Bianchi type-V perfect fluid space-time models in general relativity     

C. P. Singh  Shri Ram  Mohd. Zeyauddin 《Astrophysics and Space Science》2008,315(1-4):181-189

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Cosmological models in alternative theory of gravity with bilinear deceleration parameter     

R. K. Mishra  Avtar Chand 《Astrophysics and Space Science》2016,361(8):259

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Eddy covariance based methane flux in Sundarbans mangroves,India   总被引：1，自引：0，他引：1  

Chandra Shekhar Jha  Suraj Reddy Rodda  Kiran Chand Thumaty  A K Raha  V K Dadhwal 《Journal of Earth System Science》2014,123(5):1089-1096

We report the initial results of the methane flux measured using eddy covariance method during summer months from the world’s largest mangrove ecosystem, Sundarbans of India. Mangrove ecosystems are known sources for methane (CH₄) having very high global warming potential. In order to quantify the methane flux in mangroves, an eddy covariance flux tower was recently erected in the largest unpolluted and undisturbed mangrove ecosystem in Sundarbans (India). The tower is equipped with eddy covariance flux tower instruments to continuously measure methane fluxes besides the mass and energy fluxes. This paper presents the preliminary results of methane flux variations during summer months (i.e., April and May 2012) in Sundarbans mangrove ecosystem. The mean concentrations of CH₄ emission over the study period was 1682 ± 956 ppb. The measured CH₄ fluxes computed from eddy covariance technique showed that the study area acts as a net source for CH₄ with daily mean flux of 150.22 ± 248.87 mg m^?2 day^?1. The methane emission as well as its flux showed very high variability diurnally. Though the environmental conditions controlling methane emission is not yet fully understood, an attempt has been made in the present study to analyse the relationships of methane efflux with tidal activity. This present study is part of Indian Space Research Organisation–Geosphere Biosphere Program (ISRO–GBP) initiative under ‘National Carbon Project’.  相似文献   

String cosmological models of Bianchi type-III     

J. K. Singh  Shri Ram 《Astrophysics and Space Science》1996,246(1):65-72

A technique to generate new exact Bianchi type-III cosmological solutions of massive strings in the presence of magnetic field is presented. Starting from Tikekar and Patel's strings models in the absence and presence of the magnetic field, new solutions are obtained. Some of their physical features are discussed.  相似文献   

Gas hydrate stability zone modelling in areas of salt tectonics and pockmarks of the Barents Sea suggests an active hydrocarbon venting system     

S. Chand  J. Mienert  K. Andreassen  J. Knies  L. Plassen  B. Fotland 《Marine and Petroleum Geology》2008,25(7):625-636

The Barents Sea seabed exhibits an area of major glacial erosion exposing parts of the old hydrocarbon basins. In this region, we modelled the gas hydrate stability field in a 3D perspective, including the effects of higher order hydrocarbon gases. We used 3D seismic data to analyse the linkage between fluid-flow expressions and hydrate occurrences above old sedimentary basin systems and vertical faults. Pockmarks showed a relation to fault systems where some of them are directly connected to hydrocarbon bearing sedimentary formations. The influence of bottom water temperature, pore water salinity and geothermal gradient variation on gas hydrate stability zone (GHSZ) thickness is critically analysed in relation to both geological formations and salt tectonics. Our analysis suggests a highly variable GHSZ in the Barents Sea region controlled by local variations in the parameters of stability conditions. Recovery of gas-hydrate sample from the region and presence of gas-enhanced reflections below estimated BSR depths may indicate a prevalent gas-hydrate stable condition.  相似文献   

Gravitational instability for some astrophysical systems     

R. C. Sharma  Trilok Chand 《Astrophysics and Space Science》1991,183(2):215-224

The gravitational instability of an infinite homogeneous self-gravitating mixture through porous medium in the presence of a variable horizontal magnetic field varying in vertical directions has been considered to include, separately, the effects due to suspended particles and collisions between ionized and neutral components. The dispersion relations in both cases have been obtained. It has been found that Jeans's criterion of instability holds good even if the effects due to suspended particles, collisions, porosity, and variable magnetic field are considered.  相似文献   

Bianchi type-VI0 cosmological models in certain theories of gravitation     

Shri Ram  Prem Singh 《Astrophysics and Space Science》1993,200(1):35-46

Exact Bianchi type-VI₀ cosmological solutions to Einstein's equations are presented in vacuum and for stiff-matter in the normal gauge for Lyra's geometry and in scalar-tensor theories developed by Saez and Ballester (1985) and Lau and Prokhovnik (1986). Also cosmological solutions are obtained for pure massive strings (p-strings) and for pure geometric strings. The dynamical behaviour of the models have been discussed.  相似文献   

Dimensionality reduction of hyperspectral data using spectral fractal feature     

Kriti Mukherjee  Jayanta Kumar Ghosh  Ramesh Chand Mittal 《国际地球制图》2013,28(6):515-531

A new approach for dimensionality reduction of hyperspectral data has been proposed in this article. The method is based on extraction of fractal-based features from the hyperspectral data. The features have been generated using spectral fractal dimension of the spectral response curves (SRCs) after smoothing, interpolating and segmenting the curves. The new features so generated have then been used to classify hyperspectral data. Comparing the post classification accuracies with some other conventional dimensionality reduction methods, it has been found that the proposed method, with less computational complexity than the conventional methods, is able to provide classification accuracy statistically equivalent to those from conventional methods.  相似文献   

Training Workshop on Quaternary Setup of Arid NW Himalaya: Main focus on Ladakh     

Yogesh Ray  Naresh Rana  Zaheed Majid  Pritam Chand 《Journal of the Geological Society of India》2012,80(6):874-875

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Some Kaluza-Klein cosmological models in f(R,T) gravity theory     

Shri Ram  Priyanka 《Astrophysics and Space Science》2013,347(2):389-397

Algorithms are derived for constructing five dimensional Kaluza-Klein cosmological space-times in the presence of a perfect fluid source in the framework of f(R,T) gravity theory proposed by Harko et al. (Phys. Rev. D 84:024020, 2011). Starting from the solution of Reddy et al. (Int. J. Theor. Phys 51:3222-3227, 2012b) some classes of new solutions are generated which correspond to accelerating models of the Universe. The physical and kinematical behaviors of the models are studied.  相似文献