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Analysis, detection and correction of misspecified discrete time state space models
No full textMisspecifications (i.e. errors on the parameters) of state space models lead to incorrect inference of the hidden states. This paper studies weakly nonlin-ear state space models with additive Gaussian noises and proposes a method for detecting and correcting misspecifications. The latter induce a biased estimator of the hidden state but also happen to induce correlation on innovations and other residues. This property is used to find a well-defined objective function for which an optimisation routine is applied to recover the true parameters of the model. It is argued that this method can consistently estimate the bias on the parameter. We demonstrate the algorithm on various models of increasing complexity
Random Forests for Big Data
No full textInternational audienceBig Data is one of the major challenges of statistical science and has numerous consequences from algorithmic and theoretical viewpoints. Big Data always involve massive data but they also often include online data and data heterogeneity. Recently some statistical methods have been adapted to process Big Data, like linear regression models, clustering methods and bootstrapping schemes. Based on decision trees combined with aggregation and bootstrap ideas, random forests were introduced by Breiman in 2001. They are a powerful nonparametric statistical method allowing to consider in a single and versatile framework regression problems, as well as two-class and multi-class classification problems. Focusing on classification problems, this paper proposes a selective review of available proposals that deal with scaling random forests to Big Data problems. These proposals rely on parallel environments or on online adaptations of random forests. We also describe how related quantities -- such as out-of-bag error and variable importance -- are addressed in these methods. Then, we formulate various remarks for random forests in the Big Data context. Finally, we experiment five variants on two massive datasets (15 and 120 millions of observations), a simulated one as well as real world data. One variant relies on subsampling while three others are related to parallel implementations of random forests and involve either various adaptations of bootstrap to Big Data or to ``divide-and-conquer'' approaches. The fifth variant relates on online learning of random forests. These numerical experiments lead to highlight the relative performance of the different variants, as well as some of their limitations
La France populiste ?
No full textNote de recherche ENEF / Sciences Po-CEVIPOF, n°30Le développement du populisme constitue aujourd'hui une réalité politique dans nombre de démocraties occidentales. Le populisme s'y matérialise sous des formes diverses, à droite mais aussi à gauche de l'échiquier politique, dans une variété de contextes. Au-delà des acteurs partisans eux-mêmes, le populisme s'identifie également chez les citoyens. Il se définit comme un système cohérent d'attitudes et de représentations, dont on peut mesurer la présence et la distribution au sein des électorats. En lien avec des recherches conduites dans plusieurs pays européens et aux Etats-Unis, nous proposons une mesure empirique du populisme chez les électeurs français
A staggered scheme for the Euler equations
No full textWe extend to the full Euler system the scheme introduced in [Berthelin, Goudon, Minjeaud, Math. Comp. 2014] for solving the barotropic Euler equations. This finite volume scheme is defined on staggered grids with numerical fluxes derived in the spirit of kinetic schemes. The difficulty consists in finding a suitable treatment of the energy equation while density and internal energy on the one hand, and velocity on the other hand, are naturally defined on dual locations. The proposed scheme uses the density, the velocity and the internal energy as computational variables and stability conditions are identified in order to preserve the positivity of the discrete density and internal energy. Moreover, we define averaged energies which satisfy local conservation equations. Finally, we provide numerical simulations of Riemann problems to illustrate the behaviour of the scheme
Discontinuous shear thickening in the presence of polymers adsorbed on the surface of calcium carbonate particles
No full textInternational audienceIn the presence of dispersant molecules currently used in cement industry and based on polyethylene oxide (PEO) we found a strong discontinuous shear thickening (DST) at high volume fraction in suspensions of calcium carbonate particles. The transition was reversible and the critical shear rate and shear stress for which this instability appears are reported versus the volume fraction of particles. A model of repulsive forces between polymers, taking into account the thickness of the polymer layer and the density of adsorption on the surface of the particles, can explain the differences of critical stresses observed between these three dispersant molecules. In particular it explains why a small polymer densely adsorbed can be more efficient to repel the transition at higher stress than a larger molecule less densely adsorbed. Above the transition, we find that the suspension presents a special kind of stick-slip instability with even the presence of a negative shear rate under constant applied stress. A model is proposed which well predicts this regime by taking into account both the inertia of the apparatus and the viscoelasticity of the suspension
