Vol 60, No 9 (2018)

The modified Fisher–Kolmogorov–Petrovskii–Piskunov equation with quasilocal quadratic competitive losses and variable coefficients in the small nonlocality parameter approximation is reduced to an equation with a nonlinear diffusion coefficient. Within the framework of a perturbation method, equations are obtained for the first terms of an asymptotic expansion of an approximate solution of the reduced equation. Particular solutions in separating variables are considered for the equations determining the first terms of the asymptotic series. The problem is reduced to an elliptic integral and one linear, homogeneous ordinary differential equation.

The influence of a homogeneous medium filled with water droplets on the polarization structure of electromagnetic waves propagating in it, emitted in series with horizontal and circular (e.g., right-handed) polarization, is considered. An approach is proposed for estimating the influence of the resulting transformation of the polarization structure on the magnitude of the modified radar reflectivity, based on the use of the functional dependence of the components of the Jones vector on the angle of ellipticity and the tilt angle of the polarization ellipse. A distinguishing feature of the proposed approach consists in the relationships calculated using it for determining the modified radar reflectivity, obtained for the case of backscattering by the medium, where the orientation of the polarization basis of the medium is different from that of the measurement basis. Estimates of the modified radar reflectivity have been obtained, allowing one to determine regions with elevated values of this parameter.

A model of a stable plasma formation, based on radial quantum oscillations of charged particles, is discussed. The given plasmoid is described with the help of the nonlinear Schrödinger equation. A new phenomenon of effective attraction between oscillating charged particles is considered within the framework of the proposed model. The possible existence of a composite plasma structure is also discussed. Hypotheses about using the obtained results to describe natural long-lived plasma formations which can serve as alternative energy sources are advanced.

The semiclassical Thomas–Fermi method of calculating the electrostatic field of a multielectron atom is modified for effectively one-dimensional atoms. The main Thomas–Fermi equation and the dimensionless, one-dimensional Thomas–Fermi equation are obtained, and it is shown that within the framework of the method “one-dimensional” neutral multielectron atoms cannot exist.

The article presents recent results of the dramatically enhanced electric breakdown strength observed in the accelerating gap of a plasma-filled optical system for the formation and focusing of a wide-aperture pulsed electron beams with currents up to 80 A and energies up to 35 keV. This system is a plasma-optical diode type device in which the acceleration and formation of the electron beam occurs in the double layer between the emissive surface of the plasma cathode (electron emitter) stabilized by a fine mesh grid and the open surface of the anode plasma. The anode plasma is created by the toroidal plasma generator of original design based on the ion source with closed drift of electrons with an anode layer.

Results of investigation of the angular distribution and mass-to-charge fractions of the ion flow generated in a pulsed vacuum arc with lanthanum hexaboride and boron carbide cathodes are presented. It is shown that the discharge with such cathodes provides efficient generation of the plasma with a high fraction of boron ions with charge states from 1+ to 3+ whose total fraction is determined by the fraction of the boron atoms in the cathode material. The angular distributions of ions in the plasma flow depend on the relationship between the masses of components of cathode materials: in the case of lanthanum hexaboride cathode, the distribution of boron ions is wider than that of lanthanum ions, and in the case of boron carbide cathode, the boron and carbon ion distributions are practically identical.

The positive column of a gas discharge in helium is investigated for high-modulation-depth discharge current without stepwise ionization. The electron energy distribution function for different discharge current oscillation phases, the electron concentration, and the longitudinal electric field strength are measured in helium gas-discharge plasma. The electric field modulation effect and the change of the electron energy distribution function over the period at frequencies less than the reciprocal ambipolar diffusion time are detected.

Simulation results are compared with experimental data to define the integral breakdown criterion for the spark gaps of the switches of the LTDs with oil insulation and to determine the influence of the inductance of the trigger inductor on the delay of the switch firing. The results confirm that the shape of the output square pulse produced by the oil-insulated LTDs can be corrected as required if the trigger inductors are used to trigger the cavity switches.

Structure and dielectric properties of polymer nanocomposites based on isotactic polypropylene and iron oxide (Fe₃O₄) nanoparticles are studied. Distribution of magnetite nanoparticles in a polymer matrix was studied by scanning electron microscopy (SEM, Carl Zeiss). Dielectric properties of nanocomposites were examined by means of E7-21 impedance spectrometer in the frequency range of 10²–10⁶ Hz and temperature interval of 298–433 K. The frequency and temperature dependences of the dielectric permittivity ε, as well as the temperature dependence of log (ρ) were constructed. It is shown that introduction of the magnetite (Fe₃O₄) nanoparticles into a polypropylene matrix increases the dielectric permittivity of nanocomposites. An increase in the dielectric permittivity is explained by the increase in the polarization ability of nanocomposites. It is found that a decrease in the specific resistance with increasing temperature up to 318 K is associated with an increase in the ionic conductivity of nanocomposites. An increase in the resistance at temperatures higher than 358 K is due to the destruction of the crystalline phase of the polymer, as a result of which the distance between the Fe₃O₄ nanoparticles increases.

