Vol 63, No 1 (2018)

The hydrodynamic model of a heterophase interlayer of a liquid, which includes an epitropic liquid-crystal (ELC) layer, is supplemented with its structural-rheological model. The application of these models and the technique developed for processing the results of viscosity measurements for n-hexadecane interlayers in the tribotriads has made it possible to conduct a detailed determination of the properties of its ELC layer and the overlapped layer, such as the equilibrium thickness and viscosity, their temperature variation, and the activations energy of the viscous flow.

The method proposed here for analyzing processes in a hot plasma of noncylindrical Z-pinches is based on separation of the group of high-energy ions into a special fraction. Such ions constitute an insignificant fraction (~10%) of the total volume of the Z-pinch plasma, but these ions contribute the most to the formation of conditions in which the pinch becomes a source of nuclear fusion products and X-ray radiation. The method allows a quite correct approach to obtaining quantitative estimates of the plasma parameters, the nuclear fusion energy yield, and the features of neutron fluxes in experiments with Z-pinches.

The effect of the rate of the rise in the current to 1700 A/ms on the characteristics of a transition of units of superconducting (HTSC) modules from a superconducting to normal state has been experimentally studied. The units differed by the critical current of the HTSC tape and design. The units of HTSC modules are used as a part of the resistive superconducting fault current limiter (SFCL) for ac and dc grids. The obtained dependences should be taken into account when designing a resistive SFCL.

Tribotechnical polymer composites based on polytetrafluoroethylene with nanomodifiers of different compositions have been developed and their structure and properties have been studied.

The results of simulating the rapid microwave heating of spherical clusters of metal particles to the melting point are reported. In the simulation, the cluster is subjected to a plane electromagnetic wave. The cluster size is comparable to the wavelength; the perturbations of the field inside the cluster are accounted for within an effective medium approximation. It is shown that the time of heating in vacuum to the melting point does not exceed 1 s when the electric field strength in the incident wave is about 2 kV/cm at a frequency of 24 GHz or 5 kV/cm at a frequency of 2.45 GHz. The obtained results demonstrate feasibility of using rapid microwave heating for the spheroidization of metal particles with an objective to produce high-quality powders for additive manufacturing technologies.

Using paraffin-based magnetic nanocolloids as an example, the reasons for maxima in the temperature dependence of the magnetic susceptibility of magnetic colloids have been discussed. The behavior of these dependences in a wide temperature interval has been analyzed for colloids in solid and liquid states. It has been concluded that the maximum observed at the melting point of paraffin can be attributed to freezing Brownian degrees of freedom in magnetite coarse particles, the magnetic moment of which is intimately related to the solid matrix. The second main maximum, which arises in the solid state, is explained by the superparamagnetic-magnetically hard transition of most fine particles at lower temperatures. It has been noted that the flatness of this maximum results from the polydispersity of the magnetic nanoparticle ensemble.

We present the results of studying the effect of technological synthesis regimes of a solar furnace using the method of a partial metal reduction of one of the oxides on the phase formation of cermet composite materials of the TiO₂-CuO system. It has been established that the phase composition of the synthesized cermet composite materials depends on the carbon concentration, melting temperature and cooling rate. The dependence of the spectral-optical properties of selectively absorbing coatings on the production technology and properties of synthesized composite materials has been presented. It has been found that the coatings fabricated by melting in air with overheating at a melt cooling rate of about 105–106°C/s have the highest values of the integral absorption coefficient, α_s = 91.0–94.5%.

The structure of polycrystalline Fe films grown on an oxidized Si(001) surface at room temperature has been studied by the technique of high-energy electron diffraction. It has been found that the grain orientation in the films depends of the amount of deposited iron. In Fe films less than 5 nm thick, grains have been found to be randomly oriented. Fe films more than 5 nm in thickness exhibit the (111) texture with an axis coinciding with the surface normal. The angular dispersion of the [111] direction in the Fe lattice from the surface normal is ±25°. It has been found that as the Fe films become thicker, the (111) texture changes to the (110) texture.

Binary phase modulation is demonstrated with the aid of commercially available LC matrix. Elements of plane diffraction optics (cylindrical and spherical lenses) are fabricated and experimentally studied. Limitations related to a finite size of a pixel of a binary diffraction SLM are considered.

An acousto-optic shaper is developed for transformation of the Gaussian beam profile into almost rectangular profile. As distinct from lens devices, an acousto-optic device allows modification of the shape of the output beam in a fixed optical configuration using changes in radio control with relatively short response times of about 10 μs. The method is based on multibeam high-efficiency Bragg diffraction when the diffraction orders are overlapped with respect to angle. It is shown that the beam profile can be transformed into rectangular and more complicated profiles with an efficiency of no less than 80%. The experiments are performed using the TeO₂ crystal.

The results of measurements of the vertical component of electric field at a radio path with the permafrost at a frequency of 255 kHz have been interpreted. An analysis of the results has shown that the considered radio path exhibits the properties of a two-part impedance surface, i.e., it consists of two sections. At a distance of 70 km from a radiation source and at a frequency of 255 kHz of the electromagnetic wave, the field decreases with the distance R according to the power law as R^-1.5 and a power index takes an intermediate value between the power indices for decreasing the field in free space R^-2 and for the decrease in the field above an ideal conducting surface R^-1. With further propagation at a distance of 70–220 km, the field shows the specific behavior of a surface electromagnetic wave.

We have analyzed the tacking force exerted by a low-conductivity Ohmic plasma channel on a relativistic electron beam. It has been shown that, for the given type of evolution of the resistive hose instability of the beam along its pulse, this force substantially depends on the frequency and the increment of the increase in the given instability.

An optimal set of geometric and electrical parameters of a high-aperture electrostatic charged-particle spectrograph with a range of simultaneously recorded energies of E/E_min = 1–50 has been found by computer simulation, which is especially important for the energy analysis of charged particles during fast processes in various materials. The spectrograph consists of two coaxial electrodes with end faces closed by flat electrodes. The external electrode with a conical-cylindrical form is cut into parts with potentials that increase linearly, except for the last cylindrical part, which is electrically connected to the rear end electrode. The internal cylindrical electrode and the front end electrode are grounded. In the entire energy range, the system is sharply focused on the internal cylindrical electrode, which provides an energy resolution of no worse than 3 × 10^-3.

The matrix method has been used to calculate the coefficients of absorption of terahertz radiation in conventional (with radiation incident from vacuum adjacent to the bolometer) and inverted (with radiation incident from the substrate on which the bolometer was fabricated) bolometric structures. Near-unity absorption coefficients were obtained when an additional cavity in the form of a gap between the bolometer and the input or output window was introduced. Conventional bolometers then became narrowband, while inverted-type devices remained broadband.

The problem of 1D radiative-conductive heat transfer in a homogeneous isotropic gray medium near a planar diffuse nontransparent surface and in between parallel plates with different temperatures has been solved analytically. Nonconvective measurements of the thermal resistance of parallel-plane polyethylene foam specimens versus the number of layers (i.e., thickness) have been taken, both without and with thin screens made of aluminum foil. The applicability of the suggested theoretical approach and experimental technique for the measurement of radiative heat transfer and heat transfer by conduction in light heat-protective materials has been demonstrated.

The approach to using hydrogen as fuel, which ensures the smooth operation of autonomous power systems that use renewable energy sources (wind or solar power installations) with the stochastic mode of power generation, has been presented. The fundamental possibility of implementing the nondetonation combustion of hydrogen via the addition of ecologically clean components or a small percentage of methane has been demonstrated by methods of mathematical modeling.