revised catalog of 3828 o-rich agb stars and 1168 c-rich agb stars. we have verified data using simbad astronomical database cds (strasbourg) (http://simbad.u-strasbg.fr/simbad/), sky view virtual observatory (https://skyview.gsfc.nasa.gov/current/cgi/query.pl), infrared astronomical satellite, iris improved reprocessing of the iras survey, akari survey. the distance of the candidate is taken from gaia archive (https://gea.esac.esa.int/archive/). we carried out search of different cavity like structures around the different agb stars in iris and akari map available in the sky view virtual observatory. the steps that we followed during the search are elaborated below: step-i: inspection of the region in 10×10 in sky view virtual observatory: the parameters used during sky survey are listed below: coordinate: j2000, projection: gnomonic image size (pixel): 500×500 brightness scaling: histogram equalization step-ii: image taken on the basis of searching isolated cavity structure around agb star step-iii: extraction of flux using aladin v2.503 software(https://aladin.u-strasbg.fr/aladin.gml): the flexible image transport system (fits) images were downloaded from sky view, according to the procedure mentioned above and the fits image is processed using software aladin v2.503. region of interest the image structure located at r.a. (j2000) = 04hr 46m33.036s and dec. (j2000) = +490 56m 23.77s selected as a region of our interest. the reasons of selections are as follows: 1 the structure seems to be isolated and its size is around 3.24 pc for iris and 12.28 pc for akari in contraction. 2 there were several condensations (minima) and the features can be seen in all 4 bands of iris survey and akari survey. 3 the structure in iris is prominent in 60µm and 100µm that enable us to study the fluxes emitted from the dust and grain. 4 the structure in akari is prominent in 90µm (akari wide-s) and 140µm (akari wide-l) that enable us to study the fluxes emitted from the dust and grain. data reduction each pixel of the cavity-like region in fits images are analyzed by using aladin v2.503 which helps in data reduction. with the help of aladin v2.503 the invisible spectral photography can be reduced into desired color and analysis of the relative flux distribution in the region of interest can be done. more precisely we cannot make visible pictures and photography in ir region but, using this software we can make visible reference with color specification. so it is convenient to draw contour map, hexbin plot and marking to find desired physical parameter (e.g. flux, coordinate, etc). the aladin software can be considered as sky atlas designed by cds for research of astronomical sources through color coded display of required http://web.chungbuk.ac.kr/~kwsuh/agb.htm devendra raj upadhyay and trishna subedi/bibechana 18 (2) (2021) 154-163 156 image. aladin v2.503 allows us to visualize digitized images of any part of the sky, to superimpose entries from the cds astronomical catalogs and tables, and to interactively access related data and information from simbad and gaia archive of all known objects in the field. flux density variation we studied the flux density of all the pixel lying inside the counter level 71 for iris under 100µm and find the flux of corresponding pixels in 60µm using the software aladin v2.503 which was used to calculate the dust color temperature and mass of each pixel due to the contribution of dust. similarly, for akari we used the counter level 100 under 140 µm image and the corresponding pixels in 90 µm were obtained. here we found the regions of maximum and minimum flux and studied the density in each image of both iris and akari in a comparative manner. dust color temperature the contour map has been made in 100 m and 140 m fits. then the corresponding flux densities are calculated from the iris 60 µm image. using the ratio of the flux density in the iris 60 µm to the flux density in the iris 100 µm in the expression given below [20, 21] , dust color temperature is calculated as, �� = −96 ln �×0.643+� ….… (1) where, � = � 60�� � 100�� since, f (60µm) and f (100µm) are the flux densities at 60µm and 100µm respectively. for akari survey, following expression is used to calculate the dust color temperature [6, 20, 21], �� = −57 ln �×0.643+� ...… (2) where, � = � 90�� � 140�� since, f (90µm) and f (140µm) are the flux densities at 90µm and 140µm respectively. dust mass estimation the dust masses are estimated from the far-infrared flux densities at 100 μm image in iris and 140 μ m in akari survey. the infrared flux can be measured from the iris sky view images and images from groningen using aladin v2.503. the resulting dust mass depends on the physical and chemical properties of the dust grains, the adopted dust temperature and the distance to the object. the final expression for the dust mass [22-24], can be written as; �dust = 4aρ 3�� ���2 � �,� ..… (3) here, b(v,t) = planck’s function, which is the function of the temperature and frequency, and given by the expression; � �, � = 2ℎ�3 �2 1 � ℎ� kt−1 .….. (4) and a= weighted grain size = 0.1 μm ρ = grain density= 3000 kgm-3 qν= grain emissivity = 0 .0010 for 100μm and 0.0046 for 60μm respectively. fν= total flux density of the region whose mass is to be determined, �� = � × 5.288 × 10−9 mjysr-1 1mjysr-1=1.26×10–19kg.s–2 d = distance to the structure b(ν,t) = planck’s function. h = planck’s constant c = velocity of light ν = frequency at which the emission is observed and t= the average temperatures of the region. values of different parameters we use in the calculation of the dust mass in our interest are as follows: using these values, an expression (3) takes the form [22-24], �dust = 0.40 ���2 � �,� ....… (5) visual extinction for visual extinction we need optical depth[25] �100 = �100µ� � �,� 100 …… (6) here f100µm in kgs-2 and b(ν,t)100 is corresponding intensity of radiation which is observed at 100 µm h devendra raj upadhyay and trishna subedi/bibechana 18 (2) (2021) 154-163 157 flux in iris as proposed by wood et al. [14]. for visual extinction: �� = 15.078 1 − � −�100 641.3 …… (7) we have uses this formula for akari by calculating optical depth for τ140. for akari survey, following expression is used to calculate the visual extinction �� = 15.078 1 − � −�140 641.3 ..…… (8) where �140 = �140µ� � �,� 140 inclination angle the angle between line-of-sight and the plane of celestial object projected in the sphere is called inclination angle. holmberg (1946) [26] established a simple model to find the inclination angle of celestial objects. holmberg equation is the relation between the axial ratio ( b/a ) and the inclination angle (i), the angle between the line-of-sight and normal to the galactic plane. the flatness factor (q) = 0.33 is assumed by considering oblate spheroid. ���2� = �2 �2 −�2 �2 ……..(9) is called ‘holmberg formula’ for inclination angle [26]. 3. results and discussion in our work, the dust color temperature, intensity of radiation, dust mass and extension are measured using fits images of 60 μm, 100 μm and 90 μm, 140 μm. projection map of coordinates in r. a. and decl fig. 1 is the projection map of the right accession and declination. it show larger region of interest in fig. 1(a) iris in comparison with fig. 1(b) because we have selected image size 10×10 for iris and 0.50×0.50 in akari. but we obtained more pixels in akari because of high resolution of survey. this projection is lambert projection in nature. fig. 1: position of candidate iras 04427+4951 (a) projection of coordinates of far infrared cavities using iris survey (b) projection that of coordinates using data of akari survey. hexbin distributions of flux fig. 2 (a) show the 60 micrometer iris image flux distribution in mjysr-1 with r.a.(j2000) and decl.(j2000) in degree in iris survey. similarly, fig. 2 (b) show the 90 micrometer akari fits image flux distribution in mjysr-1 with r.a.(j2000) and decl.(j2000) in degree in iris survey. here, color ranging from violet to red indicates more emission of flux from that pixels. in both case the central region contain lesser flux in low wavelength band of both survey. devendra raj upadhyay and trishna subedi/bibechana 18 (2) (2021) 154-163 158 fig. 2: (a) represents hexbin plot of right ascension (r.a.), declination (decl.) and 60 m flux using iris survey (b) hexbin plot of right ascension (r.a.), declination (decl.) and 90 m flux of iras 04427+4951 using akari survey. mapping of flux fig. 3 (a) present the contour map of 100 micrometer iris fits image flux distribution in mjysr-1 with r.a.(j2000) and decl. (j2000) in degree in iris survey. similarly, fig. 3(b) show the 140 micrometer akari fits image flux distribution in mjysr-1with r.a.(j2000) and decl.(j2000) in degree. here, color bar ranging from red to violet indicate decrease in flux which show the cavity region of asymptotic giant branch at center in both survey. fig. 3: the contours are shown. (a) 100 μm flux (b) 140 μ m flux with right ascension (r.a.), declination (decl.) using akari survey. linear fit of flux fig. 4(a) represents the best fit between the farinfrared flux of 60 μm and 100 μm. similarly, fig. 4(b) shows the best fit relation between far-infrared flux emission in 90 μm and 140 μm. here, the data extracted from the fits image of the iris and akari survey. devendra raj upadhyay and trishna subedi/bibechana 18 (2) (2021) 154-163 159 fig. 4: (a) linear fit between flux of 60 μm and 100 μm (b) linear fit between flux 90 μm and 140 μm. both has positive slope. the best fit line obtained are: f60=0.28f100 1.16 ……..(10) f90=0.10f140 + 7.33 ……..(11) here, f60, f100, f90 and f140 are flux in mjysr-1. the slope of these line are 0.28 and 0.10 used for the calculation of dust color temperature. the coefficient of correlation 0.85 in iris data and 0.53 in akari data which shows flux at central region of infrared cavity are more diverse. mapping of dust color temperature fig. 5 presents the contour map of dust color temperature distribution. here, color means the temperature depends upon the wavelength of radiation emitted by a cloud of dust from the cavity region around agb stars. fig. 5: represents contour map of dust color temperature (a) using iris data. (b) using akari survey. the contour and color bar distinguish the color temperature of radiation. on comparing two survey data, the dust color temperature is more in iris whereas lesser in akari. it shows higher the wavelength band lesser the temperature. from this study, the dust color temperature is in the range between 22.85 k and 24.1 k with an average dust color temperature of 23.48 k in the iris survey and 14.54 k to 15.24 k with an average dust color temperature of 14.89 k in the akari survey. mapping of planck’s function fig. 6 shows intensity of radiation distributions in far-infrared radiation emitted by a cloud of dust around agb stars corresponding to dust color temperature. devendra raj upadhyay and trishna subedi/bibechana 18 (2) (2021) 154-163 160 fig. 6: contour map of planck's function (a) using iris data. (b) using akari survey. the contours and color separate the different intensities of radiation. in the given fig. 6(a) and (b), the color bar represents the radiation intensity increases from violet to red. looking at the isocontours we generated, the iris plot shows the spectral intensity decrement towards the center, but the maximum intensity lies a little away from the center. however, the akari plot shows the irregular trends in planck's function values. here, different in trend due to polytropy nature of the dust in the region around agb stars. mapping of dust mass fig. 7 present the contour map of dust mass in the cavity created due to agb wind. by calculation we obtained the average dust mass is 3.55 × 1027 kg (1.79 ×10-3mʘ) using iris fits observation and 5.34×1028 kg (2.69 × 10-2 mʘ ) in akari fits analysis. here on comparing from fig. 5, fig. 6, and fig. 7 in both survey dust mass is more in that region where dust color temperature and planck's function minimum. it shows a nearly inverse trend of dust mass with the dust color temperature, planck's function. fig. 7: contour map of dust mass using ( a) iris data. (b) contour map using akari survey. visual extinction fig. 8 (a) and (b) show the variation of dust color temperature with visual extinction in both surveys. the values are in the range of 4.3 × 10-4 3.4 × 10-4 mag in iris and 7.5 × 10-3 4.5 × 10-3 mag in akari. here, temperature has inverse relation with visual extinction in both survey. the best fit line for iris and akari data obtained are: devendra raj upadhyay and trishna subedi/bibechana 18 (2) (2021) 154-163 161 td=-0.75av +26.12 ……..(12) td=-0.23av + 16.16 ……..(13) the coefficient of correlation are -0.72 in iris data and -0.96 in akari data. this show that akari survey is more intensive and more responsive. fig. 8: the variation of dust color temperature (td ) with visual extinction ( av ) (a) for iris and (b) for akari survey. table 1: structure of the cavity in terms of extension contraction and inclination angle. table 1 shows the extension (major diameter) contraction(minor diameter), inclination angle values. here, the size of the cavity region we have selected in iris is more (36.56×12.28) pc whereas structure is small in akari image (10.02×3.24) pc since we have taken 10×10 size in iris and 0.50× 0.50. extension and contraction of the structure obtained using a simple expression l = r × θ, where r = 3000.36 pc is the distance to the structure and θ = pixel length (in radian). the value of inclination angle is nearly 900 shows cavity structure suggesting an edge-on appearance. 4. conclusions we have studied physical properties (flux variation, dust color temperature, dust mass estimation, distance, planck’s function, and extinction) of the cavity region around structure iras 04427+4951 within 10×10 for iris all-sky map and 0.50×0.50 for akari all-sky map. we focus on the dust environment of agb stars. the search of the dust structure in far-infrared (100 µm and 60 µm) of various agb stars in iris database and (140 µm and 90 µm) in akari all-sky map perform. the distance to the agb star is 3000.36 pc. the size of cavity-like structure around agb star in iris all sky map is found to be 36.56 pc×12.28 pc and akari all sky map is found to be 10.02 pc×3.24 pc. the difference in the obtained size is found due to different size during target extraction i.e., 1⁰×1⁰ for iris all sky map and 0.5⁰× 0.5⁰ for akari all sky map and also due to the independent contour map drawn for different map. from the iris and akari map, we have seen the minimum flux region is at the center of the cavity. the physical properties of a cavity of our region of interest are studied. we have extensively used the help of aladin v2.5 and python 3. we tagged each pixel and the data of flux density extracted and dust color temperature, dust mass estimation, size of the structure, inclination angle, and visual extinction. from the above study, we obtain the dust color temperature in the range between 22.85k and 24.1 k with an average dust color temperature of 23.48 k in the source extension contraction inclination angle iris 36.56 12.28 86.150 akari 10.02 3.24 86.080 devendra raj upadhyay and trishna subedi/bibechana 18 (2) (2021) 154-163 162 iris survey and 14.54k -15.24k with an average dust color temperature of 14.89k in the akari survey. the average dust mass is 3.55 × 1027 kg (1.79 ×10-3mʘ) in iris survey and 5.34×1028 kg (2.69 × 10-2 mʘ )in akari survey. the dust color temperature and dust mass show a nearly inverse relation with each other which supports our physics. the average value of spectral density is 8.75 × 10-16 wm-2sr-1hz-1 and 1.47 10-16 wm-2sr-1hz-1 using fits of iris and akari the size of the structure is found to be 36.56pc × 12.28 pc with inclination angle 86.150 in iris and 10.02 pc × 3.24 pc with inclination angle 86.08 0 in akari map. the visual extinction is found to be in the range of 4.3 × 10-4 3.4 × 10-4 mag in iris and 7.5 × 10-3 4.5 × 10-3 mag in akari. on comparing past dust properties obtain using iris and akari and our results. here, we reach an understanding of 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https://ui.adsabs.harvard. /abs/1946melus.117....3h https://doi.org/10.1086/192107 https://doi.org/10.5303/jkas.2009.42.4.081 https://doi.org/10.1111/j.1365-2966.2011.19462.x https://doi.org/10.5303/jkas.2018.51.5.5 https://doi.org/10.3847/1538-4357/ab6609 https://doi.org/10.1051/0004-6361:20030575 https://ui.adsabs.harvard.edu/abs/1993apj...409..725y https://ui.adsabs.harvard.edu/abs/1993apj...409..725y https://doi.org/10.3847/1538-4357/abbb8d https://ui.adsabs.harvard.edu/abs/1983qjras..24..267 https://ui.adsabs.harvard.edu/abs/1983qjras..24..267 https://ui.adsabs.harvard.edu/abs/1946melus.117....3h bibechana 18 (2) (2021) 130-137 130 a study of dust structure nearby white dwarf wd1334-678 ishwor nath joshi, ajay kumar jha*, binil aryal central department of physics, tribhuvan university, kirtipur *email: ajay.jha@cdp.tu.edu.np article information: received: december 31, 2020 accepted: may 26, 2021 keywords: white dwarf interstellar medium akari flux density dust color temperature abstract a low flux density region nearby white dwarf wd1334-678 in the 140 µm akari survey maps has been systematically searched and found a far-infrared cavity centerd at r.a. (j2000) = 13h38m14.4s, dec.(j2000) = −68◦40’42”, in which minimum flux is 19.5 mjy/sr at 90 µm wavelength. the physical properties (size, dust color temperature, dust mass) and thermodynamic property (planck function distribution) of the cavity using 140 µm and 90 µm akari survey data has been presented. the size of the cavity is found to be 0.17◦× 0.12◦ . the dust color temperature is found in the range 17.70 ± 0.01 k to 18.81 ± 0.01 k. the plank function distribution along major and minor diameters shows a very good agreement with sinusoidal fitting. the period of oscillation of dust particles along major and minor diameters are 3.2 wm-2sr-1hz-1arcmin-1and 1.6 wm-2sr1hz-1arcmin-1, respectively. doi: https://doi.org/10.3126/bibechana.v18i2.37439 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction the low and intermediate-mass (m < 10 mo) stars formed by nuclear burning, appears as a red giant in the region of hertzsprung-russell diagram, is called asymptotic giant branch (agb) stars [1]. when an asymptotic giant branch star exhausts the supply of hydrogen in its core, the core shrink and its temperature increases, causing the outer layers of the star to expand and cool. the star's luminosity increases, and it becomes a red giant, following a track leading into the upper right hand corner of the hr diagram (blandford& rees, 1974). the agb phase is divided into two parts, the early agb (e-agb) and the thermally pulsing agb (tp-agb). during the e-agb phase the principal source of energy is helium fusion in a shell around a core consisting mostly of carbon and oxygen. during this phase the star swells up to giant proportions to become a red giant again. the star may become as large as one astronomical unit. after the helium shell runs out of fuel, the tp-agb starts. now the star derives its energy from fusion of hydrogen in a thin shell, inside of which lies in the now inactive helium shell. however, on periods of 10,000 to 100,000 years the helium shell switches on again, and the hydrogen shells switches of a process known as a helium shell ash [2]. towards the end of their lifetime, almost all (9598%) stars lose a substantial fraction of their mass https://doi.org/10.3126/bibechana.v18i2.37439 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana ishwor nath joshi et al./ bibechana 18 (2) (2021) 130-137 131 on the asymptotic giant branch (agb) in form of massive winds, which compels them into the planetary nebula (pn) phase. the central star of pn is the white dwarf. the massive stellar wind emitted from the agb star interacts with the ambient interstellar medium. thus the structure (gas or the dust) around the white dwarf preserve the history as a fossil record of the early and late agb phase of the star. it is important to understand the shaping process of interstellar clouds as well as the nature of the emission from agb to pn phase. the white dwarf is suspected to reside within giant dust structures which may represent fossil records of its progenitor's transition from spherically symmetric to bipolar or unipolar mass loss. it can be suspected that the white dwarf is not the only one where fossil records of ancient mass loss in its neighborhood as well as signs of the resulting shaping can be traced. besides being ideal laboratories for the study of various astrophysical processes prevailing in highly excited dilute nebulae, pne and their ancestors are key objects for the understanding of the evolution of stars. in this connection, the transformation from spherically symmetric agb winds to non-spherical pne represents one of the most enduring problems of stellar astrophysics [3]. the study regarding evolved planetary system around white dwarfs has produced a separate insight into the end state of planetary system and provided that the measurements of proportion of the extra-solar planets [4]. kiss et al [5] and koenyves et al [6] investigated 462 far-infrared loops and studied their size, temperature luminosity. wienberger and armsdorfer discovered very large (90) jet like structures in the fir (far infrared) suggest in the interaction of the wind of the asymptotic giant branch (agb) stars with ambient ism matter [7]. aryal et al [8] found two giant (2.1 pc, 0.9pc) bipolar dust emission structures centered on ngc1514. this is one of the very few known cases where the history of all main mass-loss phases of the intermediate initial mass star is preserved. jha & aryal [9] performed the study of dust color distribution of two new cavity-like structures (sizes ∼ 2.7pc × 0.8pc and ∼ 1.8pc × 1pc) using iras and akari maps near pulsars. they found the difference in the average temperature in iras and akari maps to be 3.2 ± 0.9k and 4.1 ± 1.2k. a larger value of dust color temperature was found in a longer wavelength akari map than in the iras map which is not normally possible. so, we are interested to study the physical properties of far infrared cavity nearby the white dwarf wd1334678 in 90 and 140 μm akari which will give the clear hint of shaping mechanism of ism. 2. methods we found a far-infrared cavity at 90 and 140 μm akari nearby white dwarf wd1334-678. we downloaded the fits (flexible transport image system) image of a cavity structure at 90 and 140 μm. we had processed it by using the software aladin v2.5. contours were drawn to separate the minimum flux region within the structure. the corresponding flux at 90 and 140 μm at each pixel were measured in the region of interest. possible sources for the background flux were studied using the simbad database (https://simbad.ustrasbg.fr/simbad/). we adopt the following methods for calculations of flux densities, dust color temperature, planck’s function a dust mass and size of cavity in the selected region nearby the white dwarf. dust color temperature we adopt the method developed by schnee et al [10] to determine the dust color temperature of dust. the flux density of emission at a wavelength ⋋ i is given by �� = 2ℎ� ⋋� 3 � ℎ� ⋋����−1 ���⋋� −�ω� (1) where h is planck's constant, k is boltzmann's constant, c is the speed of light, nd is the column density of dust grains, � is a constant which relates the flux with the optical depth of the dust, � is the https://simbad.u-strasbg.fr/simbad/ https://simbad.u-strasbg.fr/simbad/ ishwor nath joshi et al./ bibechana 18 (2) (2021) 130-137 132 spectral emissivity index and ω� is the solid angle subtended at ⋋ i by the detector. we assumes td<< 1 and ω140 = ω90 and also ⋋ 140= ℎ� ��140 and ⋋ 90 = ℎ� ��90 , the ratio r of the flux densities at 90 and 140 µm is given as � = �(90��) �(140��) = ( 90 140 )-(3+β) [� �140 �� − 1 � �90 �� − 1 ] ω90 ω140 (2) but �140 = 103 and �90 = 160 from equation (2) becomes � =0.64-(3+β)� 103 �� − 1 � 160 �� − 1 (3) following dupac et al. [11], we use the equation, � = 1 (�+ ���) (4) to describe the observed inverse relationship between �� and �. here, � and � are free parameters found that the temperature dependence of the emissivity index fits very well with the hyperbolic approximating function. the value of � depends on dust grain properties as composition, size, and compactness. for reference, � = 0, 1 and 2 for pure blackbody, the amorphous layer-lattice matter and the metals and crystalline dielectrics respectively [12]. we used � = 2 for dust as suggested by jha & aryal (2017) [13]. for a smaller value of �� , 1 can be dropped from both numerator and denominator of equation and it takes the form � = 0.64−(3+β) . � 103 �� � 160 �� (5) taking the natural logarithm on both sides of equation (5) we get, ln(r) = ln 0.64 -(3+β)[103 �� − 160 �� ] = ln 0.64 -(3+β)[−57 �� ] (6) we find the expression for the temperature as, �� = −57 ln [�×0.64 3+� ] where � = �(90��) �(140��) (7) f(90 µm) & f(140 µm) are the flux densities at 90 µm and 140 µm, respectively. in this way, we can use equation (7) for the determination of the dust grain temperature [14]. planck’s function the power emitted by a body as radiation of different frequencies per unit surface area of the body, per unit solid angle per unit frequency is termed as spectral radiance of that body. according to planck, the spectral radiance of a body at frequency � and temperature (t) is given by [15], � �, � = 2ℎ�3 �2 [ 1 � ℎ� ���−1 ] (8) this equation is called the expression for planck's function where, �� = boltzmann's constant � = speed of light � = frequency at which the emission is observed ℎ = planck's constant and � = dust color temperature of each pixel by using the formula given by equation (8), we can calculate the planck's function of each pixels of the cavity. we finally plot graphs of planck's function versus distance along the major and minor axes to study the distribution of planck's function along the extension and compression of the cavity. the value of planck’s function depends on the wavelength (frequency) and temperature [16]. the mass of the dust within the region of interest can be calculated by the method of hildebrand (1983) [17]. 3. results and discussion structure: contour map for the systematic search on akari maps, the white dwarf wd1334-678 is located at r.a. (j2000) = 13h38m14.4s, dec. (j2000) = −68◦40’42”. the size of the cavity found nearby the white dwarf is 0.17◦× 0.12◦. using the aladin v2.5 suitable contours are made at level 1 and 50 that enclose the minimum flux density of the isolated cavity. the ishwor nath joshi et al./ bibechana 18 (2) (2021) 130-137 133 contour map of cavity the contour level 1 to 50 at 140µm as shown in figure 1 (a). fig. 1: (a) showing contour levels in fits image of far-infrared cavity nearby wd1334-678 at 140 µm. two contours at 140 µm image for the best selection of contour with major axis cd and minor axis ab and (b) jpeg image of wd1334-678 at 140 µm [18]. distribution of flux density and contour map at 140 µm the values of akari flux densities at 90 µm and 140 µm have measured using aladin2.5 software. figure2 (a) shows graph between flux at 90 µm and 140 µm. a best fit straight line is drawn on the data. the slope of the line is 0.035. using equation (7) and values of the slope of best fit line, we calculated the dust color temperature. inside the cavity, the dust color temperature found to be varied from 17.70 ± 0.01 k to 18.81 ± 0.01 k. for the minimum and maximum fluxes, no good correlation is seen whereas for the intermediate flux values, there is good correlation. fig 2 (b) shows the akari 140 µm far infrared image of the core region of the cavity located nearby white dwarf wd1334-678 having size 0.17◦×0.12◦ at r.a. (j2000) = 13h38m 14.4s, dec. (j2000) = −68◦40’42”. we got different contours levels by plotting the flux densities at 140 µm. the contour levels are at fluxes 46.14, 49.02, 51.90, and 53.82mjy/sr respectively. from fig. 2 (b), we can see that the gap between two counter levels at northern-east region is very small, while the gaps between counter levels become broaden at southern-west region. there may be external sources in northern-east region so that that the counter levels at northern region are compressed. this indicates that mass loading takes place in the middle part of the cavity. contour maps of dust color temperature and dust mass distribution fig.3a and 3b represent the dust color temperature and dust mass contour maps. from fig. 3a, in southern-east, low temperature can be seen, while higher mass can be seen in this region (fig. 3b). similarly, along north-east temperature is high, while the mass is low. it is seen that the lower the temperature higher the mass in the contour maps which is expected trend. in the core region, higher mass distribution can be seen (fig. 3b) but in that region, temperature is not low. this shows that there might be an external cause. dust mass contour map and dust color temperature contour map gives the information of the distribution of the dust mass and dust color temperature within the region of interest respectively. ishwor nath joshi et al./ bibechana 18 (2) (2021) 130-137 134 gaussian nature of dust color temperature and dust mass fig.4a and 4b represent the gaussian temperature and the gaussian mass distributions respectively. the value of standard deviation is found to be (σ) = 0.21 and mean value is (��) = 18.15 k. since the standard deviation is small, we can expect that the data values tend to be close to the mean value of the temperature i.e. small variation of data values from mean can be expected. from fig.4a, it is clear that the data are skewed right. this implies that the temperature distribution is not quite symmetric. the gaussian distribution curve is left skewed in fig. 4b. this suggests that the mass distribution has lack of perfect symmetry. the average value of the dust color temperature in the core region of the cavity is found to be 18.15 k, equal to the gaussian center (fig.4a) with an offset of 1.10 k (< 2 k), suggests that the cavity is dynamically stable [19]. generally, the gaussian distribution is found to be in the good agreement with both td and md distributions (figs. 4a, b). however, gaussian width and skewness are found to be different in these plots, suggesting an external effect, probably from any wind blowing objects. distribution of planck’s function along the extension and compression of the cavity fig. 5a and 5b represent the variation of planck’s function along major and minor diameter of the cavity respectively. the solid curve stand for the sinusoidal plot, fig. (5 a,b) clearly shows that the planck’s function first decreases along with distance for the major diameter. it goes down to a certain minimum value 1.42× 10−16 and then increases with the distance. the fluctuation of planck’s function with distance frequently implies the instability inside the cavity which is responsible for the violation of the thermodynamic equilibrium. this might tell us the presence of effect of wind blower inside the cavity. but in case of minor diameter, the planck’s function increases slightly and then decreases with the distance. here the materials are in the local thermodynamic equilibrium along the compression (minor diameter) of the cavity. so, this variation seems to make our cavity is isolated and stable. fig. 2: (a) flux density at 90 µm versus 140 µm plot. the solid line represents the best fitted line. the best fitted line and the regression coefficient are given. the r2value and the distribution of data suggests that there is no correlation between 90 and 140 µm fluxes in the far-infrared cavity. this suggests that this cavity might not be formed naturally and (b) akari 140 µm far infrared images of the core region of white dwarf cavity wd1334-678 centered at r.a. (j2000) = 13h38m14.4s, dec. (j2000) = −68◦40’42”. the color bars are given for flux density in mjy/sr.. the planck’s function of dusts found to obey sinusoidal variation along extension given by ishwor nath joshi et al./ bibechana 18 (2) (2021) 130-137 135 b (ν,t) = 1.656×10-16 + 1.697×10-17 ·sin[ � (�−3.289) 3.227 ] (10) similarly, for minor diameter planck’s function distribution is shown in fig. 5b. along the compression (minor diameter), best fit sinusoidal curve obey the equation (11) b (ν,t) = (1.592×10-16) + (1.374×10-17)·sin[� (�−0.861) 1.691 ] (11) from figures 5a and 5b, it can be concluded that dust particles are oscillating sinusodially along extension and compression with periods 3.2 wm2sr-1hz-1arcmin-1 and 1.6 wm-2sr-1hz-1arcmin-1, respectively. fig. 3: the contour map of dust color temperature (a) and dust mass (b). the contour levels are shown. fig. 4: the distribution of dust color temperature (a) and dust mass (b). the solid curve represents gaussian fits. the gaussian parameters are given. the error bar represents ±1σ of the deviation. ishwor nath joshi et al./ bibechana 18 (2) (2021) 130-137 136 fig. 5: variation of planck’s function with distance along the major (a) and minor (b) diameter of the cavity. the solid lines represent sinusoidal fit. the error bar is the standard error of the deviation. 4. conclusion we systematically searched a far infrared cavity nearby white dwarf wd1334-678 in akari maps centered at r.a. (j2000) = 13h38m14.4s, dec. (j2000) =−68◦40’42”. we studied physical (size, dust color temperature, dust mass) and dynamic (planck function distribution) properties of the cavity. we conclude our results as follows: (a) the size of the far infrared cavity is found to be 0.17◦× 0.12◦. the minimum flux density at 140µm is found to be 46 mjy/sr. the dust color temperature is found to lie in the range17.70 ± 0.01 k to 18.81 ± 0.01 k. (b) the average mass of the dust in the cavity is found to be 1.1×1025 kg. it indicates that the region is mass deficiency region, suggest the external cause (white dwarf). the white dwarf (wd1334678) might have blown and swept away the material from the region of cavity. (c) the planck function distribution along the major and minor diameter of the cavity showed non-uniform distribution, suggesting that the dust in the cavity are not in the thermodynamically equilibrium. (d) planck function distribution show sinusoidal nature. this indicates that the dust in the cavity might be oscillating in order to gain stability. the period of oscillation along extension (major diameter) and compression (minor diameter) are found to be 3.2 wm-2sr-1hz-1arcmin-1 and 1.6 wm2sr-1hz-1arcmin-1, respectively. acknowledgement we acknowledge sky view virtual observatory, akari survey, simbad database, origin5.0, origin8.0 and girl catalog. one of the author (inj) acknowledges central department of physics, tribhuvan university, kirtipur, nepal for all kind of support for his research work. references [1] f. herwig, evolution of asymptotic giant branch stars, annual review of astronomy and astrophysics 43 (2005) 435-479.. https://doi.org/10.1146/annurev.astro.43.072103.150600 [2] b. aryal and r. weinberger, dust structure around white dwarf wd1003-44 in 60 & 100 μm iras survey, himalayan physics 2 (2011) 5-10. https://doi.org/10.3126/hj.v2i2.5202 [3] b. aryal, asymmetric mass-loss from the white dwarf wd 0253+209: secret revealed, bibechana 8 (2012) 1-7. https://doi.org/10.3126/bibechana.v8i0.4806 [4] d. koester, b.t. gansicke, j. farihi, the frequency of planetary debris around young white dwarfs, astronomy and astrophysics 566 (2014)20. https://doi.org/10.1051/0004-6361/201423691 [5] cs. kiss, a. mor, l.v. tth, far-infrared loops in the 2nd galactic quadrant, astronomy & astrophysics 418 (2004) 131-141. https://doi.org/10.1051/0004-6361:20034530. https://doi.org/10.1146/annurev.astro.43.072103.150600 https://doi.org/10.3126/hj.v2i2.5202 https://doi.org/10.3126/bibechana.v8i0.4806 https://doi.org/10.1051/0004-6361/201423691 https://doi.org/10.1051/0004-6361/201423691 https://doi.org/10.1051/0004-6361:20034530 ishwor nath joshi et al./ bibechana 18 (2) (2021) 130-137 137 [6] v. koenyves, cs. kiss, a. moor, z.t. kiss, l.v. toth, catalogue of far-infrared loops in the galaxy, a&a 463 (2007) 1227-1234. https://doi.org/10.1051/00046361:20065438 [7] r. weinberger, and b. armsdorfer, a pair of 9 ° long dust jets ejected from evolved stars, astronomical society of the pacific 313 (2004) 299. 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[19] a.k. jha, b. aryal, a study of farinfrared loop at -5o galactic latitude around pulsar j1627-5547, bibechana 15 (2018) 70-76. https://doi.org/10.3126/bibechana.v15i0.18443 https://doi.org/10.1051/00046361:20065438.%20 https://doi.org/10.1111/j.1365-2966.2009.15966.x http://dx.doi.org/10.1007/s12036-018-9517-6 https://doi.org/10.1051/0004-6361:20030575.%20%20 https://ui.adsabs.harvard.edu/link_gateway/1994apjs...95..457w/doi:10.1086/192107 https://ui.adsabs.harvard.edu/link_gateway/1993apj...409..725y/doi:10.1086/172702 https://doi.org/10.3126/bibechana.v15i0.18443 guna nidhi gnawali et al. / bibechana 16 (2019) 145-153: rcost p.145 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal study on the effect of growth-time and seed-layers of zinc oxide nanostructured thin film prepared by the hydrothermal method for liquefied petroleum gas sensor application guna nidhi gnawali 1 , shankar p shrestha 2 , khem n poudyal 3 , indra b karki 2 , ishwar koirala 3* 1 advanced college of engineering and management, tu 2 patan multiple campus, tu 3 central department of physics, kirtipur, tu * email: ikphysicstu @gmail.com article history: received 12 september, 2018; accepted 1 november, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21556 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/bync/4.0/ abstract gas sensors are devices that can convert the concentration of an analytic gas into an electronic signal. zinc oxide (zno) is an important n-type metal oxide semiconductor which has been utilized as gas sensor for several decades. in this work, zno nanostructured films were synthesized by a hydrothermal route from zno seeds and used as a liquefied petroleum gas (lpg) sensor. at first zno seed layers were deposited on glass substrates by using spin coating method, then zno nanostructured were grown on these substrates by using hydrothermal growth method for different time duration. the effect of growth time and seed layers of zno nanostructured on its structural, optical, and electrical properties was studied. these nanostructures were characterized by x-ray diffraction, scanning electron microscopy, optical spectroscopy, and four probes sheet resistance measurement unit. the sensing performances of the synthetic zno nanostructures were investigated for lpg.xrd showed that all the zno nanostructures were hexagonal crystal structure with preferential orientation. sem reviled that the size of nanostructure increased with increase in growth time. band gap and sheet resistance for zno nanostructured thin film decreased with increase in growth time. zno nanostructured thin film showed high sensitivity towards lpg gas. the sensitivity of the film is observed to increase with increase in no of seed layers as well as growth time. the dependence of the lpg sensing properties on the different growth time of zno nanostructured was investigated. the sensing performances of the film were investigated by measured change in sheet resistance under expose to lpg gas. keywords: gas sensor; nanostructure; hydrothermal growth; electric nose 1. introduction monitoring the air quality especially in urban areas has become a priority due to the great amounts of pollutants released in the atmosphere which have a noxious effect on the human and animal’s health and also on the vegetation [1]. gas sensors are devices that can convert the concentration of an analyte gas into an electronic signal, and are an important component of devices commonly known as electric noses http://nepjol.info/index.php/bibechana http://dx.doi.org/10.3126/bibechana.v16i0.20960 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ guna nidhi gnawali et al. / bibechana 16 (2019) 145-153: rcost p.146 (online publication: dec., 2018) [2]. the history of gas sensors can be traced to the last century. miners are among the first groups that become aware of the importance of detecting hazardous gases in their working environment. in the early years, small animals, such as birds, were used as poor substitute for quantifiable method to measure this hazard [2]. to detect pollutant gases different kinds of gas sensor have been developed. in the past eighty years, scientists have developed various gas sensors such as electrochemical sensors, catalytic combustion sensors, infrared sensors, and diffusion fuel cell sensors [2]. these sensors have a broad range of application in chemical engineering, medical, agriculture, architecture and other fields. the first are electrolyte-based potentiometric sensors for automobile exhaust monitoring. another important type of commercial sensor is the metal oxide semiconductor gas sensor, e.g. sno2, which uses changes in resistance of the metal oxide to detect the low concentration of gases [2]. in this thesis work, we have synthesized and characterized the zno nanostructured thin film on glass substrate by hydrothermal method and used for lpg gas sensor application. for this work, at first we have deposited zno thin film on glass substrates and synthesized zno nanostructured thin film for different growth time. then this sample is characterized by using different instruments. 2. experimental set up zinc acetate dehydrate was first dissolved in mixture of ethanol and di-ethanolamine (dea) solution at room temperature. the molar ratio of dea to zinc acetate was maintained approximately 1.0 and the concentration of zinc acetate was 0.6m. the solution was stirred at 600c for 2 hours to yield a clear and homogeneous solution which served as precursor. the precursor solution was filtered through whatman filter paper [4].the prepared zinc acetate precursor was dripped on to spin coated substrate. the spinning velocity of the substrate was more than 2000 rpm initially and then 3000 rpm for 30 seconds in order to spread the colloid on to the glass with uniform thin layer. the deposited film is heated at 4200c for 10 min. after that the same coating process is repeated for different 2 layers, 3 layers, 5 layers, and 8 layers to get uniform, transparent and conducting thin film of zno. for nanostructure growth solution, zinc nitrate hexahydrate [zn(no3)2]. 6h2o, hexamethylene-tetramine (c6h12n4) (a.r. grade) and di water were used as starting materials and solvent respectively. zinc nitrate hexahydrate and hexamethylenetetramine was first dissolved in di water at room temperature. the concentration of zinc nitrate hexahydrate and hexamethylenetetramine was 0.3m. the solution was stirred at 600c for 2 hours to yield a clear and homogeneous solution which served as precursor. the precursor solution was filtered through whatman filter paper [6]. for hydrothermal growth, the prepared zno solution was taken into an air tight glass bottle. then the zno seeds layer deposited substrates was immersed in precursor solution, which solution was taken into air tight glass bottle. then that glass bottle was immersed into a preheated water bath at 70℃ for different time duration such as 2hrs, 4hrs, 6hrs, 8hrs, and up to10hrs. after cooling, the zno film were washed with de-ionized water several times, and then dried in air.the crystallinity of the zno films was determined by xray diffractometer. optical transmittance was obtained using usb 2000 photonics spectrometer. the electrical properties were determined from sheet resistance measurement. morphology and dimension of the zno nanostructures thin film was studied by scanning electron microscopy (sem).the lpg sensing propertieswere studied in a home-made gas sensor assembly comprising a temperature controller, a chromel-alumel thermocouple, an electrical heating plate, a gas chamber, and a lpg volume measurement unit. 3. results and discussion here we study the structural properties of zno seed layers and zno nanostructured thin film on glass substrates. typical xrd patterns of 8 coated zno seed layers are shown in fig.1. from table 1, we find that, the crystalline peaks with 2values can be exactly indexed to the hexagonal wurtzite structured zno (jcpds card no 03-0891). the sharp diffraction peaks indicate the good polycrystallinity of the prepared films and no peaks for other zinc compounds are detected in the different pattern. guna nidhi gnawali et al. / bibechana 16 (2019) 145-153: rcost p.147 (online publication: dec., 2018) table.1: jcpds d-values, observed d-values, intensity measured for (hkl) plane (i(hkl)), intensity of (hkl) plane taken from the jcpds card (i0(hkl)), and observed 2value of zno seed layers. fig.1: observed xrd pattern of zno seed layers and nanostructured thin film (hydrothermal growth for 10 hours). table.2: fwhm value (β), grain size (d), intensity measured for (hkl) plane (i(hkl)), intensity of (hkl) plane taken from the jcpds card (i0(hkl)), dislocation density (𝛿), dvalues and texture coefficient (tc(hkl)) of zno nanostructured thin film. texture coefficients of crystalline materials are calculated from the xrd result by using the relation [7], 𝑇𝑐(ℎ𝑘𝑙) = 𝐼(ℎ𝑘𝑙) 𝐼0(ℎ𝑘𝑙) ⁄ 1 𝑛 ∑ 𝐼(ℎ𝑘𝑙) 𝐼0(ℎ𝑘𝑙) ⁄𝑛 where tc(hkl) is the texture coefficient of (hkl) plane, i(hkl) is the intensity measured for (hkl)plane, i0(hkl) is the intensity of (hkl) plane taken from the jcpds card (card no. 03-0752) fitting in the x-ray diffraction guna nidhi gnawali et al. / bibechana 16 (2019) 145-153: rcost p.148 (online publication: dec., 2018) pattern material, n is the number of diffraction peak. the calculated texture coefficient values of zno nanostructures thin film for different (hkl) planes are shown in table 2. further investigations on the dimension of the nanostructures, grown by hydrothermal synthesis were investigated by scanning electron microscopy (sem). fig.2. shows sem image of zno film synthesized by hydrothermal route for 2 hours and fig. 3. shows the sem image of zno film synthesized for 10 hours. from this figure we find that nano sheet like structures were formed in both cases. the average dimensions of the nanostructures were measured based on the image. from figure the average thickness of plate like nanostructures was about 10 nm, which is slightly lower than the result of shao et al. [8] and li et al. [9]. from this image the average length and width of nanostructures is observed to be about 550 nm and 220 nm, respectively, which is also slightly lower than the values observed by different research group [10]. from fig.3.the average thickness of the plate like nanostructures was observed to be nearly same as the thickness at low growth time but length and width of nanostructures was nearly about 1050 nm and 525nm, respectively. comparing the sem image of zno for 2 hrs and for 10 hrs we find that with increase in growth time the dimension of area of nano sheet increased but thickness of the plate does not increase markedly. the reason for larger length in this case may be possibly due to longer growth time. fig.2: sem images of (8 coating) znonanosheet synthesized by hydrothermal route for 2hours at different resolution (a) 4µm (b) 1µm resolution. fig.3:sem images of znonanosheet synthesized by hydrothermal route for 10hours at different resolution (a) 20µm and (b) 4µm. fig.4 shows the transmittance and absorbance of zno nanostructured thin films fabricated at different growth time. from fig. 4(a) we have calculated the average transmittance of the wavelength ranging from 300-1000nm.the average transmittance is observed to decrease from 75% to 55% with increase the growth time. the decreases of transmittance of the film with growth time could be related to two factors. one is the thicker zno nanostructured thin films had larger hexagonal grain size and larger surface roughness. the other is the higher absorption effect for the thicker films. from the fig.4 (a) it is clearly observed that in all cases the transmittance is observed to be less than 75%, wavelength range 300-1000 nm, regardless the growth time. when the deposition condition like substrate temperature and other chemicals are kept fixed the value of transmittance is observed to decrease with increased in growth time. guna nidhi gnawali et al. / bibechana 16 (2019) 145-153: rcost p.149 (online publication: dec., 2018) from the graph it is observed that transmittance starts to decrease rapidly at 400 nm wavelength. from this figure we find that the absorption edges shift to high wavelength with increase in growth time. fig. 4(b). depicts the absorption spectra of the films obtained in the wavelength range of 300 to 1000 nm. the absorbance edge have been found broad and pronounced around 800 nm for all deposited films. from the graph it is clearly seen that the absorbance decreases sharply at wavelength range about 550 nm to 650 nm and then decreases gradually up to about 800 nm. beyond 800 nm, the absorbance is very low and nearly constant for all deposited zno nanostructured thin films. from the graph it is clearly seen that as growth time increases absorption edge shift to higher wavelength value. fig.4: optical transmittance and absorbance spectra of zno nanostructured thin films fabricated at 70℃ and different growth time. depending on a band structure of the material both direct and indirect transitions occur in a case of crystalline or polycrystalline material. as discussed earlier nature of optical transition and the optical band gap of these films are obtained using the relation (αhν) = a(hν-eg) n where n=1\2, for direct allowed transition, egis the energy band gap, α is the absorption coefficient. direct and indirect optical band gap of these nanostructured thin films is obtained by extrapolating the linear portion of the plot on to hν-axis. the point where the linear part of (αhν) 2 versus hν curve intersects the hν axis gives us the band gap value for allowed direct transitions; on the other hand, the point where linear part of (αhν) 1/2 versus hν curve intersects the hν axis gives us the band gap value for allowed indirect transitions[5]. fig.5. depicts the variation of (αhν) 2 versus photon energy (hν) film prepared at different growth time of zno nanostructures thin film. from the figure we see that the allowed direct band gap decrease from 3.164 ev to 3.107 ev with the increase in growth time. these values are lower than that observed by the reasearch group [48] for the zno nanostructures thin film growth by hydrothermal process. wang et al [48], also observed that the peak position of free excitonic emission redshifted from 3.3 to 3.2 ev with increasing of grain size from 21 to 64 nm. however many factors (enhanced strain, enlarged grain size and more oxygen vacancies between atom and molecule etc) influence the variation of the energy band gap. since from xrd analysis and sem analysis we have observed that with increase in growth time grain size of the znonano sheet increases. thus in our case decreases of energy band gap with increase of growth time may be due to larger size o f nanostructures. fig.5: (h) 2 as a function of photon energy (h) for the zno nanostructured thin film prepared at 70℃ and different growth time. fig.6. the sheet resistance of zno nanostructured thin film in air and in lpg flow condition at temperature 300℃ at different growth time. guna nidhi gnawali et al. / bibechana 16 (2019) 145-153: rcost p.150 (online publication: dec., 2018) we have measured sheet resistance in air as well as in presence of lpg gas by using four-point probe methods at operating temperature of 300℃. fig. 6. shows the variation of sheet resistance of zno nanostructured thin film versus growth time in air and lpg flow condition. the sheet resistance of the film is observed to decreases rapidly with growth time up to 6 hrs. beyond this time the decreases is rather slow. although many factors influence the variation of the sheet resistance. in our case decreases of sheet resistance with increase of growth time may be related to the grain size. we have observed that size of nanostructures was increased with increase in growth time. the increase in size of nanostructures led to deposition of more dense and compact film. also this led to decrease in grain boundaries which result in decrease in sheet resistance. the sheet resistance of the film for 2, 4, 6, 8, and 10 hours is observed to be 269, 244, 153, 151 and 139 kilo ohom/square, respectively. fig. 7: sensitivity versus growth time of zno nanostructured thin film at temperature 300℃ with equal volume of lpg gas. fig. 8: optical transmittance spectra of zno nanostructured films fabricated at 70℃ for different seed layers. the sheet resistance is observed to decreases with increase in the growth time of zno nanostructured thin film in similar way as in absence of lpg gas. the sheet resistance for growth time of 2, 4, 6, 8, and 10 hours is observed to be 204, 179, 111, 108, and 90 kilo ohom/square respectively. the value of sheet resistance in lpg gas is observed to be less than the value of sheet resistance in air. when the lpg gas is introduced in the gas chamber, ch4, c3h8 and c4h10 molecules present in lpg react with pre-adsorbed oxygen species. as a result the surface oxygen concentration is reduced, and electrons that were initially trapped by oxygen anions are released back in to the zno solid, leading to an increase in the conductivity of the zno surface. so that sheet resistance decreases in presence of lpg [3]. in the work of lokhande group [3] it is observed that for each film, the sensitivity increased with temperature up to 300℃and then decreased at 450℃. the sensitivity of all the films does not exhibit any significant difference at lower temperature. at a lower operation temperature, the low sensitivity can be expected because the gas molecules do not have enough thermal energy to react with the surface adsorbed oxygen species. at low temperatures the sensitivity is restricted by the speed of the chemical reaction, and at higher temperatures it is restricted by the speed of diffusion of gas molecules. at some intermediate temperature, the speed values of the two processes become equal, and at that point the sensitivity reaches its maximum. thus in the present case the operating temperature of zno nanostructured thin films was takes as 300℃ at which the zno sensor response attained its peak value. fig. 7 shows the sensitivity as a function of growth time measured at temperature 300℃ for zno nanostructures thin film obtained by hydrothermal growth technique upon exposure to lpg. the sensitivity of zno nanostructures thin film for growth time of 2, 4, 6, 8 and 10hrs are observed to be 24%, 26%, 27%, 28%, and 35%, respectively. the sensitivity is increased with growth time may be due to formation of larger nano sheet which led the higher surface area. guna nidhi gnawali et al. / bibechana 16 (2019) 145-153: rcost p.151 (online publication: dec., 2018) the fig.7 reveals that the sensitivity increased from 24% to 35% as the growth time increased from 2 hrs to 10 hrs, for gas flow rate 16.66 ml/sec, with continuous flow of lpg gas. from our observation we conclude that better sensitivity was observed at 10 hours. fig. 8 shows the transmittance of the zno nanostructured thin film fabricated at 70℃ for different seed layers. from fig.4.10 we have calculated the average transmittance of the film, in the wavelength ranging from 300-1000 nm. the average transmittance was observed to be different for different coat. the average transmittance of the film for 1, 2, 5 and 8 coats of seed layer is observed to be nearly about 60%, 65%, 50% and 65% respectively. from the fig. 8, it is clearly observed that in all case the average transmittance is observed to be less than 65% in the wavelength range 300-1000 nm, regardless the seeding layer. when the deposition condition like substrate temperature and other chemicals are kept fixed the value of transmittance changes according to change in the seeding time. from the graph it is observed that transmittance starts to decrease rapidly at lower range of wavelength. fig. 9 depicts the variation of (αhν) 2 versus photon energy (hν) film prepared at same growth time, but have different seed layers of zno nanostructured thin film. from the figure we see that the allowed direct band gap decrease from 3.175 ev to 3.092 ev with the increase the seed layers.the band gap is observed to be 3.175 ev for one coated sample, but for 2, 5 and 8 coated sample have nearly about 3.092 ev. from the figure the band gap is observed to decreases slightly with increase in seed layers. although many factors influence the variation of energy band gap, in our case the energy band gap decreased with increase of coating times of seed layers may be due to the increased in thickness of nanostructured film. for higher number of coating times of seed layers the thickness of the film may be increased, due to this band gab may be decreased. fig. 9: (h) 2 as a function of photon energy (h) for the zno nanostructured thin film at 70℃ for different layers of coating. fig.10: the sheet resistance of zno nanostructured thin film at different number of coats of seed layers in air and in lpg flow condition. we have measured sheet resistance in air as well as in presence of lpg gas by using four-point probe methods operating at temperature of 300℃. fig. 10.shows the sheet resistance of zno nanostructured thin film versus with different layers of seeding in air and lpg flow condition. the continuous gas flow rate was 16.66 ml/sec for each sample. in both case the sheet resistance of the film is observed to be decreases rapidly with seeding time up to 3 coats. beyond this the sheet resistance decreases slightly up to 8 coats. the sheet resistance of the film in air for 1, 3, 5, and 8 coats (for hydrothermal growth at 8 hours) is found to be 167, 156, 154, and 151 kilo ohom/squre, respectively. similarly the sheet resistance of the film in lpg flow condition is observed to be 129, 121, 114, and 108 kilo ohom/square respectively. there are many factors that influence the decreases in sheet resistance with increase the number of coating of seed layers. in our case the decrease of sheet resistance may be related to the number of metal centers increased. because with increase the number of coating of seed layers the number of nuclei of metal centers increased, and the film formed become denser and compact as number guna nidhi gnawali et al. / bibechana 16 (2019) 145-153: rcost p.152 (online publication: dec., 2018) of coating increases. for small number of coating, the connection between grains may be loose and thus film appears to be porous. with the increased number of coating, the films become denser. so that sheet resistance decreased with increase in seeding times. this decreases value of sheet resistance with increased number of coating is applicable to observed high sensitivity. fig.11: the sheet resistance of zno nanostructured thin film at different number of coats of seed layers in air and in lpg flow condition. fig. 12: sensitivity versus different number of coating of zno thin film. fig. 11 shows the sensitivity versus number of coating of seed layer of zno thin film at temperature 300℃ obtained by hydrothermal growth for 8hrs. from the figure we see that sensitivity of the film increases rapidly with increasing the number of coating of seed layer thin film up to 3 coats, beyond this the sensitivity increases in slow rate. this is because for small number of coating, the connection between grains is poor and thus the resistivity is high. the sensitivity of zno nanostructures thin film fabricated at temperature 70℃ for 1, 3, 5, and 8 coats (having same growth times) are found to be 22.63%, 27.54%, 28.61%, and 28.24%, respectively. the fig.12 reveals that the response range of sensor is from 22.63% to 28.24% for the different coat of znothin film at gas flow rate 16.66 ml/sec, with continuous flow of lpg gas. in our case sensitivity increased with seeding time may be due to larger surface area of nanostructures. for small number of coating, the connection between grains is loose and thus film appears to be porous. with the increased number of coating (up to three coats), number of grains increase thus increasing the surface area of film. so it is obvious that for the greater surface area, the interaction between the adsorbed gases and the sensor surface are stronger. so that sensitivity is increased with increasing number of coating of seed layers. on increasing the coatings further, the grains tend to overlap on others thus not contributing much in increasing the surface area. so we obtain a less steep curve for the 5 coated zno seed layer. the decrease in sensitivity for the 8 coated zno seed layer can be attributed to the same reason that the overlapping of more grains with increased number of coatings tend to decrease surface area significantly. from our observation we observed maximum sensitivity for 5 coated seed layers of zno. 4. conclusion in this present work, zno nanostructures were synthesized by a hydrothermal route for different growth time from zno seed layers. the effect of the growth time of zno nanostructured thin film and effect of seed layers of zno nanostructured thin film were studied. xrd showed that all the zno nanostructures were hexagonal wurtzite structure. sem reviled that the length and width of zno nanostructure increased with increase in growth time. the length and width of the nanostructure was found to be 550 nm and 220 nm for nanostructures grown for 2 hrs and 1050 nm and 525 nm for nanostructure grown for 10 hrs. band gap for zno nanostructured thin film decreased from 3.175 ev to 3.092 ev for the increasing seed layers and 3.164 ev to 3.107 ev with increased growth time from 2 hours to 8 hours, while the sensitivity for the same samples increased. the sensing performance of the zno nanostructures was observed with lpg guna nidhi gnawali et al. / bibechana 16 (2019) 145-153: rcost p.153 (online publication: dec., 2018) in air. the sensitivity of zno nanostructures was observed to be 24% to35% with increased in growth time and 22% to 28% with different seed layers. from our observation maximum sensitivity was observed at 10 hours growth time. references [1] g. m. camila, s. joop, l. martina, s. marayam, electrostatic spray deposited zinc oxide film for a gas sensor applications, j. applied surface science 253 (2007) 7483-7489. [2] m. liu, synthesis of zno nanowires and application as gas sensors, master’s diss., university of saskatchewan, department of chemistry, 2010. [3] c. d. lokhande, t. p. gujar, v. r. shinde, lpg sensing properties of zno films prepared by spray pyrolysis method : effect of molarity of precusor solution,sensors and actuators 120(2007) 551-559. [4] k. g. yim, s. m. jeon, m. s. kim, s. kim, g. nam, d. y. lee, j.s. kim, j. y. leem, hydrothermal synthesis of zno nanorods, applied physics and material science 121(2011) 214-216. [5] s. m. sze and k. n. kwok, physics of semiconductor devices, 3rd edition, wiley,2006. [6] t. h. meen, w. water, y. s. chen, w. r. chen, l. w. ji, c. j. huang, growth of zno nanorods by hydrothermal method under different temperatures,ieee, 1 (2007) 617-620. [7] l. o. lupan, s. chow, e. shishiyanu, t. monaico, v. shishiyanu, b. sontea, a. naitabdi, s. park, a. schulte, matt. resr.bulletin 44, (2009) 63-69. [8] s. shao, p. jia, s. liu, and w. bai, stable field emission from roselike zinc oxide nanostructures synthesized through a hydrothermal route, mater. lett.62:8-9 (2008) 1200-1203 [9] f. li, l. hu, z. li, and x. huang, influence of temperature on the morphology and luminescene of zno micro and nanostructure prepared by ctab-assisted hydrothermal method, j. alloys compd. 465:1-2 (2008) l14l19. [10] z. wang, x-f. quin, j. yim, and z-k zhu , aqueous solution fabrication of large-scale arrayed obelisk-like zinc oxide nanorods with high efficiency j. solid state chem. 177:6 (2004) 2144. [11] y. wang, x. jing, y. xia, a solution-phase, precursor route to polycrystalline sno2 nanowires that can be used for gas sensing under ambient conditions, j. am. chem. soc. 125 (2003) 16176-161 sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.165 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal correlation of solar wind velocity with different parameters during geomagnetic disturbances sujan dhakal1, binod adhikari1,2*, kiran pudasainee2, naryan prasad chapagain2,3 drabindra pandit1,2,3 subodh dahal4, bikash shrestha1, bhawani sapkota4, daya nidhi chhatkuli5 1st. xavier’s college, maitighar, kathmandu, nepal 2patan multiple campus, patandhoka, lalitpur, nepal 3central department of physics, tribhuvan university, kirtipur, kathmandu, nepal 4department of physics, himalayan college of geomatic engineering and lrm, kathmandu 5department of physics, tri-chandra multiple campus, kathmandu, nepal *e-mail: binod.adhi@gmail.com article history: received 29 april, 2018; accepted 04 november, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21575 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract we have studied the solar wind velocity and it’s relation with solar wind pressure, southward component of imf-bz, solar wind temperature (tsw), solar wind density (nsw) and geomagnetic indices during different geomagnetic disturbances. during disturbed days, there is a fluctuation of energy and plasma inside the magnetosphere, which changes the parameters like pressure, velocity, imf-bz, sym-h and ae indices. the solar wind velocity shows very remarkable relationship with pressure. there is weak connection of solar wind pressure with imf-bz, although it is more geoeffective. keywords: geomagnetic storm; solar wind velocity; cross-correlation analysis. 1. introduction geomagnetic disturbance is a temporary disturbance on earth magnetosphere initiated by various solar phenomena which produces abnormal condition in the interplanetary magnetic field (imf) [1]. this disturbance may occur due to solar wind, coronal mass ejection (cme), solar flare, corotating interaction region (cir) [2]. solar wind is the continuous flow of plasma coming out from the sun [3]. it has the magnetic field which recombines with earth’s magnetic field. during the process of interaction energy and plasma are resettled into the magnetosphere and the magnetic field energy is converted into thermal energy and kinetic energy [4, 5]. the earth surrounding atmosphere is heated by the supersonic collision less magnetized plasma which carried a large amount of kinetic and electrical energy from solar wind. some of this energy finds its way into our magnetosphere creating http://nepjol.info/index.php/bibechana mailto:binod.adhi@gmail.com http://dx.doi.org/10.3126/bibechana.v16i0.20960 https://creativecommons.org/licenses/by-nc/4.0/ sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.166 (online publication: dec., 2018) turmoil in geomagnetic activity resulting into geomagnetic storms, substorms as well as hildcaas (high intensity long duration continuous auroral activities) [6,7]. generally, the most intense geomagnetic storms are due to cmes whereas cirs cause less intense geomagnetic storms [8]. the intensity of the geomagnetic storm depends upon the solar wind structures [9]. a typical geomagnetic storm is caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the earth’s magnetic field [3]. both interactions increase plasma movement through the magnetosphere that increase an electric current in the magnetosphere. the impact of different solar phenomenon is measured by solar wind parameters and geomagnetic indices. geomagnetic storm cause changes in geomagnetic indices such as disturbance storm time (dst), kp, ae etc. geomagnetic indices are ground based measurements that are collected to quantify the state of the magnetosphere and it shows how the earth reacts to given wind structure. these indices perturbation give the idea of the earth’s magnetosphere which is continuously affected by the solar wind flowing from the sun’s corona [2, 10, 11]. geomagnetic indices are the measure of the geomagnetic activity which plays the significance role in describing the space weather. space weather refers to highly vulnerable conditions in the near earth geo-space environment. the geomagnetic indices are used to quantify the ability and geoeffectiveness of interplanetary solar wind structure to cause geomagnetic storms [5,6]. the increase in the solar wind pressure initially can compress the magnetosphere [11]. 2. dataset and methodology the data for this study have extracted the omni (operating mission as nodes on the internet) wave page and downloaded from the official website of nasa https://omniweb.gsfc.nasa.gov/data set for solar wind measurements. cross-correlation cross-correlation is simply a measure of statistical relationships involving two or more variables as a function of time lags applied to one of them. one can simply understand the cross correlation as a measure of similarities of two different time series function, one relative to the other. it is also known as sliding dot product or sliding inner product. its value ranges from -1 to 1 and with the highest degree of cross correlation its value is close to 1. it is the standard method to estimate the degree to which two different series are correlated. 3. result and discussion in this section, we are dealing with cross correlation of solar wind velocity with component of imf (bz) and geomagnetic indices for four different geomagnetic disturbance on different period. mainly correlation between vsw with solar wind parameter psw, sym-h and ae are analyzed. the brief discussion of the event using solar wind parameter and interplanetary parameters are discussed below. event 1: january 20, 2015 the case study presented in figure 1 represents fluctuation in solar and interplanetary parameters during 20th january 2015. the bottom panel of figure 1 shows the minimum and the maximum value of ae is 0 and 350 nt respectively. similarly, the minimum and maximum value of sym-h, bz, psw, nsw, vsw and tsw are found to be -19 nt and 36 nt, 7.82 nt and -5.95 nt, 0.93 npa and 9.75 ,5 n/cc and 50.83 n/cc, 273.4 km/s and 318 km/s, 13849 k and 53979 k. respectively. to be classified as storm, it must have sym-h ≤ -50 nt [3]. thus, it is characterized as quiet day event studies the variation of sq current over the various four quietest days of february 2003 and the results represents that sq (h) exhibits transient variations with varying amplitude [12]. the analysis was carried out on solar quiet days using hourly values of horizontal h components of geomagnetic field. sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.167 (online publication: dec., 2018) the variation of sq-h is characterized maximum around the daytime (07:00-17:00lt) and the minimum values during pre-sunrise hours between 05:00 and 06:00lt. it is clear that before the sunrise, conductivities are low due to absence of solar thermal heating. due to lack of solar thermal heating causes the ionosphere conductivities to be the weakest pre-sunrise hours over all the day throughout the year. during a geomagnetic disturbance, there is an energy input inside the magnetosphere which changes atmospheric parameters. but during quiet periods, the disturbances measurements on the ground are less significant. fig. 1: from top to bottom, the panels shows the variations of the tsw (104 k), vsw (km/s), nsw (n/cc), psw (npa), bz (nt), sym-h (nt) and ae (nt) in gsm coordinate system respectively during 20th january 2015. sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.168 (online publication: dec., 2018) figure 2 shows the cross-correlation of vsw with solar parameters and geomagnetic indices during 20th january 2015. the horizontal axis represents the scale in minutes and the vertical axis represents the cross-correlation coefficient. the red curve shows the correlation between vsw and tsw is highly positive with coefficient around 1. the sky-blue curve shows correlation between vswsym-h is moderate and sometime crosses the zero points and reaches a negative value around -0.5. the psw-bz (blue curve) shows positive correlation with correlation coefficient around 0.6 at time lag -800 minutes. similarly, the vsw-ae (pink curve) and vsw-nsw (yellow curve) shows positive correlation with correlation coefficient around +0.7 and +0.8 respectively. the vsw-psw (black curve) shows similar nature as yellow curve with correlation coefficient +0.8. here moderately and less correlated line seems to be more irregular and fluctuating than the highly correlated ones. fig. 2: cross-correlation of solar wind velocity with southward component of interplanetary magnetic field (bz), solar wind temperature (tsw), sym (h), ae solar wind density (nsw), and solar wind pressure respectively during 20th january 2015. event 2: 6-10 june 2006 figure 3 represents the fluctuation of various parameters during 6 to 10 june 2006. here, the ae has the minimum value around 23 nt at 3:00 ut and the maximum value around 1191 nt at 6:00 ut. similarly, the minimum and maximum value of sym-h is -45 nt and 16 nt respectively. the maximum value of bz component (gsm) is 10.62 nt and minimum bz component is -12.02 nt. the flow pressure lies between the range 1.01 npa to 18.26 npa. the maximum value of proton density 51.78 n/cc and the minimum value is 1.39 n/cc. the solar wind speed fluctuates between 327.9 km/s and 677.7 km/s and the solar wind temperature fluctuates between 27705 k and 192066 k. the figure 3 indicates that the hildcaa events starts at the mid-day of 6th june 2006 and continue till the beginning of 9th june 2006. during the event there is fluctuation in the values of parameters vsw, bz, psw, nsw, sym-h and ae respectively. the result obtained for this event are satisfied the criteria for hildcaa as suggested by tsurutani and gonzalez (1987). in 1995, tsurutani et al. has found that sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.169 (online publication: dec., 2018) the recovery phase is longer in the year 1974.the dst recoveries are associated with high ae values. the main reason for this is high fluctuation in interplanetary bz in the high velocity stream. with every instant of southward field turnings, there is an increase in ae and decrease in dst. the southward turnings cause magnetic reconnection and plasma injections into the night side magnetosphere. there is slight decrease in dst at each of these injections. these periods of continuous substorm activity are defined as hildcaa. the main cause of the interplanetary bz fluctuations is given by belcher and davis (1971). they have demonstrated that alfven waves are propagating away from the sun which are present in the high-speed streams leads to the bz fluctuations within the cirs leading to the irregular shaped storm main phase, and also the fluctuations that cause hildcaas in the storm “recovery phases”. [7] has described the seasonal dependence of hildcaa events to determine the solar cycle. their study clarifies that the occurrence of hildcaa events during the different phases of the solar cycle. that paper also discussed the interplanetary alfven waves by indicating high imf bz variance and normalized variance of the hildcaa events. [12,13] studied the solar wind energy during hildcaa in his phd thesis to described the electrodynamical process caused by the solar wind magnetosphere coupling for hildcaa events (high intensity, long duration continuous ae activity) [12,14]. he has also described the effect of hildcaa event on geomagnetic status and its consequence on earth’s environment by analysing the coupling mechanism between the solar wind and magnetosphere. fig. 3: from top to bottom, the panels shows the variations of the tsw (104 k), vsw (km/s), nsw (n/cc), psw (npa), bz (nt), sym-h (nt) and ae (nt) in gsm coordinate system respectively during 6-10 june 2006. sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.170 (online publication: dec., 2018) figure 4 shows the cross-correlation of vsw with solar parameters and geomagnetic indices during 610 june 2006. the horizontal axis represents the scale in minutes and the vertical axis represents the cross-correlation coefficient. in this figure, the sky-blue curve shows negative cross-correlation coefficient of around -0.90 between sym-h-vsw with a time lag around 10 minutes and it does not show any positive correlation during this event. the negative correlation signifies that if the value of vsw decreases with time then sym-h increases with increasing time and vice-versa. this means they have a negative relationship with each other. similarly, red curve shows positive correlation between vsw-psw with high correlation coefficient of about 0.9. the vsw-ae pink curve has a good positive cross-correlation with correlation coefficient of about 0.78 at zero-time lag. similarly, the vsw-psw black curve and vsw –nsw yellow curve also shows good positive cross-correlation with correlation coefficient of about 0.76 and 0.60 at 0-time lag respectively. blue curve ( vsw-bz) shows negative correlation with correlation coefficient of about -0.3 at 0 minutes time lag. fig. 4: cross-correlation of solar wind velocity with southward component of interplanetary magnetic field (bz), solar wind temperature (tsw), sym(h), ae solar wind density (nsw), and solar wind pressure respectively during (6-10) june 2006. event 3: 23 june 2015 figure 5 depicts the same parameters fluctuation as above during 23 june 2015. here, it is clearly seen the three phases of a geomantic storm. the initial phase begins early hours. the main phase of the storm begins from 2:00 to 12:00 ut. finally, the recovery phase begins from 13:00 and end at 24:00 ut. during main phase, the value of plasma speed (vsw) is around 700 km/s and the value of nsw lies between 0 n/cc to 30 n/cc and it is maximum around 1:00 ut. the value of bz shows variation between -20nt to 20nt. the value of psw is around 10 npa and the value of sym-h varies between 200 n t to -50 n t. the minimum value of sym-h -200nt suggested by gonzalez et al. 1992 indicates this event is an intense geomagnetic storm. here we have observed in sym-h with large negative value of -200nt with peak value. during this instant the solar wind speed and imf bz has maximum value of 800km/s and -20nt respectively. the value of ae is around 1600nt. this event is sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.171 (online publication: dec., 2018) due to the direct dependence of the geomagnetic storm with south-north component of magnetic field bz. according to gonzalez et al. (1992), the intense interplanetary field can be thought of a high speed stream, the intrinsic ejecta (called driver gas fields) and the shocked and compressed fields and plasma due to the collision of the high-speed stream with the slower solar wind preceding it. the greater the relative velocity, the stronger is the shock and the field compression, had investigated the effect of solar wind dynamic pressure psw, and preconditioning over 80 large magnetic storms (dst<100nt) which was occurring during solar cycle 23, and found that in the main phase of a storm, when there is a large enhancement of the dynamic pressure, there is always an increase in the dst peak value during the storm main phase, the weak psw verses vsw relationship was connected to the ring current energy losses which may be originated from different sources. the solar wind dynamic pressure has a strong relationship with the southward imf bz during the main phase of a storm, typically when the plasma flow speed value is very large, exceeding the 650 km/s value, and the dst<100nt. figure 5: from top to bottom, the panels shows the variations of the tsw (104 k), vsw (km/s), nsw (n/cc), psw (npa), bz (nt), sym-h (nt) and ae (nt) in gsm coordinate system respectively during 23 june 2015. sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.172 (online publication: dec., 2018) figure 6 represents the cross-correlation of vsw with solar parameters and geomagnetic indices during 23 june 2015. here the horizontal axis represents the scale in minutes and the vertical axis represents the cross-correlation coefficient. the pink curve shows the correlation between ae and vsw. this curve represents strong positive cross-correlation coefficient of about 0.8 at lag zero. the sky-blue curve shows good correlation between vsw-sym-h with cross-correlation coefficient of around -1 at lag of zero minutes. the negative correlation signifies that if the value of vsw decreases with time then sym-h increases with time and vice-versa. the blue curve of vsw-bz represents uncorrelated. the red curve represent correlation between vsw-tsw and it shows good correlation with correlation coefficient of about 0.75 at lag zero. similarly, the correlation between vsw-nsw and vsw-psw are represented by yellow and black color respectively. they shows good positive crosscorrelation of correlation coefficient about 0.6 at zero lag. fig. 6: cross-correlation of solar wind velocity with southward component of interplanetary magnetic field (bz), solar wind temperature (tsw), sym(h), ae solar wind density (nsw), and solar wind pressure respectively during 23 june 2015. event 4: 01 march 2011 figure 7 depicts the same parameters fluctuation as above during 1st march 2011. here, it shows that the minimum sym-h index for this event is -71 nt and the maximum sym-h index is 23 nt. the ae index range in between the minimum value of 18 nt and the maximum value is 1348 nt. the maximum bz component (gsm) is 16.16 nt and minimum bz component is -15.01 nt. the flow pressure lies between the range 3.63 npa to 9.47 npa. the maximum value of proton density 44.91 n/cc and the minimum value is 4.07 n/cc. similarly, the speed of solar wind is in between 301.0 km/s to 680.4 km/s. and temperature of solar wind varies in the range 21910. k to 5771.35. k respectively. the solar wind parameters and interplanetary magnetic field fluctuation represent this is a moderate sub storm. the growth phase begins around 8:00 ut of 1st march 2011. the expansion phase of the substorm begins from 12:00 ut of the same day. finally, the recovery phase begins from 20:00 ut. sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.173 (online publication: dec., 2018) the solar wind parameters, interplanetary magnetic field fluctuation show low values, characterizing this as moderate sub-storm. during the period of substorm the dst and imf bz has peak value of – 50nt and 15.01 nt respectively whereas other parameters such as solar wind speed, and ae has maximum value. the increases in the dst and the sym h indices after substorm onsets are related to the depolarization. this shows that about one third of the northward equatorial magnetic field variations are associated with variations in the solar wind pressure, a second third with substorm onsets, and the final third with interplanetary magnetic field reorientations in the north-south direction. substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy [13,14, 15]. these substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. the storage and release of energetic electron during substorms in the radiation belt leads to characteristic changes in auroral morphology and emission intensity in the polar ionosphere and high-latitude surface magnetic field [16,17, 18]. the occurrence rate of substorms is more frequent and more intense during geomagnetic storms [3]. the typical duration of substorm is about 2-4 hours. the length of growth, expansion and recovery phases vary from the short expansion of 15–20 min to a lengthy growth or recovery of a few hours [19,20,21]. fig. 7: from top to bottom, the panels shows the variations of the tsw (104 k), vsw (km/s), nsw (n/cc), psw (npa), bz (nt), sym-h (nt) and ae (nt) in gsm coordinate system during respectively during 1st march 2011. sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.174 (online publication: dec., 2018) figure 8 the cross-correlation of vsw with solar parameters and geomagnetic indices during 23 june 2015. here the horizontal axis represents the scale in minutes and the vertical axis represents the cross-correlation coefficient. the black curve shows the correlation between vsw and psw. the curve shows strong positive cross-correlation coefficient of about 0.9 at lag zero. the sky-blue curve shows correlation between vsw-sym-h is moderate and sometime crosses the zero points. the correlation between vsw-sym-h is represented by pink curve shows high negative cross-correlation coefficient of around 0.8 at lag of -20 minutes. the negative correlation signifies that if the value of vsw decreases with time then sym-h increases with increasing time and vice-versa. the blue curve of bzvsw represents there week correlation. the correlation between vsw-nsw (yellow curve) shows good correlation with correlation coefficient about 0.85 at lag zero. similarly, pink curve also shows good positive cross-correlation between vsw-ae with correlation coefficient of about 0.8 at zero lag. the correlation between vsw and tsw is positive with correlation coefficient of about 0.80 at lag zero. fig. 8: cross-correlation of solar wind velocity with southward component of interplanetary magnetic field (bz), solar wind temperature (tsw), sym(h), ae solar wind density (nsw), and solar wind pressure respectively 1st march 2011. 4. conclusion in this study, we have studied correlation of solar wind velocity with different solar and interplanetary indices during four different geomagnetic disturbances. this study shows the major sources of the geomagnetic disturbance are recognized to be cme, cir, etc. the interaction of solar wind component with earth’s magnetosphere can cause geomagnetic storms, substorms, supersubstorms, hildcaa, etc. the conclusions are summarized as the follows: • during disturbed days, there is a fluctuation of energy and plasma inside the magnetosphere, which changes the parameters like pressure, plasma density, velocity, imf-bz sym-h and ae indices. sujan dhakal et al. / bibechana 16 (2019) 165-176: rcost p.175 (online publication: dec., 2018) • the solar wind velocity shows positive correlation with pressure and negative correlation with sym/h in every event. • there is weak connection of solar wind pressure with imf-bz, although it is more geoeffective. • the strong correlation between solar wind pressure and velocity during storms initial phase was linked to the accelerated ring current build-up. acknowledgements the data sets for this study were downloaded from nasa website (http://omniweb.gsfc.nasa.gov/ow_min.html. and www.cosmic.ucar.edu/). we would like to thank nasa. references [1] b.t. tsurutani, w.d. gonzalez, f. tang, s. akasofu, and e. smith, origin of interplanetary southward magnetic fields response for major magnetic storms near solar maximum (1978-1979), j. geophys. res. a8 (1988) 8519 8531. doi.org/10.1029/ja093ia08p08519. 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[16] e.i. tanskanen, terrestrial substorms as a part of global energy flow, ph.d. dissertation, univ. of helsinki, helsinki, finland. 2002. [17] j. w. gjerloev, r. a. hoffman, the large‐scale current system during auroral substorms. j. geophys. res. 119(6) (2014) 4591-4606. doi.org/10.1002/2013ja019176. [18] w. d. gonzalez, b. t. tsurutani, l. alicia and g.d. clia, interplanetary origin of geomagnetic storms, space science reviews 88 (1999) 529. doi.org/10.1023/a:1005160129098. [19] e .n. parker, dynamics of the interplanetary gas and magnetic fields, astrophys. j. 128 (1958) 664–675. doi.org/10.1086/146579. [20] c.w. snyder, m. neugebauer, and u.r. rao, the solar wind velocity and its correlation with cosmic ray variations and with solar and geomagnetic activity. j. geophys. res. 68 (1963) 6361. doi.org/10.1029/jz068i024p06361. [21] w. chin-chun, r. p. lepping, effects of magnetic clouds on the occurrence of geomagnetic storms: the first 4 years of wind j. geophys. res., 107, issue a10 (2002). doi.org/10.1029/2001ja000161. https://doi.org/10.1002/2016ja022620 https://agupubs.onlinelibrary.wiley.com/action/dosearch?contribauthorstored=gjerloev%2c+j+w https://agupubs.onlinelibrary.wiley.com/action/dosearch?contribauthorstored=hoffman%2c+r+a https://doi.org/10.1002/2013ja019176 https://doi.org/10.1086/146579 https://doi.org/10.1029/jz068i024p06361 https://doi.org/10.1029/2001ja000161 bibechana vol. 20, no. 2, august 2023, 134–145 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar surface modification of nylon 6 by 50 hz dielectric barrier discharge produced in air and argon at atmospheric pressure bikash shrestha1, rajesh prakash guragain1,∗, binita sedhai1 hom bahadur baniya2, ujjwal man joshi1, deepak prasad subedi1 1department of physics, school of science, kathmandu university, dhulikhel, kavre 2department of physics, amrit campus, tribhuvan university, kathmandu, nepal ∗corresponding author. email: rayessprakash@gmail.com abstract this paper reports the use of dielectric barrier discharge (15.65 kv, 50 hz) produced in an air and argon environment at atmospheric pressure to modify the surface of nylon 6. power dissipation in air and argon dbd was determined to be 14.60 w and 12.00 w, respectively. similarly, the average density and temperature of an electron in air dbd were found to be 1.74 ×1011 cm−3 and 1.31 ev, respectively, while the values were 2.50 ×1011 cm−3 and 0.68 ev in argon dbd. the water contact angle (wca) was measured to confirm the enhancement in wettability. on treating the sample with air dbd for 15 minutes, the contact angle reduced from 134.070 ± 3.200 to 89.110 ± 3.060 while it was reduced to 82.740 ± 4.200 within 1 minute using argon. the study found that treating a hydrophobic sample of nylon 6 with dbd for a certain period of time transformed it into a hydrophilic one, and extending the treatment time further enhanced its wettability. the use of argon dbd was found to be more effective than air dbd in altering the surface properties of the sample, as the sample became hydrophilic after only one minute of treatment with argon dbd and completely wettable after three minutes. the findings suggest that air and argon dbd have potential applications in modifying the surface properties of nylon 6, which could have practical implications in the production of textiles, membranes, and other materials. keywords dielectric barrier discharge (dbd), electron density, lissajous figure, nylon 6, polymer, surface modification, water contact angle (wca). article information manuscript received: may 18, 2022; accepted: april 26, 2023 doi https://doi.org/10.3126/bibechana.v20i2.45159 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction polymers have aided in the growth of technology, applied engineering, and materials science due to their remarkable material characteristics [1]. however, polymers are frequently inappropriate for use in their pristine state as they are resistant to biological and chemical agents [2, 3]. they have low surface energy, poor wettability, printability, and other technologically significant aspects [4, 5]. as 134 http://nepjol.info/index.php/bibechana rayessprakash@gmail.com https://doi.org/10.3126/bibechana.v20i2.45159 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ bikash shrestha et al./ bibechana 20 (2023) 134-145 135 a result, surface treatment is needed to transform them into more sophisticated materials for use in many commercial applications [6]. to modify polymer surfaces, a variety of surface treatments are available, ranging from large-scale treatments to precision ones [7]. plasma treatment is one of the commonly used precise treatments as it has the ability to selectively alter the chemical and physical features of the polymer surfaces without changing their fundamental bulk properties. further, plasma treatment is resource-efficient, environmentally friendly, and treatment time is comparatively shorter [8–12]. mccord used atmospheric pressure plasmas to modify nylon fabrics and demonstrated that modification can be done without affecting the bulk properties [13]. swar et al. showed that due to the presence of amine groups, the surface of treated nylon 6 films was likely to be bio-compatible for future medical applications [14]. thomson et al. found a reduction in the concentration of oxygen in the treated surface was the main cause of the decrease in the wettability of the sample with an increase in treatment time [15]. in recent years, nylon 6 polymers have been in high demand, such as in biomedical and industrial applications. in this study, non-thermal plasma at atmospheric pressure is generated through dielectric barrier discharge at 50 hz frequency in air and argon environment. two methods: electrical and optical are used for plasma diagnostics. the water contact angle and surface free energy of samples before and after treatment were measured to study the considerable changes in the surface properties of the treated sample. 2 experimental methods 2.1 nylon 6 sample nylon 6, also known as polycaprolactam or polyamide 6, is a synthetic polymer made up of a monomer, caprolactam [16, 17]. the nylon 6 sample used in this study is shown in figure 1. the thickness of the sample is 0.32 mm and is yellow in color. the dimension of the sample used throughout the study was 2.5 cm × 2.5 cm. 2.2 experimental set-up figure 2 shows the experimental set-up of circular parallel plate electrode dbd system. the system comprises of a transparent, cylinder-shaped polycarbonate reactor that is 10 cm in diameter, 10 cm in height, and 0.5 cm thick. two circular brass electrodes of identical shape and size, each measuring 5.1 cm in diameter and 1.0 cm in thickness, are placed one on top of the other in the reactor, with a suitable gap between them. the upper electrode can be moved up and down on the vertical scale to adjust the electrode gap, whereas the lower electrode is fixed. a circular polycarbonate plate having a diameter of 9.7 cm and a thickness of 0.2 cm covering the lower electrode acts as a dielectric barrier. this inhibits the formation of arc discharges. the upper electrode is connected in series to the high ac power supply through a ballast resistor (20 mω, 2 w). the high tension to low tension ratio (ht/lt) of the step-up transformer used is 78.26. the lower electrode is grounded through the shunt resistance (10 kω, 10 w). the spacing between the electrodes had been maintained at 0.35 cm throughout the research study. 2.3 electrical and optical diagnostics one should also be familiar with the properties of the plasma being used. a well-defined insight into some quantities that describe plasma state is needed to understand plasma properties. the most elemental quantities are electron density and electron temperature. these quantities are known as plasma parameters. the most tempting feature of a plasma diagnostic approach is that it is noninvasive [18]. for electrical and optical diagnostics, an oscilloscope probe (kenwood pc-54 oscilloscope probe) is used to measure discharge current across shunt resistor. the voltage across the electrode is measured through a high-voltage probe (pintek hvp–28 hf). both the high-voltage probe and the oscilloscope probe are connected to the input channel of the digital oscilloscope (tektronix tds 2002) which records and displays voltage and current waveforms as a function of time. a small hole is drilled into the top circular base of the polycarbonate cylinder to allow the inlet of argon gas. the gas flow rate of argon was maintained at 2 l/min. a small hole is also drilled in the middle of the lateral surface of the polycarbonate cylinder, just opposite the electrode gap, for the insertion of fiber optical cable. the ocean optics usb2000+ fiber optic spectrometer is used to take optical spectra for optical characterization. figure 3 shows the photograph of the dbd system used in this research work. bikash shrestha et al./ bibechana 20 (2023) 134-145 136 figure 1: nylon 6 sample of dimension 2.5 cm × 2.5 cm. figure 2: schematic diagram of the experimental set-up. 3 results and discussion 3.1 electrical characterization figure 4 shows the variation of applied voltage and discharge current of air and argon dbd as a function of time. the applied voltage is sinusoidal in nature while the current signal consists of significant number of individual non-uniform filaments referred to as micro-discharges. dbd generally has several non-uniform filaments at atmospheric pressure [19]. 3.2 electrical diagnostics a standard approach for electrical diagnostics of dbd discharges is the lissajous figure. the chargevoltage (q-v) loop is commonly known as the lissajous figure. the power dissipated, average electron density, etc., parameters can be found from lissajous figures as a function of several parameters [20,21]. figure 3: photograph of dbd system. bikash shrestha et al./ bibechana 20 (2023) 134-145 137 (a) (b) figure 4: i(t)–v(t) signal of (a) air and (b) argon dbd. (a) (b) figure 5: lissajous figure of discharge in (a) air and (b) argon dbd . figures 5 show the lissajous figure of dbd generated in the air and argon environment at the applied voltage of 15.65 kv with an air gap of 0.15 cm. the energy consumed per cycle is given by [22]: e = 4cdvmin  1 1 + cg cd  (vmax − vmin) (1) and, the power dissipated is given by [23,24]: p = 4fcdvmin  1 1 + cg cd  (vmax − vmin) (2) where, cg = capacitance of air space, cd = capacitance of the dielectric, vmax = maximum value of applied voltage required to initiate discharge, vmin = minimum value of applied voltage, and f = frequency of input voltage. in this study, the values of vmax, vmin, c, cd, and cg obtained from the lissajous figure [figure 5(a) and 5(b)] were found to be 12.89 kv, 3.42 kv, 940.12 pf, 3195.40 pf, and 1332.01 pf, respectively in the case of air environment, while they were found to be 12.25 kv, 3.08 kv, 1230.05 pf, 3357.15 pf, and 1941.36 pf, respectively, in the case of argon environment. with these values, the energy consumed per cycle was found to be 0.29 j and 0.24 j while the power dissipated was found to be 14.60 w and 12.00 w in the air and argon environments, respectively. the average electron density (ne) is calculated by [25]: ne = jav eeµe (3) where, jav = average current density, e = electric bikash shrestha et al./ bibechana 20 (2023) 134-145 138 field in the discharge region, and µe= electron mobility which is calculated with the help of bolsig+ software. in the air environment, we found jav = 150.05 ma/cm2, e = 16.07 kv/cm, and µe= 335.12 cm2/vs. by substituting these values in equation (3), the average electron density (ne) was estimated to be 1.74 × 1011 cm−3. similarly, in the argon environment, we found jav = 180.34 ma/cm2, e = 13.00 kv/cm, and jav= 346.12 cm2/vs. by substituting these values in equation (3), the average electron density (ne) was estimated to be 2.50 × 1011 cm−3. 3.3 variation of power dissipated figure 6 shows the variation of power dissipated in the discharge in air and argon dbd at different applied voltages. it was found that as the applied voltage was increased, the power dissipated in air and argon dbd increased. this is because initially, available charged species are gaining energy from supplied voltages to cause further ionization of air and argon atoms [26]. at a particular applied voltage, the power dissipated in air dbd was found to be higher in comparison to argon dbd. air plasma consists of about 78% nitrogen. nitrogen being a diatomic molecule, its breakdown voltage is comparatively higher than argon in argon plasma [27]. 3.4 variation of average electron density figure 7 shows the variation of average electron density in air and argon dbd at different applied voltages. it was observed that when the applied voltage was increased, the average electron density was also found to be increased. this is because by increasing the voltage, the energy received by charge species also increases. as a result, kinetic energy rises, and the collisional mode shifts from elastic to inelastic. the emission of secondary electrons begins and will continue to increase as the applied voltage is increased [28]. similarly, the average electron density in argon plasma was found to be higher in comparison to air plasma at the particular applied voltage, as the high number of argon atoms gets readily ionized, resulting in a stream of secondary electrons due to the relatively lower breakdown voltage of argon plasma in comparison to air plasma. also in air plasma, a dissociative recombination process between electrons and ionized nitrogen molecules takes place [27,29]. 3.5 optical characterization the line intensity ratio method has been used to estimate electron temperature [30,31]: r1 r2 = i1 i2 i3 i4 = ( apq ars )( gp gr )( λrs λpq )( auv axy ) × ( gu gx )( λxy λuv ) exp [ −−ep − er − ex + ev kbte ] (4) where, λ is the wavelength of spectral lines, i is the intensity of spectral lines, a is the transition probability, g is the statistical weight and e is the energy of spectral lines. a. calculation of electron temperature in air dbd figure 8 shows the optical spectra of discharge in air plasma and corresponding values of intensity ranging from 300 to 460 nm at an applied voltage of 15.65 kv. from the spectral lines of the discharge in air dbd, four suitable nitrogen lines nitrogen first line ni (413.76 nm, 439.24 nm) and nitrogen second line nii (411.10 nm, 437.95 nm) were taken for electron temperature estimation. the nist database is used to obtain the values of aji, gi, and ei for these four lines [32]. table 1 shows the possible values of electron temperature and their corresponding intensity ratio values in the case of air dbd. figure 9 shows the variation of intensities ratio r1 r2 for different possible values of electron temperature. the four nitrogen lines taken have an intensities ratio equal to 1.03 which corresponds to an electron temperature of 1.31 ev. b. calculation of electron temperature in argon plasma figure 10 shows the optical spectra of discharge in argon plasma and corresponding values of intensity ranging from 300 to 900 nm at the applied voltage of 15.65 kv. from the spectral lines of the discharge in argon plasma, four suitable argon lines argon first-line ai (696.02 nm, 750.38 nm) and argon second-line aii(336.65 nm, 356.32 nm) were taken for electron temperature estimation. the values of aji, gi, , and ei for these four lines are obtained from the nist database [32,33]. table 2 shows the possible values of electron temperature and their corresponding intensity ratios values of the spectral lines in the case of argon plasma. bikash shrestha et al./ bibechana 20 (2023) 134-145 139 figure 11 shows the variation of intensities ratio r1 r2 for different possible values of electron temperature. the four argon lines taken have an intensities ratio equal to 0.49 which corresponds to an electron temperature of 0.68 ev. table 1: electron temperature (te) and intensity ratio. electron temperature (te) intensity ratio ( r1 r2 ) 0.80 13.44 0.90 7.06 1.00 4.21 1.20 1.94 1.40 1.12 1.60 0.74 1.80 0.54 table 2: electron temperature (te) and their corresponding intensity ratios. electron temperature (te) intensity ratio ( r1 r2 ) 0.60 1.88 0.65 0.78 0.70 0.37 0.80 0.11 0.90 0.04 1.00 0.02 figure 6: variation of power dissipated at different voltages. figure 7: variation of average electron density at different applied voltages. figure 8: optical emission spectra of discharge in air dbd. figure 9: variation of intensities ratio with electron temperature. bikash shrestha et al./ bibechana 20 (2023) 134-145 140 figure 10: optical emission spectra of discharge in argon dbd. figure 11: variation of intensities ratio with electron temperature. 4 surface characterization 4.1 mass loss (%) to ensure the etching and deposition of the plasma ion process, mass loss (%) calculation was done given by [34]: mass loss(%) = ( mi −mf mi ) × 100 (5) where, mi = initial mass of the sample before treatment and mf= final mass of the sample after treatment. a nylon 6 sample of dimension 2.5 cm × 2.5 cm was taken and its mass was measured in analytical balance (mg124ai). then, the sample was treated in air and argon dbd for a specified time and the mass of the treated sample was measured immediately after treatment. figures 12(a) and 12(b) show the mass loss (%) in the nylon 6 sample after being treated in air and argon dbd for specified times. initially, mass loss (%) was found to be increased on increasing the treatment time (from 5 to 15 minutes) in air dbd. then, no significant difference in mass loss (%) was found between 15 and 20 minutes of treatment time. initially, there was a 1.52% mass loss when the sample was treated for 1 minute in argon dbd. then on further increase in treatment time, there was no significant difference in mass loss (%). this might be because once all the etchable materials have been removed from the surface, the remaining material is difficult to remove, resulting in a decrease in etching rates. the re-deposition of sputtered fragments could also contribute to the decline in etching rate [34,35]. (a) (b) figure 12: mass loss (%) at different treatment times in (a) air and (b) argon dbd. bikash shrestha et al./ bibechana 20 (2023) 134-145 141 4.2 water contact angle a liquid’s ability to wet a solid’s surface is measured by the contact angle. it is the most important technique for studying the properties of a surface. the contact angle is the angle formed by a liquid at the three-phase boundary, where a liquid, gas, and solid meet [36,37]. the water contact angle is calculated using young’s equation for a perfect, uniform, and homogeneous surface at equilibrium [figure 13] and is given by [38]: cos θ = γsv − γsl γlv (6) where, θ = contact angle, γsv = solid surface free energy, γlv = liquid surface free energy, and γsl = solid/liquid interfacial free energy. in this study, the water contact angle of 2 µl distilled water kept on the sample surface was measured using a goniometer (rame hart contact angle goniometer, model 200). figures 14 (a) and 14 (b) shows the water contact angle of the controlled and treated nylon 6 sample in air and argon dbd, respectively. figure 13: schematic representation of young’s equation (a) (b) figure 14: water contact angle of the controlled and treated sample in (a) air and (b) argon dbd. bikash shrestha et al./ bibechana 20 (2023) 134-145 142 it was found that there was a decrease in water contact angle when the treatment time was increased in both air and argon plasma. the result shows that the sample became hydrophilic after being treated for 15 minutes in air dbd. whereas, the sample became hydrophilic when treated for 1 minute in argon dbd. moreover, the sample was completely wettable when treated for 3 minutes in argon dbd. the increase in the hydrophilicity of the sample after being treated in air and argon dbd could be because of the inclusion of hydrophilic groups such as co, cooh, c-oh, -oh, etc [13–15,39]. 4.3 surface free energy the surface tension of a solid can be taken as a measure of surface-free energy. the behavior of any liquid on the surface may be predicted by knowing the solid’s surface free energy. the surface free energy of solids from a single contact angle measurement of a liquid with a known surface tension is calculated by using the kwok and neumann equation and given by [40,41]: γl(1 + cos θ) = 2 √ γsγl [ 1− βl(γs − γl) 2 ] (7) where, βl = 0.0001057 (m2/mj)2. figure 15 shows the variation of surface free energy with treatment time in air and argon dbd respectively. the surface free energy of the controlled sample was (5.26 ± 1.11) mj/m2. the surface free energy of the sample when treated in air dbd for 5 minutes, 10 minutes, 15 minutes, and 20 minutes were found to be (19.23 ± 4.31) mj/m2, (27.52 ± 2.51) mj/m2, (29.78 ± 1.91) mj/m2 and (35.10 ± 1.85) mj/m2 respectively. similarly, the surface free energy of the sample when treated in argon plasma for 1 minute and 2 minutes were found to be (33.77 ± 2.63) mj/m2 and (34.26 ± 2.63) mj/m2 respectively. the result showed that the surface free energy of the sample increases as the treatment time is increased. (a) (b) figure 15: variation of surface free energy with treatment time in (a) air and (b) argon dbd. 5 conclusions a custom-designed dielectric barrier discharge system operating at line frequency and at atmospheric pressure, utilizing air and argon as working gases, was used for surface modification of nylon 6. the average electron density in both air and argon dbd was found to be in the order of 1011 cm−3. the power dissipated and average electron density in the discharge were found to be increased on increasing the applied voltage in both air and argon dbd. at a particular applied voltage, the average density of electrons in argon dbd was found to be relatively higher in comparison to air dbd. in contrast, the temperature of electrons in air dbd was found to be comparatively higher than in argon plasma. the generated air and argon dbd significantly enhanced the hydrophilicity of nylon 6, which was previously hydrophobic. in addition, the hydrophilicity and surface free energy of the sample was found to be increased by increasing the treatment time in both air and argon dbd. after 15 minutes of treatment with air dbd and 1 minute of treatment with argon dbd, the hydrophobic sample became hydrophilic. this shows that argon dbd is more effective than air dbd in the surface modification of nylon 6. these findings have implications for the surface modification of other polymers and may have practical applications in industries such as medical devices and packaging. acknowledgments the corresponding author was supported by the nepal academy of science and technology (nast), nepal through a ph.d. fellowship. the authors bikash shrestha et al./ bibechana 20 (2023) 134-145 143 would also like to acknowledge all the researchers of the plasma physics laboratory, kathmandu university who provided valuable suggestions and help for the completion of this work. references [1] md rabiul rahman et al. importance of sustainable polymers for modern society and development. advances in sustainable polymer composites, pages 1–35, 2021. doi.org/10.1016/b978-0-12-820338-5.00001-1 [2] xiaofang jia, margarita herrera-alonso, and thomas j mccarthy. nylon surface modification. part 1. targeting the amide groups for selective introduction of reactive functionalities. polymer, 47(14):4916–4924, 2006. doi.org/10.1016/j.polymer.2006.05.038 [3] m. s. b. reddy, deepalekshmi ponnamma, ruchi choudhary, and kishor kumar sadasivuni. a comparative review of natural and synthetic biopolymer composite scaffolds. polymers, 13(7):1105, 2021. doi.org/10.3390/polym13071105 [4] h. b. baniya, r. p guragain, and d. p. subedi. cold atmospheric pressure plasma technology for modifying polymers to enhance adhesion: a critical review. in progress in adhesion and adhesives, pages 841–879. 2021. doi.org/10.1002/9781119846703.ch19 [5] wei zhang, l johnson, srp silva, and mk lei. the effect of plasma modification on the sheet resistance of nylon fabrics coated with carbon nanotubes. applied surface science, 258(20):8209–8213, 2012.doi.org/10.1016/j.apsusc.2012.05.023 [6] fabienne poncin-epaillard et al. surface treatment of polymeric materials controlling the adhesion of biomolecules. journal of functional biomaterials, 3(3):528–543, 2012. doi.org/10.3390/jfb3030528 [7] s. k. nemani et al. surface modification of polymers: methods and applications. advanced materials interfaces, 5(24):1801247, 2018. doi.org/10.1002/admi.201801247 [8] r. p. guragain et al. improvement of hydrophilicity of polypropylene film by dielectric barrier discharge generated in air at atmospheric pressure. reviews of adhesion and adhesives, 9(1):153–166, 2021. 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[41] d. k. owens and r. c. wendt. estimation of the surface free energy of polymers. journal of applied polymer science, 13(8):1741–1747, 1969. doi.org/10.1002/app.1969.070130815 https://doi.org/10.1016/j.polymdegradstab.2014.10.001 https://doi.org/10.1016/j.polymdegradstab.2014.10.001 https://doi.org/10.1002/app.1969.070130815 introduction experimental methods nylon 6 sample experimental set-up electrical and optical diagnostics results and discussion electrical characterization electrical diagnostics variation of power dissipated variation of average electron density optical characterization surface characterization mass loss (%) water contact angle surface free energy conclusions bibechana 18 (2) (2021) 138-142 138 muonium behavior in n-acetylglycine-n-methylamide amba datt pant institute of materials structure science, high energy accelerator research organization (kek), 1-1 oho, tsukuba, ibaraki 305-0801, japan email: pant@post.kek.jp article information: received: march 30, 2020 accepted: june 4, 2021 keywords: muon muonium amino acid peptide bond protein abstract in muon spin rotation and relaxation (sr) method, theoretical work using firstprinciples calculations helps to understand the stopping sites and charge states of muon in the sample materials. to support the sr measurement on protein and dna, a systematic first-principles study starting from the constituents of the protein has been performed. in this work, the behavior of muonium (mu = +e-, bound state of a muon and an electron which is like a light isotope of h atom with similar chemical properties) in a n-acetylglycine-n-methylamide (agma), a part of peptide bond, is presented. it is found that the stopping site of mu is around o of unsaturated bonds between c and o in the agma. further calculations towards whole protein and dna will be performed to support sr studies. doi: https://doi.org/10.3126/bibechana.v18i2.35761 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction in order to apply the muon spin rotation and relaxation (μsr) method to study the life phenomena, k. nagamine et al initiated the sr measurements in cytochrome c protein [1, 2], dna [3] to understand the electron transfer process and aqueous biological solutions [4] to detect the concentration of oxygen in the bio-solutions. but the stopping sites of muon and its charge states in the bio-samples have not understood yet. theoretically, t. p. das et al [5, 6] reported the unsaturated bond of carboxyl group in the amino acids passivated by h is possible stopping site of muon however in real bio-samples amino acids are connected/formed to peptide bonds rather than h passivation. in our systematic theoretical study, we found the termination of main chain of computational model plays the significant role for the variation of potential energy depth for muon and muonium (mu =  +e-, bound state of a muon and an electron which is like a light isotope of h atom with similar chemical properties) in the amino acids [7]. in glycine, the stopping site of mu is estimated around o of unsaturated c=o bond [8]. in triglycine, the possible stopping site is calculated around o of the peptide bond [8] that is around the mailto:pant@post.kek.jp https://doi.org/10.3126/bibechana.v18i2.35761 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana a.d. pant / bibechana 18 (2) (2021) 138-142 139 o of central glycine moiety. in histidine and other aromatic amino acids, the stopping sites for mu is estimated around aromatic side chain [7, 9, 10]. in this paper, the stopping site of mu in nacetylglycine-n-methylamide (hereafter agma), a part of peptide bond, is presented. positive muon (+) is like a light proton (mass m  1/9 mp; magnetic moment  = 3.18 p) which acts as sensitive probe to study the local electronic and dynamic states of the materials. the muon can be produced by decay of pion. in accelerator facilities, muon can be generated by bombarding a muon production target (graphite etc.) by high energy proton beam. the muon decays (average life 2.2 s) to positron along the direction of muon spin at the time of decay. by collecting the positrons using spectrometers around the sample, the information about the interested properties of materials can be extracted. the wide time window (~ ps to few s), measurement without external perturbations (at any temperature, without external field) and characteristics of muon (100% spin polarized and asymmetric decay to positron in weak interaction) are advantages of this method over other spectroscopic/resonance methods. we can found the details of sr technique elsewhere [11, 12]. 2. method the theoretical calculations were performed using hybrid density function b3lyp with basis sets 631g(d) in gaussian 09 set of programs [13]. in the b3lyp level of calculations, both gradient and exchange correlations are included. the basis set 631g(d) describes well the orbitals of first and second rows elements. the optimization of structures with different basis sets were confirmed as mentioned in previous works [7, 10]. the initial charge state of muon is taken as mu as mentioned in the muon labelled electron method [11]. the stopping site is estimated based on the minimum potential energy (pe) for h or mu (hereafter mu) in the system. the pe in term of optimized energies for mu was calculated as, pe = e(amino acid + h) – [e(amino acid) + e(h)], where e(x) represents the minimum energy of system x. the pe for mu around electronegative sites of n-acetylglycine-nmethylamide (fig. 1) were calculated. the bader charge analysis [14] to approximate the total charge with each atom is also calculated. fig. 1: chemical formula (schematics) of nacetylglycine-n-methylamide. 3. results and discussion the potential energy for mu at different sites of agma is calculated. the relatively more deeper values of pe are found around two sites o1 and o2 (fig. 2) with pe -0.41 ev and -0.45 ev, respectively. it indicates the stopping site of mu is around o of unsaturated c=o of the agma. the bader charge analysis and highest occupied molecular orbitals (homo)-lowest unoccupied molecular orbitals (lumo) gap for mu stopping around those sites have been calculated as seen in table 1 and fig. 3, respectively. the bader charge analysis indicates that the nearby c of c=o bond acquired more negativity than other parts. it indicates the possibility of formation of radical at c after stopping of the mu nearby the o. from fig. 3, the homo-lumo gap of the system when mu stopped around o2 is relatively smaller than that stopped around o1. the negative homo energy indicates the bonding state and positive lumo energy indicates the antibonding state. a large gap (lumo-homo) in the case of mu stopping around o1 implies good thermodynamic stability of the compound, whereas a small gap suggests an easy electronic transition in the case of mu stopping around o2. a.d. pant / bibechana 18 (2) (2021) 138-142 140 theoretically, even though two possible sites for mu in agma are pointed out but the intensity of muon beam available in accelerator facilities in the worlds is not such a high to stop each mu near each c=o bonds. so, in this small part of peptide bond, agma, the mu stopping site would be around the o2. fig. 2: optimized structure of muonium in nacetylglycine-n-methylamide. fig. 3: homo-lumo gap of two possible stopping sites of muonium in nacetylglycine-n-methylamide. the gap is 0.20 a.u. and 0.15 a.u. for muon stopping around o1 and o2, respectively. table 1: bader charge analysis for agma, and mu stopping around o1 and o2. atom number of valance electrons with each atoms agma agma + mu around o1 agma + mu around o2 mu 0 0 c1 3 3 3 c2 1 2 1 c3 3 3 3 c4 1 1 2 c5 4 4 4 h1 1 1 1 h2 1 1 1 h3 1 1 1 h4 0 0 0 h5 1 1 1 h6 1 1 1 h7 0 0 0 h8 1 1 1 h9 1 1 1 h10 1 1 1 n1 8 8 8 n2 8 8 8 o1 8 8 8 o2 8 8 8 a.d. pant / bibechana 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t. adachi, y. ikedo, y. oishi, j. nakamura, p. strasser, k. kojima, s. makimura, n. kawamura, a. koda, t. ito, w. higemoto, k. shimomura, r. kadono, y. miyake, e. torikai, transportation of ultra slow muon on u-line, mlf, j-parc, jps conf. proc. 21 (2018) 011060. https://doi.org/10.7566/jpscp.21.011060 [18] .miyake, k. shimomura, n. kawamura, a. koda, p. strasser, k.m. kojima, h. fujimori, s. makimura, y. ikedo, y. kobayashi, j. nakamura, y. oishi, s. takeshita, t. adachi, a.d. pant, h. okabe, s. matoba, m. tampo, m. hiraishi, k. hamada, s. doiuchi, w. higemoto, t.u. ito, r. kadono, j-parc muon facility, muse, (2018). https://doi.org/10.7566/jpscp.21.011054 bibechana 19 (1-2) (2022) 142-149 142 142 dichotomization of quantitative variables in poverty analysis krishna prasad acahrya1, shankar prasad khanal1*, and devendra chhetry1 1central department of statistics, institute of science and technology, tribhuvan university, kirtipur, nepal email: drshankarcds@gmail.com article information: received: dec 15, 2021 accepted: jan 30, 2022 keywords: dichotomization headcount index poverty gap index square poverty gap index vulnerable abstract it has been proposed four schemes of dichotomization for the four household level quantitative variables – area of land holding, geographic accessibility to the nearest market centre, number of children under 15 and number of literate members of working-age – with justification in the selection of threshold value for each variable to dichotomize into disadvantaged and advantaged group of households using the nepal living standard survey 2010/11 data with 5988 households and 28,670 of their household members. association of each dichotomized variable with household level poverty status (poor/non-poor) was found highly significant. finally, the proposed schemes of dichotomization have tested empirically for their ability to differentiate the poor people into two categories ‘more vulnerable’ and ‘less vulnerable’ by fist estimating the three measures of poverty – head count index, poverty gap index and squared poverty gap index of each group of population and comparing the estimated measures between the disadvantaged and advantaged group of populations. statistical analysis has been performed by using ibm spss version 20. to a large extent the proposed schemes of dichotomization have found to differentiate the poor people into two groups; for example, the head count index of the disadvantaged group of the number of children under 15 is 3.1 times higher than that of the advantaged group. the results of this paper are expected to be useful to the policy makers and development planners of nepal for focusing their poverty reduction program towards the more vulnerable group of population as well as academician. doi: https://doi.org/10.3126/bibechana.v19i1-2.46407 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction several statistical methods are available for assessing the association of a dichotomous variable with a set of quantitative variables, not necessarily all continuous. when dichotomous variable is treated as dependent variable and the set of quantitative variables is treated as independent variables, the association can be assessed through logistic regression which assesses the effect of independent variables on dependent variable simultaneously. when the dichotomous variable is treated as grouping variable and the set of quantitative variables are bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal https://doi.org/10.3126/bibechana.v19i1-2.46407 https://creativecommons.org/licenses/by-nc/4.0/ acharya et al. / bibechana 19 (1-2) (2022) 142-149 143 treated as test variables, the association can be assessed through independent samples t-test which assess the association by comparing the two group means of each quantitative variable. the former method is more rigorous from both theoretical and practical point of view than the later method. however, the use of later method faces the problem of normality assumption which means each test variable has to follow normal distribution within each of the two categories of the grouping variables since the ttest was developed under this normality assumption. conceptually the normality assumption is hard to justify when a test variable is discrete. when normality assumption fails, instead of independent samples t-test it is a common practice to use mann-whitney test. nonetheless, the mann-whitney non parametric test transforms the quantitative variables into their rank orders and the test works on rank ordered data, and the test results are not easily understandable to wider users. the association between a binary variable with a set of quantitative variables having only two levels, the association can also be assessed through biserial correlation. the less frequently used method is to first dichotomize each independent variable using a rationally defined threshold value and then use either logistic regression or use chi-square test for the dichotomous variable and each dichotomized quantitative variable. several scholars have discussed the advantages and disadvantages on this less frequently used method [1-3]. sometimes, dichotomization of quantitative variable is absolutely necessary. for example, dichotomization of per capita consumption expenditure using poverty line as threshold value is absolutely necessary in measuring monetary poverty. this paper has two-fold objectives. first objective is to dichotomize the four household level quantitative variables by justifying in the selection of threshold value for each variable, and assess the association of the four dichotomized variables with the dichotomous variable poverty status (poor/non-poor). second objective is to estimate the three measures of poverty – head count index, poverty gap index, and squared poverty gap index – for all the four dichotomized variables in order to investigate the ability to differentiate poor peoples into ‘more vulnerable’ and ‘less vulnerable’ through the estimated measures of poverty. 2. materials and methods the main source of data of this study is nlss iii which provides household level data on socio-economic and demographic variables of 5,988 households and 28,670 household members. the available data on the variable ‘household poverty status’ was taken as binary variable by assigning code 1 for poor and 0 for non-poor. in this study a household is defined as poor (non-poor) depending upon the per capita expenditure of the household members falls below (above) the poverty line of nrs 19,261. the un-weighted and weighted proportions of poor households were correspondingly 18.5% and 20.0%. similarly, un-weighted and weighted proportions of poor household members were correspondingly 23.4% and 25.2%. out of many household level variables that influence the monetary poverty, only the following four quantitative variables are considered in the present study. 1. area of land holding 2. geographic accessibility to market center (defined in the present study by time taken in minutes to reach the nearest market irrespective of transport mode) 3. number of children under 15 4. human capital (defined by number of literate members of working-age (15 – 64 years)). the available data on the above four variables were dichotomized. the main reason for dichotomization of each of these variables is to divide the households into two groups: acharya et al. / bibechana 19 (1-2) (2022) 142-149 144 advantaged and disadvantaged group with respect to each variable. the rationale behind such demarcation of households is that the disadvantaged group of households would be in a more difficult position to escape out of poverty than the advantaged group of households. the process of dichotomization, particularly choosing the threshold value for each of the four quantitative variables is rationalized below. 2.1 dichotomizing households by area of land holding the available data on land holding is highly skewed (skewness = 5.55) with extremely high measure of kurtosis (excess of kurtosis = 65.15), and considerable number of households had no lands. as a result, analysis based on original data suffers from various problems. moreover, farm size is not a good determinant of poverty [4]. in this context, analysis based on dichotomizing the quantitative variable is more sensible than analyzing the data as it is. in view of this fact, the threshold value for this quantitative variable was chosen to be 0 which demarcates households into two groups one group of households each had no land (disadvantaged group) and the other group of households each had land (advantaged group). 2.2 dichotomizing households by the number of children under 15 children under 15 are considered as dependent population in the sense that their basic needs have to be fulfilled by their parents. in this context, large number children would be burden to parents. as a result large number of children aggravates poverty [5]. however, small number of children is desirable. the ideal number of children responded by women respondents on an average was 2.1 and by men respondents was 2.3 in 2011 [6]. based on these results, the threshold value of 2 is used for dichotomizing the quantitative variable. this threshold value demarcates the households into two groups one group of households each had more than two children (disadvantaged group) and the other group of households each had less than or equal to two children (advantaged group). 2.3 dichotomizing households by the number of literate working-age members in the context of nepal, number of illiterate persons in a household is major disadvantage of the poor households [5]. in view of this fact, the household level quantitative variable “the number of literate members of working-age” was selected and converted it into dichotomous variable by grouping the households into two groups: one group of households each had no literate member of working-age (disadvantaged group) and the other group of households each had at least one literate member of working-age (advantaged group). 2.4 dichotomizing households by access to nearest market the available data on access to nearest market center is highly skewed (skewness = 3.46) with high measure of kurtosis (excess of kurtosis = 16.74). the mean and median of the time taken to reach market center in minutes are correspondingly 80.63 and 30.00. the analysis based on dichotomizing the quantitative variable is more sensible rather than analyzing the data as it is. in view of this fact, the threshold value for this quantitative variable was chosen 30 minutes which demarcates households into two groups one group of households each is required more than 30 minutes to reach market center (disadvantaged group) and the other group of households each is required less than or equal to 30 minutes (advantaged group). the threshold value of 30 minutes is taken because it is a common in nepal [7]. 2.5 test of association the association of poverty status with each dichotomized variable is assessed using chisquare test and effect size of each test is measured by phi-coefficient whose values range from -1 to 1. just like the correlation coefficient, a negative value of phi-coefficient indicates that acharya et al. / bibechana 19 (1-2) (2022) 142-149 145 when one variable increases, the other decreases and a positive value indicates that when one variable increases, so does the other. 2.6 the measures of poverty in contemporary studies three measures of poverty are used. they were originated from a class of poverty measures p() introduced by foster-greer-thorbecke [8], and expressed as where  is index  0, q is the number of poor peoples, n is the total number of individuals, z is the poverty line, yi is the per capita consumption expenditure and sum of the expression within parentheses is total poverty gap expressed as a proportion of the poverty line. in particular, p(0), p(1) and p(2) correspondingly yield the three measures of poverty – such as head count index, poverty gap index and squared poverty gap index. the measure p(0) is also known as head count ratio, incidence of poverty or poverty rate. it is a simple concept to understand and, therefore, widely used in political debate. however, it does not take into account of how poor the poor are, and this issue is addressed by the measure p(1) which in simple term measures how far away the poor peoples are from the poverty line, consequently p(1) satisfies the monotonicity axiom of amartya sen [9] and larger the value of p(1) larger the investment and effort would require to alleviate poverty. however, the measure p(1) does not take into account of the inequality in distribution of per capita expenditure among poor, and this issue takes into account by the measure p(2) and consequently p(2) satisfies the transfer axiom of amartya sen [9]. the two measures – p(1) and p(2) – are difficult concept to understand and, therefore, they are not widely used in political debate but they are useful for policy makers as well as for academicians. several developing countries, including nepal, have been estimating and using the three measures of poverty for monitoring, evaluation and planning program of poverty reduction. academicians are also using three measures in their academic work [10 21]. all the statistical analysis has been performed by using ibm spss version 20. 3. results and discussions the results of this study are summarized in three tables where the first table displays the descriptive statistics of quantitative variables for the disadvantaged and advantaged group of households, the second table displays the association between the dichotomized variables with poverty status, and finally the third table provides weighted estimates of the three measures of poverty for the disadvantaged and advantaged group of population where weights are the population weights provided by cbs in the data file. table 1 shows that among the total 5,988 households, around 29% of have no land, 48% have at least three children, 26% have no literate persons of working age and 19% have poor access to market. the mean difference between advantaged and disadvantaged is highest in the variable ‘access to market’ and least is in the variable ‘area of land holding’. skewness is positive in all variables. table 2 shows that the percentage of poor households is larger among the disadvantaged group of households than among the advantaged group. within group difference in percentage of poor is highest in the variable ‘number of children under 15 and least in the variable ‘area of land holding’. all four dichotomized variables were found statistically significant with poverty status. the effect-size for each chi-square test is positive and it is minimum for the test of association between the dichotomized variable of access to market center and poverty status, and it is maximum for the test of association between the dichotomized variable of the number of children under 15 and poverty status. ( ) αq 1i i z y 1 n 1 αp  =       −= acharya et al. / bibechana 19 (1-2) (2022) 142-149 146 table 1: descriptive statistics of quantitative variables by group note: figures within parentheses are coding scheme (0 for advantaged group and 1 for disadvantaged group). the dichotomous variable poverty status – is coded as follows: 0 for non-poor and 1 for poor. ag = advantaged group and dg = disadvantaged group na: not applicable. computed from nlss-iii (2010/11) table 2: association of dichotomized variables with poverty status % of poor households within group chi-square & p-value phi-coefficient status of land holding: with land without land 15.0 27.0 114.9 (p<0.001) 0.14 number of children under 15: at most 2 at least 3 11.0 40.0 653.0 (p<0.001) 0.33 number of literate workingage members: at least one none 16.0 31.0 142.0 (p<0.001) 0.15 access to nearest market center: % of households mean std. dev. skewness status of land holding: with land (0) ag without land (1) – dg 71.2 28.8 0.36 0.00 0.55 0.000 5.00 na number of children under 15: at most 2 (0) ag at least 3 (1) dg 52.0 48.0 0.96 3.73 0.83 1.10 0.07 2.50 number of literate working-age members: at least one (0) ag none (1) dg 73.8 26.2 2.23 0.00 1.28 0.00 1.61 na access to nearest market center: having better access (0) ag having poor access (1) dg 80.7 19.3 13.91 152.96 11.42 148.86 0.12 2.77 acharya et al. / bibechana 19 (1-2) (2022) 142-149 147 having better access having poor access 11.0 26.0 206.7 (p<0.001) 0.08 computed from nlss-iii (2010/11) table 3 shows that the scheme of dichotomization for each quantitative variable is able to differentiate poor peoples as ‘more vulnerable’ and ‘less vulnerable’ very distinctly according to each of the three measures of poverty. comparison of the estimated three measures of poverty with the corresponding estimate of the national level, each estimate of each advantaged group of population is below the estimate of the national level, on the contrary each estimate of each disadvantaged group of population is above the estimate of the national level. table 3: three measures of poverty for eight groups of household population note: lv = less vulnerable and mv = more vulnerable. computed from nlss-iii (2010/11) the extent of differentiations of poor people by the scheme of dichotomization varies across the dichotomized variables. for instance, the ratio of the head count index of the more vulnerable group to that of the less vulnerable group of population is highest for the dichotomized variable of ‘the number of children under 15’ and the ratio is 3.1 showing that the head count index of the more vulnerable group is 3.1 times higher than that of the less vulnerable group of population. such ratios for the poverty gap index and the squared poverty gap index of the same dichotomized variable are correspondingly 4.0 and 4.7. whereas the ratio of the head count index of the more vulnerable group to that of the less vulnerable group of variables head count index (p(0))×100 poverty gap index p(1)×100 square poverty gap index p(2)×100 status of land holding: with land (lv) without land (mv) 21.4 32.9 4.5 7.5 1.4 2.6 number of children under 15: at most 2 (lv) at least 3 (mv) 13.5 41.4 2.4 9.6 0.7 3.3 number of literate persons of working age: at least one (lv) none (mv) 21.5 41.7 4.3 10.4 1.4 3.9 access to nearest market center: having better access (lv) having poor access (mv) 16.3 32.1 3.3 7.1 0.9 2.5 national level of estimates 25.2 5.4 1.8 acharya et al. / bibechana 19 (1-2) (2022) 142-149 148 population is lowest for the dichotomized variable of ‘the status of land holding’ and the ratio is 1.5 and such ratios for the poverty gap index and the squared poverty gap index are correspondingly 1.7 and 1.9. 4. conclusions dichotomization of a quantitative variable with the aid of a reasonable threshold value in poverty analysis is a useful strategy because this study to a large extent succeeded to show that such dichotomization scheme differentiates the poor people into two groups ‘more vulnerable’ and ‘less vulnerable’, so that the policy makers and development planners focus their poverty reduction program towards the more vulnerable people. among the more vulnerable household populations of those households having three or more children under 15 is the most vulnerable. a baffling issue ‘why the poor households tend to have large number children?’ has to be resolved because for the reduction of the number of children from the most vulnerable group of households. the currently available data fail to resolve this issue. the impact of outmigration of literate and young population for employment as well as settlement in abroad was seen in the dichotomized variable of the quantitative variable ‘the number of literate persons of working-age group’. conflict of interest authors declare that there is not any conflict of interest. acknowledgments authors would like to thank central bureau of 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[20] k. p. acharya. analysis of poverty profile by type of house of households in nepal. management dynamics 22(1) (2019) 7-10. doi: https://doi.org/10.3126/md.v22i1.30231 [21]p.uprety. measures, distribution and decomposition of poverty: an empirical analysis in nepal. nepalese j. stat. 4 (2020) 116. https://doi.org/10.3126/md.v22i1.30231 parkash pantha et al. / bibechana 16 (2019) 187-195: rcost p.187 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal study of natural background radiation in kathmandu valley parkash pantha1, tanka prasad bhusal1, buddha ram shah2, rajendra prasad koirala1* 1central department of physics, tribhuvan university, kirtipur, kathmandu 2nepal academy of science and technology, khumaltar, kathmandu *e-mail: rpkoirala@tucdp.edu.np article history: accepted 05 november, 2018 doi: http://dx.doi.org/10.3126/bibechana.v16i0.21605 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract the study of natural background radiation dose at thirty two locations of kathmandu valley has been done successfully using the instrument radalert 100. the average dose rates and annual effective dose were measured. from the measurements, the least value of average dose rate was found to be (22.3±3.9)×10-3 mr/hr for sundhara and the greatest value of average dose rate was found to be (37.7±7)×10-3 mr/hr for budhanilkantha 3. as per the annual effective dose, the least value was 0.391 msv/yr for sundhara and the greatest value was 0.661 msv/yr for budhanilkantha 3. the average annual effective dose of kathmandu valley was 0.475 msv/yr ranging from 0.391 msv/yr to 0.661 msv/yr. the values thus obtained were compared to the worldwide average value of annual effective dose, 0.48 msv/yr. also, the obtained values were compared to the legal dose limit (annual effective dose), 1 msv/yr set by international commission on radiological protection (icrp) for non-radiation workers and members of public. among these thirty two locations, eight locations were chosen such that they had larger range of the observed dose rates. those eight locations were re-observed. further, chi-square test was carried out to test whether the observed dose rates were following normal distribution or not. from the calculation, it was observed that the observed dose rates were following the normal distribution. keywords: background radiation; dose rate; effective dose; health hazard 1. introduction all the radiations have no deleterious effect on organisms. non-ionizing radiations can only cause atoms to vibrate but not capable of create separate ions. however, ionizing radiation has the sufficient energy that can remove bound electrons from atoms, resulting in the ions capable of breaking chemical bonds. both these types of radiation can be harmful to organisms but in general, ionizing radiation is far more harmful than the non-ionizing radiation [1,2]. when these radiations interact with the material they pass, the knock out electron from the electron shell that leaves the atom with a net positive charge. there are a lot of chances that the cell and even dna molecule http://nepjol.info/index.php/bibechana mailto:rpkoirala@tucdp.edu.np http://dx.doi.org/10.3126/bibechana.v16i0.20960 https://creativecommons.org/licenses/by-nc/4.0/ parkash pantha et al. / bibechana 16 (2019) 187-195: rcost p.188 (online publication: dec., 2018) may be damaged. this can lead to the cancer but, it depends upon the amount of the radiation that is absorbed [3,4]. alpha particles, beta particles, cosmic rays, gamma rays, x-rays carry energy enough to ionize atoms. ionizing radiations cannot be detected directly by human senses. devices like geiger counters are used to detect it. exposure to ionizing radiation may cause damage to living tissues, skin burns, radiation sickness and even death if the exposure is high [5]. non-ionizing radiations such as visible light, microwave, radio waves, infrared, thermal radiation (heat), black body radiation etc. do not contain enough energy to ionize atoms. [6,2]. human beings are exposed to the radiation every time and everywhere they go. during the formation of the earth about four billion years ago, it had contained many radioactive isotopes. the isotopes with short half-lives have decayed but that with long half-lives have remained till present. there are many naturally occurring radio nuclides that have half-lives of at least the same order of magnitude as that of estimated age of earth. the natural radioactive elements are present into the soil, rocks, air, food and drinking water. thus, the natural environment works as a major source of radiation to which the human beings are exposed constantly. the ionizing radiation that comes mainly from the natural sources is called natural background radiation [7,8]. people are exposed to radiation mainly from naturally occurring background radiation. human beings receive average dose of 2.4 msv annually from background radiation. this dose rate depends upon the geology and altitude level where people live [9]. this absorption rate ranges from 1 to 10 msv/yr and can be greater too. around 140,000 people in kerala and madras states in india receive doses average over 15 msv/yr from gamma radiation. this is the highest known level of background radiation that is affecting the considerable amount of population [10]. also, the average exposure is about 40 msv/yr in brazil and sudan. as far as the highest natural background radiation is concerned, the highest value is 800 msv/yr which is on a brazilian beach but, no people live there. there are different places known in the earth where natural background radiation is high. at ramsar in iran, about 200,000 people receive more than 10 msv/yr. generally u 238, u 235, th232 and to a lesser extent k40 and rb87 produce external exposure to radiation. the radiation from these sources are of low doses but they could possess serious health problems [11-13]. due to extreme hazardous health problems that may be caused by exposure from radiation, acceptable levels of radiation exposure and radiation doses have been set by different bodies based on the research in this fields. these bodies include national academy of science/national research council advisory committee on biological effect of ionizing radiation (beir), international commission on radiological protection (icrp), national council on radiation protection and measurement (ncrp), international commission on radiation units and measurements (icru), united nations scientific committee on the effects of atomic radiation (unscear), international atomic energy agency (iaea), world health organization (who) etc [14,15]. the people in a certain location receive certain amount of radiation dose from the environment they live in. the reception of the dose may be due to external or internal cause. the amount of dose that they are exposed to may sometimes be hazardous. for the public to know about the type of environment they live in and for the awareness of doses that they receive from the environment they are living or being, this type of study or research work plays a vital role. this type of surveys can be useful for the appraisal of public dose rates as well as the reference for the further studies in the environmental radioactivity [7]. the outdoor-environmental monitoring exposure rate of radiation was measured in 200 randomly chosen regions in southwest of iran using portable geiger-muller and scintillation detectors. the parkash pantha et al. / bibechana 16 (2019) 187-195: rcost p.189 (online publication: dec., 2018) exposure dose rate was found to be 28.4 µr/hr and annual average effective equivalent dose was found to be 0.49 msv. an overall population weighted average outdoor dose rate was calculated to be 49 ngy/hr. it was higher than the world-wide mean value of 44 ngy/hr, as reported by unscear in 1998, and was comparable to the annual effective dose equivalent of 0.38 msv [16,14]. a research work was carried out within the younger granite province of nigeria using the devices like solid scintillation counter and geiger muller tube. the study accounted that mean absorbed dose rates in air in the study area was 0.044 ± 0.007 µgy/hr within the basalts, 0.119 ± 0.050 µgy/hr for the basements rocks and 0.168 ± 0.003 µgy/hr within the younger granites, giving the average value of 0.106 ± 0.002 µgy/hr [17,18]. similar type of research work was carried out in south konkan, maharashtra, india. the activity concentrations from the selected villages are found to be ranging from 24.78± 0.14 to 76.38 ± 0.31 bq/kg for u 238, 30.08 ± 0.14 to 96.18 ± 0.31 bq/kg for t h232 and 105.34 ± 0.24 to 432.51 ± 0.48 bq/kg for k40. the average absorbed dose rate in air was calculated as 66.89 ngy/hr. the annual effective dose rates were varied from 0.27 msv/yr to 0.85 msv/yr with an average of 0.49 msv/yr. the mean radium equivalent activity value for soil samples of south konkan was 144.84 bq/kg [19,20]. 2. materials and methods to measure the radiation dose rate at different locations of kathmandu valley, nepal, radalert 100 was used. it is a health and safety instrument that measures alpha, beta and gamma radiations. it can be used to monitor the radiation level while working near radionuclide. it is a nuclear radiation monitoring device and counts ionizing events. the radalert 100 uses a geiger muller tube (gm tube) to detect radiation. the gm tube generates a pulse of electrical current each time radiation passes through the tube and causes ionization. the radalert 100 electronically processes these pulses to display the radiation level. each pulse is electronically detected and registers as a count. the radalert 100 displays the counts in different modes: counts per minute (cpm), milliroentgen per hour (mr/hr), total counts for a timed period. the diagram of the radalert 100 is shown in figure 1.1 [21]. fig. 1.1: radalert 100 the position of each location at which radiation dose rate measured was recorded with the help of gps system. the global positioning system (gps) is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the earth. it is maintained by the united states government and is freely accessible to anyone with a gps receiver. during the study, garmin 60 cs-gps was used to measure the location coordinate of the observation point. parkash pantha et al. / bibechana 16 (2019) 187-195: rcost p.190 (online publication: dec., 2018) during this study, different locations were marked out for the data collection at kathmandu valley which were chosen randomly such that maximum areas of the kathmandu valley were covered within the study. the gps receiver was turned on and the location coordinates were noted. at the same time, radalert 100 was also turned on. the mode switch of radalert 100 was set to mr/hr. after the radalert had turned on it does four-second system check and after one minute of turning it on, a short beep indicates that the enough information has been collected to ensure statistical validity. then, the radalert 100 was kept well above one meter from the ground of the observation point. gps receiver was kept in parallel and very close with the radalert 100. after all this, instantaneous readings of radiation dose were recorded for ten minutes at the interval of one minute and average value and range of radiation dose were noted. the location coordinates were also recorded using gps receiver. same observation processes were made for different locations but at different dates. the observations were done in thirty two locations of kathmandu valley including two locations at bhaktapur from march 18, 2016 to may 5, 2016 in between 12pm to 3pm. the average dose rate for a given location was calculated. standard deviations of dose rate were calculated using the simple statistics. eight locations were chosen that have large variations in the range of data observed. the observations were again performed in those locations. the chi-square test was used to check whether there is a relationship between two categorical variables or not i.e. it is carried out to test whether the observed data fit the known theoretical distributions (such as normal or binomial distributions) or not. for chi-square test, chi-square statistic is used which is denoted by 𝑥2and defined as, ᵡ2 = ∑ (𝑂𝑖 − 𝐸𝑖) 2 𝐸𝑖 𝑛 𝑖=1 where, oi is the observed frequency and ei is the expected frequency. if calculated value of chi-square is less than the critical value of chi-square for 𝜈degree of freedom (i.e., 𝜈 = k-1-m; k is the number of observation and m is population parameter from the sample data) at certain level of significance then, we could accept our null hypothesis at that level of significance otherwise, we reject it [22-24]. 3. results and discussion the dose rates of different locations of kathmandu valley were obtained by using radalert 100. the average dose rate for a given location was calculated. the observations were done in thirty two different locations of kathmandu valley. the observation points (locations) with their gps coordinates, average dose rates, annual effective doses, standard deviation of dose rates and range are shown in table 1. variations of average dose rates at different location are shown in figure 1.2. among thirty-two locations, eight such locations having large variation in the range of observed dose rates were re-observed. the locations were selected to be kalimati, baisdhara, kirtipur, satdobato, chabahil, new buspark gongabu, bansbari and budhanilkantha 3. the dose rates reobserved at these locations are tabulated in table 2. the frequency of the observed dose rates at budhanilkantha was plotted against the observed dose rates which is shown in the figure 1.3 along with the gaussian fit of the observed dose rates. to test whether it is normally distributed with the mean 37.04×10−3 and standard deviation 4.77×10−3 or not, chi-square test is carried out. the chi-square value for the set of observed data is calculated to be 6.406. for our observed data, having 8 degrees of freedom, the critical value of chisquare at 0.05 level of significance is 15.507. since, the calculated value of chi-square is less than the critical value at 0.05 level of significance, we can conclude that there is a good fit i.e., the observed data parkash pantha et al. / bibechana 16 (2019) 187-195: rcost p.191 (online publication: dec., 2018) are normally distributed with mean 37.04×10−3 and standard deviation 4.77×10−3. similarly, frequency of observed dose rates at other re-observed locations are plotted against the dose rates, gaussian curves are fitted and 𝑥2 test is carried out at 0.05 level of significance. from 𝑥2 test it is observed that the data are normally distributed at 0.05 level of significance. fig. 1.2: a plot of average dose rates at different locations of kathmandu valley. fig. 1.3: plot of frequency of observed dose rates with respect to the observed dose rates for budhanilkantha 3. the black spot mark indicates the frequency of observed dose rates and solid line indicates the gaussian fit of the observed dose rates. further, peak value of observed dose rates at eight re-observed locations, where there was large variation in range of observed dose rate was studied. maximum observed dose rates at eight reobserved locations are shown in figure 1.4. s un dh ar a s at do ba to p an ip ok ha ri m ai tid ev i k up on do le s or ha kh ut te b ha kt ap ur k irt ip ur la zi m pa t b al aj u c ho w k c ha kr ap at h k ot es ho w r s ur ya bi na ya k d ha pa si jo rp at i b ai sd ha ra b al uw at ar la ga nk he l p at an d ur ba r s qu ar e k al an ki b al kh u b as un dh ar a c ha uk i c ha ba hi l n ew b an es ho w r c ho bh ar k al im at i b an sb ar i b ud ha ni lk an th a1 b ud ha ni lk an th a2 to kh a ro ad , d ha pa si n ew b us pa rk , g on ga bu b ud ha ni lk an th a3 20 25 30 35 40 45 a ve ra ge d os e r at es (µ r /h r) locations average dose rates(µr/hr) parkash pantha et al. / bibechana 16 (2019) 187-195: rcost p.192 (online publication: dec., 2018) table 1: the observation points with their gps coordinates, average dose rates, standard deviation of dose rates, their range and annual effective doses at different locations of kathmandu valley. s.n locations gps coordinates average dose rates(µr/hr) standard deviation (µr/hr) range (µr/hr) annual effective doses (msv/yr) 1 sundhara n 270 42’02.66” e 0850 18’44.51” 22.3 3.9 16-28 0.391 2 satdobato n 270 39’30.0” e 0850 19’31.2” 23.0 5.4 15-30 0.403 3 panipokhari n 270 43’43.80” e 0850 19’29.30” 23.3 3.4 18-29 0.408 4 maitidevi n 270 42’10.40” e 0850 20’09.08” 23.7 4.2 17-29 0.415 5 kupondle n 270 41’12.45” e 0850 19’01.12” 24.2 3.8 19-30 0.424 6 sorhakhutte n 270 43’08.30” e 0850 18’34.00” 25.0 3.7 18-30 0.438 7 bhaktapur n 270 40’22.40” e 0850 25’20.90” 25.1 3.9 19-30 0.440 8 kirtipur n 270 40’37.60” e 0850 16’54.40” 25.2 5.3 18-33 0.442 9 lazimpat n 270 43’11.50” e 0850 19’07.00” 25.7 3.6 19-32 0.450 10 balaju chowk n 270 43’38.70” e 0850 18’15.40” 25.8 3.7 20-31 0.452 11 chakrapath n 270 44’23.30” e 0850 20’14.60” 26.0 3.6 19-31 0.456 12 koteshowr n 270 40’44.70” e 0850 20’59.70” 26.1 3.3 20-31 0.457 13 suryabinayak n 270 39’57.40” e 0850 25’24.90” 26.2 4.0 20-32 0.460 14 dhapasi n 270 45’10.80” e 0850 19’34.90” 26.3 4.1 21-33 0.461 15 jorpati n 270 43’59.50” e 0850 22’48.40” 26.4 3.8 21-32 0.463 16 baisdhara n 270 43’56.80” e 0850 18’10.10” 26.5 5.5 18-35 0.464 17 baluwatar n 270 43’38.12” e 0850 19’50.66” 26.8 4.0 20-32 0.470 18 lagankhel n 270 40’01.40” e 0850 19’21.00” 26.9 4.5 20-33 0.471 19 patan durbar square n 270 40’22.23” e 0850 19’29.52” 26.9 4.4 19-32 0.471 20 kalanki n 270 41’26.50” e 0850 16’58.8” 27.0 3.4 24-34 0.473 21 balkhu n 270 41’07.20” e 0850 17’43.20” 27.3 3.4 23-33 0.478 22 basundhara chauki n 270 44’13.80” e 0850 19’24.00” 27.7 3.7 22-34 0.485 23 chabahil n 270 43’37.30” e 0850 20’21.10” 27.8 5.0 19-35 0.487 24 new baneshowr n 270 41’18.40” e 0850 20’07.40” 28.0 3.1 24-32 0.491 25 chobhar n 270 39’44.70” e 0850 17’22.20” 28.3 3.3 24-33 0.496 26 kalimati n 270 41’53.19” e 0850 17’57.10” 29.0 5.0 20-36 0.508 27 bansbari n 270 44’48.90” e 0850 20’38.50” 29.0 4.8 23-38 0.508 28 budhanilkantha 1 n 270 46’41.22” e 0850 21’44.21” 30.2 4.7 22-35 0.529 29 budhanilkantha 2 n 270 46’47.20” e 0850 21’27.90” 31.1 4.2 26-38 0.545 30 tokha road, dhapasi n 270 44’42.40” e 0850 19’23.20” 31.3 2.7 27-35 0.548 31 new buspark, gongabu n 270 44’15.26” e 0850 18’58.20” 32.0 5.0 24-39 . 0.561 32 budhanilkantha 3 n 270 46’53.80” e 0850 21’15.20” 37.7 7.0 26-45 0.661 parkash pantha et al. / bibechana 16 (2019) 187-195: rcost p.193 (online publication: dec., 2018) table 2: a list of observed dose rates and their corresponding frequencies at budhanilkantha 3. range of observed dose rates ( ×10−3 mr/hr ) frequency 26-28 4 28-30 6 30-32 7 32-34 9 34-36 13 36-38 14 38-40 18 40-42 14 42-44 9 44-46 5 46-48 1 fig. 1.4: maximum observed dose rates at different locations where maximum variation in range of dose rate was observed. 4. conclusion natural background radiation dose at different locations of kathmandu valley was studied. altogether thirty two locations were considered under the study. among these locations, the least value of average dose rate was found to be (22.3 ± 3.9) 10−3 mr/hr for sundhara and the greatest value of average dose rate was (33.7 ± 7.0) 10−3 mr/hr for budhanilkantha 3. similarly, the least and greatest value of annual effective dose were 0.391 msv/yr and 0.661 msv/yr for sundhara and k al im at i b ai sd ha ra k irt ip ur s at do ba to g on ga bu c ha ba hi l b ud ha ni la ka nt ha -3 b an sb ar i 0 10 20 30 40 50 m ax im um o bs er ve d d os e r at es (x 10 -3 m r /h r) locations maximum observed dose rates parkash pantha et al. / bibechana 16 (2019) 187-195: rcost p.194 (online publication: dec., 2018) budhanilkantha 3 respectively. study shows that budhanilkantha 3 has highest radioactivity compared to that of others. also, among the observed locations, the locations having large variation in range of observed dose rates were re-observed. for each location, the chi-square test was carried out to test whether the observed dose rates follow normal distribution or not at 0.05 level of significance. the chi-square value, calculated for each location, appeared to be less than that of critical value of chi-square at 0.05 level of significance. we concluded that the observed dose rates follow normal distribution. as we turn around the globe, the worldwide average value of annual effective dose is 0.48 msv/yr, with its value lying within the range of 0.3 msv/yr to 0.6 msv/yr for individual countries. also, if we look upto the legal dose limit (annual effective dose) set by icrp for non-radiation workers and members of public, it accounts to be 1 msv/yr. from the study findings, we observed that the average annual effective dose of kathmandu valley is 0.475 msv/yr ranging from 0.391 msv/yr to 0.661 msv/yr. if we look at the observation locations carefully, about eleven locations have greater annual effective dose than that of worldwide value. among them, budhanilkantha 3 has the highest annual effective dose. these values of annual effective dose are less than that of legal dose limit for nonradiation workers and members of public set by icrp. hence, the natural exposure level at kathmandu valley is not hazardous to the people in the study regions. references [1] t. d. luckey et al. hormesis with ionizing radiation, crc press boca raton, 1980. 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[24] j. s. milton and j. c. arnold, schaum’s outline of introduction to proba-bility & statistics: principles & applications for engineering & the computing sciences, mcgraw-hill higher education, 1994. bibechana 18 (1) (2021) 240-253 240 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal degradation of fundamental polymers/plastics used in daily life: a review netra lal bhandari*1, ganesh bhandari1, sunita bista1, basant pokhrel1, kabita bist1, kedar nath dhakal2 1department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal 2central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal *email: netra.tu.edu@gmail.com article information: received: june 24, 2020 accepted: september 9, 2020 keywords: polyethylene polylactic acid degradation thermogravimetric analysis abstract polymers/plastics, composed of monomers in the form of chain/s, are one of the highly used materials for different purposes in daily life. abiotic and biotic processes carry out degradation of polymers. abiotic pathway occurs from thermal, catalytic and photo-degradation methods whereas biotic methods occur in presence of different type of microorganisms. the degradation of representative polymers; petroand bio-based (polyethylene and polylactic acid respectively) was explained by thermal, catalytic, biodegradation and photodegradation processes. the thermal degradation of polyethylene and polylactic acid was explained by thermogravimetric analysis (tga) curves. catalysts such as zeolites and amorphous silica-alumina were used for degradation of polyethylene whereas, tin for polylactic acids. microorganisms such as bacteria, fungus and actinomycetes help for degradation of polyethylene and polylactic acid. ultra violet (uv) radiation and hydroperoxides are used for the photodegradation of polymers. bio-based polymers are found to degrade relatively faster into environmentally compatible fragments in comparison to petro-based polymers. therefore, it is emphasized on producing bio-based polymers rather than petro-based for sustainability for addressing plastics related global environmental issues. doi: https://doi.org/10.3126/bibechana.v18i1.29619 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction daily human life without polymers is hardly expected these days because polymers have become one of the essential materials of twenty first century. natural (bio-based) and synthetic (petro-based) polymers are being widely used in these days in daily life. the worldwide estimated quantity of plastics production is increasing from 325 million tons (today) to 1100 million tons by http://nepjol.info/index.php/bibechana mailto:netra.tu.edu@gmail.com https://doi.org/10.3126/bibechana.v18i1.29619 https://creativecommons.org/licenses/by-nc/4.0/ netra lal bhandari et al. / bibechana 18 (1) (2021) 240-253 241 2050. most of the plastic materials will end in landfills and more is incinerated till today even though the rate of recycling is going up day by day. numbers of researches are being carried out for the disposal and degradation of polymers and plastics. re-use, and recycling of plastics followed by the production of bio-based eco-friendly plastics can be the sustainable tasks for upcoming human generation [1,2]. in these days, natural polymers such as cellulose, chitin, lignin, starch, pectin, natural fibers etc. and the secondary materials based on them are the research topics of scientists for different applications such as drug delivery, biocompatible dental, and surgical implants etc. [2]. similarly, many synthetic plastics such as polyethylene (pe), polyvinyl chloride (pvc), polystyrene (ps), polypropylene (pp) etc. are being used for packaging and other household applications because of their low weight, low cost and durability [3,4]. meanwhile, they contribute to the existing disposal and degradation problems in maximum. their manufacturing includes different organic and inorganic materials such as carbon, hydrogen, oxygen, nitrogen, chlorides, coal and natural gases [3-5]. polylactic acid (pla), one of the most widely used bio-plastic, exhibits high stiffness, low toughness, transparency, biocompatibility, biodegradability etc. [5]. it has a very slow crystallization rate containing high level of crystallinity as end products that dictates most of the mechanical and thermal properties [6,7]. the ductility and toughness of pla have been improved following multiple strategies such as copolymerization, plasticization, melt blending etc. with different tough polymers, rubbers and elastomers [6-11]. pla is available in the market at a price on a par with that of common plastics like polypropylene [5]. polymer degradation can be a set of complicated processes whose actual mechanism/s has not been explained till now. mostly, the degradation of polymers occurs by abiotic or biotic pathways. abiotic pathways refer to thermal, photochemical and oxidative processes whereas microorganisms and enzymes carry out biotic degradation [12-14]. photodegradation of polymers also occurs via homolytic bond celevage of ester like bonds followed by free radical chain mechanism in presence intense solar uv radiations [12,14]. biodegradation (enzymatic degradation) of polymers by the action of metabolic microorganisms such as bacteria, algae and fungi etc in presence of atmospheric oxygen from which small molecules or fragments are released into environment. this process is based on the concept of ‘carbon neutrality’ by which the generated carbon dioxide is again converted into biomass by photosynthesis [15-21]. chemical structure, functional groups, reactivity, swelling behavior hydrophilicity etc are the factors affecting the biodegradability of polymers [22,23]. pseudomonas, streptomyces, thermoactinomycetes, klebsiella, actinomycetes, nocardia, micromonospora, flavobacterium, comamonas, escherichia, mycobacterium, rhodococcus, azotobacter, alcaligenes, etc., are the common bacteria identified contributing to polymeric biodegradation [23,24]. similarly, sporotrichum, talaromyces, thermoascus, thielavia, paecilomyces, phanerochaete, ganoderma, geotrichum, cladosporium, phlebia, trametes, candida, penicillium, chaetomium, aerobasidium, etc. are the fungi identified so far taking part in polymer degradation [25,26]. it has been found from the research works that bio-based polymers degrade earlier in comparison to petro-based polymers/plastics [23]. this paper presents a brief review on advances in degradation of pla and pe as representative examples of bio-based and petro-based polymers respectively. thermal, bioand photo-degradation of these polymers along with some results/data from the literature are taken into account for the discussion. the idea will be supportive to focus the polymeric research particularly on bio-based polymers, finding the cross-linking reagent/catalyst netra lal bhandari et al. / bibechana 18 (1) (2021) 240-253 242 that easily polymerizes the corresponding biomonomers to bio-polymers for future prototype materials building, and the sustainability. it will also be useful to explain the real mechanism of polymer degradation and composting phenomenon that is remained poorly defined in polymer research till yet. 2. thermal degradation of pe thermal degradation of polymers is experimentally performed under an inert atmosphere and the process is called pyrolysis/thermolysis. the most commonly followed method is the thermogravimetric analysis (tga). in this method, 15 to 20 mg of polymer, taken in a platinum pan hanged with a spring is heated up to 600 ̊c [27-29]. abbas-abadi (2020), reported the degradation of pe at 650-850 k in n2 atmosphere at the heating rate of 30 k min-1 [30]. the tga curve of pe is presented in fig. 1 [28]. fig. 1: tga curves of pe under nitrogen (dashed line) and air (solid line) (heating rates of 9.2 and 9.0 k n min-1 for nitrogen and air, respectively). inset: derivative plot of weight loss for degradation in air [28]. figure 1 shows that pe is degraded in a single step that begins at 350 ̊c and reached zero mass at 490 ̊c in n2 atmosphere. however, degradation curve possesses some irregular trends in presence of air. the degradation of pe begins at 220 ̊c and reaches zero mass at 550 c̊ that might be for the oxidation at first, and degradation steps at the end. the thermal degradation of pe in presence of catalysts performs different behavior with respect to product yield. the catalysts such as zeolites, amorphous silica-alumina etc. are used for effective thermal degradation of pe for the increased rate of reaction [31-34]. the use of amorphous silicaalumina, during thermal degradation of pe significantly reduced the activation energy in comparison to thermal processes without catalyst/s [33-40]. the catalyst (10% by w/w of polymer catalyst ratio), dependent yields of thermal degradation of pe at 560 c̊ are presented in table 1. 3. thermal degradation of pla the mechanism of pla degradation by pyrolysis is shown in fig. 2. the thermal degradation of pla is a complex phenomenon consisting of a random main-chain scission and unzipping or decompress depolymerization reaction [41-44]. the random degradation involves intramolecular and intermolecular trans-esterifications, cis-elimination and other reactions such as hydrolysis or oxidative degradation whereas, unzipping or decompress depolymerization occurs when terminal hydroxyl groups became more concentrated [42,44-46]. thermal degradation of pla is also studied using thermogravimetric analysis (tga) [47-51]. the heating rates of 5, 10, 20, 30, 40 c̊ min-1 were used which is shown in fig. 3 (a). the tga curves of pla showed single decomposition peak at lower heating rate, the retention time required for the pla to a given temperature is longer [52]. the pyrolysis of pla was carried out in presence of catalyst. many researchers have explained the effect of catalyst in pyrolysis behavior of pla in literatures [44,52-57]. organo-catalyst such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (tbd) and 4pyrrolidinopyridine also helps in degradation of pla [58]. the tga curves for pyrolysis of pla in presence of tin as catalyst is shown in fig. 3 (b) which shows that the degradation temperature for pla decreases as the composition of tin increases [53]. netra lal bhandari et al. / bibechana 18 (1) (2021) 240-253 243 a. temperature (ᵒc) w t. l o ss ( % ) b. table 1: catalyst dependent product yield in the pyrolysis of pe at 560 ̊c [40]. fig. 2: thermal degradation of pla and pyrolysis mechanism [44]. fig. 3: (a) tga curves of pla at different heating rates (5, 10, 20 and 40 c̊ min-1) under n2 (b) tga curves of pla-sn samples at a heating rate of 5 k min-1 under n2 flow of 100 ml min-1 [52,53]. catalyst percent products ethylene propylene isobutylene 1-hexene heptane none 39.98 19.52 19.41 17.24 12.84 al2o3 (basic) 29.02 15.53 18.20 22.57 15.61 al2o3(neutral) 25.67 15.21 17.59 24.09 17.43 sio2 26.39 11.48 17.70 22.97 13.40 zeolite 23.19 11.39 17.39 28.40 17.04 netra lal bhandari et al. / bibechana 18 (1) (2021) 240-253 244 thermal degradation of bio-based polymer and petro-based polymer occurs by pyrolysis in presence of air or nitrogen. various catalysts support the pyrolysis mechanism. catalyst such as zeolites and amorphous silica-alumina are used for degradation of polyethylene whereas, tin for polylactic acid. the temperature required for pyrolysis of polyethylene in presence of catalysts is higher than that of polylactic acid. therefore, degradation of bio-based polymers required less energy and faster process than petro-based polymers. 4. biodegradation of pe pe is a representative of synthetic homo-polymers that contain repeating units of -ch2-ch2as a monomer in the polymer backbone [3]. biodegradation/composting of homopolymers is reported to occur in decades by bond cleavage with the enzymatic action of microorganisms [59]. the degradation of -ch2-ch2backbone can be enhanced by the addition of readily biodegradable compounds, such as starch, to a low-density polyethylene matrix etc. [15]. some researchers have explained the composting and biodegradation as synonymous terms but others have different arguments that in composting not only the solo microorganisms but also the microorganisms, enzymes, fungi, heat, temperature, light and moisture acts simultaneously for the degradation [60-65]. devi et al. (2015), hadad et al. (2005), abrusci et al. (2011), sowmya et al. (2014), nowak et al. (2011), usha et al. (2011), bonhomme et al. (2003) and sepulveda et al.(2002) studied the role of different temperature dependent microorganisms and corresponding enzymes for pe degradation. it has been reported that pe breaks down into simpler products (after decades) such as in biofilms, esters, unsaturated hydrocarbons, alkylhalides and others as listed in table 2 [59-66]. the comparative study of mechanism of bio-degradation and surface morphology of polymers was also explained by spectroscopic, microscopic and thermogravimetric methods. similarly, fungal degradation of pe is explained by corti et al. (2010), on the basis of fourier transform infrared spectroscopy (ftir) which is presented in fig. 4 [67]. the ftir peaks of polyethylene before and after degradation is different. the dotted line expressed the degradation of polyethylene in 6 month. the ftir spectra from polyethylene films by the fungal degradation enhance the formation of small units containing carbonyl groups. the ftir breakdown products in pre-oxidized polyethylene films as reflected by peak intensities on several functional groups. in ftir spectra several peaks shows the various functional groups such as –c=o (1743 cm1), -c=c(1640 cm-1), -oh deformation vibration (1080 cm-1) and -oh stretching vibration (3400 cm1). the appearance of new bands were possibly due to the oxidized fractions such as moieties containing -oh groups, resulting from the fungal biodegradation [67]. 5. biodegradation of pla pla is a bio-based polyester derived from starch feed stocks with a hydrolysable backbone that is susceptible to biodegradation. it is the promising candidate of biodegradable plastic [68] whose biodegradability is based on bacteria such as bacillus stearothermophilu, geobacillus thermocatenulatu, fungus, actinomycetes etc. and biochemical processes of degradation have been advanced in recent years [69]. pla undergoes biodegradation both in aerobic and anaerobic conditions [69]. it is a complex chemical hydrolysis process in presence of soil microorganism in which ester bonds of pla cleavage into carboxylic acid and alcohol with hydrion (enzyme) [69]. the different steps and possible mechanism of degradation is summarized in fig. 5. as in fig. 5 during biodegradation, pla-degrading microorganisms first produce extracellular depolymerase of pla that requires some inducers like elastin, gelatin, silk fibron and some peptides and amino acids [69-71]. netra lal bhandari et al. / bibechana 18 (1) (2021) 240-253 245 table 2: list of some microorganisms and corresponding enzymes contributing to pe degradation. fig. 4: (a) ftir spectra of control and pre-oxidized pe films incubation with fungal strain for 6 months (b) magnified region of the spectrum between 900 and 1800 cm-1 of fig. (a) [67]. the inducers contain l-alanine units, which is similar to l-lactic acid units of pla. depolymerase enzyme attack ester units of pla resulting in the formation of oligomers, dimers and monomers. finally, it decomposes to carbon dioxide, water and methane [71-74]. some pla degrading microorganisms and their corresponding degrading enzymes have been shown in table 3. results show that protease is the major enzyme that most of bacteria produce for pla degradation at 30 ºc [7580]. chaisu et al. (2013) studied the surface morphology of pla film after 30 days at 30 ̊c by the growth of aneurinibacillus aneurinilyticus on samples. the surface morphology of pla film was observed by sem analysis in secondary electron mode as in fig. 6 and shows that the pla film surfaces were smooth in controls before inoculation. however, after bacterial incubation within 30 days shows the surfaces as rough and hemispherical holes as in fig. 6(b). these sem micrographs support the pla films degradation by aneurinibacillus aneurinilyticus at optimal microorganisms pe degrading enzyme evolution of new compounds temperature ( ̊c) references aspergillus tubingensis biofilm 45 [60] brevibacillus borstelensis biofilm 30, 45 and 50 [59,61] trichoderma harzianum laccase, manganese peroxidase carboxylic acids, aldehydes, esters, ethers, and alkyl halides 50 [62] gliocladium viride, aspergillus awamori and mortierella subtilissima bionolle unsaturated hydrocarbon and saturated hydrocarbon 27 [63] streptomyces sp, psudomonas sp, bacillus, staphylococcus sp and aspergillus sp 30 [64] rhodococcus rhodochrous biofilm 60 [65] aspergillus niger and penicillium pinophilum extracellular enzyme 80 [66] netra lal bhandari et al. / bibechana 18 (1) (2021) 240-253 246 laboratory conditions. pranamuda et al. (1997), also observed the similar surface morphology of pla by amycolatopsis sp [81,83]. the degradation time of bio-based polymers and petro-based polymers is different. for complete degradation, petro-based polymers take a several years and decades as compared to bio-based polymer degradation [84-90]. a comparative study of polymer thin film degradation time in soil has been presented in table 4. for a complete degradation of polymers in soil takes several years and also depends on thickness of plastic, type of microbes, temperature, moisture content, ph of soil and soil humus. a thin film of polylactic acid in soil was degraded in 30-35 days and that of polyethylene film in 60-65 days [84,88]. further, the ether or ester bond containing polymers were degraded earlier as compared to the other hydrocarbon homo polymers. above results revealed that both bio-based and petro-based polymers under goes degradation by various microorganisms under different conditions. microorganisms such as psudomonas sp and bacillus helps for maximum degradation of polyethylene as compared to other microorganisms [64]. similarly, brevibacillus sp for degradation of polylactic acid [78]. the time required for degradation of bio-based polymer film is less as compared to petro-based polymers. further, polymers containing the ester, peptide or ether linkage degraded easily in soil with biocompatible end products as compared to hydrocarbon homopolymers. the exact degradation mechanism, isolation and culture of polymers specific bacteria and optimization of conditions for degradation and composting has not been fully studied and practiced till yet, and created the problems for the sustainable polymer waste management. 6. photo-degradation of pe it is reported that photo-degradation of most of polymers occurs in presence of highly energetic uv radiation following the mechanism of free radical formation similar to that of peroxidation reaction [91-94]. uv radiation with wavelength range of 290-400 nm can degrade pe into small units compatible to soil such as esters and lactones in presence of hydroperoxide [92,95] as presented in fig. 7. 7. photo-degradation of pla photo-degradation of polylactic acid is also carried out in presence of strong uv radiation (200-400 nm) with the formation of anhydride and carbonyl groups at the end as final product [96-100]. bocchini et al. (2010) explained the mechanism of photooxidative degradation of pla by the chain excision (intrachain β-scission). the photodegradation of pla also occurs by norrish i and ii type cleavage, followed by the formation of carbonyl groups as explained in fig. 8 [97,98]. in this mechanism the anhydride groups are formed by radicals that react with oxygen and extract a hydrogen forming hydroperoxide [98-100]. the photo-degradation of petroand bio-based polymers more often than not takes place in presence of uv radiations. the polyethylene is not easily decomposed to esters and lactones since it requires large amount of energy and high mechanical pressure. the photo-degradation of polylactic acid is relatively easier with esters and acids as common end products. therefore, biobased polymers as well as the polymers containing the ester, peptide, ether, carbonyl or amide linked polymers are relatively easier for photodegrdadation to soil compatible products as compared to polyethylene, polyvinyl choloride, polypropylene polymers. recommendation for future work many researchers proposed and explained polymer degradation in different ways. however, none of them is found absolute with respect to time, cost as well as environmental concerns. although composting or biodegradation of polymers seems to be an effective solution of polymer waste disposal, the exact degradation mechanism, isolation and culture of polymer specific microorganisms in laboratory is still missing. this review recommends researchers/readers to focus on green techniques/catalysts for polymerization of natural and bio-based monomers that contain the carbonyl, peptide or ether linkage, and easily degrades by composting or low intensity of uv radiations forming the eco-friendly end products. netra lal bhandari et al. / bibechana 18 (1) (2021) 240-253 247 fig. 5: schematic diagram of biochemical processes in pla degradation [qi et al. (2017)]. table 3: pla degrading microorganisms and corresponding enzymes. microorganisms pla degrading enzyme evaluation of degradability optimum temp. ( ̊c) references amycolatopsis sp. strain 3118 protease l-pla, film weight 30 [75] amycolatopsis sp. strain 41 protease l-pla, silk powder, casein, film weight 30 [76] lentzea waywayandensis protease l-pla, film weight 30 [77] kibdelosporangium aridum protease l-pla, film weight 30 [78] bacillus stearothermophilus d-pla, film (toc, gpc, viscosity) 60 [79] brevibacillus sp. l-pla, film (toc, gpc, viscosity) 60 [78] aspergillus oryzae rib40 cutinase dl-pla, turbidity of emulsion 37 [80] aneurinibacillus aneurinilyticus pla film 30 [81] geobacillus thermocatenulatus protease l-pla 60 [82] netra lal bhandari et al. / bibechana 18 (1) (2021) 240-253 248 fig. 6: sem micrographs showing the surface morphology of pla films after degradation by bacteria in 30 days at 30 ᵒc in liquid medium: (a) surface structure without cell inoculations, 50 µm (control no microorganism degradation), (b) surface structures with cell inoculation. table 4: degradation time of some polymer films in soil. fig. 7: peroxidation mechanism of photodegradation of pe [92]. polymer film degradation span (days) references polylactic acid 30-35 [84] polycaprolactone 35-40 [85] chitin 160-168 [86] cellulose 28-30 [87] polyethylene 60-65 [88] polyvinyl chloride 9095 [89] polystyrene 70-85 [90] netra lal bhandari et al. / bibechana 18 (1) (2021) 240-253 249 fig. 8: degradation of pla by norrish i and ii type reaction [98]. 8. conclusion in this review article, most common methods for polymer degradation that are familiar in practice such as thermal, photochemical, biochemical and enzymatic/catalytic processes have been discussed in brief taking polyethylene (pe) as a representative example of petro-based thermoplastics polymer and polylactic acid (pla) as bio-based polymer. comparing the results related to time, feasibility, cost and environmental concerns the biodegradation with composting would be the better solution of reducing plastic pollution for the sustainability. results related to composting or biodegradation showed that the bio-based polymers such as pla, polyhydroxybutyrate, copolyesters degrades easily in to environmentally compatible fragments/monomers as end products in comparison to petro-based polymers although there is very large gap in their mechanical properties. the identification of catalysts and enzymes to polymerize or crosslink the bio-based monomers to replace petro-based commodity polymers and finding the specific polymer eating (degrading) microorganisms would be the best way for the sustainability of polymer research. references [1] g-j. m. gruter, the oppoertunity of sustainable materials, 5th international symposium on advances in sustainable polymers (asp-19), proceedings (2019) 2-3. 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[99] a. copinet, c. bertrand, a. longieras, v. coma and y. couturier, photodegradation and biodegradation study of a starch and poly(lactic acid) coextruded material, journal of polymers and the environment 11(4) (2003) 169-179. [100] r. w. j. westerhout, j. waanders, j. a. m. kuipers and w. p. m. van swaaij, kinetics of the low-temperature pyrolysis of polyethene, polypropene and polystyrene modeling, experimental determination and comparison with literature data: review, industrial and engineering chemistry research 36 (1997) 1955-1964. bibechana vol. 20, no. 3, december 2023, 236–247 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar phytochemistry, biological activities, and chemical profiling of berberis asiatica keshab bhattarai, devendra dhakal, indira pandey bimala subba, khaga raj sharma∗ central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal, ∗corresponding author. email: khaga.sharma@cdc.tu.edu.np abstract this study focused on chemical profiling and assessed the total phenolic and flavonoid content as well as the antioxidant and antibacterial effect of the medicinal plant berberis asiatica. the results revealed that this plant has high concentrations of tpc (total phenol content) and tfc (total flavonoid content) of 37.686±2.728 mg gae/g and 115.568±8.012 mg qe/g, respectively. the dpph free radical scavenging assay demonstrated strong inhibition, with an ic50 of 205.7± 5.353µg/ml, and also showed robust antibacterial properties against staphylococcus aureus and klebsiella pneumoniae with a zone of inhibition (zoi) of 14 mm and 19 mm, respectively. the extract exhibited an excellent inhibitory potential against s. aureus and k. pneumoniae with a mic (minimum inhibitory concentration) of 0.39 mg/ml and 3.125 mg/ml respectively, indicating significant inhibitory action. furthermore, the mbc (minimum bactericidal concentration) for both s. aureus and k. pneumoniae was found to be 6.25 mg/ml, emphasizing the extract’s consistent bactericidal effectiveness against these bacteria. these findings underscore the potential utility of the methanolic extract of berberis asiatica as a natural antibacterial agent. gc-ms analysis of hexane fraction indicates the plant is rich in secondary metabolites, specifically 2,2-dimethyl-3-pentanol, 2-methyl-2-pentanol, 2,5dimethyl-4-hydroxy-3-hexanone, 3-hexanol, 4-methyl-2-pentanol are identified. overall, this study highlights the importance of plant-based natural products as potential sources of antioxidants and antibacterial agents that contribute to the future drug development process. keywords berberis asiatica, antibacterial activity, minimum inhibitory concentration (mic), minimum bactericidal concentration (mbc), staphylococcus aureus, klebsiella pneumoniae article information manuscript received: august 17, 2023; accepted: september 14, 2023 doi https://doi.org/10.3126/bibechana.v20i3.57711 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 236 http://nepjol.info/index.php/bibechana khaga.sharma@cdc.tu.edu.np https://doi.org/10.3126/bibechana.v20i3.57711 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ keshab bhattarai et al./ bibechana 20 (2023) 236-247 237 1 introduction traditional medicines rely on natural products to treat diseases, and modern pharmaceutical medications are often derived from natural sources [1]. in recent years, there has been an assessment of plant-derived natural products as promising candidates for drug development [2]. the medicinal plant serves as a valuable and organic reservoir of bioactive elements that play a significant role in contemporary medicine [3]. various plant-derived natural products, including alkaloids, phenols, and flavonoids, have been discovered with capabilities to induce apoptosis, and migration and exhibit potential against cancer, oxidation, diabetes, and inflammation [2, 4]. renewed interest and focus on medicinal plant research have been triggered by the rise in side effects, the emergence of new intestinal pathogens, and the increasing problem of microbial resistance [5]. in this research, we examined the antioxidant, antibacterial, and alpha-amylase inhibition properties of berberis asiatica, a medicinal plant grown in nepal belonging to the family berberidaceae. berberis plants of the berberidaceae family are extensively distributed across the globe, comprising almost 550 species [6]. genus berberis is globally recognized in traditional medicine for its potent medicinal properties. its roots and bark are employed as antipyretic, anti-periodic, and diaphoretic [7]. barberry fruits, due to their significant richness in anthocyanin content, are consumed as an antidiabetic drug [8]. among many species of berberis, berberis asiatica is widely used in traditional medicinal practices to cure diabetes and infectious diseases [9]. berberis asiatica, commonly known as chutro in nepali, is a wild shrub found in nepal between elevations of 1200 to 2500 meters. it thrives in shaded, rocky slopes, north-facing hillsides, and drier regions. this erect, spiny shrub grows up to 4 meters tall, sporting yellow bark. its leaves are simple, alternate, leathery, dark green on top, and grayish underneath, usually with 2-5 spiny teeth along the margins. the shrub produces pale yellow flowers in flat-topped clusters and dark purple berries with a sweet and sour taste [10, 11]. traditionally, different parts of berberis asiatica were used for medical purposes. root and bark have extensive use in indigenous medicine for treating various ailments, including eye and ear diseases, rheumatism, jaundice, diabetes, fever, stomach disorders, skin disease, and malarial fever [9]. these root and stem bark are integral to a renowned ayurvedic medicine, containing several alkaloids such as berberine, palmatine, jatrorrhizine, columbamine, berbamine, oxyberberine, and oxyacanthine [12]. these secondary metabolites play an important role in treating different diseases and disorders in the human body. it was reported that berberine plays a vital role in controlling diabetes by inhibiting digestive enzymes alpha-amylase and alpha-glucosidase [13]. oxidation, a fundamental metabolic procedure present in all life forms, holds particular significance in humans as it underpins the production of energy. however, these biochemical reactions create free radicals such as reactive oxygen species (ros), potentially amplifying oxidative stress and causing potential harm to essential biological components like lipids, proteins, and dna [14, 15]. as time passes, the harmful effects of ros become more prominent and are associated with aging and age-related illnesses like heart diseases, cancer, brain disorders, diabetes, and other chronic diseases [16]. furthermore, diabetes represents a significant metabolic syndrome with abnormally high blood glucose levels (hyperglycemia), and oxidative stress is closely associated with this condition, especially in individuals with type 2 diabetes [17, 18]. type 2 diabetes mellitus is a multifaceted and diverse collection of metabolic disorders marked by increased serum glucose levels, primarily resulting from deficiencies in both the function of insulin and its secretion [19]. roughly, 90 to 95 % of diabetes cases are attributed to type 2 diabetes [20]. to managing diabetes, one of the main approaches involves controlling postprandial hyperglycemia through the inhibition of the carbohydrate hydrolyzing enzyme alpha-amylase, responsible for breaking down longchain carbohydrates like starch, amylase, and amylopectin into glucose, and another is by reducing oxidative stress [14,20,21]. hence, a novel and promising drug is required in modern times to effectively manage diabetes and oxidative stress. as a result, there has been a concentrated effort to discover novel antidiabetic compounds from plants utilized in traditional medicine [22]. furthermore, medicinal plants offer a valuable source of antimicrobial agents [23]. several plants belonging to berberis are renowned for their antibacterial properties [24, 25]. notably, berberis asiatica has generated particular attention as a source of novel compounds with remarkable antibacterial activity. taking into account the aforementioned factors, this study was undertaken to explore the antioxidants, antibacterial, and α-amylase inhibition properties using in vitro assays, aiming to contribute significant insights into the holistic understanding of berberis asiatica. 2 materials and methods 2.1 chemicals all chemicals and reagents utilized in this study were of analytical grade. gallic acid, keshab bhattarai et al./ bibechana 20 (2023) 236-247 238 folin-ciocalteu’s reagent, quercetin, 2,2-diphenyl1-picrylhydrazyl (dpph), acarbose, α-amylase from porcine pancreases, 2-chloro-4-nitrophenyl-d-maltotrioside (cnpg3) were demanded from sigma-aldrich. 2.2 plant collection and preparation of extract the whole plant of the berberis asitica was collected from the arghakhanchi district of nepal growing at an altitude of 1810 m in october 2021 based on ethnobotanical approaches. the plant was verified in the national herbarium and plant laboratories godavari, kathmandu, nepal. to prepare the plant extract, freshly collected whole plant parts (leaves, bark, and roots) were washed with tap water to remove the contaminants, and the collected samples were dried and ground into a fine powder. for the extraction process, methanol was used as a solvent. due to high volatility, lower boiling point, and strong polarity, methanol is an ideal choice for the extraction process [26,27]. moreover, methanol is renowned for its ability to yield higher extraction efficiency as compared to other solvents and its efficacy in extracting a diverse range of compounds, including antibacterial compounds, antioxidants, polyphenols, flavonoids, alkaloids, and terpenoids [28–32]. furthermore, methanol is costeffective and readily available, making it an easily manageable choice as a preferred extraction solvent. 75 grams of powder was then mixed with 300 ml methanol in a conical flask and meticulously shaken to completely mix the powder in the solvent. then the conical flask was covered with aluminum foil and left to undergo cold percolation for 72 hours at room temperature. subsequently, the mixture was filtered using a muslin cloth, and filtrate was collected in a beaker. this process was repeated for subsequent 2 times to get a higher amount of the extract. the filtrate was concentrated using a rotary evaporator at a temperature of 400c, and concentrated solution was kept in the water bath for fast evaporation of the solvent. the crude extract was stored in the refrigerator at 4 0c for the subsequent evaluation of various biological activities, following the standard procedures. 2.3 phytochemical analysis the recently prepared raw extracts of b. asiatica were subjected to qualitative tests to analyze the presence or absence of various plant secondary metabolites including alkaloids, flavonoids, steroids, terpenoids, reducing sugars, saponins, tannins, cardiac glycosides, anthraquinones. for qualitative phytochemical analysis, a series of tests were carried out according to the protocols of [33,34]. 2.4 total phenolic content (tpc) to determine the tpc, the folin-ciocalteu phenol assay was employed [35,36]. the dry methanolic extract was prepared at a concentration of 5 mg/ml in 30% dmso. a sample (20 µl) of the plant extract and a standard solution of gallic acid (ranging from 10 to 80 µg/ml) was mixed with folinciocalteu phenol reagent (100 µl) and sodium carbonate (80 µl). after a 30-minute incubation, the absorbance was measured at 765 nm using a microplate reader (synergy lx, bio-tek, instruments, inc., usa). the tpc was calculated using a standard curve and expressed as milligrams of gallic acid equivalent (mg gae) per gram of plant extract. 2.5 total flavonoid content (tfc) to estimate the total flavonoid content (tfc), the aluminum chloride (alcl3) procedure was employed [37]. a 20 µl of the stock solution of the plant extract and 130 µl of the standard quercetin solution (ranging from 10 to 80 µg/ml) were loaded in 96-well plates. the standard quercetin solution was prepared by diluting a stock solution of 0.1 mg/ml. subsequently, to maintain the volume of 110 µl, distilled water was added to the plant extract in triplicate. additionally, 60 µl ethanol, 5 µl 10% alcl3, and 5 µl potassium acetate were added to each well. after a 30-minute incubation at room temperature, the absorbance was measured at 415 nm using a microplate reader (synergy lx, bio-tek instruments, inc., usa). the tfc was calculated using a standard curve and expressed as milligrams of quercetin equivalent (mg qe) per gram of plant extract. 2.6 evaluation of antioxidant activity to evaluate the free radical scavenging activity, the dpph radical scavenging assay was employed [38,39]. a solution of 0.1 mm dpph was prepared, and a stock solution of quercetin was also prepared. quercetin served as the positive control, while 50% dmso was used as the negative control. the positive control, negative control, and plant samples were loaded into separate wells of a 96-well plate in triplicate. subsequently, the dpph reagent was added to each well, followed by a 30-minute incubation period in darkness. after incubation, the absorbance at 517 nm was measured using a microplate reader. percentage inhibition of the tested sample was calculated using the following formula. %inhibition = [abs. of control-abs. of sample] abs. of control ×100 keshab bhattarai et al./ bibechana 20 (2023) 236-247 239 2.7 α−amylaseinhibitionactivity to assess the inhibitory activity of α-amylase, an in vitro assay was conducted using cnpg3 as the substrate [40]. plant samples of various concentrations (20 l) were mixed with α-amylase (80 l at a final concentration of 1.5 u/ml) and incubated at 37 °c for 15 minutes. the reaction was initiated by adding 100 l of the substrate, cnpg3 (final concentration of 0.5 mm), prepared in the buffer. the experiment was performed in a 50 mm phosphate buffer. after incubation, the absorbance was measured at 405 nm using a microplate reader. dmso (30%) was used as the negative control, while acarbose served as the standard. the inhibition percentage was calculated using the provided formula. %inhibition = [abs. of control-abs. of sample] abs. of control ×100 2.8 determination of antibacterial activity the antibacterial activity of the extract was evaluated using the agar well diffusion method on mueller-hinton agar (mha) plates [41]. the test organisms gram-positive staphylococcus aureus (atcc 25293), and gram-negative bacteria escherichia coli (atcc 25922), salmonella typhi (atcc 14028), and klebsiella pneumoniae (atcc 13883) were cultured in mueller-hinton broth. these tested bacteria staphylococcus aureus and escherichia coli were obtained from clinical isolation whereas salmonella typhi was isolated from the liver of the four-week-old chicken. these cultured bacteria were incubated at 37 0c until the turbidity reached a standardized 0.5 mcfarland unit. the mha plates were then uniformly inoculated with the microbial suspension. a stock solution of the plant extract at a concentration of 5 mg/ml was prepared. using a sterile cork borer with an 8 mm diameter, three wells were created on the agar surface. each well was filled with 50 µl of the plant extract, along with a positive control consisting of neomycin at a concentration of 1 mg/ml, and a negative control consisting of 50% dmso. these controls were included on each plate. after allowing approximately 15 minutes for the extracts and controls to diffuse into the agar at room temperature, the plates were incubated at 370c for 18-24 hours. following the incubation period, the plates were examined for the presence of clear zones of inhibition (zoi) surrounding the wells. the diameter of the zoi was measured in millimeters using a ruler, providing a quantitative assessment of the antimicrobial activity of the plant extract. 2.9 determination of minimum inhibitory concentration (mic) determination of the minimum inhibitory concentration (mic), which represents the smallest amount of compounds needed to inhibit or kill microorganisms in vitro, can be achieved through the broth microdilution method [42]. in this method, the methanolic extract of the plant exhibiting significant antibacterial activity was subjected to a two-fold serial dilution. under aseptic conditions, a sterile 96-well plate was filled with 100 µl of mueller hinton broth in each well. the extract was double diluted by adding equal volumes (100 µl) of the extract to mhb to get a series of concentrations ranging from 25 mg/ml to 0.012 mg/ml in plates. next, 5 µl of the prepared bacterial inoculums adjusted to 0.5 mcfarland standard was added in each dilution. the microplate was incubated at 37 oc for 12 to 18 hours. after incubation, 10 µl of a 0.003% resazurin solution was added to wells, followed by an additional incubation period of 2 to 3 hours. any color change from purple/blue to pink or colorless was recorded as a positive result. in this test neomycin solution was taken as positive control and dmso solution was placed as negative control. the mic value was determined as the lowest concentration at which no color change occurred, indicating the inhibition of bacterial growth by the plant extract. 2.10 determination of minimum bactericidal concentration (mbc) mbc was determined by subculturing the mic cultures on suitable agar plates. the sterile nutrient agar plate was taken in which solution from the microplate was loaded by streaking with the help of an inoculating loop. the solutions of the well showing mic value and above were loaded in the plate. the plates were incubated at 37ºc for 18-24 hours. then plates were examined for the growth of microorganisms. the tubes with a minimum concentration of extract in which the growth was completely checked were noted as the mbc of the plant extract [10]. mbc is complimentary to mic and it is the lowest concentration of antibacterial agent that has a reducing capacity of viability of initial bacterial inoculum up to 99.9%. 2.11 gc-ms profiling of chemical compounds in this study, for the chemical characterization hexane fraction was fractionated from the methanolic extract and this fraction was analyzed using gas chromatography-mass spectrometry (gcms) with an agilent 7890 gc instrument and an keshab bhattarai et al./ bibechana 20 (2023) 236-247 240 agilent 5975c inert msd with triple-axis detector. the analysis employed a gas carrier of helium at a flow rate of 1 ml/min. the sample injection volume was set at 2 µl, and the temperature program consisted of an initial temperature of 320c, followed by a ramping rate of 50c/min up to 2300c, with a final hold time of 15 minutes. the auxiliary heater was set to 2300c to ensure optimal conditions for efficient analysis. these carefully optimized analytical conditions provided valuable insights into the chemical composition of the hexane fraction, facilitating the identification and quantification of its compounds. these findings enhance our understanding of the chemical profile of b. asiatica and its potential therapeutic applications. 2.12 statistical analysis all the experiments were performed in triplicate and data were presented in ± standard error of the mean. the tpc, tfc, antioxidant assay, and enzyme inhibition were calculated by microsoft excel 2007. the ic50 value was calculated using graphpad prism software. 3 results and discussion 3.1 percentage yield the percentage yield was calculated to measure the abundance of secondary metabolites in the whole plant sample used in the study. the percentage yield of b. asiatica was found 10.66%, which is shown in table 1. 3.2 phytochemical screening of crude extract preliminary phytochemical analysis was performed for the analysis of the presence and absence of different secondary metabolites. the result of the phytochemical screening of the methanolic extract of berberis asiatica is shown in table 2. 3.3 total phenolic and flavonoid content the total phenolic content (tpc) and total flavonoid content (tfc) were estimated by constructing a calibration curve taking different concentrations of gallic acid and quercetin, against the absorbance. tpc was expressed as milligrams of gallic acid equivalent per gram (mg gae/g), while tfc was expressed as milligrams of quercetin equivalent per gram (mg qe/g). the total phenolic content of the methanolic extract of b. asiatica was determined to be 37.686 ± 2.728 mg gae/g, while the total flavonoid content was estimated as 115.568 ± 8.012 mg qe/g. 3.4 antioxidant potential at a concentration of 1000 g/ml, the crude extracts of b. asiatica demonstrated significant inhibitory activity of 89.588% against the dpph free radical. as a result, further dilution of the samples was performed to determine the ic50 value. the methanolic extract of b. asiatica exhibited noteworthy radical scavenging activity, with an ic50 value of 205.7 ± 5.353 g/ml. this result was compared to the ic50 value of the standard quercetin, which was found to be 6.29 ± 1.02 g/ml. table 1: physical characteristics and percentage yield of plant extract. plant color of extract weight of dry sample (g) weight of extract (g) b. asiatica yellow 75 8 table 2: phytochemical screening of whole plant extract. phytochemicals methanolic extract of berberis asiatica alkaloids + flavonoids + tannins saponins + terpenoids + steroids + glycosides + reducing sugars + coumarins + polyphenols + volatile oils where + represents the presence of metabolites and represents absence. keshab bhattarai et al./ bibechana 20 (2023) 236-247 241 table 3: total phenolic and flavonoid content in methanolic extract of berberis asiatica. whole plant extracts tpc (mg gae/g) tfc (mg qe/g) berberis asiatica 37.686 ± 2.728 115.568 ± 8.012 3.5 in vitro α-amylase inhibition activity the crude methanolic extracts of b. asiatica exhibited an inhibitory activity of 37.732% against αamylase at a concentration of 500 g/ml. therefore, additional dilution of the samples was not carried out to determine the ic50 value. according to the literature, it has been observed that plants contain secondary metabolites that possess properties similar to metformin, which are known to aid in the control of diabetes [43]. 3.6 antibacterial activity the methanolic extract of b. asiatica, at a concentration of 50 mg/ml, exhibited varying inhibitory effects against different bacteria. against s. aureus, moderate inhibitory activity was observed, with a zone of inhibition measuring 14 mm. however, no inhibitory effect was detected against e. coli and s. typhi. in contrast, the extract displayed a strong inhibitory activity against k. pneumoniae, as evidenced by a substantial zone of inhibition measuring 19 mm. these results indicate that the methanolic extract of b. asiatica possesses antibacterial properties, particularly against s. aureus and k. pneumoniae while showing no inhibitory effect on e. coli and s. typhi. 3.7 minimum inhibitory concentration the methanolic extract of berberis asiatica demonstrated significant antibacterial activity against two types of bacteria, namely s. aureus (gram-positive) and k. pneumoniae (gram-negative). to determine the potency of the extract in inhibiting the growth of these microorganisms in vitro, the minimum inhibitory concentration (mic) values were determined using the two-fold serial broth microdilution method. mic is expressed in terms of mg/ml. the mic shown by the methanolic extract of berberis asiatica and the standard antibiotic neomycin (positive control) against the test bacteria are summarized in table 6. the results indicate that the methanolic extract of berberis asiatica exhibited excellent inhibitory activity against s. aureus, with a mic value of 0.39 mg/ml. although the methanolic extract also demonstrated inhibitory activity against k. pneumoniae, it was less potent than the positive control neomycin. the mic value for k. pneumoniae was 3.125 mg/ml for the plant extract, whereas it was 0.0019 mg/ml for neomycin. 3.8 minimum bactericidal concentration mbc is the lowest concentration of antibacterial agent that has a reducing capacity of viability of initial bacterial inoculum up to 99.9%. mbc is complimentary to mic. methanolic extract of berberis asiatica exhibited minimum bactericidal concentration for s. aureus was 6.25 mg/ml and for k. pneumoniae was 6.25 mg/ml. the results showed that the plant extract exhibited the same mbc for s. aureus and k. pneumoniae. 3.9 chemical constituents profiling by gc-ms analysis the gc-ms analysis of the hexane extract of berberis asiatica revealed the presence of 35 compounds. the gc-ms chromatogram is shown in figure 2. the nist08 ms library was employed to compare and identify the chemical constituents. these compounds consist of ketones, alkanes, cycloalkanes, alcohol, and amines along with aromatic compounds. the profiling of chemical compounds in the hexane extract of asiatica with their retention time (rt), molecular weight (mw), and relative area percentage (%) are presented in table 8. table 4: antioxidant (ic50 ) of methanolic extract of berberis asiatica and standard quercetin. samples ic50 (µg/ml) berberis asiatica 205.7 ± 5.353 quercetin (standard) 6.29 ± 1.02 keshab bhattarai et al./ bibechana 20 (2023) 236-247 242 figure 1: antibacterial activity, mic, and mbc determination of plant extract. figure 2: gc-ms chromatogram of hexane fraction of berberis asiatica. 3.10 pharmacological importance of gcms detected compounds among the detected compounds by gc-ms, some of those compounds having the alcohol and ketone functional groups have been reported to possess pharmaceutical significance owing to their biological activities. the compound 2,5-dimethyl4-hydroxy-3-hexanone is reported to have potential therapeutic effects such as antioxidant, antimicrobial, anti-inflammatory, antidiabetic, anticancer, and also effective against alzheimer’s disease.. the compound 2-methyl-2-pentanol has been demonstrated to induce apoptosis in cancer cells, enhance the immune response to viral infections, and exhibit antimicrobial, antifungal, and antiviral activity. the compound 4-methyl-2-pentanol has been reported to act as an acetylcholinesterase inhibitor and demonstrate antibacterial and antifungal properties. furthermore, it has shown effectiveness in the treatment of alzheimer’s disease and other neurological disorders. other identified compounds like 2,2-dimethyl-3-pentanol and 3-hexanol also demonstrated antifungal, antibacterial, and antitumor activities [44]. the compound 3-hexanol can serve as an agonist for the gaba-a receptor, which plays a role in regulating neurotransmitters in the brain. meanwhile, in vitro studies of 2,2-dimethyl-3-pentanol have shown that this compound can inhibit the growth of various cancer cell lines, including those associated with breast, lung, and colon cancers [44]. the chemical profiling of the present study reported that the plant b. asiatica is the source of potential natural compounds that could be used in treating different diseases. 4 discussion a limited number of studies have been conducted to explore the bioactive metabolites of plants in nepal. being a landlocked country, nepal boasts remarkable biodiversity in its flora, resulting in a high denkeshab bhattarai et al./ bibechana 20 (2023) 236-247 243 figure 3: structures of some chemical compounds detected from gc-ms analysis of hexane fraction of berberis asiatica. table 5: zone of inhibition shown by methanolic extract of berberis asiatica against bacterial strain. bacterial strain zone of inhibition (mm) of plant extract zone of inhibition (mm) of positive control s. aureus 14 13 e. coli 16 k. pneumoniae 19 18 s. typhi 15 sity and diversity of plant species. for this research, various readily available berberis species were collected and confirmed to be berberis asiatica . the primary objective of this study was to evaluate the inhibitory effects of berberis asiatica on α-amylase, various gram-positive and gram-negative bacteria, as well as the antioxidant properties of plants. in earlier investigations, the methanolic extract of berberis asiatica exhibited a percentage yield of 6.8% [10]. however, in the current study, the percentage yield was found to be higher at 10.66%. the variation in secondary metabolites abundance can be ascribed to the distribution of the selected plant across different geographical locations, thereby affecting its overall availability of these compounds. in the previous study, the total phenolic content (tpc) and total flavonoid content (tfc) were examined in different parts of berberis asiatica , including leaves, bark, and roots. the tpc values were recorded as 132.63 mg gae/g, 52.240 ± 0.119 mg/100g, and 59.076 ± 0.219 mg/100g for leaves, bark, and roots, respectively [45]. similarly, the tfc was found to be 31.36 mg qe/g, 1.735 ± 0.396 mg qe/g, and 1.576 ± 0.197 mg qe/g for leaves, bark, and roots, respectively [45]. in the present study, a notable difference in tpc and tfc was observed in berberis asiatica compared to the previously reported results. the tpc value for this plant was reported as 37.686 ± 2.728 mg gae/g, and the tfc was recorded as 115.568 ± 8.012 mg qe/g. the plant sample collected in the present study showed higher contents of secondary metabolites which impart a significant effect on the biological activity, particularly in terms of antioxidant and antidiabetic properties. in previous research, the antioxidant activity of berberis asiatica was investigated, and the ic50 value for the root and stem bark extracts was determined to be 102.31 and 120.7 µg/ml, respectively [46]. however, in the current study, a notable difference was observed, showing a significant radical scavenging activity with an ic50 of 205.7 ± 5.353 µg/ml. the variation in the ic50 value of berberis asiatica indicates that the antioxidant potential can be influenced by multiple factors, including the extraction methods, a sample collected geographical area, and the timing of sample collection. apart from exhibiting poor inhibition of keshab bhattarai et al./ bibechana 20 (2023) 236-247 244 table 6: minimum inhibitory concentration of methanolic extract of berberis asiatica against test bacteria. bacteria berberis asiatica mic (mg/ml) positive control (neomycin) mic (mg/ml) s. aureus 0.39 0.0039 k. pneumoniae 3.125 0.0019 table 7: minimum bactericidal concentration (mbc) of methanolic extract of berberis asiatica against test bacteria. bacterial strain berberis asiatica mbc (mg/ml) positive control (neomycin) mbc (mg/ml) s. aureus 6.25 0.015 k. pneumoniae 6.25 0.0078 alpha-amylase in the current study, berberis asiatica is well-documented in some literature for its anti-diabetic properties. previous research suggests that the plant’s blood glucose and lipid regulatory effects can be attributed to berberine, a significant alkaloid present in berberis asiatica . this compound has been found to enhance insulin sensitivity by regulating the secretion of adipokines [47]. the results of the current study demonstrate that the methanolic extract of berberis asiatica exhibited significant inhibition in the growth of two bacterial strains, one gram-positive (s. aureus) and one gram-negative (k. pneumoniae), with a zone of inhibition (zoi) of 14 mm and 19 mm, respectively. this finding indicates that the plant extract possesses potent antibacterial properties, likely due to the presence of specific antibacterial agents. however, in the previous study, the crude aqueous extract of berberis asiatica stem bark demonstrated a zone of inhibition in the disk diffusion method. among the gram-negative bacteria, escherichia coli, klebsiella pneumoniae, and salmonella paratyphi-a exhibited a zone of inhibition of 8 mm [48]. this outcome suggests that our study has exhibited a notably robust antibacterial property when compared to the previous research. the results of the current study revealed that the methanolic extract of b. asiatica displayed a minimum inhibitory concentration (mic) of 0.39 mg/ml for s. aureus and 3.125 mg/ml for k. pneumoniae. notably, the plant extract demonstrated better inhibition for s. aureus compared to k. pneumoniae. the literature also reported similar findings, where the methanolic stem bark extract of berberis asiatica exhibited a mic of 312.5 µg/ml for s. aureus [10], which aligns with the mic value obtained in the present study. however, for k. pneumoniae, the aqueous stem bark extract of berberis asiatica reported in the literature exhibited a mic of 2500 µg/ml, which is higher than the mic value obtained in the present study [48]. furthermore, the methanolic extract of the berberis asiatica plant exhibited an mbc of 6.25 mg/ml for both s. aureus and k. pneumoniae, indicating the same bactericidal concentration for both bacterial strains. in comparison, the literature reported a methanolic stem bark extract with an mbc of 0.78125 mg/ml for s. aureus, which differs and shows the potential activity of the plant sample used in this study [10]. the difference in the biological activities and the richness of secondary metabolites in the plant may be attributed to the part of the plant sample used and the geographical variation of plant growth. in the chemical profiling, different secondary metabolites were identified by gc-ms analysis which includes, 3,3-dimethylpentane, cyclohexane, 2-methylhexane, 3-methylhexane, 1,3dimethylcyclopentane, 1,2-dimethylcyclopentane, heptane, methylcyclohexane, 2,2-dimethyl-3pentanol, 2-methyl-2-pentanol, 2,5-dimethyl-4hydroxy-3-hexanone, 3-hexanol. the previous study reported some of the compounds like berberine, palmatine, jatrorrhirine, oxyacanthine, oxyberberine, tetrahydropalmatine, and columbamine [7]. the gc-ms profiling in this study shows some different compounds with a richness of bioactive compounds like alkaloids, phenolic, and flavonoid compounds highlighting the pharmaceutical potential of the plant and may be a good source of such compounds in the future drug development process. the abundance of secondary metabolites may be affected due to climatic conditions, soil type, temperature, and geographical locations [49]. although the same plant species with nearby environmental conditions may vary in chemical compositions [50]. increasing the altitude contribute significantly to chemical composition, at higher altitude plant possess a higher amount of phenolic and flavonoid compounds [41]. however, at lower altitudes, there is a greater abundance of volatile organic compounds in the plants [41]. these variations in chemical composition according to altitude can be ascribed to discrepancies in the biological activity of plant extract. therefore, current research results show some different potential results as compared to the previous one. keshab bhattarai et al./ bibechana 20 (2023) 236-247 245 table 8: major chemical compounds detected by gc analysis in hexane fraction. s.n. name of compound retention time (rt) area % mol. wt. 1 3,3-dimethyl pentane 2.354 0.78 100.2 2 cyclohexane 2.479 86.25 84.16 3 2-methyl hexane 2.518 4.14 100.2 4 3-methyl hexane 2.632 3.45 100.2 5 1,3-dimethyl cyclopentane 2.758 0.40 98.19 6 1,2-dimethyl cyclopentane 2.850 0.53 98.19 7 heptane 3.036 0.55 100.2 8 methylcyclohexane 3.494 0.93 98.186 9 2,2-dimethyl-3-pentanol 10.542 0.28 116.2 10 2-methyl-2-pentanol 10.662 0.84 102.17 11 2,5-dimethyl-4-hydroxy-3-hexanone 11.252 0.58 144.21 12 3-hexanol 12.135 0.16 102.17 13 4-methyl-2-pentanol 12.490 0.18 102.174 5 conclusion in conclusion, the current study on berberis asiatica from nepal has provided valuable insights into its bioactive properties. the plant extract demonstrated significant inhibition of α-amylase and exhibited potent antibacterial activity against both gram-positive (s. aureus) and gram-negative (k. pneumoniae) bacteria. additionally, the extract showed promising antioxidant potential. moreover, there were variations in the total phenolic and flavonoid content of the plant when compared to previous findings. these differences could be attributed to various factors, such as plant parts used, extraction methods, and environmental conditions. chemical profiling revealed the presence of various secondary metabolites in the plant, and some of these compounds were also reported in the literature, further confirming the plant’s potential medicinal value. this study highlights the rich biodiversity of nepal’s flora and the importance of exploring and understanding the bioactive properties of its plant species. berberis asiatica emerges as a promising candidate for further research and development 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[50] christos koutsoukis, christos roukos, panagiotis g. demertzis, spyros kandrelis, and kaliopi akrida-demertzi. the variation of the chemical composition of the main plant species in a subalpine grassland in northwestern greece. legume science, 1(1):23, 2019. introduction materials and methods chemicals plant collection and preparation of extract phytochemical analysis total phenolic content (tpc) total flavonoid content (tfc) evaluation of antioxidant activity -amylase inhibition activity determination of antibacterial activity determination of minimum inhibitory concentration (mic) determination of minimum bactericidal concentration (mbc) gc-ms profiling of chemical compounds statistical analysis results and discussion percentage yield phytochemical screening of crude extract total phenolic and flavonoid content antioxidant potential in vitro -amylase inhibition activity antibacterial activity minimum inhibitory concentration minimum bactericidal concentration chemical constituents profiling by gc-ms analysis pharmacological importance of gc-ms detected compounds discussion conclusion devendra sir cover page copy.jpg bibechana 17 (2020) 20-27 20 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal structure-activity relationship and mm2 energy minimized conformational analysis of quercetin and its derivatives in the dpph• radical scavenging capacity gan b. bajracharya 1* , mohan paudel 2 , rajendra k. c. 2 , sajan l. shyaula 1 1 faculty of science, nepal academy of science and technology (nast), khumaltar, lalitpur, nepal 2 department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal *email: ganbajracharya@yahoo.com; gan.bajracharya@nast.gov.np article information: received: august 13, 2019 accepted: september 7, 2019 keywords: antioxidant 1,1-diphenyl-2-picrylhydrazyl flavonoid free radical ic50 sar abstract antioxidant activity of quercetin (1) and its derivatives (2-15) was evaluated by using dpph assay and ic50 values were calculated. dihedral angles α of c3-c2c1’-c6’ chain and β of o1-c2-c-1’-c2’ chain between ac and b rings of these flavones were determined by using mm2 energy minimized structures. structureactivity relationship study revealed that quercetin (1), quercetin-5-methyl ether (2), quercetin-3’-methyl ether (3) and quercetin-3’,5-dimethyl ether (4) displaying a high antioxidant activity (ic50 = 47.20-119.27 μm) possess similar dihedral angles (α 11.1-11.5º and β 6.3-6.6º). monoand/or di-methoxy substituent(s) at 3’ and 5 positions of the flavone are most suitable for the preservation of the antioxidant capacity while retaining conformational geometry. 1. introduction reactive oxygen species (ros) such as hydrogen peroxide (h2o2), singlet oxygen ( 1 o2), superoxide (o2•–), hydroxyl radicals (oh•), etc. are generated during oxygen metabolism in biological systems. imbalance between generation and elimination of ros leads cellular aging, mutagenesis, carcinogenesis, immunodeficiency syndrome, diabetes, coronary heart diseases, neurodegenerative diseases, etc. [1-3]. dietary flavonoids are considered as powerful antioxidants since they act as radical scavengers, metal chelators and enzyme inhibitors, and produce the beneficial health effects [4-7]. in several publications, the antioxidant activity of flavonoids have been evaluated using 1,1-diphenyl2-picrylhydrazyl radical (dpph•) [8], hydroxyl radical (ho•) [9], superoxide (o2• ˗ ) [10], peroxyl radical (roo•) [11], and hypochlorite (hocl/ocl ⁻ ) [12], and structure-activity relationships (sar) of flavonoids in antioxidant activity have been documented [1, 11-27]. hydrogen or electrondonating properties of flavonoids are considered to be the basis of their antioxidant activity [1, 25]. this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.25208 http://nepjol.info/index.php/bibechana mailto:ganbajracharya@yahoo.com mailto:gan.bajracharya@nast.gov.np https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.25208 gan b. bajracharya, mohan paudel et al / bibechana 17 (2020) 20-27 21 structural requirement in flavonoids for the hydrogen-donation by single-electron transfer includes ortho-dihydroxyl substituent in the b ring and c2-c3 double bond in conjugation with c-4 carbonyl group in the c ring, which expands electron delocalization for radical stabilization and determines the co-planarity of the hetero ring. quercetin, a pentahydroxy flavone (1), seems to be a paradox which satisfies these structural variations and so efficiently captures free radicals thereby exhibiting high antioxidant activity. in case of absence of a catecholic structure in b ring, the antioxidant activity is compensated by 3and/or 5hydroxyl substituent(s). blocking or removing the 3-oh group decreases antioxidant property. the dihedral angle of the b ring with respect to remaining structure in flavones is considered for strong influence on radical scavenging activity [18, 27]. however, the roles of chemical structure and underlying molecular phenomena have stayed elusive [23, 28]. the nature of rapid conjugation with glucuronosyltransferases and sulfotransferases present in the small intestine halts quercetin (1) to reach the malignant organs through gastrointestinal tract in oral therapy [29]. when the hydroxyl groups in polyphenols are methylated, the resulting compounds are much less prone to glucuronidation and sulphation, and hence are more metabolically stable increasing their bioavailablity. these underlying facts promoted us to commence a research program to study the sar of quercetin derivatives for possible enhancement of antioxidant capacity. 2. experimental chemicals and equipments quercetin (1), dpph and gallic acid were purchased from sigma-aldrich and were used as received. quercetin derivatives (2-15) used in this work were previously synthesized in our laboratory [30]. spectrophotometric analysis was performed with a cary 60 uv-visible spectrophotometer (agilent technologies). dpph radical scavenging assay the dpph assay was performed according to the procedure described by brand-williams et al. with a slight modification [31]. to generate free dpph• radical, 11.7 mg of dpph in methanol (300 ml) was stirred overnight at 0 °c and used immediately. sample solutions of the compounds 1-15 of different concentrations (5, 25, 50, 100, 250 and 500 μm in acetone) were prepared. each sample solution (0.5 ml) was mixed with freshly prepared dpph• solution (2.5 ml). a control solution was prepared by mixing acetone (0.5 ml) and dpph• solution (2.5 ml). the content was shaken well, kept in dark at room temperature for 30 min and then absorbance was measured at 517 nm against the blank solution consisting acetone (0.5 ml) and meoh (2.5 ml). the percentage of inhibition was calculated by the equation: i (%) = (1 – asample / acontrol) × 100 where, asample and acontrol are the absorbance values of the reaction mixture with and without sample, respectively. thus obtained data of % inhibitions at different concentrations were computed to calculate ic50 values by employing the equation: ic50 = (50 μm c) / m where, ic50 = concentration causing 50% inhibition of absorbance, c = intercept, m = slope of a linear curve describing dependence of % inhibition with concentration. computational analysis energy minimized structure of quercetin (1) and synthesized quercetin derivatives (2-15) were produced by using molecular mechanics part 2 (mm2) calculation, cambridgesoft’s chem3d pro 12.0.2.1076. thus optimized geometry of the structures were studied for determining the dihedral angles between the planes of the ac-ring and the b-ring employing the angels of c3-c2-c1’-c6’ (α) and o1-c2-c1’-c2’ (β). gan b. bajracharya, mohan paudel et al / bibechana 17 (2020) 20-27 22 3. results and discussion dpph assay measures the antioxidant capacity of a compound in terms of its ability to donate hydrogen atom to the free dpph• radical. the dpph• radical, which shows absorption at 517 nm, is reduced to the corresponding hydrazine when it reacts with hydrogen donors. dpph assay is considered a valid and easy assay to evaluate the sar of antioxidants [32]. some of the compounds used in this study were not completely soluble in meoh; therefore, standard procedure was slightly modified by using acetone as a dissolving solvent to prepare the sample solutions. in the dpph assay, six different concentrations of each compound were used in order to obtain ic50 value. linear regression curve of concentration versus percentage of inhibition for each compound was plotted where r 2 values were found nearly equal to 1. the slope and intercept values of linear regression curve were used to obtain the ic50 value and the result is presented in table 1. the ic50 value of quercetin (1) in dpph assay was reported by several groups and it ranged from 1.82 to 119.60 μm [26, 33-39]. in this study, compared to the parent quercetin 1 (ic50 = 47.20 µm), its monomethylated derivatives 2 (ic50 = 52.24 µm) and 3 (ic50 = 52.45 µm) have retained the antioxidant capacity in the dpph assay (table 1). the dimethylated derivative 4 also displayed antioxidant property with ic50 value of 119.27 µm. the antioxidant capacity was gradually reduced as the number of substituents other than hydroxyl group is increased. although 3,5-dioh and/or 3’,4’-dioh groups are important for scavenging of dpph• radical; however, this study showed that one (or two) of these hydroxyl group(s) can be replaced with methoxy group(s). this conclusion is also supported by moalin et al., who have reported that substitutions of methoxy group at 5 and/or 7 position(s) in ring a of quercetin (1) retain the antioxidant capacity in abts assay [27]. acetylation of free hydroxyl groups reduced the antioxidant capacity; however, quercetin 3,3’,4’,5-tetraacetate (5) and quercetin 3,3’,4’,5,7pentaacetate (6) derivatives have exhibited a mild antioxidant activity with ic50 values of 516.26 and 790.57 µm, respectively. these results also indicated that a free 7-oh group in a flavone has a crucial role. remaining quercetin derivatives (7-15) were found to be lost their dpph• radical scavenging capacity displaying ic50 value >2000 µm. olejniczak and potrzebowski have reported that a small perturbation of geometry has a great influence on bond orders in ring b in density functional theory (dft) calculation of quercetin (1) [40]. and, the change in conformers may significantly change the susceptibility for the formation of radicals and consequently alters the biological property. although molecular structure of quercetin (1) (and its derivatives as well) can be represented by exact conformation; however, the presence of many flexible hydroxyl groups and hydrogen bonding networks in the system leads a wrong conclusion in the crystal lattice provided by x-ray diffractometry (xrd). later, filip et al. have performed the conformational calculation of quercetin (1) by employing the molecular mechanics (mm) level of theory that combined with previous xrd and solid state nmr data [41, 42]. it was concluded that small changes of conformation and hydrogen bonding pattern greatly influence the bond order parameters of quercetin (1). the authors have further mentioned that no matter how precisely the conformational analysis is performed, the most important is finding of the most probable molecular conformation. the mm2 energy minimization calculation can identify the more stable conformation [43]. therefore in the present study, the mm2 calculations of the compounds 1-15 were performed. in the case of quercetin (1), the orientation of the hydroxyl groups at 3 and 3’ carbon atoms in a planar arrangement of a, b and c rings produces anti and syn conformers. herein, energy minimized structures of compounds 1-15 were computed by keeping 3 and 3’ substituents at anti fashion. the optimal conformations of the compounds obtained are depicted in figure 1 and their dihedral angles are given in table 1. gan b. bajracharya, mohan paudel et al / bibechana 17 (2020) 20-27 23 table 1: ic50 values of quercetin scaffolds (1-15) in dpph• free radical scavenging activity. the dihedral angles α = 11.5º and β = 6.6º were found in mm2 energy minimization calculation of quercetin (1), which exhibited a high antioxidant property (ic50 = 47.20 µm) (table 1, figure 1). interestingly, in comparison with quercetin (1), quercetin-5-methyl ether (2) (α 11.2º and β 6.4º), quercetin-3’-methyl ether (3) (α 11.1º and β 6.3º) and quercetin-3’,5-dimethyl ether (4) (α 11.2º and β 6.3º) showed similar dihedral angels and they were also highly efficient in scavenging of dpph• radical with the ic50 values of 52.24, 52.45 and 119.27 µm, respectively. the decrease in dihedral angles α and β decreased the antioxidant property as shown by quercetin-3,3’,4’,5-tertaacetate (5) (α = 9.2º, β = 4.6º, ic50 = 516.26 µm) and quercetin3,3’,4’,5,7pentaacetate (6) (α = 7.3º, β = 3.9º, ic50 = 790.57 µm). the mm2 calculation of remaining compounds (7-15) showed that they exist in more or less planar conformation. therefore, a slightly twisted conformation between rings b and c with dihedral angles α 11.5-7.3º and β 6.6-3.9º plays a pivotal role in preserving the antioxidant capacity of parent compound quercetin (1) and perfect planarity is merely not necessary [27]. while modifying the structure of a flavone in search of the molecule with enhanced antioxidant activity, preservation of its planarity is therefore a must. 4. conclusion in conclusion, we have evaluated the dpph• free radical scavenging capacity of quercetin (1) and its derivatives (2-15). quercetin (1) and its methoxyl derivatives 2, 3 and 4 were found as highly efficient antioxidants. the acetyl derivatives 5 and 6 exhibited a mild antioxidant capacity while other remaining derivatives (7-15) were found to be inefficient. dihedral angles α of c3-c2-c1’-c6’ chain (11.5-7.3º) and β of o1-c2-c-1’-c2’ chain compound substituents dihedral angles ic50 (μm) r 1 r 2 r 3 r 4 r 5 α° β° quercetin (1) oh oh oh oh oh 11.5 6.6 47.20 quercetin 5-methyl ether (2) oh ome oh oh oh 11.2 6.4 52.24 quercetin 3’-methyl ether (3) oh oh oh ome oh 11.1 6.3 52.45 quercetin 3’,5-dimethyl ether (4) oh ome oh ome oh 11.2 6.3 119.27 quercetin 3,3’,4’,5-tetraacetate (5) oac oac oh oac oac 9.2 4.6 516.26 quercetin 3,3’,4’,5,7-pentaacetate (6) oac oac oac oac oac 7.3 3.9 790.57 quercetin 3,3’,4’,7-tetraacetate (7) oac oh oac oac oac 7.3 1.7 >2000 quercetin 3,3’,4’,7-tetrabenzyl-5-methyl ether (8) obn ome obn obn obn 3.4 1.3 >2000 quercetin 3,4’,7-tribenzyl ether (9) obn oh obn oh obn 2.8 0.9 >2000 quercetin 3,3’,4’,7-tetrabenzyl ether (10) obn oh obn obn obn 2.7 1.1 >2000 quercetin 3,4’,7-tribenzyl-3’,5-dimethyl ether (11) obn ome obn ome obn 2.6 0.9 >2000 quercetin 3,4’,7-tribenzyl-3’-methyl ether (12) obn oh obn ome obn 2.3 0.8 >2000 quercetin 3,3’,4’,5,7-pentamethyl ether (13) ome ome ome ome ome 1.7 0.5 >2000 quercetin 3,3’,4’,7-tetramethyl ether (14) ome oh ome ome ome 1.5 0.4 >2000 quercetin 3,4’,7-trimethyl ether (15) ome oh ome oh ome 1.4 0.3 >2000 gan b. bajracharya, mohan paudel et al / bibechana 17 (2020) 20-27 24 (6.6-3.9º) between ac and b rings as can be found in quercetin (1) are suitable for the preservation of antioxidant capacity. monoand/or di-methoxy substituent(s) at 3’ and 5 positions of the flavone are most suitable for the preservation of the antioxidant capacity. free 7-oh group of a flavone also plays a crucial role in preserving of the antioxidant capacity. fig. 1: three dimensional energy minimized structure of quercetin (1) and its derivatives (2-15) with their dihedral angles α and β. gan b. 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abstract the time varying currents and voltages resulting from the sudden application of sources usually due to switching are transients. an rlc circuit is an electrical circuit consisting of a resistor, an inductor, and a capacitor, connected in series or in parallel. the transient response is dependent on the value of the different characteristics of damping factor (i.e., over damped, critically damped and under damped). we have computed the numerical solutions of second order differential equation with initial value problem (ivp) by using explicit (forward) euler method, third order runge-kutta (rk3) methods and butchers fifth order rungekutta (brk5). the observation compares this numerical solution of odes obtained by above-mentioned methods among them with necessary visualization and analysis of the error. these iterative methods will be extended and implement to analyze the transient analysis of an rlc circuit. we have examined the superiority of those methods over one another. the butchers fifth order rungekutta (brk5) method is found to be the best numerical technique to solve the transient analysis due to its high accuracy of approximations. moreover, we consider the possibility of discussion and analyze above mentioned iterative methods in the cases of different characteristics of damping factor. doi: https://doi.org/10.3126/bibechana.v18i2.31208 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction while regarding the problem of mathematical modelling in the area of engineering, physics, aeronautics, medicine, environmental science, astronomy, chemistry, biology and many other applied fields, the role of differential equation is momentous [1, 2]. meanwhile all of the differential model equation in real life appears to be nonlinear. on contrary, almost all differential equation bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:bhandari.indra@gmail.com https://doi.org/10.3126/bibechana.v18i2.31208 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana jeevan kafle et al. / bibechana 18 (2) (2021) 9-17 10 encountered in course of modelling to be solved analytical, is out of the question [1]. planetary motion under gravity, motion of simple pendulum, etc. are typical example of second order differential equation that won’t solve analytically [2, 3]. to wriggle out from such confounding situation one has to device a more rigorous alternative approach that would be simple and more pragmatic. one of such method is numerical method [3]. transients are the momentary fluctuation of energy induced upon the electrical circuit due to the time varying currents and voltages resulting from the sudden application of sources. it usually occurs at the period of switching [4]. sensitive component of the electrical circuitry such as millions of inductors, capacitors, resistors, transistor and diodes embedded inside integrated circuits are most vulnerable to this brief increase in current in voltage. an electrical system under the influence of transient condition rendered the system to an unsteady state. thus, a transient analysis is to analyze the response of an electrical circuit under these unsteady state condition [5]. if the variables do not vary with respect to time, then the state of system is said to be in a steady state otherwise it is said to be in an unsteady state. performance of any electrical circuit is measured by employing the methodology of transient analysis [16]. although transients do occur in the most apparent electrical equipment such as charger of an android phone, electric mixture, cfl bulb, iron etc. but it is not at threatening level because components are adjusted enough to handle such ailments [7]. but transient occurring in the microscopic level inside a microprocessor, motherboard and memory card could be lethal to the existence of the system. suhag (2013) [4] conducted the transient analysis of second order rlc circuit and observed the response of the system by changing the conditions from one steady state value to another. he concluded rk method was very efficient in solving second order differential equations. kee and ranom (2018) [5] studied the transient analysis of series rlc circuit under underdamped, critically damped and overdamped conditions using rk-4 with different time step size h. the accuracy of rk-4 method is determined by gradually as the step size decimates. thus, the improved rk-4 method by decreasing the step size ℎ or increasing the number of steps 𝑛 was a favorably suited method for solving transient analysis of electric circuit due to its high degree of accuracy and efficiency. henry et al. (2018) [7] undertook the task of transient analysis of a secondorder rlc circuit by employing two numerical methods viz. heun’s method and runge-kutta method. they observed that the heun’s method reaches the stable limit first, thus, converges faster but the runge-kutta 4th order method proved to be more accurate. thus runge-kutta method was recommended for transient analysis of complex electric circuits. ogbuka et al. (2008) [8] in their paper reiterated the need of a sound mathematical background and knowledge of basic laws of circuit analysis before handling the task of circuit analysis and they programmed the state equations of a sample complex circuit in two simulation software matlab and simplorer to generate transient response. deshpande (2014) [5] stated the source dc voltage applied in any circuit (rlc) constituting of energy storage device gives rise to transients and therefore estimation of the voltage was of significant importance for instrumentation and control purpose. deshpande carried out the transient analysis to this circuit by employing classical and laplace transformation method. also, in cases of over damped, underdamped and critically damped conditions were evaluated significant for natural response of rlc series circuit. laplace transform method had proved to be a better tool with respect to initialization condition in comparison to classical method. ahamad and charan (2019) [6] in order to solve initial value problem for fourth order odes presented fifth order runge-kutta method (rk5). kamruzzaman and nath (2018) [11] in their paper employed the modified euler and runge-kutta methods to discuss the numerical solution of an ode with ivp. they carried out the numerical jeevan kafle et al. / bibechana 18 (2) (2021) 9-17 11 simulation and compared the numerical solution with exact solution. maffezzoni et al. (2007) [12] presented a novel approach to the accurate timedomain simulation of non-linear circuits that employs a class of high-order implicit runge-kutta (rk) method. the properties of stability and accuracy of these rk methods were briefly reviewed while the implementation in the flow of an analog simulator was described in detail. in this work, we take a series rlc circuit with dc source which can be modelled with a second order ode. for solving ivp of ode and transient analysis, we first compared the three iterative method viz. explicit euler, third order runge-kutta (rk3) and butcher fifth order runge-kutta (brk5). brk5 method is observed to be the best method as it gives the least error compared to other two methods. brk5 method is then chosen to analyze the three-damping condition of rlc circuit. the approach of this paper is primarily analytical and comparative among the various numerical method for solving differential equation. section-2 comprises of the theoretical approach and three iterative methods with the necessary numerical formulation. section-3 depicts the simulation result and comparison of above-mentioned method. section-4 culminate the conclusion and finding of this work. 2. theory a rlc circuit constitute of three electrical elements viz. a resistor, an inductor and a capacitor. it is a second order circuit. these circuits are the most popular as they are applied to construct oscillator and tuners of radio or audio receiver [4]. in the adjacent fig. 1, the electrical elements resistor (r), inductor (l) and capacitor (ϲ) are connected in series with the d.c. source (𝑉𝑠), which we call rlc series circuit. a circuit equation is drawn to undertake the analytical solution part of a transient analysis [5]. an ordinary electrical circuitry could contain thousands of components. so, any analytical solution in such rlc circuits is virtually impossible. in such scenario numerical methods could offer a great relief to the solution of system. here, we used possible iterative methods to solve the circuit equation under the terms of transient analysis in an rlc circuit and compare different methods. the kirchhoff’s voltage law [5] is applied around the loop for 𝑡 > 0 in which the voltage source of the circuit in fig. 1 is calculated by the following: 𝑽𝑺 = 𝑽𝑹 + 𝑽𝑳 + 𝑽𝑪 fig. 1: rlc circuit [7]. the differential equations of the rlc in fig. 1 is based on method of loop currents where the fundamental relationship between the current, and the individual circuit elements (capacitance, inductance, resistance) are given by 𝑹𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 : 𝒗(𝒕) = 𝑹𝒊(𝒕), 𝑪𝒂𝒑𝒂𝒄𝒊𝒕𝒂𝒏𝒄𝒆 : 𝒊(𝒕) = 𝑪 𝒅𝒗 𝒅𝒕 , 𝑰𝒏𝒅𝒖𝒄𝒕𝒂𝒏𝒄𝒆 ∶ 𝒗(𝒕) = 𝑳 𝒅𝒊 𝒅𝒕 the second-order differential equation of the rlc circuit with constant coefficients is written as [17] 𝐿 ⅆ2𝑉 ⅆ𝑡2 + 𝑅 ⅆ𝑉 ⅆ𝑡 + 1 𝐶 𝑉 = 𝑉𝑠 𝐶 … … … (1) the series rlc circuit is analyzed in order to determine its transient characteristics once the switch is closed. equation (1) can be solved using different iterative methods [7]. the damping factor is responsible for amount by which the oscillation of a system gradually decreases with the time (𝒕). the transient response jeevan kafle et al. / bibechana 18 (2) (2021) 9-17 12 is dependent on the value of the damping factor (𝜻) [7]. in rlc circuit, the damping factor is given by 𝜁 = 𝛼 𝜔𝑜 where, 𝜶 = 𝑹 𝟐𝑳 (damping coefficient) and 𝝎𝟎 = 𝟏 √𝑳𝑪 (resonant frequency). then 𝜻 = 𝑹 𝟐 √ 𝑪 𝑳 the system is (i) over damped when 𝜻 > 1, (ii) critically damped when 𝜻 =1, and (iii) under damped when 𝜻 < 1 [4]. numerical methodologies in this section, we discuss different iterative method to solve initial value problems (ivp) for ordinary differential equations (ode). first, we introduce euler’s method, the simplest method. we will provide details on algorithm development using the euler method (explicit), third order ruge-kutta method (rk3) and butcher’s fifth order rungekutta (brk5) method [12, 13]. euler’s method consider one dimensional initial value problem (ivp) 𝒚′(𝒕) = 𝒇(𝒕, 𝒚(𝒕)), 𝒚(𝒕𝟎) = 𝒚𝟎 … … … (𝟐) the slope at the point (𝒕𝒏, 𝒚𝒏) is 𝒚𝒏+𝟏 − 𝒚𝒏 𝒉 ≈ 𝒅𝒚 𝒅𝒕 = 𝒇(𝒕𝒏, 𝒚𝒏) ⇒ 𝒚𝒏+𝟏 = 𝒚𝒏 + 𝒉𝒇(𝒕𝒏, 𝒚𝒏) … … … (𝟑) this formula (3) is forward euler’s method. third order runge-kutta (rk3) method the third order runge-kutta method (rk3) is broadly used for solving initial value problems (ivp) for ordinary differential equation (ode). the general formula for runge-kutta third order (rk3) method is shown below [15] 𝒚𝒏+𝟏 = 𝒚𝒏 + 𝒉 [ 𝒌𝟏 𝟔 + 𝟐𝒌𝟐 𝟑 + 𝒌𝟑 𝟔 ] … … … (𝟒) where 𝑘1 = 𝑓(𝑡𝑛, 𝑦𝑛), 𝑘2 = 𝑓 (𝑡𝑛 + ℎ 2 , 𝑦𝑛 + ℎ 2 𝑘1), 𝑘3 = 𝑓(𝑡𝑛 + ℎ, 𝑦𝑛 − ℎ𝑘1 + 2ℎ𝑘2) fig. 2: visualization of euler method [14]. butchers fifth order runge-kutta (brk5) method this method is distinguished by their order in the sense that agrees with taylors series solution up to terms of ℎ𝑟 where r is the order of the method [7]. in this method, we consider the ivp (2). the method is shown below [13]. 𝑦𝑛+1 = 𝑦𝑛 + ℎ 90 (7𝑘1 + 32𝑘3 + 12𝑘4 + 32𝑘5 + 7𝑘6) … … … (5) where, 𝑡𝑛+1 = 𝑡𝑛 + ℎ, 𝑘1 = 𝑓(𝑡𝑛, 𝑦𝑛), 𝑘2 = 𝑓 (𝑡𝑛 + ℎ 4 , 𝑦𝑛 + ℎ 4 𝑘1), 𝑘3 = 𝑓(𝑡𝑛 + ℎ 4 , 𝑦𝑛 + 1 8 ℎ𝑘1 + 1 8 ℎ𝑘2), 𝑘4 = 𝑓(𝑡𝑛 + ℎ 2 , 𝑦𝑛 − 1 2 ℎ𝑘2 + ℎ𝑘3), 𝑘5 = 𝑓(𝑡𝑛 + 3ℎ 4 , 𝑦𝑛 + 3 16 ℎ𝑘1 + 9 16 ℎ𝑘4), 𝑘6 = 𝑓(𝑡𝑛 + ℎ, 𝑦𝑛 − 3 7 ℎ𝑘1 + 2 7 ℎ𝑘2 + 12 7 ℎ𝑘3 − 12 7 ℎ𝑘4 + 8 7 ℎ𝑘5) we can extend above discussed iterative methods for the solution of higher order initial value jeevan kafle et al. / bibechana 18 (2) (2021) 9-17 13 problems (ivp) for ordinary differential equations (ode) and system of initial value problems (ivp) for ordinary differential equations (ode) [3, 16]. numerical formulation of rlc circuit let, 𝑣 = 𝑥 and 𝑑𝑣 𝑑𝑡 = 𝑦 𝐶 … … … (6) then equation (1) becomes ⅆ𝑦 ⅆ𝑡 = 𝑉𝑠 − 𝑥 − 𝑅 × 𝑦 𝐿 … … … (7) hence equation (6) and (7) form a system of first order differential equation [7]. let, 𝑓 = 𝑑𝑣 𝑑𝑡 = 𝑦 𝐶 and 𝑔 = 𝑑𝑦 𝑑𝑡 = 𝑉𝑠−𝑥−𝑅×𝑦 𝐿 euler’s method for rlc circuit 𝑥𝑖+1 = 𝑥𝑖 + ℎ 𝑓(𝑡𝑖 , 𝑥𝑖, 𝑦𝑖) 𝑦𝑖+1 = 𝑦𝑖 + ℎ 𝑔(𝑡𝑖 , 𝑥𝑖 , 𝑦𝑖) where h is the time step size. rk3 method for rlc circuit 𝑥𝑖+1 = 𝑥𝑖 + (𝑓1 + 4𝑓2 + 𝑓3)/6 𝑦𝑖+1 = 𝑦𝑖 + (𝑔1 + 4𝑔2 + 𝑔3)/6 where 𝑓1 = ℎ 𝑓(𝑡𝑖 , 𝑥𝑖, 𝑦𝑖), 𝑔1 = ℎ𝑔(𝑡𝑖 , 𝑥𝑖, 𝑦𝑖), 𝑓2 = ℎ𝑓 ((𝑡𝑖 + ℎ 2 ) , (𝑥𝑖 + 𝑓1 2 ) , (𝑦𝑖 + 𝑔1 2 )), 𝑔2 = ℎ𝑔 ((𝑡𝑖 + ℎ 2 ) , (𝑥𝑖 + 𝑓1 2 ) , (𝑦𝑖 + 𝑔1 2 )), 𝑓3 = ℎ𝑓((𝑡𝑖 + ℎ), (𝑥𝑖 − 𝑓1 + 2𝑓2), (𝑦𝑖 − 𝑔1 + 2𝑔2)) and 𝑔3 = ℎ𝑔((𝑡𝑖 + ℎ), (𝑥𝑖 − 𝑓1 + 2𝑓2), (𝑦𝑖 − 𝑔1 + 2𝑔2)) formulating brk5 method for rlc circuit 𝑥𝑖+1 = 𝑥𝑖 + (7𝑓1 + 32𝑓3 + 12𝑓4 + 32𝑓5 + 7𝑓6)/90 𝑦𝑖+1 = 𝑦𝑖 + (7𝑔1 + 32𝑔3 + 12𝑔4 + 32𝑔5 + 7𝑔6)/90 where 𝑓1 = ℎ 𝑓(𝑡𝑖 , 𝑥𝑖, 𝑦𝑖), 𝑔1 = ℎ𝑔(𝑡𝑖 , 𝑥𝑖, 𝑦𝑖), 𝑓2 = ℎ𝑓 ((𝑡𝑖 + ℎ 4 ) , (𝑥𝑖 + 𝑓1 4 ) , (𝑦𝑖 + 𝑔1 4 )), 𝑔2 = ℎ𝑔 ((𝑡𝑖 + ℎ 4 ) , (𝑥𝑖 + 𝑓1 4 ) , (𝑦𝑖 + 𝑔1 4 )) , 𝑓3 = ℎ𝑓 ((𝑡𝑖 + ℎ 4 ) , (𝑥𝑖 + 𝑓1 + 𝑓2 8 ) , (𝑦𝑖 + 𝑔1 + 𝑔2 8 )) 𝒈𝟑 = 𝒉𝒈 ((𝒕𝒊 + 𝒉 𝟒 ) , (𝒙𝒊 + 𝒇𝟏+𝒇𝟐 𝟖 ) , (𝒚𝒊 + 𝒈𝟏+𝒈𝟐 𝟖 )), 𝒇𝟒 = 𝒉𝒇 ((𝒕𝒊 + 𝒉 𝟐 ) , (𝒙𝒊 − 𝒇𝟐 𝟐 + 𝒇𝟑) , (𝒚𝒊 − 𝒈𝟐 𝟐 + 𝒈𝟑)), 𝒈𝟒 = 𝒉𝒈 ((𝒕𝒊 + 𝒉 𝟐 ) , (𝒙𝒊 − 𝒇𝟐 𝟐 + 𝒇𝟑) , (𝒚𝒊 − 𝒈𝟐 𝟐 + 𝒈𝟑)), 𝒇𝟓 = 𝒉𝒇 ((𝒕𝒊 + 𝟑𝒉 𝟒 ) , (𝒙𝒊 + 𝟑𝒇𝟏 𝟏𝟔 + 𝟗𝒇𝟒 𝟏𝟔 ) , (𝒚𝒊 + 𝟑𝒈𝟏 𝟏𝟔 + 𝟗𝒈𝟒 𝟏𝟔 )), 𝒈𝟓 = 𝒉𝒈 ((𝒕𝒊 + 𝟑𝒉 𝟒 ) , (𝒙𝒊 + 𝟑𝒇𝟏 𝟏𝟔 + 𝟗𝒇𝟒 𝟏𝟔 ) , (𝒚𝒊 + 𝟑𝒈𝟏 𝟏𝟔 + 𝟗𝒈𝟒 𝟏𝟔 )), 𝒇𝟔 = 𝒉𝒇 ((𝒕𝒊 + 𝒉), (𝒙𝒊 − 𝟑𝒇𝟏−𝟐𝒇𝟐−𝟏𝟐𝒇𝟑+𝟏𝟐𝒇𝟒−𝟖𝒇𝟓 𝟕 ) , (𝒚𝒊 − 𝟑𝒈𝟏−𝟐𝒈𝟐−𝟏𝟐𝒈𝟑+𝟏𝟐𝒈𝟒−𝟖𝒈𝟓 𝟕 )) , 𝒈𝟔 = 𝒉𝒈 ((𝒕𝒊 + 𝒉), (𝒙𝒊 − 𝟑𝒇𝟏−𝟐𝒇𝟐−𝟏𝟐𝒇𝟑+𝟏𝟐𝒇𝟒−𝟖𝒇𝟓 𝟕 ) , (𝒚𝒊 − 𝟑𝒈𝟏−𝟐𝒈𝟐−𝟏𝟐𝒈𝟑+𝟏𝟐𝒈𝟒−𝟖𝒈𝟓 𝟕 )) 3. results and discussion in the following sub section, we compare numerical solution of rlc circuits by above discussed numerical methods with exact solution and analyze the different characteristics of damping factor by using best superior iterative method. 3.1 comparison between analytical solution and numerical methods in this experiment, the simulation time for all the conditions is from 0 s to 20 s with the step size of ℎ = 0.1 s. moreover, we consider source voltage (𝑉𝑠) = 6 𝑉, resistance (𝑅)=1 ω, inductance (𝐿) = 1 𝐻 and capacitance (𝐶) = 0.25 𝐹 [7] for the simulation result of rlc circuit. fig. 3 describe simulation results of numerical solution of rlc circuit and exact solution under above conditions. in order to compare the accuracy of the numerical methods, the computed points of the three numerical methods are taken at the specific time. the computed point of each method is compared with the analytic solution. from the above fig. 3, we observed that the approximate solution curve obtained from the butcher fifth order runge-kutta (brk5) method is converging faster towards the analytical solution in jeevan kafle et al. / bibechana 18 (2) (2021) 9-17 14 comparison with the other two methods. this shows that there is less error between brk5 and analytical solution in comparison with other two methods (table 1). table 1 contain details of simulated results obtained for iterative methods and exact solution with error in different time slices. hence, we concluded that the brk5 method is more efficient method to approximate the solution of rlc circuit. so, in the following section, we consider three damping cases (i.e., underdamped, critically damped and over damped) for butcher fifth order rungekutta (brk5) method. in fig. 4, we simulate the results under discussed above condition with different time slices. 3.2 characteristics of damping factor by using brk5 method the different damping condition of rlc circuit and their characteristics are as discussed below: condition 1: underdamped (𝐢. 𝐞., 𝛇 < 𝟏 ) in this condition, the resistance, r must be less than 4ω in order to achieve underdamped response. in order to obtain the best numerical method for transient analysis of rlc circuit, three numerical methods are compared with the analytical solution. the three numerical methods mentioned are euler method, rk3 method and brk5 method. the experiment is conducted by taking 1ω as the value of resistor, r for the circuit [4, 5, 7]. condition 2: critically damped (𝐢. 𝐞. , 𝛇 = 𝟏) in critically damped response, the resistance, r must be equal to 4ω in order to achieve the critically damped condition. condition 3: overdamped (𝐢. 𝐞. , 𝛇 > 𝟏) in condition 3, the resistance, r must be more than 4ω in order to achieve overdamped response. the experiment is conducted by taking 6ω as the value of resistor, r for the circuit. table 2 contain all the condition for different damping factor. by the variation of the resistance (r), we can get three different damping conditions. in fig. 4, we observed that the under damped responses are a decaying oscillation decays at a rate determined by the attenuation (α) by using brk5 fig. 3: comparison of euler, rk3, brk5 and analytical solution. jeevan kafle et al. / bibechana 18 (2) (2021) 9-17 15 method. the exponential decay describes the envelope of the oscillation. here, the oscillation is sinusoidal with exponentially decaying amplitude. the critically damped response represents the circuit response that decays in the fastest possible time without going into oscillation. this consideration is important in control systems where it is required to reach the desired state as quickly as possible without overshooting. the overdamped response is a decay of the transient current without oscillation, which reach the stable state slower than the critically damped case. the quantitative description of numerical of solution under three damping condition by using brk5 method is detailed in table 3. table 1: simulated results obtained for iterative methods and exact solution with error. table 2: the values of electrical elements of series rlc circuit for three conditions [5]. time (t) (seconds) euler 𝑅𝐾3 𝐵𝑅𝐾5 exact voltage(v) voltage(v) 𝐸𝑅 (10−3) voltage(v) 𝐸𝑅 (10−3) voltage(v) 𝐸𝑅 (10−3) 0.0 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.1 0.000000 4.378000 0.116000 1.622000 0.115714 1.336000 0.114378 0.2 0.240000 3.654000 0.444083 0.429000 0.443657 3.000000 0.443654 0.3 0.696000 6.189000 0.951609 0.580000 0.951190 9.990000 0.952189 0.4 1.336800 5.764000 1.602239 0.325000 1.601968 5.960000 1.612564 0.5 2.125680 1.791000 2.357671 8.800000 2.357671 8.800000 2.366471 0.6 3.022200 7.630000 3.179275 0.555000 3.179643 1.870000 3.189830 0.7 3.984041 1.851000 4.029593 4.701000 4.030393 5.501000 4.004892 0.8 4.968810 4.868000 4.873643 0.299000 4.874908 9.034000 4.883942 0.9 5.935740 3.419000 5.680016 2.305000 5.681740 5.810000 5.692321 1.0 6.847225 2.573000 6.421720 2.932000 6.423867 7.850000 6.424652 element value condition 1 condition 2 condition 3 resistor underdamped critically damped overdamped dc (vs) 6v 6v 6v resistor r <4ω 4ω >4ω inductor l 1h 1h 1h capacitor c 0.25f 0.25f 0.25f jeevan kafle et al. / bibechana 18 (2) (2021) 9-17 16 table 3: values of three conditions of brk5 method. 4. conclusion the transient analysis of electrical circuit is analyzed using analytical method, euler (explicit) method, rk3 methods and brk5 method. with the usage of computational software, the process of obtaining results of transient analysis is done systematically and conveniently. it has been observed that the brk5 method is very efficient in solving second order differential equations. thus, we can conclude that by carrying out the transient time (s) values of brk5 method underdamped critically damped overdamped 0.0 0.000000 0.000000 0.000000 0.1 0.115714 0.105139 0.098897 0.2 0.443657 0.369312 0.330084 0.3 0.951190 0.731409 0.626944 0.4 1.601968 1.147248 0.950945 0.5 2.357643 1.585448 1.280130 0.6 3.179643 2.024237 1.602290 0.7 4.030393 2.449004 1.910937 0.8 4.874908 2.850415 2.202915 0.9 5.681740 3.222979 2.476992 1.0 6.423867 3.563965 2.733027 fig. 4 : comparison of three different damping condition by using brk5. jeevan kafle et al. / bibechana 18 (2) (2021) 9-17 17 analysis of a system, we can find out the response of the system by changing the conditions from one steady state value to another. our observation clearly shows that the under damped decay is oscillatory and exponential. however, the other two are non-oscillatory exponential decay. the decay in critically damped case is observed faster than in over damped case. this response helps in designing a system, which meets our requirements, and we can further optimize the time domain parameters of the system. references [1] n. ahamad and s. charan, study of numerical 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[10] md. kamruzzama, m.c. nath, a comparative study on numerical solution of initial value problem by using euler's method, modified euler's method and runge-kutta method, journal of computer and mathematical sciences 9(5) (2018)493-500. https://doi.org/10.29055/jcms/784 [11] p. maffezzoni, l. codecasa, d. d’amore, timedomain simulation of nonlinear circuits through implicit runge-kutta methods, institute of electrical and electronics engineers transactions on circuits and systems 54(2) (2007) 391-400. https://doi.org/10.1109/tcsi.2006.887476 [12] w. e. boyce and r. c. di prima, elementary differential equations and boundary value problems 10 (2012). [13] j.c. butcher, numerical methods for ordinary differential equations, second edition, john wiley and sons, ltd. (1933). [14] holistic numerical methods committed to bringing numerical methods to the stem undergraduate. https://nm.mathforcollege.com/ [15] c. senthilnatha, a numerical solutions of initial value problems for ordinary differential equations with euler and higher order of runge-kutta methods using matlab. international journal of engineering science invention 7(4) (2018) 25-31. [16] md. b. hossain, md. j. hossain, md. m. miah and md. s. alam, a comparative study on fourth order and butchers fifth order runge-kutta methods with third order initial value problem, applied and computational mathematics 6(6) (2017) 243-253. [17] j. santiago, circuit analysis for dummies, john wiley & sons (2013). https://doi.org/10.32628/ijsrset196142 https://doi.org/10.5923/j.ajcam.20170705.02 https://doi.org/10.1109/efea.2016.7748804 https://doi.org/10.29055/jcms/784 https://www.researchgate.net/deref/http%3a%2f%2fdx.doi.org%2f10.1109%2ftcsi.2006.887476 https://nm.mathforcollege.com/ https://www.google.com.np/search?tbo=p&tbm=bks&q=inauthor:%22john+santiago%22 bibechana 18 (1) (2021) 170-183 170 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal study of aerosol optical properties at different tourist places of nepal rejeena jha1, binod adhikari1*, dharmendra kumar singh2 1department of physics, st. xavier’s college, maitighar, kathmandu, nepal 2french national center for scientific research (cnrs) /ircelyon, villeurbanne-69100, france *e-mail address: binod.adhikari@sxc.edu.np article information: received: july 6, 2020 accepted: august 26, 2020 keywords: aerosol optical depth (aod) angstrom exponent cloud condensation cross-correlation coefficient abstract the comparative study of aerosol optical properties at different tourist places of nepal has been performed. langtang bc, lumbini, pokhara, kathmandu-bode, evk2-cnr, jomsom and kyanjin_gompa were the places chosen for observation. we have analyzed the monthly and seasonal variation of aerosol optical properties for a different year of the above-mentioned places. aod was found to be maximum in spring due to vegetation fire and land clearing for crop cultivation and, then in winter due to biomass burning, heating needs, pollution from bricks kilns, factories, and vehicles that contribute to winter haze. it consequently decreases in summer and was found to be minimum in autumn as summer constituent both dry and wet days and autumn starts with the ending of monsoon. but it was quite different in the case of pokhara where it was minimum in summer than in autumn as pokhara is the only city where maximum rainfall occurs in summer. we have also studied the relation between aod and corresponding wavelength. it was acclaimed that the aod of shorter wavelength is more than the longer one which is because of angstrom exponent. the relation between aod and precipitated water has been observed and noticed one to one correspondence except july and august. the cross-correlation between these two factors found to be very high indicating a time lag of approximately 2 months with the presence of aerosol on cloud condensation nuclei (ccn). doi: https://doi.org/10.3126/bibechana.v18i1.29906 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction nanomaterials are considered as intermediate the degrading air quality, particularly in populationdense areas, is associated with high aerosol levels (both anthropogenic and natural [1]. system of solid or liquid particles suspended by a mixture of gases [2], called aerosols, cover a wide spectrum dominated by dust, sulfate, carbon, sea salt, or mixtures of these particles [3] it is considered one http://nepjol.info/index.php/bibechana mailto:binod.adhikari@sxc.edu.np https://doi.org/10.3126/bibechana.v18i1.29906 https://creativecommons.org/licenses/by-nc/4.0/ rejeena jha et al. / bibechana 18 (1) (2021) 170-183 171 of the important factors in the current prediction of global climate change but associated with large uncertainties. it is a key component to study atmospheric physics such as radiative transfer of light waves in atmosphere and precipitation[4]. they directly affect the earth's solar radiation budget by scattering and absorbing solar and thermal radiation[5]. on the other hand, aerosols can also act as cloud condensation nuclei (ccn), impacting cloud cover, cloud properties, and precipitation, ultimately influencing the hydrological cycle [6]. an increase in aerosol concentration generally results in more numerous, but smaller, droplets for a given liquid water content, which ends up in a rise of the cloud albedo, known as the first indirect effect. further, a decrease in cloud droplet size delays and reduces precipitation processes, which is referred to as the second indirect effect. however, numerous feedbacks and interactions with the ice phase and other aspects of cloud dynamics make it difficult to tease out exactly how cloud microphysical changes due to aerosol changes affect the radiative balance, precipitation, and dynamics systematically and quantitatively [7]. moreover, aerosol plays a significant role in reducing visibility and implication in human health hazard because sub-micron aerosols can irritate the respiratory system [8]. even epidemiological and toxicological studies have shown associations between aerosols and adverse health effects [9]. the tibetan plateau (tp), the largest and highest plateau on earth, usually acts as a receptor of natural and anthropogenic aerosols from the surrounding regions, and its environment is highly sensitive to climate change and human activities [6]. the himalaya mountain located along the southern edge of the tp acts as a natural barrier for the transport of atmospheric aerosols [6]. aerosol optical depth (aod), defined as the ratio of solar radiation absorbed to the ratio of total solar radiation transmitted, determines how much direct sunlight is prevented from reaching the ground by the aerosol particles[10]. this work mainly focuses on the understanding of aod behavior concerning wavelength and precipitated water on monthly variation and also describes the seasonal variation of aod of different stations. datasets in this section, we have discussed the site's location, sources of data collection, and methodology which have been implemented on this work. we have observed aod from langtang bc, lumbini, pokhara, kathmandu-bode, evk2-cnr, jomsom, and kyanjin_gompa. langtang bc, evk2-cnr, and jomsom are in the himalayan region of nepal, pokhara. kathmandu-bode lies in the hilly region and lumbini is in the terai region of nepal. these places are considered as the major tourist places where lumbini, kathmandu-bode, and pokhara are densely populated cities, while the population of langtang bc, evk2-cnr, and jomsom are comparatively slim. pokhara is a lower-elevation suburban site with much higher aerosol load due to both the influence of local anthropogenic activities and its proximity to the indo-gangetic plains [6] over 125 brick kilns are in kathmandu-bode, which contribute significantly to atmospheric aerosols, particularly during winters. in the himalayan regions, people hugely rely on the traditional way of cooking by burning biomass (e.g. cow-dung, wood, fuel), which releases a large amount of aerosol in the atmosphere. the detailed description of the sites is given below in the table [11].the satellite data are considered as one of the main sources to describe the nature of aerosol optical properties. the data for the research was extracted from the aeronet site and this paper has used 2.0 version of data which is quality assured. aeronet uses ascii text format for data transfer to improve data transfer between systems. the aerosol robotic network is a ground-based network of standardized cimel sun and sky scanning radiometers measuring aod at multiple wavelengths from 340 to 1640 nm and retrieving other columnar optically effective aerosol properties [3] like volume, size distribution, rejeena jha et al. / bibechana 18 (1) (2021) 170-183 172 aerosol optical depth (aod), total optical depth (tod), etc. the development of the aerosol robotic network (aeronet) for monitoring aerosol optical depth provides measurements of natural and anthropogenic aerosol loading, which is important in many local and regional studies as well as global change research investigation [12]. aeronet is the ground-based sun-photometer network with over 400 stations globally. the aeronet aod is derived from direct beams of solar measurements. this study is dedicated to presenting a trend analysis at selected stations. the monthly mean as well as daily averages of aod are available at aeronet. aeronet has been providing high-quality retrievals of aerosol optical properties from the surface at worldwide locations for quite a decade. many sites have continuous and consistent records for over 10 years, which enables the investigation of long-term trends in aerosol properties at these locations: sites coordinates and elevation site description langtang bc latitude: 28.21443° north longitude: 85.60978° east elevation: 4901.0 meters the instrument located in langtang valley near yala glacier in the fenced area of the icmod met station[13]. lumbini latitude: 27.49000° north longitude: 83.28000° east elevation: 110.0 meters the site is in the southern plain of nepal, which is a part of the indo-gangetic plain [14]. pokhara latitude: 28.18664° north longitude: 83.97518° east elevation: 800.0 meters the instrument is located on the roof of shangrila village resort, on the south-western outskirts of pokhara city, nepal[15]. kathmandu-bode latitude: 27.68000° north longitude: 85.39000° east elevation: 1297.0 meters the site is in agricultural-residential setting downwind of the kathmandu city, near the village of bode, bhaktapur district[16]. evk2-cnr latitude: 27.95775° north longitude: 86.81494° east elevation: 5079.0 meters the cimel sun photometer is operated at the nepal climate observatory at pyramid (nco-p), at 5079 m asl, in the khumbu valley, nepal, close to the pyramid international laboratory[17]. jomsom latitude: 28.77821° north longitude: 83.71420° east elevation: 2825.0 meters on the roof of a single-story laboratory building at the southern corner of a plateau sticking into the wind blowing up the kali gandaki valley[18]. kyanjin_gompa latitude: 28.21126° north longitude: 85.56630° east elevation: 3862.0 meters instrument located in langtang valley near kyanjin_gompa village in the fenced area of the icmod met station[19]. 2. methodology the cross-correlation between aod and precipitable water has been observed. crosscorrelation: the measurement that tracks the movements of two variables or sets of knowledge relative to every other[20] and most importantly it is use to find the lag/lead/time of maximum correlation. here the cross-correlation between precipitated water and aod at 1020nm, 870nm, and 675nm has been observed. the term crossrejeena jha et al. / bibechana 18 (1) (2021) 170-183 173 correlations are used for referring to the correlations between the entries of two random vectors x and y, while the correlation of a random vector x is considered to be correlations between the entries of x itself, those forming the correlation of x [21]. the definition of correlation always includes a standardizing factor in such a way that correlations have values between −1 and +1 [22]. the period for this study was from jan 1st to dec 31st, 2018 of langtang bc, lumbini and pokhara, also, jan 1st to dec 31st, 2013 of kathmandu-bode and the same period of evk2-cnr and jomsom in the year 2012. a contour plot is a graphical form to depict a 3dimensional surface by plotting constant z slices, called contours, on a 2-dimensional configuration. that is, given a value for z, lines are drawn for connecting the (x y) coordinates where that z value occurs [23]. the contour has been used to observe the seasonal variation of aod in the above stations. four seasons are defined as spring (march-may), summer (june-august), autumn (september-november), and winter (decemberfebruary) to investigate the seasonal variation of aerosol optical properties of various tourist places of nepal. 3. results and discussion , in this section, we have discussed the result of monthly and seasonal variation of aod to various wavelengths and precipitated water. relation of aod with wavelengths and precipitated water first, three panels of figure 1 to figure 6 show the variation of aod to three wavelengths, 1020nm, 870nm, and 675 nm, respectively. the aod of shorter wavelength is greater than the longer wavelength and vice-versa. the angstrom exponent of aod of shorter wavelength is greater than the longer one as the wavelength dependence of aerosols is strongly influenced by their chemical and size composition as a result show by[24]. the comparison between the first three panels of aod at three different wavelengths with the precipitated water (figure 1 to figure 6) shows similar trends except in july and august (i.e., july and august mainly includes wet days of months). for a better understanding, we have implemented the crosscorrelation analysis between them. figure 7 to figure 12 represent the cross-correlation between precipitated water and aod at wavelengths of 1020nm, 870nm, and 675nm from different stations. in the figure, the blue curve represents the cross-correlation between precipitated water and aod at 1020nm, the red curve represents the crosscorrelation precipitated water and aod at 870nm and the green curve shows the cross-correlation of precipitated water and aod at 675nm. in each figure, cross-correlation coefficients are on the yaxis, and time is kept at the x-axis. the crosscorrelation coefficient of aod of wavelengths 1020nm, 870nm, 675nm and precipitated water was found to be very high i.e., ~0.9 of langtang bc in year 2018a.d, ~0.87 of lumbini in year 2018a.d, ~0.88 of pokhara in year 2018a.d, ~0.9 of kathmandu-bode in year 2013a.d, ~0.93 of evk2-cnr in year 2012a.d, ~0.95 of jomsom in year 2012a.d. these results show that the aod and precipitated water are highly correlated on all stations. as much of the removal of atmospheric aerosols occurs in the vicinity of large weather systems and high-altitude jet streams, where the stratosphere and the lower atmosphere become intertwined and exchange air with each other, mentioned by [25]. in such regions, many pollutant gases within the troposphere are often injected within the stratosphere, affecting the chemistry of the stratosphere. likewise, in such regions, the ozone within the stratosphere is brought right down to the lower atmosphere where it reacts with the pollutant rich air, possibly forming new kinds of pollution aerosols. so, for the removal of a large amount of aerosol there must occur enduring and a battery of natural calamities similar as the result of [26]. rejeena jha et al. / bibechana 18 (1) (2021) 170-183 174 fig. 1: the first three panel shows the variation of aod with respect to three different wavelengths i.e. 1020nm, 870nm and 675nm respectively and, the fourth panel shows the variation of aod to precipitated water of langtang bc in the year 2018 a.d. fig. 2: the first three panel shows the variation of aod with respect to three different wavelength i.e. 1020nm, 870nm and 675nm respectively and, the fourth panel shows the variation of aod to precipitated water of lumbini in year 2018 a.d. fig. 3: the first three panel shows the variation of aod with respect to three different wavelength i.e. 1020nm, 870nm and 675nm respectively and, the fourth panel shows the variation of aod to precipitated water of pokhara in year 2018 a.d rejeena jha et al. / bibechana 18 (1) (2021) 170-183 175 fig. 4: the first three panel shows the variation of aod with respect to three different wavelength i.e. 1020nm, 870nm and 675nm respectively and, the fourth panel shows the variation of aod to precipitated water of kathmandu-bode in year 2013 a.d. fig. 5: the first three panel shows the variation of aod with respect to three different wavelength i.e. 1020nm, 870nm and 675nm respectively and, the fourth panel shows the variation of aod to precipitated water of evk2cnr in year 2012 a.d. fig. 6: the first three panel shows the variation of aod with respect to three different wavelength i.e. 1020nm, 870nm and 675nm respectively and, the fourth panel shows the variation of aod to precipitated water of jomsom in year 2012 a.d. rejeena jha et al. / bibechana 18 (1) (2021) 170-183 176 fig. 7: represents the cross-correlation between precipitated water and aod at three different wavelength i.e. 1020nm, 870nm and 675nm of langtang bc in year 2018 a.d. fig. 8: represents the cross-correlation between precipitated water and aod at three different wavelength i.e. 1020nm, 870nm and 675nm of lumbini in year 2018 a.d. fig. 9: represents the cross-correlation between precipitated water and aod at three different wavelength i.e. 1020nm, 870nm and 675nm of pokhara in year 2018 a.d. rejeena jha et al. / bibechana 18 (1) (2021) 170-183 177 fig. 10: represents the cross-correlation between precipitated water and aod at three different wavelength i.e. 1020nm, 870nm and 675nm of kathmandu-bode in year 2013 a.d. fig. 11: represents the cross-correlation between precipitated water and aod at three different wavelength i.e. 1020nm, 870nm and 675nm of evk2-cnr in year 2012 a.d. fig. 12: represents the cross-correlation between precipitated water and aod at three different wavelength i.e. 1020nm, 870nm and 675nm of jomsom in year 2012 a.d. rejeena jha et al. / bibechana 18 (1) (2021) 170-183 178 monthly variation of aod the monthly variation shows that: aod was in increasing order from january to february at langtang, evk2-cnr, and jomsom. it was however comparatively less from august to december. this is because, these places are situated in the himalayan region: in january and february, winter biomass burning plays an important role and the significant portion of the population relies on traditional fuels such as wood, straw, and dung for cooking and heating homes too. these organic fuels deliver a heavy load of particles to the atmosphere [27] because people tend to burn them at relatively cool temperatures; this leads to incomplete combustion also stated by [28]. as winter starts with december, days are less hazy compared to january and february due to which aod is less in these months compared to january and february. august recorded decreasing aod: as of august mainly includes wet days of months. september begins with the ending of monsoon, due to which the sky is clear and aod is reduced. in figure2 and figure3, it was observed that aod is soaring in january, february, and december. this is the result of traffic and pollution from factories which also contributes to the winter haze in lumbini and pokhara [29]. figure 4 aod is observed to be increasing in january and december, this is because the maximum of brick kilns are situated in kathmandu-bode [30]. it is also in these months, the meteorological parameters showed significant fluctuations. the relative humidity was normally greater than 97%, as shown by[31]. a similar pattern is followed in lumbini. figure1, figure2, figure3, and figure4 aod are in increasing order from february to april due to land clearing and agricultural fires in various regions of nepal[6]. in figure 1-6, aod was observed to be decreasing in july due to wet days of summer [32]. nepal’s summer season comprises both wet and dry days, while in wet days aerosol is detached due to precipitation and in dry days the maximum number of aerosol goes to the atmosphere due to dry wind and pollution caused by various human activities[33]. sometimes, this maximum amount of aerosol with some amount of water molecules form a group of large clouds resulting in catastrophic rainfall. in figure5: aod is not significantly less in july, because evk2-cnr does not follow the trend of wet days or only a few amounts of rain may occur during this time. the aod can be seen increasing in figure1, figure2, figure4, figure5, and figure6 in may and june because these are the dry months of summer as similar result of [34] with no significant rainfall and most of the pollutants are drifted to the atmosphere by this dry wind. however, in figure3 aod can be seen to be decreased in june because pokhara is the only city all over nepal where the monsoon starts early and it lasts for long, so in pokhara, june comes into the wet days of summer. seasonal variation figure13-15 represents the contour plot of seasonal variation of aod at 1640nm of pokhara, kyanjin_gompa, and lumbini in the year of 2018, respectively. in the contour plot, season was placed in the y-axis, an hour was in the x-axis and aod was placed in the z-axis. it has been noticed that aod is increasing in winter and is maximum in spring and drastically decreasing in summer, however, it was more in autumn compared to summer in the case of pokhara. but aod is minimum in autumn than in summer for kyanjin_gompa and lumbini. these three-station i.e. pokhara, kyanjin_gompa, and lumbini were taken under consideration for seasonal variation which encompasses all three geographical regions of nepal. lumbini lies in the terai region, pokhara lies in the hilly region and kyanjin_gompa lies himalayan region. from the above figures, it was observed that lumbini has the aerosol of the highest optical depth compared to pokhara and kyanjin_gompa also, pokhara has less aod than lumbini but more than kyanjin_gompa. seasonal variation graphs of aod concludes that: aod was found to be increasing in winter and was rejeena jha et al. / bibechana 18 (1) (2021) 170-183 179 maximum in spring and drastically decreases in summer and was minimum in autumn, however, it was more in autumn compared to summer in case of pokhara. it is due to, increment in heating needs, vehicle traffic, and industry which contributes to winter haze in cities like pokhara and lumbini. pokhara also lies in such a region of nepal where a significant amount of biomass burning, and downwind of the indo-gangetic plains contributes to haze during winter and spring [6]. bricks production in winter also helps in the ejection of aerosol to the atmosphere in lumbini and kathmandu-bode. in the case of kyanjin_gompa, most of the population are dependent on traditional fuels such as woods, straw, dried dung for cooking and also for heating purpose in winter. these organic fuels contribute to a heavy load of particles in the atmosphere. also high himalayas is dominated by higher concentrations during winter and spring (pre-monsoon), minimal concentrations during the summer wet monsoon season, and increasing levels during the autumn (postmonsoon) [35]. spring season begins with occasional shower and pollution had contributed to spring haze, as in 2018 a.d nepal is considered as one of the most polluted countries added with the most degraded air quality. so in spring, aod was found to be maximum in all three stations. vegetation fires peak in the himalayan region in april [6], which has a large impact on all three sites. it was also observed that in summer, aod of pokhara goes to a minimum because most of the month of summer is wet days of monsoon and due to heavy rainfall maximum amount of aerosol flushes out. but in the case of lumbini and kyanjin_gompa summer includes both wet and dry days of monsoon due to which only a minimum amount of aerosol gets detach while in the wet days. autumn: the season starts with the ending of monsoon resulting in lesser aod compared to other seasons in the context of nepal [22]. autumn is also considered as the best season for outdoor activities like trekking, jungle safari, rafting, etc. as you can enjoy lots of green and blue sky pokhara significantly has lesser aod than lumbini but more than kyanjin_gompa. in summary, kyanjin_gompa does have relatively pristine environments occasionally disturbed by pollution episodes. pokhara and lumbini, however, are seriously affected by human activities. aod at pokhara and lumbini is much higher than the kyanjin_gompa in each month similar to the result of [6]. fig. 13: shows the seasonal variation of aod at 1640nm wavelength of pokhara in year 2018. rejeena jha et al. / bibechana 18 (1) (2021) 170-183 180 fig. 14: shows the seasonal variation of aod at 1640nm wavelength of kyanjin_gompa in year 2018 a.d. fig. 15: shows the seasonal variation of aod at 1640nm wavelength of lumbini in year 2018 a.d. 4. conclusion and general remarks we have investigated the aerosol optical properties at various tourist places in nepal concerning wavelength and precipitated water. besides that, we have also observed the monthly and seasonal variation of aod. we conclude our results as follows : • an inverse relationship between wavelength and aod was established because of angstrom exponent. angstrom exponent is inversely related to the standard size of the particles within the aerosol: the smaller the particles, the larger the exponent [36]. thus, it is a useful quantity to assess the particle size of atmospheric aerosols or clouds, and the wavelength dependencies of the aerosol/cloud optical properties[37]. the angstrom exponent rejeena jha et al. / bibechana 18 (1) (2021) 170-183 181 states that the optical thickness of an aerosol depends on the wavelength of light, as mentioned by [38]. • from the above result, it was clear that aerosol plays an important role in precipitation, or also we can say that they are inversely related to each other in july and august as these months include a massive rainfall in case of nepal. this result is like the result produced by [7] where they suggest that changes in precipitation were likely due to aerosol interactions. the amount of aerosol plays an important role in precipitation. if there are a large number of aerosols, then water molecules will have more options for condensation because of which small clouds are formed with no or very few precipitations as water droplets in the cloud need to reach in critical size for a downpour. however, if there are fewer aerosols in our atmosphere then more water molecules get attached to those few aerosol-forming large as well as grey clouds resulting in rainfall, hence the maximum number of aerosol flush out due to rainfall because precipitation is directly correlated with aod given by the study of [26]. • from above result it was inferred that, maximum increase in aod is in april due to vegetation fire which helps to contribute in spring haze, in different regions of nepal. adding up, acceleration of aod in january, february and december is the outcome of the bio-mass burning, wood and dung for cooking, heating needs in the stations like kyanjin_gompa, langtang bc, evk2-cnr, jomsom which is situated in himalayan region. likewise, bricks kiln, vehicle traffic, heating needs, pollution from factories are main source of aod in the stations like kathmandu-bode, pokhara and lumbini. • from the above result i.e. the reduction of aod in july in all the station except evk2cnr concludes that, all the other stations except evk2-cnr follow the trend of wet days of summer while wet days of summer include precipitation and due to which aerosol get detached from atmosphere. however, evk2-cnr do not follow the trend of wet days. also, all the stations except pokhara shows the acceleration of aod in the month of may and june because these two are considered as a dry months of summer with no significant rainfall and most of the pollutant are drifted up by dry wind. however, pokhara is the only city in nepal where monsoon starts early and last for long so june belongs to wet days of summer in case of pokhara. in summary, pokhara shows less aod than lumbini but more than kyanjin_gompa. .kyanjin_gompa shows relatively pristine environments occasionally disturbed by pollution episodes. pokhara and lumbini, however, are seriously affected by human activities. aod at pokhara and lumbini was much higher than the kyanjin_gompa in each month as the result of [6]. the result presented in this work may help to enhance more knowledge about the aerosol optical properties of different tourist places as well as all the three geographical regions of nepal. aerosol monthly, seasonal variation at different stations as well as geographical regions are elucidated based on the objective phenomenon of precipitation, wavelengths, and source emission variations. to improve knowledge about the study of its effect and control measure, more direct evidence, such as chemical sampling at different atmospheric layers, micro-pulse lidar observations from the surface, or lidar remote-sensing measurements have to be used in future studies. acknowledgment we would like to thank gian paolo gobbi of the institute of atmospheric science and climate (cnrisac) for his valuable advice and assistance during the data collection and also would like to thank brent holben and arnico panday, the coinvestigator and principle investigator of various station of aerosol in nepal for providing reliable rejeena jha et al. / bibechana 18 (1) (2021) 170-183 182 data for observation. we would also like to extend our thanks to the department of physics, st. xavier college for the support. the authors 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[38] d. g. kaskaoutis and h. d. kambezidis, investigation into the wavelength dependence of the aerosol optical depth in the athens area, q. j. r. meteorol. soc. 32 (2006) 2217–2234. https://doi.org/10.1256/qj.05.183 [39] h t tps: / /aeronet .gsfc.nasa.gov/ cgi-bin /bamgomas_maps_index_v3 https://aeronet.gsfc.nasa.gov/ bibechana 18 (1) (2021) 10-18 10 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal fabrication of open type carbonizer for the preparation of activated carbon from rice husk a. kumari dhami, a. rajbhandari (nyachhyon)* central department of chemistry, tribhuvan university, kirtipur, nepal *email: armila3@yahoo.com article information: received: may 11, 2020 accepted: june 9, 2020 keywords: rice husk open type carbonizer activated carbon methylene blue abstract activated carbon has been prepared from rice husk using laboratory fabricated open type carbonizer. the raw rice husk powder was named as rrh whereas chemically activated rice husk was named as carh. both samples were characterized by methylene blue number (mbn), iodine number (in) and surface area. the mbn and in of rrh was found to be 83 mg/g and 415 mg/g whereas carh was 99 mg/g and 716 mg/g respectively which indicate the presence of mesoporosity and microporosity of the samples. the surface area of rrh was found to be 206 m2/g while carh was found to be 531 m2/g. xrd analysis showed that the prepared materials were amorphous with some crystalline state while ftir spectra showed the presence of different functional groups such as hydroxyl, carbonyl, si-o-si bond and aromatic group on the material. the adsorption properties of prepared samples were studied by using langmuir and freundlich isotherm models. langmuir adsorption isotherm model was found to be best fitted. it showed that prepared materials have homogenous surface with monolayer type of adsorption. the maximum monolayer coverage (qm) for rrh was found to be 55 mg/g and for carh 143 mg/g. thus, results revealed that laboratory fabricated low cost open type carbonizer is suitable for the preparation of activated carbon. doi: https://doi.org/10.3126/bibechana.v18i1.28918 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction activated carbon (ac) is an inimitable form of carbon and is generally prepared from carbonaceous materials. such materials could be obtained from plant resources including agriculture wastes. some of the agricultural wastes that have been used are saw dust [1-2], rice husk [3], corncob [4], sugarcane [5], waste tea [6] and other by-product such as; almond shell [7], coconut shell [8], hazelnut shell [9], olive [10], apricot [11] and cherry stones [12]. among them rice husk is one of the eco-friendly and locally available agricultural waste that has been generated approximately 120 million tons annually from rice milling industries [13] and hence in present work, rice husk has been used as precursor for the preparation of activated carbon. rice husk is actually outer most covering of the rice grain. it contains 15-20% hemicellulose, 28-30% http://nepjol.info/index.php/bibechana mailto:armila3@yahoo.com?subject=mail mailto:armila3@yahoo.com?subject=mail https://doi.org/10.3126/bibechana.v18i1.28918 https://creativecommons.org/licenses/by-nc/4.0/ a. kumari dhami, a. rajbhandari (nyachhyon)/ bibechana 18 (1) (2021) 10-18 11 cellulose, 25-30% lignin, 15-20% silica and 10-15% moisture [14]. hemicellulose, cellulose and lignin are generally considered as a major source of activated carbon. these ac are generally prepared by carbonization technique. for carbonization, instruments like muffle furnace, tube furnace and other furnaces have been used. the temperature ranges from 100 to 18000c. such high temperature needs high energy consumption and running cost also get elevated. hence, we tried to fabricate an efficient, low cost open type carbonizer to prepare ac [15]. thus prepared activated carbon from open type carbonizer was then activated by phosphoric acid which mainly helps in dehydration of lignocellulosic material and formation of phosphate ester linkage between cellulose rings which inhibits shrinkage of structure during heat treatment. actually, activation is the way that is employed to increase surface area and porosity from the carbonized organic precursor [16]. the organic precursor consists of elementary crystallites with a large number of interstices between them. these interstices were filled with disorganized carbon residue that blocks the pore entrances due to which low porosity observed. the highly porous activated carbon with high surface area has got wider application in various fields like to remove pesticides and organic compounds from aqueous solution, to treat waste water, to purify food, beverage, to remove various dyes, for reducing organic chemicals, chlorine, heavy metals, as catalyst carriers (catalytic support) and as adsorbent for air purification [17]. in present work, activated carbon derived from rice husk was used to study the adsorption of methylene blue dye. 2. materials and method reagents the reagents such as orthophosphoric acid (h3po4), methylene blue, iodine used were of analytical grade and procured from merck company. all the experiments were carried out in distilled water. stock solution of methylene blue was prepared by dissolving 1 g of mb in 1000 ml of distilled water in volumetric flask. the 0.1 n of i2 solutions was prepared by dissolving 1.272 g of i2 and 5 g of ki in 100 ml of water and left for 24 hrs for complete dissolution. instruments the x-ray diffractometer (d2-phaser, bruker, germany) has been used to study the phase state of as prepared activated carbon. it was operated at an accelerating voltage of 40 kv and current 40 ma with cu-kα radiation (λ=1.5418ao) in the diffraction angle of 10 to 50 degrees. the surface functional group was studied by fourier transmission infrared spectroscopy (shimadzu, model no. irtracer-100, japan). the ftiir spectra were recorded at 4000-400 cm-1 wave number. fabrication of open type carbonizer open type carbonizer was fabricated by following procedure: step 1: fabrication of chamber first of all, the chamber was prepared by taking a can having 40 cm height and 20 cm diameter. it has volume of 20 l. bottom of the can was removed and a hole was made at the top of the can which has diameter of 10 cm. then, small holes have been made at the surface of the can at every 10 cm distance so that, perforated surface have been obtained. the diameter of hole is 2 cm [15]. the structure of chamber is shown in fig. 1(a). step 2: fabrication of chimney then a chimney was prepared by taking, 30 x 122 cm sized gi sheet. it was folded and clamped together to make a roll having diameter of 10 cm [15]. the figure of chimney is shown in fig. 1(b). step 3: assemble of chimney and chamber as prepared chimney was then assembled with prepared chamber by welding on the top of the chamber having hole of 10 cm as shown in fig. 1(c). in this way, open type carbonizer was fabricated. preparation of adsorbent preparation of raw rice husk (rrh) raw rice husk (rrh) was collected from rice mill. it was washed with water and allowed to dry in sunlight. after complete dryness, it was grinded into fine powder in an electric grinder and sieved through a. kumari dhami, a. rajbhandari (nyachhyon)/ bibechana 18 (1) (2021) 10-18 12 40 cm 20 cm 10 cm a b c 75μm sized sieve. thus, obtained powder is named as rrh. fig. 1: fabrication of open type carbonizer. preparation of chemically activated rice husk (carh) the rice husk was carbonized in open type carbonizer. then this carbonized carbon was impregnated with phosphoric acid in the ratio of h3po4 1:1 wt by wt. they were left for 24 hrs for proper soaking. after, that it was cleaned with distilled water till neutral ph. then the sample was dried at 1000c for 24 hrs. this dried sample was again carbonized at 4500c for 2 hrs in a muffle furnace and then cooled to room temperature. in this way, chemically activated rice husk was prepared and represented as carh. methylene blue number methylene blue number is defined as the milligram of methylene blue dye adsorbed by 1g dried activated carbon. it is a measure of the mesopore content in the activated carbon. the amount of methylene blue adsorbed from each was calculated by using equation 1, where, co is the concentration of methylene blue solution (mg/l) at starting time (t=0), ce is the concentration of methylene blue solution at equilibrium time (mg/l) which can be calculated by equation 2, v is the volume of the solution in liter and m is the mass of the adsorption in g. to determine the methylene blue number, the langmuir model has been applied. in this model, qeq plot is made as a function of ce. the langmuir parameters (qmax and k) were obtained by a least square fitting regression method. ce = absorbance slope …………………………..(1) qeq = co−ce m × v ………………………… (2) iodine number iodine number is the milligram of iodine adsorbed by 1 g of activated carbon from a 0.1n iodine solution when the equilibrium iodine concentration is exactly 0.002n. iodine number is an indication of micropore content in activated carbon (0-20a0 or up to 2 nm) by adsorption of iodine from solution. the concentration of iodine in the solution was then calculated from the total volume of sodium thiosulphate used by using equation 3. x/𝑀 = {(𝑁𝐼 × 126.93 × 𝑉𝐼) − [(𝑉𝐼 + 𝑉𝐻𝐶𝑙)/𝑉𝐹] × (𝑁𝑁𝑎2𝑆2𝑂3 × 126.93) × 𝑉𝑁𝑎2𝑆2𝑂3 }/mc …………………(3) where, ni = normality iodine solution, vi = added volume of iodine solution, vhcl = added volume of 5% hcl, vf = filtrate volume used in titration, 𝑁𝑁𝑎2𝑆2𝑂3 = normality sodium thiosulfate solution, 𝑉𝑁𝑎2𝑆2𝑂3 = consumed volume of sodium thiosulfate solution, mc = mass of activated carbon. determination of adsorption isotherm in order to evaluate adsorption capacity of as prepared activated carbon, adsorption isotherms were obtained. here, langmuir and freundlich isotherm model have been applied and the values were then obtained by using the equation 4-8. langmuir isotherm langmuir isotherm purposes that monolayer adsorption occur on solid surface with identical homogenous sites. once the active sites are covered with dye molecules, no further adsorption takes place. langmuir constant can be obtained by using equation 4. qe = qmbce 1+bce ……………………………………..(4) the linear form of langmuir expression is expressed as; ce qe = 1 qmb + 1 (qm) ce……………………………… (5) where, a. kumari dhami, a. rajbhandari (nyachhyon)/ bibechana 18 (1) (2021) 10-18 13 ce = equilibrium concentration of dye solution (mg/l), qe= equilibrium capacity of dye on the adsorbent (mg/g), qmax= adsorption capacity of the adsorbent (mg/g), and b = langmuir adsorption constant. the essential feature of langmuir adsorption isotherm can be expressed in terms of dimensionless constant called separation factor or equilibrium parameter (rl) which is obtained by equation 6. rl = 1 1+bco ……………………………………………….(6) where, co =initial concentration (mg/l) b = langmuir constant rl indicates the shape of isotherm and provides the idea of favorability of adsorption. if the rl value is greater than one, adsorption will be unfavorable. adsorption is favorable only when rl less than one and greater than zero. freundlich isotherm it is used for the non-ideal sorption that involves heterogeneous surface energy system and is expressed as equation 7. qe = kfce 1 n……………………………………….(7) the linear form can be written as; logqe = log kf + ( 1 n ). logce……………… ……..(8) where, kf and n (dimensionless constants) are the freundlich adsorption isotherm constants, kf indicates adsorption capacity and n indicates adsorption intensity. as the value of kf increases the adsorbent capacity of adsorbent also increases. the slope 1/n ranging between 0 and 1, is favorable adsorption condition. determination of surface area surface area of prepared activated carbon was obtained using langmuir isotherm plot and calculated by using following in equation 9. smb = qm.amb.nx10−20 m …………………………………….(9) where, smb = surface area qm = maximum loading amb = cross section area of one molecule of m b = 197.2 ao2 n = avogadro’s no = 6.023x1023 m = molecular weight of mb = 319.84 g mol-1 3. results and discussion preparation of raw rice husk (rrh) and chemically activated rice husk (carh) powder form of raw rice husk (rrh) and chemically activated rice husk (carh) was prepared and is shown in fig. 2. fig. 2: (a) raw rice husk and (b) chemically activated rice husk. characterization of adsorbents x-ray diffraction (xrd) x-ray diffraction analysis of the sample was carried out in order to determine the degree of crystallinity or amorphous nature of the activated carbons. the x-ray diffraction of raw rice husk (rrh) and chemically activated rice husk (carh) is shown in fig. 3. in fig. 3, pattern a is the diffraction pattern of rrh where one can see a distinct peak at 240 2θ which shows the amorphous nature although, it has some local crystalline structure with high conjugated aromatic compounds. similarly small peaks could also be observed at 350 and 450 2θ indicating semi crystalline cellulose structure [18]. the pattern b in fig. 3, is the diffraction pattern of carh. the peak in between 200 to 300 2θ indicates the crystalline silicon oxide phase in the tetragonal system (jcpdf file no.01-082-1554) [19]. in comparison to pattern a, pattern b have humplike crystalline peaks or absence of sharp peak. such a a b a. kumari dhami, a. rajbhandari (nyachhyon)/ bibechana 18 (1) (2021) 10-18 14 20 30 40 50 60 70 80 500 1000 1500 2000 2500 intensity counts 2 ɵ (degree ) a b diminishing of peak may be due to phosphoric acid activation. fig. 3: xrd pattern of (a) rrh and (b) carh. fourier transforms infrared spectroscopy (ftir) the ftir spectra of rrh is shown in fig. 4(a) which indicates the presence of –oh stretching vibration or si-oh group at around 3724 cm-1. small band around 2910 cm-1 represents c-h stretching of alkanes and stretching aliphatic bond of –ch, -ch2, -ch3 was obtained at 2341 cm-1.the band at 1500 cm-1 to 1750 cm-1 was noted and represents c=c stretching of alkenes and aromatic as well as c=o stretching of aromatic group [20]. at around 1039 cm-1, bending vibration of –ch3 group or stretching vibration of si-o-si bond of siloxane. the band around (450-800) cm-1 indicate bending vibration of si-o bond from amorphous silica. similarly, fig. 4(b) shows the ftir spectra of carh. the band at 3716 cm-1 was found to be weaker in comparison to raw rice husk which was broader which implies dehydration of water. the band at 3000 to 2500 cm-1 is due to –c-h stretching vibration, was completely diminished. at around 1576 cm-1 a weak band of c=c aromatic groups which may be due to partial modification of husk texture during impregnation process. likewise some changes in band could be observed at around 1086 cm-1 indicates the bending vibration of –ch3 group or stretching vibration of si-o-si bond of siloxane. the band observed at the region lower than 1000 cm-1 can be attributed to compounds with aromatic ring. the band at 450-800 cm-1 is assigned to bending vibration of si-o bond from amorphous silica and was found to be less intense which may be due to modification of the carbon by phosphoric acid activation [20]. determination of methylene blue number and iodine number porosity was determined by methylene blue number and iodine number. the methylene blue number and iodine number of rrh and carh are presented in table 1 and table 2. table 1: methylene blue number of rrh and carh. table 2: iodine number of rrh and carh. prepared sample implies that large number of micropores on the surface rather than mesopores i.e. iodine number is found to be greater than methylene blue number. it may be due to easy breakdown of amorphous polymers like lignin and hemicelluloses which produce micropores and crystalline form like cellulose which produce mesoporosity. in case of rrh porosity was low as indicated by low surface area (table 3) but in a. kumari dhami, a. rajbhandari (nyachhyon)/ bibechana 18 (1) (2021) 10-18 15 carh, which was carbonized and activated chemically, there was loss of volatile compounds, dehydration of lignocellulose materials as well as cleavage of the bond takes place. as a consequence, porosity developed. determination of surface area the surface area of rrh and carh were calculated using equation 9 and are tabulated in table 3. the surface area of carh was found to be 531 m2/g which was higher than rrh. it may be due to loss of volatile compounds, dehydration of lignocellulosic materials and cleavage of the bond during chemical activation and carbonization. table 3: surface area of rrh and carh adsorption isotherms in order to evaluate adsorption behavior of prepared samples, different isotherm models have been fitted. langmuir isotherm of rrh and carh langmuir isotherm of raw rice husk (rrh) and chemically activated rice husk (carh) was obtained by plotting ce/qe verses ce which is shown in fig. 5.a and fig. 5.b respectively. graph was found to be linear and fitted with langmuir model. the results or langmuir parameters which were obtained are presented in table 4. fig. 5: langmuir isotherm of (a) rrh and (b) carh. 4000 3500 3000 2500 2000 1500 1000 500 75 80 85 90 95 100 105 % t ra n s m it ta n c e wavenumber (cm-1) 3724 2910 2341 1510 1039 787 662 472 r a 4000 3500 3000 2500 2000 1500 1000 500 65 70 75 80 85 90 95 100 105 % t ra n s m it ta n c e wavenumber (cm-1) 3716 2980 1576 2330 1086 794 453 b fig. 4: ftir spectra of (a) rrh and (b) carh. a. kumari dhami, a. rajbhandari (nyachhyon)/ bibechana 18 (1) (2021) 10-18 16 table 4: langmuir parameters. freundlich isotherm for rrh and carh freundlich isotherm of raw rice husk (rrh) and chemically activated rice husk (carh) was obtained by plotting log qe verses log ce and is shown in fig. 6 (a) and (b). fig. 6: freundlich isotherm of (a) rrh and (b) carh the freundlich parameters obtained are presented in table 5. table 5: freundlich parameters. from table 4 and table 5, the correlation coefficient r2 values of langmuir isotherm and freundlich isotherm were evaluated. langmuir isotherm of carh was found to be 0.998 and of rrh was 0.977 which was higher than the value obtained from freundlich isotherm i.e. for carh it was 0.967 and for rrh it was 0.959. it shows that langmuir adsorption isotherm model was found to be best fitted. table 6: comparison of adsorption capacities of various activated carbons the results revealed that carh has solid surface with identical homogenous sites where monolayer y = 0.126x + 0.967 r² = 0.959 0 0.6 1.2 1.8 0 1 2 3 log ce lo g q e (a) y = 0.092x + 1.092 r² = 0.967 1 1.1 1.2 1.3 1.4 0 0.5 1 1.5 2 2.5 lo g q e log ce (b) a. kumari dhami, a. rajbhandari (nyachhyon)/ bibechana 18 (1) (2021) 10-18 17 adsorption took place. the active sites were first covered with dye molecules and there were no further adsorption occurred. the maximum adsorption capacity of carh was found to be 143 mg/g which was found to be higher than rrh which was also supported by high surface area of carh (table 3). similarly, the equilibrium parameter rl value was found to be less than one which revealed the favorability of adsorption. the adsorption capacity of carh was compared with literature values and found to be good (table 6). 4. conclusion it has been concluded that activated carbon can be prepared from low cost laboratory fabricated open type carbonizer. for the preparation of activated carbon, rice husk was used as a precursor. prepared materials were characterized by mb, in, surface area, xrd and ftir spectroscopy. xrd pattern of rrh and carh showed the amorphous with some crystalline nature of the materials. 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[27] m.t. uddin, m.a. islam, s. mahmud and m. rukanuzzaman, adsorptive removal of methylene blue by tea waste, j. hazard.mater.161 (2009) 5360. bibechana 19 (1-2) (2022) 201-207 201 flipping back of extrahelical guanine after methyl repair rajendra prasad koirala and narayan prasad adhikari* central department of physics, tribhuvan university, nepal email: narayan.adhikari@cdp.tu.edu.np article information: received: october 23, 2021 accepted: october 30, 2021 keywords: methylation damage dna repair intrahelical flipping distribution abstract methylation at o6 atom of guanine is a type of dna damage which can cause a cancer. this damage at o6 atom of guanine in a dna can be transferred to sg atom of cysteine in o6-alkylguanine-dna alkyltransferase (agt). flipping out of methylated guanine from its base stack is essential to give off the methyl adduct (ch3) to agt. agt receives the methyl adduct at cysteine leaving guanine demethylated, but still in flipped out orientation. the repair mechanism of dna would be completed only when the extrahelically flipped guanine returns back into the base stack, which is considered as the final step of the dna repair mechanism. here, the intrahelical flipping mechanism of repaired guanine has been studied. the work is further extended to examine the stability of hydrogen bonds between guanine and its pair partner cytosine. the overall result shows that intrahelical rotation of repaired guanine is possible and the base pairing is stable as the ordinary hydrogen bonding. doi: https://doi.org/10.3126/bibechana.v19i1-2.46430 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction genetic integrity is constantly threatened by several types of damages in dna like alkylation, deletion or crosslinking of nucleotides, structural changes etc. many endogenous (chemicals in metabolisms) and exogenous (like ultravoilets and other external agencies) factors are responsible in such dna insult [1,2]. the aberrations in dna nucleotide have both positive and negative impacts in body mechanism. alkylation, specifically methylation, in dna can regulate the gene expression and suppression, but excessive expression and suppression can harm the body [3-5]. besides these, there are many harmful effects of dna methylation. the methylation at o6 point of guanine base in a dna can cause the cancer [6,7]. a protein, o6-alkylguanine-dna alkyltransferase (agt), can be employed to bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal https://doi.org/10.3126/bibechana.v19i1-2.46430 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana bibechana 19 (1-2) (2022) 201-207 202 remove the methyl adduct from dna nucleotide [8,9]. it detects the damage, interaction at methylated vicinity and repairs the methyl damage. agt binds via minor groove of dna mediated by several nucleotide-residue pairs in dna and agt. the cysteine at 145th position of agt receives the methyl adduct as a suicidal reaction [10]. then, the dna gets free from damage. the activity of agt is then degraded and lost the binding capacity. the methylated cysteine thus deactivated and does not harm the body [11]. the extrahelical flipping of methylated guanine is one of the essential condition to repair the methyl damage from dna nucleotide [12]. when agt detects the damaged region in dna, the sidechain of arginine at 128th position of agt intercalates between the base strands and forms hydrogen bond with cytosine at the 20th position [8,13]. moreover, o6 atom at guanine leaves its pair partner n4 of cytosine. these events weaken the hydrogen bonding of methylated guanine with its partner. then, the methylated guanine rotates out from the backbone and approaches at the binding cavity of agt. thus, the methyl transfer is possible [9,14]. during the extrahelical condition, the methylated guanine is inserted into the agt active site and nearer to the methyl receiver cys145. dna and agt form a stable complex mediating several amino acids, out of them, cys145, his146, glu172, tyr114, lys165 and ser159 contributes as the major contributing amino acids [15]. cys145 is then converted to cysteine thiolate anion. then, abstraction of tyr114 proton by n3 site of o6 point of methylated guanine would occur and finally the methyl transfer takes place [15,16]. several studies have been carried out regarding the recognition of methylation damage, interaction with agt, extrahelical flipping of nucleotide and transfer of methyl adduct from dna [17-19]. as far as our best knowledge, the intrahelical flipping of repaired nucleotide has not been studied yet. to deal such process, we have taken a molecular system containing extrahelical guanine base in the double stranded dna. then, the flipping in mechanism of guanine and its stability after the base pair between this guanine and its base partner cytosine have been studied. we believe that this study conveys the complete repairing cycle of dna methylation damage at nucleotide. 2.material and methods 2.1 system setup a dna-protein complex was taken from protein data bank with pdb id 1t38 [20]. the original structure of the complex contains a double stranded dna with methylation at o6 position of seventh residue guanine and a dna repair protein, o6-alkylguanine alkyltransferase (agt). in the complex, agt was at centre of mass (com) distance 24.8 å far from the dna. to set the dna and agt at non-interacting condition, the dna is shifted manually along negative x direction with com distance 42.8 å. the 145th residue of agt, serine is mutated to cysteine (s145c) by using charmm-gui online web server [21]. the methyl adduct (ch3) was removed from guanine and then modelled the methylated cysteine in agt. the complex was solvated in water with periodic boundary condition (pbc) box of dimension (128 × 64 × 72) å3 and then added na+ and cl ions in order to neutralize the entire system. 2.2 molecular dynamics simulations all atom molecular dynamics were carried by using nanoscale molecular dynamics (namd) simulation package [22]. the simulation was executed by employing the charmm36m force field [23]. newly designed force field is used for the modified structure of cysteine. the particle mesh edward (pme) was used to treat the long-range interactions with a 12.0 å nonbonded cutoff. to remove the steric hindrance and undesired position of atoms, the prepared system was executed for energy minimization run for 10,000 steps [24-27]. the output structure of the molecular system was then used bibechana 19 (1-2) (2022) 201-207 203 as the input of equilibration run. the equilibration run was carried out for 2 ns for maintaining at 1 bar pressure and 300 k temperature. finally, production run was propagated for 10 ns by using langevin dynamics with a damping constant of 1 ps-1 under npt conditions with time step of 2 fs. to examine the stability of hydrogen bonding between targeted guanine (gua7) and its pair partner (cyt20), we also prepared a new molecular system picking out only dna system from the output structure of above 10 ns simulation run and molecular dynamics simulation was performed. the procedure of system set up is similar to the aforementioned process. the system was solvated in water of pbc box size (67 × 67 × 67) å3 and neutralized by adding na+ and clions. then, energy minimization was performed for 10,000 steps and equilibration run was executed for 2 ns at pressure 1 bar and temperature 300 k. the production run was propagated for 100 ns under npt condition. visual molecular dynamics (vmd) [28] and pymol [29] is used to visualize the molecular structure and to evaluate the various physical parameters during the analysis of outcomes of simulation. xmgrace program is used to plot the graphs. 3. results and discussion the molecular dynamics simulations have been carried out to examine intrahelical flipping back of methyl-free guanine and to evaluate the stability of hydrogen bonding between gua7 and cyt20 in double stranded dna. the formation of hydrogen bonding, variation of distance between the atoms to form the ordinary hydrogen bonding and radial distributions of interacting atoms in residues gua7 and cyt20 have been investigated from the outcomes of md simulations. 3.1 orientations and hydrogen bonding the interaction between repaired dna and methylated agt is weaker than that of the pairs of methylated dna and normal agt [9,18]. considering the degrading activity of agt after methylation, we have translated dna from agt along negative x direction maintaining the com distance at 42.8 å so that there is no significant interaction between them. in the beginning of the md simulation, the flipped out guanine (gua7) was oriented extrahelically towards the active cavity of agt as shown in fig. 1 (a). fig. 1: the structure of repaired dna and methylated agt complex. the center of mass (com) distance between the dna and agt are set 42.8 å so that there is no significant interaction between these molecules. the methylated cysteine is shown by arrowhead. in the first step, we investigated the activity of flipped out nucleotide, gua7, during 10 ns simulation time. upto the 5 ns simulation time scale, we have observed no any rotation of gua7 from its base stack, oscillated extrahelical region. after 5 ns, the flipped out nucleotide attempted to rotate inside the backbone. the rotation was observed significant during the 6 ns to 7 ns time interval and finally came back to form the ordinary pair between 9 ns and 10 ns time scale as shown in fig. 2 (a). we observed the hydrogen bonding pattern during the 10 ns simulation time. of course, hydrogen bonding play crucial role in the formation of stable structure of protein and dna, and their complex [30-32]. hydrogen bonding contributes in the formation of secondary and higher order proteins. likewise, it bibechana 19 (1-2) (2022) 201-207 204 has important role in the formation of convoluted structure of dna. specifically in dna, guanine forms three hydrogen bonds with cytosine (g ≡ c) and adenine forms two hydrogen bonds with thymine (a = t) [33,34]. in this study, the guanine was at the flipping out condition so that it was disconnected from the hydrogen bonding with its pair partner cytosine. we have investigated whether the flipped out guanine could rotate back intrahelically and form the ordinary hydrogen bonds with cytosine or not. for this, 10 ns simulation run was carried out under npt condition. till the 5 ns simulation run, gua7 has not been returned back into the base stack and so no hydrogen bond has been detected between gua7 and its pair partner cyt20. after 5 ns, the gua7 was found gradually rotated back intrahelically. the flipping back is relatively faster in 6 ns to 7 ns time scale. finally, pairing was completed before the 10 ns as shown in fig. 2 (a) and (b). fig. 2: the intrahelical flipping of gua7 during the 10 ns simulation time scale (a) five snapshots of simulation trajectories (0.0 ns, 2.5 ns, 5.0 ns, 7.5 ns and 10.0 ns) (ii) the formation of hydrogen bonds, the bonds started after the 5 ns time scale and all three ordinary hydrogen bonds form in between 9 ns and 10 ns. 3.2 distance and distribution of targeted nucleotides the distance and distribution of atoms in hydrogen bonding pair partners gua7(n1)cyt20(n3), gua7(n2)-cyt20(o2), gua7(o6)-cyt20(n4) have been estimated to investigate the flipping mechanism of targeted guanine. the variation of distance between the hydrogen bonding pairs is shown in fig. 3 (a) and the corresponding distributions are shown in fig. 3 (b). regarding the distance analysis, the atoms pair, gua7(o6)-cyt20(n4) came first within 3.5 å and formed stable hydrogen bond than that of other two pairs, gua7(n1)cyt20(n3) and gua7(n2)-cyt20(o2). after 9 ns time scale, remaining two pairs also rearranged within 3.5 å to form the hydrogen bonding. finally, all three pairs lie within 3.5 å. the distribution of such atom pairs also supported the rearrangements of ordinary hydrogen bonding pairs as shown in fig. 3 (b). fig. 3: variation in (a) distance and (b) distribution, of hydrogen bonding pairs in gua7 and cyt20 during 10 ns simulation. the distance and distribution curves in fig. 3 (a) and (b) also shows that the nucleotide remains relatively long time either intrahelical or extrahelical condition. the distribution curve shows that the probability of remaining the nucleotide between the distances 14 å to 10 å, i.e., rotational state, is very low so that distribution is also very small. distribution between 14 å to 20 å shows the extrahelical and the distribution within 10 å shows the intrahelical conditions. 3.3 stability of hydrogen bonds the sustainable hydrogen bonding pairs between pair partners gua7(n1)-cyt20(n3), gua7(n2)-cyt20(o2), gua7(o6)cyt20(n4) are very important to be an ordinary double stranded dna. if the hydrogen bonding between these pairs are not stable, the coding in bibechana 19 (1-2) (2022) 201-207 205 newly synthesized protein or dna strands can be erroneous. we observed the stability of such three hydrogen bonds in order to evaluate the correct repairing mechanism. to inspect the stability of hydrogen bonding pairs, we prepared a molecular system picking only dna from the output of above 10 ns simulation run. the system was then extended to 100 ns simulation under npt condition. the correct bonding of gua7 and cyt20 is shown in fig. 4 (a). in the beginning of the simulation, the number of hydrogen bonds was observed fluctuating to gain the correct orientation of the pair partner within 50 ns. after 50 ns time scale, all three hydrogen bonds are continuously acting to keep the pair partners in contact as shown in fig. 4 (b). this concludes that all three hydrogen bonds recover correctly after flipping back of guanine intrahelically. fig. 4: evaluation of ordinary hydrogen bonds between gua7 and cyt20 (a) three stable bonds are observed after 50 ns time scale, eventhough there are some fluctuations before 50 ns (b) the scheme of hydrogen bonds after intrahelical flipping of gua7. conclusions molecular dynamics simulation has been carried out to examine the intrahelical flipping of repaired guanine after methyl transfer. we have performed 10 ns simulation run to investigate the flipping in mechanism of guanine from its base stack and 100 ns simulation is propagated to evaluate the stability of hydrogen bonds between the repaired gua7 and its pair partner cyt20. the result is analyzed from the aspect of distance variation and distribution of hydrogen bonding pair partners. after transferring the methyl adduct to agt, the unpaired gua7 flipped back intrahelically and pairs with cyt20. this could be achieved within 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[34]s. lunell, g. sperber, study of the hydrogen bonding in the adenine-thymine, adeninecytosine, and guaninethymine base pairs, chem. phys. 46(6) (1967) 2119-2124. bibechana 18 (1) (2021) 128-133 128 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal structural analysis of cu substituted ni\zn in ni-zn ferrite d. parajuli1, 2*, k. samatha2 1 department of physics, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal. 2 department of physics, college of science and technology, andhra university, visakhapatnam, india. *email: deepenparaj@gmail.com article information: received: june 15, 2020 accepted: july 31, 2020 keywords: ni-zn ferrite cu substituted ni cu substituted zn xrd single phase spinel abstract ni-zn ferrites are soft ferrites basically popular for high frequency devices. they have low coercivity, low permeability and higher resistivity. these properties have their own benefits on one hand but on the other hand, we can make them more efficient by doping suitable element in order for tuning their properties for other applications. it this work, highly conducting cu is used for substituting ni in ni-zn ferrites and prepared ni0.5-xcuxzn0.5fe2o4 (x = 0, 0.05, 0.1, 0.15 and 0.2) samples using the sol-gel auto-combustion process. we have studied their resulting structural parameter using x-ray powder diffraction (xrd) and fourier transform infrared (ftir) spectroscopy method and compared with that of cu substituted zn ni-zn ferrites. their structures are found to be single phase cubic spinel similar to that of cu substituted zn. the lattice constant increases with cu concentration opposite to that at zn substitution. likewise, the size of the crystallites were not in monotonic change with the doping concentration in both cases due to internal strain and cation distribution. the difference in the pattern of xrd and ftir of our samples indicate their different but significant properties. the changes in the structure shows the effect of cu doping and indicates the possible interesting changes in their electric, electronic and magnetic properties. doi: https://doi.org/10.3126/bibechana.v18i1.29475 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction ferrites have general structure a2+fe2 3+o4 2 which are the structure under spinel with general formula ab2x4. here, a and b are various divalent and trivalent metal cations and, x is o, s, se etc. ‘a’ cation covers 1/8th of the tetrahedral holes and ‘b’ covers ½ of the octahedral holes. they are easy to synthesize and have simple structure for analysis. the spinel nanoferrites are useful in the fields like microwave devices, ultra-high-density magnetic encoding, coating, etc. [1-3]. they have crystallographic structure which can bring feasible change in their microstructure and electromagnetic characteristics. the study of the shape and material properties of different composition of ni-cu-zn ferrite system is increasing these days [4-7]. magnetic nanoparticles (nps) of cu2+ added nickel-zinc magnetic oxides are commonly utilized in magnetic component like rotary dy http://nepjol.info/index.php/bibechana mailto:deepenparaj@gmail.com mailto:deepenparaj@gmail.com https://doi.org/10.3126/bibechana.v18i1.29475 https://creativecommons.org/licenses/by-nc/4.0/ d. parajuli and k. samatha / bibechana 18 (1) (2021) 128-133 core, transformer and magnetic inductive core etc. in the present study, it is planned to formulate nps of cu substituted ni in ni-zn ferrites containing iron oxide as their main components using sol-gel method and compare their structure with cu substituted zn in ni-zn ferrites [8]. their investigation on cu substituted zn shows that cu substituted zn in ni-zn ferrites is appropriate for multilayer chip inductor (mlci) as magnetic material. the structural investigation of our compositions is carried out by utilizing x-ray diffraction (xrd) and fourier transform infrared (ftir) spectroscopy. 2. materials and method copper substituted ni-zn nps are prepared by solgel auto-combustion method as the precursors under considerations react readily with water and can form colloidal solution. moreover, the process is easy, simple, cheap and densification takes place comparatively at lower temperature giving chemically homogeneous sample. the starting materials are a grade 99.99% pure nickel nitrate, copper nitrate, zinc nitrate, iron nitrate and citric acid monohydrate with molecular formula (ni (no3)2·6h2o), cu (no3)3·h2o,(zn (no3)2·6h2o), (fe(no3)3·9h2o) and (c6h8o7.h2o) respectively supplied by himedia and merk india. the ferrites ni0.5-xcuxzn0.5fe2o4 samples with x = 0.0, 0.05, 0.1, 0.15 and 0.2 are prepared. the mixture of these metal nitrates and citric acid were mixed in molar ratio 1:1 and were dissolved in the distilled water to get clear solution. the solution was made neutral by adding liquid ammonia and then stirred in magnetic stirrer maintained at 100oc for 4 hr. they were then decanted and dried at normal temperature for 40 hrs. the flakes thus obtained were combusted and converted into a powder. the powder was sintered in a muffle furnace at 800 °c for 4 h at 5o/min and was used for testing several properties. we have used rigaku x-ray diffractometer (rigaku miniflex ii) incorporated with cu-kα radiation of wavelength 1.5406 å and ftir (ir prestige21, shimadzu, japan) for their structural property in analytical research laboratory, au. 3. result and discussion x-ray diffraction the xrd plots of different ni0.5-xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) samples are shown in figure 1 showing single phase cubic spinel structure according to the jcpds card no.480489 standard under fd-3m group. the lattice constant ‘a’ is determined with the following relation [9]: a = dhkl√h2 + k2 + l2 (1) where, dhkl is interplaner spacing for given hkl planes and is calculated by bragg’s law. the plot of intensity against the diffracting angle (2𝜃) for different concentration of cu, x = 0.0, 0.05, 0.1, 0.15 and 0.2 in ni0.5-xcuxzn0.5fe2o4 ferrite (nps) are shown in figure 1. the sharp peaks in the pattern shows the crystalline nature of the sample. the highest intensity (311) peak indicates the appropriate orientation in order to find the average crystallite size of all samples [10]. the peaks are almost similar with that of cu substituted zn as shown in figure 2. the maximum intensity with corresponding diffracting angle in each concentration is as shown in figure 3. the overall effect is the decrease in the maximum intensity and shifting of maxima towards lower angle side with the increment in the concentration of copper. this is due the change in ionic radii and size of crystallite. the debye-scherer’s formula gives the average size of the crystallite size [11]. 𝐷311 = 0.9𝜆 𝛽𝑐𝑜𝑠𝜃 (2) where, d311, λ, β and θ are volume-averaged crystallite size, wavelength of x-ray (1.5406å), full width at half maximum of (311) peak and diffraction angle respectively. d. parajuli and k. samatha / bibechana 18 (1) (2021) 128-133 130 fig.1: x-ray diffraction patterns of ni0.5−xcuxzn0.5 fe2o4 (x=0.0 to 0.2) ferrites nps. fig. 2: x-ray diffraction patterns of ni0.5cuxzn0.5xfe2o4 (x=0.0 to 0.2) ferrites nps [8]. the crystallite size, lattice parameters and cell volume of the composition ni0.5-xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) are listed in table 1. the crystallite size ranges from 29.01 to 42.68 nm in random order. there are mainly three factors responsible in these random changes: 1. synthesis condition (almost constant in our case) 2. stress created on adsorption (ion substitution process expands lattice parameter thereby generating inter stress and distortion in the lattice structure and hence affects the crystal growth rate and crystallite size) and 3. energy difference between metaloxygen bond (lower energy) and fe-oxygen bonds (higher energy). fig. 3: xrd patterns of maximum intensity vs angle ni0.5-xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrites nps. initially at lower concentration, the increase in lattice parameter due to the cu+2 entrance creates internal stress, decreases the growth rate of crystal and hence reduce the crystallite size [12]. as the concentration increases further, lower energy requirement for their bonding with oxygen accelerate the growth process thereby increasing the crystallite size. after sufficient bonding, the cations now begins to move from one denser site to another site sometimes with distortion of bond thereby decreasing the growth process. simultaneously, the lattice compression takes place due to the partial oxidation of ni2+ to ni3+, cu2+ to cu3+ [13-15]. the crystallite size and lattice parameter variation with concentration is as shown in figure 4 and figure 5 for cu substituted ni and cu substituted zn respectively. the lattice parameter increases with the cu2+ ions concentration. this is due to the larger ionic radius of cu2+ ions (0.73ao) [16] as compared ni2+ (0.69 å) [17] thereby expanding the unit cell or increasing lattice constant [18]. the reverse pattern is obtained in case of cu substituted zn as zn2+(0.74 ˚a) has more ionic radius than that of cu2+(0.73ao). in some cases, the lattice constant do not show the usual response if cu replace zn in the octahedral site [19]. the variation of lattice constant is more significant in smaller size of nps. d. parajuli and k. samatha / bibechana 18 (1) (2021) 128-133 131 from scherer’s formula, the diffraction peak width (β) is inversely proportional to the size of the crystallite. the increase in the lattice parameter expand the volume of unit cell accordingly. decreasing in crystallite size enhances sintering which inturn decreases the lattice defects and involved strain but facilitate the coalition of the crystals resulting the increase in particle size. fig. 4: variation of lattice constant and crystallite size of ni0.5-xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrites nps. fig. 5: variation of lattice parameters with composition of ni0.5zn0.5-xcuxfe2o4 sample (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrites nps (data [8]). ftir spectroscopy the ambiguity created in the structural parameters like crystallite size variation with concentration, can be resolved by the ftir spectroscopy. it gives the exact information about cation distribution or the functional group and the force creating vibration in the crystal by which absorption and diffraction takes place. fig. 6: ir spectra of of ni0.5-xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrite nps. fig. 7: ir spectra of of ni0.5-xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrite nps [8]. the frequency or wave number of the vibration depends on lattice parameter, lattice spacing, masses of cations and cation oxygen bonding. there are two absorption bands ʋ1 and ʋ2 around 400 cm−1 to 600 cm−1 due to two tetrahedral and octahedral sites with a-o-a and b-o-b bond vibration respectively as shown in figure 6 for cu substituted ni and figure 7 for cu substituted zn respectively. the substitution of cu shifted the absorption bands of both tetrahedral and octahedral d. parajuli and k. samatha / bibechana 18 (1) (2021) 128-133 132 sites slightly towards high frequency region as mentioned in table 2. as the bond length increases, the frequency decreases as usual. the ir spectra analysis shows the cu2+ ions in the octahedral site as in figure 6. the spectra of cu substituted zn is similar but the absorption is more indicating high atomic weight element in the composition. the study of force constants gives the complete information of cation distribution. table 1: lattice parameters of ni0.5-xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrites nps. table 2: tetrahedral and octahedral absorption bands of ni0.5-xcuxzn0.5fe2o4 ferrite nps. 4. conclusions diffraction peaks in the xrd pattern show the sample as single phase cubic spinel and the overall effect of the diffraction pattern shows that the maximum intensity peak is moving towards the lower angle side with the concentration of cu due to the reduction in ionic radii similar to that of cu substituted zn. the random pattern of crystallite size is due to the non-uniform lattice strain caused by cation distribution during doping. the lattice parameter increases with the cu2+ ions concentration due to the larger ionic radius of cu2+ ions (0.73ao) as compared to ni2+ (0.69 å) thereby increasing lattice constant. ftir supports the xrd results with slight shifting in higher frequency side due to cu doping. finally, the structural properties of ni-zn soft ferrites after doping with copper substituting with ni and zn respectively shows opposite trend for lattice parameter and random crystallite size, and different 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morang a.m. campus, tu, biratnagar, nepal analysis of aerosol optical depth and angstrom exponents over an aeronet site at pokhara, nepal jeevan regmi 1*, khem n poudyal 2, amod pokhrel 3, madhu gyawali4, anthony barinelli5 , rudra aryal5 1central department of physics, tribhuvan university kirtipur, nepal 2dept. of applied sciences, institute of engineering tribhuvan university, lalitpur, nepal 3university of california berkeley, california, usa 4san jacinto college, south campus, 13735 beamer rd, houston, tx 77089 franklin pierce university, 40 university drive, rindge, nh, usa *email: jsregmi28@gmail.com article information: received: june 14, 2020 accepted: july 27, 2020 keywords: aerosol aerosol optical depth angstrom exponent monthly mariations abstract the monthly variability of aerosol optical depth at 0.50 μm (aod0.50) and ångström exponents (ae) based on spectral aods over an aerosol robotic network (aeronet) site pokhara, are analyzed by using aerosol data of the year 2017. the aod0.50 are characterized by low average values (0.21± 0.12) in monsoon, and highest values in premonsoon (0.67± 0.14) followed by winter (0.46± 0.28) and postmonsoon (0.33±.02) with an overall mean of 0.43 ± 0.02. the average ae obtained by using aods at 0.44 μm and 0.87 μm are 1.20± 0.04 in premonsoon, 1.37± 0.05 in monsoon, 1.41±.01 in postmonsoon, and 1.37± 0.07 in winter with an annual average value of 1.35 ± 0.08. these overall variations of ae indicate that the majority of aerosol loading during the study period was mixture of fine and coarse mode aerosols and the influence of anthropogenic aerosols. the monthly average aod suggest low aerosol loading in the months of the monsoon season (june to september) than other months of pre-monsoon season (march to may) and post-monsoon season (october and november). doi: https://doi.org/10.3126/bibechana.v18i1.29448 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction aerosols are fine solid or liquid particles suspended in the atmosphere, which are embedded by anthropogenic and natural processes, have a strong contribution to perturb the overall solar radiative forcing [1-3]. hence, the sources, nature of aerosols, and its climatic impact are a topic of http://nepjol.info/index.php/bibechana mailto:jsregmi28@gmail.com https://doi.org/10.3126/bibechana.v18i1.29448 https://creativecommons.org/licenses/by-nc/4.0/ jeevan regmi et al. / bibechana 18 (1) (2021) 118-127 119 significant interest in the climate. commonly known natural aerosols are dust, sea salt, forest exudates, while anthropogenic aerosols are particulate air pollutants produced from human activities [4]. the importance of studying and measurement of aerosol physical, optical, and chemical properties have increased dramatically since the last few decades as aerosol loading is significantly growing due to urbanization and industrialization, high population density, or biomass burning. the atmosphere over the urban areas contains a concentration of particles with diameters from a few nanometers to around 100 micrometers produced mainly from a combination of primary particulate emissions from transportations, industries, power generation, and natural sources, and gases to particles conversion [5, 6]. aerosol particles from combustion sources, such as automobiles, wood burning, and power generation, can be small and are considered up to the size range of 1 micrometer (µm). the variability of climate is associated directly with aerosols by scattering and absorbing solar radiation and indirectly by modifying cloud properties [7]. most of the aerosols are scattering type and cause a cooling effect but some aerosols like black carbon, mineral dust and few organic carbons are absorber of radiation which causes warming effect in the atmosphere [8]. the aerosol produced by human activities has also contributed significantly to climate change [9, 10]. the analysis of aerosol optical properties along with meteorological parameters such as precipitation, relative humidity will give a picture of aerosol types over the aerosol observation sites [11-13]. ground-based measurement and analysis of aerosol optical properties are important for the quantitative measure of the extinction of solar radiation by aerosol scattering and absorption. since the last two decades, the direct measurement of aerosol optical properties from ground-based is increasing worldwide. the aerosol robotic network (aeronet) is one of the network which provides long-term aerosol optical data in many different areas of the world, and it has also established in pokhara. this site is one of the fast urbanizing cities of nepal with a lot of construction works, growing industrialization and rapid increase in population[14][2]. it causes to deposit anthropogenic aerosols in the atmosphere which requires a systematic, continuous and long term analysis of physical and chemical properties[15]. but there are very few studies in this region to address the impact of aerosol on climate change, crop productivity, visibility and human health. this work provides an overview of aerosol type by the analysis of aerosol optical depth (aod) and angstrom exponents (ae). a number of previous studies have classified aerosol types from ground based observations and remote sensing from satellites[16,17]. the spectral variation of aod which can be characterized by angstrom's parameters gives an idea of particle size and aerosol loading in the atmosphere [18, 19]. 1.1 theoretical background the aerosol characteristics are commonly determined by using the angstrom's parameters, α and β [20] and are related to aod as; τ(λ) = βλ−α (1) where α is the wavelength exponent that represents columnar aerosol size distribution in the atmosphere and used as a qualitative indicator of aerosol particle size and chemical composition. angstrom exponent values greater than 2 indicate small particles associated with combustion byproducts, and values less than 1 indicate large particles [21, 22] like sea salt and soil dust. the detection of high values of α is always associated with the small anthropogenic particles [23]. β is the turbidity coefficient that shows the aerosol number concentration in the vertical column of the atmosphere. the value of β generally varies from 0.0 to 0.5. the atmosphere is clean when β is less than 0.1 and turbid when it is greater than this. α at wavelengths 0.34, 0.38, 0.44, 0.5, 0.67, 0.87, and 1.02 μm are sensitive to the volume fraction of jeevan regmi et al. / bibechana 18 (1) (2021) 118-127 120 aerosols with radii less than 0.6 mm but not to the fine mode effective radius. long wavelengths 0.67 μm and, 0.87 μm are sensitive to fine mode volume fraction of aerosols, but not fine mode effective radius, while short wavelengths 0.38 μm and, 0.44 μm are sensitive to the fine mode effective radius but not the fine mode volume fraction [24]. at a wavelength, λ = 1 μm, we have τ (λ) = β, which is related to the aerosol column burden. the linear equation in logarithmic format is given by ln τ (λ) = ln β − α ln λ (2) equation 2 gives the values of angstrom's parameters α and β by least square analysis. 2. experiments and discussion research site and instrumentation the observation site pokhara is one of the important geophysical cities and an important tourist destination of nepal. it is situated at an altitude of 800.0 m above the sea level and about 200 km, by road, west of the capital city, kathmandu. the valley is surrounded by hills about 1000-2000 m high. the elevation rises from 800.0 m to over 7500.0 m over an aerial span of 25.0 km. pokhara is the region of highest precipitation rates in the country (3350 mm/year to 5000 mm/year). due to this sharp rise in altitude, the climate of the city is sub-tropical; however, the elevation keeps the temperatures moderate [25]. summers are humid and mild, and most precipitation occurs during the monsoon season (july september), winter and spring skies are generally clear and sunny. the mixing of dry westerly air masses with heated moist air masses from the bay of bengal produces strong convection over the pokhara valley, and thus results in strong updrafts. these strong convective activities are frequent in the premonsoon and monsoon seasons but do not occur during the winter season [26]. aerosol robotic network (aeronet), a federation of ground-based remote sensing aerosol networks established by nasa and photons, site in pokhara is situated on the rooftop of hotel sangrila, which is near to pokhara airport and uses (https://aeronet.gsfc.nasa.gov/cgibin/draw_map_display_inv_v3).cimel sunphotometer, which is a ground-based device to measure vertical profiles, as shown in the figure 1. fig. 1: map of nepal showing the location of pokhara (red icon) (obtained from https://www.google.com/url: nepalforeignaffairs.com). the sunphotometer used for the study is shown in inset. (photo: arnico panday) cimel sun and sky radiometer operate in two modes, direct sun measurements at 0.34 μm, 0.38 μm, 0.44 μm, 0.50 μm, 0.675 μm, 0.87 μm, 1.02 μm, 1.64 μm wavelengths and sky measurements at 0.44 μm, 0.675 μm, 0.87 μm, 1.02 μm [3, 26]. this radiometer makes direct sun measurements with a 1.2° full field of view every 15 min. these solar extinction measurements were used to compute aerosol optical depth (aod), which were automatically computed by using software and are available in the aeronet website. 0.94 μm channel is used to retrieve total precipitable water in centimeters. a study has reported the estimated uncertainty in computed aod approximately ±0.01 to ±0.02, which is spectrally dependent with higher errors in the uv region [12]. these data are available on the aeronet website, and since now, we name it as aeronet data. level 2 https://aeronet.gsfc.nasa.gov/cgi-bin/draw_map_display_inv_v3 https://aeronet.gsfc.nasa.gov/cgi-bin/draw_map_display_inv_v3 https://www.google.com/url jeevan regmi et al. / bibechana 18 (1) (2021) 118-127 121 aeronet aerosol optical data are cloud-screened and are used in this study. since the data are cloud screened and quality assured, data will not be available during cloudy days and when the sensor is wet. for this reason it is very difficult to obtain data during monsoon season. fig. 2: accumulated rainfall during monsoon 2017 as monitored by dhm, nepal. the plot is retrived from website of dhm weather on 7/21/2020. http://www.dhm.gov.np/uploads/getforecast/17972 20298sep%202017_final.docx as reported by dhm nepal, the average rainfall during monsoon season (june, july, august and september) are 670 mm, 932.5 mm, 767 mm and 714.2 mm respectively. the average maximum and minimum temperature during the monsoon season were 30.97 and 22.57 respectively. the annual rainfall in the year 2017 was 3743.3 mm. it means a significant amount of rainfall takes place in the monsoon season that can easily flush out larger aerosol particles from the atmosphere causing a larger drop in the value of aod. angstrom exponents, which were obtained by two pairs of wavelengths 0.44 μm and 0.87 μm are analyzed. daily averaged aerosol optical depth at 0.50 μm, aod0.50 and angstrom exponents based on wavelengths ranges, 0.40 μm to 0.87 μm are downloaded from aeronet pokhara site and analyzed for different months. 3. results 3.1. variability of aod0.50, ae coefficients and precipitable water the time series of daily averaged aerosol optical properties, namely aod at 0.50 μm (aod0.50), calculated ångström exponents (ae) in a broadband (0.44 μm-0.87μm) and precipitable water (pw) in cm, from january to december of 2017 are presented in figure 2 (a, b and c). the monthly averages of aod0.50, ae, and pw (in cm) along with monthly standard deviation are presented in table 1. it shows that aerosol loading is strong in the months from march to may with significant fine particles. angstrom exponent data indicate the approximation of the dominant size of fine particles in aerosol loading in all seasons. for our general reference we considered the threshold value of aod and ae for nearby region (delhi) for anthropogenic, mixed type, biomass burning and dust were taken as 0.3-1.3 and > 0.9, 0.4-0.7 and < 0.9, > 1.3 and > 0.8, and > 0.7 and < 0.6 respectively [27,28]. the significant standard deviation in the aod and ae represents for the different types of particulate components loading into the atmosphere [19, 29]. as expected in the monsoon period (june to september), the air is clean with low and stable aod. in the rainy season, in which we find a large amount of pw in the atmosphere (table 1), the monsoon period, the reduced values of aod may have been caused by differences in the production and flushing of aerosol from the atmosphere due to rain between dry and rainy seasons. both aod and ae exhibit a distinct seasonal trend, mainly in the months of pre and postmonsoon seasons. from the end of winter towards premonsoon season (march to may), the aod has an increasing trend and may be mainly due to the buildup of anthropogenic aerosols, burning of crop residue such as wheat in the regions as this season is the time of harvesting. pw is an essential http://www.dhm.gov.np/uploads/getforecast/1797220298sep%202017_final.docx http://www.dhm.gov.np/uploads/getforecast/1797220298sep%202017_final.docx jeevan regmi et al. / bibechana 18 (1) (2021) 118-127 122 parameter of the atmosphere for the overall climate change. monthly mean values, along with standard deviations (table 1), show that pw is decreasing from postmonsoon seasons to the early stage of premonsoon. fig. 2: time series of daily averaged columnar (a) aod values at a wavelength 500 nm (0.50 μm), aod0.50(b) ångström exponent (ae) with broad band 0.44 μm /0.87 μm and (c) precipitable water in cm, measured over pokhara from jan to december of 2017. the bottom scale is in julian day with 1 for january first and 365 for last day of december. jeevan regmi et al. / bibechana 18 (1) (2021) 118-127 123 table 1. monthly average of aod, ae and precipitable water (pw) and standard deviation in parenthesis for each month. the standard deviation is significant due to daily variability of aerosol optical properties and pw. 3.2. spectral dependence of aod the spectral values of aod decrease with an increased value of wavelength of light. the figure 3 shows the strong dependence of aod at a shorter wavelength and gradually decreases towards the longer wavelengths indicating the presence of fine to coarse aerosol particles. the fine mode particles are responsible for enhancing scattering that causes to make the values of aod high at a shorter wavelength, whereas coarse mode particles are responsible for lower values of aod at longer wavelength [19]. it can also be observed from the graph that the variation of aod with wavelength follows a similar trend for different seasons, as indicated in figure 3. the average value of aod is highest at pre-monsoon season followed by winter, postmonsoon, and monsoon season. the change in curvature in spectral aod in figure 3 could be due to the presence of more than one type of aerosol in the atmosphere, so characterizing them using a single value of α is only an approximation [30]. the variation of averaged aod based on different seasons with wavelength in logarithmic scale is investigated by using first order linear fit, given by equation, and calculated angstrom exponents and turbidity parameters. the ångström exponent and turbidity parameters for these different seasons based on a single year data are found as β= 0.19± 0.01 and α = 1.16 ± 0.07 (winter season), β =0.29 ± 0.01 and α= 1.13 ± 0.04 (pre-monsoon season), β =0.09 ± 0.03 and α = 1.25 ± 0.03 (monsoon season), and β =0.13± 0.01 and α = 1.22 ± 0.07 (post-monsoon season). the variation months aod_0.50μm ae (0.44/0.87) precipitable_water (pw) in cm jan 0.30(±0.12) 1.43(±0.05) 1.21(±0.22) feb 0.79(±0.33) 1.30(±0.09) 1.56(±0.25) march 0.72(±0.49) 1.27(±0.18) 1.95(±0.59) april 0.79(±0.45) 1.21(±0.22) 2.31(±0.67) may 0.52(±0.31) 1.25(±0.19) 3.06(±0.45) june 0.34(±0.18) 1.31(±0.14) 3.91(±0.46) july 0.12(±0.05) 1.41(±0.18) 4.63(±0.19) aug 0.16(±0.08) 1.39(±0.18) 4.70(±0.30) sep 0.31(±0.15) 1.41(±0.09) 3.98(±0.28) oct 0.36(±0.21) 1.40(±0.06) 2.83(±0.57) nov 0.31(±0.20) 1.41(±0.06) 1.81(±0.23) dec 0.30(±0.14) 1.37(±0.08) 1.31(±0.36) jeevan regmi et al. / bibechana 18 (1) (2021) 118-127 124 of turbidity parameters indicates for the aerosol loadings, and the order of β values perfectly matches the variation of aod values. the ångström exponents indicate for a significant contribution of fine mode particles. these α values were calculated using the mean spectral aerosol optical depth (aod) at wavelengths, λ, from 0. 34 μm to 1.64 μm. on the other hand, the seasonal α based on the spectral aod at wavelengths ranges 0.44 μm to 0.87 μm were found as α= 1.36 ± 0.06 (winter season), 1.24± 0.03 (pre-monsoon season), 1.37 ± 0.05 (monsoon season), and 1.40 ± 0.01 (post-monsoon season). in our study, α calculated using two different wavelength ranges of aod shows very little differences, with slightly higher α obtained in the ranges 0. 34 μm to 1.64 μm. fig. 3: spectral variation of aod. fig. 4: spectral variation of the mean aerosol optical depth (aod) at six wavelengths, λ, from 0. 44 μm to 1.64 μm for different seasons and linear fit in logarithmic wavelength scale. jeevan regmi et al. / bibechana 18 (1) (2021) 118-127 125 4. conclusions the monthly averaged aod over the pokhara aeronet device data shows that aerosol concentration is lower in the months from july to september than in the pre and post-monsoon season. it is associated with the regular rainfall in the region during this period. this study shows that the lower aod on these months is due to the heavy rainfall, as indicated by higher precipitable water levels during the monsoon season. the lowest columnar aod at 0.50 μm (aod0.50) characterize the lowest aerosol loading in monsoon, and highest average values in pre-monsoon followed by winter and post-monsoon. previous studies suggest that the higher value of aod during pre-monsoon and post-monsoon is due to the accumulation of aerosol loading from biomass burning and trans-boundary pollution from igp (indo gangetic plain). ae’s comparison obtained at two wavelength ranges, 0.44 to 0.87 μm and 0.34 to 1.64 μm, indicates that ae observed in the ultraviolet to infrared ranges can estimate aerosol sizes and shows that the aerosol has comparatively less impact on the infrared region. this analysis presented only oneyear aerosol optical data to represent monthly variation along with seasonal variation. therefore this study also sees the importance of further analysis of aerosol optical properties by using multi-year aerosol data along with back trajectory analysis of air masses to identify trans-boundary aerosols and source of air pollution over pokhara. acknowledgments authors are thankful to dr. arnico panday, nepal, and aeronet group of nasa, usa for sun/sky radiometers data (http://aeronet.gsfc.nasa.gov/) from pokhara site. conflicts of interest the authors declare no conflict of interest. references [1] r. p. aryal, k. j. voss, p. a. terman, w. c. keene, j. l. moody, e. j. welton, and b.n. holben, comparison of surface and column measurements of aerosol scattering properties over the western north atlantic ocean at bermuda, atmos. chem. phys. 14 (2014) 7617-7629. http://doi.org/10.5194/acp-14-7617-2014. 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https://doi.org/10.1029/2011jd016839 [30] r. pedr´os, j. a. martinez-lozano, m. p. utrillas, j. l. g´ omez-amo, and f. tena, columnintegrated aerosol, optical properties from ground-based spectro radiometer measurements at barrax (spain) during the digital airborne imaging spectrometer experiment (daisex) campaigns. j. geophys. res. 108 (d18) (2003)4571–4587. https://doi.org/10.1029/2002jd003331 https://doi.org/10.1029/2005jd006328 https://doi.org/10.5194/acp-19-245-2019 https://doi.org/10.4209/aaqr.2013.06.0219 https://doi.org/10.5194/isprs-archives-xlii-3-1493-2018 https://doi.org/10.1029/2011jd016839 https://doi.org/10.1029/2002jd003331 bibechana 18 (1) (2021) 214-230 214 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal schiff base metal complexes as a potential therapeutic drug in medical science: a critical review narendra kumar chaudhary, biswash guragain, siyanand kumar chaudhary, parashuram mishra department of chemistry, mahendra morang adarsh multiple campus, biratnagar, (tribhuvan university), nepal e-mail: chem_narendra@yahoo.com article information: received: july 3, 2020 accepted: august 2, 2020 keywords: schiff base, metal complex superbugs chemotherapeutics antibiotic abstract the discovery of new chemotherapeutics with novel bioactivities and functionalities to fight current emerging diseases has become the most significant research in pharmaceutical science. schiff bases are versatile pharmacophores that can form complexes by chelation with metals of different oxidation states. over a few decades of intensive research on metal-based drugs, schiff base metal complexes have been considered as the active field of research in coordination chemistry, owing to their valuable applications in various fields of science. as therapeutic drugs, they have potential applications as antibiotic, antimicrobial, antitumor, antiviral, anti-inflammatory, analgesic, antifungal, and many more. there has been a global threat of drug resistance in medical science in recent years because most of the pathogenic organisms are developing the ability to deactivate drug substances. for this reason, it requires urgent attention from chemical and pharmaceutical scientists to address the severe challenges of multidrug resistance. this review summarizes the current developments in the last few decades' research on the chemotherapeutic activities of schiff base metal complexes. doi: https://doi.org/10.3126/bibechana.v18i1.29841 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. background the coordination chemistry of transition metal complexes has gained momentum in recent years because of their versatile applications in various fields of chemical and medical sciences and comprises a large body of bio-inorganic chemistry research [1]. it has inspired chemical researchers to design and fabricate novel metal complexes all over the world. metal ions make the linkage between the drug substances and pathogenic organisms and thus the field of metal drug interaction chemistry is growing rapidly in the medical and chemical sciences [2]. microbial interactions with a variety http://nepjol.info/index.php/bibechana mailto:chem_narendra@yahoo.com https://doi.org/10.3126/bibechana.v18i1.29841 https://creativecommons.org/licenses/by-nc/4.0/ narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 215 of metal ions at various oxidation states are sometimes beneficial or detrimental, depending on the physical and chemical nature of the metal ions [3]. the treatment of diseases by pure herbal medicines from nature's chest has been a quest of mankind since ancient times. currently, there is a substantial decline in the use of pure herbal medicines because of the complexity of their chemical extraction and slow interaction with diseases [4]. pharmaceutical research has expanded after the second world war to include a massive screening of microorganisms for new antibiotics because of the discovery of penicillin. with the successful record of synthetic medicinal chemistry, the identification of new metabolites from living organisms would be the core pharmaceutical discovery efforts. the world is running out of antibiotics and the discovery of synthetic drugs is today's therapeutic desire for pharmaceutical research. however, many natural product-based drugs are in clinical practice that needs extensive research [5,6]. schiff base is the most familiar discovery of hugo schiff, who has called one of the founders of modern chemistry. the work of professor wohler excluded the concept of vis-vitalis theory, demonstrating that there is no metaphysical difference between organic and inorganic substances. the great pioneering work of berzelius, wohler, and hugo schiff changed the vision of thinking about organic chemical substances. professor schiff memorized himself by the word: remember that you descend from berzelius because berzelius taught chemistry to the old wohler and the old wohler taught me. professor schiff, the native of germany, has continued his research work in italy and introduced himself as an italian chemist [7,8]. after the novel work of schiff in 1864, many researchers were involved in this research field and got success in the synthesis and structural design of this class of compounds. the first metal-based drug that emerged in the late 19th century was cisplatin, whose serendipitous discovery as a potent anticancer drug unlocked the exploration of metal-based chemotherapeutic agents. it was the most effective anticancer drug in the market [9,10]. the resounding therapeutic success of cisplatin and its analogs has triggered tremendous effort in the search for alternative metal-based chemotherapeutic agents in the past few decades. since then the metal-drug interactions in the field of coordination chemistry have been focused well and considered as an active field of research [11]. therefore, there is an urgent to discover and characterize new drugs with enhanced activity, selectivity, bioavailability, and fewer side effects than conventional drugs to treat current diseases. 2. schiff base schiff bases comprise one of the most widely used families of organic compounds, formed as the condensation product of the chemical reaction of the active carbonyl group and a primary amine. their discovery and chemistry are the results of the great pioneer work of a german chemist, hugo schiff, in the year 1864. this has revolutionized chemical research in the field of coordination chemistry in the late 19th century [12,13]. in researching aniline chemistry, he studied the reactions of aniline with many other aldehydes and finally reached the discovery of the imine-based organic compound schiff base. they are also called anils, imines, or azomethines. this class of compounds is mainly recognized by the presence of an active imine (-ch=n-) group that carries a potential binding site for the metal ions through nonbonding electrons of the nitrogen atom [14]. the structural unit of schiff bases also possesses many other hetero-elements like oxygen and sulphur, as the main component elements for chelate formation with metals. the nature of donor atoms that act as coordination sites, their electronegativity, and steric factors largely determine the bonding ability of the ligands. by the presence of lone pair electrons on the n-atom, the electron-donating character of the double bond, and narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 216 the low electronegativity of nitrogen, the n-atom of the azomethine group (>c=n) acts as a very good donor site and schiff bases are considered as active ligands [15]. recently, schiff bases occupy a leading position in coordination chemistry and provide a significant attraction in creating chemical scaffolds due to their simplicity in preparation, variation in properties, biomedical, biochemical, and industrial applications [16]. there are several amines and carbonyl compounds in the library of organic chemistry that enables the synthesis of schiff bases with diverse structural features. for the synthesis of schiff bases, the basic carbonyl group may be aldehydes (aromatic or aliphatic) or a ketone. the stability of the imine group is controlled by the presence of substituent groups attached to the (>c=n) linkage. the general reaction for the formation of the schiff base is illustrated in scheme 1. scheme 1: reaction scheme for schiff base formation. where r represents an alkyl, aryl, cycloalkyl, or heterocyclic group, which may be variably substituted and r1 may be an alkyl, aryl group, or h atom. the formation of the schiff base is a reversible process and generally takes place by refluxing the mixture under neutral conditions or in the presence of acid or base catalysts. the formation is generally driven to completion by the separation of the product or removal of water. 3. metal complexes of schiff base many research papers have been published during the last few decades on the synthesis and pharmacology of schiff base metal complexes. schiff bases are versatile pharmacophores that cave in metal ions within their structural units because of the presence of various donor atoms [17,18]. transition metal complexes of schiff bases are generally formed by the chelation of schiff base ligands with metal ions at variable oxidation states. the vacant d-orbitals of metal ions make available space for the easy coordination of nonbonding electrons of donor atoms of the ligand and even sometimes, this ligation takes place by deprotonation process. there is a general rule of coordination chemistry that chelation makes the complex compounds more stable due to electron circulation inside the ring and changes the physiological profile of the complexes [19,20]. their stability increases when the chelate ring is five or six members. the aryl group bonded to the nitrogen or carbon of the azomethine group prevents them from rapid decomposition and polymerization. a lone pair electron in the sp2 hybrid orbital of azomethine nitrogen is of considerable chemical and biological importance because it makes easy coordination with metals. variation in the denticity of schiff bases makes controls the stereochemistry of metal complexes, which affects their physiological profiles. these complexes carry a wide range of applications in the catalytic chemistry, analytical, clinical, and biochemical fields. in addition, they also possess considerable physiological activities [21–23]. the multifunctional activities of such metal complexes are the prime sources of metal-based research in chemical science. many drug substances have metal ions that play a key role in the better success of biological activities [24]. several studies have described the enhanced activities of metal complexes compared to free ligands. recently, a large volume of research reports on schiff bases highlighted them as a type of potential antibiotic, which by chelation with metals further enhances their potency. chelation causes a drastic change in the biological properties of the ligands and metal moiety [25]. it has been reported that chelation is the cause and cure of many diseases, including narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 217 cancer. the present study of the research focuses on the formation of several schiff base ligands from different precursor compounds and their metal complexes with 3d-metal ions. these chelated complexes of schiff bases are easily absorbed in human intestinal cells and increase their antibacterial strength. 4. chemotherapeutic applications recent advances in coordination chemistry reveal schiff base as a privileged ligand because most of the biomolecules in the living system are structurally similar to this class of compounds. the biofunctional activity of metal-based complexes in medicine and chemotherapy has spurred the growth of interest in the scientific world in the past few decades, after the successful clinical application of cisplatin as a potential anticancer drug. therefore, metal-drug interaction in medical science is becoming a subject of great research interest [26– 28]. the transition metal chemistry of schiff bases gained momentum in the late 19th century and since then, metal-based drugs of schiff bases drew the significant interest of researchers in medical science for their immense biological activities. most of the metals are unnatural to the human body because they have no effective mechanism for their rejection and toxic behavior [29], and there has been a rapid expansion in the research and development of novel metal-based drugs with improved pharmacological properties. several medical problems that arise due to free metal ion toxicity may be ameliorated by their chelation with ligands. schiff base metal complexes have important biological applications as antibacterial, antifungal, antitumor, analgesic, anti-inflammatory, and antimicrobial agents. it has been found that some drugs have greater activity when administered as metal complexes than free organic compounds [30,31]. the discussion in this review is limited to the chemotherapeutic applications of schiff base ligands and their metal complexes. the potential biological activity of schiff base metal complexes is related to the presence of lone pair electrons that participate in the anchoring of biomolecules in the living body. most of the penicillin drugs as antibacterial agents have reported resistance against some pathogenic bacterial strains due to the formation of βlactamases enzymes, but their metal complexes show enhanced activity with them. penicillin-based schiff base ligands are versatile pharmacophores that give an easy binding template for several metal ions. the schiff base ligands (1 and 2) obtained by the condensation of amoxicillin trihydrate with pyridine-2-carbaldehyde and pyridine-3carbaldehyde are rich donor atom-containing compounds, which can easily form metal complexes through interactions with various transition metals. the schiff base ligands and their metal complexes were characterized by various spectral and physicochemical techniques and the antibacterial assay screening was assessed by the kirby-bauer paper disc diffusion technique. co(ii), ni(ii), cu(ii), and zn(ii) complexes of such ligands have shown better antibacterial activity against several bacterial pathogens such as e. coli, p. vulgaris, k. pneumoniae, and s. aureus[32,33]. bidentate ns ligands (3), obtained by the condensation of s-2-methylbenzyldithiocarbazate (s2mbdtc) with 2-methoxybenzaldehyde (2mb) and 3-methoxybenzaldehyde (3mb) form metal complexes with acetate salts of cu(ii), ni(ii) and zn(ii) metals in a 1:2 metal:ligand ratio. they were evaluated for their biological activities against estrogen receptor-positive (mcf-7) and estrogen receptor-negative (mda-mb-231) breast cancer cell lines using the mtt assay method. the cu(ii) complex showed remarkable cytotoxic activity against cancer cell lines. the dna binding study of the cu(ii) complex with calf thymus dna by spectrophotometric technique also revealed a good binding affinity [34]. schiff bases derived from 3,3'-diaminodipropylamine and different benzaldehyde derivatives were observed to have bacteriostatic activity against several pathogenic narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 218 gram-positive and gram-negative bacteria. they also responded to very good antifungal activities. matar et al. (2015) evaluated the in vitro antimicrobial activity of schiff base ligands against various strains of human pathogenic bacteria and a fungal strain, candida albicans, by a two-fold serial dilution method. the antibacterial study was done by the disc diffusion method using test samples at a concentration of 250 µg/disc. the compounds responded better inhibitory activity against gram-positive bacteria than against gramnegative and fungal strains. the antibacterial potency of the ligand (4) increased with the no2 moiety compared to h and oh in other derivatives. moreover, the schiff base (5) exhibited significant anti candida activity at a concentration of 24 µg/ml [35]. melonal is considered an interesting aldehyde used in sensory science with excellent sensory properties. chemically, it is 2,6-dimethyl-5heptanaldehyde. in one of the previous studies, cu(ii), ni(ii), co(ii), and cr(iii) complexes of schiff base ligand (6) obtained from 4fluoroaniline and 2,6-dimethylhept-5-enal were tested in vitro to examine their antibacterial and antifungal potency. an in vitro antimicrobial study was conducted against three gram-negative (e. coli, s. typhi, p. aeruginosa), three gram-positive (s. aureus, b. subtilis, b. megaterium) bacterial strains and six fungal strains (c. albicans, p. chrysogenum, a. niger, a. flavus, a. fumigatus, and c. oxysproum) at six different concentrations. the results of antifungal studies are more pronounced, but the antibacterial results are moderate. among them, the ni(ii) complex exhibited better antibacterial activity than the others. the study also revealed better antifungal activity of the co(ii) complex against penicilliumchrysogenum[36]. schiff base complexes containing a thiazole moiety bear special interest for anticancer activity. in a previous study, a schiff base ligand (7) was prepared by the condensation of salicylaldehyde and 2-amino-4-phenyl-5-methyl thiazole and it was complexed with co(ii), ni(ii), cu(ii), and zn(ii) salts. the synthesized compounds have interacted for anticancer activity study against different human tumor cell lines: mcf-7, hepg2, lung carcinoma a549, and colorectal cancer hct116. for the cytotoxicity assay, test compounds were dissolved in dmso at a concentration of 1 gm/ml and further concentration of the solutions was prepared by serial dilution technique. the cytotoxicity of the tested compounds was expressed by ic50 values, which showed a 50 % cytotoxic effect against cancer cell lines after 48 h of exposure to the tested compounds. the order of ic50 values with respect to hepg2 and mcf-7 cancer cell lines of the compounds was zn(ii) complex, ni(ii) complex, cu(ii) complex, co(ii) complex and ligand (7). for a549 cancer cell lines, the zn(ii) complex and ni(ii) complex showed anticancer activity at ic50 values of 5.30 and 9.10 µg/ml, respectively. the study also revealed potent inhibition of the zn(ii) complex (8) against human trk in all four tested cell lines [37]. electron-donating and electron-withdrawing groups present in schiff base have a profound effect in demonstrating biological functions. the hydrazide schiff bases of vanadium acetylacetonate complexes could be exemplified to show this type of behavior. such schiff bases (9 and 10) were prepared by the condensation of 4-(diethylamino)2-hydroxybenzaldehyde with 4-nitrobenzohydrazide and 4-methoxybenzohydrazide. schiff bases (11 and 12) were prepared by refluxation of 4(dimethylamino)benzaldehyde with 4-nitrobenzohydrazide and 4-methoxybenzohydrazide. their vanadium complexes were synthesized by treatment with vanadium acetylacetonate. their antibacterial profile exhibited the best activity against several strains of s. aureus and e. faecalis bacteria [38]. chitosan-based polymeric schiff base ligands and their metal complexes are highly toxic to human breast cancer cell lines. barbosa et al. (2017) prepared biopolymeric schiff bases from chitosan and salicylaldehyde derivatives and also successfully synthesized their pd(ii) and pt(ii) complexes. their structures were optimized on the narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 219 basis of various spectroscopic techniques such as ft-ir, uv-vis, 1h-nmr, 13c-nmr, and mass spectrometry. cytotoxic interaction of ligands and their metal complexes against the human breast cancer cell line (mcf-7) was done by mtt assay technique and found enhanced toxicity compared to non-modified chitosan. they reached in the conclusion that the cytotoxicity of complexes is a concentration-dependent variable. moreover, the in vitro antibacterial and antifungal tests of the compounds against pseudomonas syringae and fusariumgraminearum showed good results [39]. heterocyclic base-based schiff base ligands and their metal complexes also possess significant antibacterial, antifungal and anticancer activities. in a previous study, abd el-halim et al. (2017) prepared this type of schiff base (13) from quinoline-2-carboxaldehyde and 2-aminophenol and also synthesized various metal complexes with 1.10-phenanthroline. the antibacterial and antifungal activities were evaluated separately in vitro for all types of ligands and the metal complexes by the agar well diffusion method and the anticancer activity was estimated by the viability assay technique. cytotoxicity evaluation was carried out on two different cancerous cells (breast cancer cell line mcf-7, and colon cancer cell line hct-116). in this study, the schiff base ligand was found more potent than metal complexes [40]. however, the cu(ii) complex showed the highest ic50 against the breast cancer cell line (mcf-7). the remarkable antitumor activity of lanthanum and cerium complexes of (e)-n'-[1-(2pyridinyl)ethylidene]isonicotinohydrazoneschiff base ligand was noticed when they were tested in vitro using the mtt assay technique against the human lung cancer cell line a549, and human gastric cancer cell lines bgc823 and sgc7901. the ic50 value of free ligand was reported to be 41.8 µmol/l, 39.2 µmol/l and 43.5 µmol/l and la-complex 11.5µmoi/l, 13.3µmol/l and 15.6µmol/l against a549, bgc823, and sgc7901 cancer cell lines respectively. on the contrary, the ce-complex was found prone to inhibit the growth of cancerous cells at the concentration of 10.9 µmol/l, 12.6 µmol/l, and 14.8 µmol/l for a549, bgc823, and sgc7901 cancer cell lines respectively. based on the ic50 value of all three types of compounds, metal-based complex compounds have seemed hopefully more effective in terms of inhibiting proliferation and inducing apoptosis in tumor cell lines [41]. the mixed ligand cobalt complex of schiff bases (e)-2,4-dichloro-6(((2-hydroxy-5-nitrophenyl)imino)methyl)phenol (14) and (e)-2,4-dibromo-6-(((2-hydroxy-5nitrophenyl)imino) methyl)phenol (15) with pyridine showed significant growth inhibition activity in three human skin cancer cell lines (a431, ht-144 and sk-mel-30) [42]. the in vitro assessment of antitumor activity of (14 and 15) and their co-complexes demonstrated that the ic50 values of the co-complexes were significantly less than the free ligand. based on the comparative study, the ic50 values of co-complex of (14) were reported to be11.3±2.7µm, 17.8±3.1µm, and 19.8±4.8µm against a-431, ht-144, and skmel-30 respectively. kashyap, et al. (2018) explored the antimicrobial and cytotoxic activity of newly synthesized metal complexes derived from the schiff base of mhydroxybenzaldehyde and 4-amino antipyrine. the structure and binding of metals with the schiff base ligand were confirmed by uv-vis, ft-ir, nmr, and tga spectrum analysis. the screening of metal complexes followed by the sulforhodamineb assay against the selective human colorectal carcinoma (hct116) cancer cell lines were found very informative for the determination of their action and usefulness in the field of biomedical science. hct 116 cells were seeded at 2500 cells/well (96 well plates) and allowed to attach overnight. trichloroacetic acid was used as the cell fixing reagent and 0.4% (w/v) sulforhodamine b in 1% acetic acid as the dye reagent to find the total viable count cells in terms of ic50-values at 570nm of wavelength. the maximum permitted concentration of the complex used for their narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 220 cytotoxicity measurement was 100 µg/ml. the metal complexes of schiff base were found very prone to kill the fungi and less prone to inhibit the growth of bacteria when they were screened against the selective pathogenic gram-positive bacteria such as staphylococcus aureus (mtcc3160), and the gram-negative bacteria klebsiellapneumoniae, salmonella typhi, escherichia coli (mtcc 443) and the fungal species; aspergillusniger (mtcc 281), and candida albicans (mtcc 227). the serial dilution method was adopted to evaluate their antimicrobial affinity. the bacteria were grown in double-strength nutrient broth and fungi in sabouraud dextrose broth. similarly, the cytotoxicity of the synthesized compounds was found below the efficiency of standard 5fluorouracil drugs [43]. shaygan et al. (2018) have made a new approach for the determination of the antibacterial activity of newly synthesized co(ii) metal complexes derived from the schiff base (16 and 17) of terephthalaldehyde and ortho-aniline. they showed a remarkable bactericidal potency of the complex against bacterial pathogens such as e. coli(atcc:25922), serratiamarcescens (atcc:13880), p. aeruginosa (atcc:27853) (gram-negative bacteria), b. subtilis (atcc:6633), and s. aureus (atcc:6838) (gram-positive bacteria) [44]. the most common method of antimicrobial activity assessment like disc diffusion and broth dilution methods were found to be admitted in their work. in the disc diffusion method, first, the paper disc was impregnated in the stock solution (100µl) of the metal complex and then inoculated into the bacterial culture plate. the plate was incubated for 18-24 h at 35 °c and their antibacterial properties were recorded by measuring the diameter of the zone of inhibition in mm units. in contrast to the disc diffusion method, the broth dilution method was accomplished by the incubation of bacteria suspended in agar media in the presence of metal complex (2 to 0.00195gm/ml) at 35 °c for 18-24 h. the complex was found more effective against pseudomonas aeruginosa with a diameter inhibition zone of 17mm and a minimum inhibitory concentration value of 0.15 mg/ml. a new series of mononuclear fe(ii), co(ii), ni(ii), cu(ii) and pd(ii) metal complexes, resulting from the metalation of tetradentatemacrocyclic nitrogen ligands, were screened in vitro against two different varieties of cancer cells; one human breast cancer cells (mcf-7) and another human hepatocarcinoma cells (hep-g2). at first, the cells were plated in 96multiwell plate (104 cells/ plate) for 24 h for their attachment on the plate and to recover the monolayer of cells, and then treated with various concentrations (0, 2.5, 5, 10, 20 µg/ml) of metal complex solution. monolayer cancerous cells inoculated with metal complexes were incubated for 48 h at 38 0c in 5 % co2. in the incubated state, the cells were stained with sulfo-rhodamine-b stain and the excess staining reagent was removed by washing several times with acetic acid. the color intensity of the samples was measured using elisa reader and the cytotoxic activity of all the metal complexes was expressed as ic50 values. surprisingly, the metal complexes were found more active in destroying the toxic cells [45]. the ic50 values of the ni(ii) complex for respective mcf-7 and hep-g2 were reported to be1.6 µg/ml and 1.7 µg/ml. the destruction of cancerous cells in the rapid mode is believed due to the interaction of the schiff base with transition metals. cu(ii) metal complexes derived from the schiff base of quinoline-8-carbaldehyde and 4-aminobenzoic acid methyl ester or 4-amino-benzoic acid ethyl ester have gained importance in biomedical science. they are known as anticancer agents. the measurement of their action as toxic cell growthinhibiting agents has promoted the use of metal complexes as an excellent cytotoxic drug in the chemotherapeutic field. the cytotoxicity study of the metal complex was assessed by the mtt standard method in which the cells were seeded (5×103cells/well) in a 96-well plate, and cultured for 24 h in 5% co2 and then the metal complexes(0-100µm) were added and further incubated for 48 h. subsequently, 10µl of mtt narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 221 solution (5 mg/ml) was added into the previously incubated cells and then cultured for 5 h. the elisa microplate was used to measure and calculate the ic50 values of the compound. moreover, the complexes have shown excellent interaction for binding to dna by intercalating mode and fit well into the curved contour of the dna target at the minor groove region [46]. andiappan, et al. (2018) have investigated the anticancer property of a metal complex (19) derived from the schiff base (18) of 2,3diaminopyridine and anthracene-9-carbaldehyde ligands. they characterized compounds by physicochemical analysis (molar conductivity, ph measurement, elemental analysis) and spectroscopic techniques (ft-ir, uv-vis, mass-spectra, 1h-nmr, 13cnmr). they have reported the excellent anticancer activity of the metal complexes based on their performance against the selective vero, human breast cancer cell (mcf7), and cervical (hela) cancer cell lines [47]. the brutality of metal complexes against the selective cancerous cells was disclosed when they were treated with various concentrated solutions (5, 10, 25, 50, 75, and 100 µg/ml) of the metal complexes to find their ic50 values after their 24 h incubation. they showed that the complex with er and pr metals was more potent to inhibit the survival of vero, mcf7, and hela cells and varied when the concentration of the metal complex was changed. chioma et al. (2018) reported the antimicrobial and antioxidant properties of heteroleptic divalent metal complexes of pyrimidinyl schiff base ligand (20)with 2,2’-bipyridine and a series of divalent mn, co, ni, and zn metal ions. they synthesized the schiff base ligand (hl) by the condensation of 2-amino-4,6-dimethylpyridine with 2-hydroxy-1naphthaldehyde in the presence of acetic acid as a catalyst. the complexes were characterized by elemental analysis, conductivity, and ph measurements. they were further characterized by uv-vis, ft-ir, 1h/13c-nmr, and mass spectrometry techniques. the compounds were used against the clinical isolates of gram-positive and gram-negative bacteria for the measurement of their antibacterial activity and also treated against some selective fungal species. the results of their in vitro screening against pathogenic microorganisms proved that the compounds were effluent for antimicrobial properties. in addition, the action of schiff base ligand metal complexes as the antioxidant agent was evaluated by ferrous ion chelating assay and dpph radical scavenging assay, in which the metal complexes showed their excellent performance compared to ascorbic acid [48]. kuate et al. (2018) have reported the selective antimicrobial activity of metal complexes of schiff base ligand (21) derived from the condensation of 4-dimethylaminobenzaldehyde with glycylglycine. they were tested for antimicrobial evaluation against four bacterial and two fungal specimens via the disc diffusion technique. based on the comparative result, they reached in the conclusion that the zn and ni inclusive schiff base complexes were more efficient against c. neoformans, s. aureus, and s. thyphi pathogens than the other metal complexes with mic values of 2x10-3, 2.5x10-2, and 2x10-2 respectively [49]. in the fight against multidrug-resistant pathogens, it is advised often used narrow-spectrum antibiotics [50], i.e. the drugs showing very good activity against very selective pathogens like those in the present work are preferred. abu-khadra et al. (2018) prepared a schiff base ligand (22) from sulfacetamide (n-[4-(aminophenyl)sulfonil]acetamide) and 2thiophenecaroboxaldehyde and also synthesized a series of ag, cr, co, ni, cu, and zn metal complexes. they tried out to establish their antimicrobial activity against pathogenic grampositive, gram-negative, and some fungal species by deploying the agar diffusion technique [51]. all the complexes were found potent to inhibiting the growth of microorganisms. they reported such astonishing results with cobalt complexes narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 222 surpassing the activity of the standard antifungal agent amphotericin b, and that the cr and cu complexes were overall efficacious with activity close to the standard antimicrobials. hence, they concluded that the metal complex of (21) is prone to act as an antimicrobial agent. heteroleptic metal complexes of pyrimidinyl-based schiff base ligand also possess good antimicrobial activity against various pathogenic bacteria and fungi. in a previous study, festus et al. (2019) synthesized mn(ii), co(ii), ni(ii), and cu(ii) complexes of novel schiff base ligand (23) (2-(4,6dimethylpyrimidin-2-ylamino)naphthalene-1,4dione and 2,2′-bipyridine) and appraised them antimicrobial evaluation against s. aureus, e. coli, p. aeruginosa, b. cereus, p. mirabilis, k. oxytoca, a. niger, a. flevus, and r. stolonifer organisms following the agar-well diffusion method. for this study, they seeded 0.2 ml of 24 h grown microbial culture in each plate and bore wells with the sterile cork of 7 mm diameter and introduced the tested samples prepared at 10 mg/ml concentration in dmso. the study revealed moderate to some very good antimicrobial activity, even surpassing the control drug’s activity several times [52]. the antioxidant capacity of all the synthesized complexes was good and the ligand showed even better activity than the standard ascorbic acid. a novel bidentate schiff base ligand (24)(e)-1-(4((e)-(4-(diethylamino)-2-hydroxybenzyli dene)amino) phenyl)ethanoneoxime was synthesized by the condensation of 1-(4aminophenyl) ethanoneoxime and 4diethylaminosalicylaldehyde and metallated with co(ii), ni(ii), and cu(ii) for the formation of complexes. they are oxime functional groupcontaining metal complexes. they were screened in vitro antimicrobial study against two gram-positive bacteria (s. epidermidis and s. aureus), four gramnegative bacteria (e. coli, p. aeruginosa, salmonella, and klebsiella spp.) and a fungal species candida albicans. the results showed promising antimicrobial activity with almost all compounds against salmonella spp. and candida albicans, moderate activity against s. epidermidis and klebsiella spp., but nil activity against s. aureus, e. coli, and p. aeruginosa[53]. a good lead to narrow-spectrum antibiotics could be expected from such compounds. cisplatin, a pt-complex, is the first metal-based inorganic complex used in the treatment of human cancer that has opened the door of the unexplored world of metal-based drugs. the other schiff base platinum complexes also possess a similar type of antitumor activity. al-aghbari et al. (2019) synthesized a pt(ii) complex (26) of schiff base (25) by refluxing the ligand with k2ptcl4 in methanol for 24 h. the schiff base ligand was synthesized by refluxing a mixture of 2-(4isobutylphenyl)propanehydrazide and 2,3,4trihydroxybenzaldehyde in methanol and studied for anticancer activities. the complex showed higher cytotoxic activity than the ligand on both hela cells and pc3 cells, although both compounds were less potent than the model drug, cisplatin [54]. owing to adverse effects on human health, several metal-based drugs with antitumor activities have limited clinical applications and thus, require extensive research for the development of efficient and less toxic anti-tumor drugs. in search of such therapeutic drugs, deng et al. (2019) synthesized five pt(ii) complexes with a modified aroylhydrazone schiff base ligand (27) and studied in vitro anti-tumor activity. they observed remarkable cytotoxicity of the compounds after complexation with pt. the ic50 values of compound (28) against a549 and a549cisr cells were even lower than that of cisplatin[55]. narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 223 narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 224 narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 225 fig. 1: structures of targeted schiff base and metal complexes. narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 226 in a similar work, ambika et al. (2019) studied the anti-cancer and anti-angiogenic properties of schiff base metal complexes. they synthesized two co(iii) schiff base complexes, trans-[co(salen)(da)2]9clo4) and trans[co(salophen)(da)2](clo4) and characterized using various spectroscopic and analytical techniques. the cytotoxic activity of the newly synthesized compounds was conducted in vitro in a549 (human small cell lung carcinoma) and vero (african green monkey kidney cells) adopting the mtt assay. while assessed separately, neither the metal ion nor the free ligand showed any activity up to 200μm concentrations while the former and the latter complex exhibited the ic50 values of 80 μm and 65 μm respectively showing the better activity of the second complex. the study revealed the potential use of such metal complexes in cancer chemotherapy and as an inhibitor of angiogenesis [56]. benzimidazole belongs to such a potent scaffold that possesses a wide variety of functionalizations and coordination modes. in a study, a schiff base (29) containing a benzimidazole moiety was synthesized from 2aminobenzimidazole and o-vanillin in the presence of a few drops of acetic acid. its three copper complexes (30, 31, and 32) were synthesized, one with the pure ligand, and the other with n, n-donor heterocyclic bases such as 1,10-phenanthroline and 2,2'-bipyridyl as co-ligands. they were tested for anticancer and nsaids studies. the in vitro cytotoxicity was conducted against mcf-7 cancer cell lines of human breast, of which compound (32) exhibited much better potency. this cytotoxic activity was attributed to ros generation, as revealed by the lipid peroxidation and glutathione depletion studies. in further studies, compounds (30) and (32) showed significant anti-inflammatory and analgesic activities while assessed in vivo in albino rats and mice, at a lower concentration. the in silico studies revealed the interaction of the compounds with cox2 inhibitors; therefore the researchers forwarded the complexes (30) and (32) as promising nsaids candidates [57]. three tridented schiff base ligands (33, 34, and 35) derived from pyrrole-2-carboxaldehyde and three amino acids, viz. l-methionine, l-histidine, and ltryptophan were synthesized and complexed with palladium metal. the synthesis was carried out under inert conditions using schlenk techniques. the compounds were characterized by elemental analysis, 1h nmr, ftir, uv-vis, and conductivity measurements and found to be nonelectrolytic with square-planar geometry. the compounds were also tested for their antibacterial activity via the agar well diffusion method and the study was expanded to find out the mic values employing the micro titer plate serial dilution method. while the compounds were assessed against four gram-positive and two gram-negative bacteria, the ligands did not exhibit any antibacterial action, but the complexes (38) were much bactericidal followed by (37 and 36). this selective effectiveness is due to the indole and imidazole tails of the respective compounds [58]. saranya et al. (2020) studied the antimicrobial potency of metal complexes of tetradentate(39 and 40) schiff bases synthesized by the condensation of 2-aminophenol/o-phenylenediaminewithtrerpthaldehyde, and cu(ii), co(ii), and ni(ii) metal salts. compounds were synthesized by the general refluxation method and products were obtained from good to high yields (65-95%). antimicrobial tests were conducted against five bacterial pathogens and four fungal species. they found that the complexes were more active, if not completely resistant than the standards: antibioticampicillin and fungicide miconazole. it is noteworthy that the antibacterial activity of the metal complexes with schiff base (40) is better [59]. bao et al. (2020) synthesized a new schiff base (41) from ethanediamine and 2hydroxyphenylacetone and its cu(ii) complex (42). they were characterized and evaluated for cytotoxicity of the same against different cell lines to explore them as cancer cell growth inhibitors. the complex was found to strongly suppress the growth of eight different types of malignant cells narendra kumar chaudhary et al. / bibechana 18 (1) (2021) 214-230 227 by different mechanisms [60]. the compound was found to have ic50 value in the range of 5.13-11.68 µm and less toxicity than cis-platin in lo2 and huvec cells. 5. conclusion and future perspective the metal complexes of schiff bases are deeply rooted in medicinal chemistry. they have gained increasing attention in recent years owing to their versatile applications in various fields such as medicine, catalysis, electronics, industrial and material science. in this review, a collection of patents on schiff bases and their metal complexes during 2015-2020 has been compiled. the reviewed articles cover various antimicrobial and anticancer applications of patented schiff bases and their metal complexes. several antimicrobial and anticancer drugs are already in clinical use, but the development of antimicrobial resistance and tumor resistance necessitates the development of new potent antimicrobial and antitumor drugs. because of this, there is increasing interest in the design of effective drugs containing schiff base scaffold and metal complexes. another major area for therapeutic applications of schiff bases is their use against mycobacteria causing tuberculosis. this is a serious concern in pharmaceutics to come over from tuberculosis because of increasing resistance to already available antituberculosis drugs. considering the tremendous structural diversity of schiff bases, the available literature is insufficient to expose the boundless potential for therapeutic uses of schiff bases and their metal complexes. so, the future perspective as potent therapeutic drugs of schiff base metal complexes is the decisive commentary of this review article. references [1] f. glaser, o.s. wenger, recent progress in the development of transition-metal based photoredox catalysts, coord. chem. rev. 405 (2020) 213129. http://dx.doi.org/10.1016/j.ccr.2019.213129. 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(2020). https://doi.org/10.1016/j.jinorgbio.2020.111103. bibechana vol. 20, no. 3, december 2023, 297-308 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar effects of calcination and sintering temperatures on structural profile parameters of modified bnkt-ceramics ram prasad aryal∗, binod kumar bhattarai, bhadra pd. pokhrel department of applied sciences and chemical eng., pulchwok campus, t.u, pulchwok, lalitpur, nepal. ∗corresponding author. email: aryalram@ioe.edu.np abstract we have carried out a detailed study of synthesis and variations of structural profile parameters: lattice constants, unit cell volume, densities, porosity, crystallite size, dislocation density, and micro-strain of bmz modified bnkt (1 − x)bi0.5(na0.70k0.30)0.5tio3xbimg0.5zr0.5o3 for x = 0, 0.03, 0.06, 0.09 and 0.12 using x-ray diffraction. the conventional solid-state reaction method was used to synthesize bnkt samples. the bnkt powders were calcined at an optimized temperature of 850◦ c for 2 hours. keeping the calcination temperature fixed, optimized sintering temperature and time were also determined to be 1140◦ c for 2 hours, based on the sharpness of the peaks and densification. the nature of the xrd patterns is qualitatively similar to that observed for calcined powders; however, the reflections are sharper in sintered samples presumably due to an increase in particle size. the xrd profile reveals an almost pure perovskite structure with cubic symmetries for all samples in both calcined powders as well as sintered samples. the crystallite size, dislocation densities, and micro-strain were determined by using william-hall plots as well as the scherrer formula. it is observed that the maximum bulk density was found to be 5.88 gm/cm3 for x = 0.03 which is 96.39% of the theoretical density. the crystallite size varies from 19.84 nm to 44.15 nm with compositions for calcined powders and from 57.01 nm to 62.69 nm for sintered samples. the very low value of crystallite sizes of calcined powder indicates that the particle size is comparably very low compared to that of sintered samples. the dislocation densities and micro-strain for calcined and sintered powders were observed in the range (5.1 − 25.4) × 10−4 nm−2, and (2.54− 3.1)× 10−4 nm−2 and (1.3− 4.8)× 10−3 and (8.93− 9.90)× 10−4 respectively which are determined using the william-hall plot method. these results are also confirmed by the results obtained from the scherrer method. both results show improved profile parameters in sintered compositions than in calcination. this verifies that sintered bmz-doped bnkt powders are promising candidates for many dielectric-based energy storage applications. keywords ferroelectrics, micro-strain, crystallites size, williamson -hall plot article information manuscript received: october 31, 2023; accepted: november 2, 2023 doi https://doi.org/10.3126/bibechana.v20i3.58594 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 297 http://nepjol.info/index.php/bibechana aryalram@ioe.edu.np https://doi.org/10.3126/bibechana.v20i3.58594 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ram prasad aryal et al./ bibechana 20 (2023) 297-308 298 1 introduction lead-based ceramics materials such as lead zirconium titanate (pzt) [1] and its derivatives obtained by doping the materials such as nb, sn, la, and ba-modified (pzt) [2–5], lead titanate (pt), lead magnesium niobate-lead titanate (pmnpt) [6], etc., have ruled the commercial market of advanced ceramics for more than half a century due to their outstanding superior properties in piezoelectric devices (sensors, actuators, transducers) and in energy harvesting devices (dielectric and supercapacitors). however, during the synthesis process at high temperatures, the volatile nature of lead caused serious environmental pollution [7] which induced immediate research to develop many lead-free advanced ceramics for various application purposes. so much research work has been done and is ongoing to enhance the properties of conventional eco-friendly ceramics such as batio3 [8], bi0.5na0.5tio3 [9], k0.5na0.5nbo3 [10], bifeo3 [11], srtio3 [12], bi0.5k0.5tio3 [13] that could have efficiency comparable to that of lead-based ceramics [1]. though there are notable advancements in this area, no lead-free materials could meet the efficiency similar to leadbased materials to serve as a practical substitute for electro-ceramics applications [14–18]. among the various lead-free ceramics, bi0.5(na k)0.5tio3 (bnkt) ceramics have gradually been recognized as one of the best potential candidates for electroceramics and have been extensively studied [19,20]. one of the major problems associated with bnkt ceramics is densification because of the volatile nature of bi, na, and k, small sintering temperature range, and potassium sodium ion segregation [10, 21]. further, in material science, there should be a symbiotic relationship among the five elements i.e. composition-processing-structureproperties-applications for a long time [10]. however, researchers have not paid much attention to the processing parameters as they should be in the bnkt system. so before analyzing the microstructure profiles and their impacts on di-/piezo/ferroelectric properties, it is important to the optimization of calcination and sintering temperatures in the bnkt ceramics system to obtain highquality ceramics with enhanced electrical properties. polycrystalline solid ceramics are recognized structurally by small segments of high crystallinity. randomly oriented or textured crystallites are responsible for the formation of anisotropy of the polycrystalline particles. similarly, the random distribution of atoms in the grain boundaries causes lattice strain and imperfection sources in the lattice that can affect the structural uniformity and overall performance of the material [22, 23]. the analysis of x-ray diffraction peak profiles is a robust technique for characterizing the microstructural attributes of ultrafine-grained materials. microstructural properties of the material affect their applications. in xrd measurements, photons are dispersed assuming that the crystal is elastic so there is no manifold scattering, no variations in the wavelength, and absorption of energy. according to the kinematical theory, intrinsic factors such as planar defects, dislocations or crystallite size in the microstructure of the material are responsible for the broadening of the diffraction peaks or bands. examining the distinctive diffraction order dependence makes it possible to distinguish the influences of crystallite size and lattice strain on peak broadening. standard x-ray diffraction profile analysis procedures, such as assessing the full width at half maximum (fwhm), integral breadths, and fourier coefficient of the profiles yield information about apparent crystallite size and lattice strain [24–26]. crystallite size measures the size of coherently diffracting domains. commonly employed techniques for quantitative analysis include scherrer’s equation, the williamson-hall (w-h) method, the warren-averbuch analysis, rietveld refinement, and the pseudo-voigt function. nevertheless, the w-h method and scherrer’s equation analyses are widely employed for determining the crystallite size and strain [27]. this paper aims to find an appropriate synthesis temperature and time to have a pure phase of (1 − x)bnkt-xbmz (x = 0.00 − 0.12) polycrystalline perovskite ceramic material. as reported in the literature, bi, na, and k are volatile at high temperatures, so it is important to determine the exact synthesis temperature to get a pure bnktbased perovskite structure. next, to carry out a comparative study of the microstructural properties based on the compositions and temperatures. the contribution of crystallite size and microstrain to x-ray diffraction line broadening is analyzed by scherrer’s formula and williamson–hall plot methods. the porosities of the resulting samples are also calculated. 2 materials and methods 2.1 materials highly pure raw materials of metal oxide-based powders such as bi2o3 (99%), na2co3 (99.5%), k2co3 (99%), tio2 (99%), mgo (99%), and zro2 (99%) all from sigma–aldrich were used as starting raw materials. ram prasad aryal et al./ bibechana 20 (2023) 297-308 299 2.2 synthesis of (1-x) bnkt-xbmz powders stoichiometrically measured powders were mixed thoroughly for 12 hours at 300 rpm using ethanol and zirconia balls as ball milling media in a highenergy ball mill (pm400ma, retsch, germany). the dried slurry was calcined in the temperature range of 7000c to 9000c for 2 hours in a covered crucible. the disk-shaped green pellets were made (approximately 10mm in diameter and 1.2mm in thickness) by mixing 2% pva as binders into the powders and applying a uniaxial pressure of 10 tons. the green pellets of all the samples were kept at 5000c for 4 hours to burn off the binder and then sintered in the temperature range of 10900c to 11400c for 2 hours with a heating rate of 50c/min in closed alumina crucibles. during this period, the pellets were embedded with the calcined powders of the same composition to reduce the loss of bi and na. the perovskite crystal structure of the sintered powder sample annealed at 5000c for 8 hours was analyzed by the x-ray diffraction technique using a powder diffractometer (miniflex600, rigaku, tokyo, japan) with cukα radiation (λ = 1.5406 å) in the 2θ range from 100 to 800 with a step size of 0.020 and a 20/min scanning rate. by using archimedes’ principle, the bulk density of the sintered pellets was measured. the (1-x)bi0.5(na0.7k0.3)0.5tio3-xbimg0.5zr0.5o3 powder was obtained through ball milling and solidstate reaction by the following equation: (1− x)[0.25bi2o3 + 0.175na2co3 + 0.075k2co3+ tio2] + x 2 [bi2o3 + mgo + zro2] → (1− x)bi0.5 (na0.7k0.3)0.5tio3 − xbimg0.5zr0.5o3 + 0.25co2 (1) 3 results and discussion in this section, we have presented the results and discussion obtained by the x-ray diffraction study. we mainly focused on xrd profile parameters and their analysis. 3.1 optimization of the operating temperatures fig. 1 (a-d) shows the xrd diffraction pattern of the undoped bnkt samples calcined at various temperatures (7000c-9000c) for 2 hrs. to optimize the calcination temperature. based on peak intensities, phase formation, and impurities phases, the calcination temperature was optimized to 8500c for 2 hrs. as some sorts of small impurity phases were recorded at 8000c9000c, which may be due to the volatile nature of bi and na at high temperatures or incomplete phase formation in their high composition. in addition, low-intensity peaks were recorded at 7000c. similarly, green pellets prepared at the optimized calcination temperature were sintered at various temperatures (10900c-11600c) with a soaking time of 2 hrs. at a heating/cooling rate of 50c/min to obtain the optimized sintering temperature. fig. 2 (a-c) shows the corresponding xrd profile patterns. the sample shows some sort of known impurities (to be explained below) at all measured temperatures. based on densification [28], which is a crucial parameter of sintered ceramics for further characterization and for high device performance, temperature 11400c for 2hrs. is set to be an optimized sintering temperature with bulk density (5.78 gm/cm3). in this way, the working temperature is set up. figure 1: (a-d) xrd patterns of pure bnkt sample calcined at 9000, 8000, 8500 and 7000c respectively. ram prasad aryal et al./ bibechana 20 (2023) 297-308 300 figure 2: (a-c) xrd patterns of pure bnkt ceramics sintered at 11400, 11600, and 10900 c.. 3.2 physical, and structural analysis figures 3 (a, e) and 5 (a, e) show the xrd peak profiles of all calcined and sintered compositions (x = 0.00− 0.12) separately with enlarged versions of (110) fitted peaks in the inset, respectively. no splitting of (111) and (200) of the peaks recorded for the sintered systems shown in fig. 7 (a, b) are in good agreement with that of the former reported for other bnt-based ceramics [29, 30], which proposed a structure consisting of cubic phases [31,32] throughout the entire compositional range. a small fraction of a known impurity peak called a pyrochlore phase bi2ti2o7 [28], besides (110) and (200), were seen in some compositions (indicated by ♠) shown in fig. 5 (a). it has two reasons. first, it is the intermediate phase that can’t be transformed into the perovskite structure completely during the nucleation and crystal growth from the amorphous phase. secondly, because of the volatile nature of bi and na at high sintering temperatures, nonstoichiometric structural defects resulted in the formation of a pyrochlore structure [33–37]. figure 3: (a-e) xrd patterns of all the calcined samples (x=0.00-0.12) at 8500c along with enlarged view of (111) peak in the inset image respectively. ram prasad aryal et al./ bibechana 20 (2023) 297-308 301 figure 4: (a-e) w-h plots of all the calcined samples (x=0.00-0.12) at 8500c. figure 5: (a-e) xrd patterns of all the sintered samples (x=0.00-0.12) at 11400c along with enlarged view of (111) peak in the inset image respectively. ram prasad aryal et al./ bibechana 20 (2023) 297-308 302 figure 6: (a-e) w-h plots of all the sintered samples (x=0.00-0.12) at 11400c. figure 7: (a-b) xrd pattern of all calcined and sintered samples with enlarged peaks (110) of calcined, (111), and (200) for sintered samples respectively. figure 8: (a-b) compositional variation of lattice constant and theoretical density of calcined and sintered samples respectively. ram prasad aryal et al./ bibechana 20 (2023) 297-308 303 table 1: calculated physical and structural parameters of (1-x) bnkt-xbmz ceramics at optimized calcination and sintering temperature. calcined samples sintered samples compositions (x%) lattice constant (å) volume (å3) th. density (gm/cm3) lattice constant (å) volume (å3) th. density (gm/cm3) bulk density (gm/cm3) rel. density (%) porosity (%) 0 3.8908 58.90 6.04 3.8754 58.20 6.11 5.78 94.5 5.5 3 3.8773 58.29 6.19 3.8945 59.07 6.10 5.88 96.39 3.61 6 3.8915 58.93 6.20 3.8992 59.28 6.17 5.91 95.78 4.22 9 3.9241 60.43 6.13 3.9018 59.58 6.22 5.89 94.69 5.31 12 3.9308 60.74 6.21 3.9165 60.08 6.25 5.83 93.28 6.72 the lattice constant of sintered ceramics gradually increased and reached 3.9165 å (x=0.12), whereas it decreased at first (x=0.03) and increased in calcined ceramics with bmz contents, as shown in fig. 8 (a). the variations of theoretical and relative density (only for sintered ceramics) were plotted and shown in fig. 8 (b) and fig. 9 (c), respectively. the maximum relative density of 96.39% was recorded for the sintered composition x=0.03. the porosities of the composition vary from 0.04 0.55%. the calculated values of lattice constants, theoretical densities, relative densities, and porosities for all the compositions were also tabulated in table 1 for a comparative study. the slightly higher value of lattice parameters of calcined parameters than that of sintered samples may be due to the already complete phase formation of all samples. 3.3 microstructure analysis in 1918, paul scherrer discovered the first method to compute the crystallite size by employing his equation known as the scherrer equation [28]. this equation characterizes the broadening of the xrd pattern with crystallite size [38]. the equation is written as figure 9: fwhm of broadened x-ray line (b) schematic plot of eqn. (6) figure 10: (a,b) compositional variation of crystallite size of calcined and sintered samples via w-h plot and scherer’s equation method respectively.(c) compositional variation of relative density and porosity of sintered samples, ram prasad aryal et al./ bibechana 20 (2023) 297-308 304 figure 11: (a, b) compositional variation of dislocation density of calcined and sintered samples via w-h plot and scherer’s equation method respectively. figure 12: (a, b) compositional variation of macrostrain of calcined and sintered samples via w-h plot and scherer’s equation method respectively. β = kλ d cos(θ) (2) where β is the broadening of diffraction peaks (fwhm), k is the scherrer constant or shape factor (0.94 for fwhm of spherical crystals with cubic symmetry [39]), d is the average crystallite size, θ is bragg’s diffraction angle in degrees, and λ is the x-ray wavelength (cukα = 1.5405 å). next, the williamson-hall (w-h) plot is another method to compute the broadening of x-ray diffraction peaks contributed by crystallite size and lattice strain as they are independent of each other. according to the x-ray line profile analysis, the broadening of the x-ray line results from the microstructure of the material, which is caused by the random distribution of lattice defects within the crystal. the equations involved in the study of peak broadening are [40]. β = βcrystalline + βstrain (3) βcrystalline = kλ d cos θ (4) βstrain = 4ϵ tan θ (5) using equations (2), (3) and (4) it yields, β cos θ = kλ d + 4ϵ sin θ (6) equation (6) is also termed the expression of the uniform deformation model (udm) [11]. where ϵ is the micro-strain. equation (6) is in the form of y = mx+ c, where the slope (m = ϵ) measures the micro-strain (ϵ), and the intercept (c = kλ d ) gives the crystallite size (d) of the w-h plot as shown in fig. 9 (b). during the grain growth of the micro/nanoparticles, they experience a lot of compression and relaxation in the lattice, resulting in deviation in the lattice constant as well as an overall deviation in the lattice volume. on the other hand, the displacements of the atoms with respect to the neighboring lattice position result in strain broadening [25]. micro-strains of all samples are calculated using the following formula based on scherrer’s equation [40]. ϵ = β cos θ 4 (7) dislocation is another crucial parameter affecting the nanocrystalline materials’ microstructure and performance. it is an imperfection or error in a ram prasad aryal et al./ bibechana 20 (2023) 297-308 305 crystal associated with one side of the lattice with respect to another part of the lattice within the same crystal. imperfections in crystals such as dislocations, different vacancies, and interstitials are not uniformly flawed. the dislocation densities (δ) (length of the dislocation lines/volume) are determined by using the x-ray line profile analysis of the samples by using the following relation [40]. δ = 1 d2 (8) where d is the crystallite size obtained from both scherrer’s equation and w-h plot. the structural parameters (crystallite size, dislocation density, and micro-strain) derived from the xrd pattern by using both methods are tabulated in table 2. table 2: microstructural parameters of calcined and sintered (1-x) bnkt-xbmz ceramics via williamson-hall plot method and scherrer’s formula method. williamson-hall plot method compositions (x%) crystallite size (nm) dislocation density (nm−2) microstrain crystallite size (nm) dislocation density (nm−2) microstrain 0 23.74 1.77× 10−3 1.30× 10−3 60.34 2.75× 10−4 9.76× 10−4 3 44.15 5.13× 10−4 3.80× 10−3 57.01 3.08× 10−4 9.34× 10−4 6 19.84 2.54× 10−3 1.40× 10−3 60.34 2.75× 10−4 8.93× 10−4 9 25.86 1.50× 10−3 3.50× 10−3 62.69 2.54× 10−4 9.69× 10−4 12 36.66 7.44× 10−4 4.80× 10−3 59.6 2.82× 10−4 9.90× 10−4 scherrer’s formula method compositions (x%) crystallite size (nm) dislocation density (nm−2) microstrain crystallite size (nm) dislocation density (nm−2) microstrain 0 17.99 3.09× 10−3 2.04× 10−3 36.49 7.51× 10−4 1.01× 10−3 3 16.73 3.57× 10−3 2.22× 10−3 36.32 7.58× 10−4 1.02× 10−3 6 14.47 4.78× 10−3 2.59× 10−3 38.2 6.85× 10−4 9.67× 10−4 9 13.99 5.11× 10−3 2.67× 10−3 37.84 6.98× 10−4 9.77× 10−4 12 14.67 4.65× 10−3 2.63× 10−3 36.45 7.53× 10−4 1.01× 10−3 the values of crystallite size, microstrain, and dislocation density obtained from w-h plot and scherrer’s formula methods at two processing temperatures were tabulated in table 2. fig. 10 (a, b) shows that crystallite size varies almost in the same manner in both methods but the magnitude of crystallite sizes was quite different between the two methods. generally, the magnitude of crystallite size calculated from scherrer’s formula for non-zero residual stress is lower than the value obtained from the w-h plot. this is because the assumptions of scherrer’s formula and w-h plot were quite different as mentioned above. it was also seen that the variations of crystallite sizes in calcined and sintered temperatures were in reversed order. the calculated values are in the order of previously reported values in modified bnkt ceramics [41–43]. in comparison, there is a large variation in the average crystallite size obtained from the w-h plot method. this variation occurred as a result of the inequalities in the method of averaging the particle distribution. based on the data variations in the two methods, scherrer’s formula is more suitable for the determination of crystallite size in this study. furthermore, the larger the crystallite size, the more crystallinity in the powder. the better crystalline quality corresponds to the lower urbach energy (an indicator of the electronic quality of thin absorbing materials used in solar cells) [44,45]; so, the sintered sample will show better performance [27]. figures 11 (a, b) and 12(a, b) show the dislocation density and micro-strain variations computed via both methods, with calcined and sintered temperatures of all compositions. both parameters were varied in the same manner for both methods. normally, dislocation in a crystal indicates the defects or imperfections that affect the physical and chemical properties of the crystal. dislocation densities influence many properties of the materials and it increases with the plastic deformation inside the crystals. also, it was found that there were compositional variations in the micro-strain values of calcined and sintered samples in both cases. this strain variation could be due to the variations in size and microstructure of the particle [27]. smaller micro-strain values are seen in sintered composition compared to calcined samples in both cases. on the other hand, by increasing the micro-strain dislocation density increases but grain size decreases, and finally, these parameters reach saturation values [46, 47]. finally, the result shows the sintered compositions are the best/most applicable sample that holds the best crystalline quality (the least lattice strain, dislocation density, and leads to lower urbach energy) which enables them to the favorable candidates for optoelectronic devices. 4 conclusion the xrd results imply that the (1-x) bnktxbmz bulk ceramic powder was successfully prepared at optimized calcination (8500 c/2hrs) and sintering (11400 c/2hrs) temperatures. negligible impurity phases were detected in a few compositions. further, from the literature as well as ram prasad aryal et al./ bibechana 20 (2023) 297-308 306 peak position and shapes, both calcined and sintered samples are in a cubic phase. lattice parameters of sintered samples were increased gradually with doping concentration. micro-structure parameters (crystallite size, dislocation density, and micro-strain) were calculated using the x-ray line profile analysis technique for calcined and sintered samples separately via the w-h plot method and scherrer’s formula. the calculation of most of the crystalline parameters is associated with the corresponding crystallite size and 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transition metal dichalcogenides bhupendra sharma1, laxman chaudhary1, rajendra adhikari2 madhav prasad ghimire1,∗ 1central department of physics, tribhuvan university, kirtipur, 44613, kathmandu, nepal. 2department of physics, kathmandu university, dhulikhel, kavre, nepal. ∗corresponding author. email: madhav.ghimire@cdp.tu.edu.np abstract machine learning represents an emerging branch of artificial intelligence, centering on the enhancement of algorithms in computer programs through the utilization of data and the accumulation of research-driven knowledge. the requirement for artificial intelligence in materials science is essential due to the significant need for innovative high-performance materials on a large scale. in this report, the gradient boosting regression tree model of machine learning was applied to predict the lattice constants of cubic and trigonal mx2 systems (m=transition metal and x=chalcogen atoms). the theoretical/experimental values of the materials were compared to the predicted values to calculate the standard errors such as rmse (root mean square error) and mae (mean absolute error). the features used to predict lattice constants were ionic radius, lattice angles, bandgap, formation energy, total magnetic moment, density and oxidation states. the features versus contribution barplot has been drawn to reveal the contribution level of each parameter in the degree of [0,1] to obtain the predictions. this report provides a precise account of the prediction methodology for lattice parameters of the transition metal dichalcogenides family, a process that was previously not reported. keywords machine learning, artificial intelligence, gradient boosting regression, gradient descent, rmse, mae. article information manuscript received: august 18, 2023; accepted: september 23, 2023 doi https://doi.org/10.3126/bibechana.v20i3.57732 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the crucial advancement of human history has been manifested by the development of new materials. so a vast amount of data has been collected throughout the centuries in the discipline of material science. the database of the previous experiments can be used to expedite innovations. the rise of artificial intelligence (ai) ushers a new genesis in the development of materials. ai works on the basis of complex multilayer neural networks with magnificent data mining ability. the fusion of material science and ai methods are used to find the complex relationship between different parameters, 267 http://nepjol.info/index.php/bibechana madhav.ghimire@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v20i3.57732 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ bhupendra sharma et al./ bibechana 20 (2023) 267-274 268 predict the particular properties of materials and improve the material characterization techniques. the most favorable branch of ai in material science is machine learning (ml) [1]. recently, ml is turning out into a robust approach to study the materials with extremely fast and economical means. it works on the basis of neural networks (nn) which performs the prediction of required variables on the basis of training data. the first principle calculation of materials could now be enhanced by ml. we specifically design ml models to generate predictions based on the correlations of the database through statistical and probabilistic methods [2]. on the basis of nature of data labeling in material science, ml can be divided into two categories: supervised learning and unsupervised learning. supervised learning is a ml approach which is used to evaluate an unknown mapping from known samples where the output is labeled (examples are classification and regression). this is like ‘y’ (dependent variable) is predicted with the knowledge of ‘x’ (independent variable) trained previously [3]. in classification, there are p predictor variables x1, x2...xp on which takes values 1, 2, ..., k are trained. our motive is to find a model to predict the values of ’y’ from new values of ’x’. the classification tree algorithm is used to identify the categorical target variable of the most probable “class” [4]. also in regression models, the dependent variable is estimated due to the range of independent variable . the general linear regression model is: y = β0 + β1x+ ε where y is the dependent variable and x is independent variable. β0 is the constant term which is the intercept of the regression line on the vertical axis. β1 is regression coefficient which is actually the slope of the regression line. ε is the random error which can be used to express the effect of random factors on x [5]. meanwhile, in unsupervised learning only input samples are provided to the learning system to make cluster and to estimate probability density function. hence, the main goal of this learning system is to analyze the data, recognize a pattern and finally structure within the available set of data. figure 1: basic architecture of supervised learning. figure 2: schematic picture of stepwise machine learning. 1.1 process of machine learning the major steps involved in the process of ml are: [6] • identify the problem you want to solve using ml • collection of training data for the process • selection of ml model • preparation of accumulated data to train in ml model • test your ml system with test data bhupendra sharma et al./ bibechana 20 (2023) 267-274 269 • validation and improvement of the ml model. usually, we need to search more training data during this iterative loop. 1.2 density functional theory to machine learning recently, we have entered the fourth paradigm of science called data-driven science led by the experiments and simulations. the influence of this paradigm has led to the rise of new field called material informatics. the objective of material informatics is to discover the relationship between known standard features and materials properties such as structure, symmetry, composition, and properties of the constituent elements. the imperceptible feature property relationships beyond human capacities are recognized through ml process [7]. a combination of density functional theory and machine learning techniques provide a practical method to excavate feature-property relationships much more efficiently than by dft or experiments [8]. as the fundamental mathematical model of dft works only for ground state density so the study of excited states is limited within this method. the strongly correlated systems, such as d-electron in transition metal oxides (tmo) are solved with supplemental theories like hubbard parameter (u). to extend the proficiency of dft, various auxiliary code based models are integrated with dft codes such as vasp, quantum espresso, and wien2k. these methods are vastly computationally demanding but consistent and reliable. hence, the abundant database obtained from successful dft platforms can be fitted into appropriate ml models to steer the discovery of complex properties of materials [7]. 1.3 transition metal dichalcogenides two dimensional transition metal dichalcogenides (2d-tmds) are layered materials with robust inplane bonding and weak van der waals interactions between the planes which enables the exfoliation into thickness of two dimensional layers with single unit cell [9]. tmds are an emerging class of materials with highly attractive properties such as atomicscale of thickness, direct bandgap and strong spin orbit coupling. hence these materials accelerate the fundamental studies of novel physical phenomena with applications ranging from nano-electronics and nanophotonics to sensing and stimulation at the nanoscale [10]. the different properties of bulk tmds ranges from insulators such as hfs2, semiconductors such as mos2 and ws2, semimetals such as wte2 and tise2, to true metals such as nbs2 and vse2. the properties are mostly preserved with the exfoliation of such materials into mono or few layers with supplemental characteristics that emerges from confinement [11]. figure 3: bulk crystal structure of mos2. bhupendra sharma et al./ bibechana 20 (2023) 267-274 270 2 materials and methodology in this section, the methodology and the required programming model used in our work has been described. 2.1 data mining it is necessary to collect qualitative data for researchers to create the model for specific problems. open source databases such as materials project [12] and open quantum materials database [13] are one of reliable and representative databases. these databases could be used to extract the data set of the materials of our concern. once the collection of data is done, we need to clean the problems in data such as the data containing abnormal or redundant values. this is called data cleaning. the data cleaning steps are: • data sampling • processing of abnormal value • discretization of data • data normalization data sampling allows us to create prediction model of high performance with less data. thereafter, the removal of abnormal values maintains the accuracy of the model. the continuous features are reduced by data discretization. finally, data normalization is used to organize the columns and tables on the basis of dependencies seen in data. after these steps, the data set is split into training and testing sets to subject it into the ml model [14]. 2.2 gradient descent the objective of gradient descent algorithm is to minimize a differentiable cost function in certain number of iterations [15]. if y = mx + c is regression model then m and c are parameters. so, to find the optimum value of y, m (slope) and c (yintercept) must be minimized. then the cost function becomes: j(m, c) = n∑ i−1 (yi − (mx+ c))2 (1) this cost function is used to optimize the parameters m and c with following relation. mnew = mold − ρ ∂j(m, c) ∂m ∣∣∣∣∣ (m′,c′) (2) where, ρ is the learning rate and (m’, c’) is initial guess. similarly, cnew = ccold − ρ ∂j(m, c) ∂m ∣∣∣∣∣ (m′,c′) (3) so the cost function has to be minimized by moving in opposite direction of the gradient. the iteration process will be repeated until we reach the minimum cost function. finally, we obtain the optimized parameters for best fit in our regression model [16]. 2.3 cross-validation cross-validation technique is a resampling method in ml where the observation set is split into two subsets. the first subset is called training set and the second one is called test set. the training set is exercised to find a proper function whose predictive capacity is based on the prediction error. prediction error is calculated by applying the result of training set into the test set. in this report, we have used k-fold cross validation method because it estimates the model in finer way by training and evaluating it k-times enhancing the model performance. in this method, the dataset is partitioned into k subsets (folds), then the function is trained on the k-1 subsets. finally, the prediction error is estimated on each k-1 subsets with the help of the remaining set [17]. the other validation methods such as holdout validation that splits whole data into training and validation set could be sensitive to the initial random split and the evaluation can biased depending on the split. also, we opt k-fold cross-validation as our preferred method for model evaluation as it is most suitable for smaller datasets. ultimately, the choice of validation technique is chosen on the basis of the characteristics of our data and the research objectives. 2.4 gradient boosting regression model we have used gradient boosting regression tree (gbrt) to predict the lattice parameters of cubic and trigonal tmds. a gbrt model minimizes the prediction errors through boosting technique which compiles the set of weak models to construct a single strong model. in this technique, the prediction error is minimized sequentially by generating new decision trees. decision tree compares the values of root attribute with the real data-set attribute and on the basis of the comparison, it follows the branch and moves to the next node. the sequential process is basically a functional gradient descent where the prediction is optimized with the addition of new tree at every step, in order to minimize the cost function [18]. in this work, we have predicted the lattice constants (a, b and c) using other properties of mx2 system such as ionic radius, lattice angles, band gap, formation energy, total magnetic moment, density and oxidation number using gbrt model. the hyperparameters of gbrt model used here are bhupendra sharma et al./ bibechana 20 (2023) 267-274 271 max-depth and n-estimators. the max-depth sets the maximum depth of nodes in a tree which is set to 4. the n-estimator chooses the number of trees to be considered in our model which is set to be 500. the 3-fold cross validation is applied to the model with shuffle on mode. this means that the dataset has been split into three subsets. two of them were used for training where remaining one was used for testing the model and the data are trained and tested in shuffle mode. 3 results and discussion the interpretation of the accuracy of our model is measured on the basis of root mean square error (rmse) and mean absolute error (mae). for n observations y with n corresponding model predictions ŷ (yi, i=1,2...n), rmse and mae modeled by hodson [19] are as below: rmse = √√√√ 1 n n∑ i=1 (yi − ŷi)2 (4) mae = 1 n n∑ i=1 |yi − ŷi| (5) figure 4: barplot (i) shows the features used and their roles in the model to predict a of the cubic mx2 system (ii) shows the features used and their roles in the model to predict a of trigonal mx2 system (iii) shows the features used and their roles in the model to predict b of trigonal mx2 system (iv) shows the features used and their roles in the model to predict c of trigonal mx2 systems. the figures were generated in jupyter notebook using python codes. 3.1 lattice constants prediction for cubic systems twenty one cubic tmds that were available in materials project website has been used. we used gbrt algorithm to predict the lattice constant of such system. since in cubic system a = b = c and α = β = γ, so it is sufficient to predict one lattice constant for this structure. average rmse and mae from three validations are 2.62å and 0.824å, respectively. figure 4 (i) shows that the order of importance of the parameters is density, total magnetic moment, ionic radius of first element, formation energy, oxidation state of second element, ionic radius of second element, oxidation state of first element, and bandgap (denoted as density, totalmag, ra(pm), forme, oxb, rb, oxa, and band gap, respectively, in figure 4. so it is seen that the density has the most important role in pattern recognition by the model, and band gap has the least. this is because almost all data of cubic systems possess zero band gap. bhupendra sharma et al./ bibechana 20 (2023) 267-274 272 table 1: comparison table of predicted lattice constants versus their experimental/theoretical values in cubic mx2 system. material experimental/theoretical (a) predicted (a’) mnte2 6.69 6.17 cos2 5.51 5.58 cose2 5.84 5.89 nis2 5.61 5.71 nise2 5.94 6.13 ys2 7.83 5.87 cuse2 6.16 6.31 3.2 lattice constants prediction for trigonal systems thirty-one trigonal tmdcs have been taken from project materials to predict the lattice constants of such systems using a gbrt model. in the trigonal crystal system, the relation between major lattice parameters (lattice constants and lattice angles) is given by a= b ̸=c, α = β = 900 and γ = 1200. the calculated predictions of lattice constants are shown in table 2. figure 4(ii) shows that the prediction of a is mostly influenced by the ionic radius to draw the pattern relation, whereas the lattice angles have the least important role, primarily because the angles of all the systems are identical. the average standard errors after three validations are: rmse = 0.0542 å and mae = 0.205 å. in figure 4(ii) and (iii), a and b are equal for the trigonal system, so almost identical errors are seen in predicting b with the same feature roles. in the prediction of c, formation energy has shown the most important role in pattern recognition, while density contribution is in second place, as shown in figure 4(iv). the average standard errors after three validations are found to be rmse = 0.547 å and mae = 0.462 å. table 2: comparison table of predicted lattice constants versus their experimental/theoretical values in trigonal mx2 systems. material a a′ b b′ c c′ fete2 3.75 3.75 3.75 3.66 5.84 5.23 vte2 3.66 3.64 3.66 3.55 6.95 6.13 cote2 3.79 4.02 3.79 4.00 5.56 5.19 cute2 4.02 3.90 4.02 3.90 5.10 5.24 znte2 4.19 3.83 4.19 3.83 5.20 6.12 zrte2 3.98 3.79 3.98 3.79 7.00 6.73 4 conclusions in this work, the prediction of lattice constants of cubic and trigonal mx2 systems has been done through a gradient boosting regression model of machine learning. we have predicted a, b, and c on the basis of patterns or relationships drawn through training the algorithm with features such as ionic radius of atoms, lattice angles, bandgap, formation energy, total magnetic moment, density, and oxidation states. in the cubic system, the rmse and mae in the prediction of lattice constants were found to be 2.62å and 0.824å, respectively. in the trigonal system, the rmse of a = b and c were 0.0542å and 0.547å, respectively. whereas, the mae of a = b and c were 0.205å and 0.462å, respectively. the barplot of cubical systems shows that the contribution of density is the most significant in prediction, followed by total magnetic moment and ionic radius. whereas, the barplot of the trigonal system indicates ionic radius as the major contributor in the prediction of a = b, and formation energy as the major contributing parameter to predict c. dft calculations and experiments are discovering a plethora of materials day by day. hence, a large collection of data can be acquired in the field of 2d-tmds in the near future. the consequence is that the huge database could be used in machine learning to accelerate materials discovery with higher precision in the least amount of time. thereafter, not only lattice constants but every latbhupendra sharma et al./ bibechana 20 (2023) 267-274 273 tice parameter we desire can be predicted with extreme accuracy. applications the cubic and trigonal tmds are one of most stable, extensively researched and then advantageous form of 2d materials. predicting their lattice parameters using machine learning has numerous practical implications across materials science and related fields. these predictions can expedite materials discovery by guiding researchers toward promising tmd combinations, impacting areas like catalysis and energy storage. moreover, the precise control offered by these predictions aids in designing tmds for electronic and optical applications, influencing the development of semiconductors, photodetectors, and optoelectronic devices. this can lead to advancements in electronics, photonics, and telecommunications. they are also invaluable for materials characterization, aiding experimentalists in structural analysis techniques. experimentalists can use these predictions as reference values during structural analysis techniques such as x-ray diffraction and electron microscopy to validate the quality of synthesized samples. overall, machine learning’s role in tmd lattice parameter prediction accelerates innovation, improves materials properties, and reduces costs across a broad spectrum of applications. ethical considerations in our study, we adhere to ethical guidelines, even when utilizing data sourced from the materials project. although the data is not confidential, we uphold ethical standards because our research can have societal implications. we adhere to the materials project’s data privacy policies, and we take deliberate steps to prevent bias through the careful selection, analysis, and transparency of data. for additional information about the materials project, please visit the website [12]. acknowledgments this work was supported by a grant from unesco-twas and the swedish international development cooperation agency (sida) with twas research grant award no. 21-377 rg/phys/as-g. the views expressed herein do not necessarily represent those of unesco-twas, sida or its board of governors. part of this work was also supported by the university grants commission, nepal under ugc grant no. crg-78/79 s&t-03. we acknowledge nvidia for providing the license package of deep learning, a part of machine learning. references [1] wenqing sha, yike guo, qing yuan, shuai tang, xiaoyan zhang, shan lu, xiaojun guo, yang-chun cao, and shijin cheng. artificial intelligence to power the future of materials science and engineering. advanced 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[19] timothy o hodson. root mean square error (rmse) or mean absolute error (mae): when to use them or not. geoscientific model development discussions, pages 1–10, 2022. https://oqmd.org/ introduction process of machine learning density functional theory to machine learning transition metal dichalcogenides materials and methodology data mining gradient descent cross-validation gradient boosting regression model results and discussion lattice constants prediction for cubic systems lattice constants prediction for trigonal systems conclusions bibechana 18 (1) (2021) 83-90 83 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal facile methods of preparing pure hydroxyapatite nanoparticles in ordinary laboratories gokarna pandey1, kedar nath dhakal1, ajaya kumar singh2, suresh kumar dhungel3, rameshwar adhikari1,4 * 1 central department of chemistry, tribhuvan university (tu), kirtipur, kathmandu, nepal 2 department of chemistry, govt. v. y. t. pg autonomous college, durg, chhattisgarh, india 3 nepal academy of science and technology (nast), lalitpur, nepal 4 research centre for applied science and technology (recast), tu, kirtipur, kathmandu, nepal *email: ram.adhikari.tu@gmail.com article information received: june 1, 2020 accepted: july 2, 2020 keywords hydroxyapatite nanoparticles ftir spectroscopy x-ray diffraction bioceramic abstract the present work features some simple methods of preparing pure hydroxyapatite nanoparticles (nano-hap), a useful biomaterial, via various wet chemical methods and using biogenic sources such as eggshells and animal bone. the nano-hap hence prepared was subsequently characterized by ftir spectroscopy and xrd technique. the ftir spectra confirmed the presence of po4 3and oh ions as major functional groups in the prepared material, with some additional peaks implying the presence of co3ions and adsorbed water molecules. the xrd patterns, in agreement with the jcpds 09-432 data, demonstrated the crystalline nature of the nano-hap and confirmed the phase as being apatite. the average grain diameter of the nanocrystallites was found in the range of 15-30 nm. the preparatory methods depicted herein can be easily employed in ordinary high school laboratories having basic facilities such as availability of distilled water, some handy glasswares, common laboratory chemicals and instruments such as balance, hot air oven and furnace. doi: https://doi.org/10.3126/bibechana.v18i1.29600 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction hydroxyapatite (hap), with the chemical formula ca10(po4)6(oh)2, is one of the most attractive bioceramics for several biomedical applications due to its osteoconductive and antimicrobial properties and biocompatibility as well as lack of toxic and inflammatory responses [1-4]. hap is the major mineral constituent of human bone accounting for approximately 65 weight fraction of the latter. bone is, in fact, a nanocomposite material comprising hap mineral and collagen proteins, its properties thus largely being dependent on the nanoscale morphology. the apatite crystals are the essential parts of tooth and bone of all the vertebrates. when used as implants, the synthetic hap is able to provide a scaffold or template for new bone regeneration and growth, and supports the osteoblast adhesion and proliferation [3,4]. http://nepjol.info/index.php/bibechana mailto:ram.adhikari.tu@gmail.com https://doi.org/10.3126/bibechana.v18i1.29600 https://creativecommons.org/licenses/by-nc/4.0/ gokarna pandey et al. / bibechana 18 (1) (2021) 83-90 84 such an important bio-ceramic can be synthesized either from natural sources such as bone, corals, eggshells, body fluids, etc. or via various chemical routes including sol-gel method, mechano-chemical precipitation, hydrothermal technique, flame spray and microwave assisted method, and others [2-16]. the major mineral constituents of human bone are calcium and phosphorous with traces of other substances [17,18]. however, a considerable amount of carbonate (co3 2-) also appears to be present in the bone. the presence of co3 2ions in biological apatite is of great importance because it is the main source of lattice distortion, creating micro-stresses and crystalline defects in its surrounding area which, in turn, play a vital role in its solubility. thus, synthetic apatite should exhibit small particle size and presence of co3 2[18]. it has been demonstrated that the nanocrystalline hap (nano-hap) exhibits enhanced biocompatibility, bioactivity and mechanical performance over microcrystalline or bulk hap, which has been attributed to their unique quantum confinement effects and large surface area to volume ratio. thus the nano-hap can be used in designing superior biocompatible coatings for the implants and in developing high strength composite materials [4,12,17,18]. with the dawn of nanotechnological revolution during last few decades, and in context of unparalleled opportunities offered by these technological advances also in developing countries, the facile methods for nanomaterials synthesis are of tremendous scientific importance. there is overwhelming interest in the versatile routes for the synthesis of such materials among young scientists in their early career. taking into account the vigor of scientists of new generation towards nanomaterials and their technological implications, the objective of present work has been to demonstrate simple methods of preparing nano-hap in ordinary high school laboratories also using wet chemical methods by utilizing biogenic waste as resources. as evidence for the success of the methods used, the characterization of the materials by fourier transform infrared (ftir) spectroscopy and x-ray diffraction (xrd) are reported here. 2. experimental section 2.1 materials analytical grade calcium nitrate tetrahydrate, diammonium hydrogen phosphate, ammonium hydroxide (25%), ortho-phosphoric acid (85%), urea, calcium oxide, ethanol and ethylene-diaminetetraacetic acid (edta) were purchased from merck india ltd. egg shells and adult buffalo femoral bones were collected from local market in kathmandu. all solutions were prepared in distilled water. 