36 research outputs found
Anisotropic exponential cosmological solutions in the 4th and 5th orders of Lovelock gravity
Anisotropic exponential cosmological solutions for a space of arbitrary
dimension filled with ordinary matter in the 4th and 5th orders of Lovelock
gravity are obtained. Also we have supposed a generalization of such solutions
on an arbitrary order. All the solutions are represented as a set of conditions
on Hubble parameters.Comment: 10 page
Estimation of the influence of cloudiness on the Earth observation from space through a gap in a cloudy field
For atmospheric correction of satellite images, the problem is formulated to estimate the distance from a cloud at which its influence on the satellite image of the Earth surface can be neglected. The Monte Carlo method of conjugate trajectories is used. The gap radius in the field of continuous cloudiness at which the influence of the cloudy medium on the received signal intensity does not exceed 10 % is obtained. It is revealed that for the Lambert law of radiation reflection from the Earth surface, the curve of the dependence of the received signal intensity on the gap radius has a maximum caused by the opposite influence of light scattering by the cloudy medium and radiation reflection by the surface (adjacency effect). To further generalize the examined problem to a stochastic cloud field, the method of direct simulation of photon trajectories in a stochastic medium is compared with G. A. Titovβs method of closed equations in the gap vicinity. A comparison is carried out with the model of the stochastic medium in the form of a cloud field of constant geometric thickness consisting of rectangular clouds whose boundaries are determined by the stationary Poisson flow of points. It is demonstrated that results of calculations can differ at most by 20β30 %; however, in some cases (for some sets of initial data), the difference for the entire region of cloud cover indices is within 7 %. Β© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
New features of flat (4+1)-dimensional cosmological model with a perfect fluid in Gauss-Bonnet gravity
We investigated a flat multidimensional cosmological model in Gauss-Bonnet
gravity in presence of a matter in form of perfect fluid. We found analytically
new stationary regimes (these results are valid for arbitrary number of spatial
dimensions) and studied their stability by means of numerical recipes in
4+1-dimensional case. In the vicinity of the stationary regime we discovered
numerically another non-singular regime which appears to be periodical.
Finally, we demonstrated that the presence of matter in form of a perfect fluid
lifts some constraints on the dynamics of the 4+1-dimensional model which have
been found earlier.Comment: 14 pages, 5 figures, 1 table; v2 minor corrections, conclusions
unchange
From Big to Little Rip in modified F(R,G) gravity
We discuss the cosmological reconstruction in modified Gauss-Bonnet (GB)
gravity. It is demonstrated that the modified GB gravity may describe the most
interesting features of late-time cosmology. We derive explicit form of
effective phantom cosmological models ending by the finite-time future
singularity (Big Rip) and without singularities in the future (Little Rip).Comment: 15 pages, 7 figure
The nature of singularity in multidimensional anisotropic Gauss-Bonnet cosmology with a perfect fluid
We investigate dynamics of (4+1) and (5+1) dimensional flat anisotropic
Universe filled by a perfect fluid in the Gauss-Bonnet gravity. An analytical
solutions valid for particular values of the equation of state parameter
have been found. For other values of structure of cosmological
singularity have been studied numerically. We found that for the
singularity is isotropic. Several important differences between (4+1) and (5+1)
dimensional cases are discussed.Comment: 8 pages, 2 fig