Interplay between the glassy transition and granular superconductivity in organic materials

It is known that some (BEDT-TTF)2X layered organic superconductors undergo a glassy transition near 80 K. Our purpose is to exploit quenched disorder to get new insights on both the superconducting state (T < 12 K) and the glassy transition by studying the superconducting properties as functions of annealing time (ta) and temperature (Ta) around 80 K. The main results on the fully deuterated kappa-(BEDT-TTF)2Cu[N(CN)2]Br compound are: 1) The data can be described by a percolation cluster model. 2) At short time scales, the clusters grow with ta following a power law. 3) At large time scales the clusters grow toward a thermodynamic state following a stretched exponential law in (1 - exp(-(t/tau)beta)with beta varying from about 0.5 to 1 in our Ta range (65 - 110 K). 4) The relaxation time follows an Arrhenius law tau(T)=tau0exp(U/T) with U around 2660 K and 1/tau0 around 2x1013 s-1. 5) The asymptotic magnetization fits with a scaling law with Tg around 55K and n around 3.2. The results are consistent with a Ising spin-glass-like model.Comment: 17 pages; 4 figure

Trans-sinusal frontal approach for olfactory groove meningiomas

Background We report on our experience with the trans-sinusal frontal approach in removing olfactory groove meningiomas in the department of neurosurgery of Univesity Hospital Center of Annaba (Algeria).Methods Ten tumours were operated on by the trans-sinusal frontal approach, using a bicoronal incision, tree tumours developed on one side, and there were seven bilateral olfactosellar tumours. Our procedure : steotomy of the anterior wall of the frontal sinus was performed with an oscillating saw. The posterior wall of the sinus was resected and the tumour was removed through a real subfrontal route along the plane of the anterior skull base. Ethmoidal blood supply was early controlled at the initial stages of the operation, allowing avascular tumour debulking. Tumour extensions toward the sella and the optic canals were removed without brain retraction. Results Seven patients made a good neurologic recovery. Two was dead in the 24 hours after intervention and one four days after. Olfactory nets were preserved on the contralateral side in unilateral tumours. Conclusions The trans-sinusal frontal approach represents an excellent way for tumours developed in the central anterior skull base, especially for olfactory groove meningiomas, whatever their size

Effect of Al substitution on structural and electrical properties of Bi1.6Pb0.4Sr2CaCu2-x Mx O8+δ superconducting ceramics

In this work we study the effect on structural and electrical properties of superconducting compound Bi1.6Pb0.4Sr 2CaCu2-y My O8+δ were M=Al (with y=0-0.6). The samples were prepared by the solid-state reaction method. The samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), direct current (DC) resistivity versus temperature ρ(T) and alternative current (AC) susceptibility measurements. Structural analysis shows that the crystalline lattice structure of the prepared sample belongs, mainly, to the superconductive tetragonal phase Bi(Pb)2212. The SEM micrographs show that in the undoped sample the grain size has a random distribution with few grains greater than 5 μm. The grains are very dense and well connected. A quite different microstructure is obtained for the doped samples of which grains are more connected with a flat characteristic shape of Bi(Pb)2212 superconductors. All samples exhibit a superconducting character and Tc and the superconducting volume fraction decrease with increasing rate of aluminum

Kinetic factors in polymer adsorption at solid/liquid interfaces. Methods of study of the adsorption mechanism

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Modeling Energetic Efficiency of Coil Annealing Using Hydrogen Gas

International audienceDetermining the temperature of several steel coils, heated in a furnace traversed by hydrogen, is approached by numerical modeling using differential equations governing heat transfers involved. The resolution is performed by the method of finite differences. Convergence standards of different numerical algorithms are adjusted on the basis of a compromise precision time by the method of experimental plan. Thermal coefficients used in the model are also adjusted by the simplex optimization technique. Finally, the temperature measurement is performed in a coil for annealing of geometric configurations at different temperature set points, and the error between modeled and measured temperature is less than 10, K in mean absolute deviatio

Comportement thermomécanique de l’alliage 600 en flexion 4 points

Ce travail s’intéresse à l’endommagement de l’alliage base nickel 600 connu sous le nom commercial d’inconel 600 utilisé particulièrement au niveau des circuits primaires des réacteurs nucléaires à eau pressurisée. Ainsi, des essais de flexion 4 points sont effectués à l’aide d’un montage spécifique sous vide secondaire, dans un domaine de température répondant aux conditions réelles de fonctionnement des générateurs de vapeur s’étalant de 350 à 550°C. Le suivi de ces essais en conditions in situ par émission acoustique a permis de vérifier l’absence d’endommagement des échantillons utilisés. Les courbes des contraintes en fonction de la flèche obtenues à partir des données expérimentales qui sont la force et le déplacement conduisent à la détermination du module de Young et de la limite d’élasticité du matériau. D’autres essais, sous air et sous vapeur d’eau sont envisagés, afin de pouvoir remonter jusqu’au comportement viscoplastique de l’inconel 600 dans la gamme de température visée, par méthode inverse.Mots Clés: inconel 600; corrosion sous contrainte; oxydation; émission acoustique; flexion 4 points. This work concerns the damage of a nickel-based alloy known under the commercial name Inconel 600, usually used on the level of the primary circuits of the pressurized water nuclear reactors. The 4 points bending tests are carried out under secondary vacuum. In order to answer the real conditions of the operations, the temperature range which explored is chosen between 350°C to 550°C. The use of acoustic emission shows that there is no damage of the sample itself during such mechanical tests. From the curves of stress-strain and deflection, obtained from experimental tests; mechanical characteristics of material such as the Young modulus and the yield strength are determinate. Other tests under air and water vapour are considered in order to be able to obtain the viscoplastic behaviour of material in the range of temperature concerned by inverse method.Keywords: inconel 600; stress corrosion cracking; oxidation; acoustic emission; 4 points bending.