Technical Physics最新文献

In the presented article, a qualitative analysis of the plasmadynamic modes of operation of a magnetoplasma compressor (MPC) (specifically, an end-type MPC discharge) is performed. It is shown that the most acceptable mode for optical pumping of gas lasers in the ultraviolet (UV) range of the spectrum is the mode of inhibition of the plasma of the MPC discharge on a gas barrier (ohmic mode). Spatial distributions of plasma parameters are obtained.

The implementation of nanoantennas for optical wireless communications in the infrared (IR) and visible ranges ensures higher data transfer rates, reducing simultaneously the antenna size. The possibility to tune the performances of graphene by chemical doping or bias voltage is relevant in the development of reconfigurable nanoantennas. The goal of this research is the study of the performances (S‑parameters and radiation patterns (RPs)) of plasmonic graphene nanoantenna (PGNA) arrays, their controllability, and the possibility of frequency scanning by changing the chemical potential of graphene (by applying an external electric field) in the mid-IR range. The use of graphene, which has a controlled high electrical conductivity, and plasmonic properties in the terahertz (THz), far-IR and mid-IR ranges is one of the most promising alternatives to noble metals (Au and Ag) as plasmonic materials at optical frequencies only. Modeling the performances of PGNA arrays was carried out using the electrodynamic modeling program CST Microwave Studio 2023, which makes it possible to solve scientific problems associated with the design of graphene antennas in the IR wavelength range. The results of modeling the controllability of the characteristics (S‑parameters, RPs) of a single element of the antenna array (PGNA of rectangular geometry) and PGNA arrays at the resonant frequencies of the fundamental mode of surface plasmon polaritons (SPPs) are obtained, and the possibility of scanning in frequency upon a change in the chemical potential of graphene (by applying an external electric fields) in the mid-IR range is demonstrated. The results of modeling the performances of PGNA arrays show that with an increase in the chemical potential of graphene (in the interval of values of 0.3–1 eV), the operating frequencies are adjusted (frequency scanning) in the mid-IR range, the gain of the PGNA array increases, the RP main lobe narrows, and the RP side lobe level decreases with an increase in the number of single elements (N = 256); and better controllability of the RP main lobe is observed.

This study is aimed at the theoretical investigation of interaction of powerful energy beams with a plasma in a magnetic field, as well as at the elucidation of thermal-physics and fluid-dynamics problems in such calculations. We consider different regimes of a linearly stabilized surface discharge and estimate radiation–plasmadynamic regimes and structures in powerful emitting jets of a surface discharge. Time dependences of the main characteristics are plotted for different voltages and discharge channel lengths for argon and air.

Our experimental and theoretical investigations are aimed at determining conditions for the excitation of resonance effects in complex hydromechanical systems and the development of a diagnostic method for preventing hazardous vibronoise regimes in them. In analysis of the acoustic vibration spectrum obtained in the experiments based on acoustic resonance method, three vibronoise regimes have been singled out: the subsonic regime, the beat regime, and the resonant regime. In the beat and resonant regimes, pronounced acoustic vibrations have been detected (moderate-intensity vibrations in the beat regime and high-intensity vibrations in the resonant regime). The resonant regime of operation is distinguished by the highest acoustic vibration amplitude and can pose a threat for reliable and safe operation of power stations. It is shown that the vortex flow structuring effect can be diagnosed from the characteristic amplitude peaks in the acoustic spectrum even in the subsonic regime.

The conducted research is designed to develop scientifically sound recommendations in order to optimize design and layout solutions that ensure increased energy efficiency and operability of energy-producing installations for various purposes. The mechanisms leading to the formation of stable vortex structures in internal turbulent swirl flows occurring in complex channels of power plants are considered. The effects associated with the manifestation of the swirl flow crisis are considered. It is shown that the generation of stable vortex formations in the equipment elements of power installations can be directly related to the mechanism of excitation of dangerous vibro-resonance effects. A method for intensifying heat transfer in steam generating channels is proposed. The question of choosing the criterion of thermohydraulic efficiency for solving optimization problems is considered.

The paper provides a detailed solution to the problem of calculating the drag force of a hot ball moving in a viscous continuum. The problem is solved in the stationary case on time intervals when the heat exchange of the body with the environment does not lead to significant changes in its temperature. The limiting case is considered, when the Nusselt number is large (the thermal conductivity is small) and the temperature of the heated ball is considered constant together with the ambient temperature.

In this study, the Stokes formula permitting the calculation of the drag force for any spherical (including inhomogeneous) bodies is generalized. It is shown that in all physically interesting cases with different boundary conditions in the limiting transition to a homogeneous solid ball, the result is always the classical Stokes formula (F = 6pi eta Ru).

With the help of the Prandtl equation and using the methods of the variational calculus, we have obtained equations that make it possible to analytically determine the type of contour for which the drag force in a viscous flow past a body becomes the smallest. It is rigorously proved analytically that the longitudinal cross section of a cut of well-streamlined bodies can have different forms depending on the Reynolds number. The equations found are analyzed numerically and illustrated graphically.

With the help of the variational approach, a detailed derivation of a generalized dynamical equation is given in a particular case describing a soliton and a shock wave.

The possibility of using a circular waveguide with radial ridges and ring-shaped segments of finite thickness as resonant diaphragms in the synthesis of bandpass cylindrical waveguide filters is shown. The analysis of the electrodynamic parameters dependences on diaphragms geometrical dimensions has been carried out. Filters were synthesized and compared with experimental data.