Contours actifs localisés hybrides basés région et gradient

International audience– Nous proposons une nouvelle méthode de segmentation par contour actif implicite basée à la fois sur la statistique régionale locale dans le voisinage des pixels du level set et sur l'information de contour. L'originalité de notre approche réside dans la combinaison d'un terme régional localisé avec un terme adaptant localement l'influence d'un champ de forces extérieures basé contours de type flot de vecteurs gradients (GVF). Cette technique permet d'une part de lever la limitation de convergence imposée par le rayon de localisation des approches locales, et d'autre part de dépasser les restrictions des champs de forces basées contours lorsque le niveau de bruit impose une dégradation de la carte des contours ou lorsque des centres de divergences interdisent sa progression. Abstract – We propose a new segmentation method for implicit active contours segmentation based simultaneously on local regional statistics in the vicinity of the level set and on contour information. The originality of our approach lies in the combination of a local region term with an adaptive term that locally weights the influence of external force fields such as gradient vector flow fields. On the one hand, this technique extends the convergence horizon of localizing approaches caused by the localizing radius. On the other hand, it allows to overpower inherent restrictions of edge-based fields approaches when the level of noise hampers the edge map quality, or when the presence of centers of divergence forbids further evolution of the model

4DGVF-based filtering of vector-valued images

International audienceIn this paper, we propose a new method for vector-valued image restoration in order to reduce noise while simultaneously sharpening vector edges. Our approach is a coupled anisotropic diffusion and shock filtering scheme that exploits a new robust 4DGVF vector field tailored for vector-valued images. The proposed scheme sharpens edges in directions diffused from the entire spatio-spectral information available with a more precise and a more stable sharpening effect along the iterative processing. We validate our method on color images as well as on realistic simulations of dynamic PET images

Hybrid chiral domain walls and skyrmions in magnetic multilayers

Noncollinear spin textures in ferromagnetic ultrathin films are currently the subject of renewed interest since the discovery of the interfacial Dzyaloshinskii-Moriya interaction (DMI). This antisymmetric exchange interaction selects a given chirality for the spin textures and allows stabilising configurations with nontrivial topology. Moreover, it has many crucial consequences on the dynamical properties of these topological structures, including chiral domain walls (DWs) and magnetic skyrmions. In the recent years the study of noncollinear spin textures has been extended from single ultrathin layers to magnetic multilayers with broken inversion symmetry. This extension of the structures in the vertical dimension allows very efficient current-induced motion and room-temperature stability for both N\'eel DWs and skyrmions. Here we show how in such multilayered systems the interlayer interactions can actually lead to more complex, hybrid chiral magnetisation arrangements. The described thickness-dependent reorientation of DWs is experimentally confirmed by studying demagnetised multilayers through circular dichroism in x-ray resonant magnetic scattering. We also demonstrate a simple yet reliable method for determining the magnitude of the DMI from static domains measurements even in the presence of these hybrid chiral structures, by taking into account the actual profile of the DWs. The advent of these novel hybrid chiral textures has far-reaching implications on how to stabilise and manipulate DWs as well as skymionic structures in magnetic multilayers.Comment: 22 pages, 5 figure

Approche 4DGVF pour la restauration d'images multi-composantes

National audienceDans cet article, nous proposons une nouvelle méthode pour la restauration d'images multi-composantes afin de diminuer le bruit tout en rehaussant simultanément les contours. Notre approche repose sur un filtrage couplant diffusion anisotrope et filtre de choc qui exploite un nouveau champ de decteurs 4DGVF robuste adapté aux images multi-composantes. Le schéma proposé permet de rehausser les contours dans des directions calculées à partir de l'intégralité de l'information spatio-spectrale disponible et d'obtenir un rehaussement plus précis et plus stable au cours du traitement itératif. Nous validons notre méthode sur des images couleurs ainsi que des simulations réalistes d'images TEP dynamiques du cerveau

4-D Gradient Vector Flow : segmentation par surface active pour images multi-composantes

National audienceDans cet article, nous généralisons le flux de vecteurs gradients à la segmentation par surface active d'images 3-D à valeurs vectorielles. Nous basons notre méthode sur la définition d'un tenseur de structure multi-composantes pondéré exploitant l'intégralité de l'information de l'image pour réduire la sensibilité au bruit et améliorer la précision du modèle. Appliquée à la segmentation de volumes biologiques en imagerie par tomographie d'émission de positrons (TEP) dynamique, nous validons notre méthode sur des simulations Monte Carlo réalistes d'images TEP de fantômes numériques

4DGVF segmentation of vector-valued images

International audienceIn this paper, we extend the gradient vector flow field to the vector-valued case for robust variational segmentation of 4D images with active surfaces. Instead of only exploiting scalar edge strength in order to identify vector edges, we propagate both directions and amplitudes of vector gradients computed from the analysis of a structure tensor of the vector-valued image. To reduce contributions from noise in the calculation of the structure tensor, image channels are weighted according to a blind estimator of contrast that take profit of the deformable models framework. The proposed 4DGVF vector field is validated on synthetic image datasets and applied to biological volume delineation in dynamic PET imaging

Minyon’un düğünü

Johann Wolfgang Goethe'nin Sabah'ta yayımlanan Minyon'un Düğünü adlı romanının ilk ve son tefrikalarıTefrikada yazarın adı belirtilmemiştir

Variational segmentation of vector-valued images with gradient vector flow

International audienceIn this paper, we extend the gradient vector flow field for robust variational segmentation of vector-valued images. Rather than using scalar edge information, we define a vectorial edge map derived from a weighted local structure tensor of the image that enables the diffusion of the gradient vectors in accurate directions through the 4DGVF equation. To reduce the contribution of noise in the structure tensor, image channels are weighted according to a blind estimator of contrast. The method is applied to biological volume delineation in dynamic PET imaging, and validated on realistic Monte Carlo simulations of numerical phantoms as well as on real images

Expériences de recherche en éco-conception dans le domaine du Génie Electrique

National audienceQue ce soit en génie électrique ou dans tout autre domaine, l'écoconception est un très vaste sujet. Les travaux de recherche, que nous avons menés durant les quelques années passées et que nous poursuivons actuellement, n'en abordent qu'un volet très limité, celui que nous avons qualifié d'écodimensionnement. En effet, nous ne nous sommes penchés que sur la recherche de méthodologies d'optimisation de paramètres dimensionnels ou de matériaux en vue de trouver un optimum sur cycle de vie pour des produits dont nous ne remettons pas en question (pour l'instant) les procédés de fabrication, les architectures, les usages, etc. Les domaines traités ici sont : les transformateurs électromagnétiques, les moteurs électriques, les systèmes phovoltaïques autonomes et la distribution en courant continu dans les bâtiments

Coordinated community structure among trees, fungi and invertebrate groups in Amazonian rainforests

Little is known regarding how trophic interactions shape community assembly in tropical forests. Here we assess multi-taxonomic community assembly rules using a rare standardized coordinated inventory comprising exhaustive surveys of five highly-diverse taxonomic groups exerting key ecological functions: trees, fungi, earthworms, ants and spiders. We sampled 36 1.9-ha plots from four remote locations in French Guiana including precise soil measurements, and we tested whether species turnover was coordinated among groups across geographic and edaphic gradients. All species group pairs exhibited significant compositional associations that were independent from soil conditions. For some of the pairs, associations were also partly explained by soil properties, especially soil phosphorus availability. Our study provides evidence for coordinated turnover among taxonomic groups beyond simple relationships with environmental factors, thereby refining our understanding regarding the nature of interactions occurring among these ecologically important groups