11,434 research outputs found
Multicolor Graphene Nanoribbon/Semiconductor Nanowire Heterojunction Light-Emitting Diodes
We report novel graphene nanoribbon (GNR)/semiconductor nanowire (SNW)
heterojunction light-emitting diodes (LEDs) for the first time. The GNR and SNW
have a face-to-face contact structure, which has the merit of bigger active
region. ZnO, CdS, and CdSe NWs were employed in our case. At forward biases,
the GNR/SNW heterjunction LEDs could emit light with wavelengths varying from
ultraviolet (380 nm) to green (513 nm) to red (705 nm), which were determined
by the band-gaps of the involved SNWs. The mechanism of light emitting for the
GNR/SNW heterojunction LED was discussed. Our approach can easily be extended
to other semiconductor nano-materials. Moreover, our achievement opens the door
to next-generation display technologies, including portable, "see-through", and
conformable products.Comment: 12 pages, 4 figure
Model Hamiltonian for topological Kondo insulator SmB6
Starting from the kp method in combination with first-principles
calculations, we systematically derive the effective Hamiltonians that capture
the low energy band structures of recently discovered topological Kondo
insulator SmB6. Using these effective Hamiltonians we can obtain both the
energy dispersion and the spin texture of the topological surface states, which
can be detected by further experiments.Comment: 6 pages, 4 figure
Quantum anomalous Hall effect and related topological electronic states
Over a long period of exploration, the successful observation of quantized
version of anomalous Hall effect (AHE) in thin film of magnetically-doped
topological insulator completed a quantum Hall trio---quantum Hall effect
(QHE), quantum spin Hall effect (QSHE), and quantum anomalous Hall effect
(QAHE). On the theoretical front, it was understood that intrinsic AHE is
related to Berry curvature and U(1) gauge field in momentum space. This
understanding established connection between the QAHE and the topological
properties of electronic structures characterized by the Chern number. With the
time reversal symmetry broken by magnetization, a QAHE system carries
dissipationless charge current at edges, similar to the QHE where an external
magnetic field is necessary. The QAHE and corresponding Chern insulators are
also closely related to other topological electronic states, such as
topological insulators and topological semimetals, which have been extensively
studied recently and have been known to exist in various compounds.
First-principles electronic structure calculations play important roles not
only for the understanding of fundamental physics in this field, but also
towards the prediction and realization of realistic compounds. In this article,
a theoretical review on the Berry phase mechanism and related topological
electronic states in terms of various topological invariants will be given with
focus on the QAHE and Chern insulators. We will introduce the Wilson loop
method and the band inversion mechanism for the selection and design of
topological materials, and discuss the predictive power of first-principles
calculations. Finally, remaining issues, challenges and possible applications
for future investigations in the field will be addressed.Comment: Review Article published in , and update
Topological Nodal Line Semimetal and Dirac Semimetal State in Antiperovskite CuPdN
Based on first-principles calculation and effective model analysis, we
propose that the cubic antiperovskite material CuPdN can host a
three-dimensional (3D) topological nodal line semimetal state when spin-orbit
coupling (SOC) is ignored, which is protected by coexistence of time-reversal
and inversion symmetry. There are three nodal line circles in total due to the
cubic symmetry. "Drumhead"-like surface flat bands are also derived. When SOC
is included, each nodal line evolves into a pair of stable 3D Dirac points as
protected by C crystal symmetry. This is remarkably distinguished from the
Dirac semimetals known so far, such as NaBi and CdAs, both having
only one pair of Dirac points. Once C symmetry is broken, the Dirac points
are gapped and the system becomes a strong topological insulator with (1;111)
Z indices.Comment: 6 pages, 4 figure
Feedforward Sequential Memory Networks: A New Structure to Learn Long-term Dependency
In this paper, we propose a novel neural network structure, namely
\emph{feedforward sequential memory networks (FSMN)}, to model long-term
dependency in time series without using recurrent feedback. The proposed FSMN
is a standard fully-connected feedforward neural network equipped with some
learnable memory blocks in its hidden layers. The memory blocks use a
tapped-delay line structure to encode the long context information into a
fixed-size representation as short-term memory mechanism. We have evaluated the
proposed FSMNs in several standard benchmark tasks, including speech
recognition and language modelling. Experimental results have shown FSMNs
significantly outperform the conventional recurrent neural networks (RNN),
including LSTMs, in modeling sequential signals like speech or language.
