Association Mouvement/Géométrie pour représentations volumiques

Session: AnimationNational audienceLes modèles particulaires permettent de produire des animations riches et variées. Ils sont particulièrement adaptés à certains effets d'animation. Mais intrinsèquement, ils ne sont pas basés sur des représentations surfaciques ou volumiques d'objets. Ainsi, visualiser le mouvement qu'ils décrivent peut poser problème car ils ne contiennent souvent pas assez d'information pour reconstruire la moindre topologie spatiale sous-jacente. Plus précisément, un mouvement produit par de tels modèles peut être rendu via différentes formes géométriques et mener à autant d'interprétations visuelles, sans contrôle de l'utilisateur. À notre connaissance, il n'existe pas de méthode générique associant des mouvements basés points, comme ceux produits par un modèle particulaire, ou n'importe quel ensemble de points en mouvement, à une structure topologique. Dans cet article, nous proposons un "framework" permettant d'associer, selon les souhaits de l'utilisateur, n'importe quelle forme volumique à n'importe quel mouvement basé points, et de contrôler les changements topologiques. Il est ainsi possible de créer différents résultats visuels avec une unique description de mouvement. Ce "framework" est séparé en trois processus distincts : l'association entre particules et sommets, la définition de l'application du mouvement aux sommets du maillage, et les modifications topologiques et les événements qui les déclenchent. Nous montrons comment la manipulation de ces paramètres permet d'expérimenter différentes associations sur un même mouvement

Glucose availability and sensitivity to anoxia of isolated rat peripheral nerve

The contrast between resistance to ischemia and ischemic lesions in peripheral nerves of diabetic patients was explored by in vitro experiments. Isolated and desheathed rat peroneal nerves were incubated in the following solutions with different glucose availability: 1) 25 mM glucose, 2) 2.5 mM glucose, and 3) 2.5 mM glucose plus 10 mM 2-deoxy-D-glucose. Additionally, the buffering power of all of these solutions was modified. Compound nerve action potential (CNAP), extracellular pH, and extracellular potassium activity (aKe) were measured simultaneously before, during, and after a period of 30 min of anoxia. An increase in glucose availability led to a slower decline in CNAP and to a smaller rise in aKe during anoxia. This resistance to anoxia was accompanied by an enhanced extracellular acidosis. Postanoxic recovery of CNAP was always complete in 25 mM HCO3(-)-buffered solutions. In 5 mM HCO3- and in HCO3(-)-free solutions, however, nerves incubated in 25 mM glucose did not recover functionally after anoxia, whereas nerves bathed in solutions 2 or 3 showed a complete restitution of CNAP. We conclude that high glucose availability and low PO2 in the combination with decreased buffering power and/or inhibition of HCO3(-)-dependent pH regulation mechanisms may damage peripheral mammalian nerves due to a pronounced intracellular acidosis

Arrival angles of teleseismic fundamental mode Rayleigh waves across the AlpArray

The dense AlpArray network allows studying seismic wave propagation with high spatial resolution. Here we introduce an array approach to measure arrival angles of teleseismic Rayleigh waves. The approach combines the advantages of phase correlation as in the two-station method with array beamforming to obtain the phase-velocity vector. 20 earthquakes from the first two years of the AlpArray project are selected, and spatial patterns of arrival-angle deviations across the AlpArray are shown in maps, depending on period and earthquake location. The cause of these intriguing spatial patterns is discussed. A simple wave-propagation modelling example using an isolated anomaly and a Gaussian beam solution suggests that much of the complexity can be explained as a result of wave interference after passing a structural anomaly along the wave paths. This indicates that arrival-angle information constitutes useful additional information on the Earth structure, beyond what is currently used in inversions

Ambient-noise tomography of the wider Vienna Basin region

We present a new 3-D shear-velocity model for the top 30 km of the crust in the wider Vienna Basin region based on surface waves extracted from ambient-noise cross-correlations. We use continuous seismic records of 63 broad-band stations of the AlpArray project to retrieve interstation Green’s functions from ambient-noise cross-correlations in the period range from 5 to 25 s. From these Green’s functions, we measure Rayleigh group traveltimes, utilizing all four components of the cross-correlation tensor, which are associated with Rayleigh waves (ZZ, RR, RZ and ZR), to exploit multiple measurements per station pair. A set of selection criteria is applied to ensure that we use high-quality recordings of fundamental Rayleigh modes. We regionalize the interstation group velocities in a 5 km × 5 km grid with an average path density of ∼20 paths per cell. From the resulting group-velocity maps, we extract local 1-D dispersion curves for each cell and invert all cells independently to retrieve the crustal shear-velocity structure of the study area. The resulting model provides a previously unachieved lateral resolution of seismic velocities in the region of ∼15 km. As major features, we image the Vienna Basin and Little Hungarian Plain as low-velocity anomalies, and the Bohemian Massif with high velocities. The edges of these features are marked with prominent velocity contrasts correlated with faults, such as the Alpine Front and Vienna Basin transfer fault system. The observed structures correlate well with surface geology, gravitational anomalies and the few known crystalline basement depths from boreholes. For depths larger than those reached by boreholes, the new model allows new insight into the complex structure of the Vienna Basin and surrounding areas, including deep low-velocity zones, which we image with previously unachieved detail. This model may be used in the future to interpret the deeper structures and tectonic evolution of the wider Vienna Basin region, evaluate natural resources, model wave propagation and improve earthquake locations, among others

