Adaboost Discret Hétérogène à Contrainte Temps Réel : Application à la Détection de Piétons par Stéréovision

Session "Posters"National audienceCet article présente une méthode de détection de piétons basée sur la combinaison de classifieurs d'apparence et de profondeur. Des travaux récents ont montré l'intérêt de cette approche. Nous proposons deux contributions : 1) une étude comparative de différents classifieurs de profondeur, dans laquelle nous montrons que les meilleures performances sont atteintes par un classifieur simple, basé sur la moyenne des distances dans une sous-fenêtre de la région testée et 2) une adaptation de l'algorithme d'apprentissage Adaboost prenant en compte des classifieurs hétérogènes en terme de coût algorithmique. L'objectif de cette approche est de construire un classifieur à la fois performant en terme de taux de détection et de temps d'exécution. Nous montrons la pertinence de l'algorithme ainsi développé sur des séquences d'images réelle

Vers une détection de piétons temps réel par apprentissage de forme dans l'image de profondeur

National audienceThis paper presents a method for detecting pedestrians in a depth image, established from a pair of calibrated cameras (stereoscopic head). We propose to learn the characteristics of a pedestrian thanks to a boosting type algorithm, using weak classifiers created from simple statistical characteristics of distance within a sub-window of the area of analysis. These assumptions will then be confirmed by a second, classic detector based on analysis of the visual appearance of pedestrians. Our resulting method allows for the detection of pedestrians at a rate close to real time, using the concept of integral image, applied to the calculation of 3D descriptors. The proposed method is compared with a traditional method for detecting vertical obstacles on a real annotated video sequence. Our method reduces the number of false positives by approximately 60% compared to an obstacle-detection method, while reducing the computation time.Cet article présente une méthode pour la détection des piétons dans une image de profondeur, acquise à partir d'une paire de caméras calibrées (tête stéréoscopique). Nous proposons d'apprendre les caractéristiques d'un piéton à l'aide d'un algorithme de type boosting, à partir de classifieurs faibles issus de caractéristiques statistiques simples des distances à l'intérieur d'une sous-fenêtre de la zone d'analyse. Ces hypothèses seront ensuite confirmées par un second détecteur, classique, basé sur l'analyse de l'apparence visuel des piétons. La méthode ainsi obtenue permet une détection des piétons, à une cadence proche du temps réel, grâce à l'utilisation de la notion d'image intégrale, appliquée au calcul des descripteurs 3D. La méthode proposée est comparée à une méthode de détection d'obstacles verticaux classique sur une séquence vidéo réelle annotée. Elle permet de réduire le nombre de faux positifs d'approximativement 60% par rapport à une méthode de détection d'obstacles, tout en diminuant le temps de calcul

Effect of coarse particle volume fraction on the yield stress and thixotropy of cementious materials

International audienceIn order to help in modelling the yield stress of fresh concrete, we study the behavior of suspensions of coarse particles in a thixotropic cement paste. Our aim is to relate the yield stress of these mixtures to the yield stress of the suspending cement paste, to the time passed at rest, and to the coarse particle volume fraction. We present here procedures that allow for (i) studying a homogeneous and isotropic suspension, (ii) comparing the yield stress of a given cement paste to that of the same cement paste added with particles, and (iii) accounting for the thixotropy of the cement paste. We observe that the yield stress of these suspensions of cement paste with coarse particles follows the very simple Chateau-Ovarlez-Trung model {[}X. Chateau, G. Ovarlez. K.L. Trung, Homogenization approach to the behavior of suspensions of noncolloidal particles in yield stress fluids, J. Rheol. (2008) 52 489-506.], consistently with the experimental results of Mahaut et al. {[}F. Mahaut, X. Chateau, P. Coussot, G. Ovarlez, Yield stress and elastic modulus of suspensions of noncolloidal particles in yield stress fluids, J. Rheol. (2008) 52 287-313.] obtained with many different particles and suspending yield stress fluids. This consistency between the results obtained in various yield stress fluids shows that the yield stress of the suspension does not depend on the physicochemical properties of the suspending yield stress fluid; it only depends on its yield stress value. This shows that studies of suspensions in model yield stress fluids can be used as a general tool to infer the behavior of fresh concrete. Moreover, we show that the thixotropic structuration rate of the interstitial paste (its static yield stress increase rate in time) is not affected by the presence of the particles. As a consequence, it is sufficient to measure the thixotropic properties of the constitutive cement paste in order to predict the thixotropic structuration rate of a given fresh concrete. This structuration rate is predicted to have the same dependence on the coarse particle volume fraction as the yield stress

Adding virtual reality to the university self-access language centre. Brave new world or passing fad?

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Flows of suspensions of particles in yield stress fluids

