Phase boundary anisotropy and its effects on the maze-to-lamellar transition in a directionally solidified Al-Al2Cu eutectic

Solid-solid phase boundary anisotropy is a key factor controlling the selection and evolution of non-faceted eutectic patterns during directional solidification. This is most remarkably observed during the so-called maze-to-lamellar transition. By using serial sectioning, we followed the spatio-temporal evolution of a maze pattern over long times in a large Al-Al2Cu eutectic grain with known crystal orientation of the Al and Al2Cu phases, hence known crystal orientation relationship (OR). The corresponding phase boundary energy anisotropy ($\gamma$-plot) was also known, as being previously estimated from molecular-dynamics computations. The experimental observations reveal the time-scale of the maze-to-lamellar transition and shed light on the processes involved in the gradual alignment of the phase boundaries to one distinct energy minimum which nearly corresponds to one distinct plane from the family $\{120\}^{\rm{Al}} //\{110\}^{\rm{Al2Cu}}$. This particular plane is selected due to a crystallographic bias induced by a small disorientation of the crystals relative to the perfect OR. The symmetry of the OR is thus slightly broken, which promotes lamellar alignment. Finally, the maze-to-lamellar transition leaves behind a network of fault lines inherited from the phase boundary alignment process. In the maze pattern, the fault lines align along the corners of the Wulff shape, thus allowing us to propose a link between the pattern defects and missing orientations in the Wulff shapeComment: 26 pages, 6 figure

Hexagonal eutectic solidification patterns operating near a marginal stability point

We study the long-time dynamics of hexagonal directional-solidification patterns in bulk samples of a transparent eutectic alloy using an optical method which permits real-time observation of the growth front. A slow dilatation of the patterns due to a slight curvature of the isotherms drives the system into a permanent regime, close to the threshold for the rod splitting instability. Thus an apparently minor instrumental imperfection suffices to maintain the system near a marginal stability point. This answers the long-standing question of spacing selection in bulk eutectic growth

An experimental method for the in-situ observation of eutectic growth patterns in bulk samples of transparent alloys

We present an experimental method for the in-situ observation of directional-solidification fronts in bulk samples of transparent eutectic alloys. The growth front is observed obliquely in dark field through the liquid and a glass wall of the container with a long-distance microscope. We show that a focused image of the whole growth front can be obtained at a certain tilt angle of the microscope. At this tilt angle, eutectic fibers of about 3.5\mic in diameter can be clearly seen over the whole growth front in 400-\mic thick samples

The trajectory of subboundary grooves during directional solidification of dilute alloys

International audienceDue to their strong surface energy anisotropy, subboundaries generally do not intersect solid-melt interfaces at right angles. As a consequence, subboundary surface grooves move laterally during solidification, and thereby interact, in alloys, with the solute concentration gradients created in the liquid. We discuss the consequences of this effect during thin directional solidification at speeds (V) lower than the cellular-instability threshold V-c of the system. We show that the lateral drift of the subboundary grooves slows down (or equivalently the tilt angle of the subboundaries relative to the growth direction decreases) as V increases and vanishes as V approaches V. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved

In situ experiments in microgravity and phase-field simulations of the lamellar-to-rod transition during eutectic growth

International audienceIn recent experiments on the solidification of the binary eutectic alloy succinonitrile-(D)camphor carried out on board of the International Space Station (ISS), a transition from rod to lamellar patterns was observed for low growth velocities. The transition was interpreted in terms of a competition between a propagative instability of lamellae and a drift induced by a transverse temperature gradient. Phase-field simulations of a symmetric model alloy support this scenario: for a fixed transverse temperature gradient, the transition from rods to lamellae occurs for a critical composition at fixed velocity, and for a critical velocity at fixed composition. Since the alloy and control parameters used in experiments and simulations are different, our results strongly suggest that this morphological transition is generic for eutectic alloys

Innovative models for collaboration and student mobility in Europe

This report is based on new developments in higher education and international collaboration as collected by EADTU's Task Force and Peer Learning Activity on Virtual Mobility. The result is a report on three types of collaboration mobility: physical, blended and online. Main parameters for innovative education and mobility formats are defined as well as basic principles of international course and curriculum design. Examples illustrate the complete opportunity space between fully face to face and fully online collaboration. They relate to mobility within single courses, exchange mobility (classical Erasmus), networked programmes and mobility windows and joint programmes with embedded mobility. Mobility offers opportunities to institutions to strengthen their programmes and to students to enrich their study. They benefit from an international learning experience or following courses not provided by their own institution. The report shows concrete mobility schemes used in the membership (and beyond). It underpins policies for international networking and delivers tools to organise innovative education and mobility formats

Mémoires et enjeux du « moment 68 » dans le catholicisme (1968-2018)

International audienceLes événements de Mai 68 occupent une place particulière dans l'imaginaire français. La mémoire d'une insurrection subversive et violente s'est transformée, au fil des anniversaires et des commémorations, pour ne plus retenir que les images d’un moment joyeux d’émancipation et de libération de la parole avant de connaître tout récemment un réinvestissement politique.Le présent ouvrage entend interroger les mémoires d’un groupe particulier et hétérogène, celui des catholiques, qui a pu paraître en décalage au moment des événements et dont l’action reste encore assez largement méconnue.Solliciter la mémoire des acteurs catholiques de 68 en France permet d’approcher à la fois leur perception rétrospective et l’impact des événements sur leur parcours de vie ultérieur. Qu’il s’agisse de personnes connues (René Rémond à Nanterre) ou ordinaires (étudiants de l’aumônerie d’Assas ou ouvriers de la JOC à Clermont-Ferrand), les mémoires du vécu de 68 restent vives. Quand et comment se sont-elles fixées ? Tel est l’enjeu du premier axe parcouru dans cet ouvrage. Explorer des mémoires catholiques de 68 portées par des communautés ou des revues ancrées dans d’autres terres catholiques (Italie, Belgique, Amérique latine) permet de décentrer le regard et en contrepoint de s’interroger : les catholiques français sont-ils porteurs d’une mémoire spécifique de 68 ? Telle est la piste suivie dans la seconde partie. Interroger le devenir, sur 50 ans, des grands motifs du « moment 68 » -la Révolution politique, l’émancipation des peuples, la société de consommation et du spectacle, la libération sexuelle...- dans la sphère religieuse, politique et culturelle catholique permet de saisir les rejeux et les retournements, parfois inattendus, des idéaux de 68. Comment les catholiques français ont-ils interprété et recyclé 68 ? Telle est l’ouverture proposée dans la troisième partie

Examens télésurveillés au domicile de l’étudiant dans la formation à distance universitaire française

Presses Universitaires Du Québec (PUQ)International audienc

Examens télésurveillés au domicile de l’étudiant dans la formation à distance universitaire française

Presses Universitaires Du Québec (PUQ)International audienc