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  Subjects -> ELECTRONICS (Total: 207 journals)
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Radiophysics and Quantum Electronics
Journal Prestige (SJR): 0.362
Citation Impact (citeScore): 1
Number of Followers: 2  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1573-9120 - ISSN (Online) 0033-8443
Published by Springer-Verlag Homepage  [2469 journals]
  • Chaos and Geometrical Optics

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      Abstract: Chaotic evolution of dynamical systems is caused by the divergence of nearby orbits, i. e., by the intrinsic instability of the dynamics. The best way to see how the divergence of orbits may occur is to consider the orbits as the rays of light, i. e., within the framework of the geometrical optics. We discuss the basic mechanisms of chaos and demonstrate how the discovery of these mechanisms allowed one to enrich the geometrical optics by some new fundamental ideas and notions.
      PubDate: 2022-07-15
       
  • Dynamics of a Recurrent Spiking Neural Network in the Two-Alternative
           Choice Task

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      Abstract: We have revealed the dynamic mechanism of solving a cognitive task of two-alternative choice by an artificial recurrent network of spiking neurons. The approach to designing a functional network model is described based on machine learning methods. The formation of a modular coupling structure during training is established. The properties of the network response, which underlie the performing of a target task, are found.
      PubDate: 2022-07-15
       
  • Modulation of Weakly Nonlinear Traveling Waves in the Presence of a Damped
           Large-Scale Mode

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      Abstract: We study the modulation of weakly nonlinear traveling waves in the presence of a damped large-scale mode. The traveling wave is generated by the Marangoni convection in a thin liquid film heated from below. Against the background of the traveling wave, an additional “soft” mode arises due to large-scale surface deformations. Using the multiscale approach, we derive a set of coupled equations that describe a modulated traveling wave near the convection threshold. One of the equations is the wave envelope equation in the form of a modified complex Ginzburg–Landau equation (CGLE) that contains an additional term of the local liquid level rise. The second equation is an evolution equation for the film thickness that is derived from liquid volume conservation. It is shown that the presence of an additional large-scale mode affects the dynamics significantly. New modulational instability criteria are obtained.
      PubDate: 2022-07-14
       
  • Synchronization Regimes in an Ensemble of Phase Oscillators Coupled
           Through a Diffusion Field

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      Abstract: We consider an ensemble of identical phase oscillators coupled through a common diffusion field. Using the Ott–Antonsen reduction, we develop dynamical equations for the complex local order parameter and the mean field. The regions of the existence and stability are determined for the totally synchronous, partially synchronous, and asynchronous spatially homogeneous states. A procedure of searching for inhomogeneous states as periodic trajectories of an auxiliary system of the ordinary differential equations is demonstrated. A scenario of emergence of chimera structures from homogeneous synchronous solutions is described.
      PubDate: 2022-07-14
       
  • Lump Interactions with Plane Solitons

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      Abstract: We analyze in detail the interactions of two-dimensional solitary waves called lumps and onedimensional line solitons within the framework of the Kadomtsev–Petviashvili equation describing wave processes in media with positive dispersion. We show that line solitons can emit or absorb lumps or periodic chains of lumps, as well as interact with each other by means of lumps. Within a certain time interval, lumps or lump chains can emerge between two line solitons and then disappear due to absorption by one of the solitons. This phenomenon resembles the appearance of rogue waves in the oceans. The results obtained are graphically illustrated and can be applicable to the description of the physical processes occurring in plasmas, fluids, solids, nonlinear optical media, etc.
      PubDate: 2022-07-14
       
  • Simulation of the Business-Cycle Synchronization Processes in an Ensemble
           of Coupled Economic Oscillators

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      Abstract: We develop a dynamical model of an economic (financial) oscillator on the basis of the theory of automatic-control systems. Numerical experiments with the proposed model demonstrate the possibility of generating chaotic economic oscillations and their synchronization in an ensemble of coupled economic oscillators.
      PubDate: 2022-07-14
       
  • On a Statistical Approach to Phase Synchronization in Some Map-Based
           Neural Chaotic Spiking–Bursting Models

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      Abstract: Under coupling, a large group of chaotic spiking–bursting oscillating neurons can undergo neuronal regularization. This aspect has been studied in map-based models. Under coupling, the distribution of the return time difference is modified so that it becomes much narrower as expressed by its statistical dispersion.
      PubDate: 2022-07-14
       
  • Pedestrian-Induced Bridge Instability: The Role of Frequency Ratios

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      Abstract: 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.
      PubDate: 2022-07-14
       
  • Brightness Fluctuations of the Sunny-Path Image Depending on the Sharpness
           Setting of the Observation-System Lens

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      Abstract: We theoretically study the variation coefficient of the solar radiation reflected from a wavy sea surface as a function of the range to which the observation-system lens is focused. During the study, we revealed the possibility of existence of two different regimes of the received-signal fluctuations, namely, the single- and double-hump dependences of the variation coefficient on the lens-adjustment range. The effect of splitting one maximum of the variation-coefficient dependence on the range into two maxima is explained within the framework of simple optical models.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10147-6
       
