Premiers résultats concernant le site des Jardins de Saint-Benoît (Saint-Laurent-de-la-Cabrerisse, Aude), pôle religieux et funéraire des Corbières

Un projet immobilier est à l’origine de la découverte et de la fouille du site des Jardins de Saint-Benoît à Saint-Laurent-de-la-Cabrerisse (Aude). Il a livré un vaste cimetière, enserrant les vestiges d’une église à chevet plat. Les sépultures étudiées, de formes et d’architectures variées, témoignent de la longue durée de fonctionnement du pôle funéraire. En effet, celui-ci semble apparaître avant la fin du VIIIe siècle et perdurer jusqu’au bas Moyen Âge, période durant laquelle l’église est presque entièrement démantelée et le cimetière abandonné. La genèse du site souffre de nombreuses lacunes documentaires. Bien qu’il soit fait mention d’une fondation monastique sur le territoire de la commune (Sancti Laurentii), le bâtiment mis au jour pourrait également correspondre à l’église Saint-Benoît ou à un autre édifice cultuel, dont aucune mention ne nous serait parvenue. De même, ses modalités d’abandon demeurent incertaines. On peut toutefois évoquer le rôle éventuel de l’épidémie de peste noire de la seconde moitié du XIVe siècle, qui est la cause attestée du décès de plusieurs individus

A sparse grid approach to balance sheet risk measurement

In this work, we present a numerical method based on a sparse grid approximation to compute the loss distribution of the balance sheet of a financial or an insurance company. We first describe, in a stylised way, the assets and liabilities dynamics that are used for the numerical estimation of the balance sheet distribution. For the pricing and hedging model, we chose a classical Black & Scholes model with a stochastic interest rate following a Hull & White model. The risk management model describing the evolution of the parameters of the pricing and hedging model is a Gaussian model. The new numerical method is compared with the traditional nested simulation approach. We review the convergence of both methods to estimate the risk indicators under consideration. Finally, we provide numerical results showing that the sparse grid approach is extremely competitive for models with moderate dimension

A numerical scheme for the quantile hedging problem

We consider numerical approximations to the quantile hedging price of a European claim in a nonlinear market with Markovian dynamics. We study an equivalent stochastic target problem with the conditional probability of success as a new state variable, in addition to the asset value process. We propose numerical approximations based on piecewise constant policy time stepping coupled with novel finite difference schemes. We prove convergence in the monotone case combining backward stochastic differential equation arguments with the Barles and Jakobsen and Barles and Souganidis approaches for nonlinear PDEs. The difficulties compared to the classical setting consist in the construction of monotone schemes under degeneracy due to the perfectly correlated joint process, the unboundedness of the control variable, and the effect of the boundaries in the probability variable on the analysis. We extend the method to a class of nonmonotone schemes using higher order interpolation and prove convergence for linear drivers. In a numerical section, we illustrate the performance of our schemes by considering an example in a financial market with imperfections, and show that a standard nonmonotone scheme produces financially counterintuitive solutions

De la modélisation du broyage

Cet article recense les diverses approches mises en œuvre dans le domaine du broyage des solides depuis des décennies (approche minéralurgique, approche mécanique, approche génie des procédés et approche statistique des distributions). Ces approches disciplinaires ne peuvent à elles seules traduire toute la complexité de cette opération unitaire. Elles ne peuvent au mieux que trouver des applications limitées. Seules les approches globales, qui intègrent la complexité du matériau (densité, microstructure, ...), le procédé technologique de broyage (vertical, horizontal, à corps fixes, ...) et les caractéristiques du matériau divisé convoité, permettront de concevoir, de dimensionner ou d’optimiser l’opération de broyage industriel

Reprocessing of UV-weathered wood flour reinforced polypropylene composites: Study of a natural outdoor exposure

International audienceThis work aims to determine and understand the influence of a one-year natural UV weathering on the reprocessing of a wood-plastic composite (WPC), i.e. a wood flour reinforced polypropylene (PP) composites. Two wood flour contents (10% w/w and 30% w/w) were studied in comparison to neat PP. Injected samples of were submitted to a long-term natural outdoor exposure followed by one complete reprocessing cycle (grinding then injection). The visual aspect evolution of the surface was followed by optical microscopy. In order to understand the material physical degradation, the mechanical behaviour was measured thanks to tensile and Charpy impact tests. The assessment of the microstructural evolution was performed by differential scanning calorimetry (crystallinity ratio), rheological tests (viscosity), size exclusion chromatography tests (average molecular weights) and infrared spectroscopy analysis (chemical structure). A “regeneration” phenomenon was highlighted as mechanical properties are recovered after reprocessing. This is due to the mixing and the dilution of the degraded chains into the material as no recombination or crosslinking mechanism was detected. A comparison with an artificial UV weathering performed on the same samples and exposed in a previous study was finally investigated

