Vol 62, No 7 (2017)
- Year: 2017
- Articles: 27
- URL: https://journals.rcsi.science/1063-7842/issue/view/12456
Theoretical and Mathematical Physics
Anisotropic ellipsoidal inclusion with an anisotropic shell in an isotropic medium subjected to a uniform electric field
Abstract
An electrostatic problem has been solved for a dielectric inclusion that consists of an anisotropic core and an anisotropic shell. The inclusion is immersed in a uniform isotropic medium (matrix) subjected to a uniform electric field. It is assumed that the outer boundaries of the core and shell are ellipsoidal and become confocal after a linear nonorthogonal transformation that removes the anisotropy of the dielectric properties of the shell. Analytical expressions have been derived for the potential and strength of the electric field in the matrix and also in the shell and core of the inclusion, and an expression for the polarizability tensor of the inclusion has been deduced. It has been shown that the results agree with the well-known solutions in partial (limiting) cases.
Path-length distribution of ions reflected from a solid: Theory and computer simulation
Abstract
Theoretical methods and Monte Carlo procedure are used to study path-length distributions of ions reflected from a solid. The theoretical analysis is based on the solution of the integral Chandrasekhar equation for the Laplace transform of the distribution function. A family of curves is obtained for path-length distributions at several ion energies and mass ratios of ions and target atoms. A computer code for simulation is based on the approximation of pair collisions and a gas model of solid. The simulated results are compared with the theoretical results and published data.
Regarding the publication by G. B. Malykin and V. I. Pozdnyakova “On the Velocity of a Light Spot Moving over a Cylindrical Screen”
Abstract
It has been shown that, in the article by G. B. Malykin and V. I. Pozdnyakova “On the Velocity of a Light Spot Moving over a Cylindrical Screen” [Tech. Phys. 52, 133 (2007)], errors were made in the calculation of the velocity of a light spot moving over a cylindrical screen. As a result, incorrect formulas were obtained to calculate the velocity of the light spot as applied to classical mechanics and the Tangherlini transformation. Correct formulas for calculating the velocity of a light spot moving over a cylindrical in classical mechanics and in the Tangherlini transformation are proposed.
Atomic and Molecular Physics
Dispersion in the results of measuring the lifetime of negative ions due to their adsorption on ionization-chamber walls
Abstract
The time of extraction of negative ions from the ionization chamber of a static mass spectrometer has been measured as a value that significantly exceeds the time of their free exit from the chamber. It has been established that anomalously long ion extraction time is due to their adsorption on the ionization-chamber walls; as a result, their arrival at the analyzer tube is delayed. It has been shown that negative ions, which were initially generated as noninfinitely long-lived ones with respect to auto splitting off of an additional electron, are stabilized to everlasting ions due to adsorption, and the subsequent contribution from infinitely long-lived ions to the total ion flux reaching the recording system distorts the results of measuring the ion lifetime. It has been shown that some of the adsorbed ions are annihilated because of neutralization due to the additional electron tunneling to the surface. The probability of tunneling increases with an increase in temperature; thus, the temperature dependence of the ion lifetime is also distorted.
Gases and Liquids
Numerical simulation of the two-phase flow produced by spraying a liquid by a nozzle
Abstract
A numerical experiment on the simulation of the two-phase flow formed during spraying of a liquid by a nozzle has been described. The radial and axial velocity profiles of the droplets and gas in the free spray and in the two-phase flow through a cylindrical apparatus have been calculated and represented taking into account the early drag crisis of droplets and peculiarities of turbulent friction in the gas, which was detected in previous experiments. The distinguishing feature of the numerical model of the two-phase flow is that it employs the differential equations describing the nonstationary flow of a compressible gas as the initial equations. In transition to their difference analog, the familiar Lax–Wendorff algorithm has been used. A comparison of the results of calculations based on this model with experimental data has demonstrated their concordance.
Air flow control around a cylindrical model induced by a rotating electric arc discharge in an external magnetic field. Part I
Abstract
The structure and dynamics of a near-wall gas flow produced by a rotating electric arc discharge in an external magnetic field around a cylindrical model without an incoming flow has been investigated. The electric arc on the model has been produced by a combined electric discharge (low-current rf discharge + high-current pulse-periodic discharge). Permanent magnets with induction B ≈ 0.1 T have been placed inside the cylindrical models. Ring electrodes are arranged on the surface of the model. The structure and dynamics of the near-wall gas flow around the cylindrical model have been investigated using high-speed photography, as well as the shadowgraph and particle image velocimetry (PIV) methods.
