Dynamique hydro-sédimentaire des côtes dominées par la houle et par la marée

Les travaux de recherche que j’ai menés au cours des dix dernières années visent à améliorer la compréhension de la dynamique hydro-sédimentaire des zones littorales, en combinant analyses de mesures in situ et simulations numériques couplées vagues, courants, transport sédimentaire et évolution du fond. Le développement de modèles régionaux de vagues, de marées et de surcotes a amélioré la compréhension de la variabilité des climats de vague dans l’Atlantique Nord et des processus physiques contrôlant les surcotes et les submersions marines. Une méthode originale combinant traçages fluorescents et simulations numériques a permis d’améliorer l’estimation de la dérive littorale et de montrer sa forte variabilité en rapport avec celle des climats de vague. L’analyse des processus physiques contrôlant les embouchures tidales a montré que leur développement en période de beau temps résultait d’une forte dominance du jusant liée à l’asymétrie de la marée et que leur comblement en période hivernale résultait de la superposition de plusieurs mécanismes induits pas les vagues. Mes travaux en cours et leurs perspectives concernent : (1) la modélisation morphodynamique à long terme avec une approche 2DH et (1) l’analyse des processus physiques à court terme (interactions vagues-courants, ondes infra-gravitaires, etc.) à l’aide d’une approche 3D

CO ice photodesorption: A wavelength-dependent study

UV-induced photodesorption of ice is a non-thermal evaporation process that can explain the presence of cold molecular gas in a range of interstellar regions. Information on the average UV photodesorption yield of astrophysically important ices exists for broadband UV lamp experiments. UV fields around low-mass pre-main sequence stars, around shocks and in many other astrophysical environments are however often dominated by discrete atomic and molecular emission lines. It is therefore crucial to consider the wavelength dependence of photodesorption yields and mechanisms. In this work, for the first time, the wavelength-dependent photodesorption of pure CO ice is explored between 90 and 170 nm. The experiments are performed under ultra high vacuum conditions using tunable synchrotron radiation. Ice photodesorption is simultaneously probed by infrared absorption spectroscopy in reflection mode of the ice and by quadrupole mass spectrometry of the gas phase. The experimental results for CO reveal a strong wavelength dependence directly linked to the vibronic transition strengths of CO ice, implying that photodesorption is induced by electronic transition (DIET). The observed dependence on the ice absorption spectra implies relatively low photodesorption yields at 121.6 nm (Ly-alpha), where CO barely absorbs, compared to the high yields found at wavelengths coinciding with transitions into the first electronic state of CO (singulet Pi at 150 nm); the CO photodesorption rates depend strongly on the UV profiles encountered in different star formation environments.Comment: 5 pages, 2 figures, published in ApJ

UV photodesorption of methanol in pure and CO-rich ices: desorption rates of the intact molecule and of the photofragments

Wavelength dependent photodesorption rates have been determined using synchrotron radiation, for condensed pure and mixed methanol ice in the 7 -- 14 eV range. The VUV photodesorption of intact methanol molecules from pure methanol ices is found to be of the order of 10$^{-5}$ molecules/photon, that is two orders of magnitude below what is generally used in astrochemical models. This rate gets even lower ($<$ 10$^{-6}$ molecules/photon) when the methanol is mixed with CO molecules in the ices. This is consistent with a picture in which photodissociation and recombination processes are at the origin of intact methanol desorption from pure CH$_3$OH ices. Such low rates are explained by the fact that the overall photodesorption process is dominated by the desorption of the photofragments CO, CH$_3$, OH, H$_2$CO and CH$_3$O/CH$_2$OH, whose photodesorption rates are given in this study. Our results suggest that the role of the photodesorption as a mechanism to explain the observed gas phase abundances of methanol in cold media is probably overestimated. Nevertheless, the photodesorption of radicals from methanol-rich ices may stand at the origin of the gas phase presence of radicals such as CH$_3$O, therefore opening new gas phase chemical routes for the formation of complex molecules.Comment: 13 pages, 2 figures, 1 tabl

