3,052 research outputs found
Quantum anomalies in superconducting Weyl metals
We theoretically study the quantum anomalies in the superconducting Weyl
metals based on the topological field theory. It is demonstrated that the Fermi
arc and the surface Andreev bound state, characteristic of the superconducting
Weyl metals, are the manifestations of two underlying phenomenon, namely the
chiral anomaly and the parity-like anomaly, respectively. The first anomaly is
inherited from the Berry curvature around the original Weyl points, while the
second is the result of the superconductivity. We show that, all the
fascinating topological behavior of the superconducting Weyl metals, either
intranode FFLO or the internode BCS pairing state, can be satisfactorily
described and predicted by our topological field theory
Qubit-loss-free fusion of W states employing weak cross-Kerr nonlinearities
With the assistance of weak cross-Kerr nonlinearities, we introduce an
optical scheme to fuse two small-size polarization entangled W states into a
large-scale W state without qubit loss, i.e., state can be
generated from an -qubit W state and a -qubit W state. To complete the
fusion task, two polarization entanglement processes and one spatial
entanglement process are applied. The fulfillments of the above processes are
contributed by a cross-Kerr nonlinear interaction between the signal photons
and a coherent state via Kerr media. We analyze the resource cost and the
success probability of the scheme. There is no complete failure output in our
fusion mechanism, and all the garbage states are recyclable. In addition, there
is no need for any controlled quantum gate and any ancillary photon, so it is
simple and feasible under the current experiment technology.Comment: 7 pages, 3 figure
Eigenvalue, Quadratic Programming, and Semidefinite Programming Bounds for a Cut Minimization Problem
We consider the problem of partitioning the node set of a graph into sets
of given sizes in order to \emph{minimize the cut} obtained using (removing)
the -th set. If the resulting cut has value , then we have obtained a
vertex separator. This problem is closely related to the graph partitioning
problem. In fact, the model we use is the same as that for the graph
partitioning problem except for a different \emph{quadratic} objective
function. We look at known and new bounds obtained from various relaxations for
this NP-hard problem. This includes: the standard eigenvalue bound, projected
eigenvalue bounds using both the adjacency matrix and the Laplacian, quadratic
programming (QP) bounds based on recent successful QP bounds for the quadratic
assignment problems, and semidefinite programming bounds. We include numerical
tests for large and \emph{huge} problems that illustrate the efficiency of the
bounds in terms of strength and time.Comment: 32 pages, Department of Combinatorics & Optimization, University of
Waterloo, Canad
Larkin-Ovchinnikov state of superconducting Weyl metals: Fundamental differences between pairings restricted and extended in the -space
Two common approaches of studying theoretically the property of a
superconductor are shown to have significant differences, when they are applied
to the Larkin-Ovchinnikov state of Weyl metals. In the first approach the
pairing term is restricted by a cutoff energy to the neighborhood of the Fermi
surface, whereas in the second approach the pairing term is extended to the
whole Brillouin zone. We explore their difference by considering two minimal
models for the Weyl metal. For a model giving a single pair of Weyl pockets,
both two approaches give a partly-gapped (fully-gapped) bulk spectrum for small
(large) pairing amplitude. However, for very small cutoff energy, a portion of
the Fermi surface can be completely unaffected by the pairing term in the first
approach. For the other model giving two pairs of Weyl pockets, while the bulk
spectrum for the first approach can be fully gapped, the one from the second
approach has a robust line node, and the surface states are also changed
qualitatively by the pairing. We elucidate the above differences by topological
arguments and analytical analyses. A factor common to both of the two models is
the tilting of the Weyl cones which leads to asymmetric normal state band
structure with respect to the Weyl nodes. For the Weyl metal with two pairs of
Weyl pockets, the band folding leads to a double degeneracy in the effective
model, which distinguishes the pairing of the second approach from all others.Comment: 27 pages, 11 figure
The Design of Circuit-Measuring Collaborative Learning System with Embedded Broker
Recently, the academic community has been giving much attention to
Cooperative Learning System, a group learning method combined with pedagogy and
social psychology. It allows group members to gain knowledge through
collaborations and interactions. Nowadays, most Internet cooperative learning
systems are designed to provide students mainly with a convenient online
environment to study theoretical courses but rarely with an online environment
to operate practical instruments. Hence, this paper designed a 3D online
cooperative learning system for operating virtual instruments with
circuit-measuring function. By integrating with Virtual Reality, Remote Control
Parameter Transmission and embedded system techniques, this system gives
learners not only a cooperative learning environment via networking to jointly
operate the 3D virtual instruments (for example, multi-meters, power supplies
and oscilloscopes) but also the functions of instant messages and 3D puzzles to
interact with one another. Therefore, learners can effectively improve learning
interests and results.Comment: International Journal of Computer Science Issues, IJCSI, Vol. 7,
Issue 1, No. 3, January 2010,
http://ijcsi.org/articles/The-Design-of-Circuit-Measuring-Collaborative-Learning-System-with-Embedded-Broker.ph
Ferromagnetism and superconductivity with possible pairing symmetry in partially hydrogenated graphene
By means of first-principles calculations, we predict two new types of
partially hydrogenated graphene systems: CH and CH,
which are shown to be ferromagnetic (FM) semimetal and FM narrow-gap
semiconductor, respectively. When properly doped, the Fermi surface of the two
systems consists of an electron pocket or six hole patches in the first
Brillouin zone with completely spin-polarized charge carries. If
superconductivity exists in these systems, the stable pairing symmetries are
shown to be for electron doped case, and anisotropic for hole
doped case. The predicted systems may provide fascinating platforms for
studying the novel properties of ferromagnetism and triplet-pairing
superconductivity as well as two-dimensional spintronics
Growth on Two Limiting Essential Resources in a Self-Cycling Fermentor
A system of impulsive differential equations with state-dependent impulses is
used to model the growth of a single population on two limiting essential
resources in a self-cycling fermentor. Potential applications include water
purification and biological waste remediation. The self-cycling fermentation
process is a semi-batch process and the model is an example of a hybrid system.
