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The paper is devoted to a comparison of the results of an experimental study of a 28 GHz/25 kW gyrotron with a magnetically shielded system and the results of calculating the electron–wave interaction with the use of the ANGEL software code on the basis of a self-consistent model with an unfixed radio-frequency field structure. The good agreement between the results confirms the validity of using the developed code for creation of new gyrotrons. Comparison of various experimental data with the calculation results for the electron–wave interaction as well as for electron optics makes possible implicit reevaluation of the actual values of some important gyrotron parameters (the electron pitch factor, transverse velocity spread, etc.). [ABSTRACT FROM AUTHOR]

The paper presents a brief review of the quasiclassical wave dynamics for the nonlinear Schrödinger equation (NLSE) as applied to focusing and defocusing media. The NLSE depends significantly on the space dimension d. The two-dimensional NLSE has an additional symmetry of the conformal type with respect to the Talanov transformations (Talanov in JETP Lett. 11:199–201, 1970), which were initially found for the stationary self-focusing in a medium with the Kerr nonlinearity. A consequence of this symmetry is the Vlasov–Petrishchev–Talanov theorem (Vlasov et al. in Radiophys. Quantum Electron. 14:1062–1070, 1971) that relates the mean of the squared distribution and the Hamiltonian of the system. This theorem is valid for both focusing and defocusing media. In the quasiclassical limit, this makes it possible to construct anisotropic solutions which describe beam compression during self-focusing and quantum-gas expansion into vacuum within the so-called critical nonlinear Schrödinger equations, in particular, for the Gross–Pitaevskii equation with a chemical potential having a power-law dependence on density with the exponent ν = 2/d. For the Gross–Pitaevskii equation, the case d = 2 corresponds to a condensate of a weakly nonideal Bose gas, and the case d = 3 describe condensate of a Fermi gas in the unitary limit. For d = 3, the Gross–Pitaevskii equation in the quasiclassical limit transforms into equations of the gas dynamics with the adiabatic exponent γ = 5/3. The self-similar solutions in this approximation describe the angular deformations of a gas cloud against the background of an expanding gas. Angular deformations of such type are observed in both the expansion of quantum gases and the action of high-power laser radiation on matter. For three-dimensional supercritical focusing NLSE, the quasiclassical solutions of the collapsing type are presented, including the exact semiclassical solution described by the strong collapse regime. It is found that all such quasiclassical collapses are found to be unstable, except for the collapse that is simultaneously the weakest and the fastest collapse corresponding to the self-similar NLSE solution. The problem of post-collapse is also considered as the continuation of a weak collapse, which results in the formation of a quasistationary singularity in the form of a black hole into which energy is drawn from the surrounding collapsing region. For the NLSE with d ≥ 4, the formation of a black hole can be described in the quasiclassical approximation. It is shown that the anisotropy caused by the magnetic field significantly alters the structure of the Langmuir collapse, in particular, leads to the formation of strongly anisotropic black holes described quasiclassically. [ABSTRACT FROM AUTHOR]

By convention, water waves are studied under the assumption of their potentiality. This approximation is not always valid in natural conditions. The vorticity is introduced by shear currents, which are ubiquitous in the ocean. It is also generated in the near-surface layer as a result of wind action. When these factors are taken into account, the models developed for potential waves require refinement and generalization. This paper is devoted to a review of advances in the field of analytical description of surface vortical waves in deep water. The presentation is based on the Lagrangian approach. The focus is on the Gerstner wave, a particular exact solution of the Euler equation. Two ways of its generalization are discussed. The first suggests consideration of weakly nonlinear steady waves with a more general vorticity distribution (Gouyon waves). The second way is to construct exact solutions for waves with inhomogeneous and non-stationary pressure distribution on a free surface (generalized Gerstner waves). [ABSTRACT FROM AUTHOR]

The paper proposes an ingenious method for global ionospheric total electron content (TEC) mapping based on a phase-difference approach to the analysis of phase measurements of GNSS signals at a pair of coherent frequencies on a distributed network of ground-based receivers of the global IGS network. The proposed approach uses the representation of the ionosphere as a thin layer with the TEC distribution given by a truncated expansion into a series of spherical harmonics in the Sun-synchronous geomagnetic coordinate system. The expansion coefficients are determined by the least squares technique with a TEC positivity constraint, which is implemented by solving the corresponding linear complementarity problem. The proposed method does not require estimation of the differential code biases of both satellites and receivers, which makes it possible to combine data from various GNSS, such as GPS, GLONASS, and Galileo, within a single algorithm. The results of testing the proposed method on synthesized observation data using the real geometry of GNSS satellites, IGS receivers, and the ionosphere given by the NeQuick2 model, are presented. The results of comparing the real global ionospheric maps obtained by the proposed method and the maps of the CODE center are reported. [ABSTRACT FROM AUTHOR]

