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Synthesis and characterization of polyaniline-silica composites: Raspberry vs core-shell structures. Where do we stand?
No full textInternational audienc
On a stronger form of the Hohenberg-Kohn theorem
No full textWe prove a stronger form of the Hohenberg-Kohn theorem
A Quantile Mapping Bias Correction Method Based on Hydroclimatic Classification of the Guiana Shield
No full textInternational audienceSatellite precipitation products (SPPs) provide alternative precipitation data for regions with sparse rain gauge measurements. However, SPPs are subject to different types of error that need correction. Most SPP bias correction methods use the statistical properties of the rain gauge data to adjust the corresponding SPP data. The statistical adjustment does not make it possible to correct the pixels of SPP data for which there is no rain gauge data. The solution proposed in this article is to correct the daily SPP data for the Guiana Shield using a novel two set approach, without taking into account the daily gauge data of the pixel to be corrected, but the daily gauge data from surrounding pixels. In this case, a spatial analysis must be involved. The first step defines hydroclimatic areas using a spatial classification that considers precipitation data with the same temporal distributions. The second step uses the Quantile Mapping bias correction method to correct the daily SPP data contained within each hydroclimatic area. We validate the results by comparing the corrected SPP data and daily rain gauge measurements using relative RMSE and relative bias statistical errors. The results show that analysis scale variation reduces rBIAS and rRMSE significantly. The spatial classification avoids mixing rainfall data with different temporal characteristics in each hydroclimatic area, and the defined bias correction parameters are more realistic and appropriate. This study demonstrates that hydroclimatic classification is relevant for implementing bias correction methods at the local scale
Recurrent network dynamics reconciles visual motion segmentation and integration
No full textInternational audienceIn sensory systems, a range of computational rules are presumed to be implemented by neuronal subpopulations with di erent tuning functions. For instance, in primate cortical area MT, di erent classes of direction-selective cells have been identi ed and related either to motion integration, segmentation or transparency. Still, how such di erent tuning properties are constructed is unclear. The dominant theoretical viewpoint based on a linear-nonlinear feed-forward cascade does not account for their complex temporal dynamics and their versatility when facing di erent input statistics. Here, we demonstrate that a recurrent network model of visual motion processing can reconcile these di erent properties. Using a ring network, we show how excitatory and inhibitory interactions can implement di erent computational rules such as vector averaging, winner-take-all or superposition. The model also captures ordered temporal transitions between these behaviors. In particular, depending on the inhibition regime the network can switch from motion integration to segmentation, thus being able to compute either a single pattern motion or to superpose multiple inputs as in motion transparency. We thus demonstrate that recurrent architectures can adaptively give rise to di erent cortical computational regimes depending upon the input statistics, from sensory ow integration to segmentation
Construction du référentiel taxonomique commun TAXREF, socle pour la connaissance et l'échange de données
No full textNational audienceUne des missions du Muséum national d’Histoire naturelle (MNHN) est d’établir une synthèse de la biodiversité et du patrimoine naturel français. Dans ce contexte, il est en charge de l’élaboration du référentiel taxonomique pour la faune, la flore et la fonge, TAXREF. Ce référentiel unique liste et organise les noms scientifiques de l'ensemble des êtres vivants recensés sur les territoires français, métropole et outremer, et constitue la pierre angulaire du Système d’Information sur la Nature et les Paysages (SINP). Il est utilisé par de nombreux acteurs publics, privés et de la société civile (collectivités, conservateurs, aménageurs, enseignants, citoyens, etc.). TAXREF est de plus aligné avec d'autres référentiels taxonomiques ou nomenclaturaux internationaux.Dans cette présentation, nous aborderons les méthodes d'élaboration d'un tel référentiel, basées sur les codes de nomenclature, un modèle de données, des ressources bibliographiques et la constitution d'un réseau d'experts locaux, nationaux et internationaux, ainsi que les procédures de contrôles qui visent à parfaire un référentiel complexe de quelques 500.000 items. Nous présenterons les résultats et la stratégie d'acquisition. Nous aborderons également la Base de connaissance des espèces qui lui est liée : espèces protégées, menacées, mais également les interactions entre espèces qui proposent une vision dynamique de la biodiversité au delà de la simple approche descriptive.Un tel référentiel n'est utile que s'il est largement exploité. Nous décrirons donc les différentes mises à disposition de ce référentiel : outils de réconciliation, webservice TAXREF et webservice pour les statuts (base de connaissance). En particulier, nous décrirons la modélisation d’un thésaurus exprimé en SKOS (Simple Knowledge Organisation System) afin de produire une version de TAXREF exploitable avec les technologies du web sémantique. Nous aborderons la question du lien entre ce « TAXREF-SKOS » et d’autres thésaurus et ontologies existantes. Enfin, nous décrirons le travail en cours visant à l'exposer sur le web de données sous forme d’URI pérennes déréférençables (Linked Data)
