6,141 research outputs found
Hydrostatic pressure induced Dirac semimetal in black phosphorus
Motivated by recent experimental observation of an hydrostatic pressure
induced transition from semiconductor to semimetal in black phosphorus [Chen et
al. in arXiv:1504.00125], we present the first principles calculation on the
pressure effect of the electronic structures of black phosphorus. It is found
that the band crossover and reversal at the Z point occur around the critical
pressure Pc1=1.23 Gpa, and the band inversion evolves into 4 twofold-degenerate
Dirac cones around the Z point, suggesting a 3D Dirac semimetal. With further
increasing pressure the Dirac cones in the Gamma-Z line move toward the Gamma
point and evolve into two hole-type Fermi pockets, and those in the Z-M lines
move toward the M point and evolve into 2 hole-type Fermi pockets up to P=4.0
Gpa. It demonstrates clearly that the Lifshitz transition occurs at
from semiconductor to 3D Dirac semimetal protected by the nonsymmorphic space
symmetry of bulk. This suggests the bright perspective of black phosphorus for
optoelectronic and electronic devices due to its easy modulation by pressure.Comment: 7 pages, 9 figures, and 2 table
Iron-Catalyzed Nitrene Insertion Reaction for Facile Construction of Amide Compounds
A facile method for the construction of amide compounds from aldehydes by an iron-catalyzed nitrene insertion reaction has been developed. Both aryl and aliphatic aldehydes can directly afford the corresponding amides with an iron(II)-terpyridine (tpy) complex formed in situ as catalyst, and PhI=NTs as nitrogen source under mild reaction conditions. An ESI-MS study revealed the formation of [Fe(tpy)NTs)]+ as a reaction intermediate. © Georg Thieme Verlag Stuttgart - New York.postprin
Attribute Equilibrium Dominance Reduction Accelerator (DCCAEDR) Based on Distributed Coevolutionary Cloud and Its Application in Medical Records
© 2013 IEEE. Aimed at the tremendous challenge of attribute reduction for big data mining and knowledge discovery, we propose a new attribute equilibrium dominance reduction accelerator (DCCAEDR) based on the distributed coevolutionary cloud model. First, the framework of N-populations distributed coevolutionary MapReduce model is designed to divide the entire population into N subpopulations, sharing the reward of different subpopulations' solutions under a MapReduce cloud mechanism. Because the adaptive balancing between exploration and exploitation can be achieved in a better way, the reduction performance is guaranteed to be the same as those using the whole independent data set. Second, a novel Nash equilibrium dominance strategy of elitists under the N bounded rationality regions is adopted to assist the subpopulations necessary to attain the stable status of Nash equilibrium dominance. This further enhances the accelerator's robustness against complex noise on big data. Third, the approximation parallelism mechanism based on MapReduce is constructed to implement rule reduction by accelerating the computation of attribute equivalence classes. Consequently, the entire attribute reduction set with the equilibrium dominance solution can be achieved. Extensive simulation results have been used to illustrate the effectiveness and robustness of the proposed DCCAEDR accelerator for attribute reduction on big data. Furthermore, the DCCAEDR is applied to solve attribute reduction for traditional Chinese medical records and to segment cortical surfaces of the neonatal brain 3-D-MRI records, and the DCCAEDR shows the superior competitive results, when compared with the representative algorithms
On Jensen’s inequality, Hölder’s inequality, and Minkowski’s inequality for dynamically consistent nonlinear evaluations
Detection of Fatigue Crack Propagation in Steel Using Magnetic Measurements
For structural components which are exposed to cyclic stresses, fatigue damage could lead to a catastrophic failure. In nuclear pressure vessel systems where A533B steel is widely used as structural material, cyclic thermal expansions often create a low-cycle fatigue condition. The evaluation of fatigue damage therefore is critically important and nondestructive evaluation of fatigue damage is highly desirable from the viewpoint of both safer and longer operation lifetime
Improved Hydrogen Release from Ammonia Borane Confined in Microporous Carbon with Narrow Pore Size Distribution
This is the author accepted manuscript. The final version is available from Royal Society of Chemistry via the DOI in this record.Ammonia borane is a promising hydrogen storage candidate due to its high hydrogen capacity and good stability at room temperature, but there are still some barriers to be overcome before it can be used for practical applications. We present the hydrogen release from ammonia borane confined in templated microporous carbon with extremely narrow pore size distribution. Compared with neat ammonia borane, hydrogen release temperature of ammonia borane confined in microporous carbon with pore size of 1.05 nm is significantly reduced, starting at 50 C and with peak dehydrogenation temperature centred at 86 C. The dehydrogenation kinetics of ammonia borane confined in templated microporous carbon is significantly improved and by-products including ammonia and diborane are also completely prohibited without any catalysts involved. The remarkable fast hydrogen release rate and high hydrogen storage capacity from ammonia borane confined in microporous carbon is due to the dramatic decrease in the activation energy of ammonia borane. This is so far the best performance among porous carbon materials used as the confinement scaffolds for ammonia borane in hydrogen storage, making AB confined in microporous carbon a very promising candidate for hydrogen storage.The financial support by the Royal Society and University of Exeter is greatly acknowledged
