Dynamics of magnetized string cosmological model in f(R,T) gravity theory     

Shri Ram  S. Chandel 《Astrophysics and Space Science》2015,355(1):195-202

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Bianchi type-II string-dust universes     

Shri Ram  Prem Singh 《Astrophysics and Space Science》1992,192(2):335-338

We present an exact solution of Einstein's equations for cosmological models of Bianchi type-II filled with string dust as the source for the gravitational field. The solution represents an expanding and anisotropic universe which would give essentially an empty universe for large time. Some kinematical properties of the solution are discussed.  相似文献   

Inhomogeneous Plane Symmetric Models in a Scalar-Tensor Theory     

Shri Ram  S.K. Tiwari 《Astrophysics and Space Science》1998,259(1):91-97

For the general plane symmetric metric, some exact solutions of Einstein field equations in the scalar tensor theory developed by Saez and Ballestev are presented in vaccum and in the presence of stiff fluid. The physical and kinematical features of the models are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Early Viscous Fluid Cosmological Model with Zero-Rest-Mass Scalar Fields     

Shri Ram  C.P. Singh 《Astrophysics and Space Science》1998,260(4):541-549

Einstein field equations are considered for zero-curvature Robertson-Walker models in the case of a viscous fluid distribution interacting with zero-rest-mass scalar fields. Exact solutions are obtained for two different phases of the early universe viz. the inflationary phase and the radiation-dominated phase, by using the 'gamma-law' equation of state p = (-1). The index describing the material content varies continuously with cosmological time. The gravitational 'constant' and bulk viscosity are both allowed to depend on the cosmic time. Some physical properties of the cosmological models are also discussed.  相似文献   

Late Cenozoic geological development of the south Vøring margin,mid-Norway     

L. Rise  S. Chand  B.O. Hjelstuen  H. Haflidason  R. Bøe 《Marine and Petroleum Geology》2010

Late Cenozoic seismic stratigraphy of the Vøring continental margin has been studied in detail, with emphasis on the geological development of the Naust Formation deposited during the last 3 million years. The Kai Formation (15–3 Ma) comprises mainly biogenic ooze deposited in the Møre and Vøring Basins. In Naust time, there was a marked increase in supply of sediments from the inner shelf areas and the western part of the Scandinavian mountain range, and glaciers expanded to the shelf and reached the shelf edge several times during the last 1.5–2 million years. During early to mid Naust time the shelf was widened by westerly prograding sediment units, but for a long period the shallowest part of the Helland-Hansen Arch (HHA) formed a barrier preventing glacially derived debris from being distributed farther west. West of the HHA, mainly stratified marine and glacimarine sediments were deposited. A substantial part of these sediments were transported by the north-flowing Norwegian Atlantic Current, which redistributed suspended particles from ice streams, rivers, coastal erosion and seabed winnowing. After burial of the crest of the HHA at c. 0.5 Ma, glacial debris and slide deposits were also deposited west of this high. In the north, massive units of glacial debris were distributed beyond the crest of the HHA, also in mid Naust time, thinning westwards and interfingering with fine-grained sediments on the lower slope. The Sklinnadjupet Slide, inferred to be c. 250,000 years old, corresponds in age with an earlier huge slide in the Storegga area. An elongated area of uneven seabed topography previously interpreted as diapirs (Vigrid diapirs) on the slope west of the HHA is shown to be formed by ooze eruption from the crest of the arch and submarine sliding.  相似文献   

Re-Analysis of QPO in 3C 273 Light Curve     

P. Mohan  A. Mangalam  Hum Chand  Alok C. Gupta 《Journal of Astrophysics and Astronomy》2011,32(1-2):117-120

We have developed analysis tools to search for quasi periodic oscillations in light curves from active galactic nuclei, using the following time series techniques: Wavelets, periodogram, Lomb–Scargle periodogram, structure function and multi-harmonic analysis of variance. The analysis tools incorporate different noise models with significant levels for all the techniques that is an improvement over the previous work. By looking for consistently high significance, we make the detection of periodicities more robust. We apply this tool to a previously reported QPO (Espaillat et al. 2008) in the X-ray light curve of 3C 273 with a periodicity of ~3300 s and find that the significance is only 74% in the wavelet and fails to show up above 95% significance in the periodogram and multi-harmonic analysis of variance.  相似文献   

