Vol 43, No 1 (2017)

The interaction of a shock wave in a gas phase with a system of particles moving in this gas has been numerically simulated. The wave pattern of the nonstationary interaction of the propagating shock wave with these particles is described in detail. The mathematical model and computational technology employed is compared with experimental data on the dynamics of particles behind the shock wave. It is established that the approximate model of separate particles used to calculate relaxation of their velocities unsatisfactorily operates in the presence of a mutual influence of particles, whereby one particle can occur in the aerodynamic shadow of an adjacent particle.

The collective dynamics in an ensemble of active rotators coupled by a common pulsed field is studied. The dynamics of the ensemble is analyzed numerically for different values of system parameters. The calculated data, as functions of the synchronicity parameter, lead to a conclusion being drawn on the collective behavior of ensemble elements, the character of evolution of the ensemble field, and the dependence of the behavior of the ensemble field on the synchronicity of ensemble elements.

Experimental investigations of the possibility of directly synthesizing nanodispersed crystalline phases of titanium dioxides with rutile and anatase structures in a hypervelocity jet of electroerosion plasma generated by a coaxial magnetoplasma accelerator with titanium electrodes are presented. A powder product containing nanosized polymorphic phases of titanium dioxide with a spherical shape of particles has been manufactured.

We have experimentally studied how the Prandtl number (Pr) of a nanofluid depends on the concentration, size, and material of nanoparticles. The nanofluids were prepared using distilled water and nanoparticles of silica, alumina, titania, and zirconia. The volume concentration of particles was varied from 1 to 8% and their diameters changed from 10 to 150 nm. It is established that Pr values of nanofluids increase with the concentration of nanoparticles. The Prandtl number also significantly depends on the size of nanoparticles and decreases with increasing particle diameter.

Electrical characteristics of low-inductance capillary-type discharge have been determined by numerical model calculations, which ensure high efficiency of energy supply to a plasma column with an aspect ratio of 1: 100. The EUV argon laser based on this discharge provides a gain of g⁺ > 1 cm^–1 on the operating transition and ensures single-pass spontaneous lasing with g⁺l > 25 (where l is the active medium length).

New operation regimes of single and coupled oscillators in circuits based on planar VO₂ switches have been studied. The phenomenon of bistability is discovered, which consists in controlled switching of self-sustained oscillations by external pulses, which is a promising basis for the creation of oscillatory memory cells and implementation of pulse coupling regimes in artificial neural networks (ANNs). The duration of switch-on and switch-off pulses is no less that ~20 μs and 30 ms, respectively. It is established that the region of threshold voltages for bistable switching in coupled oscillators is much wider than in a single oscillator and the hysteresis width in the former case can reach 2 V. A regime of initiation of switching packets has been observed that models the ANN packet activity.

Spectral characteristics of spontaneous and stimulated luminescence have been studied for molecular beam epitaxy synthesized Al_xGa_1–xN/AlN solid solutions with x = 0.5 and 0.74 upon optical pumping by pulse laser radiation with λ = 266 nm. Broadband radiation spectra with a width of ~260 THz for Al_0.5Ga_0.5N and ~360 THz for Al_0.74Ga_0.26N have been obtained. The measured enhancement factors are g ≈ 70 cm^–1 for Al_0.5Ga_0.5N at λ ≈ 528 nm and g ≈ 20 cm^–1 for Al_0.74Ga_0.26N at λ ≈ 468 nm.

For the first time it has been experimentally shown that a powder of detonation nanodiamonds (DND) and a saturated acyclic hydrocarbon, mono- or dibasic alcohol, used as the reaction mixture after treatment at high pressures (5–8 GPa) and high temperatures (1300–1800°C) results in the formation of diamond single crystals up to 15 micron in size. The Raman spectrum indicates that the diamonds have a perfect of crystal structure. It has been suggested that the oriented attachment mechanism is responsible for growth of micrometer-size diamond single crystals out of DND particles with sizes of about 5 nm under these technological conditions.

It is established that increases in nanoporosity and the proportion of high-angle grain boundaries in the process of equal-channel angular pressing are the main structural factors leading to reduction in mechanical stability (durability) of microcrystalline titanium during long-term tests under creeping conditions.

