Echoes are not limited to sound reflecting off cave walls. A similar phenomenon—a delayed response following an immediate response to some stimulus—can occur after coupled oscillators are stimulated by a sequence of two input pulses. Researchers have now observed such an echo phenomenon in a system of coupled chemical oscillators.
Edward Ott of the University of Maryland in College Park, Kenneth Showalter of West Virginia University in Morgantown, and their colleagues studied a standard oscillating chemical system known as the Belousov-Zhabotinsky reaction. This light sensitive reaction involves transitions between an opaque state and one that transmits light. The team fixed more than 1000 tiny beads containing the relevant chemicals in a setup that allowed the beads—each with its own oscillation frequency—to be individually illuminated and the light transmitted through each bead to be separately detected.