New patterns in high-speed granular flows

We report on new patterns in high-speed flows of granular materials obtained by means of extensive numerical simulations. These patterns emerge from the destabilization of unidirectional flows upon increase of mass holdup and inclination angle, and are characterized by complex internal structures including secondary flows, heterogeneous particle volume fraction, symmetry breaking and dynamically maintained order. In particular, we evidenced steady and fully developed "supported" flows, which consist of a dense core surrounded by a highly energetic granular gas. Interestingly, despite their overall diversity, these regimes are shown to obey a scaling law for the mass flow rate as a function of the mass holdup. This unique set of 3D flow regimes raises new challenges for extending the scope of current granular rheological models

Density of Spherically-Embedded Stiefel and Grassmann Codes

The density of a code is the fraction of the coding space covered by packing balls centered around the codewords. This paper investigates the density of codes in the complex Stiefel and Grassmann manifolds equipped with the chordal distance. The choice of distance enables the treatment of the manifolds as subspaces of Euclidean hyperspheres. In this geometry, the densest packings are not necessarily equivalent to maximum-minimum-distance codes. Computing a code's density follows from computing: i) the normalized volume of a metric ball and ii) the kissing radius, the radius of the largest balls one can pack around the codewords without overlapping. First, the normalized volume of a metric ball is evaluated by asymptotic approximations. The volume of a small ball can be well-approximated by the volume of a locally-equivalent tangential ball. In order to properly normalize this approximation, the precise volumes of the manifolds induced by their spherical embedding are computed. For larger balls, a hyperspherical cap approximation is used, which is justified by a volume comparison theorem showing that the normalized volume of a ball in the Stiefel or Grassmann manifold is asymptotically equal to the normalized volume of a ball in its embedding sphere as the dimension grows to infinity. Then, bounds on the kissing radius are derived alongside corresponding bounds on the density. Unlike spherical codes or codes in flat spaces, the kissing radius of Grassmann or Stiefel codes cannot be exactly determined from its minimum distance. It is nonetheless possible to derive bounds on density as functions of the minimum distance. Stiefel and Grassmann codes have larger density than their image spherical codes when dimensions tend to infinity. Finally, the bounds on density lead to refinements of the standard Hamming bounds for Stiefel and Grassmann codes.Comment: Two-column version (24 pages, 6 figures, 4 tables). To appear in IEEE Transactions on Information Theor

GPU-boosted online image matching

International audienceMatching feature points between images is a key point in many Computer Vision tasks. As the number of images increases, this rapidly becomes a bottleneck. We here present how to use the power of GPUs to obtain image matching in typically 20 ms for one thousand points. This speedup makes applications like interactive image matching possible. Such a portable system, dedicated to 3D large scale reconstruction, is reported

Statistical Criteria for Shape Fusion and Selection

International audience—Surface reconstruction from point clouds often relies on a primitive extraction step, that may be followed by a merging step because of a possible over-segmentation. We present two statistical criteria to decide whether or not two surfaces are to be considered as the same, and thus can be merged. They are based on the statistical tests of Kolmogorov-Smirnov and Mann-Whitney for comparing distributions. Moreover, computation time can be significantly cut down using a reduced sampling based on the Dvoretzky-Keifer-Wolfowitz inequality. The strength of our approach is that it relies in practice on a single intuitive parameter (homogeneous to a distance) and that it can be applied to any shape, including meshes, not just geometric primitives. It also enables the comparison of shapes of different kinds, providing a way to choose between different shape candidates. We show several applications of our method, experimenting geometric primitive (planeand cylinder) detection, selection and fusion, both on precise laser scans and noisy photogrammetric 3D data

Microvertebrates of the Lourinhã Formation (Late Jurassic, Portugal)

The Upper Jurassic of Portugal has been globally known for its microfossil vertebrate fauna thanks to the Konzentrat-Lagerstätte of the Guimarota mine, which provided thousands of bone fragments, isolated teeth, and even complete specimens. Other vertebrate microfossil assemblages have been studied around the world. Besides Guimarota, no other Portuguese Jurassic assemblage has been extensively studied. Hereby is presented a revision of the state of the art on Portuguese microvertebrate record, and the first microvertebrate studies on three localities from the Lourinhã Formation (Late Jurassic) hosted by a Portuguese institution; Porto das Barcas, Zimbral, and Valmitão has provided 2,497 microvertebrates skeletal remains and teeth, from which 824 specimens have been identified, described and assessed to the conservative-most taxa. The stratigraphy and sedimentology of the localities suggest that Porto das Barcas and Zimbral were floodplain mud deposits, and Valmitão was an oxbow lake mud deposit, with a slow rate of sedimentation. The remains have been attributed to fishes, amphibians, squamates, crocodylomorphs, and dinosaurs; but unfortunately, no mammaliaform material has been collected. Paleoecological analyses suggest Zimbral and Valmitão were dominated by a terrestrial fauna and more diverse than Porto das Barcas, dominated by an amphibious fauna. The Lourinhã Formation appears to have been closer to the shoreline than American localities in the Morrison and Cloverly Formations were, but more continental than Buenache and Las Hoyas localities (Spain) with swamp to lacustrine paleoenvironments. A detailed study on 125 crocodylomorph teeth from Valmitão support the presence of Goniopholididae, at least two Atoposauridae taxa, and Bernissartiidae in the Late Jurassic of Portugal, with a fauna either dominated by relative small individuals, either juveniles or adults or small taxa