Une correspondance de modules pour les blocs à groupes de défaut abéliens

Let b be a block of a finite group G with an abelian defect group P and an inertial quotient E. Let us denote by L the semi-direct product of P and E. If E is cyclic and acts freely on P−{1}, we prove that the stable categories of Gb- and L-modules are equivalent, as a consequence of a more general result, without any hypothesis on E, about partial covering exomorphisms relating Gb with a suitable twisted group algebra _*

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à Jacques Tits à l'aube de sa sexagénie     

On the application of the modeling of the relaxation spectrum to the prediction of linear viscoelastic properties of surfactant systems

 In this work, the linear viscoelastic properties of cetyl-trimethylammonium tosilate–water system are predicted by the modeling of the relaxation spectrum. The modeled spectrum of relaxation times is of the “wedge-box” type where the “wedge” portion is located at the short-time scale of relaxation times and the “box” part covers the long-time scale. The linear viscoelastic properties are calculated through the exact relationships with the suggested spectrum. Agreement between the calculated expressions and experimental data of the moduli and the stress relaxation function is found. Comparison is also made with predictions of the empirical expressions of the Cole–Cole and the Williams–Watts models. Received: 17 December 1996 Accepted: 1 July 1997     

Microstructured polyacrylamide hydrogels made with hydrophobic nanoparticles

Poly(methyl methacrylate) nanosize particles, made by microemulsion polymerization, were dispersed in an acrylamide aqueous solution, which was polymerized in the presence of a cross-linking agent to yield microstructured hydrogels. The kinetics of swelling and the mechanical properties of these hydrogels were investigated as a function of concentration of particles. The microstructured hydrogels exhibit higher equilibrium swelling and larger Young modulus than conventional (that is, without particles) polyacrylamide hydrogel. The morphology of the microstructured hydrogels was examined by transmission electron microscopy.     

Phase behaviour of the dioctadecyldimethylammonium bromide-water system

The phase behaviour of the twin-tailed surfactant dioctadecyldimethylammonium bromide with water was studied by DSC, FT-IR, X-ray and polarizing microscope. The phase diagram of DODAB-water system is very similar to that of DODAC-water. The dihydrate is in equilibrium with isotropic solution below 55°C. Above this temperature there is a lamellar liquid crystalline region, in equilibrium with isotropic liquid and solid crystals of DODAB·2H₂O, up to 69°C. From 69 to 86°C, the lamellar mesophase is in equilibrium with ‘waxy’ anhydrous DODAB. From 86 to 116°C and very high DODAB content, there is a very narrow region of existence of inverse hexagonal mesophase, in equilibrium via a narrow biphase region with lamellar mesophase. AtT > 116°C an isotropic liquid appears. There seems to exist two different lamellar mesophases, one of them between 10 and 40 wt.% DODAB and the other between 60 and about 97 wt.% DODAB, with a biphase zone between them.     

Microstructured Polyacrylamide Hydrogels Prepared Via Inverse Microemulsion Polymerization

The synthesis by a two-stage polymerization process of microstructured polyacrylamide hydrogels with large swelling capacity and improved mechanical properties is reported. First, crosslinked polyacrylamide particles of nanosize scale are made by inverse microemulsion polymerization. These particles are then dried and redispersed in an aqueous solution of acrylamide and polymerized in the presence of a crosslinking agent. The microstructured hydrogels, in contrast to transparent conventional polyacrylamide hydrogels, are translucid due to the presence of the dispersed particles. The swelling capacity of these hydrogels increases as the particle content increases and their Young and elastic moduli (at equilibrium swelling) diminish only slightly. Mechanical tests disclose that the microstructured hydrogels have larger Young moduli than conventional hydrogels with an identical degree of swelling. Copyright 2001 Academic Press.     

