Active dry granular flows: rheology and rigidity transitions

The constitutive relations of a dense granular flow composed of self-propelling frictional hard particles are investigated by means of DEM numerical simulations. We show that the rheology, which relates the dynamical friction $\mu$ and the volume fraction $\phi$ to the inertial number $I$, depends on a dimensionless number $\mathcal{A}$, which compares the active force to the confining pressure. Two liquid/solid transitions -- in the Maxwell rigidity sense -- are observed. As soon as the activity is turned on, the packing becomes an `active solid' with a mean number of particle contacts larger than the isostatic value. The quasi-static values of $\mu$ and $\phi$ decrease with $\mathcal{A}$. At a finite value of the activity $\mathcal{A}_t$, corresponding to the isostatic condition, a second `active rigidity transition' is observed beyond which the quasi-static values of the friction vanishes and the rheology becomes Newtonian. For $\mathcal{A}>\mathcal{A}_t$, we provide evidence for a highly intermittent dynamics of this 'active fluid'.Comment: 7 pages, 7 figures, final version, accepted for publication in Europhys. Let

Travail, Développement, Souffrances et Actions

International audienceL'objectif de cette présentation est de proposer un modèle théorique paradoxal fondé sur de multiples recherches, concernant la " souffrance éthique " dans les conduites de travail. Ce modèle articule trois orientations : 1. Conditions de travail et souffrance psychique ; 2. Conduites de travail et engagement par l'action ; 3. Positivité des stratégies identitaires par la (re)valorisation du sens et la reliance (empathie en situation de travail). Partant des travaux actuels sur les risques psychosociaux dans les entreprises et les organismes publics et privés, mais surtout de leur expérience professionnelle en milieu hospitalier, les auteurs proposent une analyse paradoxale de l'investissement des personnes et de leur pouvoir d'agir dans les temporalités du projet de gestion de risques, questionnant les aspects méthodologiques, éthiques avec leur dynamiques d'actions, et un modèle psychosocial permettant de décrire et d'expliquer les conflits ou les stratégies paradoxales utilisées. Sont pris en compte les travaux sur - la déliance/reliance (Marcel Bolle de Bal, Edgar Morin et Jean-Louis Lemoigne), - les effets destructurants du mépris et la non-prise en compte de la reconnaissance des personnes (Paul Ricoeur, Axel Honneth, Jean-Marc Ferry), - les caractéristiques positives de la conduite de travail et l'importance de l'activité, ou de " l'action ", de l'engagement et de l'histoire (Ignace Meyerson, Hannah Arendt, Philippe Malrieu, Lev Vygotski, Yves Clot). Sont ensuite évoquées la dynamique des conditions de la santé au travail, les souffrances qu'elles supposent, les processus d'adaptation qu'elles font émerger, les stratégies de " prise " et de libération personnelle (personnation), les aspirations éthiques (héroïques, dramatiques, hédoniques, eudémoniques, philharmoniques) (fondées sur la résilience/endurance, sur le retrait, la quête du bien-être et du bonheur, la quête de l'harmonie mutuelle). Le blocage de ces aspirations est à rechercher dans les violences, les attachements contradictoires, les manipulations, les représentations, les politiques de gestion de crises, les interprétations psychologistes ou sociologistes s'éloignant de la complexité des situations, des organisations " capabilisatrices ", de la compréhension de l'interstructuration des conduites individuelles et collectives et des règles et modalités de concertation instituées

ICMI 2012 chairs' welcome

Welcome to Santa Monica and to the 14th edition of the International Conference on Multimodal Interaction, ICMI 2012. ICMI is the premier international forum for multidisciplinary research on multimodal human-human and human-computer interaction, interfaces, and system development. We had a record number of submissions this year: 147 (74 long papers, 49 short papers, 5 special session papers and 19 demo papers). From these submissions, we accepted 15 papers for long oral presentation (20.3% acceptance rate), 10 papers for short oral presentation (20.4% acceptance rate) and 19 papers presented as posters. We have a total acceptance rate of 35.8% for all short and long papers. 12 of the 19 demo papers were accepted. All 5 special session papers were directly invited by the organizers and the papers were all accepted. In addition, the program includes three invited Keynote talks. One of the two novelties introduced at ICMI this year is the Multimodal Grand Challenges. Developing systems that can robustly understand human-human communication or respond to human input requires identifying the best algorithms and their failure modes. In fields such as computer vision, speech recognition, and computational linguistics, the availability of datasets and common tasks have led to great progress. This year, we accepted four challenge workshops: the Audio-Visual Emotion Challenge (AVEC), the Haptic Voice Recognition challenge, the D-META challenge and Brain-Computer Interface challenge. Stefanie Telex and Daniel Gatica-Perez are co-chairing the grand challenge this year. All four Grand Challenges will be presented on Monday, October 22nd, and a summary session will be happening on Wednesday, October 24th, afternoon during the main conference. The second novelty at ICMI this year is the Doctoral Consortium—a separate, one-day event to take place on Monday, October 22nd, co-chaired by Bilge Mutlu and Carlos Busso. The goal of the Doctoral Consortium is to provide Ph.D. students with an opportunity to present their work to a group of mentors and peers from a diverse set of academic and industrial backgrounds and institutions, to receive feedback on their doctoral research plan and progress, and to build a cohort of young researchers interested in designing multimodal interfaces. All accepted students receive a travel grant to attend the conference. From among 25 applications, 14 students were accepted for participation and to receive travel funding. The organizers thank the National Science Foundation (award IIS-1249319) and conference sponsors for financial support