In this paper, following the review talk at the 33rd Russian–German Workshop on Gyrotrons and ECRH (Nizhny Novgorod, November 2–3, 2021), we use the GDT facility (Budker Institute of Nuclear Physics) as an example to discuss the physical principles and implementation of the fast-ion velocity distribution function diagnostics based on recording of collective Thomson scattering spectra of high-power millimeter-wave radiation in large-scale open magnetic traps used in fusion research. [ABSTRACT FROM AUTHOR]

Research on one of the methods for generation of high-power radiation flows in the subterahertz/terahertz frequency range using the GOL–PET facility is underway at the G. I.Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences (BINP SB RAS). This method consists in using the mechanisms of conversion of the plasma waves excited by a relativistic electron beam (REB) into an electromagnetic radiation flow. In the course of research, a number of mechanisms by which plasma oscillations are converted into radiation were revealed, and a power level of 10 MW was experimentally achieved in a directed submillimeter radiation flow with a duration of a few microseconds. This paper is devoted to the study of radiation generation as a function of the degree of compression of the REB cross section. The compression degree was varied in the experiments by varying the magnetic field distribution along the axis of the facility. The magnetic field was varied uniformly along the entire facility axis. In addition, the configuration with an increased ratio of fields in the accelerator diode and in the plasma section of the facility was considered. As a result of the experiments, it was shown that a decrease in the strength of the guiding magnetic field by a factor of 1.6 does not lead to a change in the radiation generation mechanism. [ABSTRACT FROM AUTHOR]

The multilevel fast multipole algorithm (MLFMA) is often used to speed up the solution of surface integral equations in electromagnetics. The method makes it possible to calculate electrodynamic systems with characteristic sizes of hundreds of wavelengths on a personal computer in a relatively short time (a few hours). The paper demonstrates the use of the MLFMA together with the principle of physical optics for fast calculation of microwave radiation between the elements of the mirror transmission lines. The complexity of the calculation is O(NlogN), where N is the number of elementary parts of the mirror surfaces involved in the calculation. Thus, the calculation time for a transmission line with characteristic total mirror sizes of hundreds of wavelengths is a few minutes. By using this method, it is also possible to significantly speed up the calculation of fields in oversized transmission lines, including both waveguides and mirrors, without loss of accuracy. [ABSTRACT FROM AUTHOR]

Multicavity continuous-wave gyroklystrons generating moderate powers in the short-wave part of the millimeter-wave band can be used as highly stable frequency-tunable microwave sources in such applications as radar ranging, wireless telecommunication systems for digital communications, plasma diagnostics, microwave material processing, generation of multi-charge ion beams, and high-resolution spectroscopy on the basis of nuclear magnetic resonance (NMR) and dynamic polarization of atomic nuclei. In this paper, the proposed method is used to calculate optimal parameters of a four-cavity CW gyroklystron operating in the three-millimeter wavelength band in the maximum amplification regime. The design of a gyroklystron with the operating TE011 mode is described, and the results of studying it experimentally are presented. They demonstrate that an output power of 2.5 kW is achieved at a frequency of 92 GHz with an efficiency of 25% at an accelerating beam voltage of 22 kV and a current of 0.46 A. The fact that the power and efficiency are limited by the achieved values is determined by an uncontrollable avalanche-type increase in the emission current, which is caused by the cathode heating due to its bombardment with electrons reflected from the magnetic mirror. The gain and bandwidth of the amplified frequencies, which were measured at a power level of 2 kW at a beam current of 0.3 A, were equal to 28 dB and 320 MHz (0.36%), respectively. The experimental results agree well quantitatively with the results of the calculations. [ABSTRACT FROM AUTHOR]

In this paper, the method of transforming the Mössbauer gamma radiation into a train of ultrashort pulses in a resonant nuclear absorber, which harmonically oscillates as a whole along the direction of radiation propagation [1], was generalized to the case of multifrequency absorber oscillations. Based on the example of the Mössbauer absorber 57Fe and the radioactive Mössbauer source of 14.4 keV photons 57Co, it is shown that under optimal conditions, adding new harmonics of the fundamental frequency to the law of absorber motion makes it possible to reduce the duration and increase the intensity of the generated pulses while maintaining their repetition period. An optimal law of absorber motion leading to the formation of the shortest and most intense pulses is derived. It corresponds to periodic fast displacements of the absorber relative to the source by the wavelength of resonant radiation. In this case, the duration of each individual pulse of the output radiation is determined by the duration of the constructive interference that appears and disappears with a rapid change in the relative phase between the incident field and the field coherently forward-scattered by the nuclei of the moving absorber due to the Doppler effect. The possibility of transforming quasi-monochromatic radiation into a single intense short pulse, the duration and instant of the formation of which are determined by the duration and instant of the onset of the absorber displacement, is shown. [ABSTRACT FROM AUTHOR]

The emergence of the pedestrian-induced bridge instability is conventionally associated with crowd synchrony; however, this view has been challenged. In this paper, we use a bio-mechanical pedestrian model in the form of an active inverted pendulum to analyze the average contribution of a single pedestrian to possibly uncorrelated crowd dynamics and bridge oscillations. We obtained that depending on the ratio of the bridge vibration and walking frequencies, the pedestrian can amplify bridge vibration or, surprisingly, extract energy from the bridge and damp bridge oscillations. In particular, we show that different combinations of the bridge and pedestrian step frequencies corresponding to the same or close frequency ratios can trigger two drastically different bridge dynamics, with enhanced or suppressed oscillations far from the resonances. [ABSTRACT FROM AUTHOR]

