Nous etudions le probleme du transfer de la chaleur dans unfluide incompressible, sous l'approximation de Boussinesq.Nous etudions le comportement des solutions dans laregion parabolique $|x|>!!>t^{1/2}$ : notre analyse montreque certaines normes $L^p$ des solutions, et notamment la norme d'energie,deviennent arbitrairement grandes en temps long.Il s'agit d'un travail en collaboration avec Maria Schonbek (UCSC).

I will present an atomic-to-continuum derivation in nonlinearelasticity. The atomistic model is based on a two-body interactionenergy, with a potential of the Lennard-Jones type. Performing apointwise Taylor expansion, we obtain a continuum model that predictselastic energy, sharp-interface energy and smooth-interface energy. Thisalso gives a method to describe the configuration of the atoms betweentwo consecutive sharp interfaces, which qualitatively agrees withexperiments in Ni-Mn alloys presenting microstructure.