1,666 research outputs found
Cosmological constraints on holographic dark energy models under the energy conditions
We study the holographic and agegraphic dark energy models without
interaction using the latest observational Hubble parameter data (OHD), the
Union2.1 compilation of type Ia supernovae (SNIa), and the energy conditions.
Scenarios of dark energy are distinguished by the cut-off of cosmic age,
conformal time, and event horizon. The best-fit value of matter density for the
three scenarios almost steadily located at by the joint
constraint. For the agegraphic models, they can be recovered to the standard
cosmological model when the constant which presents the fraction of dark
energy approaches to infinity. Absence of upper limit of by the joint
constraint demonstrates the recovery possibility. Using the fitted result, we
also reconstruct the current equation of state of dark energy at different
scenarios, respectively. Employing the model criteria
, we find that conformal time model is the worst,
but they can not be distinguished clearly. Comparing with the observational
constraints, we find that SEC is fulfilled at redshift with confidence level. We also find that NEC gives a meaningful
constraint for the event horizon cut-off model, especially compared with OHD
only. We note that the energy condition maybe could play an important role in
the interacting models because of different degeneracy between and
constant .Comment: 8 pages, 4 figures, accepted for publication in PR
Hierarchical Codebook-based Beam Training for Extremely Large-Scale Massive MIMO
Extremely large-scale multiple-input multiple-output (XL-MIMO) promises to
provide ultrahigh data rates in millimeter-wave (mmWave) and Terahertz (THz)
spectrum. However, the spherical-wavefront wireless transmission caused by
large aperture array presents huge challenges for channel state information
(CSI) acquisition and beamforming. Two independent parameters (physical angles
and transmission distance) should be simultaneously considered in XL-MIMO
beamforming, which brings severe overhead consumption and beamforming
degradation. To address this problem, we exploit the near-field channel
characteristic and propose two low-overhead hierarchical beam training schemes
for near-field XL-MIMO system. Firstly, we project near-field channel into
spatial-angular domain and slope-intercept domain to capture detailed
representations. Then we point out three critical criteria for XL-MIMO
hierarchical beam training. Secondly, a novel spatial-chirp beam-aided codebook
and corresponding hierarchical update policy are proposed. Thirdly, given the
imperfect coverage and overlapping of spatial-chirp beams, we further design an
enhanced hierarchical training codebook via manifold optimization and
alternative minimization. Theoretical analyses and numerical simulations are
also displayed to verify the superior performances on beamforming and training
overhead.Comment: This work has been submitted to the IEEE journal for possible
publication. Copyright may be transferred without notice, after which this
version may no longer be accessibl
Symmetric non-Hermitian skin effect with emergent nonlocal correspondence
The non-Hermitian skin effect (NHSE) refers to that an extensive number of
eigenstates of a non-Hermitian system are localized in open boundaries. Here we
predict a universal phenomenon that with local particle-hole(-like) symmetry
(PHS) the skin modes must be equally distributed on different boundaries,
manifesting a novel nonlocalization of the local PHS, which is unique to
non-Hermitian systems. We develop a generic theory for the emergent nonlocal
symmetry-protected NHSE by connecting the non-Hermitian system to an extended
Hermitian Hamiltonian in a quadruplicate Hilbert space, which maps the skin
modes to the topological zero modes and the PHS to an emergent nonlocal
symmetry in the perspective of many body physics. The predicted NHSE is robust
against perturbations. We propose optical Raman lattice models to observe the
predicted phenomena in all physical dimensions, which are accessible with
cold-atom experiments.Comment: 5+9 pages, 3+4 figure
1-(4-Methylbenzoyl)-3-[5-(4-pyridyl)-1,3,4-thiadiazol-2-yl]urea
In the title compound, C16H13N5O2S, the five non-H atoms of the urea linkage adopt a planar configuration owing to the presence of an intramolecular N—H⋯O hydrogen bond. The maximum deviation from planarity is 0.022 (2) Å. The thiadiazole and pyridine heterocyclic rings are close to being coplanar, with a dihedral angle of 6.7 (2)° between their mean planes. Intermolecular N—H⋯O hydrogen bonds link two neighbouring molecules into centrosymmetric R
2
2(8) dimers. Four C atoms and the attached H atoms of the benzene ring are disordered over two positions of equal occupancy
The continual presence of C3d but not IgG glomerular capillary deposition in stage I idiopathic membranous nephropathy in patients receiving corticosteroid treatment
BACKGROUND: Pathologic diagnosis of stage I idiopathic membranous nephropathy (MN-I) requires electron microscopy or immunohistochemistry that shows a glomerular capillary staining pattern of IgG and C3. However, it is not uncommon that renal biopsy did not obtain sufficient material for electron microscopy and that IgG and C3 staining in glomeruli largely lost at biopsy due to corticosteroid treatment. Since C3d is one of the final degradation products of C3 that is more stable in vivo, we determine if C3d staining could be used as a novel immunohistochemical marker for MN-I. METHODS AND RESULTS: 74 MN-I patients with electron microscopy proven MN-I were examined by immunoperoxidase staining of C3d. Intensive C3d staining was present in glomerular capillary like the staining pattern of IgG and C3 in MN-I. Importantly, in 40 MN-I patients who underwent corticosteroid treatment at biopsy the intensity and glomerular capillary pattern of C3d staining remained largely intact while the staining for IgG had substantially reduced and the pattern of glomerular capillary staining became unrecognizable. CONCLUSIONS: C3d glomerular capillary staining may be a novel marker for pathologic diagnosis of MN-I that is continuously present at biopsy in patient who has received corticosteroid treatment. VIRTUAL SLIDES: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/212078007573447
(E)-N′-(4-Methoxybenzylidene)benzohydrazide
In the title molecule, C15H14N2O2, the dihedral angle between the benzene rings is 5.93 (17)°. In the crystal, intermolecular N—H⋯O hydrogen bonds link the molecules into chains propagating in [010]
Simulation of Microstructure during Laser Rapid Forming Solidification Based on Cellular Automaton
The grain microstructure of molten pool during the solidification of TC4 titanium alloy in the single point laser cladding was investigated based on the CAFE model which is the cellular automaton (CA) coupled with the finite element (FE) method. The correct temperature field is the prerequisite for simulating the grain microstructure during the solidification of the molten pool. The model solves the energy equation by the FE method to simulate the temperature distribution in the molten pool of the single point laser cladding. Based on the temperature field, the solidification microstructure of the molten pool is also simulated with the CAFE method. The results show that the maximum temperature in the molten pool increases with the laser power and the scanning rate. The laser power has a larger influence on the temperature distribution of the molten pool than the scanning rate. During the solidification of the molten pool, the heat at the bottom of the molten pool transfers faster than that at the top of the molten pool. The grains rapidly grow into the molten pool, and then the columnar crystals are formed. This study has a very important significance for improving the quality of the structure parts manufactured through the laser cladding forming
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