12,564 research outputs found
Object Detection in 20 Years: A Survey
Object detection, as of one the most fundamental and challenging problems in
computer vision, has received great attention in recent years. Its development
in the past two decades can be regarded as an epitome of computer vision
history. If we think of today's object detection as a technical aesthetics
under the power of deep learning, then turning back the clock 20 years we would
witness the wisdom of cold weapon era. This paper extensively reviews 400+
papers of object detection in the light of its technical evolution, spanning
over a quarter-century's time (from the 1990s to 2019). A number of topics have
been covered in this paper, including the milestone detectors in history,
detection datasets, metrics, fundamental building blocks of the detection
system, speed up techniques, and the recent state of the art detection methods.
This paper also reviews some important detection applications, such as
pedestrian detection, face detection, text detection, etc, and makes an in-deep
analysis of their challenges as well as technical improvements in recent years.Comment: This work has been submitted to the IEEE TPAMI for possible
publicatio
Anomaly of -Dimensional Symmetry-Enriched Topological Order from -Dimensional Topological Quantum Field Theory
Symmetry acting on a (2+1) topological order can be anomalous in the sense
that they possess an obstruction to being realized as a purely (2+1) on-site
symmetry. In this paper, we develop a (3+1) topological quantum field theory
to calculate the anomaly indicators of a (2+1) topological order with a
general symmetry group , which may be discrete or continuous, Abelian or
non-Abelian, contain anti-unitary elements or not, and permute anyons or not.
These anomaly indicators are partition functions of the (3+1) topological
quantum field theory on a specific manifold equipped with some -bundle, and
they are expressed using the data characterizing the topological order and the
symmetry actions. Our framework is applied to derive the anomaly indicators for
various symmetry groups, including ,
, , , , etc, where and denote a
unitary and anti-unitary order-2 group, respectively, and denotes a
symmetry group such that elements in with determinant are
anti-unitary. In particular, we demonstrate that some anomaly of and
exhibit symmetry-enforced gaplessness, i.e., they
cannot be realized by any symmetry-enriched topological order. As a byproduct,
for symmetric topological orders, we derive their Hall
conductance.Comment: Recipe of calculating the partition function involving continuous
symmetries added, together with extra example
On Development History of Australia’s Language Policy and the Enlightenment to China’s Foreign Language Education
As is well-known, Australia is the first English country to officially make and efficiently carry out multi-lingual and plural culture in the world, whose language education policy has been highly spoken of by most linguists and politicians in the world in terms of the formulation and implementation. By studying such items as affecting factors, development history, implementing strategies of Australian language education policy under the background of multiculturalism, researchers can get a clue of the law of development of the language education policy in the developed countries and even the world. To be specific, through studying the development history of Australian language education policy under the background of multiculturalism, the paper puts forward some enlightenment and presents some advice on the China’s foreign language education
Amplitude death in nonlinear oscillators with mixed time-delayed coupling
Peer reviewedPublisher PD
Application of Time-Fractional Order Bloch Equation in Magnetic Resonance Fingerprinting
Magnetic resonance fingerprinting (MRF) is one novel fast quantitative
imaging framework for simultaneous quantification of multiple parameters with
pseudo-randomized acquisition patterns. The accuracy of the resulting
multi-parameters is very important for clinical applications. In this paper, we
derived signal evolutions from the anomalous relaxation using a fractional
calculus. More specifically, we utilized time-fractional order extension of the
Bloch equations to generate dictionary to provide more complex system
descriptions for MRF applications. The representative results of phantom
experiments demonstrated the good accuracy performance when applying the
time-fractional order Bloch equations to generate dictionary entries in the MRF
framework. The utility of the proposed method is also validated by in-vivo
study.Comment: Accepted at 2019 IEEE 16th International Symposium on Biomedical
Imaging (ISBI 2019
Freeze then Train: Towards Provable Representation Learning under Spurious Correlations and Feature Noise
The existence of spurious correlations such as image backgrounds in the
training environment can make empirical risk minimization (ERM) perform badly
in the test environment. To address this problem, Kirichenko et al. (2022)
empirically found that the core features that are related to the outcome can
still be learned well even with the presence of spurious correlations. This
opens a promising strategy to first train a feature learner rather than a
classifier, and then perform linear probing (last layer retraining) in the test
environment. However, a theoretical understanding of when and why this approach
works is lacking. In this paper, we find that core features are only learned
well when their associated non-realizable noise is smaller than that of
spurious features, which is not necessarily true in practice. We provide both
theories and experiments to support this finding and to illustrate the
importance of non-realizable noise. Moreover, we propose an algorithm called
Freeze then Train (FTT), that first freezes certain salient features and then
trains the rest of the features using ERM. We theoretically show that FTT
preserves features that are more beneficial to test time probing. Across two
commonly used spurious correlation datasets, FTT outperforms ERM, IRM, JTT and
CVaR-DRO, with substantial improvement in accuracy (by 4.5%) when the feature
noise is large. FTT also performs better on general distribution shift
benchmarks
Optical-pumping enantio-conversion of chiral mixtures in presence of tunneling between chiral states
Enantio-conversion of chiral mixtures, converting the mixtures composed of
left- and right-handed chiral molecules into the homochiral ensembles, has
become an important research topic in chemical and biological fields. In
previous studies on enantio-conversion, the tunneling interaction between the
left- and right-handed chiral states was often neglected. However, for certain
chiral molecules, this tunneling interaction is significant and cannot be
ignored. Here we propose a scheme for enantio-conversion of chiral mixtures
through optical pumping based on a four-level model of chiral molecules,
comprising two chiral ground states and two achiral excited states, with a
tunneling interaction between the chiral states. Under one-photon large
detuning and two-photon resonance conditions, one of the achiral excited states
is eliminated adiabatically. By well designing the detuning and coupling
strengths of the electromagnetic fields, the tunneling interaction between two
chiral states and the interaction between one of the chiral states and the
remaining achiral excited state can be eliminated. Consequently, one chiral
state remains unchanged, while the other can be excited to an achiral excited
state, establishing chiral-state-selective excitations. By numerically
calculating the populations of two chiral ground states and the enantiomeric
excess, we observe that high-efficiency enantio-conversion is achieved under
the combined effects of system dissipation and chiral-state-selective
excitations.Comment: 14 pages, 6 figure
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