78,769 research outputs found
Spin and Charge Structure of the Surface States in Topological Insulators
We investigate the spin and charge densities of surface states of the
three-dimensional topological insulator , 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
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
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
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
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
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
We derive tight expressions for the maximum
number of -faces, , of the
Minkowski sum, , of three -dimensional convex polytopes , and in ,
as a function of the number of vertices of the polytopes, for any .
Expressing the Minkowski sum as a section of the Cayley polytope of its summands, counting the -faces of reduces to counting the -faces of 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 -polytopes in , where .
For , the maximum values are attained when
, and are -polytopes, whose vertex sets are chosen appropriately from three distinct -dimensional moment-like curves
QuickCSG: Fast Arbitrary Boolean Combinations of N Solids
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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