Fermi-edge singularities in the photoluminescence spectrum of modulation-doped GaAs v-groove quantum wires

We report the observation of strong Fermi-edge singularities in the photoluminescence spectrum of strongly-confined, modulation-doped GaAs v-groove quantum wires. The behaviour of the singularity has been investigated at high excitation intensity, and both lattice and electrical heating. The latter produces a strong reduction of the singularity due to Fermi surface smearing, whereas, increased photoexcitation produces complex electron–hole correlation effects.     

Preparation of solid alkaline fuel cell binders based on fluorinated poly(diallyldimethylammonium chloride)s [poly(DADMAC)] or poly(chlorotrifluoroethylene‐co‐DADMAC) copolymers

A membrane or an electrode binder to be used in a solid alkaline fuel cell (SAFC) needs to (i) be insoluble in both aqueous solutions and the required fuels, and (ii) exhibit an hydroxide ion conductivity. To achieve these goals, two pathways were employed: (i) one consists of the radical copolymerization of diallyldimethylammonium chloride (DADMAC) with chlorotrifluoroethylene (CTFE) while (ii) the other one is based on the counter‐ion exchange of a poly(DADMAC) by fluorinated anions. First, the radical copolymerization of CTFE with DADMAC under various experimental conditions was achieved in yields up to 85%, and DADMAC percentages in the copolymers were higher than those in the feed compositions. To obtain insoluble copolymers, high CTFE feed contents (>70 mol %) were required. The other route consisting in the partial replacement of the Cl^? counter‐ions in the water‐soluble poly(DADMAC) by bistrifluoromethanesulfonimide (TFSI^?) did confer the starting material insolubility in water while maintaining its conductivity. When the fluorinated poly(DADMAC) was obtained from concentrated solutions of fluorinated surfactant, it was observed that the amount of counter‐ions exchanged was difficult to control, which limits optimization. Nevertheless, under diluted conditions, membranes with ion exchange capacity up to 0.7 meq g^?1, and conductivities close to 1 mS cm^?1 were obtained. Although their conductivities were low, these membranes fulfill the requirements for a SAFC membrane in terms of solubility in DMSO, water insolubility, and thermal stability (T_d,10% > 320 °C). When used in a fuel cell, as a binder in the membrane‐electrode assembly (MEA), significant improvements were noted (+50% of the open circuit voltage, +580% in current density, and +540% in accessible power). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2043–2058, 2009     

Normal automorphisms of a free pro-p-group in the varietyN 2 A

An automorphism of a (profinite) group is called normal if each (closed) normal subgroup is left invariant by it. An automorphism of an abstract group is p-normal if each normal subgroup of p-power, where p is prime, is left invariant. Obviously, the inner automorphism of a group will be normal and p-normal. For some groups, the converse was stated to be likewise true. N. Romanovskii and V. Boluts, for instance, established that for free solvable pro-p-groups of derived length 2, there exist normal automorphisms that are not inner. Let N₂ be the variety of nilpotent groups of class 2 and A the variety of Abelian groups. We prove the following results: (1) If p is a prime number distinct from 2, then the normal automorphism of a free pro-p-group of rank ≥2 in N₂A is inner (Theorem 1); (2) If p is a prime number distinct from 2, then the p-normal automorphism of an abstract free N₂A-group of rank ≥2 is inner (Theorem 2). Supported by RFFR grant No. 93-01-01508. Translated fromAlgebra i Logika, Vol. 35, No. 3, pp. 249–267, May–June, 1996.     

Growth by laser ablation of Ti-based oxide films with different valency states

x La_2/3+yTiO_3-δ perovskite (with δ≤0.5) were deposited by the laser ablation technique from Li_0.33La_0.56TiO₃ targets. Their growth onto MgO substrateswas studied as a function of the oxygen pressure. For films grown in vacuum (10^-6 mbar), a La_0.63TiO_2.5 composition was obtained, meaning that Ti³⁺ alone is present in the films, while Li ions are not incorporated under these conditions. This material shows good electric conductivity (ρ=500 mΩ cm). By contrast, insulating films with a Li_0.1La_0.70TiO₃ composition corresponding to the Ti⁴⁺ species were obtained at high oxygen pressures (>0.05 mbar). For all conditions, textured films were grown with different orientations depending on the temperature and the oxygen pressure. Received: 10 September 1997/Accepted: 24 November 1997     

The Chern character of a transversally elliptic symbol and the equivariant index

Let G be a compact Lie group acting on a compact manifold M. In this article, we associate to a G-transversally elliptic symbol on M a G-invariant generalized function on G, constructed in terms of equivariant closed differential forms on the cotangent bundle T ^* M. Oblatum 24-VII-1995     

Equipartition of the eigenfunctions of quantized ergodic maps on the torus

We give a simple proof of the equipartition of the eigenfunctions of a class of quantized ergodic area-preserving maps on the torus. Examples are the irrational translations, the skew translations, the hyperbolic automorphisms and some of their perturbations.     

A Numerical Approach for Arbitrary Cracks in a Fluid-Saturated Medium

A finite element method is proposed that can capture arbitrary discontinuities in a two-phase medium. The discontinuity is described in an exact manner by exploiting the partition-of-unity property of finite element shape functions. The fluid flow away from the discontinuity is modelled in a standard fashion using Darcy’s relation, while at the discontinuity a discrete analogon of Darcy’s relation is proposed. The results of this finite element model are independent of the original discretisation, as is demonstrated by an example of shear banding in a biaxial, plane-strain specimen.     

Algorithmes stochastiques à bruit dépendant

We introduce different ways of modeling the dependency of the input noise of stochastic algorithms. We are aimed to prove that such innovations allow us to use the ODE (ordinary differential equation) method. Illustrations in the linear regression framework and in the law of the large number for triangular arrays of weighted dependent random variables are also given. We have aimed to provide results easy to check in practice. To cite this article: P. Doukhan, O. Brandière, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Multi-criteria decision aid for the formulation of sustainable technological energy priorities using linguistic variables

Implementation of new and innovative energy technologies is a key mean towards a sustainable energy system. Currently, governments have to decide from an increasingly diverse mix of them, the ones which warrant support, including funding and other incentives for private sector efforts. However, appraising energy technologies in terms of their sustainability is a really complex task, considering the series of uncertainties and implications that have to be encountered so as to obtain realistic and transparent results. In this context, the main aim of this paper is to present a direct and flexible multi-criteria decision making approach, using linguistic variables, to assist policy makers in formulating sustainable technological energy priorities. Furthermore, its software realization will be applied to a number of technologies, in the context of the Greek Technology Foresight Programme, and the results will be presented and discussed.