An upper limit of absorption of the laser radiation in the plasma produced in a gas jet Xe target with the average density of (3–6) × 10¹⁸ cm^–3 and the effective diameter of 0.7 mm is found. It is equal to ≈50% and remains constant under any variation in this range of densities. This result contradicts both theoretical assessments that have predicted virtually complete absorption and results of earlier experiments with the laser spark in an unlimited stationary Xe gas with the same density, where the upper limit of absorption was close to 100%. An analysis shows that nonlinearity of absorption and plasma nonequilibrium lead to the reduction of the absorption coefficient that, along with the limited size of plasma, can explain the experimental results.

The possibility of growing oriented AlN films on Al₂O₃ substrates at temperatures below 300°C by plasma-enhanced atomic layer deposition was examined. The samples were subjected to X-ray phase analysis and ellipsometry. It was demonstrated that the refraction index of films deposited with plasma exposures longer than 20 s was 2.03 ± 0.03. The (0002) and (0004) reflections at 2Θ angles of 35.7° and 75.9° were present in the X-ray diffraction patterns of these samples. These reflections are typical of the hexagonal AlN polytype. The full width at half maximum of the rocking curve of reflection (0002) in the best sample was 162 ± 11 arcsec.

We present the results of studies of the optical, electrical, and mechanical properties of diamondlike carbon films prepared by plasma-chemical vapor deposition from a mixture of methane and diborane in various proportions. Upon reaching the threshold concentration (~12%) of diborane in the mixture, inclusions of a new phase start to form in the structure of the films. This leads to nonlinear dependence of the interior stresses and the surface resistance of coatings on the composition of the mixture with minimum values corresponding to a diborane concentration of about 12%.

Specific features of mechanical-stress relaxation in InGaAsP/InP heterostructures for 1064 nm laser radiation converters have been studied. It is established that stress relaxation via the formation of an ordered relief on the surface of solid-solution layers in InGaAsP/InP heterostructures with indium content up to 80% can decrease the probability of spinodal decomposition of the solid solution, enhance its photoluminescence intensity, and increase the efficiency of laser-radiation conversion.

We have studied the influence of bombardment with accelerated gas-cluster ions on the surface topography of silicon carbide and diamond. Atomic-force microscopy shows that exposure to 10-keV gas-cluster ions at a total dose above 10¹⁶ cm^–2 leads to smoothing of the surface relief. The ion-etching rate and efficiency of the surface relief smoothing as dependent on the thickness of removed layer have been estimated. Raman-spectroscopy data show that surface irradiation with gas-cluster ions does not introduce defects into the crystalline structure of irradiated material.

All-optical cells based on AlGaAs/GaAs/InGaAs laser heterostructures for a 905-nm wavelength have been developed, which operate in the regime of optical-power modulation by means of controlled generation switching between the Fabry–Perot cavity modes and high-Q closed mode. At a modulated power of 1.6 W, a mode-switching time of 1.2 ns and smaller is achieved.

A method for increasing the accuracy of estimation of the predictability time of noisy chaotic dynamics from system-related point sequences is proposed. General laws observed in the application of this method to interspike interval series of model threshold devices of two types operating in the regime of phase-coherent chaos are illustrated.

Linear and nonlinear magnetoelectric (ME) effects in lead zirconate titanate (PZT)–nickel ferrite bulk composites have been experimentally studied. The maximum values of a ME response signal for the linear and nonlinear ME effects amounted to 260 mV/A and 34 kV/m, respectively. A relationship between the linear and nonlinear ME effects is established based on analysis of experimental data.

The absolute differential cross sections of scattering of fast particles formed in processes with capture of one or two electrons from Ar atoms have been measured for 6-keV He²⁺ ions in the interval of scattering angles within 0°–2.5°. The cross sections of electron capture and electron capture with ionization have been determined as functions of the impact parameter. The probabilities of these processes are compared to the distribution of electron density in various shells of target atoms. Applicability of the models of screened Coulomb interaction potentials to description of the scattering of recharged particles is assessed.

A new modification of the Kolsky method is proposed, according to which a loaded sample is arranged in an obliquely cut tube casing. Using this configuration, it is possible to determine the shear stress of low-plasticity materials.

Absorption-controlled charge and discharge currents in cross-linked polyethylene (XPE) cable insulation before and after thermal aging have been measured. The experimental dependences were analyzed in terms of the equivalent Voigt scheme. Known parameters of the Voigt scheme were used to calculate the frequency dependences of relative dielectric permittivity, loss factor, and loss tangent of XPE films in the region of low frequencies (ω = 10^–3–1 s^–1) at high temperatures. Results of analysis of the absorption characteristics of XPE were applied to modeling of the process of thermal aging of cable insulation.