Asymptotic expansion of a semi-Markov random evolution

We determine the regular and singular components of the asymptotic expansion of a semi-Markov random evolution and show the regularity of boundary conditions. In addition, we propose an algorithm for finding initial conditions for t = 0 in explicit form using the boundary conditions for the singular component of the expansion. __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, No. 9, pp. 1234–1248, September, 2006.     

On the application of the method of matching asymptotic expansions to a singular system of ordinary differential equations with a small parameter

We consider a bisingular initial value problem for a system of ordinary differential equations with a single small parameter, the asymptotics of whose solution can be constructed in the form of power-logarithmic series on several boundary layers and an external layer. To use the method of matching asymptotic expansions, we prove theorems that permit one to make the passage between two adjacent layers and obtain a uniform estimate of the approximation to the solution by a composite asymptotic expansion.     

Behaviour of the Landau–Lifschitz equation in a ferromagnetic wire

Following a suggestion from A. Thiaville and J. Miltat, whose work and experiments are about ferromagnetic thin layers and nanowires, we study in this paper the behaviour of the Landau–Lifschitz equation in a straight ferromagnetic wire. As the diameter of the domain and the exchange coefficient in the equation simultaneously tend to zero, we perform an asymptotic expansion to precise the solution for well‐prepared initial conditions and are led to consider 2D exterior problems. Copyright © 2008 John Wiley & Sons, Ltd.     

On a singularly perturbed initial value problem in the case of a double root of the degenerate equation

We study the initial value problem of a singularly perturbed first order ordinary differential equation in case that the degenerate equation has a double root. We construct the formal asymptotic expansion of the solution such that the boundary layer functions decay exponentially. This requires a modification of the standard procedure. The asymptotic solution will be used to construct lower and upper solutions guaranteeing the existence of a unique solution and justifying its asymptotic expansion.     

On singular solutions of the initial boundary value problem for the Stokes system in a power cusp domain

The initial boundary value problem for the non-steady Stokes system is considered in bounded domains with the boundary having a peak-type singularity (power cusp singularity). The case of the boundary value with a nonzero time-dependent flow rate is studied. The formal asymptotic expansion of the solution near the singular point is constructed. This expansion contains both the outer asymptotic expansion and the boundary-layer-in-time corrector with the ‘fast time’ variable depending on the distance to the cusp point. The solution of the problem is constructed as the sum of the asymptotic expansion and the term with finite energy.     

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.     

Asymptotic expansion of solutions to the drift-diffusion equation with large initial data

We consider the large-time behavior of the solution to the initial value problem for the Nernst-Planck type drift-diffusion equation in whole spaces. In the Lp-framework, the global existence and the decay of the solution were shown. Moreover, the second-order asymptotic expansion of the solution as t→∞ was derived. We also deduce the higher-order asymptotic expansion of the solution. Especially, we discuss the contrast between the odd-dimensional case and the even-dimensional case.     

Initial layers and zero‐relaxation limits of multidimensional Euler–Poisson equations

In this paper, we consider zero‐relaxation limits for periodic smooth solutions of the time‐dependent Euler–Poisson system. For well‐prepared initial data, we construct an approximate solution by an asymptotic expansion up to any order. For ill‐prepared initial data, we construct initial layer corrections in an explicit way. In both cases, the asymptotic expansions are valid in a time interval independent of the relaxation time, and their convergence is justified by establishing uniform energy estimates. Copyright © 2012 John Wiley & Sons, Ltd.     

非线性奇摄动抛物型方程初值问题的套层解

运用了初始层函数构造了一类非线性奇摄动抛物型方程初值问题解的渐近展开式,并证明了该展开式达到任意精度的一致有效性.     

The Blowup Mechanism of Small Data Solutions for the Quasilinear Wave Equations in Three Space Dimensions

For a class of three-dimensional quasilinear wave equations with small initial data, we give a complete asymptotic expansion of the lifespan of classical solutions, that is, we solve a conjecture posed by John and Hörmander. As an application of our result, we show that the solution of three-dimensional isentropic compressible Euler equations with irrotational initial data which are a small perturbation from a constant state will develop singularity in the first-order derivatives in finite time while the solution itself is continuous. Furthermore, for this special case, we also solve a conjecture of Alinhac.     

Finite-time relaxation of the solution of a nonlinear pseudoparabolic equation

A model equation is considered that describes the relaxation of an initial perturbation in a crystalline semiconductor in the case when its electrical conductivity depends nonlocally on the field. For certain initial parameters, the effect of finite-time “cooling” is proved to occur. For other parameters, the first term of the long-time asymptotics is found and the remainder of the asymptotic expansion is estimated.     

