Single-Species Reactions on a Random Catalytic Chain

We present an exact solution for a catalytically-activated annihilation A + A \to 0 reaction taking place on a one-dimensional chain in which some segments (placed at random, with mean concentration p) possess special, catalytic properties. Annihilation reaction takes place, as soon as any two A particles land from the reservoir onto two vacant sites at the extremities of the catalytic segment, or when any A particle lands onto a vacant site on a catalytic segment while the site at the other extremity of this segment is already occupied by another A particle. We find that the disorder-average pressure $P^{(quen)}$ per site of such a chain is given by $P^{(quen)} = P^{(lan)} + \beta^{-1} F$, where $P^{(lan)} = \beta^{-1} \ln(1+z)$ is the Langmuir adsorption pressure, (z being the activity and \beta^{-1} - the temperature), while $\beta^{-1} F$ is the reaction-induced contribution, which can be expressed, under appropriate change of notations, as the Lyapunov exponent for the product of 2 \times 2 random matrices, obtained exactly by Derrida and Hilhorst (J. Phys. A {\bf 16}, 2641 (1983)). Explicit asymptotic formulae for the particle mean density and the compressibility are also presented.Comment: AMSTeX, 17 pages, 1 figure, submitted to J. Phys.

Kinetic description of diffusion-limited reactions in random catalytic media

We study the kinetics of bimolecular, catalytically-activated reactions (CARs) in d-dimensions. The elementary reaction act between reactants takes place only when these meet in the vicinity of a catalytic site; such sites are assumed to be immobile and randomly distributed in space. For CARs we develop a kinetic formalism, based on Collins-Kimball-type ideas; within this formalism we obtain explicit expressions for the effective reaction rates and for the decay of the reactants' concentrations.Comment: 15 pages, Latex, two figures, to appear in J. Chem. Phy

Scaling Model of Annihilation-Diffusion Kinetics for Charged Particles with Long-Range Interactions

We propose the general scaling model for the diffusio n-annihilation reaction $A_{+} + A_{-} \longrightarrow \emptyset$ with long-range power-law i nteractions. The presented scaling arguments lead to the finding of three different regimes, dep ending on the space dimensionality d and the long-range force power e xponent n. The obtained kinetic phase diagram agrees well with existing simulation data and approximate theoretical results.Comment: RevTEX, 7 pages, no figures, accepted to Physical Review

Influence of auto-organization and fluctuation effects on the kinetics of a monomer-monomer catalytic scheme

We study analytically kinetics of an elementary bimolecular reaction scheme of the Langmuir-Hinshelwood type taking place on a d-dimensional catalytic substrate. We propose a general approach which takes into account explicitly the influence of spatial correlations on the time evolution of particles mean densities and allows for the analytical analysis. In terms of this approach we recover some of known results concerning the time evolution of particles mean densities and establish several new ones.Comment: Latex, 25 pages, one figure, submitted to J. Chem. Phy

Intermittent random walks for an optimal search strategy: One-dimensional case

We study the search kinetics of an immobile target by a concentration of randomly moving searchers. The object of the study is to optimize the probability of detection within the constraints of our model. The target is hidden on a one-dimensional lattice in the sense that searchers have no a priori information about where it is, and may detect it only upon encounter. The searchers perform random walks in discrete time n=0,1,2, ..., N, where N is the maximal time the search process is allowed to run. With probability \alpha the searchers step on a nearest-neighbour, and with probability (1-\alpha) they leave the lattice and stay off until they land back on the lattice at a fixed distance L away from the departure point. The random walk is thus intermittent. We calculate the probability P_N that the target remains undetected up to the maximal search time N, and seek to minimize this probability. We find that P_N is a non-monotonic function of \alpha, and show that there is an optimal choice \alpha_{opt}(N) of \alpha well within the intermittent regime, 0 < \alpha_{opt}(N) < 1, whereby P_N can be orders of magnitude smaller compared to the "pure" random walk cases \alpha =0 and \alpha = 1.Comment: 19 pages, 5 figures; submitted to Journal of Physics: Condensed Matter; special issue on Chemical Kinetics Beyond the Textbook: Fluctuations, Many-Particle Effects and Anomalous Dynamics, eds. K.Lindenberg, G.Oshanin and M.Tachiy

Microscopic Model of Charge Carrier Transfer in Complex Media

We present a microscopic model of a charge carrier transfer under an action of a constant electric field in a complex medium. Generalizing previous theoretical approaches, we model the dynamical environment hindering the carrier motion by dynamic percolation, i.e., as a medium comprising particles which move randomly on a simple cubic lattice, constrained by hard-core exclusion, and may spontaneously annihilate and re-appear at some prescribed rates. We determine analytically the density profiles of the "environment" particles, as seen from the stationary moving charge carrier, and calculate its terminal velocity as the function of the applied field and other system parameters. We realize that for sufficiently small external fields the force exerted on the carrier by the "environment" particles shows a viscous-like behavior and define an analog of the Stokes formula for such dynamic percolative environments. The corresponding friction coefficient is also derived.Comment: appearing in Chem. Phys. Special Issue on Molecular Charge Transfer in Condensed Media - from Physics and Chemistry to Biology and Nano-Engineering, edited by A.Kornyshev (Imperial College London), M.Newton (Brookhaven Natl Lab) and J.Ulstrup (Technical University of Denmark

Spreading of a Macroscopic Lattice Gas

We present a simple mechanical model for dynamic wetting phenomena. Metallic balls spread along a periodically corrugated surface simulating molecules of liquid advancing along a solid substrate. A vertical stack of balls mimics a liquid droplet. Stochastic motion of the balls, driven by mechanical vibration of the corrugated surface, induces diffusional motion. Simple theoretical estimates are introduced and agree with the results of the analog experiments, with numerical simulation, and with experimental data for microscopic spreading dynamics.Comment: 19 pages, LaTeX, 9 Postscript figures, to be published in Phy. Rev. E (September,1966