Equation of state of a granular gas homogeneously driven by particle rotations

We report an experimental study of a dilute "gas" of magnetic particles subjected to a vertical alternating magnetic field in a 3D container. Due to the torque exerted by the field on the magnetic moment of each particle, a spatially homogeneous and chaotic forcing is reached where only rotational motions are driven. This forcing differs significantly from boundary-driven systems used in most previous experimental studies on non equilibrium dissipative granular gases. Here, no cluster formation occurs, and the equation of state displays strong analogy with the usual gas one apart from a geometric factor. Collision statistics is also measured and shows an exponential tail for the particle velocity distribution. Most of these observations are well explained by a simple model which uncovers out-of-equilibrium systems undergoing uniform "heating".Comment: Europhysics Letters (2013) in pres

Creating interactivity of our heritage stored in Museums: Experimentation with Château des Ducs de Bretagne History Museum of Nantes, France

International audienceFor the 2006 VRIC conference, we presented a scientific article dealing with a new way of thinking our technical heritage. We propose to preserve it as a digital object. However it does not mean beautiful 3D animation with nice static rendering; indeed, we create virtual mock-up which are dynamically operating. We use CAD software and engineering simulation tools. Nowadays the global methodology has been improved: it is named Advanced Industrial Archaeology. In this communication, we will detail a new experimentation done in partnership with a French museum: the Château des Ducs de Bretagne in France. This project deals with a physical mock-up of Nantes city built in 1899 and exposed in 1900 for the World Fair that took place in Paris, France. The heritage object is nowadays in the museum but exposed as “a fish inside an aquarium”. Thanks to a virtual system coupling a tactile screen with semantic research modules, a 3D active screen and a light pointer, it will allow the visitor to better understand the mock-up and emphasize important places of Nantes city life

Muséologie, patrimoine, humanités numériques et 3D

International audienceLa communication se propose d’approfondir les réflexions menées sur la place et le rôle des publics dans le cadre de recherches interdisciplinaires menées au sein des établissements d’enseignement supérieurs et de recherche de Nantes. A partir de cas d’études patrimoniaux, elle vise à définir une nouvelle approche de la médiation culturelle et patrimoniale et tend à établir les nouvelles bases du processus de création/recréation des espaces et objets patrimoniaux (patrimoine matériel et immatériel) à partir de nou-veaux paradigmes épistémologiques des Humanités Numériques unissant tant les approches en science humaine et sociale qu’en ingénierie 3D

Energy of a single bead bouncing on a vibrating plate: Experiments and numerical simulations

International audienceThe energy of a single bead bouncing on a vibrating plate is determined in simulations and experiments by tracking the bead-plate collision times. The plate oscillates sinusoidally along the vertical with the dimension-less peak acceleration ⌫, and the bead-plate collisions are characterized by the velocity restitution coefficient ⑀. Above the threshold dimensionless peak acceleration ⌫ s Ӎ0.85, which does not depend on the restitution coefficient, the bead energy is shown to initially increase linearly with the vibration amplitude A, whereas it is found to scale like v p 2 /(1Ϫ⑀), where v p is the peak velocity of the plate, only in the limit ⌫ӷ⌫ s. The threshold ⌫ s is shown to decrease when the bead is subjected, in simulations, to additional nondissipative collisions occurring with the typical frequency ␯ c. As a consequence, the bead energy scales like v p 2 /(1Ϫ⑀) for all vibration strengths in the limit ␯ c ӷ␯ c *. From the experimental and numerical findings, an analytical expression of the bead energy as a function of the experimental parameters is proposed. As they exhibit a wide range of unusual behaviors, granu-lar materials are the subject of intensive investigations ͓1–3͔. Because of the inelastic nature of the contacts between the grains, these systems are intrinsically dissipative. In order to explore experimentally the effects of the dissipation on the properties of granular systems, it is convenient to produce stationary states; they are achieved by continuously providing the system with energy, compensating the energy intrin-sically lost when the grains are in motion. Among these studies , one can note the experimental realization of two-dimensional (2D) granular gases, consisting of inelastic beads constituting less than one-layer coverage on a vertically shaken, horizontal plate ͓4 –8͔ ͑the experimental situation has been the framework of molecular-dynamics simulations by Nie et al. ͓9͔͒. The velocity distributions, granular temperature, pressure, as well as phase transitions have been studied as functions of the vibration strength, usually characterized by the peak plate acceleration ⌫. Nevertheless, detailed analysis of the clustering transition and of the pressure indicates that the vibrating boundary becomes inefficient to thermalize the system when the acceleration or the density of the gas are decreased. The energy input by the vibrating boundary has been the subject of several theoretical studies ͓10–13͔; the scaling law for the energy as a function of the vibration strength has been shown to depend on the shape of the boundary vibration ͑sinusoidal, sawtooth, etc.͒ and on the nature of the dissipation within the gas ͑viscous, inelastic͒. In these studies, the assumption was made that the bead impinges randomly on the boundary; we note that this is not the case when the bead collides more than once with the boundary between two collisions with another bead. One can easily show that the velocity is exponentially correlated between two successive collisions in this case. It is hence relevant to study the dynamical behavior of a single bead bouncing on a vibrating plate, and to determine the mean energy ͗E͘ of th

