Biomedical subjects

Agota Tóth

Publications and source records attributed to Agota Tóth.

6 recordsLinked to original sources

PubMed2006

Lateral instability of stationary spherical reaction balls.

Three-dimensional stability of stationary reaction balls is investigated in a system consisting of an autocatalysis accompanied by a slow decay of the autocatalyst. Radially stable stationary spherical structures become unstable to three-dimensional perturbations at small decay rate when the radius of the reaction ball is sufficiently large and the reactant diffuses faster than the autocatalyst. A thorough linear stability analysis and simulations in three spatial dimensions are carried out in the simplest system sustaining stationary reaction balls.

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PubMed2006

Migration-driven instability in the chlorite-tetrathionate reaction.

We have studied the lateral stability of planar reaction-diffusion fronts in an autocatalytic reaction between aqueous ions in an externally imposed electric field. In our experiments, migration drives the pattern formation leading to cellular structures where the sufficiently greater migrational flux of the reactant with respect to that of the autocatalyst is the driving force. The difference in electric field strength between the two sides of the thin reaction front results from the significant increase in conductivity during the reaction. The results of the theoretical analysis based on the empirical rate-law model of the reaction reproduce the behavior observed experimentally.

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PubMed2004

Nonlinear interactions in the density fingering of an acidity front.

Density fingering of the chlorite-tetrathionate reaction has been studied experimentally in a Hele-Shaw cell. The initially emerging cellular structure transforms into a single cell with constant--asymmetric and symmetric--shape in narrow reaction vessels. The interactions of fingers in wider Hele-Shaw cells lead to the coarsening of the patterns, however, splitting of fingers is observed as well. The long time evolution has been quantitatively described by the change in the mixing length, i.e., the amplitude of the patterns, and by the power-averaged cell number of the structures.

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PubMed2003

Isothermal flame balls: effect of autocatalyst decay.

The steady, spherically symmetric solutions to the reaction-diffusion equations based on a simple autocatalytic reaction followed by the decay of the autocatalyst are considered. Three parameters-the orders with respect to the autocatalyst in the autocatalysis p and in the decay q and the rate of decay of the autocatalyst relative to its autocatalytic production K-determine the steady concentration profiles. Numerical integrations for a fixed value of the order of the autocatalyst show that the concentration profiles have different forms depending on whether q /=p. In the former case, there is a critical decay rate K(crit) for solutions to exist, with multiple solutions for K<K(crit). In the latter case, there is a single solution for each value of K. This difference in the nature of the solution is confirmed by an analysis for p large. The temporal stability of the isothermal flame balls is examined, with temporally stable solutions being possible, provided that the ratio of the diffusion coefficient of the autocatalyst to that of the reactant is sufficiently small. The change in stability appears only when there are multiple solutions and is through a subcritical Hopf bifurcation.

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PubMed2003

Convective instability of an acidity front in Hele-Shaw cells.

Density fingering arising in the acid-catalyzed chlorite-tetrathionate reaction is investigated experimentally in Hele-Shaw cells of various thickness. Upward propagating chemical fronts are stable for all gapwidths examined. The initial evolution of the downward propagating planar fronts resulting in a cellular structure has been characterized by dispersion curves and it is found that the convectively unstable regime increases as the gapwidth increases. From the dispersion curves, the change in the characteristics of the most unstable mode and in the marginal wave number, separating the stable and unstable modes, is determined quantitatively.

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PubMed2002

Isothermal flame balls.

The existence of steady, spherically symmetric wave fronts ("isothermal flame balls") in chemical reaction systems exhibiting autocatalysis is demonstrated. Such solutions require relatively high kinetic orders p with respect to the autocatalytic species, with p>5, but occur even with equal diffusion coefficients. The flame balls are unstable, but have relevance as they indicate the minimum size for a perturbation to initiate a propagating front. A flame ball radius R(b) is identified and the dependence of this quantity on the autocatalytic order is determined. This shows R(b) tending to infinity as p-->5(+) and as p--> infinity, with a minimum for p approximately 6.71. Numerical computations are confirmed by asymptotic analysis appropriate for p-->5(+) and for systems with p large.

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