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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  [2467 journals]
  • Correction to: Quasi-Optical Sub-Doppler Lamb-Dip Spectrometer

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      PubDate: 2022-11-02
       
  • Antireflection Coating of a Dielectric Plate in the Microwave Band Using
           Surface Machining

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      Abstract: We present the experimental results of measuring the reflection coefficient of a microwave output window made of radiation-modified fluoroplast (Raflon™) with antireflection coating made by using surface machining. The quarter-wave antireflection coating was created by drilling shallow holes in a high-density hexagonal pattern over the plate surface. The Maxwell Garnett formula was used to estimate the value of the effective dielectric permittivity of the periodic structure, since this formula is the most suitable for approximation of effective properties of cylindrically shaped inhomogeneities. The dielectric permittivity of such a structure in the transverse direction corresponds to the value optimal for increasing the window transparency in the specified frequency range. It is found experimentally that the reflection coefficient in the band 120–140 GHz does not exceed −20 dB. The obtained results are compared with the theoretical calculation and numerical analysis in the CST Studio Suite.
      PubDate: 2022-11-01
       
  • Development of a Polarization Jet and Plasma Drifts in the Ionospheric F
           Region

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      Abstract: We consider Doppler measurements at the Yakutsk subauroral ionospheric station in the periods of the formation and development of a polarization jet above the observing station. It is shown that the times at which the vertical and horizontal velocities of the plasma drift reach their maximum values may not coincide. Comparison of ground-based measurements when observing a polarization jet and calculation of the model of a high-latitude ionosphere demonstrate that the presence of mismatched peaks of the vertical and horizontal components of the plasma drift velocity at the altitudes of the F2 layer leads to different variations in the basic parameters of the layer. It was found that in some cases, before the formation of a polarization jet, an increase in the critical frequency of the F2 layer is observed. A decrease in the ion recombination rate due to an increase in the height of the layer maximum and, consequently, accumulation of ions at these altitudes, is a possible explanation for this behavior. Such an increase in the critical frequency of the F2 layer may be an additional signature of the development of a polarization jet above the observing station.
      PubDate: 2022-11-01
       
  • Simulation of Spatial Coherence of a Multimode Signal and Response of a
           Horizontal Antenna in a Randomly Inhomogeneous Oceanic Waveguide

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      Abstract: We present simulation results for the spatial-coherence function of a multimode acoustic signal from a remote source in the horizontal plane of a randomly inhomogeneous oceanic waveguide and the angular response of the phased antenna to such a signal to estimate quantitatively the influence of the basic physical factors of the signal-field formation at the antenna input. The simulation was performed in a wide parameter range on the basis of a sufficiently general heuristic model, according to which the signal is the superposition of a finite number of plane waves with random complex amplitudes. It is shown that the most important factors include the spectrum of the longitudinal wave numbers of the normal waveguide modes, the total number and the spectrum of the intensities of the signal modes, and the mutual correlations of the mode amplitudes. Depending on the type of the wave-number spectrum, the influence of the mode-intensity spectrum turns out to be significantly different, which is indicative of the important role of the deterministic properties of the waveguide in the formation of the coherence function and the coherence scale as well as the related distortions of the antenna response to the signal compared with the case of an unbounded space. The physical interpretation of the results, which allows one to make predictive estimates of the considered characteristics in the presence of a priori information on the above-mentioned factors of the received-signal propagation, is given.
      PubDate: 2022-10-27
       
  • On the Possibility of Dust Grain Destruction by the Coloumb Explosion in
           Protoplanetary Disks

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      Abstract: We consider the dust charging processes in protoplanetary disks. It is shown that in the atmosphere of a disk, grains can acquire anomalously high positive charges, which can lead to their destruction as a result of the Coulomb explosion. The charging is due to the combined effect of radiation from a protostar and of electron and ion currents from the surrounding plasma. For typical protoplanetary disk conditions, such a process turns out to be effective both for porous dust grains of micron sizes and for submicron crystalline grains. Critical charges that are necessary for the destruction of dust grains and the charges acquired by the particles are found for their different sizes and various parameters of the dusty plasmas. Critical grain sizes as functions of the distance to the host star are calculated. It is shown that the Coulomb explosion leads to the appearance of a cascade of crushing of large dust grains. The character of the dependence of crushing conditions on the dust particle radius can lead to the formation of a bimodal grain size distribution in some areas of protoplanetary disks. One fraction corresponds to large particles that are not subject to destruction and the other, to small particles of submicron size.
      PubDate: 2022-10-27
       
  • Experimental Determination of Aerosol Particle Sizes Using Supercontinuum
           Radiation and Estimation of the Directional Pattern of Radiation from the
           Filamentation Region of Femtosecond Pulses

