Exchange rates of dimethyl sulfide between ocean and atmosphere

International audienceBiological activity plays an important role in gaseous sulfur compound exchanges between ocean and atmosphere. Indeed, this activity involves organ­ic sulfur compounds, one of which is dimethyl sulfide (DMS). This gas is rather insoluble and volatile; it escapes from the water, and oxidizes in the atmosphere to give SO$_2$ which oxidizes to sulfates.A cruise, in the Pacific Ocean, was undertaken to measure DMS at the ocean-atmosphere interface. Measurements were taken in water and in air at heights of 1, 10, and 17 m above the ocean surface. The results obtained dur­ing this voyage show a correlation between surface water and atmospheric con­centrations. These concentration gradients from surface water layer to atmo­sphere enable us to determine the ocean-to-atmosphere transfer coefficient (or piston velocity), which increases drastically (between 7 and 25 cm/hr), for wind velocities greater than 3 m/s

Utilisation d’un microscope à émission de champ pour l’étude de l’adsorption des gaz sur le molybdène au niveau du plan cristallographique

Un microscope à émission de champ, muni d’un trou-sonde, a été utilisé dans la mesure des variations du travail d’extraction, ΔΦ, d’une pointe métallique missive monocristalline en molybdène. Les valeurs ΔΦ enregistrées au niveau de divers plans cristallins, lorsque les gaz résiduels (CO et H2) sont adsorbés à saturation sur une pointe préalablement décontaminée, ont été comparées avec les données de la littérature relatives à ΔΦH2 et ΔΦCO. Il a été conclu que les gaz résiduels ne subissent pas une simple coadsorption sur le molybdène mais qu’il se produit une interaction entre ces gaz conduisant à un complexe de surface

Analyse des variations saisonnières de l'ozone antarctique dans la basse stratosphère à partir des données Lidar et Sonde de Dumont d'Urville

International audienceAverage subsidence in the Antarctic lower stratosphere for the austral fall of 1994 and 1996 and ozone destruction rates during the spring are derived from ozone measurements made at Dumont d'Urville (140. IE, 66.4S), ne comparison with POAM II data suggests that ozone destruction within the vortex starts earlier on the edge than in the centre. The vortex sampling in 1996 allows us to study the vortex confinement and to confirm its role of isolating barrier above 400 K.La subsidence moyenne dans la basse stratosphère en Antarctique pour l'automne austral 1994 et 1996 et les taux de destruction de l'ozone durant le printemps sont calculés à partir des mesures d'ozone réalisées à la station de Dumont d'Urville (140.1E, 66.4S). La comparaison avec les données Poam II suggère que la destruction d'ozone à l'intérieur du vortex commence plus tôt en bordure qu'au centre. L'échantillonnage du vortex en octobre 1996 permet d'étudier le confinement du vortex et de confir- mer son rôle de barrière isolante au-dessus de 400 K

Study of the interannual ozone loss and the permeability of the Antarctic polar vortex from aerosol and ozone lidar measurements in Dumont dUrville (66.4°S 140°E)

International audienceSystematic ground-based measurements of the ozone and aerosol stratospheric profile performed in the Dumont d'Urville (66.4°S, 140°E) Antarctic station are used to study the air subsidence in fall, the springtime ozone loss, and the vortex confinement on an interannual basis. The data obtained mostly from March to October in the 1992–1998 time period are analyzed as a function of equivalent latitude in order to discriminate the measurements performed inside, at the edge or outside the vortex. The subsidence rate derived from the ozone measurements in the lower stratosphere prior to the destruction period and from the volcanic aerosol measurements in 1992 is in good agreement with the estimation provided by radiative transfer models. The analysis of the ozone seasonal variation shows that the ozone destruction starts in the beginning of August and affects essentially the inner vortex or inner edge regions. The destruction lasts up to the end of September and low ozone values are found up to the end of October, confirming the isolation of the polar vortex above 400 K. Ozone destruction rates of the order of 3%/d in the 400–475 K region and 1.5%/d around 550 K are derived from the data obtained inside the vortex. The ozone measurements obtained in October allow to study the vortex confinement which shows the increase of the ozone meridional gradient through the vortex edge from 400 to 650 K. A fine view of the vortex edge is provided by a near daily series of aerosol lidar measurements performed in October 1992, a period when the vortex was deformed by planetary waves and slanted with respect to the vertical direction

Homogeneity of flexible metal–organic frameworks containing mixed linkers

Very sophisticated porous materials known as multivariate functional MOFs (also known as MixMOFs) can be designed using a synthesis method that starts from solutions composed of two or more different linkers. For this procedure to be successful, one must have access to techniques that characterize the homogeneity of MOF crystallites containing two different linkers. This is of particular relevance for MOFs made of 2-aminobenzene-1,4-dicarboxylate (abdc), which are excellent platforms for the introduction of additional functions by post-modification. In this paper, we show that adsorption/desorption isotherms and thermodiffraction studies on flexible structures can indirectly characterize the homogeneity of MOFs made from a mixture of linkers. Breathing pressures and temperatures for a series of MIL-53(Al) functionalized with amino tags, i.e. Al(OH)(bdc)1−n(abdc)n, were measured as a function of the amino content. The linear relationship between the CO2 breathing pressure and the amine content in the MIL-53(Al) structure clearly illustrates the homogeneity of the crystallite composition; in other words, the crystallites have the same abdc : bdc ratio. On the other hand, the functionalization of MIL-53(Al) with low amine content (10% abdc) results in a profound modification of the breathing properties triggered by the temperature. Much higher temperatures are required for full conversion of the np (narrow pore) to the lp (large pore) phase. We also suggest an interplay between coexisting np and lp microcrystalline domains that may “smooth” the breathing properties at the macroscopic level

L'église Saint-Martin-de-Castries (Hérault, 34): d'un habitat rural cartolingien à un prieuré cure dépendant de l'abbaye Saint-Guilhem-le-Désert

Dir. Agnès BergeretRapport

L'église Saint-Martin-de-Castries (Hérault, 34): d'un habitat rural cartolingien à un prieuré cure dépendant de l'abbaye Saint-Guilhem-le-Désert

Dir. Agnès BergeretRapport