Femtosecond laser irradiation of dielectric materials containing randomly-arranged nanoparticles

International audienceWe investigate femtosecond laser irradiation of dielectric materials containing randomly-arranged nanoparticles. For this, numerical modeling is performed based on three different methods: Mie theory, static solution of linear Maxwell's equations and a solution of nonlinear Maxwell's equations together with kinetic equations for free electron excitation/relaxation processes. First two approaches are used to define the static intensity distribution and to analyze the electromagnetic interaction between the nanoparticles. The third method allows us to investigate the complex dynamics of the laser-matter interaction. Multiphoton absorption is shown to be responsible for electron plasma generation in the regions of strong intensity enhancements in the vicinity of nanoparticles. The irradiation of the dielectric material leads to the elongation of nanoplasmas by the near-field enhancement perpendicular to the laser polarization and to their strong interaction resulting in periodic arrangement. Numerical results shed light on such effects as femtosecond laser-induced nanograting formation

From random inhomogeneities to periodic nanostructures induced in bulk silica by ultrashort laser

International audienceFemtosecond laser-induced volume nanograting formation is numerically investigated. The developed model solves nonlinear Maxwell's equations coupled with multiple rate free carrier density equations in the presence of randomly distributed inhomogeneities in fused silica. As a result of the performed calculations, conduction band electron density is shown to form nanoplanes elongated perpendicular to the laser polarization. Two types of nanoplanes are identified. The structures of the first type have a characteristic period of the laser wavelength in glass and are attributed to the interference of the incident and the inhomogeneity-scattered light waves. Field components induced by coherent multiple scattering in directions perpendicular to the laser polarization are shown to be responsible for the formation of the second type of structures with a subwavelength periodicity. In this case, the influence of the inhomogeneity concentration on the period of nanoplanes is shown. The calculation results not only help to identify the physical origin of the self-organized nanogratings, but also explain their period and orientation

Carleson measures and Oversampling in model spaces

The aim of this paper is to extend two results from the Paley--Wiener setting to more generalmodel spaces. The first one is an analogue of the oversampling Shannon sampling formula. The second one is a version of Donoho--Logan's Large Sieve Theorem which is a quantitative estimate of the embedding of the Paley--Wiener space into an $L^2(\R,\mu)$ space

Cooperative Communications with HARQ in a Wireless Mesh Network Based on 3GPP LTE

Publication in the conference proceedings of EUSIPCO, Bucharest, Romania, 201

Triviality of the ground-state metastate in long-range Ising spin glasses in one dimension

We consider the one-dimensional model of a spin glass with independent Gaussian-distributed random interactions, that have mean zero and variance $1/|i-j|^{2\sigma}$, between the spins at sites $i$ and $j$ for all $i\neq j$. It is known that, for $\sigma>1$, there is no phase transition at any non-zero temperature in this model. We prove rigorously that, for $\sigma>3/2$, any Newman-Stein metastate for the ground states (i.e.\ the frequencies with which distinct ground states are observed in finite size samples in the limit of infinite size, for given disorder) is trivial and unique. In other words, for given disorder and asymptotically at large sizes, the same ground state, or its global spin flip, is obtained (almost) always. The proof consists of two parts: one is a theorem (based on one by Newman and Stein for short-range two-dimensional models), valid for all $\sigma>1$, that establishes triviality under a convergence hypothesis on something similar to the energies of domain walls, and the other (based on older results for the one-dimensional model) establishes that the hypothesis is true for $\sigma>3/2$. In addition, we derive heuristic scaling arguments and rigorous exponent inequalities which tend to support the validity of the hypothesis under broader conditions. The constructions of various metastates are extended to all values $\sigma>1/2$. Triviality of the metastate in bond-diluted power-law models for $\sigma>1$ is proved directly.Comment: 18 pages. v2: subsection on bond-diluted models added, few extra references. 19 pages. v3: published version; a few changes; 20 page

Salinity change in the subtropical Atlantic : secular increase and teleconnections to the North Atlantic Oscillation

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 32 (2005): L02603, doi:10.1029/2004GL021499.Recent studies comparing shipboard data between the 1950's and the 1990's have shown significant, heterogeneous adjustments of the temperature-salinity structure of the N. Atlantic Ocean. Here, we present proxy records of temperature and salinity from aragonite sclerosponge skeletons, extending existing records of the Salinity Maximum Waters (SMW) of the N. Atlantic back to 1890. These proxy records show secular temperature increases of 1.6–2.0°C, higher than published global averages, and salinity increases of 0.35–0.5 psu, smaller than short-term secular trends recently measured. Salinity reconstructions vary more significantly on the decadal scale, showing changes that are related to low-frequency variations of the North Atlantic Oscillation (NAO). On both secular and decadal time scales, the records indicate significant thermohaline changes in the SMW, either via forcing at the surface or increasing depths of density surfaces in the Bahamas.This project was supported by National Science Foundation grants 9819147 and 0136941 (to P.K.S) and 9876565 and 0134998 (to S.R.T)