检索结果-南通市图书馆

EXACT NONREFLECTING BOUNDARY CONDITIONS FOR AN ACOUSTIC PROBLEM IN THREE DIMENSIONS

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2003年第1期21卷 15-24页

作者： Houde Han Chunxiong Zheng (Department of Mathematical Sciences, tsinghua university, beijing 100084,{2.) Department of Mathematical Sciences Tsinghua University 北京 100084

In this paper, nonreflecting artificial boundary conditions are considered for an acoustic problem in three dimensions. With the technique of Fourier decomposition under the orthogonal basis of spherical harmonics, three kinds of equivalent exact artificial boundary conditions are obtained on a spherical artificial boundary. A numerical test is presented to show the performance of the method.

关键词： Exterior problem Nonreflecting artificial boundary condition Acoustic equa-tion Three-dimensions.

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

在线全文

学校读者我要写书评

暂无评论

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 100084,{2.) Department of Mathematical Sciences Tsinghua University 北京 100084

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.

A new orthogonality relationship for orthotropic thin plate theory and its variational principle

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2005年第3期48卷 371-380页

作者： LUO Jianhui 1 , LONG Yuqiu 2.& LIU Guangdong 1 1. College of Civil Engineering, Hunan university, Changsha 410082.{3. 2. Department of Civil Engineering,{2., beijing 100084,{3. College of Civil Engineering Hunan University Changsha China Department of Civil Engineering Tsinghua University Beijing China

The thought how dual vectors are constructed in a new orthogonality relationship for theory of elasticity is generalized into orthotropic thin plate bending problems by using the analogy theory between plane elasticity problems and plate bending problems. Dual differential equations are directly obtained by using a mixed variables method. A dual differential matrix to be derived possesses a peculiarity of which principal diagonal sub-matrixes are zero matrixes. Two independently and symmetrically orthogonality sub-relationships are discovered. By using the integral form for elastic bending theory of orthotropic thin plate the orthogonality relationship is demonstrated. By selecting felicitous dual vectors a new orthogonality relationship for theory of elasticity can be generalized into elastic bending theory of orthotropic thin plate. By using the integral form a variational principle which is relative to differential form and a whole function expression are proposed.

关键词： theory of elasticity, thin plate theory, dual vectors, orthogonality relationship, orthotropic, variational principle.

Critical slope gradient for compulsory abandonment of farmland on the hilly Loess Plateau

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 1998年第5期43卷 409-412页

作者： TANG Keli+1, ZHANG Keli 1,2.and LEI Aling 1,3.1. Institute of Soil and Water Conservation, Chinese Academy of Sciences, Yangling 712.00, china 2. Department of Hydraulic Engineering, tsinghua university,{2., china 3. Water Resources C Institute of Soil and Water Conservation Chinese Academy of Sciences Yangling China Department of Hydraulic Engineering Tsinghua University Beijing China Water Resources Conservation Bureau of Yangtze River Ministry of Water Resources Wuhan China

Scientific evidence for the upper limit of farmland is proposed. Shallow gully erosion is one of erosion types distributed extensively on sloping farmland in the hilly regions of the Loess Plateau. Field observation and aerial photos interpretation, as well as laboratory experiments show that the shallow gully erosion occurring on the steeper farmland in the hilly regions of the Loess Plateau is an important factor leading to intensive erosion on slope, because of its extensive distribution and intensive runoff collection. The data on the formation, development and distribution of shallow gullies on sloping farmland indicate that critical slope gradient for shallow gully initiation ranges from 15 to 2. degrees with an average of 18.2.degrees. Therefore, it is suggested that critical slope gradient for compulsory abandonment of farmland on the hilly Loess Plateau should be kept within the critical slope gradient for shallow gully initiation to prevent shallow gully formation in order to control soil loss more effectively. But as the first step, the cultivation on the slopes with slope larger than 2. degrees where the maximum erosion occurs should be strictly forbidden.

关键词： hilly region of Loess Plateau upper limitation for farmland shallow gully erosion erosion dynamic.

