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Modelling the non-isothermal crystallization of polymers: Application to poly(ethylene 2,5-furandicarboxylate)
No full textInternational audienceSeveral equations have been compared for the modelling of semi-cristalline polymer crystallization on cooling from the melt and on heating from the glass. The temperature dependence was described with the Hoffman–Lauritzen (HL) equation, where U* and Kg were first determined by fitting the activation energy (Eα) dependency with temperature computed with an advanced isoconversional method (AIC) from DSC data. Several models were used to describe the extent of crystallization dependence, such as Sestak-Berggren and Avrami models. Simulations using Ozawa and AIC methods were performed for comparisons. It was shown that the model-free approach is able to take into account additional crystallization phenomena that are not considered in the classical HL or Avrami equations. Then, a new equation has been proposed to simulate additional phenomena occurring at the end of crystallization on heating from the glass, which are not described by the Hoffman–Lauritzen theory. The experimental finding that application of an isoconversional method to crystallization data following a HL mechanism, should lead to positive decreasing values for crystallization from the glass and to negative increasing values for crystallization from the melt was confirmed by simulations
Middle Pleistocene molluscan fauna from the Valle Giumentina (Abruzzo, Central Italy): Palaeoenvironmental, biostratigraphical and biogeographical implications
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Spectral element schemes for the Korteweg-de Vries and Saint-Venant equations
No full textNational audienceHyperbolic systems and dispersive equations remain challenging for finite element methods (FEMs). On the basis of an arbitrarily high order FEM, namely the spectral element method (SEM), we address :-The Korteweg-de Vries equation, to explain how high order derivative terms can be efficiently handled with a C0-continuous Galerkin approximation. The conservation of the invariants is also focused on, especially by using in time embedded implicit-explicit Runge Kutta schemes.-The 2D shallow water equations, to show how a stabilized SEM can solve problems involving shocks. We especially focus on flows involving dry-wet transitions and propose to this end an efficient variant of the entropy viscosity method
Territoire et biodiversité: mises en patrimoine et anticipations des acteurs. Une relecture à partir de la Haute Bénoué (Cameroun
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Catching-up process and GDP synchronisation in the European Union: Bayesian shrinkage estimation and distance-based approach
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Minimum Size Tree-Decompositions
No full textInternational audienceWe study in this paper the problem of computing a tree-decomposition of a graph with width at most k and minimum number of bags. More precisely, we focus on the following problem: given a fixed , what is the complexity of computing a tree-decomposition of width at most k with minimum number of bags in the class of graphs with treewidth at most k? We prove that the problem is NP-complete for any fixed 4 and polynomial for ; for , we show that it is polynomial in the class of trees and 2-connected outerplanar graphs
rhapsody-g simulations – I. The cool cores, hot gas and stellar content of massive galaxy clusters
No full textInternational audienceWe present the rhapsody-g suite of cosmological hydrodynamic zoom simulations of 10 massive galaxy clusters at the M_vir ∼ 10^15 M_⊙ scale. These simulations include cooling and subresolution models for star formation and stellar and supermassive black hole feedback. The sample is selected to capture the whole gamut of assembly histories that produce clusters of similar final mass. We present an overview of the successes and shortcomings of such simulations in reproducing both the stellar properties of galaxies as well as properties of the hot plasma in clusters. In our simulations, a long-lived cool-core/non-cool-core dichotomy arises naturally, and the emergence of non-cool cores is related to low angular momentum major mergers. Nevertheless, the cool-core clusters exhibit a low central entropy compared to observations, which cannot be alleviated by thermal active galactic nuclei feedback. For cluster scaling relations, we find that the simulations match well the M_500–Y_500 scaling of Planck Sunyaev–Zeldovich clusters but deviate somewhat from the observed X-ray luminosity and temperature scaling relations in the sense of being slightly too bright and too cool at fixed mass, respectively. Stars are produced at an efficiency consistent with abundance-matching constraints and central galaxies have star formation rates consistent with recent observations. While our simulations thus match various key properties remarkably well, we conclude that the shortcomings strongly suggest an important role for non-thermal processes (through feedback or otherwise) or thermal conduction in shaping the intracluster medium
Posters de médiation scientifique III : Réseaux de Tri
No full textposters de médiation scientifiqueCes posters font partie d'une série de posters que nous présentons lors de divers interventions de médiation (vulgarisation) scientifique (Fête de la Science, intervention dans des écoles, etc.). Nous essayons d'y présenter des bases théoriques (mathématiques) de l'algorithmique (Un algorithme est une suite finie et non ambiguë d'opérations ou d'instructions permettant de résoudre un problème ou d'obtenir un résultat) et structures de données (comment " coder " un nombre, une image, etc.). Ici, nous présentons une façon (un algorithme) de trier des éléments (par exemple, des nombres) grâce aux réseaux de tri. Pour les plus curieux d'entre vous, nous décrivons brièvement certains constituants élémentaires d'un ordinateur et comment ceux-ci permettent de faire des calculs (comment ils peuvent être assemblés pour trier). Ces posters sont accessibles dès l'école primaire (exceptée, peut-être, la partie relative à l'architecture des ordinateurs)