2.2 preparation of nano-hap four different methods used for the preparation of nano-hap were sol-gel method, precipitation method using calcium oxide and ortho-phosphoric acid as starting materials, precipitation method using aqueous slurry comprising of egg-shells powder and ortho-phosphoric acid solution, and calcination of animal bone. (a) sol-gel method this method was adopted from different research articles [11,12,19,20] published elsewhere. in this method, 10.8 g of calcium nitrate tetrahydrate, ca(no3)2.4h2o and 3.89 g of diammonium hydrogen phosphate, (nh4)2hpo4 were separately dissolved in 50 ml of water taken in a 100 ml conical flask for each. phosphate solution was then added drop-wise to the calcium nitrate solution maintained at temperature of 75 °c. the ph was maintained at 11 throughout the experiment using ammonia solution. the resulting solution was continuously stirred for 2 hrs and the product was allowed to cool and precipitate for 24 hrs. the aged gel thus obtained was filtered and washed with doubly distilled water and ethanol several times till the filtrate was neutral. finally, the resulting clear white powder was stored in a hot air oven gokarna pandey et al. / bibechana 18 (1) (2021) 83-90 85 maintained at 85 °c for 12 hrs for further analyses. the reaction can be represented as: 10ca(no3)2 + 6(nh4)2 hpo4 + 8nh4oh ca10(po4)6(oh)2 + 20 nh4no3 + 6h2o (b) precipitation method this method was adopted on the basis of works reported elsewhere [2,5,17,21,22]. calcium oxide (cao), ortho-phosphoric acid (h3po4), and ammonium hydroxide (nh4oh) were used as starting substances for this method. first of all, 7.955 g of dry cao powder was added to 50 ml of water taken in a 100 ml conical flask and vigorously stirred at 20 °c for 24 hrs to form aqueous suspension of ca(oh)2. then 9.732 g of 85% h3po4 was slowly added to the solution at a rate of about 1.5 ml/min. the reactants were further stirred for 24 hrs to attain the maturation stage, under constant stirring. the ph of the solution was maintained at 10 using ammonia solution. the precipitate was filtered, washed and dried in hot air oven at 85 °c for 12 hrs. the chemical reaction may be written as: 3cao+ 3h2o 3 ca(oh)2 3ca(oh)2+3h3po4 3 cahpo4+6 h2o 5ca(oh)2+ 3h3po4 ½ ca10(po4)6(oh)2+9h2o 2ca(oh)2+3cahpo4+6h2o ½ ca10(po)6(oh)2+9 h2o (c) eggshells as starting material an eggshell that primarily comprises of calcium carbonate (caco3) can be converted into calcium oxide (cao) via calcination, which can be then used as an inexpensive raw material for the hap synthesis. following the methods reported in elsewhere [6,23-25], the chicken eggs shells were collected and cleaned with tap water followed by washing with distilled water and acetic acid solution several times and dried and powdered using a grinder. the powder was hence subjected to thermal treatments in a furnace in three stages: firstly, at 150 ºc for 5 hrs to remove water and organic impurities, secondly, at 500 ºc for 3 hrs to remove any remaining organic residue, and finally at 1000 ºc for 2 hrs to transform the eggshell powder to cao. the powder was then transformed into hap in the phosphate solution using the following procedure. 5 g of calcium oxide was dissolved under constant stirring in 6 g of ortho-phosphoric acid. then 0.4 g of urea was added along with 0.8 g of edta and 100 ml of water. the ph of the solution was adjusted to 10 using ammonia solution at 75 ºc. the reaction mixture was further stirred for half an hour and then kept relaxed for 24 hrs to allow nano-hap to grow. the slurry was centrifuged at 5000 rpm for 2 min and the resulting sludge was thoroughly washed with distilled water until neutral ph. the precipitate was dispersed in 100 ml of ethanol and the mixture was sonicated for 1 hr. the residue was dried in air for 24 hrs and then at 85 ºc in an oven for 12 hrs. the reaction may be written as: caco3 cao+co2 10cao+10h2o+6h3po4 ca10(po4)6(oh)2+18 h2o (d) animal bone as starting material this method was adopted from different research papers [16,26-28]. briefly, the femoral bones of buffalo was collected from butcher shop that were then cut into small pieces and boiled in water for 3 hrs. the bone was then washed with acetone for several times to remove fats and other impurities and hence dried at 160 °c for 48 hrs. the pieces were ground to powder with particle diameter less than 450 µm. the powder was treated with 4m naoh (solid-liquid weight ratio of 1.40) for deproteinization. the content was heated at 250 °c for 5 hrs. the defatted and deproteinized powder was calcined at 700 °c for 6 hrs in a muffle furnace to obtain grayish white powder of hap. the powder was further calcined at 1000 °c for another 6 hrs to study the effect of calcination temperature. 2.3 methods for characterization gokarna pandey et al. / bibechana 18 (1) (2021) 83-90 86 4000 3500 3000 2500 2000 1500 1000 500 0 20 40 60 80 100 t r a n s m it ta n c e ( % ) wavenumber (cm -1 ) adsorbed h2o o-h o-h co3 2co3 2po4 3p-o po4 3c=o (carbon dioxide) fourier transform infrared (ftir) spectroscopy the ftir analysis was performed by using a prestige-21 ftir spectrometer (shimadzu company, japan). the spectra were collected in the range of 4700-400 cm−1 using kbr pellet method. x-ray diffraction (xrd) the crystal phase and structure of the samples were determined by bruker d2 phaser x-ray diffractometer with a monochromatic cukα radiation source (λ = 0.15418 nm) with 2θ angles ranging from 20° to 80°. the accelerating voltage of 30 kv and emission current of 10 ma were used. 3. results and discussion the phase purity and presence of major functional groups of the hap powder were attested by ftir analyses. fig. 1 shows the ftir spectrum of the hap powder chemically synthesized by sol-gel method. the spectrum is dominated by the typical po4 3 bands of crystalline apatite phase characterized by the peaks representing triply degenerate υ3 (po4 3-) asymmetric mode centered at 1021 cm-1 and 1087 cm-1 (shoulder), non-degenerate symmetric stretching mode υ1 (po4 3-) at 962 cm-1 and components of the triplet of υ4 (po4 3-) bending modes at 560 cm-1 and 470 cm-1 [2,6,12,21,23,29,30]. the broad band located between 3200-3600 cm−1, together with weak and broad band around 1627 cm−1 of h-o-h bending mode indicates the presence of absorbed water. the weak peak located at 3570 cm−1 corresponds to the vibrations of oh− ions in the hap lattices [6,24,26]. the two peaks centered near 1490 and 1426 cm-1 are assigned to the ν3 vibration mode and the weak peak at about 870 cm-1 is due to the ν2 vibration mode of free, planar co3 2ions (group symmetry d3h) [12,20,23-25]. the weak band at 2360 cm-1 can be attributed to c=o bonds from adsorbed atmospheric carbon dioxide [25]. fig. 1: ftir spectrum of hap powder synthesized by sol-gel method. in summary, the ftir spectrum shown in fig. 1 verifies, in consistence with several literatures, the success of the chemical synthesis of the hap powder. fig. 2 shows a closer look on structure of the raw eggshell and the hap. fig. 2: ftir spectra of raw eggshells powder compared with the hap from eggshells. the ir spectrum of the raw eggshell shows the strong carbonate peaks centered at 1490 cm-1 and 870 cm-1, and the sharp peak located at 710 cm-1 , which represents the absorbance by ca-o bond [31]. the weak band at 2360 cm-1 is attributed to c=o bonds from carbonate [25,32] while the broad band at around 2863 cm-1 appears due to oh stretching vibration and that around 3600 cm-1 arises due to n-h bonds due to proteins present in the raw eggshells. 4000 3500 3000 2500 2000 1500 1000 500 t ra n s m it ta n c e ( a .u ) wavenumber (cm -1 ) b) raw eggshell a) hap from eggshells o-h adsorbed h 2 o o-h co3 2po 4 3po 4 3p-o co3 2co3 2co3 2ca-o c=o (carbonate) amide (proteins) po 4 3n-h raw powder hap powder gokarna pandey et al. / bibechana 18 (1) (2021) 83-90 87 the ir spectrum of the hap powder prepared from eggshells given towards the bottom of fig. 2 is much different from the spectrum of raw eggshells as expected but contains the noteworthy peaks related to the hap phosphates such as those centered around 470, 560, 1020, and 1090 cm-1 , as compared with fig. 1. fig. 3 shows the ftir spectra of buffalo bone powder and the hap prepared from it. unlike in the eggshells, the spectrum of the buffalo bone powder, as shown in upper part of fig. 3, clearly shows the presence of phosphate peaks centered at 1090, 1040, 603, 568 cm−1 [10,32,33] as well as oh group at 3570 cm−1 [12,26,34] confirming the presence of hydroxyapatite as a major mineral component in the buffalo bone. the presence of sharp peaks in the aliphatic zone (2924 cm-1 and 2875 cm-1) due to the c-h elongation vibration together with the weak peaks at 1654 cm–1 due to the elongation vibration of c=o bonds and at 1541 cm–1 due to the deformation vibration of n-h bonds and elongation of c-n bonds in the bone powder results from the collagen protein [33-35]. fig. 3: comparison of the ftir spectra of bone powder and hap prepared there from. likewise, the presence of broad bands in the range of 3200-3600 cm-1 result from adsorbed water and carbonate band located at 1450 cm-1 arises due to the presence of caco3 in the buffalo bone [35]. the spectrum is very much similar to that of hap obtained from eggshells and sol-gel method except that it contains additional c-h peaks (2924 cm-1 and 2875 cm-1), which can be linked to the presence of residual organic impurities. the presence of carbonate peak (1450 cm-1 and 870 cm-1) [35] might imply that it still contains caco3 as impurity in the resulting hap powder, which will be later confirmed by xrd spectra as shown in fig. 5. fig. 4 shows the xrd patterns of hap powder synthesized by three different chemical methods: sol-gel method, precipitation method using eggshell and wet chemical precipitation method using cao and h3po4 as starting materials. the xrd patterns show that all the synthesized hap materials are crystalline. the peaks located at 2θ values of 26°, 29°, 32°, 34°, 40°, 47°, 50°, 53° and 64°, correspond to (002), (102), (211), (112), (202), (310), (222), (213) and (004) miller reflection planes of hap, respectively (which comply with the jcpds 09-432 data) [2,5,6,10,12,19, 23,27,30,36]. fig. 4: xrd pattern of hap powder synthesized by different methods as indicated. it is quite interesting to note that all the investigated samples have quite similar xrd patterns confirming the presence of the pure apatite phase in 4000 3500 3000 2500 2000 1500 1000 500 t ra n s m it ta n c e ( a .u .) wavenumber (cm -1 ) o-h co 3 2co 3 2po 4 3po 4 3c-h (organic impurities) amide i (collagen matrix) co 3 2po 4 3c-h b) hap from animal bone a) animal bone h 2 o o-h hap powder bone powder 20 30 40 50 60 70 80 in te n s it y ( a .u .) 2  (degrees) (002) (102) (211) (112) (202) (310) (222) (213) (004) (a) (b) (c) (a) hap from sol-gel method (b) hap from egg shell (c) hap from cao and h3po4 gokarna pandey et al. / bibechana 18 (1) (2021) 83-90 88 the prepared samples. the absence of peaks corresponding to (024), (021) etc. planes also clearly hinted the absence of phases such as βtricalcium phosphate [36]. the xrd patterns of the hap from eggshell powder shows comparatively less impurities than from other methods which confirms that the impurities content in hap can be reduced byheating the powder at higher temperatures, the same deduction as indicated by the ftir results. fig. 5 shows the xrd pattern of hap samples obtained from bone powder calcined at two different temperatures, 700 °c and 1000 °c. xrd patterns of both samples are very similar to that obtained by chemical methods. however, the presence of a quite sharp peak located at 2θ value of 29° in the hap prepared by calcination of the bone powder at 700 °c indicates the presence of considerable amount of caco3. fig. 5: xrd patterns of hap obtained from buffalo bone after calcination at 700 °c and 1000 °c. this peak, however, almost disappears when same hap powder is heated at 1000 °c, indicating that the decomposition of caco3 takes place at higher temperature. further, the hap peaks were found to become sharper with increasing calcination temperature. the results imply the advantages of attaining better purity of the hap by calcination of the bone powder at higher temperature. the diffraction peak observed at 2θ angle of 32o corresponding to the (211) plane, was chosen for the calculation of the crystallites size, as the former peak can be isolated from other peaks and is relatively sharper than the others. the average crystallite diameter was calculated by using debye scherrer formula as reported elsewhere [12]:  = k/cosθ (i) where,‘ ’ is the average crystallite size (in nm), ‘k’ is the shape factor (k = 0.9 for most of the spherical crystallites), ‘λ’ is the wavelength of the x-rays (λ = 1.54056 å for cu k radiation), ‘’ is the full width at half maximum (fwhm) (in radian) and ‘θ’ is the bragg’s diffraction angle. table 1 compares the crystallite size of hap particles prepared by various methods. it can be seen that size of the crystallites prepared by different methods lies in the range of 15-30 nm. the hap synthesized by sol-gel method was found to have smallest crystallite size while the buffalo bone powder calcined at 1000 °c produced the largest crystallites. however, the size disparity is not too large. the bone calcined at 100 °c has produced the crystals slightly larger than that calcined at 700 °c. there might also be some other factors affecting the nano-crystal size during the synthesis. table 1: average crystallite size of hap prepared by various methods calculated using equation (i). s. no. methods 2θ (°)* crystallite size (nm) 1 sol-gel 32.668 14.80 2 precipitation 32.796 28.11 3 eggshell 32.647 17.51 4 bone (powder calcined at 700 °c) 32.748 18.06 5 bone (powder calcined at 1000 °c) 32.942 29.23 * 2θ values corresponding to (211) miller planes at around 32° for each sample 20 30 40 50 60 70 80 in te n s it y ( a . u .) 2 (degrees) (211) (002) (102) (112) (202) (310) (222) (213) (004) bone calcination (700 °c) bone calcination (1000 °c) 2 q (degrees) gokarna pandeyet al. / bibechana 18 (2021) 96-103 89 4. conclusions a comparative study on simple, inexpensive, and facile approaches for the synthesis of nano-hap has been presented. it has been demonstrated that the nano-hap with reasonably high crystallinity and purity can be prepared in an ordinary senior high school chemistry laboratory. among the methods presented, the procedure employed on the animal bone offers reliable, most cost effective and greener way of preparing the nano-hap with high degree of purity and yield. the ftir spectra of all hap samples showed typical peaks centered around 470, 560, 960, 1020 and 1090 cm-1 corresponding to phosphate groups of apatite phase. all the specimens showed the presence of adsorbed water (band 3200-3600 cm-1) and vibration of ohions (3570 and 1027 cm-1) in hap lattices. the presence of peak corresponding to carbonate ions (1426-1490 and 870 cm-1) revealed the presence of impurities that might not appear on performing the experiment under inert atmosphere. the xrd results showed that all the synthesized hap samples were fairly 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[37] s.v. dorozhkin, calcium orthophosphates as bioceramics: state of the art., j. func. biomaterials 31(2010)22-107. menuka shrestha et al. / bibechana 16 (2019) 221-227: rcost p. 221 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal quality of life of elderly people living with family and in old age home in morang district, nepal menuka shrestha1*, heera kc2, prem bhattarai3, anjali mishra4, surya b. parajuli4,5 1department of nursing, purbanchal university, college of medical and allied health sciences, gothgaun, nepal 2department of nursing, purbanchal university, birat health college, biratnagar, nepal 3department of physiology, kathmandu university, birat medical college & teaching hospital, tankisinuwari, nepal 4department of community medicine, kathmandu university, birat medical college & teaching hospital, tankisinuwari, nepal 5nepal medical volunteer society, biratnagar, nepal *e-mail: mennusb@gmail.com article history: received 16 september 2018; accepted 10 november 2018 http://dx.doi.org/10.3126/bibechana.v16i0.21643 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract introduction: nepal like many other developing countries in the world is witnessing the rapid ageing of population. quality of life (qol) of elderly people is becoming even more relevant towards an ageing society. in nepal, less is known regarding special needs and quality of life of elderly people either in familial situations or in old age residences. objectives: the present study was undertaken to assess and compare the quality of life of elderly living with the family and in old age home. methodology: a cross sectional descriptive study was conducted from october 2016 to april 2017 among elderly population aged 60 years and above. a total of 50 elderly people were enrolled from old age home (oah) using total enumeration sampling technique and equal number of sample was selected from the family setting. qol of elderly was assessed using whoqol-brief questionnaire after taking informed consent from the participants. data was analyzed using spss. results: the mean scores of qol domains were better among the age group 60-70 years, males, married, literates and who had children. the mean scores of qol in physical, psychological and environmental domains were better in elderly living with the family than living in oah. low scores were found on social domain among elderly compared to other domain irrespective of their residence. conclusion: qol score among elderly is average, while social relationship domain of qol scores was found to be low. social activities should be expanded for these residents in order to promote social health. the qol which each individual possesses is very important in all aspects be it physical, psychological, social & environmental. furthermore, programs that help elderly people live in their own homes and social environments should be promoted. keywords: humans; homes for the aged; quality of life. http://nepjol.info/index.php/bibechana mailto:mennusb@gmail.com http://dx.doi.org/10.3126/bibechana.v16i0.20960 https://creativecommons.org/licenses/by-nc/4.0/ menuka shrestha et al. / bibechana 16 (2019) 221-227: rcost p. 222 (online publication: dec., 2018) 1. introduction ageing is inevitable developmental facts that bring along a number of changes in the physical, psychological, hormonal and social status. most of these changes are expected to affect quality of life of the elderly [1]. one of the greatest challenges to public health is to improve the quality of later years of life as life expectancy continues to rise [2]. who defines the concept quality of life (qol) as ‘individuals’ perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns [3]. quality of life elderly people (qol) is becoming even more relevant with demographic shift happening towards an ageing population. there are signals that concerns related to qol in elderly people are different from that of other general population. in nepalese society, there is very low awareness about special needs of elderly and caretakers are yet to understand the vitals of elderly care (physical and mental, psychological and social needs). additionally, among elderly there is difference between those living in old age homes and those living in community [4]. nepal like many other developing countries in the world is observing the rapid ageing of people. the urbanization, modern character, tendencies and values and world integration have led to change in the weakening of social values, economic structure, the erosion of societal values, and social structure such as the joint family. in this changing economic and social environment, the younger age group is searching for new identities about economic independence and redefined social roles inside, as well as outside the family. the shifting economic structure has reduced the dependence of rural families on land which has provided strength to tie between generations [5]. the problem has broad social, economic, political and health implications and is viewed as a concern by many different people-administrators, health professionals and general public. care of the elderly is also one of the priority areas in nepal. the government of nepal has also recently adopted national policy on ageing since its 9th long-term plan. above all, not much research work has been carried out in this topic in nepal, though it is a topic of concern. we believe the research will help administrators and policy makers to plan and implement necessary changes to address the special needs of elderly. the main objective of this study was to assess and compare the quality of life of elderly living with family and old age home. 2. methodology this is a cross sectional study was carried out in an old age home at birateswhor bridhashram, biratnagar and home setting at sundar haraincha municipality from october 2016 to april 2017. total sample size was 100; 50 elderly people were taken from old age home using total enumeration sampling technique and equal number of sample was taken from the home setting. elderly people aged 60 years and above were included but those elderly who were suffering from mental illness were excluded from the study. data were collected through face to face interview method. informed consent was taken from each participant and ethical approval was taken from purbanchal university department of research. quality of life was measured with the validated world health organization quality of life instrument-brief version (whoqol-bref). it evaluates perceived quality of life using 26 items categorized into physical domain (7 items), psychological domain (6 items), social relations domain (3 items), and environment domain (8 items). two items evaluates perception of general health and quality of life. each item is ranked on a 5-point likert scale. higher scores indicate higher quality of life. the physical health domain includes items on mobility, daily activities, menuka shrestha et al. / bibechana 16 (2019) 221-227: rcost p. 223 (online publication: dec., 2018) functional capacity, energy, pain and sleep. the psychological domain measures include self-image, negative thoughts, positive attitudes, self-esteem, mentality, learning ability, memory concentration, religion, and the mental status. the social relationships domain contains questions on personal relationships, social support, and sex life. the environmental health domain covers issues related to financial resources, safety, health and social services, living physical environment, opportunities to acquire new skills and knowledge, recreation, general environment (noise, air pollution, etc.) and transportation. 3. results hundred elderly people participated in the study where 50 participants from oah and 50 from the family. more than half (52% and 58%) were in the age group 6070 years in the oah and in the family setting respectively. the mean age of the respondents living in oah was 70.42±8.33 years while the mean age of respondents living with the family was 71.08±8.08 years. majority of the respondents were male, hindus and brahmin/chhetri in both the places. in oah both male and female were more or less equal in number. in oah most of the respondents (70%) were widow/widower while in the family setup 72% of the respondents were married and living together with their spouses. there were no unmarried and separated persons in the family setup. most of the respondents (68%) were found to be illiterate in the family in comparison to those living in oah (20%). in oah, most of the respondents (74%) had children while in family setup all the respondents had children (table1). age is significantly associated with the physical domain as compared to other domain. as the age increases the mean qol scores were decreasing in other domains too but it was not found to be statistically significant. the mean qol scores of psychological and environmental domains were significantly less in females as compared to males. the mean qol scores of physical and social domains were also less among females. education and marital status were significantly associated with the physical, psychological and environmental domains of quality of life. significant association was found between the elderly who had the child and psychological and environmental domains (table 2). the mean scores and comparison of qol (domain wise) between elderly people living in old age home and within family setup. significant association was found in terms of physical, psychological and environmental health among elderly people living in old age home and within family setup at p value <0.001. the mean score of physical health between elderly people living with the family (21.88±4.37) was better than the elderly people living in old age home (16.50±4.11). also, the mean score of psychological health of elderly people living with family (20.80 ±3.8) was better than those living in old age home (12.82 ±3.15). it indicates that elderly people living with the family had better psychological health than elderly people living in old age home. similarly, the mean score of environmental health of elderly living with the family (26.18±3.52) was better than those living in old age home (20.64±3.63). the mean score of qol between elderly people living with family (79.08±11.16) was better than the elderly people living in old age home (60.06±10.70). it indicates that elderly people living with family had better qol than the elderly people living in old age home (table 3). menuka shrestha et al. / bibechana 16 (2019) 221-227: rcost p. 224 (online publication: dec., 2018) table 1: distribution of socio-demographic characteristics of elderly people (n=100). variable old age home (n=50) family (n=50) n (%) n (%) age in years 60-70 years >70years 26 (52) 24(84) 29(58) 21(42) mean age in years ± sd 70.42±8.33 71.08±8.08 gender male female 26(52) 24(48) 39(78) 11(22) caste/ethnic group dalit janajati madhesi brahmin/chhetri 8(16) 12(24) 6(12) 24(48) 1 (2) 18(36) 31(62) religion hindu buddhist 43(86) 7(14) 46(92) 4(8) marital status unmarried married widow/widower divorced/separated 3(6) 7(14) 35(70) 5(10) 36(72) 14(28) have children yes no 37(74) 13(26) 50(100) table 2: association of socio demographic characteristics with domains of qol scores (n=100). variable physical (mean ±sd) psychological (mean ±sd) social (mean ±sd) environment (mean ±sd) age 60-70 years >70years p value 20.75 (4.44) 17.29 (5.06) <0.001 17.04 (5.01) 16.53 (5.74) 0.641 10.29 (1.21) 10.00(1.39) 0.268 23.80 (4.14) 22.93 (4.94) 0.343 sex male female p value 19.62 (5.21) 18.40 (4.58) 0.25 18.08 (5.33) 14.46 (4.53) <0.001 10.31 (1.40) 9.89 (1.05) 0.122 24.51 (4.52) 21.37 (3.79) <0.001 education status illiterate literate p value 17.68 (4.63) 21.11 (4.87) <0.001 14.64 (4.70) 19.57 (4.82) <0.001 9.98 (1.13) 10.39 (1.46) 0.123 21.32 (3.97) 26.07 (3.73) <0.001 marital status unmarried married divorced separated p value 20.67 (4.93) 21.98 (3.70) 16.52 (4.92) 19.40 (2.19) <0.001 15.67 (1.52) 20.00 (4.01) 14.15 (5.27) 15.00 (0.70) <0.001 10.33 (0.57) 10.48 (1.40) 9.83 (1.22) 10.40 (.548) 0.117 20.67 (0.57) 25.66 (3.46) 21.67 (4.81) 22.00 (2.00) <0.001 religion hindu buddhist p value 19.33 (4.92) 18.09 (5.82) 0.444 16.99 (5.20) 15.36 (6.39) 0.343 10.16 (1.33) 10.18 (0.98) 0.95 23.64 (4.50) 21.55 (4.39) 0.148 have children yes no p value 19.47 (5.04) 17.31 (4.53) 0.148 17.38 (5.39) 13.00 (2.82) 0.005 10.18 (1.36) 10.00 (0.81) 0.637 23.97 (4.48) 19.69 (2.75) <0.001 menuka shrestha et al. / bibechana 16 (2019) 221-227: rcost p. 225 (online publication: dec., 2018) table 3: comparisons of domains of qol by their place of living (n=100) variable (qol domains) group p value old age home (n=50) mean ± sd family set up (n=50) mean ± sd physical (mean ±sd) 16.50±4.11 21.88±4.37 <0.001 psychological (mean ±sd) 12.82±3.15 20.80±3.87 <0.001 social relationship (mean ±sd) 10.10±1.01 10.22±1.54 0.647 environment (mean ±sd) 20.64±3.63 26.18±3.52 <0.001 total qol 60.06±10.70 79.08±11.16 <0.001 4. discussion the mean score was found higher in environmental (23.41±4.52) and physical domain (19.19±5.01) as compared to social (10.16±1.30) and psychological domain (16.81±5.33) of quality of life of elderly. overall mean score of qol was found to be good but mean score for social relationship and psychological domain was comparatively lower than other domains which are similar to the other study where the physical domain of quality of life had the highest mean score 14.3 (±2.7), while the social domain had the lowest mean score 10.8 (±3.4) [6]. another study conducted in india also reported lowest score in the social domain [7]. this could be due to the growing number of elderly that face abandonment and neglect. however, other studies have reported lower scores in the physical domain compared to other domains. [8, 9]. the study revealed that age was significantly associated with physical domain. this is because the older age group had more functional limitations compared to the younger age group. similar findings was found in a study which reported impaired physical health among older age groups [6]. as growing age increases the probability of developing physical problems like musculoskeletal problems, so age was significantly associated with physical domain. women had a significantly lower quality of life in all domains compared to men. this could be because the women perceive ageing more negatively than the men. other studies reported that low quality of life scores among women and recognized their findings to feelings of unattractiveness among elderly women, which could lead to low self-esteem and also add to negative perception of ageing among elderly women [9]. marital status was significantly associated with quality of life in this study except in social domain. this is perhaps because married residents live in their homes with their spouses in the home setting. previous studies reported contradictory findings [10]. level of education was significantly associated with the physical, psychological and environmental domains of quality of life. evidence from studies suggests that people with higher level of education are more likely to engage in healthy behaviors which could improve physical health compared to those with lower level of education [11]. in addition higher level of education can improve psychological spirit, coping mechanisms [12] and social relationships [13]. higher level of education also had higher scores in the environment domain of quality of life. previous studies [14] have reported significantly better quality of life among people with higher level of education compared to those with lower level or no education, further highlighting the positive impact of higher education on quality of life. the mean score of physical (21.88±4.37), psychological (20.80±3.87) and environmental (26.18±3.52) menuka shrestha et al. / bibechana 16 (2019) 221-227: rcost p. 226 (online publication: dec., 2018) health domain was found higher among the elderly living with family than those elderly living in old age home with physical (16.50±4.11), psychological (12.82±3.15) and environmental (20.64±3.63) health domain. this finding was supported by a study which revealed that institutionalized elderly showed low level of quality of life compared to non-institutional [15]. this finding is in contrast to the study titled “quality of life between elderly people living in old age home and within family setup” where physical, psychological and environmental domain mean score was reported high among elderly living in old age home than elderly living with family [16]. similar findings was found in previous study [17]. the total mean score of qol between elderly people living with family (79.086±11.16) was better than the elderly people living in old age home (60.06±10.70) at p value <0.001. it indicated that elderly people living with family had better qol than the elderly living in old age home which was contradicted with the previous study [18] which observed that people living in old age home had good qol. social health domain’s mean score was found lowest among qol domain in both places and it was not statistically significant with residence. similar findings were revealed by other studies done in rural area of south india7and tamilnadu [19] 5. conclusion qol score among elderly was average, while social relationship domain of qol scores was found to be low. the physical health, psychological health and environmental health domains of qol were better in the people living with family than the elderly living in old age home. qol of elderly decreases as the age increases. the social relation domain revealed very poor among elderly living in both places. the qol which each individual possesses is very important in all aspects be it physical, psychological, social & environmental. only if they have fulfillment in all these aspects of life they have a high qol. recommendations despite some limitations, this community based cross-sectional study gives valuable information on the qol and its associated factors among elderly population. health education related to activity and environmental modification as well as increase in the social relationship may help in improving the qol of elderly people. further analytical studies will help in understanding the association of factors influencing qol. additionally, programs that help elderly people live in their own homes and social environments should be developed. social activities should be diversified for these residents in order to compensate for their lack of freedom. limitation of the study small sample size is the limitation of study. under reporting of chronic diseases in elderly, which has impact on qol is another limitation. we could not include some factors like mental health status, complications of chronic morbid conditions of the elderly. acknowledgement we would like to acknowledge all respondents for their cooperation, time and participation. we appreciate director of birateswor bridhasram for granting the permission and cooperation during the study. we would also like to thank purbanchal university, department of research for financial support for the successful completion of this study. conflict of interest we declare no conflict of interest. menuka shrestha et al. / bibechana 16 (2019) 221-227: rcost p. 227 (online publication: dec., 2018) financial disclosure faculty grant received from research department of purbanchal university. references [1] j. singh dr, comparative study of quality of life in aged persons. indian j of applied research 4 (2014) 1-3. 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[19] v. praveen, a.m. rani, quality of life among elderly in a rural area, int j community med public health 3 (2016) 754-757. bibechana vol. 20, no. 1, april 2023, 92-102 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar properties of dust in the north-east part of perseus cloud within the open cluster ic 348 using data from iris and akari surakshya bhattarai1, madhu sudan paudel2, shiv narayan yadav3 ajay kumar jha1,∗ 1central department of physics, tribhuvan university, nepal 2department of physics, tri-chandra multiple campus, tribhuvan university, nepal 3department of physics, patan multiple campus, tribhuvan university, nepal ∗corresponding author. email: ajay.jha@cdp.tu.edu.np,astroajay123@gmail.com abstract in this work, we have studied the dust properties of the north-east part of perseus cloud having a size of 0.5o × 0.5o located at ra (icrs): 56.14o dec (icrs): +32.15o, within the open cluster ic 348, using iris and akari data. an isolated region of size 0.39o×0.23o in iris and 0.34o×0.16o in akari data is detected within it. the infrared fluxes extracted using aladin v11.0 are used to study the dust temperature and dust mass. the distance of the selected dust structure is calculated using gaia edr3, which is 309.98 pc. the infrared flux density is found to be increased for long-wavelength data. the average dust color temperature calculated from short-wavelength iris data is more than that calculated from long-wavelength akari data, which are 26.34 k±0.11 k for iris and 17.63 k±0.02 k for akari data. the mass of dust within the entire dust structure is 0.06 m⊙ for iris data and 37.44 m⊙ for akari data. jeans mass for isolated region gives contradictory results in two surveys, for iris survey total mass is smaller than jeans mass but for akari survey the total mass is larger than the jeans mass. a good correlation between infrared fluxes is noticed for linear regression. the study background sources observed from the simbad database explore the large number of stars, x-ray sources, ysos, etc., embedded within the dust structure; some of them are responsible for dust heating and some for the contribution of dust mass. the contour map shows the identical distribution between infrared fluxes, dust color temperature and planck’s function and dissimilar distribution between dust mass and visual extinction in iris and akari data. the high temperature at the central region suggests that the core of dust structure is thermally active, radiating the large thermal radiation in comparison to the outer region. keywords perseus molecular cloud, ic 348, iris, akari, dust color temperature, dust mass. article information manuscript received: november 22, 2022; accepted: april 4, 2023 doi https://doi.org/10.3126/bibechana.v20i1.49392 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 92 http://nepjol.info/index.php/bibechana ajay.jha@cdp.tu.edu.np, astroajay123@gmail.com https://doi.org/10.3126/bibechana.v20i1.49392 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ surakshya bhattarai et al./ bibechana 20 (2023) 92-102 93 1 introduction molecular clouds are the most important structure in the interstellar medium (ism) as they are the birthplace of the star. milky way galaxy has hundreds of known molecular clouds out of which perseus molecular cloud is one of the nearby giant molecular cloud (gmc) which extends at distance from 293 pc to 321 pc from us [1]. it occupies the size of 6o×2o in the perseus constellation and holds 104 m⊙ gas and dust [2]. most of the perseus molecular cloud is invisible in optical wavelength, only two parts; open cluster ic 348 and ngc 1333 are visible in optical wavelength, but it is bright at mid and far-infrared wavelengths due to the radiation coming from dust heated by a large number of young low-mass stars [3]. open cluster ic 348 is located in the northeast part of perseus cloud which contains the old stars in comparison to the west part. there is many research about the age of the ic 348. based on hα emission from the stars in ic 348 herbig(1998) [4] estimated the age between 0.7 to 12 myr [4]. luhman(1998) [5] declared that most of the stars in ic 348 are younger than 3 myr but some stars has been formed 10 myr ago [5]. in other research, muench(2003) [6] calculated the mean age of stars ∼ 2 myr with a fluctuation of ∼ 3 myr [6]. the variation of the age of stars in ic 348 indicates the two episodes of star formation. the smaller value of mean age represents the majority of younger stars which might have been formed due to the dissolved core of perseus cloud and the old age is the indication of low-mass stars from perseus ob2 association. due to the dominance of young stars a , huge emission due to dust in far-infrared wavelength is observed in ic 348 cluster [6]. the infrared wavelength is the most crucial electromagnetic radiation in the sense that it can explore those regions of the galaxy which is invisible for optical and other short-wavelength radiation. the interstellar dust is the least contributing component of ism by mass but is very important to control the heating and cooling mechanism including complex chemical processes. interstellar dust absorbs the uv and other energetic radiation and re-radiates the absorb energy in the form of infrared radiation. in this way, infrared wavelength is the way to explore the interstellar dust within the galaxy [7]. in past, many research has been performed exploring the properties of interstellar dust using the infrared data in the region near the pulsars [8, 9], white dwarfs [10,11], agb star [12,13], supernova remnants [14, 15], fir loops [16–18][, fir cavities [18, 19], isolated nebula [20], etc., using the data from iras, iris and akari. in this work, we have used the data from iris and akari to explore the properties of dust within the molecular cloud. the dust color temperature and dust mass of the region in the north-east part of perseus cloud within the ic 348 is calculated and possible physical processes are explained. 2 materials and methodology 2.1 data in this work, we have taken data from four different sources. the iris data [21] at 60 µm and 100 µm and akari data [22] at 90 µm and 140 µm are used to calculate and compare results. the fits images in both iris and akari surveys are downloaded from skyview virtual observatory (https://skyview.gsfc.nasa.gov/ current/cgi/query.pl) and infrared flux density is extracted using aladin v2.5 and v11.0 [23]. we used the gaia edr3 from gaia archive (https: //gea.esac.esa.int/archive) for the estimation of the distance to the dust structure. the simbad database (http://simbad.u-strasbg. fr/simbad/sim-fcoo) is used to study the background sources within the dust structure. 2.2 method 2.2.1 dust color temperature estimation the calculation of dust color temperature from the iris 60 µm and 100 µm flux densities is done following the wood et al. (1994) [24] and schnee et al. (2005) [25]. the final expression for the temperature for iris 60 µm to 100 µm data is, td = −0.96 ln(r× 0.6(3+β)) (1) where r is the ratio of the flux densities at 60 µm and 100 µm and β is the spectral emissivity index, which takes the value from 0 to 2 for different materials. in this work, we used the β=2 assuming the dust as the crystalline dielectric [26]. following the wood et al. (1994) [24], the equation (1) can be changed for akari 90 µm and 140 µm as given by; td = −0.57 ln(r× 0.64(3+β)) (2) 2.2.2 dust mass and jeans mass estimation we have followed the calculation of young et al. 1993 [27] and hildebrand 1983 [28] to estimate the dust mass. the dust mass depends on the physical and chemical properties of the dust grains, the dust temperature (td) and the distance (d) to the (https://skyview.gsfc.nasa.gov/current/cgi/query.pl) (https://skyview.gsfc.nasa.gov/current/cgi/query.pl) (https://gea.esac.esa.int/archive) (https://gea.esac.esa.int/archive) http://simbad.u-strasbg.fr/simbad/sim-fcoo) http://simbad.u-strasbg.fr/simbad/sim-fcoo) surakshya bhattarai et al./ bibechana 20 (2023) 92-102 94 object. the expression of dust mass is; md = 0.4 ( svd 2 b(ν, td ) (3) where sv= f(100 µm)×5.288 × 1029 kg s2 for iris = f(140 µm)×5.288 × 1029 kg s2 for akari, b(ν,td) is the planck’s function for blackbody radiation given by, b (ν, td) = 2hν2 c2 ( 1 e hv kbtd − 1 ) (4) where, the symbols have the usual meaning. the jean’s mass gives the critical mass of matter within the cloud that needed to trigger the star formation process within the molecular cloud. it depends on the average temperature, density and size of the cloud. once we know the size and temperature of the region we can calculate the density using [7]; ρ = ( 3 4π )2/3( kbtd mhgr2 ) (5) where, kb is the boltzmann constant, td is dust color temperature, mh is the mass of hydrogen g is the universal gravitational constant and r is the radius of the molecular cloud considering the spherical shape. the jean’s mass can be calculated using the formula [7]; mj = ( kbtd mhg )3/2( 1 ρ2 ) (6) 2.2.3 visual extinction the loss of the radiation by the process of scattering and absorption is called the extinction. dust are the vital component for the extinction in interstellar medium. the visual extinction refers the extinction of visible light coming from the star caused by the dust. following the wood et al. (1994) [24], the visual extension is given by; av = 15.078 1− exp −tλ 641.3  (7) where, tλ = f (λ)/b(v, td) is the optical thickness and is the infrared flux density at long wavelength (100 µm for iris and 140 µm for akari) in si unit, and represents planck function at long wavelength. 2.2.4 inclination angle the inclination angle is the angle made by the line of sight to the perpendicular of the plane of the dust structure. for the calculation of inclination angle, we use holmberg (1946) [29] formula given by, cos2 i =  ( b a )2 − q∗2 1− q(∗)2  (8) where a and b are the major to minor diameter and q* is the intrinsic flatness of the structure. the intrinsic flatness gives the information of internal morphology of the cloud. the value of intrinsic flatness is taken from 0.23 for molecular cloud [30]. 3 results and discussion 3.1 contour levels in fits image in this work, the fits image of the selected dust structure around open cluster ic 348 in perseus cloud located at ra (icrs): 56.14o, dec (icrs): +32.15o is processed in the aladin v2.5 and v11.0 software [23]. the data of infrared flux of all 0.5o × 0.5o sized regions is extracted from all fits images, 60 µm and 100 µm in iris and 90 µm and 140 µm in akari. also, we draw isocontours based on infrared flux in long-wavelength image (100 µm in iris and 140 µm in akari) to find the isolated region. in iris 100 µm image, the isocontour at level 42, named outer-42, with infrared flux 153.43±2.24 mjy sr−1 is the largest possible contour. the other isocontours are middle-93 with flux 292.85±6.69 mjy sr−1 and inner-171 with flux 507.29±10.29 mjy sr−1. in akari 140 µm image the isocontour at level 80, named as outer-80, with infrared flux 325.47±0.71 mjy sr−1 is the largest possible contour. the other isocontours are middle-18 with flux 489.30±1.20 mjy sr−1, inner–167 (up) with flux 570.90±1.93 mjy sr−1 and inner–167 (down) with flux 575.95±1.64 mjy sr−1. the dust structure with the contours levels, geometrical center, position of maximum and minimum flux and temperature and major and minor axis are shown in figure 1. 3.2 infrared flux density the infrared flux is the basic parameter in this work from which we have calculated the dust color temperature and dust mass. for the extraction of infrared flux, the iris images of size 20 pixel×20 pixel are used so that there are total 400 data. in akari data we use the image of size 100 pixel ×100 pixel so that there are 10,000 data. the flux density from all fits images (60, 100, 90 and 140 µm) are extracted using aladin v11.0 [23]. these values of infrared flux are used to calculate the dust color temperature and dust mass within the selected structure. the statistical details of infrared flux is given in surakshya bhattarai et al./ bibechana 20 (2023) 92-102 95 table 1. in iris 60 µm and 100 µm data the maximum value of flux is found at the same position but they have a different value. similarly, in akari 90 µm and 140 µm data the maximum and minimum values of flux are at the same position but with a different value. the position of extreme values of flux in iris and akari data are at the slightly different positions but they are very close to each other in all four wavelengths. the detail of maximum and minimum infrared flux at all wavelengths with their respective position is given in table 2. table 1: the table gives the statistical information of infrared flux in both iris and akari data. iris akari f(60 µm)(mjy sr−1) f(100 µm)(mjy sr−1) f(90 µm)(mjy sr−1) f(140 µm)(mjy sr−1) max. 460.42 642.52 792.59 859.97 min. 7.31 31.32 23.82 86.07 average 60.54 143.81 107.51 255.17 range 453.11 611.22 768.76 773.89 sd 77.70 120.25 105.62 143.32 se 3.88 6.01 1.06 1.43 table 2: the table gives the coordinate of maximum and minimum value of infrared fluxes and temperature observed in iris and akari data. survey quantity maximum value coordinate [ra, dec (icrs)] minimum value coordinate:[ra, dec (icrs)] iris f(60 µm) 460.42 mjysr−1 56.16o, +32.16o 7.31 mjy sr−1 56.42o, +31.91o f(100 µm) 642.52 mjy sr−1 56.16o, +32.16o 31.31 mjy sr−1 56.42o, +31.91o td 34.48 k 55.23o, +32.17o 23.10 k 56.32o, +32.02o akari f(90 µm) 792.59 mjy sr−1 56.15o, +32.15o 23.82 mjy sr−1 56.45o, +31.91o f(140 µm) 859.96 mjy sr−1 56.18o, +32.15o 86.07 mjy sr-1 56.45o, +32.11o td 25.94 k 56.16o, +32.17o 15.37 k 56.27o, +32.01o table 3: comparison of statistics of dust color temperature in total structure and isolated region in both iris and akari data. iris akari (td)total (k) (td)isolated (k) (td)total (k) (td)isolated (k) f(60µm)mjysr−1 f(100µm)mjy sr−1 f(90µm)mjy sr−1 f(140)mjy sr−1 max. 34.48 34.48 25.94 25.94 min. 23.10 24.04 15.37 15.55 average 26.34 28.68 17.63 19.54 range 11.37 10.44 10.57 10.38 sd 2.20 2.19 1.60 2.13 se 0.11 0.20 0.02 0.04 3.3 dust color temperature the dust color temperature of each pixel is calculated using the ratio of infrared fluxes at two wavelengths as suggested by equations (1) and (2) for both iris and akari data. we choose the value of β = 2 assuming the dust in the form of crystalline dielectric [26]. the region of maximum and minimum temperature are noted in both iris and akari data, which is presented in table 2. in iris data the dust color temperature varies from 34.48 k±4.07 k to 23.10 k±1.62 k with an average value of 26.34 k± 0.11 k and range 11.38 k±2.84 k. in isolated region within the outer–40 contour, the maximum, minimum, average and range of temperature are found to be 34.48 k±2.90 k, 24.04 k±2.32 k, 28.68 k±0.20 k and 10.44 k±2.61 k respectively. in akari data the dust color temperature varies from 25.94 k±4.15 k to 15.37 k±.13 k with an average value of 17.63 k±0.02 k and range 10.57 k±2.64 k. in isolated region within the outer–80 contour, the maximum, minimum, aversurakshya bhattarai et al./ bibechana 20 (2023) 92-102 96 table 4: the table presents the dust mass and gas mass within the whole structure and isolated region in iris and akari data. the last column includes the jeans mass within the. survey (md)total (mg)total (md)isolated (mg)isolated (mj) iris 1.11×1029 kg (0.06 m⊙) 2.22 ×1031 kg (11.14 m⊙) 5.00×1028 kg (0.03 m⊙) 1.00×1031 kg (5.03 m⊙) 1.49×1032 kg (74.90 m⊙) akari 7.45×1031 kg (37.44 m⊙) 1.49 ×1034 kg (7488.59 m⊙) 1.86×1031 kg (9.34 m⊙) 3.72×1033 kg (1871.82 m⊙) 8.13×1031 kg (40.90 m⊙) table 5: the different parameters related to the linear relationship between the two infrared fluxes in iris and akari data. quantity iris akari slope 0.63 0.67 y–intercept 29.49 64.20 r2 coefficient 0.94 0.83 average td 31.76 k 21.69 k age and range of temperature are found to be 25.94 k±3.20 k, 15.55 k±1.99 k, 19.54 k±0.04 k and 10.38 k±2.60 k respectively. in both data, large fluctuation of temperature in the whole dust structure as well as in the isolated region suggests that the region is highly affected by the external factor. 3.4 dust mass and jeans mass the dust mass is estimated by using equation (3). for the calculation of the mass, we need the distance to the dust structure. the dust structure is within open cluster ic 348 in the well-known perseus cloud. we have estimated the distance to the selected dust structure using the data from gaia edr3, which is found to be 309.98 pc. this is very close to the distance of the open cluster ic 348 from literature 315 pc [5]. we calculate the mass of the structure in each pixel. the sum of the masses of all the pixels gives the total mass of the dust within the structure. after calculating the dust mass, the mass of gas is calculated by using fact that the mass of the gas in ism is about 200 times greater than the mass of the dust [31]. using that concept to the mass gas within the structure is calculated. for the estimation of jeans mass, we need average size, density and average temperature. the average size of the structure is calculated by converting the angular dimension into a linear dimension using the relation, linear dimension = distance × angular dimension. it gives the major and minor diameters. the average radius of the isolated structure is 0.85 pc or 2.60×1016 m for the iris image and 0.68 pc or 2.08×1016 m for the akari image. this shows that the isolated region is smaller in the akari image. we use the average temperature of the isolated region 28.68 k for the iris data and 19.54 k for akari data. the density of the dust in the isolated region is calculated using equation (5), which is 2.02×10−18 kgm−3 for iris data and 2.14×10−18 kgm−3 in akari data. using all these values in equation (6), jeans mass (mj) is calculated using both iris and akari data, given in table 4. from the table, it is seen that almost half of the total mass is contained within the isolated region. for akari data the total mass is higher in comparison to iris data, this is due to the higher resolving capacity of the akari data. for iris data the, jeans mass is greater than the total mass of the gas but for the akari data, the jeans mass is less than the total mass of gas within the isolated region. this gives the contradictory result. however, it can be interpreted that in akari data the size of the isolated structure is small as well the average temperature is small in comparison to the iris data. this might be the possible reason that the isolated in akari data appears a possible starforming region whereas the isolated region in iris data is not the possible star-forming region. 3.5 relation between infrared fluxes the relation between flux density obtained from 100 µm and 60 µm in iris and 140 µm and 90 µm in akari is studied using linear regression. we plotted the flux at a long-wavelength (100 µm in iris and 140 µm in akari) towards x-axis and flux at a short-wavelength (60 µm in iris and 90 µm in akari) towards the y-axis. figure 2 shows the linear relation between infrared fluxes. the slope of the straight line gives the ratio of flux which can be used to estimate the average dust color temperature. table 5 shows the various information related to the linear plot. this average temperature is quite different from the average temperature estimated in table 3. this might be due to the large value of yintercept obtained in the equation. because, our exsurakshya bhattarai et al./ bibechana 20 (2023) 92-102 97 figure 1: figure shows the 0.5o × 0.5o size view of fits image in aladin v2.5 with center at ra (icrs): 56.14o dec (icrs): + 32.15o showing three contours along with the position of geometrical center, center of structure with maximum flux, minimum flux, maximum temperature, minimum temperature and contours levels in 100 µm iris image (a) and 140 µm akari image (b) within the open cluster ic 348 in the perseus cloud. figure 2: the graph shows the best fit linear relation between infrared flux density at two wavelengths. in graph, flux at 100 µm (iris) and 140 µm (akari) are taken along x-axis and flux at 60 µm (iris) and 90 µm (akari) are taken along y axis. the straight line shows the best fitted straight, r2 and m represents the regression coefficient and slope of the straight line. surakshya bhattarai et al./ bibechana 20 (2023) 92-102 98 table 6: the table presents the contour levels, major and minor diameter and inclination in both iris and akari data. there are three contours in iris data and four contours in akari data. iris akari contours a (arcmin) b (arcmin) i (deg) contours a (arcmin) b (arcmin) i (deg) outer-42 23.59 13.80 56.48 outer-80 20.30 9.67 64.65 middle-93 18.89 9.18 63.94 middle-138 14.93 6.69 66.76 inner-171 8.57 4.80 58.38 inner–167 (up) 6.78 5.12 42.37 —inner–167(down) 6.72 2.12 77.22 figure 3: the figure shows the contour map for infrared flux at 60 µm (a), infrared flux at 100 µm (b), dust color temperature (c) planck’s function (d), dust mass (e), and visual extinction (f). in all figure ra taken is along x axis, dec is taken along y – axis and all these quantities are represented by color bar. the lines represents the isocontours for respective quantities. pectation was the equation in the form of y = mx, a straight line passing through the origin. however, the regression coefficient shows a very good correlation between the data. 3.6 contour map the variation of intensity of infrared fluxes in two wavelength, dust color temperature, planck’s function, dust mass and visual extinction is studied using a contour map as is shown in figure 3. in the contour map, it is seen that the distribution of infrared flux density is very much similar to each other in both iris and akari data. the infrared flux density for long wavelengths (100 µm in iris and 140 µm in akari) is greater than the infrared flux density at short wavelength (60 µm in iris and 90 µm in akari). in all wavelengths the infrared flux density is high towards the central region and low towards the lower-left corner. the intensity of infrared flux decreases gradually from the center towards the outer region in all wavelengths. on the other hand, the contour map of dust temperature and planck’s function are similar to each other in both iris and akari data. this is because planck’s function is simply a function of temperature at a particular wavelength. furthermore, it shows that the temperature, as well as the thermal radiation intensity, is maximum at the central region. this suggests that the central region is thermally active in comparison to the outer region. the lower left region is most thermally stable. the contour map of dust mass and visual extinction is similar. the distribution pattern is slightly different in iris and akari data. which might be due to the difference in the resolution of the image. this similarity indicates that the thick dust can cause more visual extinction. the mass distribution shows that the dust is concentrated in the lower belt, especially in the lower right regions in comparison to the other regions. 3.7 simbad background sources the background objects around the dust structure are studied using the simbad database (http: //simbad.u-strasbg.fr/simbad/sim-fcoo). there are 2665 sources in the square region of size 0.5o×0.5o within the dust structure. the maximum number of objects are star, young stellar objects (yso), x-ray source, t tauri star, variable star of orion type, sub-millimetric radio source, part of the cloud, etc. there are many other sources which are less in number but they are very important (http://simbad.u-strasbg.fr/simbad/sim-fcoo) (http://simbad.u-strasbg.fr/simbad/sim-fcoo) surakshya bhattarai et al./ bibechana 20 (2023) 92-102 99 figure 4: the figure shows the contour map for infrared flux at 90 µm (a), infrared flux at 140 µm (b), contour map for dust color temperature (c), planck’s function (d), dust mass (e) and visual extinction (f). in all figure ra taken is along x axis, dec is taken along y axis and these quantities are represented by color bar. the lines represents the isocontours for respective quantities. for contributing the dust mass within the structure under study. the mass of the dust is higher within the lower belt of the structure and maximum in the lower right portion. in this region the ism components, such as; part of cloud, dense core, sub-millimetric radio source, radio source, herbigharo object, infrared source, far–infrared sources are presented densely, as shown in figure 5. 3.8 gaussian plot the gaussian distribution with histogram is used to study the normal behavior of the distribution of dust color temperature and dust mass within the dust structure. in figure 6 we can see the gaussian distribution of dust color temperature and dust mass with a histogram. it is seen that for dust color temperature the gaussian distribution is very close to the normal distribution. but for dust mass, the gaussian distribution deviates from the normal distribution. this shows that the distribution of dust color temperature is more symmetric than the dust mass. the slight deviation of the gaussian distribution of dust mass from the normal distribution might be due to the presence of ism sources, such as; dense core, part of the cloud, radio (sub-mm) source, etc., present in the lower belt of the dust structure observed in the simbad database. 3.9 inclination angle for the calculation of inclination angle, we have calculated the major and minor axis of all contours using aladin v2.5. figure 1 shows the aladin v2.5 view of the fits image with three-level contour and major and minor diameter for the outermost contour. the major and minor diameters for the other contours are not shown in figure 1. the inclination angle is calculated using equation (8). for iris data, the inclination angle first increases from outer-42 to middle-93 and decreases from middle93 to inner-171. in akari data, there is a similar fluctuation observed in inclination angle from outer to inner contours. both data indicate that the isolated region is non-uniform and irregularly distributed in the morphological point of view. also, the value of inclination angle for outer contour indicates the isolated region is edge-on in both iris and akari data because i > 45o. the brief information about the major axis, minor axis and corresponding inclination angle for all contours in both iris and akari data are presented in table. 6 below. 4 conclusion in this work, the infrared flux, dust color temperature and dust mass of the dust structure around open cluster ic 348 in perseus cloud, located at ra (icrs): 56.14o, dec (icrs): +32.15o is studied. following are the major conclusions of this work; • the size of the dust structure is 0.5o×0.5o, which consists of an isolated dust region of size 0.39o×0.23o in iris and 0.34o×0.16o in akari data. the size of the isolated region is smaller in akari data. • the average and minimum value of infrared flux density are increased from shortwavelength to long-wavelength but this trend is violated for maximum value. • the average dust color temperature of dust surakshya bhattarai et al./ bibechana 20 (2023) 92-102 100 figure 5: the objects within the background of the dust structure which might be responsible for the contribution of dust mass are shown in the figure. the contours are same as the isocontour for dust mass in akari data. in the figure region in which the density of these objects is more the mass of dust is found higher, especially in akari data. structure is found 26.34 k±0.11 k in iris and 17.63 k±0.02 k for akari data. the low temperature in long-wavelength region is according to the wien’s displacement law. • the study of contour map shows the distribution between infrared fluxes in all wavelengths, and temperature and planck’s function in both iris and akari data are similar. the contour map of planck’s function shows that the intensity of thermal radiation is maximum at the central region. • the central part of the isolated region is hotter than the outer region representing the central region is thermally active and the outer region is thermally stable. the lower left region is thermally most stable. • contour map of dust map and visual extinction shows an identical distribution representing that the dense dust causing more extinction. however, a clear difference is observed between iris and akari data. • the distance of the dust structure is estimated using gaia edr3, which is found to be 309.98 pc. this value of the distance is very close to the distance of the open cluster ic 348 from the literature. • the study of background sources in the simbad database explores the objects which might be responsible for the contribution of dust temperature and dust mass within the dust structure. • the total mass of gas in isolated structure is found more in akari data (3.72×1033 kg) than in iris data (1.00×1031 kg). the jeans mass for the isolated structure is 1.49×1032 kg for iris data and 8.13×1031 kg for akari data. this indicates that the structure formation via gravitational collapse is possible according to akari data only. • the gaussian distribution is very close to the normal curve for dust color temperature slight deviation from the normal curve for dust mass. this might be due to the asymmetric distribution of ism sources, such as; dense core, part of cloud, radio (sub-mm) source, etc., which are observed in the simbad database. • the study of inclination angle shows that the isolated region within the dust structure is edge-on in both data. also, the isolated region is non-uniform and irregularly distributed from the morphological point of view. acknowledgments we acknowledge central department of physics, tribhuvan university, nepal, tri-chandra multiple campus, tribhuvan university, nepal and patan surakshya bhattarai et al./ bibechana 20 (2023) 92-102 101 figure 6: gaussian distribution for dust color temperature and dust mass in isolated region of both iris and akari data. m. campus, tribhuvan university, nepal for providing the academic environment. we are also grateful to the sky view virtual observatory, simbad, iris, akari, 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[31] t. henning and h. mutschke. lowtemperature infrared properties of cosmic dust analogues. astronomy and astrophysics, 327:743–754, 1997. introduction materials and methodology data method dust color temperature estimation dust mass and jeans mass estimation visual extinction inclination angle results and discussion contour levels in fits image infrared flux density dust color temperature dust mass and jeans mass relation between infrared fluxes contour map simbad background sources gaussian plot inclination angle conclusion bibechana 18 (1) (2021) 140-148 140 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal thermal properties of normal and sickled hemoglobin protein jhulan powrel1,2, narayan p. adhikari2* 1department of physics, butwal multiple campus, tribhuvan university, nepal 2central department of physics, tribhuvan university, kirtipur kathmandu, nepal *email: narayan.adhikari@cdp.tu.edu.np article information: received: june 29, 2020 accepted: august 2, 2020 keywords: thermodynamic properties sickle cell molecular dynamics hemoglobin protein abstract thermodynamic properties of sickled and normal hemoglobin protein are considered within the framework of classical molecular dynamics. here we have studied the specific heat capacity and rmsd (root mean square deviation) of both types of hemoglobin protein. our investigation reveals that the specific heat capacity and rmsd for oxygenated hemoglobin protein is higher than those of de-oxygenated sickle hemoglobin protein. it is also observed that the specific heat capacity and rmsd values of sickle hemoglobin protein decrease with rise in temperature. doi: https://doi.org/10.3126/bibechana.v18i1.29750 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction hemoglobin is the blood component consisting of heme and globin, where heme is the prothestic group containing iron and globin is the protein compound. it is responsible for the transportation of oxygen throughout the human body. heme is synthesized by mitochondrion which is fixed with iron. heme is protected by the surrounded globin protein. each single hemoglobin molecule has two globin chains, one globin chain is α and the other is β. two hemoglobin molecules combine to produce a functional tetramer. in inherited hemoglobin the amino acid sequence is changed because of the incorrect dna code (hbs). such a cell having abnormality is a sickle cell. sickle cell disease is the genetic disorder in which sudden change of hemoglobin protein occurs. the glutamic acid of both the β chain in the sixth position of normal hemoglobin protein is replaced by valine in the sickle hemoglobin which is shown in figure 1. as a result rbc changes from flexible bi-concave to strong elongated shape. thus by carrying less oxygen, the hemoglobin becomes fibrous aggregations giving the entire red blood cell a sickle shape. sickled hemoglobin protein (hbs) damages the sickle erythrocyte and causes the increase http://nepjol.info/index.php/bibechana mailto:narayan.adhikari@cdp.tu.edu.np mailto:ari@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v18i1.29750 https://creativecommons.org/licenses/by-nc/4.0/ jhulan powrel, narayan p. adhikari/ bibechana 18 (1)(2021) 140-148 141 in the density, reduction in the deformability and increase in the adhesivity which shortens the life span [1-3]. the polymerization of deoxygenated hemoglobin (hbs) is the primary and indispensable event in the molecular pathogenesis of sickle cell disease. there are many symptoms like the attacks of pain, sickle cell anemia, swelling in the hands and feet, bacterial infections and stroke. longterm pain may develop as people get older because of sickle cell anemia. on the other hand, heterozygote for the sickle gene are relatively protected against the danger of dying by malaria, as now firmly established through a number of clinical field studies from different parts of africa and asia(terai region of nepal)[4]. figure 2(a) shows the glutamate 6 of α chain in hemoglobin protein which is undergoes a mutation to valine. this mutation changes the charge on the surface of hemoglobin. the mutant protein is called sickle cell hemoglobin (hbs). valine residue 6 of the β chain of deoxy-hbs lies on the surface of the protein. this hydrophobic residue, present in each of the β chain, forms a hydrophobic contact in the neighboring β chain of another hemoglobin molecule [1, 6]. figure 2(b) shows the mutation that replaces a glutamate residue by a valine residue which reduced the solubility of the protein. luzzatto l. studied the structural abnormality of sickle hemoglobin (hbs) and noticed as this was the first time that a single amino acid replacement in a protein causes a serious disease [7]. a group of scientists, stradner and fig. 1: normal (glu) and sickle cell (val) hemoglobin [5]. co-worker studied molecular dynamical simulations [1] and developed the concept of the study from soft matter physics to complex protein mixtures [8].a potential antisickling drug is still to be discovered [9] as per pathophysiological study in the last 100 years of sickle cell disease. another group, xianqiao wang and rodney d. developed a virtual mechanical model for determining the mechanical and thermal behavior of different soft matter by using the steps of optimization of energy, making of equilibration in the system and production run [10]. an electrochemistry based study designed a technique to control and monitor the polymerization of sickle-cell hemoglobin (hbs) by looking the change in turbidity during the depletion of oxygen in a small volume of custom-built thinlayer electrochemical cell. the cell allowed the investigation of hbs polymerization as a function of hbs concentration, temperature and solution ph [11]. due to bad impact of sickle cell disease, this research work got attention on the study of thermal and transport property of sickle hemoglobin and normal hemoglobin protein. literature review also reveals that the mechanical, thermal and transport properties of normal hemoglobin and sickle hemoglobin protein around human body temperature (310 k) are not studied yet. the paper is organized with methods and methodology part in section 2, computational simulation part in section 3, results with discussion in section 4 and finally the conclusions at the last. jhulan powrel, narayan p. adhikari/ bibechana 18 (1)(2021) 140-148 142 fig. 2: (a) normal hemoglobin with glutamic acid in 6th position of beta chain (left) and (b) sickle hemoglobin protein with valine in the 6th position of beta chain (right). 2. methods and methodology theory in molecular dynamics (md), a hemoglobin protein molecule is considered inside the water for simulation. protein is the combination of a number of atoms which behaves as pair-wise interaction in between two atoms in the molecule [12]. each pair of atoms is interacted by bonded and nonbonded potentials. the molecular dynamic simulation calculates the motion of the atoms in molecules using newtonian dynamics. in standard molecular dynamics simulations the forces may come from classical inter atomic potentials [13]. the non-bonded van der waals and electrostatic are the interactive forces among the particles in the hemoglobin molecules. the total potential is obtain as, vtotal = [vbonded] + [vnonbonded] (1) or, vtotal = [vbond + vangle + vimproper + vproper] + [vlj + vcoloumb] (2) now the bond stretching potential is given by, (3) where b ijk force is constant, ijr is separation between the two bounded particles and ijb is the equilibrium bond length. again the bond angle potential is written as, )4()( 2 1 )( 20 ijkijkijkijangle kv   −= where ,ijk 0 ijk and  ijkk are the bond angle, equilibrium bond angle and the force constant respectively. now the improper dihedral potential energy is, )5()( 2 1 )( 2 0  −= ijklijklimproper kv where 0 is the equilibrium improper angle and k is the constant. similarly the dihedral potential is, )6())cos(1( 2 1 )( sijklijklproper nkv   −+= where ijkl is the proper dihedral angle, s is an angle at which the potential is maximum, n is the multiplicity and k is the barrier height. ( ) . 2 1 )( 2 ijijij b ijbond brkrv −= jhulan powrel, narayan p. adhikari/ bibechana 18 (1)(2021) 140-148 143 although lennard-jones potential(l-j) is not suitable for system where strong localized bonds may form (as in covalent system) or there is a delocalized electron sea where the ions remain (as in metals), the l-j potential helped us to understand basic points in many areas of condensed matter physics. the l-j potential for interaction between a pair of atom is given by [14], )7(4 612               −      = rr vlj   where ε is the depth of the attractive well, σ refers to the inter-particle distance and defines the strength of the interaction where the potential changes sign and r defines the length scale. the coulomb electrostatic interaction between two point charges qi and qj is defined by coulomb potential as, )8( 4 2r qq v m ji coloumb  = root mean square deviation (rmsd): rmsd is the level of equilibration and gives the deviation of the molecules from the defined position in space. it also gives the idea of occurrence of the reaction in chemical bonding. the larger the deviation from mean position less will be the stability of the system. rmsd values are calculated for all atoms of the hemoglobin protein backbone for the entire protein and for the protein excluding the last five residues[15] , which is the numerical measure of the structural difference of two states given by, ( ) ( ) ( ) )9( 2 1 t jj n j n trtr trmsd       − = =   with ( ) ( ) )10( 1 1 j n j t j tr n tr t  == where nα is the number of atoms whose positions are compared, nt is the number of time steps over which atomic positions are compared, →−rα(tj) is the position of atom α at time tj and ( )jtr is the average value of the position of atom to which the positions →−r α(tj) are being compared[15]. specific heat capacity: the specific heat capacity is the amount of heat required for raising the temperature of an object per degree of temperature increase per unit mass. thus in canonical ensemble the specific heat capacity is [16], )11( tk 2 b 22 bb v ee c − = where 2 be is square of the average of the total energies and 2 be is the average of the square of the total energy and bk the boltzmann constant. 3. computational details the proposed research is designed for working in theoretical computational method using molecular dynamics. hemoglobin protein of sickle and normal cell are obtained from the rcsb (research collaboratory for structural bioinformatics).org in pdb (protein data bank) form and then simulation is completed using namd (nano scale molecular dynamics) and vmd (visual molecular dynamics) software by following the steps of structure making, energy minimization and making of equilibration in the system. after performing various simulation steps the output data are used for the calculations of rmsd and specific heat capacity of both of the hemoglobin protein. for this simulation six systems are designed with four molecules which are then solvated with water using charmm force field (charmm 36) under following parameters: a system of oxygenated hemoglobin protein (a3n) with 4546(without water) atoms under the interaction of the bond potential and nonjhulan powrel, narayan p. adhikari/ bibechana 18 (1)(2021) 140-148 144 bonded potential inside a box with cut off distance of 12.0 å, pressure of 1 bar and temperature 310 k. a system of oxygenated hemoglobin protein(e83) with 19167(without water is 4668) atoms under the interaction of the bond potential and non-bonded potential inside a box with cut off distance of 12.0 å, pressure of 1 bar and temperature 310 k. a system of oxygenated hemoglobin protein(uvx) with 1863 atoms under the interaction of the bond potential and nonbonded potential inside a box with cut off distance of 12.0 å, pressure of 1 bar and temperature 310 k. similarly, for other three systems of sickle hemoglobin protein(hbs) there are 9112 atoms in each and interacting at the same potential as before with pressure at 1 bar, cut off distance of 12.0 å and at temperatures of 305 k, 310 k and 315 k. after equilibration of all the above six system they are energetically minimized at their corresponding constant temperature which provides their rmsd values. at last systems are further modified for nve and nvt simulation run in which we use the temperature coupling feature of namd to set the temperature of the molecules in the outer layer of the sphere to 300 k, while the rest of the bob is set to temperature of 330 k. 4. result and discussion present work was to study the rmsd as well as specific heat capacity of normal and sickle hemoglobin protein. the rmsd was calculated using the equation (9). we plotted the rmsd of hemoglobin protein against the time steps as follows; where figure 3(a) and 3(b) indicates the graph of root mean square deviations of oxygenated sickle hemoglobin protein and de-oxygenated hemoglobin protein at temperature of 310 k and obtained the rmsd as 0.8 å and 1.25 å respectively. they were found to be inc reased initially with small fluctuation and then remain constant for both at various values, i.e. the rmsd of deoxygenated hemoglobin found to be higher than of oxygenated sickle hemoglobin protein. rmsd plot of other system of hemoglobin protein were also plotted where figure 4(a) and 4(b) indicates the root mean square deviations of oxygenated hemoglobin protein and sickle hemoglobin protein at temperature of 310 k. for which the rmsd found to be increased initially with small fluctuation and then remain constant for both at various values of 1.3 å and 0.75 å respectively, i.e. the rmsd of oxygenated hemoglobin is higher than of sickle hemoglobin protein. similarly, rmsd for sickle hemoglobin protein at various temperatures were studied, where figure 5(a) and 5(b) indicating the root mean square deviations of sickle hemoglobin protein at 305 k and 315 k respectively. they are increased initially with small fluctuation and then remain constant for both at various values of 1.5 å and 1.4 å respectively i.e. the rmsd of sickle hemoglobin protein at lower temperature is higher than of sickle hemoglobin protein at higher temperature. the above figure 3(a), 3(b), 4(a) and 5(a), are the rmsd graph at 310 k for carbon monoxy-hemoglobin(s), deoxygenated hemoglobin protein, truncated heme-ligand hemoglobin and sickle hemoglobin protein respectively. correspondingly their rmsd were estimated as 0.8 å, 1.2 å, 1.3 å and 0.75 å, i.e. the rmsd of sickle hemoglobin is least(0.75 å) and of truncated ligand hemoglobin is maximum(1.3 å). thus, deoxygenated sickle hemoglobin with fibrous nature shows least deviation from the mean position, whereas of truncated ligand hemoglobin with large no of hydrogen bond and hydrophobic potential move faster with more rmsd value. similarly normal oxygenated and deoxygenated hemoglobin jhulan powrel, narayan p. adhikari/ bibechana 18 (1)(2021) 140-148 145 3 have their rmsd 1.3 å and 1.25 å respectively which are higher than both the oxygenated (0.8 å) and deoxygenated sickle hemoglobin (0.75 å). again at temperatures of 305 k, 310 k and 315 k (figure 4(b), 5(a) and figure.5 (b)) of deoxygenated sickle hemoglobin (hbs) [17] the rmsd are 1.5 å, 0.75 å and 1.4 å respectively. figure 6(a) and 6(b) are energy fluctuation and energy distribution graph during nve and nvt run. they gives the energy deviation from the mean [fig 6(a)] and energy distribution pattern [fig 6(b)] i.e. more the energy more is the velocity as well as temperature of the system of particles and hence system of protein behaving as thermometer. computationally by using namd code the average of square of the total energies and square of the average total energy of de-oxygenated hemoglobin protein(e83) were obtain as 6722047.08 kcalmol−1 and 6714152.23 kcalmol−1 respectively. on using these values the specific heat capacity of de-oxygenated hemoglobin protein was estimated as 2903 jkg−1c−1 (table 1). now for the calculation of specific heat capacity (cv), we have used the following theoretical and simulation parameters under the assumption of classical molecular dynamics: kb=0.00198657 kcal /molk, σ ∼ 8 k, t=317 k, j=1.43846 ×1020 kcal/mol. the specific heat capacity of normal and sickle hemoglobin protein were calculated by using the equation (11) and are tabulated in table 1 and table 2 for all the six systems. the average specific heat capacity of sickle hemoglobin 67.1906 3 122719662527 ( = ++ j/kg-c [table 1]) was less than of normal hemoglobin's (3587 j/kg-c, 2903 j/kg-c and 3204 j/kg-c) [table:2]. fig. 3: (a) rmsd graph of oxygenated sickle hemoglobin protein (left). (b) rmsd graph of deoxygenated hemoglobin protein (right). jhulan powrel, narayan p. adhikari/ bibechana 18 (1)(2021) 140-148 146 fig. 4: (a) rmsd graph of oxygenated hemoglobin protein (left). (b) rmsd graph of sickle hemoglobin protein (right). fig. 5: (a) rmsd graph of sickle hemoglobin protein at 305 k (left). (b) rmsd graph of sickle hemoglobin protein at 315 k (right). fig. 6: (a) energy flocculation of de-oxygenated hemoglobin protein (b) maxwell energy distribution for de-oxygenated hemoglobin protein. jhulan powrel, narayan p. adhikari/ bibechana 18 (1)(2021) 140-148 147 table 1: for normal and sickle cell hemoglobin protein at 310 k of temperature. for rmsd(å) cv(jkg−1c−1) oxygenated sickle hemoglobin protein) 0.8 3587 de-oxygenated hemoglobin protein 1.25 2903 oxygenated hemoglobin protein 1.3 3204 sickle hemoglobin protein(2hbs) 0.75 1966 table 2: for sickle cell hemoglobin protein (2hbs) at different temperature. for temp.(k) rmsd(å) cv(jkg−1c−1) sickle hemoglobin protein(2hbs) 305 1.5 2527 sickle hemoglobin protein(2hbs) 310 0.75 1966 sickle hemoglobin protein(2hbs) 315 1.4 1227 5. conclusion and concluding remarks the rmsd of normal and sickle hemoglobin protein was calculated within 0.75 å to 1.5 å which indicates that the proposed system is in the valid range(< 4 å) for molecular dynamical study. this study also reveals that the hbs at 305 k is most unstable (rmsd=1.5 å) among the considered system. the rmsd and specific heat capacity (cv) of de-oxygenated hemoglobin protein at 310 k are estimated as 1.25 å and 2903 j/kg-c [table 1] respectively. it also obvious that the de-oxygenated hemoglobin protein (average value=1906.67j/kg-c) has lower specific heat capacity than oxygenated (first three cv of table 1). it shows that at higher (315 k) temperature above 310 k the rmsd of sickle hemoglobin protein is increased due to less polymerization (sickling) of protein but increased in rmsd at lower temperature (305 k) is still not understood. we found essentiality of additional research work on the free energy calculation along with the mechanical and transport properties of sickle hemoglobin protein for its depth knowledge. acknowledgments jp acknowledges ugc, nepal for providing financial support (grant no. s&t-13-75/76) and butwal multiple campus, butwal (tribhuvan university) for providing ph. d. leave. this work is also under the grant of ugc, nepal for which npa acknowledges the ugc award no. crg-73/74-s&t-01. references [1] a. stradner et al, new insight into cataract formation â enhanced stability through mutual attraction, physics department and fribourg center for nanomaterials, university of fribourg, ch1700 fribourg, switzerland (2007). jhulan powrel, narayan p. adhikari/ bibechana 18 (1)(2021) 140-148 148 [2] w. a. eaton and j. hofrichter, sickle cell hemoglobin polymerization, advances in protein chemistry 40 (1990) 63-279. http://doi.org/10.1016/s0065-3233(08)60287-9. [3] f. ferrone, r. l. nagel, sickle hemoglobin polymerization. in: disorders of hemoglobin: genetics, pathophysiology, clinical management, steinberg mh, for get bg, higgs d, nagel rl (eds), cambridge university press (2000). [4] luzzatto, lucio., sickle cell anaemia and malaria, mediterranean journal of hematology and infectious diseases (4)1 (2012) e2012065. http://doi.org/10.4084/mjhid.2012.065. [5] d. c. rees, t. n. williams, m. t. gladwin, sickle-cell disease, the lancet 376(9757) (2010) 2018-2031. [6] j. robert, j. ouellette, david rawn, organic chemistry (second edition) structure, mechanism, synthesis (2018) pp. 929-971. [7] w. d. callister, materials science and engeenering, an introduction, john wiley sons.inc. us, (2007). [8] retrieved sept. 22th, 2018 from www.google.com/sickle cell anemia. 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[14] d. frenkel, b. smit, understanding molecular simulation from algorithms to applications 2nd ed; academic press; san diago, usa (2002). [15] c. james phillips, rosemary braun, wei wang, james gumbart, emad tajkhorshid, elizabeth villa, christophe chipot, robert d. skeel, laxmikant kale, and klaus schulten. scalable molecular dynamics with namd. journal of computational chemistry 26 (2005)1781-1802. www.ks.uiuc.edu/training/tutorials(retrivedonju ne10th2020 [16] k. huang, statistical mechanics, john wiley & sons, new york (1987). [17] j. c. phillips et al., scalable molecular dynamics with namd, j. comp. chem. 26 (2005) 17811802. http://www.google.com/sickle http://www.ks.uiuc.edu/t http://www.ks.uiuc.edu/t bibechana 19 (1-2) (2022) 97-101 97 structural and electronic properties of intercalated transition metal dichalcogenides compounds vandana b. parmar*, aditya m. vora+ department of physics, university school of sciences, gujarat university, navrangpura, ahmedabad 380 009, gujarat, india email: *vandanaparmar3996@gmail.com +voraam@gmail.com article information: received: december 31, 2021 accepted: january 30, 2022 keywords: density functional theory (dft) generalized gradient approximation (gga) quantum espresso code intercalated compound abstract the structural and electronic properties of transition metal dichalcogenides compound (tmdc) tis2 and its intercalated compound like fetis2 are reported in the present work using density functional theory (dft). the generalized gradient approximation (gga) with ultra-soft pseudopotential are used under quantum espresso code. from the theoretical data, it is concluded that, the energy band structure of the tis2 material has been a small indirect band gap and possess a semiconductor characteristic, while the doped intercalated compound like fetis2, the energy bands are overlapped in the fermi region, which possess metallic characteristics. also, fetis2 is a ferromagnetic material with spin up and spin down nature observed from the band structure data. doi: https://doi.org/10.3126/bibechana.v19i1-2.46397 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction studies of transition metal dichalcogenides compound (tmdc) have shown considerable attention during last many years. layered transition metal dichalcogenides (ltmcds) have applications in various areas including lubrication, catalysis, photovoltaics, supercapacitors, and rechargeable battery systems [1]. hence, the dimensionality of tmdc are also plays a significant role in their basic physical properties [1]. the study of structural and electronic properties of material gives a basic understanding of the materials [2]. fang et al. [3] have reported ab initio band-structure based calculations for bulk, single slab, and thin films of tix2 (x=s, se) using the localized spherical wave method. the density functional theory (dft) based formulation are found more useful for computing the structural and electronic properties of materials [4-11]. the guest 3d atom have transferred the charge from transition metal fe-atom to the self bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:vandanaparmar3996@gmail.com mailto:vandanaparmar3996@gmail.com mailto:%2bvoraam@gmail.com https://doi.org/10.3126/bibechana.v19i1-2.46397 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana bibechana 19 (1-2) (2022) 97-101 98 intercalated compound like tis2 reported by friend and yoffe [12]. the generalized chemical formula for tmdcs is mx2, where m represents the transition metal of group iv, v and vi of the periodic table and x is the chalcogens element. therefore, the tmdcs have shown more than 40 different combinations and have shown distinctive properties too. generally, in tis2, the layer of ti atom is sandwiched between two sulphur layers. both atoms are attracted with very weak van der wall’s force and having a very small indirect bandgap between them. because of this, the guest fe atom can be easily intercalated into pure tis2 compound. hence, the fe-s bonds are much stronger than the ti s bonds in such fetis2compound [13]. in both materials, the strong hybridization occurs in the 3d-states of fe, 3d-states of ti and 3p-states of s, respectively [14-19]. in electronic property calculation,the fetis2 has a spin polarized fully relativistic band structure. in which, the energy bands of tis2 are not overlapped near the fermi region while in the case of thefetis2, they are overlapped near the fermi region. according to this, the tis2 has a semiconductor nature while fetis2 has a metallic nature. 2. computational methodology all the calculations of structural and electronic properties are performed under dft environment by using quantum espresso code [20] with burai [21] in our computational laboratory. the structural optimization and the electronic properties such as band structure, density of states (dos), partial density of states (pdos) and total density of states (tdos) of the aforementioned materials are reported using generalized gradient approximation (gga) [22] with perdew–burke–ernzerhof (pbe) [23] and ultra-soft pseudopotential [24]. 3. results and discussion 3.1 structural optimization both the tis2 and fetis2 compounds are having cdi2-type layer structures. in which, the layer of ti is sandwiched between two layers of sulphur and the unit cell contains four atoms. in the unit cell the position of ti is a 1a and those of two s atoms are in 2d (1/3, 1/3,0.2501) and (2/3,1/3,-0.2501), respectively. therefore, the construction consists of s-ti-s sandwich type structure, which is shown in fig. 1. it is separated by in z direction from the van der wall’s gap [18]. in a very weak van der wall’s attraction between the interlayers of ti and s, the guest 3d atom like fe can be easily intercalant in pure tis2. therefore, the fe atom having a lattice position is 1b (0, 0, 0.5) in the structure and formulate the hexagonal crystal structure with space group p3ml [164] as shown in fig. 2. in fetis2, the lattice parameters are a = 3.4395å and c = 5.9303å. the brillouin zone (ibz) for hexagonal crystal structure is shown in fig. 3. fig. 1 – crystal structure of tis2 fig. 2 – crystal structure of fetis2 bibechana 19 (1-2) (2022) 97-101 99 fig. 3 – brillouin zone for hexagonal structure 3.2 electronic properties in electronic properties, the energy band structure, density of states (dos), total density of states (tdos) and partial or projected density of states (pdos) of the studied are reported. 3.3 band structure the energy band structures for tis2 material are plotted in fig. 4 with the path of the k points is taken on the high symmetry points. such path is of the order of →m→k→→a. the energy band structures of tis2 are displayed in the energy range of -10.0 ev to 10.0 ev. the k-path of the band structure is highly symmetric directions with the irreducible brillouin zone (ibz). generally, the energy band lines are not overlapped near at the fermi region. hence, the tis2 band structure has a semiconductor nature with small indirect bandgap [17]. fig. 4 – electronic band structure of tis2 fig. 5 – electronic band structure of fetis2 spin up fig. 6 – electronic band structure of fetis2 spin down the energy band structures of fetis2 material are shown in figs. 5 and 6. here, the energy band lines are overlapped near at the fermi region. therefore, the conduction band and valance band are crossed over to each other near at the fermi region in the energy range of -5.0 ev to 5.0 ev. hence, we conclude that the fetis2 intercalated compound has a metallic characteristic whereas tis2 has a semiconductor characteristic. also, according the spin up and spin down band structures of fetis2, the ferromagnetic nature of the said compound are observed. 3.4 density of states (dos) from the partial or projected dos, the contributions from the individual orbitals like s, p, d and f of dissimilar materials are studied [25]. here, we have applied the tetrahedral method for taking integration over the brillouin zone to compute the dos of the materials. figs. 7 and 8, show the tdos and pdos for tis2 compound. it is plotted in the energy range between -10.0 ev to 10.0 ev. in tdos below the fermi region, the electron density maximum at 9.0 states/ev at a point -3.0 ev. while, above the fermi region, the electron density maximum at 7.0 states/ev at a point 2.0 ev, respectively. the dos at the fermi region is shown minimum. the 3d-states of ti and 3p-states of s are drawn in the graph bibechana 19 (1-2) (2022) 97-101 100 of pdos of tis2. here, the 3d-states of ti are mainly contributed to the conduction band, while 3p-states of s are mainly contributed to the valance band only, which can easily be observed from the figure of pdos. therefore, the tis2 shows a semiconductor nature. fig. 7 – total dos of tis2 fig. 8 – partial dos of tis2 the tdos and pdos of fetis2 material are shown in figs. 9 and 10. it is planned in the energy range between -10.0 ev to 10.0 ev in spin up and spin down energy states. in tdos below the fermi region, the electron density found maximum at 6.0 states/ev at a point -2.0 ev in spin up dos and 3.5 states/ev at a point -4.5 ev in spin down dos, respectively. while, above the fermi region, the electron density maximum found at 2.0 states/ev at a point 3.5 ev in spin up and 4.5 states/ev at a point 2.5 ev in spin down dos, respectively. the dos at the fermi region is shown at 2.5 states/ev. similarly, in pdos of fetis2 the 3d-states of fe and ti are mainly paid to the conduction band, while 3p states of s are mostly contributed to the valance band only. hence, the metallic nature of fetis2 is easily seen. fig. 9 – total dos of fetis2 fig. 10 – partial dos of fetis2 conclusion finally, we conclude that, the structural and electronic properties of intercalated tmdc compounds are successfully caried out using quantum espresso code with burai software under dft environment with gga-pbe and ultrasoft pseudopotential. from the electronic band structure data, the semiconducting or semimetallic behaviour of tis2 and metallic nature of their interacted compound such as bibechana 19 (1-2) (2022) 97-101 101 fetis2 are easily observed. also, from the spin up and spin down electronic configuration, it is noted that the fetis2 exhibits ferromagnetic nature. acknowledgment we sincerely acknowledge the computational facility developed under dst-fist programme from the department of science and technology, government of 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(1993)4978. 23. j. p. perdew, k. burke and m. ernzerhof, phys. rev. lett. 77(1996)3865 24. http://www.quantum espresso.org/pseudopotential. 25. q. bin, z. guo-hua, li di, w. jiang long, q. xiao-ying, z. zhi, chinese phys. lett. 24 (2007) 1050. http://nisihara.wixsite.com/burai vandana b. parmar*, aditya m. vora+ department of physics, university school of sciences, gujarat university, navrangpura, ahmedabad 380 009, gujarat, india 1. introduction 2. computational methodology 3. results and discussion 3.2 electronic properties 3.3 band structure 3.4 density of states (dos) acknowledgment references bibechana 19 (1-2) (2022) 208-213 208 study on electronic properties of -uranium using ab-initio approach aditya m. vora*1 1 department of physics, university school of sciences, gujarat university, ahmedabad 380 009, gujarat, india email: voraam@gmail.com article information: received: june 7, 2022 accepted: july 20, 2022 keywords: dft electronic properties gga paw pseudopotential abstract in the present work, a density functional theory (dft) based simulation is performed to study the electronic properties of (uranium through the electronic band structure, total electron density of states (dos), integrated density of states (idos), partial density of states (pdos) and fermi -surface measurements. a generalized gradient approximation (gga) with projector-augmented wave (paw) pseudopotential is used in present computation. the hybridization between the 5𝑓 orbital and 6𝑑 orbital also has fairly influences on the electronic properties of -uranium. doi: https://doi.org/10.3126/bibechana.v19i1-2.46838 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction uranium is a typical member of the early actinide metallic elements due to its very wide range of applications in the aerospace, military weapons and nuclear industries [1-13]. in general, the -uranium occurs under normal pressure conditions [3]. many of the results related to their physical properties have been reported so far by different researchers [1-13]. in general, 5-electron-electron correlations in particular play a crucial role actinide series [10] for several years. large volume expansion upon phase transformation is observed [10]. therefore, theoretical modulations act an important role for studying the surface properties of the materials. vohra and spencer [14] have recently observed that at pressures above 116 gpa titanium converts from the hexagonal omega (c32) phase to -phase. bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal https://doi.org/10.3126/bibechana.v19i1-2.46838 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana aditya m. vora / bibechana 19 (1-2) (2022) 208-213 209 while, such structure was also studied by wentzcovitch and cohen [15] as a probable pathway for the pressure-induced conversion of magnesium from the hcp (a3) to the bcc (a2) phase. the α-uranium crystal is having an orthorhombic structure at lower 940k temperature and above it, such phase converts to the β-phase and then it converts to the γ-phase at the temperature above 1050k. the α-uranium is stated to be stable up to 70 gpa pressure and at lesser temperatures, while at higher temperatures, the γ-uranium can stabilize its bcc structure [16]. now a days, uranium is used to power commercial nuclear reactors that produce electricity and to produce isotopes used for medical, industrial, and defence purposes around the world. the study of electronic properties shows the atomic arrangement in such material and from that one can develop or study its isotopic substances for their various nuclear applications. 2. theory in condensed matter physics, the characterization of various materials depends on the computational and theoretical techniques. generally, the density functional theory (dft) is one of the foremost techniques based on the first principle. the time independent schrödinger equation for many body systems like solids, nanomaterials and other complex systems can be solved efficiently with the help of dft [17-26]. for solving the many body interactive systems, wave function method, viz. hartree and hartree-fock, based approximations are utilized. in 1964, hohenberg and kohn [27] gave the basis of the theory by saying that, all the ground state properties of a system are the special functional of the density of the ground state interacting system. this reduces the degrees of freedom of a system of n interacting particles from 3n to three coordinates. the limits faced by the theory are that the density is either constant or it varies slowly; however, the actual electronic systems do not fall in any of these categories. in 1965, kohn and sham [28] came up with a way out for these shortcomings and gave solution of many body schrödinger equation in the form of density. the exchange correlation effects fulfilling the pauli‟s principle, also portraying the coulomb potential are added to the solution, giving results using dft. local density approximation (lda) and generalized gradient approximation (gga) are such approximation that improves the results compared to the conventional wave function method such as hartree [29] and hartree-fock approximations [30]. various software packages have been developed on the basis of dft, for the computation of properties of material requiring only information of electron density and some basic crystallographic information of the material. thus, it is parameter free and hence called first principle theory. there are several computational codes are available based on the dft method. a few of them are quantum espresso (quantum open source package for research in electronic structure, simulation and optimization) [31], siesta (spanish initiative for electronic simulations with thousands of atoms) [32], vasp (vienna ab-initio simulation package) [33], wien2k [34], castep (cambridge serial total energy package) [35] and abinit [36] etc. these codes have different implementation techniques for the calculation of properties and can be used to complement each other.the density functional theory (dft) based formulation are found more useful for computing the structural and electronic properties of materials [17-26]. with the advantage of the electronic structure simulation based on density function theory (dft), the present work mainly focuses on the electronic properties viz; electronic band structure, total electron density of states (dos), partial dos, integrated dos and the fermi surface study of -uranium metal. such simulations are carried bibechana 19 (1-2) (2022) 208-213 210 out through quantum espresso package [31] working in winmostar [37] environment. the gga with pbe function are utilized to indulge the exchange correlation effects [38] along with the paw-type pseudopotential [39]. 3. results and discussion the plane waves are taken with kinetic energy cut off 20 ry and charge density cut off 80 ry are considered. while, the 𝑘 -point mesh of 4 × 4 × 4 are used to carried out the integration over the first brillouin zone. the equilibrium geometry is seen by optimizing the atomic positions of the said structure and is converged at accuracy in energy of the order of 10-6 ry. the space group of -uranium is cmcm. in which, total 4-atoms are in its conventional unit cell, with an advent of fcc crystals as displayed in figure 1. fig. 1: crystal structure of -uranium. its results from extending a cubic lattice along with two of its orthogonal pairs with a dissimilar lattice parameter. the experimentally lattice parameters are given as 𝑎 = 2.84å, 𝑏 = 5.86å and 𝑐 = 4.93 å [6]. also, all three vectors intersect at 90° angles (i.e. 𝛼 = 𝛽 = 𝛾 = 90 , hence such three lattice vectors remain mutually orthogonal to each other. the first brillouin zone of -uranium is seen in figure 2. fig. 2: the first brillouin zone of -uranium. the electronic band structure, the total electron density of states (dos), integrated dos and the partial dos are displayed figures. 3-6, respectively for -uranium. here, from figure 3, it can be observed that the several lowest bands lower the fermi level nearer to -1 ev are mostly due to 𝑓-electrons of the element. the area around fermi level is formed hence near the fermi level all bands are dominated. while, in the region above the fermi level, the contribution of 𝑠and 𝑝-electrons is dominant. the band structure was generated for major symmetry points along the path γ → 𝑋 → 𝑆 → 𝑅 → 𝐴 → 𝑍 → γ → 𝑌 . from the nature of the dos, show deep considerate to examine atomic bonding amongst -uranium molecules by the electronic distributions. figure 4 shows that the 𝑠and 𝑝-electrons profound into the atomic core of -uranium, which is not observed as valence electrons. hence, such distribution shows that the typical paw potential in quantum espresso with up to 5𝑠 and 5𝑝 electrons is adequate. besides, the 5𝑓 -electrons governs near the fermi energy 𝐸𝐹𝑒𝑟𝑚𝑖 amongst all the electrons. aditya m. vora / bibechana 19 (1-2) (2022) 208-213 211 fig. 3: electronic band structure of α-uranium. fig. 4: total density of states of α-uranium. fig. 5: integrated density of states of αuranium. fig. 6: partial density of states of α-uranium. the computed fermi surface is seen in figure 7. it is because of the restructuring from the charge density waves, the lattice deviates at particular sites and higher sensitivity of the computational methodology. fig. 7: fermi surface of α-uranium. 5. conclusion in conclusion, we studied the electronic band structure, dos, partial dos, integrated dos and the fermi surface of the -uranium using the gga approach with paw pseudopotential under dft environment. the dominance of 5𝑓state is observed nearby the fermi level. from the overlapping of 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https://www.abinit.org/ https://doi.org/10.1103/physrevlett.77.3865 https://doi.org/10.1103/physrevlett.77.3865 https://doi.org/10.1016/j.commatsci.2014.07.043 https://doi.org/10.1016/j.commatsci.2014.07.043 bibechana 18 (1) (2021) 1-9 1 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal insight of precursor concentration, particle size and band gap of zirconia nanoparticles synthesized by co-precipitation method arun bhujel1, bibek sapkota1, ram lochan aryal2, bhoj raj poudel1, sitaram bhattarai1,3, surendra k. gautam1,* 1 department of chemistry, tri-chandra campus, tribhuvan university, kathmandu, nepal 2 department of chemistry, amrit campus, tribhuvan university, kathmandu, nepal 3 center for nanomaterials, sogang university, seoul, south korea *email: sgautam2055@yahoo.com article information: received: may 14, 2020 accepted: june 8, 2020 keywords: zirconia monoclinic calcination raman spectra band gap abstract zirconia (zro2), an inorganic material, is a very fascinating material due to its high mechanical strength and fracture toughness. the synthesis is carried out by using co-precipitation method using optimum content of zirconium oxychloride octahydrate (zrocl2.8h2o) with naoh solution at calcination temperature of 700°c. the synthesized samples were characterized to ensure structural, functional, morphological and chemical composition by several techniques. the monoclinic structure has been confirmed from xrd, saed and raman spectra. the zr-o stretching vibration and zr-o2-zr bending vibrations were confirmed through ftir analysis. the well dispersed particles with spherical morphology were established through sem and tem analyses. edx spectra confirmed the formation of pure zirconium oxide. the band gap was calculated with the help of uv-vis spectra and particle size was determined form xrd data using debye scherrer’s equation. the variation of band gap and particle size compared with different concentrations of precursor solution was studied. doi: https://doi.org/10.3126/bibechana.v18i1.28958 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction nanomaterials are considered as intermediate between classical molecular scale and micron sized entities. the synthesis of nanomaterials with structural ability are great importance with unique physical and chemical properties in comparison with those bulk counterparts, and their properties based on quantum confinement effect and high surface area. recently, many studies performed on the oxide material such as tio2, al2o3, zno2, zro2 etc., among those, zirconia is very fascinating material in current technology [1]. among metal oxides, zirconia (zro2) nanoparticles have been widely studied because of their high thermal and chemical stability, mechanical strength, chemical inertness and corrosion resistance as well as high http://nepjol.info/index.php/bibechana mailto:sgautam2055@yahoo.com?subject=mail mailto:sgautam2055@yahoo.com?subject=mail https://doi.org/10.3126/bibechana.v18i1.28958 https://creativecommons.org/licenses/by-nc/4.0/ arun bhujel et al. / bibechana 18 (1) (2021) 1-9 2 water retention [2]. zirconia is one of the important ceramics used as a biomaterial that has a bright future because of its distinctive characteristic called transforming toughening, which can give it higher strength and toughness compared to other ceramics. it has unique electrical, mechanical, optical and thermal properties, which make it a good choice for applications such as: structural materials, thermal barrier coatings, solid oxide fuel cell electrolytes, and semiconductor materials. its stable photochemical properties make it directly applicable to photonics and can be used as catalyst in various reactions such as isomerization of alkanes, dehydration of alcohols, decomposition of nitrous oxide, etc. [3]. the zirconia nanoparticles can exist in a number of polymorphs at atmospheric pressure and are monoclinic (below 1170°c), tetragonal (lie in the range of 1170°c-2370°c) and cubic (above 2370°c). the tetragonal phase of zirconia is considered to be highly catalytic with low thermal conductivity and thermal coefficient compared with others. recently, a high-pressure allotropic form of zirconia (orthorhombic) has been reported, which is metastable at atmospheric pressure and reverts to the monoclinic phase [4]. various methods of synthesis of zro2 have been established and inspected including sol-gel [5], combustion [6], sonochemical [7], hydrothermal [8] and co-precipitation method [9] etc. among the various methods, co-precipitation method has been widely practiced as an efficient method for production of homogenous, high purity and crystalline oxide powders at low cost and simplicity of the method allows the mass production. furthermore, the particle with preferred shape and size can be produced if solvent, ph, solute concentration, reaction temperature, reaction time and the type of solvent conditions are optimized [10]. in this study, we report a simple and inexpensive synthesis route of pure and crystalline zro2 nanoparticles. thus obtained samples are characterized using various microscopic and spectroscopic methods. the variation of band gap and particle size is accounted with various concentrations of precursor solutions. the work is limited in terms of theoretical interpretations and experimental supports for the transition of different forms of bravais lattice upon temperature variation. this study is also bounded with 0.05m and 0.1m concentration of zirconium precursor solution to determine particle size and band gap energy. 2. materials and method synthesis the synthesis approach is very simple and does not require any special set up. zirconium oxide was prepared from the reaction between zirconium precursor solution i.e. zirconium oxychloride octahydrate (zrocl2.8h2o), which was obtained from loba chemie pvt. ltd. and alkaline solutions of sodium hydroxide (naoh), ethanol and acetone were all obtained from thermo-fisher scientific india pvt. ltd, mumbai. all the reactants used were of analytical grades and were used without further purification. distilled water was used throughout the experiments. appropriate amount of zirconium oxychloride octahydrate was dissolved in distilled water using hot plate magnetic stirrer to prepare its 0.05m and 0.1m solutions. aqueous naoh solution was mixed with above precursor solutions until the ph value became 8. the precipitate thus obtained was filtered after 15 minutes, washed with water and acetone several times and finally was dried at 100°c overnight. the samples of zro2 were calcined at 700°c for 2 hours and were coded as z1 (0.05m) and z2 (0.1m). characterization the crystalline structure, phase composition and crystallite size of the powder samples obtained from above processes were analyzed from xrd patterns obtained using cu kα radiations (λ = 1.514 å) for 2θ value ranging from 10° to 90° in x-ray diffractometer (rigaku ultima iv model). the arun bhujel et al. / bibechana 18 (1) (2021) 1-9 3 morphology of the samples was analyzed by transmission electron microscopy (technai g220 electron microscope), scanning electron microscopy (jeol-jsm-7600f). ftir (irtracer100, shimadzu) spectra of the samples were employed to identify the chemical structure of the samples in a range of 4000-400 cm-1. the uv-vis absorption spectra were obtained from uv-vis spectrophotometer (elico sl 177). the presence of a monoclinic structure was studied through raman spectroscopy (enspectra professional v.1.6.0.1822) and their atomic weight percentage was identified via edx (jeol-jsm-6700f) analysis. 3. results and discussion xrd diffraction patterns figures 1(a) and 1(b) show the xrd patterns of the as-prepared calcined samples of zirconia using 0.05m zrocl2.8h2o (z1) and 0.1m zrocl2.8h2o (z2) solutions, respectively and their corresponding lorentzian fitting. the xrd patterns show that samples exist in crystalline state which is evident from the presence of distinct diffraction peaks. the peak at (1-11) orientation have high intensity than the other peaks, which was attributed to the high crystalline nature of the particular orientation of the samples. lorentzian fitting was done for each sample to obtain fwhm value and the average grain size of the crystalline samples z1 and z2 are estimated as 28.3 nm and 33.3 nm, respectively using debye scherrer’s equation [11,12], which are comparable with the previous studies [13-15]. as the concentration of the precursor solution increases from 0.05m to 0.1m, the particle size also increased from 28.3 nm to 33.3 nm. from the diffraction patterns the peaks are indexed as monoclinic (baddeleyite) zro2 with lattice constants a = 0.377 nm, b = 0.447 nm, c = 0.476 nm and α = γ = 900 and β = 800, which are in good agreement with those of standard data (jcpds card 37-1484) [16]. the bond length of the zr-o bond is found to be 1.88 å and bond angle of o-zr-o was found to be 109.470. the molecular coordination geometry of the baddeleyite form of monoclinic crystal structure of zro2 sample (with hkl=111) drawn from avogadro’s 1.2 version is shown in figure 2. fourier transform infrared spectroscopy analysis the ftir spectra obtained for as-prepared samples z1 and z2 are shown in figure 3 where, broad absorption band particularly at about 700-750 cm-1 due to zr-o2-zr asymmetric and about 400-500 cm-1 due to zr-o stretching modes confirm the formation of zro2 phases having monoclinic structure. the ftir studies were in good agreement with the xrd pattern of the zirconia sample [1,10]. the extended spectrum in the region above 1000 cm-1 signifies the mesostructure having an amorphous surface of the sample with chemisorbed h2o molecules, which disappears at high temperature [10,17]. scanning electron microscopic study figure 4(a) displays the sem micrograph and figure 4(b) the corresponding histogram of zro2 sample (z1). sem image reveals that primary particles aggregate into secondary particles to form a cluster because of their small dimensions and high surface energy. the size of these nanomaterials is difficult to determine precisely by simple visual inspection due to agglomeration. hence, imagej software was used on the sem image to obtain the histogram as shown in figure 4(b) and the average particle size was estimated to be ~75 nm (from isolated regions with reasonable contrasts) which is bigger as compared to the size obtained from xrd data as 28-33 nm. it is simply due to the agglomeration of the particles because of the high surface energy. this implies that the growth of the size of the nanoparticle is mostly considered to be the result of the surface aggregation of colloidal particles (cluster by cluster growth), although, the surface morphology shows that the nanoparticles formed are of crystallite structure. arun bhujel et al. / bibechana 18 (1) (2021) 1-9 4 20 40 60 80 100 0 200 400 600 800 1000 1200 1400 1600 1800 2000 28 30 32 0 600 1200 1800 in te n s it y (a .u .) 2q (degrees) in te n s it y (a .u .) 2q (degrees) (1 11) (111) (a) 20 40 60 80 100 0 500 1000 1500 2000 28 30 32 0 700 1400 in te n s it y (a .u .) 2q (degrees) in te n s it y (a .u .) ) 2q (degrees) (1 11) (111) (b) fig. 1: xrd patterns of zirconia synthesized using (a) 0.05m zrocl2.8h2o (z1) and (b) 0.1m zrocl2.8h2o (z2) and their corresponding lorentzian fitting for fwhm calculation. (a) (b) fig. 2: (a) molecular coordination geometry and (b) baddeleyite form of monoclinic crystal structure of zro2 with (hkl = 111). (drawn from avogadro's 1.2 version). 2000 1600 1200 800 400 (zr-o2-zr) 729 (zr-o) 416 (zr-o2-zr) 735 t ra n s m it ta n c e (% ) wavenumber (cm-1) z1 z2 (zr-o) 489 fig. 3: ftir spectra of zirconia samples. arun bhujel et al. / bibechana 18 (1) (2021) 1-9 5 (a) 0 50 100 150 200 250 300 350 0 5 10 15 20 25 30 f re q u e n c y particle size (nm) (b) fig. 4: (a) sem image of zirconia prepared using 0.05m zrocl2.8h2o (z1) and (b) its corresponding histogram, as obtained from imagej software. figure 5 reveals the edx spectra of zro2 (sample z1) with presence of zr and o peaks which confirms the formation of pure zirconium oxide with no presence of impurities. fig. 5: edx spectra of zro2 nanoparticle (z1) synthesized from 0.05m zrocl2.8h2o. the average atomic percentage ratio of zr:o was found to be 26.95:73.05 for z1 sample as shown in table 1. table 1: edx result showing the compositions of zro2 nanoparticle (z1) transmission electron microscopic (tem) study figure 6 (a) depicts tem image of the zirconia nanoparticle (z1), which reveals that zirconia nanoparticles were almost agglomerated with a natural sensation because the surface forces such as van-der wall forces, capillary forces and electrostatic forces can be overwhelmed only against gravitational and inertial forces for particular size assortment. this image also revealed that small particles aggregate into secondary particles because of their small dimensions and high surface energy. the average size of prepared nanoparticle was also calculated from tem image by using imagej software and was found to be ~80 nm which is nearly in agreement with the size obtained from sem image. this was further clarified by the histogram and the gaussian fitting spectra as shown in figure 6(b). the tem-edx pattern is shown in figure 7(a), which also confirms the synthesis of pure zro2 due to presence of only corresponding zirconium and oxygen peaks. saed pattern as illustrated in figure 7(b) proves the characteristics diffraction rings corresponding to (1-11), (111) and (110) indices of monoclinic crystalline structure of zro2 nanoparticle [10]. element weight % atomic % oxygen 32.33 73.05 zirconium 67.77 26.95 arun bhujel et al. / bibechana 18 (1) (2021) 1-9 6 uv-vis spectroscopic analysis figure 8(a) depicts the uv-visible absorption spectra of zro2 nanoparticles synthesized from 0.05m (z1) and 0.1m (z2) zrocl2.8h2o, respectively which shows strong absorption at 360 nm and 355 nm that are shifted from the bulk zro2. this phenomenon is associated with charge transfer reaction for monoclinic phase arising from quantum confinement effect of the nanoparticle. the determination of the optical band gap is obtained by tauc's equation [18], (𝛼ℎ𝜈) = 𝐴(ℎ𝜈 − 𝐸𝑔)) 𝑛 where, a is the constant, hν is photon energy, eg is the allowed energy gap, n=1/2 for allowed direct transition and n = 2 for allowed indirect transition; α is the absorption coefficient. here α = 2.303×a t where, a is the absorbance and t is the thickness of the sample. similarly hv = 1240 wavelength (nm) . the band gap was calculated by extrapolating the curve drawn between (hν) vs (𝛼ℎ𝜈)2 to the x-axis as shown in figure 6(b) and are found to be 3.24 ev and 3.20 ev for two samples synthesized from 0.05m (z1) and 0.1m (z2) zrocl2.8h2o, respectively. hence, band gap decreases as the concentration of the zirconium precursor increases from 0.05m to 0.1m, which follows similar trend as reported in [18,19]. the variation of particle size and band gap with concentration of zirconium precursor is shown in figure 9. raman study the raman spectrum of zirconia (zro2) nanoparticle synthesized from 0.05m zrocl2.8h2o is given in figure 10, which shows a total of 18 vibrations modes corresponding to the monoclinic phase, out of which only 15 are reported by various researchers [20]. most of the raman lines were easily observable for both ag and bg conditions, but only one of the raman signals (178 cm-1) has been interpreted as an ag + bg superposition. the active peaks were observed at 178, 332, 381, 474, 558, and 636 cm-1 in raman spectra, which belong to the monoclinic phase of zirconium [1]. the peaks at 332 cm-1 and 636 cm-1 are assigned to ag mode. the peaks at 381 cm-1 and 612 cm-1 could be corresponding to the bg mode. the remaining peak at 178 cm-1 could be identified as the ag + bg mode of monoclinic zro2 phase. the exhibited bands are clearly indicating that the prepared zirconia sample possessed dominant monoclinic phase of zro2. all of the peaks are assigned to (o-o), (zr-o) and (zrzr) phonon vibration modes [20]. (a) 0 50 100 150 200 250 300 0 2 4 6 8 10 12 14 16 18 f re q u e n c y particle size(nm) (b) fig. 6: (a) tem image of zirconia nanoparticle using 0.05m zrocl2.8h2o (z1) and (b) corresponding histogram. arun bhujel et al. / bibechana 18 (1) (2021) 1-9 7 (a) (b) fig. 7: (a) tem-edx spectra and (b) saed pattern of zirconia nanoparticle using 0.05m zrocl2.8h2o. 300 350 400 450 500 550 600 650 700 3 5 5 n m 3 6 0 n m a b s o r b a n c e ( a .u .) wavelength (nm) z1 z2 (a) 1.5 2.0 2.5 3.0 3.5 4.0 eg=3.24 ev eg=3.20 ev (a h u )2 (a .u .) hu (ev) z1 z2 (b) fig. 8: (a)uv-visible absorptions spectra of zro2 nanomaterial synthesized from 0.05m and 0.1m zrocl2.8h2o & (b) corresponding plot of (hμ) vs (αhμ)2. 0.05 0.06 0.07 0.08 0.09 0.10 28 29 30 31 32 33 34 particle size band gap concentration (m) p a r ti c le s iz e ( n m ) decrease in band gap increase in particle size 3.20 3.21 3.22 3.23 3.24 b a n d g a p ( e v ) fig. 9: variation of particle size and band gap with concentration of zirconium precursor. 2 4 6 8 10 12 14 16 18 20 kev 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 cps/ev o zr zr zr arun bhujel et al. / bibechana 18 (1) (2021) 1-9 8 0 200 400 600 800 1000 1200 -1000 0 1000 2000 3000 4000 5000 6000 c o u n ts p e r fr a m e raman shift (cm -1) zro2 nanomaterial 1 7 7 .5 3 3 2 .3 3 8 0 .9 4 7 4 .1 5 5 7 .5 6 3 6 .3 6 1 5 .2 fig. 10: raman spectra of zro2 nanomaterial synthesized from 0.05m zrocl2.8h2o. 4. conclusions zirconia (zro2) nanoparticles have been successfully synthesized at two different concentrations (0.05m and 0.1m) of zirconium precursor (zrocl2.8h2o) by co-precipitation method using naoh as reducing agent. pure monoclinic phase was confirmed from xrd result, which is further ensured via raman spectra and saed pattern. the average size of nanoparticles increases from 28.3 nm to 33.3 nm with increase in the concentration of the solution from 0.05m to 0.1m. further, the presence of zr and o species was confirmed via ftir and edx analyses. the sem micrograph and tem analyses showed well dispersed spherical morphology of the sample with presence of agglomeration. the band gap value is found to decrease from 3.24 ev to 3.20 ev as the particle size increases with increase in the concentration of solution from 0.05m to 0.1m. acknowledgements this article is self-sponsored project. the authors’ appreciation is extended to department of chemistry, tri-chandra campus, tribhuvan university for providing necessary materials and laboratory for experiments. authors are thankful to ms. indira pokhrel, sogang university, south korea for sem and tem images; central department of chemistry, tribhuvan university for ftir characterization and department of physics, tri-chandra campus for raman characterization. authors also express gratitude to dr. satendra p. singh, sejong university, south korea for xrd characterization and helpful discussion. references [1] m. ramachandran, r. subadevi, w. r. liu, m. siakumari, facile synthesis and characterization of zro2 nanoparticles via modified coprecip itat ion method, j . nanoscience and nanotechnology . 18 (2018) 368-373. http://doi.org/10.1166/jnn.2018.14562. 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[20] kumari, w. li, d. wang, monoclinic zirconium oxide nanostructures synthesized by a hydrothermal route, nanotechnology. 19 (2008) 195602-195609. http://doi.org/10.1088/0957-4454/19/19/195602. http://scholar.waste.org/1307-6892/7811 https://doi.org:10.3126/jncs.v40i0.27271 http://dx.doi.org/10.1590/1982-5373-mr-2016-0196 http://dx.doi.org/10.1590/1982-5373-mr-2016-0196 http://dx.doi.org/10.1155/2013/314862 http://dx.doi.org/10.1016/j.jmst.2014.0.002 http://doi.org/10.1186/s11671-015-0780-z http://doi.org/10.1590/s1516http://doi.org/10.1590/s1516http://doi.org/10.1016/j.ssc.2008.03.020 http://doi.org/10.1088/0957-4454/19/19/195602 bibechana 18 (1) (2021) 108-117 108 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal diffusion of oxytocin in water: a molecular dynamics study khimananda acharya, rajendra prasad koirala, nurapati pantha* central department of physics, tribhuvan university, kathmandu, nepal *email: mrnurapati@gmail.com article information: received: june 6, 2020 accepted: july 11, 2020 keywords: diffusion molecular dynamics mean square displacement activation energy abstract classical molecular dynamics simulation is performed to estimate the diffusion coefficient of oxytocin in water at different temperatures, 288 k, 300 k, 313 k, 323 k, using groningen machine for chemical simulations (gromocs). the simulation is carried out using gromos43a1 force field and extended simple point charge (spc/e) water model. the stability of the system is evaluated from energy profile of potential and kinetic energy, which assures well equilibrated molecular system. the selfdiffusion coefficient of oxytocin and water is obtained from einstein’s relation and binary diffusion coefficient is obtained from darken’s relation. as temperature increases the diffusion coefficient also increases as per expectation. the diffusion coefficients of water from the present calculations agree well with the previously reported values, within the 10% of deviation. furthermore, the activation energy has been studied using arrhenius plot. doi: https://doi.org/10.3126/bibechana.v18i1.29316 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction biomolecules are the building blocks of living organisms. they have the specific physio-chemical configurations [1]. the structural variability and chemical conformation of the molecules determine the biological functioning in living cells. biomolecules work independently as well as cooperatively to perform in various body mechanisms [2]. proteins, nucleic acids, lipids and carbohydrates are the basic category of biomolecules, also called the macromolecules. some other molecules are also characterized into this class; primary metabolites, secondary metabolites, natural and artificially synthesized products [3,4]. the poly-condensation of amino acids residues forms a protein molecule. the carboxyl (-cooh) tail of an amino acid when covalently bonded to amine (nh2-) head of another amino acid by water elimination, a dipeptide molecule is formed [5,6]. http://nepjol.info/index.php/bibechana mailto:mrnurapati@gmail.com https://doi.org/10.3126/bibechana.v18i1.29316 https://creativecommons.org/licenses/by-nc/4.0/ khimananda acharya et al. / bibechana 18 (1) (2021) 108-117 109 then, the condensation of other amino acids one after another in new carboxyl tail, a long polypeptide chain is formed, which will finally be a functional protein molecule. a long polypeptide chain cannot stay in linear form, i.e., primary structure, because of difficulty in structural stability [7]. to minimize the overall energy profile, the molecule folds into various shapes, basically in alpha-helices and beta-turns. hydrogen bonds, salt bridges; and hydrophobic and hydrophilic interaction takes place to provide different stable structures of protein molecules [4]. oxytocin is a short peptide chain of nine amino acids (a nanopeptide) with the sequence cysteinetyrosine-isoleucine-glutamine-asparagine-cysteineproline-leucine-glycine (cys tyr ile gln asn cys pro leu gly, or cyiqncplg) with additional amide (-nh2) in the carboxyl terminus of glysine residue [8] as shown in fig 1(i) and its space-filling calotte (cpk) model for the visualization is shown in fig. 1(ii). its molecular formula is c43h66n12o12s2 with its molecular weight 1007 g per 193 moles (i.e., 1007:193 g/mole). it has white powdery color and is soluble in water and in butanol. a disulphide bridge is present first and sixth cysteine residues of the molecule [9,10]. oxytocin is also known as love hormones responsible for the feeling love and satisfaction. it plays role in social bonding, sexual reproduction in both sexes, milk production etc. it is best known for its role in childbirth and breast feeding [12]. during labor large amount of oxytocin release causing contraction of the uterus to facilitate birth. when the contractions are not strong to compress the blood vessels, postpartum hemorrhage (pph) can menace women's life. in this condition uterotoxic medicine like oxytocin is given to stimulate contraction and stop the bleeding [11,13]. oxytocin hormone is synthesized in pituitary gland. it is, then, released to the blood stream through the posterior lobe of the gland. some neurons and other parts of brain also produce oxytocin [14,15]. liquid contents of living body, like water, contribute to transport these hormones to various parts of the cell [16]. we believe that the study of transport properties of this hormone in water is very important to understand its mechanical properties in aqueous medium. furthermore, diffusion coefficient of nitric oxide in water had been observed through the same technique [17]. to our best knowledge, the transport properties of oxytocin in water have not been studies yet. we have performed the molecular dynamics to deal the transport properties of oxytocin. (i) (ii) fig.1: (i) molecular structure of an oxytocin molecule [11] (ii) cpk model of the oxytocin molecule. diffusion diffusion is the random process in which the matter is transported from one part of a system to another. khimananda acharya et al. / bibechana 18 (1) (2021) 108-117 110 matter is transported always from higher concentration to the lower concentration. this occurs often due to the concentration inhomogeneity and thermal agitation of the particles in a medium. diffusion is an imperative process within the human body and it is indispensable to transport of molecule within organ like lungs, kidneys, stomach, eyes etc. we realize several phenomena regarding the diffusion; like mixing of smoke in air, sugar in water, dust in air etc [18,19]. in this work, we estimate the selfdiffusion and binary diffusion coefficient of oxytocin in water. the diffusion in a homogeneous system without any chemical concentration gradient exists in it is referred the self-diffusion and the corresponding diffusion coefficient is known as self-diffusion coefficient. the extent of diffusion is physically measured in terms of self-diffusion coefficient. it is calculated using einstein’s relation [20,21], 𝐷 = lim 𝑡→∞ 〈[𝑟(𝑡)−𝑟(0)]2〉 6𝑡 (1) the term r(t) – r(0) in equation (1) is the displacement of particle from the reference position at time t, [r(t) – r(0)]2 is the square of displacement, and 〈… 〉 represents the ensemble average, thus, the expression <[r(t) – r(0)]2 > is the mean square displacement (msd) of the particle. for the system with two different substances, binary diffusion takes place. it is measured in terms of diffusion coefficient called binary or mutual diffusion coefficient [22]. 𝐷𝐴𝐵 = 𝑁𝐵𝐷𝐴 + 𝑁𝐴𝐷𝐵 (2) where, 𝐷𝐴𝐵 is binary diffusion coefficient, 𝐷𝐴, 𝐷𝐵 = self diffusion coefficient of species a and b respectively, and 𝑁𝐴, 𝑁𝐵 = mole fraction of species a and b respectively. the diffusion phenomenon is the temperature dependence phenomena. the mathematical relation for the temperature dependence is given by arrhenius equation [23]. 𝐷 = 𝐷0𝑒 −𝐸𝑎 𝑅𝑇 (3) where, d is diffusion coefficient, ea is activation energy, d0 is pre-exponential factor, r is universal gas constant and t is absolute temperature. 2. computational details system setup a pdbid 2mgo.pdb was taken from the protein data bank (pdb), an authorized pdb website (www.rcsb.org). the molecule was in complete form as our requirement, so no modification was done in the original structure. the topology and parameters for the system setup and molecular dynamics (md) simulations were taken from gromos43a1 force field [23]. while considering the water model, we should care on its compatibility with the force field parameter we have used [25]. the molecule was solvated into a cubic box of 4.07 × 4.07 × 4.07 nm3 dimension with spc/e [26] water model by gromacs 5.1.1 [27] command. the molecule was naturally chargeless, so extra ions have not been added. there were 2167 water molecules and one oxytocin molecule in the simulation box as shown in fig. 2. fig. 2: oxytocin molecule solvated in a pbc box. molecular dynamics simulations all atom molecular dynamics simulation was propagated to study the various mechanical properties of oxytocin molecule in water. khimananda acharya et al. / bibechana 18 (1) (2021) 108-117 111 gromos43a1 force field was used for the entire simulation. three basic steps: energy minimization, system equilibration and production run were carried out to deal the targeted properties. the original pdb structure has been estimated from x-ray diffraction (xrd) or nuclear magnetic resonance (nmr) techniques. the assigned coordinates for the atoms in the molecule might have steric hindrance due to the mechanical errors. moreover, hydrogen atoms are absent in original pdb, and they are added by the molecular system building software. therefore, before begin our md run, we must be sure that there is no any inappropriate geometry otherwise force acting on particle will be very large and system will be out of equilibrium and md fails. in order to get solved this inappropriate geometry and kinetic energy; system must be subjected to the process of energy minimization. in our system because of fast and reliable performance, we have decided to choose steepest-descent algorithm [29]. energy minimization run is often performed in absolute zero kelvin temperature, which is practically unachievable and unreliable for the natural environment. so, the molecular environment is so created that can be resembled in the practice in room temperature or for any natural process. we basically maintain the system that follows the statistical ensembles with appropriate macroscopic parameters; pressure, temperature and volume [30,31]. pressure coupling was made to set pressure 1 bar using barendsen barostat. for box re-scaling isothermal compressibility is set to 4.5 ×10-5 bar-1. particle mesh ewald (pme) for coulomb interaction with cut off distance 1.0 nm and fourier spacing of 0.3 was used. v-rescaling has been used for temperature coupling. equilibration run was performed at four different temperatures 288 k, 300 k, 313 k, and 323 k and was run 20 ns for each system. the appropriate system prepared from the equilibration run was propagated to study the molecular diffusion in water at assigned temperature above. production run was performed in nvt ensemble. each of the system was run 60 ns time period. 3. results and discussion we present and discuss about the energy profiles, self-diffusion coefficients of both water and oxytocin; and the output of self-diffusion coefficient is used to evaluate binary diffusion coefficients. finally, the activation energy of corresponding systems is estimated for each system. energy minimization and system equilibration the fundamental requirement of md simulation is to bring the molecular system in minimum potential energy so that the atoms in the molecule get free from atomic hindrance. the best way to achieve this condition is energy minimization run and analyzing the outcomes. energy minimization run is always run at absolute zero temperature, which ensures the minimum potential energy. fig. 3 shows the potential energy curve during the minimization run. the potential energy has been well converged and we confirmed the system to proceed for the post processing. we found potential energy -1.2015872×104 kj mol-1 in the most condition and steepest descent converged to fmax ˂ 50 × 104 kj mol-1. before commencing the md production run, the molecular system should be maintained at a thermodynamic ensemble. this can be done by md equilibration run and the outcomes were evaluated determining some thermodynamic parameters like pressure, temperature etc. these parameters have been assigned to resemble the cellular environment in human body. the best way of finding the stability of the molecular system is the calculation of density, which was not assigned for the system. we have calculated density of water and entire system including the oxytocin after equilibration run. the variation of density of water and entire system at different temperatures has been presented in table 1. because of infinite dilution, the mixture khimananda acharya et al. / bibechana 18 (1) (2021) 108-117 112 has similar order of density with that of pure water. the decreasing pattern of density on increasing temperature ensures that the system is appropriately equilibrated and is suitable for the further calculation. fig. 3: potential energy after energy minimization. energy profile we have studied energy profile under the gromos43a1 force field in md simulation. when the system is in md simulations, several interactions have been taken to calculate energy. the energy profile is contributed by many bonded and non-bonded interactions. bond interactions are bond stretching, bond angle vibration, proper dihedral and improper dihedral whereas nonbonded interactions are coulomb interaction and lj interaction. the energy profile is the graphical manifestation of these various energy interactions. to reduce the computational cost, we have kept bond length constant in our simulation with the help of constraint algorithm lincs. therefore, there is no energy profile due to bond stretching. also we found that bonded interaction energy was positive. the coulomb interaction and l-j interaction are the major contribution on the non-bonded interaction. these interactions were calculated using the list of non-bonded atom within the certain region. we use periodic boundary condition for such a purpose. the sr coulomb interaction has negative value and has dominant contribution on total potential energy. the value of l-r coulomb and coulomb reciprocal energy are significantly small. within the cutoff region, the l-j interaction has significant role, however, (l-r) l-j interaction has negligible contribution on total energy. the energy profiles of the system at four different temperatures have been studied. the energy profile for all the interaction energy with total energy at 300 k temperature is shown in fig. 4. self-diffusion coefficient of water and oxytocin self-diffusion coefficients of water and oxytocin have been calculated at four different temperatures; 288 k, 300 k, 313 k, 323 k using the einstein's relation in equation (1). the slope of corresponding mean square displacement (msd) was utilized to determine the self-diffusion coefficients in both systems. fig. 5(i) and 5(ii) show the mean square displacement curves for water and oxytocin respectively. we have carried out 60 ns md simulation for each temperature; however the linear relationship has to be required to draw the value of slope in msd versus time graph. so, we have selected 2 ns simulation run in the beginning to get the better statistics. the msds, thus, obtained were found linearly increasing with respect to time, and in turn increased the self-diffusion coefficients. the selfdiffusion coefficient of water was compared with previously reported experimental value and was found good agreement within 10%. the better agreement at higher temperature indicates that the force field parameters could have been calculated in these temperature regimes which are relevant to physiological phenomenon. khimananda acharya et al. / bibechana 18 (1) (2021) 108-117 113 table 1: temperatures and corresponding densities of system after equilibration run. fig. 4: total energy profile of oxytocin at 300 k. the simulated values and experimental values of self-diffusion coefficient of water at different temperatures are listed in the table 2. we also have calculated self-diffusion coefficient of oxytocin from the msd graph of oxytocin molecule. the simulated values of self-diffusion coefficient of oxytocin at different temperatures are listed in the table 3. in both systems, the self-diffusion coefficients are obtained as, d323 k > d313 k > d300 k > d288 k. while simulating macromolecule/s in a box, one needs to be careful about its size effect. it is a usual practice to consider the smallest possible simulating box and enlarge the space for moving molecules by applying periodic boundary condition (pbc). however, the size of the box should be sufficient to maintain the basic criteria of molecular simulations. the rule of thumb for this requirement says that the cut-off distance of different interactions under consideration should be less than the half the box size [24]. furthermore, previous coupling temperature (k) equilibrium temperature (k) equilibrium density (kg m-3) density of water (kg m-3) [32] 288 287.983±0.007 1008.71±0.07 999.13 300 299.983±0.007 1002.87±0.05 996.56 313 313.005±0.011 995.46±0.02 992.28 323 323.995±0.011 998.96±0.03 988.11 khimananda acharya et al. / bibechana 18 (1) (2021) 108-117 114 fig. 5: msd vs time plot of (i) water (ii) oxytocin at different temperatures. table 2: simulated and experimental self-diffusion coefficients of water at four different temperatures. temperature k simulated diffusion coefficient dw s (10-10 m2/s) experimental diffusion coefficient dw e(10-10 m2/s) [33] difference % 288 19.16±0.05 17.77 9.39 300 25.72±0.05 313 32.87±0.10 32.40 1.43 323 39.39±0.08 39.68 0.74 studies have shown that as far as these minimum criteria are maintained, the size of the box does not affect the main conclusions of the results [34]. we have taken care of size of the oxytocin molecule and also the cutoff distances, which are less than half-size of the simulating box in each dimension. binary diffusion coefficient the self-diffusion coefficients obtained for water and oxytocin were used to find the binary diffusion coefficients of oxytocin in water by using darken’s relation in equation (2). the calculated values of binary diffusion coefficients were found increasing on increasing the temperature. when temperature increases there is increase in thermal energy which results the decrease in density of the system and hence there is increase in diffusion coefficient. the estimated binary diffusion coefficients of oxytocin in water have been presented in table 4. khimananda acharya et al. / bibechana 18 (1) (2021) 108-117 115 table 3: simulated values of self-diffusion coefficients of oxytocin at four different temperatures. temperature k self-diffusion coefficient do s (10-10 m2/s) 288 2.24±0.32 300 2.45±0.29 313 3.75±0.26 323 4.79±0.01 table 4: simulated binary diffusion coefficients at four temperatures. temperature k binary diffusion coefficient do s(10-10 m2/s) 288 2.23 300 2.46 313 3.76 323 4.81 temperature dependency of diffusion we obtain activation energy from the slope of diffusion versus reciprocal of time as suggested by the equation (3), 𝐷 = 𝐷0𝑒 −𝐸𝑎 𝑁𝐴𝑘𝐵𝑇, and r = nakb, where na is avogadro number whose value is 6.023 × 10-23 mol-1 and kb is the boltzmann constant carrying the value 1.38 × 10-23 jk-1, meaning of remaining parameters are explained in equation (3). on taking the natural logarithm for the expression, we get, ln 𝐷 = ln 𝐷0 − 𝐸𝑎 𝑁𝐴𝑘𝐵𝑇 (4) then, the activation energy ea for diffusion was obtained from the slope of ln 𝐷 versus 1 𝑇 , called the arrhenious plot as, 𝐸𝑎 = − 𝑁𝐴𝑘𝐵 𝜕 ln 𝐷 𝜕(1/𝑇) (5) the intercept when extrapolated to the 1 𝑇 → 0 in the arrhenius plot gives the pre-exponential factor. (i) (ii) (iii) fig. 6: arrhenius diagram for self-diffusion coefficient of (i) oxytocin, (ii) water and (iii) binary mixture. khimananda acharya et al. / bibechana 18 (1) (2021) 108-117 116 the arrhenius plot of simulated value of water is shown in fig. 6(i), and that of oxytocin is 6(ii) and for their binary mixture is shown in fig. 6(iii), which were used to determine the activation energy for each condition. from the table 5, it is clear that the activation energy for oxytocin molecule and binary mixture is found to be almost equal; this is due to the infinitesimal concentration of oxytocin in our system. further, we found that there is an acceptable level of agreement between the simulated and experimental values of activation energy of water. 4. conclusions and concluding remarks the self-diffusion coefficient of water and oxytocin is obtained using einstein's relation. the binary diffusion coefficient is obtained using darken's relation. the results obtained for energy profile, the kinetic energy is proportional to absolute temperature, is as expected. the experimented and simulated value of self-diffusion coefficient of water for all temperature is within error 10 %. diffusion coefficient of water for water and oxytocin are found increasing with increase in temperature. furthermore, the dependency of diffusion with temperature is analyzed with arrhenius plot. activation energy is also calculated from the slope of these plots. we have found that the activation energy of water obtained from simulated data is differing from experimented value with an error of 17.18 %. we do not have any experimental result for diffusion of oxytocin at present time to compare our final result; however, we can be sure on our accuracy with comparing the results of simulated and experimental self-diffusion coefficient of water. acknowledgements k. acharya acknowledges the partial support from university grants commission (ugc), nepal. r.p.k. acknowledges the partial financial support from the nepal academy of science and technology (nast). references [1] p. narayanan, essentials of biophysics, new age international publishers, new delhi (2010). 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https://doi.org/10.1063/1.5132777 https://doi.org/10.1142/s0217979216502052 https://doi.org/10.1246/bcsj.46.2659 https://doi.org/10.1016/0378-4371(91)90226-3#_blank https://doi.org/10.1016/j.molliq.2011.12.008 https://doi.org/10.1021/j100308a038 https://doi.org/10.1063/1.448118 http://manual.gromacs.org/documentation/2016.4/manualhttp://manual.gromacs.org/documentation/2016.4/manualhttps://doi.org/10.1103/physreve.74.061901 https://doi.org/10.1088/0026-1394/38/4/3 https://doi.org/10.1039/b005319h https://pubs.acs.org/doi/10.1021/jp003020w bibechana 18 (1) (2021) 159-169 159 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal prediction of daily global solar radiation using different empirical models on the basis of meteorological parameters at trans himalaya region, nepal usha joshi1*, i. b. karki2, n.p. chapagain3 , k.n. poudyal4 1department of physics, patan multiple campus, tu, patan, nepal 2nepal open university, nepal 3department of physics, amrit campus, tu, kathmandu nepal 4department of physics, pulchowk campus, ioe, tu, patan, nepal *email: ushajoshik1967@gmail.com article information: received: may 30, 2020 accepted: august 9, 2020 keywords: global solar radiation pyranometer meteorological parameters regression technique empirical constants abstract global solar radiation (gsr) is the cleanest and freely available energy resource on the earth. gsr was measured for six years (2010 -2015) at the horizontal surface using calibrated first class cmp6 pyranometer at kathmandu (lat. 27.70o n, long. 85.5oe and alt. 1350m). this paper explains the daily, monthly and seasonal variations of gsr and also compares with sunshine hour, ambient temperature, relative humidity and precipitation to gsr. the annual average global solar radiation is about 4.16 kwh/m2/day which is significant amount to promote solar active and passive energy technologies at trans-himalaya region. in this study, the meteorological parameters are utilized in regression technique for four different empirical models and finally the empirical constants are found. thus obtained coefficients are utilized to predict the gsr using meteorological parameters for the years to come. in addition, the predicted gsr is found to be closer with measured value of gsr. the values are justified by using statistical tools such as coefficient of determination (r2), root mean square error (rmse), mean percentage error (mpe) and mean bias error (mbe). finally, the values of r2, rmse, mpe and mbe are found to be 0.792, 1.405, -1.014, and 0.011, respectively for model (d), which are based on sunshine hour, temperature and relative humidity. in this model, the empirical constants, a = 0.155, b = 0.134, c = 0.014 and d = 0.0007 are determined which can be utilized at the similar geographical locations of nepal. doi: https://doi.org/10.3126/bibechana.v18i1.29203 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction the sun is worshipped as god in greek mythology. the sun is source of various kinds of energies which has been proven vital from the beginning of human civilization till now. it is mainly composed of hydrogen (90%), helium and traces of other heavier elements. the fusion of hydrogen to helium http://nepjol.info/index.php/bibechana mailto:ushajoshik1967@gmail.com https://doi.org/10.3126/bibechana.v18i1.29203 https://creativecommons.org/licenses/by-nc/4.0/ usha joshi et al. / bibechana 18 (1) (2021) 159-169 160 is believed to be source of energy of sun by reducing mass almost 5 million tons per second in the form of electromagnetic radiation [1]. approximately 95% of solar radiation lies within the wavelength range of 0.3-2.4 µm, which comprises ultraviolet, visible and infrared portion of electromagnetic radiation, 1.2% lies in wavelength longer than 2.4µm and 3.6% lies in wavelength less than 2.4µm [1,2]. solar radiation reaching the earth surface gets through the constituents of the atmosphere. the earth’s atmosphere consists of o2, n2, co2, ar as permanent constituents. water vapor and particulate matters such as dust, soot, water drops and ice crystals which vary spatially as temporary constituents. these constituents modify solar radiation arriving at the earth surface by scattering, reflection and absorption [2-4]. the radiation which evades absorption and scattering and arriving on ground directly in the line from the solar disk is called direct or beam radiation [3]. the radiation received from sun after its direction has been changed by scattering from atmosphere is diffused solar radiation. consequently, the solar radiation arriving at the earth surface also known as global solar radiation(gsr) which is the sum of direct solar radiation and diffused solar radiation[3,4]. the gsr is of enormous importance as it can direct out development on low carbon trajectory [5]. study on gsr is most essential in order to design and operate the solar energy devices. hydrologists, engineers, agriculturists use solar radiation data for various purposes such as solar heating, cooking, drying, and interior illumination of buildings [5, 6]. also, manufacturers of solar equipment need to know the average gsr available in different and specific region. it is used to develop database in order to use it in active and passive energy form which could be a giant step for development of many sectors like tourism, education, industry, communication, health and scientific agriculture. one of the most used practical possibilities of renewable energy is the photovoltaic system to lighten the rural areas [7, 8]. in nepal, 83% of total population use clean energy and rest of them (22%) live in live dark region [9]. many people are still deprived of hydroelectricity, petroleum and so on. so people are forced to use kerosene lamp as an alternative to electricity. in nepal, 87% of total energy is consumed in residential areas, 6% in transportation, and 5 % in industry. in fy 2017/18, the consumption of traditional, commercial and renewable energies are 70%, 27.8% and 2.2% of the total energy respectively. the above data shows that the large percentage of consumption of traditional energy is not environment friendly and unsustainable. it creates indoor and outdoor air pollution. the consumption of imported petroleum product has increased by 5.6% as compared to previous year and huge amount of hard earned foreign currency is used to fulfil this energy demand [9]. nepal lies at most favorable solar belt in global map. hence, nepal receives sufficient and adequate amount of solar radiation throughout the country. the range of solar insolation and sunny days are 3.6 6.2 kwhr/m2/day and about 300 days in a year [10]. the annual average sunshine hour and solar insolation are 6.8 hour/day and 4.23 kwhr/m2/day respectively [11]. the solar irradiance at eastern highland is lesser than central mid-hill region and western hill of nepal. this is because of higher range of humidity, precipitation and wind at the eastern part than at western part of nepal [12]. the reliable and genuine information regarding the solar radiation for particular site can be applied in various field like hydrology, modern agriculture, solar active and passive energy, irrigation system and climate change. further, specific understanding on gsr is required to design solar energy system. even though we have necessity of solar radiation data, only few number of measuring equipment are available due to financial constraints and maintenance. so, we have to rely on several models to estimate the solar radiation based on the easily available meteorological parameters [8]. usha joshi et al. / bibechana 18 (1) (2021) 159-169 161 the commonly used empirical models to estimate solar radiation using sunshine hour with varying degree of complexity is followed by classical work of angstrom and prescott [13,14].so far various models have been developed by a number of researchers with different regression coefficients depending on meteorological parameters and locations. [7,8,15,16]. estimation of gsr using temperature and precipitation for year 2005 and 2007, using radest 3.0 software was observed [17]. similarly, estimation of gsr using empirical model based on sunshine hour, temperature and relative humidity (abdalla model) for four different places of nepal has been done [18]. the available literature shows that there is limited study of solar radiation in nepal. that is why it is necessary to develop authentic empirical constants on the basis of meteorological parameters such as temperature, sunshine hour and relative humidity. this is due to deficiency of solar energy data and lack of sense of importance of solar energy technique. in addition that, the empirical constants should be developed for every 200m altitude because of abruptly varying geographical structure as well as complex terrain with variation of altitude (60m-8848m). different types of empirical models are used to estimate daily average solar radiation using meteorological parameters for different locations of nepal. thus found empirical constants are used to predict global solar radiation. the better performing model are those models, using sunshine duration [6, 13, 14]. the main focus of this research is to validate the performance of four empirical models based on temperature, relative humidity and sunshine hour. 2. methodology description of site kathmandu valley is capital city, and a hub of cultural as well as historical heritage, inhabited by 2.5 million people. it lies at 27.70on and 85.5oe at mean elevation of about 1350m from sea level [19, 20]. it is characterized by subtropical cool temperate climate where temperature normally varies from a minimum of 2.4oc for january to maximum of 35oc for june with annual average of mean temperature normal of 18.4oc. the annual average of precipitation normal is 1454.8mm, most of which falls during monsoon [21, 22]. the data of hourly solar radiation on horizontal surface for kathmandu were collected from archives of the department of hydrology and meteorology, government of nepal (dhm/gon) for the year 2010 to 2015. daily data of sunshine hour, maximum temperature, minimum temperature and relative humidity for the site were obtained from dhm/gon. the gsr were measured using first class cmp6 pyranometer [23]. theory hg (mj/m2/day) is the measured global solar radiation at the ground surface. ho is extraterrestrial gsr which is found at the top of atmosphere of site measured in (mj/m2/day).it is calculated theoretically as [3] 𝐻𝑜 = 24 𝜋 𝐼𝑠𝑐 [1 + 0.033 cos 360 𝑛𝑑 365 ] × [cos ∅ cos 𝛿 sin 𝜔 + 𝜔 sin ∅ sin 𝛿] (1) where, 𝐼𝑠𝑐is the solar constant which is given as, 𝐼𝑠𝑐 = 1367×3600 106 mj/m2/day (2) where, nd is the day of the year, julian days starting from january 1st (nd =1) to december 31th (nd =365). ω is hour angle, ∅(rad) being latitude and δ(rad) is the declination angle whose expressions are given as, 𝛿 = 23.45 sin [ 360 365 (284 + 𝑛𝑑)] (3) and hour angle is, 𝜔 = cos−1[− tan ∅ tan 𝛿] (4) the relation of day length, the maximum feasible sunshine length for given day is given by equation, daylength(𝑁) = 2 15 𝜔 = 2 15 cos−1[− tan ∅ tan 𝛿] (5) usha joshi et al. / bibechana 18 (1) (2021) 159-169 162 there are many empirical models to estimate solar radiation reaching the earth’s surface. among them, in this research work the empirical models are selected on the basis of availability of meteorological parameters for given sites are listed in table 1. the solar radiation data which are analyzed to check the performance of above models consist of daily average global solar radiation for kathmandu for year (2010 2015). the regression technique for the models used were performed by using matlab2015rb and advanced microsoft excel software analysis. the graph is obtained with help of origin software as well as matlab. we obtained statistical errors such as root mean square error (rmse), mean percentage error (mpe), mean bias error (mbe) and coefficient of determination (r2) to validate the efficiency of used model. 3. results and discussion the correlation of daily gsr and clearness index (kt) with relative sunshine hour, difference of ambient temperature and relative humidity is shown in table 2. it shows that the clearness index on average is more correlated than gsr with given parameters. thus, the above four empirical models are utilized to predict the gsr at this region. empirical constants are found by using regression technique, and those values are used for the estimation of daily gsr from different models for different years at trans-himalaya region separately. the estimated gsr were compared with corresponding value of measured radiation. to analyze the validity of used models we perform different statistical test. the statistical indices employed in all applied models are mpe, mbe, rmse and coefficient of determination (r2). the outcomes of these statistical analysis and values of empirical constants are mentioned in table 3. in the study for the determination of gsr, we have taken various single and multiple meteorological parameter models. among those models, model d is multiple parameter model of sunshine hour, difference of temperature and average relative humidity which perform better than other models and indicates least value of rmse, mpe, mbe and highest value of coefficient of determination. the linear variation of monthly average measured and estimated gsr is shown in fig. 1 for model d for different year. it shows that there is remarkable agreement between monthly average daily gsr for different years for model d with highly acceptable value of coefficient of determination. fig: 2 shows monthly variation of gsr from 2010 to 2015. the gsr gradually increases from december to may and sharply decrease due to high frequency of rainfall as well as cloudy days in june, july, and august till september. above graph shows the value of global solar radiation received is maximum in the month of may, it is mainly due to less cloud, slow wind, less rainfall and less solar zenith angle. however, the normal trend deviates for the months of june, july and august for all the studied sites due to the fact that maximum rainfall of the year occurs in these months. in addition, lower values of gsr is found in winter season for the year 2010 to 2014. moreover, there is lower values of gsr found during august for the year 2015. fig: 3(a), (b), (c), and (d) gives the variation of gsr and maximum temperature with month. there is close agreement between maximum temperature and gsr. in june, july and august, summer season although temperature is high, there is decrease of gsr due to heavy rainfall and cloudy sky. fig: 4 (a), (b), (c) and (d) show variation of gsr and relative humidity with month. there is opposite relation between gsr and relative humidity. in these figures, there is minimum relative humidity and higher gsr in may due to dry season. however, in rainy season, there is higher relative humidity and lower gsr which is usual practice in weather. usha joshi et al. / bibechana 18 (1) (2021) 159-169 163 table 1: list of models used for the determination of global solar radiation. model symbol parameters relation angstrom-prescott model [14, 15] a n, n 𝐻𝑔 𝐻𝑜 = 𝑎 + 𝑏 ( 𝑛 𝑁 ) swarthman-oguniada model [21] b n, n, rh 𝐻𝑔 𝐻𝑜 = 𝑎 + 𝑏 ( 𝑛 𝑁 ) + 𝑐(𝑅𝐻) modified angstrom model c n, n, δt 𝐻𝑔 𝐻𝑜 = 𝑎 + 𝑏 ( 𝑛 𝑁 ) + 𝑐(∆t) modified angstrom model d n, n, δt, rh 𝐻𝑔 𝐻𝑜 = 𝑎 + 𝑏 ( 𝑛 𝑁 ) + 𝑐 (𝛥𝑇) + 𝑑(𝑅𝐻) table 2: correlation of gsr and clearness index with given parameters. variables hg relate with variables for year kt relate with variables for year 2010 2012 2014 2015 2010 2012 2014 2015 n/n 0.2417 0.2921 -0.0041 0.7066 0.607 0.7638 0.4896 0.811 δt 0.1435 0.2473 0.0731 0.6174 0.5845 0.6193 0.4532 0.7784 rh -0.6278 -0.491 -0.3686 -0.4095 -0.5593 -0.3401 -0.1508 -0.1443 table 3: statistical indicators and empirical constants for empirical models used in research for different year using daily measured data. (optimal values are bold-faced). year model statistical tools empirical constants mpe (%) mbe (mj/m2/da y) rmse (mj/m2/ day) r2 a b c d 2015 a -7.559 0.278 2.705 0.587 0.118 0.566 b -7.593 0.262 2.706 0.586 0.065 0.573 0.001 c -5.056 0.204 2.363 0.684 -0.017 0.364 0.018 d -4.871 0.148 2.310 0.698 -0.191 0.363 0.020 0.002 2014 a -3.577 0.057 2.282 0.563 0.337 0.221 b -3.582 0.051 2.281 0.564 0.323 0.225 0.0002 c -3.367 0.049 2.235 0.581 0.299 0.154 0.006 d -3.277 -0.013 2.179 0.602 0.134 0.148 0.009 0.002 2012 a -4.911 0.007 2.885 0.606 0.295 0.414 b -4.907 0.011 2.884 0.606 0.303 0.412 0.0001 c -4.837 0.006 2.873 0.609 0.282 0.386 0.002 d -4.824 -0.003 2.870 0.610 0.254 0.383 0.003 0.0002 2010 a -3.584 -0.180 2.969 0.684 0.348 0.299 b -3.058 -0.040 2.740 0.731 0.681 0.213 -0.004 c -3.410 -0.219 2.972 0.683 0.306 0.197 0.007 d -3.005 -0.070 2.759 0.727 0.636 0.167 0.004 -0.003 all daily average a -1.525 0.089 1.628 0.720 0.325 0.272 b -1.439 0.125 1.578 0.737 0.429 0.254 -0.001 c -1.025 0.039 1.408 0.791 0.229 0.140 0.013 d -1.014 0.011 1.405 0.792 0.155 0.134 0.014 0.0007 usha joshi et al. / bibechana 18 (1) (2021) 159-169 164 (a) (b) (c) (d) fig. 1: linear variation of monthly average measured and estimated gsr at kathmandu valley fig. 2: monthly variation measured gsr at kathmandu valley for the years (2010-2015). usha joshi et al. / bibechana 18 (1) (2021) 159-169 165 fig 3: monthly variation of gsr and maximum temperature at kathmandu valley for the years (2010, 2012, 2014, 2015). fig. 4: monthly variation of gsr and average relative humidity at kathmandu valley for the years (2010, 2012, 2014, 2015). (a) (c) (b) (d) (b) (c) (d) (a) usha joshi et al. / bibechana 18 (1) (2021) 159-169 166 fig 5: monthly variation of gsr and rainfall at kathmandu valley (2010, 2012, 2014, 2015). fig: 5(a), (b), (c), and (d) shows variation of gsr and precipitation with month. among the four figures rain fall is maximum in july, august and september in fig 5(a), (c) and (d). however in fig (b) rainfall is lower in august. at this time, there is lesser gsr due to local weather condition. in the summer or monsoon season the average rainfall is about 70% to 90% of whole year and remaining months remain almost dry. hence normal trend deviate for these months [24]. the maximum and minimum value of gsr are 16.79 ± 3.9 mj/m2/day and 9.35 ± 3.08 mj/m2/day in may and august respectively for year 2015. similarly, the monthly average gsr is maximum in may is 22.97 ± 4.59 mj/m2/day and minimum in december is 9.22 ± 1.74 mj/m2/day for year2010. the clearness index in july and august is low (0.25) and for those months gsr is ((10.01 ± 3.75) and (9.35± 3.08) mj/m2/day) respectively. the lower value of gsr in this month is due to frequent rain fall in monsoon season. it is mainly due to less cloud, slow wind, less rainfall and less solar zenith angle. however, the normal trend deviates for the months of june, july and august for all the studied sites due to the fact that they are rainy seasons for the site and maximum rainfall of the year occurs in these months. in table 4, total and average gsr is lower in year 2015 and more rainfall in same year. in rainy season, sky is covered by cloud and this reduces the solar radiation reaching the ground surface. not only the meteorological factors such as rainfall, sunshine duration and temperature affect the global solar radiation but also astronomical, geometrical and physical. fig: 6, shows the comparative study of seasonal variation of gsr at four different years at kathmandu valley. in the figure the maximum and minimum gsr is found at spring and winter season (a) (b) (c) (d) usha joshi et al. / bibechana 18 (1) (2021) 159-169 167 respectively. however, there is maximum fluctuation of gsr at summer season, it happens due to the presence of clouds and more rain fall during this time. in figure, standard deviation is used to compare the fluctuations in gsr. among the years 2015 has less gsr than others. fig. 7,8 shows the variation of gsr and clearness index with years in box plot. in year 2015 gsr is lower (12.662 ± 4.21 mj/m2/day) than in other year. it also seen from table 3. in year 2015, clearness index or transmittance of atmosphere is also low due to more rainfall. in 2015, gsr is slightly overestimated likewise for the year 2014, 2012, 2010 there is gradual increase in underestimation, it is due to variation of rainfall pattern and local weather condition. due to the earthquake in nepal (april 25, 2015, saturday), the air pollutants escalated, which reduced the clearness index (kt) and as a result lower global solar radiation. the prediction of gsr for 2017 for kathmandu and khumaltar is observed from empirical constants obtained from above analysis shown in fig.9. the empirical constants for model e-19, a = 0.115, b = 0.134, c = 0.014 and d = 0.0007, is used for prediction. the predicted values are slightly less than observed values for kathmandu for the month march, june and october as it depends upon meteorological parameters. the yearly predicted average value of gsr for kathmandu and khumaltar is14.56 mj/m2/day and 14.16 mj/m2/day for year 2017. the total predicted yearly gsr for kathmandu and kumaltar are 5315.16 mj/m2/day and 5169.78 mj/m2/day respectively. fig 6: seasonal variation of gsr at kathmandu for year (2010-2015). table 4: variation of gsr and rain fall in different year at kathmandu valley. year 2015 2014 2012 2010 yearly mean gsr (mj/m2/day) 12.662 ± 4.21 14.499 ± 3.45 16.683 ± 4.6 16.033 ± 5.7 yearly total gsr (mj/m2/day) 4621.594 ± 0.22 5292.228 ± 0.18 6105.823 ± 0.24 5852.224 ± 0.3 max gsr (mj/m2/day) 22.23 may 4 19.97 – 8 may 26.99 13 may 30.533sep 26 min gsr (mj/m2/day) 1.43 march 1 4.65 dec 16 2.95 -july 13 0.026 sep 29 total rain (mm) 1649.4 1579.7 1465.94 1480.9 max rain (mm) 115.5 may 11 93.1 jul 1 75mm sep 14 80.7 jul 22 winter spring summer autumn 0 5 10 15 20 25 g s r ( m j /m 2 /d a y ) seasons 2010 2012 2014 2015 tia usha joshi et al. / bibechana 18 (1) (2021) 159-169 168 gsr-2015 gsr-2014 gsr-2012 gsr-2010 6 8 10 12 14 16 18 20 22 24 26 g s r ( m j /m 2 /d a y ) range within 3iqr median line mean outliers year tia fig. 7: yearly variation of gsr for different year for given location 2015 2014 2012 2010 0.2 0.3 0.4 0.5 0.6 0.7 c le a rn e s s i n d e x (k t ) range within 1.5iqr median line mean outliers year tia fig. 8: variation of clearness index for different year at kathmandu valley. fig. 9: monthly variation of measured and predicted gsr for kathmandu and khumaltar for year 2017. 4. conclusion the maximum and minimum values of monthly average global solar radiation are found (19.29 ± 3.91) mj/m2/day and (11.15 ± 1.55) mj/m2/day in may and december, respectively. the annual average global solar radiation is about 14.97 ± 4.49 mj/m2/day which is significant amount to operate many more energy based devices .the overall performance of parameters rmse, mbe, mpe and r2 are found to be 1.405, 0.011, -1.014 and 0.792, respectively in the model d. these statistical errors showed that this research work is meaningful for the estimation of global solar radiation on the basis of sunshine hour, difference of ambient temperature and relative humidity. it indicates that the estimated values of global solar radiation can be very efficiently used to compensate for the energy deficiency in the country. it concluded that the availability of global solar radiation is very encouraging from application point of view. at the end, the predicting regression coefficients could be employed for the estimation of global solar radiation at the similar climatic locations of nepal. acknowledgment authors sincerely express deep thanks to department of hydrology and meteorology (dhm), government of nepal for providing relevant meteorological data. authors would like to give special thanks to r. bachchan, p.m. shrestha, faculty members and staffs of dept. of physics, patan multiple campus, tu, nepal and faculty members of applied sciences, ioe, pulchowk campus, tu. i would like to thank nast for providing financial support to forward my research work. references [1] k. n. liou, an introduction to atmospheric radiation, academic press (2002). [2] m. iqbal, an introduction to solar radiation, academic press, new york (1983). usha joshi et al. / bibechana 18 (1) (2021) 159-169 169 [3] j. a. duffie and w.a. beckman, solar engineering of thermal processes, john wiley & sons, ins (2013). [4] m.l. slaby, fundamentals of atmosphiric physics, acedemic press,new york (1995). [5] k. .n. poudyal., estimation of global solar radiation potential in nepal, ph.d.dissertation ioe, tu (2015). [6] d. banjade et al., estimation of global solar radiation using empirical models at benevento, italy, national seminar on power and communication sectors development (pcsd), kathmandu, nepal (2010) 41-44. [7] f. besharat et al., empirical models for estimating global solar radiation: a review and case study. renewable and sustainable energy reviews 21(2013)798–821. [8] m.j. ahmad and g.n. tiwari, solar radiation models–review. international journal of energy and environment 1(3) (2010) 513-532. [9] economic survey 2018/19, gov, ministry of finance. [10] wecs. water and energy commission secretariat, energy sector synopsis report, gov of nepal (2010). [11] j. n. shrestha et al., renewable energy in nepalprogress at a glance from 1998 to 2003, retrud03, 12-14 october, kathmandu, nepal, (2003). [12] international energy association (2010). key world energy statistics, international energy agency, paris. (2017). [13] a. angstrom, solar and terrestrial radiation, quarterly journal of the royal meteorological society 50 (1924) 121-125. [14] j. a. prescott, evaporation from a water surface in relation to solar radiation, transactions of the royal society of south australia 64 (1940) 114118. [15] m.s. okundamiya et al., evaluation of various global solar radiation models for nigeria, international journal of green energy 13(5) (2016) 505512. [16] c. augustine and m. n. nnabuchi, relationship between global solar radiation and sunshine hours for calabar, port harcourt and enugu, nigeria, international journal of physical sciences 4(4) (2009) 182-188. [17] k. n. poudyal et al., estimation of daily global solar radiation; nepal experience, measurement, 46 (2013) 1807-1817. [18] krishna r. adhikari et al., estimation of global solar radiation for four selected sites in nepal using sunshine hour, temperature and relative humidity, journal of power and energy engineering 1 (2013) 1-9. [19] central bureau of statistics, national population and housing census 2011, government of nepal, national planning commission secretariat (2012). [20] introduction (2018). www.kathmandu.gov.np. [21] p. r. pant and d. dongal, kathmandu valley profile, kathmandu metropolitan city (2009). [22] climate (2018). [online]. www.dhm.gov.np. [23] kipp and zonen, manual cma and cmp series, instruction manual, version: the netherlands (2006). [24] j. l. nayava et al., impact of climate, climate change and modern technology on wheat production in nepal: a case study at bhairahawa, journal of hydrology and meteorology 6(1) (2009) 1-14. http://www.kathmandu.gov.np/ http://www.dhm.gov.np/ bibechana 18 (1) (2021) 201-213 201 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal an overview on the non-destructive in-depth surface analysis of corrosion-resistant films: a case study of w-xcr deposits in 12 m hcl solution jagadeesh bhattarai* central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal *email: bhattarai_05@yahoo.com https://orcid.org/0000-0003-0058-079x article information: received: june 6, 2020 accepted: june 28, 2020 keywords: non-destructive angle-resolved xps in-depth analysis corrosion-resistant w-based sputter deposits abstract non-destructive in-depth analysis of the surface films formed on the sputterdeposited binary w-xcr (x = 25, 57, 91 at %) alloys in 12 m hcl solution open to air at 30 c was investigated using an angle-resolved x-ray photoelectron spectroscopic (ar-xps) technique to understand the synergistic corrosion resistance effects of showing very low corrosion rates, even lower than both alloying metals of the deposits. the average corrosion rates of these three tungsten-based sputter deposits found to be more than five orders of magnitude (between 3.1 × 10−3 and 7.2 × 10−3 mm/y) to that of chromium and also nearly one order of magnitude lower than that of tungsten metals. such high corrosion resistance of the sputter-deposited w-xcr alloys is due to the formation of homogeneous passive double oxyhydroxide film consisting of wox and cr4+ cations without any concentration gradient in-depth after immersion in 12 m hcl solution open to air at 30 c from the study of the non-destructive depth profiling technique of ar-xps. consequently, both alloying elements of tungsten and niobium are acted synergistically in enhancing high corrosion resistance properties of the alloys in such aggressive electrolyte. doi: https://doi.org/10.3126/bibechana.v18i1.29222 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction the method of looking into all components distribution in all depths/layers of a thin surface film is called the in-depth surface analysis. it can estimate the in-depth compositional variation of the thin surface (i.e., nano to micrometers) films formed on the solid substances using both destructive and non-destructive spectroscopic techniques like ar-xps, auger electron spectroscopy (aes), ion scattering so on. a comprehensive briefing of both the destructive and non-destructive in-depth compositional analyses of the thin solid surfaces was done since the 1970s by various researchers [1-9]. among these in-depth analysis techniques, the non-destructive ar-xps http://nepjol.info/index.php/bibechana mailto:bhattarai_05@yahoo.com https://orcid.org/0000-0003-0058-079x https://doi.org/10.3126/bibechana.v18i1.29222 https://creativecommons.org/licenses/by-nc/4.0/ jagadeesh bhattarai / bibechana 18 (1) (2021) 201-213 202 technique has been widely used as one of the promising in-depth compositional analyses of the thin films to investigate chemical constituents, oxidation states, binding energies and electronic structures of the surface films formed on any solid substrates after a valuable contribution of siegbahn and his co-researchers in the 1970s [10]. in principle, the in-depth information of such thin film depends on the effective escape depth of the ejected photoelectrons, which increases with an increase in the take-off angle of photoelectrons (toa) relative to the surface of the sample specimen as explained elsewhere [11-15]. therefore, the apparent compositions of the thin surface films on the corrosion-resistant alloys should be changed with the toa in the ar-xps measurements. in general, the surface sensitivity is varied by changing the toa and hence the intensity signals of the ejected photoelectrons from the sample species are located in the exterior part of the surface films at a low value of the toa [13]. for corrosion and materials scientists, the ar-xps technique becomes one of the very viable in-depth surface characterization tools to study the mechanism of very high corrosion-resistant of metals or/and alloys during the last three decades [16-32]. it allows researchers to check out successfully the constitution of homogeneous or heterogeneous passive surface films formed on the corrosion-resistant metal or/and alloys. it is purposeful for pointing out here that the chemically homogeneous nature of amorphous and nanocrystalline alloys are responsible for their high corrosion resistance owing to the formation of uniform protective passive films that can separate the bulk alloy from aggressive solutions [33]. such sputter-deposited amorphous or nano-crystalline chromium-, molybdenumand tungsten-based binary and ternary alloys showed higher corrosion resistance properties than those of alloyconstituting elements in very corrosive media [31, 33] as outlined subsequently. despite a very few information about the ar-xps measurements in the early of the 1990s [34], its applications have been widely accepted for the reason out behind showing synergistic corrosion resistance properties of the sputter-deposited binary and ternary chromium-, molybdenumand tungsten-based alloys in very aggressive electrolytes since 1995 ad. the sputter-deposited amorphous/nano-crystalline chromium-based binary and ternary alloys with alloying metals of niobium [20, 21], titanium [22], zirconium [23], and simultaneous additions of aluminum and molybdenum [17, 18] showed high corrosion resistance properties, mostly due to the formation of the homogeneous oxyhydroxide constituted passive films formed on the respective alloys surface from electrochemical, and xps with arxps analyses. furthermore, sputter deposits of the molybdenum-based binary and ternary alloys with alloying metals of tantalum [26], niobium [35], titanium [36], and simultaneous additions of chromium and nickel [37] showed high corrosion resistance properties, mostly due to the formation of homogeneous surface films formed on these sputter-deposited binary and ternary alloys without distinct heterogeneous distribution of ions. since tungsten belongs to the same family as chromium and molybdenum metals in the periodic table, similar behavior of showing high corrosionresistant properties expects for the sputterdeposited tungsten-based binary and ternary alloys in aggressive environments. a small addition of tungsten in stainless steels enhanced their passivity and pitting corrosion resistance properties of [38, 39]. very few works on the corrosion of different alloys containing small amounts of tungsten was carried out before 1995 [39-43], probably due to its high melting point and difficult to prepare tungstenbased single phase solid solution alloys with high concentrations of tungsten. to solve such a problem of the preparation of wbased alloys in a wide composition range was successfully solved using the sputter deposition jagadeesh bhattarai / bibechana 18 (1) (2021) 201-213 203 technique since 1995 ad. the sputter-deposited binary amorphous or nano-crystalline tungsten alloying with metals; chromium [44-47], titanium [48-45], zirconium [29, 53], molybdenum [54-56], niobium [57-60], and tantalum [61-64], nickel [6567], and ternary w-cr-ni [68-71] and w-cr-zr [72-79] alloys were prepared in the wide composition range and they showed higher corrosion resistance than those of alloy-constituting metals in corrosive environments of hcl, nacl, and naoh solutions. from conventional xps analysis, it was reported that the higher corrosion resistance than alloying components of these tungsten-based alloys is considered due to the formation of spontaneously passivated films which are composed of double oxyhydroxide of wox and cations of the alloying elements. among these binary and ternary tungsten-based alloys, the w-ta alloys showed highest corrosion resistance, and comparatively low corrosion resistance behavior among other binary tungsten-based alloys in very aggressive 12 m hcl solution at 30 °c [19, 31], although the sputterdeposited nano-crystalline w-cr alloys containing up to 91 at % chromium showed significantly higher corrosion resistance than its alloying tungsten and chromium metals [31, 44, 45]. in particular, the corrosion rate of the w-xcr alloys containing 25-91 at % of chromium shows more than five orders of magnitude lower than the sputter-deposited chromium and even nearly one order of magnitude lower than the corrosion rate of the tungsten deposit in 12 m hcl solution at 30 °c as shown in fig. 1 [31]. however, the sputter-deposited binary mo-xcr alloys did not exceed their corrosion rates than alloying molybdenum in 12 m hcl [25] which was noted mostly due to the formation of a heterogeneous passive film formed on the alloy surface from the non-destructive in-depth analysis technique of ar-xps. in this context, this paper focused to study the in-depth distributions of wox and cr4+ ions in the passive films formed on the binary w-xcr (x = 25, 57, 91 at %) sputter deposits in 12 m hcl solution at 30 °c, open to air using the non-destructive ar-xps technique which might be further useful to justify higher corrosion resistance properties of the alloys than those of tungsten and chromium metals. fig. 1: corrosion rates of the sputter-deposited tungsten, niobium and w-xnb alloys after immersion for 168 h in 12 m hcl solution open to air at 30 c [31] 2. materials and method preparation and characterization of w-xcr alloys the tungsten alloys containing 25, 57, and 91 atomic percentage (at %) chromium were prepared on glass substrate using dc sputtering machine as described elsewhere [44], and these alloys are called sputter-deposited w-xcr alloys. three sputter-deposited w-xcr alloys were characterized as nano-crystalline structure having an apparent grain size between 8 and 15 nm [31] from xrd patterns using scherrer formula as describes elsewhere [54, 80]. before the immersion tests and ar-xps analyses, the alloy specimens were mechanically polished with a sic paper having the grit number 1500 in cyclohexane, degreased by acetone, and dried by blowing dry air to remove the oxide film formed on the surface of the alloys as described elsewhere [81-83]. the average corrosion jagadeesh bhattarai / bibechana 18 (1) (2021) 201-213 204 rate was estimated using weight loss methods as described elsewhere [84, 85]. in-depth surface analysis of sputter-deposited w-xcr alloys the in-depth composition of the thin films formed on the w-xcr alloys was analyzed by ar-xps. before and after immersion in 12 m hcl solution, xps spectra were taken using a shimadzu esca– 850 photoelectron spectrometer with mgk (hν = 1253.6 ev) radiation for surface analyses. xps spectra peaks of tungsten, chromium, carbon, oxygen, and chlorine for the sputter-deposited nano-crystalline w-xcr (x = 25, 57 91 at %) alloys were firstly recorded over a wide binding energy region (that is, 0–1000 ev), and then the most intense peaks of the w 4f, cr 2p3/2, c 1s, o 1s, and cl 2p electrons were recorded in the binding energy range of 20 ev. the peak shift caused by the charging effect was corrected using the c 1s peak, and its value of 285.0 ev was considered for all the measured xrp spectra corrections as recommended elsewhere [86]. for the alloy specimens after immersed in 12 m hcl solution, a very weak cl 2p spectrum was detected at about 199.0 ev. however, the concentration of the chloride ion was not considered for the quantitative analyses of the surface films in this study because the intensity of the chloride ion is very low for quantitative analyses. the o 1s spectrum was composed of two peaks; the lower binding energy peak at 530.4 ev was assigned to om oxygen, and the higher binding energy peak at 532.3 ev was assigned to oh oxygen [87, 88]. the om oxygen corresponds to o2− ions, and oh oxygen corresponds to oh− ions and bound water in the surface film. the measured spectrum of w 4f electron was separated into wox 4f (oxidized w) and w0 4f (metal w) and the measured spectrum of cr 2p electron was separated into cr3+ 2p3/2 (oxidized cr) and cr0 2p3/2 (metal cr) for the sputter-deposited w-xcr alloys. furthermore, the w0 4f spectrum has consisted of w4+ 4f, w5+ 4f, and w6+ 4f spectra. the integrated intensities of the w0 4f, w4+ 4f, w5+ 4f, w6+ 4f, cr0 2p, and cr4+ 2p were obtained by the same method as those described elsewhere [31]. the photoionization cross-section of the w 4f and cr 2p3/2 electrons relative to the o 1s electrons used were 2.97 [40] and 1.71 [88], respectively. the in-depth compositions distribution in both the passive films and underlying alloy surfaces were quantitatively determined using three layers model [30] after the integrated intensities of these spectra of the w-xcr alloys were obtained. the angle between the alloy sample specimen surface and the direction of photoelectron to the detector was changed using tilted-specimen holders at 30, 45, 60, and 90 for ar-xps analysis as discussed elsewhere. 3. results and discussion the average corrosion rates of the sputter-deposited w and cr metals in 12 m hcl were estimated about 2.76  10–2 mm/y and 2.70  102 mm/y, respectively, while it was estimated nearly five orders of magnitude lower than chromium, and also about one order of magnitude lower than tungsten (i.e., about 3.1-7.2  10–3 mm/y) as mentioned above. consequently, it can be said that simultaneous additions of both w and cr improve the corrosion resistance properties of the sputterdeposited w-25cr, w-57cr, and w-91cr alloys synergistically. the causes of showing such synergistic corrosion resistance effects of tungsten and chromium of the sputter-deposited w-xcr alloys are further studied here using ar-xps analysis. ar-xps analysis of w-xcr alloys the experimental results of the ar-xps measurements are helpful to clarify the mechanism of showing the higher corrosion resistance behavior of the sputter-deposited binary w-xcr alloys than those of alloying elements in 12 m hcl solution. because the in-depth surface analyses of the spontaneously passivated double oxyhydroxide films formed on the w-xcr alloys using arxps analysis give better understandings of the tungsten jagadeesh bhattarai / bibechana 18 (1) (2021) 201-213 205 and niobium effects in the corrosionresistant nature of the alloys. the information about the indepth compositional distribution of metallic and oxidized species and anions in the passive films of the w-xcr alloys might be insightful to know whether the film is homogeneous or not. the measured spectra of w 4f electrons into the metallic w0 4f and oxidized wox 4f, and of cr 2p electrons cr0 2p3/2 and cr3+ 2p3/2 spectra were separated as shown in figs. 2 and 3 for the w-25cr and w-57cr alloys, respectively, in the given conditions. the w0 4f spectrum consisted of doublet peaks corresponds to w0 4f7/2 and w0 4f5/2 electrons at lower and higher binding energy. moreover, the wox 4f spectrum is also composed of three doublets of the overlapped spectra of three oxidized species of w4+ 4f7/2 and w4+ 4f5/2, w5+ 4f7/2 and w5+ 4f5/2, and w6+ 4f7/2 and w6+ 4f5/2 electrons, as shown in fig. 2. on the other hand, the cr3+ 2p3/2 and cr0 2p3/2 spectra consist of lower and higher binding energy peaks corresponding to oxidized and metallic cr 2p3/2 electrons, respectively, as shown in fig. 3. besides, the metallic and oxidized species for the w-91cr alloy were also separated at different toa of photoelectrons which is not shown here, however, the quantitative analysis is discussed subsequently. the quantitative results of the in-depth distributions of the apparent cationic fractions in the passive film surfaces and the apparent atomic fractions in the underlying alloy surfaces of the w-25cr, w-57cr, and w-91cr alloys as a function of toa of photoelectrons are shown in fig. 4. the wox ion is noticeably enriched with the deficiency of cr3+ ions in the passive films formed on both w-25cr and w-57cr alloys as shown in figs 4(a) and 4(b) without any concentration gradients of both cations in-depth of the film. therefore, it can be said that immersion for 5 hours or more in 12 m hci solution at 30 °c results in the preferential dissolution of chromium from the surface films of the w-xcr alloys containing less than 60 at % chromium, and tungsten becomes the main constituent of the passive film. similar results of the preferential dissolution of chromium and nickel, titanium, and niobium were reported for the high corrosion-resistant w-xcr-yni [32], w-xti [30], and w-xnb [89] alloys, respectively, in aggressive 12 m hcl solution. however, the trend of the in-depth distribution of wox and cr3+ ions in the passive film formed on the surface of chromium-rich w-91cr alloy is found to differ. fig. 2: examples of the deconvolution of (a) w 4f and (b) cr 2p spectra measured for the sputterdeposited w-25cr alloy after 5 h immersion in 12 m hcl solution open to air at 30 c. the cr3+ ions are concentrated with a deficiency of wox ions in the passive film formed on the w-91cr alloys as shown in fig. 4(c), although both metal ions are homogeneously distributed in-depth of the passive film. therefore, it can be said that a significant concentration of tungsten is necessary for maintaining the spontaneous passivation of the sputter-deposited w-25cr and w-57cr alloys because chromium is active in 12 m hcl solution [44]. jagadeesh bhattarai / bibechana 18 (1) (2021) 201-213 206 on the other hand, the chromium concentration is slightly higher than tungsten concentration in the passive film formed on the w-91cr alloys and hence the corrosion resistance properties of the chromium-rich w-91cr alloy showed nearly two times lower than those of other two tungsten-based alloys containing 25 and 57 at % of chromium as described above in fig. 1. furthermore, the metallic w is slightly deficient in the exterior of the underlying alloy surfaces, especially for w-25cr and w-57cr alloys, at low toa but it is found to be almost the same as in alloy composition. consequently, it can be said that both tungsten and chromium ions are homogeneously distributed indepth of the thin passive films formed on the sputter-deposited w-xcr alloys after immersion in 12 m hcl solution at 30 c which should be one of the reasons behind showing of the synergistic corrosion resistance properties by these sputterdeposited binary alloys in very an aggressive environment like 12 m hcl solution. the similar type of the synergistic effects of the higher corrosion resistance properties of the sputter-deposited binary [21, 23, 27, 28, 30, 31] and ternary [17, 18, 32] alloys than their respective alloying elements were reported in aggressive electrolytes mostly due to the formation of homogeneous passive films formed on the alloys from ar-xps analysis. it was reported that there was no concentration gradient of tungsten and titanium ions in-depth of the passive surface film and the underlying alloy surface of the sputter-deposited w-xti alloys after their exposure for 24 hours or more in 12 m hcl solution at 30 °c [30]. hence, it was presumed that such w-xti alloys showed significantly high corrosion resistance properties in such an aggressive chloride-containing environment [31]. the enrichment of chromium through its migration and diffusion at the outermost surface of the passive film formed on the sputter-deposited al-36cr-9mo alloy in 1 m hcl solution which was attributed to the faster dissolution of aluminum cations into the solution in comparison with that of chromium cations [17]. fig. 3: examples of the deconvolution of the (a) w 4f and (b) cr 2p spectra measured for the sputterdeposited w-57cr alloy after 5 h immersion in 12 m hcl solution open to air at 30 c. moreover, the quantitative analysis of the total wox ions in different layers/depths of the passive films of the w-xcr alloys were done as a function of toa of photoelectrons, and the results of the changes of the concentration ratios of w4+, w5+, and w6+ ions to the total tungsten ions in the depth of the w-25cr and w-57cr alloy surfaces as a function of toa are shown in fig. 5. the w6+ ion ratio in the passive films formed on both the alloys is significantly higher than those of the ratios of w4+ and w5+ ions in the exterior parts of the passive films, and the w6+ ion decreases with the increasing of toa, while w4+ ion increases with toa. the ratio of w5+ ion remains almost constant with the toa. jagadeesh bhattarai / bibechana 18 (1) (2021) 201-213 207 fig. 4: changes of the apparent cationic fractions in the passive surface films and atomic fractions in the underlying alloy surfaces of the w-25cr, 9w-57cr, and w-91cr alloys after immersion in 12 m hcl open to air at 30 c, as a function of toa of photoelectrons accordingly, w4+ ion is particularly concentrated in the interior (at 90 toa) of the passive film formed on the sputter-deposited w-xcr alloys, while the concentration of w6+ ion is higher in the exterior (30 to 60 toa) of the spontaneously passivated films. accordingly, the relative ratio of w6+ ion is higher in the exterior of the surface films and decreases with the depth of the passive film. fig. 5: concentration ratios of w4+, w5+, and w6+ ions to the total tungsten ions (wox) in the passive films formed on the w-25cr and w-57cr alloys. it is accepted by the corrosionists that the concentration of oxygen species present in the corrosion resistance passive films of the alloys is one of the characteristic properties. figure 6 shows the qualitative information of the in-depth distribution of oxygen species in which examples of deconvolution of the o 1s spectra measure for the sputter-deposited w-25cr alloy at 30, 45°, 60, and 90 toa of photoelectrons in the given conditions are shown in fig. 7. the alloy consists of a major oxygen species of o2− ion, although the peaks correspond to oh− ion and bound h2o at low toa (that is, at 30/45°) is remarkably higher than that at high toa (at 60 and 90) as shown in fig. 7. these results assumed that the ratio of [o2−]/[cations] is significantly increased with increasing the toa of photoelectrons and the ratio of [oh−]/[cations] is decreased with decreasing of the take-off angle of photoelectrons in the passive films of the alloys. consequently, the interior part of the passive films formed on the sputter-deposited w-xcr alloys is rather dry and well developed by m−o−m bridging, while the exterior part of the passive films formed on the alloys is slightly wet with oh− ion and h2o. formation of such type of passive films on the alloy surface might be one of the reasons for showing significantly high corrosion resistance properties by jagadeesh bhattarai / bibechana 18 (1) (2021) 201-213 208 the sputter-deposited nano-crystalline binary w-xcr alloys than those of their alloy constituting elements in such aggressive 12 m hcl solution. a similar kind of in-depth surface analysis results were reported from the previous studies for the corrosion-resistant sputter-deposited binary and ternary tungsten [27, 28, 30, 32, 89]-, molybdenum [17, 18, 21, 23]-, and chromium [25]based alloys in very corrosive environments. fig. 6: examples of the deconvolution of o 1s spectra measured for the sputter-deposited w-26nb alloy after immersion for 5 h in 12 m hcl at 30 c at (a) 15°, (b) 30°, (c) 60°, and (d) 90° of toa () fig. 7: ratios of [o2−]/[cations] and [oh−]/[cations] in the passive films formed on the w-25cr alloy. 4. conclusions this paper was focused to study the in-depth distributions of wox and cr4+ ions in the passive films formed on the binary w-xcr (x = 25, 57, 91 at %) sputter deposits in 12 m hcl solution at 30 °c, open to air using the non-destructive ar-xps analysis technique. the synergistic corrosion resistance effects of the simultaneous additions of tungsten and chromium in the sputter-deposited nano-crystalline w-xcr alloys are reasoned out by following findings based on the above discussion. a) the ar-xps analyses revealed that all cations of the binary w-xcr alloys are distributed homogeneously in the passivated oxyhydroxide films formed on the alloys. b) the lower corrosion rates of the w-25cr, w57cr, and w-91cr alloys than their alloying tungsten and chromium metals are mostly due to the formation of the homogeneous passive films composed of both w4+ and cr3+ ions without any concentration gradient in-depth of such oxyhydroxide passive films. c) the w4+ ion is particularly concentrated in the 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https://doi.org/10.1016/s0010-938x(77)80002-4 83 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal bibechana 19 (1-2) (2022) 83-89 real-time traffic prediction using monte carlo simulation: a case study of kantipath road, kathmandu, nepal niraj kumar shah1, prena chaudhary1, and gopi chandra kaphle1, * 1central department of physics, tribhuvan university, kathmandu, nepal email: gck223@gmail.com; gopi.kaphle@cdp.tu.edu.np article information: received: august 18, 2021 accepted: december 30, 2021 abstract this paper deals with the model development for the analysis of traffic data to improve efficiency and sustainability of the existing transportation system of a section of the kantipath road, kaiser library to jamal. the traffic data of the two extreme locations of the section of the road were keywords: traffic congestion/jam distribution characteristics composition of vehicles traffic prediction monte carlo simulation taken using digital video recorders. the data were extracted manually and statistically analyzed to test the different statistical distribution of traffic flow using kolmogorov–smirnov and shapiro–wilk test, and to find out different categories of vehicles along with their flow and peak hour. the kolmogorov–smirnov test reveals the traffic flow distribution is the same as cauchy, normal, inverse gaussian, logistic, gamma, and beta distributions. the dataset of kaiser library was used to predict the real time traffic flow of jamal employing monte carlo simulation in accordance to normal distribution. the forecasted and observed traffic flows show better agreement. doi: https://doi.org/10.3126/bibechana.v19i1-2.46394 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction traffic congestion is the increasing queue of vehicles on a road, characterized by the slow speed of the traffic flow, and set in when the number of vehicles on the road approaches the capacity of the road. when the vehicles are completely stopped for a certain amount of time, the situation is said to be a traffic jam. the problem of traffic congestion is faced in almost all the major cities due to increase in population and vehicles, and the limited availability of land for construction and expansion of roads. the traffic density, often taken as constant, may vary depending on the season, day of a week and even hour of a day. no traffic research has developed any means yet to accurately predict the condition under which a traffic jam may suddenly occur. the individual incidents such as accidents or sudden braking or slowing down amid smooth flowing traffic may cause a ripple effect leading to a sustained traffic jam [1]. http://nepjol.info/index.php/bibechana mailto:gopi.kaphle@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v19i1-2.46394 niraj kumar shah et al. / bibechana 19 (1-2) (2022) 83-89 84 due to the shortage of residential areas in the main parts of the cities, people are often found living in one part of the city while working in the other. mostly, the public vehicles are overcrowded and grimy inside, so in order to have a pleasurable commute from home to work and back, people prefer private vehicles. according to a 2011 estimate provided by the united states census bureau, a total of 132.3 million people commutes between their job and residential locations on a daily basis in the united states [2]. the problem of traffic congestion is severe in developing countries like nepal, as the influx of people in the cities is alarmingly high. according to the population census of 2011, the total residential population of the kathmandu valley is approximately 2.51 million [3], distributed in 899 km2 area, and is estimated to be 3.68 million by 2021 with an annual population growth rate of 3.9% [4]. the public transportation of the valley is mostly owned by the private companies, 97% of the registered vehicles [5], and there is no fixed schedule for the public transportation. the vehicles are mostly random and uncertain with no guided access to the roads. this leads to severe traffic congestion to the roads leading to market areas. furthermore, according to the economic survey 2015/16, the vehicles operating in the valley alone utilize 60% of imported petroleum [6]. it is estimated, from wasted time and additional fuel cost, that traffic jams in kathmandu cost the country nearly 165.0 million us dollar a year [7, 8]. this is a huge loss for a developing country like nepal. therefore, proper study of the traffic complexity of the valley is required for the improvement of efficiency and sustainability of the roads. in this context, a detailed study of the various roads of the kathmandu valley was drafted by the japan international cooperation agency. the study encourages people to use public transit and explores the goal of creating a long-term urban transportation network with high mobility, safety, and comfort. the study also predicts that if the current situation, without making some urgent changes, is left on its own, 80% of the roads inside the ring road will be immensely congested by 2022 [9]. similarly, the traffic composition of one day of the maitighar–tinkune road section of the kathmandu valley was determined in their peak hour during morning and evening time [10]. the paper also discusses the loss due to the bottleneck scenario. in 2004, the ministry of works and transport (road department) of gaborone, botswana published a book, the book facilitates the estimation of the future and present traffic demands for the need based development of infrastructures by considering the future traffic situation. it also highlights the importance of collection and analysis of traffic data on decision making during planning, design, construction and maintenance period of the road network [11]. in the year 2006, wach et al. determined the vehicles’ velocities and collision locations by the means of the monte carlo simulation method [12]. in 2009, du et al. developed a model for traffic assignment in local area networks using the monte carlo simulation by considering the turning probabilities at intersections [13]. in 2012, enright et al. in their paper presented a detailed model of bridge loading for free-flowing traffic by using the monte carlo simulation. the results obtained from this model match the measurements of five european highways [14]. in 2013, shengda et al. formulated a way for intelligent traffic lights based on the sequence of traffic flow in a single intersections exploiting complex mathematics and matlab [15]. in the same year, canaud et al. used probability hypothesis density filtering method for the real-time prediction of traffic, and showed that the probability hypothesis filtering method and the particle filter method are equally efficient [16]. the traffic forecasting techniques that are used by the researchers to predict the short-term traffic have their own advantages and disadvantages. the traffic forecasting is done on the basis of past traffic data. in 2015, mishra et al. used monte carlo simulation to speculate the short-term traffic of delhi-gurgaon expressway [17]. to the best of our knowledge, the implication of the monte carlo simulation for the traffic prediction has not been performed on any road of nepal till now. therefore, the present work has a lot of scope to improve the existing transportation system of different roads of nepal and serves as a basis for further study. niraj kumar shah et al. / bibechana 19 (1-2) (2022) 83-89 85 2. methodology 2.1 site selection and data collection data collection was done using sony handycam hdr-pj10 placed over two locations, one on the footbridge in jamal and another near the kaiser library on the section of the kantipath road in kathmandu, nepal. the site location is shown in fig. 1(a). the distance between these two places is 555 m. this section of the road is one of the busiest and a prime road leading to main market areas. the video graphic data of these two places were captured for the whole day from 8:00:00 to 19:00:00. the traffic distribution for every 15 minutes during the observation period is shown in fig. 1(b). the peak point of traffic flow was found at 9:45:00 and at 18:30:00. the observed traffic volume ranged from 4,700 to 7,500 vehicles per hour. from the traffic composition of vehicles, the percentages of two-wheelers and buses were found to be greatest and least respectively as shown in fig. 2(a). the contribution of public vehicles in the total vehicle flow was found to be almost constant and insignificant compared to private vehicles as shown in fig. 2(b). 2.2. kolmogorov–smirnov test and shapiro– wilk test a non-parametric kolmogorov–smirnov (ks) test is used to verify the goodness-of-fit and to determine whether an underlying probability distribution differs from a hypothesized distribution, or whether there is difference between two distributions [18]. this test is used when a comparison is to be made between observed sample distribution and theoretical distribution. the ks test is used to test whether the given sample has come from some specific distribution or not [19]. the test statistic is given by, fig. 1: (a) represents the site location. the red arrows indicate the spot where the video recorders were placed and (b) represents the number of vehicles passing through the section of the road on every 15 minutes interval (june 30, 2019). d = maximum |𝐹0(x) − 𝐹𝑑𝑎𝑡𝑎(x)| which measures the largest distance between the empirical distribution function fdata (x) and the cumulative empirical distribution fo (x). the null hypothesis is accepted if the test static d is less than the tabulated d value obtained from the ks table at a particular level of significance, otherwise an alternative hypothesis is accepted. the shapiro–wilk (sw) test is used to check if a random sample is from a normal distribution or not. several studies have demonstrated that the ks test, even in its corrected form, is less effecting for checking normality than the sw test [20]. the test statistic is given by, 𝑊 = 𝑛 𝑡=2 𝑎𝑡𝑦𝑡 ∑𝑛 (𝑥𝑡−𝑦) 𝑡=1 fig. 2: (a) represents the percentage of observed traffic composition and (b) represents the comparison of private and public vehicles with total vehicles on the section of the road over time. the private vehicles completely dominate over public vehicles. where n is number of observations, yt is value of ordered sample obtained by ordering the disorder sample, xt and at are tabulated coefficients. the null hypothesis is accepted if the test statistic w is greater than the tabulated w value obtained from the sw table at a particular level of significance. in this case, the sample belongs to a normal distribution. the sample does not belong to normal distribution if the alternative hypothesis is accepted. ∑ niraj kumar shah et al. / bibechana 19 (1-2) (2022) 83-89 86 2.3. model development for monte carlo simulation monte carlo simulation is a mathematical tool for simulating risk or uncertainty in a system by generating random variables. this method is widely used in computational physics, quantum mechanics, physical chemistry, and related applied fields, and they have a wide range of applications, ranging from complex quantum chromodynamics calculations to the design of materials that can protect experimentalists while working in radiation-hazardous areas [21-23]. furthermore, it can also be applied in finance and business. however, in this study, the purpose of developing the monte carlo simulation model is to predict the traffic flow. the section of the kantipath road chosen for the study purpose is selected in such a way that the road is uniform and there is no on/off ramp or direct access from the adjoining areas. so that the total inflow and outflow of vehicles remain the same. fig. 3: the normal distribution of the observed data counted on intervals of 1 minute and 20 seconds. fig. 4: (a) and (b) represents the normal q-q plot and box plot for the test of normal distribution of the sample of traffic data counted on the interval of 1 minute and 20 seconds. a random sample–taken from the dataset collected at the crossroad by the kaiser library, counted for 1 minute and 20 seconds interval each–was analyzed and the normal distribution of the sample was tested employing the ks test and the sw test statistics. the mean and the standard deviation of the fitted normal distribution were used to generate a new dataset with random probabilities, generated by the monte carlo simulation. the validation of the forecasted data was confirmed by comparing it with the dataset collected from the second location. since the forecasted traffic data was randomly generated, the statistical accuracy of the model was checked with the help of statistical t-test at 5% level of significance and by evaluating the mean absolute percentage error. from the ks statistics, the d value is found to be 0.060 which is less than the critical value 0.074 for the normal distribution and from the sw test, the statistic w value is found to be 0.983 which is greater than the critical value 0.017 and is pretty much close to 1.00. hence, from both the statistical tests, ks test and sw test, the sample was found to belong to the normal distribution. moreover, from the visual inspection of histogram (fig. 3), normal q-q plot (fig. 4(a)) and box plot (fig. 4(b)) showed that the traffic flow data were approximately normally distributed with a skewness of -0.361 (standard error (s. e.) = 0.172) and a kurtosis of -0.209 (s. e. = 0.342). 3. results and discussion 3.1. kolmogorov--smirnov test the traffic flow distribution obtained from every 15 minutes is compare with eight kinds of fig. 5: the probability density functions corresponding to different distributions for the dataset counted for every 15 minutes. niraj kumar shah et al. / bibechana 19 (1-2) (2022) 83-89 87 𝑖 𝑖 distributions, viz., cauchy, normal, log-normal, inv. gaussian, logistic, gamma, log-gamma and beta distributions using kolmogoro– smirnov test. the obtained plot for each of the distribution is shown in fig. 5. the cauchy distribution looks similar to normal distribution but with much heavier tails. the gamma and log gamma distributions appear same as normal and log-normal distributions respectively. in ks test, if critical d value 0.2406 at 1% level of significance is higher than calculated d value, then the observed and theoretical distributions are same. from the ks test, it has been found that the traffic flow distribution can be considered as the cauchy, normal, inv. gaussian, logistic, gamma, and beta distributions. the obtained results are summarized in table 1. table 1: kolmogorov–smirnov test distribution result for the data counted for every 15 minutes. 3.2 monte carlo simulation after performing about ten thousand of iterations using monte carlo simulation, a new dataset was fig. 6: (a), (b) and (c) represent the observed and predicted number of vehicles of different composition during the morning, afternoon and evening time respectively. the observed and predicted values are in well agreements. table 2: comparison of observed and predicted vehicle flow per 15 minutes generated with random probabilities in accordance with normal distribution for each category of vehicles as shown in fig. 6. the accuracy of the generated and the observed dataset was compared by computing the mean absolute percentage error (mape). mape = ( 1 ∑𝑁 (𝑥𝑖−𝑥 𝘍) ) * 100% 𝑁 𝑖=1 𝑥𝑖 where 𝑥𝑖 = observed value of measure; 𝑥′ = predicted value of measure and n = number of observations. the observed and predicted traffic flow of different vehicles during morning, afternoon, and evening hours along with their mape are presented in table 2. distribution maximum d value remarks cauchy 0.08313 same distribution normal 0.22480 same distribution log-normal 0.26007 different distribution inv. gaussian 0.22347 same distribution logistic 0.21266 same distribution gamma 0.23957 same distribution log-gamma 0.26315 different distribution beta 0.21214 same distribution mape of observed and predicted flows in the morning hour vehicles observed flow (vehicles/15mins) predicted flow (vehicles/15mins) mape (%) two wheeler 1096 1083 1.186 car & taxi 458 449 1.965 micro 92 97 5.435 bus 50 49 2.000 total 1696 1678 1.061 mape of observed and predicted flows in the afternoon hour two wheeler 1149 1138 0.957 car & taxi 436 452 3.670 micro 77 80 3.896 bus 47 49 4.255 total 1709 1719 0.585 mape of observed and predicted flows in the evening hour two wheeler 1202 1186 1.331 car & taxi 480 493 2.708 micro 79 87 5.063 bus 50 47 6.000 total 1811 1813 0.110 niraj kumar shah et al. / bibechana 19 (1-2) (2022) 83-89 88 4. conclusion by analyzing the traffic data, it was found that more than 66% and 90% of the total vehicles running on that section of the road were two wheelers and private vehicles respectively. the contribution of the public vehicles in the traffic composition on the section of the road seems to be almost constant and insignificant in comparison to private vehicle flows. this indicate the traffic congestion is mainly caused by the private vehicles. therefore, in order to reduce the traffic congestion, the government of nepal should increase the number of mass transit vehicles such as well facilitated buses. the traffic flow distribution of the study area, counted on every 15 minutes for the entire day of observation, is obtained to be same as cauchy, normal, inverse gaussian, logistic, gamma, and beta distributions. from the monte carlo simulation prediction study, following conclusions are drawn: • the monte carlo simulation turn out to be an excellent tool for the forecast of the real time traffic flow. the forecasted data obtained by the monte carlo simulation and the real-world observed data shows better agreement. • this method can be used by local agency for the forecast of traffic flow, as spreadsheet tools and formulae are the basic tools used for the monte carlo simulation. • the forecasted value of traffic flow can be used for the traffic light design. the traffic light can be adjusted in a manner to reduce the traffic congestion or for the optimum use of the available road networks on the basis of real-time advance forecasted data provided by the use of the monte carlo simulation. • this method with certain improvements can be used to develop the intelligent transport system for the traffic control strategy. references [1] g. orosz and g. stépán, subcritical hopf bifurcations in a car-following model with reaction-time delay, proc. royal soc. a 462 (2006) 2643–2670. 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[21] r. hill, b. healy, l. holloway, z. kuncic, d. thwaites, and c. baldock, advances in kilovoltage x-ray beam dosimetry, phys. med. biol. 59 (6) (2014) r183–231. [22] x. jia, p. ziegenhein, and s. b. jiang, gpu based high-performance computing for radiation therapy, phys. med. biol. 59 (4) (2014) r151– r182. niraj kumar shah1, prena chaudhary1, and gopi chandra kaphle1, * article information: keywords: 1. introduction 2.1 site selection and data collection 2.2. kolmogorov–smirnov test and shapiro– wilk test 𝑊 = 2.3. model development for monte carlo simulation 3. results and discussion 3.2 monte carlo simulation 4. conclusion references heera kc et al. / bibechana 16 (2019) 204-212: rcost p.204 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (0nline) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal inpatients nursing care provided in a tertiary hospital of nepal heera kc1*, sharmila shrestha2, ramananda chaudhary3, tara shah4, surya b. parajuli5,6 1department of nursing, purbanchal university-birat health college, biratnagar, nepal 2department of community health nursing, b. p. koirala institute of health sciences, dharan, nepal 3department of child health nursing, b. p. koirala institute of health sciences, dharan, nepal 4department of community health nursing, b. p. koirala institute of health sciences, dharan, nepal 5department of community medicine, kathmandu university-birat medical college & teaching hospital, morang, nepal 6nepal medical volunteer society, biratnagar, nepal *e-mail: heerakc2011@gmail.com article history: received 05 october, 2018; accepted 05 november, 2018 http://dx.doi.org/10.3126/bibechana.v16i0.21641 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract introduction: nursing care is necessary for every client seeking any type of healthcare such as health promotion, diagnosis, treatment and recovery. despite these facts, nurses are given less importance and their works are even unrecognized. objective: the objective of this study was to explore nursing care provided to inpatients of medical ward at b. p. koirala institute of health sciences, dharan, nepal. methodology: hospital based cross-sectional study was carried out in medical ward of b. p. koirala institute of health sciences, dharan from feb 2017 to oct 2018. data were retrieved from inpatient admission record book of medical ward of previous 15 months from the initiation of this research work. admission record book was reviewed and checked for completeness of the record. a total of 290 patients having complete records were enrolled. collected data were entered in microsoft excel and analysed by spss software. results: more than half patients (52.8%) were male and 44.8% belonged to janajati ethnicity. the major age group was 15-25 years (17.9%) with mean and standard deviation of 49.4±20.6. about 28.6 % of the patients were admitted due to cardiovascular related problems and poisoning (13.1%). most of the patients (67%) were admitted from emergency. median duration of stay was 4 days. every 8 out of 10 patients were recovered and discharged. general nursing care provided were maintenance of personal hygiene (91.03%), cannula site care (49.7%), providing psychological support (41%), ambulation (8.3%), back care (7.6%), catheter care(6.9%), passive exercise (2.4%), chest physiotherapy(3.7%), sponge bath(9.3%). specific care provided were propped-up positioning (36.2%), 2 hourly position change (23.4%), random blood sugar monitoring (12.4%), spo2monitoring (8.9%), watch for oxygen toxicity (9.3%), weight monitoring (3.1%) and pre cag (coronary angiography) care(2.1%). conclusion: maintenance of personal hygiene, cannula site care, psychological support, two hourly positioning and oral care were the common practices performed. keywords: academics and institutes; inpatients; medical ward; nursing care. http://nepjol.info/index.php/bibechana mailto:heerakc2011@gmail.com http://dx.doi.org/10.3126/bibechana.v16i0.20960 https://creativecommons.org/licenses/by-nc/4.0/ https://meshb.nlm.nih.gov/record/ui?name=academies%20and%20institutes https://meshb.nlm.nih.gov/record/ui?name=inpatients heera kc et al. / bibechana 16 (2019) 204-212: rcost p.205 (online publication: dec., 2018) 1. introduction nursing is considered as an art and a science, wherein caring forms the theoretical framework of nursing. nursing and caring are grounded in a relational understanding, unity, and connection between the professional nurse and the patient. care in nursing involves the application of art and science through theoretical concepts, scientific research, conscious commitment and purposeful efforts to include caring behaviors during each nurse-patient interaction [1]. the caring process is a fundamental activity of nursing that help attain, maintain, or recover optimal health and quality of life. nurses are differentiated from other health care providers by their approach to patient care and scope of practices. nurses practice in many specialities with differing levels of prescription authority [2]. caring includes cognitive, affective, psychomotor and administrative skills. these skills describes the value of nursing. nursing is a nurturing profession and caring is the essential component of its holistic practice, especially with the critically ill patient [3]. with better care environment, nurses reported more positive job experiences and patients too had significantly lower risks of death and failure [4, 5]. various study results indicate missed or omitted nursing care to be an independent predictor of hospital readmissions of patients [6]. for better patient outcome, electronic nursing care reminders are often being used in hospital settings to overcome the missed nursing care and aids in assessing the impact of technology on nursing practice [7]. evidences show nursing care has led to positive patients’ outcomes of morbidity and mortality across the age continuum. despite these facts, limited attention has been given to measuring nurses’ actions/behaviors in terms of care that is safe, effective, efficient, equitable, timely, and centered on patients and patients’ families [4, 8]. just as hospitals and clinicians caring for patients focus carefully on completing accurate diagnosis, appropriate and effective interventions, so do the nurses too in providing nursing care through appropriately planned nursing diagnosis. the proportion of nurses to patients, their qualifications and job description should therefore be carefully planned and managed to manage unnecessary patient death [9]. the roles of nurses have been expanded and resulted in greater job satisfaction and good patient outcome. a study conducted in australia suggest that patients who had longer nurse consultations were more satisfied (or=2.50, 95% ci: 1.43-4.35) and more enabled (or=2.55, 95% ci: 1.45-4.50). patients who had continuity of care with the same general practice nurse were more satisfied (or=2.31, 95% ci: 1.33-4.00). patients who attended practices where nurses worked with broad scopes of practice and high levels of autonomy were more satisfied (or=1.76, 95% ci: 1.092.82) and more enabled (or=2.56, 95% ci: 1.40-4.68) than patients who attended practices where nurses worked with narrow scopes of practice and low levels of autonomy. patients who received nursing care for the management of chronic conditions (or=2.64, 95% ci: 1.32-5.30) were more enabled than those receiving preventive health care [10]. due to these facts of nursing care for patient satisfaction and nursing leadership, we need to know the pattern of nursing practices delivered at tertiary care hospital. in tertiary care center, many complicated referral patients are admitted which needs significant nursing care for their better prognosis. evidence generated from this research will be helpful to formulate standard operating procedures (sops) on nursing care at ward level and entire hospital level. with these facts, we aimed to explore the nursing care provided to inpatients of medical ward at b. p. koirala institute of health sciences, dharan, nepal. 2. methodology this was a hospital based cross-sectional study carried out in medical ward of b. p. koirala institute of health sciences, dharan, nepal from feb 2017 to oct 2018. data were retrieved from inpatient admission record book of medical ward of previous 15 months from the initiation of this research work. admission record book was reviewed thoroughly and checked for completeness of the record. a total of heera kc et al. / bibechana 16 (2019) 204-212: rcost p.206 (online publication: dec., 2018) 290 patients having complete records were enrolled for the study. collected data were entered in microsoft excel and analysed by spss software. 3. results socio-demographic characteristics of inpatients in table 1, among inpatients in medical ward, more than half were male (52.8%) and 44.8% belonged to janajati ethnicity. the major age group among the admitted patient was 15-25 years (17.9%) followed by 45-55 years (16.2%) with mean and standard deviation of 49.4±20.6. as depicted by figure 1, majority of inpatients attending at b.p. koirala institute of health sciences were from sunsari (35.2%), jhapa (15.9%) and morang (15.2%) district. in figure 2, 28.6 % of the patients were admitted due to cardiovascular related problems followed by poisoning (13.1%). majority (66.5%) of patient were admitted in medical ward from emergency (66.5%) and opd (14.8%) (table 2). table 1: sociodemographic characteristics of the inpatients(n=290). sex frequency percentage male 153 52.8 female 137 47.2 ethnicity dalit 66 22.8 janajati 130 44.8 madhesi 25 8.6 muslim 5 1.7 brahmin/chhetri 64 22.1 age 15-25 52 17.9 25-35 33 11.4 35-45 42 14.5 45-55 47 16.2 55-65 40 13.8 65-75 44 15.2 75-85 27 9.3 85-95 5 1.7 mean ± sd 49.4±20.6 heera kc et al. / bibechana 16 (2019) 204-212: rcost p.207 (online publication: dec., 2018) fig. 1: distribution of inpatients visiting from different districts of nepal (n=290). pattern of diseases fig. 2: pattern of diseases reported among inpatients (n=290). mode of admission table 2: mode of admission of inpatients (n=290). mode of admission frequency percentage outpatient department (opd) 43 14.8 emergency 193 66.5 transfer from other wards 24 8.3 transfer from icu/ccu 30 10.4 15.9 5.2 35.2 1.7 15.2 8.6 2.4 3.8 4 1.7 0.7 4.1 1.4 2.8 0 5 10 15 20 25 30 35 40 india taplejung ilam udaypur bhojpur khotang dhankuta panchthar saptari morang tehrathum sunsari 0 5 10 15 20 25 30 12.1 28.6 8.6 1.4 8.3 3.8 9 2.1 3.1 13.1 2.8 0.7 2.4 1 2.1 0.3 0.3 0.3 percentage % heera kc et al. / bibechana 16 (2019) 204-212: rcost p.208 (online publication: dec., 2018) nursing care provided table 3: nursing care provided to inpatients (n=290). nursing care frequency percentage general care i/v cannula site care 144 49.7 back care 22 7.6 intake output 290 100.0 personal hygiene 264 91.03 sponge bath 27 9.3 health education on particular disease 42 14.5 psychological support 119 41.0 passive exercise 7 2.4 ambulation 25 8.6 chest physiotherapy 11 3.7 specific care positioning-propped up 105 36.2 watch for oxygen toxicity 27 9.3 2 hourly position change 68 23.4 watch for ugi bleeding 10 3.4 dressing for thrombophlebitis 1 0.3 catheter care 20 6.9 observe for bradycardia 1 0.3 endotracheal tube care 1 0.3 cardiac monitoring 5 1.7 weight monitoring 9 3.1 leg elevation 2 0.7 abdominal girth charting 3 1.0 cold sponging 2 0.6 spo2 monitoring 36 12.41 n/g tube feeding 4 1.2 ecg 4 1.2 diabetic foot care 1 0.3 preoperative care for cag 6 2.1 rbs monitoring 41 14.13 wound care 2 0.6 nursing care provided to inpatients were divided to general care and specific care which is shown in table 3. majority (91.03%) of inpatients received the care related to maintenance of personal hygiene (hair care, nail care, oral care and grooming). intravenous cannula (i/v) site care was provided to 49.7% of the inpatients based on their need. maintenance of intake output pattern was received by all patients. forty one percent of the patients were provided reassurance while almost 15 % inpatient received health education on particular disease. concerning specific nursing care 36.2 % patients were provided to maintain their position to ease their breathing, 23.2% were changed position 2 hourly and spo2 monitoring was done among 12.41%. heera kc et al. / bibechana 16 (2019) 204-212: rcost p.209 (online publication: dec., 2018) outcome of patients table 4: outcome of inpatients (n=290). outcomes frequency percentage recovered and discharge 223 76.9 expired 10 3.4 leave against medical advice (lama) 14 4.8 discharge on patient request (dopr) 19 6.6 refer to another hospital 3 1 transfer to another ward 14 4.8 transfer to icu/ccu 7 2.4 duration of hospital stay range: 1-35 days median: 4 days 4. discussion a hospital based cross-sectional study was conducted in medical ward of b. p. koirala institute of health sciences. admission record book was reviewed thoroughly and checked for completeness of the record of which 290 patients having complete records were enrolled for the study. in present study, majority (91.03%)of inpatients received the care related to maintenance of personal hygiene (hair care, nail care, oral care and grooming). oral care is one of the important nursing care among inpatients of medical ward. in a systematic review, it was found that oral hygiene have an impact on incidence and outcomes of respiratory diseases like pneumonia and chronic obstructive pulmonary disease in people living in the community and in long-term health care facilities. such incidence can be reduced by oral hygiene measures [11]. similarly another study conducted in canada supports the importance of oral care that explains a positive body image and the perception of adequate oral health are linked to increased social contacts, as well as improved health and well-being irrespective of age [12]. a study reported that oral health have an impact on daily performances where they identified difficulty of eating and enjoying food (42.3%), and speaking and pronouncing clearly (10.3%)due to inadequate oral care [13]. thus nursing personnel should provide oral care as it is one of the important nursing care to improve overall patient outcome at hospitals. in this study, one third of patients received specific nursing care that is two hourly position change. this is an important specific nursing care for bed ridden patients to prevent pressure sores which was evident by a research conducted at sweden where nursing staff used to reposition the patients who were high risk than those assessed as low risk. this led to the conclusion that repositioning and positions used in the prevention of pressure ulcers is important [14]. a research study found that, patients were repositioned frequently during the day and evening and least at night time [15]. pressure ulcers can predispose to a variety of complications that include bacteremia, osteomyelitis, squamous cell carcinoma, and sinus tracts. the three components of pressure ulcer prevention that must be considered in any patient include management of incontinence, nutritional support, and pressure relief. various electronic devices and materials have been practiced to prevent pressure ulcer [16]. however in low income countries where such devices can’t be affordable and approachable carefully heera kc et al. / bibechana 16 (2019) 204-212: rcost p.210 (online publication: dec., 2018) planned nursing care can contribute to prevent the pressure sores. in this study, intravenous cannula site care was provided to 49.7% of the inpatients based on their need. similar finding was revealed in a hospital based study conducted at johor, malaysiawhere83.7% followed the correct practice of care and maintenance of iv cannula. the researcher also suggested that nurses should know about this vital procedure in order to prevent risk and complication to the patient. therefore, iv cannula site care is one of the important nursing care and it should be followed correctly [17]. in this study maintenance of intake output was received by all patients. a research suggested that advanced heart failure, renal diseases are often associated with a variety of hemodynamic, fluid, and electrolyte derangements. this involves vigilant assessment of hydration, fluid treatment plan personalized for the specific patient, repeated and frequent reassessment of fluid and electrolyte balance, and appropriate changes in the treatment plan in response to the rapidly changing clinical situation of the patient that cannot be maintained by clinicians along. hence nursing care is utmost to such patients [18]. it helps the inpatients for better clinical outcome. in the present study 36.2 % patients were kept in propped up position to ease their breathing and spo2 monitoring was done among 12.41%. likewise study conducted in australia found elevation of the head of the bed (1-45°) was the most frequently adopted position[15]. present study also identified catheter care(6.9%), chest physiotherapy (3.7%), ambulation (8.6%), nasogastric tube feeding (1.2%), preoperative care (2.1%) and diabetic foot care(0.3%) as important nursing care provided to the patient. forty one percent of the patients were provided psychological support while almost 15 % inpatient received health education on particular disease. in a study the mean total ‘satisfaction with nursing care scale’ score was 62.08 ± 20.94, and the mean total ‘experience of nursing care scale’ was 71.97 ± 11.97. the highest satisfaction items were reported as ‘the skillfulness of nurses’ and ‘the nurses’ respect for the patients’ privacy’ concluding that patients require more individualized care from nurses regarding education, communication and comfort [19]. this suggests that nursing care is fundamental for patient satisfaction and positive image with hospital environment, rapid recovery and wellbeing. additionally, this study found that almost 8 out of 10 patients were recovered and discharged. the world alliance for patient safety reported that 10% of hospital patients in developed countries suffer an adverse event each year [20]. this is a good sign of care. patient outcome depends upon care provided by various discipline that is medical doctors, nursing professionals, paramedics, supporting staffs and even administration. it is evident that, nursing care is vital for better prognosis. in support to this, a research found that routine use of care maps was used to minimize unnecessary patient death [9]. 5. conclusion maintenance of personal hygiene, intravenous cannula site care, psychological support and two hourly positioning were common practice performed. recommendations individual level disease specific nursing care research needs to be done in a large setting. nursing care practices should be studied by using various nursing care tools and guidelines to identify the applicability and effectiveness. limitation of the study this research could not identify individual level nursing care based on disease pattern. the impact on patient outcome due to nursing care could not be established. heera kc et al. / bibechana 16 (2019) 204-212: rcost p.211 (online publication: dec., 2018) acknowledgement the authors would like to acknowledge nursing officer and ward staffs of medical ward of b. p. koirala institute of health sciences, dharan. conflict of interest we declare no conflict of interest. financial disclosure no grant or financial support has been received for this research work. references [1] t. jasmine, art, science, or both? keeping the care in nursing, the nursing clinics of north america 44(4) 2009415-21. pubmed pmid: 19850178. epub 2009/10/24. eng. 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[13] p. andersson, j. kavakure, p. lingstrom, the impact of oral health on daily performances and its association with clinical variables in a population in zambia, international journal of dental hygiene 15(2) (2017) 128-34. pubmed pmid: 26283168. epub 2015/08/19. eng. heera kc et al. / bibechana 16 (2019) 204-212: rcost p.212 (online publication: dec., 2018) [14] u. kallman, s. bergstrand, a. c. ek, m. engstrom, m. lindgren, nursing staff induced repositionings and immobile patients' spontaneous movements in nursing care, international wound journal 13(6) (2016) 1168-75. pubmed pmid: 25779932. epub 2015/03/18. eng. [15] s. latimer, w. chaboyer, b. m. gillespie, the repositioning of hospitalized patients with reduced mobility: a prospective study, nursing open 2(2) (2015) 85-93. pubmed pmid: 27708804. pubmed central pmcid: pmc5047314. epub 2015/07/14. eng. [16] s. latimer, w. chaboyer, b. gillespie, pressure injury prevention strategies in acute medical inpatients: an observational study, contemporary nurse 52(2-3) (2016) 326-40. pubmed pmid: 27228380. epub 2016/05/27. eng. [17] i. f. arbaee, ahmad nizal mohd ghazali, nurses knowledge and practice towards care and maintenance of peripheral intravenous cannulation in pantai hospital, batu pahat, johor, malaysia, malaysia: open university malaysia, 2014. [18] t. m. kear, fluid and electrolyte management across the age continuum, nephrology nursing journal :journal of the american nephrology nurses' association 44(6) (2017) 491-6. pubmed pmid: 29281773. epub 2017/12/28. eng. [19] e. kol, f. arıkan, e. i̇laslan, m.a. akıncı, m.c. koçak, a quality indicator for the evaluation of nursing care: determination of patient satisfaction and related factors at a university hospital in the mediterranean region in turkey, collegian (royal college of nursing, australia) 25(1) (2018) 51-6. [20] world health organization, world alliance for patient safety: forward programme, 2004. https://www.researchgate.net/profile/ahmad_nizal_mohd_ghazali2?_sg=w5qk_xbxxl4m_9h-uekxavfrr525_cys1ykkapwboq6xuhuupeyhrvqjhlseji3nt-i16ag.zq26jmjzmwkjujtwszoiletfiehrkoj7dgdai_hzynqhvxzwyhs0g4mi1gyzw9crrul1pvnbjimxtir2up25ow bibechana 18 (2) (2021) 68-79 68 electronic and magnetic properties of defected mos2 monolayer hari krishna neupane1, 2, narayan prasad adhikari2* 1amrit campus, institute of science and technology tribhuvan university, kathmandu, nepal 2central department of physics, institute of science and technology tribhuvan university, kathmandu, nepal *email: narayan.adhikari@cdp.tu.edu.np article information: received: december 28, 2020 accepted: april 17, 2021 keywords: dft magnetic moment monolayer spins vacancy defects abstract it is interesting to understand the effect of defects in 2d materials, because vacancy defects in 2d materials have novel electronic and magnetic properties. in this work, we studied electronic and magnetic properties of 1s vacancy defect (1sv-mos2), 2s vacancy defects (2sv-mos2), 1mo vacancy defect (mov-mos2), and (1mo & 1s) vacancy defects ((mo-s)v-mos2) in 2d mos2 material by firstprinciples calculations within spin-polarized density functional theory (dft) method. to understand the electronic properties of materials, we have analyzed band structures and dos calculations, and found that 1sv-mos2 & 2sv-mos2 materials have semiconducting nature. this is because, 1sv-mos2 & 2sv-mos2 materials open small energy band gap of values 0.68 ev & 0.54 ev respectively in band structures. but, in mov-mos2 & (mo-s)v-mos2 materials, energy bands around the fermi level mix with the orbital’s of mo and s atoms. as a result, bands are split and raised around and above the fermi energy level. therefore, mov-mos2& (mo-s)v-mos2 materials have metallic nature. we found that mos2, 1sv-mos2& 2sv-mos2 materials have non-magnetic properties, and mov-mos2& (mo-s)v-mos2 materials have magnetic properties because magnetic moment of mos2, 1sv-mos2& 2sv-mos2 materials have 0.00 µb/cell value and mov-mos2& (mo-s)v-mos2 materials have 2.72 µb/cell & 0.99 µb/cell respectively. therefore, non-magnetic mos2 changes to magnetic mov-mos2 & (mo-s)v-mos2 materials due to mo and (1mo & 1s) vacancy defects. magnetic moment obtained in movmos2& (mo-s)v-mos2 materials due to the distribution of up and down spins in 4p, 4d & 5s orbitals of mo atoms and 3s & 3p orbitals of s atoms in structures. the significant values of magnetic moment are given by distributed spins in 4d orbital of mo atoms and 3p orbital of s atoms. doi: https://doi.org/10.3126/bibechana.v18i2.33905 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ mailto:narayan.adhikari@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v18i2.33905 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana hari krishna neupane and narayan prasad adhikari / bibechana 18 (2) (2021) 68-79 69 1. introduction two dimensional (2d) materials with atomic thickness have become candidates for wearable electronic devices in the future. graphene and transition metal sulfides have received extensive attention in logic computing and sensing applications due to their lower power dissipation [1-3]. however, the lack of intrinsic band gap and non-magnetic nature of graphene limits its practical applications in widely expanding field of carbonbased devices. therefore, the transition metal dichalcogenides material (tmd) molybdenum disulphide (mos2) is a suitable candidate for logic computing (logic computing is the sequence of operations (hardware or software) performed by computers) and sensing (devices) applications. mos2 is made by mo and s atoms stacked together to give s-mo-s in a triangular prismatic arrangement [4]. the band structure of mos2 depends on the number of layers, and the single layer mos2 has a direct band gap of energy 1.80 ev [5]. the band is opened in between the lower energy band of conduction band and higher energy band of valence band. due to the wide band gap (1.80 ev), mos2 provides huge opportunities for electrical and optoelectronics [6-9]. in recent years, a lot of research has been carried out surrounding mos2, and various new electronic devices based on mos2 have emerged, including gas sensors, resistive memory, photo detectors, integrated logic circuits, signal amplifiers, flexible optoelectronic devices, solar cells and lubricants etc. [10-13]. electronic and magnetic properties of 2d pristine and defected materials are attracting properties in solid-state physics because they have potential applications in industrial as well as academic sectors. hence, it is interesting to understand the effect of defects in 2d materials [14-16]. the vacancy defects in solids causes deviation of atoms or ions from the periodicity and they are used to find innovative properties. they can be used to design new materials [17]. to our best knowledge, mo and s atoms vacancy defects (i.e. 1mo atom only, 1mo and 1s atoms together) in monolayer mos2 material have not been reported [5, 18-21]. these mo and s atoms vacancy defects in mos2 may provide significance outline for the material in device applications. therefore, in this work, we focus on the electronic and magnetic properties of mo and s atoms vacancy defects in monolayer mos2 through first-principles calculations within the frame work of density functional theory (dft), using computational tool quantum espresso. the remaining part of this paper is arranged as follows. in section 2, we introduce the computational details. main finding and their interpretation are presented in section 3. finally we draw conclusions in section 4. 2. computational methods in this work, we used spin-polarized density functional theory (dft) [22], with the quantum espresso simulation package [23] and structure visualization program xcrysden [24], to perform all the calculations. the generalized gradient approximation (gga) of perdew-burke-ernzerhof (pbe) [25] is used to describe the exchange correlation interactions. the rappe-rabe-kaxiraasjoannopoulos (rrkj) model of ultra-soft pseudopotentials is used to describe chemically active valence electrons in calculations. the kinetic energy cut-off and charge density cut-off values are set to 35 ry and 350 ry respectively for the planewave expansion. the first brillouin zone is sampling of a (10×10×1) monkhorst-pack (mp) [26] k-points grid, which is used to perform geometric optimizations. all the structures are fully relaxed by broyden-fletcher-goldfarb-shanno (bfgs) scheme [27], until the energy and force are converged less than 10-4 ry and 10-3 ry/bohr values respectively. the mesh of (6×6×1) k-points grid is used to perform all bands structure calculations and automatic denser mesh (12×12×1) k-points is used for density of states (dos) and partial density of states (pdos) calculations, where in both the cases, 100 k-points are chosen along the high symmetric points connecting the reciprocal space. the marzarri-vanderbilt (mv) [28] hari krishna neupane and narayan prasad adhikari / bibechana 18 (2) (2021) 68-79 70 smearing of small width 0.001 ry is used. in addition, we have chosen ‘david’ diagonalization method with ‘plain’ mixing mode and mixing factor of 0.6 for self consistency. in present work, we have constructed (3×3) supercell structure of monolayer mos2 from the unit cell by extending along x and y direction as shown in figure 1(a). then, we have generated stable and relaxed structures of 1s vacancy defect in mos2 (1sv-mos2), 2s vacancy defects in mos2 (2sv-mos2), 1mo vacancy defect in mos2 (movmos2) and (1mo & 1s) vacancy defects in mos2 (mo-s)v-mos2 materials as shown in figures 1(b-i). these prepared structures are used for further investigations. 3. results and discussion in this section, we reported first-principles calculations within the frame work of spinpolarized dft method to study electronic and magnetic properties of mo and s atoms vacancy defects in mos2 material. 3.1 electronic properties the electronic properties of 1sv-mos2, 2sv-mos2, mov-mos2 and (mo-s)v-mos2materials are studied by the analysis of band structures and dos calculations using dft method. the optimized and relaxed structures of mos2, 1sv-mos2, 2sv-mos2, mov-mos2 and (mo-s)v-mos2 materials are shown in figures 1(a-i) respectively. before study the band structures and dos calculations of 1sv-mos2, 2svmos2, mov-mos2 and (mo-s)v-mos2 materials, we need to understand the electronic properties of pure mos2 material. we know that the electronic configurations of valence electrons in mo and s atoms are [kr] 4d5 5s1 and [ne] 3s2 3p4 respectively. a hexagonal unit cell of monolayer mos2 on the basis of three (1mo & 2s) atoms in honeycomb lattice structure is initially constructed by using reported value [29, 30]. it is built up by single layers of s-mo-s atoms. it consists of two planes of sulphur (s) atoms and an intercalated plane of molybdenum (mo) atom which bounds with the sulphur atoms in a trigonal prismatic arrangement. each mo atom is surrounded by six first nearest neighboring s atoms. based on convergence test, we obtained the lattice constant ‘a’ for mos2 equals to 3.137å, which agrees with the reported value 3.19å [31]. the (3×3) supercell structure of monolayer mos2 is constructed by using the lattice constant which is three times that of the unit cell as shown in figure 1(a). we have done band structure calculations of mos2 supercell structure, and obtained band gap energy value 1.23 ev, this value is close to reported value 1.80 ev [26]. therefore, we also concluded that monolayer mos2 is a wide band gap semiconductor. the band structure of monolayer mos2 is shown in figure 2(a), where x-axis represents high symmetric points in the first brillouin zone and y-axis represents the corresponding energy values. in addition, we have prepared stable and relaxed structures of 1sv-mos2, 2sv-mos2, mov-mos2 and (mo-s)v-mos2 by removing 1s, 2s, 1mo and (1mo & 1s) atoms in supercell structure of mos2, with defects formation energy 0.52 ev, 0.76 ev, 0.64 ev and 0.87 ev respectively. these defects formation energy are calculated by using the standard formalism [32]; ed = et-d – (et-p+ ndµd) … (1) where, et-d is a total energy of a supercell with the defects, nd, is the numbers of atom removed from the perfect super cell to introduce a vacancy, µd is chemical potentials of defected atom in structures, et-p is the total energy of the neutral perfect supercell respectively. defects formation energy values of these materials are given in table 1. the stability of these structures is observed by binding energy calculations. higher the value of binding energy means, systems are more stable. the binding energy of materials depends upon calculated total energy of the systems, which are also given in table 1. hari krishna neupane and narayan prasad adhikari / bibechana 18 (2) (2021) 68-79 71 fig. 1: (a) (3×3) supercell structure of monolayer mos2 (b) before 1s vacancy defect in (3×3) supercell structure of monolayer mos2 (c) 1s vacancy defect in (3×3) supercell structure of monolayer mos2 (d) before 2s vacancy defects in (3×3) supercell structure of monolayer mos2 (e) 2s vacancy defects in (3×3) supercell structure of monolayer mos2 (f) before 1mo vacancy defect in (3×3) supercell structure of monolayer mos2 (g) 1mo vacancy defect in (3×3) supercell structure of monolayer mos2 (h) before 1mo & 1s vacancy defects in (3×3) supercell structure of monolayer mos2 (i) 1mo & 1s vacancy defects in (3×3) supercell structure of monolayer mos2. we calculated the inter-atomic distances of atoms in pristine and defected mos2 monolayer. it is found that compactness of the materials is decreased due to vacancy defects in structure. this is because, inter-atomic bondings are broken due to vacancy defect atom (atoms) in structures, and remaining atoms are loosely bounded to each other. the inter–atomic distances in pristine and vacancy defected mos2 materials are given in table 2. hari krishna neupane and narayan prasad adhikari / bibechana 18 (2) (2021) 68-79 72 table 1: fermi energy (ef), fermi energy shift (es), bandgap energy (eg), total energy of system (et), defects formation energy (ed), total value of magnetic moment (m), and magnetic moment due to total up & down spins states of electrons (µ) in 4p, 4d & 5s orbitals of mo atoms; 3s & 3p orbitals of s atoms in 1sv-mos2, 2sv-mos2, mov-mos2, and (mo-s)v-mos2materials. data of band structures, dos and pdos calculations of mos2, sv-mos2, mov-mos2& (mos)v-mos2materials mos2 1sv-mos2 2sv-mos2 mov-mos2 (mo-s)v-mos2 ef (ev) -1.89 -1.97 -2.02 -2.30 -2.33 es (ev) 0.08 0.13 0.41 0.44 eg (ev) 1.23 0.68 0.54 et (ry) -1741.61 -1718.60 -1696.58 -1593.42 -1570.53 ed (ev) --0.52 0.76 0.64 0.87 µ due to 4p of mo atoms (µb/cell) 0.00 0.00 0.00 0.03 0.01 µ due to 4d of mo atoms (µb/cell) 0.00 0.00 0.00 0.73 0.23 µ due to 5s of mo atoms (µb/cell) 0.00 0.00 0.00 0.03 0.01 µ due to 3s of s atoms (µb/cell) 0.00 0.00 0.00 0.04 0.02 µ due to 3p of s atoms (µb/cell) 0.00 0.00 0.00 1.89 0.72 t total value of magnetic moment m (µb/cell) 0.00 0.00 0.00 2.72 0.99 table 2: inter-atomic distances in pristine mos2 and vacancy defects mos2materials, where s-s, mo-mo and mo-s represent inter-atomic bonding in between any two neighbouring sulphur atoms, any two molybdenum atoms and nearest neighbour 1mo and 1s atoms in structures. inter-atomic distances of pristine mos2 and defected mos2 monolayer along x, y and z axis x-axis (å) y-axis (å) z-axis (å) s–s mo-mo mo-s s-s mo-mo mo-s s-s mo-mo mo-s pristine mos2 0.00 1.57 1.52 0.00 2.74 0.90 3.13 0.00 1.56 1s defect mos2 0.00 1.57 1.54 0.00 2.74 0.91 3.14 0.00 1.57 2s defects mos2 0.00 1.58 1.56 0.00 2.75 0.92 3.15 0.00 1.58 1mo defect mos2 0.00 1.61 1.58 0.00 2.78 0.95 3.15 0.03 1.60 1mo & 1s defects mos2 0.02 1.62 1.59 0.02 2.78 0.97 0.01 0.03 0.62 hari krishna neupane and narayan prasad adhikari / bibechana 18 (2) (2021) 68-79 73 we have done band structures calculations of 1svmos2, 2sv-mos2, mov-mos2 and (mo-s)v-mos2 materials as shown in figures 2(b-e) respectively, where 100 k-points are taken along the specific direction of irreducible brillouin zone by choosing γ-m-k-γ high symmetric points. also, high symmetric points in the first brillouin zone are taken along x-axis and corresponding energies are taken along y-axis. the 1sv-mos2 and 2sv-mos2 materials have opened narrow band gap of values 0.68 ev and 0.54 ev respectively as shown in figures 2(b-c). hence, the materials resemble with the nature of semiconductors. the band gap energy value of defected materials decreases with increase in defects concentrations in mos2 structure, which determines the conductivity strength of materials. thus, the strength of conductivity in 2sv-mos2 is greater than 1sv-mos2. also, conductivity of defected materials is higher than non-defected monolayer mos2 supercell structure. on the other hand, bands states of mov-mos2 and (mo-s)v-mos2 materials split and cross the fermi energy level as shown in figures 2(d-e) respectively. bands around fermi level mix with the orbital’s of mo vacancy in mov-mos2, and (1mo & 1s) vacancies in (mo-s)vmos2. the states associated with the dangling bond and reconstructed mo-s bond of vacancy occurs near the top of valence band and in conduction band, and appear as flat bands as shown in figures 2(d) and 2(e). therefore, from the band calculations, mov-mos2 and (mo-s)v-mos2 materials have metallic nature. the vacancies position of s and mo atoms in structures creates unpaired spins of electrons in sub-orbitals of mo-s atoms in structures. we have calculated the fermi energy of 1sv-mos2, 2sv-mos2, mov-mos2 and (mo-s)vmos2 materials and found -1.97 ev, -2.02 ev, -2.30 ev and -2.33 ev values respectively. these obtained different values of fermi energy are, due to unpaired total up & down spins states of electrons and movement of charges carriers in structures. we have analyzed dos and pdos calculations for the investigation of magnetic properties in materials. figures 3(a) and 3(b) represent dos and pdos plots of pure monolayer mos2; figures 4(a) and 4(b) represent total dos plots of sv-mos2 and 2sv-mos2 materials, figures 4(c) and 4(d) represent total pdos plots of 1sv-mos2 and 2sv-mos2 materials, figures 5(a) and 5(b) represent total dos plots of mov-mos2 and (mo-s)v-mos2 materials, and figures 5(c) and 5(d) represent total pdos plots of mov-mos2 and (mo-s)v-mos2 materials respectively, where the states above the horizontal line represents up spin states of electrons and a state below the horizontal line represents down spin states of electrons. 3.2 magnetic properties the induced magnetization in the materials is obtained by analysis of dos and pdos calculations of materials. the asymmetrically distributed up and down spins states of electrons in dos and pdos plots reflect, materials have magnetic properties, and symmetrically distributed up and down spins states of electrons in dos and pdos plots means, materials carry non-magnetic properties. up and down spins states of electrons in the orbitals of mo & s atoms are symmetrically distributed in dos and pdos plots of mos2, 1sv-mos2 and 2sv-mos2 materials are shown in figures 3(a) & 3(b), figures 4(a) & 4(c), and 4(b) & 4(d) respectively. magnetic moment due to up and down spins states of electrons in 4p, 4d & 5s orbitals of mo atoms and 3s & 3p orbitals of s atoms in mos2, 1sv-mos2 and 2sv-mos2 have value 0.00 µb/cell, which are given in table 1. therefore, mos2, 1sv-mos2 and 2svmos2 materials have non-magnetic properties. we have investigated magnetic properties of movmos2 and (mo-s)v-mos2 materials from the dos and pdos calculations using spin-polarized dft method. the dos and pdos of up and down spins states of electrons near the fermi level are asymmetrically distributed in mov-mos2 material as shown in figures 5(a) & 5(c) respectively. hari krishna neupane and narayan prasad adhikari / bibechana 18 (2) (2021) 68-79 74 fig. 2: (a) band structure of monolayer mos2 (b) band structure of 1s vacancy defect in monolayer mos2 (c) band structure of 2s vacancy defects in monolayer mos2 (d) band structure of 1mo vacancy defect in monolayer mos2 (e) band structure of (1mo & 1s) vacancy defects in monolayer mos2. in all band structure plots, horizontal dotted line represents fermi energy level. fig. 3: (a) total dos of (3×3) supercell structure of monolayer mos2 (b) pdos of up and down spins states of electrons in the individual orbitals of mo & s atoms in (3×3) supercell structure of mos2 material. in dos and pdos plots, vertical dotted line represents fermi energy level. hari krishna neupane and narayan prasad adhikari / bibechana 18 (2) (2021) 68-79 75 fig. 4: (a) total dos of up & down spins states of electrons in the orbitals of mo & s atoms in 1s vacancy defect in mos2 material (b) total dos of up & down spins states of electrons in the orbitals of mo & s atoms in 2s vacancy defects in mos2material (c) pdos of up & down spins states of electrons in the individual orbital of mo & s atoms in 1s vacancy defect mos2 material (d) pdos of up & down spins states of electrons in the individual orbital of mo & s atoms in 2s vacancy defects mos2 material. in dos and pdos plots, vertical dotted line represents fermi energy level. hari krishna neupane and narayan prasad adhikari / bibechana 18 (2) (2021) 68-79 76 fig. 5: (a) total dos of up & down spins states of electrons in the orbitals of mo & s atoms in 1mo vacancy defect in mos2 material (b) total dos of up & down spins states of electrons in the orbitals of mo & s atoms in (1mo & 1s) atoms vacancy defects mos2material (c) pdos of up & down spins states of electrons in the individual orbital of mo & s atoms in 1mo vacancy defect in mos2 material (d) pdos of up & down spins states of electrons in the individual orbital of mo & s atoms in (1mo & 1s) atoms vacancy defects mos2 material. in dos and pdos plots, vertical dotted line represents fermi energy level. this is because, electron’s spins degeneracy of the bands due to mo vacancy defects, bands are broken and splited. as a result, mov-mos2 material bears magnetic properties. we have also calculated the magnetic moments given by spins of electrons in 4p, 4d & 5s orbitals of mo atoms and 3s & 3p orbitals of s atoms having values 0.03 µb/cell, 0.73 µb/cell & 0.03 µb/cell; and 0.04 µb/cell & 1.89 hari krishna neupane and narayan prasad adhikari / bibechana 18 (2) (2021) 68-79 77 µb/cell in mov-mos2 material respectively. hence, total value of magnetic moment in mov-mos2 material is 2.72µb/cell. from above calculations, we know that spins states of electrons in 4d orbital of mo atoms, and 3p orbital of s atoms have dominant contributions for magnetism. similarly, the spins states of electrons in the orbital of mo & s atoms of (mo-s)v-mos2 material near the fermi energy level are asymmetrically distributed in dos and pdos plots as shown in figures 5(b) & 5(d) respectively. magnetic moment is given by spins states of electrons in 4p, 4d & 5s orbitals of mo atoms; and 2s & 2p orbitals of s atoms; in structure have values 0.01 µb/cell, 0.23 µb/cell & 0.01 µb/cell; and 0.02 µb/cell & 0.72 µb/cell respectively. the total magnetic moment in (mo-s)v-mos2 material has value 0.99 µb/cell. therefore, (mo-s)vmos2 material has magnetic properties. 4d orbital of mo and 3p orbital of s atoms give greater values of magnetic moment than magnetic moment given by other orbitals of atoms in the material. magnetic moment of mov-mos2 is higher than that of (mos)v-mos2 material because unequal unpaired (dangling) bonds are present in structures. these dangling bonds are formed due to the effects of 1mo atom vacancy defects and (1mo & 1s) atoms vacancy defects in the materials. it is also seen that spins polarization of atoms in (1mo &1s) atoms vacancy defects structure is less than 1mo atom vacancy defects structure. 4. conclusions and concluding remarks the novel properties in mos2 material are developed due to mo and s atoms vacancy defects. the electronic and magnetic properties of 1svmos2, 2sv-mos2, mov-mos2 and (mo-s)v-mos2 materials are studied through first-principles calculations within the frame work of spinpolarized dft method using computational tool quantum espresso. we have prepared stable structures of these materials, and then analyzed their band structures, dos and pdos calculations. from the band structure calculations, we found that 1sv-mos2 and 2sv-mos2 materials have open small energy band gap of value 0.68 ev and 0.58 ev in both up and down spins electronic states, which implies that 1sv-mos2 and 2sv-mos2 resemble with the nature of semiconductors. thus, conductivity of material increases with increase in its defects concentrations. on the other hand, mov-mos2 and (mo-s)v-mos2 materials have metallic properties because bands around the fermi level mix with the orbital’s of mo vacancy in mov-mos2, and (mo & s) vacancies in (mo-s)v-mos2. the states associated with the dangling bond and reconstructed mo-s bond of vacancy occurs near the top of valence band and in conduction band, and appear as flat bands. the charge densities associated in these bands are localized. from the analysis of dos and pdos calculations, we found that mos2, 1sv-mos2 and 2sv-mos2 materials have non-magnetic properties. the non-magnetic mos2 material changes to magnetic mov-mos2 and (mos)v-mos2 materials, due to 1mo atom vacancy defects in monolayer mos2 and (1mo & 1s) atoms vacancy defects in monolayer mos2 structure respectively. total magnetic moment of mov-mos2 and (mo-s)v-mos2 materials have values 2.72 µb/cell and 0.99 µb/cell respectively. significant values of magnetic moment are obtained due to the distribution of electrons spins in 4p, 4d, & 5s orbitals of mo atoms and 3s & 3p orbitals of s atoms in both materials. acknowledgments hari krishna neupane and narayan prasad adhikari acknowledge the ugc nepal award no. phd-75/76-s&t-09 and grants crg 073/74 -s&t -01 respectively. also, narayan prasad adhikari acknowledges network project nt-14 of ictp/oea. references [1] j. c. lei, x. zhang, and z. zhou, recent advances in mxene: preparation, properties, and applications, frontiers of physics 10(3) (2015) 276286. hari krishna neupane and narayan prasad adhikari / bibechana 18 (2) (2021) 68-79 78 [2] m. e. dávila, et al., germanene: a novel twodimensional germanium allotrope akin to graphene andsilicene, new journal of physics 16(9) (2014) 095002. 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[32] z. hou, et al., interplay between nitrogen dopants and native point defects in graphene, physical review b 85 (16) (2012) 165439. bibechana vol. 20, no. 1, april 2023, 27–35 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar a systematic study on material properties of water retted sterculia and bauhinia fiber krishna prasad kandel, girja mani aryal, sishir achyarya kc mahesh kumar joshi, bipeen dahal, bhanu bhakta neupane∗ 1central department of chemistry, tribhuvan university, kathmandu 44613, nepal ∗corresponding author. email: newbhanu@gmail.com abstract lignocellulose biomass forms an important component of traditional and next generation composite materials. to obtain desired properties, the biomass needs to be chemo–mechanically processed at different levels. the raw lignocellulose fiber obtained from sterculia villosa (roxb.) and bauhinia vahlii is traditionally believed to have high water stability; and therefore used in rural areas of south asian regions to secure objects submerged under water. in this research, we systematically studied several material properties of raw sterculia and bauhinia fiber samples retted for 0, 20, 30 and 55 days (n=8). water retting resulted in significant decrease in lignin and extractives content (p<0.05) and increase in cellulose content. fiber bundle strength of sterculia fiber increased with retting time (r2= 0.7) but bauhinia fiber did not show significant change (p>0.05). interestingly, water retting resulted in increased thermal stability in both fiber types. these findings suggested that the fiber studied have excellent water stability. the observed trend in mechanical and thermal properties could have resulted from crystallinity change and/or nominal fiber damage as supported by xrd and sem imaging data; respectively. these findings suggested that sterculia and bauhinia fiber biomass could be an important component of biodegradable composite materials which are intended for high wetting and/or humid conditions. keywords lignocellulose, water retting, fiber processing, cellulose fiber, mechanical strength. article information manuscript received: january 26, 2023; accepted: march 28, 2023 doi https://doi.org/10.3126/bibechana.v20i1.51793 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction lignocellulose biomass is one of cheap, environmentally friendly, and most abundant terrestrial biomass. the biomass can be obtained from leaf, seed, fruit, and bast portion of different plant species or other plant derived wastages following different processing methods [1–5]. bast fibers are the soft woody fiber obtained from phloem tissues of plant stem. the fibers are usually long and strong and form an important components of next generation materials and finding applications in waste water treatment, biomedical applications, agro and automotive industries [6–10]. cellulose 27 http://nepjol.info/index.php/bibechana newbhanu@gmail.com https://doi.org/10.3126/bibechana.v20i1.51793 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ krishna prasad kandel et al./ bibechana 20 (2023) 27-35 28 nano–composite fibers are also being explored in fabrication of fabrics having self-cleaning, antimicrobial, and uv-protection properties [11–13]. in natural state, bast fibers are cemented to the adjacent tissues by different gummy or non–cellulosic components such as wax, pectin, and lignin. to yield fiber of desired properties, the gummy components needs to be removed following different chemo-mechanical methods. retting is one of the most important degumming methods. several retting types are in practice such as chemical retting, enzymatic retting, water retting, dew retting, gel retting, ribbon retting, or their combinations [14–17]. retting, in general, removes noncellulosic components so that fiber bundles partially separate. to get fiber of optimal strength retting conditions needs to be optimized [1]. in water retting, fiber bundles are submerged in slow or stagnant water in a pond or tank normally for 2–3 weeks [15,18]. ground or tap water contain anaerobic bacterial and or fungal colonies that produce enzymes capable of hydrolyzing gummy or fiber binding components such lignin and pectin with release of galacturonic acid and sugar as major by-products [1,19,20]. this results in partial removal of gummy components so that fiber bundles partially separate. the retting conditions, such as retting time, microbial type and load, and fiber type determine the fiber quality. water retting results in putrid water and many pollutants. however, this is one of the cost effective methods and yields fibers having excellent length uniformity and strength [15, 21]. retting can also be carried out by using enzyme such as pectinase, xylanases in controlled condition. although enzymatic retting is faster (12–24 hours) and does not produce unnecessary pollutants, it results in fiber of low strength [1,18]. retting can also be done mechanically using decorticator to break fiber to fiber bonding. mechanical retting is rapid but results fiber of low quality. also, high cost limits it application in resource limited settings. as a result, traditional water retting is still being explored as viable option for obtaining fibers of various lengths and excellent strength [22]. the fiber biomass obtained from sterculia villosa (roxb.) and bauhinia vahlii plant species is believed to have excellent water stability; and therefore traditionally being used at local levels to secure objects submerged in water or in high humid conditions. it would be interesting to explore material properties of fiber water retted for different time period. in this study, two fiber types were retted in tank water for 0, 20, 30, and 55 days. retting efficiency, change in content of major chemical components, fiber strength, and thermal stability of the fiber samples were systematically investigated. we also bridge the observed end properties with the morphological and crystallinity change. finally, a brief discussion on the further implications of the research is provided. 2 materials and methods 2.1 materials the sterculia villosa (roxb.) and bauhinia vahlii plant stems ( 1 m long and 3 cm wide) were collected from digam, gulmi, nepal (hilly region, 1250 masl). bast fiber biomass was separated from the wet stem following traditional method. the stems were gently beaten around one end with a wooden log and pulled mechanically with hands. outer cuticular layer was removed from biomass using a stainless steel knife (figure 1). the samples were sun dried to remove excessive moisture and moved to lab for further study. 2.2 methods 2.2.1 water retting water retting was performed following literature reported methods with slight modifications [23, 24]. bast fiber samples were divided into four groups of 100 g each. samples were well rinsed with tap water and gently crushed to loosen the bundles. the samples were immersed in separate buckets containing 4 l of tap water (ph 7.2±1, conductivity 9± 1 µs). the samples were left open under natural conditions (temperature 20–300c and humidity 50–70%) for 20, 30 and 55 days. to minimize the excessive growth of microorganism and fouling, talk water was one third diluted in every 10 days. after each retting time, sample was washed with distilled water and oven dried at 105±20c. from the initial and final weights, weight loss% or retting efficiency was calculated. for convenience, sterculia samples retted for 0, 20, 30, and 55 days hereunder named as s0, s20, s30, and s55 and the bauhinia samples b0, b20, b30, and b55. until further characterization these samples were stored in air tight plastic bag in dark. a simple schematics of experimental design used in this work is provided in figure 1. 2.2.2 chemical analysis estimation of major chemical components viz. extractives, lignin, hemicellulose, cellulose and ash content in the water retted samples (s0, s20, s30, s55 and b0, b20, b30 and b55) was performed gravimetrically following the previously reported methods [25–28]. triplicate measurements were made in all the samples for each chemical component. for estimation of lignin, 1.000 g of extractive free dry sample was treated with 72% h2so4 (1:12.5 m/v ratio) for two hours at room temperature. the top solvent was removed with several krishna prasad kandel et al./ bibechana 20 (2023) 27-35 29 washings with distilled water. the residue was dried at 105 0c till constant weight was obtained. form the known initial and final weights, lignin content was obtained. to determine the hemicellulose 1.000 g of extractive free dry biomass was boiled in 150 ml of 0.5 mol/l naoh for 4 hours. the treated fiber content was washed several times with distilled water to neutral ph and oven dried at 1050c until constant weigh was obtained. hemicellulose content in % was obtained from the initial and final weights of the biomass. finally, cellulose content was obtained by subtracting the collective content of extractive, lignin and hemicellulose from 100. figure 1: schematic outline of the experimental design used in this work. 2.2.3 mechanical strength of fiber water retted fiber samples were preconditioned for 24 hours at 23±1 0c and 65 % relative humidity [29]. a fiber bundle strength tester (tsi instruments) with a maximum load capacity of 7 kg was used to determine fiber strength. flat fiber bundles were inserted into the pressley jaw (gauze length 15 mm) and then loaded into the tester. load was applied at a continuous rate of 1 kg/sec until the fiber bundle breaks. the load at fiber break was recorded. the broken fiber pieces was removed from the pressley jaw and weighed in an analytical balance at nearest accuracy of 0.0001. the fiber bundle strength (breaking tenacity) in g/tex was obtained from known values of breaking load, grammage, and gauge length. to achieve statistical significant result, 25 measurements were taken for each sample type. 2.2.4 xrd, tga, and sem measurements xrd data were measured in 2θ range 5–300 using a x-ray diffractometer (rigaku, uk) the voltage, scan rate and step size were 40 kv, 0.020/min, 0.020; respectively. a monochromatic from cu–kα line (λ= 1.540 a) was used as x-ray source. thermogrametric data of the fiber samples was measured using thermogravimetric analyzer (perkin elmer tga–7). 7–10 mg of fiber sample was heated in an alumina crucible in nitrogen atmosphere (flow rate 80 ml/min) at the rate of 10 oc/minute. data collection range, weighing accuracy and precision were 26-600 0c, 0.1 µg, and ± 2 0c; respectively. scanning electron microscopic images were obtained using field emission electron microscope (carl zeiss, supra 40vp) at the accelerating voltage of 15 kv. the collected images were imported in imagej (nih, usa) for further analysis. 2.2.5 statistical analysis descriptive statistical parameters such as mean, maximum, minimum, standard deviation and confidence intervals were calculated using origin pro (origin lab, usa). to test the significance difference between the data, whenever relevant, t-test was performed. 3 results and discussion 3.1 gravimetric analysis the % weight loss in sterculia fiber retted for 20, 30, and 55 days was found to be 10.5, 15.2, and 17.5 %; respectively. the corresponding numbers for bauhina fiber were 4.1, 5, 8.1%; respectively. these data suggested that sterculia fiber has higher retting efficiency than bauhinia. since retting conditions were same for both fiber types, the difference is retting efficiency could be linked to fiber origin; that is difference in chemical composition and fiber to fiber bonding. krishna prasad kandel et al./ bibechana 20 (2023) 27-35 30 figure 2: analysis of major chemical components in the fiber samples. (a) extractive. (b) lignin. (c) hemicellulose. (d) cellulose. the blue and red data points correspond to sterculia and bauhinia; respectively. the dotted lines are the linear fit to the experimental data and r2 values greater than 0.5 are only shown. figure 3: mechnical strength of the fiber samples. the dotted lines are the liner fit to the experimental data points. the error bars are the 95% ci values to the mean (n=25. the extractive, lignin, hemicellulose, and cellulose contents in the fiber samples for two fiber types in reported in figure 2. as expected, water retting resulted in decrease in extractive content with increase in retting time (figure 2a). in the 55 days retting period, the extractive content decreased significantly from 13 to 1.3 % (p<0.05) in the sterculia fiber. the corresponding decrease in bauhinia fiber was from 13.6 to 8.7 %. the weight loss could have resulted from the removal of pectin and waxy materials due to antimicrobial action. in the 55 days period, a significant decrease in lignin (p<0.05) content from 21.9 to 15.5 % was also observed in sterculia (figure 2b). the weight loss in retting depends on type of microorganism, water composition, retting time, and fiber types [4, 19]. so it is not surprising to see the observed difference in weight loss in sterculia and bauhinia fibers. hemicellulose content in both sample types did not change significantly (figure 2d). in the 55 days retting period hemicellulose changed from 28.6 to 33.2 % in the sterculia fiber. the corresponding krishna prasad kandel et al./ bibechana 20 (2023) 27-35 31 figure 4: xrd data for the fiber samples. (a) xrd data of sterculia samples retted for 0 (s0), 30 (s30) and 55 (s55) days. (b) xrd data of bauhinia samples retted for 0 (b0), 30 (b30) and 55 (b55) days. data are overlaid vertically for easy comparison. numbers in parentheses indicate the reflection planes. change in bauhinia fiber was from 31.2 to 33.6 %. in the same time period, cellulose content in sterculia fiber increased significantly (figure 2c) from 36.5% to 50% (p<0.05). a nominal change from 27 to 30% was observed in bauhinia fiber. we also measured ash content in fibers retted for 0 and 55 days. the corresponding values for sterculia and bauhinia were 6.7 and 4.7% and 6.2 and 4.4 %; respectively. the decrease in ash content could be due to partial loss of inorganic minerals and other impurities on water retting. as expected, ash change in ash content showed excellent negative correlation (r= -0.9) with extractive content. 3.2 mechanical strength the tenacity data for all the samples is provide in figure 3. in the 55 days period, the breaking tenacity of sterculia fiber increased significantly (p<0.05) from 18.3±1.6 (mean ±95% ci) to 26.9±2.7 g/tex (r2=0.73). in the same period, mechanical strength of bauhinia fiber did not change significantly (p>0.05). the increase in fiber strength in sterculia could be due to more loss in lignin from inter-fibrillar region that can lead in increased reorganization of cellulose chain thereby increasing crystallinity (later section) and strength [28]. 3.3 xrd data we measured xrd data of selected sterculia and bauhinia samples (figure 4a and b). the xrd data of all the samples resemble to that of typical cellulose material. cellulose fiber in natural form contains amorphous and crystalline regions. a broad peak at 2θ value of 15.50 orginates form the crystalline planes (1-10) and (110) and the strong peak at 2× value of ∼21.50 from (200) plane. the broad contribuation underlying the crystalline peaks is known to orignate from amorphous scattering [30]. we used deconvolution method in the 2θ range of 5–300 to get information on crystallinity index (ci) [30]. ci = ( at −aam at ) 100% (1) where, aam and at are the integrated intensity amorphous phase and total intensity of crystalline and amorphous phases; respectively. the crystallinity index in sterculia samples retted for 0, 30, and 55 days was found to be 44%, 48% and 50%; respectively. a good positive correlation (r=+0.85) between crystallinity and strength was obtained. crystallinity index increases on water retting is also reported for hemp fibers [31]. the increase in crystallinity index could be due to removal of lignin form inter–fibrillar region that can result in close packing of cellulose chains [28]. crystallinity index in bauhinia samples retted for 0, 30,and 55 days was found to be 55%, 54% and 54%; respectively. krishna prasad kandel et al./ bibechana 20 (2023) 27-35 32 figure 5: tga and dtg data for the fiber samples. (a), (b) tga and dtg for sterculia water retted for 0 (s0), 30 (s30), and 55 (s55) days. (c), (d) tga and dtg for bauhinia water retted for 0 (b0), 30 (b30), and 55 (b55) days. a poor positive poor correlation (r= +.5) was between the crystallinity change and strength was observed. this could be due to lower loss of lignin form inter–fibrillar region; consistent with data reported in figure 2b. a small peak shift in the xrd data could be due to change in relative contribution of amorphous and crystalline phases and or change in crystallite size. 3.4 thermal properties in both samples the weight loss below 1000c (figure 5a and c) is due to loss of moisture and or low volatile impurities [28, 32–34]. the weight loss between 100 to 3000c is mainly due to hemicellulose; as hemicellulose is known to be less stable than cellulose (figure 5a and c). the weight loss in 300–4000c range is mainly due to degradation of glycosidic bonding in cellulose that creates organic molecules such alkenes and additional derivatives of hydrocarbons. the weight loss beyond 4000c is mainly due lignin (5a and c) [35–37]. the main dtg peak for sterculia shifts from 3400c to 3500c in water retted samples. this suggested that water retting results in increase in thermal stability (figure 5b). it could be due increase of cellulose content and change in crystalline properties; as reported previously. the strong dtg cellulose peak in water retted sterculia samples (s30 and s55) is consistent with increase of cellulose on water retting (figure 2d). in bauhinia, dtg peak shifts from 3500c to 3550c in water retted samples (figure 5c). this suggested that thermal stability of water retted bauhinia does not change significantly on water retting. 3.5 sem imaging imaging of selected samples (6 out of 8) was performed to see any change in fiber surface morphology. a close comparison of images of the sterculia fiber retted for 0, 30, and 55 days (figure 6a, b, and c) reveals that gummy materials are significantly removed from the fiber surface and fiber bundles are partially separated. this observation is consistent with the wet loss study. similar change is observed in bauhinia fiber (frames d, e, and f). 4 conclusion to summarize, water retting efficiency and lignocellulosic content of sterculia villosa and bauhinia vahlii fiber retted for different periods was measured. in sterculia fiber, weight loss increased significantly with retting time; which is consistent with reduction of lignin, ash and extractive contents. the change was less significant in bauhinina fiber suggesting lower retting efficiency. in around krishna prasad kandel et al./ bibechana 20 (2023) 27-35 33 figure 6: sem images. a, b, and c are the images of sterculia fiber retted for 0 (s0), 30 (s30), and 55 (s55) days; respectively. d, e, and f are the corresponding images for bauhinia fiber. scale bar of 100 µm are provided in a (also applicable for b and c) and d (also applicable for e and f). 2 months retting period, mechanical strength of sterculia fiber increased significantly but that of bauhinia did not change. thermal stability of both fiber increased on water retting. these observations are also supported by xrd and sem imaging data. these findings suggested that both fiber have excellent water stability and can be explored as an important component in fabricating cellulose based composite materials that are intended for high wetting or humid conditions. references [1] m.t. paridah, a.b. basher, s. saifulazry, and z. ahmed. retting process of some bast plant fibres and its effect on fibre quality: a review. bioresources, 6:5260–5281, 2011. 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accepted: february 22, 2021 keywords: dwarf galaxies star formation rate spectra hα measurement sdss abstract in this paper, we have presented an analysis of emission lines from two dwarf galaxies. we analyzed the strongest emission lines of wavelength ranging from 4100 å to 6700 å. among these emission lines, hα and oiii have the highest intensities with 113.09×10-17 erg/s/cm2/å and 142.12×10-17 erg/s/cm2/å in the galaxies sdssj222726.64+120539.8 and sdssj162753.47+482529.3, respectively. the gaussian fit carried out in these emission lines showed the perfect fits with regression coefficient greater than 98 %, and full width half maximum (fwhm) of less than 4 å. the line ratios calculated between hα and hβ for sdssj222726.64+120539.8 and sdssj162753.47+482529.3 were 2.78 and 2.85, respectively, suggesting that the galaxies are starburst galaxies. the measurement of the hα line from both galaxies was then used to assess the rate of star formation. the star formation rate of the galaxies sdssj222726.64+120539.8 and sdssj162753.47+482529.3 was found to be 0.010 m☉ year-1 and 0.016 m☉ year-1, respectively, indicating a low rate of star formation, and the emission line metallicity was derived using the hα and nii line, which were measured to be 8.23 dex and 8.70 dex, respectively. doi: https://doi.org/10.3126/bibechana.v18i2.34067 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction galaxies evolve by colliding with their neighboring galaxies through the interaction of their environment. these collisions and mergers of galaxies due to induced gravitation has been the best-known fact about the evolutionary mechanism [1]. in extragalactic research, the pivotal question remains to find to what extent the properties of galaxies are regulated by the initial condition and environment. indeed, it has been found that the bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:astrosujan@gmail.com https://doi.org/10.3126/bibechana.v18i2.34067 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana s. p. gautam et al. / bibechana 18 (2) (2021) 43-49 44 evolution of galaxies relies heavily on their environment [2]. in understanding the evolution of the universe, studying the star formation rate in the universe or the individual galaxies can be essential knowledge. but in extragalactic astronomy, assessing the star formation and birth of a star is a difficult task [3]. the importance of star formation bursts in the low mass galaxies was not unlocked until the modeling of blue galaxies and interacting systems [4]. our primary objective is the study of galaxy formation and evolution is to gain insight into the interaction between the gaseous and stellar components of the galaxies. so, dwarf galaxies with low surface brightness but gas-rich, low-mass, low-metallicity are ideal for studying the rate of star formation, as it may give us an understanding of how gases turned into a star within that system that might imitate the early universes [5]. in addition, due to a simpler dynamic and morphological system than spiral galaxies, dwarf galaxies are considered the ideal laboratory for studying the formation of stars within the low gas surface density domain along with lower rotational shear rates [6]. while dwarf galaxies have received less attention than spiral galaxies and elliptical galaxies, they may have more cosmological importance. these dwarf galaxies are the most diffuse type of galaxies in our modern universe and are expected to be more than one in the past. as for cold dark matter (cdm), dwarf galaxies are the first to yield after big bang and are often thought to be the residue of the building blocks of massive galaxies [7]. dwarfs are the most dominant type of galaxies in the universe with relatively low mass and are the regular companion of other galaxies. they are often found in clusters of galaxies [8]. there are mainly three types of dwarf galaxies: i) spheroidal; gas-poor dwarf which is not supporting any star formations, ii) irregulars; gas-rich dwarf which supports star formation but at relatively low rates, iii) starbursting dwarf; forming star at a surprising rate [9]. blue compact dwarf (bcd) is known as an irregular dwarf since it has no uniform shape. the composition of bcd is comparable to the material type during the formation of the first stars in the early universe, making it an apt object to research and understand the process of formation of the primordial stars [10]. the paper is structured as follows: the sample chosen for this study is addressed in section ii. the methods of the study was presented in section iii. section iv contains the result and discussion part. finally, we have concluded our results in section v. 2. sample selection we have taken two dwarf galaxies for our study namely sdssj222726.64+120539.8 and sdssj162753.47+482529.3. these galaxies are among the merging dwarf galaxies listed in the catalog of paudel et al. [11]. sdss j222726.64+120539.8 is positioned in the sky at r.a.: 22h 27m 26.64, dec.: 12d 05m 39.8s with a redshift value 0.0118 whereas, sdss j162753.47+482529.3 is located in the sky at ra.: 16h 27m 53.47s, dec.: 48d 25m 29.3s with the redshift value 0.0134. the g & r band magnitudes of sdssj222726.64+120539.8 and sdssj162753.47+482529.3 are 15.68 & 15.65 mag, and 16.47 & 16.19 mag, respectively. the optical view of selected dwarf galaxies is shown in figure 1. figure 2 shows the sdss optical spectrum of the galaxies, wavelength (for both galaxies) ranging from 4100 å to 6700 å. the strongest among all those emission lines are oiii and hα in these galaxies distinctly. 3. methods we have analyzed the emission lines featured in the 2-d spectrum to study the properties such as line ratio, star formation rate, and metallicity of the dwarf galaxies. these images and spectrums were well-calibrated and no further reductions were required. the sdss fibers had an arc diameter of 3 seconds. therefore, these spectrums only cover the small area of these dwarf galaxies. we downloaded the spectrum data from the sdss server (http://skyserver.sdss.org/dr14). the observed http://skyserver.sdss.org/dr14 s. p. gautam et al. / bibechana 18 (2) (2021) 43-49 45 emission lines from the spectrum were then studied using the software origin8.5. the strongest emission lines, as shown in figure 2, were then gaussian fitted for the estimation of different statistical parameters. we also noted the parameter like fwhm, total flux, and best fits coefficients. in order to get an accurate corresponding flux of the emission line, we subtracted the continuum flux. fig. 1: optical view of sdss j222726.64+120539.8 (upper) and sdss j162753.47+482529.3 (lower). fig.2: 2-d optical spectrum of sdss j222726.64+120539.8 (upper) and sdss j162753.47+482529.3 (lower) with several prominent emission lines. the gaussian function is defined as [12, 13]: fg(x) = 1 √2𝜋σ2 𝑒 −(x−μ)2 2σ2 , (1) where, x, μ, and σ are normal random variables, mean deviation, and standard deviation respectively. the gaussian fitting of each emission lines studied with higher intensities and their respective fwhm, offset, and regression coefficients were tabulated and discussed in the later section. fwhm is the value at which the dependent variable is equal to half of its maximum value. kennticutt (1998) [4] s. p. gautam et al. / bibechana 18 (2) (2021) 43-49 46 obtained the qualitative estimation of total star formation (sfr) in the galaxies through photometry of coalescing hα lines from a large sample of galaxies. the star formation rate can be calculated as: sfr (m☉year-1) = 7.9× 10-42 σ l (hα) (ergs s-1), (2) where σl(hα) is the total luminosity of the hα line after gaussian fitting. σ l(hα) = area of gaussian fit × 10-17 × 4𝜋r2 (ergs s-1). r is the radius of the sphere and is calculated as r = d × 3.08 × 1024 cm. here, d is the luminosity distance the galaxy is from the earth which is calculated using the redshift value in mpc [13]. we used a line ratio between hα and nii to derive the emission line metallicity given by [14], 12 + log (o/h) = 8.743 + 0.462 × log (nii/ hα), (3) 4. results and discussion among the various methods used to estimate the rate of star formation, we have adopted the method of hα measurement estimated by kennicutt, 1998, easiest, commonly used method of sfr determination as it provides estimation of sfr rate from the hα emission lines of the spectra of the galaxies. we have analyzed the balmer series i.e., hα, hβ, hγ, and hδ, these lines are primarily associated with the gas-mass and star formation rate in the galaxies. the other strongest emission lines like hei, oiii, oiii, and nii were also identified to study the chemical parameters of the galaxy. the oiii is doubly ionized oxygen. figures 3 and 4 display the example of gaussian fits of two emission lines i.e. hα and nii for the galaxies sdssj222726.64+120539.8 and sdssj162753.47+482529.3, respectively. the red line displays the gaussian distribution with the error bars in the gaussian curve. we pointed out that the data observed and the gaussian distribution are in close agreement, which suggests the effectiveness of the findings. in the same way, we made the gaussian fit for other emission lines as well. tables 1 and 2 list the entire identified element with the strongest emission lines. the noted emission lines are redshift calibrated to get the corresponding emitted wavelength and are subjected to the baseline subtracted to get accurate flux. the gaussian parameters of all eight gaussian distributed emission lines are listed with their offset values. the average coefficient of regression was found to be 0.98. sdss j222726.64+120539.8 fig. 3: example of gaussian fitting of two emission lines hα (left) and nii (right) of the galaxy sdssj222726.64+120539.8. from table 1, we observed that the wavelength of 6564.63 angstroms had the highest intensity of 113.09 x 10-17 erg/s/cm2/å corresponding to the hα line of the balmer series. similarly, the second peak s. p. gautam et al. / bibechana 18 (2) (2021) 43-49 47 had an intensity of 103.05 x 10-17 erg/s/cm2/å which corresponds to the doublet oiii lines. the intensity at 5877.24 angstrom had a low value of 5.63 x 10-17 erg/s/cm2/å which resembles the hei emission line. for the calculation of the star formation rate, we used the formula described in equation 2. redshift value (z) = 0.0118 from the catalog of paudel et al. (2018) [11] was used to calculate the distance to the galaxy (d). we calculated the value of d as 49.17 mpc. the star formation of the galaxy was found to be 0.010 m☉year−1. we also estimated the line ratio of hα and hβ. it was found to be 2.78, which is slightly less than the theoretical value (hα/hβ = 2.8) [13] for the star-forming galaxies modeled by dessauges-zavadsky et al. [15]. the ratio of nii and hα was used to estimate the emission line and metallicity. metallicity indirectly traces the history of star formation, demonstrating the stability of many of the galaxies' essential physical mechanisms, such as the expulsion of metals into the ism by supernova and stellar winds, the deportation of gas through galactic outflows, and the accretion of gas from local environments in the galaxy [16]. the physical mechanism that controls the formation of stars and, most importantly, the evolution of galaxies can be understood by analyzing metallicity evolution in relation to the other essential properties of galaxies [16]. the value of emission line metallicity, calculated using equation 3, was found to be 8.23 dex. table 1: statistical parameters obtained from the gaussian fit of the emission lines of the spectrum of the galaxy sdssj222726.64+120539.8. emissions wavelength (å) peak intensities (10-17 erg/s/cm2/å) fwhm (å) area (10-17 erg/s/cm2/å) offset rsquare hδ 4102.89 7.67 2.21 19.14 -0.113 0.97 hγ 4341.69 18.32 2.32 47.26 -0.424 0.99 hβ 4862.69 40.64 2.84 40.64 -0.348 0.99 oiii 4960.295 36.89 2.75 103.05 0.142 0.98 oiii 5008.24 103.05 3.01 327.83 -0.170 0.99 hei 5877.24 5.63 3.74 23.29 0.307 0.98 hα 6564.63 113.09 3.77 458.81 -0.319 0.99 nii 6585.27 8.68 3.77 35.63 -0.041 0.99 fig. 4: example of gaussian fitting of two emission lines hα (left) and nii (right) of the galaxy sdssj162753.47+482529.3. s. p. gautam et al. / bibechana 18 (2) (2021) 43-49 48 sdss j162753.47+482529.3 from table 2, we noticed that the 4960.295 angstrom had the highest intensity of 142.12 x 10-17 erg/s/cm2/å corresponding to the doublet oiii emission line. similarly, the observed second peak had an intensity of 135.76 x 10-17 erg/s/cm2/å which corresponds to the hα line. the intensity had a low value of 8.65 x 10-17 erg/s/cm2/å which belongs to the hδ line. in a similar way as in the previous galaxy, the formula described in equation 2 was to find the star formation rate of this galaxy. the distance (d) to the galaxy was estimated to be 55.83 mpc using redshift value z = 0.0134 [11]. the star formation rate of the galaxy was found to be 0.016 m☉year-1. the line ratio between hα and hβ for this galaxy was 2.85, which is estimated to be slightly greater than the theoretical value (hα/hβ = 2.8), which is due to internal extinction. the emission line metallicity for this galaxy was also calculated using equation 3 and was found to be 8.7 dex. table 2: statistical parameters obtained from the gaussian fit of the emission lines of the spectrum of the galaxy sdssj162753.47+482529.3. 5. conclusion in this paper, we performed the gaussian fit of the strongest emission lines from the spectrum archived from the sdss server of two dwarf galaxies namely sdssj222726.64+120539.8 and sdssj162753.47+482529.3 to estimate the star formation rate, line ratio of hα and hβ, and emission-line metallicity of the galaxies. in both of the galaxies, the fwhm value corresponding to each element was below 4 å. this shows that the observed characteristic lines are in close agreement with gaussian fits. also, we calculated the star formation rate from their hα measurement as 0.010 m☉year-1 and 0.016 m☉year-1(indicating low star formation rate) and the metallicity as 8.23 dex and 8.7 dex for sdssj222726.64+120539.8 and sdssj162753.47+482529.3, respectively. in the future, the star formation rate will be estimated using fuv measurement and compared with these results. in addition, a photometric study of these galaxies will be carried out in order to observe other physical and morphological properties based on previous models. acknowledgment we would like to acknowledge d.n. chhatakuli, ph.d. scholar, central department of physics, tribhuvan university, for sharing his knowledge in this work. his previous studies inspired us to work in this field. we are also thankful to sanjay paudel, centre for galaxy evolution research, department of astronomy, yonsei university, emissions wavelength (å) peak intensities (10-17 erg/s/cm2/å) fwhm (å) area (10-17 erg/s/cm2/å) offset rsquare hδ 4102.89 8.65 2.16 26.93 -0.114 0.98 hγ 4341.69 18.56 3.86 112.57 -0.576 0.94 hβ 4862.69 47.64 3.08 161.71 -0.234 0.99 oiii 4960.295 46.50 2.82 142.94 0.245 0.99 oiii 5008.24 142.12 2.94 449.64 -0.113 0.99 hei 5877.24 7.30 3.61 27.04 0.041 0.95 hα 6564.63 135.76 3.79 549.59 0.386 0.99 nii 6585.27 14.89 3.96 60.58 0.097 0.99 s. p. gautam et al. / bibechana 18 (2) (2021) 43-49 49 seoul, south korea for providing a catalog of dwarf galaxies. we extend acknowledgment to sdss data server and origin8.5. author contributions this work was carried out under the guidance of the author b. aryal. all the authors have equal contribution throughout the work. references [1] f. schweizer, colliding and merging galaxies, science 231 (1986) 227-234. https://doi.org/10.10.1126/science.231.4735.227 [2] r. c. kennicutt-jr, the rate of star formation in normal disk galaxies, 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[16] m. c. cooper, c. a. tremonti, j. a. newman, a. i. zabludoff, a.i, the role of environment in the mass– metallicity relation, monthly notices of the royal astronomical society 390 (2008) (1) 245–256. https://ui.adsabs.harvard.edu/link_gateway/1983apj...272...54k/doi:10.1086/161261 https://doi.org/10.2298/saj1183071a https://doi.org/10.1155/2010/158568 http://fse.studenttheses.ub.rug.nl/id/eprint/15367 https://www.nasa.gov/image-feature/goddard/hubbles-true-blue-compact-dwarf https://www.nasa.gov/image-feature/goddard/hubbles-true-blue-compact-dwarf https://doi.org/10.3847/1538-4365/aad555 https://doi.org/10.1007/978-0-387-30164-8_323 bibechana vol. 20, no. 3, december 2023, 259–266 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar an accurate theoretical formula for linear momentum, force and kinetic energy chandra bahadur khadka department of physics, tri-chandra multiple campus, tribhuvan university, kathmandu-44600, nepal ∗corresponding author. email: chandrabahadur9988@gmail.com abstract the paper demonstrates that the existing mathematical formulas of linear momentum, force and kinetic energy in physics are incomplete, since such formulas have been formulated without incorporation of mass-energy equivalence relation e = mc2. therefore, new reformulations of the main equations of linear momentum, force and kinetic energy in the realm of special relativity are proposed. the proposed formulas provide same mathematical outcomes as the old formulas, displaying same behavior of the system when velocity approaches to speed of light, but, most importantly, comprise only velocity of the light and mass of object to provide well-defined expressions. if c be speed of light in vacuum, then, the modified linear momentum, force and kinetic energy are given, respectively, by formulas p = c √ m2 −mo 2, f = cm√ m2−mo 2. dm dt and ke = c2(m2−m2 0) 2m , where mo denotes the rest mass. these formulas vividly reveal that every physical variable depends solely on relativistic mass. therefore, it modifies newton’s second law of motion and states that the force depends on rate of change of relativistic mass of object rather than its velocity. in this highly interesting topic, primary purpose here has been to present a succinct and the carefully reasoned account of a new aspect of the newton’s second law of motion which properly allows to derive the new mathematical formulas of linear momentum, force and kinetic energy. keywords force, kinetic energy, linear momentum, newton’s second law of motion, special theory of relativity. article information manuscript received: june 7, 2023; accepted: september 16, 2023 doi https://doi.org/10.3126/bibechana.v20i3.55476 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction in 1687, sir isaac newton presented three laws of motion in his seminal work “principia mathematica philosophiae naturalis,” [1] which have produced most profound effect in entire field of physics to generate the mathematical expression of every dynamical variable such as linear momentum, force, kinetic 259 http://nepjol.info/index.php/bibechana chandrabahadur9988@gmail.com https://doi.org/10.3126/bibechana.v20i3.55476 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ chandra bahadur khadka/ bibechana 20 (2023) 259-266 260 energy and so on. linear momentum is a fundamental parameter of physics which is employed to provide an accurate mathematical description of every physical phenomenon. there is hardly any field of theoretical physics or law of nature which is not associated with linear momentum. one of the most important applications of the momentum is in the formulation of newtown’s second law of motion [2] which states that the rate of change of linear momentum is equal to force. in mathematical form: p = mv , f = d(p) dt = d(mv) dt (1) on the basis of newtonian mechanics, the kinetic energy due to application of this force is given by, ke = mv2 2 (2) the earliest known publication with the formula (1) is the work by mach in 1883 in his system of mechanical definitions: moving force is the product of the mass-value of body into the acceleration inducted in that body [3]. a more extensive analysis of equations (1) and (2) can be found in work [4]. in newtonian mechanics, equations (1) and (2) were stated with the fact assumption that mass m is constant. for over 200 years the equations of motion enunciated by newton were believed to describe nature correctly and the first time that an error in these laws were discovered. it was discovered by einstein in 1905. einstein gave following famous equation called principle of mass and energy equivalence [5, 6]. e = mc2 (3) where m denotes the relativistic mass and e denotes the relativistic energy (total energy of body, means sum of kinetic and resting energy). in 1908, lewis showed [7] that the principle of mass and energy equivalence equation (3) implies a relativistic mass formula of energy namely equation (4). the same derivation is given in feynman lectures on physics [8]. in 1912, tolman considered the principle of momentum conservation in a perfect inelastic collision and introduced theoretical dependence of mass from velocity based on the relativity principle [9]. m = mo√ 1− v2 c2 (4) where m0 denotes the rest mass. derivations such as that by tolman for relativistic mass are propagated in several excellent textbooks including the famous feynman’s lectures [10]. during the past few decades, many authors have written extensively on incorporation of relativistic formulas namely equations (3) and (4) to modify newtonian equations (1) and (2). the article [11] presents the original definition of acceleration in the special theory of relativity while article [12] presents the formalism of relativistic acceleration and velocities in three dimensions of space. the work [13] presents the einstein’s mass-energy equivalence and the equation of relativistic mass, momentum and energy from the newton’s second law of motion. the article [14] presents mass-energy equivalence formula e = mc2 from maxwell’s equations. ref. [15] presents a relativistic paradox which exposes the true nature and ubiquity of hidden momentum. the work [16] develops an original derivation of lorentz transformation in three-dimensional space, while work [17] shows the variation of mass in gravitational field with the use of formula e = mc2. articles [18], [19], [20] presents research on the special theory of relativity on de-broglie wavelength of a particle and on electric permittivity and magnetic permeability of electromagnetic wave. there are numerous publications [21, 22] that examine the various aspects of the special theory of relativity. hu [23] presented the derivation of the expression for the relativistic momentum and energy of relativistic particle based on relativistic addition. sunego and pin [24] presented a new derivation of the expression for momentum and energy of relativistic particle. adkins [25] obtained the special relativistic expressions for momentum and energy in a totally inelastic variant of the lewis-tolman symmetric collision. there are many publications on special relativity but, most importantly, following questions have not yet addressed carefully. above equation (3) suggests that the energy of a system depends solely on the inertial mass of system and velocity of light. the question then arises, “how do we express the mathematical formula of linear momentum, force and kinetic energy only in terms of mass and velocity of light as that of relativistic energy e = mc2?”. this paper provides the answer of this question by expressing the linear momentum, force and kinetic energy in terms of mass and velocity of light, then, in place of equations (1) and (2), we have simply, p = c √ m2 −mo 2, f = cm√ m2 −mo 2 dm dt ke = c2 2m ( m2 −m2 0 ) (5) further, mass-energy equivalence principle namely equation (3) helps in transforming above equations into following form. p = √ e2 − e2 0 c , f = e c √ e2 − eo 2 de dt , ke = e2 − eo 2 2e (6) where eo denotes the rest mass energy of system. it should be noted that for old theory namely equation (1) and (2), both variables mass m and velocity of chandra bahadur khadka/ bibechana 20 (2023) 259-266 261 object v are comprised, while for the modified theory (5) and (6), only one variable i.e., either mass or energy of system is comprised. the structure of the remainder of this paper is organized as follows. in the section 2, dynamical variables such linear momentum, force, kinetic energy and de broglie wavelength are expressed in terms of relativistic energy. in section 3, expression of linear momentum and force is transformed into modified form that involves single variable mass. further, modified formulas are employed to derive famous mass-energy equation e = mc2. some conclusions are summed up in the last section. 2 methods 2.1 relativistic momentum and force in terms of energy according to special theory of relativity, whenever an object of rest mass mo is in speed, it seems to get heavier. the following equation gives the mass of object at travelling velocity v. m = mo√ 1− v2 c2 (7) or, mc2 = moc 2√ 1− v2 c2 or, e = eo√ 1− v2 c2 where e0 = m0c 2 is the rest energy and e = mc2 is the total energy possessed by the object. squaring both sides of above equation we get, e2 = e0 2 1− v2 c2 or, 1− v2 c2 = e0 2 e2 or, v2 c2 = 1− e0 2 e2 v2 c2 = e2 − e2 0 e2 (8) or, v c = √ e2−e2 0 e or, ev = c √ e2 − e2 0 or, mc2v = c √ e2 − e2 0 or, mv = √ e2−e2 0 c p = √ e2 − e2 0 c (9) where the product of mass and velocity mv = p is the momentum of object. this equation (9) gives the relation between linear momentum p and relativistic energy e of moving object. above relation suggests that linear momentum depends upon change in energy of the system √ e2 − e2 0 . also, newton’s second law, in its most general form says that the rate of a change of a particle’s linear momentum p is given by the force acting on the particle. in mathematical form: f = dp dt using equation (9) we get, or, f = d dt (√ e2−e2 0 c ) or, f = d √ e2−e2 0 cd(e2−e2 0) d(e2−eo 2) dt or, f = 1 2c √ e2−eo 2 2e de dt f = e c √ e2 − eo 2 de dt (10) this result shows the expression of force in term of relativistic energy of system. in plain and simple terms, it means that force acting on a system depends upon change of energy due to relativistic phenomenon. equation (9) plays an important role to show the relationship between de broglie wavelength and energy of particle. de broglie wavelength is an important concept while studying quantum mechanics. the wave length λ that is associated with an object in relation to its linear momentum and mass is known as de broglie wavelength. a particle’s de broglie wavelength is usually inversely proportional to its linear momentum as follows. λ = h p using equation (9) we get, λ = hc√ e2 − eo 2 (11) equation (11) shows the expression of de broglie wavelength in terms of relativistic energy of the system. in plain and simple terms, it means that de broglie wavelength of particle depends upon change of energy due to relativistic phenomenon. further, the formula for kinetic energy ke for a particular body in terms of linear momentum is expressed as, k.e. = p2 2m using equation (9) we get, ke = 1 2m (√ e2−eo 2 c )2 or, ke = e2−eo 2 2mc2 (12) ke = (e2 − eo 2)mc2 2(mc2) 2 (12) total energy of body is e = mc2 hence, ke = (e2−eo 2)mc2 2e2 or, ke = mc2 2 (1− e2 e2 0 ) from equation (8) we have, ke = mc2 2 v2 c2 ke = mv2 2 chandra bahadur khadka/ bibechana 20 (2023) 259-266 262 above derivation suggests at once that modified formula of linear momentum namely equation (9) is completely true, since it gives correct expression of kinetic energy ke. therefore, modified expression of force namely equation (10) is also true. equation (10) is the basic law of physics on which the relation between relativistic energy and force of a system is based. rewriting equation (12) we have, kinetic energy ke = e2−eo 2 2mc2 substituting mc2 = e we get, kinetic energy ke = e2 − eo 2 2e (13) therefore, the kinetic energy associated with body can be accurately determined by knowing only relativistic energy. 2.2 relativistic momentum and force in terms of mass in special relativity, the relativistic mass is given by, m = mo√ 1− v2 c2 where c is speed of light in vacuum and m denotes the mass of body when it is moving with a velocity v. then total relativistic energy of the body of mass m is given by, e = mc2 = moc 2√ 1− v2 c2 the momentum of the body p = mv so that v = p m hence, mc2 = moc 2√ 1− p2 m2c2 or, mc2 = moc 2√ 1− p2c2 m2c4 or, m2c 4 = m2 0c 4 1− p2c2 m2c4 or, m2c4(1− p2c2 m2c4 ) = mo 2 c4 or, m2c4 − p2c2 = mo 2c4 or, p2c2 = m2c4 −mo 2 c4 p2 = ( m2 −mo 2 ) c2 (14) a particle of mass m moving with a velocity v has a wave associated with it whose wavelength according to de-broglie is given by, λ = h mv = h p p = h λ squaring both sides, h2 λ2 = p2 (15) from equation (14) and (15), we have h2 λ2 = ( m2 −mo 2 ) c2 or, λ2 = h2 c2( m2−mo 2) λ = h c √ m2 −mo 2 (16) this is the expression for de-broglie wavelength due to variation of mass with velocity. thus, equation (16) reveals the dependence of wave nature of object with relativistic phenomenon. this shows that the de-broglie wavelength associated with particle exists whenever mass of particle varies with velocity. further, the relationship between kinetic energy and momentum is given by ke = p 22m using equation (14) ke = c2 2m ( m2 −m2 0 ) (17) from relativistic variation of mass with velocity we have, m = m0√ 1− v2 c2 squaring both sides of above equation we get, or, m2 = m0 2 1− v2 c2 or, 1− v2 c2 = m0 2 m2 or, v2 c2 = 1− m0 2 m2 or, v2 c2 = m2−m2 0 m2 or, m2 −m2 0 = m2v2 c2 above equation (17) becomes, kinetic energy ke = c2 2m m2v2 c2 kinetic energy ke = mv2 2 above derivation suggests at once that modified formula of momentum namely equation (14) is completely true, since it generates correct formula of kinetic energy. from equation (17) it is seen that kinetic energy completely depends on change of mass of body due to relativistic phenomenon. kinetic energy ke = c2 2m ( m2 −m2 0 ) therefore, the kinetic energy associated with body can be accurately determined by knowing only relativistic mass of body. 3 results and discussion according to einstein, the mass of the body in motion is different from the mass of the body at rest. m = mo√ 1− v2 c2 this is the relativistic formula for variation of mass with velocity. where m0 denotes the rest mass and m denotes the relativistic mass of body. squaring both sides of above equation, or, m2 = m0 2 1− v2 c2 or, 1− v2 c2 = m0 2 m2 chandra bahadur khadka/ bibechana 20 (2023) 259-266 263 v = c √ m2 −mo 2 m (18) or, mv = c √ m2 −mo 2 or, p = c √ m2 −mo 2 the most important consequence of this equation is that linear momentum actually depends upon the change of relativistic mass. from newton’s second law of motion, f = dp dt = d(mv) dt or, f = mdv dt +v dm dt from equations (18) we get, or, f = m d dt ( c √ 1− m0 2 m2 ) + c √ 1− m0 2 m2 dm dt or, f = cm 2 √ 1− m0 2 m2 d dt ( 1− m0 2 m2 ) + c √ 1− m0 2 m2 dm dt or, f = cm 2 √ 1− m0 2 m2 2m0 2 m3 dm dt + c √ 1− m0 2 m2 dm dt or, f =  m2 0 m2 √ 1− m0 2 m2 + √ 1− m0 2 m2  cdmdt or, f = ( m2 0 m √ m2−mo 2 + √ m2−mo 2 m ) cdmdt or, f = ( m2 0 +m2−mo 2 m √ m2−mo 2 ) cdmdt or, f = m2 m √ m2−mo 2 c dm dt f = cm√ m2 −mo 2 dm dt (19) again, the total relativistic energy associated with mass m is given by, e = mc2 = moc 2√ 1− v2 c2 or, mc2 = moc 2√ 1−m2v2 m2c2 or, m2c4(1− m2v2 m2c2 ) = mo 2c4 or, m2c4 −m2v2c2 = mo 2c4 or, m2v2c2 = m2c4 −mo 2 c4 or, m2v2 = ( m2 −mo 2 ) c2 the momentum of a body is p = mv. hence, p2 = ( m2 −mo 2 ) c2 p = c √ m2 −mo 2 (20) since c is a constant, momentum p depends only on the mass of system. p α √ m2 −mo 2 above equation (20) is a fundamental formula of linear momentum that does not involve velocity of body. thus, linear momentum is always related with relativistic mass variation rather than its velocity. there is immense application of modified formula (20) as compare to old formula p = mv. since, old formula of linear momentum involves two variables m and v. therefore, it is very difficult to find explicit relation between momentum and mass due to involvement of another variable velocity v, but modified formula (20) involves only a single variable mass m. as a result, it is easy to determine the clear relationship between momentum and mass of object. rewriting equation (20), p = c √ m2 −mo 2 comparing this equation with linear equation y = µx+ c,we get y = p, µ = c, x = √ m2 −mo 2, c = o it is interesting and instructive to sketch the graph between momentum p and √ m2 −mo 2 (mass of body) taking them along y-axis and x-axis respectively. the slope of graph gives a constant c which is the speed of light in free space as shown in figure (1). the modified formula of linear momentum has huge application in physics to perceive important ground breaking results such as e = mc2. it generates new expression of force that involves single variable mass of body and excludes its velocity. let a force f act upon the body in the direction of its motion. force is the rate of change of momentum p i.e. f = dp dt from modified formula of linear momentum namely equation (20), or, f = d dt (c √ m2 −mo 2) or, f = cd √ m2−m2 0 d(m2−m2 0) d(m2−mo 2) dt or, f = c 2 √ m2−mo 2 . 2m dm dt f = cm√ m2 −mo 2 dm dt (21) the meaning of this equation is that force f upon the body explicitly depends on the rate of change of mass of object rather than the change of velocity of body. thus, this formula of force namely (21) corresponds to einstein’s mass energy formula e = mc2because both force and energy depends only upon the mass of the body rather than velocity of body. if ds be the displacement of the body due to the force, then work done by the force is given by, dw = fds substituting value of f from equation (21), dw = cm√ m2−mo 2 dm dt ds the velocity of body v = ds dt hence, dw = cmv√ m2 −mo 2 dm (22) also, from special relativity, c m = v√ m2 −mo 2 (23) chandra bahadur khadka/ bibechana 20 (2023) 259-266 264 figure 1: linear relation between momentum and mass of body. from equation (22) and (23) we get, dw = vc2 v dm or, dw = c2dm when mass of the body changes from mo and m, then total work done is given by,∫ w 0 dw = c2 ∫m mo dm or, w = (m−mo)c 2 or, mc2 = w +moc 2 where moc 2 is the energy due to rest mass of the body i.e., it’s energy when at rest with respect to the observer is called it rest energy moc 2 . similarly, mc2 is the total energy e possessed by the body. then we have, total energy (e) = work done (w) + rest energy (eo) e = (m−mo)c 2 +moc 2 e = mc2 this is known as einstein’s mass energy relation. therefore, the modified formula of force given by equation (21) is completely true because it gives exactly same as einstein mass energy equation. it is interesting and instructive to compare old formulas and modified formulas of variables such as linear momentum, force, kinetic energy and wavelength. in old formulas, dynamical variables are expressed in terms of mass m and velocity v of object as shown in table (1). exactly opposite behavior occurs when these dynamical variables are modified by using relativistic mechanics. as shown in table (1), formulas of dynamical variables in modified form depend on velocity of light c instead of velocity of object v. chandra bahadur khadka/ bibechana 20 (2023) 259-266 265 4 conclusion all possible relativistic formulas of dynamical variables such as linear momentum p, force f , kinetic energy ke and de broglie wavelength λ have been thoroughly derived in this article. the key innovated formulas of dynamical variables in terms of relativistic energy can be written from equations (9), (10), (11) and (13) as follows. p = √ e2−e2 0 c , f = e c √ e2−eo 2 de dt λ = hc√ e2−eo 2 , ke = e2−eo 2 2e according to mass-energy principle, mass may appear as energy and energy as mass. therefore, above formulas of dynamical variables can be written in terms of mass from equations (16), (17), (19) and (20) as follows. p = c √ m2 −mo 2 , f = cm√ m2−mo 2 dm dt λ = h c √ m2−mo 2 , ke = c2 2m ( m2 −m2 0 ) the relativistic energy of system e = mc2 depends on inertial mass of system. in same way, it is concluded that every physical variable depends solely on relativistic mass as shown in above equations. the most dramatic success of this paper is the modification of newton’s second law of motion which states that force f depends on rate of change of mass rather than change of velocity with time. the derivation of wellknown formula for energy e = mc2 has been derived by using modified equation of force. the primary purpose here has been to provide the possible extension of special relativity to modify the newtonian formulas of dynamical variables and lay down the basic equations of extended theories. the new formulas elucidated here will have many physical applications and it will be of interest in many other areas of theoretical physics. conflict of interest: the author declares no conflict of interest. data availability: data sharing not applicable to this article as no datasets were generated or analyzed during the current study. list of symbols f : force p: linear momentum ke: kinetic energy m0: rest mass m: relativistic mass c: velocity of light v: velocity of body e: relativistic energy e0: rest mass energy λ: wavelength references 1. i. newton, principia mathematica philosophiae naturalis (mathematical principles of natural philosophy), london 1687; motte1729; wawryzyki j. cracow: copernicus center press; 2011. 2. c. lee. infinity and newton’s three laws of motion. foundations of physics, 41:18101828, 2011. 3. e. mach, the science of mechanics-a critical and historical account of its development, the open court publishing, 1999. 4. i.v. meshchersky. equations of motion of a variable mass point in general case. st. peterburg polytechnic university news, 1:77-118, 1904. 5. a. einstein. on the electrodynamics of the moving 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force in terms of energy relativistic momentum and force in terms of mass results and discussion conclusion bibechana vol. 20, no. 1, april 2023, 1–9 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar study of aerosol optical properties in lumbini, nepal santosh sapkota1, sabin gautam2, santosh pokhrel1 aayush gautam3, kailash basnet1 , roshan kumar mishra4, jeevan regmi1,∗ 1prithvi narayan campus, tribhuvan university 2pokhara astronomical society 3birendra multiple campus, tribhuvan university 4university of maryland, baltimore county ∗corresponding author. email: jsregmi28@gmail.com abstract the mixture of different sized particles (fine and coarse) with air composition forms aerosols. increased economic activities, vehicles, and rapid urbanization made lumbini one of the heavily polluted regions in nepal. data are extracted from aeronet websites between 2013 to 2019 with standard deviation. we are mainly focused on understanding variations in aerosol optical properties: aerosol optical depth (aod), angstrom parameter (α and β), visibility, single-scattering albedo (ssa), refractive index (real and imaginary), and asymmetry parameter (ap) in the lumbini region. the maximum value of aod (675nm) in lumbini occurred mostly during post-monsoon season (0.61 ± 0.38) whereas; the values of aod were found to be lower during the monsoon season (0.18 ± 0.12). most of the aod values except monsoon season are found to be greater than 0.4, indicating a higher level of pollution in the study area. there is a weak correlation between precipitable water and aod, maximum correlation (0.04) occurs at the lowest value of aod at 440nm while the minimum (0.01) at the highest value of aod at 1020nm. the turbidity coefficient (β) has an adverse effect on visibility. the average visibility over lumbini was found to be 8.76 ± 4.95 km during the period of 2013-2019. single-scattering albedo (ssa) accretions occur at wavelengths between 440 and 675 nm, but the pattern changes from 675 nm to 1020 nm. all parameters were found to be distinct and seasonal fluctuations among this station are mainly due to the different aerosols availability such as biomass burning, mixed aerosols, and anthropogenic aerosols over the lumbini site. keywords aerosol optical depth, angstrom exponent , lumbini. article information manuscript received: october 09, 2022; accepted: march 18, 2023 doi https://doi.org/10.3126/bibechana.v20i1.48825 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction aerosols are atmospheric molecules that are either produced by anthropogenic factors (fossil fuel, burning, biomass, transportation, etc.) or by natural factors (volcanic, sea salt, desert, etc.). it has a variety of potential effects on our planet’s radiation balance. aerosols can absorb and scatter solar 1 http://nepjol.info/index.php/bibechana jsregmi28@gmail.com https://doi.org/10.3126/bibechana.v20i1.48825 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ santosh sapkota et al./ bibechana 20 (2023) 1-9 2 energy, which has an impact on cloud formation by changing the microphysics and lifetime of the clouds [1]. though a lot of information about our climate system is known, there are more parameters and associated factors that make a deep understanding of the climate system uncertain [2]. aerosols in the atmosphere are responsible for changing the climate system, reducing visibility and crop productivity, and harming human health [3]. the size and structure of aerosols vary from location to location and are influenced by pollution levels that make their optical and microphysical properties complicated [4]. studies on aerosols conducted in the past have also shown that aerosols produced by human activity can change regional temperature, the hydrological cycle, clouds, and precipitation [5]. the main difficulty in the current climatic study is to quantify regional-scale variations in aerosol concentration, composition, and size with high enough temporal and geographical resolution [6], which necessitates methods that integrate observations with atmospheric models. the combination of anthropogenic sources, and biomass burning over the igp region, which also affects the air quality in lumbini, is the main source of aerosol loading [7], which results in the creation of atmospheric black carbon (abc) [8–10]. thus, emitted particles get trapped under conducive meteorological conditions which results in the air pollution of the region [11]. several parameters, including aerosol optical depth (aod), angstrom exponent (α), turbidity coefficient (β), precipitable water (pw), single scattering albedo (ssa), visibility and asymmetry parameter (ap) has been examined in this article. ssa represents the scattering ability of the aerosol; higher ssa values denote a more scattering aerosol, while lower ssa values indicate absorbing aerosol. by analyzing ssa values, we can predict whether the aerosols have cooling or warming effect [12]. for purely scattering aerosol, the value of ssa is 1 and for pure absorbing particles, it is zero. the value of the ssa varies with the aerosol types also. for example; the value of ssa for biomass burning ranges from 0.88-0.94, for desert dust it ranges from 0.92-0.99 and it is 0.89-0.98 for urban industrial aerosol [13]. the real and imaginary parts, which make up the refractive index, are adversely influence by chemical composition [14]. the refractive index describes how atmospheric particles scatter and absorb light [15]. the real part’s higher value indicates the domination of scattering type of aerosol particles, whereas the imaginary part’s higher value shows the domination of absorbing type of aerosol particles. various kinds of aerosols, the refractive index’s real value has a range of possible values. the value of the imaginary part varies from 0.003-0.014 for urban industrial aerosols, 0.00093-0.021 for biomass burning, and 0.007-0.0029 for desert dust, and the value of real part ranges from 1.40-1.47 for urban industrial aerosols, 1.47-1.52 for biomass burning, and 1.36-1.56 for desert dust [16]. the asymmetry parameter (asy), which is affected by particle size and composition, has a value between -1 (backscattered) and 1 (forward scattered) [17]. the dependence of aerosol loading on a particular size is explained by the relationship of aod and angstrom exponents. the turbidity coefficient (β) reflects aerosol loading, whereas the angstrom exponent (α) denotes aerosol size distribution. the variation in the size of aerosol has guided by its source. the aerosol optical depth (aod) is an extinction coefficient of aerosols in the vertical direction, and it is used to describe turbidity, estimate the aerosol content of the atmosphere, evaluate the degree of atmospheric environmental pollution, and can be measured to assess the aerosol load on the atmosphere. moreover, the amount of water that comes back to the earth’s surface in the form of precipitation when the cloud condenses formed by evaporation from the surface of the earth is known as precipitable water. it is the main component of the greenhouse because it is capable of absorbing and reemitting infrared radiation. this work mainly focuses on understanding the aerosol optical properties over lumbini on monthly variation and also describes the seasonal variation. 2 data set and methodology this research is focused on the various aerosol properties over lumbini, nepal (27.67n, 83.50e, 150m elevation). lumbini is known as the birthplace of the buddha, which is located within the nepal terai region, called the land of the subtropical chain of forests marshes, and grasses. lumbini is one of asia’s most polluted regions in the terai region [18]. the major sources of air pollution are gases produced by different industries, brick-kiln, fire, and smoke. besides this, lumbini is bordered by india and lies in the igp region, so the transportation of various types of air pollutants from the northern part of india leads to an increase in the air pollution over lumbini [19]. since lumbini represents the characteristics of the terai region of nepal bordered to india especially, igp region and a historical pilgrimage site of nepal, we are motivated to study the various aspects of aerosol optical properties. aeronet robotics network (aeronet) (aeronet.gsfc.nasa.gov) has installed the cimel sunphotometer in lumbini international research institute (liri). we have used aeronet level 2, santosh sapkota et al./ bibechana 20 (2023) 1-9 3 version 3 data for our analysis which are quality assured data of lumbini site over the period of 7 years from january 2013 to december 2019 [20]. there are eight distinct ways to measure aod using a solar photometer, with wavelengths ranging from 340 nm to 1020nm [21]. the relationship between aod and angstrom exponent (α) is given by the power-law equation [22] τ = βλ−α (1) the wavelength in microns associated with aod value is denoted by λ . angstrom’s turbidity coefficient is denoted by β. equation (1) can be written in the logarithmic format as: ln τ(λ) = lnβ − α lnλ (2) ångström parameters ( α and β) were obtained from equation (2). from the spectral aod (λ), the angstrom exponent (ae) α can be further defined as: α = −d ln τaod(λ) d lnλ = ln τaodλ2 τaodλ1 ln λ2 λ1 (3) the visibility (v) of the air in km is given by the following formula [23]. β = 0.5α ( 3.912 v − 0.01162 ) (0.02472v (v − 5) + 1.132) (4) where v denotes the visibility in the atmosphere which is inversely proportional to extinction coefficient, [24]. the ratio of scattering coefficient to the extinction coefficient gives the single scattering albedo (ssa), can be expressed as: ω = σscatt σ (5) the asymmetry parameter can be calculated as, g = 1 2 ∫ π 0 cos θ′p (θ), sin θ,dθ (6) where,θ angle between incident and scattering direction. p (θ) represents the angular distribution of scattering light. figure 1: map showing the geographical location of lumbini, nepal. 3 results and discussion to acquire a qualitative knowledge of atmospheric aerosols and aerosol size, the aod and angstrom exponent (α) are often used. the parameter with low and high values indicates coarse and fine particle dominance, respectively. figure 2 shows the monthly average aerosol optical properties, namely, aod, angstrom exponent (ae) (440-870nm), and pw from january to december at lumbini with standard deviations from 2013 to 2019.the monthly average is obtained by averaging daily mean data over seven years. the highest aod (675nm) was found in the monsoon season in june (0.61 ± 0.38). due to fog, haze, and clouds, the aod is higher during the winter and post-monsoon seasons [25]. in contrast to the pre-monsoon and summer seasons, it was determined that the angstrom exponent (α) was at its maximum during the post-monsoon and winter seasons due to the influence of anthropogenic sources. the value of α was found to be greater than 1.0 in all months of the year, representing the dominance of fine mode aerosols due to combustion related anthropogenic sources. the lowest aod was found in the monsoon season in july (0.21± 0.14) due to the increment in the level of precipitable water that helps to wash out the aerosols in the atmosphere. the amount of precipitable water was shown to rise to start in january (1.23 ± 0.23), reach its peak in july (5.91 ± 0.36), and then gradually decline. in the lumbini site, the monsoon represents the rainy season and is responsible for 75 % of the annual precipitable water. the variation of aod, α, and precipitable water was found to be similar to [26], which agrees with our results. the short wavelength dominates the fine-mode santosh sapkota et al./ bibechana 20 (2023) 1-9 4 figure 2: aeronet station lumbini monthly averages of aod (440nm), angstrom exponent (440870nm), and precipitable water. figure 3: monthly average aod observed between january 2013 and december 2019 using aeronet sun/sky radiometers at 1020, 870, and 440 nm. particles at wavelengths below 870 nm, whereas the long wavelength dominates the coarse-mode particles at wavelengths over 870 nm. aods first show considerable seasonal and wavelength dependence. as wavelength rises, aods eventually decrease, as shown in fig. 3. the abundance of smaller size particles is indicated by higher aods at lower wavelengths. aods with wavelengths of (1020 nm, 870 nm, and 440 nm) and precipitable water (cm) at the lumbini station have very weak correlation coefficients of 0.01, 0.02, and 0.04 correspondingly, indicating the weak correlation represented in fig. 4. the fact that there is a weak correlation between aod’s of various wavelengths and precipitable water suggests the amount of aerosol or other particulate matter in the atmosphere decreases as precipitable water increases. the correlation coefficient was found to be higher at the lowest wavelength 440 nm with perceptible water in comparison with 870 and 1020nm. the linear regression functions of the daily aod concentration (y) with the perceptible water(x) were y = −0.01x + 0.34(r2 = 0.01) at 1020nm y = −0.02x+ 0.43(r2 = 0.02) at 870nm, and y = −0.06x+ 0.99(r2 = 0.04) at 440nm. the turbidity coefficient (β) is strongly linked with visibility impairment. a measure of the quantity of aerosol loading in the atmosphere is the turbidity coefficient. the relationship between visibility and the turbidity coefficient (α) is inverse (fig.5), indicating that visibility is affected by aerosol loading to some extent. the average visibility for the given period of time was found to be 8.76 ± 4.95 km which is significantly low and indicates lumbini having a hazy atmosphere most of the time. but few monsoon days are fairly clean with the highest visibility in july (20 km) and august (19 km). because more precipitable water washes out the aerosol load in the atmosphere during the monsoon season, visibility was found to be at its maximum. winter, post-monsoon, and presantosh sapkota et al./ bibechana 20 (2023) 1-9 5 figure 4: correlation between precipitable water and aods (1020, 870 and 440nm) of lumbini locations of nepal. figure 5: relation between visibility and turbidity coefficient (β) over lumbini from 2013 to 2019. monsoon seasons have the lowest visibility due to fog, haze, cold waves, and smoke from industries. at the lumbini station, the turbidity coefficient value was determined to be higher than 0.15, indicating a turbid atmosphere at all seasons. single scattering albedo (ssa), a metric of light extinction, is another important optical property of aerosols to make sure the aerosol’s scattering and absorption properties, which are strongly dependent on wavelength and have significant characteristics over lumbini. single scattering albedo (ssa) is calculated using the particle scattering coefficient to total extinction coefficient ratio [27]. the chemical nature and size distribution of aerosols have a significant impact on ssa [28]. pure absorption has a value of zero, while scattering has a value of one [29,30]. the reported ssa estimates for desert dust (0.78-0.94), urban and mixed aerosols (0.83-0.98), and biomass burning (0.92-0.99) [28]. the average ssa shows high wavelength dependence, increasing from 0.90 ± 0.03 at 440nm to 0.92 ± 0.03 at 675nm and dropping to 0.90 ± 0.04 at 1020nm (fig.6). the monsoon and post-monsoon seasons, respectively, have seen the highest and lowest ssa levels. the highest ssa value indicates that scattering aerosols predominate, whereas the lowest ssa value indicates that light-absorbing aerosols predominate. our values are supported by earlier research [29] that indicates the summer and post-monsoon seasons experienced the largest and least ssa, respectively. over lumbini, post-monsoon had the highest concentration of light-absorbing aerosols compared to other seasons [30]. similar trend of spectral variation of ssa was observed in pokhara [31]. the real and imaginary parts of the refractive index at the lumbini location are depicted in fig. 7. at 440 nm, the average real santosh sapkota et al./ bibechana 20 (2023) 1-9 6 figure 6: seasonal variation of ssa over lumbini from 2013 to 2019. figure 7: seasonal variation of the aerosol real and imaginary part of the refractive index over lumbini from 2013 to 2019. part of the refractive index is 1.47 ± 0.04; at 870 nm, it is 1.49 ± 0.04; and at 1020 nm, it is 1.48 ± 0.04. the real part of the refractive index reaches its maximum and minimum values during the postmonsoon and monsoon seasons, respectively, which agrees with the possible range of values as given by [27] for various types of aerosol particles and previous result for the lumbini region [26]. the hygroscopic growth of aerosol and relative humidity are responsible for the decrease in the value of the refractive index (real part) during the monsoon season. additionally, the average imaginary part of the refractive index declines from 0.01 ± 0.006 at 440 nm to 0.008 ± 0.004 at 675 nm and then remains almost constant at 870 nm and 1020 nm. in contrast to the monsoon and pre-monsoon seasons, the post-monsoon and winter seasons were shown to have greater values for the imaginary part of the refractive index. the value of the asymmetry parameter has found to be wavelength dependent. as the wavelength rises, the value of the asymmetry parameter (g) falls (fig. 8). the average value of the asymmetry parameter (g) decreases from 0.72 ± 0.02 at 440 nm to 0.64 ± 0.03 at 1020nm. the value gradually declines from 440 nm to 1020 nm during the winter, post-monsoon, and monsoon seasons while during pre-monsoon the value increases from 870nm to 1020 nm. 4 conclusion the key aerosol optical properties like aod, ae, pw, ssa, ap and refractive index over lumbini site was analyzed from 2013 to 2019 using aeronet data. it revealed some interesting features. the months of december and july were found to have the highest monthly average aod (675nm). the alpha value was found to be more than 1.0, indicating that fine mode aerosols predominated throughout the duration of a year. 75 % of the water vapour that is observable throughout the year is precipitable during the monsoon season. aod values are found to be spectral dependent. it is observed that aod value decreases with the increase in wavelength. aods of short wavelengths can give higher precision in measuring the size of aerosols. this implies that the aerosols’ size is dispersed in the atmosphere. the precipitable water observed higher during the periods when the aod is also higher indicating the possibility of the hygroscopic growth of aerosols and the dust storm from igp region. the visibility and the turbidity coefficient (β) have an inverse 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[31] j. regmi, k. n. poudyal, a. pokhrel, m. gyawali, l. tripathee, a. panday, and r. aryal. investigation of aerosol climatology and long-range transport of aerosols over pokhara, nepal. atmosphere, 11(8):874, 2020. https://doi.org/10.1364/ao.55.006199 introduction data set and methodology results and discussion conclusion bibechana 18 (2) (2021) 143-153 143 synthesis of antioxidative anthraquinones as potential anticancer agents richa k. gupta1,2, ganesh m. s. thakuri1, gan b. bajracharya1*, ram narayan jha3* 1laboratory of catalysis and frontier molecules, faculty of science, nepal academy of science and technology (nast), khumaltar, lalitpur, nepal 2central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal 3department of chemistry, tri-chandra multiple campus, tribhuvan university, ghantaghar, kathmandu, nepal *email: ganbajracharya@yahoo.com (g. b. bajracharya); ramnarayan_jha@yahoo.co.in (r. n. jha) article information: received: september 15, 2020 accepted: june 7, 2021 keywords: acetylation antibacterial antioxidant chrysophanol friedel-crafts reaction abstract antioxidant and antibacterial activities of natural anthraquinones namely chrysophanol (1) and emodin (2), and synthesized anthraquinones viz. 2methylanthraquinone (3), anthraquinone (4), 2-bromoanthraquinone (5), rubiadin (6), chrysophanol diacetate (7), rubiadin diacetate (8) and 1,8-dimethoxy-3methylanthraquinone (9) were investigated. anthraquinones 9, 3, 6, 5 and 2 exhibited a high dpph• radical scavenging capacity (ic50 = <500 μg/ml) showing their therapeutic potentiality for the treatment of cancers. these anthraquinones 1-9 have also displayed a weak to moderate antibacterial activity against bacillus subtilis. chrysophanol diacetate (7) including emodin (2) have been appeared as the valuable antibacterials. doi: https://doi.org/10.3126/bibechana.v18i2.31234 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction anthraquinones are important members of the quinone family that have profound therapeutic values as antibacterial, antifungal, anticancer, antioxidant, laxative, diuretic, estrogenic, antiinflammatory, antiarthritic, etc. [1-3]. anthraquinone structural motif is present in many natural dyes, pigments, vitamins, enzymes etc [4]. among 700 natural anthraquinones identified, about 200 compounds were isolated from plants and remaining from lichens, fungi and others [5-6]. anthraquinones are widely distributed in aloe species of liliaceae, semen cassiae and folium sennae of leguminosae, radix rubiae of rubiaceae, cascara sagrada of rhamnaceae, and also widely exist in a number of species of polygonaceae family especially in the genuses rheum, rumex and polygonum. they are more commonly available in the important herbs like rheum officinale, polygonum cuspidatum, polygonum multiflorum and polygonum bistorta. antioxidant molecules inhibit oxidation of other compounds. reactive free radicals, particularly ganbajracharya@yahoo.com%20 ramnarayan_jha@yahoo.co.in%20 https://doi.org/10.3126/bibechana.v18i2.31234 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana richa k gupta et al. / bibechana 18 (2) (2021) 143-153 144 reactive oxygen species such as superoxide (o2•−), hydroxyl (ho•), peroxyl (ro2•) and nitric oxide (no•), are produced in living organisms during metabolisms. an imbalance between the production of such free radicals and inability of the body to eliminate them through the use of endogenous and exogenous antioxidants result oxidative stress [7]. oxidative stress causes oxidative damage which eventually leads to a large number of diseases including cancers, mutagenesis, cardiovascular diseases, neurodegenerative diseases (e.g. alzheimer’s and parkinson’s diseases), immunodeficiency syndrome, diabetes, cellular aging, etc [8-10]. the important reaction used for the laboratory preparation of anthraquinones is friedel-crafts acylation between phthalic anhydrides and benzene derivatives. in conventional two steps process, oaroylbenzoic acids are first prepared in the presence of alcl3 by the friedel-crafts acylation [11]. in the second step, intramolecular condensation of aryl and o-aroylbenzoic acid is performed to produce anthraquinones using h2so4 or oleum [12], benzoyl chloride and concentrated h2so4 [13-14], benzoyl chloride and zncl2 [15], pocl3 and p2o3cl4 [16], or b(hso4)3 [17]. a eutectic mixture of alcl3 and nacl melt has also been used to prepare various anthraquinones by the friedelcrafts acylation between phthalic anhydrides and benzene derivatives [18-19]. montmorillonite k10 clay [20], alum (kal(so4)2.12h2o) [4] and mivpws (miv = zr, ti and sn; and pw = phosphotungstate) [21] as heterogeneous solid catalysts have also been explored, but these catalyst are not easily available. the synthesis of anthraquinones has received a great attention in the recent past due to their therapeutic values as well as synthetic challenges. total syntheses of some complex anthraquinones such as uncialamycin [22], dynemicin a [23], daunomycin [24], marmycin a [25], (±)brasiliquinone b [26], etc. have been reported (figure 1). synthesis of these bioactive complex molecules requires multiple steps and are therefore available in poor quantities diminishing their therapeutic usefulness. hence, our researches focus on isolation and/or synthesis of simple organic molecules and/or their derivatives (which can be easily obtained and/or synthesized in a large quantity) possessing remarkable medicinal values [27-31]. recently, we have reported isolation of two anthraquinones viz. chrysophanol (1) and emodin (2) from the rhizomes of rheum australe (figure 1) [32]. herein, we studied antioxidant capacity of these anthraquinones 1-2 as well as some newly synthesized anthraquinones 3-9. antibacterial activity of the anthraquinones 1-9 is also screened against 6 bacterial strains. fig. 1: structures of some anthraquinones with their medicinal values. 2. experimental chemicals and equipments 2,2-diphenyl-1-picrylhydrazyl (dpph) was procured from sigma-aldrich. gallic acid was purchased from sisco. analytical thin layer chromatography (tlc) was performed on 0.2 mm pre-coated kieselgel 60 f254 plate (e. merck). melting points (mp) were determined by using a thile’s tube and are uncorrected. uv-vis spectra were recorded on cary 60 uv-visible spectrophotometer (agilent). spectrophotometry was carried out by using an elisa microplate reader (epoch2, biotek instruments). ir spectra were recorded on ir tracer-100 (shimadzu) in kbr disc. richa k gupta et al. / bibechana 18 (2) (2021) 143-153 145 previously isolated chrysophanol (1) and emodin (2) were also used in this work [32]. procedures for the synthesis of anthraquinones method 1. friedel-crafts and intramolecular condensation reactions to synthesize anthraquinones 3-5 two-steps reaction protocol was followed to synthesize anthraquinones 3-5 [11-12]. briefly, phthalic anhydride (1.48 g, 10 mmol) and a benzene derivative (10 ml of either toluene, benzene or bromobenzene) were taken in a twonecked round bottom flask equipped with a magnetic stirrer, condenser, recovery bend and receiver adapter (that immersed in water containing conical flask). the content was stirred at 0 °c and then introduced alcl3 (3.07 g, 23 mmol) slowly. the reaction mixture was refluxed at 90 °c until the vapour of hcl was ceased. completion of the reaction was monitored by tlc (silica gel, hexane:etoac, 1:1). after cooling, the reaction mixture was decomposed by addition of ice water and 3m hcl (25 ml). the content was extracted with et2o (20 ml × 3), washed with dil. hcl, dried over na2so4 and filtered. the solvent was evaporated and the obtained residue was vacuum dried. in the second step, dried intermediate product was refluxed with conc. h2so4 (10 ml) at 100 oc for 1.5 hours. after cooling, ice water was added slowly to decompose the reaction mixture and then filtered. the residue on the filter paper was washed with 32% nh3 solution until neutralization followed by water. pure anthraquinones 3-5 were obtained after recrystallization using etoh. method 2. alcl3:nacl melt method to synthesize anthraquinone 6 anhydrous alcl3 (13.33 g, 100 mmol) and nacl (5.32 g, 91 mmol) were taken in a 500 ml round bottom flask and were melted at 125-130 oc. to this was added a mixture of phthalic anhydride (2.66 g, 18 mmol) and 2-methyl resorcinol (2.23 g, 18 mmol) in a small portion at a time. now the reaction temperature was raised to 165-175 oc and stirred for 30 minutes. thereafter, additional alcl3 (13.33 g, 100 mmol) was added and stirring was continued for another 30 minutes. a red solid product was formed, which was decomposed by addition of ice water (125 ml) and conc. hcl (125 ml) after cooling. the reaction mixture was extracted with et2o (100 ml × 3). the etherial layer was washed with dil. hcl, dried over na2so4, filtered and concentrated. the residue obtained was purified by flash silica gel column chromatography using mixtures of hexane/etoac to give rubiadin 6. method 3. acetylation reaction to synthesize anthraquinones 7 and 8 a mixture of chrysophanol (1) (0.254 g, 1 mmol), acetic anhydride (3.66 ml, 38.8 mmol) and pyridine (3.5 ml, 44 mmol) was stirred at room temperature for 4 hours. thereafter, ice cooled water was added dropwise to the reaction mixture for the precipitation. the precipitate was collected by filtration and the acetylated product 7 was purified by silica gel column chromatography using mixtures of hexane/etoac. to prepare anthraquinone 8, instead of chrysophanol (1), rubiadin (6) (0.254 g, 1 mmol) was used as the starting material for the acetylation reaction. method 4. methylation reaction to synthesize anthraquinone 9 a mixture of chrysophanol (1) (0.127 g, 0.5 mmol), k2co3 (0.760 g, 5.5 mmol), (ch3)2so4 (0.7 ml, 7 mmol) and dry acetone (100 ml) were taken in a round bottom flask equipped with a reflux condenser and cacl2 guard tube. the reaction mixture was refluxed for 4 hours. thereafter, the reaction mixture was cooled, filtered and concentrated. thus obtained residue was purified by silica gel column chromatography using mixtures of hexane/etoac to afford anthraquinone 9. analytical data of the synthesized anthraquinones all the synthesized anthraquinones 3-9 were analyzed by recording of mp, uv-vis spectra and richa k gupta et al. / bibechana 18 (2) (2021) 143-153 146 ft-ir spectra, and the data were compared with the available literature. 2-methylanthraquinone; 2-methylanthracene-9,10dione (3): method 1. yellow solid. yield 1.58 g, 71.1% in two steps. mp 176 oc (reported 176-178 oc) [4]. uv-vis (meoh) λmax nm: 328, 275(s), 256, 206. ir (kbr) ν cm–1: 3000 (c–h aromatic), 2950 (c–h alkyl), 1720 (c=o), 1700 (c=o), 1575 (c=c aromatic), 1285 (c–h bend) [33]. anthraquinone; anthracene-9,10-dione (4): method 1. yellow solid. yield 1.64 g, 78.8% in two steps. mp 280 oc (reported 283-287 oc) [34]. uv-vis (meoh) λmax nm: 325, 271(s), 251, 204 [35]. ir (kbr) ν cm–1: 1700 (c=o), 1590 (c=c aromatic), 1350, 1325 (c–h bend) [36]. 2-bromoanthraquinone; 2-bromoanthracene-9,10dione (5): method 1. colourless solid. yield 2.26 g, 78.7% in two steps. mp 203 oc (reported 205-206 oc) [4]. uv-vis (meoh) λmax nm: 283, 228, 205. ir (kbr) ν cm–1: 1750 (c=o), 1600 (c=o), 1525 (c=c aromatic), 1250 (c–h bend), 810 (c–br stretch), 500 [33]. rubiadin; 1,3-dihydroxy-2-methylanthraquinone; 1,3-dihydroxy-2-methylanthracene-9,10-dione (6): method 2. yellow needles. yield 2.35 g, 51.4%. mp 280 oc (reported 281-282 oc) [37]. uv-vis (meoh) λmax nm: 389, 256, 221. ir (kbr) ν cm–1: 3450 (–oh), 2950 (c–h alkyl), 1750 (c=o), 1650 (c=o), 1350 (–ch3) [38]. chrysophanol diacetate; 3-methyl-9,10-dioxo-9,10dihydroanthracene-1,8-diyl diacetate (7): method 3. yellow needles. yield 0.210 g, 62.1%. mp 204 oc. uv-vis (meoh) λmax nm: 428, 285(s), 256, 223, 202. ir (kbr) ν cm–1: 3000 (c–h alkyl), 1750 (two coalescence peaks, c=o), 1670 (c=o), 1650 (c=o), 1600 (c=c aromatic), 1300, 1275 (c–h bend) (figure 2a). rubiadin diacetate; 2-methyl-9,10-dioxo-9,10dihydroanthracene-1,3-diyl diacetate (8): method 3. yellow needles. yield 0.20 g, 59.1%. mp 164 oc. uv-vis (meoh) λmax nm: 415, 277, 244, 204. ir (kbr) ν cm–1: 2975 (c–h alkyl), 1755 (c=o), 1750 (c=o), 1680 (c=o), 1630 (c=o), 1370 (–ch3), 1275 (c–h bend), 1200 (figure 2b). 1,8-dimethoxy-3-methylanthraquinone; 1,8dimethoxy-3-methylanthracene-9,10-dione (9): method 4. yellow solid. mp. 193 oc (reported 195 oc) [39-40]. yield 0.116 g, 82.2%. uv-vis (meoh) λmax nm: 338, 256, 206. ir (kbr) ν cm–1: 2950 (c– h alkyl), 1650 (c=o), 1325 (c=c aromatic), 1275, 1230, 1010 (c–o alkoxy), 955 (c–o alkoxy). antioxidant capacity: dpph• radical scavenging assay the dpph• radical solution (concentration 0.1 mm) was prepared by overnight stirring of 3.9 mg of dpph in methanol (100 ml) at 4 ºc. four working solutions of 25, 50, 250 and 500 µg/ml concentrations were prepared for each anthraquinone sample. to 0.5 ml of the working solution, 2.5 ml of the dpph• radical solution was added. control was prepared by adding 2.5 ml of the dpph• radical solution in methanol (0.5 ml). the solutions were mixed well and were kept in dark at room temperature for 30 minutes. the absorbance was measured at 517 nm against blank solution consisting water (0.5 ml) and meoh (2.5 ml). the inhibition percentage at different concentrations was calculated by using the equation shown below. statistical analysis was done by using microsoft excel program. dpph• scavenging rate % = 1 − absorbance sample absorbance control × 100 antibacterial activity: agar well diffusion assay three gram-positive bacteria viz. bacillus subtilis, staphylococcus aureus (atcc 25952), enterococcus faecalis, and three gram-negative bacteria viz. klebsiella pneumoniae (atcc 13883), pseudomonas aeruginosa (attcc 27853) and salmonella typhimurium (atcc 14028) were used for the antibacterial assay. these bacterial strains were obtained from national endemic health care centre, teku, kathmandu, nepal. the pure bacterial cultures were streaked in the nutrient agar slants for sub-culture. thus developed each pathogenic bacterium were transferred into a separate nutrient broth by a sterile loop and incubated at 37 ºc for 24 hours. richa k gupta et al. / bibechana 18 (2) (2021) 143-153 147 stock sample solutions of each anthraquinone were prepared by dissolving 0.01 g of the sample in 1 ml of dmso (concentration 10 mg/ml). now, the sample solutions (50 µl of each) were charged into the 6 mm wells bored on agar plates. dmso was used as negative control. gentamycin (10 μg/dics) was used as positive control. the plates were then incubated at 37 ºc for 24 hours, and the zone of inhibition (zoi) produced was measured. 3. results and discussion anthraquinones synthesis following the known protocols, anthraquinones 3-6 were synthesized by the friedel-crafts acylation reaction between phthalic anhydride and benzene derivatives (toluene, benzene, bromo benzene or 2methyl resorcinol). for the synthesis of anthraquinones 3-5, a two-steps protocol – the friedel-crafts reaction using alcl3 followed by h2so4-mediated intramolecular condensation – was used (scheme 1) [11-12]. anthraquinone 6 was prepared in a single-step by the friedel-crafts acylation reaction between phthalic acid and 2methyl resorcinol using alcl3:nacl melt following a known procedure (scheme 2) [38]. synthesis of anthraquinones 3-6 were confirmed by comparing mp, uv-vis spectra and ir spectra reported in the literature. phenols are commonly acetylated with acetic anhydride in the presence of pyridine [41]. acetylations of previously isolated chrysophanol (1) and newly synthesized rubiadin (6) were thus performed under un-optimized conditions to afford the corresponding acetyl derivatives 7 and 8 in 62.1% and 59.1% yields, respectively (scheme 3). in the ir spectrum of compound 7, disappearance of a broad peak of the hydroxyl group that appeared in the ir spectrum of chrysophanol (1) at 3420 cm– 1, and appearance of two coalescence peaks at 1750 cm–1 and two sharp peaks at 1670 and 1650 cm–1 for four c=o groups confirmed its synthesis (figure 2a). in a similar way, rubiadin (6) had peaks at 3450 (–oh), 1750 (c=o) and 1650 (c=o) in the ir spectrum. on the other hand, its acetyl derivative 8 showed disappearance of the hydroxyl group peak and appearance of the two additional carbonyl peaks (all together four c=o groups at 1755, 1750, 1680 and 1630 cm–1) confirmed its formation (figure 2b). scheme 1 scheme 2 scheme 3 scheme 4 anthraquinone 9 was synthesized by following a general procedure of methylation using chrysophanol (1) as a substrate (scheme 4) [40, 38]. strong signals at 1010 and 955 in the ir spectrum richa k gupta et al. / bibechana 18 (2) (2021) 143-153 148 fig. 2: (a) ir spectrum of chrysophanol diacetate (7); (b) ir spectrum of rubiadin diacetate (8). of compound 9 were due to the two c–o stretches of newly formed methoxy groups. antioxidant capacity recently, we have reported isolation and identification of chrysophanol (1) and emodin (2) from the rhizomes of r. australe [32]. chrysophanol (1) is known as an antioxidant [42]; however, it shows no significant effect on the inhibition of cancer cell proliferation [43]. on the other hand, zhang et al. have reported that it is effective against mcf-7 breast cancer, 7901 gastric cancer, a375 melanoma and skov-3 oophoroma cells [44]. emodin (2) has more effectively inhibited the proliferation of ovarian, breast, lung, liver and prostate cancer cells [45-47]. more recently, we have studied structure-activity relationship study of quercetin derivatives in the dpph• radical scavenging capacity, and reported the substituent(s) effect [27]. since anthraquinones are known for various biological activities including antioxidant and anticancer activities, we were encouraged to synthesize a number of anthraquinones for the screening of their antioxidant potentiality. thus in the present work, we have synthesized anthraquinones 3-9 and together with previously isolated chrysophanol (1) and emodin (2) were used to determine the antioxidant potentiality using the dpph assay [48]. by using the experimental absorbance values obtained in the dpph assay, linear curves of percentage inhibition versus concentration for every anthraquinone were plotted and then ic50 values were computed. the result of dpph assay is depicted in figure 3. as can be seen in the figure, 1,8-dimethoxy-3-methylanthraquinone (9) is the most potent antioxidant (ic50 = 200 μg/ml) among other anthraquinones tested, followed by 2methylanthraquinone (3) (ic50 = 230 μg/ml), rubiadin (6) (ic50 = 259 μg/ml), and 2bromoanthraquinone (5) (ic50 = 383 μg/ml). in this study, anthraquinones 9, 3, 6 and 5 were found more effective in scavenging of dpph• radical than emodin (2) (ic50 = 400 μg/ml), which has displayed anticancer activity in several studies [4547]. rubiadin (6) has shown anticancer activity in the 3( 4,5dimethy lthiazol-2yl )2,5diphenyl richa k gupta et al. / bibechana 18 (2) (2021) 143-153 149 fig. 3: ic50 values of anthraquinones (1-9) in the dpph assay. table 1: antibacterial activity of the anthraquinones 1-9. s. n. pathogenic bacteria used zoi shown by different antharaquinones 1-9 and standard (in mm diameter)a 1 2 3 4 5 6 7 8 9 gentamycin 1 b. subtilis 9 16 11 11 8 12 10 10 8 16 2 s. aureus – 17 12 – – 11 13 – – 24 3 e. faecalis 8 – – – – – 14 – – 20 4 k. pneumoniae – – – 10 – – 9 – – 12 5 p. aeruginosa – – – – – – – – – 25 6 s. typhimurium – – – – – – – – – 18 avalues of the zoi include the diameter of well (6 mm) after 24 hours incubation against different bacterial species in the agar well diffusion assay. (–)-sign indicates no significant zoi was observed. richa k gupta et al. / bibechana 18 (2) (2021) 143-153 150 tetrazolium bromide (mtt) assay against different cancer cells (mcf7 breast cancer, mes-sa human uterine sarcoma, mes-sa/dx5 multidrug-resistant variant human uterine sarcoma, du145 prostate cancer and h460 lung cancer cells) [37]. chrysophanol (1) was found ineffective in scavenging of dpph• radical (ic50 = 1925 μg/ml). unsubstituted anthraquinone (4) was found least effective among the others. antibacterial activity the isolated and synthesized anthraquinones (1-9) were evaluated for the antibacterial activity by using the agar well diffusion assay [49]. the zoi produced by these compounds is tabulated in table 1. all investigated anthraquinones 1-9 have displayed a weak to moderate antibacterial activity against b. subtilis (zoi = 8-16 mm), while all these compounds were found ineffective against p. aeruginosa and s. typhimurium. a weak antibacterial activity of chrysophanol (1) against b. subtilis and s. aureus has already been reported [50-51]. literature search reveals that emodin (2) exhibits noticeable antibacterial activity against methicillin-resistant s. aureus, p. aeruginosa, escherichia coli, s. typhimurium, bacillus cereus and shigella sonnei [52-53]. in the present study, emodin (2) was found efficient antibacterial against b. subtilis (zoi = 16 mm) and s. aureus (zoi = 17 mm) in accordance with the literature, and in contrast, it was found ineffective against p. aeruginosa and s. typhimurium. 2-methylanthraquinone (3) (zoi = 12 mm) and rubiadin (6) (zoi = 11 mm) have displayed noticeable antibacterial activity against s. aureus. the growth of s. aureus (zoi = 13 mm), e. faecalis (zoi = 14 mm) and k. pneumoniae (zoi = 9 mm) was remarkably inhibited by chrysophanol diacetate (7), which clearly indicated that the biological activity of a compound can be significantly enhanced by the structural modification (compare antibacterial activity of parent chrysophanol 1 versus its diacetate derivative 7). unsubstituted anthraquinone (4) exhibited a weak antibacterial activity against k. pneumoniae (zoi = 10 mm). 4. conclusion anthraquinones are the potential drugs used against different diseases. we have synthesized a number of anthraquinones using known protocols, and evaluated their antioxidant and antibacterial activities. dpph• radical scavenging capacity of 1,8-dimethoxy-3-methylanthraquinone (9), 2methylanthraquinone (3), rubiadin (6) and 2bromoanthraquinone (5) were found comparatively more effective than emodin (2), a well-known compound for its anticancer activity. hence these compounds warrant further cancer cell lines studies. in addition, anthraquinones 1-9 have shown a weak to moderate antibacterial activity against b. subtilis, while they were found ineffective against p. aeruginosa and s. typhimurium. interestingly, a significant enhancement in the antibacterial activity was observed in chrysophanol diacetate (7) as compared to its parent compound 1, which is a known compound with a weak antibacterial activity. acknowledgments this work was supported by nepal academy of science and technology (nast). r.k.g. acknowledges nast-university collaborative research program for a ph.d. fellowship. references [1] m. fouillaud, y. caro, m. venkatachalam, i. grondin, l. dufossé, anthraquinones, phenolic compounds in food: characterization and analysis (l. m. l. nollet, j. a. gutiérrez-uribe, eds.), crc press, boca raton, fl (2018) pp. 130– 170. https://hal.univ-reunion.fr/hal-01657104 [2] g. diaz-muñoz, i. l. miranda, s. k. sartori, d. c. de rezende, m. a. n. diaz, anthraquinones: an overview, studies in natural products chemistry, volume 58 (a. rahman, ed.), elsevier science and technology, oxford, uk (2018). https://doi.org/10.1016/b978-0-444-64056-7.00011-8 [3] e. haciosmanoglu, f. ozkok, a. k. onsu, m. https://hal.univ-reunion.fr/hal-01657104 https://doi.org/10.1016/b978-0-444-64056-7.00011-8 richa k gupta et al. / bibechana 18 (2) (2021) 143-153 151 bektas, b. varol, s. pehlivan, synthesis of new anthraquinone derivatives and anticancer effects on breast cancer cell lines, eurasia proceed. sci. technol. eng. math. 4 (2018) 271–276. https://dergipark.org.tr/en/pub/epstem/issue/40805/ 498144 [4] b. r. madje, k. f. shelke, s. b. sapkal, g. k. kakade, m. s. shingare, an efficient one-pot synthesis of anthraquinone derivatives catalyzed by alum in aqueous media, green chem. lett. rev. 3 (2010) 269–273. http://dx.doi.org/10.1080/17518251003776877 [5] j. duval, v. pecher, m. poujol, e. lesellier, research advances for the extraction, analysis and uses of anthraquinones: a review, ind. crop. prod. 94 (2016) 812–833. http://dx.doi.org/10.1016/j.indcrop.2016.09.056 [6] d. s. seigler, plant secondary metabolism, springer science and business media, new york (2012). 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doi:%2010.1111/j.1745-7262.2008.00397.x http://dx.doi.org/10.7314/apjcp.2015.16.9.3887 https://doi.org/10.1016/s0023-6438(95)80008-5 https://doi.org/10.1016/s0023-6438(95)80008-5 https://doi.org/10.29356/jmcs.v50i2.1306 https://www.ajol.info/index.php/ajb/article/view/43147 https://www.ajol.info/index.php/ajb/article/view/43147 doi:%2010.1248/cpb.47.1121 http://dx.doi.org/10.3839/jabc.2013.030 bibechana 18 (1) (2021) 75-82 75 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal modeling and parameter analysis of deflection of a beam puskar r. pokhrel1*, bhabani lamsal2 1department of mathematics, ratna rajya laxmi campus, tribhuvan university, kathmandu, nepal 2sagarmatha engineering college, tribhuvan university, lalitpur, nepal *email: puskar.pokharel@rrlc.tu.edu.np article information: received: june 7, 2020 accepted: june 25, 2020 keywords: deflection compression forces mathematical modeling analytic and numerical solution abstract in this paper, we present the model equation of a beam when it applies compression forces on ends of the beam and carries a load. for the structural point of view, there should be a suitable model to understand the behavior under different conditions of loading of a beam. mathematical modeling is the simulation of a physical structure or physical phenomenon by constructing suitable analytic and numerical solution. we analyze the deflections of the beam by taking different structures of beam. the structures of beam depend on the compression forces on beams with different beams with different weights. we observe the deflection by applying various compression forces at the ends of the beam. the influence of the effect of some parameters appeared in mathematical formulations such as area moment of inertia (i), young’s modulus (e), load (w) and compressive force (p) on deflection variation are investigated in this paper. we analyze the results that how compression forces affect the system. we use finite difference method to solve the model equation numerically. we analyze and compare the numerical result with analytic solution. doi: https://doi.org/10.3126/bibechana.v18i1.29359 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction beams are structural components subjected to transverse gravity or vertical loading. a beam can be straight or curved and with constant crosssection or tapered. there are various types of beam depending upon the nature of the material, length, width, depth, and external forces in different positions. to decode what type of beam to be used in a structure depends upon the loading system and its potential deflection. deflection is the displacement of any point or part of beam from its original position, measured in y-direction [7]. the specific values of deflection for a given load can be found through differential equation [13]. in practice a factor of safety is generally considered and addressed in the model so as to compensate it. the deflection of a beam should be considered to make http://nepjol.info/index.php/bibechana mailto:puskar.pokharel@rrlc.tu.edu.np https://doi.org/10.3126/bibechana.v18i1.29359 https://creativecommons.org/licenses/by-nc/4.0/ puskar r. pokhrel, bhabani lamsal/ bibechana 18 (1) (2021) 75-82 76 decision in real world problems. generally, we have to know the magnitude and the position of the maximum deflection on a beam under various loading systems for a good engineering structure. the reactions and internal stresses of the beam can properly be estimated only with the proper knowledge of the deflection. various research activities on the deflection on a beam are carried out in the past decades. conway [5] observed the effect of load which is centrally located between two supports. schile and sierakowski [12] solved the problem of bending of a thin, simply supported at two points. bulte [3] modelled the deflection of a beam as fourth order ordinary differential equation. this was converted into a system of first order ordinary differential equation. the solutions were obtained numerically applying runge-kutta fourth order method, and were written in terms of elliptical functions whereas chucheepsakul et al. [4] expressed the solution in integral functions, and solved numerically by applying the shooting-optimization method and the finite element method. this is one of the classical approaches to find the deflection, and widely used to large deflection beam bending problem. banerjee et al. [1] proposed the nonlinear shooting and adomian decomposition methods (adm) to find the large deflection of a cantilever beam. tari [14] presented eulerbernoulli boundary value problem, and its deflection solutions in terms of the loading parameters. he et al. [9] included first derivative term in euler-bernoulli equation, and solved the non-linear large deflection of a beam. in such cases, the solutions show nonlinearity in their deformation behaviour. batista [2] used the general solution to derive an approximate formula that provides an explicit relation between the beam load and its midpoint deflection. ghuku and saha [7] solved the nonlinear governing equation numerically using lagrangian approach, and compared the results with experimental work. the study of the modelling of a beam and its parameter analysis plays significant role in the field of mechanical, aerospace and civil engineering. the knowledge of bending moment, shearing forces, rate of deformation and the deflection of a beam are useful in our daily life which we have encountered with structural elements such as the designing of civil engineering structures, machine and automobile frames, and aircraft components. in this paper, the model equation of a beam is presented as considering very small slope in the beam. so, the model equation is presented here by omitting the first derivative term in euler bernoulli equation. further, the deflections of a beam are analyzed for the variation of applied forces at the ends, the different loads and the young’s modulus of the beam. the model equation are numerically solved by applying the finite difference method, and it is outlined that the errors with analytic results. . 2. formulation of model equation let l be a length of a beam oa, be its radius of curvature of the beam at a distance x from origin, taken at the left hand end of the beam, after giving equal compressive force p at the ends o and b as shown in fig.1. if slopes of deflection curve are small, then the slope of elastic curve is also small, i.e., (dy/dx)2 is neglected in the formula [15] figure 1.1: the deflection of a beam with compression forces. at both ends [6]. puskar r. pokhrel, bhabani lamsal/ bibechana 18 (1) (2021) 75-82 77  = ( )1 + y1 2 3/2 y2 , where y1 = (d y / d x) and y2 =(d 2y, d x2), we get the radius of curvature for small deflection as  = 1/ (d 2y / d x2). let m be the bending moment of the section at a distance x from the origin o, i be area the moment of inertia of the beam cross-section and e be the elastic or young’s modulus of the beam material from which the beam is made, then applying the bernoulli euler law [1, 15] as m = (   ) give  =   d 2y d x2, (1) where y, x and m are variables, and e and i are constants. the bending moment m describes the amount of bending and deflection that occurs in a beam under a given loading system [6, 8]. it is defined as the sum of the moments of all forces to the left or right of the section that is under consideration. let p be compressive force applied on both ends o and a as shown in fig.1, the m = w 2 x p y (2) then from (1) and (2), the model equation is   d 2y d x2 = w 2 x p y this is ordinary differential equation which can also be written as (d 2 + n 2) y = n 2 k x, (3) where d 2 = (d 2/dx2), n 2 = p /ei, k = w / 2p. this is non-homogenous differential equation [11,13]. the general solution is y (x) = yc (x) + yp (x), where yc (x) and yp (x) are complementary function and particular integral [11]. let y = e r x be a solution of ( d2 + n 2) y = 0, then e r x ( r 2 + n 2) = 0 since e r x  0, r 2 + n 2 = 0, so that r =  i n, where i = -1 . so, complementary function [6] is yc (x) = c1 cos nx + c2 sin nx, and particular integral [7] is yp (x) = 1 d 2 + n 2       n 2w 2p x = n 2w 2p . 1 n 2       1 + d 2 n 2 -1 x = w 2p       1 d 2 n 2 + … x = w 2p x general solution of (3) is y (x) = yc (x) + yp (x) which gives y (x) = c1 cos nx + c2 sin nx w 2p x (4) applying the boundary conditions, y = 0 when x = 0, and y = 0 when x = l, we get c1 = 0 and c2 = w l 2p sin nl . substituting the values of c1 and c2 in (4) gives y (x) = w l 2p sin nl sin nx w 2p x (5) is analytic solution. 3. results and discussion we take the length of beam l = 10 m. figure 1.2 shows that the maximum deflection is 4.404 mm at 5.45 m the length of beam when it is under the action of equal and opposite compressive forces p = 65 kn at its ends and it carries a load w = 100 kg, young’s modulus e = 100 gpa and the area moment of inertia i = 3 cm2. if the applied forces at the ends are reduced by 5 kn, then the maximum deflection of the beam are reduced at the length of beam l = 5.45 m. puskar r. pokhrel, bhabani lamsal/ bibechana 18 (1) (2021) 75-82 78 figure 1.2: deflection of beam with weight w = 100 kg. the maximum deflection are 3.5842 mm, 2.9635 m, 2.4732 mm when the applied forces at the ends are p = 60 kn, p = 55 kn, p = 50 kn respectively, as shown in fig. 1.2. in the case of same compressive force, young’s modulus, and the area moment of inertia, when the loads of the beam are reduced by 10 kg, then the maximum deflection of the beam is also reduced by 0.4404 mm. when the beam carries loads w = 90 kg, w = 80 kg, w = 70 kg, then the maximum deflection at the length of beam l = 5.45 m are 3.9636 mm, 3.5232 mm, and 3.0828 mm respectively, as shown in fig. 1.3. in the case of same compressive force, load, and the area moment of inertia, when there are different types of material on the beam so that young’s modulus of the beam are increased by 5 gpa, then the maximum deflection of the beam are decreased by 0.4404 mm. when young's modulus e = 105 gpa, e = 110 gpa, e = 115 gpa, then the maximum deflection at length of the beam l = 5.45 m are 3.6838 mm, 3.1446 mm, and 2.7271 mm respectively, as shown in fig. 1.4. the maximum deflection is inversely proportional to the young’s modulus. if the ratio of stress and strain is increasing, then the maximum deflection is decreasing which is physically meaningful. 4. numerical method consider the interval r = {x : 0  x  l}, and it is subdivided into sub-interval with step size x = h where h = (l 0) / ( n + 1). the ends points are the mesh points xi = x i-1 + i h, for i = 1, 2,…n. we choose the step size h in such a way that it facilitates the application of matrix. the second order derivative is approximated [10,11,13] as d2y dx2  y i 1 2y i + y i + 1 h2 . writing w / 2 p = k, n2 = p / e i, then the model equation (3) reduces to y i 1 2y i + y i + 1 h 2 + n 2 y i = n 2 k x i. the finite difference numerical scheme is y i 1 + ( n 2 h 2 2) y i + y i + 1 = n 2k h2x i, for i = 1, 2, …,n. puskar r. pokhrel, bhabani lamsal/ bibechana 18 (1) (2021) 75-82 79 for i = 1 and applying the boundary conditions y(0) = 0 and y (l) = 0, we get y0 + ( n2 h 2 2 ) y1 + y2 = n 2 k h 2 x 1,  ( n2 h 2 2 ) y1 + y2 = n 2 k h 2 x1. for i = 2, y1 + ( n2 h 2 2 ) y2 + y3 = n 2 k h 2 x 2. for i = 3, y2 + ( n2 h 2 2 ) y3 + y4 = n 2 k h 2 x 3. for i = n, y n 1 + (n2 h 2 2 )y n + y n + 1 = n 2 k h 2 x n,  y n -1 + (n2 h 2 2)y n = n 2 k h 2x n y n + 1 = n 2 k h 2x n. the system so formed, can be written in matrix form as puskar r. pokhrel, bhabani lamsal/ bibechana 18 (1) (2021) 75-82 80         n2 h 2 2 1 0 … 0 1 n2 h 2 2 1 … ⋮ 0 1 ⋱ ⋱ 0 ⋮ ⋱ ⋱ ⋱ 1 0 … 0 1 n2 h 2 2          y1 y2 y3 ⋮ ⋮ yn 1 yn =         n 2 k h 2x 1 n 2 k h 2x 2 n 2 k h 2x 3 ⋮ ⋮ n 2 k h 2x n 1 n 2 k h 2x n table 1.1: distribution of deflection of the beam with compression force p = 65 kn and load w = 100 kg. this system is solved here by using a computing program. 5. numerical results figure 1.5 shows that numerical and analytical solution of the model equation. a beam of length l = 10 m, it carries a load w = 100 kg, young’s modulus e = 100 gpa, the area moment of inertia, i = 3 cm2 and compressive force at the ends of the beam p = 65 kn. the maximum deflection of the beam lies at x = 5.8333 m and decreases towards the extremes as shown in fig.1.5. the maximum deflection substantially increases from 3 mm to 4.5377 mm. the distribution of errors of the deflection of the beam obtained from numerical and analytic method is shown in table 1.1. the maximum error is 0.1651 and length: l [m] defl.: y [mm] numerical defl.: y [mm] analytical error () 0 0 0 0 0.8333 1.0519 1.0279 0.024 1.6667 2.0562 2.0017 0.0545 2.5000 2.9562 2.8686 2.8685 0.0876 3.3333 3.6985 3.5797 0.1188 4.1667 4.2353 4.0912 0.1441 5.0000 4.5257 4.3654 0.1603 5.8333 4.5377 4.3726 0.1651 6.6667 4.2485 4.0917 0.1568 7.5000 3.6461 3.5112 0.1349 8.3333 2.7291 2.6289 0.1002 9.1667 1.5070 1.4526 0.0544 10.000 0 0 0 puskar r. pokhrel, bhabani lamsal/ bibechana 18 (1) (2021) 75-82 81 the beam is highly deflected at the length of beam x = 5.8333 m. we see that the load of the beam plays more significant role than the horizontal for the deflection of the beam. the error in numerical solution of the deflection at the length of beam 3.3333m to 8.333m is more than from analytic solution. 6. conclusion we presented the model equation of a beam with external forces at the ends when it carries load, the area moment of inertia with material properties. we found that the variation of maximum deflection by applying the different external forces. the analytic and numerical solution of the deflection of the beam showed that the deflection depend on external forces as well as when it carries loads, the area moment of inertia and the structures. we analyzed the deflection of the beam for different horizontal compression forces from the extremities. the maximum deflection of the beam occurs at the centre of the beam and gradually decreases to zero at the extremities. the weight of the beam has major role for the deflection of the beam. we also analyzed the maximum deflection of the beam with different young’s modulus. we observed that error analysis of the solution of model equation, and we found that there was less error in the deflection of the beam between analytic and numerical results. the results can be used to estimate the failure of a beam. references [1] a. banerjee, b. bhattacharya, a.k. mallik, large deflection of cantilever beams with geometric non-linearity: analytical and numerical approaches, int. j. non-linear mech. 43 (5) (2008)366-376. https://doi.org/10.1016/j.ijnonlinmec.2007.12.020 [2] m. batista, large deflections of a beam subject to three-point bending, int. j. non-linear mech. 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[11] p. r. pokhrel, numerical methods for engineering, vidharthi pustak bhandar, kathmandu, nepal, 2018. [12] r.d. schile and r.l. sierakowski, large deflections of a beam loaded and supported at two points, int. j. non-linear mech. 2 (1967) 61-68. https://doi.org/10.1016/0020-7462(67)90019-4 [13] s.l.r.j. schilling, applied numerical methods for engineering, cenegage learning india pvt. ltd., delhi, india, 2011 [14] h. tari, on the parametric large deflection study of euler-bernoulli cantilever beams subjected to combined tip point loading, int. j. non-linear mech.49(2013)90-99. https://doi.org/10.1016/j.ijnonlinmec.2012.09.004 [15] c.m. wang, k.y. lam, x.q. he and s. chucheepsakul, large deflections of an end supported beam subjected to a point load, int. j. non-linear mech. 32(1) (1997) 63-72. https://doi.org/10.1016/s0020-7462(96)00017-0 https://doi.org/10.1038/srep46190 https://doi.org/10.1016/j.jestch.2018.04.007 https://doi.org/10.1016/j.hbrcj.2013.11.003 https://doi.org/10.1016/j.amc.2013.01.037 https://doi.org/10.1016/0020-7462(67)90019-4 https://doi.org/10.1016/j.ijnonlinmec.2012.09.004 https://doi.org/10.1016/s0020-7462(96)00017-0 bibechana 19(1-2) (2022) 160-164 160 optimization of momentum of muon beam and thickness of cell-window for muon experiment in bio-sample: a simulation study amba datt pant institute of materials structure science, high energy accelerator research organization (kek), 1-1 oho, tsukuba, ibaraki 305-0801, japan email: pant@post.kek.jp article information: received: july 05, 2021 accepted: december 31, 2021 keywords: muon muonium kapton cancer bio-samples muon spin rotation relaxation abstract in order to study the bio-samples (aqueous solutions) using muon spin rotation and relaxation (sr) method, the optimization of momentum of incident muon beam and selection of material for window of sample cell towards muon side are the initial steps for the sr measurement. rather than several experimental trials, we used to perform simulation study to optimize the momentum of muon beam and thickness of window of the sample cell. monte carlo simulation for optimization of momentum of monoenergetic surface muon beam in different material/thickness of window of the sample cell indicates that the al or kapton window of thickness less than 0.3 mm is suitable to maximize the intensity of the stopped muons (momentum between 25.8 mev/c to 29.8 mev/c) within 1 mm of water (bio-samples). this simulation will help to design the sample cell for the study of application of muon in life science. doi: https://doi.org/10.3126/bibechana.v19i1-2.46413 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal https://doi.org/10.3126/bibechana.v19i1-2.46413 https://creativecommons.org/licenses/by-nc/4.0/ amba datt pant / bibechana 19(1-2) (2022) 160-164 161 1. introduction muon spin rotation and relaxation (sr) method is being popular for study of life and materials. in this method, decay positron from the muon can be detected by spectrometer around the sample and the information about the desired properties of the material can be extracted from the time evolution of muon spectra [1]. since muon is like a light proton, and its bound state with an electron is like a light isotope of hydrogen atom, this method can be used to understand the local electronic and dynamics states of the materials. not limited to materials and life science [2-4], the muon can be used for discovery of new physics beyond standard model, nuclear physics, advancement of technology, etc [5]. in order to apply the muon to understand the properties of materials, it should be stopped in the sample material and the background should be minimized. selection of proper momentum of muon beam and optimization thickness of window of sample cell (especially for biosamples) are preliminary and the most important steps in this method. for the experiments to be performed in high vacuum and samples in which different muon charge states will be expected, especial care should be taken to select/use the material for sample cell. muon is an elementary particle which is like a light proton (m ~ 1/9 mp;  = 3.18 p) and sensitive to magnetic field. for sr experiment, high intensity muons can be generated in accelerator facilities however it is also possible to perform sr studies using cosmic muons. because of fully polarized and asymmetric decay to positron, it is used as promising tool to study the local electronic and dynamic states of materials in which it stops. moreover, its unique and wide time window (~ ps to few s) provides more advantages over other resonance techniques (nmr, esr, mössbauer, etc.) [1, 6]. when muon incident in sample, based on nature/properties of samples, muon can be found as diamagnetic muon, muonium or other states in the sample. after its average life 2.2 s, it decays to positron along the direction of muon spin at the time of decay. such positrons are collected by the detectors installed around the sample. the time evolution of polarization provides the information about the materials. so the sr method has been used in wide varieties of samples without any external perturbations [1]. in our previous study of application of muon for cancer study, we have used decay muon of momentum of 60 mev/c at riken/ral, uk [7-9]. for such beam, bio-samples of around a liter volume were used. as a next step, we plan to perform experiment in small and real biosamples rather than dilute aqueous solutions. for such purpose, the low momentum muon (surface muon of momentum ~ 29 mev/c) will be used at j-parc, japan. before such experiments, it is necessary to optimize the thickness of windows of sample cell and momentum of muon beam so that muon can stopped in the targeted region of sample. in this work, the monte carlo simulation study to optimize the momentum of muon beam and thickness of sample cell-window to maximize the stopped muon in the targeted sample is presented. 2. methodology based on materials and thickness of sample cell-window (fig. 1), the incident monoenergetic surface muon beam stops in window materials and/or sample. to optimize/estimate the thickness of the sample cell-window and momentum of muon beam, the stopping and range of ions in matter (srim-2013) monte carlo simulations code [10, 11] were used. the momentum and energy of surface muon beam are 29.79 mev/c and 4.119 mev, respectively [12]. based on transportation of beam in beamlines, the real momentum will be less than the 29.79 mev/c. fig. 1. schematic diagram of incident of muon beam in biosample. amba datt pant / bibechana 19(1-2) (2022) 160-164 162 so, the simulations were performed at different momentum and materials. among them three momentum data in two materials – aluminum (al) and kapton have been discussed here. in simulation, water is used instead of bio-sample because the aqueous bio-sample or real biosample some extent of water exists. the density of water is less than that of bio-sample so the stopping information in water is fine for bio-samples. the al of density 2.7 g/cc and kapton of density 1.42 g/cc were used in simulation. the kapton is polyimide which is used for different purposes – electric and thermal insulation, windows for high vacuum, protection layer, etc. the intensity of incident muon was taken over at least 104 events. 3. results and discussion the simulation of muon stopping in both al and kapton sheets of different thicknesses have been performed at three different momentum of monoenergetic surface muon beam. figure 2 shows the stopping range of muon in water. even the muon beam of momentum 25.79 mev/c can pass the 0.1 mm (fig. 2(a)) and 0.3 mm (fig. 2 (b)) of al cellwindow. however, in the case of 0.4 mm thickness (fig. 2 (c)), a small fraction (< 1% of incident muon) of 25.79 mev/c muon stopped in the window. furthermore, in the case of 0.5 mm thickness (fig. 2 (d)), all the 25.79 mev/c muon stopped in the window. the muon of momentum 25.79 mev/c, 27.79 mev/c and 29.79 mev/c passes through the kapton windows and stopped in water are presented in fig. 3. in the case of kapton thickness 0.05 mm (fig. 3(a)) and 0.4 mm (fig. (b)), all muons stopped in water within 2 mm depth. when the thickness of kapton is increases to 0.6 mm, only small fraction (< 1% of incident muon) of muon of 25.79 mev/c stopped in the kapton window. in the case of thickness 0.8 mm (fig. 3(c)), the 25.79 mev/c muon stopped in the kapton however other higher momentum muon passed the window and stopped in the water. with regard to monoenergetic muon beam, fig. 2. stopping range of muon beam of different momentum passed through the al window in water (a) al windows thickness, t = 0.1 mm, (b) t = 0.3 mm, (c) t = 0.4 mm and (d) t = 0.5 mm. the light blue color for water and light silver color for al are used. the line colors blue, black and red are used for momentum of muon beam 25.79 mev/c, 27.79 mev/c and 29.79 mev/c, respectively. amba datt pant / bibechana 19(1-2) (2022) 160-164 163 the stopping range difference for particular thickness is smaller (full width at half maximum is smaller) however in real beamline there is certain distribution of muon energy. in such cases low energy muon may stop in the window materials. for this reason, the selection of cell-window is quite important. if the muon stopped in window material, there is possibility of background or noise signal from the charge states of muon stopped in the windows materials. for example, muon stopped in kapton (unsaturated organic material) may form radical or muonium state however in al there will be muon in diamagnetic state. for the selection of windows material, we also need to consider about the visualization of sample for example during experiments using light/laser or if we use other visual spectroscopic detectors during sr experiment. for such purpose, the window of kapton or glass will be better than al. in addition, the chemical reaction of bio-sample with those window material should also be considered. for real bio-sample, the density will be different than the water used in this study. so, the density of particular sample also should be taken into account before selection of the cell window. conclusion the stopping range of surface muon in different thickness of al and kapton window of sample cell for sr experiment in biosample cell have been studied using monte carlo simulation. optimization of thickness of the window and momentum of muon beam shows that the thickness of al or kapton window within 0.3 mm will suitable to pass the muon beam of momentum between 25.79 mev/c and 29.79 mev/c. the thickness of windows suggested by this study will be used in the experiments to be performed in future sr experiments in aqueous biological samples. acknowledgment this work was supported by grant-in-aid for scientific research of the ministry of fig. 3. stopping range of muon beam of different momentum passed through the kapton window in water (a) kapton windows thickness, t = 0.05 mm, (b) t = 0.4 mm, (c) t = 0.6 mm and (d) t = 0.8 mm. the light blue color for water and light pink for kapton are used. the line colors blue, black and red are used for momentum of muon beam 25.79 mev/c, 27.79 mev/c and 29.79 mev/c, respectively. amba datt pant / bibechana 19(1-2) (2022) 160-164 164 education, culture, sports, science and technology (mext), japan, (grant number: 21k15583, “applications of muon in cancer research”). references [1] k. nagamine, introductory muon science, cambridge university press, cambridge, uk, 2007. 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[12] k. assamagan et al., measurement of the muon momentum in pion decay at rest using a surface muon beam, physics letters b 335(2) (1994) 231-236. https://doi.org/10.1016/03702693(94)91419-2 https://doi.org/10.1016/s0921-4526(00)00298-2 https://doi.org/10.1016/s0921-4526(00)00298-2 https://musr.ca/intro/musr/musrbrochure.pdf https://musr.ca/intro/musr/musrbrochure.pdf https://doi.org/10.1016/j.nima.2021.165561 http://www.srim.org/ https://doi.org/10.1016/0370-2693(94)91419-2 https://doi.org/10.1016/0370-2693(94)91419-2 bibechana vol. 20, no. 2, august 2023, 183–189 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar structural analysis and material selection for biocompatible cantilever beam in soft robotic nanomanipulator md. shazib uddin1, md. imran khan2, sadman bin shafiq3 shahriar sadik2, md. sohel rana1,∗, khaled mohammad shifullah bhuiya1 sabbir ahmed udoy1, md. khalid hasan rafi3 1department of mechanical engineering, rajshahi university of engineering & technology, bangladesh 2college of information engineering, yangzhou university, china 3school of mechatronics, mechanical engineering, china university of mining and technology, china ∗corresponding author. email: sohel1702110@gmail.com abstract this paper investigates the selection of appropriate materials for cantilever beams in surgical robotic nanomanipulators. cantilever beams play a crucial role in soft robotic surgery. biocompatible materials, which have minimal adverse effects on biological systems, are commonly used for these beams. using solidworks software simulation, the study assesses the flexibility of cantilever beams made from different biocompatible materials. the analysis involves varying the applied force (0.001 µn to 0.004 µn), beam length (80 µm, 120 µm, and 160 µm), and beam thickness (0.4 µm, 0.6 µm, and 0.8 µm). four materials—alumina, polyether-ether-ketone (peek), polyurethane (pur), and ti-6al-4v—are evaluated. simulation results highlight polyurethane (pur) as a suitable material for cantilever beams in nanomanipulators due to its favorable properties. these findings provide valuable insights for the design and advancement of efficient and reliable robotic nanomanipulators, advancing the field of soft robotic surgery. keywords cantilever beams, surgical robotic nano-manipulators, biocompatible materials, soft robotic surgery, simulation analysis. article information manuscript received: may 19, 2023; accepted: june 20, 2023 doi https://doi.org/10.3126/bibechana.v20i2.55037 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 183 http://nepjol.info/index.php/bibechana sohel1702110@gmail.com https://doi.org/10.3126/bibechana.v20i2.55037 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ md. s. uddin et al./ bibechana 20 (2023) 183-189 184 1 introduction the term "mechatronics" refers to the coordinated use of physical systems, information technology (it), and sophisticated decision-making throughout the design, production, and use of industrial goods and processes [1]. in the mechatronic field, the robot is a crucial term. the robotic institute of america defines a robot as "a reprogrammable, multifunctional manipulator designed to move materials, parts, tools, or specialized devices through various programmed motions for the performance of a variety of tasks," which is the definition that is currently most frequently used [2]. today, robotic nano-manipulators are used in surgery applications. nanomanipulator is a device created to control items at the nanoscale or a microscope attached to a virtual reality (vr) interface that enables the user to virtually teleport to the sample surface. due to the numerous biological and material science applications of nanomanipulator, it has recently attracted a lot of interest. nanomanipulator is demonstrated by the definition of material qualities, creation of electronic chipsets, testing of microelectronic circuits, teleoperation of operations, micro-injection, and manipulation of chromosomes and genes [3]. nanomanipulator involves a variety of scenarios, but the most common ones are those that use scanning tunneling microscopy (stm), atomic force microscopy (afm), and nanorobotic manipulator (nrm) [4]. the cantilever beam is one of the important parts of a robotic nanomanipulator in the field of soft robotic surgery applications. minimally invasive surgery (mis), particularly for abdominal procedures, has established itself as the industry standard [5]. a cantilever beam can be utilized as a part of the tool or instrument to manipulate tissues or carry out treatments at the microscopic level. typically compatible materials are used in soft robotic cantilever beams because of their flexibility. biocompatible materials are those that can interact with biological systems without harming them or producing unfavorable effects. these materials are employed in a variety of medical and healthcare applications. in neurosurgery, minimally invasive techniques are employed for the biopsy operation (fig. 1) which required precisely placing a device into a brain lesion. to access the tumor, the physician drills a hole in the skull and inserts a biopsy probe where a cantilever beam is used [6]. in gynaecologic surgery, each zeus system contains two physically separate subsystems known as "surgeon-side" and "patient-side" shown in (fig. 2). the surgeon-side console consists of two handles for operating the robotic arms and a display for documenting the surgical operation. the surgeon console controls three robotic arms that are mounted above the operating table as a component of the patient-side subsystem. the biocompatible material is used as a cantilever beam in these robotic arms [7]. in minimally invasive surgery, by replacing and increasing human skills, minimally invasive surgery (mis) can increase patient safety and the effectiveness of medical interventions [8]. the development of surgical instrumentation that can access the surgical target through numerous small entrances (fig. 3) which employed the cantilever beam. the aforementioned applications show that the cantilever beam is widely used in medical applications. these cantilever beams are composed of biocompatible materials. there is a limited number of studies that focused on single biocompatible material as a cantilever beam independently. but the response of the cantilever beam depends on the type of material, the width, length, and applied force. hence, optimization of the material and the effect of the influential parameters is important and such studies seem not to exist in the available literature. the objective of this study is to optimize the biocompatible materials and to investigate the effect of influential parameters on the response of the biocompatible materials in cantilever beam under specific conditions using the solidworks simulation software. 2 methodology this section describes the selection of the material, assumption and boundary condition, and simulation setup for the cantilever beam. 2.1 selection of the materials the author has selected four types of biocompatible materials like alumina, pur (polyurethane), peek (poly-ether-ether-ketone), and ti-6al-4v (titanium alloys). the basis of selection is discussed as follows. alumina-based bio-ceramic materials are considered one of the best materials to use in biomedical engineering because of their excellent biomechanical and biocompatibility properties [9]. the three main subcategories of bioceramics are bioinert, bioactive, and bioresorbable ceramics [10]. alumina and zirconia, two bio-inert ceramics with high mechanical and chemical stability, exhibit a "contact osteogenesis" pattern when in touch with bone tissue [11–14]. pur is a versatile elastomer that exhibits exceptional flexibility and resilience. it has superior impact resistance, low friction, and vibration damping qualities. these qualities make it ideally suited for soft robotic applications. peek is a high-performance thermoplastic that is renowned for its superior mechanical attributes, such as high strength, stiffness, and chemical resistance. it is used in soft biomedical engineermd. s. uddin et al./ bibechana 20 (2023) 183-189 185 ing applications due to its advantageous mechanical properties [15] for soft robotic applications. ti6al-4v is the alloying system titanium-aluminum vanadium type vt-6 (6al-4v, grade5, sat-64, ta6v, ti-al-v) with an average aluminum content of 6% and vanadium 4% are the most widely used titanium alloys in additive industries [16] and soft robotic applications. the mechanical properties of the materials are listed in table 1. 2.2 boundary condition and assumption the fixed end of the cantilever beam is fastened to hard support, which prevents motion in all directions. the force is applied to the cantilever beam’s free end. the cantilever beam is unrestricted in its ability to bend and move in transitional directions means movements can include bending and deflection, other than axially. the forces were varied from 0.001 µn to 0.004 µn. then the thickness and length were set up at three different values for each material: 80 µm, 120 µm, and 160 µm for length, and 0.4 µm, 0.6 µm, and 0.8 µm for thickness. however, the value of the width is kept fixed. it has been assumed that the materials will react linearly and elastically. the cantilever beam is said to be made of homogeneous materials, each of whose characteristics is thought to remain constant throughout. the cantilever beams will only experience modest deflections, keeping the beam within its elastic range. 2.3 simulation setup at first, the static structural analysis has been chosen. then 3d geometry of the cantilever beam has been developed using the sketching module employing the dimensions. after that, the material selection and settings of the material attributes have been fixed from the software database using the drop-down menu. the assumption and boundary condition has been set using the simulation module. the load, length, and thickness of the cantilever beam have been selected as the variable parameters during the simulation. the mesh is generated for the computational domain to discretize the geometry of the cantilever beam. optimization of the mesh generation has been done using the trial and error method. the finite element analysis (fea) was utilized to simulate the structural response of the beam under various loading scenarios. table 1: properties of different bio-compatible materials. properties alumina pur peek ti-6al-4v elastic modulus(n/m2) 3.7×1011 2.41×109 3.9×109 1.02×1011 poisson’s ratio 0.22 0.3897 0.4 0.31 mass density(kg/m3) 3960 1260 1310 4428.784 tensile strength(n/m2) 3×108 4×107 9.5×107 1.01×109 thermal expansion coefficient( / k ) 7.4×10−6 4×10−5 3.6×10−3 9×10−6 thermal conductivity(w/m. k) 30 0.2681 0.24 6.9 specific heat(j/ kg. k) 850 1900 1850 586.04 sources: solidworks software 3 results and discussion this section describes the simulation results of the four types of materials obtained at different influential parameters. 3.1 optimization of the materials figure 4 shows the effect of applied force on the deflection of the materials. overall, from this graph, we can easily figure out the deflection of cantilever beams made of different materials. the applied force ranged from 0.001µn to 0.004 µn. it is evident from the graph that deflection increases with increasing force. polyurethane (pur) exhibits the maximum deflection, while alumina represents the minimum deflection. peek and ti-6al-4v show a moderate level of deflection. thus, polyurethane (pur) demonstrates the greatest degree of flexibility compared to the other three materials (alumina, peek, and ti-6al-4v). as displacement is a measure of material flexibility, it can be concluded that polyurethane is the best material among the four. md. s. uddin et al./ bibechana 20 (2023) 183-189 186 figure 1: application of surgical robot with cantilever beam biopsy [2]. figure 2: (a) zeus surgical telemanipulator system. (b) robotic instrument arms and aesop endoscope arm (not sterile-draped) at the operating table [ [17]]. figure 3: envisaged surgical scenario with a manipulator [18]. figure 4: (effect of applied force on the deflection of the material [l=80 µm, width=10 µm, thick=0.6 µm]. 3.2 effect of applied force on pur deflection figures 5, 6, and 7 show the displacement of a cantilever beam made of polyurethane material with three types of loads. the values of length, width, and thickness are kept fixed, while only the forces vary. it is observed that the beam deflection increases with increasing load. 3.3 effect of beam length on pur deflection simulation results in figures 8, 9, and 10 indicate that displacement/deflection increases with increasing beam length at the micrometer scale. the values of force, width, and thickness are kept fixed. 3.4 effect of beam thickness on pur deflection figures 11, 12, and 13 depict the simulation of the cantilever beam with variable thickness. these figures show that the displacement of the beam decreases with increasing thickness. the values of force, length, and width are kept fixed. 3.5 simulation results in terms of magnitude figure 14 illustrates how the deflection of the beam changes with the applied force corresponding to the length. it is observed from the graph that as the force increases, the cantilever beam shows maximum deflection for the maximum length at 160µm, whereas for the minimum length at a length of 80µm, the cantilever beam shows the minimum deflection. moreover, figure 15 is a line graph that illustrates how the beam deflection decreases with increasing width. in this figure, it can be observed that for the maximum thickness of 0.8µm, the minimum deflection of the beam is observed, while for the minimum thickness of 0.4µm, the maximum deflection is found. these two graphs indicate that polyurethane beams with maximum possible lengths and minimum thickness exhibit greater deflection, indicating a higher level of flexibility that is expected for the surgical soft robotic application of a nanomanipulator. md. s. uddin et al./ bibechana 20 (2023) 183-189 187 figure 5: graphical result of the cantilever beam made of polyurethane (pur); l= 80 µm, width= 10 µm, thickness = 0.6 µm [f=0.001µn]. figure 6: graphical result of the cantilever beam made of polyurethane (pur); l= 80 µm, width= 10 µm, thickness = 0.6 µm [f=0.003µn]. figure 7: graphical result of the cantilever beam made of polyurethane (pur); l= 80 µm, width= 10 µm, thickness = 0.6 µm [f=0.004µn]. figure 8: graphical result of the cantilever beam made of pur at f=0.001µn, width=10 µm, thickness=0.6 µm [l=80 µm]. figure 9: graphical result of the cantilever beam made of pur at f=0.001µn, width=10 µm, thickness=0.6 µm [l=120 µm]. figure 10: graphical result of the cantilever beam made of pur at f=0.001µn, width=10 µm, thickness=0.6 µm [l=160 µm]. md. s. uddin et al./ bibechana 20 (2023) 183-189 188 figure 11: graphical result of the cantilever beam made of pur at f=0.001µn, l=80 µm, width=10 µm [thickness=0.4µm]. figure 12: graphical result of the cantilever beam made of pur at f=0.001µn, l=80 µm, width=10µm [thickness=0.6µm]. figure 13: graphical result of the cantilever beam made of pur at f=0.001µn, l=80 µm, width=10 µm [thickness=0.8µm]. figure 14: pur deflection as a function of applied force corresponding to the length. figure 15: pur deflection as a function of applied force corresponding to the thickness. 4 conclusion polyurethane cantilever beams show great potential as a nanomanipulator in the fields of robotics and biology because it shows highest flexibility. polyurethane is a flexible material with respect to biocompatibility and resilience to wear and tear. the polyurethane manipulator can provide the necessary dexterity and flexibility while working with biological systems at the molecular and cellular level. it could function more subtly inside the human body. a surgeon may work more precisely with less tissue injury using a nanomanipulator utilizing its high level of precision control. polyurethane lessens the likelihood of an adverse response when used with human body parts. as md. s. uddin et al./ bibechana 20 (2023) 183-189 189 a biocompatible material complies with scientific standards, polyurethane can be utilized in surgical procedures involving delicate human body parts. references [1] m. tomizuka. mechatronics: from the 20th to 21st century. control engineering practice, 10(9):877–886, 2002. 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[18] t. ranzani and et al. a soft modular manipulator for minimally invasive surgery: design and characterization of a single module. ieee transactions on robotics, 32(1):187–200, 2016. introduction methodology selection of the materials boundary condition and assumption simulation setup results and discussion optimization of the materials effect of applied force on pur deflection effect of beam length on pur deflection effect of beam thickness on pur deflection simulation results in terms of magnitude conclusion bibechana 18 (2) (2021) 1-8 1 investigation of some basic thermodynamic properties of nak alloy rajesh c. malan1, *, aditya m. vora2 1applied science and humanities department, government engineering college, valsad -396001, gujarat, india 2department of physics, university school of sciences, gujarat university, ahmedabad-380009, gujarat, india *e-mail: rcmgecv@gmail.com article information: received: september 30, 2020 accepted: november 30, 2020 keywords: binary liquid alloy pseudopotential thermodynamic properties abstract investigation of thermodynamic of liquid 𝑁𝑎1−𝑋𝐾𝑋 binary alloys using pseudopotential theory is reported. the potential suggested by fiolhais et al. with its individual parameters is used for entire calculation. a transferability of the potential from the solid to liquid medium is achieved for the presently reported binary alloy. the internal energy components, helmholtz free energy, entropy and total energy at various proportions of the participating alkali metals are included in the study. the comparison with the other data has been shown in the present article. exchange and correlation effect is also tested with the help of various local field correction functions. doi: https://doi.org/10.3126/bibechana.v18i2.31628 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction novelty in materials is key demand of industrial development. the successful synthesis of any material may be useful for the formation of fabrication of parts of various machineries and devices. the choice of the material has direct influence on overall performance of the device. the choice of the material must be on the base of some scientifically obtained physical and chemical properties. as per the present demand of requirement, variety of properties cannot be avail by the conventional metallic materials. the compounds and alloys are the better replacement of the pure metallic material to have combined properties in a single material. focusing on alloys, the preliminary stage of the formation also requires the exact knowledge of thermodynamical properties of the alloy. the variation of property with respect to a variation of the proportion of each metal used for the formation of alloy is to be obtained to know the required proportion for desired property. lots of work has been carried out for the thermodynamical properties of the many solid materials [1-3]. but on the other hand, the liquid materials are studied theoretically from the thermodynamical point of bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:rcmgecv@gmail.com https://doi.org/10.3126/bibechana.v18i2.31628 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana rajesh c. malan and aditya m. vora / bibechana 18 (2) (2021) 1-8 2 view very rarely [4-5]. the liquid alkali metals are widely used in the area of nuclear reactors. as having very fast chemically reactive nature even at room temperature, the study of the thermodynamical properties is of great significance. binary alloy of alkali metal is able to provide the mix properties of each of the metals of formed alloy. in the present article the focus is made on the one of the binary alkali alloys i.e., 𝑁𝑎1−𝑋𝐾𝑋 in liquid state. 2. computational methodology the well-established theory of the pseudopotential is applied for the present calculation. the potential suggested by the fiolhais et al. [6] is chosen for as the model potentials. the accuracy obtained in previous calculations [9-14] by this potential for various properties is the main reason of the selection of the potential. as the structure factor and the entropy both can easily be characterized by considering the hard sphere system, the well-known percus-yevick hard sphere reference system [10] is used. the value of the hamiltonian of the actual system can be estimated through the perturbation theory. according to the inequality of gibbs and bogoliubov [11, 12], the actual hamiltonian of the reference system is always greater than or equal to the hamiltonian of the reference system plus the perturbation part. the variational approach along with the gibbs-bogoliubov inequality has already been used to approximate the study of thermodynamical study of the metals. the present work extends the computation to the system of binary alkali alloy 𝑁𝑎1−𝑋𝐾𝑋. the electronic free energy of the binary alloys with atoms positions {𝑅1} and {𝑅2} can be written as [13, 14], fele{r1, r2} = feg + f1f2{r1, r2} (1) here, f1 and f2 are the first and second order perturbation energy terms, respectively and feg is the free energy of the electron gas that can be expressed as, feg = [ 3 10 kf 2 − 3 4π kf + ec − 1 2 γegt2] z̅. (2) to calculate the helmhöltz free energy (fh) of the alloy, the effective potential energy of the ions can be obtained by introducing the direct coulomb interaction between the ions. the expectation value of this effective potential can be given by, fps = feg + f1 + f2{r1, r2} + fm. (3) the madelung contribution (fm) shown in the above equation (3) can be given as, fm = 1 π ∫[c1 2z1 2(s11 − 1) ∞ 0 + 2c1c2(s12 − 1) + c2 2z2 2(s22 − 1)]dq. (4) the sij (i = j; 1,2) is the partial structure factors computed from the well-known relations given by as used by faber [11]. the first order perturbation term (f1) is obtained from averaged valence density (z̅̅̅) and the zeroth fourier component (α1) of pseudopotential from the following equations (5) and (6), respectively, f1 = (c1α1 + c2α2)z̅n. (5) αi = lim q→0 (wb(q) + 4ziπe2 q2 ). (6) the band structure energy or second order energy term (f2) is obtained from, f2 = 1 16π3 ∫ { c1c2(wb1 − wb1 ) 2 + c1 2wb1 2s11 +2c1c2wb1 wb2 s12+c2 2 wb2 2s22 } ∞ 0 { 1 ε(q) − 1} dq − z̅ 2 γ2(t)t2 . (7) here, wi is the screened form factor. ε(q) is the dielectric screening function. γ2(t) is the second order correction to the usual γ factor describing the low temperature electronic specific heat and is given by, γ2(t) = 2 3π2z̅ ∫ x2 x2−1 ∞ 0 f(x) { c1c2(w1 − w2)2 + c1 2w1 2s11 +2c1c2w1w2s12+c2 2w2 2s22 } (8) in which, wi is the screened form factor. while, the function f(x) is be defined as, rajesh c. malan and aditya m. vora / bibechana 18 (2) (2021) 1-8 3 f(x) = ( x2 − 1 4x ln | 1 + x 1 − x |) + 1 2 . (9) the free energy per particle (fmix) can be expressed as, fmix = c1μ1 + c2μ2 − phs n . (10) the chemical potential is obtained by following equation, μi kbt = ln [ni 2πħ2 mikbt ] 3 2 − ln(l − η) +ln [ 3xσi l − η ] + 3 2 [ 3x2 (1 − η)2 + 2y 1 − η ] σi 2 + [ πphsσi 3 6kbt ]. (11) and phs kbt = n(1 + η + η2) − 1 2 πn1n2(σ1 − σ2)2(σ1 + σ2 + σ1σ1x) (1 − η)3 (12) where, 𝑋 = 1 6 π(n1σ1 2 + n2σ2 2) (13) and y = 1 6 π(n1σ1 + n2σ2). (14) the internal energy (fint) can be given as, fint = 3 2 kbt + feg + f1 + f2{r1, r2} + fm. (15) using equations (10)-(15), fmix = 3 2 kbt − tsmix, (16) where, smix is the total entropy for alloy system and can be divided into following four parts, smix = sgas + sc + sη + sσ. (17) where, sc is the ideal entropy of mixing, sgas represents the gas term, sη corresponds to packing density η and sσ arises due to the difference in diameters of the hard sphere of participating elements of the alloy, respectively. the various contributions of the entropy can be given as, sc kb = −(c1lnc1 + c2lnc2), (18) sη kb = ln(l − η) + 3 2 [l − l (l − η)2], (19) sσ kb = = πc1c2n(σ1 − σ2)2⌊12(σ1 + σ2) − πn(c1σ1 4 + c2σ2 4)2⌋ 24(1 − η)2 (20) and sgas kb = ln [ e n ( emkbt 2πħ2 ) 3 2 ], (21) from all above required contributions, the helmhöltz free energy (fh) can be obtained as, fh = fps + fmix. (22) to estimate the screening effect over the bare-ion potential the hartree local field correction function (h) is used [15]. the other local field correction functions used over the bare-ion potential are the functions suggested by hubbard-sham (hs) [16, 17], vashishtha-shingwi (vs) [18], taylor (t) [19], sarkar et al. (s) [20], ichimaru-utsumi (iu) [21] and farid et al. (f) [22] and nagy (n) [23]. 3. results and discussion the individual parameters of the potential of fiolhais et al. [6] and the constants are used as given in the table 1. the potential parameters are directly adopted from the original work of the fiolhais et al. [6]. table 2 shows the various parts (𝐹𝑒𝑔, 𝐹1, 𝐹𝑀 and 𝐹𝑚𝑖𝑥) that contributes to the internal energy (𝐹𝑖𝑛𝑡) of the alloy. rather than calculating only internal energy (𝐹𝑖𝑛𝑡) and the helmhotz free energy (𝐹ℎ), the present calculation focused on calculation of the microscopic distributions of these energies in further contribution. the present results also compared with the others available theoretical results [14] to validate our results. it can be seen from the table 2 that the 𝐹𝑒𝑔 and 𝐹𝑀 has excellent agreement with compared results [14]. rajesh c. malan and aditya m. vora / bibechana 18 (2) (2021) 1-8 4 a very good agreement is obtained with the results of vora [14] for the results of 𝐹𝑚𝑖𝑥. this means the results generated by the potential used in present calculation and by vora [14] provides the almost same type of approximation for free electron energy, free energy per particle of the binary mixture and the madlung static electrical energy. the contributions provided by 𝐹𝑒𝑔, 𝐹𝑀 and 𝐹𝑚𝑖𝑥 are negative whereas that due to 𝐹1 is positive. out of these four parts, the 𝐹1 and 𝐹2 depend upon model potential. 𝐹1 is obtained from the zero limit of the potential. the results of the second order perturbation energy (𝐹2) for eight different local field corrections functions [15-23] are shown in the table 3. the comparision of the present result with the other theoretical available data [14] is also shown in the table 3. from the table 3, it can be observed that the results due to n-function [23] is highest for all concentration (𝑋). the hs-function [16, 17] provids the minimum exchange and correlation effect with respect to h-function [15]. the total internal energy (𝐹𝑖𝑛𝑡) of the alloys under study is shown in the table 4. the minimum deviation from the experimental value [20] is obtained for the n-function [23] and maximum for h-function [15]. however no significant effect is change is observed for any of the local field correction functions. hence, the suggested bare-ion potential is suffiently efficient to provide the screening and exchange and correlation effect. it also can b observed from the table 4 that the variation of 𝐹𝑖𝑛𝑡 from the experimental value [13] is maximum at 𝑋 = 0 is and minimum for 𝑋 = 1. thus, the potential provides the poor results when proportion of na is more and better results when proportion of k is more. various entroy contributions and total entropy 𝑆𝑚𝑖𝑥 are obtained a shown in the figure 1. the entropy contributes to the helmholtz free enrgy (𝐹ℎ) as shown in the equation [3] and [4]. the calculated helmhotz free energy (𝐹ℎ) is shown in the table 6. the results obtained for the 𝐹ℎ are found in well agreement with the experimental data [13] for 𝑋 = 1, better agreement for 𝑋 = 0.5 and reasonable agreement for 𝑋 = 0. table 1. input parameters and constants. metal ω (au) 𝒌𝒇 (au) 𝜶 (au) [6] 𝑹 (au) [6] na 227.76 0.4742 3.517 0.492 k 528.67 0.3826 3.349 0.679 fig. 1: various entropy contributions. rajesh c. malan and aditya m. vora / bibechana 18 (2) (2021) 1-8 5 table 2: 𝐹𝑒𝑔, 𝐹1, 𝐹𝑀 and 𝐹𝑚𝑖𝑥 (∗ 10−3𝑖𝑛 𝑎𝑢) 𝑿 𝑭𝒆𝒈 others [14] 𝑭𝟏 𝑭𝑴 others [14] 𝑭𝒎𝒊𝒙 others [14] 0.0 -81.61 -81.63 78.49 -213.7 -210.17 -6.45 -7.51 0.1 -81.73 -81.74 79.47 -203.1 -210.37 -6.71 -8.12 0.2 -81.73 -81.72 83.30 -194.5 -192.15 -6.93 -8.54 0.3 -81.64 -81.62 86.57 -187.5 -184.55 -7.13 -8.87 0.4 -81.48 -81.45 89.40 -182.1 -178.36 -7.32 -9.12 0.5 -81.28 -81.24 91.87 -178.0 -173.40 -7.49 -9.32 0.6 -81.05 -81.00 94.05 -175.0 -169.53 -7.64 -9.45 0.7 -80.78 -80.73 95.99 -172.9 -166.61 -7.79 -9.53 0.8 -80.50 -80.44 97.71 -171.8 -164.54 -7.92 -9.55 0.9 -80.21 -80.13 99.27 -171.5 -163.20 -8.05 -9.48 1.0 -79.90 -79.82 100.67 -171.8 -162.53 -8.17 -9.23 table 3. 𝐹2 ∗ 10−3in au 𝑿 h hs vs t s iu f n others [14] 0.0 -16.09 -15.45 -14.88 -14.63 -15.14 -14.35 -14.33 -13.27 -13.69 0.1 -70.51 -68.68 -67.09 -66.38 -67.83 -65.68 -65.61 -61.83 0.2 -74.60 -72.33 -70.23 -69.20 -71.18 -68.30 -68.18 -63.93 0.3 -61.07 -58.81 -56.55 -55.33 -57.54 -54.39 -54.24 -50.60 0.4 -43.40 -41.39 -39.23 -37.96 -40.14 -37.09 -36.92 -34.29 0.5 -27.86 -26.20 -24.30 -23.11 -25.08 -22.37 -22.20 -20.57 -19.20 0.6 -17.44 -16.15 -14.59 -13.56 -15.22 -12.98 -12.83 -11.89 0.7 -12.38 -11.40 -10.19 -9.38 -10.67 -8.94 -8.82 -8.17 0.8 -12.21 -11.46 -10.56 -9.98 -10.93 -9.66 -9.57 -8.80 0.9 -14.43 -13.83 -13.18 -12.83 -13.46 -12.58 -12.53 -11.39 1.0 -12.62 -12.22 -11.84 -11.71 -12.03 -11.54 -11.53 -10.30 -14.50 rajesh c. malan and aditya m. vora / bibechana 18 (2) (2021) 1-8 6 table : 𝐹𝑖𝑛𝑡 ∗ 10−3in au 𝑿 h hs vs t s iu f n exp [13] 0.0 -308.75 -308.11 -307.55 -307.29 -307.81 -307.02 -307.00 -305.93 -226.00 0.1 -274.13 -272.30 -270.71 -270.00 -271.45 -269.30 -269.23 -265.45 0.2 -265.74 -263.48 -261.38 -260.34 -262.32 -259.45 -259.33 -255.08 0.3 -241.92 -239.66 -237.40 -236.18 -238.38 -235.24 -235.09 -231.45 0.4 -215.82 -213.80 -211.64 -210.37 -212.55 -209.50 -209.33 -206.71 0.5 -193.46 -191.80 -189.90 -188.70 -190.68 -187.97 -187.80 -186.16 0.6 -177.62 -176.33 -174.77 -173.73 -175.39 -173.16 -173.00 -172.07 0.7 -168.35 -167.37 -166.16 -165.35 -166.64 -164.92 -164.79 -164.14 0.8 -165.04 -164.29 -163.39 -162.82 -163.76 -162.50 -162.41 -161.63 0.9 -165.06 -164.46 -163.81 -163.46 -164.10 -163.21 -163.17 -162.02 1.0 -161.87 -161.48 -161.10 -160.96 -161.28 -160.79 -160.79 -159.55 -190.00 table 5: 𝐹ℎ ∗ 10−3in au 𝑿 h hs vs t s iu f n exp [13] 0.0 -369.62 -368.99 -368.42 -368.16 -368.68 -367.89 -367.87 -366.80 -250.33 0.1 -323.36 -321.53 -319.94 -319.24 -320.68 -318.54 -318.46 -314.68 0.2 -320.67 -318.41 -316.30 -315.27 -317.25 -314.37 -314.25 -310.01 0.3 -306.24 -303.98 -301.72 -300.50 -302.70 -299.56 -299.41 -295.77 0.4 -287.95 -285.94 -283.78 -282.51 -284.69 -281.64 -281.47 -278.84 0.5 -269.63 -267.97 -266.06 -264.87 -266.84 -264.14 -263.96 -262.33 -235.90 0.6 -253.39 -252.09 -250.53 -249.50 -251.16 -248.93 -248.77 -247.84 0.7 -239.82 -238.84 -237.63 -236.82 -238.12 -236.39 -236.26 -235.61 0.8 -229.41 -228.66 -227.76 -227.18 -228.13 -226.86 -226.77 -226.00 0.9 -221.56 -220.97 -220.32 -219.97 -220.60 -219.72 -219.67 -218.52 1.0 -214.13 -213.74 -213.36 -213.23 -213.54 -213.06 -213.05 -211.81 -218.51 rajesh c. malan and aditya m. vora / bibechana 18 (2) (2021) 1-8 7 4. conclusion the thermodynamical investigation of the liquid alkali 𝑁𝑎1−𝑋𝐾𝑋 alloy has been done. the potential of fiolhais et al. [6] is found appropreate to describe the themodynamical properties of the alloy under study. the results for the internal energy (𝐹𝑖𝑛𝑡) and helmholtz energy (𝐹ℎ) are obtained and found in a good agreement at some concentration value. the present results are found to be deviated from the experimental data [13] at lower concentration. references [1] j. k. baria, analysis of thermodynamics of liquid dand f-shell metals with the variational approach, chinese physics letters 20(6) (2003) 894. https://doi.org/10.1088/0256-307x/20/6/333 [2] r.c. gosh, a.z. ahmed, and g. m. bhuiyan, investigation of surface entropy for liquid less simple metals, the european physical journal b 56(3) (2007) 177-181. https://doi.org/10.1140/epjb/e2007-00104-9 [3] p. kumar, n.k. bhatt, p.r. vyas, and v.b. gohel, the study of anharmonic properties and spd hybridization in barium at extreme environment, phase transitions 90(12) (2017) 1167-1178. https://doi.org/10.1080/01411594.2017.1326601 [4] p.b. thakor, v.n. patel, b.y. thakore, p.n. gajjar, and a.r. jani, thermodynamic properties of some simple metals in liquid phase by pseudopotential theory, indian journal of pure and applied physics 42 (2004) 684. 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https://doi.org/10.1088/0256-307x/20/6/333 https://doi.org/10.1140/epjb/e2007-00104-9 https://doi.org/10.1080/01411594.2017.1326601 https://doi.org/10.4028/www.scientific.net/ddf.263.105 https://doi.org/10.4028/www.scientific.net/ddf.263.105 https://doi.org/10.1103/physrevb.51.14001 https://doi.org/10.1063/1.5052121 https://doi.org/10.1063/1.5033189 https://doi.org/10.21272/jnep.10(3).03020 https://doi.org/10.1103/physrev.110.1 https://doi.org/10.1088/0305-4608/4/10/016 https://doi.org/10.1098/rspa.1958.0003 https://doi.org/10.1098/rspa.1965.0005 https://doi.org/10.1103/physrevb.6.875 https://doi.org/10.1088/0305-4608/8/8/011 rajesh c. malan and aditya m. vora / bibechana 18 (2) (2021) 1-8 8 electron gas at metallic and lower densities, modern physics letters b 12(16) (1998) 639-648. https://doi.org/10.1142/s0217984998000755 [21] s. ichimaru, and k. utsumi, analytic expression for the dielectric screening function of strongly coupled electron liquids at metallic and lower densities, physical review b 24(12) (1981) 7385. https://doi.org/10.1103/physrevb.24.7385 [22] b. farid, v. heine, g.e. engel, i.j. robertson, extremal properties of the harris-foulkes functional and an improved screening calculation for the electron gas, physical review b 48(16) (1993) 11602. https://doi.org/10.1103/physrevb.48.11602 [23] i. nagy, analytic expression for the static local field correlation function, journal of physics c: solid state physics, 19(22) (1986)l481. https://doi.org/10.1088/0022-3719/19/22/002 https://doi.org/10.1142/s0217984998000755 https://doi.org/10.1103/physrevb.24.7385 https://doi.org/10.1103/physrevb.48.11602 https://doi.org/10.1088/0022-3719/19/22/002 bibechana 19(1-2) (2022) 61-67 61 correlation between the magnetic and dc resistivity studies of cu substituted ni and zn in ni-zn ferrites d. parajuli1, 2*, n. murali3, k. samatha4 1research center for applied science and technology (recast), tribhuvan university, kathmandu44613, nepal 2tri-chandra multiple campus, tribhuvan university, ghantaghar, kathmandu, nepal 3department of physics, college of engineering (a), andhra university, visakhapatnam-530003, india 4department of physics, andhra university, visakhapatnam-530003, india *email: deepenparaj@gmail.com article information: received: may 04, 2021 accepted: february 03, 2022 keywords: spinel ni-zn ferrite isotropic negative-temperature coefficient multilayer chip inductors abstract cu substituted ni0.5-xcuxzn0.5fe2o4 (x = 0, 0.05, 0.1, 0.15 and 0.2) samples is synthesized using the sol-gel auto-combustion process. they have a cubic spinel structure with crystallite size in the range of 29.01–42.68 nm. the increment in the copper content increases the dc conductivity. the electrical resistivity decrease with an increase in the temperature i.e. it has a negative temperature coefficient with resistance similar to semiconductors. the remnant ratios r obtained from vsm show their isotropic nature forming single domain ferrimagnetic particles. the results are compared with ni0.5cuxzn0.5xfe2o4 (x = 0 to 0.25). the resultant material cu substituted zn is more significant than that of ni as indicated by its results and previous literature. doi: https://doi.org/10.3126/bibechana.v19i1-2.46387 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a. m. campus, tu, biratnagar, nepal mailto:deepenparaj@gmail.com https://doi.org/10.3126/bibechana.v19i1-2.46387 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana parajuli et al. / bibechana 19(1-2) (2022) 61-67 62 1. introduction microwave devices, magnetic recording, coating, etc. are the major applications of nizn spinel ferrites [1-3]. their crystal structure supports them in tuning their microstructural and electromagnetic properties which are necessary for many advanced applications. they have m2+fe2 3+o4 2composition with transitional metal (m) in tetrahedral and fe on the octahedral region of the nano ferrite. a vigorous study on their structural and magnetic properties with doping of several elements in ni-cu-zn ferrites is increasing day by day [46]. the core of rotary dy, transformer, and magnetic induction uses these types of ferrites. in some cases, the density, porosity, the interactions among the particles with canting effects affect their magnetic properties. recently, we have studied the effect of cu substitution on magnetic and dc electrical resistivity of ni-zn ferrites ni0.5zn0.5xcuxfe2o4 (x = 0, 0.1, 0.2, 0.3, and 0.4) [7], structural and morphological study of cu substituted ni/zn in ni-zn ferrite comparatively [8, 9], cd substituted ni-zn ferrites [10] and ni substituted co zn ferrites [11]. they all have spinel structures with semiconducting nature. in the present study, cu substituted nickel ferrites are prepared by the sol-gel method, and compare their magnetic and dc electrical properties with cu substituted zn in ni-zn ferrites synthesized from the citrate gel route [12, 13]. the cu substituted zn in ni-zn ferrites is appropriate for multilayer chip inductor (mlci) as magnetic material. 2. methodology a. materials the sol-gel method was used for the preparation of ni0.5zn0.5-xcuxfe2o4 (x = 0, 0.1, 0.2, 0.3, and 0.4). the nitrates of nickel, copper, zinc, iron and citric acid with 99.99% purity were used as starting materials and mixed in a 1:1 ratio. the solution was made clear with double distilled water. liquid ammonia was added dropwise with magnetic stirring at 100oc for 4 hrs. for getting the neutral solution after it was made neutral by adding liquid ammonia. the solution was then decanted and dried for 40 hrs. at room temperature. the resultant was powdered and sintered in a muffle furnace at 800 °c for 4 h at 5o/min. b. characterizations the structure of ni0.5zn0.5-xcuxfe2o4 (x = 0, 0.1, 0.2, 0.3, and 0.4) was studied with the help of an x-ray diffractometer (rigaku miniflex ii) with cukα radiation of 1.5406 å. the morphological and compositional study was made with tescan, mira ii lmh sem, and attached inca oxford edx. the functional group and room temperature magnetic properties were studied with ft-ir and ezvsmmodels respectively. the disc-shaped pellets were made with the help of a hydraulic system of 5 tons of pressure incorporating a few drops of polyvinyl alcohol as a binder. their flat surfaces were polished with gold to use as electrodes after being sintered at 800oc in a muffle furnace and used for the study of dc resistivity in two probe systems. 3. results and discussions a. magnetic properties ez-vsm used for the magnetic characterization of ni0.5zn0.5-xcuxfe2o4 (x = 0, 0.1, 0.2, 0.3 and 0.4). ferrites have higher resistivity due to unequal antimagnetic moments giving rise to higher spontaneous magnetization. moreover, they have a negative exchange integral affected by an interatomic distance which obstructs the flow of electrons [14]. however, their saturation permeability, coercivity, susceptibility, curie temperature, etc. are affected by the density of ions in their respective interstitial sites and their structure determines the hysteresis loop's shape, resistivity, ac conductivity, and dielectric constant. the doping of either magnetic or nonmagnetic extrinsic elements changes their property accordingly. the magnetic saturation, coercivity, etc. are calculated from their hysteresis curves as shown in figure 1. the obtained values of ms and hc are listed in table 1 [15]. parajuli et al. / bibechana 19(1-2) (2022) 61-67 63 table 1: ms and hc of ni0.5-xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrites concentratio n (x) ms (emu/g) hc (oe) 0.0 73.26 45.36 0.05 80.66 60.62 0.1 83.86 84.45 0.15 56.05 65.26 0.2 46.32 51.48 from table 1, ms increases up to (x ≤ 0.1) and then starts decreasing with cu2+ concentration. this is due to the distribution of cations and exchange interaction. on adding copper ions to the nickel-zinc mixture, they exchange a few magnetic ions fe3+ and ni2+ in a and bsites. the ab interaction is then increased thereby resisting antiparallel spin which ultimately raises the magnetic saturation [16]. according to weiss's molecular field theory, the mixed interaction (a-b and b-a) is more than similar a-a and b-b interaction resulting from the hysteresis loop [17]. the increment of nonmagnetic cu ion in place of zn ion decreases saturation magnetization. the occupancy of the b site by cu ion helps fe3+ ions migrate to the a-site thereby reducing magnetization in the b site and increasing in the a site. the total magnetization is obtained using neel’s [18] law, according to which m=|mb − ma|. so, the cu substituted zinc effectively works in changing the magnetic properties of the sample than nickel. b. dc electrical resistivity there is a rapid, then steady and finally constant decrease of dc resistivity of cu substituted nickel in ni-zn ferrites nanoparticles with cu concentration [19] as shown in dc resistivity vs. temperature for the cu substituted ni-zn ferrite of figure 3. a straight line is obtained from the logeρ vs. 1000/t graph showing the semiconducting nature of the ferrites under consideration. the temperature variation of dc electrical resistivity of ni0.5zn0.5−xcuxfe2o4 ferrite samples as in figure 4 indicates that all the samples have semiconducting properties. further, the temperature-dependent resistivity varied larger with the concentration of cu ion and seems more effective for x=0.15 in the case of cu substituted zinc in ni-zn ferrite. so, the resistive property is changed effectively in cu substituted zinc in ni-zn ferrite than that in cu substituted nickel. figure 1: hysteresis curves of ni0.5xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrite nps at room temperature figure 2: hysteresis curves of ni0.5zn0.5−xcuxfe2o4 (x=0.00 to 0.25) at room temperature [12] c. activation energy calculation the slope of the tangents on the plot of 1000/t versus logeρ of ni0.5zn0.5−xcuxfe2o4 is used for the calculation of their activation energies where we use the arrhenius relation parajuli et al. / bibechana 19(1-2) (2022) 61-67 64 incorporating the dynamism of hopping charge carriers due to temperature [19] as: 𝛒 = 𝛒𝐨𝐞 ( ∆𝐄 𝐊𝐓 ) (1) where, ρ and ρo are the dc electrical resistivity at temperature t and absolute zero. ∆e and k are the activation energy and the boltzmann constant. the activation energies obtained are plotted against the concentration of the cu in ni0.5zn0.5−xcuxfe2o4 are shown in figure 5. figure 3: temperature dependence of dc resistivity of ni0.5-xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrites figure 4: 1000/t versus logeρ of ni0.5zn0.5−xcuxfe2o4 samples (x = 0.00 to 0.25) [13] the variation in resistivity of the samples is according to the verwey and de boer hopping mechanism in which the electrons of the same element jump at their different valence states. as a result, fe2+ fe3+ hopping is raised for higher sintering temperature as more fe2+ ions. the ni2+  ni3+ and cu3+  cu2+ hopping can also take place simultaneously [21]. figure 5: activation energies vs. concentration (x) of the ni0.5-xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) figure 6: cu concentration vs. logeρ & ea of ni0.5zn0.5−xcuxfe2o4 (x = 0.00 to 0.25) [13] figure 6 shows the variation of activation energies and dc resistivity with cu substituted zinc concentration in ni0.5zn0.5−xcuxfe2o4 nanocrystalline ferrite samples (x = 0.00 to 0.25). from the figure, it is observed that the parajuli et al. / bibechana 19(1-2) (2022) 61-67 65 activation energies and resistivities of the samples are fluctuated more than that in cu substituted nickel in nizn ferrites but in the range of 0.53 ev to 0.67 ev. 4. conclusion the structures of the nanocrystalline ni0.5xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15, and 0.2) ferrite nps were synthesized by sol-gel auto-combustion method and confirmed their structure to have single-phase cubic spinel ferrite with the help of xrd and ftir. the magnetic measurements show that saturation magnetization, coercive forces, and activation energy are highest at x = 0.1. while the conductivity is lowest at x=0.05 in the case of cu substituted nickel. the zinc content effectively works in changing the magnetic properties of nickel. both have isotropic magnetism. in both cases, the electrical resistivity decrease with an increase in the temperature i.e. it has a negative temperature coefficient with resistance similar to semiconductors. the activation energies are varied more in the range 0.53 ev to 0.67 ev in cu substituted zinc than that in the range 0.42 to 0.51 ev. the variation in cu substituted nickel and cu substituted zinc synthesized by two different processes are due to their different 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https://doi.org/10.3126/bibechana.v18i2.34383 https://doi.org/10.1016/j.rinp.2021.103947 https://doi.org/10.1016/j.rinp.2021.103947 https://doi.org/10.3126/jnphyssoc.v7i2.38619 https://doi.org/10.1007/s10904-019-01419-2 https://www.worldscientific.com/doi/abs/10.1142/s0217984917503183 https://www.worldscientific.com/doi/abs/10.1142/s0217984917503183 http://doi.org/10.1142/s0217984917503183 https://doi.org/10.1016/j.fuel.2016.10.047 https://doi.org/10.1002/bbpc.19750790622 https://doi.org/10.1016/j.jart.2017.01.009 http://dx.doi.org/10.1016%2fj.jmmm.2014.12.006 https://www.researchgate.net/deref/http%3a%2f%2fdx.doi.org%2f10.1016%2fj.jmmm.2015.06.030?