36,026 research outputs found
Observation of Weyl nodes in TaAs
In 1929, H. Weyl proposed that the massless solution of Dirac equation
represents a pair of new type particles, the so-called Weyl fermions [1].
However the existence of them in particle physics remains elusive for more than
eight decades. Recently, significant advances in both topological insulators
and topological semimetals have provided an alternative way to realize Weyl
fermions in condensed matter as an emergent phenomenon: when two non-degenerate
bands in the three-dimensional momentum space cross in the vicinity of Fermi
energy (called as Weyl nodes), the low energy excitation behaves exactly the
same as Weyl fermions. Here, by performing soft x-ray angle-resolved
photoemission spectroscopy measurements which mainly probe bulk band structure,
we directly observe the long-sought-after Weyl nodes for the first time in
TaAs, whose projected locations on the (001) surface match well to the Fermi
arcs, providing undisputable experimental evidence of existence of Weyl fermion
quasiparticles in TaAs.Comment: 10 pages, 4 figures, see also related papers on TaAs
arXiv:1501.00060, arXiv:1502.0468
On the geometry of C^3/D_27 and del Pezzo surfaces
We clarify some aspects of the geometry of a resolution of the orbifold X =
C3/D_27, the noncompact complex manifold underlying the brane quiver standard
model recently proposed by Verlinde and Wijnholt. We explicitly realize a map
between X and the total space of the canonical bundle over a degree 1 quasi del
Pezzo surface, thus defining a desingularization of X. Our analysis relys
essentially on the relationship existing between the normalizer group of D_27
and the Hessian group and on the study of the behaviour of the Hesse pencil of
plane cubic curves under the quotient.Comment: 23 pages, 5 figures, 2 tables. JHEP style. Added references.
Corrected typos. Revised introduction, results unchanged
From Multiview Image Curves to 3D Drawings
Reconstructing 3D scenes from multiple views has made impressive strides in
recent years, chiefly by correlating isolated feature points, intensity
patterns, or curvilinear structures. In the general setting - without
controlled acquisition, abundant texture, curves and surfaces following
specific models or limiting scene complexity - most methods produce unorganized
point clouds, meshes, or voxel representations, with some exceptions producing
unorganized clouds of 3D curve fragments. Ideally, many applications require
structured representations of curves, surfaces and their spatial relationships.
This paper presents a step in this direction by formulating an approach that
combines 2D image curves into a collection of 3D curves, with topological
connectivity between them represented as a 3D graph. This results in a 3D
drawing, which is complementary to surface representations in the same sense as
a 3D scaffold complements a tent taut over it. We evaluate our results against
truth on synthetic and real datasets.Comment: Expanded ECCV 2016 version with tweaked figures and including an
overview of the supplementary material available at
multiview-3d-drawing.sourceforge.ne
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