Before revision:  Here we describe a possible physical mechanism for this distinctive set of dynamic transformations . Starting from the observation that excitable reaction-diffusion models of chemical systems can describe both localized spots and traveling waves, we augment one such model with a variable describing the spatial orientation of its chief constituent .
After revision:  Here we describe a possible physical mechanism for this distinctive set of dynamic transformations . Starting from the observation that excitable reaction-diffusion models of chemical systems can describe both localized spots and traveling waves, we augment one such model with a field describing the spatial orientation of its chief constituent .