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Dissociation photoinduite du radical trichlorométhyle: imagerie de fragmentation et spectroscopie de photoélectron femtoseconde
No full textInternational audienceHalogen-containing radicals play a key role in catalytic reactions leading to stratospheric ozone destruction, thus their photochemistry is of considerable interest. Here we investigate the photodissociation dynamics of the trichloromethyl radical, CCl3 after excitation in the ultraviolet. While the primary processes directly after light absorption are followed by femtosecond - time resolved photoionisation and photoelectron spectroscopy, the reaction products are monitored by photofragment imaging using nanosecond-lasers. The dominant reaction is loss of a Cl atom, associated with a CCl2 fragment. However, the detection of Cl atoms is of limited value, because in the pyrolysis CCl2 is formed as a side product, which in turn dissociates to CCl + Cl. We therefore additionally monitored the molecular fragments CCl2 and CCl by photoionisation at 118.2 nm and disentangled the contributions from various processes. A comparison of the CCl images with control experiments on CCl2 suggest that the dissociation to CCl + Cl2 contributes to the photochemistry of CCl3
Optical coherent manipulation of alkaline-earth circular Rydberg states
No full textInternational audienceOwing to their large size, Rydberg atoms are promising tools for quantum technologies1,2, as they exhibit long-range dipole–dipole interactions and strong coupling to external fields. Recent experiments have demonstrated their appeal for quantum simulation purposes3,4,5, even though the relatively short lifetime of optically accessible Rydberg levels imposes limitations. Long-lived circular Rydberg states6,7 may provide a solution. However, the detection of circular states involves either destructive6 or complex7 measurement techniques. Moreover, so far, alkali circular states have been manipulated only by microwave fields, which are unable to address individual atoms. The use of circular states of a different group of atoms, the alkaline-earth metals, which have an optically active second valence electron, can circumvent these problems. Here we show how to use the electrostatic coupling between the two valence electrons of strontium to coherently manipulate a circular Rydberg state with optical pulses. We also exploit this coupling to map the state of the Rydberg electron onto that of the ionic core. This experiment opens the way to a state-selective spatially resolved non-destructive detection of circular states and to the realization of a hybrid optical–microwave platform for quantum technology
On breast imaging from joint microwave and acoustic data within a Bayesian framework
No full textAvailable on IEEE XploreInternational audienceBreast cancer is most common, so early diagnosis of tumors is wished for. Microwave (MW) and ultrasound (US) are non-invasive, non-ionizing, low-cost, and can be run without registration for free pending breasts. MW is to yield high-contrast images of low resolution, the converse with US, with the benefit of the common breast structure. That is, fusion of MW and US data should produce images with both high contrast and high resolution. Here a Bayesian formalism is chosen to that effect (Variational Bayesian Approximation or VBA), edges as hidden variables, a number of hyperparameters involved as expected. Once the mathematics sketched, one insists on imaging of a MRI- derived breast model, a tumor added into it. Comparison with a joint edge-preserving contrast source inversion (JCSI-EP) in a deterministic framework will illustrate pros and cons of VBA
R&D Tax Credits across the European Union : Divergences and convergence
No full textWe examine the R&D, innovation and productivity effects of R&D tax credits (R&DTC) in 8 EU countries in the context of a proposed EU-wide "super deduction" on R&D expenditures. Esti- mating CDM-type econometric models on industry-level panel data, we find that past R&D sys- tematically feeds current R&D. The estimate of our proxy measure of input additionality during an R&DTC phase is generally close to 1, but rarely larger than 1. R&D intensity affects patenting intensity positively in Belgium, Czech Republic, France, Spain and the UK, but this relationship is R&DTC-related only in Belgium, France and Spain. Only in France and the UK do we observe a full R&D - innovation - productivity relationship. In the UK, this relationship is not affected by the R&DTC scheme. In France, a 1% increase in R&D conducted under the second to fourth phases of R&DTC (1999-2017) entails a cumulated 0.36% increase in patenting intensity, which translates to a 0.16% increase in productivity. The main policy implication of our results is that R&DTC may help the EU reach its "R&D at 3% of GDP" objective, but should not be the only instrument implemented to spur innovation and productivity in the EU
