43 research outputs found
Image Data Augmentation for Deep Learning: A Survey
Deep learning has achieved remarkable results in many computer vision tasks.
Deep neural networks typically rely on large amounts of training data to avoid
overfitting. However, labeled data for real-world applications may be limited.
By improving the quantity and diversity of training data, data augmentation has
become an inevitable part of deep learning model training with image data.
As an effective way to improve the sufficiency and diversity of training
data, data augmentation has become a necessary part of successful application
of deep learning models on image data. In this paper, we systematically review
different image data augmentation methods. We propose a taxonomy of reviewed
methods and present the strengths and limitations of these methods. We also
conduct extensive experiments with various data augmentation methods on three
typical computer vision tasks, including semantic segmentation, image
classification and object detection. Finally, we discuss current challenges
faced by data augmentation and future research directions to put forward some
useful research guidance
Magnetic eight-fold nodal-point and nodal-network fermions in MnB2
Realizing topological semimetal states with novel emergent fermions in
magnetic materials is a focus of current research. Based on first-principle
calculations and symmetry analysis, we reveal interesting magnetic emergent
fermions in an existing material MnB2. In the temperature range from 157 K to
760 K, MnB2 is a collinear antiferromagnet. We find the coexistence of
eightfold nodal points and nodal net close to the Fermi level, which are
protected by the spin group in the absence of spin-orbit coupling. Depending on
the Neel vector orientation, consideration of spin-orbit coupling will either
open small gaps at these nodal features, or transform them into magnetic linear
and quadratic Dirac points and nodal rings. Below 157 K, MnB2 acquires weak
ferromagnetism due to spin tilting. We predict that this transition is
accompanied by a drastic change in anomalous Hall response, from zero above 157
K to 200 below 157 K.Comment: 5 figures and 7 page
Third-order charge transport in a magnetic topological semimetal
Magnetic topological materials and their physical signatures are a focus of
current research. Here, by first-principles calculations and symmetry analysis,
we reveal topological semimetal states in an existing antiferromagnet ThMn2Si2.
Depending on the N\'eel vector orientation, the topological band crossings near
the Fermi level form either a double-nodal loop or two pairs of Dirac
points,which are all fourfold degenerate and robust under spin-orbit coupling.
These topological features produce large Berry connection polarizability, which
leads to enhanced nonlinear transport effects. Particularly, we evaluate the
third order current response, which dominates the transverse charge current. We
show that the nonlinear response can be much more sensitive to topological
phase transitions than linear response, which offers a powerful tool for
characterizing magnetic topological semimetals.Comment: 5 pages, 5 figure
GRB 120729A: External Shock Origin for Both the Prompt Gamma-Ray Emission and Afterglow
Gamma-ray burst (GRB) 120729A was detected by Swift/BAT and Fermi/GBM, and then rapidly observed by Swift/XRT, Swift/UVOT, and ground-based telescopes. It had a single long and smooth \gamma-ray emission pulse, which extends continuously to the X-rays. We report Lick/KAIT observations of the source, and make temporal and spectral joint fits of the multiwavelength light curves of GRB 120729A. It exhibits achromatic light-curve behavior, consistent with the predictions of the external shock model. The light curves are decomposed into four typical phases: onset bump (Phase I), normal decay (Phase II), shallow decay (Phase III), and post-jet break (Phase IV). The spectral energy distribution (SED) evolves from prompt \gamma-ray emission to the afterglow with photon index from Γγ=1.36 to Γ≈1.75. There is no obvious evolution of the SED during the afterglow. ...(Please see article full tet for complete abstract.
A Survey on Approximate Multiplier Designs for Energy Efficiency: From Algorithms to Circuits
Given the stringent requirements of energy efficiency for Internet-of-Things
edge devices, approximate multipliers, as a basic component of many processors
and accelerators, have been constantly proposed and studied for decades,
especially in error-resilient applications. The computation error and energy
efficiency largely depend on how and where the approximation is introduced into
a design. Thus, this article aims to provide a comprehensive review of the
approximation techniques in multiplier designs ranging from algorithms and
architectures to circuits. We have implemented representative approximate
multiplier designs in each category to understand the impact of the design
techniques on accuracy and efficiency. The designs can then be effectively
deployed in high-level applications, such as machine learning, to gain energy
efficiency at the cost of slight accuracy loss.Comment: 38 pages, 37 figure
Berry connection polarizability tensor and third-order Hall effect
One big achievement in modern condensed matter physics is the recognition of
the importance of various band geometric quantities in physical effects. As
prominent examples, Berry curvature and Berry curvature dipole are connected to
the linear and the second-order Hall effects, respectively. Here, we show that
the Berry connection polarizability (BCP) tensor, as another intrinsic band
geometric quantity, plays a key role in the third-order Hall effect. Based on
the extended semiclassical formalism, we develop a theory for the third-order
charge transport and derive explicit formulas for the third-order conductivity.
Our theory is applied to the two-dimensional (2D) Dirac model to investigate
the essential features of BCP and the third-order Hall response. We further
demonstrate the combination of our theory with the first-principles
calculations to study a concrete material system, the monolayer FeSe. Our work
establishes a foundation for the study of third-order transport effects, and
reveals the third-order Hall effect as a tool for characterizing a large class
of materials and for probing the BCP in band structure.Comment: 7 pages, 4 figure
Time-Reversal-Even Nonlinear Current Induced Spin Polarization
We propose a time-reversal-even spin generation in second order of electric
fields, which dominates the current induced spin polarization in a wide class
of centrosymmetric nonmagnetic materials, and leads to a novel nonlinear
spin-orbit torque in magnets. We reveal a quantum origin of this effect from
the momentum space dipole of the anomalous spin polarizability.
First-principles calculations predict sizable spin generations in several
nonmagnetic hcp metals, in monolayer TiTe, and in ferromagnetic monolayer
MnSe, which can be detected in experiment. Our work opens up the broad
vista of nonlinear spintronics in both nonmagnetic and magnetic systems.Comment: 4 pages, 2 figure
Sleep duration, brain structure, and psychiatric and cognitive problems in children
Low sleep duration in adults is correlated with psychiatric and cognitive problems. We performed for the first time a large-scale analysis of sleep duration in children, and how this relates to psychiatric problems including depression, to cognition, and to brain structure. Structural MRI was analyzed in relation to sleep duration, and psychiatric and cognitive measures in 11,067 9–11-year-old children from the Adolescent Brain Cognitive Development (ABCD) Study, using a linear mixed model, mediation analysis, and structural equation methods in a longitudinal analysis. Dimensional psychopathology (including depression, anxiety, impulsive behavior) in the children was negatively correlated with sleep duration. Dimensional psychopathology in the parents was also correlated with short sleep duration in their children. The brain areas in which higher volume was correlated with longer sleep duration included the orbitofrontal cortex, prefrontal and temporal cortex, precuneus, and supramarginal gyrus. Longitudinal data analysis showed that the psychiatric problems, especially the depressive problems, were significantly associated with short sleep duration 1 year later. Further, mediation analysis showed that depressive problems significantly mediate the effect of these brain regions on sleep. Higher cognitive scores were associated with higher volume of the prefrontal cortex, temporal cortex, and medial orbitofrontal cortex. Public health implications are that psychopathology in the parents should be considered in relation to sleep problems in children. Moreover, we show that brain structure is associated with sleep problems in children, and that this is related to whether or not the child has depressive problems