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Competition between microstructure and defect in multiaxial high cycle fatigue
No full textPas d'embargo connu sur Sherpa RomeoInternational audienceThis study aims at providing a better understanding of the effects of both microstructure and defect on the high cycle fatigue behavior of metallic alloys using finite element simulations of polycrystalline aggregates. It is well known that the microstructure strongly affects the average fatigue strength and when the cyclic stress level is close to the fatigue limit, it is often seen as the main source of the huge scatter generally observed in this fatigue regime. The presence of geometrical defects in a material can also strongly alter the fatigue behavior. Nonetheless, when the defect size is small enough, i.e. under a critical value, the fatigue strength is no more affected by the defect. The so-called Kitagawa effect can be interpreted as a competition between the crack initiation mechanisms governed either by the microstructure or by the defect. Surprisingly, only few studies have been done to date to explain the Kitagawa effect from the point of view of this competition, even though this effect has been extensively investigated in the literature. The primary focus of this paper is hence on the use of both FE simulations and explicit descriptions of the microstructure to get insight into how the competition between defect and microstructure operates in HCF. In order to account for the variability of the microstructure in the predictions of the macroscopic fatigue limits, several configurations of crystalline orientations, crystal aggregates and defects are studied. The results of each individual FE simulation are used to assess the response at the macroscopic scale thanks to a probabilistic fatigue criterion proposed by the authors in previous works. The ability of this criterion to predict the influence of defects on the average and the scatter of macroscopic fatigue limits is evaluated. In this paper, particular emphasis is also placed on the effect of different loading modes (pure tension, pure torsion and combined tension and torsion) on the experimental and predicted fatigue strength of a 316 stainless steel containing artificial defect
GARN: Sampling RNA 3D Structure Space with Game Theory and Knowledge-Based Scoring Strategies.
No full textInternational audienc
Réflexivité partagée et coopération en recherche-action
No full textInternational audienceOur contribution identifies the effects on cooperation of three modes of reflexivity within an action-research group trying to improve pedagogical practices in professional training: action-focussed socio-constructionist reflexivity producing competencies, event centered hermeneutic reflectivity producing narrative group identity and evaluative reflexivity focussing on the action-research processes and producing authorship. What roles do these variations of reflexivity play in RAEC action-research, how do they affect cooperation capacities and what can we learn from this study for facilitating the AR process in the future? Our analysis is based on seven years of participative observation and on documents.Au sein d'une recherche-action existentielle réunissant des chercheurs universitaires et des praticiens d'une vingtaine d'écoles professionnelles (CFI à Écoles de Management), nous cherchons les apports à la coopération de trois modes de réflexivité partagée : la réflexivité socio-constructiviste, centrée sur l'action produisant des compétences, la réflexivité herméneutique, centrée sur les récits d'événements produisant une identité narrative et la réflexion auto-évaluative, centrée sur la recherche-action elle-même et produisant l'autorisation (Ardoino, 1990) de ses membres. Quels rôles ces trois modes de réflexivité jouent-ils dans la recherche-action "RAEC", comment affectent-ils la capacité du chercheur collectif à coopérer et quels enseignements en tirer pour l'avenir ? Notre recherche se fonde sur une observation participante et l'analyse de documents
Enhancing the performances of P3HT:PCBM – MoS3 based H2-evolving photocathodes with interfacial layers
No full textInternational audienceOrganic semiconductors have great potential for producing hydrogen in a durable and economically viable manner, as they rely on readily available materials and can be solution-processed over large areas. With the objective of building efficient hybrid organic-inorganic photo-electrochemical cells, we combined a noble metal-free and solution-processable catalyst for proton reduction, MoS3, and a poly-(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction (BHJ). Different interfacial layers were investigated to improve the charge transfer between P3HT:PCBM and MoS3. Metallic Al\Ti interfacial layers led to an increase of the photocurrent up to 8 mA cm?2 at reversible hydrogen electrode (RHE) potential with a 0.6 V anodic shift of the HER onset potential, a value close to the open circuit potential of the P3HT:PCBM solar cell. A 50 nm thick C60 layer also works as interfacial layer, with current density reaching 1 mA cm?2 at RHE potential. Moreover, two recently highlighted figures-of-merit, measuring the ratio of power saved, Φsaved,ideal and Φsaved,NPAC, were evaluated and discussed to compare the performances of various photocathodes assessed in a three-electrode configuration. Φsaved,ideal and Φsaved,NPAC use the RHE and a non-photoactive electrode with identical catalyst as dark electrode, respectively. They provide different information especially for the differentiation of the role of the photogenerating layer and the role of the catalyst. Best results were obtained with the Al\Ti metallic interlayer, with Φsaved,ideal and Φsaved,NPAC reaching 0.64 % and 2.05 % respectively
Leaf flutter by torsional galloping: Experiments and model
No full textInternational audienceWhen wind blows on trees, leaves flutter. The induced motion is known to affect biological functions at the tree scale such as photosynthesis. This paper presents an experimental and theoretical study of the aeroelastic instability leading to leaf flutter. Experiments in a wind tunnel are conducted on ficus leaves (Ficus Benjamina) and artificial leaves. We show that stability and flutter domains are separated by a well-defined limit depending on leaf orientation and wind speed. This limit is also theoretically predicted through a stability analysis of the leaf motion. (C) 2015 Elsevier Ltd. All rights reserved
Solar Wind and planetary magnetospheres
