Strong light-matter coupling in ultrathin double dielectric mirror GaN microcavities

Strong light-matter coupling is demonstrated at low temperature in an ultrathin GaN microcavity fabricated using two silica/zirconia Bragg mirrors, in addition to a three-period epitaxial (Al,Ga)N mirror serving as an etch stop and assuring good quality of the overgrown GaN. The λ/2 cavity is grown by molecular beam epitaxy on a Si substrate. Analysis of angle-resolved data reveal key features of the strong coupling regime in both reflectivity and transmission spectra at 5 K: anticrossing with a normal mode splitting of 43±2 meV and 56±2 meV for reflectivity and transmission, respectively, and narrowing of the lower polariton linewidth near resonance

Video-based methodology for markerless human motion analysis

International audienceThis study presents a video-based experiment for the study of markerless human motion. Silhouettes are extracted from a multi-camera video system to reconstruct a 3D mesh for each frame using a reconstruction method based on visual hull. For comparison with traditional motion analysis results, we set up an experiment integrating video recordings from 8 video cameras and a marker-based motion capture system (Vicon™). Our preliminary data provided distances between the 3D trajectories from the Vicon system and the 3D mesh extracted from the video cameras. In the long term, the main ambition of this method is to provide measurement of skeleton motion for human motion analyses while eliminating markers

Video-based methodology for markerless human motion analysis

International audienceThis study presents a video-based experiment for the study of markerless human motion. Silhouettes are extracted from a multi-camera video system to reconstruct a 3D mesh for each frame using a reconstruction method based on visual hull. For comparison with traditional motion analysis results, we set up an experiment integrating video recordings from 8 video cameras and a marker-based motion capture system (Vicon™). Our preliminary data provided distances between the 3D trajectories from the Vicon system and the 3D mesh extracted from the video cameras. In the long term, the main ambition of this method is to provide measurement of skeleton motion for human motion analyses while eliminating markers

Video Capture of Skin Motion using Calibrated Fabrics

International audienceWe introduce a novel approach to capture linear and non linear motions of the skin surface due to muscle bugglings and other complex sub-surface interactions. Our method uses standard camera and consists of a video motion capture of the desired body surface covered by a stretchy and calibrated cloth. We develop a non model-based tracking method using regularity and topology of dedicated fabrics. Our tracking and 3D reconstruction methods support occlusions : we detect occlusions of 3D surfaces using temporal and spatial coherences, and are able to restart surface tracking once the occlusions have ended. The obtained 3D mesh can easily be integrated and adapted in a sequence of an animated virtual human. We demonstrate our method with the skinning of non-linear biceps deformations

FACSGen: A Tool to Synthesize Emotional Facial Expressions Through Systematic Manipulation of Facial Action Units

To investigate the perception of emotional facial expressions, researchers rely on shared sets of photos or videos, most often generated by actor portrayals. The drawback of such standardized material is a lack of flexibility and controllability, as it does not allow the systematic parametric manipulation of specific features of facial expressions on the one hand, and of more general properties of the facial identity (age, ethnicity, gender) on the other. To remedy this problem, we developed FACSGen: a novel tool that allows the creation of realistic synthetic 3D facial stimuli, both static and dynamic, based on the Facial Action Coding System. FACSGen provides researchers with total control over facial action units, and corresponding informational cues in 3D synthetic faces. We present four studies validating both the software and the general methodology of systematically generating controlled facial expression patterns for stimulus presentatio

Principal Geodesic Dynamics

International audienceThis paper presents a new integration of a data-driven approach using dimension reduction and a physically-based simulation for real-time character animation. We exploit Lie group statistical analysis techniques (Principal Geodesic Analysis, PGA) to approximate the pose manifold of a motion capture sequence by a reduced set of pose geodesics. We integrate this kinematic parametrization into a physically-based animation approach of virtual characters, by using the PGA-reduced parametrization directly as generalized coordinates of a Lagrangian formulation of mechanics. In order to achieve real-time without sacrificing stability, we derive an explicit time integrator by approximating existing variational integrators. Finally, we test our approach in task-space motion control. By formulating both physical simulation and inverse kinematics time stepping schemes as two quadratic programs, we propose a features-based control algorithm that interpolates between the two metrics. This allows for an intuitive trade-off between realistic physical simulation and controllable kinematic manipulation

