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Conductive edge-warping graphite mesas for robust structural superlubricity

Science China(Technological Sciences) 2024年第7期67卷 2040-2049页

作者： FENG WeiJia LIU Ying MA Ming PENG DeLi NIE JinHui State Key Laboratory of Tribology in Advanced Equipment&Department of Mechanical engineering Tsinghua UniversityBeijing 100084China Center for Nano and Micro Mechanics Tsinghua UniversityBeijing 100084China Institute of Superlubricity Technology Research Institute of Tsinghua University in ShenzhenShenzhen 518057China

Structural superlubricity(SSL) refers to a state of ultralow friction and zero wear when two solid surfaces slide against each other. Recent investigations have identified amorphous carbon at the edge of the graphite mesa as the primary source of friction in such SSL systems. Here, the tensile stress of metal thin film is exploited to engineer vertically conductive edge-warping graphite mesas(EWGM). Through this approach, robust SSL performance is realized, demonstrated by sliding an 8 μm side length square EWGM on an atomically smooth Au substrate for 10000 cycles at a constant voltage of 1 m V. In this SSL system,differential friction coefficients lower than 1.5 × 10^(-4) are achieved, with static contact resistance between EWGM and Au substrate as low as 28Ω and sliding contact resistance as low as 32Ω. Moreover, the EWGM exhibits SSL behavior on polished Si wafer substrates. Furthermore, because of the no-edge contact with the substrate during sliding, friction is independent of the sliding speed of the EWGM. This study presents the first successful fabrication of conductive EWGM. Remarkably, in both EWGM-Au and EWGM-Si SSL systems, the measured frictions are more than one order of magnitude lower than those of ordinary self-retracting graphite mesas with no-edge warping, and no wear is observed during extended current-carrying ***, these findings establish a solid groundwork for the future realization of macroscale conductive SSL systems.

关键词： structural superlubricity graphite mesa contact resistance tensile stress edge warping

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Optimizing the design of in situ sediment oxygen demand measurement chambers

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International Journal of Sediment research 2011年第2期26卷 222-229页

作者： HE Yun and LIU Cheng 1 Senior engineer,Dr.,China Institute of Water Resources and Hydropower research,Beijing 100038,China, 2 Prof.,Dr.,International research and Training Center on Erosion and Sedimentation,Beijing 100048,China Senior engineer Dr. China Institute of Water Resources and Hydropower Research Beijing 100038 China Prof. Dr. International Research and Training Center on Erosion and Sedimentation Beijing 100048 China

Sediment Oxygen Demand(SOD) is a key parameter for water quality analysis and for water quality modeling in rivers,lakes,estuaries and *** SOD can be measured both in the laboratory and in ***,the in situ technique appears to be the better approach for measuring SOD,as it likely to provide more representative and accurate *** order to optimize the design of in situ SOD measurement chambers,the three-dimensional flow fields in cylindrical SOD measurement chambers, commonly used for in situ measurements,have been numerically simulated by using the RNG-based k-s double equation turbulence *** chambers with three different inflow pipe configurations were *** results show that chamberⅢpresents distinct advantages over the other designs for in situ SOD measurement,because good flow mixing can be achieved and bottom sediment suspension can be avoided in the *** numerical simulation results were validated by comparison with existing results derived from laboratory *** SOD measurement chamber designed to reflect the results of the numerical simulations was successfully tested for in situ SOD measurements in both fresh and saline waters.

关键词： Sediment Oxygen Demand(SOD) Renormalization group(RNG) Velocity field In situ measurement Field tests

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A secure routing model based on distance vector routing algorithm

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Science China(Information Sciences) 2014年第1期57卷 137-149页

作者： WANG Bin WU ChunMing YANG Qiang LAI Pan LAN JuLong GUO YunFei College of Computer Science Zhejiang University College of Electrical engineer Zhejiang University School of Computer engineering Nanyang Technological University National Digital Switching System engineering and Technological research Center

Distance vector routing protocols have been widely adopted as an efcient routing mechanism in current Internet,and many wireless ***,as is well-known,the existing distance vector routing protocols are insecure as it lacks of efective authorization mechanisms and routing updates aggregated from other *** a result,the network routing-based attacks become a critical issue which could lead to a more deteriorate performance than other general network *** efciently address this issue,this paper,through analyzing the routing model and its security aspect,and presents a novel approach on guaranteeing the routing *** on the model,we present the security mechanism including the message exchange and update message security authentication *** suggested approach shows that the security mechanism can efectively verify the integrity and validate the freshness of routing update messages received from neighbor *** comparison with exiting mechanisms(SDV,S-RIP etc),the proposed model provides enhanced security without introducing significant network overheads and complexity.

