Authors:S. A. Koryagin; I. A. Balandin Pages: 171 - 185 Abstract: We consider quantum-mechanical probabilities of bremsstrahlung of photons in the case of low-energy Coulomb collisions in a magnetic field, where the scattering center so perturbs the state of the incident electron that the motion of the latter becomes quasi-bound. Quantum formulas for the spectral power of bremsstrahlung radiation are obtained from the classical formulas by replacing the Fourier amplitudes of the particle velocity with matrix elements of the velocity operator for wave functions, which are normalized by the condition of a unit flux being incident on the nucleus (or an equivalent outgoing flux), with summation over finite Landau levels and quantized values of the impact parameter. Equivalent forms of the specified matrix elements, which are expressed in terms of the Coulomb field and annihilation/creation operators for the eigenfunctions of the operator of the squared impact parameter, are presented. The obtained presentations for the spectral power of bremsstrahlung radiation in the case of quasi-bound electron motion allow one to translate the results of calculating this value in the classical limit to the quantum case, which is typical of white dwarfs with the strongest magnetic fields. PubDate: 2017-08-01 DOI: 10.1007/s11141-017-9788-9 Issue No:Vol. 60, No. 3 (2017)

Authors:P.V. Subochev; A. S. Postnikova; A.V. Koval’chuk; I. V. Turchin Pages: 233 - 239 Abstract: We developed an optoacoustic tomograph with hand-held probe designed for optoacoustic imaging of biological tissues. The hand-held probe consists of a fiber-optic bundle for delivery of pulsed laser radiation to the studied object and a cylindrical focusing 64-element antenna for the detection of optoacoustic pulses. The capabilities of the tomograph to visualize the model blood vessels were studied experimentally using electronic and electronic–mechanical scanning. The achieved axial/lateral spatial resolution is 200/400 μm, the imaging depth is 18 mm, and the maximum B-scan acquisition rate is 10 Hz. PubDate: 2017-08-01 DOI: 10.1007/s11141-017-9794-y Issue No:Vol. 60, No. 3 (2017)

Authors:A.P. Trifonov; A.A. Milogorodskii Pages: 240 - 251 Abstract: We synthesize and analyze the quasilikelihood and maximum-likelihood algorithms for estimating the pulse duration. The estimation-accuracy loss because of the a priori unknown pulse and background intensities is found. PubDate: 2017-08-01 DOI: 10.1007/s11141-017-9795-x Issue No:Vol. 60, No. 3 (2017)

Authors:V. A. Kanakov; N. A. Mironov Pages: 252 - 257 Abstract: The problem of this study involves the extraction of a speech signal originating from a certain spatial point and calculation of the intelligibility of the extracted voice message. It is solved by the method of decreasing the influence of interference from the speech-message sources on the extracted signal. This method is based on introducing the time delays, which depend on the spatial coordinates, to the recording channels. Audio records of the voices of eight different people were used as test objects during the studies. It is proved that an increase in the number of microphones improves intelligibility of the speech message which is extracted from interference. PubDate: 2017-08-01 DOI: 10.1007/s11141-017-9796-9 Issue No:Vol. 60, No. 3 (2017)

