36 research outputs found

    Anisotropic exponential cosmological solutions in the 4th and 5th orders of Lovelock gravity

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    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

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    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. Titov’s 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 20‒30 %; however, in some cases (for some sets of initial data), the difference for the entire region of cloud cover indices is within 7 %. © (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

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    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

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    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

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    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 w=1/3w=1/3 have been found. For other values of ww structure of cosmological singularity have been studied numerically. We found that for w>1/3w > 1/3 the singularity is isotropic. Several important differences between (4+1) and (5+1) dimensional cases are discussed.Comment: 8 pages, 2 fig
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