Features of the destruction of homogeneous and composite barriers during high-speed interactions with rod impactors
Abstract
The destruction of homogeneous and composite barriers with metal-ceramic intermediate layers that interact with WNiFe-90 alloy impactors has been investigated. A comparison of the results for different types of barriers was provided based on the weight equivalence, i.e., the equality of weight per unit barrier area along the thickness. The initial impact velocity was in the range of 0.8–1.1 km/s. The registration of the process from the moment of strike of impactor to the formation of the developed fragmentation flow behind the barrier was carried out by a high-speed video camera. The displacement–time dependences for the characteristic planes of the target configuration, i.e., the rear end of the impactor and the rear surface of the barrier were plotted by processing video film. An analysis of these dependences allowed us to identify the features of barrier destruction. The strong difference in the geometry of the zones of destruction and the dynamics of the process for monolithic and composite barriers has been noted.
Experimental model of the role of cracks in the mechanism of explosive eruption of St. Helens-80
Abstract
A unique mini model of explosive volcano eruption through a formed system of cracks is developed. The process of crack formation and development is simulated by electric explosion of a conductor in a plate of optically transparent organic glass submerged into water. The explosion of a wire aligned with a through hole in the plate generates shock-wave loading along the plate and forms cracks. The fundamental role of high velocity flow in crack wedging by a high power hydrodynamic flow of a pulsating explosion cavity has been demonstrated.
Plasma
Specific features of explosive decomposition of pentaerythritol tetranitrate exposed to an electron beam with an explosive emission cathode
Abstract
A comparative examination of the critical energy density of explosive decomposition of pentaerythritol tetranitrate exposed either to an electron beam of a GIN-600 accelerator (240 keV, 20 ns) with an explosive emission cathode or to this beam combined with metal low-temperature diode plasma has been performed. It has been demonstrated that the contribution of plasma to the development of explosive decomposition is appreciable at explosion probabilities P ≤ 0.2. At higher energy densities and explosion probabilities P ≥ 0.5, the contribution of plasma to the overall beam energy density did not exceed 10%.
Solid State
Dependence of the structure of ion-modified NiTi single crystal layers on the orientation of irradiated surface
Abstract
The composition and structure of Si layers implanted into titanium nickelide single crystals with different orientations relative to the ion beam propagation direction have been studied using Auger electron spectroscopy and transmission electron microscopy. The role of the “soft” [111]B2 and “hard” [001]B2 NiTi orientations in the formation of the structure of ion-modified surface layer, as well as the defect structure of the surface layers of the single crystals, has been revealed. Orientation effects of selective sputtering and channeling of ions, which control the composition and thickness of the oxide and amorphous layers being formed, ion and impurity penetration depth, as well as the concentration profile of the Ni distribution over the surface, have been detected.
Calculation of effective parameters of thermoelectromagnetoelastic layered media
Abstract
A system of layered multiferroic materials is averaged with allowance for thermal properties of layers. Matrix averaging is used to obtain effective parameters of the system. Formulas that make it possible to characterize the effect of magnetoelectroelastic coefficients of layers on thermal parameters are derived. The presence of pyrocoefficients in the system is possible even in the absence of the coefficients for the layers. The heat capacity of the system ceases to be an additive quantity and becomes dependent on permittivity and permeability of the layers owing to the interaction of the fields.
Model calculating high-speed collisions between bodies with different shapes and massive metallic obstacles
Abstract
The mathematical model of a high-speed collision between bodies with arbitrary elongation and massive metallic obstacles has been suggested. The model is based on the energy balance and stage-by-stage scheme of formation of a crater. The collision process has been considered to be the quasi-stationary penetration of the deformed impactor and inertial deepening of a crater at the final step. A comparison of the calculations with the results of numerical simulations and physical experiment has shown satisfactory agreement.
