Self-Diffusion and Collective Diffusion of Charged colloids Studied by Dynamic Light Scattering

A microemulsion of decane droplets stabilized by a non-ionic surfactant film is progressively charged by substitution of a non-ionic surfactant molecule by a cationic surfactant. We check that the microemulsion droplets remain identical within the explored range of volume fraction (0.02 to 0.18) and of the number of charge per droplets (0 to 40) . We probe the dynamics of these microemulsions by dynamic light scattering. Despite the similar structure of the uncharged and charged microemulsions the dynamics are very different . In the neutral microemulsion the fluctuations of polarization relax, as is well known, via the collective diffusion of the droplets. In the charged microemulsions, two modes of relaxation are observed. The fast one is ascribed classically to the collective diffusion of the charged droplets coupled to the diffusion of the counterions. The slow one has, to our knowledge, not been observed previously neither in similar microemulsions nor in charged spherical colloids. We show that the slow mode is also diffusive and suggest that its possible origine is the relaxation of local charge fluctuations via local exchange of droplets bearing different number of charges . The diffusion coefficient associated with this mode is then the self diffusion coefficient of the droplets

Handling Incoming Beliefs

International audienceMost logic-based approaches to knowledge and belief change in artificial intelligence assume that when a new piece of information comes up, it should be merely added to the current beliefs or knowledge when this does not lead to inconsistency. This paper addresses situations where this assumption does not hold. The focus is on the construction of Boolean standard-logic knowledge and belief bases in this context. We propose an approach to handle incoming beliefs that can require some formulas reconstruction or a form of preemption to be performed

Boltzmann and hydrodynamic description for self-propelled particles

We study analytically the emergence of spontaneous collective motion within large bidimensional groups of self-propelled particles with noisy local interactions, a schematic model for assemblies of biological organisms. As a central result, we derive from the individual dynamics the hydrodynamic equations for the density and velocity fields, thus giving a microscopic foundation to the phenomenological equations used in previous approaches. A homogeneous spontaneous motion emerges below a transition line in the noise-density plane. Yet, this state is shown to be unstable against spatial perturbations, suggesting that more complicated structures should eventually appear.Comment: 4 pages, 3 figures, final versio

Une nouvelle méthode hybride pour calculer tous les MSS et tous les MUS

Dans ce papier, nous présentons une nouvelle technique complète permettant le calcul des sous-formules maximales consistantes (MSS) et des formules minimales inconsistantes (MUS) d'un ensemble de clauses booléennes. Cette approche améliore la meilleure technique complète connue de plusieurs manières. Elle utilise à la fois une recherche locale peu coûteuse en ressources et le nouveau concept de clause critique pour améliorer un algorithme complet proposé par Liffiton et Sakallah. Cette hybridation permet l'obtention de gains exponentiels. Ainsi, des résultats expérimentaux montrent que cette nouvelle approche dépasse la meilleure méthode proposée jusque ici

Hydrodynamic equations for self-propelled particles: microscopic derivation and stability analysis

Considering a gas of self-propelled particles with binary interactions, we derive the hydrodynamic equations governing the density and velocity fields from the microscopic dynamics, in the framework of the associated Boltzmann equation. Explicit expressions for the transport coefficients are given, as a function of the microscopic parameters of the model. We show that the homogeneous state with zero hydrodynamic velocity is unstable above a critical density (which depends on the microscopic parameters), signaling the onset of a collective motion. Comparison with numerical simulations on a standard model of self-propelled particles shows that the phase diagram we obtain is robust, in the sense that it depends only slightly on the precise definition of the model. While the homogeneous flow is found to be stable far from the transition line, it becomes unstable with respect to finite-wavelength perturbations close to the transition, implying a non trivial spatio-temporal structure for the resulting flow. We find solitary wave solutions of the hydrodynamic equations, quite similar to the stripes reported in direct numerical simulations of self-propelled particles.Comment: 33 pages, 11 figures, submitted to J. Phys.

Un système argumentatif pour le raisonnement sur des ressources limitées

Dans cet article, nous proposons quelques bases pour l’argumentation déductive pour le raisonnement sur des ressources consommables et limitées. Nous nous appuyons sur une nouvelle logique, simple et proche du langage et des principes de la logique booléenne, permettant le raisonnement à partir de ressources consommables en quantité bornée. Une méthode des tableaux sémantiques pour cette logique est fournie. Enfin, pour prendre en compte la rareté des ressources consommables en argumentation, nous développons une approche pour le traitement du raisonnement argumentatif à partir des ressources consommables en quantité bornée

Second-order shape derivatives along normal trajectories, governed by Hamilton-Jacobi equations

International audienceIn this paper we introduce a new variant of shape differentiation which is adapted to the deformation of shapes along their normal direction. This is typically the case in the level-set method for shape optimization where the shape evolves with a normal velocity. As all other variants of the orginal Hadamard method of shape differentiation, our approach yields the same first order derivative. However, the Hessian or second-order derivative is different and somehow simpler since only normal movements are allowed. The applications of this new Hessian formula are twofold. First, it leads to a novel extension method for the normal velocity, used in the Hamilton-Jacobi equation of front propagation. Second, as could be expected, it is at the basis of a Newton optimization algorithm which is conceptually simpler since no tangential displacements have to be considered. Numerical examples are given to illustrate the potentiality of these two applications. The key technical tool for our approach is the method of bicharacteristics for solving Hamilton-Jacobi equations. Our new idea is to differentiate the shape along these bicharacteristics (a system of two ordinary differential equations)

Suppression de clauses redondantes dans des instances de SAT

Dans ce papier, nous étudions comment la suppression d'une partie des clauses redondantes d'une instance de SAT permet d'améliorer l'efficacité des solveurs SAT modernes. Le problème consistant à détecter si une instance contient ou non des clauses redondantes est NP-Complet. Nous proposons une méthode de suppression des clauses redondantes incomplète mais polynomiale que nous utilisons comme pré-traitement pour des solveurs SAT. Cette méthode basée sur la propagation unitaire offre des résultats intéressants notamment sur des instances très difficiles issues du monde réel

Овочівництво причорномор’я України: сучасний стан галузі в контексті інноваційного розвитку

Метою дослідження є організаційно-економічні особливості виробництва овочевої продукції відкритого ґрунту та картоплі Причорноморського регіону та підвищення їх економічної ефективності на засадах інноваційного розвитку

Piecewise Affine Registration of Biological Images for Volume Reconstruction

This manuscript tackles the reconstruction of 3D volumes via mono-modal registration of series of 2D biological images (histological sections, autoradiographs, cryosections, etc.). The process of acquiring these images typically induces composite transformations that we model as a number of rigid or affine local transformations embedded in an elastic one. We propose a registration approach closely derived from this model. Given a pair of input images, we first compute a dense similarity field between them with a block matching algorithm. We use as a similarity measure an extension of the classical correlation coefficient that improves the consistency of the field. A hierarchical clustering algorithm then automatically partitions the field into a number of classes from which we extract independent pairs of sub-images. Our clustering algorithm relies on the Earth mover’s distribution metric and is additionally guided by robust least-square estimation of the transformations associated with each cluster. Finally, the pairs of sub-images are, independently, affinely registered and a hybrid affine/non-linear interpolation scheme is used to compose the output registered image. We investigate the behavior of our approach on several batches of histological data and discuss its sensitivity to parameters and noise