Stability estimates for solutions of control problems for the Maxwell equations with mixed boundary conditions

We consider extremal problems for the time-harmonic Maxwell equations with mixed boundary conditions for the electric field. Namely, the tangential component of the electric field is given on one part of the boundary, and an impedance boundary condition is posed on the other part. We prove the solvability of the original mixed boundary value problem and the extremal problem. We obtain sufficient conditions on the input data ensuring the stability of solutions of specific extremal problems under certain perturbations of both the performance functional and some functions occurring in the boundary value problem.     

Stability of solutions of control problems for the convection–diffusion–reaction equation with a strong nonlinearity

We consider a boundary control problem for the stationary convection–diffusion–reaction equation in which the reaction constant depends on the concentration of matter in such a way that the equation has a fifth-order nonlinearity. We prove the solvability of the boundary value problem and an extremal problem, derive an optimality system, and analyze it to derive estimates for the local stability of the solution of the extremal problem under small perturbations of both the performance functional and one of the given functions.     

Solution of boundary-value problems for a degenerating elliptic equation of the second kind by the method of potentials

In this paper we study basic boundary value problems for one multidimensional degenerating elliptic equation of the second kind. Using the method of potentials we prove the unique solvability of the mentioned problems. We construct a fundamental solution and obtain an integral representation for the solution to the equation. Using this representation we study properties of solutions, in particular, the principle of maximum. We state the basic boundary value problems and prove their unique solvability. We introduce potentials of single and double layers and study their properties. With the help of these potentials we reduce the boundary value problems to the Fredholm integral equations of the second kind and prove their unique solvability.     

A majorant criterion for the total preservation of global solvability of controlled functional operator equation

We prove the unique solvability of a nonlinear controlled functional operator equation in a Banach ideal space. We also establish sufficient conditions for the global solvability of all controls from a pointwise bounded set, provided that some majorant equation for the given family of these controls is globally solvable. We give examples of controlled boundary value problems reducible to the considered equation.     

On stability of solutions of the coefficient inverse extremal problems for the stationary convection-diffusion equation

The coefficient inverse extremal problems are studied for the stationary convectiondiffusion equation in a bounded domain under mixed boundary conditions on the boundary of the domain. The role of control is played by the velocity vector of a medium and the functions that are involved in the boundary conditions for temperature. The solvability of the extremal problems is proven both for an arbitrary weakly lower semicontinuous quality functional and for the particular quality functionals. On the basis of analysis of the optimality system some sufficient conditions are established on the initial data providing the uniqueness and stability of optimal solutions under sufficiently small perturbations of both the quality functional and one of the functions involved in the original boundary value problem.     

Stability estimates of solutions to extremal problems for a nonlinear convection-diffusion-reaction equation

We consider an identification problem for a stationary nonlinear convection–diffusion–reaction equation in which the reaction coefficient depends nonlinearly on the concentration of the substance. This problem is reduced to an inverse extremal problem by an optimization method. The solvability of the boundary value problem and the extremal problem is proved. In the case that the reaction coefficient is quadratic, when the equation acquires cubic nonlinearity, we deduce an optimality system. Analyzing it, we establish some estimates of the local stability of solutions to the extremal problem under small perturbations both of the quality functional and the given velocity vector which occurs multiplicatively in the convection–diffusion–reaction equation.     

On the Question of Existence of a Solution to the Tricomi Problem for One Class of Systems of Mixed-Type Equations

We establish extremal properties of regular and weak solutions to the Tricomi problem for a system of mixed-type equations. Using a Schwartz-type alternation method, we prove unique weak solvability of the Tricomi problem under some constraints on coefficients.     

Riemann-Hilbert and Poincaré problems with discontinuous boundary conditions for some model systems of partial differential equations

We study the solvability of the Riemann-Hilbert and Poincaré problems for systems of Cauchy-Riemann and Bitsadze equations in Sobolev spaces. For a generalized system of Cauchy-Riemann equations, we pose a boundary value problem and prove its unique solvability in the Sobolev space W ₂¹ (D). By supplementing the Riemann-Hilbert boundary conditions with some new conditions, we obtain a statement of the Poincaré problem with discontinuous boundary conditions for a system of second-order Bitsadze equations; we also prove the unique solvability of this problem in Sobolev spaces.     

Integral equations in a diffraction problem on a locally inhomogeneous medium interface

We study the diffraction of an E-polarized field on a locally inhomogeneous interface of transparent media. We prove the unique solvability of the boundary value diffraction problem and obtain integral representations of the solution. We derive a system of integral equations equivalent to the original boundary value problem and prove a solvability theorem for this system.     

