Vol 59, No 6 (2016)

The results of measuring HF signals on oblique chirp sounding paths in the Eurasian region during a solar eclipse of March 20, 2015 and the neighboring days are presented. The solar eclipse took place against the background of a strong magnetic storm. It was established that during the solar eclipse on oblique sounding paths of different length and orientation the decrease in the maximum observable frequency for the F mode (MOF-F) and the lowest observable frequency for the F mode (LOF-F) was 8–14% and 22–33%, respectively. During the eclipse, the signal amplitude increased by 3–5 dB. On the Lovozero—Nizhny Novgorod path in the maximum phase of the solar eclipse, the electron density decrease in the ionospheric E and F₂ layers at the midpoint of the path reached 37% and 22%, respectively. According to the MOF and LOF variation measurements for various modes, the group delay time of radio signals, and the results of spectral analysis, it was found that in the eclipse there were wave disturbances with a period of 25 to 50 min. However, quasi-periodic variations of MOF-F and LOF-F having a a period of 50 to 80 min but which started before the eclipse were detected on some paths. Probably, in these cases, the variations were a result of the superposition of disturbances from two sources, namely, the magnetic storm and the solar eclipse.

We have developed a self-consistent physical model that improves the accuracy of calculating the characteristics of the devices based on both surface and pseudosurface acoustic waves. The model is free from restrictions inherent in the well-known method of coupled modes and other phenomenological methods for studying distributed systems. The compact relationships describing all the characteristics of the acoustoelectric transducers of all types with allowance for the possible directionality of their radiation and its propagation loss are obtained using analytical solution of the difference equations. The method for determining the spatial orientation of the elastic-polarization ellipse in an anisotropic crystal, which allows one to unambiguously calculate the phase shift between the oscillations of two coupled dynamical subsystems, i.e., elastic displacements and the corresponding electric field, is proposed. The obtained results, which considerably facilitate the task of fast and accurate design of various devices on the basis of surface and pseudosurface acoustic waves, are valid in the general case for any frequency, including the harmonics of the frequency of the fundamental acoustic synchronism.

We study the processes of radiation output from a microwave storage cavity through a superconducting interference switch, which is based on a H-junction with a superconducting switching cavity connected to the side branch of the junction for various ways of controlling the parameters of the switching cavity. It is shown that efficient control over radiation output in such a switch can be achieved by varying the resonance frequency or Q-factor of the switching cavity, as well as by varying these parameters simultaneously. It is found that in the case of controlling the resonance frequency of the switching cavity, there exists an optimal interval of the frequency variation, within which the total efficiency and extraction efficiency are maximum. When the Q-factor of the switching cavity changes, the dependence of the total efficiency and extraction efficiency on the Q-factor has the monotonic character. The mixed regime of radiation output control is also studied. The envelopes of the output compressor pulses are plotted on the basis of recurrent relationships between the amplitudes of the waves in the system for three regimes of switch operation. It is shown that pulses with an almost rectangular shape of the envelope can be formed in the regime of controlling the switching cavity by varying the Q-factor. An example of possible realization of the switching cavity is considered.

We study the influence of the ratio between the relaxation rates of the field in a cavity and the polarization of active centers on the dynamic properties of the distributed-feedback lasers by means of 1D numerical simulation. The model of a two-level active medium with strong inhomogeneous broadening of the spectral line under CW wide-band pumping that provides two- or several-mode lasing in the vicinity of the Bragg photonic band gap is used. Evolution of the dynamic spectra and oscillograms of the laser emission with decreasing Q-factor of the Bragg resonator is analyzed. It is shown, in particular, that under conditions of the dominant role of the superradiant effects, there are unique opportunities for control of both quantitative and qualitative characteristics of lasing, including the spectral width, duration, and coherence length of various pulse components of the output radiation.

Until now, significant progress has been made in synthesizing the current-switched structure of spin valves and magnetic tunnel junctions with hysteresis dependences of the resistance on the current. These structures are of interest for creation of small-size electronic memory. However, hysteresis of resistance, which is usually presented in publications, does not correspond to physical principles. In this paper, we show how the hysteresis dependence of the resistance on the current, or the conductance on the voltage, which does not contradict the energy conservation law, and the corresponding current–voltage characteristic should look like. As an example, we present the experimental current–voltage characteristic of the CO₂MnSi/MgO/Co₂MnSi magnetic tunnel junction, which agrees with the model hysteresis dependences.