Distributed Data Classification in Underwater Acoustic Sensors based on Local Time-Frequency Coherence Analysis

International audienceThis paper introduces a stochastic approach that considers the distributed classification problem for a network of underwater acoustic sensors. The proposed classifier applies the third order polynomial regression to the instantaneous frequency extracted from time-frequency representation of different classes of signals and represent the polynomial's coefficients in a threedimensional representation space. This automatic classifier is then compared to a non-parametric classifier based on the training of a standard neural network. The results of the proposed method on real data illustrate the efficiency of this algorithm, in terms of signal's characterization and lower communication bit rates between each sensor and the data center

Procédé d’agglomération et de recyclage en compactés de poudres de bauxites

National audienceLa bauxite est un minerai utilisé pour l’élaboration de l’aluminium ou directement sous forme de matière première pour la fabrication d’aluminates de calcium pour les ciments techniques. Elle est, dans ce dernier cas, essentiellement utilisée sous forme de bloc. On assiste depuis quelques années, à une raréfaction des blocs de bauxite alors que leur manipulation conduit souvent à des déchets sous forme de poussières qui ne sont pas valorisées à l’heure actuelle. L’objectif de ces travaux est de créer une nouvelle filière de recyclage de fines particules minérales pour pouvoir réutiliser cette matière première en remplacement de ressources naturelles qui s’épuisent. Ces produits sont mis en forme sous forme de compactés par compression directe. La bauxite est mélangée à du ciment et de l’eau puis introduite dans une matrice afin de subir un cycle de compression. Le compacté obtenu est ensuite stocké à température et hygrométrie contrôlées pour obtenir une hydratation maitrisée du ciment. Le compacté ainsi obtenu doit répondre à des spécifications bien précises en termes de densité, de porosité et de résistance mécanique grâce notamment aux hydrates spécifiques formés.L’outil principal utilisé pour caractériser les compactés est la micro tomographie par rayons X, qui est non destructive et permet d’observer en leur cœur même le comportement des grains et l’homogénéité en densité dans tout le volume. Les propriétés importantes des blocs telles que la porosité ou la distribution de taille des pores sont alors caractérisées grâce à l’analyse d’image des clichés de tomographie et comparé à la porosimétrie par intrusion de mercure. Cette étude de l’évolution des paramètres texturaux des compactés de bauxite doit permettre de comprendre et d’appréhender les phénomènes se déroulant pendant l’étape de compression. Il en suivra une optimisation des paramètres de compression et de mélange pour obtenir des compactés possédant les propriétés souhaitées

Hydrodynamic modelling of the tide propagation in a tropical delta: overcoming the challenges of data scarcity

Hydrodynamic

VITRUV - Science Cases

VITRUV is a second generation spectro-imager for the PRIMA enabled Very Large Telescope Interferometer. By combining simultaneously up to 8 telescopes VITRUV makes the VLTI up to 6 times more efficient. This operational gain allows two novel scientific methodologies: 1) massive surveys of sizes; 2) routine interferometric imaging. The science cases presented concentrate on the qualitatively new routine interferometric imaging methodology. The science cases are not exhaustive but complementary to the PRIMA reference mission. The focus is on: a) the close environment of young stars probing for the initial conditions of planet formation and disk evolution; b) the surfaces of stars tackling dynamos, activity, pulsation, mass-loss and evolution; c) revealing the origin of the extraordinary morphologies of Planetary Nebulae and related stars; d) studying the accretion-ejection structures of stellar black-holes (microquasars) in our galaxy; e) unveiling the different interacting components (torus, jets, BLRs) of Active Galactic Nuclei; and f) probing the environment of nearby supermassive black-holes and relativistic effects in the Galactic Center black-hole.Comment: 15 pages. The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation VLTI Instrumentation, Allemagne (2005) in pres

Examining Wikipedia across Linguistic and Temporal Borders

ABSTRACT The Web has grown to be an integral part of modern society offering novel ways for humans to communicate, interact, and share information. New collaborative platforms are forming which are providing individuals with new communities and knowledge bases and, at the same time, offering insights into human activity for researchers, policy-makers and engineers. On a global scale, the role of cultural and language barriers when studying such phenomena becomes particularly relevant and presents significant challenges: due to insufficient information, it is often hard to establish the cultural or language groups in which individuals belong, while there are technical difficulties in establishing the relevance and in analysing resources in different languages. This paper presents a framework to the end of addressing those issues by leveraging data on the use of Wikipedia. Resources available in different languages are explicitly correlated in Wikipedia along with time-stamped logs of access to its articles. This paper provides a framework to enable temporal page views in Wikipedia to be associated with specific geographic profiles. This framework is then used to examine the exchange of information between the English speaking and Chinese speaking localities and reports initial findings on the role of language and culture in diffusion in this context

James Webb Space Telescope Optical Simulation Testbed I: Overview and First Results

