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Enhancing the capacitances of electric double layer capacitors based on carbon nanotube electrodes by carbon dioxide activation and acid oxidization

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Science china(Technological Sciences) 2010年第5期53卷 1234-1239页

作者： LI ChenSha1,2,QIAO YingJie1,WU JianJun2,WANG DaZhi2 & YUAN DianBo2 1 department of Materials Science,Harbin engineering university,Harbin 150001,china 2.department of Mechanical engineering,tsinghua university,beijing 1.0084,china 1. department of Materials Science Harbin Engineering University Harbin 150001 China2. Department of Mechanical Engineering Tsinghua University Beijing 100084 China

Polarizable electrodes of electric double layer capacitors(EDLCs) were made from carbon nanotubes(CNTs).Effect of carbon dioxide activation together with acid oxidation for the electrodes on the characteristics and performances of electrodes and EDLCs was *** dioxide activation changed the microstructure of the electrodes,increased the effective surface area of CNTs and optimized the distribution of apertures of the *** oxidization modified the surface characteristics of *** on the polarizable electrodes treated by carbon dioxide activation and acid oxidization,the performances of EDLCs were greatly *** specific capacitance of the electrodes with organic electrolyte was increased from 21.8 F/g to 60.4 F/g.

关键词： carbon nanotube electric double layer capacitor scan electron microscopy

Effect of Coarse Aggregate Size on Relationship between Stress and Crack Opening in Normal and High Strength Concretes

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Journal of Materials Science & Technology 2005年第5期21卷 85-94页

作者： Jun ZHANG Qian LIU and Lin WANGDepaxtment of Civil engineering, tsinghua university, beijing 1.0084, china department of Civil engineering Tsinghua University Beijing 100084 China

Fine and coarse aggregates play an important role in the fracture of concrete. However, quantitative informationavailable on the effect of the coarse aggregate size on the fracture properties of concrete is still limited. In the presentpaper, the effect of coarse aggregate size (single grade of 5~10, 10~16, 16~20 and 20~25 mm) on stress-crackopening (σ-ω) relation in normal and high strength concretes (compressive strength of 40 and 80 MPa, respectively)was studied. The investigation was based on three-point bending tests implemented by fictitious crack analysis. Theresult shows that coarse aggregate size and cement matrix strength significantly influence the shape of σ-ω *** a given total aggregate content, in normal strength concrete, smaller size of aggregate leads to a high tensilestrength and a sharp stress drop after the peak stress. The smaller the coarse aggregate, the steeper the σ-ω *** contrast, in high strength concrete, the effect of aggregate size on σ-ω relation almost vanishes. A similar σ-ωrelation is obtained for the concrete except for the case of 20~25 mm coarse aggregate size. The stress drop afterthe peak stress is more significant for high strength concrete than that for normal strength concrete. Meanwhile, thesmaller the coarse aggregate size, the higher the flexural strength. Fracture energy and characteristic length increasewith increasing coarse aggregate size in both normal and high strength concretes.

关键词： Aggregate size Stress-crack opening relation Fracture energy Bending test

THE MEASUREMENT OF PLASTIC DEFORMATION AND CRACK GROWTH IN CRACKED SPECIMENS BY SAM

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Acta Mechanica Solida Sinica 1994年第4期7卷 347-353页

作者： Sun Xuewei Li Mingzheng (department of engineering mechanics,tsinghua university,beijing 1.0084,P.R.china) department of engineering mechanics Tsinghua University Beijing 100084 China

In this paper,scanning acoustic microscope(SAM) was used to obtain some characteristic photographs which explain the mesoscopic information of several cracked *** results on subsurface information of steel,nickel and aluminium were *** deformation and crack initiation were observed and *** length of crack propagation was *** is particularly suited to the study of many mesoscopic phenomena in material science because it can image mesoscopic subsurface feature without *** is revealed that SAM has a bright future in the field of mesomechanics.

关键词： SAM(scanning acoustic microscope) experiment mesomechanics crack

Truncation error calculation based on Richardson extrapolation for variable-step collaborative simulation

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Science china(Information Sciences) 2011年第6期54卷 1238-1250页

作者： ZHANG HeMing 1 , LIANG SiLu 2 , SONG ShiJi 1 & WANG HongWei 3 1 department of Automation, TNList, tsinghua university, beijing 1.0084, china 2 Computer and Information Management Center, tsinghua university beijing 1.0084, china 3 engineering Design Centre, engineering department, Cambridge university, Cambridge CB2 1PZ, UK 1. department of Automation TNList Tsinghua University Beijing 100084 China2. Computer and Information Management Center Tsinghua University Beijing 100084 China3. Engineering Design Centre Engineering Department Cambridge University Cambridge CB2 1PZ UK

Collaborative simulation is an effective approach to performing simulation analysis for complex systems by integrating models developed for different engineering disciplines. Collaborative simulation issues include the modeling of coupled multidisciplinary systems, and the simulation running time integration of these models that are solved parallelly. Estimation of the local truncation error of coupling models is the key to solve multidisciplinary collaborative simulation problem, which is actually used to restrict the simulation step. This paper presents a variable-step method based on Richardson extrapolation for calculating the local truncation error to solve collaborative simulation problem of multidisciplinary coupling models. Formulas for estimating the local truncation error are derived through theoretical analysis by using integration methods and interpolation technologies, respectively. The simulation experiments are illustrated to validate the accuracy and efficiency of proposed collaborative simulation algorithm in comparison with the usual combinative algorithm.

