The hydrogen peroxide-thiosulfate-Cu2+ reaction operated in a continuous flow stirred tank reactor is a pH-oscillator known to provide three different steady states, hysteresis, and oscillations. In addition to the various dynamical regimes established earlier, a question arises whether the reaction can be also excitable, whereby the system strongly responds to a small but supercritical external addition of certain chemical species. We carried out experiments aimed at finding excitability and studying response dynamics to single and repeated pulsed perturbations of varying amplitude and period. We found that the reaction displays a remarkable excitatory dynamics when forced. The available mechanism of the reaction involves several adjustable parameters, which need to be tuned so that the model corresponds to experimentally observed bifurcation diagrams. Our experimental findings are compared with numerical calculations, suggesting that the model is far from complete.
We present results of experiments focused on emergent and cooperative dynamics in a system of two coupled flow-through stirred reaction cells with diffusion-like mass exchange and a strongly nonlinear chemical reaction between hydrogen peroxide and thiosulphate catalysed by cupric ions in diluted solution of sulphuric acid. Due to complex mechanism, in which a crucial role is played by hydrogen and/or hydroxide ions, dynamics in a single cell entail multiple stationary states, excitability and oscillations conveniently indicated by measuring pH. When coupled, the system shows a plethora of dynamical regimes depending on the coupling strength and flow rate. Under certain conditions both cells display dynamics close to that in the absence of coupling, but majority of the regimes are emergent and cannot be deduced from dynamics of decoupled reactors. The most prominent is a stationary state maintaining highly acidic values of pH in one of the reactors and weakly acidic in the other. When each cell is set to display excitability and the coupled system is externally perturbed, the cells may cooperate and transmit excitations elicited by pulsed perturbations in one cell to the other. Periodic pulses induce firing patterns marked by a various degree of propagated excitations and by being periodic or irregular.
Bromate-sulfite-ferrocyanide reaction operated in the CSTR is sensitive to small but supercritical additions of either acid or base. When operated at two different kinds of steady states, this dynamical feature gives rise to activatory or inhibitory excitability. Spontaneous periodic oscillations are also sensitive to such perturbations. Periodically repeated pulse additions elicit a pattern of excitatory or oscillatory spikes that depends on the period and amplitude of the perturbations. These firing patterns are characterized by firing number defined as an average number of firings per a forcing period. Experiments with periodically pulsed additions of H + , OH -, and SO 3 2provide one-parameter and two-parameter firing diagrams. Recently, a detailed model has been formulated; using this model, we study global dynamics of the response by calculating firing diagrams under conditions corresponding to experiments. The experimental results are compared with calculations.
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