A numerical model based in nucleation and growth algorithms has been designed to compute the temporal sequences of precipitation and phase transformation kinetics in metastable solutions of polymorphic or hydrated substances. A outline of the model is made for the particular case of crystallization of several hydrated phases from nickel nitrate solutions

A fast time-domain magneto-optical technique is used to explore magnetic flux dynamics in the optically driven nonequilibrium state of Type I superconducting Pb films. It is found that the effective penetration of flux through the nonequilibrium intermediate state can be dramatically faster than through the normal metal. The system is probed through the application of rapid transient magnetic field pulses. Above the superconducting transition temperature, a direct measure of the diffusion coefficient of the magnetic field in the normal metal is obtained, on a time scale where the inhomogeneous spatial distribution of scattering sites is relevant. In the nonequilibrium superconductor the observations are dominated by coupling of the field transients to local motion of magnetic flux threading the normal domains. Studies as a function of how far the system is driven from equilibrium, and of the effect of a static applied magnetic field, indicate that the observations reflect the dynamics of normal/superconducting interfaces, and are strongly dependent on the microscopic arrangement of the intermediate state. By contrasting the response of pure Pb films to that of Pb1−xInx alloys, a comparison to Type II superconductivity is made.

We describe the influence of local magnetization on electron localization and transport properties on the insulating side of the metal insulator transition in the dilute magnetic persistent photoconductor Cd0.091 Mn0.09Te:ln. Measurements of both the temperature dependence of the transport properties, and also the dielectric constant, are reported for just one sample in which the carrier concentration n was varied by photodoping. From these results we are able to extract the carrier concentration dependence of the localization length and the permitivity of the electrons. We also report onl a new transport effect which occurs at ultra low temperatures and/or carrier concentrations very close to the metal insulator transition. We find that this mechanism is totally magnetic in origin and are able to explain it in terms of the well devewloped ideas of magnetic polarons in magnetic semiconductors.

We have previously given an exact solution [1] for the steady state of a model of the bimolecular reaction model A+B→ 0 due to Fichthorn et al. [2]. The dimensionality of the substrate plays a central role, and below d=2 segregation on macroscopic scales becomes important: above d=2 saturation sets in for finite size systems. Here we extend our treatment to give an exact account of the dynamics and show how various initial conditions develop into the segregated and saturated regimes. In certain conditions we find logarithmic relaxation which is related to the dimensionality.

There have been a number of recent investigations of segregation properties of diffusing particles in the presence of a single static trap in low dimensions. We study these properties when the diffusing particles are subject to different forms of external fields: global constant bias, random bias fields (Sinai model) and random transition rates. We discuss two measures of segregation, the distances from the trap either to the point at which the concentration profile reaches a specified fraction of its bulk value, or to the nearest unreacted particle. For the cases of global bias (both away from, and towards the trap) and random fields, we found that both measures of segregation have the same asymptotic temporal behavior, while for random transition rates they differ. We explain this difference by relating the nearest-neighbor distance measure to properties of hard-core diffusion in these systems. We also found anomalous spatial shapes for the profile in the vicinity of the trap in the random systems, as well as anomalous reaction rates.

We present theoretical calculations and Monte-Carlo simulations of a surface reaction model proposed by Fichthorn, Gulari and Ziff (1), on a geometrically disordered lattice. Here we look at this model on a percolation cluster in euclidean dimensions d=2 and d=3. We address the problem of poisoning by a foreign inert species exactly at the percolation concentration.

We discuss the various regimes of kinetic behavior of the densities of reactants for the A + B → 0 reaction from initial to asymptotic times. Scaling arguments and Monte Carlo simulations demonstrate an unexpectedly rich hierarchy of cross-overs among time exponents ir the decay law ρ ˜ t−α. For instance, in one dimension possible time domains include classical (α = 1), A + A-type (α = 1/2), Zeldovich (α = 1/4), asymptotic correlated (α = 3/4) and finally nonalgebraic (exponential) finite size regimes. Simulation and theory are consistent with respect to both exponefits and cross-over times for one and two dimensions.