PhD

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Agrobacterium Mediated Transfer Of Bacillus Thuringiensis 6E Cry Gene To Ixora Odorata
(University of Peradeniya, 2003) Bamunuarachchige, T. C.
Ixora species are quite popular among landscape architects and gardeners as hedge plants and potted ornamentals. However, infestations by pests such as Ixora leaf webber, flower webber, green horned caterpillar and looper caterpillar have become a threat to the commercial exporter, especially with strict quarantine regulations under which presence of a single pest egg may spell disaster. Most chemical methods adopted have hazardous effects on the environment and other beneficial insects and therefore, are unpopular among the buyers. As an alternative Ixora odorata var. vulcan was transformed with the cry gene of Bacillus thuringiensis strain 6e by Agrobacterium mediated gene transfer. In the process, an effective plant regeneration procedure and a gene transfer system were developed. The cry gene of Bacillus thuringiensis strain 6e was isolated, purified and cloned into the Xbal site of the T-DNA region of the Agrobacterium vector pLG121Hm via an adapter. Recombinant pLG121Hm was transferred to Agrobacterium strain LBA4404 by electroporation. Positive cry clones were confirmed by Dot blot analysis of the plasmid DNA (extracted from the electroporated strains) with Dig labeled cry probe. In vitro grown Ixora odorata shoot tips (2cm) were co-cultivated with LBA4404, harboring the Bt 6e cry cloned binary vector pLG121Hm. Co-cultivated explants were transferred to shoot multiplication medium ('/2 MS with 2mg/l BAP and 500mg/l cefotaxime) and incubated at 25001ux with a 16h photoperiod. After 4 weeks the axillary shoots were screened on selective medium (Vz MS supplemented with 200mg/l hygromycin). Hygromycin positive plants were used for the PCR analysis and Southern blot analysis. PCR analysis of the putative transformants, carried out with gits specific primers, produced the expected 1.680kb fragment in all the hygromycin positive transformants. Southern blot analysis of these with the Dig labeled Bt 6e cry probe produced positive results. The positive results of both, the PCR analysis and the Southern blot confirmed genomic integration of the Bt 6e cry gene. The transformation efficiency was 20% for the shoot tips whereas it was 40% and 30% for callus and leaf disk transformations respectively but the inability of proper regeneration made both these techniques redundant.
Teaching environment related activities at key stage one to help children in developing science process skills to attain scientific literacy in future
(University of Peradeniya, 2006) Vitharana, P. R. K. A.
Today we live in a world filled with scientific innovations due to the advancement of science and technology. Therefore society is complex and rapidly changing than ever before. In order to face the dynamic nature of the 21ˢᵗ century, an individual should possess multiple skills. The developed countries like USA are aiming to produce scientifically literate citizens to succeed challenging situations in the world. Although we are a developing nation we have to face the global society. However, this cannot be achieved within one or two years and it should start from primary level. According to the primary education reforms introduced in 1997, the primary - cycle of education has been divided into three key stages as key stage one — grades 1 and 2, key stage two ~ grades 3 and 4 and key stage three — grade five. Primary curriculum consists of four main subjects and science is integrated in Environment Related Activities (ERA.) The aim of this study was to help children in key stage one to develop science process skills through the subject ERA, that are required to be a Scientifically literate adult in future. In order to achieve the aim of the study it was conducted in three phases. In the first phase data were collected relating to ERA using classroom observation, interviews and diagnostic questionnaire. In the classroom observation twelve teachers from three schools were observed while teaching ERA and detailed fieldnotes were prepared for each lesson. With the help of the fieldnotes detailed transcripts were made with the objective of understanding the real situation in the classrooms. During the second phase, activities were planned in different themes of ERA to develop process skills of children. In the third phase those activities were piloted in three selected classrooms. Classroom observation was conducted and fieldnotes were prepared. The necessary improvements were made with the data obtained from observation and the feedback obtained from teachers. Data obtained from different sources were analysed and identified the weaknesses in teaching ERA, the types of activities suitable for developing process skills and how children developed process skills through suggested activities. It was evident from the study that many teachers had difficulties in teaching sciencerelated components of ERA due to the lack of subject matter knowledge and it led children to develop misconceptions. The students’ active participation, which is expected in the student-centred teaching, was not observed in most of the classrooms. Almost all the teachers had weaknesses in the area of professional skills. Among the most prominent of those were the introducing lessons, questioning, planning lessons, organizing groupwork and use of teaching aids. 85% of teachers were not competent in developing process skills of children especially due to the weaknesses in professional skills. Children enjoyed and actively participated in introduced activities. Children developed process skills when they engaged in simple activities with the proper guidance of the teacher. Teachers’ responses towards suggested activities indicated that children were very interested in learning through such activities and teachers motivated children to be inquisitive and investigative. Children in key stage one developed misconceptions due to the limited science background of teachers. Although there were number of Opportunities in the ERA syllabus to develop science process skills of students, they were rarely given proper guidance for that which is required to be a scientifically literate adult in future. The subject matter knowledge as well as the professional skills of primary teachers should be strengthened through workshops, allowing them to actively involve in activities where they could understand their own misconceptions and weaknesses.
Taxonomy and natural history of bees in selected areas of Sri Lanka
(University of Peradeniya, 2004) Karunaratne, Inoka
Prior to this study, taxonomic work on bees of Sri Lanka had been conducted entirely by overseas scientists commencing in 1897 and leading to the Smithsonian Surveys (1975-1986). These studies have documented 137 bee species in 27 genera. Information on their natural history is completely lacking and only a few specimens have been deposited in Sri Lanka. In the present study (a) bees collected from several districts, agroecological regions and habitats were identified (b) their floral relationships and nesting habits were recorded, (c) the subfamily Nomiinae was reviewed, (d) and bees diversity was determine in selected sites. A total of 137 bee species in 35 genera and 3 families were recorded. These included 20 previously unrecorded species and 5 genera and a species new to Science. Based on the location of the 29 collection sites, the Low Country Dry Zone, middle peneplain, and the agricultural habitats harboured the highest number of species. Floral hosts consisted of 167 species in 115 genera and 44 families. Weeds were the most preferred hosts (129 spp.) followed by crops and trees. Flowers of 6 naturalized plant species attracted an unusual number (> 20 species) of bees. According to pollen relationships, 131 bee species are generalists and 7 species are pollen specialists. Twelve species of bees are buzz pollinators of crops whose pollen is concealed in anthers. Pollen from 69 floral hosts in 27 plant families when microscopically examined and grouped into 12 pollen classes. Several stem nesting (16 spp.), ground nesting (13 spp.) and hive building (4 spp.) bees were recorded, Certain species were recorded only from their nests. Review of the subfamily Nomiinae resulted’ in 22 species in 11 genera. Sampling in different locations/habitats of the Knuckles Forest Reserve gave the highest Shannon Diversity Index for agricultural habitat in the Semi Evergreen Climatic Zone. Descriptions. identification keys, locality details and floral hosts are given for the 137 bee species recorded.
Taxonomy and distribution of hard ticks (Ixodidae) in selected areas in Sri Lanka and significance of the transmission of tick borne diseases
(University of Peradeniya, 2014) Liyanaarachchi, D. R.
