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Control of Complex Travelling Waves in Simple Inorganic Systems: The Potential for Computing
B. P. J. de Lacy Costello

We show that it is possible to control the initiation of travelling circular and spiral waves in a simple inorganic chemical reaction. The reaction is incredibly simple being based on the addition of a 2.5M solution of sodium hydroxide to an agarose gel loaded with Aluminium hydroxide (0.25–0.34 M). Under normal reaction conditions [AlCl30.28–0.34M] described in [A. Volford et al. Pattern Formation and Self Organisation in a Simple Precipitation System, Langmuir, 2007, 23(3) 961–964.] moving precipitate waves in the form of self-organised double spiral waves and simple circular fronts can be observed. These structures appear qualitatively similar to those observed in the classical BZ reaction but the evolution at the concentration ranges described is spontaneous. This paper describes a simple method for controlling the initiation of these waves by lowering the “excitability” of the system. In addition to controlling wave evolution we were able to observe collisions between mobile fragments of travelling precipitate waves. The significance of this observation is that schemes developed to describe collision based computing phenomena in complex reactions such as the BZ reaction can be applied within very simple chemical systems.We postulate that the control of such simple inorganic systems would be useful for a class of specialised chemical processors where the synthesis of useful materials via the inherent self-assembly mechanism constitutes the result of the computation.

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