  • Using the Maximum-Likelihood Method for the Angular Resolution of the
           Signal Sources in Multibase Phase Direction Finders

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      Abstract: We show that the angular resolution of the signal sources in the phase direction finders with the antenna systems in the form of linear arrays of the weakly directional elements can be reached by determining the own set of full periods of the phase difference, which are lost during the measurements, for each source. It is established that the maximum-likelihood method, which has been developed for estimating the arrival of one signal, can be used for the angular resolution of the signal sources. We show the generality of the basis for the angular resolution using the maximum-likelihood method and the method of summation of cosine functions. The estimates of the accuracy of the received-signal direction finding are given.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10152-9
       
  • Superdirective Acoustic Imaging with the Use of Flexible Microphone Arrays

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      Abstract: We consider the problem of spatial localization of a set of sound sources using flexible microphone antenna arrays. At the beginning, the problem of determining the coordinates of microphones through the use of calibration sources is solved. For this, we use optimization of the objective function, which is the norm of the difference between the measured and estimated delays in the arrival of calibration signals from sources to microphones, by unknown coordinates of the calibration sources and microphones. The results of simulation and experiment are presented, which show an acceptable efficiency of the proposed calibration technique. For acoustic imaging, MUSIC and the maximum likelihood signal classification method (MLSIC) were employed. The first method is widely known and was previously used to estimate the direction of arrival of plane waves. The second method was recently proposed and is based on the interference model, which includes M sources of a coherent field. The results of localization of acoustic sources were obtained using numerical simulation, as well as by an experiment in an anechoic chamber. It was shown that the MLSIC method has a better spatial resolution than the MUSIC method.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10148-5
       
  • Synthesis of a Wideband Diplexer Based on Interdigital Resonators for the
           Antennas Of Mobile-Communication Base Stations

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      Abstract: We study theoretically and experimentally a new design of the diplexer for mobile-communication base stations, which is based on interdigital resonators. A high-performance diplexer for operation in the frequency ranges 690–862 MHz and 880–960 MHz has been developed and manufactured. The diplexer is synthesized on the basis of an efficient combined method including the use of the coupling matrix technique, solution of eigenvalue problems for single and coupled rod-type resonators, and electrodynamic simulation of filters and the diplexer. The proposed design has a high potential for realization of diplexers with wide, moderate, and narrow passbands in the mobile-communication frequency ranges.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10150-x
       
  • Development and Experimental Study of a Pulsed Megawatt Gyroklystron
           Operating in the Long-Wavelength Part of the Millimeter-Wavelength Range
           at IAP RAS

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      Abstract: We have developed and studied experimentally a two-cavity gyroklystron operating at a frequency of 35 GHz and the cavity mode TE0 2 1 in a cryomagnet. The output radiation power achieved in the pulsed regime is 750 kW with an efficiency of 24%, a gain of 20 dB, and amplified-frequency bandwidth equal to 220 MHz (0.63%) at an accelerating beam voltage of 74 kV, a current of 42.5 A, and a pulse duration of 100 μs. An operating-frequency bandwidth equal to 310 MHz (0.89%) at a power level of 430 kW has been achieved in another variant of the gyroklystron. At fixed current and beam voltage, the limitation of the efficiency and the bandwidth of the operating frequencies is determined by self-excitation of parasitic oscillations in the output cavity at the TE2 2 1 mode. The limitation of the highest power of the output radiation at a level of 750 kW is related to the formation of a high-frequency discharge in the output cavity because of the deterioration of the vacuum in it as a result of heating the internal surface of the cavity due to ohmic losses. Strong influence of the axial distribution of the static magnetic field in the interaction space on the efficiency and the output radiation power is predicted theoretically and demonstrated experimentally. By finding an optimal longitudinal structure of the magnetic field using solenoids and magnetic shields, we have managed to increase the efficiency and the power of the gyroklystron in the experiment by 1.3 times compared to the case of a homogeneous distribution of the magnetic field.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10149-4
       
  • Screening of Quantum States of an Optical Field from a Resonant Perturbing
           Subsystem

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      Abstract: We predict theoretically the effect of screening the quantum states (including entangled ones) of an optical field from interaction with a resonant perturbing subsystem by means of coupling with other field modes in the ground (vacuum) state. It is shown that an ensemble of resonators with fields in the vacuum state is able to screen the quantum state of a group of excited resonators from interaction with a resonant two-level atom. The degree of modification of the initial quantum state is inversely proportional to the number of “screening” modes unexcited at the initial moment of time.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10151-w
       
