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An unsupervised grid-based approach for clustering analysis

Science china(Information Sciences) 2010年第7期53卷 1345-1357页

作者： YUE ShiHong1, WANG JeenShing2, TAO Gao1 & WANG HuaXiang1 1School of electrical engineering and Automation, Tianjin Key Laboratory of Process Measurement and Control, Tianjin university, Tianjin 300072, china 2department of electrical engineering, national cheng kung university, tainan 701, china School of electrical engineering and Automation Tianjin Key Laboratory of Process Measurement and Control Tianjin University Tianjin China department of electrical engineering National Cheng Kung University Tainan China

In recent years, the growing volume of data in numerous clustering tasks has greatly boosted the existing clustering algorithms in dealing with very large datasets. The K-means has been one of the most popular clustering algorithms because of its simplicity and easiness in application, but its effciency and effectiveness for large datasets are often unacceptable. In contrast to the K-means algorithm, most existing grid-clustering algorithms have linear time and space complexities and thus can perform well for large datasets. In this paper, we propose a grid-based partitional algorithm to overcome the drawbacks of the K-means clustering algorithm. This new algorithm is based on two major concepts: 1) maximizing the average density of a group of grids instead of minimizing the minimal square error which is applied in the K-means algorithm, and 2) using grid- clustering algorithms to thoroughly reformulate the object-driven assigning in the K-means algorithm into a new grid-driven assigning. Consequently, our proposed algorithm obtains an average speed-up about 10-100 times faster and produces better partitions than those by the K-means algorithm. Also, compared with the K-means algorithm, our proposed algorithm has ability to partition any dataset when the number of clusters is unknown. The effectiveness of our proposed algorithm has been demonstrated through successfully clustering datasets with different features in comparison with the other three typical clustering algorithms besides the K-means algorithm.

关键词： clustering grid-based algorithm K-means algorithm

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THREE-DIMENSIONAL NUMERICAL SIMULATION OF INTAKE MODEL WITH CROSS FLOW

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Journal of Hydrodynamics 2011年第3期23卷 314-324页

作者： HSIAO Shih-Chun department of Hydraulics and Ocean engineering national cheng kung university

The hydrodynamics of a pump sump consisting of a main channel, pump sump, and intake pipe is examined using Truchas a three-dimensional Navier-Stokes solver, with a Large Eddy Simulation （LES） turbulence model. The numerical results of streamwise velocity profiles and flow patterns are discussed and compared with experimental data of Ansar and Nakato. Fairly good agreement is obtained. Furthermore, unlike Ansar et al.＇s inviscid solution, the proposed numerical model includes the effect of fluid viscosity and considers more realistic simulation conditions. Simulation results show that viscosity affects the prediction of flow patterns and that the streamwise velocity can be better captured by including cross flow. The effects of the submergence Froude number on the free surface and streamwise velocity are also examined. The free surface significantly fluctuates at high submergence Froude number flows and the corresponding distribution of streamwise velocity profiles exhibits a trend different from that obtained for low submergence Froude number flows.

关键词： pump sump cross flow submergence Froude number Large Eddy Simulation (LES)

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Preparation and characterization of LiAl_xCo_yNi_(1-x-y)O_2 particles

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Particuology 2008年第4期6卷 252-257页

作者： Chen-Feng Kao, Kao-Heng Liu department of Chemical engineering, cheng kung university (NCKU), tainan 70101, Taiwan, china department of Chemical engineering Cheng Kung University (NCKU) Tainan 70101 Taiwan China

Lithium-aluminum-cobalt-nickel oxide LiAlxCoyNi1xyO2 particles, generally used as cathode of lithium battery, were prepared by chemical coprecipitation from an aqueous solution of LiOH, Al(NO3)3, Co(NO3)2 and Ni(NO3)2 with NH4OH. XRD, SEM and FTIR were used to examine the effect of nickel content on the product. FTIR patterns showed that increase in nickel content decreased the absorption strength of the peak of spinel structure of the product, attributed to the occupation by nickel in the aluminum sites. Particle size and electrical properties of the lithium-aluminum-cobalt-nickel oxide (abbreviated as LACNO) particles were also determined.