Shear-wave velocity structure beneath the Dinarides from the inversion of Rayleigh-wave dispersion

Highlights • Rayleigh-wave phase velocity in the wider Dinarides region using the two-station method. • Uppermost mantle shear-wave velocity model of the Dinarides-Adriatic Sea region. • Velocity model reveals a robust high-velocity anomaly present under the whole Dinarides. • High-velocity anomaly reaches depth of 160 km in the northern Dinarides to more than 200 km under southern Dinarides. • New structural model incorporating delamination as one of the processes controlling the continental collision in the Dinarides. The interaction between the Adriatic microplate (Adria) and Eurasia is the main driving factor in the central Mediterranean tectonics. Their interplay has shaped the geodynamics of the whole region and formed several mountain belts including Alps, Dinarides and Apennines. Among these, Dinarides are the least investigated and little is known about the underlying geodynamic processes. There are numerous open questions about the current state of interaction between Adria and Eurasia under the Dinaric domain. One of the most interesting is the nature of lithospheric underthrusting of Adriatic plate, e.g. length of the slab or varying slab disposition along the orogen. Previous investigations have found a low-velocity zone in the uppermost mantle under the northern-central Dinarides which was interpreted as a slab gap. Conversely, several newer studies have indicated the presence of the continuous slab under the Dinarides with no trace of the low velocity zone. Thus, to investigate the Dinaric mantle structure further, we use regional-to-teleseismic surface-wave records from 98 seismic stations in the wider Dinarides region to create a 3D shear-wave velocity model. More precisely, a two-station method is used to extract Rayleigh-wave phase velocity while tomography and 1D inversion of the phase velocity are employed to map the depth dependent shear-wave velocity. Resulting velocity model reveals a robust high-velocity anomaly present under the whole Dinarides, reaching the depths of 160 km in the north to more than 200 km under southern Dinarides. These results do not agree with most of the previous investigations and show continuous underthrusting of the Adriatic lithosphere under Europe along the whole Dinaric region. The geometry of the down-going slab varies from the deeper slab in the north and south to the shallower underthrusting in the center. On-top of both north and south slabs there is a low-velocity wedge indicating lithospheric delamination which could explain the 200 km deep high-velocity body existing under the southern Dinarides

Crustal Thinning From Orogen to Back-Arc Basin: The Structure of the Pannonian Basin Region Revealed by P-to-S Converted Seismic Waves

We present the results of P-to-S receiver function analysis to improve the 3D image of the sedimentary layer, the upper crust, and lower crust in the Pannonian Basin area. The Pannonian Basin hosts deep sedimentary depocentres superimposed on a complex basement structure and it is surrounded by mountain belts. We processed waveforms from 221 three-component broadband seismological stations. As a result of the dense station coverage, we were able to achieve so far unprecedented spatial resolution in determining the velocity structure of the crust. We applied a three-fold quality control process; the first two being applied to the observed waveforms and the third to the calculated radial receiver functions. This work is the first comprehensive receiver function study of the entire region. To prepare the inversions, we performed station-wise H-Vp/Vs grid search, as well as Common Conversion Point migration. Our main focus was then the S-wave velocity structure of the area, which we determined by the Neighborhood Algorithm inversion method at each station, where data were sub-divided into back-azimuthal bundles based on similar Ps delay times. The 1D, nonlinear inversions provided the depth of the discontinuities, shear-wave velocities and Vp/Vs ratios of each layer per bundle, and we calculated uncertainty values for each of these parameters. We then developed a 3D interpolation method based on natural neighbor interpolation to obtain the 3D crustal structure from the local inversion results. We present the sedimentary thickness map, the first Conrad depth map and an improved, detailed Moho map, as well as the first upper and lower crustal thickness maps obtained from receiver function analysis. The velocity jump across the Conrad discontinuity is estimated at less than 0.2 km/s over most of the investigated area. We also compare the new Moho map from our approach to simple grid search results and prior knowledge from other techniques. Our Moho depth map presents local variations in the investigated area: the crust-mantle boundary is at 20–26 km beneath the sedimentary basins, while it is situated deeper below the Apuseni Mountains, Transdanubian and North Hungarian Ranges (28–33 km), and it is the deepest beneath the Eastern Alps and the Southern Carpathians (40–45 km). These values reflect well the Neogene evolution of the region, such as crustal thinning of the Pannonian Basin and orogenic thickening in the neighboring mountain belts

