共查询到20条相似文献，搜索用时 15 毫秒
1.
I. Brevik V. V. Obukhov A. V. Timoshkin Y. Rabochaya 《Astrophysics and Space Science》2013,346(1):267-271
Specific dark energy models with linear inhomogeneous time-dependent equation of state, within the framework of 4d Friedman-Robertson-Walker (FRW) cosmology, are investigated. It is demonstrated that the choice of such 4d inhomogeneous fluid models may lead to a brane FRW cosmology without any explicit account of higher dimensions at all. Effectively, we thus obtain a brane dark energy universe without introducing the brane concept explicitly. Several examples of brane Rip cosmology arising from 4d inhomogeneous dark fluid models are given. 相似文献
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3.
F. Rahaman S. Chakraborty S. Das R. Mukherjee M. Hossain N. Begam 《Astrophysics and Space Science》2003,288(4):379-387
We have presented in homogeneous cosmological models within the framework of Lyra geometry. We have considered an inhomogeneous
spherically symmetric higher dimensional model in presence of a mass less scalar field whose potential has a flat part. The
scalar field is considered to be inhomogeneous. Also an inhomogeneous cosmological model is derived in a Kaluza-Klein type
of space time. The matter field is taken as an inhomogeneous distribution of fluid. It is observed that there is no singularity
at finite past in our model and the desirable feature of dimensional reduction is also possible for the extra space.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Structure formation in inhomogeneous dark energy models 总被引：1，自引：0，他引：1
We investigate how inhomogeneous quintessence models may have a specific signature even in the linear regime of large-scale structure formation. The dynamics of the collapse of a dark matter halo is governed by the value or the dynamical evolution of the dark energy equation of state, the energy density's initial conditions and its homogeneity nature in the highly non-linear regime. These have a direct impact on the redshift of collapse, altering in consequence the linearly extrapolated density threshold above which structures will end up collapsing. We compute this quantity for minimally coupled and coupled quintessence models, examining two extreme scenarios: first, when the quintessence field does not exhibit fluctuations on cluster scales and below – homogeneous dark energy; and secondly, when the field inside the overdensity collapses along with the dark matter – inhomogeneous dark energy. One shows that inhomogeneous dark energy models present distinct features which may be used to confront them with observational data, for instance, galaxy number counting. Fitting formulae for the linearly extrapolated density threshold above which structures will end up collapsing are provided for models of dark energy with constant equation of state. 相似文献
5.
Some inhomogeneous cosmological models of plane symmetry in presence of electromagnetic field have been obtained. Various physical and geometrical properties of the models with some special cases are also discussed. 相似文献
6.
Can Battal Kilinç 《Astrophysics and Space Science》1994,222(1-2):171-179
In this paper cylindrically symmetric, inhomogeneous cosmological models with heat flux, viscous fluid and electromagnetic field are obtained. Various physical and geometrical properties of the models are also discussed. 相似文献
7.
In this paper, the Einstein field equations have been solved for cylindrically symmetric and inhomogeneous cosmological models with viscous fluid. Various physical and geometrical properties of the models are also discussed. 相似文献
8.
蒋栋荣 《中国天文和天体物理学报》1995,(1)
本文对ＶＬＢＩ观测得到的河外射电源致密核ｃｏｒｅ的视角大小进行了统计研究，发现对单个源平均上视角大小近似反比于观测频率，与目前的模型相一致。在５ＧＨｚ上，在红移范围０．０４＜ｚ＜２．５内，平均的ｃｏｒｅ视角大小近似为常数，在非均匀喷流模型框架下，一种可能的解释是在河外射电源致密结构中磁场存在着演化。 相似文献
9.
D. Lorenz-Petzold 《Journal of Astrophysics and Astronomy》1986,7(3):155-170
We present a detailed study of the inhomogeneous Stephani-Krasinski solution with time-dependent curvature index. In general,
the cosmological behaviour of the models depends on six arbitrary functions of time. Such models are termed ‘private universes’
and cannot be in accord with observation in the most general case. Two simple models with changing topology are considered
as illustrating examples. In one of these models the pressure turns out to be negative and hence a violation of the weak energy
condition in the singularity theorems is possible. A brief review of other inhomogeneous cosmologies is included for the sake
of clarity. It is shown that the geodesic equation can be reduced to a complicated differential equation, which depends on
the three arbitrary functions involved. Therefore, it is difficult to obtain explicit formulas for the various observational
relations. 相似文献
10.