关键词： LiAl_xCo_yNi_(1-x-y)O_2 Chemical coprecipitation Particle size electrical properties

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A Simple Eddy Viscosity Model of Rough Turbulent Wave Boundary Layer

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china Ocean engineering 1996年第3期11卷 281-294页

作者： Hsu Tai-Wen and Lin Hwung-Yui Associate Professor, department of Hydraulics and Ocean engineering, national cheng kung university, tainan Graduate student, department of Hydraulics and Ocean engineering, national cheng kung university, tainan Dept. of Hydr. and Ocean engineering National Cheng Kung University Tainan Taiwan

A one-layer time-invariant eddy viscosity model is specified to develop a mathematical model for describing the essential features of the turbulent wave boundary layer over a rough bed. The functional form of the eddy viscosity is evaluated based on computational results from a two-equation turbulence model in which the eddy viscosity varies with time and space. The present eddy viscosity model simplifies much of the mathematical complexity in many existing models. Predictions from the present model have been compared with a wide range of experimental data. It is found that the eddy viscosity model adopted in the present study is physically reasonable.

关键词： turbulent wave boundary layer eddy viscosity wave fiction factor

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Improved performance of GaN-based light-emitting diodes by using short-period superlattice structures

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Progress in Natural Science:Materials International 2010年第1期20卷 70-75页

作者： Yi-jung LIU~1,Chien-chang HUANG~1,Tai-you CHEN~1,Chi-shiang HSU~1,Shiou-ying cheng~2, Kun-wei LIN~3,Jian-kai LIOU~1,Wen-chau LIU~1 1.Institute of Microelectronics,department of electrical engineering,national cheng-kung university, tainan 70101,Taiwan,china 2.department of Electronic engineering,Nation Ilan university,I-Lan 26041,Taiwan,china 3.department and Graduate Institute of Computer Science and Information engineering, Chaoyang university of Technology,Taichung 41349,Taiwan,china Institute of Microelectronics Department of Electrical Engineering National Cheng-Kung University Tainan 70101 Taiwan China department of Electronic engineering Nation Ilan University I-Lan 26041 Taiwan China department and Graduate Institute of Computer Science and Information engineering Chaoyang University of Technology Taichung 41349 Taiwan China

An InGaN/GaN multiple-quantum-well（MQW）light-emitting diode（LED）with a ten-period i（undoped）-InGaN/p（Mg doped）-GaN（2.5 nm/5.0 nm）superlattice（SL）structure,was *** SL structure that can be regarded as a confinement layer of holes to enhance the hole injection efficiency is inserted between MQW and p-GaN *** studied LED device exhibits better current spreading performance and an improved quality,compared with a conventional one without SL *** to the reduced contact resistance as well as more uniformity of carriers injection,the operation voltage at 20 mA is decreased from 3.32 to 3.14 V.A remarkably reduced reverse-biased leakage current(10-7-10-9A)and higher endurance of the reverse current pulse are *** measured output power and external quantum efficiency（EQE）of the studied LED are 13.6 mW and 24.8%,respectively. In addition,significant enhancement of 25.4%in output power as well as increment of 5%in EQE for the studied devices is observed, as the studied devices show superior current spreading ability and reduction in dislocations offered by the SL structure.

关键词： GaN superlattice(SL) current spreading hole confinement electrostatic discharge(ESD)

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Design,analysis and control of hybrid excited doubly salient stator-permanent-magnet motor

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Science china(Technological Sciences) 2010年第1期53卷 188-199页

作者： ZHU XiaoYong1,2 & cheng Ming1 1 engineering Research Center for Motion Control of MOE,School of electrical engineering,Southeast university,Nanjing 210096,china 2 School of electrical and Information engineering,Jiangsu university,Zhenjiang 212013,china engineering Research Center for Motion Control of MOE School of Electrical Engineering Southeast University Nanjing China School of electrical and Information engineering Jiangsu University Zhenjiang China

In this paper,a new hybrid excited doubly salient stator-permanent-magnet motor is proposed,where both permanent magnets and DC field windings are located in the *** theory,the mathematical model and design method of the motor are *** corresponding output power equation and the relationship between the flux control capability and the extended speed range are deduced in *** using an efficient "one-step" three-dimensional(3D) finite element method,the electromagnetic performances are analyzed,in which the leakage flux outside the stator circumference and end-effect are taken into *** on the operation principle of the motor,the control strategy and scheme are developed and implemented *** experimental results and finite element analysis show that the proposed motor not only maintains the advantages of doubly salient permanent magnet motors,but also offers high energy efficiency over a wide speed range,which makes the motor an interesting candidate for electric vehicles.

