Affine Surfaces With a Huge Group of Automorphisms

We describe a family of rational affine surfaces S with huge groups of automorphisms in the following sense: the normal subgroup Aut(S)alg of Aut(S) generated by all algebraic subgroups of Aut(S) is not generated by any countable family of such subgroups, and the quotient Aut(S)/Aut(S)alg cointains a free group over an uncountable set of generator

Apport expérimental à l'analyse poroviscoélastique des déformations endogènes dans un ciment pétrolier

Cementing is a crucial step of the construction phase of an oil well, which aims at ensuring zonal isolation between the different parts of the well and the environment. The protective cement annulus hydrates in external conditions of temperature and pressure that can vary widely from one job to another, and poor control of the hydration phase can lead to autogenous shrinkage that reduces the effectiveness of the cementing. In this work, we investigate an industrial predictive model for the evolution of a cement annulus, which combines a thermochemical system describing the cement hydration at the macroscopic scale and an aging viscoelastic system including poromechanics to describe the stress and strain resulting of a capillary pressure mechanism. This model makes a number of simplifying hypotheses that are necessary considering the large amount of important parameters used in the modeling of hydration shrinkage. The range of validity of these assumptions has been investigated, as well as the relevance of the selected parameters used in the model. In this scope, it has been decided to compare simulation results obtained with our algorithm derived from the original model with experimental results of hydration and of deformations obtained with external loading or caused by internal stresses. The hydration reaction was studied by standard calorimetric measurements as well as by nuclear magnetic resonance. This method is relatively new in the field of cementitious materials in comparison with other methods and offers several benefits for following long-term hydration as well as for accurate detection of the setting time of the material without requiring mechanical probing. The mechanical measurements were used to examine the material at various ages and with various curing temperatures to measure the evolution curves of mechanical modules with degree of hydration. These tests include tests using a static press, to measure the elastic properties and creep tests as well as dynamic mechanical analyzer tests to measure viscoelastic behavior. Finally, a critical analysis of some of the choices made in the modeling work has been proposed with suggestions to improve the accuracy of simulations at early age, both in terms of degree of hydration as of short-term creep strainsLa cimentation est une étape cruciale de la construction d'un puits de pétrole, qui vise à garantir l'isolation des différentes zones du puits. La couche protectrice de ciment s'hydrate dans des conditions extérieures de température et de pression qui peuvent varier largement selon les cas, et une mauvaise maîtrise de cette hydratation peut provoquer des déformations internes qui compromettent l'efficacité de la cimentation. On s'intéresse ici à un modèle industriel prédictif de l'évolution d'un annulaire de ciment, qui combine un système d'équations retranscrivant l'hydratation du matériau d'un point de vue thermochimique et un algorithme de calcul viscoélastique vieillissant faisant appel à la poromécanique pour décrire les contraintes et les déformations internes selon un mécanisme de pression capillaire. Ce modèle fait un certain nombre d'hypothèses simplificatrices, nécessaires au vu de la myriade de paramètres importants dans la modélisation du retrait d'hydratation. On s'interroge ici quant aux domaines de validité de ces hypothèses ainsi qu'à la pertinence des jeux de paramètres choisis. Pour ce faire, il a été décidé de comparer des résultats de simulation obtenus avec notre algorithme dérivé du modèle initial et des résultats expérimentaux de mesures d'hydratation et de déformations avec et sans contraintes extérieures. La réaction d'hydratation a été étudiée par des mesures standard comme la calorimétrie ainsi que par résonnance magnétique nucléaire. Cette méthode est relativement récente dans le domaine des matériaux cimentaires en comparaison des autres et possède des avantages pour les suivis d'hydratation à long terme ainsi que pour une détection précise de la prise du matériau sans recours à une sonde mécanique. Les mesures mécaniques ont permis d'étudier le matériau à plusieurs âges et avec plusieurs températures de cure afin de mesurer les courbes d'évolution des modules mécaniques avec le degré d'hydratation. Ces essais regroupent des tests statiques utilisant une presse, permettant de mesurer les propriétés élastiques, ainsi que des essais de fluage et des mesures par un analyseur visco-dynamique afin de mesurer le comportement viscoélastique. Enfin, une analyse critique de certains des choix faits dans le travail de modélisation a été proposée avec des pistes pour améliorer la précision des résultats au jeune âge, à la fois en termes de degré d'hydratation comme de fluage à court term

Corrosion behaviour of an assembly between an AA1370 cable and a pure copper connector for car manufacturing applications

The corrosion behaviour of an assembly between an AA1370 cable and a pure copper connector for wiringharnesses was studied in neutral chloride and sulphate containing solution. Electrochemical impedancemeasurements showed that the corrosion behaviour of the cable was controlled by the ingress of the elec-trolyte inside cable cavities. Further, local impedance measurements were performed on two assemblycross-sections, i.e. with and without cavities in the aluminium cable. The results provided evidence forboth the galvanic coupling between aluminium and copper and the presence of cavities in the aluminiumcable as relevant explanations for the corrosion behaviour of the assembl

Corrosion behaviour of mechanically polished AA7075-T6 aluminium alloy

In the present study, the effects of mechanical polishing on the microstructure and corrosion behaviour of AA7075 aluminium alloy are investigated. It was found that a nano-grained, near-surface deformed layer, up to 400 nm thickness, is developed due to significant surface shear stress during mechanically polishing. Within the near-surface deformed layer, the alloying elements have been redistributed and the microstructure of the alloy is modified; in particular, the normal MgZn2 particles for T6 are absent. However, segregation bands, approximately 10-nm thick, containing mainly zinc, are found at the grain boundaries within the near-surface deformed layer. The presence of such segregation bands promoted localised corrosion along the grain boundaries within the near-surface deformed layer due to microgalvanic action. During anodic polarisation of mechanically polished alloy in sodium chloride solution, two breakdown potentials were observed at −750 mV and −700 mV, respectively. The first breakdown potential is associated with an increased electrochemical activity of the near-surface deformed layer, and the second breakdown potential is associated with typical pitting of the bulk alloy

