Том 62, № 11 (2017)

The process of heat and mass transfer in a long cylindrical channel has been considered in terms of the mirror–diffuse model of the Maxwell boundary condition. The Hazen–Williams equation is used as a basic equation of the process kinetics. A constant temperature gradient is maintained in the channel. The heat and mass fluxes through the cross section of the channel versus the tangential momentum accommodation coefficient have been calculated in a wide range of the Knudsen number. The heat flux profiles have been constructed. A comparison with relevant published data has been carried out.

A modification of the method for calculation of horizontal and vertical components of monochromatic field that is generated in plane-layered medium by horizontal current flow and described using wave equation is proposed for problems of microelectronics. The proposed solution is based on the verified method of equivalent propagation constant that makes it possible to substantially reduce the amount of calculations in comparison with alternative methods based on rigorous dynamic approach. The analysis illustrates the application of the method at relatively small distances.

We have reported the results of experiments on determining the drag coefficient and the thrust coefficient of a two-bladed wind-powered engine based on the Magnus effect with rotating rough cylinders in the range of air flow velocity of 4–10 m/s (Re = 26800–90000) for a constant rotation number of a cylindrical blade about its own axis. The results show that an increase in the Reynolds number reduces the drag coefficient and the thrust coefficient. The extent of the influence of the relative roughness on the aerodynamic characteristics of the two-bladed wind-powered engine has been experimentally established.

The products of the erosion of a hollow copper electrode of an ac plasmatron operating in air have been examined. It has been shown using elemental analysis, IR spectroscopy, X-ray phase analysis, and differential thermal analysis that the main components of the erosion products are copper trihydroxide nitrate (II), copper oxide (II), copper oxide (I), and copper hydroxide carbonate (II).

The stability of dissipative states of a Bi₂Sr₂CaCu₂O₈ applied superconducting composite cooled by liquid helium or hydrogen with continuously increasing current-voltage characteristics described by a power equation has been studied. It has been shown that, under intensive cooling conditions, special conditions of thermal stabilization can exist for applied superconducting materials (technical superconductors) if the nonlinear temperature dependences of critical current density and specific resistance of the stabilizing matrix are taken into account. First, the minimum currents of existence and propagation of a normal zone can be absent. Second, the intensive cooling of a technical superconductor substantially increases the range of stable currents in the diapason of supercritical currents. Third, during the irreversible propagation of the thermal instability, the temperature of a technical superconductor can increase under conditions close to adiabatic, despite cooling by liquid coolant. These effects should be taken into account upon determining the conditions for overheating a technical superconductor. The numerical experiments have been compared with the results that follow from the thermal stabilization theory of combined superconductors, which assumes a linear temperature dependence of critical current density of a superconductor and a step-wise transition from the superconducting to normal state.

The structure of martensite in the In_95.42Cd_4.58 alloy has been studied by metallography, X-ray diffraction, dilatometry, and transmission electron microscopy. It has been shown that a massive structure built of colonies of tetragonal lamellar plates divided by a twin boundary {101}FCT is formed in the alloy under cooling below the martensite FCC → FCT transition temperature. The alloy recrystallizes after a cycle of FCT → FCC → FCT transitions with a decrease in the grain size by several times compared with the initial structure such fashion that the size of massifs and individual martensite lamella in the massif correlates with the change in the size of the alloy grain. Using thermal cycling, it has been revealed that the alloy tends to stabilize the high-temperature phase.

A two-stage process based on selective chemical etching induced by metal nanoclusters is used to fabricate nanostructured surfaces of silicon plates with a relatively low reflectance. At silicon surfaces covered with silver nanoclusters, the SERS effect is observed for rhodamine concentrations of about 10^–12 M. At certain technological parameters, the depth of the nanostructured layer weakly depends on the conditions for the two-stage etching, in particular, etching time. Under otherwise equal conditions for etching, the rate of the formation of textured layer in the p-type silicon is two times greater than the formation rate in the n-type silicon.

To increase the maximum power current density of an integrated n⁺p'Nn'p⁺-type thyristor during switching-off by a current pulse in the control circuit, the injection of electrons from the n⁺ emitter should be interrupted before the recovery of the collector p'N junction. This has been done using a rapidly increasing reverse gate current pulse with an amplitude equal to the amplitude of the power switched-off current. After the interruption of the emitter injection, the remaining current through the device is the current of holes extracted from the collector region via the gate electrode. Like in insulated gate bipolar transistors (IGBTs), the physical mechanism that limits the maximum density of the switch-off current is the dynamic avalanche breakdown, which is initiated by the holes extracted through the space charge region of the collector p'N junctions.

