Analysis by the Two-Fluids Model of the Dynamical Behavior of a Viscoelastic Fluid Probed by Dynamic Light Scattering

The dynamic properties of a model transient network have been studied by dynamic light scattering. The network is formed by microemulsion droplets linked by telechelic polymers (modified hydrophilic polymers with two grafted hydrophobic stickers). We compare the properties of two networks that are similar but for the residence time of the hydrophobic stickers in the droplets. The results are interpreted according to the so-called two-fluids model, which was initially developed for semidilute polymer solutions and which we extend here to any Maxwellian viscoelastic medium characterized by its elastic modulus and terminal time as measured by rheology. This model is found to describe consistently and quantitatively the experimental observations.Comment: novembre 200

On Finding Minimally Unsatisfiable Cores of CSPs

International audienceWhen a Constraint Satisfaction Problem (CSP) admits no solution, it can be useful to pinpoint which constraints are actually contradicting one another and make the problem infeasible. In this paper, a recent heuristic-based approach to compute infeasible min- imal subparts of discrete CSPs, also called Minimally Unsatisfiable Cores (MUCs), is improved. The approach is based on the heuristic exploitation of the number of times each constraint has been falsified during previous failed search steps. It appears to en- hance the performance of the initial technique, which was the most efficient one until now

Extraction de sous-formules minimales inconsistantes

Une sous-formule minimale inconsistante (Minimally Unsatisfiable Subformula ou MUS en anglais) représente la plus petite cause d'incohérence d'une instance SAT en terme de nombre de clauses. Extraire un ou plusieurs MUS s'avère donc très utile, car ceux-ci circonscrivent les sources d'inconsistance d'une formule CNF. Dans ce papier, une nouvelle méta-heuristique permettant l'approximation ou le calcul d'un MUS est présentée. Une comparaison avec les méthodes les plus compétitives est effectuée, et montre que le plus souvent, en pratique, cette approche surpasse les résultats obtenus par les autres méthodes existantes

Localiser des sources d'incohérence spécifiques sans les calculer toutes

International audienceNon disponibl

Automatic extraction of functional dependencies

International audienceIn this paper, a new polynomial time technique for extracting functional depedencies in Boolean formulas is proposed. It makes an original use of the well-known Boolean constraint propagation technique (BCP) in a new preprocessing approach that extracts more hidden Boolean functions and dependent variables than previously published approaches on many classes of instances

Percolation in a Model Transient Network: Rheology and Dynamic Light Scattering

Step strain experiments and dynamic light scattering measurements are perfomed to characterize the dynamic behavior of an o/w droplet microemulsion into which is incorporated a telechelic polymer. At sufficient droplet and polymer concentrations, above the percolation threshold, the system is viscoelastic and its dynamic structure factor shows up two steps for the relaxation of concentration fluctuations: the fast one is dominated by the diffusion but the slower one is almost independent of the wave vector. The terminal time of the stress relaxation tR and the slow time of the dynamic structure factor tS are both presumably controlled by the residence time of a sticker in a droplet: consistently, tR and tS are of the same order, they both vanishes at the percolation threshold according to power laws but with different exponents. We discuss these features in terms of deviations at the transition, from the usual mean field description of the dynamics of transient networks.Comment: mars 200

A STUDY ON THE FUSION REACTION 139La + 12C AT 50 MeV/u WITH THE VUU EQUATION

Recently Bownan et al. found that in the reaction 139La + 12C at 50 MeV/u a compound nucleus is formed. We simulate this reaction with a numerical solution of the VUU equation and indeed find that for a central collision the system fuses and equilibrates after 90 fm/c