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What makes for uniformity for non-contrastive self-supervised learning?

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Science China(Technological Sciences) 2022年第10期65卷 2399-2408页

作者： wang YinQuan ZHANG XiaoPeng TIAN Qi lü JinHu Key laboratory of Systems and Control Academy of Mathematics and Systems ScienceChinese Academy of SciencesBeijing 100190China School of Mathematical Sciences University of Chinese Academy of SciencesBeijing 100049China Huawei Inc. Shenzhen 518128China School of Automation Science and Electrical Engineering State Key Laboratory of Software Development EnvironmentBeihang UniversityBeijing 100191China

Recent advances in self-supervised learning(SSl) have made remarkable progress, especially for contrastive methods that target pulling two augmented views of one image together and pushing the views of all other images away. In this setting, negative pairs play a key role in avoiding collapsed representation. Recent studies, such as those on bootstrap your own latent(BYOl)and SimSiam, have surprisingly achieved a comparable performance even without contrasting negative samples. However, a basic theoretical issue for SSl arises: how can different SSl methods avoid collapsed representation, and is there a common design principle? In this study, we look deep into current non-contrastive SSl methods and analyze the key factors that avoid *** achieve this goal, we present a new indicator of uniformity metric and study the local dynamics of the indicator to diagnose collapses in different scenarios. Moreover, we present some principles for choosing a good predictor, such that we can explicitly control the optimization process. Our theoretical analysis result is validated on some widely used benchmarks spanning differentscale datasets. We also compare recent SSl methods and analyze their commonalities in avoiding collapses and some ideas for future algorithm designs.

关键词： contrastive learning self-supervised learning representation uniformity dynamics

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A Novel Structural Measure Separating Non-Coding RNAs from Genomic Backgrounds

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Tsinghua Science and Technology 2015年第5期20卷 474-483页

作者： Yingfeng wang Russell l.Malmberg liming Cai the School of Information Technology Middle Georgia State University Department of Plant Biology and Institute of Bioinformatics University of Georgia Department of Computer Science and Institute of Bioinformatics University of Georgia

RNA secondary structure has become the most exploitable feature for ab initio detection of non-coding RNA（nc RNA） genes from genome sequences. Previous work has used Minimum Free Energy（MFE） based methods developed to identify nc RNAs by measuring sequence fold stability and certainty. However, these methods yielded variable performances across different nc RNA species. Designing novel reliable structural measures will help to develop effective nc RNA gene finding tools. This paper introduces a new RNA structural measure based on a novel RNA secondary structure ensemble constrained by characteristics of native RNA tertiary structures. The new method makes it possible to achieve a performance leap from the previous structure-based methods. Test results on standard nc RNA datasets（benchmarks） demonstrate that this method can effectively separate most nc RNAs families from genome backgrounds.

关键词： RNA secondary structure RNA tertiary structure Inside algorithm

Accuracy of the half-power bandwidth method with a third-order correction for estimating damping in multi-DOF systems

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Earthquake Engineering and Engineering Vibration 2013年第1期12卷 33-38页

作者： wang Jinting lü Dandan Jin Feng Zhang Chuhan State Key laboratory of Hydroscience and Engineering Tsinghua University

A third-order correction was recently suggested to improve the accuracy of the half-power bandwidth method in estimating the damping of single DOF *** paper analyzes the accuracy of the half-power bandwidth method with the third-order correction in damping estimation for multi-DOF linear *** ratios in a two-DOF linear system are estimated using its displacement and acceleration frequency response curves,respectively.A wide range of important parameters that characterize the shape of these response curves are taken into *** show that the third-order correction may greatly improve the accuracy of the half-power bandwidth method in estimating damping in a two-DOF *** spite of this,the half-power bandwidth method may significantly overestimate the damping ratios of two-DOF systems in some cases.

