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1.
In this paper general solutions are found for domain walls in Lyra geometry in the plane symmetric spacetime metric given
by Taub. Expressions for the energy density and pressure of domain walls are derived in both cases of uniform and time varying
displacement field β. It is also shown that the results obtained by Rahaman et al [IJMPD, 10, 735 (2001)] are particular case
of our solutions. Finally, the geodesic equations and acceleration of the test particle are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
A new dark energy model in anisotropic Bianchi type-III space-time with variable equation of state (EoS) parameter has been
investigated in the present paper. To get the deterministic model, we consider that the expansion θ in the model is proportional to the eigen value s2 2\sigma^{2}_{~2} of the shear tensor sj i\sigma^{j}_{~i}. The EoS parameter ω is found to be time dependent and its existing range for this model is in good agreement with the recent observations of
SNe Ia data (Knop et al. in Astrophys. J. 598:102, 2003) and SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004). It has been suggested that the dark energy that explains the observed accelerating expansion of the universe may arise
due to the contribution to the vacuum energy of the EoS in a time dependent background. Some physical aspects of dark energy
model are also discussed. 相似文献
3.
Anirudh?PradhanEmail author Sudhir?Kumar?Srivastav Mahesh?Kumar?Yadav 《Astrophysics and Space Science》2005,298(3):419-432
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
4.
Cylindrically symmetric inhomogeneous string cosmological model in presence of electromagnetic field is investigated. We have
assumed that F
23 is the only non-vanishing component of F
ij
. To get the deterministic solution, it has been assumed that the expansion (θ) in the model is proportional to the eigen value σ
1
1 of the shear tensor σ
i
j
. The physical and geometric aspects of the model are also discussed.
相似文献
5.
Mercury in sediments of Ulhas estuary 总被引:5,自引:0,他引:5
Hg levels in water, suspended particulate matter and sediment of the Ulhas estuary are under considerable environmental stress due to the indiscriminate release of effluents from a variety of industries including chlor-alkali plants. Concentration ranges of dissolved (0.04-0.61 micro gl(-1)) and particulate (1.13-6.43 micro gg(-1)) Hg reveal a definite enhancement of levels in the estuary. The Hg burden in sediment upstream of the weir that limits the tidal influence is low (0.08-0.19 micro gg(-1)) with low C(org) content (1.8-2.9%). The high Hg content of the sediment just below the weir varies seasonally (highest concentration recorded being 38.45 micro gg(-1)) due to incremental accretion of sediment as the fresh water flow over the weir progressively decreases. The 30 km segment of the estuary sustains markedly high levels of Hg in the sediment with an exponential decrease in the seaward direction from the weir. Higher concentrations than the expected background prevail in all the estuarine cores up to the bottom, though the overall concentration decreases from about 20 micro gg(-1) in core 7 (inner estuary) to 1 micro gg(-1) in core 31 (outer estuary). The Hg in sediment is associated with C(org), while its correlation with Al, Fe and Mn is poor. The Hg profiles in cores from the Arabian Sea (stations 34, 35 and 37) have a distinct horizon of enhanced concentration in the 5-60 cm segment. Based on 210Pb dating of core 37, the sediment at the bottom of this core is inferred to have been deposited in the year 1949, roughly two year prior to the establishment of the first chlor-alkali plant and represents the background (0.06-0.10 micro gg(-1)). The Hg profiles in the offshore cores indicate a marked increase in transfer of Hg to sediment subsequent to 1980, with a peak around 1990-1992. Based on the index of geoaccumulation it is considered that the estuarine segment between stations 4 and 23 is extremely polluted, while the sediment from the open coast is moderately polluted in the top 25-30 cm with respect to Hg. The enrichment factor of Hg in the sediment is 350-700 for core 4 and decreases to 0-7 for the open-shore cores. 相似文献
6.
G. S. Khadekar Vaishali Kamdi Anirudh Pradhan Saeed Otarod 《Astrophysics and Space Science》2007,310(1-2):141-147
We assume the four dimensional induced matter of the 5D Ricci flat bouncing cosmological solution contains a perfect fluid.
The big bounce singularity of simple 5D cosmological model is studied with the cosmological term Λ=α
ρ and Λ=β
H
2 where α and β are constants and ρ and H are respectively energy density and Hubble parameter. This big bounce singularity is found to be an event horizon at which
the scale factor and mass density of the universe are finite, while the pressure is infinite.
相似文献
7.
8.
A new class of exact solutions of Einstein’s field equations with a bulk viscous fluid for an LRS Bianchi type-Ia obtained
by using a time dependent deceleration parameter and cosmological term Λ. The coefficient of bulk viscosity is assumed to
be a power function of mass density (ξ=ξ
0
ρ
n
). We have obtained a general solution of the field equations from which six models of the universe are derived: exponential,
polynomial and sinusoidal form respectively. The behaviour of these models of the universe are also discussed in the frame
of reference of recent supernovae Ia observations.
相似文献
9.
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
10.