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Item Role of total curvature on rays of non-compact Riemannian 2-manifold(2019-10-25) Malwatta, P.B.It is interesting to study the geometry of total curvature on complete open surfaces. Cohn-Vossen’s inequality states that in every connected noncompact finitely connected complete Riemannian 2-manifold 𝑀 with finite total curvature 𝑐(𝑀) and finite Euler characteristic 𝜒(𝑀), we have 𝑐(𝑀)≤2𝜋𝜒(𝑀). Huber extended this result, if a connected, infinitely connected complete Riemannian 2-manifold 𝑀 without boundary admits a total curvature 𝑐(𝑀), then 𝑐(𝑀)= −∞. The value 2𝜋𝜒(𝑀)−𝑐(𝑀) plays an important role in the study of rays on complete, noncompact Riemannian 2-manifolds. A ray 𝛾:[0,∞]⟶𝑀, on a complete, non-compact Riemannian manifold 𝑀 is by definition a unit speed geodesic every subarc of which is minimizing. Due to the completeness and non-compactness of the Riemannian 2-manifold 𝑀, there exists at least one ray emanating from every point of a manifold. If 𝐴(𝑝) is the collection of all rays emanating from 𝑝∈𝑀 and 𝜇 is the natural measure induced by the Riemannian metric then lim𝑛→∞𝜇𝜊𝐴(𝑝𝑛)⊂𝐴(𝑝) , where {𝑝𝑛} is a sequence of points of 𝑀 converging to 𝑝. Also we have the function 𝜇𝜊𝐴∶𝑀⟶[0,2𝜋] is upper semi-continous and hence Lebesgue integrable. If 𝑀 is connected, finitely connected, complete and non-compact Riemannian 2-manifold, we then investigated the relationship between 𝑐(𝑀) and the function 𝜇𝜊𝐴, proving that if 𝑀 is homeomorphic to 𝑅2 and if Gaussian curvature 𝐺≥0, then 𝜇𝜊𝐴 ≥2𝜋−𝑐(𝑀), and in particular 𝑖𝑛𝑓𝑀𝜇𝜊𝐴=2𝜋−𝑐(𝑀).Item Correlation between selected morphological and biochemical parameters in a hybrid tea population with the blister blight disease(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Weerasooriya, C.R.; Kottawaarachchi, J.D.; Ranathunga, M.A.B.; Amarakoon, A.M.T.Tea is produced from the plant species Camellia sinensis. Blister blight is a major leaf disease caused by the fungus Exobasidium vexans in tea resulting in significant yield losses, debilitation and death of tea bushes . Copper and systemic fungicides are currently used to control the disease resulting in high costs and potential residues in tea. In addition, there is a possibility of developing fungi resistance in tea plants to fungicides. Therefore, developing cultivars with resistance towards Blister blight is considered as the most suitable approach to control the disease. In the present study, the correlation between morphological and biochemical parameters was investigated with Blister blight disease with an aim to develop resistant cultivars. Twenty (20) tea samples including 18 accessions produced by crossing two parent cultivars: TRI 2043 (highly resistant to Blister blight) and TRI 3055 (highly susceptible to Blister blight) and the two parent cultivar samples were used in this study. The morphological analysis was carried out with reference to the guidelines given in the descriptors for tea by the International Plant Genetic Resources Institute (IPGRI) in 1997 and the descriptor list of the International Union for the Protection of New Varieties of Plants (UPOV) for tea (2008). Biochemical parameters were analysed following spectrophotometric methods and HPLC methods. Total anthocyanin, caffeine, polyphenol, gallic acid, epigallocatechin, catechin, epicatechin, epigallocatechin gallate and epicatechin gallate contents were determined. Results obtained for morphological and biochemical parameters were statistically analysed using the Minitab software under two categories; calculating the correlation between morphological and biochemical parameters and plotting a dendrogram for morphological and biochemical parameters separately. The Pearson correlation method was used to calculate the correlation between parameters. From the morphological parameters, a positive relationship was observed in the number of average pubescence on young leaf with the Blister blight resistance. Total anthocyanin content showed a positive relationship and epicatechin showed a low negative relationship with the Blister blight resistance. Accession 26 showed a very high total anthocyanin content (0.123 ± 0.065%), a moderate epicatechin content (0.792 ± 0.168%) and a high resistance to Blister blight disease, indicating its potential to be developed as a resistant cultivar. The experiment was duplicated, and the same results were obtained both times. Based on the results, it can be concluded that anthocyanin content can be suggested as a biochemical marker in tea crop improvement programs.Item Electrodeposition and characterization of as-deposited and annealed CdTe thin films.