Search

We describe the oligosaccharides-exchange dynamics performed by the so-called D-enzymes on polysaccharides. To mimic physiological conditions, we treat this process as an open chemical network by assuming some of the polymer concentrations fixed (chemostatting). We show that three different long-time behaviors may ensue: equilibrium states, nonequilibrium steady states, and continuous growth states. We dynamically and thermodynamically characterize these states and emphasize the crucial role of conservation laws in identifying the chemostatting conditions inducing them.

We derive a set of isometric fluctuation relations, which constrain the order parameter fluctuations in finite-size systems at equilibrium and in the presence of a broken symmetry. These relations are exact and should apply generally to many condensed-matter physics systems. Here, we establish these relations for magnetic systems and nematic liquid crystals in a symmetry-breaking external field, and we illustrate them on the Curie-Weiss and the XY models. Our relations also have implications for spontaneous symmetry breaking, which are discussed., SCOPUS: ar.j, info:eu-repo/semantics/published

Using the framework of stochastic thermodynamics, we present an experimental study of a doublet of magnetic colloidal particles that is manipulated by a time-dependent magnetic field. Because of hydrodynamic interactions, each bead experiences a state-dependent friction, which we characterize using a hydrodynamic model. In this work, we compare two estimates of the dissipation in this system: the first one is energy based since it relies on the measured interaction potential, while the second one is information based since it uses only the information content of the trajectories. While the latter only offers a lower bound of the former, we find it to be simple to implement and of general applicability to more complex systems.

We discuss the electrostatic contribution to the elastic moduli of a cell or artificial membrane placed in an electrolyte and driven by a DC electric field. The field drives ion currents across the membrane, through specific channels, pumps or natural pores. In steady state, charges accumulate in the Debye layers close to the membrane, modifying the membrane elastic moduli. We first study a model of a membrane of zero thickness, later generalizing this treatment to allow for a finite thickness and finite dielectric constant. Our results clarify and extend the results presented by D. Lacoste, M. Cosentino Lagomarsino, and J.F. Joanny (EPL 77, 18006 (2007)), by providing a physical explanation for a destabilizing term proportional to k[3 over up tack] in the fluctuation spectrum, which we relate to a nonlinear (E[superscript 2]) electrokinetic effect called induced-charge electro-osmosis (ICEO). Recent studies of ICEO have focused on electrodes and polarizable particles, where an applied bulk field is perturbed by capacitive charging of the double layer and drives the flow along the field axis toward surface protrusions; in contrast, we predict “reverse” ICEO flows around driven membranes, due to curvature-induced tangential fields within a nonequilibrium double layer, which hydrodynamically enhance protrusions. We also consider the effect of incorporating the dynamics of a spatially dependent concentration field for the ion channels.

In this commentary paper, we present some of the main ideas on deriving a modified fluctuation-dissipation theorem off equilibrium, which in the end can all be related to an approach based on a generalized Hatano-Sasa relation. This generalized Hatano?Sasa relation also contains an interesting inequality, which can be viewed as a generalization of the second law of thermodynamics to transitions between non-equilibrium states.

L'objectif de notre thèse de doctorat est d’étudier et de décrire les propriétés chimiques et mé- caniques du moteur moléculaire F1 -ATPase. Le moteur F1 -ATPase est un moteur rotatif, d’aspect sphérique et d’environ 10 nanomètre de rayon, qui utilise l’énergie de l’hydrolyse de l’ATP comme car- burant moléculaire. Des questions fondamentales se posent sur le fonctionnement de ce moteurs et sur la quantité de travail qu’il peut fournir. Il s’agit de questions qui concernent principalement la thermodynamique des processus irréversibles. De plus, comme ce moteur est de taille nanométrique, il est fortement influencé par les fluctuations moléculaires, ce qui nécessite une approche stochastique. C’est en créant deux modéles stochastiques complémentaires de ce moteur que nous avons contribué à répondre à ces questions fondamentales. Le premier modèle discuté au chapitre 5 de la thèse, est un mod- èle continu dans le temps et l’espace, décrit par des équations de Fokker-Planck, est construit sur des résultats expérimentaux. Ce modèle tient compte d’une description explicite des fluctua- tions affectant le degré de liberté mécanique et décrit les tran- sitions entre les différents états chimiques discrets du moteur, par un processus de sauts aléatoires entre premiers voisins. Nous avons obtenus des résultats précis concernant la chimie d’hydrolyse et de synthèse de l’ATP, et pour les dépendences du moteur en les différentes variables mécaniques, à savoir, la friction et le couple de force extérieur, ainsi que la dépendence en la température. Les résultats que nous avons obtenus avec ce modèle sont en ex- cellent accord avec les observations expérimentales. Le second modèle est discret dans l’espace et continu dans le temps et est décrit dans le chapitre 6. L’analyse des résultats obtenus par simulations numériques montre que le modèle est en accord avec les observations expérimenta, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

The behavior of a conductive membrane in a static (dc) electric field is investigated theoretically. An effective zero-thickness model is constructed based on a Robin-type boundary condition for the electric potential at the membrane, originally developed for electrochemical systems. Within such a framework, corrections to the elastic moduli of the membrane are obtained, which arise from charge accumulation in the Debye layers due to capacitive effects and electric currents through the membrane and can lead to an undulation instability of the membrane. The fluid flow surrounding the membrane is also calculated, which clarifies issues regarding these flows sharing many similarities with flows produced by induced charge electro-osmosis (ICEO). Nonequilibrium steady states of the membrane and of the fluid can be effectively described by this method. It is both simpler, due to the zero thickness approximation which is widely used in the literature on fluid membranes, and more general than previous approaches. The predictions of this model are compared to recent experiments on supported membranes in an electric field.

We formulate a quantitative description of backscattered linearly polarized light with an extended photon diffusion formalism taking explicitly into account the scattering anisotropy parameter g of the medium. From diffusing wave spectroscopy measurements, the characteristic depolarization length for linearly polarized light, lp, is deduced. We investigate the dependence of this length on the scattering anisotropy parameter g spanning an extended range from -1 (backscattering) to 1 (forward scattering). Good agreement is found with Monte Carlo simulations of multiply scattered light.

We formulate a quantitative description of backscattered linearly polarized light with an extended photon diffusion formalism taking explicitly into account the scattering anisotropy parameter g of the medium. From diffusing wave spectroscopy measurements, the characteristic depolarization length for linearly polarized light, lp, is deduced. We investigate the dependence of this length on the scattering anisotropy parameter g spanning an extended range from -1 (backscattering) to 1 (forward scattering). Good agreement is found with Monte Carlo simulations of multiply scattered light.