Homology of covering spaces of symmetric products of a Riemann surface

Homology and cohomology are considered valuable algebraic tools for studying topological spaces. Homology groups of the symmetric product of a Riemann surface were determined by I.G.Macdonald [9] in 1962. The main object of this project is finding the cohomology and homology groups of certain covering spaces of these spaces

Upgrading Sri Lankan natural vein graphite by purification and surface modification

Sri Lanka is well known for high quality vein graphite, containing about 95-98% of pure carbon. Vein graphite in Sri Lanka have been categorized into four structurally distinct graphite varieties, shiny-slippery-fibrous graphite (SSF), needle-platy graphite (NPG), coarse striated-flaky graphite (CSF) and coarse flakes of radial graphite (CFR). Impurity content in different structural type varies depending on the mode of occurrences and nature of graphite vein. Both chemical and physical methods are employed for removing impurities from the graphite. Among them, flotation is a versatile and selective mineral processing technique, which can be used to achieve specific separations from complex ores. Therefore the present study focuses on purification of Sri Lankan natural vein graphite by froth flotation, HCl leaching and alkali roasting followed by surface modification suitable for advance electrical applications. Graphite powder (<75 μm) from Needle Platy Graphite (NPG) and Shiny Slippery Fibrous (SSF) morphological types were used for this study. Initially 200g from both varieties were subjected to froth flotation. For HCl leaching under the chemical purification study, 3g of each graphite sample was treated with 10 vol. % HCl at 650C for 75 minutes. For the alkali roasting, 3g from each graphite sample was mixed with 35vol. % NaOH (solid: liquid = 1:2) separately and roasted at 250 0C under air for one hour. Selected graphite samples having carbon content about 99.9% were used for surface modification. Thermal oxidation was performed at 550 0C in a box furnace under air for 6 hours. Under the chemical method, graphite powder (3 g) was treated with 69% HNO3 (100 ml) under stirring at 60 0C for 24 hours. Carbon percentage of graphite was determined according to ASTM - 561 and weighing the residues. Filtrates were taken from both chemical purification techniques and analyzed by the Atomic Absorption Spectroscopy (AAS) technique. Both purified and modified graphite samples were characterized by Fourier Transform Infrared (FTIR) spectrophotometer (Nicolet 6700). The electrical conductivity measurements were performed by the d.c. four probe technique. The results revealed that the froth flotation could not make a considerable influence on purification, in contrast, both the acid leaching and alkali roasting methods revealed that Sri Lankan natural vein graphite can be purified over 99% carbon content. The surface modification study shows the formation of oxidized species on the graphite surface and the surface modification by chemical oxidation has a higher effect than the thermal oxidation. Both of the investigated graphite varieties reveal the possessing of electrical conductivity in the semi-conductivity range. Further the purification process improves the electrical conductivity, though it slightly decreases with surface modification

Leaching of fluoride from biotite mica in soil : implications for fluoride in shallow groundwater

Leaching of F− from biotite was investigated at room temperature by performing a series of short-term leach tests. The leaching of F− from biotite structure strongly depends on its weathering stage. Results of this study suggest that high concentration of F− is leached from highly weathered biotite, compared to fresh biotite. Results of dissolution experiments confirm that the organic acids in soil promote the leaching of F− from biotite compared to inorganic acids. Citric acid which is a week organic acid enhances leaching of F− from biotite structure compared to strong inorganic acid HNO3, independent of the weathering stage of biotite. Strong positive correlation between K+ and Fe2+ with F− in biotite treated with citric acid suggests that F− readily leachs into the solution through an ionic exchange and complex formation. Organic acids involve sorption and complex formation processes leading to release of F− into the solution. Our studies suggest that in the presence of organic acids F− is leached readily into water percolating through the soil. Therefore, shallow groundwater replenished by the water table may achieve high F− concentrations by this leaching process

Sedimentary signatures on the eastern coast of Sri Lanka: preliminary findings

Undisturbed sediment compiles are invaluable samples in the reconstruction of ancient depositional environments. Basically coastal sedimentation is significant as it preserves the eustatic and isostatic records as well as seasonal climate records. Present study concerns on sedimentology of recent sediments of a part of the eastern coastal lagoon area of Sri Lanka to interpret the depositional history. Spatial extent of sediments was studied by field mapping. Gradation analysis and morphology of sediments were used to identify the depositional history of sediments. The results revealed that the spatial extent of the recent sediment deposition is about 4km wide band from the present coast line including the lagoon environment that overlaid the weathered residual soil. Top sediments (up to 1m) are characterized by different layers with several depositional histories and did not indicate any remarkable clayey layer even though the locations are near to a river input and within the flood level. It can be said the inorganic input is prominent than the organic input in the eastern coastal sedimentation. The results need to be proved by other geochemical and age dating proxies

An overview of heavy metal contamination in coastal sediments of Sri Lanka

Coastal sediments are often subjected to heavy metal contamination as they reside at the marginal environments of anthropological water releases. These sediments provide the habitat for marine aquatic life of seafood. Therefore, heavy metal contamination in coastal sediments is one of the major environmental concerns. The coastal belt of Sri Lanka is highly urbanized with high population (59% of Sri Lankan population) and is mostly depend on the sea. Therefore, anthropogenic inputs of pollutants in to the marine environments have been increased during last decades.  Heavy metal contamination of the coastal sediments of Sri Lanka has been discussed by several studies, focusing on selected coastal regions. In this article, previous studies have been reviewed in order to understand the contamination status and ecological risks due to heavy metal accumulations. Despite the sampling location, the elemental distribution of coastal lagoonal sediments shows similar trend indicating the dominance of natural elemental sources rather the anthropogenic influences. The concentrations of As and Cr in sediments are high compared to the upper continental crust values which is a characteristic feature in possible source rocks, soils and sediments of Sri Lanka. The results of the previous studies indicate that coastal sediments are low to moderately contaminated but not at ecological risk. However, anthropogenic activities are highly variable across the coastal regions. Since limited results of the previous studies is not enough to get an overview of the heavy metal concentrations around the island, urgent need for a spatial and temporal geochemical database for coastal sediments of Sri Lanka is emphasized.Keywords: Contamination, coastal, metals and sediment

State estimation for dynamic weighing using Kalman filter

Dynamic weighing has become an essential requirement in a diverse range of industries. Dynamic weighing is different from static weighing in that static weighing involves determining the weight while the product being weighed is stationary whereas dynamic weighing weighs the products while they are moving. Force sensors are commonly used in these weighing systems. In static weighing, the weighed object is placed stationary on the platform and the steady state of the sensor signal is used to assess the weight. However, in dynamic weighing the sensor signal may not reach the steady state during the brief time of weighing, hence the weight is assessed for example, by averaging the tail end of the signal after it has been through a low-pass filter. The resulting mass estimates can be inaccurate for faster heavier items. It is useful to consider better ways of estimating the true weight, in high speed weighing applications. The proposed method is to employ the 1-D Kalman filter algorithm to estimate the optimal state of the signal. The improved steady state signal is then used in weight estimation. The proposed method has been tested using data collected from a loadcell when different masses pass over the loadcell. The results show a significant improvement in the filtered signal quality which is then used to improve the weight assessment