Technical Physics Letters最新文献

The possibility of use of air plasma spraying for depositing thick wear-resistant coatings when restoring brass parts in heavily loaded friction units is demonstrated. Recommendations for reducing the consumption of nonferrous metals and the coefficient of friction and increasing the service life of restored products are given.

The results of study of the adhesive strength of coatings formed by supersonic flame spraying from different powder materials are reported. The adhesive strength of the coatings has been evaluated by the adhesive method. It has been found that, in most cases, the experimental samples have been destroyed along the adhesive layer. The maximum adhesive strength of the investigated coatings is 72.8–101 MPa, depending on the type of a sprayed powder. The proposed powder materials are recommended for use in repair works for restoring operating surfaces of worn machine parts.

The results of numerical 3D modeling of freely convective heat-exchange processes in the channels of one of the main variants of a panel-radiant room-heating system with a ribbon finning system have been presented. The spatial distributions of the thermophysical parameters of free-convective air flows have been determined both in the internal and external regions of the system in wide ranges of changes in the basic operating and geometric parameters of the BS. The features of the behavior of the heat-transfer coefficients from the BS heating surfaces to the updraft have been calculated and established. The criterion dependences for calculating the Nusselt numbers on the modified Rayleigh number and other parameters of the vertical channels of the baseboard system have been proposed. A formula for calculating the specific heat removal capacity from the heating surfaces of the system’s internal elements has been obtained. It has been shown that the specific heat-removal capacity nonmonotonously depends on the ratio of the lengths of intercostal gaps in adjacent channels, at certain values of which there is an extremum. The relations between the capacities of convective and radiative heat fluxes generated in the considered heat-exchange system have been established. Recommendations on the choice of basic geometric and operating parameters that can provide an increase in heat removal by 20–30% compared to the practical BSs with a belt finning system have been given.

New experimental data on the properties of the vapor‒liquid phase equilibrium in the carbon dioxide–n-tetradecane binary system on the three selected isotherms 313.15, 333.15, and 353.15 K in the pressure range from 3.8 to 19.0 MPa are reported. The measurements have been carried out using an optical cell operating at high temperatures and pressures. The measured data of the vapor‒liquid phase equilibrium in the carbon dioxide–n-tetradecane binary system have been used to determine the critical data of the P_C–T_C curve.

A calculation method for a multirod (multichannel) hollow cathode has been proposed. This method is based on solving a system of equations written with allowance for the specific features of a real multirod cathode design. This system includes emission and thermal conductivity equations, energy balances on the cathode surface and at the cathode–plasma interface, the Langmuir and McCone equations, and a number of equations a describing gas flow in the cathode channels. The developed calculation method makes it possible to determine the key operating parameters of the cathode and the cathode region (temperature, midsection-area utilization factor, number of active wires, erosion, current density, electron current fraction, cathode potential drop, ion concentration, electric field strength, etc.) for specified geometry and operating conditions.

The effect of atmospheric electricity on the operation of fiber-optic communication lines has been studied on an electrophysical installation designed to simulate lightning in laboratory conditions. The change in the polarization state of the linearly polarized radiation transmitted over a fiber-optic cable has been measured using a high-speed polarimeter. During the experiments with a frequency of 100 MHz, a change in the polarization state has been monitored. For the first time, rapid rotations of the plane of polarization, the formation of elliptical polarization, and changes in the angle of ellipticity when exposed to atmospheric discharges on an optical cable have been recorded with precise reference. The effect of maintaining the radiation polarization state when the high voltage is turned off at an electrophysical installation has been discovered.

A theoretical study of a glow discharge in a supersonic gas flow between the central body (cathode) and the nozzle (anode) is carried out. It is a feature of such discharges that the gas-dynamic characteristics change significantly along the gas flow. This refers to the gas pressure, density, and temperature. In such a situation, the discharge location occurs at а place in accordance with the principle of least action. In a supersonic gas flow inside a nozzle, the gas density increases upstream along the central body. Therefore, in accordance with Hehl’s law, the current density increases along the central body. The theoretical model takes these features of the glow discharge into account and calculates the distribution of the internal characteristics of the discharge both along the electric field strength lines and along the stream. Тhe discharge performances in terms of spatial localization, radiation intensity, and formation of near-electrode zones have been established to depend on the magnitude of the current and the geometric parameters of the nozzle and the central body.

The results of the measurements of the roughness and longitudinal piezoelectric modulus d₃₃ of aluminum nitride films of different thicknesses obtained by vacuum magnetron sputtering are reported. The characteristics of the synthesized films are described and atomic force microscopy images of the film surface morphology are presented. It is shown that the roughness of the obtained films decreases when a nucleation layer is formed from molybdenum and the piezoelectric moduli d₃₃ of the two materials are similar.

The paper investigates the near field-interaction with a scatterer located in space R². This area is a priority in problems of medical diagnostics and defectoscopy. The process of wave propagation inside various objects is described using the Helmholtz equation. The field is induced by a point source located outside the body. The problem is reduced to the Lippmann–Schwinger integral equation. A two-step algorithm is used to search for inhomogeneities. A neural network approach has been used to filter the values obtained after a two-step algorithm. This problem arises in acoustics, electrodynamics, and flaw detection, as well as in medical diagnostics. When solving the problem numerically, the order of the matrix obtained in the calculation is about 25 thousand elements. Graphic illustrations of the restoration of the function of inhomogeneities within an object are presented. An experiment has been performed demonstrating the features of restoring object parameters using neural networks. The results show the effectiveness of the calculated data autoencoder filtering. A software package for determining the parameters of inhomogeneities within an object has been proposed and pursued.

The inverse problem of calculating coefficients in the Havriliak–Negami model has been considered in order to determine the structure of an inhomogeneous dielectric object on the basis of determining the parameters and analyzing the frequency characteristics of the relative permittivity. A method for calculating coefficients in the Havriliak–Negami model using three measurements of the complex permittivity at various frequencies has been applied. A numerical method has been developed to determine the coefficients in the Havriliak–Negami model, which is used in dielectric spectroscopy for early detection of tumors in the mammary gland.