A SUBCRITICAL HOPF-BIFURCATION IN THE METHYLENE-BLUE OSCILLATOR - EFFECTS OF IMPOSED FLUCTUATIONS

The dynamical behavior of the methylene blue-oxygen-sulfide oscillator in a continuous flow stirred tank reactor is investigated. At low flow rates oscillations of period one emerge at a supercritical Hopf bifurcation, whereas a subcritical Hopf bifurcation is observed at high flow rates. The subcritical Hopf bifurcation gives rise to hysteresis in a narrow range of flow rates. Random perturbations of the flow rate (shot noise) are amplified in the vicinity of the subcritical bifurcation. Maximal fluctuation effects are obtained if the time scale of the superimposed fluctuations corresponds to the natural frequency of the oscillator. The experimental results are in good agreement with model calculations.