Water clustering in polychloroprene

Water sorption has been studied gravimetrically for polychloroprene rubber samples, first at a fixed hygrometric ratio (98% HR) and several temperatures (25, 40, 60 and 80 °C) for samples of 1.8 and 3.8 mm thickness (Constant Temperature and Hygrometry, CTH experiments), then at fixed temperature (40 °C) and several hygrometric ratios ranging from 0 to 95% HR on samples of 0.1 mm thickness (DVS experiments). CTH experiments reveal an abnormal sorption behavior: after an apparently fickian transient period, the water absorption continues at almost constant rate, no equilibrium is observed after more than 2500 h, whatever the temperature. DVS experiments reveal a very low Henry's solubility but the formation of clusters at water activities higher than 40%. The water diffusivity is almost independent of activity below 50% HR and decreases rapidly when activity increases above 50%. Contrary to CTH experiments, equilibrium is reached in DVS and the difference is not simply linked to the well-known effect of sample thickness on diffusion rate. The results allow hypotheses such as hydrolysis or osmotic cracking to explain the abnormal sorption phenomenon to be rejected. It is suggested that clusters could be polymer-water complexes having a linear/branched structure able to grow without phase separation that could explain the reversibility of sorption-desorption cycles. The difference of behavior between thin 0.1 mm and thicker 1.8 or 3.8 mm samples could be due to an effect of swelling stresses

Oxidation of unvulcanized, unstabilized polychloroprene: A kinetic study

Thermal oxidation in air at atmospheric pressure, in the 80-140 °C temperature range and in oxygen at 100 °C in the 0.02-3 MPa pressure range, of unvulcanized, unstabilized, unfilled polychloroprene (CR) has been characterized using FTIR and chlorine concentration measurement. The kinetic analysis was focused on double bond consumption. A mechanistic scheme involving unimolecular and bimolecular hydroperoxide decomposition, oxygen addition to alkyl radicals, hydrogen abstraction on allylic methylenes, alkyl and peroxyl additions to double bonds and terminations involving alkyl and peroxy radicals was elaborated. The corresponding rate constants were partly extracted from the literature and partly determined from experimental data using the kinetic model derived from the mechanistic scheme in an inverse approach. Among the specificities of polychloroprene, the following were revealed: The rate of double bond consumption is a hyperbolic function of oxygen pressure that allows a law previously established for the oxidation of saturated substrates to be generalized. CR oxidation is characterized by the absence of an induction period that reveals the instability of hydroperoxides. The kinetic analysis also reveals that peroxyl addition is faster than hydrogen abstraction but slower in CR than in common hydrocarbon polydienes

Role of strain induced crystallization and oxidative crosslinking in fracture properties of rubbers

Tensile properties and crack propagation properties, especially critical strain energy release rate in mode I, GIC, have been used to investigate fracture properties of elastomers and their relationships with microstructure. These investigations were mainly based on a series of comparisons: first, the behaviour of polychloroprene rubber (CR), undergoing stress hardening due to strain induced crystallization (SIC) and oxidative crosslinking (OCL) was compared with that of chlorinated polyethylene (CPE), which undergoes SIC but not OCL, and with a polyurethane based on hydroxyl terminated polybutadiene (PU) which undergoes OCL but not SIC. Comparisons were also made on CR between fracture behaviour at ambient temperature, where SIC occurs and at 100°C where there is no SIC. Finally, oxidative crosslinking was used to vary in a continuous way the crosslink density in CR and PU, in order to evaluate the role of crosslinking in fracture behaviour. The results reveal the strong contribution of SIC to fracture strength. Crosslinking, even at low conversion, inhibits SIC which explains the sharp decrease of CR toughness in the early period of exposure to oxidation. When SIC has disappeared, it is possible to appreciate the effect of crosslinking on fracture behaviour. This effect, as evaluated from the density of deformation energy at rupture in tension or from GIC value, is almost negligible while the sample modulus increases regularly as a consequence of crosslinking. It appears that the toughness remains almost constant because it is under the influence of two contradictory phenomena: the negative effect of a reduction of ultimate elongation and the positive effect of a modulus increase. Such behaviour can be explained in terms of heterogeneous distribution of the lengths of elastically active chains. After long exposure, the sample behaviour becomes brittle, very high modulus values indicate that the samples approach, presumably in a heterogeneous way, the glassy state

