%e report the experimental observation of a sustained standing nonequilibrium chemical pattern in a single-phase open reactor. Considering the properties of the pattern (symmetry breaking, intrinsic wavelength), it is interpreted as the first unambiguous experimenta. evidence of a Turing structure.

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Experimental studies of the formation of Turing patterns in the (chlorine dioxide, iodine, malonic acid) reaction are performed in a spatial open gel disk reactor where all the input species are fed onto one side by a continuous stirred tank reactor. This setup is shown to fit the pool-chemical approximation used in most theoretical approaches. Nonequilibrium phase diagrams are established as a function of concentrations in the input flows. In agreement with theoretical predictions, the location of the transition from uniform steady states to Turing patterns is found to be almost independent of the concentrations of the complexing agent which controls the effective diffusion of activatory species. Extensive analytical and numerical calculations in two and three dimensions are performed on the basis of the Lengyel-Ra ´bai-Epstein kinetic model and its two-variable reduction. This particular experimental configuration is shown to minimize the problems encountered with more commonly used versions of spatial open reactors. In standard conditions, the quantitative agreement with the experiments is excellent in regard to the sketchiness of the model. Finally, we discuss the role of boundary conditions and comment on problems they raise in the use of one-side-fed open spatial reactors.

We show both experimentally and numerically that the time scales separation introduced by long range activation can induce oscillations and excitability in nonequilibrium reaction-diffusion systems that would otherwise only exhibit bistability. Namely, we show that in the ChloriteTetrathionate reaction, where the autocalytic species H + diffuses faster than the substrates, the spatial bistability domain in the nonequilibrium phase diagram is extended with oscillatory and excitability domains. A simple model and a more realistic model qualitatively account for the observed dynamical behavior. The latter model provides quantitative agreement with the experiments.