Вестник Башкирского университета

Study of the effect of acoustic wave on the boundary of "pure" liquid and bubbly one

2024-12-23T13:41:40+00:00

This work investigates the influence of equilibrium temperature and the degree of dispersion in the gas phase on the dynamics of reflecting and transmissing acoustic waves upon oblique incidence at the interface between bubbly liquid and “pure” one. To solve problems regarding the propagation of small perturbations in a liquid system with spherical vapor-gas bubbles in a flat one-dimensional and single-speed approximation, a system of macroscopic equations for mass, momentum and pressure in the bubbles was formulated.
The solution to this system of equations is sought in the form of a propagating damped wave. The paper presents a dispersion equation.
The influence of the incidence angle on the reflection and transmission coefficients was analyzed. It is shown that at any angle of incidence of the wave from the side of “pure” liquid at the interface, it transmits into the bubbly liquid.

Numerical and experimental modeling of the stability of the flow of thermoviscous fluid in an annular channel

2024-12-23T13:59:58+00:00

This paper presents the results of a study of fluid flow stability taking into account the viscosity dependence on temperature. A 45% aqueous solution of propylene glycol was used as the working fluid. The mathematical model was constructed in accordance with the basic principles of the weakly nonlinear theory of hydrodynamic stability. The experiments were conducted on a setup based on two horizontally located coaxial pipes made of transparent material. The inner pipe contained a heating element to create a temperature gradient in the cross-section of the annular channel. The transition from laminar to turbulent flow was determined visually using tinted liquid.
The calculations showed that the temperature gradient in the channel cross-section leads to a decrease in the critical Reynolds number, and the minimum critical Reynolds number decreases with an increase in the liquid thermal viscosity parameter. The calcula- tion results were convincingly confirmed by experimental data.

Investigation of the pressure waves dynamics in liquids with a hemispherical bubble zone

2024-12-23T14:21:05+00:00

The authors of the work studied two-dimensional axisymmetric wave disturbances in a pipe filled with water containing an end hemispherical bubble cluster made with a water-air bubble mixture. On the basis of results of numerical modeling, the dependence of the maximum pressure amplitude formed in the pipe on the geometric parameters of the cluster and the channel, as well as on the amplitude of the initial disturbance, was analyzed. It was established that for a hemispherical cluster with a radius of 60% or more of the channel radius, there is no amplification of the pressure wave for the considered initial volumetric concentrations. In cases where the cluster radius is less than 60% of the pipe radius, for the examined initial bubble contents, there exists a range of values for the volumetric gas content where a significant increase in wave amplitude is possible as a result of its interaction with the bubbly region.

Experimental investigation of the deposition of single droplets and particles in a viscous liquid

2024-12-23T15:09:21+00:00

The paper investigates the processes of settling of single elements of the dispersed phase structure in a liquid viscous medium.
The results of experimental modeling of the dynamics of precipitation of solid spherical particles in glycerin and in paraffin oil are presented. A good agreement has been obtained between the velocity of particles of different sizes and the velocity calculated accord- ing to Stokes' law. The dynamics of precipitation of a drop of distilled colored water in synthetic and paraffin oils has also been stud- ied. Theoretical velocity data are calculated using the Rybchinsky-Hadamard formula. It was observed that larger droplets flatten during subsidence and cease to follow the Rybchinsky-Hadamard law.

The effect of the transmission rate on the formation of endemic equilibrium in the extended SEIR model

2024-12-23T15:23:01+00:00

In this paper, we consider a modification of the standard SEIR model, which allows us to describe the formation of a dynamic equilibrium between infected and recovered in a constant population. The key point of this model is the isolation in the mechanism of infection transmission of a component directly related to the movement of people (transport processes), and direct contacts of people occurring at zero relative velocity (social contacts). Within the framework of a physico-chemical analogy, dependencies for constants of infection transfer rates are proposed for both purely transport and social mechanisms of spread. These dependencies are used in discussing the formation of nonlinear, non-stationary states in the model under consideration, which can be interpreted as states of endemic equilibrium. The dynamics of the spread of infections in the modified and standard SEIR models are compared.

