Volume 61, Nº 10 (2016)

We propose a method for calculating the potentials of the spacecraft surface, based on triangulation approximation of surfaces, the area method, and analytic calculations of the matrix elements of the Coulomb interaction. The technique described here has a wide range of applications including low, as well as geostationary and polar orbits, and increases the calculating speed and accuracy.

The distribution of electric current in a thin metal layer has been calculated for various specular reflection coefficients of its surfaces. The dependence of the conductivity on the distance from the lower surface of the layer has been analyzed. The Boltzmann kinetic equation in the relaxation time approximation has been used.

A 2D porous medium containing solid rectangular particles has been investigated using the computer simulation method. We have used the model of nonintersecting rectangles on a square lattice. An analysis of the effect of area, linear sizes, and degree of orientation of rectangles on the percolation of pores and particles of the system has been carried out for different methods of lattice filling. The resulting dependences have been compared and an explanation of the observed effects has been proposed.

The time-of-flight spectra of ions generated during the extraction of negative ions from the KI solution in water–glycerin mixture by high-strength electric field pulses are studied using a source with an interface based on a polymer track membrane. It has been shown that the ions formed in secondary processes of bombardment of the membrane surface make a considerable contribution to the observed spectra. It has been found that the peaks of negative hydrogen ions have the highest intensity in the spectrum, indicating effective emission of these ions during the bombardment of polyethylene terephthalate by secondary ions with an energy of about 6 keV. The main trends in the modification of the membrane interface to reduce the fraction of secondary ions in the ion beam have been outlined.

We have experimentally investigated the characteristics of an incompressible turbulent boundary layer on a plane plate upon the passive blowing of air through a fine-perforated surface and flushing it by supplying an external pressure flow through a wind tunnel using an intake device equipped with an attachment for draining the boundary layer on the inactive side of the plate. A stable decrease in the local values of the surface coefficient of friction, which reaches 80% at the end of the perforated region, has been detected over the length of the plate. The possibility of controlling surface friction by changing the velocity of the external flow and selecting the meshes and filters at the inlet to the flow passage has been demonstrated.

Recombination instability of a dust plasma of a non-self-sustained discharge maintained by an ionizing radiation beam has been studied for the conditions when the collisions of ions with atoms in the charged layer of a dust particle considerably affect the ion current to the particle. It has been shown that the collisions of ions elevate the stability of the plasma. The dependence of the conditions for the evolution of instability and its increment on the discharge parameters has been analyzed.

We report on the results of quantum-chemical calculation of the lattice energy in a LaF₃ superionic crystal of size 3.5 × 2.0 × 2.2 nm that contains 1200 ions with different structural configurations of fluorine ions. It has been shown that the most energetically disadvantageous configurations of fluorine ions correspond to arbitrarily (randomly) disordered nanolattices in the case when fluorine ions of all three types (F₁, F₂, and F₃) participate in their melting. It has been found that unidirectionally disordered nanolattices that contain a large number of defect dipoles of the anion vacancy–interstitial fluorine atom type with parallel dipole moments is energetically more advantageous than nanolattices with randomly disordered structure. It has been proposed that the electric field produced by a large number of parallel defect dipoles is formed in disordered LaF₃ nanolattices even at room temperatures. This makes it possible to classify microscopically small LaF₃ crystallites as promising functional materials that can be used, e.g., in modern solid-state technologies.

The stability of transport current introduced into a niobium titanium superconducting composite subjected to an external pulsed thermal perturbation has been studied. Stable states have been theoretically analyzed by solving Fourier and Maxwell equations that describe the thermoelectrodynamic states of lowtemperature superconductors with flux creep. It has been shown that, if the transport current is permanently introduced, subcritical thermal perturbations, i.e., perturbations that do not take the composite to a normal state provided that the current does not exceed the quench current, may result in the appearance of unstable current states. The higher the energy of the external thermal perturbation, the lower the instability onset current. It has been found that the degradation of the current-carrying capacity of the superconducting composite is due to intense heat release inside the superconductor, which is initiated by the thermal perturbations, and depends on the current input rate, the instant of time the current input is terminated, and cooling conditions.

We have reported on the results of analysis of the operating time of conventional laser diodes and diodes with noninjecting output sections. The reasons for shorter operating time of diodes with a single anti-reflection face of the cavity compared to diodes with two protecting coatings and emitters equipped with a fiber Bragg grating have been considered.

