检索结果-南通市图书馆

Comparison of fractal measures

在线全文

学校读者我要写书评

暂无评论

Science china Mathematics 2005年第11期48卷 1545-1553页

作者： QU Yanhui,WEN Shengyou & WEN Zhiying department of Mathematics,tsinghua university,{3. 100084,china department of Mathematics,Hubei university, Wuhan 43.062, china 1. department of Mathematics Tsinghua University 100084 Beijing China 2. department of Mathematics Hubei University 430062 Wuhan China

In this paper, the relationship between the s-dimensional Hausdorff measures and the g-measures in Rd is discussed, where g is a gauge function which is equivalent to ts and 0 < s≤d. It shows that if s=d, then Hg = c... 详细信息

In this paper, the relationship between the s-dimensional Hausdorff measures and the g-measures in Rd is discussed, where g is a gauge function which is equivalent to ts and 0 2Cd and Pg = c3.d on Rd, where constants c1, c2 and c3.are determined by where Wg, Cg and Pg are the g-Hausdorff, g-central Hausdorff and g-packing measures on Rd respectively. In the case 02Cs|F and Pg|F = c3.s|F, where the constants c1, c2 and c3.depend not only on g and s, but also on F. A criterion is presented for judging whether an s-set has the above properties.

关键词： gauge function Hausdorff measure central Hausdorff measure packing measure.

Numerical Simulation of Shrinkage Cavity Formation in Spheroidal Graphite Iron Castings Based on Micro Modeling

在线全文

学校读者我要写书评

暂无评论

International Journal of Minerals,Metallurgy and Materials 1998年第1期12卷 9-12页

作者： Wenzhen Li Baicheng Liu Shantong Jin (Metallurgy Engineering School, university of Science and Technology beijing, beijing 100083.{3.)(department of Mechanical Engineering, tsinghua university, beijing 100084,{3.) Metallurgy Engineering School University of Science and Technology Beijing Beijing 100083 China department of Mechanical Engineering Tsinghua University Beijing 100084 China

A micro-modeling method (MM) for the quantitative prediction of the shrinkage cavity formation in SGiron castings is proposed. The mathematical models describing the volume changes during the solidification ofspheroidal graphite cast iron are established based on the models of solidification kinetics. The shrinkage cavityformation of T-shaped SG iron castings is calculated with MM method. The calculated results are compared with theexperimental results. It is shown that the predicted size, shape and distribution of shrinkage cavity by MM methodare in good agreement with the measured results.

关键词： solidification shrinkage numerical simulation micro modeling spheroidal graphite cast iron

Anomalous magnetotransport in LaMn_(1-x)Te_xO_3

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2009年第7期52卷 987-992页

作者： TAN GuoTai1,2, CHEN ZhengHao3.& ZHANG XiaoZhong4,5 1 Key Laboratory of Beam Technology & Materials Modification of the Ministry of Education, Institute of Low Energy Nuclear Physics, beijing Normal university, beijing 100875,{3. 2 beijing Radiation Center, beijing 100875,{3. 3.Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, beijing 100080,{3. 4 Key Laboratory of Advanced Materials of the Ministry of Education, department of Materials Science and Engineering, tsinghua university, beijing 100084,{3. 5 beijing National Center for Electron Microscopy, tsinghua university, beijing 100084,{3. 1. Key Laboratory of Beam Technology & Materials Modification of the Ministry of Education Institute of Low Energy Nuclear Physics Beijing Normal University Beijing 100875 China 2. beijing Radiation Center Beijing 100875 China 3. Laboratory of Optical Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China 4. Key Laboratory of Advanced Materials of the Ministry of Education Department of Materials Science and Engineering Tsinghua University Beijing 100084 China 5. beijing National Center for Electron Microscopy Tsinghua University Beijing 100084 China

The LaMn1-xTexO3.δ (x=0.1, 0.2, 0.3. were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te4+, and Mn3. ions are partly converted into Mn2+ and Mn4+ due to the excess oxygen and Te doping. The magnetotransport associated with Mn2+, Mn3. and Mn4+ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn3. is much larger or less than the sum of Mn2+ and Mn4+; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn3. is close to the sum of Mn2+ and Mn4+. These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism.