Authors:D. V. Ionov; V. V. Kalinnikov; Yu. M. Timofeyev; N. A. Zaitsev; Y. A. Virolainen; V. S. Kostsov; A. V. Poberovskii Abstract: By virtue of their all-weather capabilities, the radiophysical atmospheric sensing methods allow one, in particular, to perform continuous observations of variations in the atmospheric content of water vapor being the most important natural greenhouse gas. The measurement station of St. Petersburg State University at Peterhof (59.88° N, 29.83° E) runs a number of ground-based instruments to determine total water-vapor content (TWVC) in the atmosphere. During a year period from September 2014 to September 2015, the TWVC was synchronously measured by two radiophysical methods, namely, the microwave and radio-refraction techniques, as well as the optical infrared method. Comparisons show that the average systematic and random discrepancies among the three methods amount to 0.3–0.5 kg/m2 (3–7%) and 0.4–0.6 kg/m2 (8–11%), respectively. The maximum relative differences (up to 20%) among the results of different-type measurements are observed for very small TWVC values (below 5 kg/m2). Empirical estimates of the random errors of the methods were 0.5, 0.3, and 0.3 kg/m2 for the radio-refraction, microwave, and infrared methods, respectively. The results of the TWVC measuring by the radio-refraction and microwave methods are in good agreement and yield greater values than those obtained by the optical method. The obtained discrepancies in the TWVC estimates are small compared with the published results of similar comparisons, which can, in particular, be attributed to the high spatiotemporal matching of various measurements. PubDate: 2017-10-10 DOI: 10.1007/s11141-017-9800-4

Authors:V. I. Kostylev; I. P. Gres’ Abstract: We propose an energy-like detector of signals and analyze its efficiency by an example of detecting a Gaussian signal with zero mathematical expectation and uncorrelated readouts against the background of Likhter noise with independent readouts. Analytical expressions for the probability of correct detection are obtained and statistical simulation is performed. Using particular examples, we show that the energy-like detection characteristics can be much closer to the optimal ones than those of the energy detection. PubDate: 2017-10-09 DOI: 10.1007/s11141-017-9804-0

Authors:O. I. Yakovlev Abstract: We report on the results of studying the circumsolar plasma turbulence according to the coronal sounding experiments using spacecraft signals. Statistical characteristics of the temporal fluctuation spectra of the amplitude, phase, frequency, and Faraday rotation angle of the radio-wave polarization plane are described for the solar offset distances of the ray path in the range between 3 and 40 solar radii. Information on the turbulence spectra is given and the spectral index, as well as the outer and inner turbulence scales, as functions of the heliocentric distance are presented. The effect on the measured parameters of the plasma waves is discussed and typical values of the wave periods for different distances from the Sun are given. PubDate: 2017-10-09 DOI: 10.1007/s11141-017-9797-8

Authors:Yu. A. Ilyushin Abstract: We consider the weak localization and the backscattering halo in media with strongly elongated scattering indicatrices. The earlier theory is generalized to the case of a nonuniform backscattering cross section in the rear hemisphere. Asymptotic formulas for the backscattering intensities are obtained in the low-angle diffusion approximation. PubDate: 2017-10-09 DOI: 10.1007/s11141-017-9802-2

Authors:T. D. Borisova; N. F. Blagoveshchenskaya; T. K. Yeoman; I. Häggström Abstract: We present the results of experimental studies of the parameters of HF-enhanced ion–acoustic and Langmuir plasma waves, as well as small-scale artificial field-aligned irregularities (AFAIs) when the EISCAT/Heating effective radiated power is varied from 10 to 560 MW. In the course of the experiments, a high-power HF radio wave with the alternating ordinary (O-mode) and extraordinary (X-mode) polarizations was radiated towards the magnetic zenith at a frequency of 7.953 MHz lying below the cutoff frequency of the F2 layer. A fundamental difference in the development of artificial ion–acoustic and Langmuir turbulence, which is seen as HF-enhanced ion and plasma lines in the EISCAT spectra, under the O- and X-mode HF pumping was found. The minimum values of the HF pump-wave electric fields in the ionosphere when the HF-enhanced ion and plasma lines, as well as small-scale artificial field-aligned irregularities, start to be excited, were determined from experimental data both for the O- and X-mode HF pumping. Comparison between the experimental and theoretical threshold values of the electric field required for the excitation of artificial ionospheric turbulence in thermal, Langmuir, and ion–acoustic modes in the high-latitude ionospheric F2 layer for the O-mode HF pump wave was made. PubDate: 2017-10-09 DOI: 10.1007/s11141-017-9798-7