International audienceWe study the rheological behavior of suspensions of noncolloidal spheres in yield stress fluids (concentrated emulsions). These are good model systems for understanding, e.g., the rheology of fresh concrete or debris flows, and more generally, the behavior of particles dispersed in any nonlinear material. We use magnetic resonance imaging techniques to investigate the flows of these yield stress suspensions in a concentric-cylinder Couette geometry. We extend the theoretical approach of Chateau et al. [J. Rheol. 52, 489–506 (2008)], valid for isotropic suspensions, to describe suspensions in simple shear flows, in which an anisotropic spatial distribution of particles is induced by flow. Theory and experiments show that the suspensions can be modeled by a Herschel–Bulkley behavior of same index as their interstitial fluid. We characterize the increase of their consistency and their yield stress with the particle volume fraction / in the 0%–50% range. We observe a good agreement between the experimental variations of the consistency with / and the theoretical prediction. This shows that the average apparent viscosity of the sheared interstitial material is correctly estimated and taken into account. We also observe shear-induced migration with similar properties as in a Newtonian fluid, which we predict theoretically, suggesting that particle normal stresses are proportional to the shear stress. However, the yield stress at flow stoppage increases much less than predicted. We also show that new features emerge in the rheology of the yield stress fluid when adding particles. We predict and observe the emergence of a nonzero normal stress difference at the yielding transition. We observe that the yield stress at flow start can differ from the yield stress at flow stoppage, and depends on flow history. It is likely a signature of a shear-dependent microstructure, due to the nonlinear behavior of the interstitial fluid, which makes these materials different from suspensions in Newtonian media. This is confirmed by direct characterization of shear-rate-dependent pair distribution functions using X-ray microtomography. This last observation explains why the theory predictions for the consistency can be correct while failing to model the yield stress at flow stoppage: a unique microstructure was indeed assumed as a first approximation. More sophisticated theories accounting for a shear-dependent microstructure are thus needed

Comparing Measurements of Vascular Diameter Using Adaptative Optics Imaging and Conventional Fundus Imaging

The aim of this prospective study was to compare retinal vascular diameter measurements taken from standard fundus images and adaptive optics (AO) images. We analysed retinal images of twenty healthy subjects with 45-degree funduscopic colour photographs (CR-2 Canon fundus camera, Canon™) and adaptive optics (AO) fundus images (rtx1 camera, Imagine Eyes(®)). Diameters were measured using three software applications: the VAMPIRE (Vessel Assessment and Measurement Platform for Images of the REtina) annotation tool, IVAN (Interactive Vessel ANalyzer) for funduscopic colour photographs, and AO_Detect_Artery™ for AO images. For the arterial diameters, the mean difference between AO_Detect_Artery™ and IVAN was 9.1 µm (−27.4 to 9.2 µm, p = 0.005) and the measurements were significantly correlated (r = 0.79). The mean difference between AO_Detect_Artery™ and VAMPIRE annotation tool was 3.8 µm (−34.4 to 26.8 µm, p = 0.16) and the measurements were poorly correlated (r = 0.12). For the venous diameters, the mean difference between the AO_Detect_Artery™ and IVAN was 3.9 µm (−40.9 to 41.9 µm, p = 0.35) and the measurements were highly correlated (r = 0.83). The mean difference between the AO_Detect_Artery™ and VAMPIRE annotation tool was 0.4 µm (−17.44 to 25.3 µm, p = 0.91) and the correlations were moderate (r = 0.41). We found that the VAMPIRE annotation tool, an entirely manual software, is accurate for the measurement of arterial and venular diameters, but the correlation with AO measurements is poor. On the contrary, IVAN, a semi-automatic software tool, presents slightly greater differences with AO imaging, but the correlation is stronger. Data from arteries should be considered with caution, since IVAN seems to significantly under-estimate arterial diameters

An integer linear programming approach for genome scaffolding

This paper presents a simple and fast approach for genome scaffolding, combining constraint modeling and simple graph manipulation. We model the scaffolding problem as an optimization problem on a graph built from a paired-end reads alignment on contigs, then describe an heuristic to solve this problem with the iterative combination of local constraints solving and cycle breaking phases. We tested our approach on a benchmark of various genomes, and compared it with several usual scaffolders. The proposed method is quick, flexible, and provides results comparable to other scaffolders in terms of quality. In addition, contrarily to state of the art approaches that require dedicated servers, it can be run on a basic notebook computer even for large genomes

HRAS is a therapeutic target in malignant chemo-resistant adenomyoepithelioma of the breast

Abstract Malignant adenomyoepithelioma (AME) of the breast is an exceptionally rare form of breast cancer, with a significant metastatic potential. Chemotherapy has been used in the management of advanced AME patients, however the majority of treatments are not effective. Recent studies report recurrent mutations in the HRAS Q61 hotspot in small series of AMEs, but there are no preclinical or clinical data showing H-Ras protein as a potential therapeutic target in malignant AMEs. We performed targeted sequencing of tumours’ samples from new series of 13 AMEs, including 9 benign and 4 malignant forms. Samples from the breast tumour and the matched axillary metastasis of one malignant HRAS mutated AME were engrafted and two patient-derived xenografts (PDX) were established that reproduced the typical AME morphology. The metastasis-derived PDX was treated in vivo by different chemotherapies and a combination of MEK and BRAF inhibitors (trametinib and dabrafenib). All malignant AMEs presented a recurrent mutation in the HRAS G13R or G12S hotspot. Mutation of PIK3CA were found in both benign and malignant AMEs, while AKT1 mutations were restricted to benign AMEs. Treatment of the PDX by the MEK inhibitor trametinib, resulted in a marked anti-tumor activity, in contrast to the BRAF inhibitor and the different chemotherapies that were ineffective. Overall, these findings further expand on the genetic features of AMEs and suggest that patients carrying advanced HRAS-mutated AMEs could potentially be treated with MEK inhibitors

Simulated Optical Performance of Custom Wavefront Soft Contact Lenses for Keratoconus

ABSTRACT: Purpose. Outstanding improvements in vision can theoretically be expected using contact lenses that correct monochromatic aberrations of the eye. Imperfections in such correction inherent to contact lenses are lens flexure, translation, rotation, and tear layer effects. The effects of pupil size and accommodation on ocular aberration may cause further difficulties. The purpose of this study was to evaluate whether nonaxisymmetric soft contact lenses could efficiently compensate for highe