A nonlinear singular perturbation problem

We show how the approach of Yosida approximation of the derivative serves to obtain new results for evolution systems. Using this method we obtain multivalued time dependent perturbation results. Additionally, translation invariant subspaces $Y$ of the bounded and uniformly continuous functions are considered, to obtain criteria for the existence of solutions $u\in Y$ to the equation $$ u^{\prime}(t)\in A(t)u(t)+ \om u(t) + f(t), t\in \re, $$ or of solutions $u$ asymptotica...

This is a correction to our article in the Journal of Differential Equations, Volume 76(1988).

The article deals with gradient-like iterative methods for solving nonlinear operator equations on Hilbert and Banach spaces. The authors formulate a general principle of studying such methods. This principle allows to formulate simple conditions of convergence of the method under consideration, to estimate the rate of this convergence and to give effective a priori and aposteriori error estimates in terms of a scalar function that is constructed on the base of estimates for ...

In recent years, many papers have been devoted to the regularity of doubly nonlinear singular evolution equations. Many of the proofs are unnecessarily complicated, rely on superfluous assumptions or follow an inappropriate approximation procedure. This makes the theory unclear and quite chaotic to a nonspecialist. The aim of this paper is to fix all the misprints, to follow correct procedures, to exhibit, possibly, the shortest and most elegant proofs and to give a complete ...

A sufficient condition for asymptotic stability of the zero solution to an abstract nonlinear evolution problem is given. The governing equation is $\dot{u}=A(t)u+F(t,u),$ where $A(t)$ is a bounded linear operator in Hilbert space $H$ and $F(t,u)$ is a nonlinear operator, $\|F(t,u)\|\leq c_0\|u\|^{1+p}$, $p=const >0$, $c_0=const>0$. It is not assumed that the spectrum $\sigma:=\sigma(A(t))$ of $A(t)$ lies in the fixed halfplane Re$z\leq -\kappa$, where $\kappa>0$ does not dep...

Assume that $Au=f,\quad (1)$ is a solvable linear equation in a Hilbert space $H$, $A$ is a linear, closed, densely defined, unbounded operator in $H$, which is not boundedly invertible, so problem (1) is ill-posed. It is proved that the closure of the operator $(A^*A+\a I)^{-1}A^*$, with the domain $D(A^*)$, where $\a>0$ is a constant, is a linear bounded everywhere defined operator with norm $\leq 1$. This result is applied to the variational problem $F(u):= ||Au-f||^2+\a |...

We consider perodic homogenization of boundary value problems for quasilinear second-order ODE systems in divergence form of the type $a(x,x/\varepsilon,u(x),u'(x))'= f(x,x/\varepsilon,u(x),u'(x))$ for $x \in [0,1]$. For small $\varepsilon>0$ we show existence of weak solutions $u=u_\varepsilon$ as well as their local uniqueness for $\|u-u_0\|_\infty \approx 0$, where $u_0$ is a given non-degenerate solution to the homogenized boundary value problem, and we describe the rate ...

Convergence of the solutions of nonhomogeneous linear singularly perturbed systems to that of the corresponding reduced singular system on the half-line [0, $\infty $) is considered. To include the situation on a neighborhood of initial instant, a boundary layer, a distributional approach to convergence is adopted. An explicit analytical expression for the limit as a distribution is proved.

Let $A$ and $A_{1}$ are unbounded selfadjoint operators in a Hilbert space $\mathcal{H}$. Following \cite{AK} we call $A_{1}$ a \textit{singular} perturbation of $A$ if $A$ and $A_{1}$ have different domains $\mathcal{D}(A),\mathcal{D}(A_{1})$ but $\mathcal{D}(A)\cap\mathcal{D}(A_{1})$ is dense in $\mathcal{H}$ and $A=A_{1}$ on $\mathcal{D}(A)\cap\mathcal{D}(A_{1})$. In this note we specify without recourse to the theory of selfadjoint extensions of symmetric operators the co...

The paper deals with a Dirichlet spectral problem for a singularly perturbed second order elliptic operator with rapidly oscillating locally periodic coefficients. We study the limit behaviour of the first eigenpair (ground state) of this problem. The main tool in deriving the limit (effective) problem is the viscosity solutions technique for Hamilton-Jacobi equations. The effective problem need not have a unique solution. We study the non-uniqueness issue in a particular cas...