_sg%5b0%5d=ge96v1dovi5ofp22_0rznofvnkh5cqre7vbwvw3ruapfx2knegudjcj5i8ba0lzs-kozrqsfplwm6vcbspdrbjsxnw.xpu0puavvwagqcct8npfnh9aobemiaszcdhi1_cqhorcog4acjvvnxuzj20dar3ola0xy-gkmisadftdizhuwa parajuli et al. / bibechana 19(1-2) (2022) 61-67 67 nanoparticles through auto-combustion method for multilayer chip inductor applications, nanoscale res. lett. 7(1)(2012)1–14. https://doi.org/10.1186/1556-276x-7-112 https://doi.org/10.1186/1556-276x-7-112 *email: deepenparaj@gmail.com a. materials the sol-gel method was used for the preparation of ni0.5zn0.5-xcuxfe2o4 (x = 0, 0.1, 0.2, 0.3, and 0.4). the nitrates of nickel, copper, zinc, iron and citric acid with 99.99% purity were used as starting materials and mixed in a 1:1 ratio. the soluti... b. characterizations the structure of ni0.5zn0.5-xcuxfe2o4 (x = 0, 0.1, 0.2, 0.3, and 0.4) was studied with the help of an x-ray diffractometer (rigaku miniflex ii) with cukα radiation of 1.5406 å. the morphological and compositional study was made with tescan, mira ii lm... 3. results and discussions bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal bibechana 19 (1-2) (2022) 90-96 synthesis of zno nanoparticles by chemical method and its structural and optical characterization rishi ram ghimire, ashutosh parajuli, suresh prasad gupta, krishna bahadur rai* department of physics, patan multiple campus, tribhuvan university, kathmandu, nepal *email: krishnarai135@gmail.com article information: received: march 29, 2021 accepted: june 03, 2021 keywords: zinc oxide nanoparticles williamson–hall method xrd uv-visible spectrophotometer abstract in this report, zno nanoparticles (nps) was synthesized by chemical method using zinc acetate dehydrate [zn(ch3coo)2.2h2o)] as precursors and ethanol and distilled water as solvent. sodium hydroxide (naoh) was used to maintain the ph of the solution and helps to establish the nps. the nps are characterized by xrd, uv-visible spectroscopy and sem image analysis. the xrd characterization gives the polycrystalline nature of zno nps with the size ~23 nm and ~27 nm calculated by scherrer’s method and williamson–hall method respectively. the crystalline size of these nps calculated using xrd pattern is validated by sem image analysis. using the uv-visible spectrophotometer and tauc plot method, the optical band gap of zno is found to be 3.35 ev. the uniform size distribution of nps shown in sem image and strong uv absorption shown in uv-visible spectra indicate that thus prepared nps are highly desirable for photo catalytic activity and detection applications. doi: https://doi.org/10.3126/bibechana.v19i1-2.46396 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction semiconductor nanoparticles (nps) have drawn tremendous interest in research because of its special electronic properties and unique optical properties as compared to their bulk. the large surface to volume ratio gives the unique physical properties of nps due to which it has versatile performance of nanoscale device [1]. the oxides of transition metals are very important class of semiconductors, among them zno is one of the promising oxide material having an inexpensive n-type nature and direct band gap of 3.37 ev. zno semiconductor is found in the hexagonal wurtzite structure [2]. it has been widely used in gas sensors [3], biosensors [4], transparent electrodes [5], nanogenerators [6], photodetectors 90 http://nepjol.info/index.php/bibechana mailto:krishnarai135@gmail.com https://doi.org/10.3126/bibechana.v19i1-2.46396 https://creativecommons.org/licenses/by-nc/4.0/ ghimire et al / bibechana 19 (1-2) (2022) 90-96 91 [7], solar cells [8] and photocatalysts [9] application. the existence of water molecules results hard agglomeration of nps in the formation of zn-o-zn bond which impedes the applications of zno nps [10]. the synthesis of the nps are mainly obtained using top–down approach (physical synthesis method) and bottom–up approach (chemical synthesis method). in physical method, the bulk materials are mashed to nano-size via most common mechanical millings like ball milling and ion-beam milling. so the shape and size is non-uniform and reproduction itself is usually not possible. in chemical synthesis method, nanomaterials have genuine size distribution due to the critical role of temperature, pressure, precursor concentration and capping agent. this involves controlled organization of atomic and molecular structure to form bulk materials [11]. the coating of nps to enhance the surface area with chemical and physical properties has an indispensable role for potential applications of nanomaterials. a number of efficient ways of research have been done in the application field of zno nps and its synthesis. in synthesis of zno nps, different shape and sizes are achieved from different methods [12]. the shape and size of zno nps show significant change with varying temperature. the average particle size increases with increase in synthesized temperature. also, increasing temperature lowers the band gap values [12, 13]. several fabrication techniques such as hydrothermal processing, sol-gel method, thermal hydrolysis techniques, vapor condensation method, laser ablation, spray pyrolysis are used to produce zno nps [14]. it can be synthesized through mechanical activation of reactant particles at nanoscale. this helps to manually control the grain size of the particle [15]. in glycol media, particle size has direct correlation to glycol chain length [16]. as the amount of triethanolamine is increased, the homogeneity is achieved in the particle size [17]. the shape and size can also be controlled by changing the preparation parameters [18, 19, 20]. particle size determination using x-ray diffraction (xrd) pattern and scanning electron microscopy (sem) image analysis is an important task to study the optoelectronic transport properties of nanoscale materials for its potential applications [21]. the shape and size of nanoparticles (nps) have the critical role particularly for sensing and detection. comparing the average crystallite size of zno nps estimated by scherrer method and by williamson-hall method supported with scanning electron microscopy (sem) image offer possibility of benefit for future size dependent applications. though there are several reports of synthesis of zno nps using chemical method where they have used capping agent to protect the agglomeration of the nps and make it uniform distribution. in this report, we are able to synthesize zno nps without capping agent and have a uniform size distribution using magnetic stirrer and centrifuge. the main focuses of our study is the synthesis of uniform zno nps without capping agent using the cost effective chemical method and employs the xrd analysis to determine the crystallite size of nps and validated with sem micrograph along with the optical properties such as optical band gap and absorption coefficient. so, the uniformity and strong uv-absorption of zno nps favors the applications towards the photo-catalytic and detection activity. 2. methodology synthesis of zno powder for the synthesis of zno nps, zinc acetate dihydrate [zn(ch3coo)2.2h2o)] of sigma aldrich company with purity 99.9% was used as a precursor, sodium hydroxide (naoh) of merck india with purity 99.8% and distilled water (h2o) were used as a medium and ethanol (ch2cooh) of tech-bio company with purity 99.98% was used as reagent. all the apparatus such as beaker, burette etc. were cleaned via sonication. solution of 2.01g (~2g) of zinc acetate dihydrate [zn(ch3coo)2.2h2o] was prepared in 15 ml of distilled water and 8.03g (~8g) of sodium hydroxide (naoh) of merck india company with purity 99.8% was prepared in 10 ml of distilled water. both the solutions were stirred for about six minute each then these solutions were mixed and stirred again using the magnetic stirrer. then 100 ml of ethanol (ch2cooh) of was poured in the burette and titration was performed such that white precipitate was seen on the previous solution. after the titration, the solution was again stirred using magnetic stirrer for about 15 minutes then this solution was centrifuged. now, this solution was washed one time with ethanol. at last, this solution was again washed with distilled water for more than ghimire et al / bibechana 19 (1-2) (2022) 90-96 92 five times. in this way, the zinc powder was obtained. structural and optical study the obtained zno powder was then studied using x–ray diffraction (xrd) and uv–visible spectrophotometer of model agilent cary 60. for the structural properties, xrd pattern was used. along with this, the size of the particle can be calculated via scherer method and williamson–hall method. the optical properties such as wavelength, optical band gap and absorption coefficient were studied using a uv–visible spectrophotometer. 3. results and discussion the chemical reaction that occurs during the process is shown by the following chemical equation: (zn(ch3coo)2.2h2o) + 2naoh → zno + 2nach3coo + h2o the zno colloid is formed when the zinc acetate dihydrate is completely hydrolyzed with sodium hydroxide in the ethanol solution. the zinc acetate solution, when heated, forms acetate ions and zinc ions. the zinc ions from zinc acetate bond with oh group of ethanol which gives zinc zn(oh)2 group as an intermediate state. this is the result of hydrolysis reaction of zinc acetate in the presence of fig. 1: xrd pattern of zno nanoparticle sharp peaks indicate the good crystallite of zno nps. the multiple peaks at different angle indicate the polycrystalline nature of chemically grown zno nps. the particle size in nanocrystalline zno powder is calculated using scherrer’s method and is also confirmed by williamson–hall plots. scherrer’s method determination of crystallite size using scherrer’s equation is well established non-destructive technique in crystallography. scherer’s formula in the equation 1 is used to calculate the particle size of zno nps. h2o and oh – ions. finally, it transformed into zno d = kλ βcosθ ………………………… (1) nps and washed it several times with de-ionized water to remove hydroxide and dried it above 100 ℃ for 3 hours then it turned into yellowish powder. x-ray diffraction figure 1 shows the x–ray diffraction pattern of zinc oxide nps with miller indices at different angle of diffraction. the patterns of xrd are shown in between the angle 30 to 80 (30<2θ<80). the peak position, relative intensities and the width of peaks have fundamental importance to know crystallite and size of the nps. where d is the particle size of the zno, k is the shape factor whose value varies from 0.89 to 0.94 and 0.94 is chosen for spherical nps, λ is the wavelength of the cu–kα radiations (1.5406 ǻ) used in the x–ray diffraction, β is the full-width half maximum (fwhm), and θ is the bragg’s angle of different peaks. from the xrd analysis pattern in figure 1, the bragg’s angle for different peaks (θ) and their respective fwhm (β) are used to find out the particle size of chemically synthesized zno nps. using equation 1, the particle size is calculated for different peaks of xrd pattern. the table 1 gives particle size at different bragg’s angle of each peak such that the average particle size is found to be nearly 23 nm. table 1: calculation of particle size from the scherrer’s method ghimire et al / bibechana 19 (1-2) (2022) 90-96 93 the linear fit, a straight line is obtained and then size is calculated using the y-intercept of the straight line. figure 2 shows the williamson-hall plot from which we obtained the particle size ~27 nm i.e. listed in the table 2. williamson–hall method since the scherrer’s methoth is used for nps size calculation of the single crystal or highly oriented nanomaterials. however the williamson–hall method is used for the calculation of particle size and strain induced in the polycrystalline nanomaterials. the peak broadening in the xrd pattern is the result of the size and strains. this method estimates the approximate formula to calculate the size broadening (βd) and strain broadening (βs). this is given by the equation 2 and equation 3 respectively. fig. 2: plot of βcosθ vs sinθ of zno nanoparticle table 2: grain size calculation from williamson hall plot and comparison with scherer’s method βd = kλ dcosθ …………………………. (2) βs = cεtanθ ................................................ (3) where cε is the strain component from the slope. it is clear that the size broadening (βd) varies as 1/cosθ and the strain broadening (βs) varies as tanθ. williamson and hall made an assumption that these two parameters combine and is represented by the equation 4. β = βd + βs ......................................................... (4) this shows that the combined effect of size broadening and strain broadening. further simplification and rearranging of equation 4 result in equation 5. morphology of all zno nps synthesized were obtained by scanning electron microscopy (sem) and studied through the figure 3 in which this sem image shows the different sizes of zno nps. there are about 16 to 18 number of zno nps within the range of 500 nm scale. so, this clearly tells that one nps average size is approximately equally to ~29 nm. the size of the nps from williamson–hall method is in nearly consistent with the size of nps obtained from the sem image. βcosθ = cεsinθ + kλ d …………….…… (5) comparing equation 5 with the standard equation of straight line, y = mx + c, it is seen that plot of βcosθ vs sinθ also forms a straight line with the slope equal to cε and the y-intercept equal to kλ/d. the strain component is calculated from the slope (cε) and the size component from the intercept kλ/d. williamson-hall plot was now formed by taking βcosθ in y-direction and sinθ in x-direction. using 2θ (degree) fwhm (degree) particle size (nm) 32.62813 0.32149 ~26 35.27603 0.31011 ~27 37.10811 0.34846 ~24 48.38115 0.42743 ~20 57.42788 0.38923 ~23 63.66431 0.45206 ~21 68.75777 0.46565 ~21 69.87374 0.45944 ~21 y intercept particle size (nm) scherrer’s method d (nm) 0.0053 ~27 ~23 ghimire et al / bibechana 19 (1-2) (2022) 90-96 94 where α is the absorption coefficient, h is the planck’s constant, ν is the frequency of the incident photon, a is the optical absorbance, eg is the optical band gap, and n is the nature of transition. for direct band gap, n = 2. the energy parameter is calculated using max planck equation as shown in equation 7. e = hν .................................................. (7) here ν is the ratio of speed of light c and wavelength of incident photon λ. then equation 7 can be approximated as shown in equation 8. e = 1240 λ …………………………… (8) for the calculation of absorption coefficient, beer lambert’s law is used given in equation 9. i = e−αl........................................ (9) i0 fig. 3: sem image of zno nps uv–visible spectroscopy uv–visible spectroscopy helps in understanding the optical properties of the zno nps. using it, wavelength and absorbance are obtained. then from further calculation, absorption spectrum and optical band gap are calculated. the absorption spectrum is shown in the figure 4. in the absorption spectrum at about wavelength of 370 nm, there is an absorption sharp turn. the optical band gap is then calculated using the tauc relation shown in the equation 6. where, io, i and α are the intensity of transmitted light, intensity of incident light and absorption coefficient respectively. path length (l) of the light used is 1 cm. then taking ln on both sides and some further simplification, α is calculated from the equation 10. 𝛼 = 2.303 × a ................................ (10) then using this relation, a tauc plot is drawn. for the tauc plot in the inset of figure 4, energy (hν) is plotted on the x–direction and (αhν)n is plotted on the y–direction. the tauc plot shown in the inset of figure 4 has the optical band gap of zno nps equal to 3.35 ev. 0.8 0.6 0.4 0.2 300 400 500 600 700 800 900 4. conclusion zno nps were synthesized from chemical route using centrifuge method which has a polycrystalline structure as characterized by xrd. the size distribution of nps calculated by scherrer’s method was ~23 nm and it was also confirmed by williamson–hall method which was ~27 nm. furthermore, the size distribution of nps validated with sem micrograph. the size of the nps obtained from williamson–hall method is in nearly consistent with the size of nps from the sem image wavelength (nm) fig. 4: absorption spectrum of zno. in the inset: (αhν)2 vs hν and the optical band gap energy of the zno nps. αhν = a(hν – eg) 1/n ............................. (6) and also showed uniform size distribution. the optical band gap of zno nps was calculated using tauc plot method from uv-visible spectra which was 3.35 ev. thus chemically grown uniform zno nps without capping agent having strong uv absorption can be used for photocatalytic and detection application. 48 40 32 24 16 1.5 2.0 2.5 3.0 3.5 a b so rb a n ce ( h  ) ghimire et al / bibechana 19 (1-2) (2022) 90-96 95 acknowledgement: the authors thank to professor shankar prasad shrestha from patan multiple campus and dr. dipendra das mulmi from nast for their valuable supports and suggestions. we also acknowledge s. n. bose national centre for basic sciences for sem image. references [1] k. m. m. abou el-nour, a. eftaiha, a. al warthan, r. a. a. ammar, synthesis and applications of silver nanoparticles, arab j. chem. 3(2010) 135–140. https://doi.org/10.1016/j.arabjc.2010.04.008 [2] z. l. wang, zinc oxide nanostructures: growth, properties and applications, j. phys.: condens. matter. 16(25) (2004) r829–r858. https://doi.org/10.1088/0953-8984/16/25/r01 [3] x. l. cheng, h. zhao, l. h. huo, s. gao, j. g. zhao, zno nanoparticulate thin film: preparation, characterization and gas-sensing property, sensors and actuators, b. 102(2) (2004) 248–252. https://doi.org/10.1016/j.snb.2004.04.080 [4] e. topoglidis, a. e. g. cass, b. o’regan, j. r. durrant, immobilisation and bioelectrochemistry of proteins on nanoporous tio2 and zno films, j. electroanal. chem. 517(1-2) (2001) 20–27. https://doi.org/10.1016/s0022-0728(01)00673-8 [5] t. minami, h. nanto, s. shooji, s. takata, the stability of zinc oxide transparent electrodes fabricated by r. f. magnetron sputtering, thin solid films. 111(2) (1984) 167-174. https://doi.org/10.1016/0040-6090(84)90484-x [6] p. x. gao, y. ding, w. mai, w. l. hughes, c. lao, z. l. wang, materials science: conversion of zinc oxide nanobelts into superlattice-structured nanohelices, science. 309(5741) (2005) 1700–1704. https://doi.org/10.1126/science.1116495 [7] p. sharma, k. sreenivas, k. v. rao, analysis of ultraviolet photoconductivity in zno films prepared by unbalanced magnetron sputtering, j. appl. phys. 93(7) (2003) 3963–3970. https://doi.org/10.1063/1.1558994 [8] y. hames, z. alpaslan, a. kosemen, s. e. san, y. yerli, electrochemically grown zno nanorods for hybrid solar cell applications, solar energy. 84(3) (2010) 426–431. https://doi.org/10.1016/j.solener.2009.12.013 [9] p. v. kamat, r. huehn, r. nicolaescu, a “sense and shoot” approach for photocatalytic degradation of organic contaminants in water, j. phys. chem. b. 106(4) (2002) 788–794. https://doi.org/10.1021/jp013602t [10] r. hong, t. pan, j. qian, h.li, synthesis and surface modification of zno nanoparticles, chem. eng. j., 119(2-3) (2006) 71–81. https://doi.org/10.1016/j.cej.2006.03.003 [11] k. d. sattler, ed., handbook of nanophysics. in r. k. thareja, a. mohanta, zno nanoparticles.1st edition, taylor and francis group, llc (2011). 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https://doi.org/10.1016/j.cej.2006.03.003 https://www.sciencedirect.com/science/journal/13698001 https://www.sciencedirect.com/science/journal/13698001 https://doi.org/10.1016/j.mssp.2014.07.025 https://doi.org/10.1016/j.materresbull.2011.07.046 https://doi.org/10.1088/0957-4484/17/20/013 https://doi.org/10.1016/j.matlet.2012.01.004 https://doi.org/10.4028/www.scientific.net/ddf.273-276.626 https://doi.org/10.4028/www.scientific.net/ddf.273-276.626 https://doi.org/10.4028/www.scientific.net/amr.699.133 https://doi.org/10.4028/www.scientific.net/amr.699.133 ghimire et al / bibechana 19 (1-2) (2022) 90-96 96 thickness of nanostructured zno film by spin coating technique, journal of nepal physical society, 7 (2) (2020), 119-125. https://doi.org/10.3126/jnphyssoc.v7i2.38632 [20] m. l. kahn, et al., organometallic chemistry: an alternative approach towards metaloxide nanoparticles, j. mater. chem., 19(2009) 4044-4060. https://doi.org/10.1039/b818935h [21] r. s. bisht, r. r. ghimire, a. k. raychaudhuri, control of grain boundary depletion layer and capacitance in zno thin film by a gate with electric double layer dielectric, j. phys. chem. c, 119 (49) (2015), 27813–27820. https://doi.org/10.1021/acs.jpcc.5b08761 https://doi.org/10.3126/jnphyssoc.v7i2.38632 https://doi.org/10.1039/b818935h https://pubs.acs.org/action/dosearch?field1=contrib&text1=ravindra%2bsingh%2b%2bbisht https://pubs.acs.org/action/dosearch?field1=contrib&text1=rishi%2bram%2b%2bghimire https://pubs.acs.org/action/dosearch?field1=contrib&text1=a.%2bk.%2b%2braychaudhuri https://pubs.acs.org/action/dosearch?field1=contrib&text1=a.%2bk.%2b%2braychaudhuri https://doi.org/10.1021/acs.jpcc.5b08761 1. introduction 2. methodology synthesis of zno powder structural and optical study 3. results and discussion scherrer’s method x-ray diffraction williamson–hall method uv–visible spectroscopy 4. conclusion wavelength (nm) acknowledgement: references s.b. parajuli et al. / bibechana 16 (2019) 228-235: rcost p.228 (online publication: dec., 2018) bibechana a multidisciplinary journal of science, technology and mathematics issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: research council of science and technology, biratnagar, nepal chaupadi during menstruation still a major community health challenge: perspective from mid-western nepal s. b. parajuli1*, 2, heera kc3, a. mishra1, p. bhattarai4, m. shrestha5, k. srivastav6 1department of community medicine, kathmandu university-birat medical college & teaching hospital, tankisinuwari, nepal 2nepal medical volunteer society, biratnagar, nepal 3department of nursing, purbanchal university-birat health college, biratnagar, nepal 4department of physiology, kathmandu university-birat medical college & teaching hospital, tankisinuwari, morang, nepal 5department of community health nursing, purbanchal university college of medical and allied health sciences, gothgaun, nepal 6mbbs student, kathmandu university-birat medical college & teaching hospital, tankisinuwari, nepal *e-mail: drsathii@yahoo.com article history: received 02october, 2018; accepted 10 november, 2018 http://dx.doi.org/10.3126/bibechana.v16i0.21645 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ abstract introduction: menstruation, a normal physiological process in reproductive life of female still has many misconceptions. knowledge of menstrual hygiene and menstrual sanitation practices affects the health of female. lack of awareness on menstrual care practice is a challenge for community health. objective: the objective of this study was to find knowledge and practice on menstrual hygiene; and perspective of chaupadi (menstrual shed) among the reproductive age group female. methodology: a community based mixed method study having cross sectional study as quantitative domain and phenomenological study as qualitative domain was conducted in maranthana community of pyuthan district of mid-western nepal from april 2016-september 2016. using convenient sampling techniques, 109 participants were included for cross sectional study and five of them who experienced chaupadi were enrolled for phenomenological study. one eligible participant form each household was taken after getting informed voluntary consent. collected data was entered in microsoft excel and analysed by spss and nvivo software. results: regarding knowledge, 73.7% were aware on the right age of menarche. almost 93% were aware on possible pregnancy after initiation of menstruation. many of them (34.9%) were informed on menstruation by friends. almost half (45.9%) had negative belief of use of old clean cloth during menstrual flow. regarding practice, only 40.4% used sanitary pad during their menstrual flow. most (65.1%) of them did not dispose,16.5% bury in nearby ground and 18.4% burn. more than half (60.6%) used soap-water to clean genitalia. remedial measures adopted during menstruation were taking adequate rest (44%), seeking medical advice (22.9%) and drinking plenty of fluid (13.8%). different traditional practice followed were use of separate utensils (64.2%), not allowed to see sun (75.8%), restriction togo outside (71.6%), cook food (56%), usual food intake (56.9%), worship (74.3%), eat with others (27.5%), sleep in usual bedroom (27.5%) and touch male members (28.4%). http://nepjol.info/index.php/bibechana mailto:drsathii@yahoo.com http://dx.doi.org/10.3126/bibechana.v16i0.20960 https://creativecommons.org/licenses/by-nc/4.0/ most (94.5%) of them experienced chaupadi (menstrual shed) during their menarche. the phenomenological approach found that chaupadi was common. they had various infections and ill health. mother groups were advocating to eliminate chaupadi in their locality. conclusion: the know-do gap on menstruation was evident. despite increasing awareness, people were still following traditional cultural practices. keywords:awareness; menstruation; reproductive age group; western nepal. 1. introduction menstruation is a periodic vaginal bleeding occurring every 26 to 30 days in women of childbearing age (15-49 years). it is a matter of both reproductive and environment health [1].onset of menstruation is a unique phenomenon for adolescent girls [2]. nepali society still consider it as a matter of impurity, secrecy and ashamed of being disclosure of their menarche [1,3]. it is considered unclean, and young girls are restricted from participating in household and religious activities during menstruation. these restrictions extend to eating certain foods like jaggery and papaya as well [2,4]. there is a strong traditional belief of staying in an unhygienic place (chhaupadi) for several days, not allowing to see sun, not allowing to touch male members, books, restrictions of entering holy places and cultural taboos with foods, using unclean pads and improper disposal of used pads.(1) it is a traditional practice in which females are forbidden to touch anything and are forced to live in isolation (shed) during menstruation [5].in some areas, women are expected to sleep outside in a tiny hut called a goth until they are clean again. this custom is called chaupadi, derived from two hindu words: chau, meaning menstruation, and padi, meaning women [6]. women often lacks knowledge regarding menstruation and good hygiene practices. hence, are vulnerable to reproductive organs diseases[7]. many adolescents girls are neither informed nor taught in school about menstruation as it is considered a subject not to be discussed [1,7]. a study found that female were not properly maintaining the menstrual hygiene [7]. the limited knowledge available was passed down informally from mothers, who were themselves lacking in knowledge of reproductive health and hygiene due to low literacy levels and socioeconomic status [8]. lack of menstrual hygiene was found to result in adverse outcomes like reproductive tract infections [9]. better knowledge about menstrual hygiene reduced this risk [4]. knowledge regarding puberty change, source of menstrual blood and route of urine and menstrual flow was low. moreover, water and sanitation at school, in workplaces and at home need to be addressed to reduce the need for unhygienic practices and reproductive tract infections. around half of both urban and rural women experience negative impact of peri-menstrual changes. rural women faced more challenges on dos and don’ts on certain activities while menstruating [10].the objective of this study was to find knowledge and practice on menstrual hygiene and perspective of chaupadi (menstrual shed) among the reproductive age group females of maranthana community of pyuthan district, nepal. 2.methodology a community based mixed method study having cross sectional study as quantitative and phenomenological study as qualitative domain was conducted at maranthana community of pyuthan district of mid-western nepal from april 2016-september 2016. sample size was calculated based on a research done at rural nepal where prevalence of menstrual knowledge was found to be 83.3% [11].a convenient sampling technique was used to collect data from 109 households. reproductive age (15 to 49 years) females from each household were selected for interview. five participants who experienced chaupadi were enrolled for phenomenological study. data was collected by means of face-to-face interview using a semi-structured questionnaire. the pre-testing of the question done at simariya community of sunsari district, nepal. s.b. parajuli et al. / bibechana 16 (2019) 228-235: rcost p.230 (online publication: dec., 2018) informed consent was taken and confidentiality of each participants was maintained. the collected data was entered into microsoft excel and analysed by spss and nvivo software. 3. results socio-demography in this study, 109 participants of reproductive age (15-49 years) group female were taken. the mean age of the participants was 24.82 with standard deviation of 8.12 years. majority (65.1%) of them were brahmin/chhetri by ethnicity and all of them were hindu. seven out of 10 had passed secondary level education and married. sixty percent of them were housemaker and from nuclear family (61.5%) having family size of 5.30. average monthly family income was nrs. 20,000. about 62.4% experienced menarche at the age of 13-14 years. status of knowledge on menstruation menstruation has many components. the different knowledge components on menstruation were depicted in table and figure. table 1 illustrates the different knowledge variable of menstruation such as 73.7% were aware on the right age of menarche, 67.9% were aware of menarche before their menstruation, 55% rightly reflect the definition of menstruation. almost 93% were aware on possibility of pregnancy after initiation of menstruation. many of them received information from friends (34.9%) and their mother (33%). table 1: knowledge on different variables of menstruation (n=109). variables yes (%) aware on right age of menarche 73.7 awareness on menarche before their menstruation 67.9 right definition of menstruation 55.0 possibility of pregnancy after initiation of menstruation 93.0 source of information on menarche friend mother sister teacher books 34.9 33.0 22.9 0.9 8.3 regarding knowledge on use of ideal things during menstruation, there was mixed response. the correct method, use of sanitary pad was known to 38.5% of the participants. about 45.9% said use of clean old clothes would be okay followed by any old cloth (11.9%) (figure 1). fig. 1: ideal thing to be used during menstruation (n=109). 38.5 45.9 11.9 3.7 percentage sanitary pads clean old clothes any old clothes others s.b. parajuli et al. / bibechana 16 (2019) 228-235: rcost p.231 (online publication: dec., 2018) in table 2, only 40.4% used sanitary pad during menstruation. regarding disposal of sanitary pad, 65.1% do not dispose,16.5% bury in nearby ground and 18.4% used to burn. only 60.6% used to clean genitalia during menstruation with soap-water. remedial measures adopted during menstruation were taking adequate rest (44%), seeking medical advice if needed (22.9%), and drinking plenty of fluid (13.8%). status of practice on menstruation table 2: modern practices followed on menstruation (n=109). variables yes (%) use of sanitary pad 40.4 disposal methods of sanitary pad (n=44) don’t dispose bury in nearby ground open burning 65.1 16.5 18.4 clean genitalia soap-water water 60.6 39.4 remedial measures adopted during menstruation taking rest seeking medical advice drinking plenty of fluid none 44.0 22.9 13.8 19.3 as in figure 2, different traditional practice adopted were use of separate utensils (64.2%), not allowed to see sun (75.8%), no permission to go outside (71.6%), no permission to cook food (56%), restriction of usual food (56.9%), banned for worshiping god (74.3%), used to eat in separate place (27.5%), not allowed to sleep in usual bedroom (27.5%) and restrict to touch male members (28.4%). most (94.5%) of them experienced chaupadi (menstrual shed) during their menarche. fig. 2: traditional practices during menstruation (n=109). 64.2 75.8 71.6 56 56.9 74.3 27.5 27.5 28.4 94.5 0 10 20 30 40 50 60 70 80 90 100 use of separate utensils not allowed to see sun no permission to go outside no permission to cook food restriction of usual food banned for worshiping god used to eat in separate place not allowed to sleep in usual bedroom restrict to touch male members chhaupadi (menstrual shed) during menarche % s.b. parajuli et al. / bibechana 16 (2019) 228-235: rcost p.232 (online publication: dec., 2018) chaupadi, a worse practice during menstruation was common during menarche. the five participants who had experienced chaupadi were selected for phenomenological study. the mean age of the participant was 27 year and all were literate. all participants had awareness on possible health consequences of chaupadi. four out of five were against the chaupadi practice but one said that this is very difficult to quit this practice today because it has become a part of their culture. they reflected that after few generations, it will automatically vanish. snake bite, animal bite, mental problems, social deprivation, ill health, depression were commonly found health problems during chaupadi. many organisation were working for reproductive health issues in their area but still the wrong practices were prevailed. comparing to past years, the practice of chaupadi was decreasing day by day. more awareness, social inclusion, advocacy are the common factors for decreasing trend of chaupadi. to stop the practice of chaupadi, there was need for more advocacy at individual, family and community level. different mother groups were advocating eliminating chaupadi in their locality. figure 3 depicts the illustration showing chaupadi practice in med-western nepal. different traditional social taboos are reflected through the illustration. phenomenological study findings fig. 3: illustration showing chaupadi system in mid-western nepal. 4. discussion the mean age of the participants was 24.82 years and majority (65.1%) of them were brahmin/chhetri by ethnicity and all of them were hindu. seven out of 10 had passed secondary level education and married. majority (60%) of them were housemaker and from nuclear family (61.5%). this study found that 62.4% experienced menarche at the age of 13-14 years. s.b. parajuli et al. / bibechana 16 (2019) 228-235: rcost p.233 (online publication: dec., 2018) similar result were found in another study where the mean age at menarche was found to be 13.1 year [3] and13.28 years [12]. in a study from saudi arebia, the mean menarcheal age was quite low (12.08 year) [13]. in the present study, 73.7% were aware on the right age of menarche, 67.9% were aware of menarche before their menstruation. almost similar result found in a study where 67.2% knew about menstruation before menarche [3].this study found that, 55% rightly reflect the definition of menstruation. it was more in a study from eastern nepal where 83.3% of girls knew that menstruation is a physiological process [11]. another study found that 36% were aware on definition of menstruation [3]. similarly, another study reported that participants were aware on menstruation as a physiological process (83%) [14]. every nine on ten were aware on possible pregnancy after initiation of menstruation in this study. more than one third of the participants (34.9%) were informed by friends followed by mother (33%) in the present study while in a study from eastern nepal 53.9% participants were taught about menstruation by their mother [11]. in another study, most common informant was mother (39.3%) [3]. mothers were the first informant to 56% girls [12]. this study found that 45.9% had negative belief of use of old clean cloth during menstrual flow. this study found that, 40.4% used sanitary pad during their menstrual flow. another research from eastern nepal reported only 33.3% of the respondents used sanitary pad during menstruation [11]. in this study, most (65.1%) of them did not dispose, 16.5% bury in nearby ground and 18.4% used to burn the sanitary pad. another study found that 29.5% burn, 27.9% dispose in pit or throw somewhere [3]. inanother study it was found that 75% wrap in paper/polythene bag and dispose [12]. in this study, 60.6% used to clean genitalia during menstruation with soap-water where as in another study 66.54% girls were using water to clean genitals during menstruation [15]. remedial measures adopted during menstruation were taking adequate rest (44%), seeking medical advice if needed (22.9%), and drinking plenty of fluid (13.8%) in the present study. this study found that different traditional practice followed were use of separate utensils (64.2%), not allowed to see sun (75.8%), no permission to go outside (71.6%), no permission to cook food (56%), restriction of usual food (56.9%), banned for worshiping god (74.3%), used to eat in separate place (27.5%), not allowed to sleep in usual bedroom (27.5%) and restrict to touch male members (28.4%). different studies from different places found that 55.7% not allowed to cook/touch utensils[3], 43% not allowed to enter kitchen[12], 91.6% restricted from attending religious functions[3], 70% not allowed to enter temple or participate in religious activities [3,12]. about 20 % were not allowed to touch/sit/talk with male member of family[3], 55.7% not allowed to do household chores, 16.4% forced to go away from home or in corner of room[3], 58.4% not allowed to cook and visit temples [7]. this study found that 94.5% experienced chaupadi (menstrual shed) during their menarche which is supported by a study that states that chaupadi practice, was in existence in the midand far-western regions of nepal [5]. phenomenological study from this study too supported that chaupadi was still common. but this kind of trend is decreasing comparing to past studies. dissimilarities were found where some people had desire to continue while some were against this. chhaupadi had led to bad consequences on overall health of women causing various infections, ill health, and even death. hence, it was found that various mothers groups were advocating for elimination of chaupadi from their locality. the nepal supreme court banned chaupadi in 2005 [16] but government regulation does not reach remote western regions [6]. according to a un report in 2011, within the district of accham, 95% of women were practicing chaupadi[17].girls practicing chaupadi will stop attending school every month during this time of personal isolation, therefore sustaining the inequality in education and the stigma surrounding periods. this is due in part to poor access to and knowledge about products such as sanitary pads. there is a general lack of education on menstrual hygiene in nepal, which is a direct result of persistent traditional beliefs and practices [18]. s.b. parajuli et al. / bibechana 16 (2019) 228-235: rcost p.234 (online publication: dec., 2018) families believe that misfortune will be brought on them by the gods if a menstruating woman is allowed in the home or any religious places [19]. in the eyes of many in remote villages of western nepal, ignoring chaupadi would bring ruin to everyone. beliefs on chaupadipersist even when rape and underage pregnancy are the tragic consequence [20]. women died from asphyxiation or burned to death when they built fires in the cramped sheds to shield from the himalayan winter [20]. a legislation passed by the parliament effective from august 2018 stated, “a woman during her menstruation or post-natal state should not be kept in chaupadi or treated with any kind of similar discrimination or untouchable and inhuman behaviour”. anyone who forces a woman to follow chaupadi may face a three month jail sentence or a 3000 nepalese rupee fine or both. the law was effective from august 2018 [21, 22]. the females suffer from physiological, mental and emotional stress. the conditions in the goth are deplorable. the mental, physical and reproductive wellbeing of the females are compromised as they suffer due to poor hygiene, poor nutrition, heavy workload and lack of security. their basic human rights are being denied to them [21]. 5. conclusion the know-do gap on menstruation was evident. despite increasing awareness, people are still following traditional chaupadi culture. recommendations the authors would like recommend meta-analysis and systematic review of menstrual awareness and practices related research conducted in different parts of nepal that could bring the concluding finding. in new federal health system of nepal where local bodies are responsible for developing their health policy, the need of actual awareness and practices on menstruation needs to be explored and act on its solution. limitation of the study we could not asses the different menstrual health problems and its association with knowledge and practice score. the inclusion of more sample would be better to generalization of the findings. acknowledgement authors would like to acknowledge all participants for their support, time and participation without them this study would not have been possible. the author would like to thank local leaders and health care workers for their coordination and support. conflict of interest authors declared no conflict of interest. financial disclosure authors declared no financial support or grant for this research work. s.b. parajuli et al. / bibechana 16 (2019) 228-235: rcost p.235 (online publication: dec., 2018) references [1] a. pradhan a, is menstrual hygiene and management an issue for adolescent school girls? water aid, 2009. 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[7] p. adhikari, b. kadel, s.i. dhungel, a. mandal, knowledge and practice regarding menstrual hygiene in rural adolescent girls of nepal kathmandu university medical journal 5(19) (2007) 382-386 [8] a. dasgupta, m. sarkar, menstrual hygiene: how hygienic is the adolescent girl?. indian journal of community medicine 33(2) (2008) 77–80. [9] m.n. tundia, d.v. thakrar, a study of the menstrual problems and hygiene practices among adolescents in secondary school, thiruvanthepuram indian journal of pediatrics 1 (2012)79. [10] m.l. marván, p. trujillo, menstrual socialization, beliefs, and attitudes concerning menstruation in rural and urban mexican women, health care for women international, 31(1) (2009) 53-67. [11] p. parajuli, n. paudel, s. shresth, knowledge and practices regarding menstrual hygiene among adolescent girls of rural nepal 5(1) (2017) 5. [12] a. kapoor, s. khari, knowledge, attitude and socio-cultural beliefs of adolescent girls towards menstruation 36(1) (2016) 8. [13] s. a. shaik, r.t. hashim , s.f. alsukait, g.m. abdulkader, h.f. alsudairy, l.m. alshaman, et al. assessment of age at menarche and its relation with body mass index in school girls of riyadh, saudi arabia 7(2) (2015) 8. [14] r.n. yadav, s. joshi, r. poudel, p. pandeya, knowledge, attitude, and practice on menstrual hygiene management among school adolescents, journal of nepal health research council 15(3) (2018) 212-6. pmid: 29353891. [15] m.n. tundia, d.v. thakrar, a study on menstrual hygiene practices and problems amongst adolescent girls in udaipur, rajasthan 5(8) (2018) 6. [16] the supreme court of nepal. law against chhaupadi, 2005. [17] united nations resident and humanitarian coordinator’s office, chaupdi in the far-west, 2011. available at: ttps://www.ohchr.org/documents/issues/water/contributionsstigma/others/field_bulletin_issue1_april_2011_-_chaupadi_in_far-west.pdf [18] d.n. bhatta, u.r. aryal, k. khanal, education: the key to curb hiv and aids epidemic, kathmandu university medical journal 11(42) (2013) 158-61. pmid: 24096225. [19] c. sauve, the red huts of nepal. 2014, available at: http://mindthis.ca/red-huts-nepal-isolation-duemenstruation. [20] a. gaelstel, the new york times, 2013. women in nepal suffer monthly ostracization. available at: http://pulitzercenter.org/reporting/nepal-achham-women-chaupadi-menstruation-ostracize-goth-traditionhindu-rape-violence-segregation. [21] meghna, even padman cannot save these women from the practice of chhaupadi, 2018. available at: http://www.legaldrift.com/even-padman-cannot-save-these-women-from-the-practice-of-chhaupadi/. [22] nepal finally criminalises ‘chhaupadi, 2018. available at: http://www.neweurope.eu/article/nepal-finallycriminalises-chhaupadi/. bibechana vol. 20, no. 1, april 2023, 103–112 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar analysis of phytochemicals and biological activities of rhizome of curcuma longa, aerial parts of centella asiatica, and corn silk of zea mays ayusha hyaunmikha, bimala subba∗ central department of chemistry, tribhuvan university kirtipur, kathmandu, nepal ∗corresponding author. email: bimalasubba@gmail.com abstract nepal is a storehouse of medicinal plants. medicinal plants like the rhizome of curcuma longa, the aerial part of centella asiatica, and corn silk of zea mays were used traditionally as medicine for diseases like inflammation, hepatic disorders, cough, etc. in this study, these selected plants were subjected to the analysis of phytochemical constituents, and biological activities following standard methods. phytochemical analysis of the methanolic extract of these selected plants revealed the presence of different chemical constituents such as polyphenols, flavonoids, glycosides, quinones, saponins, and tannins. c. longa rhizomes also showed the strongest dpph radical scavenging activity with ic50 of 55.06 µg/ml which was very close to standard ascorbic acid (49.09 µg/ml) than that of the aerial part of c. asiatica (72.56 µg/ml) and corn silk of z. mays (131.96 µg/ml). total phenolic and total flavonoid content was found highest in c. longa with the values of 195.95 ± 0.899 mg gea/g and 56.45 ± 4.056 mg qe/g respectively. the phenolic and flavonoid content of methanolic extract of aerial parts of c. asiatica was found to be 110.78 ± 1.984 mg gea/g and 30.00 ± 2.358 mg qe/g and corn silk of z. mays were found to be 65.92 ± 1.244 mg gea/g and 18.50 ± 1.424 mg qe/g respectively. the methanolic extract of rhizomes of c. longa exhibited high α-amylase inhibitory activity with ic50 values of 382.30 µg/ml than that of c. asiatica with ic50 value of 520.48 µg/ml and z. mays with ic50 value 593.09 µg/ml. keywords curcuma longa, centella asiatica, zea mays, phytochemical, antioxidant, anti-diabetic. article information manuscript received: march 9, 2023; accepted: april 4, 2023 doi https://doi.org/10.3126/bibechana.v20i1.52006 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction nepal has a huge number of medicinal plants and significant biodiversity, making it a perfect place to find novel medicines. according to world health organization (w.h.o.) research from 2008, traditional medicine is the major source of primary healthcare for the majority of people in the asian region [1]. plants have played a significant role in maintaining human health and improving the quality of human life. as plants contain therapeutic components, they have been used for ages to treat human illnesses [2]. curcuma longa is a perennial herb grown in trop103 http://nepjol.info/index.php/bibechana bimalasubba@gmail.com https://doi.org/10.3126/bibechana.v20i1.52006 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ayusha hyaunmikha and bimala subba/ bibechana 20 (2023) 103-112 104 ical southeast asia [3]. it is commonly known as turmeric in english and besar in nepali. mainly rhizome of c. longa has great medicinal value. in addition to flavoring and coloring food, c. longa rhizome is used for a variety of other uses [4]. rhizome is used in the treatment of various diseases like diabetes, inflammation, alzheimer, analgesic, biliary disorders, anorexia, cough, hepatic disorders, and sinusitis [5, 6]. biological activities of c. longa include those that are anti-bacterial, antiinflammatory, anti-oxidant, anti-coagulant, and anti-diabetic, according to research by bhat et al. (2015) [7]. centella asiatica is a perennial, prostrate, stoloniferous creeper herb that can have an average length of 15 cm. it is also known as "gotu kola" in many other regions of the world and "ghotapre" in nepali. its common names include "madhukaparni" in sanskrit, "brahmi" in hindi. it grows in tropical and subtropical regions and grows widely in different habitats. in nepal, it is found at a height of 96-2200 m above sea level [8]. many pharmacological effects of c. asiatica are thought to exist, including immunomodulatory, memoryimproving, cardioprotective, anti-cancer, antibacterial, anti-inflammatory, antidiabetic, and antioxidant characteristics [8, 9]. zea mays is the second most significant crop grown in nepal [10]. z. mays presents with a long and yellowish stigma known as corn silk is mostly used in clinical practice to treat gonorrhea, prostatitis, urethritis, cystitis, nephritis, and urinary stones [11]. according to b. thoudam et al 2011, the methanolic extract of corn silk had the highest level of antioxidant activity (85.2 mg/ml), while the ethyl acetate extract had the lowest (45.5 mg/ml) [2]. plants in different geographical areas show different biological activities. the extraction process as well as the methodology also impact the result of the research. a literature survey revealed that not much work has been reported on the biological activities of the rhizome of c. longa, the aerial part of c. asiatica, and corn silk of z. mays in nepal. plants differ as per climate which results in different physiological metabolites. so, we intend to choose these three plants for analysis in this study. 2 material and methods 2.1 materials the plant samples (rhizome of turmeric, aerial part of the ghodtapre, and corn silk of maize) were collected from bhaktapur and kathmandu valley based on traditional medicinal value from march to july 2018. the plants were identified by literatures and compared with the voucher specimens deposited at national herbarium and plant laboratories, godavari, kathmandu. 2.2 extraction the gathered rhizome of c. longa, the aerial part of c. asiatica, and corn silk of z. mays were rinsed with distilled water, shaded dried, powered being stored in a clean plastic bag until needed. cold percolation was used for the extraction of methanolic samples of selected plants. about 100 g shade dried ground powder of rhizome of c. longa, the aerial part of c. asiatica, and corn silk of z. mays were kept in a conical flask separately soaked in methanol. the sample was allowed to stand at room temperature for a few days before being filtered and concentrated with a rotatory evaporator. the concentrated filtrate was air-dried to obtain a solid or semisolid residue. the same process was repeated for all other selected plants. after that, the extracts were kept in air-tight vials and stored in a room at cold and dry place. 2.3 phytochemical screening the phytochemical constituent of the selected plant extract was determined using standard protocol [12]. the presence of different phytochemicals was analyzed using different specific reagents. 2.4 antioxidant activity dpph free radical scavenging activity assay was carried out. the ability of the rhizome of c. longa, the aerial part of c. asiatica, and corn silk of z. mays extracts to scavenge dpph free radicals was estimated using protocol [13]. in brief, the stock solution of each extract was prepared in methanol (10 mg/ml). by serial dilution of the stock solution, the plant samples at various concentrations (10–100 µg/ml) were added to a 100 µm solution of dpph in methanol. the absorbance of each solution was determined at 517 nm after 30 min of incubation at 37 ◦c using a uv-visible spectrophotometer. the measurement was performed in triplicates. the efficiency of the dpph free radical scavenging activity was determined by using the following equation: % scavenging = ac − as ac × 100 % where, as is absorbance of sample solution, ac is absorbance of control (dpph solution + methanol). the ic50 value is the effective sample concentration required to neutralize 50% of the dpph free radicals. ayusha hyaunmikha and bimala subba/ bibechana 20 (2023) 103-112 105 2.5 determination of total phenol content (tpc) the total phenolic content of all extracts was determined using the folin-phenol reagent as described by the standard protocol [12]. the plant samples at various concentrations of 0.125, 0.25, 0.5, and 1.0 mg/ml, were prepared by serial dilution of stock solution of plants 10 mg/ml. these diluted solutions were then incubated for 30 minutes with 10% fcr and 7% na2co3, and absorbance was measured at 760 nm about a blank for each concentration. gallic acid was used as a reference compound. the measurement was performed in triplicates. 2.6 determination of total flavonoid content (tfc) using the aluminum chloride colorimetric method with quercetin as a reference, the tfc of each extract was calculated [14]. the plant samples at concentrations of 0.125–1.0 mg/ml, were prepared by serial dilution of stock solution. the absorbance of each quantity of extract was measured at 510 nm against a blank. the measurement was performed in triplicates. 2.7 α-amylase inhibition assay to determine the antidiabetic potential of selected plants, an α-amylase inhibition assay was carried out using a standard protocol with slight modification [13]. the stock solution of each plant extract was prepared in dmso (1 mg/ml). six distinct concentrations of each extract, 1000 µg/ml, 640 µg/ml, 320 µg/ml, 160 µg/ml, 80 µg/ml, and 40 µg/ml were made by serial dilution of the resulting stock solution. similar methods were created for the commonly used acarbose as a standard compound. the blue starch iodine complex, which was detected at 630 nm, was used to identify the undigested starch as a result of enzyme inhibition. the measurement was performed in triplicates. 3 results and discussion 3.1 phytochemical analysis the micro-chemical analysis of a crude extract of the rhizome of c. longa, the aerial part of c. asiatica, and corn silk of z. mays in methanol extract depicted the presence of a class phytochemical as shown in table 1. table 1: result of phytochemical screening of the rhizome of c. longa, the aerial part of c. asiatica, and corn silk of z. mays s. n. phytochemicals curcuma longa centella asiatica zea mays 1. alkaloids + + + 2. flavonoids + + + 3. reducing sugar + + + 4. terpenoids + + + 5. saponins − + − 6. phenolic compounds + + + 7. tannis + + + 8. glycosides + + + 9. coumarins − + + 10. sterols + − + (+) means presence, and (–) means absence the crude extract of the rhizome of c. longa, the aerial part of c. asiatica, and corn silk of z. mays in methanol extract revealed the existence of a class of phytochemicals in the phytochemical study as indicated in table 1. the appearance of certain hues as viewed by a microscope confirmed the existence of phytochemical. literature reveals that the methanolic extract of c. longa consists of bioactive compounds like tannin, glycosides, flavonoid alkaloid saponin, steroids, glycosides, carbohydrates, proteins, starch, and amino acid [15,16]. similarly, c. asiatica methanolic extract comprise bioactive compounds like alkaloids, tannin, flavonoids, phenolics, saponin, glycosides, terpenoids, and steroids [17]. and methanolic extract of corn silk of z. mays contained alkaloids, tannin, flavonoids, phenolics, glycosides, terpenoids, and steroids [2]. the result of preliminary phytochemical screening for the same samples may show some variation due to different environmental factors, methods of collection of samples, time of collection, time for grinding, percolation, lab setup, and chemical grades. 3.2 antioxidant activity the dpph radical assay was carried out for all extracts by using ascorbic acid as standard according to the standard procedure and absorbance was recorded at 517 nm by a spectrophotometer (table 2). ayusha hyaunmikha and bimala subba/ bibechana 20 (2023) 103-112 106 figure 1: a plot of free radical scavenging of methanolic extracts and concentrations of plants, and ascorbic acid table 2: absorbance of dpph radical in different concentrations of ascorbic acid s.n. concentration (µg/ml) absorbance 1 10 0.639 2 20 0.567 3 40 0.429 4 60 0.297 5 80 0.169 6 100 0.061 (each value is a mean of triplicate data) the decrease in absorbance was due to a decrease in the concentration of dpph free radicals since there is a transfer of hydrogen radicals from ascorbic acid to dpph free radicals to form stable dpph-h molecule resulting in decolorization from violet to pale yellow. the plant extracts showed antioxidant properties in the preliminary tests therefore further test of all those extracts were carried out. the control used involved dpph and methanol omitting the sample extracts. accordingly, the % radical scavenging of each plant extract at different concentrations was calculated and listed in table 3. the ic50 values of methanolic extracts of c. longa, c. asiatica, and z. mays were found as 55.06 µg/ml, 72.56 µg/ml, and 131.96 µg/ml respectively (figures 1 and 2). since these values are lower than 100 µg/ml and comparable with ic50 values of the standard; ascorbic acid (49.09 µg/ml), these extracts show remarkable antioxidant activity may be due to the presence of a phenolic group. table 3: percentage of radical scavenging with different concentrations of plants extracts concentration rhizome of aerial part of corn silk of ascorbic acid (mg/ml) c. longa c. asiatica z. mays 10 13.84 9.44 1.29 17.33 20 24.58 12.03 2.71 26.65 40 40.10 29.49 19.92 44.51 60 52.00 41.13 23.80 61.57 80 71.41 55.11 28.71 78.13 the ic50 values of methanolic extracts of c. longa, was found as 55.06 µg/ml. since these values are lower than 100 µg/ml and comparable with ic50 values of the standard; ascorbic acid (49.09 µg/ml), these extracts shows remarkable antioxidant activity. this result is in agreement with the literature study which showed that the highest dpph scavenging activities were shown by the ayusha hyaunmikha and bimala subba/ bibechana 20 (2023) 103-112 107 figure 2: bar graph showing ic50 values of various methanolic plant extracts methanolic extract of c. longa. these scavenging activities of the extract could be related to the lipid–oxidation process, thus contributing to their electron transfer/ hydrogen donating ability [18]. the ethanolic extract of c. asiatica stem extract showed greater free radical scavenging than leaves extract [19]. but in this present study aerial part (stem + leaves) exhibited an anti-oxidant capacity less than c. longa but greater than z. mays. figure 3: calibration curve of gallic acid the literature revealed that the methanolic extract of corn silk of z. mays showed strong antioxidant activity at 85.2 mg/ml which may be due to the presence of phenolic and flavonoid constituents [2]. but the study showed the lower antioxidant capacity of corn silk which may be due to variations in environment, time of collection and methodology. 3.3 total phenolic content (tpc) the total phenolic compound present in the methanolic extract of two different plants was evaluated by using the folin-cocalteu reagent (fcr) according to the standard procedure given involving the gallic acid as standard. the absorbance graph for standard gallic acid is shown in figure 3. tpc values of methanolic extracts of c. longa rhizome, c. asiatica aerial parts, and z. mays corn silk were determined using a calibration curve and absorbance which are shown in the figure 4. from the result obtained from tpc, it has been found that phenolic compounds are a class of antioxidant that acts as the free radical terminator. the highest value of rhizome of c. longa methanolic extract (tpc 195.95 ± 0.89) showed high antioxidant activity than the methanolic extract of c. asiatica, and z. mays (figure 4). this result is in agreement with the literature study which showed that the highest tpc was shown by methanolic extract of rhizome of c. longa (260 ± 0.025 mg/g) [20]. the literature reviewed that the methanolic extract of c. longa was reported to be tpc of 39.38 mg gae/g. the study value is slightly lower than the reported value of literature review which could be due to variations in environmental conditions or may be due to the presence of other secondary metabolites or may be due to differences in ayusha hyaunmikha and bimala subba/ bibechana 20 (2023) 103-112 108 figure 4: tpc values of three plant samples figure 5: calibration curve of quercetin extraction methodology [18]. the therapeutic properties of c. asiatica may potentially be attributed to the presence of phenolic compounds as research in the literature revealed that phenolic compounds are the major contributors to the antioxidant activity in plants and that these compounds are also effective hydrogen donors, making them good antioxidants [21]. it was discovered that the tpc of the corn silk extract in this investigation (tpc 272.81 mg gae/100mg) was lower than the corn silk extracts reported by literature studies. this difference in tpc could be attributed to an environmental variable [22]. 3.4 total flavonoid content (tfc) according to the standard protocol and using quercetin as the reference standard, the total flavonoid compound found in the methanolic extract of selected plants was calculated. the absorbance vs concentration curve for the standard is shown in figure 5. tfc values of methanolic extracts of c. longa rhizome, c. asiatica aerial parts, and z. mays corn silk were determined using a calibration curve and absorbance which are shown in table 5. from the result obtained from tfc, it has been found that phenolic compounds are a class of antioxidant that acts as the free radical terminator. the highest value of rhizome of c. longa methanolic extract (tfc 56.45 ± 4.05) showed high antioxidant activity than the methanolic extract of c. asiatica, and z. mays (figure 6). the literature revealed that the methanolic extract of c. longa indicated the most abundant flavonoid content which supports to have several biological activities such as antimicrobial and protective compounds against plant disease [18]. methanolic extract of the rhizome c. longa contained tfc (79.36 ± 0.01), which is slightly higher than the value of this study [20]. this may be due to variations in the time of collection and environment. the presence of rutin, catechin, and quercetin in the c. asiatica leaf, root, and petiole resulted in a higher concentration of flavonoids, according to the literature [23]. higher tfc in methanolic extract contributed to a strong scavenging activity which is thought to give higher antioxidant activity. methanolic extract of corn silk showed higher tfc than water extract [22]. but in this study, the methanol extract of corn silk of z. mays showed lower tfc. the difference in result may be due to variations in altitude, and in time of collection of samples. ayusha hyaunmikha and bimala subba/ bibechana 20 (2023) 103-112 109 figure 6: total flavonoid content of different methanolic plant extracts figure 7: comparison of α-amylase inhibition % between acarbose and methanol extract of c. longa 3.5 α-amylase inhibition activity the anti-diabetic properties of methanolic extract of c. longa, c. asiatica, and z. mays were measured by taking acarbose as standard, and ic50 values were also calculated. to assess the anti-diabetic potential of chosen samples, a starch-iodine assay for α-amylase inhibition was performed. percentage inhibition of α-amylase by different concentrations of plant extracts and acarbose were calculated and these data were tabulated below table 4. the above result in table 4 demonstrated that selected plant extracts show amylase inhibition activity and there is concentration-dependent increase in inhibition percentage. c. longa extract had higher % inhibition of 80.62 at 1000 µg/ml than the c. asiatica and z.myas. acarbose as standard drug had % inhibition of 91.23 at 1000 µg/ml. ic50 values were calculated using graph obtained by plotting % inhibition against concentration and results are shown in table 7. thus, the methanolic extract of c. longa showed a lower ic50 value than that of c. asiatica and z. mays. the ic50 value of the standard was found as 85.43 µg/ml. the ic50 value of c. longa was found as 382.30 µg/ml which showed a higher antidiabetic property than that of c. asiatica and z. mays. the literature revealed that some bioactive compounds such as flavonoids, phenolic acid, and steroids are known to be bioactive antidiabetic principles. c. longa having terpenes, alkaloids, flavonoids, phenols, and sterols showed potent inhibitory activity towards alpha/beta-glucosidase [4]. in the previous study, the triterpenes compound is responsible for the biological activity of c. asiatica, and asiaticoside one of triterpene showed an activity as an antidiabetic agent [24]. the literature revealed that c. asiatica leaves possess significant antidiabetic activity [25]. but the research did not show the antidiabetic activity of the aerial part c. asiatica this may be due to variations in environment and time of collection. the methanolic extract of corn silk of z. mays showed lower antidiabetic activity than other plant extracts. this result correlates well with the fact that it possessed lower antioxidant capacity and lower phenolics. however, the percentage inhibition (64.94 ± 0.26) was not bad at 1000 µg/ml concentration. this may be due to the availability of phytochemicals like alkaloids, tannins, flavonoids, ayusha hyaunmikha and bimala subba/ bibechana 20 (2023) 103-112 110 figure 8: comparison of α-amylase inhibition % between acarbose and methanol extract of c. asiatica figure 9: comparison of α-amylase inhibition % between acarbose and methanol extract of z. mays phenolics, glycosides, terpenoid, and steroids which could be responsible for the antidiabetic potential of corn silk. the literature revealed that hexane and methanolic extract of corn silk inhibited the α-glucosidase with ic50 value ranges of 31.6 ± 0.4 µg/ml to 35.7 ± 0.6 µg/ml [26]. 4 conclusion the methanolic extracts of the three chosen plants were subjected to phytochemical analysis in this study, which revealed several chemical constituents, including polyphenols, flavonoids, glycosides, saponins, and tannins. thus, it can be concluded that the selected plants are rich in secondary metabolites. the methanolic extract of rhizome of c. longa demonstrated the strongest dpph radical scavenging action with an ic50 value of 55.06 µg/ml which is similar to standard ascorbic acid (49.09 µg/ml). the outcome showed that the highest total phenolic content was in c. longa (195.95 ± 0.899 mg gae/g) extract followed by the aerial part of c. asiatica (110.78 ± 1.984 mg gae/g extract). the extract which showed the lowest content of total phenol was z. mays (65.92 ± 1.244 mg gae/g). the total flavonoid content (56.45 ± 4.056 mg qe/g) was highest in the extract of c. longa among other plant extracts. among the setable 4: α-amylase inhibition % by different concentrations of plant extracts and acarbose concentration acarbose c. longa c. asiatica z. mays (mg/ml) (rhizome)(in %) ( aerial part) inhibition ( corn silk) 1000 91.23 ± 0.31 80.62 ± 1.04 71.47 ± 0.55 64.94 ±0.26 640 85.69 ± 0.23 69.39 ± 0.02 63.12 ± 0.16 57.55 ± 0.21 320 76.89 ± 0.34 64.74 ± 1.35 50.3 ± 0.45 42.67 ± 0.09 160 69.43 ± 0.65 53.41 ± 0.50 36.63 ± 1.03 36 ± 0.25 80 63.69 ± 0.54 31.11 ± 0.84 23.30 ± 0.53 25.82 ± 0.40 40 56.60 ± 0.31 23.75 ± 0.50 19.49 ± 1.20 17.94 ± 0.16 (each value is a mean of triplicate data) ayusha hyaunmikha and bimala subba/ bibechana 20 (2023) 103-112 111 figure 10: inhibition % vs concentration graph for acarbose table 5: comparison of ic50 values of plant extracts with the standard for α-amylase inhibition s.n. sample ic50 (µg/ml) 1 acarbose 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[23] mk mohd zainol, a abdul-hamid, f abu bakar, and s pak dek. effect of different drying methods on the degradation of selected flavonoids in centella asiatica. international food research journal, 16(4):531–537, 2009. [24] eka fitrianda, elin yulinah sukandar, elfahmi elfahmi, and i ketut adnyana. antidiabetic activity of extract, fractions, and asiaticoside compound isolated from centella asiatica linn. leaves in alloxan-induced diabetic mice. asian journal of pharmaceutical and clinical research, pages 268–272, 2017. [25] pk chauhan, ip pandey, and vinod kumar dhatwalia. evaluation of the anti-diabetic effect of ethanolic and methanolic extracts of centella asiatica leaves extract on alloxan induced diabetic rats. adv biol res, 4(1):27–30, 2010. [26] e adewole, a ojo, ao omoaghe, la enly, gs njateng, z sumera, and i jamshed. antidiabetic potential of corn silk extracts, identification and drug properties of bioactive compounds. trends med, 18(6):1–7, 2018. introduction material and methods materials extraction phytochemical screening antioxidant activity determination of total phenol content (tpc) determination of total flavonoid content (tfc) -amylase inhibition assay results and discussion phytochemical analysis antioxidant activity total phenolic content (tpc) total flavonoid content (tfc) -amylase inhibition activity conclusion bibechana vol. 20, no. 1, april 2023, 46-54 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar fabrication of uv sensing transistor based on transparent polycrystalline zinc oxide thin film using polymeric electrolyte gate dielectric rishi ram ghimire1, yam prasad dahal2 and krishna bahadur rai1,∗ 1department of physics, patan multiple campus, tribhuvan university, nepal 2department of physics, bhaktapur multiple campus, tribhuvan university, nepal ∗corresponding author. email: krishnarai135@gmail.com abstract the fabrication of electric double layer thin film transistors (edltfts) using polymeric electrolyte as gate dielectric on chemically grown polycrystalline zno thin film channel has the lower threshold voltage at 0.4 v and the saturation current at 3 µa in the dark. the lower threshold voltage is -1 v and the saturation current is 10 µa in the uv illumination. in the dark and under uv light, the off state id is 1 na and 0.3 µa respectively and under gate and uv illumination the on current shows more than 3 times enhancement. this improvement in photocurrent is due to the combined effect of gate and uv illumination. the field effect mobility of the tft is 0.06 cm2/vs in the dark and 0.16 cm2/vs under uv illumination. this increase in mobility under illumination and gate bias is due to the increase in carrier concentration and reduction of charged defects in the channel length. keywords zinc oxide, thin film transistor, electric double layer, photocurrent, field effect mobility. article information manuscript received: january 25, 2023; accepted: march 31, 2023 doi https://doi.org/10.3126/bibechana.v20i1.51788 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction low voltage operation thin film transistor (tfts) based on wide band gap semiconductor with controllable high carrier density is of considerable interest for a variety of inexpensive electronics and optoelectronic applications [1–3]. zinc oxide (zno) a wide band gap (3.3 ev) direct semiconductor having large exciton binding energy (60 mev) is one of such promising materials for many applications such as ultra mobile pcs, smart windows, transparent tablet and paper thin display etc. [4]. zno has many advantages over amorphous silicon base transistor such as high carrier mobility, high optical transparency, mechanical flexibility and processing versatility [5, 6]. high transmittance thin film transistor is becoming an important device in the display industries [7, 8]. one of the big challenges in present transistor technology is to increase the maximum attainable carrier density for high performance of the device. the chemical doping to increase the charge carrier is not suitable due to its unnecessary complexity in the physical properties of the material [9, 10]. conventional metal dielec46 http://nepjol.info/index.php/bibechana krishnarai135@gmail.com https://doi.org/10.3126/bibechana.v20i1.51788 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ rishi ram ghimire et al./ bibechana 20 (2023) 46-54 47 tric gates have relatively low dielectric constants and have the limitation of charge density accumulation [11]. therefore, the new idea for realizing the field induced surface charge density in field effect transistor is of great importance and urgency. the recent idea to modify the performance field effect transistor named electric double layer (edl) have been employed for attaining the high carrier density by using polymeric electrolyte gates [11,12]. an edl can be considered as a nano-gap capacitor with capacitance higher than that of sio2 and al2o3. previous authors have reported many results that the typical sheet carrier density attainable in conventional metal insulator semiconductor is <1x1013 cm−2. that is less than edl zno thin film transistor (tfts) (∼4x1014) [11, 13]. in contrast to the above, the combined effect of the gate bias and light in charge accumulation properties at room temperature on the standard oxide semiconductor zno have been investigated in few numbers and where this combined effects can be more significant than individual one in polycrystalline zno electric double layer thin film transistor (edltfts). many researchers fabricated tft using edl gate dielectric in single crystal or texture film however very few groups reported fabrication of tft using polymer electrolyte on chemically grown polycrystalline zno film for gate controlled uv detection. in this report the gate, controlled tft based uv detector shows three-order enhancement of drain current near the threshold voltage under uv illuminations. this large enhancement of drain current can be achieved due to the simultaneous generation of charge carrier in the presence of gate bias and uv illumination. for this, we have explored the possibility of fabrication of transparent poly crystalline zno tfts using polymeric electrolyte gate dielectric in which the switching action of the transistor requires ionic motion. here, our main interest is the control of conductivity of the tft channel by the modulation of surface charge density using gate bias and uv illumination. 2 materials and method 2.1 preparation of precursor solution and substrate cleaning zinc acetate dehydrate [zn(ch3coo)2.2h2o)] of sigma aldrich company with purity 99.9% was first dissolved in 50 ml of isopropyl alcohol [(ch3)2choh] of same sigma aldrich company with purity 99.7% . the resultant precursor solution was mixed through a magnetic stirrer at 65°c for 2 hrs. in this experiment, the final white precipitate of precursor is slowly dissolved when this mixture was mixed with diethanolamine (dea) drop wise. finally transparent clear solution was obtained as precursor for film coating on glass substrate. the glass substrate was ultrasonically treated for 30 min. in acetone and alcohol and dried on hot plate. figure 1: the flow chart of the procedure for preparing zno thin films. figure 2: schematic diagram of polymer electrolyte gated edltfts on zno surface. rishi ram ghimire et al./ bibechana 20 (2023) 46-54 48 (a) (b) figure 3: afm images of (a) 1 µm x 1 µm and (b) 5 µm x 5 µm of zno film annealed at 450°c. figure 4: particles distribution of afm image in histogram. 2.2 film growth the substrate was spin coated with sol at speed 3000 rpm for 30 sec. in air. each coating on the substrate was heated at 200°c for 10 min. in air. and the same process was repeated for various thicknesses. at last, zno thin films on the glass substrate was made ready by annealing at temperature 450°c for 1 hour. the following figure 1 shows the flowchart of the various steps of the zno thin film growth. 2.3 fabrication of edltft zno device fig. 2 shows the schematic diagram of edltfts. the electrical properties of zno tft were investigated in side-plane gate configuration. polyethylene oxide: lithium per chlorate (10:1) (peo/liclo4) [14] is used for a gate insulator whereas ti/au electrodes are evaporated on the film to fabricate source, gate and drain contacts for field effect transistor (fet) structure. the contact pads are designed using hard mask during thermal evaporation. in this device, its channel width to length ratio (w/l) is ≈ 0.25. 3 results and discussion the surface morphology of the chemically grown zno film was studied by atomic force microscopy. the phase images in scan range 1 µm x 1 µm and rishi ram ghimire et al./ bibechana 20 (2023) 46-54 49 figure 5: x-ray diffraction pattern of zno film figure 6: tauc plot from uv-vis analysis of a zno thin film to evaluate the band-gap at the x-axis intercept. 5 µm x 5 µm are depicted in fig. 3(a) and (b) respectively. the afm image analysis also confirmed that thus chemically grown films have some voids and porosity. the surface roughness of the zno film was observed about 5 nm. fig. 4 depicts the size distribution of the particles within area 1 µm x 0.5 µm. the average grain size was observed about 50 nm. fig. 5 illustrates the diffraction pattern of the film. the pattern shows all the promising peaks for different angle of diffraction. this indicates that the polycrystalline nature of the film. here it is observed that there are three main peaks in the x-ray diffraction pattern which are (100), (002) and (101) which indicate that the film are polycrystalline and randomly orientated [10, 15]. the polycrystallinity is expected due to the lack of epitaxial relationship between zno and the glass substrate. further the low deposition temperature to suppress the columnar growth also lead to polycrystallinity in the zno film [16]. the most preferential growth direction is along (002). the c/a ratio of the film is observed to be 1.6. experimental value is consistent with the theoretical value. fig. 6 shows tauc plot from uv-vis analysis of zno thin film to evaluate the band-gap after taken the absorption spectra of the film. the absorption of zno film was observed in uv region. in the spectra, sharp absorption occurs around 385 nm. the absorption edge corresponds to the intrinsic band gap of the zno. the information about the band gaps were obtained by analyzing dependence of the absorption coefficient on photon energy in the high absorption region. the optical band gap of the film was determined from the absorption spectra by the rishi ram ghimire et al./ bibechana 20 (2023) 46-54 50 figure 7: schematic illustration of electric double layer on zno channel. figure 8: sample on probe station. using the following tauc relation [17–19] (αhν) = a(hν − eg) m (1) where a is energy independent constant, h is plank’s constant, eg is the optical band gap and m is a constant that determines the type of transition. its value is taken 2 for indirect and ½ for direct transition. the band gap of the film was observed 3.22 ev. 3.1 characterization of electric double layer (edl) zno tft in this study, carriers are accumulated at sourcedrain channel with an edl by the application of the gate voltage. fig. 7 illustrates the formation of the electric double layer by using polymer electrolyte on the zno channel. when a positive bias is applied to the gate electrode, the mobile anion of the electrolyte move towards the positively charged electrode whereas the cation is moved towards the channel gate insulator interface. thus electric double layers are formed at two interfaces of the polymeric electrolyte gate material. these layers act as a nano-gap capacitors [1, 11] with high capacitance more than the conventional metal dielectric gate capacitance and able to induce the large surface charge density [14, 20–22]. the principal aim of using the polymer electrolyte is to enhance and control the charge carrier density in channel layer. the figure 8 shows the sample mounted on four probe station to the transistor characteristics in air. in this figure, s represents the source, d represents the drain and g represents the gate in tft of zinc oxide. the transfer characteristic of edltfts is measured by using kiethly source meter 2400 at room temperature. the edltfts operates as an n-channel enhancement mode device i.e. a positive gate voltage is required to induce the conducting channel. fig. 9 shows transfer curve (gate voltage vgs versus drain current id) measured at a drain voltage vds of 10 v. at low gate voltage (<1 v), the rishi ram ghimire et al./ bibechana 20 (2023) 46-54 51 figure 9: transfer characteristic (id, ig vs. vgs in dark and uv illumination). figure 10: drain characteristic with applied voltage vgs 0 to 9 v under dark (with scan speed 0.5 v/min.) channel is highly resistive, the value of resistivity is observed ≈ 3x106 ωcm. we observed the linearly increase in id above the thresh hold voltage (i.e. -1 v for uv and 0.4 v for dark). at low gate bias voltage, the gate current (ig) is very low or negative which is not shown in the graph. as the gate bias voltage increases positively, the ig also increases but still the value of ig is almost less than 3 order magnitude of the drain current at on state. this confirms that the performance of the device is not affected by the leakage current and also clearly demonstrates the n-type fet action. above the vgs >8 v, the ig starts to increase abruptly which notifies leakage ig and leads to change the drain current. this suggests that the polymer electrolyte gate dielectric is not suggestable to bias above 8v. the maximum current (id = 3 µa) is obtained at vgs= 10 v in the dark with width to length ratio (≈ 0.25) of the device. the role of gate bias voltage is to increase the no. of charge carriers, therefore the corresponding drain current is also increased without any significant change in gate current. this phenomenon occurs with increasing the gate voltage up to certain limit up to 8 v and saturated. that means no further change in carrier density in channel length due to the gate electric field. the on off ratio of the device is 103 and 30 in dark and uv illumination respectively. the lower threshold voltage at 0.4 v and saturation current at 3 µa is observed in dark, whereas the lower threshold voltage at -1 v and saturation current at 10 µa is observed in uv illumination. the off state id is 1 na in dark and 0.3 µa in uv illumination. this large change in off state current during illumination is due to the band edge absorption of the zno nanostructure thin film [14, 20, 21, 23]. the important observation of the experiment is the enhancement of the photocurrent under uv illumirishi ram ghimire et al./ bibechana 20 (2023) 46-54 52 figure 11: drain characteristic with applied voltage vgs 0 to 9 v under uv illumination (with scan speed 0.5 v/min.) nation due to the combined effect of gate and illumination. under gate and uv illumination, the on current shows more than 3 times enhancement and saturates about 10 µa. therefore, the charge carrier is increased by more than 3 times with combined effect of gate and uv light in on state. the charged defects states are neutralized by these field induced and light generated charge carriers which leads to enhance the filed effect mobility in the channel [21,24,25]. the transconductance (gm) of the edltfts is calculated from an (id) -vgs curve by using the following equation in active mode or saturation regime (vgs > vth and vds≥ (vgs – vth) [2]. gm = δid δvgs = (w/l)cinµfevgs (2) here w and l are the length and width of the channel, cin is the capacitance of the electrolyte zno interface and µfe is the field effect mobility. transconductance (gm) of 4.5x10−7 s is obtained in the edltfts with a source drain voltage of 10 v and gate bias 5 v in dark. in uv illumination, it is observed 1.21x10−6 s. from above calculation, the field effect mobility of the tft in dark is observed 0.06 cm2/vs and that of under uv illumination is 0.16 cm2/vs. this increase in mobility under illumination is due to the increase in carrier concentration in the channel length. fig. 10 and 11 shows the drain characteristatic of edltfts in dark and uv illumination respectively. the output characteristatic showed the typical saturation behaviour at low bias voltage i.e. vgs<5 v in dark and above that gate bias voltage, the drain current is linear. however, under uv illumination, the drain current is not perfectly saturated even at low gate voltage i.e. at vgs<8 v. this unsaturated behiour of drain current is due to the generation of huge charge carriers under band gap illumination. the ohmic behaviour emerged for vgs>5 v in dark and vgs>8 v under uv illumination. 4 conclusion the overall results and discussions show possibility of fabrication of edltfts by using polymeric electrolyte as gate dielectric on chemically grown polycrystalline intrinsic zno thin film channel. in the dark, the lower threshold voltage is 0.4 v, and the saturation current is 3 µa, whereas in uv illumination, the lower threshold voltage is -1 v, and the saturation current is 10 µa. the high on off ratio (≈103 in dark and 30 in uv illumination ) is achieved in the experiment by in plane gate configuration. in the dark and under uv light, the off state id is 1 na and 0.3 µa, respectively. this large change in off state current during illumination is due to the band edge absorption of the zno nanostructure thin film. in addition to this, under band gap wavelength illumination, the on current shows more than three times enhancement showing that the device can be controlled electrically by a gate as well as uv light. the important observation of the experiment is the improvement in photocurrent under uv light brought on is by the combined effects of the gate and uv illumination. the field effect mobility of the tft is 0.06 cm2/vs in the dark and 0.16 cm2/vs under uv illumination. the increase in carrier concentration in the channel length is the cause of the increased mobility under illumination. acknowledgement the authors thank to department of physics, patan multiple campus for their valuable supports and rishi ram ghimire et al./ bibechana 20 (2023) 46-54 53 suggestions. we also acknowledge s. n. bose national centre for basic sciences, kolkata and nast, nepal for afm, xrd, uv-visible spectroscopy and electrical measurements. references 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lett., 103:231105–5, 2013. 10.1063/1.4838656 [24] s. mondal, r. r. ghimire, a. k. raychaudhurib. mobility enhancement in electric double layer gated n-zno ultraviolet photodetector by synergy of gate and illumination: a photo hall study. appl. phys. lett., 106:041102–4, 2015. 10.1063/1.4906598 [25] m. k. hota, et al. electrochemical thin-film transistors using covalent organic framework channel. adv. funct. mater, 32(23):2201120, 2022. 10.1002/adfm.202201120 https://doi.org/10.5012/bkcs.2010.31.01.112 https://doi.org/10.1063/1.4975209 https://doi.org/10.1063/1.4914518 https://doi.org/10.1038/s41578-022-00473-6 https://doi.org/10.1063/1.4838656 https://doi.org/10.1063/1.4906598 https://doi.org/10.1002/adfm.202201120 introduction materials and method preparation of precursor solution and substrate cleaning film growth fabrication of edltft zno device results and discussion characterization of electric double layer (edl) zno tft conclusion bibechana 19(1-2) (2022) 68-74 68 study preferred alignments of angular momentum vector of i – magnitude sdss galaxies having redshift 0.54 – 0.60 shiv shankar prasad sah*, shiv narayan yadav department of physics, patan multiple campus, t.u., patan dhoka, lalitpur, nepal *email: shivshankarphysics@gmail.com article information: received: july 29, 2021 accepted: february 25, 2022 keywords: sdss galaxy cluster redshift angular momentum vector ism abstract we present a study of the three-dimensional orientation of spin vector of i – magnitude having higher redshift ranging from 0.54 to 0.60 with respect to the equilateral co-ordinate system. the main aim of this work is to know the orientation and projection of the spin vector of distant galaxies. the database is taken from sdss 14th data release (dr-14) and this redshift range contains 239,209 galaxies. sdss provides two – dimensional observed data, we convert it into three-dimension rotation axes of the galaxy with the help of the ‘position angle inclination method’. the expected isotropy distribution curves are obtained by removing the selection effects and performing a random simulation generating 107 virtual galaxies. to check, isotropy or anisotropy we have to carry out four statistical tests: chi-square, auto-correlation coefficient, first-order fourier series, and first-order fourier probability. in the study, we observed random orientation of spin vector of galaxies in all twenty samples and supported a strongly hierarchy model of galaxy evolution. also, the projection of spin vector is found to be isotropic in samples i01, i02, i03, i16, i17, i18, i19, and i20 and the remaining samples i04 to i15 are seen as local anisotropic due to the merging phenomenon of galaxies and tidal effect. this shows the problem in a coordinate system. doi: https://doi.org/10.3126/bibechana.v19i1-2.46389 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal https://doi.org/10.3126/bibechana.v19i1-2.46389 https://creativecommons.org/licenses/by-nc/4.0/ sah and yadav / bibechana 19(1-2) (2022) 68-74 69 1. introduction generally, all human beings think that how the universe was created or formed? this is a very interesting question or most active research work nowadays because there is no exact answer to this question was found to date. astrophysicists day by day carried on their research work to know the evolution of stars, galaxies as well as the entire universe. several authors were given different ideas about the creation or evolution of the universe. several theoretical models like hierarchy model, li model, ostriker model, pancake model, primordial vorticity model etc. was predicted which is based on their own assumption, but none of them is suitable to convince all physicist. one of the most important models which almost believe maximum astrophysicist are big-bang model. this model suggests that before the big bang space and time existed, and the entity of the universe was believed to be compressed into a singularity called space-time singularity [1]. the processes of galaxies evolution are not well understood to date. one of the main reasons is that they are made of three very different entities: stars, an interstellar medium and dark matter. galaxies contain a varying number of star systems, star clusters, and types of the interstellar medium of gas, dust and cosmic rays. the observable universe contains probably more than 170 billion galaxies [2]. the majority of galaxies are gravitationally organized into groups, clusters, and superclusters. from the formation of the first galaxies, and the way galaxy changes over a period of time the study of galaxy evolution and formation is mainly concerned with the processes that formed a heterogeneous universe from a homogeneous beginning and i think we all know it is one of the active areas of astrophysics where all the astrophysicists are concerned [3]. this paper is arranged in such a way that we present theory and formalism in section 2, methods of analysis are presented as in section 3, section 4 contains results and discussions and finally, the conclusion of this paper is presented as in section 5. 2. theory and formalism according to wiezsacker [1] and gamow [2], in order to know the origin of the spin vector of galaxies, the observed rotation of the galaxies is very important. there are only a few theories, which can describe the origin and evolution of stars, galaxies, superclusters etc., each of them with its different strengths and weakness, assumptions and predictions, especially the theories about galaxy cluster formation. there are three models which described strongly the three-dimensional orientation of spin vectors of the galaxies which are ‘pancake model’[4,5] predicts that the angular momentum vectors of galaxies are distributed primarily in parallel alignment to the reference plane, ‘primordial vorticity model’ [6-8] described that the spin vectors of galaxies tend to lie perpendicular alignment to the reference plane and ‘hierarchy model’ [9] gives the directions of the spin vectors are random alignment to reference plane. godlowskian transformation the ‘position angle inclination’ method is used to know the three-dimensional information about the orientation of the spin vector with respect to any arbitrary coordinate system (in our study equilateral coordinate system). this method was introduced by flin and godlowski [10] and it is used to calculate the orientation of the spin vector using the position angle and the inclination of the galaxy plane with respect to the equilateral plane. the polar angle (θ) and azimuthal angle (ϕ) are used to express the three-dimensional orientation of the spin vector of a galaxy by using a reference coordinate system and the polar angle (θ) is the angle between the spin vector of the galactic plane and an equilateral plane and azimuthal angle (ϕ) is the angle between the projection of a galactic spin vector onto the equilateral plane and the reference line within this plane. for equilateral co-ordinate system, the relation of θ and ϕ are given by sinθ = − cosi sinδ ± sini sinp cosδ ………………. (1) 𝑠𝑖𝑛𝜙 = −𝑐𝑜𝑠𝑖 𝑐𝑜𝑠𝛿 𝑠𝑖𝑛𝛼 + 𝑠𝑖𝑛𝑖 (∓𝑠𝑖𝑛𝑝 𝑠𝑖𝑛𝛿 𝑠𝑖𝑛𝛼 ∓ 𝑐𝑜𝑠𝑝 𝑐𝑜𝑠𝛼) 𝑐𝑜𝑠𝜃 ……………………… (2) where, i is the inclination angle, α is right ascension, δ is declination and p is position angle. the inclination angle is obtained by using holmberg formula [11] 𝑐𝑜𝑠2 𝑖 = 𝑞2−𝑞∗2 1−𝑞∗2 …………………… (3) where, q is the axial ratio (b/a) and q* is the intrinsic flatness of the galaxy. in the present work, we used q* = 0.05 for morphologically identified spiral galaxies. 3. method of analysis the database used in our present work involved galaxies with the survey region of sloan digital sky survey (sdss) those have redshift in the range 0.54 to 0.60. this database is taken from sdss 14th data release (dr-14) which contains 239,209 galaxies in our study region which have in the petro-magnitude range from 14.47 to 34.61. among these petro-range, we couldn't take galaxies with the magnitude less than 18.0 and above 22.0 because in this region galaxies distribution is very poor. now, we classified our total database of galaxies in the petro-magnitude range from 18.0 to 22.0 into 20 sample with the equal class interval of width 0.2. all 20 samples contain more than 50 galaxies individually which is suitable for study. the position and inclination angles generated by sdss survey contained more error in the results. theoretically, it is found that polar angle has cosine isotropic distribution curve whereas azimuthal angle has average isotropic distribution curve, with the condition that the database is taken free from selection effects. sdds survey database contains positional and inclination selection effect and that cause several changes in the expected isotropic distribution curves, so to remove such type of effects numerical simulation method is used which was proposed by aryal & saurer [12, 13]. in the numerical simulations, i can be distributed as α sin i, δ can be distributed as α cos δ and the variables α and p can be distributed randomly due to sah and yadav / bibechana 19(1-2) (2022) 68-74 70 the projection effects and the equations (1to 3) can be used to calculate the corresponding values of θ and ϕ. to define expected isotropic distribution curves, we used numerical simulations including 107 virtual galaxies for both θ and ϕ distributions. matlab 15a is used to write programme and input files for the simulation. galaxy clusters do not provide perfect alignment when viewing at pictures, so statistical analysis is important to check preferred alignments. in this work, we used four statistical tests: the chi-square, auto-correlation coefficient, fourier series and first order probability tests. the conditions for isotropy with the reference of godlowski [10, 14] are as follows: a. the value of chi-square probability is p(> χ2) > 0.050 b. the value of correlation coefficient lies in c/σ(c) = -1 to +1 c. the value of first order fourier coefficient lies in 𝛥11 /σ( 𝛥11) = -1.5 to + 1.5 and d. the value of first order fourier probability is p(>∆1) > 0.150, otherwise angular momentum vector is anisotropic. 4. results and discussion the polar angle (θ) gives the orientation of the spin vector of galaxies whereas the azimuthal angle (ϕ) gives the projection of spin vector of galaxies. our aim is to study the random effects concerning i-magnitude dependence of spin vectors of galaxies. for the isotropic distribution of spin vectors, the four statistical tests with isotropic range are already described in section 3. in the polar angle (θ) distribution a significant negative value of first-order fourier coefficient suggests that the angular momentum vectors of galaxies tend to be oriented perpendicular with respect to a reference coordinate system and supports ‘primordial vorticity model’ of galaxy evolution [6-8]. similarly, a significant positive value of the first-order fourier coefficient suggests that the angular momentum vectors of galaxies lie in parallel alignment to the equatorial coordinate system and support ‘pancake model’ [4,5]. also, the statistics for the azimuthal angle (ϕ) distribution, a significant positive value of first-order fourier coefficient (∆11/σ(∆11)) predicts that the projections of the spin vector of galaxies tend to lie radially towards the center reference plane. similarly, a significant negative value of (∆11/σ(∆11)) implies that the projection of the spin vector of galaxies tends to lie tangentially with the reference plane. we also study the ‘humps’ (the region where observed distributions are more than that of expected distributions) and ‘dips’ (the region where observed distributions are more than that of expected distributions) in the polar and azimuthal angle distributions. table 1 and table 2 respectively show the statistics of polar angle (θ) and azimuthal angle (ϕ) distributions of galaxies for all twenty samples. table 1: table showing the statistics of polar angle (θ) distribution of galaxies in twenty sample. the first column represents the sample, second column p(>χ2) represents the chi-square probability, third column c/c(σ) represents the auto-correlation coefficient, fourth column ∆11/σ(∆11) represents the first order fourier coefficient and last column represents first order fourier probability p(>∆1). sample p(>χ2) c/c(σ) ∆11/σ(∆11) p(>∆1) sample (i01) 0.864 +0.0 +0.0 0.999 sample (i02) 0.092 -0.5 +0.4 0.877 sample (i03) 0.767 -0.9 +0.1 0.994 sample (i04) 0.679 -0.6 +0.1 0.993 sample (i05) 0.276 -0.5 +0.1 0.980 sample (i06) 0.477 -0.0 +0.8 0.511 sample (i07) 0.812 +0.5 -0.2 0.001 sample (i08) 0.440 +0.3 +0.3 0.898 sample (i09) 0.415 +0.2 +1.5 0.106 sample (i10) 0.029 +0.7 +0.5 0.798 sample (i11) 0.313 -0.6 +1.2 0.223 sample (i12) 0.840 +0.1 -0.9 0.018 sample (i13) 0.336 -1.2 +0.3 0.937 sample (i14) 0.374 -0.8 -0.6 0.743 sample (i15) 0.639 +0.3 -0.2 0.957 sample (i16) 0.733 -1.3 +0.0 0.997 sample (i17) 0.423 -1.2 +0.2 0.971 sample (i18) 0.729 -0.2 -0.4 0.885 sample (i19) 0.099 -1.3 -0.4 0.864 sample (i20) 0.196 -0.1 -0.3 0.914 table 2: table showing the statistics of azimuthal angle (ϕ) distribution of galaxies in twenty sample. the first column represents the sample, second column p(>χ2) represents the chi-square probability, third column c/c(σ) represents the auto-correlation coefficient, fourth column ∆11/σ(∆11) represents the first order fourier coefficient and last column represents first order fourier probability p(>∆1). sample p(>χ2) c/c(σ) ∆11/σ(∆11) p(>∆1) sample (i01) 0.826 +0.7 +1.2 0.207 sample (i02) 0.456 +0.1 +0.7 0.642 sample (i03) 0.507 -0.1 +1.2 0.044 sample (i04) 0.682 +1.0 +2.0 0.015 sample (i05) 0.003 +3.3 +3.5 0.000 sample (i06) 0.000 +3.6 +4.2 0.000 sample (i07) 0.000 +15.3 +8.5 0.077 sample (i08) 0.000 +27.5 +11.1 0.000 sample (i09) 0.000 +39.9 +13.2 0.000 sample (i10) 0.000 +42.4 +14.0 0.000 sample (i11) 0.000 +26.9 +11.5 0.000 sample (i12) 0.000 +5.7 +6.0 0.000 sample (i13) 0.003 +3.1 +4.3 0.000 sample (i14) 0.011 +1.6 +3.7 0.000 sample (i15) 0.350 +0.7 +2.3 0.004 sample (i16) 0.634 -0.1 +1.4 0.134 sample (i17) 0.229 -2.2 +1.1 0.283 sample (i18) 0.708 -0.2 +1.1 0.307 sample (i19) 0.544 -0.3 +1.1 0.310 sample (i20) 0.596 -1.0 +1.4 0.135 sah and yadav / bibechana 19(1-2) (2022) 68-74 71 the second row of table 1 showed test statics for the polar angle distributions (θ) for sample i01. the value of chi-square probability, correlation coefficient, the first-order fourier coefficient, and first-order fourier probability are lies in the isotropic range. so, all these statistics suggest strongly isotropy and hence statistic suggests the random orientation of the spin vector. similarly, for the azimuthal angle distribution (ϕ) of the sample (i01) all these values of test statics lie within the isotropic range (see in the second row of table 2). all these statistics suggest strongly isotropy. therefore, the projection of the spin vector is to be noticed as random. figure 1(a): the polar angle (θ) distributions of galaxies in the sample (i01). the solid line represents the expected distributions and the solid circles with ±1σ error bars represent the observed distribution whereas the dashed line is cosine distribution is shown for the comparison. in figure 1(a), the shaded portion represents the range 40o ≤ θ ≤ 50o is called a bimodal region in which if both ‘hump’ or ‘dip’ appears means they are canceled to each other and we cannot predict the orientation of the spin vector. a dip (or hump) in the unshaded region at the range 0o ≤ θ < 40o suggests that the angular momentum vectors of galaxies tend to lie perpendicular or parallel with respect to the equatorial plane. similarly, a hump (or dip) in the unshaded region in the range 50o < θ ≤ 90o indicates that the spin vectors of galaxies are perpendicular (or parallel) with respect to the equatorial plane. in figure 1(a), the number of observations for small-angle (0o ≤ θ < 40o) are found to be 94 whereas the expected are 95. thus, the number of observed distributions is less than by only one than that of expected distributions. in this region, there is only one significant dip is seen at an angle 32.5o with an error limit ∼ 1.5σ and dip is seen because in this region there is a chance of cluster and supercluster and also three small dips are seen at angles 2.5o, 17.5o and 37.5o with the error limits ∼ 0.2σ, ∼ 0.1σ and ∼ 0.1σ respectively but we cannot consider as significant dip because less than 5% error is coming from mathematical calculation not as an observational data so we cannot accept as the error in observation and hence such type of error we are excluded. also, there are three small humps seen at angles 12.5o, 22.5o and 27.5o with the error limit ∼ 0.1σ, ∼ 0.5σ and ∼ 0.3σ respectively and these three small humps and dips are canceled to each other. for the bimodal region (40o ≤ θ ≤ 50o), the observed and expected number of observations are found to be 15 and 14 respectively such that observed and expected number of observations are nearly equal. also, no humps and dips are seen at the bimodal region. for large angles (50o < θ ≤ 90o), the observed and expected numbers are 23 and 21 respectively implies that the observed is slightly more than that of the expected solution by only two. there are two small humps seen at angles 52.5o and 87.5o with the error limits ∼ 0.5σ and ∼ 0.4σ respectively and also two small dips are seen at angles 62.5o and 72.5o with the error limit ∼ 0.6σ and ∼ 0.4σ respectively. therefore, in all together one significant dip with so many small dips and humps are seen. but all these humps and dips are cancelled to each other and hence, no preferred alignment of the spin vector is found to be noticed. thus, we have noticed that, there is a random distribution of spin vectors of galaxies in the θ distribution. figure 1(b): the azimuthal angle (ϕ) distributions of galaxies in the sample (i01). the solid line represents the expected distributions and the solid circles with ±1σ error bars represent the observed distribution wherwhereas the dashed line is the average distribution is shown for the comparison. in figure 1(b), the humps and dips in the scatter diagram of azimuthal angle (ϕ) distribution are very difficult to interpret as compared to polar angle (θ) distributions. it is because the azimuthal angle is the angle normal to the equatorial coordinate system and it ranges from 0o to 360o (or −180o to +180o) but when we take the projection of azimuthal angle on the equatorial coordinate system, we take an only range of ϕ is from −90o to +90o. the shaded portion represents the range −45o ≤ ϕ ≤ +45o. in the scatter diagram of the azimuthal angle (ϕ) distribution, a hump (or dip) in the middle (central eight bins) of the scatter diagram suggests that the direction of the spin vector is clockwise (or counterclockwise) and its projections of galaxies tend to point towards (or outwards) the center of the reference plane. similarly, a hump (or dip) at the first four and last four bins represents that the projections of the spin vector of galaxies lie tangentially towards (or outwards) to the center of the reference plane. sah and yadav / bibechana 19(1-2) (2022) 68-74 72 in figure 1(b), the number of observed distribution in central eight bins (ϕ ∼± 45o) are found to be 100 and that of expected is 92. thus, the number of the observed distribution are more than by 8 than that of expected. in this region, there is no any significant hump and dip are seen but six small humps are seen at the angles −45o, −35o, −25o, −15o, 15o and 25o with the error limit ∼ 0.3σ, ∼ 0.2σ, ∼ 0.4σ, ∼ 0.7σ, ∼ 0.2σ and ∼ 0.5σ respectively. also, for smaller angle (ϕ < −45o), the observed distribution are found to be 13 where as expected are 20 and observed distribution are less than by 7 than that of expected. in this region, there is no any hump seen but one significant dip is seen at an angle −75o with an error limit ∼ 1.5σ with two small dips are also seen at the angles −85o and −55o with the error limits ∼ 0.4σ and ∼ 0.6σ respectively. for larger angles (ϕ > 45o), the observed and expected number of galaxies are found to be equal and which is 19. also, in this region, there is no significant hump and dip are seen but two small humps are seen at the angles 75o and 85o with the both have nearly equal error limits ∼ 0.1σ and only one small dip is seen at an angle 55o with an error limit ∼ 0.5σ. therefore we found that, altogether one significant dip as well as so many small humps and dips are seen but all these humps and dips are cancel to each other and hence, no preferred alignment of projection of angular momentum vector is found to be noticed i.e random is seen. after careful examination of the statistics, graphs and hump or dip of polar and azimuthal angles, we concluded that orientation and projection of the spin vector are isotropic and hence randomly distributed in the sample i01. the sample i01 supports strongly the hierarchy model of galaxy evolution. in sample i09, the observed distribution of galaxies is 63,312 which is more among all these samples. the test statics for the θ distributions is shown in the tenth row of table 2. all these statistics suggest isotropy except first-order fourier probability which suggests an anisotropy. overall statistic sugests random orientation of the spin vector. similarly, for ϕ distributions the test statistics is shown in tenth row of table 2. all these statistics shows strongly anisotropy and a significant positive value of first order fourier coefficient suggests that the projections of the spin vector of galaxies tend to lie radially towards the center reference plane. figure 2: (a) the polar angle (θ) and (b) azimuthal angle (ϕ) distributions of galaxies in the sample (i09). the solid line shows the expected distributions and the solid circles with ±1σ error bars show the observed distribution. the cosine and average distribution (dashed) are shown for comparison. in figure 2(a), the number of observations for a small angle (0o ≤ θ < 40o) are found to be 92,511 whereas the expected are 92,217. thus, the number of observed distributions is more than 294 than that of expected distributions. there is no significant hump and dip is seen in a smaller range of angles. for region (40o ≤ θ ≤ 50o), the observed and expected number of observations are found to be 13,554 and 13,671 respectively such that an observed number of observations is less than by 117 than that of expected observations. in this region, also not any significant hump and dip are seen. for large angles (50o < θ ≤ 90o), the observed and expected numbers are 20,559 and 20,734 respectively implies that the observed distribution is less than that of the expected solution by 175. in this region, also there is not any significant hump and dip are seen and also we found so many very very small humps and dips are seen in a different range of angles. so, finally, we conclude that these small humps and dips are not considered as significant and hence, no preferred alignment is found to be noticed. thus, we have noticed that there is a random distribution of spin vectors of galaxies in the θ distribution. in figure 2(b), the number of observed distributions in the central eight bins (ϕ ∼± 45o) are found to be 87,768 and that of expected is 85,959. thus, the number of the observed distributions is more than 1,809 than that of expected observations. in this region, there are three significant humps seen at the angles −15 o, −5 o, 5 o with the error limits ∼ 2.5 σ, ∼ 2.0 σ and ∼ 1.5 σ respectively but there is only one small dip is seen at an angle 45 o with an error limits ∼ 0.8σ. also, for smaller angle (ϕ < −45 o), the observed distribution are found to be 17,874 whereas the expected are 19,122 and the observed distribution is less than by 1,248 than that of expected. in this region, there is no hump seen but two significant dips are seen at angles −85 o with an error ∼ 4.0 σ and −75 o with an error ∼ 2.5 σ. for larger angles (ϕ > 45 o), the observed and expected number of galaxies are found to be 20,982 and 21,542 respectively and the observed sah and yadav / bibechana 19(1-2) (2022) 68-74 73 distribution is less than by 560 than that of expected distributions. in this region, there is no hump seen but three small systematic dips are seen at angles 65 o, 75 o, and 85 o with all are nearly equal error limit ∼ 0.8σ. after studying the graph, preferred alignment is found to be noticed. this suggests that projections of spin vectors of the galaxies tend to orient radially towards the center of the equilateral co-ordinate system. after careful examination of the sample (i09), we found that the orientation of the spin vector is isotropic which implies random orientation and projection of angular momentum vector is preferred alignments and found to be radially towards the center of the equilateral coordinate system in the sample i09. this sample i09 supports the hierarchy model of galaxy evolution. similarly, we studied statistics and graphs of polar and azimuthal distribution of all remaining samples in which we found that all the samples have the three-dimensional orientation of the spin vector is isotropic which suggests that random orientation of spin vector and supports the hierarchy model of galaxy evolution. the projection of spin vector is found to be isotropic for sample i03 and lastly five samples i16, i17, i18, i19, and i20 which suggests that random projection of spin vector. the projection of spin vector in middle range samples i04 to i15 is found to be anisotropy and after careful study of these samples we found that projection of spin vector is radially towards the center of equilateral coordinate system. figure 3: the plot of i-magnitude (petro) versus firstorder fourier coefficient (∆11/σ(∆11)) for (a) θ and (b) ϕ distributions for all samples. we know that the preferred orientation and projection of the spin vector of galaxies can be studied by the general parameter first order fourier coefficient (∆11/σ(∆11)). the plot of petro-magnitude of i-filter and first-order fourier coefficient is shown in figure 3 above. in the figure, the shaded region shows the region of isotropy in both the polar and azimuthal angle distributions. the lower value of the i-magnitude represents the brighter galaxies. thus, along the x-axis, the brightness profile of galaxies decreases. the distance magnitude relation: mm = 5logr-5 + 2.5loge αr says that the magnitude is roughly proportional to the distance. we know that, according to hubble’s law, distance to the galaxy is proportional to its radial velocity or redshift. thus, we can roughly assume that the low magnitude galaxies (which is brighter) might have low radial velocity or redshift. in figure 3(a), we see that all these scatter points lie inside the shaded region, i.e., the isotropic region. all these points lie near the linear fit line for polar angle distribution (θ). thus, we conclude that the threedimensional orientation of spin vectors of galaxies is isotropic and is independent of the i-magnitude of galaxies. this implies that all these samples support strongly the hierarchy model of galaxy evolution. in figure 3(b), we see that for the azimuthal angle distribution (ϕ) first three points i01, i02, i03 and last five points i16, i17, i18, i19 and i20 lies inside the shaded region i.e., isotropic region this implies that the projection of spin vector is not preferred alignment and this suggests that projection of spin vector is random. and the remaining scatter points i04 to i15 lie outside the shaded region which means the projection of the spin vector is anisotropic and found that projection of the spin vector of the galaxies tend to be orient radially toward the center of the equilateral co-ordinate system. in the study of azimuthal distribution of all samples, we have seen that initially, a number of observed galaxies is less in the sample which is isotropic, after increasing the petromagnitude, a number of galaxies are increases and these high galaxies contained sample shows local anisotropic because in this region galaxies are in merging process and merged due to shearing or tidal effect to form a cluster, so the position of galaxies is not constant i.e., variable. we found that the equilateral coordinate system is not suitable for studying these maximum number of galaxies contained sample and to study such types of samples better to use galactic or super galactic co-ordinate system. further increase of magnitude the observed number of galaxies is less in the sample and hence isotropic is seen. after this observation, we conclude that an equilateral coordinate system is suitable for a smaller number of observed galaxies samples and for more observed galaxies samples we prefer better to use galactic or supergalactic co-ordinate system. hence, our study region of ifilter of redshift 0.54 to 0.60 supports a strongly hierarchy model of galaxy evolution. sah and yadav / bibechana 19(1-2) (2022) 68-74 74 comparison with previous works malla et al., [15-18] studied the non-random orientation of spin vector of supercluster s[202-002+0084] in 2019 having to mean redshift 0.084, supercluster s[195+027+0022] in 2019 that had redshift in the range 0.07 to 0.09, supercluster s[227+006+0078] in 2020 that had redshift in the range 0.07to 0.09 and supercluster s[231+030+0117] in 2020 that had redshift in the range 0.107 to 0.123. in all these three studies, they found that spatial orientation and projection of spin vector in all samples had not preferred alignments and which implies that random orientation and projection of spin vector with respect to the equilateral coordinate system. finally, their study concluded that all these four superclusters support strongly the hierarchical model of galaxy evolution. this result matches with our results in all the sample orientation of spin vector and some differences in the projection of the spin vector. our results also support strongly the hierarchy model of galaxy evolution. hence, our and their results are found to be nearly similar. conclusions in this article, we have to present a study of the imagnitude galaxies of redshift range 0.54 to 0.60 with respect to the equilateral co-ordinate system. the database is taken from sdss 14th data release (dr-14) and this redshift contains 239,209 galaxies. sdss provides two-dimensional data, we convert a twodimensional database into a three-dimensional galaxy rotation axis: polar & azimuthal angles, with the help of the method proposed by flin & godlowski [10,14]. sdds survey database contains positional and inclination selection effects and that cause several changes in the expected isotropic distribution curves, so to remove such types of effects numerical simulation method is used which was proposed by aryal & saurer [12, 13]. the main aim of this work is to know the random effects in the galaxy and to find out the relevance of the choice of the coordinate system in order to explain the true orientation scenario and projection of spin vectors of distant galaxies. for simplicity, we divide our total database into twenty samples with the help of the petro-magnitude range by considering equal sample bins. to check, isotropy or anisotropy we have to carry out four statistical tests: chi-square, autocorrelation coefficient, first-order fourier series and first-order fourier probability tests. the conclusion of our work is as follows: 1. we found in all twenty samples, three dimensional orientation of the spin vector of galaxies is isotropic with the equatorial plane and independent of the i-magnitude of galaxies. 2. the projection of angular momentum vector in the first three samples i01, i02, i03 and the last five samples i16, i17, i18, i19 and i20 are seen isotropic. 3. and, the remaining samples i04 to i15, the projection of spin vector of the galaxies are seen anisotropy and found that tend to be orient radially towards the center of the equilateral plane. 4. the sample which contains a maximum number of observed galaxies shows a local anisotropic angular momentum vector because in this region galaxies are in the merging process and merged due to shearing or tidal effect to form a cluster. 5. after this observation we conclude that an equilateral coordinate system is suitable to study, a smaller number of observed galaxies sample and for more observed galaxies sample we prefer better to use galactic or supergalactic co-ordinate system for the study of orientation and projection of angular momentum vector. 6. hence, our study region of i magnitude of redshift 0.54 to 0.60 supports strongly the hierarchy model of galaxy evolution. references [1] weizscker c. f., apj, 114, 165 (1951). [2] gamow g., phys. rev., 86, 251 (1952). [3] gamow g. & teller e., phys. rev., 55, 654 (1939). [4] doroshkevich a. g., apj, 14, l11 (1973). [5] doroshkevich a. g., shandarin s. f., & e. saar, mnras, 184, 643 (1978). [6] ozernoy l. m., 1971, astron. zh. 48, 1160; engl. transl. sov. astron. 15, 923 (1972). [7] ozernoy l. m., in longair m. s., einasto j., eds, proc. iau symp. the large scale structure of the universe. reidel, dordrecht, 79, 427 (1978). [8] stein r., a & a, 35, 17 (1974). [9] peebles, p. j. e., origin of the angular momentum of galaxies. apj, 155, 393 401(1969). [10] flin p., & godlowski, w., mnras, 222, 535 (1986). [11] holmberg e., medd. lund. astron. obs. vi, 117 (1946). [12] aryal b., saurer w., a&a, 364, l97 (2000). [13] aryal b. & saurer w., a&a, 425, 871 (2004). [14] godlowski w., mnras, 265,874 (1993). [15] malla j. r., aryal b., and saurer w., jnps, 5, issue 1, (october 2019). [16] malla j. r., saurer w., and aryal b., iau, proceedings of the international union; cambride 14 (353), 259-261, (jun 2019). [17] malla j. r., saurer w., and aryal b., bibechana, 17, 117-122, (2020). [18] malla j. r., saurer w., and aryal b., jist, 25(2), 72-79 (2020). *email: shivshankarphysics@gmail.com devendra sir cover page copy.jpg bibechana 17 (2020) 80-88 80 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal spectral analysis of aerosol optical depth over aeronet sites of nepal aashma acharya 1 , binod adhikari 1,2,* , pratik bhattarai 1 , gopal jha 1 , shambhu acharya 3 , ritesh shah 1 1 department of physics, st. xavier’s college, maitighar, kathmandu, nepal 2 department of physics, patan multiple campus, tribhuwan university, lalitpur, nepal 3 ministry of education, science and technology, singha durbar, kathmandu * email: binod.adhi@gmail.com article information received: august 26, 2019 accepted: november 30, 2019 keywords: aerosol aerosol optical depth wavelet analysis continuous wavelet transform abstract the suspended particle aerosols especially anthropogenic are recognized to have degradation in the quality of the atmosphere and one of the factors to cause uncertainty in climate. in this paper, we have investigated the trend of the parameter ‘aerosol optical depth’ and by application of spectral based wavelet analysis; we extracted spatial and temporal variation over the selected aeronet sites of nepal. we have taken the site kyanjin_gompa, lumbini, pokhara and kathmandu under the consideration of our study because of their geographical variability which is a significant factor for causing variation in local as well as global circulation of aerosols as per data retrieved from ground-based remote sensing system for the year 2018 over the site kyanjin gompa, lumbini and pokhara and for the year 2016 over the kathmandu, we extracted the periodicity and frequency of the variation in aod for each site by the application of continuous wavelet analysis on aod at three different wavelengths. on reviewing the previous studies, it is seen that the area lying at the indo-gangetic plain exhibit high aerosol loading in comparison with the himalayan foothills and central himalayas of nepal. we found not only the higher aerosol loading in atmosphere over site lumbini but also higher periodicity. likewise, we also found pokhara as highly polluted as lumbini. the invest iga tion of da ta records over the si te kathmandu has sho wn increment in aerosol loading in the year 2016 compared wi th previous years. 1. introduction besides gas molecules the atmospheric air consists of minute solid particles and liquid droplets called aerosols which are the suspension of minute solid particles or liquid droplets in the gas. atmospheric aerosols are commonly the mixture of particulate matter and atmospheric gas. this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.26507 http://nepjol.info/index.php/bibechana mailto:binod.adhi@gmail.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.26507 aashma acharya et al./ bibechana 17 (2020) 80-88 81 the term aerosol is often used in reference to pm, but technically refers to both the condensed phase particles and the gaseous medium they are suspended in. particularly they are described on the basis of size, concentration, and chemical composition. there are considerable differences in the size ranges, chemical nature and the sources of the aerosol that occur in these layers. often, the different aerosol groups clump together to form the hybrid of both the natural and anthropogenic aerosols. majority of the aerosol are naturally occurring such as dust, pollen grains, sea salt, fly ash, soot and carbon particle mixes in atmosphere by several natural processes. while the another one is anthropogenic abundant in polluted area formed due to human activities such as fossil fuel combustion, biomass burning, industrial smoke, power plants, coal mining and other several activities. the location of aerosols’ suspension in the earth’s atmosphere is varied over different surface. aerosols have 2 different types: primary and secondary aerosols. primary aerosols are atmospheric particles that are found in the atmosphere by direct injection or emission. the primary aerosol particles result either from fragmentation processes or from combustion. of course, their shape can change because of a number of physicochemical processes like humidification, gas–particle reactions, coagulation, etc. [1]. the formation of secondary aerosols can be aided and catalyzed by the primary aerosols present in the atmosphere of the earth. secondary aerosol particles appear in the carrier gas as a consequence of gas to particle conversion [2]. they serve as the centers for heterogeneous nucleation of water vapor. no aerosols – no clouds, so one can imagine how our planet would look without the secondary aerosol particles [1]. aerosols are short lived with a residence time of about a week in the lower troposphere. due to their short lifetimes and widely distributed sources, aerosols exhibit large spatial and temporal variabilities. aerosol possesses horizontal and vertical distribution over the atmosphere, which is called spatial distribution. the variation with the time is the temporal distribution. distribution of aerosols in various atmospheric layers depends upon the microphysical properties, chemical properties and environmental conditions. air pollution near the ground is closely related with the terrain; the high elevation would take advantage of the spread of contamination. the structure of pollution layer of the high elevation seems to be the same as the low elevation. the main emission mechanisms of the aerosols are related to the local circulation in the boundary layer caused by the surface temperature heterogeneity and relief and possibly connected with electrical charging of dust particles. the planetary boundary layer is an important parameter to analyze the aerosol particles vertical distribution. the pbl is the closer turbulent layer closest to the earth‘s surface. its height, which can vary mainly from 1 to 2 km at midday, is crucial to many aspects of weather and climate. the ground-based lidar can show atmospheric temporal variation (at a fixed location), while space-borne lidar can obtain atmospheric variation in space (in large-scale region). aerosol particles are mainly constrained in pbl but it also gets injected to the stratosphere. volcanic aerosols have the potential to be injected to stratosphere. volcanoes emit sulfur dioxide gas (so2), which reacts with water in the atmosphere to form sulfuric acid (h2so4). when volcanic plumes are emitted powerfully enough to reach the stratosphere the h2so4 can form a persistent haze of liquid droplets, reflecting away sunlight and cooling the earth for a year or two. aerosol optical depth is the measure of amount of light that aerosol scatter or absorbs in the atmosphere telling us the amount of direct sunlight being prevented to reach the earth surface. aerosol optical depth (aod) helps us to know the amount of the columnar atmospheric aerosol content [3] for example: urban haze, https://www.sciencedirect.com/topics/earth-and-planetary-sciences/sulphur https://www.sciencedirect.com/topics/earth-and-planetary-sciences/sulphuric-acid https://www.sciencedirect.com/topics/earth-and-planetary-sciences/plume https://www.sciencedirect.com/topics/earth-and-planetary-sciences/stratosphere https://www.sciencedirect.com/topics/earth-and-planetary-sciences/haze https://www.sciencedirect.com/topics/earth-and-planetary-sciences/droplet https://www.sciencedirect.com/topics/earth-and-planetary-sciences/earth aashma acharya et al./ bibechana 17 (2020) 80-88 82 smoke particles, desert dust, sea salt, etc. distributed within a column of air from the instrument (earth's surface) to the top of the atmosphere [4]. considering mathematically and more technically, aerosol optical depth is defined as the integrated extinction coefficient over a vertical column of unit cross section. the aerosol optical depth is measured using groundbased sun photometers or radiometers. in addition to the optical depth due to extinction of aerosol other atmospheric constituents can scatter light and must be considered when calculating the aod. the optical depth due to water vapor, rayleigh scattering, and other wavelengthdependent trace gases must be subtracted from the total optical depth in due course of obtaining the aerosol component [5]. in this paper, we will try to analyze the spectrum of aerosol optical depths in the aeronetsites of nepal using continuous wavelet transform. 2. dataset this research will be focusing on applying wavelet based spectral analysis to the time series analyzed aerosol optical depth, collected by the remote sensing using sun photometers. we have collected data from the link: (https://aeronet.gsfc.nasa.gov) . the site selection for this project is done according to the data availability for nepal to achieve maximum utilization of available data and resources. among the selected sites, each one is taken in consideration for this study on the basis of their geographical structure variability focusing on the fact that variability occur with the geographical differences. the locations of the equipment placed for the data collection are: s.n station name geographic latitude eographic longitude 1 kyanjin gompa 28.2141° n 85.5245° e 2 lumbini 27.6792° n 83.5070° e 3 pokhara 28.2096° n 83.9856° e 4 kathmandubode 27.6909° n 85.3905° e 3. methodology in this section, we discuss the methodology implement for the spectral analysis of aerosol optical depths in the aeronet sites of nepal. wavelet analysis the mathematical tools that can be used to transform data representation into its multilevel components are termed as wavelet transformation. the basics idea of wavelet is small wave, localized wave and decay amplitude on the basis of time and frequency [6-8]. originally, applied in geophysics in due course of analysis of seismic signals, the wavelet transforms were better and broadly formalized [6]. the main application of wavelet analysis is time-frequency localization. this tool provides the contribution of different frequency band of different locations [9]. the main task of this tool is to decompose the signals into the signal details that show trends as the function of time. wavelet analysis is used as the alternative to fourier transformation. when we plot time domain signals, we obtain a time-amplitude representation of the signal. this representation is not always the best representation of the signal for most signal processing related applications. in many cases, the most distinguished information is hidden in the frequency content of the signal. the frequency spectrum of a signal is basically the frequency components (spectral components) of that signal. the frequency spectrum of a signal shows what frequencies exist in the signal [10]. when we use fourier transformation as a tool for representing frequency components it gives us frequency-amplitude representation. ft gives the frequency information of the signal, which means that it tells us how much of each frequency exists in the signal, but it does not tell us when in time these frequency components exist. if we want to know, what spectral component occurs at what time (interval), then fourier transform is not the right transform to use. when the time-frequency localization of the spectral components is needed, a transform giving the time frequency https://aeronet.gsfc.nasa.gov/ aashma acharya et al./ bibechana 17 (2020) 80-88 83 representation of the signal is needed. the ultimate solution for this is wavelet analysis. wavelet transform helps us to provide the time and frequency information simultaneously, providing a time-frequency representation of the signal [10] . a more detailed description of the wavelet technique can be found in domingues et al. [7], mendes et al. [11] , ojeda et al. [12], klausner et al. [13] 4. result and discussion here, we discuss the aerosol optical depths in the different aeronet sites of nepal and their spectral analysis using continuous wavelet transform. figure 1 shows aod at three typical wavelengths 1640 nm, 1020 nm and 675 nm. the site kyanjin_gompa has maximum aerosol loading at wavelength 675nm with the variation of time in comparison to remaining two wavelengths. this logically means the submicron aerosol particles are dominant in this region than that of coarse mode aerosol. . minimum aerosol loading in atmosphere was observed during the month of january over the region kyanjin_gompa as per the aod whose value was very low ranging from 0 to 0.05 for the month january. the time series is showing episodic changes in aerosol optical depth over this region. from about the 61st day of the year 2018 which is march 2nd the aod variation is slowly rising than before. from the plot, we can observe drastic changes starting slowly from the beginning march eventually reaching its peak variability at the end of march and start of april.. winter 2018 in northern hemisphere began on saturday, december 22 and ended on thursday, march 21, 2019. with the increase in temperature, the aerosol loading is increasing from ending of march reaching maximum during mid-april. the aod during this period is ranging from 0.3 to 0.35. then with gradual decrease in variability, the aod again increase during end of april ranging from 0.15 to 0.2. the month may shows episodic variation of aod from minimum value to 0.2. with the beginning of monsoon during end of july the aod has shown tremendous decrease. it is quiet fair because rainwater washes out huge amount of aerosol particles from atmosphere. throughout the winter the variability is very low which is because of less humidity. lumbini lies in southern slope of central himalayas in the indo-gangetic plain. the starting of january shows less aerosol loading up to mid-january but the value of aod is tremendously larger than that of site kyanjin_gompa during this period ranging from 0.5 to 1. by the last week of january, the aod value exceeds 1. during this period the submicron aerosol of aod at 675 nm are dominant. from midfebruary, the value of aod exceeds by 1 ranging from 1 to 1.5. third week of may shows maximum aerosol loading for the wavelength 1020nm which shows dominance of coarse mode aerosol which are usually wind-blown dust. the last 15 days of june shows maximum aod with value 2 at 1640nm which is coarse mode particle relatively large size of aerosols along with aod at 675nm. this period is just before the starting of monsoon (pre-monsoon). during the end period of june aod value for 675nm reaches one and exceeds above one. as the monsoon start the aod at all three wavelengths decreases below 1 reaching to 0.5. the aod for 136 days of the year 2018 of pokhara is analyzed as variation with time as per as data availability by aeronet. during the month of january, the aod values are very low below 0.5 which is normal. as the february starts the aod value gradually reaches 1 which is large amount of aerosol loading in atmosphere. then the aerosol loading is gradually decreasing reaching very low value during mid-february. after the 46th day of the year (15 february) the aod value reaches 1 and exceeds gradually above 1 at the 675nm up to starting of march. pokhara has dominant level of submicron aerosols in atmosphere. on 29th of march the aerosol loading is very high over the site pokhara with the value above 1.5. this type of condition results haze formation in atmosphere affecting visibility to some extent. aashma acharya et al./ bibechana 17 (2020) 80-88 84 fig. 1: aod of different wavelength from kyanjin_gompa (top), lumbini (middle) and pokhara (bottom) of the year 2018. fig. 2: aod of different wavelength from kathmandu_bode of the year 2014 (top) and 2016 (bottom). aashma acharya et al./ bibechana 17 (2020) 80-88 85 figure 2 represent the time series of aod at three different wavelengths 1020nm, 870nm and 675nm from kathmandu-bode of the year 2014 (top) and 2016 (bottom). the wavelength 1020nm belongs to ir spectrum and the spectral channel of 870nm and 675nm belongs to red band of visible spectrum. the study of the aod over the aeronet-site kathmandu-bode exhibits dominance of aerosol particle that are detected by channel with wavelength of 675nm which signifies sub-micron aerosol particles. for the red channel, the aod above 0.02 signifies hazy condition of atmosphere and extremely hazy at aod value above 0.4. the variation of aod in the year 2014 also exhibits cyclic variation i.e. secondary maximum during the summer (aprilmay) season reaching primary maximum during pre-monsoon (june) and decreasing with approaching monsoon (july). the aod value reaches 1 with the approaching midsummer which is harmful state of atmosphere with hazy condition. with the start of may aod values exceeds 1 reaching 1.2. the time series of kathmandu exhibit high aod variation with maximum aerosol loading starting from the end of march up to june and then there is sharp decrease with start of the monsoon. on comparing the time series of 2014 with the time series of 2016 over kathmandu, it is observed that the maximum aerosol loading occurs during summer which implies that aod value shows sharp increment from the mid of march till end of the month. during this period the aod values ranged 0.4 to 0.6 in the year 2014 but in the year 2016 the aod reached 1.5 during the same period of the year. the aod value ranges 0.9 to 1.2 during 91st – 106th day of the year 2016. during the same period the aod value ranges from 0.7 to 1 for the year 2014. there is drastic decrease of aod with the start of may in the year 2016. the variation is similar for other two wavelengths. the time series analysis for the aerosol optical depth solely is unable to provide the information about the frequency spectrum. with the aim to extract dominant periodicities, morlet cwt analysis is applied on the aod value retrieved from visible spectral channel (675nm) and scalograms are presented in figure 3-7. as mentioned earlier, the continuous wavelet analysis was used to analyze the aod of daily averages data of 4 stations of nepal. the time period from 76th day to 201st (march-july) day over the site kyanjin-gompa (figure 3) shows high atmospheric modulation. we can observe presence of three dominant accumulations during this period. the variation during the 80th to 91stday of the year shows very high variation relatively than other. localized wavelet spectrum in the scalogram exhibits wave dominance over the period around 4 to 6 days. most of the power is concentrated during the period 5 to 4 days. some spectrum of 5 to 4 days is observed however its strength is lower compared to dominance period. another wavelet spectrum is obtained at about 27th to 30th day of the year 2018 with periodicity of 2 to 4 days, however, has lower strength than other. wavelet spectra as determined from the time series of the radiometer retrieved aod measurements obtained at three wavelengths for the daily averages aod values of station lumbini is shown above in figure 4. about 176th day of the year the periodicity of around 8 to 9 days is predominant. another periodicity is also present around 8th to 48th day of the year with period of around 15 days but of less intensity. similarly, figure 5 shows the periodicities observed on aod at pokhara in which dominance periodicities (scales) exhibits around 7 to 9 days during 110th to 120th day of the year. by comparing the global wavelets spectra corresponding to aod, representing kyanjin-gompa, lumbini and pokhara, it is found that the periodicity of 15 days of lumbini is maximum among all. it should be noted that this wavelength 675nm lie in the spectral region where the submicron aerosol aashma acharya et al./ bibechana 17 (2020) 80-88 86 particles in their accumulation regime contribute to the aod. these particles are believed to be mainly originated from secondary production mechanisms making them highly susceptible to anthropogenic activities (stone et al., 2010). periodicities are highly influenced by the local factors and the spatial variability of periodic features in the aods obtained [15]. thus, the results of the present study are in good agreement with the aforementioned studies. in figure 5, periodicity around 5 to 6 days is predominant during 115th day of the year with higher intensity of accumulation. another wave spectrum also shows dominance with periodicity of around 16 days. the 141st day also shows 3 to fig. 3: cwt analysis of aod from kyanjin gompa of the year 2018. fig. 4: cwt analysis of aod from lumbini of the year 2018. 5 days periodicities, however with the lower intensities. similarly, the 121st day of the year 2014 shows periodicity of 5 to 4 days. figure 6(a) and 6(b) represent the scalogram of aod of the site kathmandu-bode of the year 2014 and 2016 respectively. the dominant periodicity is at 6 to 4 days during 80th to 110th day of the year 2014. other spectra are also present but of lower intensities with much higher periodicity. comparing cwt analysis for the site kathmandu between 2014 and 2016 there is higher periodicity present during the year of 2016. this is an obvious result as the pollution is increasing every year and there is more accumulation of aerosol in the atmosphere. fig. 5: cwt analysis of aod from pokhara of the year 2018. fig. 6(a): cwt analysis of aod from kathmandu of the year 2014. aashma acharya et al./ bibechana 17 (2020) 80-88 87 fig. 6(b): cwt analysis of aod from kathmandu of the year 2016. 5. conclusion analysis of aerosol records of 4 stations with geographical variability has been carried out with the aim to extract spatial and temporal variability of aod and with the application of the continuous wavelet analysis; periodicity possessed by aod is extracted. we have represented scalogram alone for cwt analysis for qualitative glimpse rather to show statistically what can happen. we detailed unique dataset of the year 2018 for the urban site lumbini and pokhara along with the central himalayan valley kyanjin-gompa to study the variation of aerosl loading among these areas. along this location we took recent available data of kathmandu valley of the year 2016 and 2014 as a rapid urban representation. this study investigated that among three site study of 2018, lumbini has the highest aod value. this result agrees with the previous studies result that igp are the most polluted area with high aerosol loading. the site lumbini shows maximum periodicity of aerosol loading with period of 7 to 10 days. this behavior of aerosol variability is seen during pre-monsoon (around june 15) over the site lumbini and during april (around 26 april) with aod value more than 2 and 2 respectively. this is the toxic hazy condition of the atmosphere where visibility within the atmosphere decreases. the periodicity seen in kyanjin_gompa around april is of 2 to 3 days. this means aerosol loading in atmosphere of the with particular aod value up to 3 days. this study showed premonsoon is most polluted time of the year with primary maximum aod exhibiting higher days periodicity i.e. there is presence of higher intensity of aerosol for longer period during premonsoon. by investigating the dataset for kathmandu-bode it is found that the aod value of the year 2016 has increased from 1.2 to 1.6 which is obviously because of urban aerosol accumulation. studies have shown that urban cities like kathmandu have accumulation of aerosol resulting from fuel burning and construction dust. it is clear from our study that there is dominance of submicron particle in atmosphere of this site. comparing the primary maxima of the year 2016 with 2014 the periodicity has increased in 2016 from 5 days in 2014 to 6 days period in 2016. this shows accumulation of higher intense aerosol loading for longer periods. the decline in aod from early may_ june is due to early start of rainfall during the year 2016. rainfall washes out large amount of atmospheric aerosol which is also one of the factors for variation in aod. the himalayan valley according to previous studies shows aerosol loading during summer is due to transport of the pollution from the foothills and mostly due to biomass burning. although the periodicity is lower than other sites, it is clear from study that kyanjin_gompa which is a central himalayan valley has considerable presence of both the coarse mode aerosol and the submicron aerosols. this means it shows higher aod up to 0.25 in all wavelengths but at various days of the year. this study concludes that ig plains have the most polluted atmosphere, and then the himalayan foothills are the next one which includes valley like pokhara and kathmandu. aashma acharya et al./ bibechana 17 (2020) 80-88 88 acknowledgement the dataset for this study was 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40 a mixed-mode ginger and turmeric solar dryer: design, simulation, biochemical and performance analysis manoj gyawali1, ayusha acharya1, tikaram adhikari1, kiran dahal1, bhooshan kafle2, dae hyun kim3, sagar kafle1* 1 department of agricultural engineering, purwanchal campus, institute of engineering, tribhuvan university, gangalal marg, dharan, 56700, sunsari district, province no. 1, nepal 2 department of applied science, purwanchal campus, institute of engineering, tribhuvan university, gangalal marg, dharan, 56700, sunsari district, province no. 1, nepal 3department of biosystems engineering, college of agriculture and life sciences, kangwon national university, hyoja 2 dong, 192-1, chun cheon 200-701, republic of korea email: sagarkafle@ioepc.edu.np abstract postharvest loss of vegetables and fruits is higher in developing countries due to the lack of post-processing equipment. although the production of ginger and turmeric is high in nepal, farmers practices open sun drying, which leads to poor quality, and the products do not get to the market at reasonable prices. in this study, a simple, easy to assemble and disassemble mixed-mode solar dryer has been designed, fabricated, and biochemical and performance analyses were done. the dryer was designed considering the solar irradiation, sunshine hours, latitude of the location, locally available materials, moisture content (mc) of the product, and drying capacity. the computational fluid dynamics (cfd) analysis was performed using ansys fluent simulation software to predict the dryer’s temperature and air flow behavior. the experiment was carried out in november in the harvesting season of ginger. the dryer performance is compared with the open sun drying using ginger and turmeric. the biochemical properties such as oleoresin and essential oil were determined using soxhlet and steam distillation methods and compared with the product of open sun drying. the experiment results showed that ginger and turmeric took only about 14 sunshine hours to reach from 88% to 10-12% moisture content. the maximum collector and drying efficiency were recorded at about 45.32% and 31.364%, respectively. the temperature distribution inside the dryer obtained from the experiment correlated with the results obtained from the cfd analysis. the retention of essential oil was found more in product drying with dryer than open sun drying. among the various drying models, wang and singh model was found suitable for describing the drying model. it is concluded that the designed dryer is suitable for ginger and turmeric drying into a safe moisture level, ensuring product quality. doi: https://doi.org/10.3126/bibechana.v19i1-2.46386 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal article information: received: jan. 23, 2022 accepted: feb. 5, 2022 keywords: mixed-mode solar dryer ginger turmeric drying efficiency biochemical analysis mailto:sagarkafle@ioepc.edu.np https://doi.org/10.3126/bibechana.v19i1-2.46386 https://creativecommons.org/licenses/by-nc/4.0/ gyawali et al. / bibechana 19 (1-2) (2021) 40-60 41 1. introduction in developing countries, the food loss is significant; about 20-40% of agricultural products are being lost due to managerial and technical limitations of post-harvesting techniques such as storage, transportation, processing, packaging, and marketing [1]. for example, postharvest losses in fruit and vegetables in nepal are estimated at 20 to 50% [2]. however, this loss can be minimized by proper management of postharvest techniques like cold storage, drying, material handling, transportation, processing, cooling facilities, infrastructure, packaging, marketing system, etc. [3,4]. the drying technique is one of the effective methods of eliminating the problems of postharvest losses [5]. mainly, it is done for the safe storage of storing crops by reducing the water activities that lead to an increase in self-life of product. renewable energy, such as solar energy, can be effectively used for drying agricultural products, which is eco-friendly and has fewer environmental consequences. solar drying can be an encouraging substitute for open-air drying and is expected to play a more vital role in most developing countries due to the availability of a high level of solar radiation all over the year. the national average solar insolation of nepal is recorded as 4.66 kwh/𝑚2/day [6], with the energy generation capacity of 57,519 gwh [7]. with an appropriate solar dryer design, solar energy can efficiently be utilized for crop drying [8]. in this study, ginger and turmeric are chosen for the experiment due to the ginger and turmeric pocket zone is near the experimental location. so, it is readily available in the market, and study would be helpful for the farmers growing in the area. ginger (zingiber officinale) and turmeric (curcuma longa) are rhizomatous plants; their derivative products are widely used for food additives and folk medicines [9]. the fresh rhizome of ginger and turmeric is dried to prepare its derivatives such as ginger pickle, powder, and extractives such as ginger and turmeric oil. in 2019, nepal is the fourth largest ginger producer and exporter after china, india, and nigeria [10]. in 2018/19, it was cultivated in an area of 22,132 hectares (ha) and produced about 284,427 metric tons (t)[10]. however, due to nepal’s shortfall of suitable postharvest management techniques, fresh ginger is primarily exported in india (about 70% of the total production) [1,11]. on the other hand, the production of turmeric requires less investment, water, and fertilizer and has low pest/disease infestation. for the hilly region of nepal, it is considered a good cash crop [12]. in the fiscal year 2018/19, it was cultivated in 10,160 ha and produced 98,904 metric tons in nepal[10]. however, farmers still depend upon open sun drying and low-efficiency dryer for drying, which is used for making various derivatives products. the intervention of an efficient dryer would allow farmers to get market of their fresh product in production season and derivative products during the offseason. promoting such infrastructures and applied research plays a vital role to make food selfsufficient, and helps to meet the sustainable development goals (sdg) target, especially sdg 2 [13]. many studies related to the solar dryer have been conducted globally on various agricultural products for seeking the appropriate dryer with greater drying efficiency. the design, fabrication, and testing of the mixed-mode dryer [8] with their modifications on various agricultural products such as grapes [14], grains [15], red peppers [16], okra slices [17], tomatoes [18], etc. have been demonstrated in many studies. studies have shown that the mixed-mode dryer needs very little time to reach the products’ safe moisture level without compromising quality. however, very little literature has been reported regarding the drying of the ginger [19,20] and turmeric [21– 23] in the mixed-mode and other dryer types for determining the best-fitted drying models and product qualities. in nepal’s context, little literature has been reported on the application of the dryer in the prospect of the rural areas [24,25] by taking the different types of dryer such as solar cabinets, tunnel, rack dryers, etc. these studies have shown that the modifications help in improving performance and have suggested testing of the modified dryer. although some of the studies are reported in nepal to determine the drying performance, no such literature has been found that studied the performance of mixed-mode ginger and turmeric dryer. in addition, also drying temperature prediction with its distribution on drying chamber and airflow pattern have not much reported before. gyawali et al. / bibechana 19 (1-2) (2021) 40-60 42 to fulfill this gap, in this study, we have designed and fabricated a mixed-mode solar dryer, and performance analysis was conducted on ginger and turmeric drying. in addition, biochemical analysis was also investigated to evaluate ginger and turmeric’s biochemical properties (essential oil and oleoresin). further, we have done computational fluid dynamics (cfd) analysis to observe the temperature profile inside the dryer. 2. methodology 2.1 governing equations and drying models 2.1.1 the governing equation used in cfd analysis the governing equations which are to be solved in differential form for a 3-dimensional case are as follows: a) the continuity equation, which represents the conservation of mas 𝜕𝜌 𝜕𝑡 + ∇(𝜌�⃗� ) = 0 (1) here, �⃗� and 𝜌 represent the fluid velocity and density of air, respectively. b) the navier-stokes equation, which represents the conservation of momentum [26]: 𝜕 𝜕𝑡 (𝜌�⃗� ) + ∇. (𝜌�⃗� �⃗� ) = −∇𝑃 + ∇�̿� + 𝜌𝑔 + 𝑆𝑚 (2) here, 𝜏̿ and 𝑆𝑚 represent reynold’s shear stress tensor and the source term for momentum, respectively. c) the energy equation [27]: 𝜕 𝜕𝑡 (𝜌𝐸) + ∇. (�⃗� (𝜌𝐸 + 𝑃)) = ∇. (−𝑞 + 𝜏̿. �⃗� ) + 𝑆ℎ (3) here, 𝑆ℎ, 𝑞 and e represent the heat source team, the flux vector (positive inward) and the total energy (sum of internal and kinetic energy), respectively. the total energy is given by: 𝐸 = ℎ − 𝑃 𝜌 + 𝑢2 2 (4) where h is the sensible enthalpy of the air d) in the flow field, the presence of porous media is presented by the eq. (5) (8) through the source terms. in the momentum equation, the source term is composed of viscous losses and inertial losses. in the ansys fluent, this is written as: 𝜕𝑃 𝜕𝑧 = − 𝜇 𝛼 𝑢𝑧 + 𝐶 1 2 𝜌𝑢𝑧 2 (5) here, ( 1 𝛼 ) and c represents the viscous loss coefficient and the inertial loss coefficient, respectively. the equation can be applied similarly along x and y directions. ergun developed an equation for packed beds which has been applied successfully to grain beds [28]. 𝑃 𝐿 = 150𝜇(1−𝜀2) 𝑑2 𝑝𝜀3 𝑢 + 1.75𝜌(1−𝜀) 𝑑𝑝(𝜀)3 𝑢2 (6) from eq. (7) and the inertial and viscous loss coefficient were computed 𝛼 = 𝑑2 𝑝𝜀3 150(1−𝜀2) (7) 𝐶 = 3.5 𝜌(1−𝜀) 𝑑𝑝𝜀3 (8) 2.1.2 data calculation & analysis the thermal efficiency of the collector (ηc) was determined from eq. (9) and the graph of collector efficiency was plotted on an hourly basis [29]. ηc = ρv∆tcp acic (9) where, ρ is the density of air (kg/𝑚3) = 1.225 kg/𝑚3, 𝐼𝑐 is the solar radiation on the collector (primary), ∆t is the temperature elevation, 𝐶𝑝 is the specific heat capacity of air at constant pressure (kj/kg/k). the dryer efficiency (𝑛𝑑) was determined using eq. (10) [29]. 𝑛𝑑 = 𝑀𝑤ℎ𝑤 𝐴𝐼𝑡 (10) where, a is the collector area (secondary and primary), ℎ𝑤 is the latent heat of vaporization of water, 𝑀𝑤 is mass of water removed, i is solar radiation incident on the collector of dryer, and t is drying time. 2.1.3 drying models the experimental data of ginger and turmeric drying were used to develop the drying model [30]. the moisture ratio (mr) is determined using eq. (11). 𝑀𝑅 = 𝑀𝑡−𝑀𝑒 𝑀0−𝑀𝑒 (11) where, 𝑀0 is initial in dry basis and 𝑀𝑒 is the equilibrium moisture content of the sample and 𝑀𝑡 is mc on a dry basis at a time (t). during the drying process, continuous fluctuation in temperature, relative humidity, and velocity of the drying air was observed. therefore, a simplified form of moisture ratio, mr = 𝑀𝑡 /𝑀0 is selected for the dimensionless parameter. the procedures for thin-layer drying are typically used for evaluating and characterizing the drying parameters. the empirical models demonstrate the relationship between drying time gyawali et al. / bibechana 19 (1-2) (2021) 40-60 43 and moisture content using regression analysis. full-scale experiments are not feasible for various products. hence, these models are needed for simulation by using the drying model to predict the drying rate [20]. a total of 15 most used thinlayer drying models were fitted with experiment results in this study to find the best model for describing the ginger drying process (table 1). table 1: drying models used for the study to find out best-fitted model sn name of models model equations references 1 lewis mr = exp (-kt) [31] 2 page mr = exp (-kt^n) [32] 3 modified page mr = exp (-(kt)^n) [33] 4 henderson and pabis mr = a exp (-kt) [34] 5 logarithmic model mr = a exp (-kt) + c [35] 6 two-term mr = a exp (-k1t) + b exp (-k2t) [36] 7 wang and singh mr = 1 + at + bt^2 [37] 8 modified henderson and pabis mr = a exp (-kt) + b exp (-gt) + c exp ( -ht) [38] 9 verma et al. mr = a exp (-kt) + (1-a) exp (-gt) [39] 10 midilli and kucuk mr = a exp (-kt^n) + bt [40] 11 diffusion approach mr = a exp (-kt) + (1-a) exp (-kbt) [41] 12 two-term exponential mr = a exp (-kt) + (1-a) exp (-kat) [42] 13 simplified fick's diffusion equation mr = a exp (-c(t/l^2)) [43] 14 modified page equation-ii mr = exp (-k(t/l^2)^n) [41] 15 gaussian model mr = a exp (-(t-b)^2/ (2c^2)) [44] 2.2 design of dryer in this study, a mixed-mode solar dryer was designed as per the parameters such as solar radiation, sunshine hours, efficient tilt angle, etc. the optimum tilt angle for maximization of solar insolation on an annual basis is 30° [45], which is also the angle near the latitude of dharan (26.7944° n, 87.2817° e), nepal. the annual average solar radiation of dharan was found to be 3.68 kwh/m2/day [46], average solar radiation to the surface is 525.12 w/m2, and the average sunshine hour is 7 hours/day. the average ambient temperature of dharan during the daytime is about 30℃. the various researches found that the average collector efficiency of aluminum corrugated collectors was about 30% [47]. the requirement of exhaust air temperature from the collector is 50-55℃, which is used for safe drying of ginger and turmeric [48,49]. the mass of the ginger or turmeric was 5 kg for drying in the dryer, and the initial moisture content was taken as 90% (wet basis). the sunshine hour was considered as 7 hours per day and required the final moisture content to be 10%. water amount to be removed from fresh ginger/ turmeric product [50]. mrem = m( initial moisture (%)−final moisture (%) 100−final moisture(%) (12) by using eq. (12), the mass of water to be removed was 4.44 kg, and the amount of heat needed to remove the mass of water is given by eq. (13) [51]. qremove = mremover(hfg + hf) (13) at, 50 degrees celsius (assuming temperature inside the dryer), specific enthalpy of water at gyawali et al. / bibechana 19 (1-2) (2021) 40-60 44 latent heat of evaporation ( hfg) is 2357.6 kj/kg and enthalpy of water (hf) was taken as 4.18 kj/kg. hence, by using eq. (13), the amount of heat required to remove water was determined as 10,391.832 kj/kg. hence, considering 7 sunshine hours, the rate of energy required was determined as 412.37 w. the primary collector’s absorber was considered a corrugated black painted aluminum foil with absorptivity (α) 0.9. the total amount of useful heat provided by the collector [52] was determined by eq. (14) qu=ac[it(<τ.α>) -ul(tc-ta)] fr (14) where fr is the heat removal factor which was considered as 0.9, and the overall heat transfer loss coefficient was taken as 5 w/m2.°c. the plain window glass was taken with the transmissivity of 0.9, and ac is the area of the collector that is exposed to direct sunlight of solar. the < τ. α > was determined by eq. (15) by taking the diffuse reflectance of glass cover as 0.16. < τ. α >= ( τ×α 1−(1−α)ρ ) (15) using the obtained value of <τ.α> as 0.823 from eq. (15), the collector area was determined as 1.2920 m2. by considering the required collector area and the maximum utilization of solar radiation, the collector was split as a primary collector (corrugated aluminum) and secondary collector, the wall of the drying cabinet, to form a mixedmode solar dryer. so, it would also overcome the hourly variation of solar radiation and temperature. the dimension of the primary collector is 800 × 620 × 150 mm3, and secondary collector on each module is 1,140 × 496 mm2 and then to maintain the capacity of the dryer 5-10kg, the single solar collector connected with the two easily detachable cabinets having different tray dimensions supporting the inclination of a glass of cabinet 30° with horizontal. exhaust fans of 12 volts 0.32a were placed on each side of the drying cabinet and were operated by a solar panel. the exhaust fan placed on its side helped to make the force circulation of air so that the drying efficiency would be maximized. the trays were placed in such a way that the products absorbed heat directly and took heated air from the collector. the drawing of the dryer and each component detail is shown in fig. 1 and table 2 respectively. (a) (b) fig. 1: (a) sectional front view and back view of the mixed-mode solar dryer including all dimension of components in mm and (b) 3d view of the dryer created by using solidwork software for depicting each component of dryer gyawali et al. / bibechana 19 (1-2) (2021) 40-60 45 table 2: details of dryer components including their technical specifications s.n descriptions remarks (mm) 1. the dimension of the collector box 800 × 620 × 150 2. collector plate area 740 × 590 3. the thickness of the aluminum plate 1.2 4. absorber surface corrugated black 5. insulation thickness 25 6. raised of drying cabinet from ground surface 530 7. spacing of trays 140 8. the dimension of trays. tray 3 tray 2 tray 1 962 × 465 × 30 745 × 465 × 30 435 × 465 × 30 9. the thickness of the glazing surface 10 10. dimension of door 459 × 497 11. number of the fan on each end of the module 2 12. inlet of the collector 500 × 45 13. the diameter of 4 pipes for of air flowing (pvc) 38.1 2.3 cfd analysis of the solar dryer the fluid domain of the dryer was made with the support of solidworks software and ansys design modular (fig. 2). the dimensions and specifications used while making the 3d fluid domain were used according to the design. the drying bed of 5 mm was taken in each chamber for the tray. ansys fluent student 2019 r3 (academic version) was used to analyze the dryer, and meshing of the model was done according to the model’s geometry. the meshing elements and nodes were 497,428 and 96,952, respectively, which were below the optimum mesh limit provided by the ansys academic version. the boundary conditions (faces), such as inlet, outlets, outlets, woods pipes, etc., were defined during the meshing. after that, fluent was opened in serial mode, and steady-state and pressurebased analysis was used. the k-epsilon (2-eqn) with a realizable standard wall function was used for the viscous model. the discrete ordinate and solar ray tracing were used in the radiation model. the latitude and longitude were selected as the location of dharan, nepal, with a time zone of +5.45 and the sunshine factor as 1. the analysis time was taken in the month of november 23 at 12:00 pm. selected materials, along with their properties, are shown in table 3. gyawali et al. / bibechana 19 (1-2) (2021) 40-60 46 (a) (b) fig. 2: (a) 3d model of fluid domain of the dryer including trays, collector, exhaust, pvc etc. and (b) meshing of the model with tetrahedral mesh table 3: material properties of the material used in the cfd analysis of dryer [53,54] sn material density (kg/m3) specific heat capacity (j/kg-k) thermal conductivity (w/m2) 1 wood (ply wood) 700 2310 0.173 2 pipes 1467 840 0.17 3 glass (normal window glass 2300 792 0.8 4 ginger 410 3566.87 0.2916 5 aluminium 2719 871.9 202.4 similarly, the porous media was considered for the drying bed of ginger slices presented in the trays. for the bed of ginger slices, the permeability and inertial loss coefficient were determined from the eqs. (7) and (8) by considering the volume of the void and volume of the drying bed as 0.3 and the average diameter of the slices particles as 2 cm. the value of c and (1/ 𝛼) are 4,537.037 (1/m) and 680,559.144 (1/m2), respectively. the inlet is considered as pressure-based, and two outlets were provided with the mass flow rate of 0.0072 kg/sec (considering the average velocity of air exhausted from the fan as 0.75 m/sec). the absorptivity of the absorber was considered as 0.95, and transitivity and absorptivity of glass were taken as 0.9 and 0.05, respectively. the solution methods used were schemes coupled with third-order muscl for better accuracy. the solving iteration was taken as 1000. after that, post-processing was carried out to determine the temperature and velocity distribution pattern in collector and drying chambers. 2.4 construction of dryer cheap and locally available materials were used for the construction of the dryer. the dryer consists of essential parts such as a collector, drying cabinet, drying tray, and exhaust fans (fig. 3). collector was manufactured using a 1.2 mm corrugated aluminum sheet, painted black, mounted in the plywood box. the spacing of the corrugated sheet and glazing was 65 mm. a 1-inch angle-shaped aluminum frame gave the structural support by welding. . gyawali et al. / bibechana 19 (1-2) (2021) 40-60 47 fig. 3. experimental setup of the designed and fabricated mixed-mode solar dryer showing its components. ginger and turmeric slices were used for the experiments 2.5 experimental procedure the experiments were carried out in november 2019. the slices of ginger and turmeric of 2-5mm, harvested in november from bishnupadhuka, dharan, were used for drying. for the experiment 2.5 kg, each of the ginger and turmeric slices was used. the drying time started from the same point. different instruments measured different parameters of solar dryers on an hourly basis. biochemical analysis of ginger and turmeric was done by using a soxhlet apparatus method and steam distillation method (table 4). the fresh ginger samples were ground into a mesh using a manual blender, and 30g of the fresh ground ginger was added into a round bottom flask with water as a solvent. the quickfit distillation apparatus was set on a thermostatic heating mantle and maintained 100℃ for ginger and turmeric. the extraction process was set for about 20-25 minutes, and the liquid collected on the beaker was separated by a liquid separating funnel [55]. the essential oil of dried ginger was also extracted as per the equivalent of fresh ginger weight at various mc. similarly, 10g of dried ground ginger was weighed into the thimble wetted 5 ml of the ethanol solvent before fixing the thimble 100 ml of ethanol was poured on a round bottom flask and was fitted; the heating mantle was regulated to 78℃, which is the boiling point of ethanol. the setup was heated for about 1-1.5hrs until the ethanol and oil solutions were dropped from the soxhlet funnel to the round bottom flask. after that, the heating mantle was turned off, and the apparatus was left to cool down. this was distilled by distillation apparatus by maintaining the temperature of 78℃ to separate the ginger and turmeric oil [55,56]. table 4: instruments and methods used for determining physical and biochemical parameters items methods instrument used physical parameters temperature direct method mercury and alcohol thermometer (1℃) humidity psychrometric method psychrometer (1%) velocity direct method analog anemometer mc helium moisture analyzer, setting up the program time 10 min at 120 ℃. kern dlb helium moisture analyzer solar radiation pyranometer biochemical parameters oleoresin soxhlet method soxhlet apparatus essential oil steam distillation steam distillator exhaust fan solar panel ginger slices turmeric secondary collector primary collector tray 1 tray 2 tray 3 exhaust pipes inlet gyawali et al. / bibechana 19 (1-2) (2021) 40-60 48 3. result and discussion 3.1 results of cfd analysis the temperature obtained from the simulation showed that the average temperature of the tray increased from bottom to top (table 5). the air velocity was found maximum at pvc pipe sections around 3.425 m/sec. the higher temperature of the air was reached near the collector plates (fig. 4). (a) (b) (c) (d) fig. 4. cfd simulations (a) temperature distribution contours of trays and outlet which depicts that average temperature increase from lower tray to the upper tray and temperature was maximum where the tray exposed maximum sunlight (b) temperature distribution for vertical sections showing that temperature is increased from inlet to outlet, and (c-d) velocity distribution and vectors in the dryer showing that the extreme velocity at the pvc section of the dryer table 5: cfd analysis’s results which showed that the average temperature nearest to the tray increase from tray 3 to top tray 1 s.n. positions average temperature (°c) 1 inlet temperature 30 2 tray 1 (nearest) 44 3 tray 2 (nearest) 42 4 tray 3 (nearest) 40 5 collector temperature outlet) 41 6 outlet 1 43 7 outlet 2 44 gyawali et al. / bibechana 19 (1-2) (2021) 40-60 49 3.2 temperature and relative humidity variation on the dryer the ambient temperature rises from the collector pass through the drying cabinet and rises while reaching from tray 3 to tray 1 (fig 5 (a)). at first, the cabinet’s temperature rose to a small extent because the energy was used for the removal of moisture, not for the rise in the temperature of the cabinet. after the removal of some extent of mc, the temperature rose and reached a maximum level. the maximum rise temperature was found to be 48 ℃. the temperature difference was recorded as 10℃ at 12:30 in day-1 and then 15 ℃ at the 13.00 and 10:30 in day-2 and day -3 respectively. firstly, the exhaust air humidity was high because the mc on the product was greater. later reduced in the moisture content of a product did not restrict to a decrease in the relative humidity (r.h.), which is clear on the graph (fig 5 (b)). (a) (b) fig. 5. temperature and humidity over time (a) temperature variation curve of the different tray in the dryer showing that the temperature was supreme in upper trays than the lower one and (b) exhaust humidity curve of the different compartment shows that relative humidity from exhaust fan is affected by moisture content at the initial stage of drying. 3.3 drying curve the ginger and turmeric drying curve in the mixed-mode solar dryer also follows the standard food-drying curve. it took about 14 hours to reduce mc from about 88% to 10% for ginger and 85% to 12% for turmeric (fig. 6). there is a slight difference in the uniformity of the drying curve of each tray because of the rising trend of temperature from the lower tray to the upper tray (fig 7(a)-7(b)). fig. 6. ginger and turmeric drying curve shows that the time taken by the dryer is lesser than open sun drying 20 25 30 35 40 45 50 12 :3 0 13 :3 0 14 :3 0 15 :3 0 16 :3 0 9: 00 10 :0 0 11 :0 0 12 :0 0 13 :0 0 14 :0 0 15 :0 0 16 :0 0 8: 30 9: 30 10 :3 0 te m p er at u re (℃ ) time tray 1 tray2 tray 3 day-1 day-2 day-3 20 40 60 80 100 12 :3 0 13 :3 0 14 :3 0 15 :3 0 16 :3 0 9: 00 10 :0 0 11 :0 0 12 :0 0 13 :0 0 14 :0 0 15 :0 0 16 :0 0 8: 30 9: 30 10 :3 0 h u m id it y (% ) inlet humidity exhaust humidity (ginger compartment day -1 day -2 day -3 time 0 20 40 60 80 100 m c ( % ) time moisture content of ginger moisture of turmeric sun drying ginger sun drying turmeric day -1 day -2 day -3 gyawali et al. / bibechana 19 (1-2) (2021) 40-60 50 (a) (b) fig. 7:(a) variation of drying curve of turmeric on each tray and open sun drying. it shows that the drying faster in tray 1 than other one and (b) variation of the drying curve of ginger on each tray and open sun drying. it shows that the drying faster in tray 1 than other one 3.4 collector and dryer efficiency the efficiency of the collector and dryer was determined by utilizing eqs. (9) and (10), and the graph of collector efficiency was plotted on an hourly basis (fig. 8(b)). for determining efficiencies, the average radiations of five minutes in each period were taken into consideration (fig. 8(c)). the maximum collector efficiency was found at about 45.32% at 14:30. the maximum drying efficiency was recorded at approximately 26.33% at 14:00 in day -1 and 31.36% at 10:30 in day-2 which were the initial period of the experiment in each day, and its efficiency decreased later. (a) (b) 0 10 20 30 40 50 60 70 80 90 m c ( % ) time tray 1 tray 2 tray 3 sun drying turmeric day -2day -1 day -3 0 20 40 60 80 100 m c (% ) time tray 1 tray 2 try 3 sun drying ginger day -1 day -3day-2 0 0.005 0.01 0.015 0.02 1 2 :3 0 1 4 :0 0 1 5 :0 0 1 6 :0 0 1 0 :3 0 1 1 :3 0 1 2 :3 0 1 3 :3 0 1 4 :3 0 1 5 :3 0 8 :3 0 1 0 :3 0m a ss f lo w r a te ( k g /s e c ) time mass flow rate ginger compartment turmeric compartment day -1 day -2 day -3 0 10 20 30 40 50 1 2 :3 0 1 4 :0 0 1 5 :0 0 1 6 :0 0 1 0 :3 0 1 1 :3 0 1 2 :3 0 1 3 :3 0 1 4 :3 0 1 5 :3 0 8 :3 0 1 0 :3 0 e ff ic ie n c y ( % ) time collector effieciency dryer efficiency day-1 day -2 day -3 gyawali et al. / bibechana 19 (1-2) (2021) 40-60 51 (c) fig. 8. (a) mass flow rate of air from each compartment (b) drying and collector efficiency showing that they are highest in mid-day and (c) solar radiation among the three days. 3.5 biochemical evaluation the essential oil content of the dried product was found less than its initial conditions. however, it was found that the retention of essential oil was higher in the mixed-mode solar dryer. it was measured 1.66 ml (at 10% mc) and 0.5 ml (at 12.33% mc) in ginger and turmeric, respectively, in mixed-mode solar drying, which is higher than that of respective open sun drying (table 6). the oleoresin content of ginger through dryer was found similar at 10% mc to sun drying sample of mc 20.69%. the oleoresin content of the turmeric slice of the dryer of mc at 12% was also found similar to the sun drying of 28.7% mc, due to the complete drying powder was used to extract the oleoresin content of any products (table 7). table 6: essential oil determination of various samples of ginger and turmeric shows that essential oils are retained more in the products dried in the dryer rather than open sun products s.n. sample mc (%) weight of sample (g) essential oil (ml) the volume of essential oil +water (ml) ginger 1 fresh 87.75 30 2.2 84.55 2 solar dried 10.03 equivalent of fresh 1.66 86.55 3 open sun-dried 20.69 equivalent of fresh 1.5 85 turmeric 1 fresh 86 30 0.6 54 2 solar dried 12.33 equivalent of fresh 0.5 49 3 open sun dried 28.70 equivalent of fresh 0.35 51.5 table 7: oleoresin extraction of various samples of ginger and turmeric slices which shows that there are no significant changes in oil amount of products in both type of drying methods s.n. sample mc (%) sample weight (g) oil weight (g) ginger 1 dryer 10.33 10 0.614 2 open sun drying 20.69 10 0.610 turmeric 1 dryer 12.33 10 0.7134 2 open sun drying 28.70 10 0.7295 0 200 400 600 800 1000 1200 0 8 :0 0 0 8 :2 0 0 8 :4 0 0 9 :0 0 0 9 :2 0 0 9 :4 0 1 0 :0 0 1 0 :2 0 1 0 :4 0 1 1 :0 0 1 1 :2 0 1 1 :4 0 1 2 :0 0 1 2 :2 0 1 2 :4 0 1 3 :0 0 1 3 :2 0 1 3 :4 0 1 4 :0 0 1 4 :2 0 1 4 :4 0 1 5 :0 0 1 5 :2 0 1 5 :4 0 1 6 :0 0 1 6 :2 0 r a d ia ti o n ( w /m ^ 2 ) time gyawali et al. / bibechana 19 (1-2) (2021) 40-60 52 3.6 drying models fifteen thin-layer drying models were applied to determine the model that correlates with the drying curve obtained from the experiments. the statistical data of the various models and their correlated coefficients were summarized in table (8-9) and curves (fig. 910). 3.6.1 drying model of ginger the statistical analysis found that the experimental drying curve of ginger dried in the dryer was highly correlated with the wang and singh model, as compared to the other models, with a high correlation coefficient of 0.992. however, it was also found that the experimental sun-drying curve of ginger was highly correlated with the gaussian model with a higher correlation coefficient of 0.996 than other thin layer drying models. it was also clearly depicted from the top results graphs generated by curve expert professionals. hence, wang and singh model and gaussian model were used for describing the drying curves of solar-dried and sun-dried ginger slices. the drying equation model (gaussian model) for ginger slice drying in the open sun 𝑀𝑅 = 1.242815𝑒 (−( (𝑡+7.434025)2 2×10.00052 )) the drying model equation (wang and singh model) for ginger slices drying in the mixed-mode solar dryer. 𝑀𝑅 = 1 − 0.131715𝑡 + 0.004265117𝑡2 (a) (b) fig. 9. best fitted statistical analysis thin-layer drying model for ginger drying using (a) mixed-mode dryer and (b) open sun drying. figures show that the gaussian model and wang and singh model is suitable for ginger dried in the open sun and solar dryer gyawali et al. / bibechana 19 (1-2) (2021) 40-60 53 table 8: drying model for ginger (drying with dryer and open sun drying) including their model coefficients and correlation coefficient obtained from statistical analysis using curve expert professional s n model name coefficients r remarks sun drying drying with dryer sun drying drying with dryer 1 lewis k = 0.1296472 k = 0.18841 0.987706 2 0.971945 2 henderson and pabis a= 1.01896, k= 0.132145 a= 1.064303, k = 0.1928872 0.987971 2 0.97459 3 logarithmi c model a= 0.209173, k= 0.083905, c= 0.2365136 a = 1.3419, k= 0.108494, c= 0.33131 0.995560 38 0.98888 4 two term a= 0.510209, k1= 0.1321453, b= 0.5087503, k2= 0.1321458 0.987971 279 5 wang and singh a= 0.09744905, b= 0.0024375 a =-0.131715, b= 0.004265117 0.995175 0.9915 dryer 6 modified henderson and pabis a= 0.4457465, k= 0.1920674, b= 0.3087505, g= 1.927013, c= 0.3087505, h= 0.1927013 0.97459 7 verma et al. a= 45, k=0.349321, g= 0.356125 0.988542 8 diffusion approach a= 1, k= 0.12964, b= 1 a= 1, k= 0.1818841, b= 1 0.987706 2 0.971944 8 9 two term exponential a= 1.704871, k = 1.728126 a=1.918381, k= 0.2693824 0.992835 6 0.987296 10 simplified fick’s diffusion equation a= 1.018965, c= -0.09538507, l= 0.8495947 a = 1.064304, c= -62.0009, l= 17.92910 0.987971 0.974559 26 11 modified page equation-ii a = 0.9240763, k= -0.05799948, l= 1.042762, n= 1.379280 0.994794 8 12 gaussian model a = 1.242815, b= -7.434025, c= 10.0005 0.996313 sun drying gyawali et al. / bibechana 19 (1-2) (2021) 40-60 54 3.6.2 drying model of turmeric similarly, the turmeric’s sun drying and solar dried curves were also analyzed with the various thin layer drying models in curve expert professional software. it was found that the sun drying curve and dried solar curve of turmeric were highly correlated with the wang and singh model because they had a high correlation coefficient with wang and singh model as r= 0.99459559 for sun drying and r= 0.990296 for solar dried turmeric. hence, wang and singh’s model was suitable for describing the drying curves of turmeric generated from sun drying and drying with a designed dryer. the drying equation model (wang and singh model) for turmeric drying open sun: 𝑀𝑅 = 1 − 0.105147𝑡 + 0.0029729𝑡2 the drying model equation (wang and singh model) for turmeric drying in the mixed-mode solar dryer: 𝑀𝑅 = 1 − 0.13253𝑡 + 0.004296𝑡2 (a) (b) fig. 10. best fitted statistical analysis thin-layer drying model for turmeric drying using (a) mixed-mode dryer and (b) open sun drying. figures show that the wang and singh model is best fitted for turmeric in both drying methods . gyawali et al. / bibechana 19 (1-2) (2021) 40-60 55 table 9: drying models for turmeric (drying with dryer and open sun drying) including their model coefficients and correlation coefficient obtained from statistical analysis using curve expert professional sn model name coefficients r remarks sun drying drying with dryer sun drying drying with dryer 1 lewis k= 0.1356688 k = 0.1800525 0.9902106 0.97526 2 henderson and pabis a= 1.010587, k= 0.137134 a= 1.041562, k= 0.1872 0.99029288 0.976 3 logarithm ic model a= 1.09777, k= 0.1062144, c= 0.1160442 a=1.286532, k = 0.1102, c = -0.294118 0.993418 0.988 4 two term a = 0.5011, k1= 0.18726, b= 0.54041, k2= 0.1872676 0.97645 5 wang and singh a= -0.105147, b= 0.0029729 a= -0.13253, b= 0.004296 0.99459559 0.990296 open sun drying and dryer 6 modified henderson and pabis a= 2.65549, b= 0.19734, b = 0.852590, g= 0.26499, c= 0.853352, h= 0.2683422 a= 0.1738, k= 0.18720, b= 0.43383, g= 0.18772, c=0.4338, h=0.18722 0.99423666 5 0.9764525 7 diffusion approach a= 1.000, k= 0.1356688, b= 1 a= 1,k= 0.18005, b=1 0.99021063 0.975266 8 two term exponenti al a = 1.649675, k= 0.1753714 a = 1.84537, k= 0.257657 0.9933525 0.98636 9 simplified fick’s diffusion equation a= 1.0105, c= 0.667957, l= 2.207009 a= 1.04156, c= 340.8, l= 42.6 0.99029288 9 0.9764525 10 modified page equationii a= 0.93937, k= -0.95527, l= 2.7832, n = 1.2694 0.994565 4. conclusion a simple mixed-mode solar dryer was designed and constructed successfully using locally available materials. the dryer testing was done in november using ginger and turmeric. the steady-state cfd analysis was performed using ansys fluent in predicting the temperature and velocity of the air inside the collector, trays, and outlet of the dryer. gyawali et al. / bibechana 19 (1-2) (2021) 40-60 56 the experiment’s findings showed a substantial increment of the maximum temperature of around 15 ℃ in the tray of the dryer than ambient temperature. the time required for drying of the ginger and turmeric in the dryer was 14 sunshine hours from about 88% mc to 10-12% mc which was much higher than open sun drying. in addition to this, the maximum drying and collector efficiency were found to be 31.364% and 45.32%. from the result of the cfd analysis, it was found that the average temperature of the tray increased from lower trays to upper trays and maximum where trays were exposed to the sunlight, which correlates with the temperature results obtained from the experiment. the biochemical analysis performed in the essential oil and oleoresin showed that retention of the essential oil was more in the dryer product than the open sun drying product. the drying curves obtained from the dryer for ginger and turmeric were highly correlated to wang and singh model (r= 0.990296 for turmeric and 0.992 for ginger) compared to other drying models. based on the finding of the experiments, it was concluded that the designed mixed-mode solar dryer has sufficient capacity to dry food items rapidly to a safe moisture level, and simultaneously, it ensures a good quality of the 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[56] r. kanadea, d.s. bhatkhandeb, extraction of ginger oil using different methods and effect of solvents, time, temperature to maximize yield, int. j. adv. sci. eng. technol. 4 (2016) 2321–9009. http://www.ajer.org/ 1. introduction 2. methodology 2.1 governing equations and drying models 2.1.1 the governing equation used in cfd analysis 2.1.2 data calculation & analysis 2.1.3 drying models 2.2 design of dryer 2.3 cfd analysis of the solar dryer 2.4 construction of dryer 2.5 experimental procedure 3. result and discussion 3.1 results of cfd analysis 3.2 temperature and relative humidity variation on the dryer 3.3 drying curve 3.4 collector and dryer efficiency 3.5 biochemical evaluation 3.6 drying models 3.6.1 drying model of ginger 3.6.2 drying model of turmeric 4. conclusion acknowledgment conflicts of interest references bibechana vol. 22, no. 3, december 2025, 195-204 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar study of photovoltaic system performance across different geographical region of nepal sanjay lal karna1,2, ajay kumar jha3,∗, kishori yadavi4 1central department of physics, tribhuvan university, kirtipur, nepal 2department of physics, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal 3department of mechanical and aerospace engineering, institute of engineering, tribhuvan university, pulchowk campus, lalitpur, nepal 4department of physics, patan multiple campus, tribhuvan university, lalitpur, nepal ∗corresponding author. email: akjha@ioe.edu.np abstract the objective of this work is to study the photovoltaic system performance across different geographical region of nepal and its economic benefits. nepal's solar irradiation varies significantly by season, from 4.5 kwh/m² in december to 7.2 kwh/m² in may. notably, may has the highest irradiance levels, whereas december has the lowest. the himalayan region, including mustang, kehami, and jomsom, has greater irradiance levels ranging from 6 to 6.5 kwh/m²/day. the eastern half of nepal has lower irradiance values, below 4.4 kwh/m²/day. the palce of high irradiance, has current output ranges from 19 a to 27.5 a, with peak pv power of 375 w when simulated with secondary data. the simulation observation shows temperature fluctuations has influence power output, with higher power at lower temperatures. also, the power generation by pv rises with decreasing temperature and shifts to optimization voltage. the relationship between global horizontal irradiance and photocurrent is linear and increase from 9 to 19 a. at considered temperatures range the optimum creased photocurrent observed at 45°c. the economic analsyis was done considering 365 w solar pv system in nepal’s himalayan region and eastern half. the parameters use for economic analysis are payback period, return on investment (roi), and net present value (npv). the analysis show that at higher solar irradiance in the himalayan region leads to a shorter payback (15.7 years), higher roi (59.4%), and a less negative npv in comparative to the eastern half of nepal. these findings highlight the importance of knowing solar irradiance and temperature dynamics for optimizing pv system performance throughout nepal's different geographical regions. keywords global horizontal irradiance, himalayan, hilly and terai region, photocurrent, temperature, pv system performance article information manuscript received: march 3, 2025; revised july 12, 2025; accepted: july 16, 2025 doi https://doi.org/10.3126/bibechana.v22i3.76287 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 195 http://nepjol.info/index.php/bibechana akjha@ioe.edu.np https://doi.org/10.3126/bibechana.v22i3.76287 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ sanjay lal karna et al./ bibechana 22 (2025) 195-204 196 1 introduction photovoltaic (pv) cells are tools for transforming radiant energy from the solar to electrical in a sustainable manner. pv systems, which are typically consist of interconnected solar cells are shown in figure 1. these cells are designed to produce to maximum output energy. recent advances have enabled in the production of high-efficiency photovoltaic cells. they include certain multijunction solar cells approaching 50% of efficiency. the commercially accessible pv panels typically have converted efficiencies from 17% to 20% [1]. now a days, manufacturers give the electrical requirements of photovoltaic devices on the basis of standard test settings (stc). they include a controlled temperature of 25°c along with incident irradiance of 1000 w/m². to capture non-linear electrical behavior and environmental unpredictability, limited data exists on actual annual energy yield. nepal enjoys around 300 sunny days per year, offering strong potential for solar power. this makes it an ideal environment for photovoltaic technology to meet growing energy demands. however, many sites in nepal still lack essential research on solar energy. this study addresses that gap by highlighting the importance of renewable energy in nepal's context. figure 1: different types of photovoltaic cells depending on configuration [2] 1.1 research related to solar irradiance in nepal nepal's solar resource has inspired increased interest within photovoltaic systems. it is reported that roughly 1.1 million solar household systems. the nepal electricity authority has recently introduced net billing to encourage the use of rooftop solar panels. also the potential of technologies to assist governmental decisions on expanded power generation. a report by kadle et al. shows kathmandu, pokhara, butwal, nepalgunj, and biratnagar has tr rooftop solar panels potential, like 637 gwh per year in kathmandu to 50 gwh per year in butwal [3]. nepal has favourable geography and abundant solar radiation, which averages between 3.6 and 6.2 kwh/m2/day and roughly 300 days of sunshine per year. the current statistics show that both the thabang solar mini-grid (tsmg) and sugarkhal solar mini-grid (ssmg) experience their peak energy generation in april. tsmg generated 83.206 mwh/year in 2021 with 112.140 mwh/year in 2022, having a peak sun hour (psh) of 5.5 h. ssmg produced 64.14 mwh/year in 2021 as well as 68.79 mwh/year in 2022, with a psh of 5.7 h [4]. a potential solution to the energy crisis in remote areas like karnali province where about 67% of the population lacks access to the national grid is the use of pv solar mini grids. due to the region's rugged geographical region, extending the grid is challenging, making solar mini grids a more economical and efficient option with high generation potential [5]. 1.2 significant of research understanding solar energy in nepal has impacts beyond research. studying how solar radiation, temperature, and power generation interact can guide major improvements in the country’s energy system. this knowledge can help create tailored plans to optimize solar power production, boosting energy independence and protecting against price changes. identifying the best locations for solar pv can help use nepal’s vast solar resources for economic growth and rural development. developing solar infrastructure can create jobs, attract investments, and support local industries, improving socioeconomic conditions. as nepal faces climate change and environmental challenges, solar energy can reduce greenhouse gas emissions and reliance on fossil fuels. closing research gaps and fully using renewable energy can lead nepal toward a greener and more prosperous future. 1.3 research gap although there are studies on solar irradiance and power generation in nepal, important gaps remain. one key gap is understanding how geography, solar irradiance, and temperature together affect photovoltaic system performance. research on how these factors interact in nepal’s different regions, himalayan, hilly, and eastern terai is limited. these regions have diverse climates and geographical region, which likely influence solar power output differently. additionally, economic feasibility studies comparing pv system performance across these regions are rare. few studies combine technical data like irradiance, temperature effects, and sanjay lal karna et al./ bibechana 22 (2025) 195-204 197 power output with financial measures such as payback period, return on investment (roi), and net present value (npv). this lack of integrated analysis makes it hard to determine the most suitable locations for solar energy projects. overall, there is a strong need for comprehensive research that includes both technical performance and economic viability. such studies would help identify optimal areas for solar power deployment throughout nepal, considering its varied geography and climate conditions. 2 methods and materials 2.1 pv module used in this research for the computation detial of studying the nature of power generated, voltage and current, solarex msx60 pv module, a conventional 60w module made up of 36 polycrystalline cells connected in series, was used in the investigation. the pv module more detial is shown in table 1. these criteria served as the foundation for analysing the pv module's performance and attributes in the study. table 1: specification of solar pv module used in this research: solarex msx60 [6] at 25°c parameter msx60 specification maximum power (pmax) 60 w voltage at pmax (vmp) 17.1 v current at pmax (imp) 3.5 a short-circuit current (isc) 3.8 a open-circuit voltage (voc) 21.1 v 2.2 theory solar cells serve an important role in transforming solar energy into electricity, providing an environmentally friendly and renewable source of energy. solar cell technology has progressed throughout time, from single-crystal silicon to flexible film, organic, dye-sensitized, perovskite cells, etc. material enhancement, construction, contact systems, characterization techniques are used to improve solar cell performance. the shockley diode model is a popular model for solar cell analysis. it allows for extensive analysis and modelling to optimize the efficiency of solar cells and capacity, a single-diode model demonstrated in figure 2. figure 2: circuit diagram of shockley diode model of solar cell [7] the output current of an ideal solar cell is found as i = iph − is [ exp ( qvoc nskat0 ) − 1 ] (1) where iph is photogenerated current, is is saturation current, q is elementary charge of an electron, voc is open-circuit voltage of the solar cell, ns is number of cells/modules in series, k is boltzmann constant, a is ideality factor of the diode (typically between 1 and 2) and t0 is reference or operating temperature. in the ideal scenario, beam produced power is directly proportional to irradiation brightness, and photovoltaics provide a reasonable estimate. the mathematical representation of a photovoltaic cell (real/practical cell type) containing infinite rs (series resistance) along with rp (parallel resistance), then the diode current becomes id = is [ exp ( q (v + irs) nskat0 ) − 1 ] (2) when rs is taken into account, the resulting current of the module with ns cells in series becomes: i = iph − is [ exp ( q (v + irs) nskat0 ) − 1 ] (3) when the solar energy system is coupled in series and parallel, the current using equation (3) is i = np × iph −np × is [ exp ( q (v + irs) nskat0 ) − 1 ] (4) the incident flux has a relationship to the photocurrent (iph), and thus not dependent on voltage (or rs). the photocurrent generated by solar radiation along with the temperature influenced by it can be computed as iph = [isc +ki(t0 − tr)]× g gref (5) sanjay lal karna et al./ bibechana 22 (2025) 195-204 198 where ki is temperature coefficient of the shortcircuit current (in a/°c), tr is reference temperature (typically 25°c), g is actual solar irradiance (sunlight intensity) on the panel surface (in w/m²) and gref is reference irradiance, usually 1000 w/m² (standard test conditions). the single-diode model, which consists of a single diode component including five electrical parameters, constitutes one of the simplest representations of pv panels' intrinsic nonlinear features. castaner and silvestre (2002) created an implicit mathematical formula known as the usual i-v characteristic equation. i = iph − is [ e v +irs a0nvt − 1 ] − v + irs rsh (6) the thermal voltage (vt) can be mathematically stated as vt = kt/q. further circuit analysis can create a mathematical association between along with the incident ambient condition of the photovoltaic cell (radiation, g, and temperature, t) as reported [8]. 2.3 parameters analysis of deploying pv systems in different regions the methodology of this research involves a financial assessment of a solar photovoltaic system by calculating three key economic parameters: payback period, roi, and npv. first, the total initial investment cost is determined by summing the prices of solar panels, mppt controllers, installation, and battery replacements over the system’s 25-year lifespan. next, the annual energy output is estimated based on the panel’s rated power, local peak sun hours (psh), and system performance ratio. using these values, the payback period is calculated by dividing the initial investment by the annual monetary savings, derived from multiplying annual energy output by the local electricity rate. roi is then computed as the percentage difference between the total revenue generated over the system lifetime and the initial investment. finally, npv is calculated by discounting annual savings over 25 years at a chosen discount rate (6%) and subtracting the initial investment to assess the system’s present economic value. this methodology allows comparison of the solar system’s financial viability across different geographic locations with varying solar irradiance levels. 3 results and discussion 3.1 solar irradiance in nepal according to nasa's surface meteorology along with solar energy dataset, the average daily solar radiation on a horizontal plane in nepal varies significantly by season. the annual irradiation rate ranges from 4.5 kwh/m² in december to 7.2 kwh/m² in may [9]. notably, may has the highest average monthly sun irradiation, whereas december has the lowest amounts. this seasonal pattern represents the shifts in solar angle during daylight length caused by the tilt that occurs in the earth's axis with its orbit around the solar system. previous research, such as that undertaken by neupane et al. [10], has found comparable seasonal variations in sun irradiance across nepal's different geographical regions. figure 3 from the 2023 global solar atlas depicts the geographic distribution of solar radiation over nepal, offering a spatial picture of the region's solar energy potential. figure 3: solar irradiance above nepal ( [9] 3.2 current generated by pv modules at varying irradiation levels in nepal. solar irradiation varies significantly in nepal, affected primarily by topographical considerations. solar irradiation levels in the himalayan region, including mustang, kehami, as well as jomsom, are significantly higher, ranging from 6 to 6.5 kwh/m²/day. this increased irradiance causes higher current generation, with values ranging from 19 a to 27.5 a. tinje, saldang, dolphu, as well as mugu have high sun irradiation, which ranges from 5.6 kwh/m²/day to 6 kwh/m²/day, resulting in current outputs within this range. in contrast, the western area of nepal experiences significantly lower sun irradiation, average around 4.8 kwh/m²/day. in the eastern section of the country, solar irradiance values are below 4.4 kwh/m²/day. sanjay lal karna et al./ bibechana 22 (2025) 195-204 199 figure 4: pv current generated at different geographical region at 45 oc, at different region of nepal on the basis of irradiance level figures 4–6 demonstrate current-voltage characteristics at various temperatures and solar irradiation levels. it has been found that as the temperature drops, the voltage increases while the current flowing decreases. also, the current-voltage graphs show that when temperature decreases, the current switches to higher voltages before rapidly falling beyond particular voltage thresholds. the convergence of current with rising voltage occurs at around 20v at 45°c (figure 4), 22v at 25 °c (figure 5), along with 24v at 0°c (figure 6). these findings are comparable with prior research conducted on the pulchowk campus [11], indicating the validity and dependability of the provided results. the observation drops in power and current with increasing temperature is similar with the results of [12]. figure 5: v current generated at 25 oc, at different geographical region of nepal on the basis of irradiance level figure 6: pv current generated at 0 oc, at different geographical region of nepal on the basis of irradiance level the findings show solar irradiation and temperature variations across nepal significantly influence pv current output. high-irradiance areas like mustang and jomsom (6–6.5 kwh/m²/day) generate higher currents (19–27.5 a), making them ideal for solar pv system installation. in contrast, regions with lower irradiation, especially in the east and west, produce less current and require more efficient system design. additionally, lower temperatures enhance voltage, improving system performance. these support researchers, developers, and installation organizations in selecting optimal locations, designing efficient systems, and planning region-specific solar energy projects in nepal. . 3.3 power generated by pv at various irradiation levels in nepal the solar photovoltaic module's power output varies greatly across different geographical region of nepal, particularly in the himalayan region demonstrating significantly better power generation potential. specifically, in mustang, kehami, as well as jomsom, solar pv generated electricity is substantially higher than in other places, ranging up to 250 w, as illustrated in figure 7. the maximum electrical output of a solar pv module is often observed within a specified voltage range, usually between 10 and 15 v. this range shows the best working circumstances under which the pv module may produce the most power effectively. this improves the performance of solar pv system for energy extraction in specific region of nepal. sanjay lal karna et al./ bibechana 22 (2025) 195-204 200 figure 7: solar pv generated power at 45 oc, at different geographical region of nepal at difference irradiance level considering different possible temperature in context of nepal the solar power generated by pv module generated as shown in figures 7–9. on comparing the power generated across the different region of nepal with solar irradiance (figure 3 as references). the observation shows at 45°c, power generation in western part of butwal can produce up to 150 w across the terai and up to 200 w across hilly region of different places of nepal. similarly, in the region of the himalayas, solar pv systems generate significantly more power than terai and hilly region i.e. up to 250 w. the difference in power generated by solar pv is due to higher solar irradiation in the western himalayas compared to the eastern region, leading to greater power generation. figure 8: solar pv generated power at 25 oc, at different geographical region of nepal at difference irradiance level on comparison of higher irradiance level in himalayan region of nepal, especially mustang, kehami, as well as jomsom region photovoltaic solar energy generation is significantly higher than in other regions of nepal and observed up to 345 w as shown in figure 8. power output is higher in the western himalayas due to greater solar irradiation, peaking at 345 w compared to 270w in the east. this shows how geographic differences in sunlight directly affect solar pv performance, less pollution, sunshine peak hour, good orientation of solar panel, etc. in general, the solar pv power generation differs between the western along with eastern himalayas shows western himalayan region maximum at 375 w, whereas in the eastern himalayan region it can reach 300 w at considered temperature. the examination of the effect temperatures have on power generation finds a consistent pattern across many regions and conditions. with decreasing temperature, power output increases, accompanied by a shift to higher voltages. figures 7–9 show that the power convergence occurs approximately 20 v at 45°c, 22 v at 25°c, along with 24 v at 0°c. these findings are consistent with prior studies [8,13], supporting the observed phenomenon of power generation increasing voltage under varied irradiation. studying these dynamics is critical for optimising the deployment as well as efficiency of solar pv systems across various geographical locations, hence supporting the country's sustainable energy development. 3.4 impact of global horizontal irradiance on photocurrent figure 10 shows, how global horizontal irradiance effect photocurrent generated by solar pv module at different temperature in nepal (the region is consider for nepal from figure 3). on the absis of real data the three temperature scenarios (40°c, 25°c, along with 45°c) were used to measure photocurrent fluctuation. the study analysed photovoltaic cells' photocurrent production at various worldwide horizontal radiation levels, which varied from 3 kwh/m²/day to 7 kwh/m²/day. the observation shows photocurrent was linear with regard to the global horizontal irradiance as shown in figure 10. photocurrent readings ranged from 9 to 19 a at different irradiance level. also, at higher temperature the yield in photocurrent higher than lower temperature as example amount of photocurrent at 45°c is greater than that at 25°c and -40°c, emphasising the effect of temperature on the photocurrent generation. 3.5 impact of cell temperature on photocurrent figure 11 depicts the fluctuation in photocurrent depending on cell temperature, which ranges from 10.7 a to 11.5. the observation shows as the cell temperature increase photocurrent also increases. however, the fluctuation was small, and photocurrent values remained within a narrow range. also, sanjay lal karna et al./ bibechana 22 (2025) 195-204 201 the global irradiance has impact on photocurrent at different irradiance level means higher the level of irradiance higher the production of photocurrent. this shows that both irradiance and temperature have effects on photocurrent and consider panel generated current up maximum at the region of nepal where irradiance as well as temperature is both high. figure 9: photocurrent generate with global horizontal irradiance at differential temperature figure 10: photocurrent generate with global horizontal irradiance at differential temperature figure 11: cell working temperature vs photocurrent 3.6 -benefit analysis of deploying pv systems in different regions for cost-beneficial analysis of different geographical region of nepal on the basis of solar irradiances and power generation. a solar system setup consists of a 365 w panel costing npr 57,300, an mppt controller priced at npr 12,190, and installation expenses of npr 2,000. a battery system with a lifespan of 8 years, requiring three replacements over the 25-year system lifespan, adds npr 156,900 to the cost (3 batteries × npr 52,300 each). the total investment amounts to npr 228,390. the system assumes a performance ratio of 0.8, with average peak sun hours (psh) of 6.5 kwh/m²/day at himalayan region location and 4.4 kwh/m²/day at himalayan region location. electricity is valued at 15 npr/kwh, and the system is designed to operate over a 25-year lifespan. the annual energy output of a 365 w solar panel is calculated using the formula: e = 0.365 × psh × 365 × 0.8, where 0.8 is the assumed performance ratio. for the himalayan region place, with peak sun hours (psh) of 6.5 kwh/m²/day, the panel generates approximately 693.31 kwh/year, while for the eastern half place, with 4.4 psh, it produces 469.46 kwh/year. over a 25-year system lifespan, the total energy output is 17,332.75 kwh for himalayan region and 11,736.5 kwh for eastern half. the levelized cost of energy (lcoe) is then calculated as the total system cost divided by the lifetime energy output. with a total investment of npr 228,390, the lcoe is 13.18 npr/kwh for himalayan region and 19.46 npr/kwh for eastern half. the solar system, equipped with a 365 w panel and designed for daily use, can effectively support a combination of common household appliances. these include five 9w led bulbs (totaling 45w), five 5w mobile chargers (totaling 25w), and two 60w laptops (totaling 120w), resanjay lal karna et al./ bibechana 22 (2025) 195-204 202 sulting in a combined power demand of 190w. since the panel provides 365w of peak power and generates approximately 693.31 kwh/year (1.9 kwh/day) at himalayan region location and 469.46 kwh/year (1.29 kwh/day) at eastern half location, it can comfortably run these 190w loads for several hours daily—around 10 hours/day at himalayan region and about 6–7 hours/day at eastern half — demonstrating its suitability for basic residential or off-grid use. to meet a daily energy consumption of 950 wh (0.95 kwh) for 5 hours of use, a battery capacity of about 1,140 wh is needed after adding a 20% buffer for losses and cloudy days. for a 12v system, this equals roughly 95 ah, but considering a 50% depth of discharge (dod) for lead-acid batteries, the total required capacity becomes 190 ah at 12v. this setup can reliably power 5 led bulbs, 5 mobile chargers, and 2 laptops running for 5 hours daily. table 2 compares the electricity prices between solar systems and government-supplied electricity in different regions. while the levelized cost of energy (lcoe) from the solar system ranges from 13.18 to 19.46 npr/kwh—higher than the urban government rate of 10 npr/kwh—it is notably cheaper than the rural-hilly government rate of 21 npr/kwh, especially in the himalayan region where solar is about 37% cheaper. despite the higher per-unit cost of solar electricity in some areas, the overall investment in extending the government grid to remote, geographically challenging locations like mountainous villages in nepal is significantly greater. this is because the difficult terrain and dispersed settlements increase infrastructure costs, making solar systems a more viable and cost-effective solution for electrification in such offgrid areas. 3.7 payback period payback period is defined as the amount of time required for an investment to generate enough savings or revenue to recover the initial cost. it is calculated using the formula: payback period=initial investment/annual savings. where initial investment is the total upfront cost of the system, and annual savings represents the yearly financial benefit or revenue generated from the investment. a shorter payback period indicates quicker recovery of the invested capital. the solar system, with a total investment of npr 228,390, demonstrates different payback periods depending on location. in the himalayan region, the system generates 693.31 kwh/year, resulting in annual savings of npr 14,559.5 based on an electricity rate of 21 npr/kwh. this leads to a payback period of approximately 15.7 years. in the eastern half, with a lower annual output of 469.46 kwh/year, the annual revenue is npr 9,858.66, resulting in a longer payback period of around 23.2 years. these figures highlight that the system is more financially favorable in locations with higher solar radiation like the himalayan region. 3.8 return on investment return on investment (roi) measures the profitability of an investment by comparing the net gain to the initial cost. it is calculated as: roi = total savings over lifetime−investment investment ×100% where total savings over lifetime is the cumulative financial benefit gained from the investment, and investment is the initial cost. roi expresses the percentage return relative to the original investment, indicating how much profit (or loss) was made. the return on investment (roi) of the solar system varies significantly between regions due to differences in solar energy availability. in the himalayan region, the system generates a total of 17,332.75 kwh over 25 years, translating to a total revenue of npr 364,000 at the rural electricity sanjay lal karna et al./ bibechana 22 (2025) 195-204 203 rate of 21 npr/kwh. this results in an roi of approximately 59.4%, indicating a substantial gain over the initial investment of npr 228,390. in contrast, the eastern half yields a lower total energy output of 11,736.5 kwh, generating npr 246,465 in revenue over the same period, which gives an roi of only 7.9%. this means the system is much more economically beneficial in high-irradiance areas like the himalayan region, where energy production is higher and payback is quicker, while returns are minimal in lower-irradiance regions like the eastern half. 3.9 net present value net present value (npv) evaluates the profitability of an investment by calculating the present value of future cash flows discounted at a specific rate. assuming a discount rate r=6%, npv is calculated as: npv = 25∑ t=1 annual saving (t+ 0.6)t − inverstemnt assuming a discount rate of 6%, the net present value (npv) analysis reveals that the solar system yields negative returns in both locations over the 25-year lifespan. in the himalayan region, with an annual cash flow of npr 14,559.5, the npv is calculated as 14,559.5 × 11.9247 228,390 = npr 54,727.5, indicating that the system does not recover its initial investment in today's monetary terms. similarly, in the eastern half, the lower annual cash flow of npr 9,858.66 results in an even more negative npv of npr 110,850. these findings suggest that while the system performs better in high-irradiance areas like the himalayas, it still falls short of being financially viable when discounted future earnings are considered, highlighting the need for either cost reduction or subsidy support for greater feasibility. 3.10 limitations of research this study is subject to several limitations. solar irradiance in nepal varies significantly by season and region, ranging from 4.5 kwh/m² in december to 7.2 kwh/m² in may, with the himalayan regions such as mustang, kehami, and jomsom exhibiting higher irradiance (6–6.5 kwh/m²/day) compared to the eastern half, which remains below 4.4 kwh/m²/day. these variations, along with temperature fluctuations that affect current output and voltage, directly impact solar pv performance. however, the financial analysis in this study—covering payback period, roi, and npv— was conducted based solely on a single 365 w solar panel, mppt controller, installation, and battery replacement over a 25-year lifespan. furthermore, the simulation of power generation and energy output relied on secondary data rather than real-time field measurements, which may limit the accuracy and generalizability of the results across diverse geographic and climatic conditions in nepal. 4 conclusion the observation shows nepal's enormous possibilities for solar energy harnessing, specifically in the himalayan region with high irradiation levels. also, findings indicate a clear relationship between solar irradiance, the outside temperature, along with pv system performance. that means greater irradiance along with lower temperatures producing larger current and power outputs. the linear relationship between horizontal global irradiance and photocurrent demonstrates the predictability of pv system performance under changing environmental condition. these findings can help policymakers and stakeholders promote renewable energy adoption while encouraging sustainable development activities in nepal. the himalayan region is the more favorable location for solar pv deployment due to greater solar energy availability, resulting in faster cost recovery and higher returns. although both regions exhibit negative npvs, the system is more economically viable in the himalayas, while cost reductions or subsidies may be needed to improve feasibility in lower-irradiance areas like the eastern half. further study might concentrate on enhancing pv system models and incorporating energy storage options to improve grid resilience as well as stability when faced with of climate change risks. references [1] k. yoshikawa, h. kawasaki, w. yoshida, t. irie, k. konishi, k. nakano, t. uto, d. adachi, m. kanematsu, h. uzu, et al. silicon heterojunction solar cell with interdigitated back contacts for a photoconversion efficiency over 26%. nature energy, 2:17032, 2017. [2] d. hernández-lópez, e. r. de oña, m. a. moreno, and d. gonzález-aguilera. sunmap: towards unattended maintenance of photovoltaic plants using drone photogrammetry. drones, 7:129, 2023. [3] u. kafle, t. anderson, and s. p. lohani. the potential for rooftop photovoltaic systems in nepal. energies, 16(2):747, 2023. [4] s. l. karna, a. k. jha, k. yadav, and j. k. mallik. performance evaluation of solar pv sanjay lal karna et al./ bibechana 22 (2025) 195-204 204 mini grid system in nepal: a case study thabang and sugarkhal. frontiers in energy research, 11:1321945, 2024. [5] a. sedai, r. dhaka, p. koirala, s. gautam, r. pokhrel, s. p. lohani, h. moussa, and s. pol. renewable energy resource assessment for rural electrification: a case study in nepal. international journal of low-carbon technologies, 18:1107–1119, 2023. [6] solarex. msx-60 and msx-64 photovoltaic modules. https://www.solarelectricsupply. com/media/custom/upload/solarex-msx64. pdf, 1998. [7] m. diantoro, t. suprayogi, a. hidayat, a. taufiq, a. fuad, and r. suryana. shockley’s equation fit analyses for solar cell parameters from i-v curves. international journal of photoenergy, 2018. [8] b. françois, v. bernard, s. venel, and t. baldran. mc 2: a power conditioning and distribution unit for stratospheric balloons. e3s web of conferences, 16:14008, 2017. [9] global solar atlas. nasa’s surface meteorology and solar energy dataset, 2023. accessed 2023. [10] d. neupane, s. kafle, k. r. karki, and p. pradhan. solar and wind energy potential assessment at provincial level in nepal: geospatial and economic analysis. renewable energy, 181:6331, 2021. [11] m. shrestha and n. bhattarai. impact study on power generation from photovoltaic system due to change in local irradiance and temperature at kathmandu valley, nepal. journal of the institute of engineering, 12(1):1–9, 2016. [12] n. v. u. maheswari and l. j. s. shanthi. implementation of modified incremental conductance mppt algorithm in grid connected pv system under dynamic climatic conditions. indian journal of science and technology, 15(17):819–828, 2022. [13] n. mohammad, m. quamruzzaman, m. r. t. hossain, and m. r. alam. parasitic effects on the performance of dc-dc sepic in photovoltaic maximum power point tracking applications. smart grid and renewable energy, 4:113–121, 2013. https://www.solarelectricsupply.com/media/custom/upload/solarex-msx64.pdf https://www.solarelectricsupply.com/media/custom/upload/solarex-msx64.pdf https://www.solarelectricsupply.com/media/custom/upload/solarex-msx64.pdf introduction research related to solar irradiance in nepal significant of research research gap methods and materials pv module used in this research theory parameters analysis of deploying pv systems in different regions results and discussion solar irradiance in nepal current generated by pv modules at varying irradiation levels in nepal. power generated by pv at various irradiation levels in nepal impact of global horizontal irradiance on photocurrent impact of cell temperature on photocurrent -benefit analysis of deploying pv systems in different regions payback period return on investment net present value limitations of research conclusion bibechana 18 (2) (2021) 87-94 87 gps tec scintillations and tec depletion as seen from hetauda and nast, nepal for 2016 basu dev ghimire1, 2, 3,5,*, narayan prasad chapagain4, balaram khadka2, 3, gambir bidari2,, karan bhatta3,5, aditay singh thapa2 1institute of science and technology, central department of physics , tribhuvan university 2st. xavier’s college , maitighar kathmandu , nepa 3nepalese center for research in physical sciences (ncrps) 4amrit campus , tribhuvan university, kathmandu nepal 5gyan research academy for communication and education(grace), kathamndu nepal *email:basu.ghimire99@gmail.com article information: received: december 25, 2020 accepted: may 13, 2021 keywords: gps tec roti s4 index prn roti and s4 correlation abstract we analyzed global positing system total electron content (gps-tec) data of stations hetauda (27.414 0n and 85.051 0e) and nast (27.656 0n and 85.327 0e), nepal which are a part of unavco.we obtained the variation of rate of tec index (roti) and s4 index throughout the year 2016 for the two stations involved for the 32 all the pseudo random noise (prn) numbers barring prn number 4 which was inactive throughout the year. we chooses two stations data which are almost 40 km in distance and correlated the value of roti index with roti index and s4 index with s4 index and found that the roti index of hetauda is well correlated with roti index of nast with the highest being 94% for prn 10 and the lowest being -13% for prn 1. extremely low correlation between s4 index of hetauda and s4 index of nast was observed with the highest correlation being 8% in prn 3, 32 and the lowest correlation of -15% in prn 12. doi:https://doi.org/10.3126/bibechana.v18i2.33405 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction the ionosphere is composed of charged particles: ions and electrons. the composition of ionosphere varies with change of seasons, solar cycle, solar intensity and geomagnetic storms [1]. one of the major factors that causes variation in composition of ionosphere is sunlight, which ionizes gas molecules with its ultraviolet rays and releases free electrons. as the number of free electrons varies in ionosphere, so does the electron density in the ionosphere. it is one of the significant reasons for observation of major difference in electron density of day and night. this electron density is commonly defined as total electron content (tec) tec= �������� ����������. ��� https://doi.org/10.3126/bibechana.v18i2.33405 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana basu dev ghimire et al. / bibechana 18 (2) (2021) 87-94 88 where, n is electron density. tec is dependent on its path. this expression gives slant tec (stec) when the electron density along the ray path of the satellite to receiver is taken into account. while the vertical tec (vtec) can obtained, when the electron density along the perpendicular path of the satellite to receiver is taken into account [2]. global position system (gps) can be used to measure the change in the electron and ion content of ionosphere, as the gps signal’s characteristics changes while passing through the ionosphere. as gps signal travels through the ionosphere, it attenuates, delays, it’s level of attenuation, delays are determined by time it travels through the ionosphere. the ionosphere is dispersive, which means that the apparent time delay contributed by the ionosphere depends on the frequency of the signal [3, 4]. the stec is obtained from the dual frequency code measurements using the relation [2] as in equation (1). ���� = 1 40.3 × 1 �1 2 − 1 �2 2 −1 × �1 − �2 + ������ (1) where p1 is the pseudo range at l1 (it is at 1575.42 mhz (10.23 mhz × 154) ); p2 is the pseudo range at l2 (it is at 1227.60 mhz (10.23 mhz × 120)), teccal is the bias error correction. stec measured by the receiver at every 30s is used. the measured stec is corrected for the receiver differential delay teccal. in the above equation (1), teccal represents the bias error correction and is different for different satellite-receiver pairs [2] which is calculated from code error. slant tec is dependent on the ray path geometry through the ionosphere and an equivalent vertical value of tec, which is independent of the elevation of the ray path, is calculated [5]. there are two universally accepted quantities, the amplitude/phase scintillation s4/∂ø and roti that are commonly used to quantitatively describe ionospheric variations which are usually tec fluctuations. the amplitude scintillation index, s4, is the normalized root-mean square (rms) deviation of irridance, i [6]. measurements of both s4 and ∂ø can be derived from global navigation satellite system (gnss) scintillation monitoring receivers sampled at high frequencies, but the number and regional/global distribution of scintillation monitoring receivers are limited due to high costs. this scarcity of scintillation monitoring receivers restricts the extensive use of s4/∂ø indices [7-12]. the tec fluctuation index roti (which is derived from ordinary non-scintillation gnss receivers sampled at low frequencies) was first proposed by pi et al [7, 10, 12] in 1997. after that, roti has been used universally to quantitatively describe ionospheric anomalies. roti is the standard deviation of the rate of tec (rot) in a given 5 min interval. many studies have shown a close correlation between s4 and roti [10, 12-15] . fig. 1: vertical total electron content (vtec). tec, s4 data are taken by many satellites at a time. hence, the data are different from each other due to their different activation time. in order to increase the reliability of these data, the data should be separated according to their satellites. these different satellites can be separated by their pseudorandom noise (prn). the prn codes help in identification of the satellite by a receiver, while it is receiving its data. prn are used as an identification measure in code division multiple access (cdma) based satellite navigation system http://en.wikipedia.org/wiki/mhz basu dev ghimire et al. / bibechana 18 (2) (2021) 87-94 89 [16]. satellite throughout the world within a gnss constellation has a unique prn code that it transmits as part of the civilian access navigation message, which allows receiver to identify exactly which satellite(s) it is receiving [17]. 2. materials and methods the rate of tec (rot, in tecu/min) and amplitude scintillation index s4 is measured by utilizing dual-frequency gps observation phase data [7]. rate of tec abbreviated as rot computes the relative tec changes, along the signal paths from each individual to the receiver, as shown in equation (2) [12]. roti index is the standard deviation of rot over a 5 min interval in tecu/min in equation (3) [7]. rot = (∆stec)/∆t (2) ���� = < ���2 >−< ��� >2 (3) where stec is the tec along the ray path from the satellite to the receiver (in tecu/min) and ∆t in minutes represents the sampling interval. the amplitude scintillation index, s4, is the normalized root-mean square (rms) deviation of irradiance, i [6] as in equation (4). �4 = (<�2>−<�>2) <�>2 (4) data availability in this study, dual-frequency gps data was made public by unavco (https://www.unavco.org/data/gps-gnss/data-accessmethods/dai2/app/dai2.html#4char=nast;scope=statio n;samplerate=normal;4charmod=startswith.) unavco has provided civilian access to the dualfrequency gps data of it’s different receiver stations. the data is available in 1.0 compact rinex version files. we processed the data using gps tec analysis software developed by gopi seemala, affiliated to the indian institute of geomagnetism. the software converts the rinex data into ascii format separating data into various columns where values of stec, vtec, s4 index are separated according to prn numbers. we processed those ascii files and found yearly variation of roti and s4 for all the prn numbers. for studying correlation of roti and s4, we calculated a single value of roti for one day (by taking the average), did the same for s4 index and found out individual values of roti and s4 for each day of 2016 for the two stations involved and found the correlation between s4 and roti. fig. 2: map of nepal showing two gps stations taken in our study. 3. results and discussions variation of roti figure 3 and4 give us a pictorial description of the change in roti index from two stations of nepal; hetauda and nast, respectively during 2016. besides, prn 4 was inactive during 2016. technically, figure 1 gives the variation of roti + 200xprn with days. the reason for addition of 200 as a factor to the prn number is that the maximum value of roti did not exceed 200 for heatuda. we changed the factor 200 (multiplied to prn) to 400 in nast as the maximum value of roti in 2016 ranged in the high as three hundred. the lowest horizontal line in figures 3 and 4 represents the roti for prn 1, succeeded by prn 2 and so forth such that the highest vertical line represents the variation of roti for prn 32. https://www.unavco.org/data/gps-gnss/data-access-methods/dai2/app/dai2.html https://www.unavco.org/data/gps-gnss/data-access-methods/dai2/app/dai2.html https://www.unavco.org/data/gps-gnss/data-access-methods/dai2/app/dai2.html basu dev ghimire et al. / bibechana 18 (2) (2021) 87-94 90 fig. 3: variation of roti index during 2016 in hetauda, in units of tecu/min. fig. 4: variation of roti index during 2016 in nast, in units of tecu/min. basu dev ghimire et al. / bibechana 18 (2) (2021) 87-94 91 fig. 5: variation of s4 index in hetauda during 2016. in hetauda, we observed that the values of roti were high only for a specific time of the year. prn 1, 18 and 21 show high values of roti in around exactly the same time of the year during february and march. the same can be said about prn 14 and 32 which show high values of roti from midmarch until april. the fourth horizontal line from the bottom is static because we had no data of stec for prn 4. similar patterns of extended period of months where the values of roti index were high. however, for prn 9, 12 and 22, we can see that elevated values of roti can be seen, not for extended periods of months but only for single days. variation of s4 index the lowest horizontal line in figures 5 and 6 represents the s4 for prn 1, succeeded by prn 2 and so forth such that the highest vertical line represents the variation of roti for prn 32.in bothe stations, hetauda and nast, the beginning of february to the middle of march, no values of s4 index was recorded by prn 32. as prn 4 was inactive, we have a flat line for the s4 index for prn 4. for prn 25, we observed consistently high values for prn 25 during july in hetauda. very high values of s4 index for prn 24 was observed in the months of september and october. the same was true of prn 14 as well. although the values of s4 was consistently low throughout the year for prn 7, 9, 11, 22 and 23, there were a few days where the values of s4 index were high enough. in nast consistently high values of s4 index were observed for almost all prn except prn 6, 13, 27 where the values of s4 was mild throughout the year. correlation between roti from two stations figure 7 and 8 show dynamic correlation between roti of hetauda and of nast, along with s4 index of hetauda and of nast in 2016. we did observe a good correlation between the roti of two different stations but did not observe any good correlation between s4 index of hetauda and nast. however, the results show a negative correlation between roti of hetauda and roti of nast. for s4 index, 17 prns revealed negative correlation between hetauda and nast, while just prn 1 pointed to negative correlation between roti of hetauda and nast. for roti, 1 prn showed a positive correlation of less than 10% while for s4 index 8 out of the 14 prns that had a positive correlation had a correlation of less than 10% and prn 7, 21, 30 had a correlation of 0. basu dev ghimire et al. / bibechana 18 (2) (2021) 87-94 92 fig. 6: variation of s4 index in nast during 2016. fig. 7: correlation between roti from two stations at hetauda and nast. basu dev ghimire et al. / bibechana 18 (2) (2021) 87-94 93 fig. 8: correlation between s4 index from two stations at hetauda and nast. 4. conclusion the values of roti and s4 index were abruptly high in a few days when the values in other days in closer proximity were relatively small might have been due to the variation in geomagnetic parameters or might have its origins in equatorial ionization anomaly (eia), which greatly affects the values of tec in regions close to the equator. furthermore, the high correlation between roti of hetauda and nast, whereas low correlation between s4 of hetauda and nast might suggest that there is a correlation between the roti of different stations but no correlation between s4 in nepal. however, before concluding this result, we have to carry out the detial analysis of the correlation between the two parameters, roti, and s4 index throughout nepal. it is possible that due to geomagnetic storms and eia, good correlation was not observed in the two stations where we conducted our study. therefore, a detailed analysis of the roti, and s4 index throughout nepal will give a clearer picture of the tec variation in nepal. acknowledgement we would like to thank university grant commission nepal, provide fund for this research work. we would also like to thank unavco and gopi seemala for providing the data and tec software references [1] [1] r. tiwari, s. bhattacharya, p. purohit and a. gwal, effect of tec variation on gps precise point at low latitude, the open atmospheric science journal 3 (2009) 3. https://doi.org/10.2174/1874282300903010001 [2] [2] m. s. bagiya, h. joshi, k. n. iyer, 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[17] s. k. upadhyaya, g. s. pettygrove, j. w. oliveira & b. r. jahn, an introduction–global positioning system. calspace.ucdavis.edu/docs/intro-gps-final.pdf 2005) bibechana vol. 21, no. 3, december 2024, 311-320 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar experimental ftir characterization of kidney stones, dft analysis of cac2o4 and its interactions with lysozyme arjun acharya1, madan khanal1, rajesh maharjan1, kalpana gyawali1, kamal khanal1, mohan bahadur kshetri1, bhoj raj luitel2, rameshwar adhikari3,4, deependra das mulmi5, tika ram lamichhane1,∗, hari prasad lamichhane1, 1central department of physics, tribhuvan university, kathmandu 44600, nepal 2department of urology and kidney transplant surgery, tribhuvan university , teaching hospital, institute of medicine, maharajgung, kathmandu 44600,nepal 3central department of chemistry, tribhuvan university, kathmandu 44600, nepal 4research center for applied science and technology (recast), tribhuvan university, kathmandu 44600, nepal 5nanomaterials research laboratory, nepal academy of science and technology, lalitpur 44700, nepal ∗corresponding author: email: tika.lamichhane@cdp.tu.edu.np abstract kidney stone is an alarming global disease due to its rising incidence and prevalence. ftir spectroscopic analysis reveals that calcium oxalate is one of the most frequent chemical constituents in kidney stones. dft calculations indicate that the calcium oxalate can interact through charge transfer process in biological activities. among various proteins, lysozyme is one of the promoter proteins in nephrolithiasis of calcium oxalate type kidney stone. the location, conformation and interactions of calcium oxalate with the active residues of lysozyme contribute the binding energy of -4.18 kcal/mol. the characterization of kidney stones, dft calculations of calcium oxalate, and binding interactions of calcium oxalate-lysozyme complex contribute to the understanding of nephrolithiasis. keywords kidney stone; calcium oxalate; lysozyme; fourier transform infrared spectroscopy; density functional theory; molecular docking; nephrolithiasis. article information manuscript received: august 14, 2024; revised: september 25, 2024; accepted: september 26, 2024 doi https://doi.org/10.3126/bibechana.v21i3.68781 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 311 http://nepjol.info/index.php/bibechana tika.lamichhane@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v21i3.68781 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ arjun acharya et al./ bibechana 21 (2024) 311-320 312 1 introduction kidney stone is one of the oldest diseases, characterized by the formation of solid masses within the urinary system. these deposits are strongly linked to chronic kidney disease and can lead to kidney failure [1, 2]. despite increased awareness and improved treatment procedures, the prevalence of kidney stone disease is increasing globally, presenting a significant health threat [3]. the prevalence ranges from 7% to 13% in north america, 5% to 9% in europe, and 1% to 5% in asian countries [4]. in asia, the western, southern, and southwestern regions exhibit particularly high rates, with prevalence ranging from 5% to 19.1%. in contrast, east asian and northern asian regions show a lower prevalence, ranging from 1% to 8% [5]. the study in kathmandu university teaching hospital about the distribution of urinary calculi based on age, gender and types shows 54.20% cases are of 21-40 years. among the total kidney stone patients, male population (57.95%) are more prone than the female population (42.05%). again, 74.16% of the total patients are suffered from calcium oxalate and calcium phosphate type urinary calculi. non-vegetarian groups (88.70%) are found more suffered from this disease than vegetarian groups (11.30%). further, this study also suggested spectroscopic analysis of urinary calculi [6]. computed tomography (ct) urographic study in lumbini medical college, palpa, nepal shows 76.7% of urinary obstruction are due to urinary calculi. among the patients, 60.7% are male and 39.3% are female, and 46.7% of patients lie within 21-40 years [7]. in another research of urinary calculi in kathmandu pathology laboratory using biochemical techniques shows calcium oxalate as a major constituents with male to female patients ratio 1: 1.2 [8]. in a study of urinary calculi patients in shree birendra hospital, kathmandu, nepal, it is found that 69.2 % of the affected population are male and 30.8% are female. the majority of patients, 51%, fall within the age range of 31-45 years. additionally, calcium oxalate is found in 64.25% of the cases. among the ethnic groups, maximum number (30.75%) of the patients are from the janajati community, while minimum (11.25%) are from the madhesi population. geographically, 85.7% of the cases are reported in the hilly region, with 14.3% originating from the terai/madhesh region [9]. kidney stones are generally developed from calcium oxalate, calcium phosphate, magnesium ammonium phosphate, uric acid, and cystine. among all, calcium oxalate (cac2o4) is the most frequently observed in the kidney stones [10]. fourier transform infrared (ftir) spectroscopic technique is a powerful analytical tool for the prediction of chemicals in the samples through the measurement of wide range of spectra. it has high sensitivity, quantitative accuracy, and superior signal-to-noise ratio [11] and is widely used in the characterization of different types of kidney stones [12, 13]. density functional theory (dft) analysis can be employed to study the dipole moment, frontier molecular orbitals, global reactive descriptors, molecular electrostatic potential (mep), and mulliken atomic charges. these quantum mechanical properties provide insights about the potential interactions between chemical compound and protein, as explained in our previous work [14,15]. different proteins contribute as promoter in the biomineralization. in kinetic studies of calcium oxalate type crystal growth in the presence of proteins lactoferrin and lysozyme revealed that both the proteins promote crystal growth, with lysozyme exhibiting a more effective role in accelerating the growth process [16]. in our previous work, lactoferrin protein has exhibited the binding efficacy of -3.86 kcal/mol [14] and this research focuses on studying the different interactions by active amino acids of lysozyme protein and their contribution for binding efficacy with calcium oxalate at the atomic level. molecular docking analysis of protein and ligand can predict the different conformation of ligand within the selected binding pocket of target protein. it also predicts the binding affinities using different algorithms and scoring function [17]. the molecular docking of ligand with matrix proteins of kidney stones is found to be significant for studying the calcium oxalate types nephrolithiasis [18]. such studies at the atomic level will be helpful for understanding the interactions between calcium oxalate and lysozyme. current research aims to characterize the kidney stones. further, this research will study the quantum mechanical properties of calcium oxalate using dft in water solvent, along with the interactions within binding domain of promoter protein, lysozyme. this study will contribute to the understanding of globally challenged and unclear phenomena of nephrolithiasis. 2 methodology 2.1 characterization of samples kidney stones were collected from the institute of medicine, maharajgung following the receipt of approval from the institutional review committee of the institute of medicine, tribhuvan university, nepal. informed consents were taken from all respondents for the analysis of samples. the collected stones were carefully cleaned with distilled water and air-dried at room temperature, then arjun acharya et al./ bibechana 21 (2024) 311-320 313 crushed using mortar and pestle. finally, samples were characterized under ftir spectroscopy using the shimadzu iraffinity-1s spectrophotometer within the range of 400-4000 cm−1. 2.2 quantum mechanical calculations three dimensional structure of calcium oxalate (id: 33005) was obtained from pubchem, an open chemistry database at the national institutes of health, usa [19], and optimized using the dft at b3lyp/6-311++g(d,p) level of calculation in the water solvent using the integral equation formulation of the polarizable continuum model (iefpcm) in gaussian 16w software [20]. using the optimized structure, dipole moment, mulliken charges, molecular electrostatic potential (mep), highest occupied molecular orbital (homo) and lowest unoccupied molecular orbital (lumo), and density of states (dos) were calculated. the energies of homo and lumo orbitals, ionization potential and electron affinity of chemical compound were calculated using koopmans’ theorem as [21]: ionization potential, i = −ehomo (1) electron affinity, a = −elumo (2) the global reactive descriptors (chemical hardness, chemical softness, electronic chemical potential, and global electrophilicity index) were calculated using ionization potential and electron affinity as follows [21–23]: chemical hardness: η = i −a 2 (3) chemical softness: s = 1 η (4) electronic chemical potential: µ = −i +a 2 (5) global electrophilicity index: ω = µ2 2η (6) additionally, ultraviolet-visible (uv-vis) spectra were generated using the time-dependent (td)dft method at the same level of calculation in water solvent. the compound was visualized and evaluated using gaussview 6 [24] and gausssum 3.0 [25] software programs. 2.3 molecular docking the structure of human lysozyme (7xf6.pdb) was downloaded from the data center for the global protein data bank, rcsb pdb [26]. the secondary structures were analyzed by ramachandran plot using discovery studio visualizer v21.1.0.20298 [27]. the surface area, volume, and active residues in the binding region were predicted using the computed atlas of surface topography of the universe of proteins (castp) open-access online server [28]. the pdb files of protein and ligand were converted into partial charge and atom type (pdbqt) format after removal of water molecules, addition of kollmann’s charges, and integration of polar hydrogen atoms using the autodocktools [29–31]. molecular docking using autodock4 [29] was carried out within the grid points (40× 40 × 40) of grid point spacing 0.375 å along the x, y, and z axes, respectively. all the molecular docking procedures were conducted as described in our previous studies [14, 32]. finally, the best conformation of proteinligand complex was generated using the graphical user interface of autodocktools. the visualization of protein-ligand complexes were carried out using pymol 2.5.2 [33] and ligplot+ v.2.2 [34]. 3 results and discussion 3.1 experimental ftir characterization of kidney stones ftir spectroscopic analysis was carried out for forty-four kidney stones. comparing the generated spectra with literature [12,13], the samples contains whewellite, struvite, and uric acid types chemicals in pure and mixed form (figure 1). the spectra of majority of the samples show intense peaks at 1608-1613 cm−1 and 1313-1315 cm−1 with less intense peak at 1380-1388 cm−1 (figure 2) and these peaks almost match with the calcium oxalate monohydrate (whewellite) type kidney stones [12]. in our previous work, ftir spectra of calcium oxalate generated in different solvent using dft method at the b3lyp/6-311++g(d,p) level of calculation, the spectra in water solvent was closely matched with the experimental ftir spectra of whewellite [14]. figure 1: pie chart showing the distribution of chemical compositions in the samples analyzed by fourier transform infrared spectroscopic technique. arjun acharya et al./ bibechana 21 (2024) 311-320 314 figure 2: experimental fourier transform infrared spectra of the thirty-one whewellite type kidney stone samples. 3.2 quantum mechanical calculation of calcium oxalate 3.2.1 geometry optimization the optimized structure of calcium oxalate is shown in figure 3. in the present study, calculated dipole moment in water solvent is found 24.28 debye, whereas in our previous work in gaseous phase, it was 14.88 debye [14]. the dipole-dipole interactions between ligand and protein can affect the binding energy of the protein-ligand complex [35]. thus, calcium oxalate can also interact through dipole-dipole interactions with the nephrolithiatic proteins. figure 3: optimized structures of cac2o4 by the dft method at the b3lyp/6-311++g(d,p) level of calculation in water solvent. 3.2.2 frontier molecular orbitals in the electronic absorption spectra of calcium oxalate in water solvent, the wavelengths of 278 nm, 265 nm, and 231 nm are responsible for the electronic transitions (table 1). the maximum oscillatory strength is observed for wavelength 231 nm which is due to major contribution from the homo to lumo+1 transition of electrons (figure 4a and table 1). the electronic absorption of calcium oxalate in water solvent shows close agreement with the experimental finding [36] compared to the results obtained in the gas phase [14]. the majority of charge density is concentrated around the carbon and oxygen atoms in homo, lumo, and homo-1 orbitals. however, in lumo+1, the charge density localized around calcium atom (figure 4b). this visual representation reflects the charge distribution within the compound [37]. the energy gap, difference between the energies of homo and lumo orbitals, is found to be 5.90 ev (figure 4a). the number of states per unit energy interval at a given energy level in both occupied and virtual orbitals is illustrated with the dos spectrum in figure 5. the homo and lumo orbitals and the spectra of dos resemble closely each other. these results suggest that calcium oxalate can promote charge transfer process and exhibits enhanced capability for biological activities [38]. figure 4: calculated electronic absorption of calcium oxalate: uv-vis spectrum (a) and the frontier molecular orbitals significantly contributing to the electronic transitions (b). figure 5: density of state spectrum along with the occupied and virtual orbitals in calcium oxalate. arjun acharya et al./ bibechana 21 (2024) 311-320 315 table 1: calculated electronic properties of calcium oxalate. maximum absorption wavelength (nm) oscillatory strength major contributions absorption wavelength of whewellite (nm) [36] 278 0.000 homo → lumo (99%) 288 265 0.000 homo-1 → lumo (99%) 231 0.008 homo → lumo+1 (97%) 236 table 2: calculated global reactivity descriptors of calcium oxalate. ionization potential (i) (ev) electron affinity (a) (ev) chemical hardness (η) (ev) chemical softness (s) ( ev)−1 electronic chemical potential (µ) (ev) global electrophilicity index (ω) (ev) 6.48 0.58 2.95 0.34 -3.53 2.11 3.2.3 global reactivity descriptors the chemical hardness and electrophilicity index of calcium oxalate is obtained to be 2.95 ev and 2.11 ev, respectively (table 2). these positive values of chemical hardness and electrophilicity index suggest that the compound is suitable for charge transfer processes and can influence the binding energy in protein-ligand interactions [39]. 3.2.4 molecular electrostatic potential and mulliken atomic charges polar regions around the atoms of calcium oxalate are demonstrated with different color codes ranging from -0.316 a.u. to 0.316 a.u. using mep map. the intense positive potential is observed around the ca7 and negative potential is found around the o1, o2, o3, and o4 atoms (figure 6a). figure 6: mep map with contour lines (a) and mulliken atomic charges contributed by each atom (b) in calcium oxalate molecule. further, calcium atom has the maximum positive mulliken atomic charges and o1 as well as o4 show the maximum negative mulliken atomic charges (figure 6b). the variation of charges in oxygen atoms illustrates the induction effect of calcium atom to the bonded oxygen atoms. the mep map and mulliken atomic charge distribution show the similar nucleophilic and electrophilic regions in calcium oxalate. the reactive nature of the chemical compound associated with the polar property can be explained using mep and mulliken atomic charges [40]. and, the polar nature of calcium oxalate is significant for the bonded and non-bonded interactions with lysozyme protein (figure 9). 3.3 interactions of cac2o4 with lysozyme lysozyme protein (7xf6.pdb) contains an acetate ion (c2h3o2) as a native ligand, which forms non bonded interactions with ile77, trp82, ala126, and trp127 and hydrogen-bonded (h-bonded) interaction with asn78 (figure 8a). all non-glycine residues except cys134 and ser54 confine within the most allowed regions of the ramachandran plot arjun acharya et al./ bibechana 21 (2024) 311-320 316 (figure 7 and table 3), indicating that the structure of lysozyme is valid and suitable for the proteinligand interactions [41,42]. figure 7: ramachandran plots: all residues of lysozyme (a) and residues interacting with calcium oxalate (b). table 3: dihedral angle pairs (in degree) of active amino acids of lysozyme interacting with calcium oxalate. active amino acids of lysozyme protein dihedral angle (ϕ) dihedral angle (ψ) ile77 -75.37 134.83 asn78 -92.15 142.91 trp82 -110.81 -35.76 val117 -52.71 -49.32 ala126 -57.33 -30.91 trp127 -93.36 117.50 the binding pocket identified using castp (figure 8b) includes active residues glu53, asp71, gln76, ile77, asn78, trp82, val117, ala126, trp127, val128, and ala129 with a total binding pocket area 71.823 å2 and volume 49.887 å3, respectively. this result suggests that the region identified by castp closely matches with the location of native ligand, making it suitable for molecular docking between lysozyme and calcium oxalate. the visualizations of the best docked pose of lysozyme-calcium oxalate complex within the binding pocket are shown in figure 9. the residue asn78 forms h-bond, while the residues ile77, trp82, val117, ala126, and trp127 contribute in hydrophobic interactions with calcium oxalate ( figures 9b,c). these interactions contribute the binding energy of −4.18 kcal/mol (table 4). this result indicates that the binding affinity of calcium oxalate with lysozyme is slightly higher than that of lactoferrin as shown in our previous work [14]. the present molecular docking analysis suggests that the calcium oxalate, a key component in kidney stones, exhibits a high binding efficacy within the active region of the lysozyme, promoter protein in neprolithiasis. lysozyme is one of the key proteins found in the matrix of whewellite-type urinary calculi [16]. in in vivo conditions, matrix proteins of the calculi can exhibit aggregation-inducing properties, which can enhance the particle size of calcium oxalate type crystals, facilitating crystal growth in urinary tract [43]. the location, size, and type of urinary calculi in a urinary tract significantly influence the treatment modalities. calculi larger than 7 mm are unlikely to arjun acharya et al./ bibechana 21 (2024) 311-320 317 move spontaneously through urine and typically require surgical intervention. further, calculi ranging from 1.1 cm to 2.4 cm in size are ideal for breaking using the extracorporeal shockwave lithotripsy (eswl) and greater than 2 cm are recommended for percutaneous nephrolithotomy (pcnl) techniques [44–46]. among different calculi, weddellite types are relatively easy to break. in contrast, whewellite, infected struvite, and cystine offer the highest resistance to the eswl. generally, ureteroscopy (urs) is better option for treatment of cystine type calculi [44, 46]. figure 8: interactions of native ligand, acetate ion (c2h3o2), with lysozyme (7xf6.pdb) are represented by spoked arcs for nonbonded residues, green-dotted line for hydrogen bond, and written in green color for hydrogen-bonded residue using ligplot+ v.2.2 (a). the location of the binding pocket highlighted in red within the lysozyme represented using ribbon like structure generated by castp (b). figure 9: calcium oxalate (red) within the binding pocket of lysozyme (green for interacting and blue for non interacting residues) visualized using pymol (a,b). interactions of calcium oxalate with lysozyme are illustrated with nonbonded residues shown as spoked arcs, hydrogen-bonded residue indicated in green color, generated using ligplot+ v.2.2 (c). table 4: molecular docking results of calcium oxalate with lysozyme at temperature 298.15 k. energy components energy (kcal/mol) van der waals, hydrogen bond, and disolvation energy -4.16 electrostatic energy -0.02 total binding energy -4.18 arjun acharya et al./ bibechana 21 (2024) 311-320 318 4 conclusion this work is focused on the characterization of kidney stones and the study of nephrolithiasis phenomena using ftir, dft, and molecular docking approaches. the characterization of kidney stones using spectroscopic techniques reveals that the majority are composed of calcium oxalate monohydrate. the quantum mechanical properties suggest that calcium oxalate can interact through bonded and non-bonded interactions with proteins. the molecular docking analysis of calcium oxalate within the binding regions of lysozyme shows effective binding interactions. hence, lysozyme can play potential role for the development of calcium oxalate type nephrolithiasis. in summary, this research finds the distribution of the types of kidney stones and contributes to understand the phenomena of calcium oxalate type nephrolithiasis, which remains still unclear and is one of the most challenging global problems for the scientific community. further, characterization of kidney stones from different regions using a large sample size and the study of nephrolithiasis using different promoter and inhibitor macromolecules from both experimental and in silico approaches are still necessary for a detailed understanding of this global challenge. competing interests the authors declare that there is no conflict of interest. ethics approval and consent to participate this study was conducted with the approval of the institutional review committee of the institute of medicine, tribhuvan university teaching hospital, maharajgunj, kathmandu, nepal with an approval number of 117 (6-11) e2 079/080. informed consent was received from participants or their parents or legal guardians. data availability the data supporting the findings of this study are available within the article. authors’ contributions a acharya: conceived and designed the experiments, performed data analysis, prepared the figures, and wrote the manuscript m khanal: data analysis, manuscript writing r maharjan: technical support, critical feed back and revised the manuscript k gyawali: critical feed back and revised the manuscript k khanal: critical feed back and revised the manuscript mb kshetri: critical feed back and revised the manuscript br luitel: critical feedback, data analysis, and revised the manuscript r adhikari: critical feedback, data analysis, and revised the manuscript dd mulmi: critical feedback and revised the manuscript tr lamichhane: technical support, critical feedback, data analysis, and revised the manuscript hp lamichhane: critical feedback, data analysis and revised the manuscript acknowledgment we would like to express our gratitude to prof. dr. rajendra parajuli and asst. prof. pitamber shrestha, amrit campus, t. u., for their invaluable support in providing access to gaussian 16w software. additionally, we extend our sincere thanks to dr. rabindra tamang, dr. purushottam parajuli, dr. anjit phuyal, and dr. milan gyawali for their unwavering assistance in 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https://doi.org/10.1016/s0022-2836(63)80023-6 https://doi.org/10.1016/j.heliyon.2021.e08220 https://doi.org/10.1016/j.heliyon.2021.e08220 https://doi.org/10.1016/s0022-5347(17)35454-x https://doi.org/10.1016/s0022-5347(17)35454-x https://doi.org/10.5455%2faim.2014.22.309-314 https://doi.org/10.5455%2faim.2014.22.309-314 https://doi.org/10.1159/000497442 https://doi.org/10.1159/000497442 https://doi.org/10.1111/j.1464-410x.2006.06514.x https://doi.org/10.1111/j.1464-410x.2006.06514.x introduction methodology characterization of samples quantum mechanical calculations molecular docking results and discussion experimental ftir characterization of kidney stones quantum mechanical calculation of calcium oxalate geometry optimization frontier molecular orbitals global reactivity descriptors molecular electrostatic potential and mulliken atomic charges interactions of cac2o4 with lysozyme conclusion pandey and pokhrel / bibechana 19 (1-2) (2022) 27-33 27 phytochemical screening and biological activities of oxalis corniculata leaves of sindhupalchowk district, nepal kamala pandey, shanta pokhrel* department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal *email: shantabhattarai2014@gmail.com article information: received: october 30, 2021 accepted: december 27, 2021 keywords: antibacterial antioxidant ic50 phytochemical screening abstract the oxalis corniculata (oxalidaceae) is one of the most potential medicinal herbs and well known for multiple therapeutic properties (antiinflammatory, anticancer, antioxidant, antimicrobial, analgesic and diuretic activity). this study investigated phytoconstituents, antibacterial activity and antioxidant activity of oxalis corniculata leaves extract. methanol based phytochemical screening of oxalis corniculata revealed the presence of alkaloids, proteins, phenols, flavonoids, glycosides. the antibacterial activity revealed better potential inhibitory effect against gram-negative bacteria, particularly escherichia coli and salmonella typhi compared to staphylococcus aureus, a gram-positive bacterium. however, 1% methanol extract showed highest antibacterial activity against escherichia coli followed by staphylococcus aureus and salmonella typhi. antioxidant activity of the methanol extract with 2,2-diphenyl-1-picrylhydrazyl (dpph) free radical scavenging showed antioxidant activities with 3.87 µg/ml ic50 value. doi: https://doi.org/10.3126/bibechana.v19i1-2.46094 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction oxalis corniculata linn. (oxalidaceae) is one of the most useful medicinal plants having a wide spectrum of biological activity. it is commonly known as creeping wood sorrel (chari amilo in nepali) possess all the essential constituents which are required for normal and good health of humans [1]. it is a low growing herbaceous plant dispersed in damp shady places, roadsides, lawns, and in most parts of india [2] and nepal. the stem and bark of this plant utilize to treat malaria, snakebite, bronchitis and juice of the leaves are used as bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal https://doi.org/10.3126/bibechana.v19i1-2.46094 https://creativecommons.org/licenses/by-nc/4.0/ pandey and pokhrel / bibechana 19 (1-2) (2022) 27-33 28 digestive agent, antidote to reptile venom, in treating dysentery and diuretic activity [3,4]. the products of the plant include glycoside, flavonoid, protein, tannin, phenolic compounds, essential oil which are associated with medicinal and pharmacological properties of the plants. the leaves and stem of oxalis corniculata contain tartaric acid, citric acid and malic acid, also rich source of essential fatty acids like palmitic, oleic, and linoleic acid [5-7]. it is commonly used as an antibacterial, antifungal, anti-inflammatory, in wound healing, and in the treatment of jaundice, antiseptic, anemia, cancer, piles and in stomach troubles [8]. traditionally it is used in the treatment of bacterial infections and kidney stones [9]. das et al., studied the inhibitory activity of its aqueous extract and biofabricated silver nanoparticles against urinary tract infection (uti) causing bacteria and urolithiasis. it is reported that its leaves aqueous extract effectively suppressed the growth of struvite stones and resulting the dissolution of stones. furthermore, the inhibitory activity was further improved by its biofabricated silver nanoparticles [9]. the present paper is dealing with phytochemistry and biological activities of nhexane and methanolic extract of oxalis corniculata leaves. 2. materials and methods 2.1 plants extract preparation via soxhlet extraction leaves samples (oxalis corniculata) were collected from the sindhupalchowk district, nepal and washed by pure water to remove dust, soil, and other impurities. cleaned plant material was air dried in shade for 4 weeks and ground to powder and stored in clean and dry bottle. 65 g of leaves powder was successively extracted by soxhlet method in hexane followed by methanol. the process was continued (7-8 hours) until the colourless solvent appeared from plant material in the siphon. thus obtained extract was concentrated to get crude extract by rotary evaporator and stored in refrigerator for phytochemical screening, antibacterial and antioxidant property. 2.2 phytochemical screening different crude extract, prepared from soxhlet extraction were used for phytochemical screening to identify various bioactive chemical constituents like alkaloid, flavonoid, steroids, glycosides, and carbohydrates. the method employed is primarily based on the standard protocols [9]. 2.3 antibacterial screening agar well diffusion method was used to study the antibacterial activity of plant extract [10,11]. different concentration of solution (1%, 10%, and 50%) was prepared from the plant crude extract and tested against standard gram positive microbial strains staphylococcus aureus and gram negative strains escherichia coli atcc 25922 and salmonella typhi. these standard strains were collected from med micro nepal lab, kathmandu. the 50 µl of the working solution of the plant extract, dimethyl sulfoxide as negative control (nc) and 25 µl (100 mg/ml) of ofloxacin as positive control (pc) were loaded into the separated well (6 mm). the plates were incubated overnight at 37 ℃ and examined inhibition of bacterial growth indicated by a clear zone around the wells. the size of the zone of inhibition (zoi) was measured in mm. 2.4 antioxidant activity the free radical scavenging activity of methanolic extract and standard ascorbic acid solution was evaluated as their capability to react with stable 2, 2diphenyl-1-picrylhyrazyl (dpph) free radical [11,12]. its antioxidant property was determined as ic50 values which was calculated following the protocol mentioned in our previous paper [11, 13]. 3. results and discussion 3.1 phytochemical screening the phytoconstituents were identified by the color reaction with different reagents following the standard phytochemical screening methods [9]. the qualitative results were expressed as (+) for the presence and (−) for the absence of phytochemicals which is compiled in table 1. phytochemical screening of methanol extract of oxalis corniculata leaves revealed the presence of large number of bioactive secondary molecules like alkaloids, proteins, phenols, flavonoids, glycosides. pandey and pokhrel / bibechana 19 (1-2) (2022) 27-33 29 similar results are reported by kaur [14]. however, slightly different results were observed by other researchers [15,16]. this is due to the different environmental conditions and variation in altitude of plants. flavonoids, alkaloids, tannins, phenols were reported in the ethanol extract [17]. hence, the presence of various bioactive molecules makes the potential use of oxalis corniculata leaves to stop bleeding from wounds and effective in certain skin disease like warts, corns, antidote to reptile venom, dysentery and diuretic [3]. table 1. results of phytochemical screening of oxalis corniculata leaves extract s.no. phytochemicals n-hexane extract methanol extract 1 alkaloids + 2 flavonoids + 3 phenols + 4 carbohydrate 5 glycosides + 6 proteins + 7 saponins (+) indicate presence, (-) indicate absence. 3.2 antibacterial susceptibility assay the antibacterial efficacy was tested on the basis of the magnitude of zone of inhibition (in mm) and the results are presented in figure 1 and data indexed in table 2. the results suggested that, hexane extracts of oxalis corniculata leaf showed significant antibacterial activity against escherichia coli, staphylococcus aureus and salmonella typhi with zoi value 10 mm, 9 mm and 11 mm respectively in 50% concentration. but the crude hexane extract did not show antibacterial activity. the 1% concentration of methanol extract showed higher antibacterial efficacy against escherichia coli than staphylococcus aureus and salmonella typhi with zoi value 12 mm, 11 mm, and 10 mm respectively. but in 10% concentration methanolic extract showed antibacterial activity against only staphylococcus aureus with zoi value 10 mm. therefore, 1% methanolic leaf extract is more potent towards antibacterial activity than 10% of it. both nhexane and methanolic extracts showed highest zone of inhibition against gram negative bacteria salmonella typhi and escherichia coli (11 mm in 50% concentration of hexane extract and 12 mm in 1% concentration of methanol extract). taley et al. reported 6-14 mm zoi of methanol extract against staphylococcus aureus and escherichia coli [18] which support the present findings whereas mukharjee et al. showed 12 to 19 mm range of inhibition zone [19]. kathiriya et al. and rahman et al. reported that methanol and chloroform oxalis corniculata leaf extract showed higher antibacterial activity than the positive control [20, 21]. mohan and pandey concluded that the selected leaf extracts were showing highest antimicrobial activity with chloroform and ethanol extract [22]. therefore, this plant can be used for curing common diseases like diarrhea, cough, fever etc. table 2. antibacterial activity of oxalis corniculataleaf extracts on pathogenic bacteria (zoi in mm) pandey and pokhrel / bibechana 19 (1-2) (2022) 27-33 30 s. n. plant extract (solid) bacteria extracts (100 mg/ml) ofloxacin (100 mg/ml) 1. hexane 50% crude e. coli 10 0 30 s. aureus 9 0 32 s. typhi 11 0 26 2. methanol 10% 1% e. coli 0 12 30 s. aureus 10 11 32 s. typhi 0 10 26 fig. 1: images of antibacterial activity of oxalis corniculata leaf extract against (a) e. coli, (b) s. aureus and (c) s. typhi. 3.3 antioxidant activity via dpph assay the antioxidant activity of methanol plant extract was measured by using 2, 2-diphenyl-1-picryl hydrazyl radical (dpph) radical scavenging assay. antioxidants are defined as radical scavengers having strong anti-cancer activity by preventing oxidative cell damage [23], and protect the human body against free radicals and reduce the risk of disease [24]. the dpph radical assay was performed with methanol extract of oxalis corniculata leaf by using ascorbic acid as standard. the observed absorbance with different concentration of ascorbic acid and methanol extract was plotted in the graph (figure 2). c b a pandey and pokhrel / bibechana 19 (1-2) (2022) 27-33 31 table 3. radical scavenging activities of plant with methanol extract (me) and ascorbic acid. concentration (µg/ml ) 20 40 60 80 100 % of radical scavenging by methanol extract 22.05 32.68 40.80 51.25 60.98 % of radical scavenging by ascorbic acid 13.21 19.38 27.50 58.66 72.59 fig. 2: percentage radical scavenging activity vs. concentration of ascorbic acid and methanol extract. the table 3 depicts the results of radical scavenging activity of oxalis corniculata with methanol extract and ascorbic acid in different level of concentrations. higher the value of ic50 gives lower antioxidant potential describes their opposite relation. the ic50 value of oxalis corniculata leaf in methanol extract and standard ascorbic acid was found 3.87 µg/ml and 3.74 µg/ml respectively; however, poudel et al. mentioned 4.06 µg/ml as standard ic50 value of ascorbic acid for both ethanol and aqueous extract [25]. methanol extract showed slightly less antioxidant activity than the standard ascorbic acid, which is also reported by borah et al. [26]. this antioxidant activity is due to the existence of phenols and flavonoids in plant leaves, which may result the free radical scavenging effect [26]. ahmed et al. also reported good antioxidant activities of methanol extract and its sub-fractions in various solvents of oxalis corniculata [27]. tibuhwa also explored the antioxidant activities and suggested it as the source of side effect-free natural antioxidants which could be the best alternative to synthetic antioxidants in the food processing industry and also possible used in preventive medicine [28]. as antioxidants, flavonoids from these plants provide anti-inflammatory activity [29]. therefore, oxalis corniculata is used in treatment of wounds, burns and ulcer in herbal medicine [17]. conclusion methanolic and n-hexane extract of oxalis corniculata was successfully prepared from soxhlet extraction. the phytochemical screening of methanolic leaf extract revealed the presence of large number of bioactive secondary molecules like alkaloids, proteins, phenols, flavonoids, glycosides whereas n-hexane extract showed y = 15.804x 9.1429 y = 9.6429x + 12.625 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 20 40 60 80 100 r a d ic a l sc a v en g in g ( % ) concentration (µg/ml) ascorbic acid methanol extract pandey and pokhrel / bibechana 19 (1-2) (2022) 27-33 32 absence of phytochemicals. both extracts (nhexane and methanol) showed highest zone of inhibition against gram negative bacteria salmonella typhi and escherichia coli. and 1% methanolic leaf extract was found more potent towards antibacterial activity than 10% of it. similarly, the methanolic extract also showed good antioxidant activities as standard ascorbic acid. therefore, this result suggested that oxalis corniculata leaves can be used as a medicinal supplement in pharmaceutical industry as natural antioxidant having antibacterial activities. further research is needed to isolate and identify the important compounds present in the plant extracts to explore their biological activities. acknowledgements the authors are grateful to department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal for providing laboratory facilities to perform needful chemical experiments. we are thankful to medmicro nepal lab, thapathali, kathmandu, nepal, for providing the laboratory equipment’s and platform to perform antibacterial activities. references [1] a.k. kumar, k. das, m. joshipura, and n. mandal, oxalis corniculata linn. -the plant of indian subtropics, herbal tech. industry1 (2010)7-11. 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[28]d.d.tibuhwa, antioxidant potential-ities and antiradical activities of oxalis corniculata linn from tanzania, j. appl. biosci. 116 (2017) 11590-11600. doi: 10.4314/jab.v116i1.7 [29]d.e. okwu, evaluation of the chemical composition of indigeneous spices and flavouring agents, j. sci. 7 (2004) 455-459. doi: https://doi.org/10.3126/bibechana.v19i1-2.46094 the table 3 depicts the results of radical scavenging activity of oxalis corniculata with methanol extract and ascorbic acid in different level of concentrations. higher the value of ic50 gives lower antioxidant potential describes their opposite rel... bibechana 19 (1-2) (2022) 14-26 14 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal phytochemical analysis, antioxidant and antibacterial activities of methanolic rhizome extract of bergenia pacumbis: a valuable medicinal herb subas dangi, niranjan parajuli* biological chemistry lab, central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal *email: niranjan.parajuli@cdc.tu.edu.np, tel: +977-1-4332034 article information: received: november 8, 2021 accepted: december 4, 2021 keywords: bergenia pacumbis phytochemical screening antioxidant antibacterial abstract bergenia pacumbis, a perennial herb of the saxifragaceae family, usually referred to as ‘pashanbheda’ is geographically distributed within the temperate himalaya including nepal. the purpose of this study was to evaluate the phytochemical analysis as well as in vitro antioxidant and antibacterial activities of methanolic rhizome extract of b. pacumbis. the rhizome of b. pacumbis was extracted in methanol using the soxhlet apparatus and then the extract was concentrated. the rhizome extract was tested for phytochemicals using the standard protocol. the in vitro antioxidant activity of the extract was evaluated using the 2, 2diphenyl-1-picrylhydrazyl free radical scavenging assay. the 50 % inhibitory concentration (ic50) values of ascorbic acid and b. pacumbis were found to be 11.91 ± 0.03 μg/ml and 11.99 ± 0.05 μg/ml respectively that indicate b. pacumbis is a good source of antioxidant agents. the extract was further tested for antibacterial activity through the agar well diffusion method and found to be effective against staphylococcus aureus (16 mm) and klebsiella pneumoniae (12 mm). the present study validates the traditional use of b. pacumbis. doi: https://doi.org/10.3126/bibechana.v19i1-2.45963 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction http://nepjol.info/index.php/bibechana mailto:niranjan.parajuli@cdc.tu.edu.np https://doi.org/10.3126/bibechana.v19i1-2.45963 https://creativecommons.org/licenses/by-nc/4.0/ dangi and parajuli / bibechana 19 (1-2) (2022) 14-26 15 plant metabolites such as proteins, lipids, fatty acids, carbohydrates, and so on play a direct role in plant growth, development, and reproduction whereas secondary plant metabolites are used for defense against predators, parasites, and diseases, etc. [1]. plants contain a wide range of phytochemicals, such as polyphenols, alkaloids, flavonoids, tannins, carotenoids, terpenoids, quinine, and berberine, which are responsible for curing a variety of diseases and have properties including in vitro antioxidants, antimicrobial, antiviral, anti-mutagenic, anti-inflammatory, and other properties to a greater or lesser extent [2–4]. because of their adequacy, accessibility, compatibility, and feasibility, medicinal plants are an important part of primary health care [5]. in developing countries like nepal, medicinal plants play a vital supplementary role in the limited modern health care availability. world health organization (who) estimates that approximately 80 % of people in developing countries rely on medicinal plants for their basic healthcare needs [6, 7]. in industrialized countries, nearly 25 % of prescribed organic drugs and approximately 95 % of modern drugs have been derived directly or indirectly from plant sources [8, 9]. in the last few decades, the unprecedented rise in antibacterial resistant pathogenic microorganisms has increased the demand for novel/ alternative antibacterial agents [10–13]. antioxidants are a class of chemical compounds thought to protect enzymes and genetic material from structural and functional damage caused by an excess of free radicals [14]. the production of free radicals in the body that exceeds the body’s antioxidant capacity and the resulting damage is called oxidative stress [15]. oxidative stress is responsible for the pathogenesis of cardiovascular and neurodegenerative diseases, such as alzheimer's, aging, cancer, diabetes, and others [16]. destroying free radicals may help with good health [17]. phytochemicals such as polyphenols, flavonoids, ascorbic acid, tocopherols, carotenoids, etc. can absorb and neutralize free radicals and have significant antioxidant capacities [18, 19]. over the years, the demand for safe dietary natural antioxidants in pharmaceutics, nutraceuticals, cosmetics, and the food industry has grown significantly [20]. the bergenia species, commonly known as ‘pashanbheda’ (paashan = rockstone & bheda = piercing) [21], are perennial herbs native to central asia that grow widely in the temperate himalaya and are the most promising medicinal plants of the saxifragaceae family [22]. the different species of bergenia flourish well in rocky areas and on the cliffs are used for the dissolution of kidney and gall bladder stones. the root and rhizome of the bergenia species are used to cure fractured bones, fresh cuts, boils, wounds, fever, cough, vomiting, pulmonary infections, diarrhea, and ophthalmia by local peoples since ancient times in nepal, india, bhutan, and china. in addition, bergenia species have been reported with pharmacological activities such as analgesic, astringent, antiviral, antioxidant, antipyretic, antiulcer, antidiabetic, hepatoprotective, celebro-protective, gastroprotective, adaptogenic, hemorrhoidal, antilithiatic, anticancer, antihypertensive, antitussive, antiinflammatory, antimalarial, antimicrobial, antiobesity, insecticidal, diuretic, and skin whitening properties [23–25]. the virtues of bergenia species are largely attributed to their secondary metabolites such as arbutin, bergenin, catechin, gallic acid, and tannins, which are therapeutic and lead to variation in medical activities [26–28]. bergenia pacumbis (buch.-ham. ex d. don) c. y. wu & j. t. pan is traditionally used in the treatment of various human diseases in different parts of nepal. its leaves are used for the remedy of wounds, stomach ulcers, intestinal complaints, and heavy sneezing, while roots and rhizomes are used for acidity, dysentery, cough, fever, diarrhea, headache, dangi and parajuli / bibechana 19 (1-2) (2022) 14-26 16 (a) (b) kidney stone, internal injuries, and intestinal complaints [21, 29]. to treat diseases, a cup of boiled leaves in water is taken twice a day, while roots or rhizomes are crushed and boiled in water, then taken twice a day [29]. as reported by pandey et al. (2020), methanolic extract of b. pacumbis contains flavonoids and phenolic compounds such as afzelechin, arbutin, astilbin, bergenin, catechin, diosmetin, gallic acid, hyperoside, kaempferol-7-oglucoside, methyl gallate, morin, paashaanolactone, phloretin, protocatechuic acid, quercetin, and syringic acid. the scientific data related to the biological and chemical properties of b. pacumbis is scanty, hence, this study reports phytochemical analysis and antioxidant and antibacterial activities of methanolic extract of b. pacumbis. 2. methodology 2.1 chemicals and equipment the analytical grade chemicals/reagents used in the study were purchased from fisher scientific in germany. instruments such as soxhlet apparatus (borosilicate genuine, jsw), rotary evaporator (ika rv 10 digital v with ika hb 10 digital), and uv-visible spectrophotometer (shimadzu uv-vis spectrophotometer-1800) were also used in this research. 2.2 collection of plant materials the plant materials (plant & rhizomes) (figure 1) were collected in august 2018 from the salyan district (tharkot hill, altitude: 2,400 m above sea level), karnali province, nepal. the herbarium of the plant was recognized and verified as bergenia pacumbis (buch.-ham. ex d. don) c. y. wu & j. t. pan by taxonomists in national herbarium and plant laboratories, lalitpur, nepal. the rhizomes were washed with tap water, followed by sterilized distilled water, to remove adhered dust, dirt, and other foreign materials, and then dried in shade at room temperature. the dried rhizomes were powdered and then stored in an airtight polyethylene bag in a cool, dry location for ongoing studies. fig. 1. (a) aerial part and (b) rhizomes of bergenia pacumbis 2.3 extraction of plant materials the plant powder (60 g) was placed in the soxhlet apparatus and refluxed for 8 h with 360 ml methanol over a heating mantle at 63 °c. the solvent from plant extract was removed by evaporating with the help of a rotary evaporator under reduced pressure at 40 °c. the resulting extract (semisolid) was poured into a petri dish and left at room temperature to evaporate the excess solvent. the dried extract was weighed, and the percentage yield was calculated using equation (1). the dry sample was refrigerated at 4 °c until required for use. percentage yield = mass of crude extract the total mass of sample used × 100 % (1) 2.4 preliminary phytochemical screening the crude methanolic extract was subjected to qualitative tests for glycosides, flavonoids, alkaloids, phenolic compounds, terpenoids, steroids, carbohydrates, saponins, tannins, fixed oils and fats, quinones, reducing compounds, proteins, and coumarins according to the methods discussed in the literature. for the phytochemical tests, the stock solution was made by dissolving one gram of crude extract in 40 ml methanol. the related tests were mentioned below: (1) test for glycosides (keller-killiani test): with distilled water (5 ml), the crude extract (0.5 g) was shaken. to this, glacial acetic acid (2 ml) with one drop of ferric chloride solution was added, followed by sulphuric acid (1 ml) along the side of the test tube. a brown ring at the interface indicated the presence of cardiac glycosides (a violet ring may appear below the brown ring, while a greenish ring may form in the acetic acid layer) [30, 31]; (2) test for flavonoids: a) shinoda test: to 2-3 ml of crude extract, a piece of magnesium ribbon and 1 ml of concentrated hydrochloric acid were added. the presence of flavonoids was indicated by the formation of dangi and parajuli / bibechana 19 (1-2) (2022) 14-26 17 red or pink-red coloration of the solution [2, 32], and b) lead acetate test: 1 ml of crude extract was mixed with 1 ml of 10% lead acetate solution. the presence of flavonoids was indicated by the formation of a yellow precipitate [33]; (3) test for alkaloids: a) mayer’s test: the crude extract (0.5 g) was mixed with 5 ml of 1 % dilute hydrochloric acid and then filtered. a few drops of mayer’s reagent (potassium mercuric iodide solution) were added to the filtrate. the presence of alkaloids was determined by the formation of a white creamy precipitate [30, 34], and b) dragendorff’s test: the crude extract (0.5 g) was mixed with 5 ml of 1 % dilute hcl before being filtered. the filtrate was treated with a few drops of dragendorff’s reagent (potassium bismuth iodide solution). the presence of alkaloids was indicated by the formation of an orange-red precipitate [2, 30]; (4) test for phenolic compounds (ferric chloride test): in 5 ml of distilled water, the crude extract (0.2 g) was dissolved. a few drops of neutral 5 % ferric chloride solution were added to this. the presence of phenolic compounds was indicated by the formation of green, blue, or violet colored solution [32–34]; (5) test for terpenoids (salkowski test): five ml of extract solution was mixed with 2 ml of chloroform, and 3 ml of concentrated sulphuric acid was added along the side of the tube. the presence of terpenoids was indicated by the reddish-brown color at the interface [30, 31]; (6) test for steroids (salkowski test): with 2 ml of chloroform, the crude extract (0.2 g) was mixed and then 2 ml of concentrated sulphuric acid was added along the side of the test tube. the presence of steroids was indicated by the development of a reddish-brown color by the chloroform layer and green color by the acid layer [12]; (7) test for carbohydrates: a) fehling’s test: fehling a and fehling b reagents were mixed with equal parts, and 2 ml of it was added to the crude extract solution and gently boiled in a water bath. the appearance of a brick-red precipitate at the bottom of the test tube indicated the presence of carbohydrates (reducing sugars) [31, 32], and b) molisch’s test: 2 drops of molisch’s reagent were added to 2 ml of the crude extract and thoroughly shaken. along the side of the test tube, 2 ml of concentrated sulphuric acid was added. the presence of carbohydrates was determined by the formation of a reddish-violet ring at the junction of the two layers [32, 33]; (8) test for saponins (foam test): in a graduated cylinder, the extract (0.5 g) was shaken for 15 minutes with distilled water (20 ml). the presence of saponins was indicated by the formation of stable foam [12, 30]; (9) test for tannins (ferric chloride test): the extract (0.5 g) was mixed with distilled water (10 ml) before being filtered. a few drops of 5% ferric chloride solution were then added. the formation of a black or blue-green coloration or precipitate is the indication of the presence of tannins [12, 30]; (10) test for fixed oils and fats (spot test): ): in between two filter papers, a drop of the concentrated extract was pressed and then kept undisturbed. an oil strain on the paper indicated the presence of oils and fats [35, 36]; (11) test for quinones (alcoholic potassium hydroxide test): one ml of crude extract was treated with a few ml of alcoholic potassium hydroxide solution. the presence of quinones was indicated by the color change from red to blue [33, 36]; (12) test for reducing compounds (fehling’s test): the water (1 ml) was added to the extract (1 ml). to this solution, fehling’s reagent (5-8 drops) was added and then the mixture was warmed over a water bath. the presence of reducing compounds was indicated by brick-red precipitation [31, 32]; (13) test for proteins (xanthoproteic test): a few drops of concentrated nitric acid were added to the extract (1 ml). the presence of proteins was indicated by the formation of a yellowcolored solution [37]; and (14) test for coumarins (sodium hydroxide test): to about 1 ml of extract, 1.5 ml of 10 % naoh was dangi and parajuli / bibechana 19 (1-2) (2022) 14-26 18 added. the formation of yellow color is the indication of the presence of coumarins [37]. 2.5 antioxidant activity the antioxidant activity of the plant extract and ascorbic acid (standard) was assessed in vitro based on free radical scavenging ability using the 2, 2diphenyl-1-picrylhydrazyl (dpph) radical scavenging assay, which was slightly modified from the method described previously [38]. various concentrations (5, 12.5, 25, 50, 100 & 200 μg/ml) of plant extract and ascorbic acid were prepared in methanol on the clean and dry test tubes. the sample (plant extract or ascorbic acid) was taken 2 ml in each test tube. to this sample, 2 ml of the 0.2 mm methanolic dpph solutions was added [6]. the tubes were shaken vigorously for uniform mixing. these tubes were incubated for half an hour in darkness at room temperature. the control was made in the same way but without the plant extract or ascorbic acid, i.e. dpph solution in methanol. methanol was taken to collect the baseline on the spectrophotometer i.e. methanol as a blank [31]. the absorbance was measured at the wavelength (λ) = 517 nm using a uv-visible spectrophotometer (uv-1800, shimadzu). the percentage of dpph free radical scavenging activity (% inhibition) was calculated by using the formula given as equation (2). % inhibition = ac − at ac × 100 % (2) where ac denotes control absorbance and at denotes test sample (extract/standard) absorbance. then, the concentration corresponding to 50 % inhibition (ic50 value) was calculated by using a four-parameter logistic regression model in graphpad prism. the lower ic50 value is an indication of a more potent antioxidant activity [14, 39]. 2.6 antibacterial activity b. pacumbis extract was tested for the in vitro antibacterial activity against gram-negative bacteria escherichia coli atcc 25922, klebsiella pneumoniae atcc 700603, and salmonella typhimurium atcc 14028, and a positive bacterium staphylococcus aureus atcc 25923. the antibacterial activity of plant extract was assessed using the modified agar well diffusion method [40–44] as reported by kardong et al. (2013) and dwivedi et al. (2020). all glassware, media, and reagents were sterilized by autoclaving at 121 °c. the standard cultures of bacteria under study were collected. after obtaining the culture, the test organisms were streaked on nutrient agar plates [10] and incubated. from the isolated colony, gram staining was performed. the organism thus obtained were tested for their purity. the standard culture inoculum was prepared from primary culture plates. the isolated colony was sub-cultured on nutrient agar plates with the inoculating loop aseptically. it was then transferred to a tube containing sterile nutrient broth and incubated for 24 h at 37 °c. the bacterial suspension (inoculum) was swabbed uniformly onto the agar surface of mueller-hinton agar (mha) plates. the four wells of 6 mm diameter were made in the incubated media (mha) plates with the assistance of a sterile cork-borer at four equidistant points at about 1.5 cm away from the dish-wall. then 40 μl of the working solution (50 mg/ml) of plant extract was loaded into the respective well of each petri dish. at the same time, the solvent (dmso) was tested for activity as a negative control in a separate well. the cultured agar plates were loaded with 40 μl neomycin (1 mg/ml) as a positive control. one of the wells was also loaded with 20 μl neomycin plus 20 μl extract solution to study synergistic or antagonistic effect. the zone of inhibition (zoi) was measured in a millimeter unit after a 24 h of incubation period at 37 °c to determine the antibacterial efficacy. 2.7 statistical analysis dangi and parajuli / bibechana 19 (1-2) (2022) 14-26 19 all experiments were carried out in triplicate, and data were presented as the average of three replicates. for the statistical analysis, a oneway analysis of variance (anova) (p < 0.05) was used. ms excel 2013 and graphpad prism 9.2.0 (332) were used to conduct the statistical analysis and create the graph. 3. results and discussion 3.1 percentage yield of extraction the percentage yield of rhizome extract of b. pacumbis in methanol was calculated and it was found to be 28.17 %. the percentage yield of plant extraction is ascertained by the ability of solvent that depends upon the phytochemical composition, extraction procedure and conditions, and polarity of the extracting solvent [3, 33, 45]. 3.2 phytochemical screening as shown in table 1, the phytochemical screening of a crude methanolic extract of b. pacumbis rhizome revealed the presence of various phytochemicals such as cardiac glycosides, flavonoids, alkaloids, terpenoids, steroids, phenolic compounds, carbohydrates, saponins, fixed oils and fats, quinones, reducing compounds, and proteins, whereas tannins and coumarins were absent. however, the phytochemical composition may differ in different environmental conditions or stress conditions, extraction method, and type of solvent used [12, 39, 45]. it is revealed that the phytochemicals are known to have medicinal properties [46], antimicrobial [11, 47], and antioxidant activity [14, 17, 48]. for example, alkaloids show biological properties such as antimicrobial, antimalarial, anti-inflammatory, antispasmodic, cytotoxicity, and pharmacological effects. similarly, steroids have antibacterial and insecticidal properties, along with cardiotonic effects. according to research, cardiac glycosides are being used to treat cardiac arrhythmia and congestive heart failure [30]. other phytochemicals called terpenoids show medicinal properties such as antimicrobial, anticarcinogenic, antimalarial, hepaticidal, anti-ulcer, and anticancer activities [33]. according to several reports, flavonoid groups exhibited biological activities such as antioxidant, anti-viral, antimicrobial, antiinflammatory, anti-cancer, anti-angiogenic, and anti-allergic reactions [8, 38]. flavonoids are essential for plant growth and development as well as a plant defense against pests and microorganisms [49]. some flavonoids such as quercetin [22] and rutin [49] are known for their antioxidant, antiviral, anti-inflammatory, and antihistaminic activities. saponins and glycosides are important antidiarrheal agents [33]. saponins are antimicrobial, antiinflammatory, anti-malarial, anti-diabetic, antiallergic, and insecticidal [9]. saponins are also involved in plant defense systems due to their antimicrobial activity [38]. the antibacterial properties of steroids are known [40]. several studies have also shown that phenolic compounds have good antioxidant activity and a wide range of pharmacological activities such as anti-apoptosis, anti-carcinogenicity, antiaging, anti-inflammation, anti-atherosclerosis, inhibition of angiogenesis, cardiovascular protection, and endothelial function improvement [10, 39]. scientific reports support the fact that flavonoids or polyphenols lower the risk of cardiovascular disease, cancer, and diabetes [49]. the medicinal and nutritional values of food are mainly based on total phenolic and flavonoid content [9]. the presence of biologically important phytochemicals in the rhizome extract of b. pacumbis, as tested in this study, may contribute to its medicinal value and a potential source for useful drugs. pandey et al. (2020) used high-resolution mass spectrometry (hrms) to detect flavonoids and phenolic compounds in a crude methanol extract of b. pacumbis. but, according to the present study, phytochemical screening indicates the presence of other phytochemicals like cardiac glycosides, alkaloids, terpenoids, steroids, dangi and parajuli / bibechana 19 (1-2) (2022) 14-26 20 carbohydrates, saponins, fixed oils and fats, quinones, reducing compounds and proteins along with flavonoids and phenolic compounds. hence, to find the more chemical compounds present in b. pacumbis, gas chromatography-mass spectrometry (gc–ms), 1h nmr (nuclear magnetic resonance), and 13c nmr spectroscopy methods are required. according to several reports, different species of bergenia possess many phytochemicals, for example, 58 chemical compounds were found to be present in b. ciliata [24], 103 compounds were found in b. crassifolia [23], and 31 compounds were isolated from b. ligulata [21]. therefore, the phytochemicals present in b. pacumbis are responsible for the use of the plant as ethnomedicine in different parts of nepal. table 1. phytochemical screening of a crude extract of bergenia pacumbis rhizome s. no. phytochem icals screened standard test metha nol extrac t of b. pacum bis 1 glycosides kellerkilliani test + 2 flavonoids shinoda test + lead acetate test + 3 alkaloids mayer’s test + dragendor ff’s test + 4 phenolic compounds ferric chloride test + 5 terpenoids salkowski test + 6 steroids salkowsk i test + 7 carbohydra tes fehling’s test + molisch’s test + 8 saponins foam test + 9 tannins ferric chloride test 10 fixed oils and fats spot test + 11 quinones alcoholic potassium hydroxide test + 12 reducing compounds fehling’s test + 13 proteins xanthopro teic test + 14 coumarins sodium hydroxide test note: ‘+’ denotes the presence and ‘-’ denotes the absence of phytochemicals. 3.3 antioxidant activity the dpph free radical scavenging method was used to investigate the in vitro antioxidant activity of the methanolic rhizome extract of b. pacumbis because this experiment is reliable, quick, and requires a small amount of sample [20]. dpph is a very stable nitrogen-centered organic free radical with a purple color and a strong absorption at 517 nm that has been successfully used to evaluate free radical scavenging activity [3, 30]. when free radical scavengers are added, dpph is reduced to dpph-h, and its color changes to yellow due to the efficacy of antioxidants [18, 50]. the ability of a test sample to scavenge dpph free radicals determines its free radical scavenging capacity or antioxidant potential, which dangi and parajuli / bibechana 19 (1-2) (2022) 14-26 21 demonstrates its effectiveness, prevention, interception, and repair mechanism against injury in a biological system [49, 51]. the percentage of dpph radical scavenging ability (% inhibition) of plant extract and ascorbic acid were plotted against respective various concentrations (5 – 200 μg/ml) as displayed in figure 2. the percentage inhibition was found to increase with increasing extract concentration [49]. the percentage inhibition was found to be 87.36 % and 94.01 % at 200 μg/ml for rhizome extract and ascorbic acid (standard) respectively. the antioxidant activity of a substance is directly proportional to its dpph free radical scavenging power [52]. the concentration required for 50% dpph inhibition (ic50) values of ascorbic acid and b. pacumbis were found to be 11.91 ± 0.03 and 11.99 ± 0.05 μg/ml respectively that indicating the ic50 value of b. pacumbis was close to ascorbic acid. the lower ic50 value showed the rhizome extract of b. pacumbis is the potential of high antioxidant activity. pandey et al. (2020) reported that the ic50 value of the crude methanol extract of b. pacumbis rhizome was 40.87 ± 0.32 μg/ml. moreover, a variety of factors influence the antioxidant activity of plant extract, such as the test method, extraction procedure, and phytoconstituents in the extract [30, 39]. the antioxidant activity of phytochemicals varies from slight to extremely high depending upon their reactive groups. due to the lower bond dissociation energy phenolic compounds having the o–h group are more active than compounds having the n–h group [17]. further, activity also depends on the structure, molecular weight, and substitution pattern of functional groups [50]. according to a previous report by pandey et al. (2020), the major compounds identified in the extract of b. pacumbis were afzelechin, arbutin, astilbin, bergenin, catechin, diosmetin, gallic acid, hyperoside, kaempferol-7-o-glucoside, methyl gallate, morin, paashaanolactone, phloretin, protocatechuic acid, quercetin, and syringic acid. out of these various flavonoids and phenolic compounds, according to reports, bergenin, catechin, arbutin, morin, afzelechin, and quercetin show significant antioxidant activity [22]. because of their hydrogen donating ability, these compounds were able to discolor dpph solution [38, 45]. moreover, phytochemical screening of b. pacumbis performed in this study showed the presence of polyphenols, flavonoids, alkaloids, steroids, terpenoids, saponins, and reducing sugars, which may responsible for good antioxidant activity of the plant. the antioxidant activity of a plant can be figured out by phenolic and flavonoid contents [48, 53]. phenolic compounds are the key contributors in plant constituents that bestow the highest scavenging ability on free radicals [4, 19]. on the other hand, flavonoids which are subgroups of phenolic compounds [19] suppress reactive oxygen species (ros) formation [54], chelate trace elements involved in the free-radical generation, scavenge reactive species, inhibit oxidative enzymes and up-regulate or protect antioxidant defenses [16, 53, 55]. therefore, b. pacumbis could be a good source of natural antioxidant alternative to synthetic fig. 2. dpph free radical scavenging ability of b. pacumbis and ascorbic acid at various concentrations (5-200 µg/ml). dangi and parajuli / bibechana 19 (1-2) (2022) 14-26 22 antioxidants. further investigation regarding in vivo antioxidant activity and its mechanism could be considered. 3.4 antibacterial activity table 2 displays the in vitro antibacterial activity of methanolic rhizome extract of b. pacumbis in terms of zone of inhibition (zoi). table 2. antibacterial activity of the rhizome extract of bergenia pacumbis notes: a source of plant extract, b bacterial species, c antibiotic as a positive control, d plant extract dissolved in methanol for working solution, e antibiotic + solution of plant extract dissolved in methanol, to determine the synergistic or antagonistic effect, f dmso as a negative control the antibacterial activity was evaluated in comparison to neomycin (positive control) and dmso (negative control). figure 3 shows the antibacterial activity of the crude extract against bacteria tested by the agar well diffusion method. the antibacterial activity in terms of zoi was found to vary significantly with test microbes. the result revealed that the extract of b. pacumbis showed significant zoi against s. aureus (16 mm) and k. pneumoniae (12 mm) out of four bacteria viz. s. aureus, e. coli, k. pneumoniae, and s. typhimurium and zoi is statistically comparable with neomycin. the extract did not display any inhibition against e. coli and s. typhimurium. the extract portrayed the highest zoi against gram-positive bacterium – s. aureus followed by gramnegative bacterium – k. pneumoniae. the positive control exhibited the greatest inhibition, while the negative control did not exhibit inhibitory action against either of the microbes. the antibiotic plus plant extract had shown the antagonistic effect [56, 57] in all cases because the combined effect was less than the effect of either individual agent [58]. the plant extract shows antibacterial activity in a concentration-dependent manner [3, 38]. the extraction method and the solvent used also affect the antibacterial activity of the plant extract [9, 11]. the antibacterial activity was more pronounced on the gram-positive bacterium than the gram-negative bacterium due to the difference in morphological constitutions. the gram-positive bacterium contains only an outer peptidoglycan layer, which is an ineffective permeability barrier to antibacterial compounds [53]. on the other hand, the gramnegative bacterium has an outer membrane that contains lipopolysaccharide (lps) in the outer leaflet and phospholipids in the inner leaflet, as well as an inner peptidoglycan layer, making the cell wall impermeable to antibacterial compounds. the cell wall of gram-negative bacterium is more complex in a layout that acts pla nt extr act a path ogen s b zone of inhibition (zoi) in mm neom ycin (1 mg/m l) 40 μl (1) c extra ct soluti on (50 mg/m l) 40 μl (2) d neom ycin + extract solutio n (20 μl + 20 μl) (3) e dm so 40 μl (4) f b. pac umb is s. aure us 24 16 20 0 e. coli 18 0 16 0 k. pneu moni ae 22 12 21 0 s. typhi muri um 19 0 0 0 dangi and parajuli / bibechana 19 (1-2) (2022) 14-26 23 as a diffusion barrier and makes it less susceptible to antibacterial agents than the gram-positive bacterium [33, 37]. the presence of porins at the outer membrane and the active efflux processes involved in gramnegative bacterium is responsible for higher resistance [4]. therefore, the phytochemicals present in the extract are more active against the gram-positive bacterium as being better permeable into the cell structure. the broadspectrum antibacterial activity of the rhizome extract of b. pacumbis might be because of the presence of phytochemicals like alkaloids, phenolics, flavonoids, steroids, saponins, and terpenoids and these compounds could be soluble in an organic polar solvent. alkaloids and flavonoids have been known to have bactericidal effects [59, 60]. specific phenolic compounds possess potential antibacterial activity [61, 62]. it is reported that the antibacterial activity of most polyphenols is related to interactions between polyphenols and bacterial cell surfaces [63]. steroids, the important compound for sex hormones, have the strongest antibacterial properties. saponins have been reported to possess antibacterial activity [40, 43]. terpenoids are also for inhibition of bacterial growth [64]. the bacterial growth inhibition occurs through several mechanisms: (i) destruction of bacterial cell membrane and function, (ii) interruption of nucleic acid synthesis and function, (iii) inhibition of a metabolic pathway, and (iv) coagulation of cytoplasmic constituents [59, 60, 65] 4. conclusion the medicinal plant contains phytochemicals, especially secondary metabolites, that can be used to cure a variety of human ailments. the phytochemical screening tests of methanolic rhizome extract of b. pacumbis revealed the presence of a variety of phytochemicals, such as cardiac glycosides, flavonoids, alkaloids, terpenoids, steroids, phenolic compounds, carbohydrates, saponins, fixed oils and fats, quinones, reducing compounds, and proteins. the study showed that the rhizome extract possesses an astonishing potential on in vitro antioxidant activity was investigated by dpph free radical scavenging method and the good broad-spectrum in vitro antibacterial activity using agar well diffusion method. the present study found that b. pacumbis extract contains phytochemicals 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nuclear physics abstract the objective of this work is to calculate the energy eigenvalue for q-deformed hulthen potential using a gaussian hypergeometric function with centrifugal approximation factor and related thermodynamical properties. for this, we develop a mathematical model using the schrodinger wave equation to find the energy eigenvalue. in addition, the thermodynamic parameters were also calculated for q-deformed hulthen potential using the partition function. the energy eigenvalue for quantum numbers n=1 to n=5 was observed for screening parameters 0.1, 0.5, and 1. in between, 0.1 to 1 and n=1 to n=2 the energy eigenvalue ranges from -1.048 to -208.572. the energy eigenvalue for considering potential shows that decrease with increasing the quantum number which means electron are loosely bounded nucleus in an atom. also, the vibrational mean energy, vibrational mean free energy, vibrational specific heat capacity, and vibrational entropy are obtained but due to complexity, the further development of the equation is the limitation of this work. doi: https://doi.org/10.3126/bibechana.v19i1-2.46416 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/ licenses/by-nc/4.0/ bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:magnum.photon@gmail.com https://doi.org/10.3126/bibechana.v19i1-2.46416 https://creativecommons.org/%20licenses/by-nc/4.0/ karki et al. / bibechana 19(1-2) (2022) 165-169 166 1. introduction deformation hulthen potential (hp) with q-deformation is well-defined as 𝑉(𝑟) = − 𝑉0𝑒 −2𝛼𝑟 1 − 𝑒−2𝛼𝑟 here 𝑉0 = 𝑍𝑒 2𝛼 is known as coupling strength, and 𝛼 is the screening parameter [1-5]. hp has introduced to studies the detail of deuteron and has extensive applications in physics like nuclear physics, particle physics, atomic physics, condensed matter physics, etc.). hp is one of the short-range potentials like yukawa potential, which behaves as a coulomb potential at a small distance and exponentially decreases with increasing the distance from the nucleus. for spin-zero particles, klein-gordon uses hp for their equation to solve as 𝑉(𝑟) = −𝑍𝛼 exp(− 𝑟 𝑎 ) 1−exp(− 𝑟 𝑎 ) or 𝑉(𝑟) = −𝑍 𝑒2𝛿 𝑒−𝛿𝑟 1−𝑒−𝛿𝑟 different methods like the asymptotic iteration method, supersymmetry method, shift n1 expression, factorization method, nikiforov-uvarove, etc., are used to calculate energy eigenvalue for further potential. the q-deformed hp and modified inversely quadratic yukawa (qdhmiqy) potential can be represented as, 𝑉(𝑟) = − 𝑉0𝑒 −2𝛼𝑟 1 − 𝑞𝑒−2𝛼𝑟 − 𝑉1𝑒 −2𝛼𝑟 𝑟2 here 𝑉0, 𝑉1 , 𝑎𝑛𝑑 𝑞 are coupling strength and deformation parameters, respectively. such potential is used to describe different interactions such as nucleon-nucleon interactions, meson-meson interactions, the various field of nuclear physics, and quantum chemistry (hulthen, 1942 and tencan & sever, 2009). 1.1. differntent method to calcaulte energy eigenvalue 1.1.1. asymptotic iteration method this method is used to solve homogenous linear second-order differential equations defined as, 𝑦" = 𝜆0(𝑥)𝑦′ + 𝑠0(𝑥)𝑦 , here 𝜆0(𝑥) and 𝑠0(𝑥) function in 𝐶∞(𝑎, 𝑏). on taking (n+1)th and (n+2)the derivative, we get, 𝑦(𝑛+1) = 𝜆𝑛−1(𝑥)𝑦′ + 𝑠𝑛−1(𝑥)𝑦 and 𝑦(𝑛+2) = 𝜆𝑛(𝑥)𝑦′ + 𝑠𝑛(𝑥)𝑦 . here 𝜆𝑛 = 𝜆𝑛−1 ′ + 𝑠𝑛−1 + 𝜆0𝜆𝑛−1 and 𝑠𝑛 = 𝑠𝑛−1 ′ + 𝑠0𝜆𝑛−1. on taking the ratio of (n+2)th and (n+1)th and applying the asymptotic condition 𝑠𝑛 𝜆𝑛 = 𝑠𝑛−1 𝜆𝑛−1 ≔ 𝛼, the condition gives the eigenvalue of the considered equation, and we obtained 𝑦(𝑛+1)(𝑥) = 𝐶1𝜆𝑛−1 exp (∫ (𝛼 + 𝜆0)𝑑𝑡 𝑥 ) this equation yields the solution of the asymptotic consider equation as 𝑦(𝑥) = [𝐶2 + 𝐶1∫ exp (∫ (𝜆0(𝜏) + 2𝛼(𝜏))𝑑𝜏 𝑡 )𝑑𝑡 𝑥 ] 1.1.2. nikiforov-uvarov this method is used to solve the solution of an equation (e.g., schrodinger) by transformation as 𝜓′′(𝑠) + �̃�(𝑠) 𝜎(𝑠) 𝜓′(𝑠) + �̃�(𝑠) 𝜎2(𝑠) 𝜓(𝑠) = 0, here �̃�(𝑠) is polynomial of degree at most one, 𝜎(𝑠) and �̃�(𝑠) are second-degree polynomials. on applying the condition of 𝜆 = 𝜆𝑛 one can obtain the energy eigenvalue. here 𝜆 = 𝑘− + 𝜋′(𝑠) and 𝜆𝑛 = −𝑛𝜏 ′(𝑠) − 𝑛(𝑛−1)𝜎′′(𝑠) 2 , 𝜋(𝑠) is also polynomial with four values obtained by comparing the standard equation. 1.1.3. supersymmetry method to calculate the energy eigenvalue, this method assumes a particular type of wave function 𝜓𝑠 = exp[∫𝑊0(𝑟)𝑑𝑟 + 𝛽(𝑟)]𝜙𝑠(𝑟), here 𝑊0(𝑟) is supersymmetry in quantum mechanics assumed as witten superpotential, 𝜙𝑠(𝑟) is a new function, and 𝛽(𝑟) is also a wave function that leads to correct asymptotic value. as we knew schrodinger equation is used to obtain the energy eigenvalue by replacing the general wave function by 𝜓𝑠 and solving similar to the conventional method, we get energy eigenvalue for any potential. 1.1.4. factorization method in this method, the wave function for a particular coordinate system (example, schrodinger equation spherical coordinate system) contains angular and coordinate system, and this method separates the angular and radial part by factorization method known as separation of variable in general like ψ(𝑟, 𝜃, 𝜙) = 𝑅(𝑟)θ(𝜃)φ(𝜙) after separating the angular and radial parts. the radial part is defined as 𝑅(𝑟) = 𝑈(𝑟)𝐿(𝑟), here u(r) is related to potential and l(r) is associated with laguerre differential equation. the angular part is defined as θ(𝑥) = 𝑈(𝑥)𝑃(𝑥), here 𝑥 = 𝑐𝑜𝑠𝜃, p(x) related to the jacobi function. 2. theoretical formulation we have radial form part of se is 𝜓′′(𝑟) + 2𝑚 ℏ2 [𝐸𝑛𝑙 − 𝑉(𝑟) − 𝑙(𝑙 + 1)ℏ 2𝑚𝑟2 ]𝜓(𝑟) = 0 using centrifugal approximation 1 𝑟2 = 4𝛼2𝑒−2𝛼𝑟 (1−𝑒−2𝛼𝑟)2 , a radical form of se become 𝜓′′(𝑟) + 2𝑚 ℏ2 [𝐸𝑛𝑙 + 𝑉0𝑒 −2𝛼𝑟 1 − 𝑞𝑒−2𝛼𝑟 − 𝑙(𝑙 + 1)ℏ2 2𝑚 4𝛼2𝑒−2𝛼𝑟 (1 − 𝑒−2𝛼𝑟)2 ] 𝜓(𝑟) = 0 let us consider 𝑍 = 1 1−𝑒−2𝛼𝑟 then the radial form of the equation become 𝜓′′(𝑟) + 2𝑚 ℏ2 [𝐸𝑛𝑙 + 𝑉0 (𝑍 − 1) − 𝑙(𝑙 + 1)ℏ2 2𝑚 𝑍24𝛼2 (𝑍 − 1) 𝑍 ]𝜓(𝑟) = 0 (1) on solving equation (1), we get 𝜓′′(𝑍) 𝑍(𝑍 − 1) + 𝜓′(𝑍)(2𝑍 − 1) + [ 𝑚𝐸𝑛𝑙 2ℏ2𝛼2 1 𝑍(𝑍 − 1) + 𝑚𝑉0 2ℏ2𝛼2 1 𝑍 − 𝑙(𝑙 + 1)]𝜓(𝑍) = 0 (2) again supposed 𝑚𝐸𝑛𝑙 2ℏ2𝛼2 = −𝜖, 𝛿 = 𝑚𝑉0 2ℏ2𝛼2 , 𝜁 = 𝑙(𝑙 + 1), therefore equation (2) becomes 𝜓′′(𝑍) 𝑍(1 − 𝑍) + 𝜓′(𝑍)(1 − 2𝑍) + [ −𝜖 𝑍(𝑍 − 1) − 𝛿 𝑍 + 𝜁]𝜓(𝑍) = 0 (3) now asymptotic behavior of equation (3), at 𝑟 → 0 (𝑍 → 1) and 𝑟 → ∞ (𝑍 → 0), let us introduce a new function 𝑓(𝑍) as 𝜓(𝑍) = 𝑍𝜇(1 − 𝑍)𝜙𝑓(𝑍) (4) combining equations (4) and (3), we get a new equation of the form 𝑍(1 − 𝑍)𝑓′′(𝑍) + [1 + 2𝜇 − (2𝜇 − 2𝜙 − 2)𝑍]𝑓′(𝑍) − [(𝜇 + 𝜙)2 + (𝜇 + 𝜙) + 𝜁)]𝑓(𝑍) + [ −𝜖 − 𝛿 + μ2 𝑍(1 − 𝑍) + 𝜙2 − 𝜇2 + 𝛿 (1 − 𝑍) ]𝑓(𝑍) = 0 (5) now equation (5) becomes the gauss hypergeometric equation when the square bracket term equal to zero −𝜖 − 𝛿 + μ2 = 0, 𝜙2 − 𝜇2 + 𝛿 = 0 karki et al. / bibechana 19(1-2) (2022) 165-169 167 therefore, equation (5) is written as 𝑍(1 − 𝑍)𝑓′′(𝑍) + [1 + 2𝜇 − (2𝜇 − 2𝜙 − 2)𝑍]𝑓′(𝑍) − [(𝜇 +𝜙 + 1 2 + √ 1 4 − 𝜁) × (𝜇 + 𝜙 + 1 2 − √ 1 4 − 𝜁)]𝑓(𝑍) = 0 (6) the gaussian hypergeometric function (ghf), 2f1(𝑎, 𝑏; 𝑐; 𝑧) can be expressed as infinite series for |𝑧| < 1 as, 2f1(𝑎, 𝑏; 𝑐; 𝑧) = ∑ (𝑎)𝑛(𝑏)𝑛 (𝑐)𝑛 ∞ 𝑛=0 𝑧𝑛 𝑛! = 1 + 𝑎𝑏 𝑐 𝑧 1! + 𝑎(𝑎+1)𝑏(𝑏+1) 𝑐(𝑐+1) 𝑧2 2! +⋯……. here (𝑎)𝑛 ≔ γ(𝑎+𝑛) γ(𝑎) , (𝑏)𝑛 ≔ γ(𝑏+𝑛) γ(𝑏) , (𝑐)𝑛 ≔ γ(𝑐+𝑛) γ(𝑐) putting these in the above equation and simplifying we get, 𝑓(𝑍) = 𝐹1(𝑎1, 𝑏2; 𝑐1; 𝑍)2 = γ(𝑐1) γ(𝑎1)γ(𝑏1) here we consider 𝑎1, , 𝑏1 and 𝑐1 are unknown parameters whose values are expressed as 𝑎1 = (𝜇 + 𝜙 + 1 2 + √ 1 4 − 𝜁) , 𝑏1 = (𝜇 + 𝜙 + 1 2 − √ 1 4 − 𝜁) , 𝑐1 = 1 + 2𝜇 . now substituting the value of 𝑓(𝑍) with these parameters in 𝜓(𝑍) = 𝑍𝜇(1 − 𝑍)𝜙𝑓(𝑍) in this, we get 𝜓(𝑍) = 𝑍𝜇(1 − 𝑍)𝜙 𝐹1(𝜇 + 𝜙 + 1 2 + √ 1 4 − 𝜁, 𝜇 + 𝜙 + 1 2 − √ 1 4 − 𝜁; 1 + 2𝜇; 𝑍)2 if 𝑎1, 𝑏1, and 𝑐1 is equal to the negative of integer (𝑛) then hypergeometric function 𝑓(𝑍) will become a polynomial with 𝑛 = 0, 1, 2, 3, . . . , 𝑛𝑚𝑎𝑥 integer, applying quantum condition we have, 𝑎1 = −𝑛 and 𝑏1 = −𝑛. now using 𝜙2− 𝜇2 + 𝛿 = 0 to calculate the value of 𝜙 and 𝜇 from the above suitable value we get 𝜙 = ( 𝜔−𝑛 2 + 𝛿 2(𝜔−𝑛) ) and 𝜇 = ( 𝜔−𝑛 2 − 𝛿 2(𝜔−𝑛) ) where 𝜔 = √ 1 4 − 𝜁 − 1 2 = 𝜔 now to calculate the energy we have from −𝜖 − 𝛿 + μ2 = 0 and 𝜙2− 𝜇2 + 𝛿 = 0 is 𝜖 = 𝜙2. since we have 𝑚𝐸𝑛𝑙 2ℏ2𝛼2 = −𝜖 and 𝜙 = ( 𝜔−𝑛 2 + 𝛿 2(𝜔−𝑛) ), therefore we have, 𝐸𝑛𝑙 = − 2ℏ2𝛼2 𝑚 ( 𝜔 − 𝑛 2 + 𝛿 2(𝜔 − 𝑛) ) 2 (7) substituting the value of 𝛿,𝜔, 𝜁 in equation (7) we get, 𝐸𝑛𝑙 = − 2ℏ2𝛼2 𝑚 ( √ 1 4 − 𝑙(𝑙 + 1) − 1 2 − 𝑛 2 + 𝑚𝑉0 2ℏ2𝛼2 2(√ 1 4 − 𝑙(𝑙 + 1) − 1 2 − 𝑛)) 2 𝐸𝑛𝑙 = − ℏ2𝛼2 2𝑚 ( (√ 1 4 − 𝑙(𝑙 + 1) − 1 2 − 𝑛) + 𝑚𝑉0 2ℏ2𝛼2 (√ 1 4− 𝑙 (𝑙 + 1) − 1 2 − 𝑛) ) 2 (8) this equation is dependent upon the quantum number and screening parameters. it is a non-relativistic energy spectrum that was calculated using hp, which is short-range potential. table1: energy eigenvalue of q-deformed hp quantum number energy eigenvalue (𝑬𝒏𝒍) 𝑛 𝑙 𝑉0 = 1, 𝛼 = 1 𝑉0 = 1, 𝛼 = 0.5 𝑉0 = 0.5, 𝛼 = 1 𝑉0 = 0.1, 𝛼 = 1 𝑉0 = 0.1, 𝛼 = 0.1 1 0 2.20977 531 -2.2942 1.511428 202 1.047957 128 -0.37392 1 -3.909 -2.0596 3.342473 165 2.921198 927 -0.21685 2 0 3.90895 5159 2.059648 762 3.342473 165 2.921198 927 -0.21685 1 6.73920 8248 2.599411 115 6.206286 437 5.795751 457 -0.20085 2 15.4626 1915 4.680554 734 14.94963 916 14.54548 557 -0.26176 3 0 6.73920 8248 2.599411 115 6.206286 437 5.795751 457 -0.20085 1 10.5964 3495 3.497067 921 10.07684 311 9.670573 724 -0.22183 2 21.3326 1546 6.129289 967 20.82338 824 20.42043 553 -0.31551 3 44.9510 0139 12.00908 368 44.44673 472 44.04536 939 -0.54514 4 0 15.4626 1915 3.497067 921 10.07684 311 9.670573 724 -0.22183 1 21.3326 1546 4.680554 734 14.94963 916 14.54548 557 -0.26176 2 36.0774 4104 7.835599 168 27.69761 069 27.29540 443 -0.38115 3 65.6991 7677 14.47365 847 54.32147 377 53.92035 895 -0.64285 4 119.197 4276 26.83975 676 103.8209 174 103.4203 367 -1.13562 5 0 15.4626 1915 4.680554 734 14.94963 916 14.54548 557 -0.26176 karki et al. / bibechana 19(1-2) (2022) 165-169 168 1 21.3326 1546 6.129289 967 20.82338 824 20.42043 553 -0.31551 2 36.0774 4104 9.796092 271 35.57209 463 35.17038 379 -0.45783 3 65.6991 7677 17.18928 52 65.19627 857 64.79535 114 -0.75082 4 119.197 4276 30.55728 87 118.6958 413 118.2953 337 -1.28407 5 208.571 5169 52.89739 577 208.0706 136 207.6703 245 -2.17691 2.1. thermodynamic properties hp is also used to explain the electronic properties of some alkali halides, study the bound state and scattering properties, etc. moreover, statistical physics and quantum statistical mechanics help predict, interpret, analyze, etc., different thermodynamic properties such as vibrational and rotational energy levels of various molecules [6]. thermodynamics properties of hp are also studied for statistical quantum chromodynamics (qcd), nuclear matter, a color deconfined partonic phase, and the quark-gluon plasma (qgp) at sufficiently high temperature/density [7]. now to calculate the thermodynamic properties for hp, now we develop (8) equation to study the thermodynamic properties; we use the vibrational partition function for this we summarized 𝐸𝑛𝑙 as, 𝐸𝑛𝑙 = − ℏ2𝛼2 2𝑚 ( 𝑃 (𝜎 + 𝑛) − (𝜎 + 𝑛)) 2 (9) here, −𝜎 = − 1 2 + √ 1 4 − 𝑙(𝑙 + 1), 𝑃 = − 𝑚𝑉0 2ℏ2𝛼2 , since vibrational partition function is defined as 𝑍𝑣𝑖𝑏(𝛽) = ∑ 𝑒−𝛽𝐸𝑛𝑙 𝜂 𝑛=0 , 𝛽 = 1 𝑘𝑇 therefore, substituting the value of 𝐸𝑛𝑙 in 𝑍𝑣𝑖𝑏 hp with partition function modified as, 𝑍𝑣𝑖𝑏(𝛽) = ∑ 𝑒 −𝛽[− ℏ2𝛼2 2𝑚 ( 𝑃 (𝜎+𝑛) −(𝜎+𝑛)) 2 ] 𝜂 𝑛=0 (10) replacing the sum by an integral in the classical limit of equation (10), we have 𝑍𝑣𝑖𝑏(𝛽) = ∫ 𝑒 −𝛽[− ℏ2𝛼2 2𝑚 ( 𝑃 (𝜎+𝑛) −(𝜎+𝑛)) 2 ]𝜂 0 𝑑𝑛 (11) supposing 𝜎 + 𝑛 = 𝜌, equation (becomescome [8] 𝑍𝑣𝑖𝑏(𝛽) = ∫ 𝑒 ( 𝑏𝛽 𝜌2 +𝛽𝑎𝜌2+𝑐𝛽) 𝑑𝜌 𝜂+𝜎 𝜎 (12) here 𝑎 = ℏ2𝛼2 2𝑚 , 𝑏 = ℏ2𝛼2𝑃2 2𝑚 , 𝑐 = − ℏ2𝛼2𝑃 𝑚 , now equation (12) becomes 𝑍𝑣𝑖𝑏(𝛽) = 𝑒𝑐𝛽−2√−𝑎𝛽√−𝑏𝛽√𝜋 (− erf[γ1 − γ2] + 𝑒 4√−𝑎𝛽√−𝑏𝛽(erf[γ1 + γ2] − erf[ω1 + γ2 + ω2]) − ξ) 4√−𝑎𝛽 (13) where γ1 = √−𝑏𝛽 𝜎 , γ2 = √−𝑎𝛽𝜎,ω1 = √−𝑎𝛽𝜂 , ω2 = √−𝑏𝛽 𝜂+𝜎 𝑎𝑛𝑑 ξ = erf [ω1 + γ2 − ω2] and the error function well-defined as erf(𝑍) = 2 √𝜋 ∫ 𝑒𝑡 2 𝑑𝑡 𝑧 0 equation (13) plays an integral equation used to describe the thermodynamic properties of q-deformed hp. this equation described vibrational mean and free energy, vibrational entropy, and specific heat capacity. the integrals error function erf (𝑍) has essential applications in atomic physics, astrophysics, statistical analysis, etc. [9] 3. results and discussion 2.2. energy eigenvalue of q-deformed hp the energy eigenvalue is represented in atom unit with 𝑚 = ℏ = 1, at 𝑉0 = 0.5, 1 and 𝛼 = 0.5, 1. the energy eigenvalue is developed of q-deformed hp. it is beneficial to calculate the thermodynamic properties of physics fields like quantum chromodynamics, meson-meson interaction, nuclear matter color chromodynamics, etc. the nature of energy eigenvalue with quantum number is shown in figure 1, which shows that with an increased quantum number the electron bounded energy decreases which means the electron goes loosely bounded with the nucleus in an atom. figure 1: energy eigenvalue of q-deformed hulthen potential 2.3. thermodynamic properties of q-deformed hp 2.3.1. vibrational mean energy of q-deformed hp (vmeqhp) the mean vibrational energy for the hp model is obtained as, 𝑈(𝛽) = 𝜕 𝜕𝛽 (𝑙𝑛𝑍𝑣𝑖𝑏(𝛽)) 𝑈(𝛽) = 𝜕 𝜕𝛽 𝑙𝑛 ( 𝑒𝑐𝛽−2√−𝑎𝛽√−𝑏𝛽√𝜋 (−erf[γ1−γ2]+𝑒 4√−𝑎𝛽√−𝑏𝛽(erf[γ1+γ2]−erf[ω1+γ2+ω2])−ξ) 4√−𝑎𝛽 ) by solving this equation, we get, 𝑈(𝛽) = 𝑑(ln{ (𝑒𝑟𝑓[𝛤2−𝛤2])}) 𝑑𝛽 + 𝑑 ln{erf[γ1+γ2]} 𝑑𝛽 − 𝑑 ln{erf[ω1+γ2+ω2]} 𝑑𝛽 (14) 2.3.2. vibrational mean free energy of q-deformed hp (vmefqhp) the vibrational mean free energy is obtained as 𝐹(𝛽) = −𝑘𝑇𝑙𝑛(𝑍𝑣𝑖𝑏(𝛽)) 𝐹(𝛽) = −𝑘𝑇𝑙𝑛( 𝑒𝑐𝛽−2√−𝑎𝛽√−𝑏𝛽√𝜋 (− erf[γ1 − γ2] + 𝑒 4√−𝑎𝛽√−𝑏𝛽(erf[γ1 + γ2] − erf[ω1 + γ2 + ω2]) − ξ) 4√−𝑎𝛽 ) 𝐹(𝛽) = −𝑘𝑇[ln{ (𝑒𝑟𝑓[𝛤2 − 𝛤2])} + ln{erf[γ1 + γ2]} − ln{erf[ω1 + γ2 + ω2]} + ln{ξ}] (15) karki et al. / bibechana 19(1-2) (2022) 165-169 169 2.3.3. vibrational specific heat capacity of q-deformed hp (vshcqhp) the vibrational specific heat capacity (cs) is given as 𝐶𝑠(𝛽) = 𝑘𝛽 2 𝜕2 𝜕𝛽2 (𝑙𝑛(𝑍𝑣𝑖𝑏(𝛽))) 𝐶𝑠(𝛽) = 𝑘𝛽2 𝜕2 𝜕𝛽2 𝑙𝑛( 𝑒𝑐𝛽−2√−𝑎𝛽√−𝑏𝛽√𝜋 (−erf[γ1 − γ2] + 𝑒 4√−𝑎𝛽√−𝑏𝛽(erf[γ1 + γ2] − erf[ω1 + γ2 +ω2]) − ξ) 4√−𝑎𝛽 ) 𝐶𝑠(𝛽) = 𝑘𝛽 2 𝜕2 𝜕𝛽2 ([ln{ (𝑒𝑟𝑓[𝛤2 − 𝛤2])} + ln{erf[γ1 + γ2]} − ln{erf[ω1 + γ2 + ω2]} + ln{ξ}]) (16) (16) 2.3.4. vibrational entropy of q-deformed hp (veqhp) the vibrational entropy is obtained as 𝑆(𝛽) = 𝑘𝑙𝑛(𝑍𝑣𝑖𝑏(𝛽)) + 𝑘𝑇 𝜕 𝜕𝛽 (𝑙𝑛𝑍𝑣𝑖𝑏(𝛽)) 𝑆(𝛽) = 𝑘𝑙𝑛( 𝑒𝑐𝛽−2√−𝑎𝛽√−𝑏𝛽√𝜋 (− erf[γ1 − γ2] + 𝑒 4√−𝑎𝛽√−𝑏𝛽(erf[γ1 + γ2] − erf[ω1 + γ2 +ω2]) − ξ) 4√−𝑎𝛽 ) + 𝑘𝑇 𝜕 𝜕𝛽 ( 𝑒𝑐𝛽−2√−𝑎𝛽√−𝑏𝛽√𝜋 (− erf[γ1 − γ2] + 𝑒 4√−𝑎𝛽√−𝑏𝛽(erf[γ1 + γ2] − erf[ω1 + γ2 + ω2]) − ξ) 4√−𝑎𝛽 ) 𝑆(𝛽) = 𝑘[ln{ (𝑒𝑟𝑓[𝛤2 − 𝛤2])} + ln{erf[γ1 + γ2]} − ln{erf[ω1 + γ2 + ω2]} + ln{ξ}] + 𝑘𝑇 𝑑(ln{ (𝑒𝑟𝑓[𝛤2−𝛤2])}) 𝑑𝛽 + 𝑑 ln{erf[γ1+γ2]} 𝑑𝛽 − 𝑑 ln{erf[ω1+γ2+ω2]} 𝑑𝛽 (17) thermodynamical properties have error functions with different parameters and in literature [9] authors discuss its multiuse use. therefore, studying the thermodynamic properties for consideration in this paper has equal importance as discussed in the literature [8, 9]. the thermodynamic properties of the electron in considering potential is obtained in equation (14), (15), (16), and (17) showing that the thermodynamic properties depend upon quantum number also. therefore, the thermodynamic properties for considering potential depend upon quantum number as well as temperature. 3. conclusion the development of energy eigenvalue for q-deformation hp potential develops in equation (8) with the help of this energy vibrational thermodynamic properties are calculated. the development of a mathematical model for thermodynamic properties for the electron in q-deformation potential is completely new. in addition, the thermodynamic properties also depend upon the quantum number which means vary with the quantum number. for example, the thermodynamic properties of the electron in the n=1 orbit are different from the thermodynamic properties of the electron in the n=2 orbit and so on. this is because the thermodynamic properties depend upon the energy eigenvalue of the electron and the energy eigenvalue of the electron depends upon the quantum number. the developed mathematical model is based on a gaussian hypergeometric function with a partition function. to study the more detailed thermodynamic properties of an electron in considering potential one may extend the development theory because due to the complexity of mathematical derivation authors consider the limitations of their work. acknowledgment the authors would like to thank the department of physics, tri-chandra multiple campus, tribhuvan university and patan multiple campus, tribhuvan university, nepal; innovative ghar nepal, and national research council nepal for supporting this work. references [1] c.o. edet and p.o. okoi, any l-state solutions of the schrodinger equation for q-deformed hulthen plus generalized inverse quadratic yukawa potential in arbitrary dimensions, revista mexicana de fısica, 65(2019)333-344, http://www.scielo.org.mx/pdf/rmf/v65n4/0035-001x-rmf-6504-333.pdf [2] i. b. okon, o. popoola, and c. n. isonguyo, approximate solutions of schrodinger equation with some diatomic molecular interactions using nikiforov-uvarov method, advance in high energy physics, volume 2017, 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[9] e. w. ng and m. geller, a table of integrals of the error functions, journal of research of the national bureau of standards b. mathematical sciences, 73b(1)(1969)1-2. http://www.scielo.org.mx/pdf/rmf/v65n4/0035-001x-rmf-65-04-333.pdf http://www.scielo.org.mx/pdf/rmf/v65n4/0035-001x-rmf-65-04-333.pdf https://doi.org/10.1155/2017/9671816 https://arxiv.org/pdf/1812.06383.pdf https://arxiv.org/ftp/arxiv/papers/2001/2001.04799.pdf https://doi.org/10.1186/s42787-019-0014-0 bibechana vol. 20, no. 1, april 2023, 55-64 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar analysis and characterization of x-ray flare of mkn 421 using xmm-newton observation 0658801301 rajendra neupane, niraj dhital∗ central department of physics, tribhuvan university, nepal ∗corresponding author. email: niraj.dhital@cdp.tu.edu.np abstract this research work was carried out to analyze the x-ray flares in blazar mkn 421 using data from xmm-newton observation (observation id: 0658801301) that lasted for 8 hours. epic/pn data was used for statistical analysis of the light and spectrum curve in energy ranges from 0.3 to 10.0 kev. the best fit model for the spectrum was found to be the additive model (log-parabola + black-body). the measured integrated flux in the energy range of 0.3-2 kev is 5.015 × 10−10 ergs cm−2 s−1 with an associated uncertainty range of (5.010 – 5.020) × 10−10 ergs cm−2 s−1 at a 90% confidence level. similarly, the measured integrated flux in the energy range of 2-10 kev is 2.398 × 10−10 ergs cm−2s−1 with an associated uncertainty range of (2.392 – 2.405) × 10−10ergs cm−2 s−1 at a 90% confidence level. the highest peak in the light and spectrum curve indicated the presence of high energy x-ray flares. the fractional variability of 0.444 is relatively high, which indicates that the source is variable. the fall in count per second per energy around 2 kev in the spectrum curve suggests that the intensity of x-rays decreases in a power law manner after a strong flare at this energy. the countrate distribution of the observation analyzed is best described by a normal distribution which suggests that the emission mechanism in the blazar is governed by additive processes. keywords blazar mkn 421, light curve, (log-par+bbody), spectrum, x-ray flares. article information manuscript received: march 14„ 2023; accepted: march 31, 2023 doi https://doi.org/10.3126/bibechana.v20i1.53233 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction blazar mkn 421, also known as mrk 421, is a specific blazar and a type of active galactic nucleus (agn) characterized by high-energy emission from a compact central region. this emission is produced by a jet of matter moving at nearly the speed of light, which is aimed directly at the observer [1]. it is located at 11h04m27.2s and +38012’32”in right ascension and declination, and is one of the closest and brightest blazars with a redshift of z = 0.0308 [2]. the blazar mkn 421 was one of the first extragalactic sources detected at tev energies and is one of the brightest bl lac objects, particularly in the x-ray band [3]. mkn 421 is believed to be a source of high-energy cosmic rays (crs) and high-energy neutrinos (hens) and has strong em flux and spectral variability [4]. high energy crs 55 http://nepjol.info/index.php/bibechana niraj.dhital@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v20i1.53233 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ rajendra neupane and niraj dhital/ bibechana 20 (2023) 55-64 56 are the most energetic cosmic rays, with energies exceeding 1018 ev [4]. they are thought to originate from the most extreme environments in the universe, such as supernovae, gamma-ray bursts, or active galactic nuclei (agns) like mkn 421 [5]. mkn 421 has been extensively studied across the electromagnetic spectrum and is a popular target for multi-wavelength observations. this blazar is a powerful source of high-energy gamma-rays and is one of the first blazars to be detected in this energy range [6]. hens are subatomic particles with extremely high energies, and they are thought to be produced in the interactions of high energy crs with matter [7]. the detection of hens can provide valuable information about the origin and propagation of high energy crs, and their study can help us understand the most extreme processes in the universe. the electromagnetic (em) emission mechanism in mkn 421, as well as in other blazars, is thought to involve the acceleration and collision of highenergy particles in the relativistic jet. all blazars show variability in their flux and spectrum across the em spectrum, and emit jets towards earth [1]. in the case of mkn 421, it is believed that the relativistic electrons in the jet are accelerated to extremely high energies through various mechanisms, such as shock acceleration, magnetic reconnection, or turbulence [8]. these high-energy electrons then emit em radiation through various processes, such as synchrotron emission and inverse compton scattering. the study of x-rays can provide valuable information about the high-energy particles in the relativistic jet of blazars, such as their distribution and spectrum which is characterized by broad double peaked structure [9]. this structure is obtained in the logarithmic plot of versus . this information can help us constrain the mechanisms responsible for the acceleration of these particles and to better understand the conditions required for the production of hens and crs. x-rays are a good tracer of the high-energy emission in blazars, and they can be used to study the connection between the gamma-ray and the x-ray emission. this information can help us understand the underlying physical processes involved in the production of hens and crs, such as the interactions between the relativistic particles and the magnetic fields in the jet. x-rays can provide information about the physical conditions in the jet, such as the magnetic field strength, the temperature of the emitting plasma, and the density of the relativistic particles. this information can help us understand the conditions that determine the emission of hens and crs and the efficiency of their production in blazars. the observations of x-rays can help to recognize the astrophysical sources that can accelerate particles in the pev range [10]. xmm-newton data is used to study the release of the x-ray flares from the galactic and extragalactic sources like blazars, supernova remnants etc. [11]. the maximum count rate in a small interval of time that makes a bump in the light curve is due to the stronger x-ray flares [12]. we analyze the x-ray spectrum in the target sources using ‘xspec’. a light curve plots the count rate against time, while a spectrum curve plots the count rate against energy. the best fit model we obtain from the spectrum curve analysis gives insight into the physics processes responsible for the production of x-rays in the sources. yan et al. (2018) studied the x-ray flares of mkn 421 using 50 observational ids and found that all of them were best fit with a combination of two models: log-par and blackbody. this result was based on intraday observations and was consistent when different parameters were plotted against time [13]. this study found that most of the observational ids of mkn 421 showed similar results with a reduced chi-square nearly equal to one. on the basis of these findings, we have taken observational id 0658801301 of mkn 421 to investigate its flares and emission mechanism. liu et al. (1994) analyzed the 28-year historical light curve of on 231 and found periodic behavior with peaks and minima in the count rate [14]. similarly, our study also showed similar behavior with a rise and fall in the count rate and a highest peak (see fig. 1-2). vila and romero (2009) [15] used a leptonic and hadronic model for electromagnetic emission in microquasars gx 339-4 to explain the cause of high-energy neutrino emission during xray flares as the effect of relativistic jets of particles. this is based on einstein’s theory of the relativistic increase in mass with velocity. therefore, we use statistical analysis of x-ray data to understand the possible emission of very high energy neutrinos. we have used both light and spectrum curves for our analysis. in this paper, we focus on the target source blazar. 1.1 xmm-newton instruments xmm-newton is a european x-ray satellite mission with 3 high-performance x-ray telescopes and an optical monitor. it has a large x-ray collecting area and can observe sources continuously for long periods, providing highly sensitive observations within 0.15-15 kev [16]. the xmm-newton telescope is highly sensitive due to its advanced instruments, including the european photon imaging camera (epic) with ccd cameras and silicon chips [17]. the epic cameras have different readout times, with the pn cameras being faster, and are most efficient in the 0.1-10 kev energy range. rajendra neupane and niraj dhital/ bibechana 20 (2023) 55-64 57 the pn detector mode of the epic cameras is preferred due to its long lifetime and low photon pileup problems. in this study, we use epic data to focus on the study of x-ray flares. 1.2 x-ray flares and high energy particles emission mechanism the phenomenon of x-ray flares, where a large amount of energy is released in a short period of time, has been observed in various sources such as blazars. these flares occur at different frequencies in the electromagnetic spectrum [18] and contribute a small fraction to the diffuse neutrino intensity of very high energy [19]. x-ray flares can be detected by a method which is known as the semiautomatic detection procedure [20]. blazars are classified into two types, bl lac objects and optically violently variable quasars [21]. bl lacs are active galactic nuclei with relativistic jets caught at a small angle to the line of sight [1], while quasars are mostly flat-spectrum radio quasars. blazars are known for their large and quick variations in flux on timescales shorter than 1 hour [22], which is referred to as intra-day variability [23]. variations on timescales of days to weeks are called shortterm variability, and those on scales of months to the longest are known as long-term variability [24]. it is brightest in the x-ray band with the highest flux recorded 1.2 10-9 erg cm-2 s-1 for the energy range 2-10 kev [25]. the energy dissipation mechanism in blazar jets is still not understood. the spectral energy distribution of blazars shows two bumps, with the low-energy bump believed to be synchrotron radiation of relativistic electrons. the origin of the high-energy bump is still under debate, with various mechanisms proposed including inverse-compton scattering [26], relativistic proton synchrotron radiation [27], and synchrotron radiation of secondary particles from proton-proton interactions [28]. 2 materials and methodology in this section, we describe the xmm-newton archival data and data reduction techniques that have been used for our work. 2.1 data (xmm-newton archival data) xmm-newton data which is publicly available was used to study the nature of the source in the x-ray band of the electromagnetic spectrum (em). xm-newton observations can be retrieved through the xmm-newton science archive (http://nxsa.esac.esa.int/nxsa-web). observation data files (odfs) were downloaded from the xmmnewton science archive. xmm-newton science analysis software (sas) was used to reduce this data. here, epic/pn camera observations were used for our purpose because the sensitivity of epic/pn is greater than that of the mos camera [29]. here, xmm-newton analysis was performed for one observation id which is the brightest source blazar (target: mkn 421) . for the source analysis, light and spectrum curve was plotted. 2.2 data reduction techniques the xmm-newton data was processed using the science analysis software (sas) version 1.3 with the latest current calibration files (ccf). the energy range from 0.3 to 10 kev was selected for light curve extraction to ensure better quality and higher accuracy, while excluding absorption and background noise. all epic/pn observations were taken in small window mode. the source spectrum was extracted from the imaging data of the european photon imaging camera (epic), which was set between 10000 and 12000 with the "pattern==0" flag. the presence of pileup in the source was checked, and light curves were extracted from off-source circular regions to detect high background periods caused by flares. to avoid the strong photon pile-up effects in the inner source regions, event files were extracted from annular regions centered on the source position. the sas task epatplot was used to test different circular and annular regions and only single pixel events (pattern =0) with a quality-flag of 0 were accepted. for epic pn, the event list was created using epproc and for epic mos, emproc was run. a light curve was first generated in the energy range of 0.3-10 kev, and then a cleaned event list was produced using a threshold on the light curve counts. this threshold was used to determine "low background" intervals and create the corresponding good time interval (gti) file. the standard rate values were 0.4 for epic pn and 0.35 for mos data, but these values may change based on the steady light curve. the gti file produced by the tabgtigen tool was used to exclude event lists with flaring background, producing a filtered event list for scientific purposes. the tabgtigen tool was utilized to produce a good time interval file, which is devoid of soft proton flares. the source was visualized using ds9, where the source light curve was extracted from a circle and the coordinates of the source and background light curve were obtained. to correct for factors affecting the detection efficiency, such as vignetting, bad pixels, psf variations, and quantum efficiency, as well as variations affecting the stability of the detection within the exposure, like dead time and gtis, the cleaned event file was created. the spectral analysis involved generating a redistribution matrix and an( rajendra neupane and niraj dhital/ bibechana 20 (2023) 55-64 58 cillary file available on the xmm-newton sas site. finally, the source and background spectra were generated along with arf and rmf files. the spectra were grouped to ensure a minimum of 20 counts for each spectral channel. the spectral analysis of the data was performed using xspec and reduced chi square technique is used for statistical methods. initially, three different models were tried on the data, which included a power law, a broken powerlaw and a log-parabolic model. the log-parabolic model showed the best fit for the data, and was therefore selected as the main component of a new model. additional members were added to further improve the fit, and the best result was found to be a combination of a log-parabolic and a blackbody model. this best-fit model provides insight into the triggering mechanism of flares and confirms that the parameters of the system being observed are consistent with the defined model. 2.3 data analysis techniques the analysis of mkn blazar (observation id 0658801301) involves the use of both spectrum and light curve data. the data collected is of high quality with good time resolution and energy coverage. to study individual brightenings in the light curve, a simple logic is used to identify x-ray flares. the light curve displays time and count rate and allows for the study of single-peaked events. complex multi-peaked flares are broken down into fundamental events, with the peaked events contributing to x-ray flares. the light curve shows that the blazar source is very active with complicated, nonsinusoidal variations, consisting of both short and long period oscillations. similarly, the spectrum curve is plotted between energy and count rate. the flares in the spectrum curve are identified visually and modeled with elements equal to the number of flares. the fitting of the model is evaluated by analyzing the distribution of residuals, which should be constant if the flare findings are correct. bumps in the residuals indicate the presence of flares. table 1: log of the observing campaign. revolution obs. id. target start time (ut) end time (ut) duration obs. mode 2837 0658801301 mkn 421 2015-06-05 23:48:35 2015-06-06 07:51:55 29000 prime full window table 2: spectral analysis results of blazar mkn 421, with observation id 0658801301, fitted with model (logpar+bbody). model parameter model component component parameter unit value 1 1 logpar alpha 2.34 +/1.55× 10−3 2 1 logpar beta 0.22 +/4.36 × 10−3 3 1 logpar pivote(scale) 1.50 4 1 logpar norm 6.0 × 10−2+/1.55 × 10−4 5 2 bbody kt kev 0.6 +/5.5 × 10−3 6 2 bbody norm 5.1 × 10−4 +/1.11 × 10−5 the variability of a source in xmm-newton observations indicates that the brightness of the source is changing over time. the variability can be caused by various physical processes such as flares and changes in accretion rate onto a compact object like a black hole. the study of the variability of x-ray sources can provide important information about the physical conditions in the source and help to distinguish between different models or theories [30]. thus to observe variability in source, we find fractional variability which is given in eq. 1. fv r = √ s2− < σ2 err >)/ < x > (1) where s2 is the total measured variance, < σ2 > is rajendra neupane and niraj dhital/ bibechana 20 (2023) 55-64 59 figure 1: the light curve depicted as a linear-linear axis transformation, displays x-ray flares in a blazar and has been calculated by averaging the data over an 8-hour period ranging from 23:48:35 to 07:51:55. the mean squared errors, and < x > is the mean count rate [30]. when analyzing the x-ray data, a comparison of the log-normal and normal distributions is made by fitting each to a histogram plot of the count rates per second. the process of multiple events resulting from the collision of two or more events is referred to as cascade and follows a log normal distribution pattern [31]. similarly, the normal distribution model is useful for understanding the behavior of x-ray events that are generated through the summing or combining of individual events, rather than through the cascading or multiplication of events [32]. 3 data analysis and results we use both spectrum and light curves for analysis. the source is found to be located at 11:04:29.2118 and +38:12:36.775 of right ascension and declination respectively. the physical coordinate of the source is (25880.5, 27960.5). 3.1 light curve analysis the light curve is a plot between count rate and time. the light curve is shown in figure 1. in the light curve, we have plotted linear-linear axes transformation. the minimum and maximum time coordinates along the horizontal x-axis are 549935463.28 and 549965603.28 respectively. the maximum count rate coordinates along the vertical y-axis is 0.168 respectively. in figure 1, the reference line is set at 0.05. when viewed from 0.05 downwards, the first peak is found at a count rate of 0.04, followed by a second peak with a count rate of 0.034 and a third peak with a count rate of 0.03. there are also fourth rajendra neupane and niraj dhital/ bibechana 20 (2023) 55-64 60 (a) (b) figure 2: (a) left panel: mkn 421 pn spectrum curve for observation id: 0658801301. the observation was performed in imaging mode. the spectrum was fitted with a (logpar + bbody) model. xdata min = 0.421, xdata max = 14.40. ydata min = 1.08 × 10−3, ydata max = 261.9. ymodel min = 1.11 ×10−3, ymodel max = 264.3. (b) right panel: unfolded spectrum for the observation id: 0658801301. it is well described by a log-parabola (smooth red curve) + blackbody (dashed green) emission model, suffering line-of-sight. absorption. and fifth peaks with count rates of 0.026 and 0.024, respectively, and a sixth peak with a count rate of 0.019. in figure 1, when viewed upwards from 0.05, different coordinates (count rates) are observed for each peak, suggesting that the emission of x-rays in blazar is not periodic over the 8-hour observation period, indicating non-periodic intraday variability. the highest count rate above 0.15 is only observed once in the 8-hour time duration, reflecting the occasional release of relativistic jets in blazar. the highest count rate is associated with high energy, indicating a short and intense energy release. 3.2 spectrum analysis (for blazar) net count rate (cts/s) for spectrum is 2.813× 102 +/1.211 × 10-1(99.9% total). 1-220 channels are noticed. exposure time is 1.927 × 104sec. background exposure time is 1.927 × 104 sec. 7 channels (1-7) were ignored in the spectrum. the attributes or parameters we define in a model describe the properties of the x-ray flares emission mechanism. for example represents the galactic hydrogen column density which is 1022 cm−2 and set as default in software. ‘kt’ is the blackbody temperature. alpha ( is the spectral index and beta ( is the curvature parameter of the log parabola. alpha ( indicates the slope of the pivot energy. the value of alpha is set as 1.0. the value of beta varies from -4 to +4. but we have set it here as 0.45. the value of pivot energy is set as 1.5. the value of norm (normalization of the model) is set as 1.0. each parameter has values in a defined range but we have fixed it here so that it fits our model. the best-fitting results exhibit that there is a strong relationship between the parameters we defined. in the spectral analysis, xspec was used. χ2 statistics were applied during the spectral fittings process using xspec, the x-ray flares can be identified in the spectrum curve plotted between energy and counts per second per energy. the value of chi-squared is 1377.78 using 213 bins and null-hypothesis probability of 0.001 with 208 degrees of freedom. the value of reduced chisquare (χ2) = 6.624 (1377.78/208). the xspec analysis of the x-ray data from the observed source yielded a measured integrated flux of 5.015 × 10−10 ergs cm−2s−1in the energy range of 0.3-2 kev. the associated uncertainty range for this measurement is (5.010 5.020) × 10−10 ergs cm−2s−1, corresponding to a 90% confidence level. in addition, the xspec analysis also yielded a measured integrated flux of 2.398 x 10−10 ergs cm−2s−1 in the energy range of 2-10 kev. the associated uncertainty range for this measurement is (2.392 2.405) x 10−10 ergs cm−2s−1, also corresponding to a 90% confidence level. the best-fitting results for the spectrum curve is shown in figure 2. the hard and soft x-ray spectral shapes make the x-ray behavior of blazar very complex. in figure 2, it is hardened towards lower energies upto around 2 kev and softened towards higher energies (from above 2 kev). the spectrum steepens continuously after around 2 kev. the sharp fall in count rate (intensity) after this particular energy value indicates that brightness decreases after the emission of the flares. in figure 1, a light curve is compared to a spectrum curve in figure 2 to extract properties. the first peak above 0.05 in the vertical y-axis, from the rajendra neupane and niraj dhital/ bibechana 20 (2023) 55-64 61 figure 3: figure 3: the time-averaged broadband spectrum of the blazar source obtained using xmmnewton’s epic data (observation id 0658801301). the count spectra and residuals with respect to the best-fit (lp+bb) model are displayed on the left in figure 3, with the residual values on the y-axis and the fitted values on the x-axis. figure 4: normal and log-norm distribution of count per second. reference value 0.05, is referred to as the first lowest peak in figure 1, while the last peak above 0.15 is referred to as the last highest peak. the number of first lowest peaks, observed from the reference value 0.05, is the greatest in the whole observational period, and the number of last highest peaks is the least, with only one in this case. there are other intermediate peaks in between. when observing figure 2, it is found that the area under the curve between 0.5 and 1 kev is the maximum and decreases when moving towards the right within the same energy range. by comparing figure 1 and figure 2, it is observed that the lowest peak represents the lowest energy and the highest peak represents the highest energy. higher energy x-rays are emitted in smaller quantities while lower energy x-rays are emitted in greater quantities. the nature of the plot remains the same when different parameters, such as intensity, count rate, residuals, etc., are plotted with respect to either time or energy. 3.3 counts spectra with residuals in figure 3, the count spectra and the residuals are displayed to highlight the patterns in the residuals. the lower panel of figure 3 showcases the data that deviates from the horizontal line at "0" on the y-axis, which indicates the presence of high-energy x-ray emissions and flare events. the residuals are calculated by dividing the difference between the data and model by the error. the scatter points in the plot demonstrate that there is non-periodic variability in the count rate per energy in the blazar, which may indicate that the randomness in the count rate per energy is rerajendra neupane and niraj dhital/ bibechana 20 (2023) 55-64 62 sponsible for producing high energy events. 3.4 distribution plot analysis the mean and standard deviation of the count per second are 0.06 and 0.03 respectively. we have tried possible distributions to fit the data such as norm, lognorm and chi2. but the best fit distribution is the normal distribution and represents the additive model which can be interpreted as an addition of events in x-ray observation data analysis. the kolmogorov-smirnov (ks) p-value of normal distribution is 0.90. this high ks p-value indicates that the fit is good. count rate 0.05 appears frequently. the count per second with maximum value 0.16 is only one. this maximum value of count rate appeared only one time during the 8 hour observational period and can be a sign of x-ray flares. the fractional variability is 0.444. a fractional variability value of 0.444 indicates that the variability of the x-ray count rate is 44.4% of the mean squared count rate. this means that there is a significant amount of variability in the x-ray count rate of the source, and that the fluctuations are not due solely to poisson noise. this value can be used to study the variability of x-ray sources. ‘0.444’ fractional variability above the poisson noise level is indicative of physical processes in the x-ray source, such as intrinsic variability, propagation effects, intermittent variability, and correlated variability. fluctuations in the x-ray emitting regions, such as changes in the accretion rate, can lead to intrinsic variability in the x-ray count rate. propagation of x-rays through the interstellar medium can lead to additional variability in the count rate due to absorption and scattering. the x-ray source may switch on and off or show variability on different time scales, leading to additional variability in the count rate. variability in the x-ray source may be correlated with other physical processes, such as variability in the mass accretion rate, leading to additional variability in the count rate. for normal distribution fitting, aic (akaike information criterion) and bic (bayesian information criterion) are -107.57 and -55416.87 respectively and for lognormal distribution fitting the aic and bic value are -105.76 and -55140.08 respectively.this demonstrates that a normal distribution model is a better fit compared to a lognormal distribution model and indicates that x-ray events are generated by the aggregation of separate events, rather than through a multiplicative progression of events. 4 conclusion the x-ray flares in blazars can be analyzed through a double-component model that consists of the sum of log-parabola and blackbody models (logpar+bb). this model provides a good fit to the 0.3-10 kev emission data with a result of reduced chi-squared (χ2 = 6.624, and the estimated parameters include an absorbing column density of = 1022 cm-2, blackbody temperature of kt = 0.5 kev, pivot energy of 1.5 kev, spectral index of 1.0, and curvature parameter of the log-parabola of 0.45. the parameters of the blazar flare that was studied have been wellconstrained and its x-ray variability shows a nonperiodic nature in intraday. after the emission of strong flares, the x-ray flux decreases rapidly and steepens downward, especially after reaching a peak value 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[32] m. chernyakova, a. neronov, a. lutovinov, j. rodriguez, and s. johnston. xmm–newton observations of psr b1259 63 near the 2004 periastron passage. monthly notices of the royal astronomical society, 367(3):1201–1208, 2006. introduction xmm-newton instruments x-ray flares and high energy particles emission mechanism materials and methodology data (xmm-newton archival data) data reduction techniques data analysis techniques data analysis and results light curve analysis spectrum analysis (for blazar) counts spectra with residuals distribution plot analysis conclusion bibechana vol. 21, no. 3, december 2024, 272-280 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar evaluating and predicting losses from thunderbolt and fire events in nepal: a regression analysis with moving averages approach pitri bhakta adhikari*, rachana ghimere, nabraj khanal tri-chandra m. campus, saraswati sadan, ghantaghar, kathmandu, nepal ∗corresponding author. email: pbadhikari09@gmail.com abstract nepal is prone to natural disasters, including thunderbolts and fires,due to its geographical location. however, the lack of awareness and preparedness has exacerbated the impact of these disasters, as evidenced by the current serious pandemic situation. urgent attention is required in terms of financial, social, and technological development to effectively manage thunderbolt and fire incidents. this study examines the frequency and severity of thunderbolt and fire incidents in nepal over the past 48 years, revealing a concerning trend of increasing losses and incidents. despite this alarming situation, the issue remains largely overlooked. it is imperative for relevant agencies to take decisive actions to mitigate the losses caused by these disasters. implementing awareness programs and ensuring preparedness are crucial steps towards reducing the impact of disasters and safeguarding communities from their devastating consequences. keywords disaster; thunderstorm, fire, forecasting method. article information manuscript received: february 24, 2024; revised: july 20, 2024; accepted: august 17, 2024 doi https://doi.org/10.3126/bibechana.v21i3.63069 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction nepal, encompassing an area of 147,141 square kilometers, comprises diverse regions such as the hilly region, terai region, and himalayas. the increasing global warming and climate change have resulted in various significant challenges worldwide, including shortened monsoon periods, erratic rainfall, and increased occurrences of natural disasters such as thunderbolts, fires, landslides, floods, and droughts. among these disasters, thunderbolts and fires stand out as the most destructive in nepal due to its geographical diversity, making the country a hotspot for natural calamities [1]. different regions of nepal face distinct types of disasters on a daily basis, leading to numerous casualties, miss272 http://nepjol.info/index.php/bibechana pbadhikari09@gmail.com https://doi.org/10.3126/bibechana.v21i3.63069 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ pitri bhakta adhikari et al./ bibechana 21 (2024) 272-280 273 ing individuals, and widespread devastation. in the terai region, thunderbolts, droughts, and floods are predominant causes of destruction, while landslides and thunderbolts pose significant threats in the hilly region. additionally, avalanches in the himalayas region have claimed the lives of many individuals [2]. the prevalent natural disasters in nepal include thunderbolts, fires, landslides, and floods, with a focus on thunderbolts and fires in this study. fires have ecological effects on vegetation patterns in ecosystems, with both positive and negative impacts [3]. forest fires result in economic, social, and ecological damage, necessitating prioritized forest fire management through awareness programs and the utilization of forest firefighting tools to mitigate their widespread socio-economic, environmental, and ecological impacts. ignoring forest fire management could hinder nepal's overall development [4]. the majority of fire incidents occur during the pre-monsoon season, with tropical lowland, evergreen forests, and broad-leaved forests being at the highest risk, especially in areas with high tree cover density, lower elevations, and lower slopes [5]. the total burned area has seen a 0.6% increase since 2001 ad [6]. lightning phenomena involve electrical discharge within a cloud or between a cloud and the earth, while thunderbolts are characterized by a flash of light accompanied by thunder [7]. most thunderbolt incidents occur in april and may, while fires typically occur in march [8]. between 2011 and 2021 ad, no lightning incidents were recorded in november, with maximum occurrences observed during the pre-monsoon period. the number of people injured due to lightning is nearly three times the number of fatalities [9, 10]. investing in disaster preparedness and awareness programs is crucial, as demonstrated by aryal's findings that investing 1 npr before a disaster is equivalent to saving 18 npr after a disaster [11]. hazard identification can also help to prevent the fire scenarios. numerous studies have explored the variability and impacts of natural hazards, yet only a limited number have focused on analyzing historical trends and forecasting future scenarios. this research is based on the examination and projection of losses attributed to disasters, recognizing the varying degrees of destructiveness among different types. within the context of nepal, our focus lies on thunderbolt and fire, deemed particularly destructive. through this research, we aim to analyze the overall trend of disaster-related losses and utilize generalized equations to forecast future losses based on these trends. therefore, prioritizing development work and implementing preparedness and awareness programs are essential in reducing losses due to disasters. 2 methodology in conducting this research, the necessary data was sourced from the disaster risk reduction (drr) portal of the ministry of home affairs (moha). data spanning from 1971 ad to 2022 ad, covering a period of 48 years, was collected. to analyze the data, a moving average of 5 years was calculated, and each period was labeled from 0 to 47. for instance, period zero (0) represents the average from 1971 ad to 1975 ad, period one (1) represents the average from 1972 ad to 1976 ad, and so forth. graphs were plotted for various variables such as the average number of incidents, total deaths, affected families, and number of injured people over time. using the time series data, a regression equation in the form of y = a + bx was determined, where y represents the dependent variable, x represents the independent variable (time), 'a' represents the intercept, and 'b' represents the slope of the regression line. these graphs were analyzed using ms excel. the regression line, which provides insights into the effects on human lives in future years, was fitted based on the trend identified from the plotted data. error analysis was conducted by comparing observed values (y) with estimated values (y') obtained from the regression equation. the deviation between these values was calculated and plotted in tables for further analysis. the regression equation, expressed as a straight line in the form y = mx + c, was utilized for this analysis. the normal equations derived from this equation are as follows:∑ y = m ∑ x + nc (1) and ∑ xy = m ∑ x2 + c ∑ x (2) solving these equations yields the slope (m) and intercept (c) of the straight line. the formulas used to calculate the slope and intercept are as follows: m = n ∑ xy− ∑ x ∑ y n ∑ x2 −m ∑ x and, c = σy−m ∑ x n . by utilizing these formulas, the slope and intercept of the straight line are determined, providing valuable insights for the analysis. in this research, estimated values refer to those derived from the regression equation, while observed values denote secondary data obtained from the specified data source. the estimated values are selected at intervals of five consecutive years rather than encompassing all years, aiming to analyze the data distribution. subsequently, the disparity between estimated values (y) and observed values (y1) is tabulated for each variable, with this difference termed as the error “e” (defined as the variance between the two data points, estimated and pitri bhakta adhikari et al./ bibechana 21 (2024) 272-280 274 observed). this shows that the estimated values are how closely align with the observed values. overall, the data highlights the increasing frequency and severity of both disasters fire and thunderbolt-related incidents over the years, emphasizing the importance of effective disaster management and preparedness measures to mitigate their impact on communities. 3 results and discussion the data collected spans from 1971 ad to 2022 ad, with each period representing a five-year average using the moving average method. in the table provided, each row corresponds to a five-year period, labeled from zero to 46, where zero represents the average from 1971 ad to 1975 ad, 1 represents the average from 1972 ad to 1976 ad, and so forth. the table includes various metrics: 'ave. noi' represents the average number of incidents, 'ave. td' represents the average total number of deaths, 'ave. af' represents the average total number of affected family, 'ave. inj' represents the average total number of injured people due to thunderbolt. a. thunderbolt from table 1, it is observed that, the average number of incidents shows a generally increasing trend, particularly after year 34, where there is a rapid increase. the maximum number of deaths is recorded between years 34 and 42, with an average value exceeding 100. the number of affected families exhibits variability, ranging from zero to 1027 in average. this variation could be attributed to a lack of historical information or incomplete recording of disaster-related data in earlier years due to limited communication between societies. the maximum average number of injured individuals is recorded in years 45 and 46, exceeding 300. there is a notable increase in the number of injured people after year 32, indicating a significant rise in incidents resulting in injuries. the provided graph displays the total number of incidents attributed to thunderbolts, with the original data represented by the blue dotted line. the graph highlights a sharp increase in incidents in recent years. additionally, a regression line has been fitted to the data, represented by the red dotted line. this regression line serves as a predictive tool, table 1: moving average data of thunderbolt. year ave. noi ave. td ave. af ave. inj 0 5.8 5.6 44.6 11.4 1 6.6 5.8 44.6 11.0 2 8.4 7.2 44.6 11.4 3 8.6 10.0 20.6 15.4 4 6.8 8.6 0.0 8.4 5 6.6 8.2 0.0 5.8 6 5.4 7.0 0.0 5.6 7 3.4 5.6 0.0 5.2 8 4.0 3.8 0.0 9.0 9 5.4 5.0 0.0 9.0 10 4.8 4.6 0.0 8.6 11 4.6 4.2 0.0 8.6 12 5.2 4.4 0.0 9.2 13 4.8 3.4 0.8 1.8 14 4.0 4.2 0.8 4.6 15 5.4 6.6 3.0 9.8 16 9.4 12.0 3.0 14.8 17 11.4 15.2 3.0 16.0 18 20.0 24.2 2.2 25.0 19 31.0 32.6 33.8 36.8 20 32.2 32.8 31.6 33.0 21 34.4 34.0 109.0 37.4 22 45.2 45.0 789.2 59.2 23 39.4 38.2 789.2 54.6 24 32.0 32.8 757.6 49.4 25 35.8 34.2 757.6 56.8 26 39.4 40.4 680.2 63.4 27 31.4 32.2 0.0 48.0 28 38.6 42.2 324.0 64.2 29 41.4 41.2 324.2 69.8 30 40.2 44.0 324.2 73.4 31 39.8 39.4 324.2 85.2 32 46.4 42.4 325.0 109.4 33 51.2 41.6 21.4 119.8 34 64.0 53.2 153.0 141.6 35 75.8 61.2 172.6 163.4 36 94.2 73.8 528.4 195.8 37 112.6 86.6 738.4 224.4 38 121.6 100.2 1027.2 252.2 39 137.0 103.6 896.0 206.8 40 149.0 109.2 888.8 209.8 41 162.0 111.8 584.8 197.6 42 169.2 106.8 425.6 186.8 43 192.6 95.6 188.4 241.0 44 233.8 95.0 293.2 285.8 45 265.2 90.8 403.0 310.4 46 265.6 78.2 412.4 301.0 47 280.8 78.6 439.0 295.4 indicating the expected future trend of thunderbolt-related incidents. the regression line equation, expressing the relationship between the average number of incidents (y) and the independent variable (x), is: y = -47.32 + 4.70x. in pitri bhakta adhikari et al./ bibechana 21 (2024) 272-280 275 this equation, y represents the dependent variable, which is the average number of incidents of thunderbolts and x represents the independent variable, which could be time or another relevant factor. this regression equation allows for forecasting future trends in the number of thunderbolt-related incidents based on the provided data and the identified regression line. table 2: estimated and observed data of number of incidents due to thunderbolt year (x) estimated y = -47.32 + 4.70x observed y1 error e = y y1 e2 0 -47.32 5.8 -53.12 2821.734 5 -23.82 6.6 -30.42 925.3764 10 -0.32 4.8 -5.12 26.2144 15 23.18 5.4 17.78 316.1284 20 46.68 32.2 14.48 209.6704 25 70.18 35.8 34.38 1181.984 30 93.68 40.2 53.48 2860.11 35 117.18 75.8 41.38 1712.304 40 140.68 149.0 -8.32 69.2224 45 164.18 265.2 -101.02 10205.04 the figure 2 is the graph of total death of the thunderbolt. here straight line is the predicted line of average total death. from figure 2 it is clear that the total death due to thunderbolt is increasing sharply. the peak number of total deaths are seen in the year 35 to 45 and the lowest number of deaths are in the years 0 to 15. this is the regression line of average total death, y= -13.21+2.30 x. table 3: estimated and observed data of number of total deaths due to thunderbolt year (x) estimated y = -13.21 + 2.30x observed y1 error e = y y1 e2 0 -13.21 5.6 -18.81 353.8161 5 -1.71 8.2 -9.91 98.2081 10 9.79 4.6 5.19 26.9361 15 21.29 6.6 14.69 215.7961 20 32.79 32.8 -0.01 0.0001 25 44.29 34.2 10.09 101.8081 30 55.79 44.0 11.79 139.0041 35 67.29 61.2 6.09 37.0881 40 78.79 109.2 -30.41 924.7681 45 90.29 90.8 -0.51 0.2601 the figure 3 is the graph of affected family. here the straight line represents the predicted graph of affected family. there is the irregularity in the data structure. in some years the number of affected family is zero and in some years the number of affected family is high around thousand. the maximum number of affected family is seen in the years 20 to 25 and 35 to 40. the number of affected family is zero in the years 5 to 20 is zero. this could happen because in the past years there is no sufficient data available and there could be missing the data. this is the regression line of average injured people, y= 11.74 + 0.13 x. the figure 4 is the graph of injured people the straight-line is the predicted line for the thunderbolt. the graph of injured people is also in increasing order in which the graph is not that much increasing till the year 30. then after the graph is increasing sharply after the year 30 and the peak number of injured peoples due to thunderbolt is in year 45. this is the regression equation for injured people by thunderbolt, y= -57.58 + 6.32 x. pitri bhakta adhikari et al./ bibechana 21 (2024) 272-280 276 table 4: estimated and observed data of number of affected families due to thunderbolt year estimated y = -57.55 + 13.89x observed y1 error e = y y1 e2 0 -57.55 44.6 -102.15 10434.62 5 11.9 0.0 11.9 141.61 10 81.35 0.0 81.35 6617.823 15 150.8 3.0 147.8 21844.84 20 220.25 31.6 188.65 35588.82 25 289.7 757.6 -467.9 218930.4 30 359.15 324.2 34.95 1221.503 35 428.6 172.6 256.0 65536.0 40 498.05 888.8 -390.75 152685.6 45 567.5 403.0 164.5 27060.25 table 5: estimated and observed data of number of injured people due to thunderbolt year estimated y = -57.55 + 6.32x observed y1 error e = y y1 e2 0 -57.55 11.4 -68.95 4754.103 5 -25.95 5.8 -31.75 1008.063 10 5.65 8.6 -2.95 8.7025 15 37.25 9.8 27.45 753.5025 20 68.85 33.0 35.85 1285.223 25 100.45 56.8 43.65 1905.323 30 132.05 73.4 58.65 3439.823 35 163.65 163.4 0.25 0.0625 40 195.25 209.8 -14.55 211.7025 45 226.85 310.4 -83.55 6980.602 figure 1: graph of average number of incidents due to thunderbolt. figure 2: graph of average number of total death due to thunderbolt. figure 3: number of affected family due to thunderbolt. figure 4: number of injured people due to thunderbolt. pitri bhakta adhikari et al./ bibechana 21 (2024) 272-280 277 b. fire table 6 presents data on fire incidents, including moving averages for the number of incidents, total deaths, affected families, and injured people across 47 different years. in this table, the periods are labeled from 0 to 46, where 0 represents the moving average from 1971 ad to 1975 ad, and subsequent periods represent consecutive five-year averages. 'ave. noi' represents the average number of incidents, 'ave. td' represents the average number of total deaths, 'ave. af' represents the average number of affected families, 'ave. inj' represents the average number of injured people. from the table 2, it is observed that the number of incidents shows an increasing trend as the number of year approaches 47, with the maximum recorded at year 47, averaging 2542.8 incidents. year 47 corresponds to the average from 2018 ad to 2022 ad and the total number of deaths also exhibits an increasing trend, reaching its peak at year 47 with an average of 84.8 deaths. the number of affected families follows a similar pattern, increasing steadily until year 25, then reaching a peak value exceeding 10,000, before decreasing thereafter. similarly, the number of injured people shows a consistent increase over the years, with the maximum average of 345 injuries recorded at year 47. overall, the data indicates a concerning trend of increasing fire incidents, resulting in higher numbers of deaths, affected families, and injured individuals, especially in recent years. these observations underscore the importance of effective fire prevention and management strategies to mitigate the impact of fires on communities. fig. 5 is the graph of average number of incidents of fire from 1971 to 2022 ad. and the straight line is the predicted line which helps to predicts possible number of incidents in future. the number of incidents due to the fire is sharply increasing after the year 40. till the year 40 the graph is flat. this is the regression equation for number of incidents. by the help of this equation the future forecasting is possible by this the future events can be predicted. the regression line equation is y= 315.77 + 29.48 x. fig. 6 is the graph of average number of total deaths. and the straight line is the predicted line for future events. from the figure 6 the graph is increasing sharply and there is certain increase in the year 20 to 25. and then it increasing from year 35. here the straight line which gives the prediction that how many peoples would die in the latest years due to fire. the regression equation for fire which helps to predict the average total deaths in future is y = 9.76 + 1.25 x. table 6: moving average data of fire year ave. noi ave. td ave. af ave. inj 0 54.2 10.0 6859.8 5.4 1 78.4 17.0 8475.4 12.8 2 87.4 17.8 8607.0 22.8 3 87.2 16.8 8740.4 23.4 4 91.4 24.6 8972.6 22.8 5 91.8 25.0 3771.0 32.4 6 77.2 19.4 2407.4 34.8 7 71.0 19.6 2458.8 25.4 8 66.2 18.8 2893.0 27.4 9 66.4 13.0 3395.6 27.2 10 66.4 13.2 3230.4 19.2 11 61.8 14.4 3665.2 9.6 12 63.2 13.6 5214.4 9.6 13 62.8 14.2 4834.0 6.0 14 76.8 14.8 4661.8 7.8 15 78.8 13.8 4176.6 7.8 16 89.0 15.0 3803.4 10.6 17 123.6 22.6 3544.0 10.4 18 142.0 25.6 4886.0 15.0 19 136.4 30.8 6001.0 18.8 20 153.8 49.0 10089.6 26.0 21 160.4 67.8 17355.6 37.8 22 154.4 74.4 19457.4 46.8 23 134.6 73.4 17928.2 45.0 24 133.0 70.8 16486.2 41.0 25 132.8 58.8 12753.6 34.8 26 157.8 45.8 5462.0 28.6 27 134.8 33.0 2258.2 20.0 28 155.2 36.4 3995.4 20.4 29 155.6 32.6 3009.0 22.0 30 148.2 27.6 2780.2 21.6 31 122.6 25.2 2492.2 22.2 32 129.2 26.4 2091.4 25.8 33 160.6 32.8 3129.8 51.0 34 211.4 41.6 5595.8 73.4 35 259.6 50.6 6791.6 82.2 36 299.8 49.4 9192.8 93.6 37 361.0 58.0 15127.8 119.8 38 362.6 53.8 14049.8 108.4 39 474.8 54.0 11594.4 101.4 40 526.6 56.8 10164.4 103.0 41 766.2 62.6 8455.2 131.2 42 978.6 62.6 2968.6 142.4 43 1407.8 70.0 1991.0 192.2 44 1788.2 72.6 2707.6 241.6 45 2086.6 69.0 3181.6 290.8 46 2321.0 76.2 3174.4 314.4 47 2542.8 84.8 3300.4 345.0 the figure 7 is the graph of average number of total affected family by fire from 1971 to 2022 ad. and the straight line is the predicted line which helps to predicts future events. the peak number of affected peoples is seen in year 20 to 25. pitri bhakta adhikari et al./ bibechana 21 (2024) 272-280 278 and the overall graph is seen constant and has an average value of around 6500. the regression equation for average number of affected family is, y=6502.22+5.39 x. fig. 8 is the graph of total number of injured people and the straight line is the predicted line which helps to predict future events. the graph 8 shows that the number of injured peoples due to fire is also increasing and has a peak value at year 47. the graph is sharply increased after the year 30. there is no significant increase in the trend till the year 30. the regression equation for injured people by fire is, y = -37.53 + 4.37 x. while the literature is rich in studies on hazard management, there is a notable absence of research focusing specifically on the trend analysis and prediction of losses over time. this manuscript uniquely emphasizes the examination of past loss trends to forecast future losses. our observation indicates a significant upward trajectory in losses compared to previous years, especially in recent times. overall, our study aims to analyze the escalating trend in losses, particularly notable in recent years. however, it's important to acknowledge that the prediction of future losses may encounter challenges due to potential variations in the data obtained from the sources, which could introduce additional errors into the forecasting process. table 7: estimated and observed data of number of incidents due to fire year estimated y = -315.77 + 29.48x observed y1 error e = y-y1 e2 0 -315.77 54.2 -369.97 136877.8 5 -168.37 91.8 -260.17 67688.43 10 -20.97 66.4 -87.37 7633.517 15 126.43 78.8 47.63 2268.617 20 273.83 153.8 120.03 14407.2 25 421.23 132.8 288.43 83191.86 30 568.63 148.2 420.43 176761.4 35 716.03 259.6 456.43 208328.3 40 863.43 526.6 336.83 113454.4 45 1010.83 2086.6 -1075.77 1157281 table 8: estimated and observed data of number of total deaths due to fire year estimated y = 9.76 + 1.2x observed y1 error e = y y1 e2 0 9.76 10 -0.24 0.0576 5 15.76 25 -9.24 85.3776 10 21.76 13.2 8.56 73.2736 15 27.76 13.8 13.96 194.8816 20 33.76 49 -15.24 232.2576 25 39.76 58.8 -19.04 362.5216 30 45.76 27.6 18.16 329.7856 35 51.76 50.6 1.16 1.3456 40 57.76 56.8 0.96 0.9216 45 63.76 69 -5.24 27.4576 pitri bhakta adhikari et al./ bibechana 21 (2024) 272-280 279 table 9: estimated and observed data of number of affected families due to fire year estimated y = 6502.22 + 5.38x observed y1 error e = y y1 e2 0 6502.22 6859.8 -357.58 127863.5 5 6529.12 3771 2758.12 7607226 10 6556.02 3230.4 3325.62 11059748 15 6582.92 4176.6 2406.32 5790376 20 6609.82 10089.6 -3479.78 12108869 25 6636.72 12753.6 -6116.88 37416221 30 6663.62 2780.2 3883.42 15080951 35 6690.52 6791.6 -101.08 10217.17 40 6717.42 10164.4 -3446.98 11881671 45 6744.32 3181.6 3562.72 12692974 table 10: estimated and observed data of number of injured people due to fire year estimated y = -37.53 + 4.37x observed y1 error e = y y1 e2 0 -37.53 5.4 -42.93 1842.985 5 -15.68 32.4 -48.08 2311.686 10 6.17 19.2 -13.03 169.7809 15 28.02 7.8 20.22 408.8484 20 49.87 26 23.87 569.7769 25 71.72 34.8 36.92 1363.086 30 93.57 21.6 71.97 5179.681 35 115.42 82.2 33.22 1103.568 40 137.27 103 34.27 1174.433 45 159.12 290.8 -131.68 17339.62 figure 5: graph of number of incidents due to fire. figure 6: graph of number of total death due to fire. pitri bhakta adhikari et al./ bibechana 21 (2024) 272-280 280 figure 7: graph of number of affected family due to fire. figure 8: graph of number of injured people due to fire. 4 conclusion the data clearly indicates a significant increase in losses and incidents, particularly in fire and thunderbolt incidents. the period from 2018 ad to 2022 ad stands out as having peak averages of 2542.8 fire incidents and 280.8 thunderbolt incidents. graphs depicting these parameters show a sharp upward trend, highlighting the pressing need for intervention. given the continuous rise in incidents and losses, it's evident that without major actions, there is no sign of reduction in these disasters. therefore, it is imperative for the relevant agencies and the government to devise a clear plan to mitigate the losses caused by these disasters. effective disaster management strategies, including well-preparedness measures and awareness programs, are crucial in reducing both human and material losses significantly. by enhancing preparedness and raising awareness about these disasters, communities can better protect themselves and their assets, ultimately reducing the overall impact of these calamities. acknowledgment we acknowledge to ugc for the faculty research grant with the grant number: frg79/80 – s & t – 10 for providing the research grant. also, giving thanks to the tri-chandra multiple campus, tribhuvan university, for generously providing the necessary research facilities. the authors also want to thank drr portal to give the free access of the data and analysis, essential for the successful completion of our research. references [1] nepal government. nepal parichaya. kathmandu: nepal government, 2022. [2] t. d. ricardo and k. elisabeth. impacts of natural hazards and climate change on eu security and defence. publications office of the european union, 2021. [3] ramesh prasad sapkota and n. bista. firemediated biomass loss of woody species seedlings causing demographic bottleneck in the terai forests of central nepal. global ecology and conservation, october 2023. [4] hari prasad pandey. status and practical implications of forest fire management in nepal. journal of forest and livelihood, june 2022. [5] a. q. goparaju. predicting forest fire using multispectral satellite measurements in nepal. remote sensing applications society and environment, august 2021. [6] bhogendra mishra. forest fire pattern and vulnerability mapping using deep learning in nepal. fire ecology, 2023. [7] p. b. adhikari. the report of lightning in himalayan locale. the scientific world journal, 2023:article id 1888382, 10 pages, 2023. [8] t. r. linkha. disasters: spatio-temporal distribution of dhankuta district, nepal. rupantaran: a multidisciplinary journal, 2020. [9] p. b. adhikari. people deaths and injuries caused by lightning in himalayan region, nepal. international journal of geophysics, june 2022. [10] p. b. adhikari. different measurement system of lightning. european journal of applied physics, 5(3):26–31, june 2023. [11] p. aryal. occurrence of disaster events and their impact in nepal: role of government and civil society organizations to reduce the disaster risks. nepal journal of multidisciplinary research, pages 88–101, april 2023. introduction methodology results and discussion conclusion bibechana 19 (1-2) (2022) 150-159 150 estimation of global solar radiation (gsr) from the sunshine hour of guranshe, surkhet, nepal homchandra adhikari and nurapati pantha* central department of physics, tribhuvan university, kirtipur,kathmandu, nepal *email: mrnurapati@gmail.com article information: received: april 17, 2021 accepted: october 30, 2021 keywords: solar energy meteorological parameter global-solar radiation sunshine hour abstract the variation in global solar radiation (gsr) was studied by using experimental data via an automatic weather station (cmp3 pyranometer) located at guranshe (surkhet), a hilly area with elevation 2194m from the sea level. also, the estimated sunshine hour data of the area were used to calculate the gsr for the purpose of comparison with the measurements. our study finds a good agreement between the measured (15.65 mj/m2/day) and estimated/calculated (19.18 mj/m2/day) values of annual average gsr. the estimated gsr uses angstrom-prescott type model for calculating sunshine hours, and the coefficients (a=0.28) and (b=0.57) were obtained using the sangeetas and tiwari model. the annual average estimated sunshine hours was found to be 6.86hr which is suitable for gsr based applications. the measured data were used to study the seasonal, monthly and diurnal variations of gsr. the maximum and minimum values of gsr were found during the spring and summer seasons respectively. the minimum gsr in summer is because of heavy rainfall, high relative humidity, and cloud formation in the sky during the time. the coefficient of regression(r) and the coefficient of determination (r2) were obtained as r=0.881 and r2=0.776 respectively. here the high value of r (88.1%) indicates that of dependent variable (gsr) is nicely predicted by the independent variables. also the coefficient of determination (r2) tells us the strength of the relationship between two variables. doi: https://doi.org/10.3126/bibechana.v19i1-2.46408 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/bync/4.0/ bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal https://doi.org/10.3126/bibechana.v19i1-2.46408 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ adhikari and pantha / bibechana 19 (1-2) (2022) 150-159 151 1. introduction energy is one of the basic needs for all living creatures on earth surfaces without which our universe would be no more than a frozen rock. the radiation received by the earth from the sun in the form of electromagnetic radiation, that is radiant energy, is the main source of energy on the earth’s surface. renewable, nonrenewable, and ultimate sources of energy obtained on the earth's surface, among with all the energy sources, are directly or indirectly controlled by the solar energy [1]. photovoltaic and solar thermal capture is the main techniques to exploit the solar energy which are among the cheapest and fastest-growing sources of power in worldwide. according to the nepal electricity authority (nea) report of the fiscal year 2019/2020, the total population accessing electricity reached to 86% of the total households. the power stations generated a total of 3021 gwh of electricity which is 18.57% higher than the fiscal year (fy) 2018/2019 [2]. biomass, hydroelectricity, petroleum products, natural gas, and coal are the major energy resources in nepal, where 78% of people have access to grid-connected energy, 82% use solid fuels such as dung, coal, and wood as cooking energy. ninety five percent (95%) of biomass, which is casing harmful impact in environment, is predominantly used for household purposes. petroleum, an imported and non-renewable type of energy, is the second largest energy fuel in nepal [3]. hence the solar energy can be considered as one of the best, easily accessible, and renewable type of energy sources for nepal. fossil fuels directly affect the environment and human health. also they are expensive. large hydropower projects have several problems such as landslides, sedimentation, and damage to aquatic life, ecosystem, and vegetation. there are some social challenges such as rehabilitation and cultural issues. hence the solar power which is environmentally friendly, readily available, and cheap, and can be installed at any location can be a good alternative source of energy [4]. however, an accurate knowledge of the meteorological parameters and location of the site should be well known before installing solar devices. atmospheric energy balance studies, photovoltaic and agricultural studies, thermal load analysis on buildings, and meteorological forecasting should be reliable and readily available for the optimization design and performance evaluation of solar technologies [5]. energy transfer from the sun to the earth's surface in the form of electromagnetic waves is called solar radiation. different atmospheric particles like air molecules, ozone, clouds, and water vapor deplete the incoming radiation through reflection, scattering, and absorption [1]. there are other metrological/geological factors that affect the energy density of the incoming solar radiation (extraterrestrial solar radiation). they include rainfall, relative humidity, air pressure, air temperature, solar zenith angle, precipitation, latitude, sunshine duration, solar declination, and earth atmosphere [6]. here the gsr is defined as the sum of the direct, diffused, and reflected radiation. different models can be used to calculate gsr, however, the availability and the relevancy of meteorological parameters determine the model to use in particular territory. in the context of nepal, limited number of studies have been carried out on the estimation of gsr due to rare meteorological stations and lack of complete data of climatic factors. adhikari et al. (2013) estimated the gsr for biratnagar, kathmandu, pokhara, and jumla which are at adhikari and pantha / bibechana 19 (1-2) (2022) 150-159 152 72m, 1350m, 800m, and 2850m above the sea level using the angstrom-prescott model. they observed excellent agreement between the measured and estimated values of gsr where the maximum and the minimum solar radiation (sr) were found in jumla and biratnagar respectively [3]. temperature and relative humidity (rh) based models have been used by adhikari et al. (2014) to estimate the gsr. they observed that temperature and gsr have a direct relationship whereas rh and gsr have an inverse relationship. they also observed a strong correlation between the observed and estimated values [7]. the gsr was estimated and studied on a horizontal surface of nepalgunj (low altitude) by using radest 3.00 software with four models [8]. the cmp6 pyranometer was used to measure gsr at simara airport, bara nepal for the years 2009 and 2010. two models, angstrom-prescott[9], and sangeetas and tiwari models [10], were used to estimate the gsr and observed that gsr were maximum in march, april and may due to the sunny and clear weather and the minimum was found in summer. elom and nnamdi (2012) used a regression model and estimated the gsr and average temperature during the period of 11 years (1996-2006) at onitsha, nigeria, and found that model equations give excellent results and show a strong correlation between solar radiation (sr) and air temperature. they also observed 87.1% of the variation in the monthly mean daily sr on a horizontal surface [6]. kumar et al. (2013) developed a new model based on the angstrom-prescott model in north india, himanchal pradesh, and observed that by using a new model they determine the regression constant with only latitude and longitude. previous model used to use other parameters, in addition to latitude and longitude, as well and found that the new model is far better [5]. elekalachi et al. (2016) used an angstrom-type regression equation to estimate gsr on horizontal surfaces for awaka, enugu, and owerri with the data from archives of the national aeronautics and space administration (nasa) for a period of 11 years (2000-2010) [10]. here we use the empirical model to estimate the global solar radiation by estimating the sunshine hour data. in addition to the gsr and the sunshine hour, we study the impact of meteorological parameters on global solar radiation in guranshe, surkhet nepal. finally, we analyze the month and season wise gsr values and suggest the possibility of harvesting solar energy in near future. 2. theory and method description of the site the automatic weather station is located at guanshe which lies in the surkhet district and border between surkhet and dailakh. it is about 600 km west of the national capital kathmandu and is situated at latitude 28o39'22''n and longitude 81o37'45''e in the inner terai valley of nepal. it elevates 2194 m above from the sea level. it has a moderate climate, which contains the mountainous region and outer terai region. average temperature range from 37.1oc maximum to 4.5oc minimum [11]. the location of the weather station is shown in figure 1. fig.1: automatic weather station at guranshe, surkhet (provided by the department of hydrology and meteorology, government of nepal) [12]. the daily solar radiation on a horizontal surface for guranshe, surkhet was collected from archives of the department of hydrology adhikari and pantha / bibechana 19 (1-2) (2022) 150-159 153 and meteorology, government of nepal (dhm/gon) for the year of 2018. daily data of average air temperature, air pressure, relative humidity, rainfall for the site were obtained from dhm/gon. cmp3 pyranometer (figure 2) was used to measure global solar radiation on a horizontal surface. 2.2 collection of plant materials the plant materials (plant & rhizomes) (figure 1) were collected in august 2018 from the salyan district (tharkot hill, altitude: 2,400 m above sea level), karnali province, nepal. the herbarium of the plant was identified and authenticated as bergenia pacumbis (buch.ham. ex d. don) c. y. wu & j. t. pan by taxonomists in national herbarium and plant laboratories, lalitpur, nepal. the rhizomes were washed with tap water followed by sterilized distilled water to remove the adhered dust, dirt, and other foreign materials and dried in shade at room temperature. the dried rhizomes were powdered and then stored in an airtight polyethylene bag in a cool, dry location for ongoing studies. fig.2: cmp3 pyranometer [13]. theoretical detail the angstrom-prescott, and tiwari and sangeeta model [7] are used to calculate the gsr theoretically on a horizontal surface with the help of estimated sunshine hour of the year 2018 for guranshe, surkhet. the model is given by: 𝐻 𝐻𝑜 = 𝑎 + 𝑏 ( 𝑛 𝑁 ) … (1) where h is the monthly average daily gsr on the horizontal surface, ho is the monthly average daily extraterrestrial radiation, n is the monthly average daily number of hours of bright sunshine, n is the average daily number of possible sunshine, a and b are the regression constant. m. adb. elwashed and r.l syder [14] in their paper have presented a regression equation which is based on the monthly daily temperature. we use equation (2) to estimate the sunshine hour data of guranshe, surkhet. 𝑛 = 4.352 + 0.232𝑇… (2) where n is the sunshine hour and t is the average daily mean temperature. the extraterrestrial solar radiation (ho) on a horizontal surface is given by, iqbal [5] as follows: 𝐻𝑜 = 24 𝜋 ∗ 𝐼𝑠𝑐𝐸𝑜[( 𝜋 180 )𝜔𝑠(𝑆𝑖𝑛𝛿𝑆𝑖𝑛∅) + (𝐶𝑜𝑠∅𝐶𝑜𝑠𝛿𝑆𝑖𝑛𝜔𝑠)]… (3) where isc and eo are the solar constant and eccentricity correction factor which is given as, 𝐼𝑠𝑐 = 1367∗3600 106 mj/m2/day 𝐸𝑜 = 1 + 0.33𝐶𝑜𝑠 360𝑁𝑑 365 where, nd is the day of the year, julian days (1st january, nd=1 and 31th december, nd=365). ωs is hour angle, ∅ being latitude of site and 𝛿 is the solar declination which can be calculated as, 𝜔𝑠 = 𝑎𝑟𝑐𝐶𝑜𝑠(−𝑡𝑎𝑛∅𝑡𝑎𝑛𝛿) and 𝛿 = 23.45[ 360(𝑁𝑑 + 284) 365 ] adhikari and pantha / bibechana 19 (1-2) (2022) 150-159 154 the maximum possible sunshine hours or day length can be calculated as, 𝑁 = 2 15 𝑎𝑟𝑐𝐶𝑜𝑠(−𝑡𝑎𝑛∅𝑡𝑎𝑛𝛿)… (4) = 2 15 𝜔𝑠 the regression coefficients a and b are calculated by using sangeeta and tiwari model [10, 15] by, 𝑎 = −0.110 + 0.235𝑐𝑜𝑠∅ + 0.323 𝑛 𝑁 … (5) 𝑏 = 1.449 − 0.553𝑐𝑜𝑠∅ − 0.694 𝑛 𝑁 … (6) where, ∅ is the latitude of the particular location. to predict the accuracy of the model and also to know how the calculated gsr (hc) varies with measured gsr (hm) following statistical test is done 𝑅𝑀𝑆𝐸 = [∑ (𝐻𝑖𝑐−𝐻𝑖𝑚)2 𝑁 𝑛 𝑖=1 ] 1 2 … (7) where, n is the number of data i.e. several months, him is the ith measured value, hic is the ith calculated value and n is the number of observations. root mean square error (rmse) measures how much error is obtained between the calculated and the measured data set. also tells us that how the calculated gsr deviates from the measured gsr. 𝑀𝐵𝐸 = ∑ (𝐻𝑖𝑐−𝐻𝑖𝑚)𝑛 𝑖=1 𝑁 … (8) mean bias error (mbe) is an indication of the average deviation of calculated values from the measured values. 𝑀𝑃𝐸 = ∑ (𝐻𝑖𝑚−𝐻𝑖𝑐) 𝐻𝑖𝑚 ∗100𝑛 𝑖=1 𝑁 … (9) mean percentage error (mpe) is the computed average of the percentage of errors by which the calculated value of a model differs from the measurement values of the quantity being predicted. 𝑀𝐴𝐸 = ∑ |(𝐻𝑖𝑐−𝐻𝑖𝑚)|𝑛 𝑖=1 𝑁 … (10) mean absolute error (mae) measures how far calculated values are away from the measured values. hence, another statistical parameter like the coefficient of regression (r), coefficient of determination (r2) is also calculated. 2. results and discussion table 1 shows the climatic data for guranshe, surkhet, which is based on the above theoretical approach. the values of monthly mean extraterrestrial solar radiation (ho), monthly mean measured gsr (hm), the monthly mean of calculated gsr (hc), the monthly mean of daily hours of bright sunshine (n), the monthly mean of day length (n), the monthly mean of measured clearness index (hm/ho), monthly mean of calculated clearness index (hc/ho) and the monthly ratio of sunshine hours (n/n). table 1: climatic parameters for guranshe, surkhet in table 1, ho, hm, and hc are in the unit of mj/m2/day, n and n are in the unit of hours. from table 1, we can say that the value of annual extraterrestrial solar radiation (ho) found to be 31.83 mj/m2/day, measured global solar radiation (hm), calculated global solar radiation (hc) is found to be 15.65 mj/m2/day and 19.18 mj/m2/day. annually 6.86 hours of the bright sunshine hour was observed which indicates that the guranshe, surkhet is a place month ho hm hc a b n n hm/ho hc/ho n/n jan 22.08 16.35 13.73 0.29 0.55 6.26 10.4 0.74 0.62 0.6 feb 26.41 16.96 16.46 0.29 0.54 6.65 11.01 0.64 0.62 0.6 mar 31.91 22.31 20.68 0.31 0.51 7.67 11.82 0.7 0.65 0.65 apr 37 21.23 23.64 0.3 0.53 8.03 12.7 0.57 0.64 0.63 may 39.95 21.78 25.08 0.29 0.54 8.23 13.43 0.55 0.63 0.61 jun 40.95 16.51 25.34 0.29 0.55 8.23 13.8 0.4 0.62 0.6 jul 40.34 9.79 21.12 0.23 0.67 5.83 13.63 0.24 0.52 0.43 aug 37.95 9.35 19.81 0.23 0.67 5.52 12.99 0.25 0.52 0.42 sep 33.62 10.66 18.94 0.26 0.62 6.05 12.15 0.32 0.56 0.5 oct 28 17.73 17.92 0.3 0.52 7.15 11.27 0.63 0.64 0.63 nov 23 13.37 14.82 0.3 0.52 6.77 10.55 0.58 0.64 0.64 dec 20.69 11.73 12.66 0.28 0.56 5.96 10.2 0.57 0.61 0.58 average 31.83 15.65 19.18 0.28 0.57 6.86 adhikari and pantha / bibechana 19 (1-2) (2022) 150-159 155 where a high possibility of gsr can be obtained which can be the favorite place for solar farming. the value of regression constants a and b in the angstrom-prescott model, calculated by using tiwari and sangeeta model, are found to be a=0.28 and b=0.57. based on the above calculations in table1, statistical error arises between the calculated and measured value. table2 shows the analysis between the calculated value and the measured value of the guranshe, surkhet of the year 2018. table 2: statistical tools. rmse mj/m2/day mbe mj/m2/day mae mj/m2/day mpe % 5.01 3.69 3.82 -6.94 from table 2, rmse is found to be 5.01 mj/m2/day, which measures how much error is found between the calculated value and the measured value. similarly, mbe, mae, and mpe are found to be 3.69 mj/m2/day, 3.82 mj/m2/day, and -6.94%, negative value indicates that our estimated data is underestimated. the values in table 2 show good agreement between the calculated and the measured values of global solar radiation for the year of 2018. the seasonal, monthly, and daily variation of global solar radiation of guranshe, surkhet of the year 2018 is shown in figure 3, figure 4, and figure 5: fig.3: seasonal variation of gsr. fig.4: monthly variation of gsr. fig.5: daily variation of gsr. the maximum and minimum seasonal global solar radiation are found in the spring and summer season respectively. in the spring season gsr is found to be 21.77 mj/m2/day and in the summer season gsr is found to be 11.88 mj/m2/day for the year of 2018. the variation in local weather condition is the main reason for such differences. minimum gsr in the summer season is due to cloudy sky of rainy circumstances (average 9.67 mm per day). the high value of gsr in the spring season, on the other hand, is due to the less cloud, less rainfall, and less solar zenith angle. in the winter season, the more fog, large solar zenith cause lower value of gsr. from the monthly variation of gsr as shown in figure 4, it is found that the low values of global solar adhikari and pantha / bibechana 19 (1-2) (2022) 150-159 156 radiation are found in july, august and september (9.79 mj/m2/day, 9.35 mj/m2/day, and 10.7 mj/m2/day). the high values, on the other hand, are found in march, april and may (22.3 mj/m2/day, 21.2 mj/m2/day and 21.8 mj/m2/day respectively). the daily variation of gsr is shown in figure 5, and reveals that the value of gsr is continuously increasing and found a maximum (of value 22.3 mj/m2/day) in march. after attending the peck value, the gsr starts decreasing and is found to be a minimum (of 9.35 mj/m2/day) in august. it is due to the rainy season where there is high rainfall and relative humidity. the annual average gsr of the year 2018 is found to be 15.65 mj/m2/day. the maximum value of global solar radiation suggests that there is a high potential of solar energy in that place. fig.6: monthly variation of sunshine hour (red line with stars) and gsr (blue line with circles). sunshine hour indicates the sun in the clear sky seen during a certain period usually expressed in an hour. the monthly variation of the estimated sunshine hour of guranshe, surkhet is shown in figure 6, from the above graph we can say that the estimated sunshine hour (n) continuously increases from january to june. it means that the sun shining hour increases and becomes maximum hours (hr.) in april, may, and june i.e. on average 8 hours in a day. after reaching 8hr (with some fluctuations) it starts decreasing which indicates that the sunshine hour changes every day/month due to the solar declination, zenith angle, and other climatological factors. the estimated sunshine hour data indicates that it annually averages to 6.86 hours in a day at guranshe, surkhet. the variation of the measured value of gsr with the estimated sunshine hour is shown in figure 6. the trend of the gsr and sunshine hour (ssh) is similar, which indicates that the gsr has a direct relation with the ssh. in the starting month, january, sunshine hour and gsr start increasing which is consistent with the theory. after the month of june the trend of gsr and ssh both decrease which is due to the heavy rainfall and high relative humidity. after august they resume increasing and reach to the maximum values in the october. beyond october the values of ssh and gsr again decrease as per direct relationship between them. the more sunshine hour means the more radiation to the ground, which is generally found in the spring (shown in the graph). physical phenomenon like scattering and absorption of incoming radiation are also low in a clear sky of the season. the variation of global solar radiation (gsr) with meteorological parameters like air temperature, air pressure, relative humidity, and rainfall is shown in figure 7, figure 8 and figure 9. fig.7: daily variation of gsr with average air temperature for the year 2018. adhikari and pantha / bibechana 19 (1-2) (2022) 150-159 157 fig.8: daily variation of gsr with air pressure for the year 2018. fig.9: monthly variation of gsr with relative humidity for the year 2018. figure 7 shows that there is a strong agreement between the measured global solar radiation and average air temperature. it the beginning of the figure 7, both air temperature and global solar radiation increase to attain maximum and then both decrease sharply due to the cloudy days, high relative humidity, and high frequency of rainfall in july, august, and september. the annual average air temperature was found to be of 10.82oc in the year 2018. the daily variation of global solar radiation with air pressure is shown in figure 8. air pressure is the pressure exerted by the weight of air in the atmosphere of earth, which depends on the gravitational force. in figure 8, we see that as the air pressure increases global solar radiation also increases and vice versa which indicates the direct relationship between the air pressure and global solar radiation. the minimum value of air pressure is found in july i.e. 775.747hapa and maximum in october i.e. 783.45hapa. on average 780.747hapa pressure is found in the year of 2018 which is suitable for solar farming. the monthly variation of gsr with relative humidity is shown in figure 9. a strong inverse relation is found between global solar radiation and relative humidity. low relative humidity i.e. 38.59% is found in the winter season due to dry and the presence of less moisture and high relative humidity i.e. 90.50% is found in the summer season due to the presence of lots of water vapor. water in the air acts as a disturbance of gsr that falls on the ground which decreases the amount of gsr on the surface. the correct level of humidity and gsr are important for professional visitors and tourists in the place. hence the future energy harvesting project has to consider the effect of vegetation in humidity and vice versa. rainfall and water vapor in the air are the related quantities and show the similar effects (inverse relation) to gsr. from the beginning of the year i.e. from january, there is low rainfall and gsr is found to be increasing. the increase in rainfall gets accelerated after a certain month i.e. in the rainy season where the average of 9.68 mm of rainfall is found in three months: july, august, and september. the inverse relation between the gsr and rainfall can be understood in terms of cloud; the rainfall requires cloud in the sky and the presence of clouds blocks gsr. however, the rainfall fluctuates within a single month and the reciprocate effect can be seen in gsr. it has been noted that the maximum rainfall and the minimum gsr in august are found as 14.43 mm and 9.34, mj/m2/day respectively. an empirical model: finding coefficient of determination and coefficient of regression: we have used two models; (i) angstromprescott, and (ii) tiwari and sangeeta model to predict the gsr at that particular place by using correlation coefficients a, b, sunshine hour (n), extraterrestrial radiation (ho), and day length (n). the value of regression coefficient was found by using tiwari and sangeeta model. 𝐻 𝐻𝑜 = 𝑎 + 𝑏( 𝑛 𝑁 )… (1) the left-hand side of this equation is the clearness index ( 𝐻 𝐻𝑜 ). the values of a and b are found 0.28 and 0.57 (table1). the coefficient of determination (r2) and coefficient of regression (r) are determined from figure 10 where we show the graph between measured clearness index ( 𝐻𝑚 𝐻𝑜 ) and calculated clearness index ( 𝐻𝑐 𝐻𝑜 ). adhikari and pantha / bibechana 19 (1-2) (2022) 150-159 158 fig.10: measured clearness index ( 𝐻𝑚 𝐻𝑜 ) versus calculated clearness index ( 𝐻𝑐 𝐻𝑜 ) figure 10 finds the coefficient of regression (r) as 0.881 and the coefficient of determination (r2) as 0.776. the regression coefficient says us negative or positive correlation between dependent and independent variables. we find positive correlation coefficient from our calculations. this implies that the increase in dependent variable on increasing the independent variables. the coefficient of determination, which lies in between 0 and 1, is also known as the goodness of fit. it tells us how strong the relationship between two variables is. the regression coefficient 0.881 means 88.1% of the dependent variable is predicted from the information of independent variables. hence the good (high) value of regression coefficient tells us a good prediction of clearness index. for a clearer (less cloudy) day there is high value of the global solar radiation. in the figure 10, we see high values of the coefficient of regression and coefficient of determination which indicates the high to clearness index in guranshe, surkhet (for the year 2018). from the above discussion, we see that the annual average of measured and the calculated/predicted values of gsr are found to be 15.65mj/m2/day and 19.18 mj/m2/day respectively. also, the correlation coefficients are found to be a = 0.28 and b = 0.57. the gsr values from our calculations fall in same order of magnitude comparing to the previous studies at different places, like in lukla(14.51mj/m2/day),kathmandu(13.753 mj/m2/day),pokhara(16.499mj/m2/day),jum la(19.884mj/m2/day)andsimikot(16.562mj/ m2/day) [7].the comparison clearly shows that our calculation for guranshe agrees the most (within 5.4% of difference) with pokhara. this is due to similar geological and metrological situation in both the places. all the values (from our calculations and previous study) show the good potential of solar energy technology in those places. the results also inspire the authorities in sub-himalaya terrain (like surkhet), inner terai, and also other similar geographical locations of nepal to promote solar energy harvesting industries like photovoltaic solar panels, solar water heater, dye-sensitized solar cells, energy storage, rechargeable batteries and other possible applications [16]. 3. conclusions the measured gsr, calculated gsr and other meteorological parameters affecting gsr were studied by using the available data. the gsr of the year 2018 a.d. at guranshe, surkhet was measured at the horizontal surface using a cmp3 pyranometer. on the other hand, gsr and the other empirical constants have been estimated by using numerical models like: angstrom-prescott and tiwari and sangeeta model. the annual average of measured and the calculated/predicted values of gsr were found to be 15.65mj/m2/day (4.35kwh/m2/day) and 19.18 mj/m2/day (5.33kwh/m2/day) respectively. also, the correlation coefficients were found to be a=0.28 and b=0.57. the comparison in between the measured and calculated values of gsr were performed by using the methods of adhikari and pantha / bibechana 19 (1-2) (2022) 150-159 159 root mean square error (rmse), mean bias error (mbe), mean absolute error (mae), and mean percentage error (mpe). various metrological parameters like average air temperature, sunshine hour, air pressure, relative humidity were found to be affecting the values of gsr as per established relationship. our study shows that gurashe (surkhet) has similar average gsr value comparing to the other places of nepal and better agreement is seen with pokhara due to similar geological/metrological parameters. harvesting the solar energy can be helpful for solar farming and mitigating the energy crisis of the places especially where the other sources of energy are hardly accessible. having high potential of tourist destination, the regularity in energy supply through alternative source can enhance its pace of development in surkhet and similar territories of nepal. acknowledgment the authors acknowledge the department of hydrology and meteorology (dhm/gon), government of nepal for providing meteorological data relevant to the study. special thanks are due to prof. dr. k. n. poudyal, faculty member at ioe, pulchwk campus, tribhuvan university, and sanjeep sapkota for useful discussions. references [1] j. ekpe, m. nnabuchi, solar radiation in onitsha: a correlation with average temperature, scholarly j. biotechnol. 1(5) (2012)101-107. [2] nepal electricity authority, a year in review (2020). [3] k. r. adhikari, estimation of globla solar radiation for four selected sites in nepal using sunshine hours, temperature and relative humidity, j. power energy eng.1(2013)1-9. [4] p. rijal, 95.5 percent of nepalis have an electricity connection, report says, the kathmandu post (dated june-4, 2019). [5] r. kumar et al., new regression model to estimation global solar radiation using artificial neural network, adv. energy eng. 1 (2013) 66-73. [6] m. iqbal, an introduction to solar radiation, academic press, (1983). [7] k. r. adhikari et al., solar energy potential in nepal and global context, j. inst. eng. 9(2013)95-106. https://doi.org/10.3126/jie.v9i1.10675 [8] b.r. kc, s. gurung, estimation of the daily global solar radiation using radest 3.00 software at nepalgunj, j. inst. eng.12 (2016) 199-209. https://doi.org/10.3126/jie.v12i1.16903 [9] j. awasthi, k. n. poudyal, estimation of global solar radiation using empirical model on meteorological parameters at simara airport, bara, nepal, j. inst. eng. 14 (2018) 143-150 https://doi.org/10.3126/jie.v14i1.20078 [10] c. i. elekalachi et al., estimation of global solar radiation from monthly mean sunshine hour data in some cities in south eastern zone of nigeria, physics journal. 2(2016) 96-103. [11] a brief profile of surkhet district, june, 2014 kathmandu, nepal https://studylib.net/doc/6972573/a-briefprofile-of-surkhet-district [12]http://www.hydrology.gov.np/#/basin/37/i mage [photo provided by department of hydrology and meterology] [13] manual (2008), cmp6 pyranometer, kipp and zonen [14] m. h. abd el-wahed, r. l. snyder, calculating sunshine hours and reference evapotranspiration in arid regions when solar radiation data are limited, irrigation and draining, 64 (2015) 419-425 https://doi.org/10.1002/ird.1920 [15] m.h. soulouknga et al., determination of a suitable solar radiation model for the sites of chad, energy power eng.(2017) 9703722.doi: 10.4236/epe.2017.912045 [16] z.abdin et al., solar energy harvesting with the application of nanotechnology, renew. sust. energ. rev.(2013)26737-8. https://doi.org/10.3126/jie.v9i1.10675 https://doi.org/10.3126/jie.v12i1.16903 https://doi.org/10.3126/jie.v14i1.20078 http://www.hydrology.gov.np/#/basin/37/image http://www.hydrology.gov.np/#/basin/37/image https://doi.org/10.1002/ird.1920 https://doi.org/10.4236/epe.2017.912045 3. conclusions bibechana vol. 21, no. 1, april 2024, 1–11 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar seasonal variations of disasters in nepal pitri bhakta adhikari∗, nabraj khanal department of physics, tri-chandra m. campus saraswatisadan, ghantaghar, kathmandu, nepal ∗corresponding author. email: pbadhikari09@gmail.com abstract among natural disasters, landslides, floods, thunderstorms, and fires are major destructive disasters. fires, which frequently occur in the spring and winter seasons, are the main cause of death for people in every season. landslides seem to be very destructive in the summer season, floods also occur in the summer season, and thunderbolts frequently occur in the spring and summer seasons (pre-monsoon period). different disasters occur frequently in different seasons and have a significant effect on humans, and animals, and result in huge property loss. due to the geographical structure of our scenario, the destruction seems to be high in nepal. hence, the disasters cannot be stopped, but their impact can be reduced. awareness programs should be conducted to mitigate their effects. keywords different disasters; seasonal variations; effects of disaster; awareness program. article information manuscript received: april 29, 2023; revised: july 7, 2023; accepted: december 10, 2023 doi https://doi.org/10.3126/bibechana.v21i1.54503 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction nepal is situated at 28.3949 degrees north and 84.1240 degrees east. it has an area of 147,181 square kilometers and an average width of approximately 193 kilometers with a length of 885 kilometers. it is a landlocked country, comprising only 0.3 percent of asia’s total area. due to its geographical structure, nepal experiences many disasters, which can be classified into two main types: natural and manmade [1]. nepal has vast geographical variability, ranging from low-lying areas of 59 meters to the highest peak of mount everest at 8,848.86 meters, within an average range of 160 kilometers. the climate and severe weather conditions vary due to the difference in altitude and temperature across the country’s geographical structure. for example, the temperature in the terai region can reach up to 42 degrees celsius, while at the top of mount everest, it can drop to as low as minus 55 degrees celsius. this unique behavior of variability of temperature and geographical structure leads to the occurrence of various disasters [2]. most of nepal’s cities are situated along riverbanks, and the country can be divided into three main regions: the himalayas, hilly region, and terai region. in the terai region, 1 http://nepjol.info/index.php/bibechana pbadhikari09@gmail.com https://doi.org/10.3126/bibechana.v21i1.54503 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ pitri bhakta adhikari and nabraj khanal/ bibechana 21 (2024) 1-11 2 major disasters include floods, fires, thunderbolts, droughts, hailstorms, animal incidents, and snake bites. in the hilly region, major disasters include landslides, fires, floods, thunderbolts, hailstorms, etc., and in the himalayan region, the main disasters are avalanches, landslides, thunderbolts, and snowstorms [3]. earthquakes are a common natural disaster in nepal, as the country is located between two tectonic plates the indian section of the indo-australian plate and the eurasian plate. nepal is considered the 11th most seismically-prone country in the world. the most recent devastating earthquake occurred in 2015, which resulted in a significant loss of life and property [4, 5]. there are eight mountains whose heights are more than 8000 meters: mount everest, kanchenjunga, lhotse, makalu, cho oyu, dhaulagiri, manaslu, and annapurna. besides the three main rivers, karnali, koshi, and gandaki, several other rivers cause floods in different regions of nepal [6,7]. the primary causes of disasters are unplanned urbanization, climate change, and variation in geography. in the himalayan region, avalanches cause the most destruction, resulting in several losses such as loss of lives and property. in the terai region, floods and fires cause the most destruction [7,8]. the main cause of snow melting is global warming, which results in glacial lakes swelling and consequently bursting. many glacial lakes have burst, and as the snow melts, the area of the glacial lakes increases, resulting in the burst of lakes that cause the loss of human lives and property. global warming has increased the area of tchho-rolpa glacial lake from around 0.23 square kilometers to 1.7 square kilometers [9]. the complex geological structure also plays an important role in landslides in nepal. the weak rock and soil covering steep and hilly regions cause landslides. several flash floods have occurred due to the complex geology. on june 15, 2021, the flash flood from melamchi and indrawati rivers caused huge destruction in melamchi bazaar, which made a huge impact on the melamchi water supply project too [10]. similarly, other disasters such as fires, thunderbolts, epidemics, animal attacks, snake bites, hailstorms, droughts, etc., have also occurred in various parts of the country due to its complex geological and geographical structure. nepal is known as a natural hazard hotspot, experiencing frequent occurrences of natural disasters. this paper aims to explore the most frequently occurring disasters in nepal during each of the four seasons and propose strategies to control these major incidents that cause significant destruction. providing advance information about upcoming disasters like floods and landslides in endangered cities or villages can help minimize destruction. additionally, conducting awareness programs for the general population regarding disasters like fires, thunderbolts, and hailstorms can also contribute to reducing destruction. through an awareness campaign and timely information about impending disasters in high-risk areas, the loss of human lives, animals, and property can be mitigated. 2 methodology the data source is the drr portal/moha (http: //drrportal.gov.np/). many papers have been published that describe the annual destruction caused by specific disasters. however, this paper explains which disasters cause more destruction in different seasons and how they can be controlled. the paper includes the major four disasters: fire, landslide, thunderbolt, and flood, which seem to cause more destruction. the data for these four disasters in different years was noted, and the number of incidents, total deaths, and the number of injured people were taken from the drr portal/moha. however, the data may not include full information because of the lack of information about all incidents. the annual data for different disasters from 2011 to 2022 ad was taken, and the number of incidents, deaths, and injuries due to the different disasters in different seasons (winters1, springs2, summers3, and autumns4) was observed, noted, and analyzed. bar diagrams for different disasters during this time period were plotted, both annually and seasonally, and analyzed using the microsoft excel 2016 tool. the compiled file was created using microsoft word 2016. 3 results and discussion 3.1 flood nepal is vulnerable to disasters, including various natural and man-made hazards. in this study, we focus on interpreting the data related to the destruction caused by natural disasters, such as human deaths, the number of injured people, loss of wealth and property, and more. the disaster data is collected both annually and seasonally, covering the period from 2011 to 2022 ad. the collected data includes the number of incidents, total deaths, injured people, affected families, estimated losses, missing people, fully damaged private houses, and partially damaged private houses. table 1 presents the data related to the impacts of floods, table 2 focuses on landslides, table 3 presents data on thunderbolt incidents, and table 4 provides information on fire-related incidents. each table is organized separately to present the specific data observed and the impacts caused by these disasters. http://drrportal.gov.np/ http://drrportal.gov.np/ pitri bhakta adhikari and nabraj khanal/ bibechana 21 (2024) 1-11 3 table 1: incident, deaths, injuries, and damages due to flood in nepal annually years no. of incidents total deaths no. of injured no. of affected families estimated loss (lakhs) no. of missing people private houses fully damaged private houses partially damaged 2011 259 126 19 400 5121.00 93 723 448 2012 45 9 3 139 213.76 7 139 309 2013 266 131 5 892 203.27 133 263 108 2014 65 129 36 36514 149176.14 133 8622 24447 2015 15 0 6 23 165.85 3 14 4 2016 230 101 17 7123 307.12 36 583 180 2017 338 166 35 15118 264.14 42 264 13886 2018 80 17 26 1078 345.31 3 22 538 2019 206 73 20 3075 10634.95 27 452 1907 2020 98 42 11 512 494.11 37 166 48 2021 154 63 14 279 1153.92 34 481 172 2022 55 19 17 142 145.88 15 58 13 total 1811 876 209 65295 168225.48 563563 11787 42060 figure 1: graph of disaster due to flood in nepal. from table 1, it is evident that between 2011 and 2022 ad, there were 1811 flood-related incidents, resulting in 876 deaths and 209 injuries. additionally, 65295 families were affected, 563 people were reported missing, 11787 private houses were fully damaged, and 42060 private houses were partially damaged, leading to a loss of approximately rs. 168225.48 lakhs, as reported by moha. the complete data from the source is presented in table 1. the above data has been represented in the form of a bar diagram. in figure 1, the graph represents only four parameters: the number of incidents, the total number of deaths, the number of injured, and the number of missing individuals. the estimated loss and the number of private houses fully and partially damaged have been excluded from the figure as their presence may not be well-analyzed due to the high variability in the data numbers. the graph in figure 1 depicts the number of incidents, total deaths, injured individuals, and pitri bhakta adhikari and nabraj khanal/ bibechana 21 (2024) 1-11 4 missing persons. it is evident that the number of incidents remains consistently high throughout the years, while the number of missing individuals remains relatively low. notably, the destruction caused by the flood was comparatively less in 2015 compared to other years. in 2014, there was a high number of affected families, partially damaged private houses, and a significant increase in total deaths compared to other years. however, in 2015, the overall destruction caused by the flood appears to be reduced. this can be attributed to the occurrence of an earthquake that year, which affected a large number of people. as a result, people were more aware of the potential destruction caused by natural disasters, leading to a decreased impact of the flood. it is worth mentioning that in 2014, a loss of approximately rs. 149176.14 lakhs was incurred due to the flood. 3.2 landslide according to the data from the drr portal, the table below presents information on disasters. between 2011 and 2022, nearly 2785 landslide incidents occurred, resulting in 1483 deaths, 1218 injuries, 10161 affected families, 347 missing persons, 3890 fully damaged private houses, 3655 partially damaged private houses, and a loss of approximately rs. 18407.78 lakhs. the estimated loss is quite high. table 2 shows that the maximum loss due to landslides occurred in 2016, with approximately rs. 8104.42 lakhs lost. in figure 2, the graph shows the number of incidents, total deaths, number of injuries, and number of missing people due to landslides. the parameters for estimated loss, partially and fully damaged private houses, and the number of affected families were not included due to high variability in data numbers, making it difficult to analyze them in the figure. figure 2 demonstrates the variability in the number of incidents, total deaths, number of injuries, and number of missing people. the number of incidents is high compared to the number of injured people, total deaths, and missing people. in 2020, the number of incidents is high with a high number of deaths. it seems that the number of incidents has been increasing since 2018 compared to previous years. 3.3 thunderbolt in the drr portal, the information regarding missing persons and the destruction of private houses is not mentioned. therefore, table 3 only includes four parameters: the number of incidents, total number of deaths, number of injured people, and estimated loss. according to the available data, a total of 2666 incidents occurred, resulting in 1137 deaths. additionally, 3073 people were injured, and 2784 families were affected. table 2: incidents, deaths, and injuries due to landslide in nepal years no. of incidents total deaths no. of injured no. of affected families estimated loss (lakhs) no. of missing people private houses fully damaged private houses partially damaged 2011 126 110 81 32 457.27 24 100 6 2012 102 60 33 65 205.98 8 65 74 2013 97 87 57 174 1691.27 22 135 60 2014 75 113 96 491 236.66 129 143 37 2015 62 138 84 407 6.42 13 121 96 2016 234 148 144 1488 8104.42 9 358 440 2017 163 70 56 334 615.42 15 140 40 2018 320 91 126 749 1301.19 2 188 109 2019 449 86 93 3054 4051.86 11 1132 1590 2020 493 303 226 771 509.65 64 383 68 2021 337 178 134 604 346.35 31 261 118 2022 327 99 88 1992 881.29 19 864 1017 total 2785 1483 1218 10161 18407.78 347 3890 3655 pitri bhakta adhikari and nabraj khanal/ bibechana 21 (2024) 1-11 5 figure 2: graph of destruction due to landslide. table 3: incidents, deaths, and injuries due to thunderbolt in nepal years no. of incidents total deaths no. of injured people estimated loss (lakhs) 2011 120 76 138 35.30 2012 210 118 267 40.70 2013 213 147 286 28.12 2014 177 97 227 104.46 2015 148 103 187 10.00 2016 206 118 240 33.21 2017 188 85 251 91.25 2018 244 75 300 55.62 2019 383 94 451 122.08 2020 305 82 310 91.58 2021 208 55 193 177.78 2022 264 87 223 87.69 total 2666 1137 3073 877.79 pitri bhakta adhikari and nabraj khanal/ bibechana 21 (2024) 1-11 6 figure 3: graph of disaster due to thunderbolt in nepal. the table displays the average number of destruction caused by thunderbolts each year, along with the estimated loss of approximately rs 877.79 lakhs during this time period. it is noteworthy that thunderbolts did not result in any missing individuals or fully or partially damaged private houses. from figure 3, it can be observed that the number of affected families was highest in the years 2019 and 2020, coinciding with a high number of incidents. the graph indicates that as the number of incidents increases, the number of injuries and deaths also tend to rise. additionally, there is a consistent trend of significant destruction caused by thunderbolts on average. however, the estimated loss attributed to thunderbolts is comparatively lower than that of landslides, floods, and fires. 3.4 fire the data presented in this analysis is derived from the drr protal/moha and covers the period from 2011 to 2022 ad. during this time frame, a total of 19,921 fire incidents were recorded, resulting in 850 fatalities and affecting 27,073 families. the highest estimated loss due to fire occurred in 2015, amounting to approximately rs 40,573.93 lakhs. although the number of missing individuals and government house destruction were also recorded, they are not included in the analysis due to their relatively low occurrence. in figure 4, it can be observed that the number of incidents and the number of affected families were high in the interval from 2011 to 2017 ad. however, in the year 2018, the destruction decreased, but the number of private houses fully damaged by this disaster has been continuously increasing from the interval of 2018 to 2021 ad. the destruction seems to be less in the year 2022 ad. the total human loss and incidents caused by different disasters were mentioned annually in the above tables individually, and they are also presented in bar diagrams. throughout the period from 2011 to 2022, the total loss due to fire is represented in table 5 and shown in a bar diagram in figure 5. in comparison to other disasters, the maximum number of incidents occurred due to fire. pitri bhakta adhikari and nabraj khanal/ bibechana 21 (2024) 1-11 7 table 4: incidents, deaths, and injuries due to fire in nepal years no. of incidents total deaths no. of injured no. of affected families estimated loss (lakhs) private houses fully damaged private houses partially damaged 2011 2595 106 369 3022 25775.42 844 723 2012 2693 99 362 3424 22308.66 1038 834 2013 2115 56 313 2679 15524.39 880 526 2014 2852 78 345 3777 30652.52 1623 333 2015 2459 85 336 3600 40573.93 1853 287 2016 1486 63 216 2392 22942.09 1374 258 2017 1521 63 244 3460 19240.96 2276 440 2018 623 74 67 309 9200.97 664 166 2019 950 65 98 194 16795.08 1254 171 2020 1018 59 108 1554 18540.73 1958 149 2021 1118 77 133 2512 12075.28 3785 223 2022 491 25 67 150 3980.04 574 189 total 19921 850 2658 27073 237610.03 18123 4299 figure 4: graph of human and property loss due to fire. number of incidents, human loss due to flood, landslide, thunderbolt and fire in table 5, the number of incidents, total deaths, and number of injured people are recorded. other parameters were not included due to their higher variability, which would make it difficult to interpret in a bar diagram and analyze. from table 5, it can be seen that the maximum number of incidents, 19,921, occurred due to fire, followed by landslide, thunderbolt, and flood. the highest number of fatalities was caused by landslides, followed by thunderbolt, flood, and fire. additionally, a significant number of people lost their lives due to other disasters, totaling 10,196, which includes the 2015 earthquake. during the earthquake, approximately 9,000 lives were lost, and there was extensive damage and destruction of property. from figure 5, it is evident that the highest number of people were injured by thunderbolts during this time interval, followed by injuries caused by fire, landslides, and floods. among the different disasters, floods affected the maximum number of families, surpassing the impact of other disasters. more than half of the total affected families were affected by floods. regarding the damage to private houses, the earthquake caused the most significant destruction during this period. in 2015 alone, pitri bhakta adhikari and nabraj khanal/ bibechana 21 (2024) 1-11 8 more than 700,000 private houses were fully damaged and over 200,000 private houses were partially damaged. the next disaster resulting in significant house destruction is flood. in terms of estimated losses, fire caused the highest financial impact, followed by flood, earthquake, landslide, and thunderbolt. table 5: variation of disasters to human loss and number of incidents during the period 2011-2022 disasters number of incidents number of deaths number of injured people flood 1811 876 209 landslide 2785 1483 1218 thunderbolt 2666 1137 3073 fire 19921 850 2658 other disasters 4823 10196 28158 total 32006 14542 35316 figure 5: variation of disasters to incidents, human loss and injuries in twelve years. the human loss and incidents by different disasters in different seasons the different seasons, winter represented by s1, spring by s2, summer by s3, and autumn by s4, are presented here. winter includes december, january, and february; spring includes march, april, and may; summer includes june, july, and august; and autumn includes september, october, and november. the four main disasters in nepal, which account for more than half of the total incidents, are very dangerous in different seasons and can claim lives and cause injuries. these are presented in table 6, and their representations in bar diagrams of different seasons and disasters are given in figure 6, with the different disasters in different seasons shown in figure 7. from figure 6, it can be seen clearly that the most number of incidents were caused by fire in the winter and spring seasons. the maximum number of incidents occurred in spring (7223) and winter (6737), and the minimum in summer (2623) during the mentioned period. hence, awareness programs should be conducted during the winter and spring seasons about fire, and people should be made familiar with its harmful effects. similarly, during spring (1155) and summer (932), incidents occur due to thunderbolt, and awareness programs should be conducted during the pre-monsoon period. the landslide is most dangerous in summer among the four seasons, in which the maximum number of incidents and people were killed. in the summer season, the highest number of flood incidents were observed from the above figures, with 1408 incidents, 686 people losing their lives, and 176 people being injured. among the 32006 incidents of disasters, around pitri bhakta adhikari and nabraj khanal/ bibechana 21 (2024) 1-11 9 87 percent were caused by the four main disasters: landslides, floods, fires, and thunderbolts. these four disasters caused about 80 percent of the total deaths, which amounts to 4370 people, whereas the earthquake in 2015 caused around 9000 deaths. although the main disasters caused the maximum number of incidents, the number of human losses is comparatively lower than the earthquake. fire caused the highest number of incidents, while flood and landslide caused comparatively fewer incidents. the table 5 shows that the number of injuries incurred in thunderbolts is about three times higher than the number of deaths, and similarly, the number of injuries in fires is more than three times higher than the number of deaths. table 6: seasonal variation of disasters during the period 2011-2022. (a)seasons in different disaster disasters seasons number of incidents number of deaths number of injured flood winter 2 123 1408 spring 1 29 686 summer 0 14 176 autumn 0 0 0 landslide winter 39 15 21 spring 107 66 57 summer 2066 1006 844 autumn 558 392 293 thunderbolt winter 205 65 268 spring 1155 455 1472 summer 932 447 916 autumn 359 159 351 fire winter 6737 433 1027 spring 7223 264 723 summer 2623 61 418 autumn 4000 133 602 total 27803 4370 7208 (b)disasters in different season seasons disasters number of incidents number of death number of injured winter (s1) flood 2 1 0 landslide 39 15 21 thunderbolt 205 65 268 fire 6737 433 1027 spring (s2) flood 123 29 14 landslide 107 66 57 thunderbolt 1155 455 1472 fire 7223 264 723 summer (s3) flood 1408 686 176 landslide 2066 1006 844 thunderbolt 932 447 916 fire 2623 61 418 autumn (s4) flood 266 158 26 landslide 558 392 293 thunderbolt 359 159 251 fire 4000 133 602 pitri bhakta adhikari and nabraj khanal/ bibechana 21 (2024) 1-11 10 4 conclusion the maximum number of fire incidents occurred more frequently compared to other disasters. fire is the primary cause of deaths in every season. the highest number of fire incidents took place during spring and winter, while the minimum occurred during summer throughout the mentioned period. similarly, thunderbolts occur frequently during spring and summer, also known as the premonsoon period. to effectively address all types of disasters, awareness programs should be conducted based on the seasons. for example, awareness campaigns about thunderbolts should be focused on the pre-monsoon period, while floods and landslides are more prevalent during the rainy (summer) season and have a greater impact. landslides are particularly destructive during the summer season and moderately destructive during autumn, whereas winter and spring experience less destruction. a similar pattern is observed for floods, with the maximum destruction occurring in the summer season, moderate destruction in autumn, and significantly fewer incidents during winter. these disasters are primarily influenced by the geographical structure of the region, resulting in higher levels of destruction in nepal. therefore, it is crucial to conduct awareness programs in the prone zone areas during pitri bhakta adhikari and nabraj khanal/ bibechana 21 (2024) 1-11 11 these specific periods. acknowledgements first of all, we would like to express our sincere gratitude to tri-chandra multiple campus, tribhuvan university for the research facility. we are also thankful to drr portal, for the facility to observe data, which were analyzed to complete the research. references [1] information and broadcasting department, nepal government. nepal parichaya. 2022. doi: www.doinepal.gov.np. [2] pitri bhakta adhikari. death and injury of the people due to lightning in the himalayan region, nepal. bibechana, 18(2):116– 128, 2021. doi: https://doi.org/10.3126/ bibechana.v18i2.29168. [3] dinanath bhandari, sanchita neupane, peter hayes, bimal regmi, and phil marker. disaster risk reduction and management in nepal: delineation of roles and responsibilities. oxford policy management limited, united kingdom, 2020. [4] john p. rafferty. nepal earthquake of 2015. encyclopedia britannica, 2023. doi: https://www.britannica.com/topic/ nepal-earthquake-of-2015. [5] ministry of industry. department of mines and geology, 2021. ng 2021. [6] himalayan social journey. 8 out of 14 tallest peaks of the world in nepal, n.d. [7] pitri bhakta adhikari, sapana dawadi, and shanta nepal. the fatalities and injuries due to avalanche effect in the himalayan region, nepal. bibechana, 20(1):36– 45, 2023. doi: https://doi.org/10.3126/ bibechana.v20i1.42206. [8] basistha raj adhikari. flooding and inundation in nepal terai: issues and concerns. hydro nepal; journal of water, energy and environment, 12:59–65, 2013. doi: https: //doi.org/10.3126/hn.v12i0.9034. [9] government of nepal, ministry of home affairs. nepal disaster report 2019, 2019. [10] sudan bikash maharjan, jakob friedrich steiner, arun bhakta shrestha, amina maharjan, santosh nepal, mandira singh shrestha, birendra bajracharya, ghulam rasul, maxim shrestha, miriam jackson, and nishikant gupta. the melamchi flood disaster. icimod, 2021. doi: https://www.icimod.org/ article/the-melamchi-flood-disaster/. www.doinepal.gov.np https://doi.org/10.3126/bibechana.v18i2.29168 https://doi.org/10.3126/bibechana.v18i2.29168 https://www.britannica.com/topic/nepal-earthquake-of-2015 https://www.britannica.com/topic/nepal-earthquake-of-2015 https://doi.org/10.3126/bibechana.v20i1.42206 https://doi.org/10.3126/bibechana.v20i1.42206 https://doi.org/10.3126/hn.v12i0.9034 https://doi.org/10.3126/hn.v12i0.9034 https://www.icimod.org/article/the-melamchi-flood-disaster/ https://www.icimod.org/article/the-melamchi-flood-disaster/ introduction methodology results and discussion flood landslide thunderbolt fire conclusion bibechana vol. 21, no. 2, august 2024, 129-141 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar adsorption of water on vacancy defected h-bn bilayer at b and n sites madhav nepal1, ganesh paudel1, santosh aryal1 arun devkota2, hari krishna neupane1∗ 1amrit campus, tribhuvan university, kathmandu, nepal 2central department of physics, tribhuvan university, kathmandu, nepal ∗corresponding author. email: hari.neupane@ac.tu.edu.np abstract two dimensional (2d) materials are used to manufacture the various gadgets. their properties are therefore appealing. in the present work, we have studied the structural, electronic, and magnetic properties of 2d bilayer hexagonal-boron nitride (h-bn), single b vacancy defect on h-bn (b-hbn), single n vacancy defect on h-bn (n-hbn), water adsorption; on b-hbn (w-b-hbn) and on n-hbn (w-n-hbn), materials by spin-polarized density functional theory (dft) methods employing quantum espresso (qe) computational tools. the structural stability of the h-bn, b-hbn, n-hbn, w-b-hbn, & w-n-hbn materials has been investigated by determining their minimum ground state energy and binding energy, and found that they are stable materials. the pristine h-bn bilayer supercell structure is also found to be more compact than other defective configurations. by analyzing the band structures and density of states (dos) plots of these materials, we have examined their electronic properties, and found that pristine h-bn has a broad bandgap, whereas b-hbn, n-hbn, wb-hbn, & w-n-hbn exhibit semiconducting nature. the dos and partial density of states (pdos) computations of the considered materials are used to study their magnetic properties. it is found that pristine h-bn is a non-magnetic, and b-hbn, n-hbn, w-b-hbn & w-n-bn are magnetic materials. therefore, vacancy defects on pristine h-bn, and water adsorption on vacancy defected h-bn materials cause it to change from non-magnetic to magnetic. they could find use in the domain of device keywords adsorption, bilayer, defect, spin states. article information manuscript received: february 7, 2024; revised: april 4, 2024; accepted: april 5, 2024 doi https://doi.org/10.3126/bibechana.v21i2.62607 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction boron nitride (bn) stands out as the most lightweight chemical compound within the group iiiv in periodic table, having an equal distribution of boron and nitrogen atoms [1–6]. it’s structure is similar of graphene’s structure [7]. two dimensional (2d) hexagonal boron nitride (h-bn) was 129 http://nepjol.info/index.php/bibechana hari.neupane@ac.tu.edu.np https://doi.org/10.3126/bibechana.v21i2.62607 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ madhav nepal et al./ bibechana 21 (2024) 129-141 130 constructed by numerous methods including liquid and micromechanical exfoliation, chemical vapor deposition (cvd), and other novel synthetic approaches [8–10]. at room temperature and under ambient pressure, the hexagonal structure stands out as the stable phase among these various structures [11]. h-bn is originally an electrical insulator due to its wide bandgap energy of values in the range of (3.5-6.0) ev obtained from dft and gw calculations [12, 13]. h-bn is used in various fields such as tunneling devices, chemical sensors, transistors, lubricants due to their wide bandgap energy and various structural characteristics [13–17]. additionally, it exhibits a high degree of inertness towards a wide range of gas molecules, and it also be easily adjusted using various methods to attain different properties and functions [17–19] this tuning can be achieved through strategies like doping and introducing vacancy defect in the stable structure [19, 20]. the presence of vacancy defect in 2d h-bn material develops the spontaneous magnetization due to the distribution of unequal spin states of electrons in the orbitals of atoms present in the material [15, 21–23]. boron (b) and nitrogen (n) atoms in h-bn are strongly covalently bound due to their electronegativity [24]. in the meantime, nearby layers interact with one another by a weak van der waals (vdws) force [25]. h-bn is formed a sp2-hybridization between b & n atoms [26–28]. furthermore, compared to graphene, h-bn’s structure is thermally and chemically stable. it works well as a lubricant because of its lower coefficient of friction [29, 30]. h-bn has a unique set of characteristics, including atomic flatness, incredibly low roughness, and no dangling bonds on its surface [31]. young's modulus (270 nm-1) and thermal conductivity (400 wm-1k-1) of 2d h-bn are significantly higher than those of the majority of metals and ceramic materials [32–36]. h-bn bilayer is created by vertically staking two monolayers. its properties are changed when it placed in a humid environment. thus, adsorbed water molecules modify its electronic, magnetic, optical, and thermal properties [37–42]. many investigations have been conducted recently on the adsorption of water molecules on the surface of different other 2d materials. it is found that structural, electronic, and magnetic properties of defected materials are changed due to the adsorption of water molecules [14, 42]. after a thorough analysis of the literature, we found that no studies have been done on the structural, electronic, and magnetic characteristics of water adsorbed on pristine h-bn, and b & n vacancy defected h-bn bilayer materials. in the present work, we have investigated the structural, electronic, and magnetic properties of b & n sites vacancy defected bilayer of h-bn supercell structures (i.e., b-hbn & n-hbn), and water adsorption on these supercell structures (i.e., w-bhbn & w-n-hbn) respectively, by spin-polarized density functional theory (dft) methods using the computational tools’ quantum espresso (qe) codes. below is an arrangement of the remaining portions of this manuscript: in the methods and materials section, the procedures and supplies utilized in this investigation are detailed. in the results and discussion section, we present our findings and their interpretations, and in the conclusions section, we express our final thoughts. 2 material and methods the investigation of structural, electronic, and magnetic properties of single b atom vacancy defect on (4×4) bilayer supercell structure of h-bn (b-hbn), single n atom vacancy defect on (4×4) bilayer supercell structure of h-bn (n-hbn), and water molecules adsorbed on b-hbn (w-b-hbn) and n-hbn (w-n-hbn) materials was done using firstprinciples calculations based on the spin-polarized density functional theory (dft) method [42]. the generalized gradient approximation (gga) was utilized using perdew-burke-ernzerhof (pbe) exchange correlations in order to incorporate the electronic exchange and correlation effects in the dft theory [43]. pbe functional cannot adequately describe the weak van der waals (vdws) force present in bilayer supercell structures. therefore, to determine the type of vdws interaction between the interlayers of bilayer structures, semi-empirical dispersion correlated density functional theory (dftd2) technique is utilized. an effective potential for each atom in a system is used to substitute the complex effects of the motion of an atom's core electrons and its nucleus using grimme's rappe-rabekaxiras-joannopoulos (rrjk) model of ultrasoft pseudopotentials. so, we have used rrjk model of ultrasoft pseudopotentials and plane wave basis set in the convergence test. a (4×4) supercell bilayer structure of h-bn is constructed by incorporating 64 atoms, where single layer of h-bn contains 16 b atoms, and 16 n atoms. single b & n sites vacancy defected h-bn are created by randomly removing 1b & 1n atoms respectively from the upper surface of h-bn supercell structure. in single layer h-bn, b or n vacancy defect of 3.13% is formed, whereas in bilayer h-bn, b or n vacancy defect of 1.56% is produced (i.e., 1b or 1n atom out of 32 bn atoms in single layer). then, these supercell structures are optimized by calculating their kinetic energy cutoff (ecutoff), lattice parameter (a), and k-points (kcutoff), through the convergence test. they are found to be 35 ry, 4.65 å, and (22×22×1) remadhav nepal et al./ bibechana 21 (2024) 129-141 131 spectively. these optimized values are taken in the input file for relax calculations. the relax calculations of considered materials have done by using broyden-fletcher-goldfrab-shanno (bfgs) scheme [44] until the force and total energy change between two successive scf iterations are less than 10-3 ry/bohrs and less than 10-4 ry, respectively. the optimized and relaxed structures of pristine hbn, and b & n sites vacancy defected bilayer h-bn are shown in figures-1(a-c) respectively. furthermore, water molecule is adsorbed on the defected structures of b-hbn & n-hbn, respectively. then relax calculations are carried out with the broyden-fletcher-goldfrab-shanno (bfgs) scheme [43] until the force and total energy minimum values vary between two consecutive scf iterations. these values are likewise found to be less than 10-4 ry and 10-3 ry/bohrs, respectively. figures-1(d-e) displays the relax structures of water adsorbed on b-hbn (i.e., w-b-hbn) and on n-hbn (i.e., w-n-hbn) materials, respectively. to assure the accuracy of the results, the marzarrivanderbilt (m-v) smearing method is utilized in the calculations, with a small broadening width of 0.001 ry [43–47]. for self-consistency, the "david" diagonalization approach with a 0.6 mixing factor is selected. in order to do the band calculations, 200 k-points are chosen along the reciprocal lattice's high symmetry points. the sample locations in the reciprocal lattice's first brillouin zone are these kpoints. density of states (dos) and partial density of states (pdos) computations are carried out to investigate magnetic properties of materials. 