Vol 54, No 1 (2019)

The vacuum expectation value of the squared complex scalar field induced by a boundary in the de Sitter space with an arbitrary number of toroidally compactified dimensions is investigated. On the boundary, the field obeys the Robin condition and the quasiperiodicity conditions with arbitrary phases are imposed along the compact dimensions. In the expression for the vacuum expectation value, the part caused by the presence of the boundary is explicitly separated and its behavior is investigated in various asymptotic regions of the parameters of the problem.

We introduce a new exactly integrable level-crossing model of quantum semiclassical two-state problem for which the analytic solution is written in terms of the Kummer confluent hypergeometric functions. This is a constant-amplitude field-configuration describing an asymmetricin- time level-crossing process for which the laser field frequency detuning is given in terms of the Lambert-W function. The general solution of the problem for this model is written as a linear combination, with arbitrary constant coefficients, of two fundamental solutions each of which presents an irreducible linear combination of two confluent hypergeometric functions. We present the fundamental solutions and analyze the behavior of the system in the external field defined by the specific field configuration.

The single-particle states of charge carriers in the nanospherical InP/InAs/InP heterostructure are theoretically considered in the isotropic effective mass approximation and in the regime of strong size quantization. The results of numerical computations of the energy levels of charge carriers at various thicknesses of the quantizing of the InAs layer of the indicated heterophase structure are presented. It is shown that it is possible to achieve the desired value and position of the size quantization levels of charge carriers in the layer by an appropriate choice of the layer thickness. The interband optical transitions in the InAs layer are also considered. The values of the effective broadening of the band gap of the InAs layer as a function of the layer thickness are computed. By numerical computations, it is shown that the absorption has a resonant character and that the diagonal transitions dominate in the spectrum of the interband absorption. For several diagonal transitions involving both light and heavy holes, the values of threshold frequencies and absorption curves are given. In the spherical InP/InAs/InP nanoheterostructure, the photoluminescence spectra were also constructed for various temperatures close to room temperature.

We present the results of studies of the nanocomposite MWCNTs/SnO₂ hydrogen peroxide vapor sensors. The technology of manufacturing of these sensors has been developed. Because of the measurements of the temperature characteristics, the 100°C optimal operating temperature of the studied sensors has been found. The response and recovery curves of the sensors were investigated in the presence of different concentrations of hydrogen peroxide vapor in the atmosphere. A sufficiently high response was registered already at close to the threshold low concentrations of the target gas present in the air. In a double logarithmic scale, the linear dependence of the sensors response on the concentration of hydrogen peroxide vapor was observed in a certain concentration range. The minimal registered gas concentration is less than 1 ppm.

Orthorhombic DyMnO₃ ceramics were synthesized by means of standard high-temperature solid-state reaction technique. Impedance spectroscopy analysis (complex impedance Z* and complex modulus M*) were performed by using the nondestructive complex impedance spectroscopy technique in the frequency range of 100–10 MHz at different temperatures. The impedance spectroscopic plots were used to discern the intrinsic DyMnO3 grain and grain boundary contributions to the dielectric responses. The radii of semicircles in Z″ vs. Z′ plot (Z′ and Z″ are real and imaginary parts of Z*) increased with decreasing temperature, which suggest the increased grain resistance. Similarly, the radii of semicircles in M″ vs. M′ plot (M′ and M″ are real and imaginary parts of M*) suggest that the grain capacitance increased as the temperature decreased. The resistance and capacitance of grain boundaries seem to be independent of the investigated temperatures. The dielectric response from electrodes with demarking frequency was extracted from the presentation of Z′ vs. Z″/f, where f is the frequency of the applied field.

A modified Faraday rotation method is developed using a nanocell filled with cesium vapor. Formed atomic lines have a spectral width 1.5–2 times narrower than those obtained by the Faraday rotation method. In magnetic fields of B = 5000–7000 G, all the atomic transitions of the Cs D₂ lines, formed in the spectra, are spectrally resolved and identified. In particular, transitions that are forbidden at B = 0 G have been investigated, however, at certain values of the magnetic field, there is a gigantic increase in their probabilities. It is shown that the modified Faraday rotation method is convenient and efficient for high-resolution spectroscopy for Cs atoms. There is а good agreement between the experimental results and calculated values. The practical applications are also noted.

We describe a capacitive coupled plasma reactor, where the inert gas molecules are ionized by the radio frequency radiation. The control and measurement system of electrical and optical parameters of the plasma are considered. A qualitative assessment is given of the energy distribution of charge carriers.