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      Abstract: According to the results of studying the interaction of high-power femtosecond pulsed radiation from a titanium–sapphire laser with the aerosol particles of an aqueous solution of NaCl, we estimate the directional pattern of Na emission from the filamentation region. It has been found that this directional pattern is characterized by minima in angular directions of 0° and 180° and a maximum in an angular direction between 20° and 160°. Based on the results of recording of supercontinuum radiation formed in the air and scattered by aerosol particles, the features of the aerosol particle size distribution have been determined. Gradient optimization methods using graphic processors were employed to speed up calculations. The neural network was used as an optimization method.
      PubDate: 2022-10-27
       
  • Influence of a Reactive Power on the Dynamics of an Ensemble of
           Oscillators Simulated by the Phase Equations with Inertia

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      Abstract: We study the simplest artificial model of a power-network operation. The original model has a ring topology consisting of locally coupled power generators alternating with power consumers. Each node of the network is represented as a phase oscillator such as the Kuramoto oscillator with inertia. The network dynamics equations are transformed in accordance with the method of effective network model proposed in [1] and are numerically studied. The purpose of the work is to analyze the possible regimes of the nonuniform-network behavior in the presence of a reactive power in the system. We also study the joint influence of the reactive power and nonlinear dissipation of oscillators. The coefficient of inertia, which is the same for all oscillators, and the reactive power of one of the oscillators are considered as the network control parameters. The regime maps on the plane of control parameters, which were obtained for constant and nonlinear dissipation of the oscillators, are compared. The results show that the reactive power complicates the network behavior and reduces the phase-locked region. On the contrary, the nonlinear dissipation has a positive effect, leading to synchronization of the network oscillators even in the presence of a reactive power.
      PubDate: 2022-10-27
       
  • Self-Action of Ultrashort Pulses in the Self-Similar Regime

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      Abstract: We study the specific features of the evolution of spatially confined pulses with a finite amplitude and a duration of several periods of wave field oscillations both analytically and numerically. The initial equation, which describes propagation of a reflectionless ultrashort pulse, is transformed to a nonautonomous modified Korteveg-de-Vries equation after passing over to self-similar variables. In this simpler equation for the self-similar function, the dynamics of the internal structure of the wave field is determined by the competition of “dispersion” and cubic nonlinearity only. The evolution of pulses in the directions of the increasing and decreasing nonlinearity is separately considered. Numerical simulation of the problem has demonstrated that: i) the energy center of the wave packet moves nonuniformly along the propagation path, ii) a dispersion shock wave consisting of a set of solitons is excited in the rear part of a pulse propagating in the direction of increasing nonlinearity in the process of the dispersion spreading, and iii) the evolution of the pulses propagating in the direction of decreasing nonlinearity is also accompanied by excitation of a breather soliton.
      PubDate: 2022-10-27
       
  • Use of Carbon-Based Composite Materials with Anisotropic Conductivity for
           Creating Microwave Antennas

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      Abstract: We develop and test engineering solutions aimed at creating antenna devices made of carbonbased composite materials and operated in various intervals of the microwave range. The main electromagnetic characteristics of the antennas in this range are computer simulated and studied experimentally. The influence of the anisotropy of the material conductivity on the parameters of horn antennas is studied. Feasibility of using materials with anisotropic conductivity for creating antenna devices with given radio-frequency characteristics is demonstrated.
      PubDate: 2022-10-08
       
  • Microwave and Lidar Measurements of Ozone and Temperature Variations
           during Stratospheric Warmings of 2012–2015

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      Abstract: We present the results of joint observations of ozone and temperature in the middle atmosphere above Tomsk in December–January 2012–2013 and in December–February 2014–2015 during stratospheric warmings. The results of simultaneous microwave observations of ozone in Peterhof (60° N, 30° E) and Tomsk (56° N, 85° E) in the winter of 2013–2014 are also given. Ground-based microwave radiometry and laser diagnostics were used in the observations. Microwave radiometry and lidar technology allow us to study ozone and temperature variations during large-scale wave disturbances in the middle atmosphere such as stratospheric warming.
      PubDate: 2022-10-07
       
  • Capability of Bistatic Radar Systems to Solve the Problem of Detection of
           Potentially Hazardous Celestial Objects

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      Abstract: We analyze the capabilities of bistatic multipositional facilities with correlation signal processing for the purposes of enhancing significantly the efficiency of radar systems in detecting celestial objects which are potentially hazardous for the Earth, specifically, asteroids, comets, and large fragments of space debris. In particular, we consider radar systems using the forward scatter radar method, which is based on a significant increase in the bistatic efficient reflective area of the target independently of its shape and material in the case of forward scattering of the probing signal. The possibility to use natural radio sources as probing emitters is considered. The efficiency of two variants of ground-based space radar for both detection of celestial objects and monitoring of space hazards is estimated for further promising research developments.
      PubDate: 2022-10-07
       