Ticks are the most important ecto parasites of animals that cause great economic losses in several ways including the transmission of diseases. They are constantly having interactions with their natural environment affecting the risk of infection by tick-borne pathogens. Polymerase chain reaction is used to identify causative agents of tick borne diseases.The objectives of this study were to assess the distribution, host preference of tick species on domestic and wild animals and in humans of Sri Lanka providing detail description of taxonomical characters of each adult male and female tick species collected from this study with identification keys to all tick species reported in Sri Lanka. Moreover, to assess the questing tick diversity in forests and domestic environments and their abundance in forest area in Kandy district in relation to ambient temperature, relative humidity and rain fall.Further, to identify tick vectors for spotted fever and Babesia canis. Ticks were collected from animals by field visits, wild life parks, animal clinics, and through civilians. Flagging method was . carried out to collect questing ticks from Randenigala and Hantana forests and adjoining pastures, also from pastures in villages. Moreover, ticks infesting in human body were collected from Kandy district.Twenty six species were identified infesting on animals and questing on ground. PCR was conducted to spotted fever and B. canis. Taxonomical characters of adult tick species were illustrated and identification keys were prepared. Some species showed host preference and number of tick species on animals was higher than recorded. Ticks had expanded their geographical boundaries and host range. Dermacentor auratus, Haemaphysalis turturis, H aculeata, H hystricis, and H kyasanurensis , which were previously recorded only on wild animals were recorded on domestic animals. Immature D. auratus and Amblyomma testudinarium were abundant on humans and questing on human habitats . Spotted fever was positive from A. testudinarium, A. clypeolatum, A. javanense of wild animals and Rhipicephalus sanguine us of a dog, following Babesia canis from R. microplus and R. sanguineus. Wild animals could serve as natural hosts for zoonoses and dogs are significant agents to spread ticks between wild and domestic environments. This gives an alarming warning that even pathogens of diseases which unidentified yet in Sri Lanka could be introduced to humans via these animals.
Synthesis of monomers and polymers based on metal [Pd(II), Pt(II). Ni(II) and Ci(II) functionalised 3,4- Ethylenedioxythiophene complexes and their characterization
(University of Peradeniya, 2010) Velauthamurty, Kuhamoorthy
Ruthenium, palladium and platinum metals with phosphine ligands are known to have applications in various fields of catalysis, including hydrogenation, isomerization and hydroformylation reactions. The application of metal phosphine and metal-cyclam functionalised EDOT complexes in some exciting new areas currently opening up to inorganic chemists, for example modified electrodes and conducting polymers. Functionalisations of electrodes with the redox—active and catalytically active metal complexes are of particular interest, since these have potential applications in sensing, electrocatalysis and especially in electrochromics. More recently, a range of new EDOT derivatives functionalised with phosphine ligands, either pendant from the ethylene bridge (59 and 63) or attached directly to the thiophene 2- position (50) were investigated. Stable Pd(I), Pt(I) and Ru(II) complexes with these ligands were prepared. Normally tetraazamacrocycle complexes of 3d metals are electrocatalytically active. As such the synthesis and characterization of EDOT derivatives functionalised with 1,4,8,11-tetraazacyclo tetradecane (cyclam) ligand pendant to the ethylene bridge and prepared stable Cu(II) and Ni(II) complexes with these ligands were investigated. Further stable Pt(II), Pd(II) and Ru(II) bis-EDOT derivatives functionalized with phosphines (69) were prepared. Interestingly these complexes succeed in making copolymers containing intact complexes, whereas the corresponding EDOT complexes failed to give the polymer. Using the co-polymerization technique, all the complexes of copolymers were prepared. The functionalised PEDOT copolymer films were formed using electrolyte solutions containing functionalised EDOT complexes and EDOT (1:5 mole ratio; 0.01 M total monomer concentration), using repetitive scan cyclic voltammetry, on Pt, G.C, Au and ITO coated glass electrodes. The copolymer was characterized by using electrochemical methods such as cyclic voltammetry, electrochemical impedance spectroscopy, X-Ray photoelectron spectroscopy, X-Ray fluorescence spectroscopy, and Electron dispersive spectroscopy. These characterization techniques established that the polymers made in the presence of [MCI ₂(50)₂] consisted only of poly-(3,4-ethylenedioxythiophene), whereas polymers made in the presence of other meta! complexes were genuine co-polymers containing Ru(II), Pd(Il, Pt(lI) complexes. This represents a new technique for depositing catalytically-active metal complexes of functionalised PEDOT-phosphine and PEDOT-cyclam matrices, for instance, on array supports for high-throughput synthetic devices or microfluidic systems. The successful polymerization of metal-cyclam functionalised EDOT further opens up the possibility of using the electrogenerated polymers as electrocatalysts in the reduction of alkyl halides. Also it was found that this method affords a better control of the metals concentration in the polymer matrix.
Study of diversity and taxonomy of lichens in the Horton plains national park with a view to biomonitor the ecosystem health
(University of Peradeniya, 2010) Jayalal, R. G. U.
This study was carried out to provide a taxonomic description of lichen flora at Horton Plains National Park (HPNP) and correlate the distribution of lichens to ecological continuity in different forest types. In the present study, lichens from 12 transects within continuous forest and forest islands were selected using a remote sensing map of HPNP. Types of lichens and their diversity in relation to light intensity, temperature, tree species, density, height, diameter and the distribution pattern of trees within each transects were recorded. Further, ecological continuity was determined between continuous forest and forest islands using selected indicator macrolichen genera. Air quality monitoring in the HPNP was also carried out to determine the lichen species sensitivity to the disturbance or air pollution in HPNP. A total 379 lichen species belonging to 67 genera and 24 families were identified. This study documented several new lichen taxa for Sri Lanka that consists of 6 genera and 46 species. The 6 new lichen genera were composed of 3 foliose (Anzia, Menegazzia, Kroswia), 2 crustoses (Parathelium, Pleurotheliopsis) and 01 fruticose (Polichidiunr) lichens. Similarly, the 46 new lichen species were composed of 5 species of crustose, 38 species of foliose and 3 species of fruticose lichens. The total number of lichen taxa recorded in this study was move than 50 % of the lichen taxa already recorded from Sri Lanka. A principal component analysis (PCA) of site data, tree data and lichen cover shows that most lichens are highly correlated with the bark pH and light intensities. Mast of the lichens present in the study plots preferred relatively high pH range (5.0-6.0). The most dominant lichen species (314 species) within this pH range were macrolichens like Lobaria retigera, Pseudocyphellaria beccarti, Heterodermia microphylla and microlichens like ,Graphis sp. Myriotrema sp.. The number of lichen colonies increased with increasing diameter class from 5-10 cm up to 11-20 cm and they decreased with increasing diameter size of the lichen host species. The highest number of lichen colonies was found on hosts of 11-20 cm diameter class in both forest types. Smooth bark type had the highest diversity of lichens in both forest types and this was followed by smooth to rough bark type. The least lichen diversity was observed on deeply furrowed bark type in the continuous forest, while in the forest islands, this was observed on flaky bark type. Cluster analysis conducted on cover and frequency of genera selected as indicators of ecological continuity showed two marked clusters depicting continuous forest and forest patches, the former supporting fewer taxa at lower frequency and cover. Indicator taxa restricted to the forest patches included species of Nephroma and Teloschistes. Large foliose species of Pseudecyphellaria, Labaria and Sticta occurred in both forests, but at lower frequency and cover in continuous forest. The data revealed that the concentrations of ambient NO₂ and SO₂ were very low in HPNP. The variations of ambient NO₂ and SO₂ concentration during the study period showed insignificant positive correlation (p ≥ 0.05} with the rainfall pattern. Considering the variations of two pollutants with RH and number cf vehicles visiting HPNP, both pollutants had insignificant positive correlation. The IAP value obtained for the whole area of the HPNP was 54.22, This value belonged to the quality level 5 which represent the ‘very low’ pollution level. The results including lichen data and air quality data could confirm that the ambient air quality at HPNP is very high. The high diversity of lichens and the minimal levels of air pollutants suggested that the forest health at HPNP is highly conserved. Therefore, it is a must to maintain at least the current conditions of HPNP in order to conserve the forest and its biodiversity.
