Vol 59, No 7 (2016)

The formation of micropinches and X-ray sources in low-voltage, laser-induced discharges with high rates of current rise is investigated.

A technique is proposed for the determining the parameters of the equivalent circuit elements in strong inversion mode using the measurement results of the admittance of MIS structures based on n-Hg_0.775Cd_0.225Te grown by molecular beam epitaxy. It is shown that at 77 K and frequencies above 10 kHz, the capacitancevoltage characteristics of MIS structures based on n-Hg_0.775Cd_0.225Te with a near-surface graded gap layer have a high-frequency behavior with respect to the recharge time of surface states located near the Fermi level of intrinsic semiconductor. It is established that the electron concentration in the near-surface graded-gap layer exceeds an average concentration found by the Hall method by more than 2 times. The proposed technique was used for determining the temperature dependences of the insulator capacitance, capacitance and differential resistance of the space-charge region, and capacitance of the inversion layer in MIS structures based on n-Hg_0.775Cd_0.225Te without a graded-gap layer. The temperature and voltage dependences of the parameters of the equivalent circuit elements in strong inversion are calculated. The results of calculation are qualitatively consistent with the results obtained from the measurements of the admittance.

We present the results of experimental studies of internal quantum efficiency of photoluminescence of blue LED heterostructures based on multiple In_xGa_1–xN/GaN quantum wells with short-period In_yGa_1–yN/GaN superlattices containing small amounts of In at high levels of optical pumping. Introduction of an In_yGa_1–yN/GaN superlattice from the side of the n-region of a LED In_xGa_1–xN/GaN heterostructure allows to increase the value of its internal quantum efficiency presumably by reducing the quantum-confined Stark effect and Auger recombination rate.

The present research focuses on the effect that hollow carbon microspheres embedded into the polydimethylsiloxane elastomer have on the electroconductive properties of the composite material. The percolation point was experimentally determined. The dependence of electrical resistance of the syntactic foam on the content of semiconducting filler in the binder was revealed. The effect of the filler on the radarabsorbing properties was studied.

Impedance of polymer-dispersed liquid crystals modified by carbon nanofibers is studied in fields lower than the threshold field of the director reorientation of a liquid crystal. It is shown that the real and imaginary parts of the impedance obey to the relationship (Z_re – X₀)² + (Z_im – Y₀)² = R₀², where X₀, Y₀, and R₀ are the fitting parameters depending on the frequency of the exciting electric field.

Experimental studies of the effect of a barrier layer on the kinetics of thermally induced diffusion procesess and phase transformations in a layered Fe–Be syatem are investigated at the energy ~1.6 MeV. Thermal stability of the barrier layer in the Fe:O⁺ system is validated and a possibility of its use as a subsurface layer for a beryllium coating is demonstrated. For the Cu:O⁺ system it is shown that the implanted layer in the matrix comes apart already at the annealing temperature ~180°C and could not be used in a copper matrix as a subsurface barrier layer. For the first time, a method is proposed for retardation of diffusion and phase formation processes and realized in a layered iron – beryllium system using an implanted layer of oxygen ions. The sequence and characteristic times of thermally-induced phase-transformation processes taking place in the subsurface layers and in the bulk of the Fe (10 μm) systems: O⁺ – Be (0.7 μm) – ⁵⁷Fe (0.1 μm) and Fe (10 μm) – Be (0.7 μm) – ⁵⁷Fe (0.1 μm) are determined.

A new technique describing the formation of a nutation line under conditions of modulation of the constant magnetic field B₀ by a variable magnetic field is presented. Dependences of the nutation line profile (the number of peaks, their amplitudes, and widths) on the modulation field parameters and the magnetic field inhomogeneity ∆B₀ in the zone of arrangement of the nutation coil are investigated. Results of experimental investigations are presented and their comparison with theory is performed.

Dynamic (temporal) characteristics of adaptive systems imaging through the turbulent atmosphere are analyzed. The Strehl parameter is analytically calculated on the basis of the generalized Huygens–Kirchhoff principle. The conventional adaptive system with finite frequency band (or finite response time) is described as a dynamic system with constant delay. It is shown that to provide efficient distortion correction in such adaptive system, the time delay must be much less than the transport time of the coherence radius, corresponding to the average wind velocity, through the optical beam. Adaptive optical systems in which correction phase is calculated using not only the signal, but also its derivatives are also considered. It is shown that such modernization of the control algorithm of correction for phase front distortions admits much greater time delays. The time gain compared to the system with constant delay is the higher, the stronger are phase distortions in the optical wave.

Excess delay time of signals from global navigation systems used for coordinate-time support of high-orbit space vehicles caused by the refraction during sliding radio-wave propagation in the Earth’s atmosphere is estimated. Conclusions obtained are compared with the data of experimental analysis of observable GPS signals.

