INTERFACE OSCILLATIONS IN REACTION-DIFFUSION SYSTEMS ABOVE THE HOPF BIFURCATION

We consider a reaction-diffusion system of the form {u(t) = epsilon(2)u(xx) + f(u, w) tau w(t) = Dw(xx) + g(u,w) with Neumann boundary conditions on a finite interval. Under certain generic conditions on the nonlinearities f, g and in the singular limit epsilon << 1 such a system may admit a steady state solution may admit a steady solution where u has sharp interfaces. It is also known that such interfaces may be destabilized due to a Hopf bifurcation [Y. Nishiura and M. Mimura. SIAM J. Appl. Math., 49:481-514, 1989], as tau is increase beyond a certain threshold tau(h.) In this paper, we study what happens for tau > tau(h,) or even tau -> infinity, for a solution that consists of either one or two interfaces. Under the additional assumption D >> 1, using singular perturbation theory, we determine the existence of another threshold tau(c) > tau(h) (where tau(c) is allowed to be infinite) such that if tau(h) < tau < tau(c) then the systems admits a solution consisting of periodically oscillating interfaces. On the other hand if tau > tau(c,) the extent of the oscillation eventually exceeds the spatial domain size, even though very long transient dynamics can preceed this occurence. We make use of recently developed numerical software (that employs adaptive error control in space and time) to accurately compute an approximate solution. Excellent agreement with the analytical theory is observed.