Kadyrov A., Pak I., Ganyukov A., Imanov M., Balabekova K. «Research of operation of equipment for ultrasonic purification of exhaust gases of internal combustion engines» Инженерно-физический журнал, 94, № 6, с. 1442-1448 (2021)

This paper is devoted to analytical and experimental modeling of the method of ultrasonic purification of recycled exhaust gases of internal combustion engines. The scheme of the experimental stand and the procedure for conducting the experiment are given. The data on determination of the coagulation coefficient are presented. Ключевые слова: ultrasonic purification, coagulation, ultrasonic oscillations, internal combustion engine

Lesovoi S.V., Globa M.V. «Measurement of Siberian Radioheliograph cable delays» Солнечно-земная физика, 7, № 4, с. 93-97 (2021)

To achieve the maximum dynamic range of solar radio images obtained using aperture synthesis in relatively wide frequency bands 0.1–0.5% of the operating frequency, it is necessary to compensate the signal propagation delays in the antenna receive path before calculating visibility functions (hereinafter visibilities). When visibilities are corrected without delay compensation, the signal-to-noise ratio decreases due to residual phase slopes in the receiving system bandwidth. In addition to enhancing dynamic range, preliminary compensation for delays simplifies real-time imaging – no antenna gain calibration is required to get a first approximation image. The requirements for the accuracy of antenna placement are also reduced – in contrast to the measurement of the phase visibility error, the measurement of the delay is actually not so critical to the antenna position errors that are larger than the operating wavelength. The instantaneous frequency band of the Siberian Radioheliograph, which determines the minimum step for measuring the phase slope, and hence the accuracy of determining the delay, is 10 MHz. At the speed of light in an optical fiber of ∼0.7c, a step of 10 MHz makes it possible to unambiguously measure the difference between electrical lengths of cables up to 20 m and to correct antenna positions by radio observations, even if the error in the position of the antennas exceeds the operating wavelength. Correction of the band phase slopes during the observation time adapts the radio telescope to the temperature drift of delays and decreases antenna gain phase spread. This, in turn, leads to more stable solutions to systems of equations containing antenna gains as unknowns.

Globa M.V., Lesovoi S.V. «Calibration of Siberian Radioheliograph antenna gains using redundancy» Солнечно-земная физика, 7, № 4, с. 98-103 (2021)

The paper describes application of standard gain calibration using redundancy for a 48-antenna prototype of Siberian Radioheliograph. Traditionally, for calibration, the visibilities were measured only between adjacent antennas since they have the highest signal-to-noise ratio and are sufficient for phase calibration. We have shown that this limited set of visibilities did not allow using the antenna array redundancy potential and obtaining images with a high dynamic range on a permanent basis. Images without amplitude calibration contain many artifacts and require special care when analyzed. The inclusion of visibility measurement between antennas with a double step made it possible to significantly increase the accuracy of solving the system of equations for amplitudes. Images constructed using both phase and amplitude calibrations do not have visible artifacts and are more reliable.

Guglielmi A.V., Klain B.I., Potapov A.S. «On the group velocity of whistling atmospherics» Солнечно-земная физика, 7, № 4, с. 67-70 (2021)

The dynamic spectrum of a whistling atmospheric is a signal of falling tone, and the group delay time of the signal as a function of frequency is formed as a result of propagation of a broadband pulse in a medium (magnetospheric plasma) with a quadratic dispersion law. In this paper, we show that for quadratic dispersion the group velocity is invariant under Galilean transformations. This means that, contrary to expectations, the group velocity is paradoxically independent of the velocity of the medium relative to the observer. A general invariance condition is found in the form of a differential equation. To explain the paradox, we introduce the concept of the dynamic spectrum of Green’s function of the path of propagation of electromagnetic waves from a pulse source (lightning discharge in the case of a whistling atmospheric) in a dispersive medium. We emphasize the importance of taking into account the motion of plasma in the experimental and theoretical study of electromagnetic wave phenomena in near-Earth space.