3 results and discussion 3.1 structural properties the structural properties of bilayer h-bn material with single b atom vacancy defect, and single n atom vacancy defect; have been examined, along with the effects of water adsorption on these materials. this analysis is conducted by computing the bond length between b-n atoms, binding energy of the systems, interlayer distance of bilayers, and defect generation energies. first, a unit cell of bilayer h-bn material has been created by taking the optimized values of lattice parameter (a) = 4.65 å, kinetic energy cutoff = 35 ry, and k-points = 22 in the input file. then relax calculations are done to get optimized and relaxed unit cell structure of bilayer h-bn. the prepared relaxed unit cell of hbn is stretched along x-and y-directions (axes) by repeating its four times, which is called (4×4) supercell structure of h-bn bilayer is illustrated in figure-1(a). we have estimated the bond length between b-n atoms, interlayer distance between bilayer’s atoms, binding energy, and ground state energy of bilayer h-bn supercell structure, they are found to be 1.43 å, 3.72 å, -707.36 mev & -874.39 ry respectively. these values are comparable with other reported values of 2d materials [28,48]. they reflect that bilayer h-bn supercell structure is a stable material. the binding energy of bilayer h-bn is calculated by using equation-(1), [49]; (eb)d = eg(h−bn−bi)d −(eg(h−bn−mono)d + eg(h−bn−mono)p) (1) where, eb, eg(h-bn-bi) & eg(h-bn-monolayer) represent the binding energy of h-bn system, ground state energy of h-bn bilayer supercell, and ground state energy of monolayer h-bn supercell structure respectively. furthermore, we have created the b atom vacancy defected h-bn (b-hbn), and n atom vacancy defected h-bn (n-hbn) materials by randomly removing single b atom, and single n atom from the upper surface of bilayer material respectively. then calculate the minimum ground state, and binding energies of them. it is found that our considered materials (are shown in figures-1(b-c)) have minimum value of ground state energy, and maximum value of binding energy. the ground state energy, binding energy, defect formation energy, interlayer distance of bilayers, and bond length between bn atoms of b-hbn are found to be -845.39 ry, 515.36 mev, 0.21 ev, 3.72 å & 1.46 å respectively, and of n-hbn are found to be -831.69 ry, -643.36 mev, 0.16 ev, 3.72 å & 1.44 å respectively. these calculated values are comparable with the reported values of others 2d materials [28, 48]. the binding energy of defected bilayer h-bn systems (b-hbn & n-hbn) are obtained by using equation-(2), [49]; eb = eg(h−bn−bi)d − ( eg(w−hbn−mono)d +eg(h−bn−mono)p + eh2o ) (2) where, (eb)d, eg(h-bn-bi)d, eg(h-bn-mono)d & eg(h-bn-mono)p are represented by binding energy of defected system, minimum ground state energy of b or n sites vacancy defected system, minimum ground state energy of b or n sites vacancy defected monolayer h-bn and minimum ground state energy of pristine h-bn monolayer respectively. the defect formation energy of defected bilayer h-bn systems (b-hbn & n-hbn) are obtained by using equation(3), [14, 28,41]; (ed)f = ed − (ep + nbµb + nnµn ) (3) where, (ed)f, ed, ep, nb or nn & µb or µn represent the defect formation energy, ground state energy of defected monolayer of h-bn, ground state madhav nepal et al./ bibechana 21 (2024) 129-141 132 energy of pristine monolayer of h-bn, number of defected atom and chemical potential of defected atom respectively. the calculations of above parameters implies that b-hbn & n-hbn are stable materials. from above estimated values of bond length between b-n atoms in structures, it is confirmed that pristine system is more compact than defected systems. in addition, we have constructed water adsorption on b-hbn (w-b-hbn) and n-hbn (w-n-hbn) materials by adsorbing water molecule at different position (orientation) above the surface of defected layer of h-bn bilayer, and then relax calculation are done. it is found that adsorbed water molecule is appeared at 2.34 å distance above from the upper surface of defected h-bn bilayer. the water molecules were then positioned on the left, middle, and right at constant 2.34 distances in various orientations above the upper surface of the defected h-bn bilayer. their minimum ground state energy, binding energy, water adsorption energy, interlayer distance between the bilayers, and bond length between b-n atoms were then estimated. the calculated binding energies of the adsorbed water molecule at the left and right positions on the defective h-bn bilayer are found to be smaller than those of the middle location, while the ground state energy is found to be larger. higher binding energies and lower ground state energies are known to indicate that a material is more stable. thus, we have chosen w-b-hbn and w-n-hbn materials by adsorbing water molecule on the middle position at 2.34 å distance above the surface of defected layer of h-bn bilayer for further calculations. the optimized and relax structures of water molecule adsorbed on the middle position at 2.34 å distance above from the upper surface of defected h-bn bilayer (w-b-hbn & w-n-hbn) are shown in figures1(d-e). the minimum ground state energy, binding energy, water adsorption energy, interlayer distance between the bilayers, and bond length between bn atoms of w-b-hbn are found to be -880.04 ry, -515.36 mev, -0.24 ev, 3.72 å, and 1.46 å respectively, and of w-n-hbn are found to be -867.393 ry, -643.36 mev, -0.32 ev, 3.72 å, and 1.44 å respectively. these estimated values are agreed with the reported values of 2d materials [14, 28, 41, 50]. they reveal that these materials are stable materials. the binding energy of w-b-hbn & w-n-hbn are estimated by using equation-(4), [28, 41] eb = eg(w−hbn−bi)d − ( eg(w−hbn−mono)d +eg(h−bn−mono)p + eh2o ) (4) where, eb, eg(w-hbn-bi)d, eg(w-hbn-mono)d, eg(h-bn-mono)p & eh2o are represented by binding energy w-b-hbn or w-n-hbn system, minimum ground state energy w-b-hbn or w-n-hbn, minimum ground state energy of water adsorbed on b or n sites h-bn monolayer, minimum ground state energy of pristine h-bn monolayer and ground state energy of water molecule respectively. we also have compared the estimated parameters of considered systems and found that pristine h-bn bilayer supercell structure is more compact and stable than defected, and water adsorption on defected materials. pristine bilayer h-bn, b-hbn, n-hbn, w-bhbn & w-n-hbn bilayer supercell structures are shown in figures-1(a-e) respectively. 3.2 electronic properties electronic properties of pristine h-bn, single b atom vacancy defect on h-bn (b-hbn), single n atom vacancy defect on h-bn (n-hbn), water adsorption on b-hbn (w-b-hbn) & water adsorption on n-hbn (w-n-hbn) bilayer supercell materials are studied by the analysis of their band structures and density of states (dos) plots. the band structure plots of these materials are shown in figures2(a-e) respectively. in the band plots, highly symmetric points (γ−m−k−γ) within the irreducible brillion zone (bz) are plotted along the x-axis, and its corresponding energy levels are plotted along the y-axis. the horizontal blue dot line represents the fermi energy level which separates the electronic bands. the region below the fermi energy level is called valence band, and above the fermi energy level is called conduction band. to obtain the fine band structure, we have taken 200 k-points in the irreducible bz. bandgap energy is the distance between the material's lowest level of conduction band and topmost level of valence band. the pristine bilayer h-bn supercell structure's bandgap energy 4.56 ev is calculated, which indicates that material has a broad bandgap. this number is somewhat consistent with the monolayer h-bn supercell structure value that has been reported [15, 28]. figure-1(a) depicts the pristine bilayer h-bn supercell structure's electronic band states that we have obtained. compared to conduction band states, valence band states are found to be more closely spaced with the fermi energy level in band structure. consequently, we have p-type schottky barrier of pristine bilayer h-bn supercell structure. madhav nepal et al./ bibechana 21 (2024) 129-141 133 (a) (b) (c) (d) (e) figure 1: (color online) optimized and relax structures of b n sites vacancy defected bilayer hbn supercell material: (a) pristine bilayer h-bn supercell structure, (b) single boron atom vacancy defected bilayer h-bn supercell (b-hbn) material, (c) single nitrogen atom vacancy defected h-bn bilayer supercell (n-hbn) material, (d) water adsorption on b-hbn (i.e., w-b-hbn) material, and (e ) water adsorption on n-hbn (i.e., w-n-hbn) material. madhav nepal et al./ bibechana 21 (2024) 129-141 134 (a) (b) (c) (d) (e) figure 2: (colour online) band structure plots of pristine and defected bilayer h-bn materials: (a) band structure of pristine h-bn bilayer supercell material, (b) band structure of b-hbn bilayer supercell material, (c) band structure of n-hbn bilayer supercell material, (d) band structure of w-b-hbn bilayer supercell material, and (e) band structure of w-n-hbn bilayer supercell material. figures-2(b-c) display the band structures that we have created of b-hbn & n-hbn materials, respectively. it is calculated that the bandgap energies of b-hbn & n-hbn are 1.25 ev & 1.49 ev, respectively. the energy gaps between the fermi energy level and the lowest level of band states in the conduction band, and the fermi level and higher level of band states in the valence band are added up to get these values. electronic band states of valence band are observed near the fermi energy level in both materials. thus, they are known as p-type semiconducting materials. the unpaired arrangement of electronic spin-states in the atoms' orbitals within the structures is what causes the flat bands to form in the valence band of n-hbn and the conduction band of b-hbn. moreover, we have analyzed the band structures of w-b-hbn & w-n-hbn materials, which are ilmadhav nepal et al./ bibechana 21 (2024) 129-141 135 lustrated in figures-2(d-e) respectively. from these plots, we have estimated the bandgap energy of wb-hbn & w-n-hbn are found to be 0.97 ev & 1.24 ev respectively. it means, adsorbed water molecule affects the electronic states of defected systems. this is because, water molecule like to be adsorbed on the region of vacancy sites, as a result, more numbers of flat bands are appeared in the conduction band of w-b-hbn & in the valence band of w-n-hbn materials. in both materials, electronic band states of valence band are presented closely with the fermi energy level, and hence, they are ptype semiconducting materials. the estimated values of total minimum ground state energy, fermi energy, bandgap energy, binding energy, defect formation energy of studied materials are presented in table-1. table 1: estimated values of total energy (et), fermi energy (ef ), band gap energy (eg), binding energy (eb), and defect formation energy (ed) of pristine h-bn, b-hbn, n-hbn, w-b-hbn & w-n-hbn bilayer supercell materials. bilayer materials et (ry) ef (ev) eg (ev) eb (mev) ed (ev) nature of material h-bn -852.38 -2.27 4.56 -707.36 wide bandgap b-hbn -845.39 -2.93 1.25 -515.36 0.21 semiconductor n-hbn -831.69 -0.38 1.49 -643.36 0.16 semiconductor w-b-hbn -880.04 -3.07 0.97 -515.36 semiconductor w-n-hbn -867.39 -0.60 1.24 -643.36 semiconductor in addition, we have analyzed the dos plots of pristine h-bn, b-hbn, n-hbn, w-b-hbn & w-nhbn bilayer supercell materials for the investigation of their electronic properties. the dos plots of these materials are shown in figures-3(a-e) respectively, where dos states are plotted along yaxis and corresponding it energies are taken along x-axis. the vertical dot line separates the valence band and conduction band. the region toward lhs represents valence band, and region toward rhs represents conduction band. the horizontal dot line distinguishes the dos states of up-spins and down-spins. black and red colours of spin states are respectively, indicate the distributed up and down spin-states of electrons in the orbitals of atoms present in the materials. it is found that bandgap energies of pristine h-bn, b-hbn, n-hbn, w-b-hbn & w-n-hbn bilayer supercell materials have values 4.56 ev, 1.30 ev, 1.47 ev, 1.27 ev & 1.12 ev respectively. these calculated values are fairly agreed with the computed values obtained from band structure calculations [5, 28]. thus, it is also confirmed that pristine h-bn bilayer supercell is a wide bandgap material, and b-hbn, nhbn, w-b-hbn & w-n-hbn bilayer supercell structures have semiconducting nature. semiconducting materials can find usage in a variety of technologies, including memory devices, photocatalysts, integrated logic circuits, transistors, signal amplifiers, photodetectors, flexible optoelectronic devices, solar cells [9, 13,17]. 3.3 magnetic properties magnetic properties of pristine h-bn, b-hbn, nhbn, w-b-hbn & w-n-hbn bilayer supercell materials are investigated by the analysis of their density of states (dos) and partial density of states (pdos) calculations. dos gives an idea of number of electronic states per unit energy range, and pdos gives an idea of distribution of spin states of electrons in the orbital of atom present in the material [15, 23, 26]. dos & pdos plots of pristine h-bn, b-hbn, n-hbn, w-b-hbn & w-n-hbn materials are presented in the figures-3(a-e) & figures4(a-e) respectively. in dos & pdos plots, vertical dot line represents the fermi energy level which separates the electronic bands. the horizontal dot line separates the distributed up-and down-spin states. madhav nepal et al./ bibechana 21 (2024) 129-141 136 (a) (b) (c) (d) (e) figure 3: colour online) density of states (dos) plots of pristine and defected bilayer h-bn materials: (a) dos plot of pristine h-bn bilayer supercell material, (b) dos plot of b-hbn bilayer supercell material, (c) dos plot of n-hbn bilayer supercell material, (d) dos plot of w-b-hbn bilayer supercell material, and (e) dos plot of w-n-hbn bilayer supercell material. insets represent the zoom scale of dos plots. the dos & pdos plots of pristine h-bn bilayer supercell structure are shown in figure-3(a) & figure-4(a) respectively. in both plots, up and down spin states are symmetrically distributed around the fermi energy level. it indicates that magnetic moment has not yet developed. it is therefore a non-magnetic substance. we have examined the dos & pdos plots of b-hbn & n-hbn materials, which are depicted in figures-3(b-c) & figures-4(bc) respectively. asymmetric distribution of up and down spin states of electrons in atom orbitals in materials around the fermi energy level results in magnetic moments of -1.71 µb/cell in b-hbn & 1.00 µb/cell in n-hbn. as a result, both materials possess magnetic properties. the negative sign signified that down spin states of electrons contribute more than up spin states of electrons to the formation of magnetic moment in the materials. based madhav nepal et al./ bibechana 21 (2024) 129-141 137 on the calculations, we found that the magnetic moment values of b atom's 2s & 2p orbitals are 0.01 µb/cell & -0.06 µb/cell, whereas n atom's 2s & 2p orbitals have 0.14 µb/cell & -1.52 µb/cell in b-hbn. it has been demonstrated that the n atom's 2p orbital plays a major role in the magnetic moment produced in b-hbn material. in the same way, we calculated the magnetic moment of n-hbn material and found that it is 0.04 µb/cell & 0.30 µb/cell of b atoms' 2s & 2p orbitals, and 0.08 µb/cell & 0.58 µb/cell of n atoms' 2s & 2p orbitals, respectively. positive magnetic moment values show that up spin states are mostly responsible for the material's magnetic moment production. 2 (a) (b) (c) (d) (e) figure 4: (colour online) partial density of states (pdos) plots of pristine and defected bilayer h-bn materials: (a) pdos plot of pristine h-bn bilayer supercell material, (b) pdos plot of b-hbn bilayer supercell material, (c) pdos plot of n-hbn bilayer supercell material, (d) pdos plot of w-b-hbn bilayer supercell material, and (e) pdos plot of w-n-hbn bilayer supercell material. insets represent the zoom madhav nepal et al./ bibechana 21 (2024) 129-141 138 scale of pdos plots. furthermore, we have examined the dos & pdos computations of w-b-hbn & w-n-hbn bilayer supercell materials to learn more about their magnetic characteristics. figures-3(d-e) and figures-4(d-e) respectively depict the asymmetric distribution of up and down spin states of electron in the orbitals of atoms found in the materials near the fermi energy level. it indicates that they possess magnetic properties. we have estimated the magnetic moment created by the unpaired spin states of electrons in the orbitals of atoms present in the materials. in w-b-hbn, the spins in the 2s & 2p orbitals of b atoms and the 2s & 2p orbitals of n atoms have values of 0.01 µb/cell & 0.57 µb/cell, and -0.24 µb/cell & -1.69 µb/cell, respectively. additionally, the magnetic moments of the 1s of h atoms and 2s & 2p of o atom in w-b-hbn material are found to be -0.02 µb/cell, and 0.00 µb/cell & 0.37 µb/cell respectively. the total magnetic moment generated in w-b-hbn is therefore equal to -1.00 µb/cell. likewise, we computed the magnetic moment given by unpaired spin states in the 2s & 2p orbitals of b atoms, and 2s & 2p orbitals of n atoms are found to be 0.04 µb/cell & 0.00 µb/cell, and 0.00 µb/cell & -0.42 µb/cell in w-n-hbn martial respectively. also, magnetic moment given by spin states of electrons in the 1s orbital of h atoms and 2s & 2p orbitals of o atom in w-n-hbn material are found to be 0.00 µb/cell, and 0.00 µb/cell & 1.38 µb/cell values respectively. this indicates that the formation of magnetic moment in the material is primarily attributed to the 2p orbital of n & o atoms. consequently, total magnetic moment of w-n-hbn material have value -1.00 µb/cell. the estimated magnetic moment of b-hbn, n-hbn, w-b-hbn & w-n-hbn materials are illustrated in table-2. table 2: magnetic moment (µt in µb/cell) is produced by unpaired spin states of electrons in the 2s & 2p orbitals of boron, nitrogen, and oxygen atoms and 1s orbital of hydrogen atom in the pristine, defected, and water adsorbed on defected h-bn bilayer supercell structures. orbitals materials b-hbn w-b-hbn n-hbn w-n-hbn 2s of b atoms 0.01 0.01 0.04 0.04 2p of b atoms -0.06 0.57 0.30 -0.00 2s of n atoms -0.14 -0.24 0.08 -0.00 2p of n atoms -1.52 -1.69 0.58 -0.42 1s of h atoms -0.02 0.00 2s of o atom 0.00 0.00 2p of o atom 0.37 1.38 total magnetic moment (µt ) -1.71 -1.00 1.00 1.00 it can be observed from the calculations above that b & n vacancy defected atoms turn nonmagnetic pure h-bn bilayer supercell structures into magnetic ones. this is because the electrons in the remaining atoms in the structures have rearranged their unpaired spin states. however, because the unpaired electron spins around the b vacancy position in the h-bn structure are rearranged together with the adsorbed water molecule, the presence of adsorbed water on b sites h-bn weakens the magnetic moment. furthermore, the values of the magnetic moment of n vacancy defected h-bn, and water adsorbed on the vacancy defective h-bn of n sites are comparable. these values are produced in the materials as a result of the electronic spin states' unpaired configuration. we determined the magnetic moment values in h-bn materials with vacancy defects at sites b and n. these materials appear to be promising for use in a variety of devices requiring magnetic characteristics because of the appearance of magnetism. magnetism and magnetic materials are essential to many of the modern electronic equipment we use. biomedicine, molecular biology, biochemistry, diagnostics, catalysis, and nanoelectronics devices are just a few of the industrial applications for novel nanomagnetic materials that could be used. other applications include magnetic seals in motors, magnetic sensors, bank check ink, electrical power generators and transformers, magnetic recording media, computers, and more [51, 52]. therefore, key frameworks for the material to device applications may be provided by our understanding of unique electrical and magnetic phenomena on defective materials. 4 conclusion in the present work, we have studied the impact of adsorbed water molecule on single b atom vacancy defect on h-bn, single n atom vacancy demadhav nepal et al./ bibechana 21 (2024) 129-141 139 fect on h-bn by first-principles calculation based on spin-polarized dft methods through quantum espresso (qe) computational tools. firstly, we have investigated the structural properties of 2d bilayer hexagonal-boron nitride (h-bn), single b atom vacancy defect on h-bn (b-hbn), single n atom vacancy defect on h-bn (n-hbn), water adsorption; on b-hbn (w-b-hbn) and on n-hbn (w-n-hbn), materials by estimating their ground states energy and binding energy. they are found to be structurally stable materials. additionally, we have measured the interlayer distances and bond length between any two nearest b-n atoms, and found that defective materials are also shown to be less compact than perfect h-bn bilayer material. secondly, we have studied the electronic properties of considered materials by developing their band structures and dos plots. it is found that pristine h-bn has wide bandgap energy of value 4.56 ev, so is called wide bandgap material. on the other hands, b-hbn, n-hbn, w-b-hbn & w-n-hbn materials have small bandgap energy of values 1.25 ev, 1.49 ev, 0.97 ev & 1.24 ev respectively. hence, they have semiconducting properties. thirdly, we have examined the magnetic properties of pristine h-bn, b-hbn, n-hbn, w-b-hbn & w-n-hbn bilayer supercell materials, by the analysis of their dos and pdos calculations. electronic spin-states of up and down spins are symmetrically distributed around the fermi energy level in pristine h-bn, and hence it has zero value of magnetic moment. so, it is a non-magnetic material. the distribution of up and down spins is asymmetrically distributed around the fermi energy level in b-hbn, n-hbn, w-b-hbn & w-n-hbn materials. as a results, magnetic moment are developed of values -1.71 µb/cell, 1.00 µb/cell, -1.00 µb/cell & 1.00 µb/cell respectively. thus, b & n sites vacancy defected h-bn, and water adsorption on these defected materials are magnetic materials. thus, water adsorption on vacancy defected h-bn materials, and vacancy defects on pristine h-bn materials cause it to become magnetic instead of non-magnetic. they might be useful in the field of applications for devices. authorship contribution statement m. nepal: gathering information, analyzing and interpreting it, making figures and graphs, and writing the manuscript. g. poudel: gathering information, assisting with data analysis. s. aryal & a. devkota: gathering data and contributing to its analysis. h. k. neupane: developed the idea, oversaw its analysis, interpreted the findings, and thoroughly revised the manuscript. data availability if you have any questions about data reproduction, you can get the data that were used to create the figures, tables, and graphs in this paper directly from the corresponding author. declaration of competing interest the authors declare that none of the work reported in this study could have been influenced by any known competing financial interests or personal relationships. acknowledgments the authors acknowledge the condensed matter research lab cdp tu, twas research funds rg 20316, network project nt-14 of ictp/oe for the computing capacity, and prof. narayan prasad adhikari for his excellent input in reviewing the paper. references [1] l. kleinman and j. c. phillips. crystal potential and 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[52] h. x. peng, f. qin, and m. h. phan. ferromagnetic microwire composites: from sensors to microwave applications. springer, 2016. introduction material and methods results and discussion structural properties electronic properties magnetic properties conclusion bibechana vol. 20, no. 2, august 2023, 190–199 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar analysis of phytochemical, antioxidant, and α-amylase inhibition capacity of methanol extract of six plants from kaski, gulmi and rupandehi districts of nepal bimala subba1,∗, namrata subedi1, sanju parajuli2 1central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal 2botany department, central campus of technology, hattisar, dharan, nepal ∗corresponding author. email: bimalasubba@gmail.com abstract this study was designed to explore phytochemicals and biological activities of methanolic extract of six traditional medicinal plants (clerodendrum trichotomum, mallotus philipinensis, dioscorea-bublifera, rubia cordifolia, viscum articulatum) of nepalese origin. plant extracts were prepared in methanol through cold percolation. analysis of phytochemical constituent, antioxidant capacities and brine shrimp lethality assay of the test plant samples were carried out using standard methods. the 1,1-diphenyl-2-picryl hydrazyl (dpph) method was used to study antioxidant activity of different plant extracts. furthermore, starch-iodine method was used to study the inhibition effect of extract on α-amylase. phytochemical analysis showed the presence of phytochemicals like alkaloids, flavonoids, phenolic content, glycosides, reducing sugars, etc. in six medicinal plants. brine shrimp lethality assay suggested the presence of pharmacologically active compounds. total phenolic content and total flavonoid content of c. trichotomum’s leaves extract were found to be higher with 212.742 mg gae/g and 112 mg q/g respectively with strong antioxidant activity. similarly, the α–amylase inhibition of r. cardifolia’s root extract and c. trichotomum‘s leaves extract was found to be 252.44±0.55 µg/ml and 293.33± 0.81 µg/ml comparative with ic50 value 119.063±0.73 µg/ml of standard acarbose that showed remarkable antidiabetic property among six samples. the results, obtained here suggested that six medicinal plants i.e. c. trichotomum, m. philipinensis, d. deltoidea, d.bublifera, r. cordifolia, and v. articulatum, nepal origin showed biological activity by targeting multiple drug targets which justifies their traditional uses. this is the first finding that c. trichotomum‘s leaves can be a promising source for the development of natural antioxidant and antidiabetic agents. keywords c. trichotomum, m. philipinensis, d. deltoidea, d. bublifera, r. cordifolia, v. articulatum,. article information manuscript received: march 25, 2023; accepted: june 30, 2023 doi https://doi.org/10.3126/bibechana.v20i2.56226 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 190 http://nepjol.info/index.php/bibechana bimalasubba@gmail.com https://doi.org/10.3126/bibechana.v20i2.56226 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ b. subba et al./ bibechana 20 (2023) 190-199 191 1 introduction many diseases have been cured with plants by relating in various formula such as vegetables, fruit, spices, tea, decoction, etc., since ancient time. today’s modern society is slowly returning to ancient medicinal system as the number of people who still prefer using traditional folk medicines is increasing per year. plants comprise a wide diversity of compounds, especially secondary metabolites with anticancer, antibacterial, antidiabetics, antitumor, antiviral, analgesic and many other activities to a greater or lesser extent. notable examples of these secondary metabolites include phenols, flavonoids, alkaloids, terpenoids, saponins, glycosides, tannins etc. [1, 2]. antioxidants compounds have the ability to protect the body from reactive oxygen species. reactive oxygen species (ros) become toxic and cause the harmful effects like oxidative stress in absences of proper amount of antioxidants in our body. dpph scavenging (2, 2-diphenyl-1-picrylhydrazyl) assay is a popular method for screening in-vitro antioxidant of plant extract. dpph radical in methanol shows strong absorption at 517 nm. on increasing the concentration of extracts decreases the value of maximum absorbance suggest that scavenging of free radical by electron donation [3]. the types of diabetes mellitus according to the american diabetes association in 1997 are type 1, type 2, other specific types, and gestational diabetes. it is characterized by high blood sugar (glucose) levels that consequence from defects in insulin secretion, or resistant in its action, or both. normally when there is an elevated level of glucose in the bloodstream, the pancreas releases insulin which then binds a membrane protein of a cell and results a series of reactions that induce glucose transporters to move into the membrane and facilitate the movement of glucose into the cell. type 2 diabetes [t2d] is characterized by an increase in insulin resistance and decrease beta-cell function and chronic hyperglycemia. inhibition of α amylase activity is one of the alternative pathways for the control of postprandial hyperglycemia in diabetic patients. nepal has many plants with medicinal values as it is rich in biodiversity. some of them are used in traditional medicine that usually has a pharmacological or biological activity for use in pharmaceutical drug discovery and drug design and some are still not explored scientifically for medicinal values [3, 4]. the biological activities of the test plants i.e c. trichotomum, m. philipinensis, d. deltoidea, d. bublifera, r. cordifolia, v. articulatum had been reported by many research articles. although these plants are reported for their uses such antioxidant, antidiabetic, antimicrobial, reducing high blood pressure, or improving blood circulation, the same plant grown in gulmi, rupandehi, kaski district of nepal has not been explored yet. the genetic and geographical variation plays significant role for the dissimilarity of chemical constituents of the same plant. the growing stages of the concerned plant at the time of the collection also plays a role for the variation of the chemical constituents of the same plants. usually synthetic drugs contain a single active compound targeting a specific drug target but plant extracts may contain various active ingredients aiming at multiple drug targets [5]. on the basis of these reports, the present study purposes to calculate the polyphenols and flavonoids in the methanolic extract from different parts of such six medicinal plants i.e. c. trichotomum, m. philipinensis, d. deltoidea, d. bublifera, r. cordifolia, v. articulatum to determine their antioxidant potential and to evaluate its inhibitory properties on the α-amylase activities. 2 materials and methods 2.1 collection of plant materials and preparation their methanol extract various plant parts of six medicinal plants were collected from the farmland of gulmi, rupandehi, kaski district of nepal. the plants were identified with literatures and matched with the voucher specimens deposited at national herbarium and plant laboratories, godavari, kathmandu. the collected plant parts were cleaned, sliced into small pieces, and shade dried for 10-15 days. then it was ground into a powder and stored. the leaves extract of six plants was prepared by cold percolation method in methanol solvent. 2.2 chemicals and reagents the chemicals used in this study were of the commercially available analytical grade. the methanol solvent was purchased from merck, germany. similarly, porcine pancreatic α-amylase, 2,2-diphenyl1-picrylhydrazyl (dpph), and ascorbic acid were purchased from sigma-aldrich, usa. 2.3 qualitative phytochemical analysis phytochemicals were identified by various color reactions [6]. in brief, all plant materials were completely extracted by percolation with methanol and subjected to phytochemical screening. the presence of main groups of natural constituents in different extractive solutions was analyzed by using different specific reagents. b. subba et al./ bibechana 20 (2023) 190-199 192 2.4 brine shrimp lethality assay brine shrimp lethality assay was carried according to standard protocol [7]. briefly, sample stock solutions were prepared by dissolving 200 mg of each plant extract in 2 ml acetone. the test was conducted in 15 ml test tubes and sterilized artificial sea water (final volume 10 ml). from each stock solution 500 µl (equivalent to 1000 ppm), 50 µl (equivalent to 100 ppm) and 5 µl (equivalent to 10 ppm) were transferred to total nine test tubes, three test tubes for each dose level. the control was performed by adding the solvent used to dissolve the extract (acetone) in the assay. the solvent was evaporated by standing overnight. after complete evaporation of solvent, 5 ml of sea water was added to each test tube with gentle shaking to ensure that the compounds diffused adequately in the aqueous solution. ten salina nauplii were counted macroscopically in the stem of a pasteur pipette against a lighted background and transferred into each sample tube and the solutions were made to 10 ml with artificial sea water. after 24 hours, the numbers of survivor were counted with the help of disposable pipettes. the entire experiment was performed in a temperature controlled room at 28 °c under the continuous supply of light by table lamp (60 watt). the surviving nauplii were counted with the aid of a 3x magnifying glass after 24 hours. the mean mortality at the three dose levels for each extract was determined. no death was observed in the control tubes. the lc50 (lethal concentration for 50% mortality) values was determined using the probit method, as the measure of toxicity of the extracts [8]. 2.5 determination of total phenolic content in the plant extracts total phenolic content in plant extract was calculated by folin-ciocalteu colorimetric method with some modifications [9]. an aliquot of 1 ml of each leaf extract (0.5 -1.0 mg/ml) were mixed with 5 ml folin–ciocalteu phenol reagent (10%) and 4 ml of 7% na2co3 to get a total volume of 10 ml. the blue colored mixture was shaken well and incubated for 30 minutes at 40 ºc in a water bath. the absorbance of the mixture was measured at 760 nm. the samples were prepared in triplicate for each analysis and the mean value of absorbance was obtained. standard calibration curve for gallic acid in the range of 50–100 g/ml was prepared in the same manner and results were expressed as mg gallic acid equivalent (gae) per gram of extract. 2.6 determination of total flavonoid content in the plant extracts total flavonoid content was determined using the aluminum colorimetric method using quercetin as the standard [10]. an aliquot of 1 ml leaf extract of each concentration range from 0.5-1 mg/ ml in methanol was poured to 15 ml test tube containing 4 ml of double distilled water. at the 0, 5 and 6 minutes’ time interval, 0.3 ml 5% nano2, 0.3 ml of 10% alcl3 and 2 ml of 1 m naoh was added to the test tube respectively. immediately volume was maintained 10 ml by adding 2.5 ml double distill water. absorbance of the obtained pink color mixture was determined at 510 nm versus blank containing all reagents except quercetin. the samples were prepared in triplicate for each analysis and the mean value of absorbance was obtained. standard calibration curve for quercetin in the range of 50–100 g/ml was prepared in the same manner. the concentration of flavonoid was expressed as mg quercetin equivalent (qe) per gram of extract. 2.7 antioxidant assay the antioxidant activity of extract of the test plants and standard (ascorbic acid) was carried by dpph assay method, following standard protocol [11]. different concentration of plant extracts (10100 µg/ml) and ascorbic acid (10-100 µg/ml) were prepared in methanol on the clean and clear test tubes. the sample volume was taken 2 ml. to this sample volume, 2 ml of this 0.2 mm dpph solution was added. the tube was shaken vigorously for the uniform mixing. these tubes were allowed to stand in dark for half an hour. the control was prepared as above without the plant extract or ascorbic acid. methanol was used to collect the baseline on the spectrophotometer (thermo fisher scientific, genosystem-10-50. the absorbance was taken on the spectrophotometer at 517 nm. now the radical scavenging activity was calculated by using the following formula. %radical scavenging activity = controlabs − sampleabs controlabs × 100% (1) standard graph was plotted by taking the concentration on the xaxis and percentage free radical scavenging activity on the y-axis. based on this graph, ic50 value of each sample was calculated and these values of the different species were compared. the species having the lowest ic50 is considered to have the best antioxidant property. 2.8 alpha-amylase inhibition assay α-amylase inhibition assay was performed following the standard protocol [11]. this protocol is based b. subba et al./ bibechana 20 (2023) 190-199 193 on that α-amylase converts starch into sugars and plant extracts inhibits the action of α-amylase as acarbose. substrate was prepared by dissolving 200 mg starch in 25 ml of naoh (0.4 m) by heating at 100 ºc for 5 minutes and adjusting ph was adjusted to 7.0 after cooling. 400 µl of substrate solution was pre-incubated at 37 ºc for 15 min. termination of the reaction was carried out by adding 800 µl of hcl (0.1 m). then, 1000 µl of iodine reagent (2.5 mm) was added, and absorbance was measured at 630 nm. the assay was carried out in triplicates using spectrophotometer. percentage of inhibition was calculated using the formula %inhibition = ( 1− abs2−abs1 abs4−abs3 ) × 100 (2) where abs1 is the absorbance of the incubated mixture containing sample, starch, and α-amylase, abs2 is the absorbance of the incubated mixture of sample and starch, abs3 is the absorbance of the incubated mixture of the of starch and α-amylase, abs4 is the absorbance of the incubated solution containing starch. 3 results and discussion 3.1 plant collections the plants samples on this research work were selected and collected from the farmland of gulmi, rupandehi, kaski district of nepal (table 1). table1: list of plants, parts used and therapeutic use. s.n. scientific name common name used part therapeutic use 1. clerodendrum-trichotomum lapche leaves antioxidant antidiabetic antibacterial 2. mallotus-philipinensis sindoor leaves antioxidant antifilarial 3. diosocreadeltoidea vyakur rhizomes anti-inflammatory antiviral antidiarrhoic 4. dioscorea-bublifera gitto rhizomes antioxidant anti-inflammatory antidiabetic 5. rubiacordifolia majitho roots antidysentric antioxidant 6. viscumarticulatum harchur bark anticancer antioxidant table 2: phytoconstituents of test plants extract in methanol. phytochemical ct mp dd db rc va reducing sugars + + polyphenols + + + + + alkaloids + + + + + + glycosides + + + + quinones + + + + saponins + + + coumarins + + flavonoids + + + + + + where, (+) present and (-) absent, ct = c. trichotomum, mp = m. philipinensis, dd = d. deltoidea, db = d. bublifera, rc = r. cordifolia, and va = v. articulatum 3.2 phytochemical screening the results obtained from the phytochemical screening indicating the presence and absence of different types of phytoconstituents are tabulated in table 2. the different extracts of plants depict the presence of various secondary metabolites like alkaloids, glycosides, coumarins, saponins, flavonoids, terpenoides etc. these compound are supposed to be biologically active and act as anticancer, antioxidant, antidiabetic etc. [12]. due to presence of such secondary metabolites v. articulatum be the good source of such biologically active compounds and b. subba et al./ bibechana 20 (2023) 190-199 194 d. deltoidea and c. trichotomum can be inferred to be potent antioxidant, antidiabetic and antimicrobial [13–15]. flavonoids, alkaloids and phenolic compounds are a major source of compounds that act as primary antioxidants or free radical scavenger. subsequently, plants containing these phytochemicals may be used for the preparation of drug in a systematic way which may be lead to the cure of many ailments in the future [16]. so, many of selected medicinal plants can be inferred as the good source of biologically active compounds. 3.3 brine shrimp bioassay results obtained from the brine shrimp lethality assay are presented in table 3. table 3: lc50 value of plant samples in brine shrimp bioassay. name of plant extracts lc50 value µg/ml c. trichotomum 184.79 m. philipinensis 100 d. deltoidea 193.06 d. bublifera 135.93 r. cordifolia 184.79 v. articulatum 46.39 from the above calculations, sample va (bark of v. articulatum) had shown the lower lc50 value which indicates that it contains highly active compound. the result showed that lc50 of different plant extracts ranged from 46.39 to 193.06 µg/ml. v. articulatum can be inferred to have very strong cytotoxic effect. likewise, m. philipinensis, d. bublifera, c. trichotomum, r. cardifolia, and d. deltoidea were biologically active with lc50 values 100, 135.93, 184.79, 184.791, and 193.06 µg/ml respectively. so, these plants can be suggested to use as therapeutic agents as the toxicity activity on them is nominal. plant extract resulting in lc50 less than 1 mg/ml were considered toxic to the larvae. this brine shrimp lethality test was also a guide for active antitumor agent [17,18]. 3.4 total phenolic and flavonoid contents the tpc and tfc were expressed as the gae/g, and qe/g of extract using a calibration curve of gallic acid and quercetin, respectively which is shown in fig. 1 & 3. the total phenolic content of all selected medicinal plant extracts showed varied data ranging from 54.742±0.025 to 212.742±3.34 mg gae/g in c. trichotomum and d. deltoidea respectively which is shown in figure 2. the total phenol content of rest of plant extract lied between these two extremes. the results showed that the total phenolic content in c. trichotomum (ct) was highest among six selected medicinal plants. leaf extract of c. trichotomum (ct), bark of v. articulatum (va) also showed relatively high phenolic content. figure 1: calibration curve of gallic acid. figure 2: comparison of tpc in different plant extracts. b. subba et al./ bibechana 20 (2023) 190-199 195 figure 3: calibration curve of gallic acid. figure 4: comparison of tpc in different plant extracts. from the calculation of total flavonoid content in different plant extract, it was found that sample (ct) c. trichotomum has highest tfc. it was also seen that tfc in (dd) d. deltoidea was high enough. the total flavonoid content of different medicinal plants was found and the result revealed that the tfc varied from 72.39±112 mgqe/g in m. philipinensis to 109.964±1.25 mgqe/g is d. deltoidea. all the remaining plant extract showed the tfc in two extremes as shown in fig 4. the literature revealed that presence of phenols and flavonoids in plants extract had been reported to be associated with antioxidative action in biological system, acting as scavengers of singlet oxygen and free radicals. thus, greater tpc and tfc had positive correlation with greater antioxidant activities. in this study, the high value tpc (212±2.742 mgqe/g) and tfc (112±2.42 mgqe/g) could be attributed to antioxidant property of c. trichotomum [19]. 3.5 dpph free radical scavenging activity the free radical scavenging activity of methanol extractives of c. trichotomum, m. philipinensis, d. deltoidea, d. bublifera, r. cordifolia, and v. articulatum were evaluated by dpph assay. table 4 show the value of % dpph free radical scavenging activity at different concentrations of ascorbic acid, c. trichotomum, m. philipinensis, d. deltoidea, d. bublifera, r. cordifolia, and v. articulatum. the graph of concentration against the corresponding percentage radical scavenging activity of different samples was plotted fig 5 and ic50 value was determined. ascorbic acid was used as the standard in this experiment. among six different plant extract, methanol extract of leaves of c. trichotomum had the ic50 value 40.62±0.16 g/ml and rhizome of d. deltoidea had the ic50 value 41.18±0.81 very close to that of ascorbic acid i.e. 26.64±0.14 g/ml respectively. remaining plants m. philipinensis’s leaves (60.45 ± 0.99 g/ml), v. articulatum’s bark (63.12±0.85g/ml), d. bublifera’s rhizome (69.58±0.15 µg/ml), r. cordifolia’s root (89.71±0.13 µg/ml) extract had moderate antioxidant activity table 5. literature revealed that the majority of the antioxidant activity is due to the flavones, isoflavones, flavonoids, anthocyanin, coumarins, lignans, catechins and isocatechins. the obtained ic50 of methanolic extract of test samples are supported by previously reported value of the same plants from different region with slight variation in value [20, 21]. compounds like trichotomoside (phenylpropanoid glycoside), isoacteoside, jionoside d had been isolated and proved to be responsible for the antioxidant activity of c. trichotomum [22–24]. strong antioxidant activity for acetone and ethanol extract of v. articulatum bark had been reported by kakpure, 2020 [25]. while weak antioxidant activity of methanol extract of v. articulatum bark extract had been reported for plant collected from kathmandu valley by kumal et al 2020 [26]. b. subba et al./ bibechana 20 (2023) 190-199 196 table 4: % inhibition of ascorbic acid, ct, mp, dd, db, rc, va at different concentrations concentration % inhibition (µ g/ml) ascorbic acid ct mp dd db rc va 20 64.06±0.56 52.5±3.23 35.97±0.85 64.37±0.51 45.23±2.82 1.54±4.04 23.73±2.34 40 75.45±0.05 61.76±2.74 45.27±2.65 65.52±0.08 50.59±2.8 2.97±3.63 55.49±7.74 60 86.79±0.06 69.86±1.52 55.52±0.52 64.85±1.33 51.27±2.86 20.91±2.56 57.99±0.65 80 92.5±0.06 75.40±2.17 60.44±0.99 64.22±3.31 52.44±2.85 54.89±2.01 58.49±19.25 100 94.06±1 78.09±0.64 65.23±0.66 65.55±0.20 52.77±3.73 59.02±3.56 59.62±23.22 figure 5: a plot of % free radical scavenging of methanol extracts against concentration of plant extract, and ascorbic acid. ic50 values of the plant extracts along with the standard ascorbic acid is tabulated below in table 5. table 5: comparison of ic50 values of different plant extracts with ascorbic acid sample ic50 (µg/ml) ascorbic acid 26.64±0.14 c. trichotomum 40.62±0.16 m. philipinensis 60.45±0.99 d. deltoidea 41.18±0.81 d. bublifera 69.58±0.16 r. cardifolia 89.71±0.13 v. articulatum 63.12±0.91 ic50 values are expressed as mean±sd (n = 3) 3.6 alpha-amylase inhibition test alpha-amylase inhibitory activity of plant extracts was determined from quantitative starch-iodine method. alpha-amylase inhibition % values at different concentrations of standard acarbose and six plant extracts are shown in the below table 6. the graph of concentration against the corresponding percentage radical scavenging activity of different samples was plotted fig 6 and ic50 value was determined. the percentage inhibition of different plant extracts versus concentration and antidiabetic activity in term of ic50 values of different extract are given in table 7. table 6: % inhibition at different concentrations of plant extract. concentration % inhibition (µg/ml) acarbose ct mp dd db rc va 40 53.07±1.02 30±0.29 22.89±4.89 13.81±3.06 45.01±3.99 60.96±3.05 37.37±5.33 80 60.73±0.95 41±0.82 30.46±0.39 13.61±1.23 59.01±3.5 63.09±3.09 53.56±0.25 160 67.12±0.95 49±1.13 40.22±0.20 18.77±3.42 57.31±2.4 57.21±2.01 57.12±2.8 320 81.31±0.59 65±5.47 45±2.56 32.08±2.42 62.46±3.2 75.20±1.89 54.92±0.21 640 88.20±0.58 70±0.29 47.24±4.21 38.92±1.23 64.16±4.5 70.52±1.55 56.1±0.69 where ct = c. trichotomum, mp = m. philipinensis, dd = d. deltoidea, db = d. bublifera,rb =r. cardifolia, va = v. articulatum. mean % inhibition are expressed as means±sd (n = 3). b. subba et al./ bibechana 20 (2023) 190-199 197 figure 6: inhibition of α-amylase activities by plant extracts. ic50 values of the six plant extracts along with the standard acarbose is tabulated below in table 7. table 7: comparison of ic50 values of different plant extracts with standard acarbose sample ic50(µg/ml) acarbose 119.063 ± 0.73 clerodendrum trichotomum 293.33 ± 0.81 mallotus philipinensis 554.18 ± 0.75 dioscorea deltoidea 785.15 ± 0.92 dioscorea bublifera 352.71± 0.59 rubia cordifolia 252.44 ± 0.55 viscum articulatum 344.58 ± 0.61 ic50 values are expressed as mean±sd (n = 3) here, ic50 value of standard acarbose was found to be 119.063 ± 0.73 µg/ml. c. trichotomum, m. philipinensis, d. deltoidea, d. bublifera, r. cardifolia, v. articulatum showed α-amylase inhibitory activity with ic50 value 293.33±0.81 µg/ml, 554.18±0.75 µg/ml, 785.15±0.92 µg/ml, 352.71±0.59 µg/ml, 252.44±0.55 µg/ml, 252.44± 0.55µg/ml respectively in table 7. there was a dose dependent increase in percentage inhibitory activity against α-amylase by all the six plant extracts. the result obtained here are in good correlation with previously reported results [27,28]. strong antioxidant and antimicrobial activity of leaves of c. trichotomum collected from dhankuta had been reported by subba et al, 2016 [29]. among six medicinal plants, leaves of c. trichotomum is found to be good property as antidiabatic, antioxidant, phenolic and flavonoid content with low cytotoxic effect. 4 conclusion the present study revealed that the methanolic extract of the c. trichotomum’s leaves, m. philipinesis’s leaves, d. deltoidea’s root, d. bublifera’s root, r. cardifolia’s stem, v. artculatum’s bark has notable antioxidant potential and inhibitory activity on the α-amylase enzyme. these effects would be due to its important phenolic composition, whose quantitative study has revealed the varied presence of polyphenols and flavonoids. these results could justify the use of these plants in traditional medicine for the treatment various health problem including type 2 diabetes and complications. our study is the first examination of anti-α-amylase capacities of c. trichotomum leaves extract. study of chemical constituents of these plants using sophisticated technologies like nmr, hplc, etc. can provide a way for extensive research that can be used for commercial drug production with lesser or no side effects. acknowledgement central department of chemistry, tribhuvan university, kirtipur. references [1] yizhong cai, qiong luo, mei sun, and harold corke. antioxidant activity and phenolic comb. subba et al./ bibechana 20 (2023) 190-199 198 pounds of 112 traditional chinese medicinal plants associated with anticancer. life 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[29] b. subba, c. srivastav, and r. c. kandel. scientific validation of medicinal plants used by yakkha community of chanuwa vdc, dhankuta, nepal. springerplus, 5:155, 2016. introduction materials and methods collection of plant materials and preparation their methanol extract chemicals and reagents qualitative phytochemical analysis brine shrimp lethality assay determination of total phenolic content in the plant extracts determination of total flavonoid content in the plant extracts antioxidant assay alpha-amylase inhibition assay results and discussion plant collections phytochemical screening brine shrimp bioassay total phenolic and flavonoid contents dpph free radical scavenging activity alpha-amylase inhibition test conclusion bibechana vol. 22, no. 3, december 2025, 237-247 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar exploring the structural, mechanical, dynamical, thermal, electronic, magnetic, and optical properties of monolayer wte2 compound: first-principles study sukrit kumar yadav, tejendra neupane, arpan pokharel, kamal khanal, karan deuba, om shree rijal, hari krishna neupane∗ amrit campus, institute of science and technology, tribhuvan university, kathmandu nepal ∗corresponding author. email: hari.neupane@ac.tu.edu.np abstract the potential applications of materials are determined by their existing properties. in this work, we used first-principles approach to investigate the structural, mechanical, dynamical, thermal, electronic, magnetic, and optical properties of (3×3) supercell structure of tungsten ditelluride (wte2) compound using gga-pbe functional of density functional theory (dft) method. structural properties of wte2 compound are studied by measuring bond lengths between the atoms in structure, and ground state energy. it is found to be structurally stable material. electronic band structure and density of states (dos) plot shows that the material has direct band gap p-type semiconductor. magnetic properties of wte2 compound are predicted by the analysis of its density of states (dos) and partial density of states (pdos) plots, material is found to be non-magnetic in nature. the mechanical properties of considered compound are examined by the calculations of its modulus of rigidities, elastic constants, elasticity and anisotropy index. wte2 has ductile and anisotropic properties. moreover, we have examined the dynamical stability of considered material through the phonon dispersion curve, it reveals that wte2 is dynamically stable material. based on the calculations of phonon velocities and debye temperature, it is found that wte2 has low value of specific heat capacity. dielectric function, optical conductivity, absorption, transmission, and reflection coefficients of wte2 compound are examined for the exploration of its optical characteristics. at higher photon energy region, wte2 has transparent and anisotropic in nature, higher value of conductivity, lower values of absorption and reflection coefficient. hence, it can be used in the fields of electronic, optoelectronic, sensing, and energy storage devices. keywords dynamical, electronic, magnetic, mechanical, optical, thermal. article information manuscript received: march 5, 2025; revised: june 20, 2025; accepted: august 4, 2025 doi https://doi.org/10.3126/bibechana.v22i3.76349 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 237 http://nepjol.info/index.php/bibechana hari.neupane@ac.tu.edu.np https://doi.org/10.3126/bibechana.v22i3.76349 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ sukrit kumar yadav et al./ bibechana 22 (2025) 237-247 238 1 introduction two-dimensional (2d) materials are made up of a single or few layers of having a thickness of a few nanometers or less [1,2]. graphene, transitionmetal dichalcogenides (tmdcs) materials, hexagonal boron nitride (h-bn) etc. are the common examples of 2d materials [3–5]. tmdcs materials are the types of 2d materials having a structure of the form mx2, where m represents transition metals from group iv-x (w or mo), and x represents chalcogens material (te, s, or se) [6]. m is sandwiched between two layers of x atoms by forming the x-m-x honeycomb pattern [7]. there is a strong covalent bond between the atoms in each layer, but the layers are stacked together by weak van der waals forces [8]. tmdcs pose exceptional catalytic [9], photoluminescence [10] direct band gap, and water resistance properties [11]. so, they are used in the field of electronics and nanoelectronics for making devices such as transistors, integrated circuits (ics), and memory devices [9, 10]. they are used in flexible and wearable electronics, spintronics, quantum computing, and spin hall effect devices [12]. similarly, they are used in energy storage devices like batteries and capacitors, hydrogen evolution reactions, electrocatalysis, gas sensors, biosensors, thermoelectric devices, water purification technologies, and solid lubricants [13]. tmdcs are used in optoelectronic devices and photo detectors due to its tunable band structure [14, 15]. thus, 2d materials have potential applications in the fields of industrial as well as academic sectors. we have reviewed the various literature related with the tmdcs materials [16, 17] it is found that bulk wte2 has large magnetoresistance and finds application in magnetic sensors and memory devices. to our best knowledge, a comprehensive study of structural, mechanical, dynamical, thermal, electronic, magnetic, and optical properties of monolayer wte2 tmdcs material have not been studied well. these are the research gaps between the previous researcher’s works and our work. the tunability of these properties of tmdcs has made them a topic of great research. so, we are motivated to explore the structural, mechanical, dynamical, thermal, electronic, magnetic, and optical properties of (3×3) monolayer supercell structure of 2d wte2 tmdcs compound computationally by using density functional theory (dft) method employing quantum espresso as a computational tool. 2 methods and material first-principles calculations based on plane wave function and ultrasoft pseudopotentials (uspps) are performed using the density functional theory (dft) technique by employing the quantum espresso as a computational tool [17]. to handle the exchange-correlation interactions, we employed the generalized gradient approximation (gga) in perdew-burke-ernzerhof (pbe) form [18,19]. firstly, we have constructed the optimized and relaxed unit cell structure of wte2 material by using the optimized values of lattice parameter 12 bohr (6.35 å), kinetic energy cutoff 45 ry (612.25 ev), and k-points (12) through broyden–fletcher– goldfarb–shanno (bfgs) method [20]. the kpoint grid of mesh (12×12×1) is used to sample brillouin zone by using -centered monkhorst– pack (mp). the optimized and relax structure unit cell structure of wte2 is extended three times along x-and y-directions to form (3×3×1) monolayer supercell structure of wte2. then after relax calculations are done by using broyden–fletcher– goldfarb–shanno (bfgs) method [20], which gives the optimized and relax supercell structure of wte2. this structure is used for further calculations. the structural properties of considered material are studied by the calculations of its ground state energy through self-consistent field (scf) calculations where (12×12×1) k-point mesh is used. for the study of material’s electronic and magnetic properties, band structure, density of states (dos) and partial density of states (pdos) calculations are done. for this denser mesh (22×22×1) is used since denser mesh gives the smoother dos states. the mechanical and thermal properties of material are examined by the calculations of its modulus of rigidity and elastic constants through voigt-reusshill approach [21]. based on the computed values of elastic constants, we have estimated the shear modulus (g), bulk modulus (b), young’s modulus (e), poisson’s ratio (v), pugh’s ratio (b/g), debye temperature (d), longitudinal phonon wave velocity (vl), transverse phonon wave velocity (vt), and average phonon wave velocity (vavg). additionally, density functional perturbation theory (dfpt) techniques are used to analyze the dynamical properties of the materials under consideration [22]. the optical properties of wte2 compound are studied by calculating it dielectric function, optical conductivity, transmission, reflection and absorption coefficient through the uses of time-dependent ground state perturbation theory under random phase approximation (rpa) [23]. 3 results and discussion in this section, we have discussed the major findings and their interpretation of (3×3) monolayer supercell structure of 2d wte2 tmdcs compound. sukrit kumar yadav et al./ bibechana 22 (2025) 237-247 239 3.1 structural properties the structural properties of wte2 unit cell compound are studied by calculating its optimized values of kinetic energy cutoff, lattice parameters, and k-points. they are found to be 45 ry, 6.35 å, and 12 respectively. then, relax calculations are done by using (12×12×1) k-point mesh. the relax and optimized unit cell structure is extended along x-and y-axis by three times to construct its (3×3) supercell structure. the ground state energy of supercell structure is estimated through its selfconsistent fields (scf) calculations, and found to be -238.10 ev. this minimum value of ground state energy revels that wte2 is a stable material. the optimized and relax structure of wte2 supercell is shown in figure-1(a & b). figure 1: (colour online) (a) top view of (3×3) supercell structure of wte2 compound (b) side view of (3×3) supercell structure of wte2 compound. table 1: inter-atomic distance between w-w, w-te, and te-te before and after relaxation compared with previously reported values. bond length before relaxation (å) after relaxation (å) reported values (å) w–w 3.57 3.32 3.55 w–te 2.73 2.53 2.73 te–te 3.57 3.23 [24] figure-1(a) is the top view of the monolayer wte2 supercell compound from z-axis. the unit cell is hexagonal structure with alternating w and te atoms arranged in hexagonal shape. figure-1(b) shows the side view (i.e. x-axis or y-axis) of wte2 supercell material. in this view, the layer of w is sandwiched between two te layers. table-1 summarizes the bond lengths before and after the relaxation of a considered compound. before relaxation, the inter-atomic distance between adjacent w-w, w-te, and te-te atoms are found to be 3.57 å, 2.73 å, and 3.57 å respectively. whereas after relaxation the inter-atomic distance reduces to 3.32 å, 2.53 å, and 3.23 å respectively of these atoms in a structure. these values are closely agreed with the previously reported values of stable tmdcs materials [24]. hence, from these calculations, we confirmed that our considered material is a structurally stable. 3.2 mechanical, dynamical and thermal properties mechanical behavior of wte2 compound such as stiffness, deformation response, and stability under different external loads are determined by the measurement of parameters like elastic constants and modulus of rigidities (young’s modulus, shear modulus, bulk modulus), and compressibility (β). approximations like voigt (v) [25], reuss (r) [26], and hill [27] are used to calculate these mechanical parameters. the voigt model assumed uniform strain throughout crystal and calculated the upper bound of the elastic moduli whereas reuss model assumed a uniform stress across the material and calculated the lower bound of the elastic moduli. hill model calculated the parameters by averaging the results obtained from formed two models. the bulk modulus (b) measures the material’s resistance to uniform compression. in case of hexagonal system, it is determined by averaging the bulk modulus of elasticity from the voigt (bv) and reuss (br) models and given by; bh = 1 2 (bv +br) (1) the shear modulus (sh) measures the material’s resistance to shearing forces. it is determined by averaging the shear modulus from the voigt (sr) models; sh = (sv + sr) (2) for hexagonal crystal systems, the voigt approximations for the bulk modulus bv and shear modulus sv are expressed as; bv = 1 9 [2 (c11 + c12) + 4c13 + c33] (3) sv = 1 30 [ (c11 + c12) + 2c33 − 4c13 + 12c44 + 12c66 ] (4) sukrit kumar yadav et al./ bibechana 22 (2025) 237-247 240 for the reuss approximation, the bulk modulus br and shear modulus sr are defined as; br = (c11 + c12)c33 − 2c2 13 c11 + c12 + 2c33 − 4c13 (5) sr = 5 2 (c11 + c12)c33 − 2c2 13 [3bvc55c66 + (c11 + c12)c33 − 2c2 13] 2 (c55 + c66) (6) the compressibility (β) measures how much the material’s volume changes under pressure and it is given by the inverse of the bulk modulus (b) i.e. β = 1/b. for pristine wte2, young’s modulus (y) is an important mechanical property that indicates the material’s stiffness or rigidity. it measures how much wte2 deforms under stress, providing insight into its ability to resist elastic deformation. a higher young’s modulus means that wte2 is stiffer and deforms less under a given load. young’s modulus can be determined using the hill approximation, which is approximate for polycrystalline materials like wte2. the formula for young’s modulus is; y = 9bhsh 3bh + sh (7) where bh is the hill bulk modulus, which quantifies wte2’s resistance to uniform compression and sh is the hill shear modulus, which describes wte2’s resistance to shearing forces. by applying this formula, we can accurately assess how the pristine wte2 will behave under mechanical stress. for wte2, elastic anisotropy (a) measures the variation in stiffness with direction. it reflects how mechanical properties like stiffness and deformation change depending on the direction of applied force. high anisotropy (a) means wte2 behaves differently along different crystallographic directions. for hexagonal systems, it is expressed as [28]; a = 4c44 c11 + c33 − 2c13 (8) poisson’s ratio (ν) is calculated using an equation (9); ν = 3b − 2sh 2 (3b + sh) (9) the calculated values of various parameters for the examination of mechanical properties are mentioned in the table-2. table 2: estimated values of bulk modulus (b), young’s modulus (y), shear modulus (g), poisson’s ratio (ν), p-wave modulus, and pugh’s ratio (b/g) of wte2 compound. mechanical properties voigt reuss hill bulk modulus b (gpa) 14.78 -0.73 7.03 young’s modulus y (gpa) 24.74 -2.57 10.85 shear modulus g (gpa) 10.13 -1.40 4.37 poisson’s ratio (ν) 0.22 -0.08 0.24 p-wave modulus (gpa) 28.29 -2.60 12.85 pugh’s ratio (b/g) 1.46 0.52 1.61 the bulk modulus (b) of wte2 is found to be 7.03 gpa which indicates that it requires 7.03 gpa to uniformly compress its volume by 1%. hence, it is relatively compressible compared to other materials like diamond [29]. the young’s modulus (y) of wte2 is 10.85 gpa means that it is relatively flexible as compared to the material with higher young’s modulus such as steel [30]. the shear modulus (g) of wte2 is calculated as 4.37 gpa indicates that it is relatively soft in the resistance compared to the material like steel which has shear modulus of 80 gpa. a poisson’s ratio (ν ) of wte2 is found to be 0.24, which indicates that the contraction in perpendicular direction at 24.3% of the rate of elongation when stretched out in one direction. this is moderate value. it has a p-wave modulus 12.85 gpa, which means that it can efficiently transmit compressional waves. the pugh’s ratio (b/g) of wte2 material is found to be 1.61, it suggests that the material is relatively ductile [31–33]. furthermore, the kleinman’s parameter is calculated to be 0.45 which is less than the reference value 0.5 that determines the type of deformations when external perturbations are applied. thus, it suggests that bond bending is more dominant than bond stretching [31–33]. the dynamical properties (stability) of the material are determined by studying its phonon dispersion curve. phonon dispersion curve measures how the phonon frequencies (measured in terms of wavenumber) vary with wave vectors across the brillouin zone [34]. figure-2 shows the phonon sukrit kumar yadav et al./ bibechana 22 (2025) 237-247 241 dispersion curve of wte2 compound, where wave numbers (frequency) are plotted along y-axis and wave vectors (symmetric points) are along x-axis. the graph does not show any negative wavenumber which indicates the absence of negative frequency. thus, the material is found to be dynamically stable. the lower three bands are for acoustic phonons whereas the upper six bands are for optical phonons. the acoustic phonons at the center of brillouin zone (i.e. γ point) have zero frequencies. but the optical phonons have non-zero frequencies and are found to be 3.55, 5.27, 5.76, and 7.16 in units of per centimeters. the above results are consistent with previous studies [35,36]. it is seen that there is phonon band gap energy of values 0.30 per centimeter, which is calculated from the lower position of optical branches and upper position of the acoustical branches. moreover, we have investigated the thermal properties of wte2 compound by estimated its phonon velocities and debye temperature. for that we have estimated the longitudinal velocity, transverse velocity and average velocity of phonon wave of wte2 material. they are found to be 1665.76 m/s, 971.05 m/s, and 1077.12 m/s respectively. we have estimated the debye temperature of wte2 material, and found to be 85.6 k. it reflects that wte2 has a low melting point and has low value of specific heat capacity. 3.3 electronic and magnetic properties the wave functions that describe the electrons in solid can be studied by sampling on the brillouin zone (bz). highly symmetric points in the bz are used to study the material’s band structure. in the present work, we have studied the electronic properties of pristine wte2 compound with the help of band structure and density of states (dos) plots. figure-3(a & b) respectively represent the band structure and dos plots of considered material, where the horizontal dot line indicates the fermi energy level. it separates the electronic bands. the region below the fermi line is called valence band, and above the fermi line is called conduction band. figure-3(a) is the band structure of wte2 compound with high symmetric points are in the x-axis and fermi energy level is adjusted in the unit of ev along y-axis. the blue dashed line set at 0 ev is the fermi energy level. the plots in red lines (states) represent the band states of the electrons located at different points in brillouin zone. the region below the fermi level are valence bands, and the region above the fermi level are conduction bands. the plot shows a clear gap between the valence band maxima and conduction band minima. thus, monolayer wte2 shows semiconductor nature. from the calculations, the value of conduction band minimum (cbm) is found to be 0.95 ev, and the valence band maximum (vbm) is 0.04 ev both lying at symmetric points. thus, the band gap, defined as the gap between vbm and cbm, is calculated to be 0.99 ev. this value is consistent with previous reported values of materials that is in the range of (0.70 -1.18) ev. this material has direct band gap energy because cbm and vbm both lie at point which signifies that the inter-band transition of electrons happened without change in momentum. the valence band is closer to fermi level than the conduction band, this suggests the higher probability of finding holes in the valence band and material shows p-type semiconductor behavior. finally, we can conclude that pristine monolayer wte2 is a p-type and direct band gap semiconductor, and thus it has potential applications in semiconductor industries. table 3: valence band maximum (vbm), conduction band minimum (cbm), band gap energy (eg), and fermi energy (ef ) in units of ev for wte2 monolayer system. vbm (ev) cbm (ev) eg (ev) ef (ev) 0.05 0.94 0.99 0.98 figure 2: (colour online) phonon dispersion curves of wte2 compound, where frequency in term of wave numbers is plotted in y-axis and highly symmetric points are taken along the x-axis. vertical dot lines touch the highly symmetric points. sukrit kumar yadav et al./ bibechana 22 (2025) 237-247 242 figure 3: (colour online) (a) band structure of wte2 compound where high symmetric points are taken along the x-axis and corresponding energy are taken in y-axis. (b) density of states (dos) plot of wte2 compound where energy of dos states is taken along the y-axis and dos states are taken along the x-axis. the horizontal dot line represents the fermi energy level for both plots. figure-3(b) represents the dos plot of wte2 compound, where energy levels are plotted along y-axis and corresponding dos states are plotted along x-axis. the blue dashed horizontal line at 0 ev separates the upper conduction band from the lower valence band. there is a gap between valence band and conduction band of value 0.91 ev. this verifies the findings from band structure. near the immediate fermi region, both in conduction and valence band, the dos value is dominated due to w atoms. this suggests that near fermi energy level greater quantum states that are available to be occupied are due to w atoms. dos and partial density of states (pdos) calculations are used to explore the magnetic properties of material [37, 38]. pdos is the measurement of dos contributed by each sub-orbitals present in the material. electrons with opposite spin couples and the magnetic moment becomes zero leading to nonmagnetic nature. but, the presence of an unequal number of quantum states at a particular energy level, few electrons remain uncoupled contribute a non-zero magnetic moment which leads to magnetic properties. the pdos plot of wte2 compound is shown in figure-4, where energy values of electronic states are plotted along x-axis and corresponding states are plotted along y-axis. the vertical blue dashed line at 0 ev represents the fermi energy level situated at the boundary of the left valence band region and right conduction band region. the horizontal dot lines separate the distributed up-spin and down-spin states of electrons in the individual orbitals of atoms present in the material. figure 4: (colour online) partial density of states (pdos) plot of wte2 compound, where horizontal dot lines separated the up and down spin states and vertical dot line distinguish the valance band region and conduction band region and is called fermi energy level. tungsten (w) has electronic configuration [xe] 4f14 5d4 6s2 where xe represents xenon atom and tellurium (te) atom is [kr] 4d10 5s2 5p4. the contribution due to sub-orbitals present in valence shell has been plotted. the top plot is the total pdos plot of considered material. the graph is symmetrical along the horizontal line; that suggests the presence of equal number of states available for both up-spin and down-spin electrons at a given energy level. thus, the net magnetic moment of the system is zero and the material shows non-magnetic properties. the middle plot is the pdos plot of w atoms. the d-orbitals in w atom has higher pdos values as compare to its p and s-orbitals. the suborbital 5dx 2 has prominent values of pdos states near the fermi energy level whereas the sub-orbital 5dz 2 have dominant value of pdos. it means, a greater number of unoccupied pdos states are seen near the fermi energy level. the bottom plot is the pdos of te atoms. in this case, p-orbitals have larger contribution for the production of magnetic moment. near the fermi energy level, pdos states of 4pz sub-orbitals have higher peaks than the pdos states of s sub-orbitals. they reflect that there are a greater number of unoccupied orbitals are presented. the contribution of magnetic moment is due to the paring of up-and down-spins states. pdos states of both w and te atoms are symmetrical distributed around the fermi energy level in the plots. thus, it can be concluded that the net magnetic moment contributed by w and te atoms have zero. hence, the material shows nonmagnetic properties. sukrit kumar yadav et al./ bibechana 22 (2025) 237-247 243 3.4 optical properties when a material is exposed to electromagnetic (em) waves, many phenomena such as reflection, transmission, polarization of charges etc. are occurred [17]. a meticulous study of these phenomena can help to explore the potential usage of the materials in optoelectronics, energy storage, and sensing devices [26,39]. in this section, we discussed the optical properties of wte2 compound by the analysis of its dielectric function, optical conductivity, transmission, reflection and absorption coefficient. we have calculated dielectric tensor with the variation of photon energy in the range of 0 ev to 8 ev, for the study of material’s dielectric function (constant). dielectric tensor measures the dielectric constant in response to an applied electric field of material in a particular plane. the real and imaginary components of dielectric function are expressed by the relation: ε(ω) = ε1(ω) + iε2(ω) [40]. figures-5(a & b) are the imaginary and real dielectric function with respect to the photon energies plots of wte2 compound respectively, where dielectric function are taken along the y-axis and corresponding photon energy (ev) are taken in xaxis. these plots also show the variation of dielectric properties when an applied electric field is perpendicular (εzz) and parallel (εxx) and (εyy) to the plane of the material. figure-5(b) shows the elements of the real part of the dielectric tensor, which indicate the degree of dipole polarization (and thus energy-storing capacity) caused by the applied electric field [41]. polarization depends on the relative orientation of electric field to the plane of the material, where charges response due to the applied electric force. in 2d materials like monolayer wte2, there is a strong in-plane covalent bond with dense electron clouds. an applied electric field lies parallel to the plane, which caused the high polarization. whereas in the case of between layers, two layers are bounded due to weaker van der waal’s force with less electron distribution. hence, the applied electric field acted perpendicularly on the plane of material, which causes comparatively low polarization. that explained the higher value of εxx and εyy than εzz which are depicted in figure5(b). at zero frequency, there is a finite static dielectric constant of magnitude 7.87 (of εxx = εyy) and 2.69 (of εzz) raised due to strong covalent bonding and van der waals interaction. at lower frequencies of applied electric field, the charges can polarize effectively without any lag which gives the higher value of εxx, εyy and εzz in that frequency range. with the increase in frequency, charges with higher masses lag to polarize and thus resulting in a decreased polarization. it explains the decreasing value of dielectric function, and hence εzz becomes zero at 4.65 ev. the εxx and εyy of real dielectric functions become zero at 3.47 ev while εxx and εyy of imaginary dielectric functions show peaks at 3.47 ev. at that energy, the charge oscillators resonated with the applied electric field, and leading to no net polarization. hence, real dielectric function plots equal to zero. that phenomenon results maximum energy absorption. in the negative region, the material does not store energy. at higher energies, ε1 reached to zero which is due to rapid response of electron for the oscillation of electric field. it signifies that monolayer wte2 becomes transparent to high energy photons. similar results are obtained in previous computational and experimental studies of other tmdcs materials [42]. these unique properties of wte2 can be exploited in photonic and energy storage devices. the imaginary part of the dielectric function ε2 in figure-5(a) represents the energy loss (or absorption) of photons due to lagging response of electrons to the electric field (or inter-band transitions) [43]. the imaginary part of dielectric function also showed anisotropic properties. in layer, strong covalent bonding and denser electron cloud results greater energy loss and absorption than that of the out-plane region. it explained the higher value of εxx = εyy than εzz. the dielectric constant rises from zero to maximum value with several peaks and dips gradually falling back to zero with the increasing photon energy values of material. in the energy range below the band gap energy (0.99 ev) value, the dielectric function is determined to be zero. it is signifying that there are no excitonic transitions [44], and hence electrons polarize well in response to the slow changing electric field without any lag. when the energy of photons increased beyond 0.99 ev, the energy becomes sufficient for electronic transitions from valence band to conduction band. that explains the sudden increases the graph after energy more than band gap energy. at energy 2.05 ev, distinct peaks can be seen in the graph which showing the absorption of energy due to inter-band electronic transition. a dip region can be seen at energy 2.71 ev, representing the electron unavailability of transition states around this energy range. it could be explained by the change the electronic structure of material. the peaks at 4.65 ev of εzz, at 3.47 ev of εxx and εyy are obtained due to energy loss caused by resonance of charged oscillators and electric field. the material became transparent in increasing value of photon energy because there is not transition of photon in the region. this means, no energy loss occurred as a result the graph approaches to a zero value is shown in figure-5. our obtained results are liked similar with the results obtained by others authors in the reported literature [45]. when light interacts with electrons in a substance, an oscillating electric field is created, which explains optical conductivity. the induced cursukrit kumar yadav et al./ bibechana 22 (2025) 237-247 244 rent density j(ω) is given due to the oscillating electric field which is calculated as the product of optical conductivity σ(ω) and the applied electric field e(ω). it is expressed by the relation: j(ω)=σ(ω)ε(ω), where ω is the angular frequency of the applied field . studying optical conductivity is crucial to understanding how well a material can conduct electricity or release energy when exposed to light. optical conductivity is also a complex quantity that is σ (ω)=σ ′ (ω)+iσ ′′ (ω), where σ ′ (ω) is the real part measuring energy loss due to absorption and σ ′′ (ω)) is imaginary part measuring reactive components relating to energy storage and phase shift [22]. in the present work, we have calculated the optical conductivity of wte2 monolayer material. the real part of optical conductivity is related to the imaginary part of dielectric function. these two quantities are related by maxwell’s equation [23], σ ′ (ω)=ω ε0 ε2(ω). where ε0 is the permittivity of free space. thus, the plot of these two quantities is similar evident from figure-5(a) and figure-5(d). in figure-5(d), the real optical conductivity is plotted against increasing energy of light. below 0.99 ev (i.e. band gap energy value), the graph is flat and equal to zero. it suggests no electric current, hence absence of excitonic states. but, as the energy is increased above band gap energy value, the graph sharply increased. it represents the increasing conductivity. a sharp peak in graph at 2.05 ev is due to increase conductivity caused by inter-band electronic transition. an increased conductivity can be seen within the range 3 ev to 4 ev which is due to resonance of electrons with the electric field. conductivity is unaffected by additional light energy because electronic transitions are uncommon at this level. the imaginary optical conductivity σ2(ω) is related to the real part of dielectric function. figure5(c) shows the variation of imaginary optical conductivity (plotted along y-axis) with the increasing photon energy (plotted along x-axis). as the photon energy increases, the value of σ2(ω) decreases gradually below zero and makes a peak at 1.82 ev photon energy. further increasing the photon energy results in an increase in the curve below zero, and the curve touches the zero level at energy 3.32 ev. beyond this, the graph increases in the positive region making peaks and dips representing the intensity of polarization in the material. additionally, we have discussed about the absorption, reflection and transmission coefficient a material through the analysis of its photon energy plots which are shown in figure-6(a-c) respectively. at lower frequency (below band gap energy 0.99 ev), the absorption coefficient is reached zero as shown in figure-6(a). it suggests that there is no energy loss and inter-band electronic transition because there is only occurred excitonic transitions. hence, zero absorptance is possible below the energy of 0.99 ev. phonon assisted transition and inter-band electronic transition in the region of photon energy greater than 0.99 ev. thus, the absorption curve increases with increase the frequency having certain peaks. they are representing electronic transitions from valence band to conduction band. at energy 2.10 ev, a significant peak can be observed in absorption curve which is due to interband transition of electrons. a significant absorption of energy can be seen within the energy range 3 ev to 4 ev because in that region greater amount of energy loss of a material due to the resonance of electrons. beyond 4 ev photon energy, the absorption curve gradually decreases to zero because at higher energy inter-band transitions become unlikely and the materials become transparent. transmission coefficient of material is explored by carefully interpretation by the variation of transmission coefficient with the values of photon energy, which is shown in figure-6(b). transmission curve is symmetrical and inversely related to both absorption and reflection coefficient curves. the absorption or reflection curves are increased due to the decrease the value of transmission coefficient of a material and vice versa. it is also found that 100% transmissivity of material is seen below the value of photon energy 0.99 ev. this is due to no interaction between electrons and photons for inter-band electronic transition. but, energy of the photon is increased, the inter-band electronic transitions are occurred, and transmissivity of the material decreases which are illustrated in figure-6(b). decreasing the transmission coefficient of a material is due to existence of inter-band transition and resonance of electrons at 2.10 ev, and within (3-4) ev energy range respectively. the energy of photon is further increased beyond 4 ev, which reflects that there will be less value of reflection coefficient of a considered material. reflectivity represents the fraction of incident light that gets reflected from the surface of a material [31–33]. the figure-6(c) represents the variability of reflectivity of the material against the energy of the incident photons. below the photon energy 0.99 ev, the reflection curve is horizontal and equal to zero. it indicates, no reflection of incident photons. the reflection curve suddenly raised with increase of its photon energy because of increasing the interaction between photons and electrons. different peaks of reflection coefficient are seen at 1.99 ev and in between (3-4) ev photon energy. they happened as a result of a severe electron transition that caused a large amount of photon reflection. but, at high energy region, reflection coefficient approaches to zero value of photon energy which, indicates the decreasing the reflectivity. sukrit kumar yadav et al./ bibechana 22 (2025) 237-247 245 figure 5: (colour online) plots of dielectric function and optical conductivity with phonon energies, (a) imaginary part of dielectric function, (b) real part of dielectric function, (c) imaginary optical conductivity, and (d) real part of optical conductivity. all of these graphs are plotted against photon energy (ev). figure 6: (colour online) graph between photon energies with absorption, transmission and reflection coefficient, (a) absorption coefficient with photon energy, (b) transmission coefficient with photon energy, and (c) reflection coefficient with photon energy. 4 conclusions in this work, we explored the structural, electrical, magnetic, mechanical, dynamical, thermal, and optical characteristics of a wte2 monolayer supercell structure computationally by using density functional theory (dft) technique. we found that wte2 compound is structurally, and dynamically stable p-type semiconductor. from the interpretation of material’s density of states and partial density of states plots, it was found that up-and downspins states of electron in the orbitals of atoms are symmetrically distributed around the fermi energy level, and hence wte2 monolayer supercell structure has non-magnetic properties. mechanical properties of a considered material are studied by calculating the parameters like modulus of rigidities, elastic constants, compressibility, and anisotropy factor. the material is found to be ductile and anisotropic in nature. furthermore, thermal properties of a material are examined by calculating material’s phonon velocity and debye temperature. the longitudinal, transverse, average phonon velocities and debye temperature of considered material are found to be 1665.76m/s, 971.05 m/s, 1077.12 m/s and 85.6k respectively. hence, wte2 is a low melting point material. additionally, optical properties of wte2 compound are predicted through its dielectric function, optical conductivity, absorption coefficient, transmission coefficient, and reflection coefficient. at high photon energy region, wte2 has been more transparent, anisotropic nature, increasing conductivity, small values of absorption and reflection coefficients. hence, it can be used in the fields of optoelectronic and energy storage devices. acknowledgement the authors would like to acknowledge the condensed matter research lab cdp tu, twas research funds rg 20-316, network project nt14 of ictp/oe for the computing capacity, and prof. np adhikari for his excellent input on the manuscript. author contributions sky, tn, ap, 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[45] j. pešić, j. vujin, t. tomašević-ilić, m. spasenović, and r. gajić. dft study of optical properties of mos2 and ws2 compared to spectroscopic results on liquid phase exfoliated nanoflakes. optical and quantum electronics, 50(7):291, 2018. introduction methods and material results and discussion structural properties mechanical, dynamical and thermal properties electronic and magnetic properties optical properties conclusions bibechana vol. 22, no. 2, august 2025, 151-158 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar assessment of the dhobikhola river water using real-time monitoring system mandira pradhananga adhikari1∗, narendra bahadur rawal1, kabita yadav2 1central department of chemistry, tribhuvan university, kathmandu, 44618, nepal 2rajarshi janak university, janakpurdham, janakpur, nepal ∗corresponding authors. email: mandira43@hotmail.com abstract river water quality inside the kathmandu valley is deteriorating day by day due to the mixing of untreated industrial and domestic waste. till now, a few researchers have characterized the water quality of dhobikhola using traditional methods, therefore, there is a lack of enough data to identify river water quality thoroughly. with the exponential development of information technology, continuous, fine-scale, and real-time data monitoring is possible using advanced sensor probes with sophisticated data logging systems; it would be the first practice in the case of the dhobikhola river. in this study, real-time continuous monitoring and collection of large data using sophisticated sensors were performed to determine the river water quality and the sources of pollutants. the spatial variation of water quality parameters indicated that after entering the core city area, most parameters, such as conductivity and turbidity, changed more than four times, and oxidation-reduction potential (orp) turned into a negative value. the high conductivity and negative orp values are an indication of a sewer connection. daily and diurnal variations suggested that the dhobikhola river is always polluted with a negative orp value (< -50 mv). all the results suggest that it is enormously important to control the mixing of effluent into the dhobikhola rivers to revive the ecology of the aqueous system. keywords diurnal variation, oxidation-reduction potential (orp), real-time data, water pollution. article information manuscript received: january 1, 2025; revised: may 22, 2025; accepted: may 23, 2025 doi https://doi.org/10.3126/bibechana.v22i2.74121 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction dhobikhola is one of the major and most polluted tributaries of the bagmati river [1,2]. it originates from the muhanpokhari at shivpuri hill, north of kathmandu valley, and is mixed into the bagmati river at bhuddha marg, buddhanagar. it passes through the densely populated area before it merges into the bagmati river. it extends about 18.2 km [3] and covers about 31.2 square km [4]. rapid population growth with unmanaged urbanization generated excessive solid waste and sewage in core city areas inside the kathmandu valley [5]. municipal, hospital, and industrial wastes are dumped directly into the river. in addition, domestic and industrial wastewater are connected directly to the river without any treatment [6, 7]. due to the mixing of effluent and solid waste, the water quality of the 151 http://nepjol.info/index.php/bibechana mandira43@hotmail.com https://doi.org/10.3126/bibechana.v22i2.74121 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ mandira pradhananga adhikari et al./ bibechana 22 (2025) 151-158 152 dhobikhola is severely deteriorating in the present conditions [8–10], which harms the river ecosystem and the health of communities relying on it. near the source, close to shivpuri hill, the water is still clean; it is diverted for daily uses for bathing, irrigation, washing vegetables, utensils, and clothing. the study [3] reported that the sewage discharge and dumping of solid waste into the dhobikhola river started from the kapan area. the dhobikhola river is severely polluted from the chabahil area and downstream. a huge volume of wastewater from households and industries is directly connected to the river, and municipal waste is disposed of on the banks. these anthropogenic pollutants cause the degradation of the river's water quality. the study also suggested that the river is ecologically almost dead inside the core city area, causing heavy losses due to waterborne diseases. the physicochemical characterization of river water concluded that the dhobikhola river water is not potable; the observed dissolved oxygen was about 4.4 ppm, and the conductivity was 450 µs/cm [10]. similarly, a study concluded that the dhobikhola river water is black, and the alkalinity was 310 ppm [9]. the observed chlorine demand was as high as 20 ppm, suggesting the high amounts of organic/inorganic and pathogenic contaminants in the river water. the assessment of the bagmati river and its tributaries suggested that the oxidation reduction potential (orp) of the dhobikhola river varies between – 40 to -90 mv, with conductivity between 1,090 to 1108 µs/cm, and ammonia and sulphate concentrations were the highest among the tributaries of the bagmati river. the chlorine demand was as high as 38.70 ppm in winter [11]. based on the water quality index (wqi), they concluded that water quality is extremely polluted, hence unfit for domestic use. although these studies suggested that the bagmati river and its tributaries are polluted by domestic effluent, there is still a lack of enough studies, especially in the case of dhobikhola only a few studies are available. the daily deterioration of river water quality highlights the necessity to determine the pinpoint of pollutant sources. so that awareness is created among the people to carry out the treatment of industrial and domestic waste before its disposal into the river water body. to pinpoint the sources of pollutants, traditional water quality monitoring methods are not sufficient because there is a limitation of observation points, and it takes a long time to analyze the data. since the sources of pollutants are mainly domestic influents, real-time and continuous monitoring will provide the eventual and real-time water quality status. in this study, a detailed assessment i.e., the spatial, diurnal, and daily variations of river water quality of dhobikhola, was analyzed by logging continuous real-time and fine-scale data using an advanced monitoring system. this is a very new approach to monitor/characterize water quality parameters, which is the first experience, especially in the case of the dhobikhola river. since it is not possible to collect data of all water quality parameters in real-time and fine-scale basis, this study considered the orp, dissolved oxygen (do), and conductivity are the most useful parameters indicating sewer pollutants. 2 methodology data of water quality parameters were collected from nine different positions along the dhobikhola river from shivpuri hills to the buddha marga, budhanagar, the endpoint before confluence with the bagmati river (fig. 1). data were continuously collected and logged every second from 9 stations. the observation started from the farthest upstream site of the dhobikhola (dh-1, 27.763°n, 85.365°e), which is located at the entrance point (bhadrakali park, shivpuri hill) of the dhobikhola river. this observational area has a clean environment, is far from the residential area, and is mainly covered by a forest. the second and third observation sites were the sapridhunga, kapan (dh-2, 27.745on, 85.359oe), and narrow bridge, budhanilkantha (dh-3, 27.733on, 85.351oe). the dh-2 and dh-3 sites are rural areas and have little influence from newly developed residential areas. the next sampling site was gopikrishna, chabahil (dh-4, 27.722 on, 85.345 oe), a core city that started from this area. the sampling sites dh-5 and dh-6 are highly populated areas i.e., kalopul (27.712on, 85.338oe) and setopul, maitidevi (27.7on, 85.332oe) areas. other observation sites dh-7, dh-8 and dh-9 were the bijulibazar (27.692on, 85.329oe), anamnagar (27.688on, 85.326oe) and buddha marg, buddhanagar (27.687on, 85.324oe) areas. the sewer lines are directly connected to the river water in these areas (from dh-4 to dh-9) and are considered heavily polluted areas of the dhobikhola river [5] (nud). the diurnal variations were determined by collecting data at the dh-6 on 27 july and 4 august. real-time fine-scale water quality data were measured using an advanced-multi-parameter analyzer (hanna instruments, hi-9829) [11]. physicochemical parameters such as water pressure, turbidity, ph, temperature, oxidation-reduction potential (orp), dissolved oxygen (do), conductivity, salinity, total dissolved solids (tds), and global positioning systems (gps) were measured and logged on a real-time basis. mandira pradhananga adhikari et al./ bibechana 22 (2025) 151-158 153 figure 1: map of dhobikhola river including observation points. the circle with a dashed line indicates a core city area with heavily contaminated river water. 3 results and discussion 3.1 spatial variation of water quality parameters data was collected from nine different sites along the dhobikhola river (fig. 1). the physicochemical characterization of the water suggests the river's water quality. in this study, the physicochemical characteristics of water were determined along the dhobikhola river using a fixed sensor system. the data was collected from nine fixed stations. the sampling sites were chosen to find the source of pollutants, which varied water quality parameters along the space domain of the dhobikhola river. data collection started from shivpuri and ended at the budhanagar site on the same day. more than 500 data sets were collected from each station. data collection was started at 11:30 and ended at 13:30 on 19 september 2024. the observed water quality parameters were shown with a heat map (fig. 2), and data were presented in table 1. the river water temperature varied from 21.95±0.3 to 27.40±0.06 oc. as expected, the river water temperature was low initially upstream and increased slowly downstream due to time variation, i.e., air temperature (fig. 2a). the pressure of the water enhances slowly downstream (fig. 2b). the observed turbidity was as low as 42.87 ±16.55 fnu at the dh-1 and higher than 200 fnu at other observation sites except dh-3 and dh-4 (table 1, fig. 2c). the increase of turbidity downstream may be due to the mixing of soil or effluent in the river water [12]. the hydrogen ion concentration in water is characterized by ph value. water with a ph less than 6.5 could be soft while water above 8.5 could be hard and corrosive [13, 14]. ph of river water was comparatively high (7.62±02) upstream and decreased slowly to7.26±0.01near the end of the dhobikhola river (fig. 2d). observed ph falls within the who standard of natural water (6.5 to 8.5) [14]. the slightly alkaline ph of river water may be due to the presence of weak bases from soil and sand, ammonical compounds from domestic effluent and agricultural surplus [15] and/or microbial decomposition of organic matter [16]. conductivity is associated to the conductive ions present in the water. the low conductivity (123.4 ±6.39 µs/cm) was observed at dh-1, the conductivity was more than two times at dh-2 (234.28 ±2.84 µs/cm). it was increased almost continuously downstream (fig. 2e). the conductivity of river water at the last observation point (618.93±2.03) was more than five times higher than at dh-1 (123.4 ±6.39 µs). as shown in the table, total dissolved solids (tds) were low, 61.64 ± 3.2 ppm at dh-1 and linearly increased till dh-3 then drastically at dh-4, and it was almost fivefold higher at dh-9, the end of the observation site. similarly, salinity was 0.06±0.003psu at dh-1 continuously 0.30±0.001psu downstream. unusual enhancement of conductivity, salinity and tds downstream of the river suggests the inflow of municipal and industrial discharge [17] because industrial and domestic wastewater consists of a high concentration of salts [18,19]. table 1: water quality parameters at nine different sites along the dhobikhola river parameter dh-1 dh-2 dh-3 dh-4 dh-5 dh-6 dh-7 dh-8 dh-9 gps latitude 27.76289 27.74805 27.73354 27.72201 27.71214 27.69985 27.6922 27.6878 27.68722 gps longitude 85.36459 85.35872 85.35104 85.34539 85.33758 85.33245 85.32878 85.32646 85.32463 pressure [mmhg] 652.55±0.09 655.08±0.63 656.92±0.13 657.44±0.12 658.26±0.60 659.75±0.35 660.05±0.92 661.09±0.42 658.96±0.22 temperature [°c] 21.95±0.3 25.72±0.06 26.34±0.06 26.75±0.05 26.34±0.05 26.7±0.02 26.94±0.03 27.02±0.01 27.40±0.06 turbidity [fnu] 42.67±16.55 230.52±13.91 73.25±11.03 146.79±21.64 210.06±20.28 263.66±147.47 206.70±18.51 218.52±16.46 200.03±15.30 ph 7.62±0.02 7.42±0.01 7.33±0.02 7.25±0.01 7.22±0.02 7.26±0.01 7.26±0.01 7.29±0.01 7.30±0.02 orp [mv] 82.56±1.41 79.60±2.69 105.69±15.49 -44.63±24.23 -94.94±18.02 -80.72±20.33 -93.22±13.33 -70.89±21.48 -45.68±19.74 ec [µs/cm] 123.14±6.39 234.28±2.84 289.29±0.75 474.67±0.66 587.61±1.19 563.77±31.71 629.56±0.83 630.85±0.76 618.93±2.03 tds [ppm] 61.64±3.2 117.13±1.44 144.63±0.48 237.33±0.49 293.79±0.52 281.98±15.89 314.74±0.44 315.53±0.52 309.50±1.11 salinity [psu] 0.06±0.003 0.11±0.001 0.14±0.0003 0.23±0.0003 0.28±0.001 0.27±0.02 0.30±0.0004 0.30±0.001 0.30±0.001 do [ppm] 2.95±0.09 3.07±0.04 3.08±0.03 3.13±0.04 3.04±0.04 3.14±0.03 3.21±0.02 3.19±0.01 3.13±0.05 mandira pradhananga adhikari et al./ bibechana 22 (2025) 151-158 154 another vital parameter of the water quality is the dissolved oxygen (do). the variation of concentration of do was not pronounced in the river water. it was around 3 ppm in all observation sites. the oxidation-reduction potential (orp) is most prominently used in wastewater treatment to measure the water disinfection potential [20, 21]. the reducing agent present in the water decreases the orp value, and an oxidizing agent increases the orp value, hence, it reveals the biological reaction occurring in the water. the observed orp of river water was positive and higher than 50 mv upstream (82.56±1.41) and that was negative and it ranged from (-)44.63±24.23 to (-)94.94±18.02 downstream. the studies [20, 21] considered that 50 to 250 mv orp is suitable for the degradation of organic compounds and the nitrification process. the orp value between +50 and -50 mv is useful for denitrification, and between -50 to -250 mv is useful for the formation of sulfide and release of biological phosphorus. the positive orp value reveals the clean and unpolluted water upstream, and the negative value (< -50 mv) downstream suggests that the river water is extremely polluted with reducing substances from wastewater; hence, dissolved oxygen is not enough to decompose organic compounds, instead producing sulfide and biological phosphorus, generating a stinky smell. the negative orp value suggested that there is a lack of enough oxygen to decompose organic pollutants and dead tissue, which increases the contaminants, and the river water becomes toxic to aquatic animals, hence to the public. in addition, a low orp value is suitable to generate a stinky smell, which is responsible for an unhealthy environment around it. 3.2 diurnal variation of water quality parameters fine-scale and real-time data of dhobikhola river water quality parameters were collected in july and august 2024 in the monsoon period. diurnal variations of water quality parameters were plotted in fig. 4 and fig. 5. the diurnal variations showed that the temperatures of the river water varied with time in the observation sites. the maximum temperature was observed at about 3 pm on both observation days (fig. 3a). the temperature varied from 24 to 28.58 oc. the diurnal variation of ph was not pronounced, though it ranged from 7.43 to 7.56 (fig. 3b). conductivity was slightly increased initially and reached a maximum at noon and decreased slowly with time. the highest recorded conductivity was about 488 µs/cm and the lowest value was about 422 µs/cm on july 27 and it was 502 and 468 µs/cm, respectively, on august 4 (fig. 3c). dissolved oxygen (do) in water depends on atmospheric oxygen and photosynthesis. the do is consumed by biochemical and chemical phenomena [22,23]. the observed dissolved oxygen was less than 2 ppm and remained almost constant during the observation time. fig. 4a shows that the concentration of do was not affected by time and temperature during observation. a very low concentration of do indicates that it is almost impossible to survive aquatic animals on it. the orp value was negative for the whole day on july 27 and tends to the negative after 12:30 on august. the diurnal variation of orp value was distinctly different on aug 4 than that on july 27(fig. 4b). the variation of orp was negatively related to water pressure suggesting the loading of sewer which decreased the orp value (fig. 4c). figure 2: spatial variation of water quality parameters of dhobikhola (a) temperature (oc) (b) water pressure (mmhg) (c) turbidity (fnu) (d) ph (e) conductivity (µs/cm) (f) tds (ppm), (g) do (ppm), and orp (mv). mandira pradhananga adhikari et al./ bibechana 22 (2025) 151-158 155 3.3 daily variation of water quality parameters daily variations of water quality parameters of dhobikhola river were observed pre-monsoon (june), monsoon (july-august), and post-monsoon (september). the observed temperature, water pressure, ph, and turbidity were plotted in fig. 5. the water temperature ranged from 26 to 28 oc during the pre-monsoon period and reduced the temperature slightly, which ranged from 22 to 24 oc in the post-monsoon period (fig. 5a). the enhancement of water pressure was distinctly observed in the monsoon and post-monsoon periods (fig. 5b). the ph was comparatively higher in the pre-monsoon than in the post-monsoon period (fig. 5d). the decrease in ph after rainfall may be due to the dilution of alkaline pollutants in the water. a similar effect was also observed in the case of the turbidity of water (fig. 5c). a distinct daily variation was observed in the conductivity (fig. 6a). it was higher than 600 µs/cm in the pre-monsoon period and reduced to less than 500 µs/cm in the post-monsoon. the conductivity was reduced to nearly half by the rain. the total dissolved solids were a maximum on june 21 in the pre-monsoon period and a minimum on sep 16 in the post-monsoon period (fig. 6b). the dissolved oxygen was as low as 2 mg/l and remained almost constant in all observation days (fig. 6c). the orp value was always negative in the dhobikhola river, though a slight increase was observed during the post-monsoon period (fig. 6d). the dissolved oxygen and orp values indicated that the water quality of dhobikhola river was always heavily polluted. the rainfall slightly reduced the pollutants; however unable to enhance the water quality. the very low orp indicated that the water consists of organic pollutants that consume dissolved oxygen excessively. the negative orp value (<-50 mv) suggested that there were excessive amounts of organic contaminants from the sewer, which excessively reduced dissolved oxygen. the inflow of domestic effluent loaded the pollutants continuously, hence unable to dilute it by heavy rainfall even in the monsoon season. this is the reason why the dissolved oxygen remains low in all seasons. 3.4 correlation between water quality parameters correlation indicates the extent to which two variables vary together. a positive correlation shows the level to which those variables increase or decrease, whereas a negative correlation shows the level to which one variable increases as the other decreases. the correlation between different water quality parameters on different observation days was plotted in fig. 7. there are both negative and positive correlations between the two variables, however, the coefficient of determination (r2) was always low. the conductivity and ph show a negative correlation with the water pressure (fig. 7a and 7b). fig. 7c and fig. 7e show the positive correlation between conductivity and turbidity and between conductivity and ph, respectively. fig. 7d and fig. 7f show the negative correlation between orp and turbidity and between orp and conductivity, respectively. the correlation revealed the positive impact of turbidity on conductivity i.e, pollutants increased turbidity and conductivity and hence decreased orp values. the maximum value (r2 = 0.4742) was obtained for the relation between orp and conductivity. the negative relation between these two parameters suggested that domestic effluent increases conductive organic pollutants and/or microorganisms in addition to conductive ions in the river water. the contaminants use up dissolved oxygen excessively for their decomposition by decreasing the orp value. it is considered that the organic pollutants from domestic effluents increased excessive contaminants in the dhobikhola, which reduces orp excessively by using dissolved oxygen. due to the presence of excessive contaminants rain fall increased the water press however unable to dilute the contaminants noticeably in the dhobikhola river. figure 3: diurnal variation of (a) temperature, (b) ph, and (c) conductivity (ec) in the dhobikhola river. mandira pradhananga adhikari et al./ bibechana 22 (2025) 151-158 156 figure 4: diurnal variation of (a) do, (b) orp, and (c) water pressure in the dhobikhola river. figure 5: daily variation of (a) temperature, (b) pressure, (c) turbidity, and (c) ph during the monsoon season. figure 6: daily variation of (a) conductivity, (b) do, and (c) orp during the monsoon season. figure 7: correlation between different water quality parameters observed on different days in the monsoon season. mandira pradhananga adhikari et al./ bibechana 22 (2025) 151-158 157 4 conclusion this study monitored and analyzed fine-scale realtime water quality along the dhobikhola river using advanced sensor systems. the diurnal, spatial and daily variations of parameters such as temperature, ph, salinity, conductivity, total dissolved salt (tds), dissolved oxygen (do), and turbidity were recorded. the analytical results distinctly showed that the water quality of the dhobikhola river upstream (dh-1, dh-3) and downstream (dh-4 to dh9) was radically different. the conductivity was less than 200 µs/cm upstream but was nearly 250 µs/cm at the beginning of downstream and linearly increased to 630 µs/cm at the end of the observation site. further, oxygen reduction potential (orp) was positive upstream and negative at the downstream site. the low and negative value of orp is associated with contaminated water containing large amounts of reducing pollutants. the immense change in water quality parameters upstream and downstream on the same day suggests the influence of locally generated pollutants such as domestic, agricultural, and industrial effluents from the urban area. the daily variation of water quality parameters showed that river water is extremely polluted downstream, not only on a single day but almost every day. the monsoon rain is also unable to reduce pollutants to an acceptable level. the ph and conductivity were increased, but orp was decreased during the day. the correlation between the water quality parameters indicated that the pollutants increased the turbidity and conductive substances in the river water and reduced orp value to a highly unacceptable level downstream. from the analytical results, it is concluded that the solid wastes and domestic and industrial sewers loaded organic pollutants and reduced molecular oxygen excessively so that living organisms could not survive in it. in the absence of molecular oxygen, the microorganisms decompose pollutants by generating volatile matter, which is responsible for the hazardous fouling smell along the bank of the river. acknowledgement this research is supported by rajarshi janak university, janakpurdham, nepal, through the innovative idea award-2081. references [1] government of nepal, ministry of urban development. bagmati river basin improvement project, nepal initial environmental examination report. technical report, asian development bank, 2019. 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[23] t. e. aniyikaiye, t. oluseyi, j. o. odiyo, and j. n. edokpayi. physico-chemical analysis of wastewater discharge from selected paint industries in lagos, nigeria. int. j. environ. res. public health, 16:1235, 2019. introduction methodology results and discussion spatial variation of water quality parameters diurnal variation of water quality parameters daily variation of water quality parameters correlation between water quality parameters conclusion bibechana vol. 20, no. 2, august 2023, 126-133 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar caputo-fabrizio approach to numerical fractional derivatives shankar pariyar1,2, jeevan kafle2∗ 1tri-chandra multiple campus, ghantaghar, kathmandu, nepal, 2central department of mathematics, tribhuvan university, kathmandu, nepal ∗corresponding author.jeevan kafle,: jeevan.kafle@cdmath.tu.edu.np abstract fractional calculus is an essential tool in every area of science today. this work gives the quadratic interpolation-based l1-2 formula for the caputo-fabrizio derivative, a numerical technique for approximating the fractional derivative. to get quadratic and cubic convergence rates, respectively, we study the use of lagrange interpolation in the l1 and l1-2 formulations. our numerical analysis shows the accuracy of the theory’s predicted convergence rates. the l1-2 formula aims to enhance the accuracy and usability of a flexible tool for many applications in science and mathematics. we demonstrate the validity of the theory’s predicted convergence rates using numerical analysis. several numerical examples are also given to show how the suggested approaches may be utilized to determine the caputo-fabrizio derivative of well-known functions. lagrange interpolation is used in the l1 and l1-2 procedures to obtain quadratic and cubic convergence rates, respectively. the numerical study demonstrates that the l1-2 formula offers greater accuracy when compared to current approaches. in addition, it is a better apparatus for several applications in science and mathematics. due to its higher convergence rate, the l1-2 formula outperforms other available numerical methods for scientific computations. the l1-2 formula, a novel numerical method for the caputofabrizio derivative that makes use of quadratic interpolation, is introduced in this study as a conclusion. keywords caputo fractional derivatives, numerical solution, lagrange interpolation, l1 formula, l1-2 formula. article information manuscript received: april 7, 2023; accepted: april 25, 2023 doi https://doi.org/10.3126/bibechana.v20i2.53971 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction a branch of mathematics known as numerical analysis for fractional calculus is concerned with the creation and use of numerical techniques for the solution of fractional calculus-related issues [1]. the study of fractional calculus is still in its infancy and is continually changing. integrating and differentiating non-integer categories is the main concept behind it. it is extensively employed across a range of scientific and technological fields of study, including the sciences of physics, engineering, biology, eco126 http://nepjol.info/index.php/bibechana jeevan.kafle@cdmath.tu.edu.np https://doi.org/10.3126/bibechana.v20i2.53971 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ shankar pariyar and jeevan kafle / bibechana 20 (2023) 126-133 127 nomics, and others [1]. in contrast to fractional integral equations, which involve fractional integrals, fractional differential equations are defined by the presence of fractional derivatives. a system is said to have a differential order if its behavior can be correctly predicted by one of these equations, both of them, or both together [2]. models based on fractionalorder differential equations have been developed to describe complex dynamical systems and physical phenomena. to advance the theory and application of fractional order differentials, committed researchers have made substantial efforts. the fractional derivatives rule is not a collection of rules that can be applied in every situation, although the terms fractional differentiation and integration have been defined differently by various mathematicians [3]. because riemann-liouville (r-l) shows that the derivative of a constant component is not zero, it has been demonstrated that it can be difficult to calculate fractional derivatives using regular calculus. the r-l fractional derivative is the meaning of these that is most widely used. constant terms have non-zero derivatives, as demonstrated by the r-l discovery, which demonstrates that the derivative of a constant term is not zero, in the framework of classical calculus, it is difficult to analyze fractional derivatives [4, 5]. jumarie expertly overcame this difficulty in the most recent version by modernizing the idea of f.d. of the r-l category. the fractional derivative versions of caputo, grunwald-letinikov (g-l), and jumarie’s modified r-l are the most successful in avoiding the problem of non-zero derivatives resulting from a constant function [2]. while the grunwald-letinikov (g-l) term is useful for numerical applications, when it comes to analytical techniques, the concepts of r-l and caputo are especially useful. no one technique can be used to solve the linear fractional differential equations. the derivative of the mittag-leffler function (mlf) [6] can be calculated using the fractional derivative with the jumarie modification. swedish scientist ml developed the mlf for averaging divergent series at the beginning of the 20th century. given its crucial part in supplying solutions with integral and derivatives of fractional order, mlf is a special transcendental function. the fractional order derivatives or integrations of the superdiffusively transport, random walk, kinetic equation, and complex systems are readily solved by the mlf [4,7]. both the standard and extended mlf interpolate phenomena are governed by shared kinetic equations and their fractional analogs between an exponential law and a power law [8, 9]. in contrast to linear fracti,onal differential equations, which cannot be solved by a single technique, the fd of the mlf function can be derived by using the updated definition of the fd proposed by jumarie. the exponential function ez is essential for integer-order differential equations, according to theory. g.m. mittag-leffler was the first to refer to the function that is now denoted by, with its one parameter generalization [10], was cited by g.m. mittag-leffler as the source first [7]. fractional calculus can be used to solve fractional differential equations and explain odd phenomena. it is closely linked to mlf and its expansions. the two-parameter mlf, r(β) > 0, was established by goreflo et al and agarwal [11] immediately after the introduction of this version with a second complex parameter. leibniz asked l’ hospital [12] about the consequences of n = 1 2 and the nth derivative of the f(t) = t linear model. fc was developed in response to this query. leibniz discovered a paradox that had human consequences, but he also noted the creation of fc on september 30, 1695. a 34-year delay later, in 1849, he added the beta and gamma functions to it and referenced to g.h. 1849 [13]. lagrange [14] developed and published the exponent principle for integer-order differential operators in 1772. some of the most significant definitions of fc from several eminent mathematicians are given by us. numerous mathematicians, including fourier, lacroix, riemann, liouville, caputo, euler, and gl [15], were inspired by romero’s work and his citation by laplace [16] in 1812 to advance the subject of fractional calculus. they also made use of legendre’s extended factorial notation and lacroix’s simple nth-order derivative [11]. by using the laplace transform approach, humbert and agarwal [15] created a number of connections for this study. solving oscillation and relaxation equations is governed by first and second orders of linear differential equations [17,18]. caputo and fabrizio [19] in 2015 have introduced a new type of fractional derivative called cfd to remove the singular kernel. using both caputo-fabrizio and atangana-baleanu derivatives, algahtani [20] (2016) carried out a numerical comparison of the allen-cahn equation gao et al. [13] in (2014) introduced a novel fractional numerical technique, the l1-2 formula, for the caputo fractional derivative, which improved the accuracy of numerical solutions from δt2−α to δt3−α via quadratic interpolation. the aforementioned research served as an inspiration for the creation of a new quadratic lagrange interpolation l1-2 formula. the accuracy of the caputo-fabrizio derivative (cfd) was shown to be able to be increased from quadratic convergence to cubic. to the best of our knowledge, no previous l1-2 differentiation formula for the caputo-fabrizio derivative (cfd) has been presented before this study. additionally, this formula’s convergence rate shankar pariyar and jeevan kafle / bibechana 20 (2023) 126-133 128 has been developed. even though caputo fabrizio’s numerical solution, which makes use of the l1 and l2 numerical formulae, is the main emphasis of this paper, there are other numerical solutions to some specific fractional calculus functions. gao et al. [13], introduced an innovative fractional numerical method, the l1 − 2 formula, for the cfd and used nonlinear interpolation to increase the precision of the numerical calculation at different steps. our sounds show how the quadratic rate of convergence can be transformed into a cubic, even fourth-order, cfd. this study, in our opinion, is the first to support the convergence of the method and to give a new l1−2 differentiation formula for cfd. in addition to studying straightforward fractional relaxation and vibration equations, gerenflo and mainardi [11] also investigated fractional derivatives. from 1695 to 1697, leibniz wrote correspondence to j. wallis and j. bernoulli [17,18] in which he offered a potential method for differentiating fractional orders [6]. 2 preliminaries some of the priliminaries which are needed for the work are given below : definition 1 the formula below represents the gamma function’s integral γ(p) = ∫∞ 0 e−xx(p−1)dx, p > 0. because only when p > 0 does the aforementioned integral converge. the factorial function is also generalized by the gamma function, as for any positive integer p, γ(p) = ∫∞ 0 e−xx(p−1)dx = (p− 1)! [21]. definition 2 the beta function, denoted as β(p, q) with p, q > 0, is defined as the integral of xp−1(1− x)q−1 from 0 to 1. it is related to the gamma function through the formula β(p, q) = γ(p)γ(q) γ(p+q) [22]. definition 3 according to gl, the function m(x) of nth order fd with respect to x is defined by gl if α is a non-negative real number [2]. gl left sided fd:gldα a+ [m(x)] = lim n→ 0 1 hα n∑ k=0 (−1)k γ(α+ 1)m(x− kh) γ(k + 1)γ(α− k + 1) , nh = (x− a). . gl right sided fd:gldα b− [m(x)] = lim n→ 0 1 hα n∑ k=0 (−1)k γ(α+ 1)m(x+ kh) γ(k + 1)γ(α− k + 1) , nh = (b− x). definition 4 the r-l fractional integral, aixα(m(x)) = 1 γ(α) ∫ x a (x− z)α−1m(t)dt; x > a. xiaα(m(x)) = 1 γ(α) ∫ a x (x− z)α−1m(t)dt; a > x. properties p1: ai α x (k(t (x))) = k ·a iαx (t (x)). p2: ai α x (p (x)±q(x))) =a iαx (p (x))±a i α x (q(x)). p3: ai α x (n(x)±m(x)) =a iαx (n(x))±a i α x (m(x)). definition 5 under riemann-liouville, in most cases, the riemann-liouville formula defines a fractional derivative [23]. bd q t (v(x)) =  1 γ(ν−γ) ( d dx )t ∫ q b (q − t)t−γ−1v(t).dt; (t− 1) < β < t dt dxt v(x), β = t definition 6 the caputo fractional derivative is commonly used [13]. adα x(m(x)) =  1 γ(n−α) ∫ x a (x− t)n−α−1 ( d dx )n m(t).dt, (n− 1) < α < n dn dxn ·m(x); α = n (1) definition 7 mittag leffler function (mlf) of one parameter [10], eα(z) = ∞∑ n=0 zn γ(αk + 1) (2) two-parameters mlf β, r(β) > 0 [11] and agarwal [24] β, r(β) > 0 eα,β(z) = ∞∑ n=0 zn γ(α · k + β) (z, α, β ∈ c) (3) the generation of 3 in terms of series representation was introduced by prabhakar. eγ α,β(z) = ∞∑ k=0 (γ)nz k γ(α · k + β) · n! (4) where (γ)n is pochhammer’s symbol. with the aforementioned considerations in mind, we discuss the fractional operators with three-parameter generalized mittag-leffler kernels in our work. definition 8 a novel fractional derivative with no singularities in its kernel was suggested by caputo and fabrizio in their [17]. the first fractional derivative has an exponential kernel, which is similar to an exponential function. cf a dx(f(x)) = m(α) (1−α) ∫ x a e− α(x−t) (1−α) · f ′(t) · dt; m(0) = m(1) = 1 shankar pariyar and jeevan kafle / bibechana 20 (2023) 126-133 129 definition 9 interpolation: the process of figuring out the values of the functions at any intermediate point when the values of the first two points are known is known as interpolation. definition 10 linear interpolation [25]: the linear polynomial that passes through the specified coordinates (a0, b0) and (a1, b1). one method to express its formula is as follows: p1(x) = b0 a1−x a1−a0 + b1 x−a0 a1−a0 definition 11 quadratic interpolation [25]: the quadratic polynomial that passes through the specified coordinates (a0, b0), (a1, b1), and (a2, b2) may be written as p2(x) = b0m0(x) + b1m1(x) + b2m2(x), m0(x) = (x− a1)(x− a2) (a0 − a1)(a0 − a2) , m1(x) = (x− a0)(x− a2) (a1 − a0)(a1 − a2) m2(x) = (x− a0)(x− a1) (a2 − a0)(a2 − a1) in the formula above, the polynomial p (x) is known as the lagrange’s interpolating polynomial, and m0, m1, and m2 are the lagrange’s interpolating basis functions. 3 mathematical and numerical methods in caputo-fabrizio sense 3.1 l1 method for the caputo fractional derivative left caputo fractional derivatives are those fractional derivatives of a function that characterize its left-sided behavior, and the exact numerical method used to approximate them is called l1 for 0 < α < 1 c 0 dα t f(x) ≈ 1 γ(1− α) ∫ x 0 (x− s)−αf ′(s)ds (5) c 0 dα t f(xn) ≈ 1 γ(1− α) ∫ xn 0 (xn − s)−αf ′(s)ds (6) c 0 dα t f(xn) ≈ 1 γ(1− α) n−1∑ k=0 ∫ xk+1 xk (xn − s)−αf ′(s)ds now we replace first-order derivative in 6 by forward difference quotient as follows: c 0 dα t f(xn) ≈ 1 hγ(1− α) n−1∑ k=0 [f(xk+1 − f(xk)] c 0 dα t f(xn) ≈ hα γ(2− α) n−1∑ k=0 [f(xk+1)− f(xk)] [(n− k)(1−α) − (n− k − 1)(1−α)] is known as the l1 approach for caputo fractional derivative. this method is the most popular way to approximate the caputo fractional derivatives of a function. using computer tools, we have since conducted a more thorough analysis of the numerical method and compare it to the precise solution. 3.2 l2 method for the caputo fractional derivative the left caputo fractional derivative can be approximated via the l2 approach c 0 dα xf(x) ≈ 1 γ(2− α) ∫ x 0 (x− s)1−αf ′′(s) · ds, (1 < α < 2) (7)∫ a 0 f(x)dx = ∫ a 0 f(a− x)dx (8) from (7) and (8) as follows, c 0 dα xf(x) ≈ 1 γ(2− α) ∫ xn 0 (s)1−αf ′′(xn − s)ds, c 0 dα xf(xn) ≈ 1 h2(2− α)γ(2− α) (s)1−α n−1∑ k=0 [f(xn − xk+1)− 2f(xn − xk) + f(xn − xk−1)] [(xk+1) (2−α) − (xk) (2−α)] l2 method for obtaining caputo fractional derivatives is, c 0 dα xf(xn) ≈ n−1∑ k=0 wkf(xn−k) (9) such that where wk is the normalizing factor and k has a range of values between −1 and n. it is generally acknowledged that the l2 approach for caputo fractional derivative is the preferred method for approximating fractional caputo derivatives of functions. recently, a more thorough analysis of this numerical method was done, and the results were compared to the exact ones. 3.3 l1 method for the caputo fabrizio derivative the caputo fabrizio differential operator is defined below for 0 < α < 1 cf 0 dα xf(x) ≈ m(α) (1− α) ∫ x 0 f ′(s)exp[λ(x− s)]ds, λ = −α (1− α) , (10) cf 0 dα xf(xn) ≈ m(α) (1− α) ∫ xn 0 f ′(s)exp[λ(xn − s)]ds, (11) shankar pariyar and jeevan kafle / bibechana 20 (2023) 126-133 130 cf 0 dα xf(xn) ≈ m(α) (1− α) n∑ k=1 ∫ xk xk−1 f ′(s)exp[λ(xn − s)]ds (12) now, we replace first-order derivative in (13) by the forward difference quotient as follows: cf 0 dα xf(xn) ≈ m(α) (1− α) n∑ k=1 ∫ xk xk−1 exp[λ(xn − s)] [ f(xk)− f(xk−1) h ]ds (13) cf 0 dα xf(xn) = m(α) αh ∑n k=1[f(kh) − f(k − 1)h] [exp[λh(n− k)]− exp[λh(n− k + 1)] which is a derivative of the caputo fabrizio equation using the l1 method. we demonstrate how the three-point backward estimate method, which we derive from the linear lagrange method, was used to approximate the caputo fabrizio derivative. the cubic lagrange interpolation can be represented with α range of 1 < α < 2. 3.4 l1-2 method for caputo fractional derivative the cfd operator is defined below cf 0 dα y g(y) = m(α) (1−α) ∫ y 0 g′(u)exp[λ(y−u)]du, λ = −α (1−α) , α ∈ (0, 1). cf 0 dα y f(yk) = m(α) (1−α) [ ∫ y1 y0 g′(u)exp[λ(yk − u)]du + ∫ y2 y1 g′(u)exp[λ(yk − u)]du + · · · +∫ yk yk−1 g′(u)exp[λ(yk − u)]du], using the quadratic lagrange interpolation with the points (yj−2, gj−2), (yj−1, gj−1), (yj , gj) for the backward approximation first order derivative as follows, π2,jg(y) =gj−2 (y − yj−1)(y − yj) (yj−2 − yj−1)(yj−2 − yj) + gj−1 (y − yj−2)(y − yj) (yj−1 − yj−2)(yj−1 − yj) + gj (y − yj−2)(y − yj−1) (yj − yj−2)(yj − yj−1) where t ∈ [tj−1, tj ] for 2 ≤ j ≤ k and yj = jh, yj−1 = (j − 1)h. π2,j(g(y)) = gj−2 2h2 [(y − yj−1)(y − yj)]+ fj−1 h [(x− xj−2)(xj − x) + gj 2h2 [(y − yj−2)(y − yj−1)] π′ 2j(g(y)) = gj−2 2h2 [(2y − yj−1 − yj)] + gj−1 h [−2y − yj−2 + yj ] + fj 2h2 [2y − yj−2 − yj−1] cf 0 dα y g(yk) ≈ (g1 − g0) αh (δ1,k − δ0,k) + 1 α k∑ j=2 [ gj−2 2h (1− 2j) + gj−1 h (2j − 2) + gj 2h (3− 2j)(δj,k − δj−1,k)+ gj−2 − 2gj−1 + gj) h2 (yjδj,k)− (1− α) α δj,k − yj−1δj−1,k + 1− α α (δj−1,k) ] 4 test examples, relation between the function f(x) = e−x and its l1 fractional derivative d0.5f(x) figure 1: l1 fractional derivative, d0.5f(x) a continuous blue curve for the function f(x) = e−x and a dashed red curve for d0.5f(x) will be displayed on the same plot in the two pictures. the function used in the instance, f(x) = e−x, displays an exponential decline. the shape of f(x) is determined by the selected function, f(x) = e−x. the first derivative of the l1 fd, which determines the rate of change, is standardized. because the fact that the l1 fd shape uses the complete history of the function and is a non-local operator, it is typically smoother and less noisy than the first derivative. the l1 fd is thought to be less that are susceptible to outliers and data noise than other varieties of fd. example 1 using the l1 formula and the equation f(x) = sin(x) over [0, 1] at α = 0.5, the numerical results are shown in the table below. table 1: l1 formula of f(x) = sin(x) at α = 0.5. l1cd* exact error step sizes 0.8559 0.8461 0.0099 h=0.1 0.8472 0.8461 0.0012 h=0.01 0.8462 0.8461 0.000111 h=0.001 0.8461 0.8461 0.00001074 h=0.0001 0.8461 0.8461 0.0000010611 h=0.00001 shankar pariyar and jeevan kafle / bibechana 20 (2023) 126-133 131 *l1cd represents l1-caputo-derivative. table 1 displays the numerical outcomes under schemes 5 for the function f(x) = sin(x) over the range [0, 1] using the l1-caputo-der formula. there are four columns in the table • l1-cap-der: using the l1-caputo-der formula, this column represents a numerical approximation of the integral of the function f(x). • exact: the value 0.8461 is shown in this column as the integral of the function f(x) over [0, 1]. • inaccuracy: the absolute inaccuracy between the numerical approximation and the l1-caputo-der formula is shown in this column. • step sizes: the fourth column labeled "step sizes" shows the step size used for each numerical result. from the table, we can see that as the step size decreases, the numerical result obtained using the l1caputo-der formula gets closer to the exact value of the integral. the error decreases as the step size decreases, indicating that the numerical approximation is becoming more accurate. at h=0.0001, the error is less than 0.00001, which is a very small error, indicating a highly accurate numerical approximation. example 2 using the l2 formula and the equation f(x) = sin(x) over [0, 1] at α = 1.5, the numerical results are shown in the table below. table 2: l2 formula of f(x) = sin(x) at α = 1.5 l2-cd* exact error step sizes -0.6219 -0.6697 0.0478 h=0.1 -0.6653 -0.6697 0.0044 h=0.01 -0.6693 -0.6697 0.00042716 h=0.001 -0.6696 -0.6697 0.000042431 h=0.0001 -0.6697 -0.6697 0.0000042307 h=0.00001 l2-cd* represents l2-caputo derivative. table 2 indicates that for the different step sizes to approximate the function f(x) = sin(x) using the l2caputo-derivative, using the scheme 9 over the range [0, 1], α = 1.5 is the value that was utilized in the approximation. the step size has an impact on the numerical precision. a smaller step size often results in a more precise estimate, even though it takes longer to calculate. a larger step size results in a less accurate approximation even though it takes less time to compute. as a result, while choosing a step size, accuracy and computation effectiveness must be compromised. example 3 the equation f(x)=cos(4x) over the interval [0,2], with alpha=0.1 and different step sizes, can be solved using the l1-formula in the caputo fabrizio sense. table 3: l1 for cfd at f(x) = cos(4x) at α = 0.1 st*. s.s*. ex* ax* er* 20×101 10−1 -1.0811 -1.0807 3.9720× 10−4 20×102 10−2 -1.0811 -1.0811 3.9720× 10−6 20×103 10−3 -1.0811 -1.0811 3.9720× 10−8 20×104 10−4 -1.0811 -1.0811 3.9720× 10−10 acronyms: st* = steps, s.s* = steps sizes, ex* = exact, ax* = approximate, er*=error. if we observe an absolute error reduction of two orders of magnitude while simultaneously reducing the step size by one order of magnitude, this suggests a quadratic rate of convergence at the second order. in other words, not only is our progress significant but it is also happening quite rapidly. example 4 the equation f(x) = cos(4x) over the interval [0, 2], with α = 0.1 and different step sizes, can be solved using the l1 − 2(backward approximation) for caputo-fractional derivativeformula in the caputo fabrizio sense. table 4: l1-2 for cfd at f(x) = cos(4x) at α = 0.1 st*. s.s* ex* ax* er*. 2×101 1× 10−1 -1.0811 -1.0811 2.9514× 10−7 2×102 1× 10−2 -1.0811 -1.0811 2.9090× 10−11 4×101 0.05 -1.0811 -1.0811 1.8377× 10−8 if we observe an absolute error reduction of three orders of magnitude while simultaneously reducing the step size by one order of magnitude, this suggests a cubic rate of convergence at the third order. in other words, not only is our progress significant but it is also happening quite rapidly compared to l1-formula in the caputo-farbrizio sense. figure 2: your figure caption here. when step sizes h1 = 0.1, h2= 0.05, and h = 0.01 are taken in the interval [0, 2], an initial function f(x) = cos(4x) is specified, with a curve to the shankar pariyar and jeevan kafle / bibechana 20 (2023) 126-133 132 function at each step size. the figure illustrates how, as step size h is reduced, the approximate solutions found using the l1− 2 backwards approximate method approach the exact solution of the equation f(x) = cos(4x).this is so that the function’s derivatives can be approximated with greater accuracy using lower step sizes. 5 comparative analysis of a fractional derivatives the grunwald-letnikov, riemann-liouville, caputo, and l1-2 methods are examples of numerical methods for approximating fractional derivatives. below is a brief comparison of these two methods: accuracy: when the fractional derivative’s order is f and the step size is h the convergence rate of the grunwald-letnikov method is o(hα). the rate of convergence is not as rapid as other methods. • generally speaking, the riemann-liouville technique, which has a convergence rate of o(h2), is more accurate than the grunwald-letnikov method. • the caputo-fabrizio technique is quicker than the grunwald-letnikov and riemann-liouville methods, with a convergence rate of o(h2). • the quickest of all the approaches, the l1-2 caputo method converges at a rate of o(h3). efficiency: • the grunwald-letnikov approach only needs to evaluate a discrete convolution, hence it is computationally efficient. • the riemann-liouville approach can be computationally demanding since it uses numerous integrals. • utilizing a finite difference formula, the caputofabrizio technique is computationally effective. • to employ the computationally effective l1-2 caputo approach, the quadratic interpolation formula must be assessed. stability: • the grunwald-letnikov method could be numerically unstable depending on the values of the fractional derivative order and step size. • the riemann-liouville method could be numerically unstable for particular values of the fractional derivative order and integration limitations. • the caputo-fabrizio approach is often stable, however it can be sensitive to the selection of step size. • generally consistent and accurate with the l1-2 caputo approach. robustness: • the grunwald-letnikov method is a usually reliable technique that can be used to calculate fractional derivatives for a variety of functions. • the riemann-liouville approach is susceptible to the characteristics of the function being differentiated and can be constrained by the selection of integration limits. • the caputo-fabrizio method can compute fractional derivatives for a variety of functions and is generally reliable. • the l1-2 caputo method is a usually reliable technique that can be used to calculate fractional derivatives for a variety of functions. the l1-2 caputo approach is the most precise, effective, stable, and reliable of the four ways, to put it briefly. although less precise and effective than the l1-2 caputo method, the caputo-fabrizio approach is nevertheless a viable alternative. compared to caputo-based approaches, the grunwald-letnikov and riemann-liouville methods are typically less precise, less effective, and can be vulnerable to numerical instabilities. 6 conclusion our approach is different from most other domains. a unique numerical approach called as l1, l2, l1 has been devised using the linear and cubic interpolations for the numerical solution of the cfd. it uses the caputofabrizio sense and l1-2 formula. for backward/forward approximations, the fourth-order convergence rate is found for backward approximations, while the l1 and l1-2 equations provide quadratic and cubic convergence rates. the numerical outcomes were consistent with a well-known functions for different orders and varied step sizes. every one of these approaches has advantages and disadvantages. in contrast to the riemannliouville technique, which can be challenging to compute because of singularities, the grünwald-letnikov approach is simple to construct but can be slow. the l1-2 method is a promising new approach with a greater convergence rate, in contrast to the widely used caputo method, which can have accuracy problems. the particular application and the trade-offs between precision, effectiveness, and simplicity will determine the strategy to choose. investigating the l1-2 formula’s stability and resilience in the presence of noise or other error 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[25] h. s. malvar, li-wei he, and r. cutler. highquality linear interpolation for demosaicing of bayer-patterned color images. in 2004 ieee international conference on acoustics, speech, and signal processing, volume 3, pages iii–485. ieee, 2004. introduction preliminaries mathematical and numerical methods in caputo-fabrizio sense l1 method for the caputo fractional derivative l2 method for the caputo fractional derivative l1 method for the caputo fabrizio derivative l1-2 method for caputo fractional derivative test examples, comparative analysis of a fractional derivatives conclusion gohivar et al./bibechana 19 (1-2) (2022) 75-82 75 exponential temperature-dependent parameters for thermodynamic and structural properties of al-ti melt r. k. gohivar a, b*, s.k. yadavb, r.p. koiralab, d. adhikarib a central department of physics, tribhuvan university, kirtipur, kathmandu, nepal b department of physics, m.m.a.m. campus, t.u., biratnagar, nepal *email: ramesh.gohibar@mmamc.tu.edu.np article information: received: april 08, 2021 accepted: october 30, 2021 keywords: thermo-structural properties al-ti melt exponential t-dependent parameters artifacts r-k polynomials abstract thermodynamic and structural properties of al-ti melt have been estimated in the framework of redlich-kister (r-k) polynomial using linear temperature-dependent (t-dependent) interaction parameters above melting temperatures. these calculations show the existence of the artificial inverted miscibility gaps (artifacts) at temperatures 2000 k, 2500 k, and 2700 k. therefore, interaction parameters are assumed to vary exponentially with temperature and have been optimised for excess free energy of mixing. the artifacts do not appear in the calculation of these properties of the concerned alloy when these optimized parameters are used. doi: https://doi.org/10.3126/bibechana.v19i1-2.46392 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction the fabrication of materials for their various applications at high temperatures is one of the major tasks for the researcher in the field of material and metallurgical science. such high-temperature materials are used as exhaust valves and turbine blades in aerospace and automotive vehicles. titanium-based alloys are most often preferred as high-temperature materials. moreover, the altibased alloys have lightweight as well as high strength. therefore, complete knowledge of al-ti alloys is mandatory and hence several researchers so far have studied the phase diagram of this system [1– 9]. the experimental value of enthalpy of al was used to calculate the enthalpy of ti using gibbs-duhem https://doi.org/10.3126/bibechana.v19i1-2.46392 https://creativecommons.org/licenses/by-nc/4.0/ gohivar et al./bibechana 19 (1-2) (2022) 75-82 76 relation which were used to compute the enthalpy of mixing of liquid al-ti alloy at 2000 k [1]. kattner et al. [2]. analyzed the phases of stoichiometric compounds, the disordered solution phases and the ordered intermetallic compounds, and optimised the thermodynamic functions of the al-ti system. maeda et al. [3]⁠ studied the activity of the system at 2073 k and found that the observed values showed negative deviation from the raoult's law throughout the entire concentration of al. zhang et al. [4] ⁠ analyzed the al-ti system by taking nine phases and calculated excess gibbs free energy of mixing of disordered solution phases using a generalized bond energy model. witusiewicz et al. [7]⁠ modeled gibbs free energy of mixing of all phases of the system using computer-based software parrot optimizer of thermo-calc and optimised the thermodynamic parameters of the al-ti system. sudavtsova and podoprigora [8]⁠ used an isoperibolic calorimeter to determine the enthalpy of mixing of the liquid alloy at temperatures 1770 ± 5k and 1790 ± 5 k and concluded that these values are temperaturedependent. egry et al. [9]⁠ measured the thermophysical properties of the al-ti-based ternary system and compared them with the corresponding values calculated from the optimised parameters of the system of ref. [7] ⁠. novakovic et al. [10] ⁠ used quasi-chemical approximation to study the surface, dynamic and structural properties of the liquid al-ti alloy at 1973 k and predicted that al segregates on the surface phase of the solution throughout the entire concentration range. their result showed that the theoretical value of concentration fluctuations in the long-wavelength limit was found to be greater than the corresponding ideal values at very low concentration of ti (𝑥𝑇𝑖 ≤ 0.15) indicating the segregating tendency of the system in the constrained concentration range [11-13]. in this work, r-k polynomial has been used to study the thermodynamic and structural properties of liquid alloy by using the linear temperature interaction parameters. on extrapolating these values at higher temperatures, the artificial inverted miscibility gaps appeared [14-18]. with this regard, the exponential interaction parameters have been optimised and the thermodynamic and structural properties of the system have been recomputed at elevated temperatures, such as 1500 k, 2000 k, 2500 k and 2700 k in order to remove the inverted miscibility gaps. the necessary mathematical formulation is presented in the section 2, the results and discussion are presented in the section 3 and the conclusions are outlined in the section 4. 2. formulation the thermodynamic properties like excess free energy of mixing (𝐺𝑀 𝑥𝑠), enthalpy of mixing (𝐻𝑀) , and the activity of components of binary liquid alloy can be determined by using coefficients of r-k polynomial. these coefficients are called the interaction parameters of the system and are considered to be temperature-dependent. the linear temperature-dependent form of the interaction parameters can be given as 𝐿𝑖 = 𝑎𝑖 + 𝑏𝑖𝑇 (1) where ai and bi are parameters associated with the enthalpy of mixing and excess entropy of mixing respectively. likewise, the exponential temperaturedependent terms of the interaction parameters are expressed as [19]⁠ 𝐿𝑖 = ℎ𝑖exp( −𝑇 𝜏𝑖 ) (2) where hi and τi are constant parameters which are to be optimised for the preferred alloy. in the framework of r-k polynomial, the excess free energy of mixing (𝐺𝑀 𝑥𝑠) of the liquid alloy is expressed [20]⁠ 𝐺𝑀 𝑥𝑠 = 𝑥𝐴𝑙𝑥𝑇𝑖 ∑ 𝐿𝑖(𝑥𝐴𝑙 − 𝑥𝑇𝑖) 𝑖3 𝑖=0 (3) where 𝑥𝐴𝑙 and 𝑥𝑇𝑖 are concentrations of the components al and ti of the liquid al-ti alloy. using equations (2) in equation (3), one can obtain 𝐺𝑀 𝑥𝑠  = 𝑥𝐴𝑙  𝑥𝑇𝑖   ∑ ℎ𝑖 3 𝑖=0   exp (− 𝑇 𝜏𝑖 )  (𝑥𝐴𝑙  − 𝑥𝑇𝑖) 𝑖 (4) gohivar et al./bibechana 19 (1-2) (2022) 75-82 77 the general expression relating the excess free energy of mixing, enthalpy of mixing (𝐻𝑀) and excess entropy of mixing (𝑆𝑀 𝑥𝑠) is 𝐻𝑀 = 𝐺𝑀 𝑥𝑠 + 𝑇𝑆𝑀 𝑥𝑠 (5) the excess entropy of mixing can be calculated in terms of (𝑆𝑀 𝑥𝑠) given as 𝑆𝑀 𝑥𝑠 = −𝜕𝐺𝑀 𝑥𝑠 𝜕𝑇 (6) using linear parameters and exponential parameters from equations (1) and (2) in equations (3), (6) and finally in equation (5) then respective expressions for enthalpy of mixing (𝐻𝑀) are 𝐻𝑀 = 𝑥𝐴𝑙𝑥𝑇𝑖 ∑ 𝑎𝑖(𝑥𝐴𝑙 − 𝑥𝑇𝑖) 𝑖3 𝑖=0 (7a) and 𝐻𝑀 = 𝑥𝐴𝑙𝑥𝑇𝑖 ∑ (1 + 𝑇 𝜏𝑖 )3 𝑖=0 ℎ𝑖exp( −𝑇 𝜏𝑖 )(𝑥𝐴𝑙 − 𝑥𝑇𝑖) 𝑖 (7b) the partial excess free energy of the components al and ti of liquid al-ti alloy can be computed using the following relation 𝐺𝐴𝑙 𝑥𝑠 = 𝑥𝑇𝑖 2 ∑ 𝐿𝑖[(1 + 2𝑖)𝑥𝐴𝑙 3 𝑖=0 − 𝑥𝑇𝑖](𝑥𝐴𝑙 − 𝑥𝑇𝑖) 𝑖−1 and 𝐺𝑇𝑖 𝑥𝑠 = 𝑥𝐴𝐿 2 ∑ 𝐿𝑖[𝑥𝐴𝑙 − 𝑥𝑇𝑖(1 + 2𝑖)](𝑥𝐴𝑙 −3 𝑖=0 𝑥𝑇𝑖) 𝑖−1 (8) the activities of the components al and ti are calculated using the values from equations (8) then 𝑎𝐴𝑙 = 𝑥𝐴𝑙exp( 𝐺𝐴𝑙 𝑥𝑠 𝑅𝑇 ) and 𝑎𝑇𝑖 = 𝑥𝑇𝑖  exp ( 𝐺𝑇𝑖 𝑥𝑠 𝑅𝑇 ) (9) the structural property of the liquid alloy system can be analyzed by computing concentration fluctuations in the long-wavelength𝑆𝑐𝑐(0) limit . following bhatia and singh, the expression for 𝑆𝑐𝑐(0)terms of excess free energy of mixing can be given as [21] 𝑆𝑐𝑐(0) = 𝑅𝑇( 𝜕2𝐺𝑀 𝜕𝑥𝑘 2 )−1 (10) where k = al or ti and 𝐺𝑀 = 𝐺𝑀 𝑥𝑠 + 𝑅𝑇(𝑥𝐴𝑙ln𝑥𝐴𝑙 + 𝑥𝑇𝑖ln𝑥𝑇𝑖) using above relation and equation (3) in equation (10), then 𝑆𝑐𝑐(0) is expressed as 𝑆𝑐𝑐(0) = 𝑅𝑇[−2𝐿0 + (−12𝑥𝐴𝑙 + 6)𝐿1 +(−48𝑥𝐴𝑙 2 + 48𝑥𝐴𝑙 − 10)𝐿2 +(−160𝑥𝐴𝑙 3 + 240𝑥𝐴𝑙 2 − 108𝑥𝐴𝑙 + 14)𝐿3 + 𝑅𝑇 𝑥𝐴𝑙(1−𝑥𝐴𝑙) ]−1 (11) the ideal value of 𝑆𝑐𝑐(0) is calculated using the relation 𝑆𝑐𝑐 𝑖𝑑(0) = 𝑥𝐴𝑙(1 − 𝑥𝐴𝑙) 3. results and discussion in present work, we aim to study the thermodynamic and structural properties of the al-ti liquid alloy at elevated temperatures. when these properties were calculated using linear temperature-dependent interaction parameters of the r-k polynomial, there appeared unusual trends. therefore, the interaction parameters of the system were re-optimised assuming the interaction parameters to be exponential temperature-dependent. for the purpose, the linear parameters were taken from the work of witusiewicz et al. [7] ⁠ and the exponential parameters were optimised using equations (1) and (2), and are presented in the table 1. the excess free energy of mixing (𝐺𝑀 𝑥𝑠) was computed at temperatures 1500 k, 2000 k, 2500 k and 2700 k using equation (3) with the aid of the exponential parameters and the linear parameters of zhang et al. [4]⁠, witusiewicz et al. [7]⁠ and cost 507 [5]⁠ (table1). the compositional dependence of the values so obtained are plotted in figs. 1(a-d). table 1. interaction parameters for the excess free energy of mixing of al-ti liquid alloy gohivar et al./bibechana 19 (1-2) (2022) 75-82 78 reference thermodynamic interaction parameters [j/mol] cost 507 [5] l0 = -108250+38t l1 = -6000+5t, l3 =15000 this work l0 = -134188.7 exp (-5.677x10-4 t), l1 = -4343504.6 exp (-7.01x10-3 t), l3=41482.8 exp (-6.85x10-4 t) zhang et al. [4] l0=-111811.4+34.199t, l1=9746.9+7.69t witusiewicz et al. [7] l0 = -118048+41.972t, l1 =-23613+19.704t, l2 =34757-13.844t at temperature 1500 k, all the computed values of 𝐺𝑀 𝑥𝑠 were found to be in good agreement with each other at lower concentration of ti whereas the values obtained using the parameters of zhang et al. differed from the rest at higher concentration of ti. with the increase in temperatures, the results obtained using the linear parameters showed pronounced wavy natures at lower concentrations of ti (figs. 1(b-d)). these types of variations in (𝐺𝑀 𝑥𝑠) is not in accordance with the general trends. it is an indication of the appearance of an artificial inverted miscibility gap. but this artificial inverted miscibility gap has been removed using the exponential parameters. 1(a) 1(b) 1(c) 1(d) figs. 1(a-d): the compositional dependence of the excess free energy of mixing of the liquid al-ti alloy at different temperatures. gohivar et al./bibechana 19 (1-2) (2022) 75-82 79 the enthalpy of mixing(𝐻𝑀)of the liquid alloy were computed using equation (7a) and the temperature independent terms of the linear parameters of table 1. the temperature-dependent (𝐻𝑀) was computed using equation (7b) and the exponential parameters of table 1. the compositional dependence of hm so computed values is compared in fig. (2). fig. 2: enthalpy of mixing of the liquid al-ti alloy versus concentration of ti at 2000 k. 3(a) 3(b) 3(c) 3(d) figs. 3(a-d): activity of the components of the liquid al-ti alloy versus concentration of ti at different temperatures. gohivar et al./bibechana 19 (1-2) (2022) 75-82 80 the compositional dependence of the computed values of the activities of components al and ti are plotted in figs. 3(a-d). they found to be in well agreement at temperature 1500k (fig. 3(a)). with the increase in temperature of the system, it is observed that the activity of al computed using linear parameters shows negative deviation from raoult's law at lower concentrations of ti. generally, the activity shifts towards ideal values with an increase in temperatures. in this work, this general trend is observed when exponential parameters are used. the study of structural properties like concentration fluctuation in long-wavelength limit (scc (0)) gives information about the arrangement of the atoms in the initial melt. moreover, the positive or negative deviations of scc(0) with respect to its ideal value (𝑆𝑐𝑐 𝑖𝑑(0)) gives information about the nature of local arrangements of atoms, such as for 𝑆𝑐𝑐(0) > 𝑆𝑐𝑐 𝑖𝑑(0)segregating or homo-coordination behaviour is expected and for 𝑆𝑐𝑐(0) < 𝑆𝑐𝑐 𝑖𝑑(0) compound forming or hetero-coordination tendency is expected. 4(a) 4(b) 4(c) 4(d) figs. 4(a-d): the compositional dependence of the concentration fluctuations in long-wavelength limit gohivar et al./bibechana 19 (1-2) (2022) 75-82 81 (scc (0)) of liquid al-ti alloy at different temperatures. the values of 𝑆𝑐𝑐(0) have been computed using equation (11) with the aid of the linear parameter and exponential parameters from table 1 and are plotted in figs. 4(a-d). it is observed that the computed values of 𝑆𝑐𝑐(0) at temperature 1500 k are in good agreement. generally, it is observed that the computed value of 𝑆𝑐𝑐(0) gradually shifts toward the ideal value with the increase in the temperature of the liquid alloys [22]. but in the present work, it is observed that the computed values of 𝑆𝑐𝑐(0) using the linear parameters shifts beyond respective ideal values at the low concentrations of ti (figs. 1(b-d)) with the increase in the temperature of the system. the variation of 𝑆𝑐𝑐(0) beyond the ideal value can be termed as the appearance of the artificial miscibility gap. however, the presence of such trend has been removed by using the exponential temperature-dependence parameters at high temperatures. therefore, it can be concluded that the exponential temperature-dependent parameters of the interaction energy parameters well explain the thermodynamic and structural properties of the liquid al-ti system at preferred higher temperatures. 4. conclusion the linear as well as exponential temperaturedependent interaction parameters were used in the frame work of r-k polynomial to compute the thermodynamic and structural properties of liquid al-ti alloy at constrained higher temperature range, 1500-2700 k. the artificial inverted miscibility gaps (artifacts) appeared in the computed thermodynamic properties (𝐺𝑀 𝑥𝑠) and activity and structural property (scc (0)) at higher temperatures, such as 2000 k, 2500 k, and 2700 k when the interaction parameters were assumed to be linear temperaturedependent. but these gaps were found to be removed when the interaction parameters were assumed to be exponential temperature-dependent. the present study predicts that the thermo-structural properties of the system are well explained by the exponential parameters at considered higher temperature range. acknowledgment we are grateful to the central department of physics, tribhuvan university, kathmandu, nepal for the research facilities. references [1]p. d. desai, thermodynamic properties of selected binary aluminum alloy systems, j. phys. chem.ref.data.16(1987)109-124. https://doi.org/10.1063/1.555788. 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[22]g. kaptay, on the tendency of solutions to tend toward ideal solutions at high temperatures, metall. mater. trans. a phys. metall. mater. sci. 43 (2012) 531-543.https://doi.org/10.1007/s11661-011-0902-x. https://doi.org/10.1016/j.apsusc.2011.11.080 https://doi.org/10.1080/00319104.2014.999337 https://doi.org/10.1016/j.physb.2015.06.015 http://dx.doi.org/10.3126/bibechana.v12i0.11784 https://doi.org/10.1016/j.calphad.2006.02.007 https://doi.org/10.1016/j.calphad.2009.08.004 https://doi.org/10.1016/j.tca.2011.10.017 https://doi.org/10.1016/.calphad.2016.06.003 https://doi.org/10.1080/14786435.2020.1825858 https://doi.org/10.1016/j.calphad.2004.08.005 https://doi.org/10.1021/ie50458a036 https://doi.org/10.1080/00319108408080778 https://doi.org/10.1007/s11661-011-0902-x bibechana vol. 21, no. 2, august 2024, 124-128 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar radiation level over the bishnumati river bridges: a study from balaju to teku in kathmandu, nepal nirmal kc1, roshan chalise1,2,∗, anita mishra2, himali kalakhety3 raju khanal2 1patan multiple campus, patan dhoka, lalitpur, tribhuvan university, kathmandu, nepal 2central department of physics, tribhuvan university, kirtipur, nepal 3department of physics and geosciences, texas a& m university, kingsville, texas, usa ∗corresponding author: email: plasma.roshan@gmail.com abstract the presence of background radiation is ubiquitous, extending even to bridges. notably, the bridges spanning the bishnumati river are situated close to solid waste collection centers, garages, and significant religious sites such as shovabhagwati, indrayani, and kankeswori. this study aims to assess the radiation exposure levels across 14 different bridges along the bishnumati river, from balaju to teku, utilizing a professional digital geiger counter gca07w. the surveyed bridges encompass various types, including vehicle, bailey, and semisuspension bridges. results reveal that the shovabhagwati bridge exhibits the highest annual effective dose rate at 1.025 ± 0.230 msv/yr, while the nilbarahi bridge records the lowest at 0.696 ± 0.237 msv/yr. remarkably, the vehicle-cemented bridge displays elevated background radiation, attributed to the construction materials, such as cement, iron rods, and other components. the average annual effective dose across all surveyed bridges is 0.906 ± 0.230 msv/yr, remaining below the recommended dose set by the international commission on radiological protection (icrp). importantly, no harmful radiation levels are detected between balaju and teku along the bishnumati river bridges in kathmandu, nepal. this study contributes valuable insights into the radiation landscape of these structures, offering reassurance regarding public safety within the surveyed area. keywords background radiation, geiger counter, exposure, annual effective dose (aed) article information manuscript received: december 31, 2023; revised: february 2, 2024; accepted: march 7, 2024 doi https://doi.org/10.3126/bibechana.v21i2.61268 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 124 http://nepjol.info/index.php/bibechana plasma.roshan@gmail.com https://doi.org/10.3126/bibechana.v21i2.61268 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ nirmal kc et al./ bibechana 21 (2024) 124-128 125 1 introduction background radiation, a ubiquitous phenomenon in the natural environment, constitutes a continuous presence in our surroundings. individuals are consistently exposed to this natural background radiation, which varies based on factors such as the presence of radionuclides in the earth's crust, altitude, industrial activities, and anthropogenic byproducts. the decay of natural radionuclides like uranium and thorium results in the formation of radium and radon, disseminating into soil, water, plants, and air. radon, notably, stands as the largest contributor to natural radiation exposure [1] as shown in figure 1 [2]. the release of uranium into the environment occurs through natural events like forest fires, volcanic activities, weathering, and erosion of rock and soil. consequently, uranium and its decay products are assimilated by plants and animals, eventually reaching humans through inhalation, ingestion, and absorption from food, water, and air [3]. average activity levels of all radio-nuclides were found to surpass the global average, aligning with the geological and geochemical characteristics of the investigated area's rocks [4]. soil samples from diverse locations indicated the potential for radon concentrations in dwellings to exceed the recommended level of 300 bq/m3 for residential areas [5]. soil samples in the kathmandu valley displayed varying radon exhalation rates, corresponding to the indoor radon exhalation of dwellings [6]. sundhara exhibited the lowest average dose rate, while budhanilkantha recorded the highest. the kathmandu valley's average annual effective dose of 0.475 msv/yr [7] is slightly lower than the global terrestrial average of 0.5 msv/yr [3]. building materials studied in the region, except for gneiss rocks from shai hills with elevated cancer risk, were deemed safe for construction [8]. in pokhara city, diverse locations showed varying dose rates, with the average annual effective dose rate of 0.56 msv/yr falling within recommended levels and comparable to kathmandu city's average annual effective dose [9]. while numerous surveys have explored background radiation in various locations of nepal and the kathmandu valley, there is a notable gap concerning bridge structures. bridges, serving as connections between riverbanks, involve excavation during construction, potentially releasing more radon into the air and increasing concrete-related radiation. this study aims to assess background radiation on 14 bridges spanning the bishnumati river, evaluating whether the measured exposure dose exceeds reference levels. figure 1: sources of natural background radiation [2]. 2 material and methods the gca-07w professional gm counter [10], as depicted in figure 2, was used in this work to measure radiation levels at 14 different bridges spanning from balaju to teku over the bishnumati river during the period of 19-23 july 2020. the selection of bridges for this study was driven by the potential impact of local environmental factors, such as waste disposal sites and cremation centers, on background radiation levels. furthermore, the study was conducted during the covid-19 pandemic to capitalize on reduced human activity and traffic, thereby minimizing external variables that could affect the accuracy of radiation measurements. consequently, all 14 bridges spanning the bishnumati river within the core area of kathmandu city have been chosen for our present study. a geographical overview of the selected area is presented in figure 3, capturing a screenshot or picture of the original map. nirmal kc et al./ bibechana 21 (2024) 124-128 126 figure 2: gca-07w geiger counter [10]. figure 3: geographical overview of the study area with locations of the bridges. to ensure data accuracy, 30 different measuring points were sampled on each bridge. the average dose and standard deviation for each bridge were computed, considering measurements taken on the northern side, southern side, and middle of the bridges. this method allows for a comprehensive assessment of background radiation across the selected bridges, taking into account potential variations in exposure levels at different points on each structure. the gm counter was positioned one meter above the ground during data collection, with counts per minute (cpm) converted to annual exposure rates. the annual effective outdoor dose rate for background radiation was calculated using the nirmal kc et al./ bibechana 21 (2024) 124-128 127 following expression: aed = d ( msv hr ) × 8760hr yr × 0.2× 0.7 (1) where d is the outdoor dose rate, 8760 is the conversion factor of hours per year, 0.2 is the outdoor occupancy factor and 0.7 is the conversion factor [11]. 3 results and discussion the outdoor exposure rates for 14 different bridges are presented in table 1. in the table, the second to fifth columns represent the names of the bridges, their gps coordinates, average exposure rates, and annual effective dose rates, respectively. the values in the brackets of columns four and five represent their corresponding standard deviations. table 1 indicates that the shovabhagwati bridge exhibits the maximum outdoor background radiation, whereas the minimum value is observed at the nilbarahi bridge. the radiation values of the other bridges fall within these two extremes. data from the table are also presented graphically in figure 4 for better interpretation. figure 4 illustrates the annual effective dose of all 14 bridges on the bishnumati river, ranging from 0.696 to 1.025 msv/yr. the nilbarahi bridge records the minimum, while the shovabhagwati bridge shows the maximum annual effective dose. the average annual effective dose for all 14 bridges on the bishnumati river is 0.906 ± 0.230 msv/yr, slightly higher than previous works [7–9], but within the annual effective dose limit of 1 msv/yr recommended by the icrp for the public [12]. figure 4: annual effective dose of different bridges on the bishnumati river from balaju to kuleshwor (teku), kathmandu, nepal. table 1: effective dose from natural background radiation on the 14 bridges over the bishnumati river. s.n. bridges gps coordinate d (msv/yr) aed (msv/yr) 1 balaju 27.7255 n, 85.3053 e 0.720 (0.151) 0.883 (0.185) 2 miteri 27.7225 n, 85.3013 e 0.666 (0.168) 0.817 (0.206) 3 chamati new 27.7197 n, 85.2995 e 0.773 (0.181) 0.948 (0.221) 4 chamati 27.7137 n, 85.3022 e 0.736 (0.198) 0.903 (0.242) 5 shovabhagwati 27.7149 n, 85.3017 e 0.836 (0.188) 1.025 (0.230) 6 dhalko 27.7117 n, 85.3025 e 0.790 (0.235) 0.969 (0.288) 7 dallu 27.7094 n, 85.3029 e 0.786 (0.179) 0.964 (0.219) 8 dallu new 27.7088 n, 85.3027 e 0.786 (0.193) 0.964 (0.236) 9 kankeswori 27.7069 n, 85.3022 e 0.648 (0.192) 0.795 (0.235) 10 shankhadhar 27.7038 n, 85.3053 e 0.720 (0.151) 0.883 (0.185) 11 tahachal 27.7255 n, 85.3020 e 0.819 (0.160) 1.004 (0.196) 12 nilbarahi 27.7008 n, 85.3026 e 0.568 (0.194) 0.696 (0.237) 13 teku 27.6980 n, 85.3023 e 0.822 (0.233) 1.008 (0.285) 14 kuleshwor 27.6923 n, 85.3010 e 0.747 (0.147) 0.916 (0.180) nirmal kc et al./ bibechana 21 (2024) 124-128 128 the observed exposure rates in this study are lower than the global average and remain within acceptable levels. although these rates are higher than previous findings [7, 8, 9], they do not pose a major concern for public safety. therefore, the public can continue their activities without restriction, but caution is advisable. 4 conclusions this study assessed the background radiation doses of 14 bridges spanning the bishnumati river from balaju to teku. the findings reveal that the shovabhagwati bridge exhibits the highest annual effective dose rate at 1.025 ± 0.230 msv/yr, while the nilbarahi bridge records the lowest at 0.696 ± 0.237 msv/yr. notably, cemented-motorable bridges demonstrate a relatively higher radiation exposure compared to non-motorable bailey or suspension bridges. three bridges, namely shovabhagwati, tahachal, and teku, slightly exceed the recommended dose, while all other bridges maintain doses below the recommended levels. on average, the cumulative dose remains well below the limit for public exposure. consequently, it can be concluded that the background radiation levels on these bridges pose no hazard to the general public. these results establish a baseline, indicating the absence of biologically hazardous radiation pollution, rendering these bridges safe for public exposure to natural radiation. future work is recommended, including an exploration of the correlation between bridge materials and radiation levels. additionally, further investigation into seasonal radiation variations over the bridges may provide valuable insights. these avenues of research can contribute to a more comprehensive understanding of the factors influencing radiation levels on bridges and help enhance safety measures for public infrastructure. references [1] https://www.epa.gov/radtown/ background-radiation (accessed on august 15, 2020) [2] http://2.bp.blogspot.com/ohlswlruqw0/ uiaqlu13ysi/aaaaaaaaijq/cejdt4rxy54/ s1600/background-radiation1.jpg (accessed on august 10, 2020). [3] united nations scientific committee on the effects of atomic radiation. sources, effects and effects of ionizing radiation annex b. exposures from natural radiation sources. united nations: new york.,2000 [4] c. ningappa, j. sannappa, and n. karunakara. study on radionuclides in granite quarries of bangalore rural district, karnataka, india. radiation protection dosimetry, 131:495–502, 2008. [5] f. girault, a. p. gajurel, f. perriera, b. n. upreti, and p. richon. radon emanation of heterogeneous basin deposits in kathmandu valley, nepal. journal of asian earth sciences, 40:595–610, 2011. [6] p. parajuli, d. thapa, and b. r. shah. study of radon exhalation rate in soil samples of kathmandu valley using passive detector lr115. international journal of chemical and physical sciences, 4:30–39, 2015. [7] p. pantha, t. p. bhusal, b. r. shah, and r. p. koirala. study of natural background radiation in kathmandu valley. bibechana, 16:187– 195, 2018. [8] f. otoo, e. o. darko, m. garavaglia, c. giovani, s. pividore, a. b. andam, j. k. amoako, o. k. adukpo, s. inkoom, and s. adu. public exposure to natural radioactivity and radon exhalation rate in construction materials used within greater accra region of ghana. scientific african, 1:e00009, 2018. [9] s. p. gautam, a. silwal, s. acharya, and b. aryal. annual effective dose from natural background radiation in pokhara, nepal. asian journal of research and reviews in physics, 3:36–42, 2020. [10] https://www.imagesco.com/geiger/ digital-geiger-counter.html (accessed on august 15, 2020). [11] united nations scientific committee on the effects of atomic radiation. sources, effects and risks of ionizing radiation. report to the general assembly, with annexes, 1988. [12] a. d. wrixon. new icrp recommendations. journal of radiological protection, 28:161, 2008. https://www.epa.gov/radtown/background-radiation https://www.epa.gov/radtown/background-radiation http://2.bp.blogspot.com/ohlswlruqw0/uiaqlu13ysi/aaaaaaaaijq/cejdt4r xy54/s1600/background-radiation1.jpg http://2.bp.blogspot.com/ohlswlruqw0/uiaqlu13ysi/aaaaaaaaijq/cejdt4r xy54/s1600/background-radiation1.jpg http://2.bp.blogspot.com/ohlswlruqw0/uiaqlu13ysi/aaaaaaaaijq/cejdt4r xy54/s1600/background-radiation1.jpg https://www.imagesco.com/geiger/digital-geiger-counter.html https://www.imagesco.com/geiger/digital-geiger-counter.html introduction material and methods results and discussion conclusions bibechana vol. 22, no. 1, april 2025, 63-72 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar thermal properties and non-bonded interactions in human pmp2 variants: a molecular dynamics study prabin aryal, jhulan powrel department of physics, butwal multiple campus, tribhuvan university ∗corresponding author. email: prabinaryal.0d@gmail.com(pa) jhulan.sumi@gmail.com(jp) abstract charcot-marie-tooth disease, a genetic disorder linked to mutations in the peripheral myelin protein 2, currently lacks an effective cure. in this study, we have used molecular dynamics simulations, focusing on non-bonded interactions and thermal properties, to explore the effects of m114t mutation on pmp2 at the temperatures of 305k, 310k and 315k. our findings indicate that the mutation slightly destabilizes pmp2, reducing its structural integrity by decreasing hydrogen bonds and altering few salt bridges, although the differences are minimal. additionally, the mutant exhibits slightly increased thermal diffusivity. a nonlinear change in cv with temperature was also observed in both protein systems. this work further extends to verify the maxwell-boltzmann distribution law and demonstrate the gaussian nature of the temperature fluctuations in the protein systems. keywords charcot-marie-tooth 1a, comparative analysis, m114t mutant, nanoscale molecular dynamics. article information manuscript received: september 24, 2024; revised: january 13, 2025; accepted: january 15, 2025 doi https://doi.org/10.3126/bibechana.v22i1.70049 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction neurons are a type of specialized cells in the nervous system through which electrical impulses, also known as action potential, propagate to different cells in the rest of the body [1]. for efficient transmission of electrical impulses, the axons in the neurons are insulated by concentric layers of plasma membranes called a myelin sheath [2]. in the central nervous system, the oligodendrocyte cells make and maintain myelin sheath, whereas in the peripheral nervous system this is done by the schwann cells [3]. a single schwann cell forms one myelin sheath. high level of saturated long chain fatty acids is present in myelin along with fatty acid binding proteins like myelin basic protein (mbp) and peripheral myelin protein 2 (pmp2) which play a crucial role in inter-molecular cohesion with the lipids which stack the myelin layers together to form myelin sheath [4,5]. in particular, pmp2 is one of the most prevalent constituents in the myelin of the human pns [6]. mutations in pmp2 protein have been linked with various types of charcot-marie-tooth (cmt) disease [7–10], a hereditary motor and sensory neuropathy (hmsn), which primarily targets the 63 http://nepjol.info/index.php/bibechana prabinaryal.0d@gmail.com jhulan.sumi@gmail.com https://doi.org/10.3126/bibechana.v22i1.70049 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ prabin aryal and jhulan powrel/ bibechana 22 (2025) 63-72 64 peripheral nervous system [11]. one such recently discovered mutation in this protein is m114t, which was associated with the cmt type 1a disease in german and bulgarian families [10]. many attempts, including using ascorbic acid [12], have failed to cure cmt disease, as no significant improvement in nerve conduction velocity was observed. to date, no therapeutic cure exists. research on the pmp2 protein has revealed its tetragonal crystal structure in the space group p 41 21 2. its molecular weight is approximately 15 kda, and has high solubility in aqueous buffer solution. the structure of protein plays an important role in proper functioning. destabilized structures can result in the loss of function which can lead to aggregation of protein and formation of toxic species. in the case of this protein, there are ten anti-parallel β strands and two α helices [13]. there is a fatty acid, palmitate, inside the barrel shape of the protein. from the atomistic molecular dynamics simulation study of wild-type pmp2, it was found that the absence of this fatty acid increased the dynamics in the 2α helix [14]. non-bonded interactions within protein structures dictate their integrity and function, with alterations leading to misfolding and aggregates linked to diseases like alzheimer’s and parkinson’s.. the mutant protein has a similar tetragonal crystal structure, but with increased fatty acid binding ability. also, using the cd spectroscopy, the melting temperature for wildtype protein was found to be +61.6°c whereas that for m114t mutant was +49.2°c [15]. figures 1 and 2 show the chemical structures of methionine (left) and threonine (right) at the mutation site, and the normal pmp2 protein with methionine and threonine at position 114, respectively. cmt disease has a low mortality rate, with children being at relatively higher risk than adults [16]. however, there is a greater risk on the mental health of patients as they are psychologically more vulnerable. issues like depression, anger, guilt, and frustration due to lack of independence could disturb their mental peace and well-being [17]. while previous research has explored the structural and functional roles of pmp2, there has been limited focus on the effects of this specific mutations on interaction dynamics and thermal behavior. so, this research work got attention towards the comparative study of non-bonded interactions and thermal properties in normal and m114t mutant human pmp2 protein. also, no such study has yet been done at temperatures of 305 k, 310 k, and 315 k – the normal and extreme core body temperatures in humans [18, 19]. as there are many enzymatic activities essential for cellular processes, studying the changes in the thermal properties and their impact on them is crucial to understanding the effects of the mutation on the body, which can aid in the development of proper therapeutic drugs. we have presented the details regarding the methods and methodology in section 2, computational details in section 3, and the results and discussions in section 4. finally, the conclusions and concluding remarks are presented in the section 5. figure 1: chemical structure of methionine (left) and threonine (right) in the amino acid chain of pmp2 near mutation cite. figure 2: normal pmp2 protein with methionine at 114th position (left), and mutant pmp2 protein with threonine at the 114th position (right). 2 methods and methodology in molecular dynamics, different properties such as rmsd, h-bonding, salt bridge formation, etc can be estimated using the information of the trajectories of the particles in 6n-dimensional phase space. for this, at first the particles are assigned a position. then, the subsequent positions during simulation are generated by solving the equation of motion given by, mi ∂2ri(t) ∂t2 = fi {ri(t)} − γi dri(t) dt + ri(t) (1) where mi ∂2ri(t) ∂t2 , fi {ri(t)} and γi dri(t) dt are the net force on the ith atom, total force on the ith atom due to the neighbouring atoms, and damping force, respectively at time t. and ri(t) accounts for the random force that acts on the atoms [20]. both the bonded (vb) and non-bonded (vnb) potentials act on the system. if the ith and jth atom at distance rij have partial charges qi and qj, then the total potential (vt) is obtained as, v t = v b + v nb (2) prabin aryal and jhulan powrel/ bibechana 22 (2025) 63-72 65 where vb = vbond + vangle + vimproper + vproper , and vnb = vlj + vcoulomb the lennard-jones potential vlj, between a pair of atoms is given by the equation [21], vlj = 4ε [(σ r )12 − (σ r )6] (3) and the coulomb electrostatic interaction potential vcoulomb is given by the equation, vcoulomb = qi ·qj 4πϵmrij (4) 2.1 root mean square deviation (rmsd) the rmsd at an instant is the standard deviation of the position of the atom from mean position at that instance. it tells about the stability of the protein over time and can be used to compare the structure and conformation of two proteins. higher value of rmsd means reduced stability. the equation that gives the rmsd of a system [22] is, rmsd (ti) = √√√√(∑nα α=1 ( −→rα (ti) − ⟨−→rα⟩) 2 nt ) (5) with, ⟨−→rα⟩ = 1 nt nt∑ i=1 ⟨−→rα (ti)⟩ here, nα and nt respectively represent the number of atoms and number of time steps over which atomic positions are being compared, −→rα (ti) represents the position of atom α at time ti and ⟨−→rα (ti)⟩ represents the corresponding average value [23]. 2.2 hydrogen bonds hydrogen bond is a non-bonded interaction, so the bonds are not stable over time. as such, the stability and strength can be understood only by analysing the average frequency of formation of hbonds. it contributes to the elastic stiffness of the protein and its structural stability. for moderate strength h-bonding, which is mainly electrostatic, the donor-acceptor distance is 2.5 å 3.2 å [24]. in this research, cutoff distance and angle for h-bonds is taken as 3.2 å and 30◦, respectively. however, due to this approximation, the weak h-bondings will not be taken into account, which might bring some error in the observed results. 2.3 salt bridges salt bridge is a type of non-bonded interaction that exists between acidic and basic residues. if such residues are within the cutoff distance than they are counted as salt bridges. here, the oxygen-nitrogen cutoff distance for the salt bridges is taken as 3.2 å. salt bridges prevent the diffusion of solution [25]. 2.4 gaussian distribution gaussian distribution is one of the widely observed distribution identified by the probability distribution function [26], p (x) = 1√ 2πσx exp ( − (x− ⟨x⟩)2 2σ2 x ) −∞ ≤ x ≤ +∞ (6) where x is the random variable, whose expectation is ⟨x⟩ and standard deviation is σx. the temperature fluctuation of the system in the nve ensemble is expected to follow the gaussian distribution [22]. 2.5 maxwell-boltzmann distribution law according to maxwell and boltzmann [27, 28], the distribution of molecular velocity (v) of an ideal gas of molecular mass m at absolute temperature t is described by the function, f(v) = √ 2 π v2e− v2 2a2 a3 , v ≥ 0 (7) with parameter a = √ kbt m , where kb is boltzmann constant. using the expression for kinetic energy, ek = 1 2 mv2 = 3 2 kbt and with proper normalization, we get the probability distribution function for the kinetic energy [22] as, f (ek) = 2√ π 1 (kbt ) 2 3 √ ek exp ( − ek kbt ) (8) 2.6 thermal diffusivity the three-dimensional heat equation is, ∂t (−→r , t) ∂t = d · ∇2t (−→r , t) (9) the time dependence of the average temperature in the water-sphere system considered here is given by the equation [22], ⟨t ⟩ (t) = tbath +6·tinitial − tbath π2 ∞∑ n=1 1 n2 exp [ − (nπ r )2 dt ] (10) where tbath and tinitial are the temperatures of outer shell of sphere and the initial temperature of the interior of sphere, respectively. r (= 25 å) is prabin aryal and jhulan powrel/ bibechana 22 (2025) 63-72 66 radius of sphere excluding the outer shell of thickness 5 å. to fit a curve with the obtained data, we have approximated to the first 11 terms only, and the other terms are neglected. so, the expression considered here is, ⟨t ⟩ (t) = 200 + 66.87 · [ ∞∑ i=1 1 i2 · e−i2·0.0158·d·t ] (11) 2.7 specific heat capacity at constant volume (cv) molar specific heat capacity is the amount of heat required to raise the temperature of one mole of a substance by one kelvin. in namd, the specific heat capacity at constant volume can be obtained from a single nvt production simulation using the equation [29,30], cv = 〈 e2 〉 − ⟨e⟩2 kbt 2 (12) where ⟨e⟩ is the average of the total energy and〈 e2 〉 is the average of the square of the total energy. 3 computational details this research is based on the theoretical and computational techniques of molecular dynamics. for this, the structure of the wild-type and m114t mutant pmp2 proteins were obtained from rcsb.org. the pdb id of the chosen wild-type protein is 2wut and of the chosen mutant is 7nrw. then, the simulation is performed using the namd (nano scale molecular dynamics) and vmd (visual molecular dynamics) softwares. however, in molecular simulations using these softwares, there are some approximations like fixed force fields and cutoff distances which might not fully capture the long-range interactions. at first, steps for the energy minimization are performed, followed by system equilibration. finally, production simulation is run to obtain the final data. the rmsd is calculated from the equilibration output to check for the system stability before starting the production run, whereas rest of the analysis is done from the output of production run. for this, six systems are designed: two proteins, each kept at temperatures of 305 k, 310 k, and 315 k. the system's ph is set to 7.4, with a 12 å cutoff distance, 16 å pairlist distance, and an initial pressure of 1 bar. this limited cutoff for pairlist distance could lead to the interactions at the boundaries not being accounted, which might lead to inaccuracies in energy calculations; however, with a 2 fs timestep, these inaccuracies are expected to be minimal.. also, for the study of non-bonded interactions, some k+ and clare added to set the system to a 0.15 m/litre concentration; however, for the study of thermal diffusivity, no ions are placed. the proteins are solvated with tip3 water using modified charmm force field (charmm 36m). equilibration and production both are done in the nvt ensemble. the details of the setup are as follows: for the study of non-bonded interactions, the wild-type pmp2 (2wut) with 2,154 atoms is placed in a cubical water box of side length 67 å. the study is done at the three temperatures with minute difference in the total number of atoms: 28,027 atoms at 305 k, 27,972 atoms at 310 k, and 28,009 atoms at 315 k. however, in mutant protein (7nrw) with 2,151 atoms, the cubical box is of side length 65 å. the number of atoms for mutant at 305 k is 25,711, at 310 k is 25,741, and at 315 k is 25,720. the parameters, as mentioned above, are the same at all temperatures. furthermore, for the study of thermal diffusivity, both the proteins are kept inside a water sphere of radius 30 å, with wild-type protein containing 11,551 atoms and mutant containing 11,563 atoms, at temperature of 310 k. temperature coupling feature of namd is used to set the interior temperature to 300 k and that of outer shell (of thickness 5 å) to 200 k. at last, for the verification of maxwellboltzmann law, the systems are equilibrated for 100 ps in nvt ensemble at 310 k by removing the constraints — the atoms are set free to move and none of the bonds are kept rigid. the distribution is studied from the last time frame of the simulation. in addition to this, for the study of temperature fluctuation, a 1 ns production simulation is performed in nve ensemble by turning off the thermostat and barostat. this approach overlooks quantum effects, crucial in biological systems, making the results purely classical. additionally, short simulation timescales limit insights into slower or large-scale dynamics. 4 results and discussions in this section, we have presented the results of the various analyses performed on the two proteins in both graphical as well as tabular form. the positions of atoms at different instances were calculated using equation (1), the vdw and electrostatic interaction energies were calculated using equations (3) and (4), respectively. equations (5), (11) and (12) were used to calculate rmsd, thermal diffusivity and specific heat capacity at constant volume, respectively. for the verification of maxwellboltzmann law of distribution of kinetic energy, prabin aryal and jhulan powrel/ bibechana 22 (2025) 63-72 67 equation (8) was used, whereas to study temperature fluctuation in nve ensemble and to fit a curve, equation (6) was considered. the rmsd of both proteins and corresponding distribution at 305 k, 310 k and 315 k are shown in figure (3), (4) and (5), respectively. for wildtype protein, rmsd values at 305 k, 310 k and 315 k were 0.27 å, 0.27 å and 0.28 å, respectively. for mutant, rmsd values at all temperatures were approximately the same at 0.28 å. the standard deviation in the observed rmsd of both proteins at all temperatures was approximately the same with value of 0.01. the range of fluctuation of rmsd was between 0.05 å and 0.07 å, with 0.07 å being for both proteins at 315 k. increasing trend of rmsd with increase in temperature was observed. figure 3: rmsd graph of p2wt and m114t at 305 k (left), and corresponding distribution (right) figure 4: rrmsd graph of p2wt and m114t at 310 k (left), and corresponding distribution (right). figure 5: rmsd graph of p2wt and m114t at 315 k (left), and corresponding distribution (right). the number of h-bonds formed in both proteins and corresponding distribution at 305 k, 310 k and 315 k are shown in figure (6), (7) and (8), respectively. the average number of h-bonds formed was as follows: at 305 k, 81.46 with standard deviation of 4.78 for p2wt and 79.14 with standard deviation of 4.66 for m114t; at 310 k, 80.19 with standard deviation of 4.98 for p2wt and 79.29 with standard deviation of 5.03 for m114t; at 315 k, 79.91 with standard deviation of 4.83 for p2wt and 77.28 with standard deviation of 4.97 for m114t. the fluctuation in the number of h-bonds formed was between 29 to 35. gradual reduction in the formation of hbonds with increase in temperature was observed. table 1 shows the average rmsd and number of h-bonds formed in both proteins at all three temperatures. figure 6: graph of number of h-bonds formation over time in both proteins at 305 k (left), and corresponding distribution (right). figure 7: graph of number of h-bonds formation over time in both proteins at 310 k (left), and corresponding distribution (right). figure 8: graph of number of h-bonds formation over time in both proteins at 315 k (left), and corresponding distribution (right). prabin aryal and jhulan powrel/ bibechana 22 (2025) 63-72 68 table 1: for wild-type and mutant pmp2 protein at various temperatures. protein temperature (k) avg. rmsd (å) avg. num of h-bonds p2wt (2wut) 305 0.269 81.458 310 0.267 80.193 315 0.275 79.913 m114t (7nrw) 305 0.282 79.136 310 0.279 79.288 315 0.280 77.277 figure (9), (10) and (11) show the bar-plot of average occupancy of salt bridges (in å) in p2wt and m114t at 305 k, 310 k, and 315 k, respectively. salt bridges between few residue pairs were absent, shown by vacancy in the plot; taller plots indicate weaker salt-bridges. the most noticeable difference is observed in the residue pair asp18-lys22 and asp19-lys22 at 315 k. decreasing strength of salt-bridges with increase in temperature was observed. figure 9: average salt-bridge occupancy in both proteins at 305 k. figure 10: average salt-bridge occupancy in both proteins at 310 k. figure 11: average salt-bridge occupancy in both proteins at 315 k. the particles of both systems were found to follow the maxwell-boltzmann law of distribution of kinetic energy. the degree of agreement of the observed data with the theoretical distribution can be seen in figure (12). in both systems, the parameter of the observed data was about 0.61 and of the fitted curve was about 0.63. furthermore, the graph of temperature fluctuation over time in both proteins at 310 k is shown in figure (13) with the corresponding distribution shown in figure (14). the observed average temperature of the system with p2wt was 308.98 k with standard deviation of 1.47, while that with m114t was 308.83 k with standard deviation of 1.53. as expected, the distribution of temperature in nve ensemble was found to be gaussian in nature. prabin aryal and jhulan powrel/ bibechana 22 (2025) 63-72 69 figure 12: maxwell-boltzmann energy distribution at 310 k for p2wt (left), and for m114t (right). figure 13: graph of temperature vs simulation time in both proteins at 310 k. figure 14: temperature distribution at 310 k in p2wt (left), and for m114t (right). figure (15) shows the change in temperature during the course of simulation in both proteins. from the simulation, the thermal diffusivity of the p2wt was found to be 4.03× 10−7 m2s−1 while that for the m114t was 4.06 × 10−7 m2s−1, as show in table 2. prabin aryal and jhulan powrel/ bibechana 22 (2025) 63-72 70 figure 15: graph of temperature vs simulation time for heat diffusion in both proteins. table 2: for wild-type and mutant pmp2 protein at 310 k temperature. protein thermal diffusivity (m2 s-1) p2wt (2wut) 4.033× 10−8 m114t (7nrw) 4.063× 10−8 the graph of fluctuation of total energy over time in both proteins at temperature of 305 k, 310 k and 315 k are shown in figure (16), (17) and (18), respectively. the observed specific heat capacity at constant volume for both proteins at various temperatures are shown in table 3. at 305 k, p2wt was found to have specific heat capacity of 155.02 kcal/mol·k, which decreased to 146.45 kcal/mol·k at 310 k and increased again to 173.89 kcal/mol·k at 315 k. for m114t, at 305 k, the specific heat capacity was found to be 138.05 kcal/mol·k, which increased to 166.72 kcal/mol·k at 310 k and decreased back to 139.68 kcal/mol·k. table 3 also shows the observed vdw and electrostatic interaction energies along with their sum in both protein systems. these energies were found to decrease with temperature, with the p2wt system having higher energies than that of the mutant system at all temperatures. figure 16: graph of total energy fluctuation over time in both proteins at 305 k. figure 17: graph of total energy fluctuation over time in both proteins at 310 k. figure 18: graph of total energy fluctuation over time in both proteins at 315 k. prabin aryal and jhulan powrel/ bibechana 22 (2025) 63-72 71 table 3: for system with wild-type and mutant pmp2 protein at different temperatures (in kcal/mol for energies and kcal/molk for cv). protein temperature (k) vdw electrostatic sum cv (kcal/molk) p2wt (2wut) 305 8264.38 -100956.64 -92692.26 155.02 310 8139.54 -100146.00 -92006.46 146.45 315 8048.23 -99679.56 -91631.33 173.89 m114t (7nrw) 305 7589.58 -94075.41 -86485.83 138.05 310 7501.03 -93641.22 -86140.19 166.72 315 7397.91 -93043.12 -85645.21 139.68 5 conclusion and concluding remarks in this study, the rmsd of both proteins was found to be within the valid range (< 4 å). the rmsd of wild-type protein was in the range of 0.26 å to 0.27 å while that of mutant was between 0.27 å to 0.28 å. with the increase in temperature from 305 k to 315 k, the decrease in the average number of h-bonds formation—in wild-type, from 81.46 to 79.91, whereas in mutant, from 79.14 to 77.28— suggests reduction in stability of the protein; this is due to increased thermal agitation; such a drug specimen is to be chosen that can form strong nonbonded interactions with the protein, and optimized accordingly to increase the efficiency of the treatment. a notable difference in the formation of salt-bridges were observed, especially in the residue pairs asp18-lys22 and asp19-lys22 at higher temperatures, suggesting a clear difference in diffusion of solution. the mutant showed slightly better thermal diffusivity, but compared to water, both proteins were slow at conducting heat; this is vital in understanding how heat dissipation through protein takes place during drug-protein binding. the magnitude of sum of vdw and electrostatic interaction energies is higher in the system with wildtype protein suggesting a stronger non-bonded profile compared to that with mutant; it decreases with increase in temperature in both proteins which is due to increase in mean free path of the atoms. finally, the cv of both systems were found to have a non-linear (concave nature) change, with system of wild-type protein being generally higher; drugs should be designed accordingly to prevent protein denaturation caused by heat generated during drugprotein binding. this unusual variation of cv in both systems is not well understood. we found the necessity to study the variation of cv of both proteins at smaller temperature increments. additionally, studying the vdw and electrostatic interaction energies within the proteins, as well as their mechanical and other transport properties, is crucial for gaining a deeper insight into the effects of this mutation, and for the development of a therapeutic drug for cmt1a disease. acknowledgements p.a. expresses deep gratitude to all the teachers of the department of physics, butwal multiple campus for their constant support and guidance throughout this research work. he also extends his sincere thanks to his family and friends who played a pivotal role in advising and motivating him during this course. references [1] j. a. kiernan and m. l. barr. barr’s the human nervous system: an anatomical viewpoint. lippincott williams & wilkins, 2009. 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[30] j. powrel and n. p. adhikari. thermal properties of normal and sickled hemoglobin protein. bibechana, 18(1):140–148, 2021. introduction methods and methodology root mean square deviation (rmsd) hydrogen bonds salt bridges gaussian distribution maxwell-boltzmann distribution law thermal diffusivity specific heat capacity at constant volume (cv) computational details results and discussions conclusion and concluding remarks bibechana vol. 20, no. 1, april 2023, 10–20 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar porous activated carbon materials from triphala seed stones for high-performance supercapacitor applications chhabi lal gnawali1,∗, sabina shahi2, sarita manandhar3, ganesh kumar shrestha1, mandira pradhannanga adhikari2, rinita rajbhandari1, bhadra p. pokharel1 1department of applied sciences and chemical engineering, pulchowk campus, institute of engineering (ioe), tribhuvan university, lalitpur, nepal 2central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal 3tri-chandra multiple campus, kathmandu, nepal ∗corresponding author. email: chhabig123@ioe.edu.np abstract porous activated carbon materials derived from biomass could be the suitable materials for high-rate performance electrochemical supercapacitors as it exhibits high surface area due to the development of nanopores. here, we report the novel porous activated carbon from triphala seed stones by chemical activation with zinc chloride at different carbonization temperature (400-700 0c) under the nitrogen gas atmosphere. the activated carbon was characterized by fourier transform-infrared (ftir) spectroscopy, raman scattering and scanning electron microscopy (sem). nitrogen adsorption-desorption measurements was used to study the surface properties (effective surface areas, pore volumes and pore size distributions). the electrochemical measurements were performed in an aqueous 1 m sulphuric acid (h2so4) solution in a three-electrode cell set up. the specific surface area of triphala seed stones-derived porous carbon materials with well-defined microand mesopores ranges from 878.7 to 1233.3 m2 g−1 and total pore volume ranges from 0.439 to 0.626 cm3 g−1. the specific capacitance obtained by electrochemical measurement experiment was 208.7 f g−1 at 1 a g−1. these results indicate that the prepared nanoporous activated carbon material from triphala seed stones would have significant possibility as supercapacitor electrode material for high-energystorage supercapacitor applications. keywords triphala seed, chemical activation, zinc chloride, nanoporous, electrochemical measurement, supercapacitor. article information manuscript received: march 21, 2023; accepted: march 28, 2023 doi https://doi.org/10.3126/bibechana.v20i1.53432 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 10 http://nepjol.info/index.php/bibechana chhabig123@ioe.edu.np https://doi.org/10.3126/bibechana.v20i1.53432 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ chhabi lal gnawali et al./ bibechana 20 (2023) 10-20 11 1 introduction in 21st century, because of urbanization, industrialization as well as the rapid growth of population, the energy storage and the environmental pollution are considered thoughtful challenges worldwide. the continuous depletion of fossil fuel, climate change due to excessive greenhouse gases, high energy cost leads the society towards renewable as well sustainable energy sources so it is essential to develop the sustainable energy storage system with high power density and energy density. nowadays, the electrochemical energy storage systems like lithium-ion batteries, fuel cells, solar cells, supercapacitors are widely used in electronics and electrical vehicles [1–4]. so, researchers have keen interest on supercapacitors with ultrahigh power density, fast charging discharging rates, superior cycle life, low internal resistance, environment friendly, low cost, safe and easy operations [5–8]. supercapacitors, also known as electrical double-layer capacitors (edlcs), store charges at the surface of electrode material by means of electrical double layers via electrolyte-ion diffusion from electrolyte solution to the electrode. the performance of supercapacitors depends upon the electrode material. the carbon black, carbon nanotubes, glassy carbon, activated carbon-the carbonbased materials and the transition metals are commonly used for electrode materials [9]. in general, the commercial activated carbons prepared from fossil fuel-based precursors which are nonrenewable, expensive and environmentally non-friendly hence the researchers have great interest to prepare the activated carbon from the lignocellulosic materials. the biomass precursors are renewable, cheaper, easily available, environment friendly and highly porous materials. because of high specific surface area, well-developed pore size distributions, nanoporous activated carbons can be used as the suitable material for the supercapacitors to increase the specific capacitance [10–12]. in recent years, researchers have used various biomass materials and industrial wastes like lapsi seed, argan seed, peanut shell, sugarcane bagasse, wheat husk, etc. [13–19] as a raw material for the preparation of nanoporous activated carbon that can be used in the waste water treatment as well as the energy applications. they are renewable, locally available resources in large quantities as well as cost efficient and ecofriendly. triphala is well recognized polyherbal medicine comprises harro (terminalia chebula), barro (terminalia bellirica), and amala (phyllanthus emblica) have found potentially effective in ayurvedic medicine and even used for treating and preventing from cancer [20,21]. however, no research work observed on triphala seed stones for the preparation of activated carbon but phyllanthus emblica seed-derived hierarchically porous carbon materials for supercapacitor applications is recently reported [22]. because of being the pillar of ayurvedic medicine, biomass materials, low cost which are locally available in different regions of nepal, there is particular interest towards the study of preparing a nanoporous carbon material from triphala seed stones. in this contribution, we report the production of ac from triphala seed stones by chemical activation method using zinc chloride as an activating agent to study the performance of supercapacitor. the triphala seed powder was mixed with zinc chloride in 1:1 weight ratio and carbonized at different temperatures (400, 500, 600 and 700 0c) for 4 hours under the constant flow of ultrapure nitrogen gas. thus, prepared ac materials were named on the basis of carbonization temperature as mxc-z400, mxc-z500, mxc-z600 and mxc-z700 respectively. the control sample is prepared by direct carbonization at 500 0c and named as mxp-500. raman spectroscopy, fouriertransform infrared (ftir) spectroscopy, scanning electron microscopy (sem), and nitrogen adsorption/desorption isotherms are used to characterize the prepared activated carbons. the electrochemical energy-storage supercapacitance performance of the novel nanoporus activated carbon prepared from triphala seed stones by zncl2 activation also reported. the obtained ac shows high surface area 1233.3 m2g−1, and pore volume 0.626 cm3g−1 achieving excellent specific capacitance of 208.7 f g−1 at 1 a g−1. these results indicate that triphala seed, a bio-waste material, has the potential for the production of porous carbon materials to improve the performance of supercapacitors and may be useful to control the energy crisis in nepal. 2 materials and methods 2.1 preparation of activated carbon the samples acquired from local vendors were peeled and seed stone separation was done. the obtained seed stones were cleaned with distilled water several times before drying in an oven for 24 hours at 50 0c. after that, the seed stones were mechanically broken into powder and sieved through a mesh size of 300 µm for the precursor. the mxp-500, the control sample refers to directly carbonized carbon that was synthesized in a tube furnace under an inert atmosphere of nitrogen gas for four hours at 500 0c. the activated carbon was prepared through chemical activation using zncl2 as an activating agent in 1:1 ratio on the powder precursor, and the chhabi lal gnawali et al./ bibechana 20 (2023) 10-20 12 effects of different carbonization temperature (400, 500, 600, and 700 0c) were investigated. the carbonization process was carried out in a tube furnace (accumax india) with a constant supply of nitrogen gas. after cooling, the carbonized products were treated with 5 % hcl and then with distilled water until the supernatant liquid reached a ph of 7, and then dried at 1000c for three hours. the activated carbons prepared at carbonization temperatures 400, 500, 600, and 700 0c were labeled as mxc-z400, mxc-z500, mxc-z600, and mxc-z700, respectively. 2.2 characterizations of triphala seedderived carbon materials the surface area and textural properties of the mixture precursor powder and the activated porous carbon materials were investigated by different methods. precursor powder was subjected to a thermogravimetric analysis (tga) on a sii instrument (model exstar 600) from 25 to 10000c with a temperature ramp of 10 0c min−1 in a nitrogen gas atmosphere. raman spectroscopy (nrs-3100, jasco, tokyo, japan), fourier-transform infrared (ftir) spectroscopy (nicolet 4700, thermo electron corporation, waltham, ma, usa), scanning electron microscopy (sem: s-4800, hitachi co., ltd. tokyo, japan operated at 10 kv) and nitrogen adsorption/desorption isotherms (quantachrome autosorb-iq2, boynton beach, fl, usa) were used for instrumental characterization. the nitrogen adsorption/desorption isotherms estimated the total pore volume, pore size distribution, and specific surface area. using barrett-joyner-halenda (bjh) and density functional theory (dft) method, pore diameters and volumes were determined. for nitrogen adsorption isotherm, about 35 mg of sample was placed in a glass cell and degassed at 120 0c for 24 hrs before recordings. 2.3 electrochemical supercapacitance performance studies the electrochemical supercapacitance of triphala seed-derived activated carbon was studied by using cyclic voltammetry (cv), galvanostatic charge/discharge (gcd), and electrochemicalimpedance-spectroscopy (eis) measurements in a three-electrode-cell set-up in aqueous 1 m h2so4 electrolyte solution. the glassy-carbon electrode (gce) was used as the working electrode. the fine carbon powder was added to a mixture of water and ethanol (2 ml: 4:1 v/v ratio) and sonicated for 60 min to obtain a dispersion of carbon (2 mg ml−1. certain volume of the suspension (3 µl) was dropped on a clean and dry gce, and dried at 600c for 2 hrs to solvent evaporation. the mass of the active electrode-material for each system was 3 × 10−6 g. nafion solution (5 µl: 5% in ethanol) was used as the binder, after that the working electrode was dried at 80 0c for 2 hrs under vacuum. the cv, gcd, and eis measurements were performed on a chi 660e workstation (ch instruments, inc. austin, tx, usa) by taking platinum wire as the counter electrode, and ag/agcl as the reference electrode. the gcd curves obtained from the chronopotentiometry measurements is used to calculate the specific capacitance (cs) of the electrode materials as cs = i × td m×∆v (1) where, i (a) indicate the discharge current, td(s) is the discharge time, m (g) is the mass of active material on the gce electrode and (v) represent the operating voltage. 3 results and discussion 3.1 tga and ftir analysis the pyrolytic seed decomposition of mixture seed powder was studied by thermogravimetric analysis. the tga curve in figure 1a shows the recording from 25 to 1000 0c under nitrogen gas atmosphere that indicates the pyrolysis process of precursor occurred in three stages. in the first stage, weight loss happens as a result of evaporation of moisture being locked in the sample at temperatures below 250 0c. at the second stage, there is a significant weight loss between 250 and 370 0c, which is caused by the pyrolytic destruction of the cellulose and hemicellulose components along with partial decomposition of the lignin content. precursor slowly breaks down into carbon components in the third stage; hence there is no considerable weight loss above 370 0c. ftir analysis of powder (figure 1b) indicates the presence of several oxygenated surface functional groups of precursors corresponding to cellulose, hemicellulose and lignin. a broad ftir peak at 3337 cm−1 relates to the o–h stretching (str.) of the moisture water and/or alcoholic group of the cellulose. at the same time, bands at 2929 and 2850 cm−1 denote the cellulose’s aliphatic c-h (str.). the band at 1730 cm−1 corresponds to the unsaturated ester’s c=o (str.) [23]. in addition, the absorption band at 1587 and 1229 cm−1 arise from the aromatic c=c stretching and the c–o stretching in lignin, respectively. the band at 1322 cm−1 can be associated with the c-h symmetric deformation that is typical in cellulose and hemicelluloses [24, 25]. the bands in the regions 1028 cm−1 are due to alkoxy c-o (str.) or other c-o (str.) in cellulose, hemicellulose or lignin. due to the high temperature carbonizations, the ftir bands corresponding to the oxygenated surface functional group in the zncl2 activated carbon samples substantially diminished [26]. chhabi lal gnawali et al./ bibechana 20 (2023) 10-20 13 figure 1: (a) tga curve of triphala seed powder (precursor); (b) corresponding ftir spectrum. 3.2 nitrogen adsorption desorption isotherm by using nitrogen adsorption desorption isothermometry, the surface textural characteristics of produced carbon samples were investigated. the adsorption isotherm of carbons activated at various temperatures is shown in figure 2a. all of the carbon materials showed higher nitrogen adsorption at low relative pressures and significant hysteresis at high relative pressures. these isotherms combine type i and type iv, which suggests that the microand mesopore structures are hierarchical [27]. high nitrogen uptake may be attributed to the filling of micropores at low relative pressures (p/p0), but the hysteresis loop in the region of high relative pressures may be caused by capillary condensation taking place in the mesopores. while nitrogen uptake at low relative pressure appeared to increase, the integral area of the hysteresis loop decreased as carbonization temperature increased from 400 to 700 0c, indicating that there were more micropores present at higher temperatures and fewer mesopores in the carbon framework. large surface areas offered by these microand mesopore structures facilitate dye molecule dispersion on the carbon surface during adsorption [28]. the pore size distribution curves obtained by dft and bjh analysis is shown in figure 2b and 2c respectively. table 1 provides a summary of the surface textural properties of zncl2-activated triphala seed carbon as determined by nitrogen adsorption experiments. 3.3 raman spectra the image displays two distinct raman bands in the spectra. the defect or disordered phase of carbon may be responsible for the first peak (d-band) at 1350 cm−1 and the graphitic phase of carbon may be responsible for the second peak (g-band) at 1598 cm−1 . although the g-band reflects the stretching vibration of sp2 hybridized carbon atoms in the graphitic layer, the d-band represents the vibration of sp3 hybridized carbon atoms in disordered graphitic structure [29]. table 1: surface textural properties of triphala seed carbon at different carbonization temperature (ssa=total specific surface area, smic=micropore surface area, smes=mesopore surface area, vp=total pore volume, vmic=micropore volume, vmes=mesopore volume, wh=average half-pore width of micropores, dp=average pore diameter of mesopores) system ssa(m2/g) smic(m2/g) smes(m2/g) vp(cc/g) vmic(cc/g) vmes(cc/g) wh (nm) dp(nm) mxcz400 1137.7 1087.2 50.5 0.6 0.54 0.06 0.286 3.66 mxcz500 1233.3 1195.1 38.2 0.626 0.574 0.052 0.286 3.66 mxcz600 1143.8 1082.7 61.1 0.617 0.537 0.08 0.286 3.66 mxcz700 878.7 836.9 41.8 0.439 0.384 0.055 0.286 3.67 chhabi lal gnawali et al./ bibechana 20 (2023) 10-20 14 figure 2: (a)nitrogen adsorption-desorption isotherms of the carbon samples, (b) pore size distributions calculated using the dft method and (c) pore size distributions calculated from the bjh method the degree of graphitization of carbon materials is estimated by the help of ratio of the intensities of the g and d bands (ig/id). decreasing crystallinity is indicated by an increase in the ig/id ratio. the produced carbon samples exhibit ig/id ratios between 1.05 and 1.29, which point to the development of amorphous graphitic carbon with few structural defects. as the carbonization temperature is raised from 400 to 700 c , the ig/id ratio falls from 1.15 to 1.05, indicating an increase in graphitic carbon. electrical conductivity, specific area, and pore size are all impacted by the degree of graphitic structure, which impact on increasing the performance of the supercapacitor electrode [22]. 3.4 sem analysis the surface morphology of the mixture seed carbons was investigated using sem images. sem images show irregularly shaped and sized pore structure with microporous channels on their surfaces. most carbon particles are between a range of few and several tens of microns in size. the mxp500 has very less surface porosity (figure 4a-b) which in agreement with nitrogen sorption data. the mesopore structure of mxp-500 is hardly visible in the high-resolution sem image (figure 4b). the zncl2 activation results increases the surface porosity (figure 4d, f, g, h, i, j). the nitrogen adsorption isotherm results correspond with the sem pictures of the zncl2− activated samples, which show a large number of macroporous channellike structures whose frameworks comprise of micro/mesopores, indicating the formation of hierarchical pore structures. while mesopores are numerous, micropores are not easily visible in the zncl2− activated samples (figure 4d, f, g, h, i, j). 3.5 electrochemical measurements the high surface area and the hierarchically porous structure of the prepared sample motivate to calculate the supercapacitance performance. the comparison of cv profiles of mxp-500, mxc-z400, mxc-z500, mxc-z600 and mxc-z700 performed at 50 mvs−1 is shown in figure 5a. the quasirectangular profiles of all the samples exhibit the edlc-type energy storage mechanism. the weak redox peaks at 0.2-0.4 v for mxc-z400 cv curve indicate the partial contribution of pseudocapacitance to the edlc because of presence of the oxygen functionalities in the carbon material [22]. the low value of total internal current of cv curve in mxp-500 sample is due to the lack of porosity. the current output of the mxc-z700 sample is higher which indicates the sample mxc-z700 stored the chhabi lal gnawali et al./ bibechana 20 (2023) 10-20 15 figure 3: raman scattering spectra of mxp-500, mxc-z400, mxc-z500, mxc-z600, and mxc-z700. figure 4: sem images of (a, b) mxp-500; (c, d) mxc-z400; (e, f) mxc-z500; (g, h) mxc-z600; and (i, j) mxc-z700. highest energy among all the samples. by using galvano-static charge-discharge (gcd) at different current densities (1, 2, 3, 4, 5, 10, 20, 30, 40, 50 a g−1), the electrochemical charge storage mechanism was studied. figure 6a shows the gcd profiles of all the samples at 1 a g−1, including the reference carbon, which are of triangular form confirming an edlc-type charge storage mechanism. from the above result, we see that the reference sample mxp-500 shows the lowest charge discharge time whereas the mxc-z700 shows the highest charge discharge time which confirms the maximum charge storage capacity because of the nanoporous structure [30–32]. the gcd curves of all the samples have the triangular form and remains even at high current density of 50 a g−1), that confirm the effective ion diffusion mechanism at interiors of the nanoporous carbon materials at higher current densities. figure 6e shows the specific capacitance as the function of current density for all the samples. from this graph, we see that the specific capacitance of direct carbonized sample is very low as expected because of its low porosity while that of mxc-z700 is superior at all current densities from 1 to 50 a g−1. the specific capacitance was calculated by using equation (1). to investigate the diffusion kinetics of the electrolyte ions, electron-transfer resistance and double-layer charging at the electrode-electrolyte interface, the electrochemical impedance spectroscopy (eis) was conducted [33]. figure 7 shows the nyquist plot of prepared nanoporous activated carbon materials. the plots of zncl2 activated carbon samples shows the lack of semicircular component indicating ideal edlc type charge transfer. the steep rise in the low frequency region indicates the rapid ion transfer in the electrode. the series resistance of the electrode is given by the x-axis intercept of the imaginary component of impedance, which is close to 4.9 ω for the activated carbon. this low value of series resistance confirms the importance of interconnected nanoporous structure to increase conductivity during ion transfer and almost similar for all carbon samples, which indicates the surface-textural properties governed the energystorage capacity of the electrodes. 4 conclusion in conclusion, we have successfully synthesized nanoporous activated carbon materials from novel material, triphala (terminalia chebula, terminalia bellirica, and phyllanthus emblica) by chemical activation with zinc chloride (zncl2) at different carbonization temperatures (400, 500, 600 and 700 0c). surface textural properties show that the carbonization temperature play the significant role on porosity. the surface area of the prepared novel carbon materials from triphala ranges from 878.7 to 1233.3 m2 g−1 and the pore volume ranges from 0.439 to 0.626 cm3 g−1. also, we have studied the electrochemical supercapacichhabi lal gnawali et al./ bibechana 20 (2023) 10-20 16 figure 5: electrochemical -energy-storage performance by cv measurements: (a) cv curves at fixed potential sweep of 50 mvs−1; and cv curves at various sweep-rates (5, 10, 20, 50, 80, 100, 200, 300, 400 and 500 mvs−1) for (b) mxp-500; (c) mxc-z400; (d) mxc-z500; (e) mxc-z600; (f) mxc-z700 chhabi lal gnawali et al./ bibechana 20 (2023) 10-20 17 figure 6: (a) gcd profiles of all the samples at current density of 1 a g-1, cd curve of (b) mxp-500, (c) mxc-z600, (d), mxc-z700 at different current densities from 1 to 50 a g−1 and (e) specific capacitance as a function of current density for all samples. chhabi lal gnawali et al./ bibechana 20 (2023) 10-20 18 figure 7: eis results: (a) nyquist plots of different carbon materials (mxp-500, mxc-z400, mxc-z500, mxc-z600 and mxc-z700) in 1 m h2so4 electrolyte from 0.01 hz to 100 khz at an amplitude of 5 mv (b) the corresponding magnified plot. tance performance of the prepared nanoporous activated carbon in aqueous electrolyte (1 m h2so4) in a three-electrode system. because of their large surface area, large pore volume and interconnected mesopore structure, the prepared sample exhibit the excellence specific capacitance of 208.7 f g−1 at 1 a g−1. from these results we can conclude that the bio-waste material like triphala seed stones could be the potential source for the preparation of nanoporous activated carbon that will be suitable for the preparation of electrode material for high performance energy-storage supercapacitors. acknowledgement the authors would like to express sincere gratitude to dr. lok kumar shrestha, international center for materials nanoarchitectonics (wpi-mana), 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[33] hyun deog yoo, ji-hyun jang, joo-hyung ryu, yong park, and seung-min oh. impedance analysis of porous carbon electrodes to predict rate capability of electric double-layer capacitors. journal of power sources, 267:411–420, 2014. introduction materials and methods preparation of activated carbon characterizations of triphala seed-derived carbon materials electrochemical supercapacitance performance studies results and discussion tga and ftir analysis nitrogen adsorption desorption isotherm raman spectra sem analysis electrochemical measurements conclusion devendra sir cover page copy.jpg bibechana 17 (2020) 67-74 67 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal physicochemical analysis and phytochemical screening of some medicinal plants of letang municipality of morang district, nepal rijan ojha 1 , tilak prasad gautam 1 , narendra kumar chaudhary 2* 1 department of botany, mahendra morang adarsh multiple campus, biratnagar, nepal 2 department of chemistry, mahendra morang adarsh multiple campus, biratnagar, nepal * email: chem_narendra@yahoo.com article information received: august 15, 2019 accepted: november 29, 2019 keywords: ethnobotany phytoscreening active metabolites abstract ethnobotany gives the basic idea about the medicinal properties of plants. identification of active compounds of the medicinal plants and their standardization is essential for the production of new drugs. in the present work, different parts of the five medicinal plants (curcuma caesia, cheilocostus speciosus, drymaria cordata, leea macrophylla, plumbago zeylanica) were washed, air dried and crushed. three different extracts of each powdered material were prepared and standard phytochemical analysis procedure was followed for the analysis of physicochemical properties of plants and the identification of active chemical constituents. among 5 plants, the highest moisture content (14.83%) was found in plumbago zeylanica, higher total ash (9.22%) and acid insoluble ash (4.43%) were observed in curcuma caesia. phytochemical analysis revealed the presence of 12 varieties of bioactive chemicals in all 5 different plants. the plants of the area have great diversity of phytochemicals of numerous medicinal properties. in conclusions, these five important medicinal plants could be useful for the people of the locality to cure several diseases as well as to generate the source of income. 1. introduction the existence of traditional remedies in the disease treatment procedure is considered an integral part of modern pharmaceutical science. several bioingredients of natural products do play a significant role in the discovery of synthetic medicines [1]. nepal has a varied ecosystem for the cultivation of medicinal plants which has been supported by climatic and geographical diversity [2]. it is a small landlocked country situated in the lap of the great himalayas, bordered by china from the north side and india by other three sides. the variation of geographical diversity extends from snow-capped himalayas in the north to the tropical alluvial plains in the south [3]. the major land in nepal is covered by dense forests with possibilities of several medicinal plants [4]. the nepalese tribes still use medicinal herbs for the treatment of chronic diseases. the literature reported the this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ doi: https://doi.org/10.3126/bibechana.v17i0.25236 http://nepjol.info/index.php/bibechana mailto:chem_narendra@yahoo.com https://creativecommons.org/licenses/by-nc/4.0/ https://doi.org/10.3126/bibechana.v17i0.25236 rijan ojha et al. / bibechana 17 (2020) 67-74 68 tremendous effect of crude extracts of medicinal herbs on the disease curing process than the isolated ingredients and this may be due to their synergistic actions [5]. the synthetic chemicalbased drugs, besides their specific biological functions, also possess undesired side effects in the human body, so the phyto based drugs have utmost importance in medical science which has less toxic effects. the phytochemical ingredients of the medicinal plants produce defense mechanism and protect us from various diseases. in plants, the phytochemicals are produced by primary and secondary metabolism [6]. the primary metabolites are simple molecules involved in cellular process. the secondary metabolites are the active compounds which perform defense mechanism against the predator, insects, microorganisms, etc [7]. in recent years, the plants as medicine are becoming more popular due to fewer side effects, low cost and greater effectiveness than the synthetic drugs. this signifies the importance of active phytochemicals for curing different problems of the human body. the medicinal plant contains bioactive compounds such as alkaloids, flavonoids, tannins, glycosides, etc. these constituents have their own biological functions. alkaloids are heterocyclic nitrogencontaining compounds which possess antimicrobial, analgesic, anthelmintic, and antidiarrhoeal activity [8]. flavonoids are plant pigments that produce the color of the flowers and possess significant biological functions as an antimicrobial, antioxidant, antidiarrhoeal, antiinflammatory [9] and anticancer [10]. tannins are polymeric phenols having antimicrobial, and antihelmintic functions [8]. in this investigation, we carried physicochemical and phytochemical screening of five species of medicinal plants collected from the forest of letang municipality situated in province 1 of nepal. cheilocostus speciosus (j.koenig) c.d. specht, is a perennial, rhizomatous plant commonly called crepe ginger from family costaceae. traditionally the plant is used in the treatment of asthma, fungal diseases, rheumatism, diabetes and hepatoprotective disorders [11]. it is also reported that plant has various biological activities such as antibacterial, antifungal, antihelmentic, antioxidant, anti-inflammatory, analgesic, antipyretic, antistress and larvicidal [12] curcuma caesia roxb., belongs to the family zingiberaceae and is a nonconventional medicinal plant with common name black turmeric [13]. the ethnobotanical study concludes its use in the treatment of asthma, bronchitis, epileptic, gonorrheal discharges, impotency, leprosy, menstrual disorders, rheumatic arthritis pain, wounds, piles, toothache, tumors, and vomiting [14]. several studies have also reported its various biological functions such as antiallergic, antibacterial, anthelmintic, anti-inflammatory and antioxidant [15]. drymaria cordata (l.) willd. ex schult., commonly known as tropical chickweed belongs to the family caryophyllaceae. the plant has various pharmacological, traditional and nutritive values. to date, there are fewer reports available on its phytochemical profile [16]. roots are applied externally to heal pain and are alexipharmic. pharmacologically, the plant has been reported to possess antiurolithiatic [17] and anti-inflammatory activities [18]. leea macrophylla roxb. ex hornem., locally known as "ekle galeni" of family leeaceae is herbaceous shrub with big leaves. the plant has traditional uses in tonsillitis, tetanus, nephrolithiasis, rheumatism, arthritis, snake bites, sore, pain, and blood effusion [19, 20]. although the plant has great medicinal properties, there is no proper data available on the phytochemical profile [21]. plumbago zeylanica l., commonly known as ceylon leadwort or wild leadwort is a multipurpose medicinal herb of family plumbaginaceae. in several traditional systems, the plant is used in the treatment for skin diseases, rheumatic swellings, rheumatic pains, tuberculosis, leprosy, scabies diarrhea, gonorrhea, dyspepsia and ulcers [22]. it is reported that plant shows sufficient antidiarrheal properties [23], antiallergic, appetizer, anti-saturative, antianorexic, anti-haemorrhoidal, pain-reliever [24], insecticidal, antidiabetic [25], and hepatoprotective properties. 2. methods plant collection the reported plants were collected from the mahavarat hilly area of letang municipality of morang district in province 1, nepal, during midnovember of 2017. it has the highest altitude of rijan ojha et al. / bibechana 17 (2020) 67-74 69 494 m and rich in plant diversity though it falls under moist tropical forest (locally called charkoshe jungle). all of the plants were collected from their wild habitat. people also cultivate a few of them in their field, garden and private forest for quick access during their needs. the plants were identified with the help of taxonomic literature and herbarium specimens deposited in botany department of mahendra morang adarsh multiple campus, biratnagar. the voucher specimens were deposited in the same department. extraction the rhizomes of cheilocostus speciosus, and curcuma caesia, aerial parts of drymaria cordata, tuberous roots of leea macrophylla and root of the plumbago zeylanica were carefully separated, cleaned, shade dried, mechanically grinded and coarsely powdered. from each sample, 5 g powder was taken and soaked them for 24 hours in 50 ml of water, ethanol, and chloroform separately. the extracts were filtered using whatman filter paper 1. the filtrates were stored at 4 °c for further use. table 1: preliminary phytochemical tests for plant extracts. s.n. phytochemicals test observation references 1 alkaloid 2 ml of extract + 2 ml of hcl+ boil and cool + 2 drops of wagner's reagent brownish red coloration indicated the presence of alkaloid [8] 2 tanin 2 ml extract + 2 ml water + 2-3 drops of ferric chloride (5%) green precipitate indicated the presence of tannin. [26] 3 flavonoid 3 ml extract + evaporated to dryness. residue + 1-2 ml ch3ch2oh (50%) + heat + mg ribbon + 4-5 drops hcl red or orange color indicated the presence of flavonoid. [27] 4 steroid 5 ml extract + 2 ml chcl3+ 3 ml conc. h2so4 ● the reddish brown precipitate formed at the interface indicated the presence of steroid. [28] 5 glycoside 2 ml extract + 2 ml chcl3 + 1-2 ml ch3cooh formation of violet or blue to green coloration indicated the presence of glycoside. [29] 6 saponin 2 ml extract + evaporated to dryness. residue + 1 ml water + shaken vigorously. the persistent foam (1 cm in the test tube) confirmed the presence of saponin. [30] 7 emodol 2 ml extract + 1-2 ml nh3 (25%) + shaken. a cherries red color indicated the presence of emodol [31] 8 quinone 1 ml extract + 1 ml conc. h2so4 formation of red color indicated the presence of quinone. [32] 9 coumarin 2 ml extract + 3 ml naoh (10%). formation of yellow coloration indicated a positive result for coumarin. [33] 10 anthocyanin 2 ml extract + 2 ml hcl (2n) + 1 ml nh3 formation of pinkish red to bluish violet coloration indicated the presence of the anthocyanin. [29] 11 protein 2 ml extract + 1 ml naoh (40%) + 1-2 drops 1% cuso4 solution. formation of violet color indicated the presence of protein. [34] 12 reducing sugar 1 ml extract+ 2 ml water + 1 ml fehling solution (1 and 2) + heated in a water bath. a brick red precipitate indicated the presence of reducing sugar. [32] physicochemical analysis moisture content in a dry and clean petri dish, 5g of powdered material was weighted accurately. the sample was transferred in an oven at 110 ºc. it was dried until two consecutive weighings do not differ by more than 5 mg. loss of weight in terms of percentage was calculated. total ash about 2 g of dried plant material was weighed accurately in a previously ignited clean crucible. it was ignited by gradual heating until it became white. it was cooled for a while and weighed. the content of total ash in terms of percentage was calculated. acid-insoluble ash to the crucible containing total ash, 25 ml of 70 % hydrochloric acid was added and boiled gently for 5 minutes by covering with a watch glass. the cover glass was rinsed with 5 ml of hot water and the liquid was added to the crucible. the insoluble matter was collected on an ash less filter paper and washed with hot water until the filtrate became neutral. the filter paper containing insoluble matter in the crucible was ignited until a constant weight appeared. then it was cooled and weighed. the content of acid insoluble ash in terms of percentage was calculated. phytochemical screening the bioactive compounds were analyzed by the qualitative tests of extracts. it was screened for alkaloids, steroidal compounds, flavonoids, saponins, phenolic compounds, tannins, steroids, coumarins, and glycosides by using standard procedures. the methodology and the screening tests are presented in table 1. 3. results physicochemical analysis the results of the physicochemical analysis are presented in figure 1. among 5 plants, the highest moisture content (14.83%) was found in plumbago zeylanica, higher total ash (9.22%) and acid insoluble ash (4.43%) was observed in curcuma caesia. although these plants showed variation in data, the moisture content and ash content are associated with the purity and authenticity of plants [35]. these parameters of physicochemical analysis are essential for checking the quality of herbs, standardization of medicinal plants, crude drug formulation [36]. fig. 1: result of physicochemical analysis of five medicinal plants. phytochemical screening the phytochemical screening of five plants in three extracts revealed the presence of alkaloid in all except in the chloroform extract table 2. tannin was found in all the plants except in curcuma caesia. in the cheilocostus speciosus and plumbago zeylanica, tannin was absent in aqueous and chloroform extract but in drymaria cordata and leea macrophylla, tannin was absent only in chloroform extract. flavonoid was present in all five plants except in curcuma caesia, whereas all the three extracts of plumbago zeylanica revealed the presence of flavonoid. in cheilocostus speciosus it was absent in ethanolic extract and in leea macrophylla it was absent in aqueous extract. the steroid was found in all the plants and in all the extracts of cheilocostus speciosus and curcuma caesia, but it was absent in aqueous extract of drymaria cordata. in leea macrophylla it was only present in chloroform extract and in plumbago zeylanica it was only present in ethanolic extract. glycoside showed positive result in all the five plants except curcuma caesia and in all the extracts of plumbago zeylanica, but absent in chloroform extract of cheilocostus speciosus and 12.31 10.65 10.12 11.4 14.83 4.77 9.22 5.21 0.31 2.05 0.33 4.43 0.42 0.076 0.18 0 2 4 6 8 10 12 14 16 p er ce n ta g e w /w moisture content total ash acid insoluble ash rijan ojha et al. / bibechana 17 (2020) 67-74 71 drymaria cordata. in leea macrophylla it was only present in the aqueous extract. saponin was present only in four plants except in curcuma caesia. in the cheiloostus speciosus, leea macrophylla and plumbago zeylanica it was only absent in chloroform extract but in drymaria cordata it was only present in ethanolic extract. table 2: results of phytochemical screening of five medicinal plants. name of plant extracts alk. tan. flav. ster. gly. sap. emo. qui. coum. anth. pro. rs. cheilocostus speciosus aqueous + + + + + + + + + ethaonlic + + + + + + + + chloroform + + + + curcuma caesia aqueous + + + + ethaonlic + + + + + chloroform + + drymaria cordata aqueous + + + + + + ethaonlic + + + + + + + chloroform + + + + leea macrophylla aqueous + + + + + + + ethaonlic + + + + + + + chloroform + + plumbago zeylanica aqueous + + + + + + + + + ethaonlic + + + + + + + + + _ _ + chloroform + + + alk.alkaloid, tan.tanin, flav.flavonoid, gly. glycoside, sap.saponin, emo.emodol, qui. quinone, coumcoumarian, anth.anthocyanin, pro.protein and rs.reducing sugar, ‘+’ for present and ‘–’ for absent. emodole was found in cheilocostus speciosus and plumbago zeylanica. in cheilocostus speciosus it was absent in ethanolic extract and in plumbago zeylanica it was absent in chloroform extract. quinone was present only in three plants cheilocostus speciosus, curcuma caesia and plumbago zeeylanica. in cheilocostus speciosus and curcuma caesia it was present only in ethanolic extract and in plumbago zeylanica it was absent in chloroform extract. coumarin was present in all the plants except cheilocostus speciosus and all the three extracts of plumbago zeylanica. but in the majority of other plants it was absent in chloroform extract. protein and reducing sugar were present in all the plants. 4. discussion the present study justifies the presence of active metabolites in plants and the medicinal behavior is due to the presence of bioactive chemicals in them. the earlier reports have also suggested the anticancer activities of water-soluble phenolic compounds like tannins, flavonoids, coumarin[37]. the bioactivity of identified phytochemicals has also established by the previous studies [27,38]. in every research of phytochemistry, it is fundamental to choose a suitable solvent in order to dissolve desired bioactive compounds of plants inducing medicinal properties in human. in this study, the number of phytochemicals tested is in decreasing order of polarity as aqueous ˃ ethanol ˃ chloroform extract. the aqueous extract being the most polar organic extract amongst others has dissolved all the phytochemicals. the ethanol extract has also dissolved all the phytochemicals, however the frequency was high in aqueous extract. the chloroform extract was unable to dissolve alkaloid, tannin, saponin, emodol, quinone, and anthocyanin. the present study has reported the presence of phytochemical ingredients such as alkaloid, rijan ojha et al. / bibechana 17 (2020) 67-74 72 flavonoid, tannins, glycoside, reducing sugar in costus speciosus, similar to the earlier studies [12]. the physicochemical properties and phytochemicals analyzed in curcuma caesia showed correlations with previous research works [39,40]. in the drymaria cordata having less former research on phytochemistry revealed the identified phytoconstituents to be same as found in earlier researches [41,42]. in the existing works, it was also found that alkaloid, flavonoid, tannin, steroid, saponins, glycoside, reducing sugar and proteins are present in leea macrophylla [21]. the results obtained from physicochemical and phytochemical analysis of plumbago zeylanica correlates with earlier works [22,43,44]. among all the plants emodol, quinone, and anthocyanine have not been analyzed previously. the cheiloostus speciosus and curcuma caesia both have fleshy rhizomes and collected from the same habitats showed much variation in physicochemical properties and phytochemistry. the few variations in physicochemical and phytochemical properties might be due to the time of harvesting, age of the plant, environmental factor, grinding process, etc. the plants are active natural chemicals, easily available, free of costs and devoid from side effects due to which they have been considered as really helpful medicinal drug in the studied area from a long time. 5. conclusion the bioprospecting of medicinal plants through standardization with physiochemical parameters, analysis of active metabolites and reducing over exploitation of medicinal plants should get major concern in letang and other parts of nepal. the present study provides the evidence that plants contain bioactive metabolites like alkaloid, tannin, flavonoid, glycoside, saponin, steroid etc and justifies their therapeutic use. further ample work has to be performed in isolation, quantification and characterization of bioactive metabolites of flora for application in pharmaceutical industry. dissemination of current findings to the society through the concerned authorities will be fruitful to understand the importance of medicinal plants, with their cultivation and conservation urgencies leading to their processing and selling, which certainly decrease the unemployment and poverty in the region. acknowledgments the authors are thankful to peoples of letang for sharing valuable information regarding the medicinal plants and to the head, 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[44] r. tyagi, e. menghani, phytochemical screening of plumbago zeylanica : a potent herb, int. j. pharma sci. res. 5 (2014) 71–72. bibechana vol. 21, no. 1, april 2024, 37–50 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar comparative study of the dust color temperature and dust mass within the isolated dust in w51 giant molecular cloud in iris and akari data m. s. paudel1,∗, h. k. kushuwala1, s. bhattarai2 1department of physics, tri-chandra multiple campus, tribhuvan university, nepal 2central department of physics, tribhuvan university, nepal ∗corresponding author. email: mspaudel27@gmail.com,madhu.paudel@trc.tu.edu.np abstract this work presents the comparative study of the properties of dust within the w51 giant molecular cloud (gmc) located at (ra, dec) (j2000): 290.91◦, +14.51◦. in the infrared data of improved reprocessing of the iras (iris) the dust structure seems single and isolated having size 0.45◦×0.45◦ but in akari infrared survey it breaks into two isolated regions having size 0.15◦ × 0.15◦ and 0.10◦ × 0.10◦, represented by akari-i and akari-ii respectively. in iris map, 60 and 100 µm and in akari map, 90 and 140 µm image are used for extraction of the infrared flux. the dust color temperature (td) and dust mass (md) are calculated from the infrared flux and found to be 30.34 k in iris and 27.40 k and 23.55 k in akari-i and akari-ii. a linear relationship between the infrared flux at two wavelengths is found except akari-i. the dust mass per pixel in the isolated (core) region is found to be increased compared to the total study region. to quantify the relation between flux, dust color temperature, and dust mass, the regression analysis is used and observed spectrum of relation. a huge simbad background objected is found embedded in the dust cloud which might have been shaping the spatial variation of temperature and mass within the dust cloud. keywords w51 giant molecular cloud, infrared flux, dust color temperature, dust mass, iris, akari. article information manuscript received: september 26, 2023; revised: december 17, 2023; accepted: december 25, 2023 doi https://doi.org/10.3126/bibechana.v21i1.58815 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 37 http://nepjol.info/index.php/bibechana mspaudel27@gmail.com, madhu.paudel@trc.tu.edu.np https://doi.org/10.3126/bibechana.v21i1.58815 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ m. s. paudel et al./ bibechana 21 (2024) 37-50 38 1 introduction a giant molecular cloud (gmc) is a huge structure in the interstellar medium that can nurture the various phases of star formation, often called the stellar nursery. it is believed that the massive stars are formed in gmc in the milky way galaxy [1]. however, the formation of the star from the natal gmc is still an unclear topic. w51 is an example of the gmc in the milky way galaxy located at the sagittarius arm of the galaxy [2]. it is found from the latest research that an active and massive star is forming in the w51 molecular cloud. in the milky way galaxy, w51 is in the top 1% by size, top (5-10)% by mass [3], and top (50-15)% by star formation efficiency (sfe) [4]. it is found that the majority of the star has been formed within ∼ 3 myr. many hii and cluster are embedded within the cloud. moreover, w51 is hosting many objects which are revealed at different wavelengths, such as; various newly formed o stars are detected in the near-infrared wavelength, many third-generation of the massive proto-stars are detected in the midinfrared wavelength, and numerous young stellar populations are detected in the microwave, millimeter, and submillimeter wavelengths [5]. the infrared astronomy is crucial to explore the part of the galaxy into those parts where the visible light is unable to reach. in the history of infrared astronomy, infrared astronomical satellite (iras) was the first space satellite which was successful in mapping more than 96% of the milky way galaxy in the infrared (ir) wavelength [6]. infrared radiation is emitted by the hot dust molecules in interstellar medium (ism) due to the absorption of energetic radiation, such as; x-ray, ultra-violet (uv), and visible ray emitted from nearby hot star and stellar remnants. the mass budget of the interstellar dust can be studied via infrared radiation. it is believed that the dominant dust formation mechanisms are the stellar wind created mass loss in agb phase and supernova remnants (snrs) phase of stellar evolution and in ism, its abundance increases by coagulation, erosion, shattering, etc. [7, 8]. there have been many studies concerning the properties of dust using the infrared data from iras, improved reprocessing of iras survey (iris) [9], akari [10], and wide infrared survey explorer (wise) [11]. recently, the properties of the north-east part of the perseus molecular cloud is studied by bhattarai et al., (2023) [12] using iris and akari data, in which the dust color temperature (td) in iris data (26.34 ± 0.11 k) is found higher than the akari data (17.63±0.02 k) but the dust mass (md) is found higher in akari data. the spatial distribution of the infrared flux and temperature is almost similar in both iris and akari data but for dust mass and visual extinction there is a huge difference between both data. also, many background sources, such as; dense core, part of cloud, submillimeter radio source, ir, dark and reflection nebula, etc., are found within the studied region which are considered as the major contributor of the dust mass. in most of the studies td is found between 15 k and 45 k in iras/iris data, such as; 20 k to 24 k for the dust cloud nearby wd 0307+077 [13], 22.91 k to 34.58 k for the dust nearby pg 1225079 [14], 25.59 k to 36.82 k for the dust nearby wd 0011-399 [15], 22.67 k to 33.56 k for the dust nearby the supernova remnants (snrs) in galactic plane [16], 21.87 k to 24.09 k for the dust nearby wd 0352-049 [17], 23.77 k to 24.93 k nearby crich agb star 19558+3333 [18], 20.75 to 35.90 k and 22.52 to 45.63 for the dust in two different nebula [19]. in akari data td is also found in the same range, such as; 17.87 k to 43.47 k nearby pg 1225-079 [14], 16.31 k to 26.37 nearby wd 0011-399 [15] and 15.78 k to 28.86 nearby snrs in galactic planes [16] and 16.78 k to 17.71 nearby c-rich agb star 19558+3333 [18]. however, the average value of td is found less in akari data compared to iras/iris in all data. for wise data, td is found between 286.38 k nearby pg 1225-079 [14], 307.24 k to 353.72 k nearby wd 0011-399 [15], 122.55 k to 125.11 k nearby c-rich agb star 19558+3333 [18]. a higher value of td is observed in wise data. in most of the work, the relationship between the temperature and mass of dust is trying to explain. in dust clouds around wd 0352-044 in iris data [17], dust cloud around snrs in akari data [16], dust clouds around pg 1225-079 in wise and akari data [14], dust cloud around wd 0011-399 in wise data [15] the temperature and mass have an inverse relation, means higher dust mass is observed in the color map where the temperature is low and vice-versa. there are some other works in which no preferred relationship between td and md is found, for instance, dust cloud around snrs in iris data [16], dust cloud around wd 0011-399 in iris and akari data [15], dust cloud around pg 1227-079 in iris data [14], etc. the inter-relationship between td and md is found independent of the infrared survey, such as; iris, akari, and wise. more study is required for a clear conclusion. this work focused on the investigation of td and md from infrared flux within the w51 molecular cloud. infrared flux is used to calculate td and md and their distribution is analyzed. the relationship of the infrared flux with td and md as well as the between td and md is presented. the impact of the background objects embedded within the dust cloud is tried to explain. m. s. paudel et al./ bibechana 21 (2024) 37-50 39 2 sources of data the major data used for this work is flexible image transport system (fits) images of infrared flux downloaded from skyview virtual observatory (https://skyview.gsfc.nasa.gov/), for both iris [9] and akari [10]. fig.1 shows the jpeg image at a longer wavelength, i.e., 100 µm in iris and 140 µm in akari. the distance of the w51 molecular cloud is taken from genzel et al. (1981) [20]. the data from set of identification, measurement bibliography for astronomical data (simbad) [https://simbad.u-strasbg.fr/simbad/sim-fid] [21] is used to study the background objects around the study region. 3 method of analysis 3.1 infrared flux and dust color temperature the planck’s law of blackbody spectrum gives the expression for the energy density emitted from a source in a wide range of the wavelength. the planck’s law can be modified to apply for interstellar dust assuming (i) the beam emitted from each pixel in the infrared map is isothermal in nature and (ii) the beam is in thermal equilibrium along the line of sight. with these assumptions, the flux density fλi at wavelength λi is given as; [22, 23] fλi = [ 2hc λ3 i ( 1 e ( hc λikbtd ) − 1 )] ndαλ −β i ωi, (1) where td is the dust color temperature, nd is the column density of the dust grains, α is a constant related to the optical depth of the dust, β is the spectral emissivity index, and ωi is the solid angle subtended at λi by the detector. using equation (1), the ratio of the infrared flux at two wavelengths, fλ1 /fλ2 , can be modified under the assumptions that ωλ1 ≈ ωλ2 and for low dust color temperature, td, we obtain, td = −p ln [ r× q(3+β) ] (2) where, p = 96 for iris and 57 for akari data, q = 0.6 for iris and 0.64 for akari data, β is the spectral emissivity index. also, the value of the wavelengths, λ1 and λ2, taken in this work are 60 µm and 100 µm for iris and 90 µm and 140 µm for akari data. 3.2 dust mass the mass of dust in the molecular cloud can be obtained from the dust color temperature size of dust grain. the planck’s function at long wavelength can be used to estimate the dust mass more accurately. the expression of dust mass including all these quantities is given as [24,25]; mdust = 0.4 [ sνd 2 b(ν, td) ] , (3) where sν is the absolute value of flux at long wavelength, d is the distance to the dust cloud, b(ν, td) is the planck’s function for the blackbody radiation. once the mass of dust is estimated from equation (3), the dust-to-gas ratio, mgas ≈ 150mdust [24], is used to find the total mass of cloud (gas) within the molecular cloud. 3.3 inclination angle the inclination angle of the dust cloud is the angle subtended by the line of sight to the normal to the plane of the dust cloud. it is calculated using the holmberg (1946) [26] formula, which is given as: cos2 i = (b/a)2 − (q∗)2 1− (q∗)2 (4) where a and b are the major and minor axes of the cloud, and q∗ is the intrinsic flatness, which describes the internal morphology. for a molecular cloud dominated by neutral particles, its value is taken as 0.23 [27]. the cloud is said to edge-on if i > 45o and face-on if i < 45o [28]. 3.4 jeans criteria the process of stellar evolution initiates in the molecular cloud if the cloud has enough mass to enrich the gravitational compression against the gas pressure. the jeans criteria describe the minimum mass and size required to trigger the evolution process, which is a function of the density and temperature of the cloud. the density of a cloud having radius r is given as: ρ = ( 3 4π )2/3 kbt mhgr2 (5) where kb , mh , t , and g are the boltzmann constant, mass of neutral hydrogen, dust color temperature, and universal gravitational constant, respectively. the jeans mass is given as: mj = ( kbt mhg )3/2( 1 ρ )1/2 (6) to initiate the gravitational process the mass of the cloud must be greater than the jeans mass of the cloud [29]. m. s. paudel et al./ bibechana 21 (2024) 37-50 40 3.5 gaussian distribution for any natural process, we always expect the gaussian distribution if the size of the variables is large. for a continuous random variable x having mean µ and standard deviation σ, the gaussian probability distribution function is given by: f(x) = 1 σ √ 2π exp ( − (x− µ)2 2σ2 ) (7) 4 results and discussion 4.1 structure and size in far infrared image the part of the w51 molecular cloud under study has prominent emission in both iris and akari map. in iris map it is single and isolated and elongated along north-south direction. but in akari map the core part is broken into two parts. in this paper these two parts are represented by akari-i and akari-ii. the detail information about the center of the each structure, total size and size of isolated region is presented in table 1. the pixels corresponds to maximum infrared flux in long wavelength infrared data, 100 µm in iris and 140 µm in akari data, is considered as a center of the structure under study. in all three structures, the center of the structure is slightly beyond the geometrical center. the physical center is the point corresponding to the pixels having maximum flux. in this work, the size of the pixels used on the fits image are 1.5 arcmin/pixels in iris map and 0.25 arcmin/pixels in akari map. fig. 2 shows the fits view in aladin v2.5 [30] at longer wavelength (100 µm in iris and 140 µm in akari) in all three sub-structures. the major and minor axis of the isolated region of each structure can also be seen in fig. 2. the different contours seen in the fits image are the isoflux contour lines. table 1: the table presents the geometrical center, center of structure with maximum flux, and size of both total square region and isolated region. structure geometrical center (ra, dec [icrs]) center of structure (ra, dec [icrs]) size of structure inclination angle (i) total isolated iris-up 290.910◦ +14.510◦ 290.935◦ +14.513◦ 0.45◦ × 0.45◦ 0.32◦ × 0.18◦ 59.19◦ akari-i 290.920◦ +14.520◦ 290.934◦ +14.506◦ 0.15◦ × 0.15◦ 0.14◦ × 0.07◦ 62.89◦ akari-ii 290.798◦ +14.456◦ 290.797◦ +14.447◦ 0.10◦ × 0.10◦ 0.09◦ × 0.06◦ 50.01◦ figure 1: the jpeg image of the dust cloud nearby the w51 molecular cloud is shown in figure. the figure are for iris 100 µm, akari 140 µm, akari-i 140 µm, and akari-ii 140 µm, from left to right respectively. in akari 140 µm (second) figure dust cloud is seen broken clearly into two parts; akari-i and akari-ii. m. s. paudel et al./ bibechana 21 (2024) 37-50 41 figure 2: aladin v2.5 view of the fits image in iris (100 µm) and akari (140 µm) can be seen. in akari there are two structures; akari-i and akari-ii. the geometrical center, maximum flux region (center of structure), major and minor axis are shown. the different contour line are isocontours with different values for three image. the region inside the outer isocontour is descried as an isolated region and is considered separately for analysis of the result in following section. figure 3: the figure shows the linear relation between two infrared fluxes in iris (a) and akari (b and c) data for total region. here, r2 is the coefficient of determination and m is slope of straight line. table 2: statistical information of infrared flux; maximum (fmax), minimum (fmin), average (fav), range, standard deviation (σf ), and standard error (se) at both wavelengths in dust structures in iris and akari data. structure λ (µm) infrared flux (mjy sr−1) fmax fmin fav ± s.e. frange σf iris 60 17090.00 158.15 2346.46± 184.65 16932.37 3323.61 100 18277.80 427.97 3442.17± 212.98 17849.83 3833.71 akari-i 90 48455.82 2128.55 12161.23± 246.98 46327.28 8891.23 140 66261.41 2452.37 12230.88± 302.41 63809.04 10886.73 akari-ii 90 26890.39 2959.25 8947.48± 175.98 23931.14 4223.62 140 23011.31 3643.55 10923.17± 204.30 19367.76 4903.08 4.2 infrared flux density the fits image is processed in aladin v10.0 [30] software to extract the infrared flux density at two wavelengths, 60 µm and 100 µm in iris data and 90 µm and 140 µm in akari data. the w51 molecular cloud and its both parts under study lie close to the galactic plane of the milky way galaxy; therefore, the infrared flux density is very high at all wavelengths under study. the information about the maximum, minimum, average, range, and standard deviation of the infrared flux in each wavelength for all structures can be seen in table 2. infrared flux is higher for akari data compared to iris data at both wavem. s. paudel et al./ bibechana 21 (2024) 37-50 42 table 3: the table presents the maximum (tmax), minimum (tmin), average (tav), range, and standard deviation (sd) of td in total and isolated regions within the w51 molecular cloud. structure region tmax (k) tmin (k) tav ± s.e. (k) trange (k) σt (k) iris total 38.55± 4.10 25.29± 2.52 30.34± 0.16 13.26± 3.13 2.82 isolated 37.63± 2.09 28.49± 2.48 33.45± 0.27 9.14± 2.28 2.35 akari-i total 77.12± 24.86 17.01± 5.20 27.40± 0.21 60.11± 15.03 7.73 isolated 59.56± 17.20 17.01± 4.08 25.17± 0.23 42.55± 10.64 5.40 akari-ii total 30.82± 3.64 18.85± 2.30 23.55± 0.08 11.87± 2.98 1.99 isolated 27.81± 2.38 20.26± 1.40 23.06± 0.10 7.55± 1.89 1.59 table 4: the table shows the parameters in the linear fit, where r2 is the coefficient of determination and t is the dust color temperature calculated using the slope. structure region best fit equation r2 t(k) ∆t (k) iris total fs = 0.85fl − 588.35 0.97 35.37 −5.03 isolated fs = 0.98fl − 1946.38 0.94 37.30 −3.85 akari-i total fs = 0.58fl + 5029.49 0.50 20.57 +6.83 isolated fs = 0.47fl − 8504.23 0.37 19.09 +6.08 akari-ii total fs = 0.78fl + 415.54 0.82 23.00 −0.55 isolated fs = 0.93fl − 2131.05 0.70 24.71 +1.65 lengths. the flux is greater at long wavelengths for iris and akari-i structure, whereas for akariii, the maximum value of flux at short wavelength is higher, but the average value is again lower at short wavelengths. furthermore, a linear relationship is found between the flux at two wavelength both in iris and akari data. the infrared flux of total square region as well as that of isolated region of all three structures is studied using the linear regression. for this study the infrared flux at long wavelength (fl) is taken along the x-axis and short wavelength (fs) is taken along the y-axis, shown in fig 3. the coefficient of determination (r2) tells how closely the fitted data (red line) agree with the original data set (blue dots). it is found r2 is more for total square region compare to isolated region. in iris data it is very well fitted but in akari-i it is just acceptable for total data and bad fit for isolated data. for akari-ii, it is good fit. the various information related to the regression study is presented in table 4 and the graph showing the linear relationship between two infrared fluxes is seen in fig. 4. for akari-i, we found large number of background sources, such as; stars, clusters, yso, different radio sources, hii region, infrared sources, etc., which can be seen in fig. 10 (d e). also, the gaussian distribution of temperature is found more deviated from normal bell shape in fig. 7(b). moreover, the color map of infrared flux also shows the different nature of map for two wavelength in fig. 5 (a b). these all studies tell us the poor relation between infrared flux at two wavelength for akari-i region. 4.3 dust color temperature we use the method given by wood et al. (1994) [22] and schnee et al. (2005) [23] to estimate the dust color temperature (td) of the interstellar dust cloud, dependent on infrared flux density at two wavelengths for which the spectral emissivity index (β) is taken as 2, assuming the interstellar dust having crystalline dielectric characteristic [31]. table 3 presents various statistical information related to td for both the total square region as well as the isolated region in all three structures. the error in the average temperature (tav) is the standard error (σt / √ n), σt is the standard deviation, and n is the size of the data). but for maximum are minimum temperature are the half of the deviation from average value is taken. for range the average error in maximum and minimum value is used. the td is found more for akari data compare to the iris. however, the minimum value is less in akari. the range is found more than 5 k in both iris and akari data representing the dust cloud is thermally dynamic. moreover, td and its range in akari-ii is found more than akarii, representing high thermal activities in akarii. the td is found more in iris data compare to akari data. this is according to wien’s displacement law, which says the temperature is inversely proportional to wavelength. furthermore, it is seen that the higher value of maximum td is found in akari-i. in akari-i, the contour map (fig. 5(c)) as well as the gaussian plot of temperature (fig.7) shows the high temperature (more than 50 k) is found only in small regions or pixels. most of the region have temperature less than 40 k. in iris and akari-i the distribution of the temperature m. s. paudel et al./ bibechana 21 (2024) 37-50 43 table 5: dust and gas mass (kg and solar mass (m⊙) in dust structures and sub-structures. structure region md mean per pixels (kg) gas mass (kg) (in kg) (in m⊙) (in kg) (in m⊙) iris total 3.09× 1032 155.38 9.54× 1029 4.64× 1034 23307.50 isolated 1.51× 1032 76.04 1.96× 1030 2.27× 1034 11406.70 akari-i total 1.23× 1034 6172.64 9.47× 1030 1.84× 1036 925896.56 isolated 9.96× 1033 5006.92 1.79× 1031 1.49× 1036 751038.71 akari-ii total 4.47× 1033 2248.04 7.76× 1030 6.71× 1035 337205.43 isolated 2.73× 1033 1370.55 1.17× 1031 4.09× 1035 205582.88 is almost gaussian. also, the standard deviation is found maximum for the akari-i, suggesting the wide variation in the temperature distribution. the gaussian distribution of the dust color temperature on total square region in all three structures is seen in fig.7. additionally, the slope of the best fit straight line could give the average temperature. the slope (m) of the straight line is the ratio (r) of the infrared flux at two wavelengths, r = f (λlong) f (λshort) . this provides some insight to calculate the temperature using equation (2). using this method, temperature is calculated for both the total square region as well as in the isolated region. the results are presented in table 4. the deviation in temperature (∆t ) between table 3 and table 4 is also presented. the deviation is due to the value of y-intercept (c). in the linear regression method we implement, fs = r·fl+c, rather than fs = r·fl. it is evident that the deviation is more for akari-i for which the data deviated much from gaussian nature compare to other. for isolated region the deviation is less in iris and akari-i but for akari-ii it is more. the background sources at the isolated region is very much crowded for iris and akaari-i compare to akari-ii, which can be seen in fig. 10. 4.4 dust mass the mass of dust in each pixel of the dust structure is calculated using the infrared flux at long wavelength, dust color temperature, planck’s function, and the distance to the dust cloud using the method of hildebrand (1984) [24] and young et al., (1993) [25]. planck’s function is a function of temperature and wavelength. the distance to the w51 molecular cloud is taken as ∼17000 light years or ∼5410 pc [20]. the dust mass as well as the mass of gas within the total square region and isolated region of all three structures is presented in table 5. the mass of dust within the isolated region is also calculated separately. obviously, it is seen that the total dust mass in the isolated region is less than the total square region. one of the reasons is that the number of pixels included within the isolated region is less compared to the total square region. another effective reason is that the average dust mass per pixel is slightly more in the isolated region compared to the total square region. the mass of gas (mg) is calculated using the fact that mg ≈ 150md [24]. therefore, the mass of gas also follows the same trend as that of the dust mass within both the total square and isolated regions. 4.5 contour map the visualization of the infrared flux at two wavelengths, dust color temperature, and dust mass is presented in fig. 4, fig. 5, and fig. 6, respectively, for iris, akari-i, and akari-ii. the contour maps of the infrared flux at 60 µm and 100 µm for the iris structure are almost identical, as described in the regression analysis with an r2 value of 0.97. infrared flux is decreasing almost smoothly from the center to the outer region in iris data. in akari-i, the contour maps are less identical; a clear donut shape with local minima at the geometrical central part is observed in infrared flux at 90 µm, and an unbalanced dumbbell shape elongated along the diagonal is observed in infrared flux at 140 µm. the regression analysis between the fluxes at two wavelengths also shows a moderate value of r2, which is 0.50. for akari-ii, the contour maps show quite a similar distribution, both elongated along the main diagonal of the square region with a slight rise towards the right-upper part. however, the maximum value of the flux is seen at 140 µm, which is different from akari-i. the regression analysis shows a quite good value of r2, which is 0.82. the qualitative distribution inferred from the contour map is in accordance with the quantitative analysis provided by the regression method. the iris data contour map of the dust color temperature (td) also appears elongated along the main diagonal of the square region, but the overall distribution is quite different compared to the flux at both wavelengths. the maximum value of the temperature is beyond the center with maximum flux. also, the temperature is not decreasing smoothly from the maximum value towards the outer regions; however, an isolated region is m. s. paudel et al./ bibechana 21 (2024) 37-50 44 observed elongated along the main diagonal. in akari-i, the color map of the dust color temperature is very different from the infrared flux. an isolated low-temperature cavity can be seen within the region of interest, which is quite interesting. the maximum temperature is also deviated from the center, and the variation is also not smooth from its maximum value towards the outer region. only very few pixels have a higher temperature (> 50k), which can also be seen in the gaussian distribution in fig. 7. in akari-ii, the color map shows variation of td unevenly breaking into multiple subregions with multiple local minimum. the maximum temperature lies at the lower-mid-edge of the square region. the contour map of the dust mass in iris structure seems like the color map of flux at both wavelength. it shows the two maxima region at core. the pixels having maximum mass lies very close to the pixels having maximum flux. in outer region, the dust mass decreases smoothly showing the symmetric variation. a visual comparison between contour map of dust color temperature and dust mass shows a very poor correlation. in akari-i structure, the contour map of dust mass shows double maxima, concentrated near the center and elongated along the off-diagonal of square region. the mass distribution is quite similar to the infrared flux at core region at 140 µm. the contour map of temperature and mass are seen nearly inverse within the core region. the background sources, such as; hii region, infrared, midinfrared, near infrared, etc., are crowed near the isolated cavity of temperature which might be contributing huge dust at core. in akari-ii, the contour map of the dust color temperature is entirely different from the infrared flux at both wavelength. it is breaking unevenly into three sub-clumps. the background sources shown in fig 10 (c) also shows crowd of background sources in the periphery of the region where the aggregation of the dust mass is more. this is an evident that the dust mass is pushed slightly far away from the background sources. the visual comparison shows the distribution of mass almost inverse of the temperature. the quantitative relationship between temperature and mass is presented in later section. figure 4: the contour map for infrared fluxes (a and b), dust color temperature (c) and dust mass (d) for whole dust structure around w51 molecular cloud in iris map overlaid with the contour at different levels, in the interval of (x̄ ± k.σ), x̄ and σ are the mean and standard deviation of corresponding quantities, and k is the constant chosen in such a way that the contours are distributed evenly. the value of constant k is chosen [-0.5, 0, 0.5, 1, 1.5, 2.0, 2.5, 3, 3.5, 4] for flux at 60 µm, [-0.5, 0, 0.2, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5] for flux at 100 µm, [-2.0, -1.5, -1.0, -0.5, 0, 0.5, 1, 1.5, 2.0, 2.5] for td and [-0.75, -0.5, 0, 0.5, 1.0, 1.5, 2.0, 2.5] for md for outer to inner contour. m. s. paudel et al./ bibechana 21 (2024) 37-50 45 figure 5: the contour map for infrared fluxes (a and b), dust color temperature (c) and dust mass (d) for upper dust structure (akari-i) around w51 molecular cloud in akari-i map overlaid with the contour at different levels, in the interval of (x̄ ± k.σ), x̄ and σ are the mean and standard deviation of corresponding quantities, and k is the constant chosen in such a way that the contours are distributed evenly. the value of k is chosen [-0.75, -0.45, 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5] for flux at 90 µm, [-0.75, -0.5, -0.20, 0, 0.5, 1.0, 2.0, 3.0, 4.0] for flux at 140 µm, [-1.0, -0.5, 0, 1.0, 2.0, 3.0, 4.0, 5.0] for td and [-0.25, 0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0] for md form outer to inner contour. figure 6: the contour map for infrared fluxes (a and b), dust color temperature (td) (c) and dust mass (md) (d) for lower dust structure (akari-ii) around w51 molecular cloud in akari map overlaid with the contour at different levels, in the interval of (x̄±k.σ), x̄ and σ are the mean and standard deviation of corresponding quantities, and k is the constant chosen in such a way that the contours are distributed evenly. and the value of k are [1.0, -0.5, 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5] for flux at 90 µm, [-1.0, -0.5,-0.25, 0, 0.5, 1.0, 1.5, 2.0, 2.25] for flux at 140 µm, [-1.5, -1.0, 0.5, 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5] for td and [-1.0, -0.5, 0, 0.9, 1.0, 1.5, 2.0, 2.5, 3.5] for md form outer to inner contour. m. s. paudel et al./ bibechana 21 (2024) 37-50 46 figure 7: figure shows the gaussian distribution for dust color temperature for all structures. in all figure the quantities dust color temperature is taken along x-axis and their gaussian pdf are taken along y-axis. 4.6 flux-temperature-mass relation the color map with contour is quite effective to understand the spatial distribution of the infrared flux, dust color temperature and dust mass. for a quantitative analysis the color map is not adequate to give the proper information. the linear regression is used to quantify the relationship between them. the coefficient of determination (r2) is calculated for each pair of variables in all dust structure. the selected plots for which the r2 > 0.50 are presented in fig. 8. the temperature (td) is found to be increased with flux at both wavelength in iris data but no clear relation for akari data. also, the dust mass (md) is found to be increase with increase in infrared flux at both wavelength, both iris and akari data. but for flux at short wavelength the r2 >0.50 for both region in akari. in overall, it can be said that the td and md both increases with increase in infrared flux in all regions. the graph between td and md is shown fig. 9, in which all the plots have poor coefficient of determination, r2 > 0.50. however, in iris and akari data a very clear difference can be seen. in iris data, the relation is direct where as in akari, in both graph, the relation is inverse. moreover, the data in iris is more scattered compare to akari data. the value of r2 for each pair of variables is presented in table 6. 4.7 simbad background source study of the background objects within the selected region is carried out with the help of catalog available in simbad. the fig. 10 shows the background sources overlaid in the isocontour lines that are same for infrared flux at longer wavelength, i.e., 100 µm for iris and 140 µm for akari–i and akari-ii. in this work, the young stellar object (yso), yso candidates, different varieties of the radio sources, dark nebula, interstellar bubbles, hii region, star, dense core, part of cloud, etc., are numerous. for the better visualization the background objects are presented in three graph in iris data and two graph in akari-i data and single graph in akari-ii. the number of background sources within the region of iris structure is 1364, within akari-i structure is 401 and within akari-ii structure 134. there are least but very important objects, like hii region, infrared (ir), mid ir, far ir, dense core bubble, star forming regions, radio sources, etc., which are found to be concentrated within the core region of the cloud and it can be concluded that they are responsible for the huge infrared flux, temperature and mass as seen in color map of iris in fig. 4. the background objects around akari-i is more compare to akariii, the effect of which can be seen in the average value, range and gaussian curve of td. the range of td is more than 40 k for isolated region and more than 60 k for total square region which is very high compare to akari-ii [table 3], which represents more thermal instability in akari-ii due to the presentence of background sources. also, gaussian distribution of td is much deviated from normal bell shape. the color map also shows the effect of background objects in both of the akari structures. cavity of cold and massive dust region is seen in the periphery of regions where background sources are crowded. therefore, the entire dust properties, such as infrared flux, dust color temperature and dust mass can be explained on the basis of the background objects. 4.8 density and jeans mass the isolated region in each dust structure as seen in fig. 2 is studied separately for the jeans criteria, whether the mass of the cloud under the isolated structure is sufficient or not to trigger the star formation process is checked. the average size, average temperature, density, jeans mass and total mass of cloud of isolated region within clouds in iris, akari-i and akari-ii are presented in table 7. from table 1 it is clear that the size of the iris structure is largest and akari-ii is smallest. m. s. paudel et al./ bibechana 21 (2024) 37-50 47 conversely, the density of the akari-ii is found maximum and iris is minimum. but, the jeans mass (mj) is maximum for iris structure due to its large size. the value of mj is found less than the mass of the cloud in all structures. it is seen that there is no any possibility of further collapse of clouds either singly or part wise for the star formation process in the future. table 6: the coefficient of determination (r2) for each pair of variables, fs and fl represents the flux at short and long wavelength. coefficient of determination (r2) fl vs td fs vs td fl vs md fs vs md td vs md iris 0.56 0.54 0.65 0.81 0.21 akari-i 0.24 0.05 0.07 0.79 0.23 akari-ii 0.05 0.02 0.19 0.59 0.47 figure 8: the best fit straight line between the infrared flux, dust color temperature and dust mass in iris data. the r2 represents the correlation coefficient. the plot with r2 < 0.50 are not included here. figure 9: the best fit line between the td and md is seen in iris (a), akari-i (b) and akari-ii (c) is shown. in all data a poor correlation is observed. m. s. paudel et al./ bibechana 21 (2024) 37-50 48 figure 10: the figure shows the simbad sources around w51 molecular cloud, for iris (a, b and c), akari-i (d and e) and akari-ii (f). in all plot, ra is taken along x-axis, dec is taken along y-axis. the name of sources in the legend is according to the simbad. for iris and akari-i there are more graph made for the better visualization of the numerous objects. table 7: average radius, dust color temperature, density, jeans mass, and total mass of cloud in isolated regions of iris, akari-i, and akari-ii. structure radius (m) td (k) density (kg/m3) jeans mass cloud mass (kg) m⊙ (kg) m⊙ iris 6.07× 1015 33.45 4.33× 10−17 4.05× 1031 20.36 2.27× 1034 11406.70 akari-i 2.55× 1015 25.17 1.85× 10−16 1.28× 1031 6.44 1.49× 1036 751038.71 akari-ii 1.82× 1015 23.06 3.36× 10−16 8.39× 1030 4.22 4.09× 1035 205582.88 5 conclusion a comparative study of the properties of dust is performed within the molecular cloud w51 located at (ra, dec) (icrs): 290.910◦,+14.510◦, having an angular size of 0.45◦× 0.45◦, using the iris and akari data. following are the major conclusions: 1. being situated in the galactic plane, the dust cloud is very bright in both akari and iris. furthermore, it is divided into two isolated sub-structures having angular sizes of 0.15◦×0.15◦ and 0.10◦×0.10◦ in the akari map, represented as akari-i and akari-ii, respectively. 2. the average dust color temperature is found to decrease in the isolated region compared to the total region in all sub-structures. the hot region is found to lie outside the isolated region. 3. the dust color temperature follows wien’s displacement law, meaning the temperature is inversely proportional to wavelength. a lower temperature is found for akari data compared to iris data. 4. the range of temperature in all structures is found to be more than 10 k in total and 5 k in the isolated region, indicating that the structure is far from thermal stability. in akarii, the range is very high, representing huge thermal instability compared to akari-ii. 5. the regression analysis shows a linear relationship between the infrared flux at two wavelengths in iris and akari-ii, but the relation is very poor in akari-i for the isolated region. this might be the consequence of the large range in temperature. a mixed type (linear and quadratic) of relationship is m. s. paudel et al./ bibechana 21 (2024) 37-50 49 found between the infrared flux, dust color temperature, and dust mass. 6. the regression analysis shows that td is poorly correlated with md. in iris data, md is directly proportional to td, but for akari, md is inverse to td. 7. the dust mass is found to be more in both akari maps compared to iris map, even though the dust structure in iris is larger in size. moreover, the mass per pixel is more for akari maps. the mass per pixel is more in the isolated region for both iris and akari maps. 8. the simbad point sources within the study region show a large number of stars, young stellar objects (yso), interstellar medium (ism) sources, etc. ysos, stars, radio sources, masers, hii regions, infrared sources, mid-infrared sources, etc., are mostly found within the core region of akari-i and akari-ii structures. this is the manifestation of the huge infrared flux within the core region. 9. the study of density and jeans criteria shows that the dust structure is denser in akari data compared to iris data. also, akari-ii is found to be denser than akari-i. furthermore, all dust clouds deny the possibility of star formation. acknowledgements the authors want to acknowledgment to their host institution department of physics, tri-chandra multiple campus and central department of physics, tu for all types of academic support in this research work. thanks to skyview virtual observatory and simbad for the data used in this work. references [1] i. a. bonnell and m. r. bate. star formation through gravitational collapse and competitive accretion. monthly notices of the royal astronomical society, 370(1):488–494, 2006. 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[24] r. h. hildebrand. the determination of cloud masses and dust characteristics from submillimeter thermal emission. quarterly journal of the royal astronomical society, 24:267, 1983. [25] k. young, t. phillips, and g. knapp. circumstellar shells resolved in iras survey data. iianalysis. the astrophysical journal, 409:725– 738, 1993. [26] e. holmberg. on the apparent diameters and the orientation in space of extragalactic nebulae. meddelanden fran lunds astronomiska observatorium serie ii, 117:3–82, 1946. [27] m. p. haynes and r. giovanelli. neutral hydrogen in isolated galaxies. iv-results for the arecibo sample. the astronomical journal, 89:758–800, 1984. [28] a. jha and b. aryal. a study of a cavity nearby a pulsar at-60º latitude in the far infrared map. journal of nepal physical society, 4:33–41, 2017. [29] c. low and d. lynden-bell. the minimum jeans mass or when fragmentation must stop. monthly notices of the royal astronomical society, 176(2):367–390, 1976. [30] f. bonnarel, p. fernique, o. bienaymé, d. egret, f. genova, and et al. the aladin interactive sky atlas-a reference tool for identification of astronomical sources. astronomy and astrophysics supplement series, 143:33– 40, 2000. [31] x. dupac, j. p. bernard, n. boudet, m. giard, j. m. lamarre, and et al. inverse temperature dependence of the dust submillimeter spectral index. astronomy & astrophysics, 404:l11– l15, 2003. introduction sources of data method of analysis infrared flux and dust color temperature dust mass inclination angle jeans criteria gaussian distribution results and discussion structure and size infrared flux density dust color temperature dust mass contour map flux-temperature-mass relation simbad background source density and jeans mass conclusion bibechana 19 (1-2) (2022) 184-194 184 substitutional sodium doping on tungsten ditelluride: a first-principles study bibek subedi and narayan prasad adhikari* central department of physics tribhuvan university kirtipur kathmandu nepal *email: narayan.adhikari@cdp.tu.edu.np;vivek13.bs@gmail.com article information: received: january 08, 2022 accepted: july 10, 2022 keywords: first-principles calculationselectronic structures tungsten ditelluride sodium atom doping abstract for the investigation of structural, electronic and magnetic properties of pure and single sodium atom doped tungsten ditelluride monolayer, firstprinciples calculations based on density functional theory (dft) have been used. as the band gaps are on the order of the solar spectrum, they are commonly utilized in photovoltaic and opto-electronic systems. although wte2 has a wide range of technological applications in photo electrochemical cells and semiconductors, there are few theoretical and practical research on electronic structure calculations. to explore the band gap and other electronic and magnetic characteristics, we doped a single na atom into wte2 system. the substrate has two possible sites for sodium doping, one tungsten site (naw) and the other tellurium site (nate). on doping sodium atom at the tellurium site of 3×3 supercell, it seems to have metallic behaviour while the pristine form was semiconductor. the formation energies for both site doping have been estimated which predict that tellurium site doping is more preferable with lower formation energy. the te site is magnetic in nature, according to density of states (dos) estimates, with a somewhat unsymmetric dos plot. for tellurium site total magnetization is about 0.93µb while the pristine form was non-magnetic. the magnetism arises due to the redistribution of charge density as a result of adding a sodium atom as an impurity. doi: https://doi.org/10.3126/bibechana.v19i1-2.46429 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction two-dimensional (2d) materials are crystalline materials made up of single layers of atoms having thickness in the range of few nanometers or less. the importance of 2d materials has been found in electrodes, photovoltaics, and semiconductors, among bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:vivek13.bs@gmail.com https://doi.org/10.3126/bibechana.v19i1-2.46429 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana bibechana 19 (1-2) (2022) 184-194 185 other applications. these are ultrathin nanomaterials with substantial anisotropy and chemical functionality. [1]. they vary greatly in form, size, biocompatibility and degradability, as well as optical, mechanical, and chemical characteristics [2]. graphene, a single sheet of graphite, was dis-covered in 2004 and became the first known 2d substance. many more 2d materials, such as transition metal dichalcogenides (tmdc) and hexagonal boron nitrides (h-bn), were discovered after graphene. the tmdc materials follow mx2 structure, where m is a ivb-vib (ivb ti & zr, vb nb & ta, vib mo & w) transition metal and x is a chalcogen atom (s, se, te). according to the nature of the combination of transition metal and chalcogen, the resulting material can vary its properties from semiconducting to metallic and even superconducting state. also, if the bulk crystal is reduced to fewer layers, the band structure of many tmdcs changes distinctively, resulting in a unique sensitivity of tmdc properties to thickness [3]. in the bulk form, the crystal of 2h-wte2 crystallize in the hexagonal structure belonging to the space group p63/mmc which corresponds to the space group number 194. the crystal structure of wte2 are composed of van der walls-bonded te-w-te units. these stable units are wte2 monolayers, which contains two hexagonal planes of te atoms and an intermediate plane of w atom. there exists ionic-covalent interaction between these hexagonal planes in which the chalcogen atoms are (te) are arranged in trigonal prismatic structure [4]. in the monolayer of wte2, the w atom is trapped between two w atoms, which has a honeycomb structure. in wte2 structure, the bond length between two w atoms and w & te atoms are found to be 3.51 å and 2.73 å respectively. the w-te-w atoms forms the relaxed bond angle of 80.27º [5]. the band structure calculation of 2hwte2 along the high symmetry points γ-m-k-γ shows the indirect band gap of 0.81 ev with valance band maxima at γ-points and conduction band minima at between γ and k points. however, in 1hwte2, at high symmetry point k, direct band gap of 1.18 ev was observed. so, when the bulk structure is replaced by a single layer, the band gap switches from indirect to direct [4]. among the various properties, wte2 exhibit interesting properties like quantum spin hall effect and extremely large non saturating magnetoresistance in the monolayer limit [6]. the origin of large magnetoresistance is due the perfect balance between holes and electrons, which are sensitive to external pressure [7]. wte2 exhibit quantum transport properties, which includes superconductivity observed in the bulk crystal at high pressure [8], in multilayer flakes by proximity [9], and in monolayer by gating [10,11]. furthermore, it shows quantum spin hall effect up to 100 k in monolayer limit and type-ii weyl semi-metallic band structure6. despite the fact that wte2 is not a common material like all transition metal tellurides, it is briefly discussed as a member of this sub-family of tmdc due to its peculiar features, which have made it a possibility for enormous magnetoresistance and superconductivity. many theoretical and experimental works have been done on electronic and magnetic properties of wte2. the electronic band structure and density of states of pristine form is studied theoretically and experimentally. the change in band structure and other properties after the doping of the elements like h, li, be have been studied earlier. so, we are going to study the change in properties of pristine form after doping of na atom. by substituting a tungsten or a tellurium atom of pure tungsten ditelluride with a sodium atom, doping can be done. this might bring about changes in the electronic and magnetic behavior which may help keep a pace further ahead in this research eld. e. igmubor et al., in 2017 studied the doping of h, li and be on monolayer wte2. they found the formation energies of x dopant substituted for w between 3.59 and 2.61 ev. in their study, they found that liw bibechana 19 (1-2) (2022) 184-194 186 defect having formation energy of 2.14 ev was the most favorable. also, it was known that hw induced no magnetic moment while liw and bew induced magnetic moment of 3.44 and 0.05 µb respectively [5]. the element we want to dope in our system, sodium ([ne] 3s1) is soft, silvery white metal belonging to group i of the periodic table. the sodium atom has body-centered cubic crystal structure and it is paramagnetic in nature. due to the single valance electron, sodium is a good conductor of heat and electricity and is also highly reactive in nature. thus, by using substitutional doping, the sodium metal atom should fit readily into the wte2 sheet. in our work, we apply spin polarized density functional theory (dft) method to investigate the impact and variation in the electronic and magnetic properties of na doped wte2 nanosheet compared with pure wte2. following this section, we go over the computational techniques, findings and discussion and conclusions in that sequence. 2.methods and computational details we used the quantum espresso code to conduct first principles calculations to examine the stability, electronic and magnetic properties of pristine and sodium doped tungsten ditelluride in the context of density functional theory with van der waals (vdw) interactions [12-14]. the generalized gradient approximation (gga) created by three scientists perdew, burke, and ernzerhof (pbe) [15] was employed to include the electronic exchange and correlation impact in our system. we used the kresse-joubert (kj) projector augmented wave (paw) pseudopotential to replace the complex effects of non-valance (i.e., core) electrons and nucleus with an equivalent potential as a result only active valance electrons are explicitly included throughout our calculation. to avoid any chance of contact from adjoining layers of wte2, a vacuum of 20 å was made in the perpendicular direction to the plane of the wte2 mono-layer (z-axis). the geometrically optimized structure was obtained by allowing our structure to relax under broyden-fletcher-goldfarb-shanno (bfgs) [16] scheme until the change in total energy was less than 10-4 ry between two successive self-consistent field (scf) steps while each component of force acting is less than 10-3 ry/bohrs. following the relaxation calculations, we calculated self-consistent total energy. the brillouin zone of wte2 was obtained in k-space adopting monkhorst-pack technique [17] with an estimated value of mesh of k-points derived from the convergence test. we utilized a k-point mesh of 10×10×1 for relaxation calculation and a kpoint mesh of 14×14×1 for all other computation. we picked the wave function cutoff energy value of 50 ry and the charge density cutoff energy value of 500 ry using the convergence test. optimization calculation of lattice parameter was done before the relaxation calculation and the optimized value of lattice parameter was obtained as 6.715 bohr. we have also utilized ‘marzarrivanderbilt (m-v)’ [18] technique of smearing or cold smearing with 0.01 ry smearing width. in addition, for self-consistency, we used the ‘david’ diagonalization technique with ‘plain’ mixing mode and 0.7 mixing factor. 3. results and discussion in this section, we discuss about the results of calculations as well as analyze the results and interpret it. the main goal of our work is to investigate the electronic and magnetic characteristics of pristine and sodium doped tungsten ditelluride using density functional theory (dft) simulating under quantum espresso (qe). band structure, density of states (dos), and projected density of states (pdos) computations were used to explain the electronic and magnetic features of pristine and na doped 3×3×1 supercell of wte2. a. structure and formation energy by taking optimized values of ecutwfc, kpoints and the lattice parameter, we defined our system in the pwscf input file. taking the help of xcrysden, we first obtained the bibechana 19 (1-2) (2022) 184-194 187 primitive cell structure, figure(1), and then the 3×3 supercell, figure (2) using this input file. both of the primitive cell and supercell were allowed to relax using bfgs quasi-newton algorithm for structural relaxation. fig. 1 (a) top view (b) side view of wte2 primitive cell there was very slight change in the atomic position after relaxation. the corresponding bond lengths and bond angles were also changed by small amount in the primitive cell as shown in table (i). table i. optimized structural parameters of the relaxed primitive wte2 cell primitive cell (3 atoms) lattice parameter a=b=3.554å, c=20å w-te bond length 2.739å te-w-te bond length 83.010º the parameters of our investigation are in great agreement with previously investigated values, as shown in table (i). in the study of e. igumbor et al., the value of bond length between w-w and w-te atoms was found to be 3.51 å and 2.73 å respectively [5]. also, our values of bond length agree with that of e. torun et al., which are: 3.55 å and 2.73 å for w-w and w-te respectively [19]. the input file for 3×3 supercell of tungsten ditelluride was constructed and then the system was allowed to relax. it is a unit cell with 27 atom basis and size of cell three times that of primitive cell. fig. 2 (a) top view (b) side view of 3×3 supercell of wte2 monolayer the structural parameters of this supercell were calculated and presented in table (ii). table ii. optimized structural parameters of the relaxed 3x3 wte2 monolayer 3×3 supercell (27 atoms) unit cell size a=b=10.661å, c=20å w-te bond lengths 2.739å, 2.739å, 2.739å w-w bond length 3.553å, 3.553å, 3.553å w-te-w bond angles 80.863º the supercell structure shows the replication of atoms in x and y direction. the bond length and bond angles for particular atoms were also equal so the system can be said to be perfectly symmetric and homogeneous. the doping of na on the pure system produces several distortions. nearest w atoms bibechana 19 (1-2) (2022) 184-194 188 (in nate) and nearest te atoms (in na) are drawn away from the plane. as a result, the bond lengths and angles of the nearest neighbor w-te are likewise changed. the deformed structure of the system following na doping may be seen in figures (3) and (4). table iv. structural characteristics of wte2 sheet with na atom doping at w site (naw) te-na-te bond angles 77.967º, 77.967º, 77.967º te-na bond length 2.899å, 2.899å, 2.899å nearest neighbor wte-w bond angles 80.841º, 80.841º, 80.841º nearest neighbor tew bond lengths 2.799å, 2.799å, 2.799å fig. 3 (a) top view (b) side view of na substituted wte2 at te site (nate) fig. 4 (a) top view (b) side view of na substituted wte2 at w site (naw) the structural parameters of the distorted system after na doping are presented in table (iii) and (iv). table iii. structural characteristics of wte2 sheet with na atom doping at te site (nate) w-na-w bond angles 59.486º, 59.486º, 59.486º w-na bond length 3.282å, 3.282å, 3.282å nearest neighbor tew-te bond angles 81.231º, 81.231º, 81.231º nearest neighbor wte bond lengths 2.771å, 2.771å, 2.771å tables (iii) and (iv) shows that in both nate and naw system, the na atom has been repelled from the buckled plane. there occur significant increase of w-na and te-na bond length (3.282 å and2.899 å) than w-te bond length (2.739 å) in pristine form. as seen in the above tables (iii) and (iv), the nearest neighbor bond lengths and bond angles surrounding the doping site have been modified by a little amount. beyond this, we discovered structural changes in the whole sheet, with the degree of distortion decreasing as we go away from the doped atom. the stability of doped system was investigated by calculating the defect formation energy. the defect formation energy (ef ) [20] can be calculated by formula: ef = (ena ep) (e1 e2) where, ena represents the total energy of na doped wte2, ep represents the total energy of pure wte2, e1 represents the energy of single na atom and e2 represents energy of single w or te atom. by studying an isolated system of single atoms, the energy of isolated na, w and te atoms were determined using dft with suitable pseudopotentials. bibechana 19 (1-2) (2022) 184-194 189 table v. calculation of formation energy using different energy values (in rydbergs; 1 ry = 13.6 ev) formation energy of na doped wte2 at te site study in system energy (ry) na doped wte2 (ena) -13115.874 pristine 3×3 wte2 (ep) -13369.374 isolated na atom(e1) -109.167 isolated te atom(e2) -362.429 formation energy (ef) 0.238 formation energy of na doped wte2 at w site study in system energy (ry) na doped wte2 (ena) -12718.187 pristine 3×3 wte2 (ep) -13369.374 isolated na atom(e1) -109.167 isolated w atom(e2) -759.641 formation energy (ef) 0.713 the formation energy is less when na is doped at te site rather than at w site. thus, the doping of na at te site is more favorable than at w site. from the tables above, it can be seen that all of the energy of the system under investigation are negative, indicating their stability. both doped systems, however, have positive formation energies. it suggests, that amount of external energy should be given to con-struct the doped system, demonstrating its unstable character. b. electronic and magnetic properties of pristine wte2 band structure along with density of states of a quantum system is signature for the electronic properties of the material. the solution for the entire solid can be described by their nature in a single brillouin zone. the first brillouin zone of wte2 hexagonal lattice system with high symmetric points γ-m-k-γ is presented in figure (5). we plotted a highly fine and visible band structure plot using 100 kpoints in this path. fig. 5. first brillouin zone of wte2 hexagonal lattice with γ-m-k-γ high symmetric points. 1. electronic band structure of pristine wte2 in our study, band structure of pure wte2 single cell is calculated by taking the closed path γ-m-k-γ in an irreducible brillouin zone by choosing 100 k-points grid. figure (6) represents the band structure of pure wte2 unit cell with x-axis representing the high symmetric points and y-axis representing the associated energy values. the plot shows that pristine wte2 is a wide gap material having a direct band gap at k-point. from our calculation, we observed that band gap is approximately 1.071 ev with valance band maximum and conduction band minimum at k-point. the value of our observation corresponds with direct band gap of 1.18 ev as calculated by a. kumar and p.k. ahluwalia [4]. this band gap value of 1.071 ev for primitive cell of wte2 signifies that the system is semiconductor. as well as we observed spin polarized calculations on 3×3 wte2 supercell and obtained the band structures for up-spin and down-spin electrons. the band structures calculation shows that the arrangement of kohn-sham states in reciprocal space is identical for both spins. the supercell of pristine wte2 has direct band gap at γ-point with band gap value of 1.082 ev. bibechana 19 (1-2) (2022) 184-194 190 fig. 6 band structure of pristine wte2 using primitive cell, energies were calculated using the fermi energy as a reference (ef = 0.4962 ev). fig.7 band structure of pristine wte2 using 3×3 supercell, energies were calculated using the fermi energy as reference (ef=0.5053 ev). both primitive cell and supercell of wte2 shows the direct nature of the band gap. the only difference between them is that primitive cell has direct band gap at k-point while supercell has at γ-point. the change in band structure on going from pristine to supercell is due to the band folding, as the brillouin zone of the supercell is smaller than that of corresponding unit cell. this makes the bands of primitive cell in first brillouin zone to get folded into supercell brillouin zone. the supercell brillouin zone contains large numbers of horizontal looking bands, which does not resemble the original band structure. this makes the change in the band structure on going from primitive cell to supercell, however the symmetric points remain same21. band folding occurs as a result of hidden translation symmetry inside the supercell. this is because, while performing calculation on the supercell, the translational relations between unit cells within the supercell are ignored. on making larger supercell and sampling the brillouin zone at high symmetric point, the band structure is collapsed into an energy diagram. since there is still the translational symmetry, we can get band structure from such calculation by unfolding the band. that means, we can obtain unit cell band structure from supercell by unfolding it. 2. density of states (dos) of pristine wte2 the dos plot validates the band gap argument provided by the band structure plot and also provides information on the system’s magnetization. the dos plot of 3×3 supercell is shown in the figure (8) below. fig. 8 density of states for 3×3 supercell of pristine wte2. bibechana 19 (1-2) (2022) 184-194 191 from figure (8), it is clear that no spin states are available in the fermi level. it confirms the band structure plot’s conclusion that the system is semiconducting. the dos graph demonstrates the non-magnetic character of pristine wte2. our system is non-magnetic due to the symmetric distribution of accessible states for both up and down spin. another calculation we performed was projected density of states (pdos) calculations for various wte2 orbitals. the overall dos of the system is calculated by adding all of these orbital contributions together. the pdos graphic shows which orbital contributes the most to the overall states of the system around the fermi level. the pdos plot of 3×3 supercell of pristine wte2 is as follows. fig. 9 pdos for various orbitals of w and te atoms from this pdos, we observed that the valence orbitals of w and te atoms are below the fermi level. from the figure, we observe that s & p-orbitals of te and d-orbital of w make significant contribution, while the contribution due to the p-orbital of w is small and the contribution of s-orbital of w atom is almost absent. furthermore, the dos for various orbitals for both atoms in spin states up and down are perfectly symmetrical. thus, pure wte2 is a nonmagnetic material and element such as na can induce some magnetic moment on doping, which will be addressed further in the next sections. c. electronic and magnetic properties of wte2 doped with na atom the inclusion of a substitutional impurity, such as na, in the wte2 structure causes several modifications in its many characteristics. we also saw considerable alterations in band structure as a result of doping. on our doped system, we investigated spin polarized scf, dos, and projected dos computations. the calculation of formation energy of na doping on two possible sites viz. w & te and the study of stability of doping on these two sites suggests that the doping of na at te site is more favorable than w site. so, we present the change in the properties of pristine structure after doping of na at te site. 1. electronic band structure of na doped wte2 the band structure of na doped wte2 at the te site is shown in the diagram below. the spin polarized calculations were conducted to see the effect of doping on different spins. we observed that for up spin, electrons in the valance band crosses the fermi level and lies 0.13 ev above the fermi level whereas in case of down spin, no such crossover around fermi level is found and the electrons remains in the respective valance and conduction band. these new states present are due to the effect of doping. these band structure near the fermi level are notably different from those in pristine 3x3 wte2, also it is seen that energy levels of valance orbitals of w and te are also changed around the fermi level. bibechana 19 (1-2) (2022) 184-194 192 fig. 10 spin-up band structures of na doped wte2 at te site (nate), fermi level (ef = 1.3896 ev) is fixed as zero. fig. 11 spin-down band structures of na doped wte2 at te site (nate), fermi level (ef = 1.3896 ev) is fixed as zero. the band structure diagram illustrates that doping of na in wte2 sheet develop metallic character for up spin and semiconductor behavior for down spin. furthermore, in the case of up spin, the bands from the valance band transcend the fermi level and reach the conduction band, resulting in overlapping bands and, as a result, a metallic system. the bands stay in their respective bands without overlapping in the case of down spin, demonstrating the semiconducting nature of the material with a direct band gap of 1.007 ev at the γ-point. the doping specially influences near about fermi level. the fermi energy in case of doping is 1.3896 ev, which is higher than the fermi energy level of pristine form i.e 0.5053 ev. this slight increase in fermi energy level is because of the addition of na atom in place of te atom. 2. density of states (dos) of na doped wte2 the dos plot of the 3×3 supercell of na doped wte2 at te site (nate) is as follows. fig. 12 density of states plot for na doped wte2 at te site (nate) the horizontal line in figure (12) distinguishes dos for up-spin and down-spin, with states just above horizontal line denoting up-spin and those below the horizontal line denoting down-spin. the variation in dos is considerable near the fermi level. the fermi level line was free of any spin states in the original system. meanwhile, the fermi level line in a na doped system possesses specific spin states. the fermi level itself has been shifted up a bit in the dos plot too, so that the system shows metallic nature in up spin state. the distribution of accessible states in case of up and down spin is asymmetrical, so that na doped wte2 is magnetic. the asymmetrical nature of dos plot gives magnetic nature to the system with total magnetization of 0.93 µb for nate. the case was quite different for pristine 3×3 supercell, where up and down bibechana 19 (1-2) (2022) 184-194 193 dos were symmetrical and system behaves as non-magnetic. the individual w and te atom behave as magnetic materials as they have magnetic moment of 6 µb and 2 µb respectively. to see more closely on the contribution of atomic orbitals of each atom we also have presented and discussed with pdos plots as shown below. fig.13 projected density of states of doped 3×3 wte2. the pdos of na doped wte2 for spin states up and down is presented in figure (13) by taking fermi energy level as a reference represented by the vertical dotted lines. spin up and spin down states are separated by the horizontal line. from the projected dos calculations, the accessible states near fermi level for na doped wte2 at te site, are largely because of w and te atom. in case of w, 5dorbital is dominant over 5p & 6s orbitals, whereas for te, 5s & 5p-orbitals contributes significantly. due to this the system is magnetic in nature. the contribution of 5dorbital of w and 5s & 5p-orbitals of te to the magnetization is relatively greater than 3s orbitals of na. below the fermi level, te-s and w-d orbitals are dominant whereas above fermi level w-d orbitals are significant. the contribution of na-3s orbital is almost negligible. there are large number of unoccupied vacates state below fermi level for both w and te. the system has got magnetic nature with magnetic moment 0.93 µb per cell. conclusions and futureremarks we conducted first principles study to look into the stability, electronic and magnetic properties of pristine and sodium doped wte2 system. these calculations were executed under dft using gga exchange correlation functional including paw pseudo-potential implemented with quantum espresso code. the doping of na atom in the system makes various distortion in the structure. the na atom is shifted from the plane holding the w and te atoms after doping. regarding electronic properties we conclude that pristine wte2 sheet shows semi-conducting nature with a direct band gap of 1.082 ev for 3x3 supercell and direct band gap 1.071 ev for primitive cell. both primitive and supercell shows direct nature of band gap with the difference that primitive cell has band gap at k-point while supercell has at γ-point. this was due to the band folding while conducting calculation from unit cell to supercell. employment of band unfolding techniques could give us more authentic results and this could be further work that can be done to enhance our knowledge about bands and band structure. the band structure of doped system was quite different from the pristine system. the doping of na atom induces metallic character in case of up spin state with valance bands crossing the fermi levels. however, in case of down spin state, the system shows semiconducting nature with direct band gap of 1.007 ev at γ-point. in case of pristine system, we found the non-magnetic nature of the system due to the symmetric structure of density of states of both spin states up and down. however, in case of doped system, the asymmetrical distribution of density of states gives the magnetic nature to the system with total magnetization of 0.93 µb. this magnetization bibechana 19 (1-2) (2022) 184-194 194 was due to the addition of na atom in the pristine system, which caused the redistribution of charges between the doped atom and atoms of pristine system giving net magnetic moment to the system. the dos and pdos plot revealed that the magnetic nature of doped system is mainly due to the contribution of w-5d orbital. the contribution of 3s orbital of na can be seen above fermi level in small extent while below the fermi level the its contribution is almost negligible. our system can be used for the potential application in the field of magnetoresistance and superconductivity. the direct-indirect gap transition shows the possible application in various fields like solar cell, electronics and photocatalysis. the current work may be advanced to investigate the charge 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[21] w. ku, t. berlijn, c.-c. lee, et al., physical review letters 104 (2010) 216401. bibechana vol. 20, no. 3, december 2023, 248–258 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar time and space domain prediction of water quality parameters of bagmati river using deep learning methods pujan bashyal1, mandira pradhananga adhikari2,∗, nanda bikram adhikari1 1department of electronics and computer engineering, pulchowk campus, institute of engineering (ioe),tribhuvan university, lalitpur, nepal 2central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal ∗corresponding author. email: mandira43@hotmail.com;adhikari@ioe.edu.np abstract bagmati river is biologically, geologically, religiously and historically significant among the river systems of the kathmandu valley. the river is affected by five major tributaries, including manohara, dhobi khola, tukucha, bishnumati, and balkhu khola, which significantly impact the water chemistry inside the kathmandu valley. the data of water quality parameters ph, dissolved oxygen, turbidity, temperature, oxygen reduction potential, conductivity, total dissolved solids, salinity among others was collected using fixed sensors (in period of 5 seconds) and mobile sensors (with latitude and longitude) along the river. the observation is important for two reasons, one because it was collected in real-time and fine scale, which is not normally possible with traditional ways, and next such observation was done for the first time in bagmati river. the aim of this study was to predict water quality parameters of the bagmati river using machine learning time series models, specifically arima and lstm. the lstm model was designed with one input layer, one encoder layer, one repeat layer, one decoder layer, and one output dense layer to separate the output into temporal slices. additionally, a dnn model was employed for location-based prediction, utilizing two input layers for latitude and longitude and seven output layers for the seven water quality parameters considered for study. the models demonstrated promising performance, but further data collection and parameter variation are recommended for continued optimization. keywords arima, dnn, lstm, spatial prediction, temporal prediction, time series models. article information manuscript received: august 18, 2023; accepted: september 14, 2023 doi https://doi.org/10.3126/bibechana.v20i3.57736 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 248 http://nepjol.info/index.php/bibechana mandira43@hotmail.com;adhikari@ioe.edu.np https://doi.org/10.3126/bibechana.v20i3.57736 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ pujan bashyal et al./ bibechana 20 (2023) 248-258 249 1 introduction the bagmati river holds tremendous religious, historical, and ecological significance in nepal. originating from the shivapuri hills, this river passes through the culturally important pashupatinath temple and other areas in the kathmandu valley. unfortunately, the remarkable growth of population and unplanned urbanization in the kathmandu valley has led to severe deterioration of the bagmati’s water quality [1]. the water pollution poses major environmental and health hazards, demanding urgent assessment and remediation. periodic measurement of critical water quality parameters like ph, dissolved oxygen, temperature, turbidity etc. provides vital insights into the pollution levels and overall river health. however, the conventional methods of manual sample collection and lab-based analysis are extremely time-consuming, labor-intensive and expensive. the sparse, delayed data obtained through traditional monitoring is insufficient to capture the high-resolution spatio-temporal dynamics of a complex river system [1]. recent technological advances have enabled real-time, automatic and fine-scale sensing of water quality through fixed and mobile probes . additionally, machine learning models like long shortterm memory (lstm) networks and deep neural networks (dnn) have shown promise in effectively analyzing and predicting water quality data . however, these modern techniques are yet to be implemented or evaluated for bagmati river. therefore, this study aims to implement machine learning models on this data to predict the water quality parameters in time and space domain. successful implementation of this approach can provide an efficient alternative to traditional techniques for river monitoring in developing regions facing resource constraints. furthermore, the spatio-temporal insights obtained from data-driven modelling can strengthen pollution control policies and remediation efforts for the bagmati river. the bagmati river in nepal emerges as a critical focus for management due to its alarming pollution levels. stretching approximately 51 kilometers through the culturally significant kathmandu valley and covering a catchment area of around 678 square kilometers, this river holds significant biological, geological, and historical importance. unfortunately, it has been significantly impacted by the influx of pollutants from five major tributaries – manohara, dhobi khola, tukucha, bishnumati, and balkhu khola – which substantially alter its water chemistry. the uncontrolled urban growth within the kathmandu valley has led to the deterioration of the river’s water quality, with untreated sewage and waste being directly discharged into its waters. the river has devolved into a repository for solid waste, untreated domestic, industrial, and agricultural effluents. consequently, accurate prediction of water quality parameters at various gps locations along the bagmati river is imperative for effective pollution management and mitigation. the research conducted by adhikari et al. [1] endeavors to comprehensively profile and characterize pollutants in real-time and space. water quality encompasses the physical, chemical, biological, and radiological attributes that define water’s appropriateness for specific applications. parameters such as temperature, ph, dissolved oxygen, nutrients, metals, and pollutants collectively define water quality and significantly impact aquatic life, ecosystems, and human well-being. this quality is often evaluated against established standards for various parameters, including temperature, ph, oxidationreduction potential (orp), electrical conductivity (ec), resistivity (res), total dissolved solids (tds), salinity (sal), dissolved oxygen (do), turbidity (turb), biochemical oxygen demand (bod), chemical oxygen demand (cod), nitrogen, phosphorus, and pollutants like pm2.5, co2, formaldehyde, and volatile organic compounds (vocs). each parameter holds a defined range of values deemed safe for both human and aquatic life. temperature influences water’s physical and chemical properties, while ph indicates its acidity or alkalinity. ec and res reflect water’s conductivity, correlating with dissolved ion concentration. tds and sal measure dissolved solids and salts, while do is crucial for aquatic survival. turbidity gauges water clarity, with pollutants like pm2.5, co2, formaldehyde, and vocs emerging as additional concerns. the present study focuses on key parameters including temperature, ph, orp, ec, res, tds, sal, do, and turbidity. utilizing sophisticated mobile tracers and analyzers, data collection was conducted along the bagmati river using a rafting boat, as well as through a fixed sensor system stationed within the kathmandu valley. these sensors recorded real-time data of various physical parameters, including ph, conductivity, salinity, total dissolved solids (tds), dissolved oxygen (do), temperature, and turbidity. among the 14 designated data collection sites, the upstream gokarna site (b-1) represents the most remote point, situated approximately 8 kilometers from the entry point (sundarijal) of the bagmati river into the kathmandu valley. in this rural setting, the sources of pollutants are less apparent. moving along the river, the b-2 and b-3 sites are positioned just upstream and downstream of the guheshwori wastewater treatment plant, respectively. these sites encompass a blend of residential and industrial areas, including wool dying companies, medical colleges, and hotels. while the wastewater treatment plant treats sewage bepujan bashyal et al./ bibechana 20 (2023) 248-258 250 fore discharge, pollutants from various sources still affect the river. the guheshwori temple site (b4) is impacted by activities such as bathing, washing, and picnicking along the riverbanks. the gaurighat site (b-5) captures the influence of local residential areas before the river reaches the revered pashupatinath temple. this temple, of great cultural and religious significance, witnesses various practices such as bathing and rituals, including cremation. unfortunately, the ash from cremations is directly released into the river. pashupatinath temple (aryaghat) (b-6) observes the discharge of untreated wastewater and effluents from the treatment plant into the bagmati river. tilganga (b-7), just downstream of the guheshwori wastewater treatment plant, portrays the aftermath of these discharges. tinkune (b-8) reveals a disturbing sight of solid waste and sewer lines leading directly to the river, resulting in visibly dark and turbid water. the subsequent sites (b-9 to b-14) serve to assess the effects of tributaries on the bagmati river, with the thapathali site (r-11) illustrating the water quality above the highly polluted tukucha tributary. observations at the shankhamul site provide insight into daily and diurnal variations before tributaries influence the river. adhikari et al.’s research focused on the analysis of water quality parameters, highlighting the limitations of conventional fixed-point measurements in capturing spatial and temporal profiles. collecting data along the bagmati river frequently proves to be both time-consuming and costly. despite these constraints, the application of time and space domain data modeling could facilitate insightful conclusions and support the research objectives. by leveraging mathematical and statistical techniques, machine learning analyzes data, identifies patterns, and enables predictions or decisions based on the analysis. in a context marked by limited data availability, models grounded in statistical and machine learning techniques offer invaluable insights into the water quality domain. in this research, insights from the highresolution spatiotemporal data are extracted via statistical and machine learning models. autoregressive integrated moving average (arima) and long short-term memory (lstm) networks are implemented for accurate time series forecasting of water quality at fixed locations. additionally, deep neural networks (dnns) are leveraged to elucidate water quality variations along the river’s spatial profile. 2 research background water quality parameter research offers insights into water resource quality and its implications for human, aquatic life, and environmental health. by analyzing parameters such as ph, dissolved oxygen, turbidity, and nutrients, researchers can pinpoint contamination sources and assess aquatic ecosystem health [1]. however, data collection is timeconsuming and costly, compounded by complex influencing factors. predictive algorithms, like artificial neural networks and decision trees, are developed to forecast water quality parameters with limited data sets [2]. one study employs multivariate analysis (ca, pca, da) to classify river water, demonstrating the effectiveness of statistical techniques [3]. another study highlights the success of emd-lstm models in predicting various parameters [4]. a deep learning framework employing lstm networks forecasts water quality parameters based on historical data [5], and bi-s-sru models showcase higher accuracy [6]. a cnn-lstm-svr hybrid model outperforms traditional methods [7], while hybrid techniques and preprocessing enhance freshwater quality prediction [8]. the application of a bpnn-kalman filter model for river water temperature, ph, and do concentration prediction proves accurate [9]. narnet and lstm models predict wqi, while svm, knn, and naive bayes classify wqi data [10]. bayesian uncertainty processor enhances deep learning-based anns [11], and a novel mvd-based framework expands dnn application even with limited data [12]. deepst models spatiotemporal data, outperforming baselines [13]. flow’s influence on water quality parameters is studied, showing impacts on dissolved oxygen, turbidity, ph, and orp [14–18]. these studies emphasize considering river flow in water quality assessments, acknowledging its complex relationship. it is noteworthy that the traditional forecasting methods have lots of problems, such as low accuracy, poor generalization, and high time complexity. to solve these shortcomings, these days some machine learning based novel water quality parameters (wqp) prediction methods, like deep lstm learnings and deep neural networks are in practices [4,6,9,13,19–21]. in the case of bagmati river, to our knowledge so far, since there exist no such sequential time series-based ml modelling studies except a scenario-based so-called water evolution and planning (weap) [22], this research considers ml modelling as of its main scope using the following methodology. 3 methodology the first step involved collecting time series data related to various water quality parameters of interest. once the raw data is obtained, it is loaded and basic exploratory analysis is performed to understand trends, distributions, relationships etc. next, pujan bashyal et al./ bibechana 20 (2023) 248-258 251 data cleaning tasks are undertaken to prepare the data for modelling. this includes handling missing values, removing outliers, and dropping irrelevant columns or features. with clean data in place, models like arima and lstm can be initialized with suitable parameters and configurations. the models are then trained on historic data and validated by testing on a holdout dataset. training loops through iterations to minimize the loss function and update model weights and biases. validation provides insight into how well the models generalize. once the models are trained and validated, they can be used for one-step or multi-step ahead prediction on new data. the predictions are compared to actual values to evaluate model accuracy. in summary, the key steps in the methodology involve data collection, exploratory analysis, cleaning, model development and training, and final prediction. this provides a structured approach to apply time series modelling for forecasting water quality indicators. the process aims to build highly accurate and robust models. 3.1 environmental setup to run the models and other necessary programs, a dedicated gpu based resource colab provided by google research was used. excel was also used to save and open csv files, and process data. the libraries keras, tensorflow, statsmodels, pandas profiling, matplotlib, sklearn, pandas, numpy, and datetime were used. 3.2 data collection and analysis water quality data was collected by adhikari et al. at 14 fixed stations along the bagmati river using a multi-parameter sensor system. key parameters included ph, dissolved oxygen (do), and temperature. on which, descriptive statistics were generated using excel and pandas. data was visualized using pandas profiling. data was cleaned by removing outliers and parameters with high levels of missing data. the final dataset contained ph, do and temperature. 3.3 model development an arima time series model was developed using a grid search to select optimal p, d, q parameters based on lowest mse and mae. an lstm model was developed for time series forecasting, using encoder-decoder based architecture. a deep neural network (dnn) model was developed for spatial prediction at different locations. the model had four fully connected layers, adam optimizer, mae as loss function and relu activation function for each layer. 3.4 arima the arima forecasting equation for a stationary time series is a linear (i.e., regression-type) equation in which the predictors consist of lags of the dependent variable and/or lags of the forecast errors. that is: predicted value of y = a constant and/or a weighted sum of one or more recent values of y and/or a weighted sum of one or more recent values of the errors. a nonseasonal arima model is classified as an "arima (p,d,q)" model, where: • p is the number of autoregressive terms, • d is the number of nonseasonal differences needed for stationarity, and • q is the number of lagged forecast errors in the prediction equation. ŷt = µ+ϕ1yt−1+ϕpyt−p−θ1yt−1− ...−θqyt−q (1) equation 1 general equation for arima model. ϕprepresents the auto-regressive parameters; y represents the difference terms; i.e. if d = 0: yt = yt, if d = 1 yt = yt yt−1 and so on θp represents the moving average parameters; e represents the error term at each timestamp; µ is the constant. the parameters (p,d,q) imply the order of the model. while selecting the suitable order for the model, aic (akaike information criterion) and bic (bayesian information criterion) are used to evaluate the quality of statistical models by balancing their complexity and goodness of fit. the aic is a measure of the relative quality of a statistical model for a given set of data. it is defined as: aic = 2k − 2ln(l) (2) where, k is the number of parameters in the model and l is the maximum likelihood estimate of the likelihood function of the model. the aic balances the trade-off between the goodness of fit and the complexity of the model, and the model with the lowest aic is preferred. the bic is similar to the aic but places a stronger penalty on model complexity. it is defined as: bic = kln(n)− 2ln(l) (3) where, n is the sample size, k is the number of parameters in the model and l is the maximum likelihood estimate of the likelihood function of the model. the bic is based on the bayesian approach, where the model with the highest posterior probability is preferred. the bic penalizes complex models more than the aic, and the model with the lowest bic is preferred. pujan bashyal et al./ bibechana 20 (2023) 248-258 252 table 1: order of arima model for various parameters parameter p q d do 1 1 1 ph 3 1 0 temperature 0 1 0 orp 0 1 0 ec 0 1 1 tds 0 1 1 the first step converts the dataset into a time series format by setting the time column as the index and defining the water quality parameters as feature columns. this structures the data for temporal modelling. next, the stats-models library’s auto arima capability is leveraged to automatically optimize the arima parameters p, d, and q based on the data characteristics. the optimized model order provides the best starting point for the arima modelling. the dataset is then partitioned into separate training and testing sets to validate the model’s performance. the arima model is trained on the training data, and the testing data is used to evaluate the model’s accuracy. the model’s predictions are compared with the actual data in the testing set to assess its performance. the mean squared error (mse) and mean absolute error (mae) are calculated as metrics to quantify the model’s accuracy. these metrics provide insights into how well the arima model predicts the water quality parameters. figure 1: methodology followed in the research. figure 2: steps for implementation of arima model. 3.5 lstm the lstm has an input x(t) which can be the output of a cnn or the input sequence directly. h(t-1) and c(t-1) are the inputs from the previous timestep lstm. o(t) is the output of the lstm for this timestep. the lstm also generates the c(t) and h(t) for the consumption of the next time step lstm. the first step in the lstm involves converting the dataset into a time series format by setting the time column as the index and the water quality parameters as feature columns. this prepares the data for temporal modelling. next, minmax scaling is applied to normalize all features to a common 0-1 range, which aids model optimization. the dataset is then split into training and validation/testing sets in a ratio suitable for the problem, such as 80:20 or 70:30. with the data ready, the model architecture is defined by specifying the type and sequence of layers, like input, hidden and output layers, that the data will flow through. the tensorflow library provides the tools for building and running the models. the model is then compiled by configuring key hyperparameters like optimization algorithm, loss function and metrics for training. this sets up the model for the training process. the next step is to fit the compiled model on the training data for multiple epochs, which trains the model by minimizpujan bashyal et al./ bibechana 20 (2023) 248-258 253 figure 3: lstm input outputs and the corresponding equations for a single timestep. ing the specified loss function. finally, the trained model can be used to generate predictions on new validation/test data, and its performance evaluated using metrics like accuracy and loss scores. in summary, the methodology involves data preprocessing, model building, training and prediction to develop a machine learning model for water quality forecasting. the lstm architecture consists of an input layer that accepts sequences of 10-time -steps, with each step containing 9 input features. this input layer is connected to an encoder layer comprised of 100 lstm units. the encoder processes the input sequence and outputs an encoded sequence. the encoded sequence is then fed into a decoder layer, also containing 100 lstm units. additionally, a repeat vector summarizes the entire input sequence from the encoder’s final output and provides this context to the decoder at each time step. finally, a dense output layer separates the decoder outputs into distinct predictions for each water quality parameter. the model optimizes using the adam algorithm combined with a huber loss function. the huber loss provides the benefits of lower sensitivity to outliers compared to mse and lower bias than mae, as suggested in prior studies. this lstm model architecture enables effective learning of complex temporal relationships and patterns in the water quality time series data. figure 4: steps for implementation lstm model. figure 5: steps for implementation dnn model. pujan bashyal et al./ bibechana 20 (2023) 248-258 254 3.6 dnn model training models were trained using time series cross-validation with an 80-20 train-test split. model parameters were tuned to optimize performance. techniques like backpropagation and optimization algorithms like adam were used to minimize error and improve model accuracy. model performance was evaluated using metrics like mse, mae, aic and bic. 4 results and discussion the results of the arima and lstm models for the prediction of water quality parameters are summarized below: table 2: measured and predicted values for parameters at the two nearest locations parameter measured value (blue dot) predicted value (red dot) do 0 0.259856 ph 7.29 7.202224 temperature 21.64 21.34662 orp -254.6 -259.856 figure 6: plot of do values collected with mobile sensor along the river. figure 7: prediction curve: actual values vs predicted values of do (arima). figure 8: prediction curve: actual values vs predicted values of ph (arima). pujan bashyal et al./ bibechana 20 (2023) 248-258 255 figure 9: prediction curve: actual values vs predicted values of do (lstm). figure 10: prediction curve: actual values vs predicted values of ph (lstm). figure 11: epoch wise loss plot for e1d1 lstm. figure 12: epoch-wise mae curve for e1d1 lstm. figure 13: epoch-wise loss curve for dnn model at 80 : 20 validation split. figure 14: epoch-wise loss curve for dnn model at 70 : 30 validation split. 4.1 arima model the arima time series modeling approach was able to effectively capture the temporal dynamics in the water quality parameters. for dissolved oxygen (do), the model achieved an rmse of 0.519, mae of 0.2901 and r2 of 0.9760 on the test set, indicating a good model fit with minimal errors. the residuals plot showed that most residuals were clustered close to zero, signifying that the actual values were close to the predicted values. the model was able to forecast do levels reasonably accurately up to 5-time-steps ahead, with errors increasing slightly for longer forecast horizons. overall, the arima pujan bashyal et al./ bibechana 20 (2023) 248-258 256 figure 15: gps points with values measured (blue) and predicted (red) by dnn. modelling was successful in modelling the temporal variations in do and other water quality indicators. 4.2 lstm model the lstm neural network model demonstrated promising performance for short-term time series forecasting across the different water quality parameters. for temperature predictions, the model achieved the lowest error with mae scores ranging from 0.2649 to 0.2701 across 5-time-units. the errors were higher but still fairly low for other parameters like ph (mae 0.0527 to 0.0586) and dissolved oxygen (mae 1.10 to 1.49). the model was able to learn complex time-dependent patterns in the data. the epoch-wise learning curves showed that the model errors stabilized within 30-40 epochs of training. overall, the lstm model provided robust forecasts for the next 5-time-steps based on previous lags and long-term temporal contexts. 4.3 dnn model the deep neural network model for spatial prediction yielded optimal results with a 80:20 train-test split, achieving the lowest mae of around 0.15 after 30 epochs. the model training curves showed the validation loss decreasing and levelling off after 30-40 epochs across different data splits. this indicates that the model was able to learn the underlying spatial relationships between the location coordinates and water quality parameters. the multilayer architecture with increasing number of neurons in the hidden layers likely enabled the model to learn complex nonlinear feature representations. the model demonstrates potential for accurate prediction of water quality indicators like ph and do levels based on the geographic coordinates. 5 conclusion this study demonstrated the feasibility of using machine learning approaches like arima, lstm, and dnn models for predicting water quality parameters in the bagmati river in nepal. the fine-scale, real-time observation data collected provides valuable insights into the spatio-temporal dynamics of key water quality indicators like ph, do, temperature, and conductivity. the arima model was successfully implemented to capture the temporal patterns in parameters like do and ph. the lstm model also showed promising results for short-term time series forecasting of multiple water quality variables. the location-based dnn model achieved reasonable performance in predicting water quality parameters based on geographic coordinates. however, the limitations of the current dataset underscore the need for expanded data collection across wider spatial and temporal scales, as well as inclusion of more water quality indicators. addressing these limitations through continued research will further enhance our understanding of the intricate relationships between various natural and anthropogenic factors influencing river water quality. incorporating turbulence data along with spatiotemporal coordinates could have enabled examining the fluctuations in water quality parameters as water flows through different regions over time. availability of extensive datasets capturing turbulence, timestamps, and locations would have facilitated developing enhanced forecasting models and uncovering significant dynamic patterns and trends. specifically, analysis of how turbulence impacts various quality measures could lead to more sophisticated models and insights. however, investigating the role of turbulence poses certain challenges such as complex measurements and simulations. nevertheless, accounting for turbulence remains an important consideration for future work to advance pujan bashyal et al./ bibechana 20 (2023) 248-258 257 understanding of aquatic systems and devise optimal water resource management strategies. while turbulence incorporation was beyond the scope of this study, addressing the associated difficulties and limitations in follow-up research could significantly improve water quality assessment capabilities. nonetheless, this study represents an important step towards leveraging advanced ml techniques for developing accurate, real-time water quality monitoring systems. the model frameworks presented can inform future efforts to build intelligent decision support systems for water resource management, pollution control and remediation in the bagmati and similar river ecosystems. acknowledgement this research is supported by university grants commission, nepal through collaborative research grant (crg-79/80-st-01). references [1] m. p. adhikari, n. b. rawal, and n. b. adhikari. real-time fine-scale measurement of water quality parameters along the bagmati river in the kathmandu valley. nature environment and pollution technology, 20(3):1047– 1057, sep 2021. 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[22] b. k. mishra et al. assessment of bagmati river pollution in kathmandu valley: scenario-based modeling and analysis for sustainable urban development. sustainability of water quality and ecology, 9–10:67–77, 2017. introduction research background methodology environmental setup data collection and analysis model development arima lstm dnn model training results and discussion arima model lstm model dnn model conclusion bibechana vol. 21, no. 2, august 2024, 142-148 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar efficiency enhancement of solar cell using mirror concentrator mohammad ali1, mohammad m. tawhid2∗ 1european university, dhaka-1000, bangladesh 2north western university, khulna-9100, bangladesh ∗corresponding author. email: ku.tawhid@gmail.com abstract this research is done to find out a method by which the efficiency of a solar cell can be increased by using mirror concentrator to get a higher power and optimum efficiency. at first the sun lights are incident on the mirror concentrator made of plane glass and then the reflected rays are incident to the solar cell. flat mirror concentrator (fmc) has been used to increase the incident irradiance on solar panel system by concentrating the sun light ray on it and then to improve the cell performance. a comparison is made for the same pv solar panel systems using single and triple flat mirror concentrator. it is a beneficial and important theory of solar power plant sector. it can be used in household and any kind of industrial area. the fmc consists of two flat mirrors made of glass, with dimensions (170cm × 80cm) enclosed by aluminum frame and inclined to an angle 55 ° with a solar panel (160cm × 120cm) tilted at 45° from the horizon. the results indicated that when the concentrator is used with the solar panel the efficiency increased by a factor of 4.52% to 11.34%. so, the increase in efficiency of the solar cell is 6.82%. keywords mirror concentrator, reflected ray, solar cell, efficiency, inclined angle, power. article information manuscript received: march 7, 2024; revised: april 5, 2024; accepted: april 14, 2024 doi https://doi.org/10.3126/bibechana.v21i2.63560 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction solar panels will play a major role in future sustainable energy production, but they work best when sunlight hits them directly. this can be a problem when sunlight is diffused by cloud cover or the sun moves overhead throughout the day. many solar arrays actively rotate toward the sun to capture as much energy as possible. this makes them more expensive and complicated to build and maintain than stationary ones. the negative aspects of fossil fuels and non-renewable energy sources are being increasingly scrutinized due to their harmful effects on the environment. this impact has been exacerbated by the rapidly changing nature of the earth's climate in recent years, and more effort than ever is being put into renewable energy technologies in an effort to phase out non-renewable technologies and prioritize renewable energy sources. among all renewable energy sources, photovoltaics (pvs) 142 http://nepjol.info/index.php/bibechana ku.tawhid@gmail.com https://doi.org/10.3126/bibechana.v21i2.63560 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ mohammad ali and mohammad m. tawhid/ bibechana 21 (2024) 142-148 143 – commonly known to the public as solar cells – are one of the most widely researched and deployed technologies due to the abundance of sunlight that hits the earth every day. depending on what they are made of and how they are constructed, pvs can have a range of functions for converting sunlight energy into electricity. however, if they are to be realized as a primary energy source in the future, their efficiency must be increased to offset the loss of energy generated from non-renewable sources. one way to increase the efficiency of pv is to use photovoltaic/solar concentrators. however, as with most components in technology, there are many different types, all of which have different advantages and disadvantages. regardless of the type, the general principle of a solar concentrator is that it is an optical element (be it a lens, curved mirror or a flat mirror) that can be used to condense the light entering the pv, making it more efficient and converting sunlight into electricity. concentrator is a recent discovery that has a unique geometry that is attractive for solar electric generation systems needing concentration. since the industrial revolution, energy demand and economic growth have taken off simultaneously [1]. numerous renewable energy sources are being researched by various countries to meet the demand for energy [2]. research on solar energy is being conducted rapidly [3, 4]. sustainable and green energy solutions are a recent method of making this planet cleaner and safer. electrical energy share has been gradually enlarged and currently stands at 20% [5]. rers (renewable energy resources) have attracted a market, and various rer-based models have been developed [6]. there have been varying behavioral trends and levels of social acceptance of rers [7–9]. rers mainly consist of solar, wind, biomass, and hydro energy, which are freely available primary sources, in contrast with traditional fossil fuels. they are free from toxic or hazardous flow gases, making them more viable and greener. wind energy has been utilized to meet energy needs, but has limitations of cut-in, rated, and furling wind speed, which vary depending on the location. earth receives an amount of solar energy which is 6000 times greater than human energy needs [10]. solar energy has dominated the energy sector as a long-lasting technology compared to other resources. it is also projected that we will achieve zero co2 emissions by 2050 [11]. in this research, a comparison is made for the same pv solar panel systems using single and triple flat mirror concentrator. it is a beneficial and important theory of solar power plant sector. it can be used in household and any kind of industrial area. the fmc consists of two flat mirrors made of glass, with dimensions (170cm × 80cm) enclosed by aluminum frame and inclined to an angle 55 ° with a solar panel (160cm × 120cm) tilted at 45° from the horizon. the results indicated that when the concentrator is used with the solar panel the efficiency increased by a factor of 4.52% to 11.34%. so, the increase in efficiency of the solar cell is 6.82%. an important advantage of using of flat mirror concentrator is that, they are cost-effective and available in the market. it is making the usage of solar panel more feasible in developing countries of the world reducing the overall cost of electricity generation and improving the efficiency by pv solar system. another advantage, is the easy installation of this system. as output of average power has increased considerably during mid-day using mirrors, so the panels which are equipped with mirrors are also able to be used for those equipments which require high rating power inputs during that part of the day time. but cleaning of the concentrator on regular basis is a must. 2 literature review in 2023, n. s. buktukov et al. [12] researched-on determination of the electrical characteristics of the solar cell inside the solar cells. the paper presents the results of experimental studies of a solar panel with a holographic concentrator and photovoltaic cells based on gallium arsenide. the high efficiency of converting solar energy into electrical power is shown when dispersing and focusing different wavelengths on a photocell. during elaboration of the obtained volt-ampere characteristics of solar photovoltaic conversion elements, which determine the output power of the photovoltaic panel, the high potential of the developed design of the photovoltaic panel has been revealed. in the year of 2022, m. singh et al. [13] made a study to create more electricity by employing mirrors to collect more solar radiation as well as sunlight to photovoltaic cells. this improves the amount of energy that can be generated by a certain region of solar cells. the purpose of the study is to evaluate whether or not a simplified mirror technique can improve the performance of a solar cell, to determine the aspects of a solar cell that can be improved using simplified mirror techniques, and to confirm that the solar cells' performance has improved as a result of the simplified mirror techniques. the use of reflectors that are flat in form allows for an extra level of sunlight concentration to be achieved on the surface of the solar panel. in 2021, a. shariah et al. [14] established a design containing construction, installation and testing a stationary (non-tracking) concentrating system in irbid, jordan. bifacial solar cells are used in the design. two concentrator designs (with the same concentration ratio) are experimentally tested. conc-a has a parabolic shape in the lower part but flat reflecting walls, whereas conc-b has mohammad ali and mohammad m. tawhid/ bibechana 21 (2024) 142-148 144 a standard compound parabolic shape in all parts. the receiving solar cells are arranged in three distinct positions in each concentrator. the results reveal that the output power from both concentrators is affected by the placement of the receiving solar cells within the concentrator. it has also been found that concentrators with flat reflecting walls perform better than those with parabolic reflecting walls. conc-a’s power collection is ~198% greater than that of a non-concentrating device. when conc-b is used, the increase in power is ~181%. during the age of 2019, f. sh. zainulabdeen et al. [15] focused on developing a method of evaluation the effect of concentrator on the solar panel performance to get a higher power and optimum efficiency. the results indicated that when the concentrator is used with the solar panel the efficiency increased by a factor of (51%) to (64%) and the variation in efficiency () is (25.4%), the variation in maximum output power (pm) is (17%) and all solar parameters increased. in 2016, dr. ali h.al-hamadany et al. [16], they studied on two flat glass mirrors that was used as concentrator of solar panel system. the mirrors increase's the concentration of sun light ray on the solar module. anew model of solar panel system is designed by mean of software zemax in order to find best possible inclination angle of the concentrator that improves the performance of the solar panel. so, the efficiency is 59.5% for designed system with inclination angle 60° of the concentrator. in the year of 2015, m. bilal et al. [17] this paper presents the comparison performance of a pv module without reflecting mirror and with reflecting mirror and manual tracking. the values of short circuit current and open circuit voltage were measured under different conditions of tracking. the output power was calculated and the values were obtained for different combinations. findings from the experiments present that through using concentrators, a 25% mean rise of short-circuit (isc) currents with sun tracking, can be achieved. results also show that pv module with only tracking gives higher output than the system without tracking but the system with reflecting mirror and tracking gives greater output power. in 2013, basavaraj et al. [18] had a power shortfall of 70,000 megawatts while using 600.6 million kwh of energy. there were about 300 million people in india who did not have access to power. in december 2013, there was a power shortfall of 6,120 mw in south india. 2.1 solar panel solar panels are nothing but an electrical device which can transfer the light energy into electrical energy. solar panels absorb the sun's rays and convert them into electricity or heat. a solar panel is actually an assembly of solar cells, which can be used to generate electricity through photovoltaic effect. these cells are arranged in a grid-like pattern on the surface of solar panels. it can also be described as a set of photovoltaic modules, mounted on a structure supporting it. solar cells are produced depending on silicon diffusion process. installation of solar panels in homes results in combating the harmful emissions of greenhouse gases. thus, solar cell helps to reduce global warming also [19, 20]. solar panels do not lead to any form of pollution and are clean. they also decrease our dependence on fossil fuels which are limited and traditional power sources. a pv system was tested in ghardaia that produced 12.91% and 20.89% more energy using singleand dual-axis solar tracking, respectively [21]. figure 1: monocrystalline solar panels. mohammad ali and mohammad m. tawhid/ bibechana 21 (2024) 142-148 145 a mathematical model of a dual-axis solar tracking system was tested for the partial cpv technology that achieved satisfactory performance in comparison with a non-tracking system [22]. the layers are arranged in such a way that the highest energy band gap material is placed at the top, while the lowest band gap material is placed at the bottom. mj junction solar cells have a higher efficiency compared to single-junction cells. in a five-junction cell achieved efficiency of up to 40% [23]. 2.2 concentrator the concept of concentrator photovoltaic (cpv) is to use optical devices technically to concentrate the sunlight on small and efficient photovoltaic solar cells. hence, the cost will be reduced by means of replacing the cell surface by the less expensive material used for the optical devices (glass, silicon. etc.) therefore the technology has great potential for cost reduction [24] figure 1: diagram of mirror concentrator working. solar concentrators can also be used to melt materials and enforce heat engines. in the seventeenth century, lenses or burning glasses were the dominant form of concentrator. in the eighteenth and nineteenth centuries, the most popular concentrators were coneshaped or parabolic reflectors. in the early twentieth century, many large solar energy projects used parabolic trough reflectors. today's concentrators for photovoltaic system still have these basic forms. bulk lenses, however, have been ruled out because of weight and cost, and are usually replaced by thin fresnel lenses [25]. the structures and theory of concentrator solar cells are basically no different from those of nonconcentrator cells, there are some subtle differences in the theory, but they can be ignored for simplicity [26]. pin = i × a (1) efficiency η = pout ÷ pin (2) where pin is the incident power of the sun and can be calculated from multiplying the (i) solar irradiance in (w/m²) by the area of the solar cell or module (a) in square meter unit. the aim of this research is to improve the performance efficiency and reduce the cost of pv module by using a flat mirror concentrator with the solar panel system to decrease the price of the electricity production. 3 material and methods mirror concentrator was used on a rooftop where the sunlight was sufficient targeting to enhance the efficiency of solar cell to complete this research. all the arrangements was done for measuring the length and width of the solar cell and also for the concentrator. flat mirror concentrator (fmc) has been used to increase the incident irradiance on solar panel system by concentrating the sun light ray on it and then to improve the cell performance. a comparison is made for the same pv solar panel systems using single and triple flat mirror concentrator. it is a beneficial and important theory of solar power plant sector. it can be used in household and any kind of industrial area. the fmc consists of two flat mirrors made of glass, with dimensions (170cm × 80cm) enclosed by aluminum frame and inclined to an angle 55 ° with a solar panel (160cm × 120cm) tilted at 45° from the horizon. the mono crystalline silicon wafer was used for fabricating the solar cell in this research. the starting material was p-type silicon wafer. the weight and average thickness of the raw mohammad ali and mohammad m. tawhid/ bibechana 21 (2024) 142-148 146 silicon wafer were 6.47 gm and 182.5 m respectively and the crystal orientation was (100). the steps of producing the solar cell were cleaning, texturing, edge isolation and doping. in diffusion process, the technology used for the doping method was phosphorus diffusion. in this research the solar panel had a solar length = 0.16 m and solar width = 0.12 m. some people use the same principle when they use a magnifying lens to focus the sun's rays on a pile of kindling or paper to start fires. figure 2: working principle of luminescent solar concentrators (lsc). figure 3: image view of the research work. as the solar concentrators follows the sun, the sun lights fall on the reflective concentrator and reflects the concentrated solar power onto a receiver. the advantage of using a solar concentrator is that it can provide a high solar electricity. 4 results and discussion 4.1 results this research is done for a 10 w solar cell (with efficiency 3.90%) before and after using mirror concentrator by two steps. atfirst single mirror was used as concentrator for the solar cell and the efficiency was found 4.52%. after that three mirrors were used as concentrator and then the efficiency was found for the same solar cell 11.34% which is the proof of efficiency enhancement using mirror concentrator. we know, efficiency η = pout ÷ p in now, pout = v× i = 15 × 0.6 = 0.9 watt pin = 1000 wm-2 × (length × width) where solar length = 0.16 m and solar width = 0.12 m so, efficiency η = pout ÷ p in × 100 = 0.9 ÷ (1000× 0.16× 0.12) × 100 = 4.52% again, voltage v = 10.22 v, current i = 0.2208 a so, pout = 10.22 × 0.2208 = 2.257 w and pin = 1000 wm-2 efficiency η = (2.257 ÷ 19.91) = 11.34% (where solar width = 19.91 m) 4.2 discussion the experiment was done repeatedly within sunlight where the sunlight was available. from the remohammad ali and mohammad m. tawhid/ bibechana 21 (2024) 142-148 147 sult and calculation, it is obvious that if mirror concentrator can be used industrially for a solar panel, then the efficiency can be found in a high percentage. as the number or area of the concentrator is increased then the efficiency is increased also. if the area of concentrator can be increased providing the scope to receive a large amount of light, the output efficiency can be increased also. in future this research can be extended by increasing the number of the concentrator whether the efficiency enhancement is occurred or any other changes are found. it can also be done further by applying this experiment for various type concnetrator. 5 conclusion a mirror concentrator was used on a rooftop where the sunlight was sufficient targeting to enhance the efficiency of solar cell to complete this research. all the arrangements was done for measuring the length and width of the solar cell and also for the concentrator. the results obtained show that, use of plane mirror for improving the performance of the solar panels have shown impressive results. an important advantage of using of flat mirror concentrator is that, they are cost-effective and available in the market. it is making the usage of solar panel more feasible in developing countries of the world reducing the overall cost of electricity generation and improving the efficiency by pv solar system. another advantage, is the easy installation of this system. as output of average power has increased considerably during mid-day using mirrors, so the panels which are equipped with mirrors are also able to be used for those equipments which require high rating power inputs during that part of the day time. but cleaning of the concentrator on regular basis is a must. the results indicated that when the concentrator is used with the solar panel the efficiency increased by a factor of 4.52% to 11.34%. so, the increase in efficiency of the solar cell is 6.82%. as the number or area of the concentrator is increased the efficiency is increased also. it can also be done further by applying this experiment for various type concnetrator. references [1] f. meinardi, f. bruni, and s. brovelli. luminescent solar concentrators for buildingintegrated photovoltaics. nature reviews materials, 2(12):1–9, 2017. 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[26] j. g. fossum, e. l. burgess, and f. a. lindholm. solid – state electronics. solid state elec., 21:729, 1978. introduction literature review solar panel concentrator material and methods results and discussion results discussion conclusion bibechana 18 (2) (2021) 32-42 32 variability of b-value before and after the gorkha earthquake in the central himalaya and vicinity ram krishna tiwari1, 2,*, harihar paudyal2 1central department of physics, tribhuvan university, kirtipur, kathmandu, nepal 2birendra multiple campus, tribhuvan university, bharatpur, chitwan, nepal * email: tiwari.ram77@gmail.com article information: received: september 9, 2020 accepted: february 11, 2021 keywords: g-r (gutenberg richter) law b-value stress heterogeneity gorkha central himalaya abstract this study computes the b-value of gutenberg-richter relation associated with the 25 april 2015 gorkha earthquake and its aftershock sequences. for this the homogeneous catalogue of 769 earthquakes that occurred in the himalayan compressed belt and its vicinity was analyzed by three different approaches. the minimum b-values 0.60±0.07 and 0.63±0.06 were observed for windows containing gorkha earthquake. for time window before gorkha earthquake, the bvalue was noted as 0.89±0.12. it was noted 0.81±0.04 for time window between gorkha earthquake and dolakha earthquake and 0.78±0.08 for time window after dolakha earthquake. the results revealed the fact that b-value starts to decrease for strong earthquake. about 17% jumps of the b value were observed within 17 days between gorkha earthquake and its largest aftershock, the dolakha earthquake. the b-value 1.16±0.09 was obtained for the depth range of 0-10 km, 0.89±0.4 for the depth range 10-20 km and 0.65±0.08 for the depth range of 20-30 km. the results strongly support the global trends of decreasing b-value with depth in the continental crust and subduction zones. the low b-value patch observed in the west of gorkha from contour map depicts the region as the potential zone of future strong seismic activity. . doi: https://doi.org/10.3126/bibechana.v18i2.31207 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction the entire himalayan terrain and its surroundings is a highly active seismic zone on the earth. nepal lying at the center of the 2500 km long himalayan range, has encountered 19 devastating earthquakes since the twelfth century. a catastrophic earthquake (7.8 mw) on 25 of april 2015 has left the entire nation stunned with the casualty of about 8900 people. the effect was felt in some adjoining parts bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:tiwari.ram77@gmail.com https://doi.org/10.3126/bibechana.v18i2.31207 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana ram krishna tiwari and harihar paudyal/bibechana 18 (2) (2021) 32-42 33 fig. 1: map of central himalaya and adjoining region showing location of earthquake epicenter from 1 jan. 2013 to 31 dec. 2016. events with magnitude 6 and above are depicted by yellow stars. of india, bangladesh and the tibet [1]. the event was followed by hundreds of aftershocks throughout nepal, with one shock reaching a magnitude of 6.6 mb on 26 april and the major aftershock of 6.7 mb (7.3 mw) on 12 may 2015. the gorkha earthquake ruptured ~ 150 × 60 km patch of the main himalayan thrust (mht), the decollement defining the plate boundary at depth and locations of aftershocks are at or below the mainshock rupture plane [2]. the seismicity distribution and the cumulative number of events are depicted in fig. 1 and fig. 2. the fundamental seismic parameter used to describe the ensemble of earthquakes is b value of the gutenberg-richter distribution which is power law size distribution described in terms of magnitude [3]. the distribution is logn(𝑀) = 𝑎 − 𝑏𝑀 where n(m) is the number of earthquakes in the group having magnitudes ≥m. a constant parameter a is the logarithm of the total number of earthquakes with magnitudes greater than or equal to completeness magnitude that depends on the seismicity rate and the length of the observation time. the b value can be obtained from the slope of frequency magnitude distribution of the earthquakes. the spatial and temporal variation of b value is regarded as key clues for the future large earthquake precursors [4]. ram krishna tiwari and harihar paudyal/bibechana 18 (2) (2021) 32-42 34 fig. 2: time series analysis of 769 earthquake occurred in central himalayan compression zone showing events (>6 mb) for the study period. a high b value means a predominance of small earthquakes while a low b value means that the large earthquake dominates over smaller earthquakes. the b value is also associated with geotectonic features of an area so it has important value in seismology. a decreased in stress results in high b values whereas the increase in applied stress decreases b value [5-7] thus it decreases laterally with depth possibly because of increased stress [8], [9]. large heterogeneity present in material corresponds to higher b value [10]. aftershocks have large b values while foreshocks on the other hand show low b value [11], [12]. numerous workers have disclosed that foreshocks before strong earthquakes often have low b-value. the variation of b values before the mainshock usually experience three stages, an increase in the first, followed by a drop and another increase prior to the major event. [13-15]. a decrease in b value is interpreted because of stress increase prior to a seismic event [12], [16]. so, it is especially important to understand the b value of the frequency magnitude distribution. the objective of the study is to examine temporal and spatial variation of b value to understand the stress condition before and after the earthquake. ram krishna tiwari and harihar paudyal/bibechana 18 (2) (2021) 32-42 35 2. data and method a homogeneous earthquake catalogue is a prerequisite for the study of seismic activity of any region. we get 881 earthquake data (≥ 3.2 mb), for the period 1 jan. 2013 to 31 dec. 2017) from the catalogue of international seismological centre (isc) for the region 26.5 °n-30.5 °n and 79 °e-89 °e. out of these earthquakes, 112 are found to occur in adjoining tibetan normal faulting environment. since this study is limited to himalayan compressive zone, these 112 earthquakes are removed from the catalogue for further study. thus, the subset of catalogue including 769 events is prepared by considering the earthquake data within central himalaya and its closed surrounding for the period of 2013-01-01 to 2016-12-31. gardner and knopoff [17] algorithm was used for declusterising the catalogue. the catalogue is analyzed by three different approaches. first one is by dividing the catalogue into fixed event window; the second approach is by dividing catalogue into three different time window and, the third approach is by dividing the catalogue into subsets of depth ranges. the event time windows were prepared by taking 100 events with overlapping of 60 events. the magnitude of completeness (mc) is computed by the maximum curvature [18] approach using zmap-7.1 software [19]. the b-value is calculated by maximum likelihood estimation (mle) method which is not affected by large magnitude earthquake. the formula [20] for b-value estimation is 𝑏 = log10 𝑒 𝑀𝑎 − (𝑀 − ∆m 2 ) where ma is average of all magnitudes, m is minimum magnitude in the catalogue and ∆m is binning width of the catalogue. the b-value of all the 769 events is computed as 0.77±0.09 as depicted in fig. 3. fig. 3: frequency magnitude distribution of gr (gutenberg richter) relationship for the earthquake sequences for the period jan. 2013 to jan. 2017 where cum events in legend is for cumulative number of events and discrete is for discrete events. ram krishna tiwari and harihar paudyal/bibechana 18 (2) (2021) 32-42 36 frequency magnitude distribution of gr relationship for the earthquake sequences before the gorkha earthquake of mw 7.8 (from 1 jan. 2013 to 25 april 2015), between gorkha earthquake and dolakha earthquake (from 25 april to 12 may 2015) and after dolakha earthquake (from 12 may 2015 to 31 dec. 2017) are shown in figs. 4, 5 and 6 respectively. the b-value is observed to increase ~ 17% within 17 days between the gorkha earthquake and the dolakha earthquake (fig. 7). fig. 4: frequency magnitude distribution of gr relationship for the earthquake sequences (from 1 jan. 2013 to 25 april 2015) before the gorkha earthquake of mw 7.8 where cum events in legend is for cumulative number of events and discrete is for discrete events. fig. 5: frequency magnitude distribution of gr relationship for the earthquake sequences (from 25 april to 12 may 2015) between gorkha earthquake and dolakha earthquake where cum events in legend is for cumulative number of events and discrete is for discrete events. ram krishna tiwari and harihar paudyal/bibechana 18 (2) (2021) 32-42 37 fig. 6: frequency magnitude distribution of gr relationship for the earthquake sequences (from 12 may 2015 to 31 dec. 2017) after dolakha earthquake where cum events in legend is for cumulative number of events and discrete is for discrete events. fig. 7: time series analysis of b-value over the study period showing sudden jumps of bvalue after the 25 of april 2015 gorkha earthquake. ram krishna tiwari and harihar paudyal/bibechana 18 (2) (2021) 32-42 38 fig. 8: variation of b-value with time window. for time window 1 (2013/01/01 2015/04/25) b-value is lowest indicating the accumulation of stress and for time window 8 (2015/04/26 2015/05/03) b-value rises to 1.69 indicating release of stress after the large earthquake. 3. results and discussion seismic b-value for fixed 100 events window with overlapping of 60 events is given in table 1. the lowest b -va lue was observed as 0 .60±0.07 and 0.63±0.06 for first and second windows, prior to and during the gorkha earthquake (6.9 mb). it was 0.79±0.08 for the period 2015/05/01-2015/05/12 during which 6.7 mb dolakha earthquake occurred in the region. after the gorkha earthquake, the bvalue was increased to 0.85±0.08 and further up to 1.69±0.23. the b-value was found increased even after the dolakha earthquake up to 1.19±0.14 (table 1). thus, the results agree with hypotheses that bvalue decreases before a strong event and increases after the event (fig. 8). the increase in b-value indicates the releasing of the accumulated strain in the region. the frequency magnitude distribution (fmd) plots for the earthquake sequences are depicted in the figs. 3, 4, 5 and 6. the b-value is 0.77±0.09 for the entire study period. it was 0.89±0.12 before the earthquake (2013/01/012015/04/23).it was computed 0.81±0.04 between the gorkha earthquake and dolakha earthquake (2015/4/25-2015/5/12) and 0.78±0.08 after the ear thquake (2015/05/12 -2016/12/31) . the most dominant range of earthquake magnitude in this period is indicated by a-value variation of 4.977 to 5.421 (table 2). the low b-value for aftershock sequences may correspond to the generation of enormous size asperities in the hypocentral area of the mht [21] by the mainshock. these observed bvalues indicate that it is increasing after the dolakha earthquake showing the gradual release of stress in the region. the b-value variation with the depth range is given in table 3. by dividing the full depth range (0 km-100 km) into two groups (0-40 km and 30 –100 km), the b-value estimation shows variation from 0.83± 0.03 to 1.29±0.16 respect ively , indicating high strain accumulation in the crust. it is also the indication of more heterogeneous stress distribution in the depth range 0-40 km compared to the depth below 30 km. for the depth ranges of 10 km, the smallest bvalue is 0.65±0.08 for the depth range 20 km to 30 km and the highest b-value is 1.42±0.17 for the depth range 30 km to 40 km. the lowest b-value for the depth range 20-30 km may be because of increased applied stress at greater depth [8], [9]. the higher b-value (1.16 ±0.09) for the 0-10 ram krishna tiwari and harihar paudyal/bibechana 18 (2) (2021) 32-42 39 km range suggests higher heterogeneity. it may also indicate the low strength of rock’s that are present in the crust [22]. the depth versus b-value analysis for the region shows a continuous decrease from 0 km to 30 km (table 3). the b-value observed lower than the global b value of 1.0 from 10 km to 30 km reveal a highly differential stressed regime [9]. these observations also indicate the reverse relationship between b-value and differential stress in the crust. the gorkha earthquake exposed an asymmetric fault rupture scattering eastward from the epicenter [23]. the observed low b-value patch in the region (fig. 9) in conjunction with asymmetric fault rupture indicates the possibility of future earthquakes in the west of epicenter of the gorkha earthquake. table 1: seismic b-value for fixed 100 events window with overlapping of 60 events. window no. of events time period depth range (km) magnitude range mc b-value 1 100 2013/01/01 2015/04/25 2.70 99.0 3.3 6.9 4.0 0.60±0.07 2 100 2014/07/03 2015/04/25 3.50 99.0 3.3 6.9 4.0 0.63±0.06 3 100 2015/04/25 2015/04/25 3.50 28.7 3.4 6.5 4.0 0.85±0.08 4 100 2015/04/25 2015/04/25 3.50 28.7 3.2 5.2 3.7 0.87±0.08 5 100 2015/04/25 2015/04/26 7.90 28.7 3.2 6.6 3.7 0.98±0.12 6 100 2015/04/25 2015/04/27 4.50 22.8 3.2 6.6 3.9 1.16±0.21 7 100 2015/04/26 2015/04/29 4.50 22.8 3.4 6.6 3.8 1.23±0.19 8 100 2015/04/26 2015/05/03 7.60 35.0 3.4 4.8 3.8 1.69±0.23 9 100 2015/04/28 2015/05/11 4.50 19.60 3.4 5.2 3.8 0.76±0.22 10 100 2015/05/01 2015/05/12 2.20 35.0 3.5 6.7 3.6 0.79±0.08 11 100 2015/05/072015/05/12 2.20 20.30 3.4 6.7 3.9 0.85±0.11 12 100 2015/05/12 2015/05/15 0.70 35.0 3.4 5.2 3.9 1.17±0.14 13 100 2015/05/12 2015/05/27 0.70 35.0 3.4 5.6 3.9 1.19±0.14 14 100 2015/05/13 2015/07/01 4.50 35.0 3.4 5.6 3.9 1.15±0.15 15 100 2015/05/21 2015/09/02 4.50 35.0 3.45.1 3.9 1.24±0.14 16 100 2015/06/15 2016/02/23 5.70 100.0 3.2 5.3 3.6 0.89±0.08 17 100 2015/07/30 2016/08/27 5.70 100.0 3.2 5.3 3.7 0.91±0.09 18 89 2015/11/29 2015/12/31 0.70 68.0 3.2 5.4 3.6 0.97±0.12 table 2: seismic b-value and a value comparison for different period sn no of events time duration mc b-value a-value 1 769 2013-01-02 2016-12-28 3.7 0.77±0.09 4.839 2 68 2013/01/02 2015/04/23 (before mainshock) 3.7 0.89±0.12 4.977 3 354 2015/4/25-2015/5/12 (between mainshock and largest aftershock) 3.6 0.81±0.04 5.421 4 430 2015/05/12 2016/12/31 (after dolakha earthquake) 3.6 0.78±0.08 4.695 ram krishna tiwari and harihar paudyal/bibechana 18 (2) (2021) 32-42 40 table 3: seismic b-value at different depths depth mean longitude mean latitude no. of events mc b-value 0-10 84.95 28.00 345 3.8 1.16±0.09 10-20 85.21 27.95 713 3.7 0.89±0.04 20-30 83.42 28.78 55 3.6 0.65±0.08 30-40 84.33 28.55 123 3.5 1.42±0.17 0-40 85.07 28.02 957 3.6 0.83±0.03 30-100 84.65 28.49 143 3.5 1.29±0.16 fig. 9: contour map for b-value variation with depth. solid dots are b-value plotted for mean longitude and latitude (table 3) 4. conclusion the statistical parameter b-value of gr relation has been investigated. the b-value for the overall study period was found to be 0.77±0.09. before the gorkha earthquake, it was computed as 0.89±0.12. the b-value for the period between the gorkha earthquake and the dolakha earthquake was noted as 0.81±0.04. it was found decreasing even after the dolakha earthquake as 0.78±0.08. the distinct drop of b-value before two strong events is the exhibition of rupture nucleation points of stressed region of himalaya. the analysis of b-value based on fixed event window shows gradual increase after the gorkha earthquake and reaches the maximum value of 1.69±0.23 and again drops to the low value of 0.76±0.22. thus, there is a sudden variation of bvalue within a noticeably brief period of 17 days. ram krishna tiwari and harihar paudyal/bibechana 18 (2) (2021) 32-42 41 the b-value for depth range indicates the presence of heterogeneous crust with differential stress in the region. this observation of variation of b-value with depth agrees with other studies in various parts of the worlds. the contour map (fig. 9) shows low bvalue patch west of gorkha region which could be the region of future seismic activity. this study presents the stress level in the region before and after the gorkha earthquake in term of earthquake precursor parameter 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[23] j. p. avouac et al., lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake, nat. geosci. 8 (2015)708–711. https://doi.org/10.1038/ngeo2518. https://doi.org/10.1785/gssrl.72.3.373 https://doi.org/10.1785/gssrl.72.3.373 https://www.researchgate.net/deref/http%3a%2f%2fdx.doi.org%2f10.1126%2fscience.aac6383?_sg%5b0%5d=p_nspsroiszavgsrbq3dn5ivccm84iar33k0bmm1j0jqr073go_gilpwlkc9csxhq9rf-dwj3rybzohv92fopqkcww.-hp_lrpd3vj4z2smaqrwuv1llepfguolvhzp_0yptdy4kjganajpm-kega1ep4s2skqpfvlfg0rcs8sdmispxw https://doi.org/10.1785/gssrl.72.3.373 https://doi.org/10.1038/ngeo2518 bibechana vol. 22, no. 3, december 2025, 258-265 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar a dft based study of structural, electrical and vibrational properties of lifeas – a pnictide superconductor aditya m. vora department of physics, university school of sciences, gujarat university, navrangpura, ahmedabad 380 009, gujarat, india ∗corresponding author. email: voraam@gmail.com abstract by the uses of ultrasoft pseudopotential and the generalized gradient approximation (gga), we have looked at the structural, electrical and vibrational characteristics of the lifeas pnictide superconductor in the present work. there is a strong correlation between phonons and superconductivity, which is the major root of the superconductivity of iron pnictide superconductors. the superconducting characteristics of materials can be predicted using phonon properties. according to studies using density functional theory (dft), lifeas exhibits its metallic nature in the overlaying bands close to the fermi level. the dynamical stability is supported by positive frequencies in the phonon dispersion curves. keywords density functional theory (dft), generalized gradient approximation (gga), ultrasoft pseudopotential, iron pnictide superconductors, phonon dispersion curves. article information manuscript received: april 18, 2025; revised: august 13, 2025; accepted: august 16, 2025 doi https://doi.org/10.3126/bibechana.v22i3.77717 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the discovery of superconductivity in iron-based layered compounds by kamihara et al. [1] sparked a fierce search for new pnictide and chalcogenide superconductors. in early reviews and theoretical overviews, these materials were classified as a distinct class based on feas or fese layers, which are critical to superconductivity [2–10]. lifeas, a 111-type pnictide, is unique among them due to its intrinsic superconductivity without chemical doping [11, 12]. without the added complications of disorder, this material offers a clean platform for examining the underlying mechanisms. extensive experimental and theoretical studies of the structural and magnetic properties of iron pnictides have revealed strong electronic correlations [13], unusual magnetic interactions [14], and the possible coexistence or competition between magnetism and superconductivity [14–21]. while spin fluctuations are often cited as a possible glue for pairing [22], other options include electronphonon interaction or synergistic effects. however, optical and penetration-depth measurements further emphasize the complex interplay between the carrier dynamics and superconducting gap struc258 http://nepjol.info/index.php/bibechana voraam@gmail.com https://doi.org/10.3126/bibechana.v22i3.77717 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ aditya m. vora/ bibechana 22 (2025) 258-265 259 ture [16,23]. lifeas has attracted a lot of attention within this broader family due to its unusual lack of the fermi surface nesting [24], which calls into the question of conventional spin-density-wave-based pairing models. comparative first-principles simulations with related compounds such as lifep [25,26] and high-pressure experiments [27] have shown that subtle changes in the pnictogen height and lattice properties have a substantial effect on the density of states at the fermi level and, thus, the superconducting capabilities. these findings have demonstrated how important it is to understand such materials through accurate electronic structure calculations and structural optimization, which density functional theory (dft) provides. despite these strides, gaps remain. phonon dispersion data are also sparse relative to electronic structure data, and measured lattice constants for lifeas vary between experiments as well as compared to computational studies. the respective roles of spin fluctuations and lattice vibrations in superconductivity in lifeas remain controversial. also, some phonon studies indicate insufficient electron–phonon coupling to account for the observed tc [8,28], whereas others point to possible cooperative effects in the examined materails. and yet, there still remains no integrated study of structural, electronic, and vibrational properties within the same computational setting. this study conducts a systematic dft analysis of lifeas, focusing on its structure, electronic band structure, and vibrational spectra in order to fill in the gaps. by integrating these factors, the study seeks to elucidate the fundamental properties of the material that influence its superconductivity and to establish computational models that can guide later experimental and theoretical investigations. lifeas crystallizes in the tetragonal p4/nmm space group and has a matlockite structure. li1+ forms distorted lias5 trigonal bipyramids when it is bonded to five equivalent as3 atoms. these trigonal bipyramids share corners with 12 equivalent feas4 tetrahedra, edges with four equivalent feas4 tetrahedra, and edges with eight equivalent lias5 trigonal bipyramids. all li-as bonds have a length of 2.67å. fe2+ forms distorted feas4 tetrahedra by bonding with four equivalent as3 atoms, which share corners with four equivalent feas4 tetrahedra, edges with four equivalent lias5 trigonal bipyramids, and corners with twelve equivalent lias5 trigonal bipyramids. the average fe-as bond length is 2.47å. as3 is coupled to five equivalent li1+ and four equivalent fe2+ atoms in a ninecoordinate geometry [29]. figure 1: crystal structures of lifeas. currently, it is observed that simulations based on density functional theory (dft) [30–39] are more accurate when examining the physical characteristics of different materials. studying the structural, electrical, vibrational, and superconducting properties of lifeas iron pnictide superconductors under dft environment is the focus of the current work, which is motivated by the significance of the superconductivity phenomenon and its applications in many fields. 2 theory using the quantum espresso (qe) code [40], a dft based computations are carried out to investigate the structural, electrical, vibrational, and superconducting properties of lifeas. because it favours density inhomogeneity, the generalized gradient approximation (gga) with perdewburke-einzerhof (pbe) [41] functional is used to analyze the exchange correlation effects. the plane waves with a charge density cutoff of 80 ry and a kinetic energy cutoff of 20 ry are considered here. the 4x4x4 k-point mesh is used to highlight integration over the brillouin zone. in this work, the ultrasoft pseudopotentials [42] of three distinct elements—li, fe, and as are employed. since convergence tests revealed insignificant energy changes outside of this mesh, a 4×4×4 monkhorst–pack k-point mesh was used for geometry optimizations in this work to lower computational cost while maintaining accurate forces and stresses. a denser 6×6×6 mesh was used for the final electronic structure and dos calculations in order to guarantee precise brillouin zone integration and fine resolution close to the fermi level. aditya m. vora/ bibechana 22 (2025) 258-265 260 3 results and discussion figure 1 displays the optimization curves for the kinetic energy cutoff (ecut), k-grid, and the cell parameter ratio (c/a) for lifeas. using the variable cell relaxation (vc-relax) approach, the atomic location of said material and the lattice constants were first optimized. to confirm the findings, ration of the lattice parameters (c/a) was then adjusted. the relaxed parameters were achieved by applying the gga technique with ultrasoft pseudopotentials, as implemented in qe. table 1 presents a comparison among the computed optimized lattice parameter results and the available experimental outcomes [12]. in the present computation, the optimized lattice parameter is obtained a=3.790a, which found in good agreement with the available experimental data [12]. the current outcomes are found inconsistence with them with 0.1%-0.2% variations. (a) (b) (c) figure 2: optimization curves for (a) c/a, (b) e-cut, (c) k-grid for lifeas. in this work, the gnuplot [43] in figure 2 is used to plot the band structure for the given material. on the high symmetry points, γ→ z → r → x → m → a→ γ, the k-points path in reciprocal space is taken into consideration. here, the energy cutoff considered is 80 ry, while the charge density cutoff is 320 ry. in order to integrate over the brillouin zone, a 6×6×6 k-pint mesh is used. because fe is ferromagnetic by nature, a spin component is introduced for the computations in both circumstances. in other words, plots of the band structures for up and down spin are available. from the band structure study, it is observed that, the lifeas has a metallic quality, as evidenced by the overlapping of band lines close to the fermi region in figure 2. furthermore, no differences are seen between the situations of a minority and a majority. the fermi energy (ef) is found 9.6985 ev from the band structure data. (a) (b) figure 3: electronic band structure for lifeas (a) spin up (b) spin down. aditya m. vora/ bibechana 22 (2025) 258-265 261 table 1: calculated and experimental lattice parameters for lifeas. lattice constants (å) presently calculated values experimental values [?] deviation (%) a 3.790 3.791 0.1 c/a 1.6577 1.6599 0.2 the tdos and pdos for lifeas are displayed in figures 3 and 4. in this case, the fermi level electron density is seen at around 4.1 states/ev. at -10 ev, much below the ef, an electron density of about 1.8 states/ev is also detected. furthermore, there is no difference in the tdos for spin-up and spin-down situations, which would point to its superconducting nature. it is evident from the partial dos displayed in figure 4 that the 3d state of fe predominates close to the fermi area. the 4s orbital of arsenic contributes significantly below the fermi level. the density in the range of -5.0 ev to ef clearly suggests that fe and as are covalently bonded through hybridization between the fe(3d)as(3p) orbitals in fe2as2 blocks. consequently, the pnictogen bands and the 3d states of fe are what give lifeas its metallic nature. from the figure 3, the highest fermi level dos is observed around 4.2 states/ev. (a) (b) figure 4: tdos of lifeas (a) spin up (b) spin down. (a) (b) (c) figure 5: pdos of lifeas (a) li, (b) fe and (c) as. aditya m. vora/ bibechana 22 (2025) 258-265 262 in the present work, xcrysden [44] software is used to analyze the fermi surface topology of the material under investigation. the spin component is not included in the computation of the fermi surface since there is no difference between the band structure and dos for the spin-up and spin-down cases. five bands intersect the fermi energy level ef in the band structure of lifeas (figure 2). these five bands are represented by their respective fermi surfaces. they confirm that feas superconductors are often two-dimensional, as proposed by sadovskii, ivanovskii and izyumov [2–4]. figures 5(a)–(e) depict the fermi surfaces for individual bands that pass through the ef; figures 5(f) and (g) show the fermi surfaces for merged bands. the electron contribution is provided by the quasi-cylinders at the corners of the brillouin zone in the m-a direction, while the hole-like concentric cylinders are located at the zone centre (). this way, the fermi surfaces are visualized to discriminate between the occupied and unoccupied states. hence, for the aforementioned materials, fermi surfaces are created in a way that ascertains the electron contribution at the corners and the hole contribution in centre of the brillouin zone. the qe code's "phonon" package is used to calculate phonons [40]. the energy cutoff of 80 ry and the charge density cutoff of 320 ry were taken into consideration while computing the phonon dispersion of studied material. it was assumed that the k-mesh was 6x6x6. the phonon dispersion was calculated over the high symmetry sites (γ→z→r→γ) of the brillouin zone, taking into account the q-grid of 2×2×2. due to their involvement in pairing interactions, electron and hole pockets in fermi surface analysis have a major influence on superconductivity. by permitting interband scattering between electron and hole pockets, multiple pockets can improve superconductivity, particularly when spin or orbital fluctuations are involved. unconventional ± wave pairing can be facilitated by mediating spin-density-wave-type fluctuations by nesting between electron pockets at the zone corners and hole pockets at the brillouin zone center. the density of states at the fermi level is influenced by the size and shape of pockets, with higher n(ef ) typically strengthening pairing. the superconducting gap structure is influenced by electron-hole asymmetry; fully gapped states are preferred by balanced pockets, whereas nodes or anisotropic gaps may result from severe imbalance. the momentumspace "playground" for pairing interactions is defined by lifshitz transitions, which can result in abrupt changes in tc. the phonon dos and phonon dispersion curves for lifeas are shown in figure 6. the dispersion curve has 18 phonon branches, including 2 ta, 1 la, 5 lo, and 10 to mode branches. a phonon dispersion of 0 cm-1 to 695 cm-1 is computed. the lifeas crystal structure's dynamical stability is suggested by the positive phonon frequencies. the appropriately degenerate states of different optical and acoustical branches at point r are visible at 100 cm-1, 125 cm-1, 190 cm-1, 255 cm-1, 275 cm-1, 295 cm-1, 510 cm-1, and 580 cm-1. additionally, an overlapping of the acoustical and optical branches is visible at 125 cm-1. it is discovered that the highest phonon branches are very dispersive in the z-r direction. because of the overlapped, weakly dispersive optical branches, the phonon dos about 290 cm-1 has its maximum peak. there is a little band gap seen around 210 cm-1. certain peaks are identified in the phonon dos at 100 cm-1, 120 cm-1, 15 cm-1, 210 cm-1, 230 cm-1, 290 cm-1, 300 cm-1, and 315 cm-1. from the figure 6 it is observed that, the highest phonon frequency noted around at 698 cm-1 at r point. figure 6: the fermi surfaces for different bands (a)-(e) and for merged bands (f) and (g). aditya m. vora/ bibechana 22 (2025) 258-265 263 figure 7: (a) phonon dispersion curve and (b) phonon dos. 4 conclusions ultimately, we draw the conclusion that the structural, electronic and vibrational properties of lifeas, an iron pnictide superconductor are reported in the present paper. it is observed that 3s state of ‘as’ predominates in the section far below the fermi level and that the 3d states of ‘fe’ and ‘li’ are found near to and above the fermi level, respectively. the metallic character of lifeas is demonstrated by the superimposing bands near to the fermi level. furthermore, dynamic stability of aforementioned structure is suggested by the positive frequencies in the phonon dispersion curves. the author expresses heartfelt gratitude to the department of science and technology, government of india, new delhi, india, for developing the computing facility under the dst-fist program and to the university grants commission, new delhi, india, for providing financial support under the drs-sap-ii program. conflict of interest there was no disclosed conflict of interest by the author(s). references [1] y. kamihara, t. watanabe, m. hirano, and h. hosono. iron-based layered superconductor la[o1−xfx]feas (x = 0.05–0.12) with tc = 26 k. 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[44] a. kokalj. xcrysden—a new program for displaying crystalline structures and electron densities. j. mol. graph. model., 17:176–179, 1999. introduction theory results and discussion conclusions bibechana vol. 20, no. 3, december 2023, 205–212 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar characterization of carbon derived from candle by flame-soot method for counter electrodes of dye-sensitized solar cells prakash joshi1,∗, umesh lawaju2, anupam k.c3 mim nakarmi4, ramani pradhan5 1physics department, bhaktapur multiple campus, tribhuvan university, bhaktapur, nepal 2department of physics, patan multiple campus, tribhuvan university, lalitpur, nepal 3texas state university, san marcos, texas, usa 4dept. of physics, brooklyn college and the graduate center of the city university of new york,brooklyn, ny 11210, usa 5dept. of applied sciences and chemical engineering, pulchowk campus, institute of engineering, tribhuvan university, lalitpur, nepal ∗corresponding author. email: prakash.joshi@bkmc.tu.edu.np abstract candle soot, carbon samples prepared by flame-soot method, was characterized and investigated for its catalytic ability for the reduction of tri-iodide ions aiming to substitute expensive platinum based electrode used in dye-sensitized solar cells (dscs). the energy dispersive x-ray spectroscopy of the candle soot samples revealed that the soot contains 96% carbon. similarly, scanning electron microscopy images show that the candle soot consists of interconnected carbon nanoparticles of size ∼50 nm. furthermore, x-ray diffraction and raman spectroscopy showed that the candle soot consists of disordered and ordered graphitic carbons in a comparable proportion. the catalytic ability of the candle soot was compared with that of platinum by electrochemical impedance spectroscopy of the symmetrical electrochemical cells. the charge transfer resistance (rct) at the candle soot-electrolyte interface was observed to be ∼4.42 ω cm2 compared to ∼ 5.04 ω cm2 that of the platinum-electrolyte interface. the candle soot was prepared by a simple method using low-cost material; hence, it can be a low-cost and efficient counter electrode material alternate to the platinum used in counter electrodes of dscs. keywords candle soot, flame-soot method, counter electrode, catalyst, dye-sensitize solar cells, charge transfer resistance. article information manuscript received: july 17, 2023; accepted: august 26, 2023 doi https://doi.org/10.3126/bibechana.v20i3.58041 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 205 http://nepjol.info/index.php/bibechana prakash.joshi@bkmc.tu.edu.np https://doi.org/10.3126/bibechana.v20i3.58041 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ p. joshi et al./ bibechana 20 (2023) 205-212 206 1 introduction carbonaceous materials are chemically stable, readily available, and low-cost [1] and these materials have been adopted in the preparation of counter electrodes of dye-sensitized solar cells (dscs). the dscs, developed by o’ragen and gratzel in 1991, are a relatively new type of solar cells and these photovoltaic devices can be low-cost compared to silicon based solar cells [2, 3]. the major components of a dsc are photoelectrode, liquid electrolyte, and counter electrode. photoelectrode is the front electrode while the counter electrode (ce) is the back electrode, and the liquid electrolyte is enclosed in the gap between the two electrodes. both the photoelectrode and ce use a transparent and conducting fluorine-doped tin oxide (fto)glass substrate as a base. for the photoelectrode, the fto-glass substrate is coated with a few microns thick film of mesoporous nanocrystalline titanium dioxide (tio2) particles. then, a monolayer of light sensitive dye molecules is chemically adsorbed on the tio2 film. for the ce, the glass substrate is generally coated with a platinum. when the sunlight is incident at the photoelectrode, the dye molecules absorb the solar photons and inject their loosely bound electrons into the conduction band of the tio2. after diffusion of the electrons in the tio2 film, they arrive at the conducting part of the photoelectrode. the photoelectrode is connected to the ce via an external circuit with an electric load. thus, the electrons at the photoelectrode pass through the electric load in the external circuit and generate electric power. then the electrons arrive at the ce [3,4]. in order to enable the oxidized dye molecules to emit photoelectrons continuously (by absorbing the incident flux of solar photons), the dye molecules should be regenerated. the iodide ions in the electrolyte donate electrons to the dye molecules and the dye molecules are regenerated. after donating the electrons, the iodide ions are oxidized to tri-iodide ions, and they diffuse toward the ce which is generally coated with a thin film of platinum. the photoelectrons, arrived at the ce, are transferred to the diffused tri-iodide ions and the circulation of the electrons in the solar cell is completed. the triiodide ions after gaining the electrons are reduced to iodide ions [3–7]. the rate of reduction of tri-iodide ions into iodide ions is one of the factors that influence the light to electricity conversion efficiency of solar cells. swift transfer of the tri-iodide ions into iodide ions results high efficiency of the solar cells. the platinum coated on the ce enhances the rate of electron transfer [6]. however, the use of platinum in dscs has some issues like high cost of platinum and its instability in the electrolyte used in dscs [6]. hence, researchers have proposed various types of carbon as alternative catalyst to replace platinum [3–12]. out of the carbonaceous materials, carbon nanotubes [5], carbon nanofibers [3,7,8], graphene [9,10] etc. have exhibited comparable catalytic ability for the reduction of the tri-iodide ions as the platinum. however, the synthesis process of these carbons is not simple. consequently, these types of carbonaceous materials are still expensive. in 2019, joshi, lawaju, and b.k. reported the composite of mustard oil lampblack and printer toner as a low-cost and novel counter electrode material. the light to electricity conversion efficiency of the composite based solar cells was 3.20% compared to 4.18% of the platinum based reference solar cells [4]. similarly, lawaju and joshi used soybean oil lamp black/printer toner composite as another counter electrode material and reported an efficiency of 2.58% compared to 3.67% of the platinum based dscs [11]. our previous research has demonstrated that lampblack based ces can serve as a catalyst for the reduction of tri-iodide ions although the catalytic ability of the ces was not as efficient as that of the platinum based ces. herein, we have proposed low-cost and efficient ces prepared with candle soot for the reduction of tri-iodide ions in dscs. we prepared carbon samples derived from commercially available candle using flame-soot method and characterized the candle soot by using x-rays diffraction (xrd), raman spectroscopy, scanning electron microscopy-energy dispersive x-ray spectroscopy (sem-eds) for exploring structural and elemental compositions. in order to evaluate the catalytic ability for the reduction of tri-iodide ions, impedance spectra can be obtained by using either a working dsc or a dummy cell [13]. the structure of a dummy cell is simpler than that of a working dsc as it is fabricated without dye-sensitized tio2 film. a dummy cell is prepared by assembling two electrodes coated with catalyst. the electrodes are separated with a spacer and the gap between them is filled with an electrolyte [3,11,13]. a dummy cell fabricated with two identical electrodes (known as symmetrical electrochemcal cell) is generally employed in eis [3, 11, 14]. the value of the charge transfer resistance, rct at the catalyst-electrolyte interface of such cell indicates the ability of the catalyst for the reduction of tri-iodide ions. smaller value of rct at the catalyst-electrolyte interface implies better ablitity for the tri-iodide reduction [3,13] and hence high efficiency. in this research, eis of symmetrical dummy cells were carried out to evaluate the catalytic ability of the candle soot by measuring the rct. the electrodes of the symmetrical electrochemical cells were prepared by coating a film of candle soot and value of the rct at the interface of p. joshi et al./ bibechana 20 (2023) 205-212 207 the candle soot based film and electrolyte was determined. the value of the rct at the candle sootelectrolyte interface was ∼4.42 ω cm2 compared to ∼5.04 ω cm2 at the platinum-electrolyte interface. 2 experimental 2.1 sample preparation candles were bought at a grocery shop in bhaktapur and carbon (soot) was prepared by flame-soot method (low-cost, traditional and simple method for the preparation of carbon). we have been using this method of preparing carbon samples for application in supercapacitors and dye-sensitized solar cells. the procedure of preparing the candle soot is similar to that described by joshi et al., [4]. the experimental setup for the preparation of candle soot is shown in figure 1. the flame of the candle lamp was obstructed by a porcelain bowl, figure 1(a). the candle soot, deposited on the inner surface of the bowl, was collected for characterizations. a photograph of the collected candle soot sample is shown in figure 1(b). 2.2 characterization of candle soot for surface morphology and elemental composition the elemental and structural composition of the carbon samples were investigated using semeds, xrd, and raman spectroscopy. the sem and sem-eds were carried out using fei helios nanolab 400 scanning electron microscope. powder diffractometer (d2 phaser, bruker) was used for the xrd of the sample. figure 2 shows the sem images with different magnifications of the candle soot based carbon film prepared with carboxymethyl cellulose (cmc) as a binder. figure 2(a) and figure 2(b) are sem images with ∼6500x and ∼20000x magnifications, respectively. these images show porous and rough surface of the film formed by interconnected carbon particles of a few tens of nanometers; particles of size ∼50 nm were dominant ones in the film. figure 3(a) is the eds spectrum and the insets show the scanned area with elemental composition of the sample. the candle soot comprises ∼96% of carbon and ∼4% (atomic) oxygen. figure 3(b) and figure 3(c) depict the mapping of the elements in the film. figure 4 is the xrd spectrum of the candle soot. the two broad peaks centered at 2 of ∼250 and ∼420 imply that the candle soot contains mainly amorphous form of graphitic carbon [3,15]. we also performed raman spectroscopy of the samples. figure 5 shows raman spectra with two prominent peaks centered at wave number ∼1361 cm−1 and ∼1579 cm−1 which are known as d-band and gband, respectively. the d-band is attributed to disoriented or defect riched carbonaceous material while the g-band arises due to ordered or graphitic carbon [3, 15, 16]. the findings of the raman analysis is analogous to those from the xrd that the candle soot comprises both disordered and ordered forms of carbon. the portions of disordered carbon and ordered carbon (graphitic crystallites) in the candle soot were calculated by lorentzian line shapes fitting of the raman spectrum [17]. the content of disordered carbon was ∼47% compared to ∼53% of the ordered carbon and the value of id/ig was ∼0.9. figure 1: preparation of carbon soot (a) experimental setup and (b) sample of candle soot. p. joshi et al./ bibechana 20 (2023) 205-212 208 figure 2: sem images of candle soot based film with magnification of (a) ∼ 6500x and (b)∼20000x. figure 3: sem images of candle soot based film with magnification of (a) ∼ 6500x and (b)∼20000x. figure 4: xrd spectrum of the candle soot. figure 5: raman spectrum of the candle soot. 3 results and discussion the catalytic ability for the reduction of tri-iodide ions of candle soot was investigated by eis of the electrochemical symmetrical cells prepared with two identical electrodes coated with the film of the candle soot. a schematic diagram of the electrochemical cell is shown in figure 6. in order to prepare the carbon based electrodes, first of all, the paste of candle soot was prepared by mixing ∼0.1 g of candle soot with ∼1.5 ml of aqueous solution of cmc (∼2% p. joshi et al./ bibechana 20 (2023) 205-212 209 concentration). the mixture was stirred and left in an ambient environment overnight. the mixture was centrifuged to remove excessive binder solution and doctorbladed onto clean fto-glass substrates. the carbon film, coated on the fto, was dried at a temperature of ∼80 0c for 12 hours. two identical candle soot-based electrodes, prepared as described above, were assembled with a sealant and a liquid electrolyte containing iodide/tri-iodide ions (iodolyte an-50 purchased from solaronix, switzerland) was injected into the symmetrical cell. to compare the catalytic ability of the candle sootbased film, symmetrical electrochemical cells with platinum coated electrodes were also prepared. the eis of the electrochemical cells were performed using interface 1010e (gamry instruments, usa) in potentiostatic mode with 10 mv ac signals of frequencies ranging from 0.1 hz to 100 khz. figure 8 shows their equivalent circuits used to fit the nyquist plots [14,18–20]. figure 8(a) is the conventional equivalent circuit [14,20] in which rs is the series resistance. the rs is mainly attributed to the resistance of the electrodes and electrolyte of the symmetrical cell. rct is the charge transfer resistance at electrode-electrolyte interface. similarly, zn is nernst diffusion impedance and this deals with the impedance that arises from the diffusion of ions in the liquid electrolyte. cpe is a constant phase element, and this is related to the double layer capacitor formed at the electrodeelectrolyte interface [3,11,14,18–20]. the equivalent circuit shown in figure 8(a) was used to fit the nyquist plot of the platinum based symmetrical cell. for better fitting of the nyquist plot of the carbon soot based symmetrical cell, the equivalent circuit [18] shown in figure 8(b) was used. this equivalent circuit was proposed by kwon et al., to fit nyquist plots of porous carbon electrodes. in this circuit cdl is the double layer capacitor which is equivalent to cpe of the conventional equivalent circuit, figure 8(a). in addition to the circuit elements mentioned above, electron transport resistance (rtms) and trap capacitance (ctrap) were introduced in the new equivalent circuit [18]. rtms and ctrap arise because of the carbon layer [18]. according to kwon et al., carbon film is rich in superficial defects which exist mostly at grain boundaries and near carbon surface. electrons are trapped in such regions and ctrap is formed [18]. the values of the parameters like rtms, ctrap, rs, rct of symmetrical cells were obtained by curve fitting of the nyquist plots using gamry echem analyst (gamry instrument, usa). the values of rtms and ctrap were ∼0.79 ωand∼3.4 µf, respectively. for the symmetrical cells with platinum electrodes, the values of these parameters are assumed to be negligibly small as platinum is highly conducting and the thickness of platinum used at the electrode is ultrathin compared to the carbon layer [18]. rs of the symmetrical cells with platinum and candle soot were ∼24.17 ω and ∼25.75 ω, respectively, and these values are nearly equal. in a dsc, series resistance of the solar cell can affect its power conversion efficiency. an increase in series resistance of the solar cell decreases fill factor (ff), and low ff results lower efficiency of the solar cell [3]. the series resistance of the solar cell is mainly the sum of the ohmic resistances contributed from its components–photoelectrode, electrolyte, and counter electrode. as the values of the ohmic resistances of the platinum based symmetrical cell and candle soot based symmetrical cell are almost equal, it can be concluded that replacing a platinum with a candle soot in a dsc will not affect the power conversion efficiency of the solar cell. along with the similarity of the rs values of the symmetrical cells, their charge transfer resistance, rct, were also nearly equal. the values of the rctof the symmetrical cells with platinum and candle soot were ∼7.08 ω (5.04 ωcm2) and 6.21 ω (4.42 ωcm2), respectively. the rct at the catalyst-electrolyte interface of the symmetrical cells tells us effectiveness of the catalyst in the reduction of tri-iodide ions into iodide ions in the electrolyte. smaller value of rct implies a faster rate of the reduction of the tri-iodide ions [3, 11, 14, 19, 20]. hauch and georg, in 2001, mentioned that the value of the rct of the catalyst should not be more than 10 ωcm2 for the fabrication of a good dsc [14]. in this research, rct of the candle soot based electrodes was lower than 10 ωcm2. hence, the candle soot based electrodes can be used as counter electrodes of dscs. moreover, the comparable value of rct of the candle soot and platinum based cells indicate that the catalytic ability of candle soot based electrode for the reduction of tri-iodide ions was also comparable to that of the platinum based electrode. the catalytic ability of the carbon based counter electrode depends upon its surface morphology and elemental composition. the sem images shown in figure 2 revealed rough and porous surface texture of the film. this yields a larger surface area and provides a large electrolyte-catalyst interface, which can be a merit for the fast reduction of tri-iodide ions. also, the concentration of carbon in the candle soot is very high (∼96%) which could be another reason of low rctvalue of the candle soot. similarly, raman spectroscopy revealed the existence of disordered and ordered crystalline graphitic carbon in almost same proportion in the candle soot samples. ordered crystalline graphitic carbon yields high electric conductivity. on the other hand, the presence of disorded carbon or defect rich carbon in the candle soots might have contributed in the fast reduction of tri-iodide ions. graphitic crystallites exhibit a structural arrangement comprising basal p. joshi et al./ bibechana 20 (2023) 205-212 210 planes, which are parallel to the layers of graphite, and edge planes, oriented perpendicular to the basal planes [21–23]. notably, the electron transfer kinetics at the edge planes is more faster than that in the basal planes [21, 22]. generally, graphitic particles of small size contain more edge planes than those of large particles. veerappan et al., adopted submicron (700 900 nm) sized colloidal graphite (cg) and several micron sized graphite particles (ag20) for fabrication of counter electrodes of dye-sensitized solar cells. they reported that the smaller sized graphite particles (cg) have more edge planes than the larger ones. the symmetrical cells based on cg yielded lower rct than the symmetrical cell based on ag20 [22]. the candle soot in this research has a particle size of ∼50 nm and the portion of the defective carbon in the candle soot is significantly high. so, it can be expected that the candle soot contains plenty of edge planes which contributed in fast reduction of triiodide ions. figure 6: schematic of electrochemical symmetrical cells. modified from ref. [14] figure 7: nyquist plots of electrochemical symmetrical cells with (a) platinum coated electrodes and (b) candle soot coated electrodes. figure 8: quivalent circuits used to fit nyquist plots of electrochemical symmetrical cells with (a) platinum coated electrodes modified from ref. [14] and (b) candle soot coated electrodes modified from ref. [18]. p. joshi et al./ bibechana 20 (2023) 205-212 211 4 conclusion candle soot was investigated aiming to use it as a catalyst to replace expensive platinum used in dscs. the candle soot consists of carbon nanoparticles comprising ordered and disordered carbon with a high concentration of carbon (∼96%, atomic). the eis of the symmetrical electrochemical cells with the candle soot based electrodes showed that their series resistance and charge transfer resistance are nearly equal to those of the platinum based symmetrical cells. candle soot can be prepared with low-cost precursor and using simple techniques. so, this carbonaceous material can be a low-cost and efficient counter electrode material alternate to expensive platinum used in dscs. acknowledgements the authors are thankful to associate professor sudarshana shakya, bhaktapur multiple campus (bmc), surakshya ghamosu (bmc), anita bhadel (bmc), and shared research operation (sro) facility for providing opportunity to use the sem 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publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar biosorption of hexavalent chromium (cr(vi)) from contaminated water using charred tea waste puspa lal homagai, miksha bardewa, anup subedee hari bhakta oli, ram lal shrestha, deval prasad bhattarai∗ department of chemistry, amrit campus, tribhuvan university, kathmandu, nepal ∗corresponding author. email: deval.bhattarai@ac.tu.edu.np abstract the goal of this study is to develop charred tea waste (ctw) via chemical process for the removal of cr(vi) from contaminated water. batch adsorption experiments were conducted as a function of ph, initial concentration, contact time and adsorbent dosage. characterization of the adsorbent was analyzed by ft-ir and xrd. maximum adsorption capacity (qm) of the ctw was found to be 85.32 mg/g at optimum ph 2 in 120 minutes. the adsorption on ctw was well fitted to the langmuir isotherm and the kinetic data is consistent with the pseudo-second order kinetic model. the findings suggest that ctw could be an efficient and promising adsorbent for the removing cr(vi) from aqueous solution. keywords hexavalent chromium, charred tea waste, langmuir isotherm, pseudo-second order. article information manuscript received: march 14„ 2023; accepted: march 31, 2023 doi https://doi.org/10.3126/bibechana.v20i1.53458 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction access to safe drinking water is internationally recognized human right. presence of organic pollutants, inorganic pollutants and microbes are causing water pollution. presence of metals or metal ions such as cadmium, mercury, lead, arsenic, chromium, nickel, etc. in environment is causing heavy metal ions pollution which brings about an adverse effect on human health as well as aquatic flora and fauna [1]. discharge of heavy metal ions such as chromium rich effluent from tanning, leather, metallurgy and electroplating industries into water body is being a serious issue these days. its prevalence is increasing due to industrial production of dyes, leather, textiles, electroplating materials, and chemical manufacturing and some similar channels [2]. different oxidation states of chromium are present, and they all affect people differently. cr(vi) is toxic and highly carcinogenic, despite the fact that trace amounts of chromium (iii) have been reported to be necessary for proper lipid, insulin, and glucose metabolism [3]. world health organization (who) has assigned its upper permissible level in drinking water as 50 ppb [4]. chromium gets exposed to the environment via 76 http://nepjol.info/index.php/bibechana deval.bhattarai@ac.tu.edu.np https://doi.org/10.3126/bibechana.v20i1.53458 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ puspa lal homagai et al./ bibechana 20 (2023) 76-85 77 natural as well as anthropogenic routes [5]. many chromium-based materials are based on hexavalent chromium which exhibits its strong oxidizing power. hexavalent chromium either directly enters into the workers through dermal contact or enter into the human via water resource. industrial wastewater and human activities are polluting the environment more than a bearable level. studies have been undertaken using various types of adsorbents for its efficient and selective removal due to its extreme toxicity and pollution concerns. over use of heavy metals pollutes the water. the use of heavy metals has health, environmental and aquatic effects [6]. in connection to the increasing amount of cr(vi), various absorbents have been synthesized for the effective and selective removal of such heavy metal ions. among the different types of adsorbents, the biomass-based adsorbents are getting interest these days due to their non-toxic nature towards environment, low-cost and tunable functionality. in order to remove chromium from industrial effluents, varieties of methods and materials are used for the effective and efficient removal of heavy metal ions from the sources. some of the commonly used approaches are chemical precipitation, ion-exchange methods, electrochemical precipitation, chemical reduction, solvent extraction, membrane filtration or separation and so on [7]. however, many of these methods are less sensitive for adsorptive removal of heavy metal ions below the tolerance level due to lack of sensitivity or selectivity. removal of heavy metal ions by adsorption methods is the most promising for overall treatment. though different types of nanoparticles, polymers/conductive polymers, especially heteroatom containing conductive polymers [8, 9], layered compounds [10] are being used for the removal of heavy metal ions, biomass-based low-cost materials are getting interest for the effective removal of toxic metal ions form water. these adsorbents are easily available, eco-friendly, and cost effective with higher capacity of adsorption. in addition, such types of biomass-based materials can be chemically processed to increase its effectiveness. commonly, activated carbons are being widely used as adsorptive materials for waste water treatment [11,12]. commonly used waste materials used to prepare biomass-based adsorbent are banana peels, plum kernels, oil palm shells, tea leaves, saw dust, wheat bran, coconut husks, coffee grounds, rice husks, jackfruit peels and many others. in this context, most commonly used bioadsorbents are fruit gum, wheat bran, cork powder, sugar beet, rice bran, rice husk, nut shells, tea leaves and so on. each of the mentioned adsorbent capacitates to adsorb chromium form aqueous solution [5]. activated carbon is considered as a potent adsorbent with high surface area, microporosity and surface chemistry [13]. one of the biomass-based precursors for the preparation of activated carbon could be tea waste which is a common material left after the preparation of tea. nepal is rich in tea production. with the processing and refining into tea powder, tea leaves remain as residue. such waste materials can be employed for the preparation of activated carbon and further chemical treatment. furthermore, the composition of tea leaves may be different as a function of geography and climate. tea waste contains cellulose, hemicellulose, lignin and a lot of pectin in the cell walls. pectin is polysaccharides in which pectic acid and acidic polysaccharides, mainly composed of dgalacturonic acid and methyl ester, are present. tea leaves contain various polyphenols including epigallocatechin gallate (usually known as eggcg), flavonoids and other catechins [14]. large-scale hot water extraction of tea leaves is employed for the instant production of canned or bottled teas and producers have to struggle to dispose the discarded tea-leaves wastes. therefore, the use of such waste materials is highly preferable for the synthesis of activated carbon [15]. in this context, tea waste can be regarded as a potential precursor which can be used for the removals of cr(vi) ions from aqueous media. this method is benefitted by the facile mode of processing, easily available, cost-effective and environmentally friendly features [16]. the synthesis of charred carbon materials from tea waste of nepal origin has not been reported for the adsorptive removal of chromium (vi) listed in the comparison table 1. in this work, activated carbon has been prepared from the tea waste followed by charring with concentrated sulphuric acid. the objective of the present study is to find out the maximum uptake capacity of prepared charred tea waste for the removal of cr(vi) from contaminated water. batch adsorption experiments would be carried out changing the ph of solution, adsorbent dosage and contact time. the biosorbent ctw is ecofriendly and it can be incinerated with zero emission due to its natural constituents. on the other hand, the adsorbent is cost-effective since it is prepared from agricultural byproduct of tea. it could be an efficient and promising biosorbent for the treatment of cr(vi) from contaminated water. 2 materials and methods 2.1 preparation of chromium (vi) solution stock solution of cr(vi) of 1000 ppm concentration was prepared by dissolving 1.414 g of potassium dichromate in water followed by the addition of 100 ml solution of 2 n hno3. then the volume puspa lal homagai et al./ bibechana 20 (2023) 76-85 78 of the solution was made exactly 500 ml by adding distilled water. all the chemicals used in this study were of analytical grades. 2.2 preparation of charred tea waste waste tea leaves were collected from the tea shop, lazimpat, kathmandu. the tea waste was washed with distilled water several times, dried and ground. for charring process, 250 grams of ground tea waste were placed in a beaker of 1 liter capacity followed by the addition of concentrated sulphuric acid at an installment with constant stirring until the content turns to the black. in this step, ring opening of cellulose unit occurs. the reaction was left for 24 h for completion. the carbon was washed with deionized water several times to bring up to neutralization. then the sample was dried in vacuum at 50 °c for 9 h. the dried charcoal was ground in an agate mortar using pestle and sieved through 200 microns. finally, a sample was completely dried keeping in desiccator which is known as charred tea waste (ctw) and stored in an airtight bottle. 2.3 instrument used uv-visible double beam spectrophotometer (labtronics, lt-2802, india), ftir-spectrometer (perkin elmer 10.6.2, usa), digital ph meter (hana, hi2002-01 edge), four digit weighing machine (phoenix, ph2204c), hot air oven (elite oven), magnetic stirrer (labinco l34) and sieve (new dehli-110055). 2.4 sorption study stock solution of cr(vi) was used for the study of cr(vi) adsorption by charred tea waste. for this purpose, the stock solution of cr(vi) was diluted to prepare a series of solution form 10-300 ppm. the effect of dosage, effect of initial concentration, ph of the solution and contact time of the adsorption process was investigated. the ph of solution was maintained by using 0.5 n naoh and 0.5 n hcl solution where necessary. 20 mg of prepared adsorbents was taken in a stopper bottle and 25ml of chromium solution were agitated in a shaker at room temperature for 5-6 hours. then, the solution was filtered and the filtrate solution was taken. the absorbance of metal ion solution before and after adsorption was determined by using double beam uv-visible spectrophotometer. the amount of metal ion adsorbed onto adsorbent is calculated using the following relation given in equation (1). q = ( ci − ce w ) × v (1) here, q (mg/g) is the quantity of adsorbate adsorbed per unit mass of adsorbent. in the equation, v is the volume of solution in liter. w(g) is the mass of adsorbent, ci and ce are concentration of cr(vi) solution, respectively. the percentage adsorption capacity (%a) of the metal ion can be used by the relation of equation (2): percentage adsorption(%a) = ci − ce ci ×100 (2) 3 results and discussion 3.1 x-ray diffraction (xrd) analysis of adsorbents x-ray diffraction (xrd) study was carried out to study the crystalline/amorphous nature of the adsorbent. the xrd pattern of the raw tea waste (rtw) and charred tea waste (ctw) exhibit a broad peak in the 2θ range of 14-23° indicating a predominantly an amorphous nature. before and after modification, the xrd patterns of rtw and ctw are not so significantly different shown in figure 1. the amorphous biosorbent allows the cr(vi) ions adsorption by penetrating the surface rapidly, hence increase in adsorption capacity [17]. 3.2 fourier transform infra-red spectra (ftir) analysis the functional group study for the rtw and ctw materials were carried out in terms of ftir analysis in the department of chemistry, amrit campus. the ftir spectra of rtw and ctw are shown in figure 2. the broad absorption at 3200-3500 cm−1 corresponds to the –oh group of the adsorbent and small absorption band at 2917 cm−1 corresponds to the ch stretching in methylene group. the absorption band around 1704 cm−1 and1610 cm−1 correspond to the c=o and c=c group, respectively [18]. the c-oh stretching band at 1032 cm−1 of rtw got shifted and slightly deformed in ctw which could be associated with the charring process of the material [19]. the ftir spectra reveal the intensity and frequency change in the transformation of rtw to ctw indicating the involvement of chemical reaction. this happens due to breakdown of chemical bonds during the process of charring. puspa lal homagai et al./ bibechana 20 (2023) 76-85 79 figure 1: xray diffraction of rtw and ctw. figure 2: ftir spectra of rtw and ctw. 3.3 effect of ph on hexavalent chromium adsorption the ph of the adsorbate solution has been reported to be one of the variable for cr(vi) adsorption. for this study, 50 ppm of chromium(vi) solution was taken and its ph was maintained using ph meter in different reagent bottles from ph 1 to ph 5 keeping 0.02g of ctw in each bottle. from ph studies it was found that the % removal of chromium by ctw increased from 48.77% to 81.42% then again decreased up to 40.91%. the maximum percent cr(vi) removal was found to be 81.42% by which we can conclude that the optimum ph found to be 2 as shown in figure 3. this finding is in quite agreement with the reported literature [6]. below the ph 2, some of the chromium (vi) exists as h2cro4 which is hardly adsorb onto the adsorbent. from ph 0 to 6.5, chromium(vi) exists as hcro4 − (hydrogen chromate) while above this ph range chromium(vi) exists as chromate ions (cro4 2−) predominantly. at the optimum ph value, chromium exists predominantly as hcro4 − anion in aqueous media. with increasing the ph value the complexation process of cr(vi) goes on decreasing resulting into the low uptake of cr(vi). 3.4 effect of dose adsorption experiment was carried out at lab temperature (25°c) taking different weight of adsorbent to find the optimize amount of adsorbent dosage for the removal of cr(vi) from its 50 ppm aqueous solution. the upper tolerance level of chromium in drinking water is also 50 ppb. adsorption capacity of adsorbents increases upto a certain weight then it remains constant keeping in cr(vi) solution. with the increase of adsorbent dosages from 5 mg to 100 mg under the experimental conditions like ph, temperature and adsorbate concentration constant, the puspa lal homagai et al./ bibechana 20 (2023) 76-85 80 figure 3: effect of ph for adsorption of cr(vi) onto ctw. figure 4: effect of ctw dose on cr(vi) adsorption. adsorption study was carried out. low mass of adsorbent corresponds to the low active sites and high mass of adsorbent corresponds to the high active sites. with the increase of active sites, the percentage removal of cr(vi) got increased. the result shows that the percentage removal of cr(vi) increases with up to 20 mg adsorbent doses and remains almost constant for the studied adsorbent doses as shown in figure 4. the highest adsorption for 50 ppm adsorbate of cr(vi) is found to be 20 mg. 3.5 effect of concentration of cr(vi) solution the adsorption capacity of ctw can be evaluated with the help of an adsorption isotherm for the adsorption of cr(vi). as the concentration of cr(vi) ions increases, the adsorption of metal ions increases. at low cr(vi) ions concentration, the concentration of cr(vi) ions are limiting and get sufficient sites for their adsorption whereas at high concentration, the active sites on adsorbent are limiting compared to the cr(vi) concentration and hence become saturated. the absorbance of the supernatant clear liquid is measured spectrophotometrically at the maximum wavelength of after 4h equilibrium interval. a graph was plotted and used to calculate the amount of cr(vi) adsorbed. the maximum adsorption capacities of experimental results shown in fig.5 found to be 85.32 mg/g onto ctw at optimum ph2. puspa lal homagai et al./ bibechana 20 (2023) 76-85 81 figure 5: effect of concentration for adsorption of cr(vi) onto ctw. figure 6: langmuir isotherm plot for biosorption of cr (vi) onto ctw. 3.6 adsorption isotherm the correlation coefficient (goodness of fit) values for freundlich and langmuir isotherms were used to determine the applicability of the isotherms. langmuir and freundlich’s relation, equation (3) and (4), respectively, were used to calculate adsorption isotherms. ce qe = 1 qmb + ce qm (3) log qe = logkf + 1 n × logce (4) in these equations, ce(ppm) is the equilibrium concertation of adsorbate, qe (mg/g) is the amount of cr(vi) ions adsorbed per gram of adsorbent at equilibrium, qm (mg/g) is the maximum adsorption capacity, b (l/mg) is the constant. by plotting a graph of ce/qe versus ce, the value of qm and b can be evaluated. the kf (l/mg) is adsorption capacity and 1/n is adsorption intensity which indicates the relative distribution of energy and adsorption heterogeneity site. the result shows that the maximum adsorption capacity is found to be 85.32 mg/g onto ctw at the ph of 2. higher initial concentration can increase the higher adsorption of metal ions. with the increase of concentration, the adsorption process get saturated. the higher value of langmuir correlation coefficient (r2 = 0.9974) indicates the better fitness of langmuir model compared to the freundlich model. it shows that the metal ion adsorption is predominantly a unimolecular. additionally, in langmuir’s isotherm, the equilibrium parameter, the dimensionless equilibrium puspa lal homagai et al./ bibechana 20 (2023) 76-85 82 figure 7: time on adsorption of cr(vi) onto ctw. figure 8: pseudo second order adsorption kinetics of cr(vi) onto ctw. constant (kl), given by equation (5): kl = 1 1 + bci (5) where b is the langmuir constant and ci is the initial metal ion concentration. in this research work, the value of kl is between 0 and 1 indicating the nature of favorable langmuir model of adsorption isotherm. 3.7 effect of contact time for the study of effect of contact time in the adsorption process, 20 mg of adsorbent was put into the 20 ml of 50 ppm of cr(vi) solution. the ph of the solution was maintained 2 for the study. after shaking the solution for the 24 h, the content was filtered and the clear solution was processed for its concentration measurement using double beam uv-vis spectrophotometer. adsorption of cr(vi) was initially increased with increase of the contact time and remain constant. figure 7 shows that the amount of adsorption increased from 5 minutes up to 120 minutes, and then remained constant thereafter. 3.8 adsorption kinetics the experimental adsorption kinetic data can be evaluated following integrated form of pseudosecond-order kinetics model explained by ho and mckay [20] as given in equation (6). t qt = 1 k2q2e + t qe (6) puspa lal homagai et al./ bibechana 20 (2023) 76-85 83 here, qt (mg g−1) is the amount of the adsorption at time (min), k2 (gmg−1min−1) is the rate constant of pseudo-second order kinetic of adsorption. using the plot of t/qt versus time, we can calculate the values of k2 and qe. pseudo-second order kinetics plot gives the perfect straight line for the adsorption of cr(vi) onto ctw shown in fig.8. correlation coefficient r2 value is 0.992 which indicates the pseudo second order kinetic model for the adsorption. the correlation coefficient value is about unity i.e. 0.992 confirms that metal ions, cr(vi) are chemisorbed onto ctw. 3.9 biosorption mechanism the high value of qm could be associated with high surface area resulted from ring opening of cellulose, hemicellulose or lignin mass due to acid treatment in charring process. the ring opening process of cellulose increased the active surface sites during the charring process. in the hexavalent chromium having ionization process at ph2, the concentration of hcro− 4 ions are maximum. furthermore, at a low ph condition, protonation is possible due to high concentration of protons. as a result, hcro4 is electrostatically attracted to the protonated surfaces of the biosorbents, which helps it to bind to the surface of ctw (figure is not given). similarly, cr(vi) get adsorbed onto the protonated sites within the ctw by an ion-exchange mechanism [20,21]. table 1: maximum cr(vi) biosorption capacities (qm) of ctw with other reported biosorbents. sn biosorbent ph qm (mg/g) reference 1 arthrobacter viscous biomass 2.0 20.377 [21] 2 waste newspaper 3.0 59.88 [22] 3 coconut husk 2.0 29.00 [23] 4 cacktus fruit (opuntia) 2.0 18.50 [24] 5 carbon slurry 2.0 15.24 [25] 6 nutshell powder 2.0 72.12 [26] 7 coconut coir pith 2.0 76.3 [27] 8 banana peel 1.5 10.42 [28] 9 charred tea waste 2.0 85.32 present work 4 conclusion the charred tea waste was prepared by the treatment concentrated sulphuric acid into tea waste. the maximum cr(vi) uptake capacity was found to be 85.32 mg/g onto ctw at ph 2 reaching 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bioresource technology, 99(7):2218–2225, 2008. 10.1016/j.biortech.2007.05.023 [28] s. parlayici. comparative study of cr (vi) removal by bio-waste adsorbents: equilibrium, kinetics, and thermodynamic. journal of analytical science and technology, 10(1):1–8, 2019. 10.1186/s40543-019-0175-3 https://doi.org/110.1016/j.biortech.2007.05.023 https://doi.org/110.1186/s40543-019-0175-3 introduction materials and methods preparation of chromium (vi) solution preparation of charred tea waste instrument used sorption study results and discussion x-ray diffraction (xrd) analysis of adsorbents fourier transform infra-red spectra (ftir) analysis effect of ph on hexavalent chromium adsorption effect of dose effect of concentration of cr(vi) solution adsorption isotherm effect of contact time adsorption kinetics biosorption mechanism conclusion bibechana vol. 21, no. 2, august 2024, 150–158 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar thermodynamic, structural, surface and transport properties of au-cu melt s. k. yadav1∗ u. mehta1, r. k. gohivar1 1department of physics, mahendra morang adarsh multiple campus biratnagar, nepal. ∗corresponding author: email: sashit.yadav@mmamc.tu.edu.np abstract thermodynamic, structural, surface and transport properties of au-cu liquid alloy were calculated on the basis of different theoretical modeling equations. the thermodynamic properties, such as excess gibbs free energy of mixing, enthapy of mixing and activity were estimated and compared with the available experimental and literature data on the basis of simple theory of mixing (stm). the best fit values of model parameters were estimated using the experimental values of excess gibbs free energy of mixing and enthalpy of mixing of the system at 1550 k. using the same model parameters and frame, the concentration fluctuation in long wavelength limit and warren-cowley short range order parameter were calculated and analysed to understand the local arrangement of atoms in the liquid mixture. the surface tension and extent of surface segregation of atoms in the initial melt were computed using butler’s model. in transport properties, the ratio of mutual to intrinsic diffusion coefficients was calculated using stm and viscosity was calculated using kaptay equation. the system showed complete ordering tendency at its melting temperature. keywords molar surface area, ordering nature, noble metals, transition metals, surface phase. article information manuscript received: february 10, 2024; revised: march 25, 2023; accepted: may 10, 2024 doi https://doi.org/10.3126/bibechana.v21i2.66853 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the important information related to the alloy catalytic, wettability, electrical, magnetic, mechanical, etc. behaviours can be obtained by computing and analyzing the thermodynamic, structural, surface and transport properties of liquid alloys. in this regard, several researchers [1–11] working in the field of material science and engineering have made numerous attempts to access the mixing properties of different binary liquid alloys. therefore, thermodynamic, structural, surface and transport properties of au-cu liquid alloy have been studied in this work on the basis of different theoretical approaches. topor and kleppa in 1984 [12] and okamoto et al. in 1987 [13] have summarized a brief review of the literature related to the thermodynamic properties and phase diagrams of the au-cu system. later, sundman et al. in 1998 [14] used calphad approach to access the thermodynamic description of the system using the available experimental results for solid and liquid phases of the system. they successfully reproduced the experimental results by developing a theoretical framework, called com150 http://nepjol.info/index.php/bibechana sashit.yadav@mmamc.tu.edu.np https://doi.org/10.3126/bibechana.v21i2.66853 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ s. k. yadav et al./ bibechana 21 (2024) 150-158 151 pound energy formalism. they further presented optimised values of self-consistent parameters for the excess gibbs free energy of mixing for the system. han et al. in 2004 [15] used molecular dynamics simulation techniques to determine the density and specific heat of the system above and below its melting temperature. their results showed that the density of the system increased linearly with decrease in temperature and specific heat remained constant in the range 900-1900 k. in the same year, brillo et al. [16] experimentally measured the density and thermal expansion of the system and its pure components. their results were found to be consistent with those obtained by han et al. recently, kong et al. in 2018 [17] investigated the structural, thermodynamic and elastic properties of the system using first principle calculations based on density functional theory. they found that the metallic complexes, aucu, au3cu and aucu3 to be mechanically stable. from the above mentioned literature, it can be stated that their appears immense interest to access the mixing properties of au-cu system. therefore, the thermodynamic, structural, surface and transport properties of the system have been computed using different theoretical approaches in present work. 2 formulations 2.1 thermodynamic properties the thermodynamic properties of the system have been computed using the modeling equations of simple theory of mixing (stm).on the basis of the model, the excess gibbs free energy of mixing for binary liquid alloy is expressed as [18–20] ∆gxs m rt = ∫ c 0 log σ2dx = xa log γa + xb log γb (1) where xa (a=au) and xb (b=cu) are the mole fractions of atoms a and b respectively in the liquid mixture, such that xa + xb = 1. the terms ϕ, γa and γb can be given as ϕ = (ζ + 2xa − 1) exp (−ω/zkbt )/2xa (2) γa = [(ζ − 1 + 2xa)/xa(1 + ζ)]z/2 (3) γb = [(ζ + 1− 2xa)/xb(1 + ζ)]z/2 (4) ζ = 1 + 4xaxb [exp (2ω/zkbt )− 1]1/2 (5) herein, ω is called the ordering energy, is the model fit parameter and z is the coordination number. if ω < 0, then complex formation or hetero-coordinating tendency in the initial melt is expected, otherwise homo-coordinating tendency is expected. at equiatomic concentration (xa = xb = 0.5), the expression for ∆gxs m can be given as [18–20] ∆gxs m rt = ln [2z/2(1 + exp ( −ω zkbt ))−z/2] (6) once the value of ω is determined at xa = xb = 0.5, ∆gxs m can be computed in the entire composition range using the relation ∆gxs m = nkbt (xaxb ω kbt ) (7) the relation between gibbs free energy of mixing (∆gm ) and excess gibbs free energy of mixing ∆gxs m is expressed as ∆gm = ∆gxs m +rt (xa lnxa + xb lnxb) (8) the enthalpy of mixing (∆hm ) is expressed in terms of ∆gxs m as ∆hm = ∆gxs m − t ( ∂∆gxs m ∂t ) p (9) where p is the pressure of liquid mixture. using equations (7) in equation (9), one can obtain ∆hm = nkbt [xaxb ω kbt − 1 kbt xaxb dω dt ] (10) where dω/dt is the temperature derivative term of ordering energy as it is temperature-dependent and concentration independent. once the values of ∆hm and ∆gxs m are determined, the values of excess entropy of mixing ∆sxs m can be calculated using the standard thermodynamic relation ∆gxs m = ∆hm − t∆sxs m (11) the activity (ai, i = a,b) of each component of the liquid alloy is expressed in the form as [18–20] ln aa = lnxa + x2 b ω kbt (12) ln aa = lnxa + x2 a ω kbt (13) s. k. yadav et al./ bibechana 21 (2024) 150-158 152 2.2 structural properties in structural functions, the expression for concentration fluctuation in long wavelength limit (scc(0)) in terms of ∆gm and and ai can be given as [4, 11,18,21–23] scc(0) = rt ( ∂2gm ∂x2 a )−1 t,p,n = rt ( ∂2gm ∂x2 b )−1 t,p,n (14) and scc(0) = xbaa( ∂aa ∂xa )−1 = xaab( ∂ab ∂xb )−1 (15) with the aid of equation (6), equation (14) becomes scc(0) = xaxb [1 + z 2ζ (1− ζ)]−1 (16) the ideal values of scc(0) is calculated using the following equation sid cc(0) = x1x2 (17) another structural functions, warren-cowley short range–order parameter (α1) can be expressed in terms of scc(0) as [11,21,24,25] α1 = s − 1 [s(z − 1) + 1] (18) where s = scc(0) sid cc(0) (19) 2.3 surface properties the surface tension (σ) and surface concentration (xs i ) of the system have been calculated in the framework of butler’s model. according to this model, σ for binary liquid solution is expresses in the form [23,25–28] as σ = σa + rt λa ln xs a xb a + ∆gxs a,s −∆gxs a,b λa = σb + rt λb ln xs b xb b + ∆gxs b,s −∆gxs b,b λb (20) where σi is the surface tension, λi is molar surface area, xs i is the surface concentration, xb i is the bulk concentration, ∆gxs i,s is the molar surface partial excess gibbs free energy and ∆gxs i,b is the molar bulk partial excess gibbs free energy for the component i in the liquid mixture at the melting temperature of the alloy. ∆gxs i,s and ∆gxs i,b are correlated by the relation [25,27,28] ∆gxs i,s = β∆gxs i,b (21) where the value of β = 0.8181 [25, 28] has been taken for the present calculations. the molar surface area (λi) of component i in the liquid mixture can be calculated using the relation λi = fn 1 3 av 2 3 i (22) where na is the avogadro’s number and vi(= mi ρi ) is the molar volume of element i in the liquid mixture. the values of σi and vi are calculated with the help of the following relations [16,28–30] σi = σ0 i + dσ dt (t − t0) (23) and vi = v 0 i [1 + +κi(t − t0)] (24) where σ0 i is the surface tension, v 0 i is the molar volume and κi [28,29,31] is the temperature coefficient of volume expansion for ith component at its melting temperature (t0). 