30,119 research outputs found
Improved half-metallic ferromagnetism of transition-metal pnictides and chalcogenides calculated with a modified Becke-Johnson exchange potential
We use a density-functional-theory (DFT) approach with a modified
Becke-Johnson exchange plus local density approximation (LDA) correlation
potential (mBJLDA) [semi-local, orbital-independent, producing accurate
semiconductor gaps. see F. Tran and P. Blaha, Phys. Rev. Lett. 102, 226401
(2009)] to investigate the electronic structures of zincblende transition-metal
(TM) pnictides and chalcogenides akin to semiconductors. Our results show that
this potential does not yield visible changes in wide TM d-t_{2g} bands near
the Fermi level, but makes the occupied minority-spin p-bands lower by
0.25~0.35 eV and the empty (or nearly empty) minority-spin e_g bands across the
Fermi level higher by 0.33~0.73 eV. Consequently, mBJLDA, having no
atom-dependent parameters, makes zincblende MnAs become a truly half-metallic
(HM) ferromagnet with a HM gap (the key parameter) 0.318eV, being consistent
with experiment. For zincblende MnSb, CrAs, CrSb, CrSe, or CrTe, the HM gap is
enhanced by 19~56% compared to LDA and generalized gradient approximation
results. The improved HM ferromagnetism can be understood in terms of the
mBJLDA-enhanced spin exchange splitting.Comment: 6 pages, 5 figure
Quark Condensates in Nuclear Matter in the Global Color Symmetry Model of QCD
With the global color symmetry model being extended to finite chemical
potential, we study the density dependence of the local and nonlocal scalar
quark condensates in nuclear matter. The calculated results indicate that the
quark condensates increase smoothly with the increasing of nuclear matter
density before the critical value (about 12) is reached. It also
manifests that the chiral symmetry is restored suddenly as the density of
nuclear matter reaches its critical value. Meanwhile, the nonlocal quark
condensate in nuclear matter changes nonmonotonously against the space-time
distance among the quarks.Comment: 15 pages, 3 figure
Reevaluation of the density dependence of nucleon radius and mass in the global color symmetry model of QCD
With the global color symmetry model (GCM) at finite chemical potential, the
density dependence of the bag constant, the total energy and the radius of a
nucleon in nuclear matter is investigated. A relation between the nuclear
matter density and the chemical potential with the action of QCD being taken
into account is obtained. A maximal nuclear matter density for the existence of
the bag with three quarks confined within is given. The calculated results
indicate that, before the maximal density is reached, the bag constant and the
total energy of a nucleon decrease, and the radius of a nucleon increases
slowly, with the increasing of the nuclear matter density. As the maximal
nuclear matter density is reached, the mass of the nucleon vanishes and the
radius becomes infinite suddenly. It manifests that a phase transition from
nucleons to quarks takes place.Comment: 18 pages, 3 figure
Low-mass Active Galactic Nuclei on the Fundamental Plane of Black Hole Activity
It is widely known that in active galactic nuclei (AGNs) and black hole X-ray
binaries (BHXBs), there is a tight correlation among their radio luminosity
(), X-ray luminosity () and BH mass (\mbh), the so-called
`fundamental plane' (FP) of BH activity. Yet the supporting data are very
limited in the \mbh regime between stellar mass (i.e., BHXBs) and
10\,\msun\ (namely, the lower bound of supermassive BHs in common
AGNs). In this work, we developed a new method to measure the 1.4 GHz flux
directly from the images of the VLA FIRST survey, and apply it to the type-1
low-mass AGNs in the \cite{2012ApJ...755..167D} sample. As a result, we
obtained 19 new low-mass AGNs for FP research with both \mbh\ estimates (\mbh
\approx 10^{5.5-6.5}\,\msun), reliable X-ray measurements, and (candidate)
radio detections, tripling the number of such candidate sources in the
literature.Most (if not all) of the low-mass AGNs follow the standard
radio/X-ray correlation and the universal FP relation fitted with the combined
dataset of BHXBs and supermassive AGNs by \citet{2009ApJ...706..404G}; the
consistency in the radio/X-ray correlation slope among those accretion systems
supports the picture that the accretion and ejection (jet) processes are quite
similar in all accretion systems of different \mbh. In view of the FP relation,
we speculate that the radio loudness (i.e., the luminosity ratio
of the jet to the accretion disk) of AGNs depends not only on Eddington ratio,
but probably also on \mbh.Comment: ApJ accepte
TensorLayer: A Versatile Library for Efficient Deep Learning Development
Deep learning has enabled major advances in the fields of computer vision,
natural language processing, and multimedia among many others. Developing a
deep learning system is arduous and complex, as it involves constructing neural
network architectures, managing training/trained models, tuning optimization
process, preprocessing and organizing data, etc. TensorLayer is a versatile
Python library that aims at helping researchers and engineers efficiently
develop deep learning systems. It offers rich abstractions for neural networks,
model and data management, and parallel workflow mechanism. While boosting
efficiency, TensorLayer maintains both performance and scalability. TensorLayer
was released in September 2016 on GitHub, and has helped people from academia
and industry develop real-world applications of deep learning.Comment: ACM Multimedia 201
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