Comparison of methods for curvature estimation from volume fractions

This paper evaluates and compares the accuracy and robustness of curvature estimation methods for three-dimensional interfaces represented implicitly by discrete volume fractions on a Cartesian mesh. The height function (HF) method is compared to three paraboloid fitting methods: fitting to the piecewise linear interface reconstruction centroids (PC), fitting to the piecewise linear interface reconstruction volumetrically (PV), and volumetrically fitting (VF) the paraboloid directly to the volume fraction field. The numerical studies presented in this work find that while the curvature error from the VF method converges with second-order accuracy as with the HF method for static interfaces represented by exact volume fractions, the PV method best balances low curvature errors with low computational cost for dynamic interfaces when the interface reconstruction and advection are coupled to a two-phase Navier-Stokes solver

Pierre Petit, History, Memory, and the Territorial Cults in the Highlands of Laos. The Past inside the Present

Commencées en 2003, les enquêtes de terrain et les recherches en archives dont ce livre est l’aboutissement portent sur une petite vallée du Nord-Est du Laos, dans la province de Houaphan. Elles concernent un groupe de villages habités par différentes populations de langue tai (Lao, Tai « Noirs » et Tai « Rouges »), présentes également dans la province vietnamienne voisine de Son La. Outre la grande richesse des données recueillies par Pierre Petit et ses collègues de l’Université nationale d..

Geophysical investigation of the Pb-Zn deposit of Lontzen-Poppelsberg, Belgium

The drillhole information from the Lontzen-Poppelsberg site has demonstrated three orebodies and has allowed the estimation of the extension of the lodes, their dip, and the location at the ground surface. The localisation of the lodes makes them excellent targets for further exploration with geophysics. This deposit is classified as a Mississippi Valley Type (MVT) deposit. It consists mainly of Pb-Zn-Fe sulphides that display contrasting values in resistivity, chargeability, density, and magnetic susceptibility, with regards to the sedimentary host rocks. The dipole-dipole direct current (DC) resistivity and induce polarization (IP) profiles have been collected and inverted to successfully delineate the Pb-Zn mineralization and the geological structures. Short-spacing EM34 electromagnetic conductivity data were collected mainly on the top of Poppelsberg East lode and have revealed a conductive body matching with the geologically modelled mineralization. Gravity profiles have been carried out perpendicularly to the lode orientation; they show a strong structural anomaly. High resolution ground magnetic data were collected over the study area, but they showed no anomaly over the ore deposits. The geophysical inversion results are complementary to the model based on drill information, and allow us to refine the delineation of the mineralization. The identification of the geophysical signatures of this deposit permits targeting new possible mineralization in the area

Le groupe ACROE-ICA : recherche et formation en art, sciences et technologies

International audienceLe groupe ACROE-laboratoire ICA est reconnu dans le monde scientifique et dans le monde artistique pour être à l'origine de plusieurs concepts et techniques fondateurs et innovants sur la manière d'aborder le rôle de l'ordinateur et plus généralement les technologies numériques dans la création artistique. Depuis 30 ans, le groupe mène et soutient ses activités de recherche, de création et de formation au cøeur de l'interdisciplinarité Arts, Sciences, et Technologies

Introduction

“(...) -a lonely planet but a crowded stage”. Victor Alneng (2002 : 127) Depuis plusieurs décennies, on assiste un peu partout dans le monde à un développement sans précédent de la mobilité touristique impliquant des flux à la fois humains, techniques, financiers et culturels. Longtemps, deux attitudes ont prévalu au sein des sciences sociales, notamment francophones, à l’égard de ce phénomène. La première considérait le tourisme comme un objet mineur, sinon trivial; la seconde y voyait la si..

Proper Orthogonal Decomposition Analysis and Modelling of the wake deviation behind a squareback Ahmed body

We investigate numerically the 3-D flow around a squareback Ahmed body at Reynolds number Re = 104. Proper Orthogonal Decomposition (POD) is applied to a symmetry-augmented database in order to describe and model the flow dynamics. Comparison with experiments at a higher Reynolds number in a plane section of the near-wake at mid-height shows that the simulation captures several features of the experimental flow, in particular the antisymmetric quasi-steady deviation mode. 3-D POD analysis allows us to classify the different physical processes in terms of mode contribution to the kinetic energy over the entire domain. It is found that the dominant fluctuating mode on the entire domain corresponds to the 3-D quasi-steady wake deviation, and that its amplitude is well estimated from 2-D near-wake data. The next most energetic flow fluctuations consist of vortex shedding and bubble pumping mechanisms. It is found that the amplitude of the deviation is negatively correlated with the intensity of the vortex shedding in the spanwise direction and the suction drag coefficient. Finally, we find that despite the slow convergence of the decomposition, a POD-based low-dimensional model reproduces the dynamics of the wake deviation observed experimentally, as well as the main characteristics of the global modes identified in the simulation

Fluid force and symmetry breaking modes of a 3D bluff body with a base cavity

International audienceA cavity at the base of the squareback Ahmed model at Re 4 × 10 5 is able to reduce the base suction by 18% and the drag coefficient by 9%, while the geometry at the separation remains unaffected. Instantaneous pressure measurements at the body base, fluid force measurements and wake velocity measurements are investigated varying the cavity depth from 0 to 35% of the base height. Due to the reflectional symmetry of the rectangular base, there are two Reflectional Symmetry Breaking (RSB) mirror modes present in the natural wake that switch from one to the other randomly in accordance with the recent findings of Grandemange et al. (2013b). It is shown that these modes exhibit an energetic 3D static vortex system close to the base of the body. A sufficiently deep cavity is able to stabilize the wake toward a symmetry preserved wake, thus suppressing the RSB modes and leading to a weaker elliptical toric recirculation. The stabilization can be modelled with a Langevin equation. The plausible mechanism for drag reduction with the base cavity is based on the interaction of the static 3D vortex system of the RSB modes with the base and their suppression by stabilization. There are some strong evidences that this mechanism may be generalized to axisym-metric bodies with base cavity

Cristalliser l’histoire

La Thaïlande péninsulaire compte peu de vestiges archéologiques à l’exception de perles qui cristallisent des passions dévorantes. Collectées, portées, commercialisées, elles font régulièrement la une des journaux. À partir d’une enquête ethnographique réalisée auprès de la mission archéologique franco-thaïe en péninsule thaïe-malaise, cet article éclaire les pratiques de collecte de ces perles par divers acteurs locaux, et envisage les discours et représentations parfois contradictoires auxquels elles donnent lieu.Peninsular Thailand has few archaeological remains except beads that crystallize consuming passions. Collected, worn, traded, they regularly make the headlines of the local and national newspapers. Based on an ethnography conducted within the Franco-Thai archaeo-logical mission, this article investigates how the beads are collected by various kinds of local actors. It also highlights the sometimes conflicting discourses and representations they sustain