Using the Monte Carlo method, the influence of the APB-complexes (a pair of shear-induced APBs along the <110>direction and a pair of thermal APBs along the <100> direction) on the low-stability states of β-brass is investigated during an order – disorder phase transition in the CuZn alloy as an example. It is shown that the formation energy of a complex of thermal APBs is higher than that of a complex of shear APBs. The contribution of APBs into disordering is essential up to the temperature of the order – disorder phase transition. The most significant fact for the long-range order in this system is the appearance of a defect in the form of an APB; the difference in the types of APBs and the plane of their occurrence do not exert a significant influence on the long-range order behavior with the temperature variations. The types of antiphase boundaries do affect the structural-energy characteristics of the system at the temperatures below that of the phase transition. It is obvious that a system with structure defects is less ordered than a defect-free system. The presence of a defect in the form of an APB favors the onset of disordering at lower temperatures: reduction of ordering in the alloy begins in the case of thermal APBs at lower temperatures compared to the case of shear APBs. In the CuZn alloy with a complex of thermal APBs along the <100> direction the first distortions of the structural order invariably appear near the Zn–Zn boundary. In the alloy with a complex of shear-induced APBs along the <100> direction the distortions of the structural order are only observed in the regions where the boundaries intersect. The presence of antiphase boundaries influences the alloy stability during heating. The CuZn alloy without distortions of structural defects is more stable than that with APBs. It is shown that the process of disordering is accompanied by the smearing and faceting of the boundaries.

The paper deals with hydrogen transfer through Pd-23%Ag alloy membrane, the surface of which is modified by the electrolytic deposition of highly dispersed palladium. The dependence between the density of hydrogen flow and its excess pressure on the input surface of membrane is well approximated by the first-order curve. This fact indicates that the process of hydrogen permeability is defined by its dissociation on the input surface. Activation energy of this process is 47.9 kJ/mol which considerably exceeds that of the process of hydrogen transfer through palladium (22–30 kJ/mol). This confirms the fact that the chemisorption is a rate-controlling step of the hydrogen transfer through membrane.

Creation and application of the remote imaging spectrometer based on high power nanosecond terahertz source with standoff detector is reported. 2D transmission images of metal objects hided in nonconductive (dielectric) materials were recorded. Reflection images of metal objects mounted on silicon wafers are recorded with simultaneous determination of the wafer parameters (thickness/material).

The paper presents results of investigation into the special features of physics of fore-vacuum plasma sources of ribbon electron beams. The main difficulties encountered in the development of sources of this type are demonstrated. Conditions that allow one to increase the emission current density with simultaneous preservation of high degree of beam current homogeneity are determined. On the basis of the described physical features in the fore-vacuum plasma sources operation, the main directions in the development of the electron sources generating beams in the fore-vacuum pressure range are proposed.

The paper examines the oxidation of polycrystalline Cu films under the impact of ambient atmosphere in the course of extended time (from 20 to 90 days). It shows that in the case of 10 nm thick Cu films deposited onto the glass substrate by method of magnetron sputtering, one eventually observes the increase in transparency, surface resistance and surface roughness, as well as the decrease in reflection in the area of near infrared region. The most dramatic changes occur in films deposited in the pulse mode of sputtering with frequency of 3 kHz compared to films deposited in the direct current mode. Formation of sublayer ZnO:Al and 20 nm thick upper passivating layer ZnO:Al allows effectively preventing the oxidation of thin copper films under the impact of ambient atmosphere.

As a result of investigations of compressive deformation of steel specimens using a Vic-3D optical system it is found out that the regions of local deformations along two mutually perpendicular directions possess different character near the butt ends of the specimen in compression. It is underlined that the values of strains along these directions are also different. In the central part of the specimen, an oval region is formed with varied patterns of microstrain distribution. The transition from the stage of elastic strain (Region I in the stress–strain curve σ = f(ɛ)) to plastic deformation is accompanied by a transition from the chaotic diversified distribution of the spatial structural elements into long bands with a characteristic distribution pattern on the specimen surface: along the macrobands of plastic deformation from the corners and side faces of the specimen towards its center. Starting from Stage 1 and to the middle of Stage IV, the key role in the strain evolution on the surface belongs to the macrobands of localized plastic flow. At the end of Stage IV, the macrobands of plastic flow degenerate. A special focus is made on the fact that the transition from one stage to the other results in the changes of the strain field distributions on the specimen surface and is characterized by a different value of the strain hardening coefficient.

The results of studying the 2D-simulation of evolution of a diffusion channel in the KrF-laser pump discharge initiated by the pin on the cathode surface are presented. It is shown that during the pump pulse, the inhomogeneity passes successively through three stages: a plasma spot on the cathode surface, a diffuse channel, and a high-conductivity channel. From the analysis of the dynamics of spatial distribution of spontaneous emission on the B₀-X transition of the KrF molecule in such a discharge, it is obtained that the channel can work as an amplifying medium while the volumetric form of its glow is maintained. Despite the contraction of the channel into a narrow cord at the end of the pump pulse, the distribution of the radiation energy over the entire pulse has the shape of a torch with the width at the anode of ~0.6 cm.

The possibility of creating an x-ray laser with a two-frequency undulator with the help of the phenomenological model of a single-pass free-electron laser (FEL) that takes into account the beam characteristics and the undulator field is studied. The model is used to analyze the FEL dynamics, and the simulation results are compared with the experimental data. The advantages of using a two-frequency undulator in the single-pass FEL and the possibility of generating powerful x-ray radiation in it are demonstrated. The evolution of power of higher-harmonic generation in the FEL and the bunching coefficient at wavelengths of these harmonics are studied. The possibility of their further amplification until saturation in a cascade FEL matched to higher harmonics of the two-frequency undulator is demonstrated.