Technical Physics Letters

Mikhailov, V. V.; Perevaryukha, A. Y.; Trofimova, I. V.

doi: 10.1134/s1063785022110013pmid: N/A

Formalization in the form of systems of differential equations to describe sharp changes in the development of invasion processes remains an important and urgent problem for mathematical biophysics and bioinformatics. The spread of aggressive biological organisms is accompanied by the rapid phenomena of explosive increase in the dynamics of the population of these dangerous foreign species. Hardly predictable population outbreaks of small insects may continue until the total destruction of forests on large areas. This phenomenon of imbalance affects the entire environment and biochemical processes in the trophic chain of the biosystem. After a rapid uncontrolled (by natural physical factors and a biotic environment) outbreak, degradation of ecosystems and extinction of the invasive species may occur. The fundamental problem of controlling new aggressive species is very important for practical problems of the optimal use of bioresources. The generality of some situations requires special mathematical analysis, which can be constructed by analogy with physical processes with sharp transient regimes. Parametric changes and bifurcations cannot explain the change in behavior, because these reproductive characteristics of aggressive species in a specific biophysical environment are stable during evolutionary adaptation and change only gradually. The simulation of changes in the development rate of individuals in a competitive environment is considered as a hidden factor affecting the realization of critical effects in the dynamics of the population of species with a pronounced staging of ontogenesis. A hybrid model is constructed based on the system of equations describing actual changes in the metabolism rate in ontogenesis, which is applicable to populations in different states of the invasion process.

Trofimova, I. V.; Perevaryukha, A. Y.; Manvelova, A. B.

doi: 10.1134/s1063785022110025pmid: N/A

The problem of confirming the correspondence of the dynamics of biophysical processes arising from the incomplete and noisy data obtained during monitoring of the state of bioresources or statistics gathering in a series of laboratory experiments to three behavioral modes of paths of discrete dynamic systems (equilibrium, limiting cycle, or chaos) is considered. It is shown using the examples of real monitoring data and results of laboratory experiments that the data-approximation technique yields a dependence function, which excludes the observed qualitative development of the population process. Attempts to plot regression lines based on the monitoring data for dissipative paths do not yield the necessary information. Known models of biophysics with qualitative changes in the behavior are considered that use characteristics of the reproductive function that cannot be interpreted in terms of the environmental role. The Schwartz derivative depends on the third derivative of the second iteration of the function at the moment of stationary-point stability loss. Criteria for discrete dynamic systems are proposed that can be used to analyze the results of computational simulation from the point of view of biophysical adequacy of occurring nonlinear effects. It is suggested that the rate of population change in the model has a range of negative values and the population reproduction curve has at least two nontrivial stationary points. Consideration of the effect of an aggregated group, arising during invasions, in the action models facilitates an essential interpretation of the behavior of the model path. It is proposed to delimit the nonlinear effects arising in discrete iterative models. In the case of an invasive species that has penetrated into the ecosystem and caused the depletion of its vital resources, a rapid transition to collapse of the new population is possible. Our approach with two-attractor models makes it possible to predict the state of a critically low population of an aggressive intruder.

Ghyngazov, S. A.; Vasil’ev, I. P.; Boltueva, V. A.

doi: 10.1134/s1063785022110037pmid: N/A

Zirconia ceramics exhibits high functional and strength properties. The range of its application is continuously expanding. The use of nanopowders makes it possible to obtain fine-grained ceramics with improved characteristics. Zirconium dioxide has a high hardness, which ensures increased mold wear. In addition, nanoparticles are prone to agglomeration, which affects compaction upon pressing and sintering. These problems can be solved by introducing microadditives, e.g., carbon. The effect of the type and concentration of a carbon additive on the parameters of zirconia ceramics fabricated from powder raw materials synthesized by sol‒gel and plasma-chemical methods has been explored. The shrinkage of the ceramic samples of two types with carbon additives of three types (multiwalled carbon nanotubes (MWNTs), amorphous carbon, and amorphous carbon with MWCNTs) has been studied by dilatometry. It has been established that the additives do not affect the shrinkage rate and that the highest rate of shrinkage of the sample is almost equal to the shrinkage rate upon sintering of the ceramics without additives. The effect of a carbon additive on the density and microhardness of the ceramics has been determined. It is shown that the additives introduced into the ceramics fabricated from the powders synthesized by the sol‒gel technology reduce the density and microhardness, while the density of the ceramics made of the plasma-chemical powders increases up to a certain additive concentration threshold for carbon of all the types discussed in this study.

Maslova, O. A.; Ryabykh, A. V.; Beznosyuk, S. A.

doi: 10.1134/s1063785022110049pmid: N/A

We report on the results of computer modeling of the state of the H+ hydrogen ion in hypothetical aqueous solutions with different permittivities and the simulation of the passage of a free and hydrated proton through a monomeric graphene and graphenelike borophene nanolayer. The calculation was performed within the density functional theory using the BP86 functional of the generalized gradient approximation and the def2-SVPD and def2-TZVP Karlsruhe basis sets. The conductor-like polarizable continuum model with a permittivity ranging within ε = 1‒80.4 was used to describe the solvent. The modeling was carried out in the Orca 5.0.1 software package. The first part of the article describes the state of intermolecular interactions of complexes of H+ ions with water molecules. It was found that the most stable among the investigated H3O+, \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{{\text{H}}}_{5}}{\text{O}}_{2}^{ + }$$\end{document}, \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{{\text{H}}}_{7}}{\text{O}}_{3}^{ + }$$\end{document}, and \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{{\text{H}}}_{9}}{\text{O}}_{4}^{ + }$$\end{document} structures in an aqueous solution is the hydroxonium ion H3O+. This experimental fact is independent of the dielectric properties of a medium. The second part of the article describes the passage of H+ ions through a monomeric graphene and graphenelike borophene nanolayer. The mechanism of proton permeability from the first water molecule on one side to the second water molecule on the opposite side of the nanolayer is shown. The potential barrier for passage of a hydrogen ion through the graphene nanolayer was found to be 1.63 eV and the height of the barrier through the borophene nanolayer was 0.22 eV. It is demonstrated that, in all the cases, the permittivity of a medium does not significantly affect the barrier height.

Prosviryakov, E. Yu.; Sokolov, A. S.

doi: 10.1134/s1063785022110050pmid: N/A

A steady shear convective flow of a fluid moving between two rotating infinite planes (disks) is investigated. The angular velocities of the boundaries of an infinite horizontal layer are described by various quantities. In other words, the differential rotation of a medium (dynamic equilibria), instead of the solid-body rotation of the fluid (the Ekman convective flow), is studied. The exact solution of the Oberbeck–Boussinesq equations is considered. The system of equations is overdetermined, since, to determine four unknown functions for the shear convective flow, it is necessary to integrate a nonlinear system of partial differential equations from five equations. The velocity field is determined by linear forms. The temperature field and the pressure field are described by quadratic forms. The forms depend on two coordinates (horizontal or longitudinal). The form factor is determined by the connection from the vertical (third, transverse) coordinate. The exact solution used makes it possible to meet the “extra” equation (the incompressibility equation) and construct a nonlinear system of ordinary differential equations. The equations are numerically integrated to determine the hydrodynamic fields. The structure of countercurrents arising at the steady convection of a fluid is investigated. Using numerical algorithms for the systems of ordinary equations, the regions of the existence of countercurrents are built depending on the fluid parameters and boundary conditions for an infinite horizontal layer.