Adaptive directional estimator of the density in R^d for independent and mixing sequences

A new multivariate density estimator for stationary sequences is obtained by Fourier inversion of the thresholded empirical characteristic function. This estimator does not depend on the choice of parameters related to the smoothness of the density; it is directly adaptive. We establish oracle inequalities valid for independent, $\alpha$-mixing and $\tau$-mixing sequences, which allows us to derive optimal convergence rates, up to a logarithmic loss. On general anisotropic Sobolev classes, the estimator adapts to the regularity of the unknown density but also achieves directional adaptivity. In particular, if A is an invertible matrix, if the observations are drawn from X $\in$ R^d , d $\ge$ 1, it achieves the rate implied by the regularity of AX, which may be more regular than X. The estimator is easy to implement and numerically efficient. It depends on the calibration of a parameter for which we propose an innovative numerical selection procedure, using the Euler characteristic of the thresholded areas

Conception et mise en oeuvre d'un système d'actionneurs AMF répartis pour le contrôle de forme électroactif de voilures aéronautiques

En vue de l'amélioration des performances aérodynamiques dans le domaine aéronautique, le contrôle de forme de surfaces portantes peut s'avérer être une solution pertinente. Le présent mémoire vise plus particulièrement à définir une structure d'actionneur visant au contrôle d'une voilure en dévrillage. Par ailleurs, l'émergence des matériaux électroactifs ouvre de nouvelles perspectives pour la conception de fonctions d'actionneurs répartis. Ce travail exploite donc le potentiel d'une certaine classe de matériaux électroactifs : les Alliages à Mémoire de Forme (AMF). Dans un premier temps, l'étude détaille les différentes classes de matériaux actifs disponibles, ainsi que les applications aéronautiques dans lesquelles ces matériaux ont pu être mis à profit. Cette pré-étude démontre l'intérêt des AMF pour la réalisation de la fonction de dévrillage. Puis le mémoire précise la nature de l'effet de mémoire de forme, et en propose une modélisation. Un démonstrateur d'actionneur AMF linéaire réalisé au laboratoire est présenté qui démontre la faisabilité d'une cellule motrice à grands efforts et grandes déformations. Par ailleurs, une étude d'une structure de voilure réaliste permet de préciser le cahier des charges de la fonction de dévrillage. En déterminant les efforts et déplacements requis, il est possible de choisir la structure la plus pertinente et d'établir un bilan de l'actionnement. Ce bilan donne la masse et l'énergie requises par la fonction visée. Enfin, la confrontation de l'étude mécanique à la modélisation qui a été faite d'un actionneur à mémoire de forme permet d'affiner le bilan énergétique de la structure d'actionnement retenue. La validité du concept est démontrée à une échelle réduite par l'implantation de fils AMF sur une structure en caisson rigide. ABSTRACT : So as to improve the aerodynamic aircraft's behaviour, active shape control of airfoils is a solution of great interest. This report presents an actuator structure aiming at global wing-twist control. The electroactive materials oer new oppportunities in the design of distributed actuators' structures. In this context, the study investigates the performances of a specific material's category : the Shape Memory Alloys (SMA). Firstly, an overview of the available electroactive materials, and the related aeronautic applications, is presented. This preliminary study reveals the interest of SMA for wing twist control. Then, the shape memory effect is described and modelised. A laboratory-made SMA linear actuator is presented, which tends to establish the feasibility of a great stress / deformations actuated structure. Moreover, based on a detailed study of a realistic wing structure, the requirements of a significant wing-twist actuation may be precised. According to the calculated stress and strains, the most relevant structure may be given, as well as the energy and mass required at wing scale. Finally, based on both the mechanical study and the shape memory effect model, the needs of the global active wing structure may be estimated. The relevance of the actuation concept is demonstrated at small scale, thanks to the integration of SMA wires on a wing-box like structure

Direct inscription of on-surface waveguides in polymers using a mid-ir fiber laser

A detailed study of photo-inscribed optical waveguides in PMMA and polycarbonate using a mid-IR laser is presented. The wavelength of the laser is tuned near the absorption peaks of stretching C-H molecular bonds and the focused beam is scanned onto the surface of planar polymer samples. For the first time, we report the formation of optical waveguides in both polymers through resonant absorption of the laser beam. The optical properties of the waveguides were thoroughly assessed. An elliptic Gaussian mode is guided at the surface of both polymers. Insertion losses of 3.1 dB for a 30 mm long on-surface waveguide inscribed in PMMA were recorded. Such waveguides can interact with the external medium through evanescent coupling. As a proof of concept, the surface waveguides are used as highly sensitive refractometric sensors. An attenuation dynamical range of 35 dB was obtained for a liquid that matches the index of the PMMA substrate. Our results pave the way for large scale manufacturing of low cost biocompatible photonic devices

Toward an Enhanced Mutual Awareness in Asymmetric CVE

International audience—Collaborative Virtual Environments (CVEs) aim at providing several users with a consistent shared virtual world. In this work, we focus on the lack of mutual awareness that may appear in many situations and we evaluate different ways to present the distant user and his actions in the Virtual Environment (VE) in order to understand his perception and cognitive process. Indeed, an efficient collaboration involves not only the good perception of some objects but their meaning too. This second criterion introduces the concept of distant analysis that could be a great help in improving the understanding of distant activities. For this work, we focus on a common case consisting in estimating accurately the time at which a distant user analyzed the meaning of a remotely pointed object. Thus, we conduct some experiments to evaluate the concept and compare different techniques for implementing this new awareness feature in a CVE. Amongst others, results show that expertise of the users influences on how they estimate the distant activity and the type of applied strategies

