11,641 research outputs found
Anisotropic flow of Pb+Pb = 5.02 TeV from A Multi-Phase Transport Model
Anisotropic flow is an important observable in the study of the Quark-Gluon
Plasma that is expected to be formed in heavy-ion collisions. With a multiphase
transport (AMPT) model we investigate the elliptic(\emph{v}_{2}),
triangular(\emph{v}_{3}), and quadrangular(\emph{v}_{4}) flow of charged
particles in Pb+Pb collisions at = 5.02 TeV. Then We
compare our flow results with the published ALICE flow results. We found our
AMPT simulated results are consistent with ALICE experimental data
Quantum Size Effect on Dielectric Properties of Ultrathin Metallic Film: A First-Principles Study of Al(111)
Quantum manifestations of various properties of metallic thin films by
quantum size effect (QSE) have been studied intensively. Here, using
first-principles calculations, we show quantum manifestation in dielectric
properties of Al(111) ultrathin films. The QSE on the dielectric function is
revealed, which arises from size dependent contributions from both intraband
and interband electronic transitions. More importantly, the in-plane interband
transitions in the films thinner than 15 monolayers are found to be smaller
than the bulk counterpart in the energy range from 1.5~eV to 2.5~eV. This
indicates less energy loss with plasmonic material of Al in the form of
ultrathin film. Our findings may shed light on searching for low-loss plasmonic
materials via quantum size effect
Quantum anomalous Hall effect and tunable topological states in 3d transition metals doped silicene
We engineer quantum anomalous Hall effect in silicene via doping 3d
transition metals. We show that there exists a stable quantum anomalous Hall
effect in Vanadium doped silicene using both analytical model and Wannier
interpolation. We also predict the quantum valley Hall effect and electrically
tunable topological states could be realized in certain transition metal doped
silicene where the energy band inversion occurs. Our finding provides new
scheme for the realization of quantum anomalous Hall effect and platform for
electrically controllable topological states
Heavy quark correlations and the effective volume for quarkonia production
Using the Boltzmann transport approach, we study the effective volume of a
correlated heavy quark pair in a partonic medium based on their collision rate.
We find that the effective volume is finite and depends sensitively on the
momentum of the heavy quark and the temperature of the medium. Generally, it
increases linearly with time at the very beginning and the increase then
becomes slower due to multiple scattering, and finally it increases linearly
with respect to . We further find that the colliding heavy quark pair
has an effective temperature similar to that of the medium even though their
initial transverse momentum spectra are far from thermal equilibrium.Comment: 7 pages, 7 figure
Effects of Li doping on H-diffusion in MgH: a first-principles study
The effects of Li doping in MgH on H-diffusion process are investigated,
using first-principles calculations. We have identified two key effects: (1)
The concentration of H vacancy in the charge state (V) can
increase by several orders of magnitude upon Li doping, which significantly
increases the vacancy mediated H diffusion rate. It is caused by the preferred
charge states of substitutional Li in the state (Li) and of
interstitial Li in the state (Li), which indirectly reduce the
formation energy of V by up to 0.39 eV depending on the position of
Fermi energy. (2) The interaction between V and Li is
found to be attractive with a binding energy of 0.55 eV, which immobilizes the
V next to Li at high Li doping concentration. As a result,
the competition between these two effects leads to large enhancement of H
diffusion at low Li doping concentration due to the increased H-vacancy
concentration, but only limited enhancement at high Li concentration due to the
immobilization of H vacancies by too many Li
Giant Rashba-Spin Splitting of Bi(111) Bilayer on Large Band Gap InSe
Experimentally it is still challenging to epitaxially grow Bi(111) bilayer
(BL) on conventional semiconductor substrate. Here, we propose a substrate of
InSe(0001) with van der Waals like cleavage and large band gap
of 1.2~eV. We have investigated the electronic structure of BL on one
quintuple-layer (QL) InSe(0001) using density functional theory
calculation. It is found that the intermediate hybridization between BL and one