Initial layers and zero-relaxation limits of Euler–Maxwell equations

In this paper we consider zero-relaxation limits for periodic smooth solutions of Euler–Maxwell systems. For well-prepared initial data, we propose an approximate solution based on a new asymptotic expansion up to any order. For ill-prepared initial data, we construct initial layer corrections in an explicit way. In both cases, the asymptotic expansions are valid in time intervals independent of the relaxation time and their convergence is justified by establishing uniform energy estimates.     

等离子体中带小参数的高维流体动力学双极模型的渐近展开(英文)

通过渐近展开的方法,研究了等离子体中带小参数的双极Euler-Poisson方程的拟中性极限和零松弛时间极限问题.对于每一个极限,只要具有好准备的初值,就可以得到任意阶渐近展开的存在唯一性,并在最后讨论了这些极限的验证问题.     

Properties of solutions of a nonlinear system of equations

The objective of this paper is to study a highly general model system of nonlinear equations that describe propagation of nerve impulses in a cell. We prove time-local existence of a classical solution, derive sufficient conditions for the existence of a time-global solution, and consider the question of eventual smoothing of discontinuous initial values. The large-time asymptotic expansion of the solutions of the Cauchy problem is constructed. The coefficients of the principal term of the asymptotic expression for the solution of the Cauchy problem are computed in terms of the Fourier transform of the initial values.The study has been partially supported by the Russian Foundation of Basic Research (93-011-131).Translated from Nelineinye Dinamicheskie Sistemy: Kachestvennyi Analiz i Upravlenie — Sbornik Trudov, No. 3, pp. 64–93, 1993.     

Asymptotic analysis for a particle transport problem in a moving medium

In this paper we discuss the derivation of the diffusion theoryfor a linear particle transport in a moving gas. We performthe asymptotic analysis for a one-dimensional linear BGK modelproblem with a shifting Maxwellian which describes the timeevolution of the spatially dependent electron distribution functionin a moving weakly ionized host medium. The modified (compressed)Chapman-Enskog expansion procedure is applied to find the asymptoticsolution for small mean free path , showing that the differencebetween the exact and asymptotic solutions is of order ², uniformlyin time for arbitrary initial data.     

A method of asymptotic expansion of an m-parameter family of solutions for a quasilinear system of differential equations

By using the method of asymptotic expansion of anm-parameter family of solutions, we obtain the asymptotic expansion of solutions of a quasilinear system of differential equations. Institute of Mathematics, Ukrainian Academy of Sciences, Kiev. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 3, pp. 445–450, March, 1998.     

奇摄动分数阶微分方程的渐近解

本文研究了一类奇摄动非线性分数阶微分方程初值问题.利用伸长变量构造出解的形式展开式,并利用微分不等式理论,证明了解的一致有效的渐近式.所得的结果具有较好精度的近似解.     

Asymptotic solution of a quasistatic thermoelasticity problem for a slender rod

An asymptotic expansion is constructed for solving a quasistatic thermo-elasticity problem for a slender cylindrical rod in the presence of mass forces and non-linear heat sources. The algorithm for constructing the asymptotic form, based on the method of boundary functions, is fairly simple and convenient for carrying out numerical calculations. A deduction is made on the basis of the asymptotic form constructed on how to select correctly a simplified one-dimensional model so as to obtain a better approximation for the solution of the initial two-dimensional problem. An existence theorem for the solution is proved under certain conditions.     

Asymptotic Expansion for the Null Distribution of the <Emphasis Type="Italic">F</Emphasis>-statistic in One-way ANOVA under Non-normality

In this paper we derive the asymptotic expansion of the null distribution of the F-statistic in one-way ANOVA under non-normality. The asymptotic framework is when the number of treatments is moderate but sample size per treatment (replication size) is small. This kind of asymptotics will be relevant, for example, to agricultural screening trials where large number of cultivars are compared with few replications per cultivar. There is also a huge potential for the application of this kind of asymptotics in microarray experiments. Based on the asymptotic expansion we will devise a transformation that speeds up the convergence to the limiting distribution. The results indicate that the approximation based on limiting distribution are unsatisfactory unless number of treatments is very large. Our numerical investigations reveal that our asymptotic expansion performs better than other methods in the literature when there is skewness in the data or even when the data comes from a symmetric distribution with heavy tails.     

Initial Opening of a Compressor Valve

The initial opening of a compressor valve is investigated. The motion of the valve plate is essentially determined by the pressure distribution in the valve gap. Since the initial gap is extremly narrow a conventional CFD solution fails. Therefore the initial stages of the opening process are modelled by using an asymptotic expansion with respect to a small asepct ratio of the valve gap. The purpose of the analysis is to provide an initial condition for a CFD simulation of the valve dynamics. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)