Collision detection in volumetric subdivisions

La détection de collision dans des scènes complexes est un processus crucial dans les simulations physiques et les applications temps-réel. Si des performances suffisantes sont obtenues pour des scènes statiques, les approches classiques atteignent leurs limites lorsque la complexité des scènes augmente et lorsque les objets représentés deviennent déformables. Nous présentons dans cette thèse une approche générique, efficace et précise pour la détection de la collision dans le cadre de la simulation d'opérations chirurgicales. Les mobiles sont représentés par des maillages en déplacement dans un environnement déformable. Leurs sommets sont suivis dans une subdivision volumique convexe de cet espace environnant. Des particules sont continuellement lancées le long des arêtes des maillages pour détecter les collisions et suivre les contacts entre les mobiles et leur environnement. Cette méthode est couplée à un mécanisme de prédiction exploitant la cohérence temporelle et les relations d'adjacences topologiques pour réduire le nombre de tests géométriques nécessaires. Notre méthode gère la subdivision dynamique des mobiles et des zones de contact. Elle permet également de gérer efficacement les modifications géométriques et topologiques de l'environnement, telles que des coupures ou des déchirures, ou plus généralement l'ajout ou la suppression de matière. Nous expérimentons des simulations physiques basées sur la méthode des masse-ressort et du shape-matching et analysons les performances de notre méthode. Nous comparons également notre approche aux méthodes classiques basées sur des structures hiérarchiques.Collision detection in complex scenes is a critical process required for physical simulations and real-time applications. If good performance are achieved for static scenes, classical approaches reach their limits when the scene complexity increase and when the objects are deformable. We present a generic, efficient and accurate approach for collision detection which is adapted for surgery simulation. The moving objects are represented as meshes moving inside a deformable environment. The vertices are followed in a convex volumetric subdivision of the surrounding space. Particles are spanned along the edges of the meshes to detect collision and follow the contacts occuring between the moving object and its environment. This method is coupled with a forecast mechanism using temporal consistency and topological adjacency relation to reduce the required geometrical tests. Our method handles the dynamic subdivision of both the moving object and the contact area. It also allows to handle efficiently geometrical and topological changes of the environment, such as cuts, tears, or more generally any add or removal of material. We experiment physical simulation based on mass-spring and shape-matching physical models and analyse the performance of our method. We also compare our approach with classical methods based on a hierarchical structure

Collision detection in volumetric subdivisions

La détection de collision dans des scènes complexes est un processus crucial dans les simulations physiques et les applications temps-réel. Si des performances suffisantes sont obtenues pour des scènes statiques, les approches classiques atteignent leursCollision detection in complex scenes is a critical process required for physical simulations and real-time applications. If good performance are achieved for static scenes, classical approaches reach their limits when the scene complexity increase and w

Détection de collision dans des subdivisions volumiques

La détection de collision dans des scènes complexes est un processus crucial dans les simulations physiques et les applications temps-réel. Si des performances suffisantes sont obtenues pour des scènes statiques, les approches classiques atteignent leurs limites lorsque la complexité des scènes augmente et lorsque les objets représentés deviennent déformables. Nous présentons dans cette thèse une approche générique, efficace et précise pour la détection de la collision dans le cadre de la simulation d opérations chirurgicales. Les mobiles sont représentés par des maillages en déplacement dans un environnement déformable. Leurs sommets sont suivis dans une subdivision volumique convexe de cet espace environnant. Des particules sont continuellement lancées le long des arêtes des maillages pour détecter les collisions et suivre les contacts entre les mobiles et leur environnement. Cette méthode est couplée à un mécanisme de prédiction exploitant la cohérence temporelle et les relations d adjacences topologiques pour réduire le nombre de tests géométriques nécessaires. Notre méthode gère la subdivision dynamique des mobiles et des zones de contact. Elle permet également de gérer efficacement les modifications géométriques et topologiques de l environnement, telles que des coupures ou des déchirures, ou plus généralement l ajout ou la suppression de matière. Nous expérimentons des simulations physiques basées sur la méthode des masse-ressort et du shape-matching et analysons les performances de notre méthode. Nous comparons également notre approche aux méthodes classiques basées sur des structures hiérarchiques.Collision detection in complex scenes is a critical process required for physical simulations and real-time applications. If good performance are achieved for static scenes, classical approaches reach their limits when the scene complexity increase and when the objects are deformable. We present a generic, efficient and accurate approach for collision detection which is adapted for surgery simulation. The moving objects are represented as meshes moving inside a deformable environment. The vertices are followed in a convex volumetric subdivision of the surrounding space. Particles are spanned along the edges of the meshes to detect collision and follow the contacts occuring between the moving object and its environment. This method is coupled with a forecast mechanism using temporal consistency and topological adjacency relation to reduce the required geometrical tests. Our method handles the dynamic subdivision of both the moving object and the contact area. It also allows to handle efficiently geometrical and topological changes of the environment, such as cuts, tears, or more generally any add or removal of material. We experiment physical simulation based on mass-spring and shape-matching physical models and analyse the performance of our method. We also compare our approach with classical methods based on a hierarchical structure.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF