University of Rennes

About: University of Rennes is a education organization based out in Rennes, France. It is known for research contribution in the topics: Population & Catalysis. The organization has 18404 authors who have published 40374 publications receiving 995327 citations.

Skew-cyclic codes

Abstract: We generalize the notion of cyclic codes by using generator polynomials in (non commutative) skew polynomial rings. Since skew polynomial rings are left and right euclidean, the obtained codes share most properties of cyclic codes. Since there are much more skew-cyclic codes, this new class of codes allows to systematically search for codes with good properties. We give many examples of codes which improve the previously best known linear codes.

Hardness, Toughness, and Scratchability of Germanium–Selenium Chalcogenide Glasses

Abstract: Ge-Se chalcogenide glasses are characterized by relatively low hardness (0.39-2.35 GPa) and low fracture toughness (0.1-0.28 MPa.m 1/2 ). Actually, the hardness of chalcogen-rich glasses is low enough so that the brittleness parameter, B = H/K c , is lower than that of silicate glasses. Whereas hardness and Young's modulus increase with increasing germanium contents, fracture toughness follows a trend similar to that of the density and exhibits a maximum for the Ge 20 Se 80 composition, which corresponds to the rigidity percolation threshold. Optical microscopy and atomic force microscopy observations suggest that the indentation deformation proceeds by a localized shear deformation phenomenon. Glasses in the chalcogen-rich region behave viscoelastically at room temperature. As a consequence, an increase of the loading time results in a decrease of hardness and toughness.

Polymerization of enantiopure monomers using syndiospecific catalysts: a new approach to sequence control in polymer synthesis.

Abstract: The ring-opening polymerization of a mixture of enantiomerically pure but different monomers using an yttrium complex as initiator proceeds readily at room temperature to give the corresponding highly alternating polyester.

Phosphole-Containing π-Conjugated Systems: From Model Molecules to Polymer Films on Electrodes

Abstract: Two series of 2,5-dipyridyl- and 2,5-dithienylphosphole derivatives containing sigma3- or sigma4-P atoms were prepared, and their optical (UV/Vis absorption, fluorescence spectra) and electrochemical properties were systematically evaluated. These physical properties depend mainly on the natures of the 2,5-substituents and of the phosphorus moiety, and they revealed that these compounds contain extended pi-conjugated systems. Structure-property relationships were established on the basis of these experimental data and ab initio calculations on the parent molecules. The limited aromatic character and low-lying LUMO of the phosphole ring appear to be crucial for achieving a highly delocalised pi system. Electrooxidation of 2,5-dithienylphosphole derivatives affords electroactive films with low optical band gaps. As observed for the corresponding monomers, the optical and electrochemical properties of the polymers can be varied over a wide range by modifying the nature of the phosphorus moiety.