25,278 research outputs found
Interacting topological phases in thin films of topological mirror Kondo insulators
We study the interaction effects on thin films of topological mirror Kondo
insulators (TMKI), where the strong interaction is expected to play an
important role. Our study has led to the following results: (1) We identify a
rich phase diagram of non-interacting TMKI with different mirror Chern numbers
in the monolayer and bilayer thin films; (2) We obtain the phase diagram with
interaction and identify the regimes of interaction parameters to mimic bosonic
symmetry protected topological phases with either gapless bosonic modes or
spontaneous mirror symmetry breaking at the boundary; (3) For the spontaneous
mirror symmetry breaking boundary, we also study various domain-wall defects
between different mirror symmetry breaking order parameters at the boundary.
Our results reveal that the thin film TMKI serves as an intriguing platform for
the experimental studies of interacting topological phases.Comment: 11 pages, 4 figure
Performance Enhancement for High-order Gas-kinetic Scheme Based on WENO-adaptive-order Reconstruction
High-order gas-kinetic scheme (HGKS) has been well-developed in the past
years. Abundant numerical tests including hypersonic flow, turbulence, and
aeroacoustic problems, have been used to validate its accuracy, efficiency, and
robustness. However, there are still rooms for its further improvement.
Firstly, the reconstruction in the previous scheme mainly achieves a
third-order accuracy for the initial non-equilibrium states. At the same time,
the equilibrium state in space and time in HGKS has to be reconstructed
separately. Secondly, it is complicated to get reconstructed data at Gaussian
points from the WENO-type method in high dimensions. For HGKS, besides the
point-wise values at the Gaussian points it also requires the slopes in both
normal and tangential directions of a cell interface. Thirdly, there exists
visible spurious overshoot/undershoot at weak discontinuities from the previous
HGKS with the standard WENO reconstruction. In order to overcome these
difficulties, in this paper we use an improved reconstruction for HGKS. The
WENO with adaptive order (WENO-AO) method is implemented for reconstruction.A
whole polynomial inside each cell is provided in WENO-AO reconstruction. The
HGKS becomes simpler than the previous one with the direct implementation of
cell interface values and their slopes from WENO-AO. The additional
reconstruction of equilibrium state at the beginning of each time step can be
avoided as well by dynamically merging the reconstructed non-equilibrium
slopes. The new HGKS essentially releases or totally removes the above existing
problems in previous HGKS. The accuracy of the scheme from 1D to 3D from the
new HGKS can recover the theoretical order of accuracy of the WENO
reconstruction.In the two- and three-dimensional simulations, the new HGKS
shows better robustness and efficiency than the previous scheme in all test
cases
A Hopf algebra on subgraphs of a graph
In this paper, we construct a bialgebraic and further a Hopf algebraic
structure on top of subgraphs of a given graph. Further, we give the dual
structure of this Hopf algebraic structure. We study the algebra morphisms
induced by graph homomorphisms, and obtain a covariant functor from a graph
category to an algebra category.Comment: 16 page
Q factor in numerical simulations of DPSK with optical delay demodulation
A simple model is used to estimate the Q factor in numerical simulations of
differential phase shift keying (DPSK) with optical delay demodulation and
balanced detection. It is found that an alternative definition of Q is needed
for DPSK in order to have a more accurate prediction of the bit error ratio
(BER).Comment: This is a manuscript that was rejected by IEEE Photonics Technology
Letters in 2002 (Manucript #9527
Optimal Resource Allocation for Wireless Powered Mobile Edge Computing with Dynamic Task Arrivals
This paper considers a wireless powered multiuser mobile edge computing (MEC)
system, where a multi-antenna access point (AP) employs the radio-frequency
(RF) signal based wireless power transfer (WPT) to charge a number of
distributed users, and each user utilizes the harvested energy to execute
computation tasks via local computing and task offloading. We consider the
frequency division multiple access (FDMA) protocol to support simultaneous task
offloading from multiple users to the AP. Different from previous works that
considered one-shot optimization with static task models, we study the joint
computation and wireless resource allocation optimization with dynamic task
arrivals over a finite time horizon consisting of multiple slots. Under this
setup, our objective is to minimize the system energy consumption including the
AP's transmission energy and the MEC server's computing energy over the whole
horizon, by jointly optimizing the transmit energy beamforming at the AP, and
the local computing and task offloading strategies at the users over different
time slots. To characterize the fundamental performance limit of such systems,
we focus on the offline optimization by assuming the task and channel
information are known a-priori at the AP. In this case, the energy minimization
problem corresponds to a convex optimization problem. Leveraging the Lagrange
duality method, we obtain the optimal solution to this problem in a well
