Numerical and theoretical calculation of breakdown voltage in the electrical discharge for rare gases

This work has been devoted to a numerical and analytical calculus of the voltage breakdown in electrical discharge for several rare gases such as argon, krypton, neon, xenon and helium. It was performed using a fluid model 2D, which is based on the numerical solution of the two Boltzmann equations (equation of continuity and momentum), coupled to Poisson's equation to measure the breakdown voltage according to the product of the electrode spacing and the pressure. This study allowed a better comprehension of the physical phenomena occurring in the discharges. We, thus, developed a calculation, based on the empirically Paschen's law, allowing the determination of the breakdown voltage, which describes the transition from insulating gas to the conductive state. Paschen's curves of the different gases are plotted and a comparison between numerical and experimental as well as analytical results is also presented and analyzed.     

Prédiction des processus à temps continu autorégressifs via les espaces à noyau reproduisantPrediction of autoregressive processes via the reproducing kernel spaces

We study the statistical prediction of a continuous time stochastic process admitting a functional autoregressive representation. We construct an approximation of Parzen's optimal predictor in reproducing kernel spaces framework. To cite this article: F. Mokhtari, T. Mourid, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 65–70     

Theoretical study of some nitrososulfamide compounds with antitumor activity

The lowest-energy conformations of four 2-chloroethylnitrososulfamides were determined using the MM+ molecular mechanics method as implemented in Hyperchem 6.0. Some of the calculated structural parameters, angles and bonds lengths were compared with the crystal structure data of N-nitroso-N-(2-chloroethyl)-N'-sulfamoyl- proline. Using MM+, AM1 and PM3 the anti conformation was predicted to be more stable than the syn conformation in each of these compounds. With these methods we found that the relative energy of the transition state (TS) was considerably higher, but with the ab initio method using RHF with minimal basic function STO-3G we found that the syn conformation is predicted to be slightly more stable. The determination of some atomic charges of a selection of atoms on the syn, anti and TS structures of the various compounds provided some details about the nature of the transition state.     

Asymptotic behavior for Timoshenko beams subject to a single nonlinear feedback control

We consider systems of Timoshenko type in a one-dimensional bounded domain. The physical system is damped by a single feedback force, only in the equation for the rotation angle, no direct damping is applied on the equation for the transverse displacement of the beam. Moreover the damping is assumed to be nonlinear with no growth assumption at the origin, which allows very weak damping. We establish a general semi-explicit formula for the decay rate of the energy at infinity in the case of the same speed of propagation in the two equations of the system. We prove polynomial decay in the case of different speed of propagation for both linear and nonlinear globally Lipschitz feedbacks.      

Removal of Evans Blue by using Nickel-Iron Layered Double Hydroxide (LDH) Nanoparticles: Effect of Hydrothermal Treatment Temperature on Textural Properties and Dye Adsorption

Summary: The use of low-cost adsorbent has been investigated as a replacement for the current expensive methods of removing dyes from wastewater. The sorption of acid dye (Evans Blue) from aqueous effluents onto anionic clays (hydrotalcite-like) has been studied. Hydrotalcite may be an effective adsorbent of organic molecules due to its hydrophobic nature and the accessibility of its interlayer region. Ni/Fe layered double hydroxide (LDH), with a molar ratio of 3, were synthesised by coprecipitation followed by hydrothermal treatment at different temperatures (85, 100 and 140 °C) for 4 days. The materials were characterised by X-ray powder diffraction (XRD), infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption-desorption (BET). The diffractograms and FT-IR spectroscopy of the fresh materials showed that the hydrotalcite is present in all samples. The XRD pattern obtained was typical of a hydrotalcite, where the interlayer anion is CO, XRD and Infrared spectroscopy complemented each other by showing that with treatment the degree of order increased regardless of the type of treatment. Furthermore, it was shown that aging at increased temperature and pressure increased crystallinity. TEM showed that crystal size increased with aging temperature, so that growth occurred on the edges resulting in the formation of hexagonal plate shaped hydrotalcite crystals. The surface area decreased with increasing the hydrothermal treatment temperature. The effects of various parameters such as hydrothermal treatment temperature, crystallite size, contact time and calcination on the extent of adsorption were investigated. The studies of the removal efficiency of the reactive textile dye: Evans Blue (Direct Blue 53) by NiFeCO₃ HDLs showed that the effect of hydrothermal treatment temperature on adsorption increases with aging temperature. The Evans Blue (EB) removal percent increased with increasing contact time. Above the 70%, 50% and 20% of EB adsorption occurred in the first 2 min for HDL-140, HDL-100 and HDL-85°C respectively. Furthermore, it was found that the calcined materials are much more effective than the original LDH in removing Evans Bleu dye from an aqueous solution.     

Quantum Secret Sharing with Error Correction

We investigate in this work a quantum error correction on a five-qubits graph state used for secret sharing through five noisy channels. We describe the procedure for the five, seven and nine qubits codes. It is known that the three codes always allow error recovery if only one among the sent qubits is disturbed in the transmitting channel. However, if two qubits and more are disturbed, then the correction will depend on the used code. We compare in this paper the three codes by computing the average fidelity between the sent secret and that measured by the receivers. We will treat the case where, at most, two qubits are affected in each one of five depolarizing channels.     

Impact of Tween 60 on physicochemical properties and stability of Pistacia lentiscus fruit oil-in-water emulsion at a semi-low temperature

This study shows the effects of the Tween 60 emulsifier at different concentrations on the aqueous emulsion containing 5% of Pistacia lentiscus fruit oil. The rheological behavior and the droplet size distribution of cosmetic oil-in-water emulsions were investigated. This investigation was carried out by analyzing the shear flow and dynamic oscillatory followed by microscopic analysis and physical stability study for 24?hours and 4 months. During the period of 4 months, the emulsions were stored in a refrigerator at a semi-low temperature 12?°C. The physical stability test showed that the sample not emulsified yielded a creaming process after a short aging time. Flow curves of emulsions prepared with TW 60 exhibited a non-linear relationship between the shear stress σ and shear rate γ ?, which implies that the Herschel–Bulkley rheological model was the appropriate model for the shear flow. The increase of emulsifier quantities leading to an increase in the internal structure coherence, whereas the excess quantity affects the structure. Therefore, the optimal quantity proposed was 3.47%. Furthermore, the storage time at a semi-low temperature performed the stability and maintain the structure of emulsions.     

Measuring fast hydrogen exchange rates by NMR spectroscopy

We introduce a method to measure hydrogen exchange rates based on the observation of the coherence of a neighboring spin S such as (15)N that has a scalar coupling J(IS) to the exchanging proton I. The decay of S(x) coherence under a Carr-Purcell-Meiboom-Gill (CPMG) multiple echo train is recorded in the presence and absence of proton decoupling. This method allows one to extract proton exchange rates up to 10(5)s(-1). We could extend the pH range for the study of the indole proton in tryptophan, allowing the determination of the exchange constants of the cationic, zwitterionic, and anionic forms of tryptophan.