2.4 transport properties the viscosity (η) and ratio of mutual to intrinsic diffusion coefficients (dm/did) have been computed in order to analyze the transport properties of the system. on the basis of simple theory of mixing, η of binary liquid alloy can be given as [18,23] η = ηid[1− xaxb( 2ω kbt )] (25) where ηid is the ideal value of viscosity calculated using the relation [18,23,30] ηid = xaηa + xbηb (26) herein, ηi stands for the viscosity of pure component i at the melting temperature of the liquid alloy and is calculated using the relation ηi = η0i exp ( e rt ) (27) the term η0i is viscosity and e is activation energy of the component i at its melting temperature. the kaptay equation for the viscosity of binary liquid alloy can be expressed as [10,23,32] η = ( hna xava + xbvb + v e ) x(xag ∗ a + xbg ∗ b(0.155± 0.015)∆hm rt ) (28) s. k. yadav et al./ bibechana 21 (2024) 150-158 153 where g∗ i is the gibbs energy of activation of the viscous flow for pure component i and is given as g∗ i = rt ln ( ηivi hna ) (29) where h is the planck’s constant, v e is excess volume upon alloy formation which can be neglected and the rest of terms carry their usual meanings as stated above. in the framework of stm, the values of dm/did for binary liquid alloy can be estimated using the relation [18,19,23] dm did = [ 1− xaxb ( 2ω kbt )] (30) dm = xadb + xbda; da and db are the selfdiffusion coefficients of pure components a and b respectively. equation (30) can also expressed in the form as dm did = sid cc(0) scc(0) (31) herein, the terms carry their usual meanings as stated in the above sub-sections. 3 results and discussion 3.1 thermodynamic properties the model parameter (ω/kbt ) of simple theory of mixing (stm) is assumed to be temperaturedependent but concentration independent. the effect of model parameter on excess gibbs free energy of mixing (∆gm ) was analysed by arbitrarily varying the value of ω/kbt in the range ±5. the values of ∆gm were calculated at 1550 k using equations (7) and (8) in the above mentioned range of model parameter at all concentrations. the compositional dependence of ∆gm/rt so estimated are plotted in figures 1 and 2. 0.2 0.4 0.6 0.8 1.0 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6  g m /r t x au /k b t=0 /k b t=1 /k b t=2 /k b t=3 /k b t=4 /k b t=5 figure 1: effect of positive values of ω/kbt on ∆gm/rt versus xau at 1550 k. 0.0 0.2 0.4 0.6 0.8 1.0 -2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 g m /r t x au /k b t=-1 /k b t=-2 /k b t=-3 /k b t=-4 /k b t=-5 figure 2: effect of negative values of ω/kbt on ∆gm/rt versus xau at 1550 k. in the preferred model, it is assumed that if ω/kbt < 0, then ordering tendency among the atoms of liquid alloy is expected and if ω/kbt > 0, then segregating tendency is expected. it can be observed that the negative values of ∆gm/rt gradually decreased with increase in positive values of ω/kbt , except for ω/kbt = 3 (figure 1). herein, ω/kbt = 0 represents the ideal values of ∆gm/rt . the perusal of figure 2 corresponds that with increase in negative values of ω/kbt , the negative values of ∆gm/rt gradually increased. thus, the hetero-coordinating tendency or complex forming tendency in the liquid alloy gradually increased with the increase in negative values of ω/kbt . 0.2 0.4 0.6 0.8 1.0 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 s m xs/r h m /rt g m xs/rt g m xs /r t ,  h m /r t ,  s m xs /r x au this work experimental figure 3: compositional dependence of ∆gxs m/rt , ∆hm/rt and ∆sxs m/r for au–cu liquid alloy at 1550 k. the value of ω/kbt was first obtained with the help of equation (6) and experimental value of ∆gxs m [5] at xau = 0.5 and 1550 k. equation (7) was then used to calculate ∆gxs m for the system at all concentrations. in due course, the value of ω/kbt was s. k. yadav et al./ bibechana 21 (2024) 150-158 154 slightly adjusted following the method of successive approximation confirming that the obtained values were consistent with those of experimental. the best fit value of ω/kbt was determined to be −1.900. the compositional dependence of calculated and experimental values of ∆gxs m/rt are depicted in figure 3. both the experimental and computed values of ∆gxs m/rt were found to be consistent with each other at all compositions. the au–cu binary system is a regular alloy and the equilibrium values of ∆gxs m/rt are −0.47500 (this work) and −0.46611 (experimental [5]) at xau = 0.5. therefore, the system is found to be symmetric with respect to excess gibbs free energy of mixing and weakly interacting in nature (figure 3). moreover, the computed values of ∆gxs m/rt were found to be negative in the entire concentration range indicating the system to be ordering in nature at its melting temperature, 1550 k. the temperature derivative term of the model parameter (dω/dt ) was estimated using equation (10) and experimental data of hm [5]. the best fit value of 1 kb dω dt was found to be −0.5500 employing iterative process. the values of hm and sxs m were then computed at all concentrations using equations (10) and (11) at 1550 k, and above determined model parameters. the computed and experimental values of these thermodynamic parameters are plotted as a function of concentration in figure 3. 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 a cu a au a a u, a c u x au this work experimental ideal figure 4: activities of au (aau) and cu (acu) versus xau of au–cu liquid alloy at 1550 k. the maximum negative values of hm/rt were −0.33750 (this work) and −0.33864 (experimental [5]) at xau = 0.5. meanwhile, the optimum values of sxs m/r were 0.13750 (this work) and 0.12770 (experimental [5]) at xau = 0.5. additionally, the calculated and experimental values of these functions were found to be consistent with each other (figure 3). the small negative value of hm/rt revealed the system to be weakly interacting and ordering in nature at its melting temperature. the activities of the monomers au (aau) and cu (acu) of the system were estimated using equations (12) and (13) with the aid of determined value ω/kbt . the experimental and calculated values of aau and acu showed negative deviations from their respective ideal values revealing the system to be hetero-coordinating in nature. they agreed well with each other at all concentrations and 1550 k (figure 4) thereby validating the present iteration process. 3.2 structural properties the knowledge of structural functions helps to understand the nature of arrangement of atoms in the liquid alloy at microscopic level. the concentration fluctuation in long wavelength limit (scc(0)) and warren-cowley short range order parameter (α1) were calculated in structural properties. at a temperature and concentration, if the calculated values of scc(0) < sid cc(0), then the alloy shows ordering nature, i.e., there is preferential association among the unlike atoms. under the similar conditions, if scc(0) > sid cc(0), then it shows segregating nature, i.e., the association among the same type of atoms is favoured in the liquid state. figure 5: effect of positive values of ω/kbt on scc(0) for au-cu liquid alloy at 1550 k. the effect of ω/kbt on scc(0) was observed by calculating the physical quantity for ω/kbt = ±5 with the help of equation (16). the value of sid cc(0) was estimated using equation (17) throughout the entire concentration range. it can be observed that the computed values of scc(0) showed positive deviation from its ideal values for ω/kbt = 1 and 2 indicating the increase in segregating tendency in the initial melt (figure 5). beyond ω/kbt > 2, the s. k. yadav et al./ bibechana 21 (2024) 150-158 155 estimated values of scc(0) showed unusual trends. but on increasing the negative values of ω/kbt in the preferred range, the negative deviations of scc(0) from sid cc(0) increases (figure 6) revealing the gradual increase in ordering tendency in the alloy. these results are in accordance with those predicted by gibbs free energy of mixing in the above sub-section. 0.0 0.2 0.4 0.6 0.8 1.0 0.05 0.10 0.15 0.20 0.25 s c c (0 ) x au ideal /k b t=-1 /k b t=-2 /k b t=-3 /k b t=-4 /k b t=-5 figure 6: effect of negative values of ω/kbt on scc(0) for au-cu liquid alloy at 1550 k. theoretical, experimental and ideal values of scc(0) were estimated using equations (14-17) with help of determined values of model parameter and experimental value of activity [5]. both the calculated experimental and theoretical values of scc(0) showed negative deviation from sid cc(0) at all concentrations revealing the system to be complete ordering in nature at its melting temperature (figure 7). both of these values were in excellent agreement with each other. 0.2 0.4 0.6 0.8 1.0 -0.08 -0.04 0.00 0.04 0.08 0.12 0.16 0.20 0.24 s c c (0 ),  1 a au s cc (0) (this work) s cc (0) (ideal) s cc (0) (experimental)  1 figure 7: computed values of scc(0) and α1 versus xau for au–cu liquid alloy at 1550 k. in case of liquid alloys, the value of α1 can be negative, positive and zero. for a temperature and concentration, the ordering tendency is expected if α < 0, segregating tendency is expected if α1 > 0 and ideal mixing tendency is expected if α1 = 0. the values of α1 were calculated using equations (17-19) with the aid of estimated values of scc(0). the calculated values of α1 < 0 at all concentrations revealing the system to be complete ordering in nature. 3.3 surface properties the surface tension (σ) and surface concentrations of components au (xs au) and cu (xs cu) were computed using equation (20). the required input parameters for the purpose were determined using equations (21-24) with the help of values in table 1. the computed values of xs au, xs cu and σ are plotted as a function of concentration in figures 8 and 9 respectively. table 1: input parameters for surface tension [30] atom t0 ρ0 ∂ρ/∂t σ0 ∂σ/∂t (k) (kg/m3) (kg/m3.k) (n/m) (n/m.k) au 1336 17360 -1.50 1.169 -0.00025 cu 1356 8000 -0.80 1.303 -0.00023 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 xs cu xs au xs a u, x s c u x au this work ideal figure 8: computed values of xs au and xs cu versus xau of au–cu liquid alloy at 1550 k. the computed value of xs au showed positive deviation whereas those of xs cu showed negative deviation from their respective ideal values (figure 8). these findings suggested that au atoms segregate on the surface phase of the liquid mixture, whereas cu atoms remain in the bulk phase. the computed values of surface tension of individual atoms are σau = 1.1155 n/m and σcu = 1.2584 n/m at the melting temperature of the liquid alloy, 1550 k. as the surface tension of au is less than that of cu, au atom segregated in the surface phase. the computed values of σ is found to be equal to ideal s. k. yadav et al./ bibechana 21 (2024) 150-158 156 values in the concentration range xau < 0.3. but it is found to be less than ideal values in the rest of the concentrations (figure 9). moreover, the surface tension of the system gradually decreased with the increase in concentration of au. 0.0 0.2 0.4 0.6 0.8 1.0 1.12 1.14 1.16 1.18 1.20 1.22 1.24 1.26  [n m -1 ] x au this work ideal figure 9: computed values of σ versus xau of au– cu liquid alloy at 1550 k. 0.0 0.2 0.4 0.6 0.8 1.0 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 d m /d id x au figure 10: dm/did versus xau of au–cu liquid alloy at 1550 k. 3.4 transport properties in transport properties, the ratio of mutual to intrinsic diffusion coefficients (dm/did) of the system was calculated in the framework of stm. at a constant concentration and temperature, if dm/did < 1, then it indicates homo-atomic pairing tendency and if dm/did > 1, then it indicates hetero-atomic pairing tendency among the atoms of liquid mixture. equation (30) was used to calculate dm/did of the system at 1550 k. from figure 10, it can be observed that the computed values of the physical quantity is found to be greater than 1 throughout the entire concentration range thereby revealing the system to be complete ordering in nature at its melting temperature. similar results were also obtained from the investigations of thermodynamic and structural functions in the above sub-sections. table 2: input parameters for viscosity [30] atom η0 e (nsm−2) (jmol−1) au 0.001132 15900 cu 0.000301 30500 0.0 0.2 0.4 0.6 0.8 1.0 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9  [1 0-3 n sm -2 ] x au this work ideal figure 11: compositional dependence of η of au– cu liquid alloy at 1550 k. the viscosity (η) of the system was calculated on the basis of kaptay equation [10] (equations (2729)). the necessary parameters required for the process were taken from table 2. the viscosity of the system showed negative deviation from the ideal value. it increased gradually with the increase in the concentration of au (figure 11). 4 conclusion the values of the thermodynamic properties computed using the simple theory of mixing were consistent with their respective 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[32] s. k. yadav, n. chaudhary, and d. adhikari. thermodynamic, structural, surface and transport properties of au-ni liquid alloy at 1150 k. bibechana, 18(1):184–192, 2021. introduction formulations thermodynamic properties structural properties surface properties transport properties results and discussion thermodynamic properties structural properties surface properties transport properties conclusion bibechana 19 (1-2) (2022) 1-13 1 zirconium modified pomegranate peel for efficient removal of arsenite from water bhoj raj poudel1,2, dhan shree ale2, ram lochan aryal1,3, kedar nath ghimire1, surendra kumar gautam2, * , hari paudyal1, megh raj pokhrel1 1central department of chemistry, tribhuvan university, kathmandu, nepal 2department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu, nepal 3department of chemistry, amrit campus, tribhuvan university, kathmandu, nepal *email: surendra.gautam@trc.tu.edu.np article information: received: may 7, 2022 accepted: june 17, 2022 keywords: pomegranate peel as (iii) spp@zr adsorption capacity rainfall abstract we developed a novel biosorbent based on zirconium-modified pomegranate peel (spp@zr) for efficient arsenic (as(iii)) removal from water. sem, edx, xrd, and ftir were used to characterize the prepared biosorbent. the batch adsorption method was used to evaluate the adsorption viability of biosorbents for the removal of as(iii) from water. the edx analysis of saponified pomegranate peels (spp) before and after zr (iv) loading demonstrated that ion exchange was the preferred metal loading technique. as (iii) adsorption is very ph-dependent, with the maximum adsorption occurring at ph 8.0. the maximum as(iii) adsorption capacity of spp@zr was found to be 82.0 mg/g. according to isotherm and kinetic modeling studies, the experimental results fitted well with the langmuir isotherm and pseudo-second-order kinetic modeling. the spent biosorbent may be easily regenerated and reused using an alkaline solution. hence, spp@zr is proving to be a promising biosorbent for uptake of as (iii) from water. doi: https://doi.org/10.3126/bibechana.v19i1-2.45943 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction arsenic is a highly toxic naturally occurring element found in the earth’s crust [1]. the natural occurrence of arsenic in groundwater is a serious concern worldwide due to its chronic toxicity and carcinogenicity [2, 3]. arsenic contamination in groundwater has caused chronic health effects to millions of people throughout the world. [4]. in 1973, the agency bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal mailto:surendra.gautam@trc.tu.edu.np https://doi.org/10.3126/bibechana.v19i1-2.45943 https://creativecommons.org/licenses/by-nc/4.0/ poudel et al. / bibechana 19 (1-2) (2022) 1-13 2 for toxic substances and disease registry (atsdr) has ranked arsenic as the number one toxic substance. the inorganic form of arsenic is classified as a group 1 carcinogenic by the international agency for research on cancer (iarc) [5, 6]. who and usepa have recommended an allowable arsenic concentration of 10 ppb 0.01mg/l) in drinking water [7, 8]. both organic and inorganic form of arsenic is found in the environment. the inorganic form of arsenic is more toxic than the organic form. the inorganic form of arsenic in an aqueous medium is arsenite (as(iii)) or arsenate (as(v)) [9-11]. arsenic is exposed to groundwater through natural and anthropogenic activities such as volcanic emission, geochemical activity, rock, and soil weathering, combustion of fossil fuels, mining activities, agricultural chemicals, wood preservatives, industrial discharges, electroplating, pigments, dyestuffs, and paints [12-14]. several treatment techniques, such as coagulation-filtration [15], ion exchange [16], reverse osmosis [17], and adsorption [18, 19] are reported for as(iii) removal from aqueous medium. compared to others, adsorption looks more promising for the removal of trace concentration of contaminants due to cost-effectiveness, easy and simple operation, minimum production of secondary products [10, 20]. several agro waste-based products have been utilized by numerous researchers in the past to remove arsenic [1, 21-24]. zirconium (zr) is a multivalent transition metal that has recently been widely investigated for wastewater treatment processes. this increased focus might be owing to the capacity of zirconium to be impregnated onto biosorbents via interactions with functional groups. zirconium impregnation into biosorbents has been demonstrated to be effective in the highselectivity removal of po4 3-, f-, and as(iii)/as(v) [25-27]. furthermore, because zr is prevalent in the earth's crust, it might be readily accessible for environmental media rehabilitation. as a result, zr was chosen for removal of as(iii) using our previously proposed adsorbent, pomegranate peels [9]. using common agro-waste, pomegranate peels, we examined a novel form of the adsorbent substitute to conventional synthetic ion exchangers for as(iii) ion remediation. it's frequently dumped as a waste residue and may be found for free or very cheap. due to the presence of cellulose/hemicellulose, pectin, and lignin as significant ingredients and adequate hydroxyl, carboxyl, and carbonyl functional groups, it might be employed as an efficient biosorbent. this biopolymer contains 10-15% pectin, making it an excellent source of natural pectin [28]. to the best of our knowledge, this is the first study to look at the potential of zr(iv) impregnated saponified pomegranate peel (spp@zr) for adsorption of trace concentrations of as(iii) from water. the objective of this study was to investigate into the biosorption properties of the prepared novel spp@zr toward as(iii) ions in water. its adsorption kinetics and isotherms were investigated. the batch method was used to investigate the effect of various factors such as initial ph, adsorption time, and coexisting ions on the uptake of as(ii) by the spp@zr. combining experimental data and characterization results yielded the mechanisms of as(iii) biosorption onto spp@zr. 2. materials and methods 2.1. materials the pomegranate peel was washed in distilled water several times, chopped into pieces, and dried. the dried peel pieces were then crushed with a crusher, sieved to enable pass through a 120 µ mesh, and then desiccated in a hot air oven at 60-70°c for 24 hours. the dry powder prepared in this way was termed raw pomegranate peels hereafter abbreviated as rpp. chemicals of analytical grade were utilized without further purification. all the solutions were made with deionized (di) water. the zirconium oxychloride octahydrate, poudel et al. / bibechana 19 (1-2) (2022) 1-13 3 calcium hydroxide, and sodium arsenite were acquired from sigma-aldrich, new delhi, india. 2.2. preparation of the zr (iv)-loaded saponified pomegranate peel the adsorbent (spp@zr) was synthesized by the method given by our previous work. the synthesis procedure has been described in detail elsewhere [9]. 2.3.characterization the morphology and elemental composition of adsorbent were studied by scanning electron microscopy (sem; jeol, jsm-6701f, japan) with an energy dispersive x-ray (edx). x-ray diffraction (xrd) patterns were utilized to evaluate the crystallinity of the biosorbent using an x-ray diffractometer (rigaku co., japan). fourier transform infrared (ftir) spectroscopy (ir affinity -1s-shimadzu spectrometer, kyoto, japan) was used to examine the surface functional groups of the as-prepared biosorbent. 2.4.adsorption experiments batch experiments were used to assess the effects of the ph of the solution, adsorption kinetics, adsorption isotherm, and the influence of competitive ions. desorption tests were carried out to determine the adsorbent's reusability and regeneration capability. for the kinetics study, 25 mg spp@zr were added into flasks having 25 ml of 28.32 mg/l arsenite solution. the ph was maintained at 8.0 utilizing 0.1 m hno3 and 0.1 m naoh. the contents were stirred at 120 rpm using a shaker at room temperature. the equilibrium adsorption capacity (qe), adsorption capacity (qt) at a predetermined time (t), and % adsorption (%a) of as(iii) ions were evaluated according to eqs. (1), (2), and (3), respectively. qe = (co – ce) v m (1) qt = (co – ct) v m (2) % a = (co – ce) co × 100 (3) where qe and qt represent the adsorption capacity (mg g−1) at equilibrium and at a preselected time, respectively; c0, ce, and ct represent the concentrations of arsenic (mg/l) in initial, at equilibrium, and at a predetermined time (t), respectively, v denotes the volume of solution (ml), and m is the mass of spp@zr used (g). the pseudo-first-order [29] and pseudo-second-order [30] kinetic models were fitted using eq. (4) and eq. (5), respectively, to the experimental results to further elucidate the adsorption mechanism. log (qe – qt) = log qe – k1 2.303 t (4) t qt = 1 k2q 2 e + 1 qe t (5) where qe represents the equilibrium sorption efficiency, k1 (min–1) and k2 (g/mg . min) are the rate constants of pseudo-1st-order and pseudo2nd-order, correspondingly. in adsorption isotherms studies, 25 mg spp@zr was taken in various conical flasks having 25 ml as(iii) solutions ( 10 to 500 mg/l). the flasks were stirred for 8 hours at room temperature. then, samples were filtered and examined for initial and final concentrations of arsenite. the as(iii) adsorption performances were described by two isotherm models, langmuir [31] and freundlich [32] using eq. (6) and eq. (7), respectively. ce qe = 1 qm b + ce qm (6) log qe = log kf +      1 n log ce (7) where qm (mg/g) is the maximum adsorption capacity, b (l/mg) is the langmuir equilibrium constant, kf [(mg/g)(l/mg)1/n] is the freundlich constant for sorption capacity, and 1/n is the dimensionless heterogeneity factor for adsorption intensity. in addition, a poudel et al. / bibechana 19 (1-2) (2022) 1-13 4 dimensionless separation factor (rl) was used to investigate the important aspects of the langmuir model [33], which may be represented by eq. (8): rl = 1 1 + (bco) (8) the rl value infers the phenomenon of the langmuir isotherm. if rl is 0 < rl < 1 (favorable), while rl >1 (unfavorable), rl = 1 (linear), and rl = 0 (irreversible) adsorption process [34]. the effect of solution ph on as(iii) adsorption was evaluated over the wide ph range. 25 ml solution of 25 mg/l as(iii) stock solution was taken in the conical flask. after ph adjustment to a predetermined value (2-13), 25 mg of spp@zr was added to each flask. the solutions were shaken for 8 hrs. at room temperature. the equilibrium concentration of as(iii) after adsorption was measured. three levels of concentrations of each competitive ion were added to 25 mg/l as(iii) solution to study the impact of common coexisting anions (cl−, so4 2−, and po4 3−) on the removal of as(iii). furthermore, the blank sample was made using the same procedure but without the addition of coexisting anion. 0.1 m hno3 and 0.1 m naoh were used to keep the ph of the whole solution at 8. the biosorbent dose of 1 g/l was added and agitated for 8 hours at room temperature. for as(v) analysis, the filtrates were collected. the reusability of the as-prepared adsorbents was tested using four cycles of adsorptiondesorption of as(iii). after washing the spent biosorbents with 0.1 m naoh solution, the reusability of the adsorbents was tested. to test reusability, the regenerated adsorbent was used for up to four cycles. 2.5.analysis the concentrations of as (iii) in the samples were evaluated using an inductively coupled plasma mass spectrometer (icp-ms, agilent 7900, santa clara, ca, usa), while the ph of the solution was measured using a ph meter (chemi line cl-180, indiamart, india). 3. results and discussion 3.1. characterization of the adsorbents fig. 1 represents the sem images and eds spectra of spp, spp@zr, and as(iii) adsorbed spp@zr. in the sem images of the surfaces of spp (fig. 1(a)) and zr (iv)-spp (fig. 1(b)), the surfaces showed rough and uneven with micro and mesopores, which possibly provide binding sites for adsorption of as (iii) physically as well as chemically and favored the adsorption of as (iii). sem image of as (iii)-spp@zr (fig. 1(c)) shows that the pores are partially covered by the adsorbed as (iii) ion, which creates a layer that settles on the rough surfaces. in the edx of spp (fig. 1(d)), the intense peaks of ca indicate that ca is one of the major elements of the saponification product. after zr (iv) loading (fig. 1(e)) peaks of ca were decreased and the new peak corresponding to zr was appeared, which is strong evidence of the exchange of ca2+ ions from spp with zr (iv) ion during loading reaction through cation exchange mechanism. in the case of as (iii) adsorbed zr (iv)-spp biomass (fig. 1(f)), a new additional peak of arsenic has appeared. from this, it was evaluated that highly accommodation of as (iii) ion onto the surface with ligand exchanged between hydroxyl ion and arsenic anion as depicted in scheme 2. the elemental composition of spp, spp@zr, and as(iii) adsorbed spp@zr are shown in table 1. poudel et al. / bibechana 19 (1-2) (2022) 1-13 5 fig.1. sem images of (a) spp, (b) spp@zr, (c) as (ii)-spp@zr, and eds spectra of (d) spp, (e) spp@zr, (f) as (iii)spp@zr. table 1. elemental composition of spp, spp@zr, and as(iii) adsorbed spp@zr. elements spp (wt %) spp@zr (wt%) asspp@zr (wt % ) c k 41.29 44.72 38.62 o k 43.82 40.36 41.01 na k nd nd 0.42 si k nd nd 2.12 ca k 13.89 0.56 0.46 as l nd nd 3.87 zr l nd 14.35 13.49 total 100.00 100.00 100.00 the xrd curve of spp@zr is shown in fig. 2(a), where sharp peaks corresponding to the crystalline structure are not observed indicating the amorphous nature of the prepared adsorbent. in the ftir spectra of rpp (fig. 2(b)), a broad and strong peak located at around 3345 cm−1 is due to –oh stretching vibration [9]. the small peak at 2923 cm−1 is associated with the vibrations of –ch and –ch2 units. [35]. the peaks at roughly 1729 and 1613 cm−1 relate to the –coo and c=o groups, correspondingly. the c=o stretching of the carboxylic groups is responsible for the peak at 1629 cm−1. the prominent peak seen at roughly 1015 cm−1 corresponds to –c–o– linkages. after saponification (in spp), the peak observed at around 1729 cm-1 is disappeared, and a new peak appeared at around 1607 cm-1, indicating the formation of calcium carboxylate. the peak moved to 1626 cm-1 after impregnation with zr(iv) (in spp@zr), which is owing to the replacement of greater molecular weight zr(iv) for lower molecular weight ca (ii). furthermore, the intense peak at around 1076 cm−1 is associated with –zr-oh bonds [36]. it shows that zr(iv) was successfully loaded onto the biomass surface. afterward, as(iii) biosorption, the peak at around 1076 cm−1 (zr– oh) was decreased, and a new band was found at 815 cm−1 for zr–o–as vibration, showing that the hydroxyl groups were exchanged by the oxyanions of as(iii). fig. 2. (a) xrd pattern of spp@zr; (b) ft-ir of pp, spp, spp@zr before and after as(iii) biosorption. 3.2. biosorption experiments 3.2.1. effect of the ph of the solutions as(iii) adsorption onto rpp and spp@zr has been investigated in the ph range of 2.0 – 13.0. according to the findings, the % adsorption of as(iii) increases progressively from ph 2.0 to ph 8.0, then drops to ph 13. the adsorption of as(iii) was the most favorable at ph 7.0 to 10.0 poudel et al. / bibechana 19 (1-2) (2022) 1-13 6 for spp@zr as shown in fig 3. the removal efficiency of as(iii) was highest at ph 8.0. as a result, ph 8.0 was selected as the optimal ph for further adsorption test of as(iii). depending on the chemistry of the aqueous solution, as(iii) occurs primarily as a neutral species (h3aso3) at ph 7.0, while as an anionic species (h2aso3 -, and haso3 2-) at ph 7.012.0, and as aso3 3 species at ph >12.0 [18]. the ligand exchange interaction between hydroxyl ions of spp@zr and neutral as(iii) species, i.e. h3aso3, is not favourable at lower ph, resulting in minimal biosorption. at ph approximately 8.0, the anionic species of as(iii) predominate, making the exchange of hydroxyl ions by the oxyanion of as(iii) more favourable, resulting in increased adsorption of as(iii). due to competition between oxyanions of as(iii) and hydroxide ions at higher ph, as(iii) biosorption might be inhibited. when compared to spp@zr, the adsorption of as(iii) using rpp was found to be significantly poor even at optimum ph. as a result, for the subsequent experiments, only spp@zr was chosen as the adsorbent. fig. 3. effect of solution ph on as(iii) biosorption onto spp and spp@zr. 3.2.2. adsorption kinetics the influence of interaction time for the removal of aqueous as(iii) by spp@zr was studied at optimum ph of 8.0 and the results are revealed in fig. 4 (a). the adsorption of as(iii) increases rapidly at the beginning up to 1 h, whereas it becomes steady and finally attained equilibrium after 3 h. because the equilibrium was attained in less than 3 hours, the contact period in further tests was set at 8 hours to assure full sorption. the pseudo-first-order and pseudo-second-order models were fitted to the kinetic data to better clarify the kinetic process. according to eqs. (4) and (5), two plots fig. 4(b) and fig. 4(c) were drawn. table 2 shows the estimated values of kinetic parameters as well as the regression coefficient (r2). the pseudo-2nd-order model had an r2 of 0.999, which was nearer to unity than the pseudo-1storder model. furthermore, in the pseudosecond-order kinetic, the calculated equilibrium adsorption capacity (qe (cal) = 25.25 mg/g) is close to the experimental value (qe (exp)) = 24.98 mg/g. as a result, the as(iii) biosorption on spp@zr followed pseudo-second-order kinetics, signifying that chemisorption may be dominating the biosorption of as(iii). fig. 4. adsorption kinetics study of as(iii): (a) qt versus contact time; (b) pseudo-firstorder kinetics plot of spp@zr with as(iii) system; (c) pseudo-second-order kinetics plot of spp@zr with as(iii) system. poudel et al. / bibechana 19 (1-2) (2022) 1-13 7 table 2. kinetics parameters for as(iii) biosorption onto spp@zr. order r2 qe (exp) (mg/g) qe (cal) (mg/g) k1 (min -1) k2 (g /mg . min ) pseud o second order 0.99 9 24.98 25.25 8.3 0 × 10-3 pseud o-firstorder 0.88 7 24.98 7.96 22.3 × 10-3 3.2.3. adsorption isotherms the adsorption isotherm was described by evaluating the fluctuation of starting as(iii) concentration for adsorption capacity. figure 5(a) shows the adsorption isotherms of as(iii) onto spp@zr at ph 8.0 and room temperature. the results show that when the as(iii) ion concentration raised from low to high, the adsorption capacity increased fast, with a slow but steady rise until saturation (plateau) was reached at high concentrations. the increased adsorption rate early on might be explained by the increasing availability of vacant sorption sites in the adsorbent. at a high concentration area, the adsorption capacity achieved a plateau, indicating that no more sites are available for sorption. the adsorption data were studied utilizing langmuir (eq. 6) and freundlich (eq. 7) models to explain the as(iii) biosorption performance. isotherm’s parameters were determined from the slope and intercept of the respective plots, ce/qe vs ce (fig. 5(b)) and logqe vs logce (fig. 5(c)), respectively. the estimated isotherm parameters with r2 value are listed in table 3. table 3. isotherms parameters for as(iii) biosorption onto spp@zr. parameter value langmuir isotherm qm (mg g−1) 72.52 b (l mg−1) 0.064 r2 0.998 freundlich isotherm kf (mg g−1) (l mg−1)1/n 12.12 1/n 0.323 r2 0.937 the greater r2 indicated that the langmuir model was more suited to describe the biosorption behaviour of as(iii) onto spp@zr, as shown in table 2. we concluded that biosorption processes took occur on the adsorbent's surface, which was referred to as monolayer adsorption. the calculated maximum adsorption capacity (qm) of spp@zr for as(iii) was 72.52 mg/g, which provided a substantial potential for practical aqueous removal of as(iii) in comparison with several other biosorbents reported in past research in discussion (table 4). table 4. comparison of as(iii) biosorption capacities of various biosorbents with spp@zr. furthermore, the values of rl derived from eq. (8) are shown in fig. 5(d). the derived rl values ranged from 0 to 1, indicating that as(iii) adsorbent opti mal ph qm (mg/ g) refer ence zr(iv)-loaded apple peels 9.0 15.68 [37] la(iii)-loaded saponified watermelon rind 12.08 37.73 [38] zr-chitosan modified sodium alginate composite 43.19 [39] powdered almond shell 7.2 4.6 [40] modified hazelnut shell 9.0 11.84 [41] iron-coated seaweeds 7.0 4.2 [42] zro2-coated sawdust 7.0 29.0 [43] la2o3-coated sawdust 7.0 22.0 [43] iron dopped aminofunctionalized sawdust 7.0 10.1 [44] spp@zr 8.0 72.52 this study poudel et al. / bibechana 19 (1-2) (2022) 1-13 8 biosorption onto spp@zr is favourable and that the adsorbate-adsorbent surface bonding is strong. fig. 5. (a) equilibrium adsorption capacity for as(iii) onto spp@zr at various initial concentrations of as(iii); (b) linearized langmuir isotherm plot of spp@zr with as(iii) system; (c) linearized freundlich isotherm plot of spp@zr with as(iii) system; (d) value of rl as a function of initial concentration of as(iii). 3.2.4. influence of coexisting ions the influence of various coexisting ions for the removal of as(iii) ions was investigated, and the findings are shown in fig. 6. in the presence of cl−, and so4 2− at any concentration level, a small drop in % adsorption of as(iii) occurs, as seen in the figure compared to the blank. this might be because these ions have a lower binding capability than as(iii) ions. the inclusion of po4 3-, on the other hand, drastically reduced as(v) adsorption, owing to severe competition between phosphate and arsenite ions for the adsorbent's binding sites. at a phosphate concentration level of 75 mg l−1, the adsorption of arsenate drops by ~ 40%. furthermore, the chemical and structural resemblances of arsenite with phosphate in an aquatic environment account for the dramatic decrease in as(iii) adsorption in the presence of phosphate. fig. 6. effect of coexisting anions for the adsorption of as(iii) ions on spp@zr. 3.2.5. desorption and reusability of adsorbent the as(iii) ion is weakly sorbed onto the biosorbent at ph > 11, so elution of as(iii) from spent biosorbent may be accomplished with ease utilizing naoh solution. as a result, the spent spp@zr can be revived for recycling using a 0.1 m naoh solution. the adsorbed arsenite anion may have been swapped via ligand exchange reaction by hydroxyl ions in the alkali solution. for reusability, the spp@zr regenerated by naoh was washed with distilled water until neutrality. a reusability investigation of the biosorbent was performed after desorption for up to four cycles. after four consecutive cycles, the as(iii) adsorption capacity of spp@zr decreased from 86.4% to 67.3% percent, as shown in fig. 7. even after the fourth consecutive cycle, the as(iii) removal efficiency was more than 67%, showing that spp@zr was highly recyclable and a viable adsorbent for removing as(iii) from an aqueous solution. poudel et al. / bibechana 19 (1-2) (2022) 1-13 9 fig. 7. the % adsorption of as(iii) onto spp@zr in the subsequent adsorptiondesorption cycle. 3.2.6. as(iii) biosorption/desorption mechanism the as(iii) biosorption on spp@zr closely matched the pseudo-second-order kinetic, implying that the process is chemisorptiondriven. the ftir spectra of biosorbent before and after as(iii) adsorption supported this hypothesis. the band at 1076 cm−1 (zr–oh) was decreased after sorption, and a new band for zr–o–as a vibration was found at about 815 cm−1, showing that the –oh group was substituted by oxyanion of as(iii). the ligand exchange process for as(iii) biosorption utilizing spp@zr is as follows. in the removal of anionic pollutants, the loaded zr(iv) metal ion plays a crucial role. after zirconium is loaded onto spp, it forms stable chelates with pectic acid (biswas et al. 2008). due to the steric hindrance of a large polymer of pectic acid, all the positive charges of the zirconium ions are not entirely counterbalanced by the negatively charged carboxylic group. the carboxylic group neutralizes just one or two positive charges of zr(iv), with the remaining neutralized by negatively charged hydroxide ions, which are plentiful in the water. a ligand exchange process was anticipated to exchange these hydroxide ions with oxyanions of as(iii). adsorbed as(iii) may also be readily eluted utilizing naoh solution via a ligand exchange reaction between the adsorbed oxyanions of as(iii) and hydroxide ions in the solution. the mechanism of the ligand exchange process through as(iii) adsorption-desorption is depicted in scheme 1. scheme 1. adsorption and desorption mechanism for as(iii) onto spp@zr. conclusions spp@zr was synthesized and used as an effective biosorbent for removing arsenic from water in this study. based on the results of the characterizations, it was acceptable to conclude that efficient loading of zr (iv) into biomass and efficacious biosorption of as (iii) onto spp@zr were achieved. the maximum adsorption of as(iii) on spp@zr was evaluated at ph 8.0.the biosorption trailed a pseudosecond-order kinetic, implying that the process was chemisorption with higher initial adsorption rates. the langmuir model fit the equilibrium data better, indicating that monolayer adsorption occurred on a homogeneous surface of the spp@zr. the maximum adsorption capacity was evaluated as 72.52 mg/g, which was found to be higher than several other biosorbents found in the literature. furthermore, spp@zr works well in the presence of a variety of coexisting anions, and the spent adsorbent is easily regenerated and reused for up to four consecutive cycles. as a result, spp@zr can be considered a useful, costpoudel et al. / bibechana 19 (1-2) 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aggregate with crusher run dust: a comprehensive experimental investigation ishwor thapa1, nirmal prasad baral2, krishna raj adhikari∗3 1department of civil engineering, sharda university, greater noida, india 2department of civil engineering, ioe pashchimanchal campus, pokhara, nepal 3ioe pashchimanchal campus, pokhara, nepal ∗corresponding author. email: adhikarikrishna@wrc.com abstract this experiment explores the potential of crusher-run dust, a waste product from crusher plants, to enhance high-performance concrete. it investigates the effects of the partial replacement of sand with crusher-run dust in various ratios. the replacement of fine aggregate with crusher run dust has been considered for m50 grade design mix concrete with 0%, 15%, 30%, 45%, and 60%, and the change in characteristics has been considered. a superplasticizer was utilized to keep the workability between 76mm and 85mm. in this experimental investigation, the mechanical properties of concrete, such as compressive strength, flexural strength, split tensile strength, and porosity, have been examined. the results show that the characteristics of concrete improved, with the best results observed when using a 30% concentration of crusher-run dust in concrete, suggesting potential benefits for the construction industry. keywords concrete; crusher run dust; fine aggregate; strength. article information manuscript received: march 30, 2024; revised: july 14, 2024; accepted: july 23, 2024 doi https://doi.org/10.3126/bibechana.v21i3.65293 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction building is its foundation, and concrete is its primary component in civil engineering. the use of concrete in construction is generally acknowledged. as the fundamental component of today's technologically advanced construction industry, concrete plays a crucial role [1]. every part of the world uses a significant amount of concrete. an essential component of concrete is fine aggregate. because there is a rising need for concrete for the construction of infrastructure, there is a need for an alternative material that can meet the demand for fine aggregate 262 http://nepjol.info/index.php/bibechana adhikarikrishna@wrc.com https://doi.org/10.3126/bibechana.v21i3.65293 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ishwor thapa et al./ bibechana 21 (2024) 262-271 263 in concrete [2]. industries today produce a significant amount of garbage, posing health risks. another critical issue with this garbage is disposal. this trash can be successfully used in the production of concrete [3]. crusher-run dust, another waste product produced by crushing facilities, can be used successfully in concrete. based on the previous study, it was discovered that crusher-run dust’s qualities are somewhat comparable to those of fine aggregate and that it can be used in place of fine aggregate [4]. this study investigates the use of stone dust in place of natural sand in concrete. tests on the physical and mechanical characteristics of stone dust revealed enhanced compressive and flexural strengths with 40–60% replacement of stone dust, providing a cost-effective substitute for depleting natural sand resources [5]. due to excessive sand dredging, the building industry's reliance on concrete, which utilizes a lot of sand, has raised environmental issues. to replace sand in concrete, this study investigates the use of crushed limestone dust, showing favorable or equivalent results in a range of mechanical and physical qualities [6]. cementitious composites are widely utilized yet with high co2 emissions, looking for environmentally suitable substitutes such as industrial wastes (fly ash, silica fume, ggbs). this study evaluates their durability, strength, and eco-friendliness while also substituting granite quarry dust for river sand [7]. this study investigates using non-biodegradable quarry dust as a sustainable substitute for river sand in concrete. over seven, fourteen, and twenty-eight days, tests with different replacement percentages (0%, 25%, 50%, and 75%) showed enhanced flexural strength compared to conventional concrete [8]. due to strong demand and limited availability in top nations, quarry dust is being investigated to replace river sand in m50-grade concrete. according to research, adding quarry dust (0–100%) in place of river sand improves the compressive and tensile strength of concrete [9]. this study explores replacing river sand with eco-sand (a by-product of cement manufacturing) in concrete construction due to the increasing demand and cost of natural sand. results suggest 18% as the optimal replacement percentage, aiming to reduce pollution and promote environmental friendliness [10]. the study investigates the use of quarry dust as a secondary by-product to improve mechanical qualities in selfcompacting concrete (scc). it looks into replacing different amounts of river sand (0%-100%) with quarry dust as well as the addition of alcofine and silica fume. increased c-s-h concentration and decreased pores are found via microstructure analysis. the strongest result is obtained when 100% of the qd is replaced. this method not only enhances the characteristics of concrete but also minimizes quarry waste [11]. previous studies have shown that crusher-run dust, a waste product, can partially replace sand in construction projects. in the concrete production industry, tackling the environmental and economic obstacles caused by the reduced availability of natural sand resources is essential. recent research emphasizes the possibility of utilizing industrial waste as an eco-friendly option. when stone dust is used to substitute 40-60% of natural sand in concrete, it can improve compressive and flexural strengths, providing a cost-effective option. crushed limestone dust also shows favorable mechanical characteristics, making it a sustainable alternative. additionally, studies on granite quarry dust and eco-sand have revealed substantial enhancements in the strength and durability of concrete. adding quarry dust into concrete, especially in high-demand areas, enhances its compressive and tensile strengths. moreover, using crusher-run dust to partially replace sand has yielded positive outcomes, supporting the sector's efforts to promote sustainability and decrease co2 emissions. this study aims to investigate these options further, concentrating on how they affect high-performance concrete characteristics. this study focuses on the large amounts of waste generated when extracting and treating rocks at crusher plants, specifically focusing on crusher-run dust. the study aims to examine the impact of substituting some of the fine aggregates with crusherrun dust on the characteristics of high-performance concrete. this study seeks to identify the best replacement ratio that improves the mechanical characteristics of concrete, including compressive strength, flexural strength, split tensile strength, and porosity. by examining these elements, the research aims to offer an affordable and enduring substitute for natural sand, ultimately decreasing garbage and ecological footprint in the building sector. 2 research significance the importance of this research lies in its investigation of utilizing crusher-run dust, a by-product of crusher plants, as a substitute for fine aggregate in high-performance concrete. this method solves the urgent problem of decreasing natural sand and the adverse environmental effects of sand extraction by presenting a sustainable and affordable alternative material. the unique feature of the research is its thorough investigation of different substitution rates of crusher run dust in m50 grade concrete, offering a full comprehension of its potential advantages. by using this waste material, the study not only encourages effective waste disposal but also aids in the progress of eco-friendly construction methods, helping to further sustainable ishwor thapa et al./ bibechana 21 (2024) 262-271 264 solutions in civil engineering. 3 materials 3.1 cement and aggregate portland pozzolana cement was utilized in this study. according to is 1489-1:1991 [12], a binding agent's specific gravity test revealed that it was 3.12. in this study, fine aggregates with a size smaller than 4.75mm were used that had been carefully graded. the fine aggregate's specific gravity was determined to be 2.727, and its fineness modulus was found to be 2.22. the coarse aggregate's maximum size was 20 mm, and its specific gravity was 2.71. aggregate testing was done following is 383:1970 [13] and is 2386:1963. tables 1 and 2 display portland pozzolana cement's physical and chemical properties. similarly, table 3 shows the properties of fine and coarse aggregate. figure 1 illustrates the fine and coarse aggregate's particle size distribution (psd) curve. table 1: physical properties of portland pozzolana cement physical requirements units value specific gravity 3.12 specific surface area m2/kg 295 average particle size µm 27.6 soundness mm 3.42 initial setting time min 146 final setting time min 281 28-day compression strength 33mpa 53 mpa table 2: chemical properties of portland pozzolana cement chemical composition test value (%) loss on ignition 1.46 insoluble residue 7.23 mgo 4.76 so3 3.11 cl 0.03 cao 53.7 sio2 23.13 al2o3 6.27 fe2o3 1.89 k2o 0.95 free lime 1.92 table 3: properties of fine and coarse aggregate properties units fine aggregate coarse aggregate specific gravity 2.59 2.72 bulk density (loose) g/cm3 1.3 1.33 bulk density (compacted) g/cm3 1.45 1.49 fineness modulus 2.86 6.31 crushing strength 19.89% water absorption 1.21% 0.44% impact value 16.70% 3.2 crusher run dust his study used waste material called crusher-run dust from a crusher factory in fewa siltan dam, kaski, nepal. zone iii crusher-run dust was employed with a specific gravity and fineness modulus of 2.69 and 2.72. according to is 383:1970, a sieve analysis was conducted [13]. figure 2 below shows the psd of crusher run dust. ishwor thapa et al./ bibechana 21 (2024) 262-271 265 figure 1: psd of fine and coarse aggregate. figure 2: psd of crusher run dust. 3.3 super plasticiser the concrete mix required the addition of a superplasticizer (markplast-200f) to be usable. the amount of superplasticizer was chosen depending on how many slump trails were taken. concrete slump was kept within a 76mm and 85mm range. a certain amount of superplasticizer was added to make it work with the weight of the cement. table 4 presents the properties of the superplasticizer. table 4: properties of superplasticizer properties superplasticizer name markplast-200f colour tone dark brown state liquid specific gravity 1.06 chemical description polycarboxylate ether 3.4 concrete according to is 10262:2019 [14], the concrete mix design for the m50 grade was created with a goal strength of 58.25 n/mm2 and a planned mix proportion of 1:1.36:2.59 with a constant water-tocement ratio of 0.38. table 5 lists alternative mixture proportions. table 5: mix proportion for various concrete mixtures mixture cm cd15 cd30 cd45 cd60 w/c ratio 0.38 0.38 0.38 0.38 0.38 water (kg/m3) 170.60 170.60 170.60 170.60 170.60 cement (kg/m3) 448.95 448.95 448.95 448.95 448.95 fine aggregate (kg/m3) 612 520.2 428.4 336.60 244.80 coarse aggregate (kg/m3) 1167.2 1167.2 1167.2 1167.2 1167.2 crusher run dust (cd) (kg/m3) 0 91.8 183.6 275.4 367.20 super plasticizer (% by weight of cement) 0.62% 0.60% 0.58% 0.52% 0.46% ishwor thapa et al./ bibechana 21 (2024) 262-271 266 4 experiment work 4.1 preparation and testing of specimens crusher run dust, fine aggregate, coarse aggregate, and regular portland pozzolan cement were used to prepare the concrete. one of the six combinations was a control mix, while the remaining five contained various amounts of crusher run dust as a substitute for fine aggregate, including 15%, 30%, 45% and 60%. for casting, every component of the instrument was cleaned and carefully lubricated. dimensional considerations were made, ensuring that no point or corner was overlooked as this could result in slurry leakage. operations, including batching, mixing, and casting, were done meticulously. at first, aggregate weight was measured with a 0.5 g precision. each component needed for each mix, including the cement, coarse aggregate (20 mm and 10 mm), fine aggregate, crusher run dust, superplasticizer, and water, was weighed separately. the materials were first combined evenly in dry form, and then a mixture of superplasticizer and water was added. the initial mixture was made by adding between 50% and 70% water, and it was then properly mixed for 3 to 4 minutes in the mixer. the remaining water was combined with the super-plasticizer and thoroughly swirled before being added to the already-made mixture in the mixer for 2 to 3 minutes. after the necessary amount of concrete was produced, it was ensured that it was compacted and that the concrete was properly poured into the moulds. using a trowel, the top exterior of the filled mould was appropriately levelled. the prepared specimens were dried in the air for a whole day. moulds were opened and the specimen was moved to a water tank for curing after the 24hour casting period. after seven and twenty-eight days, the specimens were taken out of the tank. 21 samples for each mixture were created, including 6 cubes (150mm x 150mm x 150mm) for 7 and 28 days of compressive strength, 6 cylinders (300mm x 150mm) for split tensile strength at 7 and 28, 6 beams (100mm x 100mm x 500mm) for flexural strength at 7 and 28, and 3 cylinders (150mm x 100mm) for a porosity test at 28 days. 4.2 mixture description one concrete combination served as the control, and the other five were made with varying amounts of crusher-run dust. mixtures were given the labels cm, cd15, cd30, cd45and cd60 for identification purposes. for instance, cd30 defines a concrete mix that includes crusher-run dust in place of 30% of the fine aggregate. the results of the high-performance concrete investigation are greatly influenced by the experimental setup and conditions when using crusher-run dust to partially replace fine aggregate. characteristics of materials, such as portland pozzolana cement, fine aggregates, coarse aggregates, and crusher-run dust, have a direct impact on the performance of concrete. differences in mix ratios can change strength, workability, and durability. the precise amount of superplasticizer is important to keep the workability in the desired slump range; variations can result in mixes that are either too rigid or too watery, risking the structural strength. accurate blending and measuring guarantee even the spread of substances, averting any potential flaws and fluctuations in performance. appropriate curing conditions, such as temperature and humidity, are crucial for strengthening and decreasing porosity. furthermore, it is essential to adhere to standardized testing conditions when assessing mechanical properties such as compressive strength, flexural strength, split tensile strength, and porosity to ensure accurate and dependable results. changes in the conditions may lead to notable differences in the concrete's behaviour, complicating the determination of the effects of replacing fine aggregate with crusher-run dust. 5 results and discussion 5.1 property of fresh concrete slump cone equipment was used to measure the slump values of various mixes. the concrete was treated with a superplasticizer to keep the slump value between 75mm and 85mm. because of the larger particle size of crusher run dust compared to fine aggregate (as shown in figure 2), slump values increased as the fine aggregate replacement increased proportionately, and the need for a superplasticizer to maintain slump decreased as a result. details can be observed in table 6, which shows that while the dust content in concrete in the crusher has increased, slump value has also increased, and superplasticizer content has reduced. ishwor thapa et al./ bibechana 21 (2024) 262-271 267 figure 3: details of superplasticizer and slump measurement. table 6: details of superplasticizer and slump measurement replacement percentage of admixture slump (mm) cm 0.62% of cement 76 cd15 0.60% of cement 79 cd30 0.58% of cement 80 cd45 0.52% of cement 82 cd60 0.46% of cement 85 5.2 hardened properties of concrete 5.2.1 compressive strength the specimens' compressive strength was evaluated following is 516-1959 (is 516, 1959) the difference in average compressive strength for several specimens is depicted in figure 4. for all combinations, the compressive strength increased from 7 days to 28 days. additionally, it should be mentioned that compressive strength for the mixture of cd15 and cd30 was found to be higher than cm. well-graded crusher-run dust particles, which tend to fill pores on a bigger scale and take part in chemical reactions at each stage of the strength-gaining process, are to blame for this favorable alteration. however, compressive strength started to decline as the percentage of fine aggregate substituted with crusher run dust reached 45%, i.e., for mix cd30, and compressive strength continued declining as the percentage of crusher run dust grew in the mix. 5.2.2 split tensile strength the specimens' split tensile strength was evaluated following is 5816-1999 (is 5816, 1999). the average split tensile strength change for several specimens is shown in figure 5. for all blends, split tensile strength values increased from 7 days to 28 days. additionally, split tensile strength values for mix cd15 and dc30 were found to be greater than cm. due to the well-graded crusher-run dust particles' propensity to fill larger pores and take part in chemical reactions at each stage of the strengthgaining process, this noticeable variance was seen. however, as the substitution of fine aggregate with crusher run dust reached 30%, i.e., for mix cd30, split tensile strength decreased and continued to do so as the amount of crusher run dust in the mix increased. 5.2.3 flexural strength the specimens' flexural strength was evaluated following is 516-1959 (is 516, 1959) the average flexural strength variation for various specimens is depicted in figure 6. for all combinations, flexural strength values increased from 7 days to 28 days. in addition to having higher compressive and split tensile strengths than cm, it was determined that the cd15 and cd30 mix have higher flexural strengths. well-graded crusher-run dust particles, which have a propensity to fill pores on a bigger scale and take part in chemical reactions at each stage of the strength-gaining process, are to blame for this necessary alteration. however, the flexural strength of mix cd45 began to exhibit a fall when the amount ishwor thapa et al./ bibechana 21 (2024) 262-271 268 of crusher run dust in the mix reached 45%, and it continued to decrease as the percentage of crusher run dust in the mix increased. 5.2.4 porosity the specimens underwent a porosity test following astm c64 (2006) (astm c64, 2006). following a 28-day curing period, the porosity of concrete cylinders was assessed. as shown in figure 6, crusher run dust has better-graded particles than fine aggregate, which increases strength by lowering the proportion of invisible pores. the final data in figure 7 show that porosity values decrease up to 40.27% with an increase in replacement percentage at mix cd30; the lowest porosity value is attained. even though the porosity of the mixes cd15, cd45 and cd60 improved, the final porosity was still lower than the cm. figure 4: compressive strength and percentage increase in compressive strength in comparison to the control mix. figure 5: split tensile strength and percentage increase in split tensile strength in comparison to the control mix. ishwor thapa et al./ bibechana 21 (2024) 262-271 269 figure 6: flexural strength and percentage increase in flexural strength in comparison to the control mix. 5.2.5 multiple regression analysis multiple linear regression (mlr) analysis finds the line or curve best fitting a given data point set. due to its simplicity, a direct relationship is frequently used to resolve many technical challenges. when modeling and analyzing correlations between two or more variables in the fields of engineering and science, regression analysis is a statistical technique that is particularly helpful [15–19]. in this research work, an attempt is made to apply the multiple linear regression models to predict the compression(c), split tensile (st), and flexural strength (fs) of crusher run dust replaced concrete from slump value (sv) and porosity(p). the general representation of a probabilistic multiple linear regression model is presented in the following equation from equations (1-6). the provided multiple regression analysis equations serve as valuable tools in engineering for predicting the compressive, tensile and flexural strength of concrete at both early and long-term stages. the 7-day compression equation estimates the concrete's compressive strength after seven days, a critical parameter for assessing early performance. it considers input factors like slump value, which measures workability and porosity. on the other hand, the 28-day compression equation predicts the concrete's compressive strength after 28 days, signifying its long-term durability and structural integrity. similarly, equations 3 to 6 for st and fs follow the same pattern. these equations also incorporate the same input factors. these equations are instrumental for engineers in ensuring the quality and suitability of concrete mixes for specific construction applications, aiding in structural design and performance assessment. the experiment results showed a notable enhancement in the concrete's mechanical characteristics by substituting part of the fine aggregate with crusher-run dust. higher percentages of crusher run dust resulted in increased compressive strength, split tensile strength, and flexural strength, with peak values attained at a 30% substitution level. in particular, the compressive strength experienced a 4.93% increase, split tensile strength saw a 12.70% increase and flexural strength showed a 6.11% increase in comparison to the control mix, which is confirmed by [20–24] the improvements result from the well-graded crusher-run dust particles that better fill the gaps and aid in the chemical reactions for hydration. after surpassing a 30% replacement level, the mechanical properties started to decrease, suggesting there was an ideal replacement threshold. porosity examinations also confirmed these results, revealing a reduction in porosity of up to 30% when using replacements, which was closely linked to strength enhancement [25]. the research findings strongly support the advantages of incorporating crusher-run dust into concrete mixtures. this presents a sustainable and efficient substitute for natural sand that improves the strength and effectiveness of concrete buildings. ishwor thapa et al./ bibechana 21 (2024) 262-271 270 figure 7: average porosity (%) after 28 days. 6 conclusion the study presented a comprehensive analysis of the effects of curing time and fine aggregate substitution with crusher-run dust on the mechanical properties of concrete. firstly, the research demonstrated that the mechanical qualities of concrete exhibit significant enhancement as curing time increases from 7 to 28 days. this finding aligns with established concrete curing principles, highlighting the importance of allowing sufficient time for concrete to attain its maximum strength. moreover, the study identified a critical threshold at which a 30% substitution of fine aggregate with crusher run dust yielded maximum compressive strength, split tensile strength, and flexural strength, beyond which strength declined. this observation is vital for optimizing concrete mix designs, as it emphasizes the importance of balancing the use of crusher run dust to achieve the desired strength characteristics. additionally, the slump cone test results indicated that increased crusher run dust led to improved workability, substantiating the potential benefits of the fine aggregate replacement. the noteworthy increase of 4.93% in compressive strength, 12.70% in split tensile strength, and 6.11% in flexural strength when 30% fine aggregate was substituted with crusher run dust further underscores the practical advantages of this substitution in enhancing concrete's mechanical properties. in conclusion, this study provides valuable insights and engineering justifications for optimizing concrete mix designs by considering both curing time and the percentage of crusher-run dust substitution, ultimately leading to developing more durable and high-performance concrete structures. the results of this study have important consequences for both practical application and future research. essentially, adding crusher-run dust as a substitute for fine aggregate in concrete mixes is a practical and efficient way to enhance concrete's mechanical characteristics like compressive, tensile, and flexural strengths. this replacement improves concrete performance and encourages the use of industrial by-products, aiding in waste reduction and environmental sustainability within the construction sector. these findings reveal new opportunities for investigating the ideal ratios of crusherrun dust in different concrete mixes and use in future studies. additional research could examine the long-term durability of these modified concrete mixes and how they perform in various environmental conditions. moreover, examining the economic advantages and life-cycle evaluation of incorporating crusher-run dust into concrete manufacturing might offer an 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[24] m. dobiszewska et al. utilization of rock dust as cement replacement in cement composites: an alternative approach to sustainable mortar and concrete productions. journal of building engineering, 69:106180, jun 2023. introduction research significance materials cement and aggregate crusher run dust super plasticiser concrete experiment work preparation and testing of specimens mixture description results and discussion property of fresh concrete hardened properties of concrete compressive strength split tensile strength flexural strength porosity multiple regression analysis conclusion bibechana vol. 21, no. 2, august 2024, 113-123 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar phytochemical analysis and biological activities on solvent extracts of two traditionally used medicinal plants sangita pakka, akash budha magar, deepa shrestha, tinky sharma, khaga raj sharma∗ central department of chemistry, tribhuvan university, kirtipur, kathmandu ∗corresponding author. email: khaga.sharma@cdc.tu.edu.np abstract the plants buddleja asiatica and buddleja paniculata are two closely related species of which the former has widespread uses in traditional medicine while the latter remains relatively unexplored. the present study focused on the analysis of phytoconstituents and the estimation of different biological activities of extracts and semi-purified fractions. the ethyl acetate stem fraction and methanolic extract of the leaf of b. asiatica displayed the highest phenolic contents of 390.98 ± 5.32 and 383.72 ± 7.31 mg gae/g. tfc was measured as 207.33 ± 0.34 and 138.58 ± 0.53 mg qe/g for ethyl acetate leaf and stem fraction of b. asiatica. the highest antioxidant activity was displayed by crude stem extract of b. paniculata with ic50 35.65±0.61 µg/ml in dpph assay followed by ethyl acetate stem fraction of b. asiatica with ic50 36.17±0.92 µg/ml. the dcm leaf fraction and stem fraction of b. asiatica were found active against gram-negative and gram-positive bacteria. the median lethal concentration (lc50) in brine shrimp assay ranged from 346.96 ± 25.39 in hexane fraction of leaf to 2719.32 ± 706.5 µg/ml in crude methanol extract of b. paniculata. the present study showed these medicinal plants are rich in an important class of organic compounds that play a significant role in the cure of bacterial infection which ultimately supports pharmaceutical research. keywords buddleja asiatica, buddleja paniculata, antimicrobial, antioxidant, phytochemical, toxicity. article information manuscript received: december 30, 2023; revised: january 23, 2024; accepted: february 3, 2024 doi https://doi.org/10.3126/bibechana.v21i2.61208 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction plants have a huge importance in both traditional medicine and the modern health care system. the biological activities and therapeutic properties of medicinal plants are the results of specific or synergistic interactions of their secondary metabolites. these compounds are not required for central processes of growth and development in plants, but they are important for defense, signaling, symbiosis, metal transport, and competition [1]. they are synthesized through various biosynthesis pathways in plants [2]. about 200,000 plant secondary metabolites have been isolated and characterized with many more expected in the future [3]. specific sec113 http://nepjol.info/index.php/bibechana khaga.sharma@cdc.tu.edu.np https://doi.org/10.3126/bibechana.v21i2.61208 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ sangita pakka et al./ bibechana 21 (2024) 113-123 114 ondary metabolites may be exclusive to a particular species or group of species. the qualitative and quantitative composition of metabolites may vary within or between species and influenced by environmental stresses like nutrition, drought, temperature, and light [4]. genus buddleja belonging to the family scrophulariaceae includes more than 100 species that grow in temperate and drier regions of asia, africa, and america [5, 6]. these plants are mostly shrubs or small trees that can grow up to 5 m. buddleja species are used to treat bronchial complaints, liver diseases, and wounds and they are known to possess antimicrobial, antihyperglycemic, antioxidant activities, sedative functions, and, analgesic potential [6]. although buddleja has been used as a diuretic and topical antiseptic in traditional medicine, its phytochemical investigation has been somewhat neglected [7]. buddleja asiatica (bhimsenpati) and buddleja paniculata (narayanpati) are two species of the genus buddleja found in the kathmandu valley, nepal. b. asiatica is reported to have antihepatotoxic, antiinflammatory, analgesic, antipyretic, hypotensive, hypoglycemic, antimicrobial, neuroprotective, and anticataract properties [8]. it possesses chemical compounds like monoterpenoids, diterpenes, triterpenes, flavonoids, phenylpropanoids, and steroids [6]. a novel compound buddlin has been isolated from the plant [9]. b. asiatica is used as an additive in the preparation of fermentation starter culture in arunachal pradesh, india [10]. the leaf juice is used for treatment of gastrointestinal issues, skin conditions [11], abortifacient, cure for loss of weight [12], and, beverage fermentation [13]. root paste with rice water is used as a toner in burma [14]. in laos, the same procedure is applied to make a base for a medicine taken during childbirth, and leaves are used to treat headaches [15]. ullah et al., (2014) evaluated the cytotoxic and phytotoxic activities of b. asiatica which showed that the plant is safe for human consumption [16]. the leaves of b. paniculata are used by the indigenous chepang community of nepal in fermentation [17]. while many scholars have evaluated the biological activities and medicinal properties of b. asiatica, closely related species b. paniculata remains unexplored. the present work is a comparative study of qualitative and quantitative phytochemical analysis, antioxidant and antimicrobial, and cytotoxicity in methanol extracts and fractions of b. asiatica and b. paniculata. reactive oxygen species (ros) of both free radical and non-radical nature are produced inside the cell during mitochondrial oxidative phosphorylation or interaction with exogenous sources such as xenobiotic compounds [18]. they are involved in many signaling pathways and influence cell proliferation, necrosis, apoptosis, and gene expression in animal and host defense by programmed cell death that prevents the spread of invading pathogens in plants [19]. the steadily forming prooxidants (ros) are consumed by antioxidant molecules of enzymatic and nonenzymatic nature and a prooxidant-antioxidant equilibrium is maintained [20]. the imbalance in this equilibrium causes oxidative stress during which the highly reactive free radical can attack and cause structural damage to important biomolecules such as dna, proteins, carbohydrates, lipids, and enzymes [21]. oxidative stress promotes and assists development of various health issues including neurodegenerative diseases, diabetes, cancer, and cardiovascular diseases [22]. plant extracts and metabolites with rich antioxidant activity can prevent or delay the oxidation of substrate biomolecules and exert various health-promoting and therapeutic effects. although the exact mechanisms by which a given herbal medicine exerts its pharmacological effects are not established, most such medicinal plants are known to contain significant antioxidant activity [23]. adverse or side effects of synthetic drugs kill approximately 100,000 people in the usa each year and they are also responsible for about 8% of total hospital admission cases in the country [24]. although plant-based traditional medicines and secondary metabolites have far fewer side effects or toxicity than modern synthetic drugs due to their natural origin, they can potentially be toxic [23]. 2 materials and methods 2.1 plant collection and identification leaf and stem of b. asiatica and b. paniculata were collected from dakshinkali 1, champadevi, lalitpur, and bhaktapur 1, dudhapati, bhaktapur, nepal respectively in september 2021. the herbariums of the plant specimens were prepared and were identified at the central department of botany, tribhuvan university, kathmandu, nepal, having voucher no. tuch-210070 and tuch-210071 of b. asiatica and b. paniculata respectively. the photographs of fresh plants and herbarium are given in figure 1 and traditional uses of plants are listed in table 1. 2.2 extraction and fractionation he collected plant samples were cleaned and shade-dried up to a constant weight that was not attained. then, the plant samples were ground to powder using a mechanical grinder. 100 g of the powder was soaked with 300 ml of reagent-grade methanol solvent inside a conical flask. after 72 hours, the content in the flask was filtered using muslin cloth followed by whatman no 1 filter sangita pakka et al./ bibechana 21 (2024) 113-123 115 figure 1: (a) fresh plant sample b. asiatica (b) herbarium of plant sample b. asiatica (c) fresh plant sample of b. paniculata (d) herbarium of plant sample b. paniculata. paper. the filtrate was concentrated at a controlled temperature (40 c) and reduced pressure in a rotatory evaporator. the process was repeated after intervals of 48 hours and then 24 hours for maximum and complete extraction of phytochemicals. table 1: the plant samples used in the study, voucher number, and traditional medical uses s.n. scientific name identification no. altitude/plant growing plant parts traditional uses 1 buddleja asiatica tuch-210070 altitude-2180m leaves and stems fermentation [10, 13] coordinates27°38’ 57" n 85°17’ 58" e gastrointestinal issues, skin condition [11] abortifacient, cure for weight loss [12] toner [14] childbirth, headache [15] 2 buddleja paniculata tuch-210071 altitude-1996m leaves and stems fermentation [17] coordinates27°40’ 08" n 85°26’ 32" e 2.3 separation of semi-purified solvent fractions a series of reagent-grade solvents with increasing polarity (hexane, dcm, ethyl acetate, water) were used to separate the different solvent fractions of methanol extract. differences in the polarities of these solvents will result in the separation of plant secondary metabolites into different solvent fractions. thus, it will help isolate the active compound in future works. 20 g methanol extract was dissolved in 50 ml of distilled water in a separating funnel and an equal volume of hexane was added. the contents were shaken vigorously at first and then left undisturbed until a clear upper layer of hexane and lower layer of water formed and then both layers were collected in separate beakers. the hexane layer was concentrated in the rotary evaporator to obtain a hexane soluble fraction. the aqueous layer was subjected to further fractionation with dcm and ethyl acetate for the separation of dcm and ethyl sangita pakka et al./ bibechana 21 (2024) 113-123 116 acetate soluble fractions. 2.4 phytochemical analysis the phytochemical analysis of extracts and fractions was performed by following the procedures described by harborne (1998) and mallikharjuna et al. (2007) [25, 26]. the preliminary qualitative analysis for the presence and absence of secondary metabolites was carried out by the color differentiation method adopting separate protocols. 2.5 estimation of total phenolic content (tpc) phenolic content was measured using the folinciocalteu reagent method with slight modifications [27]. 20 µl each of different concentrations of standard (10 µg/ml to 100 µg/ml gallic acid solutions in methanol) and plant extracts (500 µg/ml in 50% dmso) were loaded in separate bores of a 96 well plate in triplicates. then, 100 µl folin-ciocaleu phenol reagent and 80 µl of na2co3 were added to each bore, and the well plate was placed in the dark. after 30 minutes, absorbance was taken at 765 nm using a microplate reader (synergy lx, biotek, instruments, inc., usa) with gene 5 software. tpc was calculated using the regression equation obtained from the gallic acid calibration curve and expressed as mg of gallic acid equivalent per gram dry extract or fraction (mg gae/g). 2.6 estimation of total flavonoid content (tfc) alcl3 colorimetric method as described by zhishen et al., (1999) was used to determine total phenolic content [28]. 130 µl of different concentrations of the standard (15.4 µg/ml to 154 µg/ml quercetin in methanol) and 20 µl of plant extracts (500 µg/ml in 50% dmso) were loaded in the bores of a 96-well plate in triplicates. 110 µl of distilled water was added to each bore containing plant extract. then, 60 µl of ethanol, 5 µl of alcl3, and 5 µl of ch3cook were added to each bore, and the well plate was placed in the dark. after 30 minutes, absorbance was taken at 415 nm using the microplate reader. tfc was calculated using the regression equation from the quercetin calibration curve and expressed in terms of milligrams of quercetin equivalent per gram dry extract or fraction (mg qe/g). 2.7 antioxidant activity dpph assay was employed to determine the antioxidant activity of plant extracts and fractions by following standard protocol [29]. 100 µl each of different concentrations of plant extracts and fractions (15.625 µg/ml to 500 µg/ml in 50% dmso) were loaded in triplicates to the bores of a 96-well plate. 100 µl of 0.1 mm dpph solution was added to each bore. the reaction mixture was placed in the dark for 25 minutes and absorbance was taken at 517 nm using the microplate reader. quercetin was used as standard and 50% dmso was used as control. the relationship given below was used to calculate the percentage of radical scavenging. graphpad prism 9 software was used to calculate the concentration of plant extract that scavenges 50% of the available free radical (ic50). 2.8 antibacterial assay the agar well diffusion method was used to measure the antibacterial activity in extracts and fractions [30]. the types of bacteria and their atcc numbers are given in table 2. overnight incubated broth cultures of test organisms were prepared in nutrient broth media. the concentration of bacteria was diluted and maintained at 0.5 mcfarland standard (106-8 cfu/ml). 100 µl of inoculum was spread on muller hinton agar (mha) plates and wells having 7 mm of diameter were bored on the plates. 20 µl of 25 mg/ml (in dmso) plant extracts were added to the bores in triplicates. then, the plates were incubated at 37 c, and the zone of inhibition (zoi) was measured after 24 hours. 100% dmso was used as control and 1 mg/ml ampicillin was used as standard. table 2: bacterial strain, type, and atcc number of test organisms bacterial strain type atcc staphylococcus aureus gram-positive 25923 bacillus subtilis gram-positive 35021 escherichia coli gram-negative 25922 klebsiella pneumoniae gram-negative 700603 2.9 antifungal activity the agar well diffusion method was used to measure the antifungal activity in plant extracts [30]. overnight incubated broth culture of test organisms fusarium solani (atcc 11712) was prepared in nutrient broth media and concentration sangita pakka et al./ bibechana 21 (2024) 113-123 117 was maintained at 0.5 mcfarland standard. 100 µl of inoculum was spread on potato dextrose agar (pda) plates and wells having 7 mm of diameter were bored. 20 µl of 25 mg/ml plant fraction solutions were added in triplicates to those bores. the plates were incubated at 37 c and zoi was measured after 48 hours. 100% dmso was used as control and 20 mg/ml cycloheximide was used as standard. 2.10 toxicity the toxicity of plant fractions was measured by using the brine shrimp assay [31]. 2 ml of each of the different concentrations of plant fractions (10, 100, 1000 µg/ml in methanol) was added in triplicates to test tubes. the solvent was evaporated using a water bath. the leftover residue in the test tube was dissolved using 5 ml of artificial seawater followed by the addition of 10 brine shrimp nauplii. the number of live nauplii was counted after 24 hours. the concentration of plant extracts lethal to 50% of the organism (lc50) was calculated from the percentage mortality versus concentration curve. 100% methanol was used as a control. 2.11 statistical analysis all the experiments were performed in triplicates. values were presented as mean ± standard error (se). comparisons were made using one-way anova followed by tukey’s test performed with spss version 29 software. values with p < 0.05 were considered statistically different. 3 results 3.1 phytochemical analysis the results of qualitative phytochemical analysis of the crude extracts are given in table 3. alc, b. asiatica crude leaf extract; asc, b. asiatica crude stem extract; plc, b. paniculata crude leaf extract; psc, b. paniculata crude stem extract; ‘+’, present; ‘-‘, absent. important phytochemicals such as polyphenols, flavonoids, and quinones are observed in the leaf and stem extracts of both plants. alkaloids were present only in leaf extracts and terpenoids were exclusive to the stem. the absence of coumarin in plc and glycoside in psc was recorded. table 3: qualitative phytochemical analysis of crude extracts group of compounds alc asc plc psc polyphenols + + + + alkaloids + + coumarins + + + glycosides + + + quinones + + + + flavonoids + + + + terpenoids + + alc, b. asiatica crude leaf extract; asc, b. asiatica crude stem extract; plc, b. paniculata crude leaf extract; psc, b. paniculata crude stem extract; ‘+’, present; ‘-‘, absent. 3.2 phytochemical analysis the total phenolic content and flavonoid content were measured using the folin-ciocalteu phenol reagent method and aluminum chloride colorimetric method respectively and the results are provided in table 4. the observed phenolic content ranged from 39.5 ± 1.18 in plc to 390.98 ± 5.32 mg gae/g in ase. the descending order of tpc in crude extracts and solvent fractions is 390.98 ± 5.32 (ase) > 383.72 ± 7.31 (alc) > 374.32 ± 5.72 (asd) > 295.57 ± 0.54 (asc) > 271.58 ± 5.83 (psc) > 177.05 ± 7.91 (pld) > 131.34 ± 3.82 (ale) > 93.6 ± 3.97 (ald) > 60.39 ± 3.48 (plh) > 39.5 ± 1.18 mg gae/g (plc). the measured amount of flavonoid content ranged from 13.44 ± 0.18 in pld to 207.33 ± 0.34 mg qe/g in ale. the descending order of tfc in crude extracts and fractions is 207.33 ± 0.34 (ale) > 138.58 ± 0.53 (ase) > 43.33 ± 0.14 (alc) > 42.48 ± 1.09 (asc) > 40.58 ± 0.58 (plc) > 37.22 ± 0.19 (psc) > 30.96 ± 0.18 (plh) > 15.41 ± 0.44 (ald) > 13.89 ± 0.32 (asd) > 13.44 ± 0.18 mg qe/g (pld). tpc and tfc values are graphically presented in figure 2 and figure 3. 3.3 antioxidant properties the antioxidant activity of the plant extract was measured using dpph assay. concentrationdependent increments in the percentage of free radical scavenging are observed (figure 4). the concentration of plant extract or fraction that scavenges 50% of available free radical (ic50) sangita pakka et al./ bibechana 21 (2024) 113-123 118 table 4: tpc, tfc, and half maximal inhibitory concentration (ic50) in dpph assay of plant extracts and fractions plant extracts and fractions tpc (mg gae/g) tfc (mg qe/g) ic50 (/) alc 383.72 ± 7.31a,b 43.33 ± 0.14a 51.91 ± 1.09 ale 131.34 ± 3.82 207.33 ± 0.34 139.70 ± 2.30 ald 93.6 ± 3.97 15.41 ± 0.44b,c 119.91 ± 0.41 asc 295.57 ± 0.54c 42.48 ± 1.09a,d 71.86 ± 1.67 ase 390.98 ± 5.32a,d 138.58 ± 0.53 36.17 ± 0.92a asd 374.32 ± 5.72b,d 13.89 ± 0.32b,e 83.59 ± 1.57 plc 39.5 ± 1.18e 40.58 ± 0.58d 374.7 ± 0.55 pld 177.05 ± 7.91 13.44 ± 0.18c,e 177 ± 0.72 plh 60.39 ± 3.48e 30.96 ± 0.18 315.3 ± 0.45 psc 271.58 ± 5.83c 37.22 ± 0.19 35.65 ± 0.61a quercetin # # 3.28 ± 0.89 ale, b. asiatica ethyl acetate leaf fraction; ald, b. asiatica dichloromethane leaf fraction; ase, b. asiatica ethyl acetate stem fraction; asd, b. asiatica dichloromethane stem fraction; pld, b. paniculata dichloromethane leaf fraction; plh, b. paniculata hexane stem fraction; * positive control; #, value not measured; values are the mean ± se (n=3); values marked by the same letter within the same column are not significantly different at p < 0.05. ranged from 35.65±0.61 in psc to 315.30±0.45 µg/ml in plc (table 4). the decreasing order of antioxidant activity is 35.65±0.61 (psc) > 36.17 ± 0.92 (ase) > 51.91 ± 1.09 (alc) > 71.86 ± 1.67 (asc) > 83.59 ± 1.57 (asd) > 119.91 ± 0.41 (ald) > 139.70 ± 2.30 (ale) > 177 ± 0.72 (pld) > 315.3 ± 0.45 (plh) > 315.30±0.45 µg/ml (plc). the ic50 values for extract and fractions were higher than 3.28 ± 0.89 µg/ml recorded for quercetin. figure 2: total phenolic content (mg gae/g) of plant extracts and solvent fractions. sangita pakka et al./ bibechana 21 (2024) 113-123 119 figure 3: total flavonoid content (mg qe/g) of plant extracts and solvent fractions. figure 4: percentage radical scavenging versus concentration (µg/ml) of plant extracts and solvent fractions. 3.4 antimicrobial properties the antibacterial and antifungal potential exhibited by the crude extracts and the solvent fractions is shown in table 5. the antibacterial activities of plant extracts were tested against an american-type culture collection of gram-positive and gram-negative bacteria. the dichloromethane fraction of the stem of b. asiatica displayed zois of 8.33 ± 0.67 mm against s. aureus and 8.33 ± 0.33 mm against k. pneumoniae. similarly, the dichloromethane fraction of the leaf of the plant displayed a zoi of 8.67 ± 0.33 mm against s. aureus. other extracts and solvent fractions did not display significant zoi. zoi of 27.5 ± 0.25 mm, 13 mm, 16.5 ± 1.25 mm, and 22 ± 0.5 mm were recorded against s. aureus, b. subtilis, e. coli, and k. pneumoniae for ampicillin used as positive standard. plant extracts and solvent fractions were found to be inactive against fungal species f. solani but the cycloheximide used as a standard displayed a zoi of 17.5 mm. the photographs of petri plates from the antimicrobial assay are given in figure 5. alc = b.asiatica crude extract, asc = b. asiatica crude stem extract, plc = b. paniculata crude leaf extract, psc = b. paniculata crude stem extract, ale = b. asiatica sangita pakka et al./ bibechana 21 (2024) 113-123 120 table 5: zone of inhibition (zoi) shown by the plant extracts and solvent fractions against bacterial and fungal strains plant extracts and fractions zoi (mm) of plant extracts and fractions s. aureus b. subtilis e. coli k. pneumoniae f. solani alc # ale # ald 8.33 ± 0.33a asc # # ase asd 8.33 ± 0.67a 8.67 ± 0.33a # plc # # pld # plh # psc # ampicillin* 27.5 ± 0.25 13 16.5 ± 1.25 22 ± 0.5 # cycloheximide* # # # # 17.5 values are the mean ± se (n=3); * positive control; -, no significant zoi; #, value not measured; a p < 0.05 versus ampicillin. ethyl acetate leaf fraction, ald = b. asiatica dichloromethane leaf fraction, ase = b. asiatica ethyl acetate stem fraction, pld = b. paniculata dichloromethane leaf fraction, plh = b. paniculata hexane stem fraction; 3.5 toxicity the results of the toxicity analysis of the crude extracts and the solvent fractions of the plants are displayed in table 6. the assay revealed the non-toxic to mildly toxic nature of plant extracts and the solvent fractions. values are the mean ± se (n=3); a p < 0.05 versus psc. the lc50 value ranged from 346.96 ± 25.39 in plh to 2719.32 ± 706.5 µg/ml in psc. the descending order of toxicity can be presented as 346.96 ± 25.39 (plh) > 353.68 ± 83.62 (ase) > 472.95 ± 51.36 (pld) > 540.46 ± 39.87 (asd) > 824.48 ± 103.54 (ale) > 971.34 ± 253.48 (alc) > 1074.83 ± 115.76 (asc) > 1362.93 ± 393.21 (ald) > 1366.7 ± 258.69 (plc) > 2719.32 ± 706.5 µg/ml (psc). table 6: half maximal lethal concentration (lc50) shown by plant extracts and solvent fractions against brine shrimp nauplii plant extracts and fractions lc50 (µg/ml) alc 971.34 ± 253.48a ale 824.48 ± 103.54a ald 1362.93 ± 393.21 asc 1074.83 ± 115.76a ase 353.68 ± 83.62a asd 540.46 ± 39.87a plc 1366.7 ± 258.69 pld 472.95 ± 51.36a plh 346.96 ± 25.39a psc 2719.32 ± 706.5 values are the mean ± se (n=3); a p < 0.05 versus psc. 4 discussion the observed results were supported by previous studies as the presence of phenols, flavonoids, glycosides, and terpenoids in the leaf of b. asiatica was reported by sai et al., (2019) and nafees et al., (2022) [13, 32]. among different plant secondary metabolites, phenolics are a large group of phytochemicals that includes a diverse family of compounds such as phenolic acids, flavonoids, phenylpropanoids, quinones, tannins, lignins, and hydroxycinammic acids [33]. among sangita pakka et al./ bibechana 21 (2024) 113-123 121 them, flavonoids are involved in pigmentation, signaling, plant growth and development, and plant defense mechanisms [34]. the significance of phenolics in the modern drug discovery process is illustrated by the fact that 17 out of 29 small molecules approved by the federal drug administration, usa in 2020 contained phenol moieties [35]. the crude methanol extracts and solvent fractions of b. asiatica and b. paniculata are found rich in phenolic and flavonoid contents but significant variations were observed between the two plant species and their crude extracts and fractions. crude extracts of b. asiatica possessed higher phenolic content than crude extracts of b. paniculata. stem extracts and fractions contained more phenolics than their corresponding leaf extract. the concentration of phenolics was higher in more polar solvent ethyl acetate 131.34 ± 3.82 (ale), 390.98 ± 5.32 (ase) than in less polar solvent dimethyl chloride 93.6 ± 3.97 (ald), 374.32 ± 5.72 mg gae/g (asd). similarly, more polar fraction pld contained higher phenolic compounds than plh. the ability of a more polar solvent to extract a higher amount of phenolic content is also mentioned by khanal et al., (2022) in bark extracts of beilschmiedia roxburghiana [36]. sai et. al., (2019) reported a tpc of 127.48±1.58 mg gae/g for 80% ethanol extracts of b. asiatica leaves [13]. the biological activities of phenolics, flavonoids, alkaloids, and terpenoids in the plant should be responsible for the traditional use of b. asiatica in gastrointestinal issues, childbirth, headache, skin conditions, weight loss, cancer, and diabetes [8, 11, 12, 15]. similar to phenolic contents, the flavonoid content was found to be higher in crude extracts of b. asiatica than in b. paniculata. also, the concentrations of flavonoids were higher in crude extracts and fractions of leaves than in stems. this is expected as high concentrations of flavonoids are reported in uv-exposed mesophyll cells that seem to act as protection for chloroplast from photo-oxidative damage [37]. more polar ethyl acetate contained significantly higher tfc 207.33 ± 0.34 (ale), 138.58 ± 0.53 (ase) than less polar dimethyl chloride 15.41 ± 0.44 (ald), 13.89 ± 0.32 mg qe/g (asd). sai et al., (2019) reported a tfc of 648.42±2.88 µg/ml for 80% ethanol extract of the leaf of b. asiatica [13, 33]. extracts and fractions with higher phenolic and flavonoid content displayed more antioxidant activity. phenolic compounds donate hydrogen atoms from their hydroxyl group and form stable, unreactive antioxidant radicals [38]. the antioxidant activity of such compounds depends upon the number and position of the hydroxyl group [39]. in addition to phenolics, el-sayed et al., (2008) isolated non-phenolic antioxidant compounds from the methanol extract of the leaf of b. asiatica [40]. previous scholars have reported ic50 values of 3.04±0.04 µg/ml for 80% ethanol extract and 16.28 µg/ml for methanol extract of the leaf of b. asiatica [13, 40]. the present and past studies confirm the presence of high antioxidant activity in b. asiatica and b. paniculata. antioxidant compounds present in medicinal plants prevent oxidation, which is the initial step of many neurodegenerative diseases and cancers [41]. they also reduce the risk of diabetes and cardiovascular diseases [22]. high antioxidant activity in b. asiatica and b. paniculata could be responsible for the traditional uses of the plants as anticancer, antidiabetic, and neuroprotective medicine [42, 43]. the plant is also used for the treatment of rheumatism in china [16]. the significant antioxidant activity in b. asiatica and b. paniculata makes them valuable medicinal plants. only the dichloromethane fractions of the leaf and stem of b. asiatica displayed significant zoi. both plants do not possess significant activity against b. subtilis, e. coli, and f. solani in the present study. the lack of zoi against k. pneumoniae for methanol extract of b. asiatica in the present study is in agreement with the study conducted by ali et al., (2011) in which no zoi was observed against k. pneumoniae for methanolic extract, hexane, and ethyl acetate fractions of whole plant, but the zois of 15 and 5 mm observed against e. coli and b. subtilis was different from the present study [12]. the essential oil of the whole plant was reported to be active against bacterial species e. coli, b. subtilis, and s. aureus and, fungal species f. solani [44]. the accumulation and concentration of plant secondary metabolites depend upon plant growth and development stage, genetics, and environmental stress such as radiation, drought, temperature, and salinity [45]. the antimicrobial activity of plant extract and fractions is subject to change with the presence or absence of specific metabolites, their concentration, and synergistic interactions. crude extracts of b. asiatica were more toxic than that of b. paniculata. the lc50 value of 971.34 ± 253.48 µg/ml for alc was higher than the reported value of 469.63 µg/ml for ethanol extract of b. asiatica leaves [16]. the same study also reported higher toxicity in leaf than bark extracts in agreement with higher toxicity in alc than asc observed in the present study. a good correlation between acute toxicity and the results of the brine shrimp lethality assay has been established in previous studies [46]. thus, the absence of toxicity means it is potentially safe for humans. 5 conclusion stem and leaf of b. asiatica and b. paniculata displayed the presence of secondary metabolites such as polyphenols, flavonoids, quinones, alkaloids, coumarins, glycosides, and terpenoids. plant extracts and solvent fractions of both plants are rich in phenolics and flavonoids and they also sangita pakka et al./ bibechana 21 (2024) 113-123 122 display significant antioxidant activity. the concentration of phenolics and flavonoids was found higher in polar solvents than in less polar ones. there is a weak correlation between phenolic and flavonoid concentration against antioxidant activity. the dichloromethane fraction of the leaf and stem of b. asiatica was found active against both gram-positive and gram-negative bacterial strains. both plants were found inactive against the fungal species f. solani. the plant extracts and solvent fractions displayed low toxicities against the brine shrimp nauplii. thus, the plants are safe for use as a source for isolating natural antioxidants rich in secondary metabolites. the crude extracts of b. asiatica displayed higher tpc and tfc along with the potential antibacterial 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[46] l. a. parra, r. s. yhebra, a. g. sardiñas, and l. i. buela. comparative study of the assay of and the estimate of the medium lethal dose (ld50 value) in mice, to determine oral acute toxicity of plant extracts. phytomedicine, 8 (5): 395–400, 2001. introduction materials and methods plant collection and identification extraction and fractionation separation of semi-purified solvent fractions phytochemical analysis estimation of total phenolic content (tpc) estimation of total flavonoid content (tfc) antioxidant activity antibacterial assay antifungal activity toxicity statistical analysis results phytochemical analysis phytochemical analysis antioxidant properties antimicrobial properties toxicity discussion conclusion bibechana vol. 21, no. 1, april 2024, 23–36 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar an investigation of vibrational analysis, thermodynamics properties and electronic properties of formaldehyde and its stretch by substituent acetone, acetyl chloride and methyl acetate using first principles analysis susmita limbu, tulsi ojha, rishi ram ghimire, krishna bahadur rai∗ department of physics, patan multiple campus,tribhuvan university, nepal ∗corresponding author. email: krishna.rai@pmc.tu.edu.np abstract this study finds the equilibrium configuration, vibrational analysis, thermodynamic properties, and electronic properties of formaldehyde and its derivatives, namely acetone, acetyl chloride, and methyl acetate, using first principles analysis. it emphasizes the impact of substituents on the carbonyl group and the need for this comprehensive analysis. the computational methods employed in this work are gaussian dft, gausssum and moltran calculations. for formaldehyde, the optimization step starts from the energy of -114.51282 hartree and gets optimized in the energy -114.5129634 hartree. similarly for acetone, acetyl chloride and methyl acetate, optimization step start from -193.74375 hartree, -613.26 hartree, -266.805 hartree and gets optimized in the energy -193.1744033 hartree, -613.2941798 hartree, 266.8358066 hartree respectively. infrared (ir) spectroscopy is used to analyze vibrational frequencies. the c-h and c=o vibrations are highlighted, showing characteristic peaks for each compound. heat capacity at constant volume, heat capacity at constant pressure, internal energy, enthalpy, entropy and gibb’s free energy change with change in temperature. among the derivative of formaldehyde, methyl acetate has the highest energy gap (i.e. 7.4222 ev) and acetyl chloride has the small energy gap (i.e. 5.6137 ev). the chemical parameters like ionization potential, electron affinity, chemical hardness, chemical potential, electronegativity, electrophilicity index, and chemical softness have been also calculated. electrostatic potential surfaces, molecular electrostatic potential, and electron density are visualized to understand charge distribution and reactivity regions. density of state spectra illustrate the density of electron states per unit energy. keywords density functional theory, electrostatic potential, homo-lumo, ir spectroscopy, thermodynamic properties, density of state. article information manuscript received: september 20, 2023; revised: december 10, 2023; accepted: december 16, 2023 doi https://doi.org/10.3126/bibechana.v21i1.58684 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 23 http://nepjol.info/index.php/bibechana krishna.rai@pmc.tu.edu.np https://doi.org/10.3126/bibechana.v21i1.58684 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ susmita limbu et al./ bibechana 21 (2024) 23-36 24 1 introduction formaldehyde is the first of the series of aliphatic aldehyde. it was discovered by butlerov in 1859 and has been manufactured since the beginning of the twentieth century. at ordinary temperature formaldehyde is colorless gas with pungent odor. because of its relatively low cost, high purity and variety of chemical reactions, formaldehyde has become one of the world’s most important industrial and research chemical. its biggest use is in the production of industrial resins, urea-formaldehyde, phenol formaldehyde and melamine form aldehyde [1–3]. formaldehyde (hcho) is a simple organic compound consisting of a carbon atom bonded to two hydrogen atoms with single bond and an oxygen atom with the carbon atom in the center, forming a carbonyl group (c=o). when the formaldehyde has its stretch by substituent acetone, acetyl chloride, and methyl acetate, the number of effects on the vibrations, electronic and thermodynamic properties appear on the carbonyl group (c=o). acetone (ch3coch3) is colorless highly volatile and flammable liquid with pungent ordor. acetyl chloride (ch3cocl) is a reactive and corrosive. methyl acetate (ch3cooch3) also known as acetic acid methyl ester or methyl ethanoate. it is colorless, flammable liquid with a fruity ordor. it is used in manufacture of flavors, fragrances and pharmaceuticals [4–6]. the presence of the methyl (ch3) groups on both sides of the carbonyl group forms the acetone. acetyl chloride is an acyl chloride, which contains a carbonyl group attached to a chlorine atom. methyl acetate is an ester, which contains a carbonyl group bonded to an oxygen atom. gustav e. lienhard and william p. jencks investigate the kinetics and mechanisms of thiol addition to carbonyl compounds, forming hemithioacetals and hemithioketals [7]. carbonyl compounds are commonly found both outdoors and indoors. their polar nature, stemming from the oxygen atom’s high electronegativity, enables a wide range of chemical reactions. moreover, the presence of substituents and conjugated double bonds further shapes their physical and chemical characteristics [8]. the substituent additivity effects in adiabatic ionization energies imply that cation molecular orbitals are not directly related to those of the neutral molecule [9]. laurence et al., investigated the impact of substituents on the basicity of carbonyl compounds through various measurements including enthalpy changes in iodine complex formation, solvent sensitivity and carbonyl stretching vibrations. the enthalpic basicity exhibited a strong correlation with protonation scales. the cumulative impact of substituents showed additive effects for enthalpy. the study concluded that inductive effects predominantly influence the basicity of carbonyl groups towards iodine [10]. an investigation that has not been performed previously regarding the equilibrium configuration, vibrational analysis, thermodynamics properties, and electronic properties of formaldehyde and its stretch by substituents acetone, acetyl chloride, and methyl acetate using first principles analysis is now essential and important for further study. therefore, this study aims to gain a deep understanding of the molecular behavior and the effects of substituents on the geometry optimization, vibrational analysis, thermodynamic properties [specific heat capacity at constant volume (cv), specific heat capacity at constant pressure (cp), internal energy (u), enthalpy (h), entropy (s) and gibb’s free energy (g) with change in temperature], highest occupied molecular orbitals (homo) and lowest unoccupied molecular orbitals (lumo) analysis, global reactivity descriptor, electrostatic potential (esp) surfaces, molecular electrostatic potential (mep), electron density (ed) and density of states (dos) of formaldehyde and its derivatives, namely acetone, acetyl chloride, and methyl acetate using density functional theory (dft) with b3lyp/6311+g(d ′ ,p ′ ) basis set together with gausssum 3.0.2 and moltran. dft method is used due to their ability to accurately describe molecular structures, vibrational spectra and other different specific characteristics and properties of title molecules. b3lyp is hybrid functional mostly used in dft and has the exchange correlation energy function in dft that incorporate a portion of exact exchange from hartee-fock theory with the rest of the exchange correlation energy from other sources. it provides accuracy for a wide range of molecular system. 6-311+g(d ′ ,p ′ ) is a basis set relatively large and includes polarization and diffuse function. it allows more accurate representation of electron density around atoms specially for the system with heavy atoms. it is the standard, split valence triple zeta basis set. its function describes the core and valence orbitals. the core orbital is a contracted gaussian type orbital made of six gaussians and the valence orbital is described by two orbitals, one contracted gaussian type orbital made of three gaussians and two gaussian type orbitals. in this study, 6-311g(d ′ ,p ′ ) is 6-311g basis set with added ’d’ polarization functions on non-hydrogen atoms and ’p’ polrizations for hydrogen. thus, it also describes a diffuse s and p functions for nonhydrogen atoms. triple zeta has much finer result than that of double zeta basis sets and is more accurate. sometimes, convergence of ab initio results is disappointingly slow with respect to basis set for non-dft methods. dft is less dependent on basis set size than wave function based method. susmita limbu et al./ bibechana 21 (2024) 23-36 25 2 methodology – computational details geometric optimization is an important in molecular mechanics. it was performed as a first task of the computational work for the formaldehyde and its substitute (acetone, acetyle chloride, methyl acetate). the optimized geometry, vibrational frequency, homo-lumo analysis and global reactivity descriptor of given molecules were computed employing the density functional theory (dft) method using gaussian 09w software program [11] employing 6-311+g(d ′ ,p ′ ) basis set based on becke’s three parameter (local, non-local, hartreefock) hybrid exchange functional with leeyang pair correlation functional b3lyp [12,13] at charge value zero. gaussian calculation is the best prepared using gauss view 6.0 interface. gaussian 09w is a general-purpose ab initio electronic structure package which can predict many properties of molecule and reaction pathways based on various uncorrelated and correlated wave function. after processing gaussian, the .log file and .chk file obtained from gaussian used to generate various surface representation and to observe various result [14]. the basis set used here is the 6-311+g(d ′ ,p ′ ) augmented by ‘d’ polarization functions on heavy atom and ‘p’ polarization functions on hydrogen atom as well as diffuse function for both hydrogen and heavy atoms [15]. thermodynamic parameter such as heat capacity at constant volume (cv), heat capacity at constant pressure (cp), entropy (s), internal energy (u), enthalpy (h), entrophy (s) and gibb’s free energy (g) were calculated using moltran software. in addition to this, gausssum 3.0.2 was used to calculate the density of states (dos). 3 results and discussion 3.1 geometry optimization geometry optimization is a method to predict the three-dimensional arrangement of the atoms in a molecules with minimum energy [16]. it is the first task to do while performing the computational work for the given molecules. figures 1(a) (b) (c) and (d) show the optimized structure, symbol and numbering of atoms of formaldehyde, acetone, acetyl chloride, methyl acetate. listed figures 1(a) (b) (c) and (d) are from the dft calculation and they have their respective total energy versus optimization step number in optimization state. for formaldehyde, the optimization step starts from the energy of -114.51282 hartree and gets optimized in the energy -114.5129634 hartree. similarly for acetone, acetyl chloride and methyl acetate, optimization step start from -193.74375 hartree, -613.26 hartree, -266.805 hartree and gets optimized in the energy -193.1744033 hartree, -613.2941798 hartree, -266.8358066 hartree respectively [17]. 3.2 vibrational analysis ir spectroscopy or vibrational spectroscopy is a tool for the measurement of interaction of infrared radiation with matter by absorption, emission or reflection. basic principle of it states molecules absorb specific frequencies that are characteristics of their structure. the interaction of the matter in infrared radiation signifies the ir spectroscopy and its spectrum shows the relationship between frequency and wave length of the infrared light (transmittance or absorption) [18]. the greater the frequency of oscillation of chemical bond, greater is the wavenumber. by using ir spectrum, it is distinguished that which chemical bond and possible functional group oscillates with how much of specific frequency that corresponds to certain amount of energy. c-h vibrations most organic molecules contain alkane residues and their general appearance can be seen in the infrared spectrum. figure 2 is the ir spectrum of formaldehyde and it reveals the presence of h-ch in-plane scissoring stretching at 2910.1248 cm−1, c-h asymmetric stretching at 1257.5142 cm−1, ch symmetric stretching at 1528.7213 cm−1, h-ch out-of-plane wagging at 1190.7995 cm−1. figure 3 is the ir spectrum for acetone having ch asymmetric stretching at 3161.0988 cm−1, h-ch assymetric stretching at 3105.5663 cm−1, c-h symmetric stretching at 3039.159 cm−1, c-h inplane scissoring at 1382.2427 cm−1 and c-c-c-h in plane rocking at 1234.2899 cm−1. figure 4 is the ir spectrum of acetyl chloride, having c-h asymmetric stretching at 3331.3231 cm−1 and 2201.8905 cm−1, c-c-h in-plane rocking at 282.2516 cm−1. figure 5 is the ir spectrum of methyl acetate having c-h asymmetric stretching at 3179.0767 cm−1, 3122.3869 cm−1, 3041.8403 cm−1, h-c-h in-plane scissoring at 1393.9274 cm−1, h-c-h out-of-plane wagging at 999.1881 cm−1. c=o vibrations the carbon-oxygen double bond formed by π − π between carbon and oxygen, and the lone pair of electrons on oxygen also determines the nature of carbonyl group. the c=o stretching is a characteristic wavenumber of carboxylic acid. the carbonyl c=o stretching vibrational mode is expected to occur in the region 1680–1715 cm−1. figure 2 is the ir spectrum of formaldehyde and it shows c=o stretching at 1816.9839 cm−1. figure 3 is the ir spectrum for acetone and it has c=o stretching at 1789.4345 cm−1. in figure 4, spectrum for c=o stretching at 1747.0313 cm−1 is obtained for acetyl chloride. figure 5 is the ir spectrum of methyl acetate showing c=0 stretching at 1821.1828 cm−1. susmita limbu et al./ bibechana 21 (2024) 23-36 26 c-o-c vibration c-c-o-c in-plane scissoring is observed at 788.341 cm−1 and c-o-c stretching at 1089.4461 cm−1 for methyl acetate is as shown in figure 5. c-cl vibrations figure 4 shows c-cl stretching of acetyl chloride molecule at 483.3359 cm−1. therefore, ir spectroscopy is used for the detailed discussion of structural changes in the given molecule. structural changes affect their vibrational spectra and provide information about the vibrational modes, vibrational frequencies and intensities of these modes. in a molecule, atoms are connected by chemical bonds, and these bonds have associated vibrational modes. the vibrational frequencies depend on factors such as bond strength, bond length, and mass of the atoms involved. when the structure of the molecule changes, the vibrational modes are influenced due to bond stretching, bending, or the introduction of new functional groups. by analyzing the vibrational spectra of a molecule, we can gain insights into its structure and chemical environment. changes in vibrational frequencies due to structural modifications can impact the entropy term in the gibbs free energy equation (∆g = ∆h t∆s) and heat capacity of the system. changes in bond strengths due to alterations in molecular structure affect the enthalpy of a reaction. the enthalpy change (∆h) is composed of contributions from bond energies and vibrational energies. stronger or weaker bonds, as indicated by shifts in vibrational frequencies, influence the enthalpy aspects of a chemical reaction. thermodynamic properties are also connected to the equilibrium constants of reactions. alterations in molecular structure, reflected in vibrational spectra, can affect the position of equilibrium by influencing the enthalpy and entropy changes. figure 1: optimized structure of (a) formaldehyde (b) acetone (c) acetyl chloride and (d) methyl acetate. figure 2: ir spectroscopy for neutral formaldehyde molecule by dft method. susmita limbu et al./ bibechana 21 (2024) 23-36 27 figure 3: ir spectroscopy for neutral acetone molecule by dft method. figure 4: ir spectroscopy for neutral acetyl chloride molecule by dft method. figure 5: ir spectroscopy for neutral methyl acetate molecule by dft method. susmita limbu et al./ bibechana 21 (2024) 23-36 28 3.3 thermodynamic analysis the formaldehyde, acetone, acetyl chloride and methyl acetate molecules taken for this thermodynamic properties analysis are based on the output file of dft calculation with b3lyp/6-311+g (d ′ ,p ′ ) basis set. moltran software was employed in computing thermodynamic parameters of formaldehyde, acetone, acetyl chloride, methyl acetate. on the basis of vibrational analysis, the thermodynamic parameter such as entropy (s), enthalpy (h), gibbs free energy (g), internal energy (u), heat capacity at constant volume (cv), heat capacity at constant pressure (cp) were obtained. while performing dft calculations the molecules was considered to be at room temperature of 298.15 k and one atmospheric pressure. figures 6, 7, 8 and 9 show the different values of thermodynamic parameters for formaldehyde, acetone, acetyl chloride, methyl acetate respectively and these depict the correlation of heat capacity at constant volume (cv), heat capacity at constant pressure (cp), internal energy (u), enthalpy (h), entropy (s) and gibb’s free energy (g) with temperature. all the entropies (s) for all the given molecules sharply increase from 10 k to 50 k and decreases the increase in rate from 50 k to 500 k. parameters such as cv, cp, u and h except g increase relentlessly with temperature going from 10 k to 500 k. these increase in thermodynamic parameters are due to enhancement of the molecular vibration intensities with increment in temperature. however, g in all the figures 6, 7, 8, and 9 decrease with increase in temperature. it is because of the g depends upon the s and as the s increases g decreases [19]. s changed shows that the atom has greater adaptability of changing its own thermodynamic system regarding the temperature [20]. the g represents the energy that is free to do useful work for spontaneous process. the s and h changes revealed that the tittle compound possess more flexibility of changing its own thermodynamic system with respect to the temperature. figure 6: correlation plot of the thermodynamic properties at different temperature of the formaldehyde. susmita limbu et al./ bibechana 21 (2024) 23-36 29 figure 7: correlation plot of the thermodynamic properties at different temperature of the acetone. figure 8: correlation plot of the thermodynamic properties at different temperature of acetyl chloride. figure 9: correlation plot of the thermodynamic properties at different temperature of the methyl acetate. susmita limbu et al./ bibechana 21 (2024) 23-36 30 3.4 homo-lumo analysis the electronic transition corresponds from homo (characterizes of electron giving) to the lumo (characterizes of the electron accepting) orbitals. both the frontier molecular orbitals (fmos) (i.e. homo and lumo) are the main orbitals taking part in the chemical reaction [21]. high value of homo energy is likely to indicate a tendency of the molecule to donate electrons to appropriate acceptor molecule of low empty molecular orbital energy. the lower value of the lumo energy shows more probability to accept electrons. the energy of the homo is directly related to the ionization potential and the energy of the lumo is directly related to the electron affinity. so, the energy gap difference between the homo and lumo is an important stability index. a higher value of the energy difference is the stability of the molecular system. low gap value refers the higher electron transition and vice versa. a large homolumo gap implies high stability for the molecule in the sense of its lower reactivity in chemical reaction [22, 23]. the electronic absorption relates to the transition from the ground to the first excited state and mainly described by one electron excitation from homo to lumo [24]. figures 10(a), (b), (c) and (d) show the three-dimensional plot of the homo–lumo of formaldehyde, acetone, acetyl chloride and methyl acetate molecules using the dft with b3lyp/6-311+g(d ′ ,p ′ ) basis set. in the figure 10(a), it is observed that -7.6708 ev of energy is required to free an electron from formaldehyde molecule and -1.7265 ev amount of energy is released while attaching an electron to neutral atom of formaldehyde. the energy gap between homo and lumo for this formaldehyde from figure 10(a) is found to be -5.9443 ev. figure 10(b) shows that ionization potential of acetone is -7.0183 ev and electron affinity for acetone is -0.7371 ev. the calculated energy difference between homo and lumo for acetone from figure 10(b) is found to be -6.2812 ev. similarly, from figure 10(c), it is observed that -7.0882 ev amount of energy is necessary to release an electron from the highest occupied orbital of acetyl chloride and -1.4745 ev energy must release to attach an electron to the lowest occupied molecular orbital of acetone. from this figure 10(c), it shows the calculated energy gap of homo and lumo for this acetyl chloride compound is -5.6137 ev. also, figure 10(d) implies that -7.6379 ev amount of energy is required to free an electron from homo of methyl acetate and -0.2157 ev energy is released while attaching an electron to the lumo of methyl acetate. this methyl acetate from figure 10(d) shows the homo-lumo gap -7.4222 ev. in addition to that, it is observed that methyl acetate has the highest stability implying lower reactivity in the chemical reactions in the sense of its higher energy gap of 7.4222 ev as compared to that of our mother compound formaldehyde (5.9443 ev). on the other hand, acetyl chloride molecule is closely stable as formaldehyde and acetone is second highest stable compound among the given molecules. kinetic stability increases with the increase of homo-lumo gap. as a result, removal of electrons from ground state homo to excited state lumo requires more energy. from the above energy gap, it is clear that the molecule (formaldehyde, acetone, acetyl chloride, methyl acetate) under investigation is very soft since it has a small homo–lumo gap. global reactivity descriptor this study introduces a range of chemical reactivity descriptors aimed at enhancing our comprehension of the properties of formaldehyde, acetone, acetyl chloride, and methyl acetate molecules. the ionization potential (ip) and electron affinity (ea) of these compounds were estimated utilizing the calculated homo and lumo energies. additionally, parameters such as chemical hardness (η), chemical potential (µ), electronegativity (χ), global electrophilicity index (ω) and chemical softness (s) for these molecules have been computed and are presented in table 1. by using homo and lumo energy values for a molecule, we can calculate the global reactivity descriptor such as hardness (η), chemical potential (µ), electronegativity (χ), electrophilicity index (ω) and softness (s) using koopman’s theorem for closed-shell molecules [25–27]. the equations (1)–(5) provide the necessary formulas for computing the chemical hardness (η), chemical potential (µ), electronegativity (χ), global electrophilicity index (ω) and chemical softness (s), and they are expressed as follows: the hardness of the moelcule (η) can be expressed as η = (i −a)/2 (1) the chemical potential (µ) of the molecule is the negative of hardness µ = −(i +a)/2 (2) the electronegativity (χ) of the molecule is given by the equation χ = (i +a)/2 (3) the electrophilicity index ()ω of the molecule is ω = µ2/2η (4) the softness of the molecule is the reciprocal of hardness s = 1/η (5) where i = ehomo called ionization potential and a = elumo called electron affinity. the ionization potential (i) and an electron affinity (a) of formaldeyde, acetone, acetyl chloride, methyl susmita limbu et al./ bibechana 21 (2024) 23-36 31 acetate are -7.6708 ev, -7.0183 ev, -7.0882 ev, 7.6379 ev and -1.72656 ev, -0.73715 ev, -1.47458 ev, -0.215786 ev respectively. usually, the compound having higher homo-lumo gap are comparatively harder [28]. the acetone molecule shows the most hardness (3.140605 ev) in its neutral state. similarly, it has the most chemical softness (0.318409 (ev)−1) in its neutral state. in table 1, chemical potential is expressed in negative values. chemical potential measures the potential energy of the substance. a more negative chemical potential suggests a molecule that is more prone to react or release energy. in this context, acetone has the most negative chemical potential, implying a high reactivity. methyl acetate has a less negative chemical potential, indicating lower reactivity. electronegativity is a measure of the ability of an atom to attract electrons in a chemical bond. from table 1, formaldehyde has the highest electronegativity value (4.698725 ev) indicating it has a strong tendency to attract electrons so it is reactive. for methyl acetate, it has the lowest electronegativity (0.489788 ev) suggesting it is less inclined to attract electrons. normally, strong electrophiles have a value greater than 1.5 ev, moderate electrophiles have a value between 0.8 ev and 1.5 ev, and marginal electrophiles have a value less than 0.8 ev [29]. table 1 shows that the acetone molecule has strong electrophiles in its neutral state with values of 1.570297 ev and the methyl acetate has the least electrophiles with the value 0.137800 ev in neutral state indicating marginal electrophiles. the moderate values are found in the formaldehyde and acetyl chloride in the neutral state with their values 1.486082 and 1.403425 respectively. chemical softness is the inverse of global hardness and represents the ease with which a molecule can accept or donate electrons. a higher softness value indicates a molecule’s greater responsiveness to electron exchange. from table 1, methyl acetate has the highest chemical softness (3.649608 ev) indicating it can more readily engage in electron transfer processes, while acetone has the lowest chemical softness (0.318409 ev) suggesting it is less responsive to electron exchange. reactivity descriptors and thermodynamic parameters are fundamental concepts in understanding chemical reactions and it allows to predict and control reactions, optimize reaction conditions, and design new chemical processes. the global reactivity descriptor associated with the electronic structure principles is also used for analyzing structures, properties, reactivity, bonding, interactions, and dynamics in the context of various physicochemical processes such as molecular vibrations, internal rotations, chemical reaction, stability of isomers, ion-atom collision, atom-filled interactions, solvent effect, etc. also, global reactivity descriptors such as electronegativity, hardness has a correlation with change in dipole moment which is a measure of ionic character of bond. figure 10: the atomic orbital compositions of the frontier molecular orbital (homo-lumo) by dft for (a) formaldehyde (b) acetone (c) acetyl chloride (d) methyl acetate. 3.5 electrostatic potential (esp) surfaces, molecular electrostatic potential (mep) and electron density (ed) esp is used for predicting sites and relative reactivity towards electrophilic attack and for studying of biological recognition and hydrogen bonding interactions and mep is used as a reactivity map displaying most probable regions for the electrophilic attack of charged point-like reagents on organic molecules [30]. it provides a visual method to understand the relative polarity of the molecule. one of the most important non-bonded interactions that can be studied with potential maps is the hydrogen bond. ed iso-surface mapped with esp depicts the size, shape, charge density and site of chemical reactivity of the molecules. figure 11(a) shows the electrostatic potential (esp) of the formaldehyde that ranges from 9.963e-3 to 9.963e-3 a. u. while the figure 11(b) for molecular electrostatic potential (mep) i.e. mapped potential susmita limbu et al./ bibechana 21 (2024) 23-36 32 ranges from -4.309e-2 to 4.309e-2 a. u. in its neutral state for the same molecule. various colors on the surface correspond to distinct electrostatic potential values, which follow a progressive order of increase: from red to orange, then to yellow, green, and finally blue. the chemical reactivity of specific locations is dictated by the molecular electrostatic potential. in this context, the negative regions represented by red and yellow, and are indicative of electrophilic reactivity, while the positive region depicted in blue signifies nucleophilic reactivity [31]. similarly, esp of the acetone ranges from 1.238e-2 to 1.238e-2 a. u. while the mapped mep ranges from -5.283e-2 to 5.283e-2 a. u. as shown in figure 12(a) and (b). figure 13(a) and (b) imply the potential of the acetyl chloride ranges from -1.367e-2 to 1.367e-2 and the mapped potential ranges from -9.480e-2 to 9.480e-2 a. u. in neutral state. likewise, figure 14(a) and (b) are the electrostatic potential having the ranges from -1.603e-2 to 1.603e-2 and mapped potential with the range from -6.020e2 to 6.020e-2 a. u. of the methyl acetate. on comparing both the esp and mep of each of the molecule, it is observed that oxygen atom is mostly tilting towards the negative potential and rest of the region is mostly feasible to the zone of positive potential. from all the figures of 11(a) (b), 12(a) (b), 13(a) (b), and 14(a) (b), we can see that the highest electronegativity is located in the carboynl group. the mep of each title molecule from figure 11(b), 12(b), 13(b) and 14(b) clearly demonstrates the present of a hydrogen atom has the most positive electrostatic potential which can be considered as possible sites for nucleophilic attack. for esp of figure 11(a), 12(a), 13(a) and 14(a), the negative potential is localized near oxygen due to the more electrophilic attack (red and yellowish region), while the positive potential is localized on the rest surface indicating nucleophilic attack. regarding the ed plot of the formaldehyde, acetone, acetyl chloride and methyl acetate from the figure 11(c), 12(c), 13(c) and 14(c) using dft method of calculation, these show uniform charge distribution and the probability of an electron being present at the specific location. table 1: global reactivity descriptors of formaldehyde, acetone, acetyl chloride, and methyl acetate molecules in neutral state. property energy (ev) values of different molecules formaldehyde acetone acetyl chloride methyl acetate global hardness (η) 2.972165 3.140605 2.806855 0.274002 chemical potential (µ) -2.972165 -3.14060 -2.806855 -0.274002 electronegativity (χ) 4.698725 3.877755 4.281435 0.489788 global electrophilicity (ω) 1.486082 1.570297 1.403425 0.137800 chemical softness (s) 0.336455 0.318409 0.356270 3.649608 figure 11: (a) esp (b) mep (c) ed by dft for formaldehyde. susmita limbu et al./ bibechana 21 (2024) 23-36 33 figure 12: (a) esp (b) mep (c) ed by dft for acetone. figure 13: (a) esp (b) mep (c) ed by dft for acetyl chloride. figure 14: (a) esp (b) mep (c) ed by dft for methyl acetate. 3.6 density of state (dos) the consideration of only homo and lumo may not provide a realistic description of the frontier orbitals, it is because of the neighboring orbitals may show quasi-degenerate energy levels in the boundary regions [31, 32]. for this reason dos has been calculated using gausssum 3.0.2 program. the most important application of the dos plot is to demonstrate the mo composition and their contributions to the chemical bonding through positive and negative charges [33]. the plot reveals to determine whether the interaction between two orbitals is of a bonding or anti-bonding nature. when the dos exhibits a high intensity at specific energy levels, it signifies the presence of numerous available states for occupation. conversely, a zero intensity indicates the absence of available states, while a negative intensity signifies an anti-bonding interaction [34]. in addition to this, he energy values presented in the homo-lumo analysis also align well with the energy gap depicted in the dos spectrum. figure 15 represents the dos plot for highest and lowest energy gap of the formaldehyde and its derivatives in the energy range from – 20 ev to 0 ev and with a full width at half maximum (fwhm) of 0.3 ev. in figure 15(a), the energy gap from dos spectrum (i.e. 5.9176 ev) is lower than 5.9443 ev for fmo of formaldehyde and it means that there are only (5.9176 ev) states available for susmita limbu et al./ bibechana 21 (2024) 23-36 34 occupation. figure 15(b) shows that acetone has 6.2825 ev number of electron state per unit volume per unit energy which is very much close to energy gap (6.2812 ev) obtained from fmo’s of acetone. similarly, figure 15(c) is the dos for acetyl chloride having 5.6233 ev unit energy per unit volume which is a little higher than energy gap (5.6137 ev) obtained from fmo’s of acetyl chloride. in figure 15(d), it is found that dos for methyl acetate having 7.1838 ev unit energy per unit volume which is less than the energy gap obtained (7.4222 ev) from fmo’s of methyl acetate. the energy values presented in the homo-lumo analysis are well coordinated with the energy gap depicted in the dos spectrum. dos spectrum for homo and lumo in figure 15 for formaldehyde and its substitutions shows exact stability of given compounds and found that methyl acetate is most stable due to o–c=o group present in it. figure 15: dos spectrum of (a) formaldehyde (b) acetone (c) acetyl chloride (d) methyl acetate at b3lyp with basis set 6-311+g(d ′ ,p ′ ). 4 conclusion this study conducted an in-depth analysis of the molecular properties of formaldehyde, acetone, acetyl chloride, and methyl acetate using various computational methods. gaussian calculations were conducted using the dft method with the 6-311+g(d ′ ,p ′ ) basis set in which the optimization process successfully minimized the energy for each molecule. infrared (ir) spectroscopy analyzed the vibrational modes of the molecules in which specific vibrational frequencies corresponding to c-h, c=o, c-o-c, and c-cl bonds were identified. thermodynamic parameters such as entropy, enthalpy, gibbs free energy, internal energy, heat capacity at constant volume, and heat capacity at constant pressure were computed and the data showed how these parameters varied with temperature and provided insights into the thermodynamic behavior of the molecules. frontier molecular orbitals (homo and lumo) were analyzed to understand the electronic structure and reactivity of the molecules. the energy gap between homo and lumo was used as an indicator of molecular stability. methyl acetate was found to be the most stable molecule due to its higher homolumo energy gap. chemical reactivity descriptors, including ionization potential, electron affinity, chemical hardness, chemical potential, electronegativity, electrophilicity index, and chemical softness, were calculated to assess the reactivity of the molecules. acetone exhibited strong electrophilic reactivity, while methyl acetate had the lowest reactivity. electrostatic potential maps were generated to visualize the polarity and reactivity of the molecules. negative potential regions indicated electrophilic sites, while positive potential regions suggested nucleophilic sites. the electron density plots showed uniform charge distribution within the molecules. dos spectra were used to analyze the molecular orbitals and their contributions to chemical bonding. the energy gaps obtained from dos analysis aligned well with the homo-lumo energy gaps, providing further validation of the molecular stability rankings. the comprehensive computational analysis provided a detailed understanding of the structural, vibrational, electronic, thermodynamic, and reactivity properties of formaldehyde, acetone, acetyl chloride, and methyl acetate. references [1] h. r. gerberich and c. g. seaman. kirkothemer encyclopedia of chemical technology. john wiley & sons ltd, 1st edition, 2001. 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[34] t. a. hajam, h. sallem, m. s. a. padhusha, and k. k. mohammed ameen. synthesis, quantum chemical calculations and molecular docking studies of 2-ethoxy-4[(2trifluoromethyl-phenylimino) methyl]. mol. phys., 118(24):1–19, 2020. introduction methodology – computational details results and discussion geometry optimization vibrational analysis thermodynamic analysis homo-lumo analysis electrostatic potential (esp) surfaces, molecular electrostatic potential (mep) and electron density (ed) density of state (dos) conclusion bibechana vol. 22, no. 2, august 2025, 93-107 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar evaluation of antioxidant, antimicrobial, and lethality activities of leaf and bark extract of alnus nepalensis d. don dipak raj jaishi, dinesh raj ojha, indra ojha, govinda bhattarai, khaga raj sharma central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal ∗corresponding author. email: khaga.sharma@cdc.tu.edu.np abstract herbal medicine has been used for centuries to treat both minor and life-threatening illnesses. this study aims to evaluate the total phenolic content (tpc), total flavonoid content (tfc), total tannin content (ttc), antioxidant potential, and various biological activities of alnus nepalensis d. don (himalayan alder) extracts. among the tested extracts, the ethanolic bark extract exhibited the highest tpc (300.6 ± 3.12 mg gae/g) and ttc (120.09 ± 3.15 mg ta/g), while the methanolic leaf extract had the highest tfc (137.21 ± 4.67 mg qe/g). in terms of antioxidant activity, the ethanolic bark extract showed the lowest ic50 value (17.55 ± 1.17 µg/ml), followed by the methanolic leaf extract (ic50 = 24.03 ± 1.59 µg/ml), with quercetin as the standard (ic50 = 3.43 ± 1.61 µg/ml). for antimicrobial activity, the ethanolic bark extract exhibited significant inhibition against escherichia coli (20 mm) and klebsiella pneumoniae (19 mm), comparable to the positive control neomycin (28 mm). notably, the dichloromethane (dcm) bark extract demonstrated the highest zone of inhibition (21 mm) against e. coli. the methanolic leaf extract exhibited a minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) of 0.78 mg/ml and 1.56 mg/ml, respectively, against k. pneumoniae, while the positive control showed mic = 0.003 mg/ml and mbc = 0.007 mg/ml. in cytotoxicity assessment, the ethanolic bark extract had an lc50 value of 80.08 µg/ml, whereas the methanolic leaf extract had an lc50 of 468.81 µg/ml. these findings highlight the medicinal potential of alnus nepalensis, suggesting its potential use as a source of bioactive compounds for developing novel therapeutic agents against infectious diseases. keywords alnus nepalensis d. don, antimicrobial activity, cytotoxicity, minimum bactericidal concentration (mbc), minimum inhibitory concentration (mic), phytochemistry article information manuscript received: august 13, 2024; revised: february 4, 2025; accepted: february 10, 2025 doi https://doi.org/10.3126/bibechana.v22i2.68759 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 93 http://nepjol.info/index.php/bibechana khaga.sharma@cdc.tu.edu.np https://doi.org/10.3126/bibechana.v22i2.68759 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ dipak raj jaishi et al./ bibechana 22 (2025) 93-107 94 1 introduction natural materials, including different parts of plants, animals, and microorganisms, have been used in medicine to heal illnesses since ancient times. fossil evidence suggests that humans have been using plants as medicine for at least 60,000 years [1]. the bioactive compounds naturally found in medicinal plants help to form various kinds of medicines, dietary supplements, and functional foods [2]. the broad therapeutic application range comprises, ease of accessibility, and safer side effects, natural products are extensively used as active ingredients for drug synthesis [3]. antioxidant, anticancer, antibacterial, antiviral, and anti-inflammatory properties have been shown by medicinal plants. natural phytochemicals known as flavonoids and other phenolic compounds are present in the leaves, fruits, barks, stems, and roots of medicinal plants. these properties have led to the use of flavonoids and other phenolic compounds in medicine for a variety of conditions [4]. oxidative stress, which is caused by oxygen-free radicals, is the primary cause of several degenerative illnesses, such as cancer, gastric ulcers, and atherosclerosis. medicinal herbs are rich in antioxidants that actively scavenge oxygen [5]. the phytochemicals contained in medicinal plants, such as phenolics, flavonoids, anthocyanins, terpenoids, and tannins, enable the prevention and treatment of disease. many therapeutic plants are excellent providers of natural antimicrobial agents, offering viable substitutes for bacterial infection treatments of disease [6]. the usage of dietary or pharmaceutical supplements was influenced by an imbalance between reactive oxygen species (ros) and the body’s natural antioxidant capacity, especially during the illness assault [7]. the chemical constituents found in medicinal plants are thought to be antibiotic, antifungal, antiviral, and shielded plants from infections [8]. primary metabolites are necessary to perform various biological activities such as translocation, photosynthesis, and respiration. secondary metabolites are those that have biological significance but are not necessary for survival. the production of primary metabolites involves several chemical processes, including methylation, glycosylation, and hydroxylation. secondary metabolites undoubtedly have more complicated side chains and structural compositions [9, 10]. phenolic compounds are a large family of secondary metabolites that are primarily present in many higher plant parts including fruits, bark, leaves, and seeds, organs, and microorganisms. phenolic substances exhibit important biological characteristics that include immunemodulating, antibacterial, anticarcinogenic, antithrombotic, anti-inflammatory, antiulcer, antiartherogenic, antiallergenic, antioxidant, and analgesic effects [11]. phenolic compounds reduce fc reagents and produce a molybdenum-tungsten blue complex [12]. the fundamental structure of flavonoids is a subclass of phenolic compounds involved in the production of plant colour in flowers, the ability to resist disease, prevent ultraviolet damage, and influence the formation of legume root nodules [13]. reactive oxygen species (ros) and reactive nitrogen species (rns) in biological systems, such as superoxide, hydroxyl, and nitric oxide radicals, may oxidize lipids and proteins in cells and damage dna [14–16]. antioxidants can lessen oxidative stress, antioxidants have been shown in several studies crucial for preserving human health as well as for diagnosing, treating, and preventing disease. antioxidants are substances that, in very small amounts found in either naturally occurring food or the human body that delay, regulate, or stop oxidative processes. the process of preventing these antioxidant molecules from oxidizing involves a variety of techniques and actions [17]. the natural antioxidant system found in the human body may scavenge produced radicals by maintaining the equilibrium between oxidation and anti-oxidation. however, exposure to radiation, alcohol, tobacco smoke, or environmental contaminants causes an overabundance of reactive oxygen species (ros) and reactive nitrogen species (rns), which disrupts the equilibrium between oxidation and anti-oxidation and causes many degenerative and chronic illnesses [18, 19]. alnus nepalensis d. don is commonly known as nepalese alder which belongs to the betulaceae family that found in gully terrace forests or river beach wetlands throughout a wide range of elevations between around 700-3600 meters [20] and is historically used to treat wounds, cuts, diarrhoea, and dysentery [21]. the analysis of phytochemicals and evaluation of biological properties of bark and leaf extracts such as antioxidant, antimicrobial, and toxicity against brine shrimp nauplii have not been well reported yet. so, the proposed research work plays a significant role in fulfilling the research gap. the major phytoconstituents which show richness reported from the genus alnus are shown in figure 1. dipak raj jaishi et al./ bibechana 22 (2025) 93-107 95 figure 1: chemical compounds reported from alnus nepalensis d. don and alnus nitida d. don 2 materials and methods 2.1 chemicals merck and scientific fischer provided analytical grade (extra pure) solvents, such as methanol, ethanol, ethyl acetate, dichloromethane, and hexane. edta disodium salt dihydrate was purchased from srl, and boric acid, calcium chloride fused, and sodium chloride were purchased from merck. fc reagent and resazurin (loba chemi pvt. ltd), mueller hinton broth, nutrient agar, and mueller hinton agar media were purchased from hiemedia. 2.2 collection and identification of the plant the bark and leaf parts of a. nepalensis d. don medicinal plant were collected from the far western region of nepal (doti). the local name, scientific name, parts of medicinal plants used, and their ethnomedical usage are shown in table 1. the taxonomic identification of a. nepalensis d. don medicinal plant was conducted by national herbarium and plant laboratories, godawari, and research officers of the herbarium center provided the voucher code 01kath163159. the photographs of the selected medicinal plant and the study area are shown in figure 2 and figure 3. figure 2: alnus nepalensis d. don. figure 3: sample collected cite. table 1: description of a. nepalensis d. don scientific name local name family parts used traditional uses reference a. nepalensis d. don utis betulaceae leaf, bark the plant parts have been used to treat wound healing, against dysentery, diarrhea, inflammation, and headaches. [21] 2.3 preparation of extract the bark and leaves parts of a. nepalensis d. don were washed thoroughly, shade dried, ground into finely divided powder, and immersed in six different solvents, ranging in polarity from more polar to less polar they are; water > methanol > ethanol > ethyl acetate, dcm > hexane. afterward, each filtrate was dried in a water bath that was kept at a temperature of up to 40 ºc. finally, they were collected in glass vials and kept at 4 ºc for further analysis. the yield percentage was calculated by using the formula: yield percentage of crude extract = weight of dried crude extract weight of sample × 100 (1) 2.4 qualitative phytochemical analysis the phytochemicals present in the crude plant extracts were qualitatively analyzed by following standard protocol [22–24]. the numerous phytochemicals, including glycosides, flavonoids, alkaloids, phenolic compounds, terpenoids, steroids, carbohydrates, saponins, tannins, fixed oils, and lipids, were screened as metabolites. 2.5 estimation of total phenolic content (tpc) the folin-ciocalteu colorimetric method was used to estimate the total phenolic content of plant extracts as described by lu et al. [25]. 20 µl of plant extract, 100 µl of 10 % fc reagent (1:10), and 80 µl of 1m na2co3 were loaded in a 96-well plates in triplicates. the reaction mixture was allowed to indipak raj jaishi et al./ bibechana 22 (2025) 93-107 96 cubate at room temperature for half an hour before a deep blue colour was observed. ultimately, a spectrophotometer was used to measure absorbance at 765 nm. the standard curve was generated which is the standard curve for gallic acid (7.5-100 µg/ml) and the total phenolic content (tpc) was measured in milligrams of gallic acid equivalent (mg gae/g) per gram of extract dry weight. 2.6 estimation of total flavonoid content (tfc) the total flavonoid content was estimated by using aluminium chloride method as described by ahmed et al. [26]. 20 µl of plant extract, 100 µl of distilled water, and 60 µl ethanol followed by 10 µl of 10% alcl3 solution and 10 µl (1m) ch3cook solution were loaded in 96-well plates in triplicates. the reaction mixture was incubated for 30 minutes at room temperature. then, absorbance was taken at 415 nm with the help of a spectrophotometer. a quercetin (10-100 µg/ml) standard calibration curve was created, and measured in milligrams of quercetin equivalent per gram of the extract’s dry weight (mg qe/g). 2.7 estimation of total tannin content (ttc) the folin-ciocalteu colorimetric method was used to estimate the total tannin content by applying standard protocol [25]. 96-well plates were filled with 10 µl of plant extract and different tannic acid concentrations (7.5-100 µg/ml). the first reading was taken at 725 nm using a microplate reader after adding 70 µl of distilled water and 50 µl of 10% fc reagent. after taking an initial reading, 70 µl of 35 % na2co3 was loaded. finally, the 96-well plate was incubated for 30 minutes and consequently, its final absorbance was taken at 725 nm. the ttc was measured as mg ta/g. calibration curves were created by plotting the graph of absorbance on the y-axis and the standard concentration on the x-axis. these curves were then used to calculate the concentrations of phenolics, flavonoids, and tannins. r2, the coefficient of determination, was determined to be between 0.9753 and 0.9997 when the data were fitted linearly. 2.8 evaluation of antioxidant activity the antioxidant activity of crude plant extract was evaluated by following a standard protocol [27,28]. the crude plant extract was diluted serially up to 5 µg/ml from 160 µg/ml concentrations but positive control quercetin was serially diluted up to 0.625 µg/ml from 20 µg/ml concentrations. 100 µl of plant extracts and positive control were loaded in 96-well plates in triplicates. after that, the initial reading was taken at 517 nm. following this, 100 µl of dpph reagent was loaded into every well and incubated for half an hour. finally, the final absorbance was taken at 517 nm. since 50% dmso and methanol were used as a negative control. the following formula was used to evaluate radical scavenging activity: radical scavenging capacity =( acontrol −asample acontrol ) × 100 (2) where, acontrol = absorbance of control, asample = absorbance of sample. inhibitory concentration (ic50) was calculated by using graphpad prism (version 8.0.2.263). 2.9 evaluation of antimicrobial activity the agar well diffusion method was applied to perform an antibacterial activity using mueller hinton agar (mha) plates [29–31]. mueller hinton broth (mhb) was used for the growth of test microorganisms, atcc 25931 shigella sonnei, atcc 43300 staphylococcus aureus, atcc 700603 klebsiella pneumonae and atcc 25312 escherichia coli respectively and it was incubated at 37 ºc for 24 hrs and its turbidity was maintained by using 0.5 mcfarland. 50 µl of plant extract, 50% dmso as the negative control, and 50% neomycin as the positive control were loaded into each well created by a cork borer. the petri dishes were then incubated for 18-24 hours at 37 °c after being left for 15 minutes to allow for diffusion. after incubation, the zone of clearance was observed and measured. 2.10 determination of minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) the minimum inhibitory concentration (mic) and minimum bactericidal concentration were determined by following the standard protocol as described by sarker et al. [32]. the 0.5 mcfarland turbidity culture in mhb was diluted 1:100 to give the bacterial inoculum a final concentration of 106 cfu/ml. 5 µl of bacteria were injected into every well of 96 well plates. a common medication called neomycin served as the positive control. the plate was covered with a sterile lid and incubated for 20-24 hrs at 37 °c. the microtiter plate wells were filled with 0.003% resazurin, and the mixture was incubated for 3 to 4 hours at 37 °c. the colour of the wells with bacterial growth changed to pink, whereas the wells without infection stayed blue. the extract’s minimum inhibitory concentration (mic) was found to be the lowest at which bacterial growth is inhibited. by streaking the contents dipak raj jaishi et al./ bibechana 22 (2025) 93-107 97 of the wells onto nutrient agar plates and incubating them at 37 °c for more than 18 hours consequently, the mic and mbc of the crude plant extracts were determined. 2.11 brine shrimp lethality activity (bsla) the toxicity of plant extracts was determined by following a standard protocol [33]. the artificial sea salt water was prepared by maintaining a ph of around 8 to 8.5 by adding 1m naoh. the plant extract was diluted in various concentrations such as 1000, 800, 500, 250, 125, 100, and 10 µg/ml. then, 4 ml of artificial sea salt water was filled in each test tube. after that, 500 µl of sample, and 10 nauplii were added to each test tube in triplicate. artificial sea salt water served as the negative control, while potassium dichromate solution was employed as the positive control. the number of dead nauplii in a test tube was counted after 24 hours, and the mortality of nauplii percentage was determined using the following formula: % mortality = number of dead nauplii total number of nauplii × 100 using the probit value table, the linear equation can be obtained as y = mx+c, where y is the probit value at 50% mortality, m is variable, and c is the intercept. x is the lethal concentration and finally, the lethal concentration (lc50) was calculated. 2.12 statistical analysis the gen5 microplate reader for data collection and analysis software was used for result processing, followed by microsoft excel. the data were reported for tpc, tfc, and ttc as the mean ± standard deviation. for antioxidants, the data were reported as mean ± standard error mean. inhibitory concentration (ic50) was calculated by using graphpad prism (version 8.0.2.263). one-way anova using tukey’s test was used for comparisons, p < 0.05 values were regarded as statistically significant. 3 results 3.1 percentage yield the yield percentage of crude extracts of bark was found to be higher in methanolic extract (19.17 %) followed by ethanol (9.23 %), ethyl acetate (3.56 %), hexane (2.81 %), aqueous (2.80 %), and dcm (2.45 %). similarly, in the case of leaves, methanolic extract had a higher percentage of yield (10.78 %) followed by ethyl acetate (10.18 %), dcm (8.92 %), ethanol (5.82 %), and hexane (5.42 %) (figure 4). figure 4: yield percentage of bark and leaf crude extracts 3.2 qualitative phytochemical analysis the results of qualitative phytochemical screening of the bark and leaf extract (in different solvents) are shown in table 2. table 2: qualitative phytochemical screening of plant extracts. phytochemicals test bark extract leaf extract alkaloids dragendorff’s test carbohydrates molish’s test + + reducing sugars fehling’s test glycosides borntrager’s test + + amino acids xanthoproteic test + + flavonoids alkaline reagent test + + phenols fecl3 test + + tannins braymer’s test + + terpenoids salkowski’s test + + anthraquinones borntrager’s test + + phytosterols salkowski’s test + + note: (+) = present, (-) = absent dipak raj jaishi et al./ bibechana 22 (2025) 93-107 98 3.3 total phenolic content (tpc) the ethanolic bark extract exhibited the maximum tpc of 300.6± 3.12 mg gae/g. the tpc of hexane bark extract was found to be the lowest which is 53.67±3.59 mg gae/g. the tpc of bark extracts ranges from 300.6±3.12 mg gae/g to 53.67±3.58 mg gae/g (table 3). the tpc of leaf extracts ranges from 254.6±5.58 mg gae/g to 73.93±3.63 mg gae/g. methanolic leaf extract had the highest tpc which is 254.6± 5.38 mg gae/g and hexane extract of the leaf had the lowest tpc which is 73.93 ± 3.63 mg gae/g respectively. ethanolic bark extract had the highest tpc than of methanolic leaf extract. the calibration curve is shown in figure 5. figure 5: gallic acid standard calibration curve. table 3: tpc for various solvent extracts extraction sources solvent type total phenolic content (mg gae/g) bark aqueous 101.8± 3.41 bark methanol 292.2± 1.74 bark ethanol 300.6± 3.12 bark ethyl acetate 124.47± 4.20 bark dcm 121.53± 1.22 bark hexane 53.67± 3.59 leaves methanol 254.6± 5.58 leaves ethanol 152.47± 2.89 leaves ethyl acetate 201.13± 3.45 leaves dcm 88.47± 2.57 leaves hexane 73.93± 3.63 3.4 total flavonoid content (tfc) dcm extract of bark had the highest tfc which is 75.99 ± 4.72 mg qe/g and hexane extract had the lowest tfc which was 50.09 ± 6.31 mg qe/g. tfc of bark extract ranges from 75.99 ± 4.72 mg qe/g to 50.09 ± 6.31 mg qe/g (table 4). the methanol leaf extract had the highest tfc which is 137.21 ± 4.67 mg qe/g and hexane extract had the lowest tfc 13.12 ± 1.84 mg qe/g. the tfc of leaf extract ranged from 137.21± 4.67 mg qe/g to 13.12 ± 1.84 mg qe/g. among all the extracts, the methanolic leaves extract had the highest tfc, which is 137.21 ± 4.67 mg qe/g than that of bark extracts. the calibration curve is shown in figure 6. figure 6: quercetin standard calibration curve. dipak raj jaishi et al./ bibechana 22 (2025) 93-107 99 table 4: tfc of bark and leaf extracts extraction sources solvent types total flavonoid content (mg qe/g) bark aqueous 62.97± 1.84 bark methanol 60.40± 2.78 bark ethanol 65.24± 2.24 bark ethyl acetate 61.76± 1.39 bark dcm 75.99± 4.72 bark hexane 50.09± 6.31 leaves methanol 137.21± 4.67 leaves ethanol 104.33± 1.39 leaves ethyl acetate 111.15± 3.87 leaves dcm 35.24± 2.24 leaves hexane 13.12± 1.84 3.5 total tannin content (ttc) the maximum ttc was found to be 120.09± 3.15 mg ta/g, in the ethanolic bark extract. hexane extract of bark had the lowest ttc which is 8.27 ± 0.45 mg ta/g. the ttc of bark extract ranged from 120.09± 3.15 mg ta/g to 8.27± 0.45 mg ta/g. the ttc of the methanolic leaf extract was found to be 43.72±3.96 mg ta/g, whereas the lowest ttc was found in ethyl acetate leaf extract which is 8.42± 1.31 mg ta/g (table 5). the ttc ranges from 43.72±3.96 mg ta/g to 8.42±1.31 mg ta/g in leaf extracts. among all solvent extracts, ethanolic bark extract had the highest ttc, and hexane extract of bark had the lowest ttc. the calibration curve is shown in figure 7. figure 7: tannic acid standard calibration curve table 5: total tannin content of bark and leaf extracts. extraction sources solvent type total tannin content (mg ta/g) bark aqueous 74.03± 5 bark methanol 86.15± 4.73 bark ethanol 120.09± 3.15 bark ethyl acetate 28.88± 3.03 bark dcm 71± 6.01 bark hexane 8.27± 0.45 leaves methanol 43.73± 3.96 leaves ethanol 28.42± 1.72 leaves ethyl acetate 8.42± 1.31 leaves dcm 15.85± 0.69 leaves hexane 9.79± 0.95 3.6 antioxidant potential hexane and ethyl acetate extracts had the highest ic50 which is > 500 µg/ml and 247.9±1.73 µg/ml respectively while ethanolic extract had the lowest which is 17.55±1.17 µg/ml (figure 8). the ethanolic extract had more antioxidant potential than all crude bark extracts. the ic50 of the standard quercetin compound was found to be 3.43 ± 1.61 µg/ml. which is five times less than ethanolic extract. the methanolic extract of the leaf had the lowest ic50 24.03 ± 1.59 µg/ml among all leaf extracts. however, the hexane and ethyl acetate extracts of the leaf exhibited the highest ic50 which are > 500 µg/ml and 464.7 ± 0.22 µg/ml respectively. the methanolic leaf extract had greater antioxidant potential and the hexane extract had the lowest antioxidant potential. the ic50 of methanolic leaf extract was eight times greater than the ic50 of standard quercetin. compared to the crude leaf dipak raj jaishi et al./ bibechana 22 (2025) 93-107 100 extracts, the ethanolic extract of bark had the highest antioxidant potential. the percent inhibition against the different concentrations of the plant extract is shown in figure 13. figure 8: bar diagram showing antioxidant potential (ic50) of bark and leaf crude extracts in different solvents at various concentrations. figure 9: a plot of % inhibition against the concentration of (a) quercetin (b) methanolic and ethanolic bark extracts (c) dcm, ethyl acetate & aqueous bark extracts (d) methanol, ethanol, ethyl acetate, and dcm leaf extracts the ic50 values of various extracts of bark and leaf and standard quercetin as a reference compound are shown in table 6. table 6: the antioxidant capacity (ic50) of the aqueous, methanol, ethanol, ethyl acetate, dcm, and hexane crude extracts of bark and leaf. part plant extracts ic50 (µg/ml) bark aqueous 62.16± 3.66 bark methanol 58.06± 0.22 bark ethanol 17.55± 1.17 bark ethyl acetate 247.9± 1.73 bark dcm 87.16± 0.87 bark hexane > 500 bark *quercetin 3.43± 1.61 leaf methanol 24.03± 1.59 leaf ethanol 42.07± 2.17 leaf ethyl acetate 464.7± 0.22 leaf dcm 55.44± 1.70 leaf hexane > 500 leaf *quercetin 3.43± 1.61 note: *quercetin = positive control 3.7 antimicrobial activity the antimicrobial activity in terms of the zone of inhibition of various crude extracts of bark and leaf against k. pneumoniae, e. coli, s. sonnei, and s. aureus respectively are shown in table 7. the ethanolic bark extract had a strong antibacterial activity with zoi of 20 mm, 15 mm, 14 mm, and 19 mm respectively against escherichia coli, shigella sonnei, staphylococcus aureus, and klebsiella pneumoniae. this was quite close to the positive control, namely neomycin 24 mm for staphylococcus aureus and shigella sonnei and 28 mm for e. coli and klebsiella pneumoniae respectively. among all extracts of bark, dcm extract shows very potent activity against e. coli with zoi 21 mm (neomycin control 28 mm). however, hexane extract had no zone of inhibition against all four bacteria which is 9 mm. this was far from the zoi of positive control which are 25 mm for klebsiella pneumoniae, 22 mm for e. coli, 20 mm for shigella sonnei, and 24 mm for staphylococcus aureus respectively. the methanolic, ethanolic, and ethyl acetate dipak raj jaishi et al./ bibechana 22 (2025) 93-107 101 extracts of leaves show good antibacterial activity against klebsiella pneumoniae, e. coli, and shigella sonnei with zoi 21, 11, and 15 mm respectively (neomycin positive control 25 mm and 24 mm). the dcm and hexane extracts of leaves had less potent antimicrobial activity against klebsiella pneumoniae, e. coli, shigella sonnei, and staphylococcus aureus respectively. the zoi shown by the bark and leaf extracts of the plant is shown in figures figure 10 and figure 11. 3.8 mic and mbc the mic and mbc of ethanolic bark and methanolic leaf extracts are illustrated in table 8. the methanolic leaf extract and the ethanolic bark extract were employed for the evaluation of mic and mbc against klebsiella pneumoniae and staphylococcus aureus, respectively. the ethanolic bark extract shows minimum inhibitory concentration (mic) against staphylococcus aureus and klebsiella pneumoniae, which are 3.12 mg/ml and 1.56 mg/ml, respectively. the mbc of ethanolic bark extract against klebsiella pneumoniae and staphylococcus aureus were found to be 3.12 mg/ml and 6.25 mg/ml, respectively. the methanolic leaf extract shows mic 1.56 mg/ml and 0.78 mg/ml against staphylococcus aureus and klebsiella pneumoniae, respectively. the mbc of the methanolic leaf extract against klebsiella pneumoniae and staphylococcus aureus was found to be 1.56 mg/ml and 3.12 mg/ml, respectively. the methanolic leaf extract exhibited the lowest mic and mbc against klebsiella pneumoniae, which are 0.78 and 1.56 mg/ml, respectively. in conclusion, methanolic leaf extract had the lowest mic and mbc against klebsiella pneumoniae. the mic and mbc of methanolic leaf and ethanolic bark extracts against klebsiella pneumoniae and staphylococcus aureus were evaluated using nutrient agar plates, and the captured images are displayed in figure 12. table 7: zoi shown by crude bark and leaf extracts against klebsiella pneumoniae, escherichia coli, shigella sonnei, and staphylococcus aureus. part plant extracts bacteria used zoi shown by the sample (mm) zoi shown by the positive control neomycin (mm) bark methanol klebsiella pneumoniae 17 28 escherichia coli 18 28 shigella sonnei 14 24 staphylococcus aureus 12 24 ethanol klebsiella pneumoniae 19 28 escherichia coli 20 28 shigella sonnei 15 24 staphylococcus aureus 14 24 ethyl acetate klebsiella pneumoniae 9 25 escherichia coli 9 22 shigella sonnei 14 20 staphylococcus aureus 13 24 dcm klebsiella pneumoniae 11 28 escherichia coli 21 28 shigella sonnei 12 20 hexane klebsiella pneumoniae 9 25 escherichia coli 9 22 shigella sonnei 9 20 staphylococcus aureus 9 24 leaves methanol klebsiella pneumoniae 21 25 escherichia coli 9 22 shigella sonnei 14 24 staphylococcus aureus 9 24 ethanol klebsiella pneumoniae 13 26 escherichia coli 11 24 shigella sonnei 9 20 staphylococcus aureus 9 20 ethyl acetate klebsiella pneumoniae 9 25 escherichia coli 9 22 shigella sonnei 15 24 staphylococcus aureus 9 24 dcm klebsiella pneumoniae 9 26 escherichia coli 9 24 shigella sonnei 9 20 hexane staphylococcus aureus 9 20 klebsiella pneumoniae 9 26 escherichia coli 9 24 shigella sonnei 9 20 staphylococcus aureus 9 20 dipak raj jaishi et al./ bibechana 22 (2025) 93-107 102 table 8: mic and mbc of methanolic leaf and ethanolic bark extracts against klebsiella pneumoniae and staphylococcus aureus. plant extracts klebsiella pneumoniae staphylococcus aureus mic (mg/ml) mbc (mg/ml) mic (mg/ml) mbc (mg/ml) ethanol-b 1.56 3.12 3.12 6.25 methanol-l 0.78 1.56 1.56 3.12 positive control 0.003 0.007 0.007 0.015 figure 10: zoi shown by the bark extract against the organism used (a) klebsiella pneumoniae (b) escherichia coli (c) shigella sonnei. figure 11: zoi shown by the leaf extracts against the microorganisms (a) k. pneumoniae, (b) e. coli, (c) s. sonnei, and (d) s. aureus figure 12: mic and mbc shown by (a) ethanolbark extract, (b) methanol-leaf extract, (c) ethanol bark extract (d) methanol leaf extract (e) positive control against klebsiella pneumoniae, and staphylococcus aureus 3.9 toxicity analysis the percentage mortality shown by the plant extract against the brine shrimp nauplii is displayed in table 9. the ethanolic bark extract showed the lowest lc50 of 80.08 µg/ml. the methanolic leaf extract had the highest lc50 of 468.81 µg/ml. the potassium dichromate served as the positive control and 50% dmso served as the negative control. all nauplii were dead in the positive control (10 nauplii), and the same number of nauplii survived in the 50% dmso solution. the lc50 of crude plant extracts. figure 13: a plot log c against probit for the determination of lc 50 of ethanolic bark and methanolic leaf extract 4 discussion the genus alnus is an alder plant mostly found in nepal’s mountainous regions, it is also found in china, india, and korea. the majority of its quite extensive applications are for the treatment of fever, diarrhoea, dysentery, inflammatory diseases, skin diseases, elephantiasis, stomachaches, and wound healing. numerous biological activities, including antidiabetic, antioxidant, hepatoprotective, and antifungal effects, are performed by a. nepalensis d. don. in previous studies, 423.49 ± 0.89 mg gae/g was the tpc of methanolic leaf extract and 408.88 ± 2.08 mg gae/g was the flavonoid content [34]. however, in this study, 254.6 ± 5.58 mg gae/g tpc and 137.21 ± 4.67 mg qe/g tfc respectively. methanolic extract of the leaf contains maximum phenolic and flavonoid levels. tpc and tfc of bark extracts were compared with alnus nitida. according to a previous study on alnus nitida (bark), methanolic bark extract had tpc 631.5 ± 1.7 mg gae/g and ethanolic bark extract had tpc 607 ± 1.97 mg gae/g respectively. similarly, 221.5 ± 2.5 mg qe/g was the reported tfc of methanolic extract of this plant [35]. however, in this study, the ethanolic bark extract had a higher phenolic level which is 300.6 ± 3.12 mg gae/g. however, the flavonoid level was higher in the dcm extract which is 75.99 ± 4.72 mg qe/g. methanolic leaf exdipak raj jaishi et al./ bibechana 22 (2025) 93-107 103 tract had maximum tpc and tfc which is 254.6 ± 5.58 mg gae/g and 137.21 ± 4.67 mg qe/g respectively. in comparison with both bark and leaf different extracts, ethanolic bark extract contained a high quantity of phenolics. but, methanolic leaf extract had a high amount of flavonoids. the overall phenolic and flavonoid contents of medicinal plants might vary depending on factors such as geographical range, plant collecting time, and climate fluctuation. phenolics and flavonoids were directly correlated with antioxidant properties. high amounts of phenolics and flavonoid phytoconstituents correlated with antioxidant properties. phenolic compounds are directly correlated with tannins. ethanolic bark extract had a high ttc which is 120.09 ± 3.15 mg ta/g. in the case of leaves, methanolic extract had a high ttc which is 43.73 ± 3.96 mg ta/g. in the previous study, methanolic leaf extract had ic50 which is 4.838 µg/ml [34]. however, in this study, ic50 of methanolic leaf extract was found as 24.03 ± 1.59 µg/ml. ethanolic bark extract had ic50 39.5 ± 2.11 µg/ml in the previous study [35]. in this study, ic50 of ethanolic bark extract found as 17.55 ± 1.17 µg/ml. in comparison with leaves and bark, ethanolic bark extract possesses good antioxidant potential. tpc and ttc values in bark extract were higher in ethanolic extract which was positively correlated with the ic50 of ethanolic bark extract. the climatic conditions and other environmental factors, antioxidant capacity, tpc, tfc, and ttc were considerably different [36]. plant extracts are more effective antioxidants because they have a special functional group of secondary metabolites [37,38]. a prior study depicts that methanolic leaf extract of a. nepalensis d. don was subjected to the antimicrobial assay against a. baumannii with zoi 14.66 mm and p. mirabilis with zoi 15.50 mm [34]. however, the methanolic leaf extract of this plant in this study possesses better antimicrobial activity against klebsiella pneumoniae with zoi 21 mm. no antimicrobial assay was carried out for the a. baumannii and p. mirabilis bacteria. instead, this antimicrobial assay was carried out against klebsiella pneumoniae, escherichia coli, shigella sonnei, and staphylococcus aureus respectively. methanolic leaf extract had zoi 14 mm against shigella sonnei. ethanolic leaf extract of this medicinal plant possesses 13 mm zoi against k. pneumoniae. 15 mm was the zoi of ethyl acetate extract against shigella sonnei. none of the remaining leaf extracts inhibit bacterial growth. in bark, ethanolic bark extract had good antimicrobial activity against e. coli with zoi 20 mm, and k. pneumoniae with zoi 19 mm. dcm extract had maximum zoi which is 21 mm against e. coli. hexane has no inhibition against subjected bacteria. ethanolic extract of bark and methanolic extract of leaf showed good antimicrobial activity against klebsiella pneumoniae and staphylococcus aureus respectively. not only phenolics and flavonoids but other phytochemicals such as vitamins, carotenoids, saponins, enzymes, and minerals showed antimicrobial activity [39, 40]. ethanolic bark extract and methanolic leaf extract of this medicinal plant showed good antimicrobial activity against k. pneumoniae and s. aureus, so, these samples were subjected to determine mic and mbc. the ethanolic bark and methanolic leaf extract medicinal plant had good mic and mbc which are 1.56 mg/ml and 3.12 mg/ml for bark and for leaf 0.78 mg/ml and 1.56 mg/ml respectively against k. pneumoniae. in comparison to ethanolic bark extract, methanolic leaf extract had potent mic and mbc against k. pneumoniae. a lethality experiment was conducted on ethanolic and methanolic extracts of bark and leaves and lc50 of ethanolic bark extract was found to be 80.08 µg/ml and lc50 for methanolic leaf extract was found to be 468.81 µg/ml. in comparison between them, ethanolic bark extract had a potent lethal activity as compared to methanolic leaf extract. dipak raj jaishi et al./ bibechana 22 (2025) 93-107 104 table 9: the number of survived nauplii after treatment with methanolic leaf and ethanolic bark extracts and their percentage mortality plant extract concentration (g/ml) total no. of survived nauplii % mortality ethanol-bark extract 10 24 20 100 18 40 125 16 46.66 250 3 90 500 8 73.33 800 3 90 1000 6 80 methanol-leaf extract 10 22 26.66 100 18 40 125 16 46.66 250 24 20 500 18 40 800 12 60 1000 8 73.33 table 10: lc50 of ethanolic bark and methanolic leaf plant extracts plant extracts linear regression equation lc50 (g/ml) ethanol-b 5.0 = 1.0244x+ 3.05 80.08 methanol-l 5.0 = 0.4499x+ 3.79 468.81 5 conclusion the present study highlights alnus nepalensis d. don as a rich source of bioactive phytochemicals, including carbohydrates, glycosides, amino acids, flavonoids, phenols, tannins, terpenoids, anthraquinones, and phytosterols. among the tested extracts, the ethanolic bark extract exhibited the highest total phenolic content (tpc) among bark extracts, while the methanolic leaf extract had the highest tpc among leaf extracts. the dichloromethane (dcm) bark extract showed the highest total flavonoid content (tfc) among bark extracts, whereas methanolic leaf extract had the highest tfc among leaf extracts. similarly, tannin content was highest in the ethanolic bark and methanolic leaf extracts. overall, bark extracts demonstrated higher phenolic and tannin content, while leaf extracts were richer in flavonoids. in terms of bioactivity, the ethanolic bark extract exhibited the strongest antioxidant potential among the bark extracts, whereas the methanolic leaf extract showed the highest antioxidant activity among leaf extracts. hexane extracts of both bark and leaves demonstrated the weakest antioxidant potential. the ethanolic and dcm extracts of bark exhibited good antimicrobial activity against escherichia coli, whereas the methanolic leaf extract showed significant antimicrobial activity against klebsiella pneumoniae. furthermore, the methanolic leaf extract demonstrated superior mic and mbc values compared to the ethanolic bark extract. the ethanolic bark extract exhibited higher toxicity, as indicated by a lower lethal concentration, compared to the leaf extract. these findings suggest that a. nepalensis d. don possesses significant antioxidant, antimicrobial, and toxicological properties, making it a promising candidate for the discovery of natural antibacterial compounds. further research is required to explore its pharmacological potential and underlying mechanisms, particularly in the development of novel therapeutic agents. abbreviations • dmso: dimethyl sulfoxide • gae/g: gallic acid equivalent per gram • qe/g: quercetin equivalent per gram • ta/g: tannic acid equivalent per gram • tpc: total phenolic content • tfc: total flavonoid content • ttc: total tannin content • ic50: half-maximum inhibitory concentration • dpph: 2,2-diphenyl-1-picrylhydrazyl • zoi: zone of inhibition dipak raj jaishi et al./ bibechana 22 (2025) 93-107 105 • mic: minimum inhibitory concentration • mbc: minimum bactericidal concentration • lc50: lethal concentration 50% funding statement this research did not receive any financial support and was conducted through the independent efforts of the authors. conflicts of interest the authors declare that there are no conflicts of interest associated with the publication of this research paper. author’s 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[40] a. a. shad, s. ahmad, r. ullah, n. m. abdelsalam, h. fouad, n. u. rehman, h. hussain, and w. saeed. phytochemical and biological activities of four wild medicinal plants. scientific world journal, 2014:1–7, 2014. introduction materials and methods chemicals collection and identification of the plant preparation of extract qualitative phytochemical analysis estimation of total phenolic content (tpc) estimation of total flavonoid content (tfc) estimation of total tannin content (ttc) evaluation of antioxidant activity evaluation of antimicrobial activity determination of minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) brine shrimp lethality activity (bsla) statistical analysis results percentage yield qualitative phytochemical analysis total phenolic content (tpc) total flavonoid content (tfc) total tannin content (ttc) antioxidant potential antimicrobial activity mic and mbc toxicity analysis discussion conclusion bibechana vol. 21, no. 2, august 2024, 83-94 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar theoretical exploration of thermodynamic characteristics in lead-free liquid alloys: zn-bi-in system sanjay kumar sah1,3,∗, indu shekhar jha2, ishwar koirala1 1central department of physics, tribhuvan university, kirtipur, kathmandu, nepal 2department of physics, m.m.a.m. campus, tribhuvan university, biratnagar, nepal 3dept. of physics, birendra multiple campus, tribhuvan university, bharatpur, nepal ∗corresponding author. email: sanjay.sah@bimc.tu.edu.np abstract the calculations of zn activities in the ternary liquid solder alloy zn-bi-in at 873 k were conducted through the application of the molecular interaction volume model (mivm). the calculated values were compared to experimental data for four different cross-sectional examinations, namely for the bismuth-to-indium ratios (xbi: xin) of 1:2, 1:1, 2:1, and 9:1. moreover, the integral excess free energy of these ternary liquid alloys was assessed using the same model parameters in order to test their validity. then, the values were compared to the relevant experimental data reported in the literature that was already in existence. a satisfactory concordance has been observed between the theoretical predictions and the experimental findings. keywords activity; integral excess free energy; solder alloys; ternary liquid alloys; molecular interaction volume model. article information manuscript received: november 21, 2023; revised: december 26, 2023; accepted: january 14, 2024 doi https://doi.org/10.3126/bibechana.v21i2.60097 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction it is possible to investigate the thermodynamic characteristics of different alloys through experimental measurements. but the experimental methods are much more costly and time-consuming, given that numerous measurements and advanced instruments are required. furthermore, experimental data are scarce for alloys with multiple components. as such, it is difficult to obtain all thermodynamic data solely through experimentation [1–4] therefore, it is more advantageous to obtain the 83 http://nepjol.info/index.php/bibechana sanjay.sah@bimc.tu.edu.np https://doi.org/10.3126/bibechana.v21i2.60097 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ sanjay kumar sah et al./ bibechana 21 (2024) 83-94 84 data through theoretical means. lead-based systems have been traditionally preferred for soldering due to their lower cost and lower melting point. however, lead is a toxic metal and has adverse effects on the environment. it can contaminate the soil, water, and air [5–8]. currently, there is a worldwide agreement to outlaw lead use. therefore, the development of soldering alternatives without lead has emerged as a crucial topic in the field of electronics [8]. in addition to comparable melting points, the new alloys ought to possess other qualities like low cost, non-toxicity, fatigue and corrosion resistance, and wetting qualities. thus, researchers have attempted to replace lead in solder alloys multiple times [8]. zinc, bismuth, and indium can be chosen as beneficial materials for lead-free solder alloys due to several advantageous properties and characteristics. these are less toxic than lead, making them more environmentally friendly alternatives. alloys of those materials can have a relatively lower melting point and often exhibit good wetting properties. they also exhibit good thermal fatigue resistance, contributing to the reliability and durability of solder joints, especially in applications where the temperature may vary. mainly, zinc imparts corrosion resistance to the solder alloys, and it is a relatively inexpensive material that is readily available [9]. various alloy systems have been developed as alternatives to traditional sn-pb (tin-lead) alloys, particularly for electronic soldering applications. here are examples of binaries, ternaries, and higher alloy systems: tin-silver (sn-ag), gold-tin (au-sn), tin-copper (sn-cu), tin-silver-copper (sn-ag-cu), aluminium-tin-zinc (al-sn-zn), tinantimony-bismuth (sn-sb-bi), tin-silver-copperantimony (sn-ag-cu-sb), and tin-silver-copperzinc (sn-ag-cu-zn), etc. [6–8, 10–15]. several geometric models are widely used in predicting the thermodynamic properties of binary, ternary, and other systems of higher complexity. these models include muggianu, kohler, chou, collinet, r-k equations, the kaptay model, etc. [16–18]. mivm is superior to other models because of the way it is formulated, which requires fewer fitting parameters (only two) [19]. mivm has the unique capability to simultaneously represent the influences of the microstate number of molecular configuration (entropy) and molecular interaction (enthalpy) on excess gibbs energy. over the past two decades, the precision and dependability of mivm in predicting the properties of liquid alloys have been substantiated [20, 21]. mivm is a model characterized by two parameters. one of the model’s most important features is its capability to forecast liquid alloy thermodynamic properties in a system of multiple component mixtures using typical physical parameters of metals in liquid form and binary infinite dilution activity coefficients alone [1]. thermodynamic activities of the components of ternary liquid alloys indium-bismuth-tin (inbi-sn), tin-gold-copper (sn-au-cu), and zincindium-tin (zn-in-sn), along with their excess gibbs free energy of mixing, have been performed by sah et al. [9, 22]. a comprehensive thermodynamic representation of the complete ternary system bi-in-zn was achieved through calphad modeling, focusing on the gibbs energy of the liquid phase [23]. utilizing a calvet-type microcalorimeter and the drop calorimetric technique, the integral enthalpies of mixing for liquid bi-in-zn alloys at 773 k were determined [24]. but there is only restricted information accessible through this system. the thermodynamic characteristics of the bi-in-zn ternary system were established utilizing the electromotive force (emf) method, employing a liquid electrolyte, as outlined by the reference [25]. nevertheless, there is presently no documentation in the literature regarding the computation of their integral excess free energy. hence, in this study, the molecular interaction volume model was utilized to determine the thermodynamic activities of the zn component in the ternary liquid alloys zn-bi-in at 873 k for the four cross-sections, namely xbi: xin = 1:2, 1:1, 2:1, and 9:1. moreover, the theoretical model was employed to compute the integral excess gibbs free energy of mixing for zn-bi-in at 873 k, considering varying concentrations of zn (xzn) across all those cross-sections. 2 methodology the mivm model states that liquid molecules behave differently from both gas molecules, which move randomly all the time, and solid molecules, which oscillate continuously at one spot but move between molecular cells in a non-random way. the cells are both mobile and identical, and the molecules in the center and those closest to them can be interchanged [26]. mivm is a fluid model based on statistical thermodynamics that takes into consideration the inherent physical characteristics of the individual pure metals that make up the alloy. molar volume (vm) and the liquid phase’s first coordination number (z) are specifically taken into account, which are dependent on temperature [19]. the excess molar gibbs energy of the liquid binary mixture, i-j, is expressed as per dong ping tao in 2000 based on the molecular interaction volume model [27]: sanjay kumar sah et al./ bibechana 21 (2024) 83-94 85 ∆gxs = rt { xi ln ( vmi xivmi + xjvmjaji ) + xj ln ( vmj xjvmj + xivmiaij ) − xixj 2 ( ziaji lnaji xi + xjaji + zjaij lnaij xj + xiaij )} (1) in this context, vmi and vmj represent the molar volumes, while xi and xj denote the molar fractions of components i and j, respectively. aji and aij are the interaction parameters associated with the pair potential energy for binary liquid alloys. zi and zj are the first coordination numbers specific to the ith and jth component metals in binary liquid alloys. t stands for the absolute temperature and r represents the gas constant. in the case of a binary liquid alloy, the activity coefficients of components i and j, denoted as γi and γj , are expressed as per tao in 2008 [26] as: ln γi = ln ( vmi xivmi + xjvmjaji ) + xj ( vmjaji xivmi + xjvmjaji − vmiaij xjvmj + xivmiaij ) − x2 j 2 [ zia 2 ji lnaji (xi + xjaji) 2 + zjaij lnaij (xj + xiaij) 2 ] (2) ln γj = ln ( vmj xjvmj + xivmiaij ) − xi ( vmjaji xivmi + xjvmjaji − vmiaij xjvmj + xivmiaij ) − x2 i 2 [ zja 2 ij lnaij (xj + xiaij) 2 + ziaji lnaji (xi + xjaji) 2 ] (3) for the system of higher orders, i.e., for a multicomponent mixture, eq. (1) becomes [27]: ∆gxs = rt { n∑ i=1 xi ln vmi∑n j=1 xjvmjaji − 1 2 n∑ i=1 zixi (∑n j=1 xjaji lnaji∑n k=1 xkaki )} (4) where n is the number of components in a mixture. the formula for the activity coefficient of the ith component, γi, is provided in the work of tao in 2008 [26] by: ln γi = 1 + ln vmi∑n j=1 xjvmjaji − n∑ k=1 xkvmiaik∑n j=1 xjvmjajk − 1 2 { zi ∑n j=1 xjaji lnaji∑n l=1 xlali + n∑ j=1 zjxjaij∑n l=1 xlalȷ × ( lnaij − ∑n t=1 xtatj lnatj∑n l=1 xlalj )} (5) the formula for zi is presented in a publication by tao in 2008 [26] by: zi = 4 √ 2π 3 ( r3mi − r3oi rmi − roi ) ρirmi exp ( ∆hmi (tmi − t) zcrttmi ) (6) the molecular number density can be determined using the equation, , where ni = 0.6022 represents the molecular number. the melting temperature and melting enthalpy are indicated by tmi and ∆hmi, respectively. zc signifies a close-packed coordination, with a value of 12 for certain liquid metals. roi represents the first peak value of the radial distribution function, and rmi is the initial value of the radial distribution function, whose expressions are as follows: roi = 0.918 dcovi (7) and rmi = σi (8) here dcovi and σi represent the atomic covalent diameter and atomic diameter, respectively. the interaction parameters associated with pair potential energy are denoted by aji and aij, according to the findings of tao et al. in 2002 as [33]: aji = exp ( −εji − εii kt ) ; aij = exp ( −εij − εji kt ) (9) here εjior εij, εii and εjj represent the pair potential energies for i-j, i-i, and j-j interactions, respectively, with k being the boltzmann constant. the activity coefficients γ∞ i and γ∞ j for components i and j in binary liquid alloys are given in the limit of infinite dilution [26] as: ln γ∞ i = 1− ln ( vmjaji vmi ) − vmiaij vmj − 1 2 (zi lnaji + zjaij lnaij) (10) sanjay kumar sah et al./ bibechana 21 (2024) 83-94 86 ln γ∞ j = 1− ln ( vmiaij vmj ) − vmjaji vmi − 1 2 (zj lnaij + ziaji lnaji) (11) equations (10) and (11) must be solved using the newton-raphson method in order to determine aji and aij. these starting values are then adjusted when component activities in liquid binary alloys are calculated using equations (2) and (3). odusote et al. (2017) [28] explained that once the appropriate values of aji and aij at a particular temperature is established, their corresponding values at different temperatures can also be derived. considering the zn-bi-in ternary liquid alloy as the 1-2-3 system, the activity coefficient of the first metal, denoted as γ1, in the system can be determined using equation (5), as explained by tao in 2001 as [29]: ln γ1 = 1 + ln ( vm1 x1vm1 + x2vm2a21 + x3vm3a31 ) − x1vm1 x1vm1 + x2vm2a21 + x3vm3a31 − x2vm1a12 x1vm1a12 + x2vm2 + x3vm3a32 − x3vm1a13 x1vm1a13 + x2vm2a23 + x3vm3 − 1 2 ( z1 (x2a21 + x3a31) (x2a21 lna21 + x3a31 lna31) (x1 + x2a21 + x3a31) 2 + z2x2a12 [(x2 + x3a32) lna12 − x3a32 lna32] (x1a12 + x2 + x3a32) 2 + z3x3a13 [(x2a23 + x3) lna13 − x2a23 lna23] (x1a13 + x2a23 + x3) 2 ) (12) likewise, the surplus gibbs free energy of mixing, ∆gxs for zn-bi-in ternary liquid alloys can be derived from equation (4) as: ∆gxs = rt  x1 ln ( vm1 x1 vm1+x2 vm2 a21+x3 vm3 a31 ) +x2 ln ( vm2 x1 vm1 a12+x2 vm2+x3 vm3 a32 ) +x3 ln ( vm3 x1 vm1 a13+x2 vm2 a23+x3 vm3 ) − 1 2 [ z1x1(x2 a21 lna21+x3 a31 lna31) (x1+x2 a21+x3 a31) +z2x2(x1 a12 lna12+x3 a32 lna32) (x1 a12+x2+x3 a32) + z3x3(x1 a13 lna13+x2 a23 lna23) (x1 a13+x2 a23+x3)  (13) 3 results and discussion the required input parameters are outlined in table 1. the values of the interaction parameters of potential energy (aji and aij) for the binary alloys, as well as the first coordination numbers (zi and zj) for the components of the binary systems, are provided in table 2. coordination numbers have been computed using the formula provided in eq. (6). by plugging in the values of vm1, vm2, vm3, z1, z2, z3, a12, a21, a13, a31, a23, and a32 into equations (12) and (13), the activities of the zn component in the zn-bi-in systems at 873 k and the excess gibbs free energy of mixing, ∆gxs, for those ternary liquid alloys at 873 k were computed for all four cross-sections of xbi: xin = 1:2, 1:1, 2:1, and 9:1. the results were then compared with the corresponding experimental values [25], as illustrated in table 3 and table 4 and depicted in figures 1, 2, 3, and 4, respectively. table 1: certain input parameters [30]. metal ∆hmi [kj/mol] roi [×10−8 cm] rmi [×10−8 cm] vmi [cm3/mol] zn 7.322 2.16 2.66 9.94(1 + 1.50× 10−4(t − 693)) bi 11.30 2.78 3.34 20.80(1 + 1.17× 10−4(t − 544)) in 3.263 2.70 3.14 16.30(1 + 0.97× 10−4(t − 430)) table 2: values of aij , aji, zi, and zj computed for a range of temperature conditions in binary alloys. i-j t [k] aij aji zi zj bi− zn 873 1.1106 0.4125 8.1043 8.9699 in− zn 873 1.008 0.7123 9.1631 8.9699 bi− in 873 1.3774 0.7545 8.1043 9.1631 sanjay kumar sah et al./ bibechana 21 (2024) 83-94 87 table 3: experimental and theoretical data on zn activities in zn-bi-in ternary liquid alloys at 873 k. xzn xbi xin azn, th. e(mv) azn, exp.∗ |azn, th.− azn, exp. ∗ | xbi : xin = 1 : 2 0.00000 ————0.00000 ——————0.09900 0.30033 0.60067 0.30081 43.3253 0.31605 0.01524 0.20410 0.26530 0.53060 0.53972 23.2751 0.53859 0.00113 0.29920 0.23360 0.46720 0.69326 14.7078 0.67636 0.01690 0.40160 0.19946 0.39894 0.80280 11.456 0.73744 0.06536 0.49120 0.16960 0.33920 0.86063 6.6841 0.83719 0.02344 0.59730 0.13423 0.26847 0.89566 4.584 0.88526 0.01040 0.69580 0.10140 0.20280 0.90833 3.3761 0.91415 0.00582 0.79760 0.06746 0.13494 0.91601 3.0964 0.92097 0.00496 0.89730 0.03423 0.06847 0.93611 1.987 0.94854 0.01243 1.00000 0.00000 0.00000 1.00000 ——————xbi : xin = 1 : 1 0.00000 ————0.00000 ——————0.09940 0.45030 0.45030 0.30020 44.5091 0.30626 0.00606 0.2017 0.39915 0.39915 0.54240 22.7301 0.54645 0.00405 0.30240 0.34880 0.34880 0.71736 13.1409 0.70513 0.01223 0.39980 0.30010 0.30010 0.83199 7.88080 0.81097 0.02102 0.50040 0.24980 0.24980 0.90211 5.05520 0.87424 0.02787 0.59860 0.20070 0.20070 0.93336 3.4939 0.91129 0.02207 0.70060 0.14970 0.14970 0.93997 2.8001 0.92826 0.01171 0.80020 0.09990 0.09990 0.93665 2.1225 0.94513 0.00848 0.89930 0.05035 0.05035 0.94450 1.5482 0.95967 0.01517 1.00000 0.00000 0.00000 1.00000 ——————xbi : xin = 2 : 1 0.00000 ————0.00000 ——————0.10030 0.59980 0.29990 0.29176 45.3836 0.29922 0.00746 0.19910 0.53394 0.26696 0.52902 24.8022 0.51716 0.01186 0.30060 0.46627 0.23313 0.71723 14.2952 0.68382 0.03341 0.40010 0.39994 0.19996 0.84696 8.6099 0.79540 0.05156 0.49980 0.33347 0.16673 0.92624 4.5123 0.88695 0.03929 0.60090 0.26607 0.13303 0.96254 4.5873 0.88518 0.07736 0.70020 0.19987 0.09993 0.96658 2.8197 0.92777 0.03881 0.80210 0.13194 0.06596 0.95496 1.6984 0.95585 0.00089 0.90070 0.06620 0.03310 0.95209 1.451 0.96215 0.01006 1.00000 0.00000 0.00000 1.00000 ——————xbi : xin = 9 : 1 0.00000 ————0.00000 ——————0.10040 0.80964 0.08996 0.26752 49.751 0.26642 0.00110 0.20050 0.71955 0.07995 0.50356 28.031 0.47462 0.02894 0.30040 0.62964 0.06996 0.69851 16.1431 0.65104 0.04747 0.39800 0.54180 0.06020 0.84287 9.2727 0.78151 0.06136 0.50050 0.44955 0.04995 0.94218 4.7572 0.88119 0.06099 0.60020 0.35982 0.03998 0.98945 1.8141 0.95291 0.03654 0.70020 0.26982 0.02998 0.99628 1.6721 0.95651 0.03977 0.80020 0.17982 0.01998 0.97816 1.2784 0.96658 0.01158 0.90010 0.08991 0.00999 0.96181 0.90330 0.97627 0.00108 1.00000 0.00000 0.00000 1.00000 ——————*experimental [25] si = ± 3.10 %, s∗ i = ± 0.0302* sanjay kumar sah et al./ bibechana 21 (2024) 83-94 88 table 4: experimental and theoretical data on zn-bi-in ternary liquid alloys’ excess gibbs free energy mixing at 873 k. xzn xbi xin ∆gxsth. [j/mol] ∆gxsexp.* [j/mol] xbi : xin = 1 : 2 0.0000 0.3333 0.6667 -1549.8 -1793.0 0.1000 0.2250 0.6750 -373.4 -143.0 0.2000 0.2667 0.5333 355.8 692.0 0.3000 0.2333 0.4667 1133.4 1429.0 0.4000 0.2000 0.4000 1763.4 2025.0 0.5000 0.1667 0.3333 2216.0 2417.0 0.6000 0.1333 0.2667 2453.4 2566.0 0.7000 0.1000 0.2000 2427.1 2460.0 0.8000 0.0667 0.1333 2073.4 2103.0 0.9000 0.0333 0.0667 1304.8 1464.0 1.0000 0.0000 0.0000 0.0 0.0 xbi : xin = 1 : 1 0.0000 0.5000 0.5000 -1635.1 -1916.0 0.1000 0.4500 0.4500 -633.3 -291.0 0.2000 0.4000 0.4000 281.1 560.0 0.3000 0.3500 0.3500 1087.3 1337.0 0.4000 0.3000 0.3000 1758.5 1984.0 0.5000 0.2500 0.2500 2260.8 2426.0 0.6000 0.2000 0.2000 2550.1 2618.0 0.7000 0.1500 0.1500 2567.7 2544.0 0.8000 0.1000 0.1000 2233.4 2209.0 0.9000 0.0500 0.0500 1433.8 1568.0 1.0000 0.0000 0.0000 0.0 0.0 xbi : xin = 2 : 1 0.0000 0.6667 0.3333 -1368.1 -1547.0 0.1000 0.6750 0.2250 -230.3 -39.0 0.2000 0.5333 0.2667 443.2 746.0 0.3000 0.4667 0.2333 1224.6 1482.0 0.4000 0.4000 0.2000 1887.7 2094.0 0.5000 0.3333 0.1667 2396.0 2501.0 0.6000 0.2667 0.1333 2700.8 2658.0 0.7000 0.2000 0.1000 2734.2 2562.0 0.8000 0.1333 0.0667 2401.5 2227.0 0.9000 0.0667 0.0333 1563.3 1619.0 1.0000 0.0000 0.0000 0.0 0.0 xbi : xin = 9 : 1 0.0000 0.9000 0.1000 -512.1 -504.0 0.1000 0.8100 0.0900 266.3 811.0 0.2000 0.7200 0.0800 1003.7 1414.0 0.3000 0.6300 0.0700 1679.0 2001.0 0.4000 0.5400 0.0600 2263.9 2506.0 0.5000 0.4500 0.0500 2719.8 2851.0 0.6000 0.3600 0.0400 2993.4 2981.0 0.7000 0.2700 0.0300 3007.9 2871.0 0.8000 0.1800 0.0200 2650.2 2506.0 0.9000 0.0900 0.0100 1744.6 1812.0 1.0000 0.0000 0.0000 0.0 0.0 sanjay kumar sah et al./ bibechana 21 (2024) 83-94 89 table 4 indicates that the theoretical and experimental values [25] of the excess free energy of mixing in zn-bi-in liquid alloys at 873 k exhibit reasonable agreement, albeit with some discrepancies. the highest errors are observed at xzn = 0.1 for all four cross-sections, specifically xbi: xin = 1:2, 1:1, 2:1, and 9:1. from the experimental work of knott et al. [25], the activity of the component zn in the zn-bi-in ternary liquid alloy can be determined by a relation given in eq. (14). ∆gzn = rt ln azn = −zfe (14) where ∆gzn is the change in gibbs free energy for the zn component, z is the valency of zn, f represents faraday’s constant (i.e., 96486 coulomb/mol), r represents the molar gas constant and e represents the measured emf of the cell, whose values for all the cross-sections of bi and in have been taken from the reference [25]. based on the information in table 3, the mean relative error (si) and mean standard deviation (s∗ i ) were computed to precisely determine the extent of the difference between the experimental and predicted data. to calculate the average relative error, equation (15) can be used. si = ±100 n n∑ i=1 ∣∣∣∣ai,th. − ai,exp.* ai,exp.* ∣∣∣∣ (15) eq. (16) can be used to get the mean standard deviation. s∗ i = ± [ 1 n n∑ i=1 (ai, th. − ai, exp. ∗)2 ] 1 2 (16) in this study, 36 experimental data points (n) were considered. table 3 reveals that according to mivm, the average relative error and mean standard deviation values are ± 3.10% and 0.0302, respectively. these values are notably lower, indicating the model’s precision in predicting the activity of the zn component in the zn-bi-in ternary liquid alloys at 873 k. table 3 makes it clear that there are some discrepancies between the theoretical and experimental values [25] of the zn component’s activities in zn-bi-in liquid alloys at 873 k, but overall there is reasonable agreement. for the cross-sections xbi: xin = 1:2, 8.86% at xzn = 0.40160, for xbi: xin = 1:1, 3.18% at xzn = 0.50040, for xbi: xin = 2:1, 8.73% at xzn = 0.60090, and for xbi: xin = 9: 1, 7.85% at xzn = 0.39800 exhibits the highest error measurement, respectively. table 4 indicates that the theoretical and experimental [25] values of the excess free energy of mixing in zn-bi-in liquid alloys at 873 k exhibit reasonable agreement, albeit with some discrepancies. the highest errors are observed at xzn = 0.1 for all four cross-sections, specifically xbi: xin = 1:2, 1:1, 2:1, and 9:1. figure 1(a) demonstrates that there is a significant positive departure from ideality in zn’s theoretical and experimental activity (azn). up to xzn = 0.2992, the deviation between the theoretical and experimental results is essentially unchanged. the experimental and theoretical values exhibit a small dispersion in the concentration range of 0.2992 ≤ xzn ≤ 0.4912. again, from xzn = 0.4912 to 1.0, the deviation between them is minor. in particular, these plots show that, as xzn increases within the parameter range of 0.0 ≤ xzn ≤ 0.4016, there is an increasing positive activity deviation from ideal raoult’s law. on the other hand, a decrease in the positive activity deviation is noted in the range 0.4016 ≤ xzn ≤ 1.0. these observations are particular to cross-sections with xbi: xin = 1:2 as their defining ratio. for zn-bi-in liquid alloys at 873 k, the integral excess free energy of mixing ∆gxs versus xzn for the cross-section xbi: xin =1:2 was plotted in figure 1(b). for this cross-section, the data indicates that there were both positive and negative values found for ∆gxs. under the same concentration, xzn = 0.6, the maximum positive values were 2453.4 j/mol (th.) and 2566.0 j/mol (expt.). the apparent discrepancy between the theoretical and experimental values of ∆gxs is more noticeable at lower xzn concentrations, especially in the concentration range of 0.0 ≤ xzn ≤ 0.5. on the other hand, the observed difference between them decreases within the concentration range of 0.5 ≤ xzn ≤ 1.0, suggesting that the two datasets are convergent. zn’s theoretical and experimental activity shows a notable positive departure from ideality, as shown in figure 2(a). the difference between the theoretical and experimental results is nearly constant up to xzn = 0.3024. in the concentration range of 0.3024 ≤ xzn ≤ 0.5986, there is a slight dispersion between the theoretical and experimental values. again, there is not much of a difference between xzn = 0.5986 and 1.0. these plots indicate that as xzn increases, there is a noticeable increase in the positive activity deviation of zn from the ideal raoult’s law within the parameter range of 0.0 ≤ xzn ≤ 0.3998. in contrast, there is a noticeable decline in the positive zn’s activity deviation in the range of 0.3998 ≤ xzn ≤ 1.0 at the crosssection, xbi: xin = 1:1. the plot of ∆gxs versus xzn for the crosssection xbi: xin = 1:1, as shown in figure 2(b), sanjay kumar sah et al./ bibechana 21 (2024) 83-94 90 figure 1: theoretical and experimental variations of (a) zn activity with respect to xzn and (b) excess free energy of mixing with respect to xzn presented for zn-bi-in liquid alloys at 873 k at the cross-section xbi:xin =1:2, expt. data taken from the ref. [25]. figure 2: theoretical and experimental variations of (a) zn activity with respect to xzn and (b) excess free energy of mixing with respect to xzn presented for zn-bi-in liquid alloys at 873 k at the cross-section xbi:xin =1:1, expt. data taken from the ref. [25]. figure 3: theoretical and experimental variations of (a) zn activity with respect to xzn and (b) excess free energy of mixing with respect to xzn presented for zn-bi-in liquid alloys at 873 k at the cross-section xbi:xin =2:1, expt. data taken from the ref. [25]. sanjay kumar sah et al./ bibechana 21 (2024) 83-94 91 figure 4: theoretical and experimental variations of (a) zn activity with respect to xzn and (b) excess free energy of mixing with respect to xzn presented for zn-bi-in liquid alloys at 873 k at the cross-section xbi:xin =9:1, expt. data taken from the ref. [25]. figure 5: comparison of excess free energy of mixing with respect to xzn presented for zn-bi-in liquid alloys at 873 k at all the cross-sections, i.e., xbi: xin =1:2, 1:1, 2:1, and 9:1. sanjay kumar sah et al./ bibechana 21 (2024) 83-94 92 indicates that there were also both positive and negative values found for ∆gxs. under the concentrations, xzn = 0.7, the maximum positive theoretical value was 2567.7 j/mol, and the maximum positive experimental value was 2618.0 j/mol at xzn = 0.6. the difference between the theoretical and experimental ∆gxs values is more noticeable at lower xzn concentrations in the range of 0.0 ≤ xzn ≤ 0.5. on the other hand, convergence occurs in the concentration range 0.5 ≤ xzn ≤ 1.0. figure 3(a) reveals a notable positive departure from ideality in zn’s theoretical and experimental activity. the deviation remains consistent up to xzn = 0.1991. the dispersion between them is slightly larger in the concentration range of0.1991 ≤ xzn ≤ 0.4998. at xzn = 0.6009, the difference between them is the maximum. again, from xzn = 0.6009 to 1.0, the deviation between them becomes smaller. according to these plots, there is a noticeable increase in the positive activity deviation from the ideal raoult’s law as xzn increases within the specified parameter range of 0.0 ≤ xzn ≤ 0.4001. on the other hand, at crosssections xbi: xin = 2:1, a decrease in positive activity deviation is observed within the following range of 0.4001 ≤ xzn ≤ 1.0. as seen in figure 3(b), the plot of ∆gxs versus xzn for the cross-section xbi: xin = 2:1 shows that ∆gxs was also found to have both positive and negative values. the maximum positive values were 2734.2 j/mol (th.) at xzn = 0.7 and 2658.0 j/mol (expt.) at xzn = 0.6. the disparity in ∆gxs values is pronounced at lower xzn concentrations, notably at 0.0 ≤ xzn ≤ 0.4. conversely, the difference diminishes at 0.4 ≤ xzn ≤ 0.6, increases at 0.6 ≤ xzn ≤ 0.8, and decreases again toward the concentration range’s end. figure 4(a) illustrates a notable positive departure from ideality in zn’s theoretical and experimental activity. the deviation remains consistent up to xzn = 0.2005. in the concentration range of 0.3004 ≤ xzn ≤ 0.7002, the dispersion between them becomes larger. again, after that, in the range of 0.7002 ≤ xzn ≤ 1.0, the deviation between them becomes smaller. according to these plots, there is a noticeable increase in the positive activity deviation from the ideal raoult’s law as xzn increases within the specified parameter range of 0.0 ≤ xzn ≤ 0.398 . on the other hand, at crosssection xbi: xin = 9:1, a decrease in positive activity deviation is observed within the following range of 0.398 ≤ xzn ≤ 1.0. as can be seen in figure 4(b), the plot of ∆gxs versus xzn for the cross-section xbi: xin = 9:1 shows that ∆gxs was also found to have both positive and negative values. the maximum positive values were 3007.9 j/mol (th.) at xzn = 0.7 and 2981 j/mol (expt.) at xzn = 0.6. the apparent discrepancy between the theoretical and experimental values of ∆gxs is more noticeable at lower xzn concentrations, especially in the concentration range of 0.1 ≤ xzn ≤ 0.3. on the other concentrations of xzn, the observed difference between them is smaller. the graphical plots of excess gibbs free energy of mixing zn-bi-in liquid alloys at 873 k for all four cross-sections, i.e., xbi: xin =1:2, 1:1, 2:1, and 9:1, have been shown in figure 5. on comparison, we found that when the molar the ratio of bi and in increases from xbi: xin =1:2 to 9:1, the maximum positive values of ∆gxs increase. furthermore, keeping the concentration of zn constant, we observe that in concentrations greater than 0.4, i.e., xzn = 0.5 to 0.9, in every case, as the ratio (xbi: xin) increases from 1:2 to 9:1, then the positive values of ∆gxs also increase. for concentrations xzn below 0.5, i.e., for each case of xzn = 0.1, 0.2, 0.3, and 0.4, as the ratio xbi:xin increases from 1:2 to 1:1, either the negative value of ∆gxs increases or the positive values of ∆gxs decrease, and afterward, as the ratio xbi: xin increases from 1:1 to 9:1, either the negative ∆gxs values decrease or positive ∆gxs values increase. for example, in a particular case, at xzn = 0.1, the negative ∆gxs values have decreased and finally shifted to positive as xbi: xin increases from 1:1 to 9:1. a positive deviation from raoult’s law, and thus a positive excess gibbs free energy for all four cross-sections, indicates that the interactions between the components in the mixture are weaker than expected based on ideal behavior. in the context of liquid alloys, a positive deviation in the activity of a component like zn suggests that the interactions between zinc atoms and the other components (bi and in in this case) are weaker in the mixture than one would predict from assuming ideal behavior. it also indicates that the partial vapor pressures of the component zn in zn-bi-in alloys at 873 k are higher than their corresponding vapor pressures in the case of an ideal mixture. furthermore, the positive values of ∆gxs for all three cross-sections indicate that after mixing, the average distance between the molecules of the three liquid metals increases, i.e., the volume of the mixture expands relative to the ideal mixture. 4 conclusion the positive deviation of the activities of the component zn (for the zn-bi-in system) at all four cross-sections of bi and in, i.e., 1:2, 1:1, 2:1, and 9:1 from ideal mixing, has been successfully explained theoretically using mivm. there is a significant positive departure from ideality in zn’s activity in zn-bi-in liquid alloys at all four cross-sections of bi and in. similarly, both the negative and positive sanjay kumar sah et al./ bibechana 21 (2024) 83-94 93 values of the excess gibbs free energy of mixing for the zn-bi-in system for all four cross-sections of xbi/xin have also been successfully explained by the same theoretical model. the maximum positive values of ∆gxs increase when the molar ratio of bi and in increases from 1:2 to 9:1 in the zn-biin system. since there is a lack of existing research on the ∆gxs of zn-bi-in liquid alloys employing the mivm model, the theoretical information on the ∆gxs of ternary liquid alloys presented in this study will be valuable for providing a more precise understanding of the thermodynamic characteristics of zn-bi-in liquid alloys. references [1] hongwei yang, bin yang, baoqiang xu, dachun liu, and dongping tao. application of molecular interaction volume model in vacuum distillation of pb-based alloys. vacuum, 86(9):1296–1299, 2012. 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(no title), 1987. introduction methodology results and discussion conclusion bibechana vol. 21, no. 3, december 2024, 221-232 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar biosorption study of cr (vi) from the aqueous solution using chemically modified biomass of a newly isolated edible mushroom waste gopal gautam khatri1, manish baskota1, anita chand1, samjhana bharati2, dasu ram paudel1∗ 1department of chemistry, tri-chandra multiple campus, tribhuvan university, kathmandu 44600, nepal 2department of chemistry, amrit campus, tribhuvan university, kathmandu 44600, nepal. ∗corresponding author: email: dasu.paudel@trc.tu.edu.np abstract despite some physiological role in human body, some metals, like hexavalent chromium, have no recognized biological benefit and are poisonous above tolerance limits. for the first time, a widely available pleurotus sajor caju (fungus) biomass was studied for the cr (vi) adsorption from an aqueous solution involving physisorption, and chemisorption. using the batch adsorption method, sorption experiments were conducted, and sorption parameters such as ph, contact time, adsorbent dose, and starting metal ion concentration were studied. the sorbent material was shown to remove up to 91.67% of the cr (vi) at a ph value of 2. it was discovered that the maximum adsorption (qmax) was 239.98 mg/g. the freundlich model was adopted for the equilibrium adsorption isotherm for cr (vi). the biosorption kinetics was ascertained by fitting pseudo-first order and pseudo-second order kinetic models for the experimental data and the pseudo-second order model was found to better describe the data. the interaction of metal ions with the carboxyl, hydroxyl, and carbonyl groups present in biomass is primarily involved in metal ions uptake. this demonstrated the potential application of mushroom residues as a low-cost and promising bio-sorbent. keywords bio-adsorbent; heavy metals; adsorption; batch study; water security. article information manuscript received: january 22, 2024; revised: may 29, 2024; accepted: june 7, 2024 doi https://doi.org/10.3126/bibechana.v21i3.62097 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 221 http://nepjol.info/index.php/bibechana dasu.paudel@trc.tu.edu.np https://doi.org/10.3126/bibechana.v21i3.62097 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ gopal gautam khatri et al./ bibechana 21 (2024) 221-232 222 1 introduction the aquatic environment is facing exceptional challenges and become one of the primary global concerns because of abandoned water pollution and unintended water security [1]. aquatic pollution knowingly affects the water quality, visibility, and water reaction mechanisms including the lack of dissolved oxygen, biodegradation processes, and photosynthesis [2]. heavy metals, dyes, and hazardous pigment effluents discharged from different sources like battery, electroplating, textile, pesticide, fertilizer, cosmetics, etc. contaminate the water sources which pose a warning to public health and ecosystems [3]. as opposed to organic contaminants, most of the heavy metals are toxic, carcinogenic, non-biodegradable and accumulate in living tissues through the food chain, causing severe damage of internal organs [4]. thus, great attention regarding the elimination of toxic heavy metals, dyes, pigments, etc. is required using a novel, low cost, and feasible technology and material. specifically, chromium is considered as a major pollutant in aquatic environment owing to its extensive use in leather, electroplating, ceramics, and other industries [5]. mostly, the cr(vi) forms like hcro4 -, cro4 2-, and cr2o7 2are strongly oxidizing and are predominantly found in surface water and aerobic soils species [6,7]. the cr(iii) is essential element for the human body and other living organism however the cr(vi) is 5-10 times toxic than cr(iii) and is classified among the top pollutants and listed as the 16th dangerous contaminant [8,9]. due to high solubility, the cr(vi) intake typically occurs through contaminated food, leakage, sea foods, skin or respiratory tract and can easily enters in stomach, kidney, and liver. the health issues related to cr(vi) include the risk of lung, nasal, sinus cancer, ulcer, anemia, damage to sperm, detriment to the male reproductive system, asthma, abdominal pain, eye irritation, etc. [10,11]. the adverse health effects of cr (vi) compelled us to solve the problem by finding a suitable method of removal from aquatic environments. remediation of heavy metals from aqueous solutions is a topic of significant interest in environmental research. among many, reverse osmosis, flotation, activated carbon adsorption, ion exchange, chemical reduction, precipitation, electrodialysis, and some traditional methods are in common practice to remove heavy metals from water and wastewater [12]. these are just a few examples of the methods used for the remediation of heavy metals from aqueous solutions. researchers continue to explore innovative technologies and materials to improve the efficiency and cost-effectiveness of heavy metal removal processes. however, the mentioned approaches are typically costly and ineffective, especially at low metal ion concentrations between 1 and 100 mg/l [13]. adsorption is a widely used method for the removal of heavy metals from water having low concentration of metal ions. materials like activated carbon, clay minerals, zeolites, and biosorbents are commonly used for adsorption due to their high surface area and adsorption capacity [14]. the solidphase byproduct of biomass pyrolysis, biomass carbon, has gained attention as a possible material to treat wastewater due to its rich functional group sites and better developed pore structure. researchers have developed cutting-edge techniques including physicochemical activation, metal loading, and organic/inorganic modification to bring biochar from the lab to the commercial sector. these techniques have produced good results in terms of increasing specific surface area, optimizing the structure of the pore layer, and changing functional groups, all of which significantly improved the pore structure and surface functional groups [15]. consequently, it is important to design a stable, earth-abundant, inexpensive, and highly effective adsorbent for water purification and heavy metal decontamination process, such as bioadsorbent [16]. a known biotic mechanism cannot dissolve toxic heavy metals from water. biosorption is a very common physiochemical mechanism that involves the adherent of atoms, ions, or molecules of dissolved solids from liquid to the surface of solid materials derived from organic sources [17]. principally, the biosorption process involves a simple chemistry where the heavy metal ions in aqueous solution bound on the surface of an adsorbent due to an imbalance between two environments creating a driving force to be adsorbed onto adsorbent. the process continues till phase equilibrium is established between the amount of solidbound adsorbate species and its fraction left behind in the solution [18]. activated carbon, seaweed, microorganisms, fermented waste, and some other generated biomasses are only a few examples of the many diverse types of bio-sorbent sources that are defined by their wide source, cheap cost, and effective adsorption capability [16–19]. moreover, mushroom-based biomasses are potent for the bioremediation of several heavy metals, dyes, organic pollutants, etc. the hemicellulose fungal cell wall, chitin, chitosan, polyuronide, polyphosphates, lipids, and proteins are the primal components of the mushroom fungus that portray the superior metal binding abilities [20,21]. studies demonstrate the use of mushrooms and fungal biomass as effective biosorbents for the removal of various heavy metals from aqueous solutions and researchers are continuously exploring novel approaches and technologies to enhance the efficiency and sustainability gopal gautam khatri et al./ bibechana 21 (2024) 221-232 223 of heavy metal remediation processes using mushrooms [22–24]. specifically, for the bioremediation of hexavalent chromium, fungal derived adsorbents are widely used, demonstrating effective removal from aqueous solutions. the mushroom substrate shows that it has an exceptional ability to adsorb cr (vi) from water. the fungus species' cell wall contains chitin, which contributed to the likely binding of the cr (vi) ions. fungal cell walls are made up of 80–90% heteropolysaccharides, proteins, lipids, polyphosphates, and inorganic ions that act as adhesive material to create the walls. a common component of fungal cell walls that has the capacity to complex metal ions is chitin. also many polysaccharides found in fungal cell walls are crucial for metal binding. it has also been discovered that some functional groups, specifically carboxyl groups, have the capacity to bind metal ions [25]. the potential of mushroom-derived waste biomaterials for the adsorption and extraction of heavy metals that are harmful from wastewater is interesting. significant recycling potential is also accessible for the waste fungal biomass adsorbent that is created. following five cycles of adsorption and regeneration. up to 85.5% of cr (vi) ions are still able to be eliminated with good effectiveness [26]. through a series of batch adsorption experiments, the study explores the effectiveness of oyster mushrooms (pleurotus platypus) for the removal of cr(iii) and cr(vi) from aqueous solutions. the results demonstrate that the ligand exchange process and electrostatic force of attractions are the main causes of the adsorption processes [27]. other several mushroom(fungus) species were reported to show great efficacy for the bioremediation of cr(vi). aspergillus carbonarius performed well with 92.43% removal of cr(vi) [28]. in this work, we derived modified pleurotus sajor caju waste-derived biomass and focused on the efficacy towards biosorption of toxic heavy metal, cr(vi), from water bodies. the impact of modified and raw pleurotus sajor caju waste-derived biomass to remove cr(vi) from synthetic aqueous solution was accessed. the 0.1 m naoh modified pleurotus sajor caju waste-derived biomass powder showed an increased sorption capacity of positively charged metal ions (cr+6) onto its surface than raw biomass possibly due to the interaction of metal to hemi cellulosic cell wall components. as a result, the addition of naoh in biomass enhances their ability of metal binding and mechanical strength as well. the sorption property was explored by analyzing the effects of contact time, adsorbent dose, ph, adsorption isotherm, starting concentration, and batch kinetics. the sem, eds, and ft-ir analysis describe the surface structure and basic chemical groups in the biomass. hence, this work suggests and found a strategic functionalization of pleutorous sajo-coju waste as potential bio-adsorbent to amplify the basic understanding of adsorption in a real aquatic environment. 2 materials and methods 2.1 materials all the chemicals (sulphuric acid, buffer tablets, potassium dichromate, 1,5-diphenyl carbazide, nitric acid, sodium hydroxide, etc) of analytical grade were purchased from thermo fisher scientific india. 1000ppm stock solution of potassium dichromate, 0.1 n nitric acid, 5n sulphuric acid, 2n nitric acid, 0.1m & 2n sodium hydroxide, 0.25% dcpi solution and buffer solutions (ph-4.0,7.0 & 9.2) were prepared in different volumes. 2.2 experimental 2.2.1 preparation of raw and modified adsorbent the mushroom was washed, shade dried, then ground to a mess size of 250 microns. a part of powered mushroom underwent 0.1m naoh treatment, followed by three hours of reflux at 80°c. the ph of the final product was then kept neutral by washing with distilled water and adding nitric acid. for two hours, the mixture was then dried in an oven set at 80°c. the products were then used for the adsorption studies and ftir was used to confirm the extent of modification [29,30]. modifying bio-adsorbents enhanced adsorption capacities, but it will increase the adsorbents' cost. therefore, a cost-benefit analysis is required. the modifying chemicals used in this study may cause impacts on the environment so the proper discharge procedures were followed. 2.2.2 determination of λmax and calibration various volume of working cr(vi) solution containing 20mg/ml were taken in 25 ml volumetric flask, acidified with 1 ml of 5 n h2so4, followed by addition of 1 ml of 0.25% of dcpi solution and remaining volume with distilled water. the absorption spectra of pink colored cr(vi)-dpci complex were recorded against blank solution. among various absorption spectra, λmax was recorded at 530 nm, using calibration curve [31,32]. 2.2.3 batch adsorption study an erlenmeyer flask is pipetted with a known concentration of metal solution that has been phadjusted, and the predetermined quantity of adsorbent is then added. the flask is shaken for the gopal gautam khatri et al./ bibechana 21 (2024) 221-232 224 specified amount of time to ascertain the concentration of adsorbate. adsorbate adsorption is dependent on a number of factors, including ph, contact time, adsorbent dosage, metal solution concentration, etc. one of these parameters was changed while keeping the others fixed in order to understand the adsorption mechanism. the equilibrium adsorption amount (qe) and the percent metal uptake by adsorbent were expressed [32,33]. qe = (ci− ce)v w mg/g (1) where, qe is the amount of metal ion adsorbed per unit mass of adsorbent, w is weight of adsorbent (g), ci is initial concentration of adsorbent dose (mg/l), ce is equilibrium concentration of adsorbate (mg/l), v is volume of adsorbate. the ratio of the adsorbate ion concentration before and after adsorption to the initial concentration of metal ions in aqueous solution determines the adsorbate removal percentage. removal percentage(r) = ci− ce ci x100 % (2) 2.2.4 adsorption isotherm the amount of adsorbate adsorbed per mass of adsorbent and the quantity of unabsorbed adsorbate remaining in the solutions at equilibrium time are related by a curve known as the adsorption isotherm. the most significant isotherms for analyzing the adsorptive behavior of an adsorbate and an adsorbent are the langmuir and freundlich adsorption isotherms. 2.2.4.1. langmuir adsorption isotherm the linear form of this isotherm is represented by the expression 1 qe = 1 qm + 1 qmklce (3) where, qe is maximum adsorption of bio-sorbent at equilibrium (mg/l), qm is theoretical monolayer saturation capacity(mg/l), kl is langmuir equilibrium constant (l/mg). langmuir constant qm and kl can be obtained as slope ( 1 qm ) and intercept ( 1 qmkl ) respectively from the linear plot of (ce qe ) vs ce. by utilizing a dimensionless constant separation factor or equilibrium parameter, the fundamental properties of the langmuir adsorption isotherm can be used to estimate the affinity between the biosorbent and the biosorbate. rl =1/1 +klc i. (4) 2.2.4.2. freundlich adsorption isotherm the freundlich adsorption isotherm assumes a heterogeneous adsorption surface and active sites with different energy. this isotherm can be explained by equation 5 [34]. qe = kfc 1/n e (5) where, kf is freundlich constant (l/g), n = freundlich exponent (g/l). the value of these factors affects the isotherm's curvature and steepness, while the value of n reveals the adsorbate's affinity for the adsorbent. this isotherm's linear form is written as: log (qe) = log (kf ) + 1 n log (ce) (6) 2.2.5 adsorption kinetics . 2.2.5.1. pseudo first order kinetic model the pseudo first order kinetics proposed by lagergren for adsorption analysis can be express in equation 7 [35]. dqt dt = k1 (qe − qt) (7) where, qe is amount of cr(vi) per gram on the surface of adsorbent at the equilibrium(mg/g), qt is amount of cr(vi)per gram on the surface of adsorbent at time ‘t’(mg/g), k1 is equilibrium rate constant of pseudo-first order kinetics. after integration and applying boundary condition, t = 0 to t = t, qt = 0, and qt = qt the linear form of the equation (7). loq (qe − loq (qt − qt) = loq qe − k1t 2.303 (8) k1 is calculated from the linear plot of log (qeqt) against time. 2.2.5.2. pseudo second order kinetic model the pseudo second order rate equation for adsorption analysis [36]. dqt dt = k2(qe − qt) 2 (9) after integration and boundary condition qt = 0 at t=0, qt = qt at t = t equation (9). t qt = 1 k2q2e + 1 qet t (10) where, k2 is equilibrium rate constant for pseudo second order kinetics, k2 and qe can be calculated from the graph of t/qt against t. gopal gautam khatri et al./ bibechana 21 (2024) 221-232 225 2.2.6 spectrophotometric methods for the determination of cr (vi) dpci method is quite suitable for the determination of cr(vi) in aqueous solution. the absorbance of the solution measured at maximum wavelength is 530 nm. 2.2.7 material characterization the fourier transform infra-red (ftir) spectroscopy was done at the central department of chemistry, tribhuvan university, kathmandu. the spectra of rpsc and mpsc were obtained with a bruker spectrometer model, using potassium bromide (kbr) pellet method. the surface morphologies of mpsc and rpsc samples were characterized by using field emission scanning electron microscope (fe-sem, model: supra 40 v p instrument zeiss co., germany) and energy dispersive x-ray spectroscopy (eds) based elemental composition in the center for university-wide research facilities (curf) of jeonbuk national university, south korea. 3 result and discussion by adopting a most generalized and simple hydroxyl functionalization technique, the waste of edible mushroom pleutorous sajo-coju was prepared as an active biomass for heavy metal (cr+6) removal from aqueous solution (scheme 1, details in experimental section). on optimizing different physicochemical parameters such initial ph, initial adsorbate concentration, contact time, adsorbed dosage, and desorption research, the sorption of cr (vi) in an aqueous solution was investigated based on raw and functionalized psc. scheme 1:schematic representation showing preparation and modification of bio-adsorbent from pluorotous sajor-caju (fungus), application for removal of cr (vi) from aqueous solution and characterization. 3.1 maximum absorbance and calibration curve study the maximum absorption wavelength for cr (vi) obtained at 530 nm was used to prepare calibration curve, shown in figure (1 a, b). 3.2 effect of contact time for cr (vi) dpci complex formation the effect of contact time on adsorption of cr (vi) at initial concentration of 50 mg/l were studied. the figure 2 showed the experimental data where gopal gautam khatri et al./ bibechana 21 (2024) 221-232 226 a rapid uptake of metal ion occurs initially and absorbance value was nearly constant from 0 to 20 minutes, the absorbance value within 20 minutes was calculated using dpci solution. the relationship between time and absorbance is shown in figure 2. 3.3 effect of ph for absorption of cr (vi) on to mpsc and rpsc figure 3 illustrates how ph affects the adsorption of cr (vi) onto rpsc and mpsc. in the instance of rpsc, removal of cr (vi) was found to be reduced as ph increased; the highest removal value was shown to be at 1.0, which is an optimum ph for rpsc. however, the highest removal value for mpcs was shown to be 2.0, and this ph is optimum for mpsc. 3.4 effect of contact time for adsorption of cr (vi) onto rpsc and mpsc the batch adsorption of a 20 mg/l metal solution with a 25 mg adsorbent was studied by assessing the impact of contact time over different time periods ranging from 10 minutes to 360 minutes. the impact of contact time on the adsorption of cr (vi) onto rpsc and mpsc is shown in figure 4. adsorption was discovered to be expanding as time value has increased. figure 1: (a) determination of max for cr (vi)-dpci complex (b) calibration curve. figure 2: effect of time on cr (vi)-dpci complex formation. figure 3: effect of ph on cr (vi) adsorption by rpsc and mpsc. gopal gautam khatri et al./ bibechana 21 (2024) 221-232 227 figure 4: effect of contact time for the adsorption of cr (vi) onto rpsc and mpsc. 3.5 effect of initial cr (vi) ion concentration for mpsc, the quantity adsorbed increased from 11.61 mg/g to 201.90 mg/g, whereas for rpsc, the amount adsorbed increased from 13.82 mg/g to 204.12 mg/g. the adsorption increased from lower concentration to higher concentration ranges (20 mg/l to 500 mg/l). these results demonstrate that, as the amounts of adsorbent increases, so does adsorption. the effects of the initial adsorbate concentration for rpsc and mpsc are shown in figure 5. figure 5: adsorption isotherm of cr (vi) onto rpsc and mpsc. 3.6 batch isotherm studies the freundlich and langmuir isotherms exhibited a linear relationship with cr (vi) adsorption onto mpsc and rpsc. figures 6 (a) and (b) illustrate respectively, the langmuir isotherm and the freundlich isotherm whose r2 value indicates that freundlich isotherm is best fitted over langmuir isotherm. this result indicates that freundlich isotherm has greater applicability. the insight into the sorption favorability in terms of correlation coefficient indicates the active sites of mpsc were dispersed throughout and the ions are adsorbed chemically on the surface. figure 6: (a) langmuir isotherm and (b) freundlich isotherm plot for the adsorption of cr (vi) onto rpsc and mpsc. gopal gautam khatri et al./ bibechana 21 (2024) 221-232 228 3.7 batch kinetic modeling the kinetic data for cr (vi) adsorption onto mpsc and rpsc was studied using pseudo-first-order and pseudo-second-order kinetic models. the comparative plot of these models is represented in figures 7 (a) and (b), respectively. from the kinetic plots for the adsorption of cr (vi), it was found that the value of the correlation coefficient (r2) for the pseudo-second-order kinetic model was higher (close to one) than that of the pseudo-first-order. the results of the experimental data were better described by pseudo-second-order kinetics. this kinetic model signifies the adsorption behavior of adsorbent across the complete range. figure 7: pseudo (a) first and (b) second order kinetic model for the adsorption of cr (vi) onto rpsc and mpsc. 3.8 effect of adsorbent dose the effect of the adsorbent dose for the adsorption of cr (vi) onto mpsc and rpsc, was studied at room temperature by varying the adsorbent amount from 25 mg to 200 mg which indicates that the adsorbent dose is directly proportional with the adsorption yet showed constant value of the % adsorption beyond 100 mg for mpsc and 160 mg for rpsc, respectively. in addition to this, % adsorption was remarkably higher in case of mpsc over rpsc for the same doze of adsorbent. figure 8 shows the effects of adsorbent dose for the adsorption of % of cr (vi). 3.9 ftir analysis ftir analysis was performed to investigate the surface functional groups of mpsc and rpsc whose spectra have been shown in figure 9 (a) and 9 (b), respectively. the graph of mpsc indicated the presence of -oh, c=o, n=n=n, n=c=s, c=n, n-o, etc., which are responsible for the adsorption of cr (vi). compounds containing these functional groups have enough ability to bind chromium as they contain double bond active sites. figure 8: effect of adsorbent dose for the adsorption of cr (vi) onto rpsc and mpsc. gopal gautam khatri et al./ bibechana 21 (2024) 221-232 229 figure 9: ftir spectra of (a) rpsc and (b) mpsc. 3.10 fe-sem and eds analysis figure 10 displays the fesem analysis of the adsorbent samples both before and after adsorption along with eds mapping and eds spectrum. prior to adsorption, the fesem images at different magnitudes for mpsc revealed a porous structure and the presence of more free sites (figure 10 a-c). the high magnification image of mpsc in figure 10c indicates the distinctive porosity, and awful rough surfaces with broken edges thus providing valuable sites for metal ion adsorption on the surface of adsorbent. after adsorption, the surface morphology of sorbent mpsc (figure 10d) showed some changes that signify the effective adsorption of metal ions on the surface of the adsorbent. the morphological change as a result of the accumulation of cr (vi) ions on mpsc led to the smooth and brighter surfaces might be due to interaction of functional group of sorbents with targeted metal ions. this revealed that a higher concentration of cr (vi) had been adsorbed using the bio-sorbent also confirmed from the eds elemental mapping obtained from the fesem. the postadsorption eds pattern of mpsc (figure 10e-i) revealed characteristic colour mapping images for carbon, nitrogen, oxygen, and chromium. moreover, the eds spectrum and the elemental distribution in figure 10j clearly depicts the significant amount of chromium and other element revealing the potency of bio-adsorbent for efficient removal of toxic metal from aqueous solution. overall, the rough surface of mpsc has a considerable effect on the capacity for adsorption [37]. figure 10: fe-sem image of (a, b, c) mpse, (d) mpsc after adsorption and (e, f, g, h, i) fesem-eds colour mapping of mpsc, (j) eds spectra of mpsc and corresponding atomic composition.. gopal gautam khatri et al./ bibechana 21 (2024) 221-232 230 4 conclusion this study provides promising evidence for the use of pleurotus sajor-coju as the potent source of a new adsorbent due to high abundance and low costing procedure. modified pleurotus sajor-coju was found to be more effective adsorbent than raw one, for the removal of cr (vi). ftir analysis confirms the presence of azide, thiocyanate, alcohol, nitro, sulphonyl chloride and oxime groups on naoh modified pleurotus sajor-coju (mpsc) which are responsible for adsorbing cr (vi) from aqueous solution. the mass of the adsorbents were reported to be amorphous, however certain peaks displayed the crystallinity of cellulose. additionally, the sem analysis of the surface 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2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar biochemical, antimicrobial, and antioxidant activities of some wild mushrooms from nepal pratiksha chaudhary, nabin panth, bimal kumar raut, nisma pokhrel nita shrestha, sajan shakya, bijaya bahadur thapa akkal dev mishra, niranjan parajuli∗ biological chemistry lab, central department of chemistry, tribhuvan university kirtipur, kathmandu, 44618, nepal ∗corresponding author. email: niranjan.parajuli@cdc.tu.edu.np abstract wild mushrooms represent a crucial dietary staple for many tribal groups throughout the world since they consist of an excellent amount of biologically active constituents including phenolic compounds, and tocopherol, and act as anti-cancer, anti-allergic, anti-obesity, anti-inflammatory compounds, etc. wild mushrooms including scleroderma citrinum, heterobasidion annosum, coriolus hirsutus, cavimalum indicum, russula sanguinea, and suillus punctatipes were studied to evaluate their phytochemicals, antimicrobial activity, antioxidant activity, toxicity and relevance as a food source along with safety concerns. initially, the total phenolic content (tpc), total tannin content (ttc), and total flavonoid content (tfc) along with antioxidant and antimicrobial activity were assessed using ethanolic extracts of mushrooms. furthermore, a brine shrimp bioassay was performed, the correlation of which with antioxidant activity, tpc, tfc, ttc, and lethal concentration (lc50) was shown by principal component analysis (pca). secondary metabolites such as glucosides, flavonoids, polyphenols, alkaloids, terpenoids, saponins, and quinones were identified using phytochemical investigations. the tpc ranged from 45.98 to 102.3 mg gae/g for the extracts, tfc from 100 to 225 mg qe/g, and ttc from 80 to 180 mg gae/g. the findings of the antioxidant studies demonstrated that s. punctatipes exhibited the highest antioxidant activity (ic50 = 16.95 µg/ml), followed by c. indicum (ic50 = 22.5 µg/ml), and c. hirsutus (ic50 = 35.34 µg/ml). likewise, s. punctatipes exhibited strong antimicrobial activity as compared to other extracts. the larvicidal efficacy against brine shrimp bioassay revealed that three mushrooms; c. hirsutus, c. indicum, and s. punctatipes—contain highly toxic chemicals while the other three are non-toxic and can be consumed to some extent. keywords wild mushroom, phytochemicals, antioxidants, antimicrobial. article information manuscript received: may 15, 2023; accepted: june 13, 2023 doi https://doi.org/10.3126/bibechana.v20i2.54887 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 161 http://nepjol.info/index.php/bibechana niranjan.parajuli@cdc.tu.edu.np https://doi.org/10.3126/bibechana.v20i2.54887 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ pratiksha chaudhary et al./ bibechana 20 (2023) 161-175 162 1 introduction mushrooms are fungi that develop fleshy, sporebearing fruiting bodies and are members of the higher groups; ascomycota and basidiomycota [1]. an ample diversity of mushrooms has long been identified as edible fungi that possess a wealth of nutritional value, low-calorie content, and an abundance of structurally varied and beneficial secondary metabolites [2]. as a beloved delicacy food source, mushrooms have long been used, and recent research into their antioxidant and health advantages further adds to their allure [3]. bioactive substances derived from fungi have long been recognized, and fungi’s secondary metabolites have been the subject of investigation [4]. medicinal chemists have considered the potential benefits of mushrooms in humans for a variety of diseases to be beneficial in drug discovery and development by offering fundamental template structures and pharmacophores of therapeutically and economically effective products [5]. the therapeutic advantages of mushrooms, which include anti-hyperlipidemic, antiinflammatory, anti-cancer, antioxidant, immunoregulatory, and cardioprotective properties, are all owing to the presence of secondary metabolites in mushrooms [6–9]. numerous bioactive constituents including tocopherols, ergosterols, lectins, ergothioneine, glutathione, vitamin d, selenium, repandiol, polysaccharide-k, and many more are reported as a source of antioxidant activity in various mushroom species [5,7,10]. likewise, striatal a, b, c, and d, effective against cancer, were isolated from cyathus striatus and showed antimicrobial properties [11]. several triterpenoids; ganoderic acid e, lucidumol a, and ganoder-manontriol, found in ganoderma lucidum demonstrated remarkable cytotoxicity against human cancer cells. poisonous mushrooms that smell bad or cause severe gastrointestinal complications are classified as non-edible species. wild edible mushrooms are a natural forest resource well recognized for their nutritional, medicinal, economic, and cultural worth [12]. meanwhile, poisonous mushrooms are frequently mistaken for edible species when ingested as wild mushrooms because of their similarity in form and color. concern is also raised about the dangerous byproducts that are produced by toxic mushrooms [13]. however, the value of wild mushrooms is increasing as a result of their phenolic compounds, which act as potent antioxidants in addition to their pharmacological, nutritional, and sensory qualities [2]. thus, it is equally crucial to explore secondary metabolites found in mushrooms. mushrooms had been used as a therapeutic agent in civilizations all over the world. it has long been known as a medicinal plant in china and other asian countries, including japan and korea, and has extended to countries such as the united states as well as eastern europe, including russia [14]. even though nature has endowed wild mushrooms with diverse economic and therapeutic significance, research on the bioactivity and potential medical benefits of available mushrooms has not been thoroughly conducted extensively. the situation is even direr in developing nations like nepal where there has only been a scant study on wild mushrooms regardless of the availability of 108 families, 357 genera, and 1291 species of mushrooms with about 159 being edible, and 74 species reported to have medicinal properties [15]. scleroderma citrinum (genus scleroderma), also called scleroderma aurantium or scleroderma vulgare horn, grows from late summer to early winter frequently seen in europe and nepal, has remarkable medicinal properties, and thus, used in the pharmaceutical industries, cosmetics, and nutritious food as well [16]. it is reported to contain bioactive compounds such as sclerocitrin, norbadione a, xerocomic acid, badione a, etc [17]. heterobasidion annosum (agaricomycetes species), also known as polyporus annosum, is a species of the bondarzewiaceae family that can grow a diameter of up to 40 cm and a thickness of 3.5 cm. it is frequently found in north america and nepal, is inedible, and has been discovered to help prevent colon cancer [18]. likewise, coriolus hirsutus commonly known as rau bhako chyau is a common hairy beechwood-grown bracket fungus that not only serves as a food source but is also reported to cure wounds in traditional nepalese communities [19]. coriolus hirsutus is a common hairy bracket fungus that is grown specifically in beechwood. it persists throughout the year, has a slightly zoned crown, is occasionally white-gray with short hairs, and is tomentose and yellowish near the border. another wild mushroom species, cavimalum indicum mostly grows in bamboo trees and very little study has been reported to date. the basidiomycota family includes russula sanguinea which grows beside coniferous trees and is mycorrhizal with softwood trees. moreover, studies on r. sanguinea, a vibrantly brightly colored mushroom, exhibit strong enzyme inhibition; antiamylase and anti-glucosidase activities along with effective antioxidant activities [20]. bioactive constituents like sangusulactones a-c, blennin a, and 15-hydroxyblennin a responsible for several pharmacological activities are found in this species [21]. suillus puntatipes, often known as puffballs, are characterized by their white-yellow cap meat mass, a layer of grayish-red-purple skin, and pores that are greenish-yellow in color. it has been demonstrated for the production of cytokinins like zeatin and ribosylzeatin [22]. the human adenosine a2a pratiksha chaudhary et al./ bibechana 20 (2023) 161-175 163 figure 1: list of some collected mushrooms. ascleroderma citrinum, bsuillus punctatipes, ccoriolus hirsutus, drussula sanguinea, eheterobasidion annosum, fcavimalum indicum. receptor, which is widely represented by many different types of cells and has an important function in controlling the activity of cells engaged in both adaptive and innate immunity, has recently been shown to be activated by the naturally occurring cytokinin zeatin riboside [23]. numerous species of mushrooms have been the subject of various research throughout the world, but only a small number of studies have focused on specific wild mushrooms. the key purpose of this research is to investigate the phytochemical content, evaluation of toxicity of mushroom extracts to some extent, antioxidant activity, antimicrobial activity, tpc, tfc, and ttc of six selected wild mushrooms from nepal along with their correlation to each other have been investigated by pca. 2 materials and methods 2.1 collection and extraction of mushroom the six different mushroom species were primarily collected during the rainy season (july-august) from different locations and were identified taxonomically at the national academy of science and technology (nast), khumaltar, lalitpur. figure 1 represents the lists of collected mushroom species and their botanical description along with pharmacological importance are mentioned in table 1. each mushroom species was thoroughly cleaned, freed of contaminants, and dried in the shade before the ethanol-based soxhlet extraction method was used to extract the mushroom powder. the extracts were concentrated using a rotary evaporator, and each extract was thoroughly extracted for 12 hours. by using this formula, the percentage yield of dried mushroom extracts was calculated: percentage yield = dry weight of extract dry weight of sample × 100% (1) the metabolites found in these mushrooms were surveyed thoroughly, thereby the chemical structures of some metabolites reported previously are illustrated in figure 2. 2.2 screening identification of the phytochemicals found in the mushroom extracts was done by chemical method. as per the previously specified procedures [24], various tests including flavonoids, glycosides, alkaloids, steroids, phenolic compounds, terpenoids, saponins, tannins, carbohydrates, fats, and fixed oils were carried out. pratiksha chaudhary et al./ bibechana 20 (2023) 161-175 164 figure 2: some potential phytochemicals found in wild mushrooms. table 1: name of mushroom, collection site, common name, family, and pharmacological application name of mushroom collection site common name family pharmacological application references s. citrinum nagarkot, kathmandu common earth ball sclerodermataceae anti-inflammatory, antiseptic properties lopusiewicz, 2018) h. annosum dhulikhel, kavre root rot fungus bondarzewiaceae used as potential candidates for bioremediation and act as antioxidants, and anti-inflammatories (sadowska et al., 2020) c. hirsutus sundarijal, kathmandu turkey tail mushroom polyporaceae potential immunomodulatory properties, anticancer properties (adhikari et al., 2005) c. indicum sundarijal, kathmandu indian mallow clavicipitaceae r. sanguinea godawari, lalitpur bloody brittle gill mushroom russulaceae anti-inflammatory, antimicrobial, antioxidant, and analgesic properties (alkan et al., 2020) s. punctatipes matatirtha, kathmandu puffball mushroom suillaceae anti-inflammatory, antioxidant, and immunemodulating properties (crafts & miller, 1974) pratiksha chaudhary et al./ bibechana 20 (2023) 161-175 165 2.3 phenolic content the total phenolic content (tpc) present in the mushroom extracts was assessed by the folinciocalteu colorimetric method [25]. initially, the gallic acid stock solution was made by dissolving 10 mg of the acid in 10 ml of ethanol (1 mg/ml). gallic acid was produced in different quantities, including 125, 250, 500, and 1000 g/ml. the stock solution was made by dissolving 10 mg of each extract in 1 ml ethanol. the concentrations of 125, 250, 500, and 1000 g/ml were obtained by sequential dilutions. then, 1 ml sample solution was taken in a test tube, to which 4 ml of 7% na2co3 and 5 ml of 10% fcr were added, shaken well, and kept at ambient temperature in the dark for half an hour. the absorbance of this blue mixture was then taken at 760 nm against control, with each experiment being carried out in a triplicate manner. to plot calibration curves at various concentrations, gallic acid was employed as the reference and written as gallic acid equivalent (mg gae/g). 2.4 flavonoid content an aluminum chloride colorimetric test was used to assess the total flavonoid content (tfc) of mushroom extracts [26]. to make a quercetin stock solution, quercetin stock solution was made by dissolving its 10 mg in 10 ml ethanol (1 mg/ml). different quercetin concentrations, including 125, 250, 500, and 1000 g/ml, were produced. ten milligrams of each extract were dissolved in one ml of ethanol to create the stock solutions. to attain the concentration of 500 g/ml, several dilutions were performed. the sample solution of concentration 10 mg/ml in ethanol was diluted to 1 ml, and successively 0.3 ml of 5% nano3, 0.3 ml of 10% alcl3, and 2 ml of 1 m naoh were added. five minutes later, 0.3 ml of 10% alcl3 was introduced after the addition of double-distilled water to the mixture. the absorbance of the pink color was then compared to the control (quercetin) at 510 nm. the experiment for each concentration was carried out thrice. 2.5 tannin content the total tannin content (ttc) was assessed by the folin and ciocalteu technique based on the work carried out by this procedure [27]. a gallic acid stock solution was prepared by dissolving 10 mg of gallic acid in 10 ml ethanol (1 mg/ml). gallic acid was produced in a variety of quantities, including 125, 250, 500, and 1000 g/ml. following the initial mixing of 0.1 ml sample solution with 7.5 ml distilled water, 0.5 ml of 10% fcr and 1 ml of 35% na2co3 were added and diluted to 10 ml by distilled water. after a thorough shaking, the blue-colored mixture was maintained at room temperature for 30 minutes in the dark. then, the absorbance at 725 nm was compared to the control. each experiment was performed three times. 2.6 activity on dpph for antioxidant assay the dpph (2,2-diphenyl-1-picrylhydrazyl) radical test was performed to determine the antioxidant activities of six different mushrooms employing the earlier-mentioned approach [28]. the molecular weight of 2, 2-diphenyl-1 picrylhydrazyl (dpph) is 394.32 da. as a result, 100 ml of 0.1 mm solution of dpph was produced by precisely weighing 0.4 mg of dpph, and dissolving it in ethanol, and was then maintained the volume at 100 ml. at first, a 100 ml solution of 0.1 mm dpph was made in ethanol along with ethanolic solutions of ascorbic acid and mushroom extract were prepared in a range of concentrations (15-500 g/ml). after thorough vortexing, 1 ml of dpph solution and 1 ml of sample were combined and left at ambient temperature for roughly 30 minutes in the dark. the absorbance was compared to the control at 517 nm. the experiment for each concentration was carried out thrice. finally, the determination of antioxidant activity was done by the equation below: dpph free radical scavenging (%) =[ a517 of control −a517 of sample a517 of control ] × 100 (2) 2.7 antimicrobial activity the antibacterial activity of the mushroom extracts was assessed by the agar well diffusion method following the standard protocol [29]. salmonella typhimurium, escherichia coli, staphylococcus aureus, and bacillus cereus, the four tested bacterial strains, were cultured in mhb media with turbidity matched with 0.5 mcfarland and swabbed in the mha plates with 1.5 x 108 cfu/ml bacterial suspension for 24 hours before the antibacterial test at 37 0c incubator. using a 6 mm cork borer, wells form in these plates, and 100 mg/ml of each extract in dmso is prepared. about 40 µl of extracts are subsequently kept in the well, along with dmso as a negative control and neomycin as a positive control. after incubating overnight at 37 0c, the plates were observed as well as the zone of inhibition was determined. 2.8 brine shrimp lethality assay the brine shrimp bioassay, to assess the cytotoxicity, was performed on each ethanolic extract following the procedure [30]. brine shrimps (artemia pratiksha chaudhary et al./ bibechana 20 (2023) 161-175 166 salina) were incubated by spreading brine shrimp eggs ( 50mg) on top of the artificial seawater-filled beaker and illuminated with a table lamp (100 watts) at a temperature of 30 0c. in brine shrimp bioassay, freshly hatched brine shrimp nauplii—the egg of artimia salina—are exposed to various solutions of certain mushroom extracts. to carry out the brine shrimp bioassay, the shrimp’s egg must hatch, which required precise equipment sterilization, the making of artificial seawater, and sample processing. the artificial seawater was prepared by following protocol [31].thus, newly hatched brine shrimp nauplii were subjected to a categorized solution of mushroom extracts, and based on their cytotoxicity against the nauplii, the bioactivity was assessed. probit analysis was used to evaluate the lc50 value (g/ml) at 95% confidence intervals. meyer and others regarded the substance with lc50 of 100 ppm to be effective (potent). the percentage mortality (%m) was also computed to confirm that the bioactive substances in the mushroom extracts were responsible for nauplii’s demise. percentage mortality (%m) = number of dead nauplii total number of nauplii × 100 (3) 2.9 statistical analysis the statistical data were analyzed by implementing r (version 4.2.2) and rstudio (version 2022.10.31). in general, we used antioxidant activity (ic50 value), tfc, tpc, ttc, and lc50 value (for cytotoxicity) for the analysis using this software, along with the correlation of these data together with principal components analysis. to determine an appropriate correlation method, it was necessary to conduct a normality test. the parameters dpph, tfc, tpc, ttc, and ic50 were subjected to the shapiro-wilk normality test to validate their skewness, normality, and kurtosis. in case the data were not found to be normally distributed, kendall rank correlation was analyzed. the coefficient of determination (r2) ranged between 0.9701 and 0.9753 after the data were linearly fitted. 2.9.1 principal components analysis high-dimensional data can be simplified using principal component analysis (pca) while maintaining the integrity of underlying trends and patterns. this is accomplished through the compression of obtained data into limited dimensions that serve as feature summaries [32]. principal components are used to deal with correlated predictors and show data in a two-dimensional space. 3 results and discussion 3.1 phytochemical screening the respective percentage yield of ethanolic extract of mushrooms is displayed in table 2, with r. sanguinea having the highest percentage yield (31.90%) and c. indium demonstrating the lowest (5.10%). the differences in the amounts of mushroom extracts may be due to the solvent’s ability, which relies on the chemical composition of the mushroom, the extraction technique, and the solvents’ polarity utilized for extraction. phytochemical investigation of mushroom extracts showed the existence of polyphenols, quinones, terpenoids, saponins, and flavonoids. all mushroom extracts except for s. citrinum consist of reducing chemicals, whereas alkaloids predominate in the extracts of s. citrinum, r. sanguinea, s. punctatipes, and c. indicum. on the contrary, only two mushroom species, namely h. annosum and r. sanguinea, demonstrated the presence of glycosides. preliminary screening of r. sanguinea indicates the presence of every phytochemical examined. the list of the phytochemicals contained in the ethanolic extract of the studied mushrooms is represented in table 3. studies on the ethanol extracts of the edible mushrooms pleutorus ostearus and coprinus comatus, by high-performance liquid chromatography (hplc), reported the existence of bioactive substances such as flavonoids, alkaloids, terpenes, glycosides, and saponins, which is consistent with the current result [33,34]. table 2: percentage yield of ethanolic extract of different mushrooms s.n. name of the mushroom species dry weight of the sample (g) dry weight of extract (g) percentage yield (%) 1 c. indicum 40 2.041 5.10 2 c. hirsutus 40 3.979 9.94 3 h. annosum 40 4.897 12.24 4 s. citrinum 40 5.232 13.08 5 s. punctatipes 40 6.235 15.58 6 r. sanguinea 40 12.76 31.90 pratiksha chaudhary et al./ bibechana 20 (2023) 161-175 167 table 3: phytochemical investigation of six wild mushroom species (note: (+) present and (-) absent) group of compounds s. citrinum h. annosum c. hirsutus c. indicum r. sanguinea s. punctatipes polyphenols + + + + + + reducing compounds + + + + + glycosides + + quinones + + + + + + saponins + + + + + + alkaloids + + + + terpenoids + + + + + + flavonoids + + + + + + several investigations have indicated that extracts from a wide variety of other mushroom species contain significant amounts of phenols, flavonoids, alkaloids, terpenoids, tannins, steroids, and cardiac glycosides [35–37]. these bioactive substances have been attributed to various biological activities, including anti-diabetic and anti-inflammatory properties by saponins, anticancer and antimalarial properties by terpenoids [38], and scavenging, antiallergenic, antiviral, antiinflammatory, and vasodilating effects by flavonoids [39]. moreover, phenolic compounds have also been acclaimed with considerable restorative benefits [34]. hence, the sufficient utilization of potent compounds could provide an important base for the study of the bioactivity of the mushrooms. 3.2 total phenolic content antioxidant activity in plants is mostly attributed to phenolic compounds, which are crucial elements with redox characteristics since hydroxyl groups help to neutralize free radicals [40]. the total phenolic contents of different mushroom extracts, expressed as mg gaes/g of the extract, are listed in table 4. among the examined mushrooms, s. punctatipes exhibited the highest phenolic content (102.3 mg gae/g), and s. citrinum was the lowest (45.98 mg gae/g). this is in contrast to a study that showed s. citrinum melanin having a greater polyphenol content responsible for increased antioxidant activity [16]. such variations in total phenolic content present in the mushrooms could be resolved by various parameters, such as harvest time, growth conditions, and environment. numerous investigations have demonstrated that phenolic compounds vary in quantity and composition at the subcellular level throughout tissues [41]. moreover, the content of simple phenolic acids such as caffeic acid, ferulic acid, etc., is typically higher in younger tissues since many phenolic acids condense later into complex phenolic compounds like flavonoids, tannins, and lignins [42]. 3.3 total flavonoid content flavonoids, possibly the most significant natural phenols, are among the most varied and common groups of natural compounds being beneficial in the context of human health [43]. the total flavonoid content was determined using the aluminum chloride colorimetric technique with quercetin as a reference and indicated as mg qes/g of extract. with s. punctatipes having the maximum flavonoid content and s. citrinum the minimum, table 4 below shows that the total flavonoid content of six mushroom extracts varied from 100 to 225 mg qe/g. it was determined that s. punctatipes with the maximum total phenolic content also contained the maximum flavonoid content (225 mg qe/g). this illustrates the positive correlation between tpc and tfc implying that there is some relationship connecting tfc and antioxidant potential [44]. our results can therefore be connected with the previous work showing the positive impact of flavonoid and phenolic content in the free radical scavenging activity [45]. 3.4 total tannin content tannins are a unique group of water-soluble polyphenols, most commonly present in various mushrooms, and are regarded as good supplies of biologically active substances in the human diet [46]. the total tannin content present in the ethanolic mushroom extracts was quantified by the folinciocalteu technique, where gallic acid was used as a reference based on the previously described procedure [47]. table 4 shows that s. punctatipes had the maximum total tannin concentration (180 mg gae/g), and it gradually decreased from c. indicum, c. hirsutus, and h. annosum, to the lowest s. citrinum (80 mg gae/g), respectively. pratiksha chaudhary et al./ bibechana 20 (2023) 161-175 168 table 4: comparison of ic50, tfc, tpc, and ttc content in various mushroom extracts mushroom extracts phenolic contents(mg gae/g tpc) flavonoids contents (mg qe/g tfc) tannin contents (mg gae/g ttc) antioxidant activity ic50 values (µg/ml) s. punctatipes 102.30 225 180 16.95 c. indicum 82.76 200 160 22.50 c. hirsutus 74.71 175 140 35.34 h. annosum 63.23 175 140 39.89 r. sanguinea 51.73 125 100 53.40 s. citrinum 45.98 100 80 138.00 3.5 antioxidant activity the dpph free radical scavenging technique was employed to assess the antioxidant activity of several ethanolic extracts of mushrooms in which the decolorization of an ethanol solution of 2,2diphenyl-1-picrylhydrazyl was observed to evaluate the mushroom extract’s ability to donate hydrogen atoms (dpph). when dpph is dissolved in ethanol, it gives a violet or purple tint that, when present with antioxidants, fade to varying degrees of yellow (dpph-h). antioxidant activity was determined in terms of ic50 value in which antioxidant activity increases as the ic50 value decreases [6]. the antioxidant property of certain prevalent edible wild mushrooms resembles their total phenolic content [48]. since, phenolic compounds in mushrooms, which include free hydrogen, contribute to the antioxidant capacity of mushroom extracts, many species of wild mushrooms demonstrated antioxidant activity [49]. the ic50 value of ascorbic acid was low i.e, 15.62 µg/ml, indicating that it exhibits the highest antioxidant activity (table 4) which implies that, in comparison to other mushrooms, s.punctatipes had the greatest antioxidant activity since its ic50 value is close to that of ascorbic acid. the suillus species are reported to have strong antioxidant activity, and thereby prevent oxidative stress in humans [50]. the mushrooms—h. annosum, c.hirsutus, and c.indicum having less than 50 µg/ml ic50 possess significant antioxidant properties, in contrast to r. sanguinea’s that exhibited greater than 50 µg/ml ic50 value. s. citrinum demonstrated the least level of antioxidant activity. as per the study, the mushroom extracts’ varying antioxidant activity was likely caused by the interaction of several phenolic chemicals found in the plant itself [51]. boletus, a wild culinary mushroom, was shown to correlate with phenolic compounds, the main group of phytocomponents that contribute to the antioxidant properties of mushroom species [52]. a recent study found that consuming 18 g of mushrooms daily might boost cellular antioxidant functions and reduce the likelihood of cancer [53]. several antioxidant components are frequently used in different foods to defend against oxidative damage caused by free-radical molecules. since the beginning of time, people have consumed wild mushrooms as a part of their diets and as a source of nutritional supplements as they exhibit good antioxidant effects [54]. moreover, the antioxidant property of mushrooms has been reported to prevent oxidative damage of lipids, proteins, and nucleic acids by neutralizing free radicals. the level of oxidative stress could be lowered by supplementing the diet with antioxidant-rich edible mushrooms [3]. due to these attributes, the use of mushrooms in several nutraceutical products is rising in popularity [55,56]. likewise, antioxidant activity, nutritional value, and healthy properties of food sources are interrelated to each other [57]. according to this, s. punctatipes which exhibited good antioxidant activity could be a potential nutrient dietary source. 3.6 antimicrobial activity the antibacterial activity of six different species of mushroom was analyzed by the agar-well diffusion technique with neomycin as standard. table 5 shows the antimicrobial activity of six mushrooms towards all four test pathogens comprising two gram-positive (s. aureus and b. cereus) and two gram-negative (e. coli and s. typhimurium) bacteria. in our experiments, the s. punctatipes demonstrated the greatest antimicrobial activity with a zone of inhibition of 12 mm and 11 mm against gram-positive bacteria while b. cereus and s. aureus, along with a zone of inhibition of 9 mm and 10 mm against gram-negative bacteria s. typhimurium and e. coli. likewise, s.citrinum, h.annosum, c.indicum, and r. sanguinea showed good antimicrobial efficacy against gram-positive bacteria, while c.hirsutus, and c.indicum, displayed antimicrobial activity against gram-negative bacteria. the variation in the outcomes of antimicrobial activity could be attributed to several variables, such as the environmental and climatic conditions in which the mushroom was grown, the choice of mushroom extracts, the choice of extraction techniques, the antimicrobial test method, and the test microorganisms. as per a previous study, pratiksha chaudhary et al./ bibechana 20 (2023) 161-175 169 the pigment β-carotene, most commonly found in suillus sp., exhibited significant antimicrobial properties towards s. aureus and e. coli [50]. numerous secondary metabolites including alkaloids, flavonoids, tannins, and other phytochemicals have been documented to affect antimicrobial activity [58]. as per the prior study, the melanin of scleroderma citrinum showed no antimicrobial effectiveness towards b. cereus, e. coli, and s. aureus, which in contrast to our present study, exhibited good antimicrobial effectiveness towards both gram-positive strains [16]. there’s a probability that some of the tested extracts from this investigation will succeed as antimicrobial medicines in the future. table 5: in vitro antimicrobial activity of mushroom extracts against selected bacterial strains zone of inhibition(mm) mushroom extract (100 mg/ml) gram-positive bacteria gram-negative bacteria s. aureus b. cereus e. coli s. typhimorium s. citrinum 9 9 6 7 h. annosum 10 9 6 7 c. hirsutus 7 7 10 9 c. indicum 10 10 9 9 r. sanguinea 11 10 7 7 s. punctatipes 12 11 9 10 neomycin 34 35 24 23 dmso solution 0 0 0 0 table 6: lc50 values of different mushroom extracts mushroom extracts lc50 (g/ml) s. citrinum 4265.8 h. annosum 14791 c. hirsutus 338.8 c. indicum 338.8 r. sanguinea 16596 s. punctatipes 257.0 table 7: kendall rank correlation coefficient dpph tpc tfc ttc lc50 dpph 1 -1 -0.96609 -0.96609 0.69007 tpc -1 1 0.96609 0.96609 -0.69007 tfc -0.96609 0.96609 1 1 -0.64286 ttc -0.96609 0.96609 1 1 -0.64286 lc50 0.69007 -0.69007 -0.64286 -0.64286 1 3.7 brine shrimp assay the brine shrimp assay is a preliminary screening method used to assess the bioactivity of crude extracts by measuring their toxicity. it has been employed to identify fungal toxins, plant extract toxicity, and cytotoxicity [59–61]. the lc50values, which represent the concentration of the extract that causes 50% mortality in the brine shrimp, are calculated using this method [62]. a lower lc50 value indicates higher toxicity. according to meyer et al.,lc50 values of less than 100 ppm are considered potent, values less than 1000 ppm are toxic, and values greater than 1000 ppm are non-toxic [63]. this study demonstrates the larvicidal activity of ethanolic extracts from different mushrooms against brine shrimp. the calculated lc50 values of the mushroom extracts analyzed in this study are listed in table 6. the concentration of these mushroom extracts and their efficiency were directly correlated. at a concentration of 1000 ppm, all mushroom extracts demonstrated high toxicity with the highpratiksha chaudhary et al./ bibechana 20 (2023) 161-175 170 est mortality rates. this suggests that three of the six mushrooms examined, coriolus hirsutus, cavimalum indicum, and suillus punctatipes, might contain highly potent toxic substances, while the other three, s. citrinum, h. annosum, and r. sanguinea, were found to be non-toxic. according to our study, the three mushrooms s. citrinum, h. annosum, and r. sanguinea were found to be non-toxic, with an lc50 value greater than 1000, which is considered non-toxic according to meyer et al. (1982). this finding of h. annosum being moderately or mildly toxic corresponds to previous findings [18]. the non-toxicity or low cytotoxicity of these mushroom species suggests that they are potentially suitable for consumption. however, when it comes to safety concerns, the edibility of the six mushrooms depends on proper examination. all mushrooms can be consumed, but one mushroom, namely s. punctatipes, should only be consumed if the cap is removed. therefore, it is important to be aware of this and conduct sufficient surveys and examinations when consuming such mushrooms. additionally, the study, classification, and production of medicinal mushrooms could benefit from the application of cutting-edge technologies such as metabolomics, proteomics, transcriptomics, and genome sequencing [64]. further studies on the toxicity and nutritional value of these mushrooms will likely reveal whether they could be a valuable addition to our diets in the near future. 3.8 statistical analyses 3.8.1 correlation according to the shapiro-wilk test, the w and pvalue were found to be 0.98676 and 0.9672, respectively. since the p-value was greater than 0.05, the data are not normally distributed. therefore, the kendall rank correlation coefficient was performed, and the results are shown in table 7. 3.8.2 principal components analysis of different variables the scree plot of the principal component analysis (pca) (figure 3) displayed two principal components that accounted for 97.7% of the overall variation. the variables tpc, tfc, and ttc showed a strong correlation with the formation of axis 1 (79.4%), while dpph and lc50 strongly contributed to the development of axis 2 (18.3%) (figure 4). this plot indicates that variables such as tfc, tpc, and ttc are negatively correlated with lc50, while variables are positively correlated with lc50 values. this means that an increase in the amount of phenolic, flavonoid, and tannin content leads to a decrease in toxicity (lethal concentration). figure 3: scree plot of principal component analysis. pratiksha chaudhary et al./ bibechana 20 (2023) 161-175 171 figure 4: principal component plot of variables. 4 conclusion mushrooms contain a variety of phytochemicals, protein, dietary fiber, vitamins, and minerals, making them suitable as food supplements for all age groups. this research focused on analyzing the phytochemicals and evaluating the biological properties of the selected wild mushrooms. the preliminary assessment effectively demonstrated their cytotoxic, antibacterial, and antioxidant characteristics. the presence of various phytochemicals can be attributed to the potential antibacterial and antioxidant properties of the examined samples. all mushroom extracts exhibited at least one phytochemical, while only r. sanguinea exhibited all tested phytochemicals. the brine shrimp bioassay demonstrated the potential toxicity of s. punctatipes, c. indicum, and c. hirsutus against brine shrimp nauplii, while s. citrinum, h. annosum, and r. sanguinea were found to be non-toxic. further studies should be conducted to analyze their bioactivity and potential toxicity. s. punctatipes exhibited the most notable antibacterial and antioxidant activity among all the mushrooms studied. additionally, s. punctatipes and c. indicum contained the highest levels of flavonoids, phenolics, and tannins. further in-depth research may lead to the discovery of substances that could serve as potential drugs or templates for new drug development. mushrooms can be a great source of antioxidants due to their high phenolic content and can be consumed when handled properly. abbreviations dmso: dimethyl sulfoxide, dpph: 2,2picrylhydrazyl-hydrate, fcr: folin-ciocalteu reagent, gae/g: gallic acid equivalent per gram, ic50: half-maximal inhibitory concentration, lc50: lethal concentration 50%, tfc: total flavonoids content, tpc: total phenolic content, ttc: total tannin content, qe/g: quercetin equivalent per gram, zoi: zone of inhibition author’s contributions n. p. supervised the research; n. panth performed lab work; p. c. and b. k. r. conceptualize and analyze data; p. c., b. k. r., n. p., n. s., and s. s. wrote the manuscript; b.b.t. and a.d.m. reviewed and edited the manuscript. references [1] m. a. naranjo-ortiz and t. gabaldón. fungal evolution: diversity, taxonomy, and phylogeny of the fungi. biological reviews, 94(6):2101– 2137, 2019. 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[64] uwe groß, elzbieta brzuszkiewicz, katrin gunka, julia starke, thomas riedel, boyke bunk, cathrin spröer, dietmar wetzel, anja poehlein, cynthia chibani, wiebke bohne, jörg overmann, oliver zimmermann, rolf daniel, and heiko liesegang. comparative genome and phenotypic analysis of three clostridioides difficile strains isolated from a single patient provide insight into multiple infection of c. difficile. bmc genomics, 19(1):1, 2018. introduction materials and methods collection and extraction of mushroom screening phenolic content flavonoid content tannin content activity on dpph for antioxidant assay antimicrobial activity brine shrimp lethality assay statistical analysis principal components analysis results and discussion phytochemical screening total phenolic content total flavonoid content total tannin content antioxidant activity antimicrobial activity brine shrimp assay statistical analyses correlation principal components analysis of different variables conclusion bibechana vol. 21, no. 2, august 2024, 180-194 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar factors associated with time to first birth after marriage: a systematic review ishwar kumar shrestha, shankar prasad khanal∗ central department of statistics, tribhuvan university, kritipur, kathmandu, nepal ∗corresponding author. email: drshankarcds@gmail.com abstract time to first birth after marriage is a particularly interesting subject, because it unveils both the social behaviors and fertility patterns. though, for a woman, who marries at an early age and gets sooner childbearing can be the health threat for both mother and child. the objective of this study is to systematically investigate significant predictors associated with time to first birth after marriage. following the prisma guidelines; three databases scopus, pubmed and embase were used to capture relevant articles. a total of 21 articles with the thorough assessment of 326 articles published in english up to 10 january 2024 were included in the final review. thirty-nine significant predictors associated with time to first birth after marriage have been explored. predictors, such as age at marriage, education, residence, contraceptive, religion, wealth index were observed as some of the major significant predictors. the findings indicate to take care of those factors in order to deal with time to first birth after marriage. understanding the impact of influential factors can be considered as important reference to formulate appropriate policy to intervene effective program as well as to plan such studies based on primary data with special reference to a certain country or region. keywords keywords: first birth interval, predictor, prisma, systematic review. article information manuscript received: january 30, 2024; revised: april 11, 2024; accepted: april 16, 2024 doi https://doi.org/10.3126/bibechana.v21i2.62448 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction time to first childbirth after marriage depends on several factors. the term time to first birth after marriage, first birth interval, first childbirth after marriage are synonymously used in this paper. it varies in place to place, country to country and region to region. age at first marriage, age at first childbirth and first birth interval (fbi) after marriage are some of the major determinants of fertility measures, influenced by a number of different co-factors of demographic, socio-economic and cultural things [1]. the interval between marriage and first childbirth is a particularly interesting subject, for it unveils both the social behaviors as well as fertility patterns with regard to reproduction. 180 http://nepjol.info/index.php/bibechana drshankarcds@gmail.com https://doi.org/10.3126/bibechana.v21i2.62448 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 181 the first childbirth is important for each individual woman. it becomes the most notable event in her life. additionally, the first childbearing of woman starts undertaking the roles of motherhood as well as added further family responsibilities. first childbirth gives woman an unseen power to establish her new roles in the family [2]. in the traditional society, a woman’s first pregnancy followed by the first childbirth constitutes an exciting moment for family and relatives, because first childbirth is an important indicator for woman to prove her ability to the continuation of future generation [3]. moreover, the length of fbi after marriage is deeply connected to fertility patterns of women, population structure and its dynamics [4]. shorter length of waiting time to the first birth of women who have got married before the age of 18 became a matter of public health with the increased risk of health care of mother and children [1,2], [5]. the shorter length of fbi is also connected to premature conception, unplanned pregnancies and high fertility, especially for the women, who marry at an early young age. marriage in young age and then immediately getting first childbirth shown to have health hazards, unforeseen economic pressure, family burden and weak social presence [6]. furthermore, it can also affect others birth patterns, as well as effects on fertility behavior and family size [7]. women’s marriage at an early young age, immediate desires of children, engaged in new family responsibilities direct to their rest of future career and quality life. such events are profoundly prevailed in the women of lower socioeconomic conditions. high education, empowerment and reproductive awareness may provide women with the power to cope with the situation against sooner childbearing and faster family growth [8]. proper knowledge of contraceptive use, work roles and empowerment make a substantial impact on women to postpone the time of first childbirth at an early young age [9], however, it can be varied according to personal behavior. women, who live in the orthodox society are directly or indirectly governed by their existing socio-cultural system. with the impact of cultural constraints, they get first marriage in young age, and sooner give first child after marriage [10]. the compliance of being a sooner parenthoods in young age and other family duties disturb women for their career development, empowerment and social status [11]. several mutually common factors, such as age at marriage, education, residence, contraceptive use [12–14], religion, wealth index, husband’s education, women’s employment status [5,15] were observed as the major determinants in playing a significant role for the time duration of getting first childbirth after marriage. on the other hand, a large number of particular single factors, which were not jointly common had been identified in many studies. these factors were also interesting and had observed as of its own significance to determine the first birth after marriage. studies conducted in different places have reported different factors, where some factors are found to be common and some are not, varying from region to region, country to country and study to study. marriage at an early young age, sooner childbearing after marriage can lead women to school dropout, disturb their career development and stop other many activities that they need to accomplish in their life. as like other influential predictors (demographic, socioeconomic, cultural and geographical) for the timing of childbearing, women’s personal beliefs and behavior also play an important role in reproduction, childbearing and fertility pattern [16]. in this backdrop, the proposition of this study has aimed to accumulate, and summarizes the significant predictors in influencing the duration of first birth after marriage. moreover, the finding of this systematic review is expected to help policy makers to formulate appropriate policy, academia and researchers for identifying new research in the field of nuptiality, and development agencies to develop effective programs utilizing the identified parameters. the finding of this study could also be useful for specific location or country or region to take care of influential factors connected with fbi, specifically where there is high prevalence of starting marriage at an early young age as well as sooner first childbearing after marriage. 2 material and methods 2.1 sources this systematic review was accomplished using prisma standards [17]. the process of systematic review is presented in fig.1. to select articles, a search in embase, pubmed and scopus were performed in december 2023 developing the following key search terms: [(“factor*” or “predictor*” or “determinant*” or “cause*”) and (“time to first birth” or “first birth interval” or “first child birth” or “waiting time to firth birth” or “time interval to first birth” or “time duration to first birth”) and (“women” or “female*”)]. the search conducted in embase and scopus were confined in title or abstract or keywords. but, the search conducted in pubmed was confined in title and abstract. in addition, an option of english language only was applied to the search filter of each database. 2.2 eligibility criteria articles matching to the outcome variable (time to first birth after marriage) were included in this systematic review. the articles further limited to the ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 182 following eligibility condition: (1) articles used time to event data, (2) peer-reviewed articles, (3) articles provided the evidence of the relationship between significant factors and outcome variable, and (4) study population of women of reproductive age who have ever married or/and at least having one live birth after marriage. for this study, outcome variable was considered to incorporate topics mostly associated with demographic characteristics, socioeconomic parameters and cultural system, including (but not limited to) age at marriage, contraceptive use, education level, geographical variation, religion and economic condition. articles based on qualitative discussions, articles measuring the outcome only based on simple summary statistics, and the outcomes based on bivariate and multivariate analysis, such as chi-square and other statistical analysis were excluded, as they generally examine either simply the associations with outcome variable or explaining the average effects of predictors on outcome variable without the reference value. 2.3 study selection the articles, initially captured from three databases embase, pubmed and scopus were managed in the zotero [18]. duplicate records identified in the sources were omitted at the first phase of data management. the unique records after removing the duplicate data were exported to rayyan [19]. to select studies, author (iks) first conducted a title review of all identified records and examined the abstract in rayyan, and removed any of those were ineligible for the review. next, author (spk) independently reviewed abstracts from the remaining records after the work was done in rayyan. in the second phase, the ineligible articles considered with the agreement of both authors were excluded. the final eligible included articles were thoroughly and independently assessed by both authors. articles receiving a doubt were resolved with the agreement of both authors. at the same time, the discrepancies occurred in identifying and extracting the information were solved by the mutual understanding of both authors. 2.4 data extraction a standardized form was designed to extract the data related to the study characteristics including; study design, study population, model used in the study and findings of the studies. both authors were independently involved in the data extraction process. any discrepancies acquired between two authors while extracting the information were resolved through the subsequent review. the extracted data were accumulated, checked, summarized and then placed in table format. table1 describes the components of the study including; ‘authors’, ‘title of the study’, ‘country’, ‘study design’, ‘sample/(source)’, ‘statistical method’ and ‘significant factors with effect size’. significant factors, as a predictor, associated with fbi after marriage were the findings measured by different statistical effect sizes (or, hr, ahr, tr, coeff., estimates based on bayesian approach) cis, p-value, etc. 2.5 quality assessment quality assessment tool produced by axis [20] was used to assess the quality of all included articles. quality of all articles were thoroughly reviewed focusing on objective, target study population, use of appropriate statistical models for analyses related to outcome variable, effect size, bias and nonresponse, consideration for confounders, study limitation and conflict of interest. all 21(100%) articles included in this review clearly specified the study objectives, target population, and the methodology used. more than 57.1% articles included in this study strongly justified sample size likely to represent the target participants, since these articles used the data either of dhs survey or the national surveys which were conducted by the respective countries. likewise, the findings and results presented in all 100% articles have clearly determined statistical significance and/or precision estimates, effect size using p-value and cis. of those, 80.1% articles were internally consistent to relate the results in the discussion and conclusion section. in regard to the issue of response bias, neither the articles raised the issues of non-response rate nor described its influences. however, articles based on cross-sectional data using nationally representative data or dhs often do not describe the information about non-response as they have used secondary data. study limitation and the potential bias were discussed in more than 52.4% of the included articles, dealing the issues of study area, selection of study methodologies and the measurements used. nearly 48% articles clearly reported about the funding source and declared the absence of conflict of interest, but 52.4% articles did not disclose anything about funding. the deceleration of conflict of interest and ethical consideration were reasonably attained by all 21 (100%) papers. most of the criteria set by axis has rationally fulfilled by the reviewed articles. the detail qa report of each article done in axis tool has maintained in separate excel file. ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 183 figure 1: prisma flowchart for the process of systematic review. 3 findings the primary search done in embase, pubmed and scopus captured a total of 326 records (fig. 1) from the sources. of the initially captured records, 58 duplicates were eliminated. the remaining 268 records were retained for title and abstract review. while going through the title and abstract screening, a total of 216 records were excluded, and a total of 52 records were selected for full review. in the full article review only 21 were matched as per the study objective, which are included in this systematic review. the articles excluded for the final review were due to different reasons. among the excluded articles, 9 were based on only summary statistics, 11 were based on bivariate or multivariate analysis using chi-square and other statistical techniques but not dealt with reference values. other 5 articles were theory based mathematical models, not discussed about outcomes and predictors, and 6 papers did not have access for its full text download because electronic versions of these papers were not available in the database. the excluded 25 papers were from different countries (korea, france, united stated, nepal, malaysia, morocco, massachusetts, taiwan, vietnam, spain, singapore, congo, canada). ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 184 references for table 1 are [4, 5, 9–16,21–31] ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 185 all twenty-one (100%) articles included in the study were based observational or cross-sectional study design, of them nine (43.9%) studies were based on primary data and remaining 57.1% studies were based on secondary data. the number of samples included in the study were ranged from 180 participants (primary data) to 186771 (dhs data of nine countries of sub-saharan africa) participants. of the reviewed articles; seven (33.3%) articles were published in between 2020 to 2023, elven (52.4%) articles were published in between 2011 to 2019, and three (14.3%) articles were published in between 1990 to 2000. ten (47.6%) of the twenty-one studies included in the review were conducted in africa (ethiopia 6, nigeria – 2, sub-saharan africa -1 and swaziland 1). of the eleven remaining studies, five were from iran, three were from india and one each from britain (uk), china and indonesia. fig. 2 represents the number of studies conducted in the country. fig.3 represents the proportion of studies by world health organization (who) regional classification. according to who regional classification; ten (47.6%) studies were captured from africa (ethiopia, nigeria, sub-saharan africa and swaziland), five (23.8%) form eastern mediterranean (iran), four (19.0%) from south east asia (india and indonesia), and one (4.8%) each from europe (britain) and western pacific (china). according to world bank country classifications by income level 202-23; six (28.6%) studies were of lowincome countries, twelve (57.1%) studies were of lower middle-income countries and one (4.8%) was of low-income & middle-income country representing by sub-sharan africa. remaining one study ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 186 was of upper middle-income country, and the another one was of high-income country. this study has explored thirty-nine significant predictors connected with fbi after marriage, where measurements of these predictors were found to be varied across studies. a detailed description of the outcome measure and how the effect size is commonly measured has indicated in table 1. the effect size of outcomes in the studies also varied significantly from study to study and place to place. the significance of effect size measured in majority of the studies were obtained either by hr or ahr or β – coefficient at 95% cis or p < 0.05. nineteen (90.5%) studies out of twenty-one explored two or more than two significant predictors connected with fbi after marriage. fifteen (71.4%) studies indicated that female’s education is one of the major determinants, associated with time to first birth after marriage, while ten (47.6%) studies indicated the place of residence as a significant factor. other two factors such as; age at first marriage and contraceptive use were explored in nine (42.9%) studies. likewise, religion was identified in five (23.8%) studies, place of region and wealth index were identified in four (19.0%) studies, and age at first sex, marriage cohort and husband education were identified in three (14.3%) studies. similarly, type of occupation, family income, employment status, contraceptive knowledge, spouse age difference and current age were identified in two (9.5%) studies. other 23 remaining single factors were not mutually common to any of the studies. fig. 4 describes the number of factors explored in the reviewed articles. figure 2: articles captured from the countries. ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 187 figure 3: studies included in the review according to who regional classification. figure 4: factors associated with fbi after marriage. 3.1 statistical models used all 21 studies incorporated in this systematic review had applied statistical model(s) considering the data as time to occur the event. the occurrence of first child birth has considered as 'event', and the time interval till the occurrence of first child birth has considered as 'time'. the time is considishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 188 ered censored for a female who did not have first child birth till the study period. the response variable is the time to first birth of females. there are different models available in statistical literature for handling the time to event data or the data related to survival analysis in order to identify the factors associated with the outcome and to quantify the effect of each independent variable on the response variable. among these methods cox proportional hazard (cph) or simply cox regression [32] is the most popular model since it is considered as the robust technique. out of these 21 studies, thirteen studies were found to be applied the cox regression model, one study had applied cox regression, loglogistic, and generalized gamma parametric model, two studies had used lognormal aft model and other two studies had used inverse weibull gamma shared frailty model. of the other remaining studies, one study used lognormal shared frailty model, another one study used bayesian weibull-gamma shared frailty model, and the other one applied loglogistic model (as shown in table1). studies applying cox regression reported regression coefficient (β) or hr (hazards ratio) which is the exponentiation of the regression coefficient ( eβ ) for each independent variable. the effect size of each independent variable used in the model along with 95% confidence interval was also reported. it is easier to interpret hr as compared to regression coefficient. the reference value of hr is 1; if the value of hr >1, it indicates the increase in the risk of the occurrence of event due to the presence of certain predictor, and if hr < 1, it shows the decrease in the risk of the occurrence of event. for an instance, if hr = 3.36 for those females who have no education with respect to those who have higher education indicates that the hazards of first birth is 3.36 times more among females with no education in comparison to females having higher education [21]. among those studies which had applied cox regression model, only 7 studies checked the proportionality of hazards assumption. proportionality of hazards assumption is required to be met for the cox ph model. none of these 14 studies had attempted for regression diagnostics tests. in order to apply the statistical model(s), if one is able to capture the distribution of time until the event occurs then the parametric model may be applied. in this study, aazbih et al.(2023) [4] had applied lognormal aft model in order to quantify the effect of independent variables on time to first birth. aft models can be used as an alternative to proportional hazards (ph) model if the constant proportionality assumption is violated [15]. time ratio (tr) with 95% confidence interval is generally reported in aft models. it is also the exponentiation of regression coefficient of a predictor. the reference value of tr is also equal to 1 similar to hr. however, the interpretation of tr is a bit different than hr. if tr >1, it signifies that the time to first birth is longer, and if tr <1, it indicates that the time to first birth is a shorter. if tr = 0.86, for those women who had not empowered for the decision of household’s expenditure in comparison with those women who had empowered for the decision of household’s expenditure. this indicates that there is shorter first birth interval for those women who had not empowered to their counterparts [4]. faruk, 2018 [15] applied cox ph model, aft models based on exponential distribution, weibull distribution and lognormal distribution, and finally selected the lognormal aft model having the minimum akaike information criterion (aic). furthermore, this study had indicated that the ph assumption was also not met by this first birth interval in this dataset. in this study, only the regression coefficient with 95% confidence interval was reported but not reported tr. both these studies; aazbih et al., 2023 [4] and faruk, 2018 [15] also did not attempt to perform regression diagnostics except the use of aic criteria. dewau et al.(2021) [5] had applied inverse-weibull gamma shared frailty regression model and reported hr for each independent predictor used in the model, which was associated with time to first birth. it was reported that the data were correlated to cluster level, and in order to capture this structure of the dataset, the shared frailty models were used. enumeration areas or clusters were used as random effects predictors in the model. by exploring different shared frailty models such as lognormal gamma, lognormal inverse gaussian, log-logistic gamma, loglogistic inverse gaussian, inverse-weibull gamma and inverse-weibull inverse gaussian, finally, the inverse-weibull gamma shared frailty was considered as the best model for this data set. in order to select the best plausible model, different criteria such as log-likelihood, aic, etc. were applied. similarly, negash & asmamaw(2022) [27] had also recommended the inverse-weibull gamma shared frailty model after exploring gompertz gamma shared frailty along with this. in order to select the best model in this study too, the same criteria was used as used by dewau et al.(2021) [5]. both the studies have examined the ph assumption, and reported hr for each independent variable associated with time to first birth. fentaw et al.(2022) [22] had explored different parametric shared frailty models including cox ph model. bayesian approach of standard weibull and weibull with gamma shared frailty model was also compared based on aic, bayesian information criterion (bic) and deviance information criteria (dic), and recommended the bayesian weibull-gamma shared frailty model as the best model in this dataset. median with 95% c.i. was reported for each predictor associated with ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 189 time to first birth. tavares(2016) [31] had applied the log-logistic regression model for the time to first child birth as the error terms follow the logistic regression. 3.2 thematic factors all identified significant factors associated with fbi after marriage are further classified into the following six thematic group namely; i) socioeconomic factor 13 (33.3%): education, household size, family income, per capita income, wealth index, ideal children, social status, husband’s education, husband’s employment, women empowerment, occupation type, employment status, insurance covered; ii) reproductive health factor 8 (20.5%): menstrual status, pregnancy termination, ever fetal loss, survival status of index child, sexual debut, contraceptive use, contraceptive knowledge, intercourse and marriage; iii) demographic factor 6 (15.4%): current age, age at first marriage, age at first sex, marriage cohort, spouse age difference, month of marriage; iv) cultural factor 5 (12.8%): ethnicity, religion, kinship, type of marriage, divorce before 1st birth; v) community factor 4 (10.3%): place of residence, place of region, partner’s race, media exposure; and vi) gender factor 3 (7.7%): sex of household head, participation in decision, desired to have a son. fig. 5 shows the distribution factors according to thematic classification. 3.3 factors explored in the region studies captured from five different regions explored a total of thirty-nine significant factors found to be associated with time to first birth after marriage. of them, twenty-one (53.8%) factors were explored in africa, twelve (30.8%) factors in the eastern mediterranean, one (2.6%) factor in europe and fourteen (35.9%) factors in south-east asia. table 2 has indicated the region wise presence of determinants associated with fbi after marriage. 3.4 common factors explored in the regions in the study ten factors were found to be mutually common for two or more than two regions. the factor “level of education” was common in five regions i.e. “south east asia”, “africa”, “eastern mediterranean”, “europe” and “western pacific” regions. the factor “place of residence” was common in africa, western pacific and eastern mediterranean regions. the factors “contraceptive used” and “wealth index” were common in “africa”, “eastern mediterranean” and “south east asia”. likewise, the factor “age at first marriage” was common in africa and western pacific regions. three factors ‘husband education’, ‘contraceptive knowledge’ and ‘employment status’ were common in africa and western pacific regions. similarly, the factor ‘type of occupation is common in africa and south east asia, the factor ‘marriage cohort’ was common in african and western pacific regions. fig.6 shows the distribution of common factors associated with fbi after marriage. figure 5: thematic determinants associated with fbi after marriage. ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 190 table 1: regional factors. regions factors n (%) africa level of education, place of residence, place of region, contraceptive use, religion, age at first marriage, marriage cohort, age at first sex, employment status, husband wealth index, spouse age difference, intercourse and marriage, ethnicity, pregnancy termination, contraceptive knowledge, media exposure, sex of household head, sexual debut, household size, type of occupation. 21 (53.8) eastern mediterranean level of education, place of residence, contraceptive use, husband education level, family income, husband’s employment, type of marriage, insurance covered, desired to have a son, kinship, partner’s race, menstrual status. 12 (30.8) europe level of education. 1(2.6) south-east asia level of education, age at first marriage, contraceptive use, employment status, husband education level, wealth index, contraceptive knowledge, current age, decision participation, per capita income, social status, type of occupation, ever fetal loss, survival status of index child. 14(35.9) western pacific level of education, place of residence, age at first marriage, marriage cohort, month of marriage. 5(12.8) figure 6: common factors associated with fbi after marriage by region. 3.5 uncommon factors of the total thirty-nine identified factors, twentythree (58.97%) factors such as; divorce before first birth, ideal children, women empowerment, husband’s employment, intercourse and marriage, ethnicity, pregnancy termination, media exposure, sex ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 191 of household head, sexual debut, household size, type of marriage, insurance covered, desired to have a son, decision participation, per capita income, social status, kinship, parent’s race, menstrual status, ever fetal loss, status of index child and month of marriage were not common both in country and the region. these twenty-three uncommon factors were explored in six countries (ethiopia -3, iran 4, india 2, nigeria -1, swaziland 1 and china -1) by twelve different studies. 4 discussion findings of this systematic review indicates that fbi after marriage is related to a number of predictors, including demographic, reproductive health, socioeconomic, cultural, gender and community. additionally, time to first birth after marriage appears to be related to certain personal behavior such as age at first sex, sexual debut, intercourse and marriage, and contraceptive use, but its relationship with other risk factors, such as pregnancy termination, ever fetal loss, menstrual status, divorce before first birth, survival status of index child, are less clear. evidence suggests a link between time to first birth after marriage with some major factors, such as “education”, “place of residence”, “age at first marriage”, “contraceptive used” [4,27], “contraceptive knowledge”, “wealth index”, “husband's education”, “women employment status”, “marriage cohort” and “type of marriage” [9, 12, 15], but few studies have been also explored the link to other factors dealing with personal behavioral and family characteristics. more than seventy-one percent of studies included in this study unveiled that females with low education were exhibited negligence behavior to take part in marriage and first childbirth. women with no formal education get married at an early age and immediately attempt to get first childbirth sooner than those with primary, and secondary or higher-level education [16]. likewise, females lived in rural areas were observed high chance of early childbirth at an early age than females in the urban areas [24]. the association between age at first marriage and fbi after marriage is inverse [29], i.e. the likelihood of a woman who is married at an early young age has higher chance to bring first childbirth sooner. a study conducted in china [14] revealed that young couples residing in rural area lack a motive to delay first childbirth. most of women staying in rural area do not need to do work away from home. their cost of raising a child is less as compared to urban couples. otherwise, desire to delay parenthood of couples might attempt in stopping the first delivery of their first pregnancy by induced abortion. in addition, most of the studies conducted in iran [29–31] highlighted that employed women had children later as compared to unemployed women. but the disagreement between childbirth and involving in economic activity occur due to the conflict of work barriers and opportunity costs of childbirth. women's engagement in economic activities can be anticipated to lead into the prolong length in delay first childbirth and reduce in the number of children, and the delayed first childbirth can be beneficial for the countries where the fertility rate is high. likewise, women who had used contraceptives after marriage can manage a long-time gap to get first childbirth than the nonusers, which help women in preventing early and unplanned pregnancy [5, 7, 21]. fbi after marriage also linked to age at marriage of women. the study conducted in ethiopia, nigeria, swaziland and iran explored that women who married below the age of 18 years had their first childbirth sooner than women who married above the age of 18 years [25]. a study conducted in britain (uk) has conceptualized the variation of fbi after marriage based on five personality qualities. these five qualities were differentiated by “extraversion”, “agreeableness”, “conscientiousness”, “neuroticism” and “openness” [31]. the study concluded that high “agreeableness”, “extraversion” and “neuroticism” expedite first birth, but too openness is correlated with delaying first birth. of these five personality qualities, openness showed strongest association with fbi after marriage, and it was also identified as the most influential factor in terms of reproductive behavior [33]. the factor "openness" is a person’s individual characteristic developed by the synthesis of education, culture, family environment and the opportunities to take part in different activities. poverty, lack of access to education, lower employment participation rate, disparities between urban and rural service facilities, geographical variation, sexual debut in early young age, early pregnancy, lack of contraceptive knowledge, lower contraceptive prevalence rate, poorer healthcare access and lower level of self-efficacy [34] are some of the increased distress in regard to the issues of marriage and first child birth. hence, understanding the reasons of these differences are essential to generate recommendations, whether it is education literacy or health literacy or women empowerment or some other factor, to participate women in decision making, provide better education and access to employment. addressing these help women to prevent from unpredicted health hazards, career constrains and livelihood challenges happening due to early age at marriage and early pregnancy after marriage. advanced time to event analysis techniques such as cox ph model, different parametric aft models including shared frailty models were found to be attempted keeping in view to capture the original structure of the dataset of time to first birth, and ishwar kumar shrestha and shankar prasad khanal/ bibechana 21 (2024) 180-194 192 to quantify the effect of independent predictor on time to first child birth. the effect sizes were reported mostly in terms of hr and tr in such a way that the interpretations are easier in comparison to regression coefficient. however, the residuals analysis of the developed models were not found attempted rigorously except using aic, bic and dic for choosing the most plausible model. this systematic review suggests that first birth after marriage plays an important role in women’s physical, psychological and reproductive health across a number of different contexts, including fertility, contraception, maternal-child health care, social status, women empowerment and sexual health. the findings of this study related to influential factors associated with fbi may be a useful reference for certain countries or regions to plan new studies based on primary data. 4.1 limitation this systematic review is not free from limitations, since the findings were focused on time-to-event data. publication bias is another limitation of this review study. we did not include gray literatures and other articles published in other databases rather than embase, pubmed and scopus. for example, the search in web of science did not perform because of access limitation. on the other hand, we only assessed articles originally published in the english language, hence other eligible articles published in other languages may have ignored. the studies based on medical concerns dealing on clinical parameters; such as anxiety disorders, depression, psychiatry, and other medical issues based on treatments were also excluded. 5 conclusion evidence shows that being an educated woman in the low-income economy is an influential determinant of getting first child in an adequate time gap. but, being a rural resident is another influential determinant of getting first child in a short gap after marriage, even if, married in an early young age. on the other hand, understanding of contraceptive knowledge and its proper use should be more announced by health services for the young couples to mitigate their reproductive health hazards and unplanned pregnancy, and to manage their birthspacing and fertility. however, the study explored thirty-nine significant factors, more than ten pronounced predictors are found to be common in five different regions that influence to the time interval of first birth after marriage. some other large number of particular single factors identified in the articles, but not mutually common to the regions are also important with its own significance in relation to first birth after marriage. the study findings can be helpful to the government and policy makers to develop appropriate policies and programs in taking care of the factors associated with shorter fbi of female, those married at an early young age. it also helpful to intervene programs effectively to make aware of about marriage at an early age, shorter first-birth spacing after marriage and its negative consequences. all of these efforts can help to mitigate challenges of health hazards occurring due to unplanned childbearing and thus manage fertility rate. conflict of 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[34] ik shrestha and sp khanal. systematic review on factors associated with female age at marriage. nepal journal of statistics, 7:67–91, 2023. introduction material and methods sources eligibility criteria study selection data extraction quality assessment findings statistical models used thematic factors factors explored in the region common factors explored in the regions uncommon factors discussion limitation conclusion bibechana vol. 20, no. 2, august 2023, 146–160 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar theoretical investigation on the structural and vibrational properties of some alkali liquid metals: a pseudopotential approach mayank h. jani∗∗, aditya m. vora∗ department of physics, university school of sciences, gujarat university, navrangpura, ahmedabad 380 009, gujarat, india ∗corresponding author. email: voraam@gmail.com ∗∗mayankjani5@gmail.com abstract along with a few elastic constants, a recently created pseudopotential is employed to examine the vibrational properties of some simple alkali metals, i.e. li, na, k, rb and cs. the phonon dispersion curves (pdc) are computed in the text. (ωl and ωt ), longitudinal sound velocity (vl), transverse sound velocity (vt), isothermal bulk modulus (b), modulus of rigidity (g), young’s modulus (y ), debye temperature (θd) of some liquid alkali metals. the second order technique used in the current work, using hubbard and beeby (hb) equations, is based on pseudopotential theory. the various percus-yevick hard sphere (pyhs) and one-component plasma (ocp) structure factors used in the current investigation are used to construct the pair correlation function g(r). the current paper makes use of three distinct forms of local field correction functions developed by hartree (h), taylor (t), and nagy (n). the current findings are found to qualitatively agree with the experimental and theoretical data that is currently available. keywords pseudopotential; liquid metals, pyhs structure factor, ocp structure factor, phonon dispersion, structural properties, vibrational properties. article information manuscript received: may 2, 2023; accepted: june 10, 2023 doi https://doi.org/10.3126/bibechana.v20i2.55552 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction since a long time, phonon dispersions and vibrational properties in liquids and gases have been explored theoretically, through computer simulation, and empirically. the most popular and useful experimental technique for determining phonon dispersion curves is neutron scattering. neutron scattering research has supplied some basic excitation in liquid metals. from copley and et al. [1] to cabrillo 146 http://nepjol.info/index.php/bibechana voraam@gmail.com mayankjani5@gmail.com https://doi.org/10.3126/bibechana.v20i2.55552 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 147 et al. [2, 3], the key experimental work sheds information on the dynamical features of alkali metals. desai et al. [4] theoretically reported the vibrational characteristics of liquid argon before this practical investigation. theoretically, phonon dispersion curves can be obtained using force constants, however even for regular and simple systems such as cubic crystals, the number of force constants required is large. as a result, for complicated systems such as liquids, phonon models that represent the ion-electron interaction are critical [5]. so, since liquid metal is a highly correlated system, the random phase approximation cannot produce an accurate picture of interaction. however, hubbard and beeby (hb) [6] has explained the vibrational properties of liquid metals quite effectively, and it may also be called a generalization of theory for the solid up to the liquid state. for the explanation of phonon in liquid metals, a stepwise generalized phonon theory of the crystal has been made. in the first solid state, there is no relative motion expected but in the other half, it is to be extended to the continuous system with the relative atomic motion which is called the liquid metals. to take the work based on the theoretical formulation, the high degree physics needed which includes the kinetics with the coupling of various modes [7, 8]. these excitations are density dependent functions so, they follow, in some manner, the structure factor variations with respect to wave numbers. the structure factor peak position falls roughly at the minima of the longitudinal frequency ωl vs. wave vector (k) plot [9]. numerous studies on the vibrational characteristics of numerous types of materials have been published [10–12]. thakor and his colleagues [12] used the hb method to calculate phonon dispersion curves. the same calculations were made for the metallic elements such as na, mg, al and pb. the acquired values in that study are consistent with the experimental data for na elements. since there are just a limited amount of experimental data points available for al, it was not displayed. vora [11] has published the phonon dispersion curves for liquid alkali metals after around a year. with the aid of the empty core model pseudopotential, he demonstrated how the curves are behaving consistently. the comparison with the experimental data available reveals that the selection of potential may be to blame for the low agreement. recently, malan and vora [12] have made another attempt to determine the pdc of liquid alkali metals. they claimed that the hb technique can be used to measure the material’s aforementioned attribute. the curves they obtained were found to be compatible with the experimental data that was available [12]. looking to the advantages of pseudopotential theory with hb approach particularly for studying the vibrational properties of studied simple liquid alkali metals are reported in the present article. for studying the vibrational properties, the structure factor s(q) and then after pair correlation function g(r) plays an important role. therefore, our motive of the present article is studying the vibrational properties of some simple liquid metals with percus-yevick hard sphere (pyhs) [13–15] and onecomponent plasma (ocp) [16–18] structure factor models with our own developed single parametric model pseudopotential. 2 computational methodology the size and locations of the longitudinal (l) and transverse (t) frequency peak positions with respect to the wave vector k are attempted to be determined in the current article. in the current investigation, the pseudopotential concept was used. the determined values of the pseudopotential parameter were applied to the newly constructed pseudopotential. when calculating the ion-interaction, the exchange and correlation effects must also be taken into consideration. to have the highest chance of predicting the astonishing results, the most appropriate exchange and correlation functions are advised. here we are using two different methods for the calculation of structure factor, i.e., pyhs [13–15] and ocp [16–18]. to obtain the structure factor by ocp method, we require a pseudopotential. for the same reason, we have applied our own generated model pseudopotential to obtain the pair distribution function with the help of which we will calculate the vibrational properties of the liquid alkali metals. the form of our newly proposed model potential in real space and corresponding bare-ion form factor in the reciprocal space is given as v (r) = −3ze2 r + ze2 r exp ( 1− r rc ) r ≤ rc = −ze2 r r ≥ rc (1) the fourier transform of such model potential is given as v (q) = −4πze2 q2ω0 [3− q2r2c 1 + q2r2c − exp(1) + {−2 + exp(1) + exp(−1)q2r2c 1 + q2r2c } cos qrc + exp(−1)qrc 1 + qr2c sin qrc] (2) here, z and e are valency and electronic charge, ω0 is atomic volume, q is wave vector, and rc is the parameter of the potential, respectively. it should be noticed that this type of pseudopotential only has mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 148 one parameter rc. within the core region, it is continuous at r = rc and becomes weaker and weaker as r decreases. two features of this form are the coulombic terms inside the core and the fluctuating cancellation brought on by the attracting and repelling concentrations of the potential outside the core. it is thought that instead of being 0 or constant, the potential outside the core should change as a function of r. this demonstrates the modification made to the ashcroft empty core model. the pseudopotential parameter d can be identified using [19] as rc = 0.51raz −1/3 (3) the pair correlation function g(r) and the pair potential must be obtained in order to carry out the computations. this method generates pair correlation function values as a prerequisite for subsequent calculations rather than directly extracting them from the experimental data. therefore, the current prediction is entirely theoretical and has no connection to any earlier experimental studies. by using the generated s(q) from the pyhs [13-15] and ocp [16-18] the g(r) par distribution function for the respective reference system can be easily obtained. here [20] is an equation for the g(r) utilized in this calculation. g(r) = 1 + ( 1 2π2ρr )∫ ∞ 0 q[s(q)− 1] sin(qr)dq(4) the structure factor equations of pyhs [13–15] can be derived as: s(q) = [1 + 24ξ (1− ξ)4y6 ( (1 + 2ξ) 2 y3(sin y − cos y) − 6ξ ( 1 + ξ 2 )2 y2 [ 2y sin y − ( y2 − 2 )] + ξ 2 (1 + 2ξ) 2 [ 4y3 − 24y ] sin y − ( y4 − 12y2 + 24) cos y + 24]−1 (5) and also, the structure factor equation with ocp method is mentioned below: s(q) = s0(q) 1 + ρβu∗(q)s0(q) (6) s0(q) = 1 1− ρc0(q) (7) ρc0(q) = 3γ q4a4α2 2 [cos (qaα1) + 2 cos(qaα2) − 3 sin(qaα1) qaα1 ] (8) where, α1 and α2 are the dimensionless parameters and also β µ∗(q) equations were taken from the mentioned reference [16–18] for the static structure factor of the ocp reference system. here while deriving the static structure factor using ocp system, we have used our own developed model pseudopotential. 2.1 phonon dispersion relation finding a single model potential that can be used to precisely compute a variety of material properties is challenging. problems arise when the physical phase shifts from solid to liquid or the other way around. in other words, not all of the properties in the liquid state can be achieved by the potential provided for the solid. we propose a new potential as stated in eq (3) to get around this problem and evaluate the phonon dispersion curves and other vibrational properties. to compute the phonon dispersion relations of liquid metals, the most frequently used approach of hubbard and beeby [6] is adopted for the calculations. with the physical argument that the product of the static pair correlation function g(r) and the second derivative of the interatomic pair potential ϕ(r) is peaked near the hard sphere diameter . hubbard and beeby [6] have derived the equations for the longitudinal phonon frequencies ωl(q) and transverse phonon frequencies ωt (q) as: ωl 2(q) = ωe 2[1− 3 sin(qσ) qσ − 6 cos(qσ) (qσ) 2 + 6 sin(qσ) (qσ) 3 ] (9) and ω2 t (q) = ω2 e [ 1 + 3 cos(qσ) (qσ)2 − 3 sin(qσ) (qσ)3 ] (10) in the above mentioned equations ωe represents the maximum phonon frequency and is given as, ωe = k ∫ ∞ 0 g(r)r2ϕ ′′ (r)dr (11) with k = 4πρ 3m (12) ϕ ′′ (r) = 4z2 r3 + ω π2 ∫ ∞ 0 f (q)q2 [ 2 sin(qr) qr3 − 2 cos(qr) qr3 − q sin(qr) r ]dq (13) with ϕ′′(r) = ∂2ϕ(r) ∂r2 the energy wave number characteristics f (q) in the above equation can be written as, f (q) = −ω0q 2 16π |v (q)|2 [εh(q)− 1] 1 + [εh(q)− 1] [1− f(q)] (14) mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 149 in the above equation v (q), εh(q), f (q) are the bare ion potential, modified hartree dielectric function and local field correction functions, respectively. the exchange and correlation screening functions from hartree [21], taylor [22], and nagy [23] were utilized here to calculate the aforementioned properties. the hartree screening function is purely static and it does not include any exchange and correlation effects. the expression for it as: f(q) = 0 (15) the taylor local field correction function [22] is a simple formula for static electron gas dielectric function, incorporating exchange and correlation effects, which generates calculated physical properties with good precession and justification. the equation for the function is follows: f(q) = q2 4k2f [ 1 + 0.1534 πkf ] (16) nagy local field correlation function [23] is used in the static mean field approximation the result is analytic and depends upon the value of the paircorrelation function at zero inter-particle separation. this analytic equation can be written as: f(q) = 1− g(0, n) + cb c2 + q2 − g(0, n) q tan−1 (q c ) (17) the parameters g(0, n)and c were taken as mentioned in the original article [23]. 2.2 elastic constants and parameters in addition to phonon dispersion curves, the current study has been expanded to determine a few constants and parameters required to provide a full bulk of liquid alkali metals. the usual equations are used to calculate the aforementioned parameters. in the long-wavelength limit of the frequency spectrum, the both frequencies i.e. transverse and longitudinal are proportional to the wave vectors and obey the relations. ωl ∝ q and ωt ∝ q ωl = vlq and ωt = vt q (18) where, vl and vt are the longitudinal and transverse sound velocities of the liquid metals respectively. equations for vl and vt are given by, vl = ωe √ 3σ2 10 and vt = ωe √ σ2 10 (19) various elastic properties are then determined by the longitudinal and transverse phonon frequencies. the bulk modulus (b), modulus of rigidity (g), young’s modulus (y) [24] and debye temperature θd [24] are calculated using following expressions, bt = ρv2l− 4v2t 3 , g = ρv2t , y = 2g(σ+1) (20) σ = 1− 2 ( v2 t v2 l ) 2− 2 ( v2 t v2 l ) (21) the debye temperature is given in terms of both the velocities as [24],beg θd = h̄ωd kb = h̄ kb 2π [ 9ρ 4π ]1/3 [ 1 v3l + 2 v3t ]−1/3 (22) here h̄ represents the planck constant, kb the boltzmann constant, ωd the debye frequency, and ρ the number density, respectively. here, θd shows the characteristic atomic motions in the liquid phase and is assumed to be constant over the temperature range of interest. for liquid metals, it is often treated as a parameter and fixed with the help of equation (14). 3 results and discussion the input parameters used in the present computation are tabulated in table 1 which are directly taken from [25, 26]. the parameters of the model potential are considered from eq. (4). table 1: input parameters and constants metal z π0 (au) t (k) ξ rc γ li 1 151.82 453.0 0.46 1.4649 210.75 na 1 277.51 378.0 0.46 1.7925 206.45 k 1 529.63 343.0 0.46 2.1877 183.35 rb 1 648.68 313.0 0.43 2.3901 187.86 cs 1 810.06 303.0 0.43 2.5539 180.21 mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 150 (a) (b) (c) (d) (e) figure 1: structure factor comparison for pyhs and ocp methods for (a) li, (b) na, (c) k, (d) rb, (e) cs mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 151 here, z, π0, t , ξ, rc and γ are valence, atomic volume, temperature, packing fraction, pseudopotential parameter, and plasma component, respectively. the respective structure factors for the liquid metals li, na, k, rb, and cs are shown in figure 1. three distinct types of techniques, including pyhs and ocp, were employed to compute the structure factors using the newly proposed pseudopotential. the currently available experimental structure factor data [27] and the computed structure factor graphs have been compared in figure 1. as shown in figure 1 for the metals under study, the pseudopotential has proven to have extremely good agreement with the current experimental results [27]. as can be shown, both methodologies for every ingredient offer superb agreement with experimental findings [27]. it can therefore be inferred that the recently created pseudopotential is particularly useful in evaluating a number of liquid metal properties. all of the information we utilized in this post was obtained using the melting point temperature. tables 2 and 3 compare the locations of the first and second peaks as well as the corresponding magnitudes of structure factors. according to waseda [27], the hard sphere structure factor shows the following features: 1. the first peak of the structural factor is symmetrical. 2. a packing fraction ξ = 0.45 is determined to have the best agreement with experimental data at temperatures just above the melting point. 3. the ratio of the second peak’s position to the first peak, α, is roughly 1.86. thus, the measured deviation from the hardsphere structure factor gives useful information in the structural study of liquid metals. therefore, from fig. 1, it has been observed that both the structure factor models give very good qualitative data in comparison with the available experimental data [27]. from the results of the first and second peak positions of the structure factor narrated in table 2, quite good agreement with the experimental value [27] due to ocp was found in comparison with pyhs. so, the ratio mentioned in table 3 calculated by both the structure factor methods is found to be consistent with experimental outcomes given in the literature [27]. it has been established that both the structure factor data are qualitatively consistent with the experimental findings [27]. as a result, when compared to the pyhs reference system, the ocp reference system gives a more accurate representation of the structure of monovalent metals. according to our research, pyhs is less useful than the ocp reference system for comprehending the structural behavior of liquid metals. the results also support the study’s usage of the newly created pseudopotential. the pair correlation function is also an important component while examining the vibrational properties of liquid metals, as it provides the statistical description of the structure of liquid metals. the g(r) has also been determined using the earlier estimated values of the structure factor. the phonon dispersion curves were generated using the various structure factor approaches in accordance with eq. (1) above, and they were contrasted with the available experimental data [27]. table 2: comparison for the first peak positions of structure factors metal first peak position and related magnitude in s(q) peak position in (å−1) related magnitude pyhs ocp expt.[27] pyhs ocp expt.[27] li 2.29 2.44 2.50 2.62 2.57 2.72 na 1.91 2.01 2.05 2.63 2.61 2.70 k 1.70 1.62 1.65 2.62 2.79 2.60 rb 1.48 1.54 1.50 2.29 2.72 2.69 cs 1.48 1.49 1.45 2.30 2.26 2.73 mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 152 table 3: comparison for the second peak positions of structure factors metal second peak position and related magnitude in s(q) peak position in (å−1) related magnitude pyhs ocp exp. [27] pyhs ocp exp. [27] li 4.28 4.74 4.70 1.32 1.21 1.20 na 3.59 3.91 3.80 1.32 1.21 1.19 k 3.21 3.09 3.00 1.31 1.18 1.19 rb 2.85 2.92 2.80 1.26 1.19 1.20 cs 2.86 2.81 2.70 1.25 1.17 1.20 table 4: ratio of the structure factor s(q) metal pyhs ocp exp. [27] li 1.86 1.94 1.88 na 1.87 1.90 1.85 k 1.88 1.90 1.81 rb 1.92 1.89 1.86 cs 1.93 1.88 1.86 table 5: comparison of first peak positions and related magnitudes in g(r) for different metals. metal second peak position and related magnitude in g(r) peak position in (å−1) related magnitude pyhs ocp exp. [27] pyhs ocp exp. [27] li 2.91 3.00 3.00 2.35 2.11 2.48 na 3.54 3.70 3.70 2.77 2.06 2.42 k 4.39 4.60 4.60 3.32 2.00 2.35 rb 4.60 4.80 4.80 3.17 2.10 2.47 cs 4.97 5.12 5.10 3.38 2.19 2.58 table 6: the comparison for the second peak positions of g(r). metal first peak position and related magnitude in g(r) peak position in (å−1) related magnitude pyhs ocp exp. [27] pyhs ocp exp. [27] li 5.60 5.72 5.70 0.74 1.07 1.22 na 6.82 6.80 6.80 0.81 1.07 1.26 k 8.47 8.70 8.70 0.89 1.05 1.23 rb 8.83 9.20 9.20 0.82 1.08 1.28 cs 9.52 9.60 9.60 0.84 1.09 1.30 table 7: the ratio (r1/r2) for the pair distribution function g(r). metal pyhs ocp exp. [27] li 1.92 1.90 1.90 na 1.92 1.83 1.83 k 1.92 1.81 1.81 rb 1.91 1.91 1.91 cs 1.92 1.88 1.88 mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 153 (f) (g) (h) (i) (j) figure 2: pair correlation function comparison for pyhs and ocp methods for (f) li, (g) na, (h) k, (i) rb, (j) cs. in a system with average number density, the probability of finding another atom at a distance r from an origin atom corresponds to g(r). the function g(r) is called the pair correlation function and is frequently used for the discussion of noncrystalline systems. the information given by g(r) is only single-dimensional, but it does provide quantitative information on non-crystalline systems [27]. therefore, the pair correlation function is one of the most important pieces of information in this study. when compared to the pyhs technique, the pair distribution functions from various reference mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 154 (k) (l) (m) (n) (o) figure 3: the phonon frequencies (solid line), (dashed line) of different element using pyhs structure factor for (k) li, (l) na, (m) k, (n) rb and (o) cs. mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 155 (p) (q) (r) (s) (t) figure 4: the phonon frequencies (solid line), (dashed line) different elements using ocp structure factor for (p) li, (q) na, (r) k, (s) rb and (t) cs mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 156 (a) (b) figure 5: metal wise comparison for ωl and ωt with pyhs method. (c) (d) figure 6: metal wise comparison for ωl and ωt with ocp method. systems show that the ocp method is considerably more in line with the experimental data [27]. the percentage variation in the first peak position q1 of the structure factor using the pyhs model with the experimental data [27] for the given elements were found to be 1.33%–12.4%, whereas for the ocp method it was calculated as 1.33%– 2.75%. for the second peak variation q2, the pyhs model gives 0.77%–18.58%, while the ocp calculation gives a variation of 1.11%–17.21% and 0.40%–9.36%, respectively, with the experimental data [27]. for the first peak of the pair correlation function g(r), the variation found for the pyhs and ocp methods for the liquid alkali metals were 2.35%– 4.56% and 0.00%–0.39%, respectively. for the second peak variation g(r), the above-mentioned models yield 0.29%–5.40% and 0.00%–0.35%, respectively. for all liquid alkali metals, the longitudinal vibration variation with regard to the wave vector, calculated using the pyhs and ocp structure factors, was examined in 3 and 4. the findings of various local field correction functions are displayed using colour coding. for the pyhs method, one can see that the hartree function [21] gives the highest value for ωl(q) and ωt (q) for all the elements except k because, for element k, the screening function of nagy [23] gives the least values. also, there are experimental data available for li, na, and rb [28, 29] elements, so the comparison is also shown in the same figures 3 and 4. it shows that our obtained results are in qualitative agreement with the available experimental data [28, 29]. also, for the elements, ωl(q) shows more oscillatory behaviour in comparison with ωt (q). in the discussion for st (q), less oscillatory behaviour was observed, and one can see that the screening function of taylor [22] gives the maximum value for all the elements, while nagy [23] gives the least value except for cs. in cs, the hartree [21] screening function shows the least results, which are very similar to the data with nagy [23]. figure 6 shows that at larger q values, greater oscillatory behaviour is found in the case of ωl(q) than in the case of ωt (q) with different structure mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 157 table 8: vibrational properties of liquid metals with pyhs structure factor parameters results li na k rb cs vl × 103cm/s h 8.3761 4.7317 3.8865 2.5546 2.0273 t 8.0555 4.0830 3.6797 2.3418 1.8110 n 5.9971 0.8279 2.2189 1.7778 1.6037 exp. [30] 2.51 others[12,13] 8.88, 8.61 3.77, 4.41 3.01, 2.97 1.92, 1.90 1.48, 1.44 vt × 103cm/s h 4.8359 2.7318 2.2439 1.4749 1.1704 t 4.6508 2.3573 2.1245 1.3520 1.0455 n 3.4624 0.4780 1.2810 1.0264 0.9259 exp. [30] 1.81 others[12,13] 5.13, 4.97 2.18, 2.54 1.74, 1.69 1.11, 1.08 0.85, 0.83 g dyne/cm2 h 1.2079 0.6928 0.4153 0.3210 0.2518 t 1.1172 0.5159 0.3723 0.2698 0.2009 n 0.6192 0.0212 0.1353 0.1554 0.1575 others[12,31] 14.10, 13.25 4.41, 6.54 2.76, 2.59 2.01, 1.90 1.45, 1.39 b×103dyne/cm2 h 2.013 1.1547 0.6922 0.5351 0.4196 t 1.8620 0.8598 0.6205 0.4496 0.3348 t 1.0324 0.0353 0.2256 0.2591 0.2626 exp. [12] 5.3 others [12, 31] 2.35, 2.21 7.35, 1.09 0.46, 0.43 0.33, 0.32 0.24, 0.23 y×1011dyne/cm2 h 3.0197 1.7321 1.0383 0.8026 0.6294 t 2.7930 1.2897 0.9307 0.6745 0.5023 n 1.5480 0.0530 0.3384 0.3887 0.3939 others [12, 31] 3.53, 3.18 1.10, 1.64 0.69, 0.65 0.50, 0.47 0.36, 0.35 θd(k) h 566.4771 261.7193 173.3101 106.4724 78.4634 t 544.7990 225.8393 164.0891 97.6051 70.0914 n 405.5852 45.7920 98.9458 74.0991 62.0717 others [12, 32, 33] 609.80, 579.46 250.85, 240.35 138.77, 134.45 82.82, 80.56 58.81, 58.46 factor methods of pyhs and ocp. this assures that longitudinal phonons alone, and not both, are responsible for group oscillations. the linear response exists in phonon dispersion curves at low q values but vanishes at larger q. this happens as a result of the velocity altering as q shifts. because all of the metals under examination, due to the hartree [21] screening function, exhibit identical oscillating behaviour, the hartree-bogolyubov (hb) approach yields reasonably fruitful results. additionally, li exhibits the maximum vibrations for all the different structure factor techniques for liquid alkali metals, but cs gives the lowest vibrations. the vibrational properties of all the abovementioned liquid metals are shown in tables 8-10. the parameters include the longitudinal velocity of sound (vl), transverse velocity of sound (vt ), modulus of rigidity (g), isothermal bulk modulus (b), young’s modulus (y ), and debye temperature (θd). the selected liquid alkali metals show screening sensitivity in the low-momentum region. furthermore, the phonons can be detected as sound waves thanks to the spectrum’s macroscopic frequency limit. as a result, the longitudinal and transverse sound velocities have been calculated using the linear component of their dispersion curves. both structure factor techniques’ predictions for vibrational properties are found to be qualitatively consistent with the theoretical or experimental findings detailed in the literature [12]. to put it another way, a property essentially has the same value for all permutations of the structure factor method, but divergence is apparent when using the screening functions. one can observe that for both methods exceptionally well results in agreement with the experimental values for vl and vt . hence, pyhs and ocp structure factor techniques for calculating the isothermal bulk modulus b provide findings that are qualitatively consistent with the experimental data for all na. similar results were found for li, k, rb, and cs as individual elements using both structure factor approaches as well as experimental data [30–35]. mayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 158 table 9: vibrational properties of liquid metals with ocp structure factor parameters results li na k rb cs vl × 103cm/s h 8.3797 4.6998 3.8307 2.5699 2.0480 t 8.0590 4.0555 3.6269 2.3559 1.8295 n 5.9996 0.8223 2.1870 1.7885 1.6202 exp. [30] 2.51 others [12, 31] 8.88, 8.61 3.77, 4.41 3.01, 2.97 1.92, 1.90 1.48, 1.44 vt × 103cm/s h 4.8320 2.7134 2.2117 1.4870 1.1824 t 4.6528 2.3414 2.0940 1.3601 1.0562 n 3.4639 0.4747 1.2626 1.0326 0.9354 exp. [30] 1.81 others [12, 31] 5.13, 4.97 2.18, 2.54 1.74, 1.69 1.11, 1.08 0.85, 0.83 g dyne/cm2 h 1.1987 0.6832 0.4043 0.3249 0.2569 t 1.1087 0.5087 0.3624 0.2730 0.2050 n 0.6145 0.0209 0.1318 0.1573 0.1608 exp. [12] 5.3 others [12, 31] 14.10, 13.25 4.41, 6.54 2.76, 2.59 2.01, 1.90 1.45, 1.39 b×103dyne/cm2 h 1.9979 1.1387 0.6739 0.5413 0.4282 t 1.8479 0.8479 0.6041 0.4551 0.3418 n 1.0241 0.0348 0.2196 0.2623 0.2680 exp. [12] 5.3 others [12, 31] 2.35, 2.21 7.35, 1.09 0.46, 0.43 0.33, 0.32 0.24, 0.23 y×1011dyne/cm2 h 2.9968 1.7081 1.0109 0.8123 0.6424 t 2.7719 1.2719 0.9061 0.6826 0.5126 n 1.5362 0.0523 0.3295 0.3934 0.4020 others [12, 31] 3.53, 3.18 1.10, 1.64 0.69, 0.65 0.50, 0.47 0.36, 0.35 θd(k) h 566.7200 259.9579 170.8222 107.1108 79.2655 t 545.0326 224.3194 161.7336 98.1903 70.8080 n 405.7591 45.4868 97.5255 74.5434 62.7063 others [12, 32, 33] 609.80, 579.46 250.85, 240.35 138.77, 134.45 82.82, 80.56 58.81, 58.46 the additional theoretical data [12, 32–35] for the modulus of rigidity g for all the elements available in the literature for comparison, and both structure factor approaches were determined to be appropriate to derive the same property. similar to young’s modulus, the statistics for all the elements were accessible, which were determined to be good in comparison to the same, and the most recent estimated debye temperature θd is extremely similar to the values actually obtained. with all three types of screening functions, it is discovered that the data obtained by the three structure factor methods are quite similar to one another. 4 conclusion from the above comprehensive study, it can be concluded that the structural and vibrational properties, i.e., phonon dispersion curves (pdc), longitudinal sound velocity (vl), transverse sound velocity (vt ), isothermal bulk modulus (b), modulus of rigidity (g), young’s modulus (y ), debye temperature (θd) of some monovalent (li, na, k, rb, cs) liquid metals using the newly developed model potential with the two different types of structure factor methods pyhs and ocp, with three types of screening functions, namely hartree (h), taylor (t), and nagy (n), are reported for the first time. it can be challenging to decide which structure factor methodology is most appropriate for computing the vibrational properties of liquid metals because each of the three approaches employed here has its own distinct identity, significance, and limitations. however, from the obtained data, we can say that the hb approach calculates precise conclusions for phonon data with the fewest parameters possible, and the ocp method gives better results in comparison with the pyhs method. we conclude that the vibrational properties of the aforementioned liquid metals may be efficiently studied by pdcs derived from the hb technique with three local field correction functions, namely h, t, and n. these formulas accurately reproduce all of the salient features of phonon dispersion curves. hence, the presently adopted model potential is found suitable when used in conjunction with the hb approach. the model potential provides less complex calculation of the vibrational properties of the metmayank h. jani and aditya m. vora/ bibechana 20 (2023) 146-160 159 als under study as it is using only a single parameter (rc). the obtained vibrational properties serve as a detailed database for further research in the field of liquid metals study. acknowldgements computer facility developed under dst-fist program from the department of science and technology, government of india, new delhi, india and financial assistance under drs-sap-ii from university grants commission, new delhi, india is highly acknowledged by the authors. references [1] j. r. d. copley and j. m. rowe. shortwavelength collective excitations in liquid rubidium observed by coherent neutron scattering. physical review letters, 32:49, 1974. 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[35] d. h. li, x. r. li, and s. wang. variational calculation of helmholtz free energies with applications to the sp-type liquid metals. j. phys. f:met. phys., 16(1986):309, 1986. introduction computational methodology phonon dispersion relation elastic constants and parameters results and discussion conclusion bibechana vol. 22, no. 2, august 2025, 122-130 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar characterization of essential ingredients for designing biopolymer-based transdermal patches prasamsha panta1,2,3, elina maharjan3, holger schönherr2,∗, rameshwar adhikari3,4,5,∗∗, achyut adhikari5, rajani malla1,∗∗∗ 1central department of biotechnology, tribhuvan university, kirtipur 44618, kathmandu, nepal 2department of chemistry and biology & research center of micro and nanochemistry and (bio)technology (cµ) physical chemistry i, university of siegen, adolf-reichwein-str.2, 57076 siegen,germany 3nepal polymer institute (npi), p. o. box 24411, kathmandu, nepal 4central department of chemistry, tribhuvan university, kirtipur 44618, kathmandu, nepal 5research center for applied science and technology (recast), tribhuvan university, kirtipur 44618, kathmandu, nepal ∗corresponding authors. email: ∗ schoenherr@chemie.uni-siegen.de ∗∗ nepalpolymer@yahoo.com ∗∗∗rajanimalla2000@gmail.com abstract the study aimed to characterize the key ingredients used in developing biopolymers-based transdermal patches using fourier transmission infrared (ftir) spectroscopy, scanning electron microscopy (sem), thermogravimetric analysis (tga), and rheological analysis. while ftir spectroscopy and sem were used to investigate the structural properties and intermolecular interaction within chitosan (ch), methylcellulose (mc), and carboxymethyl cellulose (cmc) as well as wintergreen essential oil (wg oil), the tga revealed the thermal degradation profiles of ch, mc, and cmc. rheological analyses revealed that the polymer concentration and the solvent chosen significantly influenced the processability of the polymers. tga analysis demonstrated that an initial decomposition of ch took place at 275 0c, while mc and cmc exhibited initial degradation around 260 0c. based on the structural, rheological, and thermal properties, the suitability of the characterized biopolymer for fabricating the transdermal patch was demonstrated. keywords core ingredients, transdermal patch, wintergreen essential oil, biopolymers article information manuscript received: january 27, 2025; revised: march 8, 2025; accepted: march 10, 2025 doi https://doi.org/10.3126/bibechana.v22i2.74648 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 122 http://nepjol.info/index.php/bibechana schoenherr@chemie.uni-siegen.de nepalpolymer@yahoo.com rajanimalla2000@gmail.com https://doi.org/10.3126/bibechana.v22i2.74648 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ prasamsha panta et al./ bibechana 22 (2025) 122-130 123 1 introduction transdermal patches (tp) belong to advanced noninvasive drug delivery systems. they offer sustained and controlled release of active pharmaceutical ingredients (apis) through the skin (dermal region) into the systemic circulation [1]. this process bypasses the conventional oral and injection routes [2, 3]. current trends and innovations in transdermal patches include smart patches that integrate dose monitoring and adjustable drug release via wearable electronics [4], and combination therapy through which larger molecule drugs like vaccines and peptides can be delivered. similarly, for environmentally sustainable designs, biopolymer-based patches that incorporate biodegradable polymers such as chitosan, cellulose-based polymers, gelatin, and starch can be prepared [5, 6]. among these polymers chitosan (ch), methylcellulose (mc), and carboxymethyl cellulose (cmc) have been used in combination with conventional medicines [7] essential and fixed oils [8], and herbal extracts [9] for the preparation of transdermal patches. ch, mc, and cmc are environmentally friendly and versatile biopolymers with a wide range of applications [10] such as in food industries, water treatment, cosmetics and personal care, agriculture industries, medical, pharmaceutical, and healthcare products [11], textile industries [12], painting industries, construction industries. ch is a natural biopolymer obtained by the deacetylation of chitin, where the removal of acetyl groups affords amine groups [13]. ch materials (for chemical structure see figure 1) are environmentally friendly and non-toxic materials that can also be used as an antibacterial and antifungal agent, tissue engineering, skincare, hair care, and drug delivery systems [14–16] and as dietary supplements. mc is produced by treating cellulose with methyl chloride, which makes mc water soluble to form clear viscous solutions. mc is non-toxic and non-allergic, which makes this polymer suitable for use in food and pharmaceutical industries [16]. mc can be utilized in various fields for its properties and applications as a thickener and stabilizer, gelling agent, emulsifier, wound care, food packaging [17, 18], and drug delivery system [19]. the structure of mc is illustrated in figure 1. cmc is a natural polymer derived from cellulose found in plant cell walls. cmc is produced by chemical modification of cellulose, where carboxymethyl groups (-ch2-cooh) are introduced into the cellulose backbone. cmc (see figure 1) is water-soluble, which makes it useful in various fields. the applications of cmc in different areas like thickener, binder, thickening agent, excipient, controlled release, wound dressing, and drug delivery system [20, 21]. cmc is an ideal choice for a drug delivery system capable of encapsulating the active drug. cmc exhibits film-forming properties, biocompatibility, and capacity for controlled drug release [22]. figure 1: illustration of chemical structures of chitosan (ch), methylcellulose (mc), carboxymethyl cellulose (cmc), and methyl salicylate, the primary component of wintergreen essential oil (wg oil) wintergreen essential oil (wg oil), derived from the leaves of wintergreen plants (gaultheria procumbens), commonly known as dhasingare in nepali language, is a natural pain reliever with a long history of medicinal use. the oil is composed of more than 90% methyl salicylate (chemical structure given in figure 1), a chemical compound wellknown for its pain-fighting properties [23]. it has been reported that the wg oil acts as an antiinflammatory agent, making it effective for soothing muscle pain, and joint pain, and reducing swelling [24], and thus is a common ingredient in topical pain relief products such as balms and ointments employed in the treatment of rheumatism and arthritis [25]. a key development arising from combining wg oil with biopolymers could lead to new, convenient, and affordable transdermal patches for pharmaceutical applications [26–28]. this combination of natural pain relief and innovative materials holds promise for the future of pain management. the overall characterization of biopolymers is crucial in developing any kind of drug delivery system, including transdermal patches. the present work aims at characterizing ch, mc, cmc, and wg oil to investigate their suitability as building blocks for the fabrication of medicated transdermal patches. the details on the performance of the patches will be the object of other reports (for example [29]. 2 materials and methods 2.1 materials chitosan (pcode 102433232) and carboxymethyl cellulose (pcode 1002577718) were purchased from prasamsha panta et al./ bibechana 22 (2025) 122-130 124 sigma aldrich, and low substitution methylcellulose (pcode 29217) was purchased from bdh chemicals ltd., poole england. acetic acid and glycerol were procured from thermo-fischer scientific. wintergreen (gaultheria procumbens) essential oil was purchased from annapurna pvt. ltd. in nepal. milli-q water was purified in the laboratory using a millipore direct q8 system with a resistivity of 18.2 m cm (millipore advantage a10 system, schwalbach, with millimark express 40 filter, merck, germany). all the chemicals were used as received. 2.2 characterization methods 2.2.1 scanning electron microscopy (sem) analysis ch, mc, and cmc powder samples were mounted on a sample holder using conductive carbon tape. the samples were then sputter-coated with 20 nm of gold film to avoid charging and electron beam damage. a camscan cs24 scanning electron microscope (applied beams, beaverton, or, usa), operated at an accelerating voltage of 25 kv, was used. 2.2.2 fourier transmission infra-red (ftir) spectroscopy analysis powder samples of each biopolymer were ground and mixed with potassium bromide (kbr) to form a pellet. the pellet was placed in an ftir sample holder. samples were analyzed using a bruker tensor 27 ftir spectrometer (ettlingen, germany) using 2 cm-1 of the resolution, number of scans 32 in the spectral range of 4000 cm-1400 cm-1. 2.2.3 analysis (tga) approximately 10 mg of the powder sample of each biopolymer was placed in an airtight crucible and placed in the tga instrument (q500 v6.7 build 203, eschborn, germany). the samples were analyzed from 50 0cc to 850 0cc at a heating rate of 10 oc/min. 2.2.4 rheological measurement and preparation of patch 0.5 wt.% of ch was dissolved in 1 vol.% of acetic acid, and 1 wt.% of mc and cmc was dissolved in milli-q water. the solution was stirred for 12 h and viscosity was measured using a bohlin instruments rheometer at 37 oc, measuring a system of c25 din 53019 spindle. for the preparation of the transdermal patch, after the complete dissolution of ch and mc for 12 h. the mc solution was mixed with the ch solution and mixed for 3 h in a stirring plate. then the mixture was poured in a 90 mm diameter petri plate and dried in an oven at 45 oc for 2 days. every experiment was performed 3 times and the average result along with the standard deviation has been presented. 3 results and discussion 3.1 morphology of biopolymers sem analysis was conducted to investigate the particle shape, size, and surface characteristics of the biopolymers. scanning electron micrographs (sem) of biopolymer powders, with highmagnification sem images of each sample displayed to the right, figure 2. these micrographs reveal that chitosan (ch) exhibits a flake-like morphology with a smooth, non-porous surface [30] as evident in figure 2a. notably, individual ch granules appear larger compared to mc (figure 2b) and cmc (figure 2c), potentially attributed to differences in the primary materials while preparing the polymers. figure 2: scanning electron micrographs of biopolymers: a) ch, b) mc, and c) cmc; a part of each micrograph on the left (indicated by a white rectangle) has been magnified on the right. the most common initial material for ch is chitin [30], but mc and cmc are cellulose-based materials synthesized from plant cell walls [31, 32]. the cellulose-based polymers (mc and cmc) display a fibrous structure and smaller particle sizes than ch granules [33]. in the case of ch, the degree of acetylation influences its particle morphology [34]. in contrast to ch and mc, cmc has been found to exhibit smaller particle sizes and a granular, irprasamsha panta et al./ bibechana 22 (2025) 122-130 125 regular structure, likely due to the substitution during its synthesis. other factors that may contribute to the observed structural variations among ch, mc, and cmc include processing techniques and the chemicals used during preparation. 3.2 spectroscopic characterization of biopolymers and wg oil figure 3a presents the ftir spectra of ch, mc, cmc, and wg oil, revealing subtle differences across certain spectral regions. figure 3b depicts the extended spectral region (2000 cm -1 to 600 cm -1) of the ftir spectra of the samples. the region provides a clearer understanding of the spectral similarities between mc and cmc, as well as the prominent spectral signature of methyl salicylate, a key component of wintergreen essential oil. a broad band observed around 3400 cm-1 in all samples (ch, mc, cmc, and wg oil) is characteristic of o-h stretching vibrations. in ch, this broadband further confirms the presence of both hydroxyl and amine groups [5]. consistent with previous findings by santosh kumar et al., a common band near 2925 cm-1 is observed in all attributed to c-h stretching vibration of aliphatic chains of chitosan backbone in ch [35], and methylene/methyl groups within the cellulose structures of mc, cmc and wg oil. in addition, for ch, a band at 1460 cm-1, characteristic of amine ii vibrations (n-h bending), indicates the presence of free amino groups [36]. the ch2 bending vibration of the methylene group was observed at 1322 cm-1. additionally, strong bands at 1167 cm-1 and 1089 cm-1 were assigned to c-o-c bending vibrations of glycosidic linkages (figure 1) and c-o vibration of carbohydrates was observed respectively. in the case of mc, a band characteristic of c-o-c ether linkages was observed at 1460 cm-1 [37]. c-h bending vibrations and typical glycosidic linkage in cellulose were observed at 943 cm-1. in the cmc spectrum, a characteristic peak of the carboxymethyl group was observed at 1606 cm-1, corresponding to asymmetric and symmetric stretching vibrations of coogroup [38]. c-h bending vibrations of methylene and methyl groups are observed at 1331 cm-1. finally, a band at 1064 cm-1 can be attributed to c-o stretching vibrations of polysaccharides. in the case of wg, in agreement with samira mendes et. al., a band at 1584 cm-1 was attributed to aromatic c=c stretching vibrations, indicative of a benzene ring in methyl salicylate. c-o stretching vibrations of ester linkages were observed at 1257.5 cm-1. additionally, bands at 1095 cm-1 and 763 cm-1 were assigned to c-o stretching vibrations of alcohols/ phenols and aromatic c-h bending vibrations, respectively [39]. figure 3: ftir spectroscopy analysis of a) ch, mc, cmc, and wg oil, and b) magnified view of the spectral region from 2000 cm -1 to 600 cm -1 3.3 thermogravimetric analyses of the biopolymers the plot in figure 4a represents the weight loss profile of ch, mc, and cmc. all the polymers exhibit a significant weight loss and increase in temperature, which shows the thermal decomposition of ch, mc, and cmc. among the three polymers, ch appears to have the lowest thermal stability among the three biopolymers. this might indicate that ch decomposes more easily compared to mc and cmc. it seems that cmc has the highest thermal stability because the weight loss starts at higher temperatures and indicates more resistance to thermal degradation [10, 40]. the chemical structure and composition of these biopolymers play a crucial role in determining thermal stability. figure 4b illustrates that for ch powder, the primary decomposition occurred at 274 oc, attributed to the breakdown of the polymeric structure and the cleavage of glycosidic bonds (see figure 1 for chemical structures). a final decomposition step was observed around 481 °c, which might be of different chemical bonds and functional groups within the ch structure. in the case of mc, the initial decomposition started around 260 0c, associated with the degradation of the methylcellulose and the release of volatile degradation products and small organic molecules due to the breakdown of methyl ether groups. figure 3b indicates that mc undergoes approximately 10 % decomposition at 457 oc, which might be attributed to the breakdown of complex materials that remain still during the synthesis process. in contrast to the findings of thomas et al. (2016), cmc exhibited an initial decomposition of around 38 % at 260 occ, likely due to the degradation of both carboxymethyl groups and the polymeric backbone. a second phase of decomposition occurred at about 700 occ, with an approximate weight loss of 21 %, suggesting further breakdown into similar molecules. a residual mass was observed at ca. 800 oc, likely consisting of a carbonaceous substance [41]. prasamsha panta et al./ bibechana 22 (2025) 122-130 126 figure 4: thermogravimetric analysis (tga) curves of ch, mc, and cmc a) weight loss as a function of temperature, b) derivative weight loss curves. measurements were conducted under a nitrogen flow rate of 50 ml/min within a temperature ranging from 50 0c to 850 0c. generally, higher onset temperatures indicate greater thermal stability. this notion is in agreement with earlier research works related to the stable nature of the cmc, in which the latter was used for environmental applications [42], [43]. the results demonstrate better weight degradation stability of the cmc compared to ch and mc. the tga profile shows that the initial weight loss is due to moisture release, which is almost absent in the case of ch, mc, and cmc because the samples selected for analysis were stored in closed containers and freeze-dried before analysis. 3.4 rheological analysis of biopolymers the rheological study aimed to assess the stability and overall performance of these polymers during processing and transdermal patch preparation. figure 5 illustrates the viscosity of ch, mc, and cmc as a function of concentration whereby water is used as a control solution. to simplify the preparation process, a lower concentration of ch was used to compare with the mc and cmc. despite the lower concentration (0.5 wt.%), ch exhibited a viscosity of 0.23 pa.s whereas, the viscosity of mc and cmc was much lower. in the case of mc and cmc 1 wt.% of solution was used where the viscosity was found to be 0.04 pa.s and 0.014 pa.s respectively. in mc, the observed decrease in viscosity at specific temperatures is attributed to its thermoreversible property, specifically the hydrophobic interactions of methoxy groups [44]. in the case of cmc, viscosity is significantly influenced by the degree of substitution and the ionization state of the carboxyl group [45]. the difference in viscosity is likely due to the degree of deacetylation of chitosan [46] and the alignment of electrostatic forces, especially the positively charged amino group and glycosidic linkage [47]. figure 5: the viscosity of ch, mc, and cmc solutions was determined using a rheometer concerning water. accompanying photographs represent the visual appearance of the ch, mc, and cmc solutions. from the rheology study, it can be revealed that the molecular weight of the polymer, concentration, and solvent are crucial factors that affect the viscosity of the polymeric solution. as tga analyses the decomposition and stability, rheology gives information about the flowability due to structural breakdown. 3.5 structural characterization of the transdermal patch as already mentioned earlier, details on the structure-performance correlation of the patch prepared via various processing routes have been reported elsewhere [29]. here, we report briefly the structural characterization of the patch observed by optical imaging and scanning electron microscopy (sem). the photograph of the transdermal patch prepared using ch and mc is shown in figure 6a. the sem analysis shows the surface morphology of the blank transdermal patch prepared using ch and mc (figure 6b). highly porous and uneven alignment was observed which might be due to excess exposure to temperature during the drying process and water loss via evaporation while drying (figure 6). this kind of structural arrangement might be useful for the entrapment of active pharmaceutical active ingredients (apis) especially essential oils that are well-known for pain management or pain relief. while preparing the transdermal patches, the polymeric contents, a combination of plasticizers, and viscosity aid in fabricating uniform and consisprasamsha panta et al./ bibechana 22 (2025) 122-130 127 tent structural configuration across the patch. this assessment not only ensures the adherence ability of the patch but also maintains the shelf life of the patch and the release of the drug at a controlled rate. figure 6: photograph (left) and sem micrograph (right) showing the morphology of the transdermal patch prepared using ch and mc. 4 conclusion this study has characterized the properties of the basic ingredients of a transdermal patch comprising chitosan (ch), methylcellulose (mc), and carboxymethyl cellulose (cmc) to be enriched with wintergreen oil by different techniques such as sem, ir, tga, and rheological analyses. the sem imaging of the biopolymers reveals distinct differences in their particle morphology. ch displays a smooth, non-porous, flake-like surface with larger granules compared to mc and cmc, which have fibrous structures and smaller particle sizes. ch's larger granules are likely due to its chitin base, while mc and cmc are derived from cellulose. all samples exhibit a broad ftir band around 3400 cm−1, indicating the o-h stretching vibrations. ch and wg oil also show amine (nh2) and hydroxyl groups, while mc and cmc display cellulose-related features, as expected. wg oil reveals aromatic and ester vibrations associated with the methyl salicylate. ch exhibits the lowest thermal stability, starting decomposition at lower temperatures, while cmc shows the highest stability, starting decomposition at higher temperatures and with less weight loss. mc has thermal stability similar to ch. all the biopolymers have thermal stability suitable for their use as transdermal patch fabrication. future research will focus on optimizing biopolymer ratios and properties and essential oil selection to further advance the development of effective patches for pharmaceutical applications. acknowledgments dipl. laborchem. petra frank (macromolecular chemistry group, university of siegen) is cordially thanked for her support during rheological measurements. we thank prof. ulrich jonas for access to the equipment. we thank the german academic exchange service (daad) for providing a research fellowship to pp in the frame of a binationally supervised phd project, the university grants commission for providing the phd scholarship, and the university of siegen for financial support. authors contribution pp: performing experiments, analysis of results, drafting the first manuscript; em: analysis of results, and interpretation; hs: funding acquisition, conceptualization, supervision, and editing of the manuscript; ra: co-drafting of manuscript, funding acquisition, conceptualization,and supervision; aa: supervision, and editing of the manuscript; rm: supervision, data analysis and interpretation conflict of interest statement the authors declare that 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exploring topological phase transition in pt2hg1−xtlxse3 deergh bahadur shahi, dipak bhattarai, madhav prasad ghimire∗ 1central department of physics, tribhuvan university, kirtipur, 44613,kathmandu, nepal ∗corresponding author. email: madhav.ghimire@cdp.tu.edu.np abstract the transition from trivial to non-trivial phase in two-dimensional materials are called a topological phase transition (tpt). the berry phase, non-local string order parameter, and edge states define the topological nature of the system. a newly discovered jacutingaite material pt2hgse3 is a layered material which occurs naturally in the form of minerals. the material can be exfoliated and was predicted as a quantum spin hall insulator. here, on the basis of density functional theory and tight-binding calculations, we explore pt2hg1−xtlxse3 (x = 0.25, 0.50, 0.75, 1) to understand the electronic and topological properties. we start with the parent material pt2hgse3 wherein hg is replaced partially with x amount of tl, to tune the topological phases. from the electronic structure calculations, pt2hgse3 is found to be a non-trivial semimetal in it’s bulk. upon electron doping, the material transforms to strong topological metallic phase. the topological z2 invariant calculation shows tpt in pt2hg1−xtlxse3 with weak topological insulating state (0;001) for x=0, to strong topological metal (1;000) for x=1, respectively. keywords density functional theory, jacutingaite materials, spin-orbit coupling, topological invariants, topological phase transition. article information manuscript received: september 16, 2023; accepted: november 1, 2023 doi https://doi.org/10.3126/bibechana.v20i3.58632 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction topological concept in material science has a crucial role in condensed matter and materials science. topological notion not only enhances the understanding of various physical phenomena, but also play an important role in the development and innovation in materials science [1]. the study of topological properties is thriving research area due to its promising applications in electronics and quantum computing. topology and topological invariants plays a significant role in understanding and classification of new states of matter in material science. by using the concepts of mirror chern number, chern number and topological invariant (z2) we can explain the properties and different behaviors exhibited by various quantum hall systems, topological insulators (tis), topological semimetals 309 http://nepjol.info/index.php/bibechana madhav.ghimire@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v20i3.58632 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ deergh bahadur shahi et al./ bibechana 20 (2023) 309-315 310 such as dirac, weyl and nodal line. the surface or edge effects in topological materials are found to change in several properties such as in electronic, optical, transport, magnetic, etc. [2,3] and can be detected using transmission electron microscopy. two-dimensional (2d) quantum spin hall insulator (qshi) are characterized by a gapless helical edge states with small electronic band gap in it’s bulk. though they resists interaction and disorder extending up to room temperature, the study related to qshi are limited [4,5]. topological features of the materials can be identified by calculating the z2 invariant. z2 consists of four components: ν0; ν1, ν2, ν3 based on which the material can be distinguished whether they are strong or weak topological materials. for instance, when ν0 = 1; and any of its ν1, ν2, ν3 are either 0 or 1, the material are called strong topological insulator/metal, but, if ν0 = 0 and any other invariants ( ν1, ν2, ν3) are non-zero, they are called weak topological material. among several group of materials, pt2hgse3 is one of the natural mineral of platinum group belonging to jacutingaite family discovered in 2008 [6] and successfully synthesized in 2012 [7–10]. this material has been cleaved to its monolayer and from the density functional theory (many-body g0w0 calculations, it was reported to be a qshi with a band gap of ∼0.15 ev (0.5 ev) at the dirac point [11]. qshi to quantum anamolous hall (qah) phase was also observed in monolayer of pt2hgse3 by chemical functionalization [12]. in materials belonging to topological materials, topological phase transition (tpt) can be achieved by chemical functionalization, applying magnetic and electric field, pressure and doping, etc. tpt has been observed in bilayer of jacutingaite when perpendicular electric field was applied wherein the bilayer changes from a normal insulator to qshi [13]. likewise, unconventional superconductivity was observed in monolayer of pt2hgse3 by electron and hole doping along with other exotic property such as qshi [14]. monolayer of pt2hgse3 has also been studied recently in which the material losses its symmetric behavior due to presence of ferromagnetic substrate (nibr2). charge transfer takes place at the interface resulting in spin degeneracy band gap of ∼134.2 mev and valley dependent global gap of 58.8 mev, respectively [15]. further, it was noticed that lattice defect can shift the fermi level (ef ) above the van hove singularity in pt2hgse3 , and thus can potentially serve as an effective means to regulate doping effect [16]. band inversion is one of the key parameter that dictates the nontrivial property and is associated with a bulk topological invariant. further, calculation of parities in the brillouin zone (bz) of occupied bands at the time reversal invariant momentum (trim) are used in determining the topological invariant of the system following inversion symmetry [17]. thus, in inversion symmetric system, a material with strong spin-orbit coupling (soc) strength is required to flip the maximum of the valence band to the minimum of conduction band with opposite parities at the trim point. this allows to change the phase from normal insulator (ni) to topological insulator (ti). in topological band inversion, band gap is denoted by a negative sign to distinguish it from a trivial band gap in an even topological invariant scenario. ti to ni phase transition was observed also by nonmagnetic substitution [18–20]. while the overall idea of such a transition seems intuitive, specifics are yet unknown. therefore we can expect that the band gap of a ti would decrease linearly on substitution of a lighter element with weaker soc strength. the traditional interpretation of nonmagnetic doping phase transition behavior in tis has been challenged by the low concentration (x ), say about 5% in (bi1−xinx)2se3 system. the low concentration of x in a linear band-closure system, has been carried out by several experimental groups [20,21]. essentially, a good dopant should have a shallow defect level and reach optimal solubility in its host material, however, performance of the device is significantly impacted by a few basic doping constraints. for instance, it was discovered that ntype and ptype doping in zno were challenging [22]. consequently, bipolar doping issues arise in numerous large band gap semiconductors, wherein dopants of either the n-type or p-type semiconductor can be introduced, rather than both [23]. therefore, materials’ qualities such as carrier density, mechanical strength, and magnetism are found to change through doping or alloying method [24]. here, by means of electron doping to hg site in pt2hgse3 we report that with increase in doping concentration the material undergoes topological phase transition. 2 crystal structure and computational details the crystal structure of pt2hgse3 is shown in figure 1 and belongs to space group p-3m1 (space group number 164). the crystal consist of 12 atoms in a unit cell with two structural formula unit (z = 2). unit cell of pt2hgse3 jacutingaite has two distinct position of platinum denoted as pt1 and pt2. six selenium atoms encircle pt1, while the pt2 are connected to hg atoms positioned at the middle of a planar square of selenium atoms (see fig. 1). the lattice parameters of pt2hgse3 used for our calculations are a = 7.3477 å and c = 5.2955 å with lattice angles α = 900 , β = 900 and γ = 1200. the corresponding atomic positions are [0, 0, 0] for pt1, [-1/2, 0, 0] for pt2, [1/3, -1/3, 0.3507] for hg and deergh bahadur shahi et al./ bibechana 20 (2023) 309-315 311 [-0.1804, 0.1804, 0.2492] for se, respectively. we perform the density functional theory (dft) calculations both in the scalar and fullrelativistic mode using the full-potential local orbital code (fplo) version 22.00-62 [25]. doping effects has been considered in pt2hg1−xtlxse3 (x = 0.25, 0.50,0.75 and 1) by means of virtual crystal approximation (vca) method implemented in the fplo code. the standard generalizedgradient approximation (gga) in the parametrization of perdew, burke, and ernzerhof (pbe) [26] has been used for the exchange-correlation potential. a 16×16×16 k-mesh grid was used in the irreducible bz for the self-consistent calculations. the energy and charge convergence criteria are set to 10−8 hartree and 10−6 c, respectively. figure 1: crystal structure of jacutingaite pt2hgse3 having hexagonal crystal system. 3 results and discussion electronic structure: here we show the results for the parent material pt2hgse3 and the end material pt2tlse3. from the total and partial density of states (dos) shown in figure 2a for pt2hgse3, it can be observed that the major contribution are from se-4p orbitals hybridizing with the inequivalent pt-5d, and hg-6s orbitals extending in the valence region from -1 ev upto the conduction region, with a crossover at ef . band structure for the parent material pt2hgse3 is shown in fig. 2b within scalar and full-relativistic (with soc) mode. without soc, the two dirac crossing were observed at k and h close to ef . with the application of soc, dirac points at high symmetry points are gapped with a band gap of ∼30.3 mev at point h as shown in fig. 2b (inset) followed by band inversion revealing the topological semimetallic behavior. moving on to the electronic structure of the end material pt2tlse3 which results from an electron doping via vca, the total and partial dos in the valence and conduction region are found to change abruptly. as seen in fig. 2c, total dos at ef is found to increase significantly giving rise to metallic state. the main reason for accumulation of large dos at ef is due to the electron occupancy. the total dos in pt2tlse3 is mainly contributed by se-4p with substantial contribution from pt-5d and tl-6s orbitals. the orbital-resolved electronic band structure of pt2tlse3 shows that the major contribution at and around ef are from se4px,y,z, pt-5dyz and tl-6s states. furthermore, it is interesting to note that electron and hole pocket increases along the γ a l – h path in the bz with increase in tl doping (see fig. 2 (b,d)). topological properties: we extend our study to understand the topological properties in jacutingaite materials. as is well-known, four independent topological invariants, (i.e., z2 =ν0 ; ν1 ν2 ν3) proposed by fu and kane [27] is given by (−1)ν0 = ∏ ni=0,1 δn1δn2δn3 (1) (−1)ν0 = ∏ nj ̸=i=0,1;ni=1 δn1δn2δn3 (2) connecting it with the bulk band structures of pt2hgse3 and pt2tlse3 (see fig. 2 (b, d), it reveals that at each k-point the conduction band and the valence band are gapped. this allows us to define z2 index [28]. basing on this, we perfrom z2 invariant calculations. note that, for 3d systems, odd z2 (ν0 = 1) index signify strong ti, whereas for even z2 (0 = 0) index with odd indices for the other three (ν1 ν2 ν3) characterizes the signature of weak tis. thus z2 index indicates the distribution of gapless surface states at trim in the bz of 2d surface. two fold degenerate four occupied bands between energy range -1 to 0.8 ev are used to calculate the deergh bahadur shahi et al./ bibechana 20 (2023) 309-315 312 z2 invariants by using fplo code [25]. our calculation shows that z2 index is [0;001] for pt2hgse3 and [1;000] for pt2tlse3. this clearly suggest that the parent material pt2tlse3 is a weak ti while the end material pt2tlse3 is a strong ti. z2 invariants for different values of x concentration in pt2hg1−xtlxse3 are also summarized in table 1. in a crystal lattice with inversion symmetric system, wannier charge center (wcc) are used to calculate z2 index. yu and co-workers recently predicted the topological transition in sb2mg3 by calculating the z2 invariant which was based on u(2n) non-abelian berry connection [29,30]. for this, the number of crossing to any horizontal reference line and evolution of wcc in k-space in a random direction are used to calculate the topological invariant. with odd number of crossings to a reference gives rise to z2 = 1, confirming the topological phase of system. likewise, an even number of crossing to the reference line will characterize z2 = 0, indicating a trivial phase of system. following this we computed the wcc. from our calculations of z2 for the highest occupied molecular orbital, represented by band number 88 for pt2hgse3, and band number 82 for pt2tlse3, we observed a horizontal reference line (blue line) that intersects the wcc (see fig. 3). it is interesting to note that the intersection are odd numbers (say one crossing for pt2hge3 and three crossings for pt2hgse3 which confirms that the two jacutingaite are topological materials. figure 2: density of states (a,c) and band structures (b,d) of pt2hgse3 (left) and pt2tlse3 (right). blue and red colors in fig. b represents scalar-relativistic and full-relativistic for pt2hgse3. table 1: calculation of z2 invariants. z2 invariants of different material material ν0; ν1ν2ν3 pt2hgse3 0;001 pt2hg0.25tl0.75se3 0;001 pt2hg0.5tl0.5se3 0;001 pt2hg0.75tl0.25se3 0;001 pt2tlse3 1;000 deergh bahadur shahi et al./ bibechana 20 (2023) 309-315 313 figure 3: wannier centers and reference line for band 88 of pt2hgse3 (top) and band 82 of pt2tlse3 (bottom). 4 conclusion we studied the electronic and topological properties of pt2hg1−xtlxse3 by means of density functional theory and tight-binding calculations using fplo code [25]. topological invariants z2 are computed by taking wannier function as a bloch function. pt2hgse3 is found to be a weak topological semimetal while pt2tlse3 is predicted as a strong topological metal. this is confirmed by the odd number of intersection from the wannier charge center. thus a topological phase transitions are noted in pt2hg1−xtlxse3 with weak topological insulating state (0;001) for x=0, to strong topological metal (1;000) for x=1, respectively. acknowledgments this work was supported by a grant from unesco-twas and the swedish international development cooperation agency (sida) with twas research grant award no. 21-377 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https://doi.org/10.1103/physrevb.84.075119 https://doi.org/10.1103/physrevlett.105.216406 https://doi.org/10.1103/physrevlett.105.216406 introduction crystal structure and computational details results and discussion conclusion bibechana 18 (2) (2021) 80-86 80 morphological analysis of cu substituted ni\zn in ni-zn ferrites d. parajuli 1, 2*, k. samatha1 1department of physics, andhra university, visakhapatnam, india 2department of physics, tri-chandra multiple campus, tribhuvan university, nepal *email: deepenparaj@gmail.com article information: received: january 20, 2021 accepted: may 6, 2021 keywords: spinel ni-zn ferrite sem-eds critical concentration nucleation abstract cu substituted ni in ni0.5-xcuxzn0.5fe2o4 (x = 0, 0.05, 0.1, 0.15 and 0.2) samples and cu substituted zn in ni0.5zn0.5−xcuxfe2o4 (x = 0, 0.05, 0.1, 0.15 and 0.2) is synthesized using the sol-gel auto-combustion process. recently, we have carried out their structural analysis using xrd and ftir and found a cubic spinel structure. in this paper, we have studied their morphological and compositional structure with the help of a scanning electron microscope (sem) attached with an energy dispersive spectrometer (eds). the comparative study shows that the grain size of cu substituted ni is greater than cu substituted zn in ni-zn ferrite. these smaller grain-sized ferrites is preferred for many microstructural applications. depending on the available magnetic field, sintering temperature, and atmosphere, they can have different nucleation, and hence their application mode is different. they can have a critical concentration that can tune their properties. the eds attached with the sem confirmed the proper composition of samples. doi: https://doi.org/10.3126/bibechana.v18i2.34383 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ 1. introduction ><< these spinel nanomaterials or ferrites are useful in the fields like microwave devices, ultra-highdensity magnetic encoding, coating, etc. [1-3]. they have a crystallographic structure that can bring feasible change in their microstructure and electromagnetic characteristics. if the magnetic properties of those nanomaterials can be controlled then they can be exploited in advanced applications. most of the spinel ferrite materials have an m2+fe23+o42type of structure, where, m is a transitional metal cation. m is on the tetrahedral site and fe on the octahedral site of the spinel. the study of the shape and material properties of different compositions of the ni-cu-zn ferrite system is increasing these days [4-7]. magnetic nanoparticles of cu2+ added nickel-zinc magnetic oxides are commonly utilized in magnetic components for example rotary dy core, transformer, and magnetic inductive core. similarly, the smaller grains coalesced together forming fine, mailto:deepenparaj@gmail.com https://doi.org/10.3126/bibechana.v18i2.34383 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana d. parajuli , k. samatha / bibechana 18 (2) (2021) 80-86 81 larger and non-uniform grains thereby decreasing intergranular porosity on the addition of cu+2 contents. this property leads them applicable in high-frequency devices [8, 9]. the agglomeration indicates the strong interactions between the particles and grain growth during sintering [10] however, the cadmium substitution on decreases the grain size thereby decreasing dc electrical resistivity. similarly, the magnetic saturation is decreased indicating the bb interaction i.e. interaction within the b site [11]. recently, we have carried out the structural analysis using xrd and ftir of cu substituted ni0.5-xcuxzn0.5fe2o4 (x = 0, 0.05, 0.1, 0.15 and 0.2) samples and cu substituted zn in ni0.5zn0.5−xcuxfe2o4 (x = 0, 0.05, 0.1, 0.15 and 0.2) and found cubic spinel structure [12]. in the present study, it is planned to formulate nanoparticles of cu substituted ni and cu substituted zn in ni-zn ferrites containing iron oxide as their main components using the sol-gel auto combustion method. the structure and microtexture of the material with appropriate heat treatment are analyzed. 2. experimental techniques and materials copper substituted nickel-zinc nanoparticles are prepared by the sol-gel auto-combustion method. 99.99% pure nickel nitrate, copper nitrate, zinc nitrate, iron nitrate, and citric acid monohydrate with the molecular formula (ni (no3)2·6h2o), cu (no3)3·h2o, (zn (no3)2·6h2o), (fe (no3)3·9h2o) and (c6h8o7.h2o) respectively, as the starting materials. they are mixed in such a ratio that ni0.5xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) samples are prepared. the metal nitrates and citric acid were mixed in a molar ratio of 1:1 and were dissolved in the distilled water to get a clear solution. the solution was made neutral by adding liquid ammonia. the solution was then stirred in a magnetic stirrer maintained at 100oc for 4 hr, decanted, and dried at normal temperature for 40 hr. the flakes thus obtained were combusted and converted into a powder. the powder was sintered in a muffle furnace at 800 °c for 4 h at 5o/min. similarly, ni0.5zn0.5−xcuxfe2o4 (x = 0, 0.05, 0.1, 0.15, and 0.2) are prepared with the same process in sintering temperature 900 °c in the air for 4 h and then followed by a natural cooling to room temperature. the surface morphology studies of all sintered pellets were characterized on a zeiss scanning electron microscope with accelerating voltage 10 kv available in analytical research laboratory, andhra university, india. for making pallets, few drops of polyvinyl alcohol were mixed with the powder for shaping them into disc-like pallets after pressing them in a die under the hydraulic press of 5 tons. the pallets were then made as an electrode by sintering them in 800oc in a muffle furnace and polishing their flat sides with gold. 3. results a. morphological study ` i. morphological of cu substituted ni in ni-zn ferrite the microstructural images like grain size, pores, inclusions, grain boundaries, particle size, homogeneity, defects, etc. can be obtained with the help of a scanning electron microscope. the smaller grain size with low porosity controls the unnecessary spin waves production which is essential for microwave devices. in the same way, the large grain size supports the mobility of the domain wall resulting in high permeability with low coercive value. similarly, the eddy current losses are checked by the grain boundaries acting as current barriers. the sem images (from figure 1(a) to (e)) show that the nickel, copper, and zinc are not miscible and the average size of the grain is ranging from 0.2 to 0.4μm. the grains sizes are nearly equal to in the previous report [13]. ii. morphological of cu substituted zn in nizn ferrite the microstructural morphological study to investigate the grain size, uniformity, and shape of the cu substituted zn in ni-zn ferrite sintered at d. parajuli , k. samatha / bibechana 18 (2) (2021) 80-86 82 900◦c was also done with the help of a zeiss scanning electron microscope with accelerating voltage 10 kv as shown in figure 2 (a-e). the figures show that the grain size is found to increase with copper content up to x=0.15 and then decreases for additional concentration similar to the previous reports [14, 15]. the turning point is called critical concentration. the electric and magnetic properties [16] of nanomaterials are significant for the uniform grain size and boundaries [17] measured by the linear intercept method. from the micrographs, the cupper content has improved the homogeneous spherical grain and low agglomeration similar to the result of sundararajan et al. [15]. the grain size was found to be in the ranges from 130 to 246 nm with 130 nm for base composition, 183 nm for x=0.20, and the highest average grain size is 246 nm for x=0.15 similar to the previous results [18]. b. compositional study: energy dispersive spectroscopy (eds) method the elemental composition of the ni-zn ferrites was confirmed with the help of eds and found the presence of o, fe, ni, and zn as shown in figure 3. 4. discussion generally, the single grain is the composition of several crystals. the grain size depends on the sintering temperature and atmosphere [19]. they can be from very small colloidal particles, clay, silt, sand, gravel, cobbles to boulders. sem study deals with the grain size of the materials which has a significant role in its electric, magnetic, mechanical properties, etc. further, ferrite grain size increase with temperature due to higher nucleation and copper content. as an example, ferrite grain size below 2mm transformed to cementite rather than pearlite as being small-sized austenite [20]. to get the size below 1mm, severe plastic deformation (spd) process can be used which change the plateshaped pearlite into a spherical cementite particle. this reduction in ferrite grain size from 5 to 1 μm increases the yield strength by 260 mpa. so, grain size reduction enhances the mechanical properties of the material. further, the larger grain size is best for core loss, magnetic induction, and ac permeability in the weak magnetic field. for the smaller grain size, a larger field is needed for good performance [21]. moreover, the size reduction produces the quantum confinement effect which we have studied in metal oxide semiconductor especially zno and cdo the quantum confinement effects are significant in antibacterial activities. [22-23]. (a) (b) d. parajuli , k. samatha / bibechana 18 (2) (2021) 80-86 83 (a) (c) (c) (d) (e) fig. 1: (a) to (e): fesem images for of ni0.5xcuxzn0.5fe2o4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrites (b) d. parajuli , k. samatha / bibechana 18 (2) (2021) 80-86 84 (d) (e) fig. 2: (a-e): sem micrographs of ni0.5zn0.5−xcuxfe2o4 (x = 0, 0.05, 0.1, 0.15 and 0.2) ferrites fig. 3: eds counts and elemental weight for ni0.5zn0.5fe2o4 ferrite nps 5. conclusions sem micrograph of cu substituted ni in ni-zn ferrite reveals the microstructural growth along with heat action and the average size of the grain is ranging from 0.2 to 0.4μm or 200nm to 400nm. cu substituted zn in ni-zn ferrite makes it easy for sintering thereby improving grain formation, shape, and densification. sem micrograph shows the increased grain size up to x=0.15 and then decreased for the gradual increase in the concentrations. the turning concentration x= 0.15 is the critical concentration beyond which the size is decreased and agglomeration occurs. the grain size was found to be in the ranges from 130 to 246 nm with 130 nm for base composition, 183 nm for x=0.20, and the highest average grain size is 246 nm for x=0.15. the comparative study shows that the grain size of cu substituted ni is greater than cu substituted zn in ni-zn ferrite. the smaller grain size is preferred for microstructural applications. the eds attached with the sem has given the proper composition of samples. the effect of grain size on the electric and magnetic properties will be discussed in the next paper. 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accepted: november 1, 2023 doi https://doi.org/10.3126/bibechana.v20i3.58311 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 290 http://nepjol.info/index.php/bibechana premsingh@fwu.edu.np bisup@woosuk.ac.kr https://doi.org/10.3126/bibechana.v20i3.58311 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ prem raj joshi et al./ bibechana 20 (2023) 290-296 291 1 introduction lemongrass (cymbopogon citratus) is a well-known medicinal plant in nepal. it is composed of volatile aromatic chemicals, belongs to the gramineae family, which grows primarily in tropical and subtropical region of the world [1]. they possess antibacterial, antifungal, anti-inflammatory, anticancer, antiseptic, and antioxidant properties. lemongrass is widely utilized as a flavouring agent in the food business, as well as in the pharmaceutical, cosmetic, soap, and detergent sectors [2]. essential oils can be extracted utilizing various plant parts, particularly the leaves and aerial parts. basically, plants with medicinal properties are used to extract essential oils because of their antibacterial properties against bacteria, fungal, and viral pathogens. the presence of alkaloids, phenols, and other functional groups in essential oil (eo) contributes to their antibacterial activities. essential oils derived from several medicinal plants are thought to be alternative natural antibacterial agents [3]. moreover, due to the antibacterial and antifungal properties of lemongrassextracted essential oil, it has an extensive potential to be employed in food preservatives. this sort of significant feature of essential oil can be useful and feasible for farmers in the rural locations [1]. various ethnic groups have employed plant-derived natural products as traditional medicine. the essential oil isolated from origanum onites, for example, has demonstrated considerable biological activity such as antibacterial, antifungal, and antioxidant characteristics, and it has also been shown to be useful against colon cancer [4]. similarly, the leaves of cymbopogon citratus have medicinal benefits and are a source of essential oils, as claimed by manvitha and bidya [5]. a study on cymbopogon citratus revealed pharmacological activity such as antiamoebic, antibacterial, antidiarrheal, antifilarial, antifungal, and anti-inflammatory effects. it also highlighted that antibacterial activity of lemongrass can be utilized as a supplement treatment for fever, respiratory disorders, dental hygiene, and other conditions, and it also possesses anti-diabetic and anti-cancer properties [6]. furthermore, citral compounds have also been utilized in the perfume business, cleaning wounds, and treating skin ailments. the essential oil extracted from cymbopogon citratus does not have any disturbance in antibacterial activity, whether it is extracted in water as a medium or alcohol [7]. with respect to the type of organism, the gram-positive organisms were more sensitive to lemongrass oil as compared to gramnegative organisms [8]. therefore, lemongrass essential oil can be effective against drug-resistant organisms. several studies have been conducted in the field of extraction of essential oil from different plant species, wong et al. [9] discussed the extraction of essential oil from cinnamomum zeylanicum by steam distillation and soxhlet extraction method. cinnamon essential oil has cinnamaldehyde as a mojor component. the amount of cinnamaldehyde in essential oil is high (about 90%) from steam distillation and low (about 62-73%) from soxhlet extraction. the antibacterial tests for both essential oil showed the formation of clear zones all around petri dish which confirms the antimicrobial activity. high microbial properties were shown by cinnamon essential oil against the gram-positive bacteria bacillus subtilis and gram negative bacterium escherichia coil. pandey et al. [10] discussed the extraction of essential oil from the leaves of medicinal plant s. officinalis and evaluated its antimicrobial activity. they concluded that s. officinalis is a natural medicinal plant that can be used to cure many diseases, like inflammation. hanamanthagouda et al. [11] extracted essential oils from the dried leaves of lavandula pinnata. the lavandula pinnata-extracted essential oil was found as an herbal medicine, and it shows antimicrobial activity against both bacteria and fungi. reyes-jurado et al. [12] highlighted the antimicrobial activity of essential oils against a wide range of organisms. they also found that the yield and antimicrobial activity of essential oils mainly depend on environmental conditions of the season in which plant grow and on extraction methods employed. this study includes the extraction of essential oil from the dried leaves of lemongrass using clevenger apparatus and calculating the yield of oil in percentage. with the help of the zone of inhibition, we made five welled systems, where four welled systems contain four different concentrations of essential oil while the other one contains a common antibiotic, cloxacillin, against staphylococcus aureus (gram-positive bacteria). in addition, variable concentrations of essential oil and control have provided an antibacterial property against staphylococcus aureus, gram-positive bacteria. due to its effective antibacterial activity, lemongrass-extracted essential oil is considered a naturally occurring antibacterial agent. 2 materials and methods 2.1 materials the leaves of cymbopogon nardus (lemongrass) collected from botanical garden, clevenger apparatus, distilled water, microorganism (s. aureus) collected from seti provincial hospital laboratory, dhangadhi, nepal. the media mha (muellerhinton agar), petri dish, test tube, a condenser, sterilized cotton, heating mantle, cloxacillin, zone of inhibition (zoi), measuring scale, round bottom prem raj joshi et al./ bibechana 20 (2023) 290-296 292 flask, incubator, etc. 2.2 methodology extraction of essential oil in this study, lemongrass leaves were collected from dewariya botanical garden (jokhor lake), dhangadhi, nepal. these leaves were washed properly with tap water to remove dust, mud, and foreign substances. further, these leaves were cut into small pieces and left dry in sunlight for about 30 minute until water was removed from the leaves. in addition, the extraction was carried out on clevenger apparatus with two sets in order to check the yield of the essential oil. the first set contains 200 gm of dried leaves in a round bottom flask with 1000 ml of distilled water, and the second set contains 80 gm of dried leaves in a round bottom flask having 500 ml of distilled water. the duration of distillation for both extraction was 4 hours and 15 minutes. both sets provided a successful result; the 200 gm and 80 gm leaves yielded 4.5 ml and 1.9 ml respectively. finally, after the distillation process the essential oil collected in a hard glass tube [8]. the experimental setup for the extraction of lemongrass essential is shown in the figure 1. culture of organism staphylococcus aureus was selected as the microorganism and collected from the seti provincial hospital, dhangadhi, kailali. to initiate the bacteria culture, s. aureus was mixed with nutrient broth in a test tube. mcfarland turbidity standard number 0.5 was employed as a reference to determine the concentration. the test tube containing the bacterial culture was left untouched for 4-5 hours, allowing the culture to settle. after settling period, a sterilized cotton swab was utilized to consistently distribute the bacteria on the surface of prepared media in the petri dish. the petri dish, now containing the bacteria-infused media, was then placed in an incubator set to a temperature of . the incubation period lasted for 24 hours, allowing the bacteria to grow and develop under optimal conditions [13–15]. determination of anti-bacterial property by zone of inhibition (zoi) to assess the antibacterial activity, five wells were formed in a petri dish containing s. aureus bacteria. the four wells were designated for cymbopogon nardus oil at different concentrations, including 100%, 75%, 50%, and 25% and remaining one well was designated cloxacillin (antibiotic medicine) as a positive control. the petri dishes were then placed in an incubator set at and incubated for 24 hours, ensuring no contamination occurred during this period. after incubation, the diameter of the zones of inhibition around each well was measured using a scale in millimetres. this measurement represents the extent of bacterial growth inhibition and is referred to as the “zone of inhibition” [13–15]. figure 1: clevenger apparatus setup for the extraction of lemongrass oil. 3 results and discussion to complete the entire experimentation, two extractions were performed, one with 200 gm and another with 80 gm of sun-dried leaves of lemongrass. the duration of distillation process was 4 hours and 15 minutes for both extractions. the yields obtained for 200 gm and 80 gm of lemongrass leaves were 4.5 ml (2.25%) and 1.9 ml (2.37%), respectively. the yields of these two extractions are shown in figure prem raj joshi et al./ bibechana 20 (2023) 290-296 293 2(a). to access the antibacterial activity of lemongrass oil, s. aureus (gram-positive bacteria) was selected. the result revealed that cymbopogon nardus exhibited significant antibacterial activity in comparison to a positive control i.e. cloxacillin (cox). this suggests that the essential oil of cymbopogon nardus possesses antibacterial properties that can effectively inhibit the growth of grampositive bacteria. hence, it can be used as a natural alternative against bacterial infections, further supporting its traditional use as a medicinal plant with antibacterial properties. the picture of the zone of inhibition in the five-welled system with four wells containing different concentration of eo and one well containing a positive control (cloxacillin) is shown in figure 2(b). the zone of inhibition of five-welled system is tabulated in table 1. a study conducted by timung et al. [16] found that the essential oil extracted from lemongrass leaves has a yield of 2.38%. we also obtained yield of lemongrass eo as 2.25% and 2.37% which is in agreement with timung et al. [16]. we used extracted lemongrass essential oil for testing its antibacterial activities against s. aureus (grampositive bacteria). with regard to gram-positive bacterium, s. aureus, the zoi demonstrated by the essential oils at four different levels of concentration including 100%, 75%, 50%, and 25% was 25 mm, 11 mm, 9 mm, and 0 mm, respectively. this shows as concentration increases, zoi also increases which is in agreement with naik et al. [8]. this implies that the gram-positive bacterium s. aureus can be successfully inhibited from growing by the essential oil of cymbopogon nardus due to its antibacterial capabilities. the results of this investigation demonstrate that the antibacterial activity of essential oil increases progressively as concentration of oil increased. our results clearly shows the antibacterial activity of lemongrass essential oil against s. aureus microorganism. along with s. aureus, lemongrass eo found to possess antibacterial activity against bacillus cereus, bacillus subtilis, escherichia coli, and klebsiella pneumoniae however it is found neutral against pseudomonas aeruginosa microorganism [8]. in addition, the penicillin class of antibiotics includes cloxacillin as a subtype. it is frequently employed to treat bacterial infections brought on by specific bacterial species, such as s. aureus. it might also be ineffective in combating germs that have become resistant to penicillin-based antibiotics [17]. in addition, the penicillin class of antibiotics includes cloxacillin, which had a zoi of 24 mm against s. aureus. this implies that gram-positive bacterium s. aureus can be successfully inhibited from growing by the essential oil of cymbopogon nardus due to its antibacterial capabilities. table 1: zone of inhibition (zoi) in mm of a five-welled system, four for eo and one for cox concentration of lemongrass oil (%v/v) micro-organism (bacteria) 100% 75% 50% 25% cloxacillin (cox) s. aureus (gram positive bacteria) 25 11 9 0 24 figure 2: (a) essential oil extracted from cymbopogon nardus leaves (b) zoi shown by the essential oil of cymbopogon nardus in four welled plates with four different concentrations (100%, 75%, 50% and 25%) and cloxacillin (an antibiotic medicine) in one welled plate on staphylococcus aureus. prem raj joshi et al./ bibechana 20 (2023) 290-296 294 furthermore, eo at concentration of 75%, 50%, and 25% had fewer antibacterial benefits than cloxacillin antibiotics, although eo at concentrations of 100% offered marginally more antibacterial benefits than cloxacillin antibiotics. however, several studies had already been conducted by several researchers showing that essential oils extracted from lemongrass have significant antibacterial activities. timung et al. [17] reported that citronella oil possesses significant antibacterial activity, so essential oil can be utilized for various bacterial infections. in addition, naik et al. [8] reported that gram-positive organisms are more sensitive to lemongrass oil as compared to gram-negative organisms. moreover, u et al. [18] reported that extracts of lemongrass leaves and roots possessed intermediate antimicrobial activity against s. aureus, and azizi et al. [19] mentioned that eo possessed antimicrobial and antiviral activities. similarly, the lemongrass-extracted essential oil can be used as a treatment for fungal infection and skin inflammation, as reported by boukhatem et al. [20]. lemongrass eo can be helpful in curing infections caused by gram positive and gram negative organisms [8]. pathogenic and nonpathogenic diseases can be treated by the use of eo, like garlic extracted essential oil can be used to cure patients with coronary heart diseases [21]. lemongrass eo has potential use in the medicine and surgical devices because of it’s antibacterial and antifungal property. it can also be used to modify the materials in medicinal devices so as to make such surfaces resistant to biofilm formation. it is rich in bioactives and is highly sensitive with human cells, especially has pronounced anticancer activity. this shows lemongrass eo has a potential for it’s use in the treatment of cancer [22]. along with the significant applications of lemongrass eo in medicine, it has the prominent use in the food industry due to noticeable potential against various microorganisms. mainly, it has been used in strengthening food packaging and food storage systems [23]. tzortzakis and economakis [24] also highlighted that lemongrass eo can be used as an alternative to synthetic fungicides, and it can also find an application in storage and packaging. it has a capacity to reduce the disease growth mainly by limiting the spread of pathogen and lowering the spore production. 4 conclusion medicinal plants are very important to humans because they have many benefits such as being antibacterial, antifungal, anti-inflammatory etc. the lemongrass extracted oil is used as a treatment for various infectious and respiratory diseases. a species of lemongrass, cymbopogon nardus, also possesses economic importance in the production of soap and detergent, perfume, beverages, food, and cosmetics. in this study, the leaves of lemongrass were subjected to hydro distillation using clevenger apparatus for a period of over 4 hours, which provided a 2.37% yield of eo. furthermore, the oil was then analysed to evaluate it’s antibacterial activity using zoi. the zoi for four different concentrations, such as 100%, 75%, 50%, and 25% of eo and antibiotic (cox), was approximately 25 mm, 11 mm, 9 mm, and 0 mm, and 24 mm respectively. this study clearly shows that eo from cymbopogon nardus exhibits significant antibacterial activity against s. aureus (gram-positive bacteria). the sensitivity of eo found to be enhanced at higher concentration. this finding supports the traditional use of cymbopogon nardus as a valuable plant for its antibacterial properties and suggests its potential for further exploration as a natural alternative for treating bacterial infections. along with the antibacterial activity lemongrass eo has a potential use in industries especially in food packaging and food storage. references [1] e. majewska, m. kozlowska, e. gruczynskasekowska, d. kowalska, and k. tarnowska. lemongrass (cymbopogon citratus) essential oil: extraction, composition, bioactivity and uses for food preservation a review. polish journal of food and nutrition sciences, 69(4):327–341, 2019. https://doi.org/10. 31883/pjfns/113152 [2] o. s. oladeji, f. e. adelowo, d. t. ayodele, and k. a. odelade. phytochemistry and pharmacological activities of cymbopogon citratus: a review. scientific african, 6:e00137, 2019. https://doi.org/10.1016/ j.sciaf.2019.e00137 [3] m. sayeed akthar, b. degaga, and t. azam. antimicrobial activity of essential oils extracted from medicinal plants against pathogenic microorganisms: a review. issues in biological sciences and pharmaceutical research, 2(1):1–7, 2014. http://www.journalissues.org/ibspr/ [4] k. spyridopoulou, e. fitsiou, e. bouloukosta, a. tiptiri-kourpeti, m. vamvakias, a. oreopoulou, e. papavassilopoulou, a. pappa, and k. chlichlia. extraction, chemical composition, and anticancer potential of origanum onites l. essential oil. molecules (basel, switzerland), 24(14):2612, 2019. https:// doi.org/10.3390/molecules24142612 [5] k. manvitha and b. bidya. review on pharmacological activity of cymbopogon citrahttps://doi.org/10.31883/pjfns/113152 https://doi.org/10.31883/pjfns/113152 https://doi.org/10.1016/j.sciaf.2019.e00137 https://doi.org/10.1016/j.sciaf.2019.e00137 http://www.journalissues.org/ibspr/ https://doi.org/10.3390/molecules24142612 https://doi.org/10.3390/molecules24142612 prem raj joshi et al./ bibechana 20 (2023) 290-296 295 tus. international journal of herbal medicine, 1(6):5–7, 2014. 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m. m. a. khan, j. ali, d. kurjak, and m. shahid. lemongrass essential oil components with antimicrobial and anticancer activities. antioxidants, 11(1):20, 2021. https://doi.org/10.3390/antiox11010020 [23] f. faheem, z. w. liu, r. rabail, i. u. haq, m. gul, m. bryła, m. roszko, m. kieliszek, a. din, and r. m. aadil. uncovering the industrial potentials of lemongrass essential oil as a food preservative: a review. antioxidants, 11(4):720, 2022. https://doi.org/10.3390/ antiox11040720 [24] n. g. tzortzakis and c. d. economakis. antifungal activity of lemongrass (cympopogon citratus l.) essential oil against key postharvest pathogens. innovative food science emerging technologies, 8(2):253, 2007. https://doi.org/10.3390/antiox11010020 https://doi.org/10.3390/antiox11040720 https://doi.org/10.3390/antiox11040720 introduction materials and methods materials methodology results and discussion conclusion bibechana vol. 20, no. 1, april 2023, 21–26 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar overall migration of microplastics in mineral water and non-alcoholic beverages jagjit kour1,∗, pratima bhatt1, shobha basnet2 1department of chemistry, tri-chandra multiple campus, t.u., nepal, 2zest laboratories and research center (p) ltd, nepal ∗corresponding author. email: jagjitkour00@gmail.com abstract in today’s world, packaging plays a crucial role in enhancing, enclosing, and shielding the materials that are used from procurement to handling and storage, processing, manufacturing and finally to the consumer. packaging shields a product’s contents from contamination, spoiling and makes it simple to store and transfer anywhere. man-made plastic breaks down into little particles as a result of numerous external pressures. the degradation of plastics produce nano or microplastic. health issues arise when microplastics (mps) leak from plastic food packaging and are consumed by people. though plastic packaging is abundant, consumers from developing nation are not aware of the risk associated with plastic food packaging. the purpose of this study is to demonstrate occurrence of microplastics in plastic food packaging and highlight the risks involved in consumption of microplastics. in this research, the migration of microplastics from different plastic containers were noted in accordance to the bureau of indian standards is 9845-1998. the is 9845: 1998 method was utilized in this investigation to determine the overall migration of various plastics used to package mineral water and beverages. distilled water and 3 % acetic acid (w/v) were utilized as food simulators for the analysis. the migration of microplastics in mineral water were found to range from 0.38 ppm to 0.54 ppm while in case of non-alcoholic beverages overall migration ranged from 0.29 to 75.75 ppm. among the 12 samples of non-alcoholic beverages, one sample exceeded the maximum limit of microplastics as specified by who standard. keywords microplastics, simulant, plastic, distilled water, migration . article information manuscript received: december 22, 2022; accepted: march 28, 2023 doi https://doi.org/10.3126/bibechana.v20i1.53457 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction plastics are man made synthetic polymers with different properties like low cost, lightweight, easy to excess, durability etc., due to which plastics are used in our daily life in every aspect from household to large industrial scale [1]. plastics are used in the pharmaceutical industry, agricultural industries, automobiles, storage, clothing, transportation, packaging, etc. this increases the production of plastics each day [2]. around 60% plastic packaging is used for food and beverage and rest is 21 http://nepjol.info/index.php/bibechana jagjitkour00@gmail.com https://doi.org/10.3126/bibechana.v20i1.53457 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ jagjit kour et al./ bibechana 20 (2023) 21-26 22 used for other purposes like cosmetics, medicines, etc. [3]. during storage and distribution packaging protects food against physical, chemical and biological hazards. plastics are composed of large organic molecules so they are printable, moldable and heat sealable [4]. usually plastics used for the packing mineral water and non-alcoholic beverages are polyethylene terephthalate (pet), polypropylene (pp) etc., and belong to thermoplastic group and can be recycled [5]. ethylene glycol and dimethyl terephthalate under goes polycondensation reaction to give polyethylene terephthalate. this type of plastic is used for packing food and beverages since they are stable towards temperature and moisture [6, 7]. transferring of chemicals from plastic material to food is known as leaching or migration. it is a process that follows fick’s law of diffusion. leaching can occur by direct transfer and gas transfer phase [8]. as different layers films are applied in packaging, so the chemicals from the films leach to the drinks through diffusion as well as partition method. the method of leaching chemicals from outer layer of plastic to drink is known as set-off [9]. plastic is one of the important and useful product in our life and it has made our lives easy in many ways. at the same time it also has negative impact in our life, affecting our health and environment in different ways. plastic itself is chemically inactive but different additives present in the plastics may cause chemical reactions which lead to migration. when drinks and foods are aggressive, then they react with plastic in which they are packed, in such condition chemicals from plastic leaches to drink [10]. plastic degrades into small particles like micro and nano plastic by different external forces caused by humans. article published by thompson in 2004 where he used the term microplastic which attracts the people’s attention [11]. microplastics once deposited in environment, are difficult to remove. plastic materials are degraded into microplastics and nano plastics by the photooxidation process [12]. microplastics are plastic particles of various shape, size and dimensions ranging from 1 µm to 5 mm and are not soluble in water [13]. there are two types of microplastics found in our environment, primary microplastic and secondary microplastic. micro plastics that are manufactured into small size are called primary mps where as microplastics degraded from large plastic particles are called secondary mps [14]. primary microplastics can enter directly to the environment and are made for different purposes such as for cosmetics, industrial use, personal care, cleaning products, beads, plastic pellets etc., and the secondary microplastics are obtained through fragmentation of plastic by aging [15–17]. presence of microplastic in environment increases pollution and affect the health of living beings and destroys the productivity of soil [18]. in developing nation like nepal where plastic food packaging is very abundant due to various factors such as lack of alternatives, lack of awareness and busy lifestyle. due to that microplastic leaching has become an alarming concern for people. studies and research carried out in advanced nations have properly demonstrated the qualitative and quantitative analysis of microplastic leaching and migration through use of sophisticated tools and apparatus. those advanced llevel researches have also shown the negative effects caused by microplastic leaching from plastic packaging on human health as well as the environment along with the mitigating measures and alternative approaches. however, in developing nations, these kind of esearches have not been conducted thoroughly with adequate analysis so as to aware people and provide alternatives. this research is conducted on a small scale to highlight the quantitative measurements of microplastic leaching as a result of plastic food packaging and also to relate different kind of impacts it has on environment and human health. this issue is brought forward to people’s attention and can be used for more detailed studies and research in coming days. this study is based on the quantitative determination of microplastics leached from the plastic containers packed with mineral water and nonalcoholic beverages. indian standard has specified various types of simulants and test conditions for various type of foods which is given in table 1 and 2. the choice of simulant depends upon the type of food products used, time-temperature condition and also depend upon the use of food products which is given in table 3. bureau of indian standard is 9845:1998 has classified the drinks and food products into seven categories. these drinks and foods have different simulants and test conditions, which is based on the ph and fat content of the drinks and food products which is given in table 2. in the present study simulant a (distilled water) was used for mineral water and simulant b (3 % acetic acid) was used for non-alcoholic beverages. european union (eu), bureau of indian standard (bis) set the limits for migration of microplastic for food and beverage products as 60 ppm or 60 mg/l. this is the upper limit for overall migration. if the migrating substance has color then that is not suitable for packaging drinks and foods even if the extractive value is below the limit [19]. jagjit kour et al./ bibechana 20 (2023) 21-26 23 table 1: list of food simulants. simulant a distilled water simulant b acetic acid 3 % simulant c1 ethanol 10% simulant c2 ethanol 50 % simulant d n-heptane simulant e mixture of synthetic triglycerides or sunflower oil or rectified olive oil table 2: categories of drinks and foods with simulants. s.n. type discriptions example simulant 1 1 3aqueous non-acidic foods (ph>5) without fat honey, rasgulla, yeast paste and mineral water etc. a 2 2 aqueous acidic foods with no fat (ph≤5) fruit juices, carbonated beverages, lemonade, etc. b 3 3 alcoholic beverages: a. concentration of alcohol less than 10 % b. concentration of alcohol above 10 % beers, pharmaceutical syrups whisky, wine, brandy, etc. c1 c2 4 4 fats and processed dry foods with surface fat or volatile oil, oils vegetables, ghee, biscuits, chocolates, tea and coffee powder d 5 5 non-acidic foods (ph>5) with excess fat and excess moisture content butter, bread, pastry, milk-based sweets, icecream, etc. a and d 6 6 acidic foods (ph< 5) with excess fat and excess moisture content different types of pickles, tomato ketchup, cheese, mayonnaise, etc. b and d 7 7 dry processed foods having no fat different types of cereals, pulses, dry fruits, vegetables, salt, sugars, oats, etc. no end test table 3: simulants with time-temperature conditions. s.n. conditions types of food and drinks timetemp of water timetemp of 3% acetic acid timetemp of 10 % alcohol timetemp of 50 % alcohol time-temp of n-heptane 1 high temperature heat sterilized 1, 2, 4 121 0c 2h 121 0c 2 h 66 0c for 2h 2 hot filled or pasteurized above 660c, below 100 0c 1, 2, 4, 5 and 6 100 0c 2h 100 0c 2h 49 0c for half an hour 3 pasteurized or hot filled below 66 0c 1 to 6 70 0c 2h 70 0c for 2h 70 0c for 2h 70 0c for 2h 38 0c for an hour 4 filled and stored at room temp and also in refrigerated and frozen condition 1 to 6 40 0c for 10 days 40 0c for 10 days 40 0c for 10 days 40 0c for 10 days 38 0c for an hour jagjit kour et al./ bibechana 20 (2023) 21-26 24 2 methodology test standard: the overall migration of various plastic containers were determined with is 9845:1998 method. 2.1 determination of conjugative weight of beakers it is very important for this research work to take the conjugative weight of the beakers into consideration. hence, fifteen beakers of 100 ml each were cleaned and were placed inside the oven with temperature 100 0c for 2h. then the beakers were removed from the oven and placed in side the desiccator. after cooling inside the desiccator, weight of the beakers were measured. the process of cooling and weighing were repeated till the constant weight was determined. this process of conjugative weight determination was carried out for all the beakers. 2.2 preparation of sample solution glacial acetic (3 ml) was placed in a volumatic flask and 97 ml purified water was added to form 100 ml 3 % acetic acid solution. 2.3 sample selection the samples were randomly selected from different areas inside kathmandu. sample selection was done on the basis of their storage condition, type of products mostly used by children and teenagers, plastic condition and local manufacturing products. three samples of same batch number were taken. 12 mineral water bottles of four different brands and 12 bottles of non-alcoholic beverages from four different brands were also taken for the testing (two different brands of mango drinks and two different brands of litchi drinks). 2.4 procedure the plastic bottles used for the analysis were rinsed with distilled water for three times. the ph value of each sample was noted. after that, the plastic bottles were filled to their normal capacity with their respective simulant and the lids were closed. sonication was carried out to avoid formation of bubbles. consequently, the bottles were then placed inside the oven at specified temperature for required time. then after, the plastic bottles were removed from the oven and content of each bottle was poured into the beaker. the bottle was rinsed with fresh simulant and then again poured into the same beaker. in case of mineral water sample, three plastic bottles of four different brands were taken and their ph value was read then water from plastic bottle was removed. the plastic bottles were rinsed with distilled water three times. then the bottles were filled with simulant a (distilled water) to their normal capacity and lids were closed. sonication was carried out to avoid formation of bubbles. then those filled bottles were placed inside the oven at temperature 40 0c for duration of 10 days. then the water bottles were removed and the content of each bottle was poured into the beaker whose constant weight was already measured. the bottle was rinsed with fresh simulant and then again poured into the same beaker. similarly, in case of non-alcoholic beverages, same procedure was applied but simulant b (3 % acetic acid) was used as food simulant and the time and temperature condition were also same as in case of mineral water samples. blank test was also carried out for all the samples. 2.5 calculation of extractive amount beaker content was evaporated to dryness and the beaker was kept inside the oven at 100 0c to obtain absolute dryness. then the beaker was removed from the oven and kept in the desiccator for half an hour. after the beaker was cooled, it’s conjugative weight was noted as 0.1 mg. amount of extract was calculated in ppm. similarly, blank test was also done without the sample and this process was done for all other samples. extractive amount (ex) = m/v * 1000 ppm or mg/l where, m = mass of extract in mg value of blank test and v = total volume of simulant applied for each sample in ml 3 results and discussion overall migration of microplastics in mineral water and nonacholic beverages were carried out using food simulants a (distilled water) and b (3 % acetic). it was seen that every plastic packaging leaches the microplastic in different quantities depending on type of plastic container, storage temperature, storage duration, ph value of drink and type of drink packed in the container. 3.1 from water bottles distilled water was used as food simulant in the overall migration test for mineral water bottles. amount of microplastic found in plastic bottles of mineral water is different for different brands. table 4. shows the amount of extractive for different mineral water bottles. microplastics abundance ranges from 0.38 ppm to 0.54 ppm. the migration of microplastics in mineral water are within the limit provided by eu. jagjit kour et al./ bibechana 20 (2023) 21-26 25 table 4: overall migration in mineral water. sample no. simulant (ml) amount of extractive triplicate (ppm) 1 1000 0.4466 2 1000 0.0333 3 1000 0.0666 4 1000 0.7100 table 5: overall migration in non-alcoholic beverages. sample no. simulant (ml) extractive ( ppm) 1 (lichee drink) 150 75.0560 2 (lichee drink) 170 5.6399 3 (mango drink) 250 0.4266 4 (mango drink) 250 0.2933 3.2 from water bottles 3 % acetic acid was used as food simulant for the non-alcoholic beverages. 12 samples of four different brands along with blank were studied for overall migration. table 5. shows the amount of extractive for different non-alcoholic beverage bottles. the results show that among 12 samples of mango and lichee drinks only one sample of lichee drink (sample no. 1) exceeded the limit of migration of microplastics given by eu. 3.3 from water bottles as the present study is based on the quantitative measurements only and depicts the preliminary analysis of microplastic migration based on plastic packaging of mineral water and non-alcoholic beverage that resulted in above mentioned findings. according to oßmann et al., 2018, in blank samples, 384–468 microplastic particles per liter were discovered. mineral water included anywhere between 2649 and 2857 microplastics per liter in single-use pet bottles, 4889 to 5432 microplastics per liter in multi-use pet bottles, and 6292 to 10,521 microplastics per liter in glass bottles whereas according to shruti et al. (2020), microplastics in a range of sizes (0.1-3 mm) and hues, including blue, black, and brown, were discovered in non-alcoholic beverage such as soft drinks, energy drinks, and cold tea. hence, end to end relative data is not available for comprehensive comparison. 4 conclusion the overall migration limit is 60 mg/l or mg/kg or ppm for plastic container used for food packaging as given by the eu. present study showed that the migration in mineral water occurred in the range 0.38 ppm to 0.54 ppm. however, the migration limit was within the range specified by the eu. in case of non-alcoholic beverages, overall migration of microplastics exceeded the limit provided by eu in one sample only. this might be due to the type of plastic container, storage conditions, duration of storage and quality of the drink. however, the occurrence of microplastic leaching was evident which indicates that every plastic leaches which is an environmental and health risk. this shows that long term use of these kind of drinks affect the human health gradually and especially for children the risk is very high. the microplastics are consumed along with the food and drinks and after consumption it might disrupt the metabolic activities inside the body that can cause different types of diseases in the long run. therefore, consumption of these kinds of foods and drinks packed in the plastic containers should be discouraged. alternative solutions such as use of bio-degradable plastic containers, use of paper packaging and awareness on plastic leaching to general public should be conducted. to facilitate this, relevant policies should be implemented from local bodies and government entities. moreover, traditional plastic packaging practice should be penalized and use of bio-degradable options should be promoted. acknowledgement the authors would like to extend heartfelt gratitude to the university grant commission (ugc), bhaktapur, nepal for funding the research work under the small research development and innovation grant (srdig) award no. 76/77-s and t-8 and zest laboratories and research center, balkot, bhaktapur, nepal for carrying out all the experiments for this research work. jagjit kour et al./ bibechana 20 (2023) 21-26 26 references [1] c. wang, j. zhao, b. xing. environmental source, fate, and toxicity of microplastics. journal of hazardous materials, 407:124357, 2020. 10.1016/j.jhazmat.2020.124357 [2] j. chen, w. wang, h. liu, x. xu, j. xia. a review on the occurrence, distribution, characteristics, and analysis methods of microplastic pollution in ecosystems. environmental pollution and bioavailability, 33(1):227–246, 2021. 10.1080/26395940.2021.1960198 [3] k. j. groh, t. backhaus, b. carney-almroth, b. geueke, p.a. inostroza, a. lennquist, h. a. leslie, m. maffini, d. slunge, l. trasande, a.m. warhurst, j. muncke. overview of known plastic packaging-associated chemicals and their hazards. science of the total environment, 651:3253–3268, 2019. 10.1016/j.scitotenv.2018.10.015 [4] r. m. s. cruz, b. p. m. rico, m. c. vieira. food packaging and migration. in charis m galanakis, editor, food quality and shelf life, pages 197–203. academic press, 2019. hrefhttps://doi.org/10.1016/b978-0-12817190-5.00009-4 10.1016/b978-0-12-8171905.00009-4 [5] b. geueke, k. groh j. muncke. food packaging in the circular economy: overview of chemical safety aspects for commonly used materials. journal of cleaner production, 193:491– 505, 2018. 10.1016/j.jclepro.2018.05.005 [6] j. alin. migration from plastic food packaging during microwave heating. phd thesis, division of polymer technology, kth royal institute of technology, sweden, 2011. 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microplastics leaching in local candies, pickles and yogurt packed in plastic containers. j. nepal. chem. soc., 4:128–134, 2022. 10.3126/jncs.v43i1.46960 [18] j. wang, x. liu, y. li, t. powell, x. wang, g. wang, and p. zhang. microplastics as contaminants in the soil environment: a minireview. science of the total environment, 691:848–857, 2019. 10.1016/j.scitotenv.2019.07.209 [19] bureau of indian standards. determination of overall migration of constituents of plastics materials and articles intended to come in contact with foodstuffs method of analysis, 1998. https://doi.org/10.1016/j.jhazmat.2020.124357 https://doi.org/10.1080/26395940.2021.1960198 https://doi.org/10.1016/j.scitotenv.2018.10.015 https://doi.org/10.1016/j.jclepro.2018.05.005 https://doi.org/10.48317/imist.prsm/morjchem-v4i1.4128 https://doi.org/10.3390/beverages6020037 https://doi.org/10.1016/j.dyepig.2014.10.019 https://doi.org/10.1201/b21347 https://doi.org/10.1016/j.chemosphere.2020.126790 https://doi.org/10.3389/fchem.2018.00407 https://doi.org/10.3390/su12176755 https://doi.org/10.1016/j.fooweb.2018.e00097 https://doi.org/10.1021/es302011r https://doi.org/10.1016/j.marpolbul.2019.03.019 https://doi.org/10.3126/jncs.v43i1.46960 https://doi.org/10.1016/j.scitotenv.2019.07.209 introduction methodology determination of conjugative weight of beakers preparation of sample solution sample selection procedure calculation of extractive amount results and discussion from water bottles from water bottles from water bottles conclusion bibechana vol. 22, no. 1, april 2025, 22-29 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar machine learning for predicting earthquake magnitudes in the central himalaya ram krishna tiwari1, rudra prasad poudel1,2, harihar paudyal1 1birendra multiple campus, tribhuvan university, bharatpur, chitwan, nepal 2central department of physics, tribhuvan university, kirtipur, kathmandu, nepal ∗corresponding author. email: ram.tiwari@bimc.tu.edu.np abstract human intervention cannot halt natural disasters like earthquakes, but machine learning applications expertise can be utilized to detect patterns in data and increase understanding and predictive power. recent development of machine learning models has increasingly developed interest in forecasting and predicting the magnitude of earthquakes. in this work, random forest regressor (rfr), multi-layer perceptron regressor (mlpr), and support vector regression (svr) models were employed to predict the magnitude of greater than 6 mb earthquakes that occurred in the year 2015 in the central himalaya. we noticed rfr method had been able to predict the magnitude of the gorkha earthquake (6.9 mb), the kodari earthquake (6.7 mb), and 6.5 mb magnitude earthquake (aftershock of gorkha earthquake) in comparison with the other two models. we also checked the performance of these models by three parameters mean absolute error (mae), mean squared error (mse), and root mean squared error (rmse) and noticed the better performance of rfr model. the findings illustrate that rfr is achieving better performance than the other two algorithms, as the predicted magnitudes are close to the actual magnitudes. keywords machine learning, earthquake, regressor, prediction. article information manuscript received: october 6, 2024; revised: january 7, 2025; accepted: january 12, 2025 doi https://doi.org/10.3126/bibechana.v22i1.70637 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction an earthquake is a natural disaster that strikes suddenly, between seconds to minutes, and shakes a large area of landmass, potentially killing people and damaging property. nepal, which is positioned in the center of the himalayan arc, saw many small and large earthquakes in last millennia [1–5]. the seismic activity in the himalayan region is impacted by the buildup of strain energy that happened roughly 50 million years ago during the indian plate's thrust beneath the eurasian plate [6–8]. 22 http://nepjol.info/index.php/bibechana ram.tiwari@bimc.tu.edu.np https://doi.org/10.3126/bibechana.v22i1.70637 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ram krishna tiwari et al./ bibechana 22 (2025) 22-29 23 the region has had more recent earthquakes in the past 70 years, including the 1988 udayapur earthquake of magnitude 6.6 mw, 2011 sikkim earthquake of magnitude 6.9 mw, 2015 gorkha earthquake of magnitude 7.9 mw, dolakha (kodari) earthquake of magnitude 7.3 mw, doti earthquake of magnitude 6.6 ml, and the 2023 jajarkot earthquake of magnitude 6.4 ml [8–10]. human intervention cannot halt natural disasters like earthquakes, but machine learning application expertise can be utilized to detect patterns in data and increase understanding and predictive power [11–13]. most of the machine learning (ml) algorithms fall into one of two categories: supervised learning (sl) and unsupervised learning (usl) (figure 1). figure 1: basic idea of selecting the ml algorithms. unsupervised ml for unlabelled data, and supervised ml for labelled data. in sl, the computer is instructed or trained with the labeled data. sl algorithms construct two types of predictive models, regression and classification models which approaches data in a different way. for forecasting a numerical value, regression model is used. usl includes utilizing an unlabeled dataset to train the computer, after which it uses its own judgment to anticipate outputs. the primary goal of unsupervised learning is to categorize or group the unsorted dataset according to similarities, differences, and patterns. the machines are to find the hidden patterns in the input dataset [14]. in contrast to traditional methodologies, machine learning (ml) models offer a fresh and creative way to find hidden signals and patterns. this development covers a wide range of seismic applications, such as earthquake detection and phase identification, early warning systems, ground motion prediction, seismic tomography, earthquake geodesy, seismic risk assessment, and finally earthquake prediction [15,16]. it is generally accepted that there isn't a single ideal algorithm or machine learning solution that works for all situations and datasets because algorithm performance varies on a variety of parameters. while some algorithms work better with tiny amounts of data, others are more effective with large samples of data. while some algorithms just need quantitative inputs, others demand categorical inputs. the complication of the data and the number of features that the model needs to understand and make predictions are crucial factors when picking an algorithm. to account for this, three distinct algorithms namely, random forest regressor (rfr), support vector regressor (svr), multi-layer perceptron regressor (mlpr) have been used in this work to analyse an earthquake dataset [17]. different hyper parameters have been looked at for each model that has been selected, and the predicted results have been equitably assessed with metrics like mean square error (mse), root mean square (rmse and mean absolute error (mae). 1.1 random forest a random forest algorithm builds a forest from many separate decision trees, and chooses the outcome based on the predictions offered by them. the decision nodes, leaf nodes, and root nodes make up a decision tree (figure 2). figure 2: schematic presentation of random forest algorithm. decision trees are trained using knowledge acquisition. a method splits a training dataset into branches, and then further divides those branches until a leaf node is reached [18]. splitting branches during the creation of decision trees depends on entropy and information gain. the attributes used to forecast the outcome are represented by the nodes in the decision tree. ram krishna tiwari et al./ bibechana 22 (2025) 22-29 24 1.2 support vector regression a support vector regressor (svr) is a mathematical framework designed to function as a method or strategy for optimizing a particular mathematical function concerning a provided dataset. the svr method focuses on finding the ideal hyperplane in the feature space (n-dimensional space) which in turns divides the data points into various classes [19]. the hyperplane seeks to make the distance between the closest points of various classes as large as feasible. the size of the hyperplane is determined by the quantity of features. for two input characteristics, the hyperplane essentially becomes a line whereas it turns into a 2-d plane for three input characteristics. 1.3 multi-layer perceptron regression a multi-layer perceptron regression (mlpr) consists of at least three layers: an input layer, a hidden layer, and an output layer. every layer makes use of the results from the layer before it. without input, each layer node is referred to as a neuron. the primary processing unit of the neural network, the neuron, gathers data from a variety of inputs, applies weights and bias terms, and then sends the final product to an active function that produces outputs [20]. a multilayer perceptron model primarily comprises of a back propagation model for training, and additionally, it employs a linear activation function in its hidden layers, which, when combined with multiple layers, allows it to approximate non-linear relationships in the data. figure 3: schematic presentation of multilayer perceptron algorithm where l0 stands for (layer 0) or input layer (il), l1 stands for (layer 1) or hidden layer (hl), and l2 stands for (layer 2) or output layer (ol). the study area is in the central himalaya region between latitudes of 26.5° and 30.5° and longitudes of 80° and 88°, which includes the entirety of nepal along with certain regions of india and china. the region has low to moderate seismicity (figure 4). the seismicity of the region is primarily controlled by the main central thrust (mct), main boundary thrust (mbt), main frontal thrust (mft), and several small faults that are trending north to the south [21–23]. figure 4: seismicity of the study area. also showing major himalayan thrusts std, mct, mbt, and mft from north to south, namely south tibetan detachment system, main central thrust, main boundary thrust, main frontal thrust. the earthquake occurrence mechanisms are widely regarded as unpredictable and marked by non-linear behaviors. most ongoing research in the field of ml has concentrated on exploring how neural networks can be applied to address this challenge [11,24,25]. because of conceptual, algorithmic, and computational constraints, it was challenging to construct efficient models via the early explorations, but it is now possible to use advanced models by leveraging deep neural networks (dnns) [13,26]. while going through the literature, artificial neural network (ann) in collaboration with seismic precursors were found useful to predict earthquakes. for example, back propagation neural network (bpnn) models have been used to identify unusual behaviour in radon concentrations produced by earthquakes [27]. from the assembly of radial basis function (rbf) neural networks, earthquakes in china have been predicted (y. liu et al., 2004). analysing seismic events over a period in southern california and san francisco, a model was designed, based on anns which can predict the earthquakes on monthly basis [16]. in 2009, the identical seismic considerations were incorporated with the probabilistic neural network (pnn) to predict earthquake [15]. the work [28] demonstrates that, although the occurrence of earthquakes is nonlinear and random phenomena, it is still possible to model it using methodologies of machine learning. the neural network-based method for predicting earthquakes was evaluated using data from the portuguese reram krishna tiwari et al./ bibechana 22 (2025) 22-29 25 gion of the azores, and the results showed that it successfully predicted earthquakes in july 1998 for the modified mercalli intensity (mmi) of 8, and in january 2004 for the modified mercalli intensity (mmi) of 5, respectively [29]. according to studies [15, 16] probabilistic neural networks (pnns) may be used for small and intermediate earthquake prediction while recurrent neural networks (rnns) may be utilized for earthquakes of large magnitude. according to a comparative study employing ann technology and non-linear predictability assessments, the dynamics of earthquakes in the north-east india region were found to be stochastically scaled process [30]. in a study conducted in hindukush region by the application of four machine learning algorithms on a temporal distribution of past earthquakes, the accuracy to predict the earthquakes is noticed to be 65% on linear programming boost ensemble while 58% and 62% for rnn and random forest [31]. the aim of this study is to utilize historical seismic data, including date, time, latitude, and longitude to create predictive algorithms that can predict the magnitude and compare it with the actual magnitude of the earthquakes in central himalayan region. the primary challenge is to design and train machine learning models that enhances our ability to predict earthquake magnitudes accurately, aiding in disaster preparedness and response efforts. 2 data and methodology this research is quantitative and based on quantitative earthquake data like magnitude, latitude, longitude, and focal depth. the data extracted from the international seismological centre (isc) catalog for the period between february 1, 1964, and december 27, 2022 [32], included additional entries such as event identification numbers, author names, station codes, and phase data, which were deemed irrelevant for this study and excluded. the catalog was further processed to identify missing values in critical attributes like magnitude, depth, latitude, and longitude, with incomplete records removed. the final dataset comprises 2595 earthquakes, with magnitudes ranging from 2.9 to 6.9. after compilation, the data was thoroughly cleaned, formatted, and stripped of missing or damaged entries to ensure its suitability for analysis. the three models, namely random forest regressor (rfr), multi-layer perceptron regressor (mlpr), and support vector regressor (svr) are selected over others for their proven capability to manage the inherent complexities of the dataset, such as non-linearity, high-dimensionality, and data noise [33, 34]. the data processing in this study involves configuring key hyper parameters across these models. for rfr, bootstrapping is enabled (bootstrap=true), and the model uses all features for each split (max_features=1.0), with trees growing until leaves are pure or contain fewer than 2 samples (min_samples_split=2). it employs the 'squared_error' criterion to minimize mean squared error and uses 100 trees (n_estimators=100). the mlpr is configured with the 'tanh' activation function, a learning rate of 0.001 (learning_rate_init=0.001), and 500 neurons in the hidden layer (hidden_layer_sizes=500), utilizing the 'sgd' solver for optimization. it runs without early stopping (early_stopping=false) and continues until reaching the maximum number of iterations (max_iter=100). the svr model uses an rbf kernel (kernel='rbf') with a regularization parameter (c=1.0) and an epsilon of 0.1 to control error margin, while gamma is set to 'auto'. all models are trained with random_state=0 for reproducibility, and verbose output is suppressed (verbose=false). these configurations collectively guide the data through preprocessing, transformation, and optimization steps to ensure that the machine learning models are effectively trained and evaluated.80% of the dataset was provided for training and the remaining 20% for testing, allowing for proper model evaluation on unseen data (aryal et al., 2024). thereafter, numerical optimization algorithms are employed to iteratively fine-tune the model parameters using a cost function. to evaluate the model's performance, we calculate metrics such as mean absolute error (mae), mean square error (mse), and root mean square error (rmse). finally, the machine learning model is employed to handle new data. 3 results and discussion machine learning offers promising capabilities for analyzing historical data to predict earthquake magnitudes, a task with no definitive method yet. this research leverages data from 2595 seismic events and applies random forest regressor (rfr), support vector regressor (svr), and multi-layer perceptron regressor (mlpr). these models were chosen for their ability to handle nonlinear relationships and complex geophysical patterns: rfr for robustness and feature analysis, svr for modeling nonlinearities with kernel methods, and mlpr for capturing intricate dependencies. their selection is supported by their proven reliability in similar seismological studies [33–35]. we have tested these methods to forecast the magnitude of the earthquakes that hit the central himalaya region in the year 2015 and comparison between actual magnitude and predicted magnitude are depicted by the different plots. the density magnitude plot of the dataset is depicted by figure 5. ram krishna tiwari et al./ bibechana 22 (2025) 22-29 26 figure 5: a density magnitude plot provides a visual representation of the frequency of earthquakes at different magnitudes. the y-axis represents the density of earthquakes, often measured as the number of earthquakes per unit magnitude. this shows how frequently earthquakes of different magnitudes occur within the dataset. it tends to have a higher density for smaller magnitude earthquakes and gradually decreases as the magnitude increases. a single higher peak in the plot suggests that 3.1 to 5.4 magnitudes are predominant in that region. the plot shows a steep decrease in density as magnitude increases which suggests that there are fewer large earthquakes, a typical characteristic of most seismically active regions. five earthquakes of the year 2015, namely the gorkha earthquake (6.9 mb), the kodari earthquake (6.7 mb), the magnitude 6.1 mb earthquake, the magnitude 6.5 mb earthquake and the magnitude 6.6 mb earthquake of diverse locations, are used to assess the performance of the proposed techniques. the rfr, mlpr, svr models are trained and tested through multiple cycles to refine their performance which helps to get the minimum errors [33,34,36,37]. table 1 gives the predicted magnitude and actual magnitude of above-mentioned earthquakes and heat map of predicted magnitude is presented in figure 6. figure 6: a heat map of magnitude predicted by random forest (rfr), multi-layer perceptron (mlpr), support vector regression (svr) for the gorkha earthquake, the kodari earthquake, the magnitude 6.1 earthquake, the magnitude 6.5 earthquake and the magnitude 6.6 earthquake. following the training phase, the model is validated to forecast the earthquake exceeding 6.0 in mb scale and the 3d plot of the predicted magnitude and actual magnitude plot are depicted by figure 7. table 1: predicted and actual magnitude of the earthquakes. name rfr based magnitude mlpr based magnitude svr based magnitude actual magnitude gorkha eq 6.24 4.09694 4.61592 6.9 kodari eq 5.846 4.08975 4.32297 6.7 eq6.1 3.732 4.06169 3.86912 6.1 eq6.5 5.887 4.10614 4.47054 6.5 eq6.6 4.629 4.09994 4.18434 6.6 table 2: adapted machine learning model with error and accuracy. model mae mse rmse accuracy of model random forest regressor (rfr) 0.36 0.23 0.48 0.16 multi-layer perceptron regressor (mlpr) 0.40 0.27 0.52 0.016 support vector regressor (svr) 0.35 0.24 0.49 0.13 ram krishna tiwari et al./ bibechana 22 (2025) 22-29 27 the magnitude predicted by rfr is close to the actual magnitude of the gorkha earthquake, the kodari earthquake, and the magnitude 6.5 aftershock (above 6.0 for both events) while the magnitude predicted for other earthquakes deviates from the actual value (figure 7). the magnitude predicted by svr significantly deviates from the actual values, as it predicts 4.61592 for the gorkha earthquake and 4.32297 for the kodari earthquake. the magnitude predicted by mlpr is just around 4 and almost the same for all five earthquakes and greatly deviated from the actual magnitudes. figure 7: 3d plot of predicted magnitude versus actual magnitude for the gorkha earthquake, the kodari earthquake, the magnitude 6.1 earthquake, the magnitude 6.5 earthquake, and the magnitude 6.6 earthquake using rfr, mlpr, svr. 3.1 performance evaluation the performance of rfr, svr, and mlpr is presented in table 2 and figure 8 and their accuracies are presented in figure 9. the 3d error bar in figure 8 depicts the errors produced by rfr, mlpr, and svr models. the mae, mse, and rmse errors for rfr (0.36, 0.23, 0.48) and svr (0.35, 0.24, 0.49) exhibit minimal disparity, whereas mlpr's errors are marginally elevated (0.40, 0.27, 0.52). these findings indicate that mlpr's performance is comparatively inferior to that of rfr and svr. the rfr model demonstrates superior performance in predicting earthquake magnitudes compared to the other two methods. the accuracy plot reveals that rfr achieves a slightly higher accuracy (0.16) than svr (0.13) and mlpr (0.016) (figure 9). this can be attributed to rfr's ensemble approach, which leverages decision trees to capture complex patterns in the data effectively. in contrast, svr prioritizes a smoother fit by minimizing margin violations, which may limit its ability to capture intricate details. the notably low accuracy of the mlpr model suggests that it fails to learn meaningful patterns from the data, leading to predictions that are essentially random. figure 8: 3d error bar of three different methods employed for the estimation of the magnitudes. figure 9: accuracy bar of three different methods used for the estimation of magnitudes. 