卷 62, 编号 4 (2019)

In the majority of modern radio telescopes, which are used for radio interferometry with very long baselines, a special signal is introduced into the signal chain for the phase calibration of the equipment. This signal is used during the correlation processing of the radio-astronomy observations for obtaining a synthesized response when it is required to match the signals of several frequency channels by phase and delay and to ensure control over the working capacity of the equipment and the phase stability of the signal chain during the preparation and implementation of observations. Isolation of the phase-calibration signal in the recorded data requires considerable computation resources. In this case, the computation volume increases with increasing recorded frequency domain, which can amount to several gigahertz for modern radio telescopes, such as RT-13 of the “Quasar” VLBI network. In this work, the well-known methods for measuring the parameters of the phase-calibration signal are considered, their precision is estimated, the computation efficiencies are compared, and the disadvantages of the available measuring algorithms are shown. An improved method allowing one to significantly save the computation cost without the measuring-accuracy loss is proposed, which softens hardware requirements and speeds up computations.

We propose universal formulas for the amplitudes of longitudinal and transverse plane acoustic waves, which are reflected and refracted by a plane interface of two media. The formulas are valid for liquid and gaseous media, as well as for elastic isotropic media. Advantages of these formulas are their relative clarity compared with the well-known and commonly accepted formulas, as well as a possibility to pass over from one scattering problem to another by simply replacing the corresponding wave numbers. Despite the well-known methods which are used in the calculations and rather have a methodical character, we manage to find a new type of surface waves at the interface of elastic media. These waves are characterized either by ratios of the wave numbers of transverse waves and densities, or by only the wave numbers of longitudinal waves and the ratio of the densities of media.

We present a version of the frequency-tunable gyrotron operating in a wide frequency range (0.1–0.26 THz) with an output radiation power of up to 260 kW. Multilevel analysis and combined optimization of its electron-optical and electrodynamical systems are performed. The gyrotron is designed for operation with the JASTEC-10T100 cryomagnet or its analogs. Efficiency of single-stage recovery in this system is analyzed. A collector system is proposed, which is capable of collecting electron beams effectively during gyrotron operation in the entire specified frequency range.

A change-over of the quasiparticle wave functions and spectrum under a variation in an interparticle interaction in a Bose-Einstein condensed gas of bosons confined in a one-dimensional trap with a flat potential and impermeable walls is studied analytically and numerically. An efficient approximate method of analysis is developed. It yields a solution to the self-consistent Bogoliubov and Gross-Pitaevskii equations for quasiparticles and the condensate that describes a crossover from the regime of a gas of noninteracting bosons to the regime of a gas with the interaction being strong enough to reach a Thomas-Fermi asymptotics. As a result, the characteristic function of the total number of noncondensed particles is found which, for the first time, allows one to figure out how the quantum statistics of fluctuations of the number of particles in the condensate depends on its inhomogeneity and the interparticle interaction in the case of the flat trap. The qualitative features of this dependence as well as a possibility of an experimental observation of the predicted effects in the actual traps are discussed.