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Effect of powder mixing process on the microstructure and thermal conductivity of Al/diamond composites fabricated by spark plasma sintering

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Rare Metals 2010年第1期29卷 86-91页

作者： CHU Ke, JIA chengchang, LIANG Xuebing, and chen hui school of Materials science and engineering, university of science and technology beijing, beijing 100083, china school of Materials science and engineering University of Science and Technology Beijing Beijing China

Two powder mixing processes, mechanical mixing （MM） and mechanical alloying （MA）, were used to prepare mixed Al/diamond powders, which were subsequently consolidated using spark plasma sintering （SPS） to produce bulk Al/diamond composites. The effects of the powder mixing process on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated. The results show that the powder mixing process can significantly affect the microstructure and the thermal conductivity of the composites. Agglomerations of the particles occurred in mixed powders using MM for 30 min, which led to high pore content and weak interfacial bonding in the composites and resulted in low relative density and low thermal conductivity for the composites. Mixed powders of homogeneous distribution of diamond particles could be obtained using MA for 10 min and MM for 2 h. The composite prepared through MA indicated a high relative density but low thermal conductivity due to its defects, such as damaged particles, Fe impurity, and local interfacial debonding, which were mainly introduced in the MA process. In contrast, the composite made by MM for 2 h demonstrated high relative density and an excellent thermal conductivity of 325 W.m^-1.K^-1, owing to its having few defects and strong inter-facial bonding.

关键词： metal matrix composites thermal properties sintering powder mixing

Identification of Nonlinear Dynamic Systems Using Diagonal Recurrent Neural Networks

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International Journal of Minerals,Metallurgy and Materials 1999年第2期13卷 149-151页

作者： Jing Wang hui chen(information Engmeering school, university of science and Techaology beijing, beijing 100083, china) information engineering school University of Science and Technology Beijing Beijing 100083 China

In order to apply a new dynamic neural network- Diagonal Recurrent Neural NetWork (DRNN) to the system identificationof nonlinear dynamic Systems and construct more accurate system models, the structure and learning method (DBP algorithm) of theDRNN are Present6d. Nonlinear system characteriStics can be identified by presenting a set of input / output patterns tO the DRNN andadjusting its weights with the DBP algorithm. Experimental results show that the DRNN has good performances in the identification ofnonlinear dynamic systems in comparison with BP networks.

关键词： neural network system identification intelligent control control system models learning method

Numerical calculation on temperature field of FGH95 alloy droplet during rapid solidification

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Journal of university of science and technology beijing 2003年第3期10卷 51-54页

作者： Huanming chen and Benfu Hu Materials science and engineering school, university of science and technology beijing, beijing 100083,china Physics and Electrical information engineering school, Ningxia university, Yinchuan 750021,china Univ Sci & Technol beijing Sch Mat Sci & Engn Beijing 100083 Peoples R China Ningxia Univ Phys & Elect Informat Engn Sch Yinchuan 750021 Peoples R China

The temperature field of FGH95 alloy droplet atomized by plasma rotatingelectrode processing (PREP) during solidification has been calculated through numerical analysisbased on equivalent sensible heat capacity method. And thus the relational curves among temperaturegradient of solid-liquid interface, moving velocity of solid-liquid interface and solid fractionduring solidification have been presented. The results indicate that the relation between averagetemperature gradient of solid-liquid interface and droplet size, and the relation between averagemoving velocity of solid-liquid interface and droplet size can be expressed during solidification.

关键词： FGH95 alloy droplet temperature field numerical calculation

Surface characteristics of rapidly solidified nickel-based superalloy pow-ders prepared by PREP

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Rare Metals 2003年第4期22卷 309-314页

作者： chen Huanming , HU Benfu , and LI huiying1) school of Materials science and engineering, university of science and technology beijing, beijing 100083, china2) school of Physics and Electrical information engineering, Ningxia university, Yinchuan 750021, china school of Materials science and engineering University of Science and Technology Beijing 北京 100083

The surface microstructure and the surface segregation of FGH 95 nickel-basedsuperalloy powders prepared through plasma rotating electrode processing (PREP) have beeninvestigated by using SEM and AES. The results indicate that the surface microstructure of powderschanges from dendrite into cellular stricture as the particle size of powders decrease, and thepredominant precipitates solidified on the particle surfaces were identified as MC' type carbidesenriched with Nb and Ti. It was also indicated that along with the depth of particle surfaces, thesegregation layer of S, C and O elements are thick, and that of Ti, Cr elements are thin for largesire powders while they are in reverse for median size particles.

关键词： FGH 95 nickel-based superalloy powders surface characteristics microstructure plasma rotating electrode processing

Texture Analysis of Superconducting Films Based on YBCO System

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International Journal of Minerals,Metallurgy and Materials 2000年第2期14卷 107-109页

作者： Nan chen Weimin Mao(Material science and engineering school, university of science and Technol0gy beijing, beijing 100083 china)(Department of Materials science and engineering, university of Petroleum, beijing 102200, china) Material science and engineering school University of Science and Technology Beijing Beijing 100083 China Department of Materials science and engineering University of Petroleum Beijing 102200 China

Textures in different layers of superconductors based on YBCO system are analyzed using the methods of pole figure and con-ventional φ scans. It is shown that the φ scanning technology has only 1-dimensional description and could omit some information of3-dimensional orientaion distribution, which will influence the superconductor quality The pole figure method, in contrast, demonstra-tes the orientation distribution 2-dimensionally and gives a comprehensive view of thin filIn textUr, which is a much bettCr method fortexture analysis in superconducting films, in which there is commonly an unique high sharpness textur component.