Nonlinear acoustic nondestructive evaluation (NA NDE) methods have a higher sensitivity for defect detection than standard methods. These methods use various kinds of acoustic wave interactions. In this paper, we suggest augmenting the acoustic framework and use the interaction between acoustic and electromagnetic waves. A brief review of NA NDE and medical nonlinear acoustic imaging methods is presented. Medical methods based on electromagnetic wave modulation by an acoustic radiation force are discussed where improvements using ultrasound contrast agents are suggested. The estimation of the modulation of a radar signal by a crack vibration were made based on standard static measurements. The effects of modulation of an acoustic wave by an electromagnetic field are briefly considered for the method of crack detection in metal materials. The effects considered in this paper may be used in the new methods of NDE and medical diagnostics. [ABSTRACT FROM AUTHOR]

Presents a commentary to the paper "Influence of Radiation Coherence on the Effects of Polarization Nonreciprocity of Fiber Ring Interferometers," by I. A. Andronova. Association of polarization phase nonreciprocity to the interference of counterpropagating waves; Comments on the results of the study.

It has been proved by computer simulation methods that for given antenna parameters, three parts of energy of ultrashort electromagnetic pulses, namely, energies emitted to the far zone, perceived by the receptor load, and reflected back from the antenna to the oscillator, significantly and differently depend on the duration of the leading and trailing edges of the excitation pulse. The technique proposed in the paper permits finding tradeoff solutions in the design of energetically efficient radiators intended for testing technical equipment for immunity to electromagnetic impacts. [ABSTRACT FROM AUTHOR]

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 settings. In this paper, a new approach is proposed to determine the risks of shear-induced thrombus formation. This approach is applicable for a wide range of objects including aorta and mechanical circulatory assist devices. The geometry of the vascular walls in numerical experiments is chosen to be isomorphic to that of the blood vessels in a human body. Promising ways to reduce the risks of thrombus formation activation in high blood flows have been found. The developed technique can be used by physicians to plan personalized strategies for antithrombotic therapy based on individual shear-induced platelet activation risks. [ABSTRACT FROM AUTHOR]

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 phase at each point. Two variants of the scheme were employed in the experiments: one scheme uses a magnifying lens near the sample and the other, a projection lens near the interferometer. The paper also presents the results of numerical simulation aimed at studying the ultimate capabilities of the method. A model part, on the surface of which four groups of geometric figures with different configurations were formed, was used as the test object. This allowed one to determine the limiting spatial resolution, the limiting displacement along the optical axis, the limiting angular sensitivity, and the possibility of finding the surface profile. [ABSTRACT FROM AUTHOR]

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 to the substrate surface is known with high accuracy. The possibility of forming a matrix of NV centers localized on the crystal surface is demonstrated. The results of studying the fluorescence of NV centers in such structures are presented. [ABSTRACT FROM AUTHOR]

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, and a pulse duration of 5 μs). The electrodynamic system of the generator is based on the use of a two-dimensional Bragg structure that combines the properties of a slow-wave system, which ensures efficient ˇ Cerenkov interaction with a rectilinear ribbon electron beam, and a high-Q cavity, which ensures selective excitation of the operating mode in the conditions of a significant value of the oversize parameter. The paper discusses design elements and parameters of the generator and presents the modeling results that demonstrate the possibility to achieve a stable narrow-band generation regime with a gigawatt level of the output radiation power. To ensure a mainly one-directional output of the radiation, a planar Bragg reflector was designed, which is installed in the channel for transportation of the relativistic ribbon electron beam on the cathode side of the interaction space. [ABSTRACT FROM AUTHOR]

This paper proposes, and practically implements, a technique for finding equivalent frequencies, which are attributed to the atmospheric optical depths measured by a two-channel wideband radiometric system in the millimeter wavelength range. Establishment of the equivalent frequency (averaged over the frequency response of the system) in the corresponding atmospheric transparency window makes it possible to relate wideband measurements of the optical depth with narrowband radiometric measurements used in standard calculations of integral humidity. The search for equivalent frequencies is based on a comparison of experimental data on the effective transparency in the millimeter wavelength range and integral humidity of the atmosphere by simulation of a real atmosphere using the MPM Liebe model. The developed method of consistent determination of humidity and transparency of the atmosphere in the millimeter wavelength range can be used for both millimeter-wave radioastronomy and high-performance space telecommunications. In particular, the method specifies the spectral characteristics of the measured atmospheric transparency for the studied radio astronomy site and estimates the astroclimate conditions. [ABSTRACT FROM AUTHOR]

