Vol 64, No 9 (2019)

It is shown that localized and quasi-local states exist near a thin defect layer with nonlinear properties, separating a linear medium from a Kerr-type nonlinear medium. Localized states are characterized by a monotonically decreasing field amplitude on both sides of the interface between the media. Quasi-local states are described by the field in the form of a standing wave in the linear medium and a monotonically decreasing field in the nonlinear medium. Contacts with nonlinear self-focusing and defocusing media are analyzed. The mathematical formulation of the proposed model is a system of linear and nonlinear Schrödinger equations with a potential simulating the thin defect layer, which is nonlinear relative to the field. Dispersion relations determining the energy of local and quasi-local states are obtained. The expressions for energy in explicit analytic form are indicated in the limiting cases and the conditions of their existence.

Shock-wave loading of transparent objects is studied with the aid of a theoretical method based on numerical simulation on a 3D regular mesh using an explicit solver in the Euler–Lagrange connected formulation and an experimental method using shadow photography and shadow background technique.

The formalism of the Lifshitz theory has been used for determining the pressure exerted by dispersion forces between metal and dielectric plates separated by a thin layer of a magnetic fluid. Numerical calculations are performed for gold and quartz glass plates and the magnetic fluid consisting of kerosene and magnetite nanoparticles at room temperature. For this purpose, we have used familiar representations of dielectric properties of gold and quartz glass along the imaginary frequency axis; corresponding representations have also been obtained for magnetite and kerosene. The dispersion pressure has been analyzed as a function of the distance between the plates, the volume fraction of magnetite particles in the magnetic fluid, and their diameter. At large separations between the plates, simple analytic expressions for this pressure have been derived. Possible application of results has been considered.

A periodic discharge in a liquid flow is an effective tool for modifying the surfaces of metal articles, which is aimed at increasing their durability, hardness, and corrosion resistance. Analysis of the discharge properties for determining limiting potentialities of this method and for optimizing technological regimes has revealed several formerly unknown physical phenomena. These factors must be considered for determining safety measures in implementation of industrial technologies. A new element in analysis is the inclusion of anomalous manifestations like bulbs, tracks, and filaments detected in ambient medium.

In this paper, we experimentally studied the behavior of the integral operation parameters of a Hall-effect thruster (thrust and specific thrust impulse) in two stable discharge glow modes significantly different from each other in anodic efficiency. The studies were conducted using a laboratory model of a Hall-effect thruster with an extended layer with an average discharge channel diameter of 77 mm in the discharge voltage range of 500–900 V and in the gas-flow rate range from 2 to 5 mg/s. The most striking distinguishing features of the observed glow regimes are the plasma jet shape and the discharge current value at almost identical input parameters (gas flow, discharge voltage, and magnetic field). In the entire studied range of input parameters when changing from the optimal mode (in terms of efficiency) to suboptimal, the main integral characteristics of the engine are shown to undergo a stepwise change: the discharge current increases by 10‒30% with a simultaneous relative drop in thrust by 5–15% and in efficiency by 20–40%. A detailed study of the anodic efficiency structure showed that, at abrupt rebuilding, the efficiency of using the electron current (the ratio of the ion current to the discharge current) changes, i.e., the electron conductivity in the engine discharge channel.

The results of experiments with an initiator of lithium and graphite, whose mass was 10% of the mass of the projectile, are presented. Similar initiators produce plasma with a high speed of sound and provide the initial speed of the projectile of ∼0.5 km/s. The droplet-shaped damage on the insulating wall of the accelerator channel are described. The link between the appearance of these damages and the sharp deceleration of the plasma piston (PP) is noted. A hypothesis relating the occurrence of damages to the resonant deformation of the channel under the action of a moving high-pressure front is discussed. It is shown that the hypothesis about the resonant deformation of the channel qualitatively explains the known features of the accelerator operation.

High-resolution differential scanning calorimetry has been used to study the crystallization of binary alloys with unlimited and limited solubility of their constituents. A sharp and intense emission of crystallization heat has been invariably observed immediately below the liquidus curve. Standard techniques to describe crystallization in the intercritical temperature range cannot explain the above phenomena. It is assumed that they may be associated with a large number of local microvolumes enriched with a crystallization-controlling component (concentration fluctuations) that appear in the liquid as approaching the liquidus curve. The appearance of such microvolumes precedes the spontaneous formation of many crystallites in a large volume of the liquid phase.

