C2 interpolation of spatial data subject to arc-length constraints using Pythagorean-hodograph quintic splines

International audienceIn order to reconstruct spatial curves from discrete electronic sensor data, two alternative C2 Pythagorean-hodograph (PH) quintic spline formulations are proposed, interpolating given spatial data subject to prescribed constraints on the arc length of each spline segment. The first approach is concerned with the interpolation of a sequence of points, while the second addresses the interpolation of derivatives only (without spatial localization). The special structure of PH curves allows the arc-length conditions to be expressed as algebraic constraints on the curve coefficients. The C2 PH quintic splines are thus defined through minimization of a quadratic function subject to quadratic constraints, and a close starting approximation to the desired solution is identified in order to facilitate efficient construction by iterative methods. The C2 PH spline constructions are illustrated by several computed examples

Surfaces Reconstruction Via Inertial Sensors for Monitoring

International audienceThis document deals with the new capabilities of monitoring via the surface reconstruction of stuctures with sensors' arrays systems. Indeed, we will detail here our new demonstrator composed of a smart textile equipped with inertial sensors and a set of processings allowing to reconstruct the shape of the textile moving along time. We show here how this new tool can provide very useful information from the structures

Sawing of Logs in Virtual Trees Using 3D Intersection Algorithms

Colloque avec actes et comité de lecture. internationale.International audienceThis work is issued from researches developed in the Programme of Plant Modelling Programme (AMAP) at Cirad: modelling, simulation and visualisation of trees. The goal is to extract and to visualise sawed boards from virtual trees, which are produced by the software AMAP. The initial geometric description of the trees have to be adapted to the sawing: the branches are not correctly connected to the trunk. So, in collaboration with the laboratory LMC, two approaches have been developed. The first one uses 2D-image techniques while in the second one, a new description of the surfaces is developed with some 3-D intersections algorithms to solve the problem of connections. It uses Bézier surfaces and geometrical connection techniques

Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition)

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. For example, a key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process versus those that measure fl ux through the autophagy pathway (i.e., the complete process including the amount and rate of cargo sequestered and degraded). In particular, a block in macroautophagy that results in autophagosome accumulation must be differentiated from stimuli that increase autophagic activity, defi ned as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (inmost higher eukaryotes and some protists such as Dictyostelium ) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the fi eld understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. It is worth emphasizing here that lysosomal digestion is a stage of autophagy and evaluating its competence is a crucial part of the evaluation of autophagic flux, or complete autophagy. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. Along these lines, because of the potential for pleiotropic effects due to blocking autophagy through genetic manipulation it is imperative to delete or knock down more than one autophagy-related gene. In addition, some individual Atg proteins, or groups of proteins, are involved in other cellular pathways so not all Atg proteins can be used as a specific marker for an autophagic process. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field

Methode algorithmique d'implicitisation et d'inversion. Application au lancer de rayons

INIST T 74936 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Méthode algorithmique d'implicitisation et d'inversion - Application au lancer de rayons

Le travail présenté ici a pour thème le développement et la mise en oeuvre d'une méthode d'implicitisation et d'inversion ainsi que son application à la visualisation de surfaces polynomiales et rationnelles parametrées par la technique du lancer de rayons. l'implicitisation est un problème d'élimination pour lequel les méthodes de résultant s'avèrent mieux adaptées à notre application. la méthode de dixon (1908) pour les surfaces obtenues par produit tensoriel (surfaces de bi-degré) est particulièrement bien adaptée. Nous proposons une extension algorithmique de cette méthode qui conserve ses propriétés de simplicité et de compacité. la programmation en langage REDUCE a permis une expérimentation sur de nombreux exemples: elle montre que l'équation implicite est obtenue, et ceci de façon efficace, bien que la justification théorique de l'algorithme reste incomplète. L'étude de cette dernière nous a amené à considérer les problèmes de paramétrisations non fidèles et de l'apparition de facteurs parasites. Ensuite le problème de l'inversion (identification et détermination des paramètres d'un point de la surface rationnelle) est résolu complètement. Nous proposons enfin une application numérique de ces algorithmes (en langage C) au problème de l'intersection d'une Bezier rationnelle et d'une demi-droite (rayon). les aspects de stabilité numérique et d'optimisation sont mis en avant: à chaque surface est associée une table pre-calculée, permettant d'obtenir simplement l'équation d'intersection dans le paramètre rayon. Les images données attestent des qualités numériques de cette méthode d'implicitisation-inversion

Surface reconstruction from micro-sensors and geodesics

National audienceWe are concerned with the reverse engineering problem of reconstructing physical surfaces from tangential data. These tangential data are provided by embedded sensors (micro-accelerometers and micro-magnetometers developed by the laboratory CEA/LETI) along a curve represented by a ribbon. Appropriate methods for the reconstruction of planar and spatial curves from such tangential informations have been developed and validated by a real-time demonstrator : the Morphosense ribbon. Then by placing the Morphosense on a physical surface at regular intervals along different directions, the surface is divided into a system of rectangular and triangular patches. Furthermore, it is shown that the Morphosense ribbon assumes the shape of a geodesic when laid on a smooth physical surface. Thus, specific methods for the problem of constructing rectangular or triangular surface patches, when prescribed boundary curves are required to be geodesics of the resulting surface, are presented. The possibility of constructing such surface patches is shown to depend on the given boundary curves satisfying two types of consistency constraints. The first constraint is global in nature, whereas the second constraint is a local differential condition, relating the curvatures and torsions of the curves meeting at each of the four patch corners to the angle between those curve

Modélisation Géométrique et Reconstruction de Surfaces

L'ensemble des thématiques abordées s'inscrivent dans le contexte de la modélisation et du calcul géométrique

On the interpolation of concentric curvature elements

International audienceA convex G2 Hermite interpolation problem of concentric curvature elements is considered in this paper. It is first proved that there is no spiral arc solution with turning angle less than or equal to π and then, that any convex solution admits at least two vertices. The curvature and the evolute profiles of such an interpolant are analyzed. In particular, conditions for the existence of a G2 convex interpolant with prescribed extremal curvatures are given

Apport de l'IRM dans l'orientation diagnostique des rhumatismes inflammatoires

CLERMONT FD-BCIU-Santé (631132104) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF