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Analyse comparée de méthodes de résolution du couplage conduction-rayonnement dans des matériaux hétérogènes semi-transparents
No full textInternational audienceThis article compares numerical methods developed by seven french research teams attached to the GDR CNRS 2047 TAMARYS for coupled conduction-radiation for coupled conductionradiation heat transfer resolution in heterogeneous semi-transparent media. The teams work on a common configuration, analyzing net heat flux (total, conductive, radiative) and temperature profiles. The study highlights the benefits and limitations of each approach concerning the selected configuration, with each providing a unique perspective that enhances the others.Cet article compare les méthodes numériques de simulation développées par sept équipes de recherche françaises rattachées au GDR CNRS 2047 TAMARYS collaborant pour la résolution d’un problème couplé conduction-rayonnement dans un milieu hétérogène semi-transparent. Les équipes ont travaillé sur une configuration commune, analysant les profils de températures et de flux nets (totaux, conductifs et radiatifs). Cette étude met en évidence les points forts et limites de chaque méthode au regard de la configuration choisie, chacune offrant une perspective distincte et complémentaire aux autres
Experimental and numerical study of pressure increase in a condenser during loss of cooling
No full textInternational audienceA model predicting the behavior of a PWR condenser in case of loss of cooling flow is presented. This model enables the prediction of steady state phase (for initializing the transient scenario) and the pressure evolution modelling during the stop cooling flow and restart flow phases. The resolution is based on the discretization of energy equations of fluid inside tube and tube walls and on the use of empirical correlations to consider forced convection of inside fluid and condensation on tube walls. The impact of transient phenomena such as inertia or compression of steam is studied too. In order to do so, an experimental apparatus is set up and experimental pressure inside the condenser is compared with pressure predicted numerically. The results of the simulations agreed well with the experimental data
Observation of entanglement in a cold atom analog of cosmological preheating
No full textInternational audienceWe observe entanglement between collective excitations of a Bose-Einstein condensate in a configuration analogous to particle production during the preheating phase of the early universe. In our setup, the oscillation of the inflaton field is mimicked by the transverse breathing mode of a cigar-shaped condensate, which parametrically excites longitudinal quasiparticles with opposite momenta. After a short modulation period, we observe entanglement of these pairs which demonstrates that vacuum fluctuations seeded the parametric growth, confirming the quantum origin of the excitations. As the system continues to evolve, we observe a decrease in correlations and a disappearance of non-classical features, pointing towards future experimental probes of the less understood interaction-dominated regime.Nous observons l’intrication entre des excitations collectives d’un condensat de Bose-Einstein dans une configuration analogue à la production de particules durant la phase de preheating de l’Univers primitif. Dans notre dispositif, l’oscillation du champ d’inflaton est imitée par le mode de respiration transverse d’un condensat en forme de cigare, qui excite de manière paramétrique des quasi-particules longitudinales de moments opposés. Après une courte période de modulation, nous observons l’intrication de ces paires, révélant le rôle joué par les fluctuations du vide dans l’amorçage de la croissance paramétrique. Cela confirme l’origine quantique des excitations. À mesure que le système continue d’évoluer, nous constatons une diminution des corrélations et une disparition des caractéristiques non-classiques. Ces observations ouvrent la voie à de futures explorations expérimentales du régime non linéaire qui suit, où d’autres analogies pourront être établies avec le reheating, c’est-à-dire la thermalisation de l’Univers post-inflationnaire
Réutilisation de l’Inconel® 625 dans le procédé de fabrication additive par fusion laser sur lit de poudre pour la production de pièces d’équipements navals
No full textCinématique vs. cinétique : faut-il les dissocier pour optimiser l’apprentissage moteur ?
