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Journal Cover Journal of the National Science Foundation of Sri Lanka
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  This is an Open Access Journal Open Access journal
   ISSN (Print) 1391-4588
   Published by Sri Lanka Journals Online Homepage  [48 journals]
  • Effect of cation size of iodide salt in the electrolyte on the performance
           of dye sensitised solar cells

    • Abstract: Gel polymer electrolytes (GPEs) have an upsurge interest among scientists due to their fascinating advantages such as leak proof nature, long term stability and good performance. They have been extensively tested for various devices including rechargeable cells, dye sensitised solar (DSS) cells, electrochromic devices and super capacitors. When GPEs are employed for DSS cells, the salt in the electrolyte has been known to play a major role in governing the cell performance. All DSS cells that use iodide/triiodide redox couple comprise a GPE complexed with an iodide salt. Therefore it has been accepted in principle, that GPE should assist iodide ion conductivity.In this study, GPEs based on several iodide salts were prepared and their performance in DSS cells were evaluated. As such, three different iodide salts, namely, potassium iodide (KI), zinc iodide (ZnI2) and tetrapropylammonium iodide (Pr4NI) were chosen for the study. The selection was mainly based on salts with cations having dissimilar sizes and valencies. Among them, KI based gel polymer electrolyte had the highest conductivity. However, the dye sensitised solar cell based on Pr4NI exhibited the highest performance. Gel polymer electrolyte based on ZnI2 had the lowest conductivity and also the lowest performance in DSS cells. Published on 2016-03-31 09:46:40
       
  • Performance of ion exchange resin as solid catalyst for the esterification
           of acetic acid with ethanol

    • Abstract: Esterification of acetic acid with ethyl alcohol was carried out in the presence of a cation exchange resin. The resin used was Lewatit S1467, which is commercially available at a low cost and used commonly in the water treatment industry. The catalyst pretreated with HCl showed higher acetic acid conversions. The acidic cation exchange resin treated with HCl was examined for catalyst loading, reaction temperature and reusability. The highest acetic acid conversion of 58 % was observed for acetic acid to ethanol mole ratio of 1:1 at 335 K with a 5.4 % (w/w) catalyst loading. The experimental data were fitted with the pseudo homogeneous model, and the heterogeneous models Langmuir-Hinshelwood (LH) and Eley- Rideal (ER). LH model provided a better agreement with the experimental kinetic data, and the activation energy was found to be about 58 kJmol-1. Published on 2016-03-31 09:50:52
       
  • PAGE - a simple method to detect the protective effects of medicinal
           plants against sugar induced protein damage

    • Abstract: J.Natn.Sci.Foundation Sri Lanka 2016 44 (1): 105-107 Published on 2016-03-31 10:02:37
       
  • A low-cost partially automated polarimeter for investigating skylight
           polarisation

    • Abstract: Skylight polarisation pattern in general and the positions of the polarisation neutral points in particular are important parameters in atmospheric science. The construction and operation of a low cost partially automated polarimeter for studying the polarisation pattern of skylight in the principal plane of the sun, and some results obtained for the skylight polarisation pattern using the polarimeter are presented in this paper. The polarimeter mainly consists of a collimating tube with a linear polariser and a detector consisting of a light dependent resistor controlled by a microprocessor. The degree of polarisation for a given angular distance from the sun in the principal plane of the sun was measured using the maximum and minimum currents passing through the light dependant resistor (LDR) computed through voltage measurements across the LDR. Positions of the polarisation neutral points and the maximum degree of polarisation were determined graphically using plots of the degree of polarisation as functions of the angular solar distance. The error in the neutral point positions was estimated to be 2°, while that of the degree of polarisation was estimated to be a maximum of 18 %. The measurements taken at different times on relatively clear sky days during a period of over one year provided consistent results in fairly good agreement with similar studies carried out using more sophisticated instruments as well as theoretical predictions for a molecular atmosphere. An attempt has also been made to account for any deviations of the quantitative results from those of other studies. Published on 2016-03-31 09:56:48
       