关键词： half-power bandwidth method third-order correction damping ratio estimation error two-DOF system

Modified sequential importance resampling filter

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Journal of Systems Engineering and Electronics 2015年第3期26卷 441-449页

作者： Yong Wu Jun wang Xiaoyong l Yunhe Cao National lab of Radar Signal Processing Xidian University

In order to deal with the particle degeneracy and impov- erishment problems existed in particle filters, a modified sequential importance resampling （MSIR） filter is proposed. In this filter, the resampling is translated into an evolutional process just like the biological evolution. A particle generator is constructed, which introduces the current measurement information （CMI） into the resampled particles. In the evolution, new particles are first pro- duced through the particle generator, each of which is essentially an unbiased estimation of the current true state. Then, new and old particles are recombined for the sake of raising the diversity among the particles. Finally, those particles who have low quality are eliminated. Through the evolution, all the particles retained are regarded as the optimal ones, and these particles are utilized to update the current state. By using the proposed resampling approach, not only the CMI is incorporated into each resampled particle, but also the particle degeneracy and the loss of diver- sity among the particles are mitigated, resulting in the improved estimation accuracy. Simulation results show the superiorities of the proposed filter over the standard sequential importance re- sampling （SIR） filter, auxiliary particle filter and unscented Kalman particle filter.

关键词： sequential importance resampling (SIR) evolution,current measurement information (CMI) unbiased estimation.

Numerical simulation of flow focusing pattern and morphological changes in two-phase flow inside nozzle

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Chinese Journal of Chemical Engineering 2019年第1期27卷 63-71页

作者： Jin Zhao Zhi Ning Ming lü Geng wang College of Mechanical and Electrical Engineering Beijing Jiaotong University

The flow focusing nozzle is a new type of nozzle that performs effective atomization of the discrete phase by means of high-speed motion of the continuous *** flow pattern and its morphological changes have a significant effect on the atomization, but the influence of different parameters on the morphological change of the flow pattern remains *** flow focusing pattern and morphological changes in the two-phase flow inside the nozzle were simulated numerically, based on the volume of fluid *** results demonstrate that the ratio of the nozzle-to-capillary distance and capillary diameter, the gas–liquid velocity ratio, and capillary diameter have significant effects on the flow *** the ratio of the nozzle-to-capillary distance H and capillary diameter D increases, or the capillary diameter D increases, the flow pattern tends to transform into a laminar form; however, when the gas–liquid velocity ratio V increases, the flow pattern tends to transform into a turbulence ***, we define the cone-shaped expansion rate, cone-shaped focusing rate,and cone angle in order to study the morphological changes in the cone shape inside the *** results indicate that the morphological change of the cone shape and flow pattern transformation is *** the cone shape tends to be unstable, the flow pattern changes towards flow blurring, whereas, a stable cone indicates that the flow tends to exhibit a droplet pattern.

关键词： Flow focusing Pattern transformation Morphological changes Numerical simulation

Seismic behavior of outrigger truss-wall shear connections using multiple steel angles

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Earthquake Engineering and Engineering Vibration 2016年第2期15卷 197-208页

作者： li Xian wang Wei lü Henglin Zhang Guangchang State Key laboratory for Geomechanics & Deep Underground Engineering China University of Mining and Technology Jiangsu Key laboratory of Environmental Impact and Structural Safety in Civil Engineering School of Mechanics and Civil Engineering China University of Mining and Technology

An experimental investigation on the seismic behavior of a type of outrigger truss-reinforced concrete wall shear connection using multiple steel angles is presented. Six large-scale shear connection models, which involved a portion of reinforced concrete wall and a shear tab welded onto a steel endplate with three steel angles, were constructed and tested under combined actions of cyclic axial load and eccentric shear. The effects of embedment lengths of steel angles, wall boundary elements, types of anchor plates, and thicknesses of endplates were investigated. The test results indicate that properly detailed connections exhibit desirable seismic behavior and fail due to the ductile fracture of steel angles. Wall boundary elements provide beneficial confinement to the concrete surrounding steel angles and thus increase the strength and stiffness of connections. Connections using whole anchor plates are prone to suffer concrete pry-out failure while connections with thin endplates have a relatively low strength and fail due to large inelastic deformations of the endplates. The current design equations proposed by Chinese Standard 04G362 and Code GB50011 significantly underestimate the capacities of the connection models. A revised design method to account for the influence of previously mentioned test parameters was developed.

