卷 59, 编号 3 (2023)

We study a nonlinear eigenvalue problem of a special form arising in electrodynamics. The problem is posed for a system of two equations with boundary conditions of the first kind and two additional local conditions. There is one spectral parameter in the problem, and two more parameters, which are subject to an additional constraint, occur in the above-mentioned local conditions. Thus, there are two unknown parameters in the problem: one is the spectral parameter, and the other is some additional parameter, chosen so as to ensure that there exists a nontrivial solution of the problem in question. The existence of nonlinearizable solutions of the problem is proved.

We consider a boundary value problem for a singularly perturbed system of two second-order ordinary differential equations with different powers of the small parameter multiplying the second derivatives. A specific feature of the problem is that one of the two equations of the degenerate system has a double root and the other has three nonintersecting simple roots. It is proved that for sufficiently small values of the small parameter the problem has a solution that has a fast transition in a neighborhood of some interior point of the interval. A complete asymptotic expansion of this solution is constructed and justified. It qualitatively differs from the well-known expansion in the case where all the roots of the degenerate equations are simple but also does not coincide with the expansions in the previously studied problems with double roots; in particular, the inner transition layer turns out to be single-scale.

We study the direct problem for transverse vibrations of a homogeneous beam of finite length with time-nonlocal conditions and obtain necessary and sufficient conditions for the existence of its solution. For the direct problem, the inverse problem of determining the time-dependent coefficients of the lower derivative and the right-hand side in the equation is studied. The existence and uniqueness of the solution of the inverse problem are proved. The solution is based on separation of variables, which is used to reduce the problems to an integral equation and a system of integral equations.

Based on the theory of trajectory pullback attractors, we study the qualitative behavior of weak solutions for the Bingham model with periodic conditions in the space variables. For the model under consideration, a family of trajectory spaces is introduced and the existence of pullback attractors is proved.

We consider the initial value problem for linear systems of second-order ordinary differential equations with an identically singular matrix multiplying the principal part. Sufficient conditions for the existence of a unique solution are given in terms of matrix polynomials. For such problems, multistep difference schemes are proposed. An analysis of their stability and calculations of a model example are carried out.

The problems of multiplicative control for the reaction–diffusion–convection model with coefficients that are nonlinearly dependent on the solution and also dependent on spatial variables are studied. In the case of a power-law dependence of the model coefficients on the solution, optimality systems are derived for extremum problems. With their help, estimates of the local stability of solutions of specific control problems with respect to small perturbations of both the cost functionals and one of the given functions of the boundary value problem are obtained.

The author has retracted this article. The main results of the work, namely Theorem 1 and the corollaries arising from it, have not been strictly proven: formulas (8) are valid only under the condition 
. Yet, even when the indicated condition is met, formulas (9) need to be proven. Because of this, this work in its current form should be recognized as incorrect. The author is grateful to Professor L.G. Makar-Limanov, who drew attention to the lack of correct proof of formula (8) and Professor V.V. Bakhtin, who pointed to other inaccurate statements in this article.