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Sen A.K.,Assam University | Polcaro V.F.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Dey I.,Gc College | Gupta R.,Inter-University Center for Astronomy and Astrophysics
Astronomy and Astrophysics | Year: 2010

Context. The small compact isolated dark clouds also known as "Bok globules" are believed to be ideal sites for low-mass star formation. Some of these clouds are undergoing gravitational collapse, and the ambient magnetic field plays a key role in collapse dynamics. The background star polarimetry is generally accepted as a good tool to map the magnetic field, which is responsible for the alignment of dichroic grains that produce polarization. Aims. The background star polarization when studied together with extinction is expected to help us to understand various grain properties and the role of polarimetry as a tracer of magnetic field in these star-forming clouds. With this idea, polarization and colour excess E(B-V) values for a set of background stars have been studied together to understand various astrophysical process in some star-forming dark clouds. Methods. Optical photometric observations of the three clouds CB3, CB25, and CB39 were carried out at the 2 m H.C. Telescope, India, to determine the colour excess E(B-V) of the background stars by following a technique adopted by Bernabei & Polacaro (2001, A&A, 371, 123). These three clouds were selected from a set of eight clouds previously observed by us in optical polarimetry (Sen et al. 2000, A&AS, 141, 175). Further independent spectroscopic measurements of a few selected sample stars were recently carried out during February and March 2010 from 1.52 m Cassini Telescope, Loinao, Italy, to confirm the correctness of estimated E(B-V) values obtained by this photometric technique. Results. The colour excess E(B-V) values so obtained were compared with optical polarization values obtained for the same set of stars. It was found that the measured extinction values increase with the increase in percentage polarization for the cloud CB39 and to some extent for CB25. However, for cloud CB31 no such correlation was observed. It is normally expected that the grains causing extinction should also cause polarization of the light from background stars. Any possible deviation from this under different circumstances here has been discussed in the light of the ongoing physical processes in the star-forming clouds. © 2010 ESO. Source


Astapati A.D.,Gc College | Das A.K.,Assam University
International Journal of Ecology and Environmental Sciences | Year: 2010

Present study was undertaken to estimate the seasonal variations in biomass, primary productivity and dry matter transfer in a successional grassland dominated by Imperata cylindrica at Dargakona, Barak Valley, northeast India. Monthly changes in live shoot biomass exhibited a uni-modal growth pattern during the study period. Live shoots biomass during September- October was: 606.96 to 840.88 g m-2 in burnt plot; 853.75 to 511.94 g m -2 in unburnt plot. Use of fire as grassland management tool stimulated significant accumulation of belowground biomass; found as maximum in burnt plots (1368.44 g m-2). Annual aboveground net production ranged from 653.26 to 877.96 g m-2 in burnt plot and 527.12 to 936.08 g m-2 in unburnt plot. The belowground net production was: 973.79 to 1326.65 g m-2 (burnt plot) and 764.47 to 981.34 g m-2 (unburnt plot). A greater accumulation of belowground biomass and faster recycling through decomposition was found as an adaptation to maintain the grassland ecosystem. The grassland system showed net accumulation of surplus dry matter as total organic matter input into the system was greater than the total output. Imperata grassla nd was found to be serai in nature, which is maintained under the indigenous management system of farming community. © NATIONAL INSTITUTE OF ECOLOGY, NEW DELHI. Source


Das K.N.,National Institute of Technology Silchar | Chaudhuri B.,Gc College
Advances in Intelligent and Soft Computing | Year: 2012

The maximum independent set problem (MISP) is to find the largest subset of vertices of a graph such that none of these vertices are connected by an edge (i.e., all vertices are independent of each other). It has many real life applications. In solving MISP, especially where the complexity of the graph increases, exact methods become impractical or sometimes become too slow to provide a solution. In those cases, the evolutionary heuristics are being successfully used by many researchers. In this paper, a critical review of different existing approaches in evolutionary methods to solve MISP, has been made. Later, some of the future scopes are being presented. © 2012 Springer India Pvt. Ltd. Source


Sharma G.D.,Assam University | Deb B.,Gc College
Journal of Pure and Applied Microbiology | Year: 2012

Three different types of nitrogen fixing bacteria viz, Azotobacter vinelanduii, Bacillus polymyxa and Pseudomonas fluorescens were isolated from rhizosphere of field-grown sugarcane in Barak Valley, Assam. On an average highest number of diazotrophs was recorded in rainy season, which was followed by summer season. Lowest number of diazotrophs was observed in winter season. Nitrogenase activity of Azotobacter vinelandii, Bacillus polymyxa and Pseudomonas fluorescence was 403.05, 209.15, 107.80 (nM C2H 2/h/mg protein) respectively. Data obtained in this work will hopefully contribute to future research aimed at developing reliable and effective sugarcane inoculants. Source


Dey S.,St Anthonys College | Goswami S.,Gc College | Dey T.,College of William and Mary
Journal of Health, Population and Nutrition | Year: 2013

The objective of this study is to examine the factors that influence the occurrence of childhood anaemia in North-East India by exploring dataset of the Reproductive and Child Health-II Survey (RCH-II). The study population consisted of 10,137 children in the age-group of 0-6 year(s) from North-East India to explore the predictors of childhood anaemia by means of different background characteristics, such as place of residence, religion, household standard of living, literacy of mother, total children ever born to a mother, age of mother at marriage. Prevalence of anaemia among children was taken as a polytomous variable. The predicted probabilities of anaemia were established via multinomial logistic regression model. These probabilities provided the degree of assessment of the contribution of predictors in the prevalence of childhood anaemia. The mean haemoglobin concentration in children aged 0-6 year(s) was found to be 11.85 g/dL, with a standard deviation of 5.61 g/dL. The multiple logistic regression analysis showed that rural children were at greater risk of severe (OR=2.035; p=0.003) and moderate (OR=1.23; p=0.003) anaemia. All types of anaemia (severe, moderate, and mild) were more prevalent among Hindu children (OR=2.971; p=0.000), (OR=1.195; p=0.010), and (OR=1.201; p=0.011) than among children of other religions whereas moderate (OR=1.406; p=0.001) and mild (OR=1.857; p=0.000) anaemia were more prevalent among Muslim children. The fecundity of the mother was found to have significant effect on anaemia. Women with multiple children were prone to greater risk of anaemia. The multiple logistic regression analysis also confirmed that children of literate mothers were comparatively at lesser risk of severe anaemia. Mother's age at marriage had a significant effect on anaemia of their children as well. © International Centre For Diarrhoeal Disease Research, Bangladesh. Source

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