Publications Scientifiques
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Item 2,4-Substituted-3-aza-1-thiabutadienes : a conformational study by dipolmetry(Elsevier, 1992) Cellerin, C.; Abouelfida, A.; Pradère, J.P.; Proutière, A.; Rozé, J.C.; Bouzid, Mohammed; Exner, O.Item Calculation of liquid-phase mass transfer coefficient on directional-jet trays with longitudinal partitions(Springer, 1993) Auashria, S.Item Synthèse du benzo-1,4-dioxanne en catalyse par transfert de phase = Synthesis of 1,4-benzodioxan by phase transfer catalysis(1994) Hamada, B.; Kaddour, O.; Safar, M.; Boukherissa, A.La synthèse du benzo-1,4-dioxane par interaction du 1,2-dichloroéthane avec le pyrocatéchol a lieu en présence de solvants polaires qui sont parfois très coûteux. Dans ce travail, la réaction de synthèse a été améliorée du point de vue vitesse et rendement par l'utilisation de la catalyse par transfert de phaseItem Experimental determination of work function of silver alloys(1994) Lefort, Andre; Akbi, Mohamed; Parizet, Marie-JoseModels about arc roots need a good knowledge of physical constants characterizing contact material. With pure metal, all the constants are well known; but for alloys some are not known. In this paper we relate how we have measured work function of silver alloys. Measuring method used is the Fowler one where photoelectronic current produced by different ultraviolet radiations is measured in high vacuum. Experimental set-up have been tested for pure materials and then, have been applied to some silver alloys. Results about pure metals show an evolution of the work function with temperature; it decreases when temperature increases. Results about silver-nickel alloys show a large dependence of obtained results with the preparation of contact surface. For example, polishing and cleaning induce, because of atom migration, a large modification of the ratio of the two components on surface; this phenomenon induces a variation of work function comparatively with obtained values with prLtary product. By heating alloy contact in high vacuum we have observed large variations of work function, which result from material component vaporisation by sheets. Surface analyses by electron microscope produce proves of the phenomenon. An empirical relation is given to calculate work function of binary alloy when this constant is known for each alloy componentItem Seminumerical technique for the analysis of integrated semiconductor devices(1994) Dehmas, Mokrane; Zitouni, Abdelkader; Bourdoucen, H.Item Vortex dynamics studied over a wide range of time scale in Bi-2212 Crystals(1995) Goupil, Ch.; Ruyter, A.; Provost, J.; Aouaroun, T.; Simon, Ch.Item One-dimensional brownian-motion model for transport measurements in high-temperature superconductors(1996) Goupil, Ch.; Aouaroun, T.; Thopart, D.; Hamet, J. F.; Simon, Ch.Using a one-dimensional model of Brownian motion of vortices over pinning wells, we derive a current-voltage equation assuming a distribution of the effective pinning length. The model describes linear and nonlinear regimes of the E(J) curves in a single-particle description. Thermally activated flux flow and flux flow define the two limits of the dissipative process, respectively, at very low and high current. The pinning relief is described by pinning well depth and pinning well gradient, respectively, which can be checked by resistive and current-voltage measurements. The model is then applied to a YBa2Cu3O7−δ thin film. It provides a phenomenological model of the dissipation induced by transport currentItem Study of vortex motion in a sintered high Tc superconductor by a vibrating reed technique(1996) Richard, L.; Woirgard, J.; Aouaroun, T.; Rabier, J.Using a vibrating reed technique in a subresonant excitation mode, dissipation mechanisms have been studied in sintered YBa2Cu307-, superconductors with different grain sizes. Experimental results are interpreted within the critical state model. Results deduced from vibrating reed technique are compared with ac susceptibility measurements. It is shown that both techniques give consistent resultsItem Quasi-static MoL-based approach for the analysis of multilayer transmission line structures(John Wiley & Sons, 1997) Zitouni, Abdelkader; Bourdoucen, H.; Nait Djoudi, T.Item Anisotropic resistivity measurements by a multi-terminal transport method(IOP Publishing, 1997) Aouaroun, T.; Hardy, V.; Goupil, Ch.; Warmont, F.; Villard, G.; Simon, Ch.Item Work function measurements of contact materials for industrial use(IOP, 1998) Akbi, Mohamed; Lefort, AndréThe nature of the contact material is important for the characteristics of electric arcs and particularly for the electronic emission. Work functions of new industrial materials made with silver alloys and silver oxide alloys are not known at present. An experimental set-up is described which allows work function measurements from room temperature up to 700 K. The Fowler method was used for the measurement of the work function by the photoelectric effect. As a first application of the experimental device, work functions of metals (Ag, Cu, Ni, Sn and Zn) were determined. Furthermore, the influence of industrial surface treatment such as the application of electric arcs and repeated mechanical shocks on the Ag contact work surface was studied by SEM to observe their effect on electron work function. Breaking arcs in air cause a remarkable increase in the work function of the silver contact material by progressive formation of silver oxidesItem Plastic vortex creep in the high-Tc superconductor (T1 2/3 , Bi1/3) Sr2CaCu2Ox(Elsevier, 1998) Aouaroun, T.; Hardy, V.; Simon, Ch.Item Second-peak effect in a superconducting Tl, Bi -1212 single crystal by ac susceptibility : evidence for vortex plastic behavior(American Physical Society, 1998) Aouaroun, T.; Simon, Ch.A second peak effect is observed for a ~Tl, Bi!