131 research outputs found

    Ramallah : une « capitale » déconnectée

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    National audienceRamallah reflĂšte les limites du pari des accords d’Oslo de 1993, qui rĂȘvaient d’instaurer un État palestinien dans les frontiĂšres de la Ligne verte de 1949, malgrĂ© la colonisation israĂ©lienne. L’Organisation de libĂ©ration de la Palestine, qui revendiquait JĂ©rusalem, s’était alors rĂ©signĂ©e Ă  Ă©tablir une capitale provisoire Ă  Ramallah

    Extrapolation of DEM simulations to large time scale. Application to the mixing of powder in a conical screw mixer

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    International audienceThe paper proposes an original algorithm which allows a long time scale extrapolation of DEM results at a very low computational cost. This algorithm can be adapted to any periodic processes. In this study, it is applied to the mixing process of powders within a conical screw mixer. The results are then compared with long time DEM simulations. It appears that this method is able to predict the DEM results with a very good accuracy

    Qualitative and quantitative DEM analysis of cohesive granular material behaviour in FT4 shear tester

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    International audienceThe macroscopic behaviour of cohesive granular material in the FT4 shear tester is studied using the discrete element method (DEM). The shear test is simulated faithfully to the experimental procedure (filling, compaction, pre-shearing and shearing). The angle of internal friction and the apparent bulk cohesion are the macroscopic properties analysed as a result of the variation of the microscopic parameters: the sliding friction coefficient and the adhesive surface energy. The simplified JKR model was used to account for the cohesive contact between spheres. The results of the shear test show that the adhesive forces influence the dilatancy of the granular bed and the incipient failure point. In general, the shear stress increases with the adhesive energy. The sliding friction coefficient and the adhesive energy affect the yield locus and therefore the angle of internal friction and the apparent cohesion. Two correlations were established between the angle of internal friction and sliding friction coefficient and between cohesion and adhesive energy. The effect of the initial consolidation on the shear test results is also discussed

    Essais en bassin du comportement dynamique d'une éolienne flottante sous l'action conjuguée de la houle et du vent

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    Ce travail porte sur l'Ă©tude expĂ©rimentale du comportement dynamique d'une Ă©olienne offshore flottante sous l'action conjuguĂ©e de la houle et du vent. Pour cela, un nouveau moyen d'essai permettant la gĂ©nĂ©ration de vent a Ă©tĂ© dĂ©veloppĂ© sur le bassin de gĂ©nie ocĂ©anique de l'École Centrale de Nantes. La qualification aĂ©rodynamique de ce dispositif a mis en Ă©vidence un faible taux de turbulence et une bonne homogĂ©nĂ©itĂ© spatiale. Dans un second temps, un modĂšle rĂ©duit d'Ă©olienne flottante a Ă©tĂ© dimensionnĂ© Ă  l'Ă©chelle du 1/50e suivant une mĂ©thodologie adaptĂ©e Ă  ce type d'essai. Le dimensionnement de la maquette est basĂ© sur l'Ă©olienne gĂ©nĂ©rique NREL 5MW. Cette Ă©olienne repose sur un flotteur de type semi-submersible (Dutch Tri-floater). Cette maquette a ensuite Ă©tĂ© Ă©tudiĂ©e en bassin afin de caractĂ©riser son comportement sous l'action de la houle et du vent. L'influence de la directionnalitĂ© de la houle et de fluctuations basses frĂ©quences caractĂ©ristiques d'un spectre de vent marin est aussi Ă©voquĂ©e dans ce document

    Can the evaluation of marker placement confidence be used as an indicator of gait kinematic variability?

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    IntroductionThree-dimensional gait analysis is widely used for the clinical assessment of movement disorders. However, measurement error reduces the reliability of kinematic data and consequently assessment of gait deviations. The identification of high variability is associated with low reliability and those parameters should be ignored or excluded from gait data interpretation. Moreover, marker placement error has been demonstrated to be the biggest source of variability in gait analysis and may be affected by factors intrinsic to the evaluators such as the evaluator's expertise which could be appraised through his/her experience and confidence in marker placement.ObjectivesIn the present study, we hypothesized that confidence in marker placement is correlated with kinematic variability and could potentially be used as part of a score of reliability. Therefore, we have proposed a questionnaire to evaluate qualitatively the confidence of evaluators in lower-limb marker placement. The primary aim of this study was to evaluate the reliability and validity of the presented questionnaire. The secondary objective was to test a possible relationship between marker placement confidence and kinematics variability.MethodsTo do so, test-retest gait data were acquired from two different experimental protocols. One protocol included data from a cohort of 32 pathological and 24 asymptomatic subjects where gait analysis was repeated three times, involving two evaluators. A second protocol included data from a cohort of 8 asymptomatic adults with gait analysis repeated 12 times, per participant, and involving four evaluators with a wider range of experience.ResultsResults demonstrated that the questionnaire proposed is valid and reliable to evaluate qualitatively the confidence of evaluators in placing markers. Indeed, confidence scores were correlated with the actual variability of marker placement and revealed the evaluator's experience and the subjects' characteristics. However, no correlation was observed between confidence scores and kinematic variability and the formulated hypothesis was not supported

