WELL-POSEDNESS OF A FREE BOUNDARY PROBLEM IN THE LIMIT OF SLOW-DIFFUSION FAST-REACTION SYSTEMS

We consider a free boundary problem obtained from the asymptoticlimit of a FitzHugh-Nagumo system, or more precisely, a slow-diffusion, fast-reaction equation governing a phase indicator, coupled with an ordinary differential equation governing a control variable v. In the range （-1, 1）, the v value controls the speed of the propagation of phase boundaries （interfaces） and in the mean time changes with dynamics depending on the phases. A new feature included in our formulation and thus made our model different from most of the contemporary ones is the nucleation phenomenon： a phase switch occurs whenever v elevates to 1 or drops to -1. For this free boundary problem, we provide a weak formulation which allows the propagation, annihilation, and nucleation of interfaces, and excludes interfaces from having （spacetime） interior points. We study, in the one space dimension setting, the existence, uniqueness, and non-uniqueness of weak solutions. A few illustrating examples are also included.