Characteristic signs of the universal Nelson–Kosterlitz jump of the superconducting liquid density in the temperature dependences of the magnetization of La_1–ySm_yMnO_{3 + δ} samples with samarium concentrations y = 0.85 and 1.0, which are measured in magnetic fields 100 Oe ≤ H ≤ 3.5 kOe, are detected. As the temperature increases, the sample with y = 0.85 exhibits a crescent-shaped singularity in the dc magnetization curve near the critical temperature of decoupling vortex–antivortex pairs (T_KT ≡ T_c ≈ 43 K), which is independent of measuring magnetic field H and is characteristic of the dissociation of 2D vortex pairs. A similar singularity is also detected in the sample with a samarium concentration y = 1.0 at a significantly lower temperature (T_KT ≈ 12 K). The obtained experimental results are explained in terms of the topological Kosterlitz–Thouless phase transition of dissociation of 2D vortex pairs in a quasi-two-dimensional weak Josephson coupling network.

An experiment on the simulation of the conditions for propagation of laser pulses in dense neodymium atomic vapor is proposed for the development of a technological setup for the laser separation of the ¹⁵⁰Nd isotope from a kilogram sample of natural mixture. The comparison of waveforms of laser pulses in the presence and in the absence of absorption shows that the absorption predominantly takes place at the leading edge of the pulse. The experimental distortion of the waveform is related to the saturation of absorption. The effect is well described using the calculations based on the formalism of the rate equations.

With a diaphragm placed behind the anode foil, dual runaway electron beams have been provided in helium, hydrogen, nitrogen, and air under a pressure of several torrs to several dozen torrs and a high-voltage pulse amplitude of about 250 kV. These beams consist of two pulses with commensurable amplitudes with a time interval between them of several dozen picoseconds to several hundred picoseconds. It has been shown that the breakdown of the interelectrode gap at pressures from several torrs to several dozen torrs may occur in different regimes and dual pulses of the electron beam current are registered when the initial current through the gap is below 1 kA. It has been found that a supershort avalanche electron beam that consists of one pulse is generated when the delay of breakdown equals several hundred picoseconds. It has been shown that, when the gas pressure reaches several hundred Torr, including atmospheric pressure, the runaway electrons are detected behind the foil after the termination of the supershort avalanche electron beam pulse.

Fluctuations of the supramolecular structure of albumin facies are analyzed. Two stable states of the supramolecular structure of facies are revealed at room temperature. Optical microscopy is used to assess dynamic character of the supramolecular structure of human serum albumin.

A physical model of interactions of protein molecules has been developed. The regularities of their reactivity have been studied using electrostatics methods for two histone dimers H2A–H2B and H3–H4 assembled from monomers. The formation of histone dimers from different monomers has been simulated and their ability to the formation of stable compounds has been investigated by analyzing the potential energy matrix using the condition number. The results of a simulation of the electrostatic interaction in the formation of dimers from complete amino acid sequences of selected proteins and their truncated analogs have been considered. The calculations have been performed taking into account the screening of the electrostatic charge of charged amino acids for different concentrations of the monovalent salt using the Gouy–Chapman theory.

We have described a new probabilistic method for calculating and assessing lightning striking terrestrial explosive objects using a combined criterion for the emergence of upward streamer and leader discharges from the elements of the object being protected and lightning rods taking into account the probabilistic nature of the avalanche–streamer and streamer–leader transitions, the trajectories of a downward stepped lightning leader and lightning current. It has been shown that the disregard of possible formation of uncompleted streamer discharges from the elements of the object in the electric field of a downward lightning leader, which can ignite explosive emission, decreases the rated probability of the object being damaged by a lightning stroke by several times.

We have investigated the time dependences of the strength of adhesive bonds between polymers (epoxy adhesive and polyamide) and steel 45 at various temperatures. These dependences have been determined based on the rates of two opposite processes, viz., an increase in strength due to the formation of coordination bonds between polymer molecules and Fe²⁺ ions and a decrease in strength due to ruptures of adhesive or polyamide molecules under the effect of internal stresses. The values of activation energy of these processes have been determined.

We have reported on the results of an experimental simulation of a holographic absolute ballistic gravimeter with the minimal (down to 0.5 mm) length of the trajectory of a falling test mass and rigid stabilization of its angular position. Gravimeters of this type ensure the mobile measurement of the free fall acceleration and are intended for the application in a new field of research, i.e., HF gravimetry.