Volume 59, Nº 11 (2017)

Observations of quasi-periodic intense radio emission at 2–8 GHz from the brown dwarfs with a brightness temperature of up to T_b ∼ 10¹³ K and with a fairly narrow radiation pattern initiated a series of studies in which the radiation was interpreted in terms of the electron cyclotron maser emission generated by energetic electrons with the “loss cone.” The plasma mechanism of the radio emission was excluded from consideration because it requires that the electron plasma frequency should exceed the electron gyrofrequency in the source of the radio emission, i. e., ν_p > ν_c. In this paper, we propose a coherent plasma radiation mechanism for intense radio emission from the brown dwarfs. The possibility of the formation of hot extended coronae in the magnetic loops that occur in the atmospheres of the brown dwarfs as a result of the photospheric convection is shown. The electric currents generated in the magnetic loops by photospheric convection lead to the plasma heating and elevation of the “squeezed” atmosphere. This ensures that the condition ν_p > ν_ce required for the plasma mechanism of radio emission is fulfilled at the coronal levels. In addition, the pumping mechanism supplying energetic particles into the coronae of the brown dwarfs, which maintain the long-term generation of intense radio emission from these stars, is studied. The parameters of the Langmuir turbulence explaining the observed properties of the radio emission from the brown stars are determined.

We give a mathematical rationale, an algorithm, and hardware implementation for a multichannel ionosonde–direction finder with chirp signal. The results of experimental studies of twodimensional angle–frequency characteristics on the Cyprus—Rostov-on-Don meridional obliquesounding path are presented. It is shown that both regular (terminator-related) and irregular (caused by the passage of a traveling ionospheric disturbance through the propagation path) transverse (with respect to the propagation path) horizontal gradients of the electron number density lead to a deviation of the azimuth of the high-angle ray in the direction of the N_e gradient. The experimental data are compared with the simulation results.

Within the framework of the Ginzburg–Landau theory, we study the features of the localized nucleation of the order parameter in superconducting systems with inhomogeneous effective mass m of the Cooper pairs, which is due to the spatial modulation of the diffusion coefficient and/or fluctuations in the local anisotropy axis in the sample. In the asymptotics of the weak magnetic fields H, for which the magnetic length [Φ₀/(2πH)]^1/2, where Φ₀ is the magnetic-flux quantum, is much shorter than the inhomogeneity scale, the spatial scale of the order parameter is determined by the sample-average coherence length and the regular lattice of the Abrikosov vortices is formed in the superconductor. In sufficiently strong magnetic fields H, the order parameter is localized near the minima of the coherence length ξ ∝ m^−1/2, which results in an increase in the critical temperature and destruction of the regular lattice of the Abrikosov vortices. Therefore, competition between the two superconductivity-nucleation types is observed during a gradual increase in the magnetic field, which leads to the positive curvature of the phase-transition line. We have also studied the features of the temperature dependences of the upper critical magnetic field for some model spatial mass profiles of the Cooper pairs. The obtained results are in good agreement with direct numerical calculations.

We study the potential of a method for manipulating the spectral-temporal characteristics of the Mössbauer γ photon on the basis of resonant interaction of the electromagnetic field of a single photon with an oscillating nuclear absorber. It is shown that the absorber enrichment by a resonant nuclide and an increase in its optical density allow one to considerably increase the peak probability of detecting the photon behind the absorber and improve the obtained-pulse shape. The estimates for the γ radiation of the Mössbauer nuclide ⁵⁷Co with a photon energy of 14.4 keV and a lifetime of 141 ns of the excited state, which interacts with the oscillating resonant absorber enriched by the ⁵⁷Fe nuclei, are given and the possibility of compressing the waveform of an incident photon into a train of pulses with durations of 10 ns and peak intensity two times exceeding that in the absence of the absorber is shown.