Vol 60, No 3 (2017)

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.

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.

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.

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.

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.