Investigation of quantum chemical parameters of adsorption of neutral and protonated forms of acetophenonoxim

2024-12-28T10:07:59+00:00

As part of the work performed, studies were conducted on the quantum chemical parameters of adsorption of neutral and pro- tonated forms of acetophenone oxime, global descriptors of reactivity were studied: the highest occupied molecular orbitals (HOMO), the lowest unoccupied molecular orbitals (LUMO), energy gap, ionization energy, electron affinity and the proportion of transferred electrons. Maps of HOMO and LUMO isosurfaces of neutral and protonated molecules have been constructed. On the basis of the obtained values, it is proved that the neutral form of acetophenonoxime is more preferable for the adsorption process on the metal surface than the protonated one. This phenomenon is explained by the fact that neutral molecules are more “soft” com- pounds and have low stability; therefore, they tend to transfer electrons to iron atoms with electron deficiency.

Interaction of the oxidized fraction of siberian larch arabinogalactan with acetylsalicylic acid

2025-01-07T10:34:31+00:00

The interaction of the oxidized fraction of arabinogalactan (OFAG) with acetylsalicylic acid (ASA) in aqueous solutions was studied using UV spectroscopy. It was shown that in the reaction system under study, complex compounds of the composition 1:1 are formed, when for each individual COOH group of OFAG there is one molecule of ASA. Using the method of molar ratios, the stability constants (K) of the resulting complexes were calculated in the temperature range 291–316 K. It was established: 1) at these temperatures, OFAG and ASA form fairly stable complexes (K ~ 103–104 L/mol); 2) with increasing temperature, the K values decrease. The
study of the temperature dependences of K made it possible to determine the thermodynamic parameters of complex formation.

Information system for kinetic modeling of diesel fuel hydrotreating process

2025-01-07T11:08:24+00:00

The work is devoted to the development of a kinetic model of the catalytic hydrotreating of diesel fuel using an information system. In modern oil refining, hydrotreating is used very widely. A variety of straight-run fractions and secondary products are subjected to hydrotreating: gasolines, jet and diesel fractions, vacuum gas oil, various types of oil feedstock. The kinetic modeling is based on a full-scale experiment. For calculations, we used process studies at temperatures from 340 to 380°C with a step of 20°C. A block diagram of the developed information system and the results of kinetic modeling of the hydrotreating process are given: calculated rate constants of the stages, pre-exponential factors and activation energies.

To numerical simulation of chemical interactions during temperature microconvection

2025-01-07T11:33:00+00:00

The article deals with the model equations for describing of convection fluid dynamics in microtubes. The convection is initiated with temperature gradient and described by the Boussinesq buoyancy approximation. The model is supplemented with arbitrary series of chemical reactions described on the basis of Arrhenius chemical kinetics. It is shown that the change of convection flows makes strong impact on the reaction rates. The model demonstrates a possible approach to a numerical simulation of polymerase chain reaction

Поправка

2025-01-07T11:39:02+00:00

В предыдущем номере журнала – «Вестник Башкирского университета». 2024. Т. 29. №3 – в мемориальной статье «Харрасов Мухамет Хадисович – выдающийся ученый, организатор высшего образования, государственный деятель и гражданин» не были указаны авторы.
Редакция извещает, что авторами данной статьи являются:
- Шарафуллин Ильдус Фанисович, доктор физико-математических наук, доцент, директор Физико-технического института, УУНиТ;
- Екомасов Евгений Григорьевич, доктор физико-математических наук, профессор, профессор кафедры теоретической физики Физико-технического института, УУНиТ;
- Азнагулова Гузель Мухаметовна, доктор юридических наук, главный научный сотрудник отдела теории права и междисциплинарных исследований законодательства Института законодательства и сравнительного правоведения при Правительстве РФ.
Редакция приносит свои извинения за допущенную ошибку.