A study of internal browning of two cultivars of pineapple with special reference to heat shock treatment as a control measure
(University of Peradeniya, 2002) Weerahewa, Hewa Lunuwilage Darshani
Internal browning, commonly encountered in pineapple during prolonged cold storage, is a major obstacle to long distance export of fruit under sea freight. In the present study, the internal browning of fruit of two pineapple cultivars was investigated with the view of establishing suitable postharvest physical treatments that induce tolerance to the disorder. Three-week storage trials were conducted simulating the sea freight export conditions at 10°C and 85% RH. In Mauritius, the internal browning symptoms appeared within a week of storage at 10°C initially in the marginal core tissue which subsequently spread to the surrounding flesh. But in Kew, the symptoms commenced only after 2-3 weeks of storage as isolated patches in the tissue surrounding the core. There was a clear difference in the time of incidence and pattern of symptom development between the two cultivars. The cv. Mauritius showed comparatively faster ripening and respiratory rates and greater accumulation of acids during cold storage, than the cv, Kew. In both cultivars the tissues undergoing browning displayed greater PPO, peroxidase activity and electrolyte leakage. Harvesting fruit early at 100% green stage reduced the incidence and severity of internal browning in both cultivars. Several postharvest physical treatments were tried out to induce cold tolerance of fruit. Heat shock treatment in the form of hot water dip immediately after harvest was found to induce fruit tolerance to internal browning in both cultivars and the best temperature-time combination was 38°C for 60 minutes. The treated fruit developed 75% and 50% lesser browning in the flesh and core region respectively. The overall reduction of internal browning was about 55-60%. The results obtained from different temperature-time combinations suggested that an internal tissue temperature of 36-38°C is a prerequisite for induction of fruit tolerance. Although heat treatment significantly reduced internal browning, it slowed down fruit ripening and associated changes and increased water loss compared to untreated controls. However, provision of modified atmosphere conditions to heat-treated fruit during cold storage enhanced cold tolerance by another 10% and resulted in lesser water loss, hence better appearance. The mechanism of induction of fruit tolerance following heat treatment appeared to be through production of heat shock proteins. It is possible that the cellular repair mechanisms following cold injury may be taking place more rapidly in treated fruit. A cold shock at 4°C for 60 minutes, preceded or followed by heat treatment, also - effectively reduced the internal browning of cv. Mauritius. Here the treated fruit remained firmer and showed lesser cell damage than the fruit provided with heat shock treatment alone or heat shock followed by MA. Intermittent warming of fruit during the cold storage regime also reduced internal browning cv, Mauriti
Synthesis and characterization of doped and undoped Zircon based ceramics
(University of Peradeniya, 2013) Aalahakoon, W. P. C. M.
Homogeneous and fine sized starting P?wders of both undoped and doped zircon (Fe, Y, Fe and Al co-doped) were synthesized by the sol-gel technique following controlled hydrolysis and condensation steps. The .powders were sintered for different temperatures and their structural characterization was carried out using wide range of characterization techniques such as XRD , NMR, SEM and TEM. The densities and zircon yie lds of both doped and undoped samples have found .to increase with temperature reaching a maximum at 1500°C. They show a slight dissociation beyond this temperature. A significant reduction in the starting temperature of zircon formation was observed in the Fe and co-doped sample from 1400°C to 1225°C and 1215°C respectively revealing the contribution of the dopants in zircon formation . The microstructures of both doped and undoped samples revealed they are almost fully dense. The dopants are present in the grain boundaries in all the samples indicating no substantial solid solution formation with zircon. The Fe and Al co-doped samp le is superior to all the other samples; showing promising microstructures without microcracking with fully densified zircon and high zircon yield . Almost single phase zircon was obtained at 1400°C. TEM micrographs reveal that a crystalline grain boundary phase containing some Fe and AI. This may be advantageous when high temperature creep resistance is a concern. Another set of samples were prepared with the conventional solid state sintering method and compared with the sol-gel samples. Undoped and Fe doped samples have silica in the form of both crystalline and amorphous phases whereas Y doped sample has complex microstructure with multiphases due to yttrium. Dopants are present in the grain boundaries without substituting into the zircon sub lattice. A significant feature observed in the sol-gel samples is the absence of cristobalite phase which contributes towards crack formation in the sintered bodies. Finally the electrical properties of both sets of samples were discussed. It was revealed that there is a transient current present due to some initial mobility within the samples, which masks the true conductivity values. Therefore the measured conductivity data could be due to the transient current combined with grain boundary conduction. Also it was suggested that doping does not help in oxygen vacancy migration due to the high activation energy of oxygen migration.
Synthesis and characterization of Poly(Ethylene Oxide) (PEO) - based and Polyacrylonitrile(PAN) - based polymer electrolytes to be used in Photoelectrochemical (PEC) solar cells
(University of Peradeniya, 2010) Bandara, T. M. W. J.
Dye sensitized photo-electrochemical (PEC) solar cells require solid state redox electrolyte systems with good conductivity, mechanical strength and chemical stability. Iodide ion containing polymer electrolytes are important as redox species in PEC solar cells as well as in iodide ion conducting batteries and other devices. In this work, ionic conductivity and thermal, dielectric and transport properties of some Polyethyleneoxide (PEO) and Polyacrylonitrile (PAN) based electrolyte systems and their applications in PEC solar cells were studied. Solid polymer electrolyte membranes were prepared by complexing tetrapropylammonium iodide (Pr₄N⁺I⁻) and PEO. The PEO: Pr₄N⁺I⁻+I₂ = 9:1 ratio gave the best room temperature conductivity for the electrolyte. For this composition, by incorporating the plasticizer ethylene carbonate (EC), a conductivity enhancement of four orders of magnitude was obtained. A marked conductivity enhancement was observed during the melting of the polymer crystallites and above this polymer melting temperature (Tm) the conductivity reached values of the order of 10⁻³ S cm⁻¹. The Tm decreased from 66.1 to 45.1 °C and the glass transition temperature (Tg,) decreased from -57.6 to -70.9 °C due to the incorporation of the EC. The room temperature dielectric constant increased from 3.3 for the unplasticized sample to 17.5 for the plasticized sample. It can be inferred from the dielectric results, that the iodide ion is well dissociated and despite its large size and relatively low concentration it is a relatively efficient charge carrier.All solid solar cells were fabricated with plasticized electrolytes containing PEO:Pr₄N⁺I⁻+I₂ = 9:1 and EC. Maximum photocurrent of 98 μA cm⁻² was obtained for the electrolyte composition PEO:EC = 1:1 under the irradiation of 1000 W cm⁻². The effect of incorporating Al₂O₃ filler on the properties of the plasticized electrolyte was studied using electrical and dielectric measurements, and thermal analysis. In the differential scanning calorimetry (DSC) themograms the existence of two endothermic peaks was observed on heating; one of these peaks is associated with the melting of the PEO crystallites, while the other peak at about 30°C is associated with the melting of the EC rich phase. The temperature dependence of the conductivity exhibited an abrupt conductivity increase in the 1ˢᵗ heating run due to the melting of the EC rich phase. Conductivity isotherms showed the existence of two maxima, one at ~5 % Al₂O₃ content and the other at ~15 %. The occurrence of these two‘maxima could be explained in terms of the interactions caused by alumina grains and the crystallinity of the electrolyte. However, a conductivity enhancement could not be observed in the PEO/EC/ Pr₄N⁺I⁻ electrolyte due to incorporation of Al₂O₃ filler. Enhanced ionic conductivity values were obtained for the ionic liquid tetrahexylammonium iodide containing PEO-based plasticized electrolytes. The conductivity measurements showed a marked conductivity enhancement during the melting of the plasticizer-rich phase of the electrolyte. Annealed electrolyte samples showed slightly better conductivity than non annealed samples revealing the existence of hysteresis. The optimum conductivity was shown for the electrolytes with PEO:Salt =100:15 mass ratio and this sample exhibited minimum Tg, of -72.2 °C. For this optimum PEO:Salt ratio, the conductivity of non-annealed electrolyte was 4.4x10⁻⁴ S cm⁻¹ and that of the annealed sample was 4.6x10⁻⁴ at 30 °C. The short circuit current density (/sc), open circuit voltage (Voc) and power conversion efficiency (n %) of the PEC solar cell fabricated with optimum conductivity electrolyte are 0.63 mA cm⁻², 0.76 V and 0.47% under the irradiation of 600 W m⁻² light. Gel polymer electrolytes based on PAN are potential candidates for photo-electrochemical solar cells. In this work, the plasticized gel polymer electrolyte PAN:EC:PC:Mgl₂) was studied. At 20°C the optimum ionic conductivity of 1.9x10⁻³ S cm⁻¹ was obtained for the (PAN)₁₀(Megl₂)n/₁₀(EC)₂₀(PC)₂₀ electrolyte where n = 1.5. The predominantly ionic nature of the electrolyte is seen from the DC polarization data. DSC thermograms of electrolyte with different Mgl₂) concentrations were studied and the glass transition temperatures were determined. The /-V characteristics revealed that the Isc, Voc and ɳ of the cell are 3.87 mA cm⁻², 659 mV and 2.5 % respectively under the irradiation of 600 Wm⁻².
