共查询到20条相似文献,搜索用时 34 毫秒
1.
S. K. Tripathy S. K. Nayak S. K. Sahu T. R. Routray 《Astrophysics and Space Science》2009,321(3-4):247-252
LRS Bianchi type-I string cosmological models are studied in the frame work of general relativity when the source for the energy momentum tensor is a bulk viscous stiff fluid containing one dimensional strings embedded in electromagnetic field. The bulk viscosity is assumed to be inversely proportional to the scalar expansion. The physical and kinematical properties of the models are discussed. The effects of Viscosity and electromagnetic field on the physical and kinematical properties are also investigated. 相似文献
2.
Sunil Kumar Tripathy Dipanjali Behera Tushar Ranjan Routray 《Astrophysics and Space Science》2010,325(1):93-97
Spatially homogeneous and anisotropic LRS Bianchi type-I string cosmological models are studied in the frame work of general
relativity when the source for the energy momentum tensor is a bulk viscous fluid containing one dimensional strings. A barotropic
equation of state for the pressure and density is assumed to get determinate solutions of the field equations. The bulk viscous
pressure is assumed to be proportional to the energy density. The physical and kinematical properties of the models are discussed.
The role of bulk viscosity in getting an inflationary phase in the universe is studied. 相似文献
3.
Sunil K. Tripathy Subodha K. Nayak Subrat K. Sahu Tushar R. Routray 《Astrophysics and Space Science》2009,323(3):281-287
Spatially homogeneous and anisotropic LRSBianchi type-I string cosmological models are studied in the frame work of general relativity when the source for the energy momentum tensor is a bulk viscous fluid containing one dimensional strings embedded in a magnetic field. A barotropic equation of state for the pressure and density is assumed to get determinate solutions of the field equations. The bulk viscous pressure is assumed to be proportional to the energy density. The effects of viscosity and electromagnetic field on the properties of the model are investigated. The role of bulk viscosity and electromagnetic field in getting an inflationary phase and in establishing a string phase in the universe is studied. 相似文献
4.
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
5.
Some inhomogeneous viscous fluid cosmological models in the presence of an electromagnetic field for cylindrical symmetry are obtained. To get a determinate solution, it is assumed that the coefficient of shear viscosity is proportional to the rate of expansion. The paper also discusses the behaviour of the model when viscosity is absent and comments on some other physical properties. 相似文献
6.
String cloud cosmological models are studied using spatially homogeneous and anisotropic Bianchi type VIh metric in the frame work of general relativity. The field equations are solved for massive string cloud in presence of bulk
viscosity. A general linear equation of state of the cosmic string tension density with the proper energy density of the universe
is considered. The physical and kinematical properties of the models have been discussed in detail and the limits of the anisotropic
parameter responsible for different phases of the universe are explored. 相似文献
7.
Tilted Bianchi type I cosmological models filled with disordered radiation in presence of a bulk viscous fluid and heat flow
are investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density. Some physical and geometric
properties 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
8.
Two cylindrically-symmetric cosmological models representing viscous fluid distributions when free-gravitational field of typeD where coefficient of shear viscosity is assumed to be proportional to the rate of expansion, are obtained. The behaviour of the models in the absence of viscosity and other physical properties are also discussed. 相似文献
9.
Conformally flat tilted Bianchi type V cosmological models in presence of a bulk viscous fluid and heat flow are investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density. Some physical andgeometric aspects of the models are also discussed. 相似文献
10.
Some Bianchi type IX viscous fluid cosmological models are investigated. To get a solution, a supplementary condition between
metric potentials is used. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density,
whereas the coefficient of shear viscosity is considered as proportional to scale of expansion in the model. The cosmological
constant Λ is found to be positive and is a decreasing function of time, which is supported by results from recent supernovae
observations. Some physical and geometric properties of the models are also discussed. 相似文献
11.
Anisotropic universe with cosmic strings and bulk viscosity in a scalar–tensor theory of gravitation
V. U. M. Rao G. Sree Devi Kumari K. V. S. Sireesha 《Astrophysics and Space Science》2011,335(2):635-638
A spatially homogeneous and anisotropic Bianchi type-I cosmological model is obtained in a scalar–tensor theory of gravitation
proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. Some physical
and kinematical properties of the model are discussed. It is observed that the bulk viscosity has a greater role in getting
an accelerated expansion of the universe in this theory. 相似文献
12.
