Vol 62, No 6 (2019)

Using the Hubbard model in an approximation of static fluctuations, analytical relations of anticommutator Green’s functions and energy spectra of С₃₆ fullerene and La@C₃₆ endohedral fullerene with the D_6h symmetry groups are obtained. Using the group theory methods, a classification of the energy states is performed and the allowed transitions in the energy spectra of the С₃₆ and La@C₃₆ molecules are determined.

The results of investigation of phase and elemental compositions, defect substructure states, mechanical and tribological properties of the modified surface of Steel Gr1 are presented. The process of modification consists in plasma spraying of a Ni–Cr–B–Si-based powder coating followed by its irradiation with a high-intensity pulsed electron beam. It is shown that the coating surface formed by plasma spraying contains micro- and macro-pores and is characterized by high relief. A subsequent processing of the modified surface with a highintensity pulsed electron beam of a submillisecond duration in the mode of surface layer melting is accompanied by smoothing of the coating surface, saturation of the surface layer crystal lattice with Ni, Cr, B and Si atoms, formation of submicron cells of dendritic recrystallization, precipitation of nanosized particles of the second phase, and formation of quench structure. When combined, these treatments result in the formation of a hardened layer up to 1500 μm in thickness, whose microhardness and wear resistance by 4.6–6.5 and 4 factors exceed the respective characteristics of the initial steel.

Cathodic arc deposition is used to produce ZrNbN coating with the different niobium concentration. Investigated are the elemental and phase compositions of the obtained coating, its structure and properties. It is shown that various parameters of niobium cathode discharge modify the elemental composition of ZrNbN coating. The dependencies are obtained for physical-and-mechanical and tribological properties on the niobium concentration in ZrNbN coating. It is shown that the coating with the niobium concentration of 9.8 at.% has the best properties, such as 39.4 GPa hardness, 0.03 μm roughness, 0.43 friction coefficient and not over 9.4·10^–6 mm³/(N·m) wear rate.

The paper expounds physical principles of the low-frequency piezothromboelastography method for studying viscous properties of whole blood and diagnosis of the hemostatic potential. A mathematical model of ultrasonic vibrations in a viscous fluid has been developed. An ARP-01M “Mednord” piezothromboelastograph is used to carry out a numerical experiment to study the operational modes of a piezoelectric sensor and its applicability for measuring the dynamics of the viscous properties of whole blood. It is shown that the piezoelectric sensor reaches the optimal operational mode with the configuration of the needle-resonator in the form of a rectilinear rod with a loop. The maximum sensitivity in measuring the amplitude-frequency signal characteristics with a recording piezoelement is observed at 2.95 kHz. A numerical experiment studying the influence of a viscous medium on changes in the amplitude-frequency characteristics of vibrations of the needle-resonator of the piezoelectric transducer with allowance for the viscous friction force magnitude has been performed. The viscous properties of water and glycerin are used as an example. Calculations have been performed for two limiting magnitudes of the viscous force encompassing the interval of changes of the whole blood viscosity in the process of coagulation. It is demonstrated that the method has sufficient sensitivity to changes in the viscous characteristics of blood and to the dynamics of changes of these characteristics during coagulation and hence, has high measurement accuracy.

The results of an experimental investigation of the effect of cumulation of a beam of runaway electrons formed in a high-voltage nanosecond discharge at a reduced air pressure are presented. The optimal conditions of this effect in a discharge gap in a tubular cathode – grounded planar anode geometry were achieved at an air pressure of ≈5 Pa and an interelectrode gap of 2.75 mm. An electron-beam current pulse is recorded with a high time resolution (up to about 80 ps) behind the flat foil anode. It is found out that due to this effect a through hole is formed in a 20 μm-thick aluminum foil after 2–3 discharge pulses. The results obtained suggest that the electron energy in the second part of the beam current pulse is lower than that in its first part.

WSe₂ films with thickness of two monolayers are deposited on SiO₂/Si substrates using the top-down technology. The thickness and the composition of the films are confirmed by measurements of the Raman spectra, photoluminescence, and interference contrast in three RGB channels. The luminescence of WSe₂ bilayers is studied at temperatures decreased down to 5 K. It is shown that at low temperatures, the fine structure of the emission spectrum near the direct intrinsic absorption edge is determined by the recombination of A excitons (in the ground or excited state) and various complexes (trions and excitons bound on defects). The emission spectrum near the indirect fundamental absorption edge is described by exciton luminescence processes in which the exciton energy and momentum are transferred to phonons corresponding to the Λ point of the Brillouin zone. A possible contribution of the electron-hole liquid to the emission spectrum is discussed.

