COUPLED EXCITABLE CELLS

An experimental system of two continuous stirred tank reactor cells mutually coupled via direct mass exchange through the common wall is used to study the characteristics of-the response of coupled excitable chemical reaction systems to single and periodic concentration forcing of one of the sub systems. The classical Belousov-Zhabotinskii (BZ) reaction mixture in an excitable state is used to determine the response of the system to single stimulation in dependence on the amplitude of the stimulant (AgNO3) and the intensity of the mutual mass coupling. Conditions of synchronization of firings in the cells and conditions of the failure of the propagation of excitations are studied for single stimulations. It is observed that in a certain range of the intensities of the mass coupling of the cells the increase of the amplitude of the stimulation seemingly paradoxically causes failure of the propagation of the excitation. Both synchronized and nonsynchronized periodic and aperiodic firing regimes are observed for periodic stimulations. Their dependence on amplitude and period of stimulations is determined and localization of the regions of nonsynchronized regimes of firings in the ''excitation diagram'' is made. The character and the effects of the time delay in the transfer of the excited pulse to the nonstimulated cell are also studied. Qualitative agreement between the experimentally observed behavior and the results of simulations by the Oregonator model of the BZ kinetics is found. The simulations also revealed that the failure of the single-stimulus propagation with increasing stimulation amplitude reflects the dynamics of the interplay between mass exchange and autocatalytic kinetics of Br- ion formation and depletion. The Oregonator model is also used in the simulation study of the propagation of excitation in a linear array of N-coupled cells. It is found that the single-stimulus propagation failure boundary shifts to higher intensities of coupling with increasing N, but it practically ceases to depend on N for higher N. The range of coupling strengths where the phenomenon of propagation failure with the increase of the stimulation amplitude could be observed also narrowed with increasing N.