An asymptotic solution of the Dirichlet problem for the Poisson equation on a nonperiodic frame

In this paper, the Dirichlet problem for the Poisson equation is considered in a nonperiodic framelike domain that consists of thin short strips or cylinders. We construct a complete asymptotic expansion for the solution. We obtain an estimate for the difference between the exact solution and the asymptotic one. Bibliography: 9 titles. Dedicated to Olga Arsenievna Oleinik Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 19, pp. 000-000, 0000.     

The impulsive solution for a semi-linear singularly perturbed differential-difference equation

The impulsive solution for a semi-linear singularly perturbed differential-difference equation is studied. Using the methods of boundary function and fractional steps, we construct the formula asymptotic expansion of the problem. At the same time, Based on sewing techniques, the existence of the smooth impulsive solution and the uniform validity of the asymptotic expansion are proved.     

Perturbation of Solutions with Moving Singularities

We study the Cauchy problem for a nonlinear second-order differential equation with a small parameter in the case where the exact solution has a power singularity depending on a small parameter. We propose an asymptotic method similar to the Krylov–Bogoliubov method for localizing the singularity up to the accuracy of any order and construct an asymptotic expansion of the solution in the domain of regular behavior.     

Heat distribution in an infinite rod

We construct an asymptotic expansion of the solution of the Cauchy problem for the one-dimensional heat equation for the case in which the initial function at infinity has power asymptotics.     

Asymptotic expansion of solutions in a rolling problem

Asymptotic methods in the theory of differential equations and in nonlinear mechanics are commonly used to improve perturbation theory in the small oscillation regime. However, in some problems of nonlinear dynamics, in particular for the Higgs equation in field theory, it is important to consider not only small oscillations but also the rolling regime. In this article we consider the Higgs equation and develop a hyperbolic analogue of the averaging method. We represent the solution in terms of elliptic functions and, using an expansion in hyperbolic functions, construct an approximate solution in the rolling regime. An estimate of accuracy of the asymptotic expansion in an arbitrary order is presented.     

The Topological Derivative of the Dirichlet Integral Under Formation of a Thin Ligament

We construct and justify the asymptotic expansion of a solution and the corresponding energy functional of the mixed boundary-value problem for the Poisson equation in a domain with a ligament, i.e., thin curvilinear strip connecting two small parts of the boundary outside the domain. Asymptotic analysis is required in the theory of shape optimization; therefore, in contrast to other publications, we use no simplifying assumptions of the flattening of the boundary near the junction zones.     

Formal asymptotic solution of a singularly perturbed nonlinear optimal control problem

A system of equations that arises in a singularly perturbed optimal control problem is studied. We give conditions under which a formal asymptotic solution exists. This formal asymptotic solution consists of an outer expansion and left and right boundary-layer expansions. A feature of our procedure is that we do nota priori eliminate the control function from the problem. In particular, we construct a formal asymptotic expansion for the control directly. We apply our procedure to a Mayer-type problem. The paper concludes with a worked example.     

Behavior at infinity of a solution to a matrix differential-difference equation

We obtain an asymptotic expansion for a solution to a nonhomogeneous retarded- or neutraltype differential-difference equation. The case of unbounded delays is considered. The influence is accounted for the roots of the characteristic equation. We establish the exact asymptotics for the remainder depending on the asymptotic properties of the free matrix term of the equation.     

Asymptotic expansion of the solution of a differential-difference equation of general form

We obtain an asymptotic expansion of the solution of an mth-order inhomogeneous differential-difference equation of general form. We establish an integral estimate with a submultiplicative weight for the remainder of the expansion depending on the existence of the corresponding submultiplicative moment of the right-hand side of the equation.     

On the stability and the attraction domain of the stationary solution of a singularly perturbed parabolic equation with a multiple root of the degenerate equation

We construct and justify the asymptotics of a boundary layer solution of a boundary value problem for a singularly perturbed second-order ordinary differential equation for the case in which the degenerate (finite) equation has an identically double root. A specific feature of the asymptotics is the presence of a three-zone boundary layer. The solution of the boundary value problem is a stationary solution of the corresponding parabolic equation. We prove the asymptotic stability of this solution and find its attraction domain.     

An asymptotic expansion of the solution to a system of integrodifferential equations with exact asymptotics for the remainder

We obtain an asymptotic expansion of the solution to a system of first order integrodifferential equations taking into account the influence of the roots of the characteristic equation. We establish exact asymptotics for the remainder in dependence on the asymptotic properties of original functions.     

