In this study we explored nonlinear spatial–temporal behavior in the oxidation of sulfite by hydrogen peroxide,in which thiosulfate was added to implement a negative feedback,which consequently led to a transition from propagating fronts to target patterns.Our investigation in the homogeneous system showed that increasing the concentration of hydrogen peroxide or decreasing the concentration of sulfite accelerated both the positive and negative feedbacks and therefore could facilitate the transition from front waves to target patterns.On the other hand,increasing the initial concentration of hydrogen ions or decreasing the concentration of thiosulfate mainly accelerated the autocatalytic production of hydrogen ions.The experimental observations were qualitatively reproduced with a model developed recently by Rabai and Hanazaki.In reaction–diffusion media,spontaneous formation of propagating pH fronts was obtained within a narrow range of sulfite and thiosulfate concentrations.The velocity of these traveling fronts was found to decrease with respect to increasing concentrations of thiosulfate and sulfite or decreasing concentrations of hydrogen ion and hydrogen peroxide.

The concentration of hydrogen ions is found to evolve periodically in the non-buffered chlorite-thiourea reaction.Perioddoubling,homoclinic and quasiperiodic bifurcations have been uncovered in this study.Experiments further illustrate that under the reaction conditions employed in this investigation reducing the reaction temperature favors the occurrence of complex pHo scillations.These experimental results provide new insight into the underlying mechanism of the chlorite–thiourea reaction,in particular regarding the significance of the nonlinear oxidations of sulfur(-II) compounds.

Pattern formation in glycolysis is studied with a classical reaction-diffusion allosteric enzyme model.It is found that,similar to recent experimental reports in the yeast extracts,a small magnitude local perturbation can induce transient target waves in a two dimensional oscillatory medium. An above threshold stimulation generates target waves which eventually evolve into spatiotemporal chaos upon collisions with the boundary or other wave activities.Detailed simulation studies show that the studied simple glycolytic reaction-diffusion model can support three types of spatiotemporal behaviors which are independent of the boundary conditions:(1) a spatially uniform stable steady state,(2) periodic global oscillations and (3) spatiotemporal chaos.

An approach leading to the development of spiral turbulence is reported here in an oscillatory reactiondiffusion medium,which is through the spontaneous formation of targetlike waves near the core of a spiral wave.The newly formed target wave emerges with its own characteristic frequency and propagates on top of the original spiral wave,which eventually leads to the breakup of the spiral at a location far from the spiral center.The radius of the surviving spiral segment decreases rapidly with the bifurcation control parameter.Calculation of power spectra suggests that the meandering of the spiral tip is responsible for the onset of the superimposed target and the phase desynchronization of the superimposed target waves.

In this report the decomposition and oxidation kinetics of thiourea dioxide and thiourea trioxide are investigated with a reversed-phase ion-pair high-performance liquid chromatography (HPLC) method.The HPLC method allows us to simultaneously determine and quantify several sulfur-containing reagents such as (NH2)2CSO2,(NH2)2CSO3,(NH2)2CO,and SO32- (HSO3－). Experiments illustrate that the decomposition of thiourea oxides is a first-order reaction,in which the rate constants increase with the pH of the solution.Oxidations of thiourea oxides by hydrogen peroxide are first order with respect to both reagents within the studied pH range between 4.0 and 8.0.Oxidation rate constants are measured under different pH conditions,which show that increasing the pH of the reaction solution significantly accelerates the oxidation process