Yu. V. Troshchiev

Vortex Rings and Plasma Toroidal Vortices in Homogeneous Unbounded Media. II. The Study of Vortex Formation Process

The conditions of the formation of toroidal vortices (TVs), i.e., the plasma TV and air vortex ring at atmospheric pressure, are experimentally determined. The TV formation process is numerically simulated. Local characteristics of the pulsed jet, induced flow of ambient medium (air), and forming TV at various time points are obtained. It is shown that the results of the preliminary numerical calculation are in agreement with experimental data.

Restoration of the signal and its spectral characteristics with an irregular set of measurements

An extension of the algorithm for singular value decomposition (SVD)-based restoration of the signal is suggested that makes it possible to gain information on the dynamics of spectral lines (response of the medium) recorded in a single series of irregular measurements of the signal’s integral characteristics with the help of a sliding window. The size and displacement of the window fluctuate in time. SVD-based restoration is accomplished both directly from irregular measurement data and after interpolation of the data to the nodes of a regular grid. An algorithm of signal restoration that is based on spline interpolation is also proposed. When combined with SVD-based restoration, this algorithm allows almost complete elimination of spurious frequencies. In the case of integral measurements using an irregular-size window with its center displaced, the signal restoration quality and determination of the spectral line dynamics are shown to be no worse than in the case of fluctuation-free measurements. Analysis is performed both for a model signal and for the real response considered earlier in the physical experiment.

Formation of multidomain structures in the interaction of elliptic light beams with a gas mixture

It is shown that the absorption of optical energy by vibrational levels of a gas mixture can lead to the formation of several high-temperature domains along the region of propagation of a light pulse. Point and distributed models of the interaction of laser radiation with a gas are analyzed. The control of parameters can be used to control the position of domains and their number. For practical applications (e.g., data recording in the bulk of a medium), the existence of two or more high-temperature regions in combination with the dynamics of chemical reactions may have both positive and negative effects.

Analysis of thermal regimes in media with bulk heat release

Traditional and Burnett models of heat and mass transfer in a two-element medium with heat release proportional to the fraction of one of the elements are considered. The models are analyzed using a computer program for multiparametric analysis. The varieties and characteristics of regimes in both models are investigated and compared. It is expedient to use the results of simulations, for example, in studying nonlinear processes of heat and mass transfer in new power-generating units.

Analysis of stopping and then restarting a self-regulating uranium-plutonium reactor

It is shown that it is possible to restart a reactor after it has been stopped and restore its self-regulating mode.

Diffusion coefficients in a nonideal lattice gas with high concentration gradients

Expressions for the flow of migrating particles and for the diffusion coefficient in a nonideal lattice gas are derived from the equations of chemical kinetics. The diffusion coefficients depent not only on the concentration of the chemical components the gas, but also on their gradients and surface reactions. The diffusion coefficients are linear operators: the direction of flow may deviate from the gradient even for a one-component gas. These factors are shown to be essential at high gradients.

Some methods for determination of the terahertz laser signal and the dynamics of its frequencies

The possibility of restoration of a terahertz signal transmitted through a substance and represented as a set of integral measurements is studied. Being related with substance identification, such problems are topical. In the study, two algorithms are proposed for spline-based signal restoration. Te algorithms enable one to reduce the presence of spurious frequencies. It is important that a spline with a number of nodes approximately equal to the number of measurements does not guarantee a high quality of signal restoration. The proposed algorithm, which involves the choice of the optimal number of measurements, is free from this drawback. Both a model signal and the real response of a medium are considered.

Multistability of States of a Molecular Gas with the V-T Relaxation Time Dependent on the Vibrational Energy

The possibility of realizing multistability of states under the action of IR radiation on a molecule under conditions of nonlinear absorption of light energy and dependence of the V-T relaxation time on its vibrational energy is shown. A two-wave optically bistable arrangement potentially having a highly contrasting range of states is proposed. The nonlinear dependence of the V-T relaxation time on the vibrational energy is shown to allow the realization of optical bistability based on the absorption of light energy at the frequency of the fundamental vibrational transition.

Diffusionless motion of high-absorptivity domains along the laser beam axis

A new mechanism of motion of high-absorptivity domains under the action of Gaussian beams without allowance for diffusion of the material characteristics along the direction of beam propagation is studied by computer simulation. The essence of this mechanism is the dependence of the absorption factor growth rate on the radiation intensity. As a result, high-absorptivity domains may drift from heavily to weakly irradiated regions of the medium.

High-absorption multidomain dynamic structures in layered and homogeneous chemically-active media formed by elliptical light beams

Formation of several high-absorption domains induced by elliptical laser beams in homogeneous and layered chemically active media is studied with computer simulation. An interaction pattern is found when a part of the domains can exist only within a certain time interval. In this case, stable domains can be located both in front of and behind these dynamic domains.