139 research outputs found
Imaging Ferroelectric Domains via Charge Gradient Microscopy Enhanced by Principal Component Analysis
Local domain structures of ferroelectrics have been studied extensively using
various modes of scanning probes at the nanoscale, including piezoresponse
force microscopy (PFM) and Kelvin probe force microscopy (KPFM), though none of
these techniques measure the polarization directly, and the fast formation
kinetics of domains and screening charges cannot be captured by these
quasi-static measurements. In this study, we used charge gradient microscopy
(CGM) to image ferroelectric domains of lithium niobate based on current
measured during fast scanning, and applied principal component analysis (PCA)
to enhance the signal-to-noise ratio of noisy raw data. We found that the CGM
signal increases linearly with the scan speed while decreases with the
temperature under power-law, consistent with proposed imaging mechanisms of
scraping and refilling of surface charges within domains, and polarization
change across domain wall. We then, based on CGM mappings, estimated the
spontaneous polarization and the density of surface charges with order of
magnitude agreement with literature data. The study demonstrates that PCA is a
powerful method in imaging analysis of scanning probe microscopy (SPM), with
which quantitative analysis of noisy raw data becomes possible
RealFlow: EM-based Realistic Optical Flow Dataset Generation from Videos
Obtaining the ground truth labels from a video is challenging since the
manual annotation of pixel-wise flow labels is prohibitively expensive and
laborious. Besides, existing approaches try to adapt the trained model on
synthetic datasets to authentic videos, which inevitably suffers from domain
discrepancy and hinders the performance for real-world applications. To solve
these problems, we propose RealFlow, an Expectation-Maximization based
framework that can create large-scale optical flow datasets directly from any
unlabeled realistic videos. Specifically, we first estimate optical flow
between a pair of video frames, and then synthesize a new image from this pair
based on the predicted flow. Thus the new image pairs and their corresponding
flows can be regarded as a new training set. Besides, we design a Realistic
Image Pair Rendering (RIPR) module that adopts softmax splatting and
bi-directional hole filling techniques to alleviate the artifacts of the image
synthesis. In the E-step, RIPR renders new images to create a large quantity of
training data. In the M-step, we utilize the generated training data to train
an optical flow network, which can be used to estimate optical flows in the
next E-step. During the iterative learning steps, the capability of the flow
network is gradually improved, so is the accuracy of the flow, as well as the
quality of the synthesized dataset. Experimental results show that RealFlow
outperforms previous dataset generation methods by a considerably large margin.
Moreover, based on the generated dataset, our approach achieves
state-of-the-art performance on two standard benchmarks compared with both
supervised and unsupervised optical flow methods. Our code and dataset are
available at https://github.com/megvii-research/RealFlowComment: ECCV 2022 Ora
Fault diagnosis of refrigerant charge based on PCA and decision tree for variable refrigerant flow systems
Variable refrigerant flow (VRF) systems are easily subjected to performance degradation due to refrigerant leakage, mechanical failure or improper maintenance after years of operation. Ideal VRF systems should equip with fault detection and diagnosis (FDD) program to sustain its normal operation. This paper presents the fault diagnosis method for refrigerant charge faults of variable refrigerant flow (VRF) systems. It is developed based on the principal component analysis (PCA) feature extraction method and the decision tree (DT) classification algorithm. Nine refrigerant charge schemes are implemented on the VRF system in the laboratory, which contain the normal and faulty refrigerant charge conditions. In addition, data of the online operating VRF systems are collected in this work. Firstly, data from both experimental VRF system and online operating systems are pre-processed by outlier cleaning, feature extraction and data normalization, because the original data of the VRF system usually has poor quality and complex structure. Secondly, the fault diagnosis model based on the PCA-DT method is built using the data of the experimental VRF system. In this step, the PCA method is used to obtain a new data sample which includes four comprehensive features, then the new data sample are randomly split into training and testing sets as the input of DT classifier for fault diagnosis. Thirdly, the advantages of the PCA-DT method is validated using the experimental data of different fault severity levels. Results show that the combined use of PCA and DT methods can achieve better fault diagnosis efficiency than the single decision tree method. Further, the robustness of the PCA-DT method in online fault diagnosis is verified using the data from online VRF systems. The online VRF systems have the same or different number of indoor units as the trained (experimental) VRF system. The PCA-DT method also shows desirable goodness on the online fault diagnosis process. In this sense, this work provides a promising fault diagnosis strategy for refrigerant charge faults of VRF system application
Uncertainty Guided Adaptive Warping for Robust and Efficient Stereo Matching
Correlation based stereo matching has achieved outstanding performance, which
pursues cost volume between two feature maps. Unfortunately, current methods
with a fixed model do not work uniformly well across various datasets, greatly
limiting their real-world applicability. To tackle this issue, this paper
proposes a new perspective to dynamically calculate correlation for robust
stereo matching. A novel Uncertainty Guided Adaptive Correlation (UGAC) module
is introduced to robustly adapt the same model for different scenarios.