Parties and Voters in the Populist Market : Left and right populism in France and the Netherlands
No full textInternational audienceThe literature on populism has been split, reflecting the distribution of the populist phenomenon across regions, i.e. left-wing populism in Southern Europe and Latin America, and right-wing populism in Northern Europe (Mudde and Kaltwasser 2013). There are only few cases where populist parties and voters both left and right are found to coexist and compete within the same political system. More recently, there has been a complexification of the populist ‘market’ across a number of countries, however. While competing against the mainstream, populist parties in those countries are also fishing from the same pool of voters dissatisfied with ‘old’ politics and traditional party elites, thereby competing against each other from different party system locations. Little is known of what may unite and oppose populist voters operating across both sides of the left-right spectrum in a given polity. Whilst we may expect populist voters to differ according to their attaching ideology, there may be more convergence on political attitudes –i.e. the core of populism defined as a Manichean representation of politics- as well as attitudes towards the EU which are increasingly associated with populist mobilization. In this paper, these possible commonalities of populist mobilization are examined cross-nationally from two voter surveys conducted in France and the Netherlands. Both countries provide suitable cases where relevant populist parties are found in both their radical left and radical right manifestations. This study aims to assess the relationships of varieties and/or common similarities of populism within a same context, when confronting similar institutional constraints and competitive incentives. Its findings have important implications for our understanding of the electoral dynamics of competition within a ‘populist market’, which, as recent developments in populist politics worldwide suggest, may become an increasingly relevant phenomenon across a range of actors and contexts, and a promising research area
Experimental evaluation of relative calibration in a MISO-TDD system
No full textInternational audienceWe study the transmit time reversal beamforming in a 8x1 MISO communication system at 2.68GHz. We consider the downlink time reversal transmission where a BS communicates with one user. A prototype composed by 8 antennas and designed by Orange labs acts as the BS while the user has a single antenna. The reciprocity property is destroyed by the non-symmetric characteristics of the RF electronic circuitry. We use relative calibration which is based exclusively on signal processing techniques to solve this issue. Utilizing a controlled test setup based on OpenAirInterface, the ExpressMIMO2 SDR boards, as well as a servo controlled rail, we show the feasibility of a relative calibration method through beamforming SNR measurements. We also evaluate the performance of an antenna selection scheme at the transmit side as a low-cost low-complexity alternative to capture many of the advantages of multi-antenna systems. The measurements show that the relative calibration method is performing almost optimal and that the complexity can be significantly reduced by using antenna selection
Compression d'images et de vidéos inspirée du fonctionnement de la rétine
No full textThe goal of this thesis is to propose a novel video coding architecture which is inspired by the mammalian visual system and the retina. If one sees the retina as a machine which processes the visual stimulus, it seems an intelligent and very efficient model to mimic. There are several reasons to claim that, first of all because it consumes low power, it also deals with high resolution inputs and the dynamic way it transforms and encodes the visual stimulus is beyond the current standards. We were motivated to study and release a retina-inspired video codec. The proposed algorithm was applied to a video stream in a very simple way according to the coding standards like MJPEG or MJPEG2000. However, this way allows the reader to study and explore all the advantages of the retina dynamic processing way in terms of compression and image processing. The current performance of the retina-inspired codec is very promising according to some final results which outperform MJPEG for bitrates lo wer than 100 kbps and MPEG-2 for bitrates higher than 70 kpbs. In addition, for lower bitrates, the retina-inspired codec outlines better the content of the input scene. There