We show that the radiation patterns of two-dimensional systems in the form of arrays depend on the duration of the emitted pulses. To study such systems, we propose to use the correlation length depending on the pulse duration and the emission direction. The obtained formula for the length of correlation in two-dimensional systems is convenient for description of distortions in the radiation patterns, which are caused by shortening the duration of the emitted pulses. In this paper, we consider the effect of suppression of side lobes in radiation patterns. This is a general effect, since it is related to the delay of signals from different parts of the emitting system. In particular, it is observed in optical systems of the diffraction grating type, in which a decrease in the intensity of diffraction maxima in the case of pulse duration shortening can be used as the basis for a new method of estimation (or measurement) of the duration of optical pulses. [ABSTRACT FROM AUTHOR]

The concept of Compton-type free-electron lasers (FELs) operating in short wavelength ranges with a high efficiency and power level is currently underway at the IAP RAS (Nizhny Novgorod). This concept is aimed at reducing the energy of a driving relativistic electron beam and thereby increasing the efficiency of the electron–wave interaction in FELs, as well as making the oscillator relatively compact. The basis of this concept is microwave undulators of a new type—the so-called "flying" undulators. This paper is devoted to the results of the current studies of these undulators, their simulation, and "cold" electrodynamic tests in the Ka band. For powering microwave undulators, a spatially extended narrow-band ˇ Cerenkov surface-wave oscillators (SWOs) are developed in the specified frequency range driven by Sinus-6, a high-current accelerator, with a particle energy of 0.5 MeV, a current of 5 kA, and a pulse duration of 25 ns. The required sub-gigawatt power level of output radiation combined with a high stability of the narrow-band oscillation regime is achieved under conditions of a strongly oversized oscillator by using two-dimensional distributed feedback provided in a 2D doubly-periodic slow-wave structure. The design parameters of a 32 GHz/0.5 GW SWO intended for powering microwave undulators are presented and the results of its simulation and reported. [ABSTRACT FROM AUTHOR]

The gyrotron traveling-wave tube (gyro-TWT) is a wideband version of gyrotron amplifiers, which produce pulsed or continuous-wave radiation in the millimeter-wavelength band at a power level that exceeds the powers produced by conventional TWTs with slow-wave structures and rectilinear beams by 1–2 orders of magnitude. Since 1996, researchers at the Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS) have been developing the concept of the gyro-TWT based on the use of a waveguide with a helically corrugated surface, which changes the dispersion of one of the eigenmodes in a circular waveguide radically. In this paper, we discuss several problems that arise in implementation of such devices, which many years of experimental studies have revealed, present the parameters of gyro-TWTs developed with allowance for specific applications of their end users, and discuss lines of further perfection of such amplifiers. [ABSTRACT FROM AUTHOR]

We analyze the integral parameters of resonant interaction of relativistic electrons in the Earth's radiation belts with electromagnetic ion-cyclotron waves. The analysis is based on numerical simulations. Wave packets of finite length with varying frequency and various amplitude profiles propagating from the equator are considered. The roles of three nonlinear interaction regimes, analyzed in the first part of our paper [1] for single particle trajectories, are compared. It is shown that interaction characteristics depend stronger on the electron energy and wave packet position for the wave packet with Gaussian amplitude profile than for the wave packet with constant amplitude. For the wave packet with Gaussian amplitude profile, the directed and diffusive transfer of particles in the phase space are comparable, while for the wave packet with constant amplitude the mean change in the equatorial pitch angle can be considerably (a factor of 3 to 5) greater than the standard deviation. The most significant decrease in the equatorial pitch angle and the largest fraction of the corresponding particles are obtained for particles with energies of about 1 MeV for the wave packet close to the equator. The fraction of particles which can be scattered into the loss cone after a single pass through the wave packet is 1.0-1.7%. [ABSTRACT FROM AUTHOR]

We consider the dispersion characteristics of electromagnetic waves in a plasma with strong magnetic field and equal content of relativistic electrons and positrons, whose synchrotron radiation can be the source of optical radiation of a pulsar. It is shown that when a small fraction of nonrelativistic protons with a nonequilibrium distribution function is present in the plasma, an effective instability can develop at frequencies below the first harmonic of the relativistic gyrofrequency of electrons, namely, at the harmonics of the proton gyrofrequency. This instability leads to the excitation of the O- and X-mode electromagnetic waves, which can, in principle, be related with the observed pulsar radiation. In part I of this paper, we study dispersion characteristics of low-frequency electromagnetic waves (with frequencies below the relativistic gyrofrequency of electrons) in an ultrarelativistic electron-positron plasma with an isotropic momentum distribution function of the particles. Instabilities of the O- and X-mode waves and the conditions of escape of the radiation from the region of strong magnetic field into a rarefied isotropic plasma will be considered in paper II. The results can be used in the interpretation of known experimental data on the dynamic pulsar radiation spectra obtained with high temporal and frequency resolution. [ABSTRACT FROM AUTHOR]