The measured frequency dependence of the electric impedance of a composite based on ultra-high molecular weight polyethylene reinforced with carbon nanotubes in contact with an electrolyte is presented. The behavior of the active and reactive impedance components, permittivity, and conductivity in the frequency range from 0.1 Hz to 120 MHz is analyzed. An equivalent electric circuit simulating the dispersion of the impedance of the polymer composite making contact with the electrolyte is proposed. The formation of a double electric layer at the interface between the polymer composite and electrolyte layer is demonstrated and the electrical characteristics of this layer are determined.

Zinc oxide powders made by mechanical high-energy grinding have been investigated using the methods of scanning electron microscopy, thermal nitrogen desorption, and Raman spectroscopy of infrared Fourier spectroscopy. Their structural evolution, including reduction of the average size of crystallites, increase in specific surface area, as well as changes in the number and ratio of adsorption centers, has been demonstrated. The data on the reconstruction of the surface of zinc oxide powders and multiple bond breaking in near-surface areas resulting from long-term dispersion have been presented.

The influence of shape on phase equilibria in a two-phase region between liquidus and solidus temperatures has been simulated using Si–Ge nanoparticles as an example. The shape and volume of a particle have been set by its effective radius and fractal dimension. The temperature dependence of the fractal dimension of the phases has been taken into consideration in terms of a simple geometrical model. It has been shown that decreasing the volume of a nanoparticle and its fractal dimension (which corresponds to nanoparticles of a more complicated shape) leads to narrowing down the temperature range of the heterogeneous region, changes in phase transition temperatures and equilibrium compositions of co-existing phases. It has been found that at different temperatures the dependences of the composition of the liquid phase on a particle’s morphology differ which is explained by implementing different mechanisms of reducing the surface energy.

An effect has been discovered that irradiation of a silicon sample by light changes the properties of another silicon sample several centimeters away from the former. This effect is observed if the samples are in contact with a fluoroplastic–NaCl aqueous solution system or a sodium-containing glass–water system. Results have been treated based on the earlier model of hypersonic wave generation by light in a silicon–native oxide system and the hypothesis for hypersonic wave propagation along a solid–aqueous medium interface due to the presence of Na⁺–[H₂O]_n clusters.

Vertical components of the vector potential of electromagnetic wave above two-layer strongly inductive impedance medium are determined. The solution is represented as a Sommerfeld integral. Singularities of such an integral are determined using effective parameters. The phase velocity of the surface electromagnetic wave is considered. It is shown that such a velocity is always less than the velocity of light in vacuum, so that the surface electromagnetic waves cannot be classified as the Zenneck waves for which the phase velocity is greater than the velocity of light (similarly to electromagnetic waves in waveguides).

Dielectric waveguides are being intensively studied as accelerating structures excited by an electron bunch. Rectangular dielectric structures are used both to test the principles of new accelerating schemes and to study the electric properties of filling materials. Several dielectric materials used as fillers of waveguides have anisotropic properties (sapphire, ceramic films). Anisotropy can have a significant effect on the wakefields generated by an electron bunch in a structure. The paper presents an analytical calculation of Vavilov–Cherenkov radiation generated by a relativistic electron bunch in a rectangular waveguide filled with a transversely inhomogeneous transversely isotropic dielectric. A method for constructing an orthogonal basis of the transverse operator with its subsequent use to find the wakefield is presented. A dispersion relation for the structure and expressions for the wakefield created by a point electron bunch in a transversely isotropic rectangular dielectric structure are obtained. Based on the formalism presented, parameters of an accelerating structure based on sapphire, allowing the generation of fields above 100 MV/m, are calculated.

The results of experimental studies into the application of anisotropic pyrolytic graphite (APG) as grid structures in power microwave devices with a dispenser cathode are detailed. The dependences of emission characteristics of molybdenum, hafnium, and APG in diodes and electron guns on the electron-flow power dissipated at the studied samples and on cathode temperature are presented. It is demonstrated that the power dissipation capacity of APG grid structures (without parasitic thermionic emission) is up to 20 and 9 times higher than that of molybdenum and hafnium grids, respectively.