关键词： stator permanent magnet motor hybrid excitation doubly salient finite element method flux weakening control

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Longshore Current on an Equilibrium Beach

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china Ocean engineering 1996年第2期11卷 181-192页

作者： Chang Hsien-Kuo and HsuTai-Wen’ Associate Professor, department of Civil engineering, national Chiao Tung university, 1001 Ta-Hsueh Rd.,Hsinchu, 300 Taiwan . Associate Professor, department of Hydraulics and Ocean engineering, national cheng kung university,tainan department of Civil engineering National Chiao Tung University 1001 Ta-Hsueh Rd. Hsinchu 300 Taiwan Dept. of Hydr. and Ocean engineering National Cheng Kung University Tainan Taiwan

Natural beaches tend to be concave-up rather than planar and are reasonable to be modeled by an equilibrium beach profile. A governing equation for longshore current on an equilibrium beach is derived and its analytical solution is given in this paper. Through comparisons of the present solution and field data of longshore current for a step-type beach, the present solution is found to have fairly agreeable prediction to longshore current inside the surf zone. The effects of the shape of a concave-up beach and turbulent mixing stress on longshore current inside the surf zone are discussed in the present paper.

关键词： longshore current equilibrium beach profile surf zone turbulent mixing stress

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Development of Virtual Simulation System for Remote Collaborative Surface Machining

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武汉理工大学学报 2006年第S1期28卷 68-73页

作者： R.S.Lee department of Mechanical engineering National Cheng Kung UniversityTainan 701TaiwanChina

Most researches about virtual machine tool are emphasized on simulations of machine motion and machining process for single machine. In this paper,a virtual simulation system for remote collaborative surface machining is developed. The motion command of machine tool is generated by an interpolator,which can derive synchronized motion commands according to feedrate. Thus,the system can estimate the machining time. For universal assembly of five-axis virtual machine tool,it is based on the D-H notation representation and machining constraints consideration. The remote collaborative virtual manufacturing system based on the CORBA technology is proposed in this paper. It demonstrated that the developed virtual machine tool can be used to verify and simulate the machining process for the collaboration of the surface design and manufacturing team.

关键词： virtual machine tool remote collaboration five-axis.

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Analysis of multi-objective optimisation method for main insulation structure configuration scheme of valve-side winding of ultra-high voltage converter transformer considering multi-field coupling

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High Voltage 2024年第2期9卷 296-308页

作者： Lijun Yang Zhidong cheng Li cheng Ruijin Liao State Key Laboratory of Power Transmission Equipment Technology School of Electrical EngineeringChongqing UniversityChongqingChina

Because DC conductivities of oil-paper materials can be easily affected by electric field and temperature,the electrical properties under electro-thermal coupling of oil-paper materials should be considered when optimising the insulation structure of valve-side winding of the converter *** on the finite element multi-physical field coupling simulation,the multi-objective optimisation of main insulation structure of valve-side winding is carried *** view of the high time consuming of multi-physical field calculation and the actual needs of an insulation structure optimisation,the Kriging method and technique for order preference by similarity to the ideal solution(TOPSIS)method are introduced,and combines them with NSGA-II to obtain a joint algorithm that can be used for the optimisation of insulation structure of the converter *** using the joint algorithm of multi-objective optimisation,the insulation structure configuration scheme of valve-side winding is *** can be seen from the experiment result that,on the one hand,the joint algorithm adopted can obtain the insulation structure configuration scheme that meets the design *** the other hand,when facing the configuration scheme optimisation under multi-field coupling,the computational time required by this method is only 0.15%of that required by original genetic algorithm.

关键词： converter insulation coupling

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Aging assessment of large generator insulation based on PD measurements

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Progress in Natural Science:Materials International 2005年第11期15卷 1035-1043页

作者： YUE Bo, CHEN Xiaolin, cheng Yonghong and XIE Hengkun (State Key Laboratory of electrical Insulation and Power Equipment, Xi'an Jiaotong university, Xi'an 710049, china Graduate School at Shenzhen, Tsinghua university, Shenzhen 518055, china department of electrical engineering, Tsinghua university, Beijing 100084, china) State Key Laboratory of electrical Insulation and Power Equipment Xi'an Jiaotong University Xi'an 710049 China Graduate School at Shenzhen Tsinghua University Shenzhen 518055 China department of electrical engineering Tsinghua University Beijing 100084 China

The statistical parameters of phase resolved partial discharge (PD) distribution and ultra-wideband (UWB) characteristics of PD pulse are proposed for aging assessment of large generator insulation. Multi-stress aging tests of the model generator stator bar specimens were performed and PD measurements were conducted using both digital PD detector with frequency ranging from 40 kHz to 400 kHz and UWB PD detector with bandwidth from 10 MHz to 3 GHz at different aging stages. The test results show that the skewness and UWB frequency characteristics of PD can be taken as the characterization parameters for aging assessment of generator insulation. Furthermore, the measurement results of real generator stator bars show that these methods based on statistical parameters and UWB characteristics of PD are prospective for aging assessment and residual lifetime estimation of large generator stator insulation.

关键词： partial discharge stator insulation multi-stress accelerated aging statistical parameters ultra-wideband aging assessment.

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