关键词： superconductor thin film texture YBCO pole figure

Combining Self-organizing Feature Map with Support Vector Regression Based on Expert System

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自动化学报 2005年第4期 120-127页

作者： WANG Ling MU Zhi-Chun GUO hui(information engineering school, beijing university of science and technology, beijing 100083)

A new approach is proposed to model nonlinear dynamic systems by combining SOM(self-organizing feature map) with support vector regression (SVR) based on expert system. Thewhole system has a two-stage neural network architecture. In the first stage SOM is used as a clus-tering algorithm to partition the whole input space into several disjointed regions. A hierarchicalarchitecture is adopted in the partition to avoid the problem of predetermining the number of parti-tioned regions. Then, in the second stage, multiple SVR, also called SVR experts, that best fit eachpartitioned region by the combination of di?erent kernel function of SVR and promote the configura-tion and tuning of SVR. Finally, to apply this new approach to time-series prediction problems basedon the Mackey-Glass di?erential equation and Santa Fe data, the results show that SVR experts hase?ective improvement in the generalization performance in comparison with the single SVR model.

关键词： SOM clustering SVR experts single SVR Mackey-Glass di?erential equation SantaFe data

Emotional Gait Generation for a Humanoid Robot

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International Journal of Automation and computing 2010年第1期7卷 64-69页

作者： Lun Xie Zhi-Liang Wang Wei Wang Guo-chen Yu school of information engineering, university of science and technology beijing, beijing 100083, PRC school of information engineering University of Science and Technology Beijing Beijing PRC

In this paper, an emotional mathematical model and affective state probability description space of a humanoid robot are set up on the basis of psycho-dynamics＇ psychological energy and affective energy conservation law. The emotional state transferring process and hidden Markov chain algorithm of stimulating transition process are then studied. The simulation results show that the mathematical model is applicable to the authentic affective state change rule of human beings. Finally, the gait generation experiment results of control signal and electric current tracking wave-form are presented to demonstrate the validity of the proposed mathematical model.

关键词： Emotional mathematical model humanoid robot hidden Markov chain stimulating transition process gait generation.

Complex conforming Delaunay triangulation

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science china(information sciences) 2010年第6期53卷 1130-1140页

作者： MENG XianHai 1, LI JiGang 1, YANG Qin 1, CAI Qiang 2 & chen QiMing 3 1 NLSDE, school of Computer science and engineering, BeiHang university, beijing 100083, china 2 school of Computer sciences, beijing technology and Business university, beijing 100037, china 3 school of Mechanical engineering and Automation, BeiHang university, beijing 100083, china NLSDE School of Computer Science and Engineering BeiHang University Beijing China school of Computer sciences Beijing Technology and Business University Beijing China school of Mechanical engineering and Automation BeiHang University Beijing China

A novel algorithm of conforming Delaunay triangulation for curved geometry is presented in the paper.A progress has been made for the problem puzzled Delaunay refinement where curved constraints cannot be accepted as input *** algorithm is based on a new sufficient condition for the existence of constraints in *** requires computing only the intersection between constraints and Voronoi edges or faces instead of the circum-sphere of curved *** the termination of the algorithm when small input angles exist in constraints, a weighted method is applied to ensure that the algorithm can terminate under any *** two-dimensional and three-dimensional results are also *** is shown that the algorithm has the capability of dealing with both linear and nonlinear constraints in a consistent way, without the need of maintaining triangular meshes on face constraints.

关键词： mesh generation Delaunay triangulation conforming curved constraints tetrahedralization weight

Least trace extended set-membership filter

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science china(information sciences) 2010年第2期53卷 258-270页

作者： HUANG Yi , chen ZongJi & WEI chen National Key Laboratory of science and technology on Integrated Control technology, school of Automation science and Electric engineering, Beihang university, beijing 100083, china National Key Laboratory of science and technology on Integrated Control technology School of Automation Science and Electric Engineering Beihang University Beijing China

To improve the consistency of estimation result, a least-trace extended set-membership filter (LTESMF) is presented for a class of nonlinear stochastic systems, which has linear output and unknown- but-bounded noise. Feedback technique is used instead of the intersection of ellipsoid-sets in the measurement update. The feedback parameter is optimized in order to minimize the trace of error bounded ellipsoid’s envelop matrix. A new stability analysis method was developed to prove the stochastic system’s stability by using the convergence of some measurement of the error bounded ellipsoid. Analysis result shows that the estimation error of LTESMF will converge to a bounded area. A simulation of SINS/GPS integrated alignment with large misalignment angles is conducted. The results demonstrate that the convergence speed and the consistency of LTESMF are much better than those of extended Kalman filter (EKF), in addition the steady estimation precision and computational complexity are close to that of EKF.

关键词： set-membership estimation nonlinear system convergence upper bound least trace stability analysis