Bistable system reactive

Sometimes, even spatially homogeneous chemical systems can cause bistability and show complex behavior in time. For example, autocatalysis may occur due to the particular molecular structure and reactivity of certain constituents, and reactions may evolve to new states by amplifying or repressing the effect of a slight concentration perturbation. 

The previous results as well as numerical simulations 8 J suggest that a non-equilibrium bistable reactive system may evolve by nucleation process, in agreement with the theory of nucleation-induced transitions [ 9 3and with experimental observations 10 ]], If the whole system is initially in the metastable state a, in such conditions that the lifetime of a is of the order of the observation time, spontaneous local fluctuations may form a microdroplet of the stable state y then the chemical reaction tends to extend its volume, whereas the diffusion tends to reduce it. The deterministic theory shows L J if the radius of the droplet happens to exceed a... 

Reactions taking place far from equilibrium show a number of unusual features, even at the macroscopic level. Consequently, the aim of much of the research in this area is rather different, and has concentrated on characterizing and unraveling the kinetics giving rise to behavior like oscillations, chaos and bistability. So the microscopic details of the reactive event, which are presumably like those in close-to-equilibrium systems, are not studied, but rather the complex structure of the macroscopic temporal and spatial evolution is the focus of attention. However, there is a class of phenomena which is analogous in some respects to the rate problem in systems close to equilibrium these are external noise-induced transitions between bistable states. The purpose of this article is to describe these phenomena and point out how some of the theoretical tools developed for equilibrium systems can be exploited to investigate these new rate processes. 

SPONTANEOUS BREAKING Of SPATIAL HOMOGENEITY IN A BISTABLE REACTIVE SYSTEM FAR FROM EQUILIBRIUM... 

The time evolution of an inhomogenous bistable reactive system in absence of convection is studied in the birth and death formalism. With the aid of multivariate Master Equations it is shown in simple cases that spatial homegenity can be spontaneously breaken during the passage from metastable to stable state a theory of nucleation is presented, which allows the evaluation of the nucleation rate. 

The chemical system used for our study is a chlorite-iodide-malonic acid (CIMA) reaction in an acidic (sulfuric acid) aqueous solution. The CIMA reaction exhibits a rich variety of phenomena oscillations in a batch reactor or in a CSTR [26], transient target waves in a closed Petri dish [26], bistability in a CSTR [26, 27], front structures in a Couette reactor [27-30], and Turing patterns in open gel reactors [7-10]. In our two-side-fed reactor. Figure lb, components of the reaction are distributed in the two compartments in such a way that neither compartment is separately reactive. Chlorite is only in compartment A , and malonic acid is only in compartment B thus there are opposing chemical concentration gradients in the direction normal to the plane of the gel. The other chemical species are contained in equal amounts in both reservoirs, except for sulfuric acid, which is more concentrated in compartment B than in compartment A. Note that chlorite and iodide in compartment A are at a low acid concentration they would react rapidly at high acid conditions. 

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