Decadal link between longitudinal morphological changes in branching channels of Yangtze Estuary and movement of the offshore depo-center
In estuaries, the morphology of inland and offshore areas usually evolves synergistically. This study examines the decadal link between longitudinal changes in morphology of branching channels and movement of the offshore depo-center (where sediment deposition rate is maximum) of the Yangtze River estuary, under intense human interference. Integrated data analysis is provided on morphology, runoff discharge, and ebb partition ratio from 1950 to 2017. Channel-volume reductions and change rates between isobaths in branching channels reflect the impact of estuarine engineering projects. Ebb partition ratio and duration of discharge ≥ 60 000 m3 s-1 act as proxies for the water excavating force in branching channels and runoff intensity. It is found that deposition occurs in the lower/upper sub-reaches (or further downstream/upstream channels) of the inland north/south branching channels, and the offshore depo-center moves southward or southeastward, as runoff intensity grows; the reverse occurs as runoff intensity declines. This is because the horizontal circumfluence in the Yangtze estuary rotates clockwise as ebb partition ratios of the north/south branching channels increase/decrease for increasing runoff, and conversely rotates anticlockwise for decreasing runoff. Land reclamation activities, the Deepwater Channel Project, and the Qingcaosha Reservoir have impacted greatly on longitudinal changes of morphology in the North Branch and the South Passage and on ebb partition ratio variations in the North/South Channel and the North/South Passage. Dam-induced runoff flattening has enhanced deposition in the upper/lower sub-reaches of the north/south branching channels and caused northward movement of the offshore depo-center, except in areas affected by estuarine engineering projects. Dam-induced longitudinal evolution of branching channel morphology and offshore depo-center movement will likely persist in the future, given the ongoing construction of large cascade dams in the upper Yangtze and the completion of major projects in the Yangtze estuary
On the Kinematic Signature of the Galactic Warp As Revealed by the LAMOST-TGAS Data
Using a sample of about 123,000 stars with accurate 3D velocity measurements from the LAMOST-TGAS data, we confirm the kinematic signature of the Galactic warp recently found by Schonrich & Dehnen. The data reveal a clear trend of increasing mean vertical velocity Vz as a function of absolute vertical angular momentum Lz and azimuthal velocity Vφ for guiding center radius Rg between 6.0 and 10.5 kpc. The trend is consistent with a largescale Galactic warp. Similar to Schonrich & Dehnen, we also find a wave-like pattern of Vz versus Lz with an amplitude of ∼0.9 km s-1 on a scale of ∼2.0 kpc, which could arise from bending waves or a winding warp. Finally, we confirm a prominent, localized peak in Vz near Lz ∼ 2150 kpc km s-1 (corresponding to Rg ∼ 9 kpc and Vφ ∼ 255 km s-1). The additional line-of-sight velocity information from LAMOST reveals that stars in this feature have a large, inward radial velocity of VR ∼ -13.33 ± 0.59 km s-1 and a small radial velocity dispersion of σR ∼ 25.27 ± 0.89 km s-1, suggesting that a stellar stream gives rise to this feature
H-alpha +[NII] Observations of the HII Regions in M81
In a first of a series of studies of the H-alpha + [NII] emission from nearby
spiral galaxies, we present measurements of H-alpha + [NII] emission from HII
regions in M81. Our method uses large-field-CCD images and long-slit spectra,
and is part of the ongoing Beijing-Arizona-Taipei-Connecticut Sky Survey. The
CCD images are taken with the NAOC 0.6/0.9m f/3 Schmidt telescope at the
Xinglong Observing Station, using a multicolor filter set. Spectra of 10 of the
brightest HII regions are obtained using the NAOC 2.16m telescope with a Tek
1024 X 1024 CCD. The continua of the spectra are calibrated by flux-calibrated
images taken from the Schmidt observations. We determine the continuum
component of our H-alpha + [NII] image via interpolation from the more
accurately-measured backgrounds (M81 starlight) obtained from the two
neighboring (in wavelength) BATC filter images. We use the calibrated fluxes of
H-alpha + [NII] emission from the spectra to normalize this interpolated,
continuum-subtracted H-alpha + [NII] image. We estimate the zero point
uncertainty of the measured H-alpha + [NII] emission flux to be 8%. A
catalogue of H-alpha + [NII] fluxes for 456 HII regions is provided, with those
fluxes are on a more consistent linear scale than previously available. The
logarithmically-binned H-alpha + [NII] luminosity function of HII regions is
found to have slope = -0.70, consistent with previous results (which
allowed ). From the overall H-alpha + [NII] luminosity
of the HII regions, the star formation rate of M81 is found to be , modulo uncertainty with extinction corrections.Comment: 18 pages, 7 figures, accepted for publication in the Astronomical
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