On the critical character of plasticity in metallic single crystals

Previous acoustic emission (AE) experiments on ice single crystals, as well as numerical simulations, called for the possible occurrence of self-organized criticality (SOC) in collective dislocation dynamics during plastic deformation. Here, we report AE experiments on hcp metallic single crystals. Dislocation avalanches in relation with slip and twinning are identified with the only sources of AE. Both types of processes exhibit a strong intermittent character. The AE waveforms of slip and twinning events seem to be different, but from the point of view of the AE event energy distributions, no distinction is possible. The distributions always follow a power law, even when multi-slip and forest hardening occur. The power law exponent is in perfect agreement with those previously found in ice single crystals. Along with observed time clustering and interactions between avalanches, these results are new and strong arguments in favour of a general, SOC-type, framework for crystalline plasticity.Comment: 12 pages, 10 figure

Rigorous Physicochemical Framework for Metal Ion Binding by Aqueous Nanoparticulate Humic Substances: Implications for Speciation Modeling by the NICA-Donnan and WHAM Codes

Latest knowledge on the reactivity of charged nanoparticulate complexants toward aqueous metal ions is discussed in mechanistic detail. We present a rigorous generic description of electrostatic and chemical contributions to metal ion binding by nanoparticulate complexants, and their dependence on particle size, particle type (i.e., reactive sites distributed within the particle body or confined to the surface), ionic strength of the aqueous medium, and the nature of the metal ion. For the example case of soft environmental particles such as fulvic and humic acids, practical strategies are delineated for determining intraparticulate metal ion speciation, and for evaluating intrinsic chemical binding affinities and heterogeneity. The results are compared with those obtained by popular codes for equilibrium speciation modeling (namely NICA-Donnan and WHAM). Physicochemical analysis of the discrepancies generated by these codes reveals the a priori hypotheses adopted therein and the inappropriateness of some of their key parameters. The significance of the characteristic time scales governing the formation and dissociation rates of metal−nanoparticle complexes in defining the relaxation properties and the complete equilibration of the metal− nanoparticulate complex dispersion is described. The dynamic features of nanoparticulate complexes are also discussed in the context of predictions of the labilities and bioavailabilities of the metal species

Evidence for Specific Genotype-Dependent Immune Priming in the Lophotrochozoan Biomphalaria glabrata Snail.

International audienceHistorically, the prevailing view in the field of invertebrate immunity was that invertebrates that do not possess acquired adaptive immunity rely on innate mechanisms with low specificity and no memory. Several recent studies have shaken this paradigm and suggested that the immune defenses of invertebrates are more complex and specific than previously thought. Mounting evidence has shown that at least some invertebrates (mainly Ecdysozoa) show high levels of specificity in their immune responses to different pathogens, and that subsequent reexposure may result in enhanced protection (recently called 'immune priming'). Here, we investigated immune priming in the Lophotrochozoan snail species Biomphalaria glabrata, following infection by the trematode pathogen Schistosoma mansoni. We confirmed that snails were protected against a secondary homologous infection whatever the host strain. We then investigated how immune priming occurs and the level of specificity of B. glabrata immune priming. In this report we confirmed that immune priming exists and we identified a genotype-dependent immune priming in the fresh-water snail B. glabrata

Redistribution et Plasticité pour les Interfaces Utilisateurs 3D : un Modèle Illustré

National audienceIn this paper we propose a model to handle redistribution for 3D user interfaces. Redistribution consists in changing the components distribution of an interactive system across different dimensions such as platform, display and user. Our work is based on previous models that ease the creation of 3D plastic user interfaces, interactive systems that can handle context of use modifications while preserving usability. We extended these models in order to include redistribution capabilities. The final solution lets developers create applications where 3D content and interaction tasks can be automatically redistributed across the different dimensions at runtime. The proposed redistribution process includes an automatic detection of these platforms and a meta-user interface to control the redistribution granularity. In order to illustrate this model, we describe three different scenarios of redistribution between a tablet and a CAVE for a 3D application. We show how redistribution can be used at runtime to combine these platforms, to switch seamlessly from one platform to another one and last how redistribution can be used to create a collaborative context of use

From 3D Bimanual Toward Distant Collaborative Interaction Techniques: An Awareness Issue

International audienceThis paper aims to raise the question : "How much 3D bimanual interaction techniques can be useful to the design of collaborative interaction techniques in the field of Collaborative Virtual Environment (CVE)?". Indeed, CVE involve the use of complex interaction techniques based on specific collaborative metaphors. The design of these metaphors may be a difficult task because it has to deal with collaborative issues that came from sparse research areas (Human-Computer Interfaces, Human-Human Interactions, Networking, Physiology and Social Psychology). Metaphors for bimanual interactions have been developed for a while essentially because it is a widely spread area of interest for common tasks. Bimanual interactions involve the simultaneous use of both hands of the user in order to achieve a goal with better performances compared to uni-manual interactions thanks to a natural skill that is proprioception. This collaborative aspect could certainly be a helpful entry point in the design of efficient collaborative interaction techniques extended from improved bimanual metaphors. However, the proprioceptive sense cannot be considered in the same way, and additional features must be proposed to be able to collaborate efficiently. Thus, awareness is a key to let CVE be usable and the availability of collaborative feedbacks is essential to extend bimanual interactions toward collaborative ones. In this paper, we based our study on existing work on bimanual and collaborative interaction techniques trying to draw similarities between them. We emphasize common points between both fields that could be useful to better design both metaphors and awareness in CVE