Identification and optimization of the constitutive model for die-formed expanded graphite for sealing applications

International audienceThe die-formed expanded graphite is used in industry for sealing applications subjected to extreme pressure and temperature. Its chemical inertness, excellent elastic recovery and adaptability to damaged flanges serves the sealing function. However, in some cases, the high load required for tightening leads to significant mechanical effects related to flanges bending or radial thrust. To address this effect and support the implementation of graphite seals investigations are performed to identify a constitutive model for that specific material and describe the interaction of these seals with their environment [1]. Instrumented axial die-compaction tests are performed to characterize the load-compression curve as well as the radial pressure from the sample [2], [3]. A methodology is then developed for the identification of the coefficients related to the constitutive model, assuming a Drucker-Prager Cap model, and especially the hardening behaviour, which drives the seals compression and unloading curves. The work is based on a parametric optimization and a numerical simulation close to the test device itself. The identified model is finally used for graphite seals simulation, to address mechanical interactions with their environment and comparison with tests performed with dedicated instrumented seals validate its relevance

Influence of dietary histidine level on histidine metabolism in the preruminant calf.

International audienc

Transport des acides amines dans l'aire splanchnique par le plasma sanguin et le sang chez le veau preruminant

National audienc

Influence de la vitesse d'absorption des acides amines sur le bilan hepatique chez le veau preruminant.

National audienc

Pulse protein feeding pattern restores stimulation of muscle protein synthesis during the feeding period in old rats

International audienc

Influence of ambient gas pressure and carbon adsorption on dark current emission from a cathode

International audienc

Dechlorination of ferrous archaeological artefacts in subcritical conditions: understanding of the corrosion layer transformation thanks to a multi-scale characterisation

International audienceDechlorination of ferrous archaeological artefacts is rendered necessary after excavation in order to remove chloride species present at the metal/corrosion layer interface. Indeed, when artefacts are exposed to air after a long period of burial they can suffer severe damages. This is due to the reactivation of the corrosion processes through the migration of those chlorides that provokes local acidification. In the conservation field, treatments are based on the immersion of the artefacts in alkaline bath in order to transform the chloride containing phases (akaganeite and $\beta$-Fe$_2$(OH)$_3$Cl). But specifically for artefacts of high dimensions the process can last from several months to years. An innovating approach based on treatment in subcritical conditions (180°C, 35 bars) allows to reduce by a factor of 10 the treatment duration. The optimisation of this treatment requires the determination of the reaction pathways between the initial corrosion layers and the transformed ones after treatment. Therefore synthetic phases representative of archaeological corrosion products formed in aerated environments (goethite, lepidocrocite, magnetite, akaganeite, maghemite) have been treated separately to study their transformation during the treatment. Specifically in-situ experiments under synchrotron radiation have been performed on akaganeite in order to determine the different transformation steps of this phase. The behaviour of two akaganeite, the first one obtained by laboratory synthesis and the second one from archaeological origin has been compared. Thanks to XANES at the Fe K-edge in sub-critical conditions it has been highlighted that depending on the heating rate the akaganeite transforms either in hematite or in a mix of goethite and hematite. High resolution X-ray diffraction under synchrotron has allowed to determine the evolution of the crystalline structure of the remaining akaganeite depending on the chloride content of this phase. Last the results show that the transformation kinetics depend on the origin of the precursor and that archaeological phases transform much slower than synthetic ones

Nutritional control of protein metabolism during aging

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Proposed diagnostic criteria for apathy in Alzheimer's disease and other neuropsychiatric disorders.

International audienceThere is wide acknowledgement that apathy is an important behavioural syndrome in Alzheimer's disease and in various neuropsychiatric disorders. In light of recent research and the renewed interest in the correlates and impacts of apathy, and in its treatments, it is important to develop criteria for apathy that will be widely accepted, have clear operational steps, and that will be easily applied in practice and research settings. Meeting these needs is the focus of the task force work reported here. The task force includes members of the Association Française de Psychiatrie Biologique, the European Psychiatric Association, the European Alzheimer's Disease Consortium and experts from Europe, Australia and North America. An advanced draft was discussed at the consensus meeting (during the EPA conference in April 7th 2008) and a final agreement reached concerning operational definitions and hierarchy of the criteria. Apathy is defined as a disorder of motivation that persists over time and should meet the following requirements. Firstly, the core feature of apathy, diminished motivation, must be present for at least four weeks; secondly two of the three dimensions of apathy (reduced goal-directed behaviour, goal-directed cognitive activity, and emotions) must also be present; thirdly there should be identifiable functional impairments attributable to the apathy. Finally, exclusion criteria are specified to exclude symptoms and states that mimic apathy

The Congolobe project, a multidisciplinary study of Congo deep-sea fan lobe complex: Overview of methods, strategies, observations and sampling

The presently active region of the Congo deep-sea fan (around 330 000 km2), called the terminal lobes or lobe complex, covers an area of 2500 km2 at 4700–5100 m water depth and 750–800 km offshore. It is a unique sedimentary area in the world ocean fed by a submarine canyon and a channel-levee system which presently deliver large amounts of organic carbon originating from the Congo River by turbidity currents. This particularity is due to the deep incision of the shelf by the Congo canyon, up to 30 km into the estuary, which funnels the Congo River sediments into the deep-sea. The connection between the river and the canyon is unique for major world rivers. In 2011, two cruises (WACS leg 2 and Congolobe) were conducted to simultaneously investigate the geology, organic and inorganic geochemistry, and micro- and macro-biology of the terminal lobes of the Congo deep-sea fan. Using this multidisciplinary approach, the morpho-sedimentary features of the lobes were characterized along with the origin and reactivity of organic matter, the recycling and burial of biogenic compounds, the diversity and function of bacterial and archaeal communities within the sediment, and the biodiversity and functioning of the faunal assemblages on the seafloor. Six different sites were selected for this study: Four distributed along the active channel from the lobe complex entrance to the outer rim of the sediment deposition zone, and two positioned cross-axis and at increasing distance from the active channel, thus providing a gradient in turbidite particle delivery and sediment age. This paper aims to provide the general context of this multidisciplinary study. It describes the general features of the site and the overall sampling strategy and provides the initial habitat observations to guide the other in-depth investigations presented in this special issue. Detailed bathymetry of each sampling site using 0.1 m to 1 m resolution multibeam obtained with a remotely operated vehicle (ROV) shows progressive widening and smoothing of the channel-levees with increasing depth and reveals a complex morphology with channel bifurcations, erosional features and massive deposits. Dense ecosystems surveyed in the study area gather high density clusters of two large-sized species of symbiotic Vesicomyidae bivalves and microbial mats. These assemblages, which are rarely observed in sedimentary zones, resemble those based on chemosynthesis at cold-seep sites, such as the active pockmarks encountered along the Congo margin, and share with these sites the dominant vesicomyid species Christineconcha regab. Sedimentation rates estimated in the lobe complex range between 0.5 and 10 cm yr−1, which is 2-3 orders of magnitude higher than values generally encountered at abyssal depths. The bathymetry, faunal assemblages and sedimentation rates make the Congo lobe complex a highly peculiar deep-sea habitat driven by high inputs of terrigenous material delivered by the Congo channel-levee system