A pacemaker, regularly emitting chemical waves, is created out of noise when an excitable photosensitive Belousov-Zhabotinsky medium, strictly unable to autonomously initiate autowaves, is forced with a spatiotemporal patterned random illumination. These experimental observations are also reproduced numerically by using a set of reaction-diffusion equations for an activator-inhibitor model, and further analytically interpreted in terms of genuine coupling effects arising from parametric fluctuations. Within the same framework we also address situations of noise-sustained propagation in subexcitable media.

The behavior of uncoupled chaotic systems under the influence of external noise has been the subject of recent work. Some of these studies claim that chaotic systems driven by the same noise do synchronize, while other studies contradict this conclusion. In this work we have undertaken an experimental study of the effect of noise on identically driven analog circuits. The main conclusion is that synchronization is induced by a nonzero mean of the signal and not by its stochastic character.

We report the experimental observation of Richardson dispersion and a double cascade in a thin horizontal fluid flow induced by Faraday waves. The energy spectra and the mean spectral energy flux obtained from particle image velocimetry data suggest an inverse energy cascade with Kolmogorov type scaling Ek$\propto${}k$\gamma${}, $\gamma${}$\approx${}-5/3 and an Ek$\propto${}k$\gamma${}, $\gamma${}$\approx${}-3 enstrophy cascade. Particle transport is studied analyzing absolute and relative dispersion as well as the finite size Lyapunov exponent (FSLE) via the direct tracking of real particles and numerical advection of virtual particles. Richardson dispersion with ⟨$\Delta${}R2(t)⟩$\propto${}t3 is observed and is also reflected in the slopes of the FSLE ($\Lambda${}$\propto${}$\Delta${}R-2/3) for virtual and real particles.

Wave propagation in a photosensitive, subexcitable Belousov-Zhabotinsky medium is made possible by periodic modulation of a homogeneous illumination field. The propagation can be understood in terms of an interplay between the radial expansion of the wave and the motion of its free ends as the excitability varies periodically. This description leads to a simple kinematic analysis that provides insights into the initial conditions and forcing parameters giving rise to sustained wave propagation.