Etude de la diversité géochimique de la surface de Mars, à partir des données de spectrométrie X de la mission Mars Exploration Rover. Modélisation de l'altération des roches martiennes

Depuis 2004, les rovers Spirit et Opportunity de la mission MER (Mars Exploration Rover) explorent leurs sites d'atterrissage respectifs, le cratère Gusev et les plaines de Meridiani. Ces travaux de thèse portent sur l'analyse et l'interprétation des données de l'instrument APXS (Alpha-Particle X-ray Spectrometer), situé au bout du bras articulé de chacun des rovers, dont le rôle est de déterminer la composition chimique des roches et des sols martiens par spectrométrie X. Grâce à leur surprenante longévité, Spirit et Opportunity ont pu s'éloigner à plusieurs km de leurs lieux d'atterrissage initiaux et les APXS ont analysé de nombreux échantillons fournissant des indices sur le rôle que l'eau a pu jouer dans le passé martien. J'ai d'abord choisi d'étudier cette diversité d'échantillons à l'aide d'une approche d'analyse multidimensionnelle. Ceci m'a permis de réaliser une classification des échantillons et de mettre en évidence les relations pétrogénétiques entre les roches et les sols de Gusev et Meridiani. Je présenterai les principaux résultats obtenus grâce à cette méthode ainsi que leur lien avec l'organisation spatiale et stratigraphique des échantillons. Je montrerai ensuite comment ces résultats m'ont incité à tester un modèle géochimique numérique d'altération de basalte martien par un brouillard acide de SO3. Je décrirai les hypothèses de ce modèle avant d'en comparer les résultats avec les données MER. Nous verrons enfin quelles en sont les implications, au niveau de la géologie des sites de Gusev et Meridiani et plus généralement vis-à-vis de l'histoire géologique de Mars et des conditions qui ont prévalu à sa surface dans le passé.Since 2004, the twin rovers Spirit and Opportunity of the MER (Mars Exploration Rover) mission have been investigating their respective landing sites at Gusev Crater and Meridiani Planum. This PhD thesis deals with the analysis and the interpretation of the data from the APXS (Alpha-Particle X-ray Spectrometer) instrument located on the robotic arm of each rover and whose role is to determine the chemical composition of Martian rocks and soils by X-ray spectrometry. Thanks to their extraordinary longevity, Spirit and Opportunity have been able to reach distances several km from their initial landing sites and the APXS instruments have analyzed numerous samples, yielding clues about the role that water could have played in the Martian past. In a first time, I chose to investigate this diversity of samples thanks to a multidimensional analysis technique. This allowed me to perform a classification of samples and to highlight the petrogenetic relationships between rocks and soils from Gusev and Meridiani. I will present the main results obtained with this method and their connections with the spatial and stratigraphic organisation of the samples. Then I will show how these results led me to explore a numerical geochemical model of SO3 acid fog alteration of Martian basalts. I will describe the hypotheses of this model before comparing its results with MER data. We will finally see what are the implications about the geology of the sites of Gusev and Meridiani, and more generally about the geological history of Mars and the conditions that prevailed at its surface in the past

Expeditious synthesis of 1,1-diarylethylenes related to isocombretastatin A-4 (isoCA-4) via palladium-catalyzed arylation of N-tosylhydrazones with aryl triflates

International audienceA quick and efficient entry to 1,1-diarylethylenes via the reaction of poly-oxygenated aryl N-tosylhydrazones with aryl triflates is described. The reaction employs the catalytic system Pd(OAc)2/XPhos, tBuOLi as the base and dioxane as the solvent. A variety of substituents on both coupling partner's hydrazones and triflates are tolerated. This procedure provides a complementary route to the existing methods for the access to 1,1-diarylethylenes of biological interest

Albums de littérature de jeunesse et mathématiques. L'exemple des albums codés: typologie, savoirs et tâches