A user-space file system for on-demand legacy desktop software

在线全文

学校读者我要写书评

暂无评论

Science china(Information Sciences) 2011年第6期54卷 1142-1150页

作者： ZHANG YouHui 1,2., SU GeLin 1,2.& ZHENG WeiMin 1,2.1 Department of Computer Science and Technology,{3., beijing 100084,{2. 2.tsinghua National Laboratory for Information Science and Technology,{3., beijing 100084,{2. Department of Computer Science and Technology Tsinghua University Beijing China tsinghua National Laboratory for Information Science and Technology Tsinghua University Beijing China

Some user-level virtualization technologies have been used to convert legacy software (like the existing Windows desktop applications) into the on-demand software without any modification. To give the client a friendly and compatible method to access on-demand legacy software across the Internet, this paper presents a clientend file system for this usage case. It is a Windows user-space file system based on the cloud storage (where the on-demand software is stored), which converts the local file system accesses into remote visits. Quite a few optimizations are adopted and adjusted to suit the file-access-pattern of on-demand software, including the local cache, metadata/data/software prefetch and content-addressable storage (CAS), to decrease the number of remote visits and/or to overlap IO (input/output) operations with software execution. Detailed access-pattern analyses are also presented. This file system has been implemented and tests show that it is practical for much daily-used software-a local cache of limited size can provide up to 80% hit ratio and the corresponding overhead of running-time is about 3.%. Owing to this method, on any compatible and networked computer, a user can use his/her personalized software conveniently although it does not exist on the local host.

关键词： on-demand software software as a service user-space file system cloud storage

Experimental realization of quantum cryptography communication in free space

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2005年第2期48卷 237-246页

作者： WANG Chuan1, ZHANG Jingfu1, WANG Pingxiao1, DENG Fuguo1, AI Qing1 & LONG Guilu1,2.1. Department of Physics, Key Laboratory for Quantum Information and Measurements, tsinghua Univer- sity, beijing 100084,{2. 2. Center for Atomic and Molecular NanoSciences, tsinghua university, beijing 100084,{2. Department of Physics Key Laboratory for Quantum Information and Measurements Tsinghua University Beijing China Atomic and Molecular NanoSciences Tsinghua University Beijing China

Utilizing linear optical devices, the principle of B92.quantum key distribution (QKD) protocol is demonstrated in free space with a distance of transmission of 2.2.meters. The faint laser pulses with 650 nm wavelength are used as the single photon sources. The experimental results show that the eavesdropping behavior in the signal transmission can be detected. We also discuss the problems and solutions in using the quantum cryptography communication practically. It is pointed out that one of the approaches to increasing the distance of the quantum communication is to overcome the attenuation of the single photon in transmission. This could not be solved by the use of single photon source, and new quantum communication protocols are needed to solve these problems.

关键词： quantum key distribution, free space, linear optics, faint pulses.

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

在线全文

学校读者我要写书评

暂无评论

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 100084,{2. 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, 16~2. and 2.~2. 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 2.~2. 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

Luminescence of Eu^(2.) in Strontium Aluminum Oxide System with Long Decay Property

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Chinese Chemical Letters 1998年第4期9卷 401-402页

作者： Yong QIU and Hai Tao SUN(Department of chemistry, tsinghua university,{2.) Department of chemistry Tsinghua University Beijing 100084 China

A long decay luminescent powder based upon the strontium aluminum oxide system with Eu2. as the activator was produced. It was found that the variation of the molar ratio of Al to Sr leads to a change in emission colo... 详细信息

关键词： luminescence of Eu^(2.) strontium aluminum oxide emission

Development of silicon-based microelectrode array

在线全文

学校读者我要写书评

暂无评论

Science china(Technological Sciences) 2009年第8期52卷 2391-2395页

作者： LIN JianHui1,2.3. WU XiaoMing1,2.3.4, HUANG PengSheng1,2. FENG Lei5, REN TianLing1,2.& LIU LiTian1,2.1 Institute of Microelectronics, tsinghua university, beijing 100084,{2. 2.tsinghua National Laboratory for Information Science and Technology, beijing 100084,{2. 3.Yangtze Delta Region Institute of tsinghua university, Jiaxing 3.4050,{2. 4 State Key Laboratory of Transducer Technology, Chinese Academy of Sciences, Shanghai 2.0050 china 5 Department of Biomedical Engineering, tsinghua university, beijing 100084,{2. Institute of Microelectronics Tsinghua University Beijing China tsinghua National Laboratory for Information Science and Technology Beijing China Yangtze Delta Region Institute of tsinghua university Jiaxing China Department of Biomedical Engineering Tsinghua University Beijing China

This paper introduces in details a kind of silicon-based microelectrode array. MEMS (micro-electromechanical system) technology is used in the fabrication of the microelectrode array, which is designed to perform signal recording and electrical stimulation for nerves in neural engineering. A simple fabrication process is developed. An improved model of microelectrodes is brought forward and successfully validated by the excellent match between circuit simulations and electrical measurements, including both magnitude and phase of microelectrode impedance. Compared with the simple one that is usually used, the improved model is believed to be an advance and more accurate. This modeling helps to improve the design of microelectrodes and understand the behavior of interface between electrode and cell. Furthermore, the microelectrode is proved to be a feasible tool for researches in neural engineering by successfully recording neural activities of sciatic nerve of a bullfrog.

关键词： microelectrode array MEMS neural engineering