Theoretical analysis of boundary control extremal problems for Maxwell’s equations

Under study are the extremal problems of multiplicative boundary control for timeharmonic Maxwell’s equations considered with the impedance boundary condition for the electric field. The solvability of the original extremal problem is proved. Some sufficient conditions are derived on the original data which guarantee the stability of solutions to concrete extremal problems with respect to certain perturbations of both the quality functional and one of the known functions that has the meaning of the density of the electric current.     

On the uniqueness and stability of solutions of extremal problems for the stationary Navier-Stokes equations

We consider inverse extremal problems for the stationary Navier-Stokes equations. In these problems, one seeks an unknown vector function occurring in the Dirichlet boundary condition for the velocity and the solution of the considered boundary value problem on the basis of the minimization of some performance functional. We derive new a priori estimates for the solutions of the considered extremal problems and use them to prove theorems of the local uniqueness and stability of solutions for specific performance functionals.     

On solvability of boundary integral equations of potential theory for a multidimensional cusp domain

The Dirichlet and the Neumann problems for the Laplace equation on a multidimensional cusp domain are considered. The unique solvability of the boundary integral equation for the internal Dirichlet problem for harmonic double layer potential is established. We also prove the unique solvability of the boundary integral equation for the external Neumann problem for harmonic single layer potential. Bibliography: 13 titles.     

On estimates for solutions of elliptic boundary value problems in a layer

We consider boundary value problems for elliptic operators with constant coefficients in a layer, i.e., in a domain between two parallel planes. We assume that the Lopatinskii condition and the condition of the unique solvability of an auxiliary problem for an ordinary differential operator are satisfied. We prove theorems on the solvability and smoothness of solutions in Sobolev spaces with weight of exponential type.     

Solvability of Inverse Extremal Problems for Stationary Heat and Mass Transfer Equations

We consider inverse extremal problems for the stationary system of heat and mass transfer equations describing the propagation of a substance in a viscous incompressible heat conducting fluid in a bounded domain with Lipschitz boundary. The problems consist in finding some unknown parameters of a medium or source densities from a certain information of a solution. We study solvability of the direct boundary value problem and the inverse extremal problem, justify application of the Lagrange principle, introduce and analyze the optimality systems, and establish sufficient conditions for uniqueness of solutions.     

On the unique solvability of a family of two-point boundary-value problems for systems of ordinary differential equations

We consider a family of two-point boundary-value problems for systems of ordinary differential equations with functional parameters. This family is the result of the reduction of a boundary-value problem with nonlocal condition for a system of second-order, quasilinear hyperbolic equations by the introduction of additional functions. Using the parametrization method, we establish necessary and sufficient conditions of the unique solvability of the family of two-point boundary-value problems for a linear system in terms of the initial data. We also prove sufficient conditions of the unique solvability of the problem considered and propose an algorithm for its solution. __________ Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 12, No. 4, pp. 21–39, 2006.     

Inverse coefficient problems for elliptic equations in a cylinder: II

We study sufficient conditions for the unique solvability of the inverse coefficient problem. We obtain various global sufficient conditions in the form of constraints on the signs of the given functions and their derivatives. As a corollary, we consider statements of inverse coefficient problems with overdetermination on the boundary, where the Dirichlet conditions are supplemented with the vanishing condition for the normal derivative on part of the boundary. We prove sufficient conditions for the existence of a solution in this case.     

Proof of the solvability of a system of partial differential equations in the nonlinear theory of shallow shells of Timoshenko type

We study the solvability of a system of second-order partial differential equations under given boundary conditions. To prove the existence of a solution of the system, we reduce it to a single nonlinear partial differential equation whose solvability is proved with the use of the contraction mapping principle.     

On a nonlocal problem in function theory

We consider nonlocal boundary value problems for three harmonic functions each of which is defined in its own domain. A contact condition is posed on the common part of the boundaries of these domains, and the Dirichlet or Neumann data (or mixed boundary conditions) are given on the remaining parts of the boundary. We prove the unique solvability of these problems.     

Motion of a vortex filament with axial flow in the half space

We consider a nonlinear third order dispersive equation which models the motion of a vortex filament immersed in an incompressible and inviscid fluid occupying the three dimensional half space. We prove the unique solvability of initial–boundary value problems as an attempt to analyze the motion of a tornado.     

On the uniqueness of the solution of the first two boundary value problems for the heat equation without initial conditions

We consider boundary value problems for the heat equation without initial data in the class of functions of polynomial growth at infinity. We prove the unique solvability of the first and second boundary value problems and show that the conditions at infinity are important; i.e., their weakening results in the nonuniqueness of the solution.