Free-radical polymerization of styrene in worm-like micelles

The solubilization of styrene in wormlike micelles of the cationic surfactant, cetyltrimethylammonium tosilate (CTAT), and its polymerization is examined here by UV spectroscopy, oscillatory rheometry, small angle X-ray scattering, polarizing light microscopy, and transmission electron microscopy. At low CTAT concentrations, the polymerization of styrene yields small and rigid rods in coexistence with wormlike micelles that form from the excess surfactant after the polymerization process. At high CTAT concentrations, polymeric rods (of large aspect ratio), spheroid polymer particles, and wormlike micelles coexist. The polymerization rate is second order, indicating that polymerization reactions end mainly by bimolecular termination.     

Microemulsion Polymerization Modeling Based on the Experimental Conversion Trend and its Derivative

In this work, the microemulsion polymerization modeling problem is addressed with an integrodifferential approach. The procedure was applied to experimental data, previously presented, on the microemulsion polymerization of hexyl methacrylate (C₆MA) and styrene (STY). It was found that: (i) the nucleation rate is not linear with time, as assumed before, (ii) a vitreous effect is observed even in reactions where the polymer's glass transition temperature is lower than the reaction temperature, (iii) radical entry to polymer particles and coagulation among particles are negligible, (iv) the rate decrease interval is also caused by a reduction of active sites, (v) a mechanism in which micelles provide monomer to living particles was detected, and (vi) a simple three-parameter mechanistic model was obtained, capable of describing the studied systems.     

Simultaneous determination of enrofloxacin and its primary metabolite, ciprofloxacin, in chicken tissues

Summary An HPLC method with fluorescence detection is presented for the analysis of enrofloxcin (ENR) and ciprofloxacin (CIP) in chicken tissue using sarafloxacin (SAR) as internal standard. Tissue sample preparations were carried out by adding a phosphate buffer (pH 7.4, 0.1 M), followed by extraction with trichloromethane. Fluoroquinolones were separated on a reversed-phase column with a mobile phase of aqueous phosphate buffer-acetonitrile (80:20). The concentrations of CIP, ENR and SAR eluted off the column, with retention times of 2.28, 3.30 and 4.40, respectively, were monitored by fluorescence detection atλ _ex 338 andλ _em 425 nm. The detection limit was 32 ng g⁻¹ for CIP and 10 ng g⁻¹ for ENR. The standard curves were linearly related to concentration in the range of 1 to 2000 ng g⁻¹. Recovery was determinated as 91.3% and 78.3% for ENR and CIP, respectively. The measurement of the tissue levels of ENR and CIP in the chicken after oral administration confirmed the utility of the proposed analytical methodology.     

Disodium[hydroxotetranitronitrosyl]ruthenate(II), a Photochromic Substance with Long‐lived Metastable States: Structure at 110 K,Spectroscopic and Thermal Properties

Disodium[hydroxotetranitronitrosyl]ruthenate(II) is a photochromic compound excitable with blue‐green light which exhibits at least one unusually long‐lived metastable state at low temperature. At 298 K, the compound crystallises in the space group C2/m. A reversible phase transition occurs at 240 K upon cooling, as detected by Differential Scanning Calorimetry and X‐ray powder diffraction which causes a lowering of the crystal symmetry to the space group P2₁/n. Synchrotron X‐ray single crystal diffraction and FT‐IR spectroscopy data obtained on the ground and the excited states of the title compound low temperature phase are presented.     

Ion Transport Across Liquid|Liquid Interfacial Boundaries Monitored at Generator‐Collector Electrodes

Anion transfer processes at a liquid|liquid interface were studied with an interdigitated gold band array electrode. The organic phase, 4‐(3‐phenylpropyl)‐pyridine containing Co(II)phthalocyanine, was immobilised as random droplets at the electrode surface and then immersed into aqueous electrolyte. Oxidation of Co(II)phthalocyanine at the generator electrode was shown to be associated with anion transfer from the aqueous into the organic phase. The corresponding back reduction at the collector electrode with anion expulsion was delayed by the anion/cation diffusion time across the interelectrode gap. A working curve based on a finite difference numerical simulation model was employed to estimate the apparent diffusion coefficients for anions in the organic phase (PF₆^?4^?3^?). Potential applications in ion analysis are discussed.