(Ceylon Journal of Science, 45(2), 53–59. DOI: http://doi.org/10.4038/cjs.v45i2.7388, 2016) Kumarasinghe, K. D. M. S. P. K.; De Silva, D. S. M.; Pathiratne, K. A. S.; Salim, H. I.; Abdul-Manaf, N. A.; Dharmadasa, I. M.Thin films of CdTe semiconductor materials were grown on fluorine doped tin oxide (FTO) conducting glass substrates using the technique of electrodeposition. CdSO4 at high concentrations and CdCl2, TeO2 at low concentrations were used as precursor salts for electrodeposition. The range of deposition potentials was estimated using cyclic voltammetric measurements. The electrical, optical, structural and morphological characteristics of as-deposited and annealed CdTe thin films were characterized using photo-electrochemical (PEC) cell studies, UV-Vis spectrophotometry, X-ray diffraction (XRD) and scanning electron microscopy (SEM). These particular samples were converted from n-type into p-type after heat treatment. UV-Vis spectrometric measurements for CdTe layers indicated that, the energy band gaps of 1.45±0.02 eV for both as-deposited and annealed samples which exhibited the required optical property for fabricating CdS/CdTe solar cells. Little increase in (220) and (311) peaks of XRD spectra were observed for annealed layers compared to the as-deposited material. However, annealing exhibited a small reduction of cubic phase preferential orientation (111). The optical transmission for both as-deposited and annealed CdTe samples were about 60% for wavelengths longer than about 850 nm.Item Selenium content in meals consumed for lunch by Sri Lankans and the effect of cooking on selenium content.(Ceylon Journal of Science, 46(4), 21–25. DOI: http://doi.org/10.4038/cjs.v46i4.7465, 2017) Kiridena, K. M. S. D.; De Silva, D. S. M.; Wimalasena, S.The selenium (Se) content in meals consumed by Sri Lankans for lunch, composed of fixed and random menus, was determined using Hydride Generation Atomic Absorption Spectrometer. The samples were obtained from five districts in Sri Lanka. The Se content (μg/kg) in meals of fixed and random menus was in the range of 48-70 and 53-60 respectively. These values are comparable to the daily requirement of Se (55 μg/kg) prescribed by the World Health Organization and Food and Agriculture Organization of the United Nations. There is no significant difference in Se content in meals consumed by people in the districts of Kandy, Gampaha, Kurunegala, Rathnapura, and Colombo, as well as among individual households in each district. The effects of different cooking methods on the Se content indicate that the level of Se (μg/kg) in fried chicken (30.45 - 52.49) is less than that in a chicken curry (61.38 - 84.25). The percentage loss of Se during cooking for chicken, dahl (Lens culinaris) and Gotukola (Centella asiatica) were 89.6%, 84.1%, and 79.9% respectively. The present study revealed that Se content in Sri Lankan menus provides the required Se for people. However, the different methods of cooking indicate that there is a loss of Se during cooking.Item Gestational diabetes mellitus and risk of type 2 diabetes 10 years after the index pregnancy in Sri Lankan women—A community based retrospective cohort study(PLOS ONE, 2017, DOI: 10.1371/journal.pone.0179647 /http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0179647&type=printable, 2017) Herath, H.; Herath, R.; Wickremasinghe, R.Background Women with a history of gestational diabetes mellitus (GDM) have an increased risk of type 2 diabetes mellitus (T2DM) later in life compared to women with no GDM. This study was aimed to determine the risk of developing T2DM 10 years after GDM in Sri Lankan women. Methods A retrospective cohort study was conducted in the Colombo district, Sri Lanka. 7205 women who delivered a child in 2005 were identified through Public Health Midwives in the field. Women with antenatal records were interviewed and relevant data were extracted from medical records to identify potential participants. One hundred and nineteen women who had GDM and 240 women who did not have GDM were recruited. Current diagnosis of diabetes was based on history, relevant medical records and blood reports within the past 1 year. Results The mean duration of follow up was 10.9 (SD = 0.35) years in the GDM group and 10.8 (SD = 0.31) years in the non-GDM group. The incidence density of diabetes in the GDM group was 56.3 per 1000 person years compared to 5.4 per 