4 conclusion three machines learning algorithms namely, random forest regressor (rfr), multi-layer perceptron (mlpr), and support vector regressor (svr) have been used to predict the major earthquake events that occurred in the year 2015. the study has been applied to 2595 earthquakes of magnitude range 2.9 to 6.9, collected from isc catalog, for 68 years. the results suggest that all algorithms, while providing reasonable estimates, tend to under predict earthquake magnitudes, particularly for higher-magnitude events. for example, the rfr model predicts 6.24 for gorkha earthquake (actual 6.9) and 5.85 for kodari earthquake (actual 6.7), indicating that it tends to slightly underestimate magnitudes. similarly, the mlpr model under predicts with values like 4.10 for gorkha earthquake, while the svr model also provides lower predictions, such as 4.62 for gorkha earthquake. among three algorithms rfr is found to be the superior as it estimates the magnitude close to actual magnitude. this highlights the need for further model refinement through hyper parameter tuning, feature engineering, or incorporating more detailed seismic data to enhance prediction accuracy, especially for larger earthquakes. analyzing the residuals between predicted and actual values could help idenram krishna tiwari et al./ bibechana 22 (2025) 22-29 28 tify areas where the models are underperforming and guide improvements. from the error perspective both rfr and svr do not show significant differences but as the prediction pattern is observed rfr shows the better promises. despite challenges such as imbalanced datasets, uncertainties in seismic features, and the complexity of modeling dynamic, non-linear relationships in earthquake patterns, the results of this study indicate that both the random forest regressor (rfr) and support vector regressor (svr) hold promise for prediction, 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[37] b. nadi, f. askari, o. farzaneh, s. fatolahzadeh, and r. mehdizadeh. reliability evaluation of regression model for estimating coseismic landslide displacement. iranian journal of science and technology transactions of civil engineering, 44(1):165–173, 2020. introduction random forest support vector regression multi-layer perceptron regression data and methodology results and discussion performance evaluation conclusion bibechana vol. 20, no. 3, december 2023, 213–223 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar correlative study of aerosol optical depth with precipitable water over five aeronet stations worldwide santosh sapkota1,∗, sabin gautam1, aayush gautam2, bhairab ale1 1prithvi narayan campus, tribhuvan university 2birendra multiple campus, tribhuvan university ∗corresponding author. email: ssapkota922@gmail.com abstract ground-based measurements were taken at various locations, including kathmandu bode, beijing, gandhi college (located in the south asian zone, highly polluted area), canberra, and unc gaitan (located in the south eastern zone, low polluted area), from january to december 2016. the study investigated the seasonal and inter-annual aod that were obtained using the cimel sun photometer, as a part of the aerosol robotic network (aeronet). the data showed that kathmandu (0.45±0.01), gandhi college (0.45±0.02 and beijing (0.85±0.03) had higher aerosol optical depth (aod) values compared to other stations, with beijing being a high-altitude site. the analysis found that pre-monsoon aod were higher over kathmandu (0.45±0.01), gandhi college (0.45±0.02), unc gaitan (0.28±0.001), and canberra (0.06±0.002). on the other hand, the monsoon aod was higher over beijing (0.85±0.03). the study identified factors contributing to the higher aod values in specific regions. beijing, gandhi college, and kathmandu, located in asian monsoon regions, experienced high aerosol loading due to economic activities, vehicles, urbanization, vegetation fire, land clearing for crop cultivation, as well as winter biomass burning, heating needs, and pollution from bricks kilns, factories, and vehicles. canberra and unc gaitan had higher aod values primarily due to biomass burning, household activities and dust. aod values are higher for shorter wavelengths and vice-versa. we conducted a correlation analysis between aod and precipitable water at different wavelengths and observed one-to-one correspondence. the columnar water vapor (cwv) exhibited a high correlation with aod in canberra (coefficient of determination, r2 = 0.61) at 1640 nm but had no relationship with aod in gandhi college (coefficient of determination, r2 = 0) at 1640nm. there is a weak negative correlation between aod and precipitable water over kathmandu and unc gaitan, but there is a positive correlation in canberra, beijing and gandhi college. keywords aerosol, aerosol optical depth, precipitable water. article information manuscript received: july 30, 2023; accepted: august 29, 2023 doi https://doi.org/10.3126/bibechana.v20i3.57153 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 213 http://nepjol.info/index.php/bibechana ssapkota922@gmail.com https://doi.org/10.3126/bibechana.v20i3.57153 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ santosh sapkota et al./ bibechana 20 (2023) 213-223 214 1 introduction aerosols are tiny solid or liquid particles that are suspended in the atmosphere due to both natural and manmade (anthropogenic) causes, with sizes ranging from nanometers (nm) to tens of micrometres (µm). aerosols are produced in the atmosphere through various natural and anthropogenic processes, and they get dispersed horizontally and vertically through prevailing atmospheric circulation. in recent years, there has been a substantial increase in interest in studying natural and anthropogenic aerosols because of their influence on climate through direct and indirect radioactive effects [1]. despite this, aerosols are still a major source of uncertainty in the prediction of climate change due to inadequate information on the variabilities of aerosol characteristics on regional and temporal scales [1]. aerosol optical properties, i.e., the physical and chemical characteristics of the aerosol, are responsible for diffusing or absorbing both incoming and outgoing radiation and thus have an impact on both the climate and the earth’s radiative balance [2]. in addition to their indirect effects on cloud formation, reducing visibility, and human health [3]the scientific community has become increasingly interested in suspended aerosol particles during the past few decades. the most complete variable for determining the aerosol burden in the atmosphere from ground-based equipment is aerosol optical depth (aod). this variable is employed in regional studies to describe aerosol size distribution and evaluate air pollution [4–6]. aod is measured using groundbased sun photometers between the wavelengths of 340 and 1020 nm, with extended wavelength versions also having 1640 nm [7]. south asia comprises india, china, and nepal. it is densely populated and people face environmental threats in terms of air pollution, monsoon floods, droughts and associated climate change [8]. australia and america lie in eastern asia. it was acclaimed that the aod of shorter wavelengths is more dominant than the longer ones because of the angstrom exponent [9]. anthropogenic aerosols over south and east asia can significantly change the energy balance of the earth-atmosphere system on regional scales [10]. precipitable water vapor, or simply, precipitable water is the total amount of water vapor in the zenith direction, between the underlying surface (or a surface of particular height) and the top of the atmosphere. it is crucial to monitor and comprehend how precipitable water vapor content changes because it affects atmospheric water movement, energy conversion, and the formation of clouds and precipitation [11, 12]. we analyzed the correlation between aerosol optical depth (aod) and precipitable water (pw). conducting a correlation analysis between the aerosol optical depth (aod) data and precipitable water can provide valuable insights into the proposed method for estimating the relationship between these two variables. in the present study, for the first time, we analyse aerosol characteristics from five locations spread over a large region in south asia and the southeastern zone during different seasons to examine the space-time variation in aerosol characteristics, the correlation between aod and precipitable water and the effect of long-range transport. daily measurements of aerosol optical depths in the 870nm–1640nm wavelength region made during 2016 over kathmandu bode, gandhi college, beijing, canberra, and unc gaitan are used in the study. an analysis and documentation on the monthly and seasonal variabilities in aerosol optical characteristics, attain significance in the context of air quality, air pollution and regional and global climate. 2 data and methodology this research is focused on the various aerosol properties over five stations. we have used aeronet (level 2 version 3) data for our analysis which are quality-assured data of these sites over the period of a year from january 2016 to december 2016. we have plotted a correlation analysis between aod and precipitable water. the term "correlation analysis" refers to the process of establishing a link between two (or more) quantitative variables using a scatter plot and straight-line assumptions [13]. the connection between the quantitative variables assesses both the direction and "strength" or "extent" of an association between the variables. when two variables have a correlation value of 1, it means that they are perfectly associated positively, a correlation coefficient of -1 means that they are perfectly related negatively, and a correlation coefficient of 0 means that there is no linear relationship between the two variables [14]. the coefficient of determination (r2) is calculated as the proportion of the variability in the dependent variable that is explained by the regression mode. r2 = 1− sum of square regression (ssr) total sum of squares(tss) (1) the closer r2 is to 1, the better the regression model explains the variability in the dependent variable. if r2 is closer to 0, it means that the regression model does not explain much of the variability. we performed the graphical analysis using the levenberg-marquardt least orthogonal distance method. the data were then analyzed by using non-linear regression analysis and the least square technique, and a coefficient of determination (r2) was obtained, where m is the slope, and santosh sapkota et al./ bibechana 20 (2023) 213-223 215 c is the intercept, which represents aod or pwv measurements from aeronet. a personal correlation coefficient (r) was calculated to determine the significance of the correlation. to explore the seasonal fluctuations in aerosol optical characteristics, the study establishes four distinct seasons: pre-monsoon (march–may), summer (june–september), post-monsoon (october–november), and winter (december–february). table 1: station with the geographic location of different countries of the world. sn tation name country longitude geographic latitude amsl (m) 1 kathmandu bode nepal 27.680°n 85.103°e 1297 2 gandhi college india 25.871°n 84.261°w 60 3 beijing radi china 40.005°n 116.379°e 59 4 canberra australia 35.271°s 149.111°e 600 5 unc gaitan south america 4.311°n 72.3518°w 192 3 results and discussion 3.1 variation of aod with wavelength figure 1: variation of aod with wavelengths at different stations over the world. santosh sapkota et al./ bibechana 20 (2023) 213-223 216 in contrast to unc gaitan, the difference in aod at shorter and longer wavelengths is not significant, suggesting a lower concentration of finemode aerosols. aod could not be measured over unc gaitan and kathmandu due to fog, cloudy and overcast conditions during the post-monsoon and winter seasons. aod over unc gaitan was found to be highest (0.28±0.001) and lowest (0.04± 0.001) during pre-monsoon and monsoon season. the highest value of aod is due to affected by the long-range transport of dust particles. over beijing, monthly average spectral aod, which was typically at its highest during the summer, with a high of (0.9± 0.08) in june, indicating the most intense desert dust advection. the lowest monthly mean spectral aod (0.1±0.002) occurs during the winter season, with the lowest value occurring in january. the highest and lowest monthly mean aod occurred in july and december, respectively, according to aod (750nm) data from pyrheliometer measurements [15, 16], which acquiesce with our values. moreover, the monthly average maximum aod at gandhi college value of (0.45±0.03) during premonsoon. the monthly average aod varied from 0.1±0.02 to 0.45±0.03, which is significantly less than the range seen in beijing and kathmandu. previous studies of aod (500 nm) [17] explored that the highest aod in gandhi college occurs in june indicating the majority of the year due to hygroscopic growth and biomass burning. during the pre-monsoon season, the majority of dust came from arid regions of western china and mongolia, which moved eastward, showing the dominance of coarse particles [18]. based on the values of aod, canberra is the most pristine site than other stations. the highest aod was in december (0.07±0.001), and the lowest was in june (0.02±0.008). aod values at canberra peaked in pre-monsoon (0.06± 0.002), while aod values were down in monsoon (0.01±0.002). this can be explained by the extensive and frequent wildfires over the tropical north of australia. this is likely a consequence of the relatively high rainfall during the wet season and large smoke emissions during the subsequent burning season. the rainfall likely suppressed the smoke emissions due to the high level of moisture in the air, but it also promoted the growth of vegetation, leading to an increase in smoke emissions during the subsequent dry seasons which lead to higher aod. 3.2 correlative analysis between precipitable water (pw) and aod we have calculated the coefficient of determination of aod having three different wavelengths with precipitable water. the coefficient of determination (r2) between aod and precipitable water for respective stations is mentioned in the table below. at kathmandu station, the coefficient of determination (r2) between aod and precipitable water are 0.04, 0.027, and 0.027, respectively, which indicates a weak positive correlation (fig 2). that when there is more precipitable water, there is a decrease in aerosols or particulate matter in the atmosphere. at the station, gandhi college, r2 between aod and precipitable water are 0.011 and 0.025, respectively, which suggests that aod and precipitable water are weakly correlated (fig 3). however, the coefficient of determination is found to be zero between precipitable water and aod, which has a wavelength of 1640nm implying that there is no correlation, the presence or absence of aerosol particles at 1640 nm does not have a significant impact on the amount of water vapor present. local atmospheric conditions, different altitude profiles, and statistical noise might cause zero correlation. the weak positive correlation implies that when there is precipitable water, there is an increment of aerosols or particulate matter. at station canberra, the coefficients of determination, aod and precipitable water are 0.61, 0.382, and 0.402 (fig 4). a positive correlation between aod and precipitable water was seen due to aerosol cloud interaction, bushfires and aerosol emission [19]. similarly, at station beijing, the coefficient of determination was found to be 0.108, 0.089, and 0.365 (fig 5), which indicates that the aod and precipitable water have a weak positive correlation. lastly, in the case of unc gaitan station, the coefficients of determination between aod and precipitable water are 0.084, 0.035, and 0.198 (fig 6). the negative correlation between aod and precipitable water might be due to aerosol-induced atmospheric change, microphysical effects and local pollution effects [20]. santosh sapkota et al./ bibechana 20 (2023) 213-223 217 table 2: coefficient of determination between aods having wavelength 1640, 1020, 870 nm and precipitable water. s.n. station name coefficient of determination(r2) aod (1640 nm) aod (1020 nm) aod (870 nm) 1. kathmandu bode 0.04 0.027 0.027 2. gandhi college 0.00 0.011 0.025 3. canberra 0.61 0.382 0.402 4. beijing 0.108 0.089 0.365 5. unc gaitan 0.084 0.035 0.198 figure 2: correlation between precipitable water and aod of kathmandu bode locations of nepal at different wavelengths. santosh sapkota et al./ bibechana 20 (2023) 213-223 218 figure 3: correlation between precipitable water and aod of unc gaitan, locations of india at different wavelengths. santosh sapkota et al./ bibechana 20 (2023) 213-223 219 figure 4: correlation between precipitable water and aod of canberra locations of australia at different wavelengths. santosh sapkota et al./ bibechana 20 (2023) 213-223 220 figure 5: correlation between precipitable water and aod of beijing locations of china at different wavelengths. santosh sapkota et al./ bibechana 20 (2023) 213-223 221 figure 6: correlation between precipitable water and aod of unc gaitan locations of south america at different wavelengths. 4 conclusion the aerosol optical properties as a variation of aod and its correlation with precipitable water are investigated over five stations. the values of aod with wavelengths of 870nm have a higher value than aod with wavelengths of 1020 and 1640nm. thus, aod with short wavelengths can have a higher santosh sapkota et al./ bibechana 20 (2023) 213-223 222 precision in measuring the size of aerosols. the monthly variability of the aerosol optical depth is significant over all stations due to the prevailing meteorology, airmass transport, and atmospheric conditions. monthly and seasonal variations of the aod are different for each month. the lowest aod was seen in canberra (0.03 ± 0.001) but the highest was in beijing (0.85 ± 0.02). the higher aod was seen during pre-monsoon due to agricultural activities, biomass burning and local products. the amount of aerosol plays an important role in precipitation. if there are a large number of aerosols, then water molecules will have more options for condensation because of which small clouds are formed with no or very few precipitations as water droplets in the cloud need to reach critical size for a downpour. because precipitation is strongly 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[20] s. sapkota, s. gautam, s. pokhrel, a. gautam, k. basnet, r. k. mishra, and j. regmi. study of aerosol optical properties in lumbini, nepal. bibechana, 20(1):1–9, 2023. introduction data and methodology results and discussion variation of aod with wavelength correlative analysis between precipitable water (pw) and aod conclusion bibechana vol. 21, no. 2, august 2024, 95-102 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar dwarf galaxy merger-induced star formation rate: a case study of mrk 1481 daya nidhi chhatkuli1,∗, sanjaya paudel2, amrit sedain3 binil aryal4 1tri-chandra multiple campus, tribhuvan university, kathmandu, nepal 2department of astronomy, yonsei university, seoul 03722, republic of korea 3institut für physik und astronomie, universität, potsdam, karl-liebknecht-str. 24/25, 14476 golm, germany 4 office of institute of science and technology, tribhuvan university kathmandu, nepal ∗corresponding author. email: chhatkulidn@gmail.com abstract the merger of the galaxies serves as a trigger for the increase in the galaxy’s star formation rate (sfr), which can be quantified by observing the column density of the hα line. our findings report the presence of various gas and metal emission lines, strongly indicating that the galaxy hosts very young stars and is currently undergoing active star formation processes. notably, we report a relatively high sfr of ∼ 0.0055 m⊙ yr-1 for a dwarf galaxy, alongside a metallicity level of 12 + log(o/h) ∼ 8.88 dex. our photometric analysis reinforces the notion that the galaxy is in the midst of a merger phase. additionally, the analysis indicates that the galaxy has a relatively flat shape (sérsic index ∼ 0.8), with stars distributed more broadly and less concentrated toward its center. this provides further evidence of the ongoing merger and its impact on the galaxy’s structure. the half-light radius of the galaxy is estimated to be 2.73 arcsec by using the petrosian method. keywords dwarf galaxy, galaxy merger, star formation rate, galaxy morphology. article information manuscript received: november 30, 2023; revised: january 16, 2024; accepted: january 24, 2024 doi https://doi.org/10.3126/bibechana.v21i2.60334 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction galaxies are captivating celestial entities, offering a window into the cosmos. their study provides valuable insights into the origins and dispersion of elements and energy, shedding light on the enigmatic forces of dark matter and dark energy shaping the universe [1–3]. galaxy mergers represent a crucial aspect of galactic evolution, wherein two or more galaxies combine, resulting in a single, larger entity. these mergers engender interactions among stars, 95 http://nepjol.info/index.php/bibechana chhatkulidn@gmail.com https://doi.org/10.3126/bibechana.v21i2.60334 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ daya nidhi chhatkuli et al./ bibechana 21 (2024) 95-102 96 gas, dust, and dark matter, leading to the redistribution and reconfiguration of the newly formed galaxy’s components. spanning millions to billions of years, these processes exert a profound influence on the structure, star formation history, and evolution of the resultant galaxy. additionally, galaxy mergers can trigger intense starbursts and are associated with the formation of some of the universe’s most massive galaxies. these mergers primarily occur due to gravitational forces, giving rise to major mergers between comparably sized large galaxies, minor mergers where smaller galaxies are absorbed by larger ones, cannibal mergers where a smaller galaxy is absorbed by a larger one, and tidal mergers where galactic tidal forces pull stars together. dry galaxy mergers, specifically involving galaxies with limited gas and dust, often lead to the creation of elliptical or spiral galaxies, depending on the galaxies involved, playing a pivotal role in reshaping galactic structures and features, even when their gas and dust reservoirs are depleted [4–6]. studying dwarf-dwarf galaxy mergers is important because dwarf galaxies were common in the early universe and drove galaxy mergers. yet, these mergers are often too far away to see directly, and finding low-redshift ones with dual active galactic nuclei (dagn) is tough. in a recent study, scientists found the first two dagn candidates in these mergers, known for their telltale tidal signs and dual, bright x-ray sources, likely linked to actively feeding massive black holes. more research will give us valuable insights into how galaxies grew early on, how black holes formed in their centers, and how mergers triggered star formation [7–9]. the star formation rate (sfr) measures the rate at which new stars form, driven by the gravitational collapse of interstellar gas and dust into protostars and stars. various factors influence sfr, including interstellar medium density, composition, temperature, and nearby stars. methods for sfr measurement include observations of star-forming regions, infrared surveys, and calculations based on region mass and star formation time. sfr plays a pivotal role in galaxy evolution, star distribution, and understanding galaxy formation. in galaxy mergers, sfr can significantly rise due to increased gravitational potential, compressing gas and dust and redistributing them, fostering higher star formation. studying sfr during mergers offers insights into how these events influence star formation dynamics and galaxy evolution, with a notable connection to metallicity, as higher metallicity enhances gas cooling efficiency, promoting increased sfr, while lower metallicity can suppress it, as observed in galaxies such as the milky way [10–13]. merging galaxies exhibit elevated metallicity levels compared to normal galaxies because the gas in mergers, which is abundant, gets transformed into stars, enriching the galaxy with metals. this heightened metal abundance results from the substantial star and gas content in merging galaxies. moreover, metals in merging galaxies can redistribute to other galaxies, further boosting their metallicity [8, 14–16]. galaxy morphology is a fundamental field in astronomy that explores the shapes and structures of galaxies. it enables us to uncover the secrets of how galaxies form and evolve, providing valuable insights into the broader structure of the universe. one of the major advantages of galaxy morphology is the ability to understand the various life stages of the galaxy’s evolution and the influence of external factors such as mergers [17,18]. the surface brightness profile of a galaxy, essential for understanding its structure and components like the bulge, disk, and halo, is typically determined by analyzing the distribution of light from stars and gas. the sérsic profile, a mathematical model, is developed by miguel a. sérsic, quantifies this brightness distribution, aiding in galaxy shape characterization via the sérsic index (n) – low n values suggest diffuse galaxies, while high n values indicate concentrated ones. the profile helps distinguish galaxy types, such as ellipticals and spirals, determine galaxy size (effective radius), and estimate total luminosity for mass calculations. to understand the complex dynamics and morphology of interacting dwarf galaxy, we can employ a double sérsic profile model [19]. here, we present the study of the morphology of a merging dwarf galaxy, mrk 1481, and calculate its sfr by using the flux of the emission line of the galaxy spectrum. moreover, we estimate the size and sérsic index of the galaxy. 2 material and methods 2.1 sample selection interacting dwarf galaxies present fascinating opportunities for the study of their photometric characteristics. in our investigation, we focused on a tidally interacting dwarf galaxy, mrk 1481, of low redshift (z = 0.0059) with a radial velocity of 1803 km s-1 selected from the catalog by paudel et. al, 2018 [20]. the apparent g and r-band magnitudes of the galaxy are 16.48 mag and 15.87 mag respectively. its absolute b-band magnitude is -15.49 mag. it has a stellar mass of 2.2 × 108 m⊙. this specific galaxy, mrk 1481, is situated at celestial coordinates r. a. (j2000): 13h 42m 59.4s and dec. (j2000): 52° 41' 17.88". we determined its distance to be approximately 25.03 mpc, calculated from its redshift, assuming a flat universe and adopting cosmological parameters (h0 = 71 km s-1 mpc-1, ωm = 0.3, and ω∧ = 0.7). the number of neighbors within the search criteria (sky-projected distance daya nidhi chhatkuli et al./ bibechana 21 (2024) 95-102 97 of fewer than 700 kpcs and a relative line-of-sight radial velocity of less than ± 700 km/s) is 9, and it has no satellite. notably, the mass ratio between the interacting dwarf galaxies m1 and m2 is 20. the sdss optical image and its spectrum are shown in figure 1. in the image, the blue part represents the area where stars are currently forming in the galaxy. this is mainly happening because of the gravitational pull between the two dwarf galaxies, which causes them to interact. the spectrum shows strong emission lines, which indicates that the galaxy is an emission type. figure 1: the sdss optical image of the emission-type interacting dwarf galaxy mrk 1481 is shown in the left panel and its optical spectrum is shown in the right panel. the x-axis is the rest-frame wavelength and y-axis is flux. 2.2 data analysis we examine the gas content of the galaxy by analyzing its optical spectrum obtained from the sdss data archive server (das). our analysis aims to understand the galaxy’s composition. it is important to note that we relied on archival data and didn’t apply any additional data processing to the galaxy’s spectra. to reproduce the spectra from the sdss data server, we utilize a tool called topcat. the sdss fiber, which collects this data, has a diameter of 3 arcsecs, covering only a small portion of the galaxy. the sdss optical spectrum ranges from 4,000 å to 7,000 å, encompassing key emission and absorption lines often used to study the chemical properties of stars and galaxies. we used a gaussian fit analysis to examine the prominent emission lines in the spectra, revealing a combination of hydrogen and metal lines within the galaxy. to calculate the galaxy’s star-formation rate, we applied the kennicutt initial mass function and used neutral hydrogen’s luminosity. this approach is based on [21,22]. we took a closer look at the way the interacting galaxy appears in pictures to figure out where its tidal effects come from. the major axis light profile of the galaxy is extracted by using the image reduction and analysis facility (iraf) task ellipse, and the best-fitted elliptical isophotes are drawn on the image as described by jedrzejewski [23]. to estimate the galaxy’s size, we applied the sérsic profile [24], which helps us understand how big the galaxy is. we also used photutils to see how the galaxy’s shape changes over time. this helped us getting a better idea of what the galaxy looks like by studying its brightness patterns in images. we obtained the g-band image of the galaxy from the sdss data server and employed iraf to generate the fitted image of the galaxy using the sérsic profile. in the following section, we will delve into the outcomes of our analysis. 3 results and discussion 3.1 spectroscopic analysis in our study, we focused on analyzing the galaxy’s key emission lines, including hβ , oiii5008, hα and nii6585, (see figure 2). black dots correspond to the observed flux, while the red solid lines depict the gaussian fit applied to the galaxy’s data. these lines are significant for assessing the sfr and gaining insights into the galaxy’s metallicity. the major cause of the broadening of the characteristic lines is doppler's broadening. the balmer decrement is the ratio of the fluxes in the hα and hβ lines often used to estimate the amount of dust along the line of sight. the balmer decrement is used in astronomy to measure the reddaya nidhi chhatkuli et al./ bibechana 21 (2024) 95-102 98 dening and attenuation of light from astronomical objects, particularly in the study of galaxies and nebulae. the balmer decrement is also used to determine the dependence of the balmer decrement with galaxy stellar mass and to study the evolution of the balmer decrement with redshift [25]. we calculated the value of balmer increment to be 3.15. in the context of a merging dwarf galaxy, a balmer decrement of 3.15 indicates a significant amount of dust, which affects the observed colors and spectra of the galaxy. this value suggests that the light from the galaxy is being heavily scattered and absorbed by dust, impacting the interpretation of its properties and the processes occurring within it [26–28]. the galaxy’s star formation rate determined from the neutral hydrogen line before extinction correction stands at 0.0046 m⊙yr−1. the sfr is significantly influenced by the presence of dust particles in the interstellar medium, particularly impacting the hα emission, where a substantial amount is absorbed. to address this, we calculated the galaxy’s extinction coefficient, which is measured to be 0.1997. it’s worth noting that the hβ line is less affected by dust particle interaction. consequently, after correcting for extinction, the sfr of the galaxy is 0.0055 m⊙yr−1 which is almost similar to the zhao et al. [29], where they calculated star formation as 0.0058 m⊙yr−1 and after the extinction correction, 0.0339 m⊙yr−1. this high value of sfr of this galaxy indicates that the galaxy is actively forming stars at a significant rate. the high sfr can lead to the formation of massive stars, which can then die in supernova explosions and enrich the surrounding environment with heavy elements [30]. for the full calculation of the star formation rate and the extinction correction, see [7]. we also determined the metallicity ratios for some of the prominent lines, providing insights into the galaxy’s evolution and characteristics. gasphase metallicity is commonly assessed by calculating the oxygen abundance relative to hydrogen, defined as 12 + log(o/h). this is due to oxygen’s significance in both the mass of the universe and the electron temperature of the gas. in our analysis, we found that the metallicity of our interacting dwarf galaxy stands at 8.86 dex [31] calculated as 8.69 dex). this suggests that the galaxy’s outer regions have become hotter because the ionizing photons have been absorbed by the metals, impacting their properties. a high value of metallicity means that the galaxy contains a significant number of heavy elements, such as iron, in its stellar population [32]. 3.2 photometric analysis in our study, we employed photutils to analyze the galaxy’s isophotes and their orientation, as depicted in the upper left panel of figure 3. the evident twisting in these isophotes strongly indicates that the galaxy is undergoing a merger phase, leading to continual alterations in their appearance. we have also examined how the galaxy’s ellipticity and position angle change with its radius, as depicted in the upper-right panel of figure 3. notably, the galaxy appears nearly spherical towards its center, but as we move outward, it becomes more elliptical. this suggests that the outer regions of the galaxy are becoming more elongated, indicating a potential tidal connection and influence. we used the sérsic profile to model the galaxy’s surface brightness profile, as shown in the lower left panel of figure 3. the sérsic index for the fit, represented by “n”, is 0.8, and we measured an effective radius of 6.62 arcseconds. these values indicate that the galaxy has a relatively flat brightness distribution, resembling an exponential profile. this suggests that the distribution of stars is more spread out and less concentrated toward the center. the petrosian radius is a measure of the size of a galaxy, and it is derived from the petrosian function, which helps in characterizing the overall extent of a galaxy’s light profile. it takes into account variations in a galaxy’s brightness, making it particularly useful for galaxies with diverse structures. the petrosian index is a dimensionless profile that represents the rate of change of surface brightness with radius in a galaxy's light profile. the petrosian index is useful in determining radial concentrations of galaxy light profiles and performing accurate measurements of galaxy radii [33]. in our analysis, we calculated the petrosian radius, specifically with a sérsic index (n) of 0.2, which indicates how much light is distributed at different distances from the galaxy’s center. at a distance of 2ap (twice the petrosian radius), we assume that the petrosian profile encompasses the entirety of the galaxy’s brightness. this assumption allows us to effectively capture the overall extent of the galaxy’s light distribution seen in the lower right panel of figure 3. moreover, the half-light radius of the galaxy is estimated to be 2.73 arcsec. daya nidhi chhatkuli et al./ bibechana 21 (2024) 95-102 99 figure 2: the figure illustrates the gaussian profile of the galaxy’s prominent emitted spectral lines hβ , oiii5008, hα, and nii6585. the error bars reflect the percentile error associated with the observations. we show a conservative estimate of the flux error in the plot, i.e., 10% of the observed flux provided by the sdss webpage (https://www.sdss.org/dr15/spectro/caveats/). the wavelengths given in the x-axis are redshift corrected. figure 3: caption of figure 3 is given in next page. daya nidhi chhatkuli et al./ bibechana 21 (2024) 95-102 100 figure 3 (caption): the upper left panel shows the isophotes of the interacting dwarf galaxy, mrk 1481. the green ellipses represent the contour levels of the galaxy. the upper right panel shows the radial profile of position angle and ellipticity. the brightness profile of the galaxy is illustrated in the lower left panel, where the black dots represent the observed data and the blue solid line depicts the 1d sérsic fitting of the galaxy. the lower right panel shows the radial profile of the petrosian index and cumulative intensity at the g-band. the vertical dashed line represents the petrosian radius at sérsic index 0.2 (horizontal brown line). the vertical green-colored dashed line intersects the curve at a half-light radius. 4 conclusion in our comprehensive analysis of the spectroscopic and photometric attributes of the interacting dwarf galaxy, mrk 1481, we made a noteworthy discovery. our observations revealed the presence of highly prominent gas emission lines, indicating that the galaxy is currently undergoing a starburst phase, with the formation of very young stars in progress. to quantify this star formation activity, we conducted gaussian profile fits of the emission lines and calculated the total flux, a key parameter in determining the galaxy’s star formation rate. our findings indicate a remarkably high star formation rate, measuring at 0.0046 m⊙yr−1 when using the hα lines. however, after applying an extinction correction, this rate increases to 0.0055 m⊙yr−1. this adjustment underscores the active nature of star formation within the galaxy, highlighting the intensity of this ongoing process. we also calculated the metallicity of the galaxy which comes out 8.88 dex, and it shows that the galaxy is very metal-rich and young stars are forming. additionally, we delved into the photometric characteristics of the galaxy. we employed a sérsic profile to model the galaxy, with a sérsic index of 0.8 and a half-light radius of 2.73 arcseconds. the analysis of changing ellipticity and position angle of the galaxy has led us to the observation that the galaxy is undergoing a merger, particularly at its outer regions, indicating a potential tidal connection and influence. acknowledgements daya nidhi chhatkuli acknowledges the university grants commission of nepal, for financial support (award no.: phd-75/76-s & t-13) to carry out this research. this study is based on the archival images and spectra from the sloan digital sky survey (http://www:sdss.org/collaboration/credits.html ). a brief statement on the observational data sources the sloan digital sky survey (sdss) is a comprehensive astronomical survey that has played a pivotal role in mapping the night sky and 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[33] r. geda, s. m. crawford, l. hunt, m. bershady, e. tollerud, and s. randriamampandry. petrofit: a python package for computing petrosian radii and fitting galaxy light profiles. the astronomical journal, 163(5):202, 2022. https://doi.org/10. 3847/1538-3881/ac5908 http://doi.org/10.1093/mnras/stv626 http://doi.org/10.1093/mnras/stv626 http://doi.org/10.3126/jnphyssoc.v7i4.42928 http://doi.org/10.3126/jnphyssoc.v7i4.42928 http://doi.org/10.1088/0004-6256/141/2/68 http://doi.org/10.1088/0004-6256/141/2/68 https://iopscience.iop.org/article/10.1086/316471/pdf https://iopscience.iop.org/article/10.1086/316471/pdf http://doi.org/10.1086/322874 http://doi.org/10.1086/322874 https://doi.org/10.3847/1538-3881/ac5908 https://doi.org/10.3847/1538-3881/ac5908 introduction material and methods sample selection data analysis results and discussion spectroscopic analysis photometric analysis conclusion bibechana vol. 22, no. 2, august 2025, 141-150 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar phytochemical analysis, total flavonoid and phenolic content, antimicrobial properties of lichens extract of hypotrachyna cirrhata (fr.) divakar nirmala sharma1,2, deepa karki1, bhanu bhakta neupane1,∗, achyut adhikari1,∗ 1central department of chemistry, tribhuvan university, kathmandu, 44618, nepal 2amrit campus,tribhuvan university, kathmandu, 44618, nepal ∗corresponding authors. email: achyutraj05@gmail.com (aa) bhanu.neupane@cdc.tu.edu.np (bbn) abstract despite the significant attention lichens have received for their unique secondary metabolites, research on edible varieties remains limited. the antioxidant activity of hypotrachyna cirrhata was evaluated using in vitro dpph radical scavenging assays. the total phenolic content (tpc) and total flavonoid content (tfc) of h. cirrhata were measured as 42.165 ± 0.98 mg gae/g and 11.789 ± 0.34 mg qe/g, respectively. in this assay, ethyl acetate demonstrated strong antioxidant potential with an ic50 value of 34.14 ± 0.17 µg/ml, whereas hexane showed a higher ic50 value of 74.3 ± 1.13 µg/ml, compared to the standard quercetin, which had an ic50 value of 62.87 ± 1.02 µg/ml. the methanolic extracts of the lichen demonstrated notable antimicrobial effects against pathogens, with minimum inhibitory concentration (mic) values recorded at 195.312 g/ml and minimum bactericidal concentration (mbc) ranging from 195.312 to 390.625 g/ml. the study suggested that h. cirrhata may exhibit significant levels of total phenolic content (tpc) and total flavonoid content (tfc), which are closely associated with enhanced antibacterial and antioxidant activities. keywords anti-oxidant, anti-bacterial, total phenolic content, total flavonoid article information manuscript received: november 22, 2024; revised: april 10, 2025; accepted: may 19, 2025 doi https://doi.org/10.3126/bibechana.v22i2.71936 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction lichens represent a form of symbiotic organism, composed of a mycobiont (fungus) in association with cyanobacteria or algae [1] . these organisms are capable of surviving prolonged desiccation without succumbing to starvation, thanks to their ability to sustain a slow metabolic rate. additionally, lichens exhibit extraordinary adaptability to a wide range of habitats, thriving on almost any surface and in diverse environmental conditions, from sea level to high alpine regions. they also play a 141 http://nepjol.info/index.php/bibechana achyutraj05@gmail.com bhanu.neupane@cdc.tu.edu.np https://doi.org/10.3126/bibechana.v22i2.71936 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ nirmal sharma et al./ bibechana 22 (2025) 141-150 142 role in forming biological soil crusts and are frequently found on exposed soil surfaces, walls, roofs, and rocks [2]. lichens manifest in four fundamental growth morphologies: crustose, foliose, and fruticose [3]. globally, approximately 20,000 lichen species have been documented, with nepal's catalog identifying 1,129 species, including infraspecific taxa, distributed across 237 genera and 66 families [2]. since prehistoric times, lichens have been utilized for various purposes including food, dyes, perfumes, medicinal treatments in folk traditions, and ornamental uses [4]. lichen species produce a diverse array of secondary metabolites, which have been isolated and shown to exhibit a wide spectrum of biological activities [5]. numerous lichen extracts have been employed in traditional remedies, and screening tests have frequently revealed metabolites with antibiotic [6], antimycobacterial [7], antiviral [8], antitumor [9], analgesic [10] and antipyretic [11] properties.lichens are capable of enduring extended periods of desiccation without experiencing starvation, thanks to their slow metabolic processes. these efforts seek to explore the possible medicinal uses of compounds obtained from lichens. the metabolites found in any lichen species can be produced through one of three major metabolic pathways: the polymalonate pathway, the mevalonic acid pathway, or the shikimic acid pathway [12]. these pathways not only facilitate the storage of carbohydrates but also the production of secondary metabolites [13]. lichens have garnered considerable interest from researchers due to their therapeutic potential, which is ascribed to their distinctive compounds. despite this, comprehensive data on the edibility of lichens and detailed evaluations of their culinary and medicinal applications remain limited. to investigate the biological activities of the lichen h. cirrhata (figure 1) studies have focused on their antioxidant and antimicrobial properties, alongside the identification of phytochemical constituents and the quantification of total phenolic and flavonoid content. 2 materials and methods 2.1 collection and identification of lichens lichens hypotrachyna cirrhata were collected from the makwanpur district with geographical distribution (27° 60 81.83 n, 85° 09 22.81 e) around 2300 meter in altitude. the collected lichens was identified from the national herbarium and plant laboratories, department of plant resources, godawari, lalitpur, nepal. figure 1: picture of hypotrachyna cirrhata 2.2 preparation lichen extract after meticulously removing dust particles from the lichens, they were air-dried in the shade at room temperature for two weeks and then ground into a powder. the powdered lichens were stored in paper bags for future use. a 100 g portion of the dry powder was soaked in methanol at a 1:10 ratio for 24 hours. following this, the mixture was filtered, and the filtrates were concentrated using a rotary evaporator before being dried in the air. 2.3 phytochemicals screening the solution containing extracts from the stem was tested, revealing the presence of phytochemicals such as alkaloids, steroids, tannins, saponins, glycosides, terpenoids, flavonoids, reducing sugars, and coumarins. these findings were obtained using the standardized procedure described by a. j. harborne [14]. 2.4 determination of total phenolic content the total phenolic content (tpc) in the extract was evaluated using the folin-ciocalteu reagent with some modifications to a previously established method [15]. in short, 20 l of the extract at a concentration of 0.5 mg/ml was added in triplicate to 96-well plates. then, 100 l of folin-ciocalteu reagent and 80 l of na2co3 were added to each well. the absorbance was measured at 765 nm using a microplate reader (epoch2, biotek instruments, inc., usa) and expressed in mg of gallic acid equivalents (gae) per gram of extract, based on a calibration curve created from standard gallic acid. nirmal sharma et al./ bibechana 22 (2025) 141-150 143 2.5 determination of total flavonoid content the total flavonoid content (tfc) in the extracts was determined using a method with slight modifications from a previously reported study [15]. briefly, 20 l of plant samples at a concentration of 0.5 mg/ml was added to 96-well plates in triplicate. next, 110 l of distilled water was added to each well containing the plant samples, followed by 60 l of ethanol, 5 l of alcl3, and 5 l of ch3co2k. the absorbance was measured at 415 nm using a microplate reader and was expressed as milligrams of quercetin equivalent per gram of extract. 2.6 dpph radical scavenging activity the antioxidant capacity of the extracts was assessed using a modified 96-well plate method based on the colorimetric technique [16]. quercetin at a concentration of 20 g/ml was used as the positive control, while 50% dmso served as the negative control. each well in the 96-well plate received 100 l of either the positive control (quercetin), negative control (dmso), or plant samples, all in triplicate. following this, 100 l of dpph reagent was added to each well, and the plate was incubated in darkness for 30 minutes. after incubation, the absorbance was measured at 517 nm using a microplate reader. the dpph radical scavenging activity was then calculated using the following formula: % inhibition = ( acontrol −asample acontrol ) × 100 where, asample = absorbance of the sample acontrol = absorbance of the control 2.7 antibacterial activities lichen extracts were evaluated for antibacterial activity using the agar-well diffusion method. the test microorganisms were incubated for 12 hours at 37°c after being adjusted to a turbidity equivalent to 0.5 mcfarland standards (1.5 x 10ˆ8 cfu/ml or 10ˆ8 bacteria/ml) in mhb. using a sterile cotton swab, bacteria were evenly spread across mha plates. three wells, each approximately 4 mm deep and 6 mm in diameter, were made in the cultured mha plates using a cork borer. each well was then filled with 50 µl of lichen extract (50 mg/ml in 50% dmso). separate wells were used for the negative control, containing 50 µl of 50% dmso, and the positive control, containing 50 µl of 1 mg/ml neomycin. the plates were left at ambient temperature for 15 minutes to allow diffusion, then incubated for 18 to 24 hours at 37°c. after incubation, the zone of inhibition (zoi) for each extract was measured in millimeters 2.7.1 determination of minimum inhibitory concentration (mic) the minimum inhibitory concentration (mic) is the smallest concentration of a substance required to prevent any visible bacterial growth, determined using a slightly modified version of a previously established method [17]. it measures the effectiveness of a chemical against a specific type of bacteria and is typically expressed in mg/ml or µg. the mic was assessed for methanolic extracts or other solvent fractions of the plant extract that showed significant antibacterial activity. to prepare solutions with varying concentrations from 12.5 mg/ml to 0.097 mg/ml, 100 l of stock solutions (50 mg/ml) were serially diluted twice in 96-well plates. then, 5 l of bacteria (106 cfu/ml) was added to all wells except the negative control. the plates were covered and incubated at 37°c for 18 to 24 hours. after incubation, 0.003% resazurin solution was added to each well, followed by another incubation for three to four hours at 37°c. a blue color indicated no bacterial growth, while a pink color, resulting from the enzyme reductase, signaled bacterial presence. the well with a blue color represented the mic, or the lowest concentration required to inhibit bacterial growth. 2.7.2 determination of minimum bactericidal concentration (mbc) the minimum bactericidal concentration (mbc) is the lowest concentration of a substance needed to kill specific bacteria. in mbc assay, resazurin serves as a dye that changes color upon its conversion to resorufin, signaling the presence of viable cells (figure 2). using serially diluted plant extracts, the microdilution method is used to determine this concentration following the clsi protocol [18]. for the mic, higher concentrations were applied to mha plates and incubated for 18 to 24 hours at 37°c. bacterial growth was then observed on the mha plates, and the mbc was identified as the lowest concentration where no bacterial growth occurred. figure 2: reaction for the conversion of resazurin to resorufin during mic determination. nirmal sharma et al./ bibechana 22 (2025) 141-150 144 3 results and discussions 3.1 results 3.1.1 phytochemicals screening the results from the phytochemical screening, obtained through chemical tests, are presented in table 1 which also can indicate the different compound present in h. cirrhata. table 1: phytochemical screening serial no. group of compounds h. cirrhata 1 alkaloids ++ 2 flavonoids ++ 3 terpenoids ++ 4 glycosides ++ 5 polyphenols ++ 6 quinones ++ 7 tannins ++ 8 steroids – 9 saponins – 10 fatty acids – 11 proteins (xanthoprotein) ++ 12 coumarins ++ 13 anthraquinone – 14 reducing sugar ++ note: (++) indicates presence; (–) indicates absence. 3.1.2 estimation of total phenolic content (tpc) gallic acid equivalent (mg gae/g) was used to assess the total phenolic content in the crude extracts of h. cirrhata. the standard used to calculate tpc is gallic acid. the calibration curve is built using different final concentrations of gallic acid (10, 20, 40, 60, 80, and 100) µg/ml. using the regression equation (y = 0.017x+ 0.0552, r2 = 0.9907) derived from the gallic acid calibration curve, the tpc of the extracts was determined. tpc value for h. cirrhata was found to be 42.165± 0.98mg gae/g.the calibration curve of gallic acid is shown in figure 2 and the tpc value of extracts is represented in table 2. figure 3: calibration curve of gallic acid nirmal sharma et al./ bibechana 22 (2025) 141-150 145 3.1.3 estimation of total flavonoid content (tfc) using the usual technique and quercetin as a reference, the total flavonoid concentration of the crude lichen extract was estimated. the quercetin equivalent (mg qe/g of the extract's dry weight) was used to express the tfc value. the calibration curve is constructed using varying final concentrations of quercetin (100, 80, 60, 40, 20, 10) µg/ml. using the regression equation (y =0.0179x+ 0.0273, r2 = 0.9997) derived from the quercetin calibration curve, the tfc of the extract was determined. h. cirrhata had a tfc value of 11.789± 0.34 mg qe/g. figure 3 displays the quercetin calibration curve, and table 2 displays the tfc value for the extracts of lichens h. cirrhata. figure 4: calibration curve of quercetin. table 2: total phenolic content and total flavonoid content with standard deviation of crude extract of h. cirrhata name of lichen total phenolic content (mg gae/g) total flavonoid content (mg qe/g) h. cirrhata 42.165 ± 0.98 11.789 ± 0.34 3.1.4 anti-oxidant inhibition activities the radical scavenging activity of methanolic extract of lichen and their fractions are detailed in table 3. all extracts demonstrated concentrationdependent free radical scavenging activity in the dpph assay. among the different extracts, the ethyl acetate extracts of h. cirrhata exhibited the highest radical scavenging activity, with ic50 values of 34.14 ± 0.17 µg/ml. conversely, the lowest activity was observed in the methanol extract of h. cirrhata with ic50 values of 74.3 ± 1.13 µg/ml. 3.1.5 anti-bacterial activities along with mic and mbc the following zone of inhibition of lichens extract were evaluated against their antibacterial properties against the given bacteria. salmonella typhii (atcc 14028), shigella sonnei (atcc 25931), acinetobacter baumannii (atcc19606), escherichia coli (atcc 3292), staphylococcus aureus (atcc 25923), klebsiellapneumoniae (atcc 700603), and acinetobacter baumannii (atcc 19606) and zone of inhibition was observed which are presented in table 4 and figure 4. in addition, this lichen exhibited inhibition zones of 14 mm and 16 mm at identical concentrations against shigella sonnei and staphylococcus aureus. nirmal sharma et al./ bibechana 22 (2025) 141-150 146 table 3: antioxidant activity of different fractions of h. cirrhata in ic50 values lichen (fractions) ic50 values (µg/ml) crude 74.3 ± 1.13 hexane 44.35 ± 1.23 dcm 37.56 ± 0.49 ethyl acetate 34.14 ± 0.17 quercetin 62.87 ± 1.02 note: mean values ± sd (standard deviation) were measured. figure 5: showing inhibition zone of h. cirrhata in staphylococcus aureus b) showing inhibition zone of h. cirrhata in shigella sonnei. each methanolic lichen extract was evaluated against bacteria, showing the largest inhibition zones, along with corresponding mic and mbc values (see figure 5 and table 5). the mic for shigella sonnei was determined to be 195.312 g/ml, which was also the observed mbc. for staphylococcus aureus, the mic was 390.625 g/ml, matching its mbc. additional details of the mic and mbc values are presented in table 5, along with figures 5 and 6.each methanolic lichen extract was evaluated against bacteria, showing the largest inhibition zones, along with corresponding mic and mbc values (see figure 5 and table 5). the mic for shigella sonnei was determined to be 195.312 g/ml, which was also the observed mbc. for staphylococcus aureus, the mic was 390.625 g/ml, matching its mbc. additional details of the mic and mbc values are presented in table 5, along with figures 5 and 6. nirmal sharma et al./ bibechana 22 (2025) 141-150 147 figure 6: mic of lichen extracts and antibiotics against shigella sonnei : 5–7: (a–h: 12.5–0.098 mg/ml) for h. cirrahata, 8–10: antibiotic (neomycin a–h: 250–1.95 g/ml), 11: positive control (ah: media + bacteria), 12: negative control (a–h: media only), and b)mic of lichen extracts and antibiotics against staphylococcus aureus 5–7: (a–h: 12.5–0.098 mg/ml) for h. cirrahata, 8–10: antibiotic (neomycin a–h: 250–1.95 g/ml), 11: positive control (ah: media + bacteria), 12: negative control (a–h: media only). figure 7: mbc of lichen extracts and antibiotics against (a) staphylococcus aureus and (b)shigella sonnei table 4: zone of inhibition of h. cirrhata extract against bacterial strains serial no. name of bacteria positive control (mm) h. cirrhata extract (mm) 1 escherichia coli 18 – 2 shigella sonnei 25 14 3 salmonella typhi 20 – 4 acinetobacter baumannii 24 – 5 klebsiella pneumoniae 18 – 6 staphylococcus aureus 22 16 note: (–) indicates no zone of inhibition observed. nirmal sharma et al./ bibechana 22 (2025) 141-150 148 table 5: mic and mbc values of h. cirrhata name of bacteria mic (µg/ml) mbc (µg/ml) shigella sonnei 195.3125 195.3125 staphylococcus aureus 390.625 390.625 4 discussions lichens have been traditionally employed in medicine worldwide, with much of this knowledge originating from cultural practices. the primary secondary metabolites in this species are phenolic compounds, notably depsides and depsidones [19] , [20–22]. in this study, the total phenolic content (tpc) of the methanolic extract of h. cirrhata was found to be 42.165 ± 0.98 mg gae/g, surpassing the tpc values of acetone, water, and petroleum ether extracts of r. taitensis, which were 22.87 ± 0.12, 6.3 ± 1.06, and 12.58 ± 0.082 mg gae/g, respectively [23]. this indicates higher phenolic content in h. cirrhata. similarly, the total flavonoid content (tfc) in the crude extract was 11.789 ± 0.34 mg qe/g. in the methanolic extract of ramalina lacera, the tfc was 3.97 ± 0.3 mg re/g of dry weight (dw), while in the aqueous extract, it measured 0.01 ± 0.03 mg re/g dw [24].the ethyl acetate extract of h. cirrhata demonstrated the highest radical scavenging activity, with an ic50 value of 34.14 ± 0.17 µg/ml, likely due to its abundance of phenolic compounds with hydroxyl groups that act through various antioxidant mechanisms, such as free radical scavenging [25]. r. hossei and r. conduplicans showed radical scavenging activity at 79.05% and 72.63%, respectively [26], whereas c. furcata exhibited lower antioxidant activity, with percentages of 44.83% for the acetone extract, 47.39% for the methanol extract, and 29.99% for the aqueous extract. in comparison, the methanol extract of p. sulcata showed 71% activity [27,28]. the methanolic extract of h. cirrhata displayed inhibition zones of 14 mm and 16 mm against shigella sonnei and staphylococcus aureus, with minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) values of 195.312 g/ml and 390.625 g/ml, respectively. activity against gram-negative bacteria (e.g., escherichia coli, salmonella typhi) was absent. the absence of activity against gram-negative bacteria may be due to their unique outer membrane made of lipopolysaccharides, which acts as a barrier to many antimicrobial agents. efflux pumps and selective porin channels further limit compound entry. thus, the tested compound may either lack the ability to cross this barrier or be specific to gram-positive bacteria.in contrast, the ethanolic and hexane extracts of p. tinctorum exhibited smaller inhibition zones of 9.4 mm and 7.7 ± 0.2 mm, respectively, at a concentration of 300 mg/ml against methicillin-susceptible s. aureus (mssa, atcc 25923) [29]. additionally, studies show that methanol, ethanol, and acetone extracts from various lichens exhibit antibacterial activity against gram-positive bacteria, such as b. subtilis and s. aureus, while showing limited inhibition against gram-negative bacteria [29]. 5 conclusion the study highlighted the biological potential of h. cirrhata in terms of antioxidant and antibacterial properties. lichens have garnered significant interest recently due to their unique secondary metabolites. the biological activities of lichens are attributed to the secondary compounds produced by their mycobiont. consequently, this study focused on isolating bioactive compounds that could enhance the commercial value of these lichens in the pharmaceutical industry. disclosure statement the authors do not have any conflict of 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[26] s. kumar and a.k. pandey. chemistry and biological activities of flavonoids: an overview. the scientific world journal, 2013:162750, 2013. [27] m. kosanić and b. ranković. antioxidant and antimicrobial properties of some lichens and their constituents. journal of medicinal food, 14(12):1624–1630, december 2011. https://www.academia.edu/73252019/ https://www.academia.edu/73252019/ https://onlinelibrary.wiley.com/doi/10.1002/9781119593249.ch4 https://onlinelibrary.wiley.com/doi/10.1002/9781119593249.ch4 nirmal sharma et al./ bibechana 22 (2025) 141-150 150 [28] r. sargsyan, a. gasparyan, g. tadevosyan, and h. panosyan. antimicrobial and antioxidant potentials of non-cytotoxic extracts of corticolous lichens sampled in armenia. amb express, 11(1):110, july 2021. [29] p. s. a. i. shiromi, r. p. hewawasam, r. g. u. jayalal, h. rathnayake, w. m. d. g. b. wijayaratne, and d. wanniarachchi. chemical composition and antimicrobial activity of two sri lankan lichens, parmotrema rampoddense, and parmotrema tinctorum against methicillin-sensitive and methicillin-resistant staphylococcus aureus. evidence-based complementary and alternative medicine, 2021:9985325, 2021. introduction materials and methods collection and identification of lichens preparation lichen extract phytochemicals screening determination of total phenolic content determination of total flavonoid content dpph radical scavenging activity antibacterial activities determination of minimum inhibitory concentration (mic) determination of minimum bactericidal concentration (mbc) results and discussions results phytochemicals screening estimation of total phenolic content (tpc) estimation of total flavonoid content (tfc) anti-oxidant inhibition activities anti-bacterial activities along with mic and mbc discussions conclusion bibechana vol. 22, no. 1, april 2025, 52-62 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar physicochemical, antioxidant, and antimicrobial study in nepalese honey amrita adhikari, nabin kumar thapa, anita gurung, niranjan parajuli∗ 1centarl department of chemistry, tribhuvan university, kathmandu, nepal ∗corresponding author. email: niranjan.parajuli@cdc.tu.edu.np abstract five honey samples, mostly from western nepal, were analyzed for physicochemical properties, tpc, tfc, antioxidant, and antimicrobial assays. the results were found to be within the acceptable range, while some samples had higher moisture, hmf, and total ash levels. the tpc was in the range of 8.420 to 9.920 mg gae/g and the tfc was between 0.039 to 0.103 mg qe/g. the ic50 values were calculated of which forest honey was found to have the lowest ic50 value i.e. 7.735 ± 0.008 mg/ml. additionally, samples also showed a large zone of inhibition against four pathogens. besides, the correlation between physicochemical parameters, tfc, tpc, and antioxidant activity was established by using pearson’s correlation and pca. it displayed that the variables ic50, reducing sugar, hmf, and tfc in samples were positively correlated with one another and inversely with total ash (%), acidity as formic acid (%), and moisture (%). keywords physicochemical parameters, antioxidant, antibacterial. article information manuscript received: june 4, 2024; accepted: january 16, 2025 doi https://doi.org/10.3126/bibechana.v22i1.74118 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction bees naturally generate honey as a food item through the collection of either flower nectar from the family: apidae [1] or the waste of insects that consume living plant parts and insect secretion. the honey sourced from living plant parts and insect secretion is commonly categorized as honeydew honey [2]. since ancient times, honey has been utilized to cure illnesses such as eye diseases, infections, asthma, and fatigue [3]. it is composed of minor amounts of organic acids, 15-17 % water, and approximately 80-85 % sugars, vitamins, proteins, phenols, and flavonols [4]. mainly, fructose, glucose, and sucrose are three kinds of carbohydrates found in honey. in addition, honey contains nearly all minerals in minute amounts including potassium, sodium, phosphorus, sulfur, calcium, iron, manganese, magnesium, silicon, and copper. the most prevalent mineral element is potassium, which accounts for almost one-third of the overall amount [5]. the presence of potassium, cadmium, and nickel indicates honeydew honey [6]. it is suggested that these minor elements of honey are associated with various biological activities to exemplify antioxidant, antibacterial, antiviral, antiinflammatory, antiulcer, antihypertensive, vasodilator, antihypercholesterolemic, and antitumor activity [7]. it contains various enzymes which include diastase, invertase, catalase, glucosylcerami52 http://nepjol.info/index.php/bibechana niranjan.parajuli@cdc.tu.edu.np https://doi.org/10.3126/bibechana.v22i1.74118 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ amrita adhikari et al./ bibechana 22 (2025) 52-62 53 dase, glucose oxidase, α-amylase, β-glucosidase, αglucosidase, and proteases. diastase breaks down starch into dextrin and maltose contributing to the honey quality, while invertase transforms sucrose into glucose and fructose [8]. glucose oxidase is involved in the conversion of glucose to δgluconolactone, followed by hydrolysis of gluconic acid and hydrogen peroxide, providing honey with antimicrobial properties [9]. honey could be the best choice for use in medicinal value, as in recent times, the multi-drug resistance problem has arisen and this problem can be solved by the natural products singly or in combination with drugs. besides therapeutic benefits, some honey e.g. mad honey can also pose toxicity leading to a serious food safety concern. such toxicity and hallucinating effects are due to the honey bees collecting poisonous plants nectar like rhododendron species, coriaria arborea, and tripterygium wilfordii hook f.. mad honey contains natural plant poisons, such as pyrrolizidine, tutin, triptolide and grayanotoxins [10]. the chemical makeup, taste, color, and biological activities are primarily determined by its floral origin, species of bees, climate, and geographic area, however can additionally be altered by the weather circumstances, as well as their handling, packing, and storage [11]. in nepal, five honeybee species are found. apis cerana and apis mellifera are suitable for hive management and honey production whereas apis laboriosa, apis dorsata, and apis florea are wild species [12]. among them, only apis mellifera is an exotic species, while the remaining four species are indigenous to nepal [13]. the majority of the honey produced in nepal is the multi-floral origin, but some are also unifloral origins like chiuri, mustard, buckwheat, rudilo, sunflower, and litchi honey, as well as honeydew honey from pine, spruce (salle maha), and oak (dalle maha) trees mostly in mountain region [12]. for the import and export of honey, the global standard is contained in the codex alimentarius. the codex alimentarius standard, european honey directive, and national standard are the standards that set rules for food safety, regulation, and honey authenticity [14]. it has been reported that the various physicochemical parameters including moisture, sucrose, reducing sugar, total ash, acidity as formic acid, hydroxymethylfurfural (hmf), fructose/glucose ratio, etc are widely used to analyze botanical authentication of honey. in honey, glucose and fructose are present in higher amounts whereas twenty-two different compounds such as isomaltose, maltose, sucrose, etc are present in small amounts. further, a nondigestible molecule (fructooligosaccharides) supports the growth of intestinal bacteria and helps to enhance the human digestive system. thus, it is also named as prebiotics [15, 16]. honey also contains low-fat, watersoluble vitamins and vitamin c in higher amounts, whereas the fat-soluble vitamins and vitamin b are present in small amounts [17]. nepal has a vast array of honey types and huge potential for honey production, yet it has not fully reached its capabilities in honey harvesting due to limited research and investment in nepal. thus, a key goal of this study is to explore the physicochemical parameters, antioxidant properties, and antimicrobial test, and conduct principal component analysis on varieties collected which include local, market-sourced, and forest honey. 2 materials and methods 2.1 chemicals we acquired quercetin (cas no: 117-39-5) from sigma-aldrich in germany. gallic acid (cas no: 5995-86-8) and 2, 2-diphenyl-1-picrylhydrazyl (dpph) (cas no: 1898-66-4) were purchased from molychem in india and himedia (india), respectively. growth medium (mha and mhb) were obtained from sigma-aldrich. other chemicals were bought from fisher scientific (india). 2.2 collection of honey samples samples of honey were collected from multiple places, including pokhara, rukum, lamjung, and kathmandu (table 1). the honey types studied were forest honey, mad honey, mustard honey, chestnut honey, and indian brand-marketed honey. 2.3 physicochemical parameters the physicochemical parameters included by the international honey commission for the quality control of honey such as moisture, sucrose, reducing sugar, total ash, acidity as formic acid, hydroxymethyl furfural (hmf), and fructose/glucose ratio were analyzed [18]. moisture in honey, the moisture content was analyzed by operating the refractometric method with the help of an abbe refractometer [19]. total ash content five grams of honey were subjected to a muffle furnace at 55 °c for five hours. afterward, the ash was obtained by cooling it to room temperature and then weighed [20]. acidity as formic acid acidity as formic acid is calculated by using the titrimetric method [20]. amrita adhikari et al./ bibechana 22 (2025) 52-62 54 hydroxymethylfurfural the uv-spectrophotometric method was employed to analyze and determine the levels of hmf [18]. firstly, 25 ml water and 5 g honey were added to a 50 ml volumetric flask. further, solution i and ii of 0.5 ml carrez solution were added on, mixed, and diluted with water. after filtration, 5 ml of filtrate was taken in two test tubes. in one test tube, distilled water of 5 ml was added, while the other test tube received 5 ml of a 0.2% sodium bisulfite solution as the reference. the contents within each tube were effectively blended in a vortex mixer. subsequently, the sample’s absorbance was determined at 284 nm, and the absorbance of the reference was assessed at 336 nm. finally, the hmf (mg/100 g) content was computed based on the measurements. table 1: list of honey samples collected for the study from different regions of nepal. s. n. name of sample floral source botanical classification floral location local name 1 mustard honey mustard brassica napus pokhara tori 2 forest honey forest unspecified rukum vire rukum 3 mad honey multi-floral rhododendron arboreum and forest lamjung vire pokhara 4 indian brand marketed honey market unspecified kathmandu market honey 5 chestnut chestnut castanea sativa pokhara katus ph the ph of honey was measured by a ph meter. 3 g of sample of honey was dissolved in 30 ml of water and mixed by agitating for 30 minutes. at ambient temperature, the ph of the samples was determined [21]. reducing sugar the aoac (2005) method was used to analyze reducing sugar content in honey [20]. 1 gm of honey was added in 10 ml lead acetate solution (20%) taken in a volumetric flask of 250 ml which was diluted up to the mark and filtered. the filtrate (25 ml) was combined with 100 ml of distilled water in a 500 ml volumetric flask. a few drops of 10 % potassium oxalate solution were added until no more precipitate formed. in a 250 ml conical flask, 5 ml each of fehling a and b were combined with 10 ml of distilled water, boiled, and using the sample solution to titrate and find the amount of reducing sugar content. sucrose the fehling solution method was employed to determine the sucrose content in various types of honey [22]. the quantity of sucrose present was determined using the provided formula below: sucrose % = (total reducing sugars%−reducing sugars%)×0.95 2.3.1 glucose ratio the glucose percentage was determined using an iodometric method, and this amount was deducted from the percentage of reducing sugars to calculate the fructose percentage and the fructose-to-glucose ratio. the calculations were performed using the formulas provided below [23]. glucose % = n of thiosulphate × (blank − titre) × a× 100 0.1 n × b 2× 0.1n × b where a=0.009005, b= weight pf sample fructose % = reducing sugar %−glucose % fructose : glucose ratio = fructose % glucose % impurities 50 ml of water was used to dilute each honey sample of 10 g and blended in a shaker for about 30 minutes. filtration was done and the sample obtained was kept in the oven at 103 ºc for 10 minutes and the dried filter paper was weighed [21]. by using the formula the percentage of impurity was measured. i = m2 m1 × 100% ‘i’ represents the quantity of impurities (%), ‘m1’ represents the mass of the sample taken for analysis (g), and ‘m2’ represents the mass of residue left on the filter paper after drying (g). amrita adhikari et al./ bibechana 22 (2025) 52-62 55 2.4 total phenolic content as per the study, the total phenolic content was determined using the folin-ciocalteu method with fewer adjustments [24]. gallic acid was taken as a standard (1 mg gallic acid dissolved in 1 ml ethanol to create a gallic acid solution). it was serially diluted ranging from 10 to 100 µg/ml to prepare solutions of different concentrations. for each honey sample, 5 mg/ml of honey solution was prepared by dissolving in 70 % ethanol, 20 µl (at a concentration of 5 mg/ml) was mixed with 100 µl of folin-ciocalteu’s reagent (diluted 1:10 with water), and 80 µl of 1 m aqueous sodium carbonate solution (na2co3 ). after about 30 minutes at ambient temperature, the mixture’s absorbance at 765nm was analyzed using a microplate reader. the extracts’ total polyphenolic content was expressed as milligrams of gallic acid equivalent per gram of dry weight (mg gae/g) of the extract. this analysis was done in triplicate. 2.5 total flavonoid content as outlined by pham et al., the aluminum chloride colorimetric method was utilized to determine the total flavonoid content (tfc) with minor alternations [25]. in brief, a concentration of 5 mg/ml of honey was made ready adding 70 % ethanol. subsequently, 20 µl of each extract was combined with 100 µl of distilled water and 60 µl of ethanol. subsequently, 10 µl of 10% alcl3 and 10 µl of 1m ch3cook were added to each well. quercetin was used as the standard reference. after that, the mixture was left at room temperature for 30 minutes in the shade, after which the absorbance was measured at 415 nm using a microplate reader. the overall flavonoid concentration within the samples was expressed as milligrams of quercetin equivalent per gram of dry weight (mg qe/g) of the extract. this analytical process was conducted in triplicate. 2.6 antioxidant activity the assessment of antioxidant activity was conducted by employing the stable radical 2,2-dipheny1-picrylhydrazyl (dpph) [25]. 100 µl of dpph solution in methanol (0.1 mm ) along with 100 µl of honey solution made in methanol at different concentrations (1000, 500, 250, 125, and 62.5 µg/ml) were loaded into a 96-well plate. then, it was kept in the shade for 30 minutes and the absorbance was recorded at 517 nm. further, quercetin was employed as a standard. here, a reduction from dpph radical (purple) to diphenyl picryl hydrazine (yellow) was observed at varying concentrations. the antioxidant used for the determination of the ability to inhibit dpph radical was obtained by the below equation: % scavenging = a0 −at a0 × 100% here, “ao” represents the absorbance of control, while “at” corresponds to the absorbance of dpph when exposed to a test or reference sample. 2.7 antibacterial activity the antibacterial activity of honey samples at various concentrations (10% w/v, 20% w/v, 50% w/v, and 75% w/v) against four distinct bacterial strains ( namely: e. coli, s. aureus, s. shigella, k. pneumoniae) was examined through the agar well diffusion method on mha plates [26]. a 0.5 mcfarland equivalent of microorganism inoculum in mueller hinton broth (mhb) was spread on the mha plate’s surface using an autoclaved cotton swab. wells were bored by the clean and well-sterilized cork-borer in cultured mha media. then, a concentration of 100mg/ml of honey extracts was filled into the wells. for the positive and negative control, neomycin and distilled water were used respectively and incubated at 37ºc for 18 to 24 hours. finally, the zone of inhibition (zoi) was observed and measured by a ruler in mm. 2.8 statistical analysis the ms-excel was used to do a karl pearson correlation between the variables such as physicochemical parameters, tpc, tfc, and antioxidant activity. additionally, to correlate several physicochemical data (such as moisture content, sucrose, reducing sugar, total ash, acidity as formic acid, hmf, fructose/glucose ratio, and ph), tpc, tfc, and antioxidants. further, using r studio principal component analysis (pca) was performed. pca is a dimensionality reduction technique that transforms a set of numerous variables into a smaller set that retains most of the information from the original large data [27]. pearson correlation helps to determine the degree and direction of correlation. table 2 shows the degree of correlation as follows [28]. table 2: the degree of correlation is represented by the numerical values. amount of r strength of the correlation 0.0 < 0.1 no correlation 0.1 < 0.3 low correlation 0.3 < 0.5 medium correlation 0.5 < 0.7 high correlation 0.7 < 1 very high correlation note: ‘r’ indicates karl pearson’s correlation coefficient. amrita adhikari et al./ bibechana 22 (2025) 52-62 56 3 results and discussion 3.1 physicochemical-parameters-1 the following physicochemical parameters of all samples were determined and the results were mentioned below (table 3). 3.1.1 moisture the standard set by the codex alimentarius must be below 20%. the honey sample above the set standard will undergo deterioration by fermentation [29]. the water content of mustard, market, and chestnut honey fell within the accepted range, while forest honey (24.5%) and mad honey (25.7%) exceeded the standard range. the level of moisture is determined by factors like the relative humidity of the plant source, processing techniques, and storage conditions [30]. moisture plays a crucial role in regulating microbial growth and the potential spoilage of honey through fermentation [31]. 3.1.2 total ash content the total ash content in samples is useful for the identification of honey. here, the total ash content was from 0.1 to 0.7 in which all samples were within the standard limit except forest honey with a 0.7 value and the lowest shown was market honey [32]. out of five samples, one sample (forest honey) was out of range. 3.1.3 acidity as formic acid inorganic ions, organic acids (sulfate, chloride, and phosphate), esters, and lactones are present in honey as free acidity[30]. vitamin c, protein, and phenolic acids are the proton donors and help in identifying the quality of honey. as the honey worsens its free acidity increases and fermentation is seen by the conversion of sugar to organic acids. acidity as % formic acid consists of 0.001 to 0.01%. the lowest value of acidity as % formic acid is of indian brand market honey and the highest is of mustard and forest honey which are present in an acceptable range. 3.1.4 hydroxymethylfurfural (hmf) the hmf of various samples was from 2 to 87 mg/kg of which the lowest was that of forest honey and the highest was of indian brand market honey which exceeded the given standard value. hmf levels serve as a common measure for assessing the freshness of honey, as it is typically undetectable or found in minute amounts in newly harvested kinds of honey. however, its content tends to increase due to processing and aging [33]. indian brand market honey is processed honey and is made available in the market after a prolonged period, this could potentially account for the elevated levels of hmf observed in market honey. 3.1.5 reducing sugar the reducing sugar of different samples of honey was from 63.8 to 74.3 %, in which the highest amount of reducing sugar was present in market honey and the least in mad honey. the reduced sugar content in all the analyzed samples is up to the standard range. the amount of sugar present in honey is influenced by factors such as the source of nectar from different types of flowers, the prevailing climate, additionally the methods used in handling and keeping [34]. 3.1.6 sucrose among the five honey samples, the sucrose content ranged from 0.1% to 7.2%. the lowest sucrose content (0.1%) was found in mad honey, while the highest content (7.2%) was observed in chestnut honey. the sucrose content of different honey from different places was within the standard range ( 10). 3.1.7 fructose/glucose ratio the chestnut honey exhibited a fructose/glucose ratio of 1.34, while the other honey samples showed a ratio of 1.2. the carbohydrate composition of honey is responsible for its capacity to retain moisture, prolong shelf life, react in microwaves, and enhance the development of colors and flavors. the fructose-to-glucose ratio determines the ability to crystallize honey. honey crystallizes slowly if the fructose/glucose ratio exceeds 1.3 whereas it occurs quicker when the proportion is less than 1.0 [35]. 3.1.8 ph the honey samples’ ph values varied from 3.26 to 5.80 depending on organic acids and these organic acids are responsible for the aroma and antimicrobial activity of honey. all the honey samples were within the standard ph range except the chestnut honey. the ph difference is based on the maturity period, the concentration of minerals, and chemical composition [36]. the ph of the floral and wild honey in this research work shows a resemblance with the range of ph in a study by alves et al. [37]. 3.1.9 impurities the impurities percentage in the samples was in the range of 1.11%-6.77%. the highest impurities were found in market honey. this might be due to the adulteration, additives, and inclusion of other substances during processing. amrita adhikari et al./ bibechana 22 (2025) 52-62 57 table 3: physicochemical parameters and impurities in five honey samples. s.n. name of sample moisture (%) total ash (%) acidity as formic acid ph impurity (%) hmf reducing sugar (%) sucrose (%) fructose/glucose ratio 1 mustard honey 21.3 0.2 0.01 3.26 2.50% 40 68.5 3.4 1.2 2 forest honey 24.5 0.7 0.01 4.22 4.10% 2 63.9 0.2 1.2 3 mad honey 25.7 0.4 0.004 4.42 4.66% 12 63.8 0.1 1.2 4 market honey 19.2 0.1 0.001 4.78 6.77% 87 74.3 1.0 1.2 5 chestnut honey 20.2 0.4 0.004 5.80 1.11% 68.1 7.2 1.34 6 standard range ≤ 23 ≤ 0.5 3.5-5.5 ≤ 40 ≥ 60 ≤ 10 ≥ 0.95 3.2 tpc, tfc, and antioxidant activity the tpc, tfc, and free radical scavenging activity were assessed in various honey extracts, revealing tpc value in a range of 8.420 ± 0.703 to 9.920 ± 0.649 mg gae/g, while tfc value was less than 1 mg qe/g in all the analyzed honey samples. among the collected samples, the antioxidant activity (based on ic50 value) of honey samples followed the order: forest honey > mad honey > chestnut honey > mustard honey > indian brand market honey. in comparison to the standard quercetin (ic50 value = 0.34 ± 4.11), all analyzed honey samples displayed lower antioxidant activity. these values are compared with data from similar studies on honey’s antioxidant properties and found similar results [38–41]. the tpc, tfc, and antioxidant activity (ic50 values mg/ml) are displayed in fig 1, fig 2, fig 3, and table 4. table 4: tpc, tfc, and ic50 values of different honey samples. honey samples tpc (mg gae/g) tfc (mg qe/g) ic50 (mg/ml) mustard honey 8.976± 1.395 0.053± 0.004 11.628± 0.004 forest honey 9.809± 1.345 0.039± 0.011 7.735± 0.008 mad honey 9.106± 1.473 0.044± 0.008 10.2± 0.002 indian brand market honey 9.920± 0.649 0.103± 0.066 12.51± 0.003 chestnut honey 8.420± 0.703 0.055± 0.012 10.92± 0.005 quercetin 0.34± 4.11 figure 1: bar diagram of tpc of honey samples. figure 2: bar diagram of tfc of honey samples. amrita adhikari et al./ bibechana 22 (2025) 52-62 58 figure 3: the plot of % inhibition of dpph vs concentration of different honey samples. 3.3 correlation of bioactive compound and antioxidant activity we observed the normal distribution of the response variable (antioxidant activity) (p>0.05) using the shapiro-wilk normality test [42] the linear correlation between the two variables was assessed by using the karl pearson correlation coefficient. the results of the correlation between the variables are provided in table 5. the moisture (%) exhibited a moderately negative relation with sucrose and hmf, while it displayed a strongly negative relationship with reducing sugar content (%), tfc, and ic50 value. the sucrose (%) had a minimal connection with acidity in the form of formic acid (%) and tfc. sucrose (%) demonstrated a highly negative correlation with tpc (-0.816), but a notably positive correlation with the ratio of fructose/glucose ratio (0.897). the percentage of reduced sugar exhibited a positive correlation with tfc, hmf, and ic50 values. the proportion of total ash (%) showed no significant correlation with the fructose/glucose ratio, tpc, and ph. however, it revealed a strong negative correlation between tfc and ic50 value. hmf displayed a markedly positive correlation with tfc and ic50 values. hmf has an extremely strong positive relationship with the tfc (0.909). the relationship between tpc and tfc is positive, suggesting that most of the phenolic compounds in these honey types are flavonoids. in the provided table 5, tpc and tfc exhibit a moderately negative correlation with the ic50 value for dpph free radical scavenging. this implies that higher tpc and tfc levels correspond to lower ic50 values, indicating that as the phenolic and flavonoid content increases, the honey’s ability to neutralize free radicals improves. this connection between phenolic/flavonoid content and antioxidant activity aligns with the findings of numerous studies. conversely, the correlation between tfc and ic50 value (a measure of the level of antioxidants) is positive according to the table. this suggests that antioxidant activity isn't solely attributed to flavonoids but might be influenced by other factors such as hmf, enzymes, proteins, and minor constituents. in certain instances, flavonoids might even interact with other compounds that possess antioxidant properties, potentially diminishing overall antioxidant effectiveness. similar outcomes have been observed in prior honey-related research [43–45]. table 5: karl pearson’s correlation between physicochemical parameters, tpc, tfc, and ic50. correlation moisture (%) sucrose (%) reducing sugar (%) total ash (%) acidity as formic acid (%) hmf (mg/kg) fructose/glucose ratio tpc (mggae/g) tfc (mgqe/g) ph ic50 moisture (%) 1 sucrose (%) -0.577 1 reducing sugar (%) -0.907 0.209 1 total ash (%) 0.685 -0.160 -0.827 1 acidity as formic acid (%) 0.390 -0.058 -0.548 0.502 1 hmf (mg/kg) -0.605 -0.253 0.873 -0.828 -0.447 1 fructose/glucose ratio -0.395 0.897 0.049 0.097 -0.250 -0.431 1 tpc (mggae/g) 0.097 -0.816 0.216 0.036 -0.027 0.520 -0.743 1 tfc (mgqe/g) -0.759 -0.027 0.952 -0.767 -0.696 0.909 -0.083 0.400 1 ph -0.315 0.489 0.174 0.093 -0.670 -0.195 0.792 -0.304 0.227 1 ic50 -0.752 0.326 0.833 -0.980 -0.573 0.742 0.099 -0.180 0.754 0.076 1 3.4 principal component analysis of different variables in this analysis using principal component analysis on the dataset, 50.4% of the variation is explained by the first principal component (pc1), and 31.4% is explained by the second principal component (pc2). the scree plot, shown in fig 4, visually displays the percentage of variation represented by each principal component. it reveals that there are two prominent principal components that, when combined, account for 81.8% of the total variance present in the five distinct samples of honey. the two-dimensional graph of two prominent principal components that includes 81.8% of the total variation of the data is shown in fig 5. fig 5 is a variable correlation plot that shows the relationship between the variables of honey samples. hmf, tfc, reducing sugar, and fructose/glucose showed a better representation of variables. reducing sugar, tfc, and hmf again fructose/glucose ratio, ph, and sucrose are positively correlated. kowalski et al. also showed a positive correlation with fructose/glucose ratio, ph, and sucrose[46]. ic50 is highly positively correlated with each other and negatively correlated with total ash (%), acidity as formic acid, and moisture (%). total ash and f/g ratio, acidity as formic acid, and tpc are approximately right-angled indicating no correlation between them. https://quantifyinghealth.com/report-shapiro-wilk-test/ amrita adhikari et al./ bibechana 22 (2025) 52-62 59 a pca biplot is shown in fig 6, honey samples mustard, chestnut, forest, mad, and market honey were given by points 1, 2, 3, 4, and 5 respectively and the variables were represented by the vectors. based on this biplot, points: 2, 4, and 5 have a major impact on the variability of the data and in principal components, and observations 2 and 3 share similarities in terms of their variability in their respective datasets. the components of biplot dim 1 and 2 gave 81.8% of the variance in the descriptive profile of five different samples. kowalski et al. showed the first two components of 68.67% of the variance [45]. figure 4: scree plot of the principal components. figure 5: the principal component plot of variables. figure 6: principal component biplot of observations and variables. 3.5 antibacterial activity the agar well diffusion method was employed to assess the susceptibility of four bacterial strains (e. coli, s. aureus, s. shigella, and k. pneumoniae) to various concentrations of samples, as outlined in table 6. the largest zone of inhibition (zoi), measuring 36 mm, was observed at a 50% concentration of two honey samples (chestnut honey and forest honey) against e. coli. mustard honey and market honey exhibited no significant impact on e. coli. however, market honey demonstrated the highest inhibitory effect against the other three bacterial species: s. aureus (34 mm), s. shigella (35 mm), and k. pneumoniae (30 mm). mustard honey was also ineffective against s. aureus but showed a moderate effect against s. shigella and k. pneumoniae. this study found antimicrobial activity at 50% v/v of sample concentration of almost all samples to the four microorganisms (e. coli, s. aureus, s. shigella, k. pneumoniae). fj et al. have also reported similar antimicrobial activity in all the analyzed honey samples at a concentration greater than 60% v/v against the four different microorganisms (e. coli, s. aureus, p. aeruginosa, and b. subtilis) [46,47]. in general, the zone of inhibition tended to be slightly larger for gram-negative bacteria in contrast to gram-positive bacteria. this divergence in results can be attributed to the structural characteristics of the bacteria and their distinct mechanisms of toxicity. the major antibacterial element in honey is primarily hydrogen peroxide which disturbs the structure and function of bacteria resulting in their diminished viability due to the oxidation of their constituent molecules [48]. the relative amounts of glucose oxidase, which bees create, and catalase from flower pollen affect its levels [9]. amrita adhikari et al./ bibechana 22 (2025) 52-62 60 table 6: zone of inhibition of honey samples at different concentrations. samples e. coli (mm) s. aureus (mm) s. shigella (mm) k. pneumoniae (mm) 10% 20% 50% p.c. 10% 20% 50% p.c. 10% 20% 50% p.c. 10% 20% 50% p.c. chestnut honey 12 22 36 14 8 8 9 12 12 24 26 13 0 9 10 16 forest honey 18 20 36 18 0 0 0 10 0 28 29 12 25 28 28 15 mad honey 10 22 32 19 12 22 25 0 0 22 28 11 0 0 0 0 mustard honey 0 0 0 0 0 0 0 23 22 28 30 22 25 25 30 20 market honey 0 0 0 0 18 22 34 23 24 28 35 20 28 30 30 20 4 conclusion a comprehensive examination of five honey samples gathered from diverse regions of nepal was conducted and considerable variability was found in the physicochemical parameters, tfc, tpc, antioxidant activity, and antibacterial activity. it might be due to unique geographical regions and botanical origins. the ph and impurities of all the samples examined were within the range of the quality standard except for moisture (due to premature harvest), ash content (indicates honeydew honey), and hmf (due to processing and storage conditions). indian brand market honey displayed comparatively lower antioxidant properties among the samples, possibly due to ingredient loss during processing and packaging, and exhibited lower antioxidant activity. the samples were very efficient in opposition to the tested gram-negative bacteria displaying a high zone of inhibition, 36 mm at a 50% concentration of two types of honey (chestnut honey and forest honey(r) against e. coli. market honey exhibited noteworthy inhibitory effects against s. aureus (34 mm), s. shigella (35 mm), and k. pneumoniae (30 mm). the findings of this study demonstrated the important physiochemical parameters, tpc, tfc, and potential of honey ranging from its antioxidant properties to its antimicrobial activity, suggesting it is a natural therapeutic agent. further study is necessary to identify the bioactive substances, their particular targets, and their mechanisms of operation as antioxidant and antibacterial agents. abbreviations mha muller hinton agar tpc total polyphenol content tfc total flavonoids content gae gallic acid equivalent qe quercetin equivalent dmso dimethyl sulphoxide dpph 2, 2 diphenyl-1-picrylhydrazyl ic50 concentration provides 50% inhibition mhb muller hinton broth zoi zone of inhibition mg milligram µl microliters dftqc department of food technology and quality control ihc international honey commission mgo methylglyoxal hmf 5-hydroxymethylfurfural pca principal component analysis f/g(f/g) fructose/glucose ratio cfu/ml colony-forming unit per milliliter mdr multidrug-resistant ros reactive oxygen species conflicts of interest the authors declare no conflicts of interest. authors contributions conceptualization, n.p.; methodology, a.a.; writing-original draft preparation, n.k.t, a.a.; supervision, n.p, review, a.g.; all authors have read and agreed to the published version of the manuscript. acknowledgments the authors would like to express their gratitude towards the dftqc, babarmahal, kathmandu, for laboratory support. references [1] s. samarghandian and et al. honey and health: a review of recent clinical research. pharmacognosy research, 9(2):121–127, 2017. 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[48] g. mcdonnell. the use of hydrogen peroxide for disinfection and sterilization applications. john wiley & sons, ltd, 2014. introduction materials and methods chemicals collection of honey samples physicochemical parameters glucose ratio total phenolic content total flavonoid content antioxidant activity antibacterial activity statistical analysis results and discussion physicochemical-parameters-1 moisture total ash content acidity as formic acid hydroxymethylfurfural (hmf) reducing sugar sucrose fructose/glucose ratio ph impurities tpc, tfc, and antioxidant activity correlation of bioactive compound and antioxidant activity principal component analysis of different variables antibacterial activity conclusion bibechana vol. 20, no. 3, december 2023, 275-284 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar cr3+ substitution effect on co-cu and cu-co nano ferrites on structural and morphological properties d. parajuli1,∗, n. murali2, k. samatha3 1research center for applied science and technology, tribhuvan university, kirtipur 2department of engineering physics, auce (a), andhra university, visakhapatnam, india 3department of physics, aucst, andhra university, visakhapatnam, india ∗corresponding author. email: deepenparaj@gmail.com abstract the cr3+ substituted co-cu (co0.7cu0.3fe2−xcrxo4) and cu-co (cu0.7co0.3fe2−xcrxo4) where x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.25 nanoferrite composite were prepared with the sol-gel approach. their structural, dc electrical resistivity and magnetic properties were analyzed. xrd shows the single-phase spinel ferrite. adding cr3+ ions decreases the lattice volume and the size of the crystallite respectively. fesem images show non-spherical particles on a largely uniform surface shape with decreasing grain size on doping cr3+ . the ftir pattern supports the xrd patterns for spinel ferrite. keywords nanoferrites, cr3+ substitute, xrd, fesem, ftir. article information manuscript received: september 6, 2023; accepted: october 13, 2023 doi https://doi.org/10.3126/bibechana.v20i3.58411 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the investigation of nano-scale magnetic materials and their properties is currently a highly active area of research due to their unique and captivating attributes. these properties often differ from those of larger bulk substances due to their high surface-to-volume ratio [1–3]. nanoscale particles, with applications in diverse fields such as bioprocessing, color imaging, memory storage devices, ferrofluids, and magnetic refrigeration, have gained significant attention [4–6]. ferrites can be categorized as either soft or hard based on their magnetization and demagnetization characteristics [7]. these ferrites encompass four crystal chemistry categories: spinel ferrites, garnet ferrites, magnetoplumbite ferrites, and orthorhombic ferrites [8–10]. among these, spinel ferrites, denoted by the chemical formula mfe2o4 where m represents a divalent metal cation, have emerged as the most extensively researched due to their remarkable optical and magnetic properties [11–13]. spinel ferrites find applications in sensors, electromagnets, optoelectronic components, high-frequency devices, and more [14, 15]. they exhibit exceptional attributes such as higher resistivity values, magneti275 http://nepjol.info/index.php/bibechana deepenparaj@gmail.com https://doi.org/10.3126/bibechana.v20i3.58411 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ d. parajuli et al./ bibechana 20 (2023) 275-284 276 zation, permeability, and lower eddy current losses [16]. the distinct properties of spinel ferrites can be influenced by factors such as sintering temperature, preparation methods, choice of dopant ions, particle size, and agglomeration [17–19]. extensive studies have focused on utilizing divalent and trivalent metal ions to enhance the electrical, optical, and magnetic characteristics of ferrites. notable substitutions, like replacing fe3+ with cr3+ in cobalt ferrite, have been explored without altering the spinel structure [20]. while there has been considerable exploration of divalent ion replacements, trivalent cations have not been as extensively studied as potential substitutes in spinel materials [21]. the most notable cobalt and spinel ferrite compound is cofe2o4, which possesses a combination of advantageous features suitable for high-density magnetic recording applications. these include low cost, high coercivity, mechanical hardness, and chemical stability, making it an ideal choice [22]. within this structure, half of the fe3+ ions occupy tetrahedral sites, while the remaining half occupies octahedral sites, resulting in an inverse spinel configuration [23, 24]. by substituting different metal ions into the cobalt lattice, ferrite materials with novel properties are generated. the characteristics of these materials are significantly influenced by factors such as preparation conditions, the quantity and type of substituent [17,25–28]. when non-magnetic copper is introduced as a substitution into the cobalt ferrite lattice, it is expected to induce distortions in the spinel structure [29–32]. the addition of copper results in an intriguing distribution of cations across the interstitial sites a and b within the cobalt ferrite lattice [33]. cu2+ is a jahn-teller ion with degenerate orbitals, exhibiting high electrical conductivity in its ground state [34]. the introduction of cu2+ ions can induce crystal distortions [35]. reports suggest that the positioning of cu2+ ions at a and b sites influences the extent of crystal distortion they cause [36–38]. our recent research has investigated the impact of cr3+ substitution in cobalt-copper ferrite compositions (co0.7cu0.3fe2−xcrxo4) and cu0.7co0.3fe2−xcrxo4) [2,39–42]. it was observed that the inclusion of cr3+ions in the cobalt ferrite lattice leads to a decrease in saturation magnetization due to the lower magnetic moment of cr3+ ions compared to fe3+ ions. additionally, the electrical resistivity increased as the concentration of cr3+ ions rose. this phenomenon can be attributed to the single stable oxidation state of chromium ions, which reduces the efficiency of conduction involving fe2+ and fe3+ ions, resulting in higher resistivity. various techniques have been employed to produce cobalt-copper ferrite nanoparticles [43,44]. among these, the sol-gel process, known for generating heterogeneous and crystalline nanoparticles, stands out as a chemical method capable of effectively producing ferrite nanoparticles [45]. this process involves hydrolyzing and condensing metal precursors to form a three-dimensional inorganic system. metal precursors are utilized in this lowtemperature synthesis process [46]. this study aims to investigate the structural and morphological properties of co-cu (cu0.7co0.3fe2−xcrxo4) and cu-co (co0.7cu0.3fe2−xcrxo4) nanoferrites at varying levels of x, specifically x = 0.0, 0.05, 0.1, 0.15, and 0.2. the synthesis of the samples will involve utilizing the sol-gel auto-combustion method. this analysis will employ techniques such as xray diffraction (xrd), field emission scanning electron microscopy (fesem), and fourier-transform infrared spectroscopy (ft-ir) to examine the resulting structures and morphologies. 2 experimental techniques the initial precursors for the synthesized materials include cobalt, copper, iron, chromium nitrates, and citric acid, all obtained from sigma aldrich with a purity of 98%. a chelating agent, citric acid, was used to form complexes with the metal nitrates. to create the citric acid solution, the nitrates were mixed with citric acid in a 1:1 ratio. the resulting mixture was stirred magnetically at temperatures between 80 and 900 celsius for a duration of 10-12 hours, leading to the formation of a viscous gel. this gel was then subjected to drying at 1000 degrees celsius for 6 hours. the product was decomposed using spontaneous self-ignition and subsequently powdered using a mortar and pestle. the powdered material was annealed at 11000c for 4 hours to eliminate impurities. phase identification of the cr3+ substituted co-cu (co0.7cu0.3fe2−xcrxo4) and cu-co (cu0.7co0.3fe2−xcrxo4) nanoferrites was carried out using x-ray diffraction (xrd) with a cu-k x-ray radiation source. x’pert pro software was employed to analyze the x-ray diffraction patterns within the range of 20 to 800 diffraction angles. the surface morphology and elemental distribution of the synthesized samples were studied using fesem (field emission scanning electron microscopy) models quanta 250 and fei d9393. furthermore, different vibrational modes in the prepared samples were determined using ftir (fourier-transform infrared) spectrometers, 400 ftir, and fir (farinfrared). force constants calculations v21 = 1 2πc √ k µ (1) where µ = µ1µ2 µ1 + µ2 for two atoms systems. tetrad. parajuli et al./ bibechana 20 (2023) 275-284 277 hedral and octahedral force constants kt and ko are directly proportional to the vibration frequency and molecular weights (µa, µb) by the following relations as suggested by waldron [47]: kt = 4π2c2µav 2 1 (2) k0 = 4π2c2µbv 2 2 (3) cation distribution data was used to estimate the molecular weights of aand b-sites. the molecular weights (µa and µb) and force constants (kt and ko) are directly proportional to each other. the values of tetrahedral and octahedral radii (ra and rb) can be calculated using the equations given below: ra = cobalt content×rco+copper content×rcu+ iron content × rfe and rb = 1 2 [cromium content × rcr + iron content × rfe] the theoretical lattice constants have also been estimated using the following formulae by proposing the cationic distribution of metal ions in the spinel lattice. ra = (u− 1 4 )ath √ 3−r0 (4) rb = ( 5 8 − u)ath −r0 (5) ath = 8 3 √ 3 [ (ra +r0) + √ 3(ra +r0) ] (6) where, ra and rb are radii of tetrahedral and octahedral sites respectively. ath is theoretical lattice constants. ro is the radius of the oxygen ion. u is the oxygen positional parameter. for the fcc structure, ro is 0.375. in the co-cu ferrite system, the radii of cr3+ and co2+ ions are greater than the space occupied by the oxygen ions. this will cause distortion in the cubic lattice and therefore the oxygen parameter may differ from its usual value of 3/8 [48]. 3 results and discussion 3.1 xrd study the x-ray diffraction (xrd) patterns of cr3+ substituted co-cu (co0.7cu0.3fe2−xcrxo4) and cuco (cu0.7co0.3fe2−xcrxo4) nanoferrites, where x = 0.0, 0.05, 0.1, 0.15, 0.2, and 0.25, are presented in figure 1 (a) and (b). these patterns reveal the presence of a single-phase spinel structure [?,35,49], specifically related to the fd3m space group with a card number of 22-1086 [50]. the xrd patterns exhibit distinct and well-defined peaks in the (111), (220), (311), (222), (400), (422), (511), (440), (620), and (533) planes, indicating a high degree of crystallinity that aligns closely with existing literature [28,51,52]. the values in table 1 exhibit a gradual decrease due to the substitution of cr3+ions. for cocu nanoferrites, the lattice parameter reduces from 8.4498 å to 8.4321 å, while for cu-co nanoferrites, it decreases from 8.4441 å to 8.4099 å. this decrease is attributed to the larger ionic radii of fe3+ ions (0.645) compared to cr3+ ions (0.615) [53]. 3.2 fesem analysis utilizing field effect scanning electron microscopy (fesem), the characterization of shape and grain size in cr3+ substituted co-cu (co0.7cu0.3fe2−xcrxo4) and cu-co (cu0.7co0.3fe2−xcrxo4) nanoferrites, where x = 0.0, 0.05, 0.1, 0.15, 0.2, and 0.25, has been conducted. the fesem micrographs of the synthesized nanoferrites are depicted in figures 3 (a) and (b). extensive research has been undertaken by various investigators to gain a deeper understanding of fine-grain morphology [54,55]. the fesem micrographs reveal agglomerated, spherical, refined, and densely packed magnetic nanoparticles with an average grain size ranging from 50 to 100 nm. remarkably, this study corroborates the findings by establishing a robust correlation between the grain size deduced from the observed fesem micrograph analysis and the crystallite size determined from the xrd diffraction patterns of the synthesized samples [53]. d. parajuli et al./ bibechana 20 (2023) 275-284 278 figure 1: (a) and (b): xrd images of cr3+ doped co-cu and cu-co nano ferrite. figure 2: lattice constant and crystallite size vs. composition of the cr3+ substituted co-cu and cu-co nano ferrite. d. parajuli et al./ bibechana 20 (2023) 275-284 279 table 1: experimental values for different concentrations of the samples composition (x) cr3+ substituted co-cu cr3+ substituted cu-co lattice constant (å) crystallite size (nm) lattice constant (å) crystallite size (nm) x = 0.0 8.4498 44 8.4441 19.28 x = 0.05 8.4471 34 8.4399 22.33 x = 0.1 8.4453 36 8.4099 32.92 x = 0.15 8.4419 32 8.4210 27.71 x = 0.2 8.4321 34 8.4375 30.04 x = 0.25 8.4411 28 8.4428 23.74 figure 3: (a) and (b): fesem images of cr3+ substituted co-cu and cu-co nanoferrite. the substitution flexibility within available lattice sites diminishes as particle growth occurs, particularly when the chosen substituted element exhibits a pronounced affinity for a specific site. this results in a more controlled nucleation process and particle size. it is widely recognized that cobalt and chromium ions exhibit a strong preference for occupying octahedral sites within the lattice structure [56]. 3.3 ftir analysis ftir spectroscopy is employed to analyze vibrational modes, investigate structural stability, and assess cation distribution within interstitial sites. figures 4 (a) and (b) display the typical ftir spectra of cr3+ substituted co-cu (co0.7cu0.3fe2−xcrxo4) and cu-co (cu0.7co0.3fe2−xcrxo4) nano ferrites, where x = 0.0, 0.05, 0.1, 0.15, 0.2, and 0.25. these spectra were obtained using the samples prepared by the sol-gel method, with samples sintered at 11000c for 4 hours. the transmittance spectra were executed within wavenumbers of 350 to 800 cm−1 at room temperature. notably, below 800 cm−1, the presence of two prominent absorption bands affirms the formation of a spinel structure in the synthesized ferrites [57]. furthermore, these spectra offer insights into the functional groups present in the ferrite compositions. two distinct vibrational bands, labeled v1 and v2, arise due to stretching vibrations occurring at both octahedral and tetrahedral sites. the vibrational band v1 corresponds to the stretching vibrations of m3+-o2 (m3+ = cr3+ and fe3+) bonds in octahedral sites. in contrast, the vibrational band v2 can be attributed to the intrinsic vibrations of m2+-o2 (m2+ = co2+, cu2+, and fe2+) bonds in tetrahedral sites. this distinction arises due to the shorter fe-o bond length (0.189 nm) in tetrahedral sites compared to octahedral sites (0.199 nm). consequently, all ferrites exhibit these d. parajuli et al./ bibechana 20 (2023) 275-284 280 two distinct bands, influenced by the closer coupling of fe3+ ions at a sites rather than b sites. the positions of these vibrational bands alter as the cr3+ doping density increases. this phenomenon is due to the substitution of larger fe3+ ions by smaller cr3+ ions, resulting in a change in site radius. a notable relationship between site radius and fundamental frequency is observed, where a decrease in site radius leads to an increase in the fundamental frequency [18]. the presence of substituted cr3+ ions disrupts the (fe3+ o2) connections and perturbs the lattice structure, leading to a broadening of the high-frequency absorption band [58]. table 2 provides the a and b band positions for samples at different levels of cr3+ doping. figure 4: (a) and (b): ftir spectra of cr3+substituted co-cu and cu-co nanoferrite. 4 conclusion the cost-effective sol-gel auto-combustion technique was successfully utilized to synthesize single-phase, well-crystallized ultrafine crystals of cr3+ substituted co-cu (co0.7cu0.3fe2−xcrxo4) and cu-co (cu0.7co0.3fe2−xcrxo4) nanoferrites, where x = 0.0, 0.05, 0.1, 0.15, 0.2, and 0.25. the resulting ferrite samples exhibit a face-centered cubic structure characterized by the fd-3m space group. d. parajuli et al./ bibechana 20 (2023) 275-284 281 the crystallite size of cr3+ substituted co-cu is larger than that for cu-co. notably, the cation distribution analysis indicates a preference for octahedral b-sites for co2+, cu2+, and cr3+ ions within the lattice. the force constant is directly proportional to the atomic weights of the constituents in the respective lattice sites. the data reveals that the cu-co ferrite substituted with cr is slightly more efficient than its counterpart. data declaration data can be obtained from the corresponding author on request. competing interest the authors declare they have no competing interests. references [1] s. akter, m. n. i. khan, f. ferdous, h. n. das, and i. m. syed. analysis of the influence of trivalent cr3+ doping on the structural and electromagnetic properties of cu0.5mg0.5crxfe2−xo4 nanoferrites. aip adv., 12:95015, 2022. 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[58] m. a. abdo s. f. mansour and s. m. alwan. the role of cr3+ ions substitution on structural, magnetic and dielectric modulus of manganese zinc nanoferrites. ceram. int., 44:8035, 2018. introduction experimental techniques results and discussion xrd study fesem analysis ftir analysis conclusion bibechana vol. 21, no. 3, december 2024,300-310 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar effect of blood flow through mild stenosed artery with effective viscosity bishnu prasad bhandari1,2, jeevan kafle1, chudamani pokharel1,3,∗ 1central department of mathematics, tribhuvan university, kathmandu, nepal 2nepal engineering college, pokhara university, changunarayan, bhaktapur, nepal 3dhawalagiri multiple campus, tribhuvan university, kathmandu, nepal ∗corresponding author: email: chuda.pokherel@dmc.tu.edu.np abstract normal blood flow is disrupted by aortic stenosis, which raises risks and affects the cardiovascular system. this work analyzes blood viscosity from the central core line to the arterial wall in order to look at flow parameters in arteries with minor stenosis. in order to account for effective viscosity at radial distances, fluid dynamics in axisymmetric directions are analyzed using the navier-stokes equation. additionally, analytical expressions for shear stress, pressure drop, velocity profile, and volumetric flow rate are investigated. these results contribute to our growing knowledge of vascular physiology in stenosis and emphasize the intricacy of blood flow dynamics. keywords arterial stenosis, viscosity, hematocrit, hemodynamic parameters. article information manuscript received: april 2, 2024; revised: june 23, 2024; accepted: june 24, 2024 doi https://doi.org/10.3126/bibechana.v21i3.64409 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction atherosclerotic plaque is formed by the accumulation of cholesterol, fat, and other foreign particles [1]. arteriosclerosis, specifically the abnormal thickening and hardening of the artery walls, significantly impacts the cardiovascular system. this condition can result from various poor lifestyle choices, such as smoking, physical inactivity, and an unhealthy diet. the progression of arteriosclerosis leads to notable changes in hemodynamic parameters, including flow resistance, wall shear stress, pressure distribution, and blood flow [2, 3]. stenosis in an artery often results from the accumulation of cholesterol-rich particles, leading to the formation of atherosclerotic plaques. these plaques build up on the interior walls of arteries, causing several detrimental effects [4]. heart diseases and stroke are significant global health issues, contribut300 http://nepjol.info/index.php/bibechana chuda.pokherel@dmc.tu.edu.np https://doi.org/10.3126/bibechana.v21i3.64409 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ bishnu prasad bhandari et al./ bibechana 21 (2024) 300-310 301 ing to high mortality rates [5]. when analyzing medical imaging results like angiograms or ultrasound scans, different types of stenosis shapes can indeed have specific hemodynamic implications, affecting the severity and consequences of blood flow obstruction [6]. theoretical and experimental investigations into the effects of restrictions on blood flow parameters are crucial for understanding the hemodynamics of blood flow in both physiological and pathological conditions [7–9]. hematocrit is a significant factor that influences blood viscosity. additional features that can raise blood viscosity include decreased red blood cell deformability, high red blood cell aggregation, and increased plasma viscosity [10–12]. blood velocity and hematocrit percentage are two significant factors that have been shown to influence wall shear stress in the blood flow through a tapered artery [13]. a complete blood count (cbc) is a comprehensive examination that identifies and tracks various medical disorders by analyzing hematocrit concentration, white blood cell count, and platelet count [2,14]. examined the effects of pressure gradients, wall shear stress, blood velocity, and volumetric flow rate on human carotid arteries. an increase in the hematocrit and viscosity is accompanied by a decrease in the artery wall shear stress, indicating an increase in heart rate [15]. these results highlight the way that hematocrit, catheter size, and stenosis interact to influence blood flow hemodynamics. it has been found that the impedance changes with the size of the stenosis, hematocrit, and catheter [12]. blood clotting in the human heart can be fatal, as evidenced by the correlation between hematocrit and blood pressure gradient [14]. if platelets are activated by exceptionally high shear stress near the top of the stenosis, such atherosclerosis damages the cardiovascular system by entirely blocking blood flow to the heart [16]. figure 1: schematic illustration of a stenotic artery. mandal and chakravarty [17] have shown that blood behaves like a non-newtonian fluid in arteries with small radii and at low shear rates. according to chaturani and ponalagusamy [18] blood exhibits complex rheological behavior, particularly at low shear rates, where it demonstrates a non-zero yield stress. this phenomenon is primarily due to the interactions between erythrocytes (red blood cells), which can aggregate to form structures known as rouleaux. singh et al. [16] assumed a little asymmetric stenosis along the radial direction. biswas and chakraborty [13] examined the pulsatile blood flow across a moderately stenotic tapering artery with slip velocity at the arterial wall. haldar et al. [19] have investigated the effects of blood viscosity, wall shear stress, velocity, and hematocrit percentage on blood flow in the stenosed artery. bali and awasthi [20] determined how blood viscosity varies with hematocrit and distance from the center, and how the external magnetic field affects the flow. onitilo and usman [14] examined the theory that arterial wall shear stress would be decreased by raising hematocrit and viscosity. the literature review that was previously discussed offers proof of the impact that stenosis has on blood flow. in this study, blood flow characteristics with mild stenosis were examined in relation to blood viscosity in plasma, hematocrit, and the site of stenosis. the cylindrical polar form of the navier-stokes equation has been applied in axisymmetric directions. 2 methods considering the constant blood flow in an axially symmetrical artery that has stenosis. let r0 and r represent the artery’s radius in the absence and presence of stenosis, respectively. the artery is viewed as a circular, inelastic tube. with stenosis, the radial blood flow is disregarded. blood is thought to flow exclusively in an axial direction. 2.1 model equation considering the three components of velocity and pressure at (x, y, z) and at time t are u(x, y, z, t), v(x, y, z, t), w(x, y, z, t) and p(x, y, z, t) respectively. the continuity equation in a steady-state form is [4, 21] ∂u ∂x + ∂v ∂y + ∂w ∂z = 0. (1) here, a fluid’s density is represented by ρ(x, y, z, t). an incompressible viscous fluid has a constant density, ρ. the newtonian, viscous, and incompressible fluid n-s equations are [4, 21] bishnu prasad bhandari et al./ bibechana 21 (2024) 300-310 302 ρ ( ∂u ∂t + u ∂u ∂x + v ∂u ∂y + w ∂u ∂z ) = ρgx − ∂p ∂x + µ ( ∂2u ∂x2 + ∂2u ∂y2 + ∂2u ∂z2 ) (2) ρ ( ∂v ∂t + u ∂v ∂x + v ∂v ∂y + w ∂v ∂z ) = ρgy − ∂p ∂y + µ ( ∂2v ∂x2 + ∂2v ∂y2 + ∂2v ∂z2 ) (3) ρ ( ∂w ∂t + u ∂w ∂x + v ∂w ∂y + w ∂w ∂z ) = ρgz − ∂p ∂z + µ ( ∂2w ∂x2 + ∂2w ∂y2 + ∂2w ∂z2 ) . (4) in this case, t represents the time, and the external body forces, namely gravity, are f = ρ(gx, gy, gz). the forces resulting from pressure differences are denoted by the terms ∂p/∂x, ∂p/∂y, ∂p/∂z, and the viscous forces with constant viscosity coefficient µ in the x, y, and zdirection are represented by the last term on the right. the system (1)-(4) is closed for four unknown functions u, v, w and p. if gx = 0, gy = 0, and gz = 0 are the only external body forces acting on the motion, and if the motion is steady—that is, not changing over time—then ∂u/∂t = 0, ∂v/∂t = 0, ∂w/∂t = 0, and ∂p/∂t = 0, and the motion is two-dimensional. the navier-stokes equations for fluid flow inside a cylinder can be used to predict the flow of blood through arteries. we will use r and p to represent the artery’s blood flow’s radius and pressure drop. the velocities’ components along the radial, angular, and axial directions are vr, vθ, and vz, individually. the system (1)-(4) can be expressed in cylindrical form using x = r cos θ, y = r sin θ, r2 = x2 + y2 and θ = tan−1(y/x) from cartesian coordinate (x, y, z) to polar coordinate (r, θ, z). the equation of continuity and the equation of motion are [3, 21] 1 r ∂ ∂r (rvr) + ∂ ∂z (vz) = 0 (5) ρ ( ∂vr ∂t + vr ∂vr ∂r + vz ∂vr ∂z ) = −∂p ∂r +µ ( ∂2vr ∂r2 + ∂2vr ∂z2 + 1 r ∂vr ∂r − vr r2 ) (6) ρ ( ∂vz ∂t + vr ∂vz ∂r + vz ∂vz ∂z ) = −∂p ∂z + µ ( ∂2vz ∂r2 + ∂2vz ∂z2 + 1 r ∂vz ∂r ) (7) we assume vθ = 0 in the axisymmetric flow, and p, vr, and vz are independent of θ. for a steady flow of blood, viscosity µ and density ρ are considered to be constant. v is the velocity component parallel to the z-axis. only axially symmetric flow along the z-axis has been examined, therefore if vr = 0, vθ = 0, and vz = v, then equations (6) (7) become ∂v ∂z = 0, 0 = −∂p ∂r , 0 = −∂p ∂z + µ ( ∂2v ∂r2 + ∂2v ∂z2 + 1 r ∂v ∂r ) (8) suppose pressure term as p (z) = −∂p/∂z, equation (8) reduces to −p (z) r µ = ∂ ∂r ( r ∂v ∂r ) . (9) at a radial distance r, the effective viscosity of blood is expressed as [2, 22]. µr = µp [1 + αhr] (10) where µp is a plasma viscosity, α is a constant that characterizes the dependence of viscosity on hematocrit, hr is the hematocrit at radial distance r, and αhr reflects the increased viscosity due to the presence of red blood cells. the formula describes this relationship. hr = h [ 1− ( r r0 )m] (11) here, m is the number of stenosis, m = 1 is used from (10) and (11) µr = µp [ 1 + αh− αh ( r r0 )] bishnu prasad bhandari et al./ bibechana 21 (2024) 300-310 303 put b2 = αh, b1 = 1 + b2 µr = µp [ b1 − b2 ( r r0 )] (12) 2.2 geometry of stenosis figure 1 describes the form of the stenosis that results from the layer being deposited inside a cylindrical artery. r = r0 ( 1− β 2r0 ( 1 + cos πz z0 )) (13) where β is the greatest thickness and r and r0 are the radii with and without stenosis [21]. the boundary condition as stated by [3, 21] v = { 0 at r = r, 0 at r = r0, and ∂v ∂r = 0 at r = 0 2.3 velocity profile from equations (9) and (12) pr µp ( b1 − b2 ( r r0 )) + ∂ ∂r ( r ∂v ∂r ) = 0 pr µpb1 ( 1− b2r b1r0 )−1 + ∂ ∂r ( r ∂v ∂r ) = 0. binomial expansion is used, and neglect the higher power of r, pr µpb1 ( 1 + b2r b1r0 ) + ∂ ∂r ( r ∂v ∂r ) = 0. apply boundary conditions after integration, ∂v ∂r = − p µpb1 ( r 2 + b2r 2 3b1r0 ) . again integration, v = − p µpb1 ( r2 4 + b2r 3 9b1r0 ) +a(z) (14) used boundary condition, v = 0, at r = r a(z) = p µpb1 ( r2 4 + b2r 3 9b1r0 ) then equation (14) becomes, v = p µpb1 [ 1 4 ( r2 − r2 ) + b2 9b1r0 ( r3 − r3 )] . (15) bishnu prasad bhandari et al./ bibechana 21 (2024) 300-310 304 p = 8µpb1q πr4 0 ( 1− β 2r0 ( 1 + cosπz z0 ))4 [ 1− 8b2 15b1 ( 1− β 2r0 ( 1 + cos πz z0 ))] binomial expansion is used, and neglect the higher power of β then it becomes, p = 8µpb1q πr4 0 [ 1 + 2β r0 ( 1 + cos πz z0 ) − 8b2 15b1 ( 1 + β r0 − 3β2 2r2 0 +( β r0 − 2β2 r2 0 ) cos πz z0 − β2 2r2 0 cos 2πz z0 )] . (19) pressure drop on the stenosed region is ∆p = ∫ z0 −z0 pdz from the equation (19) and then integration, we have ∆p = 16µpb1qz0 πr4 0 ( 1 + β r0 + 3β2 2r2 0 − 8b2 15b1 ) (20) if there is no stenosis i.e., β = 0 then equation (20) becomes (∆p )p = 16µpb1qz0 πr4 0 ( 1− 8b2 15b1 ) . (21) ratio of pressure drop is ∆p (∆p )p = ( 1− 8b2 15b1 + β r0 + 3β2 2r2 0 ) ( 1− 8b2 15b1 ) (22) 2.6 ratio of shear stress kapur and pokharel et al. [4, 21] have mentioned the formula τ = pr 2 . from the equation 14, τ = 4µpb1q πr3 ( 1− 8b2r 15b1r0 ) with the help of equation (13), binomial expansion is used, and neglect the higher power of δ, we get τ = 4µpb1q πr3 0 ( 1 + 3β 2r0 ( 1 + cos πz z0 ))[ 1− 8b2 15b1 ( 1− β 2r0 ( 1 + cos πz z0 ))] (23) if there is no stenosis i.e., β = 0, then equation (23) becomes, τp = 4µpb1q πr3 0 ( 1− 8b2 15b1 ) (24) the ratio of shear stress τ τp = ( 1 + 3β 2r0 ( 1 + cosπz z0 )) [ 1− 8b2 15b1 ( 1− β 2r0 ( 1 + cosπz z0 ))] ( 1− 8b2 15b1 ) (25) bishnu prasad bhandari et al./ bibechana 21 (2024) 300-310 305 3 results and discussion computational approaches provide a detailed analysis of blood flow characteristics in stenosed arteries and offer valuable insights into the physiological impacts and potential treatment choices. 3.1 velocity of blood flow through a stenotic artery figure 2(a), explains the relationship between velocity and radius for both effective and plasma viscosity. the effective viscosity is 33.05 mm s−1 at the beginning, when r = 0, and the plasma viscosity is 47.67 mm s−1. for effective and plasma viscosity receptively, the velocities are 29.82 mm s−1 and 43.40 mm s−1 for r = 1 mm. in a similar vein, an artery’s radius is 2 mm, and its effective and plasma viscosity velocities are 19.23 mm s−1 and 27.12 mm s−1, respectively. additionally, it has been noted that velocities stop at an artery’s inner wall. according to the above, velocity reaches its maximum in the center and progressively declines towards the wall for every value of plasma viscosity and effective viscosity. this simulation’s output demonstrates how effective viscosity has a significant impact on velocity, as seen in the figure. this investigation concludes that the effective viscosity has a greater impact on blood flow velocity than plasma viscosity. figure 2(b), shows how the hematocrit affects the velocity profile under the assumption that the pressure drop is constant. we’ve assumed an artery’s radius of 3 mm and pressure of 80 pa. the velocity drops from 34.96 mm s−1 to 19.73 mm s−1, or roughly 15.23 mm s−1 at r = 0, when the hematocrit rises from 0.2 to 0.8. the velocity falls from 31.34 mm s−1 to 17.84 mm s−1, or roughly 13.5 mm s−1 at r = 1 mm, when the hematocrit rises from 0.2 to 0.8. in a similar manner, the velocity drops from 20.01 mm s−1 to 11.51 mm s−1, or roughly 8.42 mm s−1 at r = 2 mm, when the hematocrit rises from 0.2 to 0.8. finally, as the picture illustrates, the hematocrit increases somewhat, followed by a quick initial reduction in velocity and a subsequent steady decrease. near the inner wall of the artery, the velocity is almost zero, and it gradually increases as we move into the center. a low hematocrit causes a quicker rate of velocity rise. figure 2: velocity variations with radial distance for a: comparison viscosity, b: various hematocrit, c: various viscosity, d: increased viscosity due to the presence of red blood cells. bishnu prasad bhandari et al./ bibechana 21 (2024) 300-310 306 figure 2(c), shows how viscosity affects the velocity profile under the assumption that the pressure drop is constant. we’ve assumed that an artery’s radius is 3 mm. the velocity drops from 32.89 mm s−1 to 14.1 mm s−1, or roughly 24.79 mm s−1 at r = 0, when the viscosity increases from 0.3 to 0.7. the velocity drops from 29.73 mm s−1 to 12.74 mm s−1, or roughly 16.99 mm s−1 at r = 1 mm, as viscosity increases from 0.3 to 0.7. in a similar vein, the velocity drops from 19.31 mm s−1 to 8.278 mm s−1, or around 11.032 mm s−1 at r = 2 mm, when viscosity increases from 0.3 to 0.7. at last, as the image illustrates, viscosity increases slightly before velocity first drops quickly and then gradually. as we move toward the center, the velocity gradually increases from zero on the inner wall. a low viscosity causes the velocity to increase more quickly. figure 2(d), describes the distribution of velocity for different values of increased viscosity due to the presence of red blood cells. here βh = b2 takes vlues (0.5, 1, 1.5, 2) and 1 + βh = b1 has values (1.5, 2, 2.5, 3). the velocity v at b1 = 1.5 and b2 = 0.5 is 10.57 mm/s. as the b1 and b2 increases the velocity decreases and becomes 8.637 mm/s at b1 = 2 and b2 = 1. the velocity at b1 = 2.5 and b2 = 1.5 is 7.863 mm/s for the constant viscosity of plasma 0.5 gram/mm s. the velocity at b1 = 3 and b2 = 2 is (7.186 mm/s for the constant viscosity of plasma (0.5 gram/mm s respectively. it is found that the blood velocity gradually diminishes with increasing increased viscosity due to the presence of red blood cells i.e the flow velocity becomes smaller and smaller as one proceeds away from the center. for equal amount of increases increased viscosity due to the presence of red blood cells of an artery, the velocity in center has maximum and in the inner wall of an artery has minimum. as we can see from the above figures, effective viscosity has a significant impact on lowering velocity, so include the effective term and increased viscosity due to the presence of red blood cells will yield better results than only considering plasma viscosity. 3.2 volumetric flow rate in a stenotic artery figure 3: volumetric flow rate a: at different position of stenosis, b,c: at different height of stenosis, d: increased viscosity due to the presence of red blood cells. bishnu prasad bhandari et al./ bibechana 21 (2024) 300-310 307 figure 3(a) explains the volumetric flow rate at various stenosis sites, and several lines are drawn to illustrate the hematocrit values rising. stenosis positions vary from 0 to 0.5 mm. the volumetric flow rate rises to 494.3 mm3 s−1 from 481 mm3 s−1, it is about 13.3 mm3 s−1 with hematocrit is 0.2, for the position of stenosis from 0 to 0.5. once more, there is an increase in the volumetric flow rate from 357.8 mm3 s−1 to 343.7 mm.3 s−1, the difference is aroud 14.1 mm3 s−1 at 0.5 for the position of stenosis changes from 0 to 0.5. the volumetric flow rate in the final scenario increases from 266.3 mm3 s−1 to 279 mm3 s−1 at 0.7, meaning that the difference in this case is 12.7 mm3 s−1. we see that there is an inverse relationship between the hematocrit and the volumetric flow rate. stenosis position and hematocrit together carry a significant danger. figure 3(b) is employed to illustrate how, for changing hematocrit, the relationship between volumetric flow rate and height of stenosis varies. different lines are created for each hematocrit in order to display the influence of hematocrit individually. the highest hematocrit value is 0.7, and the maximum height of stenosis is 0.5 mm. about the time the hematocrit is 0.2 and the stenosis grows from 0 to 0.5 mm, the volumetric flow rate drops from 507 mm3 s−1 to 216.8 mm3 s−1. in a similar manner, when the hematocrit value is 0.5, the volumetric flow rate drops from 372 mm3 s−1 to 148.7 mm3 s−1. for the hematocrit value of 0.8, the volumetric flow rate drops from 291.8 to 113 mm3 s−1. while analyzing the variations in the volumetric flow rate decrease, we observe that the variation diminishes as the hematocrit increases. the volumetric flow rate lines are nearly parabolic when the hematocrit values are 0.2, 0.5, and 0.8. this suggests that the stenosis-related change is greatest when hematocrit values are compared. hematocrit has a greater effect when the stenosis height is less than 0.2 mm. when the stenosis height is greater than 0.4 mm, all of the volumetric flow rate lines fall between 216.8 mm3 s−1 and 113 mm3 s−1 for all hematocrit values, indicating a limiting circumstance. this suggests that greater area is required to flow a greater amount, and that in such situation, hematocrit is more effective. figure 3(c), explains the relationship, given a range of plasma viscosity values, between volumetric flow rate and thickness of stenosis (δ). to show the impact of varying plasma viscosity, three lines are drawn. in this instance, the constants are hematocrit 0.5, pressure 80 pa, and radius 3 mm. the volumetric flow rate drops from 524.20 mm3 s−1 to 204.7mm3 s−1, when the height of stenosis changes from 0 to 0.5 mm for the viscosity 0.3 gram mm−1 s−1. the volumetric flow rate decreases from 314.5 mm3 s−1 to 122.8 mm3 s−1 for the viscosity value of 0.5 gram mm−1 s−1, and from 224.6 mm3 s−1 to 87.75 mm3 s−1 approximately for the viscosity value of 0.7 gram mm−1 s−1. in this sense, when viscosity increases, the volumetric flow rate drops. this figure also shows that, when other parameters remain constant and the plasma’s viscosity grows uniformly, the volumetric flow rate eventually drops. figure 3(d) describes the distribution of volumetric flow rate for increased viscosity due to the presence of red blood cells. here b2 = βh and b1 = 1 + βh takes values (0.5, 1, 1.5, 2) and (1.5, 2, 2.5, 3). the volumetric flow rate at b1 = 1.5 and b2 = 0.5 is 473 mm3/s. as the increased viscosity due to the presence of red blood cells increases the volumetric flow rate decreases for the constant viscosity and becomes 347.8 mm3 s−1 at b1 = 2 and b2 = 1. the volumetric flow rate at b1 = 2.5 and b2 = 1.5 is 281.7 mm3/s for the constant viscosity of plasma 0.5 gram/mm s and becomes 249.3 mm3/s at b1 = 3 and b2 = 2 for the same viscosity.it is found that the volumetric flow rate gradually diminishes with increasing increased viscosity due to the presence of red blood cells i.e the volumetric flow rate becomes smaller as one proceeds away from the center. for equal amount of increases in increased viscosity due to the presence of red blood cells, the volumetric flow rate at b1 = 1.5, b2 = 0.5 has maximum and at b1 = 3, b2 = 2 has minimum. 3.3 pressure gradient across the stenosis artery figure 4 describes how the ratio of pressure drop to δ varies for varying hematocrit values. since the gap used to draw these lines is so narrow, the lines appear to be practically linear curves. the pressure drop value ratio is calculated when δ is in the range of 0 and 0.5. the picture illustrates that with a hematocrit of 0.8, the pressure ratio reaches its maximum of approximately 1.323 at δ = 0.5 mm. for the hematocrit value of 0.5, the approximate ratio of pressure drop is 1.296. in the same way, 1.253 for 0.3. when the hematocrit rises within the specified range, the ratio of pressure drop increases steadily. this suggests that as the hematocrit and height of stenosis increase, the ratio of pressure drop increases progressively. the hematocrit measurement may benefit from this knowledge. bishnu prasad bhandari et al./ bibechana 21 (2024) 300-310 308 figure 4: relation between ratio of pressure drop for different values of hematocrit with different height of stenosis. 3.4 shear stress ratio acroos stenotic artery figure 5(a) explains the relationship between the shear stress ratio at various stenosis points, and several curves are produced to illustrate the increasing hematocrit levels. in this case, the stenosis length ranges from −0.5 to 0.5, and its maximal height is found at z = 0. due to the stenosis’s symmetric structure, all of the lines symmetrically increase from −0.5 to 0 and decrease after 0. it demonstrates that when stenosis position increases, the ratio of shear stress falls. the ratio of shear stress increases parabolically from the common point to z = 0, where it reaches its maximum values 2, 2.096, and 2.144 for the hematocrits of 0.2, 0.5, and 0.8, respectively. when the hematocrit increases shear stress ratio increases gradually. the conclusion from this figure is that the shear stress ratio gets increasingly parabolic and inclines gradually as the hematocrit increases. figure 5(b) shows the shear stress ratio at various stenosis heights, with distinct lines being drawn to indicate rising hematocrit values. the highest hematocrit value is 0.8, and the maximum height of stenosis is 0.5 mm. for this reason, every line increases from 0 to 0.5 because the stenosis is thought to have a symmetrical shape. this demonstrates that a uniform rise in the hematocrit also results in a uniform increase in the ratio of shear stress. shear stress increases and reaches 1.734 at δ = 0.5 mm when the hematocrit is 0.2. at 0.5, the shear stress increases and reaches 1.956 at the maximum height δ = 0.5 mm. at 0.8, the shear stress ratio increases and reaches 2.098, as depicted in the figure. this analysis concludes that as hematocrit increases, the shear stress ratio increases consistently with a uniform quantity. the ratio of shear stress falls as hematocrit decreases, and the curve takes on a parabolic shape at different positions of stenosis. on the other hand, linear curves for various stenosis heights are produced when there is a consistent rise in hematocrit levels along with a uniform increase in the shear stress ratio. figure 5: relation between ratio of the shear stress a: with various position of stenosis for different values of hematocrit, b: at different height of stenosis for different values of viscosity of plasma. 4 conclusion atherosclerotic plaque accumulation and abnormal tissue development lead to stenosis, which restricts blood flow and contributes to cardiovascular diseases like ischemia and stroke. the einstein coefficient of blood viscosity, which quantifies the resistance to flow in blood vessels, is crucial for understanding hemodynamics and vascular health. navier-stokes equations have been applied to anabishnu prasad bhandari et al./ bibechana 21 (2024) 300-310 309 lyze the einstein viscosity in an axisymmetric direction, calculating model expressions for velocity profile, volumetric flow rate, pressure, pressure drop, and shear stress in an artery. the velocity of blood is more influenced by einstein’s viscosity than plasma viscosity. a significant reduction in volumetric flow rate is observed at the maximum height of stenosis with the uniform increase in hematocrit, indicating a heightened risk of stenosis effects after incorporating effective viscosity. the ratio of pressure drop and shear stress increases linearly with the uniform increase in hematocrit, showing a linear relationship with stenosis height. blood flow biomechanical modeling holds transformative potential for clinical procedures, surgical outcomes, vascular health understanding, and innovation across bioengineering and medical research, promising enhanced patient outcomes and healthcare advancement. references [1] v. a. nosovitsky, o. j. ilegbusi, j. jiang, p. h. stone, and c. l. feldman. effects of curvature and stenosis-like narrowing on wall shear stress in a coronary artery model with phasic flow. computers and biomedical research, 30:61–82, 1997. 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[22] m. m. lih. transport phenomenon in medicine and biology, volume 184. john wiley and sons, new york: ny, usa, 1996. introduction methods model equation geometry of stenosis velocity profile ratio of shear stress results and discussion velocity of blood flow through a stenotic artery volumetric flow rate in a stenotic artery pressure gradient across the stenosis artery shear stress ratio acroos stenotic artery conclusion bibechana vol. 21, no. 3, december 2024, 213-220 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar photoluminescence properties of tm3+/ho3+/cr3+-co-doped y3alga4o12 nano-garnet phosphors for visible-nir led applications ramadevi nepal1, jyothi prasad g.m.2,3, praveena ravipati3,∗, b.d. joshi4,∗∗, d. sujatha5 1central department of physics, tribhuvan university, kirtipur, kathmandu, nepal. 2andhra university, visakhapatnam -530003, india. 3department of physics, gayatri vidya parishad college of engineering (a), visakhapatnam530048, india. 4department of physics, siddhanath science campus, tribhuvan university, mahendranagar, nepal. 5gvsm govt. degree college, ulavapadu, spsr nellore – 523292, india. ∗corresponding author: email: praveena@gvpce.ac.in ∗∗corresponding author: email:bhawani.joshi@snsc.tu.edu.np abstract trivalent lanthanide (ln3+; ln = tm, ho, cr)-doped y3alga4o12 nano-garnet phosphor powders with varying cr3+ ion concentration (0.5, 1.0, 2.0 and 3.0 mol%) were prepared using sol-gel synthesis. the prepared powders were characterized by x-ray powder diffraction (xrd), raman and photoluminescence spectroscopic techniques. phase purity, structure and crystallite size have been estimated from the xrd results. raman spectra showed the vibrational analysis of the prepared powders. excitation spectrum showed a broad band centred at 354 nm when monitored at 712 nm. under 360 nm excitation, emission spectra showed a broad band with characteristic peaks of tm3+, ho3+ and cr3+ ions. the intensity of peaks and full width at half maximum were increased up to 2.0 mol% cr3+ ion and then decreased. all the decay curves exhibited non-exponential nature with an average lifetime of 0.302 ms. the decay curves were found to be insensitive to the cr3+ ion concentration. the cie colour co-ordinates were located in the orange-red region of the cie diagram with correlated colour temperature 2261 k. the results showed that the present phosphors were suitable for the solid state light emitting diode applications. keywords tm, ho, cr, yagg, garnets, phosphors, light emitting diode article information manuscript received: february 19, 2024; revised: april 23, 2024; accepted: april 26, 2024 doi https://doi.org/10.3126/bibechana.v21i3.62845 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 213 http://nepjol.info/index.php/bibechana praveena@gvpce.ac.in bhawani.joshi@snsc.tu.edu.np https://doi.org/10.3126/bibechana.v21i3.62845 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ramadevi nepal et al./ bibechana 21 (2024) 213-220 214 1 introduction nanomaterials like nanowires or nano-phosphors can improve electron and photon management within the light emitting diodes (leds) structure, leading to reduced energy consumption and increased luminous efficiency. nanoparticles provide a high level of tunability, allowing for the customization of various properties such as colour, conductivity, and thermal management. this flexibility enables the tailoring of led materials to meet specific application requirements, leading to advancements in diverse fields, including lighting, displays, and optoelectronics. nanoparticles enable the miniaturization of led components, allowing for the creation of smaller, more compact devices. this is particularly important in the development of flexible and bendable led displays, where the use of nanomaterials helps to maintain the required structural integrity while achieving the desired flexibility. recently, research on nano-phosphors has received significant attention as these are efficient luminescent materials for leds, field emission displays and plasma displays. phosphor-converted leds has excellent properties such as less production cost and simple device structure [1]. further, near infrared (nir) broadband sources are very important for non-invasive medical diagnostics, nondestructive food measurement, bioimaging, nightvision technologies, light converters and optical amplifiers [2–6]. the conventional incandescent bulbs and halogen lamps face different problems like low efficiency, short lifetime, high working temperatures and large size which limit their applications [7]. on the other hand, nir-emitting leds have great advantages like high efficiency, long lifetime, small in size, etc. therefore, nir broad band sources with these features are highly desired in wide range of applications [8]. nir phosphor-converted leds contains a ingan blue led chip with nir-emitting phosphors which can bring together the great advantages of ingan led chips including higher thermal stability, low manufacturing cost and high luminous efficiency [9] [10]. besides, broadband and light converters can be realized by the careful selection of host material and emitting ion of nir phosphors [11]. trivalent lanthanide (ln3+) ions have been extensively employed as emitting ions for various phosphor-converted leds. among the various ln3+ ions, tm3+ is one of the most interesting ions as it provides blue and red emissions whereas ho3+ ion is famous for its green emission. therefore, many researchers have focused on the development of single phased phosphors co-doped with both tm3+ and ho3+ ions and studied the energy transfer between tm3+ and ho3+ ions excited by nir wavelength [12, 13]. in our previous work, ultraviolet excited (uv) tm3+ and ho3+ co-doped y3al4gao12 phosphors were prepared and studied their luminescence and energy transfer properties for white led applications [14]. in the present work, tm3+/ho3+:y3alga4o12 (yagg) phosphors co-doped with cr3+ ions were prepared in order to broaden and extend the spectral profile in to the nir region for broadband source applications. cr3+ ion is the interesting ion to dope into the inorganic materials owing to its deep red colours (~ 700 nm) and narrow band emissions due to the spin-forbidden 2e →4a2 transition or broadband emission (650-1600 nm) due to the spin-allowed 4t2→4a2 transition, which strongly depends on the surrounding crystal-field strength given by the host lattices [15–17]. garnets have been chosen as the host materials for this purpose owing to their excellent properties like high thermal conductivity, high chemical stability and exhibit intense luminescence when doped with ln3+ ions [18]. ln3+:y3al5o12 (yag) is the well-known commercial phosphor for led applications [19] . however, the search for the advanced phosphors with better multiple properties for display applications is still remaining as challenging task. in this regard, the chemical composition of the garnets can be changed by replacing the part of the al3+ ions with the ga3+ or fe3+ or ge3+ ions and/or y3+ ions with lu3+ or gd3+ ions. when the al3+ ions are replaced by larger ga3+ ions, the distance between dodecahedral lattice sites (where the ln3+ ion is substituted) is going to be increased. this increase in the distance between the ln3+ ions tends to decrease the interaction between them in the host matrix and in turn reduces the concentration quenching [20]. this would enhance the luminescence intensity and efficiency as well. for instance, it was predicted theoretically that the ga3+ garnets show better luminescence properties when compared to al3+ garnets [21]. the same was also observed by praveena et al., [22] where the luminescence intensity of dy3+-doped y3alga4o12 nano-garnets are higher than that of y3al4gao12 nano-garnets. hence, the authors are motivated to investigate the luminescence properties of the present tm3+/ho3+/cr3+:yagg phosphors by varying the cr3+ ion concentration. to the best of author’s knowledge, no report is found on the current study. 2 experimental technique in the present study the phosphors were synthesised by the well-know sol-gel method [23]. sol-gel synthesis is a versatile method for producing phosphors with tunable properties, including structural and optical characteristics. optimizing synthesis ramadevi nepal et al./ bibechana 21 (2024) 213-220 215 parameters can significantly impact the final product’s properties. for instance, the choice of precursors can affect the chemical composition, dopant concentration and crystal structure of the phosphor which can influence the luminescence properties. the solvent affects the solubility of precursors and the rate of hydrolysis and condensation reactions. it can also impact the porosity, homogeneity and surface area of the phosphor. the ph of the so-gel solution can influence the hydrolysis and condensation reactions, affecting the size, morphology, and crystallinity of the phosphor particles. ph adjustment can also help control the distribution of dopants in the host matrix. the temperature and duration of the sol-gel process can affect the kinetics of the reaction, influencing the phase composition, crystallinity, and particle size of the phosphor. higher temperatures and longer reaction times generally lead to larger, more crystalline particles. the drying and calcinations processes can impact the phase purity, crystallinity, and luminescence properties of the phosphor. controlled drying and calcinations can help prevent phase transformations and enhance the phosphor’s optical properties. the concentration of dopants in the sol-gel solution can affect the luminescence efficiency and colour of the phosphor. optimizing the dopant concentration is crucial for achieving the desired optical properties. the addition of additives and surfactants can influence the morphology, particle size, and dispersion of the phosphor. this can also affect the luminescence efficiency and stability of the phosphor. post-treatment processes, such as annealing or surface modification, can further enhance the structural and optical properties of the phosphor. these processes can help to improve the crystallinity, phase purity, and luminescence efficiency of the phosphor. therefore, optimizing sol-gel synthesis parameters is essential for tailoring the structural and optical properties of phosphors. considering aforementioned parameters, the following optimizing conditions were taken into consideration after performing several experiments. yagg nano-crystalline powders tri-doped with dopant concentrations of 0.1 tm3+/0.3 ho3+/x cr3+ ions (where x= 0.5, 1.0, 2.0, 3.0 mol%) were prepared [23]. nitrate forms of the precursors were dissolved into the 25 ml of 1m hno3 under stirring to get ‘sol’. ph is maintained at around 1. citric acid and peg were added to the solution in the ratio metal:citric acid:peg is 1:2:8. continued stirring for 2 h till the ‘gel’ is obtained and then heated at 90 oc for 40 h. no other additives and surfactants were used. then, the obtained yellow colour gel was first heated at 500 oc for 4 h and later at 950 oc for 16 h in an electronic furnace with air atmosphere. the final product is in the white colour nano-crystalline powder form. xrd patterns were recorded using x-ray diffractometer (philips pw 1830) using cu k radiation (1.5406 å). confocal micro-raman spectrometer (horiba jobin yvon lab ram-hr 800) was used to record the raman spectrum. excitation, emission and decay spectra were recorded by using jobin yvon flurolog – 3 spectrofluorimeter with a 450 w xenon flash lamp. all the measurements were carried out at the similar conditions. 3 results and discussion 3.1 x-ray diffraction xrd profiles of the tri-doped yagg garnet nanocrystalline powders are displayed in the fig. 1. all the diffraction peaks were well matched with the standard jcpds data card no. 89-6661 that corresponds to space group of ia-3d cubic structure. no impurity peak is identified. this indicates that the formation of single phase high purity phosphors and successful incorporation of dopant ions without causing any disruptions in the crystal structure of yagg. the well resolved sharp peaks suggest that the synthesized samples are highly crystalline in nature. from fig. 1, it is clear that the crystallinity is increased with increasing cr3+ ion concentration. the crystallite size of the powder samples was estimated using debye-scherrer’s equation dhkl = kλ/βcosϑ, where d is the average crystallite size, k is the shape factor (0.9), is the wavelength of the xrays, is the full width at half maximum (fwhm) and is the diffraction angle. the crystallite size is increased from 13.8 to 23.7 nm when the cr3+ concentration is increased from 0.5 to 3 mol%. the crystallite size was slightly reduced upon adding the cr3+ into the tm,ho-doped yagg host [14] which represents the enhanced surface area. figure 1: xrd profiles of the tri-doped yagg nano-crystalline powders. ramadevi nepal et al./ bibechana 21 (2024) 213-220 216 3.2 raman spectra the raman spectrum of 1.0 mol% cr3+ tri-doped yagg samples is shown in fig. 2. the high frequency modes (800–1000 cm-1) are associated to symmetric and asymmetric internal stretching vibrations of rigid alo4/gao4 tetrahedra and the modes lying between 450–800 cm-1 are assigned to bending motions of these tetrahedra. the remaining lattice modes (150– 450cm-1) involve rotations and translations of the alo4/gao4 groups, octahedrally co-ordinated trivalent cations and dodecahedrally co-ordinated trivalent cations [22,24,25]. figure 2: raman spectrum of tri-doped yagg nano-crystalline powder. 3.3 excitation it is well-known that cr3+ has 2e, 4a2, 4t2 and 4t1 energy levels come from the 4f term in its d3 configuration [26, 27]. the excitation and luminescence properties of the cr3+ ion depend on the relative positions of the 4t2 and 2e levels. 4t2 state is above the 2e level when the cr3+ ion locates in the intermediate-field site that results r-line emission whereas 4t2 is under the 2e level when the cr3+ ion locates in the weak-field site. figure 3 shows the excitation spectrum of 1 mol% cr3+ tridoped yagg sample monitoring at emission wavelength of 712 nm. the spectrum consists of broadband in the region 300-450 nm which corresponds to 4a2→4t1 (4f) transition of cr3+ ion [28]. from fig. 3 it is confirmed that the present samples can be excited by near uv and visible radiation that is matching with ingan led chip. figure 3: excitation spectra of tri-doped yagg sample. 3.4 photoluminescence figure 4 shows the photoluminescence spectra of tri-doped yagg nano-crystalline powders excited with the wavelength of 360 nm. the spectra have a broad band in the region 450-800 nm with sharp characteristic peaks. the peaks are located at 482, 523, 557, 582, 612, 640 and 712 nm. the peak at 482 nm corresponds to 1g4→3h6 transition of tm3+ ion, peaks at 523 and 557 nm correspond to 5f4, 5s2→5i8 transitions of ho3+ ion, peaks at 582 and 612 nm correspond to 4t2→4a2 transition of cr3+ ion, peak at 640 nm correspond to 1g4→3f4 transition of tm3+ ion and peak at 712 nm correspond to 2e →4a2 transition of cr3+ ion [14,28,30]. rai et. al., [31] also noticed the 581 and 700 nm emissions of cr3+ in lavo4 host upon excited with wavelengths of 428 and 467 nm. yao et. al., [32] also observed the similar type of sharp lines at higher wavelengths side of the 2e→4a2 transition corresponding to nd3+ ion when it is co-doped with cr3+ ion into the ca3sc2sio12 host. chen et. al., [33] reported the yb3+/ln3+/cr3+ (ln = er, ho) doped transparent glass ceramics: crystallization, ln3+ sensitized cr3+ upconversion emission and multimodal temperature sensing. an intense cr3+ upconversion luminescence assigned to the 2e→4a2 transition was observed upon 980 nm laser excitation via energy transfer from yb3+ sensitizers to er3+ activators/bridging-centers and finally to cr3+ emitting centers. zhang et. al., [34] observed the enhanced photoluminescence of gd3al4gao12 (gagg):cr3+ by energy transfer from co-doped dy3+ ions. from fig. 4, it is observed that the luminescence intensity is slightly increased up to 2 mol% of cr3+ and then decreased which represents the optimum concentration is 2.0 mol%. from fig. 4, it is noticed that the intensity variation with respect to cr3+ ion is very less and hence these ramadevi nepal et al./ bibechana 21 (2024) 213-220 217 are stable phosphors. the fwhm values of the emission band are found to be 75.3, 77.3, 88.1 and 81.2 nm for 0.5, 1.0, 2.0 and 3.0 mol% of cr3+ ion, respectively. these values are also slightly increased up to 2.0 mol% and then decreased. hence, the optimised concentration is 2.0 mol%. further, it is observed that the fwhm is higher than that of yagg:0.5tm,1.5ho host (~65 nm) [14] and mgalga0.7b0.3o4:cr3+(29 nm) at lower concentrations [35]. thus, with the addition of cr3+ ion to the yagg:tm/ho host increased the fwhm value. therefore, from the luminescence spectra it is concluded that these phosphor powders can be useful for the broadband visible-nir light emitting diode applications. figure 4: the photoluminescence spectra of tridoped yagg nano-crystalline powders. 3.5 decay spectra figure 5 shows the decay curves monitoring at 582 nm emission and excited by 360 nm wavelength. all the decay curves exhibit non-exponential nature but insensitive to the cr3+ ion concentration. the non-exponential nature indicates the energy transfer processes are involved among tm3+, ho3+ and cr3+ ions. the insensitive nature of decay curves over cr3+ ion concentration represents the absence of concentration quenching in these phosphors, which enhances the luminescence efficiency. the average lifetime is found to be around 0.302 ms which is comparable with that of cr3+:lavo4 host (0.4503 ms) [31], higher than that of cr3+-doped garnets like ygg (0.240 ms), ggg (0.160 ms), ysgg (0.140 ms), gsag (0.150 ms) and gsgg (0.120 ms) [36] and cr3+:lusco3 (0.023 ms) hosts [37]. figure 5: the decay profiles of tri-doped yagg phosphors excited at 360 nm wavelength. 3.6 energy transfer among tm3+,ho3+ and cr3+ the energy transfer among tm3+, ho3+ and cr3+ ions in the yagg host can be elucidated through the schematic energy level diagram depicted in fig. 6. when subjected to 360 nm excitation, first the tm3+ ions get excited from 3h6 to the 1d2 level. subsequently, these ions undergo non-radiative relaxation (nr) to the lower 1g4 level. following this relaxation, radiative decay of tm3+ ions to the ground state takes place, emitting photons at wavelengths 482 nm and 640 nm, corresponding to the 1g4→3h6 and 1g4→3f4 transitions, respectively. during this process, a fraction of the energy is transferred from the excited tm3+ ions to adjacent ground state ho3+ ions through energy transfer (et1): 1d2(tm) + 5i8(ho)→3f4(tm) + 5g6(ho). this phenomenon arises due to pronounced spectral overlap between the tm3+ emission (1d2→3f4) and ho3+ excitation (5i8→5g6) in the vicinity of 460 nm [14]. subsequently, the excited ho3+ ions undergo non-radiative relaxation to lower levels, followed by radiative transitions, 5f4→5i8 (523 nm) and 5s2→5i8 (557 nm). concurrently, cr3+ ions are also elevated to the 4t1 level from 4a2 upon 360 nm excitation. these ions undergo non-radiative transitions to lower levels, populating the 2e and 4t2 levels. notably, a strong yellow emission at 582 nm and a relatively weak red emission at 612 nm are observed from the cr3+ energy levels, corresponding to the 4t2→4a2 transition, along with nir emission at 712 nm associated with the 2e→4a2 transition of cr3+ ions. in addition to this, cr3+ ions transfer a portion of their energy to adjacent ho3+ ions (et2), populating the 5f4 and 5s2 excited levels of ho3+. this energy transfer is reflected in the emission spectra (fig. 4), where the intensity at 523 nm and 577 nm increases with increase in cr3+ ion ramadevi nepal et al./ bibechana 21 (2024) 213-220 218 concentration up to 2.0 mol% and then decreases. figure 6: schematic partial energy level diagram of yagg:tm,ho,cr nano-phosphors. solid lines with arrow represent the transitions between the energy levels, zigzag lines indicate non-raditative transitions (nr), and et represents energy transfer. 3.7 cie colour co-ordinates commission international de i’eclairage (cie) colour co-ordinates and chromaticity diagrams provide a globally recognized and standardized system for describing colours accurately [38]. this consistency is vital for industries to ensure colour fidelity across various materials. these co-ordinates and diagrams are used to study colour perception, human vision and lighting technologies. figure 7(a) display the cie chromaticity diagram and 7(b) represent the corresponding spectral profile of the 2.0 mol% cr3+ tri-doped yagg phosphor. the colour co-ordinates (x, y = 0.5304, 0.4611) are located in the orange-red region with correlated colour temperature 2261 k. this represents the present phosphor gives a warm light [39]. the colour co-ordinates in the present host are closer to the yagg:0.5tm,1.5ho [14], as the ratio of tm/ho concentration is same, but shifted towards orangered side with the addition of cr3+ ion. an led device fabricated with the gagg:0.1cr3+,0.01dy3+ phosphor and a 450 nm blue chip showed the cie coordinates at (0.6387, 0.2873) [34]. it appears as a milky white light in the led device and provides a bright purplish-red emission driven by a current of 20 ma. it gives a strong red emission and yields a luminous efficacy of 27.8 lmw-1. in addition, chlorophyll pigment in plants absorbs blue (400-500 nm) and red (600-700 nm) light to help photosynthetic and phototropic processes [40]. phytochrome in plants changes its state to active form in the red light (600-700 nm, peaking at 660 nm) and inactive form in the far-red light (600-780 nm, peaking at 730 nm) [41]. these two pigments respond to red light in particular to support several functionalities in plants. therefore, the tm/ho/cr-doped yagg nano-crystalline powders can also be used in the plant growth led applications. (a) (b) figure 7: (a) cie diagram (b) corresponding spectral profile of 2.0 mol% cr3+ samples. 4 conclusions tm3+/ho3+/cr3+ tri-doped yagg nanocrystalline powders were prepared by sol-gel method and are characterized by xrd, raman and photoluminescence measurements. the xrd results confirmed the formation of single phased cubic garnet structure. the raman spectrum provided the vibrational analysis of the present samples. excitation spectrum showed that these phosphors can be successfully excited with near uv led light. the photoluminescence spectra showed the broad band in the visible and nir regions with characteristic peaks of tm3+/ho3+/cr3+ions. the addition of cr3+ ion increased the fwhm value. the decay curves were invariant with the cr3+ ion ramadevi nepal et al./ bibechana 21 (2024) 213-220 219 concentration which indicates that the absence of concentration quenching. the cie co-ordinates fell in the orange-red region. the results showed that the present phosphors have potential applications in the visible-nir light emitting broadband sources and plant growth led technology. acknowledgements the authors are highly thankful to the gayatri vidya parishad college of engineering (a), visakhapatnam for providing partial financial support. ramadevi also thankful to prof. dr. leela pradhan, amrit science campus, tribhuvan university and the kailali multiple campus, farwest university, dhangadhi, kailali, for extending the laboratory facilities. references [1] e. fred et al. solid-state light sources getting smart. science, 308(5726):1274–1278, 2003. 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[41] q. sun et al. synthesis and photoluminescence properties of deep red-emitting cagdalo4:mn4+ phosphors for plant growth leds. journal of luminescence, 203:371–375, 2018. introduction experimental technique results and discussion x-ray diffraction raman spectra excitation photoluminescence decay spectra energy transfer among tm3+,ho3+ and cr3+ cie colour co-ordinates conclusions bibechana vol. 21, no. 3, december 2024, 328–335 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar thermodynamic, structural and surface properties of cu–zr liquid alloy at different temperatures: a theoretical approach shashit kumar yadav*, dipak rohita yadav, ramesh kumar gohivar, upendra mehta department of physics, mahendra morang adarsh multiple campus, tribhuvan university biratnagar, nepal. ∗corresponding author. email: yadavshashit@yahoo.com abstract quasi-lattice model has been employed to study the thermodynamic and microscopic structural properties of cu–zr liquid alloy in the temperature range 1400-1700 k. the model fit parameters required for the purpose have been optimised using the available literature data of thermodynamic properties at the melting temperature of the system, 1400 k. these model parameters have been then computed at different temperatures assuming them to be linear temperature-dependent. the surface properties of the system have been computed using butler model at above mentioned temperatures. keywords quasi–lattice test, ordering nature, segregating nature, surface tension. article information manuscript received: august 10, 2024; revised: september 27, 2024; accepted: october 1, 2024 doi https://doi.org/10.3126/bibechana.v21i3.70438 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction pure metals are inappropriate for the most of industrial uses as they are often soft and ductile. as a result, alloying is done to produce desirable composite material with low to high melting points, increased tensile strength, improved corrosion resistance and greater cost accessibility [1]. they are used in culinary utensils, automobile parts, aerospace parts, cellphone parts, medicines, military, nuclear reactors, etc. therefore, alloying phenomenon is incredibly crucial in our daily lives [2]. alloys of cu–zr have a relatively weak interaction [3] and tend to pass into the glassy state over a wide composition range. in this regard, they are used as the foundation for a wide range of bulk amorphous materials. the long-term operation of nuclear reprocessing plants is jeopardized by the management of zirconium base alloy wastes as cladding hulls [4]. hence, the system has been studied by several researchers employing different experimental techniques and 328 http://nepjol.info/index.php/bibechana yadavshashit@yahoo.com https://doi.org/10.3126/bibechana.v21i3.70438 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ shashit kumar yadav et al./ bibechana 21 (2024) 328-335 329 theoretical approaches. the butler model was used to study the surface characteristics of the system above its melting point [5]. in 2003, zaitsev et al. produced a full experimental thermodynamic description of cu-zr intermetallic complexes [3]. the knowledge of phase diagram and thermodynamic parameters including enthalpy of mixing, enthalpy of formation and heat contents are required for the purpose. the information for glass forming propensity requires knowledge of the thermodynamic and kinetic parameters of cu–zr alloys [4]. in 2008, yamaguchi et al. evaluated the standard enthalpy of formation of cu9zr2, cu51zr14, cu8zr3, cu10zr7, and cuzr2 complexes at 298.15 k [2]. the present literature review shows that the complete assessment of mixing properties of the system in liquid state is not available to date. therefore, the thermodynamic and structural properties of the cu–zr liquid alloy at 1400 k have been studied in the work on the basis of quasi-lattice test [6–10]. the model parameters required for the process have been optimised taking the thermodynamic data of ref. [11] as reference. the calculated values of thermodynamic and structural properties have been then compared with the reference data to check the validity of best fit values of so obtained model parameters. the surface tension and surface concentrations of components in the alloy have been computed using butler model [10, 12–14]. in order to analyse the mixing tendency of the system at higher temperatures, above mentioned properties have been calculated in the temperature range 1400-1700 k. 2 formalism 2.1 thermodynamics properties the complex having the stiochiometric composition aµb,µ = 2, i.e., zr2cu [11] has been assumed to be energetically stable in the alloy. according to the quasi-lattice model, the expression for excess free energy of mixing (∆gxs m ) for the preferred complex is given as [6–10] ∆gxs m = n [∆ωϕ+∆ωabϕab +∆ωaaϕaa] (1) where ϕ = x1x2 (2a) ϕab = ( 1 6 x1 + x1 2 − 5 3 x1 3 + 1 2 x1 4) (2b) ϕaa = (−1 4 x1 + 1 2 x1 2 − 1 4 x1 4) (2c) and the expression for free energy of mixing is given by ∆gm = ∆gxs m +rt [x1 lnx1 + x2 lnx2] (3) herein, ∆ω and ∆ωij ; i, j = a,b are the interaction energy parameters, termed as model parameters. r is the real gas constant and t is the absolute temperature. xi, i = a,b is the mole fraction of pure component i in the liquid alloy. let aa and ab denote the activities of the elements a (=zr) and b(=cu) in the alloy. aa and ab can be expressed as rt ln aa = ∆gm + x2 ( ∂∆gm ∂x1 ) t,p,n (4) and rt ln ab = ∆gm + x1 ( ∂∆gm ∂x2 ) t,p,n (5) the expression for the excess entropy of mixing (∆sxs m ) can be expressed in terms of ∆gxs m with the help of standard thermodynamic relation as ∆sxs m = − ( ∂∆gxs m ∂t ) p (6) using equation (2) in equation (6), one can obtain ∆sxs m = −n [ ∂∆ω ∂t ϕ+ ∂∆ωab ∂t ϕab + ∂∆ωaa ∂t ϕaa ] (7) where ∂∆ω ∂t and ∂∆ωij ∂t are the temperature derivative terms of interaction energy parameters. the enthalpy of mixing (∆hm ), ∆sxs m and ∆gxs m can be related as ∆hm = ∆gxs m + t∆sxs m (8) 2.2 structural properties the arrangement of atoms in the liquid alloys can be studied by calculating characteristics functions, such as concentration fluctuation in the long wave length limit (scc(0)), warren-cowley short range order parameter (α1) and the ratio of mutual to intrinsic diffusion coefficients (dm/did) [6, 7, 15, 16]. scc(0) can be expressed in terms of ∆gm as scc(0) = rt [ ∂2∆gm ∂xi 2 ]−1 t,p,n (9) with the aid equations (2 and 3) in equation (2.2), scc(0) can be expressed as scc(0) = x1x2 ∗ p−1 shashit kumar yadav et al./ bibechana 21 (2024) 328-335 330 with p = 1+x1x2rt (∆ωϕ” + ∆ωabϕ”ab +∆ωaaϕ”aa) (10) moreover, the expression for ideal value of concentration fluctuation in long wavelenth limit sid cc(0) as sid cc(0) = x1x2 (11) as sated above, another structural function, α1 can be expressed as [15,17,18] α1 = s − 1 [s(z − 1) + 1] (12) here, z represents the coordination number and its value has been taken to be 10 for the work. the term s in above expression is defined as s = scc(0) sid cc(0) (13) the ratio of mutual to intrinsic diffusion coefficients is expressed as [9, 19] dm did = sid cc(0) scc(0) (14) 2.3 surface properties the knowledge of surface tension and surface segregation allows us to understand and explain the mechanical behavior, phase change, catalytic activity, and other physical behaviours of an alloy . the expression for the surface tension (σ) for binary liquid alloy is given as [12,20–22] σ = σ0 1(t ) + rt a1 ln ( xs 1 x1 ) + ( ∆gxs,s 1 −∆gxs,b 1 a1 ) σ = σ0 2(t ) + rt a2 ln ( xs 2 x2 ) + ( ∆gxs,s 2 −∆gxs,b 2 a2 ) (15) where ai = molar surface area of ith component, xs i = surface mole fraction of the ithcomponent, xi= bulk mole fraction of ith component, ∆gxs,s i = partial excess free energy of the ith component in the surface phase of liquid solution and ∆gxs,b i = partial excess free energy of the ith component in the liquid solution. ∆gxs,s i and ∆gxs,b i is related by the expression ∆gxs,s i = β∆gxs,b i (16) the value of β depends on the ratio of coordination number of atoms in surface phase and bulk phase. the value of β is taken to be 0.8181 [10, 13, 20] in the work. in equation (12), σ0 i (t ) is the temperature dependent surface tension of pure ith component in the mixture that can be expressed as [14,23] σ0 i (t ) = σ0 i + (t − t0) dσ dt (17) the terms σ0 i is the surface tension of pure component at its melting temperature (t0), σ0 i (t ) is the surface tension at the required temperature t , and dσ dt is the temperature derivative term of surface tension. the expression of the molar surface area of the ith component can be given by [10,13] ai = f(v 0 i ) 2/3(nav ) 1/3 (18) the terms vi and nav are the molar volume of ith component at temperature t and avogadro’s number respectively. the term f is geometrical constant and its value is 1.000 that can be calculated using the relation [21,24] f = ( 3fb 4 ) π1/3 fs (19) herein,fb and fs are the volume and surface packing fractions. the ideal surface tension of the binary alloy is the weighted sum of surface tension of individual components present in the alloy. mathematically, σid = σ0 1(t )x1 + σ0 2(t )x2 (20) where the terms carry their usual meanings as stated above. 3 results and discussion 3.1 thermodynamic properties the model parameters required for the quasi-lattice test, have been obtained by considering the thermodynamic database of cost 507 [11] as reference. the self-consistent parameters for ∆gxs m is expressed in terms of coefficients of redlich-kister polynomial [25] in the ref. [11], table 1. table 1: interaction energy parameters for ∆gxs m parameters [jmol−1] ref. l0 = −61685.53 + 11.29235 ∗ t l1 = 8830.66 + 5.045658 ∗ t [11] ∆ω = −43271.6 + 15.680 ∗ (t − 1400) ∆ωab = 3776.065 + 1.200 ∗ (t − 1400) this wok ∆ωaa = 65496.02 + 0.010 ∗ (t − 1400) ∆gxs m for the system in terms of coefficients of r-k polynomial can be expressed as [9, 10,25] ∆gxs m = x1x2 (l0 + l1(x1 − x2)) (21) where li (in jmol−1is the coefficient of r-k polynomial depending on temperature but independent shashit kumar yadav et al./ bibechana 21 (2024) 328-335 331 of concentration. li = ai + bi ∗ t , where ai is the contribution of enthalpy of mixing ∆hm and bi is the contribution of entropy of mixing (∆sxs m ) on ∆gxs m . the expressions of ∆sxs m and ∆hm then can be obtained using the equations (6 and 8) as [9] ∆sxs m = x1x2 [b0 + b1(x1 − x2)] (22) and ∆hm = x1x2 [a0 + a1(x1 − x2)] (23) the reference values of ∆gxs m , ∆hm and ∆sxs m have been calculated using equations (21-23) with the help of parameters in table 1. the values of model parameters ∆ω, ∆ωab and ∆ωaa and their temperature derivative terms (∂∆ω ∂t , ∂∆ωab ∂t and ∂∆ωaa ∂t ) at 1400 k have been then optimised by using equations (1,2, 7 and 8) and calculated reference values of ∆gxs m , ∆hm and ∆sxs m . the best best fit values of these model parameters are presented in table 1. these model parameters are also assumed to depend only on temperature. the calculated values of these thermodynamic functions are plotted in figure 1. 0.0 0.2 0.4 0.6 0.8 1.0 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 h m /rt s m xs g m xs/rt g m xs /r t ,  s m xs ,  h m /r t x zr cost 507 this work figure 1: plot of ∆gxs m versus xzr for cu–zr liquid alloy at 1400 k. the values of ∆gxs m , ∆hm and ∆sxs m calculated using the optimised parameters of the work and cost 507 [11] are found to be consistent with each other at its melting temperature, 1400 k. the negative values of ordering energy parameter, ∆ω, signifies the compound forming behavior of the system at its melting temperature. the optimum value of ∆gxs m = −11612.8 jmol−1 and ∆hm = −17104.0 jmol−1 at xxs = 0.4, indicating the system to be asymmetric with respect to these functions, figure 1. moreover, the system is found to be weakly interacting in nature. the values of ∆gxs m of the system have also been computed at higher temperatures, 1400 k, 1500 k, 1600 k and 1700 k following the similar procedure. the calculated optimum values of ∆gxs m at xzr are −11612.8 jmol−1 at 1400 k, − − 11220.6 jmol−1 at 1500 k, −10828.4 jmol−1 at 1600 k and −10436.1 jmol−1 at 1700 k. thus, the negative values of ∆gxs m are found to gradually decrease with an increase in the temperature of the system, figure 2. these results indicate that the compound forming tendency in the liquid alloy gradually decreases with an increase in its temperature. 0.0 0.2 0.4 0.6 0.8 1.0 -12 -10 -8 -6 -4 -2 t=1400 k t=1500 k t=1600 k t=1700 k  g m xs [ kj m o l-1 ] x zr figure 2: calculated values of azr and acu versus xzr for cu–zr liquid alloy at 1400 k. activity is another important thermodynamic parameter which is greatly influenced by the values of model parameters and is reflection of ∆gxs m . the activities of components zr (azr) and cu (acu) of liquid alloy have been calculated using equations (4, 5 and 21) with the aid of parameters in table 1. 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 a cu a zr a z r, a c u x zr cost 507 this work ideal values figure 3: calculated values of azr and acu versus xzr for cu–zr liquid alloy at 1400 k. the perusal of figure 3 conveys that the calculated values of azr and acu using the model parameters of the work are found to be consistent with those calculated using the data of cost 507 [11]. the activities of these components show negative deviation from raoult’s law or their respective ideal values shashit kumar yadav et al./ bibechana 21 (2024) 328-335 332 at lower concentrations of zr indicating the system to be ordering in nature. however, values of azr approaches ideal values at higher concentration of zr. 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 a cu a zr a z r, a c u x zr t=1400 k t=1500 k t=1600 k t=1700 k ideal values figure 4: calculated values of azr and acu as a function of concentration of zr for cu–zr liquid alloy at different temperatures. the activity of the system has also been computed at above mentioned different temperatures. the calculated values of azr and acu are found to gradually increase at higher temperatures, figure 4. the deviation of calculated values from the ideal values gradually decreases. the activity of the component zr shows positive deviation from its respective ideal value at 1500 k and above in the concentration range xzr > 0.8. these results correspond the transformation from ordering to segregating nature of the system. thus, the present investigations reveal that the compound forming tendency in the alloy decreases at elevated temperatures. 3.2 structural properties 0.2 0.4 0.6 0.8 1.0 -0.2 -0.1 0.0 0.1 0.2 0.3  1 s cc (0) s c c (0 ),  1 x zr this work cost 507 ideal values figure 5: calculated values of scc(0) and α1 versus xzr for cu–zr liquid alloy at 1400 k. the ordering nature or hetero-atomic pairing and segregating nature or homo-atomic pairing tendencies in the liquid alloys can be better understood with the knowledge of microscopic structural functions. for the purpose, concentration fluctuation in long wavelength limit (scc(0)), warren-cowley short-range order parameter (α1) and ratio of mutual to intrinsic diffusion coefficients (dm/did) have been computed in the work using equations (9-14) and parameters in table 1. 0.0 0.2 0.4 0.6 0.8 1.0 0.05 0.10 0.15 0.20 0.25 s c c (0 ) x zr ideal values t=1400 k t=1500 k t=1600 k t=1700 k figure 6: calculated values of scc(0) versus xzr for cu–zr liquid alloy at different temperatures. 0.2 0.4 0.6 0.8 1.0 -0.25 -0.20 -0.15 -0.10 -0.05 0.00  1 x zr t=1400 k t=1500 k t=1600 k t=1700 k figure 7: calculated values of α1 versus xzr for cu– zr liquid alloy at different temperatures. at a given concentration and temperature, if scc(0)>sid cc , then it indicates ordering tendency in the alloy for which α1 > 1 and dm/did < 1. likewise, if scc(0)<sid cc , then it indicates segregating tendency in the alloy for which α1 < 1 and dm/did > 1. if α1 = 0, then ideal mixing tendency in the liquid alloy is expected. the calculated values of scc(0)<sid cc and α1 < 1 in the entire concentration range indicating the ordering shashit kumar yadav et al./ bibechana 21 (2024) 328-335 333 nature of the system, figure 5. moreover, values of these functions computed using the optimised coefficients of the work are found to be in reasonable agreement with those obtained using the parameters of cost 507 [11]. the values of scc(0) are also calculated at higher temperatures following the similar procedure as mentioned above. scc(0) gradually increases with an increase in temperature of the system and approaches ideal values, figure 6. the calculated values of scc(0) are found to be grater than ideal values in the concentration range xzr > 0.8 at t>1400 k. thus, it can be stated that the system changes from ordering to segregating nature at these conditions. likewise, the calculated values of α1 is found to be greater than 1 in the above mentioned conditions revealing the similar mixing tendency. 0.0 0.2 0.4 0.6 0.8 1.0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 d m /d id x zr t=1400 k t=1500 k t=1600 k t=1700 k figure 8: compositional dependence of dm/did for cu–zr liquid alloy in the temperature range 14001700 k. the calculated values of dm/did are found to be greater than 1 at all concentrations at 1400 k, melting temperature. this result reveals that the system shows hetero-coordinating tendency. meanwhile, the calculated values of dm/did decreases with gradual increase in temperature of the system. the calculated values of dm/did < 1 in the range xzr > 0.8 and t>1400 k indicating the transformation from ordering to segregating nature, figure 8. thus, the nature of temperature-dependent mixing tendency of the system predicted by thermodynamic and structural functions are in accordance with each other. 3.3 surface properties the surface tension (σ) and surface concentration (xs i ) of the system have been computed using equations (15-21) and the parameters in table 2. the above determined values of thermodynamic parameters have been used for the purpose. the calculated values of xs i are plotted as a function of concentration in figures 9. it can be observed that the calculated values of xs zr<xzr and xs cu>xcu in the entire composition range at 1400 k, figure 9. these results have been occurred as the surface tension of cu (σcu = 1.293 nm−1) is less than that of zr (σzr = 1.633 nm−1) at this temperature. hence, cu atoms segregate in the surface phase whereas zr atoms remain in the bulk phase of the liquid alloy. table 2: surface tension and density of each component of liquid alloy [23] surface tension [nm−1] σ0 zr = 1.459− 0.00024(t − 2128) σ0 cu = 1.303− 0.00023(t − 1356) density [kgm−3] ρ0zr = 6240− 0.29(t − 2128) ρ0cu = 8000− 0.8(t − 1356) 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 x cu s x zr s x z rs , x c us x zr this work ideal values figure 9: compositional dependence of calculated values of xs zr and xs cu for cu–zr liquid alloy at 1400 k. shashit kumar yadav et al./ bibechana 21 (2024) 328-335 334 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 xs cu xs zr xs z r, xs c u x zr t=1400 k t=1500 k t=1600 k t=1700 k ideal values figure 10: calculated values of xs zr and xs cu for cu– zr liquid alloy at different temperatures. the values of xs zr and xs cu have also been computed in the temperature range 1400-1700 k. it can be observed that the calculated values of xs zr are found to increase while those of xs cu are found to decrease at higher temperatures. both of these values get closure to their respective bulk concentrations or ideal values as the temperature of the system is increased, figure 10. thus, cu atoms move towards the bulk phase whereas zr atoms move towards the surface phase at elevated temperatures. 0.0 0.2 0.4 0.6 0.8 1.0 1.30 1.35 1.40 1.45 1.50 1.55 1.60 1.65  [n m -1 ] x zr this work ideal values figure 11: calculated values of σ for cu–zr liquid alloy at 1400 k. the computed values of σ of the system is found to be less than its ideal values. moreover, the surface tension of the system gradually increases with increase in concentration of zr, figure 11. the temperature-dependent variation of σ of the system is as shown in figure 12. the surface tension of the system decreases gradually and linearly with an increase in temperature of the system. 1400 1450 1500 1550 1600 1650 1700 1.25 1.30 1.35 1.40 1.45 1.50 1.55 1.60  [n m -1 ] temperature [k] x zr =0.1 x zr =0.2 x zr =0.3 x zr =0.4 x zr =0.5 x zr =0.6 x zr =0.7 x zr =0.8 x zr =0.9 figure 12: calculated values of σ for cu–zr liquid 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[25] o. redlich and a. t. kister. algebraic representation of thermodynamic properties and the classification of solutions. industrial & engineering chemistry, 40(2):345–348, 1948. introduction formalism thermodynamics properties structural properties surface properties results and discussion thermodynamic properties structural properties surface properties conclusion bibechana vol. 20, no. 3, december 2023, 285-289 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar measurement of background radiation in jhapa, ilam, panchthar, and taplejung districts of nepal arun kumar shrestha1,2, roshan nepal1, kamala shrestha1 dijan regmi1, ganesh kumar shrestha3, buddha ram shah4, ram prasad koirala5,∗ 1damak multiple campus, tribhuvan university, jhapa, nepal 2central department of physics, tribhuvan university, nepal 3pulchowk engineering campus, tribhuvan university, nepal 4nepal academy of science and technology, lalitpur, nepal 5mahendra morang adarsh multiple campus, tribhuvan university, biratnagar, nepal ∗corresponding author. email: ramprasadkoirala13@gmail.com abstract in this study, we investigated the levels of background radiation in different locations across the eastern part of koshi province, specifically in taplejung, panchthar, ilam, and jhapa. we used a portable geiger muller counter to collect data from twenty different locations, with five sites taken from each district. the average absorbed dose rate was found to be 0.243±0.035 msv/y. the highest measured value of absorbed dose was 0.335±0.041 msv/y at pathivara temple in taplejung, and the lowest was found to be 0.197±0.039 msv/y at kakarvita, jhapa. the results suggest that these four districts do not pose any radiation risk because it was below the threshold of risk (1msv/y). we also measured the variation of absorption dose with altitude which is positively correlated with altitude with a correlation coefficient of +0.57. this might be because of the surge in cosmic radiation with an increase in altitude. keywords onizing radiation, cosmic radiation, absorbed dose, g.m. counter, background radiation. article information manuscript received: august 13, 2023; accepted: october 16, 2023 doi https://doi.org/10.3126/bibechana.v20i3.57882 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction background radiation measurement is an important task to evaluate dose for general people due to various sources. these sources are categorized into three groups: primordial, cosmogenic, and human-produced, with the most abundant being naturally occurring radionuclides (i.e. primordial radionuclides) [1–4]. these radionuclides exist in each rock, soil, and water and significantly vary 285 http://nepjol.info/index.php/bibechana ramprasadkoirala13@gmail.com https://doi.org/10.3126/bibechana.v20i3.57882 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ arun kumar shrestha et al./ bibechana 20 (2023) 285-289 286 depending upon geological and geographical situations. cosmic radiation is a significant contributor to the radiation entering the earth’s atmosphere from its surroundings. the amount of cosmic radiation that reaches the earth’s surface varies depending on a number of factors, such as altitude, latitude, and solar activity [5]. in addition to these sources, the background radiation at the local level is also greatly affected by the presence of man-made sources, such as those from nuclear activities and accidents [6]. there are various regulatory bodies such as the nuclear regulatory commission (nrc) and the international atomic energy agency (iaea) that set standards for radiation exposure to ensure the safety of individuals working with radiation or living near nuclear facilities. these agencies also monitor background radiation levels to ensure they remain within safe limits [7–9]. there are several international studies reported in the literature for the measurement of background radiation levels both in outdoor and indoor areas, and the global average value for dose rate is 59 ngy/h with the range of 18− 93 ngy/h [10,11]. the first preliminary ground radiometric survey in nepal was conducted in 1977/1978 and confirmed the presence of deposition of the mineralized bodies in tinbhangale, makawanpur. pantha et al. (2018), gautam et al. (2020), dhami et al. (2020), and shrestha et al. (2023) conducted the radiometric survey in pokhara valley, kathmandu, kanchanpur, and morang district, respectively [12–15]. results showed that these areas are under normal background radiation. in nepal, there are 77 districts; therefore, the comprehensive investigation to assess background radiation levels across the country is the most important and immediate concern to the general population [16] because no further works have been obtained in the literature. similarly, people living in high-altitude regions are receiving a higher dose of radiation, but it has a lack of information. therefore, this study was carried out to provide a map of background radiation using a gm detector in eastern nepal and to estimate the annual effective dose of residents in these areas. such works become very useful for locating the high background radiation area. it is also a regulatory prerequisite for installing and operating a research reactor and nuclear power plant and testing nuclear weapons. 2 materials and methods 2.1 description of instrument the data collection in this study was performed using the gm counter model gmc-300e plus, which employs a gm tube to detect nuclear radiation. the gm tube is designed to detect radiation by producing an electric current pulse when ionization occurs due to the passage of radiation through the tube. the instrument then detects and records each pulse as a count. the gmc-300e plus is a highly portable and battery-operated device that offers three different modes for displaying the counts: counts per minute (cpm), milliroentgen per hour (mr/h), and microsievert per hour (µsv/h). it is worth noting that the gmc-300e plus is capable of detecting high-energy x-rays (0.03 − 3.0mev), beta particles (0.25 − 3.5mev), and gamma rays (0.1 − 1.25mev). this makes it an ideal device for monitoring a wide range of nuclear radiation sources in different settings. the portability of the instrument allows for easy transport, enabling data collection to be performed on-site or in the field. the three different modes of display provide flexibility in the analysis of the collected data, making it easier to compare the results with existing radiation safety standards. for quality control measures, some specifications of the instrument are shown in table 1. 2.2 study area the present study comprises data collected from the eastern part of nepal, encompassing four distinct districts, namely jhapa, ilam, panchthar, and taplejung. the total area of the site under consideration is approximately 8196 square kilometers. the geographical expanse of the region can be broadly classified into three categories, viz., the mountainous terrain, the central hilly region, and the lower terrain (plain) region. the pinnacle of the region is the kanchenjunga peak, situated in taplejung, with an altitude of 8586meters, while the lowest is marked by kechana kalan, located in jhapa, with an elevation of merely 60meters. the highest point of elevation, from where the data has been gathered, is pathivara, situated at a height of 3780meters. on the other hand, the lowest altitude, where data collection was undertaken, is an altitude of 92meters, which is at kakarvita in jhapa. the study area with the sampling locations in four districts is given in fig. 1. arun kumar shrestha et al./ bibechana 20 (2023) 285-289 287 figure 1: study area with the sampling locations. 2.3 measurement and calculations data was collected in count per minute (cpm) 10 times from a location. for conversion of this data into msv/y, eq. (1) is used [17], d(msv/y) = (m × 0.2× f × 24× 365) 1 100 (1) where, d: absorbed dose rate in msv/y m : measured value in count per minute f : conversion factor from cpm to µsv/hr 0.2 is the outdoor occupancy factor after the conversion of all data, mean and standard deviation were calculated, and all data were plotted in an error bar graph. 3 results and discussion the background radiation of the taplejung district is presented in fig. 2. the background radiation in count per minute was converted into an absorbed dose rate using eq. (1). the lowest value was observed to be (0.268∓).03)msv/y in phungling and the highest dose rate (0.335∓).041)msv/y was observed in pathivara. it may be due to the effect of cosmic radiation at higher altitudes. the average background radiation of the taplejung district was (0.289∓ 0.02)msv/y. the background radiation of the panchthar district is presented in fig. 3. the lowest dose was found to be in phidim, and the highest dose was observed in pauwa vangang. as a result, the mean background radiation of the panchthar district was (0.247 ± 0.056)msv/y. the background radiation of the ilam district is presented in fig. 4. the minimum dose rate was in jorkalash, and the maximum dose rate was in ilam bazar. the average background radiation of the ilam district was (0.225±0.015)msv/y. the background radiation of the jhapa district is presented in fig. 5. the lowest dose was found to be in kakarvita, and the highest equivalent dose rate of was observed in bhadrapur. however, the average background radiation of the jhapa district was (0.209 ± 0.011)msv/y. all these values were below the recommended value of 1msv/y set by the international commission on radiological protection (icrp) for non-radiation workers and the public. the equivalent dose of all districts where the study is conducted is plotted in fig. 6. the lowest equivalent dose rate (0.209± 0.011)msv/y was found to be in jhapa, and the highest equivalent dose rate (0.280 ± 0.026)msv/y was observed in taplejung. the average background radiation of the eastern region of koshi province was (0.242 ± 0.034)msv/y. this result also supports the increase in background radiation with altitude. the average altitude of the study areas in jhapa, ilam, panther, and taplejung is 117, 1003, 1279, and 2110m respectively. jhapa being at lower altitude has low dose rate, and taplejung, being at higher altitude, has a high dose rate. variation of absorbed dose rate with altitude has been shown in fig. 7. it shows that there is a positive correlation between altitude and absorbed dose rate, as altitude increases the exposure also increases, this might be due to the increase in cosmic radiation with an increase in altitude. arun kumar shrestha et al./ bibechana 20 (2023) 285-289 288 figure 2: background radiation of different parts of taplejung district. figure 3: background radiation of different parts of panchthar district. figure 4: background radiation of different parts of illam district. figure 5: background radiation of different parts of jhapa district. figure 6: comparative study of dose rate at different districts. figure 7: variation of background radiation with altitude. 4 conclusion the study focused on measuring the natural background radiation dose at different locations in the taplejung, panchthar, ilam, and jhapa districts. a total of twenty locations were considered for the study, and the average dose rate for four districts was found to be (0.24 ± 0.25)msv/y. it is also observed that background radiation also increases with increasing altitude. it was determined that the annual effective dose value was lower than the legally prescribed dose limits for non-radiation workers and the general public, as set by the international commission on radiological protection (icrp). therefore, the natural exposure level in taplejung, panchthar, ilam, and jhapa is not hazardous to the people residing in the study region. arun kumar shrestha et al./ bibechana 20 (2023) 285-289 289 conflicts of interest the authors declare that there are no conflicts of interest regarding the publication of this paper. acknowledgment a. k. shrestha would like to thank the university grants commission nepal for providing the ph.d. fellowship and research support grant (phd078/79-st-13). references [1] l. benedick and z. jeran. radiological of natural and mineral drinking water in slovenia. radiat. prot. dosim., 151:306–313, 2012. [2] r.p. chetri. background radiation: detection, measurement, and hazards. himalayan physics, 627:119–122, 2017. [3] k. giri et al. radiation measurement at x-ray centers of a few hospitals in kathmandu city, nepal. kathmandu university j. sci., eng. tech., 1(4):1–4, 2007. [4] a. c. geetha and h. sreedharan. review on studies in high background radian areas (hbras) of various parts of the words. int. j. adv. res. biol. sci., 3(8):163–169, 2016. [5] m.s. potgieter. solar modulation of cosmic rays. living rev. sol. phys., 10:1–70, 2013. [6] e. kam and a. bozkurt. environmental radioactivity measurements in kastamonu region of northern turkey. appl. radiat. isot., 65:440– 444, 2007. [7] j. a. centeno et al. medical geology: impacts of the natural environment on public health. geosciences, 6(8):1–3, 2016. [8] k. kanani et al. design, manufacturing, and calibration of the new models of silver gm activation counters. measurement, 153(1):107300, 2020. [9] t. f. gesell and h. m. prichard. the technologically enhanced natural radiation environment. health phys., 28(4):361–366, 1975. [10] m. gholami et al. gamma background radiation measurement in lorestan province, iran. iran. j. radiat. res., 9(2):89–93, 2011. [11] m.b. tavakoli. annual background radiation in the city of isfahan. med. sci. monit. res., 9:7–10, 2003. [12] p. pantha et al. study of natural background radiation in kathmandu valley. bibechana, 16:187–195, 2018. [13] s. gautam et al. annual effective dose from natural background radiation in pokhara, nepal. asian journal of research and reviews in physics, 3:36–42, 2020. [14] g. dhami et al. comparison of the background radiation level within kanchanpur district, nepal. journal of nepal physical society, 6(2):34–40, 2020. [15] a.k. shrestha et al. an exposure to natural background radiation in eastern nepal. damak campus journal, 11(1):1–7, 2023. [16] c. bhatt et al. environmental radiation an important concern in the himalayas (nepal). j. environ. radioact., 112:171–174, 2012. [17] m. begum et al. assessment of background radiation level in different locations of bangladesh. nuclear science and applications, 27(12):33–36, 2018. introduction materials and methods description of instrument study area measurement and calculations results and discussion conclusion bibechana vol. 22, no. 2, august 2025, 171-180 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar a spectroscopic study of the merging dwarf galaxy pgc 007782 shankar timalsina, daya nidhi chhatkuli∗ 1department of physics, tri-chandra multiple campus, tribhuvan university, ghantaghar, kathmandu, nepal ∗corresponding authors. email: chhatkulidn@gmail.com abstract we conducted a detailed spectroscopic study of pgc 007782, an interacting emissiontype dwarf galaxy. this study utilized optical spectra of emission lines to explore the system of interacting dwarf galaxies. gaussian fitting techniques were used to examine the main spectral lines (hα, hβ , hγ , sii, oiii, and nii) and determined their gaussian parameters. our investigation mainly focused on nine prominent emission lines with wavelengths ranging from 4342 å to 6733 å. among which, hα is the most prominent line with a peak intensity of 72.16 × 10−17 erg/s/cm²/å corresponds to the central wavelength of 6564 å. with the flux of 2.93 × 10−17 erg/s/cm²/å, the nii line is the weakest at the central wavelength of 6550 å. the sii line has the highest fwhm value of 4.04 å, indicating a higher gas temperature. each of these emission lines exhibits a nearly perfect gaussian profile, with a coefficient of determination exceeding 92%. utilizing the hα line, the star formation rate of pgc 007782 is calculated to be 0.014 m⊙ yr-1, indicating that active star formation is concentrated at the galaxy's core. the calculated value of balmer decrement is 4.02 which is higher than the normal value indicating the light coming out from this galaxy is being blocked by the dust particles. with oxygen abundance of 8.31dex, the physical and morphological characteristics of pgc 007782 confirmed this galaxy as a metal-poor, actively star forming blue compact dwarf (bcd) galaxy. keywords dwarf galaxy, galaxy merger, balmer decrement, star formation rate article information manuscript received: december 13, 2024; revised: january 8, 2025; accepted: may 20, 2025 doi https://doi.org/10.3126/bibechana.v22i2.72618 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction galaxies frequently come together and merge to form bigger and complex ones. this process (hierarchical) of structure formation, happens frequently in regions of many galaxies, like clusters or groups. according to smith et al. (2018) [1], galaxies interact and collide frequently in this crowded region. when galaxies merge, gas clouds are compressed causing new stars to form quickly leading to a burst of star formation [2]. merging galaxies also create long streams of gas and stars known as tidal, 171 http://nepjol.info/index.php/bibechana chhatkulidn@gmail.com https://doi.org/10.3126/bibechana.v22i2.72618 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ shankar timalsina and daya nidhi chhatkuli/ bibechana 22 (2025) 171-180 172 pulled out by gravity. these tails come together and change the shape of the galaxy [3]. dwarf galaxies are small but significant for study as they can trigger starbursts-short periods of intense star formation. galaxy formation can be affected by these starbursts, particularly in nearby galaxies [4]. these bursts of stars are very helpful for understanding how galaxies change over time and give information about dark matter [5]. when a small galaxy merges with bigger ones, the merging process mixes the gas inside the galaxies spreading heavy elements (metals) throughout the galaxy. however, the amount of metal (metallicity) can be temporarily decreased when two galaxies of similar size merge [6]. scientists use spectra of dwarf galaxies to know about them. dwarf galaxies contain stars of different gas and chemical compositions as studied by lee et al. (2018) and smith et al. (2020) [7, 8]. hα and oiii emission lines can reveal areas where stars are still forming [9,10]. information about how the galaxy's stars and metals have changed over time can be provided by absorption features [11,12]. these studies show a wide range of histories of dwarf galaxies. as star formation rate (sfr) measures how quickly gas and dust in the galaxy turn into stars, sfr is essential for understanding how galaxies grow and evolve. star formation rate of the universe has changed significantly over time. it reached its peak around redshifts z∼ 2. this period of intense star formation is called cosmic noon [13]. the star formation rate reached its maximum at that time due to the dense gas contained in the galaxies. about 75% of all stars in the universe formed between the redshift of z∼2.5 to z∼0. the sfr steadily declined after this peak. studying these periods provides valuable insight into galaxy evolution. many factors affect sfr. under the effect of gravity, higher gas density and pressure cause gas to collapse, leading to faster star formation [14]. when the metallicity is high, that is, if the amount of elements heavier than hydrogen and helium is high, higher metallicity cools the gas better, making it easier to form stars [15]. barnes & hernquist in 1996 [16] studied the sfr in galaxies. according to them, when galaxies merge, tidal forces squeeze gas clouds, causing bursts of star formation. magnetic fields have positive as well as negative influences on sfr. magnetic fields either slow down by holding gas clouds together or gathering gas to those places where stars can form easily [17]. another factor that affects the sfr is active galactic nuclei (agn). agn affects the sfr by either pushing gas to form stars or heating and removing gas, stopping star formation [18,19]. to study galaxy evolution of the universe, understanding sfr is crucial. a very high sfr can finish the gas reservoir of the galaxy, stopping future formation of stars and changing the galaxy's shape and types of stars [20]. elements like iron and carbon are released when supernova explodes, mixing these elements with surrounding gas and dust, enriching these materials in the galaxy. next generation of stars and even planets use this enriched gas and dust [21]. studying sfr overtime provides valuable information about the forces that shape them, helping us to know how galaxies and the universe have changed [22]. in this project, we present the spectroscopic study of a low redshift (z = 0.0180), metal-poor, antenna type actively star-forming merging blue compact dwarf (bcd) galaxy pgc 007782 and calculate its sfr and oxygen abundance. 2 sample selection due to their small size, low surface brightness, and dimness, dwarf galaxies are challenging to detect since they are hard to separate from surrounding stars and background noise. while massive galaxy interactions have been extensively studied, there's a lack of research on interactions between low-mass dwarf galaxies. for this reason, studying dwarf galaxies is crucial. scientists can also learn much about dark matter—an unknown substance that makes up a large fraction of the universe. not only that, because of their more easily studied stellar populations, these areas provide important information on the formation and evolution of stars. dwarf galaxies, the building component of larger galaxies, provides information about the origin and evolution of galaxies as well as how they interact with one another and with larger galaxies. to delve deep into, we have selected a low redshift (z = 0.0180) merging dwarf galaxy pgc 007782 from a catalog by paudel et al., (2018) [23] located at r. a. (j2000): 02 h 02 m 38.7600 s, dec.(j2000): -09 d 22 m 13.080 s. morphologically, pgc 007782 is an antenna type galaxy 77.06 mpc far from us. its (g – r) color is 0.30 mag and has no satellite. the apparent g and r band ab magnitude of the galaxy are 15.43 mag and 15.13 mag respectively. the radial velocity of the galaxy taken from ned is 5396 km/s. only one neighbor is found within the search criteria (within a sky-projected distance of less than 700 kpc, and a relative line-of-sight radial velocity of less than ±700 km/s). the sdss dr 12 optical image of the galaxy pgc 007782 and its spectrum are shown in fig. 1 (a) and 1 (b) respectively. we can see that the galaxy is elongated along the n-s direction and has an antenna in the southern region. the antenna indicates that it is an interacting galaxy. in the optical wavelength range of 3500 å to 7500 å, there shankar timalsina and daya nidhi chhatkuli/ bibechana 22 (2025) 171-180 173 are many emission lines which are due to different elements like hydrogen, helium, oxygen, nitrogen, sulphur and so on. the spectrum shows that the galaxy is an emission type. figure 1: (a) the sdss dr 12 optical image of interacting galaxy pgc 007782. (b) the optical spectrum of the galaxy pgc 007782. 3 data analysis to study the star-forming properties of the merging dwarf galaxy pgc 007782, this galaxy has been selected as a sample. the study will utilize data from the sloan digital sky survey (sdss), obtaining its spectrum and analyzing it using origin software. the galaxy spectrum will be extracted by using aladin software. aladin software provides a flexible viewer for astronomical images. with it, users can interactively analyze and explore astronomical objects and their attributes by seeing multi-wavelength photos and superimposing catalogs. aladin 2.5 is used to extract the archival data of the dwarf galaxy pgc 007782 from its fits file. the data will be used to plot the optical spectrum by using origin software of version 8. origin software is widely used in the field of astronomy and is one of the simplest method to create high-quality graphs, performs statistical analysis, and supports curve fitting and automation and analyze graphs. a gaussian fitting technique will be used to model data that follows a gaussian distribution or simply normal distribution. it involves fitting a gaussian function to a dataset to calculate parameters as mean, standard deviation, which characterizes the central tendency and spread of the data respectively. this model is also applied to curve fitting, signal processing and experimental analysis in a variety of fields. we measure the physical parameters of each emission line by gaussian fits, including total flux, full width half maximum (fwhm) and best-fit coefficient. mathematically, gaussian distribution function is given as; fg(x) = 1√ 2πσ2 e−(x−µ) 2σ2 2 where, x represents a normal random variable, µ represents mean deviation and, σ represents the standard deviation of the distribution. fwhm is the width at which maximum amplitude drops to half a width. a width referred to as the full width half maximum (fwhm) is reached at this point. we choose nine emission lines and their gaussian parameters based on the greater intensity, which will be described in this work along with their gaussian parameters. we will calculate the hydrogen line ratio and the star formation rate (sfr). kennicutti's [24,25] empirical formula is used for calculating the sfr providing a reliable, empirical methods to calculate the star formation rate based on observed hα luminosity. mathematically, kennicutt's empirical formula is given by equation (1). sfr (m⊙year-1) = 7.9 × 10-42 σ l (hα) (ergs s-1) (1) where l(hα) represents the total luminosity of hα line which will be calculated by using gaussian fits. l(hα) = area of gaussian fit × 10-17 × 4r2 (ergs s-1). r is the radius of the sphere which is calculated as: r = d × 3.08 × 1024 cm. here, d is the luminosity distance of the galaxy in mpc. the gas phase metallicity will be calculated by using the empirical formula given in equation (2) provided by marino et. al. (2013) [26]. 12 + log(o/h) = 8.743 + 0.462 × log (nii/ hα) (2) shankar timalsina and daya nidhi chhatkuli/ bibechana 22 (2025) 171-180 174 4 results and discussion gaussian fitting curves of the main emission lines, i.e., hα, hβ , hγ , sii, oiii and nii of the dwarf galaxy pgc 007782 are obtained. among these, sii, oiii and nii are in duplet. hα, hβ , hγ , are the balmer lines. only the prominent emission lines hα, hβ , oiii5008 and nii6585 are shown in fig. 2. observed data are presented by the black dots and the red solid line represents the gaussian fit for the observed data. it shows that the observed data follows the gaussian distribution more accurately. figure 2: the gaussian fitting curves of four prominent emission lines hα, hβ oiii and nii are shown. gaussian parametric values of the dwarf galaxy pgc 007782 obtained after fitting of gaussian curves are presented in table 1. the names of the chosen emission lines are shown in the first column whereas, column two and three show the wavelength corresponding to peak intensity (λp) in å and the peak intensity λp in (×10-17 erg/s/cm2/å) respectively. the fourth, fifth, sixth, seventh and eighth columns represent fwhm in å, area of gaussian curve in (×10-17 erg/s/cm2/å), height of gaussian curve in (×10-17 erg/s/cm2/å), off set and coefficient of determination value respectively. shankar timalsina and daya nidhi chhatkuli/ bibechana 22 (2025) 171-180 175 table 1: gaussian parameters of the observed emission lines of dwarf galaxy pgc 007782. elements λp (å) ip fwhm (å) area height offset r-square hγ 4342 26.23 2.49 68.18 25.72 +0.0036 0.97 hβ 4863 26.35 2.77 77.75 26.37 -0.0043 0.98 [o iii] 4960 19.97 2.79 65.12 21.95 +0.0042 0.99 [o iii] 5008 64.74 2.91 211.73 68.38 +0.0004 0.99 [n ii] 6550 2.93 3.65 10.79 2.78 +0.0004 0.92 hα 6564 72.16 3.85 312.60 76.20 +0.0025 1.00 [n ii] 6585 8.48 3.84 36.54 8.94 -0.0049 0.98 [s ii] 6718 15.70 4.04 50.78 11.80 -0.0013 0.99 [s ii] 6733 10.74 3.85 66.75 16.30 -0.0046 1.00 through a careful investigation of the emission lines, significant new information about the physical property and underlining process has been obtained. hα emission lines come out with highest peak intensity of 72.16 × 10-17 erg/s/cm²/å, corresponding to the wavelength of 6564 å suggesting active star formation within the galaxy. this prominent line implies that necessary hydrogen gas is being ionized by young hot stars. similarly, second and third peak intensity of 64.74 × 10-17 erg/s/cm²/å and 26.35 × 10-17 erg/s/cm²/å respectively for lines oiii and hβ lines at 5008 å and 4863 å, shows high-excitation regime that are probably driven by energetic processes near hot star or an active galactic nucleus (agn). balmer series lines hγ and hhβ show nearly comparable peak intensity. these lines give important information on the temperature and density of the ionized gas, as well as the constant ionization state throughout the galaxy [27]. nii lines are the weakest emission lines, indicating a reduced excitation or amount of nitrogen in the ionized part of the galaxy with a peak intensity of 8.48 × 10-17 erg/s/cm²/å and 2.93 × 10-17 erg/s/cm²/å, corresponding to the wavelength 6785 å and 6750 å respectively. the sii curve shows the greatest value of fwhm that is 4.04 å, indicating that the sii line has the widest width at half of its maximum intensity, compared to the other lines in the above table. also, a larger fwhm means the spectral line is wider which indicates that a larger range of wavelengths are being occupied by the line's emissions process or transition. this happens for a number of reasons such as increased temperature, increased turbulence, or a wider velocity dispersion of the substance that is emitting or absorbing [28, 29]. a large fwhm value, sometimes indicates a wider spread of velocity within the emitting or absorbing gas or a more complicated physical environment. the table also provides measurement of the fwhm for various other spectral lines observed in optical spectra, like the balmer line hγ has the lowest fwhm of 2.49 å, indicating its width when its intensity is at half of its peak. this smaller fwhm indicates that the spectral line is narrower. this narrower line indicates that the substance, that is emitting or absorbing, is limited to a narrower range of temperature or velocity. this can happen in those environments where the motion or temperature of the gas is more ordered or where there is less turbulence. the greatest gaussian area corresponds to the hα emission lines, which is 312.60 × 10-17 erg/s/cm2/å. a larger area denotes a stronger or more intense emission or absorption feature, since it suggests a greater total energy emitted or absorbed over the whole width of the spectral line. in contrast, nii has the smallest area that is 10.79 × 10-17 erg/s/cm2 /å, suggesting a lower total energy flux or intensities, showing weaker or less intense spectral features. oiii has the largest offset of 0.0042 representing a greater discrepancy between the major data point and the expected value from the models or the theoretical prediction. similarly, nii has also the smallest offset of -0.0049, indicating there is least discrepancy between the measured data point and the expected values. shankar timalsina and daya nidhi chhatkuli/ bibechana 22 (2025) 171-180 176 figure 3: comparison of the physical parameters such as area, height and fwhm for emission lines. different colors represent different parameters. green color represents height of the emission lines, sky blue color indicates area of the fitting curve and red color represents the fwhm value, for their respective emission lines. graph plot fig. 3 compares three gaussian parameters such as area, height and fwhm values of the emission lines. these features indicate total energy emitted by the lines (flux), velocity dispersion or broadening of the gas (turbulence) and, peak intensity of the line. emission lines with larger areas usually have peak intensity [30]. for example, hα line has the largest area and highest peak intensity. above plot also shows a broad fwhm value can still have a high area. however, their peak heights are lower due to the distribution of energy over a wider wavelength range. for example, sii lines have moderate area but sii lines' broader fwhm reduces their peak heights compared to lines like oiii (5008), which has a narrow width [31]. similarly, emission lines having narrower width might still have higher peak height. the oiii (5008) line has a small value of fwhm but still has a high peak, maybe due to this line emitting gas which is less turbulent or moving uniformly. a combination of high area, peak height, and broad fwhm suggests intense star formation accompanied by significant gas turbulence. modest area, modest height of the peak and narrow fwhm indicates less active regions with lower gas densities velocities. lastly, low area, low height of the peak and broad fwhm indicates low density gas with significant turbulence or outflow. through the careful examination of emission lines of dwarf galaxy pgc 007782, significant details on the physical parameters and star-forming activity are revealed. the line ratio of hα to h, is calculated to be 4.2. this is the significant deviation from the expected value of 2.8. this variation indicates the possibility of internal dust reddening within the galaxy, as dust dims the light from both lines differently, making the hα line a comparatively greater appearance. dust-rich environments within the galaxy might have affected the observed features of the emission lines as suggested by the high hα to hβ line ratio [32]. the star formation rate for dwarf galaxy pgc 007782 after extinction correction is determined to be 0.0136 m year1 by using equation (1). this calculated value indicates that the galaxy is actively producing stars at the faster rate, but as compared to the larger more massive galaxies, this galaxy forms new stars at a slower pace. the calculated value of sfr also indicates that this galaxy's current star formation is well after the cosmic noon and is still forming stars at a lower rate in the local universe. in contrast, as galaxies have consumed much of their gas and external fueling mechanism are less frequent, the local universe (z∼0) shows the steady decline in sfr. this rate for pgc 007782 while which is not as high as some other star forming galaxies nevertheless, indicates a strong star forming activity particularly for a dwarf galaxy. the emission line metallicity is calculated to be 8.31, using the line ratio of nii and hα emission lines in equation (2). it shows that pgc 007782 is a metal-poor galaxy, indicating that this is a young or not fully evolved dwarf galaxy, which is typically a blue compact dwarf galaxy. these bcds, small, irregular galaxies with rapid star formation rates appear blue, due to the presence of a larger shankar timalsina and daya nidhi chhatkuli/ bibechana 22 (2025) 171-180 177 number of young hot stars [33]. the metal poor state of pgc007782 indicates that it has not experienced significant chemical enrichment, a characteristic common to star-forming galaxies that has not yet accumulated a major heavy element accumulation. the calculated parameters of the galaxy are summarized in the fig. 3. figure 4: figure showing the horizontal bar graph summarizing the calculated parameters. initially, by measuring the area under the gaussian fitting for the hα line, the calculated value for sfr is 0.0084 mm⊙yr1. the light emitted from these galaxies has to pass through dust, which blocks some of the light, especially at shorter wavelengths. the balmer decrement i.e., the ratio of hα and hβ , indicates the presence of dust. the theoretical value for balmer decrement is 2.28, but what we calculate is 4.02, which is significantly higher. the high ratio of hα to hβ indicates that much of the hβ line is blocked by the dust, whereas hα line is not affected by the dust, making it stronger and indicating high star formation rate [34]. the extinction coefficient was applied to the hα flux and calculated to be 0.291, indicating dust along the line of sight to the observed object. this calculated value shows a moderate amount of dust between the observer and the object. after accounting for extinction, which reflects the true star formation activity, the calculated sfr is 0.014mm⊙ yr-1, which means dust hides some of the star formation activity. we use the line of [nii] and hα to calculate the metallicity i.e., the abundance of elements heavier than hydrogen and helium, which is calculated to be 8.31 dex. this value suggests that pgc 007782 has fewer heavy elements, indicating that this galaxy is a young or not fully evolved. 5 comparison with other works the sfr obtained from spectroscopic study for sdssj222726.64+120539.8 and sdssj162753.47+482529.3 is 0.010 mm⊙ yr-1 and 0.016 mm⊙ yr-1 respectively [35], which is similar to the sfr of pgc 007782 showing that all have moderate star formation activity. metallicity of these galaxies are nearly the same showing all these galaxies are metal poor. the sfr of cg 0315 is calculated to be 0.051 mm⊙ yr-1 [36], which is higher than the sfr of pgc 007782, indicating star forming activities are happening more in cg 0315. with an effective radius of 4.5 arcsecond and half-light radius of 2.60 arcsecond, cg 0315 is declared to be bcd similar to pgc 007782. the sfr for ngc 5194 (m51a) is calculated to be 3.4 mm⊙ yr-1 [37]. this shows that ngc 5194 (m51a) forms stars at the rate of around 261 times the star formation rate of pgc 007782, indicating rapid star formation process. sfr using the hα line method calculated for sdss j134326.99+431118.7 shankar timalsina and daya nidhi chhatkuli/ bibechana 22 (2025) 171-180 178 is 0.019 mm⊙ yr-1 [38] which is slightly higher than that of pgc 007782 and has a more active star forming environment. this was also conducted by using the optical spectrum of the major emission lines. sfr of galaxy ugc 4483 is calculated to be 0.008 mm⊙yr-1 [39]. this value of 0.008 mm⊙-1 is slightly lower than the sfr of pgc 007782. that means, pgc 007782 forms stars approximately 1.6 times higher. this indicates that the higher sfr galaxy has more active star forming regions or possibly more efficient star formation processes. consequently, the galaxy pgc 007782 with the higher star forming rate undergoes more rapid evolutionary changes compared to ugc 4483. this comparison highlights that galaxies can vary significantly in how fastly the formation starts, influenced by factors like their size, type and the amount of gas available for star formation. the higher rate observed in this galaxy suggests that it is currently undergoing more active star formation compared to the standard reference value. these measurements are important for understanding the process of star formation across different galaxies and their evolution over cosmic time. 6 conclusion the system of interacting dwarf galaxies is examined through optical spectra of emission lines. strongest or major emission lines are gaussian fitted in this project. we present the result of a thorough study of the emission lines of the dwarf galaxy pgc 007782 with great attention given to the principal spectral lines hα, hβ , hγ , sii, oiii, and nii. gaussian fitting techniques were used to determine the fwhm, wavelength, peak intensities and other relevant parameters of these lines. based on the observation and calculations, the following conclusions are drawn. (a) the hα emission line is the most prominent. similarly, the nii emission line is weakest reflecting reduced energy releases from this element. (b) the sii line has the largest fwhm indicating that, sii line is wider than other emission lines, possibly caused by higher temperature or more movement of the gas in the galaxy. (c) areas were represented by total flux under the gaussian curves, with hα having the largest area, indicating strong emission. similarly, the nii line has the smallest area indicating weak emission. (d) pgc 007782 is classified as a metal-poor actively star-farming blue compact dwarf (bcd) galaxy indicated by sfr (0.0136 mm⊙yr-1) and its metallicity (8.31dex). 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[39] j. brinchmann, s. charlot, s. d. m. white, and c. a. tremonti. the physical properties of star-forming galaxies in the low-redshift universe. monthly notices of the royal astronomical society, 351(4):1151–1179, 2004. introduction sample selection data analysis results and discussion comparison with other works conclusion bibechana vol. 21, no. 3, december 2024, 195-212 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar characterization of atmospheric pressure circular dielectric barrier discharge via electrical and optical methods roshan chalise1,2∗, krishna regmi2, sadip nepal2, sangat sharma1, suresh basnet1, and raju khanal1 1central department of physics, tribhuvan university, kirtipur, kathmandu 44613, nepal 2amrit campus, department of physics, tribhuvan university, kathmandu 46600, nepal ∗corresponding author. email: plasma.roshan@gmail.com abstract this research work is concerned with the comprehensive study of the electrical and optical characterization of an atmospheric pressure circular dielectric barrier discharge (apcdbd) in natural air. the effect of airflow and input voltage on the power supply’s behavior has been investigated to keep the constant electrode gap . the energy and power dissipated during the discharge per cycle are calculated by the lissajous plot and the time average of the voltage and current curve. for the optical characterization of apcdbd, light emission during the plasma discharge is examined and the electron excitation temperature, rotational temperature, vibrational temperature, and plasma density have been computed. the boltzmann plot method is used to estimate the electron excitation temperature and vibrational temperature. the rotational and also vibrational temperatures are calculated using online massiveoes software. it is found that multiple filamentary micro discharge is increased while increasing the airflow and input voltage of the power supply. energy per cycle of the discharge is increased for increasing input voltage and vice-versa in airflow. the discrepancy in the calculation of energy dissipation from discharge between time-averaged and lissajous’s plot method is estimated. however, the fluctuation is less in the lissajous’s plot method; hence, the energy calculation from the lissajous plot method is more suitable for plasma discharge. the power consumption of the plasma reactor is found to be dependent on the input of the power supply. electron excitation temperature and the rotational temperature of the discharge decrease with increasing the airflow in the discharge and increase with increasing input voltage. therefore, by using the airflow in dielectric barrier discharge, we can move closer to the room temperature of atmospheric pressure plasma. keywords boltzmann plot, electrical parameters, electron excitation temperature, lissajous curve, rotational temperature, vibrational temperature. article information manuscript received: january 19, 2024; revised: april 19, 2024; accepted: april 23, 2024 doi https://doi.org/10.3126/bibechana.v21i3.62034 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 195 http://nepjol.info/index.php/bibechana plasma.roshan@gmail.com https://doi.org/10.3126/bibechana.v21i3.62034 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ roshan chalise et al./ bibechana 21 (2024) 195-212 196 1 introduction in recent years, low-temperature atmospheric pressure plasma has received a lot of attention as it is widely used in diverse fields of science and technology [1–8]. the dielectric barrier discharge (dbd), one of the various forms of atmospheric low-temperature plasma reactors, has a wide range of industrial uses [9, 10]. at atmospheric pressure, the dbd normally operates in a filamentary discharge condition, which restricts the possibilities for its industrial application. however, specific circumstances, homogeneous dbd can be produced, and it has the potential for use in a variety of industrial processes, including plasma sterilization, thin-film deposition, material surface treatment, remediation of diesel-contaminated soil, evaluation of bio-compatibility, and many more [11–15]. in the region of non-thermal plasma where thermal nonequilibrium between the electron, ions, and neutrals exists, the electron temperature can be orders of magnitude higher than the temperature of the heavier particles (atoms, molecules, and ions). these plasma do not heat any surfaces as they come in contact with because the ions and the neutrals stay relatively cool [16]. due to these properties, it is possible to handle heat-sensitive materials, such as polymers and biological tissues, as well as lowtemperature plasma chemistry. the dbd plasma typically consists of a large number of microscopic micro-discharges or filamentary that last for only a nanosecond or microsecond. the uniformity of the dbd is highly desired for industrial applications, particularly for operations involving surface treatment [17]. due to helium gas has low breakdown voltage and the long lives of the metastable species, it is simple to create homogeneous dbds, but the process is expensive and inefficient. since argon and nitrogen are less expensive gases, it is preferable to construct a homogeneous dbd using them [18,19]. since argon’s mean free path is short at atmospheric pressure, the breakdown voltage is comparatively larger which may make the glowto-arc transition easier to occur. because of this, it is challenging to achieve large-gap homogeneous dbd in argon gas between two plane-parallel electrodes [20]. surface dielectric barrier discharge is considered to be especially promising in aerospace engineering [21,22], biomedical sciences [23], energy conversion, etc [24]. electrode materials and shapes affect the discharge modes. meanwhile, the discharge influences electrode surface [25]. in the air, at atmospheric pressure, mahoney et al. created a dielectric barrier discharge plasma. they were calculated that the power consumption for the reactor operating without gap separation ranged from a few watts to a maximum of about 14 w using voltage/charge lissajous figures. the obtained emission spectrum was mostly within the second positive system of n2 ( c3πu → b3πg ) and the first negative system of n+ 2 ( b2 ∑+ u → x2 ∑+ g ) [26]. in atmospheric air, surface dielectric barrier discharge plasma often displays filamentary and diffuse discharges [27]. however, subedi et al. reported that a consistent and uniform dbd discharge was noted between the electrodes, which have a gap of 1 to 3 mm and a 1.5 mm dielectric barrier from argon gas. the gas supply is regulated to a flow rate of 2 liters per minute. high voltage (0 to 20 kv) power supply operating at 10 to 30 khz frequency produced the discharge, with an electron density of around 1016 cm−3 and an electron temperature of about 1 ev reported [1]. compared to filamentary-mode discharges with sinusoidal excitation, it is shown that pulsed excitation over a broad voltage range can generate stable and homogeneous dbd with improved energy efficiency. furthermore, pulsedexcitation dbd uses less discharge power while producing a higher total transferred charge per voltage cycle. the critical voltage for creating homogeneous dbd can be enhanced with water electrodes, and suppressing instabilities with them is desirable for enhancing stability [28]. fang et al. found that homogeneous discharge exists only under certain conditions. the voltage range for maintaining a stable discharge is found to be wider when the barrier thickness is smaller, the gap distance is shorter and the mesh number is greater [29]. kogelheide applied a damped sinusoidal voltage waveform with oscillation periods in the microsecond time scale to study a volume and a twinning surface dbd created in various nitrogen-oxygen mixtures at atmospheric pressure. it is discovered that the oxygen concentration in the working gas mixture has a significant impact on the electron density, the lowered electric field, and the dissipated power [12]. using an insitu treatment technique, dhakal et al. produced spark dielectric barrier discharge plasma and examined the effects on seed germination and water sterilization. significant alterations were made to the liquids’ physicochemical characteristics by the plasma treatment. following an 8-minute plasma treatment, the concentrations of h2o2, no2, and no3 were raised to 30, 40, and 100 mgl−1, respectively. e. coli and s. aureus were nearly eliminated after 8 minutes of plasma treatment. moreover, after five minutes of treatment with plasma, coriander seeds germinated more easily [11]. the most fundamental characteristics in gas discharges are electron density and electron temperature, and knowing these factors is crucial for optimizing discharge performance [30]. a plasma’s electron density and temperature may be measured using a variety of techniques. the langmuir probe, microwave interferometer, laser thomson scattering, optical emission, and absorption spectroscopy are roshan chalise et al./ bibechana 21 (2024) 195-212 197 the techniques that are most often utilized. the probe method is cheaper but it disturbs the produced plasma. in atmospheric pressure plasma, discharge produced in a small gap between the electrodes, if any probe is inserted between this discharge the properties of discharge differ or discharge is not formed [31]. therefore, optical emission spectroscopy (oes) which is non-intrusive and provides abundant information about the plasma species, is a potent method that is frequently employed for plasma diagnosis as an alternative to probe measurement. the temperature, chemical species concentrations, and ionization state of the plasma may all be determined by examining and interpreting its spectra [30, 32]. recently, using the boltzmann plot technique and the assumption that the plasma is in a state of local thermodynamic equilibrium, the electron temperature in plasma in the atmospheric pressure range has been measured based on the visible spectrum. in a radio frequency-inductive discharge in the atmospheric pressure range, the existence of the local thermodynamics equilibrium (lte) condition, which must be met to use the boltzmann plot technique to determine the electron temperature, has been confirmed [33]. in this work, we have produced the atmospheric pressure circular dielectric barrier discharge (apcdbd) with an airflow system in the stainless electrode characterized by electrical and optical methods. dielectric barrier discharges (dbds) and their behavior in a variety of applications are the main subjects of current research on the electrical and optical characterization of atmospheric circular dbds. it seeks to improve material treatment procedures, comprehend plasma dynamics, and optimize reactor designs. through the use of dbd plasma, these investigations seek to improve material treatment procedures, comprehend plasma dynamics, and optimize reactor designs.to increase the efficacy and efficiency of dbd systems for uses such as surface modification, plasma cleaning, sterilization, and material treatment, the study examines electron density, ion and current density, mean electron energy, and discharge gap voltage. to explore possible applications, the research also looks at electrical breakdown, plasma production, and single filament behavior in dbds. literature has been found on using airflow in dbd configuration from natural air to reduce the temperature of discharge and comprehensive study of plasma parameters of plasma discharge like electrical parameters, delivered energy and power, electron excitation temperature, plasma density, and rotational and vibrational temperature of atmospheric pressure discharge for variation airflow and input voltage of power supply. the variation of these plasma parameters can affect treatment process of plasma application, which we have implemented in this work. 2 methodology the block diagram of the experimental setup employed in this work is shown in figure 1. the apcdbd device consists of two plane-parallel stainless steel circular metal electrodes of diameter 57.23±0.08 mm and thickness 4.36±0.07 mm, respectively: at lower electrodes are covered by a dielectric layer 2.00 mm thickness and 90.00 mm diameter. figure 1: schematic diagram of apcdbd and its real discharge snapshot. to ensure stable plasma operation, the gap that separates the electrodes is limited to 4.0 mm wide. plasma discharge flows in the gap which was produced by a high-voltage power supply (chengdu chuangyu xinjie technology co. ltd.) with an output voltage of 3-30 kv. to control the out voltage of the power supply by changing the input voltage of the power supply (0-24.00 v) dc. the natural airflow is provided on the central hole of the upper electrode by a mini air pump and is regulated by a flow meter. an oscilloscope (tektronix tbs 1052b) and a 1000 × voltage probe (pintek hpv -40) were used to measure the voltage across dbd. to monitor the discharge current or transferred charge during plasma formation, a 100 ω resistor or 10 nf capacitor was connected in series with the ground (10 × voltage probe, tektronix tpp0201) electrode. the power consumption of discharge was calculated using the lissajous curve between the applied voltage and the charge produced during the discharge. the method most commonly used for optical characterization is the extraction of the discharge’s optical emission spectrum (oes). the light that the discharge emits is detected by an optical emission spectrometer hr1-high-resolution spectrometer (aseq instrument: pixels 3648, signal-to-noise ratio 300:1, exposure time 2.5-600 ms, ccd reading time 14 ms, wavelength 200-820 nm, 10 µm slit, 0.176 nm resolution), 10.0 mm far from the discharge, with 300 ms exposure time and 30 scan average. the apcdbd plasma is generated in different airflow and input applied voltage at fixed electrode gap roshan chalise et al./ bibechana 21 (2024) 195-212 198 and electrode material. comprehensive electrical parameters such as voltage, current, charge, frequency, energy, and power were calculated as follows: discharge current (idis) and discharge voltage (vdis) is the corresponding value of current and voltage of the first micro discharge observed in the i-v curve for one complete cycle. peak-to-peak voltage vpp of the discharge is measured from peak to peak value of the sinusoidal current-voltage waveform. vp of the discharge is half of the peak-to-peak value of the vpp [34]; vp = vpp 2 (1) root mean square (rms) of sinusoidal voltage in discharge vrms is calculated as [34]; vrms = vp√ 2 (2) the frequency of the discharge is obtained as the reciprocal of the time of one complete cycle of discharge by [34] frequency(f) = 1 t (3) we have implemented two ways of calculating of energy and power of the discharge. five per cycle are carried out to calculate the energy from the voltage-current curve and lissajous plot, and results are presented per cycle with mean values with standard deviation. the first way is to calculate the time-averaged electrical energy of the plasma discharge using voltage and current curves [34]: et = ∫ v (t)× i(t)dt (4) where v (t) and i(t) are the voltage and current at the respective time, respectively. the plasma discharge’s time-averaged electrical power consumption can be calculated using [34] pt = 1 t ∫ v (t)× v (t)dt = f × et (5) the electrical power calculated by using this method typically fluctuates from cycle to cycle. after that, several cycles are required to get a converged mean value. in addition, to ensure that the current peaks are correctly recorded and provided, the data must be captured using a high sampling rate (usually a few ns) and a high bandwidth oscilloscope. there is still a problem with this approach, despite its relative simplicity and accuracy: when there are strong current peaks, it can be difficult to resolve the synchronous current accurately because its amplitude is at least one order of magnitude smaller than the current peaks [35]. to overcome this issue manley et al. (1943) developed another simple method [36] used for surface dbd plasma [37]. this method consists of placing a capacitor c between the grounded electrode and the earthing point as shown in figure 1. it is accomplished by plotting the charge curve of the inserted 10 nf capacitor throughout a full cycle as a function of the applied voltage. each period’s energy dissipated by the discharge is represented by the area inside the closed lissajous curve. the shape of the lissajous curve depends on various factors, including the frequency, amplitude, and phase relationship between the two waveforms. so, to obtain the area of the lissajous curve, the applied voltage and the charge accumulated curve are plotted. if we take one full cycle of discharge data, the area of this curve indicates the energy that the discharge releases for each cycle [36]. the energy dissipated per cycle is calculated by [36] el = area covered by lissajous (q-v) plot (6) using the lissajous (q–v plot) approach, the power dissipation across the apcdbd is calculated by multiplying energy with the current-voltage waveform frequency [36]: pl = (e × f) (7) this approach’s primary benefit is that it is more reproducible from cycle to cycle and does not suffer from bias caused by high current peaks in the computation. using this method, calculating the precise amount of electrical power utilized only requires one ac cycle. this makes sense for tests conducted in closed loops where a short loop time is required [35]. the energy and power calculation from every four full cycles of the i-v curve and presented in mean and standard deviation. optical spectroscopy is a widely used technique to measure the intensity of different wavelengths of light. because they are noninvasive and have a fast response time, spectroscopic diagnostics are useful for measuring plasma temperatures, density, and several other characteristics in plasma that can be computed with the help of optical spectroscopy. the optical emission spectra are taken ten times and presented as their mean. the plasma temperatures are categorized into four types, i.e., the electron, vibrational, rotational, and translational temperatures [38]. since there is a high frequency of energy exchange between the rotational and translational temperatures of the plasma, they are thought to be nearly equal [38,39]. however, the rotational temperature trot is typically referred to as the temperature of the kinetic gas [38]. understanding vibrational temperature tvib can help one understand the relative rates of energy exchange processes between vibration and translation [40] and is an important factor in understanding the synthesis of roshan chalise et al./ bibechana 21 (2024) 195-212 199 no2 and the quenching of o3 [41]. plasma’s vibrational and rotational temperatures are crucial factors that can impact both the target material’s surface properties and the rate at which the plasma is chemically reacting. higher vibrational temperatures have the potential to significantly accelerate chemical reactions in plasma because they indicate the presence of energy in the excited state of molecular vibration. rotational temperature describes the population of rotational levels in molecular organisms [42]. in plasma physics, electron temperature (te) is one of the most fundamental and instructive characteristics since electrons control the chemical reactions occurring within the plasma in addition to being involved in the excitation, dissociation, and ionization of atoms and molecules. since excitation mechanisms that control the distribution of excited states are primarily driven by free electrons, the kinetic temperature of the free electrons is typically correlated with the texc of the bound electrons in an atom or molecule [43]. in high-pressure plasmas, excitation temperature is commonly used. in particular, because of their close association, determining te at atmospheric pressure often depends on texc measurement. texc is near te if the system abides by the local thermodynamic equilibrium (lte). thus, measuring texc can be a useful substitute diagnostic for plasma discharge [43, 44]. numerous diagnostic methods are available for determining the electron temperature of the plasma; however, the electrostatic langmuir probe is one of the most widely used and flexible technologies for this purpose [45]. despite having a straightforward hardware setup, its application may be restricted at times because of issues with analysis, particularly when negative ions are present, a potential source of plasma disruption, and difficulties using it with large-volume plasmas. texc can also be ascertained using optical emission spectroscopy using the proper equilibrium models [44]. the boltzmann plot method is one of the most widely used techniques for measuring the temperature in lab plasmas. the radiative transfer equation for an optically thin, uniform, and isothermal plasma along the line of sight provides the basis for this calculation. the equation is linearized by taking the logarithm of both portions to get the boltzmann plot. the argument of the logarithm, a dimensionless transcendental function, must also be dimensionless [46]. the boltzmann plot technique of n(iii) species, which uses the data from the nist database [47] in table 1, is used to compute the electron excitation temperature (texc). using this approach, the lte plasma equation is [48]; ln ( λijiij aijgj ) = − ej kbtexc +k (8) the variables in equation (8) are the intensity of the transition from the i to the j state (iij), wavelength of the transition (λij), transition probability (aij), statistical weight (gj), higher energy level ej, electron excitation temperature texc, and constant k. when we plot the ln ( λijiij aijgj ) versus ej, the slope of the obtained graph (boltzmann plot) is equal to 1 kbtexc and then the electron excitation temperature is obtained. table 1: selected n(iii) peaks in optical emission spectroscopy of apcdbd and its corresponding spectroscopic data [47] for plotting of boltzmann plot. λij (nm) aij (s−1) ej (ev) gi-gj 336.734 1.27×108 39.35199 6–6 375.467 3.78×107 38.95798 4–6 377.105 5.59×107 38.95798 4–4 393.852 8.96×107 41.48118 4–6 399.863 1.76×108 42.49548 4–6 400.358 1.88×108 42.49560 6–8 the saha equation is rooted in the principles of statistical mechanics and considers the balance between ionization and recombination processes in plasma at thermal equilibrium. it provides a way to calculate the relative abundances of different ionization states of an element in plasma as a function of temperature and pressure. the plasma density is calculated from the saha-boltzmann equation [49]: ne = 2 i2a1g1λ2 i1a2g2λ1 ( 2πmekbtexc h2 )3/2 exp [ − (e1 − e2 + ej) kbtexc ] (9) the energy of ionization of a neutral atom is denoted by ej; the intensity of the same species line has a larger gap in upper energy, and the wavelengths are denoted by λ1 and λ2; the transition probabilities are represented by a1 and a2; and the statistical weights are g1, g2. rotational (trot) and vibrational (tvib) temperatures are calculated by massiveoes software [50– 52], in which measured oes spectrum is fitted with the standard spectrum and provide the results with residual error in fitting both spectra. when dealing with nitrogen plasmas or plasmas containing nitrogen, boltzmann plots or fits of the band envelopes of various bands belonging to the first negative system and/or second positive system are commonly employed [53]. so the vibrational temperature is calculated by the boltzmann plot method also. the line intensity of the vibrational transition’s spectral was provided as [54] iν′→ν′′ ∝ hc λν′→ν′′ aν′→ν′′n0 exp(− hcgν′ kbtvib ) (10) roshan chalise et al./ bibechana 21 (2024) 195-212 200 where kb, h, c, and tvib are the boltzmann constant, velocity of light, and vibrational temperature respectively, i, a, g, and λ are transition frequency, einstein coefficient and spectral term of vibrational transition and wavelength which are related to upper vibrational level (ν′) to lower vibrational level (ν”). the spectral factor can be replaced by the energy difference of the energy levels g′ ν = eν′ − e0. the vibrational energy of the excited molecules on the level of n2 (c3π) in the quantum harmonic oscillator approximation disregarding the anharmonicity constant [55]; eν(ev ) = 1.2398× 10−4(ν + 1 2 )we(cm−1) (11) where ν is the vibrational quantum number, which can be 0, 1, 2, 3,... of ground level, and we is the spacing of vibrational energy on the c3π (= -2047.17 cm−1). after applying eq. (11) in eq. (10) then we can get the semi-log equation as ln ( iν′→ν′′λν′→ν′′ aν′→ν′′ ) = c − eν′ − e0 kbtvib (12) where iν′→ν” is the intensity of transition from upper to lower state, λν′→ν′′ is the wavelength of transition, aν′→ν′′ is the transition probability, eν′ is the upper energy level with the vibrational quantum numbers. when we plot the ln ( i ν ′→ν ′′ λ ν ′→ν ′′ a ν ′→ν ′′ ) versus (eν′ − e0), the slope of the obtained graph (boltzmann plot) is equal to 1 kbtvib and then the vibrational temperature is obtained. n2 species have a high vibrational temperature, which is shown by the overpopulation of n2 vibrational states. for the boltzmann plot method, four vibrational bands are taken: ∆ν= +1 (1-0, 21), ∆ν= -1 (0-1, 1-2, 2-3), ∆ν= -2 (0-2, 1-3, 2-4) and ∆ν= +2 (2-0, 3-1) [56]. the national institute of standards and technology reference database is the source of the spectroscopic parameters needed for the boltzmann plot [47]. the parameters to obtain the vibrational temperature is based on the analysis of the n2 (c3π) or the second positive system emissions of ∆ν = ν ′ -ν ′′ , vibrational transition (ν ′′ -ν ′ ) [56], wavelength λ (nm) [55], transition probability aν ′ →ν ′′ (106 s −1) [55] and energy eν′ (ev) calculated according to eq. (11) are listed in table 2. table 2: selected wavelengths of the oes spectrum and all other parameters required to boltzmann plot of tvib [55]. ∆ν (ν ′′ -ν ′ ) λ (nm) aν ′→ν ′′ (106 s−1) e ν ′ (ev) -2 2-4 295.32 3.80 1.14 -2 1-3 296.20 4.62 0.88 -2 0-2 297.68 3.34 0.63 -1 2-3 311.67 1.65 0.88 -1 1-2 313.60 5.49 0.63 -1 0-1 315.90 8.88 0.38 0 0-0 337.10 13.90 0.12 +1 2-1 353.60 11.41 0.38 +1 1-0 357.69 13.80 0.13 +2 3-1 375.54 8.68 0.38 +2 2-0 380.49 4.81 0.13 3 results and discussion the relationship between the applied voltage and the resulting current is an important aspect of dbd plasma. initially, at low voltages, there’s little current flow due to the insulating properties of the dielectric barrier. as the applied voltage increases, the voltage across the gap exceeds the dielectric breakdown voltage, leading to the initiation of plasma discharge and a sudden increase in current [57]. the voltage fault and impulse current occur when the voltage is high enough to ionize the working gas (atmospheric air). when the applied voltage exceeds the breakdown voltage of the atmospheric air, then the micro discharge can be seen [58]. roshan chalise et al./ bibechana 21 (2024) 195-212 201 figure 2: time variation with voltage and current for the flow variation of (a) 0 lpm, (b) 5 lpm, (c) 10 lpm, and (d) 15 lpm respectively. figure 3: time variation with voltage and current for the voltage variation of (a) 12.00 v, (b) 16.00 v, (c) 20.00 v, and (d) 24.00 v respectively. figure 2 and 3 shows the plot of the discharge current and applied voltage (i-v) waveform at the flow variation at constant input voltage and variation of input voltage at constant air flow rate. the number of current pulses rises and the discharge current intensity falls as flow rates increase from 0 to 15 lpm [59, 60]. the breakdown voltage is also reduced because, when airflow is introduced roshan chalise et al./ bibechana 21 (2024) 195-212 202 into the discharge region, the breakdown moment gradually shifts towards the lower time values. the breakdown voltage drops as airflow enters the discharge space. consequently, the number of filaments rises while the intensity of the discharge current falls [61]. because of the lower breakdown voltage, more filaments with lower intensities at a fixed input power can be produced in the discharge region [62]. figure 4 (a) and (b) represent the lissajous curve of the different lpm at constant voltage and the varying voltages with constant airflow. it is observed that with increasing the input voltage and airflow, multiple micro discharges are increased in the i-v plot. so that more and more filamentary discharge is observed during the discharge region. the increase in input voltage has resulted in an increase in peak-to-peak voltages and rms voltage. the energy carried by discharge has also decreased increasing the airflow. the frequency of the discharge is independent of applied airflow. it can be seen that the power delivered by the apcdbd also decreased with an increasing the airflow as shown in the table 3. the increase in input voltage has increased the frequency. the energy and power of the apcdbd plasma increase with increasing the voltage that is shown in table 4. there is the fluctuation of energy from time-averaged and the lissajous plot method. up to 10 % fluctuation in airflow and 2 % fluctuation in input voltage. due to the fewer number of cycles measured from our oscilloscope, more fluctuation of energy occurred, these limitations result in agreement with previous results [35]. however, the fluctuation of energy per cycle is 4 % in airflow variation and less than 1 % in input voltage variation, when calculated from lissajous plot methods. figure 4: lissajous plot; charge (q) concerning the applied voltage (kv) across discharge electrode for different (a) airflow at 24.00 v input voltage, and (b) input voltage at 15 lpm airflow. table 3: electrical parameters of apcdbd for various air flows at 24.00 v input voltage. lpm vpp (kv) vrms (kv) idis (ma) vdis (kv) et (µj) el (µj) f (khz) pt (w) pl (w) 0 24.45 8.64 0.41 8.44 116.12±11.98 190.02±1.44 25.60 2.97±0.11 4.86±0.14 5 28.77 10.17 0.75 13.97 158.13±17.01 191.26±7.96 26.10 4.12±0.17 4.98±0.79 10 30.91 10.93 0.87 16.38 160.23±9.68 193.41±6.65 26.70 4.16±0.96 5.02±0.66 15 31.21 11.03 0.88 16.40 179.00±5.35 197.70±4.93 26.90 4.68±0.54 5.15±0.49 table 4: electrical parameters of apcdbd at different input voltage at 15 lpm airflow. vin (v) vpp (kv) vrms (kv) idis (ma) vdis (kv) et (µj) el (µj) f (khz) pt (w) pl (w) 12.00 30.87 10.91 0.63 5.98 172.99±4.98 156.52±2.57 22.17 3.83±0.11 3.47±0.05 16.00 32.58 11.52 0.68 7.60 172.01±3.22 162.48±3.12 22.98 3.95±0.07 3.73±0.07 20.00 33.03 11.67 0.76 8.70 176.17±4.40 174.96±5.78 24.15 4.25±0.11 4.23±0.13 24.00 33.55 11.86 0.91 9.26 165.63±8.35 186.76±9.39 25.77 4.26±0.21 4.99±0.49 roshan chalise et al./ bibechana 21 (2024) 195-212 203 when comparing this power estimating process to the time-averaged integration of the voltage and current over five ac cycles, the deviation of value per cycle is far more up to 10 % by calculating the averaged method and nominal standard deviation found in the lissajous plot method was used. 3.1 optical characteristics optical emission spectroscopy (oes) of plasma involves studying the emission of light produced during the plasma discharge and transferring these emission spectra into their wavelength and intensity values. this can provide valuable information about the plasma’s properties, such as its composition, temperature, and density. the excitation temperature, plasma density, rotational, and vibrational temperature of the apcdbd are presented here. figure 5 (a) and (b) show the oes of apcdbd plasma at different air flows and different input voltages. in our research, we have used natural air as a working gas. the intensity of the spectra decreased with increasing the airflow and increased with increasing applied voltage in the power supply observed in the blowup figure of spectra of figure 5 (b). the population of excited particles, which can be produced by one or more channels depending on the plasma conditions, is shown by the emission intensity. the intensity of the electrode field increases in the discharge zone as the applied voltage increases. more energetic electrons are produced in the discharge zone as the electrode field strength increases. after that, they accelerate radiation transitions’ higher states, producing more active particles. as a result, when the applied voltage rises, so do the intensities of the corresponding emission spectra [42]. in atmospheric air, there is approximately 78 % of nitrogen and 20 % oxygen. thus, the peak of oes spectra in apcdbd plasma has almost nitrogen and oxygen species. the major observed spectra are the second positive system (310-380 nm) of n2 ( c3πu → b3πg ) and the first negative system (390-440 nm) of n+ 2 ( b2 ∑+ u → x2 ∑+ g ) [56]. additionally, oh ( a2 ∑+ → x2π ) radicals is prominently seen at 309 nm in the spectrum of the gliding arc discharge which plays a crucial role in plasma chemical reactions such as the oxidation of gas and liquid pollutants. the nitric oxide gamma band noγ ( a2 ∑+ → x2π ) is observed in 200 to 280 nm. reactive oxygen (o) radicals are found at wavelengths 777 nm with electronic transitions 4s(3d)4d→4p(3p) [6, 36]. figure 5: optical emission spectroscopy and blow-up spectra of apcdbd for (a) various airflow at 24.00 v input, and (b) various input voltage at 15 lpm airflow. boltzmann’s plot is used to study the electron excitation temperature of the plasma. the energy level of n (iii) species of respective wavelength versus relative intensity distribution was plotted to find the electron excitation temperature of apcdbd. a boltzmann plot is a graphical representation used in spectroscopy to analyze the populations of energy levels within a system. in the context of dbd plasma, which is a type of lowtemperature plasma, a boltzmann plot can be used to understand the energy distribution of excited states of atoms or molecules in the plasma [63]. the slope of boltzmann’s plot of airflow and input voltage variation gives the value of electron excitation temperature as shown in figure 6 and 7 respectively. roshan chalise et al./ bibechana 21 (2024) 195-212 204 figure 6: boltzmann plot for the estimation of texc using n (iii) species for increasing flow variation of (a) 0 lpm, (b) 5 lpm, (c) 10 lpm, and (d) 15 lpm. figure 7: boltzmann plot for the determination of texc using n(iii) species for increasing applied voltage (a) 12.00 v, (b) 16.00 v, (c) 20.00 v and (d) 24.00 v. figure 8 and 9 represent the measured and simulated oes data fitted plot for the determination of trot and tvib by using nitrogen second positive system n2 (c3πu − b3πg) from massiveoes software for increasing flow variation for 0 lpm, 5 lpm, 10 lpm, and 15 lpm and increasing applied voltage at 12.00 v, 16.00 v, 20.00 v, and 24.00 v respectively. roshan chalise et al./ bibechana 21 (2024) 195-212 205 figure 8: measured and simulated oes data fitted plot for the determination of trot and tvib by using nitrogen second positive system (sps) n2 (c3πu − b3πg) from massiveoes software for increasing flow variation for (a) 0 lpm, (b) 5 lpm, (c) 10 lpm and (d) 15 lpm. figure 9: measured and simulated oes data fitted plot for the determination of trot and tvib by using nitrogen second positive system n2 (c3πu − b3πg) from massiveoes for increasing applied voltage (a) 12.00 v, (b) 16.00 v, (c) 20.00 v and (d) 24.00 v. roshan chalise et al./ bibechana 21 (2024) 195-212 206 trot is typically utilized as an approximation of the gas temperature (tg) since it is representative of the rotating population of the ground state and provides information on the global temperature of the plasma [64]. the average kinetic energy brought on by the rotating of particles in the plasma is referred to as rotational temperature. the molecular axes of plasma molecules can spin. the energy distribution between these rotating degrees of freedom is shown by the rotational temperature [65]. on the other hand, electron collisions are the primary source of molecular specie’s vibrational states. the non-equilibrium plasma’s chemical kinetics are significantly influenced by the vibrationally excited species, [66] because vibrational excitation plays the role of an energy reservoir [67]. figure 10 shows the typical boltzmann plot of the relative intensity distributions versus vibrational energy using nitrogen second positive system n2 (c3πu−b3πg) for flow variation of 0 lpm, 5 lpm, 10 lpm, and 15 lpm. the vibrational temperature is correlated with the average kinetic energy of the oscillating motion of the plasma’s particle constituents. atoms and molecules can oscillate about their equilibrium locations as well as other sorts of vibrations that can occur in plasma. the quantity of energy involved in these oscillations is described by temperature variations figure 10 and 11 shows a typical boltzmann plot of the relative intensity distributions flow variation and input voltage variation. after taking into account the scattered data points and fitting errors, the vibrational temperature was obtained figure 11 shows the boltzmann plot for the determination of tvib using nitrogen second positive system n2 (c3πu − b3πg) for increasing applied voltage of 12.00 v, 16.00 v, 20.00 v, and 24.00 v. figure 10: boltzmann plot for the determination of tvib using nitrogen second positive system n2 c 3πu− b3πg) for flow variation for (a) 0 lpm, (b) 5 lpm, (c) 10 lpm and (d) 15 lpm. roshan chalise et al./ bibechana 21 (2024) 195-212 207 figure 11: boltzmann plot for the determination of tvib using nitrogen second positive system n2 c 3πu− b3πg) for increasing applied voltage (a) 12.00 v, (b) 16.00 v, (c) 20.00 v and (d) 24.00 v. table 5 shows the optical parameters of apcdbd for increasing air flows at 24.00 v input voltage. as an increase in the airflow electron excitation temperature, and rotational temperature were increased, but density and vibrational temperature decreased. the plasma density decreased with increasing air flow rate is supported by previously published results [63]. table 6 shows the optical parameters of apcdbd at different input voltages at 15 lpm airflow. while increasing the input voltages of the power supply electron excitation temperature, electron density, vibrational temperature, and rotational temperature are increased. the gas breakdown between the hv electrode and the floating electrode is more likely to occur as the applied voltage increases because of the hv electrode’s extremely tiny radius of curvature and the gap, which together produce a strong electric field. following the disruption in the discharge region, the electron density rises and the plasma resistance value is very low [42]. the plasma power grows with applied voltage, and the energy input into the discharge zone rises as well, increasing the likelihood of electron-heavy particle collisions raising the rotational temperature, and highlighting the joule heating effect [68]. table 5: optical parameters of apcdbd for various air flows at 24.00 v input voltage. lpm texc (k) ne (× 1023 m−3) tvib(b.p) (k) trot(moes) (k) tvib(moes) (k) 0 15272.40 1.39 3260.87 492.51 ± 15.13 2759.99 ± 17.59 5 15226.10 1.45 3284.08 486.17 ± 17.95 2762.64 ± 18.19 10 15248.80 1.49 3307.29 474.78 ± 15.93 2777.78 ± 18.35 15 15240.90 1.54 3349.27 464.84 ± 13.56 2787.04 ± 17.85 roshan chalise et al./ bibechana 21 (2024) 195-212 208 table 6: optical parameters of apcdbd at different input voltage at 15 lpm airflow . vin (v) texc (k) ne (× 1023 m−3) tvib(b.p) (k) trot(moes) (k) tvib(moes) (k) 12.00 15241.50 1.52 3149.27 450.35 ± 16.23 2743.46 ± 18.57 16.00 15279.10 1.51 3214.45 468.44 ± 16.59 2753.47 ± 18.79 20.00 15293.60 1.53 3291.24 486.01 ± 17.75 2754.24 ± 18.99 24.00 15342.80 1.54 3337.66 496.67 ± 16.49 2787.27 ± 17.85 we have calculated all of the plasma parameters electrical and optical by available analysis techniques in a standard way. we have found our rotational temperature is a little bit more than the room temperature, however, it is decreasing lower but only airflow cannot control the temperature. for this decrement in gas temperature plasma power source is important so we need to develop a power source for reactors for developing heatsensitive plasma applications. another major thing of that such types of flat area dbd can treat thin and large surface subtracted but not possible to treat thick substrates. hence for this application, needed to change such dbd like a plasma jet. 4 conclusion in this research, comprehensive electrical and optical characterization of the atmospheric pressure dielectric barrier discharge plasma is employed by available different methods. to understand these basic parameters calculation is essential for every application of plasma. the dbd is produced in atmospheric pressure air so that easy to handle and low cost for production. the energy and power calculation is more converged by using the lissajous plot method. however, the time-averaged method has more divergent values per cycle. as the airflow increases the energy and power of discharge dissipated also goes on decreasing. similarly, as the voltage increases the power also increases concerning the parameter. the optical parameters are increased with increasing the input voltage of the power supply, however, density and rotational temperature are decreased while increasing the airflow between the electrodes of apcdbd. it also follows the standard relation of nonthermal plasma temperature order trot < tvib < texc. the plasma is in a state known as a non-thermal equilibrium when the temperatures of the electrons, vibrations, and rotations are not equal. the rotational temperature, which is assumed to be equivalent to the gas temperature, rises as the applied voltage increases and falls as the airflow increases, suggesting that the thermal effect is more pronounced at higher input voltages and lower airflow. this research work has played a crucial role in understanding the electrical and optical characterization of produced atmospheric discharges. acknowledgement roshan chalise would like to acknowledge the university grants commission, nepal for the ph.d. fellowship award (phd-78/79-s & t-16) and extend special thanks to dr. bhagirath ghimire for his guidance in the characterization methods. we acknowledge the research coordination and development council, tribhuvan university, kirtipur, nepal for the national priority research grant (tu-npar-077/78-erg-12). we also thank tirtha raj acharya, prajwal lamichhane, and oat bahadur dhakal of plasma bioscience research center, department of electrical and biological physics, kwangwoon university, seoul, republic of korea for their help in determining the vibrational temperature of discharge by boltzmann plot method. 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ie 800℃, and id 900℃; 800℃, 900℃ and 1000℃) around 2= 40.9° is related to the iron oxide (fe2o3) and is related to jcpds 89-8104). the formation of the additional peak is due to the diffusion of atoms in the heating process. the variations in crystallite size and particle size are due to iron content. their effect on magnetic properties and hence in hyperthermia are under study. keywords ni-zn ferrites, sem-edx, ftir, hyperthermia. article information manuscript received: may 7, 2024; revised: june 20, 2024; accepted: june 23, 2024 doi https://doi.org/10.3126/bibechana.v21i3.65529 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 254 http://nepjol.info/index.php/bibechana deepenparaj@gmail.com https://doi.org/10.3126/bibechana.v21i3.65529 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ d. parajuli et al./ bibechana 21 (2024) 254-261 255 1 introduction hyperthermia, the application of heat to treat disease, has ancient roots dating back to egyptian, indian, and chinese civilizations. the therapeutic use of heat was historically limited to treating infections, improving circulation, and easing muscle pain. however, its scientific exploration began in earnest in the 19th and 20th centuries. in 1866, german surgeon carl busch reported using heat to treat tumors, and in the 20th century, advancements in technology facilitated more precise applications of hyperthermia [1]. this is highly applicable in medical applications: 1) cancer treatment, 2) enhanced drug delivery, 3) immune response stimulation, 4) pain management etc. in cancer treatment, there are three hyperthermia: local hyperthermia (targets small areas, typically tumors, using external devices like microwave, ultrasound, or radiofrequency to raise tissue temperature.), regional hyperthermia (treats larger areas of the body, such as limbs or organs, often in combination with other treatments like chemotherapy.) and whole-body hyperthermia (used for metastatic cancer, raising the body's core temperature to enhance the effects of other cancer treatments.) [1] in enhanced drug delivery, hyperthermia increases cell membrane permeability, facilitating the uptake of chemotherapeutic drugs. it can enhance the efficacy of drug-loaded nanoparticles and liposomes, targeting tumor sites more effectively. in immune response stimulation, heat can stimulate immune responses by increasing the expression of heat shock proteins, which help the immune system recognize and attack cancer cells. in pain management, it is used in physiotherapy to relieve muscle and joint pain, leveraging its ability to improve blood flow and reduce muscle stiffness [1]. recent research focuses on magnetic nanoparticles that can be heated in an alternating magnetic field, providing targeted hyperthermia with minimal damage to surrounding tissues [?]. integrating hyperthermia with radiation and immunotherapy has shown promising results, enhancing treatment efficacy and reducing side effects. advances in imaging and thermal dosimetry have improved hyperthermia's precision, allowing for real-time non-invasive treatment monitoring and adjustments [2]. the extensive research conducted on the ni-zn ferrite system [3–6] has demonstrated that ni-zn bulk ferrite emerges as the optimal core material for high-frequency applications. this is due to its advantageous properties, such as high saturation magnetization, elevated curie temperature, favorable magnetic permeability, low power loss, and high dc resistivity [7, 8]. transforming bulk nizn ferrite into nanostructures offers significant potential for enhancing specific properties like saturation magnetization, initial permeability, particle size, and dc resistivity. consequently, this material holds promise for various applications, including magnetic data storage, targeted drug delivery systems, mri contrast enhancement, and serving as a heating agent in magnetic fluid hyperthermia [9, 10]. achieving desired variations in multiple parameters tailored for each application requires meticulous control over the synthesis process to produce the material in nano form. it is known that tailoring the chemical composition allows control of magnetic properties [11–13]. these properties depend primarily on the exchange interactions, which depend upon the types and concentrations of different cations present in the composition [14, 15]. numerous researchers have made efforts [16–18] to obtain the least-sized particles with superior magnetic properties in nano ni1xznxfe2o4 ferrites by choosing an appropriate zinc concentration (x). on the other hand, research has revealed that studies involving varied iron content in bulk or nano ni-zn ferrites are severely inadequate [19–21]. in any ferrite system, the arrangement of substituted ions within the structure plays a crucial role in altering the electromagnetic properties [22]. to develop a suitable material with desired characteristics, it's essential to thoroughly comprehend how different cations occupy positions within the a and b sub-lattices [23]. for instance, achieving magnetic hyperthermia necessitates materials exhibiting high saturation magnetization, low coercivity, and a significant curie temperature [24]. enhancing processing conditions and focusing on consequent magnetic properties can lead to the fabrication of superior materials for magnetic hyperthermia applications [25]. the study undertakes a methodical examination aimed at obtaining a nano ferrite composition. it aims to significantly enhance specific saturation magnetization through a comprehensive understanding of how cation distribution varies with different levels of iron content in the ferrite composition. here, we present and analyze their structural, morphological, and spectroscopic data. 2 method of preparation the sol-gel process was adopted in preparing the ni-zn nanoferrites with varying amounts of iron in the composition. the nitrates of nickel, zinc, and iron are mixed in stoichiometric proportion along with deionized water and stirred for 2 hrs and then mixed with a chelating agent polyethylene glycol (peg) (10g of peg mixed in 100ml deionized water) in 1:1 ratio and dehydrated at 100oc. the involved reactions are: (a) 0.65 ni (no3)2.6h2o + 0.35 zn d. parajuli et al./ bibechana 21 (2024) 254-261 256 (no3)2.6h2o + 2 fe (no3)3.9h2o + peg → ni0.65zn0.35fe2o4 + 8no2 + 2o2 + 24h2o (b) 0.65 ni(no3)2.6h2o + 0.40 zn(no3)2.6h2o + 1.95 fe(no3)3.9h2o + peg → ni0.65zn0.40fe1.95o4 + 7.95no2 + 1.975o2 + 23.85h2o (c) 0.60 ni(no3)2.6h2o + 0.35 zn(no3)2.6h2o + 2.05 fe(no3)3.9h2o + peg→ ni0.60zn0.35fe2.05o4 + 8.05no2 + 2.025o2 + 24.15h2o the drying resulted in a reddish gel along with reddish brown fumes of no2 [26] which further converted into fluffy ferrite mass. the water content was removed with the use of a hot air oven for 10 hours. each ferrite composition's as-prepared powder has been annealed at 400 ℃ for one hour and then allowed to cool naturally by turning off the furnace. the annealed powder was extensively crushed and made into pellets and toroids using polyvinyl alcohol as a binder. all the pellets and toroids have been heated for one hour at optimum temperatures (800 ℃ to 1050 ℃ @ 5℃/min) before being subjected to natural cooling to room temperature. the samples were further designated as ie-1000, in1050, and id-1000, where 1000 and 1050 indicate the optimum annealing temperatures. flowchart 1: preparation and characterization of ni-zn ferrites the preparation and characterization of ni-zn ferrites are shown in flowchart 1 which ensuring clarity and reproducibility for future researchers. characterization the samples have been characterized panalytical x’pert pro was used for determining the crystallographic structure. supra 55 zeiss fesem with attached edx and working with a primary e-beam at an energy of 25 kev was used for morphological study. nicolet-magna-550 ir spectrometer was used for the compositional study. detailed analysis and discussion about the observed variations in various parameters like lattice constant, and particle size, have been described as a function of iron content to finalize a composition with the desired characteristics of the magnetic hyperthermia application. 2.1 materials all the chemicals (sulphuric acid, buffer tablets, potassium dichromate, 1,5-diphenyl carbazide, nitric acid, sodium hydroxide, etc) of analytical grade were purchased from thermo fisher scientific india. 1000ppm stock solution of potassium dichromate, 0.1 n nitric acid, 5n sulphuric acid, 2n nitric acid, 0.1m & 2n sodium hydroxide, 0.25% dcpi solution and buffer solutions (ph-4.0,7.0 & 9.2) were prepared in different volumes. 3 results and discussion 3.1 xrd study the spinel structure was tested and the lattice parameter of samples was been computed from the observed bragg angles of the xrd in the range 15°– 85° with 1.5406 å wavelength x-rays. the xrd patterns of the samples in, id, and ie, ni-zn nanoferrite from 800 ℃ to 1050 ℃ are shown in figures 1 to 3. the wider peaks indicate the smaller crystallite size. the signs of nascent iron oxides are observed in the material. the intensity is increasing slowly with temperature indicating the enhancement of the crystallization. the estimated lattice parameters corresponding to the in-1050, id-1000, and ie1000 samples were 8.3746 å, 8.3774 å, and 8.3806 å respectively depending on the iron content from 50% to 51.25%. the marginal increase in the case of ie-1000 has been associated with the formation of fe2+ ions in the material processed at a higher annealing temperature and the larger ionic radius of fe2+ ions (0.78 å). the peaks (111), (220), (311), (222), (400), (422), (511), (440), (620), (533), (622) corresponds to jcpds08-0234 and are cubic spinel structure. there is one extra peak in all three samples (in 800℃; ie 800℃, and id 900℃; 800℃, 900℃ and 1000℃) around 2= 40.9° is related to the iron oxide (fe2o3) and is related to jcpds 89-8104). the formation of the additional peak is due to the diffusion of atoms in the heating process [10,27]. 3.2 fesem study at the nanoscale, the size of particles becomes crucial due to the significant variations in material properties compared to larger micron-sized counterparts. nano-sized ferrite particles, as they approach a critical diameter, display distinctive magnetic characteristics such as single domain behavior, superparamagnetism, and a lowered curie temperature. moreover, in nanoparticles with a high surface-to-volume ratio, surface spin disorder can alter magnetic properties over time. in singledomain particles, the absence of domain wall resd. parajuli et al./ bibechana 21 (2024) 254-261 257 onance shifts the operational frequency to higher ranges, making them valuable for high-frequency applications. conversely, single-domain particles of sufficiently small size may demonstrate superparamagnetism, a property crucial for applications like magnetic hyperthermia treatment. (a) (b) (c). figure 1: xrd of the (a) in sample (b) id sample and (c) ie sample subjected to various heating temperatures. fesem micrographs of these three samples support the observed microstructural changes in terms of increased porosity and compaction of reduced grains (figure 2). figure 2: fesem images of (a) in-1050 (b) id1000 and (c) ie-1000 pellet samples. archimedes' principle has been used to determine the experimental (or) bulk density of all the samples. the bulk density of the sample, dbulk = w1 w1−w2 (1) where w1 = the sample weight in air (g) w2 = the sample weight in water (g) the x-ray density is often more than the macroscopic density of a specimen which is influenced by the weight and volume of the specimen. this is because the macroscopic specimen, in contrast, exhibits minute cracks and pores. determining the x-ray density, also known as ''theoretical density'', is essential because it may be used to evaluate actual porosity by comparing it to the macroscopic density of the sintered compacts. the theoretical density or x-ray density (dx-ray) has been calculated from the lattice parameter values using the expression below [28], dx−ray = 8m na3 (2) where, m is the molecular weight of the ferrite sample, n is the avogadro number and a is the lattice parameter of the unit cell. from the values of x-ray and experimental densities, the percentage of porosity of the samples was calculated using the relation, the percentage of porosity, dx−ray − dbulk dx−ray × 100 (3) the experimental density, x-ray density, and porosity of the samples have been presented in table 1. d. parajuli et al./ bibechana 21 (2024) 254-261 258 table 1: optimum firing temperatures, bulk density, x-ray density, and percentage of porosity of in1050, id-1000, and ie-1000 samples composition optimum firing temperature (°c) bulk density (g/cm3) x-ray density (g/cm3) porosity (%) ni0.65zn0.35fe2.05o4 1050 4.498 5.355 16.0 ni0.65zn0.40fe1.95o4 1000 4.516 5.360 15.8 ni0.60zn0.35fe2.05o4 1000 4.577 5.340 14.3 it is speculated that the production of fe2+ ions in the sample processed at greater annealing temperatures is the cause of the higher bulk density of the ie-1000 composition. the larger sintering temperatures facilitate the reduction of fe3+ ions into fe2+ ions creating oxygen vacancies in the material which promotes the formation of larger grains with higher densities [27]. 3.3 edx spectra energy-dispersive x-ray spectroscopy (edx) is used to record the elemental composition of the sintered samples. figures 3 to 5 illustrate edx spectra for the id-1000, ie-1000, and in-1050 samples. the observed presence of the elements, nickel (ni), zinc (zn), iron (fe), and oxygen (o) in the spectra confirms that the nanoparticles belong to ni-zn ferrite material with no impurities. 3.4 ftir spectra figure 6 represents the room temperature ftir spectra recorded in the range from 3000 cm-1 to 300 cm-1 on the nicolet-magna-550 spectrometer using the kbr pellet for in-1050, ie-1000, and id-1000 samples. each spectrum has two significant absorption bands corresponding to fe2+ o2vibrations at tetrahedral and octahedral sites, respectively, between 592-595 cm-1 and 414-420 cm-1 [29]. the absorption band 2363 cm-1 corresponds to the atmospheric carbon dioxide absorbed on the surface of the particles during sample preparation [30]. a weak band was observed at around 470 cm-1, attributed to the splitting of the octahedral band due to the jahn-teller distortion, confirming the presence of the fe2+o2vibration band in the ferrite [31]. table 2 shows the band positions that correspond to tetrahedral and octahedral metal complexes. figure 3: edx spectra of id-1000 sample. figure 4: edx spectra of ie-1000 sample. figure 5: edx spectra of in-1050 sample. table 2: band positions and fe3+ o2bond force constants for the samples. sample (tetrahedral) cm-1 (octahedral) cm-1 fe3+-o2bond force constant (105 dyne/cm) tetrahedral (kt) octahedral (ko) in 1050 592 414 227 133 id 1000 595 417 223 135 ie 1000 593 420 228 137 d. parajuli et al./ bibechana 21 (2024) 254-261 259 in comparison to the corresponding bands of in1050, the tetrahedral band (v1) of id-1000 and octahedral band (v2) of ie-1000 exhibit a shift towards the higher wave numbers. the tetrahedral band shift suggests that zn2+ (0.60 å) ions prefer to occupy tetrahedral sites and push fe3+ ions towards oxygen ions due to the larger ionic radius of zn2+ than fe3+ (0.49 å) ion. this is expected to result in a decrease in the distance between fe3+ o2ions. the presence of a weak absorption band, 668 cm-1 could be attributed to the presence of the zn2+ ions at the tetrahedral sites [32] corresponding to the zn2+ o2tetrahedral complexes. an increase in zinc concentration resulted in a corresponding increase in band intensity (figure 7) in the id-1000 sample. figure 6: ftir spectra of ni-zn ferrites. figure 7: magnified pictures of absorption bands of ni-zn ferrite samples. due to a change in bond length at b-sites, there is a shift of the octahedral absorption band in the ie-1000 sample causing an increase in the force constant of the octahedral site when compared to the normal sample. the force constant for the fe3+ o2bond has been estimated with the help of the formula shown below [33], k = 42c22 (4) (all values are in cgs), where c is the speed of light, is the wave number and is the reduced mass for fe3+ and o2ions. table 2 shows the estimated force constants for the tetrahedral and octahedral sites. generally, there is a decrease in bond length and an increase in force constant for either site if the radius of the impurity ion is lower than the displaced ion. the concentration of displaced nickel ion and the excess iron ion is the same in the ie-1000 sample. the rise in iron concentration at octahedral sites could improve the reduced mass, besides substituting the nickel ions at octahedral sites and the process is in charge of the variations noticed in band position and force constant. to have the quantitative distribution of ions on tetrahedral and octahedral sites, effective cation distribution is needed. further, the distribution helps to discuss the changes taking place in the peak position of the absorption bands with the amount of iron content in the ni-zn system. for this purpose, the cation distribution has been proposed based on experimentally obtained saturation magnetization measurements. 4 conclusions the sol-gel process was adopted in preparing the ni-zn nanoferrites with varying amounts of iron in the composition. xrd shows cubic spinel structure except for one extra peak in all three samples (in 800℃; ie 800℃, and id 900℃; 800℃, 900℃ and 1000℃) around 2= 40.9° is related to the iron oxide (fe2o3) and is related to jcpds 89-8104). in comparison to the in-1050 bands, the id-1000 and ie-1000 samples exhibit shifts towards higher wave numbers in the tetrahedral and octahedral bands, respectively. a weak band was observed 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[33] p. a. shaikh, r. c. kambale, a. v. rao, and y. d. kolekar. structural, magnetic and electrical properties of co–ni–mn ferrites synthesized by co-precipitation method. journal of alloys and compounds, 492(1–2):590–596, mar. 2010. introduction method of preparation materials results and discussion xrd study fesem study edx spectra ftir spectra conclusions bibechana vol. 21, no. 3, december 2024, 281-289 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar comparative study of uv index in the selected sites of nepalese teritory isman mainali , prakash khadka, nurapati pantha∗ central department of physics, tribhuvan university, kathmandu, nepal ∗corresponding author. email: mrnurapati@gmail.com abstract progression and development of many underwater and terrestrial life forms are influenced by many environmental factors, including the amount of ultraviolet radiation present at water and the earth’s surface. spectral measure of solar uv radiation helps us to understand the causes of change in environment and also raise public awareness about potential threats when the index value goes higher. this paper presents the value of uv index over six different locations of nepal which are situated at different latitude and at different altitude. the numeral values of uv index during solar noon, provided by power data sets from year 2001 ad to 2021 ad, was used which were then compared with standard value categories of uv index based on who guideline. the uv index value for these locations were compared on monthly and annual basis. upon analysis, it was found that during solar noon average value of uv index above dolpa was highest with the value 9.10. the maximum value of uv index above other locations were: 8.43(birgunj), 8.13(hetauda), 6.14(rolpa) and 5.45(tulsipur) respectively. during mid-summer the value of uv index in each of these locations fall into high or very high category as per the who guideline. thus, people from these locations are vulnerable to the exposure of harmful uv radiation. this study reveals that special care should be taken during midday from june through august. keywords uv index, uv radiation, aerosols, surface albedo, altitude effect, latitude effect. article information manuscript received: july 25, 2024; revised: september 2, 2024; accepted: september 14, 2024 doi https://doi.org/10.3126/bibechana.v21i3.69319 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction uv radiation is a kind of electromagnetic radiation generated by sun and some artificial sources such as arc welders, tanning beds etc. it lies in between wavelengths of about 400nm(boarder to visible-light region) and about 100nm(boarder to x-ray region). this kind of radiation is produced by extremely hot surfaces like sun and by excitation of atoms in a gaseous discharge tube. most of the uv radiation present in sunlight is soaked up by oxygen in earth’s atmosphere to form ozone layer of lower stratosphere [1]. depending upon the interaction of wavelength 281 http://nepjol.info/index.php/bibechana mrnurapati@gmail.com https://doi.org/10.3126/bibechana.v21i3.69319 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ismah mainali et al./ bibechana 21 (2024) 281-289 282 of ultraviolet radiation with biological materials, it is classified into three divisions: a)uv-a (400-315 nm) b)uvb (315-280 nm) and c)uv-c (280-100 nm) [2]. ninety nine percent of uv radiation that reaches earth’s surface is ultraviolet a radiation and remaining 1 percent is ultraviolet b radiation while uv-c does not reach earth’s surface due to screening of ozone layer. when ozone layer depletes then more uv-b radiation reaches earth’s surface and causes many hazardous effects on organisms [3]. uv index is a tool used to measure the power of sun’s ultraviolet radiation at a specific place and time. this scale was first developed in 1992 by canadian scientists and then standardized adopted by the world meterological organization(wmo) and un’s world health organization(who). this is a linear scale and increases at constant rate. higher value of uv index represents greater threat of sunburn due to uv exposure. during night time the index has value 0 which corresponds to zero uv radiation. when it was originally designed, an index of 10 corresponded roughly to noon time summer sunlight with clear sky. the index compress several factors into a single number that gives us concept of how cautious we need to be in sun. a score of 1 or 2 implies low uv concentration, 3 to 5 implies moderate, 6 or 7 implies high, 8 to 10 implies very high and 11 and above implies extreme condition [4]. there are several factors that affects the value of uv index over the specific locations. some of the factors are as mentioned below: a. altitude the altitude plays vital role in variations of uv index level at different geographical regions. with increase in altitude the value of uv index increases and vice versa. as altitude increases, atmosphere gets thinner due to which less amount of solar radiation is absorbed or scattered. in addition, direct sun’s rays fall on the surface at higher altitude which increases the uv intensity. also the effect of reflection by snow covered mountain at higher altitude contributes to increasing uv. as per who guideline, every 1000m increase in altitude causes 10% increase in uv index [5]. b. absorption and scattering by aerosols aerosols are tiny particles that are suspended in air which are emitted either due to industrial processes or natural sources like volcanic eruption. the surface uv irradiance is affected by absorption and scattering process of atmospheric aerosols. thus, aerosols are referred to as either absorbing or nonabsorbing. the effect of these two processes are ascertained by values for aerosol optical depth(aod) and single scattering albedo(ssd). the absorption and scattering constituents of aod depends on wavelength and is likely to be proportional to λα, where α is the angstrom coefficient. the aerosols can have impact on cloud cover, cloud properties and precipitation which ultimately affect hydrological cycle [6]. significant engrossment of aerosols has been monitored under forest fires or fume from burning animal waste or plant materials, and desert dust [7]. c. scattering by clouds cloud cover is one of the compelling geophysical variate that affects surface emission at all wavelengths. cloud bears several varieties and different variety of cloud have different impact on angular distribution and intensity of surface uv radiation. in cloudless days uv irradiance is higher. generally, clouds depress the concentration of uv radiation through its absorption. but, thin clouds may even elevate the uv concentration due to dissemination from cloud particles [8]. it has been observed that short wavelength radiation is less influenced by existence of cloud compared to longer wavelength which shows the wavelength dependent effect of clouds on surface irradiance. d. surface albedo surface reflective power (surface albedo) disperse radiation upward to the airspace which increases surface uv irradiance. the estimates of surface ultraviolet rays from satellite data is also affected by snow on the ground. due to increased reflectivity from snow the estimated surface irradiance reduces. with mixture of cloud cover and snow the estimation of uv radiation becomes more complex. e. latitude at the equator uv radiation from the sun is at its peak and it decreases gradually as it moves towards the pole. the main reason behind it is during solar noon, the sun is directly overhead above equator, causing radiation to travel shortest distance through the atmosphere before striking the ground. at higher latitude, the radiation takes lengthier route through the atmosphere. f. molecular scattering under the considerations of clean atmosphere with absence of absorption, particulate scattering and reflection from the ground (i.e. albedo = 0), the only scattering is molecular scattering or rayleigh scattering. molecules of oxygen and nitrogen are smaller than the wavelength of uv and visible emission and cause rayleigh scattering. while molecules of water vapor, aerosols etc. are larger ismah mainali et al./ bibechana 21 (2024) 281-289 283 than uv visible radiation and cause mie scattering [9]. the chief variable for evaluating surface uv in rayleigh atmosphere are surface pressure and sza. g. solar zenith angle with increase of solar zenith angle(sza) the amount of radiation falling on a horizontal plane of surface of earth decreases. there are two main reasons behind it: a) the amount of solar radiation reaching the earth’s surface is proportional to the cosine of angle between normal to the surface direction of radiation. b) the relative path length of direct radiation passing through the aerosphere increases as the sun descend in the sky. the first fact states that both diffuse and direct component of surface ultraviolet rays are subjected to cosine effect. the second fact states that when sza increases to 90 degree the departing of relative path length(µ) from secant of solar zenith angle deviates notably. thus, with increase in sza direct solar beam reduces due to scattering and absorption process in the atmosphere [8]. h. absorption by atmospheric gases atmospheric gases like sulfur dioxide, ozone and nitrogen dioxide absorb uvb radiation. the diffused and direct component of surface uv emission are both absorbed by these gases. the diffused component is reduced due to absorption that occur in optical path both before and after the scattering of radiation. according to beer’s law, the direct component of surface uv radiation is inversely proportional to the secant of solar zenith angle times exponent of the coefficient of absorption at a specific wavelength. this explains the reduction of direct component. i. depletion of ozone layer the ozone layer is region of earth’s stratosphere containing layers of ozone molecules that absorb almost all of the harmful ultraviolet light coming from the sun. it is mainly present in the lower portion of earth’s atmosphere and has ability to absorb around 99 % of the harmful affecting uv radiation coming from the sun which can have negative influence on life of earth. the over time thinning of the earth’s ozone layer in the upper atmosphere due to release of chemical compounds consisting gaseous chlorine or bromine from industries or other human activities is called ozone layer depletion. one chlorine atom carries potentiality to destroy 100 ozone molecules per second [10]. ozone is strong absorber of uvb radiation. so intensity of uvb radiation on earth’s surface depends upon the thickness of ozone layer [11].the depletion of ozone layer leads to direct exposure to harmful uv radiation of the sun. the optical path of uv radiation is plainly lengthened near the surface and is obviously reduced as ozone is destroyed. uvb radiation is known to be biologically damaging. 2 effects of high uv index uv radiation has low penetrating power compared to x-rays. so its effects on the human body are limited to the surface skin. melanin is a chemical pigment present in skin which absorbs uv radiation and limits its penetration into tissues. when these pigments in cells are activated by uv radiation they migrate to the surface of the skin causing suntan. persons with fair skin are more prone to harmful effects of uv radiation as they have less melanin pigment [12]. some of the effects of over exposure to uv radiations are discussed below: a. effects on aquatic animals numerous aquatic animals, with an emphasis on fish, corals, amphibians, zooplankton, and other aquatic organisms have shown the significant role that uv radiation plays as an environmental stressor. according to a recent metaanalysis that revealed negative effects of ambient uv-b radiation on the growth and survival of a wide range of aquatic organisms (not just animals). reduced survival rates of copepods from antarctic waters and uv-exposed larval kill are two direct effects of uv on marine zooplankton. in marine copepods fed uv-exposed versus unexposed diatoms, the indirect effects of uv include reduced egg production and more deformed larvae. in juvenile atlantic salmon, increased uv-b radiation can lower growth rates and immune function; in juvenile rainbow trout, it can increase trematodes, or parasitic flatworms that cause cataracts [13]. b. effects on human health continuous exposure to the sun causes premature aging, which progressively can make skin become bulky, creased, and leathery [14]. many researches have revealed that uv radiation is likely to increase certain cataracts. uv radiation can also cause skin cancer around the eyes and degeneration of macula [15]. besides these effects, excessive exposure to ultraviolet radiation can abolish skin’s natural defense and proper functioning of the body’s ismah mainali et al./ bibechana 21 (2024) 281-289 284 immune system. unprotected exposure to uv radiation is the major cause of skin cancer. skin cancers like melanoma, and types of non-melanoma skin cancers like basal cell carcinomas and squamous cell carcinomas are immediate consequences of exposure to higher amount of uv radiation [16]. 3 methods a. measurement ideology nasa has been disseminating crucial data for the study of climate and climatic processes through its earth science research program. the nasa global energy and water exchange-surface radiation budget project (gewex srb) and ceres syn1deg edition 4.1 provide surface shortwave radiation or solar insolation, along with superior valuations of the earth’s top-of-atmosphere (toa). the solar-related data from these sources are presented on a comprehensive 10 latitude longitude grid. the power data sets simultaneously integrate these data sets. the power data sets furnish both low-energy and high-energy solar fluxes to individuals. the gewex shortwave algorithm employs a remodeled method by laszlo and pinker (1992) to solve the radiative transfer equation. it involves the use of a radiative transfer model, alongside temperature and moisture profiles taken from isccp nnhirs and cloud parameters deduced from the international satellite cloud climatology project (isccp), with supplements from 4-d data assimilation products produced with merra-2 and distributed by nasa goddard space flight center (gsfc). additionally, ozone column amounts are obtained from satellite measurements [17]. as raw data, three satellite visible radiances are utilized: the sky composite radiance, instantaneous clear-sky radiance, and the instantaneous cloud-sky radiance. these are then converted into broadband shortwave toa albedos using the angular distribution models (adm) from the earth radiation budget experiment. to find the absolute value of surface reflective power and produce a toa skyward flux, a radiative transfer model is applied. power provides the ultraviolet irradiance at all temporal levels from 2001 to the months of near real time (nrt) directly from ceres syn1deg, which is available only in all-sky conditions. b. research area the research areas are located at different latitude, longitude and altitude. shey phoksundo rural municipality lies within an elevation range of 2300 meters and 7425 meters, with a longitude 83.09000 e and latitude 29.42000 n [17, 18]. manang is located at latitude of 280 4 ′ n and longitude of 840 1 ′ e with an altitude ranging from 2000 to 6000 meters [19]. hetauda is positioned at a latitude of 270 25 ′ n and longitude of 850 2 ′ e respectively, and at an altitude of 345m from sea level [20]. paribartan rural municipality is situated at longitude 82.57000 e and latitude 28.50000 n, within an elevation range of 14001600 m from the sea level [21]. birgunj is located at a latitude of 2701 ′ n and longitude of 84052 e respectively, and the elevation of city from sea level is 91m [22]. tulsipur municipality is situated at longitude 82.29830 e and latitude 28.13110 n, and at an altitude of 725 m from the sea level [23]. furthermore, the research area are classified into three categories depending upon their altitude from sea level as: a) low altitude (birgunj and hetauda) b) moderate altitude (tulsipur and paribartan rm) and c) high altitude (shey phoksundo rm and manang). c. data analysis for a comparative study of the uv index above birgunj, dang, hetauda, rolpa, dolpa, and manang from 2001 ad to 2021 ad, data were obtained from power.larc.nasa.gov. the uv index values were derived from mean solar day measurements taken hourly and averaged to obtain monthly averages. subsequently, these monthly averages were further averaged to determine the annual average uv index value. a standard deviation test was conducted to assess the dispersion of the data points. 4 results and discussion a. annual variation and monthly variation of uv index above different locations at low altitude the average value of uv index for every month from year 2001 ad to 2021 ad is presented in table 1 below: ismah mainali et al./ bibechana 21 (2024) 281-289 285 table 1: average uvi above birgunj and hetauda, and calculated standard deviation months birgunj uv index s.d. hetauda uv index s.d. january 4.16 0.41 4.37 0.42 february 5.48 0.58 5.42 0.62 march 7.17 0.50 6.89 0.42 april 8.43 0.45 8.13 0.51 may 8.06 0.71 7.65 0.67 june 8.12 0.60 7.58 0.38 july 7.61 0.68 7.22 0.52 august 7.87 0.61 7.43 0.50 september 7.81 0.45 6.80 0.39 october 7.03 0.35 6.37 0.33 november 5.12 0.39 4.93 0.33 december 4.13 0.34 4.03 0.36 figure 1 (a): average monthly variation of uv index above birgunj and hetauda. figure 1(b): average annual variation of uv index above birgunj and hetauda. the graphs (fig:1(a)& (b)) and table 1 reveal that the uv index in birgunj reached its maximum in the year 2009 ad with the value of 7.19 and its minimum in 2021 ad with the value of 6.43. in contrast, hetauda shows slight variations in the uv index annually, with a minimum of 6.16 in 2015 and a maximum of 6.84 in 2017. both locations experience the highest uv index in april, reaching 8.43 in birgunj and 8.13 in hetauda. conversely, december records the lowest uv index values in both places. notably, the peak uv index values observed in april classify as ’very high’ according to who guidelines. the difference in local weather conditions or the accumulation of more aerosols in the atmosphere may be reasons for the lower uv index in hetauda compared to birgunj. additionally, the higher air pressure in birgunj, due to its lower altitude, implies greater global solar radiation (gsr) there than in hetauda as air pressure increases the global solar radiation [24]. at moderate altitude figure 2(a): average monthly variation of uv index above tulsipur submetropolitan and paribartan rural municipality. figure 2(b): average annual variation of uv index above tulsipur submetropolitan and paribartan rural municipality. ismah mainali et al./ bibechana 21 (2024) 281-289 286 table 2: average uvi above tulsipur and paribartan, and calculated standard deviation. months tulsipur uv index s.d. paribartan uv index s.d. january 3.43 0.37 3.73 0.41 february 4.81 0.55 5.11 0.56 march 6.51 0.45 7.05 0.47 april 7.24 0.56 7.93 0.60 may 7.11 0.74 8.14 0.77 june 6.48 0.67 7.24 0.77 july 5.87 0.45 6.52 0.55 august 5.96 0.50 7.00 0.63 september 5.77 0.32 6.68 0.41 october 5.22 0.34 6.20 0.40 november 3.68 0.24 4.40 0.29 december 3.11 0.26 3.59 0.32 based on the graphs (fig:2(a) & (b)) and table(ii) , it can be concluded that the uv index values above tulsipur and paribartan rm were highest in the year 2009 ad and lowest in 2021 ad. upon analyzing the monthly data, it is evident that the uv index peaks in april for tulsipur and in may for paribartan, while reaching its minimum in december. the maximum uv index values observed in april classify as ’high’ and in may as ’very high’ according to who guidelines. additionally, due to its higher elevation, paribartan rm experiences a higher uv index compared to tulsipur sub metropolitan. at high altitude table 3: average uvi above manang and shey phoksundo, and calculated standard deviation months manang uv index s.d. shey phoksundo uv index s.d. january 4.48 0.62 4.89 0.62 february 5.86 0.72 6.70 0.93 march 7.28 0.49 8.99 0.93 april 8.05 0.57 10.89 0.88 may 8.47 0.67 12.06 0.92 june 8.34 0.61 12.56 0.80 july 7.94 0.51 11.54 0.66 august 8.18 0.44 11.02 0.48 september 7.90 0.35 10.29 0.54 october 7.13 0.52 8.83 0.52 november 5.21 0.46 6.44 0.33 december 4.37 0.38 4.98 0.50 figure 3(a): average monthly variation of uv index above manang and shey phoksundo rural municipality. figure 3(b): average annual variation of uv index above manang and shey phoksundo rural municipality. ismah mainali et al./ bibechana 21 (2024) 281-289 287 from the table 3 and graphs (fig:3(a) & (b)) above, it can be concluded that the uv index values above manang and shey phoksundo, between the years 2001 and 2020 ad, reached their maximum in 2009 ad and minimum in 2015 ad. analysis of the monthly uv index values reveals, peaks in may for manang, and june for shey phoksundo, with minimum values occurring in december for manang and january for shey phoksundo. the higher uv index above shey phoksundo, compared to manang, can be attributed to its greater altitude. the highest uv index value in shey phoksundo illustrates the influence of altitude on uv exposure, as this region has the highest elevation among the six territories. the increase in uv concentration with altitude is due to factors such as a decrease in air molecules, aerosols, high reflectivity of the ground and clouds in the atmosphere [25]. additionally, the path length of the sun’s rays shortens with increasing altitude. there is a decrease in the uv index values between june and august, coinciding with the period of maximum precipitation and cloud covers [26]. thick cloud cover during this time lowers the amount of uv exposure. there is a slight rise in the uv index value after july. this could be attributed to a decrease in pollutants, which are flushed out due to rainfall, resulting in clearer skies [6]. despite its higher altitude, hetauda exhibits a lower uv index compared to birgunj. this difference can be attributed to the increasing aerosol content in the atmosphere and the regional-scale transport of polluted air masses [27]. a similar uv index trend was observed in kathmandu as well. despite its higher altitude, the peak uv index value recorded was 6 to 7 [28]. since both regions are industrial areas, the increasing aerosol concentration in the atmosphere has reduced the uv index due to which the effect of altitude became less dominant. upon analyzing yearly data, it is evident that the uv index peaked in the year 2009 ad, likely due to the heightened activation of factors influencing the uv index. however, there was a significant decline in the value around 2015 ad. this decline could be attributed to the arrival of primarily diffuse uv radiation caused by the accumulation of a large number of dust particles in the upper atmosphere following a devastating earthquake, which obstructed direct uv radiation. also, different parts of nepal received heavy rainfall in the same year which could also have reduced the over uv exposure [29]. furthermore, the uv index appears to have declined in all six locations after 2019. the covid-19 pandemic is undoubtedly responsible for this decline. with lockdown measures in place and no vehicular emissions, there was a significant reduction in airborne emissions of various oxides, which support the ozone layers thickening and help prevent significant amounts of incoming uv radiation. figure 4: hourly variation of uv index above birgunj, tulsipur and shey phoksundo rural municipality. the monthly variation plot clearly indicates that the minimum uv index values are observed in december or january, while the values become dominant during the summer months. there is a clear upward trend in the first half of the year and a downward trend in the second half. overall, the data analysis suggests that the uv index values in this region vary between 3 and 13. the maximum uv index values fall into the category of high and very high when compared with the standard values mentioned by the who [30]. figure 4 represents the uv index trend during the daytime. from the graph, it is evident that the uv index rises after sunrise, peaks around solar noon, and then gradually decreases, reaching zero at night. additionally, the uv index remains at zero both before sunrise and after sunset. figures 1a), 2a), and 3a) clearly illustrate that the uv index value is low during the winter season (december and january) and increases with rising temperatures in the spring and summer. the study of the uv index in various locations across nepal, conducted at different altitudes, reveals that the uv index becomes higher during april, may and june, and drops significantly in december. additionally, uv index values increase with altitude. however, in industrial areas, despite the higher altitudes, there is no significant rise in uv index levels. from a global perspective, studies of the uv index conducted at various sites across africa have shown that uv levels are higher near the equator and at higher altitudes. this highlights the impact of latitude and altitude on uv index levels at specific locations. additionally, it was observed that uv index values increase during the summer and in areas with low industrial activity, while they decrease in winter, indicating the influence of seasonal changes and aerosol levels on uv index readings [30]. all these observations suggest that the uv index rises with increasing altitude, ismah mainali et al./ bibechana 21 (2024) 281-289 288 while a higher aerosol optical depth results in a significant reduction in uv index levels [31]. furthermore, clouds usually decreases the concentration of uv radiation from reaching the earth but dispersion from thin cloud may sometime increase it [32]. the higher value of uv during summer suggests that special care should be taken to protect oneself from overexposure to uv radiation during peak hours in the summer season. after closely analysing the data, it is recommended that people in all six locations adopt measures to protect themself from the possible threats posed by excessive uv exposure between the months of march and october. by adhering to simple yet crucial practices, such as wearing protective clothing, applying broad-spectrum sunscreen, and seeking shade during peak sunlight hours, individuals in the selected area alongside most of the territories of nepal can significantly reduce the risk of sunburn, premature aging, and skin cancer [33]. additionally, staying hydrated and using moisturizer can help prevent sunburn. mountaineers are advised to wear sunglasses to protect their eyes. hikers should consider using uv-blocking filters for their gear. it’s also important to check the uv index of a location before planning outdoor activities. promoting these habits within communities can foster a culture of sun safety, ensuring that people of all ages prioritize their health while enjoying outdoor activities. 5 conclusion upon analyzing the uv index values above birgunj, hetauda, tulsipur, shey phoksundo, paribartan r.m., and manang, it is evident that during solar noon, the uv index above shey phoksundo reaches the highest levels among all locations. the maximum average uv index above shey phoksundo is 12.56, indicating an extreme risk from unprotected solar exposure, observed typically in june, while the minimum value is 4.89, recorded in december. furthermore, the maximum average uv index values above birgunj, tulsipur, paribartan, manang, and hetauda are classified as ’very high’ according to who guidelines, typically occurring in april and may. in contrast, the minimum average uv index values, classified as ’moderate’ according to who guidelines, are noted in december. in conclusion, safeguarding ourselves against the detrimental effects of overexposure to uv radiation demands a proactive commitment to safety habits. acknowledgements the authors extend their sincere gratitude to mr. sushil babu ojha from central department of physics and prof. dr. k.n. poudyal, institute of engineering, pulchowk campus, tribhuvan university, for useful discussion. additionally, heartfelt appreciation is expressed to nasa for providing the essential data required for the calculations. references [1] a. aggarwal, r. kumari, n. mehla, r. p. singh, s. bhatnagar, sharma, k. sharma, v. amit, b. rathi, et al. depletion of the ozone layer 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[29] u. joshi, i. karki, n. chapagain, and k. poudyal. prediction of daily global solar radiation using different empirical models on the basis of meteorological parameters at trans himalaya region, nepal. nepal bibechana, 18(1):159–169, 2021. [30] j.-m. cadet, h. bencherif, t. portafaix, k. lamy, k. ncongwane, g. j. coetzee, and c. y. wright. comparison of ground-based and satellite-derived solar uv index levels at six south african sites. international journal of environmental research and public health, 14(11):1384, 2017. [31] r. sharma, b. kjeldstad, and p. espy. uv index and total ozone column climatology of nepal himalaya using toms and omi data. journal of hydrology and meteorology, 9(1):45–59, 2015. [32] k. n. poudyal, b. k. bhattarai, b. sapkota, and b. kjeldstad. estimation of global solar radiation using clearness index and cloud transmittance factor at trans-himalayan region in nepal. energy and power engineering, 4(6):563–570, 2012. [33] committee on environmental health and section on dermatology. ultraviolet radiation: a hazard to children and adolescents. pediatrics, 127(3):588–597, 2011. introduction effects of high uv index methods results and discussion conclusion bibechana vol. 20, no. 2, august 2023, 200–204 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar chemical and microbial evaluation of water of rupa lake kamal prasad dhungana1, akkal dev mishra2,∗, kalpana gautam adhikari3 1department of chemistry, prithvi narayan campus, pokhara 2central department of chemistry, tribhuvan university, kathmandu 3department of microbiology, janapriya campus, pokhara ∗corresponding author. email: mishraad71@gmail.com abstract analysis of chemical and microbial features of rupa lake water was carried out in summer season by adopting accepted analytical techniques. water samples were collected at 28°c, and on-site observations were made for features like colour, odour, ph, transparency, dissolved oxygen, and free carbon dioxide. in the laboratory, the concentration of prominent mineral ions and microbial contamination were measured using accepted analytical techniques. transparency of lake water was noted 91cm and electrical conductivity 41 µs/cm indicating the presence of suspended particulate at moderately higher concentration. this water is slightly alkaline with ph of 7.2 that is accounted by domination of alkali and alkaline metal ions. presence of nitrogenous species mainly ammonium and nitrate in excess amount has detected to be major reason for rapid eutrophication in the lake. analysis of rupa lake water has shown the considerable presence of phosphate and sulphate which have added to the hardness 130 mg/l of the water as well. on the top of this fairly higher concentration of free carbon dioxide indicates presence of organic wastes in association with decaying matters. domestic sewage discharge, the use of pesticides and fertilizers in agricultural areas, as well as other solid waste dumps has caused microbial contamination and the biggest dangers to the viability of rupa lake. the risk of contamination and the eutrophication process needs to be managed by creating public awareness [1].the study shows that water quality of rupa lake is contaminated for drinking but adequately suitable for all aquatic life and ecological balance. keywords chemical features, rock weathering, eutrophication, ecological balance, microbial contamination. article information manuscript received: june 22, 2023; accepted: july 11, 2023 doi https://doi.org/10.3126/bibechana.v20i2.56526 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction lakes have diverse physical and chemical characteristics, making them valuable ecosystems for drinking water, fisheries, recreational activities, and ecological studies. the lake ecosystems are considered as one of the valuable ecosystems in the world [2]. water quality is vital for developing a healthy ecosystem, as both non-living and living factors depend on each other [3]. rivers, lakes and oceans 200 http://nepjol.info/index.php/bibechana mishraad71@gmail.com https://doi.org/10.3126/bibechana.v20i2.56526 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ k. p. dhungana et al./ bibechana 20 (2023) 200-204 201 greatly facilitated the world wide spread of the population and commerce, springs, waterfall, glaciers and snow fields. about 97% of the total available water on earth is contained in ocean, and remaining 3% is available as fresh water. among fresh water, 2% is contained in ice in accusable region and 0.7% as ground water. out of the total fresh water available on earth, only 0.25% exists in lakes and rivers at any given time, with the rest being stored in ice in inaccessible regions and groundwater [4]. the surface water is the form of oceans, rivers, lakes, ponds and streams on the earth's surface. there are about 5000 lakes in nepal out of them; ten are listed in the list of ramsar site. the water from the lakes is the source of drinking and for various household uses for rural and urban people [5]. water quality and suitability for use are determined by its taste, odour, colour, and concentration of organic and inorganic matters. contaminants in the water can affect the water quality and on the health of the people. most of the lakes of nepal are situated in the hilly region. among hill districts, the kaski district contains the largest number of lakes and all of them are located to the pokhara valley. pokhara valleyis known as the "city of lakes’ ’. phewa lake, begnas lake, rupa lake, maidi lake, khaste lake, dipang lake, nyureni lake, gude lake are the most popular lakes of pokhara valley [6]. physical characteristics such as light, temperature, transparency, pressure, water current and conductivity whereas chemical properties like dissolved oxygen, carbon dioxide, ph, alkalinity, hardness, etc. of the lake water are some of the key factors to evaluate water quality [7]. pollutants present like pb, as, hg, cd, u, etc in the water may cause serious health hazards. rupa lake has become tourism attraction spot and provides enough spaceforboating and recreation.farmers in the kaski district have formed the rupa lake rehabilitation and fisheries cooperatives limited to help protect the watershed [8]. the concentration of all minerals is related to two main factors are the abundance of chemical elements in the earth crust and the solubility of their compounds. the main anions contained in natural water are c1−, so4 2−, hco− 3 and co2− 3 and the main cations are ca2+, na+, mg2+, k+ etc [9]. all natural water contains dissolved gases but they differs in their origins such as volcanic process and degassing of the earth's mantle supply oxides and dioxides of carbon, methane, ammonia, hydrogen sulfide, hydrogen chloride, sulfurous gas [10]. some other gasesmayappearand dissolve in waterasresult ofultravioletradiation, thunderstorm discharge sulfurous gas, vapour of iodine, ammonia, carbonic acid, etc. biogenic substance these include compound of silicon, nitrogen, phosphorus, iron, etc. organic matters are composed of organic compound that have come from remains of organism such as plants and animals and their waste products in the environment [11]. main objective of present study is to examine rupa lake water for mineral ions and microbes which determine water quality for drinking, irrigation, animals and aquatic creatures as compared to who standards. this study will help in creating public awareness to safeguard lake water, conserve the lake area and maintain local ecosystem. 2 methods and materials the study area, rupa lake, is a freshwater lake located in the border of pokhara metropolitan and rupa rural municipality of kaski district, nepal. it is the third-largest lake in the pokhara valley, covering an area of about 1.35 km2, with an average water depth of 3 m and a maximum depth of 6 m. the lake is elongated north to south and is fed by perennial streams. its watershed area is 30 km2 where the main inflow of water is from talbesi stream, whereas dhovan khola is the feeder stream with its outlet tal khola at sistani ghat. it supports a number of floral and faunal species. a total of 36 species of water birds have been recorded in the lake which represents about 19 percent of the total 193 wetland-dependent birds found in nepal [12]. rupa lake is the third largest lake in the cluster of pokhara which is located at latitude of 28007’28012’n and longitude of 84005’-84010’ e. the lake is surrounded by dense forests over humus soils with hard rocks. the physical and chemical parameters such as temperature, transparency, dissolved oxygen, carbon dioxide, ph, alkalinity, hardness, dissolved solids, chloride, calcium, and magnesium were evaluated using various methods. some of other parameters such as sulphate, phosphate (po4 3-), nitrate (no3 -), ammonium (nh4 +), iron (fe2+/fe3+) were studied with the help of spectrophotometer. the concentration of potassium (k+) was estimated by flame photometer and electrical conductivity by conductivity meter [13]. all the solutions of the reagents to be used were prepared in 0.01m concentration in distilled water for titration and other reactions. spectrophotometric absorption was observed at 396 mµ-512 mµ for the detection of fe2+/fe3+ ions simultaneously. similarly, k+ ions gave purple emission with 760 nm in flame photometry at about 18000c. k. p. dhungana et al./ bibechana 20 (2023) 200-204 202 table 1: methods applied for evaluating the physico-chemical features of water. parameters methods employed transparency (cm) secchi disc method temperature (0c) standard mercury thermometer dissolved oxygen (mg/l) winkler’s iodometric titration method hydrogen ion concentration microprocessor ph meter total alkalinity (mg/l) titration method total hardness (mg/l) edta titration method total solid (mg/l) evaporation method total dissolved solid (mg/l) filtration method calcium (mg/l) titration method magnesium (mg/l) titration method chloride (mg/l) titration method in addition to this, the microbial contamination in the lake was analyzed by most probable number (mpn) method [14]. preliminary test was done by inserting durham’s tube containing lake water into macconky broth in inverted form. the change in colour into yellow indicates the presence of coliform bacteria in water and formation of colony at 37 gives its confirmation. the number of positive tubes were counted and compared with standard chart to find mpn of 100 ml water sample. figure 1: overview of rupa lake. 3 results and discussion transparency was measured at 28°c using a secchi disk method. the transparency of rupa lake was found to be 91 cm, which suggests that the presence of organic and inorganic suspended particles, silts, sediments, and debris could affect the water quality. an increase in temperature might result in a drop in the quality of water as the organic matter composition decays more quickly due to the warmer water. rupa lake has a slightly alkaline ph value of 7.2, indicating the presence of carbonates and bicarbonates of alkali and alkaline earth metals. the concentration of dissolved oxygen (do) observed in this study is 4.2 mg/l, which is lower than the standard value of 5.0 mg/l, indicating poor suitability for aquatic life. presence of carbonates, bicarbonates and hydroxides of alkali metals and alkaline earth metals like na, k, mg, ca, accounts for total alkalinity water. the lake water's total alkalinity is 52 mg/l, making it slightly alkaline, and the total hardness is 130 mg/l, which is a bit high and might impact the biotic components of the lake. the electrical conductivity (ec) of the lake water is 41 µs/cm, suggesting higher dissolved ion concentrations or high total dissolved solids (tds) values. the tds measures the amount of chemical weathering in the watershed. its amount in rupa lake in present study is found to be 50 mg/l. the variety of natural and human induced pollutant causes ink. p. dhungana et al./ bibechana 20 (2023) 200-204 203 crease in tds. the lake water's total solid matter is 136 mg/l, indicating a high level of solid materials, including dissolved and suspended solids, clay, plankton, organic waste, and inorganic precipitates. the chloride concentration of rupa lake is 14 mg/l. the primary sources of chlorine in lakes and ponds are domestic sewage and faecal deposits. it lies within the standard value prescribed by who. calcium and magnesium concentration observed are 24 mg/l and 13mg/l respectively that exceed the normal acceptable level. however the concentration of phosphate is 0.04mg\l which lies above who guideline for drinking water. the observed concentrations of nitrates, ammonia, and sulfates in rupa lake are slightly higher, possibly due to domestic runoff, industrial discharge, agricultural runoff, and natural degradation of organic matter, as well as sewage contamination. these nitrogenous sources are responsible for eutrophication in water bodies. nitrate is 0.61 mg/l, ammonia was 1.8 mg\l and sulphate is 2.6 mg\l in rupa lake water respectively. the potassium concentration of lake water sample was 1.6 mg\l. the concentration of iron in the lake water is 0.5 mg/l, which exceeds the standard value of 0.3 mg/l. the higher iron concentration may be due to weathering of ferrous and ferric ions from surrounding rocks and minerals. higher concentration of iron in lake water becomes rusty red or brown in colour that causes health hazards. it may be due to the weathering of ferrous and ferric irons from surrounding rocks and minerals. the observation of microbiological analysis performed by most probable number method revealed that the lake water contains coliform bacteria. table 2: observations of various parameters of rupa lake water. parameters rupa lake who standards (2020) parameters rupa lake who standards (2020) transparency (cm) 91 100.0 calcium (mg\l) 24 10.0 temperature (0c) 28 12-25 magnesium (mg\l) 13 5.0 electrical conductance (µs/cm) 41 40.0 phosphate(mg\l) 0.04 0.02 total alkalinity (mg/l) 52 100.0 nitrate (mg\l) 0.61 0.50 total dissolved solids (mg/l) 50 45.0 ammonia (mg\l) 1.8 1.5 total solids (mg/l) 136 120.0 iron (mg\l) 0.5 0.3 dissolved oxygen (mg\l) 4.2 5.0 sulphate (mg\l) 2.6 2.5 ph 7.2 6.5-8.5 potassium (mg\l) 1.6 2.0 chloride (mg\l) 14 20.0 free co2 (mg\l) 3.0 1.5 total hardness (mg\l) 130 50.0 4 conclusion the study of chemical and microbial features of rupa lake revealed that the water is slightly alkaline with higher concentration of suspended and dissolved minerals as compared to who water quality standards. on the top of this, the water is contaminated with coliform bacteria. the water is not suitable for drinking purposes however it is acceptable for aquaculture and irrigation. rapid eutrophication may be caused by household and industrial discharge along with decomposition of organic matters is posing severe danger to the sustainability of rupa lake. this study has indicated another challenge to the sustainability of this lake like encroachment accompanied with deforestation and sedimentation due to weathering of soils and rocks from catchment areas. right now it has become essential to conserve the lake by strict monitoring and safeguarding aquatic environment and watershed areas by creating public awareness towards local ecosystem and health hazards. acknowldgement authors would like to express sincere thanks to the department of chemistry, prithvi narayan campus, tribhuvan university, for providing the laboratory facility to conduct this research work. the university grants commission of nepal deserves thanks for financial support to carry out this research work. k. p. dhungana et al./ bibechana 20 (2023) 200-204 204 references [1] b. gautam and b. bhattarai. seasonal changes in water quality parameters and sediment nutrients in jagadishpur reservoir, a ramsar site in nepal. nepal journal of science and technology, 9:149–156, 2008. [2] r. b. raya. impact of land use on water quality of phewa-lake pokhara, nepal. in urban waters: resource or risk?, page 190, 2008. [3] p. k. neupane, m. khadka, r. adhikari, and d. r. bhuju. lake water quality and surrounding vegetation in dry churiya hills, far-western nepal. nepal journal of science and technology, 11:181–188, 2010. [4] m. l. parry, o. f. canziani, j. p. palutikof, p. j. van der linden, and c. e. hanson. ipcc, 2007: climate change 2007: impacts, adaptation and vulnerability. contribution of working group ii to the fourth assessment report of the intergovernmental panel on climate change. cambridge university press, 2007. [5] p. lamsal, k. p. pant, l. kumar, and k. atreya. sustainable livelihoods through conservation of wetland resources: a case of economic benefits from ghodaghodi lake, western nepal. ecology and society, 20(1), 2015. 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[10] d. rupakheti, l. tripathee, s. kang, c. m. sharma, r. paudyal, and m. sillanpää. assessment of water quality and health risks for toxic trace elements in urban phewa and remote gosainkunda lakes, nepal. human and ecological risk assessment: an international journal, 23(5):959–973, 2017. [11] u. r. khadka and a. l. ramanathan. major ion composition and seasonal variation in the lesser himalayan lake: case of begnas lake of the pokhara valley, nepal. arabian journal of geosciences, 6:4191–4206, 2013. [12] n. pradhan, i. providoli, b. regmi, and g. kafle. valuing water and its ecological services in rural landscapes: a case study from nepal. mountain forum bulletin, pages 32–34, 2010. [13] n. m. khadka, s. d. gautam, and p. n. yadav. a core experimental chemistry. third edition, 2010. [14] e. w. rice, l. bridgewater, and american public health association, editors. standard methods for the examination of water and wastewater, volume 10. american public health association, washington, dc, 2012. introduction methods and materials results and discussion conclusion bibechana vol. 22, no. 3, december 2025, 223-236 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar advancement of plant-based inhibitor acquired from elaeocarpus aungustifolius blume leaves to control carbon steel corrosion in simulated concrete pore solution madhab gautam1,2, dhruba babu subedi1, yuvraj paudel1 kamal t. kunwar magar1, nootan prasad bhattarai1,∗, jagadeesh bhattarai1,∗ 1central department of chemistry, tribhuvan university, kirtipur 44618, kathmandu, nepal 2department of chemistry, tribhuvan m. campus, tribhuvan university, tansen 32500, palpa, nepal ∗corresponding author. email: bhattarai_05@yahoo.com[jb], neutan08@gmail.com[npb] abstract the extraordinary compressive strength of concrete makes it one of the most popular building materials, second only to water. however, early reinforcement corrosion is a common problem with concrete structures reinforced with carbon steel (cs). this issue underscores the significance of understanding corrosion-retarding systems that incorporate inhibitors. this research evaluates the effectiveness of leaf extract from elaeocarpus angustifolius blume (leea) as an inhibitor in an aqueous saturated calcium hydroxide electrolyte that simulates a concrete pore solution (scps) with a ph level exceeding 11.5. the objective is to evaluate the corrosioninhibiting capacity of leea at 500-4000 ppm in scps to reduce the corrosion of reinforcing carbon steel (rcs) at 298k over four months or more using gravimetric weight loss (grwl) and electrochemical polarization (ecp) techniques. grwl and ecp methods yielded the maximal inhibition efficiencies of 93.9% and 81.7%, respectively, at 4000 ppm leea in scps. the results of ecp experiments demonstrated that the corrosion current density (ccd) decreased with increasing leea concentrations. this observation indicates that leea exhibits a significant inhibitory effect in the scps environments. phyto-compounds (pcs), including polyphenols, alkaloids, and flavonoids found in leea, can inhibit both cathodic and anodic (i.e., mixed) processes by promoting the best-fitting langmuir adsorption isotherm model on the rcs surface. surface analyses confirmed the corrosion-inhibiting effectiveness of leea in enhancing concrete's anti-corrosion properties through a protective layer on rcs. keywords corrosion-resistant film, phyto-inhibitor, polarization, reinforcement corrosion, polarization. article information manuscript received: april 28, 2025; revised july 28, 2025; accepted: august 3, 2025 doi https://doi.org/10.3126/bibechana.v22i3.78028 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 223 http://nepjol.info/index.php/bibechana bhattarai_05@yahoo.com neutan08@gmail.com https://doi.org/10.3126/bibechana.v22i3.78028 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ madhab gautam et al./ bibechana 22 (2025) 223-236 224 1 introduction the most widespread structural building material is reinforcement concrete because of its affordability, mechanical strength, and adaptability [1]. the reinforcement concrete structures' durability is affected by their alkaline nature of interspersed pore solution, which has a ph of around 12-14 [2]. as a result, cement paste's hydration produces a thin, passive, and stable oxide film [3] that firmly sticks to the rcs surface to prevent early corrosion deterioration. the rcs corrosion deterioration describes the premature degradation of reinforced concrete structures caused by electrochemical processes on the cs surface brought on by ambient dampness, high temperatures, carbonated conditions, and the ingress of vicious ions such as sulfates and chlorides [4]. it is the most prevalent issue in hostile (urban or industrial) and coastal environments [5]. corrosion causes concrete structures to crack, spall, and weaken, which causes reinforced concrete foundations to collapse too soon [6]. the reinforcement corrosion presents significant challenges and should be managed effectively in time [7]. synthetic waterproofing compounds are utilized for long periods as preventive concrete admixtures to mitigate corrosion of rcs [8]. unfortunately, a considerable number of these synthetic compounds have the potential to harm living beings and contribute to environmental contamination [9]. it underscores the viability of utilizing plant-based green extracts as an alternative approach for corrosion prevention in reinforcement concrete infrastructures [10]. secondary metabolites such as alkaloids, phenols, flavonoids, and others derived from plant waste—encompassing leaves, roots, stems, and bark—are particularly relevant in this context. these compounds exhibit distinctive aromatic systems, unsaturated -systems, and lone pairs of electrons associated with heteroatoms [11]. such characteristics facilitate the formation of physical and chemical adsorption layers that disrupt corrosion reactions at the interface between corroded rcs and the concrete mix that incorporates plant extracts, thereby demonstrating significant corrosion-inhibiting properties [12]. nepal ranked the world's second-richest country in forest resources after brazil, and is home to a diverse range of flora and fauna [13]. however, many forest products in nepal have been underutilized. research into their potential as environmentally friendly corrosion inhibitors for reinforced concrete (rec) is still in its early stages. some studies have documented the use of nepalese plant-based corrosion inhibitors to control the corrosion of mild steel (ms) in various electrolytes. for instance, the leaves of callistemon citrinus have been tested on ms in nacl [14], while extracts from areca catechu and laurus nobilis have been studied in a 0.5m nacl solution [15]. additionally, aegle marmelos has shown effectiveness on ms in bioethanol [16], and a range of plants including acacia catechu, terminalia arjuna, aegle marmelos, catharanthus roseus, callistemon citrinus, and laurus nobilis have all been evaluated on ms in acidic electrolytes [17]. researchers have also explored vitex negundo on aluminum and copper in biodiesel and its blends [18]. further studies have involved aegle marmelos and catharanthus roseus in both bioethanol and its blends [16], extracts of vitex negundo and catharanthus roseus on ms for waterproofing applications [11], and the stem extract of tinospora cordifolia on aluminum and copper in biodiesel-based fuels [19]. more recent studies have examined leaf extracts of mangifera indica [20] and psidium guajava [21] on ms in concrete beams and slabs. ongoing efforts continue to identify new and effective green inhibitors for rec infrastructure, including the endemic plant species elaeocarpus angustifolius blume from nepal, as a potential green inhibitor. in this context, it is meaningful to mention herein that in the domain of materials science, two synthetic and commercial waterproofing agents, along with the methanolic extract of mangifera indica leaves, had exhibited notable anti-corrosion properties, thereby warranting their recommendation for the protection of reinforced mild steel (rms) infrastructures [20]. the corrosion resistance of 1000 and 2000 ppm concentrations of m. indica extracts applied to rms within concrete surpasses that of equivalent concentrations of the commercial waterproofing agents. this enhanced performance was evidenced by shifts in halfcell potential (hcp) values toward more noble directions (i.e., < 10 % corrosion probability regions). such findings suggest that plant-based anticorrosive concrete admixtures may provide greater advantages than the utilization of conventional waterproofing chemicals [20]. hence, this study aimed to present a rationale for the integration of plantderived metabolites from elaeocarpus angustifolius blume leaf as effective anti-corrosive additives in ferroconcrete formulations. elaeocarpus angustifolius blume, commonly known as the bead tree or rudraksha, is a wellknown medicinal plant recognized for its various pharmacological and ethno-medicinal properties [22]. the name comes from greek, where "carpus" means fruit and "eleaeo" refers to olive, which reflects the olive-like appearance of the tree's fruits [22]. the elaeocarpus family includes over 360 species worldwide, with 26 species identified in nepal alone [16]. among these, e. angustifolius blume—also referred to as elaeocarpus ganitrus roxburgh and e. sphaericus gaertner—is an madhab gautam et al./ bibechana 22 (2025) 223-236 225 evergreen tree notable for its ornamental, stony endocarp, known as rudraksha [23]. according to hindu mythology, the rudraksha tree has sprouted from the tears of lord shiva, and its fully developed blue fruits are often referred to as "blueberry beads" [24]. the rudraksha tree is a large, evergreen, deciduous tree with a spreading crown that can grow to 50 and 200 feet [25]. its leaves are simple, alternate, and oblong-lanceolate, measuring 10-15 cm long. the underside of the leaves has a dull, fibrous texture, while the upper surface is bright green [26]. this tree is well-known for its spiritual and therapeutic benefits, as it produces beads with segmented ridges, believed to possess electromagnetic properties capable of dispelling negative energy [27]. research indicates that methanolic leaf extracts of the rudraksha tree (e. ganitrus) exhibit significant analgesic effects and contain alkaloids, tannins, and flavonoids [28]. additionally, methanolic leaf extracts of e. sphaericus are rich in phytoconstituents such as saponins, alkaloids, phenols, flavonoids, sterols, and carbohydrates; however, they do not contain amino acids or proteins [29]. because the leaves of this medicinal plant have a high phenol and flavonoid content and contain many classes of bioactive secondary metabolites, the bioactivity tests showed that the leaves might be a potential source of antibacterial, antibiotic, antioxidant, anti-diabetic medications [30], and other purposes like as anti-corrosive agents. however, a considerable quantity of leaves from this plant acts as debris without deriving any industrial or monetary benefits. while a limited number of studies have underscored the corrosion-inhibitory properties of the leaf extract [16] and seed extract [31] in aggressive electrolytes, there has yet to be an investigation into their efficacy in mitigating corrosion in rec. according to what we know, the methanolic leaf extract from the elaeocarpus aungustifolius blume plant was not considered a corrosion inhibitor for reinforced carbon steel in scps/reinforcement concrete in literature, which is why the present research is considered novel. therefore, this study aims to evaluate the effectiveness of leaf extracts from the elaeocarpus angustifolius blume plant (leea) as environmentally friendly corrosion inhibitors in simulated concrete pore solutions (scps) with a ph level higher than 11.5. the primary objective is to assess the viability of leea as a green corrosion inhibitor within this context. the research investigates the ability of leea to reduce the corrosion of carbon steel (cs) in scps utilizing gravimetric weight loss (grwl) and potentiodynamic polarization (pop) methods. the findings may contribute to plant-derived green inhibitors designed to mitigate corrosion in concrete reinforcement. 2 materials and method ar grade methanol and calcium carbonate were employed for the preparation of leea and saturated ca(oh)2 solution, respectively. they were with a purity of 98%. elaeocarpus aungustifolius blume leaves, as illustrated in fig. 1(a), were identified with voucher code rdp-01 and deposited at the department of plant, national herbarium and plant laboratory in godavari, lalitpur, after being collected from the tribhuvan university campus premises close to the central department of environmental sciences, tu-kirtipur, nepal. the collected leaves were placed in a shady area until completely dried and ground in an electric grinder to make leaf powder, as in fig. 1(b). about 400 grams of leaf powder of elaeocarpus aungustifolius blume were taken in 2000 ml conical flasks with 800 ml of methanol, as described elsewhere [32]. after being tightly sealed in the conical flask and thoroughly shaken, they were kept for 2 weeks or more with regular shaking, as shown in fig. 1(c). following the shaking procedure, the supernatant mixtures were kept for a few hours to separate the supernatant using filtration. excess methanol in the filtrate was removed using a rotary evaporator (ika®rv 10 digital v, germany) and water bath at 40°c, as illustrated in fig. 1(d). then, the semi-solid leaf extract of elaeocarpus aungustifolius blume (leea) was stored at 4°c. the saturated calcium hydroxide [ca(oh)2] solution, with a ph of approximately 12±0.5, was used to prepare the scps. figure 1: photos illustrating the different stages of the leea preparation: leaves of elaeocarpus aungustifolius plant (a), dried leaves powder (b), leafpowder dipped in ch3oh (c), and a solvent evaporator machine (d). for the grwl approach, fifteen thermomechanically treated carbon steel (cs) specimens, designated as 500cs (nbs marked 500 xd series), were meticulously prepared. as previously outlined in other studies, the surface preparation involved using silicon carbide paper with grits ranging from 200 to 2000 [15]. the average diameter and length of each of the 500cs pieces were 1.13 cm and 2 cm, respectively. a 5-digit micro-balance (bm-252; a&d weighing co., japan) with an accuracy of madhab gautam et al./ bibechana 22 (2025) 223-236 226 0.00001 grams was initially used to record carefully the weight of each 500cs piece (abbreviated as w0). the composition (wt.%) of the 500cs pieces is roughly 98% fe, with trace c, mn, s, and p, as described elsewhere [33]. out of the 15 sample pieces, three 500cs pieces were immersed in three 100 ml beakers containing 50 ml of scps without leea (controlled scps). similarly, twelve 500cs pieces were dipped in twelve beakers containing 50 ml scps with 5004000 ppm leea for 2802 hours to estimate the corrosion rate (cor). for this, the weight of each 500cs specimen after being exposed to it for t times (indicated as wt) was recorded after 7, 14, 28, 43, 60, 90, and 117-day immersion in each scps variant. the corrosion rate (cor) for each sample in the scps with leea concentrations ranging from 500 to 4000 ppm and in the scps without leea (control scps) was calculated using the formula provided in equation (1), as described elsewhere [34]. additionally, the estimated surface coverage () and corrosion inhibition efficiency [coie) were calculated using equations (2) and (3), respectively, as given in ref. [35]. cor(mm/y) = ∆w (g) × 87600 a (cm2)× ρ (gcm−2)×t (hrs.) (1) θ = cr(control) − cr(leea) cr(control) (2) % coie =cr(control) cr(leea) cr(control) ×100 (3) where, w = wo-wt furthermore, electrochemical analysis was performed through potentiodynamic polarization (pop) experiments using an iquant 64 potentiostat (model no.: ifc 101-32240) with a three-electrode system, as outlined in the literature [36]. the slopes of the anodic and cathodic polarization curves, derived from formulas (4) and (5), were used to calculate the corrosion potential (ecor), corrosion current density (icor), the corrosion rate (cor) based on icor or weight loss, and the corrosion inhibition effectiveness (coie) based on icor and weight loss [37]. consequently, icor-based cor was determined using tafel plots of both the anodic and cathodic curves [38]. cr(icor) = 0.13 × icor × e ρ (4) %ine(icor) = icor(control)-icor(leea) icor(control) ×100 (5) where, = 7.86 g/cm³, is density and e = 55.85, equivalent weight of 500cs pieces. the inhibitory activity of the phyto-compounds (pcs) from leea is demonstrated using langmuir adsorption isotherm [39, 40]. the linear fit plot of this isotherm allows us to estimate gads, using equation (6), as illustrated in literature [41]. cleea = 1 kads + cleea (6) in this case, kads = adsorption equilibrium constant, which helps determine the free energy change of adsorption (gads) value, as described in previous literature [42]. the phytochemical tests [32, 43] of leea were conducted to decide the presence (+) or absence () of various phytochemicals in leea. the ftir spectra were recorded in the wavenumber range of 400-4000 cm¹ using the atr mode (ir affinity1s, shimadzu corp., japan) to confirm the presence of functional groups in leea in addition to the phytochemical tests. pcs with their electronic properties identified using uv-vis spectra recorded by a uv-visible spectrophotometer (specord®200 plus, germany) across the wavelength range of 200 to 800 nm. furthermore, a high-performance quadrupole time-of-flight mass spectrometer (xevo g2-xs qtof, iit ropar, punjab, india) was employed to identify the distinct pcs in leea through liquid chromatography-mass spectrometry (lc-ms, waters corp., usa). the study examined the morphological and compositional modifications of the 500cs samples behind 2802 hours in control-scps and scps with 500 to 4000 ppm leea, using a scanning electron microscope (sem-thermo fisher scios field emission, usa, 10 kv), equipped with energydispersive x-ray spectroscopy (edax octane elect eds/edx detector, usa, 30 kv). it captured the surface images of the 500cs pieces submerged in control scps and scps with 500-4000 ppm leea using white light interferometry (wli) with a newview-9000 from zygo corp. 3 results and discussion the phytochemical tests confirmed that phenols, flavonoids, alkaloids, terpenes, saponins, glycosides, and carbohydrates are present in the leea as the main pcs, as summarized in table 1, constituted heteroatoms and unsaturated electrons and/or aromatic compounds [28]. these findings align with existing literature [30]. the pcs from leea contribute to forming a diffusion-barrier passive layer on the surface of immersed 500cs pieces through the adsorption phenomenon, which aids in controlling corrosion and is consistent with previous studies [44]. the uv-vis analysis revealed distinct peaks associated with various functional groups of leeapcs, thereby confirming the electronic transitions present in the extract, as illustrated in fig. 2(a). the uv-vis spectra of leea show absorption peaks at 472 nm, 503 nm, 535 nm, 606 nm, and 664 nm, suggesting the existence of aromatic or conjugated unsaturated systems [45]. previous study reported that the uv-vis peaks at 472 nm and 535 nm indicated the presence of terpenoids [46]. the peaks at 606 nm and 664 nm are identified as chlorophyll [47]. consequently, pbes exhibit a strong anti-corrosive effect due to their richness in secondary metabolites (sms). however, uv-vis analmadhab gautam et al./ bibechana 22 (2025) 223-236 227 ysis presents challenges in identifying specific constituents corresponding to these absorption peaks [48]. therefore, it is essential to complement uvvis findings with other analytical techniques [49], such as ftir, gc/ms, or uhplc/ms, to characterize the plant extracts, as discussed in the next sections. table 1: tests for phyto-compounds (pcs) in leea pcs result pcs result alkaloid ++ saponin + phenol +++ tanine − flavonoid ++ terpenoid ++ glycoside + carbohydrate − note: signs +, ++, +++ indicate abundance, while the sign − indicates absence. figure 2: (a) uv-vis and (b) ft-ir spectrum of leea. the results of functional groups, as shown in fig. 2(b), are confirmed in the pcs of leea by ftir analysis. the presence of nitrogen (n), sulfur (s), and oxygen (o) heteroatoms and functional groups like phenols, carboxylic acids, and amines, distinguished by their abundance and degree of unsaturation was verified by ftir spectra's values [50]. phenolic, alcoholic or amines compounds are indicated by a peak at 3345 cm¹, which correspond to the o-h or n-h stretching vibrations found in aromatic compounds [51]. an ftir peak at 2922 reflects the asymmetric stretching of c-h vibrations. other notable peaks include those associated with carbonyl c=o groups at 1708 cm¹ and c=o or c=c stretching at 1605 cm¹ [52], as well as c=c-c aromatic stretching at 1456 cm¹ [53]. these findings signify the presence of various functional groups, including alcohols, amines, ketones, acids, and unsaturated compounds. furthermore, peaks ranging from 1260 to 1380 cm¹ confirm that all plant extracts contain aromatic rings [54, 55]. a significant peak at 1200 cm¹ indicates c-n stretching vibrations, suggesting the presence of secondary or tertiary amines in the leea [56]. moreover, a peak at 1020 cm¹ corresponds to o-h or c-h bending vibrations in aromatic compounds [57]. these findings are consistent with prior studies [58]. therefore, the results of the ftir analyses support the potential application of the leea as an effective anticorrosive admixture in concrete formulations to mitigate the corrosion of reinforcement. the ftir analysis confirms the presence of diverse functional groups in the examined leea, enhancing our understanding of its chemical composition. these groups are responsible for inhibiting the corrosion of reinforcement metals in concrete infrastructures. using mass bank matching, the lc-ms analysis of the leea reported eight pcs mainly, including phenols, terpenoids, alkaloids, and flavonoid functional groups. these anticipated pcs, which assumed to be present in the extract are listed in table 2 and shown in fig. 3, are verified from phytochemical testing, uv-vis, ftir, and lc-ms analyses. table 2: major compounds present in leea analyzed from lc-ms analysis s.n. retention time (min) molecular formula & weight (g/mol) name of compounds types of compounds 1 1.853 c18h17no3 (295.1) dp-oxazole acid alkaloids 2 4.238 c12h18clno2s (275.1) dimethenamid alkaloid 3 4.864 c21h22o10 (432.4) apigenin-7-o-glucoside flavonoids 4 5.219 c21h20o11 (448.1) kaempferol-3-o-glucoside flavonoid 5 5.659 c30h52o (428.7) epifriedelanol terpenoids 6 6.149 c20h21no4 (339.1) canadine or papaverine alkaloid 7 8.000 c15h12o3 (240.1) 4’-hydroxyflavone flavonoid 8 9.498 c15h11o6 + (287.2) cyanidin flavonoid madhab gautam et al./ bibechana 22 (2025) 223-236 228 figure 3: structural formula of pcs assumed to be present in leea identified with lc-ms technique. these studies demonstrated that leea has a potent anti-corrosive impact on concrete reinforcement corrosion. it allows the chemicals in leea to attach to the cs specimens dipped in scps, either physically through weak interactions like van der waal interactions and/or chemically through ionic or co-covalent bonding [59]. the corrosion rate (cor) of immersed cs in both control scps and scps with leea concentrations was estimated using the weight loss method, and the results are plotted in fig. 4(a). the cor of the cs in scps with 1000 ppm leea is lower than that in the control scps with 500 and 2000-4000 ppm leea, indicating that leea effectively inhibits the corrosion of cs in scps with 1000 ppm leea. as shown in fig. 4(a), the cor of sample specimens immersed in scps containing 500, 2000, and 4000 ppm of leea ranged from 0.0013 to 0.0069 mm/y. in contrast, the cor in scps with 400 ppm leea was approximately 0.0017 mm/y. the 1000 ppm leea addition to the scps displayed the highest corrosion resistance. consequently, the corrosion-inhibiting efficiency was about 95% in the scps with 1000 ppm leea, as illustrated in fig. 4(b). it demonstrates the enhanced corrosion inhibition effect of 1000 ppm leea in scps. figure 4: variations of cor (a) and coie (b) of cs immersed in scps without (control) and with 500-4000 ppm leea. these findings indicate the formation of a stable and anti-corrosive passive film at the 1000 ppm leea concentration, in contrast to the other concentrations of 500, 2000, and 4000 ppm leea. also, it might be a result of the formation of a persistent adsorption layer. over time, more phytocompounds (pcs)-based inhibitor molecules may have been adsorbed onto the cs surface, which could cause the extract to desorb somewhat from the cs surface [60]. the dissolution of pcs adsorbed from leea inhibitors in the scps by the generation of a chelate between the iron atoms of cs pieces and the heteroatoms of phytoconstituents present in leea inhibitor may be the cause of the decrease negligibly in inhibition for 2802 hours immersion [61]. the corrosion inhibition of cs specimens enriched with increasing amounts of leea. the instability of the cs specimen in the control scps, which does not contain leea, may be attributed to the break of early-formed layers of cs across the metal-layer interface. this detachment can increase the corrosion rate over extended immersion times [62]. the lower cor of cs in scps containing leea concentrations ranging from 1000 to 4000 ppm is due to beneficial phytochemicals such as polyphenols, alkaloids, and flavonoids in leea. these compounds facilitate the formation of a thin passive coating film on the surface of 500cs through the adsorption of complex polyphenols or heteroaromatic chemicals [63]. according to qualitative examinations, the leea retains a variety of flavonoids, alkaloids, phenols, and terpenoids. the pcs function as key parts of the phyto-molecular interactions with the corroded surfaces of cs specimens in the scps, elucidated by the adsorption isotherm model, such as the langmuir isotherm. the molecular interaction between the corroded cs and pcs of leea is due to heteroatoms and highly conjugated aromatic electrons in the pcs [64]. overall, the use of leea as a promising inhibitor for cs in scps at different immersion times, as demonstrated by the stabilization of the highly concentrated extract to the scps. langmuir adsorption isotherm, illustrated in fig. 5 is utilized to investigate the adsorption of leea’s pcs onto the cs piece in scps across various immersion periods. it assessed the corrosion inhibition mechanism of leea on rusty cs specimens in scps with changing leea concentrations. it is meaningful to mention herein that for the linear langmuir isotherm plot, the estimated cor was based on the gravimetric weight loss (grwtl) method. figure 5 shows a linear relationship with a very high coefficient of determination (r²) that tends to unity. however, the slope is not equal to one (i.e., 1.284-1.431), indicating a fit not only to the langmuir monolayer adsorption isotherm. in corrosion inhibition studies, the standard adsorpmadhab gautam et al./ bibechana 22 (2025) 223-236 229 tion gibbs energy is frequently estimated through linear regression of the langmuir isotherm, as outlined in equation (6). figure 5: langmuir isotherm plots for cs specimens in scps with different concentrations of leea at different immersion times. in this adsorption isotherm model, the slopes of the corresponding straight lines must adhere to the requirements of the langmuir isotherm, which stipulates a slope of unity. this theoretical framework enables relatively precise estimations of the standard adsorption gibbs energy based on experimentally determined surface coverage. however, a deviation in the slope from unity to values ranging from 1.284 to 1.431, as illustrated in fig. 5, suggests non-langmuir adsorption phenomena, which may indicate the presence of multi-site adsorption or surface heterogeneity [65]. additionally, the thermodynamic analysis, based on g°ads values, suggests that the adsorption in this condition is spontaneous and involves electrostatic interactions, characteristic of physisorption [66]. the negative values of g°ads further support the favorable spontaneous nature of the adsorption process of pcs on the immersed cs surface. we have tested other adsorption isotherm models like temkin, el-awady, and freudlich adsorption models [67]. they did not fit with r² values comparatively much lower than that of the langmuir isotherm plots. consequently, the langmuir adsorption isotherm demonstrates the best fit compared with the temkin isotherm. these outcomes align with conclusions from earlier research notifying identical adsorption behaviors of pcs on corroded steel specimens in acidic environments [66]. based on the experimental results from weight loss tests, as discussed above, the corrosion inhibition efficiency and mechanism of leea adsorption onto corroded carbon steel (cs) have already been investigated. besides, the corrosion inhibition kinetics of leea on the cs surface in scps, both with and without leea, can be examined using potentiodynamic polarization (pop) analysis. the corrosion potential (ecor) values shifted to more negative (cathodic) directions without significant changes in anodic current density as a function of leea concentrations, as depicted in fig. 6. in addition, the cathodic current density (icath) and corrosion current density (icor) decreased with leea concentrations in scps, indicating the suppression of cathodic reactions on cs in the given conditions, even though there is no consistent shifting of ecor. these electrochemical properties are rendered by a protective passive film formation on the surface of the corroded cs in the scps with 500-4000 ppm leea. figure 6: plots obtained pop for cs immersed in scps with (a) 500 ppm, (b) 1000 ppm, (c) 2000 ppm, and (d) 4000 ppm leea including control scps. the corrosion rate and inhibition efficiency were determined using the corrosion potential (ecor), corrosion current (icor), and tafel slopes of the anode (anod) and cathode (cath) from potentiodynamic polarization (pop) curves through the tafel extrapolation method, as shown in fig. 6 and also summarizes in table 3. increases in aond and cath, driven by leea in scps, indicate improved polarization resistance (rp) predominantly by cathodic reduction reactions. a higher cath suggests hindered reduction processes, while an increased anod points to slower cs dissolution and potential passivation [68]. madhab gautam et al./ bibechana 22 (2025) 223-236 230 table 3: corrosion current (icor) and inhibition efficiency (icor-based/grwtl-based corie) calculations for cs immersed in scps without and with 500–4000 ppm leea, obtained from grwl and pop approaches leea (ppm) ecor (mv) icor (a/cm2) βanod (mv/dec) βcath (mv/dec) rpol (kω·cm2) icor-based corie (%) grwtl-based corie (%) blank -428.4 7.301 2.54 6.33 0.04 – – 500 -596.1 3.808 9.58 14.67 2.06 47.8 59.9 1000 -545.2 2.576 7.86 17.83 3.22 64.7 94.1 2000 -512.1 1.946 11.09 18.89 7.43 73.4 81.1 4000 -507.4 1.569 12.29 17.39 9.31 78.5 77.3 ultimately, this trend reflects the formation of a passive layer, enhanced rp, and decreased corrosion rates [69]. in literature, the coies of 4000 ppm leaf extracts of tagetes erecta [37] ziziphus budhensis [33], and sisamum indica [46] were 73.78%, 81.48%, and 81.7% (icor-based), and 67.81%, 91.22%, and 93.9% (grwl-based), respectively. in contrast, a 4000 ppm leea exhibited inhibition efficiencies of 81.7% (icor-based) and 93.9% (grwl-based), indicating the leea has shown almost the same corrosion-inhibiting efficiency for reinforced concrete as other plant extracts reported in the literature. we investigated the morphological changes of cs sample surfaces after a 2802-hour immersion in scps with 4000 ppm of leea, compared to scps under control conditions. the cs specimen immersed in control scps exhibited a severely corroded surface with several corrosion-related flaws, as shown in fig. 7(a). the significant corrosion observed was due to the prolonged exposure to the control scps, which facilitated the interaction of hostile ions with the cs surface through existing surface flaws [70]. in contrast, the sem micrographs of the pieces immersed for the same duration in scps containing 4000 ppm of leea, shown in fig. 7(b), displayed leea's remarkable anticorrosive effectiveness. the samples have smooth surfaces with minimal corrosion-related flaws and few corrosion products. the protective adsorption layers, created by leea, act as a barrier against hostile ions, reducing their ability to penetrate the surface [71]. figure 7: sem micrograph for the adsorption layer formed over cs pieces after immersion for 2802 hours in (a) control scps and (b) scps with 4000 ppm leea. the eds examination demonstrated a notable decrease in fe from 98.37% to 61.69% in the cs sample at control-scps after 2802 hours, alongside an increase in o-content to 33.13%, indicating significant corrosion product formation. conversely, samples with 4000 ppm leea for 2802 hours at scps displayed reduced corrosion, with 72.63% fe and 22.38% o, as shown in table 4. these results align with verma and khan [72], demonstrating minimal rust formation and corrosion-resistant properties on the cs surface. thus, leea effectively inhibits iron dissolution in scps, acting as a corrosion-preventive agent. table 4: edx elemental analysis of immersed cs pieces in control scps and scps with 4000 ppm leea after 2802 hours immersion specimens fe (wt.%) o (wt.%) ca (wt.%) si (wt.%) misc. (wt.%) fresh cs specimen 98.37 – 0.17 0.40 1.08 cs immersed for 2802 hrs in control scps 61.69 33.13 3.34 1.84 – cs immersed for 2802 hrs in scps with 4000 ppm leea 72.63 22.38 3.12 1.87 – the white light interferometry (wli) technique, known for its high sensitivity in corrosion studies, was employed to assess surface roughness and morphology. this method provides rapid and accurate three-dimensional (3d) and 2d topographic analysis of corroded metal surfaces, offering precise lateral and vertical resolution without physical contact [73]. figures 8(a) and 8(b) display the 2d and 3d profiles of the cs specimens after 2802 hours of immersion in 2000 ppm leea at scps. the surface roughness (sr) measured 7.059 m, lower than the 8.510 m recorded for specimens immersed in scps without the plant extract [33]. it represents a 17.05% reduction in surface roughness when leea is present, indicating its effectiveness in minimizing corrosion [74]. these results are consistent with sem analysis, further confirming the superior performance of leea as a corrosion inhibitor for immersed cs samples. madhab gautam et al./ bibechana 22 (2025) 223-236 231 figure 8: 2d and 3d wli images of the cs specimen after immersion for 2802 hrs in scps with 2000 ppm leea. the results show llea has strong corrosioninhibiting properties in scps environments typical of reinforced concrete, supported by sem/eds and wli assessments. a graphical representation (fig. 9) to elucidate the corrosion-inhibiting mechanism attributed to the adsorption of plant-derived pcs from llea on cs in scps, both in the absence of the inhibitor (control) and with concentrations of llea ranging from 500 to 4000 ppm under ambient conditions. this illustration aims to clarify the distinguished inhibiting effect of llea within scps or concrete environments, as demonstrated in fig. 9, by following the steps below. figure 9: a diagrammatic representation shows the adsorption mechanism of 4'-hydroxyflavone onto 500cs in scps with 2000 ppm leea at ambient conditions. i. the electrostatic interaction occurs between protonated pcs of leea and the positively charged fe2+ ions from cs, facilitating physical adsorption [75]. ii. coordination bonding between lone pairs (non-bonding electrons) on hetero-atoms like o or n in pcs and the unoccupied d-orbitals of fe-atoms in the immersed cs specimens may result in chemical adsorption [41]. iii. the aromatic ring and the empty d-orbitals of the fe-atoms in the rcs interact with -electrons to facilitate chemical adsorption [44]. iv. the d-electrons of fe-atoms of corroded cs specimens and the vacant anti-bonding molecular orbitals of the pcs components of leea undergo chemical adsorption, resulting in donor-acceptor interactions or retro-donation [36]. the analysis of multiple adsorption sites indicates that the phytochemicals (pcs) obtained from the leea are suitable for forming a passive adsorption layer on the surface of cs specimens, serving effectively as corrosion inhibitors. this study explores the plant-based inhibitors for the first time in concrete admixtures to prevent the corrosion of cs in scps, highlighting their environmentally friendly properties. 4 conclusions this study demonstrates that first-time use of leea effectively prevents the corrosion of cs specimens in simulated concrete pore solution (scps). results from gravimetric weight loss (grwl), potentiodynamic polarization (pop), and surface analysis like sem/eds and wli confirm the formation of a protective surface layer that slows down the corrosion rate of 500cs in scps containing 5004000 ppm leea as a concrete admixture. the optimal inhibition efficiencies achieved were 93.9% (measured by grwl) and 78.5% (measured by pop) at 4000 ppm leea in scps at room temperature. the pop measurements indicate that the cathodic reaction primarily governs the effectiveness of leea as a significant corrosion inhibitor. the langmuir adsorption isotherm suggests that the leea-based pcs create a homogeneous, singlelayer protective coating on the surface of the corroded cs through physical adsorption. this study established that the initial application of leea significantly mitigates the cs specimens when exposed to scps. the findings obtained from gwl, pop, and surface analysis techniquessem/eds and wli confirm the formation of a protective surface layer. this layer effectively reduces the corrosion rate of 500-grade carbon steel (500cs) within leea concentrations ranging from 500 nd 4000 ppm at scps, as a concrete admixture. the maximum inhibition efficiencies recorded were 93.9% (as determined by gwl) and 78.5% (as determined by pop) at a concentration of 4000 ppm leea in scps at ambient temperature. additionally, the pop measurements suggest that the cathodic reaction predominantly influences the efficacy of leea as a corrosion inhibitor for concrete environments. furthermore, the langmuir adsorption isotherm indicates that leea-based protective coatings form a uniform, single-layer protective film on the madhab gautam et al./ bibechana 22 (2025) 223-236 232 surface of corroded carbon steel through physical adsorption. compared to the 500cs sample immersed in controlled scps without leea, surface analysis using sem/eds and wli revealed that the surface of the cs remained smooth after immersion for about four months or more in leea at scps. the extract (500-4000 ppm leea) is derived from the leaves of elaeocarpus angustifolius, which are typically discarded and thus readily available at minimal or no cost. it not only ensures cost-effectiveness but also promotes environmental sustainability. the non-toxic and eco-friendly nature of the extract enhances its suitability for largescale applications in real-world infrastructure without posing any risks. acknowledgments the authors acknowledge mr. madhusudan dhakal (imr-cas in shenyang, china) for arranging wli and dr. m.a. fickenscher (university of cincinnati, usa) for providing sem/eds facilities. the authors also thank mr. r.d. pandey for his assistance in identifying plant species and preparing leea. mg acknowledges the university grant commission (ugc-nepal) for awarding his ph.d. research grants (award no.: phd-78/79-s&t-03). author contributions mg, npb & jb planned the experimentations; specimen preparation, practical works, and data examination by mg, dbs, yrp, and ktkm; analyzed the data and results overview by mg, npb, and jb; documented the manuscript draft by mg and npb, and did the conclusive edits by mg and jb. all authors read and consented to the final manuscript. conflict of interest the authors assert that they hold no conflicts of interest data availability statement upon appeal, the corresponding author(s) will supply data to reinforce their conclusions. references [1] s.s. ubayi, a. ahmad, e. ahmad, b.s. abubakar, s. dulawat, m. nuhu, u.s. ibrahim, and a. ibrahim. a review on the impact of jute fiber reinforcement on mechanical properties of 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[75] b.r. fazal, t. becker, b. kinsella, and k. lepkova. a review of plant extracts as green corrosion inhibitors for co2 corrosion of carbon steel. npj materials degradation, 6(5):1–14, 2022. introduction materials and method results and discussion conclusions bibechana vol. 22, no. 3, december 2025, 205-214 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar hydrogen bonding, spectroscopic (ft-ir and ft-raman), uv-vis, and mulliken charge analysis of guanosine-5 -diphosphate: insight from dft and molecular docking manoj kumar chaudhary1, tarun chaudhary2, bhawani datt joshi3 gulab singh verma4, rajesh kumar shukla4, tirth raj paneru5,6,∗ 1department of physics, tribhuvan university, amrit campus, institute of science and technology, kathmandu 44600,nepal 2department of physics, bageshwari multiple campus, mid-west university, kohalpur, 21900, nepal 3department of physics, tribhuvan university, siddhanath science campus, mahendranagar, 10400, nepal 4department of physics, university of lucknow, lucknow-226007, india 5central department of general science, far western university, mahendranagar, 10400, nepal 6central department of physics, tribhuvan university, kathmandu, nepal ∗corresponding author. email: tirthpaneru2015@gmail.com abstract hybrid functional b3lyp has been used for quantum chemical calculation of guanosine-5 -diphosphate (gdp) from dft approach. the intra-molecular hydrogen bonding in the title molecule was rendered from quantum theory of atoms in molecule (qtaim). the vibrations of different functional groups of the gdp have been examined theoretically from ft-ir and ft-raman calculation. the electrostatic potential (esp) surface revealed that the maximum positive potential is attributed to h4, and the highest negative potential corresponds to o31, predicting the sites for the intermolecular hydrogen bonding in the crystal packing of the title compound. the theoretical uv-vis spectrum is used to calculate the excitation energy as well as excitation state of dgp. the binding affinity of gdp with ras-related c3 botulinum toxin substrate 1 (rac1) protein is calculated from molecular docking approach. the inhibition constant of 2p2l is less than that of 2h7v; hence, the title compound is a good inhibitor of 2p2l. keywords guanosine-5 -diphosphate (gdp); aim; ft-ir; ft-raman; molecular docking. article information manuscript received: january 25, 2025; revised june 1, 2025; accepted: july 26, 2025 doi https://doi.org/10.3126/bibechana.v22i3.74596 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 205 http://nepjol.info/index.php/bibechana tirthpaneru2015@gmail.com https://doi.org/10.3126/bibechana.v22i3.74596 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ manoj kumar chaudhary et al./ bibechana 22 (2025) 205-214 206 1 introduction guanosine is a purine nucleoside with neuroprotective properties, particularly in ischemic stroke, spinal cord injury, and depression. it also reduces neuro-inflammation and oxidative stress [1]. the nucleotides guanosine 5-monophosphate (gmp), guanosine 5-diphosphate (gdp), and guanosine 5-triphosphate (gtp) are the basis of guanine-based purines (gbps). ecto-nucleotidases can convert these nucleotides into guanosine [2]. gdp is nucleotides made up of guanine, ribose and two phosphate groups [3]. it has wide applications in biological activity like: cellular signaling and metabolism. gdp is formed due to hydrolysis of guanosine triphosphate (gtp) and there is the evolution of energy which is used in cellular processes. moreover, gdp take part in the conversion of succinyl-coa to succinate and there is the production of energy [4]. when gdp is changed into gtp due to activation of g-proteins then signals are transmitted into the cell. gdp has crucial role to maintain the cell structure as well as it is involved in intracellular transport properties by the formation and deformation of microtubules [5, 6]. the functional groups present in gdp are amine group (-nh2), amide group (-c=o-n), hydroxyl group (-oh) and phosphate group (po4 2-). these functional groups have crucial role to take part in hydrogen bonding in crystal structure as well as in ligand-protein interaction. this study aims to provide insight into reactive parts of gdp by highlighting the sites of intraand intermolecular hydrogen bonding. the atomic charge on each atom of the title molecule revealed from mulliken charge analysis. the vibrational spectroscopic techniques (ft-ir and ft-raman), along with uv-vis spectroscopy, conducted through quantum chemical calculations, elucidated the vibrations and electronic transitions of significant functional groups in the compound, confirming their role in biological activity. moreover, the binding affinity of the title compound with the targeted protein was evaluated through molecular docking to assess its biological performance. 2 materials and methods quantum chemical calculation has been conducted from gaussian 16 software [7]. the exchange correlation functional b3lyp was used in this calculation [8–10]. the diffused as well as polarization functional basis set 6-311++g(d,p) is taken into consideration to obtain the more accurate result [11]. the density functional theory (dft) [12]is the wonder full technique which gives the result closer to experimental value and this is implemented in gaussian 16 software. the gaussview 06 software [13] is used to visualize the data which is obtained after calculation. the intra-molecular hydrogen bonding in the investigated molecule has been calculated from quantum theory of atoms in molecule (qtaim) by using aimall software package [14, 15]. the rdg isosurface, scatterplot, and molecular electrostatic potential mapped into the molecular surface produced by the multiwfn 8.0 and vmd 1.9.1 software packages [16, 17]. the ligand-protein interaction of gdp with predicted target rac1 is explored from autodock and discovery studio visualizer 4.5 [18, 19]. the gauss sum software has been implemented to explore the excitation state and excitation energy from uv-vis spectroscopy [20]. 3 results and discussion 3.1 atoms in molecules (aim) he intra-molecular hydrogen bonding of gdp has been explored by using qtaim analysis [15]. the judgement of intra-molecular hydrogen bonding in gdp is based on the electron density (ρbcp), laplacian of electron density (∇2ρbcp), and total electron density (hbcp) at bond critical point (bcp). if the respective value of (ρbcp) and (∇2ρbcp) lies in the range (0.0020.034) a.u and (0.0240.139) a.u, then there is the existence of hydrogen bonding [21]. the nature and strength of hydrogen bonding is identified in terms of (∇2ρbcp) and hbcp. if their values are greater than zero, then there should be weak hydrogen bond (electrostatic). if (∇2ρbcp) > 0 and hbcp < 0; then there should be partially covalent bond. if ((∇2ρbcp)) < 0 and hbcp < 0; there should be strong covalent hydrogen bond [22]. the optimized structure of the gdp with atom numbering scheme is depicted in figure 1. the molecular graph of gdp highlighting intra-molecular hydrogen bonds is presented in figure 2. the table 1 represents the bond length (å), bond angle (°) and sum of van der waal radii of interacting atoms (rh + ra). the value of (ρbcp), ∇2(ρbcp), electron kinetic energy density (gbcp), electron potential energy density (vbcp), total electron energy density (hbcp), and interaction energy (eint) at bcp for gdp is presented in table 2. the distance between interacting atoms is less than the value of rh + ra but (∇2ρbcp) > 0 and hbcp < 0 so all the four intra-molecular hydrogen bonds are partially covalent in nature. moreover, the interaction energy (eint) at bcp for o10h11...o2 is highest (8.311) kcal/mol, and the bond length h11. . . o2 is least (1.813 å) so, h11. . . o2 is the strongest intra-molecular hydrogen bond out of four. manoj kumar chaudhary et al./ bibechana 22 (2025) 205-214 207 figure 1: 3d structure of gdp obtained from b3lyp/6-311++g(d,p) level of theory figure 2: molecular graph of gdp for intramolecular hydrogen bond. table 1: geometrical parameters for intramolecular hydrogen bonds in gdp: bond length (å), bond angle (°), and sum of van der waals radii of interacting atoms (rh + ra) in å. d–h· · ·a d–h (å) h· · ·a (å) d–h· · ·a (°) rh + ra (å) c19–h39· · ·o35 1.078 2.316 134.291 2.72 c15–h41· · ·o7 1.090 2.405 135.688 2.72 o33–h34· · ·o7 0.970 2.016 161.390 2.72 o10–h11· · ·o2 0.987 1.813 148.943 2.72 table 2: topological parameters for intramolecular interaction of gdp: electron density at the bond critical point ( ρbcp), laplacian of (∇2ρbcp), electron kinetic energy density (gbcp), electron potential energy density (vbcp), total electron energy density (hbcp), and interaction energy (eint) at the bcp. interaction bond length (å) ρbcp (a.u.) ∇2ρbcp (a.u.) gbcp (a.u.) vbcp (a.u.) hbcp (a.u.) eint (kcal/mol) h39· · ·o35 2.315 0.0114 0.0427 -0.0019 -0.0069 -0.0088 -2.155 h41· · ·o7 2.405 0.0103 0.0353 -0.0014 -0.0062 -0.0076 -1.937 h34· · ·o7 2.014 0.0170 0.0710 -0.0029 -0.0119 -0.0148 -3.748 h11· · ·o2 1.813 0.0310 0.1093 -0.0005 -0.0265 -0.0270 -8.311 3.2 non-covalent interaction analysis the non-covalent interaction analysis employed a reduced density gradient (rdg) scatterplot to visualize various interactions in the chemical system using electron density and its derivative. the graph between the sign(λ2)ρ and a dimensionless parameter rdg insight into the intensity of the interaction. the value of rdg can be evaluated by the following equation: [23,24] rdg(r) = 1 2(3π2) 1 3 |∇ρ(r)| ρ(r) 4 3 different colour codes are used for different types of non-covalent interactions. weak van der waals force of attraction is represented by green with the value of sign(λ2)ρ ≈0. steric repulsion between interacting species is represented by red with the value of sign(λ2)ρ > 0 and strong hydrogen bonding interaction is represented by blue, with the value of sign(λ2)ρ < 0 [25]. the 2d-nci rdg graph and its 3d isosurface for the visualisation of non-covalent interaction are shown in figs, 3 (a) and (b). the rdg isosurface illustrates that the green colour flaky patches appeared between oxygen and hydrogen and nitrogen and hydrogen, which represent the van der waals interactions between them that are seen in the rdg scatter graph in the region of 0.01 to 0.005 a.u. the red spikes seen in the rdg scatter graph cover a wide range from 0.01 to 0.05 a.u., highlighting the repulsion between the carbon atoms of rings r1, r2, and r3, which is dominant over hydrogen bonding and van der waals force of attraction. the strong intramolecular hydrogen bond between h11 and o2 is seen in the isosurface by the blue colour, which is observed in the rdg scatter graph with blue spikes in the range of 0.03 to 0.05 a.u. nci analysis reveals that the intra-molecular hydrogen bonds h39...o35, h41...o7, and h34...o7 exhibit weak van der waals forces of attraction, while the intra-molecular hydrogen bond o10-h11...o2 is a strong hydrogen bond, which was also justified by qtaim analysis. manoj kumar chaudhary et al./ bibechana 22 (2025) 205-214 208 (a) (b) figure 3: (a) rdg scatter plot of gdp and (b) 3d isosurface showing non-covalent interactions in gdp. 3.3 spectroscopic studies he number of mode of vibration of the molecular system is explained by the relation 3n-6, where n is the number of atoms in the molecule. the gdp molecule has 43 atoms so there are 123 modes of vibration. the ft-ir and the ft-raman of the investigated molecule has been examined from same level of theory. the calculated spectrum of ftir is presented in figure 4 and the calculated ftraman is presented in figure 5. the dft calculation is used to obtain the raman intensities but it depends on the raman scattering amplitudes and the raman scattering cross-section∂σj ∂ω . the raman scattering amplitude gives raman intensity for each normal mode of vibration and is given by the relation [26,27]. ∂σj ∂ω = ( 24π4 45 ) (ν0 − νj) 4 1− exp [ −hcνj kt ] ( h 8π2cνj ) sj where sj= scattering activities, νj = predicted wave numbers for jth normal mode, ν0= wavenumber of raman excited state and h, c and k are universal constants. the calculated wavenumber is more than the experimental one due to anharmonicity. so, to reduce the calculated wave number the linear wavenumber linear scaling (wls) factor is used [28, 29]. the functional groups are the active parts of gdp and can play a vital role in biological action through different intermolecular interactions. these active parts also participate in intra-molecular hydrogen bonding. the signature of functional groups are seen in higher wavenumber in pure form but the signature at lower wave number is determined the fingerprint regions of gdp and they are in mixed mode. in this study, we only discussed the modes of vibrations related to the signature of functional groups that are seen in higher wavenumbers and are important in biological action. the vibration modes of active parts belong to a functional group and are assigned to higher wavenumber regions along with unscaled and scaled wavenumbers, which are presented in table 3. the vibrational modes associated with the active groups of gdp are discussed in detail in the following sections. 3.3.1 c=o and p=o vibrations the experimental value of n–h stretching vibrations is found in the order of (3500-3300) cm-1 [30]. in the gdp compound, asymmetric n26h2 stretching is calculated at 3493 cm1, but its symmetric stretching is calculated at 3396 cm1. the stretching of n23h vibration is computed at 3412 cm¹ with a significant peak in the ft-ir spectra. the in-plane bending of the amine group n26h2 is calculated at 1630 cm-1and 1585 cm-1with significant ir absorbance. in the title compound, the signatures of cn vibration in rings r1 and r2 are examined at 1556, 1528, and 1487 cm-1with sharp peaks. experimental oh stretching is generally found in the range (35003200) cm–1 [31]. in the title compound, the oh stretching is calculated from dft at 3633, 3621, 3619, 3517, and 3236 cm¹, corresponding to o35h, o8h, o3h, o33h, and o10h, respectively. the amine group and hydroxyl group has significant peaks in ir and raman spectroscopy and these functional groups interact with residue of amino acid which is justified in the molecular docking section. manoj kumar chaudhary et al./ bibechana 22 (2025) 205-214 209 table 3: the scaled and unscaled wavenumber along with the mode of vibration of different functional groups in gdp. unscaled wavenumber (cm−1) scaled wavenumber (cm−1) types of vibration 3841 3631 ν(oh) stretching vibration of o35h 3827 3621 ν(oh) stretching vibration of o8h 3824 3619 ν(oh) stretching vibration of o3h 3709 3517 ν(oh) stretching vibration of o33h 3681 3493 νa(nh2) asymmetric stretching of n26h2 3591 3412 ν(nh) stretching vibration of n23h 3574 3397 νs(nh2) symmetric stretching of n26h2 3394 3236 ν(oh) stretching vibration of o10h 3263 3118 r2[ν(ch)] stretching vibration of c19h 3165 3029 νa(ch2) asymmetric stretching of c13h2 3110 2979 r3[ν(ch)] stretching vibration of c17h 3104 2974 r3[ν(ch)] stretching vibration of c15h 3098 2969 νs(ch2) symmetric stretching of c13h2 3059 2933 r3[ν(ch)] stretching vibration of c16h 2994 2874 r3[ν(ch)] stretching vibration of c14h 1787 1750 r3[ν(c=o)] stretching vibration of c22=o 1661 1630 δin(nh2) in-plane bending of n26h2 1614 1585 δin(nh2) in-plane bending of n26h2 1583 1556 ν(cn) vibration of cn in ring (r1 and r2) 1554 1528 ν(cn) vibration of cn in ring (r1 and r2) 1511 1487 ν(cn) vibration of cn in ring (r1 and r2) 1505 1481 δin(ch2) in-plane bending of c13h2 1452 1431 r3[δin(ch)] in-plane bending of c17h 1439 1418 r2[δring] ring deformation of r2 1437 1416 γ(ch2) twisting of c15h2 1415 1395 r3[δin(ch)] in-plane bending of ch 1407 1387 δin(oh) in-plane bending of o33h 1384 1365 ω(ch2) wagging of c13h2 1291 1275 ν(p=o) stretching vibration of p6o7 1247 1233 ν(p=o) stretching vibration of p1o2 1166 1154 δin(oh) in-plane bending of o10h 953 946 δin(oh) in-plane bending of o8h and p6o10 stretching 871 866 δin(p6-o10-o8) in-plane bending 865 860 r2[δin(ch)] in-plane bending of c19h 863 859 r2[δin(ch)] in-plane bending of c19h 3.3.2 ch vibration the experimental c-h stretching vibration is obtained in the range (3000-3100) cm–1 [31]. in the title compound, the stretching of c19h, c17h, c15h, c16h, and c14h in the rings r2 and r3 are calculated at 3118, 2979, 2974, 2933, and 2874 cm1 , respectively being very sharp peak for c14h with higher ir absorbance. the in-plane bending of ch vibration is computed at 1431 and 1395 cm–1 in the ring r2. for ring r3, the in-plane bending of ch found to be at 860 and 859 cm–1. the asymmetric stretching vibration of c13h2 is calculated at 3029 cm–1 but symmetric stretching of c13h2 is calculated at 2969 cm–1. 3.4 electrostatic potential surface (esp) analysis the visual representation of the charge distribution on the molecular surface can be performed by the electrostatic potential surface analysis. this tool aids in the prediction of sites for the intraand intermolecular interactions by identifying the locations of electrophiles and nucleophiles [32]. the region of positive potential shown by the blue colour region corresponds to the position of the electrophile, which should be favourable for nucleophilic attack, and the negative potential region represented by the red colour is the site of electrophilic attack [33]. the molecular surface of the title compound mapped with the electrostatic potential on its van der waals surface is shown in figure 6. the blue and orange dots of the molecular electrostatic surface represent the points of minimum and maximum potential. the global minimum potential of -95.53 kcal/mol attributed to the o31 atom in the c=o group of ring r1 of gdp is the nucleophile. the maximum positive potential 113.71 kcal/mol corresponds to the h4 atom attached to the oh group in phosphate, making it the best site for nucleophilic attack. from this result, we conclude that h4 and o31 are ideal sites for intermolecular hydrogen bonding, and the crystal packing of the title compound may be contributed manoj kumar chaudhary et al./ bibechana 22 (2025) 205-214 210 by the o3-h4. . . o31 hydrogen bonding. figure 4: calculated ft-ir spectra of guanosine-5 diphosphate in the range (100-3800) cm-1 calculated from b3lyp/6-311++g(d,p) level of theory. figure 5: calculated ft-raman spectra of guanosine-5 diphosphate in the range (100-3800) cm-1 calculated from b3lyp/6-311++g(d,p) level of theory. figure 6: electrostatic potential mapped into molecular vdw surface of guanosine-5 diphosphate. 3.5 mulliken charge analysis the electronic property of atom in molecular system has been identified from mulliken charge analysis. this is calculated on the basis of distribution of electrons in the atoms as well as the formation of polarity in the molecular system [34]. this analysis helps to identify the electrophilic and nucleophilic atoms in the compound that can take part in chemical reaction with surrounding species in hydrogen bonding in crystal packing and ligand-protein interaction [35]. the distribution of charge on the heavy atoms of gdp is presented in figure 7. from this analysis it is clear that the concentration of negative charge is mainly on o2, o5, o7, c17, n29, c30, and o31. out of these atoms, the highest value of negative charge is seen on c17. this is due to shearing of charge among c16, n18 and o32 atoms. similarly, the concentration of positive charge is more across p6, n18 and c19. but the highest value of positive charge is calculated across n18. these atoms have prominent role to take part in ligand-protein reaction. figure 7: mulliken charge with hydrogen summed into heavy atoms on gdp from b3lyp/6311++g(d,p). 3.6 uv-visible spectra analysis the essential and useful technique to study the biologically active compounds is uv-vis spectroscopy. the spectrum helps in the characterization of substances and gives an idea regarding their electronic structure. the spectrum is used to check biological activity of compounds when changes are made to functional groups that insure the change in (increase or decrease) drug activity of molecules when derivatives are synthesized [35]. besides these activities, it also helps with compound stability, activity quantification, and interaction monitoring which are critical for assessing and maximizing biological activity. uv-vis spectroscopy can monitor enzyme activity in real time; it helps to study the photo stability of biologically active compounds [36]. it helps to quantify the changes in absorbance upon binding, indicating interaction mechanisms, binding constants, and binding sites. moreover, it helps to examine the electronic structure, aromatic rings, and functional group present in the compound and the band gap energy of compound to check the nature of compound whether it is semiconductor or other type of materials [37, 38]. besides that it has wide applications to measure the concentration and interaction of proteins and nucleic acids as well as it is used to study the enzyme activity. the uvvis spectra of gdp is calculated in gaseous state by employing the td-b3lyp/6-311++g(d,p) themanoj kumar chaudhary et al./ bibechana 22 (2025) 205-214 211 ory. the uv-vis spectra is plotted which is presented in figure 8. the absorption peak is obtained at 271 nm which infer that there is delocalization of -electron due to guanine base which contains conjugated double bonds and aromatic ring in gdp. in guanine base structure there is also absorption of lone pair electrons η due to presence of nitrogen (n) and oxygen (o) atoms in gdp. thus, there is transition of π → π∗ and η → π∗ electrons and in such case the order absorption wavelength is (250-280) nm. the percentage contribution of molecular orbitals along with oscillator strength, energy gap and maximum absorption wavelength is presented in table 4. the homo orbital is 114 and lumo orbital is 115. the first excited state (homo→lumo (100%)) is calculated as 4.06 ev corresponding to λmax=305.17 nm having minimum oscillator strength=0.0001. this is due to the transition of π → π∗ electrons. similarly, the second excited state is calculated at 275.06 nm (homo→l+2 (94%)) with respective excitation energy and oscillator strength 4.51ev and 0.0237. this is due to transition of π → π∗ and eta → π∗ electrons. figure 8: uv-vis absorbance of gdp in gas phase calculated with td-b3lyp/6311++g(d,p) 3.7 molecular docking molecular docking is crucial technique to explore the ligand-protein interaction. the binding sites as well as binding energy, inhibition constant and ligand efficiency are the important parameters which explain the docking analysis of ligand with predicted target (protein) [39, 40]. the target protein ras-related c3 botulinum toxin substrate 1(rac1) has been predicted from free online swisstargetprediction and two protein 2p2l and 2h7v has been downloaded from protein data bank [41, 42]. the protein has been cleaned by removing the water molecule and co-crystalized ligand. the ligand gdp and proteins 2p2l and 2h7v are prepared for docking by converting them into pdb file. after that the docking has been performed from autodock vina [18]. the binding sites have been examined from discovery studio visualizer 4.5 [19]. out of the many docked conformers the best docked conformers have been presented in figure 9. the conventional hydrogen bonds, residue of amino acid, ligand efficiency, inhibition constant and binding energy of ligand-protein interaction is presented in table 5. from molecular docking analysis it is confirmed that the binding sites in gdp are o2, o3, o5, o7, o10, o31, n29, and h34. during the molecular docking analysis of gdp with cell division control protein 42 homolog (cdc42) with the pdb codes 1ano, 1a4r and 1doa; the binding sites was found to be almost same [43]. the binding energy for 2p2l (-8.0 kcal/mol) is more than the binding energy of 2h7v (-7.4 kcal/mol). moreover, the inhibition constant of former (1.35 µm) is less (3.73 µm) than the later one. the number of conventional hydrogen bond in 2p2l is 10 and the number of hydrogen bond in 2h7v is 7. besides that, the bond length of conventional hydrogen bond in 2p2l is less than that of 2h7v. so, former is better inhibited by title compound. table 4: the conventional hydrogen bonds, residue of amino acid, ligand efficiency, inhibition constant, and binding energy of gdp. ligand protein pdb code bond length (å) binding atoms amino acid binding energy (kcal/mol) inhibition constant (µm) ligand efficiency gdp rac1 2h7v 2.54 o31 lys116 –7.4 3.73 0.26 2.68 o2 lys16 2.28 o7 lys16 2.05 o7 gly15 2.33 o7 val14 2.00 o7 lys16 2.01 o3 thr17 gdp rac1 2p2l 2.16 n29 ser41 –8.0 1.35 0.29 2.75 h34 ser41 2.80 h34 ser41 2.22 o2 lys16 2.45 o2 val14 2.32 o2 lys16 1.96 o2 gly15 1.75 o3 thr17 2.38 o5 lys16 2.31 o10 ala13 manoj kumar chaudhary et al./ bibechana 22 (2025) 205-214 212 figure 9: 2-d ligand-protein interaction of gdp with 2h7v and 2p2l pdb code of protein rac1. 4 conclusion the intra-molecular hydrogen bonding of gdp has been scrutinized from qtaim analysis and rdg scatter plot and its 3d-isosurface. four intramolecular hydrogen bonds have been identified and all are partial covalent in nature. out of them the intra-molecular hydrogen bond h11...o2 is the strongest as it has the smallest bond distance 1.8134 å and the highest interaction energy (8.3114 kcal/mol). the maximum positive electrostatic potential 113.71 kcal/mol, was observed in h4, and the maximum negative potential associated with o31 of gdp, as predicted by esp analysis. this analysis confirms that these sites are favourable for intermolecular hydrogen bonding in the solid-state structure of the title compound as well as in ligandprotein interaction analysis. the gdp molecule has 43 atoms and 123 modes of vibrations. all the vibrations are ir and raman active. the fingerprint and functional group present in the molecule have been explored. there are significant peaks for carbonyl group (c=o), amine group (-nh2), and hydroxyl group (-oh) and phosphate group (po4 2-). it is confirmed that these functional groups have prominent role for intermolecular hydrogen bonding with residue of amino acid which is verified by the molecular docking as well as mulliken charge and esp analysis. uv-vis spectra analysed that there are single significant absorbance peak at 272 nm wavelength which is correspond to the second excited state (homo→l+2 (94%)) with respective excitation energy and oscillator strength 4.51ev and 0.0237. this arises due to transition of π → π∗ and η → π∗ electrons. mulliken charge analysis confirmed that the atoms o2, o5, o7, c17, n29, c30, and o31 have negative charge and the atoms p6, n18 and c19 have positive charge. these charges take part in ligand-protein interaction which is explored from molecular docking. the protein 2p2l has more binding affinity than 2h7v protein of rac1. author contribution m.k. chaudhary: conceptualization of research activity, data analysis and manuscript writing; t. chaudhary: analysis, and drafting; g.s. verma: data calculation; t.r. paneru: supervision, writing and editing; b.d. joshi: proofreading and editing and r. k. shukla: proofreading and editing. declarations conflict of interest the authors declare no competing interests. references [1] l. e. b. bettio, j. gil-mohapel, and a. l. s. rodrigues. guanosine and its role in neuropathologies. purinergic signalling, 12:411– 426, 2016. 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[43] m. k. chaudhary, b. maharjan, g. s. verma, and r. k. shukla. hydrogen bonding and reactivity behavior of guanosine-5’-diphosphate from dft and molecular docking approach. api j. sci., 1:84–91, 2024. introduction materials and methods results and discussion atoms in molecules (aim) non-covalent interaction analysis spectroscopic studies c=o and p=o vibrations c−h vibration electrostatic potential surface (esp) analysis mulliken charge analysis uv-visible spectra analysis molecular docking conclusion bibechana vol. 22, no. 1, april 2025, 15-21 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar chemical profiling, antioxidant, and antimicrobial activities of the essential oil of matricaria recutita (chamomile) ram prasad baral1, rameshwar adhikari2, achyut adhikari1,∗ 1central department of chemistry, tribhuvan university, kathmandu, nepal 2research center applied science and technology (recast), kathmandu, nepal ∗corresponding author. email: achyutraj05@gmail.com abstract matricaria recutita, commonly known as chamomile, is extensively utilized in the pharmaceutical, cosmetic, and food industries for its medicinal and essential oil properties. local people from the karnali province of nepal use this plant against skin and vaginal infection by bacteria and fungi. this research focuses on extracting essential oil through hydro-distillation, followed by gas chromatography-mass spectroscopy (gc-ms) to identify its chemical constituents and antioxidant and antimicrobial activities against bacteria and fungi responsible for common skin infections. the gc-ms analysis of the essential oil from m. recutita identified eleven chemical components. the major constituents, with respective area percentages at retention times 37.16, 11.79, and 7.88 in the gc chromatogram, were -farnesene (46.56%), bisabolol oxide-a (11.79%), and menthol (7.88%). limonene, methyl salicylate, and -bisabolol oxide-b also constituted the lowest area percentages at 1.36%, 1.59%, and 1.62%, respectively. the essential oil exhibited significant antioxidant activity with ic50 = 0.1924 µl/ml. additionally, the essential oil exhibited notable antibacterial activity against staphylococcus aureus atcc6538p and candida albicans, displaying zones of inhibition measuring 10.64 mm and 14.44 mm, respectively. the broth method also revealed that the mic is above the 250 mg/ml range and has more potential for inhibition. keywords matricaria recutita, essential oil, gc-ms analysis, antibacterial, antifungal, antioxidant, mic and mbc . article information manuscript received: june 5, 2024; revised: december 25, 2024; accepted: january 2, 2025 doi https://doi.org/10.3126/bibechana.v22i1.66431 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction nature has shown to be a promising source of therapeutic compounds, with many modern medications derived from medicinal plants found in nature [1]. herbal medicine has recently received much attention from scientists as a supplemental or replacement therapy [2]. the world health organization (who) reports that herbal medicines are the primary source of medication for 70 – 80 % of the people in developing countries [3]. among the broad assortment of plant products, essential 15 http://nepjol.info/index.php/bibechana achyutraj05@gmail.com https://doi.org/10.3126/bibechana.v22i1.66431 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ram prasad baral et al./ bibechana 22 (2025) 15-21 16 oils (eo) have gotten much attention [4]. essential oils are made up of highly volatile chemicals that are separated by a physical process. essential oil combines oily fragrant volatile chemicals such as monoterpenes, sesquiterpenes, aromatic compounds, and their derivatives employed as antimicrobials, anti-inflammatory, sedatives, expectorants, and diaphoretics, among other things [5]. german chamomile (matricaria chamomilla) is a plant find in western europe, west asia, india, and north america is a source of chamomile essential oil, which has been used for its relaxing and restorative properties for a very long time [5]. it was historically used for anxiety and digestive problems in traditional medicine in europe and the middle east [6]. because of its anti-inflammatory, antioxidant, and antibacterial qualities, a recent study emphasizes its potential in contemporary medicine and cosmetics [7]. some of its constituents, such as chamazulene and bisabolol, are responsible for its medicinal properties [8]. investigating its chemical makeup and its uses in medicine, cosmetics, and holistic well-being are the goals of this work [9–11]. it is the common name for various daisy-like plants in the asteraceae family with yellow centers (about 1 1.5 cm in diameter) and white petals (between 12 20 in number) [12]. the essential oils are extracted from the flowering tops. chamomile has been widely used to treat wounds, skin irritation, burns, chickenpox, ear and eye infections, and nasal inflammation [9, 12, 13]; [14]. according to scientific analysis, extracted essential oils of chamomile were discovered to include bisabolol oxide a and b and other flavonoids with anti-inflammatory and antiphlogistic activities [8]. these plants are most recognized for their calming properties when eaten as tea, frequently served with honey or lemon [6]. local people from the karnali province of nepal use this plant against skin and vaginal infection [15]. much chemical and biological work has been reported in this plant but chemical and biological activities of plants from karnali province of nepal have not been reported so far [?, 12, 13,16]. this research fulfills the above gap, and we have reported chemicals from the essential oil of chamomile, antibacterial and antifungal activity of microorganisms responsible for skin infection, and antioxidant activity. 2 materials and methods 2.1 materials plant material: the german chamomile (matricaria recutita) plants were collected from the surkhet district and the plant was identified in the national plant herbarium, godawari, lalitpur, and the collection number assigned to the herbarium (collection no: 79). chemicals: anhydrous na2so4 and media for antibacterial activity test were bought from the local suppliers of himedia, india, in kathmandu. the dpph and other chemicals used in gc were purchased from merck. 2.2 methods 2.2.1 extraction of essential oil from chamomile fresh flowers were collected and chopped into pieces smaller than 10 × 10 cm, then boiled in a clevenger apparatus unit with 200 l of distilled water. after 5 – 6 hours, the oil distillation stopped and a calibrated trap was used to determine the volume of essential oils [17, 18]. the distillate's essential oils were dried over anhydrous na2so4 and stored in the freezer. 2.3 gas chromatography-mass spectrometry (gc-ms) analysis the gc-ms technique was used to identify chemical compounds present in the essential oil. the gc-ms was performed on a shimadzu gcms-qp 2010 plus equipped with a rtx-5ms capillary column with a column dimension of 60 m × 0.32 mm × 0.25 um. a capillary column that has a nonpolar stationary phase (db-5 or hp-5, f) was used for gc. the eo sample was diluted with hexane and 1 l of the essential oil sample was injected in split mode (split ratio 10:1), the injector temperature was set at 250°c [10]. helium gas was used as a carrier gas at a constant 4 ml/min flow rate. at first, the temperature was set at 50°c for two minutes, then ramped up to 200°c at a pace of 10°c per minute, and then to 250°c at a rate of 5°c per minute, total run time was 70 minutes. to begin scanning, the detector's temperature was set at 280°c and mass range to m/z 40–400 [19]. the ionization mode of the mass was 70 ev electron impact (ei). 2.3.1 antibacterial activities the mueller-hinton agar was used to prepare agar plates. chamomile eo was tested against seven bacterial strains, utilizing the well-diffusion method. overnight cultures of the respective bacterial strains, obtained from the american type culture collection (atcc), were lawn cultured on mueller hinton agar (mha). before swabbing, the indicator strains were standardized to a 0.5 mcfarland solution. using a cork borer, wells of 5 mm diameter were created on the agar plates, into which 50 µl of chamomile essential oil (prepared in 50% ram prasad baral et al./ bibechana 22 (2025) 15-21 17 dmso) was introduced, alongside positive (antibiotic) and negative (dmso) controls. the mha plates were then incubated overnight at 37°c, and the subsequent zones of inhibition were measured the following day [20] 2.3.2 antioxidant activity the dpph assay was conducted following a version of a previously established protocol [5]. specifically, 100l of chamomile essential oil at concentrations of (0.01, 0.005, 0.001, 0.0005, 0.0001, and 0.00005 g/ml) was mixed with 100l of dpph solution (0.1mm) in methanol. the reaction mixture was thoroughly shaken and incubated in darkness for 30 minutes. following incubation, the absorbance of triplicate readings was measured at 517 nm using a microplate reader (epoch tm 2 microplate spectrophotometer, bio tek instruments, usa). s.activity % = (a sample−a control) a control × 100 where s. activity is scavenging activity, a control is the absorbance of the control (dpph solution without essential oil), and a sample is the absorbance of the sample (essential oil with dpph). the ic50 value, representing the concentration at which the essential oil scavenged 50% of dpph radicals, was determined using graph pad prism 8 software (graph pad prism software, california, usa). 3 results and discussion 3.1 gas chromatography-mass spectrometry (gc-ms) analysis the essential oil was discovered as a light blue liquid with a pleasant, herbaceous aroma that smelt like straw. the components in the oil were examined using instrumental conditions set on the gc-ms and identified using direct mass spectral comparison. figure 1 shows chromatograms of chamomile extract with varied retention times. figure 1: gcchromatogram of essential oil extracted from chamomile (x-axis: time, y-axis: abundance). the chromatogram abundance v/s retention time plot revealed 11 peaks, indicating the presence of 11 phytoconstituents. table 1 shows the chemicals discovered based on retention duration and area (%). the retention time was compared with the compounds present in the nist library to identify the chemicals present in the essential oil. the mass spectra of major compounds were compared with the mass spectra of compounds available in the nist library. the principal components were discovered to include -farnesene (46.56 %), -bisabolol oxide-a (11.79 %), and menthol (7.88 %), as well as other minor components. the results revealed that essential oils isolated from matricaria recutita include -farnesene, -bisabolol oxide-a, menthol, and nine others [20,21]. the following is the molecular structure of the critical components found in matricaria recutita essential oils: figure 2: structure of major compounds of eo of matricaria recutita various compounds found in essential oil extracts of matricaria recutita from gc-ms analysis exhibit diverse pharmacological activities. farnesene, for instance, functions as an anticarcinogenic, antibacterial, and anti-fungal agent while stimulating gastrointestinal tract receptors [21, 22]. -bisabolol oxide-a showcases antiinflammatory, anti-irritant, antibacterial, and nonallergenic properties [22, 23]. menthol, commonly used in ointments, cough drops, and nasal inhalers, is medicinal and acts as an anti-fungal agent [24]. bisabolol is known for its anti-inflammatory and soothing properties, along with antimicrobial and antioxidant activities [22]. chamazulene, another ram prasad baral et al./ bibechana 22 (2025) 15-21 18 compound, exhibits anti-inflammatory and antioxidant properties, useful in reducing inflammation and oxidative stress [17, 22]. (-)--bisabolol also known for its antioxidant, anti-inflammatory, and anticancer properties, may also promote relaxation and reduce anxiety [25]. luteolin, with strong antioxidant properties, is studied for neuroprotection and reducing oxidative stress in the brain [26]. lastly, farnesene, a sesquiterpene hydrocarbon, contributes to antimicrobial activity [27]. the bioactive compounds present in matricaria recutita support its medicinal values and protect against various diseases. thus, matricaria recutita plants are considered valuable medicinal plants [20,28]. 3.2 antioxidant activity chamomile essential oil exhibited promising antioxidant activity, as evidenced by its low ic50 value of 0.1924 µl/ml compared to the standard ascorbic acid, which had an ic50 of 0.0187 mg/ml. the inhibitory percentage against the concentration graph is shown in fig. 3. figure 3: antioxidant activity of chamomile (matricaria recutita) essential oil 3.2.1 antibacterial and antifungal activities the antibacterial efficacy of the isolated chamomile (matricaria recutita) essential oil was assessed against staphylococcus aureus atcc6538p, pseudomonas aeruginosa, bacillus subtilis, enterococcos faecalis, protecus vulgaris, shigella dysenteries, escherichia coli, klebsiella pneumonia, staphylococcus epidermidis, and salmonella typhi and exhibited noteworthy antibacterial activity for staphylococcus aureus with a zone of inhibition measuring 14.44 mm, as compared to the positive control 27.00 mm, no significant activity was shown against other bacteria. antifungal activity was tested for c. albicans and showed the zone of inhibition 10.64 mm, as compared to the positive control 21.11 mm (table 2). minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc): the broth dilution method is a common approach to ascertain the minimum inhibitory concentration (mic) and the minimum bactericidal concentration (mbc) of antibiotics or other antimicrobial agents against specific bacterial strains. in this method, a range of concentrations of the antimicrobial agent is tested against the bacteria to find the lowest concentration that inhibits visible growth (mic) and the lowest concentration that kills the bacteria (mbc). in this particular study, the antibacterial activity of a 100% essential oil was evaluated against candida albicans and staphylococcus aureus using the broth dilution method. despite demonstrating antibacterial properties, the exact mic of the essential oil could not be determined. the essential oil exhibited significant inhibition at a concentration of 500 mg/ml against both candida albicans and staphylococcus aureus. however, when the concentration was reduced to 250 mg/ml, no significant inhibitory effect was observed. this suggests that the mic for the essential oil is somewhere above 250 mg/ml, indicating that concentrations below this level are not effective for antibacterial activity. these findings are visually represented in figure 4, which shows the difference in bacterial growth inhibition at various concentrations of the essential oil. figure 4: a) minimum inhibitory concentration (mic) and b) minimum bactericidal concentration (mbc) for staphylococcus aureus and c) minimum bactericidal concentration (mbc) candida albicans. ram prasad baral et al./ bibechana 22 (2025) 15-21 19 chamomile essential oil's composition varies according to species, location, extraction techniques, collection time etc. in this research, we identified the major components of chamomile essential oil, which include -farnesene (46.56%), bisabolol oxide-a (11.79%), and menthol (7.88%). compared to other research papers, our findings revealed a higher percentage of -farnesene [29]. the obtained results from stanojevic et al. (2016) showed the presence of 52 components, with the highest content of -farnesene (29.8%), -farnesene (9.3%), -bisabolol and its oxide (15.7%), chamazulene (6.4%), germacrene d (6.2%), and spiroether (5.6%) [30]. additionally, the study by kazemi (2015) reported the major compounds and their percentages in chamomile essential oil as follows: -bisabolol oxide (38%), camphene (9.11%), sabinene (4.87%), limonene (6%), 1,8-cineole (7.12%), camphor (6.54%), and -pinene (6%) [20]. amiri et al. identified the major components in chamomile essential oil as -bisabolol oxide a (17.14%), chamazulene (15.12%), en-indicycloether (6.22%), -bisabolone oxide (6.15%), noctanal (6.00%), -bisabolol oxide b (5.17%), 1,8cineole (3.86%), -terpineol (3.11%), and germacrene d (3.02%) [21]. -farnesene has shown antimicrobial properties, which could lead to its use in developing new antimicrobial drugs or as an ingredient in topical antimicrobial formulations [30]. the essential oil of chamomile from the republic of srpska's northwest exhibits significant antioxidant and antibacterial properties when compared to previous studies. in a dpph assay, the oil showed strong antioxidant activity after 90 minutes of incubation, with an ic50 value of 2.07 mg/ml [30]. our studies show much better antioxidant activity ic50 = 0.1924 µl/ml. the bacteria staphylococcus aureus is responsible for skin infection and the fungi candida ablicans for skin and vagina infection, so inhibition of this bacteria and fungi by eo of chamomile validated the ethnomedicinal uses of this plant by local people. 4 conclusion the essential oil of matricaria recutita was successfully extracted using the steam distillation method. the gas chromatography-mass spectroscopic (gc-ms) technique revealed the 11 different chemical constituents including -farnesene (46.56 %), -bisabolol oxide-a (11.79 %), and menthol (7.88 %) as major compounds. the eo of m. recutita showed significant antioxidant potential, with an ic50 value of 0.1924 µl/ml. significant antimicrobial activities against c. albicans and staphylococcus aureus atcc6538p were with inhibition zones measuring 10.64 mm and 14.44 mm, respectively. it was able to efficiently inhibit candida albicans and staphylococcus aureus at 500 mg/ml. the concentration below 250 mg/ml showed no discernible inhibition, indicating a mic greater than this amount. this suggests that eo can inhibit microbial growth above the concentration of 250 mg/ml. this work scientifically validates the use of this plant by local people for skin and vaginal infections. acknowledgment the authors would like to acknowledge the department of plant resources, thapathali, kathmandu, for gc-ms analysis. conflict of interest the authors declare no conflicts of interest. references [1] d.-c. hao. genomics and evolution of medicinal plants. ranunculales medicinal plants, 2019. 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[30] l. p. stanojevic, z. r. marjanovic-balaban, v. d. kalaba, j. s. stanojevic, and d. j. cvetkovic. chemical composition, antioxidant and antimicrobial activity of chamomile flowers essential oil (matricaria chamomilla l.). journal of essential oil bearing plants, 19(8):2017–2028, 2016. introduction materials and methods materials methods extraction of essential oil from chamomile gas chromatography-mass spectrometry (gc-ms) analysis antibacterial activities antioxidant activity results and discussion gas chromatography-mass spectrometry (gc-ms) analysis antioxidant activity antibacterial and antifungal activities conclusion bibechana vol. 22, no. 1, april 2025, 30-40 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar richards equation for the assessment of landslide hazards ramesh chandra timsina department of mathematics, patan multiple campus, tribhuvan university, kathmandu, nepal ∗corresponding author. email: rameshtimsina028@gmail.com abstract in this study, we investigate numerical simulation models for water flow in variably saturated (unsaturated) soils. these models are crucial for addressing soil-related challenges and analyzing water-related risks, particularly in the context of water resource management, soil water-induced disasters, and the agricultural impacts of global environmental changes. the richards equation is one of the most widely used models for simulating water flow in porous media, especially in unsaturated soils. however, as a highly nonlinear parabolic partial differential equation (pde), it has limited analytic solutions, which often lack precision in practical scenarios. this necessitates the development of innovative and robust numerical methods for accurate simulations. we introduce a numerical procedure that linearizes the richards equation using the kirchhoff integral transformation, followed by discretization with various time-stepping schemes. this approach enables efficient and accurate modeling of water flow. to extend its application, we integrate the numerical solution with a hydrological infinite slope stability model to evaluate landslide hazards. specifically, we calculate the factor of safety index based on an axisymmetric form of the richards equation, which helps identify potential landslidenprone areas. furthermore, our model provides a framework for predicting landslides by considering the interplay between water flow and the physical, geological, and topographical characteristics of a landscape. this integrated approach offers valuable insights for geohazard assessment and the mitigation of water-induced risks. keywords richards equation; moisture content; infinite sloe model; landslide hazards; factor of safety. . article information manuscript received: may 6, 2024; revised: january 4, 2025; accepted: january 13, 2025 doi https://doi.org/10.3126/bibechana.v22i1.65508 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction landslides occur in many regions worldwide, particularly in mountainous areas. geologically, the himalayan mountain chain, stretching approximately 2,400 kilometers, is among the most tectonically active mountain ranges on earth [1]. this vast terrain is home to millions of people and diverse ecosystems, spanning countries such as nepal, bhutan, northern pakistan, northern india, and other parts of asia. the himalayan region faces significant land sliding problems due to a combination of factors: uneven topography, dynamic geological structures, fragile and fractured rock formations, 30 http://nepjol.info/index.php/bibechana rameshtimsina028@gmail.com https://doi.org/10.3126/bibechana.v22i1.65508 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ramesh chandra timsina/ bibechana 22 (2025) 30-40 31 and heavy, concentrated rainfall during the monsoon season. these elements collectively contribute to frequent and severe landslides, posing substantial risks to lives, infrastructure, and the environment in this region. the increasing frequency of severe and concentrated rainfall events, largely driven by climate change, has significantly exacerbated landslide risks worldwide, including in the himalayan region. heavy rainfall, a primary trigger for infiltration-induced landslides, is a common occurrence across this mountainous terrain. these landslides lead to extensive destruction of natural infrastructure, damage to roads, houses, and other man-made constructions, and result in substantial annual economic losses and fatalities. in unsaturated soils, infiltration-induced landslides typically occur close to the ground surface, where heavy rainfall triggers shallow landslides. these shallow landslides commonly develop within the vadose zone, the unsaturated region above the water table, often destabilizing surface layers in foothill areas. slope failure, which governs the stability and instability of soil surfaces, is closely linked to the infiltration process. fluctuations in matric potential within unsaturated soils play a crucial role in this process. as rainfall infiltrates the soil, the resulting changes in matric potential reduce mechanical stability, triggering landslides. understanding these dynamics is critical for developing strategies to mitigate landslide hazards in regions prone to heavy rainfall. infiltration-induced landslides in the himalayas cause severe damage to lives, property, infrastructure, and the environment, especially during the monsoon season. to address these challenges, it is essential to examine the factors, underlying issues, and environmental impacts associated with such landslides. the primary cause of these landslides is surface failure, which is influenced by the interconnectedness of slope instabilities. analyzing slope stability in unsaturated soils is crucial, as it provides insights into the mechanical behavior of slope materials. a detailed study of these materials enables the calculation of the factor of safety (sf ), a conventional measure for assessing the stability of sliding surfaces along failure planes. certain weather conditions, including continuous and heavy rainfall, rapid snow melt, and abrupt weather changes, are key drivers of slope instability. these phenomena are closely tied to fluctuations in pore water pressure within the soil. during infiltration and redistribution processes, such as rainfall and post rainfall periods, pore water pressure exhibits abnormal variations. increased pore saturation leads to a rise in pore water pressure, which, when repeated cyclically, reduces the soil’s effective stress and triggers slope failure. the richards equation, a nonlinear partial differential equation, effectively governs these processes and can be applied for quantitative landslide hazard assessment. by coupling the richards equation with a slope stability model, it is possible to develop a robust framework for analyzing slope failure in relation to weather data. this integrated approach provides a powerful tool for capturing the dynamics of slope stability under various environmental conditions [2]. the accuracy and reliability of this method depend heavily on the quality and availability of soil parameters, weather data, and the physical characteristics of the landscape. by incorporating these factors, a dependable procedure for landslide hazard assessment can be tailored to specific regions, enabling precise and effective mitigation strategies [3]. in this work, we propose an approach to modeling infiltration induced landslides, focusing on the critical role of infiltration processes in predicting landslide hazards. to achieve this, the kirchhoff transformed richards equation [4] is integrated with the infinite slope stability model [5], providing a robust framework for landslide prediction. this approach incorporates various hydraulic conductivity functions, which are experimentally verified and describe the movement of water through pore spaces. these functions depend on soil and fluid properties, such as intrinsic permeability, density, viscosity, degree of saturation, shear stress, and strength. the relationships between hydraulic conductivity and moisture content are captured using established empirical formulations [6], which are critical for understanding soil behavior under different conditions. to account for slope stability, a hydrological slope stability model is coupled with the nonlinear richards equation. this integration enables the development of a comprehensive formulation for assessing landslide hazards. the new formulation emphasizes infiltration-induced landslides in unsaturated soils and captures the complex interplay between soil moisture dynamics and slope stability. the validity of the proposed approach will be tested by comparing its predictions with interpolated exact data. applications and examples will also be conducted to illustrate the practical utility of the method, demonstrating its effectiveness in accurately predicting landslide hazards in diverse scenarios. 2 background this work aims to provide an integrated understanding of hydrogeology and the mathematical framework necessary for studying water flow in unsaturated soils and infiltrationinduced landslide hazards. a key focus is on deriving water flow relations for unsaturated soils from fundamental equations at the pore scale, offering a foundation for developing governing equations for modeling water flow [4]. the study of water flow in unsaturamesh chandra timsina/ bibechana 22 (2025) 30-40 32 rated porous media requires a well-defined formulation of governing equations, supported by appropriate constitutive relationships [6], and accompanied by specific boundary and initial conditions to complete the model. typically, water flow through unsaturated soil is described using the richards equation, which is based on semi-empirical foundations first developed by buckingham (1907) [7] and later refined by richards (1931) [4]. despite its limitations and drawbacks, the richards equation remains the most widely used model for simulating water flow through both saturated and unsaturated soils. its long nstanding history of application highlights its significance, particularly in infiltration studies across various disciplines. however, solving the richards equation is challenging due to the nonlinearities in constitutive relationships, especially those involving hydraulic properties. while analytical solutions exist, they are rare and limited to specific cases requiring simplifications or substitutions. consequently, numerical solutions have become the dominant approach, with numerous techniques developed to address these challenges. however, achieving high accuracy, robustness, and cost effectiveness remains an ongoing effort. this work emphasizes the critical role of solving the richards equation in understanding complex flow phenomena in unsaturated soils. the discussion extends to the numerical challenges and computational advancements required for robust solutions. to address these issues, a qualitative analysis is presented to better understand the behavior of the richards equation and its implications for modeling and simulation. lots of numerical solution techniques were employed efficiently to solve the richards equation with the use of newton–raphson or picard iterative techniques together with finite difference or finite element or finite volume approximations. finite difference methods were used by celia and bouloutas [8] or woodward and dawson [9] or dogan and motz [10]. finite element methods are found in celia and bouloutas [8], lehmann and ackerer [ [11], simunek [12], forsyth et al. [13], katvetsi et al. [14]. mixed finite elements were used by diersch and perrochet [15], knabner and schneid [16], chavent and roberts [17]or fahs et al. [18]. manzini and ferraris [19], orgogozo et al. [20] or caviedes–voulli‘eme et al. [21] or c.e. zambra et al. [22] were used finite volume method. primary variable switching between the pressure head and water content; upstream weighting of the relative permeability; methods of lines and transformation techniques were used by celia et al. [8]; kirkland et al. [23]; tocci et al. [24]; williams et al. [25]; mathews et al. [26]; ji et al. [27]; li et al. [28]; zha et al. [29]; zhang et al. [30]. generally, numerical methods are adopted to the pressure head–based form of richards equation in saturated, unsaturated and for layered soils. however, there is a poor mass balance for unsaturated soils with unacceptable time stepping limitations. the methods which are used in pressure head–based form are also applied to mixed form of richards equation by celia et al. [8]with a strategy to evaluate the change in water content over one time step directly from the change of the pressure head. it was found that in this strategy, there is a good mass balance. but according to kirkland et al. [23] under very dry initial conditions, there was a cpu efficiency problem in this method. numerical methods of the moisture–based form of richards equation has a significantly improved performance when the infiltration phenomenon into very dry soil ( hills et al. (1989) [31], kirkland et al. (1992) [23]; forsyth et al. (1995) [13]; zha et al. (2013) [32]). but the topmost drawback of this method is that it can be used for simulating water flow in unsaturated region only. to capture and retain the beneficiary of the moisture based method wu and forsyth (2001) [13]; kirkland et al. [23] and zeng et al. (2018) [33] were improved by combining these two. kirkland (1992) [23] was introduced a new variable having different characteristic at unsaturated and saturated region in which it may be a linear function of moisture content for unsaturated soil and a linear function of pressure head for saturated or nearly saturated soil. for relatively dry initial conditions this method has a very good cpu efficiency found by williams et al. (2000) [25]. moreover, there should be defined a point in which these two methods are joined which may directly affect the accuracy and robustness of the numerical results. haverkamp et al. (1977) [6]; campbell (1985) [34]; vauclin et al. (1979) [35]; ross and bristow (1990) [36]; williams et al. (2000) [25]; ji et al. (2008) [27]; berninger et al(2011) [37]; zhang et al. (2015, 2016, 2018) [30]; li et al. (2016) [28] used kirchhoff integral transformation approach to solve the non-linear richards equation. pan and wierenga (1995) [38] laid out a special numerical method to overcome the difficulties of evaluating the integral in kirchhoff transformed approach. a second integral transform formula was introduced by williams et al. (2000) [25], interpolating the linear combination of moisture content with an arbitrary constant and the kirchhoff integral transform. indeed, this method had really a good efficiency and robustness as compared to others. to solve unsaturated flow equation with kirchhoff transformation zhang et al. (2015) [30] introduced a new numerical method as a good name finite analytic method (fam). in this method, a local analytic solution is used to form a set of algebraic equation on the kirchhoff transformed variable. this method established an accurate and efficient solution. zhang et al. (2016) [30], applied fam on ramesh chandra timsina/ bibechana 22 (2025) 30-40 33 mixed form of richards equation. also zhang et al. (2018) [30], extended it into the two–dimensional richards equation. however, its good achievement, the finite analytic method is limited only for homogeneous porous media soil. ji et al. (2008) [27], used the transient pressure head–based method and compared a steady state solution obtained from kirchhoff transformation to a steady–state solution obtained from time marching scheme. they used gardner’s constitutive relationship [39] and their result showed that the computational cost in unsaturated flow simulation can greatly be reduced and the use of kirchhoff transformation has great implication for subsurface water problems. but they only considered pseudo–heterogeneous layered porous media and limited it only to steady–state conditions. although, kirchhoff transformation method has some limitations, it seems to be very promising method for simulation of richards equation in unsaturated porous media region. following into this method, numerical errors will be reduced effectively because variations of kirchhoff head in its integral nature are much smaller than those in pressure head. indeed, when the kirchhoff transformation is employed along with some specific constitutive relations to solve nonlinear richards equation, a full linearization of the unsaturated richards equation is permitted. this linearization has an ability of analytic and semi–analytic solutions. furthermore, numerical methods for solving nonlinear richards equation are pertaining to specific constitutive relationships. the popular widespread constitutive relationships were developed by gardener, van genuchten, brooks and corey and haverkamp et al. [6]. correspondingly, they gave the well measured relationship between hydraulic conductivity, pressure and moisture content. for example, heejun suk et al. (2019) [40], obtained a numerical solution of the kirchhoff transformed richards equation in variably saturated flow in heterogeneous layered soil. this method has followed the gardener’s relationships and is used to solve the linearize partial differential equation. egidi et al. (2018) [41], used van genuchten consecutive relationship for a numerical solution of richards equation providing a simple method adaptable in parallel computing. a constitutive relationship developed experimentally by haverkamp et al. were used by liu fengnan et al. (2020) [42]to a linearized finite difference scheme for the richards equation under variable–flux boundary conditions. among these, a most robust numerical method an explicit stabilized runge–kutta–legendre super time–steeping scheme is developed [42]to solve mixed form of nonlinear richards equation with no source and sink terms and with sink terms as evapotranspiration [43] numerically adopting the constitutive relationship developed by haverkamp et al. [6]. the scheme is based on the natural phenomena taking into account the hydraulic conductivity as a function of water pressure head as a real situation with experimental data. finally, landslides in the himalayan region are driven by a variety of interconnected processes and causes. the primary factors contributing to landslide hazards include geological, morphological, physical, and humaninduced causes. among these, the foothills of the himalayas are particularly vulnerable to landslides triggered by unusual, heavy, and concentrated precipitation during the monsoon season. rainfall is the most significant triggering factor, with the onset of the monsoon frequently leading to widespread landslide occurrences and disasters. these events pose severe risks to people, infrastructure, and ecosystems, affecting countless lives and livelihoods on both large and small scales throughout the region. this paper is organized as follows : in section 3, we present the methodology along with kirchhoff transformed axi-symmetrical form of richards equation, including the numerical methods based on finite difference schemes with different time stepping and the slope failure models for landslide stability in unsaturated soils. in section 4, we show the results of the numerical procedure implemented in python. in section 5, we discuss the results and the future development of this work. 3 methodology the flow of water in unsaturated soil follows the darcy law and mass conservation equation [4]. thus, the flow phenomena can be expressed by richards equation, a highly non linear pde. however, the analytical solution of this equation is impossible, we established a robust numerical solution of this equation in (1+1)d and (2+1)d by adopting different time stepping schemes and compared their results and used the appropriate one to find the factor of safety for the prediction landslide in the potential landslide area. we have used the (1+1)d solution for bench marking and obtained the solution for axi-symmetrical form of this equation. 3.1 richards equation the axi-symmetrical form of richards equation can be written as ∂θ ∂t = 1 r ∂ ∂r ( rk(ψ) ∂ψ ∂r ) + ∂ ∂z ( k(ψ) ∂ψ ∂z ) +w, (1) where θ(ψ) and k(ψ) represent the moisture content θ(ψ) and hydraulic conductivity k(ψ), respecramesh chandra timsina/ bibechana 22 (2025) 30-40 34 tively, and w is the rate of precipitation. the function θ(ψ) and k(ψ) are taken from empirical formulas, the van genuchten and haverkamp et al. models [6, 44, 45] are the most widely used in scientific computations due to their formulation by smooth function. commonly used versions of these models can be written as: k(ψ) = ks ( 1− (αψ) n−1 )2 / (1 + (αψ)n) m/2 , (2) θ(ψ) = θr + θs − θr (1 + (αψ)n) m , (3) where α is the reciprocal value of ψ0, i.e., the air entry point [46], θs and θr are the saturated water content and residual water content respectively. ks is the value of the permeability when the soil is saturated. m, n are empirical parameters depending on the soil, also m and n have the relation: m = 1− 1 n . (4) the various hydraulic parameters, e.g., α, θr, θs, n, ks, are related to the pore size distribution and pore geometry, so they ultimately depend on the soil type and can be determined experimentally by specific laboratory tests. for implementation and to improve the results, we used the van genuchten model. 