  • Model Waveforms of Slow-Tail Sferics

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      Abstract: We simulate numerically the propagation of slow-tail sferics, which occupy a wide frequency band from 1 Hz to 10 kHz, in the spherical Earth–ionosphere cavity. The TM wave generated by a vertical lightning discharge is considered. Classic engineering models of a lightning stroke are employed. The calculations use the Williams stroke model as the field source. We assume that the upper boundary of the cavity is an isotropic horizontally stratified ionosphere, and the conductivity of each layer depends on its altitude. The day and night-time models of the vertical conductivity profile, which were used for correct description of the global electromagnetic (Schumann) resonance, are employed. The frequency dependence of the complex propagation constants of the zero- and first-order modes was found by using the full-wave solution in the form of the Riccati equation. The roots of this equation are the eigenvalues of the problem, which are found by iterations. Complex spectra of vertical electric and horizontal magnetic fields are constructed in the form of a series of modes with known propagation constants. Various source-to-observer distances in the day and night-time cavities are considered. The Fourier transform is applied to the complex field spectra to find the waveforms of the sferics. The model data allowed us to obtain the calibration curves for estimating the source-to-observer distance from the delay between the ELF slow tail and the VLF precursor. It is shown that the calibration curves are coincident for the day and night-time propagation conditions.
      PubDate: 2021-11-01
       
  • X-Ray Emission from Utracool Stars

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      Abstract: We study two possibilities of the origin of quiescent X-ray emission from ultracool stars using the examples of brown dwarfs TVLM 513-46546 and VB 10: (a) radiation from hot coronas and (b) radiation from a system of magnetic loops filled with a sufficiently dense hot plasma heated due to the dissipation of electric currents flowing in the loops. The parameters of the corona, as well as the parameters of the loops and their number, which are necessary for the implementation of the observed X-ray emission measure, have been determined. For the studied brown dwarfs, the generation of X-rays by a set of hot loops is energetically more favorable than in the case of a hot corona, which was also confirmed by the results of the analysis of quiescent microwave radiation from the brown dwarf TVLM 513-46546.
      PubDate: 2021-11-01
       
  • Electrodynamic Analysis of Eigenmodes of Spheroidal Dielectric Resonators

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      Abstract: We perform electrodynamic analysis of electromagnetic modes in a set of spheroidal dielectric resonators. The dependences of eigenfrequencies on the size of the resonators are found for a set of 5, 6, 7, and 9 spheroidal dielectric resonators. The problem is modeled numerically, and the dependence of the frequencies of coupled modes on deformations of the resonators is studied. The results can be useful in radioelectronics and biomedical applications.
      PubDate: 2021-11-01
       
  • Determination of the Velocity Profiles of Longitudinal and Shear Waves on
           the Basis of Analysis of Seismic Noise

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      Abstract: We consider a method for determining the velocity profiles of the longitudinal and shear waves on the basis of analysis of seismic noise. It is a result of improving the widely used method of passive tomography. The proposed method is based on the relation between the mutual spectrum of signals from the spaced receivers, which record two projections of the displacement vector, and the incomplete Green’s function, which corresponds to the response of the surface Rayleigh wave. Using this method, it is possible to determine the frequency dependence of both the phase velocity and ellipticity of the Rayleigh wave. In turn, the latter allows one to reconstruct the profiles of the longitudinal- and shear-wave velocities. In this work, we explain the fundamentals of the method within the framework of a simple model and propose its experimental evaluation. A comparison with the results of an independent measurement using a vibrator is given.
      PubDate: 2021-11-01
       
  • Simulation of Large-Scale Disturbances of the Near-Earth Plasma Affected
           by High-Power High-Frequency Radio Waves from the Sura Heating Facility

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      Abstract: We present the results of simulation of large-scale disturbances of the near-Earth plasma modified by high-power HF radio waves from the Sura heating facility. The numerical simulation was performed over the entire range of ionospheric altitudes, using an SAMI2 modified version for the input parameters corresponding to the in-situ measurements of the spatial structure of the disturbed region performed by the method of low-orbit radio tomography. The numerical simulation results conform to the radio tomography reconstruction data. The dynamics of the evolution and relaxation of large-scale temperature and plasma-density disturbances under the action of high-power HF radio waves from the Sura heater are studied on the basis of simulation data.
      PubDate: 2021-11-01
       
  • Comparison of Sources of Narrowband and Ultra-Wideband Electromagnetic
           Pulses in Terms of the Efficiency of their Impact on Electronic Tools

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      Abstract: We solve the problem of determination of the conditions under which the source of microwave pulses and the source of ultra-wideband electromagnetic pulses have an identical resulting impact in terms of energy on semiconductor elements of technical means without special receiving antennas. It is shown that sources of microwave pulses, whose carrier frequencies range from hundreds of megahertz to several gigahertz, reach the desired effect at lower energy costs. However, as the carrier frequency increases, their energy efficiency becomes lower, and ultra-wideband sources turn out to be more efficient in many practical cases.
      PubDate: 2021-11-01
       
 
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