  • Quasi-Optical Sub-Doppler Lamb-Dip Spectrometer

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      Abstract: We describe a new sub-Doppler spectrometer with an enlarged gas cell, which was created at the IAP RAS for high-precision laboratory measurements of molecular transitions at millimeter and submillimeter wavelengths in the interests of radio astronomy. By using a larger diameter with a shortened cell length, a calibrated attenuator for radiation power adjustment, and synthesizers with lower phase noise, it was possible to eliminate a number of shortcomings of the previous spectrometer and not only to measure with high accuracy the transition frequencies of a number of molecules taking into account hyperfine splitting, but also to study their shifts due to both pressure and radiation power. In particular, information about precise frequencies will be used to examine the inner dynamics in the star-forming regions, and also to search for variations of fundamental constants. The principle of frequency-independent cell-aperture irradiation was employed when the optical scheme of the spectrometer was designed. The examples show Lamb-dip measurements of the hyperfine structure in the CH3CN and HNCO molecular lines.
      PubDate: 2022-10-07
       
  • Determination of Integrated Water Vapor and Liquid Water Contents from the
           Measurements of Microwave Atmospheric Radiation

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      Abstract: We present an overview of the results of our studies in the field of using the radiothermal-detection method for determining the integrated water vapor content in the atmosphere and the integrated liquid water content in the clouds, as well as a general overview of modern achievements in this field. The possibilities of determining the atmospheric integrated water vapor content and the integrated liquid water content of the clouds are shown for particular examples using the ground-based measurements of the microwave atmospheric radiation simultaneously at the frequencies 22.235 and 36.000 GHz (near the water-vapor absorption line). The possibility is shown of detecting the regions of high content of liquid water in an upper overcooled part of the powerful convective clouds and using the microwave measurements for predicting dangerous weather events including thunderstorms. The prospects of using the radiothermal-detection method in meteorology on the basis of the radiophysical complex of Lehtusi Geophysical Observatory are discussed in relation to improving the technology of regional very short-term forecast (with a lead time of 2–12 h) of dangerous phenomena caused by the development of clouds and precipitation.
      PubDate: 2022-10-07
       
  • Dust Temperature Profiles in Dense Cores Related to the High-Mass
           Star-Forming Regions

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      Abstract: We obtained continuum maps at a wavelength of 350 μm for eight gas–dust clouds from the southern hemisphere using the APEX-12m telescope. The clouds are related to the regions of the formation of high-mass stars and star clusters and have dense cores. The core sizes estimated at half the maximum intensity at a wavelength of 350 μm are 0.1–0.2 pc. The core masses and gas mean densities lie in the ranges 20–1000 Mʘ and (0.3–7.3)·106 cm−3, respectively. A comparison of the obtained data at a wavelength of 350 μm with observation data of the same objects at a wavelength of 1.2 mm was carried out. From the intensity ratios at two wavelengths reduced to one angular resolution, the spatial distributions of the average dust temperature on the line of sight are calculated. Dust temperature maps in most objects correlate with intensity distributions at a wavelength of 350 μm. A decrease in the dust temperature with distance from the center is detected in most cores. The obtained dust temperature profiles in most cases turned out to be close to linear ones. Using a simple spherically symmetric model of a dust cloud, it is shown that temperature profiles close to the observed ones can be obtained under the assumption of the presence of an internal source by varying the density profile parameters and specifying a powerlaw index β of the dust emissivity dependence on frequency as a constant. It is shown that the dust temperature estimates strongly depend on the chosen value of β. It is considered how possible variations of β in the cloud can affect the results obtained.
      PubDate: 2022-10-07
       
  • Problems of Lightning Initiation and Development

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      Abstract: We review the basic issues of the initiation and development of the lightning discharge, which top the list of the most important and yet unsolved problems of atmospheric electricity. The main challenges of creating theoretical models are due to the fact that the value of the electric strength of atmospheric air exceeds the peak electric fields measured in thunderstorm clouds by approximately an order of magnitude. Among several concepts proposed to explain the process of initiation of a lightning discharge at different times, two ideas stand apart, namely, the hypothesis of the lightning birth caused by the initiation of a positive streamer from the surface of a hydrometeor and the hypothesis of lightning initiation due to the development of a runaway electron breakdown. However, none of these approaches has become universally recognized or dominant due to various difficulties. A fundamentally new mechanism of lightning discharge initiation, which has been proposed recently, is based on the noise-induced kinetic transition occurring in the stochastic field of charged hydrometeors. The proposed approach looks like a sequence of discharge activity transitions from small spatial scales to increasingly larger ones. One of the main features of the proposed hypothesis is that the generation of streamers is determined by the level of small- and mesoscale fluctuations of the electric field in the thunderstorm and is essentially independent of the large-scale field. In this case, the role of the large-scale field is to ensure interaction of the initiated streamers, when they start developing mainly in the direction specified by this field. In the final section of the review, we discuss the fundamental role of the polarity asymmetry in the processes of the initiation and further development of lightning discharges.
      PubDate: 2022-09-29
       