关键词： routing security distance vector auxiliary trustable model authentication metric

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SYNCHRONOUS EFFECT OF SLIPPING HEAVY LOADS ON RO-RO SHIP ROLLING IN WAVES

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Applied Mathematics and Mechanics(English Edition) 2006年第7期27卷 959-966页

作者：张银龙沈庆陈徐均 Second engineers Scientific research Institute of the General Armaments Department Beijing 100036 P.R.China engineering Institute of engineer Corps PLA University of Science and Technology Nanjing 210007 P. R. China engineering Institute of engineer Corps PLA University of Science and Technology Nanjing 210007 P.R.China

Common effect of wave and slip of internal vehicles will make rolling of the roll-on ship serious. This is one of the important reasons for overturn of ro-ro ships. The multibody system with a floating base is composed of ro-ro ship and slipping vehicles. Takes the rolling angle of the ship and the transverse displacements of the slipping vehicles on desk as freedoms. Making use of the analysis of apparent gravitation and apparent buoyancy, the wave rolling moment is derived. By means of dynamic method of multibody system, dynamic equations of the system are established. Taking a certain channel ferry as an example, a set of numerical calculation have been carried out for rolling response of the multibody system with a floating base of a ro-ro ship and displacements response of the slipping vehicles under common effect of free slipping vehicles and wave, and a conclusion has been drawn that the motion of the numerous free slipping heavy loads will trend to be synchronous under restraining of the side-wall bulkhead with time because of repeated collision.

关键词： ro-ro ship slipping heavy loads floating base multibodies system synchronous effect dynamics

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Modeling structured peer-to-peer systems

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The Journal of China Universities of Posts and Telecommunications 2006年第3期13卷 76-80页

作者： HAN Li LEI Zhen-ming Information engineer Institute Beijing University of Posts and Telecommunications Beijing 100876 China

Distributed network architecture and dynamic change of nodes makes the operation of structured peer-to-peer networks unpredictable. This article aims to present a research on the running rule of structured peer-to-peer networks through a mathematical model. The proposed model provides a low-complexity means to estimate the performance of a structured peer-to-peer network from two aspects： the average existent time of a node and probability of returning to a temporarily steady state of network. On the basis of the results, it can be concluded that the proposed structured peer-to-peer network is suitable for those conditions where the frequency of node change is under limited value, and this value mainly depends on the initializing time of the node. Otherwise, structured peer-to-peer network can be abstracted as a network queuing system, which is composed of many node queuing systems in a meshy way and the relation between the throughput of the node system and network system is analyzed.

关键词： peer-to-peer network distributed hash table bith and death Markov model average existent time temporarily steady state

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Target tracking of the scale and rotation problem research 25th

Target tracking of the scale and rotation problem research

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第25届中国控制与决策会议

作者： Ren Hongwei Zhao Qinjun Cheng Xingong Wang Chengyou Schools of Electrical engineer University of Jinan

ISBN: (纸本)9781467355322

In order to solve the scale and rotation problem in target tracking, a target tracking algorithm based on scale invariant feature transform and mean shift is proposed. First, template area and the target area in the extreme value point of scale space are detected ,then accurate position and scale of the feature point are detected through the simulation of three dimensional quadratic function,after that feature points of the target area and template area are matched,and error matching is removed according to the continuity of scale and angle between adjacent frame. The experimental results show that the algorithm has good tracking performance when targets angle and scale changed.