Two modern radars for diagnosis of the ionosphere by the radio-wave backscattering method, namely, the Irkutsk incoherent scatter radar at VHF (IISR, 154-162 MHz) and the Ekaterinburg coherent radar at HF (EKB, 8-20 MHz) are operated at the Institute of Solar-Terrestrial Physics, Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS). The paper analyzes the results of joint observations of strong scattering (radio aurora) on June 8, 2015. To determine the geographical position of the radio aurora, we developed original methods that take into account both the features of the radio-wave propagation and the features of the radar antenna systems. It is shown that there are areas where the spatial position of the HF and VHF radio aurora can coincide. This permits using the radars as a single complex for diagnosis of the characteristics of small-scale high-latitude irregularities in the ionospheric E and F layers. A comparative analysis of the characteristics and temporal dynamics of the radio-aurora region in the HF and VHF ranges is performed. Using the DMSP satellite data, it has been shown that the radio aurora dynamics during this experiment with the EKB radar can be related with the spatial dynamics of the localized area with high electric field, which moves from high to equatorial latitudes. It is found that due to the broader field of view, radio aurora at the HF radar was stably observed 6-12 min earlier than at the VHF radar. This permits using the EKB radar data for prediction of the radio-aurora detection by the IISR radar. [ABSTRACT FROM AUTHOR]

Dynamic nuclear polarization in strong-field nuclear magnetic resonance (NMR) spectroscopy requires terahertz radiation with moderate power levels. Nowadays, conventional gyrotrons are used almost exclusively to generate such radiation. In this review paper, we consider alternative variants of electronic microwave oscillators which require much weaker magnetic fields for their operation, namely, large-orbit gyrotrons operated at high cyclotron-frequency harmonics and Čerenkov-type devices, such as a backward-wave oscillator and a klystron frequency multiplier with tubular electron beams. Additionally, we consider the possibility to use the magnetic field created directly by the solenoid of an NMR spectrometer for operation of both the gyrotron and the backward-wave oscillator. Location of the oscillator in the spectrometer magnet makes it superfluous to use an additional superconducting magnet creating a strong field, significantly reduces the length of the radiation transmission line, and, in the case of Čerenkov-type devices, allows one to increase considerably the output-signal power. According to our calculations, all the electronic devices considered are capable of ensuring the power required for dynamic nuclear polarization (10 W or more) at a frequency of 260 GHz, whereas the gyrotrons, including their versions proposed in this paper, remain a single option at higher frequencies. [ABSTRACT FROM AUTHOR]

Observations of quasi-periodic intense radio emission at 2-8 GHz from the brown dwarfs with a brightness temperature of up to T ∼ 10 K and with a fairly narrow radiation pattern initiated a series of studies in which the radiation was interpreted in terms of the electron cyclotron maser emission generated by energetic electrons with the 'loss cone.' The plasma mechanism of the radio emission was excluded from consideration because it requires that the electron plasma frequency should exceed the electron gyrofrequency in the source of the radio emission, i. e., ν > ν. In this paper, we propose a coherent plasma radiation mechanism for intense radio emission from the brown dwarfs. The possibility of the formation of hot extended coronae in the magnetic loops that occur in the atmospheres of the brown dwarfs as a result of the photospheric convection is shown. The electric currents generated in the magnetic loops by photospheric convection lead to the plasma heating and elevation of the 'squeezed' atmosphere. This ensures that the condition ν > ν required for the plasma mechanism of radio emission is fulfilled at the coronal levels. In addition, the pumping mechanism supplying energetic particles into the coronae of the brown dwarfs, which maintain the long-term generation of intense radio emission from these stars, is studied. The parameters of the Langmuir turbulence explaining the observed properties of the radio emission from the brown stars are determined. [ABSTRACT FROM AUTHOR]

In this series of papers, we propose a method for the development of an approximate solution of the Maxwell equations in smoothly inhomogeneous anisotropic gyrotropic media with allowance for aberrations, spatial dispersion, and absorption. The connection with the aberration-free approximation equations is shown. In the first paper of the series, we propose a procedure for the development of an approximate scalar wave equation aimed at description of the single-mode propagation of wave beams. [ABSTRACT FROM AUTHOR]

Until now, significant progress has been made in synthesizing the current-switched structure of spin valves and magnetic tunnel junctions with hysteresis dependences of the resistance on the current. These structures are of interest for creation of small-size electronic memory. However, hysteresis of resistance, which is usually presented in publications, does not correspond to physical principles. In this paper, we show how the hysteresis dependence of the resistance on the current, or the conductance on the voltage, which does not contradict the energy conservation law, and the corresponding current-voltage characteristic should look like. As an example, we present the experimental current-voltage characteristic of the COMnSi/MgO/CoMnSi magnetic tunnel junction, which agrees with the model hysteresis dependences. [ABSTRACT FROM AUTHOR]

In this paper we systematize the results of studying the characteristics of the plasma-density ducts, which was conducted in 2005-2010 during the DEMETER-satellite operation. The ducts are formed at altitudes of about 700 km as a result of the ionospheric F region modification by high-power high-frequency radio waves radiated by the midlatitude SURA heating facility. All the performed measurements are used as the basis for determining the formation conditions for such ducts, the duct characteristics are studied, and the opportunities for the duct influence on the ionosphere-magnetosphere coupling and propagation of radio waves of various frequency ranges are demonstrated. The results of numerical simulation of the formation of such ducts are presented. [ABSTRACT FROM AUTHOR]