  • Modulating effects of cowpea incorporated diets on serum lipids and serum
           antioxidant activity in Wistar rats

    • Abstract: The effect of incorporation of four Sri Lankan cowpea cultivars in experimental diets on serum lipids and serum antioxidant activity (AOA) in Wistar rats was investigated. Seven-week-old male Wistar rats (five groups, five per group) were fed with 20 % fat as a control diet (CD) in comparison with 20 % fat enriched diets containing 20 % whole cowpea powder from cowpea cultivars [Bombay (BO), Waruni (WA), Dawala (DA) and MI 35 (MI)] for six weeks. A lower serum total cholesterol concentration (TC) (p < 0.05) and a higher (p < 0.05) serum AOA in WA, BO, and MI diet fed rats were observed compared to the CD fed group. Higher serum AOA in WA and BO fed rats was accompanied by the higher AOA and total phenolic content (TPC). A lower (p < 0.05) serum low density lipoprotein concentration (LDL-C) was observed in all cowpea diets fed rats, and lower (p < 0.05) serum triacylglycerol (TG) and higher (p < 0.05) high density lipoprotein (HDL-C) levels were observed in WA and MI fed groups, respectively compared to CD fed groups. Cowpea incorporated experimental diets modulate serum lipids and serum AOA in Wistar rats. Published on 2016-03-31 09:42:16
       
  • Evaluation of shear strength parameters of rail track ballast in Sri Lanka

    • Abstract: In Sri Lanka the ballasted rail tracks are the most preferred by the railway authority due to low initial investment and it continues using crushed rock as rail track ballast. Regardless of the frequent usage of these aggregates as track ballast in Sri Lanka, their shear strength characteristics have not been scientifically measured or used in design. The primary purpose of this paper is to present the investigation of shear strength properties of fresh and fouled rail track ballast in Sri Lanka using a large-scale direct shear device, which accommodates actual size ballast particles. The shear stress–strain and dilation behaviour of fresh and fouled ballast were obtained and the internal friction angle was estimated. The results showed that the shear strength of fresh ballast is higher than that of the fouled ballast and the shear strength envelope better resembled non-linear behaviour. Also it was revealed that the internal friction angle of ballast tends to reduce with age. More realistic shear strength parameters as proposed by the test results would promote state-of-the-art practice for the design of ballasted rail track foundations. Published on 2016-03-31 09:33:16
       
  • Antimicrobial constituents of Hypocrea virens, an endophyte of the
           mangrove-associate plant Premna serratifolia L.

    • Abstract: Emergence of multidrug-resistant pathogenic microorganisms has prompted a worldwide search for new antibiotics from various sources. Endophytic fungi from unique habitats are considered as potential sources of novel bioactive compounds. Sri Lankan mangrove ecosystem is such a distinctive and unexploited resource for the discovery of structurally diverse and biologically active metabolites including antimicrobials. Nine endophytic fungi were isolated from the leaves and twigs of Premna serratifolia L. from a mangrove habitat in the Negombo lagoon and the antimicrobial activities of their laboratory cultures were evaluated. The most promising antimicrobial activity was exhibited by the endophytic fungus Hypocrea virens. Bioassay guided fractionation of the organic extract of this fungus led to the isolation of two known metabolites; the antimicrobial epidithiodioxopiperazine, gliotoxin (1), and the closely related but less active bisdethiobis(methylthio)gliotxin (2). The chemical structures of the two compounds were determined by spectroscopy and confirmed by comparison of mass and nuclear magnetic resonance (NMR) spectral data with the reported values for these molecules. The minimum inhibitory concentration (MIC) values obtained for gliotoxin (1) in the current study are 0.13 μg mL-1 for Bacillus subtilis, 16 μg mL-1 for Staphylococcus aureus, 32 μg mL-1 for Methicillin Resistant Staphylococcus aureus (MRSA) and Escherichia coli, 64 μg mL-1 for Pseudomonas aeruginosa and Candida albicans fungus. This is the first study to report the isolation of endophytic fungi from P. serratifolia and their antimicrobial activities. Published on 2016-03-31 09:28:32
       
