1,470 research outputs found
SystÚme tutoriel intelligent pour la résolution de problÚmes en thermodynamique
L'enseignement stratégique a traduit plusieurs principes
de l'approche cognitive dans une démarche d'enseignement en faisant de la
résolution de problÚmes une partie importante du curriculum
scolaire. Cet article présente un systÚme tutoriel intelligent qui
accompagne l'étudiant dans sa démarche de résolution et
lui offre des interventions spécifiques et graduées, lorsqu'il
éprouve des difficultés. Le tutoriel s'appuie sur un ensemble de
catégories d'erreurs déterminées
expérimentalement et utilise le formalisme mathématique
associé au domaine d'application à travers les formules, les
hypothĂšses et les valeurs numĂ©riques. AppliquĂ© Ă
la thermodynamique, un prototype a été
expérimenté et a fourni des résultats
intéressants
Le Massif des Rehamna (Meseta marocaine) : tĂ©moin dâun changement majeur de la dynamique des plaques au CarbonifĂšre supĂ©rieur - Permien infĂ©rieur au sein de lâorogĂšne varisqueâ allĂ©ghĂ©nien
Lâabsence dâĂ©tude moderne dans le varisque marocain associant Ă©tude structurale, mĂ©tamorphique et gĂ©ochronologique freine toute avancĂ©e significative sur son Ă©volution tectonique et sur les corrĂ©lations gĂ©odynamiques avec les autres branches adjacentes de lâorogĂšne varisque-allĂ©ghĂ©nien en Europe et en AmĂ©rique du Nord au PalĂ©ozoĂŻque supĂ©rieur. Dans le massif des Rehamna (Meseta marocaine), trois Ă©pisodes tectoniques ont Ă©tĂ© mis en Ă©vidence. (1) Charriage vers le SSO de formations ordoviciennes sur le socle nĂ©oprotĂ©rozoĂŻque Ă cambrien et ses bassins intracontinentaux dĂ©vono-carbonifĂšres. Cet Ă©vĂ©nement entraĂźne un cisaillement ductile horizontal et un mĂ©tamorphisme prograde Barrovien au sein des roches enfouies. (2) Il rĂ©sulte de ce raccourcissement la formation dâun dĂŽme syn-convergent dâallongement ~EâO permettant lâextrusion des unitĂ©s infĂ©rieures et le dĂ©tachement des unitĂ©s supĂ©rieures mĂ©tamorphiques. Ces Ă©pisodes sont contraints Ă 310â295 Ma par les Ăąges 40Ar/39Ar de refroidissement et de cristallisation mĂ©tamorphique dâamphiboles et de micas. (3) Une convergence de direction ONO, orthogonal au prĂ©cĂ©dent, permet lâaccrĂ©tion finale de toutes les unitĂ©s sur le socle continental plus Ă lâouest. Les Ăąges 40Ar/39Ar de refroidissement dâamphiboles dâun leucogranite syn-tectonique et de son encaissant, ainsi que les Ăąges de cristallisation de muscovites dâune mylonite, dĂ©montrent que cet Ă©pisode prend place entre 295 et 280 Ma. La fin de lâorogĂšne varisque dans cette partie de la Meseta marocaine est contrainte par lâĂąge de refroidissement dâun batholithe granitique post-tectonique Ă 275 Ma. Ces Ă©vĂ©nements, confrontĂ©s dâabord Ă lâĂ©volution de la Meseta marocaine, sont enfin mis en relation avec la gĂ©odynamique globale des continents Laurentia et Gondwana Ă la fin de lâorogĂšne varisqueâallĂ©ghĂ©nien, montrant le changement des contraintes aux limites dans la chaĂźne au CarbonifĂšre supĂ©rieurâPermien infĂ©rieur au Maroc, en Europe et en AmĂ©rique du Nord (Appalaches).Non peer reviewe
Thermal conditions predict intraspecific variation in senescence rate in frogs and toads
Variation in temperature is known to influence mortality patterns in ectotherms. Even though a few experimental studies on model organisms have reported a positive relationship between temperature and actuarial senescence (i.e., the increase in mortality risk with age), how variation in climate influences the senescence rate across the range of a species is still poorly understood in free-ranging animals. We filled this knowledge gap by investigating the relationships linking senescence rate, adult lifespan, and climatic conditions using long-term capture-recapture data from multiple amphibian populations. We considered two pairs of related anuran species from the Ranidae (Rana luteiventris and Rana temporaria) and Bufonidae (Anaxyrus boreas and Bufo bufo) families, which diverged more than 100 Mya and are broadly distributed in North America and Europe. Senescence rates were positively associated with mean annual temperature in all species. In addition, lifespan was negatively correlated with mean annual temperature in all species except A. boreas. In both R. luteiventris and A. boreas, mean annual precipitation and human environmental footprint both had negligible effects on senescence rates or lifespans. Overall, our findings demonstrate the critical influence of thermal conditions on mortality patterns across anuran species from temperate regions. In the current context of further global temperature increases predicted by Intergovernmental Panel on Climate Change scenarios, a widespread acceleration of aging in amphibians is expected to occur in the decades to come, which might threaten even more seriously the viability of populations and exacerbate global decline.Peer reviewe
French Roadmap for complex Systems 2008-2009
This second issue of the French Complex Systems Roadmap is the outcome of the
Entretiens de Cargese 2008, an interdisciplinary brainstorming session
organized over one week in 2008, jointly by RNSC, ISC-PIF and IXXI. It
capitalizes on the first roadmap and gathers contributions of more than 70
scientists from major French institutions. The aim of this roadmap is to foster
the coordination of the complex systems community on focused topics and
questions, as well as to present contributions and challenges in the complex
systems sciences and complexity science to the public, political and industrial
spheres
A new 3MW ECRH system at 105 GHz for WEST
The aim of the WEST experiments is to master long plasma pulses (1000s) and expose ITER-like tungsten wall to deposited heat fluxes up to 10 MW/m. To increase the margin to reach the H-Mode and to control W-impurities in the plasma, the installation of an upgraded ECRH heating system, with a gyrotron performance of 1MW/1000s per unit, is planned in 2023. With the modifications of Tore Supra to WEST, simulations at a magnetic field BâŒ3.7T and a central density nâŒ6 Ă 10 m show that the optimal frequency for central absorption is 105 GHz. For this purpose, a 105 GHz/1MW gyrotron (TH1511) has been designed at KIT in 2021, based on the technological design of the 140 GHz/1.5 MW (TH1507U) gyrotron for W7-X. Currently, three units are under fabrication at THALES. In the first phase of the project, some of the previous Tore Supra Electron Cyclotron (EC) system components will be re-installed and re-used whenever possible. This paper describes the studies performed to adapt the new ECRH system to 105 GHz and the status of the modifications necessary to re-start the system with a challenging schedule
The fourth phase of the radiative transfer model intercomparison (RAMI) exercise : Actual canopy scenarios and conformity testing
The RAdiative transfer Model Intercomparison (RAMI) activity focuses on the benchmarking of canopy radiative transfer (RT) models. For the current fourth phase of RAMI, six highly realistic virtual plant environments were constructed on the basis of intensive field data collected from (both deciduous and coniferous) forest stands as well as test sites in Europe and South Africa. Twelve RT modelling groups provided simulations of canopy scale (directional and hemispherically integrated) radiative quantities, as well as a series of binary hemispherical photographs acquired from different locations within the virtual canopies. The simulation results showed much greater variance than those recently analysed for the abstract canopy scenarios of RAMI-IV. Canopy complexity is among the most likely drivers behind operator induced errors that gave rise to the discrepancies. Conformity testing was introduced to separate the simulation results into acceptable and non-acceptable contributions. More specifically, a shared risk approach is used to evaluate the compliance of RI model simulations on the basis of reference data generated with the weighted ensemble averaging technique from ISO-13528. However, using concepts from legal metrology, the uncertainty of this reference solution will be shown to prevent a confident assessment of model performance with respect to the selected tolerance intervals. As an alternative, guarded risk decision rules will be presented to account explicitly for the uncertainty associated with the reference and candidate methods. Both guarded acceptance and guarded rejection approaches are used to make confident statements about the acceptance and/or rejection of RT model simulations with respect to the predefined tolerance intervals. (C) 2015 The Authors. Published by Elsevier Inc.Peer reviewe
Radiofrequency and mechanical tests of silver coated CuCrZr contacts for the ITER ion cyclotron antenna
The ITER Ion Cyclotron Resonance Heating (ICRH) system is designed to couple to the plasma 20âŻMW of RF power from two antennas in the 40â55âŻMHz frequency range during long pulses of up to 3600âŻs and under various plasma conditions with Edge Localized Modes. Radio-Frequency (RF) contacts are integrated within the ITER ICRH launcher in order to ensure the RF current continuity and ease the mechanical assembly by allowing the free thermal expansion of the Removable Vacuum Transmission Line coaxial conductors during RF operations or during 250âŻÂ°C baking phases. A material study has been carried out to determine which materials and associated coatings are relevant for RF contacts application in ITER. In parallel, RF tests have been performed with a new prototype of Multi-ContactÂź LA-CUT/0,25/0 contacts made of silver-coated CuCrZr louvers. During these tests on a RF vacuum resonator, currents between 1.2 kA and 1.3 kA peak have been reached a few tens of times in steady-state conditions without any visible damage on the louvers. A final 62âŻMHz pulse ending in a 300âŻs flat top at 1.9 kA resulted in severe damage to the contact. In addition, a test bed which performs sliding test cycles has been built in order to reproduce the wear of the contact prototype after 30 000 sliding cycles on a 3âŻmm stroke at 175âŻÂ°C under vacuum. The silver coating of the louvers is removed after approximately a hundred cycles whilst, to the contrary, damage to the CuCrZr louvers is relatively low
Expansion of Regulatory T Cells in Patients with Langerhans Cell Histiocytosis
Frederic Geissmann and colleagues find that Langerhans cell accumulation in Langerhans cell histiocytosis results from survival rather than uncontrolled proliferation, and is associated with the expansion of regulatory T cells
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