125 research outputs found
MTGFlow: Unsupervised Multivariate Time Series Anomaly Detection via Dynamic Graph and Entity-aware Normalizing Flow
Multivariate time series anomaly detection has been extensively studied under
the semi-supervised setting, where a training dataset with all normal instances
is required. However, preparing such a dataset is very laborious since each
single data instance should be fully guaranteed to be normal. It is, therefore,
desired to explore multivariate time series anomaly detection methods based on
the dataset without any label knowledge. In this paper, we propose MTGFlow, an
unsupervised anomaly detection approach for Multivariate Time series anomaly
detection via dynamic Graph and entity-aware normalizing Flow, leaning only on
a widely accepted hypothesis that abnormal instances exhibit sparse densities
than the normal. However, the complex interdependencies among entities and the
diverse inherent characteristics of each entity pose significant challenges on
the density estimation, let alone to detect anomalies based on the estimated
possibility distribution. To tackle these problems, we propose to learn the
mutual and dynamic relations among entities via a graph structure learning
model, which helps to model accurate distribution of multivariate time series.
Moreover, taking account of distinct characteristics of the individual
entities, an entity-aware normalizing flow is developed to describe each entity
into a parameterized normal distribution, thereby producing fine-grained
density estimation. Incorporating these two strategies, MTGFlowachieves
superior anomaly detection performance. Experiments on the real-world datasets
are conducted, demonstrating that MTGFlow outperforms the state-of-the-art
(SOTA) by 5.0% and 1.6% AUROC for SWaT and WADI datasets respectively. Also,
through the anomaly scores contributed by individual entities, MTGFlow can
provide explanation information for the detection results
Frame-wise Cross-modal Matching for Video Moment Retrieval
Video moment retrieval targets at retrieving a moment in a video for a given
language query. The challenges of this task include 1) the requirement of
localizing the relevant moment in an untrimmed video, and 2) bridging the
semantic gap between textual query and video contents. To tackle those
problems, early approaches adopt the sliding window or uniform sampling to
collect video clips first and then match each clip with the query. Obviously,
these strategies are time-consuming and often lead to unsatisfied accuracy in
localization due to the unpredictable length of the golden moment. To avoid the
limitations, researchers recently attempt to directly predict the relevant
moment boundaries without the requirement to generate video clips first. One
mainstream approach is to generate a multimodal feature vector for the target
query and video frames (e.g., concatenation) and then use a regression approach
upon the multimodal feature vector for boundary detection. Although some
progress has been achieved by this approach, we argue that those methods have
not well captured the cross-modal interactions between the query and video
frames.
In this paper, we propose an Attentive Cross-modal Relevance Matching (ACRM)
model which predicts the temporal boundaries based on an interaction modeling.
In addition, an attention module is introduced to assign higher weights to
query words with richer semantic cues, which are considered to be more
important for finding relevant video contents. Another contribution is that we
propose an additional predictor to utilize the internal frames in the model
training to improve the localization accuracy. Extensive experiments on two
datasets TACoS and Charades-STA demonstrate the superiority of our method over
several state-of-the-art methods. Ablation studies have been also conducted to
examine the effectiveness of different modules in our ACRM model.Comment: 12 pages; accepted by IEEE TM
Absence of topological Hall effect in FeRh epitaxial films: revisiting their phase diagram
A series of FeRh () films were epitaxially
grown using magnetron sputtering, and were systematically studied by
magnetization-, electrical resistivity-, and Hall resistivity measurements.
After optimizing the growth conditions, phase-pure FeRh films
were obtained, and their magnetic phase diagram was revisited. The
ferromagnetic (FM) to antiferromagnetic (AFM) transition is limited at narrow
Fe-contents with in the bulk FeRh alloys. By
contrast, the FM-AFM transition in the FeRh films is extended to
cover a much wider range between 33 % and 53 %, whose critical temperature
slightly decreases as increasing the Fe-content. The resistivity jump and
magnetization drop at the FM-AFM transition are much more significant in the
FeRh films with 50 % Fe-content than in the Fe-deficient
films, the latter have a large amount of paramagnetic phase. The
magnetoresistivity (MR) is rather weak and positive in the AFM state, while it
becomes negative when the FM phase shows up, and a giant MR appears in the
mixed FM- and AFM states. The Hall resistivity is dominated by the ordinary
Hall effect in the AFM state, while in the mixed state or high-temperature FM
state, the anomalous Hall effect takes over. The absence of topological Hall
resistivity in FeRh films with various Fe-contents implies that
the previously observed topological Hall effect is most likely extrinsic. We
propose that the anomalous Hall effect caused by the FM iron moments at the
interfaces nicely explains the hump-like anomaly in the Hall resistivity. Our
systematic investigations may offer valuable insights into the spintronics
based on iron-rhodium alloys.Comment: 9 pages, 10 figures; accepted by Phys. Rev.