294 Implementation time of a lipid lowering therapy in patients with dyslipidemia: results of Prysme study

Despite the availability of specific guidelines, the management of dyslipidemia in practice is not optimal.Objective and methodologyPRYSME, a non-interventional multicentre study carried out with 1226 general practitioners, aimed to describe the implementation time of a lipid lowering treatment according to cardiovascular risk level (primary objective) and to identify its determinants. Were eligible patients treated for a dyslipidemia diagnosed less than 2 years ago. Demographic and clinical characteristics and circumstances of diagnosis and treatment initiation were collected.Results3268 patients were included (mean age: 57 years old, males: 64%). 26% were obese and 45% overweight. Only 12% had no cardiovascular risk factors (CRF) at the time of dyslipidemia diagnosis. The most frequent CRF were arterial hypertension (50%), smoking (43%), family history of premature coronary heart disease (28%), HDL-c <0.4g/l (20%) whereas 15% of the patients had a personal history of cardiovascular disease. Dietary programs were initially implemented for 98% of the patients. More than 90% were treated with a statin. The implementation time of the treatment (evaluated according to the biological confirmation of dyslipidemia), according to the initial number of CRF, was as following:0 CRF1 CRF2 CRF≥ 3 CRFSecondary preventionTotal[-3;0] months34.3%28.6%27.1%29.3%49.1%33.1%]0;3] months23.1%26.2%26.4%24.0%21.9%23.9%> 3 months42.6%45.3%46.5%46.8%29.0%43.0%Chi-2 test : P<0.001The main determinant of an early implementation of a lipid lowering therapy (≤ 3 months) was secondary prevention (OR=1.8). The number of CRF had no significant impact.ConclusionThis study underlines the lack of awareness towards cardiovascular risk factors in the management of dyslipidemia, particularly while considering the implementation time of a lipid lowering therapy

Éditorial

Créée en 1984, la Revue Archéologique de l’Ouest s’apprête à célébrer son 35e anniversaire. L’éditorial ouvrant le tome 23 en 2006 rappelait le contexte de sa naissance, les conditions de sa croissance et les adaptations alors en cours. Avec ce volume, on passait en effet d’une structure associative reposant pour une large part sur le bénévolat à un organe d’édition et de diffusion professionnel. Douze années plus tard, de nouveaux ajustements apparaissent ..

Analyse et créativité pour la conception d'interaction avec l'habitat intelligent

International audienceConcevoir des interactions pour des systèmes innovants implique une première étape dans laquelle se mêlent découverte du domaine et des contraintes, créativité et mise en situation des idées sélectionnées. Cette étape a pour objectif de s'engager avec plus de confiance dans le processus de conception. Nous exposons ici une partie de notre démarche sur de nouvelles interactions avec l'habitat intelligent. Nous avons cherché à répondre le plus efficacement à nos différents objectifs par l'association de pratiques complémentaires que nous présentons succinctement avec un retour d'expérience sur leur mise en application et leur enchaînement

Analyse géométrique des données : une enquête sur le racisme

In this paper, we present the data analysis processing of a survey about racism. The methodology is that of the analysis of structured data, inspired by specific comparisons in ANOVA, and applied to geometric data (Euclidean clouds). Its realization is done by means of the Language for Interrogating Data (LID) implemented in the EyeLID software.Dans cet article, nous présentons une démarche d'analyse statistique d'un questionnaire appliquée à une enquête sur le racisme. La méthodologie suivie est celle de l'analyse des données structurées, inspirée des comparaisons spécifiques en analyse de variance, et appliquée à des données géométriques (nuage euclidien). La mise en Ïuvre est réalisée grâce au langage d'interrogation de données (LID) implanté dans le logiciel EyeLID

From computational neuroscience to computational learning science: modeling the brain of the learner and the context of the learning activity

International audienceWe share a new exploratory action known as Artificial Intelligence Devoted to Education (AIDE) launched with the support of Inria (Mnemosyne Team) and Nice INSPÉ from Côte d´Azur University (LINE laboratory) in connection with the Bordeaux NeuroCampus. It positions artificial intelligence in a somewhat original way ... not [only] as a disruptive tool, but as a formalism allowing to model learning human in problem-solving activities