are many perspectives which concern the improvement of the retina-inspired video codec which seem to lead to a groundbreaking compression architecture. Hopefully, this manuscript will be a useful tool for all the researchers who would like to study further than the perceptual capability of the mammalian visual system and understand how the structure and the functions of the retina can in practice improve the coding algorithms.Cette thèse vise à proposer une nouvelle architecture de codage vidéo qui s’inspire du système visuel des mammifères et de la rétine. La rétine peut être considérée comme une machine intelligente qui traite le stimulus visuel de façon très efficace. De ce fait, elle représente une grande source d'inspiration pour développer de nouveaux systèmes de traitement d’image. Il y a plusieurs raisons pour cela : elle consomme peu d’énergie, elle traite des entrées haute résolution et sa façon de transformer et d’encoder de manière dynamique le stimulus visuel dépasse les normes actuelles. Nous avons souhaité étudier et proposer un codec vidéo inspiré de la rétine. L’algorithme proposé a été appliqué à un flux vidéo d'une manière simple, suivant le principe des standards de codage MJPEG ou MJPEG2000. Cette approche permet au lecteur d’étudier et d’explorer tous les avantages du traitement dynamique de la rétine en termes de compression et de traitement d’image. La performance actuelle du codec que nous avons développé est très prometteuse. Les résultats montrent des performances supérieures à MJPEG pour des débits inférieurs à 100 kbps et MPEG-2 pour des débits supérieurs à 70 kpbs. De plus, à faibles débits, le codec proposé décrit mieux le contenu de la scène d’entrée. De nombreuses perspectives sont proposées afin d'améliorer ce codec inspiré de la rétine qui semblent conduire à un nouveau paradigme en compression vidéo
Massive loops in thermal SU(2) Yang–Mills theory: Radiative corrections to the pressure beyond two loops
No full textInternational audienceWe address the loop expansion of the pressure in the deconfining phase of SU(2) Yang–Mills thermodynamics. We devise an efficient book-keeping of excluded energy-sign and scattering-channel combinations for the loop four-momenta associated with massive quasiparticles, circulating in (connected) bubble diagrams subject to vertex constraints inherited from the thermal ground state. These radiative corrections modify the one-loop pressure exerted by free thermal quasiparticles. Increasing the loop order in two-particle irreducible (2PI) bubble diagrams, we exemplarily demonstrate a suppressing effect of the vertex constraints on the number of valid combinations. This increasingly strong suppression gave rise to the conjecture in arXiv:hep-th/0609033 that the loop expansion would terminate at a finite order. Albeit the low-temperature dependence of the 2PI 3-loop diagram complies with this behavior, a thorough analysis of the high-temperature situation reveals that the leading power in temperature is thirteen such that this diagram dominates all lower loop orders for sufficiently high temperatures. An all-loop-order resummation of 2PI diagrams with dihedral symmetry is thus required, defining an extremely well-bounded analytical continuation of the low-temperature result
Scientific rationale for Uranus and Neptune in situ explorations
No full textInternational audienceThe ice giants Uranus and Neptune are the least understood class of planets in our solar system but the most frequently observed type of exoplanets. Presumed to have a small rocky core, a deep interior comprising ~70% heavy elements surrounded by a more dilute outer envelope of H2 and He, Uranus and Neptune are fundamentally different from the better-explored gas giants Jupiter and Saturn. Because of the lack of dedicated exploration missions, our knowledge of the composition and atmospheric processes of these distant worlds is primarily derived from remote sensing from Earth-based observatories and space telescopes. As a result, Uranus's and Neptune's physical and atmospheric properties remain poorly constrained and their roles in the evolution of the Solar System not well understood. Exploration of an ice giant system is therefore a high-priority science objective as these systems (including the magnetosphere, satellites, rings, atmosphere, and interior) challenge our understanding of planetary formation and evolution. Here we describe the main scientific goals to be addressed by a future in situ exploration of an ice giant. An atmospheric entry probe targeting the 10-bar level, about 5 scale heights beneath the tropopause, would yield insight into two broad themes: i) the formation history of the ice giants and, in a broader extent, that of the Solar System, and ii) the processes at play in planetary atmospheres. The probe would descend under parachute to measure composition, structure, and dynamics, with data returned to Earth using a Carrier Relay Spacecraft as a relay station. In addition, possible mission concepts and partnerships are presented, and a strawman ice-giant probe payload is described. An ice-giant atmospheric probe could represent a significant ESA contribution to a future NASA ice-giant flagship mission