Alexandre N. Carvalho

Attractors for infinite-dimensional non-autonomous dynamical systems /

The pullback attractor.- Existence results for pullback attractors.- Continuity of attractors.- Finite-dimensional attractors.- Gradient semigroups and their dynamical properties.- Semilinear Differential Equations.- Exponential dichotomies.- Hyperbolic solutions and their stable and unstable manifolds.- A non-autonomous competitive Lotka-Volterra system.- Delay differential equations.-The Navier-Stokes equations with non-autonomous forcing.- Applications to parabolic problems.- A non-autonomous Chafee-Infante equation.- Perturbation of diffusion and continuity of attractors with rate.- A non-autonomous damped wave equation.- References.- Index.-

Attractors of parabolic problems with nonlinear boundary conditions. uniform bounds

The authors study the asymptotic behavior of solutions to a semilinear parabolic problem u t −div(a(x)∇u)+c(x)u=f(x,u) for u=u(x,t), t>0, x∈Ω⊂⊂R N , a(x)>m>0; u(x,0)=u 0 with nonlinear boundary conditions of the form u=0 on Γ 0 , and a(x)∂ n u+b(x)u=g(x,u) on Γ 1 , where Γ i are components of ∂Ω . Under smoothness and growth conditions which ensure the local classical well-posedness of the problem, they indicate some sign conditions under which the solutions are globally defined in time, and somewhat more strong dissipativeness conditions under which they possess a global attractor that captures the asymptotic dynamics of the system. After that the authors study the dependence of the attractors on the diffusion. For a(x)=a e (x) they show their upper semicontinuity on e . Throughout the paper they also pay special attention to the dependence of the estimates obtained on the domain Ω and show that in certain instances the L ∞ bounds on the attractors do not depend on the shape of Ω but rather on |Ω| .

Abstract parabolic problems with critical nonlinearities and applications to Navier-Stokes and heat equations

PARABOLIC PROBLEMS WITH CRITICAL NONLINEARITIES AND APPLICATIONS TO NAVIER-STOKES AND HEAT EQUATIONS JOSÉ M. ARRIETA AND ALEXANDRE N. CARVALHO Abstract. We prove a local existence and uniqueness theorem for abstract parabolic problems of the type ẋ = Ax+f(t, x) when the nonlinearity f satisfies certain critical conditions. We apply this abstract result to the Navier-Stokes and heat equations. We prove a local existence and uniqueness theorem for abstract parabolic problems of the type ẋ = Ax+f(t, x) when the nonlinearity f satisfies certain critical conditions. We apply this abstract result to the Navier-Stokes and heat equations.

LOCAL WELL POSEDNESS FOR STRONGLY DAMPED WAVE EQUATIONS WITH CRITICAL NONLINEARITIES

In this article the strongly damped wave equation is considered and a local well posedness result is obtained in the product space HQ(Q) X L 2 (il). The space of initial conditions is chosen according to the energy functional, whereas the approach used in this article is based on the theory of analytic semigroups as well as interpolation and extrapolation spaces. This functional analytic framework allows local existence results to be proved in the case of critically growing nonlinearities, which improves the existing results.

A general approximation scheme for attractors of abstract parabolic problems

We consider semilinear problems of the form u′ = Au + f(u), where A generates an exponentially decaying compact analytic C 0-semigroup in a Banach space E, f:E α → E is differentiable globally Lipschitz and bounded (E α = D((−A)α) with the graph norm). Under a very general approximation scheme, we prove that attractors for such problems behave upper semicontinuously. If all equilibrium points are hyperbolic, then there is an odd number of them. If, in addition, all global solutions converge as t → ±∞, then the attractors behave lower semicontinuously. This general approximation scheme includes finite element method, projection and finite difference methods. The main assumption on the approximation is the compact convergence of resolvents, which may be applied to many other problems not related to discretization.

Asymptotic behaviour of non-linear parabolic equations with monotone principal part

Abstract We consider non-linear parabolic equations with subdifferential principal part and give conditions under which they posses global attractors in spite of considering non-Lipschitz perturbations. The case of globally Lipschitz perturbations of a maximal monotone operator has been addressed in Boll. Un. Mat. Ital. B (8) 2 (2000) 693–706. In the case of perturbations which are not globally Lipschitz, the main difficulty is the lack of uniqueness of solutions which at first does not even allow us to define attractors. We overcome this difficulty for problems enjoying certain regularity and absorption properties that allow uniqueness of solutions after some time has been elapsed. The results developed here are applied to the case when the subdifferential operator is the p -Laplacian to obtain existence of attractors and the existence of periodic solutions.

Existence of pullback attractors for pullback asymptotically compact processes

Abstract This paper is concerned with the existence of pullback attractors for evolution processes. Our aim is to provide results that extend the following results for autonomous evolution processes (semigroups) (i) An autonomous evolution process which is bounded, dissipative and asymptotically compact has a global attractor. (ii) An autonomous evolution process which is bounded, point dissipative and asymptotically compact has a global attractor. The extension of such results requires the introduction of new concepts and brings up some important differences between the asymptotic properties of autonomous and non-autonomous evolution processes. An application to damped wave problem with non-autonomous damping is considered.

Stability of Gradient Semigroups Under Perturbations

In this paper we prove that gradient-like semigroups (in the sense of Carvalho and Langa (2009 J. Diff. Eqns 246 2646–68)) are gradient semigroups (possess a Lyapunov function). This is primarily done to provide conditions under which gradient semigroups, in a general metric space, are stable under perturbation exploiting the known fact (see Carvalho and Langa (2009 J. Diff. Eqns 246 2646–68)) that gradient-like semigroups are stable under perturbation. The results presented here were motivated by the work carried out in Conley (1978 Isolated Invariant Sets and the Morse Index (CBMS Regional Conference Series in Mathematics vol 38) (RI: American Mathematical Society Providence)) for groups in compact metric spaces (see also Rybakowski (1987 The Homotopy Index and Partial Differential Equations (Universitext) (Berlin: Springer)) for the Morse decomposition of an invariant set for a semigroup on a compact metric space).

Lower semicontinuity of attractors for non-autonomous dynamical systems

This paper is concerned with the lower semicontinuity of attractors for semilinear non-autonomous differential equations in Banach spaces. We require the unperturbed attractor to be given as the union of unstable manifolds of time-dependent hyperbolic solutions, generalizing previous results valid only for gradient-like systems in which the hyperbolic solutions are equilibria. The tools employed are a study of the continuity of the local unstable manifolds of the hyperbolic solutions and results on the continuity of the exponential dichotomy of the linearization around each of these solutions.

A GRADIENT-LIKE NONAUTONOMOUS EVOLUTION PROCESS

In this paper we consider a dissipative damped wave equation with nonautonomous damping of the form \begin{eqnarray*} \hspace*{2.057in}u_{tt}+\beta(t)u_t=\Delta u+f(u) \hspace*{2.057in} (1) \end{eqnarray*} in a bounded smooth domain Ω ⊂ ℝn with Dirichlet boundary conditions, where f is a dissipative smooth nonlinearity and the damping β : ℝ → (0, ∞) is a suitable function. We prove, if (1) has finitely many equilibria, that all global bounded solutions of (1) are backwards and forwards asymptotic to equilibria. Thus, we give a class of examples of nonautonomous evolution processes for which the structure of the pullback attractors is well understood. That complements the results of [Carvalho & Langa, 2009] on characterization of attractors, where it was shown that a small nonautonomous perturbation of an autonomous gradient-like evolution process is also gradient-like. Note that the evolution process associated to (1) is not a small nonautonomous perturbation of any autonomous gradient-like evolution proc...