We study the possible origin of long-lasting soft X-ray flares on the AD Leo star, which were observed onboard the Extreme Ultraviolet Explorer (EUVE) spacecraft for the period of 1993-2000 [1]. These flares have relatively long rise and decay times of the radiation intensity ( τ ≈ 10 s and τ ≈ 5 · 10, respectively), as well as a relatively large emission measure EM ≈ 10cm, which exceeds by 1-3 orders of magnitude the emission measure of soft X-ray flares on the Sun. Assuming that the radiation appears in magnetic loops and basing on the observed values of the emission measure and radiation decay time, the authors of [1] determined the typical length $$ \overline{l}\approx 1.5\cdot {10}^{10} cm $$ , electron number density $$ \overline{n}\approx 3\cdot {10}^{11}c{m}^{-3} $$ , and plasma temperature $$ \overline{T}\approx 2.5\cdot 107 $$ K of the loops. This paper considers plasma heating due to dissipation of the electric currents in the coronal magnetic loops of the star induced by the photospheric convection. The large inductance of the loop as an equivalent electric circuit determines the long time of the current rise in the source and explains the observed time of plasma heating and the rise time of the X-ray radiation intensity. It is shown that the parameters of the X-ray sources in the AD Leo atmosphere agree with the parameters calculated under the assumption of simultaneous emission of a great number of loops (about 50) with electric currents greater than 10 A, which exceeds the electric currents in the solar coronal magnetic loops by 1-3 orders of magnitude. Such an exceeding can be related to the higher photospheric convection velocities on the late-type stars compared with the Sun. [ABSTRACT FROM AUTHOR]

The method considered in this paper for developing a spectroscopic database of moist-soil dielectric properties in the microwave band is based on the generalized refractive mixing dielectric model proposed in [1, 2]. This model makes it possible to derive the Debye parameters of bound and free soil water and also the maximum bound-water fraction value for different types of soil by using dielectric-constant (DC) and loss-factor (LF) measurement data as functions of the volumetric moisture content. A set of these parameters, complemented with DC and LF values for dry soil, permits one to calculate the mentioned characteristics for moist soil in the entire microwave band. In this paper, the method developed in [1, 2] is used for deriving the spectroscopic parameters of moist soils on the basis of the DC and LF data measured in [ABSTRACT FROM AUTHOR]

In this review comprising two papers, we discuss the results of studying the influence of random irregularities of a medium on nonlinear wave interactions. In this paper representing the first part of the review, we summarize the results of studying the mean fields of interacting waves in the presence of three-dimensional random irregularities and discuss the basic approximations within the framework of which these results are obtained. [ABSTRACT FROM AUTHOR]

The majority of known works on the theory of multiple scattering of electromagnetic waves in media with strong fluctuations are constrained by the assumption of statistical homogeneity of a medium. In this paper, we consider an isotropic lossy random medium, for which the principle value and multipole moments of the permittivity are invariant with respect to arbitrary rotations about a fixed symmetry axis and translations along the axis and are inhomogeneous in the radial direction. This paper is aimed at calculating the effective permittivity operator (EPO) for such a medium for the case of strong permittivity fluctuations. [ABSTRACT FROM AUTHOR]

We study the super-low-frequency field of a grounded horizontal electric dipole on a high-latitude submeridional path having a length of up to 1000 km. Unlike most of the earlier works, this paper considers the case of wave propagation along the dipole axis, where the main component of the magnetic field is radial. The frequency dispersion of the ground conductivity under the source, which determines the coefficient of excitation of the Earth-ionosphere waveguide, is found from the measurements of the field at a distance of three heights of the ionosphere. Typical parameters of propagation of super-low-frequency waves are refined allowing for specific features of the path used in the experiment. The significance of allowing for ground conductivity as the radiation propagates along low-conductivity regions is demonstrated. The regions where one of the magnetic-field components is predominant are calculated in a polar coordinate system linked to the source, as well as the regions where the both components should be allowed for. The theoretical possibility of determining the phase velocity of the wave based on the ratios of the magnetic-field components measured at longer lengths is noted. [ABSTRACT FROM AUTHOR]

This paper is devoted to an analytical study of the one-dimensional stationary system of equations for modeling of the electrode effect in the Earth's atmospheric layer with aerosols. New integrals of the system are derived. Using these integrals, the expressions for solutions of the system and estimates of the electrode layer's thickness as a function of the aerosol concentration are obtained for numerical parameters close to real. [ABSTRACT FROM AUTHOR]

We present the results of observations of the Doppler frequency shift for the radar radio signals of broadcast and exact-time RWM stations, which are scattered by small-scale artificial ionospheric irregularities. By the method described in our previous paper [1] and using the multifrequency HF Doppler radar, estimates were made for a three-dimensional vector of the drift velocity of irregularities. It is shown that the drift velocity of irregularities can vary considerably both in magnitude and direction for short periods of time. The velocity lies in a wide range of values, 20-270 m/s, but sometimes it exceeds 500-700 m/s. The most probable drift velocity ranges from 40 to 70 m/s. [ABSTRACT FROM AUTHOR]