Coviability of the social and ecological systems in Réunion Island’s National Park : Climate variability, wildfires, and the vulnerability of biodiversity
No full textInternational audienceLocated in the western side of the Indian Ocean, Réunion Island is characterized by significant dichotomies of vegetation distribution because of the topography of its mountains. The rainforests that are exposed to easterly winds are in contrast to the xeric vegetation which is protected from wind on the western side. Due to certain practices, these xeric ecosystems are particularly exposed to wildfires during winter, especially during the years of long rainfall deficits. However, relying on tests of drought index and break detection, climate data analysis shows a significant decrease in rainfall during the 1980s in the part of the island which is protected from the wind. One of the consequences of this change in rainfall patterns is the increased frequency of wildfires. This phenomenon represents a major issue for preserving the biodiversity of the Réunion Island National Park (RNP). One of the key events of the history of wildfires in the Réunion Island is the emergence of intentional or criminal fires since the creation of the National Park in 2007. These intentional fires could be considered as a protest against the creation of the Park. This work thus attempts to seek coviability between institutional actors and the population (particularly those living in the Park), in a context of climate variability. The perspective of a joint viability of the ecological system (climate / fires / plant colonization) and social systems (concerns and perceptions of the population) is part of a systemic analysis highlighting the role of the different stakeholders in the governance and the regulation of "wildfire" risks. The sustainable management of this protected area, a UNESCO world heritage site, takes us to the core issue of the coviability of ecological and societal systems
Les déterminants du choix d'un médecin généraliste par les personnes vivant avec le VIH
No full textIntroduction :<br> A l'heure d'une volonté de l'état d'un suivi alterné hôpital-ville pour les PvVIH, le suivi reste, très hospitalo-centré. Certains médecins généralistes suivent une importante file active de PvVIH et d'autres aucun. Les PvVIH s'orientent-ils vers un profil de médecin particulier? Ont-ils des critères de choix?<br>Méthodologie : <br>Nous avons réalisé une étude qualitative par entretiens semi-dirigés auprès de 12 patients atteints du VIH sur Nice et Grasse. Nous avons recueilli leur ressenti à propos de leur choix de médecin traitant et avons identifiés des critères.<br>Résultats : <br>Les critères sont similaires à ceux de la population générale avec une attention toute particulière pour, l'écoute et le soutien psychologique en premier, la connaissance globale du patient avec un suivi, une continuité des soins et une bonne coordination avec les spécialistes, et enfin un bon relationnel et une ouverture d'esprit du praticien.<br>Conclusion :<br> Les compétences demandées aux MG par les patients se retrouvent dans la formation actuelle des jeunes médecins qui devraient pouvoir assurer dans l’avenir le suivi ambulatoire des PvVI
Souffrance sexuelle : genre, norme et politique dans une pratique psychanalytique : la différence sexuelle et sa fétichisation
No full textIn psychoanalysis clinical practice, the sexual always is confronted to gender's issues ; gender as social sex butalso as a discursive category producing sexed body and questionning a particular time's subjectivity. We haveinvestigated those questions from the perspective of norms, taking into account its incorporation and attachment inthe identification process. This will involve thinking about the concept of “sexual difference” theorical and politicalshortcomings, in order to propose a clinical approach that takes into account social changes related to sexuality and toinvent new ways to « do politics ». The fetichization of sexual difference, it seems to me, is a obstacle to theoreticaland clinical work's advancement. My daily clinical practice as a clinical psychologist in the hospital urologydepartment, where I see people suffering in their sexuality, opened upfor me the benefits of a multidisciplinaryapproach, particulary in gender and feminist studies. These ones appeared to me allowing psychoanalysis to remain acritical perspective of the norms, seen as a “grammar of subjectivation” ; allow also to investigate the link betweenmodes of submission, desire of norms and sexual suffering, and lastly to be able to hear the complaint, the symptom,as a singularity, a resistance to social norms. The approach of the sexual difference seen from the gender perspectiveopen up for psychoanalysis new configurations of desire, symbolic, power and sexuation, allowing a differentarticulation of the individual and collective, of the social actor and the unconscious. We may