Authors:N.Yu. Babanov; A. V. Klyuev; S.V. Lartsov; V.P. Samarin Abstract: We study a parametric scatterer representing a quadripole of four bridge-type parametric circuits with antennas connected to the circuit arms and tuned to the pump signal and its half-wave subharmonic on the basis of simulation and full-scale experiments in the frequency range near 800 MHz. PubDate: 2017-10-09 DOI: 10.1007/s11141-017-9803-1

Authors:G. N. Ilyin; A. V. Troitsky Abstract: We present a method and algorithm for real-time determination of the tropospheric delay of a radio signal and the radiometric complex developed on their basis. The method is based on the measurement of the atmospheric thermal microwave radiation intensity at the frequencies ν 1 = 20.7 GHz, ν 2 = 32 GHz, and ν 3 = 56.7 GHz and solution of the corresponding inverse problem with respect to the atmospheric parameters (temperature, pressure, humidity, and water content) which completely determine the tropospheric delay of a radio signal. The method was experimentally tested by comparing the radio-signal delay series obtained by the radiometric method and the GLONASS/GPS data. The error of determining the wet component of the radio-signal delay was about 3 mm. PubDate: 2017-10-09 DOI: 10.1007/s11141-017-9799-6

Authors:V. L. Weber Abstract: We consider the problem of simulation of the slope field of a random surface profile, which is represented as a sum of a finite number of sinusoids with random phases. The behavior of the correlation function of the slopes is studied for equidistant and nonequidistant locations of the nodes of the model-field spectrum on the frequency axis. A new node-location method, which is based on the equalization of the amplitudes of the spectral components of the actual slope field and ensures maximum proximity of the correlation functions of the model and actual fields over the entire region of their definition, is proposed. Using this method, one can significantly reduce the number of the summed harmonics during the simulation of the sea wind waves. The problem of fluctuations of the above-water irradiance is studied using the proposed slope-simulation method and, as a result, its application efficiency is proved. PubDate: 2017-10-09 DOI: 10.1007/s11141-017-9801-3

Authors:N. A. Denisova; A. V. Rezvov Abstract: We consider reflection of electromagnetic waves from two-layer dielectric films with finite thickness, whose refractive indices vary in the direction of wave propagation, which is perpendicular to the substrate boundary. The profiles of the refractive indices of the structures having low reflection coefficients in a wide frequency range are found. The obtained results are based on exact analytical solutions of the Helmholtz equation for one type of the layered inhomogeneous dielectric medium. The possibility of creating new low-reflection wideband inhomogeneous dielectric structures is demonstrated. PubDate: 2017-09-14 DOI: 10.1007/s11141-017-9793-z

Authors:A. A. Shvetsov; M. V. Belikovich; O. S. Bol’shakov; V. G. Ryskin; F. M. Feigin; L. I. Fedoseev; A. Korabovsky; A. V. Averchenko Abstract: We present the results of development of a multifrequency method for passive remote sensing of the snow cover using spectral features of the downward atmospheric radiation in the millimeter-wavelength range. A description of the automated tri-band spectroradiometer realizing this method is provided. Preliminary results of test measurements of the snow cover parameters by means of the tri-band spectroradiometer are discussed. PubDate: 2017-09-14 DOI: 10.1007/s11141-017-9791-1

Authors:A.V. Shchekoldin; I.V. Zhuravlev Abstract: We solve the problem of the high-accuracy measurement of the moving-object azimuth by the phase method using fixed antennas. The algorithm is presented for eliminating the ambiguity when calculating the azimuth variation by this method in the case where the object is detected in the region of unambiguous azimuth determination by a radar system. The experimental results of the azimuth measurements are presented. PubDate: 2017-09-14 DOI: 10.1007/s11141-017-9792-0

