Vol 62, No 9 (2017)

The reconstruction of the spatial distribution of radiation sources in a proportional scattering medium has been considered. An exact solution of the inverse tomographic problem has been obtained by analytically solving the radiation transport equation for arbitrary distributions of radiation sources and extinction coefficient and exact boundary conditions. The type and scale of distortions associated with radiation scattering in tomographic reconstructions have been demonstrated.

We have proposed an algorithm for constructing matrix elements of the collision integral for the nonlinear Boltzmann equation isotropic in velocities. These matrix elements have been used to start the recurrent procedure for calculating matrix elements of the velocity-nonisotropic collision integral described in our previous publication. In addition, isotropic matrix elements are of independent interest for calculating isotropic relaxation in a number of physical kinetics problems. It has been shown that the coefficients of expansion of isotropic matrix elements in Ω integrals are connected by the recurrent relations that make it possible to construct the procedure of their sequential determination.

The model of effective atomic potential and the Monte Carlo method are used to calculate the charge distribution of the Kr ions that are formed due to irradiation of neutral atoms by X-ray photons at an energy of 1.3 keV. The calculated results are in good agreement with the recent experimental data and can be used for development and maintenance of gas detectors that monitor the intensity of X-ray free-electron lasers.

The effect of surface ponderomotive forces on the Kelvin–Helmholtz instability is studied in the linear formulation based on the equations and boundary conditions of the electrostatics and fluid dynamics of an ideal incompressible fluid. Conditions to be satisfied by the values of determining parameters of the problem for the transition of an unstable flow in zero electric field into a stable regime after the application of a horizontal electric field have been written in the form of inequalities. It has been shown that, at the stability bound, the wavelength of the most instable mode is independent of the ponderomotive forces. In case of a liquid with large permittivity a stable flow regime exists for which the stability condition only differs in small dimensionless values from the stability condition for the charged surface of a quiescent liquid conductor in contact with a gas at rest.

The service life of the cathode of a DC arc plasmatron continuously working with tubular electrodes that operate in the air has been considered using the semi-phenomenological approach. The thermal emission, that ensures the necessary flow of electrons, and the evaporation of the cathode material, which determines its erosion, have been taken as the basic physical phenomena that constitute the workflow. The relationships that enable the estimation of the cathode’s operating time have been obtained using the known regularities of these phenomena and experimental data available in the literature. The resulting evaluations coincide satisfactorily with the endurance test results.

We have reported on the results of an experimental investigation of the effect of inert admixtures on the threshold characteristics of the breakdown (initiation) voltage in energy-saturated materials. A physicomathematical model that describes the experimental results has been proposed.

The results of magnetic flux penetration into high-temperature superconducting composites of the second generation have been analyzed and described. The distribution of magnetic flux was observed experimentally using the magnetooptical visualization technique at various temperatures of 4.2–80 K. The experimental data have been found to coincide with the results of analytical and semi-numeric calculations of magnetic field profiles carried out for regimes of full and partial field penetration into superconducting composites. The method of estimating the critical current density based on measurements of the topography of the transverse magnetic flux has been considered, and an approach to estimating the critical current density for strips from measurements of the tangential field component has been proposed.

The lubrication of detonation-synthesis diamond additives in lubricant composites has been discussed. The mechanism of interaction between nanodiamonds and friction surface has been shown to depend on the applied load. Two models of the lubrication of nanodiamonds and the conditions for their validity have also been proposed.

The dielectric properties of polypropylene/Na⁺ montmorillonite nanoclay composites have been studied under conditions of heating and cooling. The ε(T) and tanδ(T) parameters have been measured as functions of temperature at frequencies of 10³–10⁶ Hz in the heating–cooling mode. A comparative analysis of the measured and calculated ε parameters reveals that the best agreement between the theory and experiment has been provided by the Lichteneker model. As has been established, the values of ε parameter decrease with an increase in the frequency to 6 × 10⁴ Hz, then increase, while the dielectric losses tanδ(ν) are characterized by curves with a diffused maximum at 10⁴ Hz, which increases with a rise in the nanomontmorillonite filler content. As has been shown, high montmorillonite concentrations in polypropylene favor the acceleration of dipole–relaxation processes and associated dielectric losses, as well as the whole conductivity of nanocomposites.

The intensity of light dynamic scattering by a nematic liquid crystal with negative dielectric anisotropy (ZhK-440) as a function of the constant electric field strength has been studied under different interfacial conditions. It has been shown that potential barriers that arise at the interfaces not only influence the scattering intensity, but may also radically change the form of the dependence; i.e., the curves of optical transmission in the direction of the incident beam may have a minimum under certain field strengths. At higher strengths, the cells become totally transparent again. This anomalous behavior of the transmission curve is associated with the fact that the conductivity of the cells drops below a critical value with growing field strength, as the resistance of the space charge region at the inversely biased junction of the extraction electrode rises. In addition, it has been shown that the high resistance of the cells at low voltages may be attributed not only to a low concentration of impurities in the liquid crystal, but also to a low emissivity of the injecting electrode and a weak electron affinity of the extraction electrode.