-1212 single crystal using ac susceptibility measurements. The analysis of the frequency dependence of the second peak position shows that plasticity governs the vortex dynamics on both sides of the second peak line. This suggests that no particular change in the vortex dynamics occurs by crossing this line. We propose that this second peak effect is due to the temperature activated form of the characteristic relaxation times and to the fact that the characteristic activation energy Uc and the critical current density Jc have inverse variations with the magnetic field B ~when one increases with B the other decreases!. We also propose that the time dependence of the second peak field position should indicate the vortex dynamics behavior: an increasing second peak field position with time is a fingerprint of elastic behavior while a decreasing second peak field position with time is a fingerprint of plastic behavior. The latter case agrees well with our experimental resultsItem Influence of surface roughness on the deuterium inventoryof ASDEX-UPGRADE divertor tiles(1998) Hildebrandt, D.; Akbi, Mohamed; Jüttner, B.; Schneider, W.The gas inventory of divertor target tiles used in ASDEX-UPGRADE has been analyzed by thermodesorption spectrometry (TDS°. desorbed gaseous molecules have been measured by heating up complete and cut divertor tiles. the largest samplrs '80X80mm2)could be heated up to temperatures of 1500 K and smaller ones to even higher temperatures.in addition, surface analysis techniques as auger electron spectroscopy (AES),secondary ion mass spectrometry(SIMS), nuclear reaction analysis (NRA), electron microscopy and optical surface profiling have been applied for investigating erosion and deposition phenomena. the original plasma facing surface of the tiles were graphite (EK98) and plasma sprayed tungsten, respectively. the graphite tiles were used from 1991-1995 for about 1900 discharges and the tungsten tiles in 1996 for about 800 discharges...Item Deuterium and impurity contamination of divertor tiles and collector probes of asdex-upgrade(Fusion and plasma physics, 1998) Hildebrandt, D.; Akbi, Mohamed; Jüttner, B.; Rohde, V.; Schneider, W.The uptake and release of hydrogen isotopes at the plasma-facing components in magnetic, confinement fusion devices affects the working gas recycling, the plasma behaviour and the tritium inventory [1]. This attracts considerable interest in the investigation of hydrogen trapping during plasma exposure. The most intensive plasma material interaction occurs on limiters and divertor plates. Post-mortem analysis of such components gives information on the total amount of hydrogen isotopes retained in the material after plasma exposure. Recent investigations of divertor tiles of ASDEX-UPGRADE have shown that the dominant trapped deuterium amount is contained in the deposited material at the surface [2]. This surface contamination consists mainly of carbon, boron and the hydrogenic isotopes. Movable collector probes have been applied to investigate the hydrogen trapping and impurity deposition under specific plasma conditions. In the present paper results on the impurity and deuterium contamination at the surface of collector samples are presented and compared with corresponding results from the divertor tiles. The collector samples were exposed to the scrape-off plasma of the main chamber (SOL-probe) and to the divertor plasma (DIV-probe)Item Vortex plastic creep in a superconducting crystal of Tl-2223(Elsevier, 1998) Aouaroun, Tahar; Simon, CharlesItem Pillar defects, a new type of track in Pb-irradiated Bi-2212 thin films : nanostructural study and influence on the irreversibility line(Elsevier, 1998) H ebert, S.; Hervieu, M.; Hardy, V.; Aouaroun, T.; Simon, Ch.; Provost, J.; Milani, E.; Aruta, C.; Balestrino, G.Item Speed-up of high accuracy analog test stimulus optimization(1999) Khouas, Abdelhakim; Derieux, AnneAnalog integrated circuit testing and diagnosis is a very challenging problem. The inaccuracy of measurements, the infinite domain of possible values and the parameter deviations are among the major difficulties. During the process of optimizing production tests, Monte Carlo simulation is often needed due to parameter variations, but because of its...Item Performance of an unbuffered Beta model using stochastic Petri nets(International Journal of Modelling and Simulation, 1999) Benazzouz, D.; Farah, A.Many multistage interconnection networks (MINs) and single stage interconnection networks (SSINs) have been proposed for parallel computer systems and for fast packet switching in high speed new works. The cost, performance, and fault-tolerance capability of the interconnection networks (INs) becomes very important in the design considerations of a multiprocessor systems. Several types of INs have been proposed, notably multistage and single-stage interconnection networks. There have been extensive studies on MIN (e.g., performance analysis, methods to improve the throughput, priority, etc.), but relatively little work on SSINs has appeared in the literature. In this paper we evaluate the unbuffered Beta topology of SSIN using stochastic Petri nets. We present an approximate analytical model. We analyze the random delay experienced by a message traversing the network for uniform traffic. Messages can have different sizes. Each sender can accept one packet per cycle and route it to the appropriate receiver. It is shown that the bandwidth increases when the data transfer increases. In addition, it is shown that the average transfer time increases slowly compared to the increase of processors. The power of this model is that, firstly, it presents an acceptable number of states, and secondly, the model can be easily generalizedItem Speed-up of High Accurate Analog Test Stimulus(1999) Khouas, Abdelhakim; Derieux, AnneAnalog integrated circuit testing and diagnosis is a very challenging problem. The inaccuracy of measurements, the innite domain of possible values and the parameter deviations are among the major diOEculties. During the process of optimizing production tests, Monte Carlo simulation is often needed due to parameter variations, but because of its expensive computational cost, it becomes the bottleneck of such a process. This paper describes a new technique to reduce the number of simulations required during analog fault simulation. This leads to the optimization of production tests subjected to parameter variations. In section I a review of the state of the art is presented, section II introduces the algorithm and describes the methodology of our approach. The results on CMOS 2-stage opamp and conclusions are given in sections III and IV