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We construct a stable right inverse for the divergence operator in non-cylindrical domains in space-time. The domains are assumed to be H\"older regular in space and evolve continuously in time. The inverse operator is of Bogovskij type, meaning that it attains zero boundary values. We provide estimates in Sobolev spaces of positive and negative order with respect to both time and space variables. The regularity estimates on the operator depend on the assumed H\"older regularity of the domain. The results can naturally be connected to the known theory for Lipschitz domains. As an application, we prove refined pressure estimates for weak and very weak solutions to Navier--Stokes equations in time dependent domains., Comment: v3 final version after incorporating the referee's suggestions. To appear in Ann. PDE

International audience; We aim at extending the existence theory for the equation div v = f in a bounded or exterior domain with homogeneous Dirichlet boundary conditions, to a class of solutions which need not have a trace at the boundary. Typically, the weak solutions that we shall consider will belong to some Besov space B(p.q)(S)(Omega) with s epsilon (-1 + 1/p, 1/p). After generalizing the notion of a solution for this equation, we propose an explicit construction by means of the classical Bogovskii formula. This construction enables us to keep track of a "marginal" information about the trace of solutions. In particular, it ensures that the trace is zero if f is smooth enough. We expect our approach to be of interest for the study of ;rough solutions to systems of fluid mechanics. (C) 2011 Elsevier Inc. All rights reserved.

International audience; We formulate and solve the Poisson problem for the exterior derivative operator with Dirichlet boundary condition in Lipschitz domains, of arbitrary topology, for data in Besov and Triebel-Lizorkin spaces.

In this paper, we study the weighted Korn inequality on some irregular domains, e.g., s-John domains and domains satisfying quasihyperbolic boundary conditions. Examples regarding sharpness of the Korn inequality on these domains are presented. Moreover, we show that Korn inequalities imply certain Poincare inequality.