Vol 26, No 134 (2021)
Articles
Numerical assessment of the spread dynamics of the new coronavirus infection SARS-CoV-2 using multicompartmental models with distributed parameters
Abstract
We propose multicompartmental models of infectious diseases dynamics for numerical study of the spread parameters of the new coronavirus infection SARS-CoV-2, which take into account the delay effects associated with the presence of the latent period of the infection, as well as the possibility of an asymptomatic course of the disease. The dynamics of the spread of COVID-19 in the Russian Federation was investigated, using these models with distributed parameters that formalize the interactions of the models’ compartments. The paper provides numerical estimates of the spread dynamics of the new coronavirus infection in various age groups of the population. We also investigate possible consequences of the mask regime and quarantine measures. We obtain an explicit estimate allowing to assess the necessary scope of these measures for the epidemy extinction.
Russian Universities Reports. Mathematics. 2021;26(134):109-120
109-120
On permutable strongly 2-maximal and strongly 3-maximal subgroups
Abstract
We describe the structure of finite solvable non-nilpotent groups in which every two strongly n -maximal subgroups are permutable (n = 2; 3 ). In particular, it is shown for a solvable non-nilpotent group G that any two strongly 2-maximal subgroups are permutable if and only if G is a Schmidt group with Abelian Sylow subgroups. We also prove the equivalence of the structure of non-nilpotent solvable groups with permutable 3-maximal subgroups and with permutable strongly 3-maximal subgroups. The last result allows us to classify all finite solvable groups with permutable strongly 3-maximal subgroups, and we describe 14 classes of groups with this property. The obtained results also prove the nilpotency of a finite solvable group with permutable strongly n -maximal subgroups if the number of prime divisors of the order of this group strictly exceeds n (n=2; 3 ).
Russian Universities Reports. Mathematics. 2021;26(134):121-129
121-129
Solvability conditions in the analytical form of a descriptor system of partial differential equations
Abstract
A system of first-order partial differential-algebraic equations in a Banach space with constant degenerate operators in the case of a regular operator pencil is considered. In this case, under some additional condition, the original system splits into two subsystems in disjoint subspaces in order to search for the projections of the original unknown function in the subspaces. The matching conditions for the parameters of the systems are identified. A solution of the considered system of differential-algebraic equations is constructed.
Russian Universities Reports. Mathematics. 2021;26(134):130-142
130-142
A counterexample to the stochastic version of the Brouwer fixed point theorem
Abstract
It is shown that the stochastic counterpart of the classical fixed point theorem for continuous maps in a finite dimensional Euclidean space (“Brouwer’s theorem”) is not, in general, true. This result implies, in particular, that a careful choice of invariant sets in the stochastic version of Brouwer’s theorem is necessary in the theory of stochastic nonlinear operators.
Russian Universities Reports. Mathematics. 2021;26(134):143-150
143-150
Lagrange principle and its regularization as a theoretical basis of stable solving optimal control and inverse problems
Abstract
The paper is devoted to the regularization of the classical optimality conditions (COC) - the Lagrange principle and the Pontryagin maximum principle in a convex optimal control problem for a parabolic equation with an operator (pointwise state) equality-constraint at the final time. The problem contains distributed, initial and boundary controls, and the set of its admissible controls is not assumed to be bounded. In the case of a specific form of the quadratic quality functional, it is natural to interpret the problem as the inverse problem of the final observation to find the perturbing effect that caused this observation. The main purpose of regularized COCs is stable generation of minimizing approximate solutions (MAS) in the sense of J. Warga. Regularized COCs are: 1) formulated as existence theorems of the MASs in the original problem with a simultaneous constructive representation of specific MASs; 2) expressed in terms of regular classical Lagrange and Hamilton-Pontryagin functions; 3) are sequential generalizations of the COCs and retain the general structure of the latter; 4) “overcome” the ill-posedness of the COCs, are regularizing algorithms for solving optimization problems, and form the theoretical basis for the stable solving modern meaningful ill-posed optimization and inverse problems.
Russian Universities Reports. Mathematics. 2021;26(134):151-171
151-171
Study of rigidity of a first-order algebro-differential system with perturbation in the right-hand side
Abstract
The rigidity of a dynamical system described by a first-order differential equationwith an irreversible operator at the highest derivative is investigated. The system is perturbed by an operator addition of the order of the second power of a small parameter. Conditions under which the system is robust with respect to these disturbances are determined as well as conditions under which the influence of disturbances is significant. For this, the bifurcation equation is derived. It is used to set the type of boundary layer functions. As an example, we investigate the initial boundary value problem for a system of partial differential equations with a mixed second partial derivative which occurs in the study of the processes of sorption anddesorption of gases, drying processes, etc.
Russian Universities Reports. Mathematics. 2021;26(134):172-181
172-181
Maximal linked systems on products of widely understood measurable spaces
Abstract
Maximal linked systems (MLS) of sets on widely understood measurable spaces (MS) are considered; in addition, every such MS is realized by equipment of a nonempty set with a π -system of its subsets with «zero» and «unit» (π -system is a nonempty family of sets closed with respect to finite intersections). Constructions of the MS product connected with two variants of measurable (in wide sense) rectangles are investigated. Families of MLS are equipped with topologies of the Stone type. The connection of product of above-mentioned topologies considered for box and Tychonoff variants and the corresponding (to every variant) topology of the Stone type on the MLS set for the MS product is studied. The properties of condensation and homeomorphism for resulting variants of topological equipment are obtained.
Russian Universities Reports. Mathematics. 2021;26(134):182-215
182-215
Two-sided estimates for solutions of boundary value problems for implicit differential equations
Abstract
We consider a two-point (including periodic) boundary value problem for the following system of differential equations that are not resolved with respect to the derivative of the desired function: f i t, x, x , x i =0, i= 1, n. Here, for any i = 1, n the function f i :[0, 1]× Rn × Rn ×R→R is measurable in the first argument, continuous in the last argument, right-continuous, and satisfies the special condition of monotonicity in each component of the second and third arguments. Assertions about the existence and two-sided estimates of solutions (of the type of Chaplygin’s theorem on differential inequality) are obtained. Conditions for the existence of the largest and the smallest (with respect to a special order) solution are also obtained. The study is based on results on abstract equations with mappings acting from a partially ordered space to an arbitrary set (see [S. Benarab, Z.T. Zhukovskaya, E.S. Zhukovskiy, S.E. Zhukovskiy. On functional and differential inequalities and their applications to control problems // Differential Equations, 2020, 56:11, 1440-1451]).
Russian Universities Reports. Mathematics. 2021;26(134):216-220
216-220