BOUNDARY ELEMENT METHOD WITH HIGH ORDER IMPEDANCE BOUNDARY CONDITIONS IN ELECTROMAGNETICS
No full textInternational audienceIn this paper, we study boundary element method with high order impedance boundary conditions (HOIBC) to solve Maxwell's equations. The unknowns are electric and magnetic currents J and M. We propose several formulations and study the existence and uniqueness of the solution. Then, we discretize these formulations with a finite element method based on Lagrange elements. We give numerical tests of the HOIBC solution
Étude de la réactivité des sucres dans les couplages organométalliques : application à la synthèse de glycosides biologiquement actifs
No full textSugars are molecules present in many biological and physiological processes, such as cell-cell interactions and immune responses. Their great importance has earned them a certain interest in many research projects both in the methodology of organic synthesis and in the vast field of applications of glycosylated compounds. This thesis work is devoted to the study of the reactivity of thiosugars in the presence of transition metals for the synthesis of two types of compounds: O-heterosides and S-heterosides. O-heterosides (Chapter I) are synthesized from thiosugars and carboxylic acids by following a new and innovative method, based on a coupling catalyzed by Cu(acac)₂ and allowing the production of glycosidic esters in a stereoselective way in one very short time (15 minutes in the microwave). More than twenty products have been generated with yields ranging from 17 to 91%. The S-heterosides (Chapter II and III) are formed from thiosugars and iodinated aryls according to a palladocatalyzed coupling (Pd-Xantphos-G3) of Buchwald-Hartwig-Migita. The synthesized products were the subject of two subsequent applications. In the 2nd chapter, we were interested in chiral perfluorinated sulfoximines and their coupling to thiosugars in order to combine in the same structure : S-heteroside. The properties of the synthesized compounds have been studied and the diastereoisomers of all sulfoximine-thioglycosylated products have been successfully separated. Finally, in the 3rd chapter, we proceeded to the palladocatalyzed coupling of thiosugars and azobenzenes, known for their structurally reversible character in contact with light in order to form Azobenzene-thioglycosylated compounds. The studies carried out thereafter consist in evaluating the impact of the carbohydrate part on the azobenzene pattern by examining the photochromic and physicochemical properties (water solubility) of the Azobenzene-glycosylated compounds.Les sucres sont des molécules présentent dans de nombreux processus biologiques et physiologiques, tels que les interactions cellules-cellules et les réponses immunitaires. Leur grande importance leur a valu un intérêt certain dans beaucoup de projets de recherches tant dans la méthodologie de synthèse organique que dans le vaste domaine d’applications des composés glycosylés. Ce travail de thèse est consacré à l’étude de la réactivité des thiosucres en présence des métaux de transition pour la synthèse de deux types de composés : les O-hétérosides et les S-hétérosides. Les O-hétérosides (Chapitre I) sont synthétisés à partir de thiosucres et d’acides carboxyliques en suivant une méthode nouvelle et innovante, basée sur un couplage catalysé au Cu(acac)₂ et permettant de produire des esters glycosidiques de façon stéréosélective en un temps très court (15 minutes aux micro-ondes). Plus d’une vingtaines de produits ont été générés avec des rendements allant de 17 à 91%. Les S-hétérosides (Chapitre II et III) quant à eux, sont formés à partir de thiosucres et d’aryles iodés selon un couplage palladocatalysé (Pd-Xantphos-G3) de Buchwald-Hartwig-Migita. Les produits synthétisés ont fait l’objet de deux applications postérieures. Dans le 2ème chapitre, nous nous sommes intéressées aux sulfoximines perfluorées chirales et a leur couplage aux thiosucres afin de combiner les deux motifs dans une même structure de type S-hétérosides. Les propriétés des composés synthétisés ont été étudiés et les diastéréoisomères de tous les produits de type sulfoximines-thioglycosylées ont été séparés avec succés. Enfin, dans le 3ème chapitre, nous avons procédé au couplage palladocatalysé des thiosucres et des azobenzènes, connu pour leur caractère réversible structurellement au contact de la lumière afin de former des composés Azobenzènes-thioglycosylés. Les études réalisées par la suite consistent à évaluer l’impact de la partie glucidique sur le motif azobenzènes en examinant les propriétés photochromiques et physicochimiques (hydrosolubilité) des composés Azobenzènes-glycosylés