关键词： target tracking mean-shift algorithm SIFI algorithm scale space

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Obstacle-transformer: A trajectory prediction network based on surrounding trajectories

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IET Cyber-Systems and Robotics 2023年第1期5卷 1-8页

作者： Wendong Zhang Qingjie Chai Quanqi Zhang Chengwei Wu Department of Control Science and engineer Harbin Institute of TechnologyHarbinChina

Recurrent Neural Network,Long Short-Term Memory,and Transformer have made great progress in predicting the trajectories of moving *** the trajectory element with the surrounding scene features has been merged to improve performance,there still exist some problems to be *** is that the time series processing models will increase the inference time with the increase of the number of prediction *** problem is that the features cannot be extracted from the scene's image and point cloud in some ***,an Obstacle-Transformer is proposed to predict trajectory in a constant inference ***‘obstacle’is designed by the surrounding trajectory rather than images or point clouds,making Obstacle-Transformer more applicable in a wider range of *** are conducted on ETH and UCY datasets to verify the performance of our model.

关键词： deep-learning trajectory prediction transformer

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Y_(2)O_(3)modification on nickel-rich LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)with improved electrochemical performance in lithium-ion batteries

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Journal of Rare Earths 2022年第2期40卷 309-317,I0005页

作者： Rui He Xue Bai Aijia Wei Lihui Zhang Peng Liu Zhenfa Liu Institute of Energy Resources Hebei Academy of ScienceShijiazhuang 050081China Hebei engineer research Center for Water Saving in Industry Shijiazhuang 050081China Shijiazhuang Suntec-Chem Co. LtdShijiazhuang 050000China

Doping and coating are frequently employed for the improvement of the properties of Ni-rich NCM *** this work,we prepared stable LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)materials modified withY_(2)O_(3)via a wet chemical *** order to investigate the action mechanism ofY_(2)O_(3)on NCM811,we analyzed the micro structures using X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM),and transmission electron microscopy(TEM).Also,to study the electrochemical performances,we conducted a charge/discharge test and cyclic *** results show thatY_(2)O_(3)modified NCM811 materials have good thermal stability,and proper content ofY_(2)O_(3)can effectively prevent the materials from damaging and significantly improve the electrochemical properties of the ***,1%Y2 O3 modified NCM811 material show much better cycling performance than other *** cycling at 1.0 C the 1%Y2 O3 modified NCM811 shows capacity retention of 90.1%after 100 cycles,which is higher than 69.4%for pristine *** examined the microstructures of the materials before and after *** the SEM results,we conclude that structural changes are among the key factors that lead to the degradation of the electrochemical properties of materials.

关键词： LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) Y_(2)O_(3)modification Lithium-ion batteries Rare earths

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Fatigue damage behavior of a surface-mount electronic package under different cyclic applied loads

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Chinese Physics B 2014年第4期23卷 377-384页

作者：任淮辉王习术 Longyuan Beijing) Wind Power engineer Technology Co. Ltd Department of engineering Mechanics Tsinghua University

This paper studies and compares the effects of pull-pull and 3-point bending cyclic loadings on the mechanical fa- tigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy （SEM） in-situ technology and nonlinear finite element modeling, respec- tively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure.

关键词： solder joint fatigue life hysteresis energy SEM in-situ technology

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Refraction-Diffraction Mathematical Model for Waves With Lateral Energy Transmission Mechanism and Its Verification

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China Ocean engineering 1996年第4期11卷 455-464页

作者： Xu Shikai , Wang Hongchuan Hong Guangwen engineer, Nanjing hydraulic research Institute, Nanjing, 210029 . Professor, research Institute of Coastal and Ocean engineering, Hohai University, Nanjing 210024 Nanjing hydraulic research Institute Nanjing 210029 Res. Inst. of Coast. and Ocean Eng. Hohai University Nanjing 210024

To solve problems concerning wave elements and wave propagation, an effective way is the wave energy balance equation, which is widely applied in oceanography and ocean dynamics for its simple computation. The present papaer advances wave energy balance equations considering lateral energy transmission and energy loss as the governing equation for the study of wave refraction-diffraction. For the mathematical model, numerical simulation is made by means of difference method, and the result is verified with two examples.

关键词： refraction-diffraction wave energy wave direction wave number wave height group velocity numerical simulation

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