Doklady Physics最新文献

A class of power tensor series (constitutive relations) with coefficients (material functions) that are functions of three independent invariants is considered in three-dimensional space. Based on the Hamilton–Cayley formula, the exact expressions in the form of matrix series are found for the coefficients of three-term representations of such power series. The relationship of the coefficients of direct and inverse three-term constitutive relations is derived. Cases of tensor linearity, or quasi-linearity, as well as the independence of material functions from invariants, are discussed.

On the basis of a geometrically nonlinear model of a Bernoulli-Euler beam, the influence of the amplitude and shape of the initial curvature on the nature and stability of the static equilibrium positions of the system under conditions of electrostatic and thermal effects has been studied. With the help of numerical methods of the theory of bifurcations, a complete parametric analysis of the diagrams of evolution of the equilibrium positions for beams with initial curvature in terms of symmetric and asymmetric lower modes of free vibrations is conducted. The regions in the parameter space of the values of the axial force of a mechanical or temperature nature and the strength of the electrostatic field, in which the elastic system has the property of bistability, are determined. The prospect of using the considered class of structures with projected geometry perturbations as sensitive elements of high-precision microelectromechanical sensors of various physical quantities is noted.

The problem of stabilizing spacecraft in ultralow (for the Earth, 120–250 km) orbits with the help of air-breathing electric propulsion (ABEP) using the gases of the surrounding atmosphere as a propellant is considered. Qualitative differences of air-breathing electric propulsion from traditional electric propulsion are singled out, and, based on the fundamental laws of mechanics and electrodynamics, the necessary conditions for the existence of spacecraft with an air-breathing electric propulsion engine in closed ultralow orbits are substantiated.

The grid-characteristic method on structured grids is applied to various problems related to railway-traffic safety, as well as to obtain results of full wave modeling using this method and analyzing them for a better understanding of the physical processes occurring under conditions of heavy and high-speed traffic on various sections of the track. The problem involves the consideration of traffic on a ballasted and ballastless bridge desk. In the course of computer simulation, various wave fields and dynamic distributions of pressure and components of the Cauchy stress tensor are obtained during the traffic. The calculation time during which the propagation of wave processes occurs in various bridge structures is estimated. The results obtained give an idea of wave phenomena during the traffic in the area of bridges and along the railway track as a whole.

The effect of an outside wave impact on filtration of fluids from capillaries into environmental porous media and back is considered. Two mechanisms of filtration acceleration are found. The first of them is specified with changing the permeability of environmental porous media and the surface layer of capillaries due to the wave impact. The second mechanism is caused by synchronous and in-phase vibrations of pressure in the capillary and the permeability of environmental porous media. It manifests itself only in the resonance case. Both these effects can be used for intensification of the trance-capillary exchange in medicine.

The results of simulation of a geomagnetically induced current impact on the consolidated power system of the center of Russia expected during a strong magnetic storm are represented. It is shown that a complex of factors appears during this impact that can induce the progression of a blackout: a significant decrease in voltage on a set of electrical power elements, the mass cutoff of power transmission lines under the effect of relay protection, and the dangerous heating of construction elements of power transformers.

For the first time, the transfer of the substance of a free-falling drop into a resting target fluid at the stage of formation of a primary cavity was tracked by high-speed video recording. In the experiments, water-diluted drops in a ratio of 1 : 100 ink solution or a saturated solution of baking soda with a diameter of (D = 0.43) cm fell at a velocity of U = 3.1 m/s into water or a 20% ammonium thiocyanate solution in the splash formation mode. In all experiments, the wall of the growing cavity is pierced by thin fibers containing drop material, which form an intermediate fine-structured layer. After the end of the fiber growth stage with a duration of 7–8 ms and diffusion smoothing of the concentration gradients, a liquid layer of intermediate density with a thickness of 1.5 to 0.7 mm is formed around the growing cavity. The layer is separated by a sharp boundary from the target fluid. A new group of inclined fibrous loops is formed in the wake of the collapsing cavity.

The results of comparative investigations of the parameters of pulsed cathodoluminescence of crystals and ceramics excited by runaway electron beams with a duration of 10–12 ps and by electron beams with a duration of 2 ns generated in a vacuum diode are presented. It is shown that the luminescence spectrum and the decay kinetics of the bands coincide in both cases. When excited by a beam of runaway electrons, a lower luminescence intensity is observed. In certain cases, a delay in the appearance of luminescence relative to the onset of the electron-beam action is found. The mechanism for the appearance of a delay upon excitation by the beam of runaway electrons is associated with the process of luminescence rise.

The most promising areas of research in the field of plasma aerodynamics are proposed. On the basis of the presented experimental data obtained recently, the possibilities of using the volumetric force effect on the gas flow in aerodynamic applications, which is realized with the help of near-surface electric discharges, are considered. One of these applications is to increase the length of the laminar section of the boundary layer on the swept wing in order to reduce the aerodynamic drag of the aircraft in the cruise flight mode. The second direction is associated with the control of the three-dimensional separation of the boundary layer on the elements of the mechanization of the swept wing in the take-off and landing modes. The third direction is the reduction of surface friction in the turbulent boundary layer, which is realized on most of the surface of modern near- and supersonic aircraft. The proposed studies are not only of applied, but also of fundamental importance due to the physical complexity of the studied phenomena.