Asymptotic expansion of the solution of a matrix differential-difference equation of the general form

We obtain the asymptotic expansion of the solution of an inhomogeneous matrix differential-difference equation that belongs to the retarded or neutral type. The case of unbounded delays is considered. We take into account the influence of roots of the characteristic equation. An integral estimate of the remainder with a semimultiplicative weight is obtained depending on the semimultiplicative moment of the free matrix term in the equation.     

Behavior at infinity of a solution to a differential-difference equation

We obtain an asymptotic expansion for a solution to an mth order nonhomogeneous differential-difference equation of retarded or neutral type. Account is taken of the influence of the roots of the characteristic equation. The exact asymptotics of the remainder is established depending on the asymptotic properties of the free term of the equation.     

Asymptotic behavior for a cellular replication and maturation model

We consider a nonlocal first order partial differential equation with time delay that models simultaneous cell replication and maturation processes. We establish a comparison principle and construct monotone sequences to show the existence and uniqueness of the solution to the equation. We then analyze the asymptotic behavior of the solution via upper–lower solution technique.     

Construction of global‐in‐time solutions to Kolmogorov‐Feller pseudodifferential equations with a small parameter using characteristics

Using an idea going back to Madelung, we construct global in time solutions to the transport equation corresponding to the asymptotic solution of the Kolmogorov‐Feller equation describing a system with diffusion, potential and jump terms. To do that we use the construction of a generalized delta‐shock solution of the continuity equation for a discontinuous velocity field. We also discuss corresponding problem of asymptotic solution construction (Maslov tunnel asymptotics).     

Numerical Eulerian method for linearized gas dynamics in the high frequency regime

We study the propagation of an acoustic wave in a moving fluid in the high frequency regime. We calculate the asymptotic approximation of the solution, around a mean flow, of this problem using an Eulerian method. By introducing the stretching matrix (deformation tensor for the geometrical optics rays) of the linearized Euler system, we deduce the geometrical spreading. This quantity is the key tool for computing the leading order term of the asymptotic expansion thanks to a conservation equation along the group velocity. The main contribution is to construct and implement a numerical scheme in the Eulerian framework for the eikonal equation and for the transport equation on the stretching matrix. We present numerical results for several test cases to study the convergence and validate our approach.     

Perturbation of a singular solution to the Liouville equation

We construct an asymptotic (with respect to a small parameter) solution of the Cauchy problem for the perturbed Liouville equation in the case where the unperturbed solution has singularities on timelike lines. We propose a modification of the Krylov-Bogoliubov method that, in particular, allows us to find the asymptotic corrections to the singularity lines. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 118, No. 3, pp. 390–397, March, 1999.     

Asymptotics of a solution of a discontinuous singularly perturbed Cauchy problem

We construct the asymptotic expansion of a solution of the Cauchy problem for a singularly perturbed system of differential equations whose right-hand side is discontinuous on a certain surface. We consider the case where the surface of discontinuity is crossed and estimate the remainder of the constructed asymptotic expansion.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 46, No. 11, pp. 1502–1508, November, 1994.The present work was supported by the Ukrainian State Committee on Science and Technology.     

The fluid-dynamic limit of the Broadwell model of the nonlinear Boltzmann equation in the presence of shocks

This paper studies the asymptotic equivalence of the Broadwell model of the nonlinear Boltzmann equation to its corresponding Euler equation of compressible gas dynamics in the limit of small mean free path ε. It is shown that the fluid dynamical approximation is valid even if there are shocks in the fluid flow, although there are thin shock layers in which the convergence does not hold. More precisely, by assuming that the fluid solution is piecewise smooth with a finite number of noninteracting shocks and suitably small oscillations, we can show that there exist solutions to the Broadwell equations such that the Broadwell solutions converge to the fluid dynamical solutions away from the shocks at a rate of order (ε) as the mean free path ε goes to zero. For the proof, we first construct a formal solution for the Broadwell equation by matching the truncated Hilbert expansion and shock layer expansion. Then the existence of Broadwell solutions and its convergence to the fluid dynamic solution is reduced to the stability analysis for the approximate solution. We use an energy method which makes full use of the inner structure of time dependent shock profiles for the Broadwell equations.     

Asymptotic behavior of the wave function of a system of several particles with pair interactions increasing at infinity

We construct an asymptotic representation of the wave functions of systems of two and three quantum particles with pair interactions increasing at infinity. We consider three-particle systems on the line and in the three-dimensional space. The eikonal and transport equations used to construct the asymptotic representation differ significantly from the corresponding equations in the case of decreasing potentials. We study the solution of the nonlinear eikonal equation in detail.