A dynamic theory of coherent x-radiation emitted by a divergent beam of relativistic electrons traversing a thin single-crystal plate is developed which takes into account multiple scattering of the electrons on the target atoms. The case is considered in which the target is quite thin, so that it is not necessary to take absorption of radiation into account, but the electron path in the target is quite long, so that it is necessary to take multiple scattering into account. Expressions are obtained which describe the spectral–angular characteristics of parametric x-radiation and diffracted transient radiation under these conditions. Conditions are described under which diffracted bremsstrahlung radiation can be neglected. The possibility of manifesting the effects of dynamic diffraction is investigated.

A multifield theory of bodies with microstructure is developed. As the basic model we take the structural model of a Cosserat chain consisting of particles of rectangular shape. A linear complete discrete model, a linear reduced discrete model, and a nonlinear discrete model are derived and discussed. One-period and two-period solutions are obtained, describing small oscillations of particles in one direction and in different directions. Single-field and two-field, complete and reduced Cosserat models are constructed. It is shown that the singlefield model describes one-period solutions in the chain while the two-field model describes both long-wave one-period and short-wave two-period solutions.

Amplification of conically diverging laser beams in the XeF(C-A) amplifier of the THL-100 hybrid laser system operating in the visible range (λ = 475 nm) is investigated experimentally and theoretically. Energies of 2 and 2.5 J are obtained experimentally and theoretically at the output from the XeF(C-A) amplifier for the chirped start pulse with energy of 0.8 mJ and duration of 2 ps. Patterns of changes of energy and spatial and temporal distribution of the amplified laser beam intensity are investigated theoretically. The maximal calculated energy density and the radiation pulse intensity are W_max = 100 mJ/cm² and I_max = 64 GW/cm², respectively.

Within the limits of the Hubbard model supplemented with allowance for relativistic antisymmetric Dzyaloshinskii–Moriya interaction, the spin fluctuation theory of helical band ferromagnetism is developed. The magnetic state equation is derived for the nonuniform order parameter together with expressions for the Néel temperature and the wave vector of a spin structure. The effect of pressure on the helical ferromagnetism is analyzed based on the LDA + U + SO calculations of the MnSi electronic structure at different pressures. It is shown that with increasing pressure, the effect of zero-spin fluctuations that reduce the Néel temperature is amplified, and at a pressure of 15.2 kb a quantum transition takes place accompanied by vanishing of the longrange magnetic order.

A flow of physical events (photons, electrons, etc.) is considered. One of the mathematical models of such flows is a modulated synchronous doubly stochastic flow of events. Analytical results for conditional and unconditional probabilities of erroneous decision in optimal estimation of flow states upon the criterion of the a posteriori probability maximum are presented.

The energy spectra of five fullerene C₇₆ isomers are calculated for the Hubbard model in the static fluctuation approximation. Based on the spectra obtained, the optical absorption spectra of pure fullerene C₇₆ represented by the isomer of symmetry D₂ and endohedral Lu₂@C₇₆, Sm@C₇₆, and DySc₂N@C₇₆ metal complexes are calculated. The calculated optical absorption spectra agree qualitatively well with the available experimental data, thereby indicating a need to consider the strong Coulomb interactions in the study of the π-electron fullerene subsystem.

Implementing a previously obtained, original solution of the Dirac equation for an electron in the field of a nucleus (Ze) expressed in terms of the wave function of the corresponding Schrödinger equation and its derivatives in spherical coordinates and the spin projection operator Σ₃ associated with the eigenfunction, taking into account in each component of the spinor the leading term of the expansion in the small parameter (Zα), α = e² / ħc ≈ 1 / 137, the partial probabilities W of emission of a photon (Zα)^* → (Zα) + γ have been calculated. Here two orthogonal states of the linear polarization of the photon, and also the spin states of the electron, which previously had not been taken into consideration, have been taken into account in the transverse gauge. It turns out that the probabilities W of emission of a photon per unit time for any allowed transitions are proportional to (Zα)⁴, as was previously accepted, and the selection rules for the quantum number m have the usual form ∆m = 0,±1. It was found that a spin flip does not take place during emission. In contrast to the customary situation with the selection rules for the quantum number l being of the form ∆l = ±1, for ∆m = ±1 there also exist integrals over dcosθ which are not equal to zero for undetermined odd values of ∆l. In this, and also in a fundamentally different dependence of the amplitude on the quantum numbers consist the differences from the traditional approach to the problem. Necessary conditions are formulated, under the fulfillment of which the selection rules for l are not changed, having values ∆l = ±1 for arbitrary ∆m, but it was not possible, however, to give a complete proof of these rules.