3.2 linearization techniques applying the kirchhoff integral transformation in equation 1, we let h = ψ − z and define: ϕ(h) = ∫ h 0 k(h′)dh′. (5) since k(h) > 0 from equation (2), the function ϕ(h) is strictly increasing with k(h) = k(ψ). taking derivatives of both sides of the transformation with respect to r and z, we obtain: ∂ϕ ∂r = k(ψ) ∂ψ ∂r , ∂ϕ ∂z = k(ψ) ∂ψ ∂z . (6) again, taking the derivative of equation (6) with respect to r: ∂2ϕ ∂r2 = k(ψ) ∂2ψ ∂r2 + ∂k ∂ψ ( ∂ψ ∂r )2 , (7) and ∂φ ∂z = ∂φ ∂h ∂h ∂z = k(h) ∂(ψ − z) ∂z = k(ψ) ( ∂ψ ∂z − 1 ) = k(ψ) ∂ψ ∂z −k(ψ) (8) again differentiating of equation (8), ∂2φ ∂z2 = ∂ ∂z ( k(ψ) ∂ψ ∂z ) − ∂ ∂z (k(ψ)) (9) using the equations (6),(8) and (9), the richards equation (1), takes the form ∂θ ∂t = ∂2φ ∂r2 + 1 r ( ∂φ ∂r ) + ∂2φ ∂z2 +w (10) with θ(φ) = θ(h). the corresponding initial and boundary conditions for the transformed equation (10) takes the following form .θ(r, z, 0) = φ0(r, z), rin ≤ r ≤ rout, 0 ≤ z ≤ ztop ∂φ ∂z = q(t), r > 0, z = 0, t > 0 φ(r, zbot, t) = β(t), r > 0, t > 0 ∂φ ∂r = 0, r = rout , z > 0, t > 0 .φ(rin,z, t) = β1(t), t > 0 (11) the kirchhoff transformation transformed the nonlinear equation (1) to a nonlinear parabolic equation (10). also we note that the kirchhoff transformation preserves the uniqueness of the solution for the transformed problem. 3.3 discretization techniques and implementation we have the transformed equation is in two different state variables. to solve the transformed equation (10) numerically with the prescribed initial and boundary conditions (11), it is feasible to have a single state variable. for this, and are assumed as single valued continuous functions of one another, and arranging these variables as ∂θ ∂t = ∂θ ∂φ ∂φ ∂t = ( 1 ∂φ ∂θ ) ∂φ ∂t , ∂φ ∂θ = ∂φ ∂h ∂h ∂θ , (12) differentiating (3) with respect to h, we get ∂θ ∂h = αn(θs−θr)(−m)(1+ |αh|n)−m−1n|h|n−1 ∂φ ∂h = k(h) = k(ψ), (13) using (12) and (13), the transformed richards equation (10) takes the form c(φ) ∂φ ∂t = ∂2φ ∂r2 + 1 r ( ∂φ ∂r ) + ∂2φ ∂z2 (14) ramesh chandra timsina/ bibechana 22 (2025) 30-40 35 where the functional coefficient c depends on through h as c(φ(h)) = −α nmn(θs − θr)|h|n−1 k(h)(1 + |αh|n)m+1 (15) 3.4 finite difference scheme we set up a two dimensional (r, z ) uniform grid for an axi symmetric problem in the cylinder geometry by subdividing the radial length [rn, rout ] into mr subintervals of width ∆r = rout−rin mr and the height [0, ztop] in to mz subintervals of width ∆z = ztop mz . we construct a grid (ri, zj , tn) with ri = i∆r, i = 0, 1, 2, ....,mr, zj = j∆z, j = 0, 1, 2, 3, ...mz, and tn = n∆t, n = 1, 2, 3..., n . let φni,j denote φ(ri, zj , tn). the partial differential equation (14) can be approximated using forward difference in time and central difference in space as ∂φ ∂t |(rizj ,tn) ≈ φn+1i,j − φi,jn ∆t , ∂φ ∂r |(rizj ,tn) ≈ φni+1,j − φi−1,jn 2∆r ∂2φ ∂r2 |(rizj ,tn) ≈ φni−1,j − 2φi,jn + φni+1,j ∆r2 , ∂2φ ∂z2 |(rizj ,tn) ≈ φni,j−1 − 2φi,jn + φni,j+1 ∆z2 (16) using a weighted average of the derivatives( ∂φ ∂r , ∂2φ ∂r2 , ∂2φ ∂z2 ) at the two time levels, tn and tn+1 and adopting crank-nicolson(cn) scheme , equation (14) can be discretized as φn+1 i,j − φn i,j ∆t = 1 2cni,j(∆r) 2 [ φn+1 i−1,j − 2φn+1 i,j + φn+1 i+1,j +φn i−1,j−2φn i,j+φ n i+1,j+ 1 2cni,j(∆z) 2 [ φn+1 i,j−1 − 2φn+1 i,j +φn+1 i,j+1+φ n i,j−1−2φn i,j+φ n i,j+1+ 1 4ricni,j(∆r) [ φn+1 i+1,j − φn+1 i−1,j + φn i+1,j + φn i−1,j ] (17) we collect the unknowns on the left hand side : − ( fr − f ri ) φn+1 i−1,j+(1+2fr+2fz)φ n+1 i,j − ( fr + f ri ) φn+1 i+1,j − fz(φ n+1 i,j−1 + φn+1 i,j+1) = ( fr − f ri ) φn i−1,j+(1−2fr−2fz)φ n i,j+ ( fr + f ri ) φn i+1,j − fz(φ n i,j−1 + φn i,j+1) (18) where fr = ∆t 2cni,j(∆r)2 , fz = ∆t 2cni,j(∆z)2 , f = ∆t 4cni,j(∆r) . the equation (18) is coupled at the new time level n + 1. that is, we must solve a system of (linear) algebraic equations, which we will write as ax = b, where a is the coefficient matrix, x is the vector of unknowns, b is the right hand-side. to solve the system of linear equations, we need to form a matrix system ax = b, where the solution vector x must have one index. for this, we need a numbering of the unknowns with one index, not two as used in the mesh. we introduce a mapping position (i, j ) = v(i, j ) from a mesh point with indices (i, j ) to the corresponding unknown p in the equation system. p = v(i, j ) = j (vr + 1) + i, for i = 0, 1, 2, · · · , vr, j = 0, 1, 2, · · · , vz, with this mapping, we number the points along the radial direction starting with z = 0 and then filled one mesh line at a time. in another way p = v(i, j ) = i(vz + 1) + j, for i = 0, 1, 2, · · · , vr, j = 0, 1, 2, · · · , vz. with r = 0 and then filled one mesh line at a time. from this we can get the general feature of the coefficient matrix obtained from the discretized equation (18). let ak,l be the value of element (k, l) in the coefficient matrix a, where k and l are the numbering of the unknowns in the equation system. we have ak,l = 1 for k = l corresponding to the all known boundary values. let k be v(i, j ), i.e., the single index corresponding to the mesh point (i, j ). then, for interior mesh along with boundary, we have av(i,j),v(i,j) = ak,k = 1 + (fr + fz), ak,v(i−1,j) = ak,k−1 = −fr ak,v(i+1,j) = ak,k+1 = −fr ak,v(i,j−1) = ak,k−(vz+1) = −fz ak,v(i,j+1) = ak,k+(vz+1) = −fz the corresponding right hand side vector in the equation system has the entries bk, where k numbers the equations with the given boundary values. the above mention algorithm can be used to update the transformed variable φn i,j to its value in the next time level φn+1 i,j . but we cannot advance the algorithm to the next time level φn+2 i,j without evaluating the function c(φn+1 i,j ) ramesh chandra timsina/ bibechana 22 (2025) 30-40 36 which requires computing the intermediate variable hn+1 i,j . for this , we imply the equation (13) which can be approximated as hn+1 i,j = hni,j + φn+1 i,j − φn i,j k(hni,j) . (19) 3.5 landslide stability analysis in unsaturated soil this study focuses on the modeling of infiltrationinduced landslides in unsaturated soils, specifically analyzing slope stability and instability using the axi-symmetric kirchhoff-transformed richards equation. the approach considers the variation of moisture content with water pressure head and vice versa. infiltrationinduced landslides on ground surfaces often resemble shallow landslides triggered by intense rainfall events. the problem is addressed using an infinite slope model to calculate the safety factor (sf), which serves as a key indicator of slope stability. the safety factor is defined as the ratio of resisting forces that prevent slope failure to driving forces that cause collapse. as (sf) greater than one indicates stability, while as (sf) less than one signals instability. this numerical value acts as a landslide hazard index, enabling predictions about the likelihood of landslides for given topographic conditions. the infinite slope model is adopted due to its simplicity and effectiveness, especially for shallow landslides where the failure plane is parallel to the ground surface and relatively shallow compared to the slope length. for inter connected to the moisture profile obtained from the above solution schemes we preferred the following hydrological infinite slope model sf = c zytsinβcosβ + tanφ tanβ + hθy wtanφ zytsinβcosβ (20) where c is the effective cohesion, is the moisturity, yt is the unit weight of the soil, yw is the unit weight of the water, is the angle of internal friction, z is the soil thickness, is the slope of the inclined surface. the combination of the infinite slope model (equation 20) with richards equation, allows the landslide hazard evaluation directly from weather data. in particular, the solution of richards equation will be used to obtain information about in the expression. 4 simulation results 4.1 numerical setup to demonstrate the numerical solution of the prescribed model, the numerical process developed in the above section is written in python and ran on a laptop with 2.8 ghz quad-core intel core i7 processor. we considered a specific infiltration experiment in unsaturated soil and observe the corresponding outcomes. at first the setup consisted on a landslide area having dimension 70m × 100m. the physical constituent of the landslide area is sandy soil. we use the soil parameters and characteristics relationship between the soil moisture content () and the hydraulic conductivity k () from the work of van genuchten. k(ψ) = ks [1− |∂ψ|n]− m 2 [ 1− ( ||n 1 + ||n )m]2 (21) θ(ψ) = θr + (θs − θr) (1 + ||n)m (22) the simulation starts with a uniform saturation θ = 0.1 cm3/cm3 and a constant water head ψ = −61.5 cm is maintained at the bottom boundary z = zbot. for the upper boundary z = ztop at the soil surface, a constant flux q(t) = 13.69 cm/hr for t < 0.7hr and zero normal flux condition for t > 0.7hr is maintained. to compute the approximate solution using different time-stepping schemes, we used a uniform spatial step size ∆z = 2 cm in the axial direction and a step size of ∆z = 2 cm in the radial direction. the simulation was run for 0.75 hr. for the infiltration-induced landslide, we interpolated the moisture variation obtained from the above experiment to the hydrological model for stability analysis. data was obtained from the department of hydrology and meteorology, government of nepal, and field observations in the landslide area located in yangbarak vdc, ward no. 6, shripung, panchthar district. rainfall data from the region was applied in our simulation model (equation 20). 5 results and discussion the axi symmetrical model was employed to simulate vertical water infiltration into an unsaturated homogeneous porous medium and to analyze the landslide hazards, hydrological model was used. numerical experiments were carried out by using sand column (proposed by van genuchten.) ramesh chandra timsina/ bibechana 22 (2025) 30-40 37 with finite difference schemes(ftcs, btcs, cn and rkl). since we do not have exact solution, we have used numerical solution obtain from above (rkl) finite difference scheme for one dimensional as the reference solution timsina, r.c et al. [42] for numerical experiment of two dimensional water infiltration. fig. (2) (a) shows the variation of volumetric moisture content in sand for one dimension, and fig. 2 (b) shows the comparison of different time-steeping schemes as discussed in [42]. in this numerical experiment, the function used for the hydraulic conductivity and the water content as in one dimensional case were taken from van genuchten [46]. we set the axi-symmetrical form of richards equation in an unsaturated flow into a region of sandy soil. for this, we suppose the domain is specified to be an annulus, rinner ≤ r ≤ router with rinner strictly greater than zero, other than a disk. the annular domain consists of 70 cm in length with 100 cm of annular radius. we suppose it vertically downward where the z-axis is taken as downward positive with a constant water head ψ = −61.5 cm at the left (dirichlet) boundary condition r = rin as dummy. a constant flux boundary condition (neumann) on the right r = rout is taken and a constant water head ψ = −61.5 cm at the bottom boundary z = zbottom. at the upper boundary z = 0 (the soil surface), a constant flux q(t) = 13.69 cm/hr for t < 0.7 hr and zero normal flux condition for t > 0.7 hr. the solution domain was meshed using a spatial step size of ∆z = 2 cm on the axial direction and a step size of ∆r = 2.5 cm on the radial direction and the simulation was run for 1 hr. the longitudinal water content profiles and radial water content profiles at time 0 hr and some other times are shown in figure (3) (top). from this figure, it is possible to note that the residual water content at the bottom of the annulus is reached when time t is about 0.50 hr. the moisture content contours are shown in figure (4) and corresponding surface plots of moisture content are in figure (4) (left). we observe the flow phenomena and carried out the variation of water content in the region we have prescribed. we have interconnected the above result to the infinite slope model to evaluate the safety factor. we have measured the slope angle and the thickness of the unsaturated soil as 300 and 8m. we use the parameter of effective cohesiveness is 4.4kpa, the frictional angle is 280, the soil unit weight is 23.4kn/m3. figure 6 depicts the computed results of safety factor for different pressure head observed in the experiment. the factor of safety obtained by the above model demonstrates the possibilities of surface failure and operation of landslide hazards. from figure 6 we conclude that the situation of surface failure may increases when the level of ground water is increased by heavy rainfall meanwhile the pressure head energy increase and the level of unsaturated region decrease and the possibilities of landslide increases. the axisymmetric form of richards’ equation was set in an unsaturated flow region of sandy soil. the domain was specified as an annulus, rinner ≤ r ≤ router, with rinner > 0. the annular domain is 70 cm in length and 100 cm in radius. a constant water head ψ = −61.5 cm was maintained at the bottom boundary, while a constant flux q(t) = 13.69 cm/hr for t < 0.7 hr and zero normal flux condition for t > 0.7hr were applied at the soil surface. the solution domain was meshed with a spatial step size ∆z = 2 cm in the axial direction and ∆r = 2.5 cm in the radial direction. the simulation was run for 1 hr. figures 4 and 5 show the longitudinal and radial water content profiles and the corresponding surface plots. ramesh chandra timsina/ bibechana 22 (2025) 30-40 38 the safety factor for different pressure heads and corresponding moisture content is shown in figure 6. the slope angle and thickness of the unsaturated soil were 30◦ and 8m, respectively. the effective cohesion was 4.4 kpa, friction angle 28◦, and soil unit weight 23.4 kn/m3. the results indicate an increased likelihood of surface failure with heavy rainfall. conclusion the flow of water in unsaturated soil is described by axi symmetrical kirchhoff transformed richards equation (a highly nonlinear degenerate parabolic partial differential equation) and solved it numerically and interpolate the result in the hydrological model for stability analyses for the possibilities of landslide hazards. also this work is based on illustrative numerical examples in cylindrical form, with realistic parameters. we implemented different finite difference schemes. the work presented here describes and verifies the application and accuracy of finite difference schemes to simulate flow in unsaturated porous media in axi symmetrical cylindrical formation of the land surface. however, this work presented a new super time stepping numerical scheme which was able to solve the kirchhoff transformed axi symmetrical richards equation and the findings are converges to the theoretical analysis and also the findings are in line with one dimensional approaches [42, 43]. figures 2 and 3 depicted that the numerical simulations results for the same infiltration experiment as in one dimension imposing, zero flux boundary conditions in the lateral boundary mimic the results from the one dimensional model. that is the longitudinal profile are in line with that of the one dimensional model. the numerical method is able to handle short duration infiltration and relatively easy to implement. the interpolated result shows that the prediction of landslide is possible for the available parameter depending on the constituent of the soil and nature of the land. this work can be extended to achieve to accurate prediction of massive landslide to unsaturated heterogeneous soils with abruptly changing wetness conditions. acknowledgments the author thanks the research division, university grants commission, sano thimi, bhaktapur, for the small research grant provided for this work (srdig-80/81-s&t-10). data availability the data supporting the findings of this study are included within the article. conflicts of interest the author declares no conflict of interest. references [1] r. k. dahal and s. hasegawa. representative rainfall 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[46] m. t. van genuchten. a closed–form equation for predicting the hydraulic conductivity of unsaturated soils. soil science society of america journal, 44(5):892–898, 1980. introduction background methodology richards equation linearization techniques discretization techniques and implementation finite difference scheme landslide stability analysis in unsaturated soil simulation results numerical setup results and discussion bibechana vol. 22, no. 1, april 2025, 80-84 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar (short communication) exploring the electronic and magnetic properties of half-heusler alloy comnsb: implications for spintronics binay limbu, prem sagar dahal 1central campus of technology, tribhuvan university, dharan, 56700, nepal ∗corresponding author. email: binay.805511@cdp.tu.edu.np(bl) prem.dahal@cct.tu.edu.np(pd) abstract heusler alloys have caught a lot of attention because they can be really useful in modern technology. in this study, we investigated the electronic and magnetic properties of comnsb by employing advanced computational methods rooted in density functional theory and planewave pseudo potential approach. our investigation uncovers that comnsb is a half-metallic ferromagnet with a half-metallic gap of 0 ev at the equilibrium lattice constant. the total spin magnetic moments have been computed 3µb per unit cell which is in good agreement with the slater pauling rule mt = zt − 18 for half heusler alloy. the hybridization of the eg and t2g orbitals of the co, mn, and p-orbitals of the sb are primarily responsible for the band gap. this indicates that these alloys hold great potential as functional materials for spintronics. keywords half-heusler, density of states, half-metallic, bandstructure, spintronic devices, dft. article information manuscript received: april 4, 2024; accepted: january 18, 2025 doi https://doi.org/10.3126/bibechana.v22i1.64520 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the half-heusler alloys composition is represented by the generic formula xyz where x and y are transition metal elements and z is the main group sp element. half-heusler [1] structure can be looked at as four-interpenetrating face centre cubic(fcc) lattices and has unique four crystal sites in wyckoff coordinates. half-heusler compounds crystallize in fcc c1b structure with space group f-43m. in this structure x, y and z occupy (0,0,0), (1/4,1/4,1/4) and (3/4,3/4,3/4) sites and (1/2,1/2,1/2) sites are empty. the half-metallic compounds can also be characterised by their integer value of magnetic moments which is in accordance with the slater-pauling rule mt = zt − 18 where mt is magnetization and zt is a total number of valence electron. in this project, we planned to investigate systematically the electronic and magnetic properties of half-heusler alloys comnsb. in the present time, heusler compounds having co and mn atoms pull large attention because of their 80 http://nepjol.info/index.php/bibechana binay.805511@cdp.tu.edu.np prem.dahal@cct.tu.edu.np https://doi.org/10.3126/bibechana.v22i1.64520 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ binay limbu, prem sagar dahal/ bibechana 22 (2025) 80-84 81 property of strongly ferromagnetic with the high curie temperature. heusler alloys catch the interest of many one because of possible study within the same family of series of integrating diverse magnetic phenomena like pauli paramagnetism, helimagnetism, itinerant and localized magnetism or heavy-fermionic behaviour. at fermi level at low temperture some of oxides(e.g fe3o4 and cro2) [2], double peroskites (e.g sr2fereo6) [3] and pyrites (e.g cos2) [4] which shows 100% spin-polarization. mostly half heusler [1] are used in the application fields like spin-injection devices,spin-filters [5], tunnel junctions [6] or gmr devices [7]. in most cases, half-metallicity has been lost. it is experimentally found [8] that near surfaces and interfaces half-metallic character is lost. there are also several factors which affect the half-metallic character of half heusler alloys [1]. 2 computational details in this study, we used gga method implemented in the quantum espresso software package vaersion 6.7 to investigate electronic and magnetic properties of comnsb. in order to optimize the lattice parameter of comnsb using the energy minimization method we carried out a convergence test on the kinetic energy-cutoff of the wavefunctions and the number of k-points in monk-horst pack grid on the basis of crystal structure and lattice constant of produced comnsb determine by experiment. to relax the coordinates we maintain force between atoms less than 10−3 ry/a.u using the optimized lattice parameter of comnsb. taking into account all these computed values, we evaluated the electronic structure employing the plane wave pseudo-potential approach within the quantumespresso distribution of dft. we use ultra-soft pseudo-potential from the quantum espresso page for cobalt, manganese and antimony. scf threshold was set to 10−8 and energy tolerance was set to 10−5rydberg monk-horst pack grids with dimensions of 8x8x8 were used for the sampling of the brillouin zone. the linear tetrahedral integration approach was used to calculate the density of the states. with the help of the tool xcrysden, crystal structure can be visualized. graphing and plotting are done with the help of gnuplot. 3 results and discussion 3.1 electronics properties the electronic band structure is one of the most used analytical techniques in the determination of a crystal’s first-principles electronic structure, particularly within the kohnsham framework of density functional theory [9]. electronic properties of solids can be determined and analyzed by using their band structures. it includes the fundamental components for practically all crystal characteristics. when many atoms are brought together, their interaction causes the initial atomic levels to be perturbed because the atoms in a solid are tightly packed. according to pauli’s exclusion principle, which states that no two electrons can occupy the same energy state. the orbitals are completely occupied with electrons [10]. in a solid, the valence electrons group together and compete to occupy the same energy level, creating energy bands. the core electrons, on the other hand, do not change energy levels and continue to be bound to the nuclei. within each energy band, the outcome is a continuum of energy levels. in semiconductors and insulators, a band gap forms as a result of the periodic potential of the ion cores in the material and how the electrons react to this potential. the energy range between the highest occupied and lowest vacant energy levels is known as the band gap. the material’s electronic characteristics are determined by the band gap size, which is dependent on the substance. for instance, conductors have no band gap whereas insulators have a wide band gap. materials can be categorized as conductors, semiconductors, or insulators. it depends on the width of their energy bands and the relative position of their fermi level, which is the energy level of the highest occupied state. the fermi level is located in the conduction band because the valence bands in conductors are broad and overlap. the fermi level is found in semiconductors and insulators near the top of the valence band or within the band gap. a material’s density of states (dos), or the number of electronic states per unit energy range, may also be used to describe its electronic structure. density functional simulations were used to examine the electronic structures of the comnsb [11] alloys at their equilibrium lattice constants (a=5.82350 a.u). we focus on the dos in the range of the fermi level, which is set to zero and varies from -5 to 3ev since the dos distribution at the fermi level influences the electronic characteristics. around the fermi level, it is clear that there is a significant exchange splitting between the majority-spin and minority-spin states. particularly, the bands of the minority-spin states for comnsb [11] have an indirect energy gap at the fermi level, but the majority-spin states crossing the fermi level are partially filled. as a result, comnsb shows halfmetallic [12] characteristics. the computed spinpolarized band structures for comnsb alloy at the equilibrium lattice constant along the high symmetry directions in the first brillouin zone are represented in figures 1a and 1b, respectively. we computed the band structure along the brillouin zone route γ−x−w−k−γ−l−u−w−l−k which binay limbu, prem sagar dahal/ bibechana 22 (2025) 80-84 82 figure 1: (a)unit cell and (b) optimized lattice parameter. -10 -8 -6 -4 -2 0 2 4 γ x w k γ l w u x e ne rg y [e v ] -10 -8 -6 -4 -2 0 2 4 γ x w k γ l w u x e ne rg y [e v ] figure 2: band structure plots of comnsb (a) spin-up and (b) spin-down. is shown in figure 1. we learn that comnsb’s electronic structures exhibit the typical half-metallic characteristics, the majority-spin band structures are metallic, but the minority-spin band structures are semiconducting with a band gap of 1 ev. this finding is in good accordance with findings from earlier studies [11]. the augmented spherical waves investigation was used by kübler [13] to conduct a theoretical study of comnsb [14]. he discovered a dos that was exactly like ours in terms of its size gap and the fermi level, which was situated at the left edge of the spin-minority gap. the bottom of the minority-spin conduction bands is placed at 1.3 ev, whereas the top of the minority-spin valence bands is at 0 ev [14]. the half-metallic gap for comnsb [14] is 0 ev, which is decided minimum of ec and ev. ec is the energy level of the bottom minority-spin conduction band in relation to the fermi level, and ev is the absolute value of the top minority-spin valence band energy in relation to the fermi energy. the dos nature perfectly matches the band’s results. the hybridization of the eg and t2g orbitals of the co, mn, and p-orbitals of the sb are primarily responsible for the band gap. the delocalized electrons may be responsible for co and mn’s eg and t2g orbitals contribution. 3.2 magnetic properties the spin and orbital angular momentum of electrons in their electronic shells give rise to the magnetic properties of atoms or ions. the total spin of the atom or ion is determined by the combination of the spin and angular momentum vectors of the electrons. this behaviour is regulated by the laws of quantum mechanics. it is clear from hund’s rule states are energetically favoured. three quantum numbers total spin s, orbital angular momentum l, and total angular momentum j can be used to describe the state of an atom or ion. according to the pauli exclusion principle and hund’s rule, the electronic shells of atoms are filled up. the valence orbitals of the atoms hybridize with those of neighbouring atoms when they are brought together to form a solid, creating bonding and anti-bonding states. these states are able to have electrons added to them in ways that are energetically advantageous, leading to varied magnetic behaviour in solids. some substances contain spontaneous magnetic moments, which means they have a magnetic moment even in the absence of an external magnetic field. the presence of such spontaneous moments shows that electronic spins and magnetic moments are arranged in a predictable way. the magnetic materials ferromagnets, anti-ferromagnets, and ferrimagnets all result from distinct configurations of binay limbu, prem sagar dahal/ bibechana 22 (2025) 80-84 83 -10 -5 0 5 10 -4 -3 -2 -1 0 1 2 3 4 fermi-level spin-up spin-downp d o s( st a te s/ e v) e-ef [ev] co-4d mn-4d sb-2p figure 3: total and partial density of state plots of comnsb (a) dos and (b) pdos. electronic spins and magnetic moments. by counting the number of unpaired electrons and multiplying the result by bohr’s magneton, one may get the total magnetic moment of a substance. 21 valence electrons in the comnsb half-heusler alloy contribute to magnetism. four of the 21 valence electrons will initially occupy the co and mn 4s states since these states are lower in energy than the 4p levels. seven of them are in majority-spin states for co and mn, while the other ten are in minority-spin states for co and mn. according to hunds rules, a 3d orbital has space for 10 electrons, hence the 3d orbital of majority-spin states are not entirely filled. the majority spin has a three-hole band, and the total magnetic moment for a spin should be 3µb per formula unit. table 1 contains the computed total spin magnetic moments. it is clear that these are integral values, which for comnsb equals 3µb. the total spin magnetic moments are known to be mt = zt − 18 for half-metallic, where mt is the total magnetic moment per unit cell and zt is the total number of valence electrons. these total spin magnetic moments are required to follow the slater-pauling rule [15]. in half-metals [12], the fermi energy is often confined in the minority-spin gap, which makes the spin magnetic moment integral and the number of occupied minority-spin states an integer. they have 21 valence electrons in the comnsb. according to the slater-pauling rule [15], comnsb’s total spin magnetic moment is 3µb, which is consistent with the findings of our first principles. the computed magnetic moments have been found to be in accordance with previous comnsb [14] theoretical studies. as can be observed, various atoms contribute differently to the magnetic characteristics due to differences in their spin magnetic moments. the comnsb alloy’s mn atom has the highest spin magnetic moments, while sb contributes very little to the alloy’s overall spin moment. these quantitative findings show that mn atoms, which are present in the compounds in a high spin state, account for the majority of the total spin magnetic moments. the magnetic moments of co and sb in the half-heusler alloy comnsb [14] have a negative sign. the induced magnetic polarization of the co and sb atoms is antiparallel to that of the mn atoms, as seen by the negative sign in their local magnetic moments. it also demonstrates the existence of ferromagnetic coupling in comnsb [11]. table 1: calculated total magnetic moment (mt ) for comnsb. magnetic moments in (µb) gga co -0.0879 mn 3.1275 sb -0.0605 4 conclusion with the help of dft, gga, and quantum espresso code, this paper has effectively analyzed the electronic and magnetic characteristics of comnsb. first, we created the optimized unit cell of the fcc structure of comnsb [11]. the kinetic energy (cut-off energy) with a k-point grid of 9x9x9, is discovered to be 90 ry during optimization. the estimated lattice parameter was then determined to be 5.82350 a.u, which is only 0.4% deviated from the experimental data but still extremely close to them. as a result, the lattice parameter of comnsb [11] computed with the gga approach agrees well with experimental data. the gga technique in the qe package is then used to investigate the band structure and density of states. this demonstrates that the plane-wave pseudopotential approach may be employed with the quantum espresso code to do first-principles calculations to analyze more complicated electronic and other systems. between the majority-spin and minority-spin bands of the co 3d and mn 3d states, there is a significant exchange splitting. comnsb is a half-metallic ferromagnet with a half-metallic gap of 0 ev at an equilibrium lattice constant. the total spin magnetic binay limbu, prem sagar dahal/ bibechana 22 (2025) 80-84 84 moments that have been computed is 3µb per unit cell, which is in good agreement 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https://doi.org/10.1016/j.jallcom.2011.08.017 https://doi.org/10.1103/physrevb.74.134426. https://doi.org/10.1103/physrevb.74.134426. https://doi.org/10.3126/jnphyssoc.v5i1.26938. https://doi.org/10.3126/jnphyssoc.v5i1.26938. https://doi.org/10.1103/physrevb.66.174429 https://doi.org/10.1103/physrevb.66.174429 introduction computational details results and discussion electronics properties magnetic properties conclusion bibechana vol. 21, no. 1, april 2024, 12–22 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar lattice thermal conductivity in half-heusler model compounds xnisn (x=ti, zr, hf) using slack’s model prakash khatri1,2, n. p. adhikari1,∗ 1central department of physics, institute of science and technology, tribhuvan university, kirtipur, kathmandu, nepal 2department of physics, siddhanath science campus, mahendranagar, tribhuvan university, nepal ∗corresponding author. email: narayan.adhikari@cdp.tu.edu.np abstract reducing lattice thermal conductivity (κl) that reflects the material’s heat-carrying capacity through lattice phonon vibrations is crucial for optimizing the figure of merit (zt). using density functional theory (dft) and density functional perturbation theory (dfpt), present work considers the structural, electronic, magnetic, and phonon properties of the xnisn (x=ti, zr, hf) half heusler (hh) compounds. tinisn, zrnisn, and hfnisn are identified as semiconductors with indirect band gaps of 0.43 ev, 0.47 ev and 0.39 ev, respectively, exhibiting dynamical stability. the temperaturedependent κl of hh xnisn are compared using slack’s model with two approaches for analyzing phonon velocity: elastic constants from quasiharmonic approximation (qha) as implemented in the thermo_pw code and slope of phonon bands based on dfpt. at room temperature, tinisn, zrnisn and hfnisn have κl values of 28.61 wm−1k−1, 34.61 wm−1k−1 and 29.85 wm−1k−1 respectively using phonon velocity from slopes of phonon bands based on dfpt. these values show deviation of 1.48%, 6.29%, and 5.82% to those κl values 29.01 wm−1k−1’, 36.79 wm−1k−1 and 31.59 wm−1k−1 for tinisn, zrnisn and hfnisn respectively using qha. keywords density functional theory, lattice thermal conductivity, slack’s model, phonon bands. article information manuscript received: september 16, 2023; revised: december 5, 2023; accepted: december 16, 2023 doi https://doi.org/10.3126/bibechana.v21i1.58405 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 12 http://nepjol.info/index.php/bibechana narayan.adhikari@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v21i1.58405 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ prakash khatri and n. p. adhikari/ bibechana 21 (2024) 12-22 13 1 introduction the rising energy demands but limited fossil fuels have led to a worldwide energy crisis. waste heat resulting from industrial processes, residential heating and vehicle exhaust affects the environment. the potential of thermoelectric (te) materials to utilize such waste heat energy can play a vital role on the reduction of fossil fuel usage and global greenhouse emissions [1–3]. the thermoelectric figure of merit (zt) is employed as a means to quantify the conversion efficiency of thermoelectric materials. it is expressed as [4], zt = s2σt κ (1) it depends on the material’s transport coefficients, including the seebeck coefficient (s), electrical conductivity(σ), absolute temperature (t) and total thermal conductivity κ = κele +κl, which is the sum of electronic component (κele) and lattice component of total thermal conductivity (κl). thermal conductivity (κ) is crucial for various technological advancements, including thermoelectricity and heat management applications [5,6]. the transport coefficients s, σ and κele are interdependent due to the influence of carrier concentration and effective mass. the interdependence between the kele and σ is established by the wiedemann-franz law (κele = σlt). a zt in te materials corresponds to a high power factor (pf = s2σ) and a low κl. strong electron-phonon coupling in bulk materials like half-heusler (hh) alloys imposes restrictions on simultaneous optimization of pf and reduction of k [7,8]. nowadays the primary focus is on reducing κl since efforts to manipulate κele are ineffective due to its direct correlation with σ. it is worth noting that the reduction of κl has shown limited impact on the pf. as a result, reducing κl independently of the parameters s, σ , and κele becomes crucial in optimizing zt value [9]. the lattice thermal conductivity of solid [10], κl = 1/3cvvsl, is directly influenced by the phonon velocity (vs) and mean free path (mfp) (l). by increasing the scattering of phonons, the heat flux can be reduced hindering mfp and resulting in lower κl [11]. multiple methods like grain boundary scatterings, point defects, dislocations, impurity scattering [12], nanostructuring [13], alloy scattering [14] leading anharmonicity reduce κl by scattering phonons. the dominant scattering mechanism in a material is temperature dependent. at low temperatures, grain boundary scattering are significant whereas near to debye temperature, defects act as scattering centers and above room temperature phonon-phonon scattering dominates [15, 16]. phonon boltzmann transport equation (pbte) [17] involving large numbers of linear equations are challenging to solve for κl due to high dimensionality and complexity of determining reliable ii and iii-order force constants based on atomic interactions [18]. iterative solutions based on dft calculations, such as shengbte software [19], temperature gradient molecular dynamics (md) simulations based software tools like lammps [20] require a high computational cost [20]. the debye-callaway model offers a method to estimate κl using debye temperature (θd), phonon velocity (vs), and the grüneisen parameter (υ) [21]. slack developed a model [22] (equation 3) to express the κl in semiconductors, considering the significant role of acoustic modes in heat transfer. half-heusler compounds display a wide range of thermal conductivities [7]. the presence of symmetry in hhs contributes to a decreased computational cost in comparison to more intricate systems like layered compounds or those with distorted symmetries [23]. the κl of the 18 valence electron system xnisn (x=ti, zr, hf) has been reported in many experimental and computational studies [8, 24–28]. instead of computationally expensive models, the slack model is more efficient and feasible to predict the lattice thermal conductivity (κl) and providing insights into thermal transport. to our best knowledge, a comprehensive comparison of the κl values for these compounds using slack’s model is still not available. such a comparison could be beneficial in the field of high-throughput computations to seek for the materials with ultralow or ultrahigh κl efficiently. it could eliminate the need for extensive efforts in calculating the debye temperature and grüneisen parameter, as required by alternative methods. in the present work, our primary focus is on calculating κl of hh xnisn (x=ti, zr, hf) using slack’s equation. we obtained the required parameters for the equation from two different approaches: from elastic constants by qha in thermo_pw code [29] implemented in quantum espresso and the slopes of acoustical branches of phonon bands using dfpt [30]. the paper is structured as follows: second section discusses the computational details, the third section focuses on the main results and discussion and the last section presents the conclusions and concluding remarks of present work. 2 computational details we used dft [31] in quantum espresso (version 7.1) [32] with a plane wave basis set and generalized gradient approximation (gga) method with perdew, burke and ernzerhof (pbe) exchangecorrelation functional [33]. the rrjk model [34] of ultrasoft pseudopotentials was used for calculations on structural optimization, electronic and magnetic properties. we incorporated a kiprakash khatri and n. p. adhikari/ bibechana 21 (2024) 12-22 14 netic energy cutoff of 70 ry and a charge density cutoff of 700 ry with brillouin zone integration utilized the monkhorst–pack scheme [35] with a 10 × 10 × 10 k-mesh in the first irreducible brillouin zone. the "david" diagonalization method with a mixing factor of 0.3 is employed in the self-consistent field (scf) calculations, with a convergence threshold of 10−6 ry. for band structure calculations, k-points were chosen along γ→x→w→k→γ→l→u→w→l→k, high symmetry path (figure 1(c)), in the first brillouin zone of reciprocal lattice. the density of states and partial density of states were computed through non-self consistent field (nscf) calculations with a denser mesh of 20 × 20 × 20 k-points. marzarrivanderbilt smearing [36] of broadening width of 0.005 ry was employed in all calculations. the compounds’ dynamical stability was checked via phonon dispersion calculations using density functional perturbation theory (dfpt) with a 2 × 2 × 2 q-point mesh by computing second-order derivative of the total energy with respect to atomic displacements. the slack’s equation was used for calculating κl with velocity of phonon determined using two different techniques. the first method involved the utilization the elastic parameters obtained from qha implemented in thermo_pw codes. on the other hand, the second approach employed the slopes of the longitudinal and transverse components of the acoustic branches in the phonon dispersion curve. 3 results and discussion 3.1 structural properties the xnisn (x=ti, zr, hf) half-heusler compounds are extensively studied ternary intermetallics,having an edge-centered cubic structure with a fundamental composition of 1:1:1. the structure has the specific symmetry of f 4̄ 3m with x element is the most electropositive. inside the unit cell of these compounds, three atoms (x, ni, and sn) are situated at specific in-equivalent wyckoff positions: x at 4a (0, 0, 0), ni at 4b (0.5, 0.5, 0.5), and sn at 4c (0.25, 0.25, 0.25) as shown in figure 1(a) and 1(b). we have calculated the optimized lattice parameters of xnisn (x=ti, zr, hf) by minimizing total energy of crystal with murnaghan’s equation of state [37], e(v ) = e0 + bv b′ [ 1 b′ − 1 ( v0 v )b′ + 1 ] (2) in the equation b is bulk modulus, b’ is first pressure derivative of the bulk modulus that corresponds to pressure of p=0, e0 is the equilibrium energy and v0 is the unit-cell volume that corresponds to zero pressure. the optimized lattice constant represents the minimum ground state energy, signifying the crystal’s most stable configuration. figure 2(a), 2(b) and 2(c) shows the total energy vs lattice parameter for tinisn, zrnisn and hfnisn respectively. the optimized lattice constant for tinisn, zrnisn and hfnisn are 11.259 bohr (5.958å), 11.629 bohr (6.154å) and 11.552 bohr (6.113å) respectively. the hfnisn compound exhibits smaller lattice parameters compared to zrnisn and this difference can be attributed to the lanthanide contraction phenomenon. table 1. presents the optimized lattice constants for xnisn (x= ti, zr, and hf) along with the previously reported experimental and computational data. the deviation of our calculated lattice parameter values from that in experimental reports by aliev et al. [38] are 0.63%, 0.71% and 0.76% for tinisn, zrnisn and hfnisn respectively. the calculated lattice parameter values in the present work agree with the values in computational report by öğüt, s., rabe [39] within 1.36%-2.66%, j. yang et al. [40] within 0.47%-0.66% and muta et al. [26] within 0.47%-0.71%. all the variation in lattice parameters are ≤ 2.66% and the variation could be attributed due to the choice of exchange-correlation functional utilized in the studies. figure 1: (a) conventional unit cell of xnisn (x=ti, zr, hf), (b) primitive unit cell of xnisn (x=ti, zr, hf). the blue, red, and green colors in both figures represent x, ni, and sn, respectively visualized by xcrysden. (c) brillouin zone locating symmetric points. prakash khatri and n. p. adhikari/ bibechana 21 (2024) 12-22 15 figure 2: total energy (in rydberg) vs lattice parameter (in bohr) for (a) tinisn (b) zrnisn (c) hfnisn. table 1: comparison of calculated lattice parameter (in å) of xnisn (x=ti, zr, hf) with experimental and computational results in literature. compound our work aliev et al.[38] öğüt, s., & rabe[39] j. yang et al.[40] muta et al.[26] tinisn 5.958 5.920 5.814 5.921 5.930 zrnisn 6.154 6.110 6.070 6.113 6.110 hfnisn 6.113 6.066 5.950 6.084 6.080 3.2 electronic and magnetic properties we have studied the band structures of xnisn (x=ti, zr, hf) using gga-pbe exchangecorrelation functional as shown in figures 3(a), 3(b) and 3(c). from computed band structure of xnisn compounds, all the compounds exhibit a semiconductor nature with an indirect band gap. the position of the conduction band minimum (cbm) is at the x point of the brillouin zone (bz), while the valence band maximum (vbm) is at the γ point of the bz. the tinisn, zrnisn, and hfnisn compounds exhibit band gaps (eg) of 0.43 ev, 0.47 ev, and 0.39 ev, respectively. the calculated band gap values agree with the values in computational report by öğüt, s., & rabe [39] within 8.51%-23.07%, j. yang et al. [40] within 0.00%-8.51% and zou et al. [41] within 7.69%-10.64% as shown in table 2. these deviations might be because of the different exchange correlation functional used in the calculations in different studies. in general, dft underestimates the band gaps. however, in these compounds, the experimental band gap value reported in aliev et al. [38] is smaller than the calculated value. this difference is because of the formation of an impurity band within the gap, which occurs due to the presence of ni-interstitial atoms [42]. density of states (dos) and partial density of states (pdos) plots revealing the distribution of electrons among atomic orbitals are crucial tools for understanding the electronic and magnetic properties of materials. the main contribution to the dos of xnisn near the fermi level arises from the 3d orbitals of ni in the valence band (vb), while it comes from the 3d/4d/5d orbitals of ti, zr,and hf, respectively in the conduction band (cb). the sn5p orbitals play a minor role in both the vb and cb of the material. symmetric and equal electron spin distribution in mentioned orbitals cancels magnetic moments, that explains the non-magnetic behavior in xnisn compounds. the non-magnetic behavior in these 18 vec hh is in agreement with the slater-pauling rule [43], which connects the material’s magnetic moment (m) to the number of valence electrons (z) in the unit cell as m= (z-18)µb . prakash khatri and n. p. adhikari/ bibechana 21 (2024) 12-22 16 figure 3: the electronic band structure and pdos plots of orbitals of constituent atoms (a) tinisn (b) zrnisn (c) hfnisn with the fermi level represented by a horizontal dotted line. table 2: comparison of band gap (eg in ev) of xnisn (x=ti, zr, hf) with experimental and theoretical results reported in literatures. compound our work aliev et al.[38] öğüt, s., & rabe[39] j. yang et al.[40] zou et al.[41] tinisn 0.43 0.12 0.51 0.45 . . . zrnisn 0.47 0.18 0.51 0.51 0.52 hfnisn 0.39 0.22 0.48 0.39 0.36 figure 4: phonon band diagram of (a) tinisn, (b) zrnisn and (c) hfnisn compounds. prakash khatri and n. p. adhikari/ bibechana 21 (2024) 12-22 17 3.3 phonon spectrum and dynamical stability this study presents the phonon dispersion of xnisn (x=ti, zr, hf) using dfpt as shown in figures 4(a), 4(b) and 4(c) respectively. the compounds were checked for dynamical stability using these curves. stability is indicated by real frequencies, while instability is indicated by imaginary frequencies. figure 4’s phonon dispersion curves confirms the dynamic stability of the compounds, as they lack imaginary phonon frequencies. with a primitive unit cell having 3 atoms, these compounds have three low-frequency acoustic modes and six highfrequency optical modes in their phonon dispersion curve. the equation vg = dω dk defines phonon group velocity, where optical dk branches exhibit a low group velocity due to their flat curvature, while acoustic branches show a high group velocity with a linear variation. thus, the acoustic modes play a significant role in heat transport and κl, while the optical branch has a minor impact. there is a noticeable separation between the optical and acoustic phonon modes, which decreases from tinisn to hfnisn. the low κl might be achieved in the compounds having a small phonon gap or maximum overlapping because of enhanced phonon scattering [44]. the overlapping of phonon modes increases in the order of ti < zr < hf, consequently strongly influencing the thermal transport of phonons in the same order. the maximum acoustic mode frequency for tinisn (156 cm−1), zrnisn (153 cm−1) and hfnisn (140 cm−1). the low-energy acoustic phonons have limited energy transfer during heat transport, which ultimately leads to a low κl in these materials. among these compounds, the low frequency for acoustic modes in the phonon is least for hfnisn. 3.4 estimation of lattice thermal conductivity slack’s equation [22] for calculating κl is, κl = v 1/3amθ3d γ2tn2/3 (3) the parameters in the equation are average atomic mass (m), volume per cell (v), number of atoms in the primitive unit cell (n), grüneisen parameter (γ) and debye temperature (θd). the grüneisen parameter (γ) is a measure of the strength of lattice anharmonicity in a material that influences κl. it can be determined by considering the longitudinal (vl) and transverse (vt) velocities of the lattice vibrations. our calculations are focused on determining the γ through the analysis of elastic constants [45]. grüneisen parameter (γ) is computed as, γ = 9− 12(vt/vl) 2 2 + 4(vt/vl)2 (4) the dimensionless constant a is computed as a = 2.43× 10−8 1− 0.514/γ + 0.228/γ2 (5) the vl and vt were calculated using two different techniques. the first method used the elastic parameters obtained from qha implemented in thermo_pw codes. the thermo_pw algorithm calculates the various elastic constants and utilized them to derive various elastic properties, including bulk moduli, shear moduli and young’s moduli, using the voigt-reuss-hill approximation [46, 47]. these derived elastic properties were then employed to compute sound velocities. b = c11 + 2c12 3 (6) g = c11 − c12 + c13 5 + 5(c11 − c12) 3(c11 − c12 + 4c44) 2 (7) y = 9bg 3b +g (8) the longitudinal and transverse velocity components of lattice vibration are, vt = √ g ρ (9) vl = √ 3b + 4g 3ρ (10) the average sound velocity, v = [ 1 3 ( 1 v3l + 2 v3t )]−1/3 (11) another significant factor in computing κl is the debye temperature θd, which considers the average sound velocities. the θd corresponds to the state where all phonon modes in a material are fully excited and it plays a crucial role in γ and hence κl [47]. θd determined form the average sound velocities of acoustic phonon modes [46], θd = h̄ kb ( 6π2n v )2 ν (12) the second method involves the calculation of the vl and vt by analyzing the slopes of longitudinal and transverse components of the acoustic branches respectively in the phonon dispersion curves depicted in figure 4(a), 4(b) and 4(c). when computing κl, the linear region near the γ point in the acoustic branch of the phonon dispersion curve is selected prakash khatri and n. p. adhikari/ bibechana 21 (2024) 12-22 18 because it impacts the thermal transport significantly. the region is selected with care to ensure linearity. table 3. presents the vl , vt, v, θd, γ and κl (at 300k) of xnisn compounds. the κl of determined using velocity values from phonon slopes by dfpt and qha model in thermo_pw codes, are tinisn (28.61 wm−1k−1 and 29.00 wm−1k−1), zrnisn (34.61 wm−1k−1 and 36.79 wm−1k−1) and hfnisn( 29.85 wm−1k−1 and 31.59 wm−1k−1) respectively. the results obtained from both methods show an agreement of 1.48%, 6.29%, and 5.82% for tinisn, zrnisn, and hfnisn, respectively. the variation of κl calculated using both approaches for all compounds are as shown in figure 5. both approaches calculate κl from elastic parameters but differ in the way of estimation. these approaches have varying accuracy in velocity estimations. for phonon velocity from phonon band slopes, the acoustic branches near the point in a specific and localized region of the phonon dispersion curve are analyzed. the another approach estimates the phonon velocities by calculatingthe macroscopic elastic parameters from elastic constants without explicitly considering individual phonon vibrational modes. figure 5. demonstrates the temperaturedependent nature of κl. our data shows the trend κl (tinisn) < κl (hfnisn) < κl (zrnisn) throughout the considered temperature range. as the temperature increases, the κl decreases and becomes less temperature dependent at higher temperatures. this is because of the increased lattice scattering due to increased anharmonicity. the greatest difference between values of κl from both approaches at room temperatures is for tinisn and zrnisn. the deviation in values of κl between tinisn and zrnisn is by 20.97% and 26.81% from the phonon band slope of dfpt and qha model respectively. on increasing temperature the deviation in the values of κl decreases. despite having high κl at room temperature, these compounds exhibit low κl at elevated temperatures, making them suitable for hightemperature te applications and can have better zt values. our calculated values by both approach are compared to those reported in quinn et al.[3] (ref. [3])in table 3. the calculated values of κl in present work by dfpt approach agree within (1.36%8.06%) and values by qha model agree within (0.13%-1.65%) to those values reported in ref. [3]. the κl values reported in ref. [3] used debye callaway’s model considering umklapp scattering only. however, if grain boundaries, point defects, and electron-phonon interactions were accounted, κl values would be much lower. phono3py, solving boltzmann transport equation using the relaxation-time approximation (rta-bte), reports κl values < 10 wm−1k−1 for these compounds by considering anharmonicity resulting from phonon-phonon scattering, mass disorder and grain boundary effects [48, 49]. the values κl are 14.5, 16.7 and 15.3 wm−1k−1 calculated by rtapbe approach [24], 17, 18, 19 wm−1k−1 by dft and machine learning [23] and 16.8, 17.5 and 19.5 wm−1k−1 by machine learning algorithm [25] for tinisn, zrnisn and hfnisn respectively are lesser κl than our calculated values. although our data agrees the trend with these literature but are highly overestimated. slack’s model shows a similar tendency to overestimate κl values in comparison to shengbte for nbfesb and tafesb. the κl for nbfesb and tafesb at room temperature, as estimated by shengbte, are approximately 22 and 21 wm−1k−1, while those predicted by slack’s model are higher at 24 and 26 wm−1k−1, respectively [45]. slack’s model predicts higher κl values (12.69, 18.26, and 20.83) wm−1k−1 for mcobi (m = ti, zr, and hf) in ref. [50] compared to the values (11.02, 11.14, and 10.43) wm−1k−1 in ref. [51]. slack’s method offers the main advantage of being computationally intensive, but gives only a rough estimate and lacks accuracy for κl. the main drawback is that κl is indirectly derived from either elastic constants or acoustic phonons [45, 49]. despite having limited heat transfer capabilities, modes related to the optical branch can influence κl by interacting with acoustic vibrations. slack’s method efficiently predicts both extremely low and high κl for compounds in high-throughput computations, particularly in the identification of potential thermoelectric materials. the experimental κl values are significantly lower because even if the impurity concentrations are very low, the presence of small amounts of interstitial can cause significant disorder, leading to a substantial reduction in κl [2, 26]. in order to achieve closer agreement between computational results and experimental values for κl, the consideration of phonon scattering is essential. prakash khatri and n. p. adhikari/ bibechana 21 (2024) 12-22 19 table 3: comparison of physical properties of xnisn (x=ti, zr, hf) computed using phonon band slopes in dfpt and qha in thermo_pw codes, along with a comparison to ref.[3] that reported κl values for defect-free compositions based on the debye-callaway model considering umklapp scattering. compound approach vl (m/s) vt (m/s) v (m/s) θd (k) γ κl (wm−1k−1) tinisn slopes 6060.54 3358.89 3741.69 428.51 1.64 28.61 thermo_pw 5672.68 3125.60 3467.67 397.13 1.47 29.04 ref.[3] 5426.00 3062.00 3406.00 392.00 1.58 29.00 zrnisn slopes 6021.41 3380.13 3761.50 417.54 1.60 34.61 thermo_pw 5103.90 3069.61 3394.99 376.85 1.37 36.79 ref.[3] 5498.00 3149.00 3498.00 390.00 1.53 37.40 hfnisn slopes 4900.15 2815.22 3126.77 348.65 1.51 29.85 thermo_pw 4674.76 2752.94 3049.43 339.99 1.43 31.59 ref.[3] 4191.00 2503.00 2770.00 311.00 1.38 31.40 figure 5: variation of lattice thermal conductivity of xnisn compounds with temperature using slack’s model with velocity determined from phonon bands by dfpt and qha model in thermo_pw suite. 4 conclusions and concluding remarks the properties of xnisn compounds, such as their structural, electronic, magnetic and phonon characteristics, are computed through dft and dfpt. the calculated equilibrium lattice constants for tinisn, zrnisn and hfnisn are 5.958å, 6.154å, 6.113å respectively. our study reveals that tinisn, zrnisn and hfnisn are non magnetic semiconductors with indirect bandgap of 0.43 ev, 0.47 ev and 0.39 ev, respectively. the dos near the fermi level is mainly from 3d-ni orbitals in vb and ti, zr, and hf ’s 3d/4d/5d orbitals, respectively in cb with sn-5p orbitals having minor role in both bands. the phonon dispersion confirms the dynamic stability of the systems. the overlapping optical and acoustical phonon modes increase from tinisn to hfnisn. the κl variation with temperature was assessed using slack’s model, with phonon velocity analyzed with qha model and the slope of phonon bands by dfpt. the κl has observed to decrease as the temperature increases because of phonon scattering. the room temperature κl values of 28.61 wm−1k−1, 34.61 wm−1k−1 and 29.85 wm−1k−1 for tinisn, zrnisn and hfnisn respectively using dfpt follow same trend to those values 29.01 wm−1k−1, 36.79 wm−1k−1 and 31.59 wm−1k−1 respectively by qha model. the findings obtained through both approaches exhibit an agreement of 1.48%, 6.29%, and 5.82% for tinisn, zrnisn and hfnisn, respectively. the values in present study are overestimated in comparison to prior methods. the scattering effects are to be included for matching the computational and exprakash khatri and n. p. adhikari/ bibechana 21 (2024) 12-22 20 perimental values for κl. although the compounds have high κl at low temperatures, the decreasing values of them at elevated temperatures make them promising for high-temperature te applications. acknowledgements pk acknowledges the phd grants award no. phd-79/80-s&t-14 of ugc nepal and nt-14 of ictp/eau for partial support. npa acknowledges tu-npar-077/78 erg14. references [1] g. j. snyder and e. s. toberer. complex thermoelectric materials. nature materials, 7(2):105–114, 2008. 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[51] c. toher, j. j. plata, o. levy, m. de jong, m. asta, m. b. nardelli, and s. curtarolo. high-throughput computational screening of thermal conductivity, debye temperature, and grüneisen parameter using a quasiharmonic debye model. physical review b, 90(17):174107, 2014. introduction computational details results and discussion structural properties electronic and magnetic properties phonon spectrum and dynamical stability estimation of lattice thermal conductivity conclusions and concluding remarks bibechana vol. 20, no. 3, december 2023, 326–338 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar comprehensive review of lca studies in civil engineering ishwor thapa1, nirmal prasad baral2, krishna raj adhikari3,∗ 1department of civil engineering, sharda university, greater noida, india 2department of civil engineering, ioe pashchimanchal campus, pokhara, nepal 3ioe pashchimanchal campus, pokhara, nepal ∗corresponding author. email: adhikari.krishnaraj@gmail.com abstract this review explores the application of life cycle assessment (lca) within the domain of civil engineering, aiming to provide a comprehensive overview of current research, methodologies, challenges, and future trends. lca serves as a pivotal tool for assessing the environmental impact of infrastructure projects, yet gaps persist in its integration with socioeconomic dimensions, regional considerations, and dynamic modeling. by analyzing existing literature and scholarly discussions, this review identifies research gaps and proposes directions for enhancing the applicability and effectiveness of lca in civil engineering. moreover, it examines future trends such as the integration of advanced technologies, stakeholder engagement, and policy implementation, which are poised to shape the landscape of lca practices in the civil engineering sector. ultimately, this review paper contributes to the understanding of lca’s potential to drive sustainable decision-making in infrastructure development, paving the way for more informed and environmentally conscious practices. keywords life cycle assessment, civil engineering, environment, indicator, building, road. article information manuscript received: september 12, 2023; accepted: september 27, 2023 doi https://doi.org/10.3126/bibechana.v20i3.58552 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the field of civil engineering has witnessed a growing emphasis on sustainable practices, driven by the need to address the environmental impacts of construction and infrastructure projects. in this context, lca has emerged as a powerful tool for evaluating the comprehensive environmental implications of buildings and infrastructure throughout their entire life cycle. lca assesses the environmental burdens associated with each phase of a project, from raw material extraction to construction, operation, and end-of-life scenarios. lca is particularly relevant in the construction sector, which significantly contributes to energy consumption, resource depletion, and greenhouse gas emissions. 326 http://nepjol.info/index.php/bibechana adhikari.krishnaraj@gmail.com https://doi.org/10.3126/bibechana.v20i3.58552 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ishwor thapa et al./ bibechana 20 (2023) 326-338 327 1.1 historical development the historical development of the lca can be divided into distinct periods. the years 1970 to 1990 marked the "decades of conception," during which early studies emerged, addressing environmental concerns such as energy efficiency, pollution control, and waste management. the scope of analysis expanded to include resource requirements and waste flows, with pioneering studies on beverage containers conducted by the midwest research institute and basler hofman. interest waned briefly, but by the early 1980s, it surged. the period from 1990 to 2000 saw the "decade of standardization," characterized by coordinated efforts through organizations such as setac and iso to create a framework and terminology for lca. this era also saw the integration of lca into policy documents and the emergence of impact assessment methods. the following decade, 2000 to 2010, was labeled the "decade of elaboration." diverse lca methods were explored, ranging from economic and social impacts to dynamic and risk-based assessments. the field has expanded to cover not only environmental aspects but also societal and economic dimensions. the future (2010-2030) was anticipated as the "decade of life cycle sustainability analysis," emphasizing a broader approach encompassing environmental, economic, and social indicators and spanning various levels of analysis from product to economy-wide assessments. this phase of development aims to address complex sustainability challenges through an integrated and transdisciplinary framework [1]. 1.2 need of lca in civil engineering the 2030 agenda’s 17 sustainable development goals (sdgs) were adopted by global leaders in january 2016. concurrently, the paris agreement emerged from cop21 in november 2016, uniting countries to limit global temperature rise below 2 degrees celsius. by april 2018, 175 parties had ratified the agreement, with 10 developing nations outlining climate change response plans. climate change disregards borders, as evidenced by rising greenhouse gas emissions impacting weather patterns and sea levels [2]. a distinct sdg targets urgent climate action. life cycle assessment aids sustainability experts, designers, and engineers in evaluating products and systems alongside alternatives. to ensure unbiased comparability, the international organization for standardization (iso) established global benchmarks, with the european committee for standardization (cen) enhancing assessments for specific domains such as construction materials. a new cen standard under development focuses on sustainability assessment methodologies for civil engineering projects [3]. this article provides an in-depth overview of the latest developments in life cycle assessment (lca) within civil engineering. this section covers the tools used for analysis and the databases containing life cycle inventory (lci) data. the article also includes constructive criticisms addressing both the limitations of lca and the practical challenges that have arisen. the main objective of this study is to enhance our understanding of how lca is applied in civil engineering. this, in turn, encourages the use of lca as a tool for making informed decisions in managing infrastructure projects. furthermore, this article aims to establish new criteria for designing with the environment in mind. 2 basic framework of the lca life cycle assessment (lca) is a standardized approach used to systematically analyze the environmental impacts of a product or service from its inception to its functional end. it encompasses stages such as raw material acquisition, production, usage, maintenance, and end-of-life. these impacts include resource depletion, human health, and ecological well-being [4]. despite its current application in various industries with diverse methodologies, lca’s origins date back to the 1970s. while iso standards such as 14040 and 14044 provide guidance, they lack practical specifics [5]. 2.1 phases of lca life cycle assessment (lca) consists of four distinct phases. the first phase involves defining the goal and scope of the assessment and setting the boundaries and objectives. in the second phase, the life cycle inventory (lci) is compiled, where all relevant data on inputs, outputs, and processes within the system boundary are collected. the third phase, known as life cycle impact assessment (lcia), evaluates the potential environmental impacts of the identified inputs and outputs. finally, in the fourth phase, the results are interpreted, providing meaningful conclusions and recommendations based on the assessment’s goals and findings [6]. the important phases involved in lca in civil engineering and other important issues are discussed below. figure 1 below shows the lca framework. goal and scope the lca process begins by defining the goal and scope, which are crucial for selecting methodology and categories. clear articulation of the study’s scope, purpose, and assumptions, including lifecycle phases, future scenarios, and product components is pivotal. this step, which is mandatory in each lca study, significantly shapes its direction and ensures transparent communication ishwor thapa et al./ bibechana 20 (2023) 326-338 328 post-study. the scope involves setting the system boundary and level of detail, both influenced by the intended lca result use and the subject under examination. the scope of lca varies widely based on its goal, making it essential and variable across cases [7]. life cycle inventory the life cycle inventory (lci) involves tracking the inputs and outputs related to a product, requiring extensive regional and global data. the process considers energy and raw materials as inputs, and environmental emissions such as gases, liquids, and solids as outputs. gathering data for energy, transportation, materials, and waste from sources such as factories, governments, and scientific journals is essential. lci analysis compiles input/output data within the system boundary, tailored to the study’s goal. specific case data or general databases such as ecoinvent can be used [8]. various specialized lca tools and software are available for conducting lcas with different levels of detail. life cycle impact assessment (lcia) the life cycle impact assessment (lcia) serves to evaluate the life cycle inventory outcomes of an analyzed system. in this process, the various outputs obtained from the life cycle inventory (lci) are adjusted by a factor based on the unit of measurement. this adjustment assigns the outputs to specific impact categories such as global warming, land use, water use, acidification, and eutrophication. this step is referred to as "characterization." the software provides predefined lci methods for this purpose. the quantified impact resulting from characterization can then be compared with a reference value, known as "normalization." in addition, quantified impacts can be given significance values, unique to each impact category, for the calculation of a single consolidated outcome. this process is termed "weighting." these significance values are determined on the basis of factors including economic, political, and social considerations [6]. interpretation interpretation in lca refines and explains the multitude of results to derive meaningful conclusions. interpretation amalgamates inventory analysis and impact assessment findings coherently with a predetermined goal and scope. this phase unveils potential limitations, drawbacks, and uncertainties [6]. summarizing and discussing lci and lcia results forms the interpretation stage. it leads to conclusions, recommendations, and decision-making aligned with the defined goal and scope. multicriteria analysis (mca) can yield a single weighted outcome, overcoming the need for separate results from each impact category. employing sensitivity analysis reveals if uncertain inputs significantly influence outcomes, possibly necessitating a more extensive inventory analysis [9]. 2.2 different life cycle models for lca to assess a product’s life cycle, understanding its stages is essential. the life cycle typically involves five phases: raw material extraction, manufacturing and processing, transportation, usage and retail and waste disposal. various life cycle models exist, with four common ones: cradle-to-grave analyzes impact across all five steps, whereas cradle-to-gate assesses until factory exit. cradle-to-cradle integrates recycling, closing the loop, whereas gateto-gate focuses on specific value-added processes. environmental product declarations (epds) certify lca findings, and there is a specialized wellto-wheel approach for transport fuels and vehicles, ensuring precision in emissions and energy calculations [3]. 2.3 lca tools and databases licensed software tools for lca, notably gabi, and simapro, utilize databases such as gabi, ecoinvent, elcd, u.s. lci, idea, and input-output (i-o) for comprehensive analysis. bedec-itec focuses on construction with energy, co2, and pricing data[8]. comparative reviews of constructionoriented databases highlight ecoinvent and gabi as superior, due to qualitative aspects. ecochain, oneclicklca and openlca are some other alternative lca tools. limited free databases prompt reliance on licensed options, hindering wider lca application [10]. accessible databases are essential; their absence restricts lca studies to experts using licensed software, limiting its broad adoption. table 1 below shows the advantages and disadvantages of the lca tools and database. in summary, lca tools offer valuable capabilities for assessing the environmental impacts of products and processes. however, their cost, complexity, and dependence on databases can limit their widespread adoption, particularly among smaller organizations and those with limited expertise in lca methodology. accessible and current databases are crucial for accurate and meaningful lca studies. figure 2 shows the cost optimization process through lca using different lca tools and a database. ishwor thapa et al./ bibechana 20 (2023) 326-338 329 table 1: advantages and disadvantages of lca tools and databases advantages disadvantages 1.comprehensive analysis 1.cost 2.qualitative aspects 2.limited free database 3.construction focus 3.complexity 4.alternative options 4. database dependence 5.resource intensive 6.data availability 7.subjectivity 8.constant updates figure 1: lca framework. figure 2: cost optimization through life cycle cost analysis. 3 current practice of lca in civil engineering in the current practice of life cycle assessment (lca) in civil engineering, the focus is on evaluating the environmental impacts of infrastructure projects from cradle to grave. lca considers the entire life cycle of a structure, including raw material extraction, construction, operation, maintenance, and eventual demolition or disposal. advanced software tools and databases are used to model and analyze the various inputs, outputs, and environmental burdens associated with each phase. this aids engineers in making informed decisions to minimize resource consumption, energy use, emissions, and waste generation, ultimately leading to more sustainable and environmentally conscious design and construction practices. in this review, only the structural, geotechnical, highways and construction material domains of civil engineering will be discussed. 3.1 structural engineering in the current practice of life cycle assessment (lca) in the field of structural engineering, the emphasis is on assessing the environmental impacts of building and infrastructure systems. this involves analyzing the complete life cycle of structures, considering factors such as material selection, construction methods, operational energy use, and end-of-life scenarios. engineers use specialized software and databases to quantify the environmental burdens associated with different structural options. majid bahramian & kaan yetilmezsoy conducted a two-decade study on the development of life cycle assessment of the building industry from 1995 to 2018 [11]. the analysis reveals that there was a greater emphasis on studying shorter buildings (1 to 5 floors) compared to taller ones (5 or more floors) in terms of life cycle assessment. studies on shorter buildings, mainly residential, were about twice as numerous as those on taller buildings, where commercial structures garnered more attention. most commonly studied were the stages of manufacturing and usage, with a focus on impact factors such as global warming potential and embodied energy. for tall buildings, embodied energy values varied widely from 0.533 mj/m² to 883.1 gj/m², whereas for short buildings, they ranged from 0.21 to 374.4 gj/m². in terms of ishwor thapa et al./ bibechana 20 (2023) 326-338 330 global warming potential, tall buildings emitted between 10 and 10,010 kg co2-eq/m² annually, but certain studies highlighted how timber structures could reduce emissions by 234.8 to 1338 kg co2eq/m². emissions for shorter buildings ranged from 0.07 to 35,765 kg co2-eq/m², with timber structures lowering emissions by 12.9 to 361 kg co2eq/m². lifespan varied widely, from 20 to over 100 years, for different building types in life cycle assessment. functional units, the measurement units used, also differed substantially, with most using "m²" (61%), while "whole building" was used in about 20% of studies, showing a lack of standardization. ecoinvent was the most commonly referenced database (65%) for building life cycle assessment, followed by the university of bath ice (11%), the u.s. database (9%), and the australian material inventory database (7%). among computer software tools, simapro was most frequently cited (40%), followed by athena impact estimator (7.5%) and gabi software (4%). the study underscores that variations in building aspects (design, materials), lifespan, functional units, and scope hinder direct comparisons of research findings [11]. in recent years, major focus areas in building lca research have been life cycle energy assessment, life cycle carbon emissions assessments, lca of building refurbishments, dynamic lca of buildings, uncertainty analysis in lca of buildings, integration of lca in building rating systems, integration of lca with lcc and social lca and bimbased life cycle assessment of buildings [12]. a recent study by fatma abdelaal and brian h.w. guo suggests that using building information modeling (bim) and life cycle assessment (lca) for environmentally friendly buildings is not yet fully developed. there is a significant connection between the importance of bim and lca for these buildings. the people involved view bim and lca positively, seeing their potential for integration. however, the actual use of bim and lca does not match these positive views, indicating a need for substantial efforts to effectively implement and integrate them into green buildings [13]. 3.2 highway engineering currently, researchers focus on the field of lca in highway engineering domains, including developing advanced methodologies to quantify environmental impacts, integrating lca into decisionmaking processes, and exploring innovative materials and technologies to enhance sustainability in infrastructure projects. researchers aim to optimize design and construction strategies, minimize energy consumption, emissions, and resource depletion, and promote the adoption of greener transportation solutions to create more resilient and environmentally friendly transportation systems. a study provides a comprehensive review, highlighting research gaps, including areas such as inventory analysis, and locally relevant data collection, addressing aspects such as surface roughness, noise, lighting, and albedo, considering the temporal and consequential aspects of the pavement life cycle and conducting sensitivity analyses [14]. in another study, the use of innovative construction techniques such as 3d printing is being researched [15]. a recent study gathered past research on highway pavement studies, analyzed life cycle steps and environment impact indicators and proposed a method for selecting flexible road pavement structures through stages including design, cost analysis, life cycle impact assessment, and integration of impact assessment with costs. the findings suggest that pavement with a bitumen-stabilized base containing recycled material performs best in terms of cost and environmental impact assessment, given a specific design criterion, while highlighting the influence of design parameters on pavement choices [16]. another study reviewed various lca methodologies for pavement and performed a comparative life cycle assessment (lca) to assess the environmental impacts of using recycled concrete aggregates (rcas) instead of natural aggregates in hot mix asphalt (hma) production. the analysis found that mixes with 15% and 30% rca replacements were more environmentally friendly than the conventional mixture, but the mix with 45% rca showed poorer environmental performance than the conventional mix [17]. this combined investigation of structure and environment illustrates the benefits of replacing primary natural aggregate (na) with recycled construction and demolition waste aggregate (cdw-ra) in subbase layers for flexible and semi-rigid road pavements. various pavement structures featuring a 0.30 m subbase layer constructed from four materials, including two unbound and two cement-stabilized variants using na and cdw-ra, were compared in terms of their structural behavior. additionally, the study evaluated environmental impacts through a life cycle assessment (lca) [18]. guangli made an lca framework for bridge assessment[5] and also performed lca on a soil steel composite bridge [19]. according to [20], 67 lca studies found in the literature were assessed and categorized into four groups: flexible pavement, rigid pavement, mixed pavement, and road infrastructure. the analysis revealed that 80% of the studies were conducted in developed nations, with only 20% from developing countries. a significant portion of road pavement lca studies (about 76%) concentrated on material and construction phases, primarily assessing global warming potential and energy demand. a smaller proportion (10-15%) considered a broader range of ishwor thapa et al./ bibechana 20 (2023) 326-338 331 impact categories and employed commercial software such as gabi and simapro for impact assessment. of the 67 studies, 19 pertained to flexible pavements, 4 to rigid pavements, 30 to a combination of both, and 14 to road infrastructure. notably, certain road infrastructure components, such as bridges, tunnels, drainage, lighting, and road marking, were analyzed, whereas others, such as culverts, toll plazas, and vehicle underpasses were excluded. most studies relied on secondary or background data for life cycle inventory. only 18 of the 67 studies conducted sensitivity analyses and only 6 performed uncertainty analyses. this study highlights the need to encompass all related infrastructures alongside road pavements and emphasizes a greater focus on sensitivity and uncertainty analyses within transportation sector studies. therefore, future lca studies involving road infrastructures should address these negative repercussions and incorporate social and economic impacts via multicriteria decision making to enhance lca as a robust tool for sustainable decision-making [20]. 3.3 geotechnical engineering within the domain of general geotechnical engineering literature, the primary focus of most papers is developmental aspects. these articles also explore approaches to sustainability in geotechnical engineering beyond the realm of lca and life cycle cost analysis (lcca). alternatively, they might involve evaluations of ongoing research endeavors. a study examined sustainability within the realm of geotechnical engineering, emphasizing the importance of resilience and system recovery. they investigated various assessment techniques, including geospear, lca, and lcc. the authors introduced a composite sustainability index that amalgamates resource efficiency, environmental impact derived from lca, and socioeconomic repercussions during the design process [21]. another study conducted a comprehensive review of assessments with an environmental focus on the life cycles of geotechnical systems. this exploration identified gaps that could drive future research. while the review’s scope was not all-encompassing, it yielded recommendations for future research needs. these suggestions addressed the limited coverage of impact categories in the existing literature and the absence of a standardized lca framework. the review also acknowledged the impediments posed by the availability and quality of location-specific data, alongside the complexities of evaluating diverse soil profiles and design alternatives [22]. raymond meticulously analyzed the categories of impact and environmental indicators in the life cycle impact assessment (lcia) phase. specific impact categories, such as energy and global warming, were more frequently used than others. impacts related to land use and soil received less attention, and the corresponding indicators for these categories were less developed than those related to energy and global warming [23]. in the category of ground improvement, praticò employed lcca to develop a model for the selection of stabilizers and stabilization methods for subgrade soil in lowvolume road projects. their method integrated the extra stabilization costs into the construction expenses for treated sections, consequently minimizing long-term maintenance costs [24]. regarding the category of retaining walls and slope support, zastrow evaluated 30 cost-optimized earthretaining walls using lca, relying on input data from the ecoinvent database. the quantities of concrete and steel, as well as the recycling status of steel, have implications for the resulting environmental impact [25]. similarly, das examined the sustainability and resilience aspects of slope stabilization. their sustainability evaluation encompassed lca, socioeconomic consequences, and other factors, each of which was weighted based on their relative significance. through multicriteria analysis, these weighted indicators yielded resilience and sustainability indices for each stabilization technique. the technique with the lowest index was proposed for implementation. this proposed framework enabled the integration of multiple assessment methods into a single comparable index [26]. in the remaining categories, research was less extensive, and the number of published papers was lower than that other categories. in the category of "cement related to ground improvement," chang carried out a comparative study of costs and environmental impacts between the use of biopolymers and traditional portland cement for ground improvement applications [27]. ishwor thapa et al./ bibechana 20 (2023) 326-338 332 table 2: waste materials in concrete researched in the past three years author journal waste material used r sharma [28] innovative infrastructure solutions waste coarse aggregate x peng et al [29] journal of cleaner production waste coarse aggregate a shukla et al [30] materials today: proceedings waste marble dust z he et al [31] powder technology recycled concrete powder z duan et al [32] construction and building materials waste coarse aggregate and recycled concrete powder b qi et al [33] processes recycled epoxy d yang et al [34] case studies in construction materials recycled concrete powder s vaishnavi devi et al [35] materials today: proceedings waste coarse aggregate d mostofinejad et al [36] journal of building engineering waste coarse aggregate, recycled fine aggregate, and waste glass z ma et al [37] journal of cleaner production recycled concrete powder j xiao et al [38] journal of building engineering recycled concrete powder md. jahidul islam [39] construction and building materials waste coarse aggregate fernando a. n. silva et al [40] buildings waste coarse aggregate and recycled fine aggregate j kim, h jang [41] journal of cleaner production recycled concrete powder y guo et al [42] construction and building materials recycled concrete powder a aldemir et al [43] journal of building engineering waste coarse aggregate j. jolly abraham et al [44] materials today: proceedings waste coarse aggregate i patra et al [45] sustainable energy technologies and assessments waste coarse aggregate j yang et al [46] journal of cleaner production wet-grinded submicron autoclaved aerated concrete waste k khan et al [47] materials waste marble dust a zhou et al [48] resources, conservation, and recycling engineering sediment waste h al-mosawe et al [49] buildings waste coarse aggregate ishwor thapa et al./ bibechana 20 (2023) 326-338 333 figure 3: lca for building construction. figure 4: lca for geo-technical engineering projects. 3.4 construction material table 2 provides various research that has chosen waste materials, including waste coarse aggregate, waste marble dust, recycled concrete powder, recycled epoxy, waste glass, wet-grinded submicron autoclaved aerated concrete waste, and engineering sediment waste, among others. the diverse range of waste materials explored in these studies reflects a growing interest in finding eco-friendly and cost-effective alternatives to traditional construction materials. these research efforts contribute to the broader goal of reducing environmental impact and promoting sustainability in the construction sector, potentially leading to innovative solutions and practices for the industry’s future. to gain a deeper understanding of each study’s specific findings and implications, access to individual papers is necessary. similarly, figure 4 shows the waste materials used for concrete production over the past three years. the most used waste material was waste coarse aggregate. over the past twenty years, research has been directed toward various aspects of the field. for instance, there has been a focus on incorporating construction and demolition waste (cdw) materials as aggregates into new concrete mixtures, as exemplified by references [50]. furthermore, novel design approaches, including the utilization of building information modeling (bim), have emerged, as indicated in the references [51]. additionally, other studies, such as those cited in references [52] have evaluated the environmental advantages of substituting virgin materials with cdw, while minimizing the impact on mechanical properties. within the construction field, especially in cdw, lca is commonly employed to select the optimal scenario among landfilling, recycling, and incineration, as discussed in [53]. research in the past two decades has focused on incorporating construction and demolition waste (cdw) materials in new concrete mixes, exploring design approaches such as building information modeling (bim) and assessing the environmental benefits of replacing virgin materials with cdw without compromising mechanical properties. these efforts commonly employ life cycle assessment (lca) to evaluate sustainability impacts across various phases of building and infrastructure projects, but challenges remain in integrating lca into design considerations and encompassing all lifecycle stages, as highlighted by various literature reviews [54]. zhuocheng conducted a comprehensive investigation and analysis encompassing 62 peer-reviewed articles, examining aspects such as goal and scope definition, life cycle inventory analysis, impact assessment, and interpretation of the use of timber in mass construction. these studies reveal a broad range of variations in terms of scope, duration, system boundaries, data sources, and indicators. the research covers multiple scales, including building materials, components, structures, entire buildings, and even urban contexts, with a primary focus on comparing the life cycle assessment (lca) of reinforced concrete (rc) and cross-laminated timber (clt) constructions. the articles predominantly assess indicators such as global warming potential (gwp) and life cycle energy, indicating that mass timber buildings exhibit, on average, 23.00% higher embodied energy than rc alternatives, while rc buildings demonstrate 42.68% higher embodied greenhouse gas (ghg) emissions than mass timber alternatives [55]. alireza conducted a systematic review of concrete mixtures and examined the literature concerning the environmental effects related to life cycle assessment (lca). the analysis encompassed two categories of environmental impact indicators: midpoint and endpoint. in the realm of midpoint indicators, various parameters were scrutinized, including global warming potential, water depletion, agriishwor thapa et al./ bibechana 20 (2023) 326-338 334 cultural land use, fossil depletion, particulate matter, acidification potential, embodied energy, water pollution, ozone layer depletion, eutrophication potential, human toxicity, and abiotic depletion potential. within the endpoint indicator category, discussions revolved around human health, ecosystem quality, and resource depletion. it was noted that among the various environmental impact indicators, global warming potential and acidification potential were the most frequently employed in the context of lca for concrete mixtures. in addition, the author compiled a concise summary of the stages in lca, taking into account factors such as the country of origin, system boundaries, functional units, effects of service life and compressive strength, sensitivity analysis, and the environmental impact method employed for conducting the lca. the study revealed that the "crate to gate" approach was the most commonly utilized system boundary in the lca of concrete mixes, with the cml method being the most frequently employed environmental impact assessment method [55]. 4 limitations and challenges of lca in civil engineering in the realm of civil engineering, conducting accurate lcas encounters numerous challenges. one of the foremost hurdles lies in sourcing precise and comprehensive data, given the multifaceted nature of project life cycles and the inconsistencies in data quality across sources. this is compounded by the scarcity of standardized databases and the resulting uncertainty in assessment conclusions. moreover, the fast-paced and resource-constrained environment of civil engineering projects often clashes with the time and expertise required for thorough lca. the industry’s deeply ingrained practices and limited awareness about the benefits of lca can further hinder its integration, while the absence of standardized methodologies prevents cohesive comparisons between studies. the intricacies of civil engineering projects, marked by uncertainty, cumulative effects, and adaptability, make quantifying environmental impacts and setting accurate system boundaries particularly intricate. implementing life cycle assessment (lca) in civil engineering projects presents a range of challenges that require careful consideration. foremost among these challenges is the acquisition of accurate and comprehensive data for all stages of a project’s life cycle, a task that can be alleviated through improved data management systems and collaboration with industry organizations. defining clear system boundaries, fostering interdisciplinary collaboration, and addressing the shortage of lca expertise are essential to navigating the complexity of lca. standardization efforts and adherence to established guidelines can help ensure consistent and reliable results. additionally, integrating lca into project planning, educating stakeholders, and advocating for supportive policies can help overcome resistance to change. the dynamic nature of environmental data necessitates sensitivity analysis and scenario planning, while effective communication strategies tailored to different audiences are vital for sharing lca findings. overall, these strategies can help civil engineering projects embrace lca and contribute to more sustainable infrastructure development. figure 5: waste materials used for concrete production in the past three years. figure 6: lca for construction materials in civil engineering projects. ishwor thapa et al./ bibechana 20 (2023) 326-338 335 5 research gaps and future trends in the context of civil engineering, lca is a vital tool for evaluating the environmental impacts of infrastructure projects, however, certain research gaps impede its holistic integration. while lca has primarily addressed environmental aspects, there is a need to incorporate socioeconomic considerations such as community impact and economic development. existing lca models are often static, lacking adaptability to dynamic project changes, user behaviors, and external factors. cultural influences on project outcomes are overlooked, warranting investigation into how cultural factors shape lca outcomes. resilience and adaptability also remain underexplored, as is the enhancement of data quality and availability for lca studies. moreover, lca’s focus on short-term impacts neglects longterm consequences, necessitating research to incorporate maintenance and adaptation costs. despite its policy potential, gaps persist in understanding how lca insights inform policy decisions. addressing these gaps is poised to drive lca in civil engineering toward a more comprehensive and impactful future. the future of life cycle assessment (lca) in civil engineering is expected to involve a holistic approach integrating environmental, social, and economic aspects. this includes evaluating social impacts and long-term economic viability, aided by advanced data analytics, real-time monitoring through digital twin technology, and the application of circular economy principles for waste reduction and material reuse. collaborative stakeholder engagement, machine learning, and ai are expected to enhance lca accuracy, while lca findings could play a more significant role in shaping policies and regulations. integrating lca with life cycle cost analysis will provide a comprehensive view of design trade-offs, aligning financial and sustainability objectives for more informed decisionmaking. overall, lca’s evolution in 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https://doi.org/10.1016/j.resconrec.2019.10440 https://doi.org/10.1016/j.resconrec.2019.10440 10.1016/j.buildenv.2022.109320 https://doi.org/10.1080/19648189.2022.2078885 https://doi.org/10.1080/19648189.2022.2078885 introduction historical development need of lca in civil engineering basic framework of the lca phases of lca different life cycle models for lca lca tools and databases current practice of lca in civil engineering structural engineering highway engineering geotechnical engineering construction material limitations and challenges of lca in civil engineering research gaps and future trends 102 bibechana issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: department of physics, mahendra morang a.m. campus, tu, biratnagar, nepal bibechana 19 (1-2) (2022) 102-110 analysis of sarscov-2 cases in nepal using different models oat bahadur dhakal1, roshan chalise*1,2 and raju khanal 2 1patan multiple campus, tribhuvan university, lalitpur, kathmandu 44700, nepal 2central department of physics, tribhuvan university, kirtipur, kathmandu 44613, nepal email: plasma.roshan@gmail.com article information: received: june 03, 2021 accepted: february 18, 2022 keywords: epidemic exponential model logistic model sir and sird model abstract the world has faced many epidemics during its evolution of human civilization from the influenza epidemic in 1200 bc, to severe acute respiratory syndrome sarscov-2 in 2019, each epidemic has become fatal and people have died from thousands to millions. the epidemic pattern of covid-19 in nepal is analyzed and predicted using the exponential, logistic, sir (susceptible infectious recovered), and sird (susceptible infectious recovered deceased) models. the cumulative instances of an outbreak rise exponentially at first, described by the exponential model but there is a point of inflection after some time where the curve nearly turns linear which is predicted by the logistic model. the sir and sird models are used to anticipate the number of cumulative cases of covid-19 for the 400 days based on information supplied by the ministry of health and population. based on real-time data and data from our simulation, we can conclude that by strengthening the efficiency of social isolation and lockdown, we could significantly reduce the spread of covid-19 in our country. doi: https://doi.org/10.3126/bibechana.v19i1-2.46400 this work is licensed under the creative commons cc by-nc license. https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/bibechana mailto:plasma.roshan@gmail.com https://doi.org/10.3126/bibechana.v19i1-2.46400 https://creativecommons.org/licenses/by-nc/4.0/ dhakal et al / bibechana 19 (1-2) (2022) 102-110 103 1. introduction looking back to history, infectious diseases are the companion of human beings. even in this modern era epidemic outbreaks are frequent. the different epidemic models have been extensively used for analyzing and forecasting epidemiological tactics together with unfolding of hiv, sars, influenza, and sarscov-2. mathematical models have helped in describing the quantitative facts estimating the epidemic and providing tips to the authorities in dealing with the outbreak. they use fundamental assumptions and cumulative facts in combination with parameters for numerous infectious illnesses and to identify the parameters to calculate the consequences of various involvements. the modeling also can help to determine which precautions are to be taken in future. covid-19 is of extreme difficulty as it has hastily spread throughout the globe causing widespread deaths. like many developing countries with sub-optimal health systems and capacity, nepal has already suffered significantly. the hunan seafood market in china is regarded as the first location where an outbreak of pneumonia without a known cause occurred, attracting international attention. when an outbreak first began, the chinese government responded quickly with a total lockdown and mass protection. chinese researchers discovered a novel coronavirus (cov) in patients in wuhan on january 7, 2020 [1]. this virus is genetically linked to the coronavirus that caused the sars pandemic in 2003 due to which it was given the name sars-cov-2 by the international committee on virus taxonomy (ictv) on february 11, 2020. when the number of confirmed cases reached 1, 18, 319 with 4, 292 deaths, who (world health organization) gave the name covid-19 and notified the disease as worldwide pandemic on march 11, 2020. canto et al. [2] used a variety of sird based approaches and the seir (susceptible exposed infectious recovered) model to analyze covid-19 dynamics in mexico. according to their findings, the largest number of infected cases would be reported on august 15, with a total of 5, 52, 420 infections and 58, 653 fatalities in mexico on august 1. crokidakis [3] used the siqr (susceptible infectious quarantine recovered) model to analyze data from the brazilian department of health from february 26 to march 25, 2020, to look at the early evolution of the covid-19. their results estimated that the basic reproduction number was 5.25 and the epidemic rate is doubled 2.72 days. using the sird model, chatterjee et al. [4] investigated the course of the covid-19 outbreak in india, predicted the time for infection peak. adhikari and marahatta [5] studied the pandemic of a novel corona virus in nepal using logistic, sir, and arima (autoregressive integrated moving average) model and expected that the total number of confirmed cases to be around 64,000 and the highest number of confirmed cases around 1,500 on the 111th day on july 11 from march 23, 2020. hamzah et al. [6] forecasted the worldwide covid-19 outbreaks estimating the total number of confirmed cases and its occurring time. deep learning models were used by arora et al. [7] to predict and analyze covid-19 positive cases in india. the suggested method produces high accuracy for short-term predictions, with daily predictions having an error rate of less than 3% and weekly predictions having an error rate of less than 8%. qin et al. [8] used social media search index to predict the number of new cases of covid 2019. in malaysia, alsayed et al. [9] estimated the epidemic peak and infected cases for covid-19 and anticipated the time for peak of new cases to be followed by a 30-day period of uncertainty. huang et al. [10] investigated the global covid-19 pandemic forecast trend. with a case study of wuhan, ndairou et dhakal et al / bibechana 19 (1-2) (2022) 102-110 103 al. [11] investigated the mathematical modeling of covid-19 transmission kinetics. sarkar et al. [12] used susceptible (s), asymptomatic (a), recovered (r), infected (i), isolated infected (iq), and quarantined susceptible (sq), collectively expressed sariiqsq to predict the cases of covid-19 in india. they discovered that quarantining susceptible individuals can successfully reduce the basic reproduction number by reducing the contact rate between uninfected and infected individuals. the gaussian mixture model was used by singhal et al. [13] to predict the covid-19 outbreak, the overall number of expected cases and deaths. covid-19 in asia was studied by aviv-sharon et al. [14] using a generalized logistic growth model. to anticipate the trend of the covid-19 outbreak in iran, ahmadi et al. [15] employed an epidemic projection model and least square error with percentage error. kuniya [16] predicted the epidemic peak of coronavirus disease in japan using seir model. bhandary et al. [17] analyzed the pandemic scenario of nepal during the first phase of lockdown from 23rd january 2020 to 30th april 2020. they recommended keeping social distance and a stay-at-home policy in the covid-19-affected district, as well as implementing rigorous lockdown. dmitry [18] estimated the effects of pandemic outbreaks on global supply networks using simulations based on the coronavirus outbreak scenario. they showed how to analyze and forecast the effects of epidemic outbreaks using simulation-based approach. wangping et al. [19] used extended sir model to predict and compare the trends of the covid-19 outbreak in italy and hunan, china, with covid-19 time-series data from january 22 to april 02, 2020. john et al. [20] were unable to predict the covid-19 epidemic, due to insufficient data input, incorrect modeling assumptions, and a variety of other factors. gatto et al. [21] investigated the prevalence and behavior of the covid-19 outbreak in italy, claiming that a series of mobility and human-to-human interactions restrictions reduced transmission by 45 percent. saez et al. [22] used generalized linear mixed models to examine the effectiveness of the spanish government’s response to the covid 19 outbreak. ceylan [23] used arima models to estimate the epidemiological pattern of covid-19 prevalent in italy, spain, and france from february 21 to april 15, 2020. in italy, spain, germany, and france, ding et al. [24] calculated pandemic trends and important epidemic aspects of covid-19. using the seir model they found the day for maxima of daily new confirmed cases for italy, spain, germany, and france would be on april 16, april 5, april 21, and april 19. wang [25] used mathematical models to describe applications, limitations, and potentials, implying the mathematical models that have long been employed in epidemiology to generate quantitative data and provide useful guidance for outbreak management and policy creation. bastos and cajueiro [26] used two versions of the sir model to simulate and anticipate the early course of the covid-19 pandemic in brazil. in order to determine the epidemic trend in wuhan, china, wang et al. [27] used an infectious disease dynamics seir model. giordano et al. [28] introduced sidarthe (susceptible infected diagnosed healed ailing recognised threatened extinct), a novel model that forecasts the course of an epidemic to aid in the planning of an effective control strategy. weitz et al. [29] designed and studied an epidemiological intervention model to aid in the maintenance of interactions required for the operation of critical goods and services while lowering the risk of transmission. the termination of social confinement and the danger of covid-19 re-emergence were investigated by lópez and rodo [30]. they recommended that lockdowns be maintained for at least two months to avoid the spread of the disease and the emergence of a 2nd wave of covid-19 infections. findings of a stochastic agent-based microsimulation model of the covid-19 outbreak in france were given by hoertel et al. [31]. dhakal et al / bibechana 19 (1-2) (2022) 102-110 104 a large number of works are reported on covid-19 modeling that is based in different countries, however, only a few works [5, 17] are published on forecasting the corona epidemic of nepal and also use only a few models, so we are interested to consider four models (exponential model, logistic model, sir model, and sird model) and study which one fits best with real data. this work is expected to help decision makers to estimate the development of epidemic outbreaks and their long-term effects in current and future pandemic crises. in the event of an epidemic outbreak, it can also assist in identifying essential parts of reducing risk, response, and recovery plans. 2. description of models covid-19 cases and deaths have surged over the world, requiring more attention to future epidemics and global risks. we have undertaken a comparative study of this epidemic in nepal using the four different models (exponential model, logistic model, sir model, and sird model). one of the models used is the exponential growth model which uses the following equations: (1) where variable ‘x’ is the time for required data, ‘a’ is the initial value, ‘b’ is the growth rate and ‘c’ is the time for initial data. a logistic function’s most general expression is (2) where ‘m’ stands for infection speed, ‘n’ stands for the day with the most infections, and ‘p’ stands for the total number of infected persons at the end. due to the dynamics of an epidemic, which is much faster than the birth and death rate, birth and death are often omitted in basic compartmental models. the following set of ordinary differential equations are used to define the sir [32] model (3) (4) (5) where sird model [33] is appropriate for an influenza-type disease, and helps to identify the population, who are susceptible of being infected, those who are infected, and those who have recovered and deceased. the susceptible population ns(t) decreases through contact with infected, at a rate given by , as (6) the infected population ni(t) increases through contact with infected (at a rate set by , decreases through recovery, at a rate γ, and also decreases through death, at a rate : (7) the recovered population nr(t) increases as the infected population recover, assuming that all recovered people are immune to being infected a second time in quick succession. (8) the deceased population nd(t) increases through death at a rate . (9) the fact that the member of all groups together must add up to the total population expressed as: (10) in order to introduce the effect of social distancing the equations (6) and (7) are modified as (11) where q is a function of time, represents the effectiveness of social distancing defined as , (12) with t in days, tq gives the count of number of days passed after social distancing measures are implemented, h is the heaviside step function: dhakal et al / bibechana 19 (1-2) (2022) 102-110 105 , (13) to include the effect of stopped isolation, say after tuq days (for “un-quarantine”), we modified the function q as: (14) 3. results and discussion the results of exponential, logistic, sir, and sird models are analyzed and compared with the real data of the covid-19 outbreak in nepal based on the information released by the ministry of health and population [34], government of nepal. the exponential model represents the uncontrollable spread of infection, but it cannot predict when the epidemic will terminate. it provides the idea that the number of infected cases rapidly increase in the early stages. the total infected population during january 22 to july 23, 2020, along with the prediction using the exponential model is shown in fig.1. fig. 1: total infected cases versus days started from january 22, 2020. the logistic model is that curve fitting and prediction outcomes heavily depend on past data, and it explains epidemic growth that will terminate in the future. cumulative infected case of 300 days starting from january 22, 2020, using a logistic model with real data fitted and is shown in fig. 2. the infection speed of the epidemic is found to be 9.31 along with the estimated maximum growth rate of confirmed covid-19 cases on 153 days (june 22, 2020). this calculation was made without assuming the effectiveness of lockdown, and social distancing. the total assumed population versus the number of days from 23rd march 2020 using the sir model is shown in fig. 3. it describes the covid-19 in such a way that susceptible, infected, and recovered persons were correlated to each other. when the initial date of the model was set to be 23rd march 2020 there were 2 total confirmed cases and 0 deaths. for this prediction, assumed that the total number of suspected persons will be 10,00,000 people among the total population of nepal. effective contact rate and recovery rate were considered 0.2 and 1/14 respectively. from the simulation, it is observed that the reproduction number is found to be 2.8. the peak of the infected persons is found at 110 days (which lies in the first week of july) and the curve gets flattened after 200 days. the total number of infected persons is found to be 2,75,135 along with 9,99,997 susceptible and 9,24,974 persons will be recovered up to 26th april 2021. fig. 2: cumulative infected cases versus days started from january 22, 2020. dhakal et al / bibechana 19 (1-2) (2022) 102-110 106 fig. 3: number of the assumed population versus days from march 23, 2020. considering the total susceptible population to be 106 the number of assumed population versus days (400) from march 23, 2020, without starting lockdown, is shown in fig. 4. at first, for the formulation of this model before lockdown, the assumed total population to be infected is 10,000,000 along with the data on march 23, 2020. on that day, the total number of cases was 2, deaths were 0, and recovered were 1. the reproduction number is assumed to be 2.4 along with a mortality rate of 0.004. thus, the result shows that 0.4 % (3,504) of total population will die, 87.6% (8,75,840) recover and 21.9 % (2, 18,887) will be infected after 400 days. fig. 4: number of the assumed population versus days from march 23, 2020, without lockdown effect. with the initiation of lockdown the nature of the number of population versus days (300) is shown in fig. 5. as the government of nepal has implemented lockdown from march 24, 2020, then the sird model has to be modified including different parameters such as social distancing, effective lockdown rate, introducing social distancing q0, and time of lockdown tq, which has been assigned to 0.1 and 1. introducing these parameters and implementing them 0.3 % (3,050) faced death, 76.3 % (7,62,620) recovered and 13.5% (1,34,710) get infected from covid-19. the number of infected has reduced from 2,18,887 to 1,34,710 and the number of deaths reduced from 3,504 to 3,050 with the introduction of lockdown. the prediction of future scenario after the government of nepal ended the lockdown on july 21, 2020 is depicted in fig. 6. it describes the total assumed population versus the number of days after the end of lockdown. for this, we have included that ro =2.1, m = 0.004, p=14, & q0 = 0.1, tq = 0, tuq = 120. it was found that 0.3% (3,499) faced deaths, 87.5 % (8, 74,798) recovered and 21.7% (2,16,926) get infected after the end of 400 days. the number of infected has increased from 1,34,710 to 2,16,926 with the implementation of lockdown from march 24, 2020, to july 21, 2020. fig. 5: assumed population versus the number of days from march 23, 2020, with the initiation of lockdown. dhakal et al / bibechana 19 (1-2) (2022) 102-110 107 fig. 6: total assumed population versus the number of days from march 23, 2020, with lockdown ends on july 21, 2020. conclusion in this work, we used the classic exponential, logistic, sir, and sird model to interpret the collected public data on the cumulative numbers of quarantined cases, recovered cases, and death cases from january 22 to july 23, 2020, which are published on a daily basis by the ministry of health and population of nepal [34]. the logistic model predicts the infection rate for nepal is 9.31 along with the infection number at 22 june 2020 is 19,529 ±7126. the sir model predicts the infection peak for nepal at the end of june 2020 and the total number of infected persons is found to be 2,75,135 along with 9,99,997 susceptible and 9,24,974 recovered persons after the end of 26 april 2021. sird model gives an idea of how social distancing (lockdown) helps to decrease the infection rate of covid-19. as the percentage of the total number of infected persons has decreased from 21.9 % to 13.5 % which is almost 84,177. the death trends have also decreased from 3,503 to 3,050 which are 453 less due to the implementation of lockdown. widespread social distancing can help to reduce the number of cases and limit the burden of the healthcare system. the earlier the social distancing the lower the number of cases would be. however, slacking off on social distancing could lead to a reemergence of the virus. specifically isolating the most vulnerable segments of the population can significantly reduce the overall mortality rate. the models used here are good for prediction and comparative studies. as these results depend heavily on data availability and their authenticity more realistic and continuous modeling has to be 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o. kermack and a. g. mckendrick, a contribution to the mathematical theory of epidemics, proc. r. soc. a 115 (2020) 700-721 https://doi.org/10.1098/rspa.1927.0118 [33] n. t. bailey, the mathematical theory of infectious diseases and its applications, 2nd edition (1975) london [34] ministry of health and population, nepal, https://covid19.mohp.gov.np/ 1. introduction 2. description of models bibechana vol. 21, no. 1, april 2024, 51–62 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar potential removal of arsenite from contaminated water using a fixed bed column packed with tio2-impregnated pomegranate peel powder bhoj raj poudel1,3, ram lochan aryal2, kedar nath ghimire3, hari paudyal3,∗ megh raj pokhrel3 1department of chemistry, tri-chandra multiple campus, t. u., kathmandu, nepal 2department of chemistry, amrit campus, tribhuvan university, kathmandu, nepal 3central department of chemistry, tribhuvan university, kathmandu, nepal ∗corresponding author. email: haripaudyal9@gmail.com abstract a dynamic biosorption of arsenite in a fixed bed column packed with tio2 impregnated pomegranate peel (pp@tio2) has been investigated in this work, which is important to identify the effectiveness and affordability of an adsorbent in actual practice. to create an active adsorption site for as (iii) ions, pomegranate peel powder (pp) was impregnated with tio2. under various operating parameters, the performance of a column packed with pp@tio2 for adsorbing as (iii) ions was evaluated. breakthrough curve modelling showed that the bed depth service time (bdst) and thomas models agreed well with the experimental data. the maximum column capacity of pp@tio2 using the thomas model was found to have resembled experimental value with high values of coefficient of determination. therefore from these results, we may anticipate that pp@tio2 can be a strong contender for the treatment of wastewater that has traces amount of the as (iii) ion in a fixed bed system. keywords pomegranate peel; removal; pp@tio2; as(iii); fixed bed column. article information manuscript received: november 20, 2023; revised: december 20, 2023; accepted: december 25, 2023 doi https://doi.org/10.3126/bibechana.v21i1.60048 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 51 http://nepjol.info/index.php/bibechana haripaudyal9@gmail.com https://doi.org/10.3126/bibechana.v21i1.60048 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ bhoj raj poudel et al./ bibechana 21 (2024) 51-62 52 1 introduction arsenic contamination in an aquatic environment has caused risk to aquatic plants and animals, and serious hazardous effects to humans even in very low concentrations [1, 2]. it can exist in several various oxidation states in aquatic environments, but the main states are as (iii) and as (v) [3]. arsenic is entered into groundwater not only by natural processes such as volcanic eruptions, dissolution of minerals ore, geochemical reaction, biological activities, etc., but also via anthropogenic sources such as wood preservatives, industrial effluents of metal processing, semiconductor, electroplating, mining, battery, pigments, dyestuff, and paints [4,5]. additionally, acid mine drainage wastewater contains a significant amount of arsenic [6]. studies reported that long-term exposure to arsenic concentrations above 100 ppb may cause blackfoot disease, hyperkeratosis, and cancers [7]. its contamination in food and water is the main way that humans are exposed to it. the maximum permitted limit (mcl) of 10 ppb for arsenic in drinking water has been established by the usepa and who because of its exposure concern and severe noxiousness [8–10]. as a result, effective and affordable arsenic removal techniques from polluted water are of emerging concern. conventional methods for the elimination of pollutants from contaminated water are ion exchange, electrocoagulation/co-precipitation, lime softening, reverse osmosis, ultrafiltration, nanofiltration, and resin chelation [6]. nevertheless, most approaches have practical drawbacks, including high costs, insufficient metal removal, the production and disposal of hazardous metal sludge, and unsuitability for water with traces of contaminants [11]. currently, adsorption is the most effective process for the removal of contaminants from water compared to other methods due to its simplicity, cost-effectiveness with high efficiency, potential for regeneration, and sludge-free operation [12]. recently, various low-cost non-conventional adsorbents have been utilized to sequester arsenic from contaminated water [2, 3, 13–17]. to date, most of the research on the adsorption of arsenic from aqueous solutions has been done in batch mode experiments. a sorbent utilized in this study is tio2-impregnated pomegranate peel, abbreviated as pp@tio2 hereafter. in our previous work, we focused on the as(iii) removal using pp@tio2 as an adsorbent and photocatalyst using batch mode experiment [4]. the pp@tio2 was proven to be an effective, ecological, profitable, and reusable biosorbent for sequestering arsenic from contaminated water. it was also observed that the adsorbed as(iii) was partly oxidized to as(v) on the adsorbent’s surface. the efficient application of biomassbased adsorbents for removing as(iii) in continuous flow fixed-bed column adsorption systems is not well documented [18–20]. therefore, careful attention to these details is needed to design the practical implementation of this investigated pp@tio2 and the design of industrial columns. for an industrial application or real wastewater refining, biosorption in a fixed-bed column packed with adsorbent is desirable [21–25]. thus, the laboratory size fixed-bed column’s experimental findings justify the design of an adsorption column for industrial use. as an extension of our earlier study [4], this work extensively investigated the effectiveness of pp@tio2 in as(iii) removal in a fixed-bed column mode. the biosorption capacity of spp@tio2 for as(iii) concerning some operating variables like flow rate, influent concentration, and bed depth was assessed. experimental data were used in a variety of models, including the yoon nelson, bed depth service time (bdst), and thomas models, to assess design parameters. 2 materials and methods 2.1 chemicals and instruments analytical grade chemicals were utilized without further purification in the present work. the flow of the feed solution is controlled by using a peristaltic pump (eyela mp-1000-mp-1000-h, japan), whereas that of effluent samples was collected each hour using a fraction collector (advantec sf-2120, advantec tokyo kaish, ltd., japan). 2.2 synthesis of the adsorbent (pp@tio2) the local juice trader in kathmandu, nepal, graciously provided the pomegranate peel waste. first, distilled water was used to thoroughly wash the pomegranate peels. it was then dried for 48 h at 343 to 353 k in an oven. the dry bulk was crushed and put through a copper sieve with a mesh size of 150 microns. the biopolymer’s hydroxyl groups were crosslinked by a condensation reaction using conc. h2so4 as a dehydrating agent, preventing the adsorbent from dissolving in aqueous solutions. the cross-linked pomegranate peels were made according to paudyal et al. (2017). in a round bottom flask, 15 g of raw peel powder was combined with 30 ml of conc. h2so4, which was then heated to 100°c and stirred for 24 h before cooling to room temperature. after being neutralized with sodium bicarbonate, the charred mass was once again stirred in 1 m hcl solution. it was rinsed repeatedly in distilled water until it reached neutrality, and then it was dried at 70°c in a convection oven. the term pp refers to the powder made from pomegranate peels in this manner. bhoj raj poudel et al./ bibechana 21 (2024) 51-62 53 then, pp@tio2 was prepared using a modified sol-gel method. about 10 ml of titanium (iv) nbutoxide was mixed with 15 ml of ethanol. after stirring for 30 min at room temperature, 2 g of powdered pp was added to it. then, 15 ml of a solution of 1:1:1 ethanol, deionized water, and acetic acid were added dropwise from the burette to the magnetically stirred mixture. the whole content was further stirred for 4h until sol was obtained. the sol was dried overnight at 80°c after aging at 40°c for 2 h. finally, the dried gel was ground into a powder and calcined at 400°c in a muffle furnace. the resulting pp@tio2 was stored in a plastic container before being used in the characterization and adsorption experiment. the detailed methodology for preparing pp@tio2 is shown in scheme 1. 2.3 characterization as a continuation of our previous study, the methodology and results of the characterization of pp@tio2 before and after adsorption have been described in detail elsewhere [4]. in brief, edx spectra showed peaks associated with ti after tio2 impregnation (pp@tio2), indicating that the biomass had been effectively impregnated with tio2. the edx spectra of as(iii) absorbed pp@tio2 showed an additional peak associated with arsenic. this demonstrated that arsenic had been effectively adsorbed from an aqueous solution by pp@tio2. in xrd analysis, the diffraction peaks associated with crystalline tio2 in the case of pp@tio2 emerge at 2θ = 25.2◦, 38.1◦, 48◦, 55◦, 63◦, 70◦, and 75◦. the (1 0 1), (0 0 4), (2 0 0), (1 0 5), (2 0 4), (2 2 0), and (2 1 5) planes, respectively, are represented by these peaks. this demonstrates that tio2 was successfully embedded in biomass in the form of crystalline anatase. these peaks demonstrate excellent agreement with jcpds card no. 00-021-1272 of the tio2 anatase phase. in ftir spectra of pp@tio2, the ti-o vibration, which represents the contact of tio2 with pp, is attributed to absorption peaks between 420 and 700 cm-1. this offers convincing proof of tio2 impregnation with the creation of the ti-o-c bond. in the ftir spectra of as(iii) adsorbed pp@tio2, an extra peak related to as-o vibrations was discovered at 825 cm-1 following arsenic biosorption. this supports the biosorption of as(iii) onto pp@tio2. using sem coupled with an edx spectrometer, the morphology and elemental composition of as-synthesized biosorbent were examined. the crystallinity of the pp@tio2 was determined using xrd patterns from an x-ray diffractometer. using ftir spectroscopy, the surface functionalities of the biosorbents before and after biosorption of as(iii) were examined. the xps investigations were performed by using an xps spectrometer (thermo fisher scientific, uk) to identify the elemental bonding and chemical states. 2.4 dynamic adsorption test in fix bed column as seen in figure 1, a glass column with an inner diameter of 0.8 cm and a height of 20 cm was used for the continuous adsorption test of as(iii) in a fixed bed column. for this, the pp@tio2 was soaked in di water before being packed into the column. following that, the wet adsorbent was packed into a column. the column was first filled with glass beads (5 cm), then with a layer of cotton (2 cm), and then pp@tio2 (1.4 to 4.1 cm). the column was once more packed with a 2 cm cotton layer trailed by a 5 cm glass bead layer. before the biosorption test, the column was conditioned by passing di water for 5 h at the same ph as the test solution. after this, as(iii) solution (10 mg/l) was passed into the column at the required flow rate by using a peristaltic pump. the effluent solutions for the measurement were collected at each regular interval with the help of a fraction collector. alkali solution (0.1 m naoh) was used to elute the loaded as(iii) since they had been successfully used in earlier batch tests. the effluent samples were then analyzed to measure the final concentrations of arsenic by using icp-ms. 2.5 analysis of breakthrough curve parameters it is crucial to study the breakthrough curve to evaluate a column’s biosorption performance. calculating the breakthrough curve parameters can do this. the ratio of as(iii) concentration from the effluent to the intake, ce ci , is presented against time (h) following the commencement of the flow. equation 1 provides the total quantity of adsorbate ion sorbed onto the packed column, qtotal, and the dynamic biosorption capacity, qe [21, 23]. qtotal = qa 1000 = q 1000 ∫ t=total t=0 cadsdt (1) qe = qtotal m (2) where ttotal, q, a, m, and cads stand for, respectively, the total flow period for the column to grasp exhaustion, volumetric flow rate, the area under the breakthrough curve, the quantity of biosorbent (g), the difference in the initial and the effluent adsorbate concentration. equation 3 may be used to determine the mass transfer zone [26]: mtz = z te − tb te (3) bhoj raj poudel et al./ bibechana 21 (2024) 51-62 54 where z denotes the bed height (cm); tb denotes the breakthrough time, and te is the exhaustion duration. 2.6 breakthrough curve modeling the breakthrough curve must be predicted to design and optimize the column for the biosorption process. for this, three mathematical models: the yoon-nelson model, and the bed depth service time (bdst) model, were employed in this work to examine the dynamic biosorption efficiency of pp@tio2. the column experiment conditions are presented in table 1. 2.6.1 thomas model this model assumes that mass transfer at the interface rather than chemical interactions restricts adsorption, and experimental results exhibit langmuir isotherms and second-order kinetics [27]. this is appropriate for illustrating the entire breakthrough curve [26]. the following equation 4 may be used to express the thomas model in linear form [21,28]: ln ( ci ce − 1 ) = kth q0m q = kthcit (4) where kth denotes thomas rate constant (ml/min.mg), qe represents the equilibrium biosorption capacity (mg/g), m represents the mass of biosorbent (g), and q denotes the feed rate (ml/min). the linear plot of ln (ci/ce– 1) vs t allowed for the evaluation of the values kth and qe. scheme 1: flowsheet detailing the synthesis of pp@tio2 from biomass derived from pomegranate peels. figure 1: schematic diagram for the column experiments (figure adapted with permission from biswas et al. 2008 [25], copyright, elsevier). bhoj raj poudel et al./ bibechana 21 (2024) 51-62 55 2.6.2 yoon-nelson model this model presumes that the probability of biosorption for each adsorbate ion decreases at a rate that is proportionate to its probability of both biosorption and breakthrough of biosorbent from the biosorbent [29]. in the later phases of the breakthrough curve, the yoon-nelson model, like the thomas model, may reduce the shortcomings of the adams-bohart model. the yoon-nelson model’s linear expression is presented by the following equation 5 [23,30]: ln ( ce ci − ce ) = ky n − τky n (5) where τ denotes the amount of time required for a 50% adsorbate breakthrough in minutes and ky n denotes the yoon-nelson rate constant (min−1). 2.6.3 bed depth service time (bdst) model this model predicts that bed depth and service time will be linearly related for a certain breakthrough concentration. past studies state that this model does a good job of explaining the first 10 to 50% of the breakthrough curve [7]. equation 6 provides the linear expression of the bdst model [21]: tb = n0z ciu0 − 1 kbci ln ( ci cb − 1 ) (6) where n0 is the column adsorption capacity (mg/l), tb denotes the service period of column (in hours), cb denotes the outflow concentration at breakthrough point (mg/l), and kb denotes the rate constant [l/(mg.h)]. the bdst parameters, n0, and kb, are computed from the time versus bed depth graphs. 2.6.4 adams bohrt model this model works better in situations where the effluent concentration is lower. adams-bohrts model predicts that the biosorption rate is proportional to the biosorbent concentration and the residual capacity of the solids. in the linear form, it can be written as [31], ln ( ct ci ) = kabci ×−n0 u0 kabz (7) where ci is the initial concentration (mg/l) of as(v); ct is the concentration (mmol/l) of as(v) at time t; kab is the bohart–adams model rate constant (l/min); n0 is the column saturation concentration (mg/l); z is the height of the bed (cm) in a column. 3 results and discussion 3.1 characterization as a continuation of our previous study, the adsorbents used in this study were thoroughly charbhoj raj poudel et al./ bibechana 21 (2024) 51-62 56 acterized in previous research [4]. their relevant characteristics are briefly mentioned here. 3.1.1 edx spectra adsorbent before and after as(iii) adsorption the edx spectra of pp, pp@tio2, and as(iii) adsorbed pp@tio2 are revealed in figure 2(a), figure 2(b), and figure 2(c), correspondingly. the edx spectra showed peaks associated with ti after tio2 impregnation (pp@tio2), indicating that the biomass had been effectively impregnated with tio2. the edx spectra of as(iii) absorbed pp@tio2 showed an additional peak associated with arsenic. this demonstrated that arsenic had been effectively adsorbable from an aqueous solution by pp@tio2. 3.1.2 xrd pattern of biosorbent figure 3 displays the xrd pattern of pp and pp@tio2. the absence of sharp peaks in the pp signals its amorphous nature. the diffraction peaks associated with crystalline tio2 in the case of pp@tio2 emerge at 2θ = 25.2◦, 38.1◦, 48◦, 55◦, 63◦, 70◦, and 75◦. the (1 0 1), (0 0 4), (2 0 0), (1 0 5), (2 0 4), (2 2 0), and (2 1 5) planes, respectively, are represented by these peaks. this demonstrates that tio2 was successfully embedded in biomass in the form of crystalline anatase. these peaks demonstrate excellent agreement with jcpds card no. 00-021-1272 of the tio2 anatase phase. 3.1.3 functional group analysis ftir spectra were used to confirm the functional groups on the biosorbents, as given in figure 4. in the ftir spectra of pp@tio2, the ti-o vibration, which represents the contact of tio2 with pp, is attributed to absorption peaks between 420 and 700 cm-1. this offers convincing proof of tio2 impregnation with the creation of the ti-o-c bond. in the ftir spectra of as(iii) adsorbed pp@tio2, an extra peak related to as-o vibrations was discovered at 825 cm-1 following arsenic biosorption. this supports the biosorption of as(iii) onto pp@tio2. 3.2 effect of the flow rate the impact of the flow rate of the inflowing solution on the as(iii) biosorption by pp@tio2 was investigated at different flow rates (72, 150, and 240 ml/h) and a fixed bed height (4.1 cm), and preliminary as(iii) concentration (10.0 mg/l). the breakthrough data presented in figure 5(a) indicates that a lesser time is sufficient for column breakthrough, whereas its value is increased with the decrease of flow rate. this is attributed to the possibility of channeling and short contact between the as(iii) ions and active sites of pp@tio2 bed at a higher flow rate. moreover, the treated bed volumes are determined to be 297.1, 327.7, and 349.5 at flow rates of 72, 150, and 240 ml/h, respectively. another reason for an earlier breakthrough might be because a greater volume of solution containing a greater number of as(iii) ions passed across the bed at a higher flow rate. consequently, more as(iii) ions became in contact with the adsorbent sites of pp@tio2, making them get saturated more rapidly. likewise, a higher biosorption capacity is achieved at a lower flow rate as expected. as the flow rate increased, the amount of as(iii) passed through the pp@tio2 bed containing a fixed number of active sites increased; however, the contact time between the adsorbate and adsorbent potentially reduced, which increases the possibility of channeling. because of this, the limited number of active sites are colloids or adsorbed with as(iii) ion resulting in a decrease in column adsorption capacity. the longer contact time and lesser channeling led to more efficient adsorption of as(iii) onto pp@tio2, and thus, a higher biosorption capacity was attained at a lower flow rate. figure 2: edx spectra of (a) pp, (b) pp@tio2 and (c) as(iii) adsorbed pp@tio2. bhoj raj poudel et al./ bibechana 21 (2024) 51-62 57 figure 3: xrd spectra of pp and pp@tio2. figure 4: ftir spectra of pp, pp@tio2 and as(iii) adsorbed pp@tio2. 3.3 effect of initial as(iii) concentration the breakthrough curves at varying initial as(iii) concentrations for a flow rate of 150 ml/h and a bed height of 4.1 cm are shown in figure 6(a). the treated bed volumes were 436.9, 327.7, and 145.63 for initial as(iii) concentrations of 5.0, 10.0, and 15.0 mg/l, respectively. the figure clearly shows that with increasing initial as(iii) concentration, the biosorption approached saturation more quickly, and the breakthrough time was decreased. a similar trend was reported by paudyal et al., 2013 [21]. the decrease in breakthrough time at higher concentrations is due to the contact of a large number of as(iii) at high concentrations of arsenic with active sites in the pp@tio2 bed. the biosorption capacity of pp@tio2 for as(iii) also increased (2.31 to 3.14 mg/g) with increasing initial as(iii) concentration, which can probably be attributed to the higher concentration offering more driving force for the transfer process. 3.4 effect of bed height figure 7(a) depicted the impact of bed height on the breakthrough curves regarding as(iii) biosorption onto the pp@tio2. the treated bed volumes of as(iii) solution increased from 515.5 to 625.0, and 687.8 with an increasing bed height of 1.4, 2.6, and 4.1 cm, respectively, which may relate to an extended contact duration. the evaluated as(iii) removal capacity of pp@tio2 for the bed heights of 4.1, 2.6, and 1.4 cm are presented in table 2. 3.5 modeling of the breakthrough curve this study explores the dynamic biosorption behavior of pp@tio2 using the thomas, yoon-nelson, and adams-bohart models. figures 5(b), 5(c), and 5(d), respectively, show the modeling curve of thomas, yoon-nelson, and adams-bohart models at different flow rates. figures 6(b), 6(c), and 6(d), respectively, show the modeling curve of thomas, yoon-nelson, and adams-bohart models at different as(iii) concentrations. similarly, figures 7(b), 7(c), and 7(d), respectively, show the modeling curve of thomas, yoon-nelson, and adams-bohart models at different bed heights. table 2 shows the results or dynamic parameters obtained for the adsorption of as(iii) onto the column of pp@tio2 using various models. the entire breakthrough curve may be analyzed using the thomas model. this model presupposes bhoj raj poudel et al./ bibechana 21 (2024) 51-62 58 that mass transfer at the interface limits biosorption and that the data follows second-order kinetics and langmuir isotherms. the dynamic biosorption capacity rose from 3.81 to 2.86 mg/g as the flow rate increased from 72 to 240 ml/h, whereas the thomas rate constant increased from 0.127 to 0.521 l/mg·h. in a packed bed system, homogeneous contact decreases due to channeling, which causes q0 to decline at greater flow rates. the thomas rate constant increased from 0.1992 to 0.2567 l/mg·h, and the biosorption capacity increased from 2.31 to 3.13 mg/g as the initial as(iii) concentration rose from 5.0 to 15.0 mg/l. the higher concentration gradient provided a greater driving force, and a higher amount of mass transfer occurred through the adsorbent bed, causing better biosorption capacity at the higher concentration of as(iii). similar results were observed by paudyal et al., 2013, in the case of fluoride adsorption using zr(iv) modified dried orange juice residue [21]. in the case of the yoon-nelson model, it was discovered that, with an increase in flow rate from 72 to 240 ml/h, ky n rose from 1.271 to 2.961 h-1, and τ reduced from 4.54 to 1.04 h, respectively. the ky n values fall from 1.194 to 0.047 h-1 when the bed height rises from 1.4 to 4.1 cm, while τ increases from 89.3 to 165.1 h. an increase in the ky n values from 0.996 to 5.472 h-1 and a drop in τ from 4.63 to 1.04 h was brought on by a change in the initial as(iii) concentration from 5 to 15 mg/l. the adams-bohart model, which is used to evaluate the initial part of the breakthrough curve (ct/c0 = 0 to 0.5), assumes that equilibrium is not instantaneous. when the initial as(iii) concentration was increased from 5 to 10 mg/l, the kinetic constant kab reduced from 0.175 to 0.042 l/mg·h, but it rose when the flow rate was increased from 72 to 240 ml/h from 0.063 to 0.181 l/mg·h. additionally, a rise in bed height from 1.4 to 4.1 cm caused kab to fall from 0.0725 to 0.0552 l/mg·h. with an increase in flow rate from 72 to 240 ml/h, the column saturation concentration of the adsorbent (n0) decreased from 2532 to 2195 mg/l, respectively. when the initial as(iii) concentration was increased from 5 to 15 mg/l, n0 values increased from 1.63 to 7.91 mg/l, respectively. figure 5: biosorption of as(iii) onto pp@tio2 in fixed bed system at different flow rates (a) breakthrough profile, and modeling using (b) thomas, (c) yoon nelson, and (d) adams-bohrats models. bhoj raj poudel et al./ bibechana 21 (2024) 51-62 59 figure 6: biosorption of as(iii) onto pp@tio2 in fixed bed system at different concentrations (a) breakthrough profile, and modeling using (b) thomas, (c) yoon nelson, and (d) adams-bohrats models. figure 7: biosorption of as(iii) 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[30] y.h. yoon and j.h. nelson. application of gas adsorption kinetics i. a theoretical model for respirator cartridge service life. am. ind. hyg. assoc. j., 45:509–516, 1984. https://doi.org/10.1080/ 15298668491400197 [31] g.s. bohart and e.q. adams. some aspects of the behavior of charcoal with respect to chlorine. j. am. chem. soc., 42:523–544, 1920. https://doi.org/10.1016/j.jhazmat.2007.11.030 https://doi.org/10.1016/j.jhazmat.2007.11.030 https://doi.org/10.1080/15298668491400197 https://doi.org/10.1080/15298668491400197 introduction materials and methods chemicals and instruments synthesis of the adsorbent (pp@tio2) characterization dynamic adsorption test in fix bed column analysis of breakthrough curve parameters breakthrough curve modeling thomas model yoon-nelson model bed depth service time (bdst) model adams bohrt model results and discussion characterization edx spectra adsorbent before and after as(iii) adsorption xrd pattern of biosorbent functional group analysis effect of the flow rate effect of initial as(iii) concentration effect of bed height modeling of the breakthrough curve conclusion bibechana vol. 21, no. 1, april 2024, 74–82 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar structural and cation distribution analysis of nickel-copper/nickel-magnesium substituted lithium ferrites d. parajuli1,∗, k. samatha2 1research center for applied sc. and tech., tribhuvan university, kirtipur, kathmandu, nepal 2dept. of physics, college of sc. and tech., andhra university, visakhapatnam, india ∗corresponding author. email: deepenparaj@gmail.com abstract lithium ferrite (li0. 5fe2.5o4) is a promising material due to its importance in construction and engineering. it can be crystallized in the spinel crystal structure, ab2o4, where “a” and “b” depict lattice sites named as tetrahedral and octahedral supported by oxygen ions, respectively. the xrd peaks are matched well with the jcpds card (no. 38-0259) indicating a spinel cubic crystal structure with the space group of fd3m except for for extra peak 211 in the basic lithium ferrite as an indication of the mild phase transformation from the fd3m space group to the p4132 space group. the present basic li-ferrite sample contains a mild secondary hematite phase too apart from the major spinel crystal phase. the cation distribution is also tested in this work which is important for further investigation of magnetic and dielectric properties of the ferrites. these ferrites are widely used in microwave, magnetic as well as electric energy storage devices. keywords xrd, cation distribution, lnc and lnm ferrites, mild phase transformation article information manuscript received: december 31, 2023; revised: january 30, 2024; accepted: february 1 , 2024 doi https://doi.org/10.3126/bibechana.v21i1.61270 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction lithium ferrites are considered to be one of the most versatile ferrites as it covers a large number of applications. lithium ferrites are frequently used in information storage, switching devices, and phase shifters because of their excellent rectangular hysteresis loop characteristics [1, 2]. it has a relatively high curie temperature of about 640oc, which ensures its applicability over a wide range of technically useful temperatures. at room temperature, lithium ferrite has permeability and saturation magnetization higher than those for yttrium iron garnet. it has a low cost when compared to the garnets [3]. the nickel-rich lithium ferrites 74 http://nepjol.info/index.php/bibechana deepenparaj@gmail.com https://doi.org/10.3126/bibechana.v21i1.61270 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ d. parajuli and k. samatha/ bibechana 21 (2024) 74-82 75 are also extensively used for lithium-ion batteries [4], [5]. lithium ferrite (li0. 5fe2. 5o4) is a promising material due to its importance in construction and engineering [6]. it can be crystallized in the spinel crystal structure, ab2o4, where “a” and “b” depict lattice sites named as tetrahedral and octahedral supported by oxygen ions, respectively [7]. lithium and magnesium ferrites are potential materials for applications from low frequency to microwave frequencies [8–10]. the li and mg ferrites, with their high resistivity and low eddy current losses, are useful materials for applications at microwave frequencies. they exhibit rectangular hysteresis loops, which makes them suitable for magnetic information storage devices. moreover, these materials are cost-effective with easy preparation techniques, and excellent performance over a wide range of temperatures compared to garnets that have similar applications. this has attracted scientists and technologists for widespread development of materials in different devices. ferrites are mostly, as prepared as ceramic materials by conventional methods [4, 11, 12]. the study of structural properties with xrd is related to the crystal structure, cation distribution, and surface microstructures which are composed of pores, grains, and grain boundaries. thus, structural studies are essential for understanding the variations of magnetic and electrical properties as well as developing suitable materials for microwave applications. since the observed variations in saturation magnetization (to be discussed in the next paper) would also provide valuable information about the distribution of cations in li0.5-xnixcuxfe2.5xo4 (lnc) and li0.5-xnixcuxfe2.5xo4 (lnm) (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25) ferrite systems, the discussions involved in arriving at the cation distributions can be used to verify and confirm the distributions are presented in this paper. 2 materials preparation and characterization the starting materials were reagent-grade lithium oxide, nickel oxide, copper oxide, magnesium oxide, and iron oxide powders which were mixed in appropriate stoichiometric ratio and ground for 12 hours using agate mortar and pestle in the presence of methanol to improve homogeneity. the resulting mixture was air-dried and then pre-sintered in the air for 8 hours at 750°c. the pre-sintered ferrite was again ground for 4 hours in the presence of methanol and again dried in air at room temperature. the prepared samples were designated as lnc series: li0.5-xnixcuxfe2.5xo4, (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25) and lnm series: li0.5-xnixmgxfe2.5xo4, (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25) with lnc and lnm respectively. the structural characterization of the samples li0.5fe2.5o4 were done with x ray diffractometer (rigaku). 3 results 3.1 x-ray diffraction studies typical x-ray powder diffraction patterns of li0.5fe2.5o4 (basic lithium ferrite), li0.5-xnixcux fe2.5xo4 (lnc x=0.10) and li0.5-xnixmgxfe2.5xo4 (lnm x=0.10) are shown in figures 1, 2 and 3 respectively. the xrd peaks 210, 211, 220, 310, 311, 321, 400, 421, 422, 511, 440 are matched well with jcpds card (no. 38-0259). the patterns are indexed with all the planes indicative of spinel cubic crystal structure with the space group of fd3m. however, the basic lithium ferrite shows some extra peaks with the hkl values of 211 which is indicative of a mild phase transformation from the fd3m space group to p4132 space group. from the xray diffraction studies, the lattice constant of the basic composition li0.5fe2.5o4 sintered under different conditions has been determined in this paper. this study reveals that the lattice constant does not change with the sintering conditions as is to be expected. the measured value of the lattice constant along with the values reported in the literature for the above composition are given in table1 for comparison. table 1: lattice constant values in å for li0.5fe2.5o4. present study from the literature 8.287± 0.005 8.328 [13], 8.298 [14], 8.301 [15] as is evident from the data that the values reported in the literature differ slightly from each other since the origin and method of preparation of the sample under test is different for different cases [16]. however, the observed value in the present study lies well within the reported range of latd. parajuli and k. samatha/ bibechana 21 (2024) 74-82 76 tice parameter values. this kind of transformation is more in the basic lithium ferrite, and quite less in substituted lithium ferrites. particularly, when the concentration of the ni-cu or ni-mg cations is substituted in place of li-fe ions this extra phase for transformation gradually disappears and finally for concentrations x=0.20 onwards the patterns are clearly indicative of spinel crystal structures with only fd3m space group. a marked reduction in the intensity of 210 peak and complete elimination of 211 peak in the xrd patterns of substituted samples can be clearly seen in comparison to the xrd pattern of the basic lithium ferrite. similarly, it is noticed that apart from the presence of 310 peak, the intensities of 422 and 311 peaks appear more than what the spinel crystal structure normally produces. in this case too, the differences in normal intensities of 422, 311 and 310 gradually decrease when the concentration of the substituted ni-cu or ni-mg cations increases. hence, we have made an attempt to index these extra peak intensities to the 132, 110 and 121 peaks represented by hematite (antiferromagnetic fe2o3) crystal structure and they are well matched. thus, it can be said from the above that the present basic li-ferrite sample contains a mild secondary hematite phase too apart from the major spinel crystal phase. here too, a marked reduction in the magnitude of hematite phase in the xrd patterns of substituted samples is observed when the concentration of the substituted ni-cu or nimg cations increases. 3.2 cation distribution analysis 3.2.1 observed lattice parameter the main reflection planes of the spinel structure of ferrites are identified in the x-ray diffraction patterns of the present samples as (220, 311, 400, 422, 511 and 440). using all these major peaks of the spinel structure, experimental lattice parameters were estimated for all the samples. in order to minimize the error in estimations, the obtained lattice parameters were plotted versus the nelson –riley error function [17]. the plots are straight lines with increasing trends. the observed lattice parameter can be obtained by extrapolating the lines to =90o, where all errors vanish. the estimated values of the experimental lattice parameter “aexp” as a function of composition (x) for both the lnc and lnm ferrite systems are presented in figure 4. the lattice constant has been observed to increase with concentration (x) in both the series. further, it is observed to increase steeply from x = 0.10 onwards till x=0.20 in all the substituted samples. the introduction of ni2+ and cu2+ ions in lnc series, and ni2+ and mg2+ ions in lnm series into li0.5fe2.5o4 can cause a small shift in the lithium ferrite peaks. this shift is indicative of the change in lattice constant. larger size ions, cu2+ ions in lnc series and mg2+ ions in lnm series cause the spinel lattice of the lithium ferrite to expand. this increment of the lattice parameter could be explained on the basis of ionic radii, where the radius of ni2+ ion (0.069 nm) is smaller than that of li+ (0.073 nm) and radius of cu2+ion (0.073nm) is larger than of fe3+ (0.0645 nm) ions. in lnm series, the ni2+ ions successively replace the li+ and the mg2+ (0.072 nm) ions replace fe3+ (0.0645 nm) ions. this introduction of larger size ions, i.e., cu2+ and mg2+, is likely to induce uniform strain in the lattice, as the material is elastically deformed. this effect causes the lattice plane spacing to change and the diffraction peaks to shift to a lower 2 position [18, 19]. the unit cell expands to accumulate the larger ion, so it is expected to increase the lattice parameter. the uniform increase in lattice constant with ni-cu and ni-mg substitution indicates that lattice expands without disturbing the symmetry of lattice [20]. a similar variation has also been reported by ravinder et al. [21]. 3.2.2 theoretical lattice parameter in order to match the trend of the observed lattice constants with theoretical ones in both lnc and lnm series, a careful selection of cations among the tetrahedral and octahedral sites was assigned. this has been a common practice in assigning cation distributions [22] because the cations take different values in their dimensions depending up on their occupation in particular lattice site and its corresponding coordination. for example, the ionic radius of cu2+ ions in tetrahedral (4-fold) coordination is equal to 0.57 å and in octahedral (6-fold) coordination its size becomes 0.73 å. this difference in size due to its occupation in a particular site would also naturally affect the lattice constant. in the light of this information, an attempt was made in the present work to match the lattice constant by carefully assigning the cations in aand b-sites. however, since such a distribution should also match with the cation distribution to be assigned when the theoretical and experimental magnetic moments (to be discussed in the next paper) are compared, we have put up a concentrated effort in making these assignments by synchronizing all the experimentations on these samples. d. parajuli and k. samatha/ bibechana 21 (2024) 74-82 77 figure 1: typical x-ray diffraction pattern of lithium ferrite. figure 2: typical x-ray diffraction patterns of ni-cu substituted (lnc, x=0.10) and ni-mg substituted (lnm, x=0.10) ferrite samples. theoretical lattice constant in general is calculated using the following relation [23]. ath = 8 3 √ 3 { (ra +ro) + √ 3 (rb +ro) } (1) here ra and rb are the mean radii of the tetrahedral and octahedral sites and ro is the radius of oxygen ion. in lnc series, ra = y · rtetra cu2+ + (1− y) · rtetra fe3+ (2) rb = 1 2 {(0.5− x) · rocta li+ + x · (x− y) · rocta cu2+ + (1.5− x+ y) · rocta fe3+} (3) in lnm series, ra = y · rtetra mg2+ + (1− y) · rtetra fe3+ (4) rb = 1 2 { (0.5− x) · rocta li+ + x · (x− y) · rocta mg2+ + (1.5− x+ y) · rocta fe3+ } (5) the proposed cation distributions used for the calculations of theoretical lattice constant are listed in tables 2 and 3. d. parajuli and k. samatha/ bibechana 21 (2024) 74-82 78 figure 3: typical x-ray diffraction patterns of ni-mg substituted (lnm, x=0.10) ferrite samples. tables 4 and 5 give the comparison between calculated and experimental lattice constant values. the same has been shown in the form of graph for easily depicting the trends in figure 5 and 6 respectively. table 2: the proposed cation distribution for the lnc series of samples. x a site b site 0.00 fe li0.5fe1.5 0.05 fe li0.45ni0.05cu0.05fe1.45 0.10 fe li0.4ni0.1cu0.1fe1.40 0.15 fe0.985cu0.015 li0.35ni0.15cu0.135fe1.365 0.20 fe0.925cu0.075 li0.25ni0.25cu0.175fe1.325 0.25 fe0.940cu0.060 li0.25ni0.25cu0.175fe1.325 the values of ra and rb can be calculated for both the systems lnc and lnm systems using the following expressions [23]. table 3: the proposed cation distribution for the lnm series of samples x a site b site 0.00 fe li0.5fe1.5 0.05 fe li0.45ni0.05mg0.05fe1.45 0.10 fe li0.40ni0.10mg0.10fe1.40 0.15 fe0.955mg0.045 li0.35ni0.15mg0.105fe1.395 0.20 fe0.960mg0.040 li0.30ni0.20mg0.160fe1.340 0.25 fe0.975mg0.025 li0.25ni0.25mg0.225fe1.275 the ionic radii of li+, ni2+, cu2+, mg2+, and fe3+ used in the calculations are taken from shannon [24] corresponding to tetrahedral and octahedral coordination. d. parajuli and k. samatha/ bibechana 21 (2024) 74-82 79 table 4: experimental and calculated lattice constants of lnc system. li0.5−xnixcuxfe2.5−xo4 (lnc series) x aobs acal 0.00 8.287 8.3558 0.05 8.282 8.3568 0.10 8.298 8.3578 0.15 8.364 8.3589 0.20 8.350 8.3602 0.25 8.386 8.3615 table 4: experimental and calculated lattice constants of lnm system. li0.5−xnixmgxfe2.5−xo4 (lnm series) x aobs acal 0.00 8.287 8.3558 0.05 8.336 8.3561 0.10 8.294 8.3565 0.15 8.364 8.3578 0.20 8.383 8.3581 0.25 8.350 8.3580 it can be clearly seen from the above figure that the trends of experimental and theoretical lattice constants for both the lnc and lnm series samples are optimally made to coincide within the limitations of experimental errors associated with the xrd technique, and thus the assigned cation distributions are reasonably accurate. figure 4: variations of observed lattice constant with concentration (x) of lnc and lnm series. d. parajuli and k. samatha/ bibechana 21 (2024) 74-82 80 figure 5: comparison of variations of observed and calculated lattice constants with concentration (x) in lnm series. figure 6: comparison of variations of observed and calculated lattice constants with concentration (x) in lnc series. 4 discusssion when there is a change in the lattice constant of a crystal, it can affect the distribution of cations within the crystal lattice. the lattice constant is the distance between unit cells in a crystal lattice. changes in lattice constant can occur due to various factors, such as temperature, pressure, or the presence of impurities [25]. the distribution of cations within a crystal lattice is determined by factors like the crystal structure and the size of the cations. in an ionic crystal, cations are arranged in a specific way to achieve electrostatic stability. here are a few possible scenarios when there is a change in lattice constant: if the lattice constant increases, the distance between adjacent ions also increases. cations d. parajuli and k. samatha/ bibechana 21 (2024) 74-82 81 may experience a decrease in repulsion, making it more favorable for larger cations to be accommodated within the lattice. if the lattice constant decreases, the distance between adjacent ions also decreases. smaller cations may find it more favorable to occupy the lattice sites. significant changes in lattice constants can lead to phase transitions in the crystal structure [26]. during a phase transition, there can be a reorganization of cations in the crystal lattice to achieve a more stable arrangement at the new lattice constant. changes in lattice constant can affect the substitution of cations in the crystal lattice. depending on the specific conditions, different cations may be more likely to substitute for one another. it's important to note that the behavior can vary depending on the specific crystal structure and the type of cations involved. additionally, changes in lattice constant can be associated with changes in the material's physical and chemical properties, including its electronic, optical, and mechanical properties. experimental studies and theoretical calculations are often used to understand these behaviors in specific materials. the cation distribution in a material refers to the arrangement of positively charged ions (cations) within its crystal structure. this distribution can have a significant impact on the material's properties like magnetic, electronic, electric, dielectric, optical, mechanical, chemical, phase transition, and thermal conductivity, etc. [10, 27]. understanding and controlling cation distribution is essential in the design and engineering of materials with specific desired properties for various technological applications, including electronics, catalysis, energy storage, and more. researchers often explore different cation distributions to tailor material properties for specific functions. the cation distribution can impact phase transitions in materials. changes in temperature or pressure may lead to structural transitions, and the distribution of cations can influence the ease and nature of these transitions. the details on the material properties other than the structural properties will be discussed in the next paper. 5 conclusion the xrd peaks 210, 211, 220, 310, 311, 321, 400, 421, 422, 511, 440 are matched well with jcpds card (no. 38-0259). the patterns are indexed with all the planes indicative of spinel cubic crystal structure with the space group of fd3m. however, the basic lithium ferrite shows some extra peaks with 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https://doi.org/10.1107/s0567739476001551 https://doi.org/10.1016/j.chphi.2023.100270 https://doi.org/10.1016/j.chphi.2023.100270 https://doi.org/10.1021/acs.chemmater.6b00038/suppl_file/cm6b00038_si_005.cif https://doi.org/10.1021/acs.chemmater.6b00038/suppl_file/cm6b00038_si_005.cif https://doi.org/10.1021/acs.chemmater.6b00038/suppl_file/cm6b00038_si_005.cif https://doi.org/10.2298/pac2104351m introduction materials preparation and characterization results x-ray diffraction studies cation distribution analysis observed lattice parameter theoretical lattice parameter discusssion conclusion bibechana vol. 22, no. 2, august 2025, 85-92 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar radiological assessment of the bagh bhairav temple in kirtipur, nepal using in-situ gamma ray spectrometry anita mishra∗, raju khanal central department of physics, tribhuvan university, kirtipur, nepal ∗corresponding author. email: anita.745711@cdp.tu.edu.np abstract in this work, the results of an in-situ radiological survey of the bagh bhairav complex in kirtipur, nepal, using a portable gamma ray spectrometer equipped with a gps and data logger unit is presented. the study aims to assess external exposure by evaluating and mapping external absorbed dose rates and radionuclide activity concentrations in the area. the measured absorbed dose rate in air ranged from 100.330 ngy/h to 170.506 ngy/h, with a mean value of 128.661 ± 14.637 ngy/h. the activity concentrations of the gamma radionuclides 238u, 232th and 40k, outdoor annual effective dose (aed) and excess lifetime cancer risk (elcr) were found higher than the world average values. the elevated absorbed dose rate is attributed to the high activity concentrations of gamma radionuclides present in soils, rocks at high altitudes. this study provides baseline radiological data for the bagh bhairav area and contributes to the limited radiological data available for nepal. keywords absorbed dose rate, activity concentration, aed, elcr, in-situ radiological survey, nepal article information manuscript received: october 17, 2024; revised: january 20, 2025; accepted: february 9, 2025 doi https://doi.org/10.3126/bibechana.v22i2.70839 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction human populations are continually exposed to ionizing radiation from environmental sources, which contributes to their radiation dose. high radiation doses have been reported in various parts of the world, including india, which borders nepal [1, 2]. gabdo et al. measured the mean terrestrial gamma radiation dose rate in pahang state, malaysia, to be 176 ± 5 ngy/h, with an annual effective dose rate of 0.22 msv/y for outdoor exposure [3]. a survey by taskin et al. revealed the average outdoor gamma dose rate in kirklareli, turkey, to be 118 ± 34 ngy/h [4]. ramola et al. studied the average external absorbed dose rates in the garhwal himalaya region of india from the radionuclides 226ra, 232th and 40k, finding it to be 138 ngy/h [5]. the high concentration of radionuclides in these areas is attributed to various rock types and their chemical properties. rajasthan and kerala in india have also reported higher dose rates [6, 7]. radionuclides present in building materials can further elevate radiation levels [8]. bala et al. found that the activity concentrations of 226ra, 232th, and 40k in soil and building materials in una, india, were higher than the world average [9]. in terengganu state, malaysia, the mean terrestrial gamma 85 http://nepjol.info/index.php/bibechana anita.745711@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v22i2.70839 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ anita mishra and raju khanal/ bibechana 22 (2025) 85-92 86 radiation dose rates and annual effective dose were measured to be 150 ngy/h and 0.92 msv/y, respectively [10]. gamma ray spectrometry has also been employed to study environmental gamma radiation in some selected areas of nepal [11–14]. recently, gamma ray spectrometry has found diverse applications, including lithological mapping [15], qualitative analysis of clay minerals [16], investigation of shutdown radioactivity for the experimental advanced superconducting tokamak (east) [17], radioactivity depth distribution analysis in activated concrete [18], and evaluating tropical soil processes and attributes [19]. the bagh bhairav complex is an ancient temple built in the 16th century, located in kirtipur city, a unesco tentative site (https://en.wikipedia. org/wiki/kirtipur), approximately 5 km southwest of the capital city (figure 1). the temple lies between latitudes 27.6790 27.6800 and longitudes 85.2760 – 85.2770 at an altitude of 1294.970 – 1352.410 meter. the complex consists of a large temple surrounded by many smaller temples and statues. the bricks, timber, clay mortar, stones, and clay tiles used for construction may have high concentrations of primordial radionuclides, which can produce gamma radiation and elevate background radiation levels. pilgrims and visitors regularly visit the temple, and the surrounding area is inhabited, making a radiological survey of this area essential to assess any potential radiological hazards to the public. the image of the bagh bhairav temple featured on a postage stamp issued by the government of nepal also underscores its historical significance (figure 2). the aim of this study is to evaluate outdoor external exposure in the complex and its surrounding area by measuring the absorbed dose rate in air and calculating the annual effective dose (aed) using in-situ gamma ray spectrometry. the absorbed dose is the radiation energy imparted to a unit mass of matter and aed is a measure of the energy deposited by radiation in organs and tissue per year and it measures the biological effects of radiation to humans. the measured absorbed dose rate in air will be compared with the dose rate calculated from the activity concentrations of terrestrial gamma radionuclides 238u, 232th and 40k. additionally, the associated health risks will be assessed by calculating the excess lifetime cancer risk (elcr). elcr is the difference between the proportion of people who develop or die from the disease in an exposed population and the corresponding proportion in a similar population without the exposure [20]. the acceptable range of excess lifetime cancer risk (elcr) is generally contextual and varies based on regulatory frameworks and risk management practices. as a general rule, mitigation (or any action) may not be necessary if the risks originate from natural sources and the dose remains below established thresholds, such as the icrp’s recommended limit of 1 msv/year for the public. figure 1: google map and location of the survey site. figure 2: postage stamp of nepal depicting the bagh bhairav temple. 2 material and methods the spectrometer (pgis 2) was carried in a backpack (maintained at a height of 1 m for consistency in measurements) and walked around the study area with a speed less than 2 km/h. 2.1 gamma ray spectrometry the dose rate is studied using gamma ray spectrometer (pgis 2 from pico envirotec) which can record 512 channels of data in the energy range 20 kev to 3 mev. it has auto calibration and real-time spectrum stabilization by the natural gamma photo peaks. the activity concentration of 40k is directly measured from its emission line at 1461 kev while the activity concentration of uranium and thorium decay series is measured from the gamma emission of 214bi at 1764 kev and 208tl at 2614 kev respectively. 2.2 dosimetry 2.2.1 annual effective dose (aed) the outdoor annual effective dose (aed) is calculated based on the absorbed gamma dose rate by https://en.wikipedia.org/wiki/kirtipur https://en.wikipedia.org/wiki/kirtipur anita mishra and raju khanal/ bibechana 22 (2025) 85-92 87 using the equation [1]: aed (nsv) = d ( ngy h ) ×8760h×of×cf ( sv gy ) (1) where d is the average absorbed dose rate, cf is the conversion factor, 0.7 sv/gy (to convert absorbed dose rate in air to effective dose equivalent for human), of is the outdoor occupancy factor, 20% and 8760 is hours in one year. 2.2.2 excess lifetime cancer risk (elcr) the excess lifetime cancer risk (elcr) was calculated using the equation [20]: elcr = aed × le ×rf (2) where le is the life expectancy of people (66.2 year in nepal) (http://en.worldstate. info/asia/nepal) and rf is the overall fatal risk coefficient, 0.05 per sv as recommended by icrp for the purpose of radiological protection. 2.2.3 absorbed gamma dose rate the absorbed gamma dose rate from the concentration of gamma radionuclides in rocks and soils is calculated using the equation [1]: dcalculated ( ngy h ) = 0.0417ak+0.462au+0.604ath (3) where ak , au and ath is the activity concentration (bq/kg) of 40k, 238u and 232th respectively. 3 theory the semi-empirical model based on mono-energetic radiation is the simplest approach for modeling gamma ray fields. this model uses a two-layer configuration, with the earth represented as an infinite half-space of constant density and radioelement concentration, overlaid by a layer of non-radioactive air with constant density. the observed photo peak intensity, di, is given by: di = aε 4πr2 e−µeree−µarandv (4) where ndv is the number of gamma rays of energy e0 emitted per second by the volume element dv, a is the effective cross-sectional area of the detector, ε is the photo peak efficiency of the detector for gamma rays of energy e0, µe and µa are the linear attenuation coefficients for the earth and air, respectively; and re and ra are the distances that gamma rays travel through the earth and air, respectively, with r = ra + re. 4 results the measured absorbed dose rate in air of bagh bhairav area was obtained in the range of 100.330 to 170.506 ngy/h with an average of 128.661 ± 14.637 ngy/h. the radiological map of measured absorbed dose rate in air is shown in figure 3. the dose rates were overlaid on the geo-referenced map to find the spatial variability. the higher value was observed in the surrounding area of the temple (yellow colour) with the highest value (red colour) near the temple wall as building materials are also the contributors of gamma dose. the concentrations of 40k, 238u and 232th was measured in the range of 1.130 to 5.702%, 0.590 to 20.461 ppm and 3.053 to 40.683 ppm with an average of 3.126 ± 0.749%, 6.903 ± 3.150 ppm and 18.264 ± 6.179 ppm respectively. the activity concentrations of 40k, 238u and 232th, as calculated following iaea (2003) was found in the range 701.433 to 1422.147 bq/kg with an average of 978.901 ± 161.189 bq/kg, 39.805 to 153.454 bq/kg with an average of 85.340 ± 21.423 bq/kg and 42.454 to 111.790 bq/kg with an average of 74.326 ± 13.899 bq/kg respectively. the calculated absorbed dose rates was obtained in the range 90.350 to 167.879 ngy/h with an average of 125.140 ± 18.249 ngy/h and was found nearly equal with the measured dose rate. the dose rate from the particular gamma radionuclides 40k, 238u and 232th were obtained in the range of 14.748 to 74.423 ngy/h, 3.366 to 116.744 ngy/h and 7.486 to 99.764 ngy/h respectively. the average dose rate from 40k, 238u and 232th were compared with population weighted average (table 1). table 1: absorbed dose rate compared with population weighted average [1] absorbed dose rate in air (ngy/h) gamma radionuclide 40k 238u series 232th series population weighted average 18 15 27 present study 40.806±9.786 39.386±17.976 44.789±15.153 http://en.worldstate.info/asia/nepal http://en.worldstate.info/asia/nepal anita mishra and raju khanal/ bibechana 22 (2025) 85-92 88 figure 3: measured absorbed dose rate map of bagh bhairav overlaid on (a) an imagery map (b) a topographical map showing altitude contour. the average measured dose rate and calculated dose rate were found to 128.661 ± 14.637 ngy/h and 125.140 ± 18.249 ngy/h respectively and the ratio of them (0.972) inferred no discrepancies in survey data. the variation in calculated dose rate was found more than measured dose rate in the studied area (figure 5). figure 4: contour map of absorbed dose rate in air (a), concentrations of 40k (b), 238u (c) and 232th (d). the contour maps of measured absorbed dose rate, concentrations of 40k, concentrations 238u and concentrations 232th with latitude and longitude were shown in figure 4. the variation of dose rate in the area seems smooth though it had high standard deviation. the variation of concentrations of 40k and 232th is smooth in the area while 238u concentration shows little roughness. 4.1 outdoor aed and elcr the outdoor aed was found to be 0.157 msv which is higher than the world average value of outdoor aed from terrestrial gamma dose. the elcr was calculated from outdoor aed and was found 0.519 ×10−3 which is also higher than the world average. 5 discussion the dose rate was found to be higher near the walls of the temples, as the gamma radionuclides 238u, 232th and 40k present in building materials (mud, clay bricks, and stones) also contribute to gamma radiation. these dose rates are associated with gamma radiation from the earth’s crust (sedimentary rocks of lacustrine deposits) as well as from building materials. the elevated dose rate in the complex is attributed to higher activity concentrations of primordial radionuclides in the area. the terrestrial gamma dose rate varies slightly within the complex, reflecting the activity concentrations of natural gamma radionuclides present in the soils and rocks, which have dispersed in the area due to long-lasting geological processes. the activity concentrations of the gamma radionuclides 238u, 232th and 40k were found to be higher than the world population-weighted averages of 33 bq/kg, 45 bq/kg, and 420 bq/kg, respectively [1]. figure 5: variation between measured dose rate and calculated dose rate. the shape and spread of the measured absorbed dose rates and calculated dose rate data show asymmetry, as illustrated in the histogram (figure 6). the frequency distribution of the concentrations of 238u, 232th and 40k was also found to be non-symmetric and right-skewed, with most values shifted toward the left, indicating that the mean is greater than the median (figure 6). the median, dispersion, and range of dose rates from the concentrations of gamma radionuclides 238u, 232th and 40k were compared using box-whisker plots (figure 7), with whiskers extending to 1.5 times the interquartile range (iqr). regression analysis between the activity concentrations of 238u, 232th anita mishra and raju khanal/ bibechana 22 (2025) 85-92 89 and 40k and the measured absorbed dose rate was conducted using a scatter plot (figure 8). the results of the statistical analysis are presented in table 2. hypothesis tests for histogram normal fitting and regression analysis (linear fitting) were performed at a 0.05% significance level. radiological data for soil and rocks in nepal is available for the hetauda region [21], and while some areas have been monitored for various reasons, comprehensive data is still lacking. therefore, the data from the present study will serve as baseline data for nepal. the study determined that the measured absorbed dose rate in air is higher than the world average. the ratio of the absorbed dose rates (calculated and measured) shows a discrepancy of less than 30%, indicating that the survey data is logically representative [1]. the outdoor annual effective dose (aed) calculated was found to be higher than the world average background radiation for outdoor terrestrial radiation, which is typically around 0.07 msv [1]. the outdoor aed for the study area is compared with neighbouring countries such as india (which shares similar geological and geographical conditions), china, and others (table 3). the excess lifetime cancer risk (elcr) value was also found to be higher than the world average of 0.29×10−3 [1], but the associated risk of developing cancer remains negligible. figure 6: distribution of (a) measured, and (b) calculated absorbed dose rates, activity concentrations of (c) 40k, (d) 238u, and (e) 232th. figure 7: calculated absorbed dose rates from activity concentrations of 40k, 238u and 232th. figure 8: correlation between measured absorbed dose rate and activity concentrations of (a) 40k (b) 232th (c)238u and (d) calculated absorbed dose rate. anita mishra and raju khanal/ bibechana 22 (2025) 85-92 90 table 2: statistics of the survey data measured dose rate (ngy/h) calculated dose rate (ngy/h) conc. of 40k (%) conc. of 232th (ppm) conc. of 238u (ppm) mean 128.661 124.982 3.126 6.903 18.264 median 130.195 123.916 3.092 6.538 17.581 first quartile 114.845 107.966 2.605 4.586 13.789 third quartile 138.406 140.085 3.607 8.757 22.042 standard error 0.391 0.616 0.02 0.084 0.165 standard deviation 14.637 23.077 0.75 3.151 6.181 coefficient of variation 0.113 0.184 0.239 0.456 0.338 skew 0.239 0.261 0.302 0.755 0.564 kurtosis -0.466 -0.22 0.103 0.766 0.179 table 3: comparative study of outdoor (aed) in different regions of nepal and the world s.n. sites outdoor aed (msv) references 1 hetauda, nepal 0.12 [22] 2 garhwal, india 0.17 [5] 3 una, india 0.1 [9] 4 kirklareli, turkey 0.144 [4] 5 kohistan, pakistan 0.12 [23] 6 islamabad, pakistan 0.16 [24] 7 pahang, malaysia 0.22 [3] 8 baotou, china 1.03 [25] 9 odha, india 0.17 [26] 10 mrima hill environs, kenya 0.86 [27] 11 tribhuvan university, kirtipur 0.142 [28] 12 unesco sites, kathmandu 0.148–0.186 [29] 13 tarakeshwar, kathmandu 0.15 [30] 14 bishnumati bridges, kathmandu 0.906 [31] 15 present study 0.157 – 16 world average 0.07 [1] 6 conclusions the in-situ radiological survey of the bagh bhairav complex was performed using a portable gammaray spectrometer equipped with a gps and data logger unit. the outdoor absorbed dose rate in air was found to be nearly twice the world average. the absorbed dose rate in air was compared with terrestrial data, and statistical analysis revealed a positive linear correlation between them. the distribution showed a skewed pattern and was correlated with the concentrations of terrestrial gamma radionuclides. additionally, there was a strong agreement between the measured and calculated absorbed dose rates; the ratio of the calculated to measured dose rate was nearly equal to one, indicating no discrepancies in the data. the activity concentrations of 238u, 232th, and 40k in the complex were approximately 2.5 times higher than the world average, contributing to the elevated dose rates observed. although the outdoor annual effective dose (aed) and excess lifetime cancer risk (elcr) were higher than the world averages, the outdoor 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[31] nirmal k.c. et al. radiation level over the bishnumati river bridges: a study from balaju to teku in kathmandu, nepal. bibechana, 21:124–128, 2024. introduction material and methods gamma ray spectrometry dosimetry annual effective dose (aed) excess lifetime cancer risk (elcr) absorbed gamma dose rate theory results outdoor aed and elcr discussion conclusions bibechana vol. 22, no. 1, april 2025, 41-51 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar dynamics of wter pollution concentration with uniform and exponential increment of pollutants jeevan kafle1, ranjan kumar chaudhary1, bekha ratna dangol2,∗ 1centarl department of mathematics, tribhuvan university, kathmandu, nepal 2department of mathematics,patan multiple campus, tribhuvan university lalitpur, nepal ∗corresponding author. email: bdangol37@gmail.com abstract the study focuses on the one dimensional advection-dispersion equation (ade) to study the dynamics of concentration of water pollution when the pollutants at the source is increasing uniformly and exponentially. analytical solutions are obtained by using laplace transform and numerical solutions are by finite difference method (fdm). the steady state case is studied. the dynamics of pollution concentration along the length of river channel are shown through two dimensional plots by varying the rate of added pollutants, cross sectional area of river and water flow velocity. the pollution concentration decreases along the length of river (downstream) for each analysis. the analytical and numerical solutions are shown in three dimensional plots. the analytical and numerical solutions are compared with the help of relative error. the relative errors calculated for uniform and exponential increment of pollutants at the source are compared while studying the dynamics of the concentration. the environmental and chemical engineering may substantially benefit from such studies. keywords advection, dispersion, pollutant concentration, laplace transform, finite difference, relative error. article information manuscript received: may 13, 2024; revised: january 14, 2025; accepted: january 16, 2025 doi https://doi.org/10.3126/bibechana.v22i1.65799 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the rapid and unplanned development of urbanization, unregulated industries and highly dense population in the urban areas are becoming a serious problem in the natural environment [1]. more specifically, the degradation of the natural environment are due to poor waste management, public transports, excessive use of pesticides in agriculture, deforestation, release of toxic materials from industries, unmanaged drainage and many more [1]. in some eastern philosophies, water is often metaphorically linked to human civilization. however, contamination in these water resources like pond, river and lake at the urban areas poses a significant challenge to the communities, vegetation and other species that rely on them [1]. the major causes for these water pollution are unmanaged growth of urbanization, industries, and lack of public awareness. indeed, rivers play a crucial role in aquatic ecosystems by transporting water and nutrients to various areas [2]. however, when contam41 http://nepjol.info/index.php/bibechana bdangol37@gmail.com https://doi.org/10.3126/bibechana.v22i1.65799 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ jeevan kafle et al./ bibechana 22 (2025) 41-51 42 inated with pollutants, these waterways can become hazardous to human health and other species. consumption of contaminated water or exposure to pollutants can lead to sickness and even death among both humans as well as wildlife. these highlight the critical importance of protecting water sources from pollution [3]. as per a recent world health organization (who) report, inadequate water quality is responsible for 3.1% of fatalities and contributes to 80% of illnesses [4]. in the study of water pollution, biochemical oxygen demand (bod) serves as the gauge for assessing water pollution levels [5]. this analysis employed most of the parameters outlined by pimpunchat et al. (2007), under the assumption that the predominant pollutants are biochemical wastes [6]. for instance, bagmati river is widely recognized as the most polluted river in nepal with its biochemical oxygen demand (bod) consistently on the rise [7] (see, fig. 1). the extreme bod is achieved due to the consequence of high levels of organic matter, high iron, and low dissolved oxygen [8]. industrial waste and drainage from urban dwellers are responsible for the main source of bod loads, leading to the increased concentration of the pollutants along the river. prior studies on the water quality of bagmati river revealed the degradation in its lower portion with several significant parameters that exceeded the limits set by the national surface water quality standards and classification [7]. the ongoing deterioration of water quality in the bagmati river, revered as a holy river, serves as a compelling motivation for researchers to conduct systematic studies on water pollution. pollution in river channel takes place due to disposal of waste materials from point and non-point pollution sources [5]. understanding the transport and dispersion of pollutants from the source to body across the medium can substantially contribute for identifying sources of pollution, assessing the impact of contaminants on aquatic ecosystems, guiding and implementing pollution control measures and facilitating public awareness [1]. in overall, understanding, managing, and mitigating the impacts of pollution on water resources are the important aspects in the study of water pollution [6]. to describe the pollution dispersion in the water body, physical and mathematical models are developed. physical models are small scale representations of the water body. however, numerical experiments using mathematical models can cover the larger domain. these mathematical models are divided into statistical and deterministic models [1]. statistical models rely on the analysis of historical monitoring data, while deterministic models are constructed based on mathematical description of physical processes. figure 1: polluted bagmati river (left) and bod status in bagmati river at major locations (cities) at different years (right) [8]. bod is in rise over time (t) and location (x), where the river flows downstream. more specifically, bod contents consistently exceeded the limit for moderately contaminated water (2-8 mg l−1) and even crossed the threshold for treated municipal sewage (20 mg l−1). for the mathematical models to study water pollution, various conservation equations have been developed to describe the movement of substances subject to both advection and diffusion [9]. advection refers as the transport of substances by the flow of water and dispersion refers to the spreading of substances due to concentration gradients, typically from areas of higher concentration to areas of lower concentration [6]. with the rise of environmental engineering and the need to model the transport of pollutants in underground and surface water, the advection-dispersion equation gained prominence and is developed during the latter half of the 20th century [9]. due to the reliability, the advection and dispersion equations have been emerged in several fields, including environmental sciences, chemistry, and physics. these equations are incredibly employed for the spreading of pollution which may take the form of any substance (gas, liquid or solid) or energy ( radioactivity, heat, sound, or light) [10]. marusic [11] developed a model to describe the disjeevan kafle et al./ bibechana 22 (2025) 41-51 43 persion of pollutants in systems resembling rivers over the temporal changes in pollutant concentrations. pochai et al. [12] proposed a convectiondiffusion model with constant coefficients to optimize contaminant levels in waste water treatment and successfully solved it by employing the finite element method. the primary objective was to reduce the initial cost of water treatment, thereby achieving more cost-effective treatment solutions. later on, it was extended to two dimensions by tabuenca et al. [13]. the advection-diffusion equations are employed for various prospective: prediction of the transport concentration of pollutants (johari et al. [14]); contamination of rivers (pimpunchat et al. [6]); deriving pollutant concentration field (miller et al. [15]). poudel et al. [?, 10], solving one dimensional ade for pollutant concentration with zero dispersion and steady state cases are analyzed for oxygen concentration with zero as well as non zero dispersion coefficients. finding the analytical and numerical solutions for the developed models are another important aspects of this field. lots of efforts have been made in finding analytical solutions in some states and reduced situations using different approaches. the example includes the use of laplace transform and with greens functions for pollutant concentration (carslaw and jaeger [17]; poudel et al. [10]); finite difference approach in semi-infinite mediums (savovic and djordjevich [18]); semi infinite domain with zero initial concentration (van and alves [9]); laplace transform approach for the temporally and spatially dependent solute dispersion in a onedimensional semi-infinite porous medium (kumar et al. [19]). the purpose of the study is to obtain the analytical and numerical solutions of advection dispersion equation modeled for uniform and exponential increment of pollution concentration at point source and hence observe the dynamics of pollution concentration at different spatial points along the length of the river. laplace transform technique is used for analytical solution and finite difference scheme, forward time central space scheme (ftcss) is used for numerical solution. the obtained solutions are compared with the help of relative error for more reliable result. 2 mathematical model and numerical method 2.1 the governing equation in this model developed by manitcharoen and pimpunchat (2020) [5], the involved parameters are based on the assumption that the contaminants are only due to the biochemical wastes [6]. the rate of change of the pollution concentration with position (x) and time (t) is expressed as ∂(ap ) ∂t = dp ∂2(ap ) ∂x2 − ∂(vap ) ∂x −k1 x x + k (ap )+qh(x), 0 ≤ x < l, t > 0 (1) where, h(x) is the heaviside function as suggested by chapra [20] (1997), defined as h(x) = { 1, 0 < x < l, 0, otherwise. (2) here, v is the flow velocity of water along the river, p is the pollution concentration, dp is the dispersion coefficient, k1 is the pollutant degradation rate coefficient, q is added pollutant rate, k is halfsaturated oxygen demand concentration, x represents concentration of dissolved oxygen, and a is the cross sectional area of the river [5]. pollutant of oxygen concentration quantities are considered homogeneous throughout the cross-section of river and can fluctuate over the its length. this presumption meets the requirement as proposed by dobbin [21]. for convenience, we assume that the parameters a, q, dp, and k1 remain constant both spatially and temporally [22]. the pollution concentration at the source may increase uniformly or sometimes, it may increase exponentially. the case of insignificant k (k≈0) is taken into consideration for analysis as it isnot possible to use laplace transform technique to solve advection dispersion equation [5]. from equation (1), the rate of change of the pollution concentration p1(x, t) resulting from a uniform increase in the pollution concentration at source is ∂(ap1) ∂t = dp ∂2(ap1) ∂x2 − ∂(vap1) ∂x −k1ap1 + qh(x). (3) similarly, the pollution concentration p2(x, t) resulting from exponential rise in the pollution concentration at source is ∂(ap2) ∂t = dp ∂2(ap2) ∂x2 −∂(vap2) ∂x −k1ap2+q(1−exp(−λx))h(x), (4) where the arbitrary constant λ represents the exponential pollution source term. initially, the domain is free of solutes. so, the initial condition is p (x, t) = 0, x ≥ 0, t = 0. (5) jeevan kafle et al./ bibechana 22 (2025) 41-51 44 the concentration at the origin is p0 and the concentration gradient is supposed to be zero at infinite length of course. so, boundary conditions are p (x, t) = p0, x = 0, t > 0, (6) ∂p (x, t) ∂x = 0, x → ∞, t > 0. (7) 2.2 analytical solution let the function p (x, t) is assumed to be bounded and defined for t > 0. let p̄ (x, s) be laplace transform of the function p (x, t), where s is transformed variable of t [5]. using laplace transform for equations (3) and (4), we get respectively, dpa d2p̄1(x, s) dx2 − va dp̄1(x, s) dx −k1ap̄1(x, s) +a(sp̄1(x, s)− p1(x, 0)) + q s = 0, (8) dpa d2p̄2(x, s) dx2 − va dp̄2(x, s) dx −k1ap̄2(x, s) +a(sp̄2(x, s)− p2(x, 0)) + q(1− exp(−λx)) s = 0, (9) where s > 0, x ≥ 0. the initial (5) and boundary conditions (6) and (7) are transformed respectively as p̄ (x, s) = 0, x ≥ 0, s = 0; p̄ (x, s) = p0 s , x = 0, s > 0; dp̄ dx (x, s) = 0, x → ∞, s > 0. (10) using (10) in (8), we get d2 dx2 (p̄1(x, s))− v dp d dx (p̄1(x, s))− k1 + s dp p̄1(x, s) = − q sadp . (11) auxiliary equation of (11) is m2 − v dp m− k1 + s dp = 0. (12) this is quadratic in m whose roots are m1 = v + √ v2 + 4dp(k1 + s) 2dp , and m2 = v − √ v2 + 4dp(k1 + s) 2dp . thus, complimentary function and particular integral respectively are, c1e m1x + c2e m2x and q as(k1 + s) . the solution of (8) is p̄1(x, s) = c1e m1x + c2e m2x + q as(k1 + s) . (13) using boundary condition (10), c1 + c2 = p0 s − q sa(k1 + s) . (14) differentiating equation (13) with respect to x, we get dp̄1(x, s) dx = c1m1e m1x + c2m2e m2x. again, by using boundary condition (10) in above equation, we get c1 = 0. thus from (13), required solution is p̄1(x, s) = ( p0 s − q sa(k1 + s) ) em2x + q as(k1 + s) . jeevan kafle et al./ bibechana 22 (2025) 41-51 45 also, we can write p̄1(x, s) = ( p0 s − q sa(k1 + s) ) exp (( γ − √ s+ β2 dp ) x ) + q as(k1 + s) , (15) where, γ = v 2dp , β = √ v2 4dp +k1. now, we find the solution of equation (9) by the similar process as above. using (10) in (9), we get d2 dx2 (p̄2(x, s))− v dp d dx (p̄2(x, s))− k1 + s dp p̄2(x, s) = −q(1− exp(−λx)) sadp . (16) auxiliary equation of (16) is m2 − v dp m− k1 + s dp = 0. (17) so, roots of equation (17) are m1 = v + √ v2 + 4dp(k1 + s) 2dp , and m2 = v − √ v2 + 4dp(k1 + s) 2dp . thus complimentary function and particular integral respectively are, c1e m1x + c2e m2x and q as(k1 + s) − qe−λx as(k3 + s) where, k3 = k1 − λv − λ2dp. thus, the solution of (16) is p̄2(x, s) = ( p0 s − q sa(k1 + s) + qe−λx as(k3 + s) ) em2x + q as(k1 + s) − qe−λx as(k3 + s) . (18) using boundary conditions (10) and calculating same as above, we get the solution of equation (16) as p̄2(x, s) = ( p0 s − q sa(k1 + s) + qe−λx as(k3 + s) ) em2x + q as(k1 + s) − qe−λx as(k3 + s) . it can be written as p̄2(x, s) = ( p0 s − q sa(k1 + s) + qe−λx as(k3 + s) ) exp (( γ − √ s+ β2 dp ) x ) + q as(k1 + s) − qe−λx as(k3 + s) . (19) taking inverse laplace transform to the equations (15) and (19), the respective analytical solutions of equations (3) and (4) are p1(x, t) = q ak1 (1− exp(−k1t)) + 1 2 ( p0 − q ak1 ) exp (( β√ dp + γ ) x ) erfc ( x 2 √ dpt + β √ t ) + exp (( −β√ dp + γ ) x ) erfc ( x 2 √ dpt − β √ t ) + q 2ak1 exp ( v dp x−k1t ) .erfc ( x 2 √ dpt + γ √ dpt ) + exp(−k1t)erfc ( x 2 √ dpt − γ √ dpt ) , (20) jeevan kafle et al./ bibechana 22 (2025) 41-51 46 p2(x, t) = q ak1 (1− exp(−k1t))− q ak3 exp(−λx)(1− exp(−k3t)) + 1 2 ( p0 − q ak1 + q ak3 ) . exp (( β√ dp + γ ) x ) erfc ( x 2 √ dpt + β √ t ) + exp (( −β√ dp + γ ) x ) .erfc ( x 2 √ dpt − β √ t ) + q 2ak1 exp ( v dp x−k1t ) erfc ( x 2 √ dpt + γ √ dpt ) + exp(−k1t)erfc ( x 2 √ dpt − γ √ dpt ) − q 2ak3 exp (( θ√ dp + γ ) x−k3t ) .erfc ( x 2 √ dpt + θ √ t ) + exp (( −θ√ dp + γ ) x−k3t ) erfc ( x 2 √ dpt − θ √ t ) , (21) where, θ = √ v2/4dp + vλ+dpλ2. 2.3 the steady state case taking t→∞ to the equations (20) and (21) gives the steady state case as follows p1(x, t → ∞) = q ak1 + ( p0 − q ak1 ) exp (( γ − β√ dp ) x ) , (22) and p2(x, t → ∞) = q ak1 − q ak3 exp(−λx) + ( p0 − q ak1 + q ak3 ) exp (( γ − β√ dp ) x ) . (23) now, taking x→∞ to calculate downstream pollutant concentration, we get p1(x → ∞, t → ∞) = p2(x → ∞, t → ∞) = q ak1 . (24) 2.4 numerical technique here, we use forward time and central space scheme (ftcss) to find numerical solution of equations (3) and (4). these equations in finite difference form can be written as [5], pn+1 1m − pn 1m k = dp h2 (p1m+1 − 2pn 1m + pn 1m−1)− v 2h (pn 1m+1 − pn 1m−1)−k1p n 1m + q a , (25) pn+1 2m − pn 2m k = dp h2 (p2m+1 − 2pn 2m + pn 2m−1)− v 2h (pn 2m+1 − pn 2m−1)−k1p n 2m + q a (1− exp(−λxn m)) (26) where, m and n refer to the discrete step size h and k respectively. the initial and boundary conditions (10) can be written respectively as [5] pm,0 = 0, x ≥ 0; p0,n = p0, t > 0; pm,n = pm−1,n, x → ∞, t ≥ 0. (27) the stability condition is dpk/h 2≤1/2 for the above schemes. 3 results and discussion we comparatively study the dynamics of the water pollution concentration over the river channel when the pollutants at the source increases uniformly and exponentially along with the variation of the rate of added pollutant, cross section area of the water channel, and flow velocity over time. the parametric values are extracted from the different existing literatures. for various plots to study the concentration dynamics, the values for involved parameters are taken as: dp=10 m2 hr−1, jeevan kafle et al./ bibechana 22 (2025) 41-51 47 v=4 mhr−1, a=10 m2, k1=1 hr−1, p0=1 kgm−3, q=1.02 kgm−1 hr−1 and λ=0.06289 [5]. 3.1 comparison of dynamics of concentrations p1 and p2 keeping the same parameter values, the dynamics of the pollution concentrations p1 along the river for the uniformly increasing pollutants and p2 for exponentially increasing pollutants are revealed in the fig. 2. figure 2: comparison of pollution concentrations p1 and p2 at different spatial regions when the pollutant at source increases uniformly and exponentially respectively. the concentration p2 is higher than p1 at the vicinity of the source of pollutant at x = 0 and then both saturates to the almost same level as the water flows substantially downstream. initially, at the source x = 0, pollution concentration p2 is relatively larger than that of p1 as pollutants at the source is increasing exponentially for p2 and uniformly for p1. both the concentrations decrease non-linearly over the distance and time until the flow travels 18 km. in this moment, the rate of decrement of p2 is substantially faster than that of p1. after traveling about 18 km from the source, both the concentrations decreases asymptotically. as a result, both graphs look like the same. however, they vary by the incredibly smaller margin. the applied model enables to study the dynamics for the significantly longer travel distance. however, we study only upto 30 km of travel distance. the concentration decreases rapidly for exponential increment case rather than uniformly increment form along the length of the river channel. 3.2 dynamics of concentrations p1 and p2 as rate of added pollutant varies the concentration dynamics of pollution p1 and p2 are shown in fig. 3 as the rate of added pollutants q varies for q = 0.04, 1.02 and 2.00. the dispersion rate of the pollution is the greatest when the rate of added pollutants q is the least. on the contrary, the rate is the least when q is the greatest. figure 3: evolution of pollution concentration a: p1, b: p2 at different spatial regions along the river as rate of added pollutants (q) varies. the pollution concentration decreases at slow rate as the rate of added pollutants increases. as a result, the effect of rate of added pollutants q near the upstream is very less and that near the downstream is dominant in both the cases. but in case of fig. 3b, the effect of rate of added pollutants q is very less near the origin as it is affected by exponential source term λ. for the case fig. 3a, the concentration decreases non-linearly till x=19 km and then after it goes asymptotically whereas for the case fig. 3b, it decreases non-linearly till x=21 km and then after goes asymptotically. the concentration of pollutants decreases at slow rate at any cross section of the river as the rate of added pollutants q increases. 3.3 dynamics of concentration p1 and p2 as cross section area of the river channel varies the variation of pollution concentrations p1 and p2 with different cross sectional area a of the river jeevan kafle et al./ bibechana 22 (2025) 41-51 48 channel, along the length of the river is shown in fig. 4 as the cross sectional area of the river varies for a=5, 10, 80. figure 4: evolution of pollution concentration a: p1, b: p2 at different spatial regions along the river as cross sectional area a of the river channel varies. the pollution concentration decreases as the cross sectional area of the river channel increases. when the cross sectional area of the river channel is less, then there is not enough space for pollutants to be dispersed more rapidly. thus, the concentration of pollutants remains condensed and is more for least area. thus, the pollution concentration decreases at any cross section of the river as the cross sectional area increases. the rate of decrement of concentration is more when the cross sectional area is more and is less for less area. the effect of cross sectional area is less for case fig. 4a and very less for case fig. 4b near the upstream and dominant near the downstream. the increment of pollutants is exponential in case of fig. 4b, so the concentration profile near the origin seems to be very close. but it is not so close in case of uniform increment. for the case fig. 4a, the concentration decreases non-linearly till x=21 km and then after it goes asymptotically whereas for the case fig. 4b, it decreases non-linearly till x=23 km and then after goes asymptotically. in overall, the concentration decreases along the length of river channel as cross sectional area increases. 3.4 dynamics of concentration p1 and p2 as flow velocity of the river varies the variation of pollution concentrations p1 and p2 with different water flow velocity v along figure 5: evolution of pollution concentration a: p1, b: p2 at different spatial regions along the river as the flow velocity of water v varies. the pollution concentration increases as the flow velocity of water increases. the length of the river is shown in fig. 5. with the increase of velocity, advection becomes more dominant than dispersion and hence the rate of decrement of concentration of the pollution decreases with increase in water flow velocity along the length of the river. if the water flow velocity is least, then pollutants get dispersed very near to the origin and concentration decreases so rapidly. but when water flow velocity is high then the concentration does not get chance to disperse so rapidly at the same position and hence rate of decrement of concentration becomes slower. for v=2, 4 & 6, concentration decreases non-linearly till the position x=16, 20 & 23 km in case of fig. 5a, and x=17, 21 & 25 km in case of fig. 5b, respectively and then goes asymptotically. jeevan kafle et al./ bibechana 22 (2025) 41-51 49 3.5 dynamics of the concentration as travel distance and travel time both varies we obtained the analytical and numerical solutions of advection dispersion equation (ade) with uniform and exponential increment of pollutants at origin by employing laplace transform technique and finite difference technique respectively. figure 6: analytical: a and numerical: b solution of equation (3). the both solutions do not provide exactly same values but provide nearly comparable values. fig. 6 shows the pollution concentration p1(x, t) at each grid point of time and space. in both cases fig. 6a and fig. 6b, concentration at origin is the highest and goes down as distance increases. the concentration decreases rapidly along the distance whereas it decreases slowly along time. the concentration at peak point i.e at x=30, t=3, is very less approximate to zero but not actually zero. though values of concentration obtained from analytical and numerical solutions are not exactly same, they are close to each other. thus nature of both the three dimensional plots are same but not exact. similarly, fig. 7 shows the nearly same thing as described for fig. 6 i.e. concentration at origin is the highest and decreases rapidly along the distance and slowly along the time. but concentration at origin for fig. 7 is higher than that of fig. 6. this clears that forward time central space scheme (ftcss) is somehow good scheme to solve these modeled equations but not perfect. figure 7: analytical: a and numerical: b solution of equation (4). the both solutions do not provide exactly same values but provide nearly comparable values 3.6 error analysis the solutions obtained analytically and numerically can be compared with relative error which is defined by [5], relative error = ∣∣∣∣∣panalytical − pnumerical panalytical ∣∣∣∣∣ (28) the relative errors of pollution concentrations for both the cases by h=1 and k=0.03 at t=3 hours are tabulated below. the domain for distance is taken up to 20 km from the origin to analyze the relative error between analytical and numerical solution of advection-dispersion equation (ade). table 1 shows the relative error for p1 and table 2 shows that for p2. from both the tables, table 1 and table 2, we can see that concentrations goes on decreasing with increase in distance. the relative error is less near the origin and more at far from the origin within the domain. the error for both pollution concentrations p1 and p2 is shown with the help of histogram below in fig. 8, where red colored pillar shows the analytical solution whereas green colored pillar shows the numerical solution. as the analytical and numerical solutions for p1 and p2 are compared, the relative error is higher in computing p2 rather than p1, which can be seen clearly from the tables given below. table 1: relative error of pollution concentration p1 [kg m−3] at t = 3 hours. distance (km) analytical solution numerical solution error error % 0 2.301356 2.283520 0.007750 0.770 5 0.945251 0.930611 0.015400 1.548 10 0.409821 0.399460 0.025281 2.530 15 0.193824 0.183838 0.05152 5.152 20 0.104777 0.098491 0.05999 5.999 jeevan kafle et al./ bibechana 22 (2025) 41-51 50 table 2: relative error of pollution concentration p2 [kg m−3] at t = 3 hours. distance (km) analytical solution numerical solution error error % 0 2.405330 2.427610 0.009260 0.926 5 1.089690 1.121450 0.029140 2.914 10 0.507550 0.477210 0.059770 5.977 15 0.182539 0.169762 0.069990 6.990 20 0.085641 0.092935 0.085160 8.516 figure 8: comparison of analytical and numerical solutions for water pollution concentration with uniform (left) and exponential (right) increment of pollutants at origin. in both the cases analytical as well as numerical solutions are obtained close to each other. 4 conclusion in this study, one dimensional advectiondispersion equation (ade) is applied to study the dynamics of water pollution concentration at different spatial region along the length of river as the pollutants in the source increasing uniformly and exponentially. the analytical solutions of the employed model are presented by employing laplace transform and steady state state case is studied. it has been found that concentration becomes a fixed positive constant when time and space both tends to infinity. dispersion coefficient of pollution concentration is taken to be non zero. the results show that the pollution concentration at the source is relatively larger in the case of exponentially increment than that for uniformly increment. however, as the water flows substantially, these concentrations vary with small margin due to their advection and dispersion through the medium of water. the variations of concentrations p1 and p2 are presented along the length of the river with respect to the variation in rate of added pollutants, crosssectional area of the river, water flow velocity. the results reveals that as the water flows downstream, the concentration decreases. however, their rate of decrement varies. as the rate of added pollutants increases, the concentration decreases slowly. similarly, as velocity of the water increases, the water pollution advects rather than the dispersion that slows the decrease in concentration variation. when the area of cross section of the river channel increases, there will high discharge of water through the channel. consequently, pollution concentration quickly decreases. the three dimensional plots reveal that pollution concentration is the highest at origin (source) at the initial time and it decreases over time and space. however, it quickly decreases with traveled distance rather than traveled time due to the increment of pollutants either uniformly or exponentially. the numerical solutions of the model equations are obtained by finite difference method (fdm) using forward time central space scheme (ftcss). as the analytical and numerical solutions for p1 and p2 are compared, the relative error is higher in computing p2 rather than p1. these results may be useful in better understanding the water pollution that may contribute to environmental engineering, hydrology, contaminant transport modeling and chemical engineering where the advection and dispersion of contaminants is widely applied. references [1] p. goyal and a. kumar. mathematical modeling of air pollutants: an application to indian urban city. air quality-models and applications. doi:10.5772/16840, 2011. jeevan kafle et al./ bibechana 22 (2025) 41-51 51 [2] a. s. wadi, m. f. dimian, and f. n. ibrahim. analytical solution of one-dimensional advection-dispersion equation of the pollutant concentration. journal of earth system science, 123(6):1317–1324, 2014. [3] s. a. alruman, a. f. el-kott, and m. a. keshk. water pollution: source and treatment. american journal of environmental engineering, 6(3):88–98, 2016. [4] m. haseena, m. f. malik, a. javed, s. arshad, n. adif, s. zulqar, and j. hanif. water pollution and human health. environmental risk assessment and remediation, 1(3):16–19, 2017. [5] n. manitcharoen and b. pimpunchat. analytical and numerical solutions of pollution concentration with uniformly and exponentially increasing forms of sources. journal of applied mathematics, 2020:1–9, 2020. [6] b. pimpunchat, w. l. sweatman, w. triampo, g. c. wake, and a. parshotam. modelling river pollution and removal by aeration. modelling and simulation society of australia and new zealand, pages 2431–2437, 2007. [7] b. k. mishra, r. k. regmi, y. masago, k. fukushi, p. kumar, and c. saraswat. assessment of bagmati river pollution in kathmandu valley: scenario-based modeling and analysis for sustainable urban development. sustainability of water quality and ecology, 9:67–77, 2017. [8] k. pokhrel. water quality monitoring of bagmati river basin, kathmandu valley. doctoral dissertation, amrit campus, 2023. [9] m. t. van genuchten and w. j. alves. analytical solution of the one-dimensional convectivedispersive solute transport equation volume bulletin no.1661. us department of agriculture, agricultural research service, 1982. [10] k. poudel, j. kafle, and p. s. bhandari. analytical solution for advection-dispersion equation of the pollutant concentration using laplace transformation. journal of nepal mathematical society, 4(1):33–40, 2021. [11] g. a. l. marusic. a study on the mathematical modeling of water quality in river type aquatic systems. journal wseas transactions on fluid mechanics, 8(2):80–89, 2013. [12] n. pochai, s. tangmanee, l. j. crane, and j. j. miller. a mathematical model of water pollution control using the finite element method. proceedings in applied mathematics and mechanics, 6(1):755–756, 2006. [13] p. tabuenca, j. vila, j. cardona, and a. samartin. finite element simulation of dispersion in the bay of santander. advances in engineering software, 28(5):313–332, 1997. [14] h. johari, n. rusli, and z. yahya. finite difference formulation for prediction of water pollution. materials science and engineering, 318(012005):1–10, 2018. [15] j. j. miller, n. pochai, s. tangmanee, and l. j. crane. a water quality computation in the uniform channel. journal of interdisciplinary mathematics, 11(6):803–814, 2008. [16] g. e. roberts and h. kaufman. table of laplace transforms. w. e. saunders co., philadelphia and london, 1969. [17] h. s. carslaw and j. c. jaeger. conduction of heat in solids. clarendon press, oxford, uk, 1959. [18] s. savović and a. djordjevich. finite difference solution of the one-dimensional advection– diffusion equation with variable coefficients in semi-infinite media. international journal of heat and mass transfer, 55(15-16):4291–4294, 2012. [19] a. kumar, d. k. jaiswal, and n. kumar. analytical solutions to one-dimensional advection– diffusion equation with variable coefficients in semi-infinite media. journal of hydrology, 380(3-4):330–337, 2010. [20] c. s. chapra. surface water-quality modeling. the mcgraw-hill companies, 1997. [21] w. e. dobbins. bod and oxygen relationships in streams. journal of the sanitary engineering division, 90(3):53–78, 1964. [22] g. li. stream temperature and dissolved oxygen modeling in the lower flint river basin, ga. doctoral dissertation, university of georgia, 2006. [23] g. e. roberts and h. kaufman. table of laplace transforms. w. e. saunders co., philadelphia and london, 1969. [24] d. k. salkuyeh. on the finite difference approximation to the convection-diffusion equation. applied mathematics and computation, 179(1):79–86, 2006. [25] r. k. singh, h. yabar, n. nozaki, and r. rakwal. analyzing waste problems in developing countries: lessons for kathmandu, nepal through analysis of the waste system in tsukuba city, japan. journal of scientific research and reports, 8(6):1–13, 2015. introduction mathematical model and numerical method the governing equation analytical solution the steady state case numerical technique results and discussion comparison of dynamics of blackconcentrations p1 and p2 dynamics of blackconcentrations p1 and p2 as rate of added pollutant varies dynamics of concentration p1 and p2 as cross section area of the river channel varies dynamics of concentration p1 and p2 as flow velocity of the river varies dynamics of the concentration as travel distance and travel time both varies error analysis conclusion bibechana vol. 22, no. 2, august 2025, 131-141 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar estimation of phytochemicals, antioxidant, antimicrobial, and brine shrimp lethality activities of valeriana jatamansi jones indra ojha, khaga raj sharma∗ 1central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal ∗corresponding author. email: khaga.sharma@cdc.tu.edu.np abstract herbal medicine has been widely utilized in traditional medicine for treating various ailments. this study aimed to quantify the phenolic, flavonoid, and tannin content in different plant extracts, assess their antioxidant capacity, and evaluate their antimicrobial efficacy. among the extracts tested, methanol exhibited the highest total phenolic content (tpc) at 166.5 ± 2.0 mg gae/g and total flavonoid content (tfc) at 103.87 ± 5.47 mg qe/g, whereas hexane displayed the lowest tpc (16.03 ± 2.22 mg gae/g) and tfc (8.27 ± 3.88 mg qe/g). the methanolic extract demonstrated the strongest antioxidant activity with an ic50 of 103.3 ± 1.53 g/ml, compared to the hexane extract's ic50 of 524.7 ± 0.89 µg/ml. antimicrobial testing revealed that aqueous, ethanolic, and hexane extracts effectively inhibited klebsiella pneumoniae with a zone of inhibition of 17 mm, comparable to the positive control neomycin (24 mm). the ethanolic extract showed substantial minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) values against k. pneumoniae and staphylococcus aureus (3.12 mg/ml and 6.25 mg/ml, respectively), relative to the control (0.0078 mg/ml and 0.015 mg/ml). additionally, cytotoxicity assays showed lc50 values of 1905.46 µg/ml for the ethanolic and 2137.96 µg/ml for the methanolic extract. these findings suggest that the studied plant extracts, particularly methanolic and ethanolic, have significant bioactive potential, positioning them as promising sources for future drug development against infectious diseases. keywords valeriana jatamansi, tpc, tfc, dpph, antimicrobial, mic, mbc, toxicity article information manuscript received: november 8, 2024; revised: march 16, 2025; accepted: march 17, 2025 doi https://doi.org/10.3126/bibechana.v22i2.71378 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction medicinal plants have long played a critical role in human health, providing therapeutic compounds that have been used since ancient times to manage and treat diseases. these plants, which contain bioactive compounds in various organs, serve either as direct therapeutic agents or as essential precursors for drug synthesis. a distinction exists between medicinal plants that have been scientifically validated for their therapeutic effects and those consid131 http://nepjol.info/index.php/bibechana khaga.sharma@cdc.tu.edu.np https://doi.org/10.3126/bibechana.v22i2.71378 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ indra ojha and khaga raj sharma/ bibechana 22 (2025) 131-141 132 ered medicinal but lack thorough scientific study, underscoring the need for continued research into these natural resources [1, 2]. natural materials, including plant parts, animal products, and microorganisms, have a historical foundation in medicine, with fossil evidence indicating that humans have utilized plants for medicinal purposes for at least 60,000 years. the chemical diversity found in natural compounds has developed over millions of years, providing an array of biologically active substances with potential pharmacological effects [3]. phytochemicals, the bioactive constituents produced by plants, are essential metabolites that contribute to various functions such as plant growth, pollination, and defense against pathogens. these compounds are not only crucial for plant survival but also play an important role in protecting plants from environmental stressors, including disease and uv radiation [4,5]. phytochemicals can be classified into primary and secondary metabolites. primary metabolites, like proteins, carbohydrates, and nucleic acids, are indispensable for basic plant functions, while secondary metabolites, including phenolics, flavonoids, and terpenoids, arise from more specialized metabolic pathways. these secondary compounds are often associated with defensive functions, including antibacterial, antifungal, and antiviral properties, making them of great interest for therapeutic use [6,7]. antioxidants, flavonoids, and phenolic compounds found in medicinal plants help combat oxidative stress, which is linked to degenerative diseases such as cancer, atherosclerosis, and gastric ulcers [8, 9]. one notable medicinal plant is valeriana jatamansi jones, a perennial herb from the valerianaceae family, native to the himalayan region and traditionally valued for its broad spectrum of medicinal properties [10, 11]. distributed from afghanistan to china, v. jatamansi jones has been used to treat various conditions, including neurological disorders, insomnia, and bacterial infections. its bioactive profile includes valepotriates, lignans, sesquiterpenoids, flavones, and other phytochemicals, supporting its application in ailments such as epilepsy, skin diseases, and obesity [12–14]. in addition to its historical significance in traditional medicine, studies have highlighted the plant’s anti-inflammatory, sedative, antioxidant, and neuroprotective effects [15]. despite its longstanding use, comprehensive studies examining the phytochemical composition and biological properties of the aerial parts of v. jatamansi jones remain limited. this study aims to fill this research gap by analyzing the phytochemical constituents and evaluating the biological activities of the aerial parts of v. jatamansi jones, contributing to a deeper understanding of its therapeutic potential. 2 materials and methods 2.1 chemicals for this study, high-purity analytical-grade solvents-methanol, ethanol, ethyl acetate, dichloromethane, and hexanewere sourced from merck and fischer scientific to ensure optimal extraction conditions. edta disodium salt dihydrate was supplied by srl, while merck provided additional reagents including sodium chloride, boric acid, and fused calcium chloride. key materials such as the folin-ciocalteu (fc) reagent, resazurin, and microbial culture media including mueller hinton broth, nutrient agar, and mueller hinton agar were obtained from hiemedia and loba chemi pvt. ltd. the use of high-quality reagents and culture media was essential for achieving precision in both the phytochemical analyses and microbiological assays. 2.2 plant collection and identification the aerial parts of valeriana jatamansi jones were collected from the far western region of nepal (sayal gaupalika-02, doti). details such as the scientific name, local name, plant parts used, and ethnomedicinal applications are summarized in table 1. the specimen was authenticated by research officers at the herbarium center, where it was assigned the voucher code 01kath162457. a visual representation of the v. jatamansi jones medicinal plant is provided in figure 1. figure 1: aerial parts of v. jatamansi jones indra ojha and khaga raj sharma/ bibechana 22 (2025) 131-141 133 table 1: description of v. jatamansi jones scientific name v. jatamansi jones local name sugandhawal family valerianaceae parts used aerial parts traditional uses curing blood diseases, burning sensation, cholera, skin disease, throat troubles, and ulcers. reference [16] 2.3 preparation of extract after collection, the plant material was thoroughly cleaned, followed by shade drying to preserve its phytoconstituents. it was then finely powdered in the grinding mill, ensuring a uniform consistency for further use. approximately ten grams of v. jatamansi jones powder was dissolved in 200 ml of six different solvents, ranging in polarity from more polar to less polar: water, methanol, ethanol, ethyl acetate, dichloromethane (dcm), and hexane. the content kept in maceration was shaken every 24 hours for three days. the contents were then filtered, and the filtrate was dried using a rotatory evaporator, maintaining a temperature of 4045 °c. 2.4 qualitative phytochemical analysis qualitative phytochemical screening was conducted using standard protocols [17–19] to identify various metabolites present in v. jatamansi jones. the screening targeted a range of phytochemicals, including glycosides, flavonoids, alkaloids, phenolic compounds, terpenoids, steroids, carbohydrates, saponins, tannins, fixed oils, and lipids. this analysis provided an overview of the bioactive constituents within the plant extract. 2.5 estimation of total phenolic content (tpc) the total phenolic content (tpc) of the plant extracts was determined using the folin-ciocalteu colorimetric method, as described by lu et al. [20]. in triplicate, 96-well plates were prepared with 20 l of plant extract, 100 l of 10% folin-ciocalteu reagent (diluted 1:10), and 80 l of 1m na2co3. the reaction mixture was incubated for 30 minutes at room temperature until a blue color developed. absorbance was then measured at 765 nm using a spectrophotometer. tpc was quantified as milligrams of gallic acid equivalent per gram of extract dry weight (mg gae/g), based on a gallic acid standard curve ranging from 7.5 to 100 g/ml. 2.6 estimation of total flavonoid content (tfc) the total flavonoid content of the plant extracts was assessed using the aluminum chloride method as described by ahmed et al. [21]. in triplicate, 20 l of plant extract, 100 l of distilled water, and 60 l of ethanol were added to 96-well plates. this was followed by the addition of 10 l of a 10% aluminum chloride (alcl3) solution and 10 l of 1m potassium acetate (chcook) solution. the reaction mixture was kept to incubate at room temperature for 30 minutes. absorbance was then measured at 415 nm using a spectrophotometer. the total flavonoid content was written as milligram of quercetin equivalent per gram of extract dry weight (mg qe/g), with quantification based on a standard calibration curve for standard quercetin having the value from 7.5 to 100 g/ml. 2.7 evaluation of antioxidant activity the positive control, quercetin, was serially diluted from the original concentration of 20 g/ml down to 0.625 g/ml, while the crude plant extract was diluted from 640 g/ml to 5 g/ml. in triplicate, 100 l of each diluted plant extract and the positive control were added to a 96-well plate. the initial absorbance was recorded at 517 nm. following this, each well received 100 l of dpph reagent, and the mixture was incubated for 30 minutes. the final absorbance was measured again at 517 nm. methanol and 50% dmso served as negative controls. this formula quantifies the ability of the extracts to scavenge free radicals, providing insight into their antioxidant potential [22, 23]. radical scavenging capacity = a control−a sample a control × 100 % where, acontrol = absorbance of control, asample = absorbance of sample inhibitory concentration (ic50) was calculated using graphpad prism (version 8.0.2.263). 2.8 evaluation of antimicrobial activity antibacterial activity was assessed using the agar well diffusion method on mueller hinton agar (mha) plates [24, 25]. the test microorganisms, including shigella sonnei (atcc 25931), staphylococcus aureus (atcc 43300), klebsiella pneumoniae (atcc 700603), and escherichia coli (atcc 25312), were cultivated in mueller hinton broth (mhb) and incubated at 37 ºc for 24 hours. the turbidity of the broth was adjusted to a 0.5 mcfarland standard to ensure uniform bacterial density. using a cork borer, wells were created in the agar plates, which were then filled with 50 l of the plant extract. negative control wells received 50% dmso, while positive control wells were filled with indra ojha and khaga raj sharma/ bibechana 22 (2025) 131-141 134 50% neomycin. after allowing for 15 minutes of diffusion, the petri dishes were incubated for 18 to 24 hours at 37 °c. following incubation, the zones of clearance were observed and measured to evaluate the antibacterial efficacy of the plant extract. 2.9 determination of minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) the minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) were determined following the standard procedure described by sarker et al. [26]. the bacterial inoculum was prepared to a final concentration of 106 cfu/ml by diluting the 0.5 mcfarland turbidity culture in mueller hinton broth (mhb) at a ratio of 1:100. a 5 l inoculum was then introduced into each well of a 96-well plate. neomycin served as the positive control in this assay. after sealing the plate with a sterile lid, it was incubated at 37 °c for 20 to 24 hours. following incubation, 0.003% resazurin was added to each well, and the plates were incubated for an additional 3 to 4 hours at 37 °c. wells that remained blue indicated no bacterial growth, while those that turned pink signified the presence of bacterial growth. the lowest concentration of the extract at which bacterial growth was inhibited was recorded as the mic. to ascertain the mbc, the contents of the wells were streaked onto nutrient agar plates, which were subsequently incubated at 37 °c for over 18 hours. the absence of bacterial colonies on the agar plates indicated the minimum bactericidal concentration of the crude plant extracts. 2.10 brine shrimp lethality assay (bsla) the toxicity of the plant extracts was assessed using a standard procedure [27]. the ph of the artificial seawater was adjusted to a range of 8 to 8.5 by adding 1m naoh. various concentrations of the plant extract were prepared, including 1000, 800, 500, 250, 100, and 10 µg/ml. each test tube was filled with 4 ml of the prepared seawater solution. in duplicate, 10 nauplii were added to each test tube along with 500 v. µl of the respective plant extract. potassium dichromate solution served as the positive control, while artificial seawater acted as the negative control. after 24 hours of incubation, the number of dead nauplii in each test tube was counted. the percentage of nauplii mortality was calculated using the following formula: % mortality = number of dead nauplii/total number of nauplii× 100 y= mx + c is the linear equation that may be found using the probit value table, where y is the probit value at 50% mortality, m is variable, and c is the intercept. calculating the lethal concentration (lc50). this method provided insight into the potential toxicity of the plant extracts on aquatic organisms. 2.11 statistical analysis data collection and analysis from the gen5 microplate reader were conducted using microsoft excel. the results for total phenolic content (tpc) and total flavonoid content (tfc) were reported as mean ± standard deviation. for antioxidant activity, the findings were expressed as mean ± standard error of the mean (sem). the inhibitory concentration (ic) values were computed using graphpad prism software (version 8.0.2.263). this analytical approach ensured a comprehensive evaluation of the data obtained from the experiments. 3 results 3.1 qualitative phytochemical analysis the results of qualitative phytochemical screening of the extract of v. jatamansi jones(in different solvents) are shown in table 2. table 2: qualitative phytochemical screening of plant extracts phytochemicals test plant extracts alkaloids dragendorff’s test carbohydrates molish’s test + reducing sugars fehling test glycosides borntrager’s test + amino acids xanthoproteic test + flavonoids alkaline reagent test + phenols fecl3 test + tannins braymer’s test + terpenoids salkowski’s test + anthraquinones borntrager’s test + phytosterols salkowski’s test + note: (+) = present, (-) = absent 3.2 total phenolic content (tpc) the phenolic content of the various solvent extracts of valeriana jatamansi is summarized in table 3. indra ojha and khaga raj sharma/ bibechana 22 (2025) 131-141 135 the methanolic extract exhibited the highest total phenolic content (tpc) value of 166.5 ± 2.0 mg gae/g, while the hexane extract displayed the lowest tpc value of 16.03 ± 2.22 mg gae/g, as indicated in the table below. these results highlight the significant variation in phenolic compound concentrations among the different solvent extracts. table 3: tpc values for various solvent extracts plant extracts tpc (mg gae/g) aqueous 93.9 ± 3.89 methanol 166.5 ± 2.0 ethanol 105.66 ± 5.42 ethyl acetate 74.55 ± 3.62 dichloromethane 34.18 ± 2.74 hexane 16.03 ± 2.22 3.3 total flavonoid content (tfc) the flavonoid content of the various plant extracts is presented in table 4 below. the methanolic extract demonstrated the highest total flavonoid content (tfc) value of 103.87 ± 5.47 mg qe/g, while the hexane extract exhibited the lowest tfc value of 8.27 ± 3.88 mg qe/g. these findings indicate a significant variation in flavonoid concentrations across the different solvent extracts. table 4: tfc of different solvent extracts of v. jatamansi jones plant extracts tfc (mg qe/g) aqueous 94.63 ± 6.11 methanol 103.87 ± 5.47 ethanol 93.87 ± 3.41 ethyl acetate 54.93 ± 5.61 dichloromethane 30.69 ± 4.41 hexane 8.27 ± 3.88 3.4 antioxidant activity the antioxidant activity of the plant extracts was assessed using the dpph assay, with the ic values for the different solvent extracts of valeriana jatamansi summarized in table 5. the methanolic extract exhibited the lowest ic value of 103.3 ± 1.53 v µg/ml, indicating a strong antioxidant activity. in contrast, the hexane extract showed a significantly higher ic50 value of 524.7 ± 0.89 v µg/ml, reflecting lower antioxidant capacity compared to the other extracts. these results highlight the varying effectiveness of different solvents in extracting antioxidant compounds from the plant. the inhibition of radical scavenging activity is displayed in figure 2. table 5: antioxidant potential (ic50) values of different solvent extract plant extract ic50 (g/ml) aqueous 104.3 ± 0.41 methanol 103.3 ± 1.53 ethanol 155.7 ± 0.34 ethyl acetate 161.3 ± 1.14 dichloromethane 323.8 ± 0.14 hexane 524.7 ± 0.89 quercetin (standard) 3.49 ± 2.29 note: quercetin = standard antioxidant figure 2: a plot showing % inhibition against the concentration of (a) aqueous (b) methanol, (c) ethanol, (d) ethyl acetate, (e) dichloromethane, (f) hexane extract, and (g) standard quercetin 3.5 antibacterial activity the antibacterial activity of the plant extracts was evaluated using the agar well diffusion method, targeting both gram-positive (staphylococcus aureus) and gram-negative bacteria (shigella sonnei, klebsiella pneumoniae, and escherichia coli). the results of the antibacterial tests are presented in taindra ojha and khaga raj sharma/ bibechana 22 (2025) 131-141 136 ble 6 and illustrated in figure 3. among the extracts, the aqueous, ethanolic, and hexane extracts exhibited the highest zone of inhibition against klebsiella pneumoniae, measuring 17 mm. conversely, the aqueous extract demonstrated limited antimicrobial activity against escherichia coli, with a zone of inhibition of only 9 mm. these findings suggest varying levels of antibacterial efficacy among the different extracts against the tested microorganisms. for ease of interpretation, the antibacterial activities are displayed in the bar diagram in figure 4. table 6: zone of inhibition (zoi) of plant extracts against different bacteria plant extracts bacteria zoi of sample (mm) zoi of positive control (neomycin) (mm) aqueous klebsiella pneumoniae 17 24 escherichia coli 9 22 shigella sonnei 15 24 staphylococcus aureus 15 23 methanol klebsiella pneumoniae 15 24 escherichia coli 12 22 shigella sonnei 13 24 staphylococcus aureus 12 23 ethanol klebsiella pneumoniae 17 24 escherichia coli 13 22 shigella sonnei 12 24 staphylococcus aureus 11 23 ethyl acetate klebsiella pneumoniae 15 24 escherichia coli 12 22 shigella sonnei 15 24 staphylococcus aureus 13 23 dichloromethane klebsiella pneumoniae 14 24 escherichia coli 15 22 shigella sonnei 11 24 staphylococcus aureus 10 23 hexane klebsiella pneumoniae 17 24 escherichia coli 14 22 shigella sonnei 11 24 staphylococcus aureus 11 23 indra ojha and khaga raj sharma/ bibechana 22 (2025) 131-141 137 figure 3: antibacterial test slides against different bacterial strains, kp = klebsiella pneumoniae, met = methanol, ss = shigella sonnei, eth = ethanol, sa = staphylococcus aureus, ea = ethyl acetate, e. coli = escherichia coli, dcm = dichloromethane, hex = hexane, aqu = aqueous figure 4: bar diagram showing antibacterial activity (zoi in mm) by different solvent extracts against k. pneumoniae, e. coli, s. sonnei, and s. aureus. 3.6 mic and mbc the study revealed that the ethanolic plant extract exhibited stronger antimicrobial effects than the methanolic extract, demonstrated by lower minimum bactericidal concentration (mbc) values for both k. pneumoniae (gram-negative) and s. aureus (gram-positive). specifically, the minimum inhibitory concentration (mic) and mbc values for both plant extracts against k. pneumoniae and s. aureus were 3.12 mg/ml and 12.5 mg/ml for the methanolic extract, and 3.12 mg/ml and 6.25 mg/ml for the ethanolic extract as shown in table 7. this suggests that the ethanolic extract was more effective at a lower concentration. in contrast, the positive control, neomycin, showed far lower mic and mbc values of 0.0039 mg/ml and 0.0078 mg/ml. this indicates that while the plant extracts do exhibit antimicrobial activity, they are much less potent compared to neomycin. however, the ethanolic extract still presents potential for antimicrobial applications due to its relatively lower mbc in comparison to the methanolic extract. the photographs of the experimental results are shown in figure 5 and figure 6. figure 5: well-plates showing mic values against (a) k. pneumoniae and (b) s. aureus, met = methanol, pc = positive control, eth = ethanol, and nc = negative figure 6: petri plates showing mbc of plant extract against k. pneumoniae and s. aureus, kp = klebsiella pneumoniae, met = methanol extract, sa = staphylococcus aureus, eth = ethanol extract 3.7 toxicity analysis the lethality of the plant extracts, measured by the lc50 values, showed that the ethanolic extract had the lowest lc50 at 1077.78 µg/ml, indicating greater toxicity to the brine shrimp nauplii than the methanolic extract, which had the highest lc50 at 1905.46 µg/ml table 8 and 9. in this bioassay, 50% dmso served as a negative control, in which all ten-brine shrimp nauplii survived, demonstrating that it had no toxic effects. conversely, potassium dichromate, used as a positive control, proved highly toxic, as all ten nauplii exposed to it were dead. these findings suggest that the ethanolic extract is more toxic to brine shrimp compared to the methanolic extract, with the positive and negative controls confirming the validity of the assay. indra ojha and khaga raj sharma/ bibechana 22 (2025) 131-141 138 table 7: mic and mbc values for plant extract plant extracts klebsiella pneumoniae staphylococcus aureus mic (mg/ml) mbc (mg/ml) mic (mg/ml) mbc (mg/ml) methanol 3.12 12.5 3.12 12.5 ethanol 3.12 6.25 3.12 6.25 positive control 0.0078 0.015 0.0039 0.0078 table 8: the number of survived nauplii after treatment with methanolic and ethanolic extracts and their percentage mortality plant extract concentration (g/ml) total no. of survived nauplii % mortality methanolic extract 10 25 16.67 100 23 23.33 250 21 30 500 20 33.33 800 16 46.67 1000 15 50 ethanolic extract 10 28 6.67 100 23 23.33 250 21 30 500 20 33.33 800 18 40 1000 17 43.33 table 9: the toxicity of plant extracts for both methanolic and ethanolic extracts plant extracts linear regression equation lc50 (g/ml) methanolic 5.0 = 0.4554x + 3.4823 2137.96 ethanolic 5.0 = 0.6306x + 2.9269 1905.46 this table highlights the dose-dependent effect of both methanolic and ethanolic extracts on brine shrimp mortality, with the methanolic extract demonstrating slightly higher toxicity than the ethanolic extract at higher concentrations. however, the lc50 values demonstrate the ethanol extract was found toxic than the methanolic extract. 4 discussion the study confirms that the methanolic extract of valeriana jatamansi jones is particularly rich in phenolic (166.5 ± 2.0 mg gae/g) and flavonoid (103.87 ± 5.47 mg qe/g) compounds, which were significantly higher than those in other extracts (aqueous, ethanol, ethyl acetate, dichloromethane, and hexane). phenolic compounds, known for their redox properties, contribute to antioxidant activity by acting as reducing agents, hydrogen donors, and singlet oxygen quenchers [28]. in previous research, the methanolic extract of v. jatamansi jones roots exhibited a tpc of 187.13 ± 6.8 mg gae/g and an ic50 value of 78 ± 2.9 g/ml. however, in this study, the ic50 for the methanolic extract was slightly higher at 103.3 ± 1.53 µg/ml, and the aqueous extract had an ic50 of 104.3 ± 0.41 µg/ml, showing improvement from its previous ic50 of 154 ± 4.6 µg/ml [29]. these variations from climatic and environmental factors affect antioxidant capacity, total phenolic content (tpc), and total flavonoid content (tfc) [29–31]. the collection site has a cold temperature, organic-rich soil, moderate water supply, and minimal light exposure. these conditions influence the biosynthesis of secondary metabolites, as supported by various studies. environmental changes can affect the production of certain medicinal plant species because the concentration of secondary metabolites (sms) in these plants is influenced by factors such as climate and ecological conditions [32]. plant metabolism and life depend on light because of photosynthesis. plants must therefore be able to detect the many light spectra found in solar radiation to survive [33]. additionally, a wide variety of secondary metabolites in the intricate biochemical interaction are affected by light at varying intensities [34]. temperature changes sigindra ojha and khaga raj sharma/ bibechana 22 (2025) 131-141 139 nificantly influence plant growth and the metabolic pathways involved in signaling, physiological control, and defense responses. when photosynthesis is disrupted due to extreme conditions, the temperature of the primary meteorological factors can greatly affect the composition of secondary metabolites [35]. the pearson correlation coefficients provide valuable insights into the relationships between total phenolic content (tpc), total flavonoid content (tfc), and antioxidant activity (aa), allowing us to better understand how these factors interact with one another. the strong positive correlation between tpc and tfc (r = 0.923, p = 0.009) suggests that phenolics and flavonoids might share similar biosynthetic pathways. this relationship is statistically significant at the 0.01 level. however, the negative correlations between tpc-aa (r = -0.835, p = 0.038) and tfc-aa (r = -0.922, p = 0.009) indicate that other factors may influence antioxidant activity beyond just phenolic and flavonoid contents. tpc and aa relationship is statistically significant at the 0.05 level, whereas, tfc and aa relationship is statistically significant at the 0.01 level. regarding antimicrobial activity, previous work reported that the methanolic extract of v. jatamansi jones achieved a zone of inhibition (zoi) of 19 mm against e. coli and 21 mm against pseudomonas [36]. in this study, the ethanolic and hexane extracts demonstrated the highest zoi of 17 mm, nearing the efficacy of neomycin, the positive control. ethyl acetate extract also showed moderate inhibition, with a 15 mm zoi against k. pneumoniae and s. sonnei. besides phenolics and flavonoids, other compounds like vitamins, carotenoids, saponins, enzymes, and minerals may also contribute to antimicrobial activity [37]. the study further investigated the antibacterial potency of methanolic and ethanolic extracts against k. pneumoniae and s. aureus, with mic and mbc values of 3.12 mg/ml and 6.25 mg/ml, respectively, for the ethanolic extract, and 3.12 mg/ml and 12.5 mg/ml for the methanolic extract. these results are consistent with findings from earlier research, demonstrating that v. jatamansi jones extracts possess robust antibacterial properties against these pathogens [38]. 5 conclusion in conclusion, valeriana jatamansi demonstrates significant medicinal potential due to its diverse phytochemical composition, which includes high levels of phenolics, flavonoids, and other bioactive compounds. among the solvent extracts, the methanolic extract exhibited the highest total phenolic content (tpc) and total flavonoid content (tfc), correlating with its strong antioxidant capacity. in contrast, the hexane extract displayed the lowest tpc and tfc, alongside the weakest antioxidant potential. antimicrobial activity assays revealed that the aqueous, ethanolic, and hexane extracts effectively inhibited k. pneumoniae, with the ethanolic extract showing superior minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) values, indicating a potent antimicrobial effect. additionally, the ethanolic extract’s lower lethal concentration (lc50) compared to the methanolic extract suggests enhanced toxicity, further highlighting its bioactivity. the 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[38] j. j. m. j. al zuhairi, f. jookar kashi, a. rahimi-moghaddam, and m. yazdani. antioxidant, cytotoxic and antibacterial activity of rosmarinus officinalis l. essential oil against bacteria isolated from urinary tract infection. eur. j. integr. med., 38:101192, 2020. introduction materials and methods chemicals plant collection and identification preparation of extract qualitative phytochemical analysis estimation of total phenolic content (tpc) estimation of total flavonoid content (tfc) evaluation of antioxidant activity evaluation of antimicrobial activity determination of minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) brine shrimp lethality assay (bsla) statistical analysis results qualitative phytochemical analysis total phenolic content (tpc) total flavonoid content (tfc) antioxidant activity antibacterial activity mic and mbc toxicity analysis discussion conclusion bibechana vol. 20, no. 1, april 2023, 65-75 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar a brief review on preparation and application of mwcnt-based polymer nanocomposites jyoti giri1,2,3,∗, rameshwar adhikari2,4 1dept. of chemistry, tri-chandra multiple campus, tribhuvan university kathmandu, nepal 2nepal polymer institute (npi), p. o. box 24411, kathmandu, nepal 3nepal development and research institute (ndri), lalitpur, nepal 4research centre for applied science and technology (recast), tribhuvan university kirtipur, kathmandu, nepal ∗corresponding author. email: girijys@yahoo.com abstract technological advancementalways seeks new materials with improved functional properties, particularly for smart applications. in this regard, nanotechnology is offering today wide range of novel material designs fabricated by compounding nanofillers into the polymer matrix. different allotropic forms of carbon can reinforce the properties of polymers for various applications. reinforcement depends on the dimension, shape, size and compatibility of the nanofiller with the polymer matrix. chemical modification of filler surfaces and the matrix can selectively localize the filler in the hybrid composites in the desired phase or at the interface by melt mixing or solution casting method, during compounding procedure. in this regard, the conducting nature of the additioin of multiwalled carbon nanotubes (mwcnts) into a polymer matrix fosters the conductivity into the materials. such nanocomposites can be used for numerous applications such as conducting materials, super-capacitors, light emitting devices, medical purposes etc,. this review paper focuses on different methods of preparation of mwcnt/polymer nanocomposites, their surface properties, and microbial properties etc,. keywords multiwalled carbon nanotubes (mwcnt); polymer composites; conductivity; mechanical strength; antibacterial properties. article information manuscript received: january 16, 2023; accepted: april 1, 2023 doi https://doi.org/10.3126/bibechana.v20i1.53724 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the advancing world is the gift of nanotechnology which deals specially with nanomaterial and nanocomposites. they are multiphase materials in which one or more phases of material is in nanoscale dimensions below 100 nm [1–3]. generally, a nanocomposite material has dispersing phase 65 http://nepjol.info/index.php/bibechana girijys@yahoo.com https://doi.org/10.3126/bibechana.v20i1.53724 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ jyoti giri and rameshwar adhikari/ bibechana 20 (2023) 65-75 66 called a matrix and a dispersed or reinforcing phase called a filler. these nanoscaled fillers are embedded in a continuous phase of polymer, metal or ceramics matrix [4]. almost all varieties of polymers are used as matrices such as thermoplastics; polyurethane (pu) [5], polyethylene (pe) [6], polyvinyl chloride (pvc) [7], thermosets; epoxy polyimide [8] and phenolic resin [9] and elastomers; polybutadiene (pb) [10], ethylene-octene copolymer (eoc) [11]. these fillers may be of 0 dimensional (0d), one-dimensional (1d), two-dimensional (2d) and three-dimensional (3d). 3d particles are cubical or spherical structures spread in x, y and z directions for instance boehmite [11], silica [12] and different kinds of particle. 2d particles are sheet-like layered particles spread in x and y directions for instance graphite. 1d particles are tubular or cylindrical in the structure such as singlewalled (swcnt), multiwalled carbon nanotubes (mwcnt) whereas 0d are the quantum dots which are very minute particles comprising few atoms such as fullerenes, polyhedral oligomeric silsesquioxane (poss) etc., [9–13]. the filler and matrix phases together generally give the synergetic effect to the composites which would be novel, intense and cumulated. the properties of the composites depend on the types of variables i.e., filler, their nanoscale dimension, loading degree, degree of dispersion, their size, shape, orientation and interaction with the matrix. surface area to volume ratio (a/v) with aspect ratio [a= ratio of length (l) and diameter (d)] of filler gives a good relation for the reinforcement in the composite which has been depicted in fig. 1, in which the change in the aspect ratio of a circular plate with a/v ratio was illustrated. the periodic increase in l of the platelets changes the molecule to a cylindrical form. in region a the platelete on increasing l , structure changes from 1 to 2 and 3. stage 3 is the one when its l=d and its aspect ratio becomes 1. further increase in l can be seen in region b, where the structure converts to filamental fibrous 1-dimensional structure, stage 4 [14]. fibers (such as carbon nanotubes, 1 dimensional) and platelets (such as layered silicates clay, 2 dimensional filler) have higher a/v ratios so they have high reinforcement ability [15]. therefore increasing order of reinforcement can be illustrated with respect to a/v ratio as 1>2>3 [11]. depending upon the particle size of the filler, electrical, thermal, and optical properties of the nanocomposites can be varied. the interacting phases can even alter the mechanical property of the composite by varying the modulus and strength [16]. fig. 2 and fig. 3 show the expanded interfacial surface of the filler to interact with the matrix [14]. the spherical fullerence being 3-dimensional has less tendency for agglomeration, less likely is for tubular mwcnt and sheet of graphite has least reinforcement and has possibility of agglomeration [17–19]. the nanofillers mostly in practice are alumnosilicates (clays) [20], carbon nanotubes (cnt) [8,21], nanofibres [22], ultra-dispersed diamonds (nanodiamonds) [23], fullerenes [24], other inorganic nanotubes, nanoparticles of silicon oxide (sio2), calcium carbonate (caco3), metal nanoparticles as well as fibers from biological resources. different allotropic forms of carbon have various effects in the matrix mostly for their strength, conductivity and optical property. boeing: 787 dreamliner, the aircraft is an example of mechanical reinforcement. it was made up of carbon fiber-reinforced epoxy resin. here carbon fiber induced strength and stiffness to the material and epoxy binds the fiber with significant less weight [25]. the conducting materials form the important base of industries in information technology, electronics and electrical industries etc., [26]. conducting fillers in polymers result the conductive composites which have low density, low weight, high mechanical performance, low cost and easy processability such as biobased polymer (from polylactic acid (pla) and potato starch) and cnts are one of the most interesting materials with high strength [8, 27]. the sp2 hybridization of the carbon in cnt’s form an allotropic tubular structure that can be termed into diverse architectures to form swcnt, mwcnt, nanobud etc. such carbon materials are conductive even in little amount and open different avenues of applications as polymer composites. therefore, numerous researchers are in the process throughout the world to achieve optimum best-conducting polymer composites for advanced applications. mwcnt has been incorporated into different polymers such as ethylene vinyl acetate copolymer (eva) [28], pu block [29], polystyrene (ps)/polyvinylidene fluoride (pvdf) composites [28], polyolefins [29] and polyesters [30–32]. in these systems, electrical-conducting properties, thermal, morphological, mechanical and dielectric properties are enhanced. mwcnt also worked as a compatibilizer between ps and pvdf [30]. the allotropes of carbon/polymeric nanocomposites have significant applications in numerous field nowadays. they can be used as antistatic materials [33–35], super capacitors [ [29, 35] highly conductive application (electrodes in touch screens and sensors) [28,36,37] security application, screen printing, coating materials, organic solar cells [29], printing electrodes, conductive adhesives, current limiting devices, shielding for electromagnetic protection, heater with distributed heat emission and self-regulated heaters [27, 29]. similarly light emitting device, contact bottoms of computers, laptops, mobiles, i-pads and media techniques etc. x. jyoti giri and rameshwar adhikari/ bibechana 20 (2023) 65-75 67 zhao et al., studied carbon black nanoparticles in polystyrene (ps)/polyvinylidene fluoride (pvdf) composites which induce dielectric property. [34] s. b. kondawar also mentioned that conducting nanocomposites are the noble electrodes for the application as super capacitor [32]. electronic tattoo are also some noble application of such nanocomposites [38,39]. 2 preparation of conducting polymer nanocomposites there are many techniques for compounding polymer matrix with nanofiller. some of the techniques are explained here [32]. 2.1 solution casting this is a technique where both polymer and filler are homogeneously dissolved in a solvent separately and mixed followed with sonication. the mixer solution is sonicated and cast to a desired shape and the solvent will be slowly evaporated to get a thin film of the composite [38,40]. 2.2 in-situ polymerization this is a technique by which the first polymer was synthesized. during the synthesis of polymer, at the stage of prepolymer formation fillers are incorporated and stirred well, stabilized and moulded to the desired shape. usually, the process is applicable for co-polymer with bigger units [37]. 2.3 internal melt mixing the dried polymer and fillers are blended into the rotors with specific rotation per minute (rpm), temperature and for a specific time to homogeneous compounding. depending upon the type of polymer and composites they are pre-cured and post-cured in an oven at a specific temperature. the stable composites are moulded with hydraulic pressure to obtain a plaque [18,32,33]. 2.4 twin screw extruder in this technique, dried polymers and fillers are premixed and put into a conical counter rotating a brabender with the specific speed (round per minute, rpm) of twin extruders at a higher temperature below the melting point. composites prepared are cooled with ice water to pelletized or prepared the plates with hydrolytic pressure in the specific diameter of moulds [41–46]. except for the process described above peng et al., 2008, explained the chemical synthesis, electrochemical deposition and co-deposition methods to prepare conducting polymers with carbon nanotubes. these composites have a high charging/discharging ratio so were applicable to prepare supercapacitors, batteries and fuel cells. [36]. material on the gce electrode and (v) represent the operating voltage. 3 morphological features of mwcntbased nanocomposites the morphology of the nanofiller has many effects on the nanocomposites. their dispersion and interaction with the matrix play a very important role in the mechanical and chemical properties of the materials. morphology of the composites can be investigated by different techniques; such as scanning electron microscopy (sem), optical microscopy (op) and transmission electron microscopy (tem). these techniques are efficient to locate shape, size, distribution of filler and interaction with the matrix. the expanded graphite has better conductivity in comparision to untreated graphite in composites. this could be due to continuous sea-weeds phase in expanded graphite where as untreated graphite has flakes like interrupted structure [28]. fuctionalization of the filler and matrix would increase compatibility between filler and matrix. sem micrograph of poly(butylene adipate co-terephthalate) (pbat)/mwcnt-oh shows good dispersion of mwcnt in pbat polymer which becomes more intense in acrylic acid grafted pbat. the tem micrograph of tensile fracture also supports mwcntoh get dispersed well where as mwcnt forms agglomerates on 3 wt. % loading of filler in pbat matrix [31]. feller et al., also explained sem micrograph of acrylic acid grafted pbt with ohfunctionalized graphene oxide upto 3% shows good dispersion of nanofiller [15,38].the exfoliated cnt has conductive network, assigned for the flexible continuous phase of ps matrix [47]. c-x liu and j-w choi noticed dispersion of cnt above 1 % cannot be investigated by tem due to formation of opaque nanocomposite where as sem can explain uniform dispersion of mwcnt throughout the fracture surface. sem micrograph of polydimethylsiloxane (pdms)/cnt upto >5 wt. % fillers showed good dispersion with consistent clusters up to 3µm [29]. polyaniline (pani)/cnt and polypyrrolidine (ppy)/cnt nanocomposites have cnt coated with homogeneous polymer and formed coralloid network [36]. n. g. sahoo et.al. observed smooth lattice structure of carboncarbon bond in tem image of mwcnt where as some defects are seen in cooh group functionalized mwcnt due to cooh group hanged on cnt surface. the cooh group of cnt is forming ester bond with oh group of polyurethane matrix [37]. jyoti giri and rameshwar adhikari/ bibechana 20 (2023) 65-75 68 figure 1: surface area to volume ratio a/v of a cylindrical particle of a given volume, plotted versus aspect ratio a= l/d [13,14]. figure 2: ideal structures of a fullerene (left) and a carbon nanotube (right) [14,19]. figure 3: 3d structure of graphene layers in graphite [14,19]. the sem micrograph for transverse section cut perpendicular to extrusion direction of pbt60/eea-cb40 nanocomposite show phase organization where holes and tunnels in black correspond to conductive phase containing carbon black and poly(ethylene-co-ethyl acrylate) [15]. the selective localization of carbon black (cb) was observed in morphological study of diphasic ps/pvdf/cb composite with continuous phase of ps by x. zhao et al., [30]. the interfacial connection between ps and pvdf was not clear in sem micrograph [28]. similar type of phase separation can also be observed in fig. 4 with two immisible phases of pla/pbat/mwcnt nanocomposites. on increasing pbat composition, cnt migrates towards pbat phase from pla although there is no chemical bond reported [43]. mwcnt in pla/mwcnt composites can also increase chunks and striation in nanocomposites [42]. the mwcnts also increase roughness and hydrophobicity on the surface of the polymer composites which can be seen in the sem images of polyhydroxy valerate (phbv)/mwcnt. the micrographs of nanocomposites of mwcnt varying from 0 %, 1 %, 1.5 % jyoti giri and rameshwar adhikari/ bibechana 20 (2023) 65-75 69 figure 4: sem image of pla/pbat/ mwcnt nanocomposite [19]. figure 5: sem micrographs showing fracture surface phbv/mwcnt with (a) 0 %, (b) 1 %, (c) 1.5 % and (d) 2 of mwcnt [40]. and 2 % in phbv show increasing roughness respectively as shown in fig. 5 (a, b, c and d). the 0 % of mwcnt in nanocomposites found to have smooth surface where as mwcnt in phbv found to have homogeneous dispersion of mwcnt in matrix and are incompatible to matrix resulting voids into the nanocomposites. the voids cause roughness and increasing with mwcnt see fig. 5 [40]. the data is further supported by the increasing contact angle value for surface of same nanocomposites as shown in fig 6a. the increase of θ = 55o for pure phbv to 87o on 1 % loading of mwcnt is a significant rise in hydrophobicity. moreover, the smooth and rough surfaces show a similar trend and significance on rough parts of the nanocomposite surface as shown in fig 6b [40]. 4 mechanical performance and thermostability of mwcnt-based nanocomposites polymers are class of materials in which one can induce or reinforce any properties such as mechanical, morphological or conductivity. in this regard, different reinforcing inorganic materials such as mwcnt alone or in combination with other materials such as carbon blacks, graphenes, nanodiamonds, hydrogenated cnt etc., can be incorporated into polymer materials [48, 49]. fig.7 clearly shows the reinforcing effect of increasing wt.% of mwcnt in polycarbonate. the young’s modulus is increasing with increasing concentration of mwcnt [50]. other properties like charge barrier, and conducting property can be induced into the polymer matrix by the dispersion of conductive fillers such as cnts or polymers intrinsically conductive [38, 40, 47]. the practices of researchers are with different types of polymers molded with cnt or conducting polymer to reinforce the mechanical, thermo mechanical properties and conductivity of nanocomposites. mixing a filler into the polymer may be a simple technique but the major challenge for the scientist is to make them compatible with the polymer. in comparison to neat filler, functionalized fillers of respective polarity have more good compatibility. n. g. sahoo et al., synthesized polyurethane and incorporated cooh-functionalized mwcnt by situ polymerization in a urethane matrix. the composite has good dispersion and adhesion of coohmwcnt on polyurethane matrix with pronouncing advances thermomechanical property [15]. the jyoti giri and rameshwar adhikari/ bibechana 20 (2023) 65-75 70 figure 6: (a) photographs showing increasing hydrophobicity with increasing mwcnt in phbv/mwcnt nanocomposites, (b) the bar diagram indicating the effect of increasing contact angle value on increasing mwcnt in phbv [40]. electrical conductivity in ps/mwcnt composite can be reinforced by the 2 wt-% of loading cnt [47]. 5 electrical conductivity of mwcnt based nanocomposites carbon material is one of the filler with wide conducting ability. composites of conducting filler with polymers results in conductive polymer nanocomposite which have low density, low weight, high mechanical performance, low cost and easy processability. carbon materials carbon black, carbon fibers, carbon nanotubes (cnts) have conductivity value (σ) ranges from 101 s/cm, 103 s/cm), cnts are one of the most interesting materials with high strength. the sp2 hybridization of the carbon form allotropic tubular structure and these structure modified to form single walled carbon nanotubes (swcnt), multiwalled carbon nanotubes (mwcnt), nanobud etc. such carbon materials are conductive even in little amount and opens different avenues of applications as composites with polymer. therefore numerous researches are in the process throughout the world to achieve optimum best conducting polymer composites for different advance applications. mwcnt has been incorporated into different polymers such as ethylene vinyl acetate copolymer (eva) [28], polyurethane block [29], polystyrene (ps)/polyvinylidene fluoride (pvdf) composites [30], polyolefins [31], polyesters [18, 32] and pla [51] in these system electricalconducting properties, thermal, morphological, mechanical and dielectric properties are enhanced. mwcnt also worked as compatibilizer between ps and pvdf [?]. the electrical resistivity in fig. 8 of the pbat, acrylic acid grafted pbat with mwcnt and mwcnt-oh composites were measured directly on laminated films (0.1 mm thick) with an ohmstat rt-1000 resistivity meter. the significant decrease in resistivity with the addition of conducting fillers mwcnt and mwcnt-oh by 1 wt-% can be seen in fig. 8. the electrical resistivity decreases from 1×1016 ω/sq to 1×1010 ω/sq differing by 1×106 times for pbat/mwcnt. similarly, 1 wt-% addition of mwcnt-oh in pbatg-aa decreases to 8×107 ω/sq. the difference in resistivity between 1 wt-% and 3 wt-% loading of mwcnt and mwcnt-oh is 1×102 ω/sq approximately. on adding 5 wt-% of filler the resistivity decreases more to 1×101 ω/sq. therefore upto 3 wt-% of mwcnt and mwcnt-oh sharply reduce the resistivity where as 5 and more wt-% loading of mwcnt and mwcnt-oh does not reduce in the appreciable amount. moreover, the pbat-gaa/mwcnt-oh composites have more reduction in resistivity in comparison to pbat/mwcnt. this might have happened due to the ester bond formation between arylic acid in pbat and ohgroup in mwcnt and ester bonds are always stronger than the hydrogen bond which is in between pbat and mwcnt [32]. biodegradable conducting nanocomposites with pla and mwcnt with increasing concentration of cnt in composite from 0 wt-% to 1.5 wt-% found jyoti giri and rameshwar adhikari/ bibechana 20 (2023) 65-75 71 figure 7: stress-strain curve showing reinforcement in polycarbonate by filling 2 wt-% and 5 wt-% mwcnt [50]. figure 8: the electrical resistivity of pbat, pbat-g-aa, pbat/mwcnt, and pbat-g-aa/mwcntoh composites [30]. to increase crystallization, thermal degradation and at the same time reported drop in surface resistivity [41]. c.s. wu and h.t. liao modified poly (butylene terephthalate) (pbt) by surface grafting with acrylic acid and graphene oxide was modified to acid chloride (go)-cocl) derivative. composites of such materials have found improved thermal and decreased with graphene oxide (go) and resistivity property and antistatic property [33]. 6 antibacterial properties dispersed cnt’s in nanocomposites can induce antibacterial properties. as carbon is inorganic filler spread throughout the matrix renders the bacterial growth showing by increasing hydrophobicity as mentioned above and induce antibacterial property in nanocomposites [40]. fig. 9 (a) shows the decrease in survival of bacterial colonies on fixed loading of e. coli (0.1 ml) with respect to fixed volume and time during incubation with the pbat-g-aa/mwcnt (3 wt-%). e. coli colonies grow on incubation, after 3 hours slowly the composite inhibits the growth of e. coli. in fig. 8(b), 12 hours incubation almost all colonies are disappeared [32]. the infectious bacterial growth of e. coli can be observed in the prepared composites of c.s. wu. the e. coli cell count with respect to the exposure time of the composites with bacteria was given in the fig. 8 a and b. the pbat and pbat-g-aa resist the growth of e.coli where as the increase in % incorporation of mwcnt and mwcnt-oh not only decrease in growth of e.coli but also suppress the growth of bacteria in the culture to almost zero cell count. fig. 10 shows the survival ratio of e.coli in contact with the pbat or pbat-g-aa surface. exposure of composite with bacteria upto 6 hours doesnot hinder the growth but after 6 hours exposure result concluded that increase in % of mwcnt and mwcnt-oh in composites started to decrease survival ratio of bacteria showing antibacterial effect of the composites [32]. however, enhanced biodegradation was also observed in pbat/ mwcnt nanocomposites compatibilized with zno jyoti giri and rameshwar adhikari/ bibechana 20 (2023) 65-75 72 figure 9: (a) photographs show pbat-g-aa/mwcnts (3 wt. %) samples loaded with a fixed volume (0.1 ml) of e. coli. (b) e. coli was exposed to pbat-g-aa/mwcnts (3 wt-%) for evaluation of antibacterial activity [32] . figure 10: exposure survival ratio of e. coli cells during exposure to pbat or pbat-g-aa and its composite surfaces [32]. in more than 0.2 %, indicating bacterial degradation. 7 conclusion carbon in different allotropic states a nanometric dimension of up to 100 nm becomes the nanofiller where the aspect ratio provides an interacting surface for the polymer matrix in the nanocomposite. nanocomposite can be prepared by simple techniques of compounding. filler-matrix rearrangement can be investigated by different spectroscopic methods like sem, optical microscopy (om), tem etc., which confirms that significant reinforcement, is achieved only when filler and matrix are compatible with each other. the nano-carbon materials such as mwcnt, nanodiamond, and nanoscopic graphite can be used to reinforce mechanical properties and thermostability and at the same time are capable of producing synergetic effects in their nanocomposites to reinforce mechanical properties, induce electrical conductivity as well as other functionalities in the different kinds of polymers. all such properties are boon for material science and engineering making the composites nanomaterials applicable in numerous fields in developing novel devices and technologies. acknowledgement jyoti giri wants to thank japan science & technology, sakura science exchange program and professor takahiro maruyama, meijo university, nagoya, japan for strong motivation in the field of conductjyoti giri and rameshwar adhikari/ bibechana 20 (2023) 65-75 73 ing carbon based polymer composites. references [1] q. wu et al. mechanical properties of nanomaterials: a review. nanotechnology reviews, 9:259–273, 2020. 10.1515/ntrev-2020-0021 [2] j. r. peralta-videa et al. nanomaterials and the environment: a review for the biennium 2008–2010. journal of hazardous materials, 186:1–15, 2011. doi:10.1016/j.jhazmat.2010.11.020 [3] l. a. kolahalam et al. review on nanomaterials: synthesis and applications. materials today: proceedings, 16:1–9, 2019. doi:10.1016/j.matpr.2019.07.371 [4] m. s. senthil kumar et al. effects of nanomaterials on polymer composites-an expatiate view. reviews on advanced materials science, 38:40–54, 2014. 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performance and thermostability of mwcnt-based nanocomposites electrical conductivity of mwcnt based nanocomposites antibacterial properties conclusion bibechana vol. 20, no. 3, december 2023, 316–325 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar thermodynamic, structural and surface properties of rare earth metallic alloys: au-la liquid system s. k. yadav∗ department of physics, mahendra morang adarsh multiple campus biratnagar, nepal. ∗corresponding author: email: sashit.yadav@mmamc.tu.edu.np abstract a complete information related to the mixing behaviours of au alloyed with rare earth metals or lanthanides is very scarce. therefore, an attempt has been made in this work to compute and study the temperature and concentration dependent thermodynamic, structural and surface properties of au-la liquid alloy using different theoretical approaches. the thermodynamic properties, such as excess gibbs free energy of mixing, enthalpy of mixing, excess entropy of mixing and activity of the system were computed using available coefficients of interaction energy parameters in the framework of redlich-kister polynomial. taking these as reference values, model parameters for quasi-lattice model were optimised at 1473 k. the model parameters were then determined at higher temperatures assuming them to be linear temperature-dependent. the thermodynamic and structural properties were then computed in the temperature range 1473 k-1773 k. the surface properties of the system were computed using bulter’s model using determined values of partial excess gibbs free energy of its components. present investigations revealed that the compound forming tendency of the system gradually decreased with increase in temperature of the system. keywords ordering energy, hetero-coordinating nature, segregating nature, surface segregation, surface tension. article information manuscript received: march 10, 2023; accepted: march 25, 2023 doi https://doi.org/10.3126/bibechana.v20i3.59896 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction development of lead free solders has been a great task for the researchers working in the field of materials design and fabrication. one of the most promising alternative for the purpose has been found to be the use of sn-based alloys, more precisely sn-ag-cu ternary alloys. addition of small amount of rare earth (re) elements to these alloys, increases the mechanical behaviour, creep-fatigue resistance and wetting properties [1–4]. in due course, knowledge related to the mixing behaviours of re-based liquid alloys are important. but a very few information regarding the thermo-physical properties of metallic alloys having re metals, also called lanthanide, as ingredient is available to date. in order to develop the thermodynamic database of re-based liquid alloy, the thermodynamic and structural properties of au-la liquid alloy was studied in the previous work [5]. to further enhance the procedure, the mixing properties of au-la liquid alloy have been computed and studied at different 316 http://nepjol.info/index.php/bibechana sashit.yadav@mmamc.tu.edu.np https://doi.org/10.3126/bibechana.v20i3.59896 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ shashit kumar yadav/ bibechana 20 (2023) 316-325 317 temperatures in the present work. dong et al. in 2011 [6] have summarized the details of literature associated with the works carried out by different researchers to assess the mixing properties of au-la alloy. in their work, phase relations in au-la and au-er alloys have been thermodynamically studies using calphad technique incorporated with the ab initio calculations. they calculated enthalpy of mixing of the system at 1473 k and compared them with the experimental values of fitzner et al. [7]. further, they presented the self consistent parameters of redlich-kister polynomial [8] for the excess gibbs free energy of mixing for different phases present in the alloy. they calculated the existence of different stable phases, such as aula2, aula, au2la, au51la14 and au6la. these results were found to be in good agreement with those obtained by massalski [9], except for the reaction temperature and composition involving the constitution of au2la and au51la14 phases. they found the reaction temperature to be 75 k higher and close to xau = 0.04 than observed by massalski. in the knowledge of the author of this work, the complete description of the mixing properties of the system is lacking to date. therefore, an attempt has been made in this work to study and explain the thermodynamic, structural and surface properties of the liquid alloy at different temperatures. in thermodynamic properties, such as excess gibbs free energy of mixing (∆gxs m ), enthalpy of mixing (∆hm ), entropy of mixing (∆sxs m ) and activity (ai; i = au,la) were computed using modeling equations of quasi-lattice model. in the same frame, the structural properties, such as concentration fluctuation in long wavelength limit (scc(0)), warren-cowley short range order parameter (α1) and ratio of mutual to intrinsic diffusion coefficients (dm/did) were calculated. the surface tension and surface concentrations of the system were calculated using butler’s model [10–13]. 2 formulations 2.1 quasi–lattice model this theoretical approach assumes that when two elements a and b are mixed in liquid state, the formation of the complex of the type aµbν takes place. the values of µ and ν depend upon stiochiometric compositions at which the stable phase is present and are determined from the phase diagram of the system. in this work, the existence of the complex au2la [6, 7] was considered as energetically favoured . in this regard, the expression for excess gibbs free energy of mixing (∆gxs m ) can be given as [14–16] ∆gxs m = n [φω +φabωab +φaaωaa] (1) where ω, ωab and ωaa are the interaction energy or model parameters. they are assumed to be temperature-dependent but concentration independent. φ, φab and φaa are the simple polynomials in x1 and x2, such that x1 + x2 = 1. φ, φab and φaa are expressed as [14–16] φ = x1x2 φab = x1 6 + x2 1 − 5x3 1 3 + x4 1 2 φaa = −x1 4 + x2 1 2 − x4 1 4 (2) ∆gxs m can be expressed in terms of gibbs free energy of mixing (∆gm ) as ∆gm = ∆gxs m +rt [x1 lnx1 + x2 lnx2] (3) where r (in j/(mol.k) is the real gas constant and t (in k) is the absolute temperature. the excess entropy of mixing (sxs m ) is related to ∆gxs m as ∆sxs m = − ( ∂∆gxs m ∂t ) p (4) from equations (1) and (4), one can obtain ∆sxs m = −n [ ∂∆ω ∂t φ+ ∂∆ωab ∂t φab + ∂∆ωaa ∂t φaa ] (5) herein, ∂∆ω ∂t ,∂∆ωab ∂t and ∂∆ωaa ∂t are the temperature derivative terms of interaction energy parameters. the enthalpy of mixing (∆hm ) can be related to ∆gxs m and ∆sxs m by the well known thermodynamic expression as ∆hm = ∆gxs m + t∆sxs m (6) using equation (4) in equation (6), yields ∆hm = ∆gxs m − t ( ∂∆gxs m ∂t ) p (7) the activity of component i (ai; i = au,la) in the binary solution can be expressed in terms of ∆gm as rt ln ai = ∆gm + (1− xi) ( ∂∆gm ∂xi ) t,p,n (8) using equations (1) and (3) in equation (8), one can obtain the expression for ( ∂∆gm ∂xi ) t,p,n as shashit kumar yadav/ bibechana 20 (2023) 316-325 318 ( ∂∆gm ∂xi ) t,p,n = ∆ωφ ′ +∆ωabφab ′ +∆ωaaφ ′ aa + ln ( xi 1− xi ) (9) where φ ′ and φ ′ ij are the first order derivatives of respective parameters (in equation (2)) with respect to concentration of ith element. to study and understand the arrangement of atoms at atomic level in the initial melt, the structural functions have become an essential tool. among them, the expression for concentration fluctuation in long wavelength limit (scc(0)) is expressed as [17–20] scc(0) = rt ( ∂2gm ∂x2 1 )−1 t,p,n = rt ( ∂2gm ∂x2 2 )−1 t,p,n (10) using equations (1) and (3) in equation (10), yields scc(0) = x1x2[1 + x1x2rt (∆ωφ′′ +∆ωabφ ′′ ab +∆ωaaφ ′′ aa)] −1 (11) where ϕ′′ and ϕij ′′ are the second order derivatives of respective parameters with respect to concentration (xi) and can be obtained from equation (2). the ideal values of scc(0) is obtained by the following relation sid cc(0) = x1x2 (12) the structural functions, warren-cowley short range–order parameter (α1) and the ratio of mutual to intrinsic diffusion coefficients (dm/did) can be expressed in terms of scc(0) as [13,15,18,21] α1 = s − 1 [s(z − 1) + 1] (13) with s = scc(0) sid cc(0) (14) and dm did = sid cc(0) scc(0) (15) 2.2 redlich-kister (r-k) polynomial r-k polynomial is used to model the temperaturedependent thermodynamic properties of liquid alloys. it is extensively used as modeling equations in theoretical calculations, software based computations and experimental measurements [6, 8]. in this approach, ∆gxs m is expressed as [5, 6, 8, 22] ∆gxs m = x1x2 n∑ q=0 lq(x1 − x2) q (16) where lq are the linear t–dependent coefficients or interaction energy parameters of r-k polynomial. they are expressed in the form lq = aq + bqt , where aq (in j/mol) are contributions due to ∆hm and bq (in j/mol-k) are contributions of ∆sxs m to ∆gxs m equivalent to equations 6. the partial excess gibbs free energy (∆gxs i ) of the component i in the binary liquid alloy can be given as [22] ∆gxs i = ∆gxs m + (1− xi) ( ∂∆gxs m ∂xi − ∂∆gxs m ∂(1− xi ) (17) the activity coefficient of component i in the binary solution is related to ∆gxs i as rt ln γi = ∆gxs i (18) after the computations of γi, the activity of component i can be obtained by the relation ai = xiγi (19) the values of sxs m and hm can be obtained using equations (4), (7) and (16). using equations (10) and (16), scc(0) for this system having q = 0, 1 can be obtained as [5, 23] scc(0) = rt [−2l0 + (−12x1 + 6)l1 + rt x1(1− x1) ]−1 (20) the values of other structural functions in this framework can also be obtained using equations (13-15). 2.3 butler model the surface properties, surface tension (σ) and surface concentrations (xs i ) of the system have been calculated using butler model. according to this model, σ for binary liquid solution can be given as [10–13] shashit kumar yadav/ bibechana 20 (2023) 316-325 319 σ = σ1 + rt a1 ln xs 1 xb 1 + ∆gxs 1,s −∆gxs 1,b a1 = σ2 + rt a2 ln xs 2 xb 2 + ∆gxs 2,s −∆gxs 2,b a1 (21) where σi is the surface tension, ai is molar surface area, xs i is the surface concentration, xb i is the bulk concentration, ∆gxs i,s is the molar surface partial excess gibbs free energy and ∆gxs i,b is the molar bulk partial excess gibbs free energy for the component i of the liquid mixture at the melting temperature of the alloy. ∆gxs i,s and ∆gxs i,b related by the relation ∆gxs i,s = β∆gxs i,b (22) where β = 0.8181 [11, 13] for simple liquid metals. the molar surface area (ai) of component i in the liquid mixture can be calculated using the relation ai = fn 1 3 av 2 3 i (23) where na is the avogadro’s number and vi(= mi ρi ) is the molar volume of element i in the liquid mixture. the values of σi and vi are calculated with the help of the following relations [11,24] σi = σ0 i + dσ dt (t − t0) (24) and vi = v 0 i [1 + +λi(t − t0)] (25) where σ0 i is the surface tension, v 0 i is the molar volume and λi [11,24] is the temperature coefficient of volume expansion for ith component at its melting temperature (t0). 3 results and discussion 3.1 thermodynamic properties the self-consistent parameters for excess gibbs free energy of mixing (∆gxs m ) of au–la liquid alloy were taken from dong et al. [6] (table 1). these parameters were used to calculate ∆gxs m of the system at 1473 k in the frame work of r-k polynomial [8] (equation (16)). the values so computed were considered as reference data and then quasi– lattice model was employed to determine the model fit parameters using equations (1-3). the best fit values of the model parameters were estimated assuming the existence of au2la complex and are presented in table 1. table 1: interaction energy parameters for ∆gxs m of au–la liquid alloy parameters [j/mol] reference l0 = −254446.24 + 6.00025 ∗ t l1 = −85046.07 + 2.89377 ∗ t [6] ∆ω = −264279.94476 + 8.97912 ∗ dt ∆ωab = −3042.03606 + 0.083140 ∗ dt this work ∆ωaa = −345964.24650 + 1.66280 ∗ dt the determined values of model parameters ∆ω, ∆ωab and ∆ωaa were found to have negative values (table 1). among them, ∆ω is called ordering energy parameter and its value was estimated to be −264279.94476 indicating the system to be strongly interacting in nature. the value of ∆gxs m was computed at 1473 k using the parameters from table 1 and equations (1-3). the compositional dependence of ∆gxs m of the this work along with the values computed using the parameters of dong et al. are displayed in figure 1. 0.0 0.2 0.4 0.6 0.8 1.0 -6.0 -5.5 -5.0 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 s m xs/r g m xs/rt h m /rt g m xs /r t , h m /r t , s m /r x au dong et al. [6] this work fitzner et al. [7] figure 1: compositional dependence of ∆gxs m/rt , ∆hm/rt and ∆sxs m/r of au–la liquid alloy at 1473 k. the computed values of ∆gxs m were found to be in consistent with each other at compositions thereby validating the present optimisation procedure (figure 1). the maximum negative value of ∆gxs m = −5.12014rt (this work) and ∆gxs m = −5.12991rt (dong et al.) [6] at xau = 0.6. the high negative value of ∆gxs m/rt indicates the system to be strongly interacting in nature at its melting temperature, 1473 k. moreover, the system is found to be asymmetric with respect to ∆gxs m . the enthalpy of mixing (∆hm/rt ) and excess entropy of mixing ∆sxs m/r of the system were calculated with the help of parameters from table 1 and equations (4-7). these computed values are portrayed as a function of composition in figure 1. shashit kumar yadav/ bibechana 20 (2023) 316-325 320 the extremum negative value of ∆hm/rt = −5.37922rt (this work) and ∆hm/rt = −5.38665rt (dong et al. [6]) at xau = 0.6. the high negative value of hm/rt corresponds the strong association between au and la in the assumed complex at 1473 k. further, the computed values of ∆hm/rt of this work and those of dong et al. were consistent with each other and the system is found to be asymmetric with respect this physical function. the values of ∆hm/rt were also found to be in agreement with the experimental values of fitzner et al. [7] at higher compositions of au. likewise, the maximum negative value of ∆sxs m = −0.26781r (this work) and ∆sxs m = −0.26744r (dong et al.) at xau = 0.5. the au-la liquid alloy is found to be symmetric with respect to ∆sxs m . thus, the above theoretical investigations reveal that the model parameters determined in the frame work of quasi-lattice model are fruitful in explaining the thermodynamic properties of the system. to further validate the present optimisation process, the activity of the system was computed using the same determined model parameters. the activities of the individual atoms (aau and ala) of the initial melt were calculated on the basis of rk polynomial (equations (16-19)) and quasi-lattice model (equations (8 and 9)) using the parameters from table 1. the calculated and ideal values of aau and ala are plotted as a function of concentration in figure 2. 0.0 0.2 0.4 0.6 0.8 1.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 a la a au a a u, a l a x au dong et al. [6] this work ideal figure 2: computed values of aau and ala versus concentration of au (xau) of au–la liquid alloy at 1473 k. the computed values of aau and ala were found to be much less than their respective ideal values at all compositions indicating the system to be strongly interacting in nature. both of these values, computed using the parameters of present work and dong et al., were found to be consistent with each other at all concentrations (figure 2). thus, it can be stated that the preferred model is capable of explaining the thermodynamic functions and reproducing the activity of the system. therefore, these model parameters were considered for the computations of structural and surface properties. in thermodynamic properties, ∆gxs m , ∆hm and ai; i = au,la were computed at different temperatures assuming the model parameters of quasilattice model to be linear temperature-dependent. the model parameters ∆ω, ∆ωab and ∆ωaa in correlation with their respective temperature derivatives terms ∂∆ω/∂t , ∂∆ωab/∂t and ∂∆ωaa/∂t can be expressed as [5, 13] ∆ω(t ) = ∆ω(t0) + ∂∆ω ∂t (t − t0) (26) ∆ωij(t ) = ∆ωij(t0) + ∂∆ωij ∂t (t − t0) (27) where t0 (= 1473 k) is the melting temperature of the system and t is the temperature of interest at which thermodynamic properties are to be calculated. the determined values of temperaturedependent model parameters for this liquid alloy are portrayed in table 1. 1500 1600 1700 1800 -60 -50 -40 -30 -20 g m xs [ kj m o l-1 ] temperature [k] au 10 la 90 au 20 la 80 au 30 la 70 au 40 la 60 au 50 la 50 au 60 la 40 au 70 la 30 au 80 la 20 au 90 la 10 figure 3: temperature dependence of excess gibbs free energy of mixing (∆gxs m ) for au–la liquid alloy. the values of ∆gxs m were computed using equations (1 and 2), ∆hm were computed using equations (1 and 7) and ai were computed using equations (17-19) at different temperatures with the aid of parameters in table 1. the temperature variation of ∆gxs m and ∆hm at fixed composition ratios of au and la are presented in figures 3 and 4. the compositional dependence of ai at different temperatures are plotted in figures 5 and 6. shashit kumar yadav/ bibechana 20 (2023) 316-325 321 the negative values of ∆gxs m and ∆hm decreased linearly with increased in temperature of the system. 1500 1575 1650 1725 1800 -70 -60 -50 -40 -30 -20 h m [ kj m o l-1 ] temperature [k] au 10 la 90 au 20 la 80 au 30 la 70 au 40 la 60 au 50 la 50 au 60 la 70 au 70 la 30 au 80 la 20 au 90 la 10 figure 4: variation of ∆hm with temperature of au–la liquid alloy. 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 a a u x au t=1473 k t=1573 k t=1673 k t=1773 k ideal figure 5: activity of au (aau) versus xau in temperature range 1474–1773 k. 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 a l a x au t=1473 k t=1573 k t=1673 k t=1773 k ideal figure 6: compositional dependence of activity of la (ala) at different temperatures. these results revealed the decrease in the complex formation tendency or strength of interaction between the monomers. indeed, the activities of au and la gradually increased with increase in temperature. the deviation of ai from ideal values gradually decreased with increase in temperature indicating the decrease in mixing tendency of the system (figures 5 and 6). 3.2 structural properties the information related to the local arrangement of atoms in the initial melt can be obtained form the knowledge of structural functions. in structural functions, concentration fluctuation in long wavelength limit (scc(0)), warren-cowley short range order parameter (α1) and ratio of mutual to intrinsic diffusion coefficients (dm/did) were computed in the frame work of quasi-lattice model using equations (10-15) and parameters from table 1. likewise, equations (12-15) and (20) were used to calculate these values on the basis of r-k polynomial with the aid of parameters of dong et al. (table 1). the compositional dependence of scc(0), α1 and dm/did are plotted in figures 7 and 8. 0.2 0.4 0.6 0.8 1.0 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 alpha 1 s cc (0) a lp h a 1, s c c (0 ) x au dong et al. [6] this work ideal figure 7: computed values of scc(0) and α1 of au–la liquid alloy at 1473 k. at a temperature and concentration, if scc(0)<sid cc(0), α1 < 0 and dm/did > 1, then complex formation tendency or hetero-coordinating tendency in the alloy is expected. at the same constraints, if scc(0)>sid cc(0), α1 > 0 and dm/did < 1, then self association among the atoms of alloy or homo-coordinating tendency is expected. the computed values of scc(0) showed negative deviation with respect to its ideal values in the entire concentration range indicating the system to be ordering in nature. this finding is further supported by the negative values of α1 and dm/did > 1 (figures 7 and 8). moreover, the values of scc(0) and α1 computed using the parameters of this work and dong et al. [6] were found to be consistent with each other at all concentrations. shashit kumar yadav/ bibechana 20 (2023) 316-325 322 following the similar procedure as mentioned above, the values of scc(0), α1 and dm/did > 1 were computed in the temperature range 1473-1773 k. the compositional and temperature dependence of these functions are displayed in figures 9-11. 0.0 0.2 0.4 0.6 0.8 1.0 2 4 6 8 10 12 14 d m /d id x au this work figure 8: computed values of dm/did versus xau of au–la liquid alloy at 1473 k. 0.0 0.2 0.4 0.6 0.8 1.0 0.05 0.10 0.15 0.20 0.25 s c c (0 ) x au t=1473 k t=1573 k t=1673 k t=1773 k ideal figure 9: scc(0) versus xau of au–la liquid alloy at different temperatures. the computed values of scc(0) gradually increased and got closure to its ideal values with the rise in temperature of the system above its melting temperature (figure 9). at equiatomic composition (xau = 0.5), the deviation of scc(0) from sid cc(0) were found to be −0.22529, −0.22370, −0.22211 and −0.22054 at 1473 k, 1573 k, 1673 k and 1773 k respectively. these decrease in negative deviations correspond the decrease in in compound forming tendency in the initial melt at high temperatures. this result is further supported by the decrease in negative values of α1 and decrease in positive values of dm/did with increase in temperature of the system (figures 10 and 11). at xau = 0.5, the computed values of α1 were found to be −0.47692, −0.45959, −0.44331 and −0.42814 and those of dm/did were computed to be 10.11753, 9.50450, 8.96344 and 8.48676 at 1473 k, 1573 k, 1673 k and 1773 k respectively. these results further stands in favour of those revealed by scc(0). thus, the results obtained from the investigations of structural functions are in accordance with those indicated by the thermodynamic functions in the above section. 0.0 0.2 0.4 0.6 0.8 1.0 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 a lp h a 1 x au t=1473 k t=1573 k t=1673 k t=1773 k figure 10: α1 versus xau of au–la liquid alloy at different temperatures. 1500 1575 1650 1725 1800 2 3 4 5 6 7 8 9 10 11 12 13 d m /d id temperature [k] au 10 la 90 au 20 la 80 au 30 la 70 au 40 la 60 au 50 la 50 au 60 la 40 au 70 la 30 au 80 la 20 au 90 la 10 figure 11: computed values of dm/did of au–la liquid alloy at different temperatures. 3.3 surface properties in surface properties, surface tension (σ) and extent of surface segregation (surface concentrations, xs i ) were computed in the frame work of butler model [10, 24] using equations (26-25) and parameters from table 2. the compositional dependence of xs i and σ are portrayed in figures 12 and 13 respectively. shashit kumar yadav/ bibechana 20 (2023) 316-325 323 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 xs la xs au xs a u, x s l a x au this work ideal figure 12: computed values of xs au and xs la versus xau of au–la liquid alloy at 1473 k. the surface concentration of la (xs la) showed positive deviation whereas that of au (xs au) showed negative deviation from their respective ideal values in the concentration range xs au < 0.9 (figure 12). among the two components, la has the lower surface tension (σla = 0.63360 n/m) and that of au is higher (σau = 1.13475 n/m) at 1473 k, melting temperature of the system. therefore, la segregated in the surface phase and au remained in the bulk phase of the initial melt in the range xs au < 0.9. xs au gradually increased and xs la gradually decreased with the increase in the bulk concentration of au (xau). they exceed their respective ideal values beyond xs au > 0.9 indicating exchange of their positions in the two phases of melt. the computed values σ of the system gradually increased with increased in the bulk concentration of au. it showed negative deviation from its ideal value beyond xau < 0.6 while showed positive deviation in the remaining range (figure 13). 0.0 0.2 0.4 0.6 0.8 1.0 0.6 0.7 0.8 0.9 1.0 1.1 1.2 s u rf a ce t e ns io n [n m -1 ] x au this work ideal figure 13: compositional dependence of σ of au– la liquid alloy at 1473 k. table 2: input parameters for surface tension [25] atom t0 ρ0 ∂ρ/∂t σ0 ∂σ/∂t (k) (kg/m3) (kg/m3k) (n/m) (n/mk) au 1336 17360 -1.50 1.169 -0.00025 la 1203 5955 -0.24 0.720 -0.00032 the surface tension and surface concentrations of the components of the system were also calculated at different temperatures with the aid of equations (26-25) and parameters from table 2. the compositional and temperature dependence of estimated values are presented in figures 14-16. 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 xs a u x au ideal t=1473 k t=1573 k t=1673 k t=1773 k figure 14: computed values of xs au versus xau of au–la liquid alloy at different temperatures. 0.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 xs l a x au ideal t=1473 k t=1573 k t=1673 k t=1773 k figure 15: computed values of xs la versus xau of au–la liquid alloy at different temperatures. the surface concentrations of au gradually increased and those of la gradually decreased with increase in temperature of the liquid mixture. the negative deviations of xau and positive deviation of xla from their respective ideal values eventually decreased at elevated temperature (figure 14 and 15). therefore, au atoms move from bulk to surface phase while those of la moves from surface shashit kumar yadav/ bibechana 20 (2023) 316-325 324 to bulk phase to maintain the equilibrium condition in the liquid. moreover, the surface tension of the mixture gradually decreased linearly with the increase in temperature beyond its melting temperature (figure 16). these results are as expected since the cohesive force between the components of the liquid mixture gradually decreases with the increase in temperature. 1500 1575 1650 1725 1800 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 s u rf ac e t e n si o n [n m -1 ] temperature [k] au 10 la 90 au 20 la 80 au 30 la 70 au 40 la 60 au 50 la 50 au 60 la 40 au 70 la 30 au 80 la 20 au 90 la 10 figure 16: variation of σ with temperature of au– la liquid 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[25] eric adolph brandes and g. b. brook. smithells metals reference book. elsevier, 2013. introduction formulations quasi–lattice model redlich-kister (r-k) polynomial butler model results and discussion thermodynamic properties structural properties surface properties conclusions bibechana vol. 21, no. 3, december 2024, 321-327 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar ph profile and acidity analysis of some nepalese tea brands: effects of tea type and temperature narendra kumar chaudhary∗, sanjaya thakur, sujan budhathoki, dipak baral department of chemistry, mahendra morang adarsh multiple campus, biratnagar, (tribhuvan university) nepal ∗corresponding author: email: chem_narendra@yahoo.com abstract tea is a popular beverage enjoyed throughout the world, often as a morning wake-up drink. however, excessive consumption may negatively affect health, especially for those who suffer from acidity. in this study, we report the ph values of four locally available tea brands, tokla, ridhisidhi, suman, and muna, brewed at cold and hot conditions and flavored with lemon juice as an additive to determine how conditions and additives affect acidity. hot-brewed tea had an alkaline ph range of 7.74 to 9.03, while cold-brewed tea had a reduced ph range of 7.12 to 7.23. the ph value of lemon-flavored tea ranged from 4.59 to 6.98, suggesting that its acidity may cause problems for those who are sensitive to acid. milk-based teas exhibited ph values between 6.07 and 7.4, while teas with added sugar had lower ph values. with increasing sugar concentrations, tea becomes more acidic. according to these findings, plain black tea is preferable for individuals who are sensitive to acid, whereas lemon-flavored tea may be uncomfortable for them. studying the acidity levels of nepalese tea can therefore provide valuable information about its potential health benefits. in turn, this could lead to research on how brewing techniques and ingredients affect tea chemical composition. keywords tea, ph value, acidity, lemon tea, health benefits, flavor. article information manuscript received: august 20, 2024; revised: october 1, 2024; accepted: october 3, 2024 doi https://doi.org/10.3126/bibechana.v21i3.68944 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction tea is a popular beverage worldwide, and millions of people enjoy it every day because of its refreshing taste, multiple flavors, and numerous health benefits [1]. tea, derived from the leaves of the camellia sinensis plant, is not only consumed as a daily beverage but also holds significant cultural importance, varying across regions and spanning thousands of years of history [2]. chinese emperor shen nong accidentally discovered tea around 2737 bce when some tea leaves fell into boiling water [3]. since then, tea has spread globally, becoming an integral part of various cultures [4]. each culture has devel321 http://nepjol.info/index.php/bibechana chem_narendra@yahoo.com https://doi.org/10.3126/bibechana.v21i3.68944 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ narendra kumar chaudhary et al./ bibechana 21 (2024) 321-327 322 oped unique traditions and rituals for its consumption [5]. tea consumption is an essential part of nepalese culture and economy, with several local brands producing high-quality tea [6]. the hilly region of nepal has a suitable climate, fertile soil, and abundant water, making it an ideal location for tea plantations (figure 1). the tea produced in this region is of high quality and renowned for its flavor, contributing to popularity of hills growing popularity as a destination for tea tourism. the ph of tea is an important factor that can influence its taste, and potential health benefits [7]. it is not only a refreshing beverage, but also boasts numerous health benefits, supported by scientific research [8]. some of the key health benefits associated with regular tea consumption include antioxidant properties, cardiovascular health benefits, weight management, mental health and cognitive function, immune system support, stress reduction, bone health, skin health, and diabetes management. polyphenols, such as catechins and flavonoids, help neutralize free radicals and reduce oxidative stress and cellular damage [9, 10]. in particular, green tea may help reduce the risk of certain cancers by protecting cells from dna damage and inhibiting tumor growth [11]. regular tea consumption is associated with improved cardiovascular health [12, 13]. drinking tea may help lower blood pressure, reduce cholesterol levels, and improve blood vessel function [14]. some studies have suggested that drinking tea may lower the risk of stroke, likely owing to its beneficial effects on blood pressure and cholesterol [15]. the catechin and caffeine components of tea can help boost metabolism and increase fat oxidation, potentially aiding weight loss and management [16]. this can help to regulate appetite and reduce overeating [17]. caffeine in tea provides a mild stimulant effect, and improves mental alertness. tea, especially green tea, contains l-theanine, which promotes relaxation and can enhance cognitive function by working synergistically with caffeine [18]. peppermint and ginger tea are known to aid digestion and alleviate symptoms, such as bloating and nausea [19]. polyphenols in tea can promote the growth of beneficial gut bacteria, contributing to a healthy digestive system [20]. catechins in tea have been shown to possess antimicrobial properties, that can help combat bacteria and viruses [21]. the anti-inflammatory properties of tea can contribute to better joint and bone health [22]. antioxidants in tea can help protect the skin from damage caused by ultraviolet (uv) rays, thereby reducing the risk of skin cancer and premature aging. drinking tea may also help improve skin hydration and elasticity, giving the skin a healthier appearance [23]. some studies have suggested that green and black tea can help regulate blood sugar levels, improve insulin sensitivity, and reduce the risk of type 2 diabetes [24]. figure 1: tea gardens in nepal. source: https://highlightstourism.com/2022/12/14/ tea-gardens-a-sight-seeing-in-eastern-nepal. drinking tea, which is generally considered beneficial owing to its antioxidants and other healthpromoting compounds, can pose certain health risks. tea, especially black and green tea, contains caffeine, which can cause sleep disturbances and increase anxiety levels in sensitive individuals. excessive and regular consumption of caffeine can lead to heart palpitations and increased heart rate [25,26]. the tannins present in tea leaves hinder the absorption of iron from plant-based diets. individuals with iron deficiency, pregnant women, and children are at high risk due to tannin contents [27, 28]. excessive tea consumption is associated with decreased bone mineral density and an increased risk of fractures, especially in postmenopausal women, owing to the fluoride content of tea leaves [29]. it contains oxalates, which can lead to kidney stones in sensitive individuals [30, 31]. excess tea consumption may lead to health risks due to its high heavy metal content such as pb, al, and metal fluorides [32]. because tea is acidic, some people may experience nausea, acid reflux, or upset stomachs when it is taken on an empty stomach. tea has been considered as a means of connecting people in society and is a tradition, but not only as a beverage. this study aims to measure and compare the ph values of various nepalese tea brands under different conditions, including brewing times, temperatures, and medium types. 2 experimental 2.1 materials and chemicals four local nepalese tea brands, tokla, ridhisidhi, suman, and muna tea, were selected for this study and purchased from the local market of biratnagar, nepal. distilled water was used to brew the tea samples. they were meshed to remove dirt and brewed according to standard brewing instructions. a digital ph meter was used to measure the ph of brewed tea samples. the ph variation was investigated by varying the brewing conditions, includhttps://highlightstourism.com/2022/12/14/tea-gardens-a-sight-seeing-in-eastern-nepal https://highlightstourism.com/2022/12/14/tea-gardens-a-sight-seeing-in-eastern-nepal narendra kumar chaudhary et al./ bibechana 21 (2024) 321-327 323 ing temperature changes and the addition of fresh lemon juice, milk, and sugar to the tea samples. 2.2 preparation of tea samples in each set of experiments, 2 g of dry tea was added to 200 ml of distilled water to prepare tea. the temperature of hot tea was maintained at 90 °c. various types of tea samples, including teas with milk, sugar, and fresh lemon juice, were prepared using the same procedure but in varying proportions. during preparation, the tea samples were occasionally stirred to homogenize them. the ph measurements were performed in triplicate to reduce error. the entire process of sample preparation and ph measurement is shown in figure 2. figure 2: tea sample preparation and ph measurement. 2.3 statistical analysis the origin 2018 version software was used to perform a one-way anova test to compare the mean differences between multiple groups. the data represents the mean of ph in three replications with ± standard deviation (sd). pair identification and the display of significant mean differences were accomplished through post-hoc analysis using tucky's test. the ph values of p < 0.05 were considered significant. 3 results and discussion 3.1 freshly brewed tea the flavor and stability of tea can be greatly influenced by ph. black tea had a ph value of 7.73 to 9.03 under hot conditions, whereas it drops to 7.12 to 7.22 under cold conditions. the ph values of all the freshly brewed teas were within the expected range for black tea, indicating a slightly alkaline nature. suman tea with a ph of 9.03 under hot conditions is relatively more basic than other tea brands. cooling decreased the ph of all tea brands. as reported in previous studies, fresh brewed black tea typically has a ph of 7–9 under hot conditions and a slightly decreased ph of 7.12 7.30 under cold conditions [31]. this decrease in ph under cold conditions may be due to the release of organic acids [32]. table 1 presents the ph data for all tea brands under cold and hot conditions, which are graphically illustrated in figure 3. table 1: ph of black tea in water without flavour s. n. different brands of tea ph hot condition cold condition 1 tokla 7.73 ± 0.05 7.2 ± 0.01 2 ridhisidhi 8.00 ± 0.1 7.18 ± 0.02 3 suman 9.03 ± 0.05 7.22 ± 0.025 4 muna 7.76 ± 0.03 7.12 ± 0.005 each value represents mean ph ± standard deviation (sd) figure 3: ph of black tea in cold and hot conditions. 3.2 tea with lemon flavour table 2 presents the ph data for all brands of black tea containing varying amounts of sugar and lemon juice. the ph value decreased as more sugar was added to the tea. moreover, an increased concentration of sugar (2 g) resulted in a slightly acidic ph range. likewise, adding lemon (0.1, 0.2, 0.3, and 0.4 ml), which is highly acidic (ph ~2-3) to black tea containing different levels of sugar (0.5, 1.0, 1.5, and 2.0 g) resulted in a significant drop in ph levels, narendra kumar chaudhary et al./ bibechana 21 (2024) 321-327 324 making the tea more acidic. the ph values, ranging from 4.59 to 6.97 after adding lemon to tea, are consistent with studies showing that lemon acidity (ph 2-3) lowers the overall ph of tea mixtures [33]. the ph change follows this order: suman > ridhisidhi > muna ~ tokla. this increase in acidity can enhance the antioxidant properties of tea, but might also make the tea tangier and sharper in taste. the tokla tea brand is more acidic in this context, with a ph of 4.59. a study has shown that the addition of lemon can enhance the bioavailability of polyphenols, thereby increasing the health benefits of tea. however, increased acidity may pose discomfort issues for acid-sensitive individuals [34]. the results of the variation in the ph of sugar-supplemented tea with and without lemon are graphically presented in figure 4. table 2: ph of sugar added black tea with and without lemon s. n. different brands of tea sugar content ph lemon contentblack tea black tea with lemon 1 tokla 0.5 gm 7.49 ± 0.005 6.28 ± 0.005 0.1 ml 1.0 gm 7.25 ± 0.01 5.66 ± 0.005 0.2 ml 1.5 gm 7.07 ± 0.005 5.13 ± 0.01 0.3 ml 2.0 gm 6.80 ± 0.01 4.59 ± 0.005 0.4 ml 2 ridhisidhi 0.5 gm 7.73 ± 0.015 6.97 ± 0.015 0.1 ml 1.0 gm 7.51 ± 0.015 6.39 ± 0.005 0.2 ml 1.5 gm 7.23 ± 0.02 5.86 ± 0.015 0.3 ml 2.0 gm 6.94 ± 0.015 4.77 ± 0.02 0.4 ml 3 suman 0.5 gm 8.69 ± 0.005 6.67 ± 0.005 0.1 ml 1.0 gm 8.43 ± 0.015 6.08 ± 0.01 0.2 ml 1.5 gm 8.2 ± 0.01 5.55 ± 0.02 0.3 ml 2.0 gm 7.87 ± 0.02 4.97 ± 0.02 0.4 ml 4 muna 0.5 gm 7.48 ± 0.01 6.35 ± 0.005 0.1 ml 1.0 gm 7.25 ± 0.01 5.83 ± 0.01 0.2 ml 1.5 gm 6.94 ± 0.01 5.27 ± 0.02 0.3 ml 2.0 gm 6.75 ± 0.01 4.75 ± 0.01 0.4 ml each value represents mean ph ± standard deviation (sd) figure 4: ph of sugar added black tea with and without lemon. 3.3 sugar added tea with milk adding milk to tea generally decreases its ph, making it acidic, which may be due to the buffering capacity of milk that contains proteins and calcium as its main components. the ph of the tea with 100% milk ranged from 6.07 -7.40. suman tea had the highest ph value (7.40). this suggests that it might offer the mildest flavor when milk is added. muna showed the largest decrease in ph (6.07) after the addition of more sugar to 100 % milk tea. when the milk concentration in tea decreases, the ph value increases slightly, moving toward an alkaline nature [35]. however, some studies have raised concerns that milk might decrease the absorption of certain antioxidants in tea, although the extent of this effect remains debated [36]. the variation in the ph profile of milk tea with added sugar is presented in table 3, and a bar graph showing this effect is shown in figure 5. narendra kumar chaudhary et al./ bibechana 21 (2024) 321-327 325 table 3: ph of sugar added milk tea with varying milk-water ratios s.n. different brands of tea sugar content ph milk tea without water 75% milk & 25% water 50% milk & 50% water 1 tokla 0.5 gm 6.86 ± 0.05 6.91 ± 0.01 6.94 ± 0.005 1.0 gm 6.70 ± 0.01 6.79 ± 0.005 6.86 ± 0.005 1.5 gm 6.56 ± 0.01 6.71 ± 0.005 6.77 ± 0.005 2.0 gm 6.44 ± 0.03 6.54 ± 0.005 6.62 ± 0.02 2 ridhisidhi 0.5 gm 7.19 ± 0.01 7.16 ± 0.03 7.13 ± 0.06 1.0 gm 6.99 ± 0.005 6.97 ± 0.01 6.98 ± 0.005 1.5 gm 6.78 ± 0.01 6.84 ± 0.01 6.87 ± 0.01 2.0 gm 6.59 ± 0.005 6.69 ± 0.005 6.78 ± 0.005 3 suman 0.5 gm 7.40 ± 0.01 7.30 ± 0.005 7.21 ± 0.01 1.0 gm 7.24 ± 0.01 7.17 ± 0.005 7.13 ± 0.02 1.5 gm 7.04 ± 0.005 7.03 ± 0.01 7.03 ± 0.01 2.0 gm 6.82 ± 0.01 6.85 ± 0.01 6.91 ± 0.01 4 muna 0.5 gm 6.65 ± 0.01 6.75 ± 0.02 6.83 ± 0.005 1.0 gm 6.43 ± 0.01 6.58 ± 0.01 6.73 ± 0.02 1.5 gm 6.22 ± 0.01 6.40 ± 0.01 6.62 ± 0.01 2.0 gm 6.07 ± 0.02 6.29 ± 0.01 6.52 ± 0.005 figure 5: ph of tea with different % of milk-water ratio and sugar content. 4 conclusion the ph of four local nepalese tea brands was successfully investigated and evaluated to compare their acidity and evaluate their health impacts, particularly in acid-sensitive individuals. most of the teas studied were basic in nature, and ph variation occurred after the addition of ingredients such as milk, sugar, and lemon flavors in different amounts. plain black tea is mildly alkaline to neutral, which makes it relatively safe for acid-sensitive individuals. the lemon-flavored tea is significantly more acidic, which might be due to the acidic components present in lemons. the acidity level of approximately 4.59 can be sufficiently high to induce discomfort 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[35] a. rashidinejad, e.j. birch, d. sunwaterhouse, and d.w. everett. addition of milk to tea infusions: helpful or harmful? evidence from in vitro and in vivo studies on antioxidant properties. critical reviews in food science and nutrition, 57:3188–3196, 2017. https://doi.org/10.1080/10408398. 2015.1099515 [36] m. serafini, a. ghiselli, and a. ferro-luzzi. in vivo antioxidant effect of green and black tea in man. european journal of clinical nutrition, 50:28–32, 1996. https://doi.org/10.1080/10408690091189194 https://doi.org/10.1080/10408690091189194 https://doi.org/10.1007/s12603-021-1677-4 https://doi.org/10.1007/s12603-021-1677-4 https://doi.org/10.1046/j.1523-1755.2001.00488.x https://doi.org/10.1046/j.1523-1755.2001.00488.x https://doi.org/10.1007/s13197-021-05034-3 https://doi.org/10.1007/s13197-021-05034-3 https://doi.org/10.1016/j.jfca.2013.09.010 https://doi.org/10.1016/j.jfca.2013.09.010 https://doi.org/10.5601/jelem.2017.22.3.1449 https://doi.org/10.5601/jelem.2017.22.3.1449 https://doi.org/10.1080/15428052.2018.1502114. https://doi.org/10.1080/15428052.2018.1502114. https://doi.org/10.1080/10408398.2015.1099515 https://doi.org/10.1080/10408398.2015.1099515 introduction experimental materials and chemicals preparation of tea samples statistical analysis results and discussion freshly brewed tea tea with lemon flavour sugar added tea with milk conclusion bibechana vol. 20, no. 1, april 2023, 86-91 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar mixing properties of liquid al–au alloys shashit kumar yadav, upendra mehta ram prasad koirala, ramesh kumar gohivar∗ department of physics, mahendra morang adarsh mulpiple campus tribhuvan university, biratnagar, nepal *corresponding author. email: ramesh.gohibar@mmamc.tu.edu.np abstract the thermodynamic and structural properties of liquid al–au alloy have been studied in framework of r-k polynomial using temperature-dependent energy interaction parameters at different temperatures. thermodynamic properties, excess free energy of mixing and activity, and in structural properties, concentration fluctuation in long wave-length limit have been computed at temperatures 1338 k, 1500 k and 1600 k. the properties, such as surface tension and surface concentration of the system have been computed at above mentioned temperatures using butler model. the system shows transformation from segregating to ordering in nature with increase in concentration of au. keywords r-k polynomial, al–au alloys, thermodynamic, structural and surface properties. article information manuscript received: march 21, 2023; accepted: april 2, 2023 doi https://doi.org/10.3126/bibechana.v20i1.53776 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the majority of semiconductor packages are assembled via wire bonding, which is typically regarded as the most affordable and efficient connectivity approach. the intermetallic compounds of al-au alloys are profoundly used in these metallization processes [1–4]. hence, the mixing properties of the system has been extensively investigated by several researchers [3,5–18]. the details of the literature related to the chronological investigations of phase structures and thermodynamic properties of the system till 2004 are presented by li et al. [3]. they accessed the thermodynamic properties of the system using thermo-calc (computerbased software) along with other theoretical approaches. they also presented the self-consistent temperature-dependent interaction parameters for excess gibbs free energy of mixing. later, olajire and musari used different theoretical models to investigate the thermodynamic and structural properties of the system [10]. peng et al. [19] experimentally measured the compositional and temperature dependence of density, temperature coefficient of density, molar volumes, selfand inter diffusion and viscosity of al-au liquid alloy at 1400 k. they also developed a molecular dynamics (md) model in order to computed the above mentioned properties using the experimental results [19]. later brillo and kolland [20] experimentally measured the surface tensions of the system and found that the surface tension (σ) de86 http://nepjol.info/index.php/bibechana ramesh.gohibar@mmamc.tu.edu.np https://doi.org/10.3126/bibechana.v20i1.53776 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ krishna prasad kandel et al./ bibechana 20 (2023) 86-91 87 creases linearly with temperature. further, they found that σ of the system decreased monotonically with increase in al content at 1400 k. from above literature survey, it can be stated that al-au liquid alloy has been extensively studied. therefore, an attempt has been made in this work to reassess the thermodynamic properties of the system using optimised coefficients li et al. [3] of redlich-kister (r-k) polynomial [21]. these coefficient are used to compute thermodynamic, structural and surface properties of the system at different temperatures in frame work r-k polynomial. the thermodynamic properties, such as gxs m , activity (a) and structural properties, such as concentration fluctuation in long wavelength limit (scc(0)) have been computed. the surface properties of have been computed using butler model [22] with the help of determined values of partial excess gibbs free energy of individual component of the alloy. the different modeling equations used for the present investigations are presented in the section 2, the results and discussion are mentioned in the section 3 and important conclusions of the work are highlighted in the section 4. 2 methods and methodology according to r-k polynomial, the excess free energy of mixing (gxs m ) is expressed as [21,23] gxs m = xalxau[l0 + l1(xal − xau)] (1) where l0 and l1 are coefficients of r-k polynomial, also called interaction energy parameters and are assumed to depend linearly on temperature and xal and xau are moalr fraction of constituents of liquid al–au alloy. the energy interaction parameters is linear temperature dependent and the excess free energy of mixing is expressed as gxs m = xalxau[(a0 + b0t ) + (a1 + b1t )(xal − xau)] (2) the partial excess free energy (gxs al, g xs au) of each component of liquid al–au alloy can be calculated using the relation [24] gxs al = gxs m + xau ( ∂gxs m ∂xal − ∂gxs m ∂xau ) gxs au = gxs m + xal ( ∂gxs m ∂xal − ∂gxs m ∂xau ) (3) once the values of partial excess free energy of mixing are computed, the values of activity of each component (aal, aau) in the liquid alloy is obtained by following expression aal = xal exp ( gxs al rt ) , aau = xau exp ( gxs au rt ) (4) the structural function in long wave-length limit (scc(0)) of binary liquid al–au alloy can be expressed in the following form [25] scc(0) = rt ( ∂2gm ∂x2 al )−1 t,p,n = rt ( ∂2gm ∂x2 au )−1 t,p,n (5) the analytical expression for scc(0) of liquid al– au alloy [26] is scc(0) = rt [−2l0 + (−12xal + 6)l1 +(−48x2 al + 48xal − 10)l1 + rt xal(1− xal) ]−1 (6) the information related to the arrangement of atoms in the nearest neighbourhoods of initial metallic solution can be obtained by computing parameters like concentration fluctuation in the long wave length limit (scc(0)) [25,26]. the expression for ideal value of scc(0) is calculated using the relation sid cc(0) = xalxau (7) the surface properties of the system have been studied using butler model [22, 27]. this approximation is based on the assumption of hypothetical monoatomic surface layer being in equilibrium with the bulk phase of the metallic solution. accordingly, the surface tension (σ) of the solution in terms of molar surface area (λ1) of constituent atoms is expressed as σ = σal + 1 λal (gxs al,s −gxs al,b) + rt λal ln( xs al xb al ) = σau + 1 λau (gxs au,s −gxs au,b) + rt λau ln( xs au xb au ) (8) where σal and σau are surface tension of pure components , and gxs al and gxs au are the partial excess free energy of component in the surface phase and bulk phase respectively, and xs al, x s au and xb al, x b au are the surface and bulk concentrations of al and au respectively. herein, gxs i,s = βgxs i,b, i = al,au with β = 0.8181 [22] and λiis expressed as λi = 1.00n 1/3 a ( mi ρi )2/3 (9) where na is the avogadro’s number, mi and ρi are the mass and density in the al–au alloy respectively. the expression for σi and ρi can be given as σi = σ0 i + ∂σi ∂t (t − t 0 i ) (10) ρi = ρ0i + ∂ρi ∂t (t − t 0 i ) (11) where t 0 i is the melting temperature of the ith component and t is the required temperature at which these parameters are to be calculated. krishna prasad kandel et al./ bibechana 20 (2023) 86-91 88 3 results and discussion 3.1 excess free energy of mixing the energy interaction parameters of r-k polynomial for liquid al–au alloy were taken from ref. [3] are presented in table 1. the interaction parameters of table 1 have been used in equation (1) to compute gxs m of al–au alloy at 1338 k, 1500 k and 1600 k. the computed values are plotted in figure 1. the negative value of gxs m of the system decreases with increase in temperature. the minimum value at 1338 k is found to be -19.505 kj/mol at equi-atomic composition. table 1: energy interaction parameters of liquid al–au alloy interaction parameters (j/mol) [3] l0 = −131996.19 + 36.42t l1 = 40781.83− 1.896t table 2: physical quantities of liquid al–fe alloy [28] quantities element al element au mi (kg) 0.2698154 0.19696665 t0 i 933 k 1336 k ρ0i (kg/m3) 2385 17360 dρi dt (kgm−3t−1) -0.28 -1.5 σi(mn/m) 914 1140 dσi dt (mn/(mt)) -0.35 -0.52 0.2 0.4 0.6 0.8 1 −25 −20 −15 −10 −5 0 xau g x s m (k j /m ol ) al-au alloy 1338 k 1500 k 1600 k figure 1: excess free energy of mixing of liquid al–au alloy at different temperatures. 3.2 activity the parameters of table 1 have been used in equation (3) to calculated the partial excess free energy (gxs i , i=au, al) of each component at above mentioned temperatures. the activity of components al and au (aau, aal) have been calculated using equation (4) and these values are plotted in figure 2. the activity of component al in the region of high concentration of al (xau < 0.2) shows positive deviation from raoult’s law and negative deviation at remaining concentrations. this indicates the system shows ordering nature in the region xau < 0.2 and segregating nature at remaining concentrations. both the components have a very small value of activities in the concentration range xi = 0.6 which indicates strong ordering behaviour of the system (figure 2). krishna prasad kandel et al./ bibechana 20 (2023) 86-91 89 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 aal aau xau a ct iv it y al–au alloy 1338 k 1500 k 1600 k ideal figure 2: activity of liquid al–au alloy at different temperatures. 3.3 concentration fluctuation in long wavelength limit (scc(0)) the structural function (scc(0)) of liquid al–au alloy gives an idea about the local arrangement of components al and au in the system. the function scc(0) have been calculated using energy interaction parameters of table 1 in equation (6) at above mentioned temperatures, 1338 k, 1500 k and 1600 k. the computed values are plotted in figure 3. the calculated value of scc(0) at lower concentrations of au (xau < 0.2) exceeded ideal values showing segregating nature in those region. however, these values at remaining concentration are less than ideal values indicating the ordering nature. hence, the system shows transformation from segregating to ordering nature. as the temperature of the system is gradually increased, the computed values of structural function gradually increases (figure 3). 0.2 0.4 0.6 0.8 1 0 5 · 10−2 0.1 0.15 0.2 0.25 xau s c c (0 ) al–au alloy 1338 k 1500 k 1600 k ideal figure 3: scc(0) of liquid al–au alloy at different temperatures. 3.4 surface tension (σ) surface tension (σ) of liquid al–au alloy has been calculated at above mentioned temperatures using physical parameters of table 2 and equations (8,9,10,11). the calculated values of (σ) are plotted in figure 4 as a function of concentration of au. the surface concentrations xs al and xs au of the alloy have been optimised during the computations of (σ) and are plotted in figure 5. it can be observed that the surface tension (σ) of the system at its melting temperature (1338 k) gradually increased with increase in the bulk concentration of au. as mentioned earlier, σ was also computed at different temperatures. with increase in the temperature, the values of σ gradually decreased with increase in the content of au (figure 4) and these results are similar to those obtained by [19], [20]. krishna prasad kandel et al./ bibechana 20 (2023) 86-91 90 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 1.2 xau s u rf ac e te n si o n (n / m ) surface tension of al–au alloy 1338 k 1500 k 1600 k figure 4: surface tension of liquid al–au alloy at different temperatures. 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 aau aal xau s u rf ac e c on ce n tr a ti on surface concentration of al–au alloy 1338 k 1500 k 1600 k figure 5: surface concentration of liquid al–au alloy at different temperatures. the surface concentrations of au and al (xs au and xs al) have the same value at/about xau = 0.7. with increase in xau, xs au gradually increases whereas xs al gradually decreases. at higher temperatures, the computed values of xs al gradually decreases whereas those of xs au gradually increases (figure 5). these results indicate that there is exchange of atoms between the surface and bulk phases of the liquid alloy in order to maintain equilibrium [29]. 4 conclusion present theoretical investigations show that the liquid al–au is found to be the most interacting at its melting temperature. the system shows tranformation from segregating to ordering nature. with increase in temperature, its 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[29] s. k. yadav, l. n. jha, and d adhikari. modeling equations to predict the mixing behaviours of alfe liquid alloy at different temperatures. bibechana, 15:60–69, 2018. introduction methods and methodology results and discussion excess free energy of mixing activity concentration fluctuation in long wavelength limit (scc(0)) surface tension () conclusion bibechana vol. 20, no. 2, august 2023, 175–182 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar in-vitro dissolution study of gallstone with medicinal plant extracts bijaya b.k.1, achyut adhikari1,∗ gobinda gyawali2 1central dept. of chemistry, tribhuvan university, kirtipur 44618, kathmandu 2department of fusion science and technology, sun moon university tangjeong myeon, asan si, chungnam 31460, republic of korea ∗corresponding author. email: achyutraj05@gmail.com abstract background: gallstone disease poses a substantial economic burden on healthcare systems globally, necessitating safer alternatives to current treatments like dissolution therapy and cholecystectomy. natural compounds from plants offer a potential solution, but research on their cholelitholytic activity is limited. in vitro dissolution studies are crucial for identifying effective plant-based therapies. objective: this study aims to investigate the in vitro cholelitholytic activity of six plants and ayurvedic medicines, selected based on ethnopharmacological knowledge and folk medicinal practices. methods: gallstone samples were categorized as combined cholesterol gallstones (ccgs) or black pigment gallstones based on external morphology and cross-sectional analysis. in vitro dissolution studies were conducted using extracts from bergenia ciliata, berberis asiatica, cuscuta europaea, kalanchoe pinnata, teraxacum officinale, macrotyloma uniflorum, and ayurvedic medicines (cystone®, gokshuradi, and calcury). the samples were immersed in the extracts and controls separately and incubated in a shaking water bath. the gallstone dissolution capacity was assessed by recording the dry weight of the samples at multiple time points. results: t. officinale was highly effective in dissolving black pigment gallstones, while b. asiatica exhibited superior efficacy for ccgs. m. uniflorum and c. europaea also demonstrated significant dissolution activity against black pigment gallstones. however, k. pinnata was less effective for both gallstone types. b. ciliata and c. europaea exhibited equal effectiveness against both types. ayurvedic medicine extracts were less effective compared to plant extracts. conclusion: this in vitro study showed the plants can dissolve gs effectively. however, the effectiveness of the plant to dissolve gs depends on the type of the stone. the findings from this study serve as a basis for further in vivo research. keywords gallstone, in vitro dissolution, plant extracts, combined cholesterol gallstones, black pigment gallstones. article information manuscript received: june 4 2023; accepted: june 17, 2023 doi https://doi.org/10.3126/bibechana.v20i2.55865 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction gallstones (gs), which are solid deposits formed inside the gallbladder, are mainly composed of cholesterol and bilirubin [1]. the formation of gs involves supersaturation, nucleation, crystallization, and aggregation of the insoluble components of the bile like cholesterol and bilirubin [2]. when the 175 http://nepjol.info/index.php/bibechana achyutraj05@gmail.com https://doi.org/10.3126/bibechana.v20i2.55865 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ bijaya b.k. et al./ bibechana 20 (2023) 175-182 176 concentration of these insoluble components exceeds their solubility or there is a decrease in bile acid concentration or the presence of foreign substances, gallstones form [3]. gallstone disease is a prevalent health problem that affects 10-20% of the global population [4] and is a significant contributor to morbidity and mortality [5], with an estimated global cost of $6.5 billion annually [6]. its prevalence in nepal is 4.87% with females being more affected than males [7]. therefore, gallstone disease imposes a significant economic burden on healthcare systems worldwide [8]. the treatment of gallstone disease can be done through surgery or non-surgical methods. nonsurgical methods include taking bile acids like chenodeoxycholic acid (cdca) and ursodeoxycholic acid (udca) orally (oral dissolution therapy) [9] or installing litholytic solvent like methyl tert-butyl ether (mtbe) [10], 2-methoxy-6-methylpyridine (mmp) [11], or ethylenediaminetetraacetic acid (edta) [12], directly into the gallbladder through a percutaneous transhepatic catheter (contact dissolution therapy) [13]. however, these methods have limitations due to side effects, toxicity, low efficiency [14], incomplete dissolution [15], and gallstone reoccurrence is common [16]. laparoscopic cholecystectomy, the surgical removal of the gallbladder, is considered the best option [17] but has postoperative complications such as bile leakage, bile duct injury [18], persistent pain [19], and fat intolerance [20]. due to the limitations and potential risks of current treatment options, natural compounds from plants could be a safer alternative. it is believed that herbal medicines have lesser or no side effects. while extensive studies have been conducted on the cholelitholytic activity of organic solvents, research on plants is limited, and in vitro dissolution studies are necessary to identify potential plant-based therapies. therefore, in this study, we investigated the in vitro cholelitholytic activity of six plants (selected based on ethnopharmacological knowledge and folk medicinal practices) and ayurvedic medicines available in the market. the results of this in vitro study will provide a basis for further research in vivo. 2 materials and methods 2.1 collection and pre-treatment of gallstones dr. barun kumar shah, norvic international hospital, thapathali, kathmandu, nepal has provided the gallstone samples. cholecystectomy was performed to extract gallstones from patients. altogether, 12 ccgs (from two patients) and 15 black pgs (from one patient) were collected. the collected gallstones were thrown away materials with no human tissues or genetic material. the gallstone samples were washed with deionized water and dried at 60 ℃ in an incubator until the constant weight [21]. 2.2 macroscopic classification of gallstones based on the external morphology and internal cross-sectional analysis, we categorized the gallstones into two groups: combined cholesterol gallstone (ccgs) and black pigment gallstone (black pgs). photographs of the gallstones were taken, their morphological features like shape, size, color, and internal cross-section were studied. the outer dimensions of the stone were measured with a digital vernier caliper. one gallstone from each patient was cut into equal halves using jeweler’s saw and the internal cross-section was studied. the remaining gallstones were stored on a desiccator filled with calcium chloride in a dark cabinet, and later on, they were used for in vitro dissolution with different extracts of plant and herbal medicines. 2.3 collection of plant and ayurvedic medicines the rhizomes of bergenia ciliata were collected from central nepal, parbat district, panchase. the root of berberis asiatica and tendrils of cuscuta europaea were collected from central nepal, parbat district, modi rural municipality-7, ranpu. the leaves of kalanchoe pinnata were collected from central nepal, kaski district, pokhara-15, nayagaun. leaves of teraxacum officinale were collected from central nepal, kathmandu district, kirtipur. the legumes of macrotyloma uniflorum were purchased from the local market of kirtipur, nayabazar. herbarium samples of each plant were prepared and the plants were identified from national herbarium and plant laboratories, godawari, lalitpur. ayurvedic medicines (cystone®, gokshuradi, and calcury) were purchased from arogyadham homoeopathic hospital, pokhara with the suggestion of homeopathic physician dr. bishnu prasad chapagain. the plant materials were washed with tap water, cut down into small pieces, and shed dried for two weeks. the shed dried plant samples were crushed into powder with the help of a grinding mill at the central department of chemistry. the powder samples were put into an airtight glass jar and stored at ambient temperature. 2.4 in vitro dissolution study of gallstones the dried and powdered plant samples were extracted with ethanol using soxhlet apparatus. to bijaya b.k. et al./ bibechana 20 (2023) 175-182 177 obtain crude extracts, 50 g sample powder was refluxed with 500 ml of ethanol at 40 °c until a clear solution was obtained in the thimble. the dilute extract was evaporated under reduced pressure using a rotatory evaporator at 40 °c. the semisolid crude extract obtained from rotavapor was dried at ambient temperature for several days to get the dry crude extract. the dried crude extracts were collected into 15 ml flat-bottom borosil culture tubes, labeled properly, and stored at 4 °c in a refrigerator. 50 mg/ml extract solution was prepared by dissolving 5 g of the solid crude extract in 100 ml of distilled water. the solution was slightly warmed and sonicated for half an hour, let to settle down to get a clear stock solution. the clear solution was collected into a 100 ml volumetric flask, the flask was stoppered, labeled, and stored in a refrigerator at 4 °c. two tablets of each ayurvedic medicine were powdered in a mortar and pestle and the powder was taken into the centrifuge tube with a screw cap. distilled water (10 ml) was added and the content was kept in a water bath for a night at 37 °c, centrifuged at 25 °c in a high-speed centrifuge at 8000 rpm to get clear supernatant. the clear supernatant was collected into a 100 ml volumetric flask, the flask was labeled and stored at 4 °c in a refrigerator [22]. 2.5 dissolution of gallstones with plant and medicine extracts for the in vitro dissolution study, the protocol used by igimi et al. [23] was followed with slight modification. the gallstone samples that were oven-dried (at 60 ℃) and stored in a desiccator in a dark cabinet at least for 15 days were taken for dissolution. the gallstone samples were taken, weighed, and immersed in vitro into 10 ml of the extract, positive control, and negative control separately. borosil culture tubes (15 ml volume) with round bottom and screw cap were used for the purpose. the tubes with content were put in a test tube rack and kept in a shaking water bath at 37 ℃ with gentle and constant shaking (60 rpm). the plant extracts were changed every day to minimize any effect due to saturation of the solution by dissolved components of the stone [23]. the stones were taken out of the extract by filtration through filter paper (whatman no1), washed with distilled water, transferred into a pre-weighed crucible, dried at 60 °c in an incubator for two days to get constant weight, and the weight reduced was noted [11,24]. to determine the gallstone dissolution capacity of each extract and solvent, we recorded the dry weight of the stone samples at three different time points (4, 94, and 190 h) after they were directly immersed in the solution. photographs of the stones were also taken after each time interval. the stone samples with comparable weight and size were taken for dissolution study. the average weight of different ccgs samples was 14.48±0.21 mg and that of black pgs samples was 21.46±0.22 mg. in the present research, 2% edta solution maintained at ph 9.5 adjusted with hcl and 95% ethanol was used as a positive control whereas distilled water was used as a negative control. it was found that the higher the ph of the edta solution higher is its litholytic activity [25]. the ph of 8.5 is within the harmless range to use to the human body [25], but we maintained the ph 9.5 because studies have found that this is the most effective ph at which edta shows the maximum dissolution of gs [26]. first of all, the weight dissolved by negative control at every time point was subtracted from the weight reduction value recorded for each of the preparations at respective time points to calculate the actual weight dissolved by the preparations. then the percentage dissolution was calculated by using the following formula [11,24]: %dissolution(w/w) = actual wt. dissolved initial wt. of the stone ×100 (1) 3 results 3.1 general observation and macroscopic classification of gallstones the photographs showing the external morphology and internal cross-section of the gallstone samples are given in figure 1. the gallstone sample, which is multifaceted, whitish-brown with a hard and smooth outer surface [27, 28], with a distinct inner pigmented yellow core and a white external shell (figure 1a, b) [28, 29] was classified as a combination cholesterol gallstone (ccgs). the gallstone sample, which was irregular with a rough and thin yellowish surface [27, 28], amorphous in cross-section [28, 29] with a black inner part and outer thin yellowish layer (figure 1c, d) was classified as black pigment gallstone (black pgs) [28]. furthermore, we conducted a separate study to support this macroscopic classification via uv-vis and sem-eds analysis [28]. 3.2 in vitro dissolution study of gallstones the final data obtained for cumulative dissolution of gallstone samples in different extract and solvent preparations is presented in table 1. the observation tables for recorded weight (initial, after 4 h, 94 h, and 190 h), dissolution and cumulative dissolution are included in supplementary material bijaya b.k. et al./ bibechana 20 (2023) 175-182 178 figure 1: photographs of the gallstone samples; (a) ccgs, (b) internal cross-section of ccgs, (c) black pgs, and (d) internal cross-section of black pgs (annexure 1). photographs of gallstones at different time are also given in supplementary material (annexure 2). after 190 hours, 14.3 mg of the ccgs and 8.6 mg of the black pgs was dissolved in etoh, whereas in edta, 11.5 mg of the black pgs and 5.1 mg of ccgs was dissolved. therefore, it can be inferred that the ccgs was more soluble in etoh and black pgs was more soluble in edta (table 1). figure 2 illustrates the comparative study of the final dissolution of gallstone samples in different extract and solvent preparations. it shows that e1 (m. uniflorum), e4 (c. europaea), e5 (t. officinale), and edta dissolved black pgs more effectively than ccgs, while the m2 (calcury) showed almost similar dissolution for both the stones. in contrast, e2 (b. asiatica), e3 (b. ciliata), m1 (cystone), m3 (gokshuradi), and etoh showed better dissolution for ccgs than for black pgs, while in e6 (k. pinnata), dissolution of both the gallstones was comparable. table 1: comparative study of the final dissolution of ccgs and black pgs in different extract and solvent preparations. extract or solvent weight dissolved after 190 hours (mg) ccgs black pgs e1 (m. uniflorum) 5.6 9.3 e2 (b. asiatica) 10.8 5.4 e3 (b. ciliata) 4.7 3.7 e4 (c. europaea) 7.3 8.5 e5 (t. officinale) 3.0 9.6 e6 (k. pinnata) 2.2 2.1 m1 (cystone®) 3.1 1.8 m2 (calcury) 3.9 4.0 m3 (gokshuradi) 5.8 3.5 edta (+ve control) 5.1 11.5 etoh (+ve control) 14.3 8.6 note: edta and etoh are used as positive controls and distilled water as a negative control. the data for each experiment is expressed after subtracting the data obtained for the negative control. 4 discussion close interpretation of the graph in figure 2 shows that, in e1 (m. uniflorum), e4 (c. europaea) and e5 (t. officinale), black pgs was more soluble than ccgs. among different extracts preparations (both plant and medicine), e5 (t. officinale) was the most effective for dissolving black pgs (9.6 mg). in comparison with the most effective positive control edta (11.5 mg), the efficacy of e5 (t. officinale) to dissolve black pgs can be considered as comparatively excellent. e5 (t. officinale) was more effective than another positive control etoh (8.6 mg). the efficacy of e1 (m. uniflorum) to dissolve black pgs (9.3 mg) was almost equivalent to that of the most effective plant e5 (t. officinale). this shows that e5 (t. officinale) and e1 (m. uniflorum) can effectively dissolve pigbijaya b.k. et al./ bibechana 20 (2023) 175-182 179 figure 2: the comparative study of the final dissolution of ccgs and black pgs in different extract and solvent preparations ment containing stones. moreover, this fact was further supported by the result obtained for cholesterol predominant ccgs which shows that e5 (t. officinale) and e1 (m. uniflorum) dissolved significantly lesser amount of ccgs than black pgs (3.0 mg in e5 and 5.6 mg in e1). m2 showed almost similar efficacy to dissolve both the ccgs (3.9 mg) and gsb (4.0 mg) whereas m1 (cystone®) and m3 (gokshuradi) showed better dissolution for ccgs than black pgs. similarly, e2 (b. asiatica) and e3 (b. ciliata) dissolved ccgs more effectively than black pgs. the efficacy of e6 (k. pinnata) was similar for both the stones (2.2 mg ccgs, 2.1 mg black pgs). a close inspection revealed that e6 (k. pinnata) was the least effective plant to dissolve both the ccgs and black pgs. among different plant extracts, e2 (b. asiatica) was the most effective (10.8 mg) to dissolve ccgs. in comparison with the most effective positive control etoh (14.3 mg), the efficacy of e2 (b. asiatica) to dissolve ccgs can also be considered significant. e2 (b. asiatica) was found to be more effective than another positive control edta (5.1 mg). moreover, e2 (b. asiatica) dissolved only 5.4 mg of bilirubinate predominant black pgs which was almost half of the dissolution obtained for ccgs. form all of these interpretations we can conclude that e2 (b. asiatica) is effective to dissolve cholesterol containing gallstones like ccgs. e4 (c. europaea), although, was found to be more efficient to dissolve black pgs than ccgs, there is no significant difference between the values obtained (8.5 mg of black pgs vs 7.3 mg of ccgs). dissolution of black pgs in e4 (c. europaea) is far close to the dissolution in e5 (t. officinale) with only 1.1 mg difference. on the other hand, a significant difference was obtained for dissolution of ccgs in e4 (c. europaea) and the most efficient plant e2 (b. asiatica) and positive control etoh (difference of 3.5 mg with e2 and 7.0 mg with etoh). therefore, it can safely be inferred that e4 (c. europaea) was also effective in dissolving pigment stones like gsb. among different medicine extract, m3 (gokshuradi) was the most effective to dissolve ccgs, it dissolved ccgs (5.8 mg) more efficiently than black gsb (3.5 mg, 16.20%). even though, m3 (gokshuradi) including other medicine extracts were far less effective than e2 (b. asiatica) (10.8 mg) and e4 (c. europaea) (7.3 mg) for dissolving ccgs. on the other hand, among different medicines, m2 (calcury) showed the highest dissolution for black pgs (4.0 mg). but, m3 was still less effective than e1 (m. uniflorum), e2 (b. asiatica), e4 (c. europaea), and e5 (t. officinale). therefore, it can be inferred that the medicine extracts were less effective than most of the plant extracts in dissolving gallstones. these ayurvedic medicines are recommended for oral dissolution therapy of kidney stones and not for gallstones. this fact could explain lesser efficacy of these commercial ayurvedic medicines over plant extracts in dissolving gallstones. chekroune and benamara [30] reported difbijaya b.k. et al./ bibechana 20 (2023) 175-182 180 ferent plant preparations to dissolve a significant amount of gs. about 209.37 mg, 97.42 mg, and 15.02 mg of the cholesterol-bilirubin containing gs were reduced in herniaria hirsuta extract, lemon juice, and their mixture respectively after 312 hours of immersion whereas the olive oil/lemon juice emulsion dissolved the stone with 291.1 mg weight completely after 168 hours of immersion [30]. in the present study, among all plant extracts and gallstone samples, the maximum weight reduction after 190 h was 10.8 mg in e2 (b. asiatica) for ccgs. due to the difference in immersion period of the stone, direct comparison of our report with the reported data seems to be inappropriate, however, it can be concluded that we also found in vitro cholelitholytic activity of different plant extracts. the in vitro dissolution study showed that ccgs was more soluble in etoh than in edta whereas black pgs is more soluble in edta than in etoh. the insoluble residue of ccgs was left even after 190 hours of incubation in edta (5.1 mg dissolution) whereas ccgs was completely dissolved in etoh after 94 hours (11.6 mg dissolution). the efficacy of edta to dissolve black pgs (11.5 mg) was almost double that for ccgs (5.1 mg); however, almost half of the black pgs was left undissolved even after 190 hours of incubation (annexure 1: table 3). this indicates that ccgs is easily dissolvable by using cholesterol solvent like ethanol whereas black pgs contains a greater proportion of insoluble components and it is difficult to dissolve completely both in cholesterol solvent like etoh and in calcium chelating solvents like edta. this finding is consistent with the result reported by lin et al. [24]. lee and co-worker [31] reported that 1.1 mg, 9.1 mg, and 30.0 mg of the cgs stone sample with 69.3 mg initial weight was dissolved in absolute ethanol after 3, 6, and 9 hours of incubation, respectively and the stone was dissolved completely after 18 h. in the present study, we have recorded 2.7 mg and 14.3 mg dissolution of the ccgs (wt. 14.48±0.21 mg) after 4 and 94 hours respectively. the stone was dissolved completely after 94 hours. based on this data, the dissolution we obtained in etoh for ccgs was lower than that reported by lee et al. the difference arises due to the lower concentration of etoh we used (95% etoh). in the case of black pgs (wt. 21.46±0.22 mg), etoh was not found effective and only 8.6 mg of the stone was dissolved after 190 h. the low solubility of the black pgs in etoh is due to the presence of a high concentration of insoluble bilirubinate as the main component which was confirmed by sem and eds in a separate study by our group [28]. 5 conclusion from the morphological and cross-sectional study, gallstones were classified as combined cholesterol gallstone (ccgs) or black pigment gallstone (black pgs). in vitro dissolution studies were also conducted using plant and medicine extracts, revealing that t. officinale was the most effective in dissolving black pgs, whereas b. asiatica was the best for ccgs. m. uniflorum and c. europaea were also found to be effective in dissolving black pgs, while k. pinnata was the least effective for both types of gallstones. b. ciliate and c. europaea were equally effective in dissolving both types of gs. medicine extracts were less effective than plant extracts. this in vitro study showed the plants can dissolve gs effectively. however, the effectiveness of the plant to dissolve gs depends on the type of the stone. the study suggests that further research is necessary to confirm the effectiveness of these plants in real biological systems through animal models. furthermore, the potential compound in plant that show cholelitholytic or anti-cholelithogenic activity and mechanism of action is still unknown and requires further research. the present research is limited to in vitro study. although normal human body temperature (37 ℃) was maintained while preforming in vitro dissolution study, other factors like normal bile ph is not considered. list of abbreviations gs = gallstone ccgs = combination cholesterol gallstone black pgs = black pigment gallstone cdca: chenodeoxycholic acid udca: ursodeoxycholic acid mtbe: methyl tert-butyl ether mmp: 2-methoxy-6-methylpyridine edta: ethylenediaminetetraacetic acid ethics approval and consent to participate not applicable. human and animals right no animals/humans were used for studies that are basis of this research. availability of data and materials all the data are provided in the supplementary material which is available on the publisher’s website along with the published article. bijaya b.k. et al./ bibechana 20 (2023) 175-182 181 conflict of interest the authors declare no conflict of interest, financial or otherwise. acknowledgements we acknowledge the national youth council, government of nepal, for providing a partial research grant to conduct this research. we also extend our thanks to dr. barun kumar shah, norvic international hospital, kathmandu, nepal, for providing gallstone samples. supplemetary materials supplementary material is available on the publisher’s website along with the published article. references [1] g. liu, d. xing, h. wang, and j. wu. vibrational spectroscopic study of human pigment gallstones and their insoluble materials. journal of molecular structure, 616(1-3):187–191, 2002. 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[31] lawrence l lee and john p mcgahan. dissolution of cholesterol gallstones: comparison of solvents. gastrointestinal radiology, 11:169– 171, 1986. introduction materials and methods collection and pre-treatment of gallstones macroscopic classification of gallstones collection of plant and ayurvedic medicines in vitro dissolution study of gallstones dissolution of gallstones with plant and medicine extracts results general observation and macroscopic classification of gallstones in vitro dissolution study of gallstones discussion conclusion bibechana vol. 22, no. 2, august 2025, 108-115 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar structural characterization of hdac2-mta1 complex narayan gautam1,2, narayan p. adhikari1 1central department of physics, tribhuvan university, kirtipur, nepal 2tri-chandra multiple campus, tribhuvan university, kathmandu 44613, nepal ∗corresponding author. email:narayan.adhikari@cdp.tu.edu.np abstract histone deacetylases are recruited to specific transcriptional repression complexes through interactions with corepressor proteins. this recruitment leads to chromatin condensation and transcriptional silencing. in this study, we modeled the complex structure of hdac2 with mta1 and investigated the hdac2 and mta1 interactions using all-atom molecular dynamics (md) simulation. our results show that the elm2-sant domains of mta1 wrap completely around hdac2. we identified the different types of interactions such as hydrogen bonds, salt bridges, and hydrophobic interactions. specifically, glu186, glu147, glu163, lys166, and lys124 amino acid residues of hdac2 form both hydrogen bond and salt bridge interactions with arg168, arg189, asp187, and glu195 amino acid residues of mta1. additionally, tyr15 amino acid of hdac2 form hydrogen bonds with glu195 amino acid of mta1. in addition to hydrogen bond and salt bridge interactions, we also analyzed hydrophobic interaction. keywords hdac2, mta1, molecular dynamics simulation, salt bridge, hydrogen bonding, hydrophobic interactions, solvent-accessible surface area, mm-gbsa article information manuscript received: january 19, 2025; revised: february 6, 2025; accepted: february 10, 2025 doi https://doi.org/10.3126/bibechana.v22i2.74254 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction nucleosomes are the basic units of chromatin that consist of histone and non-histone proteins in eukaryotic cells. dna is wrapped around histones that help the dna fit into the nucleus. transcription factors are proteins that interact with the dna and help to remodel the chromatin structure by repressing or expressing the transcription. when the lysine residues on the amino-terminal of histone are acetylated, the interaction between the histones and dna is weakened, and the chromatin is accessible for the transcription. the acetylation is possible due to the enzyme hats. when the acetyl group is removed with the help of hdacs from the lysine of histones on the amino-terminal, the interaction of the histone with dna is strengthened. at that time, the chromatin is inaccessible for the transcription. many studies have predicted that there is an important link between hdacs and cancer. hdacrelated interactions are known to be associated with transcriptional repression of some genes, and abnormal recruitment of hdacs to their promoter is con108 http://nepjol.info/index.php/bibechana narayan.adhikari@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v22i2.74254 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ narayan gautam and narayan p. adhikari/ bibechana 22 (2025) 108-115 109 tributed to the tumorgenesis. hdac (nurd complex) with that of mta1 have indicated a possible function of hdacs in tumor progression. mta1 also physically interacts with hdac1. mta1 is a target of heregulin (hrg) and plays a significant role in the repression of estrogen receptor (er)mediated transcription by recruiting hdacs [1]. the metastatic is regulated by different genes. out of these genes, mta proteins play crucial roles in the development and spread of cancer cells [2, 3]. histone modification is one of the important epigenetic modifications that is essential for the regulation of gene expression. histone deacetylases (hdacs) are enzymatic proteins that remove acetyl groups from histone and non-histone proteins which repress the gene expression [4,5]. hdacs are associated with different biological processes such as cellular proliferation, apoptosis, and signal transduction [6, 7]. overexpression and abnormal expression of hdacs to their promoter causes different types of diseases such as cancer, neurodegenerative disorders, hiv, diabetes, inflammation and cardiac diseases [8]. the inhibition of histone deacetylases (hdacs) results in increased acetylation of histones and various non-histone proteins, encompassing signaling mediators [9, 10], tumor suppressors [11], transcription factors [12], and dna repair proteins [13]. there are 18 members in the hdac family, divided into 4 classes based on their structure and function [14]. class i includes hdac1-3 and 8; class ii includes hdac4-7, 9, and 10; class iii includes sirtuin enzymes (sirt 1-7); and class iv comprises only hdac11, which is structurally different from the others. within class ii, there are further subdivisions: class iia (hdac4, 5, 7, and 9) and class iib (hdac6 and 10), based on their subcellular localization and expression patterns. histone deacetylases 1 and 2 are required for brain development [15] and heart development [16]. the different types of mta proteins are mta1, mta2, and mta3 [17, 18]. mta1 and mta2 are expressed ubiquitously but the expression pattern of mta3 is restricted. mta1 and mta2 are mainly found in the nucleus [19]. mta1 was originally identified through from rat metastatic breast tumors [20] after that it was found that mta1 is widely up-regulated in human tumors [21]. mta1, mta2, including hdac1, hdac2 are the subunits of nurd complex that provide the essential role of mta and hdacs proteins to the chromatin modification [22, 23]. there are different domains in the mta1 protein. bromo-adjacent-homology (bah) domain, the egl-27 and mta1 homology 2 (elm2) domain, and the swi3, ada2, ncor, and tfiii-b (sant) domains are the important domains [18]. after recruiting hdacs, the elm2 domain functions as a transcriptional repression domain [24]. the elm2 and sant domain of the mta1 establish numerous interactions with the hdac [1,25]. the structure of hdac1 in complex with mta1 from the nurd complex was reported by millard and coauthors in 2013. they reported that elm2-sant domains from mta1 wrap completely around hdac1 [25]. hdac2 contains many domains with defined functions. the catalytic domain common to all class i hdacs is formed by a stretch of more than 300 amino acids constituting a large portion of the protein [26]. a nuclear localization signal (nls) at the cterminus can only be found in hdac1 [27], whereas a c-terminal coiled-coil domain (possibly enabling additional protein-protein associations) seems to be specific for hdac2 [6]. despite previous research into interactions between hdac2 and mta1 [25], the precise nature of the hdac2-mta1 functional complex remains unknown. we used all-atom molecular dynamics (md) simulations to investigate the interactions of hdac2 and mta1. md simulations and in silico studies have successfully been used to investigate the molecular interactions, including hdacs [28, 29]. first, we predicted the structure of the hdac2-mta1 complex and performed md simulations to investigate the hdac2mta1 interactions. we identified the binding sites and crucial residues and estimated the key parameters related to the structural stability and binding affinity of the complex. 2 methods 2.1 system preparation the structure of the hdac2-mta1 complex was predicted with alphafold2 colab [30] using the fasta sequences of hdac2 (uniprot [31] accession id q92769) and mta1 (uniprot [31] accession id q13330). hdac2 and mta1 proteins have 488 and 715 amino acids, respectively. the alphafold2 prediction of the hdac2-mta1 complex was obtained with full-length sequences for hdac2 and mta1. 2.2 md simulations we utilized the namd software [32] and the charmm36m force field [33] to conduct all-atom md simulations of the hdac2-mta1 complexes, as employed in previous studies [28, 29, 34]. the simulation input files were prepared using the charmm-gui web server [35]. in cubic boxes, the systems were solvated with a tip3 water model and 150 mm nacl. the hdac2-mta1 complex, after being solvated and ion-neutralized, contained a total of 139681 atoms. the system was minimized for 10,000 steps with heavy atoms being harmonically restrained, followed by an equilibration of 100 narayan gautam and narayan p. adhikari/ bibechana 22 (2025) 108-115 110 picoseconds using the nvt ensemble. the production runs were performed using a time step of 2 femtoseconds. 2.3 data analysis the vmd software [36] was utilized to analyze simulation trajectories. chimerax [37] and vmd were utilized to effectively visualize protein structures and generate high-quality figures. the binding free energy was calculated using the mm/gbsa approach with namd, as described in previous publications [28,29,34]. the equation used to estimate binding free energy for the complex is as followed with the entropy term ignored [38]: ∆g = ghdac2−mta1 −ghdac2 −gmta1 (1) where, ghdac2−mta1 or ghdac2 or gmta1 is the sum of energy contributions due to internal (bond, angle, dihedral, and improper), electrostatic, van der waals, and solvation (polar and non-polar contributions) energies (g = einternal + eelectrostatic + evdw + esolvation). a contact distance cutoff of 3.5 å and an angle cutoff of 30 degrees were used to analyze hydrogen bonding, and the same atomic distance cutoff was used to analyze salt bridges. contact surface area was calculated using the formula [39]: contactarea = sasahdac2 + sasamta1 − sasahdac2−mta1 2 (2) where, sasahdac2 corresponds to solventaccessible surface area (sasa) of hdac2 at any time, sasamta1 to sasa of mta1, and sasahdac2−mta1 to sasa of the complex. vmd was used to measure the sasa values using the simulation trajectories. 3 results and discussion we used alphafold2 to predict the molecular structure of the hdac2-mta1 complex and performed md simulations to study into how the complex formed between hdac2 and the mta1 protein. to evaluate the structural stability of the predicted complex and identify the crucial residues that contribute to the formation, we performed an md simulation. additionally, we calculated the binding free energy and contact surface area of the hdac2mta1 complex. 3.1 prediction of the hdac2-mta1 complex figures 1(a) and 1(b) illustrate the individual complete structures of hdac2 and mta1 proteins predicted from alphafold2 respectively. although the mta1 protein exhibits a highly disordered structure with unstructured loops, hdac2 has a more stable structure. figure 1(c) illustrates the hdac2-mta1 complex structures predicted by alphafold2. this predicted model’s interface predicted template modeling (iptm) score is 0.76. model confidence is typically associated with an iptm score of 0.75 or higher [40]. to the best of our knowledge, the specific hdac2 amino acids that interact with mta1 have not yet reported. we were able to predict the structure of the hdac2mta1 complex by giving alphafold2 a full-length sequence of both hdac2 and mta1. the hdac2mta1 complex included a full-length hdac2 and mta1 sequence, as illustrated in figure 1(c). a robust cutoff of 5 å is effective in establishing solid foundations of the protein structure networks approach [41]. the amino acids in the mta1 protein strongly interact with hdac2 in several areas, including the helix, the beta sheet, and the unstructured loops. to make the system as small as possible, we removed unstructured loops and helices that were away from more than 5 angstroms from where the hdac2 and mta1 meets as shown in figure 1(d). this truncation significantly reduces the size of the system as well as the computational cost. subsequently, we performed a 500 ns md simulation of the complex that included all atoms. figure 1: (a) structure of hdac2 (b) structure of mta1(c) modeled structure of hdac2-mta1 complex; (d) structure of the hdac2-mta1 complex after removing the loops beyond five angstroms form each other. narayan gautam and narayan p. adhikari/ bibechana 22 (2025) 108-115 111 3.2 structural stability of the hdac2mta1 complex we monitored the structural stability of the hdac2-mta1 complex using rmsd measurements as shown in figure 2(a) and used simulation results to confirm hdac2-mta1 complex formation. rmsd plot shows the initial reorganizations until 280 ns, but after that the structural stability of the complex was maintained with relatively stable rmsd measurements. figure 2(b) shows the structure of the complex after 500 ns of simulation of the hdac2-mta1. figure 2: (a) rmsd of the hdac2-mta1 complex from the 500 ns simulation trajectory. (b) hdac2mta1 complex structure after 500 ns of simulation time. 3.3 major interaction involved in the complex formation and stabilization to understand the mechanism of the interaction of hdac2 with mta1, we explored their dynamics during the simulation of the complex. to identify the inter-protein interactions, we evaluated alphafold protein-protein interaction with chimerax in the predicted complex structure of the hdac2 and mta1 that lie within a 5 angstrom distance in the hdac2-mta1 complex. figure 1(d) shows the structure of the hdac2-mta1 complex, in which both proteins are within 5 angstrom to each other. alphafold believes that blue color lines have high confidence, which means residue pairs that are close to each other, and red color lines indicate that the residue pairs have low confidence. 3.3.1 hydrogen bonding between hdac2 and mta1 to predict the hydrogen bonds formed between hdac2 and mta1, we analyzed the data from the simulation trajectories. this was carried out using the analysis protocol outlined in the methods section. frequently, a specific amino acid in one protein would form hydrogen bonds with another protein via different atoms. in our simulation, we only took into account individual bonds that were occupying more than 25%. table 1 displays the occupancies of hydrogen bonds. for each pair of residues, the occupancies presented in table 1 represent the sum of hydrogen bonding contributions from various atoms within the same residue. the time evolution of each hydrogen bond established by each atom pair from the analysis of the trajectory are shown in figure 3(a). the types of atoms are shown inside parentheses. figure 3: (a) distance of hydrogen bonds formed between the residues in hdac2 and mta1. the type of atoms that are predicted to establish the contacts are provided inside parentheses of each residue. (b) orientation of residues in both hdac2 and mta1 that form the hydrogen bonds. the crucial residues are shown in licorice representation and the black dotted lines represent the hydrogen bonds. table 1: hydrogen bond occupancies obtained from the analysis of trajectories of hdac2-mta1 simulation. except tyr15-glu195 residues pair, all other residues pairs are involved in the formation of salt bridges as well as hydrogen bonds in the formation of hdac2-mta1 protein complex. hdac2 mta1 occupancy glu186 arg168 156.84% glu147 arg168 137.00% glu163 arg189 130.28% tyr15 glu195 63.64% lys166 asp187 58.24% lys124 glu195 46.00% narayan gautam and narayan p. adhikari/ bibechana 22 (2025) 108-115 112 table 2: hydrogen bond length between the atoms of the residues of hdac2 and mta1 of the final frame obtained from the 500 ns of the simulation of hdac2-mta1 complex hdac2 residues mta1 residues bond-length (å) (mean±s.d.) glu186(oe2) arg168(ne) 2.9±0.17 glu186(oe1) arg168(nh2) 2.9±0.19 glu147(oe2) arg168(nh2) 3.6±0.90 glu147(oe2) arg168(nh1) 3.4±0.79 glu147(oe1) arg168(nh1) 3.3±0.73 glu147(oe1) arg168(nh2) 3.5±0.87 glu163(oe2) arg189(ne) 3.4±0.49 glu163(oe1) arg189(nh2) 3.1±0.38 glu163(oe2) arg189(nh2) 3.2±0.48 tyr15(oh) glu195(oe1) 3.2±0.80 lys166(nz) asp187(od1) 3.4±1.31 lys124(nz) glu195(oe2) 2.8±0.26 3.3.2 contribution of a salt bridge for the formation of the hdac7-mef2a complex figure 4: (a) time evolution of formation of salt bridges between hdac2 and mta1 during the complex formation. (b),(c) and (d) orientation of the residues that formed salt bridges in licorice form. lys124 of hdac2 and glu195 of mta1 form a strong salt bridge, despite the hydrogen bond occupancy being relatively low at only 46.00%. this salt bridge is crucial for establishing the linkage between hdac2 and mta1, as shown in the figure 4(a) and 4(b) respectively. three additional salt bridges that we predicted are: glu147(hdac2)-arg168(mta1), glu163(hdac2)-arg189(mta1), and glu186(hdac2)−arg168(mta1), performed nearly equal contributions to the formation of the hdac2-mta1 complex. the salt bridges exhibit stability throughout the 500 ns simulation. the remaining salt bridge that we predicted is lys166(hdac2)-asp187(mta1) and the stability of this salt bridge remains constant throughout the simulation, except for the time period between 380 ns and 410 ns. figure 4(b) shows the precise orientation of all these residues that form the hdac2-mta1 complex within each protein. 3.3.3 contribution due to hydrophobic interactions figure 5: (a) regions of hydrophobic residues that form hydrophobic interaction between hdac2 and mta1, and (b) hydrophobic residues in hdac2 (magenta texts) that establish hydrophobic interactions with mta1 residues (orange red texts) with surface and licorice representation. the hydrophobic interactions play a crucial role in the formation and stabilization of the complex between hdac2 and mta1. our results show that there are a number of hydrophobic interactions between residues in hdac2 and mta1 across the interface. we predicted that hydrophobic residues ile54, val119, ala120, val123, leu162, leu165, ala187, phe188, ile408, ala410 of hdac2 make hydrophobic interactions with ala175, ile177, leu180, leu181, leu194, val198, trp199 of mta1. although there are many hydrophobic interactions in the formation of hdac2-mta1 complex, the crucial residues that form hydrophobic interaction is shown in figure 5(a). the zoom viewed of figure 5(a) is shown in figure 5(b) in surface and licorice representation with label. narayan gautam and narayan p. adhikari/ bibechana 22 (2025) 108-115 113 table 3: the hydrophobic interactions between the different amino acid residues of hdac2 and mta1. hdac2 mta1 ile54 val198, trp199 val119 leu194 ala120 leu194 val123 leu194 leu162 ala175, ile177 leu165 ile177, leu180 ala187 ala175 phe188 ile177 ile408 leu180 ala410 leu180, leu181 as shown in figure 5(b), the hydrophobic residues ile54 of hdac2 binds strongly with val198, trp199 of mta1. three amino acid residues val119, ala120 & val123 of hdac2 make hydrophobic cavity. in that cavity, leu194 of mta1 deeply inserted and make strong interaction. also, iile177 and ala175 of mta1 make hydrophobic interactions with leu162, ala187, and phe188 of hdac2. similarly, leu165, ile408, and ala410 of hdac2 interact with leu180 and leu181 of mta1. we have calculated the hydrophobic contact area of the hdac2-mta1 complex by using the equation as described in the method section. figure 6(a) shows the contact area measurements for the hdac2-mta1 complex. we calculated the average and standard deviation (s.d.) of all contact area values (values for each frame of entire 500 ns simulations) as shown in figure 6(a) and obtained 243.89±23.44 å2 (mean±s.d.). the time evolution of hydrophobic contact area was monitored over a 500 ns molecular dynamics simulation, as shown in figure. at the initial phase, the contact area is stable and is predominantly fluctuated between 200 and 250 å2, which represent the relatively stable interactions with minor fluctuations. after 350-500 ns, the contact area is increased, with peak values reaching approximately about 340 å2. the higher contact area after 350 ns is due to the formation of new hydrophobic contacts between ile408 and ala410 of hdac2 with leu180 and leu181 of mta1 in the rearrangement of the hdac2-mta1 complex. prior theoretical and experimental research has indicated that burying 1 å2 of the hydrophobic surface at the protein-protein interface increases the complex stabilization free energy by -15 ± 1.2 cal/mol. thus, in the case of the hdac2-mta1 complex, the hydrophobic surface area at the hdac2-mta1 interface, which measures 243.89 å2, plays a significant role in contributing approximately -3.66 kcal/mol to its stability. this suggests that hydrophobic interactions are essential in the formation and stabilization of the hdac2–mta1 complex. figure 6: (a) contact surface area measurements hdac2 and mta1 in hdac2-mta1 complex, and (b) time evolution of the non-bonded interaction energy in the hdac2-mta1 complex. we also analyzed two interactions, electrostatic and van der waals, that help to stabilize hdac2mta1 complex. electrostatic interactions are due to the charged residues in the proteins. our result estimated that these interactions are stable after 280 ns of simulation and its value was -1220.25 ± 126.65 kcal/mol. van der waals interactions are relatively weaker interactions. these interactions remained stable from the beginning to the end of our simulation. the average strength of the van der waals interactions was -237.55 ± 20.53 kcal/mol. these negative values of both electrostatic and van der waals interaction energy is favorable for the interaction of hdac2-mta1. both non-bonded interaction energies contribute to the stable binding of the hdac2–mta1 complex. this observation suggests that hdac2 and mta1 form a stable complex through multiple non-covalent interactions. 3.3.4 binding free energy of the complex in order to determine the strength of the interaction between hdac2 and mta1, we employed the molecular mechanics with a generalized born and surface area solvation (mm/gbsa) method to calculate the binding free energy of the complex. we have determined the binding free energy of the hdac2–mta1 complex using the molecular dynamics (md) simulation trajectory. the mm/gbsa binding free energy of the hdac2–mta1 complex is -223.14 ± 17.71 kcal/mol, indicating a substantial binding free energy for a stable protein–protein complex. 4 conclusions the hdac (nurd) complex with that of mta1 have indicated a possible function of hdacs in tumor progression. mta1 is a target of heregulin (hrg) and plays a significant role in the repression of estrogen receptor (er)-mediated transcripnarayan gautam and narayan p. adhikari/ bibechana 22 (2025) 108-115 114 tion by recruiting hdacs. in this work, we investigated the molecular mechanism of complex formation of hdac2 with mta1 protein, using structure predicting tool alphafold2 and performed md simulations. we obtained the hdac2-mta1 complex from molecular modeling and assessed its stability using md simulations. our results show that hdac2 interacts with mta1 through elm2sant domains as in hdac1-mta1 interaction. several hydrogen bonding interactions between the residues at the binding interface are also involved in the binding of hdac2 and mta1. in addition to hydrogen bonding, salt bridges between the interfacial charged residues are the also the major interactions involved in the binding. furthermore, hydrophobic interactions play a significant role in forming and stabilizing the hdac2-mta1 complex. our results reveal that hdac2 strongly wrapped by mta1, forming a stable complex via different interactions. our first structural characterization of the hdac2–mta1 complex outlines the molecular basis of the interaction of hdac2 with mta1, which offers valuable insights into the recruitment mechanism of the hdac complex for the transcription repression mediated by mta1. disclosure statement there are no conflicts to declare. author contributions npa supervised the project. ng performed the md simulations and analyzed the data. ng and npa contributed to the data analysis and interpretation. ng wrote the manuscript npa contributed to manuscript editing. references [1] a. mazumdar et al. transcriptional repression of oestrogen receptor by metastasis-associated protein 1 corepressor. 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[41] j. salamanca viloria et al. an optimal distance cutoff for contact-based protein structure networks using side-chain centers of mass. 7(1):2838, 2017. introduction methods system preparation md simulations data analysis results and discussion prediction of the hdac2-mta1 complex structural stability of the hdac2-mta1 complex major interaction involved in the complex formation and stabilization hydrogen bonding between hdac2 and mta1 contribution of a salt bridge for the formation of the hdac7-mef2a complex contribution due to hydrophobic interactions binding free energy of the complex conclusions bibechana vol. 22, no. 2, august 2025, 116-121 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar from linear to non-linear/chaotic pendulum: a computational study chhabi kumar shrestha1,2, krishna raj adhikari3,∗, kapil adhikari4, narayan prasad adhikari2 1department of physics, prithvi narayan campus, tribhuvan university, pokhara, nepal 2central department of physics, tribhuvan university, kirtipur, kathmandu, nepal 3department of applied sciences, pashchimanchal campus, institute of engineering, tribhuvan university, pokhara, nepal 4faculty of science and technology, gandaki university, nepal ∗corresponding author. email: adhikarikrishna@wrc.edu.np abstract in this work, we have used computational techniques to examine how the dynamics of a simple pendulum change from linear to non-linear and chaotic. the graph of phase space, angular displacement versus time, and angular velocity versus time are thoroughly examined in our analysis. a significant shift is observed in these representations, particularly in the graph of angular displacement versus time and angular velocity versus time. as the non-linearity is enhanced, we observe a progressive movement from circular to oval shapes in phase space. in damped and forced pendulum scenarios, similar patterns are observed. in these cases, the graphs display a sinusoidal pattern with a diminishing amplitude with time. surprisingly, in the phase space of the damped pendulum, a spiral type of graph is observed, demonstrating the intricate relationship between damping effects and non-linearity. this research emphasizes the separatrix’s function as a crucial cutoff point where the pendulum’s motion changes from linear to chaotic. keywords phase space; separatrix; damped pendulum; trajectory; runge-kutta method; harmonic oscillator article information manuscript received: december 12, 2024; revised: january 7, 2025; accepted: january 10, 2025 doi https://doi.org/10.3126/bibechana.v22i2.72570 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction galileo was the first to observe that the swinging time of a lamp in a cathedral remained consistent regardless of its swing’s size, at least for the small swings he could observe [1]. huygens invented the first pendulum clock in 1656 [2], which was a big step forward in timekeeping from earlier techniques. 116 http://nepjol.info/index.php/bibechana adhikarikrishna@wrc.edu.np https://doi.org/10.3126/bibechana.v22i2.72570 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ chhabi kumar shrestha et al./ bibechana 22 (2025) 116-121 117 the pendulum was thus the first oscillator of significant practical significance. the study of pendulum dynamics plays an important role in classical mechanics, and simple harmonic motion (shm) is well understood for small oscillations. if the particle in the case of periodic motion moves back and forth, then the motion is called oscillatory or vibratory motion. the harmonic motion of the simplest type, having constant amplitude and single frequency, is called simple harmonic motion. the body is said to be in simple harmonic motion (shm) if the acceleration of the body is directly proportional to the displacement and is directed always toward the mean position. if ’a’ be the acceleration of the body and ’x’ be the displacement of the body from the mean position, then acceleration ∝ displacement i.e., a ∝ x ⇒ a = −kx where ’k’ is a constant, called a force constant or spring constant, and negative sign indicates acceleration is always directed opposite to the displacement or motion of an object [3]. suppose a particle of mass ’m’ executing shm. if ’x’ be the displacement of the particle from the equilibrium position at any instant of time ’t’, then from hooke’s law restoringforce(f ) ∝ x ⇒ f = −kx ⇒ d2x dt2 = −kx m = −w2x where w2 = k m the general solution of this equation is x = a1e iw0t +a2e −iw0t phase space is the momentum, and position coordinates are set to define the dynamic system. the idea that unifies quantum and classical mechanics is crucial to understanding physics. the space of all possible states for a physical system is known as phase space in classical mechanics. friedrich henri poincare, ludwig boltzmann, and josiah willard gibbs invented the idea of phase space in the late 1800 s [4]. a dynamical system’s state varies with time, as represented by a point in phase space, and this is known as the phase trajectory. a phase plane that shows the angle θ and the angular velocity dθ dt provides a clear visual representation of the dynamics of a pendulum. certain curves or points, referred to as “attractors", are important in this graphical representation. no matter where the motion begins, attractors are crucial because they symbolize the final states that all potential pendulum trajectories can converge toward over time. in the case of real-world systems, when large angular displacement and the damping term are taken into account, a simple pendulum exhibits non-linear and chaotic behavior. while many studies have analyzed these behaviors separately, a comprehensive computational study that systematically examines the transition from linear motion to non-linearity and chaos is still lacking. this work has employed the numerical technique runge-kutta method to investigate chaotic behavior in pendulums, but further exploration is required to fill the gap between classical and modern computational approaches. this study aims to address this gap by employing a computational framework to analyze phasespace trajectories and quantify the transition from periodic to chaotic motion. understanding these transitions has important applications in fields such as seismology, robotics, and precision timekeeping, where chaotic oscillations impact system stability and performance. 2 materials and methods a simple pendulum is a heavy-point object suspended by a flexible, weightless, and inextensible string that can oscillate freely in a vertical plane. when a bob of a simple pendulum is displaced through a small angle from its mean position, then it begins to vibrate around its mean position. such motion of the point mass is called simple harmonic motion. suppose a bob of a simple pendulum of mass ‘m’ whose effective length is ‘l’. let the bob be displaced through ‘x’ such that the angle θ is very small. then various forces acting on the bob are: 1. weight ‘mg’ acting vertically downward. 2. tension ’t’ acting on a string towards the point of suspension here, weight ‘mg’ can be resolved into two components. the component mgcosθ balances tension t, and another component mgsinθ is restoring force, which causes the oscillation of the simple pendulum. according to newton’s second law, f = ma = m d2x dt2 m d2x dt2 = −mgsinθ the negative sign indicates that restoring force and displacement are in opposite directions. if we have x = lθ then above equation becomes ml d2θ dt2 = −mgsinθ d2θ dt2 = −g l sinθ (1) chhabi kumar shrestha et al./ bibechana 22 (2025) 116-121 118 using maclaurin’s theorem, we get, d2θ dt2 = −g l (θ − θ3 3! + θ5 5! − ......) (2) taking the first term of the right-hand side, we get, θ̈ = −g l θ (3) which has the solution of the form θ(t) = θ0cos √ g l t (4) its time period is t = 2π √ l g [6] 2.1 damped harmonic oscillator a harmonic oscillator is called a damped harmonic oscillator in which the oscillations are damped on account of a resistive or damping force, with its amplitude progressively decreasing to zero. when a simple harmonic oscillator is subjected to a damping force that is proportional to its velocity and an external periodic force, then we write an equation of its motion [7]. d2x dt2 + γ dx dt + ω2 0x = a0sinwt (5) where f (t) = ma0sinwt is the driving force with angular frequency ω.in the absence of driving force i.e., at a = 0, the real solutions of equation (7)at t → ∞ are: x0(t) = c1e −(γ+ √ γ2−4ω2 0)t/2+c2e −(γ− √ γ2−4ω2 0)t/2, γ2 − 4w2 0 > 0 (6) x0(t) = c1e −γt/2 + c2e −γt/2, γ2 − 4w2 0 = 0 (7) x0(t) = c1e −γt/2cos (√ −γ2 + 4ω2 0t/2 ) + c2e −γt/2cos (√ −γ2 + 4ω2 0t/2 ) γ2 − 4w2 0 < 0 (8) if a0 > 0, then the general solution is obtained from the sum of the special solution, xs(t), and the solution of homogeneous equations is x0(t). the special solution is obtained as xs(t) = asinwt+bcoswt1001[8] putting this equation in equation (7), we get, xx(t) = a0[(w 2 0 − w2)coswt+ γwsinwt] (w2 0 − w2)2 + γ2w2 (9) so, the general solution is given by x(t) = x0(t) + xs(t) (10) in the case of resonance without damping w = w0 and γ = 0. in this case, the solution becomes x(t) = c1coswt+c2sinwt+ a0 4w2 (coswt+2wtsinwt) (11) 2.2 forced damped pendulum let us consider a simple pendulum in a uniform gravitational field in which its motion is damped by the force that is proportional to its velocity and is under the action of the vertical harmonic external driving force then its equation of motion becomes [9]. d2θ dt2 + γ dθ dt + w2 0sinθ = −2acoswtsinθ (12) where θ is the angle made by the pendulum with the vertical, γ is the damping coefficient, w2 0 = g/l is the natural angular frequency of the simple pendulum, ω is the angular frequency of driving force. the 2a is the amplitude of the oscillation. 3 methodology the current study is both computational and theoretical in nature. it mainly focuses on the phasespace trajectory of the chaotic pendulum. using the runge-kutta method, a numerical solution is obtained. fortran 90 is used to run the file, and gnuplot is used to plot the phase space. fortran is used to program scientific and mathematical applications. the name fortran is an acronym for formula translation. it is a high-level programming language. there have been different versions of fortran since the 1950s when work on it began at ibm. the equation (1) can be solved by using the runge-kutta (rk) method [10, 11].from the pedagogical perspective, fortran90 offers a basic method for numerical computing. it is a well-known language for high-performance numerical computation that is very effective at solving differential equations involving large data sets. fortran is based on a numerical algorithm that aids researchers and students in expanding their understanding of numerical analysis, whereas python and matlab are based on built-in libraries. fortran 90 is an excellent tool for solving complicated physical models, such as chaotic pendulums, because it offers a better-optimized solution for iterative numerical computations. the simulation parameters chhabi kumar shrestha et al./ bibechana 22 (2025) 116-121 119 employed in this investigation are the pendulum’s length of 2.0 meters, damping coefficient of 0.5, simulation time step of 30 seconds, and angular velocity of 3.1 rad/sec. even though there are many numerical techniques, such as euler’s method and verlet integration, we have chosen to employ the rungekutta method (rk) because it offers a higher-order accurate solution and is frequently applied to nonlinear dynamical systems because of its enhanced stability. the first-order euler’s approach makes it less precise, requiring a very small time step to minimize errors. it is not dependable for long-term simulations due to its significant truncation errors. likewise, verlet integration works well in molecular dynamics simulations but is less appropriate for chaotic differential equations. 4 results and discussions in this study entitled “from linear to nonlinear/chaotic pendulum: a computational study," we investigated the changes in a pendulum system’s dynamic behavior. considering the equation θ̈ = −g l sinθ in the beginning, we tracked the pendulum’s angular displacement θ against time, which is shown in figure 2 for the angle of oscillation 90.in the linear regime—where the angular displacement remains small—the pendulum displayed simple harmonic motion, which is characterized by smooth, sinusoidal oscillations. as the amplitude increases, i.e., the angle of oscillation is increased and moved away from basic harmonic behavior, the motion becomes more complex and enters into the non-linear zone. chaotic dynamics began as the angle grew closer to and beyond 180, at which point the non-linear behavior became more noticeable. we then looked at the relationship between angular velocity and time, which is shown in figure 3. a constant amplitude was maintained by the harmonic oscillation of the angular velocity in the linear regime. significant amplitude and frequency changes were observed as the system entered the non-linear region. again considering the equation d2θ dt2 +γ dθ dt +w2 0sinθ = −2acoswtsinθ, we have plotted the graph of θ versus time, θ̇ versus time and θ̇ versus θ. when the damping term was present, additional complexity was created because energy dissipation changed the oscillatory patterns, which, over time, caused the motion to get slower gradually. plots showing the relationship between θ̈ versus θ the phase space analysis, shown in figure 4, helps us to understand the behavior of the system over time. for small oscillations, the phase-space trajectory forms closed loops, confirming agreement with theoretical expectations of simple harmonic motion. as the amplitude increases, the deviation from the simple harmonic motion is significant, leading to distortion in the phase space indicating the chaotic behavior. the separatrix is the clear indicator for such transition, marking the boundary between regular and chaotic motion and observed in the phase space plots beyond 1800. these findings are also in agreement with the theoretical models. when the pendulum enters the chaotic regime, the phasespace diagram exhibits irregular, scattered trajectories, which is consistent with known chaotic behavior in dynamical systems. similar trends were observed in the case of the damped pendulum, where damping affected the rate of energy dissipation in the system shown in figure 5, and figure 6. plots of the damped pendulum’s phase space revealed spiral paths that eventually converged to fixed points, signifying the end of the motion of the system as depicted in figure 7. figure 2: graph of θ versus t for θ = 90 and dt=0.0 similarly, the graph of angular velocity θ̇ versuss time is shown in figure 3. figure 3: graph of θ̇ versus t for θ = 90 and dt=0.0 the phase space of the nonlinear pendulum is chhabi kumar shrestha et al./ bibechana 22 (2025) 116-121 120 shown in figure 4. figure 4: graph of θ̇ versus t for dt =0.02sec figure 5: graph of θ versus t for γ = 0.5 , dt=0.01,ω = 3.1, ω0 = 3.1 figure 6: graph of θ̇ versus t for γ = 0.5 , dt=0.01,ω = 3.1, ω0 = 3.1 for γ = 0.5 , dt=0.01, ω = 3.1, ω0 = 3.1 figure 7: graph of θ̇ versus θ 5 conclusions this study offers insightful information about how linear to non-linear behavior changes in pendulum systems. it clarifies the complex dynamics underlying pendulum motion and advances our understanding of chaotic behavior by fusing rigorous analysis with numerical simulations. the findings have implications beyond theoretical issues and may be used in engineering, physics, and other disciplines. the study of non-linear dynamics and its applications to complex systems requires further investigation. 6 acknowledgments we extend my sincere gratitude to saddam hussein dhobi and sandip baral for their invaluable guidance, unwavering support, and insightful feedback throughout the entire duration of this work, “from linear to non-linear/chaotic pendulum: a computational study." one of the authors, chhabi kumar shrestha, acknowledges the ugc, nepal, for the phd grant award: phd-80/81-s&t-09. references [1] laura fermi and gilberto bernardini. galileo and the scientific revolution. courier corporation, 2003. [2] filip buyse. galileo, huygens and the pendulum clock: isochronism and synchronicity1. societate si politica, 11(2):5–12, 2017. [3] d. s. mathur. mechanics. s. chand publishing, 2007. [4] david d nolte. the tangled tale of phase space. physics today, 63(4):33–38, 2010. chhabi kumar shrestha et al./ bibechana 22 (2025) 116-121 121 [5] neha aggarwal, nitin verma, and p arun. simple pendulum revisited. european journal of physics, 26(3):517, 2005. [6] p. l. devries and r. p. wolf. a first course in computational physics. computers in physics, 8(2):178–179, 1994. [7] konstant. computational physics. http://www.physics.ntua.gr/~konstant/ computationalphysics. [8] k. n. anagnostopoulos. computational physics, vol i: a practical introduction to computational physics and scientific computing. konstantinos anagnostopoulos, 2014. [9] m. suzuki and i. s. suzuki. physics of simple pendulum. 2019. [10] d. w. zingg and t. t. chisholm. runge–kutta methods for linear ordinary differential equations. applied numerical mathematics, 31(2):227–238, 1999. [11] a. tocino and r. ardanuy. runge–kutta methods for numerical solution of stochastic differential equations. journal of computational and applied mathematics, 138(2):219– 241, 2002. http://www.physics.ntua.gr/~konstant/computationalphysics http://www.physics.ntua.gr/~konstant/computationalphysics introduction materials and methods damped harmonic oscillator forced damped pendulum methodology results and discussions conclusions acknowledgments bibechana vol. 21, no. 1, april 2024, 63–73 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar synthesis, characterization and antimicrobial study of silver nanoparticles using methanolic fraction of artemisia vulgaris leaf sandhya parajuli1, pujan nepal1, ganesh prasad awasthi2, hari bhakta oli1, ram lal (swagat) shrestha1,∗∗, puspa lal homagai1,∗∗∗, deval prasad bhattarai1,∗ 1department of chemistry, amrit campus, tribhuvan university 44613, kathmandu, nepal 2division of convergence technology engineering, jeonbuk national university, jeonju, jeollabuk-do, 54896, republic of korea ∗corresponding author. email: deval.bhattarai@ac.tu.edu.np ∗∗ swagatstha@gmail.com ∗∗∗ drplhomagai@gmail.com abstract rational selection of active biomolecules in the synthesis of nanoparticles for reducing the precursor and functionalizing the nanoparticles (nps) can offer remarkable comeback of biocompatibility and biological applicability. this work aimed at the synthesis of a cost-effective, ecofriendly, and a facile approach of silver nanoparticles (agnps) using methanolic leaf extract of artemisia vulgaris. the phytochemical constituents present in the methanolic extract were characterized by qualitative chemical tests and spectroscopic measurements and employed for the reduction of silver nitrate into silver nanoparticles. formation of agnps was monitored by uv-visible spectroscopic measurement. fourier transform infrared (ftir) spectroscopy reflected the presence of characteristic functional groups associated with the phytochemical constituents involved in the formation of nanoparticles. the crystalline phase and morphology of the nps were assessed form x-ray diffraction (xrd) spectra and field emission scanning electron microscopy (fesem), respectively. xrd pattern revealed the crystalline nature of nanoparticles with grain size of ∼ 28 nm based on the debye scherer formula. study of antimicrobial activity of agnps against gram-positive bacteria bacillus subtili, gram-negative bacteria escherichia coli, and fungus candida albicans exhibited good potential to control the bacterial and fungal growth. keywords artemisia vulgaris, leaf extract, green chemistry, agnps, antibacterial activity, antifungal activity article information manuscript received: september 6, 2023; revised: november 26, 2023; accepted: december 29, 2023 doi https://doi.org/10.3126/bibechana.v21i1.60018 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 63 http://nepjol.info/index.php/bibechana deval.bhattarai@ac.tu.edu.np swagatstha@gmail.com drplhomagai@gmail.com https://doi.org/10.3126/bibechana.v21i1.60018 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ sandhya parajuli et al./ bibechana 21 (2024) 63-73 64 1 introduction an unchecked use and misuse of antibiotics has led to the emergence of a number of antibiotic-resistant bacterial strains which is a global health concern with serious implications. development of new antibiotics has not been sufficient to cope with the raising antibiotic-resistant strains and this poses a significant challenge in the health sector. in the realm of growing threats of antibiotic resistant, it is imperative to cut down the uses of antibiotics to diminish the potential risk or to develop new class of materials with good antibacterial properties [1]. in this context, the nanoparticles' antibacterial capability may be useful in creating antibacterial medications to fight against harmful pathogenic strains. synthesis of silver nanoparticles have gained significant interest over the years especially due to their remarkable antimicrobial properties, outstanding electrical and thermal conductivities, optical and high catalytic activities, surface enhanced raman scattering, chemical stability, antibacterial, antibiofilm, wound healing and other therapeutic abilities on a par with its cost-effective production [2]. upon entering into the bacterial cell, silver ions cause to transform the dna molecules into an intensive forms and losses its reproduction power resulting into the bacterial cell death [3]. as silver displays a specific roles in catalytic, antimicrobial and biological system, synthesis of agnps has been grown as an important antimicrobial agent in contrast to the ever increasing threats posed by antibiotic resistant microbes [4]. though agnps can be synthesized by physical, chemical and biological method, the uses of toxic materials, tedious methods and high production costs of synthesis have turned the researchers towards the green synthesis method as an alternative approach for its cost-effective and biocompatible nanomaterial synthesis routs [5]. in this context, green method of nanomaterial synthesis for antibacterial applications can be the best alternative approach which uses non-hazardous, renewable, and low-cost materials as a precursor. green synthesis of nanomaterials involves the uses of secondary metabolites present in plant extracts deploying their excellent reducing, capping and stabilizing properties [6]. extensive researches are going on for the optimization of shape, size and stability of nps using biomolecules extract from the different parts of plants. recently, biosynthesis of silver nanoparticles have been carried out using artemisia absinthium, thymus vulgaris [7], zingiber officinale [8], premna integrifolia l. [9], allium cepa l. [10], salvia vertilillata [11], moringa olifera [12], etc. different parts of plant have been used to extract biomolecules for the preparation of nanoparticles. furthermore, different types of extract such as aqueous extract, methanolic extract and so on are being used for the extraction of biomolecules. methanol, being polar solvent, can extract many polar phytochemical constituents from plant which could be effective for the preparation of nanoparticles by green synthesis method. it was found that the agnps synthesis using papaya fruit showed a notable antibacterial activity against e. coli and p. aeruginosa [13]. in this research work, researchers used well diffusion technique for the study of antibacterial activities of agnps. uses of environmentally benign materials like phytochemical extracts, fungi, bacteria, and enzymes for the synthesis of nanoparticles offers numerous benefits like low-cost, availability, biocompatibility, ecofriendly, etc. recently, green synthesis of metal nanoparticles using medicinal plant such as a. vulgaris has shown potential antimicrobial, antioxidant and anti-proliferative activities [14, 15]. an essential oil of a. vulgaris consists of caryophyllene,trans-caryophyllene, thujone, thujone, 1,8 cineole, and linalool as major constituents [16]. various nanoparticles have been prepared using the plant extract of a. vulgaris. it was found that the iron nps synthesized using a. vulgaris extract were potentially useful for environmental remediation [17]. in addition, a. vulgaris is commonly found in the climate of nepal and can be cultivated for commercial scale without tedious efforts. the secondary metabolites present in such plants have remarkable reducing properties which can be correlated with the ability of plants extract for the synthesis of nanoparticles with improved characteristics. the phytochemicals present in a. vulgaris leaf extract can be employed as reducing, capping and stabilizing agent in the synthesis of silver nps. therefore, it seems rational for its use in the synthesis of silver nanoparticles. alomari et al. synthesized agnps by green synthesis method using aqueous extract of a. vulgaris leaf and studied for antimicrobial activities. silver nps prepared using this extract did not exhibit any effect on candida albicans [14]. in the similar work, rasheed et al. synthesized agnps using methanolic extract of a. vulgaris leaf and applied for their potential biomedical applications. in both cases, phytochemical tests have not been carried out. before one embarks on the green synthesis of nps, it is imperative to carry out the phytochemical test to ensure the action of phytochemical constituents in the mechanistic path of nanoparticle synthesis. rational selection of biomolecules in the synthesis of silver nanoparticles is a strategic approach to enhance their biocompatibility and broaden their biological applicability. keeping this in view, this research aimed at synthesizing the agnps by a green synthesis route ussandhya parajuli et al./ bibechana 21 (2024) 63-73 65 ing methanolic extract derived from artemisia vulgaris leaf of sainamaina, rupendehi, nepal. so far the knowledge obtained from literature, a. vulgaris of this locality has not been reported for the synthesis of agnps. at the beginning, the presence of phytochemicals in the methanolic extract of a. vulgaris was assessed and used for the synthesis of agnps. as-synthesized agnps were characterized by uv-visible spectroscopy, xrd, ftir, fesem and tem. finally, the antibacterial efficacy of assynthesized agnps were studied against the grampositive (bacillus subtilis) and gram-negative (escherichia coli) bacteria. antifungal test was carried out against candida albicans. 2 experimental 2.1 chemicals and reagents methanol (99.8% emparta), silver nitrate (99.8% qualigens) and matured sample leaves of artemisia vulgaris were collected from sainamaina municipality ward no. 11 (27°4131.9 n and 83°1539.4 e), rupandehi, nepal in september, 2022. in this work, chemicals of analytical grades were used in as-received form without further purification. 2.2 extract preparation artemisia vulgaris leaves were washed with dw, dried in the shade for two weeks followed by crushing to fine powder using a herbal medicine disintegrator (model fw177). the leaf extract was prepared by soaking 100 g of leaf powder in 750 ml methanol for 10 days. then the content was filtered using cotton muslin to obtain the extract and it was finally filtered through whatman 42. 2.3 phytochemical test to determine the presence of major chemical constituents present in the plant extracts, phytochemical tests were carried out as per the standard protocols [18, 19]. briefly, the methods adopted for phytochemical tests are as follows. test for alkaloids mayer’s test and dragendorff’s tests were performed for alkaloid test. mayer’s test: 3 drops of mayer’s reagent was added into the 2 ml of methanolic extract followed by shaking well. appearance of yellowish precipitate indicates the presence of alkaloid. dragendorff’s test: 3 drops dragendorff’s reagent was added into 2 ml extract followed by well shaking. appearance of yellowish precipitate indicates the presence of alkaloid. test for flavonoids 5 ml of dilute ammonia solution was percolated into 2 ml of methanolic extract followed by addition of conc. sulphuric acid from side of the testtube. appearance of yellow color shows the presence of flavonoids. test for terpenoids 2 ml of chcl3 was percolated into 5 ml of methanolic extract followed by slow addition of 3 ml of conc. h2so4. appearance of a reddishbrown color indicates the presence of terpenoids. test for saponins 20 ml of distilled water was added into 5 ml of extract followed by vigorous shaking. appearance of froth indicates the presence of saponins. test for quinone few drops of concentrated sulphuric acid were added into 2 ml of extract. appearance of yellow precipitate shows the presence of quinones. test for polyphenols 3 drops of 5 % fecl3 solution were added into 2 ml of extract followed by shaking well. appearance of black color indicates the presence of polyphenol. test for glycosides 3 drops of molisch’s reagent were added into 2 ml of extract followed by shaking well. then few drops of conc. h2so4 were added slowly from the side of test-tube and left to stand for few minutes. appearance of violet ring at the junction of two layers indicates the presence of glycosides. test for proteins biuret test was performed for proteins. for this, 2 ml of 5 % naoh was added into 2 ml extract followed by addition of cuso4 solution. the appearance of pink color indicates the presence of protein. 2.4 synthesis of agnps 8.2 g of silver nitrate was dissolved in 500 ml distilled water to prepare 0.01 n silver nitrate solution. silver nanoparticles were prepared by adding 10 ml and 6 ml of plant extract separately into a beaker with 30 ml of 0.01 n agno3 solution (extract precursor ratio: 1:3 agnps and 1:5 agnps, respectively) with constant stirring at room temperature. thus, formed precipitate was filtered and washed with distilled water and ethanol. then it was dried in vacuum oven at 60 °c. finally pure agnps was collected. 2.5 physicochemical characterization the phytochemical assay was based on the visual changes of the solution after chemical treatment. double beam uv visible spectrophotometer (labtronics 2802) was used to determine the formation of agnps in the department of chemistry, amrit campus, tribhuvan university, kathmandu, nepal. for this purpose, agnps was dispersed in ethanol by sonication for 15 min and taken in quartz cuvette for the measurement of sandhya parajuli et al./ bibechana 21 (2024) 63-73 66 absorbance within the window of 300-700 nm at a scan interval of 5 nm. fourier transform infrared (perkinelmer 10.6.2) spectroscopy was used to identify the functional group associated with potential biomolecules attached with silver nanoparticles in the cut off range 500-4000 cm-1 with scan interval 4 cm-1. the crystallinity and crystal phase of the obtained materials were probed by an x-ray diffraction (xrd, rigaku diffractometer, japan, cu k, = 1.5406 å) within the two theta angle of 10-80° at a scan rate of 5°/min at 0.02° steps. the surface morphology of assynthesized material was studied using field emission scanning electron microscopy (fe-sem, hitachi, tokyo, japan) equipped with energy dispersive x-ray spectroscopy (edx). the transmission electron microscopy (tem) image of as-synthesized composite nanoparticles was studied using highresolution transmission electron microscopy (hrtem, jem-2200, jeol, ltd, japan). 2.6 antimicrobial activity antibacterial and antifungal activities of 1:3 agnps, and 1:5 agnps were carried out using agar well diffusion methods. inhibitions of bacterial and fungal growth were tested in terms of zone of inhibition. microbials culture was prepared in a tryptone soy broth medium at 37 °c for 10 h. the microbial cell suspension was diluted to obtain 107 colony forming unit per milliliter (cfu/ml). then 100 µl inoculum was spread over the entire tryptone soy agar plate. sterilized agnps and control samples were placed over the agar plate containing corresponding bacteria. in this experiment, 5µl of standard kanamycin was loaded into respective sections with the help of micro pipette. kanamycin was used as standard for antimicrobial test. the plates were incubated in bacteriological incubator for 12 hrs at 37 °c. each plate was then observed for the zone of inhibition (zoi) produced by antibacterial and antifungal activity. zoi was measured by the use of ruler [20]. 3 results and discussion 3.1 phytochemical analysis in this study, initially, presence of some phytochemicals were tested by chemical test. the results obtained in this test are presented in table 1. result shows that the leaf extract did not show the presence of alkaloids but consists of bioactive substances including flavonoids, saponins, terpenoids, quinones, polyphenols, proteins, and glycosides present. for the preparation of nanomaterials, these bioactive phyto-constituents were thought to function as stabilizing and reducing agents. the study by thangjam et al., revealed that the leaves extract of artemisia vulgaris included phytochemicals such flavonoids, triterpenoids, glycosides, polyphenols, saponins, and proteins [21]. 3.2 uv-visible spectroscopy the absorbance recorded of silver nanoparticles in double beam uv-vis spectrophotometer is shown in figure 1(a). the uv-vis spectra of silver nanoparticles showed a characteristic surface plasmon resonance (spr) peak at ∼430 nm, indicating the finely dispersed agnps. in the similar experiment, agnps synthesis in aqueous solution was monitored by recording the absorption spectra at a wavelength range of 300-600 nm [22]. the peak at 430 nm was found to be a characteristic absorbance peak of the artemisia vulgaris variant metabolites and proteins, which play an important role in the reduction of silver ions into synthesized nps. our findings are in good agreement with previous reports [23–25]. in the similar work of rasheed et al., uv-vis absorbance peak of agnps synthesized using aqueous extract of a. vulgaris l. was detected at 420 nm [15]. according to the study done by alomari, prominent peak of agnps was observed at 431 nm [14]. in the same way, the agnps developed from acorous calamus rhizome extract displayed broader peak around 400 nm [26]. similarly, several researchers have reported that the peak of agnps appears to be around this region [27, 28]. comparing with these reports, the uv-vis absorbance peak observed for agnps of this work seems to be appreciable. sandhya parajuli et al./ bibechana 21 (2024) 63-73 67 table 1: showing the results obtained by phytochemical test phytochemicals presence/absence alkaloids absent flavonoids present saponins present terpenoids present quinones present polyphenols present proteins present glycosides present figure 1: (a) uv-vis spectra of 1:3 agnps and 1:5 agnps, (b) ftir spectra of a. vulgaris leaf extract only and green synthesized agnps and (c) xrd patterns of green synthesized agnps. 3.3 ftir spectroscopy the functional groups present in as-synthesized agnps were investigated using ftir spectroscopy. the ftir spectra of plant extract and assynthesized nanostructure are shown in figure 1(b). in the spectra of leaves extract, a board spectrum at 3322 cm-1 was due to the o-h bond stretching. the c–h stretching of alkane has resulted in a band at 2945 cm-1 and 2835 cm-1. the absorption band at 1655 cm-1 is due to c=o or c=c stretching of carbonyl compounds [29]. the c–h bending of alkane gives rise to band at 1449 cm-1 and 1413 cm-1. an absorption peak at 1116 cm-1 was ascribed to c-n stretching of amine, and band at 1022 cm-1 was attributed to ester and tertiary alcohol. these assigned peaks were carried out in accordance with spectrometric identification of organic compounds [30]. the functionalities present in methanolic extract of leaves of artemisia vulgaris were found to be well indexed with some previously published report [31]. 3.4 xrd the crystallite nature and size of the as-synthesized nanoparticles were carried out by using x-ray diffraction spectroscopy. the xrd patterns of the green synthesized agnps using a. vulgaris leaves extract is shown in figure 1(c). the xrd patterns of agnps were appeared at 2θ values of 27.78°, 32.35°, 38.09°, 45.53°, 54.78°, 57.53, 64.45°, 67.37°, and 76.74°. the four distinct diffraction peaks at 2θ values of 38.09°, 44.53°, 64.45°, and 76.74° were well indexed to the (111), (200), (220), and (311) reflection plane of cubic structure of silver, respectively, with jcpds card no: 90-13050, space group: fm3m [8, 32]. these data are in good agreement with those of elemike et al. on their work on agnps using a. afra [33]. furthermore, along with these representatives peaks of silver, some additional peaks values of 27.78°, 32.35°, 46.36°, 54.78°, 57.53°, and 67.37° were also observed at 2θ value which are well matched to the peaks from the jcpds card no: 76-1393 for silver oxide. presence of some of these peaks was due to the oxidation of silver during the sandhya parajuli et al./ bibechana 21 (2024) 63-73 68 long term storage before the characterization. similar studies of xrd patterns for silver nanoparticles have been reported in elsewhere [34, 35]. the average crystallite size of the green synthesized silver nanoparticles was calculated by using debyescherrer formula, d = kλ βcosθ (1) where, d = crystallite size of materials λ = wavelength of cu k radiation (0.15406 nm) θ = bragg’s angle β = corrected half width of the diffraction peak (in radian) k= shape factor which usually equals to 0.94 the most intense peaks observed in the xrd spectra are 38.09° and 45.53°. the average beta factor was used in grain size calculation. the average crystallite size of green synthesized agnps was found at around 28 nm. 3.5 fesem and edx analysis the surface morphology of as-prepared silver nanoparticles was investigated via field emission scanning electron microscopy (fesem) coupled with energy dispersive x-rays spectroscopy (edx) and elemental mapping. the surface morphology of silver nanoparticles with different magnifications are shown in figure 2. the images demonstrate the homogeneously generated, narrow size distribution of the silver nanoparticles. the formation of silver nanoparticles occurs at the nanoscale range which is facilitated by the plant metabolites in their synthesis and stabilization. similar results were also reported in the synthesis of silver nanoparticles using other phytochemical constituents [36, 37]. successful synthesis of silver nanoparticles in nanometric range is also supported by transmission electron microscopy (tem) as shown in the figure 4. the tem image clearly shows the nanosized agnps. additionally, energy dispersive x-ray with elemental mapping was carried out to ensure the synthesized product, as seen in figure 3. edx spectral analysis demonstrated higher silver counts at 3 kev and hence confirming the predominant presence of silver in the nanoparticles. silver makes up the bulk of the nanoparticle's composition (91.31 mass % and 61.84 atom %). observation of some other peaks such as peaks of carbon and oxygen in vicinity of silver major peaks corresponds to that c and o elements are characteristic of plant extract. the outcome reveals that the nanoparticles are mostly made of silver, with a little carbon and oxygen. small amount of carbon could be due to the effect of carbon tape used during fesem/edx characterization. in addition, the carbon and oxygen could be associated with phytochemicals capped onto the silver nanoparticles as methanolic extract of artemisia vulgaris leaf was used as capping and reducing agent. some amount of oxygen in edx could be associated with the oxidized silver nanoparticles upon long storage [15,38]. figure 3 represents the elemental mapping of assynthesized product and revealed the presence of c, o, and ag. 3.6 antimicrobial activities in this study, the antimicrobial activity of green synthesized agnps using avle was studied against gram-positive bacteria (bacillus subtilis), gramnegative bacteria (escherichia coli), and fungi (candida albicans) by agar well diffusion method. thus obtained results are shown in table 2. kanamycin was used as a positive control to compare with the obtained results of as-synthesized agnps to observe their antimicrobial efficiencies. green synthesized agnps showed the potential antimicrobial activity against gram-positive bacteria (bacillus subtilis), gram-negative bacteria (escherichia coli), and fungi (candida albicans). agnps of 1:5 ratio showed best efficiency as compared to 1:3 agnps and leaves extract alone. the zone of inhibitions of 1:5 agnps for bacillus subtilis, escherichia coli, and candida albican were found as 5 mm, 6 mm and 6 mm, respectively and are comparable to the positive standard control kanamycin (9 mm zone of inhibition). however, the zone of inhibitions exhibited by 1:3 agnps for bacillus subtilis, escherichia coli, and candida albican were 4 mm, 5 mm and 4 mm, respectively. these values are almost comparable to those exhibited by artemisia vulgaris extract. the result showed that as-prepared silver nanoparticles exhibited significant inhibition activities against the tested microbial. the zone of inhibition exhibited by extract, agnps and control (kanamycin) are shown in the histogram (figure 5). in the similar work carried out by rasheed et al., the antibacterial activities of nps were investigated using the disc diffusion method against 5 pathogens, namely escherichia coli, staphylococcus aureus, pseudomonas aeruginosa, klebsiella pneumonia and haemophilus influenza [15]. the highest value was recorded against s. aureus (18 ± 0.27 mm) and the lowest value was recorded against v. cholera (12 ± 0.18 mm) by agnps. however, they have not mentioned the zoi of control. similarly, in the study done by alomari [14], green synthesized agnps showed significant activity against grampositive bacteria (bacillus subtilis, staphylococcus aureus), and gram-negative bacteria (escherichia coli, pseudomonas aeruginosa), whereas the fungi (aspergillus flavus and candida albicans) showed sandhya parajuli et al./ bibechana 21 (2024) 63-73 69 highest resistance towards agnps with 0.0 inhibition zone. in the work, alomari synthesized the agnps using aqueous fraction of leaf extract of a. vulgaris. meanwhile, silver nanoparticles prepared in our work exhibited inhibition activities against fungal species, candida albicans. this could be associated with the effect of size of nanoparticles, active ingredient and phytochemicals functionalized nps. figure 2: fesem images of 1:3 agnps (a, b and c) and 1:5 agnps (d, e and f) at different magnification. figure 3: elemental mapping of silver nanoparticles (a) morphological view, (b-e) elemental mapping: (b) carbon, (c) oxygen, (d) silver, (e) carbon, oxygen and silver, (f) eds spectra (g) mass percentage and atom percentage of as-synthesized 1:5 agnps. sandhya parajuli et al./ bibechana 21 (2024) 63-73 70 figure 4: transmission electron microscopy image of as-synthesized 1:5 agnps under different scale bar. figure 5: histogram representation of antimicrobial activities of leaf extract and agnps compared to control kanamycin. sandhya parajuli et al./ bibechana 21 (2024) 63-73 71 figure 6: antimicrobial activity of green synthesized agnps against (a) b. subtilis, (b) e. coli, (c) c. albicans, and of avle against d, e, f (b. subtilis, e. coli and c. albicans, respectively). where, c+=positive control, s1= 1:3 agnps, s2= 1:5 agnps, c-= negative control, and s= plant extract. table 2: antimicrobial activity of as-synthesized agnps using artemisia vulgaris leaves extract samples zone of inhibition (mm) bacterial species fungal species bacillus subtilis 5 g+ escherichia coli 5 gcandida albicans 4 extract (100 µl) 1:3 agnps (5 mg) 4 5 4 1:5 agnps (5 mg) 5 6 6 kanamycin (5 µg/ml) 9 9 9 4 conclusion in this work, silver nanoparticles were successfully prepared by green synthesis method using the methanolic extract of artemisia vulgaris leaf. phytochemical screening of the methanolic extract ensured the presence of flavonoids, saponins, terpenoids, quinones, polyphenols, proteins and glycosides. as-prepared silver nanoparticles was characterized using uv-vis, ftir, xrd, fesem, tem, edx and elemental mapping. the agnps exhibited the surface plasmon resonance at ∼430 nm. the average particle size of the agnps was ∼ 28 nm according to debye scherer equation. this value is in agreement with those exhibited in tem image. to the biomedical point of view, the synthesized nanoparticles were found to act as good antimicrobial agents. it was confirmed that biosynthetic silver nanoparticles showed excellent antibacterial performance against gram-positive bacteria (bacillus subtilis) and gram-negative bacteria (escherichia coli), and also showed antifungal activity against candida albicans. the extract from a. vulgaris has potential value for various biomedical and pharmaceutical applications. all in all, the finding suggests a successful synthesis of silver nanoparticles by green synthetic route which is good enough to act as antibacterial and antifungal agents for biomedical applications. conflict of interest authors declare no conflict of interest. acknowledgements authors acknowledge to the department of chemistry, amrit campus, for laboratory support. sandhya parajuli et al./ bibechana 21 (2024) 63-73 72 references [1] r. penchovsky and m. traykovska. designing drugs that overcome antibacterial resistance: where do we stand and what should we do? expert opinion on drug discovery, 10(6):631– 650, 2015. 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[38] s. ahmad et al. green nanotechnology: a review on green synthesis of silver nanoparticles—an ecofriendly approach. international journal of nanomedicine, pages 5087–5107, 2019. introduction experimental chemicals and reagents extract preparation phytochemical test synthesis of agnps physicochemical characterization antimicrobial activity results and discussion phytochemical analysis uv-visible spectroscopy ftir spectroscopy xrd fesem and edx analysis antimicrobial activities conclusion bibechana vol. 22, no. 2, august 2025, 188-195 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar first principles calculations of mechanical, electronic, thermoelectric and thermal properties of zncu shashit kumar yadav∗, subash dahal, bhupal guragain , department of physics, mahendra morang adarsh multiple campus tribhuvan university,biratnagar, nepal ∗corresponding author. email: sashit.yadav@mmamc.tu.edu.np abstract the structural, mechanical, electronic and thermoelectric properties of zncu were investigated using density functional theory (dft). the perdew–burke–ernzerhof (pbe) exchangecorrelation functional within the generalized gradient approximation (gga) was employed in the quantum espresso package for the purpose. the zncu compound was found to be both mechanically and dynamically stable. analysis of its elastic and electronic properties reveals that zncu is mechanically stable, anisotropic, and exhibits metallic behavior. furthermore, thermoelectric property analysis indicates that zncu achieves its highest power factor at 300 k. the study of thermodynamic properties suggests that zncu retains mechanical stability at elevated temperatures. keywords zncu compound, quantum espresso, electronic properties, phonon, thermoelectric properties. article information manuscript received: january 10, 2025; revised: april 12, 2025; accepted: may 26, 2025 doi https://doi.org/10.3126/bibechana.v22i2.79223 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction alloying materials serve an important role in improving the qualities of materials for a variety of applications by increasing their strength, durability, and corrosion resistance. the material can be alloyed to achieve the qualities that alloy components lack for practical application [1]. there are enormous possibilities for alloying the material, but copper alloy has gained its own importance in the fields of machinery, electrical industry, and construction over the past year [2, 3]. among the different possible alloys of copper, the zncu alloy stands out due to its potential application in diverse domains. the unique combination of zinc and copper provides promising characteristics [4–8]. different research has been conducted to study the properties of the zncu alloy. for example, iwaoka and hirosawa used first principles method to calculate elastic properties of three different complex of cu-zn system to improve the stiffness of aluminum alloy [4]. similarly, liu et al. studied the structural, elastic, and electronic properties of cu-x (x = al, be, mg, sn, zn, and zr) by the first-principles calculations [8]. furthermore, tang et al. used a modified quasi-chemical model (mqm) to describe the gibbs energy of the liquid phase [9]. 188 http://nepjol.info/index.php/bibechana sashit.yadav@mmamc.tu.edu.np https://doi.org/10.3126/bibechana.v22i2.79223 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ shashit kumar yadav et al./ bibechana 22 (2025) 188-195 189 despite significant progress in material science, comprehensive studies that integrate structural, electronic, elastic, thermoelectric, and thermal properties of zncu crystal structure are still sparse. therefore, this work attempts to explain these properties of the zncu compound using the first principles calculations employing quantum espresso codes [10]. 2 computational details the first principles calculation of zncu structure was performed using the quantum espresso software package [10]. the crystal structure was first optimized by performing the vc-relax calculation using perdew-burke-ernzerhof (pbe) of scalar relativistic exchange-correlation functional and ionic potentials described by ultrasoft pseudopotential (uspp) for zn and cu downloaded from the material cloud website [11]. the plane wave cutoff energy was set to 40 ry and 320 ry was set for the wave function and charge density. the brillouin zone was determined using monkhorst-pack for self-consistent field calculation and for density of state (dos) calculation. the electronic band structure was calculated along the highsymmetry point in the brillouin zone using the path γ−x −m − γ−r−x|r−m . the bulk modulus was calculated using the murnaghan equation of state using the ev.x utility of quantum espresso [12]. furthermore, the thermo_pw [13] postprocessing tool was used to calculate the elastic constant, which allowed for the calculation of mechanical properties such as bulk modulus, young modulus, shear modulus, and poisson ratio of the material. electronic transport properties were calculated with the help of the boltztrap code [12, 14]. the output information of nonself-consistent field calculation was used as input for boltztrap software, which solves the boltzmann transport equation to determine electrical conductivity, seebeck coefficient, and thermal conductivity. the phonon calculation was executed in the phonopy package [15] using the finite displacement method on a supercell. finally, thermal properties such as heat capacity at constant volume, free energy, and entropy were calculated. 3 results and discussion 3.1 structural properties figure 1 shows the zncu crystal structure which is a tetraauricupride cubic structure in space group pm3m with all bond lengths of 2.53 å. zn is bonded with eight cu atoms in body centered geometry [16]. figure 1: crystal structure of zncu. using the first principles calculations in quantum espresso software, the total energies were minimized as a function of the lattice parameter for the material. the lattice parameter (a), bulk modulus( b0 = −v ∂p ∂v ) , and pressure derivative (b′) of the zncu crystal structure are derived by fitting the murnaghan equation of state as [17] p (v ) = b0 b′ [( v0 v )b′ − 1 ] (1) where v0 is the equilibrium volume and b′ = db/dp . the murnaghan equation of state is fitted using the ev.x tool of quantum espresso to calculate total energy as a function of unit cell volume. the obtained value of the lattice parameter is 2.96628 å, which is consistent with the experimental value of 2.959 å [4]. similarly, bulk modulus (b0) and its pressure derivative (b′) are found to be 115.00 gpa and 5.02, respectively. the obtained value of bulk modulus is in good agreement with the value in the materials project database, which is 116.00 gpa [18]; validating the present computational approaches. 3.2 vibrational properties the phonon serves as a medium for understanding transmission of vibrational energy in the material. utilizing the phonopy algorithm [15], the phonon frequency of zncu was calculated. a 2×2×2 supercell was created to collect force sets for analyzing the phonon band structures and phonon density of states (dos). the phonon dispersion curves and the corresponding phonon density of states (dos) of zncu are shown in figure 2. these calculations shashit kumar yadav et al./ bibechana 22 (2025) 188-195 190 were performed to assess the dynamical stability and lattice vibrational behavior of the compound. the phonon dispersion curve displays the vibrational frequencies along high-symmetry directions in the brillouin zone. importantly, no imaginary frequencies (i.e., frequencies below zero) are observed throughout the entire brillouin zone, indicating that the zncu structure is dynamically stable in its equilibrium configuration. the phonon spectrum features both acoustic and optical branches. the acoustic modes originate from the γpoint and extend up to about 4 thz, while the optical modes span from about 4 thz to over 6.5 thz. the separation between the acoustic and optical branches suggests a moderate mass difference between zn and cu atoms and indicates potential phonon scattering behavior relevant to thermal transport. the phonon density of state (dos) exhibits multiple sharp peaks, especially in the highfrequency region (4–7 thz), corresponding to localized optical modes. the lower-frequency region shows a more gradual increase in dos, associated with acoustic phonons. this distribution of vibrational states implies that optical phonons significantly contribute to the vibrational properties, while acoustic phonons dominate low-temperature specific heat and thermal conductivity. he phonon dos achieved is consistent with the findings of a previous study by peter et al. for β-zncu [7]. figure 2: phonon band structures and phonon dos of zncu. 3.3 elastic properties the elastic constant matrices (cij) were calculated using thermo_pw utility of quantum espresso. three independent elastic constants; c11, c12, and c44 for cubic structure of zncu were obtained. these elastic constants were further used to calculate the elastic property through voigt–reuss–hill (vrh) methods [19–22]. the relation of shear modulus (g) and bulk modulus (b) are expressed as [12,19,23] gv = c11 − c12 + 3c44 5 (2) gr = 5c44(c11 + c12) 4c44 + 3(c11 − c12) (3) g = gv +gr 2 (4) bv = br = c11 + 2c12 3 (5) b = bv +br 2 (6) similarly, young’s modulus (y ), poisson’s ratio (ν), and universal elastic anisotropy index (au ) can be calculated using the relations as [19,20,23] y = 9bg 3b +g (7) ν = 3b − 2g 2(3b +g) (8) au = 5 ( gv gr ) + ( bv br ) − 6 (9) table 1 shows the calculated values of these elastic parameters. born criteria for mechanical stability of the cubic system, i.e., c11 > 0, c44 ≥ 0, c11 ≥ |c12| and c11 + 2c12 ≥ 0 are satisfied by the calculated value of elastic constants [12,22,23]. this shows that zncu crystal is mechanically stable. furthermore, the value of bulk modulus (b0) calculated using murnaghan equation of state in the section 3.1 and voigt-reuss-hill methods using equation (3.3) are comparable with the value predicted in the material project database [18] and ref. shashit kumar yadav et al./ bibechana 22 (2025) 188-195 191 [4]. the small discrepancy in the calculated values of elastic parameters with material project database may be due to the use of different pseudopotentials. we have used pbe type pseudopotential whereas the later, ref. [18], have used pbesol type pseudopotential. table 1: calculated values of elastic parameters for zncu complex parameter this work material project [18] other [4] c11 (gpa) 152.692 134.8 – c12 (gpa) 102.697 104.7 – c44 (gpa) 96.992 75.4 – b (gpa) 119.362 116 117.4 g (gpa) 56.632 46 40.1 y (gpa) 145.975 107.7 – ν 0.295 0.33 0.34 au 2.565 3.57 3.87 figure 3: spatial dependence and 3d visualization of young’s modulus (y ), linear compressibility (β), shear modulus (g) and poisson’s ratio (ν) of zncu. shashit kumar yadav et al./ bibechana 22 (2025) 188-195 192 the bulk modulus (b) characterizes the material’s resistance to uniform compression and is intrinsically linked to its crystal structure, including the nature and length of chemical bonds . the shear modulus (g), or modulus of rigidity, quantifies the material’s response to shear stress, reflecting its ability to resist deformation caused by tangential forces that induce relative motion between adjacent atomic layers. young’s modulus (y ) represents the stiffness of the material under uniaxial tensile stress and provides a comprehensive measure of its elastic rigidity [16, 24, 25]. its higher values indicate greater resistance to deformation. the calculated value of y = 145.975 gpa, indicating moderately high stiffness, consistent with metallic bonding. additional mechanical parameters derived from the elastic moduli, namely pugh’s ratio (k = b/g), poisson’s ratio (ν), and the universal anisotropy index (au ) offer valuable insight into the bonding characteristics, mechanical behavior, and elastic anisotropy of crystalline materials [26]. according to pugh’s criterion, materials with k > 1.75a re typically classified as brittle, while those with k > 1.75 are considered ductile [19]. the calculated value of k = 2.11, indicating the material to be ductile. the calculated value of ν = 0.295 corresponding that the material exhibits metallic ductility, as predicted by k. furthermore, a universal anisotropy index of au = 1 denotes a mechanically isotropic material, whereas any deviation from this value indicates the presence of elastic anisotropy [19]. the obtained value of au = 2.565 corresponding that te material to be significantly anisotropic, which may affects its mechanical behaviour under directional stress. the directiona dependence of the elastic properties was also analyzed using the elate software [27], which processes the second-order elastic constants (cij) in voigt notation. based on the calculated values of c11, c12 and c44, table 1. the software then generated 2d and 3d plots of mechanical properties, including young’s modulus (y ), linear compressibility β, shear modulus (g) and poisson’s ratio (ν). the obtained results are summarized in table 2, and their 2d and 3d plots are visualized in figure 3. the uniform shapes of the respective plots indicate isotropy, while deviations reflect elastic nisotropy. the software utilizes distinct color schemes to represent elastic properties in 2d and 3d visualizations [27]. for y and β, green indicates positive values and red denotes negative values. in the case of g and ν, up to three colors are employed: solid green and translucent blue for positive values, and translucent red for negative values, particularly relevant for poisson’s ratio, which may become negative in specific crystallographic directions. it can be observed that the spatial dependence of y , β and g are found to be positive for the material with finite and non-negative values of respective anisotropy. figure 3. but the value of ν is found to be negative (there is presence of red colour) with infinite value of anisotropy indicating its directional dependence. table 2: variations of young’s modulus (y ), linear compressibility (β), shear modulus (g), and poisson’s ratio (ν), along with their corresponding anisotropy ratios for zncu parameter y (gpa) β (tpa−1) g (gpa) ν min max min max min max min max value 70.009 228.960 2.7926 2.7926 24.998 96.992 -0.24656 0.83841 anisotropy 3.266 1.000 3.880 ∞ 3.4 electronic properties the electronic properties of the material were investigated using dft within the pbe scalar relativistic approximation. the calculated electronic band structures, density of states (dos), and partial density of states (pdos) are presented in figure 4(a,b). the band structures of te material shows multiple bands crossing the fermi level (ef ), consistent with its metallic character, as shown in figure 4(a). notably, several highly dispersive bands are observed near ef along the γ-x, r-x, and m–γ directions, indicating the presence of high carrier mobility in these directions. in contrast, the presence of relatively flat bands around −3 ev to −2 ev corresponds to localized cu-d states, as supported by the pdos in figure 4(b). the absence of a band gap and the significant overlap of conduction and valence bands near ef suggest that zncu can exhibit good electrical conductivity. the availability of partially filled conduction states also implies the possibility of tuning thermoelectric performance through appropriate doping or carrier concentration adjustment. the pdos plot reveals that the cu-3d orbitals dominate the valence region, particularly within the energy range from approximately −4 ev to −2 ev, shashit kumar yadav et al./ bibechana 22 (2025) 188-195 193 as shown in figure 4(b). the zn-3d states contribute mainly at deeper energies (−6 ev to −3 ev), whereas the s and p orbitals of both zn and cu exhibit relatively minor contributions. the non-zero density of states at the fermi level confirms the metallic nature of zncu, which further supports the results of band structures. figure 4: electronic band structures, density of states and partial density of states (pdos) of zncu. 3.5 thermoelectric properties the thermoelectric properties of the zncu were investigated using boltzmann transport equation implemented in boltztrap2 codes [12, 14]. the calculations were basically focusing on the seebeck coefficient (s), electrical conductivity (σ/τ0), thermal conductivity (ke/τ0), and power factor (pf = s2σ/τ). the calculated values of these parameters are plotted as a function of temperature in figure 5. the seebeck coefficient exhibits a nonlinear trend, starts slightly positive from about 200 k and becomes strongly negative around/at 300 k. with further increase in the temperature of the sample, plot of seebeck coefficient gradually increases towards zero as temperature approaches 850 k. the change in sign of the coefficient indicates a crossover in carrier type dominance. its positive value indictes hole-like or p-type behaviour whereas negative value indicates electron-like or ntype behaviour. the sharp negative peak suggests dominant n-type conduction at intermediate temperatures. the plot of electrical conductivity decreases with temperature (top right panel of figure 5). this behaviour is expected for metallic semiconducting materials, in which increased phonon scattering takes place at higher temperatures thereby reducing the conductivity of material. further, the thermal conductivity of the material increases linearly with temperature (bottom left panel of figure 5). this behaviour is typical as thermal conductivity due to electrons generally increases with temperature in metallic system. the power factor combines seebeck and conductivity, which is a key quantity in thermoelectric performance. the plot of power factor stars from zero at/about 200 k and then gradually increases attaining peak value around 300 k. it decreases sharply then after with further increase in temperature (bottom right panel of figure 5). the peak near 300 k indicates optimal thermoelectric performance at room temperature. 4 conclusions the structural, mechanical, electronic, and thermoelectric properties of zncu have been systematically investigated using the first principles calculations employing quantum espresso codes. elastic constant calculations confirm the mechanical stability of the compound, satisfying the born stability criteria for cubic systems. pugh’s ratio and poisson’s ratio indicate that zncu is ductile, while the universal anisotropy index and elate visualizations reveal significant elastic anisotropy. electronic band structure analysis demonstrates that zncu exhibits metallic behavior, with no band gap across the fermi level. this metallic nature supports good electrical conductivity, which is a critical factor in thermoelectric performance. thermoelectric calculations show that zncu achieves its highest power factor at 300 k, highlighting its potential for energy conversion applications. thus, zncu shashit kumar yadav et al./ bibechana 22 (2025) 188-195 194 figure 5: temperature dependence of seebeck coefficient (s), electrical conductivity (σ/τ0), thermal conductivity (ke/τ0), and power factor (pf = s2σ/τ) of zncu. combines mechanical robustness, metallic conductivity, and promising thermoelectric performance, making it a potential 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[27] gaillac r, pullumbi p, coudert fx. elate: an open-source online application for analysis and visualization of elastic tensors. journal of physics: condensed matter. 