Vol 63, No 5 (2018)

On the basis of the solution to the equation for a single-particle density matrix, the momentum distribution is obtained for a light-particle impurity placed in an ordered system of heavy particles and interacting with them with the amplitude U₀. The effect of the value of U₀/T₀ on the functional form of the momentum distribution is investigated. It is shown that the momentum-distribution function obtained within the perturbation theory up to the terms ~(U₀/T₀)² retains its form also outside the region of applicability of the perturbation theory; however, the relative magnitude of the correction is much smaller than that given by the perturbation theory.

The results of experimental investigations of the micronozzle-chocking phenomenon under diffusion combustion of a hydrogen microjet at a high outflow velocity in the case of ignition of hydrogen near the nozzle cut are presented. It is found that the cause of micronozzle chocking is the heating of the nozzle walls from the flame-neck region retained up to transonic velocities and preventing nozzle cooling and the passage of the hydrogen jet to the supersonic-flow velocity. It is shown that hydrogen ignition far from the nozzle cut with a developed hydrogen supersonic flow into the flooded space leads to the disappearance of the flameneck region, flame detachment from the nozzle cut, and, correspondingly, termination of the nozzle heating and the possibility of the microjet coming out at the supersonic-flow velocity for the hydrogen jet. It is established that the flame-neck region is a stabilizing factor for the subsonic combustion of a hydrogen microjet up to transonic velocities. In the second case, the presence of supersonic cells stabilizes the supersonic diffusion combustion of the hydrogen microjet.

The boundary-value problem for a block structure consisting of an elastic half-space that occupies the lower part of a Cartesian coordinate system and interacts with two block elements in the form of unbounded wedges with right angles at the vertices is considered. The horizontal boundaries of the wedges are rigidly connected with the half-space boundary, and vertical ones are parallel planes. We consider the antiplane problem for cases where the distance between the vertical boundaries of block elements is present or absent. By the example of a three-dimensional problem degenerating into a two-dimensional one, it is shown that an initial earthquake is possible, like in the case of using Kirchhoff plates instead of three-dimensional block elements.

The application of variational methods to the problems of optimal control for a decrease in the intensity of temperature oscillations of the environment on the basis of the choice of the physical and geometrical structure of heterogeneous constructions is proposed. The necessary optimality conditions are developed for the optimal-design problems under study in the variational statement. On the basis of the constructive analysis of the necessary optimality conditions, the qualitative regularities of the optimal heterogeneous structures are established, which makes it possible to estimate the efficiency of the existing heat-shielding constructions and to find in which direction it is necessary to improve their heat-shielding ability to achieve the ultimate possibilities for a decrease in the temperature-action intensity.