In this theoretical paper, we propose a method for measuring the temperature profile in the active topsoil of the Arctic tundra using observations of the brightness temperature for two different polarizations of the radiation at frequencies of 1.4, 6.93, 7.3, and 10.7 GHz. A multifrequency physical model of microwave emission of bare soil, a dielectric model of the Arctic tundra soil, and temperature profiles, which were measured in the active topsoil at the Toolik field station on the Alaska North Slope, were used to calculate the observed values of the brightness temperature. Temperature profiles were retrieved from the observed values of the brightness temperature in the approximation of a piecewise-linear profile of topsoil temperature during 2010-2011. Correlation analysis of the temperature profiles measured at the Toolik station and retrieved from the radiometric data has shown that in winter the error of measurement of the soil temperature at depths of 0.6 and 16.0 cm in terms of the variance (correlation coefficient) does not exceed 2.3 (0.98) and 7.2 (0.62°C), respectively. In summer, the error of measurement of the soil temperature using the radiometric method is two times less than in winter. [ABSTRACT FROM AUTHOR]

This paper aims at analyzing the broadband part of electromagnetic emission from thunderclouds in a frequency range of tens of kilohertz to hundreds of megahertz. A model of the intracloud lightning discharge formation is presented. The lightning formation is described as a stochastic growth of the branching discharge channels, which is determined by the electrostatic field. The dynamics of the electric field and of the charge distribution over the lightning structure is calculated deterministically. The effect of the initial charge density in the cloud and the parameters of the conducting channels on spatio-temporal characteristics of the currents and structure of the lightning discharge is studied. The discharge radio emission is calculated by summing up the radiation fields of each channel at the observation point. The standard model for a separate discharge current is adopted, and the electromagnetic radiation in the far zone is estimated. It is found that the obtained frequency spectra exhibit a universal power-law behavior. The results of the modeling agree with known experimental data. [ABSTRACT FROM AUTHOR]

Although optical tools for measuring the surface-wave characteristics provide the best spatial and temporal resolutions compared with other methods, they face some difficulties while converting the results of indirect measurements into the absolute levels of waves. In this paper, we propose a combined optical method for measuring the 3D spectral density of the heights and the time realizations of the surface-wave profiles. The method involves, first, synchronous recording of the optical-brightness field on a rough-surface area and the surface-oscillation measurement at one or several points and, second, filtering of the spatial image spectrum, so that the filter parameters are also chosen from the condition of maximum correlation of the reconstructed and measured surface oscillations at one or two points. The second part of this work deals with the results of measuring the multi-dimensional wave spectra on the basis of the proposed method. [ABSTRACT FROM AUTHOR]

Correction of aberrations is regarded as one of the most successful applications of diffractive optical elements in the optical system. The ways of overcoming these negative properties of the diffractive elements as spherochromatism and power spectral selectivity are presented. Using the technique given in this paper, a compact plastic-lens refractive-diffractive objective, which can operate in a wide spectral range including the visible and near-infrared radiation, has been designed. [ABSTRACT FROM AUTHOR]

This paper is devoted to experimental studies of interaction between intense acoustic fields and their interfaces. In particular, we discuss the results of experimental studies of the spatial variation of the profile and spectrum evolution of an intense acoustic wave reflected from an acoustically soft boundary. The distance between the source aperture and the surface approximately corresponds to the coordinate of the last diffraction maximum in the axial distribution of the acoustic field at the pump frequency. The radiation intensity was chosen in such a way as to ensure the nonlinear wave interaction both before and after the reflection. It is shown that antiphased interaction between harmonics in the reflected wave formed before the boundary and the harmonics formed after the refection leads to a significant variation in the profile and spectrum of the reflected wave, which determines the further formation of nonlinear waves. Propagation of the reflected wave is accompanied by an intense rise in signal amplitude in the compression phase and the formation of a new shock-wave front. A nonmonotonic decay as a function of the harmonic number is observed in the harmonic amplitude distribution. This feature of the spectrum behavior takes place in the increasingly low-frequency part of the spectrum as the distance from the boundary increases. [ABSTRACT FROM AUTHOR]

The second part of this paper continues the discussion of possibilities for combining functionally different types of biomedical characterization of tissues using optical coherence tomography (OCT). In the first part, polarization-sensitive imaging and conventional approaches to elastographic mapping in OCT were considered. Here, we consider an unconventional approach to elastographic mapping based on the analysis of variability of OCT images of the deformed tissue, omitting the stage of the displacement-field reconstruction. We also discuss methods for quantification of blood flow and visualization of microvasculature, some of which have much in common with the elastographic approach based on the analysis of temporal variability of OCT frames. This similarity looks especially promising in the context of combining multiple contrast mechanisms to enable prospective multimodal OCT scanners, as is essential for biomedical progress given the complex and heterogeneous nature of real biological tissues. [ABSTRACT FROM AUTHOR]