La notion de résultats dans quatre entrées disciplinaires du français
No full textInternational audienceThis paper questions the notion of result in French didactics through the study of scientific articles published in four issues of the journal Repères (2018-2020) on four disciplinary objects: writing, literature, spelling and lexicon. It looks at the discourses, the parameters that construct the results, the content of the results and the typologies of research.Cette communication interroge la notion de résultat en didactique du français à travers l'étude d'articles scientifiques parus dans quatre numéros de la revue Repères (2018-2020) portant sur quatre objets disciplinaires : l'écriture, la littérature, l'orthographe et le lexique. Elle s’intéresse aux discours, aux paramètres qui construisent les résultats, au contenu des résultats et aux typologies des recherches
Les discours meurtriers aujourd'hui
No full textInternational audienceSuivant la voie ouverte par le philologue allemand Victor Klemperer, à partir d’une perspective interdisciplinaire, ce livre a pour objet la description et l’analyse des discours extrémistes actuels les plus violents. Il s’intéresse plus particulièrement aux appels au meurtre et à leurs légitimations politiques ou religieuses, du djihadisme contemporain au suprématisme blanc. Les différents auteurs tentent de décrire et d’analyser ces discours, dits « meurtriers », dans leurs formes, leurs soubassements et leurs effets. En mettant au cœur même de la désignation la question du rapport entre discours et actes, la dénomination « discours meurtriers » peut permettre le repérage de traits caractéristiques, ainsi que le relevé de modes opératoires et d’enjeux sociaux ou subjectifs propres à ces énoncés ou à ces langages. Ils interrogent cette performativité propre aux propagandes idéologiques actuelles, où le discours tend à se précipiter dans l’action, au lieu de la suspendre ou de l’élaborer. Les discours meurtriers peuvent recouvrir les discours de haine par les passions destructrices qu’ils véhiculent ou qu’ils suscitent, mais ils se distinguent par l’incitation ou l’appel au meurtre et sa justification, ainsi que par des effets d’anéantissement clairement repérables. L’actualité montre jusqu’à la caricature, au-delà de la propagande et de la terreur déployée par l’autoproclamé « État islamique », combien il est urgent d’interroger ce qui est peut-être en train d’arriver aujourd’hui, dont les langages pourraient être à nouveau l’instrument et le symptôme. Il est en effet crucial de chercher à comprendre pour tenter de prévenir ces forces du discours au service du négatif et de l’anéantissement de toute altérité
Genesis of morpho-kinematic lopsidedness in minor merger of galaxies
No full textInternational audienceAn m = 1 lopsided asymmetry is common in disc galaxies. Here, we investigate the excitation of an m = 1 lopsidedness in host galaxies during minor mergers while choosing a set of 1:10 merger models (with varying orbital configurations, morphology of the host galaxy) from the GalMer galaxy merger library. We show that a minor merger triggers a prominent m = 1 lopsidedness in stars of the host galaxy. The strength of the m = 1 lopsidedness undergoes a transient amplification phase after each pericenter passage of the satellite, in concordance with past findings of exciting an m = 1 lopsidedness by tidal encounters. However, once the merger happens, and the post-merger remnant readjusts itself, the lopsidedness disappears in short time-scale (∼ 500 − 850 Myr). Furthermore, a delayed merger can drive a prolonged (∼2 Gyr) lopsidedness in the host galaxy. We demonstrate that the m = 1 lopsidedness rotates with a well-defined pattern speed which is much slower than the m = 2 bar pattern speed, and is retrograde with respect to the bar. This gives rise to a dynamical scenario where the Inner Lindblad resonance of the m = 1 lopsidedness falls in between the corotation and the Outer Lindblad resonance of the m = 2 bar mode. A kinematic lopsidedness also arises in the host galaxy; the resulting temporal variation closely follows that of the density lopsidedness. The minor merger also triggers a transient off-centred stellar disc-dark matter halo configuration due to the tidal encounter with the satellite