78,769 research outputs found

    Spin and Charge Structure of the Surface States in Topological Insulators

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    We investigate the spin and charge densities of surface states of the three-dimensional topological insulator Bi2Se3Bi_2Se_3, starting from the continuum description of the material [Zhang {\em et al.}, Nat. Phys. 5, 438 (2009)]. The spin structure on surfaces other than the 111 surface has additional complexity because of a misalignment of the contributions coming from the two sublattices of the crystal. For these surfaces we expect new features to be seen in the spin-resolved ARPES experiments, caused by a non-helical spin-polarization of electrons at the individual sublattices as well as by the interference of the electron waves emitted coherently from two sublattices. We also show that the position of the Dirac crossing in spectrum of surface states depends on the orientation of the interface. This leads to contact potentials and surface charge redistribution at edges between different facets of the crystal.Comment: Use the correct spin operator. Changes affect the surface states spin structure, but not the spectru

    Spin and charge structure of the surface states in topological insulators

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    pre-printWe investigate the spin and charge densities of surface states of the three-dimensional topological insulator Bi2Se3, starting from the continuum description of the material [Zhang et al., Nat. Phys. 5, 438 (2009)]. The spin structure on surfaces other than the (111) surface has additional complexity because of a misalignment of the contributions coming from the two sublattices of the crystal. For these surfaces we expect new features to be seen in the spin-resolved angular resolved photoemission spectroscopy (ARPES) experiments, caused by a nonhelical spin polarization of electrons at the individual sublattices as well as by the interference of the electron waves emitted coherently from two sublattices. We also show that the position of the Dirac crossing in the spectrum of the surface states depends on the orientation of the interface. This leads to contact potentials and surface charge redistribution at edges between different facets of the crystal

    The space of ultrametric phylogenetic trees

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    The reliability of a phylogenetic inference method from genomic sequence data is ensured by its statistical consistency. Bayesian inference methods produce a sample of phylogenetic trees from the posterior distribution given sequence data. Hence the question of statistical consistency of such methods is equivalent to the consistency of the summary of the sample. More generally, statistical consistency is ensured by the tree space used to analyse the sample. In this paper, we consider two standard parameterisations of phylogenetic time-trees used in evolutionary models: inter-coalescent interval lengths and absolute times of divergence events. For each of these parameterisations we introduce a natural metric space on ultrametric phylogenetic trees. We compare the introduced spaces with existing models of tree space and formulate several formal requirements that a metric space on phylogenetic trees must possess in order to be a satisfactory space for statistical analysis, and justify them. We show that only a few known constructions of the space of phylogenetic trees satisfy these requirements. However, our results suggest that these basic requirements are not enough to distinguish between the two metric spaces we introduce and that the choice between metric spaces requires additional properties to be considered. Particularly, that the summary tree minimising the square distance to the trees from the sample might be different for different parameterisations. This suggests that further fundamental insight is needed into the problem of statistical consistency of phylogenetic inference methods.Comment: Minor changes. This version has been published in JTB. 27 pages, 9 figure

    The Immune Overreaction Phenomena in Severe Sars-cov-2 Human Infections

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    The immunology of Sars-cov-2 human infection is known to be complex. One of the facets   of its complexity  is the occurrence  of immune over reaction phenomena  in its severe forms. Such forms stands as  a challenge for laboratory diagnostics and clinicians due its further complexity. The objective of the present mini-review was to explore these immune over-reaction phenomena [IORP ]among the severe infection forms .The noted IORP in severe  covid-19 were as;  two,the innate immno-thrombi [microthrombi]  and the hyper-cytokine-mia[cytokine storm],one cross-road IORP as an unrestrained activation of complement system and two adaptive IORP as an autoimmune phenocopy[ Neutralizing autoantibody producing B cell autoimmune pheno-copy of the type I Interferons ] as well as the Viral sensor [ Dynamics of the MAIT immune cells ]. These phenomena  are resolved on reaching  the possible  case  recovery. Keywords: Adaptive ,cross-road ,innate ,immune ,over-reaction, phenomena ,sars-cov-2. DOI: 10.7176/JHMN/85-09 Publication date: January 31st 202