Authors:A. V. Shvets; A. P. Nickolaenko; V. N. Chebrov Abstract: We present the results of analyzing the response of the Schumann-resonance frequencies to the Xray solar flares. A special technique, by which a sharp variation that is present in all the resonant modes, but is hidden by regular variations combined with stochastic fluctuations is singled out using the weighted average frequency, has been developed. On the basis of comparison of the response shape and the flare intensity, the parameters of the statistical relationship between the frequency variations and the X-ray radiation intensity were analyzed and determined for the nonlinear regression model. It has been shown that an increase in the resonant frequency is proportional on the average to the logarithm of the X-ray radiation intensity to the power of 1.7. The magnitude of changes in the cavity frequency is related with the corresponding changes in the characteristic “magnetic” height of the conductivity profile of the lower ionosphere and compared with the results of the independent analysis performed by measuring VLF radio signals. PubDate: 2017-09-14 DOI: 10.1007/s11141-017-9789-8

Authors:I. A. Gotyur; D. M. Karavaev; V.M. Krasnov; Y.V. Kuleshov; A.B. Lebedev; A. N. Meshkov; G. G. Shchukin Abstract: By combining the global atmospheric model NRLMSISE-00 and the humidity model of the Northern hemisphere (GOST 26352-84), we developed a model for calculation of the dielectric permittivity of the atmosphere along the radio-wave propagation path. Microwave radiometry data were used to test the model. The difference between the model and measured values of the zenith wet delay of radio waves in the troposphere averaged 1–3 cm for a r.m.s. deviation of 4.7–5.3 cm. PubDate: 2017-09-14 DOI: 10.1007/s11141-017-9790-2

Authors:A. V. Shchekoldin; I. V. Zhuravlev Abstract: We solve the problem of measuring the radial velocity of a moving object under nonlinear variation in the Doppler phase with respect to time. The algorithm for measuring this velocity with high accuracy, which allows one to coherently accumulate the signal to improve the signal-to-noise ratio, is described. Compared with the existing analogs, the developed algorithm makes it possible to reduce the amount of calculations. PubDate: 2017-09-01 DOI: 10.1007/s11141-017-9786-y

Authors:A. V. Vodopyanov; M. Yu. Glyavin; A. G. Luchinin; S. V. Razin; A. V. Sidorov; A. P. Fokin Abstract: We studied the glow of the plasma of a pulse discharge ignited in nitrogen by high-power focused radiation of a terahertz-wave gyrotron (a radiation frequency of 0.67 GHz, a pulse duration of 20 μs, and a power of 40 kW). The pressure in the discharge chamber varied in the range 0.1–350 Torr. It was found that at high pressures (more than 50 Torr), long-term (about 1.0–1.5 ms), a non-monotonic afterglow exists after the end of the terahertz pulse, whose intensity can exceed the plasma glow intensity significantly (by several times) during the action of the terahertz radiation pulse on the plasma. At pressures below 50 Torr, the afterglow duration proves to be significantly shorter, specifically, about several tens of microseconds. The observed long-term afterglow is radiation in certain vibrational bands of the second positive system of N2 and is due, evidently, to the processes of associative excitation of electron levels in nitrogen molecules with the participation of long-living metastables \( {\mathrm{N}}_2\left({\mathrm{A}}^3{\varSigma}_{\mathrm{u}}^{+}\right) \) . PubDate: 2017-09-01 DOI: 10.1007/s11141-017-9784-0

Authors:D. V. Aleksandrov; A. P. Anyutin; I. P. Korshunov; A. D. Shatrov Abstract: We study plasmon resonances, which arise in the two-dimensional problem of diffraction of a plane wave on a gold cylinder with an elliptical shape of the transverse cross section. Numerical and asymptotical methods are used to find scattering and absorption spectra in the visible range. A simple analytical solution of the problem is found for a cylinder with an elongated shape of the transverse cross section. It is shown that in the case of normal incidence of a plane wave, a single quasistatic plasmon resonance is excited in such a cylinder. PubDate: 2017-09-01 DOI: 10.1007/s11141-017-9782-2