2016;28(27):275201. https://next-gen.materialsproject.org/materials/mp-987 https://next-gen.materialsproject.org/materials/mp-987 introduction computational details results and discussion structural properties vibrational properties elastic properties electronic properties thermoelectric properties conclusions bibechana vol. 20, no. 2, august 2023, 113–125 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar sol-gel synthesis, characterization of zno thin films on different substrates, and bandgap calculation by the tauc plot method d. parajuli1,2,∗, sandip dangi1, bhumi raj sharma3 nunu lal shah1, devendra kc4 1department of physics, tri-chandra multiple campus, ghantaghar, kathmandu 2research center for applied science and technology, tribhuvan university, kirtipur 3department of physics, janapriya multiple campus, pokhara, kaski 4myrveien 13, 9740 lebesby, norway ∗corresponding author. email: deepenparaj@gmail.com abstract the sol-gel spin coating method was used for the preparation of the zinc oxide which was coated over polymer, transparent, and glass translucent substrates and characterized with the help of a uv-vis spectroscope. the wavelength bandgap of those samples was found to be 296nm, 310.5nm, and 330nm respectively. the actual band gap of zno is 388nm. similarly, their optical bandgap energy calculated by the tauc plot method were 3.641ev, 3.385ev, and 3.495 ev respectively. the transparent polymer slide has the lowest wavelength bandgap and the translucent glass slide has the highest. further, the bandgap’s value differs from its actual value to the difference in the absorption process due to the presence of the substrate. these results suggest that the choice of substrate can significantly impact the optical properties and performance of the zinc oxide thin film. this result can be applied in developing and optimizing zinc oxide thin films for various purposes, such as in solar cells, sensors, and optoelectronics. by carefully selecting the substrate, it may be possible to tailor the bandgap energy and other optical properties of the thin film to better suit the specific application. keywords zinc oxide, thin films, bandgap, spin coating method, a sol-gel method, uv spectroscope. article information manuscript received: march 10, 2023; accepted: april 16, 2023 doi https://doi.org/10.3126/bibechana.v20i2.54115 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction extensive research is conducted these days on metal oxides in nanoparticle form due to their diverse potential applications in various fields, such as agriculture, medicine, industry, and technology. the metal oxides being researched include copper, zinc, tin, magnesium, zirconium, silver, titanium, cerium, and others. among these, zinc oxide (zno) is particularly important due to its electronic and 113 http://nepjol.info/index.php/bibechana deepenparaj@gmail.com https://doi.org/10.3126/bibechana.v20i2.54115 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ d. parajuli et al./ bibechana 20 (2023) 113-125 114 optical properties, radiation stability, low cost of production, and non-toxicity. it has a high bandgap of 3.37 ev at room temperature and is commonly used in semiconducting oxide thin films, which are extensively utilized in solar cells, sensors, leds, surface acoustic devices, cosmetics, and paintings. previously, a study was conducted on sol-gel synthesized zno deposited on a glass slide [1] which will be studied further with other options in this work. zno is also utilized in organic and solar hybrid cells [2–5] in the form of a buffer layer for the cathode buffer layer, and it performs efficiently in both bulk and 2d forms, with thin films proving more effective than bulk ones. due to its versatility and various uses, zno is produced on a large scale [6] these days. znos are typically n-type with a wide bandgap of 3.37 ev [7] and have bands in the uv and visible light regions [8]. during the growth process, the interstitial sites, vacancies, or anti-sites of oxygen, zinc, and other factors may affect the final product’s parameters. zno’s point defect has an electron mobility of approximately 300 cm2 v−2 s−1 for bulk zno and around 1000 cm2 v−2 s−1 for zno nss, increasing the capacity for electron transfer. additionally, zno is active in oxidation and reduction processes. however, zno only has the capacity to absorb uv radiation, which is a narrow window of electromagnetic radiation and is difficult to excite the electron-hole pair. moreover, it can be scratched by light and decompose in higher and lower ph-valued solvents [9]. it can dissolve in highly acidic or basic media under proper biasing [10]. however, the limitations of zno can be overcome by using a composite of zno with other metals, such as doping, as described in previous literature. there are many processes for the preparation of nanomaterials [11–17]. the thin film zno [18] can be prepared with different methods like a deposition [19], sol-gel [20], vacuum evaporation [21], sputtering [22,23], successive ionic layer adsorption and reaction (silar) [24], pyrolysis [25], etc. we have incorporated the simplest but well-controlled stoichiometry [26], method called sol-gel followed by spin coating [27]. the solgel method as shown in figure 2 uses metal alkoxides m (or)n [derived from weak acids r-oh] and alkoxysilanes for their reaction in radial or all direction [28]. we have taken zn (no3)2 for zno synthesis [29]. the substrate for coating was transparent glass, translucent glass, and polymer slide. they were examined under a uv vis spectroscope. for spin coating, the substrate is mounted on a rotating system (10,000 rpm) whose centrifugal force spread the zno solution uniformly around the slide against surface tension and viscous force thereby creating the thin film of micro to the nanometer range. it is not effective for samples with a large area of the substrate. only 5% of the sample is distributed over the slide and the rest 95% is flung off [30]. the thickness of the sample is dependent on various parameters and given: h = ( 1− ρa ρa0 )( 2ηm 2ρa0ω2 )1 3 (1) where,ρ , η, m, and ω are the density, viscosity, evaporation rate, and angular speed of the slide respectively. the slides can be systematically coated [30]. the tauc plot method was used to calculate the band gap energy in which the energy is on the xaxis and (αhν)2 on the y-axis. a tangent line on the curve at α = 0 touches a point on the x-axis is the optical bandgap energy of the materials. to get the curve first, we have to begin the tauc plot. the equation (αhν)2 = k(hν − eg) is known as tauc and davis-mott relation [31]. this relation is used to find the optical bandgap energy of a thin film of zinc oxide from uv-v is absorption spectroscopy. in this equation, α is the absorption coefficient ‘hν′ is the incident photon energy, k is the energy-independent constant and eg is the optical band gap energy of the zinc oxide. in this equation, ‘n’ represents the nature of the transition. for direct gap semiconducting material, n=2. figure 1: the beer lambert’s law. d. parajuli et al./ bibechana 20 (2023) 113-125 115 in uv-v is spectroscopy, the data which is given to us have wavelength and absorbance. therefore, we have to convert wavelength to energy and need to calculate the absorbance coefficient (α) from absorbance data. we use the max planck equation energy from wavelength, i.e. eg = hν (2) where h is planck’s constant and ν is the frequency of uv-vis light incident on the substrate in which the thin film of zinc oxide is coated. we know that, ν = c λ (3) putting equation (2) in equation (1), eg = hc λ (4) where c is the speed of light and putting the values in equation (4), we get, eg = 6.62× 10−34js× 3× 108m/s λ eg = 19.854× 10−26jm λ (5) in equation (4) the energy is in joule, we have to convert it into electron volts. we know, 1ev = 1.602 × 10−19j , therefore energy in equation (4) can be converted as follows: eg = 19.854× 10−26ev m 1.602× 10−19λ eg = 12.393× 10−7ev m λ where 10−9m = 1nm eg = 12393 ev nm λ (6) in equation (6), we have to put the value of the wavelength in the nanometer obtained from the uvv is spectroscope when uv-v is light incident in zinc oxide. in this project work, we have used origin software to convert wavelength to energy with help of equation (6) which can be seen in figure 1. the coefficient of absorption (α) is obtained by plotting (αhν)2 on the y-axis where ‘hν′ is the incident photonic energy. using beer lambert’s law, we can calculate ‘α’ from absorbance data [32,33]. in figure 1, i is the intensity of transmitted light, io is the intensity of incident light, ‘α′ is the absorption coefficient and l is the path length in which absorbance takes place. from beer lambert’s equation, i = ioe −αl (7) we can modify equation (7) as i i0 = e−αl taking logs on both sides, log i i0 = loge−αl log i i0 = −αlloge log i0 i = αlloge as we know, absorbance(a) = log i0 i so we can write as, a = αlloge α = a 1 lloge where,loge = 0.4343, then we can write, α = a 1 0.4343l α = 2.302× a l as we took the thin film of zinc oxide so the path length = 10mm = 1cm α = 2.302× a 1cm α = 2.302×acm−1 (8) the unit of absorbance coefficient would be cm−1 because 2.303 is a constant and absorption is a dimensionless quantity. thus using equation (7), the absorption coefficient is calculated with the help of origin software which can be seen in figure 1. now combining equation (7) with energy to get our desire tauc relation i.e. (αhν)n = (absorption coefficient × energy)n (αhν)n = (2.303×a× hν)n (9) equation (9) gives the value of (αhν)2 with the unit (ev cm−1)2. then, a graph is plotted with energy (hν/λ) on the x-axis and (αhν)2 on the y-axis. then, draw a tangent line on the curve where α=0. the point where it touches the axis is the optical bandgap energy of the materials. d. parajuli et al./ bibechana 20 (2023) 113-125 116 2 materials and methods the work mainly can be divided into three parts: 1) to obtain a thin film of zinc oxide by the sol-gel method and 2) analysis of the zinc oxide coated thin films over different glass slides using uv-v is spectroscope, and 3) calculation of the optical band gap energy of a thin film of zinc oxide with the help the tauc plot method. steps 1 and 2 are schematically shown in figure 2. the preparation of zno solution in the laboratory of recast, tu is shown in figures 3-13. the reaction taken in preparing zno is shown in the following reaction: zn (no3)2 + ch2ch (oh) → zno + ch2ch (oh) + 2no2 + o in this work, the slides can be cleaned by keeping them in the solution of water and detergent for 1hr 30 minutes followed by distilled water washing, ethanol, and acetone. the slides are then dried in a hot air oven for the complete removal of moisture from the surface. we have used polyvinyl alcohol (pva) as a chelating agent and zinc nitrate as a precursor for the production of zinc oxide nanoparticles. at first, 1 ± 0.05 gm of pva was mixed with 100ml of distilled water and stirred at 800c for 45 minutes in a magnetic stirrer. next, zinc nitrate of 2.974 ± 0.05gm in 100ml of pure distilled water and stirred in a magnetic stirrer. an equal volume (20ml) of each solution is mixed and stirred in a magnetic stirrer at room temperature ( 230c while experimenting) for 3hrs of time duration. the solution was again stirred for the next 5 hrs. at 500c to form a thick hot solution. cooled to room temperature to obtain a gel solution. then, we added a few drops of methanol help of a volumetric pipette and stirred for the next 15 min at normal temperature to get the clear gel-type solution. the gel solution was coated over the clean glass slide by keeping a few droplets of the gel-type clear solution over the spin coater (we have used the cpu 12v dc fan as the spin coater which can be seen in figure 10) and spinner for the next 50 second. the resulting slide was heated for 10 minutes at 2000c in a preheated hot air oven and cool them to room temperature. the systematic diagram of the sol-gel synthesis of zinc oxide over a glass slide is given in figure 2. then, obtained thin film of zinc oxide is analyzed with the help of a uv-vn is spectroscope. figure 2: a schematic view of the sol-gel process for the zno thin film processing. figure 3: dissolving pva with distilled water at 80oc. figure 4: mixing pva and zinc nitrate solution. d. parajuli et al./ bibechana 20 (2023) 113-125 117 figure 5: stirring the mixed solution for 3 hrs. figure 6: stirred continued for 5hrs. at 50oc. figure 7: normal temperature solution preparation. figure 8: adding methanol and stir the solution for 15 minutes. figure 9: formation of clear gel solution. figure 10: coating gel over the slide to get a thin film. figure 11: heating the coated thin film at 200oc in a hot air oven. figure 12: thin film of zinc oxide. d. parajuli et al./ bibechana 20 (2023) 113-125 118 figure 13: zno-coated transparent and translucent glass/polymer slide . 3 results and discussion 3.1 xrd study the x-ray diffraction (xrd) pattern in figure 14 displays the crystallographic planes (100), (002), (101), (102), (110), (103), (200), (112), (201), (004), and (202) at θ values of 31.760, 34.440, 36.240, 47.560, 56.660, 62.900, 66.420, 67.960, 69.140, 72.640, and 76.980, respectively, which matches with the jcpds card number 01-089-1397 [20, 34, 35] the presence of sharp and narrow peaks indicates that the zno nps are highly crystalline. furthermore, the sample exhibits a single-phase wurtzite structure, which is a hexagonal closepacked crystal structure commonly observed in zno [25]. the average crystallite size is obtained with the help of sherrer’s d = kλ β cos θ formula„ where d is the particle size of the zno, k is the shape factor whose value varies from 0.89 to 0.94 and 0.94 is chosen for spherical nps, is the wavelength of the cu–k radiations (1.5406 ) used in the x–ray diffraction, β is the full-width half maximum (fwhm), and θ is the bragg’s angle of different peaks. the average particle size of the zno nanoparticle was found at 39nm. the particle size and strain can induce the broadening of the xrd peaks. 3.2 sem study the scanning electron microscope (sem) image of a pure zno crystal is shown in figure 15 where oxygen and zinc atoms are represented by large and smaller spheres. the morphology of the composition agrees well with the previous literature [36]. figure 14: x-ray diffraction (xrd) patterns of zinc oxide nanoparticles. figure 15: tsem image of zno nanoparticles. d. parajuli et al./ bibechana 20 (2023) 113-125 119 3.3 uvv is spectroscope study uv-visible spectroscopy is an analytical technique used to measure the absorption or transmission of discrete wavelengths of uv or visible light by a sample, compared to a reference or blank sample. this method is suitable for both organic and inorganic compounds, and the pattern observed in the spectroscopic data depends on the reflective or absorptive properties of the sample. uv spectroscopy is simple, versatile, cost-effective, and nondestructive. spectrophotometers are used to measure the absorption or transmission of light as a function of the wavelength that passes through a sample. however, exposure to uv light can damage organic samples, which is a potential risk associated with this technique. to better understand how a uv-vis spectrophotometer works, it is essential to consider its main components. several variations of the instrument exist, but a typical system usually includes a light source, a monochromator, a sample holder, a detector, and a data acquisition system, as illustrated in figure 16. the light source generates the uv or visible light, and the monochromator selects specific wavelengths. the sample holder holds the sample in place and ensures uniform exposure to light, while the detector measures the amount of light absorbed or transmitted by the sample. finally, the data acquisition system records the spectral data, which can be analyzed to determine the properties of the sample. figure 16: a simplified schematic of the main components in a uv-vis spectrophotometer [37]. in this process, a steady source of light like a xenon lamp is needed for uv and visible light range. a deuterium lamp is used for the uv light range. a tungsten or halogen lamp is needed for visible range. the determination wavelength range needed for the substrate material, the uncoated substrate is taken as the sample and identified as the baseline wavelength and was found to be in the range 190-600 nm for uv characterization. a wavelength selector is used in the spectrophotometer to set the wavelength in its baseline range. then the light of a wavelength within the baseline range is passed through the coated sample and characterized with respect to a reference uncoated sample. in this work, we developed a thin film of zinc oxide over 1) transparent glass slides, 2) translucent glass slides, and 3) transparent polymer slides as in figures 12 and 13 respectively. their optical properties were studied with a uv visible spectrometer and calculated their bandgap energy with the help of the tauc plot method as follows: 3.3.1 uv-v is spectroscopy for transparent polymer slide the spectrum obtained from uv-visible spectroscopy (figure 17) shows a maximum peak at 296nm, as the bandgap wavelength of zno. however, the actual bandgap wavelength of the bulk zno is reported to be 388nm [38–40]. this discrepancy may be attributed to the use of substrates that diminish the absorption of radiation. further, the nanograin of the different substrates differs in the value of the optical energy band [41–43]. in contrast, the uncoated transparent polymer slide showed no such peak as seen in figure 18. further, the tauc plot method was used to calculate the bandgap energy of zinc oxide coated on a transparent polymer slide, yielding a value of 3.77ev, as illustrated in the corresponding figure 19. d. parajuli et al./ bibechana 20 (2023) 113-125 120 figure 17: uv-visible spectrum of a thin film of zinc oxide coated over a transparent polymer slide. figure 18: uv-visible spectrum of uncoated over transparent polymer slide. figure 19: the optical absorption coefficient (hv)2 of zinc oxide-coated transparent polymer slide as a function of the photon. figure 20: uv-visible spectrum of a thin film of zinc oxide coated over a transparent glass slide. figure 21: uv-visible spectrum of uncoated over a transparent glass slide. d. parajuli et al./ bibechana 20 (2023) 113-125 121 figure 22: the optical absorption coefficient (hv)2 of zinc oxide-coated transparent glass slide as a function of the photon. 3.3.2 uv-vis spectroscopy for transparent glass slide the uv-visible spectrum as in figure 20 indicates that the maximum peaks are located at 310.5nm as the band gap wavelength of zno. however, it is important to note that the actual band gap wavelength of bulk zno nanoparticles is 388nm [38–40], which is higher than the measured value. this discrepancy may be due to the substrate materials used for coating zinc oxide, which reduced the absorption of radiation. further, the nanograin of the different substrates differs in the value of the optical energy band [41–43]. in contrast, figure 21 shows no such peak for the uncoated transparent polymer slide, and the deflection begins at a wavelength of 310.5nm. the bandgap energy of the zinc oxide coated over a transparent glass slide was calculated with the help of the tauc plot method and found 3.68ev as in figure 22. figure 23: uv-visible spectrum of a thin film of zinc oxide coated over a translucent glass slide. figure 24: uv-visible spectrum of uncoated translucent glass slide. 3.3.3 uv-v is spectroscopy for translucent glass slide the uv-visible spectrum displayed in figure 23 reveals that the maximum peaks are observed at a wavelength higher than 331.5nm. however, the actual band gap wavelength of zno nanoparticles is known to be 388nm [38–40], which is higher than the measured value. this difference in the measured and actual values may be attributed to the subd. parajuli et al./ bibechana 20 (2023) 113-125 122 figure 25: the optical absorption coefficient (hv)2 of zinc oxide-coated translucent glass slide as a function of the photon. strate materials used for coating zinc oxide affecting the absorption processes of radiation. further, the nanograin of the different substrates differs in the value of the optical energy band [41–43]. conversely, figure 24 shows no such peak for the uncoated transparent polymer slide, and the deflection initiates at a wavelength of 331.5nm. the bandgap energy of the zinc oxide over a transparent polymer slide was found to be 3.59ev with the help of the tauc plot method as in figure 25. the actual wavelength, peak wavelength, and optical bandgap of zno thin film for different substrates are listed in table 1 and the computational values of zno are listed in table 2. table 1: actual wavelength, peak wavelength, and optical bandgap of zno thin film for different substrate. transparent polymer transparent glass translucent glass peak wavelength (nm) with a substrate 296 310.5 331.5 bandgap energy (ev) 3.77 3.68 3.59 actual wavelength of zno without substrate (nm) [38–40] 388 388 388 table 2: computational values of zno with different models. computational values of zno bandgap [44] 3.39 (hse) 3.57 ev gw 3.30ev zno wurtzite 4 conclusion the thin films of zinc oxide over different substrates were developed with the sol-gel spin coating method and characterized with the help of a uv-v is spectroscope. the wavelength bandgap of each substrate such as 296nm (polymer substrate), 310.5nm (for transparent glass substrate), and 331.5nm (for translucent glass substrate), and the band energy of zinc oxide coated over the different substrates is 3.77ev (transparent polymer slide), 3.68ev (transparent glass slide), 3.59 ev (translucent glass slide). the transparent polymer slide has the lowest wavelength bandgap and the translucent glass slide has the highest. the tauc plot method was used to calculate the bandgap energy. these results suggest that the choice of substrate can significantly impact the optical properties and performance of the zinc oxide thin film. the result is that the polymer is more transparent than the glass. so, we can incorporate polymers where more transparency is needed. this result can be applied in developing and optimizing zinc oxide thin films for various d. parajuli et al./ bibechana 20 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uvv is spectroscope study uv-v is spectroscopy for transparent polymer slide uv-vis spectroscopy for transparent glass slide uv-v is spectroscopy for translucent glass slide conclusion bibechana vol. 22, no. 3, december 2025, 266-279 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar assessing the antioxidant antibacterial and toxic potential of quercus floribunda lindl bark govinda bhattarai, dipak raj jaishi, and khaga raj sharma∗ central department of chemistry, tribhuvan university, kirtipur, kathmandu, nepal ∗corresponding author. email: khaga.sharma@cdc.tu.edu.np abstract since ancient times, herbal medical practitioners have been treating a wide range of conditions, from basic to life-threatening, with traditional or folk remedies. phytochemicals are incredibly helpful in defending against numerous diseases in human beings. due to their affordability and lack of side effects, herbal medicines have replaced synthetic drugs in many countries. the goal of the present study is to analyze the total phenolic content (tpc) and total tannin content (ttc) by the folin-ciocalteu method, total flavonoids content by the aluminum chloride method, dpph radical scavenging activity, evaluation of antimicrobial activity by agar-well diffusion method and evaluation of cytotoxic activity of crude extract. the dried bark of the quercus floribunda lindl was powdered, and then the extract was prepared in different solvents chosen based on their polarity using the cold maceration technique. among different crude extracts, ethyl acetate extract has a high tpc (127.23 ± 1.65 mg gae/g), and dichloromethane (dcm) has the lowest tpc (9.25 ± 0.69 mg gae/g). also, hexane extract shows high tfc (61.72 ± 4.01 mg qe/g), and ethanolic extract shows the least tfc content (3.97 ± 1.03 mg qe/g). furthermore, ethanolic extract had the highest ttc which is 49.91 ± 1.06 mg tae/g, and least ttc value in hexane extract which is 5.51 ± 1.3 mg tae/g. along with this, methanolic extract showed good antioxidant ability with ic50 of 12.70 ± 0.37 µg/ ml. in the case of the antimicrobial susceptibility test, the ethanolic and ethyl acetate extract of bark was found to be effective against escherichia coli (atcc 25912) with a zone of inhibition of 15 mm, equal to positive control, and neomycin. ethyl acetate extract is also found effective against shigella sonnei (atcc 25931) with a zone of inhibition of 22 mm. the minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) were also estimated in two different bacterial strains. for methanolic extract, the mic value for gram-positive staphylococcus aureus (atcc 43300) was 3.125 mg/ml, and gramnegative shigella sonnei was 3.125 mg/ml, and the mbc was 25 mg/ml for both strains. the methanolic extract shows good cytotoxicity against brine shrimp nauplii with lc50 of 40.55 µg/ml. thus, from the overall study, the bark of quercus floribunda lindl could be used as a natural source to isolate antibiotics and antioxidants. keywords quercus floribunda lindl, antimicrobial, antioxidant, cytotoxicity, phytochemistry. article information manuscript received: april 25, 2025; revised september 8, 2025; accepted: september 11, 2025 doi https://doi.org/10.3126/bibechana.v22i3.77948 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 266 http://nepjol.info/index.php/bibechana khaga.sharma@cdc.tu.edu.np https://doi.org/10.3126/bibechana.v22i3.77948 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ govinda bhattarai et al./ bibechana 22 (2025) 266-279 267 1 introduction nature is a remarkable indicator of the numerous phenomena of coexistence. the foundation for treating human illnesses is natural items derived from plants, animals, and minerals. right now, there is a growing demand for and acceptance of medicinal herbs. plants undoubtedly contribute significantly to ecosystems by offering vital services [1]. almost every region in the world has a remarkable history of using medicinal plants to benefit humankind. this amazing knowledge has been passed down from generation to generation by traditional healers. the deep understanding of this natural medicine paradigm has remained unchanged despite modernization and cultural changes. a new revolution in the treatment of diseases might undoubtedly be brought about by phytochemical research combined with pharmacological thinking in light of traditional uses [2]. significant medications like atropine, codeine, digoxin, morphine, quinine, and vincristine are derived from plants and the secondary metabolite components of those plants. plants have a long history of usage in both modern "western" medicine and some traditional medical systems [3]. humans could choose which plant tissues to consume based on their observation that certain plant tissues, such as fruit, leaves, or roots of certain species, improved their state of mind. aromatic and medicinal plants are a valuable source for creating novel medications and treating physical and mental health issues [4]. the pharmaceutical industry developed various commercial synthetic medications, the past was referred to as the "synthetic era". continuous usage of synthetic medications over time resulted in serious side effects and microbial resistance. large populations cannot pay the high cost of synthetic pharmaceuticals to profit from them. a worldwide movement has emerged in recent decades that has centered on green medicines because of their low side effects and affordability. the discovery of medicinal plants was crucial to the creation of modern herbal remedies because allopathy is unable to fully treat several illnesses, including cancer, liver disorders, and arthritis. when there are no adequate anti-diabetic, anti-inflammatory, anti-arthritic, or chemotherapy drugs available, the bioactive components of medicinal plants are utilized [5]. plant-based products are expected to be worth $83 billion globally, and this sector is still expanding. moreover, it is estimated that up to 60% of anticancer medications and about 25 % of contemporary drugs are derived from natural sources. the who estimates that between 65%-80% of people in underdeveloped nations currently use medicinal plants as a form of treatment. since just 15% of the world's 300,000 plant species have been assessed to establish their pharmacological potential. research highlighting the value and effectiveness of therapeutic plants is being conducted across the globe in a variety of nations at different stages of development [6]. according to the world health organization, a plant is considered medicinal if it contains chemicals that have therapeutic value or serve as precursors for the semi-synthesis of chemotherapeutic medications (who). plants consist of several parts, including leaves, stems, rhizomes, bark, seeds, flowers, and fruits. these plant sections consequently contain chemical substances that are useful for medicinal purposes [7]. according to bhattarai and ghimire, 143 species of commercial medicinal aromatics plants (maps) were evaluated from the himalayan gradient [8]. a total of 161 species of medicinal plants have been reported to be used by the tamang community in makwanpur district [9]. the meche people have been reported to use 64 plant species from the jhapa district [10]. quercus floribunda, also known as the tilonj oak, green oak, moru, or mohru oak, is a species of oak that is endemic to afghanistan, pakistan, nepal, and the western himalayas of india. it is usually found at elevations between 2,000-3,000 meters (6,6009,800 feet) above sea level. the tree is an evergreen and an important species for fuelwood and fodder, with a dense crown that reaches up to 30 meters (98 feet) [11]. quercus floribunda has a straight trunk that may grow up to 45 meters in height and 2 meters in diameter. it also has a dense crown. as the bark ages, it becomes dark grey or dark reddish brown and exfoliates in uneven woody scales. the bright green, 4-8 cm long, lanceolate to elliptic moru leaves can have smooth or spiky edges. catkins in male inflorescences are 8 cm long. the length of the female spikes is 4 cm. the fruit is an ovoid or oblong, brown, 2 cm long acorn with a sharp tip that grows alone on the branches from the previous year [12]. quercus species, commonly referred to as oaks, are a significant genus within the fagaceae family. it is found extensively in tropical climates and temperate woodlands in the northern hemisphere. numerous constituents have been employed in conventional medicine to address and prevent a range of human diseases, including diarrhea, ulcerative gastritis, asthma, hemorrhoids, and wound healing. bioactive chemicals, including triterpenoids, phenolic acids, and flavonoids, have been linked to a variety of biological activities, including antiinflammatory, antibacterial, hepatoprotective, antidiabetic, anticancer, gastroprotective, antioxidant, and cytotoxic properties [13]. the decoction or infusion include styptic, hemostatic, antibacterial, antifungal, and antiseptic efgovinda bhattarai et al./ bibechana 22 (2025) 266-279 268 fects. it is taken orally to treat conditions like severe diarrhea, dysentery, and hemorrhages. it is used topically on the outside to treat burns, wounds, and a range of skin disorders, hemorrhoids, and irritation of the anal, vaginal, and oral mucosa. it can also be used as a mouthwash to treat gum disease and toothaches. plant extracts can be used in lotions and ointments to aid in the healing of wounds [14]. the quercus species yields the wellknown acorn, which is used in traditional medicine together with bark and leaves. these parts of the plant are used as antiseptics or to treat gastrointestinal issues. both people and animals eat acorns because of their nutritional value. oak wood is valuable for its color, durability, and resistance to fungal deterioration in the wood industry as well as for wine maturation in oak barrels [15]. the analysis of phytochemicals and evaluation of biological properties of bark extracts, including antioxidant, antimicrobial, and toxicity against brine shrimp nauplii, have not been well reported yet. so, the proposed research work plays a significant role in fulfilling the research gap. the major phytoconstituents previously reported from the genus quercus are shown in figure 1 figure 1: structure of different phenolic compounds previously reported from quercus species. 2 materials and methods 2.1 chemicals ethyl acetate, hexane, dcm, ethanol, and methanol solvents were purchased from merck in germany and thermo fisher scientific in india. similarly, gallic acid and folin ciocalteu (fc reagent) and other chemicals from loba chemie. dimethyl sulfoxide (dmso) (silico research laboratory, india), acetic acid (control drug house, gujarat, india), quercetin, 2,2diphenyl-1-picrylhydrazyl (dpph) (srichem, maharashtra, india), potassium acetate (loba chemie, pvt ltd., mumbai, india), sodium carbonate anhydrous, tannic acid, ferrous nitrate, müller hinton broth (mhb), muller hinton agar (mha), and nutrient agar (na) growth nutrient agar were purchased from himedia lab, mumbai. 2.2 collection and identification of the plant based on the indigenous knowledge from the local user and literature survey, the plant was collected from the himali gaupalika bajura district at 2500m, latitude 29.53°n and longitude 81.67°e. after plant collection, the plant parts needed to be processed for the herbarium. the herbarium was created once the plant had fully dried and was taken to the national herbarium and plant laboratories in godavari, lalitpur, for identification. the plant was identified as quercus floribunda lindl by the national herbarium and govinda bhattarai et al./ bibechana 22 (2025) 266-279 269 plant laboratories. the voucher code is provided as kath163578. the photograph of the herbarium and collection sites of q. floribunda is shown in figures 2 and 3. figure 2: photograph of the herbarium of q. floribunda. figure 3: maps of sample-collecting sites.. the phytochemicals flavonoids, gallotannin, and ellagitannin were found in the aqueous bark extract of quercus acutissima. this plant could be used to block 5-reductase activity and testosterone-induced sebum synthesis in rats; it decreased androgenrelated pathogenes of acne, testosterone conversion, and sebum synthesis [16]. the methanolic extract of the same species contains phenolic acids and could show anticancer activity against breast cancer cell lines, cervical cancer cells, human t lymphocyte cells, human colon cancer cell lines, and human embryonic kidney cells [17]. the ethanolic leaf extract of quercus salicina blume depicts a vasodilatation effect on porcine coronary artery endothelium and good antioxidant activity [18]. the quercus sideroxyla shows antihyperglycemic activity, maintaining the glucose levels at more stable levels by inhibiting the -amylase enzyme [19]. the aqueous extract of the same species consists of gallic acid, catechin, epicatechin, procyanidins, and proanthocyanidins, and these phytochemicals show antioxidant activity [20]. 2.3 preparation of extract the bark of this plant was collected, cleaned, shade dried, sliced into small pieces, and dipped in six different solvents based on polarity: aqueous, methanol, ethanol, ethyl acetate, dcm, and hexane. after 72 hours, filtration was done using filter paper, and the solvents were re-suspended for 48 hours and consecutively for 24 hours one last time. every time, the filtrates were collected and concentrated under a vacuum in a rotatory evaporator at 40 °c. the extracts were collected in glass vials and stored at 4 ºc for future analysis. the following formula was utilized for the calculation of the yield percentage of the crude extract. 2.4 qualitative phytochemical analysis the presence of secondary metabolites, alkaloids, flavonoids, polyphenols, lignins, tannins, steroids, and saponins was determined by observing a color change in the chemical process, and phytochemicals found in different extracts were qualitatively identified by following the standard protocol [21]. 2.5 estimation of total phenolic content (tpc) the folin-ciocalteu colorimetric method was used to estimate the total phenolic content of plant extracts [22–24]. in triplicate, 96-well plates were loaded with 20 µl of plant extract, 100 µl of 10% fc reagent (1:10), and 80 µl of 1m na2co3. before an intense blue color was noticed, the reaction mixture was left to incubate at room temperature for 30 minutes. finally, absorbance at 765 nm was measured using a spectrophotometer. the total phenolic content (tpc) was measured in milligrams of gallic acid equivalent (mg gae/g) per gram of extract dry weight, and the standard curve was created, which is the standard curve for gallic acid (7.5100 µg/ml). 2.6 estimation of total flavonoid content (tfc) the total flavonoid content was estimated by using the aluminum chloride method as described by ahmed et al. [24, 25]. in triplicate, 96-well plates govinda bhattarai et al./ bibechana 22 (2025) 266-279 270 were loaded with 20 µl of plant extract, 100 µl of distilled water, and 60 µl of ethanol, followed by 10 µl of 10% alcl3 solution and 10 µl (1m) ch3cook solution. at room temperature, the reaction mixture was incubated for half an hour. then, using a spectrophotometer, absorbance was measured at 415 nm. a standard calibration curve for quercetin (10-100 µg/ml) was developed and quantified in milligrams of quercetin equivalent per gram of the dry weight of the extract (mg qe/g). 2.7 estimation of total tannin content (ttc) the folin-ciocalteu colorimetric method was used to estimate the total tannin content by applying the standard protocol [26]. tannic acid concentrations ranged from 7.5 to 100 µg/ml, and 10 µl of plant extract was added to 96-well plates. then, 50 µl of 10% fc reagent and 70 µl of distilled water were added, and a microplate reader was used to capture the initial reading at 725 nm. after that, 70 µl of 35% na2co3 was injected following the first measurement. the ultimate absorbance of the 96-well plate was measured at 725 nm after it had been incubated for 30 minutes. ttc was expressed as mg tae/g. 2.8 evaluation of antioxidant activity the antioxidant activity of crude plant extract was evaluated by following a standard protocol [27,28]. the crude plant extract was diluted serially up to the required concentrations, but the positive control quercetin was serially diluted up to 0.625 µg/ml from 20 µg/ml concentrations. in triplicate, 100 µl of plant extracts and a positive control were added to 96-well plates. the first reading was then obtained at 517 nm. after that, each well received 100 µl of dpph reagent, which was then incubated for 30 minutes. at 517 nm, the ultimate absorbance was measured. because methanol and 50% dmso were employed as negative controls. the following formula was used to evaluate radical scavenging activity: radical scavenging capacity = ( acontrol −asample acontrol ) × 100 (1) where, acontrol = absorbance of control, asample = absorbance of sample. inhibitory concentration (ic50) was calculated by using graphpad prism (version 8.0.2.263). 2.9 evaluation of antimicrobial activity the agar well diffusion method was applied to perform an antibacterial activity using mueller-hinton agar (mha) plates [29, 30]. the test microorganisms, escherichia coli, klebsiella pneumonae, staphylococcus aureus, and shigella sonnei, were cultivated in mueller-hinton broth (mhb) and incubated for 24 hours at 37 ºc. its turbidity was maintained at 0.5 mcfarland. 50 µl of plant extract, 50% dmso as the negative control, and 50% neomycin as the positive control were added to each well created by a cork borer. the petri plates were incubated for 18 to 24 hours at 37 °c after being left for 15 minutes to allow for diffusion. after incubation, the zone of clearing was measured and tracked. 2.10 of minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) the minimum inhibitory concentration (mic) and minimum bactericidal concentration were determined by following the standard protocol as described [31]. a final concentration of 106 cfu/ml was obtained for the bacterial inoculum by diluting the 0.5 mcfarland turbidity culture in mhb 1:100. each well of the 96-well plates received an injection of 5 µl of bacteria. the positive control was a popular drug called neomycin. a sterile lid was placed over the plate, and it was incubated at 37 °c for 20 to 24 hours. 0.003% resazurin was added to the microtiter plate wells, and the mixture was incubated at 37 °c for three to four hours. while the wells without infection remained blue, the wells with bacterial growth became pink. the lowest concentration at which bacterial growth is inhibited was determined to be the extract's minimum inhibitory concentration (mic). the mic and mbc of the crude plant extracts were ascertained by streaking the well contents onto nutrient agar plates and then incubating them at 37 °c for over 18 hours. 2.11 brine shrimp lethality assay (bsla) the toxicity of plant extracts was determined by following a standard protocol [32]. by adding 1m naoh, the ph of the artificial sea salt water was kept between 8 and 8.5. different quantities of the plant extract, including 1000, 800, 500, 250, 100, and 10 µg/ml, were diluted. each test tube was then filled with 4 ml of artificial seawater. 10 nauplii and 500 µl of sample were then added in triplicate to each test tube. the positive control was a potassium dichromate solution, while the negative control was artificial sea salt water. after 24 hours, the number of dead nauplii in a test tube was counted, and the following formula was used to calculate the % mortality of nauplii: using the probit value table, the linear equation can be obtained as y = mx+c, where y is the progovinda bhattarai et al./ bibechana 22 (2025) 266-279 271 bit value at 50% mortality, m is the variable, and c is the intercept. x is the lethal concentration, and finally, the lethal concentration (lc50) was calculated. 2.12 statistical analysis the data was collected by using a gen5 microplate reader. data analysis was carried out by using microsoft excel. tpc, tfc, and ttc were reported as the mean ± standard deviation. mean ± standard error reported for antioxidants. half maximal inhibitory concentrations (ic50) were calculated by using graph pad prism (version 8.0.2.263). the comparisons were made by using a one-way anova test. values with p < 0.05 were considered statistically different. 3 results 3.1 percentage yield the highest yield percentage was found in the aqueous extract, which is 15.24% followed by methanol (11.29 %), ethanol (9.53 %), ethyl acetate (3.35 %, dcm (0.71 %), and the lowest yield percentage of 0.4% in hexane extract. this is because the aqueous solvent is more polar than other solvents, and the bark might contain highly polar compounds. the bar diagram of the % yield of different solvent extracts is shown in figure 4. figure 4: showing the yield percentage in different solvent extracts. 3.2 qualitative phytochemical analysis qualitative phytochemical screening of different solvent extracts of q. floribunda is shown in table 1. table 1: qualitative phytochemical screening of plant extracts. phytochemicals test aqueous methanol ethanol ethyl acetate dcm hexane alkaloids dragendorff’s test + + + + + carbohydrates molish’s test + + + + + protein test biuret test flavonoids alkaline reagent test + + + + terpenoids salkowski’s test + + + + tannins braymer’s test + + + + phenolic test fecl3 test + + + + anthraquinones borntrager’s test + + + + note: (+) = present, (-) = absent. 3.3 total phenolic content (tpc) the tpc of this plant ranges from 127.23 ± 1.65 mg gae/g to 9.25 ± 0.69 mg gae/g (figure 5). the bark of quercus floribunda lindl showed the highest tpc value in ethyl acetate extract (127.23 ± 1.65 mg gae/g) followed by aqueous (123.23 ±4.28 mg gae/g), methanol (111.13 ± 1.55 mg gae/g), ethanol (93.65 ± 2.23 mg gae/g), and hexane (9.29 ± 0.26 mg gae/g), and least value in dcm (9.25 ± 0.69 mg gae/g). the tpc values are significantly different from each other at p < 0.05. the calibration curve is shown in figure 6. 3.4 total flavonoid content (tfc) the tfc of q. floribunda ranges from 61.72 ± 4.01 mg qe/g to 3.97 ± 1.03 mg qe/g (figure 7). the plant quercus floribunda lindl possesses the highest flavonoids in hexane extract (61.72 ± 4.01 mg qe/g), followed by dcm (50.21 ± 0.93 mg qe/g), aqueous (6.98 ± 0.93 mg qe/g), ethyl acetate (6.12 ± 1.47 mg qe/g), methanolic (4.08 ± 0.67 mg qe/g), and the lowest value in ethanol extract (3.97 ± 1.03 mg qe/g). values are significantly different from each other at p < 0.05. the calibration curve of quercetin is shown in figure 8. 3.5 total tannin content (ttc) the ttc of quercus floribunda lindl ranges from 49.91±1.06 mg tae/g to 5.51±1.3 mg tae/g. the maximum ttc was found in ethanolic extract (49.91±1.06 mg tae/g), followed by methanolic extract (49.51±3.33 mg tae/g), ethyl acetate (47.35±1.69 mg tae/g), aqueous (37.27±2.96 mg govinda bhattarai et al./ bibechana 22 (2025) 266-279 272 tae/g), dcm (14.78±1.39 mg tae/g), and the least content in hexane extract (5.51±1.3 mg tae/g) (figure 9). values are significantly different from each other at p < 0.05. the calibration curve of tannic acid is shown in figure 10. figure 5: standard calibration curve of gallic acid.. figure 6: total phenolic content in the various solvent extracts. figure 7: standard calibration curve of quercetin. figure 8: total flavonoid content in various extracts. 3.6 antioxidant activity the dpph free radical inhibition by various plant extracts was shown through a graphical representation (figures 11 and 12). based on the result obtained in the bark of quercus floribunda lindl possesses good antioxidant activity. among the different extracts, the methanolic extract shows good antioxidant activity with an ic50 of 12.70 ± 0.37 µg/ml, followed by ethanolic extract ( 17.08 ± 0.48 g/ml), ethyl acetate (21.38 ± 0.66 g/ml), and aqueous extract had the least antioxidant potential, with its ic50 of 29.31±1.24 µg/ml. the antioxidant potential of dcm and hexane extract is weak (> 500). antioxidant values are significantly different from each other at p < 0.05. the bar diagram of ic50 of different solvent extracts of this plant is shown in figure 13. 3.7 antimicrobial activity the result showed the minimum zone of inhibition for the dcm and hexane extract, which confirmed their least anti-bacterial activity. in comparison to the positive control (neomycin), the aqueous extract also does not show a good zone of inhibition. the aqueous extract showed a good zone of inhibition for e. coli 10 mm and staphylococcus aureus 15 mm. methanolic (14 mm), ethanolic (15 mm), and ethyl acetate (15mm) extracts showed a good zone of inhibition in e. coli, which is exactly the same as a positive control (15mm). methanolic and ethanolic extracts showed the same zone of inhibition (20mm) against staphylococcus aureus, whereas for the same bacteria, the positive control showed 25 mm of zoi. for klebsiella pneumoniae, methanol, ethanol, and ethyl acetate showed comparable zoi of 15 mm, 16 mm, and 16 mm, respectively, and the positive control showed 28 mm of zoi for the same bacteria. in the same manner for shigella sonnei, ethyl acetate extract showed a good zoi of 22 mm, whereas the positive control showed 25 mm. also, methanolic and ethanolic exgovinda bhattarai et al./ bibechana 22 (2025) 266-279 273 tracts showed comparable zoi of 19 mm and 20 mm, respectively. the antibacterial activity of different solvent extracts in terms of zoi is shown in table 2. figures 14 and 15 are the test slides against different microorganisms. table 2: zone of inhibition (zoi mm) shown by various extracts of quercus floribunda lindl against different bacteria and neomycin as a positive control. crude extract shigella sonnei klebsiella pneumoniae staphylococcus aureus escherichia coli aqueous 14 9 15 10 methanol 19 15 20 14 ethanol 20 16 20 15 ethyl acetate 22 16 18 15 dcm 12 12 11 8 hexane 9 9 9 9 positive control 25 28 25 15 negative control figure 9: standard calibration curve of tannic acid. figure 10: total tannin content in various extracts of quercus floribunda lindl. figure 11: standard curve of dpph inhibition by quercetin. figure 12: plot of dpph inhibition against the concentration of (a) aqueous extract, (b) ethyl acetate extract, (c) methanol extract, and (d) ethanol extract. govinda bhattarai et al./ bibechana 22 (2025) 266-279 274 figure 13: bar diagram showing the antioxidant potential of bark crude extracts in different solvents at various concentrations. figure 14: the zoi shown by the aqueous extract against the bacterial strains. sa = staphylococcus aureus, kp = klebsiella pneumoniae, e. coli = escherichia coli, ss = shigella sonnei figure 15: zoi of methanol, ethanol, ethyl acetate, dcm, and hexane extract against different bacterial strains. meoh = methanol extract, ss = shigella sonnei, etoh = ethanol extract, sa = staphylococcus aureus ea = ethyl acetate extract, kp = klebsiella pneumoniae, dcm = dichloromethane extract, e.coli = escherichia coli, pc = positive control, nc = negative control 3.8 minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) methanolic extract showed the mic and mbc value for both bacterial strains (3.12 mg/ml and 25 mg/ml, respectively, where the positive control (neomycin) shows mic 0.78 mg/ml for both bacterial strains. the mbc value was 6.25 mg/ml for shigella sonnei and 3.12 mg/ml for staphylococcus aureus for neomycin. ethanolic extract showed mic against staphylococcus aureus and shigella sonnei was 1.65 mg/ml, but mbc was different for staphylococcus aureus, 25 mg/ml, and more than 25 mg/ml for shigella sonnei. the mbc was more than 25 mg/ml for shigella sonnei by ethanolic extract because the bacterial growth in the petri dish was not completely inhibited or killed, so more than 25 mg/ml will be the required concentration to kill the bacteria completely. similarly, for ethyl acetate extract, it was found that 3.125 mg/ml. mic value for shigella sonnei and 1.652 mg/ml for staphylococcus aureus, and for both bacterial strains, the mbc value was 25 mg/ml. table 3 depicts the mic and mbc of different solvents against two bacteria. the results of mic and mbc are shown in figure 16. table 3: mic and mbc values of different extracts for gram-positive (staphylococcus aureus) and gramnegative (shigella sonnei). extract type mic (mg/ml) mbc (mg/ml) shigella sonnei staphylococcus aureus shigella sonnei staphylococcus aureus methanol 3.125 3.125 25 25 ethanol 1.562 1.562 >25 25 ethyl acetate 3.125 1.652 25 25 positive control 0.781 0.781 6.25 3.125 govinda bhattarai et al./ bibechana 22 (2025) 266-279 275 3.9 brine shrimp lethality activity (bsla) the percentage mortality along with the lc50 of the methanolic extract is shown in table 4. the methanolic extract had good lethal potential against brine shrimp nauplii. from bsla, the lc50 value for the methanolic extract was found to be 40.55 µg/ml. a plot of probit against log c is shown in figure 17. table 4: brine shrimp activity for the methanolic extract of the plant sample. extract type concentration (µg/ml) surviving nauplii after 24 h mortality % lc50 value (µg/ml) methanol 1000 24 80.00 40.55 800 17 56.66 500 22 73.33 250 20 66.66 100 16 53.33 10 12 40.00 figure 16: showing mic and mbc values of three different extracts (methanol, ethanol, and ethyl acetate) along with the positive control (neomycin). figure 17: a plot of probit against log c. 4 discussion all the species of quercus floribunda lindl are useful medicinal plants. the different parts of quercus species are used in various treatments, where the bark of this species is used as an astringent, antiarthritic, and for other disorders [13]. since there is no more work in pharmacognosy of this species, my research mainly focuses on the bark of the quercus floribunda lindl plant, which is widely distributed in the range of the himalayas (25003000 m), nepal. different extraction solvent shows different yield percentages. the aqueous yield is maximum, showing maximum polar constituents in the bark of this plant, and minimum in hexane, showing minimum presence of non-polar compounds in the bark. this study found the same result, where the yield was maximum in the polar solvent. according to this study, to improve extraction efficiency, a combination of polar and nonpolar solvents should be used [33]. in this species, there is no specific research related to this work, so the data are correlated with other species of the same genus. in phytochemical screening of the bark of quercus floribunda lindl, it was found that the bark of the plant is highly rich in different classes of bioactive compounds, alkaloids, flavonoids, steroids, tannins, carbohydrates, and saponins. this result can be correlated to the study carried out in different species of the quercus genus by different researchers [34]. the bark of quercus gluca contains tannins, carbohydrates, saponins, phenols, and quinones, which make it a medicinally active plant. also, according to [13], the quercus genus contains various classes of compounds such as glycosides, terpenoids, flavonoids, phenolic acids, fatty acids, sterols, and tannins. the bark of quercus floribunda lindl had the highest tpc value in ethyl acetate extract (127.23 ± 1.65 mg gae/g), with the lowest value in dcm (9.25 ± 0.69 mg gae/g). there is no more significant difference in tpc value between the dcm and hexane extracts. also, the study finds ethanol extract had the lowest tfc value (3.97 ± 1.03 mg qe/g), and hexane had the maximum value (61.72 ± 4.01 mg qe/g). the bark of quercus floribunda lindl shows the maximum ttc in aqueous extract (37.27±2.96 mg tae/g) and the least in hexane extract (5.51±1.3 mg tae/g). there is no specific research conducted on this species within this solvent and bark, so it is difficult to correlate the data. thus, the data were correlated with different species of the same genus and another part of the bark in the same plant. a study conducted by ahmad et al. 2023 [35] on aerial part leaves and galls found the maximum tpc value and tfc value in acetonic extract, 66.9 ± 0.05 g gae/mge govinda bhattarai et al./ bibechana 22 (2025) 266-279 276 and 38.4 ± 0.72 g qe/mge, respectively. thus, the bark of q. floribunda lindl has more phenolic and flavonoid content than the aerial part. a study conducted in the bark of q.faginea by ferreira et al. 2018 [36] found maximum tpc (630.3 mg gae/g), tfc(207.7 mg catechin equivalents (ce)/g), and tannin (220.7 mgce/g) in ethanol-water extract. this shows that the bark of q. faginea contains more phenolic compounds, flavonoids, and tannins. among six solvent extracts, the methanolic extract shows good antioxidant activity with an ic50 of 12.70 ± 0.372 µg/ml, followed by ethanol, ethyl acetate, and aqueous. the ic50 value for the crude extracts of dcm and hexane was greater than 500 µg/ml, indicating a low level of antioxidant activity in these extracts. according to the research carried out by ferreira et al. 2018 [36] in the bark of q. faginea ic50 was 2.6 µg/ml in polar ethanol-water extract, showing more antioxidant activity in comparison to q. floribunda lindl. this variation in results is due to climatic conditions, altitude variation between the collected samples, and correlated species from the literature. the value reported by sánchez-burgos et al., 2013 [37] for anti-oxidant activity in leaves of different species (q. resinosa, q. grisea, q. laeta, and q.obtusata) ranges from 150 – 450 µg/ml, which is more than compared to aqueous extract (29.31±1.24 µg/ml) of quercus floribunda lindl. this data shows the bark of quercus floribunda lindl is more antioxidant than the above-mentioned plants. from the antibacterial study in the bark of quercus floribunda lindl, it was found that the gram-negative e. coli was inhibited equally by ethanol and ethyl acetate, with a zoi of 15 mm, exactly as a positive control. this shows the bark of this plant is a potent source of antibiotics against e. coli. for gram-positive staphylococcus aureus, methanolic and ethanolic extracts show a zoi of 20 mm, a minimal zone of inhibition for hexane extract and dcm, confirming their low levels of antibacterial activity. a poor zone of inhibition is also seen in the aqueous extract when compared to the positive control (neomycin). the bark of quercus floribunda lindl shows antibacterial activity. there is no exact paper to correlate the anti-microbial result. of this species, but it was found by sarwar et al., 2015 [38] that the leaves of q. incana have significant antibacterial activity for both gram-positive and negative. the n-butanol extract of leaves shows 32 mm and 28 mm zoi against a.niger and a. flavus, respectively also 19 mm for micrococcus leuteus. this data shows that the quercus genus has good antibacterial properties. this supports the bark of quercus floribunda lindl also acts as a good source of antibiotics. similarly, according to iqbal et al., 2023 [33], the bark of q. glauca shows good antibacterial properties, whereas the methanolic extract shows a maximum zoi of 13.33mm against klebsiella pneumoniae, which is similar to the methanolic extract of the bark of quercus floribunda lindl. (15 mm). mic and mbc values were determined for gram-positive (staphylococcus aureus) and gram-negative (shigella sonnei) bacteria. for both bacterial strains, methanolic extract demonstrated the same mic values and mbc values for both strains (3.125 mg/ml and 25 mg/ml, respectively). ahmad et al., 2023 [35] found that nuts of quercus floribunda lindl are moderately cytotoxic against brine shrimp nauplii. this investigation revealed that methanolic extract from the bark of quercus floribunda lindl exhibits good toxicity against brine shrimp nauplii with an lc50 of 40.55 µg/ml. 5 conclusion phytochemical screening in the bark of quercus floribunda lindl revealed that the bark extract included phenol, flavonoids, tannins, terpenoids, carbohydrates, and alkaloids. it was based on the result of yield percentage and phytochemical screening for the extraction process; methanol, ethanol, and ethyl acetate are good solvents. the results of the comparison of tpc, tfc, and ttc of six different crude extracts found the highest tpc in ethyl acetate and the lowest in dcm. the tfc was highest in hexane and lowest in ethanolic extract. likewise, the ttc value was highest in the aqueous extract and the lowest in the hexane extract. on the evaluation of the antioxidant activity of various crude extracts of quercus floribunda lindl’s bark, the methanolic extract shows good antioxidant properties, followed by ethanol, ethyl acetate, and aqueous extract. as a consequence, this finding has demonstrated that the presence of phenols' antioxidant activity is directly related. dcm and hexane extract were found to be less potent for scavenging free radicals. so, from the above-mentioned results of methanolic, ethanolic, and ethyl acetate extracts, it was concluded that these extract shows good antimicrobial activity and toxicity assay. ethanol and ethyl acetate showed a good zone of inhibition for e. coli, which is equal to the positive control, neomycin. methanolic and ethanolic extracts showed a maximum zone of inhibition for staphylococcus aureus, about the positive control, neomycin. for klebsiella pneumoniae, all three extracts showed moderate zoi in comparison to the positive control, neomycin. ethyl acetate extract showed maximum zoi for shigella sonnei. these extracts showed comparable zones of inhibition for different bacteria. from the calculation of mic and mbc of these three extracts against shigella sonnei and staphylococcus aureus, it was govinda bhattarai et al./ bibechana 22 (2025) 266-279 277 concluded that for the methanolic extract, the minimum required concentration to inhibit was 3.125 mg/ml for both bacteria, and to kill the bacteria completely, the required concentration bacterial growth. the mic and mbc values are also comparable for these three extracts. from all these results, it was concluded that the methanolic extract is more potent for the toxicity assay. therefore, further research is necessary to completely comprehend this plant's medical potential. this plant has a wide range of biological properties, so this plant has great biological importance and could be used as a source of natural antimicrobial and antioxidant agents. abbreviations dmso: dimethyl sulfoxide gae/g: gallic acid equivalent per gram qe/g: quercetin equivalent per gram tae/g: tannic acid equivalent per gram tpc: total phenolic content tfc: total flavonoid content ttc: total tannin content ic50: half-maximum inhibitory concentration dpph: 2,2-diphenyl-1picrylhydrazyl zoi: zone of inhibition mic: minimum inhibitory concentration mbc: minimum bactericidal concentration lc50: lethal concentration 50% funding statement this research did not receive any financial support and was conducted through the independent efforts of the authors. conflicts of interest the authors declare that there are no conflicts of interest associated with the publication of this research paper. author’s contribution • govinda bhattarai: performed laboratory work, writing, review, editing, and original draft. • dipak raj jaishi: writing, reviewing, formal analysis, and editing • khaga raj sharma: writing, reviewing, editing, supervision, and conceptualization acknowledgments the authors express their gratitude to the national herbarium and plant laboratories, godawari, nepal, for their assistance in the identification of the plant. references [1] f. jamshidi-kia, z. lorigooini, and h. aminikhoei. medicinal plants: past history and future perspective. journal of herbmed pharmacology, 7(1):1–7, 2017. 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[38] r. sarwar, u. farooq, a. khan, s. naz, s. khan, a. khan, a. rauf, h. bahadar, and r. uddin. evaluation of antioxidant, free radical scavenging, and antimicrobial activity of quercus incana roxb. frontiers in pharmacology, 6:277, 2015. introduction materials and methods chemicals collection and identification of the plant preparation of extract qualitative phytochemical analysis estimation of total phenolic content (tpc) estimation of total flavonoid content (tfc) estimation of total tannin content (ttc) evaluation of antioxidant activity evaluation of antimicrobial activity of minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) brine shrimp lethality assay (bsla) statistical analysis results percentage yield qualitative phytochemical analysis total phenolic content (tpc) total flavonoid content (tfc) total tannin content (ttc) antioxidant activity antimicrobial activity minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) brine shrimp lethality activity (bsla) discussion conclusion bibechana vol. 22, no. 3, december 2025, 215-222 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar first-principles investigation of graphitic carbon nitride (gcn)monolayer embedded with transition metals (ni, pd, and pt) as a no sensor guna nidhi poudel, pitamber shrestha, narayan prasad rijal, shree ram sharma, leela pradhan joshi, rajendra parajuli∗ department of physics, amrit campus, tribhuvan university, kathmandu, nepal ∗corresponding author. email: rajendra.parajul@ac.tu.edu.np abstract adsorption of nitric oxide on ni, pt, and pd-embedded graphitic carbon nitride (gcn) has been studied computationally using density functional theory. transition metal (tm) embedded in gcn exhibits significantly higher adsorption energy compared to pristine gcn. this study finds that pt-embedded gcn shows a high adsorption energy of -4.560 ev, which is greater than that of other tm-embedded gcns. while no gas showed physisorption on the pristine gcn, it exhibited strong chemisorption on the tm-embedded systems. when functional transitional metals are embedded on its surface, along with the adsorption of no, new energy states are introduced near the fermi surface, which modifies the electronic properties of the system. also, the changes in the band states of the system are noticed. furthermore, non-magnetic gcn is found to be magnetic when pt is embedded in it. keywords dft, graphitic carbon nitride (gcn), electronic and magnetic properties, adsorption. article information manuscript received: november 24, 2024; revised july 29, 2025; accepted: august 3, 2025 doi https://doi.org/10.3126/bibechana.v22i3.71498 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the rapid growth of industrialization and vehicles around the globe has been one of the major sources of pollutant gasses such as co, no2, so2, o3, no, etc., and no [1] is considered one of the most threatening ones. this gas affects the environment heavily and negatively impacts the ecological balance and human health [2]. as the concentration of no [3] in the atmosphere has increased rapidly over the past few years, it has been tantamount to developing a cheap, environment-friendly, and efficient technique to remove or at least effectively reduce such a pollutant gas from the atmosphere. several attempts have been made to address this problem using catalytic processes and various other techniques [4]. however, the effectiveness of these approaches remains highly uncertain. materials that possess properties such as chemical inertness, hardness, high surface area, and a tunable band gap have shown promise in adsorbing pollutants like nitric oxide (no). graphitic carbon nitride (gcn), a two-dimensional and layered material composed of carbon and nitrogen atoms, is found to have those 215 http://nepjol.info/index.php/bibechana rajendra.parajul@ac.tu.edu.np https://doi.org/10.3126/bibechana.v22i3.71498 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ guna nidhi poudel et al./ bibechana 22 (2025) 215-222 216 properties. a graphitic carbon nitride (gcn) sheet is composed of carbon and nitrogen atoms with sp2 hybridization [5, 6] where the bond of partial n atoms is connected with two neighbors, and the c atom remains unsaturated [7, 8]. this enables it to adsorb foreign elements, molecules, etc. to gain stability. there are two types of structures of gcn, tri-s-triazine (c6n7) and triazine (c3n3), of which the former is the stable structure, and because of this, gcn nanosheets have been reported in the literature with remarkable interest concerning their adsorption behavior, catalysis, and photo catalysis [9, 10]. the space between the triazine group in gcn is the important center for the trapping of the cations, transitional metal, and the molecule with large radii inside it [11]. figure 1: the optimized structure of unit cell of gcn. d.k. gorai et al. [2] studied the adsorption behavior of no gas over os, ir, and pt embeddedgcn by vasp software with pbe-gga exchange correlation. they have found that no is adsorbed physically with gcn but chemically with os, ir, and pt-embedded gcn. they concluded that the ir-embedded gcn can be considered a promising candidate for sensing no gas and its elimination from the atmosphere. basharnavaz et al. [3] studied fe, ru, and os-embedded gcn for the no gas sensor by using the quantum espresso simulation package. these authors found that os -osembedded gcn is the promising candidate for the elimination of the no gas from the environments as compared to the other two metals-embedded gcn. xu et al. [12] studied the adsorption behavior and electronic states of poisonous gas molecules, like hcn, so2, h2s, and no, on gcn and mo atomembedded gcn. further, the study of charge transfer analysis in their report indicates that h2s acts as a donor, while hcn, so2, and no act as acceptors. density of states (dos) study shows that hcn, so2, and h2s make the system inclined towards semimetallic, while the adsorption of no onto moembedded gcn contributes to smaller magnetic properties. furthermore, basharnavaz et al. [13] reported the adsorption properties of so2 gases over the transition metal/p–codoped gcn with quantum espresso software. also, they reported that in transition metal (co, rh, and ir), ir/p–codoped system with the highest eads i.e. 3.52 ev can be effectively used for the removal and sensing of so2 gas from the polluted environment. similarly, to explore high photocatalytic activity gu et. al. [14] adopted the carbon vacancies and hydroxyls in gcn. the authors found from both computational and experimental characterization that the removal of photocatalytic no from the ch-cn nanosheet was heavily attributed to the synergistic effects of carbon vacancies and hydroxyls. metals such as ag-, li-, na-, and k-doped gcn demonstrate the highest adsorption energy for no2 as investigated by zhang and co-workers [15] by using the dmol3 package. they concluded their research by alluding that ag-, li-, na-, and k-doped gcn are potential candidates for gas molecule sensors with unique and high sensitivity for no2. furthermore, basharnavaz et al. [16] investigated no2 adsorption behavior on co, rh, and ir-embedded gcn, whereas transition metal-embedded gcn shows chemisorption of no2 gas with dramatic changes in conductivity and a large reduction in band gap energy. their result shows that the wrinkle structure of tm-embedded gcn is found to exhibit a sharp close peak near the fermi level and the huge amount of charge transferred from d -orbitals of the tm atoms to p orbitals of no2 gas. apart from the above-mentioned reports, gcn as an adsorbent with various adsorbates, including metal embedded gcn, has been documented in many literature. in one of the previous works [2], it has been extensively studied for pt-embedded gcn; however, ni and pd-embedded gcn monolayers as no gas sensors have not been reported so far. our main objective in this paper is to compare pt-embedded gcn as a no sensor with the aforementioned relevant reports and to perform similar types of work with pd and ni-embedded gcn. 2 computational details ab initio calculations have been performed by vienna ab initio simulation package (vasp) [17] with generalized gradient approximation (gga) by using exchange-correlation functional perdewburke ernzerhor (pbe) [18]. the k-point sampling of the brillouin zone was obtained using a 5×5×1 grid centered at the gamma (γ) point using the monkhorst pack scheme [19]. to depict the interactions between ion cores and valence electrons, we utilized the paw potential as a pseudopotential [20, 21]. kinetic energy cutoff 550ev is set up for plane-wave basis set expansion, limiting the total number of plane waves in calculations. we maintained system stability by implementing a convergence constraint of 107 ev in energy difference between successive self-consistent total energy calculation. guna nidhi poudel et al./ bibechana 22 (2025) 215-222 217 table 1: band gap (eg) in ev, adsorption energy (eads) in ev, magnetic moment (mtot) in µb , the distance between n and o (dn–o) in å, the distance between tm = ni, pd, pt and n of no (dtm–n) in å, the distance between tm = ni, pd, pt and nedge of gcn (dtm–ned) in å. property eg (ev) eads (ev) mtot (µb) dn–o (å) dtm–n (å) dtm–ned (å) no – – – 1.170 – – gcn 1.300 – – – – – gcn-ni 0.710 – – – – 1.83 gcn-pd 0.150 – – – – 2.00 gcn-pt 0.120 – 1.4000 – – 1.92 gcn-pt [2] 0.068 – 1.6641 – – 2.384 gcn-no 1.120 -0.807 – 1.171 – – gcn-ni/no 0.540 -4.270 0.0000 1.173 1.60 1.87 gcn-pd/no 0.100 -4.386 0.0000 1.175 1.72 2.03 gcn-pt/no 0.090 -4.560 0.0001 1.180 1.76 2.04 gcn-pt/no [2] 0.000 -4.790 0.0004 1.182 1.742 2.207 after applying these criteria, all atoms in the structures were allowed to relax, and subsequent calculations were carried out. however, the tetrahedron method was used to compute the band structure and density of state (dos) calculations. for band structure computations, a set of 50 k-points was specifically chosen to span the high-symmetry points connecting the reciprocal space. this selection allows for a detailed analysis of how the energy bands evolve along this path in reciprocal space. to perform density of state calculations, the reciprocal space k point grid (20 × 20 × 1) was selected. the adsorption energy eads for the adsorption of no gas over the gcn system is calculated from: eads = egcn−no − (egcn + eno) (1) where egcn-no is the total energy of gcn with no, egcn is the total energy of gcn and eno is the total energy of an isolated no gas. similarly, eads for adsorption of no gas over tm (ni, pd, pt)-gcn system is calculated from: eads = etm−gcn−no − (egcn + eno + etm ) (2) where etm--gcn -no is the total energy of tmgcn with no, egcn is the total energy of gcn, eno is the total energy of an isolated no gas and etm is the energy of transition metal. a negative value is related to the exothermic process, and the adsorption process becomes thermodynamically stable. 3 results and discussion the previous studies illustrated that the heptazinebased structure is more favorable than the triazinebased structure [22,23]. the optimized structure of pristine gcn is shown in fig. 1. the structure of the unit cell contains three types of n atoms, such as nedge, ninner, and nbridge, and two types of c atoms, such as cinner and cbridge, as shown in fig. 1. the optimized value of the lattice constant was obtained to be 7.1 å, which is comparable to experimental and theoretical findings reported in the literature [2, 3, 24,25]. in a 2 × 2 supercell, there are vacancies between 4 unit cells where different atoms and molecules can be embedded. to prevent interlayer interactions, a substantial vacuum distance of 18 å was implemented along the z direction. the relaxed structures of pristine gcn, ni, pd, and pt-embedded gcn, and ni, pd, and pt-embedded gcn with adsorbed no gas are shown in fig.2. from this figure, it is observed that the pd and pt atoms are placed almost at the middle position (symmetrical place) of the gcn, whereas the ni atom is almost asymmetrically placed in the gcn. this may be because the atomic radii of the pd and pt are greater than those of the ni atom, which form a strong bond with the n atom of gcn. in addition, it is observed that the nitrogen atom of the no gas is positioned above the vacancy site of the pristine gcn. at this site, the optimization energy is higher than at other possible positions of no. furthermore, the optimized structures show that the adsorption of no gas on the gcn and tm-gcn system contributes to the structural distortion, and also noticeably changed shape of the systems from planar structure to buckled structure as the buckled structure is more stable than the planar structure [26]. the adsorption energy for the no gas on pristine gcn and ni, pd, and pt-embedded gcn were calculated using eqs.1 and 2. the values thus obtained are presented in the third column of table 1, and they are found to be 0.807, 4.270, 4.386, 4.560 ev for the no gas on pristine gcn and ni, pd, and pt embedded gcn respectively. in the last row of table 1, nearly the same result has been reported by gorai et al. [2] for pt-embedded gcn. based on this result, it can be inferred that the no gas on gcn has low adsorption energy, whereas the guna nidhi poudel et al./ bibechana 22 (2025) 215-222 218 no gas on pt-embedded gcn has the highest adsorption energy. the adsorption energy is higher in the case of pt-embedded gcn due to strong electronic hybridization between the pt-5d orbitals and the n-2p states gcn. this acceptor-donor interaction leads to significant charge transfer from the metal’s d-orbitals to the no molecule, thereby enhancing the adsorption energy. in contrast, for pdembedded and ni-embedded gcn, the d-orbitals are either fully occupied (pd: 4d10) or more localized (ni: 3d8), which limits their capacity for effective back-donation to the adsorbate. as a result, the weaker orbital overlap and reduced charge transfer lead to lower adsorption energies. the optimized nitric oxide bond length (dno) has been given in the first row (fifth column) of table 1. it has been found that the bond length of this molecule changes when it is adsorbed by gcn and tm-gcn and this is in line with the previous work [2] as is seen in table 1. figure 2: optimized structure of pristine and tmembedded gcn before and after no adsorption (a) pristine gcn (b) ni-embedded gcn (c) pdembedded gcn (d) pt-embedded gcn. the values for dno on gcn, ni, pd, and ptembedded value of dno on pt-gcn suggests that the separation gcn were found to be 1.171, 1.173, 1.175, and 1.180 å respectively (fifth column of table 1). the maximum value of dno on pt-gcn suggest that the separation of polarization of charge between n and o is greatest in pt-embedded gcn [27]. based on the above mentioned results, it can be concluded that no interaction between the ptembedded gcn is stronger than the ni and pdembedded gcn system. further, the n atom of no and the nedge atom of gcn (before and after no adsorption) both interact with the tm atom of tm-gcn. these bond distances have been shown in the last column of table 1. on the other hand, the distance between n of gcn and tm also increases before and after the adsorption of no. this indicates weak hybridization between n of gcn and tm. additionally, the distance between pt and n of gcn for no adsorbed pt-gcn is the largest compared to another case. figure 3: spin-polarized electronic band structure of pristine gcn, ni-embedded gcn, pd-embedded gcn, and pt-embedded gcn before and after no adsorption. to get the electronic properties of the pristine gcn, ni, pd, pt-embedded gcn, no adsorbed gcn, and no adsorbed ni, pd, pt-embedded gcn, we performed the electronic polarized band structure of above aforementioned system by ggapbe approximation. new energy states are noticed near the fermi level when ni, pd, and pt are embedded in gcn and after the adsorption of no gas on the gcn monolayers. asymmetry seen in spinup and spin-down density of state calculations show that the magnetic characteristics guna nidhi poudel et al./ bibechana 22 (2025) 215-222 219 figure 4 figure 4: spin-polarized total density of states and partial density of states for gcn, tm embedded gcn, no adsorbed gcn, and no absorbed tm-embedded gcn. figure 4 shows spin-polarized total density of states and partial density of states for gcn, tmembedded gcn, no adsorbed gcn, and noabsorbed tm-embedded gcn. a similar type of result has been reported in previous study [2] also. the pristine gcn shows the semiconducting nature and it is observed that the band gap (eg) for this system is 1.30 ev. it is lower than the experimental value (2.7 ev), since the pbe, the exchangecorrelation functional method, usually underestimates the band gap energy. a similar sort of discrepancy has been found in the literature when the pbe functional was used for the band gap calculations [28–31]. the bandgap energy of the gcn significantly decreases after embedding ni, pd, and pt in the gcn system, as shown in table 1 and fig.3. the band lines corresponding to spin up and spin down of the pure and no adsorbed pristine gcn, ni, and pd, pt embedded gcn, are depicted in fig. 3. the lines in both the conduction band (cb) and valance band (vb) of spin up and spin down of the pure and no adsorbed pristine gcn, ni, and pd embedded gcn are seen overlapped showing symmetric, which indicates the materials to be non-magnetic. on the other hand, vb and cb band lines of the pt-gcn and no adsorbed pt-gcn are asymmetric, indicating the materials to be magnetic with magnetic moments 1.4000, and 0.0001 µb respectively. previous work [2] also shows similar values fairly confirming this result. it has been observed that after the no adsorption on the pt-embedded gcn, there is a considerable drop in the magnetic moment. this may be due to the strong hybridization between the 5d-orbitals of pt with the p-orbital of the n atom of the no. to understand more about the electronic and magnetic properties resulting from no adsorption on both pristine gcn monolayers and tm-gcn monolayers, spin-polarized partial density of states (pdos) and total density of states (tdos) have been calculated for all the systems. tdos and pdos before and after no adsorption exhibit a significant change, as illustrated in fig 4. there is significant increase in dos in tm-embedded gcn with comparable to the gcn. in these systems, the embedded metals serve as a bridge, facilitating an enhanced hybridization between the gas molecule and the g-c3n4 monolayer. the symmetric tdos and pdos were observed in pure and no adsorbed pristine gcn, pure and guna nidhi poudel et al./ bibechana 22 (2025) 215-222 220 no adsorbed ni and pd-embedded gcn (first, second, and third rows of fig 4). there is symmetry observed between the spin-up and spin-down channels in pure and no adsorbed pristine gcn, pure and no adsorbed ni, and pd-embedded gcn in the first, second, and third rows of fig 4. thus, it can be inferred that these materials do not seem to exhibit magnetic behavior. in pt-gcn, the absence of symmetry between the spin-up and spin-down states results in the manifestation of a magnetic moment in this system. however, no adsorbed ptgcn shows almost symmetry between spin up and spin down in tdos and pdos diagrams, indicating almost negligible magnetic moment. 4 conclusion the adsorption behavior of the toxic gas no on ni, pd, and pt-embedded gcn has been studied using the first-principles method. it is evident from structural properties and adsorption analysis depicted in the optimized diagram that no is physically adsorbed into gcn, whereas it is chemically adsorbed into ni, pd, and pt-embedded gcn. further, ni is positioned asymmetrically, while pd and pt are symmetrically placed within the gcn cavity. additionally, from adsorption energy calculations, we may say that no tends to adsorb more on pt-embedded gcn than on ni, and pdembedded gcn. the band energy of all systems is found within the range of semiconducting materials. from the electronic properties that were calculated from the gga-pbe dft method, it can be inferred that gcn, tm-embedded gcn (tm=ni, pd), no adsorbed gcn, no adsorbed ni and pd embedded gcn are non-magnetic materials. thus, like other pollutants as well as toxic gases, metal-embedded gcn has been seen to adsorb no, as shown by other theoretical and experimental studies. acknowledgments this work is supported by the international science program (nep01), uppsala university, sweden for computing resources, and the partial financial aid for gnp is provided by the university grants commission (ugc master grants, grant no. mrs77/78-s&t-127), nepal. author contributions guna nidhi poudel: conceptualization, methodology, investigation, visualisation, data curation, formal analysis, validation, writing original draft pitamber shrestha: validation, formal analysis. narayan prasad rijal: writing, review & editing. shriram sharma: validation, formal analysis. leela pradhan joshi: project administration, formal analysis. rajendra 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[31] d. r. lawati, h. k. neupane, d. k. chaudhary, p. shrestha, r. p. adhikari, l. p. joshi, and r. parajuli. structural, mechanical, electronic and optical properties of mgzno3 perovskite: first-principles study. journal of physics and chemistry of solids, 181:111547, 2023. introduction computational details results and discussion conclusion bibechana vol. 21, no. 2, august 2024, 103-112 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar geometrical interpretation of space contraction in two-dimensional lorentz transformation chandra bahadur khadka department of physics, tri-chandra multiple campus, tribhuvan university, kathmandu-44600, nepal ∗corresponding author. email: chandrabahadur9988@gmail.com abstract this paper points out that the transformation equations for the spatial and temporal coordinates between two frames of reference in the existing generally accepted version of the lorentz transformation are deficient, since transformation equations are based on one dimensional motion between inertial frames. therefore, all possible space-time coordinate transformation equations between moving and stationary frames by prolonging lorentz transformation in a two-dimensional plane are thoroughly proposed in this article. if v denotes the relative velocity between stationary frame (x, y) and moving frame (x ′ , y ′ ), then the transformation equations along x and y-axis under two-dimensional lorentz are given, respectively, by the formulas x ′ = ( x− vtx√ x2+y2 ) √ 1− v2 c2 and y ′ = ( y− vty√ x2+y2 ) √ 1− v2 c2 . in this work we conclude that length and breadth of a rectangle appears to be shortened to the observer when there is the relative velocity between the rectangle and observer along both x and y-axis. in particular, we present a concise and carefully reasoned account of a new aspect of lorentz transformation which decently allows for the determination of space-time coordinates transformation equations in two dimensions of space. keywords frame of reference, lorentz transformation, space contraction, special relativity. article information manuscript received: september 5, 2023; revised: january 10, 2024; accepted: january 19, 2024 doi https://doi.org/10.3126/bibechana.v21i2.62271 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the theory of special relativity [1, 2] at the current time stands as a universal theory comprising the relativistic nature of mass and the common space-time arena in which all fundamental phenomena occur. the well-known lorentz transformation equations [3] form the basis of einstein’s special relativity and give the transformation equations for spatial and temporal coordinates in two frames of reference on the basis of constancy of light and its independence with relative velocity between source and observer. 103 http://nepjol.info/index.php/bibechana chandrabahadur9988@gmail.com https://doi.org/10.3126/bibechana.v21i2.62271 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ chandra bahadur khadka/ bibechana 21 (2024) 103-112 104 there are many wellknown written texts on the formulation of relativistic mechanics. the relativistic space-time coordinate formulas were presented in 1904 by lorentz [3], and later that the lorentz transformation was simplified and clearly recorded on 5th june 1905 by poincare [4], who gave it a form very close to its contemporary version: x ′ = x− vt√ 1− v2 c2 , t ′ = t− xv c2√ 1− v2 c2 y ′ = y, z ′ = z (1) where y, z,y ′ and z ′ are coordinates along the direction perpendicular to the direction of motion. on 30 june 1905, einstein published his work [5] where based on the postulate of constant speed of light, he derived the correct transformation of coordinates, law for addition of velocities and mass energy equivalence principle. lewis and tolman [6] extended the relativity principle and introduced the theoretical dependence of mass on velocity. derivations such as that by poincare for space-time coordinates transformation between inertial frames and by tolman for relativistic mass are propagated in several excellent textbooks, including famous feynman’s lectures [7]. there are some known research results about the extension of lorentz transformation for determination of space time coordinate transformation along various directions. there are research papers that provide a deeper sense of the concept of relativity with the universal frame of reference [8] and all possible experiments to falsify such theories were conducted in [9]. in the article [10], new mathematical formalism of special relativity was developed. research is also conducted on the practical aspects of relativity [11]. in ref. [12], the trajectory of a relativistic particle in 1+1 dimensions was obtained in the representation of lobachevsky geometry. the dynamics of a relativistic particle that does not have an electric charge and is under the action of an external force has been analyzed on the basis of the special theory of relativity in work [13]. pagano et al [14] have discussed different roles of lorentz transformation in classical wave propagation theories and in relativistic mechanics. karplyuk et al [15] showed how the factorization of an arbitrary lorentz transformation is performed as a sequence of a spatial rotation and a boost. using the lorentz transformation, alex-amor et al [16] had shown that a particular class of space-time modulated gratings behave effectively as moving media. ref. [17] presents a concise and carefully reasoned account of a new aspect of gravitational redshift theory revealing the change of mass with gravity. furthermore, ref. [18] points out the possible extension of special relativity to derive the new mathematical formulas of linear momentum, force and kinetic energy. a recently published research article [19] shows the simultaneous contraction of length, breadth and height of cuboids by developing three-dimensional lorentz transformation. there are many publications on special relativity with important theoretical results. the lorentz transformation equations in most of the literature to date are formulated based on onedimensional motion along x-axis between inertial frames governed by equation (1). equation (1) generates the space contraction along the x-axis only and can’t explain spatial behavior along y and zdirections. therefore, it manifests the inadequacy of the current form of lorentz transformation, especially the need for the inclusion of relative motion along both x and y-directions between inertial frames of reference. here, we present the corresponding modified lorentz transformation in two dimensional xy plane by introducing the relative motion between inertial frames along both x and y-directions simultaneously. the modified transformation equations, in place of equation (1) are: x ′ = x− vxt√ x2+y2√ 1− v2 c2 , y ′ = y − vyt√ x2+y2√ 1− v2 c2 t ′ = t− v √ x2+y2 c2√ 1− v2 c2 , z ′ = z (2) comparing equations (1) and (2), the space coordinates transformation take place along only x-axis in old transformation (1) and time depends only on x coordinate while the space coordinates take place along both x-axis and y-axis in modified transformation (2) and time depends on both x and y coordinates. with above motivation, the structure of this paper is systematically arranged as follows. in section 2, the transformation equations along both x and y-axis have been displayed by introducing the relative motion between inertial frames in the twodimensional xy plane. in section 3, based on modified transformation equations, formulas of length and breadth contraction of a rectangle in a moving frame are obtained for the first time. some conclusions are summed up in the last section. 2 methods 2.1 the equation of wave front of light let two frame of reference s and s' such that s' frame of reference is moving with uniform velocity v as shown in figure (1). let origin o and o' of two co-ordinate system coincide at t = t′ = 0 and a source of light is flashed at the origin o at t = 0, when o and o' coincide. then, in view of chandra bahadur khadka/ bibechana 21 (2024) 103-112 105 constancy of speed of electromagnetic wave with respect to the motion of two frames of reference, each observer at o and o' claim to be at the center of the spreading spherical wave front of light pulse. when light is at point p, let space-time co-ordinate measured by the observer o and o' be (x, y, z, t) and (x′, y′, z′, t′) respectively. since both the observers are at the center of the same expanding wave front, the equation of wave front in frame s and frame s' must be equal. x2 + y2 + z2 − c2t2 = x ′2 + y ′2 + z ′2 − c2t ′2 (3) since there is no relative motion along zdirection then, z = z ′ = 0 above equation (3) reduces to x2 + y2 − c2t2 = x ′2 + y ′2 − c2t ′2 r2 − c2t2 = r ′2 − c2t ′2 (4) 2.2 geometrical calculations in figure (1), θ be the angle made by line op with positive x-axis in s frame of reference. draw pq' and pq perpendiculars on x'-axis and x-axis respectively. in right angled triangles pq'o' and pqo, (i) angle opq = angle o'pq' (same angle) (ii) angle pqo = angle pq'o' = 90° (iii) angle qop = angle q’o’p (remaining angle) therefore, angle qop = angle q'o'p' = θ. in right angled triangle o'pq' po′2 = o′q′2 +q′p 2 or, r ′2 = x ′2 + y ′2 (5) also, sinθ = pq ′ po′ = y ′ r′ cos θ = q ′ o ′ po′ = x ′ r′ (6) similarly, in right angled triangle opq po2 = oq2 +qp 2 , r2 = x2 + y2 (7) also, sinθ = pq op = y r cos θ = oq op = x r (8) 2.3 transformations equations in two dimensions, there is relative motion between inertial frames along both x and ydirections simultaneously. let r and r' be position of point p measured from frame of reference s and s' respectively. in figure (1), frame s' moves with velocity v in xy plane making an angle θ with positive xaxis of stationary frame. therefore, velocity v has two components vx = v cos θ and vy = v sin θ along x-axis and y-axis respectively. thus, the transformation equation from frame s to s' are y ′ = γ(y − vyt) x ′ = γ(x− vxt) where vy = v sin θ and vx = v cos θ be component of velocity along y and x-axis in s frame of reference respectively, then above transformation equation becomes, y ′ = γ(y − vtsinθ) x ′ = γ(x− vtcosθ) where γ denotes the lorentz factor. now, we have, y ′ = γ (y − vtsinθ) r (9) x ′ = γ (x− vtcosθ) r (10) chandra bahadur khadka/ bibechana 21 (2024) 103-112 106 figure 1: the inertial system s and s’ in two dimensional planes now, radius vector r' in s' frame of reference from equation (5) is r ′2 = x ′2 + y ′2 substituting value from transformation equations (9) and (10), r ′2 = γ2 ( x− vxt r )2 + γ2 ( y − vyt r )2 or, r ′2 = γ2 ( x2 − 2vtx2 r + v2x2t2 r2 + y2 − 2vty2 r + v2y2t2 r2 ) or, r ′2 = γ2 ( x2 + y2 − 2tv ( x2+y2 r ) + t2v2 ( x2+y2 r2 )) using equation (7) we get, or, r ′2 = γ2 ( r2 − 2vtr2 r + t2v2r2 r2 ) or, r ′2 = γ2 ( r2 − 2tvr + t2v2 ) or, r ′2 = γ2(r − vt)2 r ′ = γ(r − vt) (11) this is the transformation equation from frame s to frame s' in term of radius vector when there is relative motion along x and y-axis simultaneously. again, the transformation equations from frame s' to s are y = γ ′ (y′′ + v ′ yt ′ ) x = γ ′ (x′′ + x ′ yt ′ ) where v′y = vsinθ and v′x = vcosθ be component of velocity along y and xaxis respectively, then above transformation equations becomes, y = γ ′ (y′′ + vsinθt ′ ) x = γ ′ (x′′ + vcosθt ′ ) substituting value of sinθ and cosθ from equation (6) we get, y = γ ′ ( y ′ + vy ′ t ′ r′ ) (12) x = γ ′ ( x ′ + vx ′ t ′ r′ ) (13) now, radius vector in s frame of reference from equation (7) is r2 = x2 + y2 substituting value from transformation equation (12) and (13), r2 = γ ′2 ( x ′ + vx ′ t ′ r′ )2 + γ ′2 ( y ′ + vy ′ t ′ r′ )2 or, r2 = γ ′2 ( x2 + 2vt ′ x ′2 r′ + v2x ′2t ′2 r′2 + y ′2 + 2vt ′ y ′2 r′ + v2y ′2t ′2 r′2 ) or, r2 = γ ′2 ( x ′2 + y ′2 + 2vt ′ ( x ′2+y ′2 r′ ) + v2t ′2 ( x ′2+y ′2 r′2 )) using equation (5) we get, or, r2 = γ ′2 ( r ′2 + 2vt ′ r ′2 r′ + v2t ′2r ′2 r′2 ) or, r2 = γ ′2 ( r ′2 + 2vt ′ r ′ + v2t ′2 ) or, r2 = γ ′2 ( r ′ + vt ′ )2 or, r = γ ′ (r ′ + vt ′ ) (14) this is the transformation equation from frame s' to frame s in term of radius vector when there is relative motion along x and y-axis simultaneously. 2.4 the lorentz transformation equations the transformation equation relating r' and r can be written from equation (11) and (14) as, r ′ = γ(r − vt) and r = γ ′ ( r ′ + vt ′ ) or, r = γ ′ ( γ(r − vt) + vt ′ ) or, r = γ ′ γr − γ ′ γvt+ γ ′ vt ′ or, t ′ = r γ′v − γ ′ γr γ′v + γ ′ γvt γ′v or, t ′ = γt+ r γ′v − γr v or, t ′ = γ [ t− r v ( 1− 1 γγ′ )] (15) equation (3) gives equation of wave front, or, r2 − c2t2 = r ′2 − c ′2t ′2 substituting value of r' and t' from (11) and (15), we get r2−c2t2 = γ2(r−vt)2−c2γ2 [ t− r v ( 1− 1 γγ′ )]2 chandra bahadur khadka/ bibechana 21 (2024) 103-112 107 or, r2−c2t2 = γ2r2−2γ2rvt+γ2v2t2−c2γ2t2+ 2c2γ2t rv ( 1− 1 γγ′ ) −c2γ2 r2 v2 ( 1− 1 γγ′ )2 or, r2 − c2t2 = r2 [ γ2 − c2γ2 v2 ( 1− 1 γγ′ )2] + rt [ −2γ2v + 2c2γ2 v ( 1− 1 γγ′ )] + t2 ( γ2v2 − c2γ2 ) equating the coefficients of r2 ,rt and t2 on both sides, γ2 − c2γ2 v2 ( 1− 1 γγ′ )2 = 1 (16) −2γ2v + 2c2γ2 v ( 1− 1 γγ′ ) = 0 (17) γ2v2 − γ2c2 = −c2 (18) from equation (18) −γ2 ( c2 − v2 ) = −c2 γ2 = c2 (c2−v2) = 1 1− v2 c2 γ = 1√ 1− v2 c2 (19) further, γ2 = 1 1− v2 c2 or, 1− v2 c2 = 1 γ2 or, v2 c2 = 1− 1 γ2 (20) from equation (17), we have, −v + c2 v ( 1− 1 γγ′ ) = 0 or, −v2+c2 ( 1− 1 γγ ′ ) v or, v2 = c2 ( 1− 1 γγ′ ) or, v2 c2 = ( 1− 1 γγ′ ) (21) comparing equations (20) and (21) we get, 1− 1 γ2 = ( 1− 1 γγ′ ) or, 1 γ = 1 γ′ or, γ = γ ′ = 1√ 1− v2 c2 therefore, the required transformation equation from (11) is r ′ = r−vt√ 1− v2 c2or, √ x′2 + y′2 = √ x2 + y2 − vt√ 1− v2 c2 (22) from (15) we get, t ′ = γ [ t− r v ( 1− 1 γγ′ )] using equation (21) we get, or, t ′ 1√ 1− v2 c2 [ t− r v . v2 c2 ] or, t ′ = t− rv c2√ 1− v2 c2 or, t ′ = t−v √ x2+y2 c2√ 1− v2 c2 the inverse lorentz transformation equations are obtained by interchanging the coordinates and changing v by −v in above transformation equations as follows. r = r ′ +vt ′√ 1− v2 c2 or, √ x2 + y2 = √ x′2+y′2+vt ′√ 1− v2 c2 t = t ′ + v √ x′2+y′2 c2√ 1− v2 c2 (23) these equations convert measurement made in frame s' into those in frame s. from these equations it is thus amply clear that space time coordinates transformation equations in two-dimensional space (xy plane) depend upon both x and y coordinates. 3 results and discussions the transformation equation from moving frame to stationary frame of reference when there is relative motion along x and y-axis can be written from equations (12) and (13) as follows. y = γ ′ ( y ′ + vy ′ t ′ r′ ) = y ′ + vy ′ t ′ r′√ 1− v2 c2 (24) x = γ ′ ( x ′ + vx ′ t ′ r′ ) = x ′ + vx ′ t ′ r′√ 1− v2 c2 (25) above equations can be modified by using equation (6) as follows, y = γ ′ ( y ′′ + vt′sinθ ) = y ′ +vt′sinθ√ 1− v2 c2 x = γ ′ ( x ′′ + vt′cosθ ) = x ′ +vt′cosθ√ 1− v2 c2 now, radius vector in s frame of reference from equation (7) is r = √ x2 + y2 using equations (24) and (25) we get, or, r = √√√√(x′+ vx ′ t ′ r ′√ 1− v2 c2 )2 + ( y′+ vy ′ t ′ r ′√ 1− v2 c2 )2 or, r = √√√√√( x′+ vx ′ t ′ r ′ )2 + ( y′+ vy ′ t ′ r ′ )2 (√ 1− v2 c2 )2 or, r = √ x2+ 2vt ′ x ′2 r ′ + v2x ′2t ′2 r ′2 +y′2+ 2vt ′ y ′2 r ′ + v2y ′2t ′2 r ′2√ 1− v2 c2 or, r = √ x′2+y′2+2vt′ ( x ′2+y ′2 r ′ ) +v2t′2 ( x ′2+y ′2 r ′2 ) √ 1− v2 c2 chandra bahadur khadka/ bibechana 21 (2024) 103-112 108 substituting the value r ′2 = x ′2 + y ′2 we get, or, r = √ r′2+2vt′ ( r ′2 r ′ ) +v2t′2 ( r ′2 r ′2 ) √ 1− v2 c2 or, r = √ r′2+2vt′r′+v2t′2√ 1− v2 c2 or, r = √ (r′+vt′) 2√ 1− v2 c2or, r = r ′ + vt ′√ 1− v2 c2 (26) this is the required transformation equation in terms of radius vector. this process of mathematical calculation reveals that transformation equations (24) and (25) in terms of x and y coordinates are separated form of transformation equation (26). putting value of r andr ′ on equation (26) we get, √ x2 + y2 = √ x′2 + y′2 + vt ′√ 1− v 2 c2 (27) case(i): when there is relative motion along single dimension say x-axis, then y = y ′ = 0. as a result, equation (27) becomes, √ x2 = √ x′2+vt ′√ 1−v 2 c2or, x = x ′ + vt ′√ 1− v2 c2 (28) which is the desired ordinary lorentz transformation equation of space coordinate along x-axis. case (ii): when there is relative motion along single dimension say y-axis, then x = x ′ = 0. as a result, equation (27) becomes,√ y2 = √ y′2+vt ′√ 1−v 2 c2or, y = y ′ + vt ′√ 1− v2 c2 (29) which is the desired ordinary lorentz transformation equation of space coordinate along y-axis. consider two frames of references s and s ′ such that s ′ frame is moving with velocity v in two dimensional xy plane as shown in figure (2). consider a rectangle abcd in stationary frame of reference. let (x1, y1) and (x2, y2) are coordinates of point a and c measured from s frame while( x1 ′ , y1 ′ ) and ( x2 ′ , y2 ′ ) are coordinates of point a and c measured from s ′ as shown in figure (2). let length and breadth of rectangle are taken along x-axis and y-axis respectively, then the length of the rectangle along ab in figure (2) is given by, l0 = x2 − x1 (30) this length l0 of the rectangle in stationary frame of reference is known as proper length. the inverse lorentz transformation equation along xaxis can be written from equation (25) as follows. x1 = x1 ′ + vx1 ′ t ′ r1 ′√ 1− v2 c2 x2 = x2 ′ + vx2 ′ t ′ r2 ′√ 1− v2 c2 putting these values in equation (30) we get, l0 = x2 ′ + vx2 ′ t ′ r2 ′√ 1− v2 c2 − x1 ′ + vx1 ′ t ′ r1 ′√ 1− v2 c2 or, l0 = x2 ′ −x1 ′ + vx2 ′ t ′ r2 ′ − vx1 ′ t ′ r1 ′√ 1− v2 c2 or, l0 √ 1− v2 c2 = x2 ′ − x1 ′ + vx2 ′ t ′ r2 ′ − vx1 ′ t ′ r1 ′ or, x2 ′ − x1 ′ = l0 √ 1− v2 c2 + vx1 ′ t ′ r1 ′ − vx2 ′ t ′ r2 ′ or, x2 ′ − x1 ′ = l0 √ 1− v2 c2 + vt ′ ( x1 ′ r1 ′ − x2 ′ r2 ′ ) or, l = l0 √ 1− v2 c2 +vt ′  x1 ′√ x′2 1 + y′21 − x2 ′√ x′2 2 + y′22  (31) where l = x2 ′ − x1 ′ be the length of rectangle along x-axis in frame s ′ called improper length, r1 ′ = √ x′2 1 + y′21 be radius vector measured froms ′ of point a having coordinate ( x1 ′ , y1 ′ ) and r2 ′ = √ x′2 2 + y′22 be radius vector measured froms ′ of point c having coordinate ( x2 ′ , y2 ′ ) . similarly, breath of the rectangle along bc in figure (2) is given by, b0 = y2 − y1 (32) chandra bahadur khadka/ bibechana 21 (2024) 103-112 109 figure 2: length and breadth contraction of the rectangle figure 3: relative geometrical shape of rectangle chandra bahadur khadka/ bibechana 21 (2024) 103-112 110 this breadth b0 of the rectangle in stationary frame of reference is known as proper breadth. the inverse lorentz transformation equation along yaxis can be written from equation (24) as follows. y1 = y1 ′ + vy1 ′ t ′ r1 ′√ 1− v2 c2 y2 = y2 ′ + vy2 ′ t ′ r2 ′√ 1− v2 c2 putting these values in equation (32) we get, b0 = y2 ′ + vy2 ′ t ′ r2 ′√ 1− v2 c2 − y1 ′ + vy1 ′ t ′ r1 ′√ 1− v2 c2 or, b0 = y2 ′ −y1 ′ + vy2 ′ t ′ r2 ′ − vy1 ′ t ′ r1 ′√ 1− v2 c2 or, b0 √ 1− v2 c2 = y2 ′ − y1 ′ + vy2 ′ t ′ r2 ′ − vy1 ′ t ′ r1 ′ or, y2 ′ − y1 ′ = b0 √ 1− v2 c2 + vy1 ′ t ′ r1 ′ − vy2 ′ t ′ r2 ′ or, y2 ′ − y1 ′ = b0 √ 1− v2 c2 + vt ′ ( y1 ′ r1 ′ − y2 ′ r2 ′ ) or, b = b0 √ 1− v2 c2 +vt ′  y1 ′√ x′2 1 + y′21 − y2 ′√ x′2 2 + y′22  (33) where b = y2 ′ − y1 ′ be the breadth of rectangle along y-axis in frame s ′ called improper breadth, r1 ′ = √ x′2 1 + y′21 be radius vector measured froms ′ of point a having coordinate ( x1 ′ , y1 ′ ) and chandra bahadur khadka/ bibechana 21 (2024) 103-112 111 r2 ′ = √ x′2 2 + y′22 be radius vector measured froms ′ of point c having coordinate ( x2 ′ , y2 ′ ) . from equations (31) and (33), it is seen that both length and breadth of rectangle appear to be shortened to observer in frames ′ if there is relative motion between rectangle and observer along both x-axis and y-axis. on the other hand, the length of the rectangle appears to be shortened keeping breadth fixed if there is relative motion along the x-axis only. similarly, the breadth of the rectangle appears to be shortened keeping length fixed if there is relative motion along y-axis only. a neat depict of space contraction in one and twodimensional motion is shown in figure (3). figure (3) shows that a square in one stationary frame appears to the observer in the other frame in one dimensional motion (say along x-axis) to be rectangle due to contraction along x-axis. a square gets shortened in both x and y-directions if there is relative motion along both x and y-axis simultaneously as shown in figure (3). the transformation equations along the x and y-axis that give rise to such phenomena of shortening in spatial coordinates have been meticulously presented in table (1). from the table, it is clearly seen that the modified lorentz transformation represents the generalization of ordinary transformation (one-dimension system). therefore, the modified transformation is the description of the behavior of the space-time coordinate transformation happening in two dimensions of space. 4 conclusions all possible space-time coordinate transformation equations by introducing relative motion between inertial frames in two dimensional xy-plane have been thoroughly outlined in this article. on the basis of transformation equations, it is definitely possible to obtain space contraction along the x and y-axis simultaneously. the corresponding length and breadth contraction of rectangle when there is relative motion along both x and y-axis can be written from equation (31) and (33) as follows. l = l0 √ 1− v2 c2 + vt ′ ( x1 ′ √ x′2 1+y′2 1 − x2 ′ √ x′2 2+y′2 2 ) b = b0 √ 1− v2 c2 + vt ′ ( y1 ′ √ x′2 1+y′2 1 − y2 ′ √ x′2 2+y′2 2 ) from these equations, it should be concluded that both length and breadth of a rectangle appear to be shortened when there is relative motion along both x and y-directions. also, the transformation equation for temporal coordinate can be written from equation (23) as follows, t ′ = t−v √ x2+y2 c2√ 1− v2 c2 this equation reveals that time depends upon both x and y coordinate when there is relative motion along both x and yaxis. when moving frames ′ in figure (1) moves along x-axis only, then y = y ′ = 0, hence above equation reduces to, t ′ = t− vx c2√ 1− v2 c2 which is the required transformation equation of time in ordinary lorentz transformation (one dimensional system along x-axis). hence, modified transformation is just an extended form of ordinary transformation in a two-dimensional plane. an extensive analysis of transformation of temporal and spatial coordinates between inertial frames can be obtained via the natural extension of lorentz transformation in two dimensional spaces. the mathematical relations illuminated here will have many applications for manifestation of structure of space-time coordinate transformation between inertial frames of reference and will play an important role in many other areas of theoretical physics, especially those which are connected with relativistic mechanics. conflict of interest the author declares no conflict of interest. data availability statement data sharing not applicable to this article as no datasets were generated or analyzed during the current study. funding this research did not receive any specific grant from funding agencies in the public, commercial or not for profit sectors. references 1. a. einstein, relativity: the special and the general theory-100th anniversary edition, princeton university press, princeton, new jersey, 2019. 2. r. szostek. derivation of numerous dynamics in the special theory of relativity. open physics, 17(1):157-166, 2019. 3. h. a. lorentz. electromagnetic phenomenon in a system moving with any velocity smaller than the that of light. proceeding of the royal netherlands academy of arts and sciences, 6:809-831, 1904. 4. h. poincare. on the dynamics of the electron. in proc. academic sciences, 140:15041508, 1905. 5. a. einstein. on the electrodynamics of the moving bodies. annalen der physik, 17(10):891-921, 1905. 6. g. n. lewis and r. c. tolman. the principle of relativity and non-newtonian mechanics. in proceedings of the american academy of arts and sciences, 44:709-726, 1909. chandra bahadur khadka/ bibechana 21 (2024) 103-112 112 7. r. feynman, r. b. leighton and m. sands, the feynman lectures on physics, vol.1: the new millennium edition; mainly mechanics, radiation and heat.vol.1. basic books, 2011. 8. r. szostek. explanation of what time of kinematics is and dispelling myths allegedly stemming from the special theory of relativity. applied sciences, 12(12):1-19, 2022. 9. k. szostek and r. szostek. the concept of mechanical for measuring the 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karplyuk, m. kozak and o. zhmudskyy. factorization of the lorentz transformations. ukrainian journal of physics, 68(1):19-24, 2023. 16. a. alex-amor, c. molero and m. g. silveirinha. analysis of metallic spacetime gratings using lorentz transformations. physical review applied, 20(1):014063, 2023. 17. c.b. khadka. determination of variation of mass with gravity. journal of nepal physical society, 9(1):129-136, 2023. 18. c.b. khadka. an accurate theoretical formula for linear momentum, force and kinetic energy. bibechana, 20(3):259-266, 2023. 19. c.b. khadka. derivation of the lorentz transformation for determination of space contraction. st. petersburg state polytechnical university journal. physics and mathematics, 16(3):115-130, 2023. introduction methods the equation of wave front of light geometrical calculations transformations equations results and discussions conclusions bibechana vol. 22, no. 1, april 2025, 1-14 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar computational evaluation on spectroscopic (ft-ir, raman), electronic, biological, and nlo properties of cirsilineol by dft, admet, and molecular docking method tirth raj paneru1,4, poonam tandon2, bhawani datt joshi3,∗ 1department of general science, far western university, kanchanpur, nepal 2department of physics, university of lucknow, lucknow-226007, india 3department of physics, siddhanath science campus, tribhuvan university, mahendranagar, 10400, nepal 4central department of physics, tribhuvan university, kirtipur, kathmandu, nepal ∗corresponding author. email: bhawani.joshi@snsc.tu.edu.np abstract cirsilineol is a natural product that has pharmacological characteristics and is used to prevent the growth of cancer. this study aims to investigate the spectroscopic, electronic, and biological properties of drugs and predict their suitability for drug-like candidates to inhibit prostate cancer. the computational evaluation was performed with density functional theory (dft) at b3lyp/6-311++g(d,p) level of theory and drug-like characteristics rendered from admet analysis. spectral measurement for ir and raman provided evidence of intramolecular hydrogen bonding of the oh group in ring r1. the electronic transition properties of the title compound were determined using td-dft with a polarized continuum model in solvent ethanol, resulting in a blue shift in absorption wavelength. the electrostatic potential mapped with the van der wall surface predicted effective electrophiles and nucleophiles, allowing for the layout of intraand intermolecular hydrogen bonds. the pharmacological properties of cirsilineol determined by admed analysis confirmed that it is non-toxic. to assess the biological performance of cirsilineol, molecular docking was performed with protein codes 1e3g and 1gs4, which showed inhibition action with binding affinity -7.7 and -7.8 kcal/mol, respectively. keywords cirsilineol, vibrational spectra, electrostatic potential, admet, van der waals surface, uv-vis spectra. article information manuscript received: september 25, 2024; revised: december 7, 2024; accepted: december 21, 2024 doi https://doi.org/10.3126/bibechana.v22i1.70126 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 http://nepjol.info/index.php/bibechana bhawani.joshi@snsc.tu.edu.np https://doi.org/10.3126/bibechana.v22i1.70126 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ tirth raj paneru et al./ bibechana 22 (2025) 1-14 2 1 introduction plant-derived products have pharmacological characteristics, so they have been used as medications for various types of diseases without harmful effects to the normal cells in body [1]. flavonoids are pharmacologically significant phytochemical compounds found in fruits vegetables, and plant leaves [2]. the plant artemisia vestita was used in traditional chinese and tibetan medicine for joint pain and inflammatory disease, which produces cirsilineol, also known as 4,5-dihydroxy-3,6,7-trimethoxyflavone and has antimicrobial, antioxidant, and anticancer properties [3, 4]. research has demonstrated that it possesses anti-tumor properties and reduces the growth of human cancer cells [5]. owing to its anticancer properties, it has been utilized for treating breast, prostate, and lung cancers, as well as other types of carcinomas, by enhancing the immune system [6,7]. the literature reveals the curative and anticancer properties of cirsilineol using experimental and theoretical approaches [6,7]. paneru et al. conducted a theoretical study on the conformational analysis, stability, reactivity, and drug potential of cirsilineol from dft [8]. literature indicates that raman and ir spectra with vibrational analysis, non-linear optical properties as well as electron transition properties based on uv-vis spectra analysis, have not been conducted yet. this study is primarily focused on the investigation of vibrational spectra, electronic transitions, and the more exact prediction of reactive sites in cirsilineol. for this study, quantum chemical calculations were performed on the title molecule using density functional theory and the b3lyp hybrid functional with basis set 6-11++g(d, p). this study uses potential energy distribution calculations to conduct a comprehensive spectroscopic investigation. the electrostatic potential was determined by the esp surface analysis, which provides information about the reactive sites of the molecule. the nonlinear optical (nlo) properties of the title compound were also investigated in terms of dipole moment, polarizability, and hyperpolarizability to provide insight into its use as an nlo material. the natural charges on each atom were determined by natural population analysis (npa). the drug-like properties and toxicity of the molecule were also evaluated by admet analysis. finally, molecular docking was carried out to evaluate the anti-cancer effect of cirsilineol against protein codes of androgen receptor by detecting binding sites and binding affinity of the title molecule with the target protein codes. 2 materials and methods 2.1 computational details geometry optimization of the molecule should require to commence the present work, which was accomplished by density functional theory in the gaussian 09 software package [9, 10]. the computations were carried out with the hybrid functional b3lyp in the basis set 6-311++g(d,p), the correlation effect, as proposed by lee, yang, and parr, and the exchange interactions, as presented by becke, are both described by the b3lyp hybrid functional [11–13]. the electronic transition in orbitals was visualized using gaussview 05 [14] . the confirmation of ir and raman frequencies, as well as the optimized structure of the molecule, was identified using chemcraft software [15]. through the use of harmonic approximation, the ir absorption and raman intensity of the optimized structure were determined. multiwfn 8 and vmd 1.9.4 software were used to map the electrostatic potential (esp) with the molecular van der wall surface [16, 17]. with the polarized continuum model (pcm), the uv-vis absorption of cirsilineol demonstrating electronic transition on molecular orbital was rendered in gaseous and solvent phases, using the td-dft/b3lyp/6-311++g(d,p) level of theory [18, 19]. the density of state (dos) spectrum was produced with the gausssum 3.0 software, with a full width at half maximum (fwhm) of 0.3 ev [20]. the energy gap in the dos spectrum was then compared with the energy gap between highest occupied molecular orbital (homo) and lowest unoccupied molecular orbital (lumo). to evaluate the admet properties of cirsilineol, the swiss adme and pkcsm online web tool was used [21,22]. auto dock tools (adt) version 1.5.4 has carried out the molecular docking of the molecule [23]. finally, the binding positions of the title molecule with the pdb codes of the androgen receptor were displayed using discovery studio visualizer 4.5 [24]. 3 results and discussion 3.1 geometry optimization the compound cirsilineol (cid 162464) was downloaded from the pubchem database, [25] and optimized using density functional theory with the b3lyp/6-311++g(d,p) level of theory. the ground state energy of cirsilineol was found to be -767078.745 kcal/mol, which is identical to the energy (-767080.126 kcal/mol) for the most stable conformer of cirsilineol as evaluated by paneru et al. using the same level of theory [8]. the optimized structure of cirsilineol with a numbering scheme on the atoms is shown in fig. 1. the optimized structure was used for further study of the tirth raj paneru et al./ bibechana 22 (2025) 1-14 3 title compound. 3.2 vibrational assignment the use of vibrational spectroscopy, such as fourier-transform infrared (ft-ir) and raman, can generate important insights into the interactions and structure of molecules. cirsilineol consists of 41 atoms with (3n-6) 117 modes of vibration, all of those being ir and raman active. the spectral wavenumbers for ir and raman were calculated at the b3lyp/6-311++g(d,p) level of theory, but they were overestimated due to anharmonicity, so they were reduced using the wavenumber linear scaling (wls) factor [26]. the vibrational wavenumber calculations and potential energy distribution assignment were performed in gar2ped in accordance with pulay's recommendations [27, 28]. the raman intensity was not directly obtained from dft calculations it can be obtained from the raman scattering cross-section. raman scattering cross-section is proportional to the amplitude and provided by the following relation [29]. ∂σj ∂ω = ( 24π4 45 ) (ν0 − νj) 4 1− exp [ hcνj kt ] ( h 8π2cνj ) sj where, h, c, and k as a universal constant. sj and νj be the scattering activity and predicted wavenumber of jth mode , and ν0 be the wavenumber related to the excited state. simulated spectra are produced by convoluting each predicted vibrational mode with the computed raman and ir intensities using a lorentzian line shape with a full width at half maximum (fwhm) of 8 cm-1 [30]. table 1 displays both the unscaled and scaled wavenumbers for ft-ir and ft-raman, as well as their ped distribution. the graph of ir absorbance plotted against the scaled wavenumber, adjusted using the wls factor derived from dft calculations, is presented in fig. 2. the graph for the raman spectra obtained by plotting the graph between raman intensity and scaled wave number is shown in fig. 3. using the potential energy distribution in table 1, and the ir and raman spectra shown in figures 2 and 3, we illustrated the vibrational modes associated with the functional groups, rings, and methyl groups of cirsilineol in the following sections. 3.2.1 o-h vibrations cirsilineol has two oh groups on rings r1 and r3. this group may be reactive parts of molecules, allowing it to participate in intraand intermolecular hydrogen bonds. the stretching vibration of the free o-h group in ring r3 is 3624 cm-1, while the stretching vibration of the o-h group in ring r1 is 3064 cm-1. the stretching vibration of free oh in a similar type of flavonoid, such as kaempferol, was computed to be 3626 cm-1; in quercetin, 3640, 3598 cm-1; in myricetin, computed to be 3546, 3608 cm-1; and in catechol, computed to be 3647 cm-1 using b3lyp/6-31+g(d,p) level of theory. these are in agreement with our result [31]. the stretching vibration of the o-h group in ring r1 was found to be lower, confirming the presence of o4-h31. . . o5 intra-molecular hydrogen bonding. the o-h vibration of rings r1 and r3 showed a sharp peak in both ir and raman spectra, whereas the vibration of o-h in ring r1 shifted to the lower frequency in ir and raman spectra. the deformation of o-h groups occurred at 1415 and 1195 cm-1. 3.2.2 o-ch3 vibrations there are three methyl moieties in cirsilineol, and each one can vibrate in the different ways, including stretching, deforming, and rocking. the methyl group exhibits asymmetric stretching in the range of 2970-2950 cm-1 and symmetric stretching in the range of 2880-2860 cm-1. asymmetric deformations should fall within 1470-1430 cm-1, while symmetric deformations should be within 1380-1370 cm-1 [32]. asymmetric stretching of the methyl group was computed to be 3009, 3006, 3002, and 2941 cm-1, whereas symmetric stretching was obtained at 2977, 2972, 2900, 2899, and 2886 cm-1. the asymmetric deformations of the methyl group were calculated at 1489, 1486, 1480, 1470, 1465, and 1464 cm-1, while the symmetric deformations were determined at 1459, 1458, and 1447 cm-1. methyl moieties were found to be rocking at 1203, 1195, 1188, 1156, and 1155 cm-1. these observations have shown that the calculated wavenumbers for various vibrations falls within the range reported in the literature. figure 1: optimized structure of cirsilineol showing intra-molecular hydrogen bonding (oh. . . o) and numbering scheme on atoms. tirth raj paneru et al./ bibechana 22 (2025) 1-14 4 figure 2: calculated ir spectra of cirsilineol at the b3lyp/6-311++g(d,p) level of theory. figure 3: calculated raman spectra of cirsilineol at the b3lyp/6-311++g(d,p) level of theory. 3.2.3 vibrations in ring r1 ring r1 consists of one c-h moiety and three c-o moieties. the stretching, in-plane bending, and out-of-plane bending should all be in the range 3100-3000 cm-1, 1350-950 cm-1, and 1100-600 cm-1, respectively [33]. stretching of ch was calculated to be 3076 cm-1, with in-plane bending at 1170 cm-1 and out-of-plane bending at 835 cm-1. c-c stretching in ring r1 occurred at 1651, 1617, 1566, 1697, 1632, 1364 and 1303 cm-1. c-o stretching was obtained at 1224 cm-1 with a 22% ped contribution, whereas other c-o stretching had a lower ped contribution. because the ch3 group is attached to the c-o group, the inplane and out-of-plane bending contributes significantly less in ped. the ring showed trigonal deformation at 712 cm-1 and asymmetric deformation at 576 cm-1, with a lower contribution from ped. additionally, the ring showed puckering and torsion at 768 and 629 cm-1. their contribution with the peak observed in ir and raman spectra. 3.2.4 vibrations in ring r2 ring r2 contains one c-h moiety and one c=o group. the stretching vibration of c-h was obtained at 3076 cm-1 with in-plane deformations and out-of-plane deformations computed at 1281, 1272 cm-1, and 850, 844 cm-1 respectively. the in-plane bending of c-h is a lower ped contribution. the stretching of co occurred at 1605 and 1586 cm-1 with ped contributions of 21% and 15%, respectively; the lower ped contribution of the co group is due to its participation in hydrogen bonding with the o-h group of ring r1. the stretching vibration of c=o aligns with those of myricetin at 1603 and 1570 cm-1, as well as with quercetin at 1604 and 1571 cm-1 [31]. c-c stretching in ring r2 was calculated at 1586 and 1281 cm-1. the asymmetric torsion, trigonal deformation, asymmetric deformation, and ring puckering occurred at 693, 524, 891, and 738 cm-1, respectively, but had a lower ped contribution. 3.2.5 vibration in ring r3 in ring r3, there are three c-h groups with two co groups attached to hydrogen and methyl groups. the c-h stretching wavenumber were obtained at 3092, 3064, and 3022 cm-1, while the in-plane bending was computed at 1529 and 1178 cm-1, and the out of plane bending were occurred at 925 and 812 cm-1. the stretching of c-o was computed at 1529, 1303, and 1272 cm-1, while its in-plane bending and out-of-plane bending were computed at 560 and 467 cm-1, respectively, with lower contribution in ped. the c-c stretching in the ring was determined at 1605, 1604, 1426, 1415, 1374, and 1293 cm-1. the trigonal and asymmetric deformations in the ring occurred at 1272, 1052 cm-1 and 675, 642, 536, and 524 cm-1, respectively. the puckering and asymmetric torsion values were calculated at 878, 741, 738, and 583 cm-1 and 812, 583, 467, and 449 cm-1, respectively. tirth raj paneru et al./ bibechana 22 (2025) 1-14 5 tirth raj paneru et al./ bibechana 22 (2025) 1-14 6 tirth raj paneru et al./ bibechana 22 (2025) 1-14 7 3.3 density of states (dos) when an electron transitions from the valence band to the conduction band, it results in a definitive change in the density of states [34]. the density of state spectra produced in the gausssum 3.0 software with a full width at half maximum (fwhm) of 0.3 ev. the dos spectrum for cirsilineol in the gaseous and solvent phase ethanol is shown in fig. 3. bonding interaction is suggested by a positive value on the dos spectrum, anti-bonding is indicated by a negative value, and no bonding is indicated by a zero value. the green lines in the spectrum represent the highest occupied molecular orbital (homo), while the red lines represent the lowest unoccupied molecular orbital (lumo). acceptor orbitals are represented by virtual orbitals, and donor orbitals are represented by occupied orbitals. the high intensity of dos represent multiple state of occupation at that energy level [35]. it was found that the energy gap in the dos spectrum and the homo-lumo gap in cirsilineol were identical. cirsilineol is more reactive in the ethanol solvent and stable in the gaseous medium because the energy gap in the solvent phase was found to be less than that of the gaseous phase. 3.4 uv-v is spectrum and electronic transition uv-vis spectroscopy is the most fundamental tool for analyzing the absorption properties of pharmacological molecules, allowing us to better comprehend intraand intermolecular interactions [36]. in this study, the uv-vis spectrum was plotted in gaseous and solvent phase ethanol using td-dft in the ief-pcm model to analyze the electronic transition between homo and lumo [37]. table 2 presents the major electron transitions along with their corresponding excitation energies, absorption wavelengths, and oscillator strengths. fig. 4 displays the uv-vis absorption spectra of cirsilineol in gaseous medium and solvent (water, ethanol, and methanol). the transition from homo→lumo is the first excited state has an absorption wavelength of 363.40 nm with excitation energy of 3.41 ev in a gaseous medium and an absorption wavelength of 359.80 nm with excitation energy of 3.44 ev in solvent ethanol. the absorption in solvents shifted to a shorter wavelength is a blue shift, because the polarity of solvent increases. the decreases in absorption wavelength in solvent ethanol are due to the transition from n→π∗ [38]. figure 5 depicts the significant transition between homo and lumo of cirsilineol in gaseous and solvent ethanol. the solvent facilitates charge transfer more readily than a gaseous medium; hence, the band gap in a solvent decreases, which increases its reactivity. figure 3a:density of states spectrum of cirsilineol in (a) gaseous and (b) solvent (etoh) phases. figure 4: the uv-vis absorption spectrum of cirsilineol (in gas and solvent phases). figure 5: major transition between homo and lumo in gaseous and solvent etoh phases. tirth raj paneru et al./ bibechana 22 (2025) 1-14 8 3.5 electrostatic potential (esp) surface analysis the foundation for the biological activity of a drug molecule can be laid by understanding the intermolecular interactions in molecules through the use of the electrostatic potential surface [39]. esp displayed to the surface extrema of cirsilineol is shown in fig. 6. the points of minimal and highest esp were indicated in the figure by the blue and orange spots [40]. the regions of positive and negative potential on the molecule's surface were represented by the colors blue and red, respectively. the global minimum potential of the molecule was determined to be -38.38 kcal/mol, which is attributed to o5. the global maximum potential was found to be 56.88 kcal/mol, corresponding to h38. the largest positive potential on h38 is due to its attachment to oxygen, which attracts a large number of electrons from h38. this shows that the most effective electrophile and nucleophile for participating in intermolecular interactions are h38 and o5, respectively. the intermolecular hydrogen bonding formed by intermolecular interaction h38. . . o5 can form the crystal-packing of cirsilineol. all hydrogens in the molecule have positive potential, while oxygen has negative potential. 3.6 natural population analysis mullikens charges are highly sensitive to the choice of basis sets; hence, natural population analysis is an alternative to it, which better describes the electron distribution in the compounds [41]. the natural population analysis determines the natural atomic orbitals and their occupancies and provides a natural atomic charge on each atom [42]. the natural charges on each atom of cirsilineol calculated at b3lyp/6-311++g(d,p) level of theory are presented in table 3. the graph plotted between natural charges and each atom of the cirsilineol is also shown in fig. 7. all the hydrogen atoms have positive charges, with h31 being the most electrondeficient and exhibiting the highest positive charge. therefore, h31 is the most favorable site for nucleophilic attack. conversely, all the oxygen atoms have negative charges, with o4 and o5 displaying the highest negative charges and possessing excess electrons. consequently, o4 and o5 are potential sites for electrophilic attack. due to this consequence the intra-molecular hydrogen bonding o4h31. . . o5 was formed. c16, which has the highest negative charge of -0.3396 e, behaves as a nucleophile, while c12 exhibits the highest positive charge of 0.4840 e and acts as an electrophile. figure 6: esp mapped molecular vdw surface of cirsilineol. tirth raj paneru et al./ bibechana 22 (2025) 1-14 9 figure 7: distribution of natural charges calculated from natural population analysis. 3.7 nonlinear optical (nlo) properties when the electromagnetic field interact with the molecule it will causes formation of new field, change in phase, amplitude, frequency and other propagation properties of incident field which related with the nonlinear optical properties [43]. it gives key information in frequency shifting, optical communication, switching, data storage as well as signal processing [44]. the calculation of static dipole moment µ0, mean polarizability |α0| , anisotropy of polarizability (∆α), and first order hyperpolarizability β0 of the most stable conformer of title molecule has been carried by using dft at b3lyp/6-311++g(d,p) level of theory from the relations [45]: µ0 = ( µ2 x + µ2 y +µ2 z ) 1 2 |α0| = 1 3 (αxx + αyy + αzz) ∆α = 2− 1 2 [ (αxx − αyy) 2 + (αyy − αzz) 2 + (αzz − αxx) 2 + 6α2 xx ] 1 2 β0 = [ (βxxx + βxyy + βxzz) 2 + (βyyy + βxxy + βyzz) 2 +(βzzz + βxxz + βyyz) 2 ] 1 2 the components of static dipole moment, first order hyperpolarizability, mean polarizability and anisotropy of cirsilineol molecule are shown in table 4. from the table it was found that cirsilineol have static dipole moment µ0 was found to be 4.009 debye, first order hyperpolarizability β0 found to be (16.173×10-30 esu), and anisotropy of polarizability was found to be (107.698×10-24 esu). these values are larger than that of urea, hence it encourages the title molecule can be considered as an excellent nlo material [46]. 3.8 admet properties analysis most pharmaceuticals in clinical trials fail to reach the market due to their limited potential and side effects, making the development of new medications difficult. admet analysis evaluates the absorption, distribution, metabolism, excretion, and toxicity of drug molecules [47]. the swissadme tool determined that cirsilineol has a molecular weight of 344.32, with four rotatable bonds, seven h-bond acceptors and 2 donors, 142.160 å2 topological polar surface areas (tpsa), and 91.44 molar refractivity. the bioavailability score and lipophilicity were found to be 0.55 and 2.53 respectively. all of these physicochemical parameters fall within the range of lipinsky rules for drug likeness; hence cirsilineol can be used as an antimicrobial drug [48]. the solubility, tpsa, flexibility, molecular weight and lipophilicity except saturation of the title compound lie within the pink region of the radar plot given in fig. 8 (a) indicating that cirsilineol is excellent in terms of bioavailability. the diagram of the boiled egg model in fig. 8 (b) indicates that the red dots are located within the white region, suggesting that cirsilineol is effectively absorbed in the gastrointestinal tract and enhances bioavailability [49]. the pharmacokinetic properties determined by the online tool pkcsm as well as the admet properties for the title compound in terms of suitability for human administration are presented in table 5. cirsilineol has 100% intestinal absorption and a solubility of -3.326 mol/l, which is higher than tirth raj paneru et al./ bibechana 22 (2025) 1-14 10 -4 mol/l. additionally, it has a skin permeability of -2.75 cm/h, indicating desirable pharmacologic properties for absorption and distribution [50]. if the volume of distribution (vds) is high, the drug will be distributed in plasma rather than tissue, which is in the desirable range for the title compound. bbb and cns permeability were determined to be 0.738 (log bb) and -3.116 (log ps), respectively, indicating that they were unable to cross the blood-brain barrier and central nervous system. additionally, it has a good metabolism and excretion, with a clearance of 0.638 (ml/min/kg). it is not positive to toxicity of ames, indicating that it is mot mutagenic. the anticipated maximum dose for humans to be tolerated was 0.275 (mg/kg/day), which suggests a moderate level of tolerance. finally, the fact that it responds negatively to enzyme inhibitory capacity, hepatotoxicity, and skin sensitivity suggests that it is not harmful. hence, each of these qualities supported the medicinal nature of cirsilineol. 3.9 molecular docking molecular docking is a computational technique used to understand how drug molecules bind with the target receptor with the preferred orientation and find the binding affinity between them [51]. it has been reported that cirsilineol shows anticancer effects against human cancer cells, including prostate cancer. literature has reported that androgen receptors have been associated with the progression of prostate cancer and are known to play a crucial role in male reproduction [52, 53]. cirsilineol inhibits the development of prostate cancer cells through the stimulation of ros-mediated apoptosis [7]. in this study, we performed molecular docking with androgen receptor protein codes 1gs4 and 1e3g, which were downloaded from the protein data bank [54]. the water was taken out of the protein and kollmann's charge was added in order to identify the active sites of the protein for a grid box of 60åx60åx60å with a spacing of 0.375 å. figure 9 displays the binding modes illustrating the various interactions between cirsilineol and the protein codes 1e3g and 1gs4. for the protein codes 1e3g and 1gs4, the binding affinity and various docking evaluation parameters are shown in table 6. the active binding sites of protein codes 1e3g and 1gs4 both are confirmed at the centre having coordinates x = 6.786, y = 27.710 and z = 11.102. the binding affinity with 1e3g and 1gs4 were found to be -7.7 and -7.8 kcal/mol respectively. the inhibition constant for 1gs4 was found to be less as compared to 1e3g and rmsd between the initial structure and docked structure is 0.58 å for 1gs4 hence title compound is a potential inhibitor of 1gs4. figure 8: (a) boiled-egg permeation plot and (b) bioavailability radar plot of cirsilineol. figure 9: docking of different protein codes of androgen receptor with cirsilineol showing best binding modes and interactions tirth raj paneru et al./ bibechana 22 (2025) 1-14 11 4 conclusion in this study, we employed dft calculations to analyze the vibrational bands (ft-ir and raman) associated with various moieties of cirsilineol. the ft-ir and raman spectra were simulated, and the stretching vibrational wavenumber of the oh group in ring r1 was found to be lower due to the existence of intra-molecular hydrogen bonding o4h31. . . o5. the dos spectrum indicates an electron transition from the valence band to the conduction band, suggesting that the band gap in the ethanol solvent is 3.92 ev, while in the gaseous medium it is 3.97 ev. this suggests that the title compound is more reactive in an ethanol solvent. the transition of electrons between homo and lumo is the first excited state for both gaseous and solvent mediums, with absorption wavelengths of 363.40 nm and 359.80 nm, respectively. the decrease in wavelength in the solvent indicates a blue shift, and there is a transition from n→*. the electrostatic potential mapped with the van der waals surface showed that the global minimum and maximum potential of cirsilineol were determined to be -38.38 kcal/mol for o5 and 56.88 kcal/mol for h38, respectively. this implies that o5 and h38 tirth raj paneru et al./ bibechana 22 (2025) 1-14 12 are the effective nucleophile and electrophile, which could lay the groundwork for intermolecular hydrogen bonding in crystal packing. natural population analysis predicted that o4 and h31 atoms had the highest negative and positive charge, respectively, supported the intra-molecular hydrogen bonding o4-h31. . . o5. the nlo study confirmed that cirsilineol can be used as an nlo material. admet analysis confirmed that the title compound is nontoxic and orally accepted. finally, molecular docking with the androgen receptor shows that it has the lowest binding affinity of -7.8 kcal/mol with the protein code 1gs4 and the lowest inhibition constant, suggesting that cirsilineol may be an inhibitor of 1gs4. acknowledgments t.r. paneru acknowledges dst, india for granting a partial fellowship (insa/dstisrf/2023/nep/08/13), and b.d. joshi acknowledges the university grant commission (ugc), nepal for partial financial support to this work under the faculty research grant (frg-79/80s&t-05). author contributions t.r. paneru: writing-original draft, investigation, and formal analysis; p. tandon: software and supervision; b.d. joshi: writing-review, editing, and supervision. data availability the data supporting the findings of this study are available from the corresponding author upon reasonable request. references [1] d.k. patel. health benefits, therapeutic applications, and recent advances of cirsilineol in the medicine: potential bioactive natural flavonoids of genus artemisia. emiddt, 23:894–907, 2023. 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[54] p.w. rose, b. beran, c. bi, w.f. bluhm, d. dimitropoulos, d.s. goodsell, a. prlic, m. quesada, g.b. quinn, j.d. westbrook, j. young, b. yukich, c. zardecki, h.m. berman, and p.e. bourne. the rcsb protein data bank: redesigned web site and web services. nucleic acids research, 39:d392–d401, 2011. introduction materials and methods computational details results and discussion geometry optimization vibrational assignment o-h vibrations o-ch3 vibrations vibrations in ring r1 vibrations in ring r2 vibration in ring r3 density of states (dos) uv-v is spectrum and electronic transition electrostatic potential (esp) surface analysis natural population analysis nonlinear optical (nlo) properties admet properties analysis molecular docking conclusion bibechana vol. 22, no. 1, april 2025, 73-79 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar fabrication of cu: zno thin film sensor for ethanol vapor detection rabin simkhada1, dalton r. gibbs2, soma dhakal2, dipak oli1, rishi ram ghimire3, deependra das mulmi4,∗, leela pradhan joshi1,∗ 1dept. of physics, amrit campus, tribhuvan university, kathmandu, nepal 2virginia commonwealth university, dept. of chemistry, richmond, va, 23284, usa 3dept. of physics, patan multiple campus, tribhuvan university, kathmandu, nepal 4nanomaterials research laboratory, nepal academy of science & technology, khumaltar, nepal ∗corresponding author. email: deependra.mulmi@nast.gov.np(dm) leela.pradhanjoshi@ac.tu.edu.np(lp) abstract for a long time, metal oxide semiconductor (mos) based gas sensors have been widely used in domestic, commercial, and industrial sectors to detect harmful gases. the performance of such sensors is significantly enhanced by appropriate doping of suitable materials into mos such as zno and sno2. this work showcases the design, analysis, and use of a cu-doped zno (cu: zno) film tailored for detecting traces of ethanol vapor at lower temperatures. herein, various cu: zno films have been fabricated on glass substrates using a spin coater followed by annealing at 600 0c for 1 hour in a muffle furnace. so-prepared samples have been characterized using x-ray diffraction, energy dispersive analysis x-ray (edax), uv-visible spectrophotometer, and scanning electron microscopy (sem). the xrd analysis showed a polycrystalline nature with preferred orientation along (100) and (002) crystal planes. the morphology study showed their porous and granular surface structure. these films' elemental analysis demonstrated the good incorporation of cu into the zno matrix. the uv-visible results showed a significant decrease in the band gap from 3.28 ev for undoped zno to 3.20 ev for cu: zno films. ultimately, as-prepared cu: zno thin films were used for sensing ethanol vapor at temperatures ranging from 100 0c to 300 0c. the result showed a maximum sensitivity of 70.60 % at a reduced temperature of 140 0c at 4% cu: zno thin, which implies that cu: zno is suitable for developing the gas sensors for upcoming future generations. keywords polycrystalline, spin coating, gas sensor, metal oxide semiconductor. article information manuscript received: october 6, 2024; revised: january 13; accepted: january 17, 2025 doi https://doi.org/10.3126/bibechana.v22i1.70639 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 73 http://nepjol.info/index.php/bibechana deependra.mulmi@nast.gov.np leela.pradhanjoshi@ac.tu.edu.np https://doi.org/10.3126/bibechana.v22i1.70639 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ rabin simkhada et al./ bibechana 22 (2025) 73-79 74 1 introduction over the last few decades, the rapid increase of the global population has exploited excessive nonrenewable natural resources, which produce numerous harmful gases [1, 2]. it has become one of the greatest environmental risks to health [3]. if the normal concentration of these gases exceed, then they cause long-term health hazards to people that may lead to heart disease, lung cancer, and respiratory infections [4–6]. so, there is an instant need for effective gas sensors to detect and reduce these problems. several devices are available for tracking pollutants and dangerous gases, which are very expensive, time-consuming, and hardly used in real-time situations. to reduce the abovementioned problems, there is a greater demand for costeffective, accurate, portable, and reliable gas sensors. in recent times, several metal oxide semiconductors have been used to detect pollutant gases and organic vapor including zno, tio2, fe2o3, sno2, mgal2o4, cutio2, and many more [7–9]. among these, zno has been considered one of the most promising materials for detecting toxic gases as it has a wide band gap, high exciton energy, chemical stability, more electron mobility, a high surface area, and is nontoxic and abundant in nature. [10–14]. most zno sensors follow the surfacecontrolled sensing mechanism. nonetheless, there are still certain problems with gas sensitivity, such as high operating temperatures, huge response and recovery times, and poor sensitivity percentages of gas response. fabrication of zno gas sensors with very good sensitivity and selectivity for spotting toxic and explosive gas leakages is a major challenge, mainly because of their high operating temperatures [15]. so, it is critical to discover a practical method for creating zno nanostructures with high sensitivity and superior stability [16]. doping of the metal is frequently used to enhance the sensing behavior of the metal oxide semiconductors (mos) [17]. in this work, copper is doped in a different weight ratio into zno over a glass substrate. copper (cu) is known for its excellent electrical and thermal conductivity, ductility, and resistance to corrosion [18]. cu doped zno exhibits properties that are favorable for sensing [19, 20]. the most popular and inexpensive type of alcohol, ethanol, is widely used in the chemical industry, brewing, medicine, pharmaceuticals, personal care products, fuel, and laboratory [4, 21]. long term use and high dose exposure of ethanol cause a weakened immune system, and leadto health hazards to living beings. there is an urgent need for the detection of such lethal gases with effective sensing materials. this work reports on the synthesis of undoped and cu doped zno for detecting traces of ethanol vapor at reduced temperatures than reported values. there is a significant challenge in establishing a stable device using any oxide material due to the physisorption and chemisorption of moisture from the atmosphere, which gradually degrades the quality of the films and changes the performance of the device. to avoid this practical limitation, the device can be kept in a vacuum before use; however, this restricts and limits its application. selectivity is a major challenge for this device. for example, the device responds to various alcohols (ethanol, methanol, butanol), water vapor, and ammonia. therefore, the solution is to identify a selective dopant that can capture only certain types of molecules. mass production using a low-cost chemical method is suitable, but it still lacks reproducibility. this limitation can be mitigated using vacuum techniques like pld, sputtering, or thermal evaporation; however, the cost would be high for mass production. once the selectivity of the device towards the target molecules is achieved, the application becomes feasible, and at least a disposable, low-cost device can be made using a simple chemical method. this research is beyond the scope of mass production; it focuses solely on how the cu dopant changes the responsivity of the device to ethanol vapor. 2 experimental details 2.1 materials the materials used to fabricate cu: zno films were copper chloride dihydrate, zinc acetate dihydrate, ethanol, labolene, acetone and distilled water. all the chemicals used in this experiment were of analytical grade. figure 1: schematic diagram for zno film preparation. 2.2 deposition of zno film thin films of 0.5m undoped and cu-doped zno were synthesized using a spin coater. the zinc acetate dihydrate salt dissolved in ethanol, while copper chloride was dissolved in ethanol solution separately. these two solutions were added and stirred for 60 minutes at 60 0c in a magnetic stirrer. five rabin simkhada et al./ bibechana 22 (2025) 73-79 75 solutions were prepared without doping and varying cu from 1% to 4% as a dopant. these solutions were left to age for 24 hours at room temperature before film deposition. microscopic glass substrates were first cut into an appropriate size, then cleaned using labolene and acetone, and finally rinsed with distilled water. subsequently, they were dried in a hot air oven at 150 0c for 2 hours. the speed and spinning time of the spin coater were set to 3000 rpm for 30 seconds. this process yielded undoped and cu: zno layers of 1%, 2%, 3%, and 4% concentration on the glass substrate. 2.3 characterization structural characteristics of as-prepared thin film were characterized by using x-ray diffractometer (xrd). interplanar spacing (d) is calculated by using bragg’s law [22] 2dsinθ = nλ where, λ is the wavelength of the x-ray, n and θ represent order of diffractions and bragg’s angle, respectively. further, average crystallite size (d) was computed using the relation of debye–scherrer formula [23] d = 0.9λ βcosθ where β represents the fwhm of the sharp peak. the surface morphology and elemental analysis of the undoped and cu: zno was studied using scanning electron microscopy (sem) and energy dispersive x-ray (edax). on the other hand, optical properties of zno and cu: zno were investigated using uvvisible spectrophotometer (cary 60, agilent technology). the optical band gap energy of the thin films can be found by extending the linear segment of (αhν)2 on the x-axis. the formula employed for calculating the band gap is provided as follows: αhν = a(hν ± ep − eg) n where a is a constant, h is the planck constant, ν is the frequency of radiation and n is a constant that determines the type of the optical transition. similarly, the sensitivity of thin films was evaluated by using formula [24] s = ra −re ra × 100% where ra is the resistance of thin film measured in the air and re is the resistance of thin film measured at ethanol vapor exposure. 3 results and discussion 3.1 scanning electron microscopy scanning electron microscopy [25] is important as it helps for better understanding of surface textures of as prepared samples by providing high-resolution images. figures [2] (a), (b), (c),(d) and (e) show the sem images of undoped zno, 1%, 2%, 3%, and 4% cu doped films at resolution of 500 nm, respectively. these sem images clearly showed a grainy-like structure with a decrease in particle size for cu: zno films. insets in each figure show the sem images captured at 100 nm resolution. figure 2: sem images of (a) undoped zno (b) 1% cu: zno (c) 2% cu: zno (d) 3% cu: zno (e) 4% cu: zno. 3.2 energy dispersive x-ray analysis edax is generally used for elemental analysis of prepared materials [26]. here, the different elements present in as-prepared thin films are analyzed. figure [3] (a) and (b) demonstrate the edax spectra of undoped and 1% cu: zno thin films, respectively. the results show the presence of zn, o along with traces of other elements of c, si, and ca are presented in the inset of figure [3] (a). figure [3](b) illustrates edax of cu: zno. in this case, the atomic percentage of copper is quantified as 1.91% in the 1% cu thin film. edax confirms the successful incorporation of cu into the zno lattice and provides quantitative elemental composition. an optimal cu concentration ensures improved sensor performance, while excessive doping can introduce defects that degrade conductivity and response stability. figure 3: (color online) edax spectrum of: (a) undoped zno and (b) 1% cu doped zno. 3.3 structural analysis the surface morphology and grain size of the zno nanostructure play a major role in sensing and detection of gases. the structural analysis of undoped rabin simkhada et al./ bibechana 22 (2025) 73-79 76 and doped zno was performed by x-ray diffraction. the x-ray diffraction (xrd) pattern consists of a number of peaks indicating zno films were polycrystalline in nature. figure [4] depicts the xrd pattern of zno with different concentrations of cu ranging from 0% to 4%. three intense peaks were observed at 33.19 0 (100), 35.86 0 (002) and 37.68 0 (101) for undoped zno thin film that were found to be consistent with the zno peaks of jcpds values. figure 4: (color online) xrd pattern for undoped and cu doped zno thin film. table 1: comparison between the calculated interspacing distance (d), standard jcpds d-spacing, and corresponding crystallite size. cu-zno (2θ) (°) calculated d (å) jcpds d (å) crystallite size d(å) average d (nm) % 0% 33.19 2.6978 2.8142 279.60 28.17 35.86 2.5027 2.6033 329.39 37.68 2.3859 2.4759 236.02 1% 33.28 2.6950 2.8142 281.76 26.09 35.93 2.4960 2.6033 241.68 37.76 2.3812 2.4759 259.32 2% 33.20 2.6968 2.8142 274.61 26.06 35.86 2.5028 2.6033 243.25 37.67 2.3864 2.4759 263.98 3% 33.16 2.6998 2.8142 256.09 26.47 35.82 2.5047 2.6033 273.14 37.64 2.3841 2.4759 265.13 4% 32.51 2.7525 2.6882 260.70 23.90 35.18 2.5498 2.4952 225.23 36.97 2.4302 2.3797 233.79 the xrd major peaks observed were well aligned along the growth direction implies wurtzite structure of zno with no observable defects. additionally, other minor peaks are also found in xrd patterns. these results vividly agree with the previously reported work [27–30]. table [1] shows a comparison between the calculated interplanar spacing distance (d), standard jcpds d-spacing and the corresponding crystalline size (d). the calculated value of d is compared with the standard jcpds card number of 36-1451 [31]. the calculated value of interplanar spacing is found to be less than the jcpds value, which may be due to the impurities in zno. the average crystallite sizes were of 28.17 nm, 26.09 nm, 26.06 nm, 26.47 nm, and 23.90 nm for undoped,1%, 2%, 3%, and 4% of cu doped zno, respectively. notably, these results vividly agree with the sem results. table 1 clearly shows the decreasing d value for cu doped zno. 3.4 optical analysis the optical band gap of thin films was calculated from tauc plot. figure [5] illustrates the band gap of undoped and cu: zno thin films. the band gaps for each film are calculated by extrapolating the linear portion of the respective curve. it is found that the band gap value of undoped zno thin films was 3.28 ev. when cu is doped into zno, the band gap decreases and found to be minimum 3.17 ev at 4% cu: zno. this reduction in the band gap might be due to the position of cu at nearby substitutional sites. further, cu doping might have introduced some additional energy levels in the zno near the valance band and conduction band edge, although the momentum of holes and electrons remain constant [32]. figure 5: (color online) bandgap of undoped and cu doped zno. 3.5 sensor application the zno sensor experiences a change in resistance when gas molecules interact with its surface. in normal conditions, oxygen molecules are absorbed onto the zno surface and ionize into oxygen species by capturing electrons from the conduction band. this process creates a surface depletion layer, which increases the sensor’s resistance [33]. when ethanol molecules come into contact with the zno surface, these oxygen species interact with the ethanol and release the trapped electrons back into the conduction band. doping zno with cu introduces additional charge carriers, typically in the form of holes or electrons which increases the material’s conductivity.this modification enhances the material’s rabin simkhada et al./ bibechana 22 (2025) 73-79 77 sensitivity by increasing the interaction strength between the target gas molecules and the sensing surface. furthermore, the presence of cu dopants alters the surface chemistry of zno, leading to improved selectivity by facilitating specific gas adsorption mechanisms. copper doping can alter the band structure of zno, potentially narrowing the band gap. these changes can improve electron mobility and facilitate the transfer of electrons when gas molecules interact with the sensor. which translates to higher sensitivity. figure [6] shows the sensitivity measurements of undoped and cu doped zno for ethanol vapor. the injection of ethanol is 1000 ppm for each sample. we have calculated the sensitivity of fabricated thin films by measuring the resistance in air (ra) and in gas (re). when zno films are exposed to air, oxygen molecules are adsorbed on their surface by attracting an electron from the conduction band . consequently, the resistance becomes high which may reduce conductivity. however, when ethanol gas is exposed to the film, gas reacts with the adsorbed oxygen ions on the surface of thin films and donates electrons back into the conduction band. as a result, conductivity increases compared to the undoped one. the optimum sensitivity of samples performed at the corresponding temperature is presented in table [2]. it showed that the sensitivity increases with the increment in the cu concentration. the sensitivity of pristine zno is only 16.57% at an operating temperature of 200 0c. conversely, the sensitivity of cu: zno rises while increasing the cu concentration. the maximum sensitivity of 70.60 % is found at cu: zno (4%) at an operating temperature of 140 0c, which is followed by 3%, 1% & 2% cu: zno with the corresponding temperatures of 180 0c, 200 0c & 200 0c respectively. the systematic decrease in operating temperature was observed from 200 0c for undoped to 140 0c for the 4% cu: zno films. figure 6: (colour online) sensitivity of undoped and cu: zno thin film with temperature variation. table 2: maximum sensitivity of samples performed at various operating temperatures. sample maximum sensitivity (%) operating temperature (°c) 0% cu:zno 16.57 200 1% cu:zno 54.54 200 2% cu:zno 50.29 200 3% cu:zno 59.21 180 4% cu:zno 70.60 140 as the cu concentration increases, the crystalline size of the film slightly decreases, increasing the grain boundaries and surface roughness, which in turn increases the surface area, making it favorable for sensing applications. edx analysis is used to determine the cu wt.% in the elemental composition. in the case of 1% cu doping in zno, it shows 4.25 wt.% of cu, along with other elements, which leads to a significant enhancement in sensitivity from 16% to 54% towards ethanol vapor. 3.6 sensing mechanism the zno sensor operates by detecting resistance changes caused by gas interactions with its surface. under normal conditions, oxygen molecules are adsorbed on the zno surface, where they ionize into oxygen species by capturing electrons from the conduction band. this electron capture results in the formation of a surface depletion layer, which increases the sensor's resistance [33, 34]. when ethanol gas encounters the zno surface, the oxygen species react with the ethanol molecules, releasing the trapped electrons back into the conduction band. this electron return reduces the depletion layer, thereby lowering the sensor's resistance. the effectiveness of a gas sensor is influenced by factors such as sensitivity, selectivity, thermal stability, and response speed, which are largely determined by the shape, size, and surface morphology of the sensing material. figure 7: (color online) depleted region at gb (a) under ambient condition (b) under ethanol condition. in zno sensor, depleted layers are formed in inrabin simkhada et al./ bibechana 22 (2025) 73-79 78 dividual nano-crystallites as well as in grain boundary (gb) regions due to the adsorption of oxygen molecules in ambient condition. oxygen species from the atmosphere capture the electrons at the surface of zno, therefore, the negative charges would be trapped at the surface and grain boundary (gb) regions [fig. 7]. trapping of negative charge causes the band bending upward. as a result, gb potential (φgb ) and gb depletion width (ω) are formed which control the carrier transport through the gb region. in the presence of deoxidizing gas like ethanol, electrons trapped by oxygen molecules are returned the zno film and decreased potential (φgb) and increased the conductivity [20,25,33]. 4 conclusion this work concludes with the successful fabrication of undoped and cu: zno thin films for ethanol sensing. the xrd results confirmed the polycrystalline hexagonal wurtzite structure of zno. edax values confirm the doping of cu into the zno matrix. likewise, sem images showed that the as-prepared thin films are porous and grainy structured with the reduction of grain size for cu doping film. the band gaps of cu: zno significantly decreased with the increment of cu concentration as compared to undoped zno. more importantly, when the cu concentration was 4%, the maximum sensitivity of 70 % for ethanol exposure was at 140 0c. based on these results, it can be concluded that cu: zno holds significant potential in the field of gas sensing and might be useful to facilitate superior gas sensing performance, particularly in detecting ethanol vapor. acknowledgements the authors would like to thank the international science program (isp), uppsala university, sweden for supporting the atmospheric and material science research group at the department of physics, amrit campus through nep01 for conducting this work. declaration of conflict of interest there is no known conflict of interest by the authors. references [1] b. p. j. d. l. costello, r. j. ewen, n. guernion, and n. m. ratcliff. sens. actuators b. sens. actuators b, 87:207, 2002. 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[34] k. ozawa, t. hasegwa, k. edamoto, k. takahansi, and m. kamada. j. phys. chem. b, 106(36):9380–9386, 2002. introduction experimental details materials deposition of zno film characterization results and discussion scanning electron microscopy energy dispersive x-ray analysis structural analysis optical analysis sensor application sensing mechanism conclusion bibechana vol. 22, no. 3, december 2025, 248-257 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar eco-friendly synthesis of silver nanoparticles using withania somnifera root extract: characterization, phytochemical profiling, and evaluation of antimicrobial activity ratna bahadur thapa1, shankar datt ojha2, sujan dhungana2, laxmi tiwari2, devendra khadka3,4, milan babu poudel5, megh raj pokhrel4, janaki baral2, bhoj raj poudel2* 1department of chemistry, damak multiple campus,t.u., damak nepal 2department of chemistry, tri chandra multiple campus, t.u., kathmandu, nepal 3department of chemistry, tribhuvan multiple campus, t.u., tansen, palpa, nepal 4central department of chemistry, t.u,kirtipur, kathmandu, nepal 5department of convergence technology engineering, jeonbuk national university, jeonju, jeollabuk-do 54896,republic of korea ∗corresponding author. email: bhoj.poudel@trc.tu.edu.np abstract silver nanoparticles (ag nps) were synthesized using a green chemistry approach, utilizing withania somnifera (ashwagandha) root extract, whose phytochemicals acted as eco-friendly, non-toxic reducing agents. the synthesized agnps were characterized using x-ray diffraction (xrd), uv-visible spectroscopy, fourier transform infrared spectroscopy (ftir), scanning electron microscopy (sem) and energy dispersive x-ray spectroscopy (eds). xrd analysis confirmed the crystal structure of the ag nps and estimated their size to be 10 nm. uv-visible spectroscopy showed a characteristic absorption peak, confirming the formation of agnps. ftir analysis identified functional groups associated with the phytochemicals in the root extract, which may contribute to nanoparticle stabilization. sem images revealed the spherical morphology of the ag nps, while eds analysis confirmed the presence of silver in the synthesized nanoparticles. the phytochemical examination of ashwagandha found secondary metabolites, including phenolic, alkaloid, and flavonoid compounds. the synthesized ag nps were assessed for their antimicrobial activity against staphylococcus aureus, escherichia coli, and candida albicans, demonstrating significant efficacy markedly against gram-positive bacteria. this finding highlights the role of ashwagandha-mediated ag nps in sustainable np formation and antimicrobial applications. keywords antimicrobial activity, phytochemical analysis, root extract, ag nps, withania somnifera. article information manuscript received: march 9, 2025; revised: august 5, 2025; accepted: august 8, 2025 doi https://doi.org/10.3126/bibechana.v22i3.76471 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 248 http://nepjol.info/index.php/bibechana bhoj.poudel@trc.tu.edu.np https://doi.org/10.3126/bibechana.v22i3.76471 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ratna bahadur thapa et al./ bibechana 22 (2025) 248-257 249 1 introduction nanoscience involves the investigation and modification of materials on a nanoscale, generally defined as being between 1 and 100 nanometers (nm). nanoscience has rapidly evolved and gained considerable attention in research with industry worldwide [1]. nanoparticles (nps) exhibit distinct electrical, optical, chemical, and catalytic characteristics that set them apart from larger bulk substances, making them highly important for many applications [2,3]. bio-nanotechnology is the backbone of nanotechnology; it combines biotechnology and nanotechnology to develop eco-friendly and biosynthetic methods for synthesizing nanomaterials [4]. metallic nps, including agnps, gold, titanium, copper, and zinc, are widely studied for their superior performance in various applications. agnps are widely recognized for their potent antimicrobial activity, which makes them highly valuable across many fields, including medicine, food science, agriculture, and environmental remediation. their effectiveness stems from their ability to inhibit microbial growth, contributing to advancements in numerous applications [5, 6]. the process of synthesizing agnps has advanced over time, with earlier chemical reduction techniques frequently using harmful chemicals that present health and environmental hazards [7]. in response, green or eco-friendly synthesis methods have gained attention, utilizing natural materials such as plant extracts, microbes, and biopolymers to create nps without harmful chemicals, making the process more secure and environmentally friendly [8]. agnps exhibit multifunctional properties that have led to their widespread applications in medicine, catalysis, and environmental remediation [9,10]. compared to metals like gold and platinum, silver offers cost-effective and scalable synthesis, particularly when biosynthetic routes are adopted. furthermore, biosynthetic methods using plant-derived compounds such as polyphenols and proteins as reducing agents enhance the environmental friendliness and cost-efficiency of ag nps formation [11]. however, challenges related to scalability, cost, and labour intensity remain in np synthesis. withania somnifera is widely recognized as ashwagandha (figure 1). it contributes to ayurvedic medicine and is renowned for its numerous positive health effects, including anti-swelling, oxidative stress-reducing, adaptogenic, and antimicrobial [12]. with its ability to thrive in arid regions and poor soils, ashwagandha is widely cultivated in india, nepal, the middle east, and parts of africa [13]. the utilization of plentiful natural resources, including botanical extracts, further emphasizes the potential of green synthesis techniques. the plant is rich in various bioactive entities that enhance its therapeutic benefits [14]. among many plant-based sources, ashwagandha has emerged as an intriguing candidate for the synthesis of agnps. figure 1: arial part and root of withania somnifera (ashwagandha) plant. the eco-friendly ag nps synthesis using withania somnifera root extract presents a sustainable alternative to conventional methods, harnessing the plant’s natural phytochemicals for both reduction and stabilization. this method supports environmental sustainability and can elevate the antimicrobial properties of agnps by leveraging the synergistic interaction with bioactive compounds derived from plants [15]. this finding explores the synthesis of agnps using withania somnifera root extract. research highlighted the characterization, phytochemical profile, and antimicrobial properties of the nps. various analytical techniques, including xrd, sem, and uv-visible spectroscopy, will be utilized to assess the size, morphology, and ag nps' stability. the phytochemical composition of withania somnifera compounds will be examined to lead to the formation of nps. additionally, ashwagandha-based agnps of antimicrobial activity will be assessed against bacterial, fungal, and viral pathogens, aiming to evaluate their potential applications in medical and biotechnological fields. the findings of this research will further promote the use of plant-based materials in np synthesis, offering novel solutions for creating safe, efficient, and sustainable nanomaterials. 2 materials and methods 2.1 materials in the laboratory experiments, distilled water and analytical-grade chemicals were utilized. silver nitrate (agno3), and sodium hydroxide (naoh) were obtained from thermo fisher scientific india pvt. ltd., india. 2.2 collection and preparation of ashwagandha root extract the roots of ashwagandha plant were collected from their natural habitat in tapoban forest of ratna bahadur thapa et al./ bibechana 22 (2025) 248-257 250 marma rural municipality-4, darchula district, sudurpashchim province, nepal (29.738° n, 80.821° e) between march and april 2024. the plant was harvested during the cooler morning hours. the roots were carefully washed with clean water, then sliced into smaller segments and allowed to dry in a shaded area for two weeks. after the drying period, the roots were processed into a fine powder using a mechanical grinder. for the extraction, 10 grams of the powdered ashwagandha were soaked with 100 ml distilled water in a beaker. the solution was heated to 60° c and stirred for 30 minutes with a magnetic stirrer. afterwards, the mixture was allowed to cool to a suitable temperature, filtered using whatman filter paper, and stored at 4°c for later use. 2.3 phytochemical screening the hydro-methanolic root extract, prepared by the cold percolation of 30 g of powder, yielded 12 g of crude methanolic extract, which was subsequently used for the qualitative screening of phytochemicals. the analysis followed established protocols incorporating slight modifications based on insights from earlier studies [16–18]. 2.4 synthesis of agnps agnps were synthesized using a green method under optimized conditions. a 0.001 m agno solution was prepared by dissolving 0.17 grams of agno in 1000 ml of distilled water. in a typical reaction, 50 ml of this solution was mixed with 20 ml of freshly prepared ashwagandha root extract, added dropwise under continuous magnetic stirring at 600 rpm. the reaction was conducted at ambient temperature (~25 °c) and a neutral ph of 7.0, maintained by not adding any acid or base. the total reaction time was 30 minutes, during which the color change from pale yellow to dark brown indicated the formation of agnps. these parameters were selected based on reported optimal conditions for plant-extract-mediated silver nanoparticle synthesis. 2.5 characterization of agnps 2.5.1 uv-vis spectroscopy when materials absorb ultraviolet and visible light (200–600 nm), they produce the ultraviolet-visible spectrum. the agnps produced using ashwagandha root extract were characterized by a uvvisible spectrophotometer (specord 200 plus, analytik, jena, germany). 2.5.2 xrd analysis the crystallographic information of synthesized agnps was investigated using a d2 phaser, bruker with cu k radiation. the scanning was performed over a 2 range of 30°-90° utilizing a step size of 0.2003 2.5.3 ftir analysis ftir analysis was conducted using a perkinelmer spectrometer with spectrum ir (version 10.6.2 to determine the functional groups found in the root extract responsible for the synthesis of ag nps within the spectral range of 500-4000 cm1. 2.5.4 fe-sem and eds analysis the morphology and elemental composition of agnps were analyzed using a field emission scanning electron microscope (fe-sem, hitachi, japan) equipped with an energy-dispersive x-ray spectroscopy (eds) detector. 2.6 antimicrobial effectiveness the antimicrobial effectiveness of agnps and root extract was evaluated against three specific microbial strains: escherichia coli (atcc 8739), which is a gram-negative bacterium; staphylococcus aureus (atcc 6538p), a gram-positive bacterium; and candida albicans (atcc 2091), a fungal organism. the assessment utilized the agar-well diffusion technique to compare their effectiveness with that of a standard antibiotic. each culture was incubated under optimal conditions, ensuring precise measurement of inhibition zones and clear differentiation between microbial responses. all antimicrobial experiments were conducted in triplicates. the data are expressed as mean ± standard deviation (n=3). 2.6.1 media preparation a liquid broth (lb) medium was made by mixing 13 grams of lb powder (from sisco research laboratories pvt. ltd., india) into 1 litre of distilled water. this mixture was subsequently sterilized in an autoclave set at 121°c and 15 psi for 25 minutes. after sterilization, it was allowed to cool to 50 °c. once cooled, 5 ml portions of the medium were aseptically distributed into pre-sterilized 15 ml falcon tubes. the tube was then inoculated with a bacterial culture and incubated for 1 day for bacterial cell growth. to ensure accuracy and reproducibility, it is crucial to maintain aseptic techniques throughout the process and to verify that the incubation conditions are optimal for the specific bacterial strains being studied. ratna bahadur thapa et al./ bibechana 22 (2025) 248-257 251 2.6.2 media plated and antimicrobial assay preparation muller hinton agar (mha) plates were made by dissolving 39 grams of mha powder (sisco research laboratories pvt. ltd., india) in one litre of distilled water. after mixing, the solution was sterilized in an autoclave at 121°c and a pressure of 15 psi for 25 minutes. following autoclaving, the medium was allowed to cool to approximately 50°c before being dispensed into sterile petri dishes, with each plate receiving 25 ml of the prepared agar. before the antimicrobial assay, each plate (stored in the refrigerator) was labelled with the corresponding sample name. by using a sterile cotton swab, a 150 µl aliquot of bacterial suspension was spread evenly on the surface of the agar. wells were then created in the agar to accommodate the test samples and standards. for plant extracts, samples were loaded with 50 mg/ml concentration dissolved in dmso, while nps were added at approximately 30 mg per well. a kanamycin solution (5 mg/ml; 10 µl) was used as a positive control to assess bacterial strain comparability. similarly, for antifungal evaluation, itraconazole (20 mg/ml; 10 µl) was introduced into the designated wells as a standard reference. the plates were incubated at 37°c for 24 hours, and the effects were evaluated. 2.7 data analysis the data obtained was analyzed and plotted using origin 2024b software. 3 results and discussion 3.1 phytochemical screening the phytochemical components in the ashwagandha root extract that contributed to the reduction and stabilization of agnps were analyzed qualitatively. results of phytochemical screening indicate that hydro-methanolic root extract is rich in secondary metabolites (test result in table 1). alkaline reagent tests were done in the presence of flavonoids [17], and alkaloids were found using hager’s test [18]. the test showed positive results for saponins, as indicated by the froth test [17]. terpenoids and steroids were also detected through positive results in the salkowski test [18]. tannins were presented as evidenced by the lead acetate test [18]. additionally, quinone was identified through the concentrated hydrochloride (hcl). the presence of glycosides and phenolic compounds was confirmed using sodium hydroxide and ferric chloride tests [16]. these compounds, extracted with polar solvents, have an inherent polarity that aids in np formation and stabilization. table 1: phytochemical screening of the hydro-methanolic root extracts of ashwagandha s. n secondary metabolites tests result 1 flavonoid test alkaline reagent test + 2 alkaloids test hager’s test + 3 saponins test froth test + 4 terpenoids and steroids test salkowski test + 5 tannins lead acetate test + 6 quinone test conc. hcl + 7 glycosides naoh + 8 phenolic fecl3 + note: “+” indicates the presence of the phytochemical content. 3.2 green synthesis of agnps the environmentally friendly formation of agnps can be achieved using extracts from plants that are abundant in various bioactive substances, including phenolic acids, terpenoids, and proteins. these compounds serve as natural reducing agents in the synthesis process. these biomolecules aid in converting metal ions into stable nps, offering a greener alternative that minimizes the use of harmful chemicals. these compounds help reduce metal salts to nanoscale particles, such as converting ag+ to ag° in ag nps synthesis. ashwagandha, known for its antioxidant properties, is particularly effective in reducing silver ions to agnps. in this process, an aqueous ashwagandha extract is combined with agno under constant stirring. the bioactive compounds present in plant extract assist in the reduction of silver ions (ag+) by providing electrons, which results in the formation of agnps. this process often involves a noticeable colour change due to spr, typically shifting the solution's colour to a shade of brownish-blue [19]. the neutral ph (~7) and ambient temperature maintained during the ratna bahadur thapa et al./ bibechana 22 (2025) 248-257 252 synthesis likely favored the reduction kinetics and stabilization of agnps by phenolic and flavonoid constituents in the extract. the 30-minute reaction time aligns with other rapid green synthesis protocols reported in the literature [20]. figure 2 illustrates the green synthesis route of agnps using withania somnifera root extract, showing the key steps: preparation of plant extract, reduction of ag ions, and stabilization of nanoparticles by bioactive phytochemicals. figure 2: representative diagram of green synthesis of ag nps. 3.3 characterization of agnps 3.3.1 uv-vis spectroscopy analysis ag nps synthesized using withania somnifera root extract were confirmed through uv-vis spectroscopy, which displayed a broad absorption spectrum between 300–600 nm. a clear peak at 433 nm is observed, as illustrated in figure 3(a). the optical absorption peak observed at 433 nm corresponds to surface plasmon resonance (spr), a hallmark feature of metallic agnps. the spr peak arises from collective oscillation of conduction electrons on the nanoparticle surface in resonance with incident light [20]. the peak position varies based on the morphology and size of the nps, with smaller particles generally exhibiting a blue shift. the broad spectral profile indicates a certain level of polydispersity, a common trait in green synthesis methods [21]. figure 3: (a)ultraviolet-visible absorption spectra (b) tauc plot indicating an apparent optical energy gap (~2.25 ev), derived from quantum confinement effects in agnps. the energy gap of ag nps differs from that of macroscopic silver due to quantum confinement effects [22]. in bulk form, silver behaves as a metal with no band gap since the conduction and valence bands overlap. however, when silver is reduced to the nanoscale, especially at smaller particle sizes, a shift in optical properties resembling a band gap can develop. for ag nps, this energy gap typically ranges between 2.0 ev and 4.0 ev, affected by the surrounding and size conditions of the particle. this optical gap, observed through techniques like uv-visible spectroscopy, is linked to plasmonic resonances rather than the electronic bandgap found in semiconductors. however, band gap governs the material's electrical properties and is essential in determining whether a material behaves as a conductor, semiconductor, or insulator [23]. agnps energy gap (eg) determined through the tauc method [24,25]; (αhν)1/m = c(h− eg) here, = absorbance coefficient, c = constant, h = planck's constant, = photon frequency, eg = optical band gap, and m = ½ for direct band gap semiconductors. additionally, an optical energy gap of 2.25 ev was calculated using the tauc method (figure 3 (b)). while this value mimics a "bandgap," it is not a true electronic bandgap as seen in semiconductors. instead, it reflects quantum confinement effects and plasmonic behavior associated with the small size of agnps. as agnps are metallic, their conduction and valence bands overlap in bulk; however, at the nanoscale, localized surface effects and interaction with light can produce apparent optical transitions that resemble a bandgap [21,22]. 3.3.2 ftir analysis the analysis using ftir was conducted to determine the functional groups that play a role in the synthesis and stabilization of ag nps. in figure 4, the ftir spectra of the plant extract is shown in ratna bahadur thapa et al./ bibechana 22 (2025) 248-257 253 black, while those of the synthesized agnps are represented in red. in the ftir spectrum of the plant extract, several distinctive peaks are observed, with a prominent absorption band at 3307 cm¹. the presence of hydroxyl groups in the extract has been indicated by the vibrations associated with o–h stretching [26]. the peak observed at 2940 cm¹ corresponds to asymmetric c–h stretching, suggesting that alkyl groups are present. furthermore, the bands identified at 1607cm¹ and 1408 cm¹ are associated with c=c and c–h vibrations, respectively. additionally, the spectrum feature at 1028 cm¹ is attributed to c–o stretching, a characteristic often associated with alcohols or phenolic compounds [27]. a band at 608 cm¹ was associated with c–h bending vibrations. the presence of ag nps resulted in significant changes, with all spectral bands showing weaker intensity in comparison to the original plant extract. this indicates that ag nps were successfully formed. notably, the reduced intensity of the o– h stretching vibration at 3307 cm-1 suggests that hydroxyl groups played a role in the synthesis of the nps. moreover, the shifts observed in the c=c (1593 cm-1) and c–o (1016 cm-1) absorption peaks provide further evidence of the involvement of these functional groups during the formation process. it is believed that various functional groups such as hydroxyl, and carbonyl are integral to not only the reduction of silver ions but also the stabilization of the nps [28]. figure 4: (ftir spectra of agnps (black) and root extract (red). 3.3.3 xrd analysis xrd is a powerful method used to examine the size and crystalline structure of materials by analyzing the diffraction patterns produced when xrays interact with a sample. the crystalline structure of withania somnifera-based ag nps was analyzed using xrd as shown in figure 5. the observed diffraction peaks at 2 angles of 37.8°, 44.3°, 64.4°, 77.2° and 81.2° correspond to the miller indices (111), (200), (220), (311) and (222) respectively. these peaks suggest the presence of a facecentred cubic (fcc) crystal structure. these results were validated by comparing them to the jcpds database (file number: 01-087-0717) [29]. some of the observed peaks were attributed to partial oxidation of silver, which occurred during longterm storage before characterization. the average crystallite size of powdered agnps was estimated using scherrer’s equation [30], d = kλ βcos θ in this eqn, the following variables are defined: d refers to the size of the crystallite or grain, k is the dimensionless shape factor, which is set at 0.9, represents the wavelength of the x-ray radiation being utilized, denotes bragg’s angle expressed in radians, and indicates the full width at half maximum, also measured in radians. the most intense diffraction peak appeared at 37.8°. the size of the crystallites in the agnps was measured to be 10.57 nm. this calculation was based on the xrd data, which includes detailed information on peak positions and angles, crucial for determining the crystallite size. figure 5: xrd patterns of ag nps. 3.3.4 sem/eds analysis the surface features and elemental percentage of the formed ag nps were examined through sem and energy-dispersive x-ray spectroscopy (eds). sem image captured at a scale bar of 0.5 m is presented in figure 6, showing spherical particles with consistent size distribution and noticeable agglomeration of the ag nps. when ag nps are heated indirectly, they tend to cluster together, leading to the electronic coupling between the metal ratna bahadur thapa et al./ bibechana 22 (2025) 248-257 254 particles. this interaction causes a shift in the spr to higher wavelengths, accompanied by a higher intensity in the uv-visible spectrum, in contrast to the behaviour of individual particles [31]. the synthesis method, purification steps, and drying conditions are key factors affecting the agglomeration, dispersion, stability, and size distribution of ag nps [32]. silver was found to be the most abundant element, comprising 56.9%, followed by carbon at 29.7%, and oxygen at 13.5%. a prominent peak confirmed the presence of silver metal. the peaks corresponding to oxygen and carbon, as seen in figure 6, are attributed to organic components from the proteins or enzymes in the extract, as well as the carbon tape used during the measurement process [33]. 3.4 antimicrobial evaluation the agar diffusion method was used to perform antimicrobial activity, adhering to established guidelines [34]. the zone of inhibition (zoi) served as the primary indicator to gauge antimicrobial effectiveness. the size of the zoi created on bacterial cultures was assessed to determine the antimicrobial activity of plant extracts, as shown in table 2. the zoi for each microbial strain was measured in millimeters and reported as mean ± sd (n = 3). atcc (american type culture collection) was the source for the microbial reference strains that play an essential role in standardizing and distributing these materials, ensuring reproducibility and reliability across scientific research and industrial applications. figure 6: sem image and eds spectrum of synthesized ag nps. table 2: antimicrobial screening of withania somnifera extracts strain reference culture type control (c+) (mm) ag nps (mm) plant extract (mm) e. coli atcc8739 gram-negative 25.0 ± 0.4 21.3 ± 0.4 0.0 s. aureus atcc6538p gram-positive 26.1 ± 0.4 22.4 ± 0.4 0.0 c. albicans atcc2091 fungi 27.2 ± 0.4 20.2 ± 0.4 0.0 note: zoi = zone of inhibition in mm. kanamycin (positive control, c+), concentration of 5 mg/ml. dmso was used as a negative control and showed no activity. the antimicrobial activity of ashwagandha extract on e. coli was tested using the atcc 8739 reference strain, with a positive control for comparison. the positive control produced a zoi of 25 mm, while ag nps exhibited a zoi of 21 mm against the strain, shown in figure 7(a), which suggests that ag nps demonstrate considerable antibacterial properties against e. coli. the antimicrobial effect of ashwagandha extract against s. aureus was assessed using the atcc 6538p reference strain, with a positive control for comparison. the zoi for positive control was 26 mm, while agnps showed a zoi of 22 mm against this strain, as shown in figure 7(b). these findings demonstrate that ag nps have significant antibacterial activity against s. aureus. antimicrobial activity of agnps possesses notable antimicrobial activity against c. albicans which was tested using the atcc 2091 reference strain, with a positive control for comparison. the zoi for the positive control was 27 mm, while agnps showed a zoi of 20 mm against this strain, as depicted in figure 7(c). figure 7: zone of inhibition for (a) e. coli, (b) s. aureus, and (c) c. albicans. 3.5 antibacterial mechanism of agnps agnps exhibit antimicrobial properties through both direct and indirect mechanisms. a key factor in their effectiveness is the continuous release of ag, which plays a crucial role in bacterial inhibition. these ions have a strong affinity towards proteins, allowing them to attach to bacterial cell walls and membranes, figure 8. this interaction disrupts membrane integrity, increasing permeability and leading to structural instability. once silver ions enter the cell, they disrupt the activity of respiratory enzymes, leading to the production of ratna bahadur thapa et al./ bibechana 22 (2025) 248-257 255 reactive oxygen species (ros) and hindering the synthesis of atp. the oxidative stress caused by ros damages essential cellular components, including lipids, proteins, and dna [35]. additionally, silver ions bind to dna, disrupting replication and transcription, which hampers cell division and ultimately leads to bacterial death [36]. they also interfere with ribosomal function, inhibiting protein synthesis and disrupting cellular processes [37,38]. figure 8: mechanism for the antimicrobial activity of ag nps.. beyond ion release, ag nps themselves contribute to bacterial inhibition. when bacteria encounter certain substances, they gather on their surfaces and infiltrate the cell wall. this infiltration disrupts the internal structures and causes the leakage of cellular materials, ultimately leading to cell death. moreover, ag nps interfere with bacterial signaling pathways by dephosphorylating tyrosine residues on peptide substrates, disrupting essential regulatory functions. this disruption inhibits bacterial proliferation and promotes cell death. through this combination of silver ion activity, nanoparticle interaction, and interference with cellular functions, ag nps demonstrate broadspectrum antimicrobial efficacy [39,40]. 4 conclusions ag nps synthesis using ashwagandha root extract provides an environmentally friendly and effective method for np formation. the synthesized nanoparticles were characterized through uv-vis spectroscopy, ftir, xrd, and sem/eds; this led to the formation of nps that were spherical and crystalline in shape, measuring 10.57 nm in size. ag nps are stabilized by phytochemicals, including alkaloids, saponins, and phenolic compounds found in the extract. the nps exhibited enhanced antimicrobial effectiveness against gram-positive and gram-negative bacteria, displaying larger inhibition zones and reduced mic values compared to the extract on its own. these results underscore the potential of ashwagandha-derived ag nps for medical and environmental purposes, highlighting the significance of green synthesis in promoting sustainable nanotechnology. future studies should aim to refine synthesis conditions and investigate additional applications to fully exploit the capabilities of these nps. future research will focus on finding the quantitative phytochemical profiling. this study had some limitations, lack 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[40] p. kharel, m. d. manandhar, s. k. kalauni, s. awale, and j. baral. isolation, identification and antimicrobial activity of a withanolide [ws1] from the roots of withania somnifera. nepal j. sci. technol., 12:179–186, 2011. introduction materials and methods materials collection and preparation of ashwagandha root extract phytochemical screening synthesis of agnps characterization of agnps uv-vis spectroscopy xrd analysis ftir analysis fe-sem and eds analysis antimicrobial effectiveness media preparation media plated and antimicrobial assay preparation data analysis results and discussion phytochemical screening green synthesis of agnps characterization of agnps uv-vis spectroscopy analysis ftir analysis xrd analysis sem/eds analysis antimicrobial evaluation antibacterial mechanism of agnps conclusions bibechana vol. 21, no. 2, august 2024, 159-170 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar comparative study of machine learning based prediction of supercapacitance performance of activated carbon prepared from bio-based materials kirti bir rajguru1, sujan bhandari2, ganesh kumar shrestha1, chhabi lal gnawali1,∗, bhadra prasad pokharel1 1department of applied sciences and chemical engineering, pulchowk campus, institute of engineering (ioe), tribhuvan university, lalitpur, nepal 2central department of physics, tribhuvan university, kirtipur, kathmandu, nepal ∗corresponding author: email: chhabig123@ioe.edu.np abstract the performance of electrochemical double-layer capacitors (edlcs) is evaluated by the capacitance of activated carbon (ac) electrodes. the capacitance of ac electrodes is influenced by many factors such as precursor type, activation method, pore structure, surface chemistry and electrolytic properties. in this paper, we present a comparative study of machine learning based prediction of surface area, mesopore volume and total pore volume of activated carbon for energy storage applications. the ml models were trained on a dataset of synthetic data that were generated from the limited number of experimental data and which included the activation temperature, methylene blue number and iodine number of the activated carbon (ac). the best performing ml model was random forest and xgboost model. the results of this study can be used to optimize the production of activated carbon and improve its performance in energy storage applications. keywords machine learning; activated carbon; energy storage; capacitance. article information manuscript received: january 31, 2024; revised: april 18, 2024; accepted: april 23, 2024 doi https://doi.org/10.3126/bibechana.v21i2.62465 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 159 http://nepjol.info/index.php/bibechana chhabig123@ioe.edu.np https://doi.org/10.3126/bibechana.v21i2.62465 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ kirti bir rajguru et al./ bibechana 21 (2024) 159-170 160 1 introduction a data based method called the machine learning algorithm has been applied as a substitute tool to deal with a number of real-world problems. creating models and techniques that enable computers to learn from data and make predictions or judgments without being explicitly programmed is a key component of the artificial intelligence field of machine learning [1, 2]. it is utilized in a variety of programs, including recommendation engines, natural language processing, and identifying pictures. there are various types of machine learning such as unsupervised machine learning and supervised machine learning. in supervised machine learning, the algorithm develops predictions or classifications based on input data after learning from labeled training data. unsupervised machine learning uses an unlabeled data collection as its foundation [3]. supercapacitors, also known as electrochemical capacitors, are an intermediate form of energy storage between batteries and ordinary capacitors. supercapacitors can store more energy than regular capacitors due to their substantially higher energy density. supercapacitors have received a lot of interest recently, due to its potential applications in a wide range of fields, such as consumer electronics and renewable energy systems. whereas batteries, store energy chemically, supercapacitors do so electrostatically [4, 5]. supercapacitors rely on the rapid movement of ions to store and release energy quickly. larger surface area and appropriate pore volumes enhance the device’s energy and power density. optimizing these parameters help in designing energy storage materials that can store more energy, charge and discharge faster, and has improved overall performance and durability in various applications [6–9]. fossil fuels can lead to energy crisis due to their finite supply and environmental impact. transitioning to renewable energy source is essential to mitigate these issues. activated carbon is highly porous form of carbon with a large surface area. activated carbon (ac) is prepared from various carbonaceous material such as peat, wood, etc. in this study, the methylene blue number (mbn), iodine number and temperature were utilized to predict the surface area, mesopore volume, and total pore volume of produced activated carbon by using machine learning algorithm [10, 11]. a larger surface enhances the size of room for interaction between the electrolyte and electrode material. more active places for electrochemical processes to take place can be made possible by this, increasing the amount of energy stored and accelerating the rate of charge/discharge. larger pores called mesopores allow ions to pass through them and enter and exit the material [12]. a higher mesopore volume ensures better ion accessibility and diffusion within the material, which improves the overall charge/discharge efficiency and, the device’s power performance. total pore volume includes all sizes of pores, from microspores to mesopores. it is a measure of the overall storage capacity for ions [13, 14]. this research employs statistical and experimental data, to assess the most suitable model for the prediction of more accurate dataset. the aspiration is to employ machine learning techniques which enhance comprehension of the interplay between different aspects of activated carbon and surface area, mesopore volume and total pore volume. this, in turn, will streamline and enhance the precision of experimental guidance for future experiments [15,16]. 1.1 machine learning models there are different types of machine learning models that can be used to predict the electrochemical properties of activated carbon and its features, as they can capture the non-linearity in the data. among all these models, we selected those that were most suitable for our data type so that we can predict the electrochemical features of the ac with high degree of accuracy. various studies like that of ziang, su, wang, donthula has been done in the use of machine learning for prediction of different types of properties of activated carbon [17]. 2 materials and methods 2.1 experimental terminalia chebula seed stones were used for the preparation of activated carbon(ac). terminalia seeds were collected from the market and cleaned to remove any impurities. phosphoric acid was used as an activating agent. terminalia seeds powder was mixed in a phosphoric acid solution. the impregnation process ensured that the seeds powder absorbed the acid solution uniformly. the impregnated powder was subjected to tubular furnace, typically in the range of 400°c700°c. it helped in the formation of development of pores and the removal of the volatile components. the phosphoric acid acted as a dehydrating agent and helped the carbon substance (activated carbon) to develop holes. to get rid of any remaining acids or other contaminants, the prepared activated carbon was thoroughly rinsed with distilled water. the synthesized activated carbon (ac) was analyzed by determining its iodine number, methylene blue number, surface area, mesopore volume and total pore volume [18–20]. we took eight data for each feature of methylene blue number, iodine number, surface area, mesopore volume, and total pore volume. kirti bir rajguru et al./ bibechana 21 (2024) 159-170 161 2.2 computational 2.2.1 data collection figure 1: heatmap of regression values of different input and output features of ac. figure 2: box plot featuring range of input and output values of features of the ac. figure 3: histogram of all the inputs and output features. the data from the experimental method was used to define the range and variance of each of the resultant values obtained using formulas for specific capacitance, surface area, mesopore volume, and total pore volume. the synthetic data was generated using the algorithm of producing random number but in range and variance obtained from the experimental data. the large number of synthetic data generation is crucial for machine learning as it helps to expand the dataset, making the model more robust and capable of better generalization. this broader dataset can lead to improved training and more accurate predictions. machine learning algorithms often require a significant amount of diverse data to effectively learn patterns and relationships. the details of the generated data can be studied using the heat map, the box plot and histogram shown in figure 1, 2 and 3 respectively. by creating synthetic data that closely resembles the original experimental data, we provide the algorithm with more examples which will potentially enhance its performance. the large number of data were generated. to generate a normal random distribution value firstly, we limited the range of input and out values by using an algorithm function. finally, the generated value is scaled to fit within the range as mentioned above. these techniques ensured that the synthetic data closely resembles our experimental data [21,22]. 2.2.2 machine learning process firstly, the data were checked for missing values and missing values were computed using mean. in the following process, firstly the importance of input features and their order of importance were noted for each output feature as shown in the figure 3. methylene blue number was the most important parameter for the prediction of mesopore volume followed by temperature and iodine number respectively. finally, iodine number, methylene blue number and temperature in the same order are important for prediction of total pore volume. to ensure fair treatment of features, we applied scaling to bring all the features to a similar scale. random forest model was used to calculate feature importance. the normalized reduction in the criterion brought by each feature was guided our selection process. a variety of machine learning algorithms were chosen based on their relevance to the task. the dataset was partitioned into training and validation sets in the ratio of 80:20. subsequently, each algorithm underwent training using the training data, enabling them to grasp underlying patterns [23]. analysis of the results provided insights into algorithm performance, guiding the refinement of the approach for improved outcomes in subsequent iterations [24]. kirti bir rajguru et al./ bibechana 21 (2024) 159-170 162 figure 4: feature importance of input variables for output of ‘’surface area". figure 5: feature importance of input variables for output of total pore volume. figure 6: feature importance of input variables for output of ‘ ’mesopore volume’ ’. 2.2.3 proposed model selection there are several machine learning algorithms that are suitable for regression tasks. in this paper following machine learning algorithms were described. linear regression a fundamental approach model connects between input variable and a continuous output using a linear equation. linear regression is a fundamental statistical method used for modeling the relationship between a dependent variable and one or more independent variables. the rationale behind linear regression is being simple and interpretable and can be used for robust regression and classification tasks. it assumes a linear relationship between the variables, attempting to find the best-fitting straight line (or hyperplane in higher dimensions) through the data points [25]. if the true relationship between the input feature and surface area is not linear, linear regression may not capture it. the goal of linear regression is to find the coefficients that minimize the sum of squared differences between the predicted values and the actual values in the training data. this is often done by using techniques like ordinary least squares (ols) or gradient descent [26]. ridge regression ridge regression, a regularization method in linear regression, introduces a penalty term based on the l2 norm of coefficients to mitigate overfitting and multi-collinearity [27]. lasso regression similar to ridge, lasso adds a penalty, but it tends to create simpler models by encouraging some feature contributions to become zero. both ridge and lasso are used when dealing with multicollinear data. both lasso and ridge assume linearity and independence. regularization helps to mitigate overfitting, but their performance depends on the true underlying relationship [28]. decision tree regression this method dissects data into hierarchical decision structures to predict the target output. a decision tree is a widely used machine learning algorithm for both classification and regression tasks [29]. it is a tree-like model where an input is passed through a series of binary decisions based on the values of its features. each decision node in the tree represents a feature, and the branches from that node represents the possible feature values. the leaf nodes of the tree contain the predicted output or class. when a new input is given, it traverses the tree based on the feature values, following the decisions at each node, and finally arrives at a leaf node that provides the predicted class (classification) or value (regression). decision trees tend to over-fit noisy data and feature importance may not accurately reflect the true kirti bir rajguru et al./ bibechana 21 (2024) 159-170 163 relevant features of data. random forest regression an ensemble technique constructs multiple decision trees and averages their predictions, by enhancing accuracy and avoiding overfitting. random forest is a machine learning algorithm used for both classification and regression tasks. it is an ensemble method that builds multiple decision trees during training and combines their outputs to make predictions. by introducing randomness in tree construction and feature selection, random forest reduces overfitting and improves generalization. it is a powerful and versatile algorithm often used for complex datasets and can provide valuable insights into feature importance. random forests addresses decision tree limitations by averaging predictions across multiple trees. they handle non-linearites better but may still struggle with subtle relationships [30]. support vector regression (svr) support vector regression is to used determine a regression line that best suits the data, allowing some flexibility around the line. support vector regression (svr) is a machine learning algorithm that is used for regression tasks. it is an extension of support vector machines (svm) and is particularly useful while dealing with continuous or numeric target variables. svr works by finding a hyperplane that best fits the data points which minimizes the error within a certain margin.svr uses different kernel functions (such as linear, polynomial, radial basis function, etc.) to map the input data into a higher dimensional space, which can help to capture complex relationship between variables. svr can model non-linear relationships effectively. the choice of kernel function impacts the performance [31]. gradient boosting regression an ensemble strategy that sequentially builds weak learners, with each one rectifying the errors of its predecessor. gradient boosting adapts well to complex patterns but might over fit if not tuned properly. cat boost regression a gradient boosting algorithm proficient in handling categorical features; can be configured to run without displaying training progress. cat boost is a gradient boosting machine learning algorithm which particularly well suits for categorical features. it stands for "categorical boosting." similar to other gradient boosting methods, cat boost also builds an ensemble of decision trees to make predictions. cat boost also includes features like automatic handling of missing values, built-in cross validation, and the ability to monitor training progress. it has gained popularity for its ease of use, efficiency, and competitive performance on various machine learning tasks [32]. xg boost regression another robust gradient boosting algorithm designed to overcome limitations of traditional gradient boosting. it is important to assess dataset size, feature complexity, interpretability, and computational resources while choosing the most suitable algorithm for research paper. 2.2.4 model evaluation in this research, a comprehensive evaluation of the model’s performance is carried out to assess its generalizability and stability. the technique of crossvalidation is employed, which involves partitioning the dataset into subsets for both training and validation purposes. this allows us to test the model’s ability to perform consistently across different subsets of data, ensuring that it can handle a variety of scenarios effectively. to gauge the accuracy and reliability of the model, appropriate evaluation methods are applied. these methods could encompass metrics such as mean squared error (mse), root mean squared error (rmse), mean absolute error (mae), and possibly more domain specific metrics tailored to the nature of the dataset. these metrics collectively offer insights into the model’s predictive performance and its closeness to the actual experimental data [33] a crucial aspect of this analysis involves a comparison between the actual experimental data and the model’s predicted values for specific characteristics like capacitance, surface area, mesopore volume, micro pore volume, and total pore volume. by contrasting these values, researchers can quantify the model’s accuracy in predicting intricate material properties. the degree of agreement between the predicted and actual values will offer insights into the model’s capability to capture the underlying relationships within the data. in the context of terminalia chebula seeds, the effectiveness of the model in predicting the material’s characteristics is a focal point of analysis. the findings obtained through rigorous evaluation methods shed light on how well the model can capkirti bir rajguru et al./ bibechana 21 (2024) 159-170 164 ture the nuanced features of the activated carbon derived from these seeds. researchers will interpret the results to discern the strengths and limitations of the model in reproducing the complex properties of the material. this interpretation forms a critical part of the paper, as it guides the reader in understanding the implications of the study’s outcomes and its broader implications for the field. catboost and xgboost combine ensemble power with categorical feature handling. they perform well but require tuning [34,35]. 2.2.5 model evaluation parameters in the field of predictive modeling and statistical analysis, the selection of appropriate performance metrics is of paramount importance. this choice determines how effectively a model’s predictions are evaluated and compared against actual values. four commonly employed metrics for this purpose are mean squared error (mse), root mean square error (rmse), mean absolute error (mae), and r-squared [36]. mean squared error mean squared error is a widely utilized metric that quantifies the average squared differences between the model’s predicted values and the actual observed values. by squaring the errors, mse emphasizes larger deviations and penalizes them more than smaller errors. this characteristic makes mse sensitive to outliers and may lead to models that are overly focused on minimizing large errors [37]. the following formula is used to calculate the mean squared error: mse = 1 n n∑ i (yi − ȳ 2) (1) were, mse= mean squared error n= number of data points yi= observed values ŷi= predicted values root mean squared error root mean square error is derived from mse, rmse is the square root of the average of squared errors. it has an advantage of presenting errors in the same unit as the target variable, making it more interpretable. rmse offers insights into the spread or dispersion of prediction errors. while it retains the sensitivity to outliers, the square root transformation mitigates the influence of extreme values [38, 39]. the formula to calculate root mean square error is given as: rmse = √ mse (2) mean absolute error mean absolute error calculates the average of the absolute differences between predicted and actual values. unlike mse, it treats all errors equally, making it less sensitive to outliers. this characteristic makes mae a favorable choice where outliers should not disproportionately affect the evaluation. however, it may lack the emphasis on larger errors that mse provides. the following formula used to calculate the mean squared error: mae = ∑n i (yi − ȳi) n (3) where, mae=mean absolute error yi=prediction xi= true value n= total number of data points r-squared r-squared measures the proportion of the variance in the dependent variable that is explained by the independent variables in the model [40]. it offers insights into the goodness of fit and the model’s explanatory power. higher r-squared values indicate a larger portion of the variability in the data is accounted by the model. nevertheless, it is important to note that r-squared can be misleading when applied to complex models, as it tends to increase with the addition of more variables, even if they are not meaningful [40]. the following formula used to calculate the r-squared: r2 = 1− ssr sst (4) while selecting the appropriate metric for evaluating a model’s performance, researcher’s must consider the nature of the data, the goals of the analysis, and the desired balance between sensitivity to errors and robustness to outliers [41]. in many cases, a combination of these metrics can provide a more comprehensive assessment of a model’s strengths and weaknesses, contributing to a more thorough and nuanced interpretation of results. 3 results and discussion 3.1 statistical analysis of datasets table.1: depicts the entirety of the generated dataset. within this dataset, the variables exhibited mesopore volume size ranging from 0.3 to 0.899 cm3/g and surface area from 800.09 to 1999.70 m2/g. to assess the degree of dispersion for each kirti bir rajguru et al./ bibechana 21 (2024) 159-170 165 variable, we employed mean values and their corresponding standard deviations(sd). additionally, the range of each variable was captured through the utilization of minimum and maximum values. complementing these measures, quartile ranges were furnished to provide supplementary insights into the distribution’s central tendency. “sd" typically stands for "standard deviation," which measures the amount of variation or dispersion in a set of values. so, "sd mean" could refers to the standard deviation of the mean, indicating how much the average value varies from the overall average. 3.2 machine learning prediction 3.2.1 model evaluation nine (9) machine learning models were employed based on the testing dataset. table.2: displays the error values for various models, including support vector re gression, linear regression, ridge regression, decision tree regression, and random forest regression, together with surface area, mesopore volume and total pore volume. table.2: error values for the three outputs using different machine learning models. 3.2.2 comparative analysis with chemical methods we compared ml predictions (e.g. using random forest, gradient boosting, etc.) with traditional methods. ml models outperform traditional methods due to their ability to capture intricate patterns. ml models benefit from larger datasets, whereas traditional methods can work with smaller samples. ml implementation involved computational costs, but traditional methods required expensive equipment. ml models handled noisy data better, but traditional methods were robust even with limited data. 3.2.3 hyperparameter tuning hyperparameter tuning is the process of selecting the best combination of hyperparameters for a machine learning model which optimizes its performance in a given task. hyperparameters are parameters that are not learned by the model during training, but rather set before training begins, such as learning rate, regularization parameter, number of hidden layers, etc. the selection of appropriate hyperparameters can greatly impacts the performance of a machine learning model. for example, using a high learning rate may cause the model to converge quickly but also result in unstable results or overshooting the optimal solution, while a low learning rate may cause the model to converge slowly but also result in more stable and accurate results. similarly, selecting an appropriate value for regularization can help to prevent overfitting, while choosing the optimal number of hidden layers or neurons can impact the model’s ability to learn complex patterns in the data. hyperparameter tuning involves searching through a range of hyperparameters using various techniques such as grid search, random search and bayesian optimization to find the combination that results in the performance on a validation set. by optimizing the hyperparameters, the model’s accuracy and generalization ability can be improved [42]. hyperparameter tuning in random forest is the process of finding the optimal values for the hyperparameters of the model which maximize its performance on a given dataset. hyperparameters are values set before training the model that control its behavior, such as the number of trees in the forest, maximum depth of each tree, and minimum number of samples required to split a node. kirti bir rajguru et al./ bibechana 21 (2024) 159-170 166 kirti bir rajguru et al./ bibechana 21 (2024) 159-170 167 hyperparameter tuning in random forest is the process of finding the optimal values for the hyperparameters of the model that maximize its performance on a given dataset. hyperparameters are values set before training the model that control its behavior, such as the number of trees in the forest, the maximum depth of each tree, and the minimum number of samples required to split a node. for each of the model we have calculated the evaluation metrics like mae, mse etc. and also the best parameters so that we can get the best pathway for each model. 4 conclusion fossil fuels contribute to air pollution, greenhouse gas emissions, and environmental degradation. supercapacitors can help to reduce these effects by providing efficient energy storage and recovery, especially in applications like electric vehicles and renewable energy systems. they can capture and release energy quickly, minimizing the need for constant fossil fuel consumption. using supercapacitors can lead to cleaner air and reduced carbon emissions, promoting a more sustainable energy kirti bir rajguru et al./ bibechana 21 (2024) 159-170 168 landscape. a model that predicts the surface area, mesopore volume and total pore volume of biobased activated carbon was created using various machine learning algorithms. the machine uses the input features namely temperature, methylene blue number and iodine number, and the test circumstances. the prediction performance of the random forest regressor and cat boost regressor models was superior than that of the ann, ridge, mlp, gbr, dtr and svr models. the multifaceted correlations between input parameters such iodine amount and methylene blue number and output variables include surface area, mesopore volume, and total pore volume have been studied using machine learning (ml). in addition, ml might be used for generating models for prediction that includes surface area, mesopore volume, and total pore volume. by using surface area, mesopore volume, and total pore volume, machine learning algorithms can assist researchers in choosing the best model and in enhancing the efficacy and reliability of the energy storage process. machine 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[42] y. y. chia, l. h. lee, s. shafiabady, and d. isa. a load predictive energy management system for supercapacitor-battery hybrid energy storage system in solar application using the support vector machine. applied energy, 137:588–602, 2015. introduction machine learning models materials and methods experimental computational data collection machine learning process proposed model selection model evaluation model evaluation parameters results and discussion statistical analysis of datasets machine learning prediction model evaluation comparative analysis with chemical methods hyperparameter tuning conclusion bibechana vol. 22, no. 2, august 2025, 181-187 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar comparative ph analysis of synthetic and natural cleaning agents: implications for eco-friendly and dermatological safety narendra kumar chaudhary∗, mandip yadav, sujan budhathoki dipak baral, janak adhikari, ajaya bhattarai 1 department of chemistry, mahendra morang adarsh multiple campus, biratnagar, tribhuvan university, nepal ∗corresponding authors. email: chem_narendra@yahoo.com abstract cleaning agents are essential for maintaining hygiene in domestic and industrial settings, and their ph plays a critical role in determining their safety and efficacy. this study analyzed the ph profiles of locally available synthetic (soaps, shampoos, and detergents) and natural cleaning agents (aloe vera and reetha) in dilute solutions to evaluate their implications for skin health and environmental safety. the results showed neem kanti patanjali (nkp) and no. 1 soaps exhibited near-neutral to mildly alkaline ph (6.88–7.95), making them suitable for skin applications. dove and sunsilk (ss) shampoos have slightly acidic profiles (6.35–6.85), aligning with the scalp's natural ph. detergents like surf excel and ariel were strongly alkaline (8.16–8.59) suggesting effective cleaning but possibly being harsh on sensitive skin. natural cleaning agents exhibited eco-friendly properties, with aloe vera having a mildly acidic ph of 5.40–5.79, and reetha being near neutral to slightly alkaline, with a ph of 7.36–7.74. in all samples, dilution reduced alkalinity or acidity, emphasizing the importance of using the correct concentrations. these findings highlight the need for ph-balanced formulations to ensure compatibility with human skin and minimize environmental harm. future research should focus on optimizing product formulations for skin health, biodegradability, and ecological safety while promoting sustainable cleaning practices. keywords cleaning agent, shampoo, ph behavior, soap, skin compatibility, dermatological safety article information manuscript received: may 17, 2025; revised: may 24, 2025; accepted: may 26, 2025 doi https://doi.org/10.3126/bibechana.v22i2.78901 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction cleaning refers to washing clothes and dishes and maintaining personal hygiene to ensure a healthy, safe, and pleasant environment. it involves removing dirt, organic matter, salts, and visible soil from objects and surfaces using water, and various cleaning products [1,2]. cleaning agents play a vital role in daily life, helping prevent the spread of pathogens 181 http://nepjol.info/index.php/bibechana chem_narendra@yahoo.com https://doi.org/10.3126/bibechana.v22i2.78901 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ narendra kumar chaudhary et al./ bibechana 22 (2025) 181-187 182 in homes, healthcare settings, and industrial environments [3]. these agents are generally categorized as synthetic or natural and are available in liquids, powders, sprays, granules, or solids [2]. understanding their ph behavior is critical, as cleaning agents are commonly used in aqueous solutions. the ph of a diluted cleaning agent influences its effectiveness, compatibility with human skin, and environmental impact [4]. for instance, acidic agents are effective for removing mineral deposits but may irritate the skin or harm ecosystems if improperly disposed of. alkaline agents are suitable for cleaning grease and oils but may disrupt the natural ph of skin and pose environmental risks [5, 6]. in contrast, neutral agents tend to be milder, offering safer options for both skin and nature. since human skin has a slightly acidic ph of 4.5 to 5.5, cleaning products with extreme ph levels can lead to skin issues such as irritation, dryness, or allergic reactions [7, 8]. environmental concerns also arise from the discharge of cleaning solutions into water bodies, where altered ph levels can negatively affect aquatic organisms and soil microbiota [9, 10]. therefore, evaluating the ph behavior of cleaning agents is essential to ensure both personal and environmental safety. synthetic cleaning agents, such as soaps, shampoos, detergents, bleaches, and degreasers, are widely used due to their high efficacy and affordability [8]. these agents typically contain synthetic surfactants, petrochemicals, dyes, and fragrances, which enhance their cleaning power but may pose risks to health and the environment over time [1,11]. repeated exposure to such chemicals can lead to skin problems, particularly in individuals with sensitive skin. moreover, synthetic cleaning waste can pollute water sources, disrupt aquatic ecosystems, and contribute to toxic buildup [12]. natural cleaning agents, on the other hand, are formulated with eco-friendly ingredients such as baking soda, citric acid, vinegar, and essential oils. these products are generally safer for both human health and the environment because of their mild ph and biodegradable nature. often marketed under the umbrella of "green cleaning", these agents emphasize not only safe ingredients but also sustainable manufacturing, packaging, and disposal practices [13]. as the demand for eco-conscious products increases, refining the formulation of natural cleaning agents is essential to ensure they remain effective and safe. this research aims to analyze the ph behavior of nine synthetic and two natural cleaning agents in dilute solutions and assess their implications for skin health and environmental safety (table 1). comparing their ph profiles will help to promote sustainable cleaning practices, inform consumer choices, and guide the development of safer and more eco-friendly products. 2 experimental 2.1 materials four different types of cleaning agents such as commercial soaps, shampoos, detergents, and natural products, were selected in this study and purchased from local markets in biratnagar, nepal. the commercial soaps analyzed were liril soap, dettol soap, neem kanti patanjali soap (nkp), and no. 1 soap (n1), while the shampoos included head & shoulders (hs), clinic plus (cp), sunsilk (ss), and dove. the detergents studied were surf excel (se), clean add (ca), 2-in-1, and ariel. additionally, natural agents such as aloe vera gel (avg) and indian soapberry (reetha) (isb) were included to provide a broader perspective on cleaning performance and safety. distilled water was used as the diluent to ensure consistent and uncontaminated conditions for the ph measurements. figure 1 shows images of some commercial and natural cleaning agents studied. analytical grade reagents and standard laboratory equipment were used throughout the study. figure 1: cleaning agents under study. 2.2 preparation of sample solutions the preparation of different sample solutions was done using different techniques. six different solutions for soaps and detergents were made by dissolving 0.2 gm and 0.25 gm of the samples, respectively, in 50 ml to 100 ml volumes of distilled water. these were prepared at room temperature with gentle stirring to ensure complete dissolution. for shampoos, 1.5 ml of each was diluted with distilled water to create volumes ranging from 25 to 75 ml and mixed gently to achieve a homogenous solution. natural product sample solutions, such as aloe vera gel and reetha (indian soapberry), were made by dissolving 0.5 gm of each in 50–100 ml of distilled water while stirring to ensure uniform dispersion [14,15]. narendra kumar chaudhary et al./ bibechana 22 (2025) 181-187 183 figure 2: preparation of sample solutions. 2.3 ph measurement a digital ph meter (mars auto ph meter) was used to measure the ph of the prepared solutions. the meter was calibrated with standard buffer solutions at ph 4.0, 7.0, and 10.0 prior to each set of measurements. to prevent cross-contamination, the electrode was rinsed with distilled water and blotted dry before immersion in test solutions. the experiments were conducted at room temperature, and the ph readings were recorded after stabilization on the meter display. the ph of each sample was measured in triplicate, and the average values were calculated for analysis. trends in alkalinity, acidity, and buffering capacity were revealed by tabulating the results, which were categorized according to sample types, including soap, shampoo, detergent, and natural products. quality control procedures included making fresh solutions to prevent contamination or deterioration, cleaning glassware thoroughly with distilled water, and checking the accuracy ph meter on a regular basis. table 1 lists the composition details and other pertinent data for every cleaning agent under study. 3 results and discussion the ph levels of various soaps, shampoos, detergents, and natural cleaning agents were measured in different volumes of distilled water to evaluate their ph behavior and compatibility with skin and fabric. 3.1 soaps the ph analysis of various soaps revealed distinct trends in alkalinity and neutrality upon dilution with distilled water. the ph of liril soap decreased from 7.4 at 50 ml to 6.97 at 100 ml, transitioning from slightly alkaline to almost neutral, suggesting its mild nature. dettol soap showed a reduction in ph from 7.28 to 6.68 as the water volume increased, aligning with its formulation for antibacterial activity at mildly acidic to neutral ph levels. nkp soap demonstrated a comparable behavior, with ph ranging from 7.31 to 6.88, suggesting its suitability for skincare due to its mild nature. no. 1 soap, initially more alkaline at 7.95, became closer to neutral at 6.78 after dilution, making it appropriate for general use. these findings demonstrate the varying degrees of alkalinity and neutrality of soaps, which can influence their compatibility with skin health and applications, depending on their ph behavior during dilution [11, 16–18]. it is narendra kumar chaudhary et al./ bibechana 22 (2025) 181-187 184 therefore likely that dilution reduces the buffering capability of the solutions. the ph values for each soap with different amounts of distilled water are shown in table 2, and figure 3 provides a visual representation of these values. table 2: ph of different soaps at varying volumes of distilled water. s.n. volume of distilled water (ml) mass of soap (gm) liril dettol no. 1 nkp 1 50 0.2 7.40 7.28 7.95 7.31 2 60 0.2 7.26 7.00 7.84 7.18 3 70 0.2 7.15 6.88 7.51 7.12 4 80 0.2 7.07 6.78 7.38 7.08 5 90 0.2 7.00 6.73 7.27 7.00 6 100 0.2 6.97 6.68 6.78 6.88 figure 3: ph of different soaps at varying volumes of distilled water. 3.2 shampoos the ph of shampoos plays a crucial role in their effectiveness and compatibility with hair and scalp health. head & shoulders (hs) shampoo exhibited a ph range of 7.14 to 6.66, and supports its anti-dandruff properties, as slightly acidic formulations are kinder on the scalp. with an initial ph of 6.78 and a steady decline to 6.35, clinic plus exhibits mild acidity that is unlikely to be damaging to hair or the scalp. sunsilk demonstrated minimal variation in ph (6.83 to 6.62), suggesting a stable formulation suitable for regular use. dove demonstrated a steady drop in ph from 6.85 to 6.48, highlighting its standing as a mild and moisturizing product. these findings highlight the importance of ph-balanced formulations in maintaining scalp health and preventing hair damage, as excessively alkaline products can disrupt the natural structure of hair, and lead to issues like dryness and breakage [19,20]. the ph information for each shampoo with different amounts of distilled water is shown in table 3 and is graphically depicted in figure 4. table 3: ph of different shampoos at varying volumes of distilled water. s.n. volume of distilled water (ml) volume of shampoo (ml) hs cp ss dove 1 25 1.5 7.14 6.78 6.83 6.85 2 35 1.5 7.10 6.65 6.80 6.78 3 45 1.5 7.05 6.60 6.75 6.69 4 55 1.5 7.00 6.54 6.72 6.63 5 65 1.5 6.85 6.48 6.70 6.54 6 75 1.5 6.66 6.35 6.62 6.48 figure 4: ph of different shampoos at varying volumes of distilled water . 3.3 detergents the ph analysis of four detergents, such as surf excel, clean add, 2-in-1, and ariel, were found to have a uniformly alkaline ph, which makes them suitable for removing tough stains. surf excel and 2-in-1 detergents exhibited identical ph ranges from 8.59 to 8.19, highlighting their strong alkanarendra kumar chaudhary et al./ bibechana 22 (2025) 181-187 185 line properties. similar patterns were seen in clean add, where ph levels marginally dropped from 8.56 to 8.20. the alkaline profile of ariel detergent was maintained, although its range was somewhat smaller, ranging from 8.42 to 8.16. these ph values align with the general characteristics of laundry detergents, which are formulated to be alkaline for efficient cleaning of dirt, grease, and oils. however, because high-ph solutions are harsh, improper rinsing may eventually cause fabric damage, even though their alkalinity guarantees effective stain removal [21]. the ph values for each detergent with different amounts of distilled water are shown in table 4 and are visually represented in figure 5. table 4: ph of different detergents at varying volumes of distilled water. s.n. volume of distilled water (ml) mass of detergent (gm) surf excel ariel 2 in 1 clean add 1 20 0.25 8.51 8.42 8.59 8.56 2 30 0.25 8.45 8.35 8.49 8.48 3 40 0.25 8.40 8.30 8.38 8.43 4 50 0.25 8.35 8.25 8.33 8.39 5 60 0.25 8.21 8.19 8.24 8.23 6 70 0.25 8.18 8.16 8.19 8.20 figure 5: ph of different detergents at varying volumes of distilled water. 3.4 natural cleaning agents the ph levels of natural agents such as aloe vera and indian soapberry (reetha) have been studied to understand their suitability for various applications. aloe vera exhibits a mildly acidic nature, with its ph increasing from 5.40 at 50 ml to 5.79 at 100 ml. the natural ph of human skin, which normally falls between 4.5 and 5.5, is closely matched by this mild acidity, making it advantageous for skincare and calming applications. on the other hand, indian soapberry (reetha) shows a near neutral ph profile, varying from 7.74 to 7.36. this neutrality makes reetha suitable for use as a natural cleaning agent for both skin and fabric, as it is less likely to cause irritation or disrupt the skin's natural ph balance [22–24]. table 5 summarizes the ph data for these natural agents in different volumes of distilled water, and figure 6 shows the data graphically, giving a thorough overview of their characteristics. table 5:ph of different natural agents at varying volumes of distilled water. s.n. volume of distilled water (ml) mass of soap (gm) ph (aloe vera) ph (reetha) 1 50 0.5 5.40 7.74 2 60 0.5 5.43 7.66 3 70 0.5 5.48 7.58 4 80 0.5 5.59 7.49 5 90 0.5 5.65 7.42 6 100 0.5 5.79 7.36 narendra kumar chaudhary et al./ bibechana 22 (2025) 181-187 186 figure 6: ph of different natural agents at varying volumes of distilled water. 4 general discussion the study highlights the critical role of ph in determining the suitability and safety of personal care and cleaning products. the majority of soaps and shampoos have a ph that is close to neutral to slightly acidic, which is in line with the skin's normal ph range of 5.4 to 5.9. this makes them appropriate for use on the skin and scalp [25]. in contrast, detergents are strongly alkaline, reflecting their primary purpose of cleaning fabrics but necessitating thorough rinsing to avoid irritation or damage from residual traces [26]. dilution with distilled water consistently lowered the ph across all tested samples, likely due to the reduced concentration of acidic or alkaline ions. among personal care products, items like neem kanti patanjali soap, dove shampoo, and aloe vera demonstrated mild ph levels, minimizing the risk of disrupting the skin’s acid mantle. furthermore, detergents' strong alkalinity makes them potentially harmful to sensitive skin if they are not properly rinsed out of fabrics [27]. natural cleaning agents such as reetha and aloe vera were found to have ph profiles suitable for ecofriendly and non-damaging cleaning applications, offering a sustainable alternative to synthetic products. this research highlights the importance of understanding ph profiles to optimize product applications and ensure user safety. it also emphasizes that maintaining a ph balance close to natural skin levels is essential for preventing issues such as dryness, irritation, or disruption of the skin's natural barrier. by tailoring formulations to appropriate ph levels, manufacturers can enhance product efficacy while minimizing adverse effects on users and the environment. 5 conclusion the compatibility of soaps, shampoos, detergents, and natural products with skin and hair health is highlighted by the study of their ph levels. most of the soaps tested ranged from neutral to mildly alkaline and were influenced by the volume of distilled water used during preparation. liril soap had a ph of 7.4 to 6.97, indicating mild alkalinity suitable for cleaning without harsh effects. dettol soap showed a slightly lower ph range (7.28 to 6.68), making it more skin-friendly. neem kanti patanjali and no.1 soaps also displayed mild alkalinity, supporting their cleaning efficacy while maintaining skin compatibility. shampoos such as head & shoulders, clinic plus, sunsilk, and dove had ph values from slightly acidic to neutral, aligning with the natural scalp ph (5.4–5.9). this balance is vital for maintaining hair health and preventing dryness or irritation. in contrast, detergents like surf excel and ariel exhibited higher alkaline ph values (8.59 to 8.16), reflecting their strong cleaning action but potentially harsh effects on sensitive skin. natural products showed varied profiles: aloe vera was acidic (ph 5.40–5.79), aligning with the skin's natural acidity and aiding hydration and healing, while reetha ranged from neutral to mildly alkaline ph (7.74–7.36), and offering gentle cleaning properties. the study underscores the importance of selecting products with ph levels compatible with skin and hair health to 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[27] d. mijaljica, f. spada, and i. p. harrison. skin cleansing without or with compromise: soaps and syndets. molecules, 27, 2022. introduction experimental materials preparation of sample solutions ph measurement results and discussion soaps shampoos detergents natural cleaning agents general discussion conclusion bibechana vol. 21, no. 3, december 2024, 290-299 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar characterization of the molecular interactions between kaiso and ctcf using alphafold2 and molecular dynamics simulations bidhya thapa1,2, narayan prasad adhikari1,∗ 1central department of physics, tribhuvan university, kirtipur, kathmandu, nepal 2padma kanya multiple campus, tribhuvan university, bagbazar, kathmandu, nepal ∗corresponding author. email: narayan.adhikari@cdp.tu.edu.np abstract zinc finger (zf) protein ctcf is an architectural protein that plays a crucial role in global chromatin organization and remodeling via its interaction with several protein partners. the interaction between kaiso and ctcf regulates the enhancer-blocking function of ctcf. despite the important biological function of their interactions, structural characterization of the kaiso-ctcf complex has yet to be carried out. in this work, we have employed molecular modeling and md simulation to predict the complex between kaiso and ctcf and investigate its structural features. we have employed alphafold2 to predict the optimum complex between kaiso and ctcf and md simulation to explore the detailed dynamics of the interaction involved in complex formation and stabilization. we predicted the key residues and their interactions involved in the binding of kaiso to ctcf. our results show that the hydrophobic interaction between the inter-facial residues plays a significant role in forming the kaisoctcf complex. in addition, several non-covalent interactions, such as hydrogen bonds and electrostatic and van der waals interactions, stabilize the complex. the significant value of hydrophobic contact area and binding free energy signifies the stability of the predicted kaisoctcf complex. keywords kaiso, ctcf, protein-protein interactions, alphafold2, md simulation. article information manuscript received: august 16, 2024; september 5, 2024; accepted: september 14, 2024 doi https://doi.org/10.3126/bibechana.v21i3.68838 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction zinc finger (zf) protein kaiso is a transcription factor that regulates various cellular functions, such as gene expression, cellular differentiation, development, and cancer progression [1–7]. kaiso was first identified as the binding partner of armadillo repeat protein p120 catenin [3]. it contains three classical c2h2 zf domains that are involved in dna recognition and binding [4, 8]. the highly conserved hydrophobic n-terminal btb/poz domain is involved in interactions with other proteins 290 http://nepjol.info/index.php/bibechana narayan.adhikari@cdp.tu.edu.np https://doi.org/10.3126/bibechana.v21i3.68838 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ bidhya thapa and narayan prasad adhikari/ bibechana 21 (2024) 290-299 291 as well as in homodimerization [9]. kaiso has dual specificity for dna binding. it recognizes the doubly methylated cpg dinucleotides (mcpgmcpg) in the core site as well as the sequence-specific kaiso binding site (kbs), having the nucleotide sequence tcctgcna, in dna [4, 8]. kaiso recruits nuclear co-repressor complex via its btb/poz domain to mediate the transcription repression in a methylation-dependent manner [9]. depending on the context and cell type, it acts as a transcription repressor [8–10] or an activator [11]. kaiso is implicated in regulating various genes involved in development and cancer. high levels of kaiso expression are observed in multiple human cancers, such as lung [2], colon [12], breast [1], and prostate [13]. ccctcbinding factor (ctcf) protein is a ubiquitous multi-functional transcription factor that binds with the thousands of tissue-specific and conserved sites spread throughout the genome [14–16]. ctcf was initially identified as the zf protein binding with a ctc-rich sequence in the c-myc promoter [17]. it is a 727 amino acid long protein containing 11 zf domains, two transcriptions repression domains, and nand c-terminal unstructured loops [18]. specifically, zf 4-7 are directly involved in dna binding, whereas other zf domains enhance the stability of the ctcfdna complex [19]. the ctcf binding sites are primarily present in intergenic regions but also in the enhancer, promoter, and within the gene bodies [15,20]. it regulates gene expression both as a transcription repressor [21] as well as an activator [17], in different cellular contexts. most importantly, it acts as an enhancer blocker by blocking the communication between an enhancer and target gene promoter and hence preventing transcriptional activation [22,23]. ctcf is an architectural protein that plays a crucial role in global chromatin organization and remodeling via its interaction with several protein partners [14]. in addition, it also participates in genomic imprinting, gametogenesis, and the early stages of mammalian development.̧ becaiter18use of its methylation-sensitive binding with dna and transcription insulation activity, ctcf allows the accurate expression of the imprinted genes in the h19–igf2 locus [23,24]. kaiso interacts with ctcf protein via the btb/poz domain and negatively regulates its enhancer blocker function [25]. interaction between kaiso and ctcf is physiologically significant because both proteins are observed to be co-expressed in many cells. both kaiso and ctcf are ubiquitously expressed proteins that are mainly present in the nucleus [3, 26]. the kaiso consensus-sequence kbs is positioned close to the ctcf binding site on the human 5’ -hs5 insulator at the -globin gene cluster. the close positioning of the kbs sequence significantly reduces the enhancer-blocking of the globin insulator [25]. in addition, the kaiso-ctcf interaction is highly specific, as ctcf does not interact with other poz domain-containing proteins such as bcl-6, plzf, and hic-1 [25]. the kaisoctcf interaction inhibits ctcf binding to its target sites, and it might be used to down-regulate the undesirable enhancer-blocking activity in specific cell types. similarly, since the poz domain of kaiso is involved in recruiting the nuclear corepressor complex to mediate transcription repression, this interaction might regulate the transcriptional activity of kaiso. in addition, the poz domain is involved in the homodimerization of kaiso (daniel et al., 1999). interactions of kaiso with ctcf could possibly affect its homodimerization and, thereby, other kaiso-mediated activity [25]. defossez et al. (2005) have shown that the cterminal region of ctcf binds with kaiso. the amino-acid residues 640-724 in ctcf are reported to be involved in the interactions with the poz domain of kaiso. however, no experimentally solved structure is available for this complex because of the largely unstructured and flexible nature of this region. in addition, the specific binding region and key residues involved in the interactions are not identified. identification of key residues involved in the interactions of the protein with its binding partner is essential to understand the structural features of the complex and their binding affinity. in this work, we used the neural network-based modeling method alphafold2 to predict the complex between ctcf and kaiso. furthermore, we optimized this interaction using md simulation and assessed the structural stability of the predicted complex. we predicted the key residues involved in the formation of the complex. in addition, we investigated the dynamics of the interactions that are responsible for the binding of the poz domain of the kaiso with ctcf. our results show that the -sheet consisting of two parallel -strand interacts with the c-terminal end of the poz domain. as the poz domain in kaiso is highly hydrophobic and the -sheet in ctcf contains several hydrophobic residues at the binding site, hydrophobic interactions play a significant role in forming the kaiso-ctcf complex. in addition, several hydrogen bonds, electrostatic, and van der waals interactions stabilize the complex. the considerable value of binding free energy suggests that the predicted complex is stable. 2 materials and methods 2.1 protein structures and molecular modeling the input sequences for the kaiso and ctcf proteins were taken from the uniport knowledgebase (uniprotkb) [27]. the complete structure of the bidhya thapa and narayan prasad adhikari/ bibechana 21 (2024) 290-299 292 kaiso and ctcf, shown in figures 1a and 1b, were modeled using the neural network (nn)-based alphafold2 implemented in colabfold [28–30]. colabfold is an accelerated approach to structure prediction that combines the fast homology search of optimized multiple sequence alignment (msas) generation by mmseqs2 (many-against-many sequence searching) [30]. we used colabfold v1.5.5: alphafold2 using mmseqs2. the c-terminal region of ctcf is reported to interact with the btb/poz domain of kaiso [25]. using this information, the amino acids 640-724 in the c-terminal domain were taken as input sequences for ctcf. similarly, the residues 1-120 in the btb/poz domain were taken as the input sequence for kaiso. the complex between kaiso and ctcf was modeled using the colabfold. we used the prediction model alphafold2_ptm for the monomer prediction, whereas the kaiso-ctcf complex was predicted using the alphafold2_multimer_v3 prediction model. the number of recycles controls the number of times the prediction is repeatedly fed through the model. for monomeric prediction, the number of recycles is chosen to be 3 (num_recycles=3). however, we have used 20 recycles (num_recycles=20) for complex prediction using alphafold2_multimer_v3. the recyle_early_stop_tolerance, which specifies when to stop the recycling, was chosen to be 0.0 for monomer and 0.5 for multimer. in addition, we used a single random seed to initialize the prediction (num_seed =1). similarly, to optimize the msa, we set the max_msa parameter to auto and the msa_mod to mmseqs2_uniref_env. similarly, we used the unpaired_paired pair_mod, which pairs sequences from the same species and unpaired msa. the rank one model predicted from colabfold was used as the input structure of the kaisoctcf complex for molecular dynamics simulation and further analysis. 2.2 system setup and molecular dynamics simulations the system input files for the md simulation were prepared using the solution builder package of the charmm-gui web server [31]. the system was solvated using tip 3p water in a cubical box with a 10 å padding around the complex and neutralized by adding 0.15m of nacl, which resulted in the system containing 36,210 atoms in the box with dimensions of 73 × 73 × 73 å3. all-atom md simulations were performed with the namd 2.14 package [32] using charmm36m force field [33], an improved force field for folded and intrinsically disordered protein. standard md protocol was followed for the simulation as in our previous works. [34–36]. briefly, the energy minimization of the system was carried out for 10,000 steps using the conjugate gradient and line search algorithm. the equilibration run was performed for 125 ps with a 1 fs integration time step at 300k. during the equilibration run, the protein’s heavy atoms were harmonically restrained with a force constant of 1.0 kcal/mol/å for the backbone and 0.1 kcal/mol/å for the side chain. the particle mesh ewald (pme) method [37] was employed to calculate the long-range interactions. the cut-off distance of 12 å taken for non-bonded interactions. the nosé hoover langevin method with a piston period of 50 fs and a decay of 25 fs was used to control the pressure. similarly, the temperature was controlled by employing the langevin temperature coupling with a friction coefficient of 1ps-1. the production run was propagated for 350 ns in npt condition at 300 k and 1 atm pressure, taking a 2 fs time step. 2.3 system setup and molecular dynamics simulations the md simulation trajectories were analyzed using visual molecular dynamics (vmd) [38]. vmd was also used for visualization and image rendering purposes. the mm/gbsa binding free energy was estimated using namd. the hydrogen bond plugin in vmd was used to analyze the complex's inter-protein hydrogen bonding. the heavy atom distance cut-off of 3.5 å and bond angle cut-off of 30° were used to calculate hydrogen bonds. similarly, the solvent-accessible surface area (sasa) of the proteins and complex was estimated using vmd. the non-bonded interaction energies were calculated using the namd energy plugin in vmd. 3 results and discussion we performed modeling and md simulation to predict the complex between kaiso and ctcf and investigated the structural stability and dynamics of the interactions in the kaiso-ctcf complex. the optimum complex between kaiso and ctcf was predicted using alphafold2-multimer implemented in google collaboratory, colabfold. the md simulation was employed to assess the structural integrity of the predicted complex and identify the major residues involved in forming and stabilizing the kaiso-ctcf complex. in addition, we studied the dynamics of the non-covalent interactions, such as hydrogen bonding, hydrophobic, electrostatic, and van der waals interactions, during the simulation. we also estimated the hydrophobic contact area between kaiso and ctcf as well as the binding free energy of the kaiso-ctcf complex. bidhya thapa and narayan prasad adhikari/ bibechana 21 (2024) 290-299 293 3.1 modeling of the kaiso-ctcf complex the amino acid residues 641-727 in the c-terminal region of ctcf were predicted to be involved in the interactions with the btb/poz domain of kaiso [25]. based on this information, we selected 641-727 residues from the canonical sequence of ctcf and used them to create a complex with the btb/poz domain of kaiso. as shown in figure 1a, the cterminal region of ctcf is the unstructured loop. solving the crystal structure of the protein-protein complex with large unstructured loops is experimentally challenging. in such conditions, computational techniques such as molecular modeling and md simulations guide the structure prediction and characterization. the ctcf residues 641-727 were predicted to be involved in the interactions with the btb/poz domain of kaiso [25]. based on this information, we selected 640-727 residues from the canonical sequence of ctcf and btb/poz domain residues 1-120 of kaiso as the input sequence in the colabfold v1.5.5: alphafold2 using mmseqs2 to predict the complex. the kaiso-ctcf complex was predicted using the alphafold2_multimer_v3 prediction model. the materials and methods section explains the details of the parameters and conditions used for the complex prediction. we chose the complex with rank one, with a predicted local distance difference test (plddt) score of 75.5 and a predicted template modeling (ptm) score of 0.65. the ptm score greater than 0.5 indicates that the predicted complex is close to the true structure. since the btb/poz domain of kaiso has a stable structural domain (figure 1b), the predicted lddt of kaiso residues in the range of 10-117 is greater than 80, whereas the lddt of most of the ctcf residues is less than 50. however, the predicted lddt score of the ctcf residues in the range 670690, which are involved in binding with kaiso, is greater than 60. figure 1c shows the kaiso-ctcf complex predicted by colabfold. since all-atom md simulation is computationally expensive, we truncated the complex by taking the regions likely involved in interactions. since only the residues 666-690 in ctcf are within 5 å of kaiso, they are most likely to interact with it. therefore, we truncated the predicted complex by taking residues 662-692 for ctcf and 9-120 for kaiso. as the btb/poz domain of kaiso is a stable domain, we have taken the entire domain as an input structure to maintain its stability. figure 1d shows the kaiso-ctcf complex used for all-atom md simulation. the predicted kaiso-ctcf complex is stable throughout the simulation and features several interprotein interactions that stabilize it, as shown in figure 2a. figure 1: (a) the full-length structure of ctcf highlighting the residues 640-727 in the c-terminal domain in magenta. (b) the complete structure of the kaiso showing the btb/poz domain in green. (c) kaiso-ctcf complex structure predicted from colabfold. (d) structure of the kaiso-ctcf complex used for the md simulation. 3.2 structural stability of the complex we estimated the root mean square deviation (rmsd) of the predicted kaiso-ctcf complex to assess the structural integrity. the time evolution of the rmsd of the complex was calculated using the initial frame of the simulation as the reference structure. the protein backbone atoms were used to calculate the rmsd values. as shown in the bidhya thapa and narayan prasad adhikari/ bibechana 21 (2024) 290-299 294 rmsd plot in figure 2b, the kaiso-ctcf complex undergoes structural reorganization up to 200 ns of the simulation and becomes stable. the average rmsd of the complex settles down to nearly 3.5 å. individually, the ctcf shows larger structural variation compared to the btb/poz domain of kaiso, owing to its flexible structure compared to the stable btb domain of kaiso. we used the md simulation trajectories after 200ns, where the system is properly stabilized, to estimate the average properties of the system. in addition, to analyze the flexibility of each residue in the complex, we calculated the root mean square fluctuation (rmsf) of individual residues using the backbone c atoms. as shown in figures 2c and 2d, the rmsf of kaiso residues is significantly stable compared to the residues in ctcf. as expected, the extremities of both proteins are highly flexible due to a lack of interactions with another protein. in kaiso, except for the loop containing residues 6266, most residues have rmsf of less than 2 å. in ctcf, the residues in 668-676 and 680-689 that are involved in interaction with kaiso have lower rmsf, indicating higher stability. 3.3 major interactions in the kaiso-ctcf complex we investigated the various non-covalent interactions involved in forming and stabilizing the complex between kaiso and ctcf. as shown in figure 2a, the kaiso-ctcf complex has several hydrophobic, hydrogen bonding, and ionic interactions. we explored the detailed dynamics of these interactions during the simulation. hydrophobic interactions the btb/poz domain of kaiso and the -sheet in the binding site of ctcf contain multiple hydrophobic residues. therefore, several inter-protein hydrophobic interactions are present at the binding interface of the kaiso-ctcf complex. figure 3a shows the representative snapshot of the md simulation showing the hydrophobic interactions in the kaiso-ctcf. our results predict that the val673 and ile684 in ctcf make hydrophobic interactions with val93 and leu98 of kaiso. similarly, ile90, leu101, and ile102 in kaiso create hydrophobic grooves with val686, ile671, and ala669 in ctcf. in addition, ile113 and leu116 of kasio interact with ala669 of ctcf. moreover, phe112 in kaiso makes hydrophobic contact with pro667 and val668 in ctcf. figure 2: (a) kasio-ctcf complex at the end of 350 ns md simulation. (b) time evolution of the rmsd measurement of the kaiso-ctcf complex. rmsf measurements of the (c) ctcf and (d) ctcf residues in the kaiso-ctcf complex during simulation. bidhya thapa and narayan prasad adhikari/ bibechana 21 (2024) 290-299 295 figure 3: (a) representative structure of the kasio-ctcf complex during the simulation highlighting the hydrophobic interactions at the binding interface. (b) time evolution of the hydrophobic contact area between the kaiso and ctcf during the simulation. we calculated the hydrophobic contact area between kaiso and ctcf to estimate the contribution of the hydrophobic interactions to the stability of the complex. the hydrophobic contact area is the hydrophobic surface buried at the binding interface between two proteins upon complex formation. the higher the contact area, the greater the interacting surface between the interacting partners, which leads to the greater stability of the complex [39]. we calculated the contact area from the sasa of individual proteins and complex using the following equation [39]. contact area = (skaiso+sctcf−scomplex) 2 where skaiso, sctcf, and scomplex are the hydrophobic sasa of the kaiso, ctcf, and kaisoctcf complex. figure 3b shows the time evolution of the hydrophobic contact area between the kaiso and ctcf. the average hydrophobic contact area for the last 150 ns of the simulation trajectories is 365 ± 54 å2. previous studies have shown that the burial of 1 å2 of hydrophobic surface area at the binding interface contributes about -15 ± 1.2 cal/mol [39, 40] of free energy to stabilize the complex. therefore, the 365 å2 of the hydrophobic contact area of the kaiso-ctcf complex contributes about -5.5 kcal/mol to its stability. therefore, hydrophobic interactions are crucial in the kaisoctcf complex formation and stabilization. hydrogen bonds interactions we analyzed the inter-protein hydrogen bond interactions between the kaiso and ctcf using the criterion explained in the methods section. the time evolution of the total number of hydrogen bonds between inter-facial residues in the kaisoctcf complex is shown in figure 4a. as the complex undergoes structural reorganization till 200 ns and becomes stable, we used the simulation trajectory of 200-350 ns to estimate the occupancy percentage of the hydrogen bonds. figure 4b shows the occupancy percentage of major hydrogen bonds involved in forming the kaiso-ctcf complex. as more than one pair of atoms are involved in forming hydrogen bonds in a given residue pair, the occupancy percentage included in figure 4b is the aggregation of all hydrogen bonds formed within a given residue pair. figure 4c shows the atomic details of the significant inter-protein hydrogen bonds in the kaiso-ctcf complex. since most of the residues in the binding interface are hydrophobic, the backbone atoms are involved in hydrogen bonding. even with the polar residues, hydrogen bonds are formed between backbone atoms as the side chains are orientated away from the binding interface (figure 4c). the backbone nitrogen of lys689 in ctcf forms a hydrogen bond with the oxygen atom of glu115 in kaiso. this bond is formed around 125 ns and remains consistently stable after 150 ns, as shown in figure 4d. similarly, the hydrogen bond between gly117 in kaiso and lys689 in ctcf becomes stable after 150 ns. in addition, the backbone nitrogen and oxygen of val93 in kaiso form hydrogen bonds with the backbone atoms of gln672 and glu674 in ctcf, respectively. these bonds are formed at the start of the simulation and remain stable throughout (figure 4d). in addition, the bidhya thapa and narayan prasad adhikari/ bibechana 21 (2024) 290-299 296 arg92(kaiso)glu674(ctcf) is the only major hydrogen bond formed between the side chains of kaiso and ctcf. figure 4: (a) time evolution of the total inter-protein hydrogen bonds in the kaiso-ctcf complex during the simulation. (b) percentage occupancy of the major hydrogen bonds in the kaiso-ctcf complex. (c) details of the major inter-protein hydrogen bonds in the kaiso-ctcf complex (shown in the licorice structure). the dotted lines represent the hydrogen bonds. (d) time evolution of the distance between the heavy atoms forming major inter-protein hydrogen bonds in the kaiso-ctcf complex. ionic interactions the ionic interactions result from the electrostatic attraction between the side chains of the charged residues at the binding interface between two proteins. the negatively charged side chain of glu674 in ctcf makes ionic interaction with the positively charged side chains of arg92 and arg94 of kaiso. similarly, the glu115 in kaiso makes ionic interactions with the side chains of lys663, lys689, and lys690 in ctcf. in the kaiso-ctcf complex, a strong, consistent salt bridge is not formed between these charged residues, as their heavy atom pairs are beyond 3.2 å during most of the simulation time. nevertheless, the arg92 and arg94 in kaiso make transient salt bridges with glu674 in ctcf. these ionic interactions enhance the binding of these two proteins to form a stable complex. we further estimated the contribution of the non-bonded interaction in stabilizing the kaiso-ctcf complex. we calculated the average values of non-bonded interaction energy using the last 150 ns of the simulation trajectory. the electrostatic and van der waals interactions contribute about -199 ± 72 kcal/mol and -56 ± 10 kcal/mol to the total energy of the complex. bidhya thapa and narayan prasad adhikari/ bibechana 21 (2024) 290-299 297 3.4 binding free energy of the complex we estimated the binding free energy of the kaisoctcf complex using molecular mechanics with a generalized born and surface area solvation (mm/gbsa) approach [41–43]. previous studies have shown that the mm/gbsa method has some limitations in calculating the absolute binding free energy of the complex and tends to overestimate the binding free energy [44, 45]. however, it is a computationally efficient way to calculate the relative binding energy of a complex. as in our previous works [36, 46, 47], we used namd to calculate the mm/gbsa energy using the simulation trajectories from the last 150 ns of the simulation, where the complex is properly stabilized. the binding free energy of the kaiso-ctcf complex is -45.1 ± 5.2 kcal/mol. even though the mm/gbsa approach overestimates the binding free energy [45], comparing this value with our previous works [46, 47] using the same method indicates a stable complex between kaiso and ctcf. 4 conclusion in this work, we employed the neural networkbased modeling method alphafold2 and md simulation to predict the complex between the kaiso and ctcf and investigated the structural features of the predicted kaiso-ctcf complex. we predicted the specific binding region as well as the key residues and their role in forming and stabilizing the complex. in addition, we studied the atomiclevel detailed dynamics of various inter-protein noncovalent interactions to understand the complex formation between the ctcf and kaiso. our results show that the residues 662-690 towards the end of the c-terminal end of ctcf, containing a -sheet with two parallel -strands, bind with the btb/poz domain of kaiso. our simulation results reveal that hydrophobic interactions between the inter-facial residues are crucial in forming the stable complex between kaiso and ctcf. in addition, several hydrogen bonding and ionic interactions are essential for binding two proteins. similarly, electrostatic and van der waals interactions also contribute to complex stabilization. the significant value of hydrophobic contact area and binding free energy indicate the stability of the predicted complex. to the best of our knowledge, it is the first computational work in modeling the kaiso-ctcf complex and investigating its structural features. previous studies have reported that kaiso-ctcf interaction negatively regulates ctcf insulator activity [25]; our first structural characterization outlines the molecular basis of the interaction of kaiso with ctcf. acknowledgments bt and npa acknowledge support from the research coordination and development council (rcdc) of tribhuvan university grants number tu-npar-077/78-erg 14. bt acknowledges the phd fellowship and research support grant (award number phd-78/79-s&t-15) from the university grants commission (ugc), nepal. author contributions bt performed the modeling and md simulation, analyzed the data, and wrote the manuscript. npa supervised the work and contributed to data analysis and interpretation. data availability the data supporting the findings of this study are available from the corresponding author upon reasonable request. references [1] bi bassey-archibong et al. kaiso depletion attenuates the growth and survival of triple negative breast cancer cells. cell death & disease, 8(3):e2689–e2689, 2017. 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[47] bidhya thapa and n p adhikari. investigating molecular interactions between kaiso and nuclear co-repressor using molecular simulations. aip advances, 14(6), 2024. introduction materials and methods protein structures and molecular modeling system setup and molecular dynamics simulations system setup and molecular dynamics simulations results and discussion modeling of the kaiso-ctcf complex structural stability of the complex major interactions in the kaiso-ctcf complex binding free energy of the complex conclusion bibechana vol. 21, no. 3, december 2024, 241-253 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar phytochemical analysis and digestive enzymes inhibition study of beta vulgaris sabina khatri, akash budha magar, tinky sharma, khaga raj sharma∗ central department of chemistry, tribhuvan university, kirtipur, kathmandu ∗corresponding author. email: khaga.sharma@cdc.tu.edu.np abstract beta vulgaris is an annual crop grown for its edible roots and leaves. it is traditionally used for the treatment of diabetes, cancer, obesity, heart problems, kidney problems, and liver diseases. the present work is centered on the phytochemical analysis and assessment of antioxidant, antimicrobial, and antidiabetic activities, and toxicity in the root and leaf extracts and solvent fractions. tpc and tfc were measured using the folin-ciocalteu phenol reagent method and alcl3 colorimetric method respectively. antioxidant and antidiabetic activity were measured with dpph assay and α-glucosidase enzyme inhibition assay. antimicrobial activity was determined with the agar disc diffusion method and brine shrimp assay was performed to measure toxicity. phytochemical analysis revealed the presence of phenols, flavonoids, glycosides, saponins, tannins, terpenoids, and alkaloids. the ethyl acetate fraction of the root contained the highest amount of phenolics with 84.35 ± 0.94 mg gae/g. total flavonoid content was found highest in the hexane fraction of root at 150.48 ± 1.10 mg qe/g. the ethyl acetate fraction of the root displayed an ic50 of 3.92 ± 0.06 µg/ml in the dpph assay. the plant extracts and fractions possessed weak α-glucosidase enzyme inhibition activity. they were inactive against bacterial species of escherichia coli, bacillus subtilis, staphylococcus aureus, klebsiella pneumoniae, and fungal species of fusarium solani. toxicity assay found the plant to be non-toxic against the brine shrimp nauplii with the lowest lc50 value being 1166.36 ± 100.21 µg/ml for the hexane fraction of leaf. the study finds b. vulgaris to be rich in phytochemicals and antioxidant activity with weak α-glucosidase enzyme inhibition activity. it is non-toxic to brine shrimp larvae. keywords beta vulgaris, α-glucosidase, dpph, antidiabetic, antimicrobial, toxicity. article information manuscript received: march 20, 2024; revised: april 16, 2024; accepted: april 17, 2024 doi https://doi.org/10.3126/bibechana.v21i3.63978 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 241 http://nepjol.info/index.php/bibechana khaga.sharma@cdc.tu.edu.np https://doi.org/10.3126/bibechana.v21i3.63978 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ sabina khatri et al./ bibechana 21 (2024) 241-253 242 1 introduction humans have been using plants as both food and medicine. dietary plants contain many important secondary metabolites besides basic nutrients. the secondary metabolites in such food act as functional components that can prevent or treat diseases [1]. many plants used in traditional medicines are also consumed as spices, vegetables, and fruits. they are known as functional foods and defined as ‘foods or dietary components that may provide a health benefit beyond basic nutrition’ [2]. the functional food market has grown due to an increase in the health consciousness among the modern population. medicinal or functional food plays a supporting role in modern medicine in the treatment of illness. so, it is essential to explore the phytochemicals and biological activities in our fruits and vegetables and assess their medicinal value. beta vulgaris subsp. vulgaris, commonly known as beetroot is an annual crop plant from the chenopodiaceae family [3]. its wild forms are distributed from europe, and north africa to western asia whereas cultivated beetroots are grown worldwide and commonly consumed in our daily diets [4]. b. vulgaris is rich in minerals and vitamins [5]. proximate analysis by kale et al., (2018) has revealed the composition of the plant as 1.35 ± 0.2% proteins, 7.59 ± 0.4% carbohydrates, 0.3 ± 0.1% fats, 1.9 ± 0.2% dietary fibers, 1.4 ± 0.2% ash, and 87.4 ± 0.3% moisture [6]. alkaloids, terpenoids, steroids, flavonoids, tannins, saponins, and glycosides in root extracts and flavonoids, tannins, oxalate, anthocyanins, saponins, phenolics, carotenoids, and phytate in leaf extracts of b. vulgaris has been detected in previous studies [7]. the plant is used in traditional medicine for the treatment of diabetes, cancer, obesity, heart, kidney, and liver diseases, and it also improves the immune system and hematopoietic system [8–10]. b. vulgaris has also been used for dandruff, diminished libido, constipation, and gastrointestinal and musculoskeletal pain [11]. in addition to traditional uses, the plant has displayed remarkable biological activities in different scientific studies. rehman et al., (2021) observed significant protein denaturation inhibitory activity, acetylcholinesterase inhibitory activity, and red blood cell stabilizing activity in root and leaf extract of b. vulgaris [12]. mzoughi et al., (2019) have revealed the antioxidant and antidiabetic potential of the plant [13]. the roots of the plant displayed anticancer and antibacterial activities in a study by el-beltagi et al., (2018) [14]. the plant has also gained significant attraction in scientific research because of its high nitrate (no3 -) content that promotes health aids for cardiac ailments through endogenic nitric oxide (no) synthesis [15]. it is widely consumed and utilized to develop food coloring agents [16]. b. vulgaris is a source of a class of bioactive compound, ‘betaine’ that shows a hepatoprotective effect by increasing the expression of the quinone reductase enzyme [17]. beetin 27 (be27) is a protein isolated from b. vulgaris that contains antiviral and cytotoxic activities [18]. additionally, aqueous extract of the plant has been used in the biosynthesis of zno nanoparticles that display antimicrobial, anticancer, and antidiabetic activity [19]. due to its high nutritional and medicinal properties, b. vulgaris has attracted many scholars over the years and there have been many studies regarding its nutritional and pharmaceutical activities. the present study adds brine shrimp toxicity assay and comparative phytochemical and biological analysis of the plant using methanol extract and hexane, ethyl acetate, dichloromethane, and aqueous fraction of root and leaf of b. vulgaris to the ongoing research on the plant. the findings of the present study may guide future work regarding the isolation, purification, and characterization of active metabolites from b. vulgaris. diabetes mellitus is a chronic metabolic disorder characterized by high levels of blood sugar and caused by insulin deficiency or insulin resistance [20]. synthetic antidiabetic drugs are associated with adverse effects including hypoglycemic coma, weight gain, and kidney and liver diseases [21]. so, the world health organization (who) recommends the treatment of diabetes using medicinal plants that are cheap, effective, and contain fewer side effects [22]. the antidiabetic potential of many fruits and vegetables remains unexplored. so, there is a need to study antidiabetic activity present in our food plants to lower the risk of diabetes with appropriate diets and possible discovery of noble antidiabetic compounds. overproduction of highly reactive oxygen and nitrogen species during various metabolic processes in our bodies causes oxidative stress [23]. during oxidative stress, reactive oxygen and nitrogen species oxidize and damage important biomolecules like lipids, proteins, dna, and rna [24]. this leads to chronic diseases and disorders including cancer, diabetes mellitus, cataract, cardiovascular disease, neurodegenerative diseases, asthma, and rheumatoid arthritis [23]. antioxidants are bioactive compounds that are involved in preventing or postponing the oxidation of particles or molecules and protecting our health and well-being [25]. antioxidants may be enzymatic or non-enzymatic and endogenous or exogenous. the correlation between the intake of antioxidant-rich pomegranate juice and its positive impact on health has been observed in previous studies [26]. antioxidants in foods assist in preventing oxidative stress-related diabetes, obesity, hypertension, cardiovascular and chronic sabina khatri et al./ bibechana 21 (2024) 241-253 243 inflammation disease, and display neuroprotective and anticancer activity [27]. foodborne diseases and infections cause about 600 million hospital cases and 420,000 deaths each year [28]. most of such infections are caused by the growth of pathogenic bacteria and fungi in foods. in addition to health risks, food spoilage is associated with environmental and resource costs [29]. synthetic preservatives like benzoates, caffeine, saccharin, and sorbic acid are known to produce side effects such as asthma, heart defects, diabetes, and dermatitis [30]. so, there is an urgent need for antimicrobial agents of natural origin that are effective, safe for human consumption and display minimal side effects. many edible plants display significant antimicrobial activity and they are considered as sources of inhibitory substance against foodborne pathogens [31]. traditional medicines of natural origin are widely regarded as safer alternatives to modern synthetic drugs. a previous study reported that the fatalities caused by adverse reactions to modern pharmaceuticals were more than 100,000 whereas herbal medicines were responsible for less than 24 deaths each year [32]. nevertheless, evaluation of toxic and other side effects is incorporated in the assessment of medicinal properties of plants for their potential toxicity and bioactivity, but the safety assessment of edible and cultivated plants is generally ignored as they are considered safe for human consumption. an adequate study of medicinal food requires an assessment of its cytotoxic activity to increase confidence in human consumption and potential pharmaceutical developments. figure 1: photographs of fresh plant sample, herbarium, sample size collection, and drying of plant samples. 2 materials and methods 2.1 chemicals and reagents the 4-nitrophenyl -d-glucopyranoside (cas no: 3767-28-0), α-glucosidase enzyme (cas no: 900142-7), and quercetin (cas no: 117-39-5), were procured from sigma-aldrich (germany). dpph was purchased from hi-media (india) and gallic acid was purchased from molychem (india). analytical grade (extra pure) organic solvents like methanol, hexane, ethyl acetate, dcm, dmso, and other chemicals used in the experimentation were purchased from merck and fischer scientific (india). 2.2 equipment the equipment used during the study were mortar and pestle, glassware, an electric grinder, a weighing scale (pioneer, dhaus), a rotary evaporator (buchi re111), a hot air oven (griffin-grundy), a microplate reader (synergy lx, bio tek, instruments, inc., usa), water-bath (clifton), pipettes, vials, micropipettes (erba bihot). 2.3 plant collection and identification leaf and root samples of the plant were harvested from the cultivated site in bhaktapur, nepal in august 2021. the altitude and coordinates of the collection site are given in table 1. the plant was identified by the central department of botany, tribhuvan university, kathmandu, nepal as herbarium sample tuch-210075. photographs of plant samples are given in figure 1. sabina khatri et al./ bibechana 21 (2024) 241-253 244 table 1: traditional medicinal uses of the plant name of the plant identification no. altitude/plant growing plant parts medicinal uses and health benefits obesity, diabetes, and cardiovascular disease [8, 9] beta vulgaris tuch-210075 altitude 1401 m roots cancer, heart disease [10] 85° 25’ 48” e, 27° 40’ 14” n. leaves dandruff, diminished libido, constipation, gastrointestinal, and musculoskeletal pain [11] hypertension and endothelial function [4] food coloring [16] 2.4 extraction and fractionation plant samples were cleaned, shade-dried to a constant weight, and ground to powder. the cold percolation method was used for the extraction of phytochemicals. 250 g root powder and 250 g leaf powder were soaked in reagent grade methanol (500 ml) in separate conical flasks at a temperature of 21 0c for 72 hours. the flasks were shaken vigorously after every 24-hour interval. then, the contents were filtered with a clean muslin followed by the whatman-1 filter paper. a rotatory evaporator was used to concentrate the filtrate at reduced pressure and 40 0c temperature. solvent fractions of methanol extract were isolated using hexane, dichloromethane, ethyl acetate, and water. 20 g methanol extract was dissolved in 50 ml of distilled water in a separating funnel and an equal volume of hexane was added. the contents were vigorously shaken and then left undisturbed until clear layers of hexane at the top and water at the bottom were formed. the hexane layer was concentrated in the rotary evaporator at reduced pressure and 40 c temperature. the aqueous layer was subjected to further fractionation with dichloromethane and ethyl acetate. 2.5 phytochemical analysis the qualitative and preliminary analysis of the plant extracts was performed according to the standard procedures as described by savithramma et al., (2011) [33]. 2.6 total phenolic content (tpc) the folin-ciocalteu reagent method as described by slinkard et al., (1977) was employed to measure the tpc [34]. 20 µl gallic acid solution (10 to 80 µg/ml in methanol) and 20 µl of each extract and fraction (500 µg/ml in 50% dmso) were loaded in triplicates in a 96-well plate. to each bore, 100 µl of folin-ciocalteu reagent and 80 µl of na2co3 solutions were added and the 96-well plate was placed in the dark for 30 minutes. then, a microplate reader was used to measure the absorbance at 765 nm. a regression equation obtained from the absorbance versus concentrations of the gallic acid curve was used to calculate tpc. it was expressed as milligrams of gallic acid equivalent per gram (mg gae/g) of extract and fraction. 2.7 total flavonoid content (tfc) the alcl3 colorimetric method as described by marinova et al., (2005) was used to estimate the total phenolic content [35]. 130 µl standard quercetin solution (10 to 80 µg/ml in methanol) and 20 µl of 500 µg/ml plant extracts and fractions in 50% dmso were loaded in a 96-well plate. it was followed by adding 110 µl of deionized water to the bores containing plant extracts and fractions. subsequently, each bore received 60 µl of ethanol, 5 µl of alcl3, and 5 µl of ch3cook. then, the 96-well plate was placed in the dark. a microplate reader was used to measure the absorbance at 415 nm. a standard absorbance versus concentration of quercetin curve was constructed and tfc was calculated using its regression equation. it was expressed as milligrams of quercetin equivalent per sabina khatri et al./ bibechana 21 (2024) 241-253 245 gram (mg qe/g) of extract and fraction. 2.8 antioxidant assay the dpph assay was used to measure the antioxidant activities [36]. 100 µl of plant extracts and fractions at concentrations 1.5625, 3.125, 6.25, 12.5, 25, and 50 µg/ml in 50% dmso were loaded to the bores of a 96-well plate in triplicates. to each bore, 100 µl dpph solution (0.1 mm in methanol) was added and the 96-well plate was placed in the dark. after 30 minutes, a microplate reader was used to measure the absorbance at 517 nm. quercetin and 50% dmso were used as the standard and control respectively. the following formula was used to calculate the percentage of radical scavenging percentage scavenging = a1 −a2 a1 × 100 where a1=absorbance of control a2=absorbance of sample graphpad prism 9 software was used to calculate the ic50 (half maximal inhibitory concentration) values of extracts and fractions. 2.9 antidiabetic assay the α-glucosidase enzyme inhibition assay was used to measure the in-vitro antidiabetic activities [37]. 20 µl each of 0.5 unit/ml α-glucosidase enzyme and 500 µg/ml plant extracts were premixed inside the bores of a 96-well plate. then, 120 µl of potassium phosphate buffer (ph 6.8) and 40 µl of pnpg substrate were added. after 15 minutes of incubation at 37 °c, the absorbance of the reaction mixture was measured at 405 nm. the reaction mixture with the volume of plant extract replaced by an equal volume of buffer solution was used as a control. the following formula was used to calculate the percentage of enzyme inhibition percentage inhibition = a1 −a2 a1 × 100 where a1=absorbance of control a2=absorbance of sample 2.10 antibacterial assay the agar disc diffusion method with slight modifications was used to measure antibacterial activity [38]. the list of pathogenic bacteria, type, and atcc numbers are given in table 2. bacterial broth cultures were prepared in nutrient broth media and incubated overnight. then, the inoculum (0.5 mcfarland standards) was transferred to sterilized muller-hinton agar (mha) plates using sterile cotton swabs. discs impregnated with 50 µl of plant extracts and fractions (25 mg/ml) were placed on the surface of mha plates using sterilized forceps. once all discs were in place, the plates were covered with lids, inverted, and then incubated at 35 c for 18 hours. then, zones of inhibition (zoi) were measured. ampicillin (1 mg/ml) and 100% dmso were used as standard and control respectively. table 2: names of the bacteria, types, and atcc number bacteria type atcc klebsiella pneumoniae gram-negative 700603 escherichia coli gram-negative 25922 bacillus subtilis gram-positive 35021 staphylococcus aureus gram-positive 25923 2.11 antifungal assay the antifungal activities in extracts and fractions were measured using the disc diffusion method [38]. the fungal species fusarium solani (atcc 11712) was used as a test organism. the broth culture of the test organism was prepared in nutrient broth media and incubated overnight and then the inoculum (0.5 mcfarland standards) was spread on potato dextrose agar (pda) plates. discs impregnated with 50 µl of 25 mg/ml plant extract and fractions were placed on the surface of the pda plate. the plate was covered with lids, inverted, and then incubated at 35 0c for 18 hours. zois were measured after incubation. cycloheximide (20 mg/ml) and 100% dmso were used as standard and control respectively. 2.12 toxicity the brine shrimp lethality assay was used to measure toxicity [39]. 2 ml of each of the plant extracts and fractions at concentrations 10, 100, and 1000 µg/ml in methanol were added to different test tubes in triplicates. 2 ml of methanol was used as the control. the solvent was evaporated to dryness sabina khatri et al./ bibechana 21 (2024) 241-253 246 using a water bath. after this, artificial seawater (5 ml) was used to redissolve the leftover residue in each test tube. then, 10 matured brine shrimp larvae were transferred to each test tube. the numbers of surviving brine shrimp nauplii in each test tube were counted after 24 hours. the concentration of plant extract and fraction that kills half of the test organisms (lc50) was calculated from the percentage mortality versus concentration curve. 2.13 statistical analysis all the tests were performed in triplicates and the results are expressed as mean ± se. the results are compared using one-way anova followed by tukey’s test with the help of spss version 29 software. the values with p < 0.05 were considered statistically different. 3 results 3.1 phytochemical phytochemical analysis the preliminary phytochemical analysis found phenols, flavonoids, glycosides, saponins, tannins, terpenoids, alkaloids, and carbohydrates in both root and leaf extracts of b. vulgaris (table 3). protein was detected only in the root extract of b. vulgaris. table 3: phytochemical constituents in plant extracts. group of compounds brc blc alkaloids + + phenols + + flavonoids + + glycosides + + tannins + + terpenoids + + saponins + + reducing sugars + + proteins + brc: crude extract of roots, blc: crude extract of leaves. ‘+‘ present, ‘-‘ absent. brc: crude extract of root, brh: hexane fraction of root, brd: dichloromethane fraction of root, bre: ethyl acetate fraction of root, bra: aqueous fraction of root, blc: crude extract of leaf, blh: hexane fraction of leaf, bld: dichloromethane fraction of leaf, ble: ethyl acetate fraction of leaf, bla: aqueous fraction of leaf. # positive standard, nd: values not determined. values are the mean ± se (n=3). values followed by the different letters in the same columns are not significantly different at p < 0.05. sabina khatri et al./ bibechana 21 (2024) 241-253 247 3.2 total phenolic and flavonoid content b. vulgaris contained a significant amount of phenolics and flavonoids, and the observed results are presented in table 4. the descending order of phenolic content was 84.35 ± 0.94 (bre) > 83.39 ± 0.35 (blc) > 71.51 ± 0.66 (bld) > 42.04 ± 1.14 (brd) > 39.73±0.28 (ble) > 34.53±0.18 (brh) > 33.04 ± 1.58 (bra) > 26.51 ± 1.19 (blh) > 25.75 ± 0.27 (brc) > 15.87 ± 2.28 mg gae/g (bla). similarly, the descending order of tfc was found as 150.48±1.10 (brh) > 63.46±0.94 (bra) > 39.39 ± 0.84 (bld) > 24.27 ± 0.70 (bre) > 19.34±0.93 (brd) > 9.16±0.44 (blc) > 7.94±0.18 (brc) > 6.31±0.22 (ble) > 2.49±0.13 (blh) > 2.40± 0.06 mg qe/g (bla). (a) (b) figure 2: a) correlation between total phenolic content and ic50 in dpph assay. b) correlation between total phenolic content and percentage of α-glucosidase inhibition. 3.3 antioxidant potential ic50 value of ethyl acetate and dichloromethane fractions of leaves and ethyl acetate and hexane fractions of roots were determined as they displayed the highest radical scavenging activity during screening. these fractions displayed remarkable antioxidant activity. the highest activity was observed in bre with half maximal inhibitory concentration of 3.92 ± 0.06 µg/ml followed by bld (6.07 ± 0.16 µg/ml), brh (15.5 ± 1.02 µg/ml), and ble (30.41 ± 0.85 µg/ml) (table 4). the ic50 of quercetin was 3.9 ± 0.07 µg/ml. figure 3: percentage radical scavenging against concentrations (µg/ml) of plant extracts, solvent fractions, and quercetin. sabina khatri et al./ bibechana 21 (2024) 241-253 248 3.4 antidiabetic potential the percentage of α-glucosidase enzyme inhibition for plant extracts and fractions at concentrations of 500 µg/ml is given in table 4. the descending order of percentage enzyme inhibition is 35.36 ± 0.29 (brh) > 32.16 ± 0.88 (bla) > 29.29 ± 0.29 (bre) > 26.64 ± 1.15 (ble) > 24.66 ± 0.72 (blh) > 21.01 ± 0.58 (bld) > 17.93 ± 0.57 (bra) > 14.07 ± 0.90 (brd) > 10.31 ± 0.38 (blc) > 5.35 ± 0.19 (brc). 3.5 antimicrobial activity plant extracts and fractions did not display significant zoi against bacterium and fungal strains used in the study. photographs of petri plates are given in figure 4. ampicillin used as a standard was found to be most potent against k. pneumoniae with zoi 34 mm, followed by b. subtilis (32 mm), s. aureus (23 mm), and e. coli (23 mm). cycloheximide used as standard in antifungal assay displayed a zoi of 15 mm against f. solani (table 5). figure 4: antimicrobial activities of plant extract and fractions against bacterial and fungal strains (a. fusarium solani, b. escherichia coli, c. bacillus subtilis c. staphylococcus aureus, e. klebsiella pneumoniae.) table 5: antimicrobial activity (zoi) shown by the extract and solvent fractions. plant extracts k. pneumoniae s. aureus b. subtilis e. coli f. solani #ampicillin 34 23 32 23 nd #cycloheximide nd nd nd nd 15 # positive standard, nd: values not determined. 3.6 toxicity against brine shrimp nauplii the toxicities of plant extracts and fractions were measured in terms of their ability to kill brine shrimp nauplii and the results are given in table 6. the plant extracts and fractions did not display significant toxicities in the assay. all the lc50 values were well over 1000 µg/ml. the ascending order of lc50 is 1166.36 ± 100.21 (blh) < 1195.83 ± 115.34 (ble) < 1573.90 ± 145.26 (blc) < 1807.78 ± 270.77 (brc) < 1906.72 ± 285.36 (bre) < 2337.71 ± 570.09 (brd) < 2711.11 ± 170.05 (bld) < 4079.84 ± 809.06 (bra) < 5287.16 ± 393.51 (brh) < 5692.20 ± 381.99 g/ml (bla). sabina khatri et al./ bibechana 21 (2024) 241-253 249 table 6: median lethal concentration (lc50) for plant extract and solvent fractions in brine shrimp lethality assay. plant extracts lc50 (µg/ml) brc 1807.78 ± 270.77a brh 5287.16 ± 393.51b brd 2337.71 ± 570.09a,c bre 1906.72 ± 285.36a bra 4079.84 ± 809.06b,c blc 1573.90 ± 145.26a blh 1166.36 ± 100.21a bld 2711.11 ± 170.05a,c ble 1195.83 ± 115.34a bla 5692.20 ± 381.99b values are the mean ± se (n=3). values followed by the different letters are not significantly different at p < 0.05. figure 5: percentage mortality versus concentrations (µg/ml) of plant extracts and solvent fractions. 4 discusion the present study detected the presence of phenolics, flavonoids, glycosides, tannins, alkaloids, and carbohydrates in the methanol extract of the root. all these secondary metabolites are also reported in the literature [40, 41]. however, ahmad et al., (2013) have reported the absence of proteins and saponins in root extract [40]. extracts and fractions of b. vulgaris displayed a significant amount of phenolics and flavonoids in the present study. the amount of tpc and tfc in different plant extracts were significantly different from each other at p < 0.05. the crude extract of the root displayed higher tpc than the crude extract of the leaf, but tfc was found to be higher in the crude extract of the leaf than in the root. the slightly higher concentration of flavonoids in leaf extract is due to the accumulation of flavonoids in leaves [42]. the highest amount of phenolics was recorded for the ethyl acetate fraction of the root whereas the hexane fraction of the root contained the most flavonoid content in the present study. observed tpc of 25.75 ± 0.27 mg gae/g for brc was found intermediatory between previously reported values of 11.23 ± 0.13 mg gae/g by ahmad et al., (2013) and 39.75 ± 2.32 mg gae/g by edziri et al., (2019) [40, 43]. similarly, the tfc of 7.94 ± 0.18 mg qe/g was found comparable to 6.41 mg qe/g as reported by odoh et al., (2012) and lower than 20.73 ± 1.25 mg sabina khatri et al./ bibechana 21 (2024) 241-253 250 qe/g as reported by edziri et al., (2019) [43, 44]. the number and concentrations of phytochemicals in fruits and vegetables depend upon factors such as cultivar variation, agronomic practices, environmental stress, food processing, and storage methods [45]. appropriate measures should be taken to preserve the pharmacological activities of fruits and vegetables during the processing, storing, and cooking stages. phenolic compounds exert health-promoting effects and therapeutic activities such as antioxidant, antidiabetic, antimicrobial, anticancer, and analgesic functions [46]. these compounds are synthesized from shikimate pathways. the structural feature of phenolics consists of one or more hydroxyl groups with carbon skeletons [47]. they mainly exert their pharmaceutical effect due to their antioxidant activity. the current investigation found a strong negative correlation (r = -0.804, p < 0.003) between total phenolic content and the ic50 value in the dpph assay. the correlation is graphically presented as a linear regression plot in figure 2(a). such correlations are also reported in the literature [48]. flavonoids are a type of phenolic compound with significant pharmacological importance. they are effective against oxidative stress, bacteria, viruses, malaria, and hiv, and are responsible for natural pigmentation and flavor in many fruits and beverages [49]. the presence of various plant secondary metabolites and the high concentrations of phenolics and flavonoids indicate the high potential of b. vulgaris in pharmacological research. the ethyl acetate, hexane and dichloromethane fractions of roots and leaves of b. vulgaris displayed high antioxidant activities. the percentage of free radical scavenging increased with the increase in the concentrations of plant fractions (figure 3). antioxidant activities in the ethyl acetate fraction of the root and dichloromethane fraction of the leaf were similar to that of standard quercetin at p < 0.05 indicating the possibility of the presence of an active compound. the high antioxidant activity in b. vulgaris also makes it an ideal natural food preservative. the antioxidants in fruits and vegetables are mainly due to polyphenols, carotenoids, or vitamins [50]. further work involving gc-ms and lc-ms analysis could identify specific active principals responsible for bioactivity. previously, edziri et al., (2019) have reported ic50 values in abts and dpph assay of methanol extract of root as 359.65 and 254.76 µg/ml respectively [43]. the dpph ic50 value of 3.92 ± 0.06 µg/ml for bre was comparable to the ic50 values of 2.32 ± 0.72 µg/ml and 2.20 ± 0.72 µg/ml for root and leaf extracts reported in the literature [12]. α-glucosidase inhibitors competitively bind with α-glucosidase enzyme and reduce the rate of disaccharide hydrolysis and subsequent glucose absorption in the blood [51]. thus,α-glucosidase enzyme inhibition assay was used in the present study to measure antidiabetic activity. the plant extracts and fractions displayed weak inhibition activities in the present study. however, a previous study by mzoughi et al. (2019) has reported the ic50 values for ethanolic leaf extract as 0.13 mg/ml and 1.03 mg/ml in α-glucosidase inhibition assay and -amylase inhibition assay respectively [13]. variations in ic50 values may have arisen due to the differences in environmental stress, cultivar variation, or extraction solvent. mechanism of antidiabetic activity in plants includes blocking of liver gluconeogenesis, stimulation of insulin secretion and sensitivity, inhibition of glucagon secretion, prevention of glucose absorption in the intestine, and reabsorption of glucose in the kidneys [52]. a previous study has found an increase in the number of β-cells of the islet of langerhans in streptozotocin-induced diabetic rats on oral administration of 2 g/kg b. vulgaris extract for 28 days [53]. this indicates antidiabetic activity in the plant may involve stimulation of insulin secretion and inhibition of digestive enzymes. the α-glucosidase inhibition assay displayed a mild positive correlation (r = 0.413, p < 0.024) with total flavonoid content. the graphical representation of such correlation is given in figure 2(b). the leaf extracts and fractions lacked significant zones of inhibition against bacterium and fungal species at a concentration of 25 mg/ml. the findings in this study agreed with the observations made by rauha et al., (2000) in which they reported the absence of activity against c. albicans, a. niger, e. coli, and s. aureus for 500 µg of 80% methanol extract of b. vulgaris tuber [54]. another study reported zoi of 2 mm against s. aureus for leaf aqueous extract while methanol extract was found to be inactive [55]. ethanolic extract of the roots displayed zois of 12.54 ± 0.35, 8.37 ± 0.21, and 0 mm against s. aureus, b. cereus, and a. niger respectively in the study conducted by el-beltagi et al., (2018) [14]. thus, there are differences in the antibacterial activity reported in various studies. these differences may be due to variations in the number and concentration of secondary metabolites caused by genetic and environmental factors, the solvent used for extractions, concentrations used, and bacterial susceptibility. the cytotoxic activity in plant extracts and fractions was measured using a brine shrimp lethality assay. the assay is a reliable method for estimating preliminary cytotoxic activity. lagarto parra et al., (2005) have reported a significant correlation between the brine shrimp assay and oral lethality in mice [56]. in the present study, all lc50 values were higher than 1000 µg/ml. so, the plant is sabina khatri et al./ bibechana 21 (2024) 241-253 251 relatively safe for human consumption, a fact evident from its worldwide cultivation and inclusion in kitchens. observed percentage mortality increased with the increase in concentration of plant extracts as shown by figure 5. 5 conclusion the medicinal food b. vulgaris contains important phytochemicals such as alkaloids, phenols, flavonoids, glycosides, tannins, terpenoids, and saponins. the extracts and fractions of the plant possess high concentrations of phenolics and flavonoids and display significant antioxidant activities. thus, the consumption of the plant could reduce the risk of chronic diseases associated with oxidative stress. the plant displayed weak αglucosidase inhibition activity that was significantly correlated with total flavonoid content. the plant is found to be inactive against f. solani, k. pneumoniae, e. coli, b. subtilis, and s. aureus. it is not toxic to the brine shrimp nauplii. thus, the inclusion of b. vulgaris in the diet will have potential pharmacological benefits due to the presence of important phytochemicals. further isolation, purification, and characterization of active metabolites coupled with in-vivo studies may lead to increased use of the plant as a medicinal food. besides the medicinal properties, the plant could be used as a potential source of secondary metabolites that impart high food value from the aspects of nutraceutical properties. acknowledgment the authors would like to acknowledge the central department of botany, tribhuvan university, kathmandu, nepal for taxonomical identification of the plant. references [1] y. zeng, y. li, j. yang, et al. therapeutic role of functional components in alliums for preventive chronic disease in human beings. evid. based complement. altern. med., 2017:article id 9402849, 2017. 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[56] a. lagarto parra, r. silva yehbra, i. guerra sardiñas, and l. iglesias buela. comparative study of the assay of artemia salina l. and the estimate of the medium lethal dose (ld50 value) in mice, to determine oral acute toxicity of plant extracts. phytomedicine, 8(5):395–400, 2001. introduction materials and methods chemicals and reagents equipment plant collection and identification extraction and fractionation phytochemical analysis total phenolic content (tpc) total flavonoid content (tfc) antioxidant assay antidiabetic assay antibacterial assay antifungal assay toxicity statistical analysis results phytochemical phytochemical analysis total phenolic and flavonoid content antioxidant potential antidiabetic potential antimicrobial activity toxicity against brine shrimp nauplii discusion conclusion bibechana vol. 22, no. 2, august 2025, 159-170 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar multiscale study of interaction between sars-cov-2 protein and human receptor complex roshan sigdel, jhulan powrel, nurapati pantha∗, narayan prasad adhikari central department of physics, tribhuvan university, kathmandu, 44618, nepal ∗corresponding authors. email: mrnurapati@gmail.com abstract this study explores the binding mechanism of key binding pockets (s19 q24 a475 and t500 r357) in the severe acute respiratory syndrome coronavirus 2 (sars-cov-2) spike protein and the human angiotensin-converting enzyme 2 (hace2) receptor complex using molecular dynamics (md) simulations and first-principles calculations. the binding pockets were extracted from the 6lzg protein-protein complex, and the input systems were prepared using charmm-gui for molecular dynamics, pymol for structural modifications, and a quantum input generator for first-principles calculations. md simulations were conducted to assess the stability of the binding pockets and to analyze key interactions, including hydrogen bonding, electrostatic, and van der waals interactions. root mean square deviation (rmsd) calculations indicated fluctuations within the system. first-principles calculations, based on density functional theory (dft) and hybrid functionals, were used to compute the binding energies of residues within the binding pockets, which were found to be negative, suggesting no significant intra-pocket binding. electronic property analysis revealed that the behavior of key amino acid residues is largely governed by p-orbitals and atomic chemical structure, with minimal influence from crystal symmetry near the fermi level. moreover, ethylation of residues a475 was determined to be ineffective in disrupting the interaction between sars-cov-2 and the hace2 receptor. keywords sars-cov-2, protein structure, binding pockets, receptor complex, amino acids article information manuscript received: february 19, 2025; accepted: may 22, 2025 doi https://doi.org/10.3126/bibechana.v22i2.75792 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 1 introduction the severe acute respiratory syndrome-like coronavirus (sars-cov-2) epidemic that started the covid-19 pandemic in wuhan, china, in december 2019 swiftly expanded into a serious global health and economic problem. the virus quickly spread worldwide in 2020, creating widespread illnesses, posing a severe threat to the worldwide population, and intensifying into a global crisis, according to reports of the first human transmission in december 2019. according to the who, this disease has been responsible for more than 630 million recorded cases and 6.5 million fatalities worldwide so far [1, 2]. there are many different strains of the big virus family known as coronaviruses. most viruses affect cats, camels, chickens, and bats. coronaviruses are unique in that they can spread from one species to another through 159 http://nepjol.info/index.php/bibechana mrnurapati@gmail.com https://doi.org/10.3126/bibechana.v22i2.75792 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ roshan sigdel et al./ bibechana 22 (2025) 159-170 160 “cross-species transmission" or “spillover" meaning that a virus that initially infects one species might change in a way that makes it possible to infect another species. the covid-19 pandemic started this way; the virus probably originated in bats before spreading to humans via an intermediary animal host. direct, indirect, and close contact with sick people can spread coronaviruses to others. the virus-containing saliva and respiratory secretions can be expelled by infected people when they exhale, talk, cough, or sneeze. people can then contract the virus by coming into contact with these infected secretions, either by touching contaminated surfaces and then touching their mouth, nose, or eyes or by being close to an infected person who expels infected droplets [3–5]. the first human coronaviruses were detected in the 1960s in patients’ nasal discharge linked to the common cold. named for their crown-like spikes, these viruses caused global outbreaks in the past. severe acute respiratory syndrome coronavirus (sars-cov) emerged in 2002, while middle east respiratory syndrome coronavirus (merscov) surfaced in 2012. in 2019, sars-cov-2 was identified in china, causing covid-19 and sparking a pandemic. these coronaviruses are believed to have evolved from bat origins, with some reports suggesting rodent origins for cov-oc43 and hku1. studies indicate cov-oc43’s transmission to humans around 120 years ago, highlighting their prolonged presence in human populations [6, 7]. coronaviruses are categorized into four genera based on phylogenetic relationships and genomic structure: alphacoronavirus, betacoronavirus, gammacoronavirus, and deltacoronavirus. alphacoronavirus and betacoronavirus mainly infect mammals, including humans, while gammacoronavirus and deltacoronavirus target birds. human coronaviruses hcov-229e, hcov-nl63 (alphacoronavirus), hcov-oc43, and hcov-hku1 (betacoronavirus) cause common colds. more severe outbreaks, like sars-cov, mers-cov, and sars-cov-2, stem from betacoronavirus. while both alpha-covs and beta-covs lead to mild illnesses, sars-cov, mers-cov, and sars-cov-2 can result in severe, life-threatening diseases [4, 8]. coronaviruses are composed of positive singlestranded rna and nucleoprotein (n), encased within a lipid bi-layer containing spike glycoprotein (s), membrane protein (m), envelope glycoprotein (e), and hemagglutinin esterase (he) [4, 8–10]. the rna genome’s length ranges from 26 to 32 kb. sars-cov-2, a beta-cov, exhibits a spherical structure with crown-like spikes measuring 60-140 nm in diameter and 9-12 nm in spike length. sarscov-2 shares about 80 % nucleotide sequence identity with sars-cov [4,9, 11]. since the emergence of the covid-19 pandemic, numerous scientists have devoted their efforts to unravelling the complex mechanisms by which sarscov-2 interacts with the hace2 receptor. despite significant progress in vaccine development, many people continue to suffer from the virus, highlighting the need for a deeper understanding of the virus’s nature and binding mechanisms. developing more effective vaccines and drugs remains a significant challenge that requires continued research and innovation. [8, 12]. here, we perform a multiscale study combining molecular dynamics (md) simulations and quantum espresso (qe) calculations to investigate the binding mechanism between sarscov-2 and hace2. in md, we analyze hydrogen bonds, van der waals (vdw), and electrostatic interactions within two key binding pockets: s19 q24 a475 and r357 t500, where a475 and t500 are sars-cov-2 residues, and the rest belong to hace2. following this, we use quantum expresso codes to conduct quantum mechanical calculations, focusing on the relaxation of these binding sites, estimating the system’s total energy and individual residue contributions, and exploring their electronic properties, such as density of states (dos) and band structures. roshan sigdel et al./ bibechana 22 (2025) 159-170 161 figure 1: binding pockets s19 q24 a475 and r357 t500 in the sars-cov-2 protein and hace2 receptor complex, based on coordinates from the 6lzg.pdb file. 2 computational methods 2.1 molecular dynamic simulation molecular dynamics (md) simulations were executed utilizing the namd simulation package, employing the 6lzg pdb file from the rcsb protein data bank website, representing the sars-cov-2 (wild type) complex and hace2 proteins [8, 13]. the simulation system was solvated within a water environment to mimic the cellular milieu, and periodic boundary conditions were imposed to emulate an infinite system. to ensure charge neutrality and maintain the desired ph, a balanced number of positive (na+) and negative (cl−) ions were introduced. specifically, for the s19 q24 a475 binding pocket, 2 na+ ions and 2 cl− ions were added, and for the r357 t500 binding pocket, 3 na+ ions and 4 cl− ions were incorporated. the charmm36m force field was chosen to describe the interactions in the simulations, providing a comprehensive representation of the system’s behaviour. the simulation protocol commenced with energy minimization, spanning 5 ns for each isolated binding pocket and 100 ns for the sars-cov-2-hace2 complex within the nvt ensemble at 310k. subsequently, a production run of 5ns was carried out for each isolated binding pocket and 100ns for the sars-cov2-hace2 complex under npt conditions. the resultant data from the production run underwent visual molecular dynamics (vmd) analysis. structural stability assessment was performed through root mean square deviation (rmsd) calculations using the rmsd trajectory tool in vmd. the simulation trajectories used vmd analysis tools to identify and analyze bonded and non-bonded interactions. 2.2 first principles calculations an in-depth analysis of the density of states (dos) and band structures was conducted for two distinct systems. these systems consisted of amino acid residues from hace-2, sars-cov-2, and their constituent amino acids. first-principles calculations were performed using the quantum espresso algorithm. the electronic exchange and correlation effects were incorporated into the system through the pbesol functional developed by john p. perdew. this hybrid density functional, employed by pbesol, combines the exchange from a hartree-fock calculation with the correlation from a density functional description, which are two distinct types of functionals in density functional theory (dft) [14]. andrea dal corso’s projector augmented wave (paw) pseudopotential, obtained from the quantum espresso website, was used to replace the complex effects of the motion of an atom’s core (i.e., non-valence) electrons with an effective potential. this ensured that only the chemically active valence electrons were explicitly considered throughroshan sigdel et al./ bibechana 22 (2025) 159-170 162 out the entire calculation [15]. the structure was optimized using the broyden-fletcher-goldfarbshanno (bfgs) scheme and was allowed to relax until the total energy change between two successive self-consistent field (scf) steps was less than 10−7 ry, and each component of the acting force was below 10−4 ry/bohrs [16]. a degauss value of 0.001 ry was used, with “occupation” fixed and “smearing” applied in various systems depending on the number of electrons present. the david diagonalization method was employed with the “plain” mixing mode and a mixing value of 0.4 to ensure self-consistency. to prepare for subsequent calculations, the optimal convergence values for the kinetic energy cutoff and k-point sampling were determined. these choices were made to enhance the accuracy of the calculations while minimizing computational expenses. since the system lacked a crystalline nature, it was necessary to transform it into a crystalline arrangement by encapsulating it within a cell. this adaptation was required to enable the accurate execution of first-principles calculations. since the system’s crystalline size is not fixed for band calculations, a k-path was generated using the “seek-path" tool from material cloud [17], following the suggested path γ–x | y –γ–z | r–γ–t | u–γ–v | γ–x ′ | y ′–γ–z ′ | r′–γ–t ′ | u ′–γ–v ′, where γ represents the brillouin zone center, and other points denote symmetry-related locations within the reciprocal space. the band structure analysis primarily focuses on the r–γ–t segment, with corresponding k-points. 3 results and discussion 3.1 root-mean-square deviation(rmsd) 0 2 4 6 8 10 12 14 0 1 2 3 4 5 d is ta n c e ( å ) time (ns) average (a) 0 2 4 6 8 10 12 14 16 18 0 1 2 3 4 5 d is ta n c e ( å ) time (ns) average (b) 1 1.5 2 2.5 3 0 20 40 60 80 100 d is ta n c e ( å ) time (ns) average (c) figure 2: time evolution of rmsd of the isolated system of s19 q24 a475 (2a) and t500 r357 (2b) binding pockets of s protein and human ace2 complex during the 5 ns simulation run, and of the system containing sars-cov-2 spike protein and hace2 receptor complex during the 100 ns simulation run (2c). the figure in 2 illustrates the rmsd values for a range of systems, including isolated single binding pockets (s19 q24 a475, and t500 r357) within the s protein and human ace2 complexes, as well as the complete s protein and human ace2 complexes. specifically, the rmsd fluctuations for inroshan sigdel et al./ bibechana 22 (2025) 159-170 163 dividual isolated binding pockets, such as s19 q24 a475 and t500 r357 within the s protein and human ace2 complexes, exhibit variations spanning 14.25 å to 0.91 å and 16.85 å to 0.74 å, respectively. on the other hand, the rmsd fluctuations for the s protein and hace2 complexes themselves range from 3.78 å to 1.115 å. regarding average rmsd values, the isolated binding pockets (s19 q24 a475 and t500 r357) and the s protein and hace2 complexes demonstrate values of 6.27 å, 5.78 å, and 2.05 å, respectively. further examination of the rmsd values over time reveals that the isolated system containing only binding pockets (s19 q24 a475 and t500 r357) fluctuations start at 1.35 å and 1.19 å, respectively, and fluctuate in between their respective maximum and minimum values. the most pronounced fluctuations occur between 1.9 ns and 2.3 ns, as well as between 3.99 ns and 4.6 ns for s19 q24 a475, and between 0.36 ns and 0.85 ns, as well as between 3.75 ns and 4 ns for t500 r357. eventually, the rmsd values stabilize at a relatively constant level. similarly, the rmsd values for the s protein and hace2 complexes initially fluctuate, with significant variations between 26.8 ns and 36.8 ns and between 59.6 ns and 62 ns. ultimately, these values also reach a steady state. the results indicate that both the s protein and hace2 complexes and the isolated system containing only binding pockets s19 q24 a475 and t500 r357 maintain relatively consistent rmsd values, suggesting structural stability in the molecular dynamics simulation. the more significant fluctuations observed in the isolated system can be attributed to the absence of interactions with other amino acids in the s protein and hace2 complexes. 3.2 hydrogen bonds 0 0.5 1 1.5 2 2.5 3 3.5 4 0 1 2 3 4 5 n u m b e r o f h -b o n d time (ns) average (a) 0 0.5 1 1.5 2 2.5 0 20 40 60 80 100 n u m b e r o f h -b o n d time (ns) average (b) 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 n u m b e r o f h -b o n d time (ns) average (c) figure 3: time evolution of the number of hydrogen bonds (h-bonds) formed between s protein and hace2 (s19 q24 a475 and t500 r357) for the isolated system during 5ns simulation runs (3a), and (3c) and the system containing sars-cov-2 spike protein and hace2 receptor complex for pocket s19 q24 a475 during 100 ns simulation runs (3b). to calculate the number of hydrogen bonds between amino acid residues of binding pockets a475 s19 q24 and t500 r357 of the sars-cov-2 s protein and the ace2 receptor, we utilized the vmd extension hydrogen bonds with a 3.5 å cut-off distance for hydrogen bond formation. roshan sigdel et al./ bibechana 22 (2025) 159-170 164 table 1: occupancy percentage of hydrogen bonds in the s19 q24 a475 and t500 r357 binding pocket of the s protein-hace2 complex hydrogen bonds occupancy % for s19 q24 a475 binding pocket ser19-side—ala475-side 1.60% ala475-main—gln24-main 0.80% ala475-main—gln24-side 2.40% ser19-main—ala475-main 4.00% ser19-main—ala475-side 4.00% gln24-main—ala475-side 0.80% for s19 q24 a475 binding pocket from total sars-cov-2 spike protein-hace2 complex ser19-side—ala475-main 41.12% ser19-main—ala475-main 7.19% gln24-side—ala475-main 6.99% for t500 r357 binding pocket arg357-main—thr500-main 3.20% arg357-main—thr500-side 6.40% thr500-side—arg357-side 0.80% arg357-side—thr500-main 2.40% arg357-side—thr500-side 3.20% figure 3 illustrates the dynamic changes in hydrogen bond counts for various binding pockets within the s protein and human ace2 complex. the isolated systems of s19 q24 a475 and t500 r357 exhibit fluctuating hydrogen bond counts ranging from 0 to 4 and 0 to 3, respectively. similarly, the binding pocket within the sars-cov-2 spike protein and hace2 receptor complex, namely s19 q24 a475, experiences hydrogen bond fluctuations from 0 to 2. notably, no hydrogen bonds were observed between amino acid residues t500 and r357 in the t500 r357 binding pocket of the sarscov-2 spike protein and hace2 receptor complex. the total number of hydrogen bonds between the hace2 receptor and s protein amino acid residues for the isolated systems of s19 q24 a475 and t500 r357 binding pockets are 6 and 5, respectively. the corresponding binding pockets within the sarscov-2 spike protein and hace2 receptor complex are 3 and 0, respectively. detailed hydrogen bond occupancy percentages are summarized in table 1. from table 1, the isolated binding pockets exhibit minimal hydrogen bonding with very low occupancy percentages. this indicates that the hydrogen bonds involving amino acids s19, q24, and a475 are insignificant enough to confirm stable binding. however, the same binding pocket comprising s19, q24, and a475 in the complete complex shows a significant hydrogen bond contribution, particularly between ser19 (side chain) and ala475 (main chain). this discrepancy arises because isolating a specific binding pocket by removing all other binding pockets alters the system’s environment, demonstrating that amino acids from other binding pockets also influence the hydrogen bonding within a given binding pocket. similarly, the binding site involving t500 and r357 in the complete complex does not exhibit any hydrogen bonding. however, small hydrogen bonds are observed in the system containing only the t500–r357 binding pocket, isolated from all other binding sites. this behaviour reinforces that interactions between binding pockets are critical in modulating hydrogen bonding within individual pockets. 3.3 vdw or electrostatic interactions electrostatic and van der waals interactions are critical non-covalent interactions prevalent in biological systems. these interactions are crucial in both intermolecular and intramolecular binding between biomolecules. in proteins, charged amino acids attract or repel each other due to electrostatic interactions. meanwhile, van der waals interactions occur due to the temporary asymmetry of electron density around an atom, which creates a dipole moment. this dipole moment is responsible for the attractive force at longer distances and the repulsive force at shorter distances. our study analyzed vdw, or electrostatic interactions between amino acid residues within two binding pockets (s19 q24 a475 and t500 r357) found in the spike protein and hace2 receptor complex. we examined the electrostatic and van der waals forces between these residues using an isolated system approach. we compared the results of our analysis with those obtained from systems containing roshan sigdel et al./ bibechana 22 (2025) 159-170 165 the s19 q24 a475 and t500 r357 binding pockets of the sars-cov-2 spike protein and hace2 receptor complex, respectively. in both the isolated system and the system containing the sarscov-2 spike protein and hace2 receptor complex, the interactions among amino acid residues within the s19 q24 a475 and t500 r357 binding pockets are characterized by significant non-bonded interaction energies, which are primarily composed of van der waals and electrostatic contributions. for the system involving the sars-cov-2 spike protein and hace2 receptor complex, the average electrostatic contribution, van der waals interaction, and non-bonded interaction energies are (-12.64 ± 0.19) kcal/mol, (-0.9996 ± 0.043) kcal/mol, and (-13.64 ± 0.18) kcal/mol, respectively, for the s19 q24 a475 binding pocket; and (1.61 ± 0.13) kcal/mol, (-0.93 ± 0.02) kcal/mol, and (0.675 ± 0.124) kcal/mol, respectively, for the t500 r357 binding pocket. on the other hand, the isolated system of the s19 q24 a475 and t500 r357 binding pockets shows negligible electrostatic contribution, van der waals interaction, and non-bonded interaction energies. the average values for these interactions are (-5.46 ± 1.92) kcal/mol, (-0.022 ± 0.042) kcal/mol, and (5.48 ± 1.91) kcal/mol, respectively, for the s19 q24 a475 binding pocket; and (-8.104 ± 1.797) kcal/mol, (0.017 ± 0.0788) kcal/mol, and (-8.09 ± 1.76) kcal/mol, respectively, for the t500 r357 binding pocket. -100 -50 0 50 0 1 2 3 4 5 e n e rg y ( k c a l/ m o l) time (ns) elec vdw non-bonded (a) -30 -25 -20 -15 -10 -5 0 5 10 15 0 20 40 60 80 100 e n e rg y ( k c a l/ m o l) time (ns) elec vdw non-bonded (b) -80 -60 -40 -20 0 20 40 0 1 2 3 4 5 e n e rg y ( k c a l/ m o l) time (ns) elec vdw non-bonded (c) -15 -10 -5 0 5 10 15 0 20 40 60 80 100 e n e rg y ( k c a l/ m o l) time (ns) elec vdw non-bonded (d) figure 4: variation of electrostatic (elec) and van der waals (vdw) interaction energies between the amino acid residue of s protein and amino acid residue of hace2 for the isolated system of s19 q24 a475 and t500 r357 binding pocket, (4a) and (4c), and for the system containing sars-cov-2 spike protein and hace2 receptor complex for s19 q24 a475 and t500 r357 binding pocket, (4b) and (4d). the nonbonded interaction in both the isolated systems and the system containing the sars-cov2 spike protein and hace2 receptor complex are primarily driven by van der waals and electrostatic interactions. however, the magnitudes of nonbonded interaction energies are higher in the latter case. the van der waals interaction remains relatively stable by examining the electrostatic, van der waals, and total nonbonded interaction plot in figure 4. at the same time, fluctuations are more pronounced in the electrostatic interaction. consequently, these fluctuations lead to considerable variations in the overall nonbonded interaction energy, the sum of van der waals and electrostatic interactions. notably, these fluctuations are less intense in the isolated systems of binding pockets within the s protein and human ace2 complex compared to the system containing the sars-cov-2 spike proroshan sigdel et al./ bibechana 22 (2025) 159-170 166 tein and hace2 receptor complex. 3.4 energy calculations we employed an scf input file for a comprehensive quantum mechanical analysis, calculating the total energy alongside fermi energy, kohn-sham states, and energy eigenvalues. our objective was to uncover the binding energy within two specific binding pockets of the sars-cov-2 spike protein and hace2 receptor complex. this was achieved through a range of first-principles calculation setups utilizing quantum espresso, adjusting lattice parameters (a, b, and c) based on system size (table 2). table 2: lattice parameters, crystal structures, and total energies of various systems for two binding pockets. system lattice parameters (a=b=c) in å crystal structure total energy of systems of binding pockets (ry) ethane -42.8747 for s19 q24 a475 binding pocket s19 q24 a475 11.9112 cubic -544.2074 s19 q24 11.9112 cubic -412.7575 s19 5.07 cubic -172.6133 q24 8.1787 cubic -240.1767 a475 4.9275 cubic -131.4759 ethylated a475 6.4988 cubic -172.4018 ethane 5.5738 cubic -42.8747 for t500 r357 binding pocket t500 r357 15.9037 cubic -471.5230 r357 11.790 cubic -278.4724 t500 5.5738 cubic -193.1114 ethane 5.5738 cubic -42.8747 the binding energy of each binding pocket can be determined by utilizing the ground state energy values of the individual amino acid residues of the sars-cov-2 spike protein and the hace2 receptor. the binding energy for the systems is calculated using the following equation: • binding energy for s19 q24 a475 binding pocket ebinding = es19+eq24+ea475−es19−q24−a475 (1) ebinding = −0.0584ry • binding energy for t500 r357 binding pocket ebinding = et500 +er357 −et500−r357 (2) ebinding = −0.0607ry • binding energy for ethylated a475 ebinding = ea475 + ec2h6 − eethylateda475 (3) ebinding = −1.9488ry where, es19, eq24, and er357 represent the energies of the amino acid residues of the hace2 receptor, ea475 and et500 represent the energies of the amino acid residues of the sars-cov-2 spike protein, and ethylated energy of ea475 is eethylateda475. additionally, es19−q24−a475 and et500−r357 represent the total system energies of each binding pockets. understanding the interaction between the sarscov-2 spike protein and the hace2 receptor complex is vital for understanding viral infection mechanisms, but predicting amino acid binding accurately was challenging due to the absence of a fixed geometry. analysis of the s19 q24 a45 pocket revealed that the calculated binding energy of −0.0584 ry is negative, suggesting no binding, which contradicts the actual situation within the pocket. in reality, the amino acid residues are bound through hydrogen bonds, van der waals forces, and electrostatic interactions [8]. similar inconsistencies are seen in pockets t500 r357 (with binding energy −0.0607 ry), which bind via van der waals or electrostatic interactions. factors like body fluids, temperature, and bulk protein interactions that are unaccounted for in our system can influence binding. our isolated site approach might lead to negative binding energies, indicating unbinding. the effect of ethylation was investigated on residue a475. the a475 ethylated complex was -1.9488 ry in binding energy, indicating a state of instability. the ethylation modification did not succeed in enhancing the stabilization of the hace2sars-cov-2 binding complex, suggesting that the strategy is ineffective in destabilizing the binding interface between the amino acid residues of the sars-cov-2 protein and the hace2 receptor complex. roshan sigdel et al./ bibechana 22 (2025) 159-170 167 3.5 density of states (dos) and bands the band structure of solids, stemming from quantum forces on isolated atoms, governs their electronic and optical traits, pivotal in materials science. electrons adhere to pauli exclusion, occupying valence bands while leaving the conduction band accessible. the band gap, devoid of orbitals, separates them and emerges from electron-ion interactions. materials are classified based on the band gap: conductors (small/zero gap), semiconductors (0.1-4 ev), and insulators (>4 ev). conductors allow easy electron flow, semiconductors suit electronics, and insulators hinder electricity [18]. the density of states (dos) characterizes available quantum states in a solid’s energy range, impacting electronic, transport, and magnetic traits. calculating dos reveals energy band distribution, shedding light on electron behaviour. 3.5.1 for s19 q24 a475 binding pocket the figures (5a and 5b), (5c and 5d), (5e and 5f), (5g and 5h), (5i and 5j), and (5k and 5l) depict the band and dos structures, along with pdos highlighting orbital and atomic contributions, for the hace2 receptor’s amino acid residue (s19 and q24), sars-cov-2’s amino acid residue (a475), s19 q24, s19 q24 a45, and ethylated a475 respectively. starting with s19, it exhibits n-type semiconductor behaviour with a band gap of 2.52 ev. the presence of conduction bands close to the fermi surface suggests it can act as an electron donor. the band contributions in the conduction and valence bands, as seen in figures 5a and 5b, are primarily attributed to the p-orbital of carbon and nitrogen atoms, respectively. the band structures near the fermi level do not significantly vary with high symmetric points, indicating that crystal symmetry does not significantly affect electronic states. moving on to the q24 system, it falls within the wide energy gap semiconductor category with a band gap of 3.3798 ev. like s19, the p-orbital of carbon and oxygen atoms predominantly contributes to the conduction band, while the p-orbital of oxygen mainly influences the valence band. like before, the band structures around the fermi level remain relatively unchanged across high symmetric points. a475, on the other hand, exhibits ntype semiconductor behaviour with a band gap of 2.4808 ev. its conduction bands’ proximity to the fermi level facilitates electron movement, making it an effective electron donor. the p-orbitals of carbon and nitrogen atoms play a significant role in the conduction and valence bands, similar to s19 and q24. again, the band structures near the fermi level show minimal variation with high symmetric points. in the s19 q24 system, the interaction between s19 and q24 results in a system with a band gap of 3.0851 ev. this places it in the wide energy gap semiconductor regime. the p-orbital of carbon atoms and some contribution from oxygen are notable in the conduction band, while the valence band’s behaviour is akin to that of s19 and q24. despite the binding, the electronic properties align more with q24, and the band structures near the fermi level remain largely consistent. the s19 q24 a475 system also demonstrates semiconductor characteristics with a band gap of 2.2652 ev. the band contributions in the conduction and valence bands resemble those of the individual amino acids. importantly, after the interaction, the system’s semiconductor nature still aligns with that of the hace2 receptor, indicating a shift in properties towards hace2 characteristics. the band structures around the fermi level exhibit no significant changes due to the interaction. finally, ethylated a475 exhibits p-type semiconductor behaviour with a band gap of 3.4036 ev. the valence band’s proximity to the fermi level indicates electron acceptance characteristics. interestingly, the ethylation of a475 transforms its properties from n-type to wide energy gap p-type semiconductors. despite this shift, the band contributions from the p-orbitals of carbon and oxygen atoms persist, and the band structures near the fermi level display slight variations across high symmetric points. this suggests that ethylation does not dramatically impact the electronic structure at these energy levels. roshan sigdel et al./ bibechana 22 (2025) 159-170 168 -8 -6 -4 -2 0 2 4 6 8 r γ t fermi level e -e f (e v ) high symmetric points -8 -6 -4 -2 0 2 4 6 8 0 5 10 15 20 25 fermi level dos (no. of states per ev) (a) 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 -6.00 -4.00 -2.00 0.00 2.00 4.00 6.00 p d o s ( n o . o f p ro je c te d s ta te s p e r e v ) e-ef (ev) sum s-orbital p-orbital 0.00 2.00 4.00 6.00 8.00 10.00 12.00 -6.00 -4.00 -2.00 0.00 2.00 4.00 6.00 p d o s ( n o . o f s ta te s p e r e v ) e-ef (ev) carbon nitrogen hydrogen oxygen (b) -6 -4 -2 0 2 4 6 r γ t fermi level e -e f (e v ) high symmetric points -6 -4 -2 0 2 4 6 0 50 100 150 200 250 300 fermi level dos (no. of states per ev) (c) 0 50 100 150 200 250 300 350 400 -8 -6 -4 -2 0 2 4 6 8 p d o s ( n o . o f p ro je c te d s ta te s p e r e v ) e-ef (ev) sum s-orbital p-orbital zoomed region 0 50 100 150 200 -8 -6 -4 -2 0 2 4 6 8 p d o s ( n o . o f s ta te s p e r e v ) e-ef (ev) carbon nitrogen hydrogen oxygen zoomed region (d) -8 -6 -4 -2 0 2 4 6 8 r γ t fermi level e -e f (e v ) high symmetric points -8 -6 -4 -2 0 2 4 6 8 0 5 10 15 20 25 fermi level dos (no. of states per ev) (e) 0 2 4 6 8 10 12 14 -8 -6 -4 -2 0 2 4 6 8 p d o s ( n o . o f p ro je c te d s ta te s p e r e v ) e-ef (ev) sum s-orbital p-orbital 0 1 2 3 4 5 6 -8 -6 -4 -2 0 2 4 6 8 p d o s ( n o . o f s ta te s p e r e v ) e-ef (ev) carbon nitrogen hydrogen oxygen (f) -5 -4 -3 -2 -1 0 1 2 3 4 r γ t fermi level e -e f (e v ) high symmetric points -5 -4 -3 -2 -1 0 1 2 3 4 0 2000 4000 6000 8000 10000 fermi level dos (no. of states per ev) (g) 0 200 400 600 800 1000 1200 -5 -4 -3 -2 -1 0 1 2 3 4 p d o s ( n o . o f s ta te s p e r e v ) e-ef (ev) sum s-orbital p-orbital zoomed region 0 100 200 300 400 500 600 700 800 -5 -4 -3 -2 -1 0 1 2 3 4 p d o s ( n o . o f s ta te s p e r e v ) e-ef (ev) carbon nitrogen hydrogen oxygen zoomed region (h) roshan sigdel et al./ bibechana 22 (2025) 159-170 169 -3 -2 -1 0 1 2 3 4 r γ t fermi level e -e f (e v ) high symmetric points -3 -2 -1 0 1 2 3 4 0 500 1000 1500 2000 2500 fermi level dos (no. of states per ev) (i) 0 200 400 600 800 1000 1200 1400 -5 -4 -3 -2 -1 0 1 2 3 4 p d o s ( n o . o f p ro je c te d s ta te s p e r e v ) e-ef (ev) sum s-orbital p-orbital zoomed region 0 200 400 600 800 1000 -5 -4 -3 -2 -1 0 1 2 3 4 p d o s ( n o . o f s ta te s p e r e v ) e-ef (ev) carbon nitrogen hydrogen oxygen zoomed region (j) -4 -2 0 2 4 6 8 r γ t fermi level e -e f (e v ) high symmetric points -4 -2 0 2 4 6 8 0 20 40 60 80 100 fermi level dos (no. of states per ev) (k) 0 5 10 15 20 -6 -4 -2 0 2 4 6 8 10 p d o s ( n o . o f p ro je c te d s ta te s p e r e v ) e-ef (ev) sum s-orbital p-orbital 0 2 4 6 8 10 -6 -4 -2 0 2 4 6 8 10 p d o s ( n o . o f s ta te s p e r e v ) e-ef (ev) carbon nitrogen hydrogen oxygen (l) figure 5: figures (5a), (5c), (5e), (5g), (5i), and (5k) illustrate the band and dos structures for the s19, q24, a475, s19 q24, s19 q24 a475, and ethylated a475 systems, respectively. figures (5b), (5d), (5f), (5h), (5j), and (5l) display the orbital-projected density of states and atom-projected density of states for the s19, q24, a475, s19 q24, s19 q24 a475, and ethylated a475 systems. 3.5.2 for t500 r357 binding pocket r357 has a wide energy gap n-type semiconductor nature with a 3.3505 ev band gap, featuring bands at the fermi level. band contributions near the fermi level stem mainly from p-orbitals, oxygen, and nitrogen atoms. the preserved band structure symmetry suggests a critical role in the sarscov-2 binding mechanism. the semi-metallic nature and fermi-level states suggest potential interactions with other molecules. t500, a p-type semiconductor, possesses a 2.881 ev band gap with carbon and nitrogen-driven conduction and valence bands near the fermi level. symmetry analysis reveals minimal changes near the fermi level, implying consistent electronic properties. t500 r357 exhibits a 3.4137 ev band gap with n-type semiconductor behaviour, mirroring hace2’s properties post-interaction. band contributions involve p-orbitals, carbon, nitrogen, and oxygen atoms. the consistent band structure near the fermi level hints at the modification after binding, indicating potential for drug design. 4 conclusions our study involved three molecular dynamics simulations: two on isolated binding pockets (s19 q24 a475 and t500 r357) and one on the full sars-cov-2 spike protein-hace2 receptor complex. these simulations (5ns, 5ns, and 100ns) aimed to reveal binding mechanisms by assessing stability and amino acid interactions, including hydrogen bonds, electrostatic, and van der waals forces. rmsd values confirmed stability, with the isolated s19 q24 a475 system averaging 6.27 å, 5.78 å for t500 r357 system, and the full complex averaging 2.05 å. non-bonded interactions, particularly van der waals and electrostatic forces were stronger in the full complex than in isolated pockets, with significant electrostatic fluctuations. first-principles calculations revealed negative binding energies for specific amino acid interactions, though real-world conditions could alter these results. ethylation of a475 was found to have minimal impact on binding. density functional theory analyses highlighted the electronic properties of key amino acids, showing strong p-orbital contributions with limited crystal symmetry effects near the fermi level. these findings deepen our understanding of the binding mechanisms between sarscov-2 and hace2, offering valuable insights for developing therapeutics aimed at disrupting viral interactions. roshan sigdel et al./ bibechana 22 (2025) 159-170 170 acknowledgements r. sigdel sincerely expresses his gratitude to the university grants commission (ugc) for its financial support. the authors acknowledge the computing facilities provided by the tribhuvan university research coordination and development council (rcdc) through the national priority grants tunpar-077/78-erg-14. references [1] ben hu, hua guo, peng zhou, and zheng-li shi. characteristics of sars-cov-2 and covid19. nature reviews microbiology, 19(3):141– 154, 2021. 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[18] john singleton. band theory and electronic properties of solids, volume 2. oxford university press, 2001. https://covid19.who.int/ https://covid19.who.int/ introduction computational methods molecular dynamic simulation first principles calculations results and discussion root-mean-square deviation(rmsd) hydrogen bonds vdw or electrostatic interactions energy calculations density of states (dos) and bands for s19 q24 a475 binding pocket for t500 r357 binding pocket conclusions bibechana vol. 22, no. 3, december 2025, 280–290 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar thermodynamic and surface properties of al-cu-fe-si-ti liquid alloy n. dahal1,2,3, u. mehta2, r. k. gohivar2, r. p. koirala2, s. k. yadav2* 1central department of physics,tribhuvan university, kirtipur 2department of physics, mahendra morang adarsh multiple campus, tribhuvan university biratnagar, nepal. 3department of physics,sukuna multiple campus,tribhuvan university, sundarharaincha ∗corresponding author. email: sashit.yadav@mmamc.tu.edu.np abstract the thermodynamic and surface properties of the al-cu-fe-si-ti liquid alloy were systematically investigated using theoretical models. these properties were investigated at different cross-sections from fe and ti corners. for the comparative study, the excess gibbs free energy of mixing for the liquid alloy was determined using the muggianu, kohler, and chou models, based on the thermodynamic database of constituent binary subsystems available in the literature. the activity of the system was calculated using chou model. the activities of al, fe, si, and ti showed negative deviations from raoult’s law, confirming strong complex-forming tendencies, whereas cu exhibited positive deviations, highlighting its weaker interaction and tendency toward segregation. these deviations diminished with increasing temperature, indicating that elevated thermal energy reduces ordering interactions and promotes random mixing. the surface tension of the alloy was calculated using butler equation with the aid of thermodynamic database. present investigations revealed that compositions enriched with elements of intrinsically higher surface tension exhibited larger overall surface tension values. surface segregation studies demonstrated that al possesses the strongest surface affinity, followed by si, while ti is the least surface-active element. these findings provide crucial insights into the thermodynamic stability and interfacial behavior of multicomponent al–cu–fe–si–ti liquid alloys, which are essential for optimizing their processing and applications. keywords al-cu-fe-si alloy, chou model, thermodynamic modeling, r-k polynomial, surface tension. article information manuscript received: august 19, 2025; revised: september 9, 2025; accepted: september 12, 2025 doi https://doi.org/10.3126/bibechana.v22i3.83332 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 280 http://nepjol.info/index.php/bibechana sashit.yadav@mmamc.tu.edu.np https://doi.org/10.3126/bibechana.v22i3.83332 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ n. dahal et al./ bibechana 22 (2025) 280-290 281 1 introduction the development of alloys has been driven by the need to engineer materials with tailored properties for scientific and technological applications. among these, al-based multicomponent alloys are widely used in aerospace and automotive industries due to their lightweight, high strength, wear resistance, and cost-effectiveness [1]. their recyclability properties further make them superior to polymer-based materials. the addition of fe to al enhances mechanical strength [2], while al-cu alloys can form quasicrystalline structures, exhibiting low thermal conductivity and high corrosion resistance [3]. incorporating si into al-cu-fe alloys promotes quasicrystalline phase formation, improving fluidity, reducing porosity, and enhancing strength [4–6] . similarly, ti-based alloys are favored in aeronautics and aerospace for their high strength-to-weight ratio, low density, excellent corrosion resistance and high melting temperature. however, their poor oxidation resistance at high temperatures can be mitigated by surface modification, where ti concentration is reduced by alloying with oxidation-resistant elements that preferentially segregate to the surface [7]. experimental investigation of alloys in molten states faces significant challenges, including high reactivity of elements at elevated temperatures, time-consuming procedures, high costs, and the need for advanced instrumentation [8]. the theoretical modeling complements the experimental study by exploring a vast range of compositions and temperature-dependent structures, saving time and resources. in this regard, different theoretical models such as collinet [9], hillert [9, 10], kohler [9, 11, 12], muggianu [9, 12, 13], toop [11, 12, 14] and chou’s (also known as general solution model, gsm) [12,15,16] models are collectively recognized as geometric models, have been developed to explore mixing properties of ternary and higher order liquid alloys. notably, the chou model and symmetric geometric models like muggianu and kohler are often considered more appropriate than asymmetric geometric models for analyzing highly intricate multi-component alloys [9]. these computational approaches have been widely employed to assess the thermo-physical properties of ternary liquid alloys [11–14, 17, 18] and quaternary systems [8, 19–21]. notably, arslan and dogan [9] applied these models to predict the thermodynamic behavior of the fe-cr-ni-mg-o quinary system, while dogan et al. [13] investigated the ni-cr-co-al-mo system. extending this further, dogan and arslan [22] analyzed the ni-cr-co-al-mo-ti-cu system, leveraging thermodynamic databases of constituent binary subsystems to enhance predictive accuracy. moreover, a comprehensive investigation of the al-cu-fe-si-ti liquid alloy remains unexplored, with no theoretical or experimental data reported to date. therefore, this study is designed to explore the thermodynamic and surface properties of al-cu-fesi-ti liquid alloy using theoretical modeling equations. the common fundamental concept of these models is that the behavior of alloys is the cumulative effects of their binary subsystems with a specific weightage assigned to each. 2 formalism 2.1 thermodynamics properties excess gibbs free energy of mixing ∆gxs m is a thermodynamic function that has a strong influence on the mixing behavior of alloys. for binary liquid alloys, the respective parameter ∆gxs ij is expressed in the form of redlich-kister (r-k) polynomial as [10–12,23] ∆gxs ij = xixj ∑ aν ij(xi −xj) ν (1) where xi and xi are the concentrations of the components in the binary alloys. aν ij are the coefficients of the r-k polynomials. the expression for ∆gxs m of multi-component liquid alloy is obtained by adding ∆gxs ij with suitable probability weight assigned to each [11, 14, 20, 21,24] ∆gxs m = σm ij,i ̸=jwij∆gxs ij (2) where, i, j = 1, 2, 3, ....m depending upon the components of the alloy. for quinary alloy, m=5 and hence ∆gxs m can be expressed as ∆gxs m = w12∆gxs 12 +w13∆gxs 13 +w14∆gxs 14 +w15∆gxs 15 +w23∆gxs 23 +w24∆gxs 24 +w25∆gxs 25 +w34∆gxs 34 +w35∆gxs 35 +w45∆gxs 45 (3) the term wij is the probability weight assigned to binary pairs of the multi-component alloy, expressed as wij = xixj xi(ij)xj(ij) (4) where xi and xj are the concentrations of the components in the quinary system and xi and xj are the concentrations of the components in the constituent binary subsystem. the selection of later two terms depends upon the preferred theoretical model. for example, muggianu model [9, 13] xi(ij) = ( 1 + xi − xj 2 ) , xj(ij) = ( 1 + xj − xi 2 ) (5) n. dahal et al./ bibechana 22 (2025) 280-290 282 kohler model [9, 13] xi(ij) = xi xi + xj , xj(ij) = xj xi + xj (6) chou model [9, 13] xi(ij) = xi +σm k=1,k ̸=i,jx kξki(ij) (7) herein, ξki(ij) are the similarity indices of component k to component i in ij subsystem, expressed as [14,17,21] ξki(ij) = η(ij, ik) η(ij, ik) + η(ji, jk) (8) the term η(ij,ik) in equation (8) is the square of deviation, expressed in the form η(ij,ik) = ∫ 1 0 (∆gxs ij −∆gxs ik ) 2dxi (9) the activity coefficient γi of ith component in the multi-component liquid alloy is related to partial excess gibbs free energy (∆gxs i ) as [12,25] rt ln γi = ∆gxs i (10a) once γi is calculated, the activity (ai) of the respective component can be calculated using the relation ai = xiγi (10b) ∆gxs i is calculated in terms of integral excess gibbs free energy of mixing (∆gxs m ) of the quinary system as [9] ∆gxs i = ∆gxs m + m∑ j=1 (δij − xj) ∂∆gxs m ∂xj (11) where δij is the kronecker delta function. 2.2 surface properties the surface tension (σ) of a quinary liquid alloy is calculated using the analytical expression of butler’s model [11,12,14,23,26,27] σ = σi + rt ai ln xs i xb i + ∆gxs i,s −∆gxs i,b ai (12) here, σi(i = 1, 2, 3, 4, 5) is the surface tension of the individual component at temperature of interest t, r is the molar gas constant, and xs i and xb i are the concentrations of the component i in the surface phase and the bulk phase respectively. ∆gxs i,s and ∆gxs i,b are respectively the partial excess free energy for the surface phase and the bulk phase of the individual component, and are related as ∆gxs i,s = β∆gxs i,b [11,20,26,28] . the term β is semiempirical parameter and its value depends upon the state and type of the atoms of the liquid mixture. ai is the surface area of the monolayer of one mole of pure element i and it can be calculated using the relation [23,26] ai = fn 1/3 a (mi/ρi) 2/3 (13) where f is called geometric factor and its value depends upon the type of crystal of the atoms in the mixture and the terms na, mi and ρi are the avogadro’s number, molar mass of element i and density of the element i respectively. the value of f is calculated from the relation [17,23,26] f = (3fb/4) 2/3(π1/3/fs) (14) with fb and fs are the volume and surface packing fractions respectively. 3 results and discussion 3.1 thermodynamic properties table 1: interaction energy parameters of the binary sub-system of al-cu-fe-si-ti liquid alloy system aν ij [jmol−1] reference a0 ij -67094+8.56*t al-cu a1 ij 32148-7.12t t [29] a2 ij 5915-5.89 t a0 ij -91976.5+22.13*t al-fe a1 ij -5672.58+4.8728*t a2 ij 121.9 a0 ij -11340.1-1.23*t al-si a1 ij -3530.93+1.35993*t a2 ij 2265.39 a0 ij -108250+38*t al-ti a1 ij -6000+5.00*t [30] a2 ij 15000 a0 ij 36088-2.33*t cu-fe a1 ij 324.53-0.0327*t a2 ij 324.53-0.033*t a0 ij -39688.86+14.27*t cu-si a1 ij -49937.13+29.79*t a2 ij -31810.6+18.008*t a0 ij -19330+7.651*t cu-ti a1 ij 0 [24] a2 ij 9382-5.45*t a0 ij -62273.8+5.70*t fe-si a1 ij -5491.468 a2 ij -18821.54+22.07*t a0 ij -164434.6 +41.98*t fe-ti a1 ij -21.52*t [30] a2 ij 0 a0 ij -255852.17+21.87*t si-ti a1 ij 25025.35-2.00*t a2 ij 83940.65-6.71*t n. dahal et al./ bibechana 22 (2025) 280-290 283 figure 1: excess gibbs free energy of mixing (∆gxs ij ) of binary sub-systems of al-cu-fe-si-ti liquid alloy at 1950 k experimental as well as theoretical studies of the binary subsystems of al-cu-fe-si-ti are available in literature. hultgren et al. [31] have compiled the experimental data of thermodynamic parameters of many binary subsystems, which is one of the popularly cited sources in the study of alloy. the previous studies showed that the binary sub-systems al-cu [32–34] , al-fe [23, 35–38] , alsi [32, 39] and al-ti [36, 40, 41] are ordering alloys whereas cu-fe sub-system is reported to have segregating nature [2,42–44]. additionally, cu-si [45], cu-ti [46, 47], fe-si [48, 49] and si-ti [50–52] have been investigated to have ordering nature. the theoretical approaches applied in this study treat the thermodynamic and surface properties of a multicomponent liquid alloy as the sum of the corresponding properties of all binary subsystems, with specific weightages assigned to each. the excess parameters of a binary liquid alloy are expressed in terms of redlich-kister (r-k) polynomials. the optimized coefficients of the r-k polynomials for the binary subsystems of the al-cu-fe-si-ti liquid alloy were obtained from the literature and are presented in table 1. the excess gibbs free energy of mixings of the binary sub-systems (∆gxs ij ) of the quinary liquid alloy were calculated at 1950 k using aforementioned and are plotted in figure 1. among the 10 binary sub-systems, cu-fe was found to have positive (∆gxs ij ) with peak value of 7.880 kjmol−1 at cu50fe50. the rest of all were found to have negative (∆gxs ij ) with the peak values of −13.00 kjmol−1 at al40cu60, −12.20 kjmol−1 at al50fe50, −2.230 kjmol−1 at al50si50, −8.540 kjmol−1 at al50ti50, −3.200 kjmol−1 at cu40si60, −1.100 kjmol−1 at cu50ti50, −20.60 kjmol−1 at fe50si50, −12.80 kjmol−1 at fe50ti50 and −53.30 kjmol−1 at si50ti50, figure 1. these results indicate that the cu-fe subsystem is segregating in nature, whereas the others exhibit ordering behavior, with si-ti being the most ordering, followed by cu-ti, fe-si, al-cu, al-si, al-ti, al-fe, and cu-si. (a) (b) figure 2: ∆gxs m of al-cu-fe-si-ti liquid alloy at 1950 k from (a) fe corner at cross-section xal : xcu : xsi : xti = 4:1:2:3 (b) ti corner at crosssection xal : xcu : xsi : xti = 1:2:3:4. as cu-fe is the only segregating subsystem and siti is the strongest ordering subsystem among all binaries, this work focuses on exploring the excess gibbs free energy of mixing (∆gxs m ) and the activities of the components in the al-cu-fe-si-ti liquid alloy from the fe and ti corners. in this regard, ∆gxs m of system was calculated at 1950 k at cross-section xal : xcu : xsi : xti = 4:1:2:3 from fe corner and at xal : xcu : xfe : xsi = 1:2:3:4 from ti corner in the framework of chou, muggianu and kohler models for comparison process. for the purpose, equations (2-9) along with the required parameters from table 1 have been utilized. the calculated values of ∆gxs m from the preferred models are consistent with each other (figure 2(a,b)) thereby validating the present computational apn. dahal et al./ bibechana 22 (2025) 280-290 284 proaches. (a) (b) figure 3: compositional variations of ∆gxs m for al-cu-fe-si-ti liquid alloy at 1950 k from (a) fe corner (b) ti corner at 1:2:3:4,4:1:2:3,3:4:1:2,2:3:4:1 and 1:1:1:1 fixed compositions of other atoms. additionally, the values of ∆gxs m were calculated from the fe and ti corners at fixed compositions of the remaining atoms in the ratios 1:2:3:4, 4:1:2:3, 3:4:1:2, 2:3:4:1 and 1:1:1:1 using the chou model (figure 3 (a,b)).the optimum values of ∆gxs m from the fe corner were found to be −27.720, −20.340, −13.260, −15.460, and −19.580 kjmol−1 for the above-mentioned cross-sections xal : xcu : xsi : xti =1:2:3:4,4:1:2:3,3:4:1:2,2:3:4:1 and 1:1:1:1 respectively, figure 3(a). these results suggest that, at a particular fe concentration, the strength of interaction between the components increases with an increase in the concentrations of si and ti, whereas it decreases with an increase in cu concentration. this is because higher si and ti concentrations promote the formation of the most energetic and ordering complexes of si– ti, fe–si, and fe–ti. conversely, increasing the cu concentration reduces the number of ordering pairs, which lowers the magnitude of the negative ∆gxs m value. the present investigation also reveals that the strength of quinary interaction in the alloy is dominated by binary pairs interactions of si–ti in the cross-sections xal : xcu : xsi : xti=1:2:3:4, 4:1:2:3 and 1:1:1:1, fe-si and fe-ti interactions in 3:4:1:2 and 2:3:4:1. the maximum negative values of ∆gxs m calculated from the ti corner are −29.280, −25.010, −17.900, −14.500, and −21.950 kjmol−1 for the cross-sections xal : xcu : xfe : xsi = 1:2:3:4, 4:1:2:3, 3:4:1:2, 2:3:4:1 and 1:1:1:1 respectively, figure 3(b). these results indicate that increment in the concentrations of fe and si have greater influence on increasing ∆gxs m of the system from the ti corner. the maximum ∆gxs m values in the quinary compositions are lower than the maximum ∆gxs ij value of the si-ti binary system at the composition si50ti50. this suggests that the robustness of the quinary interaction is surpassed by that of the si–ti binary interaction. further, the strength of the quinary interaction is dominated by si–ti interactions in the cross-sections 1:2:3:4, 4:1:2:3, and 1:1:1:1; by cu–ti, fe—si, and si—ti interactions in 3:4:1:2; and by cu—ti and fe—ti interactions in 2:3:4:1. 3.2 activity the activities of the components of the al–cu–fe– si–ti liquid alloy were calculated at 1950 k and higher temperatures in the aforementioned crosssections using equations (10) and (11) within the framework of the chou model. the activities of the components calculated from the fe corner at the cross-section xal : xcu : xsi : xti = 3:4:1:2 are illustrated in figure 4(a). it can be observed that the activity of fe (afe) exhibits a small negative deviation from ideal behavior, indicating its tendency to form complexes with other components. at xfe = 0.1, the activities are aal = 0.10, acu = 0.31, asi = 0.008 and ati = 0.043. as the fe concentration increases (i.e., the concentrations of the other components decrease), the activities of al, si, and ti decrease steadily, whereas the activity of cu initially increases despite its decreasing concentration, figure 4(a). after reaching a maximum of 0.46, acu decreases with further increases in fe concentration. this behavior can be explained by the segregating nature of the cu-fe system and the ordering tendency of the other binary subsystems. increasing the fe concentration favors the formation of complexes between fe and the other elements, except cu. consequently, cu shows a stronger tendency to leave the solution, which initially raises its acn. dahal et al./ bibechana 22 (2025) 280-290 285 tivity. however, at higher fe concentrations, the very low concentrations of all other components are available in the liquid mixture, including cu which leads to a reduction in the activities of al, cu, si and ti. moreover, afe increases gradually with increase in its concentration as expected. (a) (b) figure 4: activity of components of al-cu-fe-si-ti liquid alloy at 1950 k (a) fe corner at cross-section xal : xcu : xsi : xti = 3:4:1:2 (b) ti corner at cross-section xal : xcu : xfe : xsi = 1:2:3:4. the activity of ti (ati), calculated from the ti corner, shows a negative deviation from ideal behavior (figure 4b), indicating its strong tendency to form complexes throughout the entire concentration range. at xti = 0.1, the activities of the other components are found to be aal = 0.05, acu = 0.46, afe = 0.09 and asi = 0.08. with increasing ti concentration or decreasing concentrations of al, cu, and fe, the activities of al, cu, and fe increased, reaching maximum values of aal = 0.064, acu = 0.599 and afe = 0.110, before decreasing again with further reductions in their respective concentrations. this trend arises from the strong complexforming tendency of si and ti, as evidenced by their large negative ∆gxs m , which dominates over the weaker ordering tendencies of the other binary subsystems. at equiatomic composition, the activities follow the order acu>aal>afe>ati>asi. figure 5: variation of activity of components with temperature at composition al20cu20fe20si20ti20. the variation of the component activities with temperature at equiatomic composition (al20cu20fe20si20ti20) was also studied in the present work. the activities of al, fe, si, and ti increase with rising temperature whereas that of cu decreases (figure 5). al, fe, si, and ti exhibit negative deviations from ideality, indicating their complex-forming nature in this alloy. however, this tendency diminishes at elevated temperatures, leading to an increase in their activities. in contrast, cu shows a positive deviation from raoult’s law, reflecting its segregating behavior. consequently, the activity of cu decreases as temperature rises. 3.3 surface properties the surface tension (σ) of the liquid alloy was calculated at 1950 k and higher temperatures using the butler equation. for this purpose, the surface tensions, densities, their temperature variations, and melting temperatures of the individual alloy components, listed in table 2, were taken from the literature [53]. by employing these parameters along with the determined values of partial excess gibbs free energy of mixing (∆gxs i ) of the individual components in equations (11) and (12), the surface tension of the quinary system was evaluated from both fe and ti corners by varying the concentration of the corner element from 0.1 to 0.9. these values were calculated at aforementioned cross-sections as a function of concentration and are displayed in figure 6(a,b). n. dahal et al./ bibechana 22 (2025) 280-290 286 table 2: input physical parameters for surface tension at melting temperature (t0) [53] parameter element al cu fe si ti tm [k] 933 1360 1809 1683 1958 ρ0 [kg m−3] 2385 8000 7030 2524 4110 ∂ρ ∂t [kg m−3 k−1] -0.28 -0.801 -0.833 -0.3487 -0.226 σ0 [n m−1] 0.914 1.285 1.872 0.865 1.65 ∂σ ∂t [n m−1 k−1] -0.00035 -0.00013 -0.00049 -0.00013 -0.00026 (a) (b) figure 6: surface tension of the al-cu-fe-si-ti liquid alloy at 1950 k calculated from (a) fe corner and (b) ti corner. in the fe corner, calculations were performed for the cross-sections xal : xcu : xsi : xti = 1:2:3:4, 4:1:2:3,3:4:1:2, 2:3:4:1 and 1:1:1:1, as illustrated in figure 6(a). at xfe = 0.1, the computed σ values are 1.12, 0.84, 0.95, 0.92, and 0.94 nm−1 for the respective cross-sections. with increasing bulk concentration of fe, the surface tension of the liquid alloy gradually increases in each cross-section. among the alloy components, ti exhibits the highest surface tension (σti = 1.6487 nm−1) and al the lowest (σal = 0.558 nm−1) at 1950 k, table 2. therefore, at a given fe concentration, the alloy’s surface tension is maximized in the cross-section with the largest proportion of ti and minimized in the cross-section with the largest proportion of al. this demonstrates that the surface tension of the quinary liquid alloy increases with increasing ti concentration and decreases with increasing al concentration. the surface tension of the liquid alloy was also calculated from the ti corner for the cross-sections xal : xcu : xfe : xsi = 1:2:3:4, 4:1:2:3, 3:4:1:2, 2:3:4:1 and 1:1:1:1, shown in figure 6(b). at xti = 0.1, the computed values of σ are 1.043, 0.81, 0.90, 1.07, and 0.94 nm−1 for the respective crosssections. the maximum surface tension, observed at the cross-section xal : xcu : xfe : xsi = 2:3:4:1, is attributed to the higher proportions of cu and fe, both of which have relatively large surface tensions, table 2. conversely, the minimum surface tension is observed at the cross-section xal : xcu : xfe : xsi = 4:1:2:3, resulting from the lower proportions of cu and fe and the higher proportions of al and si, which have comparatively lower surface tensions. these findings demonstrate that the surface tension of the liquid alloy increases in compositions where elements with inherently higher surface tensions are present in greater proportions. figure 7: variation of surface tension of al–cu–fe– si–ti liquid alloy with temperature. n. dahal et al./ bibechana 22 (2025) 280-290 287 variation of surface tension of the quinary alloy with temperature was studied at different compositions, out of which variation at five different assembly of atoms of the liquid alloy is demonstrated in figure 7. surface tension of the liquid alloy is observed to decrease at elevated temperature, implying the decrease in the atomic interactions among the constitute atoms of the liquid mixture. this result further justifies the the mixing tendency predicted by the previously determined thermodynamic functions of the system at elevated temperatures. (a) (b) figure 8: surface concentrations of components of al-cu-fe-si-ti of liquid alloy calculated from (a) fe corner at cross-section xal : xcu : xsi : xti = 3:4:1:2 (b) ti corner at cross-section xal : xcu : xfe : xsi = 1:2:3:4. the surface concentrations of the components (xs i , i = al,cu, fe, si, t i) of the quinary system were computed as a function of fe and ti concentrations in different cross-sections. as shown in figure 8(a), at the cross-section xal : xcu : xsi : xti = 3:4:1:2, the surface concentrations of atoms at 1950 k are found to be xs al = 0.66359, xs cu = 0.20645, xs fe = 0.0.034397, xs si = 0.07484 and xs t i = 0.020699, while the corresponding bulk concentrations are xal = 0.24, xcu = 0.32, xfe = 0.20, xsi = 0.08 and xti = 0.16. these results indicate a strong tendency of al atoms to segregate at the surface, while the other atoms preferentially remain in the bulk phase. the surface concentration of fe increases gradually at first and then rises sharply with increasing bulk fe concentration. in contrast, the surface concentration of al decreases markedly, whereas si and ti concentrations decrease gradually. interestingly, the surface concentration of cu initially increases despite a decrease in its bulk concentration, but after reaching a maximum value, it decreases again. this unusual behavior of cu can be attributed to the strong ordering tendency of the other elements with fe, which reduces the likelihood of cu forming bonds with them. as a result, cu atoms preferentially migrate toward the surface phase. a similar variation in the surface concentration of al atoms has been reported in the ti-al-si ternary liquid alloy by yadav et al. [28]. in the ti corner at the cross-section xal : xcu : xfe : xsi = 1:2:3:4, the surface concentrations are found to be xs al = 0.351316, xs cu = 0.159499, xs fe = 0.04691, xs si = 0.419739 and xs t i = 0.022489, corresponding to bulk concentrations of xal = 0.08, xcu = 0.16, xfe = 0.24, xsi = 0.32 and xti = 0.20 (figure 8(b)). in this region, al and si exhibit a strong tendency to segregate into the surface phase, while cu, fe, and ti preferentially remain in the bulk phase. moreover, the surface concentration of ti increases gradually at first and then rises sharply with increasing bulk ti concentration. conversely, xs si decreases as bulk concentration of ti increases. the concentrations of al, cu, and fe at the surface initially rise with decreasing bulk concentration, reaching a peak before declining again. this unusual behavior is attributed to the dominant presence of si and the strong ordering tendency of the si-ti system, which influences the distribution of al, cu and fe at the surface. at equiatomic composition, the overall extent of surface segregation tendency of the alloying elements follows the order al>si>cu>fe>ti>. we have also calculated the temperature dependence of the surface concentrations at a fixed composition, al20cu20fe20si20ti20, figure 9. the surface surface concentrations of the components at this composition are found to be xs al = 0.620774, xs cu = 0.139894, xsfe, = 0.031593, xs si = 0.186671 and xs t i = 0.021066 at 1950 k. this implies the highest surface segregating nature of al and lowest surface segregating nature of ti among the components in this composition too. further, the surface concentration of fe and ti appears to be enn. dahal et al./ bibechana 22 (2025) 280-290 288 hanced with rise in temperature, whereas, surface concentration of al, cu and si appears to decrease at higher temperature. figure 9: variation of surface concentrations of the components of al–cu–fe–si–ti liquid alloy with temperature. 4 conclusion the thermodynamic analysis of the al-cu-fe-si-ti liquid alloy reveals that its multicomponent behavior is primarily governed by the interactions within its binary subsystems. among the ten binaries, cu-fe exhibits a segregating tendency with positive excess gibbs free energy of mixing, while the remaining systems show ordering behavior, with siti being the strongest ordering pair. the calculated quinary ∆gxs m values from both fe and ti corners confirm the consistency of chou, muggianu, and kohler models, thereby validating the present computational approach. the quinary alloy exhibits stronger negative ∆gxs m values when si and ti concentrations are high, emphasizing the dominance of si-ti, fe-si, and fe-ti interactions. conversely, higher cu concentration reduces ordering, leading to weaker interactions. comparison with binary interactions shows that the robustness of quinary ordering does not surpass the strong si-ti binary interaction at 1950 k. overall, the alloy’s thermodynamic stability is strongly influenced by the cooperative effects of ordering pairs, particularly siti, fe-si, and fe-ti, while cu tends to weaken the interaction strength due to its segregating nature with fe. this tendency of the quinary system is further justified by the results of activity, the other thermodynamic function. the surface tension of the quinary system increases at each crosssection with the increase in concentrations of fe and ti. the surface tension rises in alloy compositions enriched with elements that naturally possess higher surface tensions. at the cross-section xal : xcu : xsi : xti = 3:4:1:2 and from fe corner, al atoms segregate at the surface, while the other atoms preferentially remain in the bulk phase. from ti corner at xal : xcu : xfe : xsi=1:2:3:4, al and si exhibit a strong tendency to segregate into the surface phase, while cu, fe, and ti preferentially remain in the bulk phase. at equiatomic composition, the overall extent of surface segregation tendency of the alloying elements follows the order al>si>cu>fe>ti>. temperature elevation systematically decreases both surface segregation and deviations in activities, confirming that the system approaches an ideal random distribution at higher temperatures. references [1] c. corti. 22nd santa fe symposium on jewellery manufacturing technology, 18–21 may 2008 albuquerque, new mexico, usa. gold bulletin, 41(3):269–271, 2008. 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[53] j.j. valencia and p.n. quested. thermophysical properties. modeling for casting and solidification processing, 189, 2001. introduction formalism thermodynamics properties surface properties results and discussion thermodynamic properties activity surface properties conclusion bibechana vol. 21, no. 3, december 2024, 233-240 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher: dept. of phys., mahendra morang a. m. campus (tribhuvan university) biratnagar computational analysis of clot formation risk in diabetes: a mathematical modeling approach shabab akbar, rohit kumar sharma, mo sadique, kshiteendra mohan jaiswal, purnima chaturvedi, vivek kumar, sapna ratan shah∗ school of computational & integrative sciences, jawaharlal nehru university, new delhi 110067, india ∗corresponding author: email: sapnarshah@mail.jnu.ac.in abstract diabetes (type 1 or type 2) is a serious condition that can make blood clot more easily. this can cause heart attacks and strokes, which are very dangerous. our approach integrates physiological data, hemodynamic principles, and mathematical equations to simulate blood flow dynamics and clot formation processes within the vasculature of diabetic individuals. by incorporating key factors such as altered blood viscosity, resistance to flow, endothelial dysfunction, and platelet aggregation, we obtained insights into the complex interplay between diabetes related factors and clotting propensity. changes in blood composition, such as increased levels of fibrinogen and other clotting factors, can make blood thicker and more prone to clotting and the reason for increased resistance to flow and viscosity. as blood clots enlarge in blood vessels, they obstruct blood flow, increasing resistance. this makes blood movement harder. clot size also affects nearby blood viscosity. accumulating cells and clotting factors thicken blood, worsening circulation. larger clots heighten flow resistance and viscosity, potentially causing issues like tissue damage. thus, larger clots worsen blood flow and cardiovascular health. through computational simulations, we explored various scenarios to assess the impact of different parameters on clot formation risk, thereby offering valuable insights for the development of preventive strategies and targeted interventions for diabetic patients. keywords clot formation, diabetes mellitus, mathematical modeling, cardiovascular complications, platelet aggregation. article information manuscript received: april 19, 2024; revised: april 23, 2024; accepted: june 6, 2024 doi https://doi.org/10.3126/bibechana.v21i3.64973 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 233 http://nepjol.info/index.php/bibechana sapnarshah@mail.jnu.ac.in https://doi.org/10.3126/bibechana.v21i3.64973 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ shabab akbar et al./ bibechana 21 (2024) 233-240 234 1 introduction in diabetes, blood tends to clot more easily, which can lead to serious problems like heart attacks and strokes. it is important to manage diabetes carefully to reduce this risk. recent data from the international diabetes federation (idf) underscores the alarming scale of the epidemic, with 537 million adults aged 21–80 living with diabetes in 2021, a number projected to soar to 784 million by 2045. the disease exacts a heavy toll, causing 6.9 million demise in 2021 alone, translating to one in every two seconds. moreover, diabetes ranks as the third most prevalent comorbidity in covid-19 cases, leading to increased disease severity, and adverse outcomes, including admission in icu and at last death. it is considered a silent epidemic, with its prevalence steadily increasing globally and posing significant public health challenges. all these statistics underscore the urgent need for effective interventions and policies to curb diabetes epidemic and its associated complications [1–4]. diabetes is a chronic disorder characterized by high blood glucose levels and is associated with a myriad of complications, including cardiovascular diseases figure.1. one of the major cardiovascular complications of diabetes is the increased risk of thrombotic events, such as myocardial infarction and stroke, attributed to the formation of blood clots within the vasculature [5–8]. despite advances in understanding the pathophysiology of diabetic vascular complications, the precise mechanisms underlying the heightened clot formation risk in diabetic individuals remain incompletely understood [9–13]. mathematical modeling and computational simulations offer a powerful approach to elucidate the complex hemodynamic and biochemical processes involved in clot formation, providing valuable insights into the interplay between diabetes related factors and thrombotic propensity [14–18]. diabetes is commonly categorized into two primary types: type 1 and type 2. in type 1 diabetes, pancreas doesn’t produce enough insulin, while type 2 diabetes, more prevalent form, arises when the body becomes resistant to insulin or doesn’t produce sufficient amounts. symptoms may include heightened thirst, hunger, fatigue, weight loss, frequent urination, infections, blurry vision, and slow wound healing [19–24]. both type 1 and type 2 diabetes can increase the risk of blood clotting, but the mechanisms may differ between the two types. in type 1 diabetes, where the body does not produce enough insulin, the risk of blood clotting may be related to factors such as hyperglycemia (high blood sugar levels), which can lead to damage of blood vessels and impair blood flow. additionally, individuals with type 1 diabetes may have other risk factors such as increased levels of clotting factors in the blood. in type 2 diabetes, which is characterized by insulin resistance or reduced insulin production, the risk of blood clotting may be higher due to factors such as obesity, inflammation, and metabolic abnormalities associated with insulin resistance. these factors can contribute to changes in blood vessel function and increased clot formation. both types of diabetes can predispose individuals to blood clotting, but the specific mechanisms and risk factors may vary [10,21]. figure 1: normal artery with diseased artery with a blood clot. addressing these risk factors through lifestyle modifications and targeted interventions is crucial in combating the diabetes epidemic and reducing its burden on individuals and healthcare systems alike [25–30]. diabetes can lead to severe complications that affect various parts of the body, including heart, blood vessels, eyes, teeth, kidneys, nerves, and may ultimately result in demise. diabetic complications often necessitate amputations, causing permanent disability [31–36]. diabetic patients has to face more higher risk of blockage and heart strokes compared to the general population. diabetic neuropathy, a type of nerve damage resulting from high blood sugar levels, is another common complication, particularly affecting the feet and increasing the risk of foot ulcers, infections, and subsequent limb amputations, especially when combined with poor blood flow [37–42]. diabetic retinopathy, characterized by hurting to the tiny blood vessels in retina, is a leading cause of blindness worldwide, affecting nearly one million individuals. additionally, diabetic nephropathy, which damages the small blood vessels in the kidneys, leads to kidney disease and can eventually cause kidney failure, representing one of most prevalent causes for kidney failure [43–47]. in this study, we presented a computational analysis of clot formashabab akbar et al./ bibechana 21 (2024) 233-240 235 tion risk in diabetes using a mathematical modeling approach. our research aims to unravel the intricate mechanisms that contribute to the increased thrombotic risk in diabetic patients [48–51]. by leveraging mathematical models and computational simulations, we simulated various scenarios to explore the impact of diabetes related factors, such as altered blood rheology, endothelial dysfunction, and platelet hyperactivity, on clot formation dynamics. through comprehensive analyses of hemodynamic parameters, clot formation kinetics, and biochemical pathways, we aim to elucidate the underlying mechanisms driving clot formation in diabetic individuals [52–56]. the significance of clot formation risk in diabetes lies in its potential to lead to severe and life-threatening complications. diabetes is associated with an increased propensity for blood clot formation, a condition known as hypercoagulability. additionally, diabetic individuals are more susceptible to developing blood clots in smaller blood vessels, leading to conditions like deep vein thrombosis (dvt) and pulmonary embolism (pe). therefore, understanding and mitigating the risk of clot formation in diabetes is crucial for preventing adverse cardiovascular outcomes and improving patient outcomes. this computational approach allows us to integrate diverse physiological and pathological factors into a unified framework, providing a holistic understanding of the complex interplay between diabetes and thrombotic risk. by elucidating the key determinants of clot formation in diabetes, our study aims to identify potential therapeutic targets and strategies for mitigating the heightened thrombotic risk associated with this prevalent metabolic disorder [51,57–60] ersonalized interventions aimed at reducing the burden of cardiovascular complications in diabetic patients. 2 formulation of the problem our mathematical model incorporates several key factors implicated in the pathogenesis of clot formation in diabetes, including altered blood viscosity, endothelial dysfunction, and platelet aggregation. the model is based on fundamental principles of hemodynamics, fluid mechanics, and biochemical kinetics, represented by a system of differential equations describing the dynamics of blood flow and clotting processes within the vascular network. parameters such as blood glucose levels, lipid profiles, and inflammatory markers are integrated into the model to capture the systemic effects of diabetes on vascular health [61, 62]. in this study, we considered, a scenario where a narrowing in the artery, known as stenosis, forms asymmetrically along the artery’s length but maintains symmetry around its circumference. this narrowing depends on both the axial distance along the artery, denoted as z, and height of stenosis. in this situation, radius of artery, denoted as r(z), can be expressed as below: r(z) r0 = { 1− [l (m−1) 0 x− xm] d ≤ z ≤ d+ l0, 1 otherwise. (1) where x =z-d. in simpler terms, let’s break down the equation. we are talking about an artery with a blockage, which reduces its radius compared to its original size. the variable r(z) represents the current radius of the artery with the blockage, while r0 represents its original, unobstructed radius. the length of the blockage is denoted by l0 and d indicates where along the artery it is located. the parameter m, which must be greater than or equal to 2, describes the shape of the blockage. when m=2, it means the blockage is axially symmetric. finally, there is another parameter, a, which is determined by the specific values of these variables and parameters [10,31,36,50]. a = δ mm/(m−1) r0 lm 0 (m− 1) this equation helps us find the maximum height of the blockage in the artery, indicated by the symbol . it is determined by factors such as the location of the blockage along the artery (z), its length (l0), and the shape parameter (m). the expression also involves a fractional calculation, with the result being the maximum height of the blockage. 2.1 conservation equation and boundary condition the equation describing the steady, and fullydeveloped flow of blood in an artery, under the conditions of laminar flow and incompressibility, simplifies as: 0 = −∂p ∂r + 1 r ∂(rτ) ∂z 0 = −∂p ∂r (2) the coordinates (z, r) represent the positional measurements, with z indicating the direction along the artery’s axis, and r denoting measurements perpendicular to the artery’s axis. coordinates (z, r) are used for pinpointing locations within artery. the coordinate z represents positions along the artery’s length, while the coordinate r measures distances perpendicular to the artery’s axis. this system allows for precise spatial referencing within the artery, aiding in the analysis of various phenomena occurring within its structure. the following conditions at the boundaries are applied to find the solution of the aforementioned equations. shabab akbar et al./ bibechana 21 (2024) 233-240 236  ∂u ∂r = 0 at r = 0 u− 0 at r = r(z) τ is finite at r = 0 p = p0 at z = 0 p = pl at z = l (3) 2.2 casson’s fluid model casson’s model is often expressed [16,27]:{ τ1/2 = τ 1/2 0 (µ)1/2(−du dr ) 1/2, if τ ≥ τ0 (dudr ), if τ < τ0 (4) with τ0 = −( dp dz ) rc 2 where µ shows casson’s viscosity coefficient, rc represents radius of plug flow region, 0 indicates yield stress, and represents wall shear. the rate at which volume flows through a particular point in the system, as described by equation (16), is termed as: q = π ∫ r 0 r(−du dr )dr (5) upon integrating equation (17) with the assistance of equations (16) and (3), we obtain the following result: q = πr4 8µ (−dp dz )[1− 16 7 ( rc r )1/2+ 4 3 ( rc r )− 1 21 ( rc r )4] (6) equation (18) can be rewritten as; q = πr4 8µ (−dp dz )f(ȳ) with f(ȳ) = [1− 16 7 (ȳ)1/2 + 4 3 (ȳ)− 1 21 (ȳ)4] where ȳ = rc r << 1 the pressure gradient, as derived from the equation above, can be expressed as below: −dp dz = 8µq πr4f(ȳ) (7) by integrating equation (19) with the boundary conditions, it is obtained: ∆p = p − p0 = 8µq πr4f(ȳ) ∫ l 0 dz (r(z)/r0)4f( ¯y(z)) (8) resistance to flow, also known as resistive impedance, is represented by the symbol and is defined as below: λ = pl − p0 q (9) resistance to flow, obtained from above equations as a reference, can be expressed as follows: λ = 1− l0 l + f0 l ∫ d+l0 0 dz (r(z)/r0)4f( ¯y(z)) (10) where f0 = [1− 16 7 ( rc r )1/2 + 4 3 ( rc r )− 1 21 ( rc r )4] apparent viscosity (µapp) is defined as below: µapp = 1 (r(z)/r0)4f(ȳ) (11) shear stress at wall may be obtained as below; τr = [τ 1/2 0 + (−µ du dr ) (12) 3 results our computational analysis unveils the intricate ways in which diabetic conditions, characterized by hyperglycemia, dyslipidemia, and chronic inflammation, exert profound effects on blood rheology and endothelial function, thereby predisposing diabetic individuals to heightened clot formation. through detailed simulations, we observe that the diabetic milieu significantly alters key hemodynamic and biochemical parameters, creating a prothrombotic environment within the vasculature [34,50,52]. specifically, our model demonstrates that increased blood viscosity, attributed to elevated levels of circulating glucose and lipids, impedes blood flow and promotes stasis, facilitating clot formation. moreover, impaired endothelial nitric oxide production, a hallmark of diabetic endothelial dysfunction, disrupts the delicate balance between prothrombotic and antithrombotic factors, further exacerbating thrombotic propensity. figure 2: resistance to flow with stenosis shape. shabab akbar et al./ bibechana 21 (2024) 233-240 237 figure 3: viscosity with stenosis size. interestingly, our simulations elucidate a nonlinear relationship between blood glucose levels and clot formation risk, with acute hyperglycemic spikes exerting particularly pronounced effects on platelet reactivity and activation of the clotting cascade. these findings underscore the importance of glycemic control in mitigating acute thrombotic events in diabetic patients. additionally, our sensitivity analyses highlight the potential efficacy of multifaceted interventions targeting various pathophysiological pathways implicated in clot formation. by integrating blood glucose lowering strategies, lipid-lowering therapies, and antiplatelet agents, our model suggests synergistic effects in reducing clot formation risk and attenuating the burden of cardiovascular complications in diabetes [6,16,45,51]. figure.2. show that as blood clots expand in size within the blood vessels, they create obstructions that impede the flow of blood. this obstruction results in an increase in resistance to blood flow, making it more difficult for the blood to move past the clot. the larger the clot, the greater the resistance it presents to the flow of blood. this increased resistance can lead to higher pressure within the blood vessel upstream of the clot and decreased pressure downstream, altering blood flow patterns and potentially causing complications such as ischemia or tissue damage. therefore, as clot size increases, so does the resistance to blood flow, which can have significant implications for overall cardiovascular health and function. figure.3. show that as blood clots grow larger within the vasculature, they exert significant effects on blood viscosity, the thickness or stickiness of blood. this increase in viscosity arises from several factors. first, the clot traps various blood components, including red blood cells and platelets, within its structure, leading to a concentration of blood constituents in the vicinity of the clot. additionally, the formation of fibrin, a protein essential for clot structure, results in the creation of a dense meshwork that impedes blood flow [4,15,23,50]. as more platelets aggregate to the clot site, they further contribute to the viscosity of the surrounding blood. the obstruction caused by a larger clot alters the flow dynamics within the blood vessel, influencing shear forces and pressure gradients, which in turn affect viscosity. ultimately, the growth of blood clots leads to an increase in local blood viscosity, impacting blood flow dynamics and potentially exacerbating thrombotic events. overall, our computational approach offers valuable insights into the complex interplay between diabetes-related factors and thrombotic propensity, providing a framework for identifying novel therapeutic targets and optimizing treatment strategies for diabetic individuals at increased risk of thrombotic events [24,32,52]. by elucidating the underlying mechanisms driving clot formation in diabetes, our research aims to pave the way for personalized interventions aimed at mitigating the heightened thrombotic risk associated with this prevalent metabolic disorder. 4 conclusion our study underscores the utility of mathematical modeling and computational analysis in elucidating the complex interplay between diabetes and thrombosis. by integrating physiological data and computational simulations, we provided mechanistic insights into the pathophysiology of clot formation in diabetes and identify potential therapeutic targets for mitigating thrombotic complications in diabetic individuals. the computational framework developed in this study offers a valuable tool for assessing clot formation risk, optimizing treatment strategies, and guiding clinical decision-making in diabetic patients. as blood clots grow larger within the blood vessels, they create obstructions that impede the flow of blood. this obstruction increases the resistance to blood flow, making it more challenging for blood to move past the clot. at the same time, the clot’s size can also affect the viscosity of the blood in the vicinity of the clot. as more blood cells and clotting factors accumulate around the clot, the viscosity of the blood in that area can increase. both increased resistance to flow and higher viscosity can further impede blood circulation, potentially leading to complications such as ischemia or tissue damage. therefore, as the clot size increases, both resistance to flow and viscosity are likely to increase, exacerbating the clot’s impact on blood circulation and overall cardiovascular health. shabab akbar et al./ bibechana 21 (2024) 233-240 238 references [1] j. d. hoffman and s. frankel. numerical methods for engineers and scientists. crc press, boca raton, fl, usa, 2018. 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[62] s. singh. effects of shape of stenosis on arterial rheology under the influence of applied magnetic field. international journal of biomedical engineering and technology, 6(3):286–294, 2011. introduction formulation of the problem conservation equation and boundary condition casson’s fluid model results conclusion bibechana vol. 22, no. 3, december 2025, 291-298 issn 2091-0762 (print), 2382-5340 (online) journal homepage: http://nepjol.info/index.php/bibechana publisher:dept. of phys., mahendra morang a. m. campus (tribhuvan university)biratnagar in silico molecular docking and admet analysis of the phytochemicals of kalanchoe pinnata (lam.) pers. as potential modulators of the mineralocorticoid receptor against cardiovascular diseases ram lal (swagat) shrestha1,2,3, manila poudel2, sujan dhital1,2, nirmal parajuli 1,2, ashika tamang 1,2, safal adhikari 1,2, shiva m.c. 1,2, aakar shrestha 2, timila shrestha 1,2, samjhana bharati 1,2, binita maharjan 1,2, bishnu p. marasini2,3,4,*, jhashanath adhikari subin 2,5,* 1department of chemistry, amrit campus, tribhuvan university, lainchaur, kathmandu 44600, nepal 2kathmandu valley college, syuchatar bridge, kalanki, kathmandu 44600, nepal 3institute of natural resources innovation, kalimati, kathmandu 44600, nepal 4nepal health research council, ministry of health and population, ramshah path, kathmandu 44600, nepal 5bioinformatics and cheminformatics division, scientific research and training nepal p. ltd, bhaktapur 44800, nepal ∗corresponding author. email: bishnu.marasini@gmail.com [bpm] subinadhikari2018@gmail.com [jas] abstract cardiovascular diseases represent a leading global health challenge, with a pronounced impact in low and middle-income countries. the mineralocorticoid receptor (mr), a key transcription factor in cardiovascular disorders, has been linked to hypertension, heart failure, and myocardial infarction. this study aims to investigate the potential of the phytochemicals in kalanchoe pinnata (lam.). pers., a plant known for its traditional medicinal uses, in modulating mr activity through in silico approaches. twenty phytochemicals belonging to different classes of organic molecules from the plant were subjected to computational screening to assess their interaction with the mr (pdb id: 5l7e). mr was treated as a flexible receptor, and molecular docking was performed in a solvated environment. the molecule astragalin among the test molecules showed a promising binding score of -9.209 kcal/mol, which is comparable to the native ligand's score of -9.619 kcal/mol. admet predictions, including toxicity classification, revealed that most of the compounds demonstrated favorable gastrointestinal absorption and varying degrees of blood-brain barrier permeability. toxicity evaluations revealed that several compounds exhibited moderate to low toxicity, with both astragalin and patuletin classified as class 5, indicating a relatively higher level of safety compared to other phytochemicals, and a class comparable to the native compound (class 6). these findings suggested that phytochemicals of k. pinnata hold potential for further investigation as modulators of mr activity, with implications for drug development in cardiovascular diseases. keywords: flexible molecular docking, computational approach, desolvation, docking score, pharmacokinetics, drug-likeness . article information manuscript received: july 1, 2025; revised: august 29, 2025; accepted: september 11, 2025 doi https://doi.org/10.3126/bibechana.v22i3.80853 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 291 http://nepjol.info/index.php/bibechana bishnu.marasini@gmail.com subinadhikari2018@gmail.com https://doi.org/10.3126/bibechana.v22i3.80853 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ ram lal (swagat) shrestha et al./ bibechana 22 (2025) 291-298 292 1 introduction cardiovascular (cv) disease refers to a group of conditions that affect the heart and blood vessels. this includes hypertension, heart attack, stroke, heart failure, and other heart disorders [1]. cv disease is the leading cause of death worldwide, disproportionately affecting lowand middle-income countries more severely than high-income countries [2, 3]. the mineralocorticoid receptor (mr) is a transcription factor belonging to the steroid receptor family. activation of the mineralocorticoid receptor is associated with various cv system disorders, such as hypertension, heart failure, and myocardial infarction [4, 5]. the increase in mr expression in the heart and blood vessels with age contributes to the higher incidence of cv diseases in the elderly [6, 7]. enalapril and metoprolol are frequently prescribed for the treatment of cv conditions like hypertension and heart failure. despite their effectiveness, these drugs may cause side effects, including dizziness, headaches, weakness, a drastic decrease in white blood cell count, proteinuria, and severe allergic reactions. to address these issues, this study focuses on exploring plant-based compounds as potential alternatives [8, 9]. medicinal plants are recognized for containing compounds that may be valuable in treating diseases or in drug development [10, 11]. kalanchoe pinnata (lam.) pers., a succulent herb, has long been utilized in traditional medicine to treat heart conditions, kidney stones, and cancer [12, 13]. they are used in folk medicine to relieve stomach pain and to treat gastritis, diarrhea, dysmenorrhea, liver disorders, fever, female infertility, genitourinary infections, snake and scorpion bites, leprosy, cough, asthma, kidney stones, arthritis, cv diseases, and general tiredness [14]. the plant extract exhibits antihypertensive activity as reported by various authors [15,16], and forms the premise for this work. discovering new leads for a well-known target is a pivotal phase in drug development. two primary approaches are employed: experimental highthroughput screening to sift through extensive compound libraries for potential leads, and computational methods that leverage structural data of the protein binding site [17]. to reduce the cost and time associated with extensive in vitro and in vivo experiments for identifying potential compounds in drug discovery and development, the use of in silico approaches is on the rise [18–20]. this technique employs a docking server to identify novel ligands for receptors with known structures, facilitating the screening of multi-compound databases for molecules that fit a receptor's binding site, thus eliminating the initial need for wet lab experiments [21–23]. this study involves an in silico screening of compounds from k. pinnata to assess their potential to modulate the mr protein and for molecularlevel understanding of the relevant pathways associated with the modulation. 2 methodology 2.1 ligand search twenty phytochemicals of k. pinnata were identified from the literature (google scholar, researchgate, pubmed, sciencedirect) and are presented in table 1 along with their pubchem cid. the compounds' structured data files (sdf) were downloaded from the pubchem database [23]. 2.2 protein target search probable targets were identified using the superpred web server (https://prediction.charite. de/) [24]. it is used for predicting the potential target proteins for a given set of ligands. a percentage bar indicates the probability of the ligand binding to the protein. this probability is based on structural similarity, binding affinity, and other computational predictions. the protein target with the highest probability, which was commonly found among all the ligands, was chosen. other factors considered during this process included ensuring the protein resolution was below 2 å, no mutations were present, and a native ligand was present. eventually, a mineralocorticoid receptor target (pdb id: 5l7e) with a resolution of 1.86 å was chosen with a native ligand (6q0). the structural data of the protein was retrieved from the rcsb protein bank (https://www.rcsb.org/) in pdb format.. 2.3 ligand optimization the native ligand (6q0) was optimized before molecular docking by the use of the avogadro program [25]. it is an advanced software for editing and visualizing molecules, used in computational chemistry, molecular modeling, and bioinformatics for optimizing molecular geometries [26]. the universal force field (uff) was utilized to optimize the molecular geometries of the compounds, the conjugate gradient method was employed, and energy convergence was adjusted to 10-8 units to reduce their structural complexities [27,28]. alongside the native ligand, the same optimization process was applied to all the 20 compounds. after the optimization, it was saved in pdb format for molecular docking calculations. https://prediction.charite.de/ https://prediction.charite.de/ ram lal (swagat) shrestha et al./ bibechana 22 (2025) 291-298 293 2.4 protein structure optimization the pdb structure with pdb id of 5l7e was opened in the pymol program. when the water molecules are removed from a protein, it is known as the holoprotein. after the native ligand is extracted, the resulting structure is called the apoprotein. the extra chain present in the target was removed, polar hydrogens were added, and it was subsequently saved in pdb format. 2.5 molecular docking calculations ligand-protein docking is an optimization problem focused on predicting the position and pose of a ligand that achieves the lowest binding energy within the receptor's active site. docking aids in predicting the favorable binding geometries of a small molecule within a target protein's binding site and estimating the docking score of the resulting complex [29]. for the docking purpose, a web-based tool known as the dockthor (rigid receptor approach) (https://www.dockthor.lncc.br/) [30] was used. for this, the apo form of the protein, native ligand, and the test compounds were utilized in pdb form. initially, to validate the molecular docking protocol, the approach used by adhikari subin and shrestha (2024) was followed. the apoprotein and native ligand were uploaded to the server, and the following parameters were applied: grid center (x: 9, y: 14, z: 11), grid size (x: 16, y: 16, z: 16), discretization: 0.17, number of evaluations: 1,000,000, population size: 750, and number of runs: 24 [31]. subsequently, the test compounds were docked using the same parameters as those for the native ligand. the docking score measures the strength of the interaction between the target and the molecule. it reflects the free energy change upon binding on a comparative basis, with more negative values indicating stronger interactions [30,32,33]. 2.6 protocol validation via rmsd calculation root mean square deviation (rmsd) measures the average distance between atoms in a predicted model and a reference structure, assessing how well the predicted model aligns with the experimental or reference structure. lower rmsd values indicate a better fit, reflecting a more accurate prediction of the ligand's binding mode to the target protein [34]. an rmsd value below 2.0 å [35] is widely accepted as the benchmark for distinguishing between successful and unsuccessful reproductions of a known binding mode [29,36]. the heavy atom rmsd was calculated for the native ligand with the best binding affinity. 2.7 protein-ligand interactions plip server (https://plip-tool.biotec.tudresden.de/plip-web/plip/index) was used for visualizing three-dimensional representations of protein-ligand interactions [37]. 2.8 admet properties and toxicity class identification the in silico properties for absorption (gastrointestinal absorption and p-glycoprotein substrate/inhibitor status), distribution (blood-brain barrier permeability), metabolism (cytochrome p450 inhibition or substrate status), and excretion (clearance) were evaluated using the swissadme server (https://www.swissdock.ch/). the toxicity class was determined through the protox 3.0 server (https://tox.charite.de/protox3/). it classifies compounds into six toxicity classes (1 to 6) based on their predicted lethal dose (ld50) and potential toxic effects. class 1 represents the most toxic compounds, while class 6 represents the least toxic. 3 results and discussion 3.1 molecular docking protocol validation by superimposing the co-crystallized native ligand with the docked ligand, the heavy atom rmsd was calculated to be 1.79 å, indicating that the docking protocol was reliable and predicted the ligand's https://www.dockthor.lncc.br/ ram lal (swagat) shrestha et al./ bibechana 22 (2025) 291-298 294 binding pose (figure 1). the parameters were determined to be effective in capturing the presumed global minima of the protein-ligand adduct. 3.2 binding affinity and strength of interactions the binding affinity of -9.691 kcal/mol found by the docking of the native ligand against the target suggested a strong interaction (table 2). the lower (more negative) the binding energy, the more stable and stronger the binding between molecules [38]. among the proposed compounds, astragalin (complex 1) exhibited the best binding affinity of -9.209 kcal/mol, which is the closest to that of the native ligand. similarly, complex 2 (patuletin) demonstrated a binding affinity of -8.572 kcal/mol indicating slightly weaker interactions as compared to complex 1. figure 1: superimposition of co-crystalized native ligand 6q0 (brown) with docked ligand (green) (heavy atom rmsd= 1.79 å). 3.3 present in the protein-ligand complexes proteins interact with other small molecules to enhance or inhibit biological functions. in proteinligand interactions, a few key residues play a pivotal role in recognizing counterparts and maintaining the affinity that binds the ligand to its receptor [39]. identifying these key residues is essential for understanding protein function, analyzing molecular interactions, and guiding future experimental procedures [40]. the interactions between different ligands and the target are illustrated in figure 2. table 2 shows that the native ligand formed hydrogen bonds with arg817 at a distance of 3.29 å. the distances between the ligand and the amino acids reveal the proximity of their interaction within the protein binding site. the shorter the distance, the stronger the interaction. in this context, the h-bonding interaction involving leu769 in complex 1, with a distance of 1.71 å, can be considered the strongest overall. similarly, the interaction with met807 in complex 2 is the strongest among all residues, with a distance of just 1.92 å. the key amino acid residues (arg817, trp806, leu769) involved in the interactions between astragalin (complex 1) and the target protein are nearly identical to those observed in the interaction between the native ligand and the protein. this suggests that the ligand binds at the catalytic site of the protein and is therefore capable of modulating it. (native) (1) (2) figure 2: 3d interactive representations of the key interactions of the ligand with active site residues in protein-ligand complex (native, 1 (astragalin), and 2 (patuletin)). ram lal (swagat) shrestha et al./ bibechana 22 (2025) 291-298 295 3.4 admet analysis the admet data via the swissadme server and its analysis provided key insights into the absorption properties of the molecules. molecules (triacontane and hentriacontane) were found to be insoluble with low gastrointestinal (gi) absorption. their high lipophilicity (logp of 11.95 and 12.34, respectively) poses formulation and absorption challenges. in contrast, palmitic acid displayed high gi absorption, along with moderate solubility and permeability across the blood-brain barrier (bbb), making it a promising candidate. bersaldegenin3-acetate, while soluble and showing high gi absorption, was not bbb permeant and had moderate lipophilicity (logp of 2.08). most of the molecules adhered to lipinski's rule of five, except astragalin, which had a high topological polar surface area (tpsa) of 190.28 å² and a low logp value of -0.24, making it unable to permeate the gi tract and, therefore, unlikely to enter the bloodstream [41] (table 3). the low gastrointestinal absorption of astragalin could potentially be improved through nanoparticle delivery, glycoside hydrolysis, or other formulation strategies such as lipid-based carriers and prodrug approaches. palmitic acid and cardenolide were the only compounds identified as bbb permeant, indicating their ability to cross the bbb and potentially target central nervous system (cns) disorders. however, the boiled-egg model, based on tpsa and logp values, revealed that 7 out of the 20 molecules did not fall within the specified range for bbb permeation or high gastrointestinal absorption (supplementary figure 1). this limitation suggested that these molecules may not be as effective as orally administered or cns-targeting compounds [42]. of the 20 molecules analyzed, 12 did not inhibit any of the major enzymes (cyp1a2, cyp2c19, cyp2c9, cyp2d6, and cyp3a4) (supplementary table 1). this indicates that these molecules are less likely to disrupt the metabolism of other medications, thereby lowering the risk of drug-drug interactions [43]. this is particularly significant for patients on multiple drugs, as it suggests that these 12 molecules are unlikely to lead to adverse effects associated with the buildup of other drugs metabolized by these cyp enzymes [44]. the excretion properties of the phytocompounds were evaluated based on their clearance rates (ml/min/kg), revealing significant differences among the molecules. astragalin demonstrated a low clearance rate of 3.126 ml/min/kg, suggesting that it remains in the body for a longer period before being eliminated. in contrast, pseudotaraxasterol and campesterol exhibited higher clearance rates of 19.75 ml/min/kg and 16.512 ml/min/kg, respectively (supplementary table 2). this indicates that they are rapidly cleared from the body, reducing the risk of accumulation and potential toxicity. efficient excretion minimizes the chances of toxic buildup or prolonged exposure, making these molecules less likely to cause long-term toxicity compared to those with slower clearance rates. most of the molecules (11) were classified under class 4 toxicity, indicating they are harmful and can lead to significant health effects at higher doses (890 mg/kg). however, they are less likely to be fatal than classes 3, 2, and 1. three molecules (triacontane, hentriacontane, and bersaldegenin-3acetate) were classified as class 3, which are toxic at moderate doses, while two were in class 5, indicating they are less toxic but still harmful at very high doses. three molecules (taraxerol, pseudotaraxasterol, and epigallocatechin) were determined to have class 6 toxicity, suggesting they have low or negligible toxicity and are generally safe at typical exposure levels (7000 mg/kg). one molecule, identified as cardenolides, was categorized in class 2, indicating high toxicity with potentially fatal effects at relatively low doses (34 mg/kg) (supplementary table 3). this suggests that even small ram lal (swagat) shrestha et al./ bibechana 22 (2025) 291-298 296 amounts could pose serious health risks, highlighting the need for caution in handling and potential therapeutic applications. for any practical use, such as in drug development or herbal preparations, rigorous dose optimization, careful monitoring, and safety assessments would be essential to prevent toxic effects. additionally, formulation strategies or structural modifications may be required to mitigate toxicity while preserving any beneficial biological activity. astragalin, although inactive across specific toxicity endpoints such as carcinogenicity, immunotoxicity, mutagenicity, and cytotoxicity, was classified in a safe toxicity class (class 5). it demonstrated favorable outcomes in molecular docking studies, justifying further exploration. note: water solubility is indicated as: insoluble (-), poorly soluble (+), moderately soluble (++), and highly soluble (+++). and rejection in the table indicates the violation of 2 rules of lipinki. the admet properties of several reference drugs (enalapril, metoprolol, ramipril, and digoxin) commonly used in the management of cv diseases are shown in supplementary table 4. with the highest tpsa (203.06 å²), digoxin may struggle to cross cell membranes, leading to its lower gi absorption and poor bbb permeability. all the drugs, except digoxin, showed high gi absorption, suggesting they are effectively absorbed orally. despite digoxin being classified as class 1 in toxicity, it is still used for the intervention of cv diseases. the ligand we studied, astragalin, is classified as class 5 in toxicity and has good solubility and bbb permeability. the phytochemicals astragalin and patuletin from k. pinnata demonstrated significant binding affinity to the mineralocorticoid receptor in molecular docking studies, suggesting their potential as modulators. furthermore, their admet profiles indicate favorable solubility, good gi absorption, and bbb permeability, along with lower toxicity levels, making them promising candidates for cv drug development. 4 conclusion the results of this study underscore the potential of kalanchoe pinnata phytochemicals as modulators of the mineralocorticoid receptor, with significant implications for cv disease management. the molecular docking analysis revealed that the phytochemical astragalin exhibited strong binding affinities close to the native ligand, suggesting its potential effectiveness in modulating mr activity. furthermore, the admet analysis indicated that most of the studied compounds demonstrated favorable pharmacokinetic properties, including good gastrointestinal absorption, toxicity endpoints, and acceptable toxicity levels, with several compounds falling within safe toxicity classes. 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m. campus (tribhuvan university)biratnagar enhanced electronic and magnetic performance of mos2 monolayer via tc & nb impurities defect and water adsorption on impurities defected materials hari krishna neupane1,∗∗, prakash khatri2, arun devkota2 narayan prasad adhikari2,∗ 1amrit campus, institute of science and technology tribhuvan university, kathmandu, nepal 2central department of physics, institute of science and technology, tribhuvan university, kathmandu, nepal ∗corresponding author. email: narayan.adhikari@cdp.tu.edu.np ∗∗email: hari.neupane@ac.tu.edu.np abstract this study examined the effect of tc & nb impurity atoms on mos2 (tc-mos2 & nb-mos2), and adsorption of water molecule on impurities defected mos2 (tc-w-mos2 & nb-w-mos2) material from first-principles calculations. by the estimation of their ground state energy and binding energy, they are stable 2d materials. from band structure and density of states (dos) calculations, tc & nb impurities affect the nature of pristine mos2. it is found that tc-mos2 has n-type & nb-mos2 has p-type semiconducting nature. water interaction on tc-mos2 & nb-mos2 slightly changes the electronic properties and impacts the bandgap, which enhanced the electronic performance of material than that of pristine mos2. the magnetic properties of tc-mos2, nb-mos2, tc-w-mos2, and nb-w-mos2 are analyzed and found to exhibit an uneven distribution of up-spin and down-spin states of electrons in the orbital of atoms near the fermi level. it reflects that they have magnetic properties. the non-magnetic mos2 material changes in to weak magnetic defected-mos2 materials due to the presence of tc, nb and adsorbed water molecule. it means, impurity defects add to magnetic properties of pristine mos2. magnetic properties on defected mos2 occurred due to the dominant contributions of spin states of 4d-orbital of mo, tc, nb atoms, and 3p-orbital of s atoms in the structures. this study highlights the impact of tc & nb impurity atoms and adsorbed water molecule on impurities defected mos2. the studied materials have potential applications in the fields of catalysis, nanoelectronics, biomedicine, and magnetic sensors on the basis of their electronic and magnetic properties. keywords adsorption, defect, fermi, impurity, semiconducting. article information manuscript received: august 10, 2023; accepted: september 1, 2023 doi https://doi.org/10.3126/bibechana.v20i3.57470 this work is licensed under the creative commons cc by-nc license. https://creativecommons. org/licenses/by-nc/4.0/ 224 http://nepjol.info/index.php/bibechana narayan.adhikari@cdp.tu.edu.np hari.neupane@ac.tu.edu.np https://doi.org/10.3126/bibechana.v20i3.57470 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ hari krishna neupane et al./ bibechana 20 (2023) 224-235 225 1 introduction two-dimensional (2d) transition-metal dichalcogenides (tmdcs) are a type of compound that consists of a transition metal from group iv-x (e.g., mo or w) and a chalcogen element (s, se, or te) arranged in the form mx2 [1]. these compounds can have a variety of properties, including metallic (such as vs2 and nbs2), semiconducting (such as mos2and ws2), or insulating (like hfs2) [2, 3]. tmdcs have a structure where one layer of m atoms is sandwiched between two layers of x atoms, and these layers are held together by van der waals (vdws) force. their structure is composed of a honeycomb pattern [4, 5]in which the three atomic planes (chalcogen-metal-chalcogen) stack to create the individual layers of the material [6]. the mos2 monolayer is a semiconducting tmds material that has mo and s atoms stacked together in an s-mo-s configuration, which results in a direct bandgap of 1.80 ev [5–9]. the unique properties of hexagonal tmds materials include their atomic-scale thickness as well as their direct bandgap in its electronic band (wide bandgap exotic semiconductor), which can vary depending on the stacking order [3, 7, 10]. the weak interlayer forces, strong spin-orbit coupling, and robustness of mos2 make it an attractive material for electronic and mechanical applications due to its layered structure [11–13]. due to its high on/off current ratio and higher carrier mobility at room temperature, mos2 has applications in field-effect transistors (fets) and photodetectors [14, 15]. 2d semiconductors, both in the form of monolayer and multilayer, have a wide range of applications. they include usage in transistors, signal amplifiers and integrated logic circuits [16]. they also have potential uses in photocatalysts, solar cells, spintronics, flexible optoelectronics, nanoelectronics, nanophotonic, nanosensing, energy harvesting, photovoltaic solar cells, photocatalytic cells [17–19], dna sequencing, biological and chemical sensors, lubricants, and catalytic surfaces for hydrogen storage in technology and industrial sectors [20,21]. the electronic properties of 2d materials can be affected by external factors such as strain, electric field, pressure, temperature, doping, and defects. this means that the properties of tmdcs can be adjusted by controlling the environment they are in [22–25]. it is interesting to study how 2d materials like tmdcs interact with various solvents, such as water, due to their atomically flat surfaces which allow for different hydrophobic and long-range interactions [26, 27]. the areas around the edges and vacancies in 2d materials are highly sensitive to the adsorption of molecules, which can change the electronic and magnetic properties of the layers by distorting their arrangement [24, 28]. the way that h2o interacts with mos2 can vary depending on where it is adsorbed [29]. the way that 2d materials interact with other materials, biomolecules, solvents and ions is affected by the structure of water at the interface [30–32]. the ability to tune the electronic structure of 2d-tmds is made possible by the strong relationship between defects and chemical dopants in these materials, as well as the stacking of multiple monolayers [33, 34]. mos2 based devices are used in moisture environment too, so mos2-based devices can also be used in moist environments. however, the adsorption of water molecules on the monolayer mos2 can lead to waterinduced oxidation and the formation of molybdenum trioxide (moo3), which causes the loss of lubricity [35, 36]. various studies have revealed that the accumulation of hydrocarbon contaminants in the air can cause mos2 to become more hydrophobic over time, and this can affect the material’s electrical or structural properties [37]. despite the amount of research on the interaction of mos2 with water, the interactions of impurity-defected mos2 with water have not been thoroughly examined. understanding these interactions could lead to the development of more efficient 2d materials-based biological and chemical sensors for medical devices [38]. crystalline structures inevitably contain defects, or deviations in the arrangement of atoms or ions, and are considered a necessary consequence of entropy considerations in solids [39, 40]. imperfections in solid materials, such as the replacement of an atom with a foreign atom or the removal of an atom from the structure, are known as impurity and vacancy defects respectively. these defects play a crucial role in altering and utilizing the undesired properties of the material [41]. these defects can lead to the discovery of new electronic, magnetic, mechanical, and transport properties in materials. this can have potential applications in various fields including catalysis, nanoelectronics, biomedicine, magnetic sensors, and more. it is crucial to study the properties of 2d materials with defects and how they are affected by these imperfections [42,43]. previous studies have investigated the structural, electronic and magnetic characteristics of a pure mos2 monolayer [8, 9], but the effect of impurities such as tc, nb on mos2 and water absorbed on impurities defected mos2 have not been reported. the current study aims to examine the impact of the impurity atoms on mos2 using firstprinciples calculations that combine spin-polarized density functional theory (dft) method. the remainder of the paper is structured as follows: the methodology and computational details used in the study are discussed in section 2, the findings, results and discussion are presented in section 3, and hari krishna neupane et al./ bibechana 20 (2023) 224-235 226 the final conclusions of the work are outlined in section 4. 2 methods and mateials the study carried out structural optimization, electronic and magnetic properties calculations using density functional theory (dft) method [44] implemented in the quantum espresso code [45] using ultra-soft pseudopotentials (uspps). the grimme model of uspp suggests the use of the rappe-rabekaxiraas joannopoulos (rrkj) model to describe weak van der waals (vdws) interactions in the system. this model of uspps includes only the chemically active valence electrons in the calculations, which reduces the complexity of the effects caused by the motion of non-valence electrons of an atom and its nucleus [46]. the valence electronic configuration in h, c, mo, o, s, tc and nb atoms of our system are h: 1s2; o: [he] 2s22p4; s: [ne] 3s2 3p4; mo: [kr]4d5 5s1; tc: [kr] 4d5 5s2 and nb: [kr] 4d5s1 respectively. we used a (3×3) supercell structure of monolayer mos2 to perform our calculations. first, we created the unit cell of mos2 using the xcrysden (structure visualization software) and quantum espresso (qe) computational tools. we have used an experimental lattice parameter of value 3.19 å in the input file. we then converged the kinetic energy cut-off value, k-points, and lattice parameters. we then constructed impurity defects in mos2 by replacing the central mo atom with nb and tc respectively and then water molecule adsorbed on impurity defected mos2 are shown in fig. 1(a-d) respectively. the study also used a plane wave basis set and generalized gradient approximation (gga) with perdew, burke, and ernzer (pbe) to incorporate electronic exchange and correlation (xc) potential in the calculations [47]. the plane wave basis set is used to implement kinetic energy cutoff and charge density cutoff in the calculations. the kinetic energy cutoff used is 35 ry and the charge density cutoff is 10 times the kinetic energy cutoff, which is 350 ry, for all systems using uspps for plane wave expansion. a (8×8×1) k-mesh generated using the monkhorst-pack (m-p) scheme is used to integrate the brillouin zone (bz) during self-consistent calculations and structure optimization in the first irreducible brillouin zone [48, 49]. the calculations are stopped when the total energy and force reached a threshold of 10-4 ry and 103 ry/bohrs respectively to ensure accurate results. the optimization of all structures is done using the broyden-fletcher-goldfarb-shanno (bfgs) [50] algorithm until the change in total energy is less than 10-4 ry and the force is less than 10-3 ry/bohrs between two consecutive scf iterations. the calculations used a small broadening width of 0.001 ry using the marzarri-vanderbilt (m-v) smearing method to ensure the accuracy of the results [51]. the "david" diagonalization method with a mixing factor of 0.6 is chosen for self-consistency. in order to study magnetic properties, spin-polarized density of states (dos) and partial density of states (pdos) calculations are performed. the systems are relaxed by using optimized values of kinetic energy cutoff, charge density cutoff, k-points, and lattice parameters. the self-consistent total energy calculations are done after the relaxation. the band calculations are done by selecting 100 k-points along the high symmetry points in the reciprocal lattice. these k-points are the sampling points in the first brillouin zone of the reciprocal lattice. before calculating the density of states (dos) and partial density of states (pdos), non-self-consistent (nscf) calculations are done using an automatic denser mesh of (16×16×1) k-points, with a verbosity setting of "high" and an occupation setting of "tetrahedra". 3 results and discussion in this section, we discussed in detail about the structural, electronic, and magnetic properties of pristine mos2, tc & nb impurities defected mos2 materials, and water adsorption on impurities defected mos2 materials. the analysis is based on spin-polarized dft method of calculations. 3.1 structural analysis in this section, we have discussed the structural properties of pristine mos2, nb & tc impurities defected mos2, and water adsorbed on impurities defected mos2 materials. firstly, we have prepared unit cell of mos2 and check its stability by calculating its ground state energy and binding energy, it is found to be stable 2d material. after that, we have prepared (3×3) supercell structure of mos2 by extending unit cell along x-and y-axis, which is used for further calculations. so, we examined the stability of (3×3) supercell structure of mos2 by estimating its ground state energy -1741.61 ry and binding energy 6.83 ev, and found that it is stable material. this estimated binding energy value is comparable with reported value of other stable 2d materials [52, 53]. the binding energy of mos2 is found by using equation (1) [24]; (eb)mo−s2 = [emos2 −nemo −n ′es]/n” (1) where, (eb)mo−s2 is the binding energy per mos2 pair, emos2, emo & es are the ground state energy of mos2, single mo & single s atoms respectively, n & n’ respectively represent the number of mo atom & s atom present in supercell structure, n” indicates the total number of atoms present in supercell structure. moreover, we have constructed tc impurity defected mos2 (tc-mos2) material by hari krishna neupane et al./ bibechana 20 (2023) 224-235 227 replacing mo sites atoms from stable (3×3) supercell structure of mos2, and then relax calculations are done. the minimum ground state energy of value -1774.07 ry and maximum binding energy of value 7.32 ev are obtained at the center position of mo atom of tc-mos2, is shown in fig. 1(a). this value is close with reported value of other 2d materials [52, 53]. similar procedure is done for the fabrication of nb impurity defected mos2 supercell structure (nb-mos2). the estimated ground state energy and binding energy of nb-mos2 are found to be -1711.97 ry & 6.42 ev respectively. the estimated binding energy of nb-mos2 agrees with reported value of other 2d martials [52, 53]. hence, nb-mos2 is a stable 2d material, is shown in fig. 1(b). the binding energy of tc-mos2 and nb-mos2 are obtained by using equation (2) [24]; (eb)tc/nb−mo−s2 =[ etc/nb−mos2 −nemo −n ′es −n ′′etc/nb ] /n ′′′ (2) where, (eb)tc/nb−mo−s2 is the binding energy per tc-mos2 pair, etc/nb−mos2, emo, etc/nb & es are the ground state energy of tc/nb-mos2, single mo, single tc or nb & single s atoms respectively, n, n’ & n” respectively represent the number of mo atom, number of s atom, and number of tc or nb atom present in impurities defected mos2 supercell structure, n” ’ denotes total number of atoms present in defected supercell structures. furthermore, water molecule is adsorbed on different positions at 2.45 distance above the surface of tc-mos2 & nb-mos2, it is found that adsorbed water molecule (i.e., physio-adsorption) is at 2.45 distance vertically from the center position of mos2 are more stable materials, which are shown in fig. 1(c-d). this is because they have minimum ground state energies (-1810.08 ry of tc-w-mos2 & -1747.98 ry of nb-w-mos2 respectively), and maximum binding energies (7.89 ev of tc-w-mos2 & 6.98 ev of nb-w-mos2 respectively) than other positions of adsorbed water molecule on defected mos2. these binding energies are fairly agree with reported value of other stable 2d materials [52,53]. we have also estimated the adsorption energy of water molecule with tc-mos2 & nb-mos2 by using equation (3), and found to be 2.17 ev & 2.08 ev respectively. they are comparable with the reported values of water adsorption on 2d materials [9, 25, 27]. hence, water adsorbed defected materials are stable 2d materials. ea = etc/nb−mos2 + eh2o − etc/nb−w−mos2 (3) where, ea is the adsorption energy of water molecule with tc-mos2 or nb-mos2 materials, etc/nb−mos2 & eh2o, are the ground state energy of tc-mos2 or nb-mos2 and adsorbed water molecule respectively. from the estimation of binding energies of tc-mos2, nb-mos2, tc-w-mos2 and nb-w-mos2 materials, we concluded that tc impurity defected mos2 are more compact than nb impurity defected mos2 structure. 3.2 electronic and magnetic properties solid materials are made up of a large number of atoms, each with discrete energy levels for their electrons. when two similar atoms are brought together, their atomic orbitals overlap and split into distinct energy levels for the molecule, forming a continuous range of energy known as an energy band. understanding the band structure and density of states (dos) of a solid material provide insight into its electronic properties. magnetic properties of materials are explored by analyzing of their density of states (dos) and partial density of states (pdos). therefore, electronic and magnetic properties of tc & nb impurities defected mos2 materials (tc-mos2 & nb-mos2), and water adsorbed on tc & nb impurities defected mos2 materials (tc-w-mos2 & nb-w-mos2) are studied by analyzing their band structure, dos and pdos plots. the band structures of tc-mos2, nb-mos2, tc-wmos2 and nb-w-mos2 are shown in fig. 2(a-d) respectively. to understand the electronic properties of tcmos2, nb-mos2, tc-w-mos2 and nb-w-mos2 materials, band structure and dos calculations are performed. for that, we have chosen first brillouin zone of the reciprocal lattice. the x-axis of the band structure plot represents the high symmetric points γ-m-k-γ of the first brillouin zone, with the -center being one of these points, and the y-axis corresponds to energy values. a total of 100 k-points are selected along these high symmetry points, which define a sampling path and irreducible region within the brillouin zone. in an ideal condition where the crystal is not under nonuniform strain or has imperfections. the repetition of the sampling path will cover the entire space of the brillouin zone. the band structure diagrams also have a horizontal dotted line, which represents the fermi energy level. as seen in the band structure of tc-mos2, band states of conduction band are moving closer to the fermi energy level than that of valence band due to the rearrangement of spin states of electrons in the 3s, 3p orbitals of s atoms with 4d, 5s orbitals of tc atom in structure. hence, number of charge carriers in conduction band are greater than that in the valence band. it reveals that tc-mos2 is a n-type semiconducting material having direct bandgap energy 1.01 ev at hari krishna neupane et al./ bibechana 20 (2023) 224-235 228 (a) (b) (c) (d) figure 1: (colour online) supercell structure of (a) tc impurity defect on mos2 (tc-mos2 ), (b) nb impurity defect on mos2 (nb-mos2 ), (c) water adsorbed on tc impurity defected mos2 (tc-w-mos2 ), and (d) water adsorbed on nb impurity defected mos2 (nb-w-mos2 ). (a) (b) (c) (d) figure 2: (colour online) band structure plots of; (a) tc-mos2, (b) nb-mos2, (c) tc-w-mos2 and (d) nb-w-mos2. in figures, the horizontal dotted line represents the fermi level, and the vertical dotted line intersects at high symmetry points. hari krishna neupane et al./ bibechana 20 (2023) 224-235 229 γ-point. this result is deviating from the properties of pristine mos2 [5–7], due to the presence of tc impurity defects. we have estimated the bandgap energy of nb-mos2 material by the analysis of it band structure calculations and found direct bandgap energy 1.10 ev in between the conduction band minima and valence band maxima at high symmetry γ-point. band states of valence band lies closer to the fermi energy level than the band states of conduction band. this is because unpaired arrangement of spin states in the 3s, 3p orbitals of s atoms with 4d, 5s orbitals of nb atom in structure. we concluded that nb-mos2 is a p-type semiconductor material. this property is different than of pure mos2 [6,7], which is attributed due to the presence of nb impurity defects in nb-mos2. we have also analyzed the density of states (dos) plots of tc-mos2 & nb-mos2 materials are shown in fig. 3(a-b) respectively. it is found that distributed upspin and down-spin states open bandgap energy due to the presence of unpaired spin states in the orbital of tc & nb atoms with s atoms respectively in structures. it also confirmed that tc-mos2 is a n-type and nb-mos2 is a p-type semiconductor material. from the analysis of above calculations, we concluded that impurity defects enhanced the electronic conductivity in materials. semiconducting materials have wide applications due to their reliability, compactness and low cost; they are having probable future. thus, p-type and n-type semiconductors find a wide variety of applications in the fields of memory, sensing, electronic, spintronic, optoelectronic devices [38,42,43]. electronic properties of material are affected due to presence of moisture [25, 32]. so, we have investigated the electronic properties of water adsorbed on impurities defected mos2 through band structure and dos plots. the band structures of tc-w-mos2 & nb-w-mos2 are shown in fig. 2(cd) respectively. in the band structure of tc-wmos2, a direct bandgap of 1.13 ev is observed at -point. its fermi energy level being closer to the conduction band, which indicates that tc-w-mos2 exhibits n-type semiconductor. the bandgap energy of tc-w-mos2 has slightly greater value than that of tc-mos2 material because adsorbed water molecule reduces binding energy (losses lubricity). it is observed that band states are slightly repelled towards conduction band from fermi energy level in band structure is shown in fig. 2(c). this is also confirmed by the analysis of its dos plot is shown in fig. 3(c). in dos plot, bandgap energy is computed in between upper level of valence band and lower level of conduction band of distributed upand down-spin states of electrons in the orbital of atoms present in the material. furthermore, we have computed the bandgap energy of nb-w-mos2 material on the basis of band structure and dos plots, are shown in fig. 2(d) & 3(d) respectively. the band structure of nb-w-mos2 reveals a direct band gap of 1.23 ev at γ-point, which coupled with the fermi energy being positioned near the valence band, indicates that nb-w-mos2 has p-type of semiconducting properties. this obtained result is slightly deviated from the semiconducting behavior of pure mos2, which is due to the presence of adsorbed water molecule and nb impurity defect on mos2. to confirm the predicted nature of nb-w-mos2, we have analyzed the dos of it and found that distributed upand down-spin states are appeared near the valence band is shown in fig. 3(d). this confirmed that it has p-type semiconducting properties. water molecule can interact with impurities, altering their electronic and chemical states and subsequently modifying the band structure, and hence inflate the electronic properties than that of pristine mos2. additionally, water adsorbing on the surface of mos2 can form a thin layer of water molecules and influence the electronic properties of the material. this can result in the creation of new energy levels leading to new electronic states and modifications to the bandgap energy. effect of impurities (tc & nb) defect on pristine mos2 and adsorbed water molecule on impurities defected mos2 initiate to switch in band structures and dos plots. as a result, fermi energy, fermi shift, total ground state energy, bandgap energy, and binding energy of defected materials have changed than that of pristine form, they are presented in table-1. the reason of shifting band states in band and dos from pristine to defected systems are; h atom has one unpaired up-spin electron in 1s orbital, o atom has paired spins in 2s orbital and paired electrons in 2px sub-orbital, and unpaired electrons in 2py and 2pz sub-orbitals. the mo atom has one unpaired up-spin electron in 5s orbital and one in 4d orbital with sub-orbitals 4dxy, 4dxz, 4dyz, 4dx2−y2 , 4dz2 . tc atom has paired spins in 5s orbital and one unpaired up-spin electron in 4dxy, 4dxz, 4dyz, 4dx2−y2 & 4dz2 sub-orbitals. nb atom has one unpaired up-spin electron in 5s orbital, one unpaired electron in 4dxy, 4dxz, 4dyz & 4dx2−y2 and one vacant in 4dz2 sub-orbital. the s atom has paired spins in 3px sub-orbital and one unpaired up-spin electron in 3py & 3pz sub-orbitals. these different electronic configurations affect the electronic and magnetic properties of materials. the magnetic properties of materials can be evaluated by analyzing their density of states (dos) and partial density of states (pdos). these plots provide insight into the distributions of electrons with upand down-spins within the material. when the distributions are symmetrical, meaning that the number of upand down-spins of electrons are equal, magnetic moments of the electrons canceled hari krishna neupane et al./ bibechana 20 (2023) 224-235 230 out, resulting in non-magnetic properties. however, when the distributions are asymmetrical, there are more upor down-spins of electrons, it leads to a net magnetic moment, resulting in magnetic properties. this occurs when electrons of the atoms are not paired, meaning the presence of unpaired upand down-spins of electrons in the atomic orbitals create certain magnetic moment, leading to magnetic properties of the material. in other words, the dos and pdos calculations of spin-polarized systems reveal the distributions of electrons with opposite spins in the material. if the number of electrons with opposite spins are equal, the material is non-magnetic. but, if the distributions are asymmetrical, the material has magnetic properties. the reason is that electrons with opposite spins can pair up, which cancels out their magnetic moments. but, if there are more electrons with one spin direction, the material will have a net magnetic moment, making it magnetic. the pdos plot of tcmos2, nb-mos2, tc-w-mos2 and nb-w-mos2 are presented in fig. 4(a-d) respectively. dos plots (fig. 3(a-d)), and pdos plots (fig. 4(a-d)) come up with the information’s of distributed spin states in electronic orbitals of atoms present in the materials. the dos plots of considered materials give insight into how the impurities and adsorbed water molecule affect the electronic and magnetic properties of mos2. hence, dos used to understand how the defects and adsorbed water molecule influenced the electronic and magnetic properties of materials. the detail investigation of magnetic properties of tc-mos2, nbmos2, tc-w-mos2 and nb-w-mos2 materials, we have analyzed pdos plots. in pdos analysis, we especially focused the impact of distributed electronic spin states in the orbitals of atoms present in the materials. it shows how the electrons are spread among different orbitals and how impurities and water exposure affect these distributions, providing a deeper understanding of how these factors affect the magnetic properties of materials. in dos & pdos plots of tc-mos2, nb-mos2, tc-wmos2 and nb-w-mos2, we found that the distributions of up-spin and down-spin electronic states near the fermi level are asymmetrical. we determined the net magnetic moment arising from upspin and down-spin of electrons in each orbital of the constituent atoms. magnetic moment in the 4p, 4d & 5s orbitals of mo atom have 0.03 µb /cell, 0.11 µb /cell & 0.00 µb /cell; 3s & 3p orbitals of s atoms have 0.00 µb /cell & 0.05 µb /cell; and 4p, 4d & 5s orbitals of tc atom has -0.01 µ b /cell, -0.03 µb /cell & 0.00µb /cell values in tc-mos2 material. total magnetic moment of tc-mos2 is found to be 0.15 µb /cell, and the magnetic moment based on integrated density of states (idos) is also estimated to be 0.15 µb /cell. the magnetic moment generated in tc-mos2 is mainly due to the 4d orbital of mo, 3p orbital of s, and 4d orbital of tc atoms. thus, tc-mos2 is considered a magnetic material. the magnetic properties of nb-mos2 are investigated by the analysis of its pdos plot. it is determined that the 4p, 4d & 5s orbitals of mo atoms contributed 0.01 µb /cell, 0.09 µb /cell, & 0.00 µb /cell magnetic moments respectively. additionally, the magnetic moment carried out by 3s & 3p orbitals of s atoms have 0.00 µb /cell & 0.01 µb /cell; 4p, 4d & 5s orbitals of nb atoms have -0.02 µb /cell, -0.08 µb /cell & 0.00 µb /cell respectively. total magnetic moment of nb-mos2 is found to be 0.01 µb /cell. the same value of magnetic moment of nb-mos2 is determined by integrated density of states (idos) calculation. the dominant contribution of magnetic moment by 4d orbital of mo, 3p orbital of s, and 4d orbital of nb atoms in nb-mos2. hence, nb-mos2 is a weak magnetic material. table 1: bandgap energy (eg), fermi energy (ef), fermi energy shift (es), total ground state energy (et), and binding energy (eb) of mos2, tc-mos2, nb-mos2, tc-w-mos2, and nb-w-mos2 materials. materials ef (ev) eg (ev) es (ev) et (ry) eb (ev) mos2 -1.89 1.80 -1741.61 6.83 tc-mos2 -0.83 1.01 1.06 -1774.07 7.32 nb-mos2 -2.26 1.10 -0.37 -1711.97 6.42 tc-w-mos2 -1.01 1.13 0.88 -1810.08 7.89 nb-w-mos2 -2.42 1.23 -0.53 -1747.98 6.98 hari krishna neupane et al./ bibechana 20 (2023) 224-235 231 (a) (b) (c) (d) figure 3: (colour online) dos plots of (a) tc-mos2, (b) nb-mos2, (c) tc-w-mos2 and (d) nb-w-mos2. in figures, horizontal dotted line separates the spin states, vertical dotted line indicates the fermi level, and inset represents the dos plots large range of energy level. (a) (b) (c) (d) figure 4: (colour online) (a) pdos plot of individual up-spin and down-spin states of electrons in the orbitals of mo, s & tc atoms of tc-mos2 material, (b) pdos plot of individual up-spin and down-spin states of electrons in the orbitals of mo, s nb atoms of nb-mos2 material, (c) pdos plot of individual up-spin and down-spin states of electrons in the orbitals of mo, s, tc, h o atoms of tc-w-mos2 material, and (d) pdos plot of individual up-spin and down-spin states of electrons in the orbitals of mo, s, nb, h & o atoms of nb-w-mos2. in figures, horizontal dotted line separates the spin states, vertical dotted line indicates the fermi level, and inset represents the pdos plots of large-scale energy range. hari krishna neupane et al./ bibechana 20 (2023) 224-235 232 table 2: total magnetic moment (µ) of tc-mos2, nb-mos2, tc-w-mos2, and nb-w-mos2 materials obtained by asymmetrically distributed up-spin and down-spin of electrons in various orbitals of different atoms. orbitals / materials tc-mos2 nb-mos2 tc-w-mos2 nb-w-mos2 µ of 4p-mo 0.03 0.01 0.03 0.00 µ of 4d-mo 0.11 0.09 0.12 0.08 µ of 5s-mo 0.00 0.00 0.00 0.00 µ of 3s-s 0.00 0.00 0.00 0.00 µ of 3p-s 0.05 0.01 0.03 0.01 µ of 4p-tc -0.01 0.01 µ of 4d-tc -0.03 -0.04 µ of 5s-tc 0.00 0.00 µ of 4p-nb -0.02 0.00 µ of 4d-nb -0.08 -0.07 µ of 5s-nb 0.00 0.00 µ of 2s-o 0.00 0.00 µ of 2p-o 0.00 0.00 µ of 1s-h 0.00 0.00 total (µ) µb/cell 0.15 0.01 0.15 0.02 furthermore, we have estimated the magnetic properties of tc-w-mos2 and nb-w-mos2 materials by interpretating their pdos plots. the magnetic properties of tc-w-mos2 are predicted by the estimation of distributed electronic spin states in the individual orbital of each atom present in the structure. the 4p, 4d 5s orbitals of mo atoms have magnetic moments 0.03 µb /cell, 0.12 µb /cell 0.00 µb /cell respectively in structure. also, 3s 3p orbitals of s atoms have magnetic moments 0.00 µb /cell 0.03 µb /cell; and 4p, 4d 5s orbitals of tc atom has magnetic moments 0.01 µb /cell, -0.04 µb /cell 0.00 µb /cell respectively. similarly, we have estimated the magnetic moment generated by 2s 2p orbitals of o atom have values 0.00 µb /cell 0.00 µb /cell; and 1s orbital of h has value 0.00 µb /cell. the total magnetic moment of tc-w-mos2 is obtained 0.15 µb /cell. we also have estimated the magnetic moment 0.15µ b /cell based on integrated density of states (idos). the magnetic moment in tc-w-mos2 is mainly created by the dominant effect of 4d orbital of mo, 3p orbital of s, and 4d orbital of tc atoms. therefore, tc-w-mos2 is considered to be a magnetic material. in nb-w-mos2 , the magnetic moment is observed in 4p, 4d, 5s orbitals of mo atoms have 0.00 µb /cell, 0.08 µb /cell 0.00 µb /cell respectively. the magnetic moments given by 3s 3p orbitals of s atoms have values 0.00 µb /cell 0.00 µb /cell respectively. the 4p, 4d 5s orbitals of nb atom has magnetic moments of 0.00 µb /cell, -0.07 µb /cell 0.00 µb /cell; and 2s & 2p orbitals of o has magnetic moments of 0.00 µb /cell 0.00 µb /cell, while the 1s orbital of h atom has a magnetic moment of value 0.00 µb /cell. the total magnetic moment of nb-w-mos2 is found to be 0.02 µb /cell. magnetic moment of nb-w-mos2 also estimated through integrated density of states (idos), and found to be 0.02 µb /cell. the main source of magnetic moment in nb-w-mos2 is 4d orbitals of mo, 4d orbitals of nb, and 3p orbital of s atoms in the structure. thus, nb-w-mos2 is weak a magnetic material. from the above calculations of magnetic moment in the materials, we found that impurity atoms on mos2 , and adsorbed water molecule on impurities defected mos2 intensified the magnetic properties in the materials. the detail calculations of magnetic moment of tc-mos2 , nb-mos2 , tc-w-mos2 and nb-w-mos2 materials by the analysis of individual electronic orbital of atoms are given in table-2. 4 conclusions structural, electronic, and magnetic properties of tc-mos2, nb-mos2, tc-w-mos2 and nb-w-mos2 materials have been explored by spin-polarized density functional theory (dft) method with van der waals (vdws) corrections (dft-d2) approach through computational tool quantum espresso. it is found that tc-mos2, nb-mos2, tc-w-mos2 and nb-w-mos2 are stable materials. the nature of materials has been studied through their band structure and density of states (dos) calculations, and the result showed that all materials have narrow bandgap semiconducting properties. the bandgap energy of tc-mos2, nb-mos2, tc-w-mos2 and nb-w-mos2 have values 1.01 ev, 1.10 ev, 1.15 ev and 1.23 ev respectively. the electronic band states of conduction band are appeared close to the fermi energy level of tc-mos2 tc-w-mos2, and hence they are n-type semiconductor materials. on the other hand, band states of valence band are aphari krishna neupane et al./ bibechana 20 (2023) 224-235 233 peared near the fermi energy level than the band states of conduction band in band structure and dos plots of nb-mos2 nb-w-mos2 materials. it reflects that they have p-type semiconducting properties. the presence of impurities in mos2 and adsorbed water molecule on impurities defected mos2 affects the semiconducting behavior of pure mos2 by shifting the band states with respect to fermi energy level. band structure calculations and dos analysis revealed that the impact of water molecules on the surface of mos2 can alter its electronic properties, leading to the creation of new energy levels and modifications to the bandgap, resulting in new electronic states. magnetic properties of considered materials are studied on the basis of their density of states (dos) and partial density of states (pdos) calculations, and found that all materials have magnetic properties. magnetic moment of materials is developed due to presence of unpair electronic spin states in the individual orbitals of atoms present in the material. the estimated magnetic moment of tc-mos2, nb-mos2, tc-w-mos2 and nb-w-mos2 have values 0.15 µb /cell, 0.01 µb /cell, 0.15 µb /cell 0.02 µb /cell respectively. the significant values of magnetic moment are given in materials due to the presence of unpaired spin state in the 4d orbitals of mo atoms, 3p orbital of s atoms, and 4d orbitals of tc nb atoms. hence, electronic and magnetic properties are enhanced in the materials due to the presence of impurity atoms on mos2 and adsorbed water molecule on impurities defected mos2. references [1] m. chhowalla, h. s. shin, g. eda, l. j. li, k. p. loh, and h. zhang. the chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. nature chemistry, 5(4):263–275, 2013. 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