关键词： multidisciplinary systems collaborative simulation variable-step algorithm error estimation

THE GLOBAL ARTIFICIAL BOUNDARY CONDITIONS FOR NUMERICAL SIMULATIONS OF THE 3D FLOW AROUND A SUBMERGED BODY

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Journal of Computational Mathematics 2003年第4期21卷 435-450页

作者： Hou-de Han Xin Wen (department of Mathematical Sciences, tsinghua university, beijing 1.0084, china) department of Mathematical Sciences Tsinghua University Beijing 100084 China

We consider the numerical approximations of the three-dimensional steady potential flow around a body moving in a liquid of finite constant depth at constant speed and distance below a free surface in a channel. One vertical side is introduced as the upstream artificial boundary and two vertical sides are introduced as the downstream artificial boundaries. On the artificial boundaries, a sequence of high-order global artificial boundary conditions are given. Then the original problem is reduced to a problem defined on a finite computational domain, which is equivalent to a variational problem. After solving the variational problem by the finite element method, we obtain the numerical approximation of the original problem. The numerical examples show that the artificial boundary conditions given in this paper are very effective.

关键词： Ship wave Potential flow Global artificial boundary condition Finite element method.

Investigation of ZSM-5/MCM-41 Composite Molecular Sieve for Reducing Olefin Content of FCC Gasoline

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china Petroleum Processing & Petrochemical Technology 2009年第4期11卷 10-17页

作者： Ji Dekun~(1,2) Li Shuyuan~1 Ding Fuchen~2 Chi Yaoling~2 (1.Chemical engineering School,china university of Petroleum(beijing),beijing 102249 2.department of Chemical engineering,beijing Institute of Petrochemical Technology) Chemical engineering School China University of Petroleum (Beijing) Beijing 102249 China department of Chemical engineering Beijing Institute of Petrochemical Technology China

ZSM-5/MCM-41 composite molecular sieve was prepared by the nano-assembling *** ZSM-5 molecular sieve,the MCM-41 molecular sieve,the ZSM-5/MCM-41 mechanical mixture and the ZSM-5/MCM-41 composite molecular sieve were characterized by X-ray powder diffractometry,N_2 adsorption isotherms,temperature programmed desorption of ammonia and scanning electron microscopy and their properties were *** FCC gasoline as the feed,activities of different molecular sieves for reducing olefin content were investigated in a continuous high-pressure micro-reactor unit under the following conditions:a reaction temperature of 400℃,a reaction time of 2 h,a weight hourly space velocity of 3h^(-1),and a reaction pressure of 2.0 *** results showed that the HMCM-41 molecular sieve had low reaction performance,and the HZSM-5 molecular sieve demonstrated high aromatization activity,while the ZSM-5/MCM- 41 composite molecular sieve exhibited a best olefin-reducing performance because of its high isomerization activity and moderate aromatization *** a largest olefin-reducmg capability and a reasonable distribution of products,the composite molecular sieve was more suitable for FCC gasoline upgrading compared to other three catalysts.

关键词： ZSM-5 MCM-41 composite molecular sieve FCC gasoline olefin reduction

The reliability of the improved e^N method for the transition prediction of boundary layers on a flat plate

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Science china(Physics,mechanics & Astronomy) 2012年第5期55卷 837-843页

作者： SU CaiHong1,2 1 department of mechanics,Tianjin university,Tianjin 300072,china 2 Tianjin Key Laboratory of Modern engineering mechanics,Tianjin 300072,china 1. department of mechanics Tianjin University Tianjin 300072 China2. Tianjin Key Laboratory of Modern Engineering Mechanics Tianjin 300072 China

The transition criterion in the improved eN method is that transition would occur whenever the velocity amplitude of disturbance reaches 1%-2% of the free stream velocity,while in the conventional eN method,the N factor is an empirical *** this paper the reliability of this key assumption in the improved eN method is checked by results of transition prediction by using the Parabolized Stability Equations(PSE).Transition locations of an incompressible boundary layer and a hypersonic boundary layer at Mach number 6 on a flat plate are predicted by both the improved eN method and the PSE *** from both methods agree fairly well with each other,implying that the transition criterion proposed in the improved eN method is reliable.

关键词： transition prediction boundary layer eN PSE

Non-linear Identification Based on the Method of Gauss Functions

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Communications in Nonlinear Science and Numerical Simulation 1997年第3期2卷 39-44页

作者： Qing ZHANG & Chongde LU (department of Thermal engineering, tsinghua university ,beijing, 1.0084) department of Thermal engineering Tsinghua University Beijing 100084 China

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关键词： identification the method of gauss functions whole optimization

New evidence for lack of CMB power on large scales

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Science china(Physics,mechanics & Astronomy) 2010年第3期53卷 567-570页

作者： LIU Hao1 & LI TiPei1,2,3 1 Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, beijing 100049, china 2.department of Physics & Center for Astrophysics, tsinghua university, beijing 1.0084, china 3 department of engineering Physics & Center for Astrophysics, tsinghua university, beijing 1.0084, china 1. Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China2. Department of Physics & Center for Astrophysics Tsinghua University Beijing 100084 China3. Department of Engineering Physics & Center for Astrophysics Tsinghua University Beijing 100084 China

A digitalized temperature map is recovered from the first light sky survey image published by the Planck team, from which an angular power spectrum of the cosmic microwave background (CMB) is derived. The amplitudes of the low multipoles (low-l) measured from the preliminary Planck power spectrum are significantly lower than those reported by the WMAP team. Possible systematical effects are far from enough to explain the observed low-l differences.

关键词： cosmology cosmic microwave background data analysis