Solitons are a well-studied subject in many domains of nonlinear physics, including hydrodynamics, plasma physics, optics, etc. However, it has been demonstrated only recently that they can be realized in systems of microwave electronics. This review presents the results of analyzing theoretically the formation mechanisms of envelope solitons of two types. The first type is the self-induced transparency

The loss of stability of the blood liquid state causes changes in the blood aggregation, resulting in thrombus formation. Intravascular thrombus formation is intensely studied within modern biophysics by the methods of mathematical simulation. Determining the conditions of shear-induced platelet activation has opened an opportunity for the estimation of thrombus formation risks in particular clinical

We consider the Alfvén wave self-interaction in a plasma with thermal misbalance. To describe this process, a system of truncated equations is obtained that allows using a relatively simple algorithm for its numerical solution. The obtained truncated system describes the self-interaction of Alfvén waves under various conditions of thermal misbalance and thermal instabilities. The results obtained by

We use the qualitative, simplified modeling, and approximately self-consistent nonlinear-optical approaches to explain the nature of the regime under which relativistically intense laser pulses propagate in a plasma to distances exceeding the Rayleigh length considerably, as was found earlier by numerical simulation. Such a regime requires certain matching of the size of the laser spot with the plasma

We consider direct and inverse problems of geophysical hydrodynamics, associated with prediction, posterior analysis, and variational assimilation of observational data. The focus is on numerical algorithms for solving problems with incomplete information (initial and boundary conditions). Along with the classical algorithms, an approach to setting and solving these problems developed in the works

We study mutual synchronization in a system of two delay-coupled gyrotrons. The results of the bifurcation analysis are presented in the approximation where the delay time is short compared with the oscillation onset duration. The conditions of the stability of in-phase and antiphase synchronization regimes are analyzed for various values of parameters. Synchronization regions are plotted on the detuning–coupling

We describe in detail the construction of numerical fourth- and sixth-order schemes using the Magnus expansion for solving the Zakharov–Shabat system, which makes it possible to solve accurately the direct scattering problem for the nonlinear Schrödinger equation. To avoid numerical instabilities inherent in the procedure of solving the direct scattering problem, high-precision arithmetic is used.

This review includes a description of the origin and evolution of the term “dark matter” as an observationally needed element of the Universe structure. The first context of this term was in fact a “missing mass” which was discovered as a deficit of luminous matter to explain all the observed gravity governing the motion inside galaxies and between them. Generally, the missing mass can be explained

This work is a review of recent results, which have been obtained within the framework of the mathematical theory of dynamical chaos and are related to the discovery of its third new form, the so-called mixed dynamics. This type of chaos considerably differs from its two classical forms, namely, conservative chaos and dissipative chaos, and the main difference is that attractors and repellers can intersect

We present the results of simulation of image recognition using invariant correlation filters. The possibilities of exploiting color information and preprocessing for quality improvement of subpixel image correlation matching are shown.

We analyze spatial characteristics of the four-wave radiation converter in a two-component medium consisting of a transparent liquid and nanoparticles with allowance for the gravity force. It is shown that allowing for the gravity force acting on nanoparticles affects significantly the efficiency of conversion of low spatial frequencies. Three ranges of effective nanoparticle masses (small, intermediate

The reconstruction methods, which are based on compressed sensing (CS), make it possible to record and reconstruct information basing on its sparse or compressed representation. In this work, we study resistance of CS-based single-pixel imaging to partial loss of the intensity of the recorded radiation from an object with a limited area of the detector. The problem was solved experimentally by implementing

We propose an original way to produce several thin helical electron beams using one common magnetic system. The proposed systems with broken azimuthal symmetry of the emission surface of the adiabatic magnetron-injection gun (MIG) can be used in multibarrel gyrotrons. Specific features of the new system are analyzed on an example of MIGs optimized for gyrotron operation at a frequency of 140 GHz and

We study the L-41 KD/84, and RD cells cultured as a monolayer on a glass substrate. This work is aimed at studying the laws of variation in the speckle-dynamics signals in space and time in the image plane of a monolayer of cells for high optical magnifications, different rates of the environmental-temperature variations, exposure to other virus types, and after the cell defrosting. It is shown that

This work is aimed at creating the theoretical basis for the method allowing one to layer-by-layer reconstruct the parameters which characterize the processes occurring in small regions of living cells. The problem of the speckle dynamics in the object-image plane, which is caused by random variations in the optical paths of the waves in various layers inside the cell, is theoretically solved for a

We describe experimental studies of the recording of the relief of a diffusely reflecting surface using a shear interferometer. The interferometer uses a Michelson scheme, but the mirrors serve to combine two identical beams displaced with respect to each other. In this case, interference arises between the neighboring points having different phases. The interference pattern reflects the change in

