Anionic polymerization of ethylene oxide with cryptates as counterions: 2

A kinetic study of the anionic polymerization of ethylene oxide has been made in tetrahydrofuran at 20°C, with the cryptate Cs⁺ + [TC] as counterion, [TC] being a spheroidal macrotricyclic ligand. Conductance measurements have been made on THF solutions of ?₄BCs + [TC]. Ionic associations higher than cryptated ion pairs are negligible for living end concentrations lower than 3 × 10^?4 moll^?1. k_± and the alkoxide ion pair dissociation constant K_D were determined from both sets of kinetic data obtained with and without added salt knowing the value of k_? from kinetic data performed with K⁺ + [222] as counterion. Free alkoxide ions are about twenty times more reactive than cryptated caesium ion pairs.     

Polymer electrolytes

Summary The room temperature conductivity of lithium salts dissolved in polyethylene oxide, proposed as polymer electrolytes, is shown to decrease drastically upon storage. The crystallization process, which is responsible for that ageing, can be blocked, if two further components are added : an elastomer copolymer butadiene-acrylonitrile and a macromer of polyoxyethylene. In addition, a crosslinking process must be carried out.     

Preparation of optically active poly β-propiolactones

Racemic -methyl--n-propyl--propiolactone is readily polymerized with zinc and cadmium chiral glycolates leading to optically active polyesters. The stereoelectivities observed are lower than for oxiranes and thiiranes with the same initiator system. A value of rotatory power for pure enantiomer _o, is deduced from NMR measurements in the presence of chiral solvent. The structure of polymers is discussed on the basis of NMR results.     

Feeding rats with liposomes or fish oil differently affects their lipid metabolism

Two n‐3 polyunsaturated fatty acid (PUFA)‐rich diets differing in their chemical and physical forms were given to rats during 2 wk. Liposomes [phospholipids (PL) organized in bilayer structures] made from a natural marine lipid extract or a mixture of fats containing fish oil [similar fatty acids esterified in triacylglycerols (TAG)] were used. The influence of n‐3 PUFA dietary sources on plasma parameters, i.e. TAG, cholesterol and PL concentrations, was investigated. A similar hypotriglyceridemic effect of n‐3 PUFA from liposomes or fish oil was observed. In contrast, feeding rats with liposomes led to different PL and cholesterol patterns. In the plasma of rats fed liposomes, total cholesterol amounts were positively correlated with PL levels. Liposome and fish oil feedings caused a marked increase in the amounts of n‐3 PUFA, which occurred mainly at the expense of n‐6 PUFA. However, the enrichment in n‐3 PUFA in the different plasma lipid classes differed substantially when ingested in the form of fish oil or liposomes. These results were interpreted in terms of different lipid bioavailability and metabolic fate during the digestive steps and in the liver, with the dietary source.     

Crack–Tip Toughness of a Soft Lead Zirconate Titanate

Crack–opening displacement (COD) measurements were performed on a commercial lead zirconate titanate (PZT). The intrinsic fracture toughness (or crack–tip toughness) of this material was determined using a new evaluation procedure, which takes into account the near–tip CODs and complete crack profile CODs. The crack–tip toughness K _I0 was determined from an extrapolation of COD data obtained at various loading stages, thus avoiding the complications caused by subcritical crack growth in PZT. Results for plane strain and plane stress condition are presented.     

Cellulose nanocrystal-mediated assembly of graphene oxide in natural rubber nanocomposites with high electrical conductivity

This study reports a green and powerful strategy for preparing cellulose nanocrystal (CNC)/graphene oxide (GO)/natural rubber (NR) nanocomposites hosting a 3D hierarchical conductive network. Due to good dispersibility and amphiphilic nature of CNC, well dispersed CNC/GO nanohybrids were prepared. Hydrogen bonding interactions between CNC and GO greatly enhanced the stability of the CNC/GO nanohybrids. CNC/GO nanohybrids were introduced into NR latex under sonication and the mixture was cast. Self-assembled CNC/GO nanohybrids preferentially dispersed in the interstice between latex microspheres allowing the construction of a 3D hierarchical conductive network. By combining strong hydrogen bonds and 3D conductive network, both electrical conductivity and mechanical properties (tensile strength and modulus) have been significantly improved. The electrical conductivity of the nanocomposite with 4 wt% GO and 5 wt% CNC exhibited an increase of nine orders of magnitude compared to the nanocomposite with only 4 wt% GO; meanwhile, the electrical percolation threshold was 3-fold lower than for NR/GO composites.     

Mathematical morphology on hypergraphs,application to similarity and positive kernel

The focus of this article is to develop mathematical morphology on hypergraphs. To this aim, we define lattice structures on hypergraphs on which we build mathematical morphology operators. We show some relations between these operators and the hypergraph structure, considering in particular transversals and duality notions. Then, as another contribution, we show how mathematical morphology can be used for classification or matching problems on data represented by hypergraphs: thanks to dilation operators, we define a similarity measure between hypergraphs, and we show that it is a kernel. A distance is finally introduced using this similarity notion.     

Licence de brevet et partage du risque: Résultats de simulation

Annals of Telecommunications - Le partage du risque est une des raisons les plus souvent avancées pour expliquer les clauses financières des contrats de licence. Pour autant, aucune...     

Classical and variational multiscale LES of the flow around a circular cylinder on unstructured grids

The effects of numerical viscosity, subgrid scale (SGS) viscosity and grid resolution are investigated in LES and VMS-LES simulations of the flow around a circular cylinder at Re=3900 on unstructured grids. The separation between the largest and the smallest resolved scales in the VMS formulation is obtained through a variational projection operator and finite-volume cell agglomeration. Three different non-dynamic eddy-viscosity SGS models are used both in classical and in VMS-LES. The so-called small-small formulation is used in VMS-LES, i.e. the SGS viscosity is computed as a function of the smallest resolved scales. Two different grid resolutions are considered. It is found that, for each considered SGS model, the amount of SGS viscosity introduced in the VMS-LES formulation is significantly lower than in classical LES. This, together with the fact that in the VMS formulation the SGS viscosity only acts on the smallest resolved scales, has a strong impact on the results. However, a significant sensitivity of the results to the considered SGS model remains also in the VMS-LES formulation. Moreover, passing from classical LES to VMS-LES does not systematically lead to an improvement of the quality of the numerical predictions.