共查询到20条相似文献，搜索用时 468 毫秒
1.
Exact solutions of the field equations for a Bianchi type-I space-time, filled with a viscous fluid and cosmological constant,
are obtained. We utilize the constancy of deceleration parameter to get singular and non-singular solutions. We investigate
a number of solutions with constant and time-varying cosmological constant together with a linear relation between shear viscosity
and expansion scalar. Due to dissipative processes, the mean anisotropy and shear of the model tend to zero at a faster rate. 相似文献
2.
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
3.
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
4.
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
5.
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
6.
If we admit the bulk and shear viscosity coefficients to be homogeneous in all the stages of the cosmic evolution and the fact that these can be expressed in terms of the metric coefficients, we obtain some cosmological models that are exact solutions of Einstein's equations. The metric utilized is the one of Szekeres's class II and the curvature source is a viscous fluid without heat flux. 相似文献
7.
Bianchi type V viscous fluid cosmological model for barotropic fluid distribution with varying cosmological term Λ is investigated. We have examined a cosmological scenario proposing a variation law for Hubble parameter H in the background of homogeneous, anisotropic Bianchi type V space-time. The model isotropizes asymptotically and the presence of shear viscosity accelerates the isotropization. The model describes a unified expansion history of the universe indicating initial decelerating expansion and late time accelerating phase. Cosmological consequences of the model are also discussed. 相似文献
8.
Bulk viscous cosmological models of universe with variable deceleration parameter in Lyra’s Manifold
N. Ibotombi Singh S. Romaleima Devi S. Surendra Singh A. Sumati Devi 《Astrophysics and Space Science》2009,321(3-4):233-239
FRW models of universe in the presence of viscous fluid are investigated in the cosmological theory based on Lyra’s Manifold. By considering the deceleration parameter to be a variable and the viscosity coefficient of bulk viscous fluid to be a constant, exacts solutions have been obtained from which three forms of model of the universe are derived. The physical properties of the models are also investigated. 相似文献
9.
The motivation of this paper is to investigate two viscous fluid cosmological models in General Relativity in which the expansion
is only in two directions i.e. one of the Hubble parameters
is zero. In the first model, coefficient of shear viscosity is assumed to be constant while in the second model, the coefficient
of shear viscosity is proportional to the rate of expansion in the model. Here no additional condition is assumed except for
coefficient of shear viscosity. These models are new and different from those models obtained by Bali and Jain (1987, 1988)
in which free gravitational field was assumed to be Petrov Type D and non-degenerate for Marder (1958) metric and coefficient
of shear viscosity is proportional to the rate of expansion in the model. The various physical and geometrical aspects 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
10.
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
11.
The object of this paper is to investigate the behaviour of electromagnetic field in inhomogeneous cosmological models obtained for viscous fluid distributions. The various particular cases when both the electromagnetic and viscosity are absent, are also discussed. 相似文献
12.
Bianchi Type I Bulk viscous fluid tilted cosmological model without shearviscosity is investigated. The behaviour of the model in presence andabsence of bulk viscosity is discussed. The physical and geometricalconsequences of the models are also discussed. 相似文献
13.
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
14.
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
15.
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
16.
Subhabrata Majumdar Ravi Subrahmanyan 《Monthly notices of the Royal Astronomical Society》2000,312(4):724-732
In the context of cold dark matter (CDM) cosmological models, we have simulated images of the brightness temperature fluctuations in the cosmic microwave background (CMB) sky owing to the Sunyaev–Zel'dovich (S–Z) effect in a cosmological distribution of clusters. We compare the image statistics with recent ATCA limits on arcmin-scale CMB anisotropy. The S–Z effect produces a generically non-Gaussian field and we compute the variance in the simulated temperature-anisotropy images, after convolution with the ATCA beam pattern, for different cosmological models. All the models are normalized to the 4-yr COBE data. We find an increase in the simulated-sky temperature variance with increase in the cosmological density parameter Ω0 . A comparison with the upper limits on the sky variance set by the ATCA appears to rule out our closed-universe model: low-Ω0 open-universe models are preferred. The result is independent of any present day observations of σ 8 . 相似文献
17.
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
18.
Nawsad Ali 《Journal of Astrophysics and Astronomy》2013,34(3):259-271
The present study deals with spatially homogeneous and anisotropic axially symmetric Bianchi type-I cosmological model with time variable cosmological term Λ in the presence of bulk viscous fluid. The Einstein’s field equations are solved explicitly by time varying deceleration parameter q. Consequences of the four cases of phenomenological decay of Λ have been discussed which are consistent with observations. Physical and kinematical parameters of the models are discussed. 相似文献
19.
S. K. Tripathy S. K. Nayak S. K. Sahu T. R. Routray 《Astrophysics and Space Science》2008,318(1-2):125-131
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 embedded in electromagnetic field. A barotropic equation of state for the pressure and density is assumed to get determinate solutions of the field equations. The bulk viscosity is assumed to be inversely proportional to the scalar expansion. The physical and kinematical properties of the models are discussed. The effect of viscosity and electromagnetic field on the physical and kinematical properties is also investigated. 相似文献
20.
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