Emissions from grassland burning in Kaziranga National Park,India – analysis from IRS-P6 AWiFS satellite remote sensing datasets     

K. V.S. Badarinath  T. R. Kiran Chand  V. Krishna Prasad 《国际地球制图》2013,28(2):89-97

Biomass burning from vegetation fires is an important source of greenhouse gas emissions. In this study, we quantify biomass burning emissions from grasslands from the highly sensitive Kaziranga National Park, Assam, Northeast India. Most of the fires in the park are ‘controlled burning fires’ set by the park officials for management purposes. We evaluated the short-term impacts of fires and the resulting air pollution through integrating biomass burnt information from satellite remote sensing datasets. IRS-P6 Advanced Wide Field Sensor (AWiFS) data during March and April corresponding to dry season were evaluated to delineate the burnt areas. These burnt area estimates were then integrated with biomass data and emission factors for quantifying the greenhouse gas emissions. Results suggested that of the total study area of 37,822 ha, nearly 3163.282 ha has been burnt during March, 2005. Within one month, the burnt area increased to 7443.92 ha by April, i.e., from 8.36% to 19.68%. In total, biomass burning from the grasslands contributed to 29.65 Tg CO₂, 1.19 Tg CO, 0.071 Tg NOx, 0.042 Tg CH₄, 0.0625 Tg total non-methane hydrocarbons, 0.152 Tg of particulate matter, and 0.062 Tg of organic carbon and 0.008 Tg of black carbon during April. The importance of ‘fire’ as a management tool for maintaining the wildlife habitat has been highlighted in addition to some of the adverse affects of air pollution resulting from such management practices. The results from this study will be useful to forest officials as well as policy makers to undertake some sustainable forest management practices to maintain an ideal habitat for Kaziranga's wildlife.  相似文献   

Hypersurface-homogeneous bulk viscous fluid space–times with time-dependent cosmological term     

M. K. Verma  Shri Ram 《Astrophysics and Space Science》2010,326(2):299-304

Some hypersurface-homogeneous cosmological models with bulk viscous fluid and time-dependent cosmological term are investigated. These expanding, shearing and non-rotating cosmological models of the universe evolve from initial big-bang singularities and give an essentially empty space for large times. Some physical and geometric behaviors of these models are also discussed.  相似文献   

Bulk viscous fluid hypersurface–homogeneous cosmological models with time varying G and Λ     

Shri?Ram  M. K. Verma 《Astrophysics and Space Science》2010,330(1):151-156

Hypersurface–homogeneous cosmological models containing a bulk viscous fluid with time varying G and Λ have been presented. We have shown that the field equations are solvable for any arbitrary cosmic scale function. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of the energy density. Exact solutions of Einstein’s field equations are obtained which represent an expanding, shearing and accelerating/decelerating models of the universe. The physical and kinematical behaviours of the models are also discussed.  相似文献   

Geophysical expression of natural recharge in different geological terrains     

Hodlur GK  Singh UK  Das RK  Rangarajan R  Chand R  Singh SB 《Ground water》2003,41(6):857-866

Behavior of the Dar-Zarrouk parameters--longitudinal unit conductance, transverse unit resistance, longitudinal resistivity, and transverse resistivity--has been compared with the behavior of the natural recharge in two geological terrains. Contour patterns of the geophysical parameters and those of natural recharge have been analyzed and a qualitative relation in their behavior was recognized. Graphical comparison of the geophysical and hydrogeological parameters clearly illustrates a qualitative relationship between the two parameters. Use of such qualitative relation in the field of ground water exploration and management studies is explained. A modest beginning is attempted to arrive at a quantitative relation between natural recharge and Dar-Zarrouk parameters.  相似文献