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Boundary element analysis for elastic and elastoplastic problems of 2D orthotropic media with stress concentration

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Acta Mechanica Sinica 2005年第5期21卷 472-484页

作者： Xiushan Sun Lixin Huang Yinghua Liu Zhangzhi Cen Department of Engineering Mechanics Tsinghua UniversityBeiiing 100084 China College of Civil Engineering and Architecture Guangxi University Nanning 530004 Guangxi China

Both the orthotropy and the stress concentration are common issues in modem structural engineering. This paper introduces the boundary element method （BEM） into the elastic and elastoplastic analyses for 2D orthotropic media with stress concentration. The discretized boundary element formulations are established, and the stress formulae as well as the fundamental solutions are derived in matrix notations. The numerical procedures are proposed to analyze both elastic and elastoplastic problems of 2D orthotropic me- dia with stress concentration. To obtain more precise stress values with fewer elements, the quadratic isoparametric element formulation is adopted in the boundary discretization and numerical procedures. Numerical examples show that there are significant stress concentrations and different elastoplastic behaviors in some orthotropic media, and some of the computational results are compared with other solutions. Good agreements are also observed, which demonstrates the efficiency and reliability of the present BEM in the stress concentration analysis for orthotropic media.

关键词： Boundary element method (BEM) . Fundamental solution . Orthotropic medium . Stress concentration .Elastic and elastoplastic problems

Fabrication of 2D ZnO Nanosheet Thin Film by a Simple Two-Step Approach

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稀有金属材料与工程 2006年第A3期35卷 642-643页

作者： Ning Wang Hong Lin Jianbao Li Xiaozhan Yang Jun Yang Chunfu Lin State Key Lab of New Ceramics ＆ Fine Processing Department of Materials Science ＆ Engineering Tsinghua University Beijing 100084 China

In this paper,2D single-crystalline ZnO nanosheets thin film was fabricated successfully on silicon wafer by a simple two-step ***,SEM and TEM were used to characterize the phase structures and morphologies of ZnO nan... 详细信息

关键词： ZnO nanosheets crystal growth thin film

Microstructures and Toughness of Weld Metai of Ultrafine Grained Ferritic Steel by Laser Welding

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Journal of Materials Science & Technology 2004年第6期20卷 755-759页

作者： XudongZHANG WuzhuCHEN ChengWANG LinZHAO YunPENG ZhilingTIAN DepartmentofMechanicalEngineering TsinghuaUniversityBeijing100084China CentralIron&SteelresearchInstitute Beijing100081China

3 mm thick 400 MPa grade ultrafine grained ferritic steel plates were bead-on-plate welded by CO2 laser with heat input of 120-480 J/mm. The microstructures of the weld metal mainly consist of bainite, which form is lower bainite plates or polygonal ferrite containing quantities of dispersed cementite particles, mixed with a few of low carbon martensite laths or ferrite, depending on the heat input. The hardness and the tensile strength of the weld metal are higher than those of the base metal, and monotonously increase as the heat input decreases. No softened zone exists in heat affected zone (HAZ). Compared with the base metal, although the grains of laser weld are much larger, the toughness of the weld metal is higher within a large range of heat input. Furthermore, as the heat input increases, the toughness of the weld metal rises to a maximum value, at which point the percentage of lower bainite is the highest, and then drops.

关键词： Laser welding Ultrafine grained steel Microstructure Toughness

Verification of Interdomain Routing System Based on Formal Methods

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tsinghua Science and Technology 2009年第1期14卷 83-89页

作者：臧志远罗贵明殷翀元 tsinghua National Laboratory for Information Science and Technology (TNList) School of SoftwareTsinghua University

In networks, the stable path problem （SPP） usually results in oscillations in interdomain systems and may cause systems to become unstable. With the rapid development of internet technology, the occurrence of SPPs in interdomain systems has quite recently become a significant focus of research. A framework for checking SPPs is presented in this paper with verification of an interdomain routing system using formal methods and the NuSMV software. Sufficient conditions and necessary conditions for determining SPP occurrence are presented with proof of the method＇s effectiveness. Linear temporal logic was used to model an interdomain routing system and its properties were analyzed. An example is included to demon- strate the method＇s reliability.

关键词： interdomain routing system stable path problem software verification linear temporal logic

Facile Synthesis of Long,Straight and Uniform Copper Nanowires via a Solvothermal Method

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稀有金属材料与工程 2006年第A3期35卷 644-645页

作者： Chunfu Lin Hong Lin Ning Wang Xing Zhang Jun Yang Jianbo Li Xiaozhan Yang State Key Lab of New Ceramics ＆ Fine Processing Department of Materials Science ＆ Engineering Tsinghua University Beijing 100084 China

Copper nanowires were facilely prepared via a solvothermal *** this method,cetyitrimethylammonium bromide (CTAB) was used as a soft template,copper nitrate was an inorganic precursor,and absolute ethanol served as a reducing agent as well as a solvent.X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the as-prepared copper *** as-prepared copper nanowires are fairly uniform and *** majority of them are longer than 100μm and some even longer than 200μ***,most nanowires are quite *** addition, The mechanism of the growth process of copper nanowires was discussed.

