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Phase shifts between four Belousov-Zhabotinsky (BZ) oscillators are applied to encode phase patterns in an experimental network consisting of four reactors. Oscillations are established in a focus of the BZ reaction, which is sinusoidally driven by an applied electrical current. In addition to the global electrical coupling by the sinusoidal function the four reactors are electrically coupled by an optimized feedback function including time delay. Two of three possible phase patterns can be encoded in this Hopfield-type network of four reactors. With a phase pattern in which all four reactors are in-phase, one of the two stored phase patterns is recalled with a 50% probability. This indicates that the two encoded patterns have the same dynamic stability. It is possible to reversibly switch between the two patterns by adding Ce 4+ solution. Higher order phase patterns permit a higher phase resolution. The phase method provides for a large amount of information to be stored and recalled in a multiunit network. Numerical calculations with the seven-variable Györgyi-Field model of the BZ reaction are in good agreement with the experimental results. Generic similarities with the so-called binding problem in neurology are discussed.

The effect of the stirring rate and stirring sense on the bifurcation points of the mcillatory domain of the minimal bromate system in a stirred flow reactor is studied experimentally and computationally using nonpremixed feedstrcams. Stirring below -lo00 rpm shifts both the "lower" (supercritical) and the 'upper" (subcritical) Hopf bifurcations to higher values of the flow rate as the stirring rate is decreased. The position of the Hopf bifurcations as well as the size of the oscillatory domain were also affected when the fedstreams were permuted or, alternatively, when the direction of stirring was r e v e d . The positions of the Hopf bifurcations were no longer affected at high stimng rates (>-lo00 rpm), but they showed different limiting values depending on which in-flow configurations or stirring sense was used. This behavior is confirmed by a phenomenological stirring model that assumt8 the presence of small subvolumes in the immediate vicinity of the entry ports.The stirring sense is introduced in the model by an inequality in the mass exchange rates between the subvolumes. IntroductionStudies of stirring and mixing processes in a continuous-flow stirred tank reactor (CSTR) have shown that even in well-stirred local concentration gradients exist, and the case of ideal mixing cannot be attained. Local variations in electrode potentials in the reactive C102-/I-system were found using movable microelectrodes.' Fluctuations in this system were also detected by UV absorption.2 The mixing process of two nonreactive liquids was investigated by CARS This noninvasive method, which does not interfere with the turbulent flow, has excellent temporal and spatial resolution at constant temperature. Pronounced concentration gradients occurring in the vicinity of the entering ports were found which are compatible with the existence of substantial heterogeneities in the domains close to the inflow ports, in which the entering reactants exhibit higher concentrations than in the bulk. The heterogeneities are subsequently dissipated by vigorous stirring of the solution within the CSTR, when the flow is stopped.Imperfect mixing can strongly affect the dynamics of nonlinear systems. The dependence of transitions between different stationary states of bistable systems on the stirring rate has been extensively studied both experimentally and computationally in the minimal bromate system,>I0 the C102-/1-reaction,"-I6 the C102-/S2032-system," the I03-/H3As03 reaction,'8-20 the Yautocatalatorn,21 and the Schlbgl model?2-24 The critical flow rates, at which transitions between multiple steady states take place, have been seen to vary considerably with changes in the stirring rate. Changing the stirring rate has even led to the onset of completely new dynamical features:21 Oscillations were induced in the C102-/I-r e a c t i~n , '~~'~ whereas computations of the H3As03/I03-system show tristability.20 Transitions from periodic to aperiodic regimes were reported in the Belousov-Zhabotinskii (BZ) reaction in a CSTR when the stirring rat...

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