Synthesis and characterization of some peo-based nano composite polymer electrolytes
(University of Peradeniya, 2008) Pitawala, H. M. J. C.
An electrolyte is an essential component of an electrochemical power source. It is a medium with high ionic conductivity and negligible electronic conductivity. From the practical point of view, conventional liquid electrolytes have many drawbacks such as electrolyte leakage, electrolyte corrosion, weight and complex design, leading to a large volume expansion. Owning to their potential ability to replace the traditional liquid electrolytes in electrochemical cells, high molecular weight poly(ethylene oxide) (PEO) based polymer electrolytes are emerging as the best candidates to be used as polymer electrolytes. Although these electrolytes have high solvation power, complexion ability and ion transport directly connected with alkaline salt (Li⁺), their, the ionic conductivity at ambient temperatures (10⁻⁷-10⁻⁶ S cm⁻¹) is not high enough for most practical applications. In order to overcome this problem, many strategies have been attempted, such as the inclusion of cross-linking agents to form networks, incorporating low molecular weight additives and inorganic fillers. Among these, the incorporation of nano-sized ceramic oxide fillers, to the conventional PEO-salt matrix has been regarded as one of the most promising methods. However, systematic and detailed studies of such nano- composite electrolytes are still lacking. In the present work, different types of PEO- based nano composite polymer electrolytes have been synthesized using common solvent casting method and characterized them mainly using Complex Impedance Spectroscopy (CIS) and Differential Scanning Calorimetry (DSC). The surface morphology of some selected samples has been studied using Scanning Electron Microscope (SEM). For the system, PEO: LiTf, the addition of nano— sized alumina fillers have increased the ionic conductivity of the polymer salt complex giving the maximum conductivity enhancement for the samples with 15 wt. % Al₂O₃. The conductivity at 25 °C increased from 3.5x10⁻⁷ S cm⁻¹ to 2.1x10⁻⁵ S cm⁻¹ due to the addition of 15 wt. % Al₂O₃. Incorporating ethylene carbonate (EC) with (PEO)₉ LiTf + 15 wt. % Al₂O₃ polymer electrolyte resulted in further increase in conductivity, from 2.1x10⁻⁵ S cm⁻¹ to 1.5x10⁻⁴ S cm⁻¹ at room temperature. In (PEO)₉LIBF₄ : Al₂O₃ : (EC/PC) system, the combined effect of the plasticizer and the filler on ionic conductivity and thermal properties of the polymer electrolyte, (PEO)₉LiTF, have been studied in detailed and the maximum conductivity enhancement was observed for the polymer electrolyte, (PEO)₉LiTf + 15 wt.% Al₂O₃+ 50 wt.% [ 75% EC+ 25% PC], with a room temperature conductivity value of σRT; (max) =1.2x10⁻⁴ S cm⁻¹. In the system, (PEO)n,LiBF₄, (n = 3, 6, 8, 10, 12, 15, 20), the composition, n = 12, showed the highest conductivity of 8.7x10⁻⁶ S cm⁻¹ at the room temperature ( 25 °C) among different Li / EO ratios. The addition of nano- porous alumina filler to this electrolyte (with n = 12) increased the ionic conductivity of the polymer salt complex giving the maximum conductivity enhancement for the sample with 15 wt. % Al₂O₃ [σRT (max) = 6.1x10⁻⁵ S cm⁻¹]. The ionic conductivity enhancement due to the incorporation of filler is evidently associated with the surface interactions of the filler with ionic species. One possible mechanism is the creation of favorable conducting pathways through Lewis acid-base type interactions of ionic species with O/OH surface groups on filler grains. The effect of filler on Tg suggest that the filler particles interact with main chain dynamics of the host polymer presumably through Lewis acid-base type interactions between the ether oxygen and filler surface groups leading to a lowering of the Tg. The filler also impedes crystallization and increases the amorphous phase content of the polymer electrolyte. Therefore, it is evident that a major contribution to the conductivity enhancement comes from the structural modifications associated with the polymer host caused by the filler.
Synthesis, characterization and electrical properties of some solid polymer electrolytes based on Poly(Ethylene Oxide), Peo
(University of Peradeniya, 2000) Bandra, L. R. A. K.
