Résolution de certains modules instables et fonction de partition de Minc

One constructs minimal injective resolutions for certain unstable modules that appear to be the mod 2 cohomology of Thom spectra. The terms of the resolution are tensor products of Brown–Gitler modules and Steinberg modules introduced by S. Mitchell and S. Priddy. A combinatorial result of Andrews shows that the alternating sum of the Poincaré series of the considered modules is zero. One gives homotopical applications of this result. To cite this article: D.H.H. Nguyen et al., C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Discrimination of metallosupramolecular architectures in solution by using diffusion ordered spectroscopy (DOSY) experiments: double-stranded helicates of different lengths

The translational diffusion coefficients of various helicates have been determined by using NMR diffusion spectroscopy (Diffusion Ordered SpectroscopY, DOSY), in order to investigate the individual behaviour of the helicates according to their length (different nuclearities; 1-5 metals), to the nature of the metal involved (CuI or AgI), as well to their bulkiness due to the presence of substituents on the periphery of the assembly. Furthermore, the spectrum of a mixture of helicates belonging to the same series, but with different lengths and nuclearities, showed the signals of each component, with no observable cross-linking, confirming the self-recognition properties of the helicates.     

Effect of aqueous acetic, oxalic, and carbonic acids on the adsorption of europium(III) onto alpha-alumina

Chemical retention, i.e., partition of the element between aqueous solution and mineral surface, is a key phenomenon for assessing the safety of possible nuclear waste disposal. For this purpose, the sorption of Eu(III) onto a model mineral-alpha-alumina-is studied here, including the effects of groundwater chemistry: pH and concentrations of small organic and inorganic ligands (acetate, oxalate, and carbonate anions). This work presents some experimental evidence for a synergic mechanism of sorption of europium-ligand complexes onto the alumina. Only cationic complexes were necessary to consider to model experimental results. Using the ion-exchange theory (IET) and a corresponding restricted set of parameters-exchange capacities and thermodynamic equilibrium constants-the whole set of sorption experiments of Eu(III) cationic species onto the alpha-alumina was modeled under various chemical conditions.     

Aging of an unstable w/o gel emulsion with a nonionic surfactant

We study an unstable highly concentrated emulsion of water droplets in oil with a nonionic surfactant. A technique of light diffusion coupled to a rheometer allows simultaneous measurement of average droplet radius and emulsion shear elastic modulus during time. Over the studied range of volume fraction (from 71 to 95%), we show that Princen and Kiss’ (J Colloid Interface Sci 112:427–437, 1986) model does not apply. A dimensional analysis based on the hypothesis of dominant van der Waals forces is proposed for nonionic surfactants, which is in good agreement with experimental data. We also show that the measured average droplet volume increases linearly with time and that the coalescence rate strongly depends on the volume fraction in relation with different topological conformations of droplets.

Fast propagation for KPP equations with slowly decaying initial conditions

This paper is devoted to the analysis of the large-time behavior of solutions of one-dimensional Fisher-KPP reaction-diffusion equations. The initial conditions are assumed to be globally front-like and to decay at infinity towards the unstable steady state more slowly than any exponentially decaying function. We prove that all level sets of the solutions move infinitely fast as time goes to infinity. The locations of the level sets are expressed in terms of the decay of the initial condition. Furthermore, the spatial profiles of the solutions become asymptotically uniformly flat at large time. This paper contains the first systematic study of the large-time behavior of solutions of KPP equations with slowly decaying initial conditions. Our results are in sharp contrast with the well-studied case of exponentially bounded initial conditions.     

Imidazol(in)ium-2-Carboxylates as N-Heterocyclic Carbene Ligand Precursors for Ruthenium Metathesis Initiators

Summary: Imidazol(in)ium-2-carboxylates were used as N-heterocyclic carbene (NHC) ligand precursors to convert the [RuCl₂(p-cymene)]₂ dimer into three ruthenium-arene complexes of the [RuCl₂(p-cymene)(NHC)] type. The decarboxylation of NHC · CO₂ betaines also provided a convenient synthetic path to prepare five well-known ruthenium-NHC catalysts for olefin metathesis and related reactions, including the second generation Grubbs and Hoveyda–Grubbs catalysts, via ligand exchange with phosphine-containing, first generation ruthenium-benzylidene or indenylidene complexes. Both procedures are particularly attractive from a practical point of view, because NHC · CO₂ adducts are stable zwitterionic compounds that can be stored and handled with no particular precautions.     

Supramolecular structures in nanocomposite multilayered films

We investigate the multilayered structures of poly(ethylene)oxide/montmorillonite nanocomposite films made from solution. The shear orientation of a polymer-clay network in solution combined with simultaneous solvent evaporation leads to supramolecular multilayer formation in the film. The resulting films have highly ordered structures with sheet-like multilayers on the micrometer length scale. The polymer covered clay platelets were found to orient in interconnected blob-like chains and layers on the nanometer length scale. Inside the blobs, scattering experiments indicate the polymer covered and stacked clay platelets oriented in the plane of the film. The polymer is found to be partially crystalline although this is not visible by optical microscopy. Atomic force microscopy suggests that the excess polymer, which is not directly adsorbed to the clay, is wrapped around the stacked platelets building blobs and the polymer also interconnects the polymer-clay layers. Overall our results suggest the re-intercalation of clay platelets in films made from exfoliated polymer-clay solutions as well as the supramolecular order and hierarchical structuring on the nanometer, via micrometer to the centimeter length scale.