27,982 research outputs found
Implicit and electrostatic Particle-in-cell/Monte Carlo model in two dimensional and axisymmetric geometry I: analysis of numerical techniques
We developed an implicit Particle-in-cell/Monte Carlo model in
two-dimensional and axisymmetric geometry for the simulations of the
radio-frequency discharges, by introducing several numerical schemes which
include variable weights, multigrid field solver, etc. Compared to the standard
explicit models, we found that the computational efficiency is significantly
increased and the accuracy is still kept. Numerical schemes are discussed and
benchmark results are shown. The code can be used to simulate practical
reactors.Comment: accepted by Plasma Source Sci. Tec
Interatomic Coulomb interaction and electron nematic bond order in FeSe
Despite having the simplest atomic structure, bulk FeSe has an observed
electronic structure with the largest deviation from the band theory
predictions among all Fe-based superconductors and exhibits a low temperature
nematic electronic state without intervening magnetic order. We show that the
Fe-Fe interatomic Coulomb repulsion offers a natural explanation for the
puzzling electron correlation effects in FeSe superconductors. It produces a
strongly renormalized low-energy band structure where the van Hove singularity
sits remarkably close to Fermi level in the high-temperature electron liquid
phase as observed experimentally. This proximity enables the quantum
fluctuations in to induce a rotational symmetry breaking electronic bond
order in the -wave channel. We argue that this emergent low-temperature
-wave bond nematic state, different from the commonly discussed
ferro-orbital order and spin-nematicity, has been observed recently by several
angle resolved photoemission experiments detecting the lifting of the band
degeneracies at high symmetry points in the Brillouin zone. We present a
symmetry analysis of the space group and identify the hidden antiunitary
-symmetry that protects the band degeneracy and the electronic
order/interaction that can break the symmetry and lift the degeneracy. We show
that the -wave nematic bond order, together with the spin-orbit coupling,
provide a unique explanation of the temperature dependence, momentum space
anisotropy, and domain effects observed experimentally. We discuss the
implications of our findings on the structural transition, the absence of
magnetic order, and the intricate competition between nematicity and
superconductivity in FeSe superconductors.Comment: Final version. Published in PRB. 15 pages, 6 figures, and 2 table
Implicit and electrostatic Particle-in-cell/Monte Carlo model in two dimensional and axisymmetric geometry II: Self-bias voltage effects in capacitively coupled plasmas
With an implicit Particle-in-cell/Monte Carlo model, capacitively coupled
plasmas are studied in two-dimensional and axisymmetric geometry. Self-bias dc
voltage effects are self-consistently considered. Due to finite length effects,
the self-bias dc voltages show sophisticating relations with the electrode
areas. Two-dimensional kinetic effects are also illuminated. Compare to the
fluid mode, PIC/MC model is numerical-diffusion-free and thus finer properties
of the plasmas are simulated.Comment: Submitted to Plasma Sources Sci. Techno
The Production of and in decays
Considering and as and , we
study the productions of and in exclusive weak decays of
meson by the improved Bethe-Salpeter(B-S) Method. Using the relativistic
B-S equation and Mandelstam formalism, we calculate the corresponding decay
form factors. The predictions of the corresponding branching ratios are:
and . That will provide us a new way to observe
the and in the future, as well as to improve the knowledge
of meson decay.Comment: 15 pages, 7 figure
Chiral Lagrangians with to one loop
We construct the Lorentz-invariant chiral Lagrangians up to the order
by including as an explicit degree of
freedom. A full one-loop investigation on processes involving
can be performed with them. For the Lagrangian, one obtains
38 independent terms at the order and 318 independent terms
at the order . For the Lagrangian, we get 33
independent terms at the order and 218 independent terms at
the order . The heavy baryon projection is also briefly
discussed.Comment: 23 pages,8 tables. Less terms are found with more constraints.
Version accepted by PR
The weak decay to and by Bethe-Salpeter method
Considering and as and
states, the semileptonic and nonleptonic of decays to and
are studied by the improved Bethe-Salpeter(B-S) Method. The form
factors of decay are calculated through the overlap integrals of the meson wave
functions in the whole accessible kinematical range. The influence of
relativistic corrections are considered in the exclusive decays. Branching
ratios of weak decays to and are predicted. Some of
the branching ratios are: and . These results may
provide useful information to discover and and the
necessary information for the phenomenological study of physics.Comment: arXiv admin note: substantial text overlap with arXiv:1605.0909
Urban Traffic Dynamics: A Scale-Free Network Perspective
This letter propose a new model for characterizing traffic dynamics in
scale-free networks. With a replotted road map of cities with roads mapped to
vertices and intersections to edges, and introducing the road capacity L and
its handling ability at intersections C, the model can be applied to urban
traffic system. Simulations give the overall capacity of the traffic system
which is quantified by a phase transition from free flow to congestion.
Moreover, we report the fundamental diagram of flow against density, in which
hysteresis is found, indicating that the system is bistable in a certain range
of vehicle density. In addition, the fundamental diagram is significantly
different from single-lane traffic model and 2-D BML model with four states:
free flow, saturated flow, bistable and jammed.Comment: 4 pages, 5 figure
How target waves emerge in population dynamics
Based on a multi-agent model, we investigate how target waves emerge from a
population dynamics with cyclical interactions among three species. We show
that the periodically injecting source in a small central area can generate
target waves in a two-dimensional lattice system. By detecting the temporal
period of species' concentration at the central area, three modes of target
waves can be distinguished. Those different modes result from the competition
between local and global oscillations induced by cyclical interactions: Mode A
corresponds to a synchronization of local and global oscillations, Mode B
results from an intermittent synchronization, and Mode C corresponds to the
case when the frequency of the local oscillation is much higher than that of
the global oscillation. This work provides insights into pattern formation in
biologic and ecologic systems that are totally different from the extensively
studied diffusion systems driven by chemical reactions.Comment: 10 Pages, 5 figure
Bidirectional selection between two classes in complex social networks
The bidirectional selection between two classes widely emerges in various
social lives, such as commercial trading and mate choosing. Until now, the
discussions on bidirectional selection in structured human society are quite
limited. We demonstrated theoretically that the rate of successfully matching
is affected greatly by individuals neighborhoods in social networks, regardless
of the type of networks. Furthermore, it is found that the high average degree
of networks contributes to increasing rates of successful matches. The matching
performance in different types of networks has been quantitatively
investigated, revealing that the small-world networks reinforces the matching
rate more than scale-free networks at given average degree. In addition, our
analysis is consistent with the modeling result, which provides the theoretical
understanding of underlying mechanisms of matching in complex networks
A global estimation of the lower bound of the privacy amplification term for decoy-state quantum key distribution
The privacy amplification term, of which the lower bound needs to be
estimated with the decoy-state method, plays a positive role in the secure key
rate formula for decoy-state quantum key distribution. In previous work, the
yield and the bit error rate of single-photon state are estimated separately to
gain this lower bound. In this work, we for the first time take the privacy
amplification term as a whole to consider this lower bound. The mathematical
description for the correlation between the yield and the bit error rate of
single-photon state is given with just two unknown variables. Based on this, we
obtain the global estimation of this lower bound for both BB84 protocol and
measurement-device-independent protocol. The results of numerical simulation
show that the global estimation can significantly improve the performance of
quantum key distribution
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