In recent decades, a considerable interest has been focussed on polymer electrolyte materials, prepared by complexing suitable polymers with selected metal salts to give electrolyte membranes of interest for the development of electrochemical devices. The most classic example is the combination of poly(ethylene oxide), PEO, and lithium salts (LiX), which in fact are being explored for the development of high-energy density rechargeable batteries. Polymer electrolytes suitable for secondary lithium batteries are thoroughly studied in order to achieve better performance in terms of high ionic conductivity at room temperature and stability against lithium electrodes. However, one major problem of PEO based electrolytes is that the conductivity assumes practically acceptable values only at high temperatures around 100 °C. The objective of the present work is to study the characteristics of PEO based solid polymer electrolytes. This thesis focuses on enhancement of ionic conductivity and ionic transport mechanisms in these electrolytes. Efforts have been made to increase the ambient temperature conductivity by decreasing the crystallinity and increasing the segmental mobility of the polymer by the incorporation of salts and plasticizers into PEO. The two systems, PEO-LiCF₃SO₃ and PEO-LIN(CF₃SO₂)₂, have been chosen for this work, Low molecular weight PEGM (Mw, = 400), EC and PC were used as conventional plasticizers. Furthermore, nano-composite electrolytes i.e. plasticized polymer-salt electrolytes with an added ceramic filler of small particle size, such as Al203, has been found to enhance ionic conductivity. The addition of finely dispersed non-miscible particles in a polymer electrolyte generally enhances the ion conductivity, PPFEMO (Mw = 4000) was introduced as a new type of plasticizer for PEO based polymer electrolytes. There are, up to now, no other examples of mixing this type of ‘electrolyte with non-miscible liquids except with the PEO based electrolytes with PPFEMO systems presented here. The system PEO-LiX, with the addition of PPFEMO is a bi-phase stable emulsion. The micro-droplets present in the emulsion prevent or retard the crystallisation of the electrolyte when it is cooled from the melting temperature to ambient temperature. The ion conductivity below the melting point temperature maintains stable values as long as the re-crystallisation is prevented. The characteristics of the electrolytes were investigated by Complex Impedance Spectroscopy, Complex Dielectric Spectroscopy, Differential Scanning Calorimetry and tranference number measurements. The temperature dependence of the conductivity was studied in 8detail for all materials. Dielectric properties, dynamical mechanical properties, glass transition temperature and degree of crystallinity of these materials were also discussed in detail. For the systems, PEO-LiCF₃SO₃, PEO-LiN(CF₃SO₂)₂, PEO-LIN(CF₃SO₂),-EC/PC and PEO-LiN(LiCF₃SO₂)₂-PPFEMO, the dielectric measurements reveal two peaks in the imaginary part of the dielectric function, a high frequency peak in the GHz region attributed to the α- process of the pure polymer, and a lower frequency ‘ion-pair’ peak in the MHz region, the intensity whose is found to be dependent upon the concentration of the salt present in the polymer-salt complex. Considerable amounts of ion pairs were present in both plasticized and unplastisized polymer electrolytes and if the relaxation frequency can be taken as a probe of the local flexibility of the polymer chain it can be concluded that the conductivity increases in parallel to the increases in the local flexibility of the polymer segments.
Synthesis of Hydroxyapatite nanomaterials for their potential use in fabrication of bone-Implants
(University of Peradeniya, 2015) Wijesinghe, W. P. S. L.
Recently, all over the world, hydroxyapatite (HA) nanomaterials and biocompatible prostheses coated by HA nanomaterials have widely been used in broad range of applications. However, current synthesis techniques of HA nanomaterials and preparation methods of HA coated bone implants (prostheses) are very expensive. Therefore, development of low cost and simple preparation methods for HA nanomaterials and bone implants have become one of the most important research areas in the globe. Furthermore, currently , bone implants and their raw-materials are imported to Sri Lanka with very high- costs. As a result, development of materials for bone-implants is very important for the reduction of medical expenses of Sri Lanka. This research work focuses on synthesis of HA nanoparticles and their nanocomposites using simple, novel and economical methods . This research work also attempts on development of thin-films of HA and TiO₂/HA on metallic implants through the Atomized Spray Pyrolysis (ASP) technique in order to produce biocompatible bone implants . Moreover, synthesis of HA nanoparticles dispersed PMMA matrix is introduced in order to replace expensive metallic biomaterials in medical applications. In order to prepare HA nanoparticles, simple and economical method is devised using calcium and orthophosphate . Since naturally occurring calcium carbonate minerals can be used to prepare calcium sucrate, HA nanoparticles can be synthesized from these minerals which is a great effort on high value-addition to these minerals. Both needle-like and spherical hydroxyapatite nanoparticles are synthesized with this method and the effect of synthetic temperature and calcination on morphology , crystallite size and crystallinity are studied . Triton X-100 is used to prepare HA colloids in order to control the aggregation of HA nano particles . A novel, simple and low-cost technique is devised to prepare hydroxyapatite coated titanium metal (TiM) implants . TiO₂/HA nanocomposites are synthesized and deposited on TiM and Ti₆AL₄V surfaces in order to produce TiO₂/HA coated implants. The HA/polymer nanocomposites such as HA/poly(methyl methacrylate) (HAlPMMA), HA/poly(acrylic acid) (HA/PAA) and HA/stearic acid (HA/SA) are synthesized under in-situ and ex-situ preparation methods with their respective monomers and polymers. While polymerization of MMA into PMMA, the HA/SA is dispersed in to the reaction medium in order to produce HA nanoparticles dispersed PMMA matrix. Porous HA is synthesized using calcium sucrate on nano-CaCO₃ template s to use in biomedical applications . Furthermore , Eppawala apatite (EPAP) was directly converted into high purity HA nanoparticles by removing F and Cl from EPAP. All these novel methods and products are important to reduce the production cost of the HA nanoparticles, HA composites and biocompatible prostheses in order to use in biomedical fields.
Stability, strain and speed of polypyrrole actuators
(University of Peradeniya, 2010) Jafeen, Mohamed
Polypyrrole doped with large immobile dodecyl benzene sulfonate (PPy/DBS) anions operating in aqueous electrolytes is one of the successful and low cost systems suitable for the use as soft actuators. However, considerable improvement in the performance of the PPy/DBS actuators is still required for successful applications of these actuators. The present work aims to get a better understanding of the processes associated with actuation mechanism of PPy/DBS actuators so as to improve their performance. A second aim has been to use the unique physico-chemical environment of polypyrrole to determine hydration numbers of cations. The PPy/DBS films were prepared electrochemically with ‘constant currents and characterized using cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), optical absorption spectroscopy, and force- displacement measurement techniques. The electrochemical processes associated with the actuation of the PPy/DBS films in alkali halide and alkali earth halide chloride aqueous electrolytes having varying concentrations were investigated. The redox behaviour of the films in electrolytes having various concentrations shows that the cathodic peak potentials during the cathodic reduction of the films depend on the concentration of the cycling electrolytes used. The results also indicate the necessity of water in the right amount in the cycling electrolytes to ease the reduction process. Cyclic voltammetric studies at different sweep rates show that the mobility (diffusion) of counter ions into the PPy/DBS film is larger in concentrated electrolytes having smaller cations. In highly concentrated alkali halide aqueous electrolytes, the mass of a PPy/DBS film at the end of each redox cycle is found to drift. The change in mass depends on the concentration of the cycling electrolytes used and the number of cycles. The mass drift during cycling can be controlled by interchanging the cycling electrolytes. The electrochemical stability of PPy/DBS films in aqueous alkali halide electrolytes depends strongly on the concentration of the electrolyte used. While the cycling capacity in dilute electrolytes decreases significantly after about 50 cycles, the capacity remainsthe same even at the 300ᵗʰ cycle in highly concentrated electrolytes indicating that the films are more stable in highly concentrated alkali halide electrolytes. This is an important result with respect to the usability of this type of actuator. Very thin nano-sized (nm thick) PPy/DBS films were also prepared using electrochemical polymerization and characterized using EQCM measurements. The results show that ionic motion in nano-sized thin PPy/DBS films during redox cycling in alkali halide aqueous electrolytes has similar characteristics as those of ionic motion in comparatively thicker PPy/DBS films. The results further indicate that the initial layers of a PPy/DBS film are somewhat different in structure from the layers added later in the film. The hydration numbers of metal cations in aqueous electrolytes were determined using the novel physico-chemical environment of polypyrrole. The primary hydration numbers obtained for alkali, alkali earth and alkali rare earth metal cations in respective chloride aqueous electrolytes having various concentrations (0.02 M — 1 M) are: Lit⁺ : 5.5-5.3; Na⁺: 4.5-4.3; K⁺ : 2.3-2.5; Rb⁺ : 0.9-0.8 ; Cs⁺ : ~0; Mg²⁺ : 10.4-10.6 ; Ca²⁺ : 7.9-8.1; Sr²⁺ : 5.7-6.1; Ba²⁺ : 3.0-3.1; Y³⁺ : 13.6- 13.8; La³⁺: 9.0-9.1. ‘The values of the primary hydration numbers of these metal ions are found to remain constant in the above aqueous electrolytes having concentrations up to 1 M. For all cations the primary hydration numbers show an approximate linear variation with the total charge per surface area of each cation, which is a measure of the surface charge density. The model using the surface charge density may well be the best simple model for primary hydration number of a metal ion. Furthermore the primary hydration numbers of metal cations in highly concentrated aqueous electrolytes are smaller than those in dilute electrolytes and the free water in highly concentrated electrolyte is absolutely a ‘different kind of water’ containing loosely bound water molecules rather than entirely free molecules. Electro-chemo-mechanical behaviour of PPy/DBS actuators was investigated using the computer automated Force-Displacement setup. Experiments demonstrated that the electrochemical strain of a PPy/DBS actuator in aqueous electrolytes depends on of the actuation frequency and on the type of cations in the cycling electrolytes. At high actuation frequencies, strains depend solely on the cation plus the hydrated water molecules (i.e. on the hydration number) and At low frequencies, on the other hand, the strain depends on the sum of the hydrated water molecules and those inserted by an osmotic process. Between the two frequency regions the strain decreases significantly. Therefore, the highest speed of response (larger strain at high actuation frequency) for PPy/DBS actuators is achievable in the cycling electrolytes containing cations having larger hydration numbers.
