90 research outputs found
Hommage Ă Bertrand Dorny (1931-2015)
Depuis 2003, un peu avant NoĂ«l, je trouvais dans ma boĂźte aux lettres une enveloppe matelassĂ©e en papier kraft, lĂ©gĂšrement bombĂ©e, et je savais qui en Ă©tait lâexpĂ©diteur. CâĂ©tait Bertrand Dorny. Il mâenvoyait ses vĆux dans une boĂźte dâallumettes quâil avait eu soin de rendre unique. Elle contenait un minuscule livre manuscrit, en forme de dĂ©pliant. Le texte Ă©tait de lui. Chaque annĂ©e, je me promettais dâĂȘtre la premiĂšre Ă lui souhaiter la bonne annĂ©e et je nâai jamais rĂ©ussi. Fin 2015, je nâa..
Nitrogen sorption as a tool for the characterisation of polysaccharide aerogels
Supercritically dried aerogels of several polysaccharides (chitin, chitosan, alginate, alginic acid, k- carrageenan, and agar) have been characterised by physisorption ofN2. Surface areas as high as 570m2 gâ1 have been measured. The nature of the functional groups of the polysaccharide significantly influences the adsorption of N2 on the surface of the aerogel. The net enthalpy of adsorption increases with the polarity of the surface groups of the polymer, in the order chitin < agarâ€chitosan < carrageenan < alginic acidâŒalginate. The surface area and the mesopore distribution of the aerogels depend both on the dispersion
of the parent hydrogel and on the behaviour of each polymer in the drying treatment. Aerogels which retain the dispersion of the parent hydrogel are mainly macroporous (pores larger than 50 nm) while materials liable to shrink upon solvent exchange form mesoporous structures
The role of argumentation in online epistemic communities: the anatomy of a conflict in Wikipedia
International audienceThis research aims to investigate the processes by which knowledge objects â in this case Wikipedia pages on astronomy â are elaborated, in online communities, focussing on the role of argumentative interactions
DNA-catalyzed Henry Reaction in Pure Water and the Striking Influence of Organic Buffer Systems
In this manuscript we report a critical evaluation of the ability of natural DNA to mediate the nitroaldol (Henry) reaction at physiological temperature in pure water. Under these conditions, no background reaction took place (i.e., control experiment without DNA). Both heteroaromatic aldehydes (e.g., 2-pyridinecarboxaldehyde) and aromatic aldehydes bearing strong or moderate electron-withdrawing groups reacted satisfactorily with nitromethane obeying first order kinetics and affording the corresponding ÎČ-nitroalcohols in good yields within 24 h. In contrast, aliphatic aldehydes and aromatic aldehydes having electron-donating groups either did not react or were poorly converted. Moreover, we discovered that a number of metal-free organic buffers efficiently promote the Henry reaction when they were used as reaction media without adding external catalysts. This constitutes an important observation because the influence of organic buffers in chemical processes has been traditionally underestimated
Mesoporosity changes from cambium to mature tension wood: a new step toward the understanding of maturation stress generation in trees
International audienceIn order to progress in the understanding of mechanical stress generation, the mesoporosity of the cell wall and its changes during maturation of poplar (Populus deltoides x P. nigra) tension wood (TW) and opposite wood (OW) were measured by nitrogen adsorptionâdesorption. Variations in the thickness of the gelatinous layer (G-layer) were also measured to clarify whether the mesoporosity change simultaneously with the deposition of the G-layer in TW. Results show that mesoporous structures of TW and OW were very similar in early development stages before the deposition of G-layers. With the formation of the S2 layer in OW and the G-layer in TW, the mesopore volume decreased steeply before lignification. However, in TW only, the decrease in mesopore volume occurred together with the pore shape change and a progressive increase in pore size. The different patterns observed in TW revealed that pores from G-layers appear with a different shape compared to those of the compound middle lamella, and their size increases duringthe maturation process until stabilising in mature wood. This observation strongly supports the hypothesis of the swelling of the G-layer matrix during maturation as the origin of maturation stress in poplar tension wood
Chitosan as efficient porous support for dispersion of highly active gold nanoparticles: design of hybrid catalyst for carbon-carbon bond formation
