Acceptor formation in Mg-doped,indium-rich GaxIn1?xN: evidence for p-type conductivity

We report on the Mg-doped, indium-rich Ga_xIn_1−xN (x < 30). In the undoped material, the intrinsic electron density is very high and as a result there is no detectable photoconductivity (PC) signal within the range of temperatures of 30 <T < 300 K. In the Mg-doped material however, where the conductivity is reduced, there is a strong PC spectrum with two prominent low-energy peaks at 0.65 and 1.0 eV and one broad high-energy peak at around 1.35 eV. The temperature dependence of the spectral photoconductivity under constant illumination intensity, at T > 150 K, is determined by the longitudinal-optical phonon scattering together with the thermal regeneration of non-equilibrium minority carriers from traps with an average depth of 103 ± 15 meV. This value is close to the Mg binding energy in GaInN. The complementary measurements of transient photoluminescence at liquid He temperatures give the e-A⁰ binding energy of approximately 100 meV. Furthermore, Hall measurements in the Mg-doped material also indicate an activated behaviour with an acceptor binding energy of 108 ± 20 meV.     

A critical experiment at HFR of 19 March 2008

In this paper, we present the critical experiment performed in March 2008 in the high-flux reactor (HFR) to reproduce physical conditions similar to the core light water introduction accident. We present the HFR, the context of the study and two Monte Carlo models: TRIPOLI4 – JEFF3.1 and MCNP – ENDF/BVII. All comparisons between calculations and experimental results show, within both models, that the safety rods efficiencies, in AIC alloy, are always underestimated in normal as well as in accidental configuration of the reactor.     

Examen de "L'expertise psycholégale: Balises méthodologiques et déontologiques".

Reviews the book, L'expertise psycholégale: Balises méthodologiques et déontologiques (1999). This collective under the direction of Louis Brunet wants to give a progress report on knowledge and the practice of psychological expertise. The work considers the general aspects of it and particularly ethics and the deontology, as well as the specific fields. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of the metal–support interface in the total oxidation of carboxylic acids over Ru/CeO2 catalysts

Depending on the support morphology and the metal/support contact, Ru/CeO₂ catalysts show very different behavior in catalytic wet air oxidation of acrylic, succinic and acetic acids. TEM and electron diffraction studies favor the hypothesis of a specific role of ceria in oxygen transfer from gas phase to metal sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Efficiency of a Gas‐Liquid Contactor for the Oxygenation of Activated Sludge: Assessment of Mass Transfer Coefficient

The aim of this work is to investigate a co‐current air‐liquid downward flow bubble column with air entrainment by liquid injection nozzle in order to use it as an aerator in activated sludge treatment plants. The study concerns the determination of mass transfer efficiency by measuring the mass transfer coefficient, k_La, both in clean water and in activated sludge. In clean water, this parameter is determined by three methods, i.e., gassing out method, absorption with chemical reaction and off‐gas method. In activated sludge medium, k_La values are measured by two methods, i.e., sludge reoxygenation and the hydrogen‐peroxide method. The values of k_La obtained in clean water are compared to those obtained in sludge, enabling the assessment of the α factor, i.e., ratio of oxygen transfer coefficient sludge/clean water. The results are in good agreement with those reported previously in the literature.     

Comparative study of 2-group and diffusion theories for the calculation of the neutron noise in 1D 2-region systems

In this paper, the neutron noise, i.e. the stationary fluctuations of the neutron flux around its mean value, is calculated in 2-group P₁ and diffusion theories for a 2-region slab reactor using Green’s function technique. The applicability of diffusion theory for different types and locations of the perturbation, as well as different frequencies, is assessed. Material data, i.e. nuclear cross-sections and kinetic parameters, representative of a Light Water Reactor (LWR) and of a Heavy Water Reactor (HWR), respectively, are used in this work. It is demonstrated that for practical situations in LWRs and HWRs, there is no significant advantage to use P₁ theory since diffusion theory gives acceptable results. The largest deviations between the two formalisms are observed in regions of large gradients of the static neutron flux, such as close to the reflector interface and close to the perturbation. Such observations are in agreement with theoretical expectations. This study also indicates that neglecting the effect of cross-section perturbation on the diffusion coefficient gives a rather small impact on the solution. This allows drastically simplifying the determination of the neutron noise. When using numerical techniques for such a determination the memory requirements and computational effort can be significantly reduced.     

Impact of gold nanoparticles combined to X-Ray irradiation on bacteria

Recent increase of multi drug-resistant bacteria represents a crucial issue of public health. As novative approaches are required to face that problem, those emerging from nanotechnology are of great interest. In that context we propose the possibility to use gold nanoparticles combined with ionising radiation to destroy pathogenic bacteria. For that, we investigated the potential X-Rays enhanced reduction of bacterial cell viability, following nanoparticle exposure, on a bacterial model,Escherichia coli. Our first concern was to confirm the absence of toxicity of the colloidal solution used. Then, we developed an X-Ray irradiation system and showed that gold nanoparticles increased the efficiency of ionising radiation to induce bacteria cell death.     

Ruby micro-piezospectroscopy in GdAlO3/Al2O3(/ZrO2), Er3Al5O12/Al2O3(/ZrO2) and Y3Al5O12/Al2O3(/ZrO2) binary and ternary directionally solidified eutectics

The fluorescence from (naturally present) Cr³⁺ impurities was used to measure the residual stress in the alumina phase of six melt-grown ceramic eutectic composites associating gadolinum aluminum perovskite (GAP), erbium aluminum garnet (EAG) or yttrium aluminum garnet (YAG) with α-alumina and cubic zirconia. Such measurements are reported for the first time in the GAP containing eutectics.In the usual hydrostatic assumption, we conclude to a residual compression in the range of ～70–400 MPa depending on the sample composition. The validity of the hydrostatic assumption is questioned when a microscope is used for the measurements.     

Experimental study of droplet vaporization in a fluidized bed

The injection of liquid in a hot fluidized bed is used in many industrial processes. The larger droplets are likely to engulf particles and create agglomerates that should be avoided when a fast vaporization is expected. A new model is proposed to estimate the chances of agglomeration based on a critical bed temperature below which agglomerates form. This critical temperature for safe operating conditions is based on heat transfer between the particles and the liquid and takes the porosity of the solid into account. The model could be applied to pure and multi‐component mixtures and has been validated experimentally.     

Stability of supported platinum catalysts in aqueous phase under hydrogen atmosphere

Two supported platinum catalysts (1.0 wt.% Pt/alumina (D=51%) and 1.0 wt.% Pt/silica (D=41%)) were treated at room temperature under nitrogen or hydrogen in aqueous media of various pH (pH=0.7, HCl; pH=6, water; pH=10, NH₄OH). Then, the catalysts were filtered, dried and activated following various procedures. The dispersions of the different samples were determined from transmission electron microscopy (TEM) and/or chemisorption measurements.

On preoxidized samples, a sintering of platinum is observed under hydrogen bubbling whatever the pH of the solution and it is higher on the silica support. An in situ reduction allows to prevent the metal accessibility loss on alumina and to restrict that observed on silica. Otherwise, the activation mode (direct reduction or calcination–reduction) can modify the platinum accessibility of the Pt/alumina catalyst treated in HCl medium.