Laser spectroscopy measurements of neutron-rich tellurium isotopes by COMPLIS

Laser spectroscopy based on resonant ionization of laser-desorbed atoms has been used to study the neutron-rich tellurium isotopes with the COMPLIS facility at ISOLDE-CERN. Isotope shifts and hyperfine structures of several neutron-rich Te isotopes: ^120?136Te and ^{123 m?133 m}Te have been measured. From the hyperfine structure we have extracted magnetic and quadrupole moments. Changes in the mean square charge radii have been deduced and their comparison with the known data for the other elements near Z?=?50 is presented. The experimental δ?<?r ²> values are compared with those obtained from relativistic mean field calculations.     

Synthesis and characterization of new polyamides based on Diphenylaminoisosorbide

New aromatic polyamides were synthesized by the microwave‐assisted polycondensation of an optically active isosorbide‐derived diamine with different diacyl chlorides in the presence of a small amount of N‐methylpyrrolidinone. Polymers with inherent viscosities between 0.22 and 0.73 dL/g were obtained corresponding to molecular weights up to 140,000 g/mol. With interfacial polymerization or the Higashi method, lower molecular weight polymers were obtained with inherent viscosities in the range of 0.04–0.36 dL/g. Differential scanning calorimetry measurements clearly demonstrated the high thermal stability of these polymers (mp = 180–300 °C) and the absence of decomposition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6480–6491, 2005     

Dynamics of the Water–Oil Front for Two-Phase, Immiscible Flow in Heterogeneous Porous Media. 1 – Stratified Media

We study the evolution of the water–oil front for two-phase, immiscible flow in heterogeneous porous media. Our analysis takes into account the viscous coupling between the pressure field and the saturation map. Although most of previously published stochastic homogenization approaches for upscaling two-phase flow in heterogeneous porous media neglect this viscous coupling, we show that it plays a crucial role on the dynamics of the front. In particular, when the mobility ratio is favorable, the viscous coupling induces a transverse flux that stabilizes the water–oil front, which follows a stationary behavior, at least in a statistical sense. Calculations are based on a double perturbation expansion of equations at first order: the local velocity fluctuation is defined as the sum of a viscous term related to perturbations of the saturation map, on one hand, plus the perturbation induced by the heterogeneity of the permeability field with a base-state saturation map, on the other hand. In this first paper, we focus on flows in stratified reservoirs, with stratification parallel to the mean flow. Our results allow to predict the evolution of large Fourier mode of the front, and the emergence of a stationary front, for favorable mobility ratios. Numerical experiments confirm our predictions. Our approach is applied to downscaling. Extension of our theory to isotropic media is presented in the companion paper.     

Regioselective and efficient halogenation of 4,5-unsubstituted alkyl 3-hydroxypyrrole/3-hydroxythiophene-2-yl-carboxylates

Substituted heterocycles, such as pyrrole and thiophene, are commonly found in the field of pharmaceutical and material sciences. Here we studied the reactivity of 4,5-unsubstituted alkyl 3-hydroxypyrrol-2-yl-carboxylates and 4,5-unsubstituted alkyl 3-hydroxythiophen-2-yl-carboxylates in different halogenation conditions, due to their interest as building blocks in the synthesis of bioactive compounds and materials. We describe herein the regioselective monohalogenation of 3-hydroxypyrroles and 3-hydroxythiophenes in mild conditions with common halogenation agents. The selectivity of the halogenation was studied. Optimized one-step reaction conditions were found for monobromination and monochlorination. Finally, we observed that bromination with N-bromosuccinimide (NBS) took place at the C4 position of the heterocycle, while chlorination with SO₂Cl₂ led to C5-halogenated derivatives.     

On a hyperbolic conservation law of electron transport in solid materials for electron probe microanalysis

The prediction of X-ray intensities based on the distribution of electrons throughout solid materials is essential to solve the inverse problem of quantifying the composition of materials in electron probe microanalysis (EPMA) [3]. We present a hyperbolic conservation law for electron transport in solid materials and investigate its validity under conditions typical for EPMA experiments. The conservation law is based on the time-stationary Boltzmann equation for binary electron-atom scattering. We model the energy loss of the electrons with a continuous slowing-down approximation. A first order moment approximation with respect to the angular variable is discussed. We propose to use a minimum entropy closure to derive a system of hyperbolic conservation laws, known as the M1 model [11]. A finite volume scheme for the numerical solution of the resulting equations is presented. Important numerical aspects of the scheme are discussed, such as bounds for the finite propagation speeds, as well as difficulties arising fromspatial discontinuities in thematerial coefficients and the scaling of the characteristic velocities with the stopping power of the electrons.We compare the accuracy and performance of the numerical solution of the hyperbolic conservation law to Monte Carlo simulations. The results indicate a reasonable accuracy of the proposed method and showthat compared to the MonteCarlo simulation the finite volume scheme is computationally less expensive.