  • Development of High-Power Long-Pulse Submillimeter-Wave Free-Electron
           Lasers on the Basis of the Linear Induction Accelerator Complex

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      Abstract: The high-power long-pulse submillimeter-wave free-electron laser (FEL) is developed jointly by the Institute of Nuclear Physics and the Institute of Applied Physics on the basis of the linear induction accelerator complex, which forms electron beams with a particle energy of 5–20 MeV, a current of 2 kA, and a duration of 200 ns. The studies are aimed at achieving power levels of 0.1–1.0 GW and an energy of 10–100 J in pulses of radiation in the indicated range. We present the results of electron-optical experiments, in which electron beams with parameters acceptable for their efficient application in FELs were formed. Helical pulse undulators have been developed for the build-up of operating transverse oscillations of electrons. The possibility to use modified Bragg cavities, which are based on the coupling of propagating and quasi-critical waves and capable of ensuring stable narrow-band generation at significantly large (as compared with the wavelength) transverse dimensions of the interaction space, is analyzed as the key component of the electrodynamic system of a generator. The results of the simulating and cold testing of this type of cavities for operation in the submillimeter-wave range with a channel diameter exceeding 20 wavelengths are presented.
      PubDate: 2022-09-29
       
  • A Vector Algebraic Description of the Solar-Path Phenomenon

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      Abstract: We propose a theoretical model of the solar path, which has been developed for the first time using the vector-algebra methods. The formulas describing the average brightness of the solar radiation reflected from the wavy water surface are derived taking into account the finite angular dimensions of the directional patterns of the light source and the photodetector of the observation system. A new model of the distribution function of the visible slopes of the sea surface observed in the oblique geometry is developed.
      PubDate: 2022-09-29
       
  • Selection of Simulating Signal-Like Interference in Radar Systems with
           Internal Coherence

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      Abstract: We propose and study a method of defense against intelligent simulating signal-like active interference on the basis of an assessment of the coherent properties of radar signals. The signalcoherence measure, which is defined as the entropy of the signal-energy distribution over the eigensubspaces of the signal correlation matrix, is proposed as a selection criterion. The main factors, which influence the coherence degree of radar signals, are analyzed. The computation cost during the implementation of the proposed method for estimating the quantitative measure of the signal coherence is estimated. The results of the full-scale experimental studies, which employ various types of aircraft (with a propeller engine and turbojets) and the special equipment, i.e., a repeater of simulating signal-like interference, are presented. The estimated degree of coherence of the signals from real airborne objects and the simulating signal-like interference, which has been obtained during the experimental studies, confirms the possibility of selecting the simulating signal-like interference by the proposed method.
      PubDate: 2022-09-29
       
  • Features of the ELF/VLF Wave Generation and Propagation Processes during
           Ionospheric Modulated High-Frequency Heating

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      Abstract: We consider the results of observations of the ELF/VLF horizontal magnetic field of the ionospheric source using a high-latitude network of PGI stations in the heating experiment of 2016 at the EISCAT/Heating facility. We have discovered that at frequencies close to the frequency of the first transverse resonance of the Earth–ionosphere waveguide (∼1.8 kHz), the amplitude of the horizontal magnetic field of the ionospheric source at the Barentsburg station (located 961 km from the heating facility) often exceeded the amplitudes at the mainland stations located closer to the heater (the nearest station Lotta is 395 km away). With all other conditions being equal, at frequencies considerably different from the frequency of the first transverse resonance, this effect was not observed. We identified and analyzed two possible physical mechanisms that can be responsible for the observed effect. The first is related to a fairly low decay of waves with frequencies close to the frequency of the first transverse resonance of the Earth–ionosphere waveguide when propagating above a highly conductive sea surface with a high reflection coefficient. The second is due to the non-uniformity of the radiation pattern of the ionospheric source. Numerical modeling of the generation and propagation of ELF/VLF waves in the Earth–ionosphere waveguide was carried out and the contribution of the proposed mechanisms was estimated. It is shown that the radiation pattern of the source does not have a notable effect and the experimental data are explained only by taking into account the high conductivity of the lower boundary of the waveguide along the EISCAT—Barentsburg path and low conductivity along the EISCAT—Lotta path. The state of the ionosphere is assessed and a family of electron density profiles for which a similar effect can be observed is obtained.
      PubDate: 2022-09-29
       
  • 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
      DOI: 10.1007/s11141-022-10170-7
       
 
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