attain a psychoanalyticalapproach that doesn't see as pathology, gender, sex and sexuality's configurations which contest the binary conceptionof sexual difference and its assignations, withing the central question, the political treatment of “ difference”.Le sexuel à l’oeuvre dans la clinique psychanalytique s'avère toujours traversé par des enjeux de genre, genre commesexe social mais aussi comme catégorie discursive produisant le corps sexué et questionnant la subjectivité d'uneépoque. Cette thématique est analysée du point de vue de la question des normes et de la prise en compte de sonincorporation et de son attachement dans les processus d'identification. Il s'agira de penser les insuffisancesthéoriques et politiques de la notion de « différence sexuelle » pour une clinique qui souhaite prendre en compte leschangements sociaux relatifs à la sexualité et inventer de nouvelles manières de « faire de la politique ». Unefétichisation de la différence sexuelle m'est apparue un obstacle majeur aux avancées du travail théorico-clinique. Maclinique au quotidien comme psychologue clinicienne en service d'urologie à l'hôpital accueillant des personnessouffrant dans leur sexualité m'a invité à m'enrichir de l'apport de la pluridisciplinarité, et particulièrement des étudesde genre et féministes. Celles-ci me sont apparues comme pouvant permettre à la psychanalyse de demeurer undispositif critique à l'endroit des normes, envisagées comme grammaire de la subjectivation. De penser le lien entremode d'assujettissement, désir de normes et souffrance sexuelle et d'entendre la plainte, le symptôme dans sasingularité et comme résistance psychique aux normes sociales. L'approche de la différence sexuelle sous l'angle dugenre propose à la psychanalyse d'autres configurations du désir, du symbolique, du pouvoir et de la sexuation pourainsi articuler l'individuel et le collectif, le sujet social avec le sujet de l'inconscient. Ainsi pouvons nous penserpsychanalytiquement sans les pathologiser les configurations de genre, sexe et sexualité contestant la conceptionbinaire de la différence sexuelle et ses assignations, avec la question centrale du traitement politique que l'on souhaitefaire de la différence
A finite element method with overlapping meshes for free-boundary axisymmetric plasma equilibria in realistic geometries
No full textInternational audienceExisting finite element implementations for the computation of free-boundary axisymmetric plasma equilibria approximate the unknown poloidal flux function by standard lowest order continuous finite elements with discontinuous gradients. As a consequence, the location of critical points of the poloidal flux, that are of paramount importance in tokamak engineering, is constrained to nodes of the mesh leading to undesired jumps in transient problems. Moreover, recent numerical results for the self-consistent coupling of equilibrium with resistive diffusion and transport suggest the necessity of higher regularity when approximating the flux map. In this work we propose a mortar element method that employs two overlapping meshes. One mesh with Cartesian quadrilaterals covers the vacuum chamber domain accessible by the plasma and one mesh with triangles discretizes the region outside. The two meshes overlap in a narrow region. This approach gives the flexibility to achieve easily and at low cost higher order regularity for the approximation of the flux function in the domain covered by the plasma, while preserving accurate meshing of the geometric details outside this region. The continuity of the numerical solution in the region of overlap is weakly enforced by a mortar-like mapping
Une place pour les technologies smartphones et les Réseaux Sociaux Numériques (RSN) dans les dispositifs institutionnels de l’alerte aux inondations en France ?
No full textInternational audienceEn cas d’alerte aux inondations, l'information en temps réel et sa diffusion à un large public sont des éléments cruciaux pour limiter les comportements à risque, détecter les premiers dommages ou préparer les acteurs locaux à gérer la crise. Pour répondre à un tel enjeu, les Réseaux Sociaux Numériques (RSN) et les applications smartphones apparaissent, de plus en plus, comme des solutions logicielles pouvant compléter, de façon positive, les dispositifs institutionnels, notamment grâce à la dynamique des contenus partagés et aux nombreuses interactions sociales dont ils sont le support. Alors que plusieurs pays (Etats-Unis, Norvège, Pays-Bas, Suède, Philippines) utilisent déjà ces outils, et même si le Ministère de l'Intérieur a lancé une application urgentiste nommée SAIP le 8 juin 2016, la population et les services de l’Etat sont beaucoup plus réticents en France, la défense de la propriété des données individuelles, le manque de crédit attribuée aux messages, le non respect des standards internationaux, les verrous technologiques étant les premiers facteurs de blocage évoqués. Dès lors, cet article propose d’évaluer les apports et les limites des tels outils à partir de plusieurs retours d’expérience, de discuter de leur place par rapport aux dispositifs existants et de dégager des pistes de recherche qui pourraient être explorées par les scientifiques, en allant au-delà d'une simple opportunité contextuelle