National audienceL'album codé fait partie du paysage de littérature de jeunesse. Nous montrons ici l'intérêt de l'étude d'albums codés en classe pour des apprentissages en mathématiques. Afin de situer l'album codé, nous présentons une typologie des albums de littérature de jeunesse pour la classe de mathématiques. Ensuite, nous analysons les savoirs mathématiques sous-jacents à l'étude d'albums codés (codage, symbolisme, logique en particulier) en montrant l'intérêt pour l'apprentissage de la schématisation en résolution de problèmes. Nous présentons également des pistes d'activités pour la classe qui comprennent des tâches de lecture et des tâches de création d'albums codés

Palladium-catalyzed coupling of N-tosylhydrazones with ortho substituted aryl halides: synthesis of 4-arylchromenes and related heterocycles

International audienceA convenient and efficient procedure for the synthesis of 4-arylchromenes, thiochromenes, and related heterocycles via a four step-sequence has been developed. The first three steps, which involve hydration of alkynes, hydrazones formation, and their Pd-coupling with ortho substituted aryl halides, furnished stereoselectively Z-trisubstituted olefins without any purification of the intermediates generated in each stage. These latter proved to be suitable precursors, in the last step, for the synthesis of the desired heterocycles of biological interest.

Idiopathic club foot treated with the Ponseti method. Clinical and sonographic evaluation of Achilles tendon tenotomy. A review of 221 club feet

SummaryThe Ponseti method applied to treating idiopathic club foot consists in placing successive corrective casts, possibly an Achilles tendon tenotomy, then derotation braces, a method that has proven its efficacy. This study compared 221 cases of club foot treated with this method between 2002 and 2007 divided into two groups, based on whether or not Achilles tendon tenotomy was performed. Assessment was both clinical and sonographic. We observed clear improvement of the results in the group that underwent Achilles tendon tenotomy and a significant difference in the rate of secondary surgery. The sonographic evaluation also showed improvement of the morphological results. We now systematically propose Achilles tendon tenotomy however severe club foot may be

Morphological analyses of small and medium size landforms in Scandia Cavi and Olympia Undae, Northern circumpolar region of mars

This article presents a systematic morphological analysis of the topographic landforms at Olympia Undae and Scandia Cavi in the northern circumpolar region of Mars. The study has been performed using images from Mars Express and Mars Reconnaissance Orbiter, as well as topographic profiles from Mars Global Surveyor of 200 small and medium-size geological landforms (16 km diameter on average). The main morphometric parameters of these landforms have allowed their classification into three groups that include cratered structures, non-cratered structures, and complex irregular structures. In the cratered group, three subgroups can be distinguished: cratered cones, impact craters and undifferentiated craters. In turn, the non-cratered group includes two subgroups: peaked domes and simple domes. Their possible relation to internal, surface and impact processes is discussed

Mineralogy and chemistry of cobbles at Meridiani Planum, Mars, investigated by the Mars Exploration Rover Opportunity

Numerous loose rocks with dimensions of a few centimeters to tens of centimeters and with no obvious physical relationship to outcrop rocks have been observed along the traverse of the Mars Exploration Rover Opportunity. To date, about a dozen of these rocks have been analyzed with Opportunity’s contact instruments, providing information about elemental chemistry (Alpha Particle X‐ray Spectrometer), iron mineralogy and oxidation states (Mössbauer Spectrometer) and texture (Microscopic Imager). These “cobbles” appear to be impact related, and three distinct groups can be identified on the basis of chemistry and mineralogy. The first group comprises bright fragments of the sulfate‐rich bedrock that are compositionally and texturally indistinguishable from outcrop rocks. All other cobbles are dark and are divided into two groups, referred to as the “Barberton group” and the “Arkansas group,” after the first specimen of each that was encountered by Opportunity. Barberton group cobbles are interpreted as meteorites with an overall chemistry and mineralogy consistent with a mesosiderite silicate clast composition. Arkansas group cobbles appear to be related to Meridiani outcrop and contain an additional basaltic component. They have brecciated textures, pointing to an impact‐related origin during which local bedrock and basaltic material were mixed