Technical Physics最新文献

The characteristics of phase equilibria in cytane−propane/butane and diphenyl−propane/butane systems have been investigated in the temperature interval 403–443 K and the pressure range 1.0−6.8 MPa using a high-pressure optical cell. Type-I phase behavior has been found.

The paper deals with aspects of the development of a methodological approach to normalizing the supply voltage quality in an electrical network by developing an algorithmized method for determining the rational installation location of symmetrization equipment in a motor-loaded electrical complex. The developed method makes it possible to implement processes aimed at ensuring efficient operation of the electrical complex in the presence of an electric motor load under low-quality supply voltage conditions. The proposed method based on software provides design procedures for calculating various options for symmetry and for choosing the most cost-effective technique. Attention is focused on the main criteria for evaluating decisions made in designing the location of symmetrization equipment in the electrical complex. The architecture and basic functional features of the application software as a tool for implementing the calculation method are reviewed. The software is intended for electrical calculations in the design, modernization, and operation of electrical networks. It includes drawing schematic diagrams of sections of electrical complexes with installed symmetrization equipment. The results are presented of experimental studies demonstrating the effectiveness of the developed method in solving problems of voltage symmetry in the supply electrical network. It is obvious that the developed approach based on automatic selection of locations for symmetrization equipment depending on the operating conditions of electric motor load makes it possible to automate the design procedures for voltage normalization in the electrical network. It minimizes voltage asymmetry in power supply and contributes to improving the operational reliability of low-voltage asynchronous motors. The study findings and prospects of using the developed approach are considered both for solving complex design problems and for the economic justification of local design solutions. A detailed analysis and formalization of the study results with relevant conclusions were carried out.

A method is proposed for determining the transport characteristics used in the macroscopic heat- and mass-transfer equations for multicomponent media. The method has been based on the kinetic theory of gases. To generalize this theory to a multicomponent medium, its approximation by a basic binary medium has been used. In this study, a two-level approach has been developed, which combines the description of macroscopic processes in multicomponent gaseous media with the microscopic description based on the Boltzmann equation.

Background. The relevance of the topic of this work is due to the need to reduce the level of penetrating interference and improve the quality of the useful signal received by the on-board active interference station. Goal. Improving the quality and functional parameters of on-board frequency-selective systems and structures by adjusting the amplitude–frequency characteristics (AFCs) of filters. Methods. The system analysis of the main parameters, modeling of the frequency characteristics of attenuation and the standing wave voltage coefficient, expert assessments, and research tests have been used. Materials. To improve the characteristics of the filters, it is proposed to adjust (control) the AFCs of the filters. The schemes and topologies of correctors are given. It is shown that with the help of thin-film and thick-film correctors, various frequency response distortions can be eliminated, the slope of the characteristic can be adjusted, and the depth of the AFC dip can be changed. Results. The proposed schemes, designs, and topologies of correctors make it possible to adjust the slope of the characteristics up to 16 dB, change the depth of their dip, maintain the voltage standing wave ratio within 1.35–2.5 in the operating frequency range, reduce the frequency response nonuniformity to 0.2 dB, and the noise factor to 2.3–2.4 dB. To ensure such a level of performance during the adjustment process, it is required to carry out an individual combined adjustment of the resistors in the range from –10% to +30% or functional adjustment according to a template. At the same time, the flare discharge method provides a higher time stability of the frequency response adjustment indicators and a higher yield of suitable products as compared to the laser method. Conclusions. The proposed method of adjusting the AFCs of the filters in a frequency-selective system makes it possible to improve the quality of the useful signal received by the active interference station. Adjusting the frequency response by adjusting the resistances of the corrector resistors by the flare discharge method provides a higher temporal stability of the parameters than the laser adjustment.

The paper presents studies devoted to the study of the heat capacity of propylene homopolymers and propylene–ethylene copolymers, comparison of the data obtained with the composition of macromolecules and the molecular weight of polymers. The paper considers the influence of the molecular weight and ethylene groups on the specific heat capacities of polypropylenes, found by differential scanning calorimetry.

The influence of montmorillonite on the polymerization and properties of photocurable resin has been investigated. It has been shown that montmorillonite added to the binder composition does not retard the curing reaction and does not suppress UV curing. Montmorillonite improves the elasticity modulus and does not influence the glass transition temperature of UV-cured compositions.

The problem of positional control of the service gates in a shipping lock as a multidimensional control object with lumped parameters is considered. A general formulation of the problem is given, including requirements for the final and intermediate states. To solve the problem, it is proposed to use a production model of the regulator in the form of a system of rules. The numerical method for solving the problem is based on presenting the control algorithm in the form of an a priori non-fixed and time-varying system of rules determined during the control process. The presented results of numerical modeling confirm the effectiveness of the proposed method for determining the positional control of objects of this type.

Cooling of a modified surface by a dispersed flow of distilled water has been investigated experimentally, and the results have been compared with cooling of an unmodified surface. The modification of the heat-exchange surface of the copper working region has been performed by processing with a high-energy electron beam; as a result, a unique microporous surface has been obtained. The macrograph of the modified surface has been obtained and profiles have been measured using a profile meter. Four series of experiments for various heat carrier parameters have been performed for the modified and unmodified surfaces. The excess pressure of the heat carrier at the sprayer input was (4–14) × 10⁵ Pa, the mass flow rate of the heat carrier (distilled water) was (2.1–4.3) × 10^–3 kg/s, and the spraying density varied in the limits (3.0–6.1) kg/(m² s). The variations of the heat flux densities for these surfaces were compared. The convective component and the component of the phase transition of the removed heat flow during cooling the surface by a dispersed flow were estimated, and the conclusion was made concerning the key contribution of the phase transition to this process was made. The amount of evaporated liquid for the considered cooling modes were compared, and the dependence of this quantity on the heat flux density was obtained. The maximal heat flux density during the cooling of the surface by a dispersed flow attained 8.5 MW/m².

The problem of hemodynamics (i.e., blood circulation in vessels resulting from the difference in the hydrostatic pressures in different parts of the circulatory system) has been investigated. For the differential problem in the hemodynamic model of heart, a difference scheme has been constructed and the convergence of the approximate solution to the exact solution has been substantiated. A numerical solution is obtained for the model problem of a single-chamber heart.

Several samples of nano-oil with different concentrations of dielectric and conductive nanoparticles are prepared to describe the electrophysical characteristics of nanofluids. Permittivity and conductivity of the nanofluids are experimentally measured. The processed experimental results are compared with the calculated results obtained using the Nielsen formula. The comparative analysis shows qualitative agreement of the calculated and experimental values of permittivity and a significant difference between the experimental and calculated dependences of conductivity on the concentration of particles. Such a difference between the calculated and experimental results is due to the adsorption of ions on the surface of the particles and their subsequent sedimentation. A decrease in the conductivity can be due to a decrease in the number of mobile particles and the fact that they have significantly less mobility compared to ions in the presence of weak electric fields. Additional measurements of the conductivity of nanofluids with particles of silicon dioxide and added oleic acid reproduce the observed decrease in the conductivity.