    QuickCSG: Fast Arbitrary Boolean Combinations of N Solids

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    QuickCSG computes the result for general N-polyhedron boolean expressions without an intermediate tree of solids. We propose a vertex-centric view of the problem, which simplifies the identification of final geometric contributions, and facilitates its spatial decomposition. The problem is then cast in a single KD-tree exploration, geared toward the result by early pruning of any region of space not contributing to the final surface. We assume strong regularity properties on the input meshes and that they are in general position. This simplifying assumption, in combination with our vertex-centric approach, improves the speed of the approach. Complemented with a task-stealing parallelization, the algorithm achieves breakthrough performance, one to two orders of magnitude speedups with respect to state-of-the-art CPU algorithms, on boolean operations over two to dozens of polyhedra. The algorithm also outperforms GPU implementations with approximate discretizations, while producing an output without redundant facets. Despite the restrictive assumptions on the input, we show the usefulness of QuickCSG for applications with large CSG problems and strong temporal constraints, e.g. modeling for 3D printers, reconstruction from visual hulls and collision detection

    The International Urban Energy Balance Models Comparison Project: First Results from Phase 1

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    A large number of urban surface energy balance models now exist with different assumptions about the important features of the surface and exchange processes that need to be incorporated. To date, no com- parison of these models has been conducted; in contrast, models for natural surfaces have been compared extensively as part of the Project for Intercomparison of Land-surface Parameterization Schemes. Here, the methods and first results from an extensive international comparison of 33 models are presented. The aim of the comparison overall is to understand the complexity required to model energy and water exchanges in urban areas. The degree of complexity included in the models is outlined and impacts on model performance are discussed. During the comparison there have been significant developments in the models with resulting improvements in performance (root-mean-square error falling by up to two-thirds). Evaluation is based on a dataset containing net all-wave radiation, sensible heat, and latent heat flux observations for an industrial area in Vancouver, British Columbia, Canada. The aim of the comparison is twofold: to identify those modeling ap- proaches that minimize the errors in the simulated fluxes of the urban energy balance and to determine the degree of model complexity required for accurate simulations. There is evidence that some classes of models perform better for individual fluxes but no model performs best or worst for all fluxes. In general, the simpler models perform as well as the more complex models based on all statistical measures. Generally the schemes have best overall capability to model net all-wave radiation and least capability to model latent heat flux

    The maximum number of faces of the Minkowski sum of three convex polytopes

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    We derive tight expressions for the maximum number of kk-faces, 0kd10\le{}k\le{}d-1, of the Minkowski sum, P1+P2+P3P_1+P_2+P_3, of three dd-dimensional convex polytopes P1P_1, P2P_2 and P3P_3 in Rd\reals^d, as a function of the number of vertices of the polytopes, for any d2d\ge{}2. Expressing the Minkowski sum as a section of the Cayley polytope C\mathcal{C} of its summands, counting the kk-faces of P1+P2+P3P_1+P_2+P_3 reduces to counting the (k+2)(k+2)-faces of C\mathcal{C} which meet the vertex sets of the three polytopes. In two dimensions our expressions reduce to known results, while in three dimensions, the tightness of our bounds follows by exploiting known tight bounds for the number of faces of rr dd-polytopes in Rd\reals^d, where rdr\ge d. For d4d\ge{}4, the maximum values are attained when P1P_1, P2P_2 and P3P_3 are dd-polytopes, whose vertex sets are chosen appropriately from three distinct dd-dimensional moment-like curves

    QuickCSG: Fast Arbitrary Boolean Combinations of N Solids

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    QuickCSG computes the result for general N-polyhedron boolean expressions without an intermediate tree of solids. We propose a vertex-centric view of the problem, which simplifies the identification of final geometric contributions, and facilitates its spatial decomposition. The problem is then cast in a single KD-tree exploration, geared toward the result by early pruning of any region of space not contributing to the final surface. We assume strong regularity properties on the input meshes and that they are in general position. This simplifying assumption, in combination with our vertex-centric approach, improves the speed of the approach. Complemented with a task-stealing parallelization, the algorithm achieves breakthrough performance, one to two orders of magnitude speedups with respect to state-of-the-art CPU algorithms, on boolean operations over two to dozens of polyhedra. The algorithm also outperforms GPU implementations with approximate discretizations, while producing an output without redundant facets. Despite the restrictive assumptions on the input, we show the usefulness of QuickCSG for applications with large CSG problems and strong temporal constraints, e.g. modeling for 3D printers, reconstruction from visual hulls and collision detection
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