Désorption induite par photons et électrons dans des glaces moléculaires

The deposition of energy in the form of electronic excitations in molecules condensed on cold surfaces (10-100 K) can lead to the desorption of some of these molecules. This basicsurface science process has consequences in a variety of fields, two of which are of concern here : astrochemistry and vacuum dynamics. Photon and Electron-Induced desorption are studied in this manuscript for thin films of condensed molecules (ices), e.g. CO, H2O, NO or CH4. The first objective is to obtain a quantification of the desorption of the various desorbing species, and to look for the parameters that affect the efficiency of the process. The second objective is to understand the mechanisms of evolution and relaxation of the initial electronic excitations that lead to desorption. Photon-induced desorption is studied at LERMA using synchrotron radiation in the VUV range (5-14 eV) and soft X-ray range (520-600 eV). This allows to obtainspectrally-resolved information, which is crucial both for model implementation and fundamental understanding of the mechanisms. Electron-induced desorption is studied at CERN in the 150-2000 eV range. The results expand the available data on UV photodesorption and allow to determine the relevance of electron or X-ray desorption for astrochemistry. Progress has also been made on the understanding of mechanisms, particularly on the role of energy or particle transport from the bulk to the surface of the ice, on indirect desorption, or on the desorption of ions in the soft X-ray range. A new experimental set-up has also been developed at LERMA forlaser desorption and laser spectroscopy experiments, allowing quantum-state and kinetic energy resolved measurements of desorbed molecules.L’excitation électronique de molécules condensées sur des surfaces froides (10-100 K) peut mener à la désorption de certaines de ces molécules. Ce processus fondamental a des conséquences dans de nombreuses disciplines, dont deux ont guidé ce travail : l’astrochimie et la dynamique du vide dans les accélérateurs. La désorption induite par photons et électrons est étudiée pour des films amorphes de molécules condensées (glaces) telles que CO, H2O, NO ou CH4. Un objectif de cette thèse est la quantification de la désorption des différentes espèces, et d’explorer les paramètres pouvant affecter l’efficacité du processus. Le second objectif est de déterminer l’évolution et la relaxation des excitations électroniques initiales et par quel mécanisme cela mène à la désorption. La photodésorption est étudiée au LERMA en utilisant le rayonnement synchrotron dans la gamme du VUV (5-14 eV) et des X mous (520-600 eV). Cela permet d’obtenir une information spectrale cruciale pour la compréhension des mécanismes et pour l’implémentation dans les modèles. La désorption induite par les électrons est étudiée au CERN dans la gamme d’énergie 150-2000 eV. Les résultats obtenus étendent les données de photodésorption UV disponibles et permettent de déterminer la pertinence de la désorption par les électrons ou les rayons X pour l’astrochimie. Des progrès sont faits dans la compréhension des mécanismes, notamment sur le rôle du transport d’énergie ou de particules depuis l’intérieur de la glace vers la surface, ou sur la désorption indirecte. Un nouveau dispositif expérimental a aussi été mis en place au LERMA pour des expériences de désorption par laser et de spectroscopie laser, permettant d’obtenir l’énergie interne et cinétique des molécules désorbées

Compression of a Stearic Acid Surfactant Layer on Water Investigated by Ambient Pressure X-ray Photoelectron Spectroscopy

We present a combined Langmuir–Pockels trough and ambient pressure X-ray photoelectron spectroscopy (APXPS) study of the compression of stearic acid surfactant layers on neat water. Changes in the packing density of the molecules are directly determined from C 1s and O 1s APXPS data. The experimental data are fit with a 2D model for the stearic acid coverage. Based on the results of these proof-of-principle experiments, we discuss the remaining challenges that need to be overcome for future investigations of the role of surfactants in heterogeneous chemical reactions at liquid–vapor interfaces in combined Langmuir–Pockels trough and APXPS measurements

Immune Response and Mitochondrial Metabolism Are Commonly Deregulated in DMD and Aging Skeletal Muscle

Duchenne Muscular Dystrophy (DMD) is a complex process involving multiple pathways downstream of the primary genetic insult leading to fatal muscle degeneration. Aging muscle is a multifactorial neuromuscular process characterized by impaired muscle regeneration leading to progressive atrophy. We hypothesized that these chronic atrophying situations may share specific myogenic adaptative responses at transcriptional level according to tissue remodeling. Muscle biopsies from four young DMD and four AGED subjects were referred to a group of seven muscle biopsies from young subjects without any neuromuscular disorder and explored through a dedicated expression microarray. We identified 528 differentially expressed genes (out of 2,745 analyzed), of which 328 could be validated by an exhaustive meta-analysis of public microarray datasets referring to DMD and Aging in skeletal muscle. Among the 328 validated co-expressed genes, 50% had the same expression profile in both groups and corresponded to immune/fibrosis responses and mitochondrial metabolism. Generalizing these observed meta-signatures with large compendia of public datasets reinforced our results as they could be also identified in other pathological processes and in diverse physiological conditions. Focusing on the common gene signatures in these two atrophying conditions, we observed enrichment in motifs for candidate transcription factors that may coordinate either the immune/fibrosis responses (ETS1, IRF1, NF1) or the mitochondrial metabolism (ESRRA). Deregulation in their expression could be responsible, at least in part, for the same transcriptome changes initiating the chronic muscle atrophy. This study suggests that distinct pathophysiological processes may share common gene responses and pathways related to specific transcription factors

Suivi du contenu en azote de la solution du sol d'une rizière après placement d'urée

A comparative trial was conducted on a rice field planted and not planted to rice. Following up the nitrogen content of soil solutions during the trial enabled to specify relationships between soil-plant and nitrogeneous fertilizers (urea in the form of supergranules or perlurea applied in bands). A slower hydrolysis of urea was reported in treatments without rice, especially when urea was applied in the form of supergranules. Ammonium concentrations were very high after urea supergranules applications (1,000 ppm) and lesser when urea was applied in bands (55 to 99 ppm). The detailed examination of the evolutive curves of these concentrations pointed out a pseudo-delay effect in root uptake, the effect being more particularly sensible when supergranules were used. This can be explained if we assume a critical concentration threshold (about 100 ppm) beyond which root uptake becomes highly efficient. When urea is applied in the form of supergranules, roots would progress from the periphery to the center of the area of nitrogen diffusion. So the supply of plants at their request, added to the very marked decrease of losses linked to deep placements, would explain why urea is more efficient when applied in the form of supergarnules

Etude à l'aide d'urée enrichie en 15N de la fertilisation azotée du riz inondé à Madagascar

Les travaux comprennent trois étapes : - la comparaison entre supergranules d'urée, la perlurée et une solution d'urée placés à 1 cm ou 10 cm de profondeur. L'essai mené à Ansirabé a montré que la profondeur de localisation était le facteur le plus important. - des apports fractionnés de supergranules ou de perlurée : les supergranules apportés à 21 ou 42 j après repiquage donnent les meilleurs résultats. - une cinétique de prélèvement de l'azote. L'essai mené près d'Arivonimamo a permis de montrer la bonne efficacité des supergranules d'urée. La dynamique de prélèvement est expliquée par la forte proportion de NH3 (relativement à NH4) régnant dans la sphère de diffusion de l'ammoniaque dérivée du supergranule

Comparative effects of the application of prilled urea and urea supergranules on flooded rice in Madagascar

UMR SYSTEM : équipe AMPLUSInternational audience