L’arrière-plan idéologique de la réforme scolaire au Japon

Une réforme de l’école a débuté au Japon en 1992, pour voir une accélération après 2000. Elle a visé à repenser le fonctionnement et le rôle du système scolaire, et à lui conférer davantage d’autonomie et de compétitivité, en mettant les écoles en concurrence et en procédant à diverses dérégulations. Le présent article examinera les arguments avancés par les tenants de la réforme pour justifier celle-ci, puis en exposera les grandes lignes, pour enfin se pencher sur ses effets depuis 2000-2002, en relation avec l’évolution de la société japonaise, depuis l’éclatement de la bulle économique en 1991-1992.A school reform started in Japan in 1992 and speeded up after 2000. It aims at rethinking the role the school system plays and the way it works ; and giving it more self-government and competitiveness by developing competition between schools and creating some deregulations. First the article examines the arguments that the supporters of the reform have put forward to justify it ; then it explains the outlines of the reform ; finally it focuses on the effects it has had since 2000-2002 in connection with the evolution of the Japanese society since the burst of the economic bubble in 1991-1992.Una reforma de la escuela empezó en Japón en 1992, para ver una aceleración después del 2000. Pretendía volver a pensar el funcionamiento y el papel del sistema escolar, y conferirle más autonomía y competitividad poniendo las escuelas en competencia y procediendo a diversas desregulaciones. El presente artículo examinará los argumentos expuestos por los defensores de la reforma para justificarla, después expondrá sus grandes líneas, para estudiar por fin sus efectos desde 2000-2002, en relación con la evolución de la sociedad japonesa desde la explosión de la bola económica en 1991-1992.Eine Schulreform hat in Japan 1992 angefangen, und hat sich 2000 beschleunigt. Sie zielte darauf ab, die Funktionsweise und die Rolle des Schulsystems neu durchzudenken und ihm mehr Autonomie und Wettbewerbsfähigkeit zu verleihen, indem sie die Schulen in Wettbewerb treten lie_ und verschiedene Deregulierungen einführte. Vorliegender Artikel untersucht zuerst die Argumente der Befürworter der Reform zur Rechtfertigung dieser Ma_nahmen, stellt deren Richtlinien und beobachtet schlie_lich ihre Auswirkungen seit 2000-2002, in Zusammenhang mit der Entwicklung der japanischen Gesellschaft seit dem Platzen der Spekulationsblase 1991-1992

Effect of corrosion on the fatigue life and fracture mechanisms of 6101 aluminum alloy wires for car manufacturing applications

An innovative solution for the automotive industry is to replace the copper used for wiring harnesses with aluminum alloys, such as the aluminum–magnesium–silicon 6101 alloy. Wiring harnesses are composed of thin strand arms obtained by a wire drawing process. These strands are susceptible to exposure to a corrosive environment and fatigue solicitations simultaneously. The fatigue endurance of this alloy was studied using the stress-life approach for three metallurgical states representative of three colddrawing steps. Fatigue tests performed in corrosive media tests highlighted a strong decrease of the 6101 alloy lifetime due to fatigue–corrosion interactions and a modification of failure modes

Corrosion Behavior of 6101 Aluminum Alloy Strands for Automotive Wires

Microstructural states produced by each step of the manufacturing process leading to the production of automotive strand arms in 6101 aluminum alloy (AA6101) for wiring harnesses were investigated in relation to their corrosion behavior in NaCl solution. The observed corrosion morphology,i.e., pitting corrosion or intergranular corrosion, was strongly dependent on the precipitation state, i.e., mainly the presence of intergranular Mg2Si precipitates. A ‘grain size – corrosion resistance’ relationship was also evidenced with an ennoblement of the corrosion potential for wires heavily cold drawn, which were characterized by a nanometric grain size. Dislocation density as well as the homogeneity of alloying element distribution were also found to be relevant parameters for explaining the electrochemical behavior of each microstructural state. Plastic deformation and recrystallization phenomena occurring during the manufacturing process were found to be associated with redistribution of alloying elements, which impeded the formation of intergranular Mg2Si precipitates. Therefore, in the present study, the cold drawing process was found to increase the intergranular corrosion resistance of AA6101

Pitting corrosion of 17-4PH stainless steel manufactured by laser beam melting

The pitting corrosion behaviour of a 17-4PH martensitic stainless steel (MSS) manufactured by power bed laser beam melting (LBM) was compared to that of a wrought MSS. More noble pitting potentials were measured for LBM samples, probably due to a smaller size of NbCs as compared to wrought MSS. The metastable pits were less numerous, but had a higher nucleation rate and longer life time for the LBM samples compared to the wrought MSS. This was explained by assuming a decrease in the repassivation ability of LBM samples due to small gas pore

Towards Hybrid CAA with ground effects

CAA based on the Linearised Euler Equations (LEE) is applied to propagate aerodynamic sound over an extended distance including ground effects. The LEE are coupled to data from an LES via an acoustic analogy to follow-up the sound from the source to the extended far field: the complete chain is illustrated on the sound generated by a cylinder in a M ∼ 0.2 and Re ∼ 48000 flow. A very good agreement is found in free field between the approach based on the Ffowcs-Williams & Hawkings (FWH) analogy only and the combined FWH-LEE approach. The ability of the combined approach to handle complex boundary conditions is illustrated on the same data set with a rigid and a grassy ground