Radiophysics and Quantum Electronics最新文献

We study experimentally an atmospheric pressure discharge sustained by the millimeter-wave gyrotron radiation in an argon flow. The spatial distribution of gas temperature in the plasma jet emerging from the conical nozzle of a waveguide plasmatron has been measured by two independent methods. Using the method of optical interferometry and the method of thermosondes, it is shown that even with a microwave heating power of several tens of watts, it is possible to create a weakly ionized plasma at the nozzle exit, in which the gas temperature reaches about 1000 K and declines uniformly in the postdischarge area. The interferometric method applied in this work makes it possible to obtain an instantaneous complete spatial picture of the gas temperature distribution in the plasma torch during a single passage of a probing laser beam through the medium under study. This permits one to observe the complex dynamics of convective processes during the outflow of plasma and hot gas from the hole in the plasmatron.

We study the possibility of increasing the peak power of ultrashort sub-gigawatt pulses of Cherenkov superradiance (SR) based on the effect of the self-compression that occurs in the process of formation of microwave solitons with self-induced transparency (SIT solitons) due to the cyclotron resonance interaction with a rectilinear (passive) electron beam. In order to enhance the selfcompression efficiency, it is proposed to use a two-stage scheme, each section of which is optimized taking into account the parameters of the incoming signals, specifically, the superradiance pulses or SIT solitons. Simulations show that the proposed scheme allows increasing the peak power of a 90 GHz SR pulse from 150 MW to 1 GW.

We study analytically the statistical (Anderson) localization of the wave beam propagating in a structure of evenly placed waveguides with random parameters. We explore in detail the suppression of the diffraction broadening of the wave field in a randomly inhomogeneous medium in the continuum limit. A dispersion equation for the mean field is obtained from statistical averaging of the Helmholtz equation. The structure of the dispersion equation considerably differs from the parabolic dispersion law (typical of homogeneous media in the quasioptical approximation). The surface of the wave vectors defined by this equation (the refractive-index surface) has points where the curvature changes sign. In the theory of wave processes, this indicates that the diffraction is suppressed for the wave beams propagating in the so-called special directions in space, which corresponds to the Anderson localization. Evolution of such wave beams is considered on the basis of presenting the field as the Fourier integral of the spectrum of initial distribution over the transverse wave number. The asymptotic evaluation of the integral shows that the Anderson localization is described by the Airy beams. The transition region is studied numerically. Similar conclusions are also drawn in the case of a discrete problem.

This review presents a state-of-the-art analysis in the field of application of fractional calculus to dynamic problems in solid mechanics with moving loads. It includes papers devoted to the study of the dynamic behavior of structures carrying moving loads and made of a viscoelastic material and/or resting on viscoelastic foundations, the damping properties of which are described by models with fractional derivatives. A large number of numerical and experimental studies in this field gives grounds for using fractional-derivative models in dynamic contact problems. Issues on the action of moving oscillating loads in the form of systems with one or several degrees of freedom are also considered.

We obtain an analytical expression for the decision statistics for detecting signal-like active interference based on an estimate of the eigenvalues of a sample correlation matrix. The exact decision statistic is derived from a rigorous expression for the likelihood ratio and obtained on the basis of the generalized likelihood ratio including that for short samples. Using the exact decision statistic, we obtain detection curves (the dependence of the probability of correct detection on the signal-to-noise ratio) for various process-sample lengths. Dependences of the probability of correct detection on the phase-fluctuation value are given and it is shown that signal-to-noise ratio for detecting the signal-like interference in the case of a given probability of correct detection significantly increases with decreasing phase fluctuations of the interference.

We consider the scattering of long-wavelength radiation by two parallel cylinders within the framework of the quasistatic approximation, which is valid when the diameters of the cylinders and the gap between them are much smaller than the radiation wavelength. Using the conformal transformation, we obtain an analytical solution to the two-dimensional problem, which agrees well with the computer calculations. The found Green’s function allows calculating higher expansion orders.

We consider the interaction of relativistic electrons with finite-length packets of electromagnetic ion-cyclotron waves in the Earth’s radiation belts. On the basis of the numerical simulation by the test particle method, we study the dependence of the interaction characteristics on the length and amplitude of the wave packet both in the linear and nonlinear regimes. The fluxes of the particles precipitating to the loss cone as a result of the considered interaction are calculated. We show that both in the linear regime and under the regime of force bunching caused by the direct influence of the Lorentz force on the electron phase, the decrease in the packet length expands the interaction region to low energies outside the range of resonance values for the central packet component. Such an interaction can lead to precipitation of hundreds-keV electrons into the ionosphere. Nonlinear effects lead to saturation of the precipitation flux at the limiting level corresponding to the strong pitch-angle diffusion.

We present the results of studying the refractive index of ultrashort waves, which is calculated on the basis of meteorological measurements of the atmospheric-soil measuring complex. The diurnal and seasonal dynamics of the behavior of the refractive index and its gradient in the lower 10- meter layer of the troposphere in the Ivolginsk basin in the Republic of Buryatia are considered. It is found that in summer, meteorological conditions that favor the negative refraction of UHF waves arise. It determined that the greatest influence on the general gradient of the refractive index in this season is exerted by the gradient of its humidity component, which depends on the vertical distribution of atmospheric humidity. Due to intense insolation, the Earth’s surface is heated, which leads to active evaporation of the soil moisture and its subsequent condensation in the atmosphere.

This paper analyses the problems of measuring the parameters of a repetitive periodic signal with the monobit (binary 1/0 or signed binary ±1) quantization, which is called “rough statistics” here. The consideration is carried out in relation to radio equipment with phased antenna arrays using spatiotemporal sampling. The system constructed is based on the Monte Carlo method. Randomization of noninformative parameters of the processed signals is used for linearization of the quantization nonlinearity. This paper brings into balance the conventional approach based on an extensive increase in resources (that is, an increase in the resolution and rate of the analogto-digital converter) and the alternative approach involving an increase in the sample size.

We present the results of radar experiments performed on the Sura facility after its upgrade in 2020–2021. Anomalous enhancement of the radio echo up to 40 dB above the radio background level during a lunar radar session on October 17, 2022 at a frequency of 8925 kHz is reported. Arguments in favor of the ionospheric nature of this phenomenon are presented.