Strong light-matter coupling in bulk GaN-microcavities with double dielectric mirrors fabricated by two different methods

Two routes for the fabrication of bulk GaN microcavities embedded between two dielectric mirrors are described, and the optical properties of the microcavities thus obtained are compared. In both cases, the GaN active layer is grown by molecular beam epitaxy on (111) Si, allowing use of selective etching to remove the substrate. In the first case, a three period Al0.2Ga0.8N / AlN Bragg mirror followed by a lambda/2 GaN cavity are grown directly on the Si. In the second case, a crack-free 2,mu m thick GaN layer is grown, and progressively thinned to a final thickness of lambda. Both devices work in the strong coupling regime at low temperature, as evidenced by angle-dependent reflectivity or transmission experiments. However, strong light-matter coupling in emission at room temperature is observed only for the second one. This is related to the poor optoelectronic quality of the active layer of the first device, due to its growth only 250 nm above the Si substrate and its related high defect density. The reflectivity spectra of the microcavities are well accounted for by using transfer matrix calculations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3477450

A study on the use of the PACS bolometer arrays for submillimeter ground-based telescopes

A new kind of bolometric architecture has been successfully developed for the PACS photometer onboard the Herschel submillimeter observatory. These new generation CCD-like arrays are buttable and enable the conception of large fully sampled focal planes. We present a feasibility study of the adaptation of these bolometer arrays to ground-based submillimeter telescopes. We have developed an electro-thermal numerical model to simulate the performances of the bolometers under specific ground-based conditions (different wavelengths and background powers for example). This simulation permits to determine the optimal parameters for each condition and shows that the bolometers can be background limited in each transmission window between 200 and 450 microns. We also present a new optical system that enables to have a maximum absorption of the bolometer in each atmospheric windows. The description of this system and measurements are showed.Comment: 9 pages, 12 figures, to be published in the Proceedings of SPIE Vol. 6275, "Astronomical Telescopes and Instrumentation, Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III

Multiple-View Threedimensional Paper Sheet Reconstruction

Smoothly bent paper-like surfaces are developable. They are however difficult to minimally parameterize since the number of meaningful parameters is intrinsically dependent on the actual deformation. Previous generative models are either incomplete, i.e. limited to subsets of developable surfaces, or depend on huge parameter sets. Our first contribution is a generative model governed by a quasi-minimal set of intuitive parameters, namely rules and angles. More precisely, a flat mesh is bent along guiding rules, while a number of extra rules controls the level of smoothness. The generated surface is guaranteed to be developable. The second contribution is an automatic multi-camera 3D reconstruction algorithm. First of all, the cameras and a sparse structure are reconstructed from the images using Structure-from-Motion method. A 2D parametrization of the reconstructed points is computed by dimensionality reduction. This parameterization is used to initialize the proposed model since it easily allows us to estimate the surface curvature. The initial model parameters are eventually tuned through model-based bundle-adjustment.Les surfaces de type papier, lorsqu’elles ne présentent pas de pli franc, sont mathématiquement décrites par des surfaces développables. Ces dernières sont difficiles à paramétrer de manière minimale car le nombre de degrés de liberté significatif dépend de la déformation. Les modèles existants sont incomplets ou dépendent de grands jeux de paramètres redondants. Notre première contribution est un modèle génératif contrôlé par un jeu quasi-minimal de paramètres intuitifs. Le principe est de plier une surface plane autour de règles de guidage. Un certain nombre de règles de lissage contrôle la régularité de la surface ainsi générée, qui par construction approche une surface développable. Notre deuxième contribution est un algorithme d’estimation du modèle proposé à partir de plusieurs images. Tout d’abord, les caméras et une structure 3D éparse de la surface de l’objet sont reconstruites. Une paramétrisation 2D de ces points est ensuite calculée par une méthode non-linéaire de réduction des dimensions. Cette paramétrisation est essentielle pour évaluer la courbure d’une surface passant par les points reconstruits, nécessaire à l’initialisation des paramètres du modèle. Enfin, un ajustement de faisceaux ajuste les paramètres du modèle afin de raffiner la surface en minimisant l’erreur de reprojection