关键词： copper nanowires solvothermal method template

Some Issues in Quantum Information Theory

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Journal of Computer Science & Technology 2006年第5期21卷 776-789页

作者：段润尧季铮锋冯元应明生 State Key Laboratory of Intelligent Technology and Systems Department of Computer Science and Technology Tsinghua University Beijing 100084 P.R. China

Quantum information theory is a new interdisciplinary research field related to quantum mechanics, computer science, information theory, and applied mathematics. It provides completely new paradigms to do information processing tasks by employing the principles of quantum mechanics. In this review, we first survey some of the significant advances in quantum information theory in the last twenty years. We then focus mainly on two special subjects： discrimination of quantum objects and transformations between entanglements. More specifically, we first discuss discrimination of quantum states and quantum apparatus in both global and local settings. Secondly, we present systematical characterizations and equivalence relations of several interesting entanglement transformation phenomena, namely entanglement catalysis, multiple-copy entanglement transformation, and partial entanglement recovery.

关键词： discrimination entanglement transformation quantum computing quantum information

Preparation and Characteristics of Nanoscale Diamond-Like Carbon Films for Resistive Memory Applications

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Chinese Physics Letters 2010年第9期27卷 225-228页

作者：富迪谢丹张晨辉张笛牛洁斌钱鹤刘理天 institute of Microelectronics Tsinghua University Beijing 100084 tsinghua National Laboratory for Information Science and Technology Beijing 100084 State Key Laboratory of Tribology Tsinghua University Beijing 100084 Institute of Microelectronics Chinese Academy of Sciences Belting 100029

We propose diamond-like carbon （DLC） as the resistance change material for nonvolatile memory applications. Nanosecale DLC films are prepared by filtered cathodic vacuum arc technique and integrated to W//DLC/W structure devices. The deposited DLC film has a thickness of about 20nm and high spa fraction content. Reversible bistable resistive switching from a high resistance state to a low resistance state, and vice versa, is observed under appropriate unipolar stimulation pulses. High resistance switching ratio （larger than a thousand times） and low level of switching power （about 11 μW） are demonstrated. We propose that the mechanism of the repetitive resistive switching is the growth and breakage of conductive sp2-like filaments in the predominantly sp3-type insulating carbon upon applications of voltage pulses, which is consistent with the experimental results.

关键词： Carbon Carbonates Carbonation Packaging materials Films Integration Grain legumes

Analysis and Design of Tapered Slot Antenna for Ultra-Wideband Applications

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tsinghua Science and Technology 2009年第1期14卷 1-6页

作者：姚远陈文华黄斌冯正和张志军 Department of Electronic Engineering Tsinghua University

The tapered slot antenna, such as Vivaldi, has been widely used due to its ultra-wideband, high gain, simple feed structure, and easy fabrication. However, there is no rigorous analytical theory for this type of antenna. This paper analyzed the metal parts of a tapered slot antenna in a conical coordinate system with the medium analyzed in rectangular coordinates. This mixed mode gave an approximate analytical form for the tapered slot antenna with the field distribution and radiation characteristics. A planar tapered slot antenna was proposed according to the results of the analysis methods. Measured and simulated results demonstrate the antenna performance. The antenna shows good impedance matching over a wide bandwidth of 9 GHz, from 2 GHz to 11 GHz, and good radiation patterns. It is suitable for ultra-wideband applications.

关键词： planar antenna tapered slot antenna ultra-wideband (UWB) Vivaldi

Difference in electron-and gamma-irradiation effects on output characteristic of color CMOS digital image sensors

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Rare Metals 2004年第2期23卷 165-170页

作者： MENGXiangti KANGAiguo ZHANGXimin LIJihong HUANGQiang LIFengmei LIUXiaoguang ZHOUHongyu InstituteofNuclearEnergyTechnology TsinghuaUniversityBeijing100084China InstituteofLowEnergyNuclearPhysics BeijingNormalUniversityBeijing100875China

Changes of the average brightness and non-uniformity of dark output images,and quality of pictures captured under natural lighting for the color CMOS digital image sensorsirradiated at different electron doses have been studied in comparison to those from theγ-irradiated sensors. For the electron-irradiated sensors, the non-uniformity increases obviouslyand a small bright region on the dark image appears at the dose of 0.4 kGy. The average brightnessincreases at 0.4 kGy, increases sharply at 0.5 kGy. The picture is very blurry only at 0.6 kGy,showing the sensor undergoes severe performance degradation. Electron radiation damage is much moresevere than γ radiation damage for the CMOS image sensors. A possible explanation is presented inthis paper.

关键词： semiconductor technology irradiation damage electron and gamma irradiation color CMOS image sensor output characteristic Si