Vol 61, No 9 (2016)
- Year: 2016
- Articles: 28
- URL: https://journals.rcsi.science/1063-7842/issue/view/12368
Theoretical and Mathematical Physics
Numerical simulation of the ablation of thin molybdenum films under laser irradiation
Abstract
Laser irradiation of a molybdenum film on a quartz substrate is numerically studied. The simulated results prove the experimental effect lying in a threefold decrease in the size of the ablation region in comparison with the focal spot. The numerical experiment proves the hypothesis on the two-stage ablation of metal film with the primary formation of oxide phase. It is demonstrated that oxidation leads to a selective decrease in the thermal resistance of the film along the vertical direction, so that the anisotropic character of the ablation is enhanced.
Multiphysical simulation analysis of the dislocation structure in germanium single crystals
Abstract
To grow high-quality germanium crystals is one of the most important problems of growth industry. The dislocation density is an important parameter of the quality of single crystals. The dislocation densities in germanium crystals 100 mm in diameter, which have various shapes of the side surface and are grown by the Czochralski technique, are experimentally measured. The crystal growth is numerically simulated using heat-transfer and hydrodynamics models and the Alexander–Haasen dislocation model in terms of the CGSim software package. A comparison of the experimental and calculated dislocation densities shows that the dislocation model can be applied to study lattice defects in germanium crystals and to improve their quality.
Numerical simulation of high-gradient magnetic filtration
Abstract
We have reported on the results of a numerical simulation of high-gradient magnetic filtration of ultradisperse corrosion products from water coolants. These results have made it possible to establish optimal technical characteristics of high-gradient magnetic filters. The results have been used to develop test samples of high-gradient magnetic filters (HGMFs) with different magnetic systems to purify technological water media of atomic power plants from activated corrosion products.
Model of a neural network inertial satellite navigation system capable of estimating the earth’s gravitational field gradient
Abstract
A model for recognizing inertial and satellite data on an object’s motion that are delivered by a set of distributed onboard sensors (newtonmeters, gyros, satellite receivers) has been described. Specifically, the model is capable of estimating the parameters of the gravitational field.
Gases and Liquids
Difference in the conditions and characteristics of evaporation of inhomogeneous water drops in a high-temperature gaseous medium
Abstract
The evaporation of water drops of initial mass 5–15 mg on a stationary graphite substrate, as well as inhomogeneous drops with solitary solid inclusions, during heating by high-temperature combustion products has been investigated experimentally. Experiments have also been carried out with analogous inhomogeneous drops moving through combustion products. The possibility of two mechanisms of phase transformations of inhomogeneous liquid drops has been established. The scales of the effect of the area of the inclusion surface (up to 20%) and the initial mass of water (up to 90%) on the characteristics of the evaporation of inhomogeneous drops have been determined.
Calculation of the drag and heat transfer from a sphere in the gas flow in a cylindrical channel
Abstract
A numerical experiment on the simulation of heat transfer from a sphere to a gas flow in a cylindrical channel in the Stokes and transient flow regimes has been described. Radial and axial profiles of the gas temperature and the dependences of drag coefficient Cd of the body and Nusselt number Nu on Reynolds number Re have been calculated and analyzed. The problem of the influence of the early drag crisis for a sphere on its heat transfer to the gas flow has been considered. The estimation of this phenomenon has shown that the early drag crisis of the sphere in a strongly turbulent flow causes a reduction in heat transfer from the sphere to the gas by three to six times (in approximately the same proportion as for its drag coefficient).
Plasma
Electric charge of a lightning ball
Abstract
The electric charge of a lightning ball is found by comparing the electrohydrodynamic stabilities of a charged drop in an electrostatic suspension and a lightning ball floating in a superposition of the gravitational field and the surface electric field. It has been assumed that the electric field strength at the surface is limited by a breakdown value. For a lightning ball radius of 15 cm, its charge is estimated as several microcoulombs. Accordingly, the density of electrostatic energy accumulated in the lightning ball is on the order of one-hundredth of a joule per square centimeter. The density of the material that constitutes the lightning ball has been estimated for the case when the electric field strength at the site of its origination is several times higher than that in fine weather. The density of the lightning ball turns out to differ from that of air by only a few percents.