D. R. K. Reddy R. L. Naidu T. Ramprasd K. V. Ramana 《Astrophysics and Space Science》2013,348(1):241-245
A locally rotationally symmetric(LRS) Bianchi type-II space-time is considered in the frame work of a modified theory of gravitation proposed by Canuto et al. (Phys. Rev. Lett. 39:429, 1977) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. A special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento B 74:182, 1983) is used to obtain determinate solution of the field equations. We have also used the barotropic equation of state and the bulk viscous pressure is assumed to be proportional to the energy density. The physical and kinematical properties of the model are also discussed. 相似文献
13.
In this paper we have investigated some LRS Bianchi type-V cosmologicla models representing a viscous fluid distribution with a null electromagnetic field and streaming neutrinos. Various physical and kinematical features of these models have also been explored. 相似文献
14.
T. Vidya Sagar C. Purnachandra Rao R. Bhuvana Vijaya D. R. K. Reddy 《Astrophysics and Space Science》2014,349(1):479-483
A spatially homogeneous and anisotropic Bianchi type-III space-time is considered in the framework of a scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961) in the presence of bulk viscous fluid containing one dimensional cosmic strings. We have found a determinate solution of the field equations using the plausible physical conditions (i) a barotropic equation state for the pressure and density, (ii) special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento B74:182, 1983), (iii) shear scalar is proportional to scalar expansion and (iv) the trace of the energy tensor of the fluid vanishes. We have also assumed that bulk viscous pressure is proportional to energy density. Some physical and kinematical properties of the model are, also, discussed. 相似文献
15.
The paper consists of some exact solutions for a homogeneous Bianchi type VI0 universe. The material distribution is taken to be a magnetized bulk viscous fluid in presence of massive cosmological string. We assume that current is flowing along x-direction. Therefore, the magnetic field is in yz-plane. For deterministic model of the universe, we assume that shear (σ) is proportional to the expansion (θ) and ζ θ=constant=ξ where ζ the coefficient of bulk viscosity and θ the expansion in the model. The physical and kinematical parameters of the models thus formed are discussed. 相似文献
16.
K. S. Adhav S. D. Katore R. S. Rane K. S. Wankhade 《Astrophysics and Space Science》2009,323(1):87-90
In this paper, we have investigated spatially homogeneous isotropic Friedmann cosmological model with bulk viscosity and zero-mass
scalar field in Lyra manifold. The cosmological models are obtained with the help of the special law of variation for Hubble’s
parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983) and power law relation. Some physical properties of the models are discussed. 相似文献
17.
Exact solutions are obtained for an isotropic homogeneous universe with a bulk viscous fluid in the cosmological theory based on Lyra’s geometry. The viscosity coefficient of the bulk viscous fluid is assumed to be a power function of the mass density. Cosmological models with time dependent displacement field have been discussed for a constant value of the deceleration parameter. Finally some possibilities of further problems and their investigations have been pointed out. 相似文献
18.
In this paper, we have constructed a five dimensional LRS Bianchi type I cosmological model with wet dark fluid (WDF) in general relativity with the matter field described as bulk viscosity. It is found that in presence of bulk viscosity an inflationary effective stiff fluid cosmological model is obtained, whereas in absence of bulk viscosity the wet dark fluid degenerate to stiff fluid. Some physical and geometrical properties of the model are also discussed. 相似文献
19.
S. K. Tripathy S. K. Nayak S. K. Sahu T. R. Routray 《Astrophysics and Space Science》2009,323(1):91-96
Bianchi type-I string cosmological models are studied in Saez-Ballester theory of gravitation when the source for the energy
momentum tensor is a viscous string cloud coupled to gravitational field. The bulk viscosity is assumed to vary with time
and is related to the scalar expansion. The relationship between the proper energy density ρ and string tension density λ are investigated from two different cosmological models. 相似文献
20.
Some Bianchi type I viscous fluid cosmological models with a variable cosmological constant are investigated in which the
expansion is considered only in two direction i.e. one of the Hubble parameter
is zero. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density whereas the coefficient
of shear viscosity is considered as constant in first case whereas in other case it is taken as proportional to scale of expansion
in the model. The cosmological constant Λ is found to be positive and is a decreasing function of time which is supported
by results from recent supernovae Ia observations. Some physical and geometric properties of the models are also discussed. 相似文献