Study of selenium clusters

The aim of this paper is to study the properties of selenium clusters produced by vapor condensation technique. Simulation of nucleation process up to 50 atoms are in favour of a structure close to the amorphous structure. Doubly charged clusters are also obtained in the mass spectra.     

Effect of reducing gas on the hydrogen production by thermo-oxidation of water over 1%Rh/Ce0.6Zr0.4O2

We have studied the effect of the reducing gas (H₂, CO and CH₄) on the hydrogen production by thermo-oxidation of water over the 1%Rh/Ce_0.6Zr_0.4O₂ catalyst prepared by impregnation. The catalyst is characterized by hydrogen chemisorption (Hc), before and after catalytic decomposition of water, temperature-programmed desorption, temperature-programmed reduction, X-ray diffraction and scanning electron microscopy. The catalyst is reduced in situ at 500 °C (4 h) under H₂, CO or CH₄ flows and flushed with Ar gas. Then, pulses of water (1 μL/pulse) are injected at 500 °C under Ar flow (30 mL/min). The results show clearly that the reducing gas has a strong effect on the H₂ production which follows the order: H₂?>?CH₄?>?>?CO. H₂ chemisorption measurements at room temperature highlight a strong metal–support interaction over fresh reduced catalysts which decreases after water decomposition (reduced centers?+?H₂O?→?oxidized centers?+?H₂).

     

Measurement of neutral gas temperatures in nitrogen-corona discharges

The temperature of neutral gas of the nitrogen-corona discharge has been measured using a Mach-Zehnder interferometer. The variation of the optical path in the interferometer has been measured, together with the refraction index. Density variations were also calculated. Values of measured temperatures of the neutrals in the corona discharge were obtained under both positive and negative coronas.     

Convergence of the Brun algorithm over the field of formal power series

The aim of this paper is to study multidimensional continued fraction algorithm over the field of formal power series. In the case of the Brun algorithm by using its homogenous version, we prove that it converges.     

Structure of small rare earth clusters

Rare earth clusters are produced by the inert gas condensation technique. The observed size distribution shows large peaks atn=13, 19, 23, 26, 29, 32, 34, 37, 39, 45, ... The beginning of this sequence (up to 34) has been already observed in argon clusters and recently by our group in barium clusters; this sequence may be interpreted in terms of icosahedral structures corresponding to the addition of caps on a core icosahedron of 13 atoms.     

Experimental studies on selenium cluster structures

In this paper, we report properties of selenium clusters produced by vapor condensation technique. Impact electronic ionization is performed on clusters in the size range from 2 to 36 atoms. The measured ionization potentials exhibit small oscillation corresponding to the wiggles observed on the mass distribution. An attempt to connect these experimental observations with the geometrical structure of the molecules is made in the discussion.     

Formulation and Optimization by Experimental Design of Low-Fat Mayonnaise Based on Soy Lecithin and Whey

The main objective of this study is to develop a new formula for a diet mayonnaise-like sauce without cholesterol. Emulsifying power is provided by the use of soy lecithin and the total fat content was limited to 16%. Droplet size measurement of employed mayonnaise samples at different times show that the largest diameter of fat does not exceed 18.5 µm with a yield stress of 56.1 Pa. Results of stability to centrifugation reveal that the absence of the supernatant oily layer ensures the stability of the emulsion. Using the experimental design method, the number of trials can be limited to a number of 16 experiments, and best formulation of the mayonnaise (without cholesterol) was obtained.     

Sorption of basic dyes onto granulated pillared clays: thermodynamic and kinetic studies

Effect of the granulation process onto the thermodynamic and kinetic sorption parameters of two basic dyes (Basic Yellow 28-BY 28 and Basic Green 4-BG 4) was evaluated in the present work. The charge surface properties of the surfactant-modified aluminium-pillared clay (CTAB-Al-Mont-PILC) particles were not modified, and the isoelectric point remains constant after high shear wet granulation. The Gibbs free energy of both BY 28 and BG 4 sorption was negative and decreased with the granulation; the endothermic nature of the sorption process was confirmed by the positive values of ΔH°. Adsorption kinetics of the two dyes, studied at pH 6 and 150 mg L(-1), follow the pseudo-first order kinetic model with observed rate constants of 2.5-4.2×10(-2) min(-1). The intraparticle diffusion model, proposed by Weber and Morris, was applied, and the intraparticle plots revealed three distinct sections representing external mass transfer, intraparticle diffusion and adsorption/desorption equilibrium. Diffusion coefficients, calculated from the Boyd kinetic equation, increased with the granulation and the particle size. Pseudo-first order kinetic constants, intraparticle diffusion rate constants and diffusion coefficients were determined for two other initial concentrations (50 and 100 mg L(-1)) and include in a statistical study to evaluate the impact of granulation and initial concentration on the kinetic parameters. Kruskal-Wallis tests, Spearman's rank order correlation and factor analysis revealed a correlation between (i) the diffusion coefficients and granulation, and between (ii) the intraparticle diffusion rate constants and initial concentration.     

Ultrasonic measurements of particle retention by a porous medium

Ultrasound transmission and reflection are utilized to characterize the particle retention in depth of fluid-saturated porous samples under a flow of silt solution. The effect of the concentration of particles in the fluid is investigated via measurements of “comparison coefficients” which are the ratio of the Fourier transforms of the reflected (transmitted) signals before and after the particle flow. Numerical computations of the latter coefficients using Biot-Stoll’s theory are compared to the experimental data. The frequential evolution of physical parameters such as bulk and shear moduli are sought. To this end, a gradient descent algorithm is utilized to minimize the differences between the experimental and calculated comparison coefficients. Several concentrations of suspended particles are investigated to check the validity of this inversion method and a good agreement between theory and experiments is observed.