1,721,009 research outputs found
Reduction waves in the two-variable Oregonator model for the BZ reaction
No full textNumerical simulations of the two-variable Oregonator in a one-dimensional reaction–diffusion model are undertaken to show the formation of single reduction pulses. These are seen to exist over relatively narrow ranges of the (dimensionless) kinetic parameters and arising in the derivation of the Oregonator model, though they are seen for all values of the diffusion coefficient ratio considered. For the smaller values of a direct transition from single reduction pulses to wave trains is found. For equal diffusion coefficients, , this transition involves a sequence of complex spatio-temporal dynamics, including localized oscillatory behaviour and the successive spreading of a region in the reduced state. The present results are compared with results from the three-variable Oregonator and the Rovinsky–Zhabotinsky models for the BZ reaction, as well as with previous experimental observations
Collective behavior of a population of chemically coupled oscillators
No full textExperiments are performed in which a large number (∼104) of relaxation oscillators are globally coupled through the concentration of chemicals in the surrounding solution. Each oscillator consists of a microscopic catalyst-loaded particle that displays oscillations in the concentrations of chemical species when suspended in catalyst-free Belousov−Zhabotinsky (BZ) reaction solution. In the absence of stirring, the uncoupled particles display a range of oscillatory frequencies. In the well-stirred system, oscillations appear in the surrounding solution for greater than a critical number density of particles (ncrit). There is a growth in the amplitude of oscillations with increasing n, accompanied by a slight increase or no change in frequency. A model is proposed to account for the behavior, in which the transfer of activator and inhibitor to and from the bulk medium is considered for each particle. We demonstrate that the appearance and subsequent growth in the amplitude of oscillations may be associated with partial synchronization of the oscillators
Role of Differential Transport in an Oscillatory Enzyme Reaction
No full textAs a result of the bell-shaped pH-rate characteristic of enzymatic processes, feedback may arise in enzyme reactions having non-neutral products. This special type of product activation has been shown to lead to self-sustained pH oscillations in an enzyme-loaded membrane. We investigate the possibility of oscillations in a model of the urea–urease reaction, prompted by the recent experimental discovery of feedback in this reaction. An open system is considered in which acid and urea are transported to a cell containing the enzyme. Using linear stability analysis we determine the range of transport coefficients limit cycles may exist for and show that differential transport is required for oscillations in a class of compartmentalized enzyme processes similar to the urea–urease system. We demonstrate that although the transport rate of acid (kH) must be greater than that of urea (kS) for oscillations in a urease-loaded membrane, bistability is possible for kS ≥ kH
Scroll waves in the Belousov-Zhabotinsky reaction: exploitation of O2- effect on the ferroin-catalysed system
No full textEffect of oxygen on wave propagation in the ferroin-catalysed Belousov-Zhabotinsky reaction
No full textLoss of coherence in a population of diffusively coupled oscillators
No full textThe authors investigate the relationship between the natural frequency distribution of diffusively coupled chemical oscillators and their entrainment by pacemakers. The system consists of micrometer-sized catalyst beads which are coupled to their neighbors by diffusion of the activator/inhibitor species through the catalyst-free Belousov-Zhabotinsky (BZ) reaction solution. The frequency distribution is measured as a function of the beads’ number of neighbors. With the maximum number of neighbors, either target waves or disordered patterns are observed in the reaction domain and there is a shift to higher frequencies than those observed in the natural frequency distribution. The loss of coherence between neighbor oscillators is quantified by a decrease in the phase synchronization index. The experimental results are reproduced in simulations which demonstrate that the decrease in the degree of synchronization is correlated with the appearance of a small fraction of permanently excited beads in BZ populations of high mean frequency and/or large width
A path to patterns
No full textScientists have long been intrigued by a mechanism first predicted by Alan Turing that leads to self-organizing chemical patterns. Now they have a guide to creating them experimentally
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