Status and mechanisms of insecticide resistance in anopheline vectors of malaria in Sri Lanka
(University of Peradeniya, 2007) Perera, M. D. B.
Resistance to insecticides was studied in the major malaria vector An. culicifacies, and secondary vector An. subpictus in five districts (i.e. Anuradhapura, Kurunegala, Moneragala, Puttalam and Trincomalee) of Sri Lanka during January 2001 to January 2005. Adults were collected using cattle baited trap huts. Larvae were collected from natural breeding habitats. Adult bioassay experiments were carried out with World Health Organization (WHO) discriminative dosages of DDT, malathion, fenitrothion, propoxur, lambda-cyhalothrin, cyfluthrin, cypermethrin, deltamethrin, permethrin and etofenprox,according to WHO standards. Metabolic resistance by carboxylesterase, glutathione S- transferase (GST) and monooxygenase based mechanisms were determined by biochemical, synergist and metabolic techniques. Target site insensitivity was studied by biochemical assays and gene sequencing. Resistance in other potential malaria vectors from Anuradhapura was also studied. Both species were highly resistant to DDT in all the collected places. Malathion and fenitrothion resistance was high in all the places except An. culicifacies in Kurunegala (susceptible to both) and Puttalam (susceptible to fenitrothion). Populations were highly resistant to permethrin in Anuradhapura and Trincomalee. All the populations were susceptible to cypermethrin and cyfluthrin. An. subpictus from Anuradhapura, Kurunegala and Puttalam were resistance to lambda-cyhalothrin. All An. subpictus populations had low susceptibility fo deltamethrin. Etofenprox tolerance was highest in Anuradhapura An. subpictus. Carboxylesterase activities were higher in An. culicifacies. Native PAGE resolved one elevated isozyme band from each species. Thin layer chromatography analysis of metabolized mosquito homogenates showed the presence of malathion carboxylesterase mechanism in all the populations except for Kurunegala An. culicifacies. AChE was more sensitive to insecticides in Kurunegala and Trincomalee An. culicifacies populations and highest insensitivity was observed from Trincomalee An. subpictus population. High GST activities in both species explained their high resistance to DDT. Quantitative and qualitative changes of carboxylesterases, and insensitive target site AChE were found to be responsible for organophosphorus resistance in Anuradhapura, Moneragala, Puttalam and Trincomalee An. culicifacies populations. Synergist and biochemical studies revealed that monooxygenases provide pyrethroid resistance. An. subpictus, An. nigerrimus and An. peditaeniatus showed resistance to propoxur showing the high exposure of their breeding sites to agricultural insecticides. An. nigerrimus and An. peditaeniatus have developed insecticide resistance mainly due to elevated monooxygenase activities. Leucine to phenylalanine substitution (TTA to TTT) in sodium channel regulatory gene was detected from Anuradhapura An. subpictus and was almost identical to the mutation identified in An. gambiae s.s. of South Africa. This indicates an independent origin of the same mutation in two geographically isolated species due to the constraints for evolving different mutations without interrupting the physiological role of the target site. It appears that pyrethroid resistance of Sri Lankan An culicifacies is mainly caused by monooxygenases and that of An. subpictus is mainly by mutated sodium channel genes.
Structure-activity studies of arly alkenes and synthesis and use of chiral inductors in iridoid synthesis
(University of Peradeniya, 2000) Priyadarshani, A. M. A.
This thesis consists of two parts. Part one of the thesis describes the synthesis of insecticidal active aryl alkenes. Previous study of Zingiber purpureum had shown the presence of an aryl alkene, (E)- 1-(3’,4’-dimethoxyphenyl)butadiene which was active against Aedes aegypti with LC₅₀ of 6.5 ppm and against the bruchid, Callosobruchus maculatus with LC₅₀ of 2 mg. The compound also showed oviposition deterrent and ovicidal effects against the bruchid. The aryl alkene was however unstable when exposed to light and air. Structurally related compounds, were therefore synthesized in order to study the structure-activity relationship to obtain stable aryl alkenes with the same or enhanced activity. Arylalkenes were synthesized using the Wittig reaction. Aromatic aldehydes substituted with hydroxy and methoxy groups at different positions on the aromatic ring were reacted with ylides of different length (1 to 4 carbons). Para methoxy substituted aryl alkenes were generally found to have strong insecticidal activity against Callosobruchus maculatus in the residual film bioassay. In the seed treatment bioassay, these compounds showed oviposition deterrent and ovicidal effects against the bruchid. However the result against Aedes aegypti did not show any consistent pattern in relationship between structure and activity. Part two describes the synthesis of Gastrolactole, which is a key intermediate in the synthesis of sex pheromones, Nepetalactoles and some Iridoidal compounds. Some Nepetalactones, Nepetalactoles and other terpenoids with iridoidal skeleton are chemical messengers among aphids. The key step in our synthesis is an intramolecular [4+2]-cycloaddition of an enamine derivative of 8-oxocitral, wherein the enamine moiety acts as the chiral inductor. 2-Methyl-, fert-Butyl-, Phenyl-indoline were used as chiral inductors in the cycloaddition step and three different cycloaddition products were obtained in different diastereomerical ratios. 2-Phenylindoline was the best chiral inductor for the cycloaddition step judging by the yield of the reactions and the diastereomerical ratios of the products. Racemic 2-phenylindoline was resolved into its enantiomers separated by first converting them to urea derivatives using (R)-(+)-a-methylbenzylisocyanate. The diastereomers of the urea derivative were then separated by medium pressure column chromatography and finally they were released as separate samples of (R)- and (S)-2- phenylindoline after reaction with diborane in refluxing THF. The enantiomeric purity of the two enantiomers were checked by chiral gas chromatography.
Studies on ovary, ovule and anther culture of cocos Nucifera L. (Coconut)
(University of Peradeniya, 2008) Perera, P. I. P.
