Vol 513, No 1 (2023)

A new type of vortex structures in the 3D ferromagnet is predicted – the vortex rings. It was established by experimental methods that these structures have finite energy. The nature of the interaction of pairs of such rings in the simplest cases was investigated.

Current trends in developing high-energy lasers with pulse energies in the tens and hundreds of joules are considered. Active media are analyzed for their use in such lasers. Yb:YAG active crystalline and ceramic elements (AE) of Russian production are experimentally investigated at temperatures from 100 K to 295 K. The data of the AE cryogenic cooling system are presented. A diode pumping system for AE and a homogenizer of its radiation are described. The physical and technical characteristics of the pumping system are given. Fresnel losses, absorption losses, and losses due to amplified spontaneous emission (ASE), which reduce the energy stored in an inverted population, are experimentally measured. The results of measuring the gain in multipass circuits with different sets of AEs are presented.

Expressions are obtained for operators of concentration of electric field strength and displacement on the surface of inclusions in matrix composite depending on shape and volume fraction of inclusions in material. These operators relate the fields on the inclusion surface on the matrix side with the average values of the electric field strength and displacement in the composite sample.

In this work, for the first time, an exact solution of the contact problem of interaction with a multilayer base of two semi-infinite stamps, the ends of which are parallel to each other, is constructed. Stamps are assumed to be absolutely rigid, and the distance between them can have any finite value. The task is an important stage in the algorithm for constructing models of a new type of crack in materials of different rheologies. The mechanism of destruction of the medium by cracks of a new type is radically different from the mechanism of destruction of the medium by Griffiths cracks, and has so far been poorly studied. Griffiths formed his cracks with a smooth border as a result of compression from the sides of an elliptical cavity in the plate. Cracks of a new type have a piecewise smooth border, resulting from the replacement of an ellipse with a rectangle compressed from the sides. The problem considered in the article can be considered as the result of the formation of a new type of crack with absolutely rigid banks and deformable lower boundary. Thanks to it, after the solution, it becomes possible to switch to deformable stamps and a crack of a new type in the rheological medium. The solution of this problem turned out to be possible due to the construction of exact solutions of the Wiener–Hopf integral equations on a finite segment. The paper shows how the solution of one of the previously unsolved problems allows us to investigate and solve exactly other problems, to identify previously unknown properties and resonances. As a result of constructing an exact solution to the problem, the fact that the solution of dynamic contact problems for stamp systems is not unique was confirmed and a dispersion equation for finding resonant frequencies was constructed.

A method is proposed for constructing exact solutions to boundary value problems of the theory of elasticity in a rectangle with stiffeners located inside the region (an inhomogeneous problem). The solutions are represented by series in Papkovich–Fadle eigenfunctions, the coefficients of which are determined explicitly. The method is based on the Papkovich orthogonality relation and the theory of expansions in Papkovich–Fadle eigenfunctions developed by the authors in homogeneous boundary value problems of the theory of elasticity in a rectangle (the biharmonic problem). The solution sequence is demonstrated with the example of an even-symmetric problem for a rectangle the sides of which are free, and an external load acts along the stiffener located on the axis of symmetry of the rectangle.

The presented work examines the combustion of a hydrogen microjet flowing from a curved channel with a round micronozzle. Jet flows that are generated using rectilinear and curved channels differ in that in the second case, Dean vortices make a noticeable contribution to the formation of the jet and its combustion. The interaction of the latter with Kelvin–Helmholtz vortices, the formation of which is typical for flows with a velocity shift, causes changes in combustion characteristics. They include spatial distortions of the laminar flame zone near the nozzle exit, the area of turbulent combustion downstream, as well as the turbulent flame in the conditions of its separation from the nozzle exit and the cessation of laminar combustion in the initial section of the flow. The results of these studies provide an opportunity to better understand the combustion features of hydrogen microjets under conditions of their hydrodynamic instability.

Rectilinear motion of a body controlled by a movable internal mass in a medium with a quadratic resistance is considered. Conditions are obtained that ensure translation of the body with a velocity changing periodically. The average speed of the motion is determined. Conditions that guarantee the maximum average speed are established.

The monolithic design of the compact bandpass filter X-band is made on technology of multilayered printed circuit boards. A quarter-wave stripline resonators of the filter have two conductors divided by the layer prepreg having low parameters which is bonding together a design. This eliminates influence of prepreg on the characteristics of the devices, ensuring good repeatability of filters in mass production. For increase the high-frequency stopband of filter, one of the conductors of each resonator is cut in half by a transverse slit. The constructive sizes of the device were obtained by parametric synthesis using the electrodynamic analysis of its 3D model. The experimental data of five-order filter are in good agreement with the electromagnetic simulation of filters 3D model. An experimental device has a central frequency of the passband of 10 GHz and fractional bandwidth of 5.7%, its dimensions and weight are 18.0 × 5.4 × 2.1 mm and 0.5 g. The important advantage of the developed design is the possibility of its installation on the board using the surface mounting method.