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Use of Microbial Biofilms to Assess Groundwater Quality in Karstic Ecosystems
No full textInternational audienceKarstic aquifers are particularly vulnerable to contaminations but, unlike surface waters, biological indicators of their groundwater quality are lacking. We propose a methodology based on microbial biofilms developed on artificial substrates (clay beads) to evaluate groundwater quality. Clay beads were incubated every 2 months over 18 months in three karstic stations characterised by contrasting nutrient and organic matter inputs from their catchments. After every 2‐month incubation, microbial biofilms on clay beads were analysed for biomass, hydrolytic and dehydrogenase activities, and prokaryotic community structure. NH 4 + , NO 3 − , PO 4 3− and dissolved organic carbon (DOC) concentrations were also measured in groundwater during the experiment. Biofilm biomass and activities were not positively correlated with nutrient and DOC concentrations in groundwater probably due to biofilm growth inhibition by antibiotics in the station having the highest nutrient and DOC concentrations. In contrast, the diversity of prokaryotes in biofilms was positively correlated with nutrient and DOC availability. In the studied heterotrophic karstic stations, the quantity of resources originating from the catchments determined the diversity but also the prokaryotic community structures of biofilms. We selected several microbial taxa as potential indicators of groundwater quality. The next step will be to test their applicability in other karstic ecosystems
On the partial Grundy coloring of graphs
No full textInternational audienceIn a proper vertex coloring of a graph, a Grundy vertex is a vertex colored with color c and adjacent to any color 1 to c-1. A partial Grundy coloring of a graph is a proper coloring of its vertices where any color admits at least one Grundy vertex. The partial Grundy number of a graph is the maximum number of colors used in a partial Grundy coloring of this graph. In this article we consider this parameter for some classes of graphs, in particular -free graphs, regular graphs, Cartesian and direct products of graphs
Near real-time monitoring of volcanic deformation and lava flows from multi-angular Capella Space SAR imagery
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Spatially-Controlled Planar Guided Crystallization of Low-Loss Phase Change Materials for Programmable Photonics
No full textInternational audiencePhotonic integrated devices are progressively evolving beyond passive components into fully programmable systems, notably driven by the progress in chalcogenide phase-change materials (PCMs) for non-volatile reconfigurable nanophotonics. However, the stochastic nature of their crystal grain formation results in strong spatial and temporal crystalline inhomogeneities. Here, we propose the concept of spatially-controlled planar Czochralski growth, a novel method for programming the quasi-monocrystalline growth of low-loss Sb2S3 PCM, leveraging the seeded directional and progressive crystallization within confined channels. This guided crystallization method is experimentally shown to circumvent the current limitations of conventional PCM-based nanophotonic devices, including a multilevel non-volatile optical phase-shifter exploiting a silicon nitride-based Mach-Zehnder interferometer, and a programmable metasurface with spectrally reconfigurable bound state in the continuum. Precisely controlling the growth of PCMs to ensure uniform crystalline properties across large areas is the cornerstone for the industrial development of non-volatile reconfigurable photonic integrated circuits
Direct Fluoroformylation of the C3 ‐Position of Indoles with 2,4‐Dinitro(trifluoromethoxy)benzene as Fluorocarbonyl Source
No full textInternational audienceWe herein report the direct fluoroformylation of indoles and other heteroaromatic cycles. Acyl fluorides are very useful moieties in coupling reactions with or without metal. However, they are usually obtained from the corresponding carboxylic acids or from aryl halides in pallado‐catalyzed carbonylation/fluorination reactions. Our method uses fluorophosgene generated in situ from 2,4‐dinitro(trifluoromethoxy)benzene (DNTFB) as a fluoroformylating agent without any metal and from carboxylic acid‐free heteroaromatic rings. Moreover, our method can be telescoped with amidification reactions in a one‐pot process
Confinement Effects on the Rh <sup>III</sup> Cp* / Polyoxometalate System in Photochemical CO <sub>2</sub> Reduction Reactions: Porous Organic Polymer Versus Metal–Organic Framework
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The two-step scenario of the Messinian Crisis (Clauzon et al. , 1996): a specification supported by new data
No full textInternational audienceMany papers refer in a revised way to the two-step scenario of the Messinian Crisis conceived by Clauzon et al. (1996). The present paper recalls the basis for the two-step scenario and discrepancies with the later modified version, completed by new data supported by extensive micropaleontological analyses. Our interpretation of the Sicilian Eraclea Minoa section as belonging to a peripheral basin is the centre of the debate. We show the great amplitude of fluvial erosion during the peak of the crisis, which for the Rhône River, exceeded 400 km upstream of the present shoreline. Based on dinoflagellate cysts, we also recall the reasons for supporting the occurrence of three successive Lago Mare episodes of two different origins. The first and third episodes constitute phases of high sea-level exchanges between the Mediterranean and the Paratethys respectively just before the onset of paroxysm and after it. The second episode is due to overflowing Paratethyan waters from the Aegean Basin just before the end of paroxysm. Similarly, the demonstration of the marine reflooding of the Mediterranean Basin prior to the Zanclean is repeated. We emphasize dissimilarity between basins, focussing in particular on those, isolated or perched ones, which were continuously filled by waters during the desiccation phase: western part of the Alboran Sea and southeastern part of the Levantine Basin (marine waters), Apennine Foredeep (fresh waters), and Aegean Basin (brackish waters). The