The optical properties of InGaAs/GaAs quantum dot heterostructures that are doped by manganese and chromium during growth by Metal-organic vapor phase epitaxy have been studied. Surface topography photoluminescence spectra measurements have demonstrated the possibility of controlling the spectral characteristics of the structure by varying quantum well growth conditions and sizes in the presence of impurity atoms. Research results are explained by the peculiarities of InAs nanoclusters formation on the GaAs surface in the presence of Mn and Cr atoms.

Application of negative corona discharge in the course of recording leads to an increase in the holographic sensitivity of the Cu–As₂Se₃ structure and diffraction efficiency of the recorded holographic gratings and the relief gratings fabricated with the aid of chemical etching. Positive corona discharge impedes the recording of holographic gratings in the Cu–As₂Se₃ structure. The Cu–As₂Se₃ structure exhibits the properties of a negative photoresist under irradiation in the presence of the negative corona discharge. In addition, the dissolution selectivity substantially increases due to the corona discharge.

A two-crystal high-transmission acousto-optic monochromator is developed and studied. The transmittance of the monochromator can substantially be increased and the scheme can be simplified using the reflection from a face of the acousto-optic cell as a separating polarizer. The intervals of parameters of acousto-optic interaction (angles and wavelengths) that correspond to high efficiency of the monochromator are found. Characteristics of two high-transmission monochromators with different parameters of the acousto-optic interaction are determined.

The results of the chromatographic–mass spectrometric analysis of a mixture containing a compound with low protonation efficiency have been given. A software package for preliminary processing of mass spectra is used for determining the peak parameters of the compound ions. The reliability of the processing results has been confirmed by comparison with the tabular data for the isotope masses and the isotopic composition of the component. The mass spectrum has been interpreted by calculating the peak areas and centroids together by evaluating the standard deviation of the center of the peak. The results of processing the mass spectrum using the mMass program have been given.

The solubility of helium in α- and β-quartz single crystals, optical quartz crystals, and Pyrex glass has been studied by the method of thermal desorption of helium from crystals preliminarily saturated in the gaseous phase in the temperature range T = 323–1123 K and saturated vapor pressure P = 0.6–31 MPa. It has been shown that the behavior of the solubility of helium in quartz crystals is described by exponential dependences on the reciprocal temperature. The solubility of helium in quartz single crystals is almost independent of temperature. For all kinds of samples, the solubility varies in proportion to the saturated vapor pressure and attains values of (6.2 ± 0.3) × 10¹⁵ cm^–3 in single crystals for P = 25.5 MPa, T = 873 K, and (8.64 ± 0.04) × 1019 cm^–3 in optical quartz for P = 31 MPa and T = 373 K. It has been shown that the solubility of helium in quartz single crystals can increase upon an increase in the concentration of defects in the crystal as a result of multiple thermal cycling of samples in the course of measurements. Possible mechanisms of the dissolution of helium in quartz have been studied, and the results have been compared with those obtained by other authors.

We have reported on a new method for obtaining a liquid-metal field emitter. The treatment of a porous crystal of GaP binary semiconducting compound with high-voltage pulses in a vacuum has made it possible to obtain stable structures on its surface in the form of discrete gallium clusters. These structures exhibit high emission properties, including stable currents at a level of a few microamperes, as well as the high uniformity of the distribution of emission nanocenters over the surface.

A microstructural analysis of the human serum albumin (HSA) samples dehydrated on a glass substrate from solutions with different concentrations of protein has been performed. The structuring effect of salt (NaCl) on the variations in the morphology of HSA interfaces has been shown experimentally. The substantiation of some structural effects has been given by taking into consideration the supramolecular organization and the polyelectrolyte nature of the protein molecule.

It has been shown that the use of the survival function of the Weibull distribution shifted along the ordinate axis allows one to increase the accuracy of the approximation of the normalized profile of an erosion zone in the area from the axis to the maximum sputtering region compared with the previously suggested distribution function of the extremum values. The survival function of the Weibull distribution is used in the area from the maximum to the outer boundary of an erosion zone. The major advantage of using the new approximation is observed for magnetrons with a large central nonsputtered spot and for magnetrons with substantial sputtering in the paraxial zone.

A study has been carried out of the effect on the discharge-charging processes of a current source of surface-active bonds of carbon structures used as additives in the composition of a negative electrode material. A mechanism has been proposed based on the conclusions derived from the Kossel–Stranski molecularkinetic theory, which explains the growth of 3PbOPbSO₄H₂O crystals upon the introduction of carbon materials. It has been established that the presence of carbon additives in the composition of the negative electrode material of starter lead-acid batteries increases the capacitance of 20-h discharge mode by up to 5% and the discharge duration by cold scrolling current to a final voltage of 6 V at negative temperatures of–18°C and–30°C by 3–4.5% and 9–13%, respectively.