The effect of the time of thermolysis (thermal degradation) on the absorption spectra, specific resistivity, and concentration of holes of partially dehydrochlorinated polyvinyl chloride films has been studied. The number of conjugated carbon double bonds in films has been determined as a function of the time of thermolysis.

Scanning electron microscopy, atomic force microscopy, and cyclic voltammetry have been used to perform a complex comparative study of the structure of hydrogen fuel cell electrodes consisting of nanostructured platinum on carbon black and electrodes containing a proton-conducting Nafion polymer introduced into the electrode in the form of a solution and in a precoagulated state. It has been shown that, in the latter case, the specific area of electrochemically active platinum increases significantly (by up to two times).

A study of the photocatalytic activity of commercial and mechanically activated zinc oxide powders has been carried out based on the example of the decomposition of Brilliant Green. The goal of this work was to study the effect of the grinding time (0, 1, 3, 5, and 7 min) on the structure of zinc oxide and its photocatalytic activity under visible and ultraviolet (UV) radiation. It has been found that, when UV radiation is used, the constant of the dye oxidation rate for samples activated for 1 min increases compared with unactivated powders, whereas further mechanical activation leads to a decrease in the photocatalytic activity. When using visible radiation, samples activated for 1 min showed the minimum photocatalytic activity and further mechanical activation led to an increase in the efficiency of photocatalysis.

We have considered a permutation entropy method for analyzing chaotic, noisy, and chaotic noisy series. We have introduced the concept of permutation entropy from a survey of some features of information entropy (Shannon entropy), described the algorithm for its calculation, and indicated the advantages of this approach in the analysis of time series; the application of this method in the analysis of various model systems and experimental data has also been demonstrated.

The spatial dynamics of the resistive hose instability of a relativistic electron beam has been studied for the case when the charge neutralization time is much longer, on the order of, or much shorter than the current compensation time. It has been found that the growth of this instability has the highest increment when the charge neutralization time is on the order of skin time.

The electrical performance of amorphous carbon thin films obtained by the ion beam sputtering of a carbon target in argon has been investigated. It has been shown by the Raman spectroscopy method that these films have a graphite-like structure. It has also been found by conductivity and thermopower studies that the hopping mechanism of conductivity with a variable length of hops over localized states near the Fermi level changes to the mechanism of hopping over the nearest neighbors as the temperature rises from 77 to 190 K. Near room temperature, electrotransport is provided by variable-length hops over localized states at the tail of the valence band.

This work is devoted to the mathematical modeling of the temperature effect on the stability of H2A–H2B and Н3–H4 histone dimers by studying their behavior in different temperature regimes of 20–50°C. The study of the thermal stability of these two dimers in aqueous solutions at different temperatures has revealed their multifarious behavior at temperatures at 20–50°C. Analysis has shown that dimer Н3–H4 is prone to aggregation due to an increase in the force of linking between histones Н3 and H4. Studies of the behavior of histone dimer H2A–H2B have disclosed different temperature transitions in its structure with a maximum peak at a temperature 45°C.

We have studied the thermal regime of a self-heated hollow cathode in combined low-current (1–5 A) dc discharge and high-current (up to 100 A) pulsed-periodic discharge and the influence of the pulsed parameters on the current-voltage characteristic of the high-current discharge. It has been shown that, after the application of a voltage pulse (200–500 V), the discharge current attains its peak value and is stabilized over a time of ~100 μs. The discharge voltage in the quasi-stationary discharge stage exceeds the continuous discharge voltage at the same current by many times and depends on the mean value of the current in the discharge gap. The interpretation of the form of the I–V characteristics of the pulsed discharge is based on the dynamics of heating and cooling of the cathode surface layer and on the variations in the integral temperature of the cathode.

The problem of reconstruction of dynamic systems in the presence of noise using series of interburst intervals is solved. It is shown that the reconstruction procedure can be applied to strongly nonlinear noisy oscillatory processes. The results make it possible to generalize the method for analysis of dynamic systems with respect to recovery time to a wide variety of neuron oscillators.