4,651 research outputs found
Bulk-Fermi-Arc Transition Induced Large Photogalvanic Effect in Weyl Semimetals
The surface Fermi arc, as a hallmark of Weyl semimetals (WSMs), has been well
known in current research, but it remains a challenge to unveil novel phenomena
associated with the Fermi arc. Here, we predict a heretofore unrecognized
process in WSMs, namely, the photoinduced transition between the bulk states
and the Fermi arc. We find this process is significant and can lead to a large
effective three-dimensional shift current on the boundaries with the Fermi arc
in wide terahertz range. Moreover, due to the low symmetry of the boundaries,
the surface photogalvanic effect predicted here can appear in a large class of
WSMs that do not have bulk shift current. Hence, our work not only unveils a
hidden photogalvanic effect in WSMs but also suggests that all the WSMs are
promising material candidates for developing efficient terahertz
photodetectors.Comment: 6 pages, 5 figure
ATMSeer: Increasing Transparency and Controllability in Automated Machine Learning
To relieve the pain of manually selecting machine learning algorithms and
tuning hyperparameters, automated machine learning (AutoML) methods have been
developed to automatically search for good models. Due to the huge model search
space, it is impossible to try all models. Users tend to distrust automatic
results and increase the search budget as much as they can, thereby undermining
the efficiency of AutoML. To address these issues, we design and implement
ATMSeer, an interactive visualization tool that supports users in refining the
search space of AutoML and analyzing the results. To guide the design of
ATMSeer, we derive a workflow of using AutoML based on interviews with machine
learning experts. A multi-granularity visualization is proposed to enable users
to monitor the AutoML process, analyze the searched models, and refine the
search space in real time. We demonstrate the utility and usability of ATMSeer
through two case studies, expert interviews, and a user study with 13 end
users.Comment: Published in the ACM Conference on Human Factors in Computing Systems
(CHI), 2019, Glasgow, Scotland U
Analysis of nonlinear suspension power harvest potential
Because the power consumption of a controlled suspension is huge, the power harvest potential of a nonlinear controlled suspension is analyzed. Instead of simplifying the suspension to a linear model or adopting some control strategies to solve the problem, this paper investigates the effect of the nonlinear characteristics on the power harvesting potential. A mathematic model is introduced to calculate the nonlinear vibration, and the amount of harvested power was obtained using the multi-scale method. A numerical validation is carried out at the end of this study. The results show that the investigated mechanical parameters affect both the vibration amplitude and the induced current, while the electric parameters only affect the induced current. The power harvesting potential of the nonlinear suspension is generally greater than the linear suspension because the frequency band of the actual pavement also contains bandwidth surrounding the body resonance point. The only exception occurs if the vehicle travels on a road with a particular profile, e.g. a sine curve. To optimize harvested power, it is better to consider the nonlinear characteristics rather than simplifying the suspension to a linear model
Planar Hall effect in topological Weyl and nodal line semimetals
Using symmetry analysis and semiclassical Boltzmann equation, we
theoretically explore the planar Hall effect (PHE) in three-dimensional
materials. We demonstrate that PHE is a general phenomenon that can occur in
various systems regardless of band topology. Both the Lorentz force and Berry
curvature effects can induce significant PHE, and the leading contributions of
both effects linearly depend on the electric and magnetic fields. The Lorentz
force and Berry curvature PHE coefficient possess only antisymmetric and
symmetric parts, respectively. Both contributions respect the same crystalline
symmetry constraints but differ under time-reversal symmetry. Remarkably, for
topological Weyl semimetal, the Berry curvature PHE coefficient is a constant
that does not depends on the Fermi energy, while the Lorentz force contribution
linearly increases with the Fermi energy, resulting from the linear dispersion
of the Weyl point. Furthermore, we find that the PHE in topological nodal line
semimetals is mainly induced by the Lorentz force, as the Berry curvature in
these systems vanishes near the nodal line. Our study not only highlights the
significance of the Lorentz force in PHE, but also reveals its unique
characteristics, which will be beneficial for determining the Lorentz force
contribution experimentally.Comment: 9 pages, 5 figure
5-Arc transitive cubic Cayley graphs on finite simple groups
AbstractIn this paper, we determine all connected 5-arc transitive cubic Cayley graphs on the alternating group A47; there are only two such graphs (up to isomorphism). By earlier work of the authors, these are the only two non-normal connected cubic arc-transitive Cayley graphs for finite nonabelian simple groups, and so this paper completes the classification of such non-normal Cayley graphs
GNNLens: A Visual Analytics Approach for Prediction Error Diagnosis of Graph Neural Networks
Graph Neural Networks (GNNs) aim to extend deep learning techniques to graph
data and have achieved significant progress in graph analysis tasks (e.g., node
classification) in recent years. However, similar to other deep neural networks
like Convolutional Neural Networks (CNNs) and Recurrent Neural Networks (RNNs),
GNNs behave like a black box with their details hidden from model developers
and users. It is therefore difficult to diagnose possible errors of GNNs.
Despite many visual analytics studies being done on CNNs and RNNs, little
research has addressed the challenges for GNNs. This paper fills the research
gap with an interactive visual analysis tool, GNNLens, to assist model
developers and users in understanding and analyzing GNNs. Specifically,
Parallel Sets View and Projection View enable users to quickly identify and
validate error patterns in the set of wrong predictions; Graph View and Feature
Matrix View offer a detailed analysis of individual nodes to assist users in
forming hypotheses about the error patterns. Since GNNs jointly model the graph
structure and the node features, we reveal the relative influences of the two
types of information by comparing the predictions of three models: GNN,
Multi-Layer Perceptron (MLP), and GNN Without Using Features (GNNWUF). Two case
studies and interviews with domain experts demonstrate the effectiveness of
GNNLens in facilitating the understanding of GNN models and their errors.Comment: 15 page
- …