Thermokinetic model of fracture of heterogeneous materials and peculiarities of its numerical realization under the action of RF electromagnetic fields
Abstract
The fracture of rocks has been investigated theoretically and experimentally. The model of evolution of micro- and macrocracking under the action of electromagnetic fields with the help of rf electrodes has been proposed. The calculation of the fields of temperature and thermoelastic stresses makes it possible to study the evolution of macrocracking and to establish the directions of evolution in the case of their 3D configuration. The mechanisms of the formation of a main crack for regions with different tensile stresses have been established. The main crack can evolve towards the range of tensile stresses lower than the ultimate tensile stress. The possibility of controlling the evolution of the main crack by selecting stresses over the length of the crack formed and the heating time has been demonstrated.
Physical Science of Materials
Investigation of the stability of electrical properties of reduced LiNbO3 crystals
Abstract
The instability of the electrical properties of lithium niobate single crystals of congruent composition subjected to reducing thermochemical treatment has been investigated by impedance spectroscopy. It has been shown that the subsequent heating of the reduced lithium niobate samples in dry air up to 380 K or higher is accompanied by the progressive increase in their electric resistance, which is due to the oxidization of the crystal surface layers.
Formation of thin graphite films upon carbon diffusion through nickel
Abstract
Experimental results on the synthesis of thin graphite films with the aid of annealing of nickel films on carbon substrate are presented. Highly oriented pyrolitic graphite is used as the substrate to provide structural quality of the deposited nickel film. It is shown that the cyclic annealing of the structure with intermediate cooling leads to crystallization of primary amorphous carbon into a film consisting of flakes of vertical graphene. The process of graphite formation is discussed.
Method for producing graphite and alumina thin films
Abstract
A simple comprehensible method for producing graphite and alumina films has been suggested. The optical properties of a graphite suspension in toluene and a suspension of natural clay with a high content of alumina particles in water have been studied. It has been found that the optical density of the suspensions varies from layer to layer, and the lowest optical density has been observed in upper layers. Graphite and aluminum films have been prepared by taking samples from different depths. The microstructure of the films has been examined. It has turned out that alumina particles coalesce into regularly shaped objects in the form of snowflakes. In addition, alumina films obtained from samples taken from different depths of the suspension have different thicknesses. In thin and thick films, the particle size is 0.29 and 2.81 μm or more, respectively.
Solid State Electronics
Charge transfer and thermopower in TlGdS2
Abstract
The temperature dependences of the dc conductivity and thermoelectric coefficient of TlGdS2 in the temperature interval of 77–373 K have been studied for the first time. It has been found that, at low temperatures (114–250 K), the compound has conductivity of the p-type and charge transfer in its energy gap follows the hopping mechanism. The main parameters of localized electronic states in the energy gap have been determined.
Lasing in microdisks with an active region based on lattice-matched InP/AlInAs nanostructures
Abstract
The emissivity of unstrained quantum-dimensional InP/AlInAs nanostructures and their lasing properties in microdisk cavities prepared by wet etching have been studied. For as-prepared structures, it has been found that they radiate owing to quantum-dimensional InP islands 50–300 nm in diameter. At temperatures below 160 K, whispering gallery modes have been observed in the microdisks. Experimental data on the PL intensity for microcavity modes versus the pump power, which were obtained at liquid helium temperature, have made it possible to find the lasing threshold, 50 W/cm2. The half-width of the laser line at above-threshold powers equals 0.06 nm, which corresponds to a Q factor of 15 000.
Physics of Nanostructures
Influence of annealing at temperatures above the solidus temperature on the structure and galvanomagnetic properties of Bi92Sb8 solid-solution thin films
Abstract
The influence of the annealing temperature from the interval between the solidus and liquidus temperatures of Bi92Sb8 solid solution on its structure and galvanomagnetic and thermoelectric properties has been studied. It has been shown that films of bismuth–antimony solid solution grown by thermal evaporation in a vacuum will have a large-grained structure after annealing at temperatures higher than the solidus temperature of the solid solution. It has been found that these films offer the lowest resistivity, the highest relative magnetoresistance, and the highest mobility of charge carriers. As the annealing temperature approaches the liquidus temperature, the probability that a dendritic structure will form and antimony-enriched regions will appear grows. This causes an increase in the charge carrier concentration and a decrease in the resistivity with a decrease in the relative magnetoresistance and charge carrier mobility.
