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

Orner l’espace liturgique aux IXe et Xe siècles : synthèse sur l’art de la céramique polychrome ornementale en Bulgarie

La production et l’utilisation de l’art de la céramique polychrome architecturale dans la décoration de plusieurs églises de Constantinople ont été révélées en 1907. Les interrogations sur leur origine deviennent entières avec la découverte en 1909 par Iordan Gospodinov de plaques similaires à pâte blanche dans les fouilles du monastère de Patleĭna, situé dans le rayonnement de la deuxième capitale du 1er royaume bulgare médiéval (Preslav), établie par Siméon Ier (893-927). Cette région est en effet durant cette période le lieu de l'installation de complexes monastiques mais aussi de la construction de nombreuses églises. Cette vie artistique et spirituelle intense reflète en réalité la politique de ce roi qui souhaite élever son jeune État bulgare au rang des foyers artistiques proches que sont Thessalonique et Constantinople. La situation géographique de ces terres, les désignant par ailleurs comme un point de confluence où se mêlent des héritages antiques et différentes influences issues de mouvements migratoires de populations diverses, nécessite de s’interroger sur les sources d’inspirations et sur les savoirs techniques qui ont pu marquer leur production artistique. Durant la période médiévale, les dirigeants, animés d’une volonté d’affirmer leur puissance face à Constantinople, entretiendront une relation passionnelle avec cette dernière perçue autant comme une concurrente que comme un modèle. Il n’est donc pas surprenant de voir dans la décoration de constructions civiles et religieuses sous Siméon Ier l’apparition de la céramique polychrome architecturale, utilisée dans les mêmes périodes qu’à Constantinople comme décor pariétal. Leur origine – Preslav ou Constantinople – tout comme celle des artistes-artisans a éveillé de nombreux débats. Les études récentes ont toutefois pu éclaircir certains aspects dont, notamment pour le cas de Preslav, que cet art original a été produit localement. Actuellement, cinq grands complexes d'ateliers de fabrication de ce type de céramique ont pu être identifiés dans le bassin de Preslav mais les connaissances sur la diffusion et sur le développement de cette décoration architecturale demeurent incertaines.Cette étude propose de ce fait de dresser une synthèse des connaissances acquises sur cet art jusqu’à aujourd’hui afin, je l’espère, d’approfondir une réflexion sur leur interaction avec l’édifice et le fidèle. Orner l’espace liturgique dans le sens d’« ornare », c’est-à-dire décorer une surface dans le but de sublimer harmonieusement un lieu afin qu’il soit à la hauteur de la gloire de Dieu, prend également une tout autre dimension en devenant un moyen de transmission de messages spirituels et de pouvoirs. Composées de deux catégories – l’ornemental et le figuré –, ces céramiques participent tout comme la mosaïque, la peinture ou la sculpture à figurer le monde céleste sur terre mais aussi à montrer, comme l’explique Cyprien de Carthage (IIIe siècle), que le fidèle doit, tout comme l’église, être ornementé, édifier son intérieur en le parant de l’éclat de la vraie lumière et de vertus. Derrière cette décoration fabriquée sur la demande de commanditaires, nous assistons non seulement à une volonté d’accroître la foi du croyant mais surtout d’exprimer une puissance en touchant la sensibilité du fidèle.The production and use of the art of architectural polychrome ceramics for the decoration of several churches in Constantinople was revealed in 1907. The questions regarding their origin become complete with the discovery in 1909 by Iordan Gospodinov of similar plates with white paste in the excavations of Patleĭna monastery, located in the vinicity of the second capital of the First medieval Bulgarian kingdom (Preslav), established by Simeon I (893-927). During this period, this region has seen the installation of monastic complexes but also of the construction of numerous churches. This intense artistic and spiritual life effectively reflects the politics of a king who wished to elevate his young Bulgarian state to the rank of the nearby artistic centers of Thessaloniki and Constantinople. The geographical location of these lands, which also designate it as a confluence point where the ancient heritage and different influences from the migratory movements of different populations are mixed, begs the question of the sources of inspiration and the technical knowledge which may have marked their artistic production. During the medieval period, leaders who are motivated by a desire to assert their power in the face of Constantinople maintain a passionate relationship with Constantinople, perceived as both a rival and a model. It is therefore not surprising to see in the decoration of civil and religious constructions under Simeon I the appearance of architectural polychrome ceramics, used in the same periods as in Constantinople, as a parietal decoration. Their origins - Preslav or Constantinople - as well as that of the artists-artisans, have aroused many debates. Recent studies however, have been able to clarify some points, including in the case of Preslav, that this original art was produced locally. Currently, five large workshops of this type of ceramic have been identified in the Preslav basin, but the knowledge of the diffusion and development of this architectural decoration remains uncertain.This study therefore proposes to draw up a synthesis of the knowledge acquired on this art up to the present day in order, I hope, to propound a reflection on their interactions with the building and the believer. To ornate the liturgical space in the sense of "ornare", that is to say decorating a surface with the aim of harmoniously sublimating a place so that it is worthy of the glory of God, also takes on a completely different meaning by becoming a mean of transmitting spiritual messages and powers. Composed of two categories - ornamental and figurative -, these ceramics participate, together with mosaics, painting or sculpture, to represent the heavenly world on earth but also in showing, as Cyprian of Carthage (3rd c.) explains that the believer must just as the church is ornate, to build his interior by filling it with the brightness of true light and virtues. Behind this decoration, made on the request of patrons, we witness not only a desire to increase the faith of the believer but above all to express a power by touching the sensitivity of the faithful

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