Density modulations in an elongated Bose-Einstein condensate released from a disordered potential

We observe large density modulations in time-of-flight images of elongated Bose-Einstein condensates, initially confined in a harmonic trap and in the presence of weak disorder. The development of these modulations during the time-of-flight and their dependence with the disorder are investigated. We render an account of this effect using numerical and analytical calculations. We conclude that the observed large density modulations originate from the weak initial density modulations induced by the disorder, and not from initial phase fluctuations (thermal or quantum).Comment: Published version; 4+ pages; 4 figure

Anderson Localization of Expanding Bose-Einstein Condensates in Random Potentials

We show that the expansion of an initially confined interacting 1D Bose-Einstein condensate can exhibit Anderson localization in a weak random potential with correlation length \sigma_R. For speckle potentials the Fourier transform of the correlation function vanishes for momenta k > 2/\sigma_R so that the Lyapunov exponent vanishes in the Born approximation for k > 1/\sigma_R. Then, for the initial healing length of the condensate \xi > \sigma_R the localization is exponential, and for \xi < \sigma_R it changes to algebraic.Comment: published versioon (no significant change compared to last version

Quasi-localization and quasi-mobility edge for light atoms mixed with heavy ones

A mixture of light and heavy atoms is considered. We study the kinetics of the light atoms, scattered by the heavy ones, the latter undergoing slow diffusive motion. In three-dimensional space we claim the existence of a crossover region (in energy), which separates the states of the light atoms with fast diffusion and the states with slow diffusion; the latter is determined by the dephasing time. For the two dimensional case we have a transition between weak localization, observed when the dephasing length is less than the localization length (calculated for static scatterers), and strong localization observed in the opposite case.Comment: LaTeX, 5 pages, 3 figures. The manuscript has been changed following the Referees' constructive criticism and is accepted for publication in EPJ

Chimie des matériaux hybrides

Année sabbatique : le cours n’a pas eu lieu

Embodied Artificial Intelligence through Distributed Adaptive Control: An Integrated Framework

In this paper, we argue that the future of Artificial Intelligence research resides in two keywords: integration and embodiment. We support this claim by analyzing the recent advances of the field. Regarding integration, we note that the most impactful recent contributions have been made possible through the integration of recent Machine Learning methods (based in particular on Deep Learning and Recurrent Neural Networks) with more traditional ones (e.g. Monte-Carlo tree search, goal babbling exploration or addressable memory systems). Regarding embodiment, we note that the traditional benchmark tasks (e.g. visual classification or board games) are becoming obsolete as state-of-the-art learning algorithms approach or even surpass human performance in most of them, having recently encouraged the development of first-person 3D game platforms embedding realistic physics. Building upon this analysis, we first propose an embodied cognitive architecture integrating heterogenous sub-fields of Artificial Intelligence into a unified framework. We demonstrate the utility of our approach by showing how major contributions of the field can be expressed within the proposed framework. We then claim that benchmarking environments need to reproduce ecologically-valid conditions for bootstrapping the acquisition of increasingly complex cognitive skills through the concept of a cognitive arms race between embodied agents.Comment: Updated version of the paper accepted to the ICDL-Epirob 2017 conference (Lisbon, Portugal

Hybrid Nanocomposites with Tunable Alignment of the Magnetic Nanorod Filler

For many important applications, the performance of polymer-anisotropic particle nanocomposite materials strongly depends on the orientation of the nanoparticles. Using the very peculiar magnetic properties of goethite ({\alpha}-FeOOH) nanorods, we produced goethite-poly(hydroxyethyl methacrylate) nanocomposites in which the alignment direction and the level of orientation of the nanorods could easily be tuned by simply adjusting the intensity of a magnetic field applied during polymerization. Because the particle volume fraction was kept low (1-5.5 vol \%), we used the orientational order induced by the field in the isotropic phase rather than the spontaneous orientational order of the nematic phase. At the strongest field values (up to 1.5 T), the particles exhibit almost perfect antinematic alignment, as measured by optical birefringence and small-angle X-ray scattering. The results of these two techniques are in remarkably good agreement, validating the use of birefringence measurements for quantifying the degree of orientational order. We also demonstrate that the ordering induced by the field in the isotropic suspension is preserved in the final material after field removal. This work illustrates the interest, for such problems, of considering the field-induced alignment of anisotropic nanoparticles in the isotropic phase, an approach that is effective at low filler content, that avoids the need of controlling the nematic texture, and that allows tuning of the orientation level of the particles at will simply by adjusting the field intensity

On a model of magnetization switching driven by a spin current: a multiscale approach

International audienceWe study a model of magnetization switching driven by a spin current: the magnetization reversal can be induced without applying an external magnetic fi eld. We first write our one dimensional model in an adimensionalized form, using a small parameter $\epsilon$. We then explain the various time and space scales involved in the studied phenomena. Taking into account these scales, we fi rst construct an appropriate numerical scheme, that allows us to recover numerically various results of physical experiments. We then perform a formal asymptotic study as $\epsilon$ tends to 0, using a multiscale approach and asymptotic expansions. We thus obtain approximate limit models that we compare with the original model via numerical simulations

Chemists and the School of nature

International audienceBiomimetism is an umbrella covering a variety of research fields ranging from the chemistry of natural products to nanocomposites, via biomaterials and supramolecular chemistry. . It is an informal movement and the concept itself is so loose that one can wonder whether biomimetism is more than a slogan forged by chemists in order to hop on the "green" bandwagon. Or could it bring a revolution into chemistry with a profound transformation of its practices

Environnement de test pour un système temps-réel de performance en musique mixte

National audienceA Master 2 internship report done at the IRCAM (the Institute for Research and Coordination in Acoustics/Music). Subject : Test environments for a real-time mixed music system. This report concerns an automatic generation of real time test model based suites using UPPAAL tools. -Specification with timed automaton, test execution using UPPAAL extensions and conformance management - are points studied in the report. An offline procedure using coVer is developed and described in the appendix.Ce document est un mémoire de fin de Master2 Informatique STL de l' Université Pierre et Marie Curie qui s'est déroulé à l'IRCAM (Institut de Recherche et coordination Acoustique/Musique). Ici, nous allons aborder le sujet du test sur un système temps réel embarqué et plus précisément de génération automatique de tests basée sur modèle pour systèmes temps-réel. - La spécification par automates temporisés, l'exécution des tests grâce à des outils du logiciel UPPAAL, la gestion d'une conformité pour rendre le bon verdict selon un environnement en temps réel - sont des points étudiés dans ce rapport. Une procédure offline utilisant coVer est développée et décrite dans l'annexe