Peeling the Onion: Hierarchical Reduction of Data Redundancy for Efficient Vision Transformer Training
Vision transformers (ViTs) have recently obtained success in many
applications, but their intensive computation and heavy memory usage at both
training and inference time limit their generalization. Previous compression
algorithms usually start from the pre-trained dense models and only focus on
efficient inference, while time-consuming training is still unavoidable. In
contrast, this paper points out that the million-scale training data is
redundant, which is the fundamental reason for the tedious training. To address
the issue, this paper aims to introduce sparsity into data and proposes an
end-to-end efficient training framework from three sparse perspectives, dubbed
Tri-Level E-ViT. Specifically, we leverage a hierarchical data redundancy
reduction scheme, by exploring the sparsity under three levels: number of
training examples in the dataset, number of patches (tokens) in each example,
and number of connections between tokens that lie in attention weights. With
extensive experiments, we demonstrate that our proposed technique can
noticeably accelerate training for various ViT architectures while maintaining
accuracy. Remarkably, under certain ratios, we are able to improve the ViT
accuracy rather than compromising it. For example, we can achieve 15.2% speedup
with 72.6% (+0.4) Top-1 accuracy on Deit-T, and 15.7% speedup with 79.9% (+0.1)
Top-1 accuracy on Deit-S. This proves the existence of data redundancy in ViT.Comment: AAAI 202
Atmospheric deposition and river runoff stimulate the utilization of dissolved organic phosphorus in coastal seas
In coastal seas, the role of atmospheric deposition and river runoff in dissolved organic phosphorus (DOP) utilization is not well understood. Here, we address this knowledge gap by combining microcosm experiments with a global approach considering the relationship between the activity of alkaline phosphatases and changes in phytoplankton biomass in relation to the concentration of dissolved inorganic phosphorus (DIP). Our results suggest that the addition of aerosols and riverine water stimulate the biological utilization of DOP in coastal seas primarily by depleting DIP due to increasing nitrogen concentrations, which enhances phytoplankton growth. This “Anthropogenic Nitrogen Pump” was therefore identified to make DOP an important source of phosphorus for phytoplankton in coastal seas but only when the ratio of chlorophyll a to DIP [Log10 (Chl a / DIP)] is larger than 1.20. Our study therefore suggests that anthropogenic nitrogen input might contribute to the phosphorus cycle in coastal seas
Uncertainty-inspired Open Set Learning for Retinal Anomaly Identification
Failure to recognize samples from the classes unseen during training is a
major limit of artificial intelligence (AI) in real-world implementation of
retinal anomaly classification. To resolve this obstacle, we propose an
uncertainty-inspired open-set (UIOS) model which was trained with fundus images
of 9 common retinal conditions. Besides the probability of each category, UIOS
also calculates an uncertainty score to express its confidence. Our UIOS model
with thresholding strategy achieved an F1 score of 99.55%, 97.01% and 91.91%
for the internal testing set, external testing set and non-typical testing set,
respectively, compared to the F1 score of 92.20%, 80.69% and 64.74% by the
standard AI model. Furthermore, UIOS correctly predicted high uncertainty
scores, which prompted the need for a manual check, in the datasets of rare
retinal diseases, low-quality fundus images, and non-fundus images. This work
provides a robust method for real-world screening of retinal anomalies
Research on the Jumping Control Methods of a Quadruped Robot That Imitates Animals
At present, most quadruped robots can move quickly and steadily on both flat and undulating ground; however, natural environments are complex and changeable, so it is important for a quadruped robot to be able to jump over obstacles immediately. Inspired by the jumping movement of quadruped animals, we present aerial body posture adjustment laws and generate animal-like jumping trajectories for a quadruped robot. Then, the bionic reference trajectories are optimized to build a trajectory library of a variety of jumping motions based on the kinematic and dynamic constraints of the quadruped robot. The model predictive control (MPC) method is employed by the quadruped robot to track the optimized trajectory to achieve jumping behavior. The simulations show that the quadruped robot can jump over an obstacle of 40 cm in height. The effectiveness of the animal-like jump control method is verified
Simulation of High-Performance Surface Plasmon Resonance Sensor Based on D-Shaped Dual Channel Photonic Crystal Fiber for Temperature Sensing
This paper presents and numerically analyzes a refractive index sensor based on side-polished D-shaped two-channel photonic crystal fiber (PCF) and surface plasmon resonance (SPR). The effects of pore duty ratio, polishing depth, and thickness of a Nano-Titania sensitizing layer on sensor performance are studied, and the sensor performance is analyzed and optimized. The results show that the sensitivity of the Nano-Titania sensitized sensor can reach 3392.86 nm/RIU and temperature sensitivity of the sensor is increased to 1.320 nm/K, and the amplitude sensitivity of the unsensitized sensor can reach 376.76 RIU−1. In addition, the influence of titanium dioxide layer on the mode field diameter of PCF fiber core is also studied. It is found out that the sensor with a 50 nm thick titanium dioxide film has a larger mode fiber diameter, and is more conducive to coupling with single-mode fiber. Our detailed results contribute to the understanding of SPR phenomena in hexagonal PCF and facilitate the implementation and application of SPR-PCF sensors
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