We give a review of both our own original scientific results of the development of superconducting receivers for sub-terahertz astronomy and the main leading concepts of the global instrumentation. The analysis of current astronomical problems, the results of microwave astroclimate research, and the development of equipment for sub-terahertz radio astronomy studies justify the need and feasibility

In this work, we solve the problem of detecting the connectivity in the ensemble of radioengineering oscillators of chaos with a delay in the own dynamics by two widespread methods, namely, the method of Granger conditional causality and the method of partial directed coherence. Both approaches are based on the empirical predictive models. The estimates are tested for significance using the surrogate

We demonstrate the possibility to use focused beams of millimeter-wave radiation to heat ceramic materials locally with the purpose of manufacturing sintered products on the basis of such materials by additive methods. The results of experiments on layer-by-layer sintering of ceramic hydroxiapatite samples heated by a gyrotron facility operating at a frequency of 24 GHz are presented.

In this work, we consider the problem of noise location of a moving acoustic source using the aperture synthesis. In this case, it is assumed that the signal, which is emitted by the source, is incoherent in time. Such a scenario is the most interesting from the practical point of view since actual sources mainly have continuous radiation spectra. It is assumed that, in addition to the sea noise, interference

We consider the maximum-likelihood algorithm for detecting a rapidly fluctuating sequence of ultra-wideband quasi radio signals with an arbitrarily shaped modulating function and unknown amplitude and initial phase, in the case where such a sequence is observed against the background of the Gaussian white noise. The structure and the statistical characteristics of this algorithm are found and its statistical

This paper summarizes the results of studying the creation of localized ensembles of NV centers in a single-crystal diamond. The diamond was doped with nitrogen during its CVD growth. Due to the use of a microwave CVD reactor, in which a rapid (a few seconds) change in the composition of the gas mixture is realized, thin (nanometer thick) doped diamond layers were obtained, the position of which relative

We study experimentally the electron distribution functions in longitudinal velocities in actual (non-modeled) operating regimes of a two-cavity gyroklystron. It is shown that as the beam’s magnetic compression factor α increases, the distribution function is transformed smoothly from the quasi-Gaussian to a multi-peak one. The main region of this evolution is longitudinal bunching of the beam, which

We show that during phase locking of the oscillations of a megawatt-level gyrotron by a relatively weak external monochromatic signal, the phase and frequency modulation of the gyrotron radiation due to the low-frequency fluctuations of the accelerating voltage and current decreases severalfold compared to the autonomous regime. The calculations were performed using the example of two megawatt-level

We analyze theoretically millimeter-wave surface-wave generators based on relativistic ribbon electron beams within the framework of the averaged quasioptical model, as well as using direct numerical modeling by the Particle-in-Cell method. The regime of excitation of π modes and the regime of the backward-wave oscillator based on a surface wave are studied. The possibility to achieve generation of

We study a new modification of the Bragg structures based on the coupling of traveling and quasicritical waves, as well as the possibility to use it as an electrodynamic system of free-electron masers (FEMs) and lasers (FELs). It is shown that inclusion of quasicritical waves in the feedback loop allows one to improve significantly the selective characteristics of Bragg structures and ensure the stable

We discuss the concept of creating sources operated in the sub-terahertz/terahertz frequency range with a multi-megawatt power level and based on the coherent spontaneous emission of intense electron bunches. The possibility of forming such bunches is due to the development of modern photo injection systems. The results of theoretical analysis and computer simulation of the dynamics of electron bunches

We study the possibility of using the technology of 3D photopolymer printing with subsequent metallization of working surfaces for developing electrodynamic components of microwave devices. The technology applicability is considered by examples of mockups of a profiled helical waveguide for a microwave undulator of a Compton free-electron laser and a periodic slow-wave system of a backward-wave oscillator

As part of the creation of a unique T-15MD tokamak with a magnetic field of 2 T and an aspect ratio of 2.2, the first one of a series (8 pieces) of microwave setups of a megawatt power level for electron–cyclotron plasma heating and current drive was developed and successfully tested. The setup includes a gyrotron, power supplies, a microwave radiation transmission line, and a fast (response time is

This work is devoted to the studies performed at the Institute of Applied Physics of the Russian Academy of Sciences and aimed at the development of the photoinjector accelerator complex, which ensures formation of the electron bunches with charges of up to 100 pC and particle energies of 3 to 5 MeV. The key elements of the complex are described, namely, the accelerating cavity powered by the klystron

The project of a high-power, spatially developed, planar surface-wave W-band generator with two-dimensional distributed feedback is developed jointly by the Institute of Applied Physics of the Russian Academy of Sciences and the Institute of Nuclear Physics of the Russian Academy of Sciences on the basis of the ELMI accelerator (an electron beam with a particle energy of 1 MeV, a current of 2–5 kA