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Assistance robotique au service de l’apprentissage et du réapprentissage de gestes moteurs : Optimisation de l’interaction humain-robot
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Triboelectric charging properties of ABS and PS granules with different concentration of Brominated flame retardants
No full textInternational audienceWaste plastics are a significant source of pollution as they contain substances identified as persistent organic pollutants (POPs), such as brominated flame retardants (BFRs). These substances are added to many polymer materials to comply with safety flammability standards, to enhance their fire resistance, delay ignition, slow the spread of fire, or delay the time of flashover. BFRs are released from plastic materials into the environment during use, disposal, and recycling; they require careful management to reduce the risks associated with their dangerous nature for human health. Among the plastics found in WEEE, Acrylonitrile Butadiene Styrene (ABS) and Polystyrene (PS) are the most prevalent, as their excellent insulating and mechanical properties render them essential for the electrical and electronic equipment sector. However, their high flammability makes them particularly targeted for the addition of high levels of BFRs to enhance their fire resistance and comply with safety standards. Moreover, their similar surface properties and close mass density values significantly limit wet separation methods, such as density and flotation methods. In this case, tribo-electrostatic separation might be a low-cost, low-polluting solution that can preserve the original properties of plastic. Tribo-electrostatic separation was chosen over wet methods because it is a dry process that requires no chemical pretreatment, no expensive wetting reagents, and also eliminates wastewater treatment issues. This method exploits the differences in triboelectric properties of ABS and PS, enabling their separation without altering their chemical structure, which is critical for preserving recyclability. The aim of this paper was to investigate the effect of the presence of BFR with different concentrations in ABS and PS materials on their triboelectric charging characteristic and tribo-electrostatic separation process of brominated ABS and PS particles. The tribocharging properties of brominated plastic particles were studied by a fluidized bed tribocharger. The brominated polymers used in the tribocharging experiments were BFR-free ABS, 0.23 % BFR ABS, 4.6 % BFR ABS, BFR-free PS, 0.23 % BFR PS, and 4.6 % BFR PS, produced by CRITT France, using hexabromobenzene as a model of BFR. In the first part of the experiments, this work investigated the influence of the tribocharger wall material, the triboelectric behavior of BFR ABS and PS plastics, their charge density evolution over time, and finally the effect of tribocharging duration. In the second part of the experiments, tribo-electrostatic separation tests were conducted on different mixtures (BFR-free ABS/BFR-free PS, 4.6 % BFR ABS/4.6 % BFR PS, etc.)
Coupling a gas gun with an X-pinch x-ray source to perform x-ray diffraction under shock loading
No full textInternational audienceX-ray diffraction is an appropriate technique to probe crystalline materials and better understand their response under shock loading, particularly when they experience phase transition. This technique was already used at various large-scale facilities. Here, we present an alternative way to perform x-ray diffraction under shock loading at the laboratory scale by coupling an X-pinch x-ray generator with a single stage gas gun. This x-ray source is capable of generating a single polychromatic x-ray flash shorter than 100 ns. Preliminary static diffraction tests gave promising results, and then, an experimental apparatus was set up to perform in situ x-ray diffraction in a shock-loaded material. X-ray diffraction is performed in reflection at the interface between the studied sample and an anvil window to ensure a homogeneous pressure state within the probed region. A specific target configuration was designed to synchronize the x-ray emission with the temporary shocked state. The synchronization is achieved by the use of a trigger chain whose adjustable delay is chosen prior to the experiment based on the expected travel time of the shock wave throughout the target. The technique was successfully used to investigate the solid–solid phase transition of tin between β and γ phases. Results indicate a satisfying synchronization between the shock wave arrival and the x-ray emission. Diffractograms under shock loading show a disappearance of the static ambient figure (parent phase) and the development of a new diffraction pattern (daughter phase)
Validation of a pole with a force sensor for field studies on Nordic walking
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Synthesis, microstructural characterization and transport properties of a new (Ti2Nb)AlC2 ternary nanolaminate carbide solid solution.
No full textInternational audienceA new (Ti2Nb)AlC2 MAX phase solid solution is synthesized by hot isostatic pressing a powder mixture of sub-stoichiometric titanium carbide, niobium and aluminum. It is demonstrated that the synthesis temperature and Al content are key parameters to obtain a large volume fraction of 312 MAX phase solid solution. Rietveld refinement allows determining the cell parameters which are shown to vary from one sample to another. Thus, (Ti2Nb)AlC2 is not a line compound but a disordered solid solution. The 312 MAX phase solid solution formation mechanism is discussed considering intermediate phases observed by scanning electron microscopy and analysed using energy dispersive X-ray spectroscopy. Finally, transport properties are characterized. It is demonstrated that electron-phonon coupling is more efficient than in Ti3AlC2 and Ti3SiC2