We study a one-dimensional stationary system of equations comprising the continuity equation for the ion concentration with the recombination effects taken into account and the Gauss law for the electric field. This system gives a simplified description of various phenomena in ionized medium theory and is used, in particular, for modeling of the electrode effect in the atmospheric surface layers with the turbulent diffusion effects neglected. Using the integral of the system and a phase portrait in the ion concentration plane, we offer a complete classification of types of solutions of the system, examine their properties, and deduce some analytical relations between the ion concentration and the electric field. The basic equations of classical electrode effect theory are obtained for some classes of solutions within the framework of this approach. Correct formulations of the problems are discussed. New classes of solutions, for which there are layers with infinitely increasing conductivity and charge density are described. The Appendix illustrates, in both analytical and graphical form, the results obtained in the main part of this paper on the basis of qualitative reasoning for parameters close to real. Analytical expressions for the fields and ion concentrations are given for all types of solutions. Relations for the distances between electrodes and analytical relations describing the properties of the spatially localized solutions are presented. [ABSTRACT FROM AUTHOR]

Recent years yielded important experimental results in the field of studying the middle- and the upper-atmospheric discharges initiated by the lightning strokes. These results have been obtained using the most widespread measurement method related to the high-speed high-sensitivity visibleband cameras and the spectroscopy, which is the most rapidly developing method of observation of the upper-atmospheric flashes. Both methods are used during the ground-based, as well as the balloon- and satellite-borne observations. The above-mentioned methods are reviewed in this paper. [ABSTRACT FROM AUTHOR]

We describe the results of studying experimentally a high-power (hundreds of kilowatts) pulsed (pulse duration of about 30 μs) subterahertz gyrotron with the generation frequency corresponding to one of the atmosphere transparency windows. The gyrotron with an operating frequency of 0.67 THz, a power of more than 200 kW and an efficiency of 20-25% was used in the experiments on ignition of a localized discharge in a plasma. The paper presents the data about measurements of the temperature field of the emitter, calorimetric measurements of the power and efficiency of the gyrotron, and the design of the quasioptical converter of radiation to a narrow wave beam. The first experiments with the terahertz discharge in a focused wave beam of the gyrotron are briefly described. [ABSTRACT FROM AUTHOR]

The results on the aerosol-size spread influence on dissipative instability of aerosol flow in a cold weakly ionized collisional plasma, which were obtained in the first part of this paper [], are used for the Mars (altitudes 70-100 km) and Titan (altitudes 900-1200 km) atmospheric conditions. The threshold charges and characteristic space-time instability scales are quantitatively estimated. [ABSTRACT FROM AUTHOR]

One of the important problems of communication, navigation, and diagnostics of inhomogeneous media is multipathing, in which the signal propagates on different paths between the points of emission and reception. In this paper, using a numerical simulation we explore the capabilities of the spatial signal processing to eliminate the effects of multipath signal propagation in a smoothly inhomogeneous medium. It is shown that the multipathing effects disappear after the spatial processing based on double weighted Fourier transform in the presence of multipath propagation in a medium with irregularity scales both more and less than the Fresnel radius. [ABSTRACT FROM AUTHOR]

Based on the correlation and ranging methods, we developed an algorithm determining the coordinates of moving sources of wideband noise. The main advantage of this algorithm is the ability to eliminate the ambiguities of determining the target coordinates arising in the multistatic systems. To test the proposed algorithm, a laboratory passive multistatic radar system was designed and assembled. This paper describes the parameters of the experiment conducted using this system. The obtained results are discussed and analyzed. [ABSTRACT FROM AUTHOR]

In this series of papers, we propose a method for development of an approximate solution of the Maxwell equations in smoothly inhomogeneous anisotropic gyrotropic media with allowance for aberrations, spatial dispersion, and absorption. Evolution equations for wave beams are obtained, and a method for their numerical solution is developed. The relation of the quasi-optical evolution equation to the aberration-free equation for wave beams is shown, and a general solution to the latter equation is found. The applicability conditions for the aberration-free equation have been written explicitly. Methods of allowance for dissipative aberration effects within the framework of the nonaberrational approximation are described. [ABSTRACT FROM AUTHOR]

We consider the problem of coordinated spatial signal processing at the base stations of modern high-throughput wireless cellular systems using orthogonal frequency division multiplexing (OFDM) and adaptive antenna arrays. In the existing OFDM systems with coordinated multi-point (CoMP) transmission, the user throughput gain is achieved via co-channel interference mitigation by means of coordinated transmit beamforming at the base stations. For such schemes, it is assumed that each base station transmitter is equipped with linear antenna array comprising a set of elements with the same vertical polarization. In this paper, a new approach to spatial coordination is studied using the joint coordination of the signal polarizations at the transmitting base stations whose antenna arrays are made of pairs of mutually orthogonal antenna elements. In this case, co-channel interference mitigation among the base stations is achieved via the adaptive choice of the signal polarization at each transmitting antenna array. An algorithm of coordinated spatial signal processing with polarization selection is proposed in this work and the system throughput is analyzed for the proposed CoMP scheme. [ABSTRACT FROM AUTHOR]