Evolution of a vortex in gas-discharge plasma with allowance for gas compressibility
Abstract
The dynamics of a vortex tube in a compressible medium with the Rayleigh energy release mechanism has been considered theoretically. The analytic theory of this phenomenon is constructed and various approximations have been considered. The range of applicability conditions for the vortex formation theory has been extended substantially. It has been shown based on the model of a plasma as a Rayleigh medium that, for a certain relative orientation of the vortex axis and the electric field vector at an air pressure of tens of Torr, a vortex tube in the glow discharge plasma is destroyed over time intervals on the order of hundredths of a second. It has been found that allowance for the compressibility leads to an increase in the rate of vortex destruction. For this medium, the time dependences of the tangential velocity in a vortex tube have been calculated for various initial parameters. The similarity rules for the given phenomena and the universal dependence of the vortex tube dynamics have been obtained.
Hard X-ray source based on low-impedance rod pinch diode
Abstract
The results of experiments on the formation of a low-impedance diode in a rod pinch diode configuration preliminarily short-circuited by a radial foil have been described. The low-impedance diode is formed as a result of detachment of the foil (accelerated by the current of a high-current generator) from the anode rod. It has been shown that, by changing the shape of the anode tip, the thickness of the aluminum foil, and its position relative to the anode tip as by reconnecting the current via the foil and rod plasma, it is possible to obtain from one to several sequential hard X-ray pulses.
Solid State
Dynamic strain aging of the materials characterized by the Peierls plasticity mechanism
Abstract
A synergetic model is proposed to describe the influence of dynamic strain aging on the plasticity of materials that is controlled by the Peierls barriers overcome by dislocations. The immobilization of dislocations by the impurities concentrated in the dislocation cores is taken into account. The behavior of calculated deformation curves is studied as a function of the material parameters and the mechanical test conditions.
Size effect in the formation and failure of stable current states in composites based on high-temperature superconductors
Abstract
The influence of the transverse size of a composite wire based on a high-temperature superconductor on the dynamics of its thermoelectrodynamic properties at constant-rate current input has been studied. The physical mechanism behind the formation of stable regimes, which are characterized by the nonuniform distribution of the electric field and transport current over the cross-sectional area of the composite, has been determined. It has been shown that the critical current density of the superconducting composites determined from their current–voltage characteristic have lower and upper boundaries of electric voltages, which outline the allowable measurement range. It has been found that, when the input current completely penetrates into the composite, conditions for its stability are governed by the size effect. The essence of this effect is that conditions for current state stability in superconducting composites with the same cross-sectional area but various cross size differ. The conditions for the absence of unstable states in the composite the cross section of which is partially filled with the transport current have been formulated.
Multistable current states in high-temperature superconducting composites
Abstract
Conditions for current instabilities that arise in high-temperature superconducting composites with essentially nonlinear dependences of the critical current densities and resistivity on the temperature and magnetic induction have been studied. The analysis has been conducted in terms of zero-dimensional models, which has made it possible to formulate general physical mechanisms behind the formation of currents states in superconducting composites according to the external magnetic field induction, cooling conditions, and the properties of the superconductor and cladding. The possible existence of current and temperature stable steps, as well as stable steps of the electric field strength, in the absence of the superconducting–normal transition, has been demonstrated. Reasons for instabilities under multistable current states have been discussed.
Physical Science of Materials
Nanoindentation of a hard ceramic coating formed on a soft substrate
Abstract
The hardness and Young’s modulus of the thin hydroxyapatite-based coatings deposited by RF magnetron sputtering onto magnesium alloy, titanium, and steel substrates are studied. As the penetration depth increases, the hardness and Young’s modulus of these coatings are found to tend toward the values that are characteristic of the substrates. It is shown that the difference between the values of hardness and Young’s modulus at small penetration depths (h < 80–100 nm) can be caused by the difference between the physicomechanical properties inside the coatings and that this difference at large penetration depths (h > 100 nm) can be induced by an additional effect of the strength properties of the substrate material.