Undulator radiation (UR) of some elliptical undulators with multiperiodic magnetic fields of sin-sin and sincos configuration is investigated, as is also UR of a planar and a spiral undulator in the presence of additional harmonics of the magnetic field. Exact analytical expressions for the UR spectrum and the intensity in terms of generalized special Bessel functions are obtained; the corresponding Bessel coefficients are derived. Comparison of the obtained results with the available experimental data for real devices along with numerical simulations confirms the accuracy of the analytical formulas. The possibility of generation of a strong fifth UR harmonic induced by the third harmonic of the undulator field is demonstrated. In free electron lasers (FELs) this effect leads to the generation of a strong fifth harmonic of coherent radiation against the background of a weak third harmonic. In a spiral undulator with a third harmonic of the field, large values of the Bessel coefficients are obtained for the fifth UR harmonic; this makes it possible to use such an undulator as a prebuncher, i.e., to bunch electrons, at the wavelength of the fifth harmonic in a cascade FEL with amplification of the higher harmonics. The corresponding FEL is modeled.

A linear correlation has been established between the empirical parameter D of the Enkel equation for the viscosity and the vitrification temperature T_g of inorganic glasses, which is discussed within the framework of the model of delocalized atoms. From an analysis of this correlation, certain information on the vitrification and the viscous flow of glass-forming liquids follows. The value of D is an unambiguous function of the atom delocalization energy.

Research was done on electrical conductivity and thermal conductivity of AgSbSe₂ in the temperature range of 80–330 K. It was demonstrated that charge transfer in AgSbSe₂ is carried out by means of hopping conductivity of carriers over localized states. The localized state radius and densities of localized states at the Fermi level were calculated. It was demonstrated that high defectiveness of AgSbSe₂ leads to the low value of lattice thermal conductivity.

A model of the p–n junction that adequately describes the non-quasi-static effects of accumulation and relaxation of nonequilibrium charge carriers is considered. In this case, the diffusion charge equation is written in a closed form resolved with respect to the diffusion charge. This allowed computer programming of this model to be performed without user-defined recursion resolving the differential equation with respect to the diffusion charge. As a result, the non-quasi-static model of the p–n junction has been realized as an equivalent circuit containing only conventional quasi-static elements of computer-aided design systems.

Resonant interaction of an elastic plate with an air bypassing it and leading to the development of a wind instability is studied. The dispersive equation of bending vibrations is derived and investigated. Conditions for bending wave amplification and non-transmission are found. The spectrum of complex natural vibration frequencies is determined for a plate with finite dimensions, pivotally fixed at the ends and located in air flow bypassing it. The main parameters of the wind instability are determined.

Results of experimental investigations of the dispersion of the refractive index n(ν) and of the absorption coefficient α(ν) of a ZnGeP₂ crystal in the frequency range 0.3–1 THz are presented. Their comparative analysis is performed. The spectra obtained can be used for real-time diagnostics of the material quality that requires integral characterization. The most informative spectral range in which considerable differences between the absorption coefficients are observed is determined to be 400–800 μm.

The process of production of an H (h; A) boson of the Minimal Supersymmetric Standard Model and a heavy fermion pair in arbitrarily polarized \( {e}^{-}{e}^{+}\to H\left(h;\kern0.5em A\right)f\overline{f} \) collisions is considered. Analytical expressions for the differential cross sections of the processes are obtained, and peculiarities of the behavior of the cross sections and the angular and spin asymmetries are investigated as functions of the energies and emission angles of the particles.

The current – voltage characteristics of nBn structures based on HgCdTe grown by molecular beam epitaxy (MBE) on GaAs substrates in the temperature range 9–300 K were experimentally studied. The choice of technological parameters of nBn structures was determined by the possibilities of creating infrared detectors for the 3–5 μm spectral range (MWIR). Structures with various compositions (from 0.67 to 0.84) and thicknesses (from 120 to 300 nm) of the barrier layers were studied. It was established that the composition in the barrier layer exerts the greatest influence on the type of current–voltage characteristics. For a composition equal to 0.84, the current density at small reverse bias is much lower than that for structures with lower compositions in the barrier. For structures with pronounced temperature dependence of the current density, activation energies were found that ranged from 66 to 123 meV. Studies of nBn structures with various electrode areas have shown that for high current densities, leakage along the lateral walls plays an important role. Possible mechanisms for the formation of current – voltage characteristics in MWIR nBn structures based on MBE HgCdTe are discussed.

At the end of the article the acknowledgement should be added: “This work was financially supported by a grant from the Russian Science Foundation (project No. 17-19-01374)”.