It is shown how the techniques that yield anisotropic and inhomogeneous solutions of the Einstein-Liouville equations for Friedmann-Robertson-Walker (FRW) spacetimes can be used to demonstrate the existence of anisotropic and inhomogeneous FRW solutions of the Einstein-Boltzmann equations, thereby providing a possible relativistic kinetic theory basis (and consequently a more self-consistent basis) for tilting imperfect fluid FRW cosmological models (based on a set of phenomenological laws of relativistic thermodynamics). 相似文献
11.
We derive a new class of inhomogeneous cosmological models to verify that in the limit of large cosmological time, some models approach the Friedmann-like universe. We investigated also the contribution of the viscosity to the production entropy. Finally, we estimated the anisotropy present in the models in the asymptotic limits and comparated the results obtained with the corresponding models without viscosity. 相似文献
12.
Andrei Mesinger Steven R. Furlanetto 《Monthly notices of the Royal Astronomical Society》2008,385(3):1348-1358
One well-known way to constrain the hydrogen neutral fraction, , of the high-redshift intergalactic medium (IGM) is through the shape of the red damping wing of the Lyα absorption line. We examine this method's effectiveness in light of recent models showing that the IGM neutral fraction is highly inhomogeneous on large scales during reionization. Using both analytic models and 'seminumeric' simulations, we show that the 'picket-fence' absorption typical in reionization models introduces both scatter and a systematic bias to the measurement of . In particular, we show that simple fits to the damping wing tend to overestimate the true neutral fraction in a partially ionized universe, with a fractional error of ∼30 per cent near the middle of reionization. This bias is generic to any inhomogeneous model. However, the bias is reduced and can even underestimate if the observational sample only probes a subset of the entire halo population, such as quasars with large H ii regions. We also find that the damping wing absorption profile is generally steeper than one would naively expect in a homogeneously ionized universe. The profile steepens and the sightline-to-sightline scatter increases as reionization progresses. Of course, the bias and scatter also depend on and so can, at least in principle, be used to constrain it. Damping wing constraints must therefore be interpreted by comparison to theoretical models of inhomogeneous reionization. 相似文献
13.
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
14.
Families of inhomogeneous models filled with a stiff perfect fluid and radiation have been derived in which there is no flow of total momentum. The models are the generalizations of those of Bianchi Type VI
h
and are discussed for some particular forms of the arbitrary functions appearing in them. 相似文献
15.
In this paper, we have investigated plane symmetric inhomogeneous cosmological models in the presence of massless scalar field
in modified theory of general relativity when source of the gravitational field is a perfect fluid. The physical and geometrical
aspects of the models together with singularity involved in the models are also discussed.
PACS Nos.: 04.50. + h•4.20.Cv• 4.20.Dw 相似文献
16.
In this paper, the Einstein field equations have been solved for inhomogeneous cylindrically symmetric space times with string source. Certain physical and geometrical properties of the models have been examined. 相似文献
17.
In this paper inhomogeneous cosmological models with perfect fluid distributions in presence of electromagnetic field is obtained. Various physical and geometrical properties of the model in presence of electromagnetic field are also discussed. 相似文献
18.
利用新的太阳附近２５ｐｃ内的Ｇ矮星金属含量分布函数,本文在假定星际介质丰度非均匀情况下,讨论了四种化学演化模型的合理性．结果表明,简单模型和坍缩模型与实际情况相差较大,而ＰＩＥ模型和ＰＰＹ模型不仅对金属含量分布函数拟合较好,而且传统的Ｇ矮星问题也可以得到解释．这表明太阳附近可能受银晕影响较小． 相似文献
19.
The extinction curves of single clouds, seen towards the stars HD 147165, 179406 and 202904, have been modelled using various mixtures containing both the bare and inhomogeneous (composite and/or multilayer) grains. It has been shown that the models composed of the bare graphite and silicate grains together with the multilayer grains containing silicates, organic refractory and water ice, are more useful in explaining extinction under the reduced cosmic abundances. The models based on Mathis' composite grains or on Greenberg & Li's core-mantle grains can also provide quite good fits of the extinction and the measured scattering parameters, but still require an excessive amount of carbon which results in too large a C/O ratio. The inhomogeneous grains essentially contribute to the extinction in practically the whole wavelength range of our extinction curves. As a rule, such grains have quite wide size distributions, centred at around 100 nm, although graphite grains are mainly of small sizes. 相似文献
20.
Some cylindrically symmetric inhomogeneous cosmological models for perfect fluid distributions with electromagnetic field
are obtained. To get a determinate solution, a supplementary condition between metric potentials is used. Various physical
and geometrical properties of the models with some special cases are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献