Optics
Influence of acoustic anisotropy of paratellurite crystal on the double acousto-optic Bragg light scattering
Abstract
Influence of acoustic anisotropy on acousto-optic interaction in optically and acoustically anisotropic media is theoretically and experimentally studied. A specific type of acousto-optic diffraction is analyzed with allowance for the phase-matching conditions for two diffraction maxima. Analytical expressions for the phase-mismatch parameters versus the angle between the phase and group velocities of acoustic wave are derived. Light intensity in the diffraction peaks is numerically calculated, and experimental data on the diffraction in the paratellurite crystal at an acoustic walk-off angle of 54° are presented.
Determination of gyrotropic characteristics in tetragonal zinc and cadmium diphosphide crystals
Abstract
We have reported on the results of an investigation of the gyrotropic properties of zinc and cadmium diphosphide tetragonal crystals. It has been found that the regime of obtaining crystals affects the specific rotation of the light polarization plane in a cadmium diphosphide. It has been shown that the dispersion of optical activity in the polarizer–optically active crystal–analyzer system leads to oscillations in the transmission spectra under certain conditions. The peculiar optical properties of gyrotropic crystals placed in between two polarizers can be used to construct optical filters.
Generation of 1D interference patterns of Bloch surface waves
Abstract
Interference patterns of Bloch surface waves with a period that is significantly less than the wavelength of incident radiation are formed using dielectric diffraction gratings located on the surface of photonic crystal. The simulation based on electromagnetic diffraction theory is used to demonstrate the possibility of high-quality interference patterns due to resonant enhancement of higher evanescent diffraction orders related to the excitation of the Bloch surface waves. The contrast of the interference patterns is close to unity, and the period is less than the period of the diffraction structure by an order of magnitude.
Combined weak-current discharge in a copper-vapor laser
Abstract
We have considered the application of a new method of pumping of active media on metal vapors by a combined weak-current discharge. A distinguishing feature of a weak-current discharge compared to the method for the traditional pumping of self-contained lasers is the regime of lower energy input to the discharge. Using this regime, it is possible to realize a pulsed-periodic form of the discharge with laser pulses of various shapes and durations at low current amplitudes (several amperes). Additional pulsed-periodic discharge is used to heat the active zone.
Simulation and study of material with diffuse scattering in the near- and mid-IR spectral ranges
Abstract
Fabrication of efficient scattering materials based on uniform layer of metallized fine powder on the surface of thermoplastic polymer is analyzed. Spectra of diffuse reflection and scattering indicatrix of the materials in the near- and mid-IR spectral ranges are studied.
Electrophysics, Electron and Ion Beams, Physics of Accelerators
Application of aluminum and titanium foils in low-energy wide-aperture electron accelerators
Abstract
We have reported on the results of theoretical and experimental investigations of characteristics of aluminum and titanium foils used in devices to extract electron beams from wide-aperture low-energy accelerators with a high current density. The mechanical properties of foils at different temperatures and the electron beam transmission and absorption coefficients have been compared. The results of analyzing the dependences of the efficiency of the electron beam extraction from accelerators on the type of the electron–optical system, material, and thickness of the foil for various sizes of extraction windows and the same type of the slot support grids have been presented. We have proposed an analytic model for calculating the temperature of the foil in the unit cell of the support grid. The electron transmittance and absorbance, as well as the temperature regimes of the foils, have been calculated using different methods.
Physical Electronics
Proton-beam writing channel based on an electrostatic accelerator
Abstract
We have described the structure of the proton-beam writing channel as a continuation of a nuclear scanning microprobe channel. The problem of the accuracy of positioning a probe by constructing a new high-frequency electrostatic scanning system has been solved. Special attention has been paid to designing the probe-forming system and its various configurations have been considered. The probe-forming system that best corresponds to the conditions of the lithographic process has been found based on solving the problem of optimizing proton beam formation. A system for controlling beam scanning using multifunctional module of integrated programmable logic systems has been developed.
