Intricate patterns of wave propagation are exhibited in a chemical reaction-diffusion system with spatiotemporal feedback. Wave behavior is controlled by feedback-regulated excitability gradients that guide propagation in specified directions. Waves interacting with boundaries and with other waves are observed when interaction terms are incorporated into the control algorithm. Spatiotemporal feedback offers wide flexibility for designing and controlling wave behavior in excitable media.

Propagating wave segments are stabilized to a constant size and shape by applying negative feedback from the measured wave area to the excitability of the medium. The locus of steady-state wave size as a function of excitability defines the perturbation threshold for the initiation of spiral waves. This locus also defines the excitability boundary for spiral wave behavior in active media.

Solid-state NMR spectroscopy is used to characterize the interaction of L-cysteine with gold nanoparticles. The experiments show that there are two types of cysteine in the gold-cysteine complex, with nearly equal populations. We postulate that cysteine forms a two-layer boundary around the gold nanoparticles. The first layer is made of cysteine molecules forming a thiolate bond with the gold surface and having its charged amino and carboxyl groups oriented away from the gold surface. The second layer has its amino and carboxyl groups oriented toward the first layer and its sulfur group oriented away from the gold particles.

We characterize the spatiotemporal evolution of a photosensitive Belousov-Zhabotinsky medium that is made up of coupled oscillatory cells with randomly distributed frequencies. The medium evolves from an initial state of multiple wave sources to a synchronized state governed by a single wave source. The synchronization occurs via a competition between the sources, which arises when the oscillators are not identical but have slightly different natural frequencies. The evolution of each cell is monitored to demonstrate frequency and phase synchronization of the inhomogeneous cellular medium, and a simple kinematic description for the advance of the phase-diffusion wave is presented.

The synchronization of two distributed Belousov-Zhabotinsky systems is experimentally and theoretically investigated. Symmetric local coupling of the systems is made possible with the use of a video cameraprojector scheme. The spatial disorder of the coupled systems, with random initial configurations of spirals, gradually decreases until a final state is attained, which corresponds to a synchronized state with a single spiral in each system. The experimental observations are confirmed with numerical simulations of two identical Oregonator models with symmetric local coupling, and a systematic study reveals generalized synchronization of spiral waves. Several different types of synchronization attractors are distinguished. DOI: 10.1103/PhysRevE.68.026205 PACS number͑s͒: 82.40.Qt, 05.45.Xt, 05.65.ϩb, 47.54.ϩr Synchronization phenomena are of fundamental importance in physical, chemical, biological, and technical systems. The synchronization of coupled chaotic oscillators has attracted much attention in recent years, and complete, phase, lag, and generalized synchronization have been distinguished in such systems ͓1͔. These concepts have been applied in the analysis and interpretation of experimental data from the cardiorespiratory system ͓2͔, paddlefish cells ͓3͔, the human brain ͓4͔, and in the contexts of population dynamics ͓5͔ and communication with chaotic lasers ͓6͔. Recently, synchronization phenomena in spatially extended systems have attracted increasing attention. Identical synchronization and phase synchronization have been observed in systems exhibiting spatiotemporal chaos ͓7-9͔.In this paper, we describe experimental and theoretical studies of the synchronization of two locally coupled domains of excitable media exhibiting spiral wave behavior. We have used the photosensitive Belousov-Zhabotinsky ͑BZ͒ reaction ͓10͔, which is particularly convenient for studies on influencing existing patterns or generating new ones by the application of various types of external forcing ͓11-13͔, or by local ͓14͔, nonlocal ͓15͔, or global ͓16͔ feedback mechanisms. The identical synchronization of chemical wave patterns has been previously observed in a BZ system with diffusive cross-membrane coupling ͓17͔. Here we study two domains of excitable media that are locally coupled to each other by means of a video camera-video projector setup through a coupling algorithm, which leads to weaker than identical synchronization ͓18͔.Prior to each experiment, the projected image was adjusted at each pixel by an iterative algorithm to ensure a spatially uniform illumination field, upon which all subsequent projected images were based. The local concentration of oxidized catalyst was recorded with a video camera, and the recorded image was divided into an array of square cells. In all experiments, the lateral size of each cell was much smaller than the spiral wavelength. The medium was partitioned into two square regions separated and surrounded by an unexcitable boundary generated with high-intensity light. The corresponding...