Том 8, № 1 (2016)

In this paper we examine the possibility of using approximations of elementary functions for the analytical solution of meteor physics equations, used to describe the trajectory and to evaluate the defining parameters of meteoroids entering the Earth’s atmosphere. We show the possibility of replacing the analytical solution with the combination of two elementary functions along one parameter. We provide estimates for the error of the proposed replacement. We investigate the magnitude of error in the function which arises in the approximation of meteoric observational data.

This article presents the results of ab initio quantum simulation of graphite-like structure formation from amorphous carbon. It is devoted to explaining a resistivity switching mechanism in experiments on phase-change memory. In this work, a two-scale molecular dynamics model is used, which consists of Car-Parrinello quantum molecular dynamics (CPMD) and modified Ehrenfest molecular dynamics. The results of simulation point out to the appearance of a layered graphite-like molecular structure at an increase in temperature. These changes in the atomic configuration can be considered as a second-order phase transition in nanostructured material, which leads to threshold resistivity switching. For calculations, the IBM BlueGene/P supercomputer installed at the Faculty of Computational Mathematics and Cybernetics of Moscow State University was used.

Numerical solution of the Vlasov–Maxwell equations in a three-dimensional (3D) model for the interaction between a powerful electromagnetic field of laser radiation and electron–proton plasma with a supercritical density yields kinetic functions of electron and proton distribution versus time. In this work, such kinetics are analyzed in detail, which makes it possible to elucidate the mechanism underlying the important effect of the considered interaction, i.e., the effect of proton acceleration up to very high energies of dozens megaelectron-volts. This mechanism consists in transferring the momentum of the incident electromagnetic wave enhanced by the reflection effect of this wave to the proton component of the plasma. Qualitatively, these results are consistent with the physical experiments of the last decade. The paper also presents the calculation results for the distribution of all (six) components of the electromagnetic field inside the plasma with account for violation of the plasma electroneutrality. This work studies the kinetic properties of the plasma and is a continuation of our previous publications.

The recent progress in the methods for the study of the three-dimensional structure of porous and composite materials (microtomography, confocal microscopy, and FIB-SEM) and the significant improvement in the available computational resources make it possible to simulate various processes directly in the three dimensional geometry of samples of such materials (pore-scale modeling) in order to determine their effective properties or to get a more detailed understanding of the studied processes, such as filtration. In this work, we solve the Stokes equation by the finite-difference method using schemes of the second and fourth orders of accuracy in a three-dimensional domain whose geometry reproduces the microstructure of the investigated rock samples. The numerical values of permeability obtained for a sample of sandstone are consistent with the data of laboratory measurements.

Analyzing the efficiency of preventive measures based on probability relations of reliability theory demonstrates that these measures principally rank below nondestructive testing (defectoscopy, or flaw detection), which represents a direct diagnostic method for preventing failures and accidents. The proposed mathematical model rests on the interpretation of nondestructive testing as observations of the current state of the basic reliability parameter, namely, the failure rate. Analytical relations of the model are obtained using Kolmogorov’s equations for the limiting probabilities of the state graph of an item–defectoscope system. The model has the following parameters: the failure and restoration rates of an item, the probabilities of errors of the first and second kind of the faults' detection, and the frequency of item testing. The results demonstrate the technological and economic efficiency of flaw detection. Here, the frequency of testing is more important for economic efficiency than small probabilities of errors. The model can be used to optimize performance specifications for the design of flaw detection equipment. The numerical examples approximately correspond to conditions of offshore industry.