The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a tabletop workbench to study aspects of wavefront sensing and control for a segmented space telescope, including both commissioning and maintenance activities. JOST is complementary to existing optomechanical testbeds for JWST (e.g. the Ball Aerospace Testbed Telescope, TBT) given its compact scale and flexibility, ease of use, and colocation at the JWST Science & Operations Center. We have developed an optical design that reproduces the physics of JWST's three-mirror anastigmat using three aspheric lenses; it provides similar image quality as JWST (80% Strehl ratio) over a field equivalent to a NIRCam module, but at HeNe wavelength. A segmented deformable mirror stands in for the segmented primary mirror and allows control of the 18 segments in piston, tip, and tilt, while the secondary can be controlled in tip, tilt and x, y, z position. This will be sufficient to model many commissioning activities, to investigate field dependence and multiple field point sensing & control, to evaluate alternate sensing algorithms, and develop contingency plans. Testbed data will also be usable for cross-checking of the WFS&C Software Subsystem, and for staff training and development during JWST's five- to ten-year mission.Comment: Proceedings of the SPIE, 9143-150. 13 pages, 8 figure

The VLTI / PIONIER near-infrared interferometric survey of southern T Tauri stars. I. First results

Context : The properties of the inner disks of bright Herbig AeBe stars have been studied with near infrared (NIR) interferometry and high resolution spectroscopy. The continuum and a few molecular gas species have been studied close to the central star; however, sensitivity problems limit direct information about the inner disks of the fainter T Tauri stars. Aims : Our aim is to measure some of the properties of the inner regions of disks surrounding southern T Tauri stars. Methods : We performed a survey with the PIONIER recombiner instrument at H-band of 21 T Tauri stars. The baselines used ranged from 11 m to 129 m, corresponding to a maximum resolution of 3mas (0.45 au at 150 pc). Results : Thirteen disks are resolved well and the visibility curves are fully sampled as a function of baseline in the range 45-130 m for these 13 objects. A simple qualitative examination of visibility profiles allows us to identify a rapid drop-off in the visibilities at short baselines in 8 resolved disks. This is indicative of a significant contribution from an extended contribution of light from the disk. We demonstrate that this component is compatible with scattered light, providing strong support to a prediction made by Pinte et al. (2008). The amplitude of the drop-off and the amount of dust thermal emission changes from source to source suggesting that each disk is different. A by-product of the survey is the identification of a new milli-arcsec separation binary: WW Cha. Spectroscopic and interferometric data of AK Sco have also been fitted with a binary and disk model. Conclusions : Visibility data are reproduced well when thermal emission and scattering form dust are fully considered. The inner radii measured are consistent with the expected dust sublimation radii. Modelling of AK Sco suggests a likely coplanarity between the disk and the binary's orbital planeComment: 19 pages, 11 figure

Phase Referencing in Optical Interferometry

One of the aims of next generation optical interferometric instrumentation is to be able to make use of information contained in the visibility phase to construct high dynamic range images. Radio and optical interferometry are at the two extremes of phase corruption by the atmosphere. While in radio it is possible to obtain calibrated phases for the science objects, in the optical this is currently not possible. Instead, optical interferometry has relied on closure phase techniques to produce images. Such techniques allow only to achieve modest dynamic ranges. However, with high contrast objects, for faint targets or when structure detail is needed, phase referencing techniques as used in radio interferometry, should theoretically achieve higher dynamic ranges for the same number of telescopes. Our approach is not to provide evidence either for or against the hypothesis that phase referenced imaging gives better dynamic range than closure phase imaging. Instead we wish to explore the potential of this technique for future optical interferometry and also because image reconstruction in the optical using phase referencing techniques has only been performed with limited success. We have generated simulated, noisy, complex visibility data, analogous to the signal produced in radio interferometers, using the VLTI as a template. We proceeded with image reconstruction using the radio image reconstruction algorithms contained in AIPS IMAGR (CLEAN algorithm). Our results show that image reconstruction is successful in most of our science cases, yielding images with a 4 milliarcsecond resolution in K band. (abridged)Comment: 11 pages, 36 figure

Thermal and microstructure study of the chip formation during turning of Ti64 β lamellar titanium Structure

In recent years, many titanium alloys have emerged, each of them associated with a range of different heat treatments. Thus, several microstructures have been studied to varying degrees. For example, the Ti64 titanium alloy, mostly known for its α + β structure, can display a different state: the structure, inducing nonstandard mechanical behavior. This work presents chip formation in this specific microstructure where a strong heterogeneity is observed and where the shear band formation is a function of the relationship between the shear direction and the microstructure orientation. From these reasons, major differences are found in the chip morphology, within the same cutting condition, in comparison to the bimodal structure where a single chip morphology is obtained for each cutting condition. A section of this paper is devoted to the presentation of the β microstructure where different configurations can be seen within the same chip. Next, the influence of cutting conditions on the chip formation is studied. To highlight the specific chip formation process, a temperature model has been developed and combined with cutting force analysis to understand clearly the specificity of the chip formation for this structure. Finally, the discussion explains the different chip formation scenarios according to the workpiece microstructure to be cut

Grid Computing for Climate Processing on South America

O projeto LAG-Clima quer estabelecer um ambiente de computação em grade de processamento e compartilhamento de dados. O objetivo é manter uma rede de interconexão entre instituições na América do Sul para previsão climática em meso-escala e disponibilizar dados. Plataforma de softwares: BRAMS (código meteorológico de meso-escala), OurGri