The drift of spiral waves toward regions of higher light intensity was observed experimentally in the ruthenium-catalyzed Belousov-Zhabotinsky reaction. A light gradient can thus be used to manipulate optical information in new computational systems based on photochemical media. The drift of a gradient that is rotationally invariant in space is three to four times as fast as that of a translationally invariant gradient. Simulations based on the use of a cellular automaton, which is made isotropic by a semirandom distribution of cells, are in agreement with the experimental results.
We present experimental evidence for a "granular clock." We use a setup in which vertical vibrations (10-20 Hz) of a bidisperse granular medium cause horizontal oscillations (periods in the order of minutes) between two connected compartments. Moreover, we present the first experimental evidence for full segregation of smaller particles into one compartment, leaving the larger ones in the other compartment. Simulations, using a simple model, describe phenomenologically the observed oscillations.
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