Towards an efficient multiscale modeling of low-dimensional reactive systems: study of numerical closure procedures

In this paper, we present a study on how to develop an efficient multiscale simulation strategy for the dynamics of chemically active systems on low-dimensional supports. Such reactions are encountered in a wide variety of situations, ranging from heterogeneous catalysis to electrochemical or (membrane) biological processes, to cite a few. We analyzed in this context different techniques within the framework of an important multiscale approach known as the equation free method (EFM), which "bridges the multiscale gap" by building microscopic configurations using macroscopic-level information only. We hereby considered two simple reactive processes on a one-dimensional lattice, the simplicity of which allowed for an in-depth understanding of the parameters controlling the efficiency of this approach. We demonstrate in particular that it is not enough to base the EFM on the time evolution of the average concentrations of particles on the lattice, but that the time evolution of clusters of particles has to be included as well. We also show how important it is for the accuracy of this method to carefully choose the procedure with which microscopic states are constructed, starting from the measured macroscopic quantities. As we also demonstrate that some errors cannot be corrected by increasing the number of observed macroscopic variables, this work points towards which procedures should be used in order to generate efficient and reliable multiscale simulations of these systems.Comment: 15 pages, 11 figure

Stochastic efficiency of thermodiffusion: an extended local equilibrium approach

The recently established connection between stochastic thermodynamics and fluctuating hydrodynamics is applied to a study of efficiencies in the coupled transport of heat and matter on a small scale. A stochastic model for a mesoscopic cell connected to two macroscopic reservoirs of heat and particles is developed, based on fluctuating hydrodynamics. Within this approach, the fluctuating separation and thermodynamic efficiencies are defined. The conditions required to observe bimodal distributions of these efficiencies are determined, and the evolution of these distributions is investigated in the large-size and in the long-time limits. The results obtained are not restricted to thermodiffusion and can be generalized to systems where efficiency is defined as a ratio of stochastic state variables or dissipation rates.Comment: Figure 11 is corrected when compared to the published versio

Structural constraints limit the regime of optimal flux in autocatalytic reaction networks

Autocatalytic chemical networks play a predominant role in a large number of natural systems such as in metabolic pathways and in ecological networks. In this work, we present a theoretical framework that identifies the thermodynamic conditions under which autocatalytic networks run optimally in a non-equilibrium stationary state. Our theory shows that the overall reaction associated with the network is aligned with the thermodynamic force that drives the system out of equilibrium. We also demonstrate that the thermodynamic force required to operate at a maximal flux obeys universal constraints that are independent of the kinetics, but solely determined by the stoichiometry of the overall process and by the structural properties of the underlying chemical reaction network.Comment: 27 pages, 5 figures, 1 tabl

On the stochastic thermodynamics of reactive systems

We develop a theoretical framework for the stochastic thermodynamics of reactive systems. We show that the transition probabilities per unit time of reactive events must satisfy specific constraints, in order for stochastic approaches to lead to physically meaningful results in the macroscopic limit. We discuss how these constraints affect the properties of stochastic fluxes and forces, and entropy production. We also see how they can be used to derive various expressions of fluctuation theorems.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Stochastic thermodynamics based on an Einstein-Boltzmann definition of fluctuating entropy

Stochastic thermodynamics is an extension of classical nonequilibrium thermodynamics to small systems, where fluctuations are expected to play an important role. A central difficulty met when developing such an extension is how to define a nonequilibrium fluctuating entropy. Typically, the expression used is based on Gibbs' formula for entropy at equilibrium. In this work, we show that one can construct an alternative framework for stochastic thermodynamics based on an extension of Einstein's formula connecting the probability of fluctuations and entropy around equilibrium states. We compare the two approaches and discuss, in particular, how they lead to different interpretations of what a stochastic entropy and entropy production represent.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Modélisation des réactions de surface à l'échelle mésoscopique

Mesoscopic Modeling of Chemical Surface ReactionsReactions such as those encountered in heterogeneous catalysis form a specific class of non-equilibrium, nonlinear systems: they take place on low-dimensional supports, the surfaces, exhibiting a particularly restricted geometry. Because of this geometrical restriction, fluctuation-induced nanometric self-organization can spontaneously arise and can lead to a compartmentalization of the reactants and the products. We use mesoscopic stochastic simulations and theoretical approaches to model the dynamics at these scales and to understand the connection between the microscopic details of the processes and the macroscopic rate laws for concentrations. In particular, we study the propagation of waves, the emergence of coherent oscillatory and explosive behaviors and apply these techniques for the modeling of experimental systems such as the H2+O2/Rh reaction with co-adsorbed potassium or the NO+H2 reaction on platinum.Doctorat en sciences, Spécialisation chimieinfo:eu-repo/semantics/nonPublishe

Les piles à combustible :principes, faisabilité et impact écologique

info:eu-repo/semantics/nonPublishe

Reaction-diffusion approach for the description of co-adsorbed interacting species

info:eu-repo/semantics/publishe

Structure and dynamics in low-dimensional reactive systems

info:eu-repo/semantics/nonPublishe