Electron spectroscopy of iron disilicide
Abstract
We have reported on the results of a complex investigation of iron disilicide FeSi2 using characteristic electron energy loss spectroscopy, inelastic electron scattering cross section spectroscopy, and X-ray photoelectron spectroscopy. It has been shown that the main peak in the spectra of inelastic electron scattering for FeSi2 is a superposition of two unresolved peaks, viz., surface and bulk plasmons. An analysis of the fine structure of the spectra of inelastic electron scattering cross section by their decomposition into Lorentzlike Tougaard peaks has made it possible to quantitatively estimate the contributions of individual energy loss processes to the resulting spectrum and determine their origin and energy.
Short Communications
On the theory of the ionization-induced drag of fast charged particles
Abstract
The moments in the theory of deceleration of fast charged particles colliding with an oscillator have been considered in the dipole approximation. In this approximation, the problem has been solved exactly, and the moment of the oscillator has been determined from the initial state |m> = |0> in the form of the sum of 1D integrals. The method considered here makes it possible to calculate the moments for ion velocities close to atomic velocities (v ~ va).
Dynamic properties of a Josephson junction balanced comparator with Coulomb blockade
Abstract
The dynamics of a Josephson junction balanced comparator with Coulomb blockade has been analyzed. An expression for the time resolution in the case of a linearly increasing gating voltage pulse has been derived with regard to the Bloch inductance. It has been shown that the time resolution depends on the Bloch inductance of small Josephson junctions. Estimates have confirmed the feasibility of a subpicosecond time resolution for balance Josephson comparators with Coulomb blockade.
Electroplasma coatings based on silicon-containing hydroxyapatite: Technology and properties
Abstract
IR analysis and the plasma deposition of silicon-containing hydroxyapatite powder have been carried out. It has been shown that the coating exhibits developed morphology and consists of molten powder (including nanosize) particles uniformly distributed over the entire surface. The adhesion characteristics have been calculated and scanning electron microscope images of the resultant coating have been analyzed.
IR spectroscopic investigation of the structure of water–fuel microemulsion for diesel engines
Abstract
The structures of a microemulsion formed by a surfactant (ammonium oleate), water drops of a linear size of 1–3 µm, and a diesel fuel has been investigated using IR spectroscopy. It has been found that ammonium oleate molecules in the microemulsion are dissociated on the positive NH4+ ion and the negative ion of the remaining part of the molecule, which forms the hydrogen bond with water molecules. This increases the rate of water, evaporation and leads to the more complete combustion of the diesel fuel. As a result, the concentration of harmful nitrogen oxides and soot particles in the exhaust gas of the diesel engine decreases.
High-transmission spectrograph with a large range of simultaneously measured energies of charged particles
Abstract
Computer simulation has been performed for a high-transmission electrostatic spectrograph, and charged particle energies in the range Emax/Emin = 25 and 50 have been measured simultaneously. The spectrograph has been designed in the form of two coaxial cylinders with plane endface electrodes; the cylinder of a larger diameter has been cut into fragments with a potential that varies according to a linear law. For this device, the geometric and electrical parameters that ensures a beam that focuses in the entire range of recorded energies with the energy resolution interval (0.4–1.1)% are determined in the regime when the object under investigation is placed outside the field.
Rapid determination of the gas temperature in magnetooptical traps
Abstract
We have considered a simple method for estimating the gas temperature in a magnetooptical trap. In this method, only one of three laser beams in the magnetooptical trap is shut down. Then, the light scattered by the atoms of the remaining beams makes it possible to observe the spread of the atoms in real time without using additional lasers. An analysis of the measuring data has convincingly proved their conformity with theoretical estimates. This method can be useful for the approximate express analysis of the magnetooptical trap performance.