    Effect of Cyclosporine on Left Ventricular Remodeling After Reperfused Myocardial Infarction

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    ObjectivesThis study examined the effect of a single dose of cyclosporine administered at the time of reperfusion on left ventricular (LV) remodeling and function by cardiac magnetic resonance 5 days and 6 months after myocardial infarction.BackgroundIn a human study, administration of cyclosporine at the time of acute reperfusion was associated with a smaller infarct size.MethodsTwenty-eight patients of the original cyclosporine study had an acute (at 5 days) and a follow-up (at 6 months) cardiac magnetic resonance study to determine LV volumes, mass, ejection fraction, myocardial wall thickness in infarcted and remote noninfarcted myocardium, and infarct size.ResultsThere was a persistent reduction in infarct size at 6 months in the cyclosporine group compared with the control group of patients (29 ± 15 g vs. 38 ± 14 g; p = 0.04). There was a significant reduction of LV end-systolic volume (and a trend for LV end-diastolic volume; p = 0.07) in the cyclosporine group compared with the control group, both at 5 days and 6 months after infarction. There was no significant difference between the 2 groups in either global LV mass or regional wall thickness of the remote noninfarcted myocardium at 5 days or 6 months. Attenuation of LV dilation and improvement of LV ejection fraction by cyclosporine at 6 months were correlated with infarct size reduction.ConclusionsCyclosporine used at the moment of acute myocardial infarction reperfusion persistently reduces infarct size and does not have a detrimental effect on LV remodeling. These results are preliminary and must be supported by further studies. (Ciclosporin A and Acute Myocardial Infarction; NCT00403728

    Acceleration and interannual variability of creep rates in mountain permafrost landforms (rock glacier velocities) in the European Alps in 1995–2022

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    Cryospheric long-term timeseries get increasingly important. To document climate-related effects on long-term viscous creep of ice-rich mountain permafrost, we investigated timeseries (1995–2022) of geodetically-derived Rock Glacier Velocity (RGV), i.e. spatially averaged interannual velocity timeseries related to a rock glacier (RG) unit or part of it. We considered 50 RGV from 43 RGs spatially covering the entire European Alps. Eight of these RGs are destabilized. Results show that RGV are distinctly variable ranging from 0.04 to 6.23 m a−1^{−1}. Acceleration and deceleration at many RGs are highly correlated with similar behaviour over 2.5 decades for 15 timeseries. In addition to a general long-term, warming-induced trend of increasing velocities, three main phases of distinct acceleration (2000–2004, 2008–2015, 2018–2020), interrupted by deceleration or steady state conditions, were identified. The evolution is attributed to climate forcing and underlines the significance of RGV as a product of the Essential Climate Variable (ECV) permafrost. We show that RGV data are valuable as climate indicators, but such data should always be assessed critically considering changing local factors (geomorphic, thermal, hydrologic) and monitoring approaches. To extract a climate signal, larger RGV ensembles should be analysed. Criteria for selecting new RGV-sites are proposed

    Determination of rapid Deccan eruptions across the Cretaceous-Tertiary boundary using paleomagnetic secular variation: 2. Constraints from analysis of eight new sections and synthesis for a 3500-m-thick composite section

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    International audienceThe present paper completes a restudy of the main lava pile in the Deccan flood basalt province (trap) of India. Chenet et al. (2008) reported results from the upper third, and this paper reports the lower two thirds of the 3500-m-thick composite section. The methods employed are the same, i.e., combined use of petrology, volcanology, chemostratigraphy, morphology, K-Ar absolute dating, study of sedimentary alteration horizons, and as the main correlation tool, analysis of detailed paleomagnetic remanence directions. The thickness and volume of the flood basalt province studied in this way are therefore tripled. A total of 169 sites from eight new sections are reported in this paper. Together with the results of Chenet et al. (2008), these data represent in total 70% of the 3500-m combined section of the main Deccan traps province. This lava pile was erupted in some 30 major eruptive periods or single eruptive events (SEE), each with volumes ranging from 1000 to 20,000 km 3 and 41 individual lava units with a typical volume of 1300 km 3. Paleomagnetic analysis shows that some SEEs with thicknesses attaining 200 m were emplaced over distances in excess of 100 km (both likely underestimates, due to outcrop conditions) and up to 800 km. The total time of emission of all combined SEEs could have been (much) less than 10 ka, with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence (so-called ''big red boles''). The number of boles, thickness of the pulses, and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end. On the basis of geochronologic results published by Chenet et al. (2007) and paleontological results from Keller et al. (2008), we propose that volcanism occurred in three rather short, discrete phases or megapulses, an early one at $67.5 ± 1 Ma near the C30r/C30n transition and the two largest around 65 ± 1 Ma, one entirely within C29r just before the K-T boundary, the other shortly afterward spanning the C29r/C29n reversal. We next estimate sulfur dioxide (likely a major agent of environmental stress) amounts and fluxes released by SEEs: they would have ranged from 5 to 100 Gt and 0.1 to 1 Gt/a, respectively, over durations possibly as short as 100 years for each SEE. The chemical input of the Chicxulub impact would have been on the same order as that of a very large single pulse. The impact, therefore, appears as important but incremental, neither the sole nor main cause of the Cretaceous-Tertiary mass extinctions
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