Récit historique et objet technique : outil de valorisation mutuelle

National audienceDans le domaine de l’histoire des techniques et du patrimoine matériel, l’informatisation est massive, autant sur le plan de l’écriture, que des sources (archives) ou de la valorisation. Cependant les articulations entre ces plans (archive, recherche, valorisation) restent faibles. Ce travail propose un outil numérique de gestion de contenu historique (récits et sources) pour documenter et valoriser les objets du patrimoine technique. En fonction des situations, différentes interfaces permettent d’accéder aux connaissances, une interface de navigation en 3D est ici proposée en exemple. L’objet technique et le travail de l’historien sont conjointement valorisés

Récit historique et objet technique : outil de valorisation mutuelle

National audienceDans le domaine de l’histoire des techniques et du patrimoine matériel, l’informatisation est massive, autant sur le plan de l’écriture, que des sources (archives) ou de la valorisation. Cependant les articulations entre ces plans (archive, recherche, valorisation) restent faibles. Ce travail propose un outil numérique de gestion de contenu historique (récits et sources) pour documenter et valoriser les objets du patrimoine technique. En fonction des situations, différentes interfaces permettent d’accéder aux connaissances, une interface de navigation en 3D est ici proposée en exemple. L’objet technique et le travail de l’historien sont conjointement valorisés

Application de l’analyse de l’hétérogénéité aux indices comparatifs d’incidence et de mortalité par cancer de l‘estomac au Québec, 1984-1988.

Cet article présente l'analyse d'hétérogénéité selon la méthode développée par Gail (1978). Elle examine si les rapports de mortalité (local/national) dans les différents groupes d'âges sont identiques, ceci étant une condition nécessaire pour que les indices comparatifs de mortalité décrivent valablement les données. De plus, comme cette méthode est analogue à l'analyse de variance, la population peut être partitionnée selon une hypothèse à tester. Nous l'avons appliquée à l'incidence et à la mortalité par cancer de l'estomac au Québec de 1984 à 1988.This article presents the heterogeneity analysis according to the method developped by Gail (1978). This method was used to assess if mortality data (local/national) are similar among different age groups, this latter being one of the conditions for comparative mortality ratings describe the data with validity. Moreover, this method being comparable to the variance analysis, the population may be split up according to some hypothesis to be tested. We have applied it to the incidence and mortality of stomach cancer in Québec from 1984 to 1988

A case study of capitalisation and valorisation of our technical heritage

International audienceFor the 2008 CIRP Design conference, we have presented a scientific article dealing with a new way of thinking our technical heritage: we would like to preserve it as a digital object. Project deals with a physical mock-up of Nantes city built in 1899 and used for the Universal exposition in France in 1900 in Paris. The heritage object is nowadays in the museum but exposed as a fish inside an aquarium. Thanks to a virtual system coupling a tactile screen with semantic research modules, 3D active screen and light pointer, it will allow the visitor to better understand the mock-up and emphasize important places of Nantes city life. However it does not mean beautiful 3D animation with nice static rendering; indeed, we create virtual mockups which are dynamically operating. We use CAD software and engineering simulation tools. Nowadays the global methodology has been improved: it is named Advanced Industrial Archaeology. In this communication, we will detail a new experimentation done in partnership with a French museum: the Château des Ducs de Bretagne in France. This project deals with a physical mock-up of Nantes city built in 1899 and exposed in 1900 for the World Fair that took place in Paris, France. The heritage object is nowadays in the museum but exposed as “a fish inside an aquarium”. Thanks to a virtual system coupling a tactile screen with semantic research modules, a 3D active screen and a light pointer, it will allow the visitor to better understand the mock-up and emphasize important places of the city. The mock-up represents our industrial heritage with old shipyards of Nantes