关键词： anchor truss suffer welded reinforced stiffness tensile desirable properly frames

The Hilbert expansion of the Boltzmann equation in the incompressible Euler level in a channel

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Science China Mathematics 2025年第1期 39-88页

作者： Feimin Huang Weiqiang wang Yong wang Feng Xiao Academy of Mathematics and Systems Science Chinese Academy of Sciences School of Mathematical Sciences University of Chinese Academy of Sciences Key laboratory of Computing and Stochastic Mathematics (Ministry of Education) School of Mathematics and StatisticsHunan Normal University

The study of the hydrodynamic limit of the Boltzmann equation with physical boundary is a challenging problem due to the appearance of the viscous and Knudsen boundary *** this paper,the hydrodynamic limit from the Boltzmann equation with the specular reflection boundary condition to the incompressible Euler equations in a channel is *** on the multi-scaled Hilbert expansion,the equations with boundary conditions and compatibility conditions for interior solutions,and viscous and Knudsen boundary layers are derived under different scaling,***,some uniform estimates for the interior solutions,and viscous and Knudsen boundary layers are *** the help of the l2-l∞framework and the uniform estimates obtained above,the solutions to the Boltzmann equation are constructed by the truncated Hilbert expansion with multiscales,and hence the hydrodynamic limit in the incompressible Euler level is justified.

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An analytical model for electrode-ceramic interaction in multilayer piezoelectric actuators

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Acta Mechanica Sinica 2007年第2期23卷 199-208页

作者： B.l.wang J.C.Han Center for Composite Materials Harbin Institute of TechnologyHarbin 150001China

The present paper develops an analytical model for multi-electrodes in multi-layered piezoelectric actuators, in which the electrodes are vertical to and terminated at the edges of the medium and electroelastic field concentrations ahead of the electrodes in the multilayer piezoelectric actuators are examined. By considering a representative unit in realistic multilayers, the problem is formulated in terms of electric potential between the electrode tips and results in a system of singular integral equations in which the electric potential is taken as unknown function. Effects are investigated of electrode spacing and piezoelectric coupling on the singular electroelastic fields at the electrode tips, and closed-form expressions are given for the electromechanical field near the electrode tips. Exact solution for un-coupled dielectrics is provided, where no piezoelectric coupling is present.

关键词： Actuators . Piezoelectric materials . Electrodes. Multilayer. Fracture mechanics

CAlCUlATION OF SECOND PHASE PARTIClE-GRAIN BOUNDARY INTERACTION RANGE

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Acta Metallurgica Sinica(English letters) 2008年第1期21卷 8-14页

作者： X.l. wang Y.H. Wei W. wang l.F. Hou College of Materials Science and Engineering Taiyuan University of Technology Taiyuan 030024 China Baosteel Technology Center Baoshan Iron ＆ Steel Co. Ltd. Shanghai 201900 China Manuscript received 20 December 2006

On the basis of the grain boundary equation by HeUman and corresponding analysis of Worner, this article deals with the interaction range between the second-phase particle （SPP） and grain boundary （GB） as viewed from the applicability of grain boundary equation. Also, a new expression describing the interaction range has been derived, which solves the problem in theory that the interaction range between SPP and GB can only be qualitatively analyzed previously. It is shown that given the interaction position between SPP and GB, the interaction range can be quantitatively determined by use of this expression.

关键词： Second-phase particle Grain boundary Pinning force Surface free energy