A structural investigation of the passive film on iron and iron/chromium alloys

The Electrochemical Polarisation, Photocurrent Spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS) techniques have been used to study the passive film on pure iron and iron alloy samples containing up to 25% chromium. The material used in this work was prepared both as bulk and thin films. The bulk samples were passivated electro- chemically at various anodic potentials whereas the film ones were either fully converted into passive films by simple immersion in various solutions for one week or electrochemically at various anodic potentials. The Fe and Fe/Cr film samples used in the electrochemical passi­vation were deposited onto gold substrate and those passivated by immersion were deposited directly onto mylar. Polarisation curves for both the bulk and film materials were recorded. They suggest that the electrochemical behaviour of the two materials is similar. The wavelength and potential dependence of the photocurrent spectra were also recorded for the bulk and film samples of Fe and Fe/Cr alloys. The data were analysed to obtain the effective optical band gaps and flat band potentials of the passive films respectively. These results also show that the two materials are similar. Furthermore, the photocurrent data suggest that the passive film on Fe/Cr alloys consists of Fe(III) and Cr(III) phases. The fluorescence EXAFS above the Fe and Cr K-absorption edges of the passive film on Fe and Fe/Cr alloy films has been recorded both in-situ and en- situ. The spectra obtained in these studies were analysed to obtain average Fe-O and Fe-Fe separations as well as Cr-0 and Cr-Cr ones. These results together with a detailed examination of the XANES suggest that the passive film on iron in the absence of chromium is best described as a disordered 7—FeOOH-like structure and that on Fe/Cr alloys as well as on pure Fe passivated in chro­mate solution contains two simultaneous phases of disordered 7-FeOOHand Cr(OH)j. The structure of the chromium containing phase of the passive film was found to be independent of the source of chromium whether it was present in the alloy or it was incorporated from the passivating solution. The EXAFS data show also that the structure of the passive film is insensitive to drying. The results obtained in these studies have enabled the determination of the structure of the passive film on iron and iron/chromium alloys and the rôle played by chromium in improving the corrosion resistance of iron and its alloys has been identified. These conclusions are discussed in the light of other structural investigations of the passive film

Contribution à un cadre de spécification et conception d'IHM de supervision à base de services web dans les systèmes industriels complexes (Application à une raffinerie de sucre)

Ce mémoire présente une contribution à la conception d IHM sous la forme d un cadre méthodologique global en vue de la spécification de l IHM de supervision en tenant compte des pistes de conception et méthodologiques visant à intégrer un développement d applications interactives orienté services sous les angles du GL, de l IHM, tout en ayant une vision métier. En d autres termes, il prend la forme d une démarche s appuyant sur des méthodes, et des modèles issus du GL d une part, des technologies et ingénierie du web et de la gestion des processus métiers d autre part. Dans ce cadre, nous mettons en avant les différentes étapes du processus complet tout en focalisant sur les premières étapes allant jusqu à la spécification de l IHM et tenant compte des spécificités des services web.Nous avons appliqué le cadre proposé en vue de démontrer ou valider les principes fondateurs sur une étude de cas représentative relative à la supervision d un procédé industriel d une raffinerie de sucre du groupe agro-alimentaire CEVITAL de Béjaïa (Algérie).Les perspectives de recherche visent notamment l amélioration et l extensibilité de la démarche d une part et ce qu inspire cette approche comme solutions techniques pour les ingénieurs concepteurs, puis comme défis ou nouvelles problématiques pour les ergonomes d autres part.This thesis presents a contribution to the HMI design which consists of a global framework towards the supervisory HMI specification. It s based on some research on design and methodologies aiming to integrate interactive service oriented applications developpement from the software engineering and the HCI points of view under a business vision. This framework is based on models and methods issued from software engineering on the one hand, and on web technologies and business processes on the other hand. We highlight the different phases of a complete design process where focusing mainly on the first steps towards the HMI specification step taking into account the specificities of the web services.We have applied the proposed framework so that to validate its main principles on a representative study case relative to the supervision of the sugar refinery industrial process, at CEVITAL (an agro-alimentary industrial group based in Béjaïa, Algéria).The research perspectives aim notably to the enhancement and extensibility of the framework on the one hand, and investigate on what this approach inspires like technical solutions to the design engineers and ergonomic challenges to the ergonomists on the other hand.VALENCIENNES-BU Sciences Lettres (596062101) / SudocSudocFranceF

Outil de modélisation et de génération d'un échantillon multidimensionnel des pixels d'un imageur CMOS

International audienc

Maximum Lifetime Target Coverage in Wireless Sensor Networks

International audienceThe challenge in the deployment of wireless sensor networks is to ensure the coverage of targets with high energy efficiency, particularly when coverage constraint and energy constraint must be taken into account. Many algorithms have been suggested over the years to enhance network lifetime as sensor nodes are powered by batteries. These algorithms divide a set of sensor nodes into a number of subsets which can monitor all targets. The subsets are either joint or disjoint. In this paper, we propose an efficient method to compute the maximum lifetime target coverage. Our proposed method is centered around a target that is covered by a minimum number of sensor nodes. Based on this approach, we also propose an algorithm to expand the network lifetime which guarantees the monitoring of all targets by forming subsets of sensor nodes. Our obtained results are compared with the work reported in [1]. They are also compared with a method of computing the maximum lifetime target coverage (MLTC). The results obtained by simulation show that the proposed algorithm enhances the network lifetime, which illustrates the efficiency of this algorithm

Oxidation-Induced Surface Roughening of Aluminum Nanoparticles Formed in an Ablation Plume

International audienceNanoparticles formed within an ablation plume produced by the impact of a nanosecond laser pulse on the surface of an aluminum target have been directly measured using small-angle x-ray scattering. The target was immersed in an oxygen-nitrogen gas mixture at atmospheric pressure with the O_{2}/N_{2} ratio being precisely controlled. The results for an increasing oxygen content reveal remarkable effects on the morphology of the generated particles, which include a decrease in the particle volume but a marked increase in its surface ruggedness. Molecular dynamics simulations using a reactive potential and performed under similar conditions as the experiment reproduce the experimental trends and show in detail how the shape and surface structure of the nanoparticles evolve with increasing oxygen content. This good agreement between in situ observations in the plume and atomistic simulations emphasizes the key role of chemical reactivity together with thermodynamic conditions on the morphology of the particles thus produced