15,055 research outputs found
Doubled Conformal Compactification
We use Weyl transformations between the Minkowski spacetime and dS/AdS
spacetime to show that one cannot well define the electrodynamics globally on
the ordinary conformal compactification of the Minkowski spacetime (or dS/AdS
spacetime), where the electromagnetic field has a sign factor (and thus is
discountinuous) at the light cone. This problem is intuitively and clearly
shown by the Penrose diagrams, from which one may find the remedy without too
much difficulty. We use the Minkowski and dS spacetimes together to cover the
compactified space, which in fact leads to the doubled conformal
compactification. On this doubled conformal compactification, we obtain the
globally well-defined electrodynamics.Comment: 14 pages, 4 figure
Time domain analysis of superradiant instability for the charged stringy black hole-mirror system
It has been proved that the charged stringy black holes are stable under the
perturbations of massive charged scalar fields. However, superradiant
instability can be generated by adding the mirror-like boundary condition to
the composed system of charged stringy black hole and scalar field. The
unstable boxed quasinormal modes have been calculated by using both analytical
and numerical method. In this paper, we further provide a time domain analysis
by performing a long time evolution of charged scalar field configuration in
the background of the charged stringy black hole with the mirror-like boundary
condition imposed. We have used the ingoing Eddington-Finkelstein coordinates
to derive the evolution equation, and adopted Pseudo-spectral method and the
forth-order Runge-Kutta method to evolve the scalar field with the initial
Gaussian wave packet. It is shown by our numerical scheme that Fourier
transforming the evolution data coincides well with the unstable modes computed
from frequency domain analysis. The existence of the rapid growth mode makes
the charged stringy black hole a good test ground to study the nonlinear
development of superradiant instability.Comment: 7 pages, 6 figures, and 5 tables. References adde
The Quasi-normal Modes of Charged Scalar Fields in Kerr-Newman black hole and Its Geometric Interpretation
It is well-known that there is a geometric correspondence between
high-frequency quasi-normal modes (QNMs) and null geodesics (spherical photon
orbits). In this paper, we generalize such correspondence to charged scalar
field in Kerr-Newman space-time. In our case, the particle and black hole are
all charged, so one should consider non-geodesic orbits. Using the WKB
approximation, we find that the real part of quasi-normal frequency corresponds
to the orbits frequency, the imaginary part of the frequency corresponds to the
Lyapunov exponent of these orbits and the eigenvalue of angular equation
corresponds to carter constant. From the properties of the imaginary part of
quasi-normal frequency of charged massless scalar field, we can still find that
the QNMs of charged massless scalar field possess the zero damping modes in
extreme Kerr-Newman spacetime under certain condition which has been fixed in
this paper.Comment: 30 pages, many figures, to appear in JHE
Serum cystatin C and chemerin levels in diabetic retinopathy
Peer reviewedPublisher PD
The origin of p-type conduction in (P, N) co-doped ZnO
P mono-doped and (P, N) co-doped ZnO are investigated by the first-principles
calculations. It is found that substitutive P defect forms a deep acceptor
level at O site (PO) and it behaves as a donor at Zn site (PZn), while
interstitial P (Pi) is amphoteric. Under equilibrium conditions, these defects
contribute little to the p-type conductivity of ZnO samples since the formation
energy of PZn is much lower than that of Pi or PO when EF is below mid-gap (a
prerequisite p-type condition). Zinc vacancies (VZn) and PZn-2VZn complex are
demonstrated to be shallow acceptors with ionization energies around 100 meV,
but they are easily compensated by PZn defect. Fortunately, PZn-4NO complexes
may have lower formation energy than that of PZn under Zn rich condition by
proper choices of P and N sources. In addition, the neutral PZn-3NO passive
defects may form an impurity band right above the valence band maximum of ZnO
as in earlier reported (Ga,N) or (Zr,N) doped ZnO. This significantly reduces
the acceptor level of PZn-4NO complexes, and helps improving the p-type
conductivity in ZnO.Comment: 25 pages, 7 figure
Semantic Graph Convolutional Networks for 3D Human Pose Regression
In this paper, we study the problem of learning Graph Convolutional Networks
(GCNs) for regression. Current architectures of GCNs are limited to the small
receptive field of convolution filters and shared transformation matrix for
each node. To address these limitations, we propose Semantic Graph
Convolutional Networks (SemGCN), a novel neural network architecture that
operates on regression tasks with graph-structured data. SemGCN learns to
capture semantic information such as local and global node relationships, which
is not explicitly represented in the graph. These semantic relationships can be
learned through end-to-end training from the ground truth without additional
supervision or hand-crafted rules. We further investigate applying SemGCN to 3D
human pose regression. Our formulation is intuitive and sufficient since both
2D and 3D human poses can be represented as a structured graph encoding the
relationships between joints in the skeleton of a human body. We carry out
comprehensive studies to validate our method. The results prove that SemGCN
outperforms state of the art while using 90% fewer parameters.Comment: In CVPR 2019 (13 pages including supplementary material). The code
can be found at https://github.com/garyzhao/SemGC
1-[6-(9H-Carbazol-9-yl)hexyl]-2-phenyl-1H-benzimidazole
The molecule of the title compound, C31H29N3, contains a hexyl chain, a coordination unit (benzimidazole) and a functional group (carbazole). The benzimidazole ring is not coplanar with either the phenyl ring or the carbazole system, making dihedral angles of 43.26 (3) and 39.03 (2)°, respectively. The dihedral angle between the phenyl ring and the carbazole system is 24.42 (3)°. The hexyl Cβ atom (with respect to benzimidazole) deviates by 1.124 (2) Å from the benzimidazole plane, although the Cα atom lies in the plane. The hexyl Cβ atom (with respect to carbazole) deviates by 1.315 (1) Å from the carbazole plane, although the Cα atom lies in the plane. The crystal structure is stabilized by intermolecular C—H⋯π interactions
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