Moreover, FSMNs can be learned much more reliably and faster than RNNs or LSTMs
due to the inherent non-recurrent model structure.Comment: 11 pages, 5 figure
Competitive Inner-Imaging Squeeze and Excitation for Residual Network
Residual networks, which use a residual unit to supplement the identity
mappings, enable very deep convolutional architecture to operate well, however,
the residual architecture has been proved to be diverse and redundant, which
may leads to low-efficient modeling. In this work, we propose a competitive
squeeze-excitation (SE) mechanism for the residual network. Re-scaling the
value for each channel in this structure will be determined by the residual and
identity mappings jointly, and this design enables us to expand the meaning of
channel relationship modeling in residual blocks. Modeling of the competition
between residual and identity mappings cause the identity flow to control the
complement of the residual feature maps for itself. Furthermore, we design a
novel inner-imaging competitive SE block to shrink the consumption and re-image
the global features of intermediate network structure, by using the
inner-imaging mechanism, we can model the channel-wise relations with
convolution in spatial. We carry out experiments on the CIFAR, SVHN, and
ImageNet datasets, and the proposed method can challenge state-of-the-art
results.Comment: Code is available at
https://github.com/scut-aitcm/Competitive-Inner-Imaging-SENe
Magnetisms in -type monolayer gallium chalcogenides (GaSe, GaS)
Magnetisms in -type monolayer GaX (X=S,Se) is investigated by performing
density-functional calculations. Due to the large density of states near the
valence band edge, these monolayer semiconductors are ferromagnetic within a
small range of hole doping. The intrinsic Ga vacancies can promote local
magnetic moment while Se vacancies cannot. Magnetic coupling between
vacancy-induced local moments is ferromagnetic and surprisingly long-range. The
results indicate that magnetization can be induced by hole doping and can be
tuned by controlled defect generation.Comment: 5 page
Automatic construction of Chinese herbal prescription from tongue image via CNNs and auxiliary latent therapy topics
The tongue image provides important physical information of humans. It is of
great importance for diagnoses and treatments in clinical medicine. Herbal
prescriptions are simple, noninvasive and have low side effects. Thus, they are
widely applied in China. Studies on the automatic construction technology of
herbal prescriptions based on tongue images have great significance for deep
learning to explore the relevance of tongue images for herbal prescriptions, it
can be applied to healthcare services in mobile medical systems. In order to
adapt to the tongue image in a variety of photographic environments and
construct herbal prescriptions, a neural network framework for prescription
construction is designed. It includes single/double convolution channels and
fully connected layers. Furthermore, it proposes the auxiliary therapy topic
loss mechanism to model the therapy of Chinese doctors and alleviate the
interference of sparse output labels on the diversity of results. The
experiment use the real world tongue images and the corresponding prescriptions
and the results can generate prescriptions that are close to the real samples,
which verifies the feasibility of the proposed method for the automatic
construction of herbal prescriptions from tongue images. Also, it provides a
reference for automatic herbal prescription construction from more physical
information.Comment: 17 pages, 10 figure
TopoTag: A Robust and Scalable Topological Fiducial Marker System
Fiducial markers have been playing an important role in augmented reality
(AR), robot navigation, and general applications where the relative pose
between a camera and an object is required. Here we introduce TopoTag, a robust
and scalable topological fiducial marker system, which supports reliable and
accurate pose estimation from a single image. TopoTag uses topological and
geometrical information in marker detection to achieve higher robustness.
Topological information is extensively used for 2D marker detection, and
further corresponding geometrical information for ID decoding. Robust 3D pose
estimation is achieved by taking advantage of all TopoTag vertices. Without
sacrificing bits for higher recall and precision like previous systems, TopoTag
can use full bits for ID encoding. TopoTag supports tens of thousands unique
IDs and easily extends to millions of unique tags resulting in massive
scalability. We collected a large test dataset including in total 169,713
images for evaluation, involving in-plane and out-of-plane rotation, image
blur, different distances and various backgrounds, etc. Experiments on the
dataset and real indoor and outdoor scene tests with a rolling shutter camera
both show that TopoTag significantly outperforms previous fiducial marker
systems in terms of various metrics, including detection accuracy, vertex
jitter, pose jitter and accuracy, etc. In addition, TopoTag supports occlusion
as long as the main tag topological structure is maintained and allows for
flexible shape design where users can customize internal and external marker
shapes. Code for our marker design/generation, marker detection, and dataset
are available at
http://herohuyongtao.github.io/research/publications/topo-tag/.Comment: Accepted to TVC
A Synthetic Approach for Recommendation: Combining Ratings, Social Relations, and Reviews
Recommender systems (RSs) provide an effective way of alleviating the
information overload problem by selecting personalized choices. Online social
networks and user-generated content provide diverse sources for recommendation
beyond ratings, which present opportunities as well as challenges for
traditional RSs. Although social matrix factorization (Social MF) can integrate
ratings with social relations and topic matrix factorization can integrate
ratings with item reviews, both of them ignore some useful information. In this
paper, we investigate the effective data fusion by combining the two
approaches, in two steps. First, we extend Social MF to exploit the graph
structure of neighbors. Second, we propose a novel framework MR3 to jointly
model these three types of information effectively for rating prediction by
aligning latent factors and hidden topics. We achieve more accurate rating
prediction on two real-life datasets. Furthermore, we measure the contribution
of each data source to the proposed framework.Comment: 7 pages, 8 figure
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