Indirect ultraviolet photodesorption from CO:N2 binary ices - an efficient grain-gas process

UV ice photodesorption is an important non-thermal desorption pathway in many interstellar environments that has been invoked to explain observations of cold molecules in disks, clouds and cloud cores. Systematic laboratory studies of the photodesorption rates, between 7 and 14 eV, from CO:N2 binary ices, have been performed at the DESIRS vacuum UV beamline of the synchrotron facility SOLEIL. The photodesorption spectral analysis demonstrates that the photodesorption process is indirect, i.e. the desorption is induced by a photon absorption in sub-surface molecular layers, while only surface molecules are actually desorbing. The photodesorption spectra of CO and N2 in binary ices therefore depend on the absorption spectra of the dominant species in the subsurface ice layer, which implies that the photodesorption efficiency and energy dependence are dramatically different for mixed and layered ices compared to pure ices. In particular, a thin (1-2 ML) N2 ice layer on top of CO will effectively quench CO photodesorption, while enhancing N2 photodesorption by a factors of a few (compared to the pure ices) when the ice is exposed to a typical dark cloud UV field, which may help to explain the different distributions of CO and N2H+ in molecular cloud cores. This indirect photodesorption mechanism may also explain observations of small amounts of complex organics in cold interstellar environments.Comment: 21 pages 5 figure

Mapping and Describing Geospatial Data to Generalize Complex Models: The Case of LittoSIM-GEN

For some scientific questions, empirical data are essential to develop reliable simulation models. These data usually come from different sources with diverse and heterogeneous formats. The design of complex data-driven models is often shaped by the structure of the data available in research projects. Hence, applying such models to other case studies requires either to get similar data or to transform new data to fit the model inputs. It is the case of agent-based models (ABMs) that use advanced data structures such as Geographic Information Systems data. We faced this problem in the LittoSIM-GEN project when generalizing our participatory flooding model (LittoSIM) to new territories. From this experience, we provide a mapping approach to structure, describe, and automatize the integration of geospatial data into ABMs

A Survey of UV Bright Sources Behind the Halo of M31

We have performed a wide-area ultraviolet (UV) imaging survey using the GALaxy Evolution eXplorer (GALEX) to search for bright, point-like UV sources behind M31's extended halo. Our survey consisted of 46 pointings covering an effective area of ~50 deg^2, in both the far-UV and near-UV channels. We combined these data with optical R-band observations acquired with the WIYN Mosaic-1 imager on the Kitt Peak National Observatory 0.9m WIYN telescope. An analysis of the brightness and colors of sources matched between our photometric catalogs yielded ~100 UV-bright quasar candidates. We have obtained discovery spectra for 76 of these targets with the Kast spectrometer on the Lick 3m telescope and confirm 30 active galactic nuclei and quasars, 29 galaxies at z > 0.02 including several early-type systems, 16 Galactic stars (hot main-sequence stars), and one featureless source previously identified as a BL Lac object. Future UV spectroscopy of the brightest targets with the Cosmic Origins Spectrograph on the Hubble Space Telescope will enable a systematic search for diffuse gas in the extended halo of M31.Comment: 10 pages, 10 figures. Accepted to MNRA

Automating vertical services deployments over the 5GT platform

This article presents a system for 5G networks that makes it possible to meet the diverse needs of vertical industries simultaneously sharing the same physical infrastructure. Orchestration, network slicing, edge computing, and federation are key technologies enabling industry verticals to have their own virtual networks, which might require aggregating transport networking and computing fabric, from the edge up to the core and cloud. Three novel building blocks are defined to meet these challenges in an automated manner: a vertical slicer as the entry point to create services and request slices, a service orchestrator to manage the services and decide their placement and allocation of required resources, and a mobile transport and computing platform virtualizing infrastructure networking and computing resources in an integrated manner. An experimental evaluation of the developed system shows its feasibility and confirms some of the benefits expected