Fast Selective Elimination of Spiral Waves

The Tris(2,2'-Bipyridyl)Ruthenium-Catalysed Belousov–Zhabotinsky Reaction

The Belousov – Zhabotinsky (BZ) reaction is the prototypical oscillating chemical reaction. The tris(2,2'-bipyridine)ruthenium-catalysed BZ reaction (often simply referred to as the ruthenium-catalysed BZ reaction) displays photosensitivity and has been widely exploited for examination of the effects of illumination on nonlinear reaction kinetics. In this review, we investigate the behaviour of the ruthenium-catalysed BZ reaction. The mechanism of the reaction is analysed and we examine how light sensitivity is incorporated into kinetic models of the reaction. The temporal dynamics of the photosensitive reaction is presented and, finally, we discuss the extraordinary wealth of behaviour that has been observed in the spatially-distributed system when perturbed by visible light.

Surfactant-induced gradients in the three-dimensional Belousov-Zhabotinsky reaction

Scroll waves are prominent patterns formed in three-dimensional excitable media, and they are frequently considered highly relevant for some types of cardiac arrhythmias. Experimentally, scroll wave dynamics is often studied by optical tomography in the Belousov-Zhabotinsky reaction, which produces CO(2) as an undesired product. Addition of small concentrations of a surfactant to the reaction medium is a popular method to suppress or retard CO(2) bubble formation. We show that in closed reactors even these low concentrations of surfactants are sufficient to generate vertical gradients of excitability which are due to gradients in CO(2) concentration. In reactors open to the atmosphere such gradients can be avoided. The gradients induce a twist on vertically oriented scroll waves, while a twist is absent in scroll waves in a gradient-free medium. The effects of the CO(2) gradients are reproduced by a numerical study, where we extend the Oregonator model to account for the production of CO(2) and for its advection against the direction of gravity. The numerical simulations confirm the role of solubilized CO(2) as the source of the vertical gradient of excitability in reactors closed to the atmosphere.

Survival versus collapse: abrupt drop of excitability kills the traveling pulse, while gradual change results in adaptation

Excitable media show changes in their basic characteristics that reflect temporal changes in the environment. In the photosensitive Belousov-Zhabotinsky (BZ) reaction, excitability is decreased by illumination. We found that a traveling pulse failed to propagate when a certain level of light intensity was switched on abruptly, but the pulse continued propagating when the light intensity reached the same level gradually. We investigated the mechanism of adaptation of pulse propagation to the change in light intensity using two mathematical models, the Oregonator model (a specific model for the photosensitive BZ reaction), and the FitzHugh-Nagumo model (a generic model for excitable media). The appearance of a characteristic such as adaptation is shown to be a general feature for a traveling pulse in excitable media.

Desensitization effects in the ruthenium-catalyzed Belousov-Zhabotinsky reaction

The influence of visible light on the velocities of spiral waves in the [Ru(bpy)](3)(2+) -catalyzed Belousov-Zhabotinsky (BZ) reaction is well documented. However, there are only few reports showing the effect of the way a change in the applied intensity is made, or on "desensitization" or "memory" type phenomena. In this paper, we present observations showing significant changes in spiral tip dynamics without varying the light intensity during the course of the experiments. We produce further evidence showing that changes in wave velocity and inhibitory effects are depending on whether the increase in intensity is applied in one large step or in a number of smaller steps. Also, the tip trajectories before and after the spiral waves have been subjected to an increase and subsequent decrease in intensity levels are different, suggesting a change in excitation of the system. The experimental results are separated into two groups depending on the light sensitivity of the system and the behavior of the spiral tip. Simulation results demonstrate that the different tip trajectories observed in the experiments can be modeled by only varying the excitation threshold. Our observations indicate that there must be at least two different competing pathways for the reaction mechanism not only in the oscillatory BZ system but also in excitable media and that intermediates may also play an important part in determining the excitation of the system and not just the initial concentrations of the reactants.