关键词： colossal magnetoresistance La-Te-Mn-O magnetotransport

Ultralight X-type lattice sandwich structure (Ⅱ):Micromechanics modeling and finite element analysis

在线全文

学校读者我要写书评

暂无评论

Science china(Technological Sciences) 2009年第9期52卷 2670-2680页

作者： ZHANG QianCheng1,CHEN AiPing 2,CHEN ChangQing2,3.& LU TianJian2 1 State Key Laboratory for Mechanical Behavior of Materials,School of Material Science and Engineering,Xi’an Jiaotong university,Xi’an 710049,china 2 MOE Key Laboratory for Strength and Vibration,School of Aerospace,Xi’an Jiaotong university,Xi’an 710049,china 3.department of Engineering Mechanics,AML,tsinghua university,beijing 100084,china State Key Laboratory for Mechanical Behavior of Materials School of Material Science and Engineering Xi’an Jiaotong University Xi’an China MOE Key Laboratory for Strength and Vibration School of Aerospace Xi’an Jiaotong University Xi’an China department of Engineering Mechanics AML Tsinghua University Beijing China

The methods of homogenization and finite elements are employed to predict the effective elastic constants and stress-strain responses of a new type of lattice structure,the X-structure proposed by the authors in a companion paper. It is shown that in most cases the predictions by the equivalent homogenization theory agree well with the experimental and 3.dimensional finite element calculated results. The theoretical and numerical study supports the argument that the X-structure is superior to the pyramid lattice structure in terms of mechanical strength.

关键词： sandwich panel lattice structure equivalent homogenization finite element model

Fault prediction model based on evidential reasoning approach

在线全文

学校读者我要写书评

暂无评论

Science china(Information Sciences) 2010年第10期53卷 2032-2046页

作者： SI XiaoSheng 1,2 , HU ChangHua 1 & ZHOU ZhiJie 1,2 1 Unit 3.2, Xi’an Institute of Hi-Tech, Shaanxi, Xi’an 710025, china 2 department of Automation, tsinghua university,{3., china 1. Unit 3.2 Xi’an Institute of Hi-Tech Shaanxi Xi’an 710025 China2. Department of Automation Tsinghua University Beijing 100084 China

In order to deal with fault prediction problems that involve both quantitative and qualitative in-formation for nonlinear complex system, a new fault prediction model is established based on the evidential reasoning (ER) approach, and an optimal learning algorithm for training ER-based prediction model is pre-sented based on the mean square error (MSE) criterion. This prediction model inherits the advantages of ER approach, which can deal with precise data, incomplete data and fuzzy data with nonlinear characteristic. In this model, the input signals transformed using rule based information transformation technique, are aggregated by analytical ER approach, and then the outputs of prediction model are constructed according to the types of system outputs. In addition, two fault decision criteria are defined to conduct fault identification. To overcome the difficulty in determining model parameters accurately and subjectively, a nonlinear optimization model is constructed and the optimal parameters are obtained. Two experimental studies are conducted to evaluate the performance of the proposed model. The results show that the established prediction model and the presented parameters optimization methods can deal with fault prediction problem effectively.

关键词： fault prediction evidential reasoning belief distribution nonlinear optimization

FL-FN-MOGA Based Traffic Signal Control

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Systems Engineering and Electronics 2003年第3期14卷 14-23页

作者： Wei Wu & Zhang Yi department of Automation, tsinghua university, beijing 100084, P. R.{3. department of Automation Tsinghua University Beijing 100084 P. R. China

In this paper, a traffic signal control method based on fuzzy logic (FL), fuzzy-neuro (FN) and multi-objective genetic algorithms (MOGA) for an isolated four-approach intersection with through and left-turning movements is presented. This method has an adaptive signal timing ability, and can make adjustments to signal timing in response to observed *** 'urgency degree' term, which can describe the different user's demand for green time is used in decision-making by which strategy of signal timing can be determined. Using a fuzzy logic controller, we can determine whether to extend or terminate the current signal phase and select the sequences of phases. In this paper, a method based on fuzzy-neuro can be used to predict traffic parameters used in fuzzy logic controller. The feasibility of using a multi-objective genetic algorithm ( MOGA) to find a group of optimizing sets of parameters for fuzzy logic controller depending on different objects is also demonstrated. Simulation results show that the proposed methed is effecfive to adjust the signal timing in response to changing traffic conditions on a real-time basis, and the controller can produce lower vehicle delays and percentage of stopped vehicles than a traffic-actuated controller.