Apennine Foredeep cannot be the reference for the entire Mediterranean with respect to its evolution during the crisis. During the crisis, water exchanges between the Aegean Basin and the Eastern Paratethys (Dacic Basin, Black Sea) were impossible through the Marmara region because of the development of two opposed fluvial networks. Such exchanges existed thanks to a gateway that was probably located within the Balkans. Investigations around the Levantine Basin point to areas submitted to fluvial erosion during the crisis paroxysm and nearby areas, which might have received marine waters from the Red Sea. Much information is still to be discovered and that more progress is still needed in order to fully decipher this outstanding event.De nombreux articles se réfèrent opportunément mais sous une forme revisée au scénario en deux temps de la Crise messinienne de Clauzon et al. (1996). Cet article rappelle les fondements de ce scénario et les dissemblances avec les autres versions, le tout appuyé par de nouvelles données riches en analyses micropaléontologiques. Notre interprétation de la coupe d’Eraclea Minoa (Sicile) comme relevant d’un bassin périphérique est au centre du débat. Nous montrons l’ampleur de l’érosion fluviatile pendant le paroxysme de la crise qui, pour le Rhône, s’est propagée jusqu’à 400 km en amont de l’actuel littoral. Nous rappelons les arguments en faveur de l’existence de trois épisodes Lago Mare distincts chronologiquement et de nature différente mis en evidence par les kystes de dinoflagellés. Les premier et troisième épisodes résultent des phases d’échanges réciproques à haut niveau marin entre Méditerranée et Paratéthys peu avant le déclenchement du paroxysme et après celui-ci. Le second épisode est dû au déversement des eaux paratéthysiennes issues du bassin égéen peu avant la fin du paroxysme. De même, la démonstration du réennoiement du bassin méditerranéen antérieurement au Zancléen est réitérée. L’accent est mis sur la disparité entre bassins, notamment ceux qui sont restés isolés ou perchés et alimentés en eau pendant la phase de dessiccation: partie occidentale de la Mer d’Alboran et partie sud-est du basin levantin (eau marine), avant-fosse apenninique (eau douce), et basin égéen (eau saumâtre). Il est évident que le processus qu’a connu l’avant-fosse apenninique ne peut plus servir de modèle pour l’ensemble du bassin méditerranéen. Les échanges entre bassin égéen et Paratéthys orientale (basin dacique, Mer Noire) ne pouvaient s’effectuer par la région de Marmara, siège pendant la crise de deux réseaux fluviatiles de sens opposé, mais par un corridor probablement intra-balkanique. Les résultats sur le pourtour du bassin levantin laissent entrevoir des secteurs soumis à l’érosion fluviatile lors du paroxysme de la crise à côté de secteurs ayant pu bénéficier d’entrées d’eaux marines de la Mer Rouge. Il reste encore beaucoup à découvrir et à comprendre pour démystifier complètement cet événement hors normes
Éducation et démocratie : approches philosophiques. Introduction générale
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L’énigme du calice dans Bouvard et Pécuchet
No full textInternational audienceQuelques jours avant de mourir le 8 mai 1880, Gustave Flaubert élaborait l'épisode sur la botanique, un des derniers de son roman Bouvard et Pécuchet. À cette fin, et inspiré par une phrase de Rousseau sur le calice des fleurs qui « manque à la plupart des liliacées », il avait rédigé une note en forme d'énigme botanique : trouver une plante commune, poussant en Normandie au mois d'avril, qui serait d'une famille qui dérogerait à une règle générale chez les plantes (« Toute plante a des feuilles, un calice et une corolle »), mais qui elle-même dérogerait à cette exception au sein de sa famille (une exception à l'exception). Sans grande familiarité avec la botanique, Flaubert prétendait prédire l'existence d'une telle plante, alors que l'énigme suscitait la circonspection chez ses amis plus savants. Une enquête de Maupassant lui a permis d'examiner des solutions possibles d'abord parmi les Renonculacées puis les Rubiacées, où la shérarde lui a semblé répondre à son attente. Cet épisode laisse toujours plusieurs questions sans réponse, auxquelles nous tentons d'apporter des éclairages, qui nécessitent un regard botanique sur cette énigme : pourquoi Rousseau a-t-il écrit « la plupart » ? Pourquoi Flaubert a-t-il refusé la première solution de Maupassant ? Pourquoi a-t-il accepté la seconde ? La shérarde était-elle en 1880, et est-elle aujourd'hui une bonne solution à son énigme ? Quels mécanismes naturels ou épistémologiques, produisent les exceptions aux exceptions ? Comment cette plante imaginaire peut-elle devenir le terrain de confrontation de conceptions différentes de la nature et de la connaissance, du XIXe au XXIe siècle ? ABSTRACT. A few days before his death on May 8, 1880, Gustave Flaubert was working on the episode about botany, one of the last in his novel Bouvard and Pécuchet. To this end, inspired by a sentence by Rousseau about the calyx of flowers, which "is missing in most liliaceae," he wrote a note in the form of a botanical enigma: to find a common plant, growing in Normandy in April, that would belong to a family that deviated from a general rule among plants ("Every plant has leaves, a calyx, and a corolla"), but which itself would deviate from this exception within its family (an exception to the exception). Without much familiarity with botany, Flaubert claimed to predict the existence of such a plant, while the enigma aroused caution among his more knowledgeable friends. An investigation by Maupassant allowed him to examine possible solutions, first among the Ranunculaceae and then the Rubiaceae, where the sherardia seemed to meet his expectations. This episode still leaves several questions unanswered, which we will attempt to shed light on, requiring a botanical and historical perspective on this enigma: why did Rousseau write "most"? Why did Flaubert reject Maupassant's first solution? Why did he accept the second? Was the sherardia in 1880, and is it today, a good solution to his enigma? What natural or epistemological mechanisms produce exceptions to exceptions? How can this imaginary plant become the battleground for different conceptions of nature and knowledge, from the 19th to the 21st century
