Biomedical subjects

F Baras

Publications and source records attributed to F Baras.

12 recordsLinked to original sources

PubMed2002

Three-state model for cooperative desorption on a one-dimensional lattice.

We develop a master equation approach to the dynamics of immobile reactants on a one-dimensional lattice, in the presence of two different species undergoing cooperative desorption. A common feature of all the schemes studied is the strong dependence of the final coverage on the initial conditions, associated with the lack of ergodicity of the invariant state. Our approach leads to full agreement with Monte Carlo simulations, both asymptotically and transiently.

Journal Article↗

PubMed2002

Oscillatory reactive dynamics on surfaces: a lattice limit cycle model.

Complex reactive dynamics on low-dimensional lattices is studied using mean-field models and Monte Carlo simulations. A lattice-compatible reactive scheme that gives rise to limit cycle behavior is constructed, involving a quadrimolecular reaction step and bimolecular adsorption and desorption steps. The resulting lattice limit cycle model is dissipative and, in the mean-field limit, exhibits sustained oscillations of the species concentrations for a wide range of parameter values. Lattice Monte Carlo simulations of the lattice limit cycle model show locally the emergence of sustained oscillations of the species concentrations. Random fluctuations of the concentrations, clustering between homologous species, and competition between the various clusters/species cause the in-phase oscillations of neighboring sites. Distant regions oscillate out of phase and spatial correlations decay exponentially with the distance. The amplitude and period of the local oscillations depend on the system parameters.

Journal Article↗

PubMed2000

Hydrodynamic fluctuations in the kolmogorov flow: nonlinear regime

In a previous paper [I. Bena, M. Malek Mansour, and F. Baras, Phys. Rev. E 59, 5503 (1999)] the statistical properties of linearized Kolmogorov flow were studied, using the formalism of fluctuating hydrodynamics. In this paper the nonlinear regime is considered, with emphasis on the statistical properties of the flow near the first instability. The normal form amplitude equation is derived for the case of an incompressible fluid and the velocity field is constructed explicitly above (but close to) the instability. The relative simplicity of this flow allows one to analyze the compressible case as well. Using a perturbative technique, it is shown that close to the instability threshold the stochastic dynamics of the system is governed by two coupled nonlinear Langevin equations in Fourier space. The solution of these equations can be cast into the exponential of a Landau-Ginzburg functional, which proves to be identical to the one obtained for the case of an incompressible fluid. The theoretical predictions are confirmed by numerical simulations of the nonlinear fluctuating hydrodynamic equations.

Journal Article↗

PubMed1999

Hydrodynamic fluctuations in the Kolmogorov flow: linear regime.

The Landau-Lifshitz fluctuating hydrodynamics is used to study the statistical properties of the linearized Kolmogorov flow. The relative simplicity of this flow allows a detailed analysis of the fluctuation spectrum from near equilibrium regime up to the vicinity of the first convective instability threshold. It is shown that in the long time limit the flow behaves as an incompressible fluid, regardless of the value of the Reynolds number. This is not the case for the short time behavior where the incompressibility assumption leads in general to a wrong form of the static correlation functions, except near the instability threshold. The theoretical predictions are confirmed by numerical simulations of the full nonlinear fluctuating hydrodynamic equations.

Journal Article↗

PubMed1999

Reaction-controlled cooperative desorption in a one-dimensional lattice: a dynamical approach.

The spinlike dynamics of immobile reactants in a one-dimensional lattice is analyzed for two representative systems involving cooperative desorption. An exact combinatorial approach is worked out. Its failure to reproduce the results of microscopic simulations is shown to be associated with the lack of sufficiently strong ergodic properties, as a result of which the final state depends strongly on the initial conditions. A dynamical approach to the problem based on the Master equation description is subsequently developed, leading to full agreement with the microscopic simulations.

Journal Article↗

PubMed1996