关键词： Traffic signal control Fuzzy logic Fuzzy-neuro Multi-objective genetic algorithms.

Effects of Si Content and the Addition Amount of Al-3. Master Alloy on the Solidification Structures of Hypoeutectic Al-Si Alloys

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2001年第3期20卷 168-173页

作者： Donghui Wang,Jianguo Li, Yankang Zheng, Bingzhe Bai department of Materials Science and Engineering, tsinghua university, beijing 100084,{3. Tsing Hua Univ Dept Mat Sci & Engn Beijing 100084 Peoples R China

Effects of Si content and the addition amount of Al-3. master alloy on the solidification structures of hypoeutectic Al-Si alloys were studied. The addition amounts of the master alloy were 0.2%, 0.4%, 0.7% and 1% (mass fraction, so as the follows), respectively. The Si content of Al-Si binary alloys investigated varied from 1% to 11%. The observation of macrostructures of non-refined samples showed that 3. Si constitutes a transition point at which the minimum grain size can be obtained. It was also found that Al-3. master alloy can shift the transition point towards a higher Si value when its addition amount increases, making this point appear at 4%, 5% and 6% Si as its addition amount increases up to 0.4%, 0.7% and 1%, respectively.

关键词： Al-3. master alloy hypoeutectic Al-Si alloy grain refinement

A quantification model for apoptosis in mouse embryos in the early stage of fetation

在线全文

学校读者我要写书评

暂无评论

Science china(Life Sciences) 2009年第10期52卷 922-927页

作者： WANG PengFei1, FU JianHua1, MA WanYun1, CHEN DieYan1, Lü DanYu2 & BAI WenJia3.1 Key Laboratory for Atomic and Molecular Nanosciences of Education Ministry, department of Physics, tsinghua university, beijing 100084,{3. 2 department of Anatomy & Histology and Embryology, School of Basic Medical Sciences Peking university Health Science Center, beijing 100083.{3. 3.department of Automation, tsinghua university, beijing 100084,{3. 1. Key Laboratory for Atomic and Molecular Nanosciences of Education Ministry Department of Physics Tsinghua University Beijing 100084 China 2. department of Anatomy & Histology and Embryology School of Basic Medical Sciences Peking University Health Science Center Beijing 100083 China 3. department of Automation Tsinghua University Beijing 100084 China

Apoptosis is the most important inducement and modulator for embryos in the early stage of fetation, i.e. after the 8-cell stage, mostly the morula and blastula stage, to proceed to the stage of nonlinear development. Using a two-photon laser scanning microscopy (TPLSM) system, we obtained 3.dimensional (3.) fluorescent images of preimplantation mouse embryos. A model for quantification was established. The statistical results for the spatial location of apoptosis bodies in embryos was obtained following image processing, as well as investigation of the kinetics of apoptosis. It was found that most (70%) apoptosis occurred in the trophectoderm, and the departure between the centroid and geometric center of embryos had a step transition when embryos developed into the 3.-cell stage, which was consistent with the theoretical prediction that the blastocele would induce a symmetry break of the distribution of cells in embryos.

关键词： apoptosis preimplantation mouse embryo TPLSM quantification model

Shrinkage Behaviour of Spheroidal Graphite Cast Iron in Green and Dry Sand Molds for the Benchmarking of Solidification Simulation

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2001年第6期17卷 610-614页

作者： Wenzhen LI and Baicheng LIU department of Mechanical Engineering, tsinghua university, beijing 100084,{3. Jiarong LI beijing Institute of Aeronautical Materials, beijing 100095,{3. [Manuscri Tsing Hua Univ Dept Mech Engn Beijing 100084 Peoples R China beijing Inst Aeronaut Mat Beijing 100095 Peoples R China

The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inoculation, casting modulus, mold type (green or dry) and pouring temperature within specific ranges of these variables. Based on the orthogonal experiments, the metallurgical and processing parameters of the minimum casting shrinkage and the maximum casting shrinkage were obtained, and the effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroids graphite cast iron castings were discussed. Finally, two regression equations relating these variables to the formation of shrinkage porosity were derived based upon the orthogonal experiments conducted.

关键词： Shrinkage Behaviour of Spheroidal Graphite Cast Iron in Green and Dry Sand Molds for the Benchmarking of Solidification Simulation Graphite Simulation Cast