129 research outputs found
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
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