Breeding in coconut is hampered by the lack of homozygous lines for hybrid production and a clonal propagation method. Thus the present study was undertaken to develop suitable techniques for production of dihaploids (DH) via anther and ovule culture. Further, the unfertilized ovary was tested as a novel explant for clonal propagation through somatic embryogenesis. The suitable developmental stages of explants were determined by a detailed histological study on inflorescence development. Consistent callogenesis was observed when unfertilised ovaries at -4 stage were cultured in CRI 72 medium containing 100 μM 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.1% activated charcoal. Callusing was improved by application of Thidiazuron (TDZ). Embryogenic calli were sub-cultured into somatic embryogenesis induction medium containing 66 μM 2,4-D followed by maturation medium devoid of any hormones. Germination of somatic embryos and shoot formation was induced by addition of 6-benzyl aminopurine (BAP) and Gibberellic acid (GA₃) while 2-isopentyl adenine (2iP) increased the frequency of plant regeneration. Histological studies illustrated the sequence of events during somatic embryogenesis while genetic stability of calli and somatic embryos was confirmed by ploidy analysis. In situ hybridization indicated that the cell cycle controlling gene, Rb is a potential marker to assess regeneration potential of cultures. Induction of embryogenesis in ovules failed while anther culture gave promising results. Embryogenic calli / embryoids were produced when anthers at 3 WBS stage, pre-treated at 38°C for 6 days, were cultured in Eeuwens Y₃ liquid medium containing 9% sucrose, 100 μM 2,4-D and 0.1% activated charcoal. Androgenic response was enhanced by combining 2,4-D with 1- naphthalene acetic acid (NAA) and cytokinins (2iP and kinetin). Use of phytagel- solidified medium promoted plant regeneration. Anther orientation of ‘abaxial surface up’ promoted formation and germination of embryoids. Histological studies revealed that the origin of calli/embryoids were from pollen. Ploidy analysis revealed that some of these structures were haploid whereas the others were diploid. Microsatellite marker analysis revealed that all the tested samples containing diploid chromosome complement were DHs. To the best of our knowledge, this was the first successful attempt of obtaining haploid calli/embryoids and DH plants via anther culture in coconut.
Satellite based forecast system for Yellowfin tuna fishery in the Indian ocean
(University of Peradeniya, 2015) Rajapaksha, J. K.
Yellowfin Tuna is the major export among Sri Lanka fishery products to Japan and European markets. Even the demand for quality fish in local and international markets are increasing, Sri Lanka has not invested sufficiently enough to increase its fishing capacity, specifically to increase the efficiency. One of the major drawbacks of the fishing industry in Sri Lanka is the long search time of fishing grounds causing high operational cost and as a consequence, low quality fish landings . These weaknesses can overcome by enhancing fishing technology, and one such improvement would be the minimizing catch uncertainty, or identifying fishing grounds that can address most of such problems. This research was carried out to understand the relationship of catch rates with the prevailing oceanographic conditions. In the meantime, the dynamic oceanographic conditions were related with various satellite observations and, predictive models were generated to infer the oceanographic parameters with satellite observations. Finally, an operational fishing ground forecast system was developed for Yellowfin Tuna in the Indian Ocean . Oceanographic parameters such as sea surface temperature, sea surface chlorophylla and the sea surface height from remote sensing satellite data were analyzed with Yellowfin tuna catch obtained from Sri Lankan longliners during a three year period. High frequency catch rates were observed in the regions where sea surface temperature varied primarily between 27.0-30.5°C, sea surface height between 205- 215 cm and sea surface chlorophyll concentration between 0.1-0.7 mg m⁻³. The degrees of differences between the empirical cumulative distribution function and catch-weighted cumulative distribution of the three variables were statistically significant (p < 0.01). The results obtained from a Generalized Additive Model have shown that the space-time factor is well above the oceanographic parameters which are also in significant levels (p < 0.001). The time and space factor represent the migratory pathway which is an important predictor for Yellowfin tuna. The inter-annual variability of oceanographic parameters were found consi stent with high catch rates . Further, to account for the vertical migration of Yellowfin tuna, an algorithm was developed to predict accu- rate fishing depth based on the subsurface thermal structure. This algorithm is capable of predicting isotherm depth using sea surface height and sea surface temperature with spatial resolution of 1° grids . Combining the depth prediction model and habitat preferences of Yellowfin tuna, a fishing grounds forecasting methodology was developed based on near real-time satellite observations. A subsurface temperature prediction algorithm was developed using sea surface observation from satellites with relatively high accuracy. Also, it was concluded that satellite derived oceanographic parameters; sea surface temperature, sea surface chlorophyll , and sea surface height can be used to predict potential fishing grounds of Yellowfin tuna in the Indian Ocean.
Solid polymer electrolytes based on polyacrylonitrile and organically modified ceramics ( Ormocers)
(University of Peradeniya, 2000) Perera, G. A. K. Sandhya
PAN based electrolytes were made by complexing EC and PC with different salts namely, CuCNS, Cu(CF₃SO₃)₂, Mg(CIO₄)₂, and LiCF₃SO₃ Sample preparation was done using the hot pressed technique. All systems yielded free standing electrolyte films. System with 21 mol% PAN : 30 mol% EC : 45 mol% PC : 4 mol% CuCNS has a room temperature conductivity of 3.3 x 10⁻⁵ S cm⁻¹ while the system with 20 mol% PAN : 41 mol% EC : 34 mol% PC : 5 mol% Cu(CF₃SO₃)₂ has a room temperature conductivity of 4.1 x 10⁻³ S cm⁻¹ Conductivity variations with temperature of the two systems show Arrhenius and VTF behaviours respectively. Former system seems to be an anionic conductor and the latter system a mixed conductor with cationic and electronic contributions. Electrolytes made with Cu(CF₃SO₃)₂ has been used in cells of the form, Cu/PAN: EC: PC : Cu(CF₃SO₃)₂ / PPy : DBS where DBS stands for polypyrrole polymerized in the presence of DBS. Open circuit voltage was approximately 180 mV. A capacity of about 12 μA h under a load resistor of 50 kΩ was obtained. When Mg(CIO₄)₂ was incorporated with PAN : EC : PC, a room temperature conductivity of 3.2 x 10⁻³ S cm⁻¹ can be obtained from the composition 18 mol% PAN : 64 mol% EC : 14 mol% PC : 4 mol% Mg(CIO₄)₂ . Conductivity variation with the temperature takes the form of Arrhenius behaviour. Secondary solid state cells have been fabricated with this electrolyte in the form, Mg / PAN : EC : PC : Mg(CIO₄)₂ / PPy : DBS. Open circuit voltage lies around 1.5 V. Estimated capacity values are around 0.18 mA h. System based on LiCF₃SO₃ has a room temperature conductivity of 1.2 x 10⁻³ S cm⁻¹. Corresponding composition is 15 mol% PAN : 42 mol% EC : 36 mol% PC : 7 mol% LiCF₃SO₃. Conductivity variation with temperature followed VTF behaviour. Stability of the electrolyte with lithium is somewhat acceptable. Test cells in the configuration, Li / PAN : EC : PC : LiCF₃SO₃ / PPy : X (X : CF₃SO₃, DBS’, AS) have open circuit voltages around 4 V. It is possible to get more than 800 cycles with an efficiency of 99.95%. Artificial muscles in the form, PPy : X / PAN : EC : PC : LiCF₃SO₃ / PPy : X (X : CF₃SO₃, DBS’) have been fabricated. Their movements were observed between two voltages. It is seen that the movements are faster when the assembly is thin. Ormocer electrolytes are having somewhat considerable conductivity values. But, those values should be enhanced further to make them proper candidates for applications. Concept of all solid state cells may be feasible with ormocers.
