Doklady Rossijskoj akademii nauk. Fizika, tehničeskie nauki

In solving many practically important problems of hydroacoustics, the properties of the fan interference structure of the signal intensity field are used, which in the shallow sea in the coordinates “distance – frequency” are largely determined by the value of the waveguide invariant β (S.D. Chuprov invariant) close to one. Below, the properties of the waveguide invariant are studied in the near acoustic illumination zone (NAIZ) of the deep sea, and it is found that its values are unstable – when the propagation conditions change, the waveguide invariant varies widely and is not an invariant. It is shown that in the NAIZ the use of the phase-energy invariant β_ef is more promising, since in the NAIZ it is equal to one with high accuracy and stable. It is also discovered for the first time that, under certain conditions, coherent addition of Fourier components on the complex plane is possible in the NAIZ if, when summing the spectral components of complex spectra along the ridges, an adjustment for phase variation is introduced. With such processing, in the case of stationary noise, the probability of detecting weak signals can significantly increase.

Within the framework of the averaged approach, the frequency multiplication mode in a relativistic gyrotron in the 300 GHz range was studied. It is shown that under conditions of selective excitation of oscillations on the ТЕ_33,2 mode at the fundamental cyclotron harmonic, it is possible to generate radiation with a frequency of 1.5 THz and a power of up to 1.5 kW on the ТЕ_165,7 mode with excitation of the fifth harmonic of the gyrofrequency. A three-dimensional simulation of the gyrotron by the large particle method was performed, on the basis of which a narrowing of the generation zone at the main cyclotron harmonic was shown in comparison with that calculated within the framework of a simplified model, which leads to a limitation of the power of terahertz radiation at the level of 200 W.

It is shown for the first time that using the method of Raman spectroscopy allows one to determine the content of conjugated octadecatrienoic (K-C18:3) acids in oil at their content of 8 wt. % at least. It is found that it is possible to reliably distinguish the isomers of the K-C18:3 acids containing conjugated (in punicic and α-eleostearic acids) and non-conjugated (in α-linolenic acid) C=C bonds by their Raman spectra. The obtained results can be used to develop efficient and non-destructive techniques for analyzing the composition and quality of oils, which contain conjugated octadecatrienic polyunsaturated fatty acids, and dietary supplements based on them.

It is suggested the concepts of the longitudinal electric not binding to walls of a camera discharge creation in the supersonic flows and its application for ignition and flame holding of the fuel combustion.

For the first time, the exact solution of the static contact problem of the frictionless action of a rigid die in the form of a semi-strip on an anisotropic multilayer composite material is constructed by the block element method. Previously, these important tasks in structural engineering practice, electronics, physics, and other fields were not solved. The difficulty in solving these contact problems with anisotropy, in comparison with the isotropic case, consists in the difficulty of describing the spectral properties of such mathematical objects as Green's functions and symbols of integral equations. Using existing numerical methods, it is possible to describe the behavior of the concentration of contact stresses at the stamp boundary in cases of isotropic materials. However, it was not possible to construct an accurate solution for the distribution of contact stresses in the anisotropic case under a semi-strip stamp, together with features at the boundary. For the first time, a solution was constructed reflecting the real distribution of contact stresses and their concentrations under the stamp. The solution obtained in the work tends to the solutions obtained for a strip or a quarter of the plane when the semi-strip degenerates into these areas.

A theoretical assessment of the minimum oxygen content in tungsten powder was carried out and compared with experimental results for passivated powder. The assumption of particles being spherical in size and distributed according to a lognormal law was used. Using this method, the thickness of the oxide layer in tungsten powders recovered at temperatures of 650, 800 and 950 °С (and with average size 1.53, 2.26 and 4.54 μm) was estimated and it turns out to be much larger than the monomolecular layer: 50, 10, 5 nm, respectively.

This paper presents an approach to a qualitative change, by 12 to 17 dB and more, of the low-frequency sound absorption inside and outside the transport vehicles. In the approach, the problems are solved of designing the composites of polymer matrixes with inorganic and biopolymer polydisperse phases, and of modeling, measuring and analyzing the sound-absorbing properties of thin mono-/bilayer structural elements based on the new composites. Validity of the approach is confirmed by correctness of the physical, chemical and measurement methods used, and by the results of experimental studying the test-models of the composites. These research results can be used in the current developing and prospective designing the aircraft for various purposes, and other types of transport vehicles.