Mesure et prédiction des déformations et contraintes résiduelles lors du refroidissement d’un stratifié composite thermoplastique

International audienceCooling of thermoplastic composite parts inevitably leads to the development of residual stresses, which may have negative consequences on the final part health. Modelling their development during cooling therefore appears as an interesting solution to optimize the process parameters and limit the stresses intensity. This study proposes a coupled model accounting for heat transfer, crystallization kinetics and mechanical behavior of thermoplastic composite laminate. This latter is treated according to the modified lamination theory, which is for the first time adapted to the study of a thermoplastic composite during cooling, with temperature dependent properties. This is made possible by the use of an incremental linear elastic law, which also accounts for the crystallization shrinkage and thermal expansion of the material. The model is applied to the study of an unsymmetric laminate, which leads to estimated stress and strain states. These latter are compared with experimentally measured strains, highlighting an excellent agreement which validates the proposed moLe refroidissement des pièces composites thermoplastiques durant leur mise en oeuvre mène inexorablement au développement de contraintes résiduelles. Ces contraintes peuvent être néfastes pour la santé finale de la pièce et il convient de prédire leur développement au cours du procédé afin d'optimiser celui-ci et ainsi limiter l'impact des contraintes sur le matériau. Cette étude propose un modèle de prédiction du développement des contraintes résiduelles au cours du refroidissement d'un composite thermoplastique à fibres continues de verre et matrice PA66. Celui-ci prend en compte les transferts thermiques, la cinétique de cristallisation ainsi que le comportement mécanique du composite au cours de son refroidissement. Ce dernier est traité à l'aide de la théorie modifiée des stratifiés qui est adaptée pour la première fois au refroidissement d'un composite thermoplastique dont les propriétés thermomécaniques varient avec la température. Ceci est rendu possible à l'aide d'une formulation incrémentale de la loi de comportement linéaire élastique, prenant en compte les retraits d'origine thermique et de cristallisation. Appliqué au cas d'un empilement asymétrique, le modèle permet de prédire contraintes et déformations résiduelles. Ces dernières sont comparées à des mesures expérimentales pour évaluer la fiabilité du modèle développédel

A step-economical multicomponent synthesis of 3D-shaped aza-diketopiperazines and their drug-like chemical space analysis

A rapid and atom economical multicomponent synthesis of complex aza-diketopiperazines (aza-DKPs) driven by Rh(I)-catalyzed hydroformylation of alkenylsemicarbazides is described. Combined with catalytic amounts of acid and the presence of nucleophilic species, this unprecedented multicomponent reaction (MCR) enabled the formation of six bonds and a controlled stereocenter from simple substrates. The efficacy of the strategy was demonstrated with a series of various allyl-substituted semicarbazides and nucleophiles leading to the preparation of 3D-shaped bicyclic aza-DKPs. Moreover, an analysis of their 3D molecular descriptors and “drug-likeness” properties highlights not only their originality in the chemical space of aza-heterocycles but also their great potential for medicinal chemistry

Early liver transplantation for severe alcohol-related hepatitis not responding to medical treatment: a prospective controlled study

peer reviewedBackground: Early liver transplantation for severe alcohol-related hepatitis is an emerging treatment option. We aimed to assess the risk of alcohol relapse 2 years after early liver transplantation for alcohol-related hepatitis compared with liver transplantation for alcohol-related cirrhosis after at least 6 months of abstinence. Methods: We conducted a multicentre, non-randomised, non-inferiority, controlled study in 19 French and Belgian hospitals. All participants were aged 18 years or older. There were three groups of patients recruited prospectively: patients with severe alcohol-related hepatitis who did not respond to medical treatment and were eligible for early liver transplantation according to a new selection scoring system based on social and addiction items that can be quantified in points (early transplantation group); patients with alcohol-related cirrhosis listed for liver transplantation after at least 6 months of abstinence (standard transplantation group); patients with severe alcohol-related hepatitis not responding to medical treatment not eligible for early liver transplantation according to the selection score (not eligible for early transplantation group), this group did not enter any further liver transplantation processes. We also defined a historical control group of patients with severe alcohol-related hepatitis unresponsive to medical therapy and non-transplanted. The primary outcome was the non-inferiority of 2-year rate of alcohol relapse after transplantation in the early transplantation group compared with the standard transplantation group using the alcohol timeline follow back (TLFB) method and a prespecified non-inferiority margin of 10%. Secondary outcomes were the pattern of alcohol relapse, 2-year survival rate post-transplant in the early transplantation group compared with the standard transplantation group, and 2-year overall survival in the early transplantation group compared with patients in the not eligible for early transplantation group and historical controls. This trial is registered with ClinicalTrials.gov, NCT01756794. Findings: Between Dec 5, 2012, and June 30, 2016, we included 149 patients with severe alcohol-related hepatitis: 102 in the early transplantation group and 47 in the not eligible for early transplantation group. 129 patients were included in the standard transplantation group. 68 patients in the early transplantation group and 93 patients in the standard transplantation group received a liver transplant. 23 (34%) patients relapsed in the early transplantation group, and 23 (25%) patients relapsed in the standard transplantation group; therefore, the non-inferiority of early transplantation versus standard transplantation was not demonstrated (absolute difference 9·1% [95% CI –∞ to 21·1]; p=0·45). The 2-year rate of high alcohol intake was greater in the early transplantation group than the standard transplantation group (absolute difference 16·7% [95% CI 5·8–27·6]) The time spent drinking alcohol was not different between the two groups (standardised difference 0·24 [95% CI −0·07 to 0·55]), but the time spent drinking a large quantity of alcohol was higher in the early transplantation group than the standard transplantation group (standardised difference 0·50 [95% CI 0·17–0·82]). 2-year post-transplant survival was similar between the early transplantation group and the standard transplantation group (hazard ratio [HR] 0·87 [95% CI 0·33–2·26]); 2-year overall survival was higher in the early transplantation group than the not eligible for early transplantation group and historical controls (HR 0·27 [95% CI 0·16–0·47] and 0·21 [0·13–0·32]). Interpretation: We cannot conclude non-inferiority in terms of rate of alcohol relapse post-transplant between early liver transplantation and standard transplantation. High alcohol intake is more frequent after early liver transplantation. This prospective controlled study confirms the important survival benefit related to early liver transplantation for severe alcohol-related hepatitis; and this study provides objective data on survival and alcohol relapse to tailor the management of patients with severe alcohol-related hepatitis. Funding: The present study has been granted by the French Ministry of Health—Programme Hospitalier de Recherche Clinique 2010