Chemical foaming extrusion of poly(lactic acid) with chain-extenders: Physical and morphological characterizations

International audienceThe effects of an epoxide-based chain-extender (CE) on the properties of poly(lactic acid) (PLA) foams obtained by chemical foaming extrusion using 4 wt.% of chemical foaming agent (CFA) were studied. PLA/CE blends with different weight ratios of CE were initially processed using a co-rotating twin-screw extruder. PLA/CE foams were then produced using a single-screw extruder. Various PLA/CE foams characterizations, including solution viscosity, thermal properties (DSC, TGA), cellular structure (void fraction, cell size, open cell content), mechanical and dynamic rheological behaviors, were investigated. Results show that the addition of CE enhances the viscosimetric average molecular weight and rheological properties (viscosity and storage modulus) of PLA, but it has no significant effects on the thermal properties of PLA, except the occurring of a cold crystallization. The CE incorporation also led to a decrease in the void fraction of cellular PLA, in the cell size and in the open cell content and to an increase in the cell density. Furthermore, the tensile mechanical properties such as yield stress and elongation at break of cellular materials increased with the addition of CE

Reprocessing of wood flour reinforced polypropylene composites: Impact of particle size and coupling agent on composite and particle properties

International audienceThis work aims to understand the degradation induced by multiple injection molding cycles on numerous properties of wood flour reinforced polypropylene (PP) composites. The influence of the initial wood particle size was studied as well as the influence of the addition of polypropylene grafted with maleic anhydride (PPgma) as a coupling agent at a given rate. Biocomposite compounds (20wt% of wood flour) are produced by twin-screw extrusion. Then, multiple injection and grinding cycles were performed (up to 7 cycles) to obtain normalized samples. The evolution of the wood flour particle characteristics is first assessed by SEM observation, size measurements and nanoindentation experiments. Then, the evolution of the PP matrix microstructure is determined by SEC tests (average molecular weight measurements), rheometer tests and DSC (polymer crystallinity). Finally, material mechanical properties are measured at a macro-scale thanks to tensile tests. Our experimental results show that the composite mechanical properties remain quite stable after 7 processing cycles despite wood flour degradation and PP degradation

Development of poly(lactic acid) cellular materials: Physical and morphological characterizations

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Under Glass Weathering of Hemp Fibers Reinforced Polypropylene Biocomposites: Degradation Mechanisms Based on Emitted Volatile Organic Compounds

International audienceThe durability of hemp fibers reinforced polypropylene biocomposites was investigated after one year under glass exposure. Volatile organic compounds emissions were assessed using a new passive sampling method. Degradation pathways were examined in order to understand the weathering mechanisms. The polymer matrix was decomposed into oxygenated products due to UV rays and high temperatures. As regards hemp fibers, different degradation steps of the carbohydrates were highlighted according to the nature of the detected furans. At a non-weathered state, dehydrations preceded the ring-opening mechanism, often catalyzed by Maillard reactions. The further cyclization induced the formation of 2-or 5-substituted furans emitted by non-weathered materials. Reactions between identified products after weathering which were not yet found in literature were proposed in this paper. They often implied a keto-enol tautomerism but also dehydrations that induced the formation of 3-and 4-substituted furanones. These differences can be explained by a primary decomposition of carbohydrates favored at a non-weathered state and a secondary one occurring at a weathered state

Reprocessing of artificial UV-weathered wood flour reinforced polypropylene composites

This work aims to determine and understand the influence of UV weathering on the reprocessing of a wood-plastic composite (WPC), i.e. of a wood flour reinforced polypropylene (PP) composites. Two wood flour contents (10% w/w and 30% w/w) were studied in comparison with neat PP. Compounds were produced by twin-screw extrusion. Then, ISO1A “dog bone” samples were obtained by injection molding and exposed to an artificial UV weathering using a xenon arc climatic chamber in order to simulate a long-term outdoor exposure. After this weathering stage, photo-degraded samples were submitted to grinding and injection cycles and characterized through different experimental technics. The visual evolution of the surface was followed by optical microscopy and scanning electron microscopy. In order to understand the material physical degradation, the mechanical behavior was measured thanks to tensile, Charpy impact and DMTA (Dynamic Mechanical Thermal Analysis) tests. The assessment of the microstructural evolution was performed by differential scanning calorimetry (crystallinity ratio), size exclusion chromatography (average molecular weights) tests and infrared spectroscopy (chemical structure). Additional rheological tests assessed assumptions on degradation mechanisms