Acoustics, Acoustoelectronics
Triple Bragg diffraction in paratellurite crystal
Abstract
Triple Bragg diffraction in a paratellurite crystal has been considered for the case when the plane of diffraction is oblique to the optical axis of the crystal. It has been shown that effective photoelastic constants for isotropic and anisotropic diffraction depend on the inclination of the plane of diffraction insignificantly. Triple Bragg diffraction of 0.63-μm coherent radiation in paratellurite at a 47.3-MHz slow acoustic wave has been experimentally demonstrated. For an optical power of 0.69 W delivered to a piezoconverter, the relative intensities of diffraction orders equal ~0.4, 0.4, 0.1, and 0.1, respectively.
Physical Electronics
SK analysis of the volt-ampere characteristics in graphene-based nanocomposite field emitters
Abstract
A method that enables the online processing of the experimental field emission data for the large-area emitters has been developed. This is based on an analysis of the SK diagram of volt-ampere characteristics and the plotting of a calibration grid for the efficient microscopic parameters, such as the work function, the area of emission and the coefficient of the amplification field. The application of this technique has enabled us to elucidate the behavior of a graphene-based nanocomposite emitter while changing the voltage. The noise characteristics, as well as their correlation with adsorption and desorption processes, have also been analyzed.
Photoemission of the K/W(100) system in the O2 atmosphere
Abstract
Simultaneous adsorption of potassium and oxygen on W(100) is studied using the threshold photoemission spectroscopy. A metal potassium film is formed on W(100) in the course of coadsorption of potassium and oxygen at the first stage. At the second stage, the film is transformed into a dielectric layer with the K2O2 stoichiometry.
Experimental Instruments and Technique
Development of a gas-inlet system into the ion source of an atom injector of Globus-M tokamak and the optimization of the atomic beam parameters
Abstract
A new gas-inlet system in the gas-discharge chamber of an ion source has been developed that makes it possible to adjust the arc discharge burning mode and the parameters of the plasma ion emitter. The measurements of the main electrotechnical parameters of the ion source and signals of secondary-emission probes have been performed. Based on the obtained data, the profile of power distribution in a beam has been restored. The optimum form of the control signal for the gas inlet valve of the atom injector of the spherical Globus-M tokamak has been selected.
Influence of neutron irradiation on etching of SiC in KOH
Abstract
The effect of reactor neutron irradiation on the etch rate of SiC in potassium hydroxide has been studied. In the case of high irradiation doses (1019–1021 cm–2), the etch rate of silicon carbide has been shown to drastically rise, especially in the [0001]Si direction. This considerably mitigates the orientation anisotropy of polar face etching. After high-temperature annealing (up to 1200–1400°C), a higher etch rate of irradiated crystals persists. The results have been explained by the high concentration of radiation-induced (partially clustered) defects they contain.
Short Communications
Correlation between reversion of signs of the electric field in the near-cathode plasma and anode fall potential in a short DC glow discharge
Abstract
Relatively simple probe and optical experiments were performed, confirming the presence of two main scenarios for the formation of the longitudinal characteristics of a short (without positive column) glow discharge. 1. At low pressures, when there is a single point of sign reverse of the electric field at the maximum of the plasma density, the anode fall is negative and the magnitude of the anode fall is small, there is no ionization and the anode area is dark. 2. Upon an increase in pressure, two points of field reversal are to be expected, the sign of the anode fall is positive and the anode fall of potential is comparable to the gas ionization potential; therefore, the intensive ionization directly at the anode, which glows brightly, takes place.
Transformation of a Taylor cone into a frustum upon discharge in viscous dielectric liquids
Abstract
The specifics of behavior of viscous electrolytes (exemplified by glycerol) subjected to spark discharges with direct connection of electrodes and in the induced charge mode have been studied. The transformation of a Taylor cone into a frustum, the stable existence of which depends on the polarization time, has been observed for the first time with cyclic discharges in the interelectrode space localized between an anodepolarizable viscous dielectric liquid (glycerol) and an overhanging cathode-polarizable metal electrode. The frustum development criteria (high dynamic viscosity and electric strength of the solution and low conductivity) have been determined.
Quantum neuristor: From theory to experiment
Abstract
Based on modern advances in electronics and optoelectronics, experimental and theoretical works on verifying the quantum-optical model of a living neuron have been outlined for the purpose of designing a quantum neuristor, which is a new element of neural network informatics.