Volume 6(1)

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Now showing 1 - 5 of 11
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    Sensitivity of Dengue Fever Transmission Model with respect to Parameters
    (Eastern University, Sri Lanka, 2009) S. S. N. Perera
    Dengue is the most common mosquito-borne viral disease in human. Motivated by the failure of current methods to control dengue fever, we study the sensitivity of the dynamics of the dengue transmission model with respect to parameters with aim to identify the most important parameters in order to control dengue. Three dimensional model (consisting susceptible, infective host population and infective vector population) is considered. Deriving the sensitivity equation we study the variation of the host/vector infective population with respect to parameters. Effective contact rates (human to vector and vector to human), death rate of vector population and the probability of susceptible host can permanently be immunized are considered as parameters. Results report that variation of the dynamics of the model with respect to these parameters is significant on the control point of view.
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    First record of new exotic Mealybug species, Phenacoccus solenopsis Tinsley, 1898 (Hemiptera: Pseudococcidae), its Host range and abundance in the Eastern Sri Lanka.
    (Eastern University, Sri Lanka, 2009) M. Prishanthini, M. Vinobaba
    Mealybugs (Hemiptera: Pseudococcidae) are a small group of sap sucking insect pests which cause severe economic damage to wide range of homegarden, horticultural and field crops. Therefore, a survey of mealybugs in Batticaloa District of Eastern Sri Lanka was conducted to gather information on their species composition, distribution and pest status. Among the different species identified, the cotton mealybug, Phenacoccus solenopsis Tinsley was found to be the predominant species comprising about 70% of the collected specimens. This species has not been previously reported to occur in Sri Lanka. It now appears to be widespread in the Eastern parts of the country. This is an exotic species originated from USA. The new mealybug was identified by the authors and confirmed as Phenacoccus solenopsis Tinsley by Dr.C.J.Hodgsn, Department of Biodiversity and Systemic Biology, National museum of Wales, Cardiff, Wales, UK. This first record of P.solenopsis in Sri Lanka, where it was found infesting mainly on shoe flower plants Hibiscus rosa-sinensis. The description of the adult female cotton mealybug is presented in this paper. Samples were collected from twenty five different locations within the study area and twenty six plant species from ten different families were recorded as hosts with various levels of infestations. In addition the abundance of P.solenopsis on the shoe flower plant, which is the major hosts in the homegardens, shows a clear seasonal variation and during the period of study two generations were found. Among the climatic factors, rain fall affects significantly on the abundance of this species. The implications of the introduction of this exotic polyphagous pest species and its potential threat to agriculture in Sri Lanka are discussed in this paper.
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    Antimicrobial activity of Trichoderma polysporum
    (Eastern University, Sri Lanka, 2009) R. Kapilan, A. C. Thavaranjit
    Antibiotics producing microorganisms found in nature are not only use full in medicinal purposes but are very useful in plant disease management, enzyme production, etc. Trichoderma sp. Is one of the most common genera of fungi in soils and other natural habitat consisting of organic matter. Trichoderma sp. was isolated from soil and characterized into 8 different isolates based on colony, vegetative and reproductive structures. Antifungal and antimicrobial activities of those activities of those isolates were studied against Pythium ultinum, Rhizoctonia solani, Fusarium oxyporium, Bacillus sp. Escherichia coli, Pseudomonas sp. and Streptococcus sp. One of the isolates (Isolate No.5) showed marked effect on antimicrobial activity against Rhizoctonia solani, Bacillus sp. and Pseudomonas sp. and isolate was identified as Trichoderma polysporum. Further studied on fungal, bacterial, protozoan and nematode bioassay was done by using the crude extract of Trichoderma polysporum in methanol and distilled water. Antifungal compound was effective in methanol extract where as antibacterial compound was effective in water extract. The organism produced volatile and water soluble antibiotics and showed significant inhibition on the formation of sclerotia of Rhizoctonia solani. Antiprotozoan activity was also observed but there was no effect on the motility of nematode. The enzyme amylase which is widely used in the industries was also produced by this organism
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    Comparision of Parasites fauna of economically important fish from Batticaloa lagoon
    (Eastern University, Sri Lanka, 2009) V. Sujarajini, P. Vinobaba
    This study focused on a comparison of the parasite fauna in several different economically important fish such as Etroplus suratenscis, Tachysurus spp., Glossogobius giuri, Ophiocephalus striatus, Oreochromis mossambicus and Ambassis commersoni at two locations within Batticaloa lagoon. Ergasilus parvitergum, Dermoergasilus amplectens, Caligus curtus, Lernaenicus sparatte, Procamellanous lonis and Acanthocephala sp., were the most common, and the occurrence of parasites among the fin fishes of Batticaloa lagoon was wide spread. The parasite genera E. parvitergum were the most prevalent on Etroplus suratensis whereas P. lonis and C. curtus was more common on Glossogobius giuris, whilst L. sparatte was more common on Oreochromis mossambicus; C. curtus and D. amplectens on Ambassis commersoni, and Acanthocephala sp. and P. lonis were more common on Tachysurus.
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    Predicting three-dimensional fractal dimensions of electrical discharges using two-dimensional projections
    (Eastern University, Sri Lanka, 2009) D. Amarasinghe, U. Sonnadara
    Three dimensional electrical discharge patterns are simulated to compare the three dimensional structure with the two-dimensional projections of the same. The discharge patterns are simulated using a stochastic dielectric breakdown model. Fractal techniques are used to characterize the morphological structures of the simulated discharge patterns. The discharge patterns are simulated on a 50x50x50 cubic lattice and the fractal dimensions in both three-dimensions and two-dimensions are estimated using the sand box fractal dimension estimation method. The complexity of the simulated electrical tree patterns is strongly dependent on the exponent of the cell potential 'rj'. When the value of the exponent was increased, the growth patterns effectively lost their fractal structure and became a curve with dimension 1. The fractal dimension of the three-dimensional growth patterns and two-dimensional projections when the exponent is close to unity (?1&1) are 1.84 and 1.53 respectively. A strong linear correlation was found between the simulated three-dimensional structures and their two-dimensional projections when the dimension is less than 2. This relation can be used to estimate the three-dimensional fractal dimension from two-dimensional views of complex electrical discharges.