Specifically, a variance-based uncertainty estimation is employed to adaptively
adjust the sampling area during warping operation. Additionally, we improve the
traditional non-parametric warping with learnable parameters, such that the
position-specific weights can be learned. We show that by empowering the
recurrent network with the UGAC module, stereo matching can be exploited more
robustly and effectively. Extensive experiments demonstrate that our method
achieves state-of-the-art performance over the ETH3D, KITTI, and Middlebury
datasets when employing the same fixed model over these datasets without any
retraining procedure. To target real-time applications, we further design a
lightweight model based on UGAC, which also outperforms other methods over
KITTI benchmarks with only 0.6 M parameters.Comment: Accepted by ICCV202
Comparative analysis of potential vorticity between persistent rainstorm and extreme intense rainfall events during the Yangtze-Huaihe Meiyu period
In this study, based on the rainfall measurements from weather stations over China and atmospheric reanalysis products from the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) during the period of 1979-2020, the dynamic mechanisms and differences of persistent rainstorm (PRS) events and extreme intense rainfall (EIR) events over the Yangtze-Huaihe Meiyu domain (YMD) are revealed from the perspective of potential vorticity (PV)-forced vertical motion. According to the improved definitions of PRS and EIR events, 24 PRS events and 24 EIR cases are identified over the YMD during the Meiyu period from 1979 to 2020. Composite analyses for the two types of events demonstrate that the most intense rainband of PRS events is mainly located in the Yangtze River and over the southern regions of it, while for the EIR, the most intense rainband is located in the Yangtze River and over the northern regions of it. The PRS events are found to be closely related to tropical atmospheric intraseasonal oscillation, during which the upper-tropospheric South Asian high extends more eastward, while the northwestern Pacific subtropical anticyclone in the lower and middle troposphere shifts more westward. Thus, the dry and cold air with high-PV around the upper-tropospheric westerly jet located more southward latitudes tends to intrude equatorward and downward, converging with the warm and moist air from the southwest in the lower and middle troposphere to form Meiyu front. However, the EIR events are more dependent to a greater extent on the upper-tropospheric divergence on the southern side of the westerly jet located more northward latitudes and PV-forced downward-intruding cold air. The quantitative diagnoses of PV budget for EIR events show that before and during the peak of intense rainfall, the net negative PV tendency in the upper troposphere is mainly dominated by the negative vertical PV advection, while the positive PV tendency in the middle and lower troposphere is mainly caused by the PV generation due to the vertically non-uniform diabatic heating and vertical PV advection. The vertical velocity decomposition of a typical EIR event further demonstrates that the component of ascending velocity forced by the vertical increase of horizontal PV advection plays an important role in triggering the EIR event
Atomic-Scale Tracking Phase Transition Dynamics of Berezinskii-Kosterlitz-Thouless Polar Vortex-Antivortex
Particle-like topologies, such as vortex-antivortex (V-AV) pairs, have
garnered significant attention in the field of condensed matter. However, the
detailed phase transition dynamics of V-AV pairs, as exemplified by
self-annihilation, motion, and dissociation, have yet to be verified in real
space due to the lack of suitable experimental techniques. Here, we employ
polar V-AV pairs as a model system and track their transition pathways at
atomic resolution with the aid of in situ (scanning) transmission electron
microscopy and phase field simulations. We demonstrate the absence of a
Berezinskii-Kosterlitz-Thouless phase transition between the room-temperature
quasi-long-range ordered ground phase and the high-temperature disordered
phase. Instead, we observe polarization suppression in bound V-AV pairs as the
temperature increases. Furthermore, electric fields can promote the vortex and
antivortex to approach each other and annihilate near the interface. The
elucidated intermediate dynamic behaviors of polar V-AV pairs under thermal-
and electrical-fields lay the foundation for their potential applications in
electronic devices. Moreover, the dynamic behaviors revealed at atomic scale
provide us new insights into understanding topological phase of matter and
their topological phase transitions.Comment: 19 pages and 4 figure
- …