  • On the powers of tests for homogeneity of regression coefficient vectors
           under synchronised order restrictions

    • Abstract: We consider a multivariate multiple linear regression model and study the problem of testing homogeneity of regression coefficient vectors under synchronised order restrictions when the covariance matrices are common but unknown. Synchronised order restrictions are the generalisation of the multivariate isotonic order restrictions. Synchronised order restricted test could be applied to a situation where the values of some parameters increase, those of some other parameters decrease, and those of the rest of the parameters have no restriction, simultaneously. For this problem, some test statistics were proposed and some inequalities among their powers were obtained in the past. This showed that the proposed test statistics may equally be good in terms of their powers. In the present paper, we mathematically prove that the strict inequalities hold among the powers of the test statistics. Thus we attain an exact comparison among the powers of the test statistics indicating more accurate and stronger results than those obtained in the past. Published on 2016-03-31 09:27:30
       
  • Volatile constituents of tea stems (Camellia sinensis L.O. Kuntze) as
           semiochemicals to attract low country live wood termite (Glyptotermes
           dilatatus Bugnion & Popoff), in Sri Lanka

    • Abstract: Low country live wood termite (LCLWT), Glyptotermes dilatatus Bugnion & Popoff is one of the major insect pests of low grown tea in Sri Lanka. The present study was aimed at investigating the chemical constituents and the attractant effects of tea stem volatiles isolated from different tea cultivars on the behaviour of alates of G. dilatatus. Volatile extracts of decayed and healthy stems of susceptible cultivars (TRI 2023, TRI 4042) and resistant cultivars (TRI 2027, TRI 4049) were collected. The attractant effects of stem extracts on termite alates were evaluated using the olfactometer bioassay. Volatile extracts of decayed stems obtained from the four tea cultivars were more attractive to alates than that of the healthy stems. The responses of alates to volatile extracts from decayed stems of TRI 2023, TRI 2027, TRI 4042 and TRI 4049 were 37 ± 0.04, 34 ± 0.04, 36 ± 0.035 and 32 ± 0.04, respectively whereas the responses of alates to volatile extracts from healthy stems TRI 2023, TRI 2027, TRI 4042 and TRI 4049 were 16 ± 0.03, 13 ± 0.03, 14 ± 0.38 and 16 ± 1.5, respectively.The analysis of volatile extracts from decayed stems using Gas Chromatography-Mass Spectrometry led to the detection of 96 compounds in the four tea cultivars. Among them 15 compounds were common in all four tea cultivars and n-hexadecanoic acid and 9,12-octa decadienoic (Z,Z) acid were identified as the major constituents of decayed tea stems. Compound mono(2-ethylhexyl) phthalate was identified as the major constituent in healthy stem volatiles. Mono(2- ethylhexyl) phthalate and n-hexadecanoic acid were present in both types of tea cultivars and they can be developed as an alternative method to control the test insect. Published on 2016-03-31 09:16:44
       
  • The magnetisation of two ferromagnetic spheres placed randomly in a
           magnetic field

    • Abstract: The main objective of this research is to study the uniform magnetic field both inside and outside of two randomly placed ideal ferromagnetic spheres. The expressions are given for the scalar magnetic potentials both inside and outside the spheres. In addition, the expressions for the magnetic field intensity outside and the magnetic flux density inside are also derived. The magnetic potential outside the spheres is obtained by the superposition of the potentials due to the two spheres and the potential corresponding to the external magnetic field, while the scalar magnetic potential inside each sphere is solved by imposing the exact boundary conditions known from the solution of the outside field. Finally, the numerical results with the given accuracy are generated from the expressions derived. Published on 2016-03-31 09:11:22
       
 
 
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