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Discovering properties about arrays in simple programs

International audienceArray bound checking and array dependency analysis (for parallelization) have been widely studied. However, there are much less results about analyzing properties of array contents. In this paper, we propose a way of using abstract interpretation for discovering properties about array contents in some restricted cases: one-dimensional arrays, traversed by simple "for" loops. The basic idea, borrowed from [GRS05], consists in partitioning arrays into symbolic intervals (e.g., [1,i - 1], [i,i], [i + 1,n]), and in associating with each such interval I and each array A an abstract variable AI; the new idea is to consider relational abstract properties ψ(AI, BI, ...) about these abstract variables, and to interpret such a property pointwise on the interval I: ∀l ∈ I, ψ(A[l], B[l],...). The abstract semantics of our simple programs according to these abstract properties has been defined and implemented in a prototype tool. The method is able, for instance, to discover that the result of an insertion sort is a sorted array, or that, in an array traversal guarded by a "sentinel", the index stays within the bounds

Fourniture d'un état initial du patrimoine culturel maritime sur les communes littorales du Parc naturel marin d'Iroise, sur les îles comprises dans son périmètre et sur l'espace maritime.

contrat de recherch

Dewetting of Low-Viscosity Films at Solid/Liquid Interfaces

International audienceWe report new experimental results on the dewetting of a mercury film (A) intercalated between a glass slab and an external nonmiscible liquid phase (B) under conditions of a large equilibrium contact angle. The viscosity of the external phase, η_B, was varied over 7 orders of magnitude.We observe a transition between two regimes of dewetting at a threshold viscosity of η_B* ≈ (ρ_Ae|S̃|)^1/2, where ρ_A is the mercury density, e is the film thickness, and |S̃| is the effective spreading coefficient. For η_B η_B*, the regime is viscous. The dewetting velocity is constant and scales as V ≈ |S̃|/η_B in the limit of large η_B. We interpret this regime by a balance between the surface energy released during dewetting and the viscous dissipation in the surrounding liquid

Atlas du patrimoine maritime culturel du Finistère: dans un objectif d'aménagement du territoire et de hiérarchisation des opérations à effectuer

48 planches cartographiques, en ligne début 2009 sur le site web http://www.cg29.fr/Le patrimoine maritime culturel est un élément primordial et souvent oublié du développement durable des littoraux, contrairement au patrimoine naturel. Il existe pourtant, au sein de nos sociétés en mutation, un « risque culturel » de se couper du passé et par là même de perspectives d'avenir. Pour redresser cette situation et répondre à la nécessaire prise en compte des héritages maritimes – témoins de la diversité dans le temps et dans l'espace des relations Homme/mer et supports des identités territoriales présentes et futures – un atlas du patrimoine maritime culturel a été entrepris à la demande du Conseil Général du Finistère et soutenu par la région Bretagne. L'atlas a été conçu et exécuté dans le cadre d'une recherche/action pluridisciplinaire (géographes, historiens, ethnologues) mise en œuvre depuis trois ans par l'Observatoire du Patrimoine Maritime Culturel du laboratoire Géomer (UMR LETG – 6554 – CNRS) de l'IUEM (Institut Universitaire Européen de la Mer) en appui des politiques publiques. L'observatoire travaille en étroite concertation avec un « groupe ressource » constitué de personnalités compétentes dans les différents rayons d'action de l'étude : élus, archéologues sous-marins, spécialistes de l'équipement portuaire, de l'éclairage des côtes... L'objectif principal de cet atlas du patrimoine maritime culturel des communes littorales du Finistère, le premier du genre, destiné aux élus et aux principaux acteurs du littoral, est de faciliter le passage du diagnostic à l'action, du simple inventaire des héritages maritimes à des propositions d'aménagement du territoire dans une démarche de Gestion Intégrée des Zones Côtière (GIZC). Le but n'est pas de figer les territoires littoraux à partir de représentations issues du passé mais de leur permettre d'évoluer dans l'avenir en intégrant leur originalité culturelle et humaine considérée comme une ressource non délocalisable à forte potentialité humaine et économique

Phase separation in molecular layers of macromolecules at the champagne-air interface

Bubble and foam stability, which are essential for the hallmark of champagne, rely on the concentration of amphiphilic macromolecules originating from the grape, which form molecular layers at the interface between champagne and gas. Ellipsometry and Brewster angle microscopy experiments were conducted at the air–champagne interface to analyse the lateral organization of the layers of macromolecules. Several kinds of phase separations – leading in some cases to two-dimensional foams – were identified. At the beginning of layer formation, condensed domains develop at the expense of dilute domains. Thereafter, phase separations occur within the condensed domains. These findings may allow advances in the implementation of methods predicting bubble and foam stability of champagnes