Soil carbon sequestration in eucalyptus grandis forest plantations of Sri Lanka along a chronosequence of forest age
(University of Peradeniya, 2015) Premetilake, M. M. S. N.
Managing forest plantations to sequester atmospheric carbon in soil has drawn the scientific attention as a way of reducing global warming and improving soil quality. In Sri Lanka, the area of forest plantations has substantially increased over the past few decades and, more than 20% of these are represented by Eucalyptus species. However, carbon sequestration in Sri Lankan Eucalyptus forest plantations, especially focussing on soil, has not been fully understood. Therefore, soil carbon sequestration potential of Eucalyptus grandis W. Hill, forest plantations in the intermediate zone of Sri Lanka was studied over a chronosequence of age (4, 10, 19 and 27 years after establishment) and compared with patana grassland (the land use before afforestation), a natural tropical evergreen forest and a tea (Camellia sinensis) plantation in the same zone. The factors that affect soil carbon sequestration were also examined. Six 20 m x 20 m experimental plots were established in each land use. Above ground parameters such as tree heights, Diameter at Breast Height (DBH), crown width, tree density and diversity of understory were recorded. Litter dry mass and major litter nutrients were measured. Soil samples were collected at two depth levels (0-15 cm and 15-30 crn). Total Organic Carbon (TOC), Microbial Biomass Carbon (MBC), Permanganate Oxidizable Carbon (OC) and Water Soluble Carbon (WSC) were measured. Moisture content (SMC), texture, bulk density, pH, a-pinene concentration, major soil nutrients, fungi: bacteria ratio and microbial biomass nitrogen content in soil were also determined. The data were analysed via the mixed modelling approach to eliminate pseudo-replication in the experimental design. Above ground and below ground carbon stocks were calculated. The results indicated that total height, DBH and crown width of E. grandis trees increased significantly with stand age while tree density had decreased due to thinning practices operated under the clear cutting silvicultural system. Although there was no statistical significance, the aboveground carbon stocks showed tendency to increase with stand age. Therefore, overstory contribution for carbon sequestration apparently increased with stand age. The understory vegetation density and diversity showed negative relationship with stand age exhibiting a decline in understory 's contribution for carbon sequestration with increasing stand age. The declining trend in nutrient levels of litter after crown closure also could influence slow mineralization of litter leading to increased carbon sequestration in soil. Soil moisture content (SMC), soil acidity and a- pinene concentration in soil increased significantly with stand age improving carbon sequestration potential of E. grandis plantation soil. Most of the soil nutrients displayed a declining trend up to a certain level. The stable carbon (SC) stock in 0-15 cm soil layer after 27 years of afforestation was 9.07 ± 2.21 t ha⁻¹ , which was 36, 34 and 10 fold higher than those of patana grassland, natural forest and tea plantation, respectively. From these results, it could be concluded that the E. grandis plantations increase particularly stable soil carbon storage along a chronosequence of age. Therefore, in the perspective of carbon sequestration, the presence of E. grandis plantatio ns is advantageous, especially when the trees get older.
Semisynthesis and bioactivities of lichen substances
(University of Peradeniya, 2007) Thadhani, Vinitha Moolchand
Lichens constitute a class of small perennial plants, which are a combination of two organisms a fungal partner (mycobiont) and one or more photosynthetic partners (photobiont) growing together in symbiotic association. In an attempt to isolate compounds from natural sources, three lichens, namely Parmotrema grayana, Cladonia sp. and Heterodermia obscurata were chemically investigated. Isolated compounds were subjected to various bioassays. Chemical investigation of these lichens ted to the isolation of atranorin (1), + usnic acid (2), divericatic acid (3), methyl haematommate (4), methy] orsellinate (5), orcinol (6), orsellinic acid (7), lecanoric acid (8), zeorin (9), methyl-β-orcinolcarboxylate (10), lobaric acid (11), and sekikaic acid (12). The depsides divericatic acid (3), lecanoric acid (8), sekikaic acid (12), and the depsidone lobaric acid (11) showed very significant antioxidant activity in SOIT, the IC₅₀ values being lower than the standards (propyl gallate). Simple aromatic compounds namely orciniol (6) and orsellenic acid (7), showed high urease inhibition, even higher than the standard thiourea. Methyl- 6-orcinolcarboxylate (10), methyl orsellinate (5), and the triterpenoid zeorin (9), showed significant inhibition against a-glucosidase, with IC₅₀ values several folds less than the respective standard. The second part of thesis deals with the conversion of major lichen metabolites into minor ones and testing their bioactivities The depiside, erythrin (13) isolated in 7.6% yield from Roccella montagnei was successfully converted into its isomeric diphenyl ether 15 via a Smiles rearrangement. Oxidative coupling of these diphenyl! ether using palladium (II) acetate, lead to an efficient and unambiguous approach to substituted dibenzofurans. To the best of our knowledge this is the first report on the formation of diphenyl ethers and dibenzofurans using naturally occurring depsides, via Smiles rearrangement. The oxidative coupling of fully protected diphenyl ether 17 led to dibenzofuran 18 and 19. Dibenzofuran 19, earlier synthesized by completely synthetic route, has been converted to pannaric acid (24) and schizopeltic acid (25) derivatives by previous workers. Thus, our synthesis of the dibenzofuran 19 constitutes a formal synthesis of the above natural products, in a resourceful manner. Although fully protected diphenyl ethers such as compound 17 had been used previously in the preparation of dibenzofurans, unprotected diphenyl ethers had not been subjected to oxidative coupling in the presence of palladium acetate. Oxidative coupling of free carboxylic acid containing diphenyl ethers 15 and 16 led to the dibenzofurans 21 and 20, respectively. The dibenzofuran 20 and 21 are structural analogue of naturally occurring dibenzofuran hypostrepsilic acid (27). Thus this study opens way to form these new analogues in a versatile manner using oxidative coupling of carboxylic acid containing dipheny] ethers such as 15 and 16. Even though the bioactivities of hypostrepsilic acid (27) and its related class of dibenzofurans are not known, very interestingly, their structural analogues 20 and 21, showed very promising activities. Both dibenzofurans showed very good activity in DPPH radical scavenging assay, and dibenzofuran 21 also was active in SOI radical scavenging assay. Dibenzofuran 20 showed antibacterial activity against Pseudomonas aeruginosa, whereas dibenzofuran 21 showed very high β- glucuronidase enzyme inhibitory activity at level higher than the standard. The final part of thesis deals with the structure-reactivity relationship of lichen compounds (both natural and synthetic) in various bioassays. Comparison studies revealed that depsides, and depsidones showed good.antioxidant activity in SOI due to the extended conjugation of such compounds. Thus lichens have natural mechanisms or components to combat oxidative stress, which is probably why they we have shawn very promising antioxidant activities in SOI assay. On the other hand, the synthetic dibenzofurans showed good activity in DPPH assays. Interestingly, all the simple aromatic compounds, namely orsellinic acid (7), orcinol (6), methyl-β-orcinolcarboxylate (10), methyl haematommate (4), and methyl orsellinate (5) showed very good inhibition against the enzyme urease. Comparison studies also revealed that by simple conversion such as hydrolysis of the depside brings about drastic change to the respective bioactivity. For example, erythrin (13) was inactive against all the fungi tested whereas methyl orsellinate (5), showed significant antifungal activity against all the tested fungi.

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