structure. It is shown that in order to maximize the system energy efficiency,
the optimal number of task input-bits at each user and the AP are monotonically
increasing over time, and the offloading strategies at different users depend
on both the wireless channel conditions and the task load at the AP. Numerical
results demonstrate the benefit of the proposed joint-WPT-MEC design over
alternative benchmark schemes without such joint design.Comment: 7 pages, 3 figures, and Accepted by IEEE ICC 2019, Shanghai, Chin
A Multi-scale Monte Carlo Method for Electrolytes
Artifacts arise in the simulations of electrolytes using periodic boundary
conditions (PBC). We show the origin of these artifacts are the periodic image
charges and the constraint of charge neutrality inside the simulation box, both
of which are unphysical from the view point of real systems. To cure these
problems, we introduce a multi-scale Monte Carlo method, where ions inside a
spherical cavity are simulated explicitly, whilst ions outside are treated
implicitly using continuum theory. Using the method of Debye charging, we
explicitly derive the effective interactions between ions inside the cavity,
arising due to the fluctuations of ions outside. We find that these effective
interactions consist of two types: 1) a constant cavity potential due to the
asymmetry of the electrolyte, and 2) a reaction potential that depends on the
positions of all ions inside. Combining the Grand Canonical Monte Carlo (GCMC)
with a recently developed fast algorithm based of image charge method, we
perform a multi-scale Monte Carlo simulation of symmetric electrolytes, and
compare it with other simulation methods, including PBC+GCMC method, as well as
large scale Monte Carlo simulation. We demonstrate that our multi-scale MC
method is capable of capturing the correct physics of a large system using a
small scale simulation.Comment: 14 pages, 11 figure
Bi-Directional Differentiable Input Reconstruction for Low-Resource Neural Machine Translation
We aim to better exploit the limited amounts of parallel text available in
low-resource settings by introducing a differentiable reconstruction loss for
neural machine translation (NMT). This loss compares original inputs to
reconstructed inputs, obtained by back-translating translation hypotheses into
the input language. We leverage differentiable sampling and bi-directional NMT
to train models end-to-end, without introducing additional parameters. This
approach achieves small but consistent BLEU improvements on four language pairs
in both translation directions, and outperforms an alternative differentiable
reconstruction strategy based on hidden states.Comment: Accepted at NAACL 201
Solve Traveling Salesman Problem by Monte Carlo Tree Search and Deep Neural Network
We present a self-learning approach that combines deep reinforcement learning
and Monte Carlo tree search to solve the traveling salesman problem. The
proposed approach has two advantages. First, it adopts deep reinforcement
learning to compute the value functions for decision, which removes the need of
hand-crafted features and labelled data. Second, it uses Monte Carlo tree
search to select the best policy by comparing different value functions, which
increases its generalization ability. Experimental results show that the
proposed method performs favorably against other methods in small-to-medium
problem settings. And it shows comparable performance as state-of-the-art in
large problem setting.Comment: Was previously submitted to ICAPS201
Modeling aggressive market order placements with Hawkes factor models
Price changes are induced by aggressive market orders in stock market. We
introduce a bivariate marked Hawkes process to model aggressive market order
arrivals at the microstructural level. The order arrival intensity is marked by
an exogenous part and two endogenous processes reflecting the self-excitation
and cross-excitation respectively. We calibrate the model for an SSE stock. We
find that the exponential kernel with a smooth cut-off (i.e. the subtraction of
two exponentials) produces much better calibration than the monotonous
exponential kernel (i.e. the sum of two exponentials). The exogenous baseline
intensity explains the -shaped intraday pattern. Our empirical results show
that the endogenous submission clustering is mainly caused by self-excitation
rather than cross-excitation.Comment: 9 pages, 7 figure
Mellin Transform and Image Charge Method for Dielectric Sphere in an Electrolyte
We revisit the image charge method for the Green's function problem of the
Poisson-Boltzmann equation for a dielectric sphere immersed in ionic solutions.
Using finite Mellin transformation, we represent the reaction potential due to
a source charge inside the sphere in terms of one dimensional distribution of
image charges. The image charges are generically composed of a point image at
the Kelvin point and a line image extending from the Kelvin point to infinity
with an oscillatory line charge strength. We further develop an efficient and
accurate algorithm for discretization of the line image using Pad\'e
approximation and finite fraction expansion. Finally we illustrate the power of
our method by applying it in a multiscale reaction-field Monte Carlo simulation
of monovalent electrolytes.Comment: 20 pages, 7 figures, version to be published in SIAM J. Appl. Mat
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