We analyze the motion of the electron beam in the collector of a gyrotron with the shielded magnetic system. The methods of optimization of the collector are proposed, depending on the limitations imposed on its transverse dimensions. Calculations are performed for collectors of the technological gyrotrons capable of operating in a wide range of magnetic fields (1.0–1.8 T), which allows generating

Coherent subterahertz radiation in the continuous-wave regime was obtained in a large-orbit gyrotron (LOG) operated at a high harmonic of the cyclotron frequency. An electron–optical system containing a gun with a cusp followed by a section of adiabatic magnetic compression with a factor of 1000 ensures the formation of a 30 keV/0.7 A helical axis-encircling electron beam with acceptable velocity spread

Experimental study of the influence of resonant reflection of the operation mode on the gyrotron generation regimes is a topical problem of modern high-power vacuum electronics. In this work, we formulate the requirements for the external resonant reflection system and propose its development variants. We consider resonant reflectors of two types, which are intended for experiments with a gyrotron

We study the possibility to make a gyrotron generating a power of several kilowatts at a radiation frequency of 1 THz, which will be used in promising plasma studies. In 2008, a pulsed largeorbit gyrotron (LOG) generating a power of 0.4 kW at the third cyclotron harmonic and an operating frequency of 1 THz was implemented successfully. We update this device to create a plasma source of extreme ultraviolet

We present the results of studying the passband properties of gyroklystrons theoretically and experimentally and analyze the main causes of limitations in the bandwidth of the frequencies that they amplify. It is shown that in the range of low beam currents, where the electron velocity spread is rather low, the amplification bandwidth of a two-cavity gyroklystron is close to the bandwidth of the output

We study the oscillation regimes for the model of a gyrotron with a fixed Gaussian longitudinal field structure and three modes of an equidistant spectrum (an operation mode and two satellites symmetrically spaced by frequency) during autonomous operation and under the action of an external monochromatic signal. The two-parameter (dimensionless current and the cyclotronresonance mismatch for an operating

Based on the analysis of electron–wave interaction, we study the possibility of developing a gyrotron that is able to provide a megawatt output power in quasi-continuous (long-pulse) oscillations at both first and second gyrofrequency harmonics. For selective excitation at the second cyclotron harmonic when the operating current is significantly higher than its starting value, we propose to lock the

We study theoretically the possibility to widen the frequency tuning bandwidth of the generation of subterahertz gyrotrons by using strong signal reflections by periodic structures of the Bragg type installed in the output line. It was shown earlier that wideband tuning is possible in gyrotrons with short cavities, where the use of such cavities reduces the sensitivity of excitation of higher longitudinal

We propose a method for two-stage compression of laser pulses, which makes it possible to shorten laser pulses of tens of picoseconds to an optical period with an energy efficiency of tens of percent. The method involves sequential use of the Raman compression (compression to a duration of tens of femtoseconds and the self-compression of the pulse to the field period when exciting the wake plasma wave

We consider the problem of predicting the channel characteristics for the high-mobility users of the LTE communication system. An algorithm is proposed for predicting the channel coefficients on the basis of a parameterized autoregressive model whose parameters should be estimated using the superresolution methods of spectral analysis. Using numerical simulation and the system-level simulator, we estimate

We analyze the features of energetic electron precipitation (with the maximum energy E ≥ 150 keV) from the Earth’s radiation belt into a magnetically conjugate region of the ionosphere (relative to the Sura facility) during modification of the ionospheric F2 region by high-power HF O-mode radio waves in the regime of their continuous radiation. Precipitation was recorded by the DEMETER satellite at

We consider the Bose-condensate population statistics for a gas of interacting particles confined into a three-dimensional cubic trap with different boundary conditions at a low temperature. Behavior of the mathematical expectation and variance of the condensate population with the system size increase corresponding to the transition to a thermodynamic limit at constant temperature and density of the

We study the properties of the cyclotron amplification of whistler-mode waves during their propagation in the Earth’s magnetosphere in the presence of large-scale density inhomogeneities such as the plasmapause or density ducts. Wave propagation is considered within the framework of the geometrical optics with the use of cold plasma density profiles measured onboard the Van Allen Probes satellites

We model the diffraction of a plane TE-polarized electromagnetic wave by a parabolic structure consisting of N parallel circular cylinders, where N ∼ 50. The problem of diffraction of a plane wave by a cylinder with arbitrary coordinates of its center is solved. The coupling of individual structural elements is not allowed for in the performed calculations. The field behavior in the vicinity of the

