Understanding mechanisms of drying of a cellulose slurry by magnetic resonance imaging

Cellulose - This study concerns the spatial evolution of the internal components of a macroscopic sample of cellulose slurry during its convective drying. In a first stage, some water is extracted...     

A comparative study on structural and optical properties of ZnO and Al-doped ZnO thin films obtained by ultrasonic spray method using different solvents

Transparent conducting ZnO and Al doped ZnO thin films were deposited on glass substrate by ultrasonic spray method. The thin films with concentration of 0.1 M were deposited at 350 °C with 2 min of deposition time. The effects of ethanol and methanol solution before and after doping on the structural, optical and electrical properties were examined. The DRX analyses indicated that ZnO films have nanocrystalline nature and hexagonal wurtzite structure with (1 0 0) and (0 0 2) preferential orientation corresponding to ZnO films resulting from methanol and ethanol solution, respectively. The crystallinity of the thin films improved with methanol solution after doping to (0 0 2) oriented. All films exhibit an average optical transparency about 90%, in the visible range. The band gaps values of ZnO thin films are increased after doping from 3.10 to 3.26 eV and 3.27 to 3.30 eV upon Al doping obtained by ethanol and methanol solution, respectively. The electrical conductivity increase from 7.5 to 15.2 (Ω cm)⁻¹ of undoped to Al doped ZnO thin films prepared by using ethanol solution. However, for the methanol solution; the electrical conductivity of the film is stabilized after doping.     

An electron transfer approach to the preparation of highly functionalized anthraquinones

A series of highly functionalized quinones was prepared by an original reaction of 2,3-bis(chloromethyl)-1,4-dimethoxyanthraquinone (6) with various nitronate anions under electron transfer reaction conditions.     

Optoelectronic properties of SnO_2 thin films sprayed at different deposition times

This article presents the elaboration of tin oxide(SnO_2) thin films on glass substrates by using a home-made spray pyrolysis system. Effects of film thickness on the structural, optical, and electrical film properties are investigated. The films are characterized by several techniques such as x-ray diffraction(XRD), atomic force microscopy(AFM), ultravioletvisible(UV–Vis) transmission, and four-probe point measurements, and the results suggest that the prepared films are uniform and well adherent to the substrates. X-ray diffraction(XRD) patterns show that SnO_2 film is of polycrystal with cassiterite tetragonal crystal structure and a preferential orientation along the(110) plane. The calculated grain sizes are in a range from 32.93 nm to 56.88 nm. Optical transmittance spectra of the films show that their high transparency average transmittances are greater than 65% in the visible region. The optical gaps of SnO_2 thin films are found to be in a range of 3.64 e V–3.94 e V. Figures of merit for SnO_2 thin films reveal that their maximum value is about 1.15 × 10-4-1?atλ = 550 nm. Moreover, the measured electrical resistivity at room temperature is on the order of 10-2?·cm.     

Propriétés probabilistes des processus GARCH périodiques

This Note examines the probabilistic structure of a GARCH-type stochastic difference equation with periodically time-varying parameters. We propose necessary and sufficient conditions ensuring the existence of stationary solutions, geometrically ergodic (in the periodic sense) and having finite higher-order moments. To cite this article: A. Bibi, A. Aknouche, C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

A conditional least squares approach to PGARCH and PARMA–PGARCH time series estimation

In this Note, a conditional least squares (CLS) estimates for periodic GARCH (PGARCH) models with martingale difference centered squared innovations is developed. The approach is extended to the PARMA–PGARCH models. We establish the strong consistency and the asymptotic normality for our estimate.     

Numerical simulations of large falling drops

The numerical simulation in a two‐phase medium of falling drops allows their velocities and shapes during the fall to be calculated. The terminal velocities and shapes for bromoform and chlorobenzene drops falling into water have been obtained. Although the method used calculates the flow inside and around the drop, it has not been possible to give results independent of the spatial discretization and the boundary effects. However, taking these influences into account, the numerical results agree with the experimental data given and the study consists of a good validation of the SURFER code used. Copyright © 2004 John Wiley & Sons, Ltd.     

Preparation de membranes hydrophiles obtenues par le greffage de la n-vinylpyrrolidone dans le poly(chlorure de vinyle)

PVC films were radiation-grafted in NVP-methanol solutions. Unusual kinetics relations were observed: an increase in monomer concentration or in temperature decreased the reaction rate. These effects are attributed to a higher mobility of the growing chains leading to faster chain termination and resulting in a drop of the overall rate and shortening of grafted chains. The graft copolymers swell homogeneously in water and in methanol. The swelling rate and limiting swelling ratio increase linearly with the grafting ratio. The swelling ratio was found to depend on chain length, being higher for short chains. An irreversible increase of the swelling ratio was found by raising the temperature. These unusual swelling properties of the grafted films are attributed to strong interactions between pyrrolidone groups and the Cl atoms of the PVC.