In this case, a well-stirred tank is partially drained, and subsequently
refilled using fresh medium when the concentration of both resources (assumed
to be pollutants) falls below some acceptable threshold. We consider the
process successful if the threshold for emptying/refilling the reactor can be
reached indefinitely without the time between successive emptying/refillings
becoming unbounded and without interference by the operator. We prove that
whenever the process is successful, the model predicts that the concentrations
of the population and the resources converge to a positive periodic solution.
We derive conditions for the successful operation of the process that are shown
to be initial condition dependent and prove that if these conditions are not
satisfied, then the reactor fails. We show numerically that there is an optimal
fraction of the medium drained from the tank at each impulse that maximizes the
output of the process.Comment: 21 pages, 6 figure
A Detection and Segmentation Architecture for Skin Lesion Segmentation on Dermoscopy Images
This report summarises our method and validation results for the ISIC
Challenge 2018 - Skin Lesion Analysis Towards Melanoma Detection - Task 1:
Lesion Segmentation. We present a two-stage method for lesion segmentation with
optimised training method and ensemble post-process. Our method achieves
state-of-the-art performance on lesion segmentation and we win the first place
in ISIC 2018 task1.Comment: 5 pages, 9 figures, Ranked 1st place in ISIC 2018 task1, title
updated and results adde
SimGNN: A Neural Network Approach to Fast Graph Similarity Computation
Graph similarity search is among the most important graph-based applications,
e.g. finding the chemical compounds that are most similar to a query compound.
Graph similarity computation, such as Graph Edit Distance (GED) and Maximum
Common Subgraph (MCS), is the core operation of graph similarity search and
many other applications, but very costly to compute in practice. Inspired by
the recent success of neural network approaches to several graph applications,
such as node or graph classification, we propose a novel neural network based
approach to address this classic yet challenging graph problem, aiming to
alleviate the computational burden while preserving a good performance.
The proposed approach, called SimGNN, combines two strategies. First, we
design a learnable embedding function that maps every graph into a vector,
which provides a global summary of a graph. A novel attention mechanism is
proposed to emphasize the important nodes with respect to a specific similarity
metric. Second, we design a pairwise node comparison method to supplement the
graph-level embeddings with fine-grained node-level information. Our model
achieves better generalization on unseen graphs, and in the worst case runs in
quadratic time with respect to the number of nodes in two graphs. Taking GED
computation as an example, experimental results on three real graph datasets
demonstrate the effectiveness and efficiency of our approach. Specifically, our
model achieves smaller error rate and great time reduction compared against a
series of baselines, including several approximation algorithms on GED
computation, and many existing graph neural network based models. To the best
of our knowledge, we are among the first to adopt neural networks to explicitly
model the similarity between two graphs, and provide a new direction for future
research on graph similarity computation and graph similarity search.Comment: WSDM 201
Novel anisotropic spin singlet pairings in CuBiSe and BiTe
Possible anisotropic spin singlet pairings in BiX (X is Se or Te) are
studied. Among six pairings compatible with the crystal symmetry, two novel
pairings show nontrivial surface Andreev bound states, which form flat bands
and could produce zero bias conductance peak in measurements like point contact
spectroscopy. By considering purely repulsive short range Coulomb interaction
as the pairing mechanism, the dominant superexchange terms are all
antiferromagnetic, which would usually favor spin singlet pairing in
BiX. Mean field analyses show that the interorbital pairing interaction
favors a mixed spatial-parity anisotropic pairing state, and one pairing
channel with zero energy surface states has a sizable component. The results
provide important new information for future experiments.Comment: 13 pages, 2 figures, 3 table
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