Synchronization of neural activity plays an important role for processing of information in the brain. In this work, we study the dynamics of a neural network with plastic synaptic connections under the action of a spatially localized stimulus. It is established that synchronization of all the network neurons by a local action is possible in a certain range of periodic stimulation. The network forms

We present the results of the ground-based microwave measurements of evolution of the vertical ozone content in the middle atmosphere above Nizhny Novgorod (56°20' N, 44° E) in the winter of 2017–2018. The results are compared with the satellite-based sensing data obtained using the MLS instrument onboard the Aura satellite and the ERA5 reanalysis data. In particular, the degree of the dependence of

We study experimentally the spectral characteristics of low-frequency current fluctuations in tungsten filaments of lighting lamps in the ranges of frequencies 2.5・10−4 – 5・10−1 Hz and temperatures 1260 – 2600 K. To decrease the influence of the edge effects and increase the measurement accuracy, we use subtraction (compensation) of the constant component of the current. Application of special schemes

We analyze the resonant interaction of energetic electrons with auroral kilometric radiation (AKR). Possible regimes of such an interaction are studied on the basis of a numerical solution of the particle motion equations in a given field of a quasi-monochromatic AKR wave packet. It is shown that for realistic wave amplitudes 0.2–0.4 V/m, the interaction can be highly nonlinear. As a result of nonlinear

We analyze the temporal and spatial variability of the satellite-measured brightness temperature above the ocean in the frequency range of resonance absorption in the atmospheric water vapor and the humidity characteristics of air, as well as their interrelations in the regions of the development of tropical hurricanes and their propagation from the initiation areas. The examples illustrating the possibility

Global navigation satellite systems (GNSS), such as GPS, GLONASS, Galileo, and Bei-Dou/Compass are widely used for solving a variety of research and applied problems. This work considers the use of GNSS signals for monitoring of the ionosphere to provide an ionospheric error correction in radio-engineering systems in quasireal time. The problems arising in this case, among which the absolute ionospheric

We consider the problem of using the concept of a virtual antenna array in a MIMO radar for estimating the angular location of the target in the presence of signals reflected from the ground surface. The formal criteria of realizability of a virtual antenna array are formulated. Various antenna configurations are analyzed theoretically. The restrictions on the location of the receiving and transmitting

We propose a fundamentally new scheme of the multibarrel gyrotron. As an example, we consider three promising variants of implementation of the scheme with a generation frequency of about 140 GHz or its multiple in the case of operation at higher cyclotron harmonics. A variant of a multibarrel gyrotron with wide-range continuous frequency tuning about 13.1 GHz is discussed. The possibility of operating

We study the emergence of steady wave packets in the form of envelope solitary waves (envelope solitons) which evolve from localized pulse-type initial conditions in the long-term evolution within the framework of the Ostrovsky equation. Ostrovsky equation derived in 1978 describes weakly nonlinear oceanic waves affected by the Earth’s rotation. Subsequently it became clear that this equation is universal

We numerically simulate filtration noise within the framework of the earlier proposed model for the generation of acoustic noise as a result of excitation of relaxation self-oscillations. The simulation is performed for typical parameters of reservoir rocks. As a result, appearance of the radiation frequencies observed in the experiment is demonstrated. It is also shown that due to the nonlinear interaction

On the basis of using the Jones vectors and matrices, we develop the polarization-modulation method for determining the aircraft bearing and roll by the radio-beacon radiated waves with orthogonal linear polarization, which was proposed in [1]. The waves are simultaneously radiated from two points with the known coordinates, which are spaced in the measurement plane. The engineering realization of

We present the results of a theoretical calculation and an experimental study of double-sided antireflective processing of a dielectric plate by creating a specially profiled corrugated structure on its surface. Such a structure allows one to minimize the reflection coefficient of an electromagnetic wave to a level of about −30 dB within a range of at least one octave. This antireflective effect can

We propose a small-scale transport model of the electric-discharge tree formation and analyze its implementation for a characteristic case of the thundercloud conditions. The following innovative features of the model can be emphasized: no connection to the spatial grid, high spatiotemporal resolution, and allowance for the asymmetry of the development of the positive and negative streamers and the

We describe a method for joint analysis of the night-sky snapshots and total electron content (TEC) variation maps and present a dynamic spatiotemporal configuration of the TEC variation intensity in the ionospheric airglow region in the red line of atomic oxygen (λ = 630 nm) stimulated by high-power radio waves from the Sura facility. The measurements were performed on the 29th of August, 2016. Two-dimensional

We present the results of the studies of propagation of longitudinal acoustic waves in the media with a power-law hysteresis nonlinearity. Exact analytical solutions for the self-similar periodic waves propagating in such media without changing their forms are given. The spectral characteristics of these waves are studied.