1000 person years in non GDM group giving a rate ratio of 10.42 (95% CI: 6.01–19.12). A woman having GDM in the index pregnancy was 10.6 times more likely to develop diabetes within 10 years compared to women with no GDM after controlling for other confounding variables. Delivering a child after 30 years, being treated with insulin during the pregnancy and delivering a baby weighing more than 3.5 Kg were significant predictors of development of T2DM after controlling for family history of diabetes mellitus (DM), GDM in previous pregnancies, parity and gestational age at delivery. Conclusions Women with GDM had a 10-fold higher risk of developing T2DM during a 10-year follow up period as compared to women with no GDM after controlling for other confounding variables.Item Host gene expression analysis in Sri Lankan melioidosis patients.(PLoS Negl Trop Dis 11(6), 2017) Krishnananthasivam, S.; Jayathilaka, N.; Sathkumara, H.D.; Corea, E.; Natesan, M.; De Silva, A.D.Melioidosis is a life threatening infectious disease caused by the gram-negative bacillus Burkholderia pseudomallei predominantly found in southeast Asia and northern Australia. Studying the host transcription profiles in response to infection is crucial for understanding disease pathogenesis and correlates of disease severity, which may help improve therapeutic intervention and survival. The aim of this study was to analyze gene expression levels of human host factors in melioidosis patients and establish useful correlation with disease biomarkers, compared to healthy individuals and patients with sepsis caused by other pathogens.Item Synthesis, Optimization, and Performance Demonstration of Electrospun Carbon Nanofiber–Carbon Nanotube Composite Sorbents for Point-of-Use Water Treatment(American Chemical Society., 2016) Peter, K.T.; Vargo, J.D.; Rupasinghe, T.P.; De Jesus, A.; Tivanski, A.V.; Sander, E.A.; Myung, N.V.; Cwiertny, D.M.We developed an electrospun carbon nanofiber–carbon nanotube (CNF–CNT) composite with optimal sorption capacity and material strength for point-of-use (POU) water treatment. Synthesis variables including integration of multiwalled carbon nanotubes (CNTs) and macroporosity (via sublimation of phthalic acid), relative humidity (20 and 40%), and stabilization temperature (250 and 280 °C) were used to control nanofiber diameter and surface area (from electron microscopy and BET isotherms, respectively), surface composition (from XPS), and strength (from AFM nanoindentation and tensile strength tests). Composites were then evaluated using kinetic, isotherm, and pH-edge sorption experiments with sulfamethoxazole (log Kow = 0.89) and atrazine (log Kow = 2.61), representative micropollutants chosen for their different polarities. Although CNFs alone were poor sorbents, integration of CNTs and macroporosity achieved uptake comparable to granular activated carbon. Through reactivity comparisons with CNT dispersions, we propose that increasing macroporosity exposes the embedded CNTs, thereby enabling their role as the primary sorbent in nanofiber composites. Because the highest capacity sorbents lacked sufficient strength, our optimal formulation (polyacrylonitrile 8 wt %, CNT 2 wt %, phthalic acid 2.4 wt %; 40% relative humidity; 280 °C stabilization) represents a compromise between strength and performance. This optimized sorbent was tested with a mixture of ten organic micropollutants at environmentally relevant concentrations in a gravity-fed, flow-through filtration system, where removal trends suggest that both hydrophobic and specific binding interactions contribute to micropollutant uptake. Collectively, this work highlights the promise of CNF–CNT filters (e.g., mechanical strength, ability to harness CNT sorption capacity), while also prioritizing areas for future research and development (e.g., improved removal of highly polar micropollutants, sensitivity to interfering cosolutes).Item Dissolution and aggregation of zinc oxide nanoparticles at circumneutral pH; a study of size effects in the presence and absence of citric acid(The University of Iowa, ProQuest Dissertations., 2011) Rupasinghe, R.A.Understanding the size dependent dissolution of engineered nanoparticles is one important aspect in addressing the potential environmental and health impacts of these materials as well as their long-term stability. In this study, experimental measurements of size dependent dissolution of well-characterized zinc oxide (ZnO) nanoparticles with particle diameters in the range of 4 to 130 nm have