International audienceMacroporous catalyst was obtained by dispersing nanosized gold in the fibrils of the chitosan matrix, followed by CO2 supercritical drying of the resulting hybrid material. The accessible gold nanoparticles are highly active for carbonâcarbon cross coupling reactions
De la complexation des cations aux matĂ©riaux d'intĂ©rĂȘt (les gels ionotropiques d'alginate)
Les alginates, polysaccharides extraits des algues brunes, sont des copolymĂšres Ă blocs linĂ©aires formĂ©s d'unitĂ©s mannuronates (M) et guluronates (G). Leur structure dĂ©pend de la source naturelle. La complexation de cations divalents ou trivalents (sauf Mg2+) par les fonctions carboxylates conduit Ă la formation d'un hydrogel. Pour approfondir l'Ă©tude de la formation des gels ionotropiques d'alginate, des hydrogels et des aĂ©rogels sĂ©chĂ©s en conditions supercritiques ont Ă©tĂ© caractĂ©risĂ©s Ă plusieurs Ă©chelles par diffĂ©rentes techniques. L'analyse orbitalaire ab initio de petits complexes a montrĂ© la formation de liaisons covalentes fortes avec les mĂ©taux de transition alors que les alcalino-terreux ne mettent en jeu que des interactions Ă©lectrostatiques. Selon le rapport M/G et la nature des cations, diffĂ©rents rĂ©gimes structuraux ont pu ĂȘtre identifiĂ©s par des mesures SAXS (~10-200Ă
) : des gels fibrillaires ou formĂ©s d'agglomĂ©rats interconnectĂ©s. Les propriĂ©tĂ©s mĂ©caniques des hydrogels et les surfaces spĂ©cifiques des aĂ©rogels correspondants sont directement reliĂ©es Ă ces morphologies. La prĂ©sence simultanĂ©e de plusieurs mĂ©taux dans les gels peut induire des effets coopĂ©ratifs dans la formation mais aussi dans les propriĂ©tĂ©s des matĂ©riaux. De nouvelles mĂ©thodes ont Ă©tĂ© mises au point pour contrĂŽler la synthĂšse de gels hĂ©tĂ©ro-cationiques, en considĂ©rant les effets d'affinitĂ©.Sur la base de cette Ă©tude, des synthĂšses originales de matĂ©riaux fonctionnels nano-structurĂ©s ont Ă©tĂ© dĂ©veloppĂ©es. Certains ont Ă©tĂ© construits directement dans le rĂ©seau d'alginate en exploitant les cations de gĂ©lification ; d'autres ont nĂ©cessitĂ© le sacrifice de la matrice pour former des oxydes simples ou mixtes nanocristallins.Alginates, polysaccharides produced by brown algae, are linear block-copolymers formed by mannuronate (M) and guluronate (G) units. Their structure depends on the natural source. The coordination of divalent or trivalent cations (except Mg2+) with the carboxylate functions leads to the formation of a hydrogel. In order to get some insight in ionotropic alginate gel formation, hydrogels and supercritical dried aerogels were analysed through various characterizations at different scales. The ab initio molecular orbital analysis on small complexes revealed strong coordination-covalent bonds in the transition metal complexes, whereas only ionic interaction occurs between the alkaline-earth cations and the carboxylates. Depending on the M/G ratio and the nature of the cation, different structural regimes were identified by SAXS analysis (~10-200Ă
) : well-defined fibrillar gels or gels with multiple junction nature. The mechanical properties of the hydrogels and surface areas of the resulting aerogels are directly related to these morphologies. The concomitant presence of different metals in the gel can bring cooperative effect for the formation but also for the properties of the materials. New methods to control the synthesis of hetero-cationic gels were implemented, taking into account the affinity effects. On the basis of this study, we developed new nanostructured functional materials synthesis. Some were built directly in the alginate network using the gelling cations. Others needed to sacrifice the matrix to form nanocrystalline single or mixed oxides.MONTPELLIER-Ecole Nat.Chimie (341722204) / SudocSudocFranceF
15 000 volumes à la réserve des livres rares
Si le département des estampes s\u27est spécialisé dans la collection des artist\u27s book, un genre né à la fin des années 1960 (lire l\u27article de Marie-Cécile Miessner en page 36), la réserve des livres rares a constitué une collection de livres d\u27artistes dont l\u27origine remonte aux livres illustrés par des peintres, dans le dernier quart du XIXe siÚcle. Responsable des collections des XX et XXIe siÚcles, Marie-Françoise Quignard présente la constitution du fonds, l\u27un des plus importants au monde
Editorial on Special Issues âAerogelsâ and âAerogels 2018â
International audienc
Des hydrocolloïdes aux matériaux mésoporeux (application en catalyse)
MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF
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