HOMOCLINIC CHAOS IN CHEMICAL-SYSTEMS

We first focus on complex dynamical phenomena generated by chemical kinetics in homogeneous media. We comment on the alternating sequences of periodic and chaotic states observed in some experiments on the Belousov-Zhabotinsky reaction when conducted in a continuously stirred tank reactor. We present numerical results obtained with a seven-variable Oregonator model which reproduce most of the features of the experimental sequences. We discuss the origin and the nature of the chemical chaos encountered along these sequences in terms of the chaotic orbits which exist on the way to homoclinicity. We construct Poincare map models which reduce to either multi-humped or multi-branched ID maps in the strong area contraction limit. We report on a recent experiment which provides evidence that the iteration scheme deduced from the time-series of ''spiral-type' strange attractors satistifies the symbolic dynamics predicted by Sil'nikov's theory of homoclinic chaos. We then investigate spatio-temporal pattern forming phenomena in a one-dimensional reaction-diffusion system with equal diffusion coefficients. When imposing a concentration gradient through the system, this model mimics the sustained stationary and periodically oscillating ''front structures'' observed in recent experiments conducted in an open Couette flow reactor. We emphasize the possibility that the oscillations of the spatial structure become chaotic. We report on numerical simulations of a diffusion-induced intermittent bursting phenomenon that is likely to be observed in bench experiments. We elaborate on the interpretation of this intermittent occurrence of spatially localized structures in an extended system in terms of Sil'nikov's homoclinic chaos.