QL InSe(0001) results in the formation of bands with giant
Rashba spin splitting in the large band gap of the substrate. Furthermore the
Rashba parameter can be increased significantly by tensile strain of
substrate. Our findings provide a good candidate substrate for BL growth to
experimentally realize spin splitting Rashba states with insignificant effect
of spin degenerate states from the substrate
sd2 Graphene: Kagome Band in Hexagonal lattice
Graphene, made of sp2 hybridized carbon, is characterized with a Dirac band,
representative of its underlying 2D hexagonal lattice. Fundamental
understanding of graphene has recently spurred a surge of searching for 2D
topological quantum phases in solid-state materials. Here, we propose a new
form of 2D material, consisting of sd2 hybridized transition metal atoms in
hexagonal lattice, called sd2 graphene. The sd2 graphene is characterized with
bond-centered electronic hopping, which transforms the apparent atomic
hexagonal lattice into the physics of kagome lattice that may exhibit a wide
range of topological quantum phases. Based on first-principles calculations,
room temperature quantum anomalous Hall states with an energy gap of 0.1 eV are
demonstrated for one such lattice made of W, which can be epitaxially grown on
a semiconductor surface of 1/3 monolayer Cl-covered Si(111), with high
thermodynamic and kinetic stability.Comment: Phys. Rev. Lett.(2014), In press. It includes main text and 5
figures. Supplemental material is available upon reques
Quantum dynamical speedup in correlated noisy channels
The maximal evolution speed of a quantum system can be represented by quantum
speed limit time (QSLT).We investigate QSLT of a two-qubit system passing
through a correlated channel (amplitude damping, phase damping, and
depolarizing).By adjusting the correlation parameter of channel and the initial
entanglement,a method to accelerate the evolution speed of the system for some
specific channels is proposed.It is shown that, in amplitude damping channel
and depolarizing channel,QSLT may be shortened in some cases by increasing
correlation parameter of the channel and initial entanglement, which are in
sharp contrast to phase damping channel.In particular, under depolarizing
channels, the transition from no-speedup evolution to speedup evolution for the
system can be realized by changing correlation strength of the channel.Comment: 8pages, 5 figure
Implicit Distortion and Fertility Models for Attention-based Encoder-Decoder NMT Model
Neural machine translation has shown very promising results lately. Most NMT
models follow the encoder-decoder framework. To make encoder-decoder models
more flexible, attention mechanism was introduced to machine translation and
also other tasks like speech recognition and image captioning. We observe that
the quality of translation by attention-based encoder-decoder can be
significantly damaged when the alignment is incorrect. We attribute these
problems to the lack of distortion and fertility models. Aiming to resolve
these problems, we propose new variations of attention-based encoder-decoder
and compare them with other models on machine translation. Our proposed method
achieved an improvement of 2 BLEU points over the original attention-based
encoder-decoder.Comment: 11 pages, updated detail
Dynamical speedup of a two-level system induced by coupling in the hierarchical environment
We investigate the dynamics of a two-level system in the presence of an
overall environment composed of two layers. The first layer is just one
single-mode cavity which decays to memoryless reservoir while the second layer
is the two coupled single-mode cavities which decay to memoryless or
memory-keeping reservoirs. In the weak-coupling regime between the qubit and
the first-layer environment, our attention is focused on the effects of the
coupling in the hierarchical environment on the non-Markovian speedup dynamics
behavior of the system. We show that, by controlling the coupling in the
second-layer environment, the multiple dynamics crossovers from Markovian to
non-Markovian and from no-speedup to speedup can be realized. This results hold
independently on the nature of the second-layer environment. Differently, we
find that how the coupling between the two layers affects the non-Markovian
speedup dynamics behavior depends on the nature of the second-layer
environment.Comment: 8 pages, 5 figures, Any comments are welcome
- β¦