408 research outputs found

    Prediction of Stable Ground-State Lithium Polyhydrides under High Pressures

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    Hydrogen-rich compounds are important for understanding the dissociation of dense molecular hydrogen, as well as searching for room temperature Bardeen-Cooper-Schrieffer (BCS) superconductors. A recent high pressure experiment reported the successful synthesis of novel insulating lithium polyhydrides when above 130 GPa. However, the results are in sharp contrast to previous theoretical prediction by PBE functional that around this pressure range all lithium polyhydrides (LiHn (n = 2-8)) should be metallic. In order to address this discrepancy, we perform unbiased structure search with first principles calculation by including the van der Waals interaction that was ignored in previous prediction to predict the high pressure stable structures of LiHn (n = 2-11, 13) up to 200 GPa. We reproduce the previously predicted structures, and further find novel compositions that adopt more stable structures. The van der Waals functional (vdW-DF) significantly alters the relative stability of lithium polyhydrides, and predicts that the stable stoichiometries for the ground-state should be LiH2 and LiH9 at 130-170 GPa, and LiH2, LiH8 and LiH10 at 180-200 GPa. Accurate electronic structure calculation with GW approximation indicates that LiH, LiH2, LiH7, and LiH9 are insulative up to at least 208 GPa, and all other lithium polyhydrides are metallic. The calculated vibron frequencies of these insulating phases are also in accordance with the experimental infrared (IR) data. This reconciliation with the experimental observation suggests that LiH2, LiH7, and LiH9 are the possible candidates for lithium polyhydrides synthesized in that experiment. Our results reinstate the credibility of density functional theory in description H-rich compounds, and demonstrate the importance of considering van der Waals interaction in this class of materials.Comment: 34 pages, 15 figure

    Perception de la Chine à l’ère du coronavirus: Analyse textométrique de la grande presse française de janvier à juillet 2020

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    Cette étude examine les titres et chapeaux médiatiques sur la Chine dans trois grands quotidiens nationaux de la presse écrite française (Le Figaro, Libération, Le Monde) lors de la crise du coronavirus entre janvier et juillet 2020. À l’aide de la méthode textométrique et son outil, des analyses quantitatives et qualitatives sont réalisées au fil du temps pour chaque journal et entre les trois journaux au regard du nombre total d'articles, des contenus, de l’évolution lexicale et des indices du ton d’écriture. Les résultats montrent que la couverture médiatique de la Chine a évolué au long de la crise du coronavirus, et que le ton global semble plutôt défavorable teinté de jugements d’opinions. Cependant, des différences significatives existent dans chacun des trois quotidiens nationaux

    Tentative de Définition de la Compétence de Communication à l’Usage des Interprètes de Dialogue

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    Cet article concerne l’interprétation, un métier perçu socialement en termes d’activité de communication mais ne bénéficiant que d’un nombre très limité d’études peu élaborées sur le sujet. Nous proposons donc d’aborder ce thème à travers le concept de la compétence de communication dans le contexte particulier de la pratique du métier d’interprète de dialogue. Cette tentative de définition, à laquelle nous nous attachons, relève d’un objectif central: préciser les dimensions de la compétence de communication en interprétation de dialogue. L’objet de notre étude visera, d’abord à identifier les idées qui ont contribué à l’élaboration de la notion de compétence de communication. Puis, sur un mode pragmatique, notre préoccupation sera de constituer éventuellement un cadre permettant de théoriser les conditions interactionnelles propres à l’interprétation de dialogue afin de tenter d’apporter quelques éléments permettant de définir la compétence de communication de l’interprète

    Traduire Pour le Dictionnaire Chinois-Français: Les Chengyu

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    Cet article met l’accent sur la traduction des chengyu pour un dictionnaire bilingue chinois-français. Sur l’essentiel, il pose la question de l’usage de certaines stratégies pour l’élaboration d’une entrée sous forme d’expression idiomatique. La première partie est constituée de points de vue généraux concernant la méthodologie à observer lors de la traduction d’un dictionnaire bilingue. Les parties suivantes traitent des caractéristiques du chengyu et de l’approche traductionnelle pour une troisième voie consistant en un ensemble d’équivalences tenant de la langue et de la culture

    Double-Electrode Arc Welding Process: Principle, Variants, Control and Developments

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    Double-electrode gas metal arc welding (DE-GMAW) is a novel welding process in which a second electrode, non-consumable or consumable, is added to bypass part of the wire current. The bypass current reduces the heat input in non-consumable DE-GMAW or increases the deposition rate in consumable DE-GMAW. The fixed correlation of the heat input with the deposition in conventional GMAW and its variants is thus changed and becomes controllable. At the University of Kentucky, DE-GMAW has been tested/developed by adding a plasma arc welding torch, a GTAW (gas tungsten arc welding) torch, a pair of GTAW torches, and a GMAW torch. Steels and aluminum alloys are welded and the system is powered by one or multiple power supplies with appropriate control methods. The metal transfer has been studied at the University of Kentucky and Shandong University resulting in the desirable spray transfer be obtained with less than 100 A base current for 1.2 mm diameter steel wire. At Lanzhou University of Technology, pulsed DE-GMAW has been successfully developed to join aluminum/magnesium to steel. At the Adaptive Intelligent Systems LLC, DE-GMAW principle has been applied to the submerged arc welding (SAW) and the embedded control systems needed for industrial applications have been developed. The DE-SAW resulted in 1/3 reduction in heat input for a shipbuilding application and the weld penetration depth was successfully feedback controlled. In addition, the bypass concept is extended to the GTAW resulting in the arcing-wire GTAW which adds a second arc established between the tungsten and filler to the existing gas tungsten arc. The DE-GMAW is extended to double-electrode arc welding (DE-AW) where the main electrode may not necessarily to be consumable. Recently, the Beijing University of Technology systematically studied the metal transfer in the arcing-wire GTAW and found that the desired metal transfer modes may always be obtained from the given wire feed speed by adjusting the wire current and wire position/orientation appropriately. A variety of DE-AW processes are thus available to suit for different applications, using existing arc welding equipment

    Continuous Acetone–Butanol–Ethanol (ABE) Fermentation with in Situ Solvent Recovery by Silicalite-1 Filled PDMS/PAN Composite Membrane

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    The pervaporation (PV) performance of a thin-film silicalite-1 filled PDMS/PAN composite membrane was investigated in the continuous acetone–butanol–ethanol (ABE) production by a fermentation–PV coupled process. Results showed that continuous removal of ABE from the broth at three different dilution rates greatly increased both the solvent productivity and the glucose utilization rate, in comparison to the control batch fermentation. The high solvent productivity reduced the acid accumulation in the broths because most acids were reassimilated by cells for ABE production. Therefore, a higher total solvent yield of 0.37 g/g was obtained in the fermentation–PV coupled process, with a highly concentrated condensate containing 89.11–160.00 g/L ABE. During 268 h of the fermentation–PV coupled process, the PV membrane showed a high ABE separation factor of more than 30 and a total flux of 486–710 g/m2h. Membrane fouling was negligible for the three different dilution rates. The solution-diffusion model, especially the mass transfer equation, was proved to be applicable to this coupled process.<br/
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