Vol 59, No 12 (2017)

The results of theoretical modeling of the process of formation of a nanosecond discharge in a coaxial discharge gap filled with a high-pressure gas are presented. Two cardinally different evolution scenarios of the nanosecond discharge are addressed: A) in a uniformly volume pre-ionized gas medium and B) in a strongly spatially-nonuniform initially-ionized region near the cathode with a small curvature radius. Relying on the minimal mathematical model of a high-voltage discharge and the description of the physical kinetics of runaway electrons, it is shown using the Boltzmann kinetic equation that the amplitude and duration of a current pulse of runaway electrons and their energy spectrum strongly depend on the mode of gas preionization in the gap. In particular, the other conditions being equal, near-cathode initiation gives rise to the generation of a large group of low-energy runaway electrons within the late current-switching stage. The volume-homogeneous gas preionization can reduce the number of fast electrons by nearly two orders of magnitude compared to the regime without preionization.

Spectral-luminescent and lasing characteristics of rhodamine 6G in porous aluminum oxide films anodized under various conditions are investigated. Lasing is obtained without external resonator in the longitudinal scheme under excitation by the second harmonic of Nd³⁺:YAG-laser radiation. The threshold pump power densities are in the range 3.5–15 MW/cm² depending on the anodizing conditions. Wherein, the lasing line narrows down from 12 to 5 nm.

In this work, emission spectra of Ne and Ar atoms in an inductive discharge are simulated. The influence of the alternating electric field generated by this discharge on the spectral characteristics of light sources is studied. Based on the results of calculations, the regularities in the behavior of spectral characteristics of Ne and Ar atoms in the electric field have been revealed. Practical applications of the simulation results are considered.

Colloidal solution of iron oxide nanoparticles is synthesized by nanosecond pulsed laser ablation (Nd:YAG laser, 1064 nm, 7 ns, and 180 mJ) of a metallic iron target in water, and nanocrystalline powder is prepared from this solution by vacuum drying. A composition and structure of the material obtained are investigated by methods of electron microscopy, x-ray diffraction, and optical spectroscopy. It is established that oxide particles with average size of about 5 nm and Fe₃O₄ magnetite structure are mainly formed during ablation. Preliminary investigation of magnetic properties of the prepared nanoparticle powders shows that they can be in ferromagnetic and/or superparamagnetic states.

A mismatch between the coordinates of a particle and its reconstructed image is measured and investigated. Possible reasons for inaccurate measurement of the particle coordinates under the same conditions of digital hologram recording and reconstruction are discussed.

Noncommutative integration of the Dirac equation on Lie groups with a right-invariant metric and an invariant electromagnetic field tensor is considered. An electromagnetic field, admitting a noncommutative reduction of the Dirac equation, but not admitting either diagonalization of the squared Dirac equation or separation of variables, is found.

A cosmological model of an inflationary Universe is considered that is induced by the generalized form of the equation of state for a fluid in a spatially flat Friedmann–Lemaître–Robertson–Walker Universe. A cosmological model of a fluid that describes an inflationary Universe with a type-IV singularity is investigated. Values of parameters in the equation of state of the fluid near singularities are found. Finally, we consider the correspondence of the theoretical values of the inflation parameters leading to singular inflation of type IV with the experimental data obtained from observations made by the Planck mission.

The half-wave resonance of ultra-thin conductors produced by different technologies is investigated within 8.2–15.5 GHz frequency range using an open quasi-optical resonator. A comparison of the theoretical and experimental results show that for glass-coated and drawn microwires, both fabricated from alloys with specific conductivity of over 10⁵ S/m, the experimental value of the microwire resonant length is less than the theoretical. Supposedly, this is due to the surface effect including the nanoscale transition layer of microwires. Dependence diagrams are obtained for microwires made of alloys with natural ferromagnetic resonance. It is shown that the half-wave length resonance of the latter is considerably longer than that of microwires with a similar value of specific conductivity, but without magnetic properties.

The paper presents the experimental results on thermomechanical stability of the structure and the evolution of microstructure of the type ВТ1-0 nanostructured titanium. The cyclic tests are performed within the temperature range of 30–350°С.

The results of investigation of characteristic features of modification of the structural-phase state of the surface layer of a TiC–(Ni–Cr) cermet composite under irradiation by a pulsed electron beam in the discharge plasma of inert gases with different atomic masses and ionization energies are presented. The effect of modification of the structural-phase state of the composite surface layer on its strength is analyzed under conditions of threepoint bending.

The paper examines physical properties of foam glass material modified with 0.3 mass% nano-sized zirconium dioxide. It presents experimental data on the foam glass structure on micro- and meso-levels. The authors make a conclusion about influence and mutual subordination of structural levels in the glass materials. The presence of nanocrystallites (25 nm) located in the amorphous matrix in an ordered fashion and the pore packing that is correct from the symmetry standpoint provide for the enhanced strength of the porous structure. Findings show that the introduction of nano-sized zirconium dioxide leads to the emergence of a hierarchical and mutually subordinate system. The paper concludes that small additions of zirconium oxide have a positive effect on physical and mechanical properties of foam glass material.

Frequency-temperature spectra of the complex permittivity are studied for proton semiconductors and dielectrics using the methods of a quasi-classical kinetic theory of dielectric relaxation (the Boltzmann kinetic theory) in the linear approximation with respect to the polarizing field in the radio frequency range at temperatures T = 50-450 K. The effect of the quantum transitions of protons on the Debye dispersion relations is taken into account for crystals with hydrogen bonds (HBC) at low temperatures (50-100 K). The diffusion coefficients and the mobilities under electrical transfer of protons in the HBCs are constructed at high temperatures (100-350 K) in a non-linear approximation with respect to the polarizing field.

It is shown that two previously developed approaches to the construction of nonlinear interactions in higher-derivative theories (Eur. Phys. J., C74 (2014); J. Phys., A49 (2016)) lead to equivalent nonlinear models. A substitution of variables that is invertible on the mass shell is presented, which maps the classical trajectories of one of the models onto the trajectories of the other model.

Using the method of transmission electron microscopy, the features of structural-phase state of an internally oxidized V–Cr–Zr–W alloy following severe plastic deformation by the method of torsion on Bridgeman’s anvils are investigated. A quantitative evaluation of the parameters of grain and defect structure is performed and the characteristic dimensions and phase composition of fine disperse particles are determined. The main factors controlling the special conditions of formation of nanostructured states are analyzed.

Propagation of a two-dimensional electromagnetic pulse in an array of semiconductor carbon nanotubes with impurities is investigated. The parameters of dipole moments of impurities are determined. The Maxwell equation and the equation of motion for dipole polarization are jointly solved. The dynamics of the electromagnetic pulse is examined as a function of the dipole moment. It is shown that taking polarization into account does not have a substantial effect on the propagation process, but alters the optical pulse shape.