been measured and compared at circumneutral pH (pH 7.5). Enhanced dissolution was found for the smaller particles with the largest enhancement observed in Zn2+(aq) concentrations for 4 nm diameter ZnO nanoparticles compared to larger-sized particles. Interestingly, size dependent dissolution was observed even though the nanoparticles aggregated with hydrodynamic diameters on the order of 1-3 µm in diameter. Although these results are found to be in qualitative agreement with theoretical predictions used to predict the dissolution of solids, a linearized form of the Kelvin equation to calculate a bulk dissolution value for ZnO and a surface free energy yielded quantities inconsistent with known literature values. It is therefore concluded that deviations from solubility behavior from classical thermodynamics are due to a lack of the detailed knowledge of the surface free energy as well as its dependence on the details of the surface structure, surface properties, including the presence of different surface crystal facets and adsorbed ligands, as well of aggregation state. The presence of citric acid significantly enhances the extent of ZnO dissolution for all sizes such that no significant differences were observed for total Zn2+(aq) concentrations for nanoparticles between 4 to 130 nm. This can be attributed to ligand enhanced dissolution of ZnO nanoparticles where there is no dependence on size. PREVIEW v Adsorption of citrates onto ZnO nanoparticles was observed using ATR-FTIR spectroscopy. A reversal of surface charge of ZnO nanoparticles was observed upon adsorption of citrates. Adsorption of negatively charged Cit3- onto ZnO nanoparticles make the surfaces negatively charged and this result in a repulsion between nanoparticles eventually leading to a lesser extent of aggregation. Formation of a stable suspension was also observed in the presence of citric acid. These trends observed in aggregation pattern are of great environmental and biological importance as citric acid is abandon in the environment as well as in human body.Item Nanocrystals of a Metal–Organic Complex Exhibit Remarkably High Conductivity that Increases in a Single-Crystal-to-Single-Crystal Transformation(American Chemical Society., 2014) Hutchins, K.M.; Rupasinghe, T.P.; Ditzler, L.R.; Swenson, D.C.; Sander, J.R.G.; Baltrusaitis, J.; Tivanski, A.V.; MacGillivray, L.R.Ag(I) is used to form a π-stacked metal–organic solid that exhibits remarkably high electrical conductivity. The solid undergoes a single-crystal-to-single-crystal [2+2] photodimerization to generate a 1D coordination polymer with over 40% higher conductivity. The Ag(I) complex represents the first example of an increase in conductivity resulting from a [2+2] photodimerization. Density of states calculations show a higher contribution from Ag(I) ions to the valence band in the photodimerized solid, supporting the increase in conductivity.Item Dissolution of ZnO nanoparticles at circumneutral pH: a study of size effects in the presence and absence of citric acid(American Chemical Society., 2011) Mudunkotuwa, I.A.; Rupasinghe, T.; Ming Wu, C.; Grassian, V.H.Understanding size-dependent processes, including dissolution, of engineered nanoparticles is essential in addressing the potential environmental and health impacts of these materials as well as their long-term stability. In this study, experimental measurements of size-dependent dissolution of well-characterized zinc oxide (ZnO) nanoparticles with particle diameters in the range of 4 to 130 nm have been measured at circumneutral pH (pH 7.5) and compared. Dissolution was found to be enhanced with smaller ZnO nanoparticles compared to larger-sized particles, even though the nanoparticles were present in solution as aggregates with hydrodynamic diameters on the order of 1–3 μm in size. The presence of citric acid significantly enhanced the extent of ZnO dissolution for all sizes, and the greatest enhancement was observed for the 4 nm particles. Although these results are found to be in qualitative agreement with theoretical predictions, a linearized form of the Kelvin equation to calculate a surface free energy yielded quantities inconsistent with expected values from the literature. Reasons for this inconsistency are discussed and include potential deviations of solubility behavior from classical thermodynamics as a result of a lack of detailed knowledge of surface structure and surface properties, including the presence of different surface crystal facets, and the aggregation state.