No full textInternational audienceSolar Wind interacts with solar system objects by exchanging momentum and energy. This transfer is particularly effective in the case of weakly magnetized bodies (Mars, Venus and comets) and small magnetosphere (Mercury).This interaction contributes to the erosion of the gaseous envelop and to the atmospheric dynamic and has therefore an important consequence on the atmospheric evolution of these objects. The electromagnetic coupling with these neutral environments takes place through ionization processes: ionization by solar photons, electron impact ionization (incident plasma electrons ionize the upper atmosphere), and charge exchange between ionized and neutral particles producing a cold ion and a fast neutral. At Mars, as the solar wind flow approaches the ionospheric region, more and more of ions originating from the planet are incorporated. This mass loading becomes more important as we approach the object, contributes to the loss of momentum of the flow, and leads to a pile-up and a twist of magnetic field lines around the object, creating an induced magnetosphere. Meanwhile, Mercury has an intrinsic magnetic field that forms a magnetosphere that is to say, a region governed by the ''planetary'' magnetic field and confined by the Solar Wind and IMF. The magnetosphere is also populated by ions with a planetary origin.The main structures of the solar wind plasma interaction with Mars and Mercury can be usually described using a steady state picture; however time-dependent effects play important roles. In the last couple of years we try to address the response of weakly magnetized bodies and small magnetospheres to different time-dependent drivers. Responses of transient events, such IMF rotation or Solar Wind dynamic pressure variation, to induced and intrinsic magnetospheres are compared by means of sophisticated 3D simulation
Measurement of the underlying event activity using charged-particle jets in proton-proton collisions at 2.76 TeV
No full textsee paper for full list of authorsInternational audienceA measurement of the underlying event (UE) activity in proton-proton collisions is performed using events with charged-particle jets produced in the central pseudorapidity region (abs(eta[jet]) 0.5 GeV, in the azimuthal region transverse to the highest pt jet direction. By further dividing the transverse region into two regions of smaller and larger activity, various components of the UE activity are separated. The measurements are compared to previous results at 0.9 and 7 TeV, and to predictions of several Monte Carlo event generators, providing constraints on the modelling of the UE dynamics
Optimization of Drug Delivery by Drug-Eluting Stents
No full textInternational audienceDrug-eluting stents (DES), which release anti-proliferative drugs into the arterial wall in a controlled manner, have drastically reduced the rate of in-stent restenosis and revolutionized the treatment of atherosclerosis. However, late stent thrombosis remains a safety concern in DES, mainly due to delayed healing of the endothelial wound inflicted during DES implantation. We present a framework to optimize DES design such that restenosis is inhibited without affecting the endothelial healing process. To this end, we have developed a computational model of fluid flow and drug transport in stented arteries and have used this model to establish a metric for quantifying DES performance. The model takes into account the multi-layered structure of the arterial wall and incorporates a reversible binding model to describe drug interaction with the cells of the arterial wall. The model is coupled to a novel optimization algorithm that allows identification of optimal DES designs. We show that optimizing the period of drug release from DES and the initial drug concentration within the coating has a drastic effect on DES performance. Paclitaxel-eluting stents perform optimally by releasing their drug either very rapidly (within a few hours) or very slowly (over periods of several months up to one year) at concentrations considerably lower than current DES. In contrast, sirolimus-eluting stents perform optimally only when drug release is slow. The results offer explanations for recent trends in the development of DES and demonstrate the potential for large improvements in DES design relative to the current state of commercial devices
Access to New Endoperoxide Derivatives by Electrochemical Oxidation of Substituted 3-Azabicyclo[4.1.0]hept-4-enes
No full textInternational audienceA series of substituted 3-azabicyclo[4.1.0]hept-4-ene derivatives were prepared and analysed by cyclic voltammetry. Preparative aerobic electrochemical oxidation reactions were then carried out. Three original endoperoxides were isolated, characterised and subjected to antimalarial and cytotoxicity activity assays
Physique des particules au delà du modèle standard : Matière noire, inflation et saveurs
No full textThis thesis has been focusing on beyond the Standard Model aspects of particle physics and their implication in cosmology. From the early times of the universe evolution, to current low energy supersymmetry and colliders phenomenology, various works have been achieved using mostly an effective, low energy formulation, at several different periods of the Universe History.Namely, models of Inflation are presented as effective single field theories arising from supergravity, string inspired UV completion models. Furthermore, models of dark matter including a mediator particle are studied with the use of effective higher dimensional operators that are generated explicitly from microscopic underlying theories. Such models were able to produce interesting results for explaining recent measurements on the X-rays spectrum of galaxy clusters. Finally, the study of flavour changing processes in the Dirac gaugino supersymmetric extensions of the Standard Model was explored in details, predicting some challenging signatures that are to be searched for at the next run of the LHC.Cette thèse se concentre sur l’étude des aspects de la physique au delà du modèle standard et de ses applications à la cosmologie. Depuis les temps reculés de l’évolution de l’Univers, jusqu’à la supersymétrie de basse énergie et à la phénoménologie des accélérateurs, des travauxvariés ont été réalisés utilisant pour la majeure partie une formulation de basse énergie, et ce à des stades différents de l’Histoire de l’Univers.En effet, des modèles d’inflation sont présentés sous l’angle de théories effectives (à un champs) provenant de théories de hautes énergies issues de la supergravité et de la théorie des cordes. De plus, des modèles de matière noire incluant la présence d’une particule médiatrice sont étudiés à l’aide d’opérateurs effectifs de dimensions supérieures, générés explicitement à partir d’une théorie microscopique sous-jacente. De tels modèles semblent expliquer de récentes mesures du spectre de rayons X mesuré dans certains cluster de galaxies. Enfin l’étude des